On the negative initial phase of major 2010-2014 tsunamis

Abstract:

Major tsunami events occuring in the years since 2010 in the Pacific Ocean have been recorded by an unprecedented number of instruments deployed both in the open ocean and along coastal margins. Open, or deep-ocean instruments are especially valuable in that they provide high precision observations, have a lower level of background noise than coastal counterparts, and are free from the distortion effects of coastal bathymetry and topography. We take advantage of these observations to investigate the prevalence of a negative wave (trough) leading the first positive wave observed by the more than 40 deep-ocean bottom pressure recorders and approximately 200 tide gauges that were in operation over this time period. We consider two major events: 2010 Chile, and 2011 Tohoku, and present negative trough signatures for 2012 Haida Gwaii and 2014 northern Chile. Careful investigation of tsunami arrival at each deep-ocean site highlights the role filtering techniques may play in masking phenomenon such as the leading negative wave that is the basis of this study. The main focus of this investigation is to characterize the scale and repeatability of the phenomenon rather than provide a definitive explanation as to the cause.