Yutao Shi

A rupture blank zone in middle south part of Longmenshan Faults: Effect after Lushan Ms7.0 earthquake of 20 April 2013 in Sichuan, China

On April 20, 2013, the Lushan Ms7.0 earthquake struck at the southern part of the Longmenshan fault in the eastern Tibetan Plateau, China. The shear-wave splitting in the crust indicates a connection between the direction of the principal crustal compressive stress and the fault orientation in the Longmenshan fault zone. Our relocation analysis of the aftershocks of the Lushan earthquake shows a gap between the location of the rupture zone of the Lushan Ms7.0 earthquake and that of the rupture zone of the Wenchuan Ms8.0 earthquake. We believe that stress levels in the crust at the rupture gap and its vicinity should be monitored in the immediate future. We suggest using controlled source borehole measurements for this purpose.

Lithospheric shear wave velocity and radial anisotropy beneath the northern part of North China from surface wave dispersion analysis

Rayleigh and Love wave phase velocities in the northern part of the North China are obtained from ambient noise tomography in the period range of 8–35 s and two plane wave earthquake tomography at periods of 20–91 s using data recorded at 222 broadband seismic stations from the temporary North China Seismic Array and permanent China Digital Seismic Array. The dispersion curves of Rayleigh and Love wave from 8 to 91 s are jointly inverted for the 3-D shear wave structure and radial anisotropy in the lithosphere to 140 km depth. Distinct seismic structures is observed from the Fenhe Graben and Taihang Mountain to the North China Basin. The North China Basin from the lower crust to the depth of 140 km is characterized by high-velocity anomaly, reflecting mafic intrusion and residual materials after the extraction of melt, and by strong radial anisotropy with Vsh > Vsv, implying horizontal layering of intrusion and alignment of minerals due to vigorous extensional deformation and subsequent thermal annealing. However, low-velocity anomaly and positive radial anisotropy are observed in the Fenhe Graben and Taihang Mountain, suggesting the presence of partial melt in the lithosphere due to the mantle upwelling and horizontal flow pull.

Origin of intraplate volcanism in northeast China from Love wave constraints

The tectonic source for widespread volcanism in northeast China has not been completely understood. We develop a 3-D SH velocity model in NE China that provides new constraints to the origin of the volcanism. The 3-D model is constructed from fundamental mode Love waves at the periods of 20-125 s recorded at 269 broadband seismic stations. The Changbai Mountain is characterized by a significant low velocity in the lower crust and uppermost mantle, which probably results from mantle upwelling due to the subduction of the Pacific plate. A fast and thin mantle lid of ~75 km is present beneath the Songliao Basin, indicating lithosphere extension from back-arc rifting. The slow velocity in the middle and fast velocities in the south and north at 75-115 km depths in the Songliao Basin suggest complex mantle flow with upwelling and downwelling. Unlike the other volcanic fields (Changbaishan volcano, Jingpohu volcano and Abaga volcano), the Halaha volcano has high velocity in the lower crust and upper mantle, implying a limited melt supply from mantle source recently. The subduction-induced upwelling leads to complicated small-scale mantle convection, which is responsible for the intraplate magmatism in northeast China.