Study On The Activity Of Diaojiangfu 's Fault

Both Xiaojiang fault and Dien Bien Phu fault are important block boundaries extends deep into crust, the observation of GPS showed that mass of Tibetan plateau flowing eastward and rotate clockwise when blocked by Tarim, Alxa, Sichuan block,, then as E-SE boundary, continuous deformation cross the Red river fault. Research of the north south seismic belt southern segment focus on Indochina, there is no unified definition about the boundary of lateral extrusion and the north south seismic belt, further discussion of the relation between Xiaojiang fault and Dien Bien Phu fault has important significance on completing research of the regularity of strong earthquakes and crustal motion in China.Method of tectonic, neotectonic setting, the evolutionary history of faults, medium property are base on collect, analysis, digesting former domestic and foreign scholar’s data, Achievements to research the relationship between xiaojiang and Dien Bien Phu fault; To improve the accuracy of Seismicity analysis, base on seismic catalog in research area (19°～27°N,101°～104°E) form1900to2014and3702events obtained by the double difference method from2000january to2014july, three dimensional visualization by GIS platform and selected out earthquakes which related to faults, and analysis temporal and spatial distribution of its activity; Data of crustal stress and focal mechanism solution been used to research stress state of region and faults, occurrence, compare to latest crustal deformation data. There are some basic understandings:1. Properties of block on both sides of Xiao Jiang fault,and Dien Bien Phu Fault are visible difference. Shan-tailand ancient continental nuclei and indochina ancient continental nuclei in indochina block have Precambrian crystalline basement, and south china block is a ancient fold system formed in early Paleozoic’s caledonian orogeny,they have denser crust, anomaly of geomagnetic and gravity are weakly variation, have the characteristics of the overall stability. Positive and negative anomaly of geomagnetic and gravity are alternate in the flabby sichuan-yunnan block. Simao-Lanping block continue the low density trend of sichuan-yunnan block. 2. Since the neotectonic movement, Xiaojiang fault and Dien Bien Phu fault are large scale sinistral strike sliping, controling the differential movement of blocks in region., they have similar seismogenic model:seismic activities decreased after a magnitude larger than6.0earthquake, then coming with a earthquake magnitude larger than6.0. The Dien Bien Phu fault has a longer quiet period, possible coming with a larger earthquake. Seismic Activity in rsearch area keep lower than average20year long after a peak period of magnitude larger than6.0from1970to the1983Lai Chau earthquake., Form2000to2014, that is no earthquake as magnitude lager than5.0. Deapth of great earthquake on Northern segment of Xiaojiang fault distributed in0km～60km, from middle segment to Dien Bien Phu fault are concentrated in33km and10km. Analogously, minor earthquake in northern distributed deeper than southern. Focal mechanism solution showed that seismic activity in research area are mostly strike-slip, crust stress is nearly horizontal. In neighboring region of Xiaojiang fault, principal compressive stress is strike NW-SE, of Dien Bien Phu Fault is NNW-SSE, principal compressive stress is nearly horizontal, fracture plane vertical tilt.3. Fault activity in research area are mostly strike-slip. When Crustal stress has been limited by Xiao Jiang fault and Dien Bien Phu Fault, base on the intensity and angle with fault, inverse activity and stress vector turn round suddenly. The observation of GPS reference to every stable blocks showed that deformation vectors turning when encountered south China block and Khorat block.In conclusion, Xiaojiang fault and Dien Bien Phu fault have septated strong and weak blocks, are catastrophe belt of geophysical field, crust stress, crust deformation, seismic activity had similarity with each other, consider them as the boundary of tibetan plateau lateral extrusion is suitably.Many aspects of research can be improved at present because of lack of sesmic data.