Rayleigh wave tomography of China and adjacent regions

Abstract

[1] This paper presents a tomographic study on the S wave velocity structure of China and adjacent regions. Group velocity dispersions of fundamental Rayleigh waves along more than 4000 paths were determined with frequency-time analysis. The study region was divided into a 1°Â 1°grid, and velocities in between grid nodes were calculated by bilinear interpolation. The Occam's inversion scheme was adopted to invert for group velocity distributions. This method is robust and allows us to use a fine grid in model parameterization and thus helps to restore a more realistic velocity pattern. Checkerboard tests were carried out, and the lateral resolution was estimated to be 4°-6°in China and its eastern continental shelves. The resulting group velocity maps from 10 to 184 s showed good correlation with known geological and tectonic features. The pure path dispersion curves at each node were inverted for shear wave velocity structures. The threedimensional velocity model indicates thick lithospheres in the Yangtze and Tarim platforms and hot upper mantles in Baikal and western Mongolia, coastal area and continental shelves of eastern China, and Indochina and South China Sea regions. The Tibetan Plateau has a very thick crust with a low-velocity zone in its middle. Beneath the crust a north dipping high-velocity zone, mimicking a subducting plate, reaches to 200 km in depth and reaches to the Kunlun Mountains northward. In northern Tibet a low-velocity zone immediately below the Moho extends eastward then turns southward along the eastern edge of the plateau until it connects to the vast low-velocity area in Indochina and the South China Sea.INDEX TERMS: 7218 Seismology: Lithosphere and upper mantle; 7255 Seismology: Surface waves and free oscillations; 9320 Information Related to Geographic Region: Asia;

Crustal Velocity Structure of the Northeastern Tibetan Plateau from Ambient Noise Surface-Wave Tomography and Its Tectonic Implications

“…The shear-wave velocity and Moho depth in the initial models are referred to the deep seismic sounding profiles (Xu et al, 2002;Zhao et al, 2004;S. Li et al, 2006), tomography results (Huang et al, 2003;Wang et al, 2003Wang et al, , 2007Maceira et al, 2005), and receiver functions (Pan and Niu, 2011; Ⓔ Fig. S1, available in the electronic supplement to this article).…”

Improved Surface Wave Dispersion Models, Amplitude Measurements and Azimuth Estimates

“…The dispersion data set has been derived from a variety of regional and global studies including the following: global surface wave group velocities from earthquakes derived using IMS data (Stevens and McLaughlin, 1996), augmented with additional measurements derived from IMS data; surface wave phase and group velocity dispersion curves from underground nuclear test sites (Stevens, 1986;Stevens and McLaughlin, 1988), calculated from earth models for 270 paths (test sitestation combinations) at 10 frequencies between 0.0 15 and 0.06 Hz; phase and group velocity measurements for western Asia and Saudi Arabia from Mitchell et al(1996) for 12 paths at 17 frequencies between 0.012 and 0.14 Hz; the global phase velocity model of Ekstrom et al (1996) for 9 periods between 35 and 150 seconds calculated for each grid block from a spherical harmonic expansion of order I = 40; group velocity measurements for Eurasia from Ritzwoller et al (1996) and Levshin et al (1996) for 20 frequencies between 0.004 and 0.1 Hz with 500 to 5000 paths per frequency; Antarctic and South American group velocity measurements from the University of Colorado Ritzwoller et al, 1999); high frequency Eurasian dispersion measurements from University of Colorado (Levshin et al, 2003); dispersion measurements from Central Asia made by Los Alamos National Laboratory (Yang et al, 2002); data from China (Huang et al, 2003); and data from the New Madrid region from Mancilla (2001). Figure 2 shows the frequency distribution of group velocity and phase measurements in our data set, excluding the phase velocities derived from the global phase velocity model of Ekstrom et al (1996).…”

Improved Surface Wave Dispersion Models and Amplitude Measurements

“…For frequencies below 0.03 Hz these data are much slower than other data in the same region; consequently we have removed all the Los Alamos data below 0.04 Hz. Another set comes from Huang et al (2003) and consists of more than 285,000 data points (9730 paths) from China. These data include unrealistically fast paths crossing cells with water at frequencies higher than about 0.06 Hz.…”