汶川8.0级特大地震的断裂特性与强地面运动的关系

doi:10.3969/j.issn.0253-4967.2015.04.010

摘要/Abstract

摘要：

2008年汶川8级地震的发震构造是高角度铲形逆冲断层, 伴随这种类型地震的远近场强地面运动在中国是第1次被记录到。综合汶川地震发震构造、破裂过程和强地面运动峰值加速度的资料, 探讨高角度铲形逆冲断裂作用与强地面运动的关系。结果显示, 龙门山断裂带内强地面运动峰值加速度明显大于断裂带外的台站, 前者可达后者的2倍多。同时, 该地震强地面运动具有很大的垂直分量, 近断层垂直分量大于水平分量。结合远场资料, 发现龙门山断裂带上盘峰值加速度垂直分量总体上大于下盘, 上盘垂直分量的衰减比下盘慢。不考虑远场的高值异常, 水平分量似乎也存在上盘效应, 但目前无证据表明这些异常应该被剔除。另外, 远场地面运动特征显示, 相对于反方向, 沿同震断层扩展方向(NNE)的峰值加速度水平分量衰减较慢, 垂直分量的这种方向效应不明显。考虑到汶川地震破裂浅、断面陡和以垂直形变为主这3个显著的同震构造特性, 近场和远场地面运动记录反映出位错类型和台站的实际断层距的控制作用。正因为汶川地震高角度铲形逆冲断裂结构的特殊性, 导致其地面运动与普通逆断型地震强地面运动的同震效应在某些分量上相同, 其他分量存在差异。

关键词: 汶川地震, 高角度铲形逆冲断层, 断裂作用, 强地面运动, 峰值加速度

Abstract:

The 2008 M_S8 Wenchuan earthquake occurs on a high angle listric thrust fault. It is the first time that the near and far field strong ground motion was observed for such special type thrust earthquake. This paper jointly interprets the distribution of peak acceleration of ground motion data with seismogenic structure and slip propagating process to investigate how high angle listric thrust fault controls the pattern of strong ground motion. We found that the distribution of peak acceleration of strong ground motion during the Wenchuan earthquake has four distinctive features: 1)The peak acceleration of ground motion inside the Longmenshan fault zone is large, that is, nearly twice as strong as that outside the fault zone; 2)This earthquake produces significant vertical ground motion, prevailing against horizontal components in the near field; 3)The far field records show that the peak acceleration is generally higher and attenuates slower versus station-fault distance in the hanging wall. It is doubtful that the attenuation of horizontal components also has the hanging wall effect since no evidence yet proving that the unexpected high value at long distance need be omitted; 4)As to the attenuation in directions parallel to the source fault(Yingxiu-Beichuan Fault), the far field records also exhibit azimuthal heterogeneity that the peak acceleration of horizontal components decreases slower in the north-northeastern direction in which the co-seismic slip propagates than that in the backward way. However, the attenuation of vertical component displays very weak heterogeneity of this kind. Synthetically considered with shallow dislocation, high dip angle, and prevailing vertical deformation during co-seismic process of the Wenchuan earthquake, our near and far field ground motion records reflect the truth that the magnitude of ground motion is principally determined by slip type of earthquake and actual distance between the slipping source patches and stations. As a further interpretation, the uniqueness of high angle listric thrust results in that the ground motion effects of the Wenchuan earthquake are similar to that due to a common thrust earthquake in some components while differ in the others.

Key words: Wenchuan earthquake, high angle listric thrust fault, faulting, strong ground motion, peak acceleration, hanging wall effect

中图分类号:

P315.2

黄蓓, 张培震, 张冬丽, 李小军. 汶川8.0级特大地震的断裂特性与强地面运动的关系[J]. 地震地质, 2015, 37(4): 1055-1069.

HUANG Bei, ZHANG Pei-zhen, ZHANG Dong-li, LI Xiao-jun. the faulting characteristics of 2008 wenchuan m_s8.0 earthquake and its relation with strong ground motion[J]. SEISMOLOGY AND GEOLOGY, 2015, 37(4): 1055-1069.

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