effect of contact surface area on frictional behaviour of dry and saturated rock joints abstract frictional behaviour of joints faults is of great importance in many geo engineering applications across different scales it is known that the joint surface roughness is one of the critical parameters controlling the frictional behaviour of rock joints while nominal normal and shear stresses acting across the joint asperities are calculated based on overall shearing area the actual normal and shear stresses can be much greater due to smaller actual contact area the actual contact area on the other hand is known to be related to the joint surface roughness in order to investigate the effect of contact area on the shear behaviour of rock joints an extensive set of direct shear experiments at different normal stresses on dry and saturated shale limestone and sandstone tensile joints were undertaken to compare the frictional properties of natural and artificial samples synthetic samples were also fabricated and their frictional properties were evaluated results of this study revealed that the predominant parameter controlling the frictional strength is the actual contact area while the common models in predicting the shear strength of rock joints were unable to fit the experimental data based on nominal contact area the results based on actual contact area fit the measured values accurately in addition it was observed that when the actual contact area is considered mohr coulomb criterion is sufficient to fit the experimental data irrespective of the rock type joint surface roughness or whether dry or saturated this highlights that the mohr coulomb criterion can appropriately predict the frictional strength if the actual contact area can be estimated more importantly the results showed that the surface roughness cannot dictate the shear behaviour of rock joints without considering the actual contact area

the critical slip distance for seismic faulting experimentally based friction laws1 2 have been found to predict virtually the entire range of observed behaviour of natural faults3 4 these laws contain a critical slip distance l which plays a key role in determining the degree of fault instability the size of the zone of earthquake nucleation the frictional breakdown width and the proportion of pre and post seismic slip to co seismic slip in laboratory measurements l is found to be about 10 5m but modelling results show that it must be about 10 2m if natural earthquake behaviour is to be simulated the discovery that fault surfaces are fractal over the scale range 10 5 105 refs 5 6 even for faults with large net slip has confused the problem of scaling this parameter from laboratory experiments to natural faults because fractal surfaces have no characteristic length here i show that geometrically unmated fractal surfaces when in contact under a normal load develop a characteristic length in their contact because long wavelength apertures close under load whereas short wavelength apertures may remain open this critical distance may be identified with l and calculations based on fault topography data show that at seismogenic depths it will be in the range anticipated from the earthquake modelling studies

effect of asperity order on the shear response of three dimensional joints by focusing on damage area the shear resistance of rock joints has always been of paramount importance in stability analysis of surface and underground rock structures many parameters influence the shear strength of rock joints among which surface asperity is highly crucial that has encouraged many researchers to work on among the pioneers working on the subject patton 1 was the first researcher who systematically studied the effect of joint asperity using simple physical models with two dimensional toothshaped asperity patton proposed the following bilinear shear strength criterion

potential vorticity diagnosis of the severe convective regime part ii the impact of idealized pv anomalies abstract idealized numerical experiments are conducted to understand the effect of upper tropospheric potential vorticity pv anomalies on an environment conducive to severe weather anomalies are specified as a single isolated vortex a string of vortices analogous to a negatively tilted trough and a pair of string vortices analogous to a position error in a negatively tilted trough the anomalies are placed adjacent to the tropopause along a strong upper level jet at a time just prior to a major tornado outbreak and inverted using the nonlinear balance equations in addition to the expected destabilization beneath and adjacent to a cyclonic pv anomaly the spatial pattern of the inverted balanced streamfunction and height fields is distorted by the presence of the horizontal pv gradient along the upper tropospheric jet stream streamfunction anomalies are elongated in the cross jet direction while height and temperature anomalies are elongated in the along jet direction the amplitude of the inverted

synoptic scale variability of the polar and subpolar tropopause data analysis and idealized pv inversions the synoptic scale variability of the polar and subpolar tropopause is investigated based on radiosonde and european centre for medium range weather forecasts reanalysis data in combination with idealized potential vorticity pv inversions a regression analysis is performed to examine the relationship between the relative vorticity at tropopause level the tropopause displacement the static stability above the tropopause and the anomalies of tropopause temperature and potential temperature the results are compared with regression coefficients computed from a large number of pv inversions generally a cyclonically influenced tropopause is lower warmer and potentially colder than average and the static stability above the tropopause is reduced the opposite is true under anticyclonic influence typically a cyclonic vorticity of 10 5s 1 is associated with a decrease of the tropopause height by 150 200 m correspondingly the mean vertical temperature gradient in the lowermost 2 km above the tropopause decreases by 0 2 0 3 k km 1 moreover an increase of the tropopause height by 1 km is associated with a temperature decrease by 3 5 k and an increase of the potential temperature by 6 8 k except for the last one these values do not depend significantly on the strength and the sign of the tropopause anomaly distinct annual cycles are observed in parts of the polar regions most of the relations found in the data can be reproduced with the pv inversions except for the observed linearity for large tropopause displacements which is not always reproduced very well the annual cycles can be partly explained with the aid of the pv inversions copyright 2002 royal meteorological society

misalignment of the orientation of fractures and the principal axes for p and s waves in rocks containing multiple non orthogonal fracture sets summary azimuthal anisotropy in rocks can result from the presence of one or more sets of partially aligned fractures with orientations determined by the stress history of the rock a shear wave propagating in an azimuthally anisotropic medium splits into two components with diverent polarizations if the source polarization is not aligned with the principal axes of the medium in the presence of two or more non orthogonal sets of vertical fractures the symmetry of the medium may be approximated as monoclinic with a horizontal plane of mirror symmetry if in the absence of fractures the rock is transversely isotropic ti with the symmetry axis perpendicular to the bedding plane for such a medium the fast and slow polarization directions for vertically propagating shear waves are not parallel or perpendicular to any of the fracture planes but lie in directions given by the principal axes of a second rank fracture compliance tensor this tensor is independent of the normal compliance of the fractures it follows that for vertical propagation of shear waves in a vertically fractured ti medium any number of arbitrarily oriented vertical fracture sets is equivalent to two mutually perpendicular fracture sets provided that the seismic wavelength is large compared to the size of the fractures for ovsets typical of surface seismic acquisition the p wave velocity at fixed ovset varies with azimuth as cos 2 w w 0 where w is the azimuth measured with respect to the fast polarization direction for a vertically polarized shear wave w 0 depends on both the normal and the shear compliance of the fractures and may diver from zero if the ratio of the normal to shear compliance of the fractures varies significantly between fracture sets if this ratio is similar for all fractures w 0 0 and the principal axes of the variation in p wave velocity with azimuth for fixed ovset are determined by the principal axes of the second rank fracture compliance tensor

