Tomographic Determination of 3-D Crustal Structure in Changbaishan-Tianchi Volcano Region

Abstract

Using reflection traveltimes of P wave from the 3-D deep seismic sounding experiment carried out in Changbaishan-Tianchi volcano region, we have reconstructed 3-D crustal interfaces and crustal velocity images by seismic tomography technique. The interface images show that the crustal depth increases generally from NW to SE, the Ma'anshan-Sandaobaihe and Fu'erhe-Hongqihe faults are two main deep faults in the region. Variation in crustal thickeness is especially obvious on both sides of Ma'anshan-Sandaobaihe fault, which runs across Tianchi crater in NNE direction. This indicates that there is an abrupt variation belt of crustal thickness or a deep crustal fault at this position. The velocity images show that an obvious low-velocity anomaly of P wave exists around Tianchi at the depth of 10km. It becomes a nearly SN-oriented low-velocity anomalous strip at the depth of 15km, which extends about 80~90km in SN direction and 30~40km in EW direction. With the increase of depth, the low-velocity anomalous strip can still be found on the west side of Tianchi, but with smaller scale. At this point, it becomes more concentrated and presents higher perturbation. This changing image of P-wave velocity anomaly illustrates the spatial distribution of the magma system under Tianchi volcano to a certain extent.