九二一集集地震之餘震(Mw≧6.0)震源破裂滑移分佈; Slip Distribution of Mw ≧6.0 aftershocks of the 1999 Chi-Chi,Taiwan, Earthquake

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Title:	九二一集集地震之餘震(Mw≧6.0)震源破裂滑移分佈;Slip Distribution of Mw ≧6.0 aftershocks of the 1999 Chi-Chi,Taiwan, Earthquake
Authors:	顏銀桐;Yin-Tung Yen
Contributors:	地球物理研究所
Keywords:	921;震源破裂;波形逆推;921;slip;inversion
Date:	2002-06-21
Issue Date:	2009-09-22 09:53:46 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	1999年9月21日1時47分，在台灣中部發生了芮式規模7.3的強烈地震，座落於一西部逆衝帶上的典型逆衝斷層導致此次地震。自從921集集大地震之後，餘震頻頻不斷，範圍幾乎遍佈了整個台灣中部區域。此次研究之規模大於六以上的餘震為格林威治標準時間（GMT）1999年9月20日18時3分、18時11分、18時16分、21時46分發生之四個餘震，以及另外9月22日0時14分及9月25日23時52分之二個餘震。氣象局在短時間內定出位置、規模和深度，而六百多個自由強震站記錄也同時在地震發生後即馬上紀錄，提供了研究這些餘震的波形資料。此外，中央研究院BATS（Broadband Array In Taiwan For Seismology）觀測網也經由Kao and Chen（2000）透過地震矩張量逆推同時解得震源深度及震源機制，本研究也利用其結果作為理論計算上之基本參數。利用Takeo採用結合Kennett and Kerry（1979）的反射、透射係數矩陣（Reflection-Transmiission coefficient matrix method）與Bouchon（1981）的離散波數法（Discrtet-Wavenumber method），計算出假設在水平地層內一點震源所有全波形之理論格林函數並加進震源機制後推算出理論位移波形。於斷層模型上採Finite fault approach，將一個有限斷層其看待為許多子斷層所構成，假設一測站的相關參數所計算之理論波形，則為所有子斷層的貢獻的疊加波形。以此觀念，計算出選取測站之理論波形，並和實際波形進一步採用Mori and Hertzell（1990）發展的逆推方法計算出斷層面上的錯動量分佈。所求得之結果分別為：Af1 – 主要錯動區域在震源周圍範圍，傾向往西南破裂，最大錯動量分別約為 7.6 m（P043）及 9 m（P197）；Af2 – 主要錯動區域在震源東邊區域，往下方破裂，最大錯動量分別約為125 cm（P229）及125 cm（P313）；Af3 – 主要錯動區域在震源北邊範圍，最大錯動量分別約為150 cm（P336）及150 cm（P189）；Af4 – 主要錯動區域在震源西北邊範圍，傾向下方破裂，最大錯動量分別約為8 m（P085）及 7 m（P353）；Af5 – 主要錯動區域在震源南邊範圍，最大錯動量分別約為250 cm（P324）及 180 cm（P194）；Af6 – 主要錯動區域在震源西南範圍，最大錯動量分別約為 380 cm（P042）及 424 cm（P188）。而研究中也歸納出，在考量測站包覆性下選取較遠測站時，速度構造分區是應該被考慮的。另外，將921主震錯動量分佈結果做相關比較結果，六個餘震之破裂區大致分佈於主震幾乎無錯動量之區域，向西逆衝之斷層面相對於另一斷層面有著較小的擬合誤差解，與西部逆衝構造有著構造上的一致性。 We investigate the waveforms of several Mw ³6.0 aftershocks to examine the corresponding fault geometry and the distribution of slip on the fault of the aftershocks. The time points and locations that certainly happened in our investigated aftershocks are very close to each other. As a result, those aftershocks are mixed up and fault range and plane are difficult to be defined. One objective of this investigation is to obtain the distributions of slip of several (Mw ³6.0) aftershocks of Chi-Chi earthquake. In the aspect of synthetic waveform, we use the following steps to obtain. First, a fault plane was discretized into many subfaults to imply a finite fault. Then we calculate the point source response on the subfaults and combine all subfaults response. The point source responses for the strong motion synthetics are computed using a layered velocity structure with a frequency-wavenumber integration scheme. In addition, linear least-square inversion procedure that is adopted by Hartzwll and Heaton (1983) could obtain the subfaults dislocations when the best fit to the displacement waveforms between observation and synthetic could be got. A matrix of smoothing constraints also are taken into consideration. The transverse component of the Taiwan strong-motion stations (TSMIP) was used to analyze with detrend and intergrated twice the accelograms to displacements. These aftershocks are located in the eastern of Central Mountain Ranges and there are rare stations there. We must select more information from farther stations to carry analyses out, hence the velocity structure is considered attentive. The results from these aftershocks will thus be related to the mainshock to understand the general picture of the Chi-Chi earthquake sequence.
Appears in Collections:	[Graduate Institute of Geophysics] Electronic Thesis & Dissertation

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