High-resolution, deep tow, multichannel seismic and sidescan sonar survey of the submarine mounds and associated BSR off Nicaragua pacific margin

Bathymetric and conventional multichannel seismic surveys offshore Nicaragua and Costa Rica have revealed numerous mud mounds beneath which the generally widespread BSR is not well imaged. However, many of the mounds are partially capped by patches of authigenic carbonate crusts, so it was not clear if the semitransparent seismic facies and the apparent gaps in the BSR beneath the mounds are real or due to poor normal-incidence seismic penetration through the cap rocks. To address these problems, a high-resolution seismic survey was carried out over the continental slope of the Nicaraguan Pacific margin using a deep towed multichannel seismic streamer (DTMCS) along with a sidescan sonar system (DTS) to image submarine mud mounds and the associated BSR. The proximity of the very short (39 m active length) but high-resolution 17 channel streamer to the seafloor of the deep towed system allows greatly improved lateral resolution whereas the relatively large source-receiver offset allows the undershooting of the cap rocks. For the first time our data show that the BSR in many cases continues but rises beneath the mounds. This is consistent with the advection of deep warm fluids and thus increased heat flow through the mounds. The occurrence of mud mounds seems to be controlled by the locations of faults.