Seismic Hazard Analysis for the Philippines 1988

8/8/2019 Seismic Hazard Analysis for the Philippines 1988

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Natural Hazards 1 (1988) 27-44 . 27 1988 by Kluw er Academic Publishers.

S e i sm ic H azard An a lys i s f or Th e Ph i l ip p in esS . S . S UManila Observatory, P.O. Box 1231, Manila, Philippines D404(Received: 2 June 1987; rev ised: 24 Augus t 1987)Ab s t r a c t . T w o s a m p l e p r o b a b i l i s ti c h a z a r d m a p s f o r t h e P h i l i p p i n e R e g i o n a r e c o m p i le d . I n t h e s e a r e s h o w nv a r i o u s le v e ls o f e x p e c t ed h o r i z o n t a l g r o u n d a c c e l e r a ti o n f o r s o m e g i v e n a n n u a l p r o b a b i l i ty o f e x c e e d e nc e ,n a m e l y , f o r 0 . 1 % a . p . e , a n d f o r 0 . 0 1 % a . p . e . S u c h h a z a r d m a p s a r e n e e d e d b y s t r u c t u r a l e n g i n e e r s f o rc o m p i l i n g s e is m i c z o n i n g m a p s . T h e h a z a r d m a p s a r e d e r i v e d f r o m s o u r c e - z o n e o r s e i sm o g e n i c m a p s ,w h i c h , in t u r n , a r e c o m p i l e d f r o m s e i s m o g r a p h ic , g eo l og i c, a n d g e o t e c t o n ic d a t a . M u c h w e i g h t i s p u t o ng e o t e c to n i c d a t a r a t h e r t h a n o n s e i s m o g r a p h i c d a t a . T h e f o r m e r l e n d s s u p p o r t t o e x t r a p o l a t i n g t o m u c hl o n g e r p e r io d s o f ' e x p o s u r e t i m e ' o r l o n g e r p e r i o d s o f r e c u r r e n ce .Key words . H aza rd ana l y s i s , r is k ana l y s i s , s e is m i c zon i ng , p robab i l i s t i c .

1. Introduct ionSe i sm o l o g i s t s m a k e a d i s t i n c t i o n b e t w e e n s e i sm i c h a z a r d a n d s e ism i c r isk . Se i sm i ch a z a r d is d e f in e d a s t h e p r o b a b i l i ty o f o c c u r r e n c e o f a s p ec if ie d le v el o f g r o u n dsh a k i n g w i t h i n a sp e c i fi e d p e r i o d o f t i m e . Se i sm i c r isk , o n t h e o t h e r h a n d , i s d e f i n e da s t h e e x p e c t e d ( o r p r o b a b l e ) b u i l d i n g d a m a g e ( o r l o ss o f o r i n j u r y t o l if e) , g i v e n t h ep r o b a b i l it y t h a t s p e ci fi ed le v el s o f g r o u n d s h a k i n g o c c u r .

2 . B a c k g r o u n dS t r u c t u r a l e n g i n e e r s in t h e P h i l ip p i n e s , i n d e s i g n i n g b u i ld i n g s a c c o r d i n g t o s o m e c o d e ,su c h a s t h e U n i f i e d B u i l d i n g C o d e , w o u l d l ik e t o s e e t h e e x i s t en c e o f a s e ism i c h a z a r dm a p . S u c h a m a p w o u l d e n a b l e t h e m t o a s s i g n a s e is m i c z o n e n u m b e r o r s e is m i c s a f e t yf a c t o r t o e a c h b u i l d i n g t h e y d e s ig n d e p e n d i n g u p o n i ts s it e l o c a t i o n a n y w h e r e in t h ePh i l i p p i n e s .

T w o k i n d s o f q u a s i - h a z a rd m a p s h a v e h e r e to f o r e b e en c o m p i l e d a n d u s e d b u t t h e yc o n t a i n i n h e r e n t s h o r t c o m i n g s t h a t a s t r ic t ly p r o b a b i l is t ic h a z a r d m a p a v o i d s . T h ef ir s t is a m a p b a s e d s o le l y o n r e c o r d e d s e is m i c it y . T h i s k i n d o f m a p f o c u s e s o ne p i c e n t e r c o n c e n t r a t i o n s a n d f a il s t o g e n e r a l i z e t o l i k e l y a r e a s o f f u t u r e s e i sm i c i ty .F u r t h e r m o r e , i t f a il s t o s p e c if y t h e t y p e o f h a z a r d o u s g r o u n d m o t i o n . T h e s e c o n d t y p eo f m a p is b a se d o n r e c o r d e d m a x i m u m i n te n s i ty o f g r o u n d m o t i o n b u t s till f a il s t og e n e r al iz e t o f u t u r e a r e a s o f h a z a r d o u s g r o u n d s h a k i n g . B e s id e s , s u c h a m a p t e n d s t oo v e r s t a t e t h e h a z a r d i n r e g i o n s w h e r e t h e f r e q u e n c y o f o c c u r r e n c e i s q u i t e l o wc o m p a r e d t o o t h e r m o r e s e is m i c a ll y a c t iv e a r e as . A s t ri c tl y p r o b a b i l is t i c h a z a r d m a p ,i t w i ll b e s e en , a v o i d s a ll t h es e s h o r t c o m i n g s o f t h e t w o p r e v i o u s t y p e s o f m a p s .


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28 s.s . SuThe first set of probabilistic hazard maps for the Philippines was introduced by this

author in September of 1979 as a result of a pilot project of the Southeast AsiaSeismological Program undertaken by the UNDP in cooperation with the UNESCO.It was envisioned that eventually a more detailed and definitive set of maps would becompiled. As a continuance of this work, seismic source zones were revised in 1985(Su, 1985) and again in 1986. This last revision is incorporated into this paper andcontains some radical changes from the 1985 version (which will be pointed out lateron) and thus paved the way for finalizing the hazard maps that are presented here.

