西藏高原北界之崑崙斷層地震破裂特性分析：結合地震、地質及衛星資料; Rupture Characters of the Kunlun Fault: Integrated Analysis from Seismological, Geological and InSAR Data

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题名:	西藏高原北界之崑崙斷層地震破裂特性分析：結合地震、地質及衛星資料;Rupture Characters of the Kunlun Fault: Integrated Analysis from Seismological, Geological and InSAR Data
作者:	溫怡瑛;Yi-Ying Wen
贡献者:	地球物理研究所
关键词:	地震;超剪切破裂速度;斷層應力轉移;supershear rupture velocity;earthquake;stress transfer on fault
日期:	2009-02-25
上传时间:	2009-09-22 09:54:34 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	由於印度板塊持續向北碰撞，造成西藏高原往東擠出脫逸，因而在高原形成許多大型走滑斷層。而位於西藏高原北界的崑崙斷層即為一條左側滑移運動強烈的活動斷層帶，其沿著崑崙山的南緣發展，綿延約2000公里。自1937年開始，崑崙斷層上陸續發生5個規模大於7的左移機制地震，且在地理位置上互補展開，暗示崑崙斷層上的5個大地震彼此之間的關係與區域構造運動的相連性。因此本文主旨在結合所有可獲得之資料，包括地震波記錄、地質資料、衛星資料等，深入分析崑崙斷層上最近期的兩個大地震--1997年瑪尼地震與2001年崑崙地震之破裂特性，以及速度變化與破裂特徵、斷層構造幾何等的相關性，並進一步探討崑崙斷層上地震間之應力轉移與區域構造間的關聯。針對2001年崑崙地震，野外地質資料不僅提供建立斷層模型的精確資訊，亦輔助遠震波形記錄進行聯合逆推求得良好斷層滑移分布模型；爾後經由順推模擬區域表面波檢驗破裂速度變化之分析結果發現，在400公里長的破裂過程中確實有超剪切破裂速度發生，但並不需要超過P波速度。而在最大破裂速度?6.0 km/s的S-3及S-4區段分別觀察到2公里寬的滑移分隔現象與最大可達8公里寬的破裂帶等與高速破裂相關的斷層特徵，暗示速度變化與斷層破裂能量的關連性。另一方面，1997年瑪尼地震傾角近乎垂直且雙向破裂的特性，使解析度有限的地震波資料難以判斷最佳斷層模型，而高解析度且包含斷層周圍廣泛區域之衛星影像資料的加入，則輔助了分辨不同斷層滑移模型造成的地表變形差異，決定其斷層模型為西段向北傾、東段向南傾，此一致於2001年崑崙地震的破裂斷層皆向南傾。兩個地震大部分的滑移分布都集中在深度0?10公里的淺部，其斷層破裂特徵也展現與斷層介面強度及斷層幾何之間的關聯性。而兩者明顯的左側滑移機制符合西藏高原向東擠出脫逸現象；除此之外，計算5個歷史大地震的庫倫應力變化結果指出，每個地震都發生在之前已破裂地震造成的應力上升區；而檢視地震序列的時空關係後亦發現，地震沿著崑崙斷層從左往右循環發生，這些都顯示西藏高原區域構造活動主導了在崑崙斷層上發生的地震行為模式。 The roughly east-west sinistral strike-slip Kunlun fault, one of the faults that accommodates the eastward extrusion of Tibet plateau, is an example of large scale slip partitioning in the continental crust. Since 1937, five large (M>7) earthquakes have occurred along different segments of the Kunlun fault, and all show distinct left-lateral strike-slip motion. In this study, we utilize most of the available data, including seismological, geological and InSAR data, to analyze the rupture properties of the two recent large earthquakes on the Kunlun fault—the 1997 Manyi earthquake and the 2001 Kunlun earthquake. Then, we will discuss the stress transfer on the Kunlun fault and the relationship between the fault and the regional tectonics. The comprehensive studies by using seismological, geological and InSAR data allow us to have a complete investigation on fault geometry and rupture characters. We first determine the nearly 400 km long finite-fault slip distribution of the 2001 Kunlun earthquake by inverting the teleseismic waveforms and using geological field observation as additional constraints. The geological field observations provide well-determined fault geometry and constrain the amount of slip at the surface. Then, forward modeling of regional surface waves was performed to estimate the variation of the speed of rupture propagation during faulting. We find that the rupture velocity peaked at around 6.0 km/s (supershear velocity, but not exceeding P-wave velocity) in the third and fourth segments (S-3 and S-4), where the maximum offset with a broad fault zone was observed. The significant variation in rupture velocity indicates differences in the partition of the earthquake fracture energy during faulting. On the other hand, the bilateral rupture and the nearly vertical dipping make it difficult to determine the optimal fault model of the 1997 Manyi earthquake. However, the high resolution and wide coverage InSAR data helps to identify the ground deformation variations derived from the different fault slip models. The preferred fault model of the 1997 Manyi earthquake is that the west segment dipps to the north and the east segment dipps to the south. This is consistent with fault geometry of the 2001 Kunlun earthquake, which is dipping to the south for all segments. The Coulomb stress transfer of the five large earthquakes and the spatial and temporal revolution of the earthquake sequence on the fault provide not only implications on tectonic involvement of the Kunlun fault to the eastward extrusion of Tibet, but also the earthquake triggering mechanism along a mature fault system.
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