Study On The Pre-Earthquake Anomaly Characteristics Of B-Value In The North-South Seismic Belt

The G-R relation is by far one of the best universal statistical relationships in seismicity research and is the most used parameter among all seismicity parameters.The b value is not only a sign of measuring the level of seismic activity in a certain area,but also a means of tracking the concentration,transfer and monitoring of the destructive earthquake incubation process.The b value has been widely used in the practice of medium and long-term forecasting.It is one of the important seismological research methods in the determination of the danger zone of medium-and long-term strong earthquakes and plays an important role.It is mainly used in the prediction of the three elements of strong earthquakes.In the location prediction,b-value spatial scanning results are usually used to determine the spatial distribution characteristics of the stress level of the underground medium,and the location and urgent scale of strong earthquakes in the future may be analyzed and determined.In terms of time prediction,the main Analyze the urgency of strong earthquakes through anomalous changes in the time series of seismic b-values;large earthquakes tend to occur in areas with stress lockouts,use seismic b-value changes to extract anomaly information before major earthquakes occur,and use b-value spatial distribution characteristics to analyze current active fault With the relative level of stress accumulation,the risk level of strong earthquakes in different fault zones is studied.In this paper,with earthquakes of magnitude 6 or above in the north-south seismic belt(N20° ~ 43°,E95° ~ 110°)as the research object since 2000,the spatio-temporal anomalies of b values before 22 earthquakes that are relatively independent in time and space have been analyzed.In 12 of the 22 earthquake cases,the b value of the small earthquake before the earthquake appears low value anomaly,and the abnormal characteristics are obvious.The abnormal form of the b value of the small earthquake before the earthquake is also different,which can be generally classified into two kinds of pre-earthquake anomaly forms.The second type is the pattern of continuous decrease of b value before the earthquake,and the pattern of rise of b value appears 1 ~ 2.5 years before the earthquake,which is called the pattern of "decrease-increase-earthquake".In the case of "type I" anomaly,the duration(or reduction process)of low b value before the earthquake is about 1~2 years.;In the case of the second type of anomaly,there is an obvious low-value abnormal process about 3 years before the earthquake,and the b-value of small earthquake rises obviously about 1 to 2 years before the earthquake.Different regional seismic anomaly characteristics of the b value space difference obvious,22 cases,15 earthquakes in space before there is an obvious low value anomaly b,in the focal region and its adjacent area before the earthquake are low value anomaly,present different scales and earthquake happens at low or low margin,low further confirmed b values have a certain relationship with regional stress level.On the basis of summarizing b-value anomalies before earthquakes,the physical mechanism of low-b-value anomalies and the factors affecting the analysis results are discussed,and the application prospect of b-value in the risk determination of strong earthquakes is prospected.