A comparative study of far-field tsunami amplitudes and ocean-wide propagation properties: insight from major trans-Pacific tsunamis of 2010–2015

Abstract

Copyright © The Author(s) 2018. We studied ocean-wide propagation properties of four recent trans-Pacific tsunamis based on deep-ocean measurements across the Pacific Ocean. First, we analyzed and simulated the 16 September 2015 tsunami generated by the Illapel (Chile) earthquake (Mw 8.4) and compared its ocean-wide propagation with those of three other events: the 2014 Iquique (Mw 8.2), 2010 Maule (Mw 8.8) and 2011 Tohoku (Mw 9.0). The Illapel and Maule tsunami sources are located close to each other and we reconstructed the source spectrum of the larger (i.e. Maule) tsunami by applying spectral deconvolution using the smaller (i.e. Illapel) tsunami as the empirical Green's function. The initial negative phase was found for all four events with durations of 8–29 (Iquique), 20–35 (Illapel), 22–70 (Maule) and 40–79 (Tohoku) min, with the maximum amplitudes of 0.11–0.26, 0.4–0.7, 0.5–2.9 and 1.9–2.5 cm, and the amplitude ratios to the first elevation phases of 20–40 per cent, 22–41 per cent, 29–61 per cent and 12–67 per cent, respectively. Unlike other studies, our results revealed that the duration ($${D_{ini}}$ $) and amplitude ($${A_{ini}}$ $) of the initial negative phase are directly proportional to the earthquake magnitude ($${M_w}$ $) with equations: $${M_w} = \;6.129 + 1.629\;{\rm{log}}( {{D_{ini}}} )$ $ and $${M_w} = \;8.676 + 0.706\;{\rm{log}}( {{A_{ini}}} )$ $. No relationships were observed between these parameters (i.e. $${D_{ini}}$ $ and $${A_{ini}}$ $) and distance from the source. The amplitudes of far-field DART waves do not vary with distance or strike angle, and depend only on the $${M_w}$ $. The average far-field deep-ocean amplitudes ($${A_{tsu}}$ $) for the Iquique, Illapel, Maule and Tohoku tsunamis were 0.9, 1.7, 6.0 and 15.0 cm, respectively, yielding the equation: $${M_w} = \;8.245 + 0.665\;{\rm{log}}( {{A_{tsu}}} )$ $.