Showing papers on "Slip (materials science) published in 1989"

Simulations of contact-line motion: Slip and the dynamic contact angle

Abstract: Molecular-dynamics simulations of two immiscible fluids confined between solid walls and sheared in a Couette geometry were performed as a function of shear rate for a range of wall and fluid properties. Changes with capillary number in the interface shape and dynamic contact angle were consistent with previous analytic results. Computed velocity fields showed that the usual no-slip boundary condition broke down within \ensuremath{\sim}2 atomic spacings from the contact line. The slip appears to be associated with the breakdown of local hydrodynamic theory at atomic scales.

An analysis of the low temperature, low and high strain-rate deformation of Ti-6Al-4V

Abstract: The deformation behavior of Ti−6Al−4V at temperatures between 76 and 495 K, strain rates between 0.001 and 3000 s−1, and compressive strains to 0.3 has been investigated. Measurements of yield stress as a function of test temperature, strain rate, and prestrain history are analyzed according to the model proposed by Kocks and Mecking. The mechanical threshold stress (flow stress at 0 K) is used as an internal state variable, and the contributions to the mechanical threshold stress from the various strengthening mechanisms present in this alloy are analyzed. Transmission electron microscopy (TEM) is used to correlate deformation substructure evolution with the constitutive behavior. The deformation substructure of Ti-6-4 is observed to consist of planar slip in the α grains at quasistatic strain rates. At high strain rates, deformation twinning is observed in addition to planar slip. Increasing the temperature to 495 K is seen to alter the deformation mode to more random slip; the effect of this on the proposed deformation model is discussed.

Magnitude of Late Quaternary Left-Lateral Displacements Along the North Edge of Tibet

Abstract: Images taken by the earth observation satellite SPOT of the Quaternary morphology at 18 sites on the 2000-kilometer-long Altyn Tagh fault at the north edge of Tibet demonstrate that it is outstandingly active. Long-term, left-lateral strike-slip offsets of stream channels, alluvial terrace edges, and glacial moraines along the fault cluster between 100 and 400 meters. The high elevation of the sites, mostly above 4000 meters in the periglacial zone, suggests that most offsets resulted from slip on the fault since the beginning of the Holocene. These data imply that slip rates are 2 to 3 centimeters per year along much of the fault length and support the hypothesis that the continuing penetration of India into Asia forces Tibet rapidly toward the east.

Slip Effects in Capillary and Parallel Disk Torsional Flows of Highly Filled Suspensions

Abstract: The shear viscosity material function of a highly filled suspension consisting of a Newtonian poly(butadiene acrylonitrile acrylic acid terpolymer) matrix, PBAN, mixed with an ammonium sulfate filler at 60% by volume was studied. Both capillary and parallel disk torsional flows were employed. The rheological characterization revealed strong slip of the suspension at the walls over a broad range of shear stresses in both types of flows. The slip velocity increased approximately linearly with the shear stress. In capillary flows, above a critical shear stress, flow took place in a pluglike manner, owing to slip at the wall. The experimental findings were further elucidated to determine the slip layer thickness and the apparent shear viscosity behavior of highly filled suspensions at high shear stress at the wall values. It was concluded that the slip effects dominate the flow of highly filled suspensions and the true flow and deformation characteristics of the highly filled suspensions may be overshadowed by slip at the walls.

Sensing skin acceleration for slip and texture perception

Abstract: The authors present a scheme for sensing small accelerations of the outer skin covering the fingers of a manipulator. The sensor is constructed with a thin rubber skin covering a soft inner layer of foam rubber. This decouples the skin from the manipulator structure, isolating it from structural vibrations and facilitating the tracking of object surfaces. An accelerometer attached to the inner surface of the skin measures the large local accelerations produced when areas of the skin catch and snap back as the sensor moves against a surface. The authors present experimental confirmation of the ability to detect the onset of slip, and discuss the sensor response to various surface texture parameters. >

Numerical analysis of the shear and thermal creep flows of a rarefied gas over a plane wall on the basis of the linearized Boltzmann equation for hard-sphere molecules

