Relative vertical deformations in La Union, Philippines revealed by Holocene coral microatolls …rwg-tag.bravehost.com/Conferences/RPTaiwan_Abstracts.pdf · 2009. 9. 9. · EARTH

EARTH SCIENCES INTERNATIONAL CONFERENCE, PHILIPPINES | 36

Relative vertical deformations in La Union,

Philippines revealed by Holocene coral

microatolls

M.I. Abigania1,2, F.P. Siringan2,3*, G.M. Besana-Ostman1,4* and Y. Yokoyama5

1Geology and Geophysics R&D Division, Philippine Institute of Volcanology and Seismology – Department of Science and Technology (PHIVOLCS-DOST), Philippines

2National Institute of Geological Sciences, University of the Philippines, Diliman, Quezon City, Philippines

3Marine Science Institute, University of the Philippines, Diliman, Quezon City, Philippines

4Department of Geological Sciences, University of North Carolina at Chapel Hill, NC, USA

5Department of Earth and Planetary Sciences, University of Tokyo, Japan

*present address

Abstract Coral microatolls have long been used as good indicators of relative sea level change especially in an actively deforming region. Relative vertical deformations possibly associated with paleoseismic events are reconstructed from the morphology of living and emergent coral microatolls in Paraoir, Balaoan, La Union facing Manila Trench in the Philippines. The living microatolls exhibit emergence throughout their life history by having a domal raised center and down-stepping terraces towards the rim. The highest level of survival

(HLS) of the annual growth rings seen in x-radiograph of the sampled living microatoll showed short periods of gradual submergence (2-4 mm/yr) in between abrupt relative sea-level falls. These are possibly periods of relaxation phase corresponding to interseismic adjustments. Two episodes in the coral’s band pattern are marked by a decrease in the extension rate of the growth bands. One took place in ca. 1938 and another in ca. 1963. Incidentally, a Ms 7.0 earthquake occurred offshore of Ilocos associated with Manila Trench in 1938. The decrease in growth rate might be due to increased turbidity brought by elevated sediment load from rivers due to landslides upstream triggered by the earthquake. Rapid submergence of ~2cm ca.1938 is possibly tectonic as a Ms 7.6 and 7.0 earthquake events in offshore northwest Luzon occurred in 1934 and 1938 respectively. Whereas, the growth rate pattern and rapid submergence noted in ca. 1963 might be correlated with two earthquake events offshore of Pangasinan in 1963 and offshore of northwest Ilocos in 1964. can be correlated with the growth pattern in ca.1964. Oceanographic effects on sea level like the sea surface temperature changes in the South China Sea was also recorded in the coral, marked by a 2-3 cm gradual submergence and emergence in the growth rings from 1989 to 2006.


Emerged microatolls 1km south of the sampled living coral predominantly exhibit a “cup-like” morphology having two exterior raised rims with gentle outward slopes and abrupt down-steps toward the center. One of the sampled microatoll less than 1 m in diameter shows an initial hemispherical growth for 23 years which then experienced a possible sudden emergence of 6 cm followed by a relative sea level stability for about 4 years. An abrupt submergence of 6.5 cm followed that allowed for a catch-up growth band pattern for 9 years before its final emergence of ~1 m. More complex topography can be seen in larger microatolls of more than one meter in diameter indicating other

earlier events of relative sea level changes. The final emergence of the reef at about 1.4 kyBP lead to the demise of the microatolls . This sea level fall is also recorded in other places in the Philippines. The study can most probably identify other events older than the known historical record along Manila Trench.


Electromagnetic, geochemical and thermal

studies on Taal Volcano (Philippines) from

2005 to present

P.K.B. Alanis1, J. Zlotnicki2, J.P. Sabit1, Y. Sasai3, J. M. Cordon1, M. Harada4, J.P. Toutain5, E.U. Villacorte1, A. Bernard6, H. Hase7, J.T. Punongbayan1, T. Nagao8 and R.U. Solidum Jr1.

1Philippine Institute of Volcanology and Seismology, C. P. Garcia Avenue, U. P. Campus, Diliman, Quezon City, Philippines 2CNRS, UMR6524, UMS 833-UBP Observatoire de Physique du Globe de Clermont-Ferrand, 24 avenue des landais, 63177 Aubiere Cedex, France 3Disaster Prevention Division, Tokyo Metropolitan Government, Nishi-Shinjuku, 2-8-1, Shinjuku-ku, Tokyo 163-8001, Japan 4Centre for Frontier Electronics and Photonics, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan 5Laboratoire des Mecanismes de Transfert en Geologie, UMR5563, Observatoire Midi-Pyrenees, 14 avenue Edouard Belin, 31400 Toulouse, France 6Laboratoire de Geochimie et Mineralogie Appliquee, Universite Libre de Bruxelles, CP160/02, avenue FD Roosevelt 50, 1050 Brussels, Belgium 7Geological Survey of Japan, AIST, Tsukuba, Ibaraki 305-8567, Japan 8Earthquake Prediction Research Centre, Tokai University, 3-20-1, Orido, Shimizu-ku, Shizuoka 424-8610, Japan

Abstract Taal Volcano is one of the most active volcanoes in the Philippines. Its first recorded eruption was in 1573. It has since erupted 33 times resulting in hundreds of casualties and large damages to property. In 1995, it was declared one of the 15 Decade Volcanoes. Beginning in the early 1990s it has experienced several phases of abnormal activity, including seismic swarms, episodes of ground deformation, ground fissuring and hydrothermal activities. In January 2005, several felt earthquakes drove inhabitants living near the volcano to evacuate.

Joint self-potential (SP), total magnetic field (TMF), ground temperature, and carbon dioxide (CO2) soil degassing surveys along with satellite thermal imaging were begun in Taal Volcano in 2005, which aims to study the geothermal activity occurring in the volcano. These surveys are repeated regularly and several permanent and continuous TMF and SP stations were also established on the northern part of the volcano, as well as on the northeastern shore of the Main Crater Lake (MCL). The results from these combined studies indicate strong thermal transfers and degassing in the area of Daang Kastila on the northern flank of the volcano along E-W trending fissures. These fissures may be linked to the Main Crater Lake at its northern border as well as to thermal sources near the Main Crater Lake shoreline. This latter


thermal source is a possible location of future eruptive activity.

In order to identify the centre of the geothermal activity, we conducted measurements of the lake topography, TMF, surface water temperature as well as CO2 concentrations on the surface of MCL in March, 2008. A new mound, which appeared between the years 1986 and 2008, was found near the NNE coast of MCL. The mound (a topographic high at a depth of 40 m) is non-magnetic and coincides with the position of thermal anomaly emerged during the volcanic crisis in the early 2005. This area could be the outlet of magmatic fluids, which is connected to the vent from the magma reservoir at depth.


Harnessing ICT and high performance

computing for environmental monitoring

and hazard mitigation

The Philippine e-Science Grid Program, Department of Science and Technology - Advanced Science and Technology Institute, Diliman, Quezon City, Philippines 1101

Abstract

The Advanced Science and Technology Institute (ASTI), a research and development institute under the Department of Science and Technology (DOST), is mandated to conduct research and development in the advanced fields of Information and Communications Technology (ICT) and Microelectronics.

Over the years, ASTI's programs and projects have focused on providing more significant contributions to national development through ICT and Microelectronics. ASTI has been involved with a number of collaborations with government, academe, and industry to carry out high-impact projects that contribute to agriculture, distance education, weather forecasting, education, environmental monitoring, disaster mitigation, among others.

Environment stands as one of the priority research areas of ASTI. The Institute’s activities on the area are to conduct R&D and develop technologies and products that will have useful and critical applications in disaster and hazard mitigation, as well as in monitoring environmental health and safety.

Among the focus areas include: weather notification system; remote data monitoring/ sensing/ acquisition for research and disaster mitigation; and, real-time environmental data monitoring and acquisition.

ASTI continues to build and strengthen its capabilities in the areas of Sensor and Warning Systems Development and Deployment, and High-Performance Computing, among others. ASTI is currently implementing the Philippine Real-time Environment Data Acquisition and Interpretation for Climate-related Tragedy (PREDICT) Prevention and Mitigation. PREDICT aims to improve weather forecasting using a system of automated weather stations (AWS) that can remotely send weather parameters to a central server using the nationwide cellular network. The received data is then processed and analyzed to come up with weather bulletins for general information.

ASTI also initiated the Philippine e-Science Grid (PSciGrid) Program, which was conceptualized in response to the emerging need of the Filipino scientific community for a national high-performance computing facility. PSciGrid aims to establish a grid computing infrastructure in the Philippines that will provide internet-accessible e-Science solutions to a diverse community of researchers and scientists in the academe and government. Through the PSciGrid


Program, ASTI has set up a high-performance computing (HPC) facility with installed applications for meteorology.

ASTI’s future activities in relation to geoscience include the following:

1. Development of a web-based federated geospatial information system (FedGIS) for use in hazard mapping and assessment. The FedGIS is envisioned to be a collection of geospatial databases and other databases brought and integrated together for disaster risk management using a collection of networking and computing technologies for high-availability and real-time access. Essentially, FedGIS aims to provide a tool for scientists and decision-makers to make a more precise forecast of events, better allocate resources, and save lives.

2. Participation in a regional

initiative on earthquake monitoring that simulates global and regional (continental-scale) seismic wave propagation. The data that will be generated will be critical in understanding the earth’s inner structure.


Caught off guard: the January 2009

flooding of Mindanao, Philippines

L.T. Armada1, D.V. Faustino-Eslava1, G.P. Yumul, Jr.1,2, R.C. Viado3 and C.B. Dimalanta1

1National Institute of Geological Sciences, University of the Philippines, Diliman, Quezon City, Philippines 2Department of Science and Technology, Bicutan, Taquig City, Metro Manila, Philippines 3Philippine Council for Industry and Energy Research and Development, Department of Science and Technology, Bicutan, Taquig City, Metro Manila, Philippines

Abstract

Popularization of global climate change issues has led to international, national and local government initiatives aimed at combating its effects. However, despite efforts at preparing communities for the many geologic hazards that are projected to become more frequent with the changing climatic conditions, local communities remain ill prepared for the dangers that face them.

In January 2009, unexpectedly heavy precipitation accompanied an otherwise ordinary weather phenomenon which affected nearly the entire country. However, abnormally larger amounts of rain fell on the island of Mindanao in the southern Philippines. This elevated amount of precipitation was

attributed to Tropical Depression Auring and the existence of a cold front in the region. The total amounts of precipitation exceed 160% of the thirty-year average for most areas in Mindanao. As a consequence, catastrophic floods and landslides devastated numerous communities in the region. This report presents an account of the series of disasters that affected the cities of Cagayan de Oro, Gingoog, Bislig and the township of Maco in Compostela Valley.


Deformational styles of sedimentary

packages in offshore south Bondoc

Peninsula, Luzon, Philippines

M. Aurelio1, E. Cutiongco2, J. Foronda3, K.J. Taguibao1, Z. Calucin1 and M. Forbes3

1National Institute of Geological Sciences, University of the Philippines, Diliman, Quezon City, Philippines 2Pearl Energy Limited, 80 Raffles Place, UOB Plaza 2, #12-20, Singapore 3Philippine National Oil Company – Exploration Corporation, Energy Center, Fort Bonifacio, Taguig, Philippines

Abstract

Recently acquired 2-D seismic profiles and gravity data in the offshore area between Bondoc Peninula and Burias Island, South Luzon, Philippines, are interpreted in the context of known structural styles observed onshore and in relation to paleo- and neo-tectonic regimes in the region.

