Understanding paleo-earthquakes in the Kuril Trench based on Late-Holocene tsunami deposits in the distal region from wave sources, northern Hidaka, Hokkaido, Japan

Abstract

Geological evidence, such as tsunami deposits, is crucial for studying the largest rupture zone of the Kuril Trench in Hokkaido, Japan, due to its poor historical record. Although 17th-century tsunami deposits are widely distributed across Hokkaido, the presence of multiple wave sources during that period, including the collapse of Mt. Komagatake, complicates the correlation with their wave sources. Understanding the regional distribution of these tsunami deposits can provide valuable data to estimate the magnitude of megathrust earthquakes in the Kuril Trench. The northern part of Hidaka, Hokkaido, where tsunamis from multiple wave sources are expected to overlap, is distant from the Kuril Trench. To clarify the depositional history of tsunami deposits in such distal areas, evaluating the influence of the depositional environments on the event layer preservation becomes even more critical. We conducted field surveys in Kabari, located in the northern Hidaka region, identifying three sand layers from the 10th to the 17th century and two layers dating beyond 2.3 thousand years ago. The depositional ages of most sand layers potentially correlate with tsunami deposits resulting from the Kuril Trench earthquakes. Utilizing reconstructed paleo-sea level data, we estimated that most sand layers reached approximately 2 m in height. However, it is noteworthy that the latest sand layer from the 17th century exhibited an unusual distribution, more than 3 m in height. This suggests a different wave source as the Mt. Komagatake collapse. The discovery of multiple sand layers and their distributions is crucial to constraining the maximum magnitude of giant earthquakes in the Kuril Trench and understanding the volcanic tsunami events related to Mt. Komagatake.

Wave sources of the 17th-century tsunami deposits in western Hokkaido, Japan using sediment transport modeling

“…2 and 3). The KS1 layer shows the inverse to normal grading structure and is induced by the inundation over the beach ridge because it contains coarse-grained sand that is constated of the beach ridge and beach sand (Nakanishi et al, 2024). The Komagatake model also reproduces the features of the KS1 layer in the grading structure by bedload and suspension and poor sorting (Fig.…”

“…In Kabari, the 17th-century tsunami deposits were reported by Takashimizu et al (2017) and reexamined by Nakanishi et al (2024). They found a total of ve sand layers in the peat layer and reported that the two sand layers were different event layers that occurred in the 15th-17th century.…”

“…1cd). The elevation is reconstructed based on the depth of the 17th-century volcanic ash layers from core samples (Nakanishi et al 2024). The sand sources are de ned from 1944 aerial photographs and eld surveys (Fig.…”

“…These multiple wave sources may have generated tsunamis in the 17th century and tsunami deposits in the coastal areas. Although the single layer of 17th-century tsunami deposits has been reported (Takashimizu et al 2007(Takashimizu et al , 2017Nakanishi et al 2014;Nakanishi et al 2022b), Nakanishi et al (2024) reported two layers of tsunami deposits during the 15th-17th centuries in Kabari, northern Hidaka (Fig. 1a).…”