摘要
This is the first of two papers that describes a regional tomography investigation, which combines P-wave arrival times of both regional and teleseismic earthquakes to obtain 3D mantle structures of East Asia up to 1 000 km depth. The most important findings of this tomography study are reported in this paper as follows. （1） No fast P-wave velocity anomalies can be related to subducted oceanic slabs beneath the 660 km discontinuity; instead the subducted oceanic slabs become flattened and stagnant within the transition zone. （2） The high velocity anomalies in the transition zone extend up to 1 500 km to the westward of the active trenches, which is a unique feature in the worldwide subduetion systems. （3） Slow P-wave velocity anomalies are visible up to -250 km underneath most of the East Asia on the east of 115°E, similar to the area of the stagnant slabs. These observations have important implications for the geodynamic process at depths beneath the East Asia, which might in turn control the widespread Cenozoic volcanism and associated extensional tectonics seen at the Earth＇s surface.
This is the first of two papers that describes a regional tomography investigation, which combines P-wave arrival times of both regional and teleseismic earthquakes to obtain 3D mantle structures of East Asia up to 1 000 km depth. The most important findings of this tomography study are reported in this paper as follows. （1） No fast P-wave velocity anomalies can be related to subducted oceanic slabs beneath the 660 km discontinuity; instead the subducted oceanic slabs become flattened and stagnant within the transition zone. （2） The high velocity anomalies in the transition zone extend up to 1 500 km to the westward of the active trenches, which is a unique feature in the worldwide subduetion systems. （3） Slow P-wave velocity anomalies are visible up to -250 km underneath most of the East Asia on the east of 115°E, similar to the area of the stagnant slabs. These observations have important implications for the geodynamic process at depths beneath the East Asia, which might in turn control the widespread Cenozoic volcanism and associated extensional tectonics seen at the Earth＇s surface.
基金
grants(B-11440134,S-12002006)to Dapeng Zhao from the Japan Society for the Promotion of Science
Support for Shunping Pei came from a postdoct grant of Peking University
supported by the Chinese Academy of Sciences(No.KZCX2-EW-QN102)
the National Natural Science Foundation of China(Nos.41074041,90814002 and 40125011)
