Primary Inversion Study On The Seismic Physical Forecast In Northeast Of China

In this paper the Northeast of China is selected as the area of seismic physical forecast, because the earthquake activities in this area have better orderliness and clearer dynamical mechanism. From 1900 to nowadays, the deep-focus (mb≥6.0) and shallow-focus (Ms≥5.0) earthquakes in Northeast China are obvious grouped activities and the spatial temporal correlation. The shallow-focus strong earthquake group is now in 5th period after finished 4 periods. The mid-strong earthquakes in Northeast China are sourcing from the subduction of the Japan sea plate. The major earthquake's migratory direction on the subduction zone in the Sea of Japan produces important effect for the space distribution of the shallow earthquakes in Northeast China. The earthquakes occur in Songliao basin and its periphery when the angle between Tanlu fracture zone and migratory direction is larger (α≥70o); it takes place nearby the Tanlu fault zone when the angle is smaller (α<70o).A three-dimensional earth's crust Finite Element Model of Northeast China is established as the model of seismic physical forecast, when studying the earthquakes in earth's crust of Northeast China (from 1900 to 1999). The FEA model is based on Northeast China seismic,geology,three dimension partitions and structure of wave velocity and so on. After mechanic simplified, an ANSYS FEA model is built; displacement of Japanese nosedive was simplified to a displacement force per year that applied to corresponding place of the model. Spring elements of different stiffness are used to stimulate other non-force implement boundary.According to many attempts, checking displacement input direction of the FEA model, analysis epicenter of Suihua earthquake in 1942 and Dedu group earthquakes in 1986 and model calculation to corresponding given year, contrast of maximal main pressure stress vector is so close. The model replies the stress field condition of given district. To lower the stress concentration and make the model in more reasonable condition, regional physical parameter and spring element stiffness was adjusted; before Tongliao earthquake in 1942 and Haicheng earthquake in 1975, the model was calculated step by step, there are many huge stress concentrations in earthquake area. And the whole regional maximal stresses are located at epicenter nearby. According to three aspects checking, we conclude that FEA model is reasonable for physical forecast model. Exerts the displacement load take the year as the unit (to start from 1900 to calculate to 1999) neighbor, used the adjustment earthquake to have the region model natural parameter means simulation actual earthquake to have the stress release effect, after gradually deduced the computation to withdraw the Mises stress to take the research object. Through to the estimated data statistical analysis, proposed may occur approaches in the different active time the position the around two earthquakes to occur the gap time interval cumulative stress increase, took in the certain region the earthquake has the quantitative target which the rule and further forecast, and through shakes the example analysis to the Inner Mongolian Boketu and the Liaoning Haicheng two areas to give the illustration.This article when the earthquake, the spatial rule which already occurs took the datum, the inversion studies its mechanics rule. The preliminary achievement is: Yalu River breaks and the Arun River broken ground area is the low stress collection central area, has 5.5 magnitude of above earthquakes possibilities not to be big, but the earthquake has the frequency high, shakes sends the gap approximately for 24 years, has the probability which double shakes to be higher. The Haicheng - gold state area is the high stress collection central area, has about 6.0 magnitude or the higher magnitude earthquake probability is higher, shakes sends the gap approximately for 35 years. The pine distant basin north and south beginnings and ends Tongliao area and south Bei River breaks by the northern area also is a stress concentration higher region, has 5.9 magnitude of about earthquakes probabilities higher, but the earthquake has the frequency not to be high, looked from the computing time and the cumulative energy, the present 5th active issue of in two area has the earthquake possibility to be bigger.Regarding computation regularity not ideal data and inversion research process itself, also may summarize very many valuable experiences. The result indicated that, may from the thin finite element grid, increase more faults, the establishment controllability strong dynamic numerical model as well as the quantitative careful consideration earthquake occurs when adjust the model the natural senate to amount to aspect and so on degree which the stress releases and restores further thoroughly studies.