IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS002 Poster presentation 1787
Processes affecting tsunamis propagating towards wide continental
shelves, and their role in coastal impacts
Dr. Chris Wilson
K. J. Horsburgh, B. J. Baptie, A. Cooper, D. Cresswell, R. M. W. Musson, L.
Ottemoller, S. Richardson, S. L. Sargeant
We investigate the propagation of tsunamis, towards the European shelf break, from a source at the
Azores-Gibraltar Fault Zone in order to explore aspects of oceanographic interest for tsunami
propagation over a broad continental shelf. We use six different initial conditions, based on the
November 1755 Lisbon earthquake, to force a nested model of the northeast Atlantic. The sensitivity of
tsunami propagation to tides, Earth's rotation, and topographic forcing is examined. Our results show
that topographic features at the shelf edge interact with the almost planar wave front, forming complex
intensified beams. The practical consequences of this interaction are highly variable wave heights
around affected coasts over very local scales. Despite this, wide continental shelves afford a degree of
protection from tsunamis. Due to refraction and wave spreading only a fraction of the tsunami energy
reaches the northwest European shelf, which itself provides a further buffer through reflection and
frictional dissipation. We find that even with an earthquake of magnitude 8.7 Mw, and a fault
orientation favourable to northward energy transfer, the hazards for European shelf seas are
comparable to those during winter storm conditions. The uncertainties arising from the combination of
source orientation and bathymetric interaction suggest that any assessment of tsunami risk, for places
where they are likely, should consider a large ensemble of initial conditions.
Keywords: tsunami, shelf, model