time variation of b and qc at mt etna 1981 1987 abstract time variations of seismic attenuation qc and of the coefficient b in the frequency magnitude formula are presented for mt etna during 1981 1987 significant variations of both parameters were found suggesting long period variations of the physical state of the volcano

rate dependence of ae activity during frictional sliding 1 a velocity step test was performed to examine effects of the macroscopic sliding rate on ae activity during steady state frictional sliding on a pre cut fault in a granite sample both the amplitude frequency relation and the number of ae events per unit displacement changed in response to a change in the macroscopic sliding rate both the ae activity and its rate dependence evolved with sliding the rate dependence of cumulative seismic energy calculated from the ae activity shows a positive correlation to that of friction coefficient suggesting that the rate dependence of seismic energy is one of the origins of rate dependent friction because the seismic energy is a part of frictional energy loss further the rate dependence of seismic energy is much larger than that of friction meaning that a ratio of seismic energy to frictional energy loss depends on the macroscopic sliding rate

seismic and aseismic preparatory processes before large stick slip failure natural earthquakes often have very few observable foreshocks which significantly complicates tracking potential preparatory processes to better characterize expected preparatory processes before failures we study stick slip events in a series of triaxial compression tests on faulted westerly granite samples we focus on the influence of fault roughness on the duration and magnitude of recordable precursors before large stick slip failure rupture preparation in the experiments is detectable over long time scales and involves acoustic emission ae and aseismic deformation events preparatory fault slip is found to be accelerating during the entire pre failure loading period and is accompanied by increasing ae rates punctuated by distinct activity spikes associated with large slip events damage evolution across the fault zones and surrounding wall rocks is manifested by precursory decrease of seismic b values and spatial correlation dimensions peaks in spatial event correlation suggest that large slip initiation occurs by failure of multiple asperities shear strain estimated from ae data represents only a small fraction 1 of total shear strain accumulated during the preparation phase implying that most precursory deformation is aseismic the relative contribution of aseismic deformation is amplified by larger fault roughness similarly seismic coupling is larger for smooth saw cut faults compared to rough faults the laboratory observations point towards a long lasting and continuous preparation process leading to failure and large seismic events the strain partitioning between aseismic and observable seismic signatures depends on fault structure and instrument resolution

fractal structure of spatial distribution of microfracturing in rock summary a constant stress fracture experiment of oshima granite was carried out at the confining pressure of 40mpa hypocentres of 2064 acoustic emissions were located during the experiment using the correlation integral we found that the spatial distribution of hypocentres of acoustic emission is a fractal and that the fractal dimension decreases with the evolution of rock fracturing the spatial distribution of earthquake s hypocentres reveals fractals ranging from regional to worldwide distribution if we extrapolate from laboratory measurements it is possible to predict the occurrence of large earthquakes by the decrease in the fractal dimension

assessment of mineralogical and petrographic factors affecting petro physical properties strength and cracking processes of volcanic rocks abstract microtextural features influence the petrophysical and mechanical properties of rocks including the elastic properties and cracking processes under axial loads volcanic rocks with varying microtextural characteristics and compositions were evaluated to assess the effect of the main constituents mineralogical petrographic and micro structural features on the petrophysical properties elastic properties and strength furthermore detailed analyses were also used to understand the cracking processes under axial loads the analyses of the cracking processes were completed on thin sections obtained from the mechanically tested specimens the results from the quantitative mineralogical and petrographic studies and observations from thin sections revealed that the mineral mass fractions have an effect on the specific gravity and loss on ignition loi values on the other hand unconfined compressive strength ucs and elastic properties are mostly affected by petrographic variables e g mineral content the ucs values tend to decrease with a relative increase in the groundmass with respect to the phenocryst content and vice versa biotite is the only mineral that influences the ucs individually geometric features e g feret s diameter and perimeter of opaque minerals and biotite are determined to be important constituents influencing the young s modulus under axial loads crack propagation is strongly dependent on the proportional distribution of the phenocryst and groundmass it was observed that increasing groundmass content leads to predominantly axial cracks the cracks tend to bend or propagate as a boundary crack when they reach the boundary of an unaltered phenocryst thus axial and shear cracks co exist with increasing amounts of phenocrysts which hinders crack propagation occasionally cracks can penetrate the altered or opaque phenocrysts depending on the degrees of orientation with respect to applied load of the same minerals furthermore the synthesis of the measurements obtained from ucs tests and thin section observations reveals that an increase in the amount of phenocrysts which promote the formation of more shear cracks in addition to axial cracks causes an increase in the radial strain and poisson s ratio the other factors investigated had minor effects on physical and mechanical properties of studied rocks

evolution of microseismicity during frictional sliding we have done frictional sliding experiments on inada granite in double shear and monitored the acoustic emission ae produced and temporal changes in the microseismic b value where b is defined as the log linear slope of the ae frequency amplitude distribution using both rough and smooth ground simulated fault surfaces we have found i the maximum amplitudes of ae events during stable sliding are strongly dependent on the surface roughness with smooth ground surfaces giving smaller maximum ae amplitudes ii b values are related to the surface topographic fractal dimensions so that in steady state stable sliding smooth surfaces exhibit lower b values than rough surfaces iii the b value falls before stick slip instability the change of b with slip we interpret in terms of evolving fractal crack damage during frictional sliding of the fault surfaces

strain rate and temperature dependence of omori law scaling constants of ae data implications for earthquake foreshock aftershock sequences 1 little is known about the temperature and strain rate dependence of acoustic emission ae activity ae hence we carried out a preliminary series of flow through triaxial compression tests on porous sandstones at different temperatures and strain rates the ae data exhibits clear foreshock and aftershock sequences with respect to the dynamic failure of the test specimen significant ae activity starts less than 5 min before sample failure irrespective of the strain rate the increase in the ae event rate is steeper and the foreshock exponent p is smaller in the slow strain rate tests it could be the reason why there are no easily recognisable foreshock sequences for most individual earthquakes the aftershock decay parameter p is a linear function of test temperature as it has also been inferred for natural seismicity the seismic b value decreases systematically with increasing deformation rate suggesting a greater proportion of small cracks in the slow strain rate tests hence the ae activity is a function of both strain rate and temperature

the influence of foliation on the fragility of granitic rocks image analysis and quantitative microscopy fabric dependent anisotropy is important in understanding the mechanical behaviour of foliated rocks because the foliation creates mechanically weak discontinuities using optical microscopy a foliation index fix was calculated for a group of granitic rocks in southern sweden that displays a range of textures from foliated to nonfoliated image analysis from scanning electron microscope with backscattered detector sem bse images was used in order to measure the rock texture of these samples the analyses were compared with the los angeles la test which measures resistance of rock aggregate to fragmentation the results demonstrate that the measured grain size shape and spatial arrangement are important parameters controlling the fragility of the rock both the texture and foliation must be taken into account to obtain a significant relationship with the mechanical analyses we suggest that this alternative method could be a helpful tool for predicting a rock s suitability as an aggregate as it gives a better understanding of the material properties compared to mechanical testing

