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Seismic studies of the crustal structure beneath the Three Gorges Reservoir (TGR) region in Central China have been limited by the sparse and uneven distribution of seismic stations. To increase the station coverage, we made three deployments of a mobile seismologic array in the TGR region during the three summers from 2008 to 2010. Here we present interpretations along a west-east profile through the central TGR region based on new seismic waveform data and a velocity model constrained by regional earthquake data. Two strong mid-crustal reflection interfaces at depths around 10 and 20 km are seen under the TGR. The shallow reflector defines the bottom of the Zigui (秭归) basin. The new waveform data show that the amplitude of the Moho reflection is quite weak, and beneath theMoho, there is a strong reflector around 54-km depth. It is likely that in the TGR region, the Moho is a gradient rather than a sharp boundary. We speculate that the gradient Moho and the 54-km-deep reflector in the upper mantle in the TGR region may be by-products of the Qinling (秦岭)-Dabie (大别) orogen.

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Ruichang-Yangxin earthquake is another moderate earthquake in Yangxin-Jiujiang area since 2005 Jiujiang-Ruichang M 5.7 earthquake. In order to more understand the seismic activities in this area, we study the moment tensor solution and the seismogenic structure of the Ruichang-Yangxin earthquake. Precise earthquake relocation shows that the mainshock occurred on the southwestern part of the NE-trending fault and aftershocks are distributed not only along the NE-trending fault but also along its conjugated NW-trending fault. By comprehensive analysis on the earthquake distribution, characteristics of isoseismal curve, focal mechanism, and regional structure characteristics, it is inferred that this earthquake is caused by the NE-trending Tanlu fault. In addition, it has close relationship with the conjugated NW-trending fault as well. Many researches have shown that the junction area is the earthquake-prone area, and should be paid more attention to. And our study also proves this viewpoint.