morphological features of shear formed fractures developed in a rock bridge abstract rock bridges are commonly encountered in incipiently jointed rock masses and the problem of their failure has a significant influence on the safety of involved engineering practices although many research have been conducted to look into the geometrical or mechanical properties of rock bridges before failure the properties of them after failure have rarely been investigated in this study we carried out an investigation on the morphological features of newly formed fractures developed in a rock bridge the influence of the applied normal stress and the joint persistence on the fracture morphology was systematically examined in terms of failure mechanism and grasselli s model the research results demonstrated that the development of the fractures in a rock bridge can be attributed to tensile failure mechanism or shear failure mechanism it was found that the tensile failure mechanism produces more curvilinear and rougher fractures than the shear failure mechanism moreover the fractures developed in a rock bridge were anisotropic with asymmetric asperities along the shearing plane i e maximum possible contact area a0 is less than 0 5 which is considerably distinguished from that developed in an intact rock through splitting the present study would promote our knowledge of rock bridges and contribute to the development of shear strength criterions

determination of shear failure regions of rock joints based on point clouds and image segmentation abstract to better understand the shear mechanical behaviour the information value iv and the fractal theory ft models are employed to determine the shear failure regions of rock joints under the low effective normal stress conditions first high density point clouds of rock joints at the initial stage pre shearing were collected using a laser scanning technology and four topography parameters slope angle horizontal orientation elevation difference and curvature were produced from point clouds to represent the mesostructure features second direct shear testing were conducted at the end stage post shearing and shear striae on the rock joints were measured to assess shear failure regions based on image segmentation third by combining morphological features with experimental observations correlation analyses are performed to investigate the influences of topography parameters on shear failure behaviors of rock joints based on iv and normalized weight wi similar findings are observed from the two algorithms indicating that horizontal orientation has a larger impact on shear failure than the other three parameters furthermore under the low normal loading the shear failure of rock joints are more likely to occur in regions with a slope angle in the range of 30 to 40 a horizontal orientation in the range of se to sw facing shear direction an elevation difference in the range of 0 15 to 0 30 mm and a curvature in the range of 1000 to 200 mm 1 and 200 to 1000 mm 1 it is notable that the effect of normal loads level on shear failure regions should not be neglected eventually a model is developed to predict the shear failure regions of rock joint and receiver operating characteristic roc analyses show that shear failure determinations based on the proposed model match the actual situation

rate dependent mechanical behavior of rough rock joints abstract the influence of shear rate on the mechanical behavior of rough rock joints prepared using a molding method was examined by testing jointed samples of four rock joint groups which were obtained from the underground caverns of the huangdao state oil reserves in china the tests were performed using a jaw 600 coupled shear flow machine under constant normal load cnl conditions shear rate and joint roughness coefficient jrc were the two primary considerations in this study the results indicate that the peak shear strength is controlled by shear rate and joint roughness shear rate has a nonlinear relationship with the peak shear strength whereas joint roughness exhibits good linearity with a high correlation coefficient 0 97 except for results under a shear rate of 24 0 mm min furthermore shear rate affects the damage incurred by the rock joints as illustrated by the acoustic emission of rock joints monitored by a pac acoustic emission system the joint surface breaks earlier with increased shear rate furthermore because of the more rapid generation of macrocracks under higher shear rate the corresponding cumulative acoustic emission ae count and ae energy are inversely proportional to the shear rate a new shear strength criterion that considers both shear rate and joint roughness was developed based on the experimental results and barton s shear strength criterion then the validity of this proposed criterion was verified with an average estimated error of 10 539 using the shear strength values of rock joints proposed by barton indicating that the new criterion is capable of providing an accurate estimate of shear strength for rough rock joints under different shear rates

structural anisotropy of normal fault surfaces abstract precise description of natural fault surfaces is indispensable to understanding the geometry mechanics and fluid transport properties of faults profiles of fault surfaces in the wasatch fault zone and oquirrh mountains utah are measured at 30 increments within the fault plane to determine the directional anisotropy of surface roughness at wavelengths between 10 3 m and 30 m and then compared with profiles of larger scale fault surfaces surface anisotropy and an increasing ratio of surface amplitude to wavelength are consistent with self affine fault topography at wavelengths between 1 mm and approximately 5 km fractal dimension of surface profiles generally decreases systematically as the angle to the slip direction increases directional anisotropy is described by an azimuthal scaling function k sin 0 or af af max 1 sin 1 where and af are the amplitude to wavelength ratio and anisotropy factor respectively at azimuth measured clockwise relative to slip direction within the fault surface and 0 is the amplitude to wavelength ratio parallel to slip direction k 90 0 is an anisotropy coefficient and increases systematically with spatial wavelength on the fault surface characterization of natural fault surfaces provides parameters such as fractal dimension d intercept log c of power spectra profile variance and variation in anisotropy factor af which are needed to generate fractal models of natural fault surfaces using spectral synthesis we generate sample models which illustrate the differences between fault surfaces characterized by constant versus azimuthally varying fractal dimension the latter model surfaces contain low amplitude corrugations superimposed on elongate ridges which parallel slip direction this surface texture resembles that of natural fault surfaces that refract across lithologic layering or are cut by secondary faults such as r and r shears

transport and mixing in the extratropical tropopause region in a high vertical resolution gcm part i potential vorticity and heat budget analysis abstract a high vertical resolution general circulation model gcm output has been analyzed to clarify transport and mixing processes in the extratropical tropopause region the high resolution gcm with a vertical resolution of about 300 m above the extratropical upper troposphere allows simulation of fine atmospheric structures near the tropopause such as the extratropical tropopause transition layer extl and the tropopause inversion layer til the high resolution gcm realistically simulates fine thermal and dynamic structures in the extratropical tropopause region the thickness and maximum stability of the simulated til are consistent with observations the high resolution output was analyzed using a zonal mean potential vorticity pv equation to identify dominant transport processes in the extratropical tropopause region in the northern hemisphere extratropics during winter mean downward advection sharpens the pv gradient between the tropopause and 20 k below it whereas latitudinal variati

coupled hydromechanical modeling of rock fractures under normal stress in this paper a nonlinear poromechanical model is developed for a single rock fracture under normal stress the fracture is represented by a set of voids and the progressive fracture displacement

influence of fracture geometry on shear behavior abstract laboratory research during the past 10 years has explained many critical links between the geometrical characteristics of fractures and their hydraulic and mechanical behavior one of the remaining research challenges is to directly link fracture geometry with shear behavior including behavior in response to changes in normal stress and shear direction this paper describes results from a series of shear tests performed on identical copies replicas of a natural granite fracture based on these tests we developed a method using image processing techniques to identify and quantify damage that occurs during shearing we find that there is a strong relationship between the fracture s geometry and its mechanical behavior under shear stress and the resulting damage using a three dimensional geostatistical model of the fracture surfaces we analyze the dependence of the size and location of damage zones on the local geometry and propose an algorithm for predicting areas that are most likely to be damaged during shearing in a given direction