3. MethodThe probabilistic approach to seismic hazard analysis that is adopted here, as it wasin the U.S. and Canada, follows the methodology of Cornell (1968), and of Algermissenet a l . (1982). According to this approach, one takes into account three distinct regions:first, the source or seismogenic region; second, the site where hazard is estimated; andthird, the intervening region between the source and the site. The biggest and mostdifficult step is the detailed specification of the source zones. The resulting map ofsource zones has to be based not only on seismographic (instrumental) and macroseis-mic data (such as felt intensity) but also on geology and geotectonics. It will be seenlater that the map of the source zones and the final hazard maps will bear strikingsimilarities.

Epicenters in seismogenic regions are treated statistically both spatially and tem-porally: that is, they are given a random distribution both in space and in time.

In the spatial distr ibution of epicenters, one assumes that within a given source orfault line, an earthquake is equally likely to occur at one point as at any other point.Thus, the probability density is a constant, i.e., evenly distributed within the source.To find the cumulative probability one integrates over the entire source area or theentire fault length.

In the temporal distribution of earthquakes, the Poisson model has been chosenhere, as is frequently done, because o f its simplicity in concept and in hazard estimation.Other models, such as the Markov model, could have been used.

In addition to the random distribution of epicenters in space and time within theseismogenic region, there is also the magnitude-frequency distribution or the magnitudeprobability function which is statistically derived from earthquake frequency data.This distribution gives the probability of an earthquake falling within a certainmagnitude range.

4. Scope of the Data for This StudyThe earthquake data that provided the basis for the present hazard analysis cover aperiod of twenty years: from 1964 to 1983. They include epicenters from latitude 0 to lat itude 24 , and f rom longitude 116 to 130E. Despite this short period of theseismographic database, it is the backing of the geologic and geotectonic data that


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SEISMIC HAZARDANALYSIS FOR THE PHILIPPINES 29lends support to extrapolations to future 'exposure times' of the order of 500 yearsor more.

5 . S o u r c e Z o n e s5 . 1 . P r o c e d u r eThe procedure consists of two parts. The first part is a rough delineation of the sourcezone boundaries based on seismographic data. The second part is a more refined ordetailed delineation of the zone boundaries by recourse to geotectonic data.

5.2. P a r t ISeismographic data (epicenter, focal depth, magnitude) include those of 3872 earth-quakes in the Philippine region from 1964 to 1983. These are shown in the epicentralmaps of Figures 1 and 2, taken from Su (1985). From this database, two contour mapswere prepared: one for energy flux and one for the b-values of the magnitude-frequency relation (Figures 3 and 4). F rom the overlay of these four maps a generalrough-approximation map of the seismogenic zones was prepared. This is shown inFigure 5 (taken from Su, 1985).

5.3. P a r t HBased on published literature on the geology and tectonics of the Philippines, thezones of Part I are re-defined and subdivided. As mentioned above (in 'background'),the 1985 version of the source zones (Su, 1985) has been revised. The revised versionsare shown in Figures 6 and 7. The main feature of the revision is that faults (Zones9 to 18) are now treated separately from nonfaults (Zones 1 to 8). Other details of therevision will be described as each zone is taken up.5.3.1. Z o n e 1 . Zone 1, the East Luzon subduction zone, has a different subdivisionfrom its 1985 version. The former 1D, the transform fault, is now Zone 17. Thepresent 1D lies east of 1C. IA and 1C are at present seismically much more active than1B and 1D (Lewis and Hayes, 1983). Focal mechanisms for Zone 1 are predominantlyof the thrust type while those of Zone 4 (which is contiguous to 1A and 1C) aregenerally of the strike-slip type (Lewis and Hayes, 1983, citing Cardwell e t a l . , 1980;Seno and Kurita, 1978; Fitch, 1972; Katsumata and Sykes, 1969). Negative free-airgravity anomaly in 1A and 1C is interpreted as indicating crustal downwarping anda precursor to rupture (Lewis and Hayes, 1983).High seismicity, focal mechanism solutions, and seismic sounding profiles showRecent (Pleistocene) to Present underthrust ing in 1C (Cardwell e t a l ., 1980). However,the absence of active volcanism, and the lack o f a well-defined Benioff zone and ofearthquakes deeper than 200 km show that current subduction is young.


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S E I S M I C H A Z A R D A N A L Y S I S F O R T H E P H I L I P P I N E S 33116 118 e 120

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34

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F i g . 5 . P r e l i m i n a r y s e i s m o g e n i e z o n e s .5.3.2. Z o n e s 2 a n d 3 . The transcurrent Philippine Fault, which was the former Zone3 of the 1985 version, is now Zone 9. The present Zone 2 and Zone 3 comprise thePhilippine Trench (2B and 3B) and its Quaternary volcanic forearc (2A and 3A)(Divis, 1980). Nor th latitude 12 separates Zone 2 from Zone 3. Zone 2 has a poorlydeveloped Benioff zone that dips westward to a depth of about 100 km (Cardwell e ta l . , 1980). Zone 3 has a better developed Benioff zone that extends to a depth of about200 km south of Samar, as shown by intermediate earthquakes. Considerably deeperearthquakes are found east of Mindanao and southward to Talaud Island.

The relative shallowness of the dipping lithosphere in Zones 2 and 3, together withthe lack of significant Quaternary volcanism in Eastern Mindanao and Samar (Lewisand Hayes, 1983), coupled with the evidence from seismic reflection profiles showing


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SEISMIC HAZARD ANALYSIS FOR THE PHILIPPINES 35

-25SOURCE ZONES Nos. I fo B

(FAULTS FINITE-WIDTH SOURCE ZONESARE IN A SEPARATE MAP)

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Fig. 6. Source zones Nos. 1 to 8 (faults = Finite- Width Source Zone s are in a Separate Map).

no w e l l -de ve lope d a c c r e t iona r y p r i sm in the f o r e a r c re g ion ( H a m i l ton , 1979 ; Ka r ig ,1975 ; Ka r ig a nd S ha r m a n , 1975) s t r ong ly sugge s t t ha t t he p r e se n t subdu c t ion e p i sodem a y ha ve be gun on ly in Qua te r na r y t im e , a nd i s s t i l l p r opa ga t ing sou thwa r d to thee a st o f T a l a u d a n d H a l m a h e r a i sl an d s ( C a r d w e ll e t a l . , 1980 ; M ur ph y , 1973).5.3.3. Z o n e 4 . Zo ne 4 is the dou b le f o r e a r c a s soc ia te d wi th the M a n i l a Tr e nc h wh ic hlie s we s t o f Luz o n ( Le wis a nd Ha ye s , 1983 ; C a r dw e l l e t a l . , 1980; Ka r ig , 1973) . 4B an d4D a r e the ' i nne r' vo lc a n ic f o r e a r c wh i le 4A a n d 4C m a ke u p the ' ou te r ' nonvo lc a n icforearc .


