Earthquake Temporal And Spatial Structure And Risk Assessment In Sichuan-Yunnan Area

There are many active faults in Sichuan and Yunnan,which are the regions with the most frequent strong earthquakes in China.Meanwhile,the earthquake magnitude is large and the focal depth is shallow,which is easy to cause serious earthquake disasters and huge loss of economic property and casualties.In this study,based on the historical seismic data of Sichuan-Yunnan area,the spatial-temporal symmetry characteristics were analyzed and the trend was judged,and the seismic risks based on the social and economic statistical data of different cities were evaluate,so as to provide some theoretical and practical basis for regional seismic risk management.The theoretical basis of this study is the space-time symmetry structure of major natural disasters.The logical system is "law of time symmetry structure---law of space symmetry structure---judgment of earthquake magnitude,epicenter and time---evaluation and countermeasures of earthquake risk pattern".To be specific,the commensurability theory was used to judge the time trend of the historical earthquake sequences in Sichuan-Yunnan area,Sichuan Province and Yunnan Province,and analyze the symmetrical law of earthquake time in different regions with the method of butterfly structure diagram and commensurability structure system,and finally obtain the judgment results of earthquake time trend.In space,the spatial longitude and latitude range of future earthquakes were judged by the characteristics of meridional and latitudinal migration,and the spatial-temporal trend of earthquakes in Sichuan-Yunnan area,Sichuan Province and Yunnan Province was judged,and the judgment results of earthquake epicenter trend was obtained.Based on the conclusion of future seismic trend judgment and the classical natural disaster risk evaluation system,the seismic risk evaluation index of Sichuan-Yunnan area was constructed from the perspective of the dangerousness of disaster factors,the exposure of hazard-affected body and the stability of hazard inducing environment,and the then seismic risk distribution map of Sichuan-Yunnan area was drawn.The specific conclusions are as follows:1)Time symmetry structure and trend judgment result.From 1930 to 2018,the studies on seismic time symmetry of Sichuan-Yunnan are and Sichuan and Yunnan regions indicated that earthquakes with M≥6.9 in Sichuan-Yunnan area had stronger signals between 2020 and 2022,among which the seismic signals in 2020 were stronger.The random probability of earthquake occurrence was 62.5%,and the confidence level was 58.82%.The judgment results of earthquake trend M≥6.25 in Sichuan also showed that the signals between 2020 and 2022 were stronger,but the random probability and undeclared level of earthquake are relatively low.The random probability and unreported level of earthquake confidence in 2020 were 47.06%and 44.44%,respectively,and it was only 17.64%and 16.67%in 2022.The seismic trend judgment results of M≥6.25 in Yunnan indicated that the seismic signals in 2020 and 2021 were stronger,but the seismic signal in 2020 was stronger,the random probability of earthquake occurrence was 55.0%,and the confidence level of non-reporting was 52.38%.2)Spatial symmetry structure and trend judgment results.The studies on the space migration change of Sichuan-Yunnan region from 1930 to 2018 indicated that the earthquake space of M≥6.9 in Sichuan-Yunnan region presented a symmetric distribution with 280N and 101.5°E as the symmetric axis,and every five earthquakes presented "three in north and two in south,three in east and two in west" along the axis of symmetry.Every three earthquakes were divided into a group to analyze their space rotation characteristics,and the spatial triangle was counterclockwise,so it was judged that the next seismic space was roughly 21.13°N-28°N,97.52°E-101°E;The seismic space of N≥6.25 in Sichuan presented a reverse with 31°N and 102.7°E as the symmetry axis,and the spatial triangle rotated clockwise.It was judged that the spatial range of the next earthquake was approximately 31°N-34.32°N,102.7°E-105°E.The seismic space of M≥6.25 in Yunnan presented a symmetric distribution with 24°N and 101.5°E as the symmetry axis,and the migration change in the upward latitudinal direction was "two in south and 3 in north" and "3 in south and 2 in north",and in the longitudinal direction,the west side of the symmetry axis migrated and the both sides of the symmetry axis had a skipping migration.3)Combination of space-time symmetry and risk assessment As for the earthquake risk in Sichuan-Yunnan region,the earthquake risk in Sichuan Province was higher than that in Yunnan Province.The earthquake risk in Sichuan Province presented a spatial distribution pattern of high in the west and low in the east.The earthquake risk level in the eastern and southern Sichuan was relatively low,while the earthquake risk level in the western and northern Sichuan was relatively high,and central Yunnan was the area with high earthquake risk.This is mainly attributed to the degree of relief and regional space position.The western Sichuan and the northern Sichuan are located in the Longmenshan Fault Zone and Sichuan-Yunnan diamond block,where the earthquake activity is frequent and regional relief is high,increasing earthquake damage.Central Yunnan is located in central Yunnan block,where the historical earthquake location is concentrated,and there is a high risk and high sensitivity,so that the regional earthquake disaster risk is higher.4)Earthquake risk management and countermeasures in Sichuan-Yunnan area.Based on the study on the space-time symmetry of earthquake and earthquake risk assessment in Sichuan-Yunnan area,the risk management measures were put forward for before earthquake,during earthquake and after earthquake.Before the earthquake,the high-risk window of earthquake in Sichuan-Yunnan region was identified mainly from the theory and practice,and then the propaganda education of earthquake disaster preparedness of community residents was strengthened.During the earthquake,from the perspective of residents’ self-help and escaping in public places,it is suggested that the principle of high-rise building suspension self-help "333" should be adopted and the suspension safety angle and automatic voice guidance should be set in public places.After earthquake,risk prevention mainly aims at seismic secondary disasters such as landslide,debris flow and common diseases,including residents relocation,disease prevention and so on.Sichuan-Yunnan region is an area with frequent earthquake disasters in our country,and its terrain,fault zone and ground motion peak acceleration and other factors increase the earthquake disaster loss,but these are immutable factors.The focus on reducing the earthquake disaster risk is to reasonably plan population and economic development of areas with high seismic risk,and the housing construction structure should be anti-seismic,and the residents’ capability of self-help and disaster reduction consciousness in earthquake should be strengthened.