2008年青海大柴旦6.3级地震及发震背景研究

The 2008 Ms6.3 earthquake in the Dacaidan region,Qinghai province and its seismotectonic setting

2008年11月10日青海省大柴旦地区发生6.3级地震,打破了青海省境内55个月的6级地震平静,该次地震可能是对2008年5月12日汶川8.0级地震在青藏块体内部应力调整的响应.通过该次地震及其发震断裂周缘地震震源机制解的分析认为,本次地震发震断裂活动性主要以逆冲为主并兼有走滑特性.对本次地震的发震断裂大柴旦—宗务隆山断裂带开挖探槽,探槽剖面揭露该断裂带在晚更新世—全新世早期有过明显活动;断裂带周缘历史地震的分布特征表明断裂带新的活动明显向南迁移;这与野外调查结果断层活动不断向山前迁移相一致.根据对青藏块体内部地震活动性分析认为,青藏高原内部中强震活动有顺时针螺旋迁移的特征,这一活动特征与GPS观测的青藏块体内部应力顺时针调整相一致,这一特征可能代表了青藏块体内部地震活动的一种新规律.基于对这种规律的认识和祁连地震带的大震构造孕育条件,祁连地震带东南部地区应倍受关注.

A M,6.3 earthquake occurred in the Dacaidan region, Qinghai province on 10 November 2008, breaking the 55 months-long quiet of the province. It was probably the response to stress adjustment within the Qinghai-Xizang block cause by the Wenchuan M,8.0 event on 12 May 2008. The analysis of focal mechanisms of this shock and other events surrounding its seismogenic fault suggests that this fault is dominated by thrusting with a strike-ship component. To investigate this fault, we have dug some trenches on the Dacaidan-Zongwulong shan fault zone. The trench profile reveals that this fault was very active during late Pleistocene-early Holocene time. Distribution of historical earthquakes around the fault indicated that the new activity of the fault shifts toward south, consistent with the continued migration of faulting to the range front observed in field investigations. The study on seismicity in the Qinghai-Xizang block suggests that the moderate and large earthquake in the block tend to migrate in a clockwise rotation, which coincides with the clockwise rotation of GPS velocity vectors. It is likely a new rule of earthquake in the block. Based on this insight and tectonic conditions for major earthquakes of the Qilianshan seismic zone, we suggest that much attention should be focused on the southeast of the Qilian shan zone.