Coseismic and postseismic Coulomb stress changes on surrounding major faults caused by the 2015 Nepal MW7.9 earthquake
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摘要: 2015年尼泊尔MW7.9地震重烈度区从震中向东延伸,致灾范围包括尼泊尔、印度北部、巴基斯坦、孟加拉和中国藏南地区,其应力调整对邻区和周边活动断裂可能产生重要影响.本文基于地震应力触发理论,采用岩石圈地壳分层黏弹性位错模型,计算了尼泊尔MW7.9地震引起的周边断裂,特别是青藏高原活动断裂的同震和震后库仑应力变化.结果显示,尼泊尔地震同震效应引起大部分震区库仑应力升高,余震主要分布在最大同震滑动等值线外部库仑应力升高区域;少量余震靠近最大滑动量区域,可能该区域积累的地震能量在主震期间没有完全释放.尼泊尔地震同震库仑应力对青藏高原,特别是中尼边境区域活动断裂有一定影响.亚东-谷露地堑南段、北喜马拉雅断裂西段、当惹雍错-定日断裂和甲岗-定结断裂同震库仑应力升高,其中当惹雍错-定日断裂南端,北喜马拉雅断裂西段同震库仑应力变化峰值超过0.01 MPa;帕龙错断裂、班公错断裂、改则-洞措断裂库仑应力降低,其地震发生概率有所降低.震后应力影响方面,未来40年内黏弹性松弛作用导致北喜马拉雅断裂、改则-洞措断裂和喀喇昆仑断裂整体应力卸载;藏南一系列正断层震后应力持续上升,其中帕龙错断裂南段受到震后黏弹性库仑应力影响,由应力阴影区逐渐转化为应力增强区,当惹雍错-定日断裂南段应力进一步加强,震后40年其南端应力变化峰值达到0.1345 MPa,亚东-谷露断裂南段应力亦持续增强.藏南正断层的地震活动性值得进一步关注.Abstract: The high-intensity region of the 2015 Nepal MW7.9 earthquake, that extends eastward from the epicenter, affecting Nepal, northern India, Pakistan, Bangladesh and southern Tibet of China. Since the adjustment of coseismic and postseismic stress could have significant effect on the adjacent areas and surrounding major faults, the study of the coseismic and postseismic stress is crucial for the seismic hazard assessment in these regions. Based on Coulomb failure stress triggering theory and the crustal layering elastic dislocation model, we calculated the coseismic and postseismic stress along surrounding faults induced by the Nepal earthquake and discussed the triggering of the aftershocks by the main event.#br#USGS provided the coseismic slip model of the 2015 Nepal MW7.9 earthquake. The historical earthquake focal mechanism was regarded as the actual geological fault parameter and the receive fault plane. We calculated coseismic and postseismic stress along surrounding faults induced by 2015 Nepal MW7.9 earthquake based on the PSGRN/PSCMP code.#br#The analysis of coseismic stress indicates some important results: The 2015 Nepal MW7.9 earthquake enhanced the static stress on most of the epicentral region. Most of the aftershocks occurred in the positive stress zone. The coseismic stress was increased on the south segment of Yadong-Gulu rift, the west segment of North Himalaya fault, Tangra Yumco rift and the Jaggang-Dinggyê rift, especially on the south end of the Tangra Yumco rift and the west segment of the North Himalayan fault, where the Coulomb stress was increased by more than 0.01 MPa. Coseismic stress released on the Palung Co fault, Bangong Co fault and Gerze-Dongco fault. Moreover, viscoelastic relaxation effect would unload the stress along the North Himalayan fault, Gerze-Dongco fault and Karakorum fault in the next 40 years, while the postseismic stress on a series of normal faults in southern Tibet would rise, which means that the stress shadow on the southern section of the Palung Co fault would gradually disappear, and the stress of the Tangra Yumco rift would further be strengthened. In 40 years after the earthquake, the Coulomb stress peak in this area would be about 0.1345 MPa, which is significantly over the stress threshold. The stress on the Yadong-Gulu rift would also be increased. #br#The high-intensity region of 2015 Nepal MW7.9 earthquake, extended eastward from the epicenter, parallel to the Main Himalayan Thrust. Of the total, 90% of the aftershocks occurred in the positive stress zone, while few aftershocks are located in stress shadow. Coseismic stress on optimal fault plane could explain the characteristic of aftershock distribution. Post-seismic relaxation would enhance the stress on some normal faults (such as the Palung Co fault, Tangra Yumco rift and Yadong-Gulu rift) in southern Tibet. For the high locking depth and lack of historical earthquakes, the seismic activity of the normal faults in southern Tibet deserves further attention.
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Key words:
- Nepal earthquake /
- Coulomb stress changes /
- Viscoelastic relaxation /
- Seismic hazard
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