Study Of Moderate-Strong Seismic Intensity Attenuation Relations In Sichuan-Yunnan And Its Adjacent Areas

China is one of the worst-earthquake countries in the world, and the severely destructive earthquakes brought great losses to people's life and property as well as economic construction. Sichuan-Yunnan and its adjacent area is intensely affected by earthquakes, accumulating abundant historical earthquake data, especially those at medium-strong magnitudes. Now the area still suffers frequent earthquake strikes, so it is of great practical meaning to study the pattern of intensity attenuation in the area. Under the present economical situation in China, it is of vital importance to find out the way to perform seismic safety assessment and quickly determine the affected range in the target area. This paper tries to study on the pattern of intensity attenuation and distribution in the target area, hoping to get a distributional model of intensity attenuation that is suitable to this area. Hence, the researchers could carry out a quick simulation of the intensity distribution area of the earthquake, and go on to assist the quake relief forces to launch the emergency relief work.The historical earthquakes in Sichuan-Yunnan and its adjacent area is systematically sorted, ending up with 91 typical earthquakes with magnitude≥6.0, the data are digitalized with GIS, and finally the data are obtained about the length and area of the intensity distribution of these historical quake cases. Considering the tectonic environment of epicenter and the topography conditions of the affected area, these quake data are classified into southwest China region and Sichuan Basin region respectively. At present, the commonly used intensity attenuation model is oval model, which means the intensity attenuates along prolate axis and minor axis. According to the formula I=a+bM+clg(R+R0), the writer fits the prolate and minor axis data at different intensities obtained with the oval model, and gets the pattern of intensity attenuation in southwest China region, basin region, and the whole area. Through comparing the previous research results and the present data, and combining intensity correction, the writer gets an intensity attenuation pattern that is more correct and more suitable to the target area.The various intensity areas are fitted, resulting in the formula dealing with the relationship among area, magnitude and intensity--S=exp(a-bI+cIM). Then, the area relationship and the attenuation pattern along the prolate and minor axis is integrated, the simulated isoseismal map is superimposed and compared with real earthquake cases, and the intensity attenuation pattern of the oval model is further modified. The statistical results need to be modified by the head-trail-limiting principle, adjusting the envelope curve and the high-intensity area by intensity migration.Different earthquakes have their respective applicative models. It is convenient for the regular medium-strong earthquakes to use oval model for intensity attenuation assessment. But when it comes to the large earthquakes with definite ruptures, obviously it's more suitable to apply fault distance model and buffer area analysis to get intensity attenuation assessment. Analyzing the historical earthquake cases after 1970, the writer gets the relation between earthquake magnitude and rupture length, as well as the relation between earthquake magnitude and buffer distance (d) in buffer area analysis. Among the earthquakes with magnitude≥7.5,such parameters as earthquake magnitude can decide the distribution of the whole buffer area, and its simulation results are close to real quakes. Through further analysis, and by using buffer area analysis, the writer obtains some preliminary achievements about the intensity distribution assessment.After studying the intensity attenuation pattern and intensity distribution model, the writer integrates the patterns and models that are obtained by using VB and ArcGIS into a plug-in module. Under the circumstance that basic earthquake parameters are already known, the researchers can apply the integrated software and quickly get the intensity distribution condition of a certain quake, and then provide support to the emergency work.