| On August 8,2017,the Jiuzhaigou Ms7.0 earthquake occurred on the eastern edge of the Bayan Har block in southwestern China,causing loss of life and property.Jiuzhaigou Scenic Area was also severely damaged.Earthquake is a direct manifestation of fault movement.Strong earthquakes are characterized by great destructive power and wide disasters.This makes the exploration of earthquake seismogenic mechanism and earthquake prevention and disaster reduction one of the important scientific goals of earth science.InSAR,as one of geodetic surveying technologies,is becoming an efficient earth's surface deformation monitoring method,which can provide a wide range of remote sensing observation data for spatial feature interpretation of deformation,surface damage analysis,and inversion for source mechanism.Particularly,the combination and successful application of geodetic surveying technology and seismic fault dislocation theory has made the inversion for the earthquake source model with geodetic deformations as constraints an important means of scientific understanding of the seismic mechanism.In this paper,using Sentinel-1A wide-format SAR image data,the deformation field of Jiuzhaigou earthquake is extracted by DInSAR two-track processing.The deformation field is elliptical,and the long axis is along NW direction.The deformation on the west side of the epicenter is greater than the east side.The deformation of the ascending track shows that the maximum lifting in the line of sight is 0.09 m and the maximum settlement is 0.21 m.The deformation of the descending direction shows that the maximum lift in the line of sight is 0.13 m,and the maximum settlement is 0.07 m.The earthquake did not cause obvious surface rupture lines.In order to construct the seismogenic fault model of the Jiuzhaigou earthquake,this paper takes the deformation field of ascending and descending extracted by DInSAR technology as the constraint,sets a uniform sliding single fault model,and searches for the optimal solution of the fault geometric parameters in the solution space.The latitude and longitude of the upper left corner of the seismogenic fault is 103.7°E,33.4°N,and fault is 42 km long and 31 km wide with the strike of 152° and the dip of 66.4°.When inverting for the fine non-uniform sliding distribution of the fault,in order to improve the difficulty of determining the optimal size and over smoothness of the commonly used rectangular dislocation element model,the fault is segmented based on the triangular dislocation elements that determine the adaptive size of the dislocation element according to the matrix resolution.The results of fault slip distribution show that the Jiuzhaigou earthquake is a seismic event dominated by left-lateral strike-slip,with a maximum slip of about 0.82 m at the depth of about 10 km.Coulomb stress changes caused by earthquakes are important triggers for subsequent surface or underground rupture events.This paper discusses the triggering effect of the Songpan earthquake in 1973,the Songpan earthquakes in 1976,and the Wenchuan earthquake in 2008 on the Jiuzhaigou earthquake.The cumulative effect of three earthquake events in the epicenter of the Jiuzhaigou earthquake is an increase in stress,that is,there is a triggering effect.Then the static Coulomb stress of the Jiuzhaigou seismic fault slip at 5 km,10 km,15 km and 20 km depth is calculated.The stress changes of the Jiuzhaigou earthquake at different depths in the ground have a good consistency with the subsequent seismic distribution.In this paper,the influence of Jiuzhaigou seismic fault motion on the stress changes of surrounding faults is calculated.The results show that the stresses in the northern section of the Minjiang fault and the northern section of the Huya fault increase significantly,reaching 0.5 bar,and there is no strong earthquake for a long time in the northern section of the Minjiang fault.Therefore,the risk of future earthquakes in the northern section of the Minjiang fault increases. |
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