2001年昆仑山口西8.1级地震地表破裂带

SURFACE RUPTURE ZONES OF THE 2001 EARTHQUAKE M_s 8.1 WEST OF KUNLUN PASS,NORTHERN QINGHAI-XIZANG PLATEAU

20 0 1年 1 1月 1 4日昆仑山口西 8.1级地震是近 5 0年来在我国大陆发生的震级最大、地表破裂最长的地震事件。地震地表破裂带全长 42 6km ,宽数米至数百米 ,总体走向 90°～1 1 0°,具有明显的破裂分段特征 ,自西向东由 5条次级破裂段组成。各破裂段又由若干更次级左阶或右阶斜列的破裂组成 ,具有自相似的分形结构特征。地震破裂带以左旋走滑为主 ,倾滑量很小。宏观震中区位于库赛湖东北 93.0°～ 93.5°E一带的昆仑山南麓断层谷地内。最大地表同震左旋水平位移 6.4m ,最大垂直位移为 4m。地表水平位移沿地震破裂带走向出现 6个峰值 ,各峰值之间存在相对独立的衰减序列 ,这表明此地震具有多点破裂特征。

The 2001 M _s =8.1 west of Kunlun Pass earthquake is the largest and associated with the longest surface rupture having occurred on the Qinghai-Xizang Plateau since 1951. Delineating the rupture characteristics of this event may help us to better understand the current state of stress and the evolution of the Qinghai-Xizang Plateau. The mainshock ruptured the whole Taiyanghu-Kushuihuan, Bukadaban-Kusaihu faults, and the western part of the Kunlun Pass fault, and was probably a continuation of seismic activity that began approximately four years earlier with the M _s=7.9 Mani earthquake 300 km to the northwest. Although it is not known whether there was large earthquake during the period of historical record, abundant scarps and left-laterally offset geomorphic features of Holocene age indicate that the fault is active and that it might produce large earthquakes.The trend of this surface rupture faulting zone is 90°～110°. The fairly linear trend of the fault on the surface suggests that the fault is vertical or subvertical over much of its length. From west to east, the five principal faults of the mainshock are the Taiyanghu-Kushuihuan, Buka Daban Peak, west Kusai Lake, east Kusai Lake, and Kunlun Pass faults. The total length of these overlapping surficial fault rupture strand is ca. 426 km. All but the Taiyanghu-Kushuihuan fault is 64～103 km long. Two primary characteristics of the fault zone are the en echelon geometry of the principle faults and the predominance of sinistral slip. The characteristic en echelon structure of strike-slip faults is observed at all scales along the 2001 rupture. Secondary splays and Riedel shears existed on all scales.The maximum surface left-lateral strike-slip is 6.4±1.4 m, with as much as 4 meters of vertical slip.