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3 6 s . s . s u

2 0P HIL IP P IN E F A ULT S

( A S F I N I T E -W I D T H S O U R C E Z O N E S )

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af ter Phi lippine Bu reau of M ines, 1981.1 2 0I 1 I I I I [ I I 1 2 5I I i I I , , , ,

Fig. 7. Philippine faults (as Finite-W idth Sou rce Zon es). (After Philippine Burea u of Mines, 1981.)

S e i s m i c i t y i s m u c h h i g h e r i n 4 C t h a n i n 4 D ; a l s o r e l a t iv e l y h i g h e r in 4 A t h a n i n 4 B .4 B a n d 4 D a r e m a r k e d b y p r e s e n t ly a c ti v e v o l c a n o e s a n d Q u a t e r n a r y c o n e s ( C a rd w e l le t a l . , 1980) .

F o c a l m e c h a n i s m s o l ut io n s o f e a r th q u a k e s i n th e N o r t h L u z o n R i d g e (4 B ) a r ep r e d o m i n a n t l y o f t h e s t ri k e -s l ip t y p e S o m e o f t h e s e a r e l e ft - la t e ra l a n d s o m e a r er i g h t - l a t e r a l .5 .3 .4 . Z o n e 5 . Z o n e 5 is t he M a n i l a T r e n c h . I t h a s a B e n i o f f z o n e t h a t d i p s 4 0 e a s t w a r d . T h e d i p a n g l e i n c re a s e s to a l m o s t 9 0 a s o n e p r o c e e d s s o u t h w a r d t o M a n i l a


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SEISMIC HAZARD ANALYSIS FOR THE PHILIPPINES 37Bay. The Benioff zone extends to a depth of about 200 km (Hayes and Lewis, 1984).South of latitude 13 , the Manila Trench changes its trend from north-south tonorthwest-southeast, and curves towards the Mindoro Strait. This is believed to bedue to the collision of the subducting lithosphere with the North-Palawan (Calamian)micro-continental block (Lewis and Hayes, 1984).

Seismicity is lower in the trench itself (5A) than in the forearc (5B). Present dayvolcanic activity in the forearc is an indication of convergence between the SouthChina Sea Plate and Luzon (Hamburger e t a l . , 1983). Convergence rate is estimatedat about 10 to 20ram per year (Hayes and Lewis, 1984).5.3.5. Z o n e 6 . Zone 6 comprises the Negros Trench and the Sulu Trench (6A) andtheir volcanic forearcs (6B). Seismicity is relatively low in this subduction zone. Thereare relatively few shallow earthquakes of the thrust type in the Negros Trench.However, seismic reflection profiles show sediments being underthrusted to the eastalong the Negros Trench (Cardwell e t a l . , 1980; Hamilton, 1979). There is no clearlydefined Benioff zone; but there are intermediate earthquakes suggesting that thelithosphere is being subducted eastward (Cardwell e t a l . , 1980).

The Sulu Ridge (6B) parallels the Palawan Ridge which has no seismicity at all. TheSulu Ridge is associated with a subduction that occurred from late Cenozoic toPleistocene (Cardwell e t a l . , 1980).

The Negros Trench and the Sulu Trench are considered to be one tectonic unit(Divis, 1980). Kanlaon is an active volcano on Negros Island.5.3.6. Z o n e s 7 a n d 8 . The former 7A of the 1985 version is now subdivided into 7A(the Cotabato Trench) and 7B (the forearc to the east-northeast) in the presentversion. The former 7B is now Zone 8 which is subdivided into 8A (western anddeeper part of the dipping lithosphere) and 8B (eastern and shallower part of thelithosphere).

Zone 7 and Zone 8 cover the same geographic area. Zone 7 is the shallowerstructure. Zone 8 is the deeper structure which is the northern extension of theMolucca Sea Plate. This plate had buckled and dips both westward and eastward. Itssurface expression is the Sangihe Ridge. Zone 8 is the westward dipping portion ofthe Molucca Sea Plate. It is characterized by intermediate earthquakes (8B) and deepearthquakes (8A), as far down as 680 km (Cardwell e t a l . , 1980).5.3.7. F a u l t s ( Z o n e s 9 t o 18 ) .. Following the division of Philippine faults into trans-current, normal, and thrust faults according to the Philippine Bureau of Mines (1981),three transcurrent, two normal, and three thrust faults are considered very probablyseismically active. In addit ion, two transform faults are added. Thus, a total of tenfaults are selected as source zones.

In the context of the methodology commonly in use, there are two possible waysof viewing faults. One is to regard them as line sources; the other is to treat them asfinite-width sources. In regarding them as line sources, as for example in McGuire's


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38 s.S. su'Frisk ' program (1978), additional fault parameters such as rupture length have to beconsidered. In treating them as finite-width sources, their parameters are no differentfrom those of Zones 1 to 8 earlier described.

A test was made to compare the results of treating a fault as a line source and asa finite-width source. The results agree very closely. Thus, as a measure of convenience,faults are considered finite-width sources and included in the same computat ion usedfor Zones 1 to 8.5.3.8. Tr a n s c u r r e n t F a u l t s ( Zo n e s 9 t o 1 1 ) . Zone 9 is the transcurrent Philippine Faultthat extends over 1200 km from Lingayen Gul f in Luzon to the Davao Gul f south o fMindanao (Allen, 1962). Krause (1966) suggests that it extends south of Mindanaoalong a submarine scarp into the Talaud Islands. Movement is left-lateral strike-slip(Ranneft et a l . , 1960; Allen, 1962; Rutland, 1968). Morante and Allen (1974) studiedthe geomorphic effects of the 1973 Ragay Gulf earthquake and found a left-lateraldisplacement of 3.2 m near the Tayabas Is thmus o f Southern Luzon. This was laterconfirmed by an earthquake focal mechanism solution of Lewis and Hayes (1983).Other earthquakes (1937, 1973, 1975) studied by Acharya and Aggarwal (1980) havefocal mechanisms that can be correlated with the left-lateral movement along thefault. Geomorphic features in other parts of Luzon, Masbate, and Leyte likewiseindicate left-lateral movements (Allen, 1962).

