Geological Society of America

T119 Geological Records of Earthquakes and Tsunamis on Passive and Active Margins Coasts

Monday, 5 November 2012
1:30 PM - 5:30 PM
207D

SUCCESSES AND CHALLENGES OF PALEOTSUNAMI INVESTIGATIONS ALONG THE KURIL-KAMCHATKA SUBDUCTION ZONE

Paper number: T119-7
Program: Technical Sessions
Time: 2:55 PM – 3:15 PM

Authors

Breanyn MacInnes Presenting Author
Central Washington University, Ellensburg, WA
Tatiana Pinegina
Institute of Volcanology and Seismology, Petropavlovsk-Kamchatskiy, N/A
Joanne Bourgeois
University of Washington, Seattle, WA
N.G. Razzhigaeva
Far East Division, Russian Academy of Sciences, Vladivostok, N/A

Abstract

Over a decade of fieldwork traversing coastlines from the southern Kuril Islands to central Kamchatka has revealed recurrence rates of tsunamis along the Kuril-Kamchatka subduction zone. We identified these rates using the number of tsunami deposits in coastal excavations within time intervals determined by local tephra and radiocarbon chronologies. Observed rates commonly between one tsunami every 50-150 years in the last few millennia are some of the highest in the world. Sparse records up to ~6000-8000 years old show tsunami recurrence rates roughly comparable to the last few millennia at sites where coastal stratigraphy is particularly well preserved. Time periods with the most frequent tsunamis do not appear to be synchronous along the subduction zone. Implications of the spatial and temporal variability are an area of ongoing research.

In addition to determining simplified tsunami recurrence rates, we also differentiated larger vs. smaller tsunamis at some sites— a result of particular importance for understanding regional tsunami hazards. Excavation elevations and locations combined with reconstructed shorelines (using tephrochronology and ground-penetrating radar) enabled minimum estimates of paleo-runup or paleo-inundation. Particularly large tsunamis (those with runup > 10-20 m, depending on the site) commonly occur every 200-300 years along the Kuril-Kamchatka trench.

Many challenges for interpreting paleotsunami data remain. For example, direct comparison of individual tsunamis between sites is not straightforward— an issue that can make it difficult to relate along-trench paleotsunami extent to modern examples and to relate tsunami recurrence to megathrust segmentation. Additional challenges include the effect of time averaging (the choice of time interval used in recurrence rate calculations), gaps between and variations in sites with deposit preservation, potential tsunamis from non-seismic sources, and the scarcity of sites where paleoshoreline reconstructions are possible.