长岛地区分维结构变化与区域地震活动关系及短临前兆特征

本文研究了长岛附近地区地震分维结构及月频度趋势性变化与渤海、山东及邻区大范围中强地震活动的关系,得出:大区中强以上地震活跃阶段,研究区存在分维结构,小震活动频度出现趋势性增强;中强以上地震活跃期间分维值较低,活跃阶段将要结束时分维值较高,进入地震平静阶段分维结构不存在。还研究了长岛小震月频度变化的短临前兆特征,得出长岛区地震活动对本区Ms4级以上地震、200公里范围内4.5级以上地震及主震为4.0级的震群、600公里范围内5.5级以上地震,长岛月频度一般在震前1至5个月内会出现8或14次以上的异常现象。反映了长岛小震活动对监视渤海及邻区大范围中强以上地震活动具有一定的窗口作用。

RELATIONSHIP BETWEEN THE FRACTAL STRUCTURE VARIATION IN CHANGDAO AREA AND THE AREALSEI SMICITY AND SHORT-TERM AND IMPENDING PRECURSOR FEATURE

In this paper, the author has studied the realtionship between the seismic fractal structure and monthly frequency tendency variation in the areas near Changdao and the medium-strong earthquake activity in Bohai sea, Shandong and its neighbourhood. The results show that in an active period of medium-strong or above earthquake activity in the three large areas, there exists the fractal structure and the frequency of small-magnitude earthquake activity appears higher tendentiously in the"window"area; in an active period of higher-magnitude earthquake activity, the fractal value is lower while at the end of the period it is higher; and the fractal structure will disappear when the quiet stage of earthquake activity comes. In addition, the short-term and impending precursor feature of the monthly frequency variation of small earthquake activity in Changdao area has been studied. The results reveal that if the abnormal phenomena of the monthly frequency of the earthquake activity in Changdao area emerge 8 or 14 times or more, then, in one or five months the following earthquakes will occur, including earthquakes (M = 4.0)in the three large areas; events (M=4.5) and swarm earthquakes with a main shock (M = 4.0) within the range of 200 km$ and ones (M=5.5) within the range of 600 km. The conclusions show that the small earthquake activity in Changdao area is related to the medium-strong earthquake activity in Bohai sea and its neighbourhood. Changdao is an "earthquake window".