Showing papers on "Slip (materials science) published in 2013"

Time and Space Distribution of Coseismic Slip of the 2011 Tohoku Earthquake as Inferred from Tsunami Waveform Data

Abstract: A multiple time window inversion of 53 high‐sampling tsunami waveforms on ocean‐bottom pressure, Global Positioning System, coastal wave, and tide gauges shows a temporal and spatial slip distribution during the 2011 Tohoku earthquake. The fault rupture started near the hypocenter and propagated into both deep and shallow parts of the plate interface. A very large slip (approximately 25 m) in the deep part off Miyagi at a location similar to the previous 869 Jogan earthquake model was responsible for the initial rise of tsunami waveforms and the recorded tsunami inundation in the Sendai and Ishinomaki plains. A huge slip, up to 69 m, occurred in the shallow part near the trench axis 3 min after the rupture initiation. This delayed shallow rupture extended for 400 km with more than a 10‐m slip, at a location similar to the 1896 Sanriku tsunami earthquake, and was responsible for the peak amplitudes of the tsunami waveforms and the maximum tsunami heights measured on the northern Sanriku coast, 100 km north of the largest slip. The average slip on the entire fault was 9.5 m, and the total seismic moment was 4.2×1022 N·m ( M w 9.0). The large horizontal displacement of seafloor slope was responsible for 20%–40% of tsunami amplitudes. The 2011 deep slip alone could reproduce the distribution of the 869 tsunami deposits, indicating that the 869 Jogan earthquake source could be similar to the 2011 earthquake, at least in the deep‐plate interface. The large tsunami at the Fukushima nuclear power station is due to either the combination of a deep and shallow slip or a triggering of a shallow slip by a deep slip, which was not accounted for in the previous tsunami‐hazard assessments. Online Material: Table of estimated slip for all subfaults at 0.5 min invervals.

Stable creeping fault segments can become destructive as a result of dynamic weakening

Abstract: Faults in Earth’s crust accommodate slow relative motion between tectonic plates through either similarly slow slip or fast, seismic-wave-producing rupture events perceived as earthquakes. These types of behaviour are often assumed to be separated in space and to occur on two different types of fault segment: one with stable, rate-strengthening friction and the other with rate-weakening friction that leads to stick-slip. The 2011 Tohoku-Oki earthquake with moment magnitude M_w = 9.0 challenged such assumptions by accumulating its largest seismic slip in the area that had been assumed to be creeping. Here we propose a model in which stable, rate-strengthening behaviour at low slip rates is combined with coseismic weakening due to rapid shear heating of pore fluids, allowing unstable slip to occur in segments that can creep between events. The model parameters are based on laboratory measurements on samples from the fault of the M_w 7.6 1999 Chi-Chi earthquake. The long-term slip behaviour of the model, which we examine using a unique numerical approach that includes all wave effects, reproduces and explains a number of both long-term and coseismic observations—some of them seemingly contradictory—about the faults at which the Tohoku-Oki and Chi-Chi earthquakes occurred, including there being more high-frequency radiation from areas of lower slip, the largest seismic slip in the Tohoku-Oki earthquake having occurred in a potentially creeping segment, the overall pattern of previous events in the area and the complexity of the Tohoku-Oki rupture. The implication that earthquake rupture may break through large portions of creeping segments, which are at present considered to be barriers, requires a re-evaluation of seismic hazard in many areas.

Ultrastrong Mg Alloy via Nano-spaced Stacking Faults

Abstract: Mg alloys are among the lightest alloys but they are usually weak. Here we report a new mechanism to make them ultrastrong while maintaining good ductility. Stacking faults with nanoscale spacing were introduced into a Mg–8.5Gd–2.3Y–1.8Ag–0.4Zr (wt%) alloy by conventional hot rolling, which produced a yield strength of ∼575 MPa, an ultimate strength of ∼600 MPa, and a uniform elongation of ∼5.2 %. Low stacking fault (SF) energy enabled the introduction of a high density of SFs, which impeded dislocation slip and promoted dislocation accumulation. These findings provide guidance for developing Mg alloys with superior mechanical properties.

