Sediment-Related Disasters Caused by the Nagano-ken Hokubu Earthquake in the Heavy Snow Season

Abstract

Mountain slopes covered in deep snow were hit by seismic motions during the Nagano-ken Hokubu Earthquake on March 12, 2011, resulting in avalanches, slope failures, and deep-seated landslides. Sediment-related disasters occurred at places which had geologically weak structures such as faults and fractured rock masses and/or topographical features that were prone to receiving concentrated earthquake acceleration. However, the key characteristic was the interaction between snow cover and sediment-related disasters during and after the earthquake. Fast-moving layers of air and suspended snow particles were also produced when fast debris flows crashed into accumulated snow, destroying peripheral areas along the path of the debris flows. Furthermore, a landslide occurred about 1 month after the earthquake on a slope that was likely to have been loosened by the seismic motions. The numbers of slope failures and landslides were very small compared to the Niigata-ken Chuetsu Earthquake of a similar scale, which was probably attributable to the physical and/or mechanical properties of snow cover.