Fault models of unusual tsunami in the 17th century along the Kuril trench

K Satake,S Yamaki,F Nanayama

doi:10.1186/bf03352848

K Satake, S Yamaki + Show 1 more

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https://doi.org/10.1186/bf03352848

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Abstract

AbstractGeologic evidence has shown that unusual tsunami deposits are traced as high as 18 m above the current sea level or as far as 1–4 km inland from the shoreline on the Pacific coast of eastern Hokkaido, and that such unusual tsunamis have recurred at about 500 year interval with the most recent event in the 17th century. We computed coastal tsunami heights along the Hokkaido and Sanriku coasts and inundation at five coastal marshes in Hokkaido where the tsunami deposits were mapped. Three types of faults were tested: giant fault, tsunami earthquake and interplate earthquake models. The giant fault model, with the largest seismic moment, yields the lowest tsunami heights and smaller inundation than the distribution of tsunami deposits in Hokkaido, while the tsunami heights are largest in Sanriku. The tsunami earthquake model yields little inundation in Hokkaido and the smallest heights in Sanriku. The interplate earthquake model produces the largest tsunami heights and inundation in Hokkaido, reproducing the distribution of tsunami deposits on the Nemuro coast. The multi-segment interplate earthquake with variable slip (10 m on Tokachi and 5 m on Nemuro segment) can reproduce the distribution of tsunami deposits on the Tokachi coast as well, and considered as the best source model for the 17th century tsunami, although the Sanriku tsunami heights are more than 3 m, exceeding an inferred detection threshold of historical documents. The seismic moment is estimated as 8 × 1021N m (Mw8.5). Comparison with the recent 2003 Tokachi-oki earthquake indicates that the 17th century tsunami source was longer and located further offshore at shallower depth.

Highlights

Great (M > 8) earthquakes have recurred along the southern Kuril trench, where the Pacific plate subducts beneath northern Japan at a rate of about 8 cm/yr (Earthquake Research Committee, 2004)
We assumed that the 17th century topography of marshes is the same as today, except for the giant fault model where we considered the coseismic crustal deformation
The tsunami heights from the giant fault are in general lowest, 2 to 6 m

Summary

Introduction

Great (M > 8) earthquakes have recurred along the southern Kuril trench, where the Pacific plate subducts beneath northern Japan at a rate of about 8 cm/yr (Earthquake Research Committee, 2004). Prehistoric tsunami deposits underlie coastal marshes and lagoons (Nanayama et al, 2003) or coastal cliffs (Hirakawa et al, 2005) along 200 km of eastern Hokkaido’s Pacific coast Such unusual tsunami deposits, found much further inland than those from the historical earthquakes along the Kuril trench or across the Pacific ocean, have been attributed to unusual earthquakes along the Kuril trench with an average recurrence interval of about 500 years, and the most recent tsunami was dated in the 17th century (Nanayama et al, 2003). Coastal geology indicates that the eastern coast of Hokkaido has uplifted by about 1 m in the 17th century (Atwater et al, 2004) Such uplift, repeated at about 500 year interval (Kelsey et al, 2006), has been interpreted due to postseismic slip on the deeper part of interplate earthquakes (Sawai et al, 2004). We will show that a multi-segment interplate earthquake with large and non-uniform slip can best explain the paleotsunami evidence

Summary of Paleoseismological and Historical Data

Erimo km Akkeshi

Numerical Computations of Tsunami Inundation

Conclusions