Abstract

At some submarine calderas in Japan and New Zealand, moderate-sized earthquakes with seismic magnitudes of M5–6 repeated every decade. They unusually caused large tsunamis with a maximum wave height of about a meter at coastal tide gauges. For exploration of the unknown mechanism of the peculiar volcanic tsunamis, we utilized tsunami and seismic data of the earthquakes to find a source model that explains both datasets. The model indicates that the trapdoor faulting, containing a large intra-caldera fault slip of 5 m and deformation of its sill-like magma chamber, took place in the submarine calderas and generated large tsunamis. Similarities of the repeating earthquakes reflect the decadal recurrence of trapdoor faulting due to continuous magma supply beneath the calderas, implying its potential of submarine eruptions. In conclusion, our discovery of recurrent volcanic tsunamigenesis by moderate-sized trapdoor faulting underscores our need to monitor such submarine calderas for assessing tsunami hazards.

Recent preprint can be found at: https://www.essoar.org/doi/abs/10.1002/essoar.10510526.1