Evaluating 3-D Crustal Velocity Models In North China Using Regional Seismic Travel Time And Rayleigh Wave Vertical-Horizontal Amplitude

Due to the differences in research methods and data,there may exist multiple velocity models in the same area,but the reliability of these models usually lacks systematic and objective assessment.This study is divided into two major parts.In the first part of this study,we will compare the observed direct arrival time data of Pg-wave and Sg-wave of 1749 earthquakes from 2009 to 2016 recorded by 131 seismograph stations of the National Seismological Network in North China,with the predicted travel time data from four 3-D crustal velocity models in North China using the fast marching method.Then,using statistical analysis we evaluate the relative merits of these four models with respect to the real underground structures.The results show that the large-scale pattern generally shows consistency for these four models.Within the entire study area,the model proposed by Shen et al.(2016;referred to as the "S model")is relatively better than the model proposed by Fang et al.(2010,referred to as the "F model")and Duan et al.(2016;referred to as "D model").The Crust 1.0 model(Laske,2013;referred to as "C model")is relatively worse.We think that the reasons for this result are related to the differences in data used in model construction and the associated resolution.For different tectonic units in the study area,the D model performs better in the southwestern part of the Yanshan orogenic belt,northwestern part of the Taihang Mountain foreland tectonic belt,and the Cangxian uplifted area.The F model performs better in the central part of Taihang Mountain Uplift,northern part of the Cangxian uplifted area,the Huanghua Depression,and the Yanshan fold belt regions.The S model appears better in the western block,the Shanxi Depression area,the Taihang Mountain foreland tectonic belt,and the Jizhong Depression area.There is no obvious large continuous area where the C model performs better.In the other part of this study,we will compare the measured ZH amplitude ratio data which the periods from 20s to 80s(interval 5s)at each station in the study area of 717 earthquakes from October 2006 to August 2009 recorded by 180 seismograph stations of the North China Seismic Array,with the predicted corresponding ZH amplitude ratio data from four 3-D crustal velocity models in North China using the forward calculation method.Then,using statistical analysis we evaluate the relative merits of these four models with respect to the real underground structures.The results show that the large-scale pattern generally shows consistency for these four models.Within the entire study area,the S model is relatively better than the F model and D model,The C model is relatively worse.For different tectonic units in the study area,the D model performs better in south of the western block and the.Yanshan fold belt.The F model performs better in the Jizhong Depression area.The S model appears better in the Cangxian uplifted area,the Taihang Mountain foreland tectonic belt,North of the western block,and southeast of the Yanshan orogenic belt,and There is no obvious contiguous area where the C model performs better.In this study,two kinds of data are used to evaluate the four three-dimensional crustal velocity structure models in North China.The overall evaluation results are consistent.But there are differences in the evaluation of some structural units.Considering the large errors in the evaluation of using the ZH amplitude ratio data,comprehensive consideration is given to consider that the result of using travel time data is more reliable.And our study has certain positive significance for further improving the accuracy of the regional crustal velocity models and the earthquake location based on 3-D models.