contrasts of seismic velocity density and strength across the moho abstract we provide an overview of contrast of elastomechanical parameters across the moho basically contrasts in seismic wave velocities density and yield strength these can be regarded as dynamic and quasi static endmembers of elastomechanical parameters of the crust mantle transition with respect to practical applications they are closely related because seismic investigations play the role of exploring the earth structure and physical state forming the boundary conditions for determining density and rheological models we address both average global moho models and petrophysical and structural factors that cause deviations from the global averages such as variations in moho depth temperature and rock composition fabric anisotropy and macro scale heterogeneity besides principle considerations these factors are put in a regional context in order to demonstrate how they are related to past and present tectonic processes seismic velocity and density contrasts are found between 0 and 25 whereas strength or viscosity contrasts may be orders of magnitude higher but may vanish as well or show a discontinuity of higher order only especially oceanic and old cratonic crust and near moho mantle may appear as a rheological unit although they are seismically well distinguishable in terms of seismic velocities the moho may vanish mainly under the influence of serpentinization or eclogitization originally defined as a first order discontinuity in seismic velocity the moho has turned out to be an interface across which other seismic properties such as seismic velocity gradients anisotropy and heterogeneity scale parameters can change strongly too however knowledge of these parameters as well as their relation to the rheology of the crust mantle transition is still restricted to local or regional examples so no global conclusions can be drawn

mt etna a model for the 1989 eruption abstract during the 1989 eruption of mt etna one of the most important in the last 20 years in terms of effusion rate a pair of fractures formed on the slopes of the southeast crater cone and propagated in a few days trending ca northeast and southeast with large quantities of magma being drained from the northern fracture in contrast the southern fracture after a short initial eruptive phase grew by 5 km in five days without eruptive or seismic activity when the fracture system crossed the southern scarp of the valle del bove wall some 6 km se of the active crater an intense seismic swarm started in the same area this lasted about four days and consisted of several hundred events clustering in a small focal volume although such a sequence of failure events contains elements of compatibility with a shallow dyke intrusion it did not lead to the expected flank eruption which would have threatened settlements just a few kilometres from the distal end of the fracture the question arises therefore whether or not the fracture system was dyke related and if so to what extent we attempt here to answer such a question by integration and interpretation of the available field observation and geophysical data indeed field observation constraints on the southern fracture system and the typical depth 2 km of the swarm do not contain evidence for shallow dyke emplacement beneath the lowermost part of the sse fracture conversely the inferred direction and shape of the tremor source the location and extent of a gravity anomaly observed a few months before the eruption the near horizontal migration of the seismic focii during the swarm and the change with time of related focal mechanisms lead us to hypothesize that the extreme development of the fracture system at its south was due to a deeper intrusion beneath the southern slope of the volcano

effect of sliding rate on the activity of acoustic emission during stable sliding the mechanical and statistical characteristics of acoustic emission ae events during stable sliding are investigated through a laboratory experiment using a granite specimen with a pre cut fault numerous ae events are found to be generated on the pre cut fault indicating that microscopically unstable fracture occurs during macroscopically stable sliding the composite focal mechanism solution of ae events is determined from the first motion directions of p waves the determined mechanism is consistent with the double couple one expected for the slip on the pre cut fault the source radii of large ae events are estimated to be about 10 mm from the widths of the first p wave pulses these indicate that the ae events are generated by shear fracture whose faulting area is a part of the pre cut fault plane the occurrence of ae events as a stochastic process approximately obeys the poisson process if the effect of mutually dependent events consti tuting clusters is corrected the observed amplitude frequency relation of ae events approximately follows a power law for a limited amplitude range as the macroscopic sliding rate increases the number of ae events per unit sliding distance decreases this rate dependence of the ae activity is qualitatively consistent with the observation that the real area of contact between sliding surfaces decreases with an increase in the sliding rate as reported in the literature

aftershock detection thresholds as a function of time results from the anza seismic network following the 31 october 2001 ml 5 1 anza california earthquake we examine aftershock detectability thresholds for events in the initial part of the 31 october 2001 m l 5 1 sequence in southern california this sequence occurred directly below the broadband anza seismic network which recorded continuous waveform data at 13 azimuthally well distributed stations within the study region seven had epicentral distances 20 km of the 608 aftershocks 0 m l 2 8 in the initial 2 hr of this sequence the first five aftershocks recorded were only identifiable at stations within 30 km after applying a high pass filter using a cluster radius 1 1 km of 200 representative aftershocks we track the maximum seismogram amplitude versus earthquake magnitude this relationship helps us quantify the visibility of aftershocks within the mainshock coda and assess our detection capabilities we estimate that detectable aftershocks within the mainshock coda include 1 those over magnitude 3 that are within 15 km of the network centroid that occur 12 sec or more into the sequence and 2 those over magnitude 2 that are within 30 km of the centroid of the network that occur 60 sec or more into the sequence we find a lack of large aftershocks in this sequence the largest aftershock m l 2 8 is substantially smaller than the mainshock m l 5 1 we suggest this relatively large magnitude differential is dictated by a combination of factors that includes complexity of the san jacinto fault system and the lack of large earthquakes in the region in the past 20 years online material quicktime movies juxtaposing a 3 2 aftershock in the coda of a 5 1 mainshock

numerical heat and fluid flow modeling of the panorama volcanic hosted massive sulfide district western australia exceptional exposure of the archean pilbara block in western australia reveals a cross section through an archean massive sulfide hosting volcanic succession with underlying subvolcanic intrusion in the panorama district a numerical model based on available detailed geologic information has been constructed to simulate heat and fluid flow in the panorama district the modeling provides insight into the evolution of the hydrothermal system and evaluates key geologic parameters and their influence on fluid flow hydrothermal circulation and the genesis of massive sulfide orebodies the model simulates important aspects of the panorama massive sulfide district such as temperature distribution relative alteration zonation and the size and distribution of orebodies predicted temperatures ranging from 150oc at the top of the volcanic pile to 400oc at the andesite diorite interface are comparable to temperature estimates based on previously published oxygen isotope mapping modeled fluid discharge temperatures are highest for the sulphur springs deposit 300o 400oc and lower for the kangaroo caves and other deposits 250o 350oc the most favorable conditions to reproduce the orebodies and their related alteration zonation occur at anisotropic rock permeabilities comparable to the upper oceanic crust 10 15 10 14 m2 and higher fault permeabilities 10 14 10 13 m2 with a specific fault arrangement similar to that mapped in the field the 4 6 million metric tons mt sulphur springs orebody is predicted to form in less than 5 000 yr assuming a hydrothermal fluid with seawater salinity 10 ppm base metal concentration and a low deposition efficiency 10 other deposits form above the faults under similar conditions a large range of base metal concentrations in the fluids can account for the known orebodies but high temperatures 250oc and high flow velocities 10 7 m s are necessary to produce the observed alteration patterns and distribution of ore deposits results indicate that the establishment of a significant hydrothermal system capable of forming economic massive sulfide deposits is favored in fresh volcanic rock packages that have not been affected by earlier compaction or alteration under these conditions economic massive sulfide orebodies 5 mt of 10 zn cu may form in a few thousand years although the overall lifespan of the hydrothermal system may be between 30 000 and 200 000 yr depending on the variations in rock and fault permeability with time

