Research Of WenChuan Earthquake Zone's Structural Feature And Equilibrium Effect

Longmen Shan fault in the the intersection site of Qing-Zang Plateau and Yang-Zi splice.It is a strong fold uplift Since cenozoic, length of 500km, width of 30km, NE-SWdistribution,Intersection with the Daba Mountain in the north,Southwest was cut by Xianshuihe fault.The structure with a series of roughly parallel to the imbricate thrust zone structure,a typical structural features of thrust, with the development of pre-expansion mode. In this paper, the Longmen Shan region as the study area,The specific geographic coordinates28.8°N～33°N,101°E～106.5°E.In April and June period measured in the study area south-east towards a cross-section, the contrast of fault and isostatic anomaly before and after the earthquake.The Outset of profile is Longchang,pass Jianyang, Chengdu, Lixian, end at maerkang,The measured data of after eartkquake, in addition to this measured data, found no other information.Because the complexity of the region,in order to better complete inversion,the paper developed several new methods: walsh filter, expansion of the three direction,based on Hartley's horizontal and vertical first derivative,Euler deconvolution based on Hartley Transform ,improved normalized total gradient method.Walsh transform proposed byamerican mathematician Walsh in 1923 based on Square-wave function, in the early 70 century, after the release of fast Walsh transform, as in the Walsh domain provided the conditions to solve the problem. Today a lot of data filtering and field separation methods during operation does not recognize the shortcomings of mutation information, walsh transform the nature of a square wave, the boundary can be well highlighted features, this feature has been widely used in segmentation of well logs, paper to walsh transformation applied to the magnetic data processing to achieve separation filtering and field operations, Walsh power spectrum by finding the "break point" or threshold point of the filtering, and field separation, theoretical model results show that this method can better filtering and field separation completed work and for the Walsh transform step effect of the existence of the means used be resolved diplomatically.In the gravity and magnetic data processing, are often the first to expand the edge of the original data processing. Commonly used methods of expanding edge decay to zero and the cosine expansion fold edge method, these two methods are obvious boundary effect, the present exception for the measuring point measured not only by the impact of geological targets, but also by a certain range from around other geological effects, proposed a three-edge method of the direction of expansion. C direction is the principle method of expanding edge of a measuring point in three different directions at the same time expand the edge, taking the average of boundary expansion as the final result of the expansion side, this can be integrated around the geological impact, reducing the boundary effect, and the geological characteristics of different forms of the method is applicable to all. The results from the theoretical model can be found that the expansion method is not only a good side to complete the expansion of border operations, and maximize the retention of the boundary information. Hartley transform is derived based on the re-magnetic spectrum and the horizontal and vertical first derivative formula, experimental results show that the Hartley transform to calculate the derivative of the results relative to other methods and theory of numerical difference is less derivative, and the error analysis, error 5, % of the shows that this method can the completion of the derivative calculation.Euler deconvolution method (Euler inversion method) is an automated source location estimated market potential field inversion method. Gradient data measured in the absence of the case, the derivation of potential field anomalies during the high-frequency noise is amplified, so that divergence of the Euler inversion results. This article will be based on Hartley's horizontal and vertical first derivative applied to the Euler deconvolution method to achieve inversion, effectively improve the retrieval accuracy, and Hartley transform-based Euler deconvolution of the fault model Retrieval, experimental fracture in the inversion result in the performance of the Euler form.Gravity gradient of law by the Soviet scientists BM Beryozkin in the 20th century, put forward 60 to 70 years, and it is a heavy use of high-precision anomaly and magnetic anomaly data to determine the source distribution method. Normalized total gradient method because no additional conditions, calculation is simple, and can semi-quantitatively determine the location of geological bodies are widely used to study the detection of oil and gas or oil and gas structures. Be noted that the method is also applied to magnetic anomaly. Now calculate the total gradient of gravity normalized common method is to use sine series derivative, exponential function to the next extension, the stability of poor results obtained, in order to suppress oscillations under the effect of delay in the process of carrying out by the introduction of a smooth factor . However, this method is not very good to complete normalized gradient of gravity calculation, because one of its derivative methods have low accuracy; second smoothing filter can better enhance the extension process stability. To solve the above problems, this article will use Hartley transform method to obtain the first derivative of, and the development of new smoothing filter, multi-bit derivative by contrast can be seen that the accuracy of this method over traditional methods of high precision through model tests show that the method of calculation accuracy and stability are significantly improved, the final gravity normalized gradient and phase diagram of the characteristics of the study area were identified faults.Euler deconvolution method in the area of regional gravity data inversion, the redrawing of the fracture patterns in the region. Euler deconvolution method and the normalized total gradient method on the profile after the earthquake, gravity and magnetic anomaly data in the inversion, obtained after the earthquake faults in the area of basic distribution, and regional gravity data on the use of kriging interpolation of seismic survey lines acquired before the Bouguer gravity anomaly, and the inversion of the profile. Before and after the earthquake by earthquake rupture patterns of the contrast can be found two changes: one Dujiangyan - Jiangyou fault changes: before the earthquake the fault is a north west orientation basement fault, the upper part of the fault after the earthquake occurred four different directions of small fracture (or fracture zone), resulting in such changes may be due to the earthquake rupture process of a small production. Second, the emergence of new fault: seismic data show that in Dujiangyan - Jiangyou (F5) had a fracture of the east southeast orientation of deep faults, both in gravity and magnetic field in the display. The fault shall be buried fault, because smaller fracture width may be smaller scale before measuring, no fault was found that the existence of this need in future research attention.Analysis of the earthquake before and after isostatic anomaly changes,preliminary analysis of the cause。Utilizing bouguer gravity anomaly inversion to get the change of Mohuo surface.Finally,According to different fault patterns,changes in Moho depth and isostatic anomaly, Formation of the earthquake and the impact was described.