Structure and Significance of S-wave Velocity and Poisson’s Ratio in the Crust beneath the Eastern Side of the Qinghai-Tibet Plateau

Abstract

The receiver functions of body waves of distant earthquakes obtained for the regions beneath 41 digital stations (Lhasa and GANZ in Tibet, Mandalay and Rangoon in Myanmar, SHIO in India, CHTO in Thailand, and station network in Sichuan and Yunnan) were used to invert for S-wave structure in the crust and upper mantle in Sichuan, Yunnan, and their surrounding areas. Meanwhile the distribution characteristics of the Poisson's ration and the crustal thickness in Sichuan and Yunnan areas were also obtained. Results indicate that the depth of Moho beneath the eastern side of Qinghai-Tibetan plateau varies strikingly. It is obvious that the greatest changes in crustal thickness occur in a north-south direction. The crustal thickness decreases from north to south, being as thick as 70 km in eastern Tibet, the northern portion of our area of interest, and less than 30 km in Chaing Mai and Rangoon, the southern portion of our area. There are, however, exceptions regarding the trend. The thickness exhibits an east-west variation trend in the area from Ma'erkong-Kongding in Sichuan to Lijiang in Yunnan. In general the Jinpingshan-Longmenshan fault and Anninghe fault can be taken as the boundaries of this exception area. The thickness in Kongding in the west is 68 km, while it is only 39 km in Yongchuan in the east. Moreover the Poisson's ratio values in the blocks of central Sichuan and SichuanYunnan Diamond are high, and a low velocity layer in the crust of this area can be obviously detected. The distribution characteristics of the high Poisson's ratio and the low velocity of the crust in this block correspond to the tectonic structure, being in contrast with the surrounding areas. Combining with the distribution features of the modern tectonic stress field, it is deduced that the Sichuan-Yunnan area is probably the channel through which the materials of the lithosphere flow eastward.

Thailand's crustal properties from tele-seismic receiver function studies

“…4a and b using a Vp of 6.5 km/s. All of our results for both CHTO and CMMT stations agree well with each other and are within an acceptable level when compared with other studies (Bai et al, 2010;Crotwell and Owens, 2005;Hu et al, 2008;Trabant et al, 2012;Wongwai, 2011). Only the results from Tadapansawut et al (2012) and from the CRUST 2.0 model (Bassin et al, 2000;Laske et al, 2000) are much higher than the others.…”

“…Since CMMT and CHTO are located in the same borehole, and the tele-seismic data from the CHTO station has been used extensively before in many publications (Bai et al, 2010;Crotwell and Owens, 2005;Hu et al, 2008;Trabant et al, 2012;Wongwai, 2011), we therefore Bassin et al (2000). The small squares are from Wongwai (2011) in the lower half and Tadapansawut et al (2012) in the upper half.…”

A 3‐D Shear Wave Velocity Model for Myanmar Region

“…To improve the spatial coverage of the region, we also include 22 IRIS broadband stations (station name and operation period can be found in Table S1 in the supporting information) in and around Myanmar. Some of these stations have been used in previous studies to obtain 1 ‐ D velocity structures beneath the stations (Bai et al, ; Hu et al, ; Mitra et al, ; Noisagool et al, ; Singh et al, ); we compare these with our results for verification and discussion (see section ). As shown in Figure , the average station spacing (~150 km) is too coarse to apply modern array processing techniques, such as crustal‐scale RF common‐conversion‐point stacking (Zhu, ).…”

Crustal structure beneath the Indochina peninsula from teleseismic receiver functions

“…Since there is only a single maximum in the H ‐κ contour map for a reasonable range of values, ‘average’ values of H and κ for the crust can be determined. For the three IRIS stations, H and κ have been estimates previously: H = 44.1 ± 0.3 km; κ = 1.705 ± 0.015 for KMI, H = 32.0 ± 0.2 km; κ = 1.708 ± 0.010 for QIZ [ Chen et al , 2010] and H = 29.6 ± 0.8 km; κ = 1.878 ± 0.026 for CHTO [ Hu et al , 2008]. Our results are in good agreement with those studies, except for the κ estimates by Hu et al [2008], who used a limited number of records.…”