Article,
Probability of a given-magnitude earthquake induced by a fluid injection
Geophysical Research Letters, 34 (22): L22314+ (Nov 27, 2007)
DOI: 10.1029/2007GL031615
Abstract
Fluid injections in geothermic and hydrocarbon reservoirs induce small
earthquakes (-3 < M < 2). Occasionally, however, earthquakes with
larger magnitudes (M \~ 4) occur. We investigate magnitude distributions
and show that for a constant injection pressure the probability to
induce an earthquake with a magnitude larger than a given value increases
with injection time corresponding to a bi-logarithmical law with
a proportionality coefficient close to one. We find that the process
of pressure diffusion in a poroelastic medium with randomly distributed
sub-critical cracks obeying a Gutenberg-Richter relation well explains
our observations. The magnitude distribution is mainly inherited
from the statistics of pre-existing fracture systems. The number
of earthquakes greater than a given magnitude also increases with
the strength of the injection source and the tectonic activity of
the injection site. Our formulation provides a way to estimate expected
magnitudes of induced earthquakes. It can be used to avoid significant
earthquakes by correspondingly planning fluid injections.
