Danre P., De Barros L., Cappa F., Ampuero Jean-Paul. (2022). Prevalence of aseismic slip linking fluid injection to natural and anthropogenic seismic swarms. Journal of Geophysical Research : Solid Earth, 127 (12), e2022JB025571 [16 p.]. ISSN 2169-9313.
Auteurs
Danre P., De Barros L., Cappa F., Ampuero Jean-Paul
Source
Journal of Geophysical Research : Solid Earth, 2022,
127 (12), e2022JB025571 [16 p.] ISSN 2169-9313
Anthropogenic fluid injections at depth induce seismicity which is generally organized as swarms, clustered in time and space, with moderate magnitudes. Earthquake swarms also occur in various geological contexts such as subduction zones, mountain ranges, volcanic, and geothermal areas. While some similarities between anthropogenic and natural swarms have already been observed, whether they are driven by the same mechanism, or by different factors, is still an open question. Fluid pressure diffusion or aseismic deformation processes are often proposed to explain observations of hypocenters migration during swarms, while recent models suggest that swarm seismicity is rather triggered by fluid-induced aseismic fault slip. Here, using a global compilation of 22 natural and anthropogenic swarms, we observe that duration, migration velocity, and total moment scale similarly for all swarms. This supports a common driving process for both natural and induced swarms. The scaling relations are similar to those found for slow slip events. These observations highlight the prevalence of fluid-induced aseismic slip as main driver of earthquakes migration during swarms. After quantifying aseismic slip released in the swarms, we propose an approach to estimate the seismic-to-total moment ratio, which we then compare to a theoretical estimation that depends on the migration velocity of the swarm and the effective stress drop. Our findings lead to a generic explanation of the process driving earthquake swarms that might open new possibilities to monitor seismic swarms. Plain Language Summary Earthquake swarms are a particular type of seismic activity, during which a sequence of many earthquakes occurs without being initiated by a larger one. Swarms can be induced by anthropic hydraulic injections at depth, like during geothermal power exploitation and massive storage of diverse fluids (i.e., wastewater, CO2) in porous reservoir formations. Natural earthquake swarms are also observed in a large variety of geological contexts. Previous works showed that natural and injection-induced swarms share some similarities, like the migration of seismicity. However, their underlying processes remain unclear. Here, we explain the observed similarities in both types of swarms by a model in which earthquakes are triggered by the propagation of an aseismic slip transient, which in turn is induced by pressurized fluid circulation. This model reconciles a suite of independent observations made over different length and time scales and provides a generic explanation of the driving process for the migration of earthquake swarms.
