Triggering of Seismicity by Pore-pressure Perturbations: Permeability-related Signatures of the Phenomenon

Abstract

We consider various cases of seismicity, induced by artificial fluid injections in boreholes. Like many other authors, we support the hypothesis that to a large extent the triggering of this seismicity is caused by a diffusive process of the pore pressure relaxation in porous (or fractured), saturated rocks. We show that if this hypothesis is correct, then the spatio-temporal distributions of the seismic events must have several specific features related to the effective permeability of the rock. As a rule the fluid injectioninduced seismicity obeys such features. These features can be indications of the diffusive and even hydraulic nature of the seismicity triggering process.From this point of view we analyze the spatio-temporal distribution of the late aftershocks of the Antofagasta (northern Chile) 1995 earthquake. These aftershocks were concentrated in a plane, an approximately 3 km-thick spatial zone. This thin seismogenic layer is a part of the South American subduction zone. The time-distance distribution of the aftershocks along this layer indicates that they could be triggered by a diffusion-like process. Possibly, such a process is the relaxation of the pressure perturbation caused in the pore fluid by the main Antofagasta event. We estimated the permeability required to explain the spatio-temporal distribution of the aftershocks by such a triggering mechanism. The obtained value, 60 mD, is very large. However, it is realistic for a long-time existing and large-scale fault zone.

A new method to estimate location and slip of simulated rock failure events

“…A general stress drop in the specimen due to fluid injection results in a non-critically stressed specimen at later times. This behavior observed in the simulation agrees very well with the results from laboratory experiments and from field observations (cf Stanchits et al, 2011;Shapiro et al, 2003)…”

“…Field observations show a similar correlation between (micro-) seismic events and estimated fluid front (e.g. Shapiro et al, 2003).…”

“…In experiments, the fluid front is estimated from the injected volume and fitting the solution of a linear diffusion equations to the AE Stanchits et al, 2011 from the occurrence of seismic events (e.g. Parotidis et al, 2003;Shapiro et al, 2003). In our numerical simulation we determine the fluid front from the saturation equation.…”

From velocity and attenuation tomography to rock physical modeling: Inferences on fluid‐driven earthquake processes at the Irpinia fault system in southern Italy

“…Therefore, we suggest that the dominant mechanism triggering the microseismicity at the Irpinia fault zone is the pore pressure increment, induced by fluid diffusion in the host rock medium [Dvorkin et al, 2000;Shapiro et al, 2003]. In fact, the presence of fluids inside the fault gauge may enhance seismicity due to lubrication mechanisms and by an increase of pore pressure in the medium embedding the faults.…”

Evidence for triggering of the Vogtland swarms 2000 by pore pressure diffusion

“…Besides for borehole fluid injections, pore pressure diffusion (described by either the coupled or uncoupled equations) as triggering mechanism has been proposed for various case studies: e.g., for reservoir (large artificial lakes) induced seismicity [ Howells , 1974; Talwani , 2000], for water table changes in large basins connected with microseismicity [ Costain and Bollinger , 1991; Lee and Wolf , 1998], for volcanic seismicity in Italy [ Saccorotti et al , 2002], and for aftershocks of large earthquakes [ Nur and Booker , 1972; Bosl and Nur , 2002; Jonsson et al , 2003; Shapiro et al , 2003; Miller et al , 2004; Koerner et al , 2004]. …”