shear behavior of greenschist along foliation plane considering anisotropy the shear behavior of rock mass along its structural plane i e joint bedding plane and foliation plane plays a key role in determining rock strength which is highly anisotropic the shear behavior along the foliation plane is rarely addressed from engineering geology point of view in the effect of anisotropy of on the shear behavior along foliation plane not to mention the effect of anisotropy in this study the direct shear behavior of greenschist along the foliation plane is investigated using both intact and sheared greenschist samples identical concrete replicas for the sheared greenschist samples are prepared using 3d scanning and printing in this study and sheared in four directions i e 0 90 180 and 270 under four normal stresses left sigma text n sigma text c 0 1 0 2 0 3 0 4 right the intact greenschist samples show significantly higher shear strength compared to the sheared samples due to the bonding strength along foliation plane the shear behavior of greenschist along foliation plane is anisotropic due to the 3d roughness of foliation plane and the anisotropic behavior diminishes as the normal stress increases moreover the replicas of sheared greenschist samples shows same shear strength as the sheared greenschist samples thus suggesting that the concrete is suitable for simulating greenschist shear behavior including the peak shear strength residual shear strength and stiffness which also hints that the shear behavior of the sheared greenschist is dramatically controlled by surface roughness of the joint rather than rack by comparing the results of the shear greenschist with concrete replicas

the mechanics of lubricated faults insights from 3 d numerical models 1 the weakening mechanisms occurring during an earthquake failure are of prominent importance in determining the resulting energy release and the seismic waves excitation in this paper we consider the fully dynamic response of a seismogenic structure where lubrication processes take place in particular we numerically model the spontaneous propagation of a 3 d rupture in a fault zone where the frictional resistance is controlled by the properties of a low viscosity slurry formed by gouge particles and fluids this model allows for the description of the fault motion in the extreme case of vanishing effective normal stress by considering a viscous fault response and therefore without the need to invoke in the framework of coulomb friction the generation of the tensile mode of fracture we explore the effects of the parameters controlling the resulting governing law for such a lubricated fault the viscosity of the slurry the roughness of the fault surfaces and the thickness of the slurry film our results indicate that lubricated faults produce a nearly complete stress drop i e a very low residual friction coefficient 0 01 a high fracture energy density eg few 10s of mj m2 and significant slip velocities vpeak few 10s of m s the resulting values of the equivalent characteristic slip weakening distance d0eq 0 1 0 8 m depending on the adopted parameters are compatible with the seismological inferences moreover in the framework of our model we found that supershear ruptures are highly favored in the case of enlarging gap height we can have the healing of slip or even the inhibition of the rupture quantitative comparisons with different weakening mechanisms previously proposed in the literature such as the exponential weakening and the frictional melting are also discussed

historical shear deformation of rock fractures derived from digital outcrop models and its implications on the development of fracture systems abstract the initiation and development of fractures in rocks is the key part of many problems from academic to industrial such as faulting folding rock mass engineering reservoir characterization etc conventional ways of evaluating the fracture historical deformations depend on the geologists visual interpretation of indicating structures such as fault striations fault steps plumose structures etc on the fracture surface produced by previous deformations and hence suffer from problems like subjectivity and the absence of obvious indicating structures in this study we propose a quantitative method to derive historical shear deformations of rock fractures from digital outcrop models doms based on the analysis of effects of fault striations and fault steps on the shear strength parameter of the fracture surface a theoretical model that combines effects of fault striations fault steps and isotropic base shear strength is fitted to the shear strength parameter the amount of fault striations and fault steps and their occurrences are estimated and the historical shear deformations can be inferred the validity and the effectiveness of the proposed method was proved by testing it on a constructed fracture surface with idealized striations and a fracture surface with clear fault steps the application of this method on an example outcrop shows an intuitive idea of how the rock mass was deformed and that the distribution occurrence and mode of new fractures are strictly controlled by preexisting fractures and hence emphasizes the importance of preexisting fractures in modeling the development of fracture systems

the tropopause in the polar regions abstract the polar and subpolar tropopause in both hemispheres is investigated using the ecmwf reanalysis era data from 1979 to 1993 and radiosonde data from 1989 to 1993 both the thermal and the dynamical criteria are applied to each dataset the tropopauses derived from the radiosonde data are used to validate the era derived tropopauses and to investigate the sharpness of the tropopause the validation reveals that the era data are well suited for the determination of the tropopause a comparison between the thermal and the dynamical tropopause shows a very good agreement except for polar winter and there is clear evidence that the dynamical criterion is more appropriate in winter the results show that the annual cycle of the polar tropopause can be classified into three different patterns a single wave with a tropopause pressure maximum in winter and a minimum in summer is typical for the subpolar parts of eastern siberia and north america a double wave with pressure maxima in spring and autumn

static stability in the extratropical tropopause region abstract idealized axisymmetric anomalies of potential vorticity pv on a midlatitude f plane and their related response in terms of balanced wind and temperature are investigated with special focus on the static stability in the tropopause region the pv anomalies are specified such that they can be interpreted as the result of conservative advection in the tropopause region across the gradients of a prescribed background atmosphere with piecewise constant buoyancy frequency squared n2 related cyclones and anticyclones are treated identically except for the sign of the tropopause potential temperature anomaly composite profiles of n2 are computed for which the thermal tropopause is used as a common reference level and where the number of cyclones in the composite equals the number of anticyclones one obtains a pronounced peak of n2 just above the tropopause and slightly enhanced values below the tropopause in comparison with the background profile within the framework of pv inversion various mechan

roughness of natural fault surfaces the roughness of fault surfaces is important in the mechanics of fault slip and could play a role in determining whether sliding occurs via earthquakes or fault creep we have made preliminary measurements of the power spectral density of several fault surfaces over the wavelength range from 10 5 to 1 m using field and laboratory scale profilimeters the fault surfaces are strongly anisotropic profiles parallel to the slip direction have amplitudes about one order of magnitude lower than those perpendicular to the slip direction over most of the wavelength interval measured fault roughness perpendicular to the slip direction is similar to the roughness of natural joints the greater smoothness in the slip direction presumably represents wear resulting from slip combining our data with previous measurements of the roughness spectrum of the san andreas fault shows that fault surfaces are fractal over nearly eleven orders of magnitude in wavelength

