dc.description.abstract | On December 26, 2006 at 20:26 and 20:34, two successive earthquakes with the same magnitude 7.0 on the Richter scale occurred in the southeast Taiwan Strait near HengChun
peninsula, with one epicenter approximately 38.4 km southwest of HEN station, and another is located in 33.1km west of NEN station.The Central News Agency is reporting that it is the strongest earthquake to hit HengChun in one hundred years. The earthquake not only caused casualties and building damages, but also damaged several undersea cables, disrupting telecommunication services in various parts of Asia. Besides, in Nanwan area of HengChun suffered some disasters of soil liquefaction, it implies that the nonlinear soil response might occur during earthquake.
The data we use include weak motion records observed by KAU stations during the period from 1993 to 2004 and 2006 HengChun earthquakes, which were collected by the Taiwan
Strong Motion Instrumentation Program (TSMIP) of Central Weather Bureau (CWB).We use the Horizontal-to-Vertica(H/V) Spectral Ratio Method to conduct the analysis in this study because a good rock referent site is hard to find in PingTung alluvial plain. From the analysis of weak motion of H/V Fourier spectrum, we find the magnification near the seacoast, the site effect exists from 0.5~2Hz, and that above 2Hz the contour high area move toward the inland. Follow the result of above we can infer the thickness of accretion in PingTung plain is getting deeper from the direction of northeast toward southwest.
The aim of this study is to research whether the nonlinear soil response occurred or not during the HengChun earthquake. Two characters of nonlinear soil response from earthquake spectrum between weak and strong motions :(1)the dominant frequency of weak motion is larger than strong one; (2) the soil amplification factor have the same result as former. From our result, we find most of the nonlinear soil response usually occurred in soft alluvial plain near shore area of Kau-Ping plain.And the nonlinear soil response in the western part of HengChun are not obviously, on the contrary, we can see apparent nonlinear response in the eastern valley of hill-zone. The liquefaction site, Nanwan area, besides frequency band 1~3Hz, we can’t see the phenomenon of deamplification from the spectra between weak and strong
motions in most frequency, because the phenomena of liquefaction was caused by the local refill soil of ground surface. | en_US |