Constraints on S-wave velocity structures of the lithosphere in mainland China from broadband ambient noise tomography

摘要

In this study, a 3-D S-wave velocity model of the lithosphere in mainland China down to 150 km depth was determined from ambient noise data. First, we collected 2-year continuous waveforms recorded by 1031 broadband stations of the China Regional Seismic Network and NECESSArray. Then, by applying the procedures of noise cross-correlation and time-frequency domain phase-weighted stacking, we obtained the interstation empirical Green's functions of Rayleigh waves. We measured the group and phase velocity dispersions at periods of 5-125 s from the EGFs and inverted both group and phase velocities for the S-wave velocity model. Our model revealed that the lithospheric thickness in the northern Songliao basin is similar to 70-110 km. A weak high-velocity anomaly that is discontinuous in the vertical direction was detected beneath the southern Songliao basin, which may indicate that the lithosphere is delaminated in this area. The model also revealed that deep (> 150 km) high-velocity lithospheric roots exist beneath the Ordos and Sichuan basins. The lithospheric thicknesses in eastern parts of the Northeast China Block, the North China Craton, and the South China Block are only 60-100 km, which may be the result of a series of deep processes caused by the subduction of the Pacific plate to the Eurasian plate that produced strong lithospheric thinning in eastern China. The lithospheric thickness within the Tanlu fault belt is generally thinner than that in the adjacent areas of the fault belt, and the S-wave velocity of the mantle lithosphere beneath the fault belt is also lower than that beneath the adjacent areas, indicating that the Tanlu fault belt is a deep fault belt cutting through the lithosphere.