Estimation of Local Site Effects by the Multiple Transfer ...mynces.org/download/2018/ProceedingMNCES2018/76_Zaw Lin Kya… · Case Study: Yogyakarta City, Java Zaw Lin Kyaw1, Junji

The Second Myanmar National Conference on Earth Sciences (MNCES, 2018) 981

November 29-30, 2018, Hinthada University, Hinthada, Myanmar

1Lecturer, Dr., Department of Geology, Meiktila University 2Professor, Dr., Department of Urban Management, Kyoto University 3Lecturer, Department of Geology, Meiktila University

Estimation of Local Site Effects by the Multiple Transfer Function Method,

Case Study: Yogyakarta City, Java

Zaw Lin Kyaw1, Junji Kiyono

2 and May Thet Aye

3

Abstract

Indonesia, one of the countries in the world, is located in highly seismic area. It is surrounded by the Circum Pacific Belts. Yogyakarta city is situated at the southern part of the volcanic

arc island of central Java. The city and the province accordingly are prone to geohazards

especially earthquakes as well as geological problems. The 27th May 2006 earthquake hit the

Provinces of Yogyakarta, with its epicenter estimated at about 30 km south of Bantul district

in Yogyakarta Province. The magnitude scale reached Mw 6.3. Subsequently, about 750

aftershocks have been reported, with the largest intensity recorded at 5.2. Based on latest

available information, more than 5,700 precious human lives have already been lost. About

9,000 individuals are estimated to have been injured, though estimates vary up to 20,000

individuals. The objective of this research is to simulate the prominent periods of the seismic

motions in the Yogyakarta city by utilizing the multiple transfer function model. There are 12

bore-hole sites in the research area to calculate the VS30 values. The period values are varying

from 0.44 to 0.50 sec and 0.45 to 0.67 sec. The period map illustrates that significant amplification occurs in the research area. This research indicates that the periods are useful

parameter for characterization of ground motion simulation. Finally, the period map of the

transfer function method will relate to the damage area of the research city for the future

earthquake.

Keywords: Site effects, Multiple transfer function method, Periods and Central Java

Introduction

Java Trench, deeps submarine depression, in the eastern Indian Ocean that extends

some 2,000 miles (3,200 km) in a NW-SE arc along the southwestern and southern

Indonesian archipelago. It is located about 190 miles (305 km) off the southwestern coasts of

the islands of Sumatra and Java. Its slopes exceed 10° and descend to a maximum depth of

6.75 km, the deepest point in the Indian Ocean. It constitutes an extensive subduction zone,

where the seafloor of the tectonic plate to the west is being forced under the stable plate to the

east. It is an active volcanic and seismic zone.

Recent earthquake disasters in Indonesia, such as the 2006 Yogyakarta (6.3 Mw, 5749

deaths) and the 2009 Padang (7.5 Mw, over 1100 deaths) earthquakes, highlight the urgent

need for measures to reduce earthquake fatalities. Yogyakarta-Bantul area has been seriously

damaged by Yogyakarta earthquake on 27th

May 2006. The severity of past earthquake

damage is considered to be closely related to ground structure the vibration characteristics of

the ground to enable appropriate seismic design of structures and to devise effective

earthquake disaster prevention systems in the region (USGS, 2006).

Location of the Study Area

The Yogyakarta city is located at the southern part of the volcanic arc of Java Island. It

is only about 30 km from the Merapi volcano to the north which reaches the elevation of 2911

m above sea level and the most active volcano in Indonesia. It is about 10 km from the coast

of the Indian Ocean to the south. It is situated at the center of the Yogyakarta Special

Province and in the middle part of Yogyakarta depression. This depression was actually a

graben which was filled by Merapi laharic flows. It can be defined as NE-SW elongated

depression zone and spans for 20 km wide and 40 km length from the Yogyakarta city to the

982 The Second Myanmar National Conference on Earth Sciences (MNCES, 2018)


Indian Ocean. It is initiated by extrusions of two major volcanic centers; Kulon Progo

Mountains and Southern Mountains, during Cenozoic and was formed as a volcano-tectonic

depression since Oligo-Miocene or earlier (Karnawati et al., 2006).

