Ground structure and natural disaster

Prof. Nishimura began this seminar by asking students "What is a disaster?". Disaster occurs at the points of contact between humans and nature. Whether various natural phenomena become disasters or the blessings of nature depends on the influence of humans.

In Japan, after the enactment of the disaster measures basic law, the number of fatalities due to disasters decreased suddenly, except in 1995 when the Hanshin-Awaji earthquake occurred. Frequent disasters include debris-avalanches, landslides and landslips. At the same time, earthquakes occur frequently in Japan. We cannot tell when an earthquake will occur, however we can estimate the damage of the earthquake in advance by examining the ground layer conditions. Soft ground is shaken well.

The types of disasters in a certain area have characteristic trends. For example, in Hyogo prefecture, flash floods and landslides occur frequently. Flash floods are induced by the weathering of granite. As for landslides, they have close connections with the geologic stratum (the layers of sand, clays, and volcanic ash).