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How water injection at depth influences faults and their potential to generate earthquakes ?

In a new study published in Science Advances, an international team of researchers (Cappa, Scuderi and co-authors) has developed unique laboratory and in-situ experiments to inform a hydromechanical model aiming at understanding how a fault responds to known fluid pressure perturbations. The results shed light on the mechanics of fault slip, seismic and aseismic. The paper is published in Science Advances(March, 2019).


Publication : 14/03/2019
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Earthquakes are among the most catastrophic and least predictable of all natural hazards. Since the 1960s, the exponential increase of energy-demand has stimulated the use of new techniques for the extraction of oil and gas. However, the drawback of the massive extraction of oil is the underground reinjection of energy-coproduced wastewater. Injecting fluids underground can cause earthquakes if those fluids find their way into fault zones that are ready to slip seismically. But understanding the inner workings of fluid-filled faults is challenging because researchers have been limited in how close they can get to study them. This represents a major barrier to unveiling how faults slip when driven by fluid pressure, and a serious limitation in explaining many observations of natural and induced earthquakes, and other slip processes.

A very promising observation

Combining exceptionally well controlled experiments with computer simulations of fluid injection and rupture on a fault, the authors explain how fault slip is induced by fluid pressure in a natural fault. A very promising observation is that the deformation processes at the decametric scale are quantitatively consistent with fault slip and frictional properties measured in the laboratory at the centimetric scale. The study shows for the first time that fluid injection experiments on laboratory and natural faults reveal a similar phase of fault opening and accelerating creep up to the main instability,suggesting a common underlying mechanism that is scale-independent. 

Cappa, Scuderi and co-authors have thenused the results from laboratory experiments to inform a three-dimensional hydromechanical model to test if these properties are consistent with the in-situ observations and shed light on the origin of aseismic deformation and seismicity. The model predictions are consistent with observed fault slip at field scale. The research team finds that aseismic slip initiates within the pressurized region, however, earthquake nucleation is suppressed because the size of the fluid pressurized region remains small compared to the area that would be required to nucleate an earthquake. Nonetheless, sustained aseismic creep can accumulate shear stress beyond the pressure front favoring seismicity in nearby prone areas.

To understand fault mechanics

This new work is not only a first-order advance in filling the gap between laboratory and field scale experiments to understand fault mechanics and their hydromechanical properties, but it also provides a framework to understand how coupling between fault slip and fluid flow promotes stable fault creep during fluid injection, and how seismicity can be triggered indirectly by the injection due to loading of non-pressurized fault patches by aseismic creep.

Finally, this study suggests that bringing together laboratory and field experiments with computer simulations allow to make important progress in understanding fault mechanics resulting from fluid injection, and will inform theories of how fluids at great depths cause fault motions and their potential to generate earthquakes.

The paper is published in Science Advances (March, 2019) and is titled "Stabilization of fault slip by fluid injection in the laboratory and in-situ"by Frédéric Cappa of the Université Côte d'Azur in Nice and Institut Universitaire de France in Paris, Marco Maria Scuderi and Cristiano Collettini of La Sapienza University in Roma, Yves Guglielmi of LBNL in Berkeley, and Jean-Philippe Avouac of Caltech in Pasadena. Funding came from the Agence Nationale de la Recherche (ANR HYDROSEIS, grant No. ANR-13-JS06-0004-01, andIDEX UCA JEDI, grant No. ANR-15-IDEX-01) in France, the MarieSklodowska-Curie(grant n° 656676)and the European Research Council (ERC GLASS, grant n° 259256) in Italy.

 

 

Figure Cappa

Figure: Experiments of fault deformation induced by fluid injection in the lab and in-situ.Fault opening and accelerating creep occur in the pressurized area (in blue), whereas, at its limit and beyond, critical amount of accumulated shear stress (in red) caused by propagating aseismic creep can trigger earthquakes.

Credit: Frédéric Cappa, Université Côte d’Azur, CNRS, Observatoire de la Côte d’Azur, IRD, Géoazur, France; Marco Maria Scuderi, La Sapienza University, Italy.

Contacts :

Frédéric Cappa, Université Côte d’Azur, CNRS, Observatoire de la Côte d’Azur, IRD, Géoazur, France. Email : cappa@geoazur.unice.frand Frederic.CAPPA@univ-cotedazur.fr

Marco Maria Scuderi, La Sapienza University, Italy. Email : marco.scuderi@uniroma1.it

Cristiano Collettini, La Sapienza University, Italy. Email :cristiano.collettini@uniroma1.it

Yves Guglielmi, Lawrence Berkeley National Laboratory, USA. Email : yguglielmi@lbl.gov

Jean-Philippe Avouac, California Institute of Technology, USA. Email : avouac@gps.caltech.edu

 

Reference :Cappa, F., Scuderi M.M., Collettini C., Guglielmi Y., Avouac J.P. (2019), Stabilization of fault slip by fluid injection in the laboratory and in situ, Sci. Adv.5, eaau4065, doi: 10.1126/sciadv.aau4065