Kim, M.S. and Woo, S.B., Eom, H.M., 2013. Propagation of abnormal wave on 25 April 2008 at the West Coast of South Korea
On 31 March 2007, abnormal waves suddenly hit the West Coast of South Korea, causing heavy casualties and huge economic loss. Since the cause of wave generation is unknown, we aim to study the direction of wave propagation by investigating the abnormal wave signal recorded in the tidal stations. To determine the propagation direction of abnormal waves, we analyzed tidal level observation data at 1-min intervals, provided by the Korea Hydrographic and Oceanographic Administration (KHOA). To remove tidal components, wavelet decomposition, which filters wave periods ranging from 2 to 60 min, was performed. If the daily maximum amplitude exceeding 95% confidence interval of the total daily maximum amplitudes appeared simultaneously at more than three tidal stations, the day was defined as the day when abnormal waves occurred. Because of nonstationarity and localized peak in the time domain, wavelet analysis can be suitable for analyzing the power spectrum and wave period of abnormal waves. The time when maximum total power spectrum of the decomposed time series appears for the first time is considered the arrival time of the abnormal wave. The distance of crest line propagated by the abnormal wave was calculated by considering the arrival time difference between stations and long wave speed. The abnormal wave is assumed to propagate along a tangent to a circle with radius equal to the distance which the abnormal waves moved. Based on these considerations, we found that the propagation direction of the abnormal waves on 31 March 2007 was from the northwestern corner of the West Sea to the West Coast of South Korea. Similarly, abnormal waves that occurred on 25 April 2008 were propagated from the northwestern corner of the West Sea to the east–southeast.