全球地震活动性的定量研究(三)--全球地震带的划分和Ⅰ,Ⅱ,Ⅲ带的地震活动
QUANTITATIVE STUDIES OF GLOBAL SEISMICITY (3) --REDIVISION OF GLOBAL SEISMIC BELTS AND SEISMIC ACTIVITIES OF THE BELTS I, II, III
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摘要: 本文根据板块相互作用的原理,对全球地震带作了新的具体的划分:Ⅰ带为美洲西海岸地震带;Ⅱ带为太平洋西北边缘地震带;Ⅲ带为大洋岛弧地震带;Ⅳ带为亚欧地震带;Ⅴ带为全球海岭地震带。各带地震活动水平从强到弱的顺序是Ⅲ,Ⅱ,Ⅰ,Ⅳ,Ⅴ。求出本世纪各年Ⅰ,Ⅱ,Ⅲ三带的地震活动性指数A(b),并对A(b)指数随时间的变化作了最大熵谱分析和周期图分析。结果显示Ⅱ,Ⅲ两带的周期成分与Ⅰ带有明显不同。Ⅰ带的变化较平稳,富于短周期成分,在1942年和1960年有两个峰期;Ⅱ带从1964年以来处于长趋势下降阶段,至八十年代已降至极小;Ⅲ带的五十年代事件效应显著,其变化趋势能较好地代表全球地震活动的变化总趋势。Ⅱ,Ⅲ两带有较强的长周期变化成分,可能与太平洋板块的面积较大有关。Abstract: In this paper, the global seismic belts are redivided into five divisions based on the principle of plate interactions. The first belt (1) is the west coastal range of the Americas; the second belt (II) is the northwestern margin of the Pacific ocean; the third belt (III) is the oceanic island arcs between the Indian and Pacific oceans; the fourth belt (IV) is the Eurasia; the fifth belt (V) is the global oceanic ridges. The order of the seismicity level of each belt from high to low is III, II, I, IV, V. The seismicity indexes of the belts I, II, III, for each year of the present century are calculated. The maximum entropy analysis and the periodogram analysis are made for the temporal variations of the A(b) indexes. It is shown that the periodic composition of the variations for the belts II and III is quite different from that for the belt I. The variation of the belt 1 is comparatively smooth and abundant of short-period components with two peaks in 1942 and 1960 respectively. The variation of the belt II had been in a phase of long-term decrease since 1964 and reached the lowest point in 1984. The effect of the 1950s event in the belt III whs prominent. The variation of the belt III can be a good representative of the general trend of the variation of the glowal seismic activity. The variations of the belts II and III have stronger long-jeriod components which may be attributed to the vast area of the Pacific Plate.