Surface Wave Dispersion Measurements and Tomography from Ambient Seismic Noise Correlation in China

摘要

We performed ambient noise tomography of China using the data from the China National Seismic Network and surrounding global and PASSCAL-type stations. For most of the station pairs, we retrieve good Rayleigh waveforms from ambient noise correlations using a few months to several years of continuous data at all distance ranges across the entire region (over 5000 km) and for periods from about 70 s down to about 8 s. We obtained a total number of 33,800 station-pairs (paths) and measured Rayleigh wave group and phase velocities. We inverted the Rayleigh wave dispersion measurements for dispersion maps at periods from 8 to 70 s. The dispersion maps correlate nicely with surface geology. A major feature of the ambient noise method is that the whole process is completely repeatable with different time segments, which make it possible to evaluate the uncertainties. We adopt a bootstrap method to quantify the errors in the Rayleigh wave group velocity dispersion measurements and the tomographic maps. Most of the pairs show similar dispersion curves between different runs and small standard deviations, indicating good data quality and convergence of the Green function. Group velocity at long period end generally has a larger error, which is consistent with the notion that the long period needs longer time to converge. The best retrieved periods are from 10 to 30 s with the optimal period of around 15 to 20 s. We invert the Rayleigh group and phase dispersion maps for 3D shear-wave velocity structure. The 3D model shows some remarkable features that correlate with surface geology.