Eight other large earthquakes, namely, of 1893, 1901, 1911, 1924, 1937, 1941, 1947,1948, had their epicenters along or very near the fault zone (Rowlett and Kelleher,1976). Thus seismicity gives evidence that the Philippine Fault is presently active, atleast in some parts. Additional evidence from geology, such as the sharpness of faultscarps, disrupted soil horizons and stream offsets confirmed that the fault has beenactive since Quaternary time (Lewis and Hayes, 1983). Certain surface deformationsnear and along the fault have been associated with historical earthquakes such asthose of 1869, 1879, and 1893 (Allen, 1962).

In Central Luzon, the fault divides the mountainous Cordillera Central in the northfrom the lowlands of the Central Valley Basin in the south.Past episodes of intense activity along the fault have been placed in Late-Mioceneand Post-Pliocene (Rutland, 1968).

Zone 10 is another transcurrent fault, the Tablas Lineament that is traceable forabout 350 km from Western Panay northward through Tablas Island to the TayabasIsthmus (Phil. Bureau of Mines, 1981). Allen (1962) pointed out that it might beconjugate to the Philippine Fault and thus, right-lateral.

Zone 11 is the third transcurrent fault, called the Mindanao Fault. It is traceablefor about 400 km. from the Davao Gul f northwestward to the Sindangan Valley ofNorthern Zamboanga (Phil. Bureau of Mines, 1981; Gervacio, 1964). On its north-west end there is a possibility it might be a high-angle thrust; but it is believed to bemore probably a transcurrent fault.

There is a fourth transcurrent fault, the Ulugan Fault in the Island of Palawan, butit is considered inactive because its seismicity is practically nil.


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SEISMIC HAZARD ANALYSIS FOR THE PHILIPPINES 395.3.9. N o r m a l F a u l ts ( Z o n e s 1 2 a n d 1 3) . Z o n e 12 is a n o r m a l f a u l t o n t h e n o r t h e a s ts id e o f M i n d o r o . Z o n e 13 is t h e C o t a b a t o N o r m a l F a u l t o n t h e s o u t h w e s t f la n k o fM i n d a n a o . A n o t h e r n o r m a l f a u lt , th e M a r i k i n a F a u l t l o c a te d e a s t o f M a n i la , is n o ti n c l u d e d h e r e b e c a u se i t i s c o n s i d e r e d i n a c t i v e .5.3.10. Thrus t Faul t s (Zones 14 to 16) . Z o n e 14 is t h e Z a m b a l e s T h r u s t F a u l t o n t h ew e s t e r n p a r t o f L u z o n , t h a t i s, n o r t h o f M a n i l a B a y . Z o n e 15 is a th r u s t f a u l t o n t h es o u t h w e s t si de o f M i n d o r o . Z o n e 16 is a t h r u s t f a u l t o n t h e w e s t e r n fl a n k o f P a n a yI s l a n d .

T h e s e r ie s o f t h r u s t f a u l t s a l o n g Z a m b o a n g a P e n i n s u l a a r e n o t i n c l u d e d h e r eb e c a u se t h e y a r e c o n s i d e r e d t o b e i n a c t i v e .5.3.11. Tra n s f o rm F a u l t s ( Zo n e s 1 7 a n d 1 8 ) . Z o n e 17 is a t r a n s f o r m f a u l t a t a b o u tn o r t h l a t i tu d e 1 5.5 d e g re e s, l in k i n g t h e E a s t L u z o n T r e n c h ( Z o n e 1 ) w i t h t h e P h i l ip -p i n e T r e n c h ( Z o n e s 2 a n d 3) ( L ew i s a n d H a y e s , 1 9 8 3 ; H a m b u r g e r et al . , 1983).C o n f i r m a t o r y e v i d e n ce c o n s i s t o f c o n c e n t r a t e d s e is m i c it y , s h a r p b a t h y m e t r i c lo w , a n df o c al m e c h a n i s m s o l u t io n s o f t w o e a r t h q u a k e s ( S e no a n d K u r i t a , 1 9 78 ; C a r d w e l l e tal. , 1980).

Z o n e 18 is a t r a n s f o r m f a u l t r u n n i n g a l o n g t h e V e r d e i s la n d p a s s a g e n o r t h o fM i n d o r o . S u p p o s e d l y i t l in k s t h e M a n i l a T r e n c h a n d t h e N e g r o s T r e n c h . T h i si n t e r p r e t a t i o n f i n d s c o n f i r m a t i o n i n th e i n t e n s e o r c o n c e n t r a t e d s e is m i c it y n o r t h o fM i n d o r o ( W o l f e a n d Se lf , 1 98 3) . I ts s e n se o f m o v e m e n t is b e l ie v e d t o b e l e f t -l a t e r a l( L e wi s a n d H a y e s , 1 98 4) .

6 . A t t e n u a t i o nT o c h a r a c t e ri z e t h e a t t e n u a t i o n p r o p e r t ie s o f th e i n t e rv e n i n g r e g i o n b e t w e e n t h eso u r c e a n d t h e s i te , t h e a t t e n u a t i o n c o e f f i c ie n t s o f Su (1 98 0) we r e a d o p t e d f o r t h ee n t i r e Ph i li p p i n e s , t h a t is , w i t h o u t d i s t i n c t i o n o f so u r c e z o n e s . Va l e n z u e l a et al . (1985)m a d e a n e f f o r t t o d e r iv e a t t e n u a t i o n c o e f fi c ie n ts f o r e a c h o f th e S o u r c e Z o n e s 1 t o 8 .H o w e v e r , s i nc e th e i r r es u l ts w e r e s o m e w h a t i n c o m p l e t e a n d t e n t at i v e , t h e y ar e n o ti n c o r p o r a t e d i n t h i s s t u d y .

