| The Global Risk Report points out that the earth will face risk threats brought by extreme weather events and major natural disasters in the next 10 years.The vulnerability of hazard-affected bodies has substantially increased with the rapid development of urbanization,population,and economy in cities.A large number of casualties and property losses is anticipated once a disaster occurs.As "the most serious disaster among calamities," earthquakes are characterized by strong suddenness,high destructiveness,and multiple secondary disasters.Earthquakes severely threaten the sustainable development of the social economy.The Sichuan-Yunnan region accounts for 9.43%of the total population of the country.More importantly,with its complex geological structure and frequent earthquakes,this region is an ideal test site for earthquake trend judgment and research.It also serves as a key prevention and control area for earthquake prevention and disaster reduction in China.Studying the temporal and spatial distribution characteristics of earthquake disasters in the Sichuan-Yunnan region is crucial to improving the safety of regional earthquake disasters and realizing regional sustainable development.Determining the future occurrence trends of earthquakes;assessing the level of earthquake disaster risk in different regions and their main controlling influence factors;integrating regional earthquake prevention,earthquake resistance,and disaster relief resources;and formulating effective regional earthquake prevention measures are equally important.On this basis,the method system of temporal-spatial symmetry of natural disasters is integrated in this study.Based on regional disaster system theory and risk society theory,geographical research methods are employed to judge the future trend of earthquake disasters in Sichuan and Yunnan.These methods include such as wavelet analysis method,nuclear density estimation method,co-occurrence analysis method,commensurability method,information entropy,comprehensive index method,and geographic detectors.The correlation between the factors(the relative number of sunspots and the change of the earth's rotation speed)and the seismic activity in Sichuan and Yunnan is also discussed.In addition,an evaluation index system is constructed to assess the earthquake disaster risk level of each state and city in the Sichuan-Yunnan region.After analyzing the main factors affecting the risk levels of earthquake disasters in various regions,corresponding risk management countermeasures are formulated.The results indicate the following:(1)Significant spatiotemporal statistical pattern exists in the seismic disaster.The frequency and energy release of historical earthquakes in the Sichuan-Yunnan region are periodic.The spatial distribution of epicenters is concentrated.On an annual scale,the occurrence frequency of earthquakes alternately exhibits "active period" and"quiet period." The energy release cycle oscillates most strongly at 27 years,with 1930,1946,and 1978 as the nodes.This cycle presents the characteristics of "slow increase—slow decrease—rapid increase—rapid decrease." The high-density earthquake center migrates from southwest to northeast,and the seismic activity changes from global activity to local activity.On a monthly scale,large-magnitude earthquakes have a higher possibility of occurrence in months with a high frequency of small-magnitude earthquakes.The energy release period oscillates most strongly at 26 months.The cumulative release of seismic energy in January,February,May,June,July,August,September,November,and December shows a trend of increasing fluctuations.The cumulative release of seismic energy in March,April,and October presents a decreasing trend.The "high-low" density centers of earthquakes are distributed in a jump-like manner in space.The high-density centers exhibits the characteristics of northeast-southwest circular migration.On a daily scale,an earthquake occurs every day in the past 120 years.The energy release period oscillates most strongly in 40 days.The high-density centers of earthquakes in the past 365 days are mainly concentrated near the Deyucuo-Yinmahu fault zone.(2)The seismic disaster signal is definite in 2022,2026 and 2029.A correlation is observed between seismic activities in different fault zones in the Sichuan-Yunnan area.The temporal-spatial symmetry of the seismic time series after noise reduction is considerable.The Lancangjiang,Xiaojiang,and Xianshuihe faults are the core nodes of the correlation model of the Sichuan-Yunnan fault zone.In terms of temporal symmetry,an earthquake(Ms?5.9)will occur in the Lancangjiang fault-Honghe fault and another(Ms?5.3)in the Xianshuihe fault-Lijiang-Xiaojinhe fault in 2022.An earthquake(Ms?5.6)will occur in the Xiaojiang fault-Deyucuo-Yinmahu fault in 2029.An earthquake(Ms?5.0)with strong signals will occur in the Longmenshan fault in 2026.Regarding spatial symmetry,the Lancangjiang fault-Honghe fault earthquake presents a spatial trilateral symmetrical structure,which exhibits the spatial migration law of "two similarities and one difference." The symmetry axis in the meridian direction is 101.10°E and 24.00°N and 23.06°N are the symmetry axes in the latitude direction.Thus,the next earthquake will occur in the area southwest of the axis of symmetry.The Xiaojiang fault-Deyucuo-Yinmahu fault has a symmetry axis of 27.65°N in the latitude direction and 109.90°E in the meridional direction,showing the spatial migration law of "four similarities and one difference" and "three similarities and one difference," respectively.Hence,the next earthquake will move westward.The Xianshuihe fault-Lijiang-Xiaojinhe fault is symmetrical with 29.50°N in the latitude direction and 101.05°E in the meridional direction,demonstrating the spatial migration law of "three similarities and one difference" and "two similarities and one difference,"respectively.The Longmenshan fault earthquake presents a spatial trilateral symmetrical structure.Its symmetry axis in the meridian direction is 103.60°E,showing a distribution law of "two west and three east." Its symmetry axis in the latitude direction is 31.50°N,and each group has an epicenter falling on the axis of symmetry.Therefore,the next earthquake will occur in the area west of the axis of symmetry.