The foreshock analysis technique based on the LURR method and its application in Sichuan-Yunnan region
The Load-Unload Response Ratio(LURR)theory is a medium-to-short-term earthquake prediction method that relies on the dynamic changes in rock constitutive relationships.However,determining the direction of tectonic shear stress in practice can be challenging.This study focuses on foreshocks and proposes a new approach to determine the direction of tectonic shear stress.When an earthquake with a magnitude 4 or higher occurs,the changes in Coulomb Failure Stress(CFS)along the slip direction of the earthquake are calculated to assess its loading/unloading states induced by the earth tide.This information can then be utilized to detect the possibility of subsequent strong earthquakes.In the study area of the Sichuan-Yunnan region(20°N-35°N,96°E-106°E),the loading/unloading states of M4.0+foreshocks for all M6.0+earthquakes since 2000 were analyzed.It was discovered that most foreshocks occurred during the loading process.Further analysis of the loading/unloading states of all M4.0+earthquakes in the past 10 years revealed that non-foreshocks are more likely to occur during the unloading process.By combining this information with probability gain analysis,the following conclusions are drawn:(1)If there are at least two consecutive earthquakes of magnitude 4.0 or above occurring in the seismogenic area and all of them are in the loading process,the probability of a strong earthquake occurring in the following days is higher;(2)If an earthquake occurs during the unloading process,there is little likelihood of a strong earthquake occurring in the following days.Additionally,the analysis of the loading/unloading states of M4.0+earthquakes since November 2022 suggests higher stress accumulation levels in the southeastern Sichuan,southern Yunnan,and northwestern Yunnan regions.This indicates a need for increased attention to the risk of strong earthquakes in these areas.
Load-Unload Response Ratio(LURR)Significant earthquakes with magnitude 4.0 and aboveFocal mechanism solutionTidal stressLoading/unloading states
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