Step-over of strike-slip faults and overpressure fluid favor occurrence of foreshocks:Insights from the 1975 Haicheng fore-main-aftershock sequence,China  

作　　者：Xinglin Lei Zhiwei Wang Shengli Ma Changrong He 

机构地区：[1]Geological Survey of Japan,AIST,Tsukuba,305-8567,Japan [2]State Key Laboratory of Earthquake Dynamics,Institute of Geology,CEA,Beijing,100029 China

出　　处：《Earthquake Research Advances》2024年第1期36-46,共11页地震研究进展（英文）

基　　金：jointly funded by the National Key Research and Development Project(2018YFC1503301);the National Natural Sciences Foundation of China(NSFC)(U1839211);the fundamental scientific research project of the Institute of Geology,China Earthquake Administration(IGCEA2123)。

摘　　要：This study analyzed and summarized in detail the spatial and temporal distributions of earthquakes,tidal responses,focal mechanisms,and stress field characteristics for the M 7.3 Haicheng earthquake sequence in February 1975.The foreshocks are related to the main fault and the conjugate faults surrounding the extension step-over in the middle.The initiation timing of the foreshock clusters and the original time of the mainshock were clearly modulated by the Earth's tidal force and coincided with the peak of dilational volumetric tidal strain.As a plausible and testable hypothesis,we proposed a fluid-driven foreshock model,by which all observed seismicity features can be more reasonably interpreted with respect to the results of existing models.Together with some other known examples,the widely existing step-over along strike-slip faults and associated conjugate faults,especially for extensional ones in the presence of deep fluids,favor the occurrence of short-term foreshocks.Although clustered seismicity with characteristics similar to those of the studied case is not a sufficient and necessary condition for large earthquakes to occur under similar tectonic conditions,it undoubtedly has a warning significance for the criticality of the main fault.Subsequent testing would require quantification of true/false positives/negatives.

关 键 词：Haicheng earthquake Seismogenic fault ETAS FORESHOCK Deep fluid 

分 类 号：P315[天文地球—地震学]