Mechanisms Of Uneven Seismic Activity And Earthquake Fault Interaction

The generation of a earthquake is detendned by the evolution of seismic source and the influencefrom outside. The complexion of seismiclty is due to the earthquake interaction of seismic faultactivity and the change of seismic generation process caused by the interaction. In this paper, aphysical model of earthquake generation and seismicity is designed to study the mechanics oftriggered earthquake and heterogenelty of earthquake magnitude distributlon based on friction rate-state dependent and fault interaction theory.(1) The study on the triggered and inhibited regional seismicity and its mechanismIt is thought the first evidence of triggered small earthquakes by big earthquake that the LandersEarthquake in Amenca triggered seisndcity increasing in 14 regions with epicenter up to l250km. Inthis paper, the studies on the seismicity within several hundred kilometers around the epicenters of theHyogo-Ken Nanbu, Japan, M=7.2 earthquake and the Tangshan, China, M=7.8 earthquake show thatseisndcity increased remarkably in many regions. A quantitative statistic method is used to test theslgnificance of these change to the correlation between the seismicity increasing and the two bigearthquakes and the results show that the increasing of seismic rate is significance and is caused by thetwo big earthquake and called regional triggered seismicity. Though the regional triggered seisndcityis not common, it provides us valuable observational evidence to understand the physical intrinsic ofthese complex phenomena. In other hand, regional seismicity night be inhibited by big earthquake.For example, during several ten years, after the San Francisco M=8 earthquake in l906 and the SanheM=8 earthquake in l679, seismicity decreased remarkably within several hundred kilometerssurrounding the eplcenters. In this paper, we studied the mechanism of "regional seismicity inhibition"due to the interaction of parallel faults in viscoelastic medium. The Coulomb Static Stress Changemodel is applied and a mathematics-physics model with friction rate-state dependent constructive lawls designed to understand the mechanism of regional triggered seismicity. The results demonstrate thatthis model could explain some features of regional seismicity triggrring.(2) Interaction among strong earthquake and its mechanism.The Xianshuihe Fault Zone in southwestern China is noted for its hlgh intensity and frequencyselsmicity. Based on the comprehensive analysis on the geologic structure, selsmic surface fissure andfocal mechanism solution, the elastic dislocation models of earthquakes above M(1/4) since the lastseisrnic active episode of the Xianshuihe Fault Zone are set to study the regional static stressevolution and analyze the correlatlon between it and the strong earthquake occurrences since l893.The results show that the earthquakes above M7 and majority of earthquake above M5(1/4) occurred in Places with Positive Coulombmb Failure S阶" change(ACFSCFS)·In addition,the effectofreglonal static ＼ stress change due to the big e tthquakes in Xianshuihe FanFault Zone on the neighbouring fault zone is analyzed and the possible place of future s血ng earthqu业e is predicted pre皿rily．一 Tha tampealspSCICI CICS比dllg Of山e HO勺UUll,＊milli,M＝8．6 lll ribthqUUkU UUd山e GCICCg,＊hCC, M＝8．000n…OO卜CISSXCCpd0001．Alldll悦IC山dOCCdollllloddof山OHOlyOOllllllnbqll＊1llSSCtIO calculate the ACFSCFS due to it and the resalt shows that the CFSCFS on seismogenic fault plane of the Gulang earthquake IncfCased and the Gulang e tthquake is pfo口D口tCd by Mout tCn years． (3)The breading ofmagnitude－地quency relation curve and its mechanism． The hetefogeneity of seismicity is also displayed by the discontinuity of statistic featufC of som seisndc para。ter in addition to the phenomena mentioned above．A t…l...