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Description
Human-induced earthquakes, triggered by fluid injection or extraction, have become a growing concern in energy-related activities. These events occur when fluid pressure changes destabilize faults, leading to rupture that propagates away from the hypocenter as two crack tips. While theoretically the rupture should be symmetric, many large earthquakes exhibit strong asymmetry, propagating predominantly along one direction. Understanding this behavior is key to assess seismic hazard related to fluid injection in underground formations.
In this work, we study how poroelastic coupling influences rupture directivity in earthquakes induced by fluid injection. Using fully coupled hydromechanical simulations of poroelastic media with rate-and-state faults, along with analytical solutions, we conduct a dimensionless analysis to study the propagation patterns. We quantify the degree of relative symmetry using two parameters: the proportion unilateral rupture and the directivity ratio established by Dempsey & Suckale (2016).
Our results show that rupture directivity varies significantly with the injection distance and the initial fault stresses, and range from nearly symmetric to strongly unilateral. We find that rupture asymmetry is driven by the undrained effect caused by coseismic slip, and the pressure distribution prior to the earthquake. Higher confinement stresses and injection points closer to the fault favor symmetric ruptures. Conversely, lower tectonic stresses and farther injection distances promote asymmetric ruptures. We also find that fault permeability anisotropy further enhances the rupture asymmetry.
These findings help clarify how poroelastic effects govern rupture behavior in injection-induced earthquakes, offering a feasible explanation for the frequent occurrence of almost-unilateral ruptures. This knowledge is valuable for predicting the preferred direction of an induced earthquake based on injection location and rock confinement, which is valuable for underground storage operations in the energy industry.
Acknowledgements
This research was supported by the Spanish Agencia Estatal de Investigación and the Ministerio de Ciencia, Innovación y Universidades (10.13039/501100011033) and by “EDFR/EU” through grant HydroPore II (PID2022-137652NB-C43).
| References | Rupture directivity and poroelastic coupling in earthquakes induced by fluid injection (2025); S. Andrés, D. Santillán, J.C. Mosquera & L. Cueto-Felgueroso; Eng. Fract. Mech., 322, 111123, doi.org/10.1016/j.engfracmech.2025.111123 Impact of fault permeability anisotropy on the nucleation and rupture of injection-induced earthquakes (2026); D. Santillán, R. Juanes, S. Andrés & L. Cueto-Felgueroso; Comput. Geotech., 189, 107613, doi.org/10.1016/j.compgeo.2025.107613 Collective properties of injection-induced earthquake sequences: 1. Model description and directivity bias (2016); D. Dempsey and J. Suckale; J. Geophys. Res. Solid Earth, 121, 3609-3637, doi.org/10.1002/2015JB012550 |
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| Country | Spain |
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