以中尺度反射震測法研究屯子腳斷層活動機制及構造上的意義; Investigating Active Mechanisms of the Tuntzuchiao Fault by Multiple-scaled Reflection Seismic Methods

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題名:	以中尺度反射震測法研究屯子腳斷層活動機制及構造上的意義;Investigating Active Mechanisms of the Tuntzuchiao Fault by Multiple-scaled Reflection Seismic Methods
作者:	李奕亨;Yi-Heng Li
貢獻者:	地球物理研究所
關鍵詞:	橫移斷層;新竹-台中地震;屯子腳斷層;中尺度反射震測;花狀構造;Hsinchu-Taichung Earthquake;Tuntzuchiao Earthquake Fault;mid-scale reflection seismic survey;flower structure;strike-slip fault
日期:	2009-06-30
上傳時間:	2009-09-22 09:55:04 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	1935年新竹-台中地震為台灣地震記錄史以來災害最大的地震，該地震在地表上形成長達15公里的右移地表破裂，即屯子腳地震斷層。2002年重起的震測調查研究發現，在幾乎消失的斷層跡象下所呈現的震測構造影像，指出屯子腳斷層並非簡單的右移斷層而已，而是架構在複雜的地體構造地及應力環境下所孕育之新期斷層活動。本研究使用兩種尺度的反射震測方法：結合石油工業尺度震測在深度及跨距的優勢及中尺度淺層反射震測的高解析度，偵測橫移斷層系統的細部構造。本研究在屯子腳沿線區域佈置多條中尺度反射震測，解析斷層附近的淺部地層構造；另外利用大尺度震測剖面架構區域構造，並建立二者的相關性，以研判屯子腳斷層花狀構造在區域新期構造活動上所扮演的角色。結果顯示：屯子腳斷層為壓縮型之花狀構造（Positive flower structure），為在壓應力環境下的橫移斷層所形成，地層在接近斷層的部位逐漸隆起，在斷層中心呈穹隆狀、伴隨近垂直錯移面，地表上則形成雁行張裂的次構造。單次地震事件錯移的範圍可達數百公尺，並已累積數公里的規模。根據沿斷層線的震測剖面觀察，屯子腳斷層東北端應力作用及變形量最大，向西南逐漸減弱，遇清水斷層前應已終止。因屯子腳斷層屬右移走向滑移型態，斷層系統向東延伸進入三義斷層下盤，北側地盤在東側接觸帶相對擠壓三義斷層上盤，因此屯子腳斷層東段地層變形較為明顯。本研究認為屯子腳斷層與早第三紀基盤向上發育的張裂正斷層系統息息相關，這些於中新世台灣西部海域張裂盆地所發展的正斷層系統一直延伸進入台灣外麓山帶，當上新世菲律賓海板塊向西北擠壓影響到前陸盆地時，原本位於被動大陸邊緣張力環境，逐漸轉變為壓力環境，同時主應力場受到北港高區邊界影響，在台中后里一帶形成有利於發展右移斷層之應力環境。潛伏於第四紀地層下之古正斷層再活動，產生右移剪切，並在上覆的上新世晚期以後沈積的地層形成花狀構造，而屯子腳斷層下伏之泰安斷層可視為先導斷層或弱面。根據后里河階群的發育特徵、GPS地殼變形監測及震測構造影像等線索，均顯示屯子腳斷層至少活躍於晚更新世，並延續到現今，目前該構造仍持續累積應力，相當的活躍，在地震防災工作上值得注意。 The 1935 Hsinchu-Taichung Earthquake (M=7.1) in northwestern Taiwan that induced the greatest damage in the Taiwan’s earthquake history, was marked by a 15 km surface rupture, the Tuntzuchiao Earthquake Fault. Although the present topography dose not indicate much active evidence, the structural variation underneath the Holocene terrace deposit is relatively wild. The Tuntzuchiao Fault is not only a strike-slip faults of pure shear, but also grows with a complex structure developing under the transitional tectonic stress fields. This study provides insights of regional structures and seismic characters near the fault’s shear zone by combining the middle-scale shallow reflection seismic method and the large-scale petroleum seismic survey. After detailed seismic profile analysis, we propose that the Tuntzuchiao Fault is a strike-slip fault which develops as a “positive flower structure” under the compressional condition. The formations near the fault were up-rised and formed an arched zone. Shear stresses resulted in a duplex fault within the deformed area. The fault faded to the southwest, but was greatly deformed when the fault colliding with the hanging-wall of the San-I Fault in its northwestern corner. The Tuntzuchiao fault strongly related with the reactivation of the regional normal fault system. The pre-existing normal faults in northwestern Taiwan developed in neogene and extended into the onshore area. The stress field changed into compression while the Pliocene orogeny occurred. The pre-existing normal faults were reactivated to form a strike-slip fault circumstance under compressional stresses, which developed positive flower structures. The pre-existing “paleo-normal fault” can be identified as a precursor. The reactivation of pre-existing normal faults and stress field transition control the main neotectonic activities in northwestern Taiwan. In the study region, the trajectories of maximum stresses converge toward, and perpendicular to, the front of the Peikang Basement. Model results suggest that the chance of forming large-scale wrench faults is much less than that of forming conjugate strike-slip faults of pure shear. All the evidences including terrace generation, GPS crustal deformation and seismic profiles indicate that the Tuntzuchiao Fault is still quite active and should not be ignored in the earthquake mitigation studies.
顯示於類別:	[地球物理研究所] 博碩士論文

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