Characteristics Of Coseismic Surface Rupture Of Five Modern Strong Earthquakes In And Around The Central Bayanhar Block Using Multi-source Remote Sensing Images

The continuous collision between the Indian plate and the Eurasian plate since the Late Cretaceous led to the rapid uplift of the Tibetan Plateau,resulting in extensive deformation and the development of a large number of geological structures.The Bayanhar block is a Class II active block within the Tibet Block,it is enclosed by a series of late Cenozoic active faults.These active faults regulate the strain caused by the eastward "escape" of plateau material through earthquakes.In the past hundred years,there have been 15 earthquakes above M7 around the boundary and interior of Bayanhar block,making it the focus of extensive academic attention.Coseismic surface rupture is the permanent deformation on the surface of the earth,after the rupture of the seismogenic fault in the middle and upper part of the crust.The surface rupture zone indicates the deep structural characteristics and preexisting tectonic environment of seismogenic faults to a certain extent,and plays an important role in the study of the geometry,kinematics and dynamics of seismogenic faults.Using remote sensing data to study the characteristics of the current strong earthquake rupture zone with time is of great significance for the study of historical earthquake rupture.Satellite remote sensing data has the advantages of large observation area,strong timeliness,high resolution,convenient acquisition and no restriction of ground conditions,which can reduce the restriction of natural and man-made conditions on field investigation to a great extent.Since the 21 st century,with the emergence of satellite remote sensing data with sub-meter resolution,it is possible to use remote sensing to conduct comprehensive and in-depth research on plateau earthquakes.Based on the theory of seismic geology,this paper takes the coseismic surface rupture of five recent strike-slip earthquakes in the central part of Bayanhar Block as the research object,and chooses multi-period remote sensing data before and after earthquakes to identify the changes of surface rupture zone over time.The following preliminary understandings are obtained:1)Affected by surface effects such as scour and erosion,the surface rupture zone passing through young terraces,alluvial fans,gully and river channels will be transformed within a short time after the earthquake,so it can not be identified on remote sensing images.Older landforms are less affected by surface action,and more complete and dense surface rupture zones can often be identified on the image.2)The surface rupture zone developed in the quaternary strata with low weathering resistance is easy to be destroyed by external forces.The loose and unconsolidated quaternary surface is not conducive to the long-term preservation of the rupture zone,which affects the recognition degree of the rupture zone in remote sensing images.The bedrock strata have better resistance to weathering,and the surface rupture zone is more recognizable than the quaternary strata in the image of the same period.3)The recognizable length of most earthquake surface rupture zones on remote sensing images first decreases rapidly with time,and then slowly decreases with the increase of earthquake elapsed time,and the change rate of length presents a trend of first fast and then slow.The larger the initial rupture scale,the longer the surface rupture zone can be preserved on the image.4)The recognition degree of the surface rupture zone in the image is affected by the surface action process such as the geomorphic location and climate change,as well as the scale of the rupture zone and the spatial resolution and time phase of the remote sensing image.The integrity investigation of the surface rupture zone of the present strong earthquake can rely on the emergency scientific investigation and the satellite and aerial image data shortly after the earthquake,but the identification of the surface rupture zone of the uninhabited area and the historical strong earthquake mainly relies on the satellite image which has long passed away.Through the information of the rupture zone remaining on the older geomorphic surface,a more complete surface rupture zone can be recovered than that directly observed on the surface.