Large earthquakes and tsunamis recorded in limestone caves

Abstract

Speleothems in limestone caves are precipitated during CO₂ degassing from groundwater supersaturated with calcite. Stalagmites, a type of speleothem that develops from the cave floor, grow upward at around 10-100µm a year. Paleoenvironmental information such as the Asia-monsoon activity and the vegetation changes on the upper cave surface can be obtained from detailed geochemical analysis of stalagmites along a growth direction. Episodic events like earthquakes are indicated by flaws in the speleothems. Absolute ages of the events can be obtained by U-Th dating and UV-fluorescent annual lamina counting in speleothems. We reviewed possible records remaining in limestone caves during large-scale earthquakes and tsunamis around the world, and discussed the effects of a large scale tsunami on 500-year records of Mg/Ca, δ¹³C and Sr/Ca ratios of two stalagmites from the Shiraho-Saonetabaru Cave Site, near the Shiraho beach, Ishigaki, Okinawa.