Research On The Potential Source Model Of Seismic Hazard Analysis In Strong Earthquake Tectonic Area

In this paper,the Xianshuihe fault zone and surrounding area are taken as the research demonstration area to study the seismic hazard assessment method in the strong earthquake tectonic area.This region is a narrow and densely populated area with complex seismic structures and frequent historical large earthquakes and huge risks of earthquakes and geological disasters on the South-north seismic belt of China.It is also a key focus area of earthquake prevention and disaster reduction in China.Therefore,it is particularly necessary to carry out research on earthquake risk assessment methods adapted to local seismotectonic evironment.The serious seismic risk is undoubtedly caused by the Holocene strike-slip faults as well as other medium-strong earthquakes.The Xianshuihe faults mainly comprise seven active fault segmentations charactered by characteristic earthquake model throughout this densely populated region.In order to achieve this,we conducted the following research:(1)For the large earthquakes that may occur on the active fault section,especially the Xianshuihe fault zone,it has typical seismicity of characteristic earthquake.The three-dimensional fault plane source is established according to the three-dimensional structural parameters of the characteristic fault.The characteristic earthquake model is assumed as the magnitude-frequency relationship for the large earthquake.The BrownianPassage-Time Model and Poisson model are adopted as the probability density function to describe the recurrence of characteristic earthquake simultaneously.Four magnitude-fracture empirical relationships were used to comprehensively evaluate the magnitude and the mean recurrence period of characteristic earthquake.Finally Seismic hazard parameters is obtain in different time windows in BrownianPassage-Time Model.It is noteworthy that magnitude of characteristic earthquake,recurrence period and aperiodic factors are important factors that affect time-dependent seismic hazard.(2)In order to reflect this spatial inhomogeneity that the background seismic activity has obvious clustering and banding in the strong earthquake tectonic zone,gridded point source model is adopted.The ellipse smoothing algorithm is used to estimate earthquake occurrence rate assumed to the truncated G-R distribution..The obtained seismic hazard has a spatial correlation with the distribution of the background earthquake,it si very effective to solve problem that cannot deal with spatially non-uniformity of background earthquake in the traditional potential seismic source zone method.(3)For the moderate-strong earthquake activity between the background earthquake and the characteristic earthquake in the strong earthquake tectonic area,earthquake distribution in space and time still have been curtained by active fault partly,so the enveloping area of several faults is used as its potential source area,like the classical plane potential source model,using the equivalent average seismic depth,the magnitude range is from the upper limit of background earthquake to the second-large magnitude of the characteristic fault,the seismic activity is follow the Poisson process truncated GR distribution.The spatial distribution function is used to reflect the non-uniformity of the earthquake between the potential sources.By integrating the full probability of the three different potential source models,the predicted ground motion in more probability(return period of 475,2475)and period of response spectrum(peak,0.2 s and 1 s)are evaluated.(4)Based on the focal parameters of the three-dimensional fault plane source in the probabilistic seismic hazard analysis,the deterministic seismic hazard assessment based on the scenario earthquake is performed to obtain the simulation results of the near-fault ground motion.Due to absence of the recurrence rate which is most difficult to determine,the deterministic result would be regarded as the maximum credible ground motion of the Xianshuihe fault zone in this method with clear physical mechanism,which can be used to constrain the upper limit of the ground motion at small probability level in the probability seismic hazard analysis.By comparing the two results of DSHA and PSHA,the result at probability of exceedance 2% in 50 years in 30 km buffer zone is basically consistent with the deterministic result.