Crust and uppermost mantle P-wave velocity stricture of the North China:Constraints from joint inversion of local earthquake body-wave traveltimes and gravity anomalies
North China is a typical case of studying the destruction of craton,and it is also one of the regions with the most intense and frequent strong continental earthquake activity.Studying the crust and mantle velocity structure in this area can provide important deep constraints on the understanding of the formation and evolution of cratons and the mechanism of occurrence strong intraplate earthquakes and volcanoes.Using P-wave traveltime data recorded by 202 permanent seismic stations and 360 temporary stations employed in the North China and Bouguer gravity anomalies,we obtain the crust and uppermost mantle velocity structure of the North China by joint inversion method.The introduction of gravity data can not only restrict the crust and mantle structure more reasonably,but also effectively improve the imaging ability of shallow and marginal regions with sparse ray distribution.The results show that the shallow layers of the Ordos block and the North China Plain show obvious low-velocity anomalies,which may be related to thick and soft sedimentary layers.An obvious P-wave high-velocity anomaly in the upper crust of eastern Ordos is observed,which is speculated to be correlated with the Paleoproterozoic khondalite belt.Below Datong volcano,there are obvious low-velocity anomalies at depth range of 15 25 km and 25～40 km,which are connected and presumed to be related to the multi-stage magmatic emplacement caused by the upwelling of mantle hot material.The Sanhe-Pinggu 8.0 earthquake and the Xingtai M 7.2 earthquake are both occurred in the brittle upper crust with underlying low-velocity anomalies.Under the regional dynamic loading effect,the ductile intra-crust creep will lead to the local accumulation of elastic strain energy in brittle upper crustal rocks,which will cause earthquakes.
North ChinaGravity anomaliesLocal earthquake traveltimesJoint inversionP-wave velocity
NETL
NSTL
万方数据
