HISTORICAL SEISMICITY OF THE OFFSHORE FUJIAN GUANGDONG REGION

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.