Recent Earthquakes that Hit Areas Covered and/or Underlain by Pyroclastic Matters and Their Impacts on Lifelines

Abstract

Two major earthquakes highlighted in this review article are the 2016 Kumamoto Earthquakes and the 2018 Hokkaido Eastern-Iburi Earthquake. These two events that hit the southern and northern Japanese islands known as Kyushu and Hokkaido, respectively, have one thing in common from geological and geotechnical viewpoint; the quake-hit areas are covered and/or underlain by volcanic matters. These volcanic matters such as pumice and volcanic ash have crushable nature that can cause large ground deformations, thus resulting in significant service interruption of lifelines and hindering quick recovery of the quake-hit areas. The phenomena to be discussed in this article include a never-seen-before ground subsidence that occurred on a flood plain west of Mt. Aso in Kyushu, and multiple landslides in Hokkaido with the total area of the exposed bare earth reaching 13.4 km²; the largest area that we’ve ever recorded since the Meiji era. The observed geometric features of the multiple landslide masses have a striking resemblance to those in a past event; the fact thus inspires a feeling of hope that this resemblance will allow for quick estimation of runout distances of these landslide masses with a simple empirical equation.