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Title:: Discussion on the Mechanism of Short-term Anomalies for Cross-fault Short-leveling before the 2016 Menyuan M_S6.4 Earthquake

Author(s):: ZHANG Xi¹; BAI Zhuoli¹; LIU Xia²; (1.The Second Monitoring and Application Center,China Earthquake Administration,Xi'an 710054,Shaanxi,China)(2.The First Monitoring and Application Center,China Earthquake Administration,Tianjin 300180,China)

Keywords:: the Menyuan earthquake; cross-fault deformation; short-term precursors; meta stable-meta instable state

摘要:: 2016年门源M_S6.4地震发生前6个月,祁连山断裂带上距震中200 km内的跨断层流动短水准场地异常剧增; 震前2个月观测到以正断为主的协同性群体异常变化。通过分析跨断层短水准异常的时空演变与提炼灰色关联度指标,结合定点连续形变与小震活动等辅助信息,探讨其异常机理。结果显示:祁连山断裂带跨断层短水准在门源地震前短期阶段至少呈现出偏离线性阶段的亚稳态特征,应力释放与断层协同活动已经开始; 同时也存在显示亚失稳状态特征的可能。

Abstract:: In six months before the 2016 Menyuan M_S6.4 earthquake,there were quite more anomalies of mobile cross-fault short-leveling sites within 200 km from the epicenter of the Qilianshan Mountain fracture zone,and collaborative group anomalies dominated by normal features were observed in two months before the earthquake.In this paper,based on the analysis of temporal and spatial evolution of cross-fault deformation and the extraction of the grey relativity index,combined with the auxiliary information of fixed-point continuous deformation and small earthquake activities,we discussed the anomaly mechanism.The results show that the short-leveling observation of cross-fault of Qilianshan Mountain fracture zone at least displayed a meta-stable feature in the short-term stage before Menyuan strong earthquake,deviating from the linear stage,which already had reflected the beginning of stress release and fault synergy,and did exist the possibility of reflecting the characteristics of meta-instable state.