The Yogyakarta Special Province has four major regencies and Yogyakarta city which

is located between Latitude 7˚ 24ʹ S - 8˚ 00ʹ S and Longitude 110˚ 001ʹ E - 110˚ 36ʹ E as

shown in Figure 1. The area of the city of Yogyakarta is 32.5 square kilometres (12.5 square

miles). The study area is about 480 square kilometers (Fig. 1).

Figure (1). Location map of the research area

Problem Statements

Four districts in the Yogyakarta province (Sleman, Bantul, Gunung and Kulon Progo)

and the central Java province (Magelang, Boyolali, Klaten and Purworejo) were affected. The

earthquake reduced hundreds of buildings to rubble, disrupted essential services and damaged

roads and airport runways. The high population density living in close proximity to the

epicenter explains these high numbers. In addition, the volcano Merapi, close to the epicenter,

increased activity following the earthquake.

The Yogyakarta-Bantul area is also mainly built on the unconsolidated deposits which

tend to amplify the earthquake motion in a wide range of periods that envelopes the response

periods of a wide range of structures and infrastructure systems. Both traditional and modern

designed structures had been destroyed hard. The traditional houses are normally built of

brick or stone masonry, with few in concrete block masonry walls, supporting a timber roof

with tiles. The foundations are commonly stone rubble. Either severe damage or partial to

total collapse although many engineered structures and modern reinforced concrete structures

were suffered (Elnashai, 2006).

Purpose of the Study

The main objectives of the present study are to evaluate the strong ground motion in

the research area in the following three categories:

1) To develop the multiple reflections analysis for SH-wave simulation program that can

conduct the period (sec) and magnification factors in the research area,

2) To simulate the ground motion by using the bore-hole and shear wave velocity in the study

area,

3) To evaluate the period maps of the transfer functions in the Yogyakarta city area.



General geology of the Research Area

Yogyakarta city sits in a broad depression between two groups of roughly north

running mountains where Kulon Progo Mountains are to the west and Southern Mountains to

the east. The towering Merapi volcano caps the northeast end of the depression. Yogyakarta

city is a rapidly growing population center that occupies a depression with known Quaternary

succession and located on young volcanic sediment of Merapi volcano site. Figure (2) shows

the geological map of the Yogyakarta-Bantul area.

The geology of the Yogyakarta depression area is influenced by active plate tectonic

activities such as the volcano and subduction of Indian-Australia oceanic plate below the

Eurasia continental plate. To the west, an intensively faulted dome of andesitic breccia and

lava flows occurred. Meanwhile, to the east at the Yogyakarta depression area, steep

mountains of volcanic rocks as well as limestone with karst landscape are exposed

(Karnawati et al., 2006).

Figure (2). Geological map of the Yogyakarta-Bantul area (Rahardjo et al., 1995)

Yogyakarta depression area is mainly composed of the lithologic units of Pre-

Tertiary, Tertiary and Quaternary age. The Pre-Tertiary rocks constitute as the basement and

consist of metamorphic rocks, and these units are restrictedly cropped out in the north of

Southern Mountains region. In Yogyakarta depression area, the most dominant rock units are

volcanic rocks and the young volcanic deposits which are derivatives of the Merapi volcano

from the north. The following lithologic distribution and rock formations’ descriptions are

based on the previous studies of McDonald et al. (1984) and Rahardjo et al. (1995) that

studied ground data in Yogyakarta area. The different lithologic units were resulted by the

Tertiary Orogeny in this area. The rocks exposed in the western part of the province range in

age from Middle Eocene to Pliocene while those in the Eastern part from Oligocene to

Pliocene.

Sambiputu Formation

Alluvium

Young volcanic deposits

of Merapi valcano

Sentolo Formation

Djonggrangan Formation

Kebobutak Formation

Wonosari Formation

Kepek Formation

Nglanggran

Formation Semilir Formation

Tms

Legend

Fault

Yogyakarta

Bantul



Past Earthquakes Events around Yogyakarta Area

Earthquake sources may also be identified from records of historical seismicity.

