Comparison Among the Three Peak Ground Acceleration Models in Bengkulu Province, Indonesia

Transcription

1 IOSR Journal of Applied Geology and Geophyic (IOSR-JAGG) e-issn: , p-issn: Volume 5, Iue 1 Ver. I (Jan. - Feb. 2017), PP Comparion Among the Three Peak Ground Acceleration Model in Bengkulu Province, Indoneia Tati Zera, Sutrino, Agu Budiono Department of Phyic, Faculty of Science and Technology, Ilamic State Univerity Syarif Hidayatullah, Jl. Ir. H. Juanda 95 Ciputat 15412, Indoneia Abtract: Bengkulu Province i a region located on the a ubduction zone in the Wet coat of Sumatra. It a highly prone and rik of earthquake. One of the important effect of earthquake i Peak Ground Acceleration (PGA). Thi value i needed to determine the trength of the foundation of the building to be contructed. Thi article preent comparion among the three PGA model in Bengkulu province, Indoneia. Reearch on the three model of PGA in the firt generation, namely; Eteva, Pathwardan and Croue have been teted and compared on the Bengkulu area baed on hitorical data of earthquake with magnitude, M 4 SR and hypocenter, H 100 km that occurred in The model produce 4.16 to gal Eteva, Pathwardan 72, 6 to and to gal Croue i on the PGA. In general, thee three model produce the ame map, in which the maximum value PGA i at Mukomuko in North Bengkulu and in Kaur in South Bengkulu. Keyword: Croue Model, Eteva Model, Hypocentre, Pathwardan Model, Peak Ground Acceleration. I. Introduction Bengkulu Province i located on the wetern part of Sumatra Iland. Thi area i located at the confluence of two tectonic plate, i.e. the Indo-Autralian plate and the Euraian plate. Regional meeting of the two plate i known a ubduction zone, which become the main generator large earthquake. The movement generated by the colliion of two plate create the formation of active fault in the wetern part of Sumatra. Thu, in the frame of geotectonic, Bengkulu wa lying in a ubduction zone, located between two active fault - Semangko fault and Mentawai fault. The above condition led to Bengkulu a earthquake-prone area that ha a very frequent occurrence of earthquake and ha an index of eimicity. Due to the frequent earthquake in Bengkulu, then led to the emergence of ground movement. One of the parameter of ground movement caued by earthquake i the PGA ued in geotectonic and mechanical engineering. PGA i one of the key factor to analyze the potential damage caued by the earthquake. Phyically, PGA i one of the parameter of ground motion caued by earthquake that are important in geotectonic and engineering mechanic. By knowing the value of thi PGA we can determine how deep and trong the foundation of a building mut be made o a to have reitance to earthquake. A the other parameter of ground movement caued by earthquake, can be decribed mathematically that the ground motion attenuation i the relationhip between the parameter of the ditance to the location of earthquake eimic recording [1]. Thi reearch i the tudy of the three model of the firt generation method of attenuation applied to the Bengkulu ubduction area with the aim to looking for model are mot appropriate for the region to be analyzed further alignment with regional condition. II. Literature Review The tudie on the ground movement parameter had taken in a long time and continuouly ince the firt generation until today. A number of tudie on the maximum ground motion parameter etimation have been carried out and publihed. Likewie, the variou tudie on the relationhip between the value of the PGA and the value of Peak Ground Velocity (PGV) with MMI cale have been made to variou area. David J Wald [2] had done o in California area, Liu Sing [3] for the Taiwan region, and Danciu & Telenti [4] did well in the area of Greece. In 2012, Pailoplee [5] alo publihed a imilar tudy in the area of Myanmar. In Indoneia, Hadi e.t al [6] ha conducted an analyi of Bengkulu Earthquake parameter data baed on Single and Multi Station. A number of other tudie with different method about the value of PGA had been done and in general get the concluion that the geological oil condition in the area were oberved very deciive of the PGA value that obtained. The geological condition that it mean i the denity of the oil, where the more olid ground in an area, the maller value of the PGA i obtained. Thi i conitent with the fact that the building i built on a olid ground tructure at the time of the earthquake damage i lighter than building built on land that i le dene tructure [1]. DOI: / Page