Low Coseismic Friction on the Tohoku-Oki Fault Determined from Temperature Measurements

Abstract: The frictional resistance on a fault during slip controls earthquake dynamics Friction dissipates heat during an earthquake; therefore, the fault temperature after an earthquake provides insight into the level of friction The Japan Trench Fast Drilling Project (Integrated Ocean Drilling Program Expedition 343 and 343T) installed a borehole temperature observatory 16 months after the March 2011 moment magnitude 90 Tohoku-Oki earthquake across the fault where slip was ~50 meters near the trench After 9 months of operation, the complete sensor string was recovered A 031°C temperature anomaly at the plate boundary fault corresponds to 27 megajoules per square meter of dissipated energy during the earthquake The resulting apparent friction coefficient of 008 is considerably smaller than static values for most rocks

Microscopic and Macroscopic Physics of Earthquakes

Abstract: Frictional melting and fluid pressurization can play a key role in rupture dynamics of large earthquakes. For faulting under frictional stress σ_ƒ, the temperature increases with σ_ƒ and the earthquake magnitude, M_w. If the thickness of the heated zone, w, is of the order of a few mm, then, even for a modest σ_ƒ, the temperature rise, ΔT, would exceed 1000° for earthquakes with M_w = 5 to 6, and melting is likely to occur, and reduce friction during faulting. If fluid exists in a fault zone, a modest ΔT of 100 to 200° would likely increase the pore pressure enough to significantly reduce friction for earthquakes with M_w = 3 to 4. The microscopic state of stress can be tied to macroscopic seismic parameters such as the seismic moment, M_0, and the radiated energy, E_R, by averaging the stresses in the microscopic states. Since the thermal process is important only for large earthquakes, the dynamics of small and large earthquakes can be very different. This difference is reflected in the observed relation between the scaled energy ẽ = E_R/M_0 and M_W. The observed ẽ for large earthquakes is 10 to 100 times larger than for small earthquakes. Mature fault zones such as the San Andreas are at relatively moderate stress levels, but the stress in the plate interior can be high. Once slip exceeds a threshold, runaway rupture could occur, and could explain the anomalous magnitude-frequency relationship observed for some mature faults. The thermally controlled slip mechanism would produce a non-linear behavior, and under certain circumstances, the slip behavior at the same location may vary from event to event. Also, slip velocity during a large earthquake could be faster than what one would extrapolate from smaller earthquakes.

How fast does water flow in carbon nanotubes

Abstract: The purpose of this paper is threefold. First, we review the existing literature on flow rates of water in carbon nanotubes. Data for the slip length which characterizes the flow rate are scattered over 5 orders of magnitude for nanotubes of diameter 0.81-10 nm. Second, we precisely compute the slip length using equilibrium molecular dynamics (EMD) simulations, from which the interfacial friction between water and carbon nanotubes can be found, and also via external field driven non-equilibrium molecular dynamics simulations (NEMD). We discuss some of the issues in simulation studies which may be reasons for the large disagreements reported. By using the EMD method friction coefficient to determine the slip length, we overcome the limitations of NEMD simulations. In NEMD simulations, for each tube we apply a range of external fields to check the linear response of the fluid to the field and reliably extrapolate the results for the slip length to values of the field corresponding to experimentally accessible pressure gradients. Finally, we comment on several issues concerning water flow rates in carbon nanotubes which may lead to some future research directions in this area.

Slip planes in bcc transition metals

Abstract: Slip in face centred cubic (fcc) metals is well documented to occur on {111} planes in 〈110〉 directions. In body centred cubic (bcc) metals, the slip direction is also well established to be 〈111〉, but it is much less clear as to the slip planes on which dislocations move. Since plasticity in metals is governed by the collective motion and interaction of dislocations, the nature of the relevant slip planes is of critical importance in understanding and modelling plasticity in bcc metals. This review attempts to address two fundamental questions regarding the slip planes in bcc metals. First, on what planes can slip, and thus crystallographic rotation, be observed to occur, i.e. what are the effective slip planes? Second, on what planes do kinks form along the dislocation lines, i.e. what are the fundamental slip planes? We review the available literature on direct and indirect characterisation of slip planes from experiments, and simulations using atomistic models. Given the technological importan...

