Globally Scattered 2011 Tohoku Tsunami Waves From a Seafloor Sensor Array in the Northeast Pacific Ocean

Modeling of tsunami wave propagation for forecasting focuses on the arrival time and amplitude of the earliest tsunami waves reaching coastlines. The complex later tsunami wavefield, in which scattering is predominant, poses additional hazards due to possible constructive interference of coherent packets of wave energy. However, almost no data sets exist to characterize the geographical sources and temporal evolution of the scattered waves. Here we show how recordings of the 2011 Tohoku tsunami by an array of pressure gauge sensors in the northeastern Pacific Ocean reveal coherent waves that are produced by scattering from distant coastlines including South America and Antarctica, as well as multiple seafloor fracture zones, ridges, and island chains. Multiple signal classification analysis and backward propagation ray tracing provide tight constraints on the origin of each scattered phase and resolve simultaneous wave arrivals from different scatterers. Incoming waves from constant back azimuths occur over time durations of several hours, revealing the time persistence of specific geographical scatterers. The results can advance numerical predictions of tsunami wave impact because they provide direct evidence for the necessity of incorporating both local and distant bathymetry over a range of length scales and for long time durations, to account for the azimuthal dependence of scatterer strength.