CLUSTER ANALYSIS OF STRONG EARTHQUAKES OCCURRED IN BOHAI SEA,YELLOW SEA AND THE COASTAL AREAS

The spatial distribution of strong earthquakes(M≥6)occurred in Bohai sea,Yellow sea and the coastal areas has been studied by the method of cluster analysis in the paper.Based on the results of study,the macroseismic active regions and some scattered strong earthquakes have been determined.The strong earthquakes occurred in Bohai sea are generally consistent with those occurred in the coastal areas of Hebei,Shandong or Liaoning provinces in period and region,and are characterized by high intensity;The south yellow sea macroseismic region has a style of its own with multiphase activities which is not related colsely to the coastal strong earthquakes and is characterized by high frequency;The North Yellow sea is a less active region;The Korean peninsula macroseismic region can be considered as an individual one which has not extended to the Yellow sea.Tectonic explanation for each region has been given in the paper and it has been proposed that space-time differences exist in strong earthquakes occurred in the sea area,so different countermeasures should be taken in earthquake prevention and disaster mitigation in the coastal areas and the sea areas.