seismic characteristics and seismic hazard assessment source region of the 2015 nepal earthquake mw 7 8 in central himalaya seismicity and seismic characteristics like b value fractal dimension energy release and recurrence period are assessed for the region 80 e 89 e and 26 n 31 n which includes the 2015 large nepal earthquake mw 7 8 in central himalaya the international seismological centre isc catalogue of earthquakes with mb 3 8 for the period august 1964 january 2013 are used the b values are estimated using the maximum likelihood and least square methods the fractal dimension is estimated using the correlation integral method the events are also used for estimating radiated energy in the region the probability of occurrence of moderate earthquakes mb 5 0 using isc data and mw 6 0 using usgs data for the period 1964 2015 during a specified interval of time is estimated on the basis of three probabilistic models namely weibull gamma and lognormal the model parameters are estimated by the maximum likelihood estimates it is found that there is a 99 probability for occurrence of at least one earthquake mb 5 0 in this region in a time window of 2 3 years from the year 2013 and in 20 30 years for an earthquake mw 6 0 from the year 2015 the b value maps identified variable stressed zones and the fractal dimension maps fractal characteristics of the active fault zones the energy release map identified the zones of higher and lower energy release the percent probability maps prepared using the poisson distribution identify the zones of higher and lower probability earthquakes and thus indicate the areas of future probable earthquakes

fracture toughness and fracture roughness interrelationship in thermally treated westerly granite this paper presents an experimental work aimed at assessing the correlation between fracture toughness k ic and fracture roughness for a series of westerly granite specimens thermally treated up to 850 c mode i fracture toughness as a function of thermal treatment is determined using cracked chevron notched brazilian disc specimens the degree of roughness of the resultant fracture surfaces is analyzed with the aid of a high accuracy high precision stereo topometric measurement system roughness and toughness values display a negative correlation as a function of temperature fracture toughness decreases with increasing temperature due to the gradual opening of grain grain boundaries in response to thermal stresses mode i fractures preferentially follow these weakened grain grain boundaries which in addition to the thermal expansion of individual grains result in rougher failure profiles with increasing temperature at low temperature a distinct anisotropy in roughness was observed in all fracture surfaces with higher roughness value perpendicular to the direction of fracture propagation however higher treatment temperatures resulted in the homogenization of fracture roughness in all directions these results confirm the important link among petrofabric analysis fracture toughness and fracture roughness in response to thermal treatment

the relationship between slickenside surfaces in fine grained quartz and the seismic cycle abstract well polished or reflective fault surfaces with or without linear striae indicating the sliding direction are commonly referred to as slickensides this study examines the development of slickensides which are now exposed along the surface trace of a large seismically active normal fault zone in dixie valley nevada u s a geologic and mineralogic constraints indicate the slickenside surfaces formed at depths of less than 2 km and temperatures less than 270 c the slickenside surface material is composed of greater than 98 quartz with less than 2 kaolinite and iron oxide transmission electron microscope tem observations reveal that the slickenside surface material has an extremely fine yet variable grain size 0 01 1 m and an unusual nonequilibrium texture characterized by irregular grain boundaries and low dislocation density angular fragments in the cataclasite to either side of the slickensides provide clear evidence of cataclasis crystallographic preferred orientation in the slickenside surface material indicates that non brittle continuous deformation occurred within 0 1 10 mm of the fault surfaces in many areas non brittle continuous deformation must have alternated with cataclasis because some fragments in the cataclasite have strong preferred orientations we suggest that in the dixie valley slickensides continuous deformation and the development of crystallographic preferred orientations occurred at relatively low strain rates during the interseismic period while cataclasis occurred at higher strain rates associated with seismic events the wide range of strain rates occurring within a fault zone during the earthquake cycle may be an essential element in the formation of fine grained glassy slickensides both at dixie valley nevada and many other areas

state of stress and modern deformation of the northern basin and range province constraints on the current stress regime of the actively extending northern basin and range province are provided by deformation data focal mechanisms and fault slip studies hydraulic fracturing in situ stress measurements borehole elongation breakouts analyses and alignment of young volcanic vents the integrated data indicate significant variations both in principal stress orientations and magnitudes an approximately e w least principal stress direction appears to characterize both the eastern and western margins of the basin and range province whereas in the active interior parts of the province extension occurs in response to a least principal stress oriented nw to n60 w the contrast in stress orientations between the province boundaries and in the interior suggests that along the margins the least principal stress direction may be locally controlled by the generally northerly trending profound lithospheric discontinuities associated with these margins active deformation along the southeastern and western province margins is characterized by a combination of strike slip and normal faulting focal mechanisms along northeastern province margin wasatch front and in central nevada indicate a combination of normal and oblique normal faulting temporal regional and depth dependent variations in the relative magnitudes of the vertical and maximum horizontal stresses can explain much of the observed variations in deformation styles however some depth variation in faulting style inferred from focal mechanisms may be apparent and simply a function of the attitude of fault planes being reactivated evidence for significant temporal variation or multiple cycles of variation in relative stress magnitude comes from the sierran front basin and range boundary region where recent earthquakes are predominantly strike slip whereas the profound relative vertical relief across the sierra frontal fault zone in the last 9 10 m y implies a normal faulting stress regime using the best data on stress orientation relative stress magnitudes are constrained from slip vectors of major earthquakes and young fault displacements analysis of well constrained slip vectors in the owens valley california area indicate that large temporal variations in the magnitude of the approximately n s oriented maximum horizontal stress are required to explain dominantly dip slip and strike slip offsets on subparallel faults similar faulting relations are observed throughout much of the boundary zone between the basin and range sierra nevada including the walker lane belt along the eastern province margin in the wasatch front area in utah available data suggest that the maximum and minimum horizontal stresses may be approximately equal at depths of 4 5 km earthquake focal mechanisms in this area suggest more variability in relative magnitude of the two horizontal stresses with depth furthermore superimposed sets of young fault striae along a segment of the wasatch fault also indicate temporal variations of relative stress magnitudes sources of regional and temporal variations in the stress field may be linked to variable shear tractions applied to the base of the brittle crust related to intrusion thermally induced flow and the influence of the san andreas plate boundary although difficult to date accurately the fault slip data suggest that the temporal variations in relative magnitudes stress may occur on the time scale of both a single major earthquake cycle 1000 5000 years and multiple earthquake cycles 10 000 years

the destiny of a clast within a molten pseudotachylyte vein pseudotachylytes are important markers that can indicate the thermal state during a coseismic slip failure and provide indirect information about the level of stress and sliding velocities attained during that time window on the other hand survivor fragmented clasts embedded in the quenched material are also very impor tant in that they provide information about the energy spent to create new fracture surfaces in this paper i study the temperature evolution of clasts subjected to the heat dissipated by a just formed molten pseudotachylyte pt vein in particular i find the analytical solutions for the temperature evolution within the pt vein the surrounding undamaged host rock and inside a clast according to the proposed model the numerical results show that the clasts tend to preferentially melt in the inner part of the pt vein i e they are completely assimilated by the pt in contrast some clasts can survive far from the pt vein center my solutions although based upon a simplified model can provide a theoretical framework to predict the maximum size of the survived clasts at a given distance from the pt center the distribution of these survivor clasts follows a power law relation in terms of their radius and its features generally agree with field and laboratory observations

quantitative three dimensional description of a rough surface and parameter evolution with shearing note roches reference lmr article 2002 005view record in web of science record created on 2006 11 09 modified on 2016 08 08