Keywords Seismic horizons, sedimentary packages, basin formation, tectonic inversion

Introduction Published materials in studies of offshore areas in inter-island seas of Luzon in the Philippines are generally few and sporadic. If any, these studies have been based on regional geophysical data such as

gravity and magnetics gathered through air-borne techniques (e.g. Pineda and Aurelio 1990, Bischke et al. 1990). In 1986, the then Bureau of Energy Development of the Philippines published a comprehensive summary of the sedimentary features of Philippine basins, based primarily from regional data. Detailed studies have been confined to areas surveyed by independent workers, mostly from the petroleum industry. In 1989, studies more specific to the Visayan Sea area were published in Porth and Von Daniels. This paper presents recent and detailed data (primarily seismic profiles, magnetic and gravity data) gathered in the offshore area south of Bondoc Peninsula in Southern Luzon, Philippines. The offshore data is integrated with onshore observations to gain a comprehensive understanding of the structural geology and tectonic character of the region. A preliminary effort to understand the implications of this structural and tectonic nature to petroleum exploration is attempted.

Methodology Offshore data (seismic profiles and bathymetry) gathered in 2007 (complimented with older profiles) were processed and interpreted. Among others, seismic processing involved signal deconvolution, stacking and velocity migration. Software-aided interpretation


allowed 2D and 3D appreciation of interpreted stratigraphy and structures. Seismic profiles were interpreted along with topographic contours and bathymetry, and compatible available map information from other works. The relationship between offshore seismic data and stratigraphy was established using onshore data as well as from few offshore wells.

Summary of Onshore Geology:

Southern Bondoc Penisula –

Burias Island The study area is located between Bondoc Peninsula and Burias Island in Southern Luzon (Figure 1). Bondoc Peninsula is a large anticlinorium with an anticlinorial axis oriented roughly N-S in the south and bends NWesterly to the north (Aurelio et al. 1990, Aurelio et al. 1991, Aurelio 1992). It is underlain by a pre-Tertiary volcano-ophiolitic basement topped by several sedimentary packages aged Eocene to Recent. The older sequences, including portions of the volcano-ophiolitic basement and Eocene-Oligocene volcanoclastics and limestones form the core of the anticlinorium and are exposed mostly at the northern and central sections of the peninsula as structural windows. Younger clastic sequences starting from Oligo-Miocene turbidites but passing into younger and generally shallower and more calcareous deposits cover the rest of the peninsula. The degree of deformation in these younger sedimentary sequences intensifies towards the southern half of the peninsula.

Burias Island, located to the SE of Bondoc Peninsula, presents a

similar stratigraphy, with indurated Eocene volcanoclastics forming the structural core and exposed in Sombrero Island and on the NW coasts of the the main island (Aurelio 1992). This core is topped by carbonates and clastic sequences generally showing shallower depositional features towards younger deposits and exposed widely over the island.

In Bondoc and Burias, three major unconformities since the Eocene are observed to separate several structurally-distinct sedimentary packages (Aurelio 1992). The oldest unconformity (~NP21) separates Eocene limestones from Oligo-Miocene turbidites while the middle unconformity (~NN5) marks the contact between these strongly-deformed E. Miocene turbiditic sequences with L. Miocene shallow marine clastics and carbonates. The youngest unconformity (~NN11) separates the L. Miocene clastics from the youngest sedimentary sequences.


Figure 1. Summarized geology of the Bondoc Peninsula – Burias Island area (Marinduque Island also shown) based from Aurelio (1992). Bathymetry is from GEBCO, topography is from SRTM. Offshore structures (red lines) in the Sibuyan Sea area are from Sarewitz and Lewis (1991). Approximate location of seismic profile presented in Figure 2 is shown. See text for discussion.

Summary of Observations from

Seismic Profiles

Figure 2 shows a seismic profile in the study area and its structural interpretation. A strong seismic reflector (Horizon 1 – H1) believed to be the equivalent of Late Oligocene – Early Miocene limestone and carbonate sequences exposed in Bondoc peninsula, appears as a folded and faulted horizon. The longer fold axis is generally oriented NNW-SSE, expressed in an anticline-syncline sequence plunging to the NNW. The shorter fold axis orients sub-perpendicular to the longer fold axis on an ENE-WSW direction. The NNW plunge allows the reflector to emerge on the seabed southeastwards in the direction of Burias Island, where the same mid-Tertiary limestones are exposed. Faulting is in the form of compressive faults but which show indications of initial normal faulting.

Above the H1 horizon is a package generally characterized by incoherent reflections on its lower half but by strong to moderately folded and truncated reflectors on its upper half. This sequence, together with the upper section of the H1 horizon, is affected by thrust-fold style deformation with the thrust plane – fold axis striking almost parallel to the longer fold axis of H1.

The truncation of the sequence overlying the H1 horizon is represented by a faintly to moderately visible horizon (H2) characteristic of an angular unconformity. Above H2 is a generally coherent seismic package occasionally affected by moderately- to steeply-dipping normal faults forming half-grabens and horsts biased towards a westerly basinal dip. The block-tilted unit is capped by a thin, generally undeformed sequence.


Figure 2 Seismic profile (top) between Bondoc Peninsula and Burias Island (location shown on Figure 1) and its interpretation (bottom). Vertical scale is two-way travel time in seconds. See text for discussion.

The H1 and H2 horizons correspond to the two most recent unconformities discussed in the summarized geology of the study area.

On the SW flank, a rugged seabed slope falls abruptly to the WSW suggesting instability. Reflectors are highly disturbed, often truncated by steeply dipping faults cutting through seabed.

Concluding Remarks The complex deformational style observed in the sedimentary packages in the offshore area between Bondoc Peninsula and

Burias Island is the result of multiple tectonic events known to have affected the region and nearby areas. These tectonic events involved basin deposition at different depths and time intervals, punctuated by compressional periods in between. The alternance of extensional (basin formation) and compressional (as in the case of collision) tectonic regimes often brings about tectonic inversion processes, which may generate geologic structures favourable for hydrocarbon accumulation.


Acknowledgements

M. Aurelio, holder of a Pearl Energy Professorial Chair in Energy Research, wishes to thank Pearl Energy Limited and PNOC-EC for allowing use of part of their data in this paper.

References [1] Aurelio, M.A., Rangin, C., Barrier, E. and Müller, C. Tectonique du segment central de la faille Philippine. Comptes Rendues - Academie de Science t310, SII (1990), 403-410.

[2] Aurelio, M.A., Barrier, E., Rangin, C. and Müller, C. The Philippine Fault in the late Cenozoic evolution of the Bondoc-Masbate-N. Leyte area, central Philippines. Journal of Southeast Asian Earth Sciences 6, 3/4 (1991), 221-238.

[3] Aurelio, M.A. Tectonique du segment central de la faille philippine: etude structurale, cinématique et evolution géodynamique. Thèse de doctorat de l'Université de Paris 6, Université Pierre et Marie Curie, Académie de Paris, T 92-22, France (1992) 500 p.

[4]Bischke, R. E., Suppe, J. and Del Pilar, R. A new branch of the Philippine Fault system as observed from aeromagnetic and seismic data. Tectonophysics, 183, 1-4 (1990), 243-264.

[5] Bureau of Energy Development, Philippines. Sedimentary basins of the Philippines: their geology and hydrocarbon potential. Bustamante Press, Inc., Manila, Philippines (1986).

[6] Pineda, M.J.Y. and Aurelio, M.A. New insights on the tectonics of the Southern Luzon-Northern Visayas region (from aeromagnetic data): a preliminary report. In: The Third Annual Geological Convention, December 5-7, 1990, Q.C. Philippines. Abstracts, p. 54.

[7] Porth, H. and Von Daniels, C.H., Eds., 1989. The sedimentary formations of the Visayan Sea Basin. Geologisches Jarbuch, 70, B, (1989), 428 p.

[8] Sarewitz, D.R. and Lewis, S.D. The Marinduque intra-arc basin, Philippines: Basin genesis and in-situ ophiolite development in a strike-slip setting. Geological Society of

America Bulletin, 103 (1991), 597-614.


Sibuyan Sea Fault, Marinduque Fault and

Philippine Fault (Ragay segment): New

insights from GPS data

T. Bacolcol1,3, S.-B. Yu2 and R. Solidum Jr.1

1Philippine Institute of Volcanology and Seismology – Department of Science and Technology, PHIVOLCS Bldg., C.P. Garcia Ave., University of the Philippines Campus, Diliman, Quezon City, Philippines 1101 2Institute of Earth Sciences, Academia Sinica, Nankang, Taipei, Taiwan 3Département de Géotectonique, Université Pierre et Marie Curie, 4 place Jussieu, T26, E1, Paris, France

Abstract

Data gathered in October 2005 and in June 2008 from the 11-point GPS network in Ragay-Bondoc were combined with other survey data from 22 other nearby points to calculate for the surficial velocity rates and to determine patterns of deformation for the three major crustal structures straddling Southern Luzon namely: Sibuyan Sea Fault, Central Marinduque Fault and the Philippine Fault along the Ragay-Bondoc.

As expected, calculations with respect to Palawan showed NW-directed movements for all the points included in the network. Surficial velocities range from 33 mm/yr in Sibuyan Island to about 90 mm/yr in Virac. Based on the vector magnitude and direction and as complemented by seismicity data, it appears that the Philippine Fault in Ragay Gulf is locked. It is

also probable that the on-land extension of the Sibuyan Sea Fault is the 30-km, northwest-trending Central Marinduque Fault in Marinduque Island. The gathered data also showed that Central Marinduque Fault is probably creeping at 15 mm/yr, which would explain for the sparse seismicity recorded along its length. Another major information gathered from these GPS data is the recognition of a significant NW movement (about 33 mm/yr) between Palawan and the group of islands on the east (Marinduque, Banton and Sibuyan). This would imply that the suture zone between Palawan and the Philippine Mobile Belt is located still further west of Marinduque and Romblon.


Mid-Holocene sea-level changes in Poro

Point, La Union using morphostratigraphic

indicators

N.P. Baluda1, F.P. Siringan2 and A.M.F.A. Lagmay1


2Marine Science Institute, University of the Philippines, Diliman, Quezon City, Philippines

Abstract

Vertical land motions during the mid-Holocene along the coast of Poro Point, San Fernando, La Union (Northwestern Luzon, Philippines) were delineated from the stratigraphy of uplifted coral reef sequence, micromorphology of Porites sp. microatolls, and overall geomorphology of the area. Four 14C dates from corals within the raised reef sequence yielded ages ranging between 6605 and 6220 yr bp. The topographic profile and elevation of the uplifted landforms as well as 28 flat-topped Porites sp. microatolls, with 11 being eroded, were determined using an EDM. Age-elevation relationships indicate (1) the presence of faults across the study area and (2) multiple episodes of sea level change with magnitudes of rise and fall in the order 50 to 70 centimeters within this 385-year interval.


