The rocks beneath the coastal plain of Georgia were at the center of the most fundamental tectonic events to shape eastern North America: continental collision around 290 million years ago to form the super continent of Pangea; continental breakup leading to the formation of the Atlantic Ocean beginning around 230 million years ago; and one of the biggest magmatic events in Earth’s history around 200 million years ago, the Central Atlantic Magmatic Province. A record of these events and possible relationships between them is preserved by structures in the crust of southern Georgia, including a suture between two different types of continent, the largest failed rift basin along the east coast of North America and igneous rocks from the Central Atlantic Magmatic Province. We will collect seismic refraction data, which can be used to image structures in the crust to understand these tectonic events. During March 2014, over 1000 geophones will be deployed along a ~300-km-long profile across the suture and the basin, which will record sound waves generated by a series of controlled blasts spaced ~20 km apart. The speed that sound waves travel through rocks varies with rock type. We will use these data to create velocity models that reveal the distribution of igneous rocks, variations in the thickness of the crust and variations in crustal composition. Besides a better understanding of fundamental tectonic processes, other benefits of this program include training and education of students, and characterization of basins and igneous rocks that might be good targets for carbon sequestration.
It is hard to believe that just a few days ago, the hotel had 30+ college students
roaming the hallways and the parking lot was full of SUV’s washed in clay, sand and
mud. When most of the second phase of the SUGAR project had come to a halt, there
was still work to be completed by the Seismic Source Team (SST). In order to
understand why, let me take you through the work schedule of the SST.
Dr. Harder and I drove to Atlanta on July 1st after completion of the ENAM
project in North Carolina and began scouting the shot-holes we would need to drill, load
and stem i.e. fill before the shot dates, which were scheduled for August 7th and 8th for
Line 2 and August 14th for Line 3. When scouting, you want to ensure that the shot-hole
locations selected have good, accessible roads and enough space for the drillers as well as
work crew to move in and out of easily. However beforehand, you want to ensure that
you have the permits to access different properties and have the correct keys for the
property entrance/exit gates, which Donna took care of. Scouting holes took 4 days
before drilling began on July 7th until July 29th.
An example of a good, accessible road for the drillers and SST to use.Pick a lock, any lock. One of the entrance/exit gates to a shot location. Thankfully, we
had the key. I just had to test it on each lock to open the gate. A typical workday would consist of waking up at 6:30 am, eating breakfast at 7
am and leaving to work at 7:30/8 am. We would arrive on site about an hour later and the
drillers would set up and begin drilling. This would take about 2-3 hours at some holes
and 3-4 hours at others. The last hole composed of hard rock took about 14 hours to
complete. That does not include the time it took for us to stem the hole. We would
prepare the charges to load into the hole when the drillers had ~20 ft left to drill. They
drilled up to ~80 ft at the 2 shot-holes on the ends of Line 2 and ~70 ft for the remaining
13 shot-holes. For Line 3, they drilled all 11 holes to ~60 ft. After drilling and loading
the charges into the ground, Dr. Harder would lead the drillers to the next shot-hole while
Galen, Yogi and I would stay behind to stem the hole with gravel, sand and plug it with
bentonite. We would also check the detonators to make sure they worked before heading
off to the next shot-hole to repeat the process. On average, we would drive anywhere
from 100 – 200 miles per day depending on what we were doing and where we needed to
Yogi (Victor Avila, left) and Galen preparing 2 charges to be lowered into the shot-hole. Each charge contains 2 detonators attached to 2 boosters indicated by the sets of wires.The drillers lowering the charge into the hole with Yogi carefully holding the detonator (orange wire) chords. On the left is the water truck and to the right is the drill rig."The Beast" with a 1.1 Explosives placard after transporting the source materials to the shot location.Galen taking a GPS waypoint of the loaded shot-hole while Ashley tests the detonators to ensure that they are working.Dr. Harder (left) and Kent splicing the wires at one of the shot-holes to connect the detonators in order to shoot. The routine changed once drilling was complete. We made our way to Vidalia
where we met with Donna, Dan and everyone at the instruments center and began
preparing our equipment for the nights we were going to shoot. Shots would start at 11
pm and last until as late/early as sunrise depending on the weather conditions as well as if
the detonators would connect. The days that the deployment team members were
flagging and deploying instruments, we were busy driving to shot-holes and cleaning the
ones that blew out. The idea is that you make the shot-hole location look the way it did
before the shot took place.
