Research On The Relationship Between Vegetation Cover Change And Earthquake Intensity Before And After The Earthquake

After a destructive earthquake occurs,how to quickly obtain earthquake situation information,draw a seismic intensity distribution map,and accurately assess the earthquake disaster situation is a key issue for post-earthquake emergency rescue.At present,the change factor of vegetation has not been used for the assessment of intensity,but this factor has the following advantages:(1)There are mature methods and methods for vegetation cover inversion;(2)The calculation is simple and time-saving;(3)There are many remote sensing data sources for inversion of vegetation cover.This article aims to explore the relationship between the changes in vegetation coverage before and after the earthquake and the intensity,and to analyze whether the changes in vegetation coverage before and after the earthquake can be used as a reference basis for evaluating the intensity.In the current research,there are no mature theories and methods to obtain areas where vegetation coverage is completely reduced by the earthquake.This paper uses the image difference method to obtain the vegetation coverage changes before and after the earthquake without considering other influencing factors.The result may be affected by natural conditions,Therefore,the five-year image data that are in phase with the earthquake before and after the earthquake are selected to obtain the change in vegetation coverage in each year,and the maximum natural change in vegetation coverage is obtained by the method of Maximum Value Composites(MVC).The maximum natural change in vegetation coverage is used to remove the effects of natural conditions.At the same time,considering the susceptibility of geological disasters(the probability of vegetation destruction),the slope is added for analysis,and the special changes in vegetation coverage before and after the earthquake are obtained,that is,the changes in vegetation coverage that may be caused by the earthquake.Convert the final image raster data into point data,extract the pixel points with drastically reduced vegetation coverage,and use nuclear density analysis to convert the discrete pixel points into continuous distribution of area data to reflect the characteristics of pixel point density distribution,fit the results obtained above withthe seismic intensity.In this article,four earthquake cases of Jiuzhaigou Ms7.0earthquake,Wenchuan Ms8.0 earthquake,Yaan Ms7.0 earthquake,Ludian Ms6.5earthquake were analyzed in detail.In order to monitor the continuous change of vegetation coverage over time,according to the time when the earthquake occurred,3consecutive time modis image data were selected before and after the earthquake.The change in vegetation coverage before and after the earthquake will be obtained two results,and compares the two results,the conclusion points out:1?Regardless of other influencing factors,the relationship between changes in vegetation coverage and intensity before and after the earthquake:In the Jiuzhaigou earthquake,the vegetation coverage obtained before and after the earthquake from two consecutive images after the earthquake decreased drastically,reflecting the direction of the long axis of the intensity;In the Wenchuan earthquake,the vegetation coverage of the two consecutive images after the earthquake before and after the earthquake decreased drastically,the former image can reflect the location of the high-intensity area with severe damage,and the latter image can reflect the direction of the long axis of the intensity;In the Lushan earthquake,the dramatic reduction in vegetation coverage before and after the earthquake from two consecutive images before the earthquake can reflect the direction of the long axis of the intensity;In the Ludian earthquake,the dramatic reduction in vegetation coverage before and after the earthquake from two consecutive images after the earthquake could not reflect the distribution characteristics of the intensity.2?Relationship between special changes in vegetation coverage and intensity before and after the earthquake:(1)The relationship between the overall distribution of pixel points and intensity:In the Jiuzhaigou earthquake,the pixel points extracted from two consecutive images after the earthquake have the same distribution direction as the long axis of the intensity;In the Wenchuan earthquake,the pixel points extracted from two consecutive images after the earthquake were densely distributed in the high intensity area;In the Lushan earthquake,the pixel points taken from two consecutive images before the earthquake and the area where the pixel points are concentrated in the latter image arein the same direction as the long axis of the intensity;In the Ludian earthquake,the pixel points extracted from two consecutive images after the earthquake could not reflect the distribution characteristics of the intensity.(2)The relationship between the analysis results of pixel density and intensity:The Lushan earthquake,regardless of the influence of other factors,the change in vegetation coverage before and after the earthquake is consistent with the change trend in vegetation coverage under natural conditions,special changes in vegetation coverage before and after the earthquake are not obvious,therefore,the fitting results of the pixel point kernel density analysis obtained by the method of this article and the intensity are poor.The Jiuzhaigou Earthquake,Wenchuan Earthquake,Ludian Earthquake,through this method,obtained the special changes in vegetation coverage before and after the earthquake,and the results of the pixel point nuclear density analysis have a good fit with the seismic intensity,which can reflect the long axis of the intensity direction,location of high intensity area.This paper initially proved through research that the changes in vegetation cover before and after the earthquake can reflect the distribution characteristics of the intensity,that is,there is a certain relationship between the changes in vegetation cover before and after the earthquake and the intensity,however,the vegetation damage phenomenon is different in different earthquakes,and the intensity distribution characteristics can be reflected differently.By comparing the results of the four earthquake cases,it is found that the vegetation coverage reduction caused by the earthquake is obvious when the intensity reaches X,and the intensity range is VI-IX,the phenomenon is not obvious.When evaluating the intensity,the vegetation change can be used as the basis for reference according to the actual situation.In future research,you can also choose different remote sensing data sources,explore more other methods to obtain the vegetation cover changes caused by the earthquake,and analyze the relationship between it and the seismic intensity.