Control of Seismicity Migration in Earthquake Swarms by Injected Fluid Volume and Aseismic Crack Propagation

Abstract

The evolution of fluid injection‐induced seismicity, generally characterized through the number of events or their seismic moment, depends on, among other factors, the injected fluid volume. Migration of seismicity is observed during those sequences and might be caused by a range of mechanisms: fluid pressure diffusion, fluid‐induced aseismic slip propagating along a stimulated fault, interactions between earthquakes. Recent theoretical and observational developments underline the important effect on seismicity migration of structural parameters, like fault criticality, or injection parameters, like flow rate or pressurization rate. Here, we analyze two well‐studied injection‐induced seismic sequences at the Soultz‐sous‐Fôret and Basel geothermal sites, and find that the evolution of the seismicity front distance primarily depends on the injected fluid volume. Based on a fracture mechanics model, we develop new equations relating seismicity migration to injected fluid volume and frictional and structural properties of the fault. We find that the propagation of a fluid‐induced aseismic slip front along the stimulated fault, triggering seismicity, explains well the observations made on the two sequences. This model allows us to constrain parameters describing the seismicity front evolution and explains the diversity of migration patterns observed in injection‐induced and natural earthquake swarms.

Pressure dependence of permeability in cracked rocks: experimental evidence of non-linear pore-pressure gradients from local measurements

“…It was generally considered during fluid injection into the subsurface that the front of microseismicity follows closely the pore pressure diffusion front (Shapiro & Dinske, 2009). In the last years, some publications have supported the view that the micro-seismicity front is more likely to be related to the propagation of a slow slip front, while the pore pressure diffusion front lags behind (Bhattacharya & Viesca, 2019;Danré et al, 2024;Eyre et al, 2019;Garagash et al, 2017;Guglielmi et al, 2015). To mitigate potential geological hazards associated with fluid pressure, a better understanding of the pore pressure diffusion and distribution laws in crystalline and/or low porosity/tight rocks is important.…”