geometric scale invariance genesis and self organization of polygonal fracture networks in granitic rocks abstract we documented polygonal fracture networks in the tuolumne intrusive suite sierra nevada batholith by collecting data on the size orientation and length of fractures and fracture bound polygons in nearly isotropic granitic rocks polygonal fracture networks are constrained to sheets of rock sub parallel to the underlying rock with the sheets bound above and below by fractures i e free surfaces data indicate that most geometric characteristics of the polygonal fracture networks are scale invariant large m scale networks exhibit the same geometry as small cm scale networks a linear correlation exists between sheet thickness and average polygon size polygons within the networks are anisotropic with the degree of anisotropy correlated with the degree of sheet curvature the preferred orientation of the polygons correlates with the inclination of the sheet with long axes of polygons parallel to sheet strike based on geometry we suggest that the polygonal fracture networks in granitic rocks observed in this study formed from temperature fluctuations that caused thermal expansion and contraction in the rock repeated cycles of expansion contraction led to the initiation and propagation of fractures within the network we propose that the observed fracture patterns are not a product of extrinsic conditions but rather a product of interactions between fractures implying that the polygonal fracture networks are self organizing systems

fault model for preseismic deformation at parkfield california we construct an earthquake instability model to estimate precursory faulting and ground deformation before the next moderate m 5 5 6 earthquake on the san andreas fault near parkfield california the quasi static model simulates fault slip fault shear stress and ground deformation for all stages of repeated earthquake cycles unstable slip which is the analog of a moderate parkfield mainshock is caused by overall failure of a postulated strong area or patch of the fault zone the brittle patch and surrounding weaker viscous fault are defined by the sign of a spatially varying coefficient of a slip rate dependent fault law stable failure of the patch leading up to mainshock failure causes slip rate to increase at depth amplitudes and timescales of the resulting preseismic deformation anomalies are found for the current earthquake cycle at parkfield starting just after the 1966 mainshock in two ways in the first way we vary parameter values in a sequence of simulations so as to find the simulation giving best agreement with locations moments and recurrence times of past moderate earthquakes and also with fault creep and trilateration line length changes since the 1966 mainshock in the second way we assign values of most parameters from laboratory friction experiments and a temperature depth profile inferred from heat flow data overall agreement between model results and observations is comparable for the two methods in all simulations preseismic deformation anomalies arise from slip rate increase near the model earthquake focus and start several years or less before instability preseismic anomalies in surface fault creep and line length are always too small to detect in current measurements however for some simulations constrained mainly by field data the predicted anomalies in borehole dilatation are large enough to detect

novel grain based model for simulation of brittle failure of alxa porphyritic granite abstract a grain based model gbm is generally employed by many researchers to simulate the microcracking process of crystalline brittle rock by the distinct element method in this study a novel grain based model ngbm in two dimensional particle flow code 5 0 pfc2d 5 0 is proposed to emulate the brittle failure of crystalline rock first the ngbm scheme is introduced in which the flat joint model is employed to model the contacts in mineral grains and the smooth joint model is assigned to the grain interface contacts then compressive tests are performed using alxa porphyritic granite and the strength values are fitted with the hoek brown failure criterion third a ngbm was generated based on the petrographic texture of realistic rock such as mineral constituents grain size and distribution the input microscale parameters are carefully calibrated according the experimental results finally this model is applied to study the microcracking process of alxa porphyritic granite and the influence of spatial distribution of minerals it is found that a relatively high ratio of uniaxial compressive strength to tensile strength of each mineral or synthetic samples can be reproduced by the ngbm moreover the simulated results show this model can capture the nonlinear characteristic of the hoek brown failure criterion after modeling numerous mineral grains were cut across which is consistent with the actual experimental observation the tensile crack is over the shear crack in the models while the number of intra grain shear crack increases dramatically with increasing confining pressure in addition the numerical results indicate that the effect of spatial distribution of minerals has limited influence on the evolution of microcracks but has great impact on microcrack distribution in summary the proposed ngbm in pfc2d can well reproduce the realistic failure process of granitic rocks under different loading conditions

fluid induced rupture experiment on fontainebleau sandstone premonitory activity rupture propagation and aftershocks 1 a 14 porosity fontainebleau sandstone sample diameter 40 mm length 88 mm was loaded tri axially under 100 mpa confining pressure and 240 mpa differential stress in drained conditions and under constant load pore pressure water was raised until failure was triggered during the experiment elastic wave velocities and permeability were monitored while more than 3000 acoustic emissions ae were located prior and after failure ae locations show that macroscopic fracture propagated from a large nucleation patch at speeds comprised between 0 1 and 4 m s number of ae hits per second followed omori s law with exponents of 0 92 and 1 18 pre and post failure respectively no quiescence was observed post failure except where rupture initially nucleated from fast depressurization of the pore space induced secondary aftershocks located within the fracture plane possibly indicating a heterogeneous fault geometry after rupture of lower permeability that compacted during the release of pore pressure

microseismic properties of a homogeneous sandstone during fault nucleation and frictional sliding summary the formation and evolution of faulting in three initially intact oil saturated specimens of clashach sandstone is examined under conditions of constant strain rate loading at three different confining pressures simulating the effect of tectonic loading at different depths in the earth s upper crust after a fault is formed the specimens are slid for a time and then the initial confining pressure is increased to simulate the long term recovery of strength expected in the earth the differential stress u and natural acoustic emissions ae are measured during the three separate phases of fault nucleation sliding and strengthening at the end of each individual phase the fluid permeability is measured by a pulse decay technique at constant stress the ae are interpreted using a mean field theory for damage evolution which calculates a mean crack length c from the seismic event rate n and the b value and a mean energy release rate g from u and c c and g both increase non linearly in the nucleation stage and are associated with large fluctuations in the scaling exponent b in contrast the b value remains almost constant at a value near unity in the sliding phase even when the fault is mechanically strengthened small fluctuations in g observed during sliding may be associated with the breaking of individual asperities the relative stability of b combined with a relatively constant sliding stress implies that frictional sliding has all the hallmarks of a self organized critical soc phenomenon in contrast the fresh fracture of intact rock shows a continuum of states with power law scaling at a variety of b values where b is negatively correlated to g during the fault nucleation stage the implied subcritical crack growth index n obtained from the ae data shows a distinct break of slope during the failure of the intact specimens from n 2 consistent with a theoretical transition from stable damage to dynamic instability a possible mechanism is the transition from local mechanisms dominated by dilatant hardening negative feedback to microcrack coalescence positive feedback interpreted in this way the results imply that the organized coalescence of microcracks to form a fault occurs before the ultimate strength peak stress is reached this emphasizes the fact that local mechanisms of softening or hardening do not always scale simply to the macroscopic rheology in a heterogeneous medium the fluid permeability reduces steadily throughout all phases of deformation testament to the self sealing nature of deformation in porous sedimentary rocks

how geometrical constraints contribute to the weakness of mature faults increasing evidence that the san andreas fault has low shear strength1 has fuelled considerable discussion regarding the role of fluid pressure in controlling fault strength byerlee2 3 and rice4 have shown how fluid pressure gradients within a fault zone can produce a fault with low strength while avoiding hydraulic fracture of the surrounding rock due to excessive fluid pressure it may not be widely realised however that the same analysis2 4 shows that even in the absence of fluids the presence of a relatively soft gouge layer surrounded by harder country rock can also reduce the effective shear strength of the fault as shown most recently by byerlee and savage5 as the shear stress across a fault increases the stress state within the fault zone evolves to a limiting condition in which the maximum shear stress within the fault zone is parallel to the fault which then slips with a lower apparent coefficient of friction than the same material unconstrained by the fault here we confirm the importance of fault geometry in determining the apparent weakness of fault zones by showing that the apparent friction on a sawcut granite surface can be predicted from the friction measured in intact rock given only the geometrical constraints introduced by the fault surfaces this link between the sliding friction of faults and the internal friction of intact rock suggests a new approach to understanding the microphysical processes that underlie friction in brittle materials

