Fault slip controlled by gouge rheology: a model for slow earthquakes

Abstract

S U M M A R YDuring 1997 several slow earthquakes have been recorded by a geodetic interferometer located beneath Gran Sasso, central Italy. The strain rise times of the events range from tens to thousands of seconds and strain amplitudes are of the order of 10 −9 . Amplitudes scale with the square root of the rise time and this suggests a diffusive behaviour of the slip propagation along the fault. In this work, we develop a model in which slip diffusion is the result of the presence of a gouge layer between fault faces, with a viscoplastic rheology. The fluid velocity field in the gouge layer diffuses in the directions of fault length and fault thickness, with different characteristic times. This model reproduces the relation between amplitude and rise time of measured strain signals. Synthetic straingrams, obtained for a horizontally layered, flat Earth and a source located a few kilometres from the instrument, are in agreement with observed signals.

InSAR observations of aseismic slip associated with an earthquake swarm in the Columbia River flood basalts

“…The depth and age of the Trinidad sediments are nearly the same as the depth and age of the CRBG interbed sediments. This model of aseismic slip is similar to viscous fault gouge models proposed to explain aseismic slip in Italy [ Bonafede et al , 1983; Amoruso et al , 2004]. We expect that much of the slow updip and along‐strike seismicity migration shown in Figure 6 is diffusion of the resultant pressure pulse similar to that observed in the 2000 Vogtland swarm [ Parotidis et al , 2003; Hainzl and Ogata , 2005].…”

Slow rupture of an aseismic fault in a seismogenic region of Central Italy

“…[8] A seismic moment time history, compatible with the observed signals, is computed following a viscoplastic-gouge model for slow slip propagation [Amoruso et al, 2002] and is nearly exponential in shape. Displacement of the monuments of the interferometer is computed for point sources in a flat layered Earth by using the AXITRA code [Cotton and Coutant, 1997].…”

Slow earthquakes and low frequency tremor along the Apennines, Italy

“…This scaling and spectral behaviour indicates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category. The observed scale dependence of rupture velocity for these events can be explained by either a constant low-stress drop model or a diffusional constant-slip model (already proposed in the 1D case by Amoruso et al 2004). This new scaling law may unify a diverse class of slow seismic events and lead to a better understand-ing of the plate subduction process and large earthquake generation, but different models have also been proposed (Schwartz et al, 2007).…”