This paper presents a new model to study the friction between rough surfaces with random distribution of the asperities, taking into account the contact mechanics. The results obtained show that as the surface separation decreases, the normal and friction forces increase and the coefficient of friction decreases. This model predicts higher friction forces and coefficient of friction than the model based on the Hertzian contact model. The sensitivity of the coefficient of friction to material properties is investigated using two sets of material properties. Assuming that the standard deviation and the radius of the asperities are constant, the first set investigates the variation of the adhesion energy, length of Burgers vectors, and elastic modulus parameters for the base material silicon. In the second set, real materials such as silicon, Fe, Cu, Au, and Ag are studied in contact with a silicon substrate. The results show that the friction coefficient decreases with the increase of the adhesion energy and increases with the increase of the length of Burgers vectors and elastic modulus.

The Bakharden-Quchan Faulted Zone is located in central Part of thrusted-folding belt of kopeh Dagh in NE border of Iran-Turkmenistan with array of active right lateral strike-slip faults by trending NW-SE that their ends have bent to joint blind faults in thrusts. Mechanism changing faults to reverse have caused to increase stress, shortening by thrusting in their ends bending. Most of the historical and instrumental earthquakes have distributed around faulted system of Bakharden-Quvhan Zone. Seismicity results of this zone with microseismics and computing parameters of b-value, fractal dimension (D) and mapping of local stresses distribution could have achieved us precious data on crust tension distribution, mechanism faults and system fault changes during time and place of probable occurrence future earthquakes. In neo-tectonic active zone b < 0/6 to 1/1 and D changes between zero to 2. If b< 0/6 and D closes to zero, faults and earthquakes will concentrate in asperities with high rate of stress but if b> 0/6 and D closes to 2 faults and earthquakes will scatter in whole of zone with low rate of stress. Occurrence of major earthquakes are not far away expectation in edge of asperities although there is a possibility that they gradually loss energy to get inactive because the seismology way of releasing energy in these faults is, when group of faults approach to motion threshold are increased b-values and other group of faults are accumulating energy, so their b-values are decreased.

Introduction: This article's objective is to explain slip distribution on faults and understanding further the processes of earthquakes and fault slip, and how they are related. Yet, rare were the studies that tried to compare these slip distributions. Few studies did so, but mainly focused on characterizing the earthquake slip complexity. The overall slip distribution patterns were not considered. Hence, the questions related to the average shape of earthquake slip distributions are still opened.The profiles of maximum and mean slip that extracted from the models in this article allow total slip variations along both fault strike and dip to be studied. The general idea that followed is that analyzing many earthquakes together provides a way of smoothing their individual peculiarities (such as specific slip complexities), so that common, general properties, may emerge.Aim: The present study investigated characterizing average slip distributions on earthquakes beyond their individual heterogeneity.Methods: An auto correlation method was used to define an effective length at which zones of zero (or small) slip is not contributing, even when localized between slip patches. A collection of one-dimensional profiles was prepared, each is given as D(x) (D is displacement or slip; x is position along fault length or width). Hence, all profiles are mathematically comparable and can be analyzed similarly, with a general procedure.Results: While earthquakes are complex features with highly heterogeneous mechanical conditions on their planes (due to pre-stresses, static and dynamic stress loading/unloading by neighboring ruptures, host rock properties, etc…), they share some common, generic properties that appear when a large number of events are examined together: most produce triangular slip profiles (»70% are asymmetric) with well defined, long linear tapers. Triangular slip distributions on earthquake faults seem to be self-similar, suggesting that they attest to a scale-invariant mechanical behavior. Most slip profiles are asymmetric, suggesting different behaviors at the two edges of the major asperity.Conclusion: The maximum and mean slip profiles draw a triangular and asymmetric average curve, while three dominant degrees of asymmetry are revealed. The observation of triangular slip distributions therefore attests to a common, general property of faults, regardless of their scales and kinematics. The area broken during this “first stage” appears as the “major asperity” that shapes the total triangular slip distribution.Most of the moment is released by rupture of this area. This rupture produces dynamic stress overshoot in the surrounding fault plane. This overshoot makes some unfavorably stressed (or in inappropriate energetic conditions) portions of the fault plane in conditions to slip. The linear trends in the final slip profile are taken to be associated with the progressive dissipation of the energy provided by the dynamic rupture of the main asperity.

The characteristics of near-fault ground motion are investigated considering heterogeneous slip distribution on the fault plane. Areas on the fault plane with large slip in compare with the average slip on the fault are known as asperity. The characteristics of strong ground motions in near-fault area are strongly affected by faulting parameters such as asperity location, maximum slip of asperity, rise time and rupture velocity on the fault plane. Based on theoretical Green’s function for infinite media, the near-fault pulse is simulated for finite fault model with different faulting specifications. Then, the variations of each fault parameter and site to fault distance on near-fault pulse characteristics are numerically examined and discussed. 

