Enigmatic tsunami waves amplified by repetitive source events in the
southwest of Torishima Island, Japan
Abstract
On 9 October 2023 (JST), mysterious tsunamis with a maximum wave height
of 60 cm were observed in Izu Islands and southwestern Japan, although
only seismic events of body-wave magnitudes mb 4–5 have been documented
in the southwest of Torishima Island. To investigate the source process,
we analyze tsunami waveforms recorded by an array network of
ocean-bottom pressure gauges. A stacked waveform of 16 records suggests
recurrent arrivals of multiple wave trains. Deconvolution of the stacked
waveform by a tsunami waveform from the first event revealed over 10
source events that intermittently generated tsunamis for
~1.5 hours. The temporal history of this sequence
corresponds to the origin times of T-phases estimated by an ocean-bottom
seismometer, and the mb 4–5 seismic swarm, implying a common origin.
Larger events later in the sequence occurred at intervals comparable to
the tsunami wave period, causing amplification of later phases of the
tsunami waves.