3D Costa Rica - Hongo Mounds (2001)

The plate tectonic setting offshore Costa Rica is characterized by tectonic erosion. While such margins ar etypically sediment-starved, they also comprise a setting of basal erosion and strong tectocnic deformation and subsidence. In the course of this, deep reaching faults evolve, which may connect down to the plate boundary. Mud mounds were observed at the margin, marking pathways for deep fluid sources and migration pathways.

To investigate the associated structures around such mud mound, the Hongo mound area had been selected for a 3D seismic survey during R/V  Meteor Cruise M54-1 in 2001-

The Hongo Mounds are in the main focus of the M54/1 Cruise, because they are located at a position of the margin where the oceanic plate boundary is being subducted, where a major thermal boundary is found, and where significant indications for fluid venting had been found during previous cruises. It is also the location of the subduction of a large ridge structure, which in turn must have created major sediment deformation and may have initiated or enhanced mud diaprism and/or fluid and gas venting.

The area was first surveyed in an overview grid to image the regional sedimentation and deformation patterns and to have a first look at the mound area. For precise planning of the 3D survey, the wider vicinity of the mound area was the target of the second grid, before in the third step a 3D box of 2.4 x 3.2 km was filled with 61 seismic lines at 40 m spacing.

The quality of brute stacks and onboard processing was limited due to high electronic noise levels originating from the vessel’s engine, and results can only be shown after careful processing. Although signal penetration seemed to be sufficiently high, reaching a BSR reflection at 800 ms TWT, further structural elements are rare probably the result of massive deformation.