resolution dependence of the tropopause inversion layer in an idealized model for upper tropospheric anticyclones abstract this note investigates the dependence of the extratropical tropopause inversion layer til on numerical resolution in an idealized modeling framework axisymmetric upper tropospheric anticyclones are constructed by specifying potential vorticity pv and solving the nonlinear pv inversion problem the pv distribution has a smooth but near discontinuous change of pv across the tropopause in a transition zone with vertical depth for fixed the strength of the til changes with changing resolution until the transition zone is resolved by a fairly large number of grid points the quality controlled numerical solutions are used to study the behavior for 0 this limit can lead to very strong tils but no indications for divergent behavior were found

characterization of fault zones there are currently three major competing views on the essential geometrical mechanical and mathematical nature of faults the standard view is that faults are possibly segmented and heterogeneous euclidean zones in a continuum solid the continuum euclidean view is supported by seismic gravity and electromagnetic imaging studies by successful modeling of observed seismic radiation geodetic data and changes in seismicity patterns by detailed field studies of earthquake rupture zones and exhumed faults and by recent high resolution hypocenter distributions along several faults the second view focuses on granular aspects of fault structures and deformation fields the granular view is supported by observations of rock particles in fault zone gouge by studies of block rotations and the mosaic structure of the lithosphere which includes the overall geometry of plate tectonics by concentration of deformation signals along block boundaries by correlation of seismicity patterns on scales several times larger than those compatible with a continuum framework and by strongly heterogeneous wave propagation effects on the earth s surface the third view is that faults are fractal objects with rough surfaces and branching geometry the fractal view is supported by some statistical analysis of regional hypocenter locations by long range correlation of various measurements in geophysical boreholes by the fact that observed power law statistics of earthquakes are compatible with an underlying scale invariant geometrical structure by geometrical analysis of fault traces at the earth s surface and by measurements of joint and fault surfaces topography

are topographic data sets fractal the scale invariant properties of fractal sets make them attractive models for topographic profiles because those profiles are the end product of a complex system of physical processes operating over many spatial scales if topographic data sets are fractal their power spectra will be well represented by lines in log log space with slopess such that 3 s 1 the power spectra from a digital elevation model 30 meter sample spacing of the sierra nevada batholith and from seabeam center beam depths 425 meter sample spacing along a flowline in the south atlantic are curved straight sections in the spectra can be identified but the slopes of those sections are strongly dependent upon the particulars of the data analysis fractal geometry must be used with caution in the discussion of topographic data sets

measurement and characterisation of spatial distributions of fractures abstract a variety of line sample 1 d and map 2 d datasets of faults and joints has been used to investigate the spatial distributions of fractures and to test techniques of fractal analysis the natural fracture datasets have been supplemented by synthetic datasets with known characteristics the fault datasets investigated range in scale from regional to outcrop and the joint datasets are derived from outcrop 1 d datasets were analysed by the spacing population interval counting and fracture number interval counting techniques 2 d datasets were analysed by box counting and fracture number box counting techniques results indicate that fracture spacing can be characterised in line samples using either the 1 d interval counting technique or more simply by measuring the spacing population as the cumulative frequency distribution of spaces between adjacent fractures tectonic faults frequently show a power law spacing population indicating fractal dimensions of between 0 4 and 1 0 but except for outcrop data truncation effects degrade the analysis unrefined joint datasets commonly show negative exponential or lognormal spacing cumulative frequency distributions however single orientation joint sets are characterised by a regular spacing and are therefore non fractal for both fault and joint map data box counting techniques do not yield the power law relationship between box size and the number of boxes that is expected of fractal geometries it is concluded that 2 d box counting techniques are too insensitive to characterise the many different parameters of a fracture array the fracture density technique appears not to discriminate between very different fracture patterns and therefore does not provide useful results a fracture pattern incorporates several attributes e g size distribution orientation linkage density roughness each of which may scale independently and each of which may be fractal with its own fractal dimension full characterisation of fracture patterns will therefore require independent analysis of each of these attributes

seismic wave propagation through material containing partially saturated cracks summary expressions for the wave speeds and attenuation of elastic waves through material containing aligned cracks are available in an approximation valid up to second order in the number density of cracks and for wavelengths that are long compared with the size of the cracks conditions within the crack may vary from dry stress free to fluid or solid filled the situation where cracks are partially filled with liquid and part with gas is very different from either extreme of dry or liquid filled cracks since the liquid is forced to flow laterally within a crack at the expense of the more compressible gas by tensions or compressions imposed normal to the plane of the crack expressions are derived here which enable the range of internal crack conditions to be extended to the case of partial saturation in the formulae for the propagation characteristics of waves of long wavelength through material containing such cracks

evaluation of existing criteria in estimating shear strength of natural rock discontinuities abstract as evident from the literature there are a number of shear strength criteria proposed by different researchers in spite of that barton s jrc jcs model is probably the most widely used criterion in routine engineering environments ease of determining the input parameters and efficiency in estimating the shear strength are the two key aspects which make this criterion widespread in rock engineering activities when the shear strength criteria existing in the literature had been analyzed by the authors it became apparent that the difficulty levels or eases involved in determining the input parameters of eleven criteria including barton s criterion are broadly comparable however the existing criteria do not seem to have been compared in terms of their practicality applicability while estimating shear strength of real natural rock discontinuities in the present investigation a total of 196 direct shear tests were performed on natural discontinuities of three distinct rock types i e granite quartzite and sandstone from india at normal stresses within a range of 0 22 2 01 mpa the estimated shear strengths were compared to the determined shear strengths the efficacies of the eleven shortlisted criteria in estimating shear strength of real natural rock discontinuities were critically evaluated the criteria emerged to be the most efficient in this regard were highlighted and plausible reasons behind all the findings of this study were also explained