7 . H a z a r d E v a l u a t i o n a t t h e S i t e7.1. TheoryI n a c c o r d a n c e w i t h t h e t h e o r y g i v e n b y A l g e r m i s s e n et al . (1982), F ( a ) i s d e f i n e d a st h e p r o b a b i l i t y t h a t t h e a c c e l e r a t i o n ( A) w i l l n o t e x c e e d a c e r t a i n l e v e l ( a ) , g i v e n a ne a r t h q u a k e w i th m a g n i t u d e ( M ) g r e a te r t h a n a c e r ta i n th r e s h o l d M ( m i n i m u m ) .1 - F(a ) is t h e n t h e c o r r e s p o n d i n g p r o b a b i l i t y o f e x c ee d e n c e a n d t y p i c a l l y h a s t h es h a p e o f a n e x p ( - a ) c u r ve . I f v is t h e a n n u a l r a t e o f e v e n t s w i t h M > M ( m i n i m u m ) ,t h e n v ( 1 - F ( a ) ) is th e a n n u a l n u m b e r o f ex c e e d e n ce n , t h a t i s, a n n u a l n u m b e r o f


14/18

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e v e n t s w i t h a c c e l e r a t i o n e x c e e d i n g th e l e v e l a . 1 /n is t h e n t h e re t u r n p e r i o d , R ( y ) , f o rt h e a c c e l e r a ti o n l ev e l a . T h e q u a n t i t y e x p [ - t v ( l - F ( a) )] o r e x p [ - t / R ( y ) ] o re x p [ - tn ] e x p r es s es a p r o b a b i l i t y o f n o n e x c e e d e n c e f o r t h e e x p o s u r e t i m e t , a n d t h isi s ca l led F ( a , t ) . T h e q u a n t i t y 1 - F ( a , t ) is th e c o r r e s p o n d i n g p r o b a b i l i t y o f e x c e e d-e n c e. T h e a b o v e r e a s o n i n g a s s u m e s t h a t t h e F ( a ) ' s f o l l o w a P o i ss o n d i s t ri b u t i o n , t h a ti s, t h e y a r e i n d e p e n d e n t o f o n e a n o t h e r f o r s u ff ic i e n tl y l a r g e a.

I n t h e p r o g r a m , t h e e x p e c t e d a n n u a l n u m b e r o f ex c e e d e n c e n is fi rs t c a l c u l a te d f r o mt h e p a r a m e t e r s o f t h e m a g n i t u d e - f r e q u e n c y r e l a t i o n w h i c h a r e s t at is t ic a ll y d e r i v e d


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S E I S M I C H A Z/~ .R D A N A L Y S I S F O R T H E P H I L I P P I N E S 41

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120 12s t3o ]I | I * ! I I * i i

In tens i t ies (g) a t 0 .0001 r isk ( risk = An nu al Pro babi l i ty o f Exceedence) .

f r o m r e c o r d e d s e is m i c i ty . T h i s is c a l c u l a t e d f o r d i f f e r e n t d e s i g n a t e d l e v e ls o f a c c e l e r a t i o no r i n t e n s i t y . I n o t h e r w o r d s , f o r e a c h a c c e l e r a t i o n l e v el a , t h e r e is a n n(a) w h i c h i s t h ee x p e c t e d n u m b e r o f e v e n ts p e r y e a r t h a t e x c e e d th e s p e c if ie d a c ce l e r a ti o n . F r o m t h is ,t h e q u a n t i t y 1 - e x p ( - n ) , w h i c h is t h e a n n u a l p r o b a b i l i t y o f e x c e e d e n c e , i s e v a l u a t e d .T h i s i s t h e s a m e e x p r e s s i o n f o r 1 - F(a, t ) , s h o w n a b o v e , w i t h t h e e x p o s u r e t i m et = 1 . C o n v e r s e l y , b y p r e - s p e c if y i n g d i f f er e n t d e g r e es o f a n n u a l p r o b a b i l i t y o f e x c e e d -e n c e , t h e c o r r e s p o n d i n g e x p e c t e d a c c e l e r a t i o n o r i n t e n s i t y m a y b e e v a l u a t e d b yi n t e r p o l a t i o n .


16/18

4 2 S . S . S U7 . 2 . R e s u l t sT w o h a z a r d m a p s a r e s h o w n i n F i g u r e s 8 a n d 9 . F i g u r e 8 s h o w s e x p e c t e d a c c e le r a t i o nc o n t o u r s ( i n % g ) f o r a n n u a l p r o b a b i l i t y o f e x c e e d e n c e 0 . 0 0 1; F i g u r e 9 f o r a n n u a lp r o b a b i l it y o f e x c ee d e n c e 0 . 0 0 0 1 . I n a c c o r d a n c e w i t h t h e e x p r e s si o n :1 - F ( a , t ) = 1 - e x p ( - n t ) w h i c h i s t h e p r o b a b i l it y o f e x c e e d e n c e i n t y e a r s, t h ea c c e l e r a t io n v a l u e s i n th e 0. 0 01 m a p s h o u l d r e a c h a 5 % p r o b a b i l i t y o f e x c e e d e n c e i n5 0 y e a r s; 1 0 % p r o b a b i l i t y i n 1 0 0 y e a rs . T h e a c c e l e r a t i o n v a l u e s i n t h e 0 . 0 0 0 1 m a ps h o u l d r e a c h a 5% p r o b a b i l it y o f e x c e e d e n c e i n 5 0 0 y e ar s ; 1 0 % p r o b a b i l i t y i n 1 0 0 0y e a r s .

O n e c a n d e t e c t s o m e s i m i la r it y b e t w e e n t h e s h a p e o f th e c o n t o u r s o f F i g u r e s 8 a n d9 a n d t h e s h a p e o f th e b o u n d a r i e s o f t h e s o u r c e z o n e s i n F i g u r e s 6 a n d 7 . T h i s i sg e n e r a l l y e x p e c t e d . S t a t i s t ic a l u n c e r t a i n t y i n t h e a c c e l e r a t i o n v a l u e s i n th e h a z a r dm a p s ( F i gu r e s 8 a n d 9 ) h a v e b e e n s t u d ie d b y t h o s e w h o u s e t h e C o r n e l l m e t h o d .A c c e p t a b l e v a l u e s a r e p l u s o r m i n u s 2 0 t o 2 5 % o f t h e c o n t o u r v a l u e s .

