2008年汶川Ms8．0地震北川以北段地表破裂变形的主要样式

REPRESENTATIVE PATTERNS OF COSEISMIC DEFORMATION ALONG SURFACE RUPTURE NORTH TO BEICHUAN CITY OF 2008 WENCHUAN M_s8.0 EARTHQUAKE

2008年5月12日发生的汶川地震是由青藏高原东部龙门山断裂的活动所导致。震后的调查表明,北川县城以北的断裂段破裂了约90km。在北川县城以北,不同地点沿地震地表破裂所展现的地表变形差异很大,可能反映了断裂附近地表特性的变化。文章主要从5个典型地点来阐述5种代表性的地表变形模式。前两个地点,在北川县城以北几公里,反映了近地表基岩中的一种变形和从基岩向松散堆积物过渡区的一种变形模式。与此两种断裂陡坎变形不同,中间的两个点则阐述了褶皱陡坎,它们反映了2008年地震中断裂断错在地表以下终止的不同情形。最后一个点位于汶川地震地表破裂的北端,可能代表了当地表破裂结束时地表变形的模式。在北川以北段地表破裂上典型地点的详细测量的基础上,通过归纳野外获得的地表变形资料,构建出汶川地震地表破裂北川以北段的基本变形模型。

The May 12, 2008 ,Ms8.0 Wenchuan Earthquake was the result of the activity of the Longmenshan Fault, a thrust fault zone in the eastern margin of the Tibet Plateau. Field investigation after earthquake discovers that the Northern Yingxiu - Beichuan Fault ruptured the surface about 90km north to Beichuan City during the earthquake. The deformation shows greatly pattern differences along the rupture, which may reflect the varied nature of surface breaking. In this paper, we present deformation patterns observed from five representative sites. The first two sites （the North Beichuan City site and the Shilinzi Village site） are several kilometers away from each, displaying a pattern of deformation in bedrocks and a pattern of deformation at the transition from bedrock to unconsolidated cover. The central two sites （the Fenghuang Village site and the Mowan Village site）demonstrate folding scarps which may indicate slipping depth during earthquake. The final site （the Pingxi Village site） is at the northern termination of the Wenchuan Earthquake surface rupture,which may represent a pattern when the fault terminates rupturing the ground surface. Based on field survey on these sites we constructed schematically five deformation models, which are Simple thrust scarp, Hanging wall collapsed fault scarp, Multiple thrust scarps, Warping scarp, and Monoclinal folding scarp,along the Wenchuan Earthquake surface rupture.