Tsunamis and meteotsunamis observed offshore of the South Kuril Islands

Abstract:

Initiated by the strong Kuril Islands (Simushir) earthquake and tsunami of 15 November 2006, the Institute of Marine Geology and Geophysics (IMGG), Yuzhno-Sakhalinsk, Russia, deployed a network of bottom pressure recorders (BPRs) in bays and harbours of the South Kuril Islands (offshore from Shikotan, Kunashir, and Iturup islands). To investigate the local resonant properties of different bays/harbours we used long-term series of background oscillations and estimated topographic admittance functions for each site. The deployed instruments measured several tsunamis, including the 2007 and 2009 Kuril Islands (Simushir), 2009 Samoa, 2010 Chile and 2011 Tohoku tsunamis. At the same time, these BPRs recorded several strong tsunami-like oscillations associated with atmospheric activity (“meteotsunamis”). Two most interesting events of 3-4 August 2010 and 15-16 October 2011 were induced by an intense thunderstorm and by a fast moving atmospheric front, respectively, passing through the region. The second event is of particular interest because it created 50-80 cm sea level oscillations and strong currents (of several knots) in bays of Shikotan Island; we analyzed these oscillations together with simultaneous high-precision records of atmospheric pressure. In general, tsunami and meteotsunami events recorded at the same sites enabled us to estimate and compare the corresponding spectral characteristics of the events, including spectral ratios of tsunami (meteotsunami)/background, which are free from the topographic effects and describe the source. We also used DART 21401 in the vicinity of the South Kuril Islands to examine the spectral transformation and amplification of the waves approaching the coast. We found that most of the spectral properties of tsunamis and meteotsunamis are quite similar; however, tsunami spectra have certain features related to the specific source, while meteotsunami spectra are more uniform.