the heat and fluid transfer associated with the flanges on hydrothermal venting structures we present a simple model of the heat transfer and fluid flow associated with flanges which have been observed on some of the sulphide structures formed at sites of hydrothermal venting on the endeavour segment of the juan de fuca ridge 1 we show that the majority of the heat transferred by a flange is conducted across its upper surface except in flanges which are vigorously overflowing in which case it is through convective heat transfer associated with the overflowing we calculate that the flux of hydrothermal fluid through a typical non overflowing flange of area 1 m2 and with upper surface temperature in the range 10 80 c is of the order of 10 100 cm3 s with an associated heat flux of 104 105 w this heat flux is small compared to the largest black smoker plumes at endeavour which have a heat flux of the order 107 w in isolation in a relatively quiescent environment the hydrothermal plume associated with such a flange would rise about 20 40 m into the overlying stratified water column in comparison to the largest smokers in the endeavour vent field which have been observed to ascend about 180 m 2 flange derived plumes may therefore contribute to the production of the thermal and chemical anomalies in the water column below the neutral buoyancy height of the large smoker plumes our model of the temperature structure of a flange suggests that only the upper few centimetres of a flange have a temperature below 300 c this suggests that high temperature 110 c micro organisms may only thrive in the upper few centimetres of the flange

seismic and magnetic susceptibility anisotropy of middle lower continental crust insights for their potential relationship from a study of intrusive rocks from the serre massif calabria southern italy abstract we investigated the relationships between fabric seismic and magnetic anisotropy on lithotypes representative of a continental crust exposed in the serre massif southern italy in particular from five granitoids and one metagabbro cubes were cut according to the fabric elements and seismic properties up to 400 mpa confining pressure were measured with a triaxial multi anvil apparatus we also calculated the elastic properties based on the mineral content and composition in granitoids measured average compressional wave velocity vp of the fracture free aggregate at 400 mpa is 6 2 km s whereas average shear wave velocity vs is 3 6 km s with poisson s ratio ranging from 0 240 to 0 257 related to the modal proportions of quartz in metagabbro average vp and vs at 400 mpa are 6 9 km s and 3 7 km s respectively results showed that intrinsic velocity distribution after microcracks closure depends on progressive alignment of anisotropic minerals such as biotite amphibole and pyroxene with maxima velocities localized within the foliation plane mean magnetic susceptibility k m of the granitic rocks is 6 si units indicating that paramagnetic minerals such as biotite and amphibole control the intensity of magnetic anisotropy comparison of seismic and magnetic anisotropies highlighted the different role of constituting minerals over the petrophysical properties moreover a positive correlation between seismic and magnetic anisotropy has been recognized indicating that biotite and amphibole contribute to the petrophysical and textural anisotropy in the middle crust conversely in metagabbro the anisotropy of magnetic susceptibility ams is controlled by magnetite and pyrrhotite although these form

petrographic features as an effective indicator for the variation in strength of granites abstract the textural characteristics of four different granites from the lower himalayan regime in north western pakistan have been examined in relation to their effect on the mechanical nature of rock detailed petrographic examination and subsequent quantitative qemscan analysis provide better understanding of the difference between their textures three of the granite types are slightly altered grade ii whereas the other has a higher degree of alteration and corresponds to alteration grade iii the mechanical properties determined for each granite type include unconfined compressive and tensile strength elastic modulus p wave velocity schmidt hardness and dry density statistical analyses combined with post test petrography demonstrate textural control on mechanical properties the important petrographic characteristics influencing mechanical behaviour include modal concentration and grain size of individual minerals mean grain size of rock and distribution of grain size within a rock recrystallization of minerals along boundaries has a pronounced effect on increased strength of granites texture however has a significant influence on the variation of strength of granites with similar alteration grade

geomechanical characterization of the miocene cuitzeo ignimbrites michoacan central mexico abstract volcanic rocks especially ignimbrites exhibit complex mechanical behaviours due to their large variation in welding porosity textural and granulometrical characteristics moreover there is a lack of knowledge of how alteration processes affect their intrinsic properties main objective of this research is to characterize the physical mechanical and hydraulic behaviour of different lithofacies of the cuitzeo ignimbrites mexico these volcaniclastic mixtures of lithics and pumice supported by a fine rich matrix are characterized by different textural and granulometric features a general lithostratigraphic section and geological mapping of the study area were accomplished to attain the temporal and spatial distribution of the ignimbrites strength deformation and the failure mode of selected lithofacies were directly related to micro textural and granulometric characteristics by a series of uniaxial and pre and post failure non destructive analyses e g ultrasonic pulse velocity and x ray image tomographies results for four different lithofacies were compared allowing us to explore the variation in the mechanical properties associated with characteristics derived from diagenesis petrophysical properties show that there is a large dependence on the textural characteristics and particularly on the pumice fragments content results derived from laboratory observations and x ray image reconstruction analysis show that the main differences in the average values of porosity are associated to the geometry and morphology of the grains and pore network these are closely related to the stress strength relationship and the mode of failure of each specimen in general the strength for all lithofacies tends to increase linearly with several of the physical properties e g ultrasonic pulse velocity bulk density slake durability tests demonstrate that a large part of the mechanical degradation could be attributed to swelling during wetting drying cycles this decay is significant in lithofacies with groundmass rich in expansible clays

influence of orthoclase phenocrysts on point load strength of granitic rocks abstract the point load index test involves loading cylindrical block or irregular rock samples between two conical platens until sample failure the point load strength index is determined using failure load and sample dimension is widely and variously used in engineering geological studies therefore a comprehensive knowledge about the factors that could influence the index value is necessary this paper explores the effects of orthoclase phenocryst dimension on the point load strength index is of granitic materials from turkey in this context point load strength values of 117 granite core samples were determined the granites used in this study included orthoclase phenocrysts as important mineral constituents high resolution image was obtained from the freshly fractured surface of each sample the ratio of orthoclase phenocrysts rop on the failure surface was determined using image analysis when point load strength values were correlated with the ratios of orthoclase phenocrysts an inverse relationship emerged issues in order to minimize the influence of orthoclase phenocrysts on the point load strength were discussed

