New study of basement and seismogenic structure in Ilan Plain
Speaker: Cheng-Wei Shih
Department of Earth Sciences, National Central University, Taiwan
Abstract
The Ilan Plain is surrounded by the high mountains of the Hsuehshan Range to the Northwest and the Central Range to the South. It's also considered as a delta fan formed as a back-extension of Okinawa Trough. Inside the Ilan Plain, most sediment is unconsolidated Quaternary alluvium and covered with 200m to 1400m thicknesses on the Miocene basement. Such a sediment–basement interface might have important implications for earthquake hazard assessments. Therefore, we analyze the seismogenic structure and the imaging underground of Ilan Plain in several geophysical methods. And the data shows NW–SE extension at high angle to a fault plane, which cannot be explained from a simple strike-slip nor a simple normal event as well. It is best explained by significant component of tensile source with centimetre-scale of opening on a 15-km-long fault extending from 1 to 13 km depth. With the numerous of earthquakes and high values of site amplification in Ilan plain, we must do more research to protect our security in this area.
References
Lai, K. Y., Chen, Y. G., Wu, Y. M., Avouac, J. P., Kuo, Y. T., Wang, Y., Chang, C. H. and Lin, K. C., The 2005 Ilan earthquake doublet and seismic crisis in northeastern Taiwan: evidence for dike intrusion associated with on-land propagation of the Okinawa Trough, Geophys. J. Int., 179, 678-686, 2009.
Chang, C. H., Lin, T. L., Wu, Y. M., and Chang, W. Y., Basement Imaging Using Sp Converted Phases from a Dense Strong-Motion Array in Lan-Yang Plain, Taiwan, Bulletin of the Seismological Society of America, Vol. 100, No. 3, pp. 1363–1369,