Terrane characteristics and configuration

in Northwestern Mindoro and their

implications

A.P.B. Canto1, R. Tamayo Jr.1, C. Dimalanta1, D. Faustino-Eslava1, G. Yumul Jr.1,2, K.L. Queaño3 and E. Marquez4

1Rushurgent Working Group, National Institute of Geologic Sciences, University of the Philippines, Diliman, Quezon City, Philippines

2Department of Science and Technology, Bicutan, Taguig Metro Manila, Philippines

3Mines and Geosciences Bureau-Department of Environment and Natural Resources, North Avenue, Quezon City, Philippines

42009 Centennial Faculty Grant Awardee, Department of Physical Sciences and Mathematics, University of the Philippines Manila, Padre Faura St., Ermita, Manila, Philippines

Abstract

Mindoro represents a tectonically complex island in central Philippines; the evolution of which and its importance to arc – continent collision along the western Philippines remain unclear. On northwestern Mindoro including the offshore islands of Lubang and Ambil, remnants of multiple collision events appear as NW-SE oriented tectonic slices that are separated by southwest verging thrust faults, essentially parallel to the trend of the currently active Manila Trench. A profile from the trench to Central Mindoro indicates

the presence of distinct terranes: the Middle Oligocene Amnay Ophiolite and the Mesozoic Halcon Metamorphics. A Late Pliocene to Early Pleistocene dated sequence consisting of sandstone and limestone with minor mudstone and conglomerate (Balanga Formation) unconformably overlies the two terranes.

Aside from the age variance, the Amnay Ophiolite and Halcon Metamorphics differ in petrological and geochemical characteristics and origin, as well. The former corresponds to an exhumed piece of the South China Sea crust, whereas the latter correlates to a metamorphosed continent derive fragment. Isolated ophiolitic blocks previously identified to compose the Mangyan and Lubang – Puerto Galera Ophiolites are enclosed by schists of the Halcon Metamorphics. Preliminary results suggest these peridotite and volcanic blocks have affinity with mid-oceanic ridge materials, which contrast with the chemistry of the Amnay Ophiolite. We propose the Mangyan and Lubang – Puerto Galera Ophiolite represent megaclast materials, which were incorporated into the Halcon Metamorphics protolith. As such, the Halcon Metamorphics could well be the metamorphosed equivalent of the accretionary complexes currently exposed in northern Palawan and northwest Panay. Metamorphism must have occurred prior to the Late Eocene as constrained by the Lasala Formation sedimentary package that unconformably overlies the Halcon Metamorphics.


These preliminary results support the presence of two terranes in northwestern Mindoro, the ages of which increase toward the interior of the island. The older terrane could represent the metamorphosed edge of the micro-continental block that rifted from the East Asian margin at this site of arc – continent suturing in western Philippines. Active movement along the Manila Trench and the Central Mindoro Fault enhances the exhumation of the basal units of the terranes thereby promoting higher susceptibility of the island to mass wasting processes.


A plate tectonic mechanism fluid migration

in the convergent margin, southwestern

Taiwan

W.-B. Cheng1, S.-K. Hsu2 and C.-H. Chang3

1Department of Environment and Property Management, Jinwen University of Science and Technology, Taiwan 2Institute of Geophysics, National Central University, Taiwan 3Central Weather Bureau, Taiwan

Abstract

In a subduction zone, the most likely source of the fluid would be water contained in the hydrous minerals of the subducting oceanic crust, because dehydration of clay minerals in sediments is completed at depths shallower than 10 km. Therefore, the sources and pathways of upward expelled fluid flow on the accretionary prism of southern Taiwan have been the subjects of intense debate. This paper investigates velocity structure of the active plate boundary in southwestern Taiwan by joint analysis of gravity anomaly and seismic arrival time data. P and S-P arrival time data from 3,238 earthquakes. In addition to CWBSN permanent networks, seismic data include the Central Weather Bureau permanent networks and a temporary network consisting of 11 ocean bottom seismometers (OBSs) that was deployed to detect the aftershocks of the 2006 (ML7.1) Henchun earthquake occurred beneath southern Taiwan. The total

available OBS data set consists of ~700 detected earthquakes, from which around 500 could be well located where about 450 events have been used in simultaneous inversion for hypocenters, three-dimensional Vp and Vp/Vs models for the study area. Gravity data are used to improve the model for the offshore area, where it is poorly sampled by local earthquakes. This study found three crustal anomalies: (1) two prominent high velocity/high Poisson's ratio anomalies in the mid to lower crust beneath the eastern coastal and offshore area; (2) several volumes of relatively high-velocity/high Poisson's ratio rocks in the upper- to mid-crust beneath the Central Range; (3) a thin low-velocity zone is detected above the subducting Eurasian slab in the mantle wedge and earthquakes are distributed along the transition zone between this thin low-velocity zone and the high-velocity Eurasian slab. Based on gravity modeling and our resulting velocity and Poisson's ratio models suggest that the subduction decollement, which is characterized beneath the continental shelf can be traced landward into a duplex structure in the lower crust near southern Taiwan. This study also suggested that the geochemical and geologic setting in a convergent plate boundary exerts specific controls on the formation of a bottom simulating reflections and the inferred distribution of gas hydrates. This crustal thickening occurred above the locked plate


boundary and uplifts the continental margin should raising stored gas hydrate out of the stability zone and thus destabilizing them to release methane in the region east to the deformation front. Continuous sedimentation could ensure carbon supply according to the very high sedimentation rate despite the dissociation of gas hydrates due to uplift in active margin.


Rapid seismic tsunami warning for the

South China Sea Region

P.-F. Chen

Institute of Geophysics, National Central University

Abstract

The widespread tsunami hazards of the 2004 Sumatra-Andaman Is. Earthquake prompted us to build a tsunami warning system for the South China Sea Region. We adopt the principle that tsunami waves can be expressed as a linear combination of unit tsunamis and then divide the potential source region (the Taiwan-Luzon trench) into sub-regions of squares, called unit tsunami event (Lee et al., 2005). The propagation of each unit tsunami event is simulated using the COMCOT package (Liu et al., 1998). We store the resulting unit tsunami waveforms of selected tidal stations in database for further uses. In a real tsunamigenic earthquake, the predicted tsunami waveform of a certain tidal station is then synthesized by linear combinations of unit tsunamis form the database, similar to the concept of green function. The coefficients of unit tsunamis are determined by on-site seafloor displacements which are usually calculated by the earthquake parameters (longitude, latitude, depth and seismic moment tensor). We will also implement the fast seismic source inversion method using W phase to retrieve the seismic source in a near real time fashion (Kanamori and Rivera, 2008). W phase is a long period phase arriving before S wave,

which make the W phase source inversion method effectively for rapid and robust tsunami warning purposes (Kanamori and Rivera, 2008). The purpose of this study is to build a seismic tsunami warning system for the South China Sea region by combining the W phase source inversion method and the unit tsunami method.

References [1] Lee, H.-J., Y.-S. Cho and S.-B. Woo, Quick tsunami forecasting based on database, Tsunamis: Case Studies and Recent Developments, K. Satake (ed.), 231-240, 2005.

[2] Liu, P. L.-F., S.-B. Woo and Y.-S. Cho, Computer programs for tsunami propagation and inundation, Cornell University, 1998.

[3] Kanamori, H., and Rivera. L, Source inversion of W phase: speeding up seismic tsunami warning, Geophys. J. Int., 175, 222-238 doi:10.1111/j.1365-246X.2008.03887.x


Applications of 2-D resistivity surveys in

characterizations of active faults in Luzon:

Implications for fault occurrence beneath

the Bataan Nuclear Power Plant

M. Collado1 and C.A. Arcilla2

1Department of Agriculture 2National Institute of Geological Sciences

Abstract

Resistivity surveys have found wide applications in determining groundwater levels and, when used with other geophysicial and geological parameters, provide imaging of the subsurface. Given the presence of active segments of the Marikina Valley Fault system in Metro Manila, we conducted several resistivity profiles across areas where there were visible surface ruptures due to the fault. The intention was to test the usefulness of the resistivity method in detecting the continuation of the fault beneath the surface. We present 2-D inverted resistivity profiles across active fault segments and demonstrate that there are enough geophysical contrasts to distinguish the subsurface fault signature with that of the bedrock. Since the controversial Bataan Nuclear Power Plant is thought to be built on top of a fault, we employed four resistivity lines around the building, using closely-spaced electrodes in a Wenner array, in an attempt to image the fault if it existed.

Comparing results of the BNPP resistivity survey with our numerous surveys on active faults, we conclude that there are no anomalies that indicate faults or fractures underneath and along the vicinity of the nuclear building. This study, however, DOES NOT preclude the existence of fault/s close to the vicinity of the nuclear building that may be outside the range of the resistivity profile lines. The data presented, however, arguably rules out the existence of a fault beneath the nuclear plant. It must be noted that the “existence” of such a fault was one of the main reasons why the BNPP was never operated.


Petrographic and geochemical data from

the Klondyke and Zigzag Formations:

Implications on the oceanic to island arc

evolution of the Baguio Mineral District,

Philippines

C.B. Dimalanta1, G.P. Yumul Jr.1,2 and R.A. Concepcion1

1Rushurgent Working Group - Tectonics and Geodynamics Group, National Institute of Geological Sciences, College of Science, University of the Philippines, Diliman, Quezon City, Philippines 1101 2Department of Science and Technology, Bicutan, Taguig, Metro Manila, Philippines

Abstract

This study presents a petrographic and geochemical examination of the clastic rock units that underlie the Baguio Mineral District and the nearby areas. The results obtained from this investigation will offer clues on the evolution, not only of northern Luzon, but of the Philippine island arc system as well.

Petrographic examination of samples collected from the sedimentary units in the Baguio Mineral District show that the Zigzag Formation samples have more quartz but less plagioclase compared to the Klondyke, Amlang and Cataguintingan Formation samples. Lithic fragments are more abundant in the Klondyke Formation sandstone samples. The major and immobile trace element data suggest that the Klondyke, Amlang and

Cataguintingan Formation samples were derived from a mafic source whereas samples from the Zigzag Formation indicate derivation from intermediate to felsic igneous rocks. These results suggest that the Zigzag Formation was derived from an active continental margin setting whereas the Klondyke, Amlang and Cataguintingan Formations are associated with an oceanic island arc environment.

Introduction

The amount of literature documenting the application of petrography and geochemistry to the study of sedimentary rocks has increased over the last years. These techniques are now being applied to investigations of the sedimentary units capping the basement rocks in the Philippines. The Cretaceous to Eocene sandstone sequence in Palawan was investigated by Suzuki et al. (2000). A significant amount of quartz grains and lithic acidic fragments was noted during the petrographic examination of the sandstone samples. In terms of the geochemical characteristics, high SiO2 and low FeO plus MgO values were obtained for the samples. This suggests derivation from a continental source region which is consistent with existing


models that Palawan is a fragment derived from the southern margin of mainland Asia.

This work presents the petrographic and geochemical compositions of clastic units from the Baguio Mineral District and nearby areas (Figure 1). The results are used to constrain the composition and tectonic setting of the source rocks. This, in turn, will give insights into the geologic evolution not only of Northern Luzon but also of the whole Philippine island arc system. The results contained herein will also help build up the database on the petrographic and geochemical compositions of sedimentary units in the Philippine island arc system, which, at the moment, is almost lacking.

Clastic units in the Baguio

Mineral District Zigzag Formation

The Zigzag Formation, best exposed along Kennon Road, is subdivided into the Early to Middle Miocene Upper Zigzag and Oligocene Lower Zigzag members which are separated by an unconformity (Peña and Reyes, 1970). The alternating layers of red and green sandstones and siltstones comprise the Lower Zigzag member. Upper Zigzag, on the other hand, is made up of massive, well indurated and oligomictic conglomerates consisting dominantly of basalt to basaltic andesite clasts.

Klondyke Formation

A thick sequence of coarse clastic rocks, polymictic conglomerate, conglomeratic sandstones, sandstones, flow breccias, vitric tuffs, with minor shales and

siltstones characterize this formation (Leith, 1938). This is best observed along Marcos Highway, Naguilian Road, Asin Road and the lower portion of Kennon Road. Previous studies revealed that the Klondyke Formation has well-defined proximal, midfan and distal slope portions. A Middle to Late Miocene age was assigned to this unit based on calcareous nannofossil assemblage (De Leon et al., 1991).