quantitative methods for analyzing the roughness of the seafloor the bathymetry of the world ocean has been mapped using a variety of acoustic sounding instruments and traditional contouring methods prior to this study relatively few quantitative studies have been focused on the detailed morphology of the seafloor the work of most investigators has generally dealt with the analysis of seafloor relief without regard to spatial frequency or concern for obvious morphologic anisotropies a brief review of previous work is presented and is accompanied by an identification of the specific applications and limitations of those approaches the availability of more precise digital sounding data coupled with the development of higher resolution sonar mapping instruments e g deeptow seamarc now make it possible to investigate quantitatively many important aspects of seafloor relief and the geological processes responsible for its formation typical bathymetric contour maps represent a low frequency deterministic model of the seafloor to describe the higher frequency variability or roughness of the seafloor requires the development of an appropriate statistical method for generating a valid stochastic model new methods are developed herein which allow valid statistical models of the variability of oceanic depths to be derived from existing digital bathymetric soundings the smooth contoured surface often preserved as a geographic grid of depths when supplemented by such a roughness model can provide an essentially complete statistical description of the relief statistical models of seafloor roughness are also valuable tools for predicting acoustic scattering and bottom loss and in addition contain a wealth of information for more comprehensive interpretations of deep sea relief forming geological processes to allow the variability of depths to be described as a function of scale spatial frequency the amplitude spectrum is employed as the fundamental statistic underlying the model since the validity of the amplitude spectrum depends upon the assumption of a statistically stationary sample space a computer algorithm operating in the spatial domain was developed which delineates geographic provinces of limited statistical heterogeneity within each of these provinces a spectral model is derived by fitting the amplitude estimates with one or two two parameter power law functions using specialized regression techniques the distribution of resultant model parameters is examined for a large test area adjacent to the coast of oregon 42 45 n 130 124 w which includes several contrasting geologic environments the distribution of roughness corresponds generally with the various physiographic provinces observed in the region within some provinces additional complexities are apparent in the roughness model which cannot be inferred by simply studying the bathymetry these patterns are related to a variety of geological processes operating in the region such as the convergence of the continental margin and the presence of a propagating rift on the northern gorda rise in contrast a very large area of the continental margin off the east coast of the united states was found to have in common a single distinct amplitude spectrum this amplitude spectrum is almost identical to that found from the tufts abyssal plain region off the west coast of the united states spectra from both of these areas can be clearly separated into two straight line segments of different slope the two segments of these spectra are interpreted as reflecting two dominant relief forming processes the higher frequency band representing a sedimentary regime and the lower frequency band representing an underlying tectonic volcanogenic regime in many cases the calculated roughness statistics are not constant for data collected along different ship track directions this is due to the anisotropic nature of the seafloor relief a simple model is developed which describes the roughness statistics as a function of azimuth the parameters of this model quantify the anistropy of the seafloor allowing insight into the directionality of the corresponding relief forming processes and the physical meaning of the derived model statistical parameters finally the model is used to successfully predict the roughness of a surface at scales much smaller than those resolvable by surface sonar systems the model regression line derived from a hull mounted sonar is compared to data from deep towed sonars and bottom photographs the amplitude of roughness is predicted to within half an order of magnitude over five decades of spatial frequency and this prediction capability can probably be improved even further the stochastic models presented also demonstrate the potential for closely approximating the full two dimensional nature of some areas of the seafloor with only four statistical parameters these parameters can be estimated from random ship track data given a sufficient number of tracks and range of headings

asperities barriers characteristic earthquakes and strong motion prediction recent results from paleoseismology suggest that earthquakes recurrent on a given fault may often have the same characteristic length and amount of slip stable asperities and barriers which survive many earthquakes can explain these results the activity of volcano usu japan since 1977 which produced a dacite dome with a total upheaval of 180 m offered a great opportunity to study the recurrence behavior of a fault seismologists at hokkaido university revealed a family of repeated earthquakes with nearly the same amount of slip generated from the same fault plane on the crater wall along which the dome moved upward this family can be explained by the existence of a stable asperity on the crater wall and is called the asperity type family they found however another type of family of earthquakes which share the same fault plane but show a great range of variation in the amount of slip the behavior of the latter family can be explained by the presence of weak barriers over a fault plane defined by strong stable barriers and this family is referred to as the barrier type family this type of earthquake model has been used successfully in the interpretation of observed strong motion acceleration spectra from california and the results reveal the stability of local stress drop among different earthquakes the agreement found between local stress drops estimated from strong motion data and those inferred from geological observation supports the possibility for predicting earthquake strong motion directly from geological observation of the causative fault

numerical study of flow anisotropy within a single natural rock joint the paper investigates the flow anisotropy within a natural joint subjected to mechanical shear the cubic law is the simplest way to describe fluid flow through rock joints but because of rock wall roughness deviations from this model have been observed the reynolds equation usually gives better results in this study micro scale roughness is taken into account to define a reduced coefficient of permeability numerical simulations have been carried out by applying darcy s law to the rock joint described as an equivalent porous medium the numerical simulations are based on experimental data obtained by hans phd grenoble 2002 from a series of hydromechanical shear tests on a rock joint replica the numerical results have been compared to the experimental ones and to the results obtained by applying the reynolds equation to assess the relevance of the simulations for the fracture studied the approach proposed herein can reproduce relatively well the experimental flow anisotropy and provides consistent values of flow rates whereas the reynolds equation tends to give higher flow rates

deformation phenomena in jointed rock the role of rock joints in rock mass deformation phenomena is described individually joints display concave shaped stress closure curves under normal loading and convex shaped stress displacement curves under shear usually accompanied by dilation the deformation behaviour of rock masses depends on the relative magnitudes of these components of closure shear and dilation the deformation of a rock mass may result in dramatic changes in the joint apertures and conductivities conversely changes in joint water pressure cause changes in joint aperture which affect the overall deformation of the rock mass examples of compaction in jointed reservoirs and leakage phenomena in pressure tunnels are cited each of which may be caused by changes in effective stress the presence of rock joints is seen to affect stress slabbing phenomena in tunnels and is the suspected cause of depth dependent contrasts of stress in sedimentary rocks the phenomenon of hydraulic shearing of joints is discussed with particular

fine scale structure of the extratropical tropopause region 1 a vertically high resolved climatology of the thermal and wind structure of the extratropical tropopause region is presented the climatology is based on data from 80 u s radiosonde stations covering the period 1998 2002 time averages for each radiosonde station are computed using the tropopause as a common reference level for all vertical profiles within the mean a strong inversion at the tropopause in the mean vertical temperature gradient is uncovered that is temperature strongly increases with altitude within the lowermost stratosphere this tropopause inversion layer exists on average throughout the investigated extratropics about 30 n to 70 n accordingly the static stability parameter shows considerably enhanced values within the lowermost extratropical stratosphere compared to typical extratropical stratospheric values further aloft conventional averages are not able to capture the tropopause inversion layer mean profiles of the horizontal wind show behavior qualitatively corresponding to thermal wind balance winter and summer exhibit distinctly different climate states in the extratropical tropopause region an approximated potential vorticity is considered and found to be close to well mixed within the troposphere as well as within the tropopause inversion layer this suggests the view of the tropopause inversion layer as representing a dynamically active atmospheric layer some potential implications are discussed

thermal versus dynamical tropopause in upper tropospheric balanced flow anomalies this paper systematically investigates differences between the thermal and the dynamical tropopause for upper tropospheric balanced flow anomalies idealized cyclonic and anticyclonic anomalies are considered which are either axisymmetric or plane symmetric given a distribution of potential vorticity pv the inversion problem is solved numerically to obtain the corresponding balanced flow i e wind and temperature the control parameter is the aspect ratio of the pv anomaly which governs the partitioning into a thermal and a dynamical anomaly for pv anomalies of intermediate and tall aspect ratios the location of the thermal tropopause differs significantly from the location of the dynamical tropopause the thermal tropopause is rather indistinct for intermediate aspect ratios while it is sharp and well defined for both tall and shallow anomalies a barotropic deformation flow field superimposed on a plane symmetric anomaly induces an ageostrophic wind which modifies the static stability throughout the pv anomaly such that the thermal and dynamical tropopauses evolve differently recent observations concerning the correlation between the thermal and ozone tropopauses can be interpreted consistently in terms of the present results

