Tulane geoscientist helping researchers understand rare north Louisiana earthquakes

A Tulane University geoscientist has installed seismic monitoring equipment in northwest Louisiana following an unusual series of earthquakes in the Coushatta area of Red River and DeSoto Parishes, including the largest inland earthquake recorded in state history.

Since December, at least 14 earthquakes with a magnitude greater than 2.5 have been detected in north Louisiana, according to the U.S. Geological Survey. Smaller earthquakes were missed owing to large detection instrument spacings. The most significant occurred on March 5 near Coushatta and measured magnitude 4.9. Several additional earthquakes, including one measuring magnitude 4.4, were recorded March 9 within minutes of one another.

Cynthia Ebinger, the Marshall-Heape Chair in Geology in Tulane University's School of Science and Engineering, traveled to the region to deploy instruments that will help scientists better understand the source of the seismic activity.

- Cynthia Ebinger, School of Science and Engineering

"Scientists at the U.S. Geological Survey have used new data from instruments we recently installed to relocate the earthquakes," Ebinger said. "They are occurring in crystalline rocks much deeper than any of the industrial activity and along an ancient fault line."

Five additional earthquakes were recorded in the most recent sequence, and scientists expect the activity may continue.

The earthquake cluster has drawn attention in part because it aligns with the Haynesville-Bossier Shale formation, one of the largest natural gas production regions in the United States. Scientists have documented cases in other states where wastewater injection from oil and gas production can trigger earthquakes under certain geological conditions.

"Throughout the U.S. and elsewhere, we've learned that injecting wastewater produced during oil and gas extraction back into deep wells can cause earthquakes," Ebinger said. "Over time, the added weight of the injected water can put pressure on ancient faults and cause them to reactivate."

Still, researchers say determining the exact cause of the Louisiana earthquakes will require further analysis.

"The question of natural earthquakes versus human-induced earthquakes does not have a simple yes-or-no answer," Ebinger said. "But the increase in the number and magnitude of earthquakes over the past 15 years since we've had local monitoring suggests something is changing."

Ebinger leads Tulane's Geophysics and Active Tectonics Research (GATR) Laboratory, which studies the forces that deform Earth's crust and shape tectonic plate boundaries. Her research focuses on tectonic and volcanic processes in continental rifts and passive margins and their implications for earthquake hazards, energy resources and the evolution of Earth's plates.

The monitoring effort builds on previous work by Tulane and other researchers. Between 2019 and 2022, a team of geoscientists installed seismometers across parts of the state to establish a baseline for earthquake activity and better understand Louisiana's subsurface structure.

"Those instruments measure vertical and horizontal ground motions so small they can't be detected at the surface," Ebinger said. "Our goal was to establish a baseline for earthquake activity to inform state planners and to better understand Louisiana's subsurface structure."

That monitoring revealed clusters of small earthquakes and suggested activity in some areas was increasing over time. A new Tulane array of instruments installed in October captured the recent earthquakes, providing researchers with detailed data about the sequence.

The instruments measure earthquake locations, depths, directions of fault movement and ground acceleration - the shaking people at the surface may feel.

The monitoring network is connected to the U.S. Geological Survey's National Earthquake Information Center, which allows data from Louisiana to be analyzed alongside seismic information from across the country.

"Owing to the quick USGS response, Tulane data are now monitored remotely and automatically transmitted to a national automated system that collates and uses information from Texas, Arkansas, Mississippi and throughout the United States," Ebinger said. "That allows scientists to quickly analyze earthquake locations and ground shaking and then combine those results with older data to visualize the subsurface faults."

Research students are using aftershocks and other measurements to better understand the fault systems responsible for the earthquakes and to improve hazard assessments.

"We are using aftershocks to map out the fault plane or multiple fault planes," Ebinger said. "We're also measuring ground acceleration so engineers can use that information for hazard zoning and improved ground-shaking maps."

For residents, the key factors that determine risk are the size of earthquakes and how strongly the ground shakes.

"Earthquakes happen all the time," Ebinger said. "The important factors are the magnitude of the earthquake and the ground acceleration it produces. Fortunately, we now have instruments in place to collect that critical information."