Investigating Near-surface Structure under the West-central Taiwan by the Reflection Seismic Medthod
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Abstract
The Chelungpu and Changhua faults are very important structure line under the west-central Taiwan. Several seismic reflection surveys were conducted to investigate the seismogenic structure of the 1999 Chi-Chi earthquake in central Taiwan. Two 40 km-long seismic profiles that crossed the area near the epicenter were acquired using the deep reflection method with a targeting depth of 10 km, to search for the decollement boundary. One of the obtained section shows a clear reflection event that dips to the east by 40o until reaching 8 km where the earthquake source was located. This slant event is unambiguously related to the thrusting Chelungpu fault surface. The Changhua fault is a long fault (80km), extending a long western border of three gravel terraces in west-central Taiwan. It represents the western-most thrust fault in the deformation front of Taiwan¡¦s western foothill. Photogeologic studies indicate that it could be an active fault, as it has apparent lineation and fault scarp. In this study, we used the shallow reflection seismic method to map the near-surface structure around the fault. Besides these shallow reflection , we also used many CPC deep seismic reflection lines to delineate the structures in the fault zone. The 3D structure of the fault surface can be deduced using this cost-effective approach. Although the depth imaged may be limited (e.g., 3 km), shallow seismic data still provides reliable information for the study of large rupture, and to make beter plans for deep wells that might be drilled in this area in the feture.
References
Wang,C.Y., S.Y.Kuo, W.L.shyu, J.W.H,2003: Investigating Near-surface Structures under the Changhua Fault, West-central Taiwan by the Reflection Seismic Method. TAO,vol14,NO.3,343-367
(Abstract) (Full text)
Wang,C.Y., C.L.LI, F.C.Su,..,2002: Structural Mapping of the 1999 Chi-Chi Earthquake Fault, Taian by Seismic Reflection Methods.TAO,vol13,NO.3,211-2
(Abstract) (Full text)