臺灣地區中、大規模地震震源上揚時間之評估

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Title:	臺灣地區中、大規模地震震源上揚時間之評估 Estimating the Rise Time for Moderate- and Large-Sized Earthquakes in Taiwan
Authors:	黃瑞德
Contributors:	地質學系
Keywords:	上揚時間破裂時間震源輻射能量震源時間函數動應力降靜應力降震源自相似性 rise time rupture time radiated seismic energy source time function dynamic stress drop static stress drop source self-similarity
Date:	2020
Issue Date:	2020-09-30 14:35:36 (UTC+8)
Abstract:	震源上揚時間是震源動力學中的重要參數之一，也是強地震動模擬時不可或缺的因子。由於上揚時間小於整個震源歷時數倍之多，因此不易從整個震源歷時中分離出來。在此，本研究提出一個做法，先利用非負解時間域解迴旋得到震源時間函數，之後將震源時間函數轉換到頻率域，並以-2模型求震源時間函數頻譜所對應的拐角頻率，接著由拐角頻率求其震源破裂時間，最後，再從整個震源歷時扣除破裂時間，得到上揚時間。上揚時間可用來估算動應力降，動應力降可估算震源輻射能量，更能進一步規範靜應力降的評估；而上揚時間與地震矩的關係，也牽涉到地震是否具有震源自相似性的議題。過去台灣地區有關於震源上揚時間的研究並不多，本研究希冀能有系統地建立臺灣地區中、大規模地震震源上揚時間的分析，並探討上揚時間與地震矩的關係，以進一步了解屬於台灣地震特有的孕震特徵。本研究為二年期計畫，在第一年計畫中，先利用遠震P波資料分析ML大於6.0地震的上揚時間；第二年則以台灣地區地震網收錄的地震資料分析ML介於5和6之間地震的上揚時間。 Source rise time is one of curial dynamic parameters for earthquakes; meanwhile, it is also a key factor to simulate strong ground motion. The rise time is many times less than the entire source duration, so it is not apt to be separated from the source duration. In the proposal, we propose a way to estimate the rise time. First, the source time function is determined by using non-negative time-domain deconvolution. Subsequently, we calculate the Fourier spectrum of the source time function and estimate the corner frequency following the -2 model. At last, we determine the rupture time from the estimated corner frequency, and then the rupture time deducted from the source duration obtain the rise time, which is used to calculate the dynamic stress drop. In addition, the radiated seismic energy can be estimated from the dynamic stress drop; then the dynamic stress drop would restrict the estimation of the static stress drop. Relationship between the rise time and seismic moment can be an indicator to investigate whether the source self-similarity exists. Previous studies on the rise time for Taiwan’s earthquakes are insufficient. The proposal make an attempt to systematically analyze the rise time for moderate-sized earthquakes in Taiwan. Furthermore, further probing the source self-similarity would be a significant issue to understand the seismogenic features for Taiwan’s earthquakes. The duration of this proposal is designed to be three years. In the first year, the target is to analyze the rise time for ML  6.0 earthquakes by using teleseismic P waves. In the second year, we estimate the rise time for 5  ML < 6.0 earthquakes by using local seismic data in Taiwan.
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