W. Knight

Kuril Islands tsunami of November 2006: 2. Impact at Crescent City by local enhancement

[1] Crescent City (CC) is particularly susceptible to tsunami attack. The combination of tsunami signal enhancement by both distant bathymetric features and local nearshore resonance seems to be responsible for this behavior. Application of global tsunami propagation models to the Kuril Islands Tsunami of November 2006 in the companion paper (Kowalik et al., 2008) delineated the importance of distant bathymetric features for both tsunami wave amplification and for increased duration of the tsunami arriving at CC. These distant features were responsible for delivering the late, high-energy signal, which was delayed by 2 hours from the predicted arrival time. Additional local amplification and increased duration are caused by the shelf bathymetry adjacent to CC. As the initial tsunami arrives at CC, the shelf trapping mechanism tends to excite the gravest of the natural modes. This oscillation is slowly shifted toward the natural mode closest to the period of the incident tsunami wave packet. Short-duration wave trains tend to influence the tsunami response at CC harbor in such a way that 1 hour after the first wave arrival a much stronger wave will be generated owing to the tendency of the shelf to initially ring at the frequency of the gravest mode. Practical implications of distant and local amplification relate to the potential hazard near CC, highlighting the need for awareness of the tsunami signal duration. In this respect, two timescales are important for this event: the 2-hour time delay due to distant bathymetric features and the 1-hour delay due to local offshore bathymetry.