Other clastic units

Aside from the Zigzag and Klondyke Formations, samples were also collected from sedimentary units in the nearby La Union area. These include the Amlang and Cataguintingan Formations. The Amlang Formation is a “flysch-type” sequence of thin, rhythmically interbedded sandstones, shales and minor conglomerates (Lorentz, 1984). A gradational contact separates the basal portion of the Amlang Formation from the Klondyke Formation. A Middle to Late Miocene age is assigned to this unit based on the calcareous nannofossil assemblage (Catinaster sp., Discoaster pentaradiatus and Sphenolithus abies) (De Leon, pers. comm.).

A sequence of tuffaceous sandstones interbedded with siltstones, shales and conglomerates with some limestone lenses makes up the Cataguintingan Formation (Lorentz, 1984). An unconformity serves as the boundary between the Cataguintingan Formation and the Amlang Formation. This formation has been given a Late Pliocene age based on the molluscan shell fragments, echinoid spines, ostracods and red algae (Maleterre, 1989).


Petrographic results

Twenty-two fine- to medium-grained sandstone samples were petrographically examined and point counted. Angular to sub-angular grains comprise the sandstone samples and these are embedded in <15% clay matrix. The cement, on the other hand, is usually in the form of calcite and quartz overgrowth.

The samples from the Zigzag Formation are mainly composed of quartz (60-80%). The quartz crystals are mostly monocrystalline, non-undulatory and devoid of inclusions. These characteristics commonly imply that the quartz might have been derived from the surrounding volcanic rocks as a result of weathering and erosion (Tucker, 2001).

A considerable amount of plagioclase minerals (17-30%) are also present in the Zigzag samples but this is much less than the number of plagioclase grains observed in the Amlang (45-58%) and Klondyke (25-50%) Formations. Abundant plagioclase crystals are indicative of a compositionally immature sandstone since plagioclase is a labile mineral. Compositional maturity reflects the weathering process in the source area and the degree and extent of reworking and transportation (Tucker, 2001). It is also evident that some of the plagioclase grains of the Klondyke samples exhibit zoning while some are almost completely altered into calcite.

Lithic fragments, which are mostly in the form of volcanic clasts, are common in the Klondyke (15-30%) samples.

Provenance and tectonic

setting

An examination of the geochemical compositions of sedimentary rocks can offer useful information on the composition of its source area or source rocks. When plotted on the discrimination diagram for provenance using the major elements, most of the Klondyke, Amlang and Cataguintingan samples plot in the mafic igneous provenance field. The Zigzag samples show derivation from both intermediate igneous rock sources and mafic igneous provenance (e.g. Yan et al., 2007).

Some workers are not too eager to use the Rb versus K2O diagram arguing that these elements are quite mobile during diagenesis or metamorphism. But when the diagram is used along with other plots, some useful information may still be derived. The samples from the Baguio Mineral District can be divided into two groups based on the K and Rb contents. Low K, Rb and K/Rb ratios exhibited by the Klondyke, Amlang and Cataguintingan samples suggest derivation from basic igneous rocks (Figure 2). The Zigzag samples, in contrast, are characterized by high K, Rb and K/Rb ratios typical of rocks derived from intermediate to felsic igneous rocks.

To determine the tectonic setting of the provenance region, Roser and Korsch (1986) proposed plotting the SiO2 versus K2O/Na2O values (Figure 3). This diagram differentiates oceanic island arc environments from more evolved arcs (i.e. active continental margins or continental island arcs). The K2O/Na2O ratios of the Zigzag Formation samples are generally higher compared to the ratios of


the Klondyke, Amlang and Cataguintingan Formation samples. This suggests that the sediments that make up the Zigzag Formation samples were derived from an evolved arc. Conversely, the Klondyke, Amlang and Cataguintingan Formation samples have lower K2O/Na2O and indicates that their sediments were derived from oceanic island arcs.

Conclusions

The clastic units from the Baguio Mineral District and the nearby areas were analyzed in terms of their petrography and geochemistry. The results show that the sediments of the Zigzag Formation were sourced from intermediate to felsic igneous rocks within an active continental margin setting. Mafic source rocks from an oceanic island arc setting comprise the sediments of the Klondyke, Amlang and Cataguintingan Formations.

Acknowledgements This work was supported by the National Research Council of the Philippines, Department of Science and Technology, Commission on Higher Education and National Institute of Geological Sciences. Our thanks also go to T.A. Tam III, E.G.L. Ramos, A. Imai for help in the fieldwork and in the processing of samples.

References [1] De Leon, M.M., Tamesis, E.V. and Militante-Matias, P.J. 1991. Calcareous nannofossil study of the Klondyke Formation section along km posts 278-251, Marcos Highway, Baguio City – Pugo, La Union Province, Philippines. Journal of the Geological Society of the Philippines 47, 35-92.

[2] Dimalanta, C.B. and Yumul, G.P.Jr. 2009. A geochemical approach on the provenance

signatures of the Klondyke and Zigzag Formations and its implication on the oceanic to island-arc setting evolution of the Baguio Mineral District, Philippines. Terminal Report, National Research Council of the Philippines, 36pp.

[4] Leith, A. 1938. Geology of the Baguio gold district. Philippine Department of Agriculture and Communication Technology Bulletin 9, 38.

[5] Lorentz, R.A.Jr. 1984. Stratigraphy and sedimentation of the Late Neogene sediments on the southwest flank of Luzon, Central Cordillera, Philippines. Journal of the Geological Society of the Philippines 38, 1-24.

[6] Maleterre, P. 1989. Histoire sedimentaire, magmatique, tectonique et metallogenique d'un arc cenezoic deforme en regime de transpresion: La Cordillere Centrale de Luzon, a l'extremite de la faille Philippine, sur les transects de Baguio et de Cervantes-Bontoc, Contexte structural et geodynamique des mineralisations epithermales auriferes. Universite de Bretagne Occidentale, Brest, France. Doctoral thesis. 304pp.

[7] Peña, R.E. and Reyes, M.V. 1970. Sedimentological study of a section of the “Upper Zigzag” Formation along Bued River, Tuba, Benguet. Journal of the Geological Society of the Philippines 24, 1-19.

[8] Roser, B.P. and Korsch, R.J. 1986. Determination of tectonic setting of sandstone-mudstone suites using SiO2 content and K2O/Na2O ratio. Journal of Geology 94, 635-650.

[9] Suzuki, S., Asiedu, D.K., Takemura, S., Yumul, G.P.Jr., David, S.D.Jr. and Asiedu D.K. 2000. Composition and provenance of the Upper Cretaceous to Eocene sandstones in Central Palawan, Philippines: Constraints on the tectonic development of Palawan. Island Arc 9, 611-26.

[10] Tucker, M.E. 2001. Sedimentary Petrology: An Introduction to the Origin of Sedimentary Rocks. 3rd edition. Blackwell Science Ltd, USA, 262 pp.

[11] Yan, Y., Xia, B., Lin, G., Cui, X., Hu, X., Yan, P. and Zhang, F. 2007. Geochemistry of the sedimentary rocks from the Nanxiong Basin, South China and implications for provenance, paleoenvironment and paleoclimate at the K/T boundary. Sedimentary Geology 197, 127-140.


Figure 1. The sedimentary formations in the Baguio Mineral District and nearby areas were sampled for petrographic and geochemical analyses (Dimalanta and Yumul, 2009).

Figure 2. Binary diagram using K and Rb to characterize the source rocks of the Baguio Mineral District sedimentary units (Dimalanta and Yumul, 2009).

Figure 3. Discrimination diagram from Roser and Korsch (1986) shows the Zigzag Formation samples mostly occupying the active continental margin (ACM) field whereas the other samples plot within the oceanic island arc (ARC) field. PM is passive margin (Dimalanta and Yumul, 2009).


Liquefaction potential assessment of

Malabon & Navotas cities, Philippines

J.R. Dungca

De La Salle University-Manila 2401 Taft Ave., Malate, Manila, Philippines

Abstract

The geotectonic setting of the Philippines makes it prone to various types of seismic related hazards. The devastating Luzon earthquake of 1990 is one of the most recent manifestations of this phenomenon and it has also opened opportunities to better understand the liquefaction phenomenon. Many areas in the Philippine archipelago including Malabon and Navotas are believed to have deposits of potentially liquefiable sand exist and are presently used for residential, commercial or industrial purposes. These cities may suffer tremendous losses in terms of lives and properties not only because of the violent shaking of the structures but mainly because of the liquefaction of the foundation soils due to the thick liquefiable sand layer predominantly underlies them. It is in this premise that this study was initiated to be able to make effective liquefaction potential assessments for selected areas vulnerable to liquefaction. The city of Malabon and Navotas are two places which are in the outer ring of Metro Manila. These are some of the cities which are fronting Manila Bay. These cities are known to experience frequent

flooding due to typhoons, and during high tides. Furthermore, these cities became significant to the Philippine government and the general public as pertaining to the rate of recurrence and severity of flooding, specifically during monsoon seasons and events of high tide and due to the developing global warming, and the substantiation of studies showing evidences of ground subsidence in the said areas. Assessment of liquefaction potential of the Malabon and Navotas was conducted by collecting SPT borehole data and evaluating the SPT “N” values using the semi-empirical procedures of Idriss and Boulanger (2004) for evaluating liquefaction potential during earthquakes. Thus, the factors for safety against liquefaction that was computed from the assessment procedures were analyzed.


Parallelisms between the Bangong-

Nujiang in Tibet and the Philippine suture

zones

D. Faustino-Eslava1*, J.A. Aitchison2, R.A. Tamayo, Jr.1, G.P. Yumul Jr.1,3 and C.B. Dimalanta1

1Rushurgent Working Group - Tectonics and Geodynamics Group, National Institute of Geological Sciences, College of Science, University of the Philippines, Diliman, Quezon City, Philippines 1101 2Department or Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong 3Department of Science and Technology, Bicutan, Taguig, Metro Manila, Philippines

Abstract

The geology of the Tibetan plateau documents amalgamations of various terranes successively added to the Eurasian plate during the Paleozoic to Mesozoic eras. Major structural features of the plateau run east-west, parallel to the paleo-trenches. One of these suture zones is the Bangong-Nujiang suture (BNS) which transects the plateau’s interior and is characterized by numerous exposures of Jurassic–Cretaceous ophiolites and ophiolitic mélanges, associated thick sequences of Jurassic flysch and Middle to Late Cretaceous sedimentary and volcanic rocks. The Philippines is similarly characterized by accretions of various terranes juxtaposed

within and against the island arc system. Most of these terranes and the general structural features of the country are generally distributed or oriented parallel to the length of the archipelago and its bounding subduction systems. Reconstruction of the Cretaceous Asian margin in Tibet suggests a similar geographic setting to the present Southeast and Eastern Asian region, with several marginal basins, some underlain by developed oceanic crusts, while others remain floored by continental lithosphere. This presentation discusses these parallelisms in the hope of understanding the geodynamic histories of both the more ancient BNS and the younger and presently active Philippine suture zones.


