Some Damage Observations in Ryukyu Limestone Caves of Ishigaki and Miyako Islands and Their Possible Relations to the 1771 Meiwa Earthquake

Journal of The School of Marine Science and Technology,Vol.5 No.1

Some Damage Observations in Ryukyu Limestone Caves
of Ishigaki and Miyako Islands and
Their Possible Relations to the 1771 Meiwa Earthquake

Omer AYDAN and Naohiko TOKASHIKI

	Abstract

	The quantification of the seismic past of regions during non-instrumental period is important for seismic design and disaster mitigation. The utilization of damage to speleothems of caves as one of tools of paleo-seismology has been recently receiving a particular attention.However, there is no such a study in Japan so far.This study is first attempt by the authors to study on the possibility of the utilization of damage to speleothems of caves for quantifying past earthquakes. The authors investigated the cave of Ishigaki Island and Nakabari cave of Miyako Island in relation to the 1771 Meiwa earthquake,which was estimated to had occurred on a fault between Ishigaki and Miyako Islands. The traces of the damage to speleothems were found in the caves.Some of traces observed can be directly associated with the 1771 event while the rest may indicate much earlier large seismic events.There is no doubt that the utilization of damage to speleothems of caves is an important tool for the quantification of the seismic past. However, one must pay great attentions on the other possible causes of damage due to non-seismic origin. Since similar damage to speleothems could exist in caves in other seismically active parts of Japan,the authors have been considering to extend this study to caves in such areas.