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 observed with optical electron (scanning transmission) microscopy. For slip velocity 1 m s −1 normal stresses 0.3 to 1.3 MPa, dramatic slip‐weakening behavior was observed. X‐ray diffraction analysis additional friction experiments on pure kaolinite indicate dehydration during slip. The critical distance D c is...

Compressional, shear wave velocities and their ratio, V p / s , were measured along with porosity variations during wet dry hydrostatic compaction of Bleurswiller sandstone, a 25% Vosgian sandstone. At first, increase in pressure was accompanied by simultaneous both as expected. critical effective confining P *, large mechanical decrease observed that due to pore collapse grain crushing. Theoretically, two different processes are affecting the elastic counteracting ways cataclastic...

We observe the nucleation phase of in‐plane ruptures in laboratory. show that is composed two distinct phases, a quasi‐static and an acceleration stage, followed by dynamic propagation. propose empirical model which describes rupture length evolution: The described exponential growth while inverse power law time. transition from to accelerating related critical length, scales inversely with normal stress accordance theoretical predictions, surfacic power, may be intrinsic property interface....

We measured Vp/Vs ratios of thermally cracked Westerly granite, Carrara marble and 4% porosity Fontainebleau sandstone, for an effective mean pressure ranging from 2 to 95 MPa. Samples were fluid‐saturated alternatively with argon gas water (5 MPa constant pore pressure). The experimental results show that at ultrasonic frequencies, ratio saturated specimen never exceeded 2.15, even as low MPa, or a lithology which the Poisson's minerals is high 0.3 (calcite). In order check these against...

In order to investigate the effects of fluid and frequency on elastic properties, we performed hydrostatic experiments an Icelandic basalt specimen under both dry saturated conditions. This is characterized by a bimodal porosity, i.e., cracks equant pores. The properties ‐bulk moduli in our case‐ were investigated high pressure through two experimental methods: (1) classical one using ultrasonic P‐ S‐waves velocities (frequency 10 6 Hz), (2) new one, oscillation tests −2 Hz). condition, data...

Delineating Deep Faults Most large, damaging earthquakes initiate in Earth's crust where friction and brittle fracture control the release of energy. Strong can occur mantle too, but their rupture dynamics are difficult to determine because higher temperatures pressures play a more important role. Ye et al. (p. 1380 ) analyzed seismic P waves generated by 2013 M w 8.3 Sea Okhotsk earthquake—the largest deep earthquake recorded date—and its associated aftershocks. The ruptured along fault...

Supershear earthquake ruptures propagate faster than the shear wave velocity. Although there is evidence that this occurs in nature, it has not been experimentally demonstrated with use of crustal rocks. We performed stick-slip experiments Westerly granite under controlled upper-crustal stress conditions. systematically occur when normal exceeds 43 megapascals (MPa) resulting drops on order 3 to 25 MPa, comparable inferred by seismology for earthquakes. In our experiments,...

Abstract We report macroscopic stick‐slip events in saw‐cut Westerly granite samples deformed under controlled upper crustal stress conditions the laboratory. Experiments were conducted triaxial loading ( σ 1 > 2 = 3 ) at confining pressures ranging from 10 to 100 MPa. A high‐frequency acoustic monitoring array recorded particle acceleration during allowing us estimate rupture speed. In addition, we record drop dynamically and show that dynamic measured locally close fault plane is almost...

Failure mode is intimately related to porosity change, and whether deformation occurs in conjunction with dilatation or compaction has important implications on fluid transport processes. Laboratory studies the inelastic failure behavior of carbonate rocks have focused very porous compact end‐members. In this study, experiments were conducted Solnhofen limestone intermediate investigate interplay dilatancy shear controlling brittle‐ductile transition. Hydrostatic triaxial compression...

Rocks in the Earth's crust contain variable amount of cracks, depending on deviatoric and confining stress levels, pore pressure, temperature conditions. Crack damage results effects that have been investigated for a long time, particular, decrease elastic wave velocity development anisotropy. In this paper, we focus cracked rocks develop method to calculate both anisotropy dispersion fluid‐saturated rock. We show analytic expressions can be derived properties terms crack density tensor...