anisotropy of flow in a fracture undergoing shear and its relationship to the direction of shearing and injection pressure abstract the work presented deal with the effects of shear direction and injection flow rate on the directional anisotropy of the flow for a given normal stress also is related to these effects the evolution of the intrinsic transmissivity of the fracture in relation to the shear direction and tangenital displacements particularly for small displacements tests are performed on mortar replicas of a natural fracture so that the fracture roughness and void space geometry are the same for each test three shear directions are defined these tests results show that the evolution of the intrinsic transmissivity of a fracture depends on the shear direction particularly for small displacements less than 0 5 mm and that shearing induces noticeable modifications in flow direction

tropopause folds and cross tropopause exchange a global investigation based upon ecmwf analyses for the time period march 2000 to february 2001 1 a new methodology is proposed to identify folds of the dynamical tropopause taken as the 2 potential vorticity pv units pvu isosurface from global analysis data sets from the european centre for medium range weather forecasts ecmwf it consists of a three dimensional subdivision of the atmosphere into stratospheric and tropospheric parts and a subsequent examination of multiple tropopause crossings in vertical profiles of the analyses the method is applied to a 1 year period starting in march 2000 seasonal mean fold frequency distributions show that folds occur preferentially in the subtropics with maximum frequencies of about 30 pronounced maxima are located in the subtropical bands that extend from 20 e to 120 e on both hemispheres during summer generally subtropical folds are comparatively shallow deep folds occur most frequently in midlatitudes during winter over eastern north america and the western north atlantic with maximum frequencies of about 1 detailed investigation of the relationship between individual folds and cross tropopause exchange events reveals that on the average individual folds in the extratropics are associated with larger exchange mass fluxes compared to the subtropics however due to the much higher frequency of subtropical folds the percentage of exchange events that are associated with tropopause folds is larger near 20 40 latitude 50 70 than further poleward 20 30 during winter and 10 20 during summer this indicates that tropopause folds are the key feature for cross tropopause exchange in the subtropics whereas in the extratropics other tropopause structures are at least of equal importance

paris basin vsps case history establishing combinations of fine layer or lithologic anisotropy and crack anisotropy from modelling shear wavefields near point singularities summary this paper examines shear wave splitting in multi offset vsps at a borehole site in the paris basin and demonstrates that the sedimentary structure must have at least orthorhombic anisotropic symmetry it is suggested that the most likely cause for such an orthorhombic symmetry is the combination of fine layer or lithologic anisotropy and crack anisotropy transition zones close to shear wave singularities where there are rapid changes of shear wave polarizations and delays can account for the anomalous observed waveforms observations of large variations in shear wave polarizations in propagation directions close to point singularities are probably the first positive identification of the effects of singularities in sedimentary basins

euclidean and fractal models for the description of rock surface roughness accurate description of the topography of rock surfaces is essential because surface roughness affects frictional strength the flow of fluids in joints and fractures the seismic behavior of faults and the formation of gouge and breccia in fault zones real rock surfaces can be described using self similar and self affine fractal models of surface roughness if a surface is self similar a small portion of the surface when magnified isotropically will appear statistically identical to the entire surface if a surface is self affine a magnified portion of the surface will only appear statistically identical to the entire surface if different magnifications are used for the directions parallel and perpendicular to the surface at least two parameters are required to describe a fractal model one parameter typically describes how roughness changes with scale while the other specifies the variance or surface slope at a reference scale the divider method and the spectral method are in common use to determine the best fit fractal model from surface profile data power spectra from self similar surfaces have slopes of 3 on log log plots of power spectral density versus spatial frequency while spectra from self affine surfaces have slopes other than 3 power spectra can be interpreted with greater facility if dimensionless amplitude to wavelength ratios are contoured on plots of power spectral density versus frequency the topography of many natural rock surfaces including both fractures and faults is approximately self similar within the 6 5 order of magnitude wide wavelength band of 10 m to 40 m within smaller wavelength bands natural rock surfaces may exhibit self affine behavior

crack distributions which account for a given seismic anisotropy summary the effect of microfractures or small scale inclusions within earth structures may be measured seismically wavespeeds as a function of wave normal direction lead to effective or mean elastic parameters and the difference between these and the values for unfractured material is related to parameters for the size distribution and internal conditions of the cracks or inclusions thus it appears that measurement of the seismic wavespeeds for a sequence of different propagation directions can lead to information about fractures or inclusions within the rock even though the scale size of this microstructure may be very small compared with a wavelength however the crack parameters are continuous functions of orientation and the elastic parameters for the material provide values for only 21 independent quantities this is enough to describe the crack distribution in terms of spherical surface harmonics up to fourth order only the relationship between the effective elastic parameters and t he crack distribution is accurate to second order in the number density which limits the applications to materials where the contribution of microfractures is less than 10 per cent the relationships referred to above show that inherent material anisotropy is equivalent to a distribution of hypothetical cracks embedded in an isotropic material it then follows that the effect of microfractures in an anisotropic solid may be calculated by imposing both systems of cracks real and hypothetical on an isotropic matrix for which solutions are known

the role of fracture surface roughness in macroscopic fluid flow and heat transfer in fractured rocks abstract rock fractures are major conduits for fluid flow in fractured rocks and the convective heat transfer between rock fracture surfaces and circulating fluid is a critical issue in heat recovery in fractured rocks it has been demonstrated that fracture surface roughness has a significant influence on the mechanical hydraulic thermal and transport behavior of single fractures this study aimed to assess the effects of local surface roughness of fractures on fluid flow and heat transfer processes at the macroscopic scale of fracture networks two distributions of joint roughness coefficient jrc were determined based on the jrc data in oskarshamn forsmark sweden and bakhtiary iran two empirical models relating hydraulic apertures to mechanical apertures were considered a total of ninety one realizations that considered different jrc distributions and empirical models of mechanical hydraulic apertures were studied the results show that fracture surface roughness can affect the fluid flow and heat transfer processes in fracture networks to various extents mainly depending on the empirical models of mechanical hydraulic apertures in other words the role of fracture surface roughness in macroscopic fluid flow and heat transfer in fractured rocks is critical when using a model of mechanical hydraulic apertures that predicts significant reduced hydraulic apertures discrete fracture networks models with the normal distribution of jrc are less permeable than those with the lognormal distribution of jrc using the fitting parameters of in situ jrc data

