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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/5368


    Title: 高密度地震資料分析及其用於台灣中部及東部孕震構造之研究;Applications of a dense seismic network data on the study of seismogenic structures of central and eastern Taiwan
    Authors: 張建興;Chien-Hsin Chang
    Contributors: 地球物理研究所
    Keywords: 九二一集集大地震;斷層;Chi-Chi earthquake;fault
    Date: 2004-04-12
    Issue Date: 2009-09-22 09:52:38 (UTC+8)
    Publisher: 國立中央大學圖書館
    Abstract: 台灣地區多元化的地震觀測網,提供了豐富與良好的地震研究資料。中央氣象局於1990年將台灣之地震儀全面更新為現代數位觀測儀器,至2003年全島設有70個短週期速度型及86個強震儀的即時觀測站,並且設置685個自由場強震站。過去十多年,尤其歷經九二一集集大地震,這些觀測網蒐錄了龐大的地震資料,極利於地震相關研究。本研究即以台灣現代地震網高密度、高品質的觀測資料,藉由較佳的地震定位方式,重新處理近十多年來發生在地殼深度範圍內的地震資料,包括台灣中部之災害地震以及東部之密集地震,分析其孕震構造,並探討這些孕震構造在台灣板塊運動架構下之意涵。 本研究探討一維地震定位法(1DLOC)、三維地震定位法(3DLOC)、聯合震源定位法(JHD)、雙差分地震定位法(hypoDD)及結合測站修正之三維地震定位(3DCOR)之優缺點,針對資料特性找出最佳定位方式。以1998年瑞里地震序列為例,結果顯示3DCOR最能提升整組地震群之精度。P波初動資料所決定的震源機制解顯示,瑞里地震為一逆衝型態斷層,震源機制走向角53º,傾角42º及滑移角為121º。根據震源位置、震源機制及餘震分布型態,本研究推測瑞里地震有可能為大尖山斷層錯動所引發。 本研究結合即時地震監測網及自由場強震網所蒐錄的資料,重定九二一集集主震之震源初始破裂位置為120.816ºE、23.853ºN,深度8.0公里。根據重定的震源位置及P波初動資料顯示,集集主震為一逆衝斷層型態之震源機制,走向角5º,傾角34º及滑移角為65º。另外亦討論主震後一小時之餘震,發現與薄皮逆衝理論之構造形態極為吻合。兩個主要餘震:嘉義地震與彰化地震序列,亦仔細重新定位,發現有構造上之意義,可能與北港基盤高區周圍之不連續構造線有關。至於其他餘震分布於主震的外圍位置上。 利用3DLOC與hypoDD兩階段定位方式重定台灣東部6446筆淺源地震,以及分析38個ML≥5.0之震源機制解,探討台灣東部的孕震構造,結果顯示,花東縱谷向下延伸是一個向東傾斜之地震帶,推測可能為歐亞板塊與菲律賓板塊之縫合邊界。在縱谷的西側中央山脈區主要為淺源的正斷層地震分布,其主要成因應為造山地殼擠壓抬升所形成。在縱谷東側的淺源地震主要呈現逆衝型態之機制,尤其是北緯23.5°以南區域,反應出源自東南方向之壓應力,斷層面的走向大都平行花東縱谷。然而,在北緯23.5°以北的區域則雜有正斷層及走向滑移的震源機制。由花東縱谷南、北震源機制之分歧表現,以及前人於此地區以海階定年與GPS速率分析之研究,推測海岸山脈大約在北緯23.5°(秀姑巒溪)處可能存在有一個構造分界。由重新定位的地震分布看來,在此構造分界以南,縱谷地震帶其震源機制呈現單純的逆衝斷層型態,在此構造以北,菲律賓海板塊已經開始向北隱沒並且向西彎曲,而其上方物質有順時旋轉(GPS)之現象,因此出現較為複雜的震源機制解。大體而言,重定後的地震分布與震源機制反映出與大地構造一致的特性。 The Central Weather Bureau (CWB) starts the modern digital earthquake monitoring from 1990. The CWB seismic network (CWBSN) currently includes 70 weak motion and 86 strong motion real time stations, and 685 free-field strong motion stations. In the past ten years, a large amount digital waveforms were recorded by the CWBSN. It offers a rich data set for seismological study. Four different earthquake locating programs are evaluated: 1) three-dimensions velocity structure location (3DLOC), 2) layered model joint hypocenters determination (JHD), 3) double-difference earthquake location algorithm (hypoDD), and 4) three-dimensions velocity structure with stations corrections location (3DCOR). The 1997 Rueyli earthquake sequence were used to test the performance of different methods. We found that the 3DCOR can greatly improve the location precision. The Rueyli mainshock was relocated to 120.660ºE, 23.510ºN at the depth of 5.6 km, deeper than the original CWBSN value of 2.8 km. Using this new location, a first-motion fault-plane solution shows that this earthquake is a thrust event with strike 53º, dip 42º, and rake 121º. Based on the hypocentral distribution pattern and the focal mechanism, the Rueyli earthquake was probably caused by faulting in the Tachienshan fault. The 1999 Chi-Chi earthquake in Taiwan represented the island's largest inland seismic event of the last century. Abundant high-resolution digital seismic data were recorded by CWBSN. In this study, I relocated the mainshock to be 23.853ºN, 120.816ºE at the depth of 8 km. The focal mechanism was of a thrust type with strike 5º, dip 34º and rake 65º based on the new location and the first motion polarities. I also analyzed the 1-hr aftershocks. They were mixed up in the records and not easy to isolate individual ones. The 1-hr aftershocks show good correlation with the tectonic pattern predicted by the thin-skinned thrust model. Two significant aftershocks: Chiayi and Changhua earthquake sequences are also discussed. They reveal interesting relations with structures of the Peikang-High. Some fault systems claim the responses for the aftershock sequence distribution patterns. We relocated 6446 shallow earthquakes and determined focal mechanism solutions of thirty-eight ML ≥ 5.0 events in the eastern Taiwan region (bounded by 22.7ºN, 120.8ºE ; 24.5ºN, 121.5ºE; 24.3ºN, 122.3ºE and 22.5ºN, 121.6ºE). The results suggest that the distribution of the relocated earthquakes generally agree with the fault plane determined from the focal mechanism solutions. The Longitudinal Valley (LV) is an east-dipping seismic suture zone that separates two different tectonic regions. On the left-hand side, shallow earthquakes and normal fault-type focal mechanism were found in the Central Range region. But on the right-hand side, most events occurred in the Philippine Sea Plate (PSP) were of the thrust-type, especially for the south portion and a few normal and strike-slip focal mechanism events were observed in the north portion. The tectonics of the eastern Taiwan can be classified from south and north into two regions, and there may exist a structure or boundary at about latitude 23.5°N with a strike of N110°E. In the northern portion of the eastern Taiwan, the plate boundary appears to be an east-dipping plane defined by the earthquake distribution. The focal mechanism solutions determined in this zone show thrust type faulting and agreed with this boundary plane (strike N20°E and dip about 50°). On the other hand, the southern part of the eastern Taiwan is a simple tectonics condition. The EP subducts to the east under the PSP. The LV is a suture zone dipping to the east, and most events occurred on the right-hand side of the LV. Focal mechanism solutions of these events were thrust-type with strike about N25°E and dip 54° to the east.
    Appears in Collections:[地球物理研究所] 博碩士論文

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