Paleotsunamis in the Middle Kuril Islands -- Implications for a Seismic Gap (and in View of Recent Events) (abstract)

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Geological Sciences

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Two great earthquakes occurred in the middle Kurils on 15 Nov 2006 (Mw 8.3) and 13 Jan 2007 (Mw 8.1). These earthquakes were the first big events in the short (< 300-yr) historical catalogue of this segment of the Kuril- Kamchatka subduction zone. This segment had been identified as a "seismic gap," and some researchers suggested that in this gap, seismic energy was low or released by slow-event earthquakes. In the framework of NSF-funded "Kuril Biocomplexity Project" (ARC-0508109, Ben Fitzhugh PI), we participated in international expeditions to the Kurils in summers of 2006 and 2007. One of many tasks of this project is paleoseismological research. During field work, the paleseismology team visited most Kuril islands, with a focus in 2007 on the middle Kurils, especially Simushir and Matua. We make multiple excavations along measured profiles and use marker tephra and radiocarbon dating for age control. Moreover, we now can compare paleotsunami deposits with deposits left last winter. Even before the great subduction-zone earthquake of 15 Nov 2006, we had field evidence of large prehistoric tsunamis in the middle Kuril Islands, indicating that this segment of the subduction zone has been seismically very active, comparable to other parts of the Kuril-Kamchatka system. Analysis of our data gave us preliminary tsunami frequencies of one (large) event every 50-300 years. On NE Simushir Island, paleotsunami deposits are present on marine terraces 3-20 meters high, with recurrence intervals of 200 years and less, the interval increasing with elevation and distance from shoreline. A number of these deposits are more extensive than the tsunami deposit from 15 Nov 2006. On S Matua Island, multiple paleotsunami deposits are present on marine terraces 4-15 meters high, with recurrence intervals of 300 years and less. A number of these deposits are from tsunamis comparable to or larger than that of 15 Nov 2006, which had its maximum expression on Matua. For a real estimation of earthquake and tsunami risk, we need to know paleoearthquake magnitude and its connection to tsunami intensity. The 2006 & 2007 events give us a unique opportunity to compare their tsunami height, inundation, and deposit parameters with the same from more ancient tsunamis. Using preliminary data from summer 2007, we estimate that tsunamis with intensity comparable to or bigger than 15 Nov 2006 have occurred in the middle Kurils every 250-500 years over the last few thousand years. It is reasonable to assign earthquakes greater than Mw 8 to these deposits.

This abstract is available in Eos.


Eos (Transactions, American Geophysical Union)

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