FW: [Report] Seismicity triggered by fluid injection–induced aseismic slip

· PERSPECTIVE
SEISMOLOGY
Earthquakes induced by fluid injections
1. Francois H. Cornet<http://www.sciencemag.org/search?author1=Francois+H.+Cornet&sortspec=date&submit=Submit>
+<http://www.sciencemag.org/content/348/6240/1204.short>Author Affiliations
1. Institut de Physique du Globe de Strasbourg, 5 Rue René Descartes, F 67084 Strasbourg Cedex, France.
1. E-mail: francois.cornet@unistra.fr<mailto:francois.cornet@unistra.fr>
In the early 1960s, the U.S. Army unintentionally triggered some seismic activity by injecting waste fluids into the basement rock beneath the Rocky Mountain Arsenal, near Denver, Colorado (1). It is now recognized that an increase in the pressure applied by the fluids that fill fractures and faults at depth balances progressively the normal stress exerted through the rock on these fractures but leaves the shear stress supported by these surfaces unchanged. According to friction laws, when the fluid pressure gets too high and the effective normal stress gets too low, shear motion starts. This motion is generally considered to be mostly seismogenic, that is, to be the source of earthquakes that may reach in some localities magnitudes larger than 5, or even 6, as was observed upon filling the Koyna Dam in India in the early 1960s. Today, the phenomenon of fluid-induced seismicity has become a societal concern wherever injection of large quantity of fluids at depth is involved. On page 1224 of this issue, however, Guglielmi et al. (2) report that water injected in a natural fault at a depth of 282 m generates nonseismic motion. That is, the ground displacements take place at slow velocities (≈4 µm/s), with only very small microseismic activity.
Read the Full Text<http://www.sciencemag.org/content/348/6240/1204.full>


INDUCED SEISMICITY
How to observe fault injections in real time
1. Brent Grocholski<http://www.sciencemag.org/search?author1=Brent+Grocholski&sortspec=date&submit=Submit>
Faults in the ground are known to deform in response to procedures such as wastewater injection that change the pore pressure. Guglielmi et al. took a crack at monitoring this process in real time with a controlled fluid injection into an inactive fault (see the Perspective by Cornet). Reactivating the dead fault induced aseismic slip, which triggered small earthquakes. These observations can inform models of how friction is related to slip rate. The technique can also be applied to field-scale monitoring of seismicity-inducing wastewater injections.


Feed: Science: Current Issue
Posted on: Friday, 12 June 2015 10:00 AM
Author: Yves Guglielmi
Subject: [Report] Seismicity triggered by fluid injection–induced aseismic slip

Anthropogenic fluid injections are known to induce earthquakes. The mechanisms involved are poorly understood, and our ability to assess the seismic hazard associated with geothermal energy or unconventional hydrocarbon production remains limited. We directly measure fault slip and seismicity induced by fluid injection into a natural fault. We observe highly dilatant and slow [~4 micrometers per second (μm/s)] aseismic slip associated with a 20-fold increase of permeability, which transitions to faster slip (~10 μm/s) associated with reduced dilatancy and micro-earthquakes. Most aseismic slip occurs within the fluid-pressurized zone and obeys a rate-strengthening friction law μ=0.67+0.045ln(vv0) with v0 = 0.1 μm/s. Fluid injection primarily triggers aseismic slip in this experiment, with micro-earthquakes being an indirect effect mediated by aseismic creep. Authors: Yves Guglielmi, Frédéric Cappa, Jean-Philippe Avouac, Pierre Henry, Derek Elsworth


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