Crustal structure beneath China from receiver function analysis

Abstract

[1] We collected and processed a large amount of high-quality broadband teleseismic waveform data recorded by the 48 Chinese National Digital Seismic Network stations to estimate large-scale lateral variations of crustal thickness and V p /V s ratio (hence Poisson's ratio) beneath China. A statistical method was used to select mutually coherent receiver functions at each station, which yielded over 200 traces for most of the stations. With the conventional HÀk (the crustal thickness and V p /V s ratio) approach, there is a large trade-off between H and k. Consequently, multiple maxima are frequently observed in the HÀk domain. We introduced a weight function that measures the coherence between the P-to-S conversion and the reverberation phases at each HÀk grid to reduce the trade-off. A 4th-root stacking method was further applied to reduce uncorrelated noise relative to the linear stack. These modifications turned out to be very effective in reducing the HÀk trade-off and yielded reliable estimates of crustal thickness and V p /V s ratio. The crust beneath eastern China is as thin as 31-33 km and the underlying Moho is relatively flat and sharp. In the western part of China, the crust is considerably thicker and shows large variations. The Moho is observed at about 51 km depth along the Tian Shan fold system and about 84 km deep beneath the central part of the Tibetan Plateau. The transition occurs at the so-called N-S belt between about 100°and 110°E, which is featured by unusually high seismicity and large gravity anomalies. The average V p /Vs ratio over the mainland China crust is about 1.730 (s = 0.249), significantly lower than the global average 1.78 (s = 0.27) of the continental crust. This lower V p /V s ratio may suggest a general absence of mafic lowermost crustal layer beneath China.

Crust and upper mantle structure and its tectonic implications in the South China Sea and adjacent regions

“…Along the coastal region of the South China and Indochina, there is a high gradient transition zone with $20-30 km Moho depth. To the north and west of this zone, the typical continental Moho with the burial depth ranging from 30 to 40 km is observed, matching exactly with the estimates by Wu et al (2004) and other results (Zeng et al, 1997;Hu et al, 2005;Zhang and Wang, 2007;Chen et al, 2010). The crustal thickness near the eastern Tibet and Yangtze Block increases dramatically to greater than 50 km, which is very similar to the previous findings (e.g., Yao et al, 2008).…”

“…The S-velocity 4.00 km/s is an optimal criterion which is determined by searching the best fit between the Moho depths derived from receiver functions (Bai et al, 2010;Chen et al, 2010;Wang et al, 2010;Kieling et al, 2011) and the S-velocity contours derived from the S-velocity model. Thus the depth of the 4.00 km/s contour closely corresponds to Moho depth over much of the region.…”

The role of rifting in the development of the continental margins of the southwest subbasin, South China Sea: Insights from an OBS experiment

“…Among all the three different methods of measuring the β-factors where the receiver function and the ambient tomography inverted the crustal thickness of around 30 km (Chen et al 2010;Zhou et al 2012). …”

Rifted margins: Ductile deformation, boudinage, continentward-dipping normal faults and the role of the weak lower crust

“…Rifting could have started from the orogenic collapse of the Cretaceous Yenshanian orogen (Chen, 2010) and mainly occurred from the Early Eocene to the Oligocene (Briais et al, 1993;Barckhausen and Roeser, 2004).…”