Research On Characteristics Of Gravity Erosion After Earthquake Based On Multi-source Earth Observation Technology

After the Wenchuan earthquake,geological disasters occurred frequently in Wenchuan County,resulting in strong landslides,gravity erosion and sediment yield,which seriously affected the production and construction activities and the safety of people’s lives and property in the disaster area.It is difficult to identify and extract the gravity erosion area,and it is difficult to obtain the quantitative parameters such as the amount of erosion due to the complex topography and the strong randomness of gravity erosion.In this paper,Wenchuan County,which was the hardest hit area of 5·12Wenchuan earthquake,was taken as the study area.Combined with the mass occurrence of major geological disasters,ALOS PALSAR and Sentinel 1A radar images are used as data sources,and Mai and offset are used to analyze the geological hazards The vertical deformation of the landslide area is obtained by tracking radar interferometry technology,and then the vertical deformation field of multi-phase disasters in the study area is obtained by cutting and fusing the range of incoherent area identified by optical remote sensing improved by radar coherence.Combined with GIS hydrological analysis and manual editing,the overlaying analysis of slope body and watershed erosion units was carried out,and the quantitative parameters such as erosion amount and erosion modulus were estimated and extracted,and the gravity erosion characteristics of different erosion units were analyzed.Taking the watershed as an example,the variation law of influence factors with scale was analyzed.The results show that:1)Using multi-source remote sensing data,radar remote sensing,optical remote sensing and GIS technology,a high-precision gravity erosion deformation field can be established,and then the erosion area,erosion amount,erosion modulus and other parameters of slope body and basin erosion unit can be statistically estimated,and the characteristics of gravity erosion and the relationship between gravity erosion and influencing factors can be analyzed.2)There is a positive correlation between slope gradient and erosion modulus.In the range of 500 m～1500 m,the gravity erosion amount of previous slopes is the largest,and the development degree of gravity erosion is the highest.The erosion parameters are positively correlated with the height difference of slope,and the increasing trend remains unchanged from 2008 to 2010,and slows down from 2017 to2019.The slope aspect of erosion units is concentrated in the South and Southeast,and the erosion amount accounts for more than 80%.3)After the earthquake,the intensity of gravity erosion in the basin unit decreased year by year.The dominant range of erosion area height difference is between 2000 m and 3000 m,and the amount of erosion is positively correlated with the elevation difference.There is a positive correlation between the area of gravity erosion and the elevation of the basin.The erosion area of>2500 m is relatively high,and the distribution of erosion amount is consistent in the average elevation range of all levels of basins.The proportion of erosion in the basin with slope range of 25°to 40°accounted for more than 83%.There is a negative correlation between the erosion modulus and the distance between the basin and the main fault zone.The erosion area and the amount of erosion within 15 km from the fault zone are the largest,accounting for more than 50%of all previous disasters.4)The influence of watershed scale change on the change of impact factors is different,and the impact factors of watershed erosion have certain scale change characteristics.There is a linear relationship between the gully length and the drainage area.With the increase of basin area,the basin perimeter also increases gradually.When the basin area increases to 20 km~2,the contribution rate of basin area increase to basin perimeter increases significantly.There is a positive correlation between the elevation difference and the drainage area,and the increasing trend gradually slows down when the basin area is more than 10 km~2.There is a significant negative correlation When the basin area is less than 20 km~2,the fluctuation value decreases rapidly.When the basin area is more than 20 km~2,the decreasing trend of the fluctuation degree is slow down.When the basin area is more than 35 km~2,the fluctuation degree basically remains unchanged.When the drainage area is less than 10 km~2,the increasing trend slows down.When the drainage area is greater than 10 km~2,the increase trend of river network density will remain unchanged after it is reduced to a certain range.5)The basin scale is characterized by basin area,and the main controlling factors of different scales are quite different.Taking the basin erosion unit in the study area as an example,20 km~2can be used as an interval point at the basin scale.For the basin with an area of more than 20 km~2,the basin perimeter,area,river network density,elevation and elevation difference are the main control factors of gravity erosion.For the watershed less than 20 km~2,the main influencing factors are gully length gradient,river network density,elevation difference and elevation.