The influence of surface roughness magnitude and direction on dry static friction coefficient between two similar steel samples has been studied through an experiment. A testing apparatus has been designed and fabricated to measure the friction coefficient for a few forms of surface asperity. The average, maximum and minimum values of static friction coefficients among steel samples have been measured and numerically proposed in terms of some discrete values of the surface roughness, base and counter body angles. Correction coefficient defined as the ratio of maximum to minimum friction coefficient has been found on the result basis. According to the results of the experiments, dry static friction coefficient between two similar steel samples is affected by both magnitude and direction of surface roughness. Under the condition of static equilibrium, the Colomb - Amonton formula has been used to determine friction coefficient between samples. The flexibility and mass of the string have been neglected, and the reservoir pendulum-like swinging and the water movement therein have been avoided within the experiments.

Nowadays, Barton’ s Joint Roughness Coefficients (JRC) are widely used as the index for roughness and as a challenging fracture property. When JRC ranking is the goal, deriving JRC from different fractal/wavelet procedures can be conflicting. Complexity increases when various rankings outcome from different calculation methods. Therefore, using Barton’ s JRC, we cannot make a decision based on the proven mathematical theories because each method has a different rank. Ideally, these rankings must be equal but, in practice, they are different for each method. To solve this problem and to achieve a robust and valid ranking for JRC, Condorcetand Borda count methods have been used. These methods have been proposed as fusion approaches. Re-ranking of JRC using different methods integrated with Condorcet showed confusion in ranking of the JRC4, JRC5, and JRC6 profiles. This ambiguity is equal to equalizing decision conditions about all the three at the examination of the winners, losers, and draws in pairwise matrices. Therefore, Borda Count was applied and resulted in robust rankings. In fact, a new approach for a roughness measurement is presented. A new JRC ranking called JRCN is introduced. This new ranking shows a lower sum of squared errors (0. 00390) in comparison with the original JRC ranking method (0. 00410) and ranked JRCN1 to JRCN10. Thus it is proposed to consider JRCN as a new and improved version of JRC rankings.

In this article, we studied the dynamic fracture process of Bam earthquake. In two presented models stress heterogeneity on the fault plain was modeled as barrier or asperity and friction included as slip-weakening relationship. Results of models were constrained by near field ground motion recorded in Bam station. In the first model, fracture starts form a weak asperity which its waves surround the neighbor barrier and break it down. In the second model, another asperity is included in southern part of the fault. Breaking barrier releases two fracture fronts traveling in two different regimes. One of them travels faster than shear waves and goes to the intersonic velocity. The other front travels with 0.74 shear wave velocity and makes the largest pulse of the record. Both models predict the slip rate successfully, but the second model is more consistent with the real data.

Effect of discontinuities roughness including tooth-shaped asperity, rough undulating and smooth plane having different orientations respect to confining pressure on the strength of rock under triaxial stresses has been investigated in this research. 15 groups of specimens having three types of discontinuities roughness and five types of slope angles from 0 to 90 degrees have been successfully prepared and tested under triaxial stresses. The axial strength of rough undulating and tooth-shaped asperity discontinuities decreases a little with increasing slope angle from 30 to 45 degrees under constant confining pressure and in general the axial strength of smooth plane discontinuities having different orientations is less than the axial strength of rough undulating and tooth-shaped asperity discontinuities under the different confining pressures. For tooth-shaped asperity discontinuities having orientation angles 45 degrees, failure also occurred at the body of the specimens particularly with increasing the confining pressure. Sliding occurred at the one side of tooth-shaped asperities of discontinuity having orientation angles of 60 degree under uniaxial loading and displacement took place at the direction of discontinslopeuities. But tooth-shaped asperities were broken along the discontinuities under the higher confining pressures. The effect slope angle on the axial strength decreases with an increase of confining pressure and rate of reducing the axial strength increases with an increase of discontinuity roughness. As, the strength of specimens having very rough discontinuities under high confining pressures approaches to the strength of massive (intact) rock. The maximum axial strength to the minimum axial strength ratio (Rtriax) has high value for the zero confining pressure and it decreases sharply as a negative power function of confining pressure then approaches to a constant value.

When two bodies slide on each other the asperities are engaged and deformed which causes the dynamic friction. By superposing ‎ultrasonic oscillation to one of the bodies, the friction force is reduced. The experiments show that the friction force may be reduced by ‎about 60 percent depending on material properties and the kinetics of the two bodies. This phenomenon is widely used in metal forming ‎and metal cutting. This phenomenon may be used as a replacement of lubricants in such processes due to its higher efficiency and less ‎pollution effects. In this research an elastic-plastic model for the surface contact is given which is capable of predicting the friction force when ultrasonic ‎vibrations are superimposed to macroscopic motion. The result of this model is compared with that of the experimental values. The ‎differences between these values are shown to be less than 10 percent. The result of the model is also compared with that of the Dong ‎model. The comparison show that the present model ‏‎ has better accuracy of the Dong model.