Abstract: Shear flow and thermal creep flow (flow induced by the temperature gradient along the boundary wall) of a rarefied gas over a plane wall are considered on the basis of the linearized Boltzmann equation for hard‐sphere molecules and diffuse reflection boundary condition. These fundamental rarefied gas dynamic problems, typical half‐space boundary‐value problems of the linearized Boltzmann equation, are analyzed numerically by the finite‐difference method developed recently by the authors, and the velocity distribution functions, as well as the macroscopic variables, are obtained with good accuracy. From the results, the shear and thermal creep slip coefficients and their associated Knudsen layers of a slightly rarefied gas flow past a body are derived. The results for the slip coefficients and Knudsen layers are compared with experimental data and various results by the Boltzmann–Krook–Welander (BKW) equation, the modified BKW equation, and a direct simulation method.

Effect of chromium on properties of Fe3Al

Abstract: The effects of the addition of chromium on several properties of Fe3Al, including tensile strength and ductility, fracture behavior, and slip and dislocation characteristics, were studied. Alloying with up to 6 at. % chromium results in an increase in room temperature ductility from approximately 4% to 8–10%. Along with this increase in ductility, the addition of chromium produces a change in fracture mode from transgranular cleavage to a mixed mode of intergranular-transgranular cleavage, and a change in slip behavior from coarse straight slip to fine wavy slip. These phenomena are discussed in terms of the effect of chromium on the antiphase boundary energies and dislocation characteristics.

A cohesive zone model for dynamic shear faulting based on experimentally inferred constitutive relation and strong motion source parameters

Abstract: To understand constitutive behavior near the rupture front during an earthquake source shear failure along a preexisting fault in terms of physics, local breakdown processes near the propagating tip of the slipping zone under mode II crack growth condition have been investigated experimentally and theoretically. A physically reasonable constitutive relation between cohesive stress τ and slip displacement D, τ = (τi − τd)[1 + α log (1 + βD)] exp (−ηD) + τd, is put forward to describe dynamic breakdown processes during earthquake source failure in quantitative terms. In the above equation, τi is the initial shear stress on the verge of slip, τd is the dynamic friction stress, and α, β, and η are constants. This relation is based on the constitutive features during slip failure instabilities revealed in the careful laboratory experiments. These experiments show that the shear stress first increases with ongoing slip during the dynamic breakdown process, the peak stress is attained at a very (usually negligibly) small but nonzero value of the slip displacement, and then the slip-weakening instability proceeds. The model leads to bounded slip acceleration and stresses at and near the dynamically propagating tip of the slipping zone along the fault in an elastic continuum. The dynamic behavior near the propagating tip of the slipping zone calculated from the theoretical model agrees with those observed during slip failure along the preexisting fault much larger than the cohesive zone. The model predicts that the maximum slip acceleration be related to the maximum slip velocity and the critical displacement Dc by , where k is a numerical parameter, taking a value ranging from 4.9 to 7.2 according to a value of τi/τp (τp being the peak shear stress) in the present model. The model further predicts that be expressed in terms of and the cut off frequency fmaxs of the power spectral density of the slip acceleration on the fault plane as and that in terms of Dc and fmaxs as . These theoretical relations agree well with the experimental observations and can explain interrelations between strong motion source parameters for earthquakes. The pulse width of slip acceleration on the fault plane is directly proportional to the time Tc required for the crack tip to break down, and fmaxs is inversely proportional to Tc.

