抄録
General relationship between the areal distribution of earthquake-induced landslides and the earthquake magnitude was discussed based on an investigation of more than 100 reports on 37 earthquakes which occurred in Japan after the middle of the last century. Occurrence of superficial slides, which were usually less than 104m3 in volume of debris, was analysed on the maps of small-scale (about 1/500, 000). The larger slides are not suitable for the analysis in order to find the general relationship, because their occurrences are rather rare and usually controlled by particular geologic conditions.
The longest distances from either the epicenter (p) or the surface fault (f) of the earthquake to the outer margin of the area where superficial slides occurred densely (D) or sparsely (d) at the quake were measured, and designated as Dp, Df, dp, and df, respectively.
Several relations among Dp, Df, dp, df, and M, the earthquake magnitude, were noticed.
1) For each earthquake the following relations were recognized.
Df≤Dp and df≤dp
2) Although a considerable variation was observed in the distances measured for a given M, they were, on the whole, correlated positively to the M.
3) The following semilogarithmic relation was roughly recognized between M and Df*, the maximum of Df for each M.
log Df*=a M+b
Where a and b are constants.
Similar trends were observed for Dp*, df*, and dp*, which were the maxima of Dp, df, and dp for each M, respectively. Values of a and b were calculated preliminarily, e.g. a approximated 1 for Df* and df*, and 0.5 for Dp* and dp*, while b is about 6.1 and 5.4 for Df and df* respectively and about 2 and 1.7 for Dp* and dp* respectively, when distances were measured in km. But further investigation based on more information would be necessary.
4) A few exceptions were recognized and cause were proposed tentatively.
5) Earthquakes of the magnitude less than 6 seem not to induce so many landslides.
These general relations are usefull, after suitable adjustments for the local variation, for a rough estimation of the area where superficial slides will be induced by an earthquake, of which the magnitude and epicenter can be estimated from informations on active faults.
