昆仑山口西8.1级地震西破裂带尾端破裂特征

TIP STRUCTURES OF THE WESTERN SEGMENT OF SURFACE RUPTURE ZONE OF THE M_S 8.1 WEST OF KUNLUN MOUNTAIN PASS EARTHQUAKE

20 0 1年 11月 14日昆仑山口西 8.1级地震的地表破裂带 ,宏观上可明显分为东、西两段。野外考察表明 ,8.1级地震地表西破裂带分布于库水浣湖—太阳湖之间 ,总体走向为 2 85°～ 2 90° ,全长约 2 5km ,以左旋走滑为主。西破裂带具有典型的左旋走滑末端效应 ,该段西端位于库水浣湖以西的冲沟沟床中 ,破裂带总体走向由NWW向转为 2 4 0°方向 ,表现为一系列走向 30°～ 4 0°、长 5～ 15m不等的斜列张裂缝及走向NW -SE的挤压脊组合 ;东端位于太阳湖西岸阶地上 ,破裂带总体走向由 10 5°～110°转为N5 0°E左右 ,NE向构造张裂缝与NW向挤压脊交错排列 ,总体表现为棋盘格状 ,并在太阳湖边消失。分析认为 ,昆仑山口西 8.1级地震地表西破裂带为一独立的地震事件所形成的形变带 ,昆仑山口西 8.1级地震具有多点破裂的特征。

On November 14, 2001, an earthquake of magnitude M S8.1 occurred to the west of the Kunlun Mountain Pass. This event has produced a nearly east west striking surface rupture zone of more than 400 km in length. Macroscopically, this surface rupture zone can be distinctly divided into the western and eastern segments. Field investigation has revealed that the western segment of the rupture zone extends from the Kushuiwan Lake (35°57′36.2″N, 90°15′34.6″E) to the Taiyang Lake (35°55′34.0″ N, 90°32′52.2″E), having a total length of about 25km and a general strike of 285°～290°dominated by left lateral strike slip. The western segment of the rupture zone exhibits a typical tip effect of left lateral strike slipping. The western tip of this segment occurs on the gully bed to the west of the Kushuiwan Lake, where the general strike of the rupture zone turns from NNW to S60°W. The ruptures here consist of a series of 30°～40° striking en echelon tensile fractures of 5～15m in width, and NW SE striking compression ridges. The eastern tip of this segment is located on the terrace at the western bank of the Taiyang Lake. The strike of the rupture zone here turns from 105°～110°to about N50°E. The rupture zone is characterized by the crisscross arrangement of NE trending tensile fractures and NW trending compression ridges, appearing as a tessellated structure and ending at the shores of the Taiyang Lake. According to the tip structures of the western segment of the surface rupture zone, the distribution feature of the western segment and its relation to the eastern segment of the rupture zone, as well as the characteristics of the Eastern Kunlun Fault and available seismic observational data, it is suggested that the western segment of the rupture zone was produced by an independent seismic event, and that the M S8.1 west of Kunlun Mountain Pass earthquake is characterized by multi spot fracturing.