The Brittle-Ductile Transition in Silicon. I. Experiments

Abstract: The experiments described in this paper investigate the fundamental processes involved in the brittle–ductile transition (BDT) in silicon, and form the basis of a new theoretical model (see following paper). The fracture (or bending) stresses of four-point bend specimens of silicon containing semicircular surface cracks, introduced by surface indentation, were determined over a range of temperatures and strain rates. A sharp transition, characterized by a rapid increase in fracture stress with temperature, occurs at a temperature ( T c ) that depends on the strain rate and the doping of the material used; these data are used to derive activation energies, which are found to be equal to those for dislocation glide. At temperatures above the sharp transition region, the specimens deform by macroscopic plastic yielding. Etch pitting experiments show that below T c no significant dislocation activity occurs; the sharp brittle–ductile transition is associated with a sudden growth of well-defined dislocation arrays from certain points on the precursor flaw, before fracture occurs. These only appear in a dynamic test at T ≽ T c ; at T = T c , they form only when the applied stress intensity factor K is of the same order as that for brittle failure ( K Ic ) at T T c . These experiments suggest that at T ≈ T c , a 9nucleation9 event precedes the generation of avalanches of dislocations when K ≈ K Ic . Static tests show that dislocations can be made to move from crack tips of K value as low as ca . 0.3 K Ic . Above the transition region general plasticity occurs, with slip being concentrated particularly around and spreading from the precursor flow. A 9warm-prestressing9 effect is observed, whereby the low-temperature fracture stress is increased by prestressing above T c .

Dynamic rupture modeling with laboratory‐derived constitutive relations

Abstract: A laboratory-derived state variable friction constitutive relation is used in the numerical simulation of the dynamic growth of an in-plane or mode II shear crack. According to this formulation, originally presented by J. H. Dieterich, frictional resistance varies with the logarithm of the slip rate and with the logarithm of the frictional state variable as identified by A. L. Ruina. Under conditions of steady sliding, the state variable is proportional to (slip rate)−1. Following suddenly introduced increases in slip rate, the rate and state dependencies combine to produce behavior which resembles slip weakening. When rupture nucleation is artificially forced at fixed rupture velocity, rupture models calculated with the state variable friction in a uniformly distributed initial stress field closely resemble earlier rupture models calculated with a slip weakening fault constitutive relation. Additional rupture models are calculated in which rupture nucleation is achieved naturally, with numerical simulations of the quasi-static response of the fault leading to the onset of unstable, dynamic rupture. When rupture nucleation with the state variable friction law takes place naturally, a large fraction of the fault accelerates before accelerating slip is concentrated in what ultimately becomes the rupture nucleation patch. The state evolution accompanying this accelerating slip leads to higher average rupture speeds or a more rapid rupture acceleration to near P wave rupture speeds. Rupture models are also calculated for the seismological asperity problem, that is, the failure of a highly stressed fault patch surrounded by a region of zero stress drop. Dynamic overshoot of slip into the region of zero stress drop roughly agrees with a simple energy balance analysis; the final size of the rupture is proportional to the square of the size of the high stress patch. Earlier frictional stability analyses have led to the definition of a critical fault patch size for rupture nucleation. This critical patch size is generally different from critical crack lengths determined from crack tip energy balance considerations applied to a simpler slip weakening law. In the model calculations, dynamic rupture does not nucleate if the starting patch size is less than the critical patch size. This is consistent with the frictional stability analyses. Thus these model calculations suggest that dynamic rupture following a state variable friction relation is similar to that following a simpler fault slip weakening law. However, when modeling the full cycle of fault motions, rate-dependent frictional responses included in the state variable formulation are important at low slip rates associated with rupture nucleation. The critical rupture nucleation dimension appropriate for a slip weakening fault does not predict the critical nucleation dimension for a state variable fault.

