Numerous deep]seated landslides have occurred in southern Wakayama and Nara prefectures, with over 1,000mm of rainfall caused by typhoon no.12 in 2011, which resulted in a great deal of damage. We need to consider future action for deep]seated landslides, and contemplate evacuation for the occurrence of deep]seated landslides as they have recently increased in incidence. Deep]seated landslides and the rainfall index are dominated by long]term rather than short]term rainfall indicators, but few concrete case studies are available.
We studied C]band rainfall mesh data in the southern part of Nara Prefecture after typhoon no.12 to elucidate the rainfall index relevant to deep]seated landslides.
We found that a deep]seated landslide happened around the end of the rainfall event after typhoon no.12, and that a deep]seated landslide occurred after 700\800mm of rainfall fell in 48hours with at least 900\1,000mm of total rainfall.
However, a clear relationship could not be found for rainfall totals of 1,400mm. We did not find a clear relationship between the rainfall index and deep]seated landslides, although a correlation between a higher tendency for a large]scale landslide and a greater number of deep]seated landslides was confirmed in the medium]to long]term rainfall index.We found that the excess probability of rainfall is highly correlated with deep]seated landslide.

Key wordsFdeep]seated landslide, rainfall analysis , probable rainfall