CAREER: Fluid-driven Deformation in Underground Salt Caverns and Wastewater Injection Sites

Earthquakes caused by human activities - such as wastewater injection, geothermal extraction, and underground carbon storage - tend to be small. With notable exceptions, such as the 2016 Pawnee Oklahoma earthquake, these earthquakes often hide below cultural seismic noise. This presents a challenge for both monitoring and detecting them.

It impedes studying their causes and assessing corresponding hazards. In the U.S., regions that have been free of earthquakes are now pressed to find reliable ways to address earthquake risks. Research on induced seismicity has expanded in the last decade; but studies have mostly focused on known hotspots in Arkansas, Colorado, Kansas, Ohio, Oklahoma, Texas, and Wyoming.

Yet, it is expected that induced earthquakes will occur in regions which did not face this threat before. It is, thus, critical to monitor and catalog the natural baseline seismicity in these regions before induced earthquakes happen; this allows detecting when seismicity rises above background levels and assessing the risks. One such location is the State of Louisiana.

It is currently at the threshold of implementing CO2 storage and increased oil and gas exploration. However, Louisiana lacks a statewide seismic network and monitoring program to assess seismic hazards. Here, the researchers integrate research and education in the aim to understand human-driven changes in Louisiana.

Deploying geophysical and seismic instruments, they study three key locations related to human activities and resources. These locations are: 1) in northwest Louisiana, a region with high wastewater injection rates; 2) an underground storage cavern, where ground motions have been reported and nearby sinkhole formation has occurred (with precursor earthquake activity); 3) across the Baton Rouge fault that also acts as a patchy barrier for salt water.

Integrating multiple data types, the team gradually unveils the new threats Louisiana is facing. The project also provides support to an early-career female scientist, one postdoctoral researcher, and graduate and undergraduate students. It includes the establishment of student-focused regional workshops, notably on Machine Learning applications in Geophysics.

The project also fosters broadening participation in science, e.g., by involving students from the Southern University at Baton Rouge, a Historically Black University. This project is jointly funded by the Geophysics Program and the Established Program to Stimulate Competitive Research (EPSCoR).

The project is an integrated geophysical study of multiple data types. It produces a detailed characterization of fluid-involved crustal deformation. The results have important societal implications for energy corridors undergoing rapid human change.

They characterize the largely unknown deformation of the subsurface beneath a region that supplies a major part of the U.S. oil and gas. This region is challenged by ongoing subsidence, groundwater salinization, and increasing seismicity associated with wastewater disposal from hydrocarbon exploration. The seismic arrays installed at three key locations not only measure the levels of seismicity, but also constrain the poorly understood aseismic deformation.

Indeed, innovative techniques are applied, such as Fracture Seismic imaging, that image fluid-filled networks by using harmonic resonances within fractures. Seismological methods are integrated with GPS data analysis to understand the deformation budget of the crust. This approach provides insight into the pattern of crustal deformation driven by human activities.

One expected outcome is the first high-resolution mapping of fracture geometry and connectivity, subsurface material properties, and seismic and aseismic deformation in the region. The study, thus, has far-reaching impacts on our general understanding of fluid-driven processes and their effects on crustal deformation.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.