Reply on RC2

Abstract

Consecutive Mw 7.0 and Mw 6.9 submarine earthquakes occurred offshore Hengchun Peninsula, Taiwan on 26 December 2006. A small tsunami was generated, and recorded at tide gauge stations for the first time. This important event attracted public interest as it was generated by doublet sources and demonstrated tsunami risk in Taiwan. This study analyzed tide gauge tsunami waveforms and numerical simulations to understand the source characteristics and resulting tsunami behaviors. The maximum wave heights at three stations were 0.08 m (Kaohsiung), 0.12 m (Dongkung), and 0.3 m (Houbihu), and only Houbihu recorded the first wave crest as the largest. The tsunami durations were 3.9 h at Dongkung, and more than 6 h at Kaohsiung and Houbihu. Spectral analyses detected dominant periodic components of spectral peaks on tsunami waveforms. The period band from 15.5–26.6 min was identified as the tsunami source spectrum, and the approximate source area for the consecutive tsunamis was constrained to be 800 km2. Comparing the simulated tsunami waveforms to observed tsunami waveforms showed that the GCMT focal mechanisms explained the observations at all three stations better than the USGS solutions. Numerical simulations based on real and hypothetical bathymetry examined its influence on the transmission of tsunami waves. The results revealed that wave trapping was connected to wave refraction caused by bathymetry. Trapped waves interfered with incident waves at shelf edges amplified tsunami waves and prolonged oscillations, which explained unusual observations recorded by the tide gauges. These elucidate the generation of the consecutive 2006 tsunamis, and consequent tsunami behaviors in southern Taiwan, contributing essential knowledge for tsunami warning and coastal emergency response in Taiwan to reduce disaster risk.