Evaluation of tsunami source scenarios in the caribbean sea and simulation of wave height, a TIME project activity

INTRODUCTION

Colombia has extended coastlines on both the Pacific Ocean and the Caribbean Sea. But, while its Pacific coasts are close to a very active and tsunamigenic subduction zone and have sustained several disasters, the tsunami hazards at its Caribbean coasts - both continental and insular - are yet unknown, but basically perceived as insignificant and, in any case, much smaller than those caused by swell episodes during the annual hurricane seasons. On a regional scale, tsunami hazards are also regarded as a lesser concern, compared to rather frequent disastrous hurricanes.

The available historical cataloges (Grases, 1994; Lander & Lockridge, 1989) do not list any tsunami impact on Colombian coasts. However, the lack of historical events cannot be conclusive; the recurrence periods of large earthquakes in the Caribbean are rather long and smaller events may have passed unrecorded, among the very frequent - in fact, yearly - ocurrences of swell due to hurricanes, and due to the lesser attention to natural events during periods of war and buccaneer activity. But the Caribbean is indeed a seismocally active region; its rims -from Guatemala over the Greater and LesserAntilles, Venezuela, Colombia, Panamá and part of Costa Rica - are plate margins (Fig. 1). While long segments of this margin are lateral or extensional tectonic features, others from Hispaniola to Trinidad and in front of Colombia and Panamá - are subduction zones. There is no record yet of a Caribbean-wide tsunami, but local tsunamis have been reported from many areas, over most of the active segments of its rim and mainly in the Antilles Arc; the best known event is probably the 1692 Port Royal (Jamaica) disaster.

In order to provide foundations for decisions and to assess the need for tsunami mitigation measures for Colombia's Caribbean coasts, including a recently proposed regional tsunami warning system, we have made a preliminary evaluation of tsunami hazards, covering the most likely sources, earthquakes, although volcanic and submarine landslide tsunami are also possible, at much lower frequency. With a deterministic approach, using using available seismotectonic and historical information, we analized one by one the regional seismotectonic features, to identify the most likely sources of tsunami which could threaten the coasts of Colombia. To obtain an estimate for probable tsunami wave heights, numerical simulations of wave generation and propagation were performed, using the shallow water equations as implemented in the TIME routines.