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1923年关东 M7.9地震的密集余震活动消失之后,在南关东地区已持续了几十年的地震活动平静可能是众所周知的事实。在最近10年左右环绕关东地震的震源区,由于相继发生 M≥6.0的破坏性的较大地震,因而可观测到地震活动从地震平静中逐渐恢复。地震活动恢复的特征是:1)在一些特定局部区域发生较大地震之前,小震震级随时间逐渐增大;2)震中分布在环绕关东地震的震源区形成面包圈状图形;3)地震活动以10—20 km/a 的特征速度从震源区.的外围向内区迁移,这与南关东及其周围地区地壳运动的迁移速率相同(Yamada,1973;Fujii,1979; Ishii 等,1980)。比较南关东地区各局部地震带地震活动随时间的恢复过程,可以看出地震活动的恢复有好几年的时间滞后。从震级 M 随时间的增长速率来判断,在今后10年左右可以预期有几个6级地震在地震恢复过程中发生。在本文中应强调的是:考虑到地震活动的显著恢复,对南关东地区的地震预报与灾害评估可选用更实际的方法。
After the disappearance of the intensive aftershocks of the M8.9 Kanto earthquake in 1923, the quietness of seismic activity that has lasted for decades in the southern Kanto region may be a well-known fact. In the focal area surrounding the Kanto Earthquake in the recent decade or so, it has been observed that the seismic activity gradually recovered from the earthquake calm due to the occurrence of a devastating earthquake of magnitude M ≥ 6.0. The characteristics of seismic activity recovery are: 1) the magnitudes of the small earthquakes gradually increase with time before the occurrence of larger earthquakes in some special local areas; 2) the epicenter distribution forms a donut-shaped pattern in the source region around the Kanton Earthquake; 3) The characteristic velocity of 10-20 km / a migrates from the outer periphery of the source region to the inner region, which is the same as the migration rate of the crustal movement in the South Kanto region and its surroundings (Yamada, 1973; Fujii, 1979; Ishii et al., 1980). It can be seen that the restoration of seismic activity has lagged behind several years by comparing the time-course recovery of seismic activity in various seismic zones in the southern Kanto region. Judging from the rate of increase of the magnitude M over time, it is expected that several magnitude 6 earthquakes will occur during the earthquake recovery process in the next 10 years or so. In this paper, it should be emphasized that, taking into account the significant recovery of seismic activity, a more practical method may be selected for the earthquake prediction and disaster assessment in the South Kanto Region.