Gravity, seismic refraction and resistivity

signatures in Northwest Panay, Philippines:

Subsurface imaging of a terrane boundary

using geophysical methods

J.A.S. Gabo1*, C.B. Dimalanta1, E.G.L. Ramos1, L.T. Armada1, K.L. Queaño2,3, R.A. Tamayo Jr.1, G.P. Yumul Jr.1,4, E.J. Marquez5

and D. Faustino-Eslava1

1Rushurgent Working Group - Tectonics and Geodynamics Group, National Institute of Geological Sciences, College of Science, University of the Philippines, Diliman, Quezon City, Philippines 1101 2Mines and Geosciences Bureau – Central Office, Department of Environment and Natural Resources, North Avenue, Diliman, Quezon City, Philippines 1101 3Earth and Materials Science and Engineering Department, Mapua Institute of Technology, Intramuros, Manila 4Department of Science and Technology, Bicutan, Taguig, Metro Manila, Philippines 5University of the Philippines, Padre Faura, Manila, Philippines

Abstract

Northwest Panay is composed of two terranes: the Buruanga Peninsula and the northern portion of the Antique Range (McCabe et al., 1982; Tamayo et al., 2001). These two terranes are believed to be affected by the collision between the Palawan Microcontinental Block

and the Philippine Mobile Belt during the Miocene (Yumul et al., 2005; Gabo et al., 2009). The boundary between these two terranes is the Nabas Fault, located at the neck of Buruanga Peninsula (Zamoras et al., 2008). The Northern portion of the Nabas Fault is buried beneath Plio-Pleistocene and Quaternary sediments.

To investigate this terrane boundary in Northwest Panay, gravity, seismic refraction and resistivity surveys were conducted. The gravity method results show that the Buruanga Peninsula exhibit higher gravity anomaly values than the rocks from the Antique Range. This change in gravity anomaly values can be observed to occur at the neck of the peninsula, where the Nabas Fault is located. There is a sudden drop in the gravity anomaly values at the location of the Nabas Fault. The shallow seismic refraction and resistivity surveys conducted at the neck of the Buruanga Peninsula agree with the gravity data. Modeling of the geophysical data shows that there is a sudden decrease in density and resistivity in the area between the Buruanga Peninsula and the Antique Range terranes. Even though it is covered with thick alluvial deposits, the area at the neck of Buruanga Peninsula consistently shows a sudden decrease in gravity, density and resistivity values in the geophysical survey results. These results are


evidence of the presence of the Nabas Fault, the terrane boundary between the Buruanga Peninsula and the Antique Range. This structure is believed to be an east-verging thrust fault that was generated due to the collision between the Palawan Microcontinental Block and the Philippine Mobile Belt (Zamoras et al., 2008).

References [1] McCabe, R., Almasco, J.N. and Diegor, W. 1982. Geologic and paleomagnetic evidence for a possible Miocene collision in Western Panay, central Philippines. Geology 10, 325-329.

[2] Gabo, J.A.S., Dimalanta, C.B., Asio, M.G.S., Queaño. K.L., Yumul, G.P.Jr. and Imai, A. 2009. Geology and Geochemistry of clastic sequences from Northwest Panay (Philippines): Implications for provenance and geotectonic setting. Tectonophysics, http://dx.doi.org/10.1016/j.tecto.2009.02.004

[3] Tamayo, R.A. Jr., Yumul, G.P. Jr., Maury, R.C., Polve, M., Cotten, J. and Bohn, M. 2001. Petrochemical Investigation of the Antique Ophiolite (Philippines): Implications on Volcanogenic massive sulfide and podiform chromitite deposits. Resource Geology 51, 2, 145-164.

[4] Yumul, G.P., Jr., Dimalanta, C.B., Tamayo, R.A., Jr. 2005. Indenter Tectonics in the Philippines: Example from the Palawan Microcontinental Block – Philippine Mobile Belt Collision. Resource Geology 55, 3 189-198.

[5] Zamoras, L.R., Montes, M.G.A., Queaño, K.L., Marquez, E.J., Dimalanta, C.B., Gabo, J.A.S. and Yumul, G.P.Jr. 2008. The Buruanga Peninsula and the Antique Range: Two contrasting terranes in Northwest Panay, Philippines featuring an arc-continent collision zone. Island Arc 17, 443-457.


Holocene coral reef development and sea-

level rise of northwestern Luzon,

Philippines

S.-Y. Gong1, F.P. Siringan2, C.-C. Shen3, K. Lin3 and C.-F. Dai4

1Department of Geology, National Museum of Natural Science, Taichung, Taiwan ROC

2Marine Science Institute, University of Philippines, Quezon City, Philippines

3Department of Geosciences, National Taiwan University, Taipei, Taiwan ROC

4Institute of Oceanography, National Taiwan University, Taipei, Taiwan ROC

Abstract

Holocene coral reefs occurred extensively along the west coasts of Luzon. During the reef development, the eustatic sea level rose as a result of glacier retreat. Meanwhile, Luzon was also uplifted due to neo-tectonism. These reefs thus offer an archive of eustatic and neotectonic history of western Luzon. To study the Holocene coral-reef growth and sea–level changes in the Philippines, this study drilled three boreholes on a raised Holocene reef at Currimao, northwestern Luzon, and establishes a new sea level record during the early-mid Holocene with 230Th-dated corals. The cores cover a depth interval from 3.8 m above present sea level (PSL) to 26.7 m below PSL and consist of four lithofacies including (1) reef facies,

(2) bioclastic facies, (3) clayey facies and (4) tuffaceous facies. The ages of fossil corals vary from 6,588 ± 27 ya at 1.4 m below the PSL to 9,855 ± 42 ya at 22 m below PSL. Results of this study show that the minimum sea level, relative to the western Luzon coast, was about 25m below PSL when reef started about 9.9 ka. During 9.2-8.2 ka, reef accretion rate was as high as 13 m/ky. A reef backstepping that likely resulted from rapid sea-level rise took place about 8-7 ka. Sea level then rose to near PSL at about 6,862 ± 28 ya before the reef was uplifted by tectonics. The sea-level curve of Currimao is generally similar to that of the Western Australia coast but about 10 m higher than that of Tahiti at about 9.9 ka.


Geohazard of submarine landslides in the

northern South China Sea

S.-K. Hsu, K.-T. Chen, C.-Y. Ku, Y.-C. Yeh and C.-H. Tsai

Institute of Geophysics, National Central University, Chung-Li 32001, Taiwan

Abstract

Large and fast-moving turbidity currents can incise and erode continental margins and cause damage to artificial structures such as telecommunication cables on the seafloor. In this study, we show several sites of submarine landslides in the South China Sea. The submarine landslides may be triggered by earthquakes and then produce turbidity currents. Strong turbidity currents could jeopardize artificial construction at sea. For example, the 2006 Pingtung earthquake off SW Taiwan has triggered several submarine landslides and turbidity currents along the Kaoping canyon. In consequence, eleven submarine cables across the Kaoping canyon and Manila trench were broken in sequence from 1500 m to 4000 m deep. The full-scale calculation of the turbidity current velocities are calculated along the Kaoping canyon channel from the middle continental slope to the adjacent deep ocean. The results show that turbidity current velocities vary downstream at steps of 20 m/s, 3.7 m/s and 5.7 m/s which demonstrate a positive relationship between turbidity current velocities

and bathymetric slopes. In the northern South China Sea, the deposits of submarine landslides (mass transported deposits, MTD) are distributed at foots of continental margins, canyon channels or foots of seamounts. The MTD is generally displayed in terms of acoustic transparency in seismic profiles. As evidenced by the violent cable breaks happened in the case of the 2006 Pingtung earthquakes, the destructive power of turbidity current to underwater facilities is clearly underestimated.


East Luzon Trough: An inactive

subduction zone

A.M.F. Lagmay, R. Peña, M.A. Aurelio and M.L.G. Tejada

National Institute of Geological Sciences, University of the Philippines, Diliman, Quezon City, 1101 Philippines

Abstract

The East Luzon Trough is an intra-plate depression separated from the Philippine Trench by the E-W sinistral Polillo Fault. It is flanked to the east by the Benham Rise. Unlike the Philippine Trench, the East Luzon Trough is not a well-defined steep depression, which broadens further into a domal-like structure at about 16˚N latitude and disappears northeastward. At first glance, the East Luzon trough appears to be a continuation of the Philippine Trench, but being shallower and without a well-defined Wadati-Benioff Zone, it is believed to be a nascent subduction zone. The presence of an inactive accretionary prism to the west of the trough indicates the existence of an ancient subduction zone that has since become inactive. The collision of Benham Rise with the eastern side of northern Luzon led to the cessation of west-verging subduction of the West Philippine Basin and the flipping of subduction to the east along the Manila Trench. The present East Luzon Trough may be considered either as a rejuvenation of its ancient counterpart or as a clogged subduction zone. Nevertheless, several features of the East Luzon

Trough make it different from normal subduction zones.

• A review of the seismicity

along the East Luzon Trough reveals that it lacks the deep seismicity exhibited by subduction related to trenches.

• Absence of Late Neogene magmatism along the northern Sierra Madre Range related to subduction.

• Undeformed marine sedimentary carapace over crumpled sediments in the accretionary prism

• GPS measurements indicate that the West Philippine Basin in the region of Benham Rise moves in lockstep with Northern Luzon.

The accretion of Benham Rise to the eastern seaboard of northern Luzon has led to a reorganization of the boundary of the Philippine Sea Plate. In accordance with the tectonic map of Bird (2003), the tectonic deformation zone constituting northern Luzon has become a plate boundary zone with respect to the Eurasian Plate.


Re-visit the West Philippine Basin after 1/4

century

C.-S. Lee

Institute of Applied Geosciences, National Taiwan Ocean University, Keelung, 202 Taiwan

Abstract In mid-1980, the evolution of West Philippine Basin was one of the interesting, but also a controversial tectonic problem. This is due to: (1) the basin is one the largest marginal basin in the world, (2) the available data at that time showed that this is either a normal ocean basin or a back-arc basin, (3) the basin is remote from the major land area and is not so easy to conduct the marine research, and (4) the area is on the major track of the typhoon and the planned survey could be easily altered. For these reasons, the existing dataset is like a puzzle and the scientific debit is continuing, even up to today. In the last 1/4 century, particularly in the last 10 years, under the encouragement of United Nations Law of the Sea Convention, every neighboring country (including China, Japan, Philippine, Palau, and Taiwan) are entering the area for a 200 - 500 miles Continental Shelf Survey. Because of this new data, we are able to re-examine the evolution of the West Philippine Basin, particularly on the age, spreading rate, spreading direction and the reconstruction of the whole basin. Through this exercise, we found several interesting subjects, such as an episode of very fast

spreading rate and the over-lapping spreading centers in the north of West Philippine Basin, resembling to that of the East Pacific Rise today. The estimated age is very close to the 45 ma major change of the Pacific Plate motion. How are the plates evolved? What are the responses of the deep crust? Is this will impact our understanding of the modern plate tectonics? In our detail bathymetry survey, we also begin to realize that the Eocene West Philippine Basin is covered with a lot of today-inactive submarine volcanoes. Because of being at the 5000 – 6000 m deep sea environment, the sedimentation rate is probably very low; therefore, the volcanic summits are clearly exposed. The West Philippine Basin is one of the well-known big tuna fishing ground. Is the volcano taken by the tuna as their favorite dwelling? The deep-sea ROV surveys also show the thick manganese crust and a high density of the manganese nodules. Can the volcanic summits and manganese crust become our future deep resources? Our understanding of the deep sea is believed just at begin.