State of stress and modern deformation of the Northern Basin and Range Province

Abstract: Constraints on the current stress regime of the actively extending northern Basin and Range province are provided by deformation data (focal mechanisms and fault slip studies), hydraulic fracturing in situ stress measurements, borehole elongation (“breakouts”) analyses, and alignment of young volcanic vents. The integrated data indicate significant variations both in principal stress orientations and magnitudes. An approximately E-W least principal stress direction appears to characterize both the eastern and western margins of the Basin and Range province, whereas in the active interior parts of the province extension occurs in response to a least principal stress oriented NW to N60°W. The contrast in stress orientations between the province boundaries and in the interior suggests that along the margins the least principal stress direction may be locally controlled by the generally northerly trending profound lithospheric discontinuities associated with these margins. Active deformation along the southeastern and western province margins is characterized by a combination of strike-slip and normal faulting. Focal mechanisms along northeastern province margin (Wasatch front) and in central Nevada indicate a combination of normal and oblique-normal faulting. Temporal, regional, and depth-dependent variations in the relative magnitudes of the vertical and maximum horizontal stresses can explain much of the observed variations in deformation styles. However, some depth variation in faulting style inferred from focal mechanisms may be apparent and simply a function of the attitude of fault planes being reactivated. Evidence for significant temporal variation (or multiple cycles of variation) in relative stress magnitude comes from the Sierran front-Basin and Range boundary region where recent earthquakes are predominantly strike slip, whereas the profound relative vertical relief across the Sierra frontal fault zone in the last 9–10 m.y. implies a normal faulting stress regime. Using the best data on stress orientation, relative stress magnitudes are constrained from slip vectors of major earthquakes and young fault displacements. Analysis of well-constrained slip vectors in the Owens Valley, California, area indicate that large temporal variations in the magnitude of the approximately N-S oriented maximum horizontal stress are required to explain dominantly dip-slip and strike-slip offsets on subparallel faults. Similar faulting relations are observed throughout much of the boundary zone between the Basin and Range-Sierra Nevada (including the Walker Lane belt). Along the eastern province margin in the Wasatch front area in Utah, available data suggest that the maximum and minimum horizontal stresses may be approximately equal at depths of <4–5 km. Earthquake focal mechanisms in this area suggest more variability in relative magnitude of the two horizontal stresses with depth. Furthermore, superimposed sets of young fault striae along a segment of the Wasatch fault also indicate temporal variations of relative stress magnitudes. Sources of regional and temporal variations in the stress field may be linked to variable shear tractions applied to the base of the brittle crust related to intrusion, thermally induced flow, and the influence of the San Andreas plate boundary. Although difficult to date accurately, the fault slip data suggest that the temporal variations in relative magnitudes stress may occur on the time scale of both a single major earthquake cycle (1000–5000 years) and multiple earthquake cycles (10,000+ years).

An apparatus and a method for determining the slip resistance of shoes and floors by simulation of human foot motions.

Abstract: An apparatus to measure the coefficient of kinetic friction (mu k) between the shoe sole and the underfoot surface was constructed, and a method including criteria to evaluate the risk of slipping during walking was developed. The apparatus is a prototype stationary step simulator capable of simulating the movements of a human foot and the forces applied to the underfoot surface during an actual slip, and the drainage capability of the contact surface between the shoe sole and the flooring when different lubricants or contaminants are used. The apparatus consists of a movable artificial foot controlled by a computer with the aid of three hydraulic cylinders. The frictional force (F mu), the normal force (FN) and their ratio (mu k = F mu/FN) are measured with a two-way force platform when the foot slides along its surface. Two separate gait patterns, heel-side (mu k 1) and sole-slide (mu k 2) gait pattern, are used for the evaluations. The method classifies studied shoe, lubricant and underfoot surface combinations into five slip resistance classes according to the measured mu k 1. The slip resistance assessments are specified with some complementary safety criteria, e.g., the ratio mu k 1/mu k 2. The reliability of the developed measurement method was assessed in an international comparison test. According to available results discussed in this paper, our method seems to be valid and the slip resistance measurements seem to be repeatable.

Liquid flow in pores: Slip, no-slip, or multilayer sticking.

Abstract: The Hagen-Poiseuille flow of a Lennard-Jones liquid through a cylindrical pore formed by regularly arranged fixed atoms is studied by molecular-dynamics (MD) simulations. Different flow patterns develop depending on the strength of the wall-fluid interaction, the strength of the gravitational-type driving force, the thermodynamic state, and also on the mechanism of heat dissipation. In spite of the high driving forces necessary in MD it is found that up to two molecular layers may stick at the wall which confirms recent experimental findings.

