Primary Study On Surface Deformation Characteristic And Faulting Behavior At Yingxiu Town, The Epicenter Of Ms8.0 Wenchuan Earthquake

Ms 8.0 Wenchuan Earthquake shocked everyone, and after the earthearth, research on Longmenshan Area where the earthquake occured interested geological researchers all around the world. But now the study on Wenchuan Earthquake is still in the stage of collecting basic data, which means further study is very necessary and many issues are unsolved. All along, study on Beichuan-Yingxiu Fault which is considered as seismogenic fault of Wenchuan Earthquake is not sufficient with the representation that many scientific problems involving it, such as activity rate, activity, recurrence intervals of strong earthquakes, seismic deformation characteristic and so on is still in argument. So, Yingxiu Town where the Central Fault's activity charactertistic behaves obviously is selected as research object in this paper. Primary study on seismic surface deformation and faulting behavior of Central Fault (Beichuan-Yingxiu Fault) is done by methods such as topographic analysis, field geological investigation, trench excavation, geological profile analysis and so on.Those below are main content of the paper and research methods that were adopted:1) Seismic surface deformation characteristic and some quantificational results such as deformation width, deformation amount in Yingxiu Town where seismic surface deformation is very obvious are obtained by field geological mapping and structural topographic surveying with the help of surveying machine.2) Terrace T2 at Zhongtanpu in the north of Yingxiu Town where Central Fault (Beichuan-Yingxiu Fault) is chosen as trench spot after topographic map analysis and field investigation. And then, paleoseismic events and faulting behavior of Beichuan-Yingxiu Fault are obtained by paleoseismic trench analysis and testing OSL samples.3) Age value of the four terraces well developed at Yingxiu Town is gotten by collecting and testing dating samples. Terrace T4 whose profile is very well is sampled and analyzed systemically. And we did fine topographic surveying at Zhongtanpu where structural scarps on four terraces, and scarp height of every terrace is obtained. Combining the age value of every terrace, we got vertical uplifting rate of Central Fault in different time scale and did primary analysis.4) On the base of work done above, primary analysis on seismic risk and uplifting rate of Central Fault is done.Main consequences of paper are below:1) Seismic surface deformation characteristic at Yingxiu Town shows us that seismic rupture plane develops along previous fault plane, which is evidence of in-suit recurrence model of earthquakes. Seismic surface deformation mainly performs vertical displacement in Yingxiu Town, the epicenter of Ms8.0 Wenchuan Earthqauke. The width of seismic surface deformation at Yingxiu Town is about 60m, uplifting amount 2.72m.2) Since 4.6±0.8ka ago, or in later Holocene, vertical uplifting rate of Beichuan-Yingxiu Fault is 1.17±0.236mm/a, while since 24.5±5.5ka ago, or in later Pleistocene and middle Holocene, the rate is 0.53±0.12mm/a. Lower limit of uplifting rate is 0.931±0.137mm/a since 46±4.6ka ago, or in middle and later Pleistocene.3) Paleoseismologic earthquake occured at Yingxiu Town between 4.93±0.86ka ago and Wenchuan Earthquake.