Seismicity Research Of Fenwei Seismic Zone

The Fenwei Seismic Zone is consisted of a series of fault basins that weregenerated in Late Cenozoic. The zone is not only a typical basin-range structure, butalso one of the main seismic active zones in China. The earthquakes occurredfrequently in this zone. Eight earthquakes of M≥7.0and two earthquakes of M≥8.0were recorded in this region. Therefore, it is significant to research the seismicity andgenetic machanics of earthquakes in the Fenwei seismic zone for predictingearthquakes and mitigating seismic hazards.The earthquake catalog is the base of the seismicity study, because the integrityof the earthquake catalog is an important factor for the reliability of seismic analysis.In the article, the author arranges the historical catalog of earthquakes with M≥4.7(434) in Fenwei Seismic Zone. And the author analyzes the completeness ofearthquake catalog using the b-value curve method, earthquake annual rate methodand proportional method. The results show that: the catalog of earthquakes with M≥6.0is complete since the year of1456; the magnitude M≥4.7is basic complete from1473.At the same time, the article using two methods (MBS and GFT methods)analyzes the completeness of earthquake catalog with ML≥1.0, according to theseismic station network phases in Fenwei Seismic Zone since1970. The results showthat the catalog of earthquakes with ML≥2.5is complete in the base stationconstruction period (from1970to1977); the minimum magnitude of completeness is2.2in the station adjustment and telemetry stations construction period (from1978to1997); the minimum magnitude of completeness is from2.0to2.1in the stationdigital period (from1998until now). The minimum magnitude of completenessaccompanied by the construction of seismic station is decreased, which reflects agradual improvement of the earthquake monitoring capabilities.The Acceleration Moment Release(AMR) is accepted by many scholars, andthere is great potential application in seismic hazard analysis and moderate-termearthquake prediction. This article breaks the previous ideology that using Matlabfunction to fit power function. We use the endless enumeration and nonlinear leastsquare method to fit the time to failure analysis function. This method can reduce the fitting error. At the same time, the author analyze the character of temporal and spatialdistribution before a moderate-term earthquake by combing the space cumulativestrain distribution and moment release acceleration. The method makes up for thedefects that only using AMR method produce a blank phenomenon, because of therestriction of the number of earthquakes. At the base of the complete catalog, we usethe method of b value, cumulative strain release and the acceleration moment releaseto analyze eight magnitude M≥5.0in the Fenwei Seismic Zone since1970. Theresults show that there are different levels of b value before these earthquakes, andthey also appear varying degrees strength of earthquake moment release.Through analyzing the seismicity of the historical devastating earthquakes andthe modern earthquakes, the results show that: there is north south migrationphenomena of the earthquakes with magnitude M≥6.0in Fenwei Seismic Zone. Thenext earthquake about magnitude6.0will likely happen in the Linfen basin or theWeihe basin in south of Fenwei Seismic Region. Accumulate strain and release from1970may have a8to10years cycle, and large strain release may happen in the nextseveral years. There is a significant empty energy release area between Datong andHuaian in Yanqing Datong basin zone. And there is the same phenomenon in thesouthwest of Yuncheng basin and the northeast of Weihe basin. Both the two zonesshould attract enough attention.