Investigation Of Paleoearthquakes,Slip Rate And Analysis Of Strong Earthquake Risk On The Qianning Segment Of Xianshuihe Fault

The Xianshuihe fault zone is located in the southeastern margin of the Tibetan Plateau, plateau internal har and Sichuan Yunnan two strong activity of sub block boundary zone, is one of the in the modern world the most active fracture belts. Along the fault zone, since the 7 magnitude earthquake in Kangding in 1725, there are 6.9major earthquakes in the history, the average recurrence interval is about 31 years.The risk of large earthquakes in the future has been concerned by scholars at home and abroad. Especially since 2008, the East and south of the block boundary zone occurred in Wenchuan in 2008 8, 2010 7.1 and 2013 Yushu Lushan 7 disaster and devastating earthquake, the Xianshuihe fault zone in Kangding- Kazakhstan salad also occurred in the 2014 period of Kang 6.3 earthquake, 2015, Tibet in the southern margin of the Himalaya plate boundary zones and the Nepal great earthquakes of magnitude 8.1, the Xianshuihe fault zone will not be affected by the occurrence of a larger earthquake once again become the focus of attention, fault zone and its surrounding areas have been delineated as government departments there are key monitoring danger zone 7 big earthquakes may be obtained, fault recurrence behavior of large earthquakes detailed and reliable basic data and understanding is one of the urgent task of seismic geological work.Qianning segment wherein the water river fault with NW single structure section of the southern most, along Qianning segment of the research work mainly completes at the beginning of the eighties to the nineties, trench is single, along the fault trough valley brae or scarps excavation of small trenches, generally only revealed near the main faults of tectono filling wedge, dating samples for sediments containing carbon,carbon sink effect, mixed age and sampling difficulties and other issues. In recent years, ancient earthquake research, especially trench location choices and dating techniques etc., have great development, in order to obtain fault zone is more detailed and reliable surface rupture type earthquake based information and knowledge to provide technical support. The booming based on small unmanned aerial vehicle(s UAV) super low altitude digital photography technology, and in recent years, thedevelopment of AMS measurement technology, provides a new technique to obtain the dislocation content active fault accurate and reliable fault activity rate. Field investigation found that, along the Xianshuihe fault zone Qianning segment, the Longdeng in the vicinity of the fault activity in Late Quaternary fault landform is very well developed, the local residual fault trough depression may be preserved more complete Holocene fault recorded in pond sediment plug is fracture of earthquake surface rupture history and activity rate of the ideal place.To sum up, on the one hand, the Xianshuihe fault zone is more detailed and reliable basic data and knowledge is needed to carry out the work; on the other hand,along the Xianshuihe fault zone Qianning segment Longdeng remaining studies fault earthquake surface rupture history and activity rate of the ideal place, on the basis of previous work, in recent years has made considerable progress or development is active tectonics and paleo seismic technology research based on should can get some of the more informative and reliable basic data and knowledge, for the future seismic risk assessment provides scientific basis. Therefore, the paper selected topic as "Investigation of Paleoearthquakes, Slip Rate and Analysis of Strong Earthquake Risk on the Qianning Segment of Xianshuihe Fault".The main research contents of this paper are:(1) the Xianshuihe fault zone Qianning segment Longdeng place ancient seismic fine research along the Xianshuihe fault zone Qianning segment, carefully select a developmental sedimentary sequence stratigraphy, event location relatively complete preservation, 3D excavation combined trench, to carry out fine ancient earthquake research, in order to obtain relatively more credible ancient earthquake sequence.(2) Qianning segment late Quaternary activity rate estimation-- a dry high precision acquisition of Nanjing late Quaternary activity of the dislocation and dislocation occurred in a period, and to estimate the fault in the late Quaternary since at different times the average rate of.(3) the future strong earthquake risk assessment of the dry Ning section: Based on the results of the research of the ancient earthquake and the rate of the activity, therisk assessment of the future strong earthquakes in the future is carried out.The technical scheme adopted in this paper is:(1) data processing and analysis to collect and collation of Xianshuihe fault belt of the previous research data and knowledge, historical earthquakes and modern seismic data and high resolution digital image data, and on the platform of GIS with remote sensing image processing technology will be the Xianshuihe fault zone Qianning segment of the topography, geography, geology and seismic catalogue data for fusion processing and analysis.