闽粤海外的历史地震活动

HISTORICAL SEISMICITY OF THE OFFSHORE FUJIAN GUANGDONG REGION

闽粤海外地震集中分布于晚更新世以来活动最为强烈的近岸海域断裂靠近南澳和泉州的两个地段.1918和1906年南北两段分别发生过7.3和6.1级地震.笔者以这两次地震的仪器测定参数为准,通过宏观资料对比,参考地震背景,估定各早期地震的参数,编制了历史地震序列表.南、北两区地震活动基本同步,所记最大地震均在7.3级左右.大震以前,地震活动常有增强.主震后余震频繁,但强余震多发生在1至几年以后.15世纪晚期以来,出现过两次地震活动高潮:第一次在1600年前后,两区各发生43级以上地震8次,其中南区最强为6.7级,北区约7.5级;第二次在19世纪初,南区地震18次,最强达7.3级,北区仅6.1和5.5级地震各1次.1942年以来,整个地带极少中强震活动.究竟系“减震作用”影响,还是北区正在酝酿较强地震,值得深入研究.

The earthquakes offshore Fujian and Guangdong provinces concentrated along the two segments near Nan'ao in the south and Quanzhou in the north of the off coast fault, which is very active since the late Pleistocene. In 1918 and 1906, two earthquakes with magnitudes 7-3 and 6-1 respectively occurred in the south and the north regions. With the instrumentally determined seismic parameters of these two earthquakes as standards , the author evaluated the parameters of the historical earthquakes by comparing their macroseismic materials with consideration of the geological background. As a result , chronological tables of historical earthquakes of the south and the north regions were compiled.The seismic activity of the two regions synchronized basically, and the strongest earthquakes recorded were both around M7.3. Seismic activity usually intensified before the occurrence of strong events .Aftershocks were frequent, but strong aftershocks usually occurred one to several years after the main shock. Two high tides of seismic activity occurred since the late 15th century. Around 1600, eight earthquakes each with magnitude over 4.3 occurred in both of the two regions. The magnitude of the strongest shock in the south region is 6.7, that in the north region is 7.5. The second high tide occurred in the early 20th century. Among the 18 earthquakes that occurred in the south region, one was of magnitude 7.3; whilst only two earthquakes with magnitudes 6.1 and 5.5 respectively occurred in the north region. Further, medium to strong earthquakes never occurred since 1942. Whether this is the ' mitigation effect' of strong shocks, or a big earthquake is brewing in the north region is worth intensive study.