Historical accounts of ground-shaking effects can be used to confirm the occurrence of past

earthquakes and to estimate their geographic distributions of intensity. When sufficient data

are available, the maximum intensity can be determined and used to estimate the location of

the earthquake epicenter and the magnitude of the event. Although the accuracy of locations

determined in this way depends strongly on population density and the rate of earthquake

recurrence, a geographic pattern of historic epicenters provides strong evidence for the

existence of earthquake source zones. Since historical records are dated, they can also be used

to evaluate the rate of recurrence of earthquakes, or seismicity, in particular area.

The most important earthquakes that stroke Yogyakarta are in 1840, 1867 and 1875

(Newcomb and McCann, 1987). Table (1) presents limited information on recorded

earthquakes and earthquakes dating back to 1840 that resulted in significant damage or

fatalities. Figure (3) displays the historical seismicity in Java Island.

Table (1). Historical earthquake around Yogyakarta area (Husein et al., 2008 and USGS,

2013b)

Date Latitude

(South)

Longitude

(East)

Richter Scale, Intensity, or

the Reported description

Depth

(km)

1921 Sept 11 11.35˚ S 110.76˚ E 7.5 (Ms) -

1924 Nov 12 7.30˚ S 109.50˚ E - -

1924 Dec 2 7.30˚ S 109.90˚ E - -

1937 Sept 27 8.88˚ S 110.65˚ E 7.2 (Ms) -

1943 July 23 8.60˚ S 109.90˚ E 8.1 90

1955 May 29 10.30˚ S 110.50˚ E 6.38 (Ms) -

1957 Oct 12 8.30˚ S 110.30˚ E 6.4 -

1974 Sept 7 9.80˚ S 108.48˚ E 6.5 (Ms) -

1979 July 24 11.15˚ S 107.71˚ E 6.9 (Ms) 31

1979 Nov 2 7.66˚ S 108.25˚ E 6.0 (Ms) 25

1981 Mar 14 7.20˚S 109.30˚ E 6.0 33

1992 June 9 8.47˚ S 111.10˚ E 6.5 106

2001 May 25 8.62˚ S 110.11˚ E 6.2 56

2004 Aug 19 9.22˚ S 109.58˚ E 6.3 55

2005 July 19 8.55˚ S 111.07˚ E 5.5 33

2006 May 27 7.96˚ S 110.45˚ E 6.3 10

2006 July 17 9.295˚ S 107.35˚ E 7.7 40

2007 August 8 5.968˚ S 107.65˚ E 7.5 289

2009 Sept 02 7.809˚ S 107.26˚ E 7.0 49

2010 Jan 10

2011 April 03

7.907˚ S

9.786˚ S

107.87˚ E

107.749˚ E

5.1

6.7

65

24



Figure (3). Historical seismicity in Java Island (Mw>4.0 and 1840-2013) (USGS, 2013b)

Theoretical Background

Multiple Reflections Analysis for SH-Wave

Transfer Function (1) by (Yoshida and Suetomi, 2004),

It is noted that the shear wave velocity structures were calculated by using empirical

equations, which mainly contributed on SPT, values (Yoshida and Suetomi, 2004) for

comparative analysis:

Vsi = 102 Ni0.292 (1≦Ni≦25) (for sandy soil) (1)

Vsi = 80.6 Ni0.331 (1≦Ni≦50) (for clayey soil) (2)

where, N is average number of blows in SPT. Besides, the soil classification is decided by

using the results of site investigation of standard penetration testing at twelve bore holes. The

average values of N are used for determining the soil classification on each site. The average

values of N until a depth of 30-40 m at the sites surrounding the studied area vary from 10 to

32.

