Abstract: Because b-value can be used as an indicator to measure the level of crustal stress,the seismicity pattern recognition based on b-value is considered as one of the most intuitive methods for earthquake forecast research and experiments. The intense seismicity in the Sichuan-Yunnan region makes the area to be an ideal field for earthquake forecast experiment. We investigated the spatial and temporal variations of b-values before nineteen earthquakes with M≥6.5 in the Sichuan-Yunnan region from 1981 to 2008 using regional small earthquake data. The results show that spatial b-value variations portending M≥6.5 earthquakes in the Sichuan-Yunnan region are insignificant. Less than 50%of the major earthquakes occurred in the regions with low b-values relative to the entire study area. In terms of temporal evolutions,the b-values in seismic source regions showed a systematic drop before the occurrence of earthquake. They showed an obvious decreasing trend during the period one year prior to strong earthquakes in 58%of the seismic source regions. Combined with other geological and seismological data,the short-term seismicity data can provide certain enlightenment for the estimation of potential seismic hazard in specific regions.

Key words: earthquake activity, b-value, spatiotemporal pattern, Sichuan-Yunnan region

摘要： 由于地震活动性参数b值能够反映地壳环境应力的大小,因此基于b值的地震活动性图像研究成为地震预测研究和实践最直观明了的方法之一。川滇地区地震活动频繁,是检验各种地震预测方法的理想实验场。为了研究川滇地区b值分布与强震活动的关系,利用过去40多年的小震资料分析了该区域1981年以来19次M6.5地震与b值的时空分布关系。结果表明: 虽然川滇地区b值空间分布特征与强震活动之间关系并不显著,不到50%的强震发生在b值小于区域平均值的地区, 但是震前b值的时间分布呈现系统地下降,58%的震源区的b值在强震前出现显著下降趋势。结合其他的地震、地质资料,较短时间内的地震活动性资料可以为特定地区的地震潜在危险性的判定提供一定的启示。

关键词: 强震活动, b值, 时空分布, 川滇地区