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

scaling of rock friction constitutive parameters the effects of surface roughness and cumulative offset on friction of gabbro we describe experiments in which large 14 40 cm nominal contact area blocks of gabbro were sheared in a direct shear apparatus at room temperature 5 mpa normal stress and slip velocities from 0 1 to 10 m s the apparatus was servocontrolled using a displacement feedback measurement made directly between the gabbro blocks two surface roughnesses were studied rough produced by sandblasting and smooth produced by lapping with 60 grit and accumulated displacements reached 60 mm measurements of surface topography were used to characterize roughness and asperity dimensions step changes in loading velocity were used to interrogate friction constitutive properties both rough and smooth surfaces showed appreciable displacement hardening the coefficient of friction for rough surfaces was about 0 45 for initial slip and 0 7 after sliding 50 mm smooth surfaces exhibited higher and a greater tendency for unstable slip the velocity dependence of frictiona b and the characteristic friction distanced c show systematic variations with accumulated displacement for rough surfacesa b started out positive and became negative after about 50 mm displacement andd c increased from 1 to 4 m over the same interval for smooth surfaces a b began negative and decreased slightly with displacement andd c was about 2 m independent of displacement for displacements 30 mm rough surfaces exhibit a second state variable with characteristic distance about 20 m the decrease ina b with displacement is associated with disappearance of the second state variable our data indicate thatd c is controlled by surface roughness in a complex way including but not limited to the effect of roughness on contact junction dimensions for bare rock surfaces the data show that simple descriptions of roughness such as rms and peak to trough are not sufficient to inferd c our observations are consistent with a model in whichd c scales with gouge thickness

structure of the plumbing system at tungurahua volcano ecuador insights from phase equilibrium experiments on july august 2006 eruption products understanding the plumbing system structure below volcanoes and the storage conditions temperature pressure volatile content and oxygen fugacity of erupted magmas is of paramount importance for eruption forecasting and understanding of the factors controlling eruptive dynamics phase equilibria experiments have been performed on a tungurahua andesite ecuador to shed light on the magmatic conditions that lead to the july august 2006 eruptions and the parameters that controlled the eruptive dynamics crystallization experiments were performed on a representative august 2006 mafic andesite product between 950 1025oc at 100 200 and 400 mpa and nno 1 and 2 and water mole fractions in the fluid xh2o from 0 3 to 1 water saturation comparison of the natural phenocryst assemblage proportions and phenocryst compositions with our experimental data indicates that the natural andesite experienced two levels of ponding prior to the eruption during the first step the magma was stored at 400 mpa 15 16 km 1000oc and contained ca 6 wt dissolved h2o in the second step the magma rose to a confining pressure of 200 mpa 8 10 km where subsequent cooling down to 975oc and water degassing of the magma led to the crystallization of reversely zoned rims on pre existing phenocrysts the combination of these processes induced oxidation of the system and overpressure of the reservoir triggering the july 2006 eruption the injection of a new hot volatile rich andesitic magma from 15 16 km into the 200 mpa reservoir shortly before the eruption was responsible for the august 2006 explosive event our results highlight the complexity of the tungurahua plumbing system in which different magmatic reservoirs can co exist and interact in time and are the main controlling factors of the eruptive dynamics

relationship between density compressive strength tensile strength and aggregate properties of andesites from hungary aggregate properties and strength parameters of four andesites from two operating hungarian quarries of nogradkovesd one lithotype and gyongyossolymos three lithotypes are presented in this paper air dry water saturated and freeze thaw subjected specimens were tested on core drilled cylindrical specimens and the aggregate properties were also determined from the remaining part of the drilled rock blocks tensile strength values rapidly decreased from air dry to water saturated and finally to freeze thaw subjected specimens linear relationships between air dry and water saturated bulk densities and between ucs and modulus of elasticity were found micro fabric influences strength and aggregate parameters of studied andesites fine porphyritic andesite has the highest ucs and tensile strength and the best micro deval results while coarser porphyritic andesite has lower strength and aggregate parameters test results were compared with previously published rock mechanical data of intermediate and basic igneous rocks a good exponential correlation was found between micro deval and ucs values of this paper and previously published data sets but there was no indication that micro deval values correlate well with los angeles values

the control of mineral constituents and textural characteristics on the petrophysical mechanical pm properties of different rocks of the himalaya abstract petrophysical and mechanical pm properties of a rock are primarily controlled by its mineral constituents and various textural parameters similar rock types in different tectonic setups may be characterized by different mineralogical compositions and textural properties because they might have suffered different deformational processes this paper presents a study on the mineralogical and textural control on various pm properties in quartzites granitoids gneisses metabasics and dolomite collected from different tectonic set ups the inter relationships among mineral constituents various textural parameters unconfined compressive strength ucs schmidt hammer rebound r value seismic wave both p and s waves velocity and their attenuation characteristics were obtained using regression analyses it has been concluded that there exists no relation between ucs and seismic wave velocity in quartzite granitoids and gneisses moderate positive relationship in metabasics and strong negative relationship in dolomite it has further been noted that in quartzite and dolomite monominerelic rocks grain size dominantly control the seismic wave velocity as the relatively coarser grained samples have higher seismic wave velocity whereas ucs is strongly controlled by grain size as well as the quantity and the orientation of the weak minerals like muscovite biotite calcite etc in gneisses and granitic gneisses preferred orientation of minerals especially the mica minerals although in present small quantity is the main factor controlling ucs and seismic velocity both these properties increase with the increase in intensity of preferred alignment of minerals whereas in metabasics it is the presence of amphibole pyroxene minerals feldspar that dominantly controls the seismic wave velocity

the effect of weathering on pore geometry and compressive strength of selected rock types from turkey weathering processes cause important changes in rock porosity besides porosity distribution of pore sizes is significant for the identification of changes due to rock weathering and its effects on fabric the formation of secondary porosity in different types of rock taken from different parts of turkey was examined and the results are presented in this paper the aim of this study was to observe changes in porosity due to weathering effective porosity mercury intrusion porosimetry and optical and scanning electron microscopy were used to evaluate the changes in pore geometry of the rocks additionally the dry density water absorption and uniaxial compressive strength of the rocks at different weathering stages were determined analysis of experimental data showed that microstructure of the rocks in relation to weathering is the main feature which controls their physical and mechanical properties the study revealed that fabric characteristics particularly the pore and fracture geometry are very important characteristics for assessment of the behaviour of weathered rock

statistical approach of the influence of petrography in mechanical properties and durability of granitic stones the influence of petrographic features on the strength of granitic stones is a wide studied topic which finds different correlations depending on the research and the granite type the aim of this article was to provide an accurate statistical analysis in which the amount of analysed data did not imply any doubt about the representativity of the samples and the accuracy of the results the focused principal component analysis was used because it allows to explain a determinate property in relation to several variables in addition the expression of the results was done as a simple and graphical representation that allowed to interpret the results in a global way data of texture mineralogy and strength of 12 granites were obtained in this study and were completed by those of more than 100 granites obtained from the literature the durability of the twelve granite characterized was also assessed a thermal fatigue test was carried out in 5 5 5 cm cubes revealing that the thermal expansion experimented by the different minerals was enough to produce variations in the crack network even if temperature was lower than the microfissuration threshold

seismic scaling exponents as a tool in detecting stress corrosion crack growth leading to the september october 1989 flank eruption at mt etna volcano the september october 1989 flank eruption at mt etna marked a change in the recent eruptive style of the volcano seismicity at mid order of months and short order of days time preceding the eruption onset has been analysed by means of d scaling exponent inferred from the seismic b value that represents the scaling exponent of fracture length distribution time evolution of d preceding the eruption onset revealed a general increase of d 9 to 4 months prior the eruption onset intermittent rates of d decreases and increases 4 to 1 month steady values of d 1 month and sharp decreases of d marking the eruption onset integration of these results with ground deformation data reveals that at mt etna stress corrosion crack growth enhanced by fresh magma arrival is a plausible mechanism for weakening the country rock by promoting crack growth and the coalescence of major faults

