Research On Block Fault Activity In Sichuan-yunnan Region Under The Constraints Of GPS Results

With the improvement of GPS observation technology and the continuous practice and exploration in geodesy and geodynamics,space geodetic technology has made rapid development and provided new technical means for studying earth science.Since the 20 th century,with the development and application of GPS station construction in China,we have accumulated a wealth of observation data.On this basis,China's earthquake research has achieved fruitful results,but at the same time,there are still many unsolved problems.In China,there are more than 3,000 years of historical earthquake records,the earthquake is widely distributed and the intensity is high.Due to national conditions,the earthquake has caused significant losses.Located in the southeastern part of the Qinghai-Tibet Plateau,the Sichuan-Yunnan region is one of the regions with the strongest seismic activity in mainland China.Since the20 th century,the earthquake activity in this area has been high,and earthquakes,especially the danger of strong earthquakes,need to be paid more attention.The activity level of the active fault is an important indicator of the stress state of the earthquake fault,and it is also an important source parameter of the seismic mechanics driving mechanism.Therefore,it is of great significance to study the seismic characteristics such as the slip rate,the degree of lockout,and the sliding loss of active faults in studying seismic activity and seismic hazard.This paper takes the main active faults in the Sichuan-Yunnan region as the research object,and combines the previous research results of the region to divide the Sichuan-Yunnan region into nine active plots.On this basis,using the multi-period GPS horizontal velocity field data in the study area,the current motion rate of the main fault zone in the Sichuan-Yunnan region is calculated by the fault profile analysis method.Then,based on the block model and the dislocation model,the DEFNODE negative dislocation inversion is used.The program obtains the degree of blockage of the fault zone and the spatial distribution of the sliding loss.Then,combining the calculation results,the inversion results and the previous research results,the seismic hazard of the main fault zone in the study area is analyzed.The main conclusions are as follows:1.The Lijiang-Xiaojinhe fault zone has increased the slip-slip component of the fault zone after the Wenchuan earthquake.The current strike-slip rates of the north,south and south sections are 2.8±0.5mm/a,6.5±0.5mm/a and 2.7±2mm/a,respectively.Before and after the Wenchuan earthquake,the fault zone has a high degree of occlusion and an increasing trend.2.The Longmenshan fault zone is a fault zone with strong lockout.After the Wenchuan earthquake,the degree of blockage in the northern segment is weakened.The fault zone is broken and unlocked after the Wenchuan earthquake.The fault zone is further unlocked after the Lushan earthquake.The Longmenshan fault zone tends to be stable after the Wenchuan earthquake.The current strike-slip rate is 6.3±1.1mm/a and the slip-slip rate is 4.5±1.0mm/a.3.The Longriuba fault was affected by the Wenchuan earthquake,which promoted the strain accumulation of the fault and the degree of the lock was enhanced.The current slip rate of the fault is 7.3±1.4mm/a,and the tilting slip component is1.9±1.0mm/a.With the compression of the Qinghai-Tibet Plateau and the Sichuan Basin,the region has conditions for major earthquakes.The tectonic activity of the Xianshuihe fault zone is strong.The inversion results show that the current strike slip rate in the northern segment of the fault zone is11.8±2 mm/a,and the slope slip rate is 1.7 mm/a.The current strike slip rate in the southern segment is 10.6±2.0 mm./a,the rate of tilting is 1.8 mm/a.5.The Xiaojiang fault zone is obviously segmented.The northern section is greatly affected by the Wenchuan earthquake.The degree of blockage is strengthened.The depth of the blockage reaches 18 km after the earthquake from 12 km before the earthquake.The current strike rate of the fault zone is 9.7±1.2.Mm/a.6.The current strike slip rate of the Honghe fault zone is 6.7±0.8mm/a,and the dumping rate is 1.8±0.5mm/a.The overall degree of blockage of the fault zone is high,and the strain accumulation velocity of the northern segment increases with time.The future seismic hazard of the fault is worthy of attention.