Haiti 2010 REPONS – Rapid Enriquillo Plaintain Offshore Neotectonic Study

March 13th, 2010

From left to right back to front: Chris Sorlien, Marie-Helene Cormier, John Deibold, Sean Gulick, Bob Wilson, Harold Johnson, Jake Deming, John Templeton, Katie Mishkin, Nano Seeber, Marcy Davis, Matt Hornbach, Roby Douilly, Nicole Braudy, Cecilia McHugh, Nicole Dieudonne, Steeve Symithe

La Fin

March 12th, 2010

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.

Non-stop surveying and coring and coring and surveying (2.5 days remain)

March 10th, 2010

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.

Devastation

March 9th, 2010
Three full days of small boat operations allowed Marcy, Sean, Matt, and Hal to capture the devastating effects within a coastal community on the Bay of Petit Goave. In addition to the information they gathered from surveying the seafloor, the direct effects from the earthquake were apparent on land. The coastal tent communities, obviously prepared for those who lost their homes, were surrounded by rubble, situated at an angle, and with evidence of flooding. We are unsure whether the angle is due to tectonic uplift or subsidence of the land, but with further analysis of our geophysical data we should be able to answer these questions in the near future.
This tent community is situated in an area where two rivers converge, leading us to believe it was a site of significant flooding. This was apparent by the submerged trees and water lines on remaining structures. The small boat group witnessed a helicopter landing on this site with a mass of yellow-shirt (likely UN) workers arriving to aid the Haitians. It was at a fortunate time since many of the people thought that our group were aid workers and were requesting assistance and food. The island as shown in the pictures below was also like affected by either uplift or subsidence, as it is tilted as well.   The small boat captured a great shot of the Endeavor recovering the CHIRP as they were returning to the boat.
One of our newest goals is to do some surveying in an area where rebuilding of Port -au-Prince is proposed. We are led to believe there is high earthquake risk there as well and would hopefully prevent another disaster if this is true.

Earthquake at sea

March 6th, 2010

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.

Picture descriptions:

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 Found a Fault!

March 5th, 2010

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.

Photos from Coring

March 3rd, 2010

Coring

March 3rd, 2010

Below are some additional coring photos.  See caption for description.

Sedimentology!

March 1st, 2010
Today was a thrilling day for the sedimentologists. It was the first day of gravity coring. We cored in a deep basin (>1000 m water depth) where based on our CHIRP data we hypothesized sediment deposited due to the recent earthquake activity. It is possible to link sediment layers to recent or historical events based on the type of sediment (i.e., grain size), how it is deposited, and using geochemistry to determine its age. We began coring at 11am Monday morning and were finished around 9pm, with nearly full cores (182 and 133 cm). We are really hopeful because these two core sites were 2.5 km from each other and both cores reveal very similar event layers. During a high energy event, such as an earthquake, the heaviest sediments are deposited first. Therefore, we would expect sands, shell fragments, gravels to be at the bottom of the event layer. The finest sediments would remain suspended in the water column until they eventually settle to the bottom of the seafloor. Visually, this lithology is noted in both cores, at similar depths. Contacts in sediment cores mean there is a notable change in sediment type with depth. Both cores revealed several contacts at comparable depths, meaning these areas were influenced by the same physical processes. Perhaps something as large as the recent earthquake. We will bring these cores back to the laboratories at Columbia University and Queens College to study them for geophysical properties, better understand their sedimentology using laboratory techniques, and determine if the sedimentation was recent and how fast they accumulated (using radionuclides). Radionuclides adsorb to sediment particles and provide us with a chronology because they decay at a particular known rate.  We can determine what the activity is of radionuclides associated with a particular sediment depth and then back calculate to determine the age of these sediments. Radionuclides such as Beryllium-7 with a half life of 53 days or thorium-234 with a half life of 30 days are useful for understanding if sedimentation was recent. In other words, if we find that our surface sediments have any beryllium or thorium activity, it means they were deposited by this earthquake that occurred on January 12.
Pictures provide you with a visual of how we collected gravity cores. It takes several hours to collect one core because water depths were about 1700 m and the wire is deployed from 20-40 m/min. However, when that core returns and there is sediment inside of it, we all rejoice!
Another picture is included of what some believe are eroded hillsides from the recent earthquake activity.

Reunion with the onshore geologists

February 28th, 2010

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.