March 4 2010
Yesterday we crossed the main southern plate boundary fault, the Enriquillo-Plantain Garden fault, in water shallow enough to run HW’s sidescan sonar and the rented multibeam bathymetry. The ship was going along in deep water and the projection of the fault was charted to be deep. But, the bottom came up quickly at the fault to 12 m depth, even though charted much deeper, so we won’t be doing that again in that way. Right now, they are getting ready to launch the zodiac in the same area with the mini-chirp, which is run off of batteries (I assume auto batteries or something about that size). This will show the depth and if there is young sediment, maybe 10 meters below sea floor. If deep enough, the ship can then fully survey later.

Side-scan sonar gives the reflectivity of the sea floor, and multibeam bathymetry gives the depth across a width. The sidescan showed a bright lineament that strike 260 deg azimuth, which is the azimuth of the main part of the fault. It seemed to me from the screen capture that was distributed to the participants that the lower part of the scarp was brighter. Perhaps that is the last earthquake or couple of earthquakes that broke to the sea floor. But, we don’t know if it was the 2010 earthquake yet; we don’t know yet whether it broke the sea floor.
Chris