Surface Wave Dispersion Measurements and Tomography From Ambient Seismic Noise in China
Annual rept. no. 1, 20 Dec 2006-20 Dec 2007
ILLINOIS UNIV AT URBANA DEPT OF GEOLOGY
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We have recently performed ambient noise tomography of China using the new national China Seismic Network and surrounding global and regional stations. For most of the station pairs, we can retrieve very good Rayleigh waves from ambient noise correlations using 18- months of continuous data at all distance ranges 100 km to 5000 km and for periods down to about 8 s. We obtain Rayleigh wave group velocity dispersion measurements using a frequency-time analysis method and construct Rayleigh wave group velocity maps for periods from 8 s to 60 s. Our preliminary dispersion maps show significant features that correlate with surface geology. Two major features stand out in particular. First, the major basins with thick sediment deposition correlate well with slow group velocities at shorter periods 10 to 20 s. The major basins, including Tarim, Junggar, Qadaim, Sichuan, Bohai, Songliao, Southern North China, and Jianghan, are all well delineated by slow velocities. Second, variations in crustal thickness correlate with group velocities for periods around 30 s. The major trend of crust thickening from the east to west is well represented by the velocity decreases from east to west. We propose several methods to estimate the reliability and error of Rayleigh wave dispersions derived from the ambient noise.