Chapters authored
Magnitude‐Frequency Distribution of Slope Failures in Japan: Statistical Approach to a True Perspective on Volcanic Mega‐Collapses
The relationship between magnitude and frequency of mega‐collapses (i.e., sector collapses), mainly of volcanic edifices, in Japan is examined by using existing datasets for volcanic mega‐collapses and smaller but more frequent events. Statistical analysis of these datasets showed that the magnitude‐frequency distribution of slope failures with volumes greater than or equal to 107 m3 can be expressed by a simple exponential function: logN(x) = a – bx, where N(x) is the cumulative number of mass‐movement events with magnitude ≥x. When this function was fitted to the datasets, the slope coefficient, b, was 0.7 or 0.8. The frequency distribution of mega‐collapses was similar to that of smaller (volume >105–6 m3) events. Records from the past millennium in Japan suggest that this magnitude‐frequency relationship may be applicable to the last several tens of thousands of years. Therefore, it is possible to predict event probability and the recurrence interval of events of a certain magnitude. In this way, mega‐collapses with a volume of over 109 m3 may be estimated to occur at least every 1000–2000 years somewhere in Japan. Therefore, mega‐collapses in Japan should not be considered “rare”; rather, they are “normal” events on a geomorphological timescale.
Part of the book: Updates in Volcanology