Susceptibility of microseismic triggering to small sinusoidal stress
perturbations at the laboratory scale
Abstract
Small transient stress perturbations are prone to trigger
(micro)seismicity. In the Earth’s crust, these stress perturbations can
be caused by various sources such as the passage of seismic waves,
forcing by tides, or hydrological seasonal loads. A better understanding
of the dynamic of earthquake triggering by stress perturbations is
essential in order to improve our understanding of earthquake physics
and our consideration of seismic hazard. Here, we study an experimental
sandstone-gouge-filled fault system undergoing combined far field
loading and periodic stress perturbations (of variable amplitude and
frequency) at crustal pressure conditions. Microseismicity — in the
form of acoustic emissions (AE) — strains, and stresses, are
continuously recorded in order to study the response of microseismicity
as a function of loading rate, amplitude and frequency of a periodic
stress perturbation. The observed AE distributions do not follow the
predictions of a Coulomb failure model taking into account both constant
loading and oscillation-induced strain rates. A susceptibility of the
system’s AE response to confinement pressure amplitude is estimated,
which showcases a linear relation between confinement pressure amplitude
and the AE response amplitude, observations which agree with recent
higher frequency experimental results on dynamic triggering. The
magnitude-frequency distribution of AEs is also computed. Oscillations
in Gutenberg-Richter b-value are observed in experiment catalogues but
are not quantified. Our experiments may help complement our
understanding of the influence of low inertia stress phenomena on the
distribution of seismicity, such as observations of dynamic triggering
and seismicity modulation by solid earth tides or seasonal loading.