Transfer Function (2) by Ohta and Goto (1987),

VS = 62.48N0.218H0.228F (3)

where VS = Shear wave velocity (m/s)

N = N-value of SPT

H = depth (m)

F = Coefficient of soil type

F = 1.000 (For clay)

F = 1.073 (For sand) and F = 1.199 (For gravel)

Hypocenter

Depth

0-100 km

101-300

4



Research Analysis

Evaluation of the Shear Wave Velocity Structures

The soil classification is decided by using the results of site investigations of standard

penetration testing at 12 bore holes as example of figures (4) and (5). The average values of N

are used for determining the soil classification on each site. The average values of N until a

depth of 30-40 m at the sites surrounding the eastern part of Yogyakarta city vary from 10.00 to

32.00.

The S-wave velocity structures which give such satisfactory results are at 12 drilling

sites and comparison of drilling site, S-wave velocity and SPT are shown in example of figures.

(4) and (5). Generally, the predominant periods of the transfer functions are more important and

applicable for determination of S-wave velocity because it is more stable and well reflects to

sediment depth and S-wave velocity. It was received the realistic shear wave velocities and

reliable thickness of soil layers and depths of lose sediment from these twelve drilling sites of

S-wave velocity structures. The values of S-wave velocity from the twelve drilling sites were

generally calculated between 150 and 350 m/s. Therefore, it is clearly found that it was utilized

to take the S-wave velocity from the twelve drilling sites to calculate the predominant periods.

According to the comparison of these drilling stations, all drilling sites are normally

related to the soft soils which are sand especially fine-sand, medium-sand, coarse-sand, silt and

clay. Moreover, all drilling sites are greatly corresponded the S-wave velocity and the SPT.

Figure (4). Comparison of drilling site, S-

wave velocity and SPT in

Book store-UGM, Yogyakarta

Figure (5). Comparison of drilling site, S-wave

velocity and SPT in Hotel Grage

Ramayana Yogyakarta

The relationship of soils and the predominant periods of the ground

The characteristics of seismic waves during earthquakes were mainly influenced by the

local site conditions. The unconsolidated soil deposits tend to amplify certain frequencies of

ground motion and extend the duration of the shaking which may cause further earthquake

damage. According to the geological site conditions, the expected variation in the ground

motion makes it necessary to perform a more detailed seismic hazard assessment as the

research area. The nature and distribution of earthquake damage is strongly affected by the

response of soils which is controlled in layers part by the mechanical properties of soil.

Based on the fundamental periods of the ground for each observation site, the hard soil

has never seen in the Yogyakarta city because the smaller than 0.2 sec of the fundamental



periods of the ground did not fine by the theoretical calculation. For areas where the young

volcanic sediments of the research area, the fundamental period identified from the S-wave

velocity are mostly in the range of 0.44 - 0.67 sec (Figs. 6 to 9), therefore these fundamental

period obtained may indicate the presence of generally soft (or loose) sediments in the young

volcanic sediment of study areas. The results may confirm the suitability of using the S-wave

velocity of transfer functions as a geophysical exploration tool in those structures with

significant impedance contrast between sedimentary layers and the assume bedrock. Thus the

ground motion amplification due to soft soils, common in urban of Yogyakarta city, is a major

contributor to increasing damage and number of casualties. Table (2) displays the theoretical

calculation of predominant periods of the transfer function I and II.

Figure (6). Comparison of period (sec) by using the transfer functions in Yogyakarta City

T = 0.44 sec

MF = 2.775

T = 0.53 sec

MF = 2.911

T = 0.48 sec

MF = 2.797

T = 0.56 sec

MF = 3.053

T = 0.44 sec

MF = 2.826

T = 0.50 sec

MF = 3.091




T = 0.48 sec

MF = 2.847

T = 0.67 sec

MF = 3.166

T = 0.48 sec

MF = 3.125

T = 0.63 sec

MF = 3.386

T = 0.50 sec

MF = 2.825

T = 0.59 sec

MF = 3.644




T = 0.45 sec

MF = 2.790

T = 0.48 sec

MF = 3.281

T = 0.44 sec

MF = 2.580

T = 0.59 sec

MF = 3.214

T = 0.45 sec

MF = 2.927

T = 0.50 sec

MF = 3.208




The Distribution of Periods [sec]

The period is useful parameter for characterization of ground motion simulation. As

shown in figure (10), the period values are varying from 0.44 to 0.50 sec. The high period value

is related to the damage region for the future earthquakes. The high periods are observed at

around the Kantor Pajak and University Atmajaya areas where can be served damage in the

future earthquake. Because these areas are located on the depression area where are composing

the soft sediment of the young volcanic deposit of Mt. Merapi volcano. The low periods are

evaluated around Yogyakarta city and south of that city.

