Distribution of Intra-Crustal Low Velocity Zones beneath Yunnan from Seismic Ambient Noise Tomography
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Previous studies have reached consensus that low velocity zones are widespread in the crust beneath Yunnan region. However, the relationships between the low velocity zones and large faults, earthquake distribution are less investigated by available studies. By analyzing the seismic ambient noise recorded by Yunnan Seismic Networks and Tengchong volcano array, we construct a 3D crustal shear wave velocity model for the Yunnan region, which provides more details of the distribution of intra-crustal low velocity zones in all of Yunnan. The distribution of low velocity zones shows different features at different depths. At shallow depths, the results are well correlated with near surface geological features. With increasing depth, the low velocity zones are gradually concentrated to the northern part of our study area, most likely reflecting variations in crustal thickness beneath the Yunnan region. The low velocity zones are truncated at depth by several large faults in Yunnan. It is interesting that most strong earthquakes (Ms≥5.0) occurred in Yunnan are distributed in low velocity zones or the transition zones between low and high velocity anomalies within the upper-to-middle crust. The crustal structure is composed of a brittle, seismically active upper-to-middle crust and a warm, aseismic lower crust.
Key wordsambient noise tomography crustal structure low velocity zone fault strong earthquake
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We thank the editors and two anonymous reviewers for their useful comments. We thank T. B. Yanovskaya of Leningrad State University for providing the 2D tomography software and Robert Herrmann from Saint Louis University for his Computer Programs in Seismology (CPS) software package. We are also grateful to Prof. Huajian Yao, University of Science and Technology of China, Hefei, China, for providing the software package to extract the phase dispersion curves. Figures 1 and 5–8 are constructed using the GMT software (Wessel and Smith, 1998). Seismic data are provided by Yunnan Seismic Networks. This study was financially supported by the National 973-Project (No. 2013CB733303), the National Natural Science Foundation of China (No. 41474093), and the Key Natural Science Foundation of Hubei Province (No. 2014CFA110). The final publication is available at Springer via https://doi.org/10.1007/s12583-017-0815-8.
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