The Effect of Tide Level on the Tsunami Response of Coastal Harbors

Abstract

The tsunamis generated by the February 27, 2010 Chilean earthquake and the great Japan Tohoku earthquake on March 11, 2011 arrived at several Pacific Coast harbors when the tide levels were at low tides and persisted for several tidal cycles. Despite the significant difference in the recorded wave amplitude observed at Crescent City harbor between these two events, the energy spectrum as a function of frequency has been found to contain several spikes corresponding to the frequency range of 3 × 10 ିସ~1 0 × 10 ିସ Hz. This pattern in spectral density is different from several prior tsunamis observed and analyzed for Crescent City Harbor as presented by Lee, Xing and Magoon (2008). In the present study we present the reasons behind the differences in the response behavior associated with these two events. We prove that they are due to the effect of tide levels. We also show that in order to correctly decipher the resonant response characteristics to incident wave the response curves should be expressed as a function of the dimensionless wave number. The tsunami waves recorded at tide gauge station in San Diego Harbor (Southern California) are also analyzed and discussed.

Harbour Resonance Under Impact of Powerful Tsunami

“…The multiple resonant modes are also observed on normal days with no tsunami influence. Xing, et al (2010) and Lee, et al (2012) Figure 8, the profiles of spectra density distribution are fairly similar between normal day response and tsunami event response. The primary resonant mode is 22.1 minutes on July 21 st , 2008, and 21.9 minutes on March 11 th , 2011.…”

“…The primary resonant mode is 22.1 minutes on July 21 st , 2008, and 21.9 minutes on March 11 th , 2011. The multiple spikes are observed in both charts, which provides Lee, et al (2012) basis to prove that multiple resonant modes universally exist as the background energy content on normal days. Tsunami comes with bigger waves than regular long waves on normal days, and the difference in energy level is due to the wave amplitude.…”

“…Therefore, plenty of earlier studies have been devoted on simulating harbour oscillation based on frequency domain. A frequency domain study by Lee, Huang, Kou and Xing (2012) has found that during powerful tsunamis, such as the February 27 th , 2010 Chilean tsunami and the March 11 th , 2011 Tohoku tsunami, the Crescent City harbour in Northern California responded in a very different manner when compared with prior tsunami events as shown in Lee, Xing and Magoon (2008). As in Figure 1, the spectral analysis of the recorded water level at the tide gauge station revealed many resonant peaks between 2×10 -4 Hz and 10×10 -4 Hz.…”

“…Wave Spectra at Tide Gauge Station in Crescent City on (a) Normal Day; (b) Tohoku tsunami(Xing, et al 2010 andLee, et al 2012) …”