correlation of microseismic and chemical properties of brittle deformation in locharbriggs sandstone constant stress rate loading the exit pore fluid was analyzed after the tests for the concentration of dissolved ions and acoustic emission was monitored in real time throughout the tests the exit pore fluid silica concentration and microcrack damage derived from the acoustic emission ae data both exhibited an exponential increase during the strain hardening phase of deformation damage parameters inferred from the ae data predict the stress strain curves adequately or at least up to the point of strong microcrack coalescence the damage parameters and silica signal were strongly correlated by a power law relationship the observed environment and strain rate dependence of mechanical properties can hence be attributed uniquely to time dependent crack growth by the stress corrosion mechanism index terms 1045 geochemistry low temperature geochemistry 5102 physical properties of rocks acoustic properties 5104 physical properties of rocks fracture and flow keywords stress corrosion acoustic emission silica dissolution subcritical crack growth deformation rate brittle fracture citation ojala i o b t ngwenya i g main and s c elphick correlation of microseismic and chemical properties of brittle deformation in locharbriggs sandstone j geophys res 108 b5 2268 doi 10 1029 2002jb002277 2003

mainshocks are aftershocks of conditional foreshocks how do foreshock statistical properties emerge from aftershock laws 1 the inverse omori law for foreshocks discovered in the 1970s states that the rate of earthquakes prior to a mainshock increases on average as a power law 1 tc t p of the time to the mainshock occurring at tc here we show that this law results from the direct omori law for aftershocks describing the power law decay 1 t tc p of seismicity after an earthquake provided that any earthquake can trigger its suit of aftershocks in this picture the seismic activity at any time is the sum of the spontaneous tectonic loading and of the activity triggered by all preceding events weighted by their corresponding omori law the inverse omori law then emerges as the expected in a statistical sense trajectory of seismicity conditioned on the fact that it leads to the burst of seismic activity accompanying the mainshock in particular we predict and verify by numerical simulations on the epidemic type aftershock sequence etas model that p is always smaller than or equal to p and a function of p of the b value of the gutenberg richter law gr and of a parameter quantifying the number of direct aftershocks as a function of the magnitude of the mainshock the often documented apparent decrease of the b value of the gr law at the approach to the mainshock results straightforwardly from the conditioning of the path of seismic activity culminating at the mainshock however we predict that the gr law is not modified simply by a change of b value but that a more accurate statement is that the gr law gets an additive or deviatoric power law contribution with exponent smaller than b and with an amplitude growing as a power law of the time to the mainshock in the space domain we predict that the phenomenon of aftershock diffusion must have its mirror process reflected into an inward migration of foreshocks toward the mainshock in this model foreshock sequences are special aftershock sequences which are modified by the condition to end up in a burst of seismicity associated with the mainshock foreshocks are not just statistical creatures but are genuine forerunners of large shocks as shown by the large prediction gains obtained using several of their qualifiers

dynamics of microscale precursors during brittle compressive failure in carrara marble microscale heterogeneities influence failure mechanisms in the crust to track the microstructural changes in rock samples when loaded until failure we employed a novel experimental technique that couples dynamic x ray microtomography imaging with a triaxial deformation apparatus we studied the brittle failure of carrara marble under triaxial compression dynamic tomographic data revealed the spatial organization of microfractures and damage increments characterizing the precursory activity toward catastrophic failure we quantified the emergence of scaling relationships between microstructural parameters including total damage volume incremental damage volume the largest connected microfracture and the applied differential stress the total volume of microfractures accumulated from the beginning of the experiment as well as the incremental damage showed power law increase the growth of the largest connected microfracture was related to differential stress as a power law with divergence at failure the microfracture volume increments were distributed according to a power law with an upper cutoff that itself spanned the entire volume toward failure these characteristic features of brittle failure in carrara marble under compression are in agreement with theoretical models that consider failure as a critical phase transition we also observed that very close to failure several power law relationships broke down which we interpret to be related to the coalescence of the largest microfractures in a finite size volume scaling laws and associated exponents computed from our data are compared with predictions made from theoretical and numerical models our results show that precursors of macroscopic brittle failure in carrara marble follow predictable trends

a study on the time dependent microfracturing and strength of oshima granite abstract uniaxial compressive loading experiments where axial strain rate or dilatant volumetric strain rate was kept constant were carried out using a servo controlled hydraulic testing machine the rock studied was oshima granite in order to investigate the effect of the strain rate on the strength a theory based on the assumption of redistribution of the pre existing microcracks due to subcritical crack growth was examined results expected from the theory were well borne out by the observations the strength was expressed by power functions of both axial strain rate and dilatant strain rate the stress corrosion index of oshima granite appeared to be 31 3 which agreed well with the values reported previously when the axial strain rate was held constant the acoustic emission rate increased exponentially and the b value the exponent in the frequency magnitude relation of the acoustic emissions decreased with increasing applied stress when the dilatant volumetric strain rate was kept constant the acoustic emission rate and the b value remained constant and independent of the stress increase furthermore when the dilatant strain rate was held constant at a higher value the b value was constant at a lower level as the decrease in the b value indicates the higher dilatant strain rate the b value is one of the most useful key parameters in the fracture predictions

correlation of mineralogical and textural characteristics with engineering properties of selected granitic rocks from turkey abstract granitic rocks show a variety of engineering properties that may affect quarrying operations tunneling mining slope stability and the use of rock as a construction material the physical and mechanical properties are a function of the mineralogical and textural characteristics of the rock the purpose of this study is to apply correlation analysis to investigate the relationships between petrographical and engineering properties of granitic rocks a variety of granitic rock samples from different parts of turkey were subjected to petrographic studies the same samples were then tested to determine specific gravity dry and saturated unit weight water absorption effective and total porosity sonic velocity schmidt hardness point load strength index uniaxial compressive strength tensile strength and modulus of elasticity the relationships between these properties and the petrographical characteristics are described by simple regression analyses the study revealed that the influence of the textural characteristics on the engineering properties appears to be more important than the mineralogy it also determined that the types of contacts grain mineral shape and size significantly influence the engineering properties of the granitic rocks

acoustic energy release during the laboratory seismic cycle insights on laboratory earthquake precursors and prediction machine learning can predict the timing and magnitude of laboratory earthquakes using statistics of acoustic emissions the evolution of acoustic energy is critical for lab earthquake prediction however the connections between acoustic energy and fault zone processes leading to failure are poorly understood here we document in detail the temporal evolution of acoustic energy during the laboratory seismic cycle we report on friction experiments for a range of shearing velocities normal stresses and granular particle sizes acoustic emission data are recorded continuously throughout shear using broadband piezo ceramic sensors the coseismic acoustic energy release scales directly with stress drop and is consistent with concepts of frictional contact mechanics and time dependent fault healing experiments conducted with larger grains 10 5 m show that the temporal evolution of acoustic energy scales directly with fault slip rate in particular the acoustic energy is low when the fault is locked and increases to a maximum during coseismic failure data from traditional slide hold slide friction tests confirm that acoustic energy release is closely linked to fault slip rate furthermore variations in the true contact area of fault zone particles play a key role in the generation of acoustic energy our data show that acoustic radiation is related primarily to breaking sliding of frictional contact junctions which suggests that machine learning based laboratory earthquake prediction derives from frictional weakening processes that begin very early in the seismic cycle and well before macroscopic failure

