between sakhalin and the coastline of the japanese archipelago , there is a band of areas where the magnitude 7 class earthquakes frequently occur that is referred to as the japan sea eastern margin mobile belt . サハリンから日本列島沿岸に沿って海嶺やマグニチュード7クラスの地震の多発域が帯状に連なっており、これを日本海東縁変動帯と呼ぶ。
this process is considered to be the reason that floods (fukuchiyama and yura-gawa river ) frequently occur , since the river water is held up during times of heavy rain as a result of the very gradual inclination of rivers running in the basin , and the bottleneck caused around the outlet . 盆地内の河川勾配が非常に緩く、出口付近がボトルネックとなって大雨時に停滞し度々洪水を引き起こす（福知山と由良川）というのは、こういう形成履歴を持つためであろうと考えられる。
