Seismo-acoustic Investigations of Mud Diapirs Offshore Northern Costa Rica

The erosive subduction system offshore Pacific Costa Rica is characterized by numerous mud domes of up to 100 m heights located on the overriding plate. A series of multi-disciplinary investigations has shown the mounds in the northwestern domain, opposite subducting East Pacific Rise material, to be of diapiric origin. As shown by two case studies over the single large Mound Culebra and the group of Hongo mounds, respectively, the properties of the subducting plate gravely influences the development of the mounds. Based on observations in multi-frequency seismo-acoustic data, the continental slope is subdivided into regions dominated by fast downslope sediment transport, enhanced accumulation, and slow trenchward migration. Inferred deep faults are thought to control diapir location. Fluid venting near the mud domes has been documented by various geochemical and geological techniques. Heat flow values estimated from the depth of a gas hydrate BSR indicate non-vigorous, possibly deteriorating activity at the mounds with decreasing distance from the deformation front. Distinct anomalies are seen related to several morphological features such as, in addition to Mound Culebra, a nearby fault scarp as well as a circular, crater-like structure. Comparison of the target areas highlights the role of subducting morphological differences.