TCDP井下地震儀陣列之波形分析斷層帶的衰減特性; The Q Value of the Chelungpu Fault Zone derived from TCDP Borehole Seismometers

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Title:	TCDP井下地震儀陣列之波形分析斷層帶的衰減特性;The Q Value of the Chelungpu Fault Zone derived from TCDP Borehole Seismometers
Authors:	李孟潔;Meng-Chieh Lee
Contributors:	地球物理研究所
Keywords:	斷層帶;衰減特性;Q value;Fault zone
Date:	2009-06-29
Issue Date:	2009-09-22 09:57:08 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	集集地震後，Taiwan Chelungpu-fault Drilling Project (TCDP) 在台中大坑設置七部井下地震儀陣列垂直分布於車籠埔斷層主要滑移面之上下盤。利用此井下地震儀陣列之資料，本研究探討斷層帶的衰減性質，以期望進一步了解地震發生後斷層帶構造之特性。為了避免地層側向影響，我們選取入射角小於10度之微地震資料，利用非線性逆推擬合觀測振幅頻譜及頻譜比值之線性迴歸方法，分別得到總路徑衰減運算子(t)，再配合井測速度構造，分析此斷層帶之衰減特性。研究結果顯示，S波的衰減效應較P波的衰減效應有較明顯的變化，其主要為S波資料所呈現的衰減結果較不穩定。而沿著斷層帶的垂直方向上，深度1.1公里至2公里之平均Qp為73、Qs為81，其Qp小於Qs的現象可能與斷層帶的低速特性影響其路徑行為有關。在深度0.95公里至1.1公里範圍內，其平均Qp為48；Qs則以以井下地震儀西側方向入射的震波資料估算，其數值平均為28。根據本研究所得的Q值和前人在斷層帶上的Vp/Vs值和Q質特性的研究，我們推論車籠埔斷層低Qp、Qs值的原因主要是由於斷層帶的高孔隙率及富含流體的性質所造成的影響。 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.
Appears in Collections:	[Graduate Institute of Geophysics] Electronic Thesis & Dissertation

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