Heavy rainfall and snowmelt cause sediment disasters. The wetter the soil moisture is, the higher the sediment disaster frequency becomes. In addition, antecedent precipitation and snowmelt influence sediment disaster generation. We investigated the moisture environment around the epicenter before and after the Iwate]Miyagi Nairiku earthquake of2008 based on an antecedent soil moisture index (ASI30) using AMeDAS data (precipitation, air temperature, snow depth). In order to calculate ASI30, amount of snowmelt during snow cover period was estimated using advanced degree]day method. The ASI30 was highest during the snowmelt season and after heavy rainfall more than 100mm. When the earthquake occurred, the ASI30 values at the Matsurube and Komanoyu sites were 18.0 and 20.4mm, respectively. These values did not appear to affect the damage caused by the earthquakes. Previously recorded ASI‚R‚O values after heavy rainfall events or during the snowmelt seasons of heavy snowfall years were larger than were those recorded after the earthquakes. It was important to advance the remediation activity of the disaster, and to continue the monitor around the epicenter in the future.

Key wordsFantecedent soil moisture index, advanced degree]day method, heavy rainfall, snowmelt