Low Coseismic Shear Stress on the Tohoku-Oki Megathrust Determined from Laboratory Experiments

Abstract: Large coseismic slip was thought to be unlikely to occur on the shallow portions of plate-boundary thrusts, but the 11 March 2011 Tohoku-Oki earthquake [moment magnitude (Mw) = 9.0] produced huge displacements of ~50 meters near the Japan Trench with a resultant devastating tsunami. To investigate the mechanisms of the very large fault movements, we conducted high-velocity (1.3 meters per second) friction experiments on samples retrieved from the plate-boundary thrust associated with the earthquake. The results show a small stress drop with very low peak and steady-state shear stress. The very low shear stress can be attributed to the abundance of weak clay (smectite) and thermal pressurization effects, which can facilitate fault slip. This behavior provides an explanation for the huge shallow slip that occurred during the earthquake.

The Betic-Rif Arc and Its Orogenic Hinterland: A Review

Abstract: The Betic-Rif arc is one of the smallest and tightest orogenic arcs on Earth, and together with its extensional hinterland, the Albor´ an Domain, it formed between two colliding continents. The region provides examples of a range of tectonic processes that are not predictable from the rules of rigid-plate tectonics. The AlborDomain reveals two stages of subduction and accre- tion, with different thermal histories and mechanisms of exhumation. The external Betic-Rif thrust belt illustrates four processes that create an arcuate orogen and a strongly divergent pattern of slip vectors: (a) the interaction between the westward moving Albor´ an Domain and the converging African and Iberian margins, (b) divergence in relative motion due to extension within the Albor´ an Domain, (c) slip partitioning onto strike-slip faults within the arc, and (d ) vertical-axis rotations resulting from oblique convergence on the limbs of the arc.

Frictional properties of shale reservoir rocks

Abstract: [1] We performed laboratory friction experiments on shale samples from three hydrocarbon reservoirs to assess compositional controls on fault slip behavior accompanying hydraulic stimulation. The samples span a range of clay and total organic content from ~10 to 60% by weight and demonstrate fine-scale heterogeneity within each reservoir. Friction measurements demonstrate strong dependence of strength and rate-state constitutive properties on shale composition. Shale samples with clay and organic content above ~30% by weight show coefficient of friction ~0.4 and consistently velocity-strengthening behavior, while those below this threshold show increased strength and velocity-weakening behavior. This transition in frictional strength and stability suggests a change in the shale grain packing framework from rigid clast supported to clay mineral and organic matter supported. Measurements of gouge dilatancy further support these relationships, showing a negative correlation with clay and organic content. Critical slip evolution distance exhibits similar dependence on composition, implying common micromechanical mechanisms for the observed transition in frictional behavior. We performed microstructural characterization of the experimental samples and observe changes in the gouge load-bearing framework and shear localization features consistent with these mechanical data. While these results can be applied generally to infer slip stability on faults in clay-bearing sedimentary rock, we employ the experimental data to place constraints on microearthquake magnitudes and the occurrence of slow shear slip on preexisting faults during hydraulic stimulation in shale reservoirs.

Design principles for superamphiphobic surfaces

Abstract: To predict the properties of superamphiphobic layers we analyzed the wetting of a square and a hexagonal array of vertical pillars composed of spheres (radius R) partially sintered together. Apparent contact angles above 150° are obtained by pinning of a non-polar liquid surface at the underside of the top sphere resulting in a Fakir or Cassie state. Analytical equations are derived for the impalement pressure in the limiting case A0 ≫ R2, where A0 is the area of the regular unit cell containing a single pillar. The case of close pillars is investigated numerically. By balancing forces at the rim of a drop, we calculate the apparent receding contact angle. To describe drag reduction of a flowing liquid we calculate the apparent slip length. When considering pressure-induced flow through cylindrical capillaries of radius rc, significant drag reduction occurs only for thin capillaries. The mechanical stability with respect to normal forces and shear is analyzed. Nanoscopic silica glass pillars would be able to sustain the normal and shear stresses caused by capillary and drag forces. For a high impalement pressure and good mechanical stability A0 should be small and R (respectively the neck diameter) should be large, whereas a large A0 and a small R imply low contact angle hysteresis and high slip length.