mineral precipitation in the walls of black smoker chimneys a quantitative model of transport and chemical reaction a quantitative model of transport and chemical reaction is developed to examine the interplay of physical and chemical processes controlling the evolution of black smoker chimneys diffusion and advection yield steady state profiles of temperature and concentration across a porous wall bound on one side by hydrothermal fluid and on the other by seawater the pressure gradient is estimated from the fluid dynamics of high velocity flow inside the chimney parametric studies reveal the importance of diffusion driven by gradients in activity coefficients resulting from the strong thermal gradient the model wall is a series of vertical layers each with specified physical properties chemical reaction calculated assuming chemical equilibria for the local temperature and concentration conditions significantly modifies the physical properties of the wall as it evolves model calculations demonstrate the sensitivity of mineral zonation to the physical environment and can be used to re create the aging of chimneys inferred from petrologic studies

preseismic fault creep and elastic wave amplitude precursors scale with lab earthquake magnitude for the continuum of tectonic failure modes tectonic faults fail in a continuum of modes from slow earthquakes to elastodynamic rupture precursory variations in elastic wavespeed and amplitude interpreted as indicators of imminent failure

power law singularity as a possible catastrophe warning observed in rock experiments the question which type of signals can be determinately related to catastrophic rupture in heterogeneous brittle media still remains open here we report a specific precursor of catastrophic rupture i e a power law singularity of responses based on rock experiments our experimental observations show that the singularity with power exponent b where b 0 51p0 10 meanps d appears ahead of catastrophic rupture in some rocks and the singularity does not appear at all for gradual failure it is indicated that the power law singularity can emerge well only close to catastrophic rupture and thus it could serve as a specific warning for catastrophic rupture to address the potential forewarning of imminent catastrophic rupture a fitting process based on the data before catastrophic rupture was developed to determine the two unknowns related to the occurrence catastrophe point uf and the power exponent bu it is demonstrated that the power law singularity appears only in the vicinity of catastrophe and that the power law singularity does not occur for gradual failure

the effect of mineralogy and textural characteristics on the strength of crystalline igneous rocks using image based textural quantification abstract the attempts made to understand and quantify the relationship between rock texture and engineering properties have been accompanied by some ambiguities and uncertainties and the majority of the approaches though focusing on particular rock types have not been so successful for even the same rock types from other regions this study therefore was aimed to investigate the relationship between the texture and strength properties of a wide range of crystalline igneous rocks along with more aspects of textural analysis for this purpose fifteen fresh samples of crystalline igneous rocks belonging to the stone quarries of the nw iran were collected and subjected to compressive and tensile strength tests ucs and bts thin sections of the samples were used to prepare the full mosaic image layers in three different optical conditions about 18 000 mineral grains were manually traced on the processed images and the obtained vector data was used for the quantification of various textural parameters including size metrics shape descriptors microfabric indices and mineral content different phase considerations full phasic monophasic multiphasic and phase ratio were applied to derive the textural characteristics of the individual and multiple minerals and their proportional ratio finally simple linear regression analysis was performed to evaluate the relationship between the texture and strength properties the results indicated that the newly developed quartz to feldspar size ratio qfsr indicator was the only textural parameter that could be significantly correlated with both compressive and tensile strength in a wide range of rock types the results also highlighted the fact that the role of quartz and feldspar encountered with different rock failure mechanisms could be different in fact the tensile strength was obviously affected by the size and content of k feldspar while the compressive strength showed a more complicated mechanism and seemed to be controlled by the interference effects of plagioclase and quartz textural properties furthermore the study indicated that the influence of grain size on the rock strength was more important than the grain shape or mineral content

omori law for eruption foreshocks and aftershocks 1 using the 1973 2009 worldwide catalogs for m 4 8 seismicity and vei 0 volcano eruptions we compare the properties of seismic damage patterns contemporary with eruption with the properties of foreshocks and aftershocks of classic tectonic earthquakes using superposed epoch analysis we demonstrated that the seismicity rate after eruption decreases as a power law similar to the omori law of earthquake aftershocks we further show that a complete mapping of omori law of earthquake aftershocks onto eruption aftershocks does exist as rerup t k0 10 vei t c p volcanic explosivity index vei being an empirical measure that exponentially scales with eruption size close to 0 4 is the value reported for m 5 6 5 earthquakes from the same catalog the p values are in the 0 7 range i e robustly smaller than the 0 9 1 0 range for earthquake aftershocks we estimated in the volcanic area k value for eruptions is 2 10 times smaller than for earthquakes and it scales with vei values all those parameters characterize a slower damage relaxation after eruptions than after earthquakes when earthquakes foreshock rates are proposed to be independent of the main shock magnitude we resolved a strong increase in foreshock rates including an increase of the p value of the inverse omori law prior eruptions with eruption size these patterns all emerging from mean field analysis are evidence of the volcanic eruptions being contemporary with a stochastic brittle damage in the earth crust these results suggest a generic damage relaxation within the earth crust as power law distributed after or before events the loading and relaxation exponents and the damage rate emerge as being controlled by the loading rate as reported during lab scale experiments the more impulsive the loading i e km s for the slip velocity during earthquakes against km h for dyke propagation the faster the relaxation 0 9 1 0 p values for earthquakes aftershocks against 0 7 for eruptions aftershocks before eruptions the larger the impending events the higher the p values all the observations converge toward the amplitude and frequency of the stress step to drive the omori law parameters as qualitatively reproduced by the rate and state friction law response of brittle crust faults to loading

bayesian confidence intervals for the magnitude of the largest aftershock aftershock sequences which follow large earthquakes last hundreds of days and are characterized by well defined frequency magnitude and spatio temporal distributions the largest aftershocks in a sequence constitute significant hazard and can inflict additional damage to infrastructure that is already affected by the main shock therefore the estimation of the magnitude of a possible largest aftershock in a sequence is of high importance in this work a bayesian predictive distribution and the corresponding confidence intervals for the magnitude of the largest expected aftershock in a sequence are derived using the framework of bayesian analysis and extreme value statistics the analysis is applied to 19 well known aftershock sequences worldwide to construct retrospectively the confidence intervals for the magnitude of the subsequent largest aftershock by using the statistics of early aftershocks in the sequences

temporal variations in seismicity during quasi static and dynamic rock failure abstract a comprehensive model is presented which can explain temporal fluctuations in seismic b values in the period leading to mechanical failure in terms of the underlying physical processes of time varying applied stress and stress corrosion enhanced crack growth under conditions of constant strain rate the form of the b value anomaly in the period leading to failure depends on the form of the stress time relationship for the case where dynamic failure occurs at peak stress after a period of strain hardening the model predicts a single cusp like b value anomaly reaching a critically low value of 0 5 at failure for the physically most realistic case where dynamic failure is preceded by a period of precursory strain energy release during strain softening the model predicts two minima in the b value separated by a temporary maximum or inflection point these fluctuations in the b value are consistent with reported intermediate term and short term earthquake precursors separated by a period of seismic quiescence for the case of quasi static cataclastic flow the b value mirrors the stress and never falls to the critical value because there is no critical rupture new results from a series of controlled laboratory experiments are presented in which microseismic event rates and b value were monitored contemporaneously with stress time data for all variants of the stress time relationship recent field observations of temporal changes in seismicity rates and b value preceding major earthquakes are also reported both data sets exhibit b value anomalies which are consistent with the model predictions

