The BGR Slide Off Costa Rica: Preconditioning Factors, Trigger, and Slide Dynamics

The Pacific Margin of Costa Rica is an area of intense tectonic deformation and repeated slope instability. Several processes are assumed to affect the long-term stability of the slope. Convergence-related seamount subduction and erosion are the primary reasons for large-scale failures at the lower slope. A second type of smaller slope failures occurs on the upper slope coincident with the landward termination of the regional Bottom Simulating Reflector (BSR). The coincidence of the BSR boundary and the position of slide headwalls might suggest a close genetic relationship. In this paper we present a detailed analysis of the so called "BGR Slide", a small-type submarine landslide located on the upper slope offshore the Golfo de Nicoya. The 60 m-high headwall is embedded in an area characterized by small canyon structures on the continental slope in water depths where the regional BSR reaches the sea floor. The slide with a volume of similar to 0.3 km(3) affected an area of similar to 8 km(2). OUT acoustic data set suggest faults and migrating fluids playing key roles as preconditioning factors for slope failure, while there is no clear indication for the occurrence of gas hydrates in the headwall region. Furthermore, we assume that an external trigger, e.g., an earthquake, finally initialized the sediment mobilization.