Tomographic imaging of the upper crustal structure beneath the Xinfengjiang reservoir area

作者：Yang Zhuo-Xin^*; Liu Bao-Feng; Wang Qin-Cai; Zhao Cui-Ping; Chen Zhang-Li; Zhang Xian-Kang

来源：Acta Geophysica Sinica, 2013, 56(4): 1177-1189.

DOI：10.6038/cjg20130413

• Xinfengjiang reservoir area
• Artificial earthquake and natural earthquake
• Joint inversion of travel times
• 3-D fine structure of the upper crust
• Rreservoir-induced earthquakes

A three-dimensional temporary seismic array with 50 stations was deployed in an approximately 50 km X 40 km region around the Xinfengjiang reservoir to receive seismic waves generated by artificial sources from different azimuths. The local earthquakes occurred in the area from March 2009 to May 2010 were recorded by 20 stations of the seismic array and 5 permanent seismic stations. With the inversion method without model blocks, both reflection waves generated by the artificial sources from Moho at critical distances and direct waves from local earthquakes are used to reconstruct the 3-D images of P,S velocity and V-P/V-S perturbation of the upper crust under the seismic array. The results show that the upper crust structures below the Xinfengjiang reservoir area have significant differences between the eastern and the western region. The structure is complicated in the east of the reservoir where the faults intersect mutually. Under the reservoir, the NNW striking Shijiao-Xingang-Baitian fault zone has complex lithology and structural features, and from Xingang to Shuangtang, it probably extends down to 8 km depth. The fault zone of nearly NE direction cuts crust deep. There are through shallower and deeper high-velocity ratio zones in both the canyon and near the east of the Xinfengjiang dam, especially in the western deep water canyon region of Xinfengjiang dam, along the river there is a steep fault fracture zone. The high-velocity ratio zones provide a good channel for water infiltration. The west of reservoir is a relatively stable tectonic region, where intact and hard granite rock with low permeability has been affected little by reservoir water. The occurrence of Xinfengjiang reservoir-induced earthquakes is closely related to the deep structure environment. The upper crustal medium property in the canyon and near the east of the dam is obviously laterally heterogeneous. The micro earthquakes are located in the specific parts of medium physical property and structure. It is suggested that the "soft" and "hard" staggered media environment possibly leads to occurrence of dip-slip normal fault type micro earthquakes.

• 出版日期2013-4
• 单位中国地震局地震预测研究所; 中国地震局地球物理勘探中心