张广伟， 雷建设

中国地震局地壳应力研究所(地壳动力学重点实验室)， 北京 100085



2015尼泊尔MS8.1地震中等余震震源机制研究

张广伟， 雷建设*

中国地震局地壳应力研究所(地壳动力学重点实验室)， 北京 100085

本研究利用西藏台网记录的波形数据，采用gCAP方法反演了2015年4月25日尼泊尔MS8.1大震5次中等余震(5.0≤MS≤6.5)及西藏定日MS5.9地震震源机制解.结果显示，6次地震包含2个正断、2个走滑及2个逆冲型地震.其中2个正断型地震位于主震的东北方向，即发震断层的上盘，表明该区域受到主震同震位移的影响，表现出应力拉张的变化特征；2个走滑型地震在主震破裂的东南方向上，说明随着破裂往东南方向延伸，余震的走滑分量增强；另外2个逆冲型地震位于5月12日MS7.5强余震区域，与MS7.5地震的滑移状态一致，可能与主震同震位移引起该区域处于应力挤压状态密切相关.这些结果表明，尼泊尔MS8.1主震发生后，由于同震位移的影响，不同区域处于不同的应力状态，从而使中等余震表现出不同的震源类型.

震源机制解； 中等地震； 尼泊尔MS8.1地震； gCAP方法

Using the digitally broadband seismic data recorded by the Xizang network stations, we obtained focal mechanisms of six moderate-sized earthquakes with the generalized Cut and Paste (gCAP) inversion method. This method divides three-componental waveforms into Pnl and surface wave segments, and allows adjustable time shifts between observed and synthetic waveforms, which reduce the influence of uncertainties in the 1-D velocity model used.

Our results show that the six moderate-sized earthquakes present different source types, two events for normal types, two events for strike-slip types, while the rest two events for thrust-fault types. The six earthquakes with different types are located at different regions, respectively. The two normal-fault earthquakes are distributed to the northeast of the mainshock and they are situated in the hanging wall of the fault. These normal-fault sources may be due to the tension stress change caused by the coseismic slip. The two strike-slip sources are located between the mainshock and the May 12MS7.5 strong aftershocks, suggesting that the strike-slip component is getting larger with the southeast extension of the fault. The two thrust-fault earthquakes are also interpreted as a compressional stress change due to the mainshock coseismic slip. Intergrating these focal mechanism solutions with the aftershock distribution, we conclude that different source types of these moderate-sized earthquakes in different regions all might be due to different stress regime caused by the coseismic displacement.Keywords Focal mechanism; Moderate-sized earthquake; NepalMS8.1 earthquake; gCAP method

1 引言

据中国地震台网中心测定，北京时间2015年4月25日14时11分26秒，尼泊尔发生MS8.1大地震，震中位置28.2°N、84.7°E，震源深度20 km.截至5月6日，尼泊尔境内已经造成至少7566人丧生，超过14500人受伤(中国地震局，2015).强震还引发珠穆朗玛峰雪崩，部分基地大本营被掩埋.此次地震震中距离尼泊尔首都加德满都约80 km，其余震由近西北向近东南方向迁移，震源深度多集中在20 km以上(图1)，属于浅源型地震，因……