Shot-hole 7 on Line 3. It looks like a regular hole, but it is actually about 5ft deep and has a 5ft diameter cavity.Using the backhoe to clean up the above shot-hole.After clean up!!
I can honestly say there was never a dull moment while working on the SST. I
remember Donna saying at our farewell dinner something along the lines, “We do all this
work for just a disk of data, but it’s all worth it.” She could not have summed it up any
better than that.
Here’s to another successful project….salud!
Ashley Nauer - UTEP
HUGE THANKS to all the volunteers who worked so hard to make this project such a great success. It was a pleasure working with you and getting to know you all. Also mega thanks to all the landowners who were kind enough, and trusting enough, to let us put a source on their property. None of this could have happened without your generosity and spirit of curiosity. Thanks so much.
Controlled blasts in deep holes are the source of sound waves for our program. We set them off in the middle of the night because that is when it is quietest along the county and state roads where our instruments are shallowly buried on profiles across eastern Georgia and listening for sound waves. During the nights of Aug 7, 8 and 11, our blasting experts Steve Harder, Galen Kaip and Ashley Nauer prepped and detonated 25 blasts along our lines, with some help from other enthusiastic scientists (like me). Our shots have between 200 and 1600 lbs of explosives – mostly ammonium nitrate emulsion. At each shot, we connect a long wire between the drill hole and a blast box, move back a safe distance from the shot site, wait for the appointed time, and set off the blast. The blast box is used to detonate the shot at a very accurate time. There were two shooting teams, and each has different time windows for blasting to ensure that we only do one blast at a time. If two blasts occurred at the same time, the sound waves could interfere with one another.
Ashley Nauer and Kent Anderson wire up a shot.
“Recovered a Texan at stop 20858. This one doesn’t seem to be working correctly, whenever I press it it just tells me things like “The Cowboys are America’s team” and “Bush was an American hero”. Weird.
Loaded up with Texans and geophones
“Stop 20804. Everything’s fine, except some guy came out of the woods and bit Brent. All he’s saying now is “brains” and is acting super creepy. I’ll keep an eye on it and only use the shovel if necessary”
“Team4 is Done! I repeat again, 4 is done! Heading back to the sweet onion city! ☺”
“Team gruesome twosome on our way back to the hub”
“We are gonna skip installing 21520 because both sides of the streets are well maintained yards and there’s not a great place to put a Texan”
“We’re done! Just kidding haha. We’re on our second!”
“We’re in the zone”
“All geophones buried --- I am beat. Where’s a can of spinach when ya need one, lol”
“Still digging. Still have not reached China. Will attempt again on next hole”
“On 20186 and we lost our bubble level. We even dug up the last geophone to see if I accidentally buried it”
“We just deployed our last station, 20224. Can we go to Jekyll Island?”
Donna Shillington, LDEO
Natalie Accardo - Columbia University, LDEO
Students practice digging holes and deploying Texans
near our hotel in Vidalia, Georgia.
Students and PASSCAL personnel take over the instrument center
filling 2,000 Texans with D-cell batteries.
The "battery party" comes to an end as the last Texans are filled and
the boxes are rearranged for easy late-night programming by the PASSCAL team.
Freshly delivered pallets of boxes holding all the science equipment
The PASSCAL team re-arranged the boxes into a T for their own devious reasons :)The trusty Silverado loaded down with 2000 pounds of batteries! (Dan for scale).
