Tsunami Measurements in Bays of Shikotan Island |
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| Authors: | Georgy Shevchenko Alexander Shishkin Grigory Bogdanov Artem Loskutov |
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| Institution: | (1) Russian Academy of Sciences, Institute of Marine Geology and Geophysics (IMGG), Nauki str. 1b, Yuzhno-Sakhalinsk, Russia |
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| Abstract: | Bottom pressure gauges deployed in bays of Shikotan Island (South Kuril Islands) recently recorded two tsunamis: the Simushir
(Kuril Islands) tsunami of January 13, 2007 generated by a local earthquake with magnitude M
w = 8.1 and the Peruvian tsunami of August 15, 2007 generated by a distant earthquake, M
w = 8.0. The records enabled us to investigate the properties of these two tsunamis and to estimate the effect of the regional
and nearshore topography on arriving tsunami waves. Eigen periods and spatial structure of resonant oscillations in particular
bays were examined based on results of numerical modeling. Significant amplification of the fundamental (Helmholtz) resonant
modes in Malokurilskaya Bay (19 min) and in Krabovaya Inlet (29 min) and some secondary modes was caused by the Simushir tsunami.
The considerably different geometry and bottom topography of these bays, located on the inner coast of the island, determine
the differences in their eigen periods; the only mutual peak, which was found in both basins, had a period of 5 min and was
probably related to the source features. The Peruvian tsunami was clearly recorded by the bottom pressure gauge in Tserkovnaya
Bay on the outer (oceanic) coast of the island. Three dominant periods in the tsunami spectrum at this bay were 60, 30 and
19 min; the latter period was found to be related to the fundamental mode of the bay, while the other two periods appear to
be associated with the shelf resonant amplification of tsunami waves arriving in the region of the South Kuril Islands. The
prevalence of low-frequency components in the observed tsunami spectrum is probably associated with the large extension of
the initial source area and faster decay of short period waves during the long trans-oceanic tsunami propagation. |
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