Dynamic analyses of abandoned mines in Mitake (Japan) during earthquakes

The 2003 Miyagi Hokubu and 2011 Great East Japan earthquakes induced severe damage to abandoned mines and resulted in many collapses. As a result of these damages, there is a growing concern on the seismic response and stability of areas situated above the abandoned lignite mines in Japan due to urbanisation in recent years. In this paper, the authors present and discuss the outcomes of their studies on the dynamic characteristics of ground and amplification of ground motions above abandoned mines. In addition to the effects of some parameters associated with extraction, some topographic effects on ground motions in areas with abandoned mines are also investigated and the results are presented. It is clearly shown that ground amplifications may be quite large on the abandoned mines where extraction is carried out by using the room-and-pillar or long-wall mining technique. The ground amplifications may be three to five times that at the base and be particularly larger near steep cliffs.