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

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 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.

Three‐dimensional density modeling of the EGM2008 gravity field over the Mount Paekdu volcanic area

“…The surveys were performed by the Research Center of Exploration Geophysics (now the Geophysical Exploration Center) of the China Seismological Bureau (now the China Earthquake Administration) and the State University of New York (SUNY) at Binghamton [Tang et al, 1998;Zhang et al, 2002aZhang et al, , 2002bYang et al, 2005]. Previous results of deep seismic soundings along the two seismic lines allowed four velocity layers (C1, C2, C3, and Moho in Figure 3a) to be identified.…”

“…[11] The most significant feature in the two seismic profiles is a series of LVZs in the crust directly beneath Mount Paekdu between 10 km depth and the Moho [Zhang et al, 2002a[Zhang et al, , 2002b. Here the P wave velocity is approximately 2%-4% slower than that in the surrounding crust ( Figure 3a).…”

“…However, there was a notable discrepancy among the results regarding estimates of the location of the LVZ. Recent seismic interpretations [Song et al, 2007] were used to infer the presence of a midcrustal LVZ under the region 70 km to the north of Mount Paekdu, whereas most results prior to that study [e.g., Tang et al, 1998;Zhang et al, 2002aZhang et al, , 2002b indicated the LVZ as being directly beneath Mount Paekdu. The receiver function study of Hetland et al [2004] suggested an alternative in which the LVZ is thought to be located under both areas.…”

“…The studies of Song et al [2007] result in only one LVZ located north of Mount Paekdu ("2" in Figure 3b). C1, C2, and C3 mark the velocity interfaces after Zhang et al [2002aZhang et al [ , 2002b.…”

“…The most notable differences between the interpretations of crustal velocities is the location of the low-velocity zones (LVZs). Zhang et al [2002aZhang et al [ , 2002b assumed that a vertical series of LVZs ( Figure 3a) extends from approximately 10 km down to the Moho under Mount Paekdu (point "P" in the upper part and "1" in the lower part. The studies of Song et al [2007] result in only one LVZ located north of Mount Paekdu ("2" in Figure 3b).…”