Characteristics of the 2011 Great Tohoku Tsunami on the Russian Far East Coast: Deep-Water and Coastal Observations.

The source region of the catastrophic Tohoku tsunami of 11 March 2011 was not far from the Russian Far East coast. The Sakhalin Tsunami Warning Center at Yuzhno-Sakhalinsk issued an Alert for threatened coasts of the Kuril Islands and Kamchatka; the observed tsunami heights were up to 2-2.5 m along the Pacific coast of the Kuril Islands. The tsunami was clearly recorded by a number of coastal tide gauges and by deep-ocean bottom pressure stations located in the vicinity of the Kuril Islands, as well as by the Russian open-ocean DART station 21401, located eastward from the South Kuril Islands. The data from other DART stations, in particular those located near Japan and the Aleutian Islands, were used for comparison. The records from these instruments were used to estimate the major characteristics of the tsunami waves, including arrival times, maximum heights, durations of the signal and main wavelength periods, as well as for comparison with the results of numerical modelling. In contrast to deep-sea stations where the first waves were the highest, at Russian coastal sites the highest waves occurred several hours after the arrival of the first tsunami wave. Further analysis indicated significant differences in spectral characteristics of tsunami waves propagating eastward toward North America and those directed in the northeast direction towards the Russian Far East. The main peaks of the eastward propagating tsunami waves were relatively high-frequency (periods ranging from 6-8 to 15-20 min), while those propagating in the northeast direction were mainly low-frequency (ranging from 25-40 to 60-80 min). Additionally, pronounced spectral peaks with similar long periods were found in the 'middle-field' records at Hanasaki (on the northeastern coast of Hokkaido Island), at Yuzhno-Kurilsk (Kunashir Island) and at Malokurilsk (Shikotan Island). At remote stations, the resonant periods associated with local topographic features were predominant in the spectra. [ABSTRACT FROM AUTHOR]