Spatial extent of the mid- to late Holocene sedimentary record of
tsunamis along the Southern Kuril Trench, Hokkaido, Japan
Abstract
Infrequent megathrust earthquakes, with their complex cycles and rupture
modes, require a high-resolution spatiotemporal record of tsunami
inundations over thousands of years to provide more accurate long-term
forecasts. The geological record suggests that Mw>8
earthquakes in the Kuril Trench occurred at intervals of several hundred
years. However, uncertainties remain regarding the rupture zone, owing
to the limited survey areas and chronological data. Therefore, we
investigated the tsunami deposits in a coastal wetland of southeastern
Hokkaido, Japan, to characterize the tsunamis that have originated from
the Kuril Trench over the last 4000 years. On the Erimo coast, more than
seven sand layers exhibited the common features of tsunami deposits,
such as sheet distributions of several hundred meters, normal grading
structures, and sharp basal contacts. According to numerical tsunami
simulations, the 17th-century sand layer could be reproduced by using a
multiple rupture zone model (Mw~8.8). We used
high-resolution radiocarbon dating and tephras to correlate the tsunami
deposits from the last 4000 years with those reported from regions
~100 km away. The tsunami history revealed here shows
good agreement with histories of adjacent regions. However, the
paleotsunamis reported to have occurred in regions > 200 km
away include some events that differ from those in this study, which
suggests a diversity of Mw>8 earthquakes in the Kuril
Trench. We clarified the history and extents of earthquake-generated
tsunamis along the southwestern end of the Kuril Trench, which were
previously unknown. Our results provide a framework for magnitude
estimations and long-term forecast of earthquakes.