The 2009 Samoan and 2010 Chilean tsunamis recorded on the Pacific coast of Russia
Two remote tsunamis were recorded on the Pacific coast of Russia: a relatively weak Samoan tsunami of September 29, 2009 and a much stronger Chilean tsunami of February 28, 2010. In the area of the South Kuril Islands, records were obtained using autonomous bottom pressure gauges of the Institute of Marine Geology and Geophysics (IMGG). Additionally, for the oceanic coast of the Kamchatka Peninsula, Paramushir, and Bering Islands we used data transmitted from coastal tide gauges of the Russian Tsunami Warning Service (TWS). The maximum trough-to-crest heights of the Samoan tsunami were about 30-40 cm, and were recorded about 3 hours after the first tsunami arrival. The maximum Chilean tsunami trough-to-crest wave heights were 218 cm at Severo-Kurilsk, 187 cm at Tserkovnaya Bay (Shikotan Island), and 140 cm at Khodutka Bay (Kamchatka Peninsula). The time between first and maximum waves reached 4 hours. Strong sea level oscillations for both events range for a long time: about 15-17 hours. The Samoan tsunami induced high-frequency oscillations; a considerable increase in spectral energy in the tsunami spectrum was observed at periods of 4 to 20 minutes. In contrast, the Chilean tsunami induced low-frequency oscillations; the dominant periods were 30 to 80 minutes. A probable reason for these differences is the different extensions of the source areas (the Chilean source was much larger than the Samoan source) and the different energy radiation directions from the sources. Local topography resonant effects were the main reason of well-expressed peaks in power spectra in different areas: with a period of 10 minutes (Khodutka Bay), 19-20 minutes (Malokurilskaya and Tserkovnaya bays), 29 minutes (Krabovaya Inlet), and 43 minutes (Avachinskaya Guba and Nikolskoe).
Год публикации: 2013
Ключевые слова: Tsunami measurements, Tsunami Warning Service, Kuril Islands, long waves, resonant mode, bottom pressure gauge, spectral analysis
Tsunami measurements in bays of Shikotan Island
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 Mw=8.1 and the Peruvian tsunami of August 15, 2007 generated by a distant earthquake, Mw=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.
Год публикации: 2011
Ключевые слова: Tsunami measurements, Kuril Islands, long waves, eigen oscillations, resonant mode, bottom pressure gauge, spectral analysis, seiches, numerical modeling