[J06-1] The spectrum of fault-zone deformation processes (from slow slip to earthquake) I

[J06-1-06] Laboratory observations of slow stick slip: implications for slow earthquakes and the spectrum of fault slip behavior

^○Marco Maria Scuderi¹, Elisa Tinti², Cristiano Collettini¹ (1.La Sapienza University of Rome, 2.Istituto Nazionale di Geofisica e Vulcanologia (INGV) Rome)

invited

Seismic and geodetic observations show that fault slip occurs via a spectrum of behaviors that include slow earthquakes and tectonic tremor. These phenomena have been observed in a variety of tectonic environments worldwide, however the underlying processes are poorly understood. Here we show results from lab experiments on simulated fault gouge. We used the double direct shear configuration and varied the loading system stiffness (k) to produce the full spectrum of stick-slip behaviors, with durations ranging from 10-3 to 1 second. We measured frictional rheology and elastic wave properties throughout the stick-slip cycle for slow and fast events. At the end of the experiments we also collected the resulting fault zone microstructure. When the loading stiffness is greater than the fault zone critical rheologic stiffness (kc) we observe stable frictional sliding. For k≈kc we document emergent slow-slip events from steady shear. When kc>k we observe audible stick-slip. Stick slip stress drop and event duration vary systematically as a function of the ratio k/kc. For both slow- and fast- slip events, P-wave velocity (Vp) begins to decrease prior to the stress drop and the maximum slip velocity during failure coincides with the largest drop in Vp. Microstructural observations show that with accumulated strain, deformation localizes along sharp shear planes consisting of nanometric grains, which favor the development of frictional instabilities. Once this fabric is established, fault fabric does not change significantly with slip velocity, and fault slip behaviour is mainly controlled by the interplay between fault rheological properties and the stiffness of the loading system. As applied to tectonic faults, our results suggest that a single fault segment can experience a spectrum of fault slip behaviour depending on the evolution of fault rock frictional properties and elastic conditions of the loading system.