During earthquakes, frictional heating on the fault plane induces a temperature rise and thus pore pressure rise, which is known as thermal pressurization (TP). Coseismic mineral dehydrations may occur because of this increase are included within TP framework. Dehydrations modeled source term for total volume change sink they endothermic. The reaction occurs slipping zone when threshold T s reached. Dehydration kinetic using first‐order rate. Using energy fluid mass conservation, we derive...

Effects of thermal crack damage on the rupture processes a fine‐grained granite were investigated under triaxial stress, water (wet) and argon gas (dry) saturated conditions, at room temperature. Thermal cracking was introduced by slowly heating cooling two samples La Peyratte up to 700°C, which compared intact specimens. For each rock sample, hydrostatic test first carried 90 MPa effective pressure (5 constant pore pressure). The then deformed failure strain rate 2.10 −6 s −1 , 30 pressure....

[1] Triaxial tests on gypsum polycrystal samples are performed at confining pressure (Pc) ranging from 2 to 95 MPa and temperatures up 70°C. During the tests, stress, strain, elastic wave velocities, acoustic emissions recorded. At Pc ≤ 10 MPa, macroscopic behavior is brittle, above 20 becomes ductile. Ductile deformation cataclastic, as shown by continuous decrease of velocities interpreted in terms microcrack accumulation. Surprisingly, ductile strain hardening also accompanied small...

Abstract We present a series of high‐velocity friction tests conducted on Westerly granite, using the Slow to HIgh Velocity Apparatus (SHIVA) installed at Istituto Nazionale di Geofisica e Vulcanologia Roma with acoustic emissions (AEs) monitored high frequency (4 MHz). Both atmospheric humidity and pore fluid (water) pressure conditions were tested, under effective normal stress in range 5–20 MPa target sliding velocities V s 0.003–3 m/s. Under two consecutive drops observed. The first one...

Abstract Conventional triaxial tests were performed on three sets of samples Tournemire shale along different orientations relative to bedding (0°, 45°, and 90°). Experiments carried out up failure at increasing confining pressures ranging from 2.5 160 MPa, strain rates between 3 × 10 −7 s −1 −5 . This allowed us determine the entire anisotropic elastic compliance matrix as a function pressure. Results show that orientation principal stress plays an important role brittle strength, with 45°...

Earthquakes result from weakening of faults (transient decrease in friction) during co-seismic slip. Dry weaken due to degradation fault asperities by frictional heating (e.g. flash heating). In the presence fluids, theoretical models predict thermal pressurization fluid. However, experimental evidence rock/fluid interactions dynamic rupture under realistic stress conditions remains poorly documented. Here we demonstrate that relative contribution and depends on fluid thermodynamic...

Abstract Conventional triaxial tests were performed on a series of samples Tournemire shale along different orientations relative to bedding (0°, 90°). Experiments carried out up failure at increasing confining pressures ranging from 2.5 80 MPa, and strain rates between 3 × 10 −7 s −1 −5 . During each experiment, P S wave elastic velocities continuously measured many raypaths with respect maximum compressive stress. This extensive velocity measurement setup allowed us highlight the presence...

Earthquake ruptures dynamically activate coseismic off-fault damage around fault cores. Systematic field observation efforts have shown the distribution of main faults, while numerical modeling using elastic-plastic material models has demonstrated evolution during earthquake ruptures. Laboratory scale micro-earthquake experiments pointed out enhanced high-frequency radiation due to damage. However, detailed fracturing mechanisms, subsequent and its contribution overall energy budget remain...

Abstract In this study we use the precursory acoustic emission (AE) activity during nucleation of stick‐slip instability as a proxy to investigate foreshock occurrence prior natural earthquakes. We report on three experiments performed cylindrical samples Indian metagabbro under upper crustal stress conditions (30–60 MPa). AEs were continuously recorded by eight calibrated sensors experiments. Seismological parameters (moment magnitude, corner frequency and stress‐drop) detected (−8.8 ≤ M w...

Abstract The quartz α → β transition is a displacive phase associated with significant change in elastic properties. However, the properties of at high‐pressure and temperature remain poorly constrained experimentally, particularly within field ‐quartz. Here, we conducted an experimental study on during which P‐wave velocities were measured in‐situ pressure (from 0.5 to 1.25 GPa) (200–900°C) conditions continental lower crust. Experiments carried out samples microcrystalline material (grain...