Study On Present-day Deformation In The Central Segment Of The Altyn Tagh Fault Zone By Time Series InSAR

As a boundary fault zone between the Tibetan Plateau and the Tarim Basin,the Altyn Tagh left-lateral strike-slip fault zone has undergone multi-period complicated geological evolution,with large-scale and strong penetrability and seismic activity.It plays a regulatory role in the deformation and the eastern extrusion of material of the Tibetan Plateau.Since the 1960 s and 1970 s,many scholars have gathered in this research area and achieved some breakthroughs in geology.However,there are still many controversies about the Altyn Tagh fault zone,such as activity patterns,slip-slip rates,and deformation patterns.This is mainly due to the large scale of the Altyn Tagh fault zone which tatal length is about 1700 km,coupled with the constraints of high altitude and severe weather.All of these lead to sparsely populated and uneven distribution of existing research data.All these have limited further understanding and exploration of the structure and movement patterns of the Altyn Tagh fault zone.In addition,the seismic distribution in the Altyn Tagh fault zone since 1900 has showed a significant 5th-level seismic calm area in the central segment(Mangya-Subei).In recent years,many Ms?5 earthquakes with maximum magnitude of Ms 6.6,occurred successively around the calm area,and the increase of small earthquakes and accumulative strain release since 2002.Therefore,it contributes to the study and prediction of earthquake risk in this area obtaining the fine kinematics of the central segment of the Altyn Tagh fault zoneInSAR(Synthetic Aperture Radar Interferometry)technology has provided a new method for spatial geodesy,global and regional scale mapping and deformation monitoring since 1980 s,which enabling continuous observation at all weather,high resolution,and large spatial scales.The time series InSAR technology based on the analysis of long-term serial SAR data can effectively decrease the influence of DEM error and atmospheric phase delay on the deformation signal,and further improve the accuracy of InSAR deformation monitoring,This makes it possible to use the InSAR technique to monitor the slow and large deformation caused by the inter-seismic tectonic movements of active faults.This article research the 90.8°-91.58°E area of the central segment of the Altyn Tagh fault zone using the ALOS PALSAR data from 2007 to 2010 and SBAS InSAR techniques.We obtain the time series deformation of the research object,also invert for the slip rate and locking depth of the area.The main research content is as follows:1.The tectonic movement background and seismicity data of the Altyn Tagh fault zone are collected and sorted out.The distribution and evolution history of the faults in the central segment of the Altyn Tagh fault zone have been clarified.The earthquake catalog of the area has been collected,and it has been found that there is no strong earthquake record in the region between Mangya and Subei.Nowadays,a significant small earthquake section is formed.2.The research status is elaborated in detail of InSAR technology in tectonic deformation monitoring,and the key technologies of InSAR applied in inter-seismic deformation observation are studied.Mainly include: Optimal combination of time and space baselines in SBAS InSAR data pairing;Selection of unwrapping and filtering methods for low-coherence regions;Selection of ground control points(GCP)in orbit refinement;Comparison and selection of flattening methods;Reasonable estimation of residual terrain in SBAS inversion.3.The present-day tectonic deformation field in the central segment of the Altyn Tagh fault zone was obtained using SBAS InSAR technology.The results show that:(1)LOS direction deformation on north and south parts of the main Altyn Tagh fault were approximately concentrated around-35~-60 mm and-9~11 mm respectively.(2)The deformation of Xorkol Basin is the largest that as a result of controlled by the strike slip movement of the Altyn Tagh fault.(3)The LOS direction deformations in Jinhong Mountain and Xorkol Daban area are negative,which is different from the positive deformation in other areas in the south part.It is speculated that Jinhong Mountain and Xorkol Daban area have a tendency of growth and expansion.4.The strike-slip rate and locking depth of the Altyn Tagh fault were inverted by the two-dimensional strike-slip fault buried-dislocation model.The results show that:(1)The strike-slip rate at three sections were 6.1 mm/a,5.3 mm/a,and 7.9 mm/a from west to east;(2)The corresponding locking depths were 9.5 km,6.8 km,and 12.3 km from west to east.(3)The geolocation of inverse fault is coincide with the Xorkol seismic rupture zone.5.The relationship between rate changes and surrounding seismic events was analyzed.The results show that the deformation characteristic of the central segment of the Altyn Tagh fault zone is complex,and surrounding seismic events may affect the strike-slip rate of the fault zone.6.The SBAS InSAR results of the Altyn Tagh and surrounding area show that:(1)Deformation result is related to the terrain intensity and may be related to the low precision of the selected reference SRTM DEM in mountainous area.(2)The vertical deformation map shows that the uplift of the Jinyan mountain is about 60-55 mm,while the south of the main Altyn Tagh fault is almost 0mm,indicating that there is a remarkable orogenic process in the Altyn Tagh at present.(3)the Jinyan mountain and the Xorkol basin form a composite fault structure,which is the main adjustment model of strain and stress during the transition fault movements.