Crust‐ Mantle Structure of the Changbaishan Tianchi Volcanic Region and its Vicinity: An Exploratory Study and Inferences

Abstract

Abstract Using 2‐D ray tracing software package, the crustal and upper‐mantle velocity structure and deep features of the Changbaishan Tianchi volcanic region and its vicinity are studied through travel‐time fitting and synthetic seismogram computation with deep seismic sounding (DSS) data acquired along the Changbai‐Dunhua profile. The results show that the crust of this region is separated into the upper crust and the lower crust by the interface C 2 . The upper crust is 19–23km thick and P‐wave velocity is 6.00–6.25 km/s. The lower crust is 12–17km thick, which is composed of a homogeneous velocity layer and a crust‐mantle transition layer 6–9km thick. Crustal thickness is 31–33km in Dunhua and becomes gradually greater southeastwards to its maximum value of 39km in the Tianchi volcanic region. In the Tianchi volcanic region, there exists a low‐velocity body in the crust, whose velocity is about 0.15 km/s lower than that of the adjacent medium. Results of seismic profiling, seismic tomography, and magnetotelluric sounding suggest that in Tianchi volcanic region there is a low‐velocity, low‐density, and low‐resistivity anomalous body, which may indicate the existence of a magma chamber in the crust.