T = 0.44 sec

MF = 2.938

T = 0.50 sec

MF = 3.208

T = 0.48 sec

MF = 2.821

T = 0.40 sec

MF = 2.821

T = 0.48 sec

MF = 2.711

T = 0.45 sec

MF = 2.924



In figure (11), according to the period values based on the multiple reflection analysis

for SH-wave method in the 12 bore-hole sites, the south of the study area especially Golo,

Janturan, Sorosutan and Giwangan sites have high level of risk (0.59-0.67 sec). The eastern part

of Yogyakarta city has the medium level of risk while the northeast of the study and west of

Yogyakarta city area has the low level of risk (0.45-0.53 sec). The results show that a better

distribution of the period, since the medium to high level of risk reflects the present of the

structures related to the VS30 of assume bedrock.

Table (2). The theoretical calculation of predominant periods of the transfer function I and II

No. Name X Y Z (ft)

Depth (m)

Periods I-(sec)

Periods II-(sec)

1 Book Store UGM 431,155 9,140,746 455 29 0.48 0.63

2 Bank BPD 429,448 9,139,416 395 35 0.48 0.45

3 Hotel Aston 433,024 9,139,653 415 40 0.44 0.5

4 Kantor Pajak 435,732 9,141,782 469 40 0.48 0.45 5 Giwangan 432,758 9,134,483 277 35 0.44 0.5

6 Sorosutan 431,845 9,135,282 269 35 0.48 0.67

7 Janturan 432,354 9,135,986 306 30 0.48 0.56 8 Golo 431,800 9,135,975 307 30 0.44 0.53

9 Hotel Grage

Ramayana

429,984 9,138,640 390 20 0.45 0.55

10 Jl. Mangkubumi 429,911 9,139,165 393 25 0.44 0.59

11 JL. Remujung 430,235 9,137,928 371 25 0.45 0.48

12 University Atmajaya 435,386 9,139,730 428 20 0.5 0.59

Figure (10). Period map of the transfer

function (1) in Yogyakarta city

Figure (11). Period map of the transfer

function (2) in Yogyakarta city



Conclusion

The multiple reflection of the soil layers program is conducted to simulate the strong

ground motion in Yogyakarta city based on the S-wave velocity and drilling sites. Especially,

the predominant periods of the transfer functions I and II are varying from 0.44 sec to 0.67

sec respectively. The high period of the research area will be basically influenced for future

structural building development and high way, and mitigation of socio-economic impacts in

research area. The heavy and high buildings with the high periods of ground motion will be

severely affected during future earthquakes. The results from this research well approve that

the high periods are performed the thick sediment thickness and dominated in S-wave

velocity. In the future seismic motion, the high periods will be mainly related to the damage

area of the Yogyakarta city.

Acknowledgements

This research was officially organized at the Graduate School of Engineering, Kyoto University, Japan

and financially supported by the scholarship program (the short-term research program to Japan, SRJP-2017) of

AUN/SEED-Net (JICA). We are grateful to JICA (Japan International Cooperation Agency) and AUN/SEED-

Net (ASEAN University Network/Southeast Asia Engineering Development Network) for providing me

opportunity and financial support to carry out this research. Moreover, We would like to acknowledge our graduate to the officers of JICA program from JICA-Kansai, Japan, Thailand and Myanmar for a continuous

support and help during the present study from 22nd October 2017 to 20th November 2017.

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Estimation of Local Site Effects by the Multiple Transfer ...mynces.org/download/2018/ProceedingMNCES2018/76_Zaw Lin Kya… · Case Study: Yogyakarta City, Java Zaw Lin Kyaw1, Junji