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.