Earthquake fault dynamics: Insights from laboratory experiments

2011

Earthquakes have long been recognized as resulting from a stick–slip frictional instability. The development of a full constitutive law for rock friction now shows that the gamut of earthquake phenomena—seismogenesis and seismic coupling, pre-and post-seismic phenomena, and the insensitivity of earthquakes to stress transients—all appear as manifestations of the richness of this friction law.

Rendiconti Lincei-scienze Fisiche E Naturali, 2010

Despite considerable effort over the past several decades, the mechanics of earthquake rupture remains largely unknown. Moderate- to large-magnitude earthquakes nucleate at 7–15 km depth and most information is retrieved from seismology, but information related to the physico-chemical processes active during rupture propagation is below the resolution of this method. An alternative approach includes the investigation of exhumed faults, such as those described here from the Adamello Massif (Italian Alps), and the use of rock deformation apparatus capable of reproducing earthquake deformation conditions in the laboratory. The analysis of field and microstructural/mineralogical/geochemical data retrieved from the large glacier-polished exposures of the Adamello (Gole Larghe Fault) provides information on earthquake source parameters, including the coseismic slip, the rupture directivity and velocity, the dynamic friction and earthquake energy budgets. Some of this information (e.g., the evolution of the friction coefficient with slip) can be tested in the laboratory with the recently installed Slow to HIgh Velocity Apparatus (SHIVA). SHIVA uses two brushless engines (max power 280 kW) and an air actuator in a rotary shear configuration (nominally infinite displacement) to slide solid or hollow rock cylinders (40/50 mm int/ext diameter) at: (1) slip rates ranging from 10 μm s−1 up to 9 m s−1; (2) accelerations up to 80 m s−2; and (3) normal stresses up to 50 MPa. In comparison to existing high-speed friction machines, this apparatus extends the range of sliding velocities, normal stresses and sample size. In particular, SHIVA has been specifically designed to reproduce slip velocities and accelerations that occur during earthquakes. The characterization of rock frictional behavior under these conditions, plus the comparison with natural fault products, is expected to provide important insights into the mechanics of earthquakes.

Pure and Applied Geophysics PAGEOPH, 1986

Science, 2006

Melt produced by friction during earthquakes may act either as a coseismic fault lubricant or as a viscous brake. Here we estimate the dynamic shear resistance (tauf) in the presence of friction-induced melts from both exhumed faults and high-velocity (1.28 meters per second) frictional experiments. Exhumed faults within granitoids (tonalites) indicate low tauf at 10 kilometers in depth. Friction experiments

Journal of Geophysical Research, 2000

We investigate the impact of variations in the friction and geometry on models of fault dynamics. We focus primarily on a three-dimensional continuum model with scalar displacements. Slip occurs on an embedded two-dimensional planar interface. Friction is characterized by a two-parameter rate and state law, incorporating a characteristic length for weakening, a characteristic time for healing, and a velocity-weakening steady state. As the friction parameters are varied, there is a crossover from narrow, self-healing slip pulses to crack-like solutions that heal in response to edge effects. For repeated ruptures the crack-like regime exhibits periodic or aperiodic systemwide events. The self-healing regime exhibits dynamical complexity and a broad distribution of rupture areas. The behavior can also change from periodicity or quasi-periodicity to dynamical complexity as the total fault size or the length-to-width ratio is increased. Our results for the continuum model agree qualitatively with analogous results obtained for a one-dimensional Burridõe-Knopoff model in which radiation effects are approximated by viscous dissipation. context of a three-dimensional continuum model and a one-dimensional Burridge-Knopoff model. In our studies, dynamical complexity refers to observations of a

2011

Fault lubrication and earthquake propagation in thermally unstable rocks Email alerting services articles cite this article to receive free e-mail alerts when new www.gsapubs.org/cgi/alerts click Subscribe to subscribe to Geology www.gsapubs.org/subscriptions/ click Permission request to contact GSA http://www.geosociety.org/pubs/copyrt.htm#gsa click official positions of the Society. citizenship, gender, religion, or political viewpoint. Opinions presented in this publication do not reflect presentation of diverse opinions and positions by scientists worldwide, regardless of their race, includes a reference to the article's full citation. GSA provides this and other forums for the the abstracts only of their articles on their own or their organization's Web site providing the posting to further education and science. This file may not be posted to any Web site, but authors may post works and to make unlimited copies of items in GSA's journals for noncommercial use in classrooms requests to GSA, to use a single figure, a single table, and/or a brief paragraph of text in subsequent their employment. Individual scientists are hereby granted permission, without fees or further