2 Comparion Among the Three Peak Ground Acceleration Model in Bengkulu Province, Indoneia 2.1. Gegraphical Condition of Bengkulu Bengkulu province i located on the wet coat of Sumatra at '- 3 31' latitude and 101 1' ' Eat Longitude. Adminitratively, Bengkulu i bordering on the north by Wet Sumatra, to the outh by Lampung, on the wet by the Indian Ocean and on the eat by Jambi and South Sumatera. Geographical condition of Bengkulu are hown in Fig. 1. Bengkulu i a province located in the wetern of Bukit Barian with an area of ± ,33 km 2. Bengkulu conit of 10 ditrict/citie i.e. South Bengkulu, Rejang Lebong, North Bengkulu, Kaur, Seluma, Mukomuko, Lebong, Kepahiang, Central Bengkulu, and Bengkulu City. The adminitrative area of Bengkulu extend from the border of Wet Sumatra to the border of Lampung by a ditance of approximately 567 kilometer. Bengkulu ha everal mall iland are uninhabited well a Enggano, a well a the iland are uninhabited, Mega iland and other mall iland. Figure 1. Geographical condition Bengkulu Province Baed on the tate of nature and it location, the region of Bengkulu ha different height from ea level. The tate of the province' altitude varie greatly, ranging from m covering 35.8% of the area of Bengkulu, m i the lope of the Bukit Barian mountain reache 31.60%, m cover 20.50% of the total area of Bengkulu and the region with an altitude of over 1000 meter above ea level to the peak of Bukit Barian mountain range which generally i an area of volcanic activity and tectonic area of about 12.10%. In geomorphology, Bengkulu can be divided into four part form region, namely: 1. Coatal Plain Thee plain are along the coat, which tretche from Mukomuko until the Padang Guci, generally thi area i narrow and there are bain and wetland. 2. Alluvial Plain Thi plateau i elongated at the back of the coatal plain which ha wide-ranging between 5-10 Km, thi area generally have fairly high oil fertility. 3. Plain Fold Thi area extend almot parallel to the alluvial plain with an altitude between meter above ea level. Thee area include the following Lumbuk Pinang, Beringin, Tambun and Hulu Sungai Ipuh. 4. Volcanic Region Thi region occupie mot of the Bukit Barian range, which i a mountain path faulting and complex volcanic eruption outide the center of Bengkulu. Phyically Bengkulu compoed of andeite lava rock covered by volcanic breccia ediment, clay tone, pumice, and wamp alluvium rock ediment. Thee natural condition were vulnerable to natural hazard, uch a earthquake, ground crack and ubidence, eroion, landlide, flood, and ea torm, while the tunami danger ha never been recorded in actual condition. Bengkulu area i located between the maonry pre-tertiary, tertiary volcanic rock and alluvial. In Bengkulu few tertiary formation encountered, epecially ki crytalline which include the type of gene and glimmer ki, in addition, there i plutonic rock-granite until heartland granite. Limited preading in a mountainou area Bukit Barian, among other in the outheat of Gunung Patah (North Bengkulu) Triaic formation i in the outheat and wet of the Curup (Rejang Lebong) coniting of Jani late fliti kwariti beide andtone, calcareou filit, limetone, and the kind of tuff which i rather wide pread up to the border DOI: / Page

3 Comparion Among the Three Peak Ground Acceleration Model in Bengkulu Province, Indoneia area of South Sumatra. In the wet and northeat of Muara Aman there i a formation of tertiary found in mountainou area Bukit Barian. The young tertiary formation ha a very broad ditribution area on the hill of wetern of the Bukit Barian. The rock type i mainly compoed of andtone and clay which arranged in a pleated tructure. On the other hand, there i a kind of old andeite in the form of a bulge in the Bukit Barian back of volcanic region [7] Tectonic Frame of Sumatera Iland. Sumatra iland form the wetern end of the Indoneian archipelago. Regionally, the tectonic frame of Sumatra can be een in the Fig. 2. Sumatra i compoed of two main part, the wet i dominated by the preence of the oceanic plate, being eat i dominated by the preence of continental plate. Baed on gravity, magnetim and eimic the thickne of oceanic plate i about 20 kilometer, and the thickne of the continental helf about 40 kilometer [8]. Figure 2. Tectonic frame of Sumatera Iland The tectonic hitory of Sumatra i cloely linked with the tart of the event of a colliion between the Indian-Autralian plate and Southeat Aia, about 45.6 million year ago, which reulted in a erie of ytematic change of the relative movement of the plate i accompanied by change in the relative velocity between the plate following extruion activitie happened to them. The India-Autralia plate motion which initially ha a peed 86 mm / year decreaed to 40 millimeter / year due to the colliion proce (Char-hin Liu et all, 1983 in [9]). And then the peed ha increaed to about 76 millimeter/year (Sieh, 1993 in [10]). Thi colliion proce ultimately reulted in the formation of many fault ytem Eatern India. The chematic of Sumatran ubduction ytem i hown in Fig. 3. DOI: / Page

