Study On Shallow Seismic Activity Model In Taiwan Region

Seismic activity analysis is the basic preliminary work for seismic hazard analysis and seismic zoning map compilation.Taiwan is located on the circum-Pacific seismic belt,and is one of the regions with frequent earthquakes in my country.The region has a long history of seismic observation,and the samples of seismic observation data are complete,which is suitable for seismic activity and risk analysis.By utilizing three different catalog declustering methods and three maximum likelihood estimation methods,the seismic activity parameters of the Taiwan region were calculated.Based on various seismic activity parameter models,the seismic hazard of Taiwan Island was calculated.The results indicate that different declustering methods significantly affect the probabilistic seismic hazard analysis.This paper collects earthquake catalog datasets with focal depths above ML2.0 and focal depth less than 350 km from 1900 to 2022 from the website of the Taiwan Meteorological Bureau(CWB).The earthquake magnitude in this earthquake catalog is unified as the moment magnitude Mw.Based on this earthquake catalog data set,the characteristic of seismic activity in Taiwan is analyzed,and the historical evolution of the lower limit for completeness magnitude MC recorded in different periods in Taiwan is discussed.The currently popular Gardner-Knopoff declustering method is used to delete the foreshocks and aftershocks in the earthquake catalog,and three time-distance windows are selected,namely Gardner-Knopoff(1972),Grünthal(Stiphout et al.,2012)and Uhrhammer(1986)),the corresponding mainshock catalog was obtained by calculation.The results show that different declustering methods have a significant impact on the earthquake catalog.The Gardner-Knopoff declustering method and the Uhrhammer time-distance windows parameter are recommended to remove foreshock events and aftershock events in this paper.We suggest that epistemic uncertainty resulting from various declustering approaches should be considered in probabilistic seismic hazard analysis.Stepp(1971)method is used to analyze the completeness of the earthquake catalog in Taiwan,and the completeness time of each magnitude bin is given according to the time when the estimated variance of the average earthquake occurrence rate of each magnitude bin deviates from the expected regression line,which avoids epistemic uncertainty introduced by human subjective judgment.Finally,using the maximum likelihood estimation methods of Weichert(1980),Bender(1983)and KijkoSmit(2012),the activity parameters in the G-R relationship in Taiwan are estimated.In order to verify the results of our estimated seismicity parameters,and to study the influence of subduction zone hypocenters on seismic hazard,this paper selects the Taiwan Strait and its surrounding areas for trial calculation of seismic hazard.The classic probabilistic risk analysis method proposed by Cornell(1968)was adopted,and the attenuation relationship established by Yu et al.(2013)was selected.The calculated results of hazard assessment based on two different seismicity activity models,obtained through two different declustering methods using Gardner-Knopoff and Uhrhammer,were compared with the seismic ground motion parameter zoning map of China(GB18306-2015)and the results of TEM PSHA2020 version for Taiwan region to validate the scientific rationality of the hazard assessment results.The research results of this paper can provide data input for subsequent probabilistic seismic hazard analysis in Taiwan region,and also provide reference of calculation seismic activity parameters method for the next seismic ground motion parameters zonation map of China.