experimental and numerical study of asperity degradation in the direct shear test abstract in this paper the shear behaviour and mechanisms of asperity degradation of rock joints under direct shear tests were studied using numerical and experimental approaches pfc2d was used for numerical simulations in which the intact material is simulated by a dense packing of circular particles bonded together at their contact points and by breakage of these bonds under loading regimes the damage process is simulated the joint interfaces were simulated by a newly developed modified smooth joint model in which micro scale slip surfaces are applied at contacts between particles of upper and lower blocks of the shear box in order to study the ability of this numerical approach in reproducing the shearing mechanisms and asperity degradation of rock joints in direct shear tests a comparative study was carried out against the physical experiments experimental and numerical direct shear tests were carried out on saw tooth triangular joints with the base angles of 20 and 30 under different normal stresses three shearing mechanisms of sliding surface wear and asperity shearing off were observed in these experiments the comparison of the shear behaviour and mechanisms of asperity degradation of physical and numerical experiments showed that the results of numerical models are in good agreement with physical experiments and this numerical approach can reproduce the shear behaviour of rock joints under different loading conditions

geometrical evolution of interlocked rough slip surfaces the role of normal stress abstract we study the evolution of slip surface topography using direct shear tests of perfectly mating surfaces the tests are performed under imposed constant normal stress and constant slip rate conditions to a sliding distance comparable to the roughness scale of the studied surfaces prismatic limestone blocks are fractured in tension using four point bending and the generated surface topographies are measured using a laser profilometer the initially rough fracture interfaces are tested in direct shear while ensuring a perfectly mating configuration at the beginning of each test the predetermined sliding distance in all tests is 10 mm and the sliding velocity is 0 05 mm s a constant normal stress is maintained throughout the tests using closed loop servo control the range of normal stresses applied is between 2 mpa and 15 mpa after shearing the surface topographies are re scanned and the geometrical evolution is analyzed we find that surface roughness increases with increasing normal stress under normal stresses below 5 mpa the surfaces become smoother compared to the original geometry whereas under normal stresses between 7 5 mpa and 15 mpa the surfaces clearly become rougher following shear statistical spectral analyses of the roughness profiles indicate that roughness increases with length scale power spectral density values parallel to the slip orientation are fitted by power law with typical power value of 2 6 corresponding to a hurst exponent of 0 8 assuming self affine roughness this power value is consistent for the post sheared surfaces and is obtained even when the original surface roughness does not follow initially a power law form the value of the scaling law prefactor however increases with increasing normal stress we find that the deformation associated with shearing initially rough interlocked surfaces extends beyond the immediate tested surface further into the intact rock material the intensity of the damage and its spatial distribution clearly increase with increasing normal stress wear loss is measured by subtracting the post shear surface from the pre shear surface matrices using known reference points our measurements indicate that wear loss and roughness evolution are both positively correlated with the mechanical shear work applied during the experiments we argue therefore that normal stress plays a significant role in the evolution of interlocked surfaces such as geological faults and strongly affects the energy partitioning during slip

characterization of fault roughness at various scales implications of three dimensional high resolution topography measurements accurate description of the topography of active fault surfaces represents an important geophysical issue because this topography is strongly related to the stress distribution along fault planes and therefore to processes implicated in earthquake nucleation propagation and arrest to date due to technical limitations studies of natural fault roughness either performed using laboratory of field profilometers were obtained mainly from 1 d profiles with the recent development of light detection and ranging lidar apparatus it is now possible to measure accurately the 3 d topography of rough surfaces with a comparable resolution in all directions both at field and laboratory scales in the present study we have investigated the scaling properties including possible anisotropy properties of several outcrops of two natural fault surfaces vuache strike slip fault france and magnola normal fault italy in limestones at the field scale digital elevation models of the fault roughness were obtained over surfaces of 0 25 m2 to 600 m2 with a height resolution ranging from 0 5 mm to 20 mm at the laboratory scale the 3 d geometry was measured on two slip planes using a laser profilometer with a spatial resolution of 20 m and a height resolution less than 1 m

estimation of the joint roughness coefficient of rock joints by consideration of two order asperity and its application in double joint shear tests abstract joint roughness has a significant influence on the shear behavior of rock joints many different statistical parameters have been used to estimate the joint roughness coefficient jrc of rock joints depending on what is most easily available and convenient six statistical parameters z2 sf rp 1 log z2 logsf and r p 1 of ten typical roughness profiles were calculated at different sampling intervals si the results indicate that the jrc of rock joints could not be accurately estimated by using only a single statistical parameter because the first order and second order asperities of joints have different effects on shear behavior a classified and weighted fitting formula jrc 16 09 logz21st 12 70 logz22nd 33 75 si 5 0 mm 0 5 mm is proposed to estimate the jrc shear tests on sandstone joints indicate that the maximum jrc along the shear direction is appropriate to represent the total joint surface and estimate the shear strength this formula was adopted to estimate the jrc in double joint shear tests and the results show that the mechanical behavior of double parallel joints is closely related to the interlayer rock and the weaker joint under lower normal stress the interlayer rock does not fracture and the weaker joint determines the peak shear strength of the rock specimen in contrast under higher normal stress the peak shear strength is attained when the tensile fractures initiate in the interlayer rock and it has also relevancy to the jrc of double joints and interlayer thickness

fractal geometry in the san andreas fault system it has been noted that the spatial distribution of earthquakes and the mode of strain release in the san andreas fault system is related to the complexity of fault geometry because of their rough appearance over many length scales faults can be regarded as fractal surfaces direct estimates of fractal dimension d of portions of the san andreas fault system between the northern gabilan range and the salton sea including the postulated extent of the great 1857 fort tejon earthquake are obtained from measured fault lengths analogous to the lengths of coastlines as discussed by mandelbrot regions characterized by complicated fault geometry are associated with larger values of d based on fault traces mapped at a scale of 1 750 000 d is 1 3 for this reach of the fault defined as a 30 km wide band about a main fault trace for that part near parkfield which could be associated with the nucleation of the 1857 earthquake d is 1 1 at this same scale d is 1 4 for the san andreas and related faults near san bernardino where the 1857 rupture stopped compared to 1 2 for the san andreas san juan fault segments near the point of arrest of the 1966 parkfield earthquake at finer map scales 1 24 000 and 1 62 500 critical lengths of 500 m and 1 km are identified which might relate to the extent of off san andreas fault offsets the critical lengths also suggest that fault geometry is not self similar if this fractal geometry persists through the seismic cycle it may be possible to use a quantitative measure of complexity to explain the occurrence of great and characteristic earthquakes along a given reach of fault

the examples of earthquake preparation in kamchatka and japan abstract a recently proposed predictive parameter rtl was tested using seismological catalogues of kamchatka and japan we analysed three earthquakes in kamchatka with m 7 and disastrous hyogo ken nanbu kobe earthquake in japan with