4 Comparion Among the Three Peak Ground Acceleration Model in Bengkulu Province, Indoneia Figure 3. Schematic cro-ection of the Sumatran plate boundary [11] Bengkulu i located in the outhern part of Sumatra Iland that give the appearance of tectonic pattern: 1. Sumatra Fault how a lide right en echelon pattern and i located at 100 ~ 135 kilometer above the ubduction. 2. The location of volcanoe generally eat-ea or near the fault. 3. Arc bain formed modet advance, with a depth of 1-2 kilometer and detroyed by a major fault. 4. The ridge arc relatively cloe to the face, coniting of a ingle anti form and imple form. 5. Mentawai Fault and homoclinal ridge, which are eparated by a ridge arc bain face to face and relatively intact. 6. Slope angle of ubduction i relatively uniform. III. Experiment Method Attenuation of Ground Motion i the proce or formulation of ground movement caued by the earthquake (acceleration, velocity, deviation) or the intenity of the earthquake that continue to hrink to it ditance from the earthquake ource. Mathematically, the attenuation of ground motion i a relationhip between the earthquake parameter (acceleration, velocity, deviation, intenity, or earthquake magnitude) with the ditance to the location of the earthquake recorder (the ditance of the epicenter, hypocenter, the hortet ditance). The influencing factor of the ground motion are the earthquake magnitude and the ditance to the ite, Earthquake Source Mechanim (Shallow crutal and ubduction Earthquake) and ite condition. Specific ground motion attenuation equation propoed by (Mc. Guirre, 1974 in Prawirodikromo [1]) and preented by (Dowrick, 1982 in Prawirodikromo [1]) in a form: Y b2 M b3 b1 *10 ( R ) (1) The development of further reearch on method of categorizing attenuation phae - development phae into 3 group (Dougla, 1991 in Prawirodikromo [1]), 1. Firt Generation on Bae Rock, Peak Ground Analyi (PGA) 2. Second Generation, Peak Spectral Analyi (PSA) 3. Third Generation, Next Generation Attenuation (NGA) Thi reearch wa conducted to tet the three model of acceleration of ground motion attenuation of the firt generation (Pathwardan, Eteva and Croue) for Bengkulu region located on the wetern coat of Sumatra. The model propoed by Pathwardan uing 23 event and the 32 record ubduction earthquake that occurred in Japan. The reulting empirical model i a follow: ln Y ln M 1.05( R 0.864exp(0.463 M ) (2) Under the California earthquake that ha been corrected and evaluated tatitically, Eteva obtain empirical model a follow: 5600*exp(0.8M ) Y 2 ( R 40) (3) The next attenuation function developed by Croue baed on earthquake data with ubduction mechanim taken from the Cacadia ubduction zone in wetern North Pacific. Croue formulate the empirical model a follow: DOI: / Page

5 Comparion Among the Three Peak Ground Acceleration Model in Bengkulu Province, Indoneia ln Y M 2.09ln( R 63.7 * 0.128M * h (4) In thi cae the Pathwardan and Eteva model i expreed in unit of cm/ec 2 while the Croue expreed in gal, where 1 gal = 10-3 cm/ec 2. Thee three model are elected to find the uitability of the model for the ubduction zone with the object elected reearch area, Bengkulu which wa in the area of ubduction too. Furthermore, the value of the ground motion acceleration (Y) i referred to a the PGA. In thi tudy will be determined and then map the value PGA in three model, empirical method of attenuation of the firt generation a decribed above by uing hitorical data of earthquake in 2273 from the year with 4 Mb of magnitude and depth of 100 km (hallow earthquake) that occurred in the area of Bengkulu with limit LS and BT. To get the value of the PGA of three model which will be determined performed tep - tep a follow: 1. Filter the data according to predetermined criteria baed on parameter of earthquake, time occurrence, magnitude, latitude, longitude, and hypocenter. 2. Convert value of body magnitude (Mb) to urface magnitude (M). 3. Make grid on map. 4. Determine the ditance to the epicenter grid coordinate. 5. Determine the ditance hypocenter. 6. Determining the value of the PGA. 7. Mapping the PGA value obtained. IV. Reult and Dicuion Calculation of the three model, Pathwardan, Eteva and Croue how that the firt two model give maximum PGA value at the ame location ( of latitude and of longitude) i in Mukomuko ditrict located in North Bengkulu. While Croue model give different reult with the reult of the maximum PGA gal ( of latitude and of longitude) in the Kaur ditrict in the South Bengkulu. The reult can be een in Table 1. Table 1. The Maximum PGA poition on Bengkulu Model Range of PGA value Maximum PGA poition (gal) Latitude Longitude Sub Ditrict Pathwardan Kaur Eteva Kaur Croue Muko Muko The plotting of the value of PGA reult on the map of Bengkulu for all three model provide different contour, but generally howed imilar reult to each other. Each mapping of PGA for Pathwardan model with a range of value gal can be een in Fig. 4. The Eteva model have a range of value 4: gal can be een in Fig. 5 and the Croue model ha a range of PGA value gal can be een in Fig. 6. Figure 4. Contour map of PGA by Pathwardan model Figure 5. Contour map of PGA by Eteva model DOI: / Page

