Study On 3-D Potential Seismic Source Models And Their Applications On Probabilistic Seismic Hazard Analysis

Potential source zones are 2-D in the current probabilistic seismic hazard analysis methods. Within these zones, earthquake focuses are simplified as points or lines and they distribute uniformly. In fact, earthquakes distribute non-uniformly in 3-D space, these non-uniform distributions have great influence on seismic hazard of sites near earthquake focuses. The geometric sizes and its attitudes of rupture surfaces that generate earthquakes with great magnitude have great influence on seismic hazard of near sites, and it is unreasonable if we still take the focuses as points or lines. Under this circumstance, we proposed three models to characterize the.3-D distributions of potential earthquakes with low to middle magnitude and the 3-D spreads of potential earthquakes with large magnitude, and studied their applications on probabilistic seismic hazard analysis.The general characteristics of earthquake hypocenter depth distributions in China were given by analyzing shallow earthquakes (depth < 70 km), which were recorded with modern instruments and contain depth information with orientation precision 1 and 2 after 1970. Different depth distribution functions to which focuses yield, normal distribution functions, were given for different geotectonic zones to depict the difference among hypocenter depth distributions in different zones. It is assumed that depth distribution of future potential hypocenters yield to the distribution characteristics similar to the above-mentioned ones. Considering the degree to which the basic data had been studied, in order to utilize the recent obtained research results, two methods which take into account the 3-D spatial distribution characteristics of seismic potential sources are proposed for improving the current probabilistic seismic hazard analysis methods. According to the seismicity model of low to moderate earthquakes (XU Guangyin, 1998), we constructed a 3-D potential source distribution model to characterizing the spatial distributions for low to moderate earthquakes. According to the non-uniform distribution models of earthquakes in potential sources (GAO Mengtan and XU Guangyin, 1996), we constructed a potential seismic source body model to depict the distribution characteristics of spatial concentration for large earthquakes. In this paper the seismic hazard analysis method that takes into account 3-D spatialhypocenter distributions of low to moderate earthquakes was adopted to calculate the seismic hazard for selected sample areas in Yangtse River middle reach seismic province where seismicity is characterized by low to moderate earthquakes. The seismic hazard analysis method applying potential seismic source body model was adopted for potential earthquakes with magnitude 6 and greater, and the method considering 3-D spatial hypocenter distributions of low to moderate earthquakes was also adopted for potential earthquakes with magnitude less than 6 in Beijing and adjacent areas where seismicity is very strong, rich in seismotectonics data and the delineated potential sources are relatively creditable. Considering uncertainties of precision and quantity of earthquake data used in statistical hypocenter depth distribution studies, we also adopted single-depth model and uniform-depth model of earthquake hypocenters as comparative models for method study of considering hypocenter depth factor in probabilistic seismic hazard analysis methods and we drew the following conclusions.(1) Probabilistic seismic hazard analysis methods that take into account 3-D spatial distributions of potential hypocenters have-great influence on results of seismic hazard analysis and regional seismic zoning.(2) The depth change of future potential hypocenters have great influence on the results of probabilistic seismic hazard analysis of sites near potential hypocenters, so the probabilistic seismic hazard analysis in which potential hypocenters are simplified as point sources should take into account the parameter of hypocenter depth, especially for earthquakes with small or m...