Basal and non-basal dislocation slip in Mg-Y

Abstract: The activation of non-basal slip systems is of high importance for the ductility in hcp Mg and its alloys. In particular, for Mg–Y alloys where a higher activation of pyramidal dislocation slip causes an increased ductility detailed characterization of the activated slip systems is essential to understand and describe plasticity in these alloys. In this study a detailed analysis of the activated dislocations and slip systems via post-mortem TEM and SEM-EBSD based slip band analysis in 3% deformed Mg–3 wt% Y is presented. The analysis reveals a substantial activity of pyramidal dislocations with different Burgers vectors. The obtained dislocation densities and active slip systems are discussed with respect to atomistic simulations of non-basal dislocations in hcp Mg.

Seismic and Aseismic Slip Along Subduction Zones and their Tectonic Implications

Abstract: Results of detailed mechanism studies of great earthquakes are used together with their repeat times to determine the amount of seismic slip along various subduction zones. Comparison of the seismic slip with the rate of plate motion suggests that, in Chile, and possibly Alaska, the seismic slip rate is comparable to the rate of plate motion while, in the Kuriles and Northern Japan, the seismic slip constitutes only a very small portion, approximately 1/4, of the total slip. In the Sanriku region, and to the south of it, the relative amount of seismic slip is even smaller. These results suggest that in Chile and Alaska the coupling and interaction between the oceanic and continental lithosphere are very strong, resulting in great earthquakes with a very large rupture zone, and in break-off of the undergoing lithosphere at shallow depths. In the Kuriles and Northern Japan, the oceanic and continental lithosphere are largely decoupled, so that the slip becomes largely aseismic, and the rupture length of earthquakes reduced. The reduced interaction at the inter-plate boundary may allow the oceanic lithosphere to subduct more easily and to form a continuous Benioff zone extending to depths. It may also facilitate ridge subduction beneath island arcs, which may play an important role in the formation of marginal seas such as the Japan Sea. The decoupling is also evidenced by silent or tsunami earthquakes [e.g., the 1896 Sanriku earthquake], great intra-plate normal-fault earthquakes [e.g., the 1933 Sanriku earthquake], and crustal deformation. A natural extension of this concept of inter-plate decoupling is the spontaneous sinking of the oceanic lithosphere with a consequent retreating subduction. Retreating subduction may be an important mechanism in the format ion of marginal seas such as the Philippine Sea, and explains the complete lack of major shallow earthquake activity along some subduction zones such as the Izu-Bonin-Mariana arc.

Acoustic emissions document stress changes over many seismic cycles in stick-slip experiments

Abstract: [1] The statistics of large earthquakes commonly involve large uncertainties due to the lack of long-term, robust earthquake recordings. Small-scale seismic events are abundant and can be used to examine variations in fault structure and stress. We report on the connection between stress and microseismic event statistics prior to the possibly smallest earthquakes: those generated in the laboratory. We investigate variations in seismic b value of acoustic emission events during the stress buildup and release on laboratory-created fault zones. We show that b values mirror periodic stress changes that occur during series of stick-slip events, and are correlated with stress over many seismic cycles. Moreover, the amount of b value increase associated with slip events indicates the extent of the corresponding stress drop. Consequently, b value variations can be used to approximate the stress state on a fault: a possible tool for the advancement of time-dependent seismic hazard assessment. Citation: Goebel, T. H. W., D. Schorlemmer, T. W. Becker, G. Dresen, and C. G. Sammis (2013), Acoustic emissions document stress changes over many seismic cycles in stick-slip experiments, Geophys. Res. Lett., 40, 2049–2054, doi:10.1002/grl.50507.

