On the Leading Negative Phase of Major 2010–2014 Tsunamis

Abstract

Time series observations from instruments sited in the deep ocean and along coastal margins of the Pacific during major tsunami events in the years since 2010 were systematically processed. Examination of these records during four events, 2010 Chile (Maule), 2011 East Japan (Tohoku), 2012 Haida Gwaii and 2014 Chile (Iquique), show the prevalence of a small negative phase leading the first major positive tsunami wave, a phase that is not typically reproduced by current modelling approaches. We present leading negative phase signatures in examples from the more than 40 deep-ocean bottom pressure and approximately 200 tide gauge records investigated for this study. High sampling rate time series (15-s) were given greater weight in our investigation than the more readily available 1-min series. Careful investigation of tsunami arrival at each deep-ocean site highlights the role filtering techniques may play in misleading researchers or masking specific tsunami features such as the leading negative phase that is the basis of this study. The main focus of this investigation is to characterise the scale and repeatability of the phenomenon in support of recent similar findings rather than to provide a definitive explanation as to the cause. In general, our findings are in good agreement with and support the theoretical results of Watada et al. (J Geophys Res Solid Earth 119:4287–4310, 2014).