2008

A number of recent studies suggest that dynamic slip on earthquake faults may trigger consistent frictional weakening or lubrication, a feature enhanced at relatively high slip rates (of the order of 1 m/s). Here we present the first clear seismological evidence of a progressive fault weakening under dynamic earthquake slip. The weakening increases with the estimated amount of heat rate (and resulting temperature increase) generated on the fault by frictional heating, indicating the presence of some thermally-activated weakening processes. The observed effect seems stronger for less mature slip systems, suggesting that confinement of heat or fluids is less effective on faults which possess a wider damage zone.

Journal of Geophysical Research, 2008

Frictional properties of natural kaolinite-bearing gouge samples from the Median Tectonic Line (SW Japan) have been studied using a high-velocity rotary shear apparatus, and deformed samples have been observed with optical and electron (scanning and transmission) microscopy. For a slip velocity of 1 m s À1 and normal stresses from 0.3 to 1.3 MPa, a dramatic slip-weakening behavior was observed. X-ray diffraction analysis of deformed samples and additional high-velocity friction experiments on pure kaolinite indicate kaolinite dehydration during slip. The critical slip-weakening distance D c is of the order of 1 to 10 m. These values are extrapolated to higher normal stresses, assuming that D c is rather a thermal parameter than a parameter related to a true characteristic length. The calculation shows that dimensionally, D c / 1/s n 2 , where s n is the normal stress applied on the fault. The inferred D c values range from a few centimeters at 10 MPa normal stress to a few hundreds of microns at 100 MPa normal stress. Microscopic observations show partial amorphization and dramatic grain size reduction (down to the nanometer scale) localized in a narrow zone of about 1 to 10 mm thickness. Fracture energy G c is calculated from the mechanical curves and compared to surface energy due to grain size reduction, and energies of mineralogic transformations. We show that most of the fracture energy is either converted into heat or radiated energy. The geophysical consequences of thermal dehydration of bonded water during seismic slip are then commented in the light of mineralogical and poromechanical data of several fault zones, which tend to show that this phenomenon has to be taken into account in most of subsurface faults and in hydrous rocks of subducted oceanic crust.

Journal of Geophysical Research, 1996

The coefficient of friction and velocity dependence of friction of initially bare surfaces and 1-mm-thick simulated fault gouges (< 90 gm) of Westerly granite were determined as a function of displacement to >400 mm at 25øC and 25 MPa normal stress. Steady state negative friction velocity dependence and a steady state fault zone microstructure are achieved after-18 mm displacement, and an approximately constant strength is reached after a few tens of millimeters of sliding on initially bare surfaces. Simulated fault gouges show a large but systematic variation of friction, velocity dependence of friction, dilatancy, and degree of localization with displacement. At short displacement (<10 mm), simulated gouge is strong, velocity strengthening and changes in sliding velocity are accompanied by relatively large changes in dilatancy rate. With continued displacement, simulated gouges become progressively weaker and less velocity strengthening, the velocity dependence of dilatancy rate decreases, and deformation becomes localized into a narrow basal shear which at its most localized is observed to be velocity weakening. With subsequent displacement, the fault restrengthens, returns to velocity strengthening, or to velocity neutral, the velocity dependence of dilatancy rate becomes larger, and deformation becomes distributed. Correlation of friction, velocity dependence of friction and of dilatancy rate, and degree of localization at all displacements in simulated gouge suggest that all quantities are interrelated. The observations do not distinguish the independent variables but suggest that the degree of localization is controlled by the fault strength, not by the friction velocity dependence. The friction velocity dependence and velocity dependence of dilatancy rate can be used as qualitative measures of the degree of localization in simulated gouge, in agreement with previous studies. Theory equating the friction velocity dependence of simulated gouge to the sum of the friction velocity dependence of bare surfaces and the velocity dependence of dilatancy rate of simulated gouge fails to quantitatively account for the experimental observations. EXPERIMENTAL FAULTS of slip when the sample strength is lowest and the friction velocity dependence is the most negative, changes in dilation rate are systematically smaller (Figure 5c, inset c2), similar to the initially bare surface response (Figure 4c). These observations can be quantified by determining the net thickness changes described by tz = AL / AlnV [Marone and Kilgore, 1993] and the changes in dilation rate A(dL / d5)ss / AlnV Example 1