Abstract:

The seismic tomography can provide both fine Pwave and Swave velocity structures of the crust and upper mantle, and also a Poisson’s ratio image from the seismic velocities via proper computation. However, it is unsure that Poisson’s ratio images have any advantages comparing with the Pwave and Swave velocity images. In this study, the high resolution seismic tomography is applied to the determination of detailed 3D crustal P and Swave seismic velocities structure as well as Poisson’s ratio images under the eastern part of North China region. Results of Poisson’s ratio imaging show a high Poisson’s ratio(highPR)anomalies located in HengshanNorth TaihangZhangjiakou(HNTZ)region, showing Poisson’s ratio imaging can provide new geophysical constraints for the regional tectonic evolution. HNTZ region shows prominent and continuous highPR anomalies in upper crust, extending down to the middle crust with thickness up to about 26 km. According to petrophysical property measurements and other geological data, this crustal Poisson’s ratio anomaly may be explained by the upper mantle partial melting and basaltic magma underplating during the Mesozoic era，related to the lithospheric thinning in North China craton.

Key words: seismic tomography；North China；craton crust；Poisson&rsquo, s ratio anomaly；magma underplating