Study On The Present-day Crustal Deformation Characteristics Of Keping Block By GPS Measurements

Tianshan,the youngest resurrected orogenic belt inland,has complex geological structures,frequent strong earthquakes and frequent small earthquakes since the Cenozoic.It also become one of the hotspots in geosciences at home and abroad.In recent years,the vigorous development of space geodesy technology represented by GPS and In SAR technology has provided excellent technical means for studying the characteristics of crustal movement.It has been widely used in crustal deformation monitoring research and achieved fruitful research results.Located in front of the South Tianshan Mountains,the Keping block has a typical significance during the Cenozoic tectonic evolution of the Tianshan Mountains.Although many scholars at home and abroad have obtained a broad understanding of the GPS deformation rate in the Tianshan area,which ranges from 10 to 20 mm / a.However,the interior of the Keping block was split into two different regions by the Piqiang fault with crustal shortening rate and seismic activity.These problems are still remain unclear.Limited by the natural traffic conditions in the study area,the GPS points are sparsely distributed and with large space that lead to few GPS-based geodetic survey results in this area.Based on the GPS points encrypted by the Earthquake Administration of Xinjiang Uygur Autonomous Region observed from 2014 to 2018 totally 3perid data around the research area,we takes the Keping block as the main research object and use the GAMIT / GLOBK software to calculate the velocity field results relative to Eurasia,which filled and enriched the GPS research results in this area to some extent.Based on this,we can make use of profile method to obtain the activity rate of multiple rows of thrust nappies in the block.By using the mature negative dislocation inversion software,we can calculate the locking coefficients and sliding loss distribution characteristics of the Kepingtage fault,Piqiang fault and Maidan fault in the study area,which has certain reference significance.The main results and conclusions obtained are as follows:1.Compared with the Eurasian framework,we have more abundant and reliable GPS velocity field displacement characteristics in this area.The GPS speed of each station in this area change from 13 to 17 mm / a.And the direction of movement is the NNE direction as a whole,which is basically close to the magnitude of previous GPS speed in the area.2.From the perspective of the maximum and minimum principal compressive strains,the places with the largest principal and tensile strains are concentrated in the Keping block.The place with the highest shear strain rate is on the west side of the north end of Piqiang fault,with a value of(20~30)× 10-9.According to the existing research results,the place with the largest shear strain rate usually indicates the possibility of earthquake.3.According to the two-dimensional dislocation model,the strike-slip rate we calculated was 1 ~ 5mm / a,which was close to the result of 4mm / a obtained by Yang Shaomin.The vertical cross section of multiple rows of nappies inside the block shows that the internal slip rate of each nappe is between 0 and 5 mm / a.4.The Kepingtage fault has a stable change in fault locking,with a complete locking depth within 20 km,a partial fault locking between 20 and 40 km,and a fully creeping state below 40 km.5.The Piqiang fault has a fault locking depth of less than 10 km,a partial locking state between 10 and 30 km,and a fully creeping state below 30 km.The slip deficit rate is between 0 and 2 mm / a,which is greater than 1 mm/a at 0 to 15 km.and less than 1 mm/a at 15 to 30 km.When reached to 30 km below,the slip deficit rate becomes zero finaly.6.The fault locking situation of the Maidan fault is complicated,and there are obvious stratification phenomena.The fault locking depth gradually decreases from the southwest segment to the northeast end,and gradually decreases from 35 km to less than 10 km.The slip deficit rate is between 0 and 3 mm/a across the whole fault.The slip deficit rate in the southwest segment is between 2 and 3 mm/a and the depth gradually transitions from 35 km to about 20 km.The depth of the slip loss rate at the southwestern end of the Maidan fault(75 °-76 °)is obviously low,which is likely to be affected by the deep structure of the large dextral strike slip fault—the Talas-Fergana fault zone.