| The spatial distribution and deformation characteristics of the coseismic surface fracture zone not only record the information of seismic rupture and fault movement,but also reflect the regional stress and crustal movement.The geomorphological offset caused by fault activity also contains important information about the process of earthquake rupture.The displacement distribution established by this method is helpful to understand the recurrence behavior of earthquakes and evaluate the earthquake disasters of faults.Therefore,the investigation of the post-earthquake surface fracture zone and the construction of displacement distribution are of great significance for understanding the tectonic activity of seismogenic faults.Most of the early work is based on traditional field investigation,but the harsh climate environment in the earthquake area and secondary disasters after the earthquake limit the development of field work.With the development of high-precision topography observation technology,obtaining geomorphological images by remote sensing satellite,lidar scanning,UAV and other methods can greatly reduce the constraints of natural conditions,and the data accuracy has been improved,which is helpful to the study of detailed geomorphology.In recent years,the new Sf M(Structure from Motion)photogrammetry method provides an effective technical means to quickly obtain post-earthquake high-resolution topographic data,which can obtain 3D geomorphological features in a large scale and in a short time without terrain constraints.In this paper,Sf M photogrammetry is applied to Xinjiang Fuyun fault.The Fuyun fault is located in the southwest edge of the Altai Mountains.The Fuyun M8.0earthquake occurred in 1931.The linear characteristic of the earthquake surface rupture zone is obvious.A large number of tectonic landforms related to strike-slip activities such as right-lateral gully dislocations,compressional uplifts and pull-apart basins have been developed,which are still well preserved several decades later.After the earthquake,many scholars have carried out geological mapping of the earthquake surface rupture zone,but there is a lack of detailed description of the distribution of the earthquake surface rupture zone,and the differences in displacement markers and measurement techniques.It results in the deviation of many kinds of basic data,such as co-seismic displacement,slip displacement and so on.Therefore,through photogrammetry,the high-precision terrain data about Fuyun fault are obtained.on the basis of previous studies,the shape and displacement distribution of surface fracture zone are further supplemented and modified to improve the investigation into 1931 Fuyun earthquake rupture zone.In this paper,based on aerial photogrammetry Sf M technology,a digital elevation model(DEM),with a resolution of 1m about the surface rupture zone of Fuyun earthquake is generated,which can reflect the micro-structural geomorphology and is suitable for detailed geomorphology research in a small scale.Combined with the shadow and color change of DEM data,the surface deformation characteristics such as seismic cracks and seismic mole cracks are identified,the surface rupture tracks are drawn in detail,and the surface rupture zone of Fuyun earthquake is segmented through the distribution of its geometric and tectonic geomorphological features.Taking the gully as the landform marker of the fault,the right-lateral horizontal displacement of the gully is obtained by identifying along the fault and combining with the Dispcalc measurement software.Based on the displacement of the gully,the slip displacement distribution along the fault is obtained,and the coseismic displacement distribution of the Fuyun earthquake in 1931 is extracted from it.By calculating the cumulative offset probability density(COPD)of slip displacement distribution,the recurrence of strong earthquakes is simply analyzed from the clustering,and the rupture propagation characteristics are analyzed by combining the segmentation characteristics of the surface rupture with the coseismic displacement distribution.The main conclusions of this paper are as follows:(1)the detailed surface fracture morphology and deformation characteristics.According to the geometric and structural geomorphological features of surface rupture,it can be divided into four segments S1,S2,S3 and S4 from north to south,which are connected by compressional uplift or pull-apart basin.The surface deformation is mainly characterized by shear carck,as well as transpressional cracks and tension cracks.At the junction and transition of surface rupture,there are structural geomorphological phenomena such as mole crack,ridge and pull-apart basin.(2)more complete displacement distribution and 1931 coseismic displacement distribution.The horizontal displacement of 550 groups of gullies are measured to establish the displacement distribution of Fuyun fault,and the displacement value are generally between 0.9m-94.8m.From the clustering characteristics of the four segments of COPD,the multiple relation of 3-4 times of the coseismic displacement is identified,which represents four earthquake events including the 1931 earthquake.Combined with the previous research results,194 groups of gully horizontal displacements were extracted as coseismic displacements in 1931,with an average value of(5.06 ± 0.13)m,which is equivalent to the coseismic displacement produced by similar magnitude.The slip distribution of coseismic displacement along the strike represents four continuous waves,with high gradient changes of displacement on both sides of the wave,forming three grooves together with adjacent waves respectively,and the position of the groove also corresponds to the connection of the four segments of surface rupture.(3)The 1931 Fuyun earthquake was a cascade rupture formed by four rupture segments.The "rainbow" coseismic displacement distribution reflects four complete stress drops,indicating that the surface rupture of the four segments is a complete independent fault segment,and the surface rupture is likely to break through the step area.The step area of S1 and S2 and the connection of S3 and S4 is not enough to stop the propagation of rupture here,and the bending angle of S2 and S3 will not prevent the propagation of rupture.In a word,high-resolution topographic data enriches the detailed investigation and displacement distribution of the surface rupture zone of Fuyun earthquake,and further demonstrates the good application value of high-resolution topographic data in the study of active tectonics. |
PDF Full Text Request