Active Deformation Processes in Alaska, Based on 15 Years of GPS Measurements

Abstract: We present a comprehensive average velocity field for Alaska, based on repeated GPS surveys covering the period 1992―2007, and review the major results of previously published papers that used subsets of this data The spatially and temporally complex pattern of crustal deformation in Alaska results from the superposition of several processes, including postseismic deformation after the 1964 earthquake, spatial variations in plate coupling/slip deficit, translation and rotation of large crustal blocks or plates, and a large slow-slip event in Cook Inlet Postseismic deformation from the 1964 earthquake continues today, mainly caused by viscoelastic relaxation, and causes trenchward motion The behavior of the shallow seismogenic zone along the Alaska-Aleutian megathrust is characterized by dramatic along-strike variability The width of the inferred seismogenic zone varies over along-strike distances that are short compared to the width The along-strike distribution of locked and creeping regions along the megathrust is consistent with the persistent asperity hypothesis A large slow-slip event occurred in upper Cook Inlet in 1998―2001, and a smaller event in the same area in 2005―2006 No sign of slow-slip events has been found in segments that are dominated by creep, which suggests that creep there occurs quasi-statically The overriding plate in Alaska is subject to considerable internal deformation, and can be described in terms of the independent motions of at least four blocks: the Bering plate, the Southern Alaska block, the Yakutat block, and the Fairweather block

Control of slippage with tunable bubble mattresses

Abstract: Tailoring the hydrodynamic boundary condition is essential for both applied and fundamental aspects of drag reduction. Hydrodynamic friction on superhydrophobic substrates providing gas–liquid interfaces can potentially be optimized by controlling the interface geometry. Therefore, establishing stable and optimal interfaces is crucial but rather challenging. Here we present unique superhydrophobic microfluidic devices that allow the presence of stable and controllable microbubbles at the boundary of microchannels. We experimentally and numerically examine the effect of microbubble geometry on the slippage at high resolution. The effective slip length is obtained for a wide range of protrusion angles, θ, of the microbubbles into the flow, using a microparticle image velocimetry technique. Our numerical results reveal a maximum effective slip length, corresponding to a 23% drag reduction at an optimal θ ≈ 10°. In agreement with the simulation results, our measurements correspond to up to 21% drag reduction when θ is in the range of −2° to 12°. The experimental and numerical results reveal a decrease in slip length with increasing protrusion angles when θ ≳ 10°. Such microfluidic devices with tunable slippage are essential for the amplified interfacial transport of fluids and particles.

The habitat of fault-generated pseudotachylyte : Presence vs. absence of friction-melt

Abstract: Anticipated frictional dissipation during seismic rupture is such (10-100 MW/ m 2 ) that melting on fault planes should be widespread provided slip is well-localized. However, despite evidence of slip localization throughout the upper crustal seismogenic zone, fault-hosted pseudotachylyte is rare and largely restricted to crystalline host rocks. In such rocks, pseudotachylyte fault-veins inferred to have been through a melt phase (commonly, T ∼ 1200 °C) have typical thicknesses of millimeters to centimeters and occupy low-displacement faults that only occasionally show evidence of reshear. Wall-rock damage adjacent to fault-veins is often remarkably slight but erratic injection veins may extend 40-60 km depth in subduction settings. Their apparent scarcity raises the question as to whether pseudotachylyte is rarely generated (perhaps because of dynamic lowering of shear resistance), or is rarely preserved in recognizable form. Estimates of melting energies for 1-10 mm thick fault-veins (∼ 4-40 MJ/m 2 ) are mostly higher than estimates of seismic fracture energy (0.1-10 MJ/m 2 ) and radiated seismic energy (0.1-10 MJ/m 2 per meter of slip), except for large displacements. Fault-hosted pseudotachylytes thus appear to be the product of high-stress (τ > 100 MPa) rupturing associated with fault initiation in mostly dry, intact crystalline crust.