We Found a Fault!

We have been extensively surveying a nearshore area, a site where the onshore portion of the Enriquillo-Plaintain Garden Fault most likely extends offshore. A few days ago, as we were working our assigned geophysical instrument shift (multi-beam, side-scan, CHIRP), we simultaneously realized we were transversing a fault. The uproar among geologists was invigorating. Sitting infront of the computer monitors and noting the changes of the seafloor as we scanned our survey lines, there was no doubt we detected a key area. On the CHIRP computer monitor, the seafloor shifted depths abruptly. In the multi-beam data, there was a stair-like (terraced) pattern, and as the side-scan provides a crisp image of the seafloor, we noted an actual suture in the seafloor. To provide some kind of idea of how this seafloor is presented to us on a computer screen, included are images of the reflectivity profile of the CHIRP and a map of the seafloor generated from multi-beam data (although not images of an exact fault). As we were following a rough bathymetric map (as this area has had minimal bathymetric surveying) and we were attempting to get as close to the shore as possible within the depth range possible for the Endeavor, we had a risky encounter with the seafloor in 12 m water depth. To avoid a potential disaster in shallow depths, the following day, Matt Hornbach, Marcy Davis, Hal Johnson, and Kevin (Endeavor crew member) took the zodiac out for the day to survey shallow nearshore regions. Equipped with a small CHIRP and a side-scan sonar, they had a very productive day of surveying and plan to continue in a shallow inland bay the following day.

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