Earthquake source parameters and stress distribution in the Adak Island region of the central Aleutian Islands, Alaska

Abstract: Source parameters have been systematically determined for all earthquakes with Mw≥5 that occurred between 172°W and 179°W longitude in the Adak Island region of the central Aleutian Islands during 1977-March 1987. We relocate the events using a plate velocity model developed for the region and use two alternative methods of depth determination. The first method uses arrival times of direct and prominent reflected phases, primarily pwP. The second method uses broadband P wave displacement seismograms in an inversion for source depth. The analysis of these events provides a well-constrained data set for the study of stress release along an active subduction zone. Three earthquakes, which occurred seaward of the trench axis, are located just below the crust-mantle interface and show extension nearly perpendicular to the trench axis. Seven events occurred in the Wadati-Benioff zone. Sixty-four events are located in the main thrust zone, and, except for five unusual events, are characterized by thrust mechanisms with one nodal plane dipping north at a shallow angle. In cross section the thrust zone appears as a thin (10–15 km thickness) interplate region which extends from 15 to 50 km depth. A 10°–15° average discrepancy between observed slip vector azimuths and the predicted relative motion direction between the Pacific and North American plates exists for these events. The observed slip vectors are oriented more normal to the trench than is predicted by plate motions. Five earthquakes, which occurred as aftershocks to the May 7, 1986, earthquake (Mw = 8.0), in the crust of the overriding plate have strike-slip mechanisms consistent with right-lateral motion on arc-parallel fault planes. Observations of slip vectors along the whole Aleutian arc show a similar trend to that observed in the Adak Island region. The largest differences (∼30°) between observed and predicted slip azimuths occur around 175°E. We propose a model of plate interaction in which a portion of the along-arc motion occurs along a weak strike-slip shear zone in the upper plate, near the volcanic line. The slip azimuths in the main thrust zone fit this model well, if the amount of transcurrent slip occurring in the upper plate is ∼60% of the arc-parallel relative plate motion. A consequence of the model is along-arc extension of the overriding plate between the accretionary wedge and the volcanic line, especially in the western part of the Aleutian arc. Calculations based on a tectonic model by Geist et al. (1988) for the formation of arc summit basins through block rotation and translation, suggest that along-arc extension has been significant since late Miocene or early Pliocene.

Mechanics of slip and fracture along small faults and simple strike‐slip fault zones in granitic rock

Abstract: We exploit quasi-static fracture mechanics models for slip along pre-existing faults to account for the fracture structure observed along small exhumed faults and small segmented fault zones in the Mount Abbot quadrangle of Calfornia and to estimate stress drop and shear fracture energy from geological field measurements. Along small strike-slip faults, cracks that splay from the faults are common only near fault ends. In contrast, many cracks splay from the boundary faults at the edges of a simple fault zone. Except near segment ends, the cracks preferentially splay into a zone. We infer that shear displacement discontinuities (slip patches) along a small fault propagated to near the fault ends and caused fraturing there. Based on elastic stress analyses, we suggest that slip on one boundary fault ends and caused fracturing there. Based on elastic stress analyses, we suggest that slip patches preferentially led to the generation of fractures that splayed into the zones away from segment ends and out of the zones near segment ends. We estimate the average stress drops for slip events along the fault zones as /similar to/1 MPa and the shear fracture energy release rate during slip as 5/times/10/sup 2//minus/2/times/10/sup 4/ J/m/sup 2/. This estimate ismore » similar to those obtained from shear fracture of laboratory samples, but orders of magnitude less than those for large fault zones. These results suggest that the shear fracture energy release rate increases as the structural complexity of fault zones increases. /copyright/ American Geophysical Union 1989« less

