Paleotsunami Recurrence And Inundation Estimates From Shoreline Reconstructions In The Central Kuril Islands

Abstract:

Paleotsunami records from the central Kuril Islands clearly show prolific tsunami activity in the region for the past few millennia. Investigations of stratigraphy at two sites on Matua Island reveal 16-19 deposits in 3,300 years and as many as 34-36 deposits at one site on Simushir Island in 2,350 years. Average tsunami recurrence intervals on Matua are on the order of ~150 years between events, and ~65 years on Simushir. While these intervals are short, they are comparable to other parts of the Japan-Kuril-Kamchatka subduction zone. All survey locations show shortening recurrence intervals toward the present, especially in the last 600 years when tsunami recurrence averages 55-75 years on Matua and 45 years on Simushir. The shorter recurrence intervals may due in part to preservation bias, but shorter rates in the same time interval have not been observed on the rest of the subduction zone.

Recent tsunamis in 2006 and 2007 from Mw 8.4 and 8.1 earthquakes with 5-20 m runup and 100-400 m inundation provide a test case to compare paleotsunami inundation. Shoreline reconstructions were calculated using tephra deposition on prograding beach ridge plains. On Simushir, tsunamis at least 11 m higher than the 2006 and 2007 tsunamis occurred every ~300 years. Tsunamis on Matua with slightly farther inundation than 2006 and 2007 occurred every ~215 years while those that inundated at least 100 m farther every ~750 yrs.