UC San Diego

The Great Chilean Earthquake of 22 May1960 generated a tsunami that caused widespread damage along the Pacific Rim, including at Crescent City, CA. Coincidentally, the water level fluctuations at Crescent City were successfully recorded by two Stevens Type A-35 paper-chart water level recorders installed as part of a U.S. Army Corps of Engineers study of harbor seiche. Data is available on 35 paper rolls from each of two locations in the harbor, Citizen's and Dutton's docks. Eleven rolls at each of the two docks were scanned and digitized covering the time period from 17:34, 20 May to 08:32, 31 May 1960 (PST). Digitization was performed at a sample rate of 1 Hz allowing high resolution analysis of the data. Chapter 1 documents the procedures used to obtain the digital time series of water levels at the two docks. A frequency domain investigation of the harbor response is presented in Chapter 2. Background data prior to the onset of the tsunami were used to estimate an admittance function at both docks, the result suggests the presence of edge wave resonances over the adjoining shelf as well as of individual harbor modes. Spectral ratios (of tsunami divided by background spectra) show amplification of the tsunami relative to the normal background. Frequency domain coherence and phase estimates as well as spectrograms at the two stations further show tidal modulation of the harbor response at frequencies at and somewhat above those characterizing the tsunami