Threshold height of coastal cliffs for collapse due to tsunami: Theoretical analysis of the coral limestone cliffs of the Ryukyu Islands, Japan

Stability analyses were made for both gravity- and wave-induced collapses of coastal cliffs with a vertical failure surface, to determine the threshold cliff height for tsunami-induced collapses. The models proposed in this study have two distinct parameters characterizing the cliff height. Calculations of the critical notch depth from these models show that gravity-induced collapses occur on cliffs of any height, whereas the threshold cliff heights for tsunami-induced collapses are controlled by the height of the tsunamis. The relation between the threshold cliff height and the tsunami height is represented by a power-law function.