Resonance characteristics and impact of the 2006 Pingtung tsunami in southern Taiwan

Tsunami resonance excitation induces tsunami amplification, persistent oscillation, and strong current velocities, which may enlarge coastal hazards in tsunamigenic areas. Historically, the 2006 Pingtung earthquake doublet triggered tsunamis that affected the south Taiwan coast. Studying the resonance features based on past tsunamis is important for assessing tsunami hazards and obtaining critical disaster mitigation information. Here, we elucidate the tsunami resonance oscillation and its impacts along the south Taiwan coast based on synthetic assessment of tsunamis induced by the 2006 Pingtung earthquake doublet. A numerical simulation was performed to replicate the 2006 Pingtung earthquake doublet tsunamis. Then, spatially integrated spectra were obtained via spatiotemporal analysis. The results were compared to tsunami spectra at tide gauges to identify the main oscillation modes, suggesting the main oscillation modes had 13-50 min periods during the 2006 Pingtung earthquake doublet tsunamis. The tsunami resonance oscillations were analyzed based on the main oscillation modes. In the 2006 Pingtung earthquake doublet tsunamis, edge waves occurred along the south Taiwan west coast in most oscillation modes. The Hengchun Peninsula prevents tsunami oscillation transmission, and only part of the oscillation energy at certain periods propagates to the east coast. Furthermore, the spectral amplitude distribution migration across the period domain revealed that energy amplification is a frequency-dependent phenomenon and is responsible for the large tsunami heights and strong tsunami-induced current velocities distributed along the south Taiwan coast during this past tsunami.