Probabilistic Seismic Hazard Analysis in Thailand and Adjacent Areas by Using Regional Seismic Source Zones Santi Pailoplee 1*, Yuichi Sugiyama 2 and Punya Charusiri 1 1. Earthquake and Tectonic Geology Research Unit (EATGRU), c/o Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand 2. Active Fault Research Center, National Institute of Advanced Industrial Science and Technology (AIST) 7, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japan *Corresponding author e-mail: pailoplee.s@gmail.com Extended Abstract We conducted probabilistic seismic hazard analysis for Thailand and adjacent areas by using a method proposed by Cornell (1968). We produced seismic hazard maps showing peak ground acceleration (PGA) and Modified Mercalli Intensity (MMI). Twenty-one seismic source zones (Charusiri et al., 2005) (Fig. 1), which cover all of Thailand and extend into adjacent areas, were employed. The seismicity data used in this study was a merged data set covering 1963-2007 from several international earthquake catalogues and a single Thai catalogue. We selected the strong ground-motion attenuation model, proposed by Kobayashi et al. (2000) (Fig. 2), for this study by applying 121 existing attenuation models (Douglas, 2001) to recorded strong ground-motion data and choosing the model that best fit our data. Seismic hazard analysis was carried out for 2,521 grid points on a 0.25 x 0.25 mesh within a rectangle defined by longitudes 92-106 E and latitudes 0-21 N. The resulting PGA maps for 2% probability of exceedance for s of 10 to 100 years suggest that ground motion of 0.4 to 1 g may occur in northern and western Thailand and from 0 to 0.4 g in other parts of our study area (Fig. 3). The maximum MMI in northern, western, and southern Thailand may reach levels VI, V, and IV, respectively (Fig. 4). Our result seems to be slightly different from that of Palasri (2006). The seismic hazard analysis presented here is an important step toward an accurate evaluation of seismic hazard potential in Thailand and adjacent areas. Further work is needed to refine the analysis. More observations of strong ground motion in the region are needed and further seismo-tectonic research should be encouraged. Key words: seismic hazard analysis; probabilistic approach; seismic source zone; earthquake catalogue; Thailand 405
Figure 1 Location map showing 21 seismic source zones covering Thailand (gray shading) and adjacent areas (Charusiri et al., 2005). Figure 2 Comparison of published strong ground-motion attenuation models with recorded strong ground-motion data (blue s q u a r e s ) f o r a 5. 1 earthquake (after Palasri, 2006). 406
a. 2% probability of exceedance in 10-year b. 2% probability of exceedance in 30-year c. 2% probability of exceedance in 50-year d. 2% probability of exceedance in 100-year Figure 3 Probabilistic seismic hazard maps of Thailand and adjacent areas showing the distribution of Peak Ground Acceleration (PGA) that exceeds 2% probabilities for s of 10, 30, 50, and 100 years. 407
a. % of ground shaking IV (MMI) in 50-year b. % of ground shaking V (MMI) in 50-year c. % of ground shaking VI (MMI) in 50-year d. % of ground shaking VII (MMI) in 50-year Figure 4. Probabilistic seismic hazard maps of Thailand and adjacent areas showing the probabilities (%) that ground shaking will be equal to or greater than levels IV, V, VI, and VII (Modified Mercalli Intensity) for s of 50 years. 408
References Charusiri, P., Choowong, M., Charoentitirat, T., Jankaew, K., Chutakositkanon, V., Kanjanapayont, P., 2005. Geological and physical effect evaluation in the tsunami damage area for restoration and warning system. Technical report submitted to Department of Mineral Resources, Bangkok, Thailand. (unpublished) Cornell, C.A., 1968. Engineering seismic risk analysis. Bulletin of the Seismological Society of America 58, 1583 1606. Douglas, J., 2001. A comprehensive worldwide summary of strong-motion attenuation relationships for peak ground acceleration and spectral ordinates (1969 2000). Imperial College of Science, Technology and Medicine, Civil Engineering Department, London. ESEE Report 01-1, 138 p. Kobayashi, S., Takahashi, T., Matsuzaki, S., Mori, M., Fukushima, Y., Zhao, J.X., Somerville, P.G., 2000. A spectral attenuation model for Japan using digital strong motion records of JMA87 type. Proceedings of the 12th World Conference on Earthquake Engineering, 30 January 4 February 2000. Auckland, New Zealand. Palasri, C., 2006. Probabilistic seismic hazard map of Thailand. M.S. thesis, Department of Civil Engineering, Faculty of Engineering, Chulalongkorn University, Thailand. 409