Temporal and spatial variation characteristics of seismic apparent stress in the Ningxia region
In this paper,over 300 earthquakes with ML≥2.5 that occurred in Ningxia and its adja-cent regions since 2010 were selected.The apparent stress values and relevant seismic source pa-rameters for these earthquakes were calculated.After accounting for the influence of magnitude,the seismic apparent stress values for four distinct regions of Ningxia were obtained,and the correlation between apparent stress and seismic activity level was analyzed.Results show the following:(1)The border area between Ningxia and Inner Mongolia,as well as the area from Xiangshan to Tianjingshan,generally exhibit relatively low apparent stress.Notably,no considerable variations in apparent stress are observed before or after notable earthquakes.This phenomenon can possibly be attribu-ted to the generally low level of seismic activity in these regions.(2)During 2016-2020,the apparent stress of ML2.5-2.9 earthquakes in the Wuzhong-Lingwu area demonstrates an anom-alous increasing-decreasing pattern,which may be related to the Lingwu ML3.6 earthquake swarm and ML4.5 earthquake in 2021.(3)The apparent stress of ML≥ 2.5 earthquakes from Haiyuan to Liupan Mountains exhibit an anomalous increasing-decreasing trend from 2015 to 2020,and the differential apparent stress shows a high-value anomaly from 2016 to 2017,which may be related to the Guyuan ML4.9 earthquake in 2017.(4)The anomalously high apparent stress values in Ningxia are mainly distributed in the north-east direction,which aligns with the northeastward extrusion direction of the northeastern margin of the Qinghai-Xizang block,reflecting alternating levels of seismic activity in adjacent regions:the seismic activity level from Haiyuan to Liupan Mountains is high,while that in the adjacent Xiangshan-Tianjingshan area is low;the level of seismic activity in Wuzhong-Lingwu area is high,while that in the adjacent border area between Ningxia and Inner Mongolia is low.The characteristics of seismic activity and regional stress state in the Ningxia area can be effectively understood by studying the correla-tion between seismic apparent stress and seismic activity.
apparent stressseismic activity levelNingxia and its adjacent regions