Natalie Accardo - LDEO
Galen Kaip prepares the source charges (white tubes) on the truck bed as
the drillers complete a shot hole.
The source team carefully lowers the prepared seismic charges into the complete shot hole.
Ashley Nauer (red hat) stands waiting with shovel in hand to fill the remaining height of
the hole with sand and gravel.
The drill team monitors the process of spudding, the very first stage of drilling the
shot hole, for SUGAR line 2.
The source team and drill team push on late into the night to ensure the completion of the
final shot for the entire SUGAR experiment.
We collected similar data in western Georgia last year during the first phase of the SUGAR experiment imaging these same features. During that field program, we deployed 1200 seismometers and set off 11 controlled blasts along a 250-mile-long line, which felt like a big project at the time. But this year, we will go even bigger! In eastern Georgia, we need to span an even larger area to encompass our geological targets. One of the reasons that we need to look at a bigger swath of the earth is that there is a debate about the location of the suture here – it could be as far north as Milledgeville, GA or as far south as Baxley, GA. (In case you are not up on your Georgia geography, those towns are ~100 miles apart). This means longer profiles, more instruments and more blasts! We will deploy a total of 3000 seismometers and detonate 25 blasts along two profiles. The longer profile spans 350 miles from Winder, GA to the Florida-Georgia state line near St Mary’s Georgia. Stay tuned!
Donna Shillington, LDEO
To record these lower-crustal and upper-mantle phases as “first arrivals”, where they are not obscured by the arrival of energy from shallow paths, we use long lines. Long lines mean lots of receivers and lots of driving to deploy and recover these instruments. We could have used lots of sources instead, but the blasts we used to get seismic energy into the lower crust and upper mantle in this experiment take a lot of time and money to setup. Receivers are much cheaper, so we used a lot of them. (For similar wide-angle/long-offset work at sea, airgun sources are cheaper than putting seismometers on the seafloor, so we use many shots and a smaller number of receivers out there.)
To someone who hasn't seen a seismic source shot before, there really isn't a good way to describe what a good shot feels like, except as something you haven't felt before. We had a number of students watching L1-05 being shot, since this location is quite close to Americus. The video of L1-05 is completely lacking in drama, which is a good thing; but that shot gave us all a great ride. The 100 pounders 06 and 07 were also surprisingly good.
We made gathers for most of the shots today. The dataset is fantastic, and 05, 06 and 07 produced super record sections. L1-08 committed most if its energy to the air, but it shook the ground nicely and I've got a feeling those data are going to be great too.
South-central part of the seismic line. The yellow line is team 5's section. We have been in a relatively rural part of Georgia and as a result have not encountered many locals save a few who have stopped to ask if we are ok. However, we have seen quite a few interesting things that are quite out of the ordinary (to me at least).
Friendly Muscovy duck.Rocks in a stream bed with associated pink spongy material (?)
Spanish moss.Linguoid (current) ripples on a washed out road. We have also seen quite a few old abandoned farm houses in various stages of aging...
Meghan and Nate getting it done!Along the way the cars have taken quite a beating and have actually held up pretty well. Although there have been a few instances where people got stuck, I think that the people with the toughest job will be the guys that have to detail the cars upon their return...
The large disparity in fuel grade gas prices.
A ~perfectly leveled geophone (it's harder than you'd think).Hopefully this random selection of pictures was entertaining. Up next we will post about last night's "shots." In the meantime, I can say that they were all successful with varying degrees of excitement. The most important thing is that all of our hard work is being realized as the instruments are recording refractions from buried geology that will help us unravel some of the mystery that surrounds events that happened in this area long ago.
James Gibson, LDEO
Adrian Gutierrez, 13 March 14
7:30 am: Leave Georgia Southwestern State University, where we are staying, and head to the site8:20 am: Arrive at site 8:30 am: Start drilling and take geological samples every 5 ft.
11 March 2014
9 March 14
5 March 2014