forecast model for great earthquakes at the nankai trough subduction zone an earthquake instability model is formulated for recurring great earthquakes at the nankai trough subduction zone in southwest japan the model is quasistatic two dimensional and has a displacement and velocity dependent constitutive law applied at the fault plane a constant rate of fault slip at depth represents forcing due to relative motion of the philippine sea and eurasian plates the model simulates fault slip and stress for all parts of repeated earthquake cycles including post inter pre and coseismic stages calculated ground uplift is in agreement with most of the main features of elevation changes observed before and after the m 8 1 1946 nankaido earthquake in model simulations accelerating fault slip has two time scales the first time scale is several years long and is interpreted as an intermediate term precursor the second time scale is a few days long and is interpreted as a short term precursor accelerating fault slip on both time scales causes anomalous elevation changes of the ground surface over the fault plane of 100 mm or less within 50 km of the fault trace

micro textural effects on crack initiation and crack propagation of andesitic rocks abstract the onset of dilation and uniaxial compressive strength ucs of rocks are known to be affected by mineralogical petrographic and microstructural features therefore micro textural variations are essential for understanding variation in strength and failure behaviour of rocks in this study volcanic rock samples with different micro textural characteristics from different locations in turkey were evaluated the mechanical tests revealed considerable variations in unconfined uniaxial compressive strength and the crack initiation ci threshold the ucs ranges between 108 289 mpa and ci ranges between 46 130 mpa detailed quantitative petrographic and mineralogical analyses were carried out on each tested specimen to understand these strength variations additionally microstructural studies were carried out on thin sections before and after mechanical perturbation to analyze 1 the effect of the main constituents of the rock specimens and mineral heterogeneity on crack initiation and propagation and 2 the orientation and distribution of micro and macro cracks formed during laterally unconfined compression the synthesis of mechanical mineralogical petrographic and microstructural data suggests that both the crack initiation threshold and peak strength are influenced by the ratio of the area of fine grain groundmass grains smaller than 200 m to amphibole and plagioclase phenocrysts in addition ci and ucs decrease with an increasing normalized area of biotite phenocryst

omori s power law aftershock sequences of microfracturing in rock fracture experiment a time series of acoustic emissions ae in basalt was measured under constant uniaxial compression some bursts of ae events considered to be the main shock and aftershock sequences were observed two models describing the aftershock sequences the exponential decay model n t k exp pt and the omori s power law model n t k c t p where n t denotes the occurrence rate of aftershocks at time t were examined with the progress of the fracturing process the bursts changed from the exponential decay type to omori s power law type and the p value of omori s power law aftershock sequences decreased these results indicate that microfracturing gains a longer tail with the evolution of the fracture process the reproduction of omori s power law aftershock sequences of ae events suggests that the self similarity of rock fracturing holds good over a range from microfracturing to large earthquakes

effects of slip slip rate and shear heating on the friction of granite the stability of fault slip is sensitive to the way in which frictional strength responds to changes in slip rate and in particular to the effective velocity dependence of steady state friction ss ln v this quantity can vary substantially with displacement temperature and slip rate to investigate the physical basis for this behavior and the possible influence of shear heating we slid initially bare granite surfaces in unconfined rotary shear to displacements of hundreds of millimeters at normal stresses n of 10 and 25 mpa and at room temperature we imposed step changes in slip rate within the range 10 2 to 103 5 m s and also monitored frictional heating with thermistors embedded in the granite the transient response of to slip rate steps was fit to a rate and state dependent friction law using two state variables to estimate the values of several parameters in the constitutive law the first 20 mm of slip shows rising friction and falling ss ln v further slip shows roughly constant friction ss ln v and parameter values suggesting that a steady state condition is reached on the fault surface at v 10 m s ss ln v 0 004 0 001 at higher rates the response is sensitive to normal stress at n 25 mpa granite shows a transition to effective velocity strengthening ss ln v 0 008 0 004 at the highest slip rates tested at 10 mpa granite shows a less dramatic change to ss ln v 0 at the highest rates the maximum temperature measured in the granite is 60 c at 25 mpa and 103 5 m s temperatures are in general agreement with a numerical model of heat conduction which assumes spatially homogeneous frictional heating over the sliding surface the simplest interpretation of our measurements of ss ln v is that the granite is inherently velocity weakening ss ln v 0 mimics velocity strengthening these results have implications for the frictional behavior of faults during earthquakes high slip rates may cause a switch to effective velocity strengthening which could limit peak coseismic slip rate and stress drop for fluid saturated faults strengthening by this mechanism may be partly or fully offset by weakening due to thermal pressurization of a poorly drained pore fluid

the dilatancy diffusion hypothesis and earthquake predictability the dilatancy diffusion hypothesis was one of the first attempts to predict the form of potential geophysical signals that may precede earthquakes and hence provide a possible physical basis for earthquake prediction the basic hypothesis has stood up well in the laboratory where catastrophic failure of intact rocks has been observed to be associated with geophysical signals associated both with dilatancy and pore pressure changes in contrast the precursors invoked to determine the predicted earthquake time and event magnitude have not stood up to independent scrutiny there are several reasons for the lack of simple scaling between the laboratory and the field scales but key differences are those of scale in time and space and in material boundary con ditions coupled with the sheer complexity and non linearity of the processes involved upscaling is recognized as a difficult task in multi scale complex systems generally and in oil and gas reser voir engineering specifically it may however provide a clue as to why simple local laws for dila tancy and diffusion do not scale simply to bulk properties at a greater scale even when the fracture system that controls the mechanical and hydraulic properties of the reservoir rock is itself scale invariant

assessment of rock geomechanical quality by quantitative rock fabric coefficients limitations and possible source of misinterpretations abstract rock microfabrics were quantified by image measurement system petrographic image analysis of thin sections along with common measured parameters grain area and size length of major and minor axes and their orientation some quantitative parameters aspect ratio grain boundary smoothness and fabric coefficients micropetrographic quality index k texture coefficient tc indexes of interlocking t and grain size homogeneity g were determined the reliability of these parameters for the evaluation of geomechanical properties was tested on the set of granitic rocks showing pronounced variability in rock mechanical properties none of the tested rock fabric coefficients or parameters proved a close correlation to rock mechanical properties except grain size based on experimental findings the grain size is along with porosity the controlling factor of rock mechanical properties of genetically and mineralogically similar rocks obliteration of the real effects of rock fabric parameters on the mechanical properties of rocks by application of complex fabric coefficients disables their practical use in petrography applied to geomechanics

mineralogical controls on the engineering behavior of hydrothermally altered granites under uniaxial compression effective engineering characterization of granites altered through processes of kaolinization is critical for safe extraction and design of slopes for the china clay industry in south west england by considering this important issue representative samples taken from a range of decomposition grades of altered granite were used to assess the controlling influence of changes in mineralogy on uniaxial compressive strength elastic modulus dry density and ultrasonic velocity dramatic reduction in uniaxial compressive strength occurs between alteration grades ii and iii analysis of acoustic emission data constrained by evaluation of scanning electron microscope sem images and strain gauge deformation readings has been used to identify crack propagation stages during uniaxial compression quantitative evaluation of mineralogy was determined from x ray diffraction xrd analysis of representative samples in order to establish relationships between mineralogy such as kaolinite and uniaxial compressive strength for the different alteration grade material the results of the testing confirm that the degree of alteration or kaolinization and associated changes in mineralogy of the granite is directly related to reduction in uniaxial compressive strength and dry density