A summary of geochemical study on Taal

Lake system: Searching proxies for

detecting of Taal volcano eruption

H.-C. Li1, X. Xu2, D.-R. Wen1, N.-J. Wan1, T.-S. Kuo1, R.U. Solidum Jr.3, J. Sincioco3, P.K.B. Alanis3 and Nora Campita3

1Department of Earth Sciences, National Cheng-Kung University, Tainan, Taiwan 70101, ROC

2Department of Earth System Science, University of California, Irvine, CA 92697, USA

3Philippine Institute of Volcanology and Seismology, Quezon, Philippines 1101

Abstract

Taal Lake is located in Batangas Province of central Philippines (14°0.01'N, 120°59.1'E), with a surface area of 267 km2, a maximum depth of 176 m and an elevation of 3 m above sea level. The lake occupies the famous Taal Volcano system which consists of a 15×22-km prehistoric caldera. The 5-km-wide Taal Volcano Island which has 47 craters and 4 maars, lies in the north-central Taal Lake. With 34 recorded eruptions, Taal Volcano is one of the 16 monitored volcanoes by the Global Volcanism Network. During the past 3 years, we have conducted several trips to Taal and measured water temperatures at different stations and depths; collected water samples from Taal Lake, Main Crater Lake, springs, streams, wells and rains in the area; taken three gravity cores

from water depths of 15m and ~100m and one 64-m long drill core from the western shore of Taal Lake; and sampled a few outcrops of volcanic and lake deposits in the area. The measured water temperatures ranging from 26.5 to 29oC show that the thermal gradient of Taal was very weak during the late Novembers in 2006 and 2007, perhaps due to thermal input from the Taal Volcano Island and bottom of Taal Lake. The deepest part of Main Crater Lake is 61m with a constant water temperature of 31oC throughout the depth. We have analyzed geochemical properties including concentrations of Na, K, Mg, Ca, Al, Fe, Mn, Sr, Ba, Co, Ni, Cu, Zn, Pb, As, Ti, Cr, and Cd, and isotopic values of δD, δ

18O and δ

87Sr in the water samples. From these results, we conclude: (1) High concentrations of Na, K, Mg, Ca, Al, Fe, Mn in geothermal fluid at Taal are from input of volcanic water, dissolution of volcanic rocks, and incursion of seawater. However, the major ions are introduced by both seawater and geothermal inputs, so that they could not be used as index of volcanic activity. (2) Among trace and heavy metal elements, Fe, Mn, Cu and Zn may be used as indicators of volcanic activity. (3) Isotopic composition of Taal Lake bias from MWL indicates mixing of isotopically heavy geothermal fluid and isotopically light surface input. Therefore, heavier δ

18O values of the lake recorded in the lake


sediments may reflect increased geothermal fluid caused by volcanic activity. (4) δ

87Sr of Taal Lake reveals mixing of three end-members including surface runoff, geothermal fluid and seawater. The δ87Sr value of the geothermal fluid is about 1000ppm lower than that of the lake waters. Therefore, δ87Sr may be a good indicator of volcanic activity. Our most significant study is on a 120-cm long gravity core, Core TLS2, retrieved from 15-m water depth of Taal Lake. Sixteen AMS 14C dates were made on plant remains at different layers of the core, matching very well with the bomb 14C curve determined in tree rings. The distribution of the bomb 14C profile allows us to establish the chronology of the core which yields a constant sedimentation rate of 2.04cm/year spanning the past 60 years. Based on this chronology, living plants around Taal Lake may have a lower initial ∆14C (-30‰) compared to the Modern Standard. For this core, we have measured pore water content, weight loss by 0.5NHCl leaching, TOC, TON, δ

18O and δ

13C of TIC, δ13C of TOC and

δ15N of TON, and concentrations of Na, K, Mg, Ca, Fe, Mn, Sr, Ba, Cu, Zn, Pb, Li in the acid-leachable phase. The annual resolution δ

18O and δ13C records provide us detailed variations of the lake’s hydrological, biological and sedimentary history. Carbonate was precipitated in isotopic equilibrium with the lake water at ~30oC which is close to the measured water temperature. The δ18O and δ13C of TIC co-vary in the core, because of changes in surface water input and geothermal input. In general, when there is more input surface water, both δ18O

and δ13C of the lake goes lighter

due to dilution effect. The lake productivity at this time will be lower, and carbonate precipitation is less. When the lake experiences less surface water input and/or more evaporation, δ

18O and δ13C of

the lake goes heavier due to the hydrological balance and increased lake productivity. However, when the volcanic activity increases, significant amount of hydrothermal input and deep CO2 input will lead to increase of lake’s δ

18O and δ13C.

Both carbonate and organic carbon will decrease due to the influence of volcanic input. This situation was occurred around 1991. However, if a volcanic eruption causes significant amount of dead carbon from vegetation and organism in and around the lake, the lake’s δ13C will be depleted. At the time, the δ18O and δ

13C of the lake goes the opposite way. The 1965 eruption may be an example of such a case. With the detailed geochemical profiles of Core TLS2, we have found anomalies of high concentrations of Fe, Mn, Cu, K and heavy δ

18O and δ13C values of TIC

around 1991-1994 when the Taal volcano was active. These proxies may be considered as indicators of geochemically monitoring volcanic activity for long-term prediction.


Seismic monitoring at Taal Volcano in the

Philippines

C,-H. Lin1, R.U. Solidum, Jr.2, T.-M. Chang3 and B.C. Bautista2

1Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan

2Philippine Institute of Volcanology and Seismology, Quezon, Philippines

3National Center of Research on Earthquake Engineering, Taipei, Taiwan

Abstract

Since the Philippines is located in the “Ring of Fire”, there are more than 20 active volcanoes in the Philippines, such as Pinatubo, Mayon, Bulusan, Kanlaon and Taal. Among them, Taal volcano is only 60 km south to Manila, the capital of the Philippines. Thus, volcanic monitoring in Taal volcano becomes one of the major hazard works in the Philippines. In order to improve the understanding of general seismic characteristics at Taal volcano, we have deployed a seismic network to record volcanic earthquakes in the Taal volcanic area since Feb. 2008. This seismic network consists of seven short-period seismic stations with a sampling rate of 100 Hz. Among them, three stations on the volcanic island within the main Crater Lake have also added with long-period sensors for detecting any long-period tremors. Some micro-earthquakes have been detected from the continuous seismic data at the seismic network. The preliminary results show the seismicity at the Taal volcanic area

has been low recently, except some seismic swarms in Aug. and Sept. 2008. In addition to the continuation of seismic monitoring at Taal volcano, we will carefully examine the seismic data for finding any volcanic earthquakes or tremors.


Extreme climate events: Implications of El

Niño Southern Oscillation (ENSO) and

coping with its impacts in the Philippines

D.F. Ortega, F.D. Hilario and N.T. Servando

Philippine Atmospheric, Geophysical and Astronomical Services Administration, Department of Science and Technology, Quezon City, Philippines

Abstract

The highest rainfall variability in the Philippines was well documented and is greatly associated with the ENSO events which exhibited two phases, the El Niño (warm) and La Niña (cold). The El Niño conditions typically result in warm temperature anomalies and increased chance of below normal (drier) rainfall across the country. While the La Niña (cold) exhibits the reverse manifestations, usually increased rainfall and below normal temperature anomalies. The climate-related hazards brought by the extreme climate event in the country are in the form of flooding, landslides, drought and high temperatures. Changes in the usual climate pattern in the country as effected by the ENSO event are typically manifested in the monsoon activity, frequency of tropical cyclone and onset and termination of rain. Adverse impacts of ENSO events have been experienced in the country although beneficial ones were also assessed but to a lesser degree. To address these harmful

impacts of extreme events, mitigating factors are being initiated and continuously being improved by the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA), which include the seasonal climate forecast (SCF). This paper will illustrate the different impacts of ENSO events in the country, its monitoring, prediction and the ways of coping with the negative effects, identifying the challenge of bringing the understanding of the climate science that can be used in risk management.


Utilizing calcareous nannofossils as

paleoproductivity proxies in Sulu Sea core

sediments

A.M. Peleo-Alampay1, D.N. Tangunan1, F.P. Siringan2, R. Maneja2, J.L. Soria2 and Z. Liu3

1National Institute of Geological Sciences, College of Science, University of the Philippines, Diliman, Quezon City, Philippines 2Marine Science Institute, University of the Philippines, Diliman, Quezon City, Philippines

Abstract Calcareous nannoplanktons (coccolithophores) are marine haptophyte algae which thrive in the photic zone. These organisms are sensitive to changes in the temperature, water movement, salinity and chemistry of the surface waters of the ocean. Their calcareous skeletons are important contributors to the deep sea sediments, making them valuable recorders of variations in climate and sedimentation. This research aims to use calcareous nannofossils from core sediments to determine productivity changes in Sulu Sea through time.

This study investigates calcareous nannofossils from two sediment cores collected from the Sulu Sea in southwestern Philippines during Philex cruise Leg 2 onboard R/V Melville in December 2007. These two core sites from the southeastern Sulu Sea subbasin were chosen for their difference in productivity based on present-day chlorophyll data. The high

productivity site, Core MC10 is located closer to the coast of Zamboanga Peninsula at 8°23.10’N, 122°09.15’E and 4022m water depth while Core MC8 is located in the central portion of the sub-basin at 8°38.97’N, 121°31.83’E and 4492m water depth.

A distinct difference in the distribution of total nannofossils is apparent from the two cores studied. Nannofossil abundance was very low (1-16 x 106 liths/ gram sediment) to zero in most of the sample intervals in the top ~38 cm of Core MC 8-8. Abundances start to increase at 38-39 cm depth (1920±30 years). In the other core (MC 10-3), nannofossils are present throughout, ranging from 207-626 x 106 liths/ gram sediment, except for a sharp excursion at 25 cm depth yielding only 75 x 106 liths/ gram sediment. This may reflect differences in nannofossil productivity, consistent with chlorophyll data today. Sandy silt horizons in Core MC10-3 generally yielded more nannofossils.

The nannofossil assemblages from both cores are of relatively lower diversity typical of restricted marginal sea assemblages and dominated by three (3) species. This type of assemblage is prevalent on the eastern and western coasts of the South China Sea. In both cores, Gephyrocapsa oceanica, G. ericsonii and Florisphaera profunda have the highest abundances downcore. Umbilicosphaera sibogae and


Calcidiscus leptoporus, the next most abundant taxa in Core MC10-3 comprise less than 10% of the total nannofossils.

In Core MC 8-8, F. profunda abundance increases from the bottom of the core, reaching its peak at 44cm. Thereafter the counts start to decline until it reaches a steady low at 38 cm (1920 ± 30 years) continuing up to present time. The high F. profunda at the lower portion of the core is joined by equally high amounts of G. oceanica.

The overall calcareous nannofossil distribution in Core MC 10-3 shows a higher productivity environment. This is evidenced by the very good anticorrelation between F. profunda and G. oceanica counts downcore. G. oceanica represents the upper photic zone dwellers which are advantaged during upwelling events. The inverse relationship shown by these two species in this core is therefore validation of the use of F. profunda as a productivity signal indicator for this Sulu Sea core.

Two lobes of F. profunda increases can be seen from the MC 10-3 record: the first starting from the bottom ending at 25 cm and the next starting immediately after and tapering down to core top. These are interpreted as strong non-upwelling (low primary productivity) signals in Sulu Sea basin history. The older low productivity event is more significant since the other coccolithophorid indicators such as Umbilicosphaera sibogae and Helicosphaera carteri, high nutrient species, show significant decreases during this time. In both records, the non-productivity lobes are

interrupted by the sudden low at 25 cm (~1000-1100 years ago). This abrupt decrease which seemed to affect most of the coccolithophorid record in the basin (F. profunda included) can be interpreted as a dissolution signal owing to the shallowing of the CCD or an increase in the terrigenous input into the basin from erosional processes onland. This latter phenomenon can be seen to some extent in slightly higher Al2O3 and TiO2 and Y values together with total organic carbon.


