Observation of the 2009 Samoa tsunami by the NEPTUNE-Canada cabled observatory: Test data for an operational regional tsunami forecast model

Abstract

As part of the NEPTUNE‐Canada cabled seafloor observatory, an array of six high‐precision bottom pressure recorders was installed in the late summer of 2009 at depths from 100 to 2600 m seaward of the southwest coast of Vancouver Island in the northeast Pacific. The instruments transmit 1‐sec bottom pressure data at roughly 0.1 mm equivalent sea level height to the Data Management and Archiving System (DMAS) at the University of Victoria. On September 30, 2009, the array recorded waves of 2.5 to 6 cm amplitude associated with the transoceanic tsunami generated by the Mw = 8.1 Samoa earthquake in the South Pacific. These open‐ocean observations were uncontaminated by coastal effects, demonstrating that NEPTUNE records from future tsunami events can be effectively used as realtime input to a regional numerical tsunami forecast model. We validate this proposition by showing that wave forms simulated by the regional model using the leading train of waves of the 2009 event are in good agreement with observed tsunami records for both the shelf stations and nearby coastal tide gauges. Tsunami waves simulated by this model are also significantly more accurate for local regions than those determined by global‐scale tsunami models. This ability to assimilate “pristine” open‐ocean data from the cabled observatory into an operational tsunami forecast model makes it possible to provide updated wave information that could help mitigate the impact of future tsunamis approaching the west coast of British Columbia and northern Washington State.

The open ocean energy decay of three recent trans‐Pacific tsunamis

“…The ensuing tsunami had a maximum runup on the Samoa coast of 17.6 m and was responsible for 189 fatalities [ Okal et al ., ]. The high‐resolution (15 s) DART records from this event were used to estimate the tsunami parameters and to compare these parameters with numerical model results [ Thomson et al ., ]. Figure a shows maximum computed amplitudes for the 2009 tsunami waves and estimated E 0 values (see Table S1 of the supporting information for numerical values of the computed E 0 and t 0 estimates).…”

Parallel Infrastructures and Systems for Near-Field Tsunami Detection and Impact Assessment

“…NEPTUNE Canada's cable array is located off the west coast of Vancouver Island. Included among its devices are high precision, rapid sampling bottom pressure recorders (BPR) that are able to resolve the spatial and temporal structure of sea level disturbances associated with tsunami waves [12]. The BPRs record seafloor pressures at 1-second intervals and are capable of measuring surface wave elevations on a sub-millimetre scale.…”

Tsunami Wavefield Reconstruction and Forecasting Using the Ensemble Kalman Filter

“…Japan has such networks along the Japan Trench (S‐NET; Yamamoto et al, ) and the Nankai Trough subduction zone (DONET; Kawaguchi et al, ). The Cascadia subduction zone has instruments from Northeast Pacific Time‐Series Undersea Networked Experiments (NEPTUNE)‐Canada (Thomson et al, ) and Ocean Observatories Initiative cabled arrays (Toomey et al, ). Offshore data can be used to invert for tsunami initial conditions (Tsushima et al, ) or to reconstruct the tsunami wavefield using sequential data assimilation methods (Gusman et al, ; Maeda et al, ).…”