1976年松潘7.2级地震主要预报依据的审查及前兆异常特征的讨论

1976年8月16日四川省松潘7.2级地震,震前曾作了预报。本文介绍了这次地震预报的主要依据和地震前兆异常的主要特点。

EXAMINATION OF THE MAIN PREDICTION BASES AND DISCUSSION ABOUT THE PREMONITORY CHARACTERISTICS FOR THE SONGPAN EARTHQUAKE OF 1976, M=7.2

The Songpan earthquake of magnitude 7.2, occurred on August 16, 1976, was predicted beforehand. The main prediction bases are as follows.1. Changes in seismicity pattern and seismic wave velocity.2. Crustal deformation.3. Anomalous changes in radon content and electric resistivity at the Songpan seismo-logical station and precursors at other stations and amateur seismological observation points.4. Anomalous phenomena related to ground water, animal behavior, meteorologic factors and so on in the Songpan-Longmen Mountain region.In this paper, the main prediction bases at that time are examinated. We consider that most of anomalous phenomena are reliable and the main prediction bases are valid. They are still worthy of reference in the work of earthquake prediction.The major premonitory characteristics of this earthquake are as follows:1. Although the foreshock activity was not remarkable, the earthquake occurred in the anomalous background of seismicity. In wider areas, we got some information about the earthquake prediction on the basis of the study of the lack of earthquakes （M≥4） for a long time in Sichuan Province, the systematic migration of foci of large earthquakes （M≥7） in the Chuan-Dian region and the Chuan-Qian block and the correlative earthquakes （M≥4） in the Sichuan basin.2. The medium and long-term premonitory characteristics are evidently different from the short-term and impending earthquake ones in time and space. After the medium and long-term anomalies, appearance of various kinds of anomalous phenomena in greater regions may be regarded as an important signal of the fact that a large earthquake develops from the medium and long-term stage into the short-term stage. It may be regarded as a mark of impending earthquake that a drastic increase in various kinds of anomalous phenomena takes place in the region with the medium and long-term premonitory anomalies.3. Relative quiet of anomalous phenomena in the epicentral region just prior to the earthquake is another characteristic, it was an important cause of the 'south' deviation of the place determined at that time when the short-term prediction was made.