Geochemical heterogeneity of volcanic

rocks from the Fragante Formation,

Northwest Panay, Central Philippines

A.dC. Perez1, D.V. Faustino-Eslava1, J.A.S. Gabo1, G.P. Yumul Jr.1,2, R.A. Tamayo Jr.1, K.L. Queaño1,3, C.B. Dimalanta1 and L.T. Armada1

1Rushurgent Working Group-Tectonics and Geodynamics Group, National Institute of Geological Sciences, College of Science, University of the Philippines, Diliman, Quezon City, Philippines

2Department of Science and Technology, Bicutan, Taguig City, Philippines 3Lands Geological Survey Division, Mines and Geosciences Bureau-DENR, North Avenue, Quezon City

Abstract

Following a major landslide incident in Guinsaugon, Southern Leyte in Central Philippines, the Mines and Geosciences Bureau-Department of Environment and Natural Resources (MGB-DENR) immediately set out to rationalize and speed up the implementation of the National Geohazards Mapping and Assessment Program. This program intends to adequately and comprehensively address and mitigate the possible effects or impacts of geological hazards, particularly landslide, flood and coastal erosion. The program has five components namely: (1) capacity building, 2) data acquisition, generation and

integration, (3) conduct of field survey, (4) generation of geohazard maps, and (5) conduct of information and education campaign (IEC), including installation of warning signages. To date, a total of 1348 municipalities have been assessed and 311, 1:50,000 landslide and flood susceptibility maps have been produced. The MGB has also assessed 2,383 line kilometers of coastal areas in the country. Although the efforts of the MGB-DENR and other government agencies have helped significantly in strengthening the country’s capacity in minimizing and mitigating the impacts of natural hazards, recent events still indicate some lapses particularly in the implementation by the local government of the recommendations set forth by the said agencies. These events include the landslides in Itogon, Benguet in northern Luzon and in Maco, Compostela Valley in eastern Mindanao, both events occurring in September 2008. More recently, a flashflood occurred in August 2009 in Botolan, Zambales that wiped out several communities. These examples clearly demonstrate the consequences when information and recommendations pertaining to disaster preparedness and mitigation are not taken seriously.


Geohazard mapping in the Philippines: The

Mines and Geosciences Bureau

experience

K.L. Queaño Lands Geological Survey Division, Mines and Geosciences Bureau-DENR, North Avenue, Quezon City

Abstract

Following a major landslide incident in Guinsaugon, Southern Leyte in Central Philippines, the Mines and Geosciences Bureau-Department of Environment and Natural Resources (MGB-DENR) immediately set out to rationalize and speed up the implementation of the National Geohazards Mapping and Assessment Program. This program intends to adequately and comprehensively address and mitigate the possible effects or impacts of geological hazards, particularly landslide, flood and coastal erosion. The program has five components namely: (1) capacity building, 2) data acquisition, generation and integration, (3) conduct of field survey, (4) generation of geohazard maps, and (5) conduct of information and education campaign (IEC), including installation of warning signages. To date, a total of 1348 municipalities have been assessed and 311, 1:50,000 landslide and flood susceptibility maps have been produced. The MGB has also assessed 2,383 line kilometers of coastal areas in the country.

Although the efforts of the MGB-DENR and other government agencies have helped significantly in strengthening the country’s capacity in minimizing and mitigating the impacts of natural hazards, recent events still indicate some lapses particularly in the implementation by the local government of the recommendations set forth by the said agencies. These events include the landslides in Itogon, Benguet in northern Luzon and in Maco, Compostela Valley in eastern Mindanao, both events occurring in September 2008. More recently, a flashflood occurred in August 2009 in Botolan, Zambales that wiped out several communities. These examples clearly demonstrate the consequences when information and recommendations pertaining to disaster preparedness and mitigation are not taken seriously.


Continuous monitoring along the Valley

Fault, the Philippines

R.-J. Rau1, Y.-P. Wen1, H.-K. Hung1, T.C. Bacolcol2, P.K.B. Alanis2 and R.M. Lumbang2

1Department of Earth Sciences, National Cheng Kung University, Tainan, Taiwan

2Philippine Institute of Volcanology and Seismology, PHIVOLCS Building, C.P. Garcia Avenue, University of the Philippines Campus, Diliman, Quezon City, Philippines

Abstract

Manila in the central segment of the Luzon arc, with a population of about 10 million, is subject to threatening from strong earthquakes on nearby faults and on more distant plate boundary faults. For the past 400 years Manila may have experienced more than six damaging earthquakes, but with no specific seismogenic sources identified. Paleo-seismic and neotectonic studies indicate that the 135-km long Valley Fault system on the northeastern edge of the Metro Manila is a right-lateral fault; however, the modern mode of deformation as well as its earthquake potential remains unclear. The purpose of this study is to estimate the earthquake potential of the Valley Fault system and its impact on the Manila metropolitan area by using continuous GPS observations along the fault. We have installed six dual-frequency GPS and six single-frequency GPS stations along the Valley Fault system since April,

2008. With the ~one year GPS continuous monitoring, we shall present the GPS results and the inferred mode of crustal deformation of the Valley Fault system in the meeting.


Late Holocene sediment facies and relative

sea-level changes along the Pampanga-

Angat delta, Northern Manila Bay

J.L.A. Soria1, F.P. Siringan2, Y. Yokoyama3 and K.S. Rodolfo4 1Marine Science Institute, University of the Philippines, Diliman, Quezon City, Philippines 1101 2Marine Science Institute, University of the Philippines, Diliman, Quezon City, Philippines 1101 3 Ocean Research Institute, University of Tokyo, 1-15-1 Minami-dai, Tokyo 164-8639 , Japan 4Department of Earth and Environmental Sciences, University of Illinois at Chicago, IL, USA

Abstract

Paleo-environmental changes along the delta complex on the bayhead of Manila Bay during the late Holocene were established using near-surface core stratigraphy. Mollusks and diatoms were used as proxies for salinity. Radiocarbon dates from peats and mollusks provided age control. Knowledge of previous changes may help in understanding present-day processes on the delta plain. The delta plain, occupied by wetlands on the bayhead of Manila Bay was formed mainly during a period when sea level was higher than present from about 5,500 to 1,400 yBP. Four parasequences were identified within an overall

shallowing upward sequence. The ages of the parasequences correspond to the timing of relative stillstands in the reconstructed regional fluctuations of sea level from rocky coastlines in the Philippines. Faulting also plays a role in delta evolution. Relative vertical motions across the Lubao Lineament, which could be as much as 3.5 meters over the past 1,500 yBP, helped maintain the position of the wetland and dryland boundary along the western margin of the delta plain. Aside from faulting, natural sediment compaction also contributes to subsidence. In recent years, however, anthropogenic activities such as excessive groundwater extraction have enhanced subsidence contributing greatly to delta-wide worsening floods.

79


Figure 1. 2001 Landsat image (band 4) of the Pampanga-Angat delta plain. The wetlands corresponding to the dark-colored areas in the lower delta plain are easily distinguished from the light-colored dry lands. The stratigraphy of selected cores taken across the delta plain is shown in Figure 2 (transect A) and Figure 3 (transect B).

Figure 2. Near-surface stratigraphy of selected cores along the Hagonoy-Bocaue coastal plain in Bulacan.


Figure 3. Near-surface stratigraphy of selected cores along the Lubao-Masantol coastal plain in Pampanga.

Acknowledgements This study is an offshoot of a DA BAR-funded project of F.P. Siringan and K.S. Rodolfo entitled “Net sea level change in the Pampanga Delta Region: Causes and Consequences”. Supplemental funding came from a thesis research grant 040415 TNSE of the University of the Philippines (UP)-Office of the Vice Chancellor for Research and Development to J.L.A. Soria. Field assistance and logistics were provided by the National Institute of Geological Sciences and Marine Science Institute of the University of the Philippines-Diliman.


Disaster risk management using sensors:

Early warning systems for landslides,

slope failures and debris flow

M.C. Talampas1, J.J. Marciano Jr.2, S.G. Catane3 and M.A.H. Zarco4

1Instrumentation Robotics and Control Laboratory, Institute of Electrical and Electronics Engineering, University of the Philippines Diliman, Quezon City 1101 2Instrumentation Robotics and Control Laboratory, Institute of Electrical and Electronics Engineering, University of the Philippines Diliman, Quezon City 1101 3National Institute of Geological Sciences, University of the Philippines Diliman, Quezon City 1101 4Geotechnical Engineering Group, Institute of Civil Engineering, University of the Philippines Diliman, Quezon City 1101

Abstract

A system consisting of alternation instrumentation for monitoring slope deformation and piezometric water level was designed and developed as an early warning system for landslides, slope failures and debris flows. The landslide monitoring system is composed of a sensor column array that is buried vertically underground. The sensor column consists of pipe segments each containing triaxial accelerometers for measuring tilt, and capacity type sensors for water content measurements. A modified

version of the Casagrande type piezometer is also integrated into the sensor column for purposes of measuring excess pore water pressure. Measurements taken in each segment are accessed via the Controller Area Network (CAN) communications protocol. The sensor column and piezometer are capable of communicating wirelessly with a central based station via a Wireless Fidelity (WIFI) link. Data is collected stored, process and displayed via the Python�based GUI on the base station. The sensor column and piezometer is tested on laboratory bench-scale landslide box. Tests are performed on slopes built from cohesionless material under steady state seepage conditions. A mathematical model assuming a Mohr-Coulomb elasto-plastic type material is developed. The resulting coupled unconfined fluid flow and limit equilibrium problem is solved using the finite element method. Results of the experiments show close agreement with deformation patterns and failure mechanism predicted by the model.


Crustal growth and mantle source

evolution in the Philippines

M.L.G. Tejada

National Institute of Geological Sciences, University of the Philippines, Diliman, Quezon City, Philippines 1101

Abstract

The present location of the Philippine archipelago along a complex boundary among three plates, Eurasian, Philippine, and Indo-Australian, makes it a natural laboratory for studying and understanding the early stages of continental growth. Prior to this present stage, the archipelago may have undergone previous histories of multiple arc and back-arc basin generation, crustal accretion, as well as tectonic displacements from a more southerly location. The arc’s tectonic evolution from its birth to its present stage of development is reflected in the available data from combined studies of igneous rocks of Cretaceous to recent ages, which also reveal a record of the changing or evolving mantle source regions that accompanies the arc’s evolution.

The results of the geochemical study of ~100 Ma basement rocks of the eastern margins of Luzon, the largest island, suggest that an Indian MORB-type mantle may have underlain the archipelago since the Cretaceous. This mantle signature continues to be tapped by the younger volcanic products and plutonic rocks emplaced along the

eastern side of the island. The western margin of the island is currently being modified by active subduction and collision with the Eurasian margin. As a result, the geochemical signatures of igneous rocks suggest that local processes tend to modify the nature of this pre-existing mantle as a result of changing tectonic setting and subduction recycling of materials from previously rifted fragment of the Eurasian margin.


