Geografia Distribuo de Tertremaj Domagoj kun Speciala Referenco al la Efikoj de la Nankaido Tertremo, la 21-an de Decembro, 1946, en Koti Prefektejo, Sikoku, Japanujo.

Abstract

Concerning the relations between geomorphological ground conditions and earthquake damages throughout the Prefecture of Kochi, Shikoku, Japan, due to the Great Nankaido Earthquake of December 21st, 1946, we have noticed several interesting facts:i) On the sandy ground of beach ridges, damages were found only in those parts, where the basement bed rock lies deep, or where some kind of soft mud layers lies beneath sand, or where the ground consists of very soft sand, which has been deposited in very recent years or accumulated by wind blow. On the contrary, there was scarcely any damage, where the bed rock lies near the surface, or where hard materials such as pebbles or stones lie under the sandy ground, or where the surface sand are consolidated. Practically, of course, some of the above mentioned conditions coexist complicatedly combined in the same place.ii) There were severe damages on swampy low lands behind the beach ridge.iii) Even on alluvial plains, we found patches of rather slight damages among otherwise severe damages. Under those patches of slight damages stony layers were usually found as is the case on beach ridges.We have examined the hardness of the surface ground by a simple hand-boring stick of about 1m. length.Existence of the stony layers under the ground was conjectured by the distribution of Cl' contents in underground water. Where there are stony layers under the ground, underground water flows constantly and the Cl' contents must be small. On the contrary, underground water cannot flow easily in clay, mud or fine sand layers, and the Cl' contents must become great there. A typical example of the above two cases was encountered in the town of Nakamura, where the geographical distribution of earthquake damages clearly agrees with the Cl' contents distributions. (Fig. 10)