Abstract While the fracture (rupture) dynamics of strike-slip earthquakes has been clarified to a practically acceptable level, the mechanical characteristics of shallow dip-slip seismic events remain unexplained owing to the shortage of the near-field seismological observations and the analytical difficulties at the rupture tip of an interface (fault plane) in the proximity of a free surface. In this contribution, utilizing the techniques of finite difference modeling and dynamic photoelasticity, the fracture dynamics of a dip-slip fault plane located near a free surface is studied numerically as well as experimentally. Each two-dimensional fracture model may contain a flat fault plane (initially welded interface) that dips either vertically or at an angle (e.g. 45 degrees) in a monolithic linear elastic medium (representing rocks). The time-dependent development of wave field associated with the crack-like rupture along every fault plane is recorded. Both numerical and experimental observations indicate when the fault rupture that is initiated at some depth approaches the free surface, four Rayleigh-type waves are produced. Two of them move along the free surface as Rayleigh surface waves into the opposite directions (in the hanging wall or footwall) to the far field, and the other two propagate back downwards along the fractured interface into depth. These downward interface waves may considerably govern the stopping phase of the dynamic fracture, and according to the seismological recordings, they seem to have existed during the rupture process of the 2011 off the Pacific coast of Tohoku, Japan, earthquake. In the case of an inclined fault plane, the interface and Rayleigh waves interact with each other and a shear wave possessing concentrated energy (corner wave) is generated and causes stronger disturbances in the hanging wall. The existence of the downward interface and corner waves, first numerically predicted in 2005 by Uenishi and Madariaga, seems to have been confirmed by this series of laboratory fracture experiments.

ABSTRACT Exploration in trachyandesitic Mount Sabalan, near the town of Meshkin-Shahr in north western Iran, indicated that this area hosts geothermal reservoir. In this study, we determine the direction of principal stresses using structural geology features exposed on the surface. These features include slickensides and fault steps. Analysis of the recorded slickenside traces in six districts was carried out using multiple inverse method. Results of the analyses indicated that the direction of the three principal stresses in every district is independent of the others. However, in all districts, maximum principal stress is vertical, minimum and intermediate principal stresses are horizontal. One of the applications of stress direction is in the design of hydraulic fracturing. Since the permeability of this reservoir is rather low, this stimulation technique could be a solution for enhancing productivity. Direction of the minimum stress dictates the geometry of created fracture. In this case the fracture would propagate vertically. 1. Introduction 1.1. History of Project In 1974, for assessment of geothermal resources potential in Iran some primarily studies including aeromagnetic and gravimetric operation have been done in area more than 8300 km2. After a long standby, in 1990 previous documents were reviewed and resistivity operations were conducted. According to the resistivity anomalies and geochemical alteration Meskin- Shahr (Northwestern Sabalan) introduced as the first geothermal potential in Iran. So, three exploration (production) wells up to 3200, 3176 and 2260 m and two injection wells up to 650 m have been drilled. Completion investigations such as logging and flow tests indicated that temperature of reservoir is about 240°C and permeability of reservoir is medium to low. Permeability is one of the important factors in using captured heat. Base on some calculations and estimations, it is essential to increase permeability by artificial methods. To increase permeability, we suggest hydraulic fracturing. During the hydraulic fracturing, artificial fractures are created in reservoir. Created fractures extend perpendicular to minimum horizontal stress. So, by knowledge of principal stress directions, we can determine artificially fractured geometry and drill the injection wells in the best direction. In this study, we try to determine direction of the in-situ stresses in Meskin-Shahr geothermal field using multiple inverse method. 1.2. Regional Geology Study area is located around the Sabalan Mountain in Ardabil province, northwestern Iran (Fig. 1). Geological setting of this area such as lithology and tectonics is controlled by Sabalan volcano activities. Volcanic structure is spot and stratovolcan like Stromboli volcano in Italy. Central volcano erupted on the main conjugated fracture over the paleohorst with E-W trend. According to published studies, volcanic activity in Sabalan started Eocene and resumed in Pliocene by eruption of trachyandesitic to andesitic lava flow through the main caldera. After caldera collapsing in Early Pleistocene, central caldera partially filled by trachyandesit–trachydacite 1394 lava flows [1]. The study area is located in complex compressional zone between Iran, Arabia and Eurasia plates in Alborz- Azerbaijan structural zone.

