Structure of S-Wave Velocity in the Crust-Upper Mantle and Tectonic Setting of Strong Earthquakes Beneath Yunnan

• Published in: Chinese journal of geophysics 2011-05, Vol.54 (3), p.286-298
• Main Authors: ZHANG, Xiao‐Man, HU, Jia‐Fu, HU, Yi‐Li, YANG, Hai‐Yan, CHEN, Jia, PENG, Heng‐Chu, WEN, Li‐Min
• Format: Article
• Language: English
• Subjects: Fundamental Rayleigh surface wave; Phase velocity dispersion; S-wave velocity structure; Seismogenic background; Strong earthquakes
• ISSN: 0898-9591; 2326-0440
• DOI: 10.1002/cjg2.1611

A technique of phase‐matched filter is applied to extract the fundamental Rayleigh surface waves from 47 seismic events recorded at 65 digital seismic stations deployed in Yunnan and its adjacent region. The phase velocity dispersion between two stations located at the same great circle with the epicenter in the period range 10 to 80 s is computed by the inter‐station Green's function. The dispersions within 152 pairs of the stations are extracted from 2000 waveforms, and then the S‐wave velocity structure down to a depth of 200 km is obtained by inversion. Our results reveal an overall trend of crustal thickness variation beneath Yunnan from north to south, decreasing gradually from 60 km to 30 km. The Moho has uplift and depression locally, featuring one uplift and two depressions. Additionally, the lithosphere structure varies significantly across the Red‐river fault. Beneath the Baoshan, Wanding, Cangyuan and Simao areas that belong geologically to the Yunnan‐Myanmar‐Thailand block, there exists a low‐velocity zone extending from depth 70 km to 120 km. In contrast, on the east side of the fault, the Central‐Yunnan block has only a small low‐velocity zone in the upper mantle beneath the Kangdian palaeo‐uplift, and the S‐wave velocity for most of the area ranges from 4.4 to 4.6 km/s.