Stratigraphic records of tsunamis along the <scp>J</scp>apan <scp>S</scp>ea, southwest <scp>H</scp>okkaido, northern <scp>J</scp>apan

<jats:title>Abstract</jats:title><jats:p>The stratigraphy of tsunami deposits along the <jats:styled-content style="fixed-case">J</jats:styled-content>apan <jats:styled-content style="fixed-case">S</jats:styled-content>ea, southwest <jats:styled-content style="fixed-case">H</jats:styled-content>okkaido, northern <jats:styled-content style="fixed-case">J</jats:styled-content>apan, reveals tsunami recurrences in this particular area. Sandy tsunami deposits are preserved in small valley plains, whereas gravelly deposits of possible tsunami origin are identified in surficial soils covering a <jats:styled-content style="fixed-case">H</jats:styled-content>olocene marine terrace and a slope talus. At least five horizons of tsunami events can be defined in the <jats:styled-content style="fixed-case">O</jats:styled-content>kushiri <jats:styled-content style="fixed-case">I</jats:styled-content>sland, the youngest of which immediately overlies the <jats:styled-content style="fixed-case">K</jats:styled-content>o‐d tephra layer (1640 <jats:styled-content style="fixed-case">AD</jats:styled-content>) and was likely formed by the historical Oshima‐Ohshima tsunami in 1741 <jats:styled-content style="fixed-case">AD</jats:styled-content>. The four older tsunami deposits, dated using accelerator mass spectrometry <jats:sup>14</jats:sup><jats:styled-content style="fixed-case">C</jats:styled-content>, were formed at around the 12th century, 1.5–1.6, 2.4–2.6, and 2.8–3.1 ka, respectively. Tsunami sand beds of the 1741 <jats:styled-content style="fixed-case">AD</jats:styled-content> and <jats:italic>circa</jats:italic> 12th century events are recognized in the <jats:styled-content style="fixed-case">H</jats:styled-content>iyama <jats:styled-content style="fixed-case">D</jats:styled-content>istrict of <jats:styled-content style="fixed-case">H</jats:styled-content>okkaido <jats:styled-content style="fixed-case">I</jats:styled-content>sland, but the older tsunami deposits are missing. The deposits of these two tsunamis are found together at the same sites and distributed in regions where wave heights of the 1993 tsunami (<jats:styled-content style="fixed-case">H</jats:styled-content>okkaido <jats:styled-content style="fixed-case">N</jats:styled-content>ansei‐<jats:styled-content style="fixed-case">o</jats:styled-content>ki earthquake, <jats:styled-content style="fixed-case">M</jats:styled-content>w = 7.7) were less than 3 m. Thus, the 12th century tsunami waves were possibly generated near the south of <jats:styled-content style="fixed-case">O</jats:styled-content>kushiri <jats:styled-content style="fixed-case">I</jats:styled-content>sland, whereas the 1993 tsunami was generated towards the north of the island. The estimated recurrence intervals of paleotsunamis, 200–1100 years with an average of 500 years, likely represents the recurrence interval of large earthquakes which would have occurred along several active faults offshore of southwest <jats:styled-content style="fixed-case">H</jats:styled-content>okkaido.</jats:p>