- 2018-05-11 09:28
Yuyang She1, Huajian Yao1,2*, Qiushi Zhai1, Fuyun Wang3, Xiaofeng Tian3
1Laboratory of Seismology and Physics of Earth’s Interior & School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui, China
2Mengcheng National Geophysical Observatory, University of Science and Technology of China, Mengcheng, Anhui, China
3Geophysical Exploration Center, China Earthquake Administration, Zhengzhou, Henan, China
*Corresponding Author: Huajian Yao (email@example.com)
ABSTRACT：A large volume airgun shot experiment was conducted during October 10th-20th 2015 in the Yangtze River in Anhui province of eastern China. This area is an important polymetallic metallogenic belt and mineral resource base. In order to better understand the structure in this area, we perform 3-D high-frequency surface wave tomography to investigate the shallow crustal shear velocity structure in the middle-lower Yangtze River region, using airgun signal recorded by dense arrays in this experiment. The direct surface wave tomographic method with period-dependent raytracing is used to invert all surface-wave group-velocity dispersion data in the period band 0.1-1.6 s simultaneously for 3D variations of shear velocity structures in the shallow crust. Our results show a good correspondence to the geological features, with relatively high shear wave speed in the metallic deposit fields and low shear wave speed mainly along the Yangtze River. Our shallow crustal velocity model can provide useful information for future geophysical exploration of concealed deposits and help us better understand the shallow tectonic features in this area.
Figure 1. Topography, plate boundary, faults, river systems, cities, and receiver locations in the study area. Receiver locations are shown as red triangles deployed by Geophysical Exploration Center, China Earthquake Administration. Yellow circles represent the 20 fixed shot sites in the ‘Yangtze River Project of Geoscience’. The orange dash lines represent the plate boundary. The orange line along the Yangtze River represents the Changjiang Fault (CJF). The thin black lines represent other faults including the Tanlu Fault (TLF).
Figure 2. Schematic illustration of the metallic deposit fields in the MLYMB, based on the map of Pang et al. (2014). Four large metallic deposit fields in the study area are marked as the eclipses. M1: AnQing; M2: LuZong; M3: TongLing; M4: NingWu; TLF: Tanlu Fault: CJF: Changjiang Fault.
Figure 3. (a) Recorded waveform data in the 0.1-2 s period band from the shot site D08 to stations after linear stack (204 shots). (b) 3-component records by a station in the 0.6-0.8 s period band from the shot site D06. (c) Particle motion of the waveform in the gray shaded window in (b). The big point represents the start point of the particle motion. (d) Period-Group velocity diagram from time-frequency analysis of the vertical (Z) component data in (b). The black band in (d) represents high surface wave energy for group velocity dispersion extraction.
Figure 4. The final shear velocity model obtained from the 3-D inversion. (a-d) give the shear velocity structure at four depths: 200, 400, 600, and 800 m. Only regions of good resolution are shown. The triangles represent the stations. The three red straight lines , and in (b) represent the three vertical profiles shown in Figure 5. The four red circles M1-4 in (c) represent the high-velocity anomaly regions corresponding to the four metallic deposit fields in Figure 2.
Figure 5. Shear velocity structure along the profiles (a) , (b) and (c) with their locations shown in Figure 4b. The location of four metallic deposit fields (M1-4) and the Yangtze River are also marked above each