Abstract At the Sarcheshmeh mine, the design and stability analysis is very critical due to the existence of major features such as faults and dikes, and relation of various joint sets with the geometrical form of the pit. Western area of Sarcheshmeh mine includes various types of failures, commonly structural failure type such as Sarcheshmeh pseudowedge failure. This type of failure consists of large and weak blocks of weathered highly jointed andesite surrounded by a fault and important joints. Existence and extension of near parallel faults filled with pyrite-clay in the western wall of Sarcheshmeh mine along with the geometry of this wall results in special slide conditions which need to be considered during mine expansion project. There are some limitations in using limit equilibrium methods to analyze this type of sliding. This paper analyzes Sarcheshmeh pseudowedge failure using three dimensional distinct elements method. The influence of effective parameters on the stability of such failures is quantitatively calculated and proper solutions are discussed. 1. Introduction The Sarcheshmeh porphyry copper-molybdenum deposit is located in southern Iran, at 30 degree N lat., 56 degree E long. It is currently the largest open pit mine in Iran. Western area of Sarcheshmeh mine includes various types of failures, commonly structural failure type such as Sarcheshmeh pseudowedge failure. This type of failure consists of large and weak blocks of weathered highly jointed andesite. Due to intersect of a fault with the rock mass surrounding the walls of this area (figure 1), various wedge-like rocks have been progressively sliding on the fault plane [1]. Sarcheshmeh mine is being expanded as a result of cut off grade reduction. Existence and extension of near parallel faults has made pseudowedge failure a new challenge in expanding western area of Sarcheshmeh mine. Most parts of this rare failure are kinematically stable but they will become instable with time and therefore they can not be kinematically analyzed. In limit equilibrium analysis, the stability is investigated regardless of its relation with displacements and safety factor is calculated based on static condition. Therefore, when displacements occur in a slope, limit equilibrium methods are not suitable to evaluate the effect of such displacements on total stability of the slope [2]. An example of such analysis has been done on Sarcheshmeh pseudowedge failure [3]. Numerical methods are available to analyze and model this phenomenon according to observations. This paper analyzes Sarcheshmeh pseudowedge failure using three-dimensional distinct elements method. The influence of effective parameters on the stability of such failure is quantitatively calculated and proper solutions are discussed. 2. Geological Settings Porphyry ores, such as Sarcheshmeh, are the most complex geological environments in terms of fracturing. The Sarcheshmeh deposit is related to the Late Tertiary granodioritic stock which intruded the early Tertiary volcanics. The deposit 560 was intruded by intra-mineralization and post mineralization dikes and intrusives [4].

ABSTRACT: A numerical failure model of rock, RFPA(Rock Failure Process Analysis), is used to simulate the process of rock failure under different confining pressures, including acoustic emission produced by rock failure. We find that the spatial distribution of acoustic emission (A E) event locations is fractal and has very good statistical self-similarity in different confined conditions. The fractal dimension D decreases progressively in the rock failure process. In other words, the AE event locations become more and more ordered. The fractal dimension D becomes eventually smaller in the specimen under higher confining pressure. l. INTRODUCTION Acousticemission (AE), as a transientelastic wave generated by the rapid release of energy within a material, is a ubiquitous phenomenonassociated with rock fracture and has provided a wealth of Information regarding the failure process In rock (Lockner). In other words, the AE activities in rocks represent the damage process of rock failure. Fractal Geometry has been widely used for the description of irregular phenomena in various scientific fields recently. It is a powerful tool not only for studying complex shapes, but also for describing damage phenomena with statistical characteristics. Hirata et al.conducted a creep test on Oshima granite at 40 MPa confining pressure and about 85% fracture strength. He found that the spatial distribution of AE in rocks is a fractal, and that the fractal dimension decreases with the evolution of rock fracturing (Hirata, 1987). Patience A. Cowie et al presented a numerical rupture model to simulate the growth of faults in a tectonic plate. They explored in detail the time evolution of the capacity (D0), information (D1), and correlation (D2) fractal dimensions (Cowie, 1995, I 993). recently, a numerical approach for simulating damage initation and related propagation of seismic energy during brittle rock failure, RFPA 2d (Rock Failure Process Analysis), was presented by Tang C. A. et al (Tang. Chen & Tang, 2000). However, almost the whole research work on rock failure aspects using RFPA has been concentrated on the qualitative analysis on fault propagation, the spatial distribution of AE and the location of deformation. In this paper, fractal concepts will be used to evaluate quantitively the evolving degree of disorder in the spatial distribution of AE event locations and the propagation of faults in rock failure under different confining pressures. lt is found that the defined fractal dimension decreases through the loading step.Inother words, it turns out thatthe distribution of AE becomesprogressively more ordered with the development of faults,f rom the initial loading to the main failure. 2. MODEL DESCRIPTION The demand for new tools, which may contribute to a better understanding of failure mechanisms of brittle rocks. initiated the development of RFPA. Mathematically, the RFPA code is a combination of the linear finite clement method (FEM) and continuum mechanics method capable of simulating non-linear and discontinuous mechanical behavior. In all cases. the models simulate plane strain compression of the specimens, which may be applied either uniaxially or biaxially.