Earth Sciences, University of California, Santa Cruz, California, USA. P. J. Lynett ..... experimental data, Ser. Pap. 21, Tech. Univ. Denmark, Lyngby, Denmark.
GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L10608, doi:10.1029/2004GL021918, 2005
Offshore breaking of impact tsunami: The Van Dorn effect revisited D. G. Korycansky Center for the Origin, Dynamics and Evolution of Planets, Institute of Geophysics and Planetary Physics, Department of Earth Sciences, University of California, Santa Cruz, California, USA
P. J. Lynett Coastal and Ocean Engineering Division, Department of Civil Engineering, Texas A&M University, College Station, Texas, USA Received 4 November 2004; revised 11 April 2005; accepted 15 April 2005; published 19 May 2005.
[1] We report on calculations of the shoaling and off-shore breaking of typical wavetrains from sub-km impactors into the deep ocean. We use the COULWAVE code to compute the propagation of waves through simple bathymetry profiles typical of the North American Pacific coast and the Gulf of Mexico. Numerical results are consistent with those predicted by nonlinear shoaling theory. Our primary result is that large long-period waves of the type considered should indeed break far offshore, as suggested by W. G. Van Dorn for similar waves generated by underwater explosions. Typical breaking distances range from 3 – 17 km for the Pacific coast, and up to 200 km for the Gulf coast. The inclusion of bottom friction affects the results; for very gentle slopes like the Gulf coast, a modest amount of bottom friction supplies enough dissipation to suppress wave breaking. Citation: Korycansky, D. G., and P. J. Lynett (2005), Offshore breaking of impact tsunami: The Van Dorn effect revisited, Geophys. Res. Lett., 32, L10608, doi:10.1029/ 2004GL021918.
1. Introduction [2] The Sumatran earthquake and tsunami of 26 December 2004, with the accompanying horrific damage and loss of life, focused the world’s attention on these catastrophic events. Tsunami generated by the impacts of asteroids and comets into the Earth’s oceans have been recognized as a potentially catastrophic risk to the Earth’s population [e.g., Chapman and Morrison, 1994; Hills et al., 1994; Atkinson et al., 2000]. A peculiarity of ocean impacts is the potential global effects of an impact that would otherwise be of only regional or local importance should it occur on land. This is, of course, due to the ability of waves to propagate on global scales in the oceans. Chapman and Morrison [1994] find that the greatest risk from impactors a few hundred meters in size is due to tsunami. The overall risk peaks in the 200 – 300 m range, according to linear analysis of wave propagation [Ward and Asphaug, 2000, 2003]. A recent quantitative assessment by S. R. Chesley and S. N. Ward (Impact-generated tsunami: A quantitative assessment of human and economic hazard, submitted to Natural Hazards, 2005) suggests that tsunami due to impactors of diameters under 2 km may affect (on an annualized basis) O(100) people and do ten million dollars worth of damage, with a mean loss scenario of ten billion dollars in events Copyright 2005 by the American Geophysical Union. 0094-8276/05/2004GL021918
occurring on the average once every 5000 years. They find that half of the tsunami risk comes from impactors of diameter
