The Q Value of the Chelungpu Fault Zone derived from TCDP Borehole Seismometers

• Main Authors: Meng-Chieh Lee, 李孟潔
• Other Authors: Kuo-Fong Ma
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/v6x28n

碩士 === 國立中央大學 === 地球物理研究所 === 97 === After the 1999 Chi-Chi earthquake, the Taiwan Chelungpu-fault Drilling Project (TCDP) was conducted at Dakeng, Taichung City. The TCDP hole-A is 2-km deep, and a slip zone at the depth of 1111m was identified. After a successful drilling, in Novemeber 2006, a 7-level vertical borehole seismic array (TCDP BHS) was installed in the TCDP hole-A, where covers the slip fault zone of Chelungpu fault including hanging wall and foot wall. In this study, we used the waveform data from the TCDP borehole seismic array to analyze the attenuation property of the Chelungpu fault zone. In order to avoid the lateral effect from layer structure, we chose the micro_earthquakes, which have incidence of less than 10 degree. Using the Least-Squares Estimation of Nonlinear Parameters (LSQENP) method and spectral ratio method, we obtained the value of attenuation for the operator (t*), Combining the well determined seismic velocity structure from logging data, we further estimate the attenuation factor (Q value) of the Chelungpu fault zone. For the layer from the depth of 1.1 km to 2 km, the average values of Qp and Qs are 73 and 81, respectively. We suggested that the lower value of Qp than Qs might be related to the path effect of the low velocity zone in the fault zone. In the layer from the depth of 0.95km and 1.1km, we obtain the average Qp of 48; and the average Qs of 28, as determined from the events incidence from western of the borehole. Comparing with other studies on the attenuation property of the fault zone, we suggest that the low Qp and Qs value in the Chelungpu fault zone might be a associated with the high porosity and fluid-rich property of the fault zone.