The Mystery of 2010 Chilean Earthquake Generated Tsunami Waves at Crescent City Harbor

The tsunami generated by the 2010 Chilean earthquake was recorded at several tide gauge stations along the Pacific coast from 02/27/2010 to 03/02/2010. The marigram at the tide gauge station in Crescent City Harbor in Northern California is analyzed in detail because Crescent City is well known for its tsunami vulnerability. The energy spectrum as a function of frequency has been found to contain several spikes corresponding to the frequency range of 3×10^-4 ~ 8×10^-4 Hz. This behavior is different from several prior tsunamis observed and analyzed for Crescent City Harbor. A finite element numerical model has been used to compute the resonant response at Crescent City Harbor to incident waves with different wave directions. It is found that the spectral spikes are associated with the first fundamental mode of oscillation at the dimensionless wave number kl = 1.10 for different water depth due to the varying tide levels (0.6 to 3.9 meters). A closer view of the spectral density curves found that everyday tide gauge record also contained the same multi-spectral-spikes because of the significant variation of water depth from low tide to high tide. In order to correctly decipher the resonant response characteristics to incident wave the response curve plotted as a function of the dimensionless wave number is essential.