Probabilistic Seismic Hazard Analysis In Xichang Region Based On Ground Motion Simulations

China is one of the countries with the most serious earthquake disaster in the world,so it is necessary to make accurate and quantitative assessment of seismic hazard in seismically active areas in China.In the southwest of Sichuan Province,complex tectonic activities formed the Anninghe fault zone and the Zemuhe fault zone.The two faults have generated intense and frequent seismic activity,putting millions of people in the area around Xichang at risk of strong earthquakes and earthquake-induced geological disasters.In this paper,the seismic hazard of Xichang area is taken as the main research objective,the probabilistic seismic hazard analysis is combined with stochastic finite-fault ground motion simulation,and the seismic hazard curve of several field points including Xichang is obtained,as well as the seismic hazard zoning map of Xichang area under different exceedance probability conditions.The main research contents of this paper are as follows:(1)Based on the collation and statistical analysis of the historical earthquake information in the surrounding areas of Xichang and the existing research results of geological structure and seismic activity,several scenario earthquakes with specific epicentre,magnitude and focal depth are set on the Anninghe fault zone and Zemuhe fault zone,which have the greatest impact on the seismic hazard of Xichang City.(2)The stochastic finite-fault simulation method is used to simulate ground motion of all the scenario earthquakes.The simulation input parameters about the source,propagation path and site effect are determined,the simulated ground motion time history of each virtual observation point is synthesized,the simulated ground motion parameters such as peak value and acceleration response spectrum are extracted,the spatial distribution of simulated earthquake intensity is drawn,and the characteristics of the ground motion simulation results such as rupture directivity are analyzed.Finally,the peak parameter simulation values of all virtual observation points are compared with the attenuation relationship established by predecessors based on the measured seismic records,so as to verify whether the simulated ground motion is in accordance with the reality.(3)Based on the stochastic finite-fault simulation input parameters determined before,a large number of simulated ground motion parameters of calculation field points in the surrounding area of Xichang are obtained on the basis of multiple stochastic ground motion simulations for each scenario earthquake condition,and the conditional exceedance probability value under the given value of each condition is obtained by statistical method,combined with the probabilistic seismic hazard analysis method.The seismic activity parameters of the fault zone,such as the annual average occurrence rate,b value and spatial distribution function,were determined,so as to draw the seismic hazard curve of each field point in the study area.Then,according to the calculation results,the ground motion parameter values of each field point in the study area were obtained under four different exceedance probability levels,namely,the 50-year exceedance probability 63%,10%,2%and the annual exceedance probability 0.01%.Thus,the seismic hazard zoning maps corresponding to four fortification levels of frequent earthquakes,basic earthquakes,rare earthquakes and very rare earthquakes in Xichang area are drawn.As a research on the prediction of ground motion in the future,the results are of great significance to the earthquake prevention and disaster reduction of Chinese cities.From the point of view of earthquake protection,the simulation results of strong vibration observation records can directly reflect the strength of ground motion,which is helpful to evaluate the macroscopic intensity of earthquake,post-earthquake emergency rescue and post-disaster loss assessment,and also provide the design parameters of ground motion for engineering structure analysis.The simulated ground motion influence field based on the scenario earthquake can be directly compared with the historical or future earthquakes in Xichang area.Based on the probabilistic seismic hazard analysis results of scenario earthquakes and ground motion simulations,including the seismic hazard curve and the seismic hazard zoning map,the quantitative evaluation of seismic hazard in the study area can be carried out directly,so as to provide scientific basis for earthquake prevention and relief work.The research methods and results of this paper will have great potential in the future after continuous improvement,and provide a reference for the next generation of zoning map compilation.