2015年新疆皮山MS6.5地震震源机制及余震序列定位

doi:10.3969/j.issn.0253-4967.2016.03.016

摘要/Abstract

摘要：

利用新疆台网记录的波形数据，采用gCAP方法反演得到2015年7月3日新疆皮山M_S6.5地震的最佳双力偶节面解。其中，节面Ⅰ走向97°，倾角27°，滑动角51°；节面Ⅱ走向318°，倾角70°，滑动角107°；最佳矩心深度12km，矩震级M_W6.4；结合余震分布推断此次地震的发震断层为节面Ⅰ，主震破裂表现为逆冲型地震。同时，采用双差定位法对1 014个地震进行相对定位，得到937个重定位地震事件，结果显示余震序列沿NWW向单侧扩展，展布长度约50km；震源深度主要分布在25km之上，且浅部地震较多；深度剖面显示在主震处断层面向SW倾斜，表现为上陡下缓的铲形逆冲断层特征，与主震破裂节面倾角具有较好的一致性。另外，余震序列空间分布展示出塔里木块体向西昆仑造山带下插入，且沿余震扩展的NWW方向，断层面倾角呈现逐渐增大的趋势，可能表明断层在向NWW破裂的过程中走滑分量逐渐增强。此次皮山地震是青藏高原N向挤压塔里木块体的结果，进一步印证了印度板块与欧亚板块的持续碰撞对青藏高原及周边地震活动具有强烈的影响。

关键词: 皮山M_S6.5地震, 震源机制, 双差定位, 逆冲断层

Abstract:

Using the digital broadband seismic data recorded by Xinjiang network stations, we obtained focal mechanism of the July 3 Pishan, Xinjiang, M_S6.5 earthquake with generalized Cut and Paste(gCAP)inversion method. The strike, dip and rake of first nodal plane are 97°, 27°, 51°, and the second nodal plane are 318°, 70°, 107°. The centroid depth and moment magnitude are calculated to be 12km and 6.4. Combining with the distribution of aftershocks, we conclude that the first nodal plane is the seismogenic fault, and the main shock presents a thrust earthquake at low angle. We relocated 1014 earthquakes using the double-difference algorithm, and finally obtained 937 relocated events. Our results show that the earthquake sequences clearly demonstrate a unilateral extension about 50km nearly in NWW direction, and are mainly located above 25km depth, especially the small earthquakes are predominately located at the shallow parts. Furthermore, the focal depth profile shows a southwestward dipping fault plane at the main shock position, suggesting listric thrust faulting, which is consistent with the dip of the mainshock rupture plane. The spatial distribution of aftershocks represents that the Tarim block was thrust under the West Kunlun orogenic belt. In addition, the dip angle of the fault plane gradually increases along the NWW direction, possibly suggesting a gradual increase of strike-slip component during the NWW rupturing process. From above, we conclude that the Pishan M_S6.5 earthquake is the result of Tibet plateau pushing onto the Tarim block from south to north, which further confirms that the continuous collision of India plate and Eurasia plate has strong influence on the seismic activity in and around the Tibet plateau.

Key words: Pishan M_S6.5 earthquake, focal mechanism, double-difference relocation, thrust fault

中图分类号:

P315.3

张广伟, 张洪艳, 孙长青. 2015年新疆皮山M_S6.5地震震源机制及余震序列定位[J]. 地震地质, 2016, 38(3): 711-720.

ZHANG Guang-wei, ZHANG Hong-yan, SUN Chang-qing. MECHANISM OF THE 2015 PISHAN, XINJIANG, M_S6.5 MAINSHOCK AND RELOCATION OF ITS AFTERSHOCK SEQUENCES[J]. SEISMOLOGY AND GEOLOGY, 2016, 38(3): 711-720.

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