(3)The economically developed region is the area with high risk of earthquake disaster.Major spatial differences are noted in the fatalness of disaster-inducing factor,stability and susceptibility of disaster hazard-pregnant environment,the vulnerability of hazard-affected bodies,and the comprehensive risk of earthquake disasters in the Sichuan-Yunnan region.Regarding the fatalness of disaster-inducing factor,the high-risk areas are mainly distributed in the Hengduan Mountains and the valleys of the north-south mountain system.The medium-risk areas are primarily distributed in the northwestern margin of the Sichuan Basin.The low-risk areas are majorly distributed in the eastern Sichuan Basin and Yunnan Plateau.Concerning the stability and sensitivity of the hazard-pregnant environment,the high-risk areas are mainly distributed in the Hengduan Mountains.The medium-risk areas are distributed in the Yunnan Plateau,in the western part of the north-south mountainous valley area.The low-risk areas are distributed in the Sichuan Basin.In terms of the vulnerability of hazard-affected bodies,the high-value areas are mainly distributed in the central Sichuan Basin and Kunming on the Yunnan Plateau.The median areas are majorly distributed in the east and west of the Sichuan Basin.The low-value areas are located on the edge of the Sichuan Basin and in the underdeveloped areas of the Yunnan Plateau,the valley areas of the northern and southern mountain systems,and the Hengduan Mountains.For the comprehensive risk of earthquake disasters,the high-risk areas are concentrated in the developed areas of the Sichuan Basin and Yunnan Plateau,with the higher-risk areas concentrated in the Hengduan Mountains.The medium-risk areas are concentrated in the western part of the northern and southern mountain valleys.The lower-risk areas are concentrated in the southern and northern margins of the Sichuan Basin and the eastern Yunnan Plateau,and the low-risk areas are distributed in the eastern part of Sichuan and Yunnan.(4)Seismic ability is the dominant factor affecting the earthquake risk level.Factors influencing the classification of earthquake disaster risk levels vary in different administrative regions in Sichuan and Yunnan.Road density,water supply pipeline density,and gas supply pipeline density are the primary factors influencing the earthquake disaster risk level in the Sichuan-Yunnan region,with all single-factor explanatory power values higher than 0.75.Specifically,hazard-affected body is the main controlling factor influencing the earthquake disaster risk levels in the Sichuan Basin and the central Yunnan Plateau;disaster-inducing factor,the northern and southern mountainous valleys;disaster-inducing factor and hazard-pregnant environment,the Hengduan Mountains.Moreover,social factors mainly affect the earthquake disaster risk level in 19 cities with relatively high levels of urbanization(including Chengdu,Zigong,and Luzhou);natural environmental factors,7 ethnic minority autonomous prefectures and cities with low urbanization levels(including Zhaotong,Baoshan,and Pu'er);social and natural factors,11 prefectures and cities with intermediate levels of urbanization(including Guangyuan and Ya'an).(5)3C scheme has been proposed to be the seismic disaster adaptation strategy.Clarifying the main controlling factors of earthquake disasters in different states and cities,formulating earthquake disaster management countermeasures by the"3C" risk management model according to local conditions,and improving urban resilience in a "four-in-one" manner can effectively improve the ability of cities in Sichuan to resist earthquake disasters.The "3C" risk management model relies on three levels of the disaster relief main body(city,county,and community)to formulate the phased management strategy of "3P" before the disaster,"3I" during the disaster,and"3R" after the disaster.Urban resilience can be improved in a "four-in-one" manner from the four dimensions of management resilience,institutional resilience,team resilience,and individual resilience.Finally,the resilience,response,adaptation,and recovery capabilities of cities in Sichuan and Yunnan to earthquake disasters can be enhanced.Wenchuan County and Chengdu City are selected as representatives of mixed disaster-inducing and social disaster-inducing cases to analyze the shortcomings in earthquake disaster risk management.Corresponding risk management countermeasures are then formulated to improve the sustainable development of the county/city under the high risk of earthquakes.The innovations and main contributions of this research are three-fold.(1)A theoretical system of disaster temporal-spatial symmetry was constructed,in which the correlation between seismic activities was quantified,the methods for researching seismic scope were finely screened.The logic of the research process and the accuracy of disaster trend judgment were enhanced,and the view of comprehensive research on disaster science was expanded.(2)Two research perspectives were considered,namely,the perspective of combining geological structure and trend judgment and the perspective of combining temporal and spatial trend judgment and earthquake disaster risk assessment.Specifically,the historical activity law the of Sichuan-Yunnan earthquake was revealed,the periodicity of seismic energy release was recognized,the future temporal and spatial trends of earthquakes in different tectonic units were analyzed,the risk of earthquake disasters in different regions was evaluated,and the scientificity of identifying high-risk areas of earthquake disasters was improved.(3)Three management modes were proposed.The "3C" earthquake risk management framework was designed,and the phased management strategies of "3P"before the disaster,"3I" during the disaster,and "3R" after the disaster were summarized.Disaster risk management countermeasures for different cities under the high risk of earthquakes were also accurately formulated at each stage.In a "four-in-one"manner,urban resilience can be enhanced,and the efficiency and effectiveness of earthquake prevention and disaster reduction can be effectively improved. |
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