6 Comparion Among the Three Peak Ground Acceleration Model in Bengkulu Province, Indoneia Figure 6. Contour map of PGA by Croue model Although the Croue model give the different reult in detail, the maximum value of the PGA i located in the Mukomuko, while the two other model - Pathwardan and Eteva - delivering maximum value in Kaur, but in general the three model howed a imilar pattern to each other. Thi pattern i clearly viible on a contour map, which, overall of Bengkulu have the PGA in the range of blue (low) to maroon (high). The maximum PGA value are at two location, namely Mukomuko on the northern tip of Bengkulu and Kaur on the outhern tip of Bengkulu which in thi cae i maroon. Thi i the conformity with the hitorical data on Bengkulu earthquake and urrounding area which claified a high eimicity index. Thi i becaue of Bengkulu and urrounding area located in earthquake-prone line in the colliion zone of Indoneia, Autralia and Euraia plate that form the Sumatran Trench that alway move 7 cm/year with an angle N20 0 E [12]. In addition Bengkulu wa flanked by two active fault; Mentawai and Semangko. By obtaining two of the three model of ubduction zone that have given imilar reult, howing that both model are uitable for Bengkulu area. To get a more appropriate model among that two model, need to be done further reearch by teting againt with everal other model of the firt generation and teting with meaurement data to obtain the alternative model for Bengkulu. V. Concluion The calculation of the value of PGA with three model ha been obtained that the two model (Pathwardan and Eteva) produce maximum PGA value at the ame location (Kaur ditrict in South Bengkulu). Meanwhile, Croue model produce maximum PGA value in Mukomuko ditrict in North Bengkulu. Although three model give the different value, the contour map of the PGA how the imilarity to each other. By obtaining two correponding reult how two model that are appropriate for the area of Bengkulu. Thee reult need to be teted by further reearch by other model of the firt generation and examine it with a calculation baed on the reult of direct meaurement. Reference [1] Prawirodikromo, W, Seimologi Teknik dan Rekayaa Kegempaan (Putaka Pelajar, Yogjakarta, 2012). [2] Wald, David, Quitoriano, J V, and Heaton, TH, Relationhip Between Peak Ground Acceleration, Peak Ground Velocity, and Modified Meercalli Intenity in California, Earthquake Spectra, 15(3), 1999, [3] Sung, Kun-Sung, Attenuation Relationhip of Peak Ground Acceleration and Velocity for Crutal Earthquake in Taiwan, Bulletin of the Seimological Society of America, 95(3), 2005, [4] Telenti, G-Aki and Danciu, L, Empirical Relationhip Between Modified Mercalli Intenity and Engineering Ground Motion Parameter in Greece, Bulletin of the Seimological Society of America, 98(4) 2008, [5] Pailoplee, S, Relationhip between Modified Mercalli Intenity and peak ground acceleration in Myanmar, Natural Science, 4, 2012, [6] Imul, Hadi, Suhendra, and Efriyadi, Studi Analii Parameter Gempa Bengkulu Berdaarkan Data Single-Station dan Multi-Station erta Pola Sebarannya, Berkala Fiika, 13(4), 2010, [7] acceed June 20, [8] Warren, Hamilton, Tectonic of the Indoneian Region (United State Government Printing Office, Wahington, 1979). [9] Natawijaya, DH, Neotectonic of the Sumatran Fault and Paleogeodey of the Sumatran Subduction Zone, doctoral di, California Intitute of Technology, Paadena, [10] Sieh, K & Natawijaya, DH, Neotectonic of Sumatran Fault, Indoneia, Journal of Geophyic Reearch, 105, 2000, [11] McCaffrey, R, The Tectonic Framework of the Sumatran Subduction Zone, Annual Review of Earth and Planetary Science, 37, 2009, [12] Hidayat, N and Haryanto, H S, Tektonik dan Pengaruhnya Terhadap Gempa di Sumatera Bagian Selatan, Alami, 2(3), 1997, DOI: / Page