After an evening filled with grab sampling (picture) and one last gravity core, we said farewell to our H aitian colleagues. However, as Roby and Steven will continue their studies of Haitian tectonics and Nicole’s role in the Bureau of mines necessitates further collaboration, it is not goodbye, but until we meet again.
Currently, we are surveying in the Baie de Saint Marc (picture), an area proposed for the rebuilding of Port-au-Prince. Based on our geophysical data, there are several steep inclines in coral reef complexes, however, further processing and analysis of data is required to further understand these implications. Marine terraces (picture) are very evident on land (uplifted fossil reefs in stair-like pattern) suggesting tectonic activity in this vicinity.
The Endeavor crew has been assembling waterproof floatable bags filled with food and fishing supplies, tossing them toward fishing boats as we sail by them. We also have some miscellaneous food items (apples, candy bars) on hand to toss to nearby fishermen.
Surveying will come to a completion this afternoon when we will begin our 3-day trek to Florida. Although we have successfully achieved even beyond some of our goals, this only marks the beginning of our geophysical and sedimentological studies in Haiti. This expedition has allowed us to ascertain areas to focus future research efforts to best understand the geological history of Haiti’s Southern Peninsula.
We have really accomplished a lot in our two weeks of surveying off-shore of Haiti’s Southern Peninsula. Our survey has transversed many seismically affected regions where we can focus our efforts on carefully scanning fault scarps and areas potentially altered by this earthquake or previous earthquake activity. Small boat work was especially successful, as after processing the data they were able to trace the scarps found in the shallow offshore regions to those on land. Matt immediately contacted the onshore geologists directing them to where they should focus their land surveying. Our work will be nicely complimented by the number of cores we have collected in the range of marine settings allowing us develop a “big picture” understanding for this seismically active region. A total of 18 gravity cores and 3 multi-cores in counting, have been collected in deep basin areas reaching depths beyond 1700 m to perched basins, channel settings, and reef rubble regions (<100 m water depth). The sediment will help us understand the images that are created from our surveying. We will have a better understanding for their structure, what they are composed of, and how they fit into the larger fault network. This expansive core collection will help us understand the scale of the area affected by normal deposition versus event-related deposition, the origin of sediments and where and how they accumulate during an event indicating more discrete regions of tectonic movement, and allow us to calculate a recurrence interval for earthquakes to help predict future events.
A few nights ago, the onshore geologists from the Texas Geophysical Institute and USGS met us at sea where we have a brief meeting to discuss our progress and where to focus our efforts.
Sean Gullick, scientist onboard from the Texas Geophysical Institute, had a phone interview with NPR discussing the pertinence of our research, our scientific goals, and how this is can benefit the long-term sustainability of Haiti. This interview will be posted once it is released.
Now we know what a p-wave from an earthquake feels like while at sea. We were sailing peacefully when the whole ship began to rattle. It was brief, but immediately after, our onshore correspondent informed us that the ground was shaking in Haiti, estimating a magnitude of 4.6. The physical shaking would have been a direct result from the propogation of a p-wave (primary wave) resulting from surface movement. Now that surface conditions have changed we have to start our mapping all over again…(just kidding!)
Surveying continues as we try to delineate fault scarps and fill in nearshore areas where shallow subsurface faults most likely transverse. We were successful collecting one gravity core and one multi-core today in an area where we believe the sediment is a debris flow resulting from the recent Earthquake. Visually, at least 2 events are apparent in these cores. We will process the sediments for grain-size and short-lived radionuclides when we return to New York. Grain-size is important for understanding the energy of a system. Larger and denser grains require more energy to be transported, so a landslide resulting from an earthquake would potentially transport larger grains than are commonly deposited in this environment.
We are sailing pretty close to land, so have been able to see some more detail of coastal features and scenery.
Image captured while sailing adjacent to marine terraces, fossil coral reef platforms that have been recrystallized to limestone. They are above sea level due to a likely combination of tectonic uplift and sea level fall (~4 m higher 4,000 years ago).
Image of a fishing sailboat that has been interested in our activities the last few days.
The Endeavor cook, Amanda, displays a dangerous assortment of nightly snacks. This isn’t even all of it.
Scientists at work (Cecilia McHugh and Nano Seeber).
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.
Below are some additional coring photos. See caption for description.
Late this morning we began surveying using the side-scan sonar attached to the starboard side of the boat and flying the CHIRP beyond the aft (backside) of the ship. Now we have our first depiction of the subsurface from the CHIRP as well as some detail of the surface features from the side-scan up. We are most interested in reflectors indicating recent changes in the subsurface (i.e, suture zones, sediment mass movement) which may pinpoint fault lines. Based on these features evdient in the CHIRP data, we have chosen areas to collect sediment, which will provide a more detailed record for recent seismic history in Haiti.
This afternoon, a group of geologists who have been working on shore met the Endeavor where we were able to deliver some onshore surveying supplies. Pictures of this reunion are included.