A dislocation model for the earthquake cycle at convergent plate boundaries

Abstract: SUMMARY A kinematic model for the earthquake cycle at convergent plate boundaries has been constructed on the basis of dislocation theory. We model the lithosphere-asthenosphere system by a stratified semi-infinite medium under gravity, consisting of an elastic surface layer, an intervening layer with Maxwell viscoelasticity, and an elastic substratum. The steady motion of plate convergence is naturally represented by uniform slip at a constant rate on the upper boundary of the descending oceanic plate. The occurrence of interplate earthquakes is regarded as a perturbation of the steady state plate motion, and represented by a periodic sequence of step slips on a finite seismic zone of the plate interface. Based on dislocation theory we can show that the steady slip on the interface deeper than the lithosphereasthenosphere boundary does not contribute to surface deformation in the steady state. Accordingly the surface deformation associated with the earthquake cycle is given by the superposition of viscoelastic responses to the steady slip on the interface shallower than the lithosphere-asthenosphere boundary, the steady backslip on the seismic zone, and the periodic sequence of seismic slips. We have computed cyclic patterns of vertical displacements at the free surface for two representative cases, taking account of gravity effects. The patterns of vertical displacements differ notably in the latter stage of the cycle depending on whether or not the seismic zone extends through the entire thickness of the lithosphere. After the completion of one earthquake cycle, our model yields a certain amount of permanent deformation resulting from the steady plate convergence. The pattern of the permanent deformation, that is characterized by steep uplift on the continental side, sharp subsidence at the plate boundary, and gentle uplift on the oceanic side, is irrespective of the cyclic process of stress accumulation and release repeated on the seismic zone. The earthquake cycle model developed here provides a possible explanation for the formation of earthquake-origin marine terraces.

The morphology of strike‐slip faults: Examples from the San Andreas Fault, California

Abstract: The dilatational strains associated with vertical faults embedded in a horizontal plate are examined in the framework of fault kinematics and simple displacement boundary conditions. Using boundary element methods, a sequence of examples of dilatational strain fields associated with commonly occurring strike-slip fault zone features (bends, offsets, finite rupture lengths, and nonuniform slip distributions) is derived. The combinations of these strain fields are then used to examine the Parkfield region of the San Andreas fault system in central California.

Comparison of seismic waveform inversion results for the rupture history of a finite fault : Application to the 1986 North Palm Springs, California, earthquake

Abstract: The July 8, 1986, North Palm Springs earthquake is used as a basis for comparison of several different approaches to the solution for the rupture history of a finite fault. The inversion of different waveform data is considered; both teleseismic P waveforms and local strong ground motion records. Linear parametrizations for slip amplitude are compared with nonlinear parametrizations for both slip amplitude and rupture time. Inversions using both synthetic and empirical Green's functions are considered. In general, accurate Green's functions are more readily calculable for the teleseismic problem where simple ray theory and flat-layered velocity structures are usually sufficient. However, uncertainties in the variation in t* with frequency most limit the resolution of teleseismic inversions. A set of empirical Green's functions that are well recorded at teleseismic distances could avoid the uncertainties in attenuation. In the inversion of strong motion data, the accurate calculation of propagation path effects other than attenuation effects is the limiting factor in the resolution of source parameters. The assumption of a laterally homogeneous velocity structure is usually not a good one, and the use of empirical Green's functions is desirable. Considering the parametrization of the problem, any degree of fault rupture complexity can be described in terms of a linear parametrization for slip amplitudes. However, a nonlinear parametrization for rupture times and slip amplitudes can have a distinct advantage over a simple linear one by limiting the number of unknown parameters. Regardless of the choice of data or the type of parametrization, the model or solution will be affected by the choice of minimization norm and the type of stabilization used.

Low‐frequency source characteristics of the great 1960 Chilean earthquake

Abstract: The low-frequency nature of the great 1960 Chilean earthquake, the Earth's largest recorded event, is characterized, and a source model composed of three events with a combined seismic moment of 5.5 × 1023 N m and a duration of 1500 s is presented. The results show conclusively that large-scale slip, which is only observed at low frequencies, preceded the main shock. Complex amplitude measurements of normal mode data in the band 1.0–5.0 mHz, recorded at eight vertical component stations, comprise the data set. In this band the earthquake source is assumed to be described by a line source propagating at a constant rupture velocity. The data set is the basis for a sequence of least squares inversions to determine the seismic moment, rupture velocity, spatial slip distribution, and the temporal slip function. The data are best explained by a source model that begins 1150 s before the main shock with an event of moment 1.9 × 1023 N m and rise time of 300 s, a main shock with moment of 3.2 × 1023 N m and for which most of the low-frequency energy was released beginning about 50 s after the short-period origin time, and an event 350 s later with moment of 0.4 × 1023 N m. The uncertainty in the moment estimate of the great 1960 Chilean earthquake is about 50% and is due primarily to the probable range of fault plane dip, which is not well constrained at this time.

