强震水化学前兆场特征

研究了唐山、松潘两次７级以上强震的水化学前兆场特征。结果表明，两次强震水化学前兆场有相似的特征。在震源区，水化趋势性异常和短临突变异常所占的比例大，远离震源区所占的比例小，且有逐渐减小的趋势；在震源区，水化趋势性异常起始的时间早，远离震源区异常起始的时间晚，趋势异常的形态均为逐渐升高。水化学前兆场的形成与区域应力场有关，但与震源应力场关系密切，可能起主导作用的是震源应力场。

FEATURES OF HYDROCHEMICAL PRECURSORY FIELDS FOR STRONG EARTHQUAKES

The features of Hydrochemical precursory fields of the Tangshan and Songpan Ms>7. 0earthquakes have been studied. The results show that the precursory fields of the two earthquakes have the similar property. The proportion of long-term and imminent anomalies to all anomalies is inversely proportional to epicentral distances. The long-term and imminent anomalies in the focal areas emerge earlier than those in the area far away from foci. All thelong-term anomaly patterns show gradually rising. The formation of hydrochemical precursory field has something to do with regional stress field,but has even closer relation with focal stress field. Focal stress field in the precursory process may play a main role.