(2) the Longdeng place probe trench excavation and ancient earthquake fine study, the high resolution remote sensing imagery solution interpretation and field survey combined, along Qianning segment carefully chosen Longdeng Township on the south side of a sedimentary sequence stratigraphy, event preserved relatively intact and is conducive to the acquisition of 14 C sample locations, excavation three-dimensional trench. Investigate groove profile information from the 1 / 20 scale accuracy is recorded in detail: fracture and stacked stratigraphic relations, event layer(including colluvial wedges and buried soil, tectonic wedge, filling wedge, determine the ancient earthquake occurred in the period of time and sequence. The formation sequence analysis of the local environment around the spot is carried out by using the stratigraphic information recorded in a number of exploration grooves to further define the age of the paleo earthquake events.(3)Longdeng in the vicinity of broken fault landforms, no computer measurement and activity rate estimate-- choose to break the fault landform Longdeng area, use the UAV aerial photography and digital image acquisition, by differential GPS control and geometric correction and post digital image processing,interpretation and analysis of punching groove level of horizontal displacement,combined with field survey, to obtain dry Ning segment since the late Quaternary in different periods the cumulative amount of dislocation and the latest events coseismic displacement. Comprehensive analysis of probe trench excavation obtained terrace age and events in and gully(water) accumulation of the relationship between theamount of dislocation, combined with the previous research data, the estimation of dry Ning segment since the late Quaternary in different periods of activity rate.(4) preliminary analysis of Qianning segment earthquake risk, Qianning segment(ancient) earthquake recurrence behavior analysis based on, ancient seismology angle,historical seismicity angle and activity rate angle Qianning segment of the strong earthquake risk of comprehensive analysis.The main conclusions of this paper are:(1) since the Xianshuihe fault zone Qianning segment about 9000 years ago happened five times(ancient) seismic events, events in order(8070-6395 BC),(5445-5125 BC),(4355-4180 BC),(625-1240 AD) and 1893 dry Ning earthquake.(2) Qianning segment of large earthquake recurrence behavior does not follow the characteristic earthquake recurrence model, early recurrence interval of about1000 to 2700 years to(4355-4180 BC after the incident, there have been about 5000 years long quiet period, and later entered active period, 1000 yr B.P. around since the two surface rupture of large earthquakes.(3) based on aerial drones and field measured to obtain the amount of dislocation,and combined with exploratory groove chronostratigraphic estimated get Qianning segment dating back approximately the last 1000 years the average rate of about2.8mm/a, dating from about 11000 years the average rate of about 1.6mm/a, dating back about 3 million years since the activity rate about 1.7mm/a.(4) single from the ancient earthquake recurrence interval(about 1000 years) and from the elapsed time(123 years) point of view, Qianning segment recent earthquakes above magnitude 7 is unlikely. However, if the whole fresh water river fault zone in the past 200 years since the large earthquake dense occurrence, the more likely to occur in the near future more than 7 earthquake.The main progress of the thesis is:On the basis of previous work, access to the Xianshuihe fault zone Qianning segment more complete ancient earthquake sequence of events and rate of Late Quaternary activity based on the ancient earthquake research results, analysis ofQianning segment of large earthquake recurrence behavior and recent seismic risk accumulated based information and knowledge.Main problems existing in the paper:(1) the reliability of the estimation results of the integrity and activity rate of the ancient seismic events is always a difficult problem in the study of active tectonics and paleo earthquakes. In spite of the control and analysis of all aspects of the research and the acquisition of the dislocation, the paper still has some uncertainty.(2) the obtained Qianning segment dating from about 1000 years since activity at a rate of about 2.8mm/a, dating back about 11000 years since the movement rate is1.6mm/a, dating from about 3 million years since the activity rate about 1.7mm/a, far less than the results of previous studies. The reasons for the need for more work to be tested and discussed.Next working direction:Along Qianning segment and the Xianshuihe fracture belt to carefully selected trenching sites, informative carry out ancient earthquake careful research and activity rate estimation, and the Longdeng place compared with each other, complement,maximize reduce uncertainty in the course of the study, to recognize fault surface rupture behavior and evaluate fracture recent seismic risk to provide more reliable data, is the main direction of the next step work.