Surface rupture and damage characteristics of the 2023 MS6.2 Jishishan earthquake,Gansu
On December 18,2023,an earthquake of MS6.2 occurred in Jishishan County,Gansu Province(102.79°E,35.70°N)with a focal depth of about 10 km.The earthquake was dominated by compressional thrusting with a small component of dextral strike-slip motion.According to the results of on-site emergency investigation,the epicenter of this earthquake was located on the East Jishishan fault(EJSSF),which is part of the southeastern segment of the North Lajishan fault zone(NLJSF).Near the epicenter,the EJSSF is composed of four secondary faults,including Jishixia fault(JSXF),Daduncun fault(DDCF),Zhaomuchuan fault(ZMCF),and Dahejia fault(DHJF),forming a relatively complex geometric pattern.Multiple tectonic fractures with two dominant directions and echelon fracture zones were formed along these secondary faults,and a small amount of centimeter-scale coseismic thrusting(dislocation value 2～4 cm)and right-lateral dislocation(dislocation value 3 cm)phenomena were formed along the DDCF,ZMCF and DHJF.Based on the results of previous small earthquake localization,it is concluded that the three secondary faults include the DDCF,ZMCF and DHJF of the EJSSF constitute the seismogenic structure of this earthquake.In fact,this is an earthquake event caused by the activity of secondary faults during the process of EJSSF expanding towards the interior of the Linxia Basin.Geological and geomorphic evidence indicates that the main fault(JSXF)has been active during the Holocene,the stress of the region may not be completely released by this earthquake,and the risk of larger earthquakes occurring in the future should be given sufficient attention.This earthquake also triggered a series of geological hazards and building damages such as different types of collapses,landslides,rolling rocks on slopes,liquefaction-mudflows and house damages,causing hundreds of casualties and severe economic losses.Through the investigation and analysis of the earthquake damage characteristics in different parts of the typical loess tableland in Dadun Village of the meizoseismal area,it was found that the earthquake caused severe collapse and damage to the old houses and walls built early on the upper part of the loess tableland,while causing multiple slope instability phenomena such as collapses,landslides,and surface tensile fissures of varying scales on the slope part of the middle of the tableland.The surface cracks and earthquake damage to houses in the lower part of the tableland were relatively minor.Considering that the site amplification effect of the upper part and slope of the loess tableland is one of the important reasons for the severe disasters caused by this earthquake,subsequent consideration should be given to the necessity of targeted earthquake-resistant fortifications for village houses and engineering construction on the loess tableland.
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