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从1900年到1975年每年 M≥8.0的地震数目的波动比泊松过程中预计的要大。然而,在1907—1975年期间发生的地震和泊松分布符合得很好。1900—1906年期间发生的 M≥8.0级地震的数目之大(114次中的30次)未必是由于偶然。在简化假定的条件下进行的能量计算证明,正如安德森在1974年所提出的,大约一世纪一次的地震活动增加可能是日长度的同生变化(contemporaneous change)触发的。根据泊松过程,其后的地球旋转速率较小波动不能引起每年 M≥8.0级地震数目的重大偏差。
The number of earthquakes with M≥8.0 per year from 1900 to 1975 is more than predicted in the Poisson process. However, the earthquakes and Poisson distributions that occurred between 1907 and 1975 fits well. The large number of M ≥ 8.0 earthquakes that occurred during 1900-1906 (30 out of 114) did not have to be by accident. Energy calculations under simplifying assumptions prove that, as Anderson proposed in 1974, the increase in seismic activity of about a century may have been triggered by a contemporaneous change in daily length. According to the Poisson process, the subsequent small fluctuations of the Earth’s rotation rate can not cause major deviations in the number of M≥8.0 earthquakes each year.