小滇西地区M≥5地震前b值时空变化特征

Study of Variation Characteristics of b Value Before M≥5.0 Earthquakes in the Western Region of Yunnan

同时使用完整地震目录和去余震目录,采用最大似然法对小滇西地区进行b值时空扫描,研究该地区M≥5.0地震前b值的时空变化特征。结果显示:2种地震目录b值时间曲线的整体变化趋势无明显的差异,去余震目录的空间扫描结果低值异常更加突出;小滇西地区M≥5.0地震前,b值随时间变化趋势呈现出多样化的特征,但是75%的地震发生之前,该地区处于低b值状态;该地区M≥5.0地震均发生在低b值区域或者高低b值过渡地区。另外,在不同空间尺度的b值时间曲线中,均发现了较长时间的低b值现象,尽管起始时间不同,但是结束时间相同,分析认为该现象可能是2014年盈江M6.1地震的前兆异常。因此,小滇西地区低b值是本区M≥5.0地震的一个异常指标,可以根据空间扫描的低b值地区确定未来可能的震源位置,但是b值无法单独作为一个临震指标,需要与其他地震活动性参数联合使用;b值时间曲线上的长期低值,可能是较大地震的前兆异常。

We use both complete earthquake catalog and de-aftershock catalog to conduct the spatio-temporal scanning of b value in the western region of Yunnan province by using the maximum likelihood method to search for the spatio-temporal variation characteristics of b value before M≥5.0 earthquakes in this region.The temporal scanning results show that there is no significant difference in the overall trend of the two seismic catalogs,while the spatial scanning results show that the low b value anomalies of the de-aftershock catalogs are more prominent.Before these M≥5.0 earthquakes in the western region of Yunnan,the time curve of b value present diversified characteristics,but the whole region was in a low b value state before 75%(6/8)M≥5.0 earthquakes,and all of the M≥5.0 earthquakes in this region occurred in areas with low b value or transition zone with high and low b value.And we also find that there is a long period state of low b value in different area.Although the starting time is different,the ending time is the same.We believe that the phenomenon might be the precursor of the 2014 Yingjiang M6.1 earthquake.According to the results,a conclusion can be drawn;low b value in the western region of Yunnan is a precursor of M≥5.0 earthquakes in this region,and we can determine the possible source location of M≥5.0 earthquakes in the future according to the low b value area in the spatial scan.However,the b value cannot be used to predict earthquakes occurred in several days alone,and needs to be used in combination with other seismicity parameters.Long period state of low b value in time curve maybe a precursor of big earthquakes.