Shaking Things Up: LSU’s Seismeauxbile Helps Identify Weak Spots in New Orleans Levee System
BATON ROUGE - If you’ve ever been on LSU’s campus, you probably noticed the Seismeauxbile. It’s hard not to. Parked behind the Howe-Russell Geoscience Complex, its purple-and-gold body draws quite a few confused glances. And its “Cajun-ized” spelling of mo (meaux!) evokes laughter and some university pride. But most are unaware of the Seismeauxbile’s true purpose – and of the mind behind the machine, Associate Professor of Geology and Geophysics Juan Lorenzo.
Though its spirited décor is fun and light-hearted, its mission is serious science – structural seismology, the forms and faults of Earth.
“Since I was young, I’ve been fascinated by Earth processes. Everything is governed by them, whether you’re looking for oil or studying how the Earth began,” said Lorenzo. “It’s all based on the same fundamental processes.”
It’s the mystery behind these ancient processes, primarily the fact that no one truly understands why most of the activity below the Earth’s crust happens, that really piques Lorenzo’s curiosity.
“Think about it,” he said. “After all this time and all this research, we still don’t know exactly why earthquakes happen. Plates move almost constantly, but earthquakes are relatively rare. They only happen when the moving rocks hit a snag. But why doesn’t that happen more often?”
Although not an earthquake specialist, Lorenzo does study seismology, using sound waves (up and down) and shear waves, which travel side-to-side, to “see” from tens to thousands of feet below the Earth’s surface. This is useful for determining what lies beneath … whether it’s valuable minerals, water deposits or even underground caverns and valleys.
“We use explosions, which vary in size from being quite modest to pretty impressive, to generate recordable movement below ground,” said Lorenzo. “It works a bit like medical imaging does. We use sound to measure solids … when the waves run into liquid, or perhaps empty space, our readouts indicate as such.”
Lorenzo and his team of students travel widely to put their skills to good use. They have traveled often to study a giant fault line in central Chile. Recently, their work was supported by a national copper company there.
“The copper deposits in Chile are generally found next to great faults, pathways for crustal water. So, the company hires us to find the buried fault. The students benefit from learning how and why water moves from depths of 40 miles or more, and the company benefits from learning where deposits might be located. It’s definitely a win-win,” said Lorenzo.
Lorenzo’s most recent research now focuses on something of a Louisiana icon – the New Orleans levees. After Hurricane Katrina and the failure of the city’s barrier levees, the levee boards charged with their upkeep were reorganized, and new legislation dictated that a geologist sit on each one. After that, Lorenzo and his team started work.
“This is an instance where good government and legislation fueled good science, which leads to the development of better tools, which in turn leads to the ability to ask more, and better, questions,” said Lorenzo.
He and his team travel to the levees frequently. Using the Seismeauxbile, the mobile lab they’ve developed, they distribute “geophones,” small sensory devices that translate ground movement into seismic readings. These geophones are so seismographically-sensitive that they will record the movement of an ant along the area of interest. Using an ATV, they string out several geophones, then place a metal plate on the ground and essentially hit it with a hammer to create sound waves. Shear waves are created by shaking it from side to side. Sounds simple, right? Wrong.
“It’s not just that the equipment is so sensitive,” said Lorenzo. “It’s that it’s also relatively delicate, extremely heavy and there’s a lot of ground to cover. We have managed to speed the process by connecting the geophones together into a long seismic snake, which we pull slowly behind our ATV.”
It’s a slow and tedious project, especially during hot Louisiana summers when the group might consist of Lorenzo and a single student. But the work is important, and knowing that problems cannot be addressed until they are identified keeps the group motivated.
“There is a direct relationship between natural soil makeup and the strength of a levee system,” said Lorenzo. “When a levee is so vital to a city’s survival, it necessitates lots of upkeep and maintenance. Our job is to get a ‘picture’ of the problem early on and define its boundaries.”
Once their seismic readings have identified the size and scope of a potentially problematic area in the levee, the information is passed to the levee board so the appropriate preventative measures can be taken.
“We’re not solving problems,” he cautioned. “We’re identifying them. It’s the first step in a complicated process.”
Since Lorenzo’s methods are comparatively quick and inexpensive, they are of immense value to the area. Natural subsidence and slumping are ongoing problems in levee systems, and maintenance, which traditionally includes rigorous visual inspections and protection of the groundcover, can be difficult and time-consuming. But in New Orleans, where the annual threat of hurricanes is never far from thought, time is a precious commodity.
“As a seismologist, simply working in Louisiana is a learning experience,” he said. “Here, sound travels faster in the air than it does in the ground. But to work in such a unique climate and geographical location and also have the opportunity to make a real impact with research is a once-in-a-lifetime opportunity.”
For more information on the LSU Department of Geology & Geophysics, visit http://www.geol.lsu.edu/.