大地震的破裂方向性和尺度率(I)~(III)

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Title:	大地震的破裂方向性和尺度率(I)~(III)
Authors:	黃瑞德
Keywords:	破裂方向性表面波相延遲時間破裂歷時斷層參數尺度律
Date:	2008-2010
Issue Date:	2009-09-04 15:01:02 (UTC+8)
Abstract:	大地震發生時，由於大的破裂錯動和延展，經常造成震波波寬隨方位(測站)的變化，這現象稱為破裂方向性。Ben-Menahem (1961)首先提出有限源理論描述大地震的破裂方向性現象，並依此可決定大地震的破裂長度、破裂速度、破裂方位等等。基本上，破裂方向性對地震觀測的影響，包括造成波傳時間的延遲和震波頻譜出現節點。已有數種方法可進行破裂方向性的分析，包括體波或表面波的解迴旋得到相對震源時間函數、高頻 P 波的輻射能量分析、相延遲時間等等。Hwang et al. (2001)利用1999 集集地震主震和兩個餘震的相延遲時間差評估震源歷時隨方位的變化，得到集集地震的斷層參數。 Hwang et al. (2001)或表面波解迴旋方法的限制在於需找到與主震一致的小地震(包括震源深度、位置和震源機制的一致)，才能進行分析。本研本研究依照Hwang et al. (2001) 的觀念，提出一個新的方法來計算因地震的破裂方向性所導致的延遲時間。本研究依照全球的相速分布圖計算地震至測站的理論相延遲時間，再與所觀測的相延遲時間比較，可得出每個測站所觀測到的震源歷時。此法的優點在於不需要找到在主震附近的小地震來進行分析。藉由本研究所提的方法能有系統的分析大地震的斷層參數，進而建立一個新的震源尺度率，增進對地震破裂物理行為的了解。本研究為三年期計畫，第一年著重於新方法的發展，務必使新方法能穩定的計算；第二年，利用新的方法評估一些歷史地震的斷層參數，如1960 年智利大地震、1964 年阿拉斯加大地震等等，並系統性評估一些近代大地震的斷層參數；第三年，持續分析大地震的斷層參數，並總結先前分析的斷層參數，以建立新的震源尺度率。 The wave-duration variations of seismic-wave with the station azimuth are usually observed following a large earthquake because of its large faulting and extending. This phenomenon is generally called rupture directivity. Ben-Menahem (1961) first proposed the finite moving source theory to account for the effect of rupture propagation on far-field seismograms. Basically, the source finiteness would result in a time delay in wave propagation, and weaken amplitude, showing up as a number of nodes in the Fourier spectra. Rupture directivity analysis for large earthquakes has been carried out by many methods, including deconvolution of P-waves or surface-waves, analysis of high-frequency P-wave radiation, and so on. Hwang et al. (2001) used phase-delay time differences between the main shock and its two large aftershocks to derive the rupture directivity of the 1999 Chi-Chi earthquake and determine its fault parameters. In this study, I propose a new approach to calculate the source-process time varying with the station azimuth based on the method of Hwang et al. (2001). This method, different from previous approaches, mainly calculate the theoretical phase-delay time from a global map of surface-wave phase-velocity. The source-process times with the station azimuth can be obtained when the observed phase-delay times of surface waves subtract the theoretical phase-delay times. I use the observed source-process time with the station azimuth to estimate the fault parameters of large earthquakes. Basically, the duration of this proposal is designed to be three years. The program of the first year is to develop the new method estimating the source-process time and estimate the fault parameters of several recent large earthquakes. In the program of the second year, the fault parameters of some historical larges earthquakes will be estimated through the proposed method, and the estimation of those of the latest large earthquakes will hold. In the program of the third year, I will establish a new scaling law of earthquake source from results estimated previously.
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