Abstract:From 2008 to 2012,the integrity of observation data of earthquake monitoring network in Inner Mongolia was above 96.3％,and the monitoring ability and data integrity at eastern Inner Mongolia （41 ° ～ 51 ° N,114.5 ° ～ 124.6 ° E） were more outstanding than other regions.Combined with the actual geological structure and seismic activity characteristics of eastern Inner Mongolia,we select the earthquakes of ML≥2.0 at study area （41 ° ～ 51 ° N,114.5 °～124.6 ° E） from 2008 to 2012 to calculate the average wave velocity ratio there and its variation.As the comprehensive analysis on existing research data may impact the uncertainty of calculation,we use Multi-station method to make the results more accurate and reliable.Calculation results show that the average wave velocity ratio at study area from 2008 to 2012 is 1.709 4,and basic range is between 1.690 5～1.732 8.Through the analysis of two moderate earthquakes at research area,we find that the temporal change of wave velocity ratio at the eastern region of Inner Mongolia show some significant anomaly,which satisfies the law of ＂decline-low value-recover-seismogenic＂ and there is a change in the abnormal period after the earthquake,the change rate is about 3％.After drawing the spatial contour of wave velocity ratio at that region,we found that the high values within the area are mainly distributed along Daxinganling,showing the spatial distribution of a trend of low West high East and low North high South.In terms of the geological structure,high values of wave velocity ratio in a range of 1.73 ～ 1.78 are mainly concentrated in Balihan fault,Beipiao-Chaoyang fault and Chifeng-Kaiyuan fault.Combined with the seism-geological background of study area and the change of wave velocity ratio in recent one or two years,it could be concluded that the stress variation of underground medium in eastern Inner Mongolia is more significant,with certain geological conditions of the occurrence of moderate and strong earthquake.Because the data we use here do not contain the analog seismic record before 2008,it does not show the complete seismic record and the whole change trend of wave velocity at eastern Inner Mongolia,moreover,there are few seismic stations at eastern Inner Mongolia region and they are distributed very unevenly,the results are just preliminary.With the enrichment of digital observation data in the future,we can do more detailed studies in this area.