R e f e r e n c e sAch ar y a , H . K . an d A g g awa l , Y . P . : 1 9 80 , Se i smic i ty an d t ec to n ic s o f th e Ph i l ip p in e Is l an d s, J. Geophys.

R es . 85, 3239-3250.Algermissen, S. T., Perkins, D . M ., Th enh aus, P . C., H ans on, S. L., and Bender, B . L.: 1982, Prob abilist ic

e s t ima te s o f ma x imu m a cce le r a t io n an d v e lo c i ty in r o ck in th e co n t ig u o u s U n i t ed S ta t e s , U .S . G eo l .Su r v ey O p en - f il e R e p o r t 8 2 -1 0 33 .Al l en , C . R . : 1 9 62 , C i r cu m- Pac i f i c f au l t in g in th e P h i l ip p in e - T a iwan r eg io n , J . Geophys. Res. 67, 4795~

4812.B a lce , G . R . , M ag p an tay , A . L . , an d Zan o r i a , A . S . : 1 9 7 9 , Tec to n ic scen a r io s o f t h e Ph i l ip p in es an d

n o r t h e r n I n d o n e s i a n r e g io n , P a p e r p r es e n te d a t t h e E S C A P C C O P - I O C M e e t i n g o n t h e G e o l o g y a n dTec to n ic s o f Eas t e r n I n d o n es ia , B an d u n g , 9 - 1 4 Ju ly .B a lce , G . R . , En c in a , R . Y . , Mo m o n g a n , A . L . , an d L a r a , E . D . : 1 9 80 , Ge o lo g y o f th e B ag u io d i s t ri c t an d

i t s imp l i ca t io n s o n th e t ec to n ic d ev e lo p me n t o f Lu zo n C en t r a l C o r d i l l e r a , Geol. Paleonto l . Southe as t As ia21, 265-287.

Balce , G. R . and Ga rcia , L . C . : 1985 , Seism otectonics of the Phi l ipp ines , in S o u t h ea s t A s i a A s s o c i a t io n o fS e i s mo l o g y a n d E a r t h q u a ke E n g in eer in g , S er i e s o n S e i s mo l o g y , Vol. 4, pp. 809-843.B en Av r ah a m, J . : 1 9 7 8, Th e e v o lu t io n o f mar g in a l b as in s an d ad jacen t sh elves in ea s t an d so u th eas t As ia ,Tec t o n o p h ys i c s 45, 269-288.

B o win , C . , Lu , R . S ., Lee , C . S ., an d Sch o u ten , H . : 1 9 78 , P la t e co n v e r g en ce an d acc r e t io n in th e Ta iw an -Lu zo n r eg io n , Bul l . Am. Assoc. Pet ro l . Geol . 62, 1645-1672.

C ar d we l l , R . K . , I sack s , B . L . , an d Kar ig , D . E . : 1 9 8 0 , Th e sp a t i al d i s t r ib u t io n o f ea r th q u ak es , f o ca lmec h an i sm so lu t io n s , an d su b d u c ted l i t h o sp h e r e in th e Ph i l ip p in es an d n o r th eas t e r n I n d o n es ian i sl an d s,in Th e Tec t o n i c a n d Geol og ic E vo l u t i o n o f t h e S o u t h ea s t A s i a n S ea s a n d I s la n d s ( A G U m o n o g . 2 3 ) , V o l .1, pp. 1-36.

Chr is t ian , L . B . : 1964, Pos t -o l igocen e tec ton ic h is tory of the Ca gay an B asin , Ph i l ipp ines , Phil . Geologist18, 114-147.Corne l l , C . A . : 1968 , Eng ineer ing se ismic r isk analysis , Bul l . Sei s . Soc. Am. 58, 1583-1606.De B o er , J . , Od o m , L . A . , R ag lan d , P . C . , Sn id e r, F . G . , an d T i l f o r d , N . R . : 1 9 8 0 , Th e B a taan Or o g en :

eastward subduct ion , tec ton ic ro ta t ions and volcan ism in Western Pacif ic (Phi l ipp ines) , Tec t o n o p h ys i c s63, 251-282.Div is , A . F. : 1980 , Th e pet ro lo gy and tec ton ics of recent vo lcan ism in the cen tra l Ph i l ipp ine is lands, in T h e

Tec t o n i c a n d Geolo g ic E vo l u t i o n o f S o u t h ea s t A s i a n S ea s a n d l s l a n d s ( AGU mo n o g . 2 3 ) , Vo l . 1 , p p .127-144.


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S E IS M I C H A Z A R D A N A L Y S I S F O R T H E P H I L IP P IN E S 43Div i s , A . F . : 1 9 83 , Th e g eo lo g y an d g eo ch emis t r y o f Ph i lip p in e p o r p h y r y co p p e r d ep o s i t s , i n The Tectonic

and Geologic Evolution o f Southeast Asian Seas and Islands (AGU monog. 27) , Vol . 2 , pp . 173-216 .Fi tch , T . and M olnar , P. : 1970 . Fo cal mechan ism along incl ined ear thqu ake zones in the Indonesia Phi lip -

p ine reg ion , J. Geophys. Res. 75, 1431-1444.Fi tch , T . : 1972 , Pla te convergence , t ranscu rren t faul ts , a nd in terna l defo rma t ion ad jac ent to South eastAsia and the Western Pacif ic , J. Geophys. Res. 7 7 , 4 4 3 ~4 4 6 0 .Fu l l e r, M . et al.: 1 9 8 3 . Pa leo mag n e t i sm o f Lu zo n , i n The Tectonic and Geologic Evolution of Southeast