Slip distribution of the 19 September 1985 Michoacan, Mexico, earthquake: near-source and teleseismic constraints

Abstract: We simultaneously invert the strong-motion velocity records and the long- and intermediate-period teleseismic P waveforms of the 19 September 1985 Michoacan, Mexico, earthquake to recover the distribution of slip on the fault using a point-by-point constrained and stabilized, least-squares inversion method. A fault plane with strike fixed at 300° and dip fixed at 14° is placed in the region of the earthquake hypocenter and divided into 120 subfaults. Rupture is assumed to propagate at a velocity of 2.6 km/sec away from the hypocenter. Synthetic near-source ground motions and teleseismic P waveforms for pure strike-slip and dipslip dislocations are calculated for each subfault. The observed data are then inverted to obtain the amount of strike-slip and dip-slip displacement required of each subfault. We also invert the data sets using a time-window procedure where the subfaults are allowed to slip up to three times. This approach relaxes the constraint of fixed subfault rupture time imposed by a constant rupture velocity. Inversion of the strong-motion data alone yields a slip model similar to the solution previously obtained using only teleseismic waveforms. This result supports the use of teleseismic waveform data for the derivation of fault dislocation models in the absence of strong-motion recordings. Our simultaneous inversion of both data sets suggests that rupture during the Michoacan earthquake was controlled largely by the failure of three major asperities located along the length and down the dip of a 150-km segment of the Cocos-North America plate boundary. The solution contains three major source regions including an 80 km by 55 km source near the hypocenter with a peak slip of 6.5 meters. Two additional sources are present on the southeast portion of the fault about 70 km away from the hypocenter. One of these sources, with a peak slip of 5 meters, covers a 45 km by 60 km area and extends downdip from a depth of about 10 km to 24 km. The third source region is somewhat smaller (30 km by 60 km area, 3.1-meters peak slip) and extends further downdip at depths between 27 km and 39 km. Aftershock activity following the earthquake was associated mainly with the two shallow sources. These two sources are separated by the aftershock zone of the 1981 Playa Azul earthquake.

Geosynthetic reinforced soil structures

Abstract: An approach for stability analysis of geosynthetic reinforced earth structures over firm foundations is presented. The approach involves both internal and external stability analyses. The internal stability analysis is based on variational limiting equilibrium and satisfies all equilibrium requirements. Two extreme inclinations of reinforcement tensile resistance are investigated: orthogonal to the radius defining the geosynthetic sheet, and horizontal, signifying the as‐installed position. Although a horizontal positioning requires slightly longer anchorage to assure pullout resistance, the slip surface is shallower when compared to the orthogonal case. As a result, the required total embedment length is longer for the orthogonal inclination. The external stability analysis is an extension of the bilinear wedge method and it allows a slip plane to propagate horizontally along a reinforcing sheet. The results for both the internal and external stability analyses are conveniently presented in the form of d...

Asymmetric X-ray Line Broadening of Plastically Deformed Crystals. II. Evaluation Procedure and Application to (001)-Cu Crystals

Abstract: In paper I [Groma, Ung~ir & Wilkens (1988). J. Appl. Cryst. 21, 47-53] a theory was developed to interpret the asymmetric X-ray line broadening of plastically deformed crystals. It was shown that the dislocation structure can be described by five distinct parameters, namely the dislocation density, the mean quadratic spatial fluctuation of the dislocation density, the effective outer cut-off radius, the dipole polarization and the spatial fluctuation of the dipole polarization of the dislocation structure. In this paper a procedure is developed to evaluate these parameters from the Fourier transform of the line profiles. The theory and this procedure are tested by applying it to the asymmetric line profiles of tensile-deformed Cu single crystals orientated for ideal multiple slip. The asymmetry of these profiles is assigned to the dipole polarization of the dislocation cell structure and is directly correlated to residual long-range internal stresses. It is shown that the data can be interpreted in terms of the quasi-composite model of the dislocation cell structure developed earlier for the same material.