2011年云南腾冲5.2级双震发震机理

Mechanism of the 2011 Tengchong,Yunnan,M_S5.2 double earthquakes

本研究联合使用观测震相到时和波形互相关数据,采用双差法对2011年6月20日与8月9日发生在云南腾冲的5.2级双震及其余震序列进行重定位,并采用gCAP(generalized Cut and Paste)方法反演了该双震全矩张量解.结果显示,双震震中位于龙川江断裂的西侧,余震序列在深度上为一个倾斜的柱状体,且倾向腾冲火山区;6月20日和8月9日5.2级地震均表现为体积缩小的闭合型破裂,包含有显著的非双力偶成分,但后者包含的非双力偶成分相对明显减小.这些结果表明,云南腾冲5.2级双震及余震活动可能与火山下方的地壳岩浆作用密切相关,龙川江断裂为热物质向上运移提供了通道,而双震型地震的发生可能与首次地震的破裂体积缩小挤出的流体作用于断裂密切相关.

On 20 June and 9 August 2011 two Ms5.2 earthquakes occurred in the Tengchong volcanic area, and we call them the double earthquakes because both their origin times and earthquake hypocenters are all close to each other. For better understanding the rupture mechanism of these double earthquakes, we inferred their full moment tensor solutions and relocated their seismic sequences. Using the arrival times collected from observation bulletins and obtained from the waveform cross-correlation method, we relocated the Ms5.2 double earthquake sequences with the double-difference location algorithm. These data were recorded by the CEA Crustal Institute temporary and Yunnan provincial permanent seismic stations. We obtained the full moment tensor solutions of double earthquakes with the generalized Cut and Paste （gCAP） inversion method. The gCAP method includes the parameters ζ and χ representing the strengths of the ISO and CLVD terms, respectively.Our results show that the epicenters of these double earthquakes are located west of the Longchuanjiang fault, and their aftershocks are a column tilted toward the Tengchong volcanic area with depth. The 20 June and 9 August Ms5.2 2011 double earthquakes are a kind of earthquakes with the volume-closed rupture mechanism having an obvious non-double-couple component, and the latter is much weaker in the non-double-couple component. The bootstrap test shows the values of the parameters ζ and χ are all located in their 95% confidence intervals, which demonstrates the reliability of non-double-couple components in our results. These results suggest that the Ms5.2 double earthquakes and their aftershocks are closely associated with the crustal magmatism under the Tengchong volcano and the Longchuanjiang fault provides a channel for hot material upwelling. We conclude that the occurrence of double earthquakes could be closely related to the obvious reduction in the rupture volume of the first earthquake,which leads to the extrusion of fluids that affect the fault again.