The magma system of Changbaishan-Tianchi Volcanic region is studied with three-dimensional deep seismic sounding (DSS) technique. The results show that the magma system of Changbaishan-Tianchi volcanic region, mainly characterized by low velocity of P wave, can be divided into three parts in terms of depth. At the depth range of 9~15 km, the distribution of the magma system is characterized by extensiveness, large scale and near-SN orientation. This layer is the major place for magma storage. From the depth of 15 km down to the lower crust, it is characterized by small lateral scale, which indicates the "trace" of magma intrusion from the upper mantle into the crust and also implies that the magma system most probably extends to the upper mantle, or even deeper.(less than 8-9 km deep), the range of magma distribution is even smaller, centering on an SN-oriented area just north of the Tianchi crater. If low velocity of P wave is related to the magma system, it then reflects that the magma here is still in a state of relatively high temperature. In this sense, the magma system of Changbaishan-Tianchi volcanic region is at least not "remains", in other words, it is in an "active" state.

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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 C2. 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.

A 637 km long wide-angle seismic reflection and refraction profile was carried out in the northeast margin of Tibet plateau, which crosses A'nyemaqen suture belt in the north-south direction. The crust section obtained from the seismic data shows that the depth of the Moho is about 48∼51 km. The crust is slightly thicker in the south than in the north and it varies smoothly toward the north along the profile with different structures in the various tectonic blocks. The clearly identified overcritical reflections P3, P4 on the seismic record sections indicate that the lower crust features multi-layer structure and strong reflectivity in this area. There are severe deformations on the interfaces of the crust, and low velocity distributions on the south of Aba arcuate fault and near A'nyemaqen suture belt. The low velocity zone in the mid and lower crust beneath A'nyemaqen suture belt may be explained as the extension of the suture belt into the crust. The crust structure from the West Qinling fold zone to Songpan-Garze block is characterized by strong reflections from the mid and lower crust, and relatively weak Moho reflections on the seismic record sections.