Crustal and Uppermantle Structure of Northeast China from Ambient Noise and Teleseismic Earthquake Rayleigh Wave Tomography

Abstract:

We obtained a new 3-D crustal and upper mantle shear wave velocity model of NE China from joint inversion of ambient noise data and teleseismic earthquake Rayleigh wave data using two-plane surface-wave tomography. Two-year continuous seismic records of 289 stations from the (portable) NECESSArray and the (permanent) CEA array were analyzed and phase velocity maps were obtained from period bands from 6s to 140s. S-wave velocity models were inverted by using a Markov chain Monte Carlo method. The resulting 3-D velocity model clearly shows a low velocity anomaly in the uppermantle of the Changbai mountain region associated with Cenozoic magmatism. Combined with the published body-wave tomography results we interpret this low velocity zone as the large-scale asthenospheric mantle upwelling and decompression melting related to the subduction of the Pacific Plate, which caused rifting and volcanic activities since 30 Ma ago. Fast velocity anomalies are observed in the upper mantle down to nearly 200 km depth beneath the Songliao basin. The high velocity anomaly may reflect a cooled mantle lithosphere since the formation of the basin. The two stages of lithospheric stretching of the basin from 157 to 102 Ma are followed by cooling, thickening of the lithosphere, and thermal subsidence. Slow velocity anomalies are also observed beneath the Dalainoer and Halaha volcanos in the Xing’an-Mongolia. These slow velocity anomalies could be caused by small-scale mantle convection due to undulations of lithospheric thickness in the region.