Low temperature thermochronology of

Buruanga Peninsula, Panay Island, Central

Philippines

M. Walia1, T.F. Yang1, T.K. Liu1, L.S. Teng1, W.M. Yuan2, G.P. Yumul Jr. 3,4 and C.B. Dimalanta4

1Department of Geosciences, National Taiwan University, Taipei, Taiwan

2China University of Geosciences, Beijing, 100083, China

3Department of Science and Technology, Bicutan, Taguig, Metro Manila


Abstract

Buruanga Peninsula forms the westernmost part of Panay Island, Central Philippines and is part of the Palawan continental fragment, which was formerly attached to the south-eastern China. It acted as the leading edge of the moving continental fragment and collided with Philippine Belt followed by convergence beneath the latter. Getting information about the timing of the collision event is crucial in understanding the evolution of the archipelago. Samples collected from Buruanga Peninsula were dated using fission track (FT) and 40Ar/39Ar techniques to constrain the timing of the collision of Philippines arc with Palawan continental block. First time reported fission track dates of zircon and apatite are combined with 40Ar/39Ar dates of biotite and

hornblende to obtain ages over a range of closure temperatures of about 110°C to 510±50°C. The age data suggest two consecutive tectonic events at 9-12 Ma and 16-17 Ma that resulted in the exhumation of rocks. This exhumation may be related to the collision events. Due to different closure temperatures of the FT and 40Ar/39Ar systems it is possible to recognize both Cenozoic and Mesozoic tectonic events in the area. Furthermore, these ages can be used to define the intrusion time of the diorite besides giving an estimate of the timing of arc-continent collision in Panay Island.


Middle Pliocene El Niño events recorded in

fossil corals of the Tartaro Formation,

Province of Bulacan, Central Luzon,

Philippines

T. Watanabe1, A. Suzuki2, T. Kase3, S. Minobe1, Y. Maac-Aguilar4, K. Kameo5, K. Minoshima2, R. Wani3 and H. Kawahata6

1Hokkaido University, Japan

2Agency of Industrial Science and Technology, Japan

3National Science Museum, Japan

4Mines and Geosciences Bureau, Department of Environment and Natural Resources, Philippines

5Chiba University, Japan

6University of Tokyo, Japan

Abstract

In the study of future climates, the Middle Pliocene Warm Period (PWP) can be an analog for the impending global warming. This period is characterized by significantly warm climate with high global surface temperature ranging from 3° to 5°C higher than today. Attested by many paleoclimate archives and several climate model studies, this time slice is rather preferred in simulating future climate because many conditions that prevailed during that time matches well with modern values. Also, continents then were virtually in the same geographic positions and the living flora and fauna are still extant. One thing that remains

controversial in previous records of the PWP is the role of El Niño-Southern Oscillation (ENSO) in the greenhouse warming due to lack of information about seasonal to inter-annual variability of sea surface water in low latitude regions.

In the Philippines, well-preserved Middle Pliocene (3.5-3.8 Ma) coral fossils discovered from Madlum River, central Luzon provided 35-years coral oxygen isotopic evidences with monthly resolutions. These fossils were collected from muddy sand layers of the Tartaro Formation exposed along the Madlum River in the vicinity of barrios Tartaro and Sibul, San Miguel, province of Bulacan. Based from associated fossil contents and sedimentary features, the corals are inferred to be part of a coral mound deposited in an intertidal to subtidal setting. The Porites coral blocks from Tartaro were sliced into slabs and X-rayed to observe the density of growth banding. Powdered microsamples from each band were processed for isotope analysis. Results of these analyses showed several significant attenuations of seasonal amplitude in the 18O/16O ratios of PWP coral record which were also detected in recent corals during modern El Niño events. These findings suggest that east-western movements of the Western Pacific Warm Pool (WPWP) were active that caused ENSO events during the warm period. The average sea surface temperatures in Luzon during that


time records to about 2-4°C higher than today. Results of analysis also indicate that the corals are not calcified during ENSO periods.


Plate boundary geometry of the northern

Manila Trench: Inference from seismic and

bathymetric data

Y.-C. Yeh and S.-K. Hsu

Institute of Geophysics, National Central University, Chung-Li, Taiwan

Abstract

The Manila Trench marks as the plate boundary that western Philippine Sea plate has overrided the oceanic lithosphere of the South China Sea (SCS). The northern part of the SCS crust was created between magnetic isochron C17 (i.e. 37 Ma) and isochron C10 (i.e. 28 Ma) and is terminated in the north by a fossil transform boundary, the Luzon-Ryuku transform plate boundary (LRTPB). Due to a deeper basement topography, the crust north of LRTPB could be an older oceanic crust or a rifted continental crust. In short, the age of the northern SCS is gradually older from south to north. The new collected multichannel seismic data demonstrate more intense normal faulting north of LRTPB than south of LRTPB. In addition, outer rise normal faulting mechanism earthquakes extraordinary clustered northeastern of the LRTPB

around 120。10’ E, 20。 30’ N which are evidenced by the new seismic profiles and detailed bathymetry data. Moreover, the intersection of the LRTPB and the accretionary prism shows indentation bathymetry which implies the southeastern end of the LRTPB

could be one of the key role that cause the change of the Manila Trench orientation from NE-SW to NW-SE.


A dislocation model for crustal

deformation along the fault system in

Luzon

S.-B. Yu1, Y.-J. Hsu1, C.-C. Yang2, T. Bacolcol3 and R.U. Solidum3 1Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan 2Institute of Geophysics, National Central University, Taoyuan, Taiwan 3Philippine Institute of Volcanology and Seismology, Quezon City, Philippines

Abstract

The Philippine Fault system is a result of the oblique convergence between the Philippine Sea plate and the Sundaland Block/Eurasia plate. It is a left-lateral strike slip fault that trends in N 30°- 40°W and transects the Philippine archipelago from the northwest corner of Luzon to the southeast end of Mindanao for about 1200 km. For studying crustal deformation along the Philippine Fault system, eight GPS surveys were conducted from 1996 to 2008 in the Luzon region through a joint effort by the Institute of Earth Sciences, Academia Sinica and the Philippine Institute of Volcanology and Seismology. Summing up the 12-year survey-mode GPS data in the Luzon region and continuous GPS data in Taiwan, along with other 14 IGS sites in the Asia-Pacific region, we use the GAMIT/GLOBK software to calculate the coordinates of each site and obtain the GPS time series. Then

the interseismic velocity field in the Luzon region is derived by utilizing QOCA software. The velocity field in the Luzon region gradually increases from south to north with respect to the Eurasia plate. The velocity vectors to the west of the Philippine Fault range from 44 to 59 mm/yr, while that to the east of the fault are from 59 to 79 mm/yr. The azimuths of velocity vectors range from 285° to 314°. This indicates that there is significant internal deformation in the Luzon Arc. Based on the GPS observed 1996-2008 velocity field in the Luzon region and using the interseismic crustal deformation model of Matsu’ura et al. (1986), we invert for the fault geometry parameters and fault slip rates of the Philippine Fault. The fault dip and width are fixed to be 89° and 30 km, respectively. The inverted results indicate that the average left-lateral strike-slip rate of southern segment is 20.6 mm/yr, and northern segment is 32 mm/yr. The block motion is 31 (95% confidence interval, 23~35) mm/yr with azimuth of 332° (323°~341°). Because the density and aperture of the current GPS array are insufficient, it is not able to successfully detect crustal deformation of the entire fault system and strain partition between the branch faults.


Climate change adaptation in the

Philippine context

G.P. Yumul Jr.1, 2, C.B. Dimalanta1, N.T. Servando3 and N.A. Cruz3


2Department of Science and Technology, Bicutan, Taguig City, Philippines

4Philippine Atmospheric, Geophysical and Astronomical Services Administration, Department of Science and Technology, PAGASA Science Garden, BIR Road, Quezon City, Philippines

Abstract

Climate change, involving both natural climate variability and anthropogenic global warming, has been a major concern of the world today. Negotiations within the United Nations Framework Convention on Climate Change is ongoing. It is hoped that by December 2009, substantial agreements would be reached in the Copenhagen UNFCCC negotiations. Within the context of the Bali Action Plan involving the four pillars of: a) Mitigation; b) Adaptation; c) Technology Transfer and d) Financing, it is hoped that the world will be better prepared by 2012 when the Kyoto Protocol ends.

It is in this light that the different climate change-related initiatives in the Philippines would be looked into. Considering the archipelagic

nature of the Philippines and being a very minor emitter of greenhouse gases, adaptation is the Government’s national policy. Measures involving both disaster risk management and climate change adaptation are being implemented especially in the community level. This is with the end in view of mainstreaming both disaster risk management and climate change adaptation in a changing climate regime.

The progress that are being achieved, the issues and challenges recognized and possible solutions to gaps encountered will be presented

.


Paleoclimatic implications of Late

Cretaceous planktonic foraminifera from

the mid-latitude ODP holes 758A, 761B and

762C, Indian Ocean

M.A. Zepeda1,2

1Department of Earth and Materials Science and Engineering, Mapua Institute of Technology, Intramuros, Manila, Philippines 2Paleontolgy Unit/PETROLAB, Lands Geological Survey Division, Mines and Geosciences Bureau, North Avenue, Diliman, Quezon City, Philippines

Abstract

A detailed biostratigraphic and statistical analysis of faunal assemblage of Ocean Drilling Program (ODP) sites from the mid-latitude showed great variability and instability in the paleoclimatic conditions in the Indian Ocean during the late Cretaceous (late Santonian to Maastrichtian). Faunal composition, species diversity and equitability, species distribution, ratios of climatic index species and paleoclimatic curves were used to deduce paleoclimatic conditions. The paleoclimatic curves constructed showed particularly striking and similar trends for most of the sites studied. Three paleoclimatic intervals namely, Interval 1 (late Santonian to early Campanian), Interval 2 (late Campanian to middle Maastrichtian), and Interval 3 (late Maastrichtian) can be identified in the paleoclimatic curves. Interval 1

(late Santonian to early Campanian) suggests a relatively warm paleoclimate as evidenced by: an abundance of Tethyan and warm indices; high species diversity and equitability; and high positive values in the paleoclimatic curves. Interval 2 (late Campanian to middle Maastrichtian) indicates warm and cool fluctuations as depicted by: the mixture of Tethyan and Austral species within the Transitional realm; varying abundances of warm and cool water species; fluctuations in the species diversity, equitability and climatic curve values, with a pronounced negative peak during the latest Campanian. This peak represents the coolest interval of the late Santonian to Maastrichtian as reflected by the preponderance of cool indices; low species diversity and equitability and high negative values in the paleoclimatic curve. Interval 3 (late Maastrichtian) marked another warm interval due to: a shift in the dominance of cool indices to warm indices; high diversity and equitability; and high positive values in the paleoclimatic curve. Such results imply that paleoclimatic conditions in the Indian Ocean during the late Santonian to Maastrichtian are very unstable. This instability could be attributed to an interplay of several geologic and tectonic events (i.e. break of the southern Gondwanaland continents, seafloor spreading and subsidence between Antarctica, Australia and New


Zealand; northward drift of South America from the Antarctic Peninsula; global rise in sea level during the middle Campanian; and opening, re-emergence and closure of gateways) which occurred in the Indian Ocean before, during and after the identified paleoclimatic intervals. To summarize, the paleoclimatic conditions from the late Santonian to early Campanian period of the sites under study, fluctuated from warm-Tethyan (Holes 761B and 762C) during the late Santonian; warm-Transitional (Holes 758A, 761B and 762C) during early Campanian; Transitional with varying Tethyan and Austral influences (Holes 758A, 761B and 762C) during the late Campanian to middle Maastrichtian; Tethys with Transitional influence (Holes 758A and 761B) and Transitional with pronounced Tethyan influence (Hole 762C) during the late Maastrichtian.

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Relative vertical deformations in La Union, Philippines revealed by Holocene coral microatolls …rwg-tag.bravehost.com/Conferences/RPTaiwan_Abstracts.pdf · 2009. 9. 9. · EARTH