Deformation Characteristics And Seismic Hazard Evaluation Of The Haiyuan Fault Based On GPS

The Haiyuan-Liupanshan fault,an active tectonic feature at the northeastern margin of the Tibetan Plateau,is the boundary that separate the first-order blocks between the Tibetan block and the Alaxan and the Ordos block.The deformation characteristics of the Haiyuan-Liupanshan fault is an important basis for defining tectonic deformation occurring in the Tibetan Plateau,and also one of the basic research of the continental dynamics.It is of great significance for the study of formation and evolution as well as the deformation process of the Tibetan Plateau,meanwhile,is of great significance for our understanding of the seismogenic mechanism of earthquakes.A high seismic hazard is estimated along the Haiyuan-Liupanshan fault by researches of paleoearthquakes,tectonic activity of faults,strain accumulation and seismicity.As a result,research on the deformation characteristics and seismic hazard evaluation of the Haiyuan-Liupanshan fault is not only one of the hot topics in the study of crustal deformation,but also has practical value.In this paper,we use the block model,the elastic block model and the three-dimensional elastic half-space model and the strain rate computing method to invert for the deformation and strain parameters of the Haiyuan-Liupanshan fault in both shallow and depth based on GPS.On the basis of the above results,we analyzed the seismic hazard in the northeastern Tibetan Plateau.The main work and conclusions are as follows:1.221 GPS stations with an occupation of three to eight epochs over the time spanning from 1999 to 2015 were collected.The GPS data were processed using the GAMIT/GLOBK software and a new velocity field was derived under the Eurasia-fixed frame.We analyzed the deformation characteristics of the northeastern Tibetan Plateau after taking out the rigid rotation part of the GPS velocities.2.We inverted for the slip rates,the fault locking and the slip rate deficit and the moment accumulation rates of the Haiyuan-Liupanshan fault.Along the Haiyuan fault,the results show3.2-6.2 mm/yr of left-lateral strike-slip,and the strike-slip transformed into thrusting deformation(2.8-3.5 mm/yr)along the Liupanshan fault.The results suggest full coupling down to 10 km along the Haiyuan fault.Significant portions from the Jinqianghe fault to the Maomaoshan fault,however,are locked to 17-23 km depth.The Liupanshan fault is locked to15-20 km depth.High seismic moment accumulation rates are interpreted along the“Tianzhu seismic gap”and the Liupanshan fault.3.The coulomb stress accumulation rates along the Haiyuan fault were calculated.We also calculated the second invariant of the strain rate tensors on the surface of the northeastern Tibetan Plateau.The two strain rates have a corresponding consistency in space.Faults with“deep coupling”,such as the“Tianzhu seismic gap”and the Liupanshan fault,show a relatively low magnitude of strain rates.While faults with“shallow coupling”,such as the Haiyuan segment,the Tuolaishan segment and the Lenglongling segment,show the opposite.4.On the basis of the crustal deformation and strain characteristics of the Haiyuan-Liupanshan fault,we did a seismic risk assessment along the fault zone.We took the seismogenic fault of the 2015 Nepal M_w7.9 earthquake for reference,and we also took the stress triggering effect of the 2016 Menyuan M_w6.4 earthquake into consideration.As a result,we infer that a greater possibility of nucleation for a future event on the Jinqianghe fault,the Maomaoshan fault and the Liupanshan fault exist.