日本内陆地震活动的迁移与扩散

本文研究了日本内陆及其外围海域发生大地震后的地震活动迁移现象。在所研究的6个震例中,一个共同的特点是,地震活动的迁移总是沿着地壳内的活动地质构造带发生。有时可以根据地震活动的迁移来进一步确定活动构造带的存在。把板块边缘地区的地震活动类比为沿着力学偶合平面迁移和扩散,我们可以认为,岛上的活动构造带对应着地壳块体的力学相互作用边界。地震迁移的形式可能不只一种。在我们所研究的震例中发现了以下特征:地震迁移速度约为几km/年;大地震震源区之间存在着地震空区;在每一条地震带上有一定的地震活动周期。地震迁移的一种可能机制是:由于地壳块体的相对运动,在其边界上的凹凸不平区造成了构造应力集中,这些凹凸不平区相继地发生破裂,形成了地震迁移。

MIGRATION AND DIFFUSION OF SEISMIC ACTIVITY OBSERVED IN THE JAPANESE ISLANDS

Migrations of seismic activity observed after large earthquakes which occurred in and near the Japanese Islands are investigated, A common feature of migrational phenomena in the six cases which are studied in this paper is that migration occurred along geological tectonic zones, Sometimes existence of active tectonic zone is reconfirmed by the appearance of migrational phenomena, Analogizing to plate boundary regions where seismic activity is known to migrate or diffuse along mechanically coupled plane, we can consider that inland active tectonic zones correspond to mechanically interacting boundaries of crustal blocks. It is likely that more than one type exist in miqrational phenomena. In the cases we investigated following characteristics are observed that velocity of migration is about several km/year, seismic gaps remain between focal regions of large earthquakes, and there are seismically active periods in each seismic belt. A possible mechanism of migration is successive break down of asperities in which tectonic stress concentrates by relative movement of crustal blocks.