川滇地区7级大震前中强震震源机制变化

分析了 70年代以来 ,川滇地区发生的 8次 7级大震前 5年内 ,发生在大震孕震区和震源区内的中强震震源机制解时空分布。结果表明 ,最早中强震发生在大震震源区或其附近 ,其发震应力场与区域构造应力场一致 ,与大多数大震发震应力场一致或接近。大多数中强震震源破裂特征与大震明显不同。之后有多次中强震发生在距大震震源区较远的大震孕震区内其他地方 ,它们的发震应力场往往经历了与区域构造应力场和大震应力场一致与不一致的多次交替变化。大震前最后 1个中强震也发生在距大震震源区较近的地方 ,其发震应力场与大震发震应力场明显不一致 ,偏转了 30°～ 5 0° ,或更多 ,大多数也与区域构造应力场不一致 ,有的中强震发震断裂破裂特征与大震不一致。大震前中强震震源机制的变化 ,反映了大震孕育过程的不同阶段 ,区域构造应力场的时空调整变化和增强过程 ,以及由此引发的构造断裂异常活动 ,揭示出与大震发生有关的应力场和震源破裂特征信息

Variation of Moderate- Strong Source Mechanism before Great Earthquake with M7 in Sichuan- Yunnan Areas

Time - space distribution of source mechanism resolution ofmoderate - strong earthquakes in earthquake - developing and source areas has been analyzed 5 years before 8 earthquakes of M7 in Sichuang - Yunnan areas since 1970'. The results show that moderate - strong earthquakes occur around source area and nearby in earlier time. The earthquake - generating stress field is identical with regional tectonic stress field, which is identical with that most of earthquakes. Feature of source rupture in most of moderate - strong earthquakes is obviously different with great earthquakes. Afterwards, many moderate - strong earthquakes occur within seismogenic area far from source area. Generally, their earthquake- generating stress field has experienced alternate variations, which is identical or non - identical with regional tectonic and source stress fields. The last moderate - strong earthquake before great earthquake occurs near the place of source area. The earthquake - generating stress field of moderate - strong earthquake is obviously not identical to that of great earthquake, which deflects 30° - 50° or more. Most of them are not identical to tectonic stress field. Some of rupture features of seismic faults of moderate - strong earthquakes are not identical to that of great earthquake. The variation of source mechanism of moderate - strong earthquake reflects the different stages during the process of seismogenesis and anomalous activity of tectonic fault, which reveals information, related to great earthquake.