Meter-scale stress heterogeneities and stress redistribution drive complex fracture slip and fracture growth during a hydraulic stimulation experiment
Abstract
We investigated the induced seismicity, source mechanisms and mechanical responses of a decameter-scale hydraulic stimulation of a pre-existing shear zone in crystalline rock, at the Grimsel Test Site, Switzerland. The analysis reveals the meter-scale complexity of hydraulic stimulation, which remains hidden at the reservoir-scale. High earthquake location accuracy allowed the separation of four distinct clusters, of which three were attributed to the stimulation of fractures in the damage zone of the shear zone. The source mechanism of the larger-magnitude seismicity varied by cluster, and suggests a heterogeneous stress field already prevailing before stimulation, which is further modified during stimulation. In the course of the experiment, stress redistribution led to the aseismic initiation of a tensile-dominated fracture, which induced seismicity in the fourth of the identified seismic clusters. The streaky pattern of seismicity separated by zones without seismicity suggests fluid flow in conduits along existing fracture planes. The observed sub-meter scale complexity questions the forecasting ability of induced seismic hazard at the reservoir scale from small-scale experiments. Show more
Publication status
publishedExternal links
Journal / series
Geophysical Journal InternationalVolume
Pages / Article No.
Publisher
Oxford University PressSubject
Induced seismicity; Earthquake source observations; Creep and deformation; Fracture and flow; Permeability and porosityOrganisational unit
02282 - SCCER-SoE / SCCER-SoE03476 - Giardini, Domenico / Giardini, Domenico
02818 - Schweiz. Erdbebendienst (SED) / Swiss Seismological Service (SED)
Funding
ETH-35 16-1 - Towards an improved understanding of anthropogenic earthquakes: Exploiting the Grimsel controlled fault slip experiment (ETHZ)
169178 - A decameter-scale reservoir stimulation experiment - the full hydro-mechanical response of a fault zone to high-pressure water injection (SNF)
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