Near-field propagation of tsunamis from megathrust earthquakes

We investigate controls on tsunami generation and
propagation in the near-field of great megathrust earthquakes
using a series of numerical simulations of subduction and
tsunamigenesis on the Sumatran forearc. The Sunda
megathrust here is advanced in its seismic cycle and may be
ready for another great earthquake. We calculate the seafloor
displacements and tsunami wave heights for about 100
complex earthquake ruptures whose synthesis was informed
by reference to geodetic and stress accumulation studies.
Remarkably, results show that, for any near-field location:
(1) the timing of tsunami inundation is independent of slipdistribution
on the earthquake or even of its magnitude, and
(2) the maximum wave height is directly proportional to the
vertical coseismic displacement experienced at that location.
Both observations are explained by the dominance of long
wavelength crustal flexure in near-field tsunamigenesis. The
results show, for the first time, that a single estimate of vertical
coseismic displacement might provide a reliable short-term
forecast of the maximum height of tsunami waves.

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