Asian Seas and Islands ( A G U mo n o g . 2 7 ) , Vo l . 2, p p . 7 9 -9 5 .Ger v ac io , F . C . : 1 9 6 4, A S tu d y o f th e Tec to n ic s o f t h e Ph i l ip p in e Ar ch ip e lag o , Phil. Geologist 20, 51-75.Ham b u r g e r , M . W . , C a r d we l l, R . K . , an d I sack s, B . L .: 1 9 8 3 , Se i smo tec to n ic s o f t h e No r th e r n Ph i l ip p in e

Island arc, in The Tectonic and Geologic Evolution of Southeast Asian Seas and Islands ( A G U m o n o g .27), Vol. 2, pp. 1-22.Ham i l to n , W. : 1 9 79 , Tec to n ic s o f th e I n d o n es ian r eg io n , U .S . Geo l . Su r v ey Pr o f. P ap e r 1 0 78 .Haw k in s , J . W. an d Ev an s , C . A . : 1 9 8 3 . Geo lo g y o f th e Zamb a le s R an g e , Lu zo n , Ph i l ip p in e I s l an d s :

ophio l i tes der ived f rom an is land arc-back arc basin pai r , in The Tectonic and Geologic Evolution ofSoutheast Asian Seas and lslands (AGU monog. 27) , Vol . 2 . pp . 95-123 .

Hay es , D . E . an d Lu d wig , W. J .: 1 9 6 7 , Th e M an i l a T r en ch an d Wes t Lu zo n Tr o u g h : I I . Gr av i ty an dmag n e t i c measu r emen t s , Deep Sea Res. 14, 545-569.

Haye s, D. E. and Lewis , S. D. : 1984 , A geoph ysica l s tudy o f the M ani la Tre nch , L uzon , Phi l ipp ines: I .c rusta l s t ructure , g rav i ty , and reg ional tec ton ic evolu t ion , J. Geophys. Res. 89, 9171-9195.

Ka r ig , D . E. : 1973 , Pla te conve rgenc e between the Phi l ipp ines and the Ryu kyu Is lands, Marine Geol. 14,153-168.

Ka r ig , D . E. : 1975 , Basin genesis in the Phi l ipp ine Sea , In i t ia l Repo r t o f the De ep Sea Dr i l l ing Pro jec t 31 ,pp. 857-879.

Kar ig , D . E .: 1 9 8 3 , Acc r e t ed t e r r an es in th e n o r th e r n p a r t o f t h e Ph i l ip p in e Ar ch ip e lag o , Tectonics 2,211-236.

Kar ig , D . E . an d S h a r man I l i , G . F . : 1 9 7 5. Su b d u c t io n an d acc r e t io n in tr en ch es , Bull. Geol. Soe. Am. 86 ,377-389.Kar ig , D . E . an d W ag eman , J . M . : 1 9 7 5 , S t r u c tu r e an d sed imen t d i s tr ib u t io n in th e n o r th wes t co r n e r o fthe West Phi l ipp ine Basin , In i t ia l Repor t o f the Deep-Sea Dr i l l ing Pro jec t 31 , pp . 615-620 .

Ka t su m a ta , M. an d Sy k es , L . R . : 1 9 6 9 , Se ismic ity an d t ec to n ic s o f t h e W es t Paci fi c: I zu - M ar ia n a -C a r o l i n e a n d R y u k y u - T a i w a n r e gi o ns , J. Geophys. Res. 74, 5923-5948.

Kr au se , D . C . : 1 9 6 6 , Tec to n ic s , mar in e g eo lo g y , an d b a th y m et r y o f t h e C e leb es Sea - S u lu Sea r eg io n , Bull.Geol. Soc. Am. 77, 813-832.Lewis , S . D . an d Hay es , D . E . : 1 9 83 , Th e t ec to n ic s o f n o r th w ar d p r o p ag a t in g su b d u c t io n a lo n g Eas te r nLuzon , Phi l ipp ine I slands, in The Tectonic and Geologic Evolution of Southeast Asian Seas and Islands( A G U m o n o g . 2 7 ) , Vo l . 2 , p p . 5 7 -7 8 .

Lewis , S. D. and H ayes, D. E . : 1984 , A geop hysica l s tudy of the M ani la T rench , Luzo n , Phi lippines: 2 .f o r ea r c b as in s t r u c tu ra l an d s t r a t ig r ap h ic ev o lu t io n , J . Geophys. Res. 89, 9196-9214.Lu d wig , W. J ., Hay es , D . E . , an d Er v in g , J . I. : 1 9 6 7 , Th e M an i l a T r en ch an d W es t Lu zo n T r o u g h : I .B a th y met r y an d sed imen t d i s t r ib u t io n , Deep-Sea Res. 14, 533-544.Lu d wig , W. J . : 1 9 70 , Th e M an i l a T r en ch an d W es t Lu zo n T r o u g h : I I I . Se ismic r e f r ac tio n measu r emen t s ,Deep-Sea Res. 17, 553-571.M cCaff rey , R . , Silver , E . A . , and R ai t t , R . W.: 1980 , Crus ta l s t ructure o f the M oluc ca Sea co l l i s ion zone,Indonesia , in The Tectonic and Geologic Evolution o f Southeast Asian Seas and Islands ( A G U m o n o g . 2 3 ),Vol. 1, pp. 161-178.

M cGu i r e , R . K . : 1 9 7 6, Fo r t r an co m p u te r p r o g r am f o r se ismic r isk an a ly s is , U .S . G eo l . Su r v ey Op en - f i l eRepor t 76-67 .M cGu i r e , R . K . : 1 9 7 8 , FR I SK : co m p u te r p r o g r am f o r se ismic r isk an a ly s is u s in g f au lt s a s ea r th q u ak esources , U.S. G eol . Survey Open-f ile R epo r t 78-1007.Mc Ken z ie , D . P . an d M o r g an , W. J . : 1 9 69 , Ev o lu t io n o f t ri p l e ju n c t io n s , Nature 224, 125-133.

M i tch e l l , A . H . G . , H er n an d ez , F . , an d d e l a C r u z , A . P .: 1 9 8 5 , C en o zo ic ev o lu t io n o f t h e Ph i l ip p in eAr ch ip e lag o , J. Southeast Asian Earth Sei. 1.

M o o r e , G . F . : 1 9 8 1 , Ge o lo g y o f So u th e r n M in d an ao , Ph i l ip p in es (ab s t rac t ) , EOS Trans. AGU 62, 1086.M oore , G . F . and Si lver , E . A. : 1983 , Col l i s ion process in the nor thern M oluc ca Sea , in The Tectonic and

Geologic Evolution o f Southeast Asian Seas and Islands ( A G U mo n o g . 2 7 ) , Vo l . 2 , p p . 3 6 0 - 37 2 .


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4 4 s . s . s uMo ran te , E . M. and A l len , C . R .: 1974 , D is p lacem en t on the Ph i l ipp ine f au l t du r ing the Ra gay G ul fE ar thqu ake o f 17 M arch 1973 ( abs tr ac t ), Abs tr . Geol . Soc. Am. 5, 744-745.Murauch i , S . et al.: 1973, S truc ture o f the Sulu Sea and the Celebe s Sea, J . Geophys. Res. 78, 3437-3447.Mu rphy , R . E . : 1973 , T he M an i la T ren ch-W es t T a iwan Fo ldbe l t : A f l ipped s ubduc t ion zone , Bull . Geol .

S o c . Ma l a ys . 6, 27-42.Ph i l ipp ine Bureau o f M ines : 1963 , Geological M a p o f the Philippines.Phi l ipp ine Bureau o f Mines : 1981 , Geology and Minera l Resources o f the Phi l ipp ines , Vol. 1.Rannef t , T . S . N. , Hopkins , R. M. J r . , Froel ich , A. J . , and Gwinn, J . W. : 1960, Reconnaissance geologyand oi l possibil it ies of Min dan ao, Bul l . Am. Assoc. Pet ro l . Geol . 44 , 529-568.Row let t , H. and Kell iher , J . : 1976, Evo lving seismic and tec tonic pat terns a long the wes tern marg in of thePhil ippine Sea Plate , J. Geophys. Res. 81, 3518-3524.Ru t land , R . W . R . : 1968 , A tec ton ic s tudy o f pa r t o f the Ph i l ipp ine Fau l t zone , Quar t . J . Geol. Soc. Lond on123, 293-325.Schweller , W . J . and K ar ig , D . E . : 1982 , E m placem en t o f the Z am bales o ph io l i t e in to the W es t L uzo nM a r g i n , Bul l . Am. Assoc. Pet ro l . Geol .Schweller, W. J. et al .: 1983 , Or ig ina l s e t t ing and em placem en t h i s to ry o f the Z am bales oph io l i te , L uzon ,Phil ippines, f rom s trat igraphic e vidence, in Th e Tec t o n i c a n d Geo lo g ic E vo l u t io n o f S o u t h ea s t A s i a n S ea s

a n d I s la n d s (AGU monog. 27) , Vol . 2 , pp . 124-138.Seno , T . and Ku r i t a , K . : 1978 , Foca l m echan is m and tec ton ics in the T a iwan-P h i l ipp ine r eg ion , J . P h ys .E a r t h 26, $249-$263.

Su, S . S . : 1980, At tenu at io n o f in tens i ty with epice ntral d is tance in the Phil ippines , Bul l . Sei s . Soc. Am. 70,1287-1291.Su, S. S.: 1985, Seismic sou rce zon es o f the Philippines, in S o u t h ea s t A s i a A s s o c i a t i o n o f S e i s mo l o g y a n d

Ear thqua ke Engineer ing , Ser ies on Sei smo logy, Vol. 4, pp. 793-808.S u k a m t o , R . et al.: 1979 , T he geo logy and tec ton ics o f Ha lm ahera and i ts s u r round ings ( abs tr ac t) , P r o c .

M ee t i n g o n t h e Geo l o g y a n d Tec t o n i c s o f E a s t e r n Ind o nesi a.T ay lo r , B . and H ayes , D . E . : 1980, T he t ec ton ic evo lu t ion o f the Sou th Ch ina Sea bas in , in Th e Tec t o n i c

a n d Geo l og ic E vo l u t i o n o f S o u t h ea s t A s i a n S ea s a n d I s la n d s (AGU monog. 23) , Vol . 1 , pp . 89-104.T ay lo r , B . and H ayes , D . E . : 1983 , Or ig in and h i s to ry o f the Sou th C h ina Sea bas in , in Th e Tec t o n i c a n dGeo lo g ic E vo l u t i o n o f S o u t h ea s t A s i a n S ea s a n d I s la n d s (A GU m on og . 27 ) , Vo l . 2 , pp . 23 -56 .Uyeda , S . and M cCabe , R . : 1983 , A pos s ib le m echan is m o f ep i s od ic s p read ing o f the Ph i l ipp ine Sea , inAccre t ion Tec tonics in the Circum -Paci f i c Reg ions M. Has h im oto and S . Uy eda ( eds.) (T okyo) , pp .291-306.

Valenzuela , R. G. , Garc ia , L . C. , and A mb ubu yog , G. F . : 1985, Assessmen t of seismic in tens i ty of Phi l ip-pine his tor ical ear thquakes , in S o u t h ea s t A s i a A s s o c i a t i o n o f S e i s mo l o g y a n d E a r t h q u a ke E n g in eer in g ,S er i e s o n S e i s mo l o g y , Vol. 4, pp. 743-792.Weissel , J . K . : 1980, Eviden ce for Eocen e oceanic crus t in the Celebes bas in , in The Tectonic an d GeologicE vo l u t io n o f S o u t h ea s t A s i a n S ea s a n d I s la n d s (A GU m on og . 23 ), Vo l . 1, pp . 37 -47 .

Wolfe , J . A. : 1981, Phi l ippine geochronology, J. Geol . Soc. Phi l ippines 35, 1-30.Wolfe , J . A. and Self , S . : 1983, S tructural l ineaments and neogene volcanism in southwes tern Luzon, inTh e Tec t o n & a n d Geo lo g ic E vo l u t i o n o f S o u t h ea s t A s i a n S ea s a n d I s l a n d s (A G U m onog . 27 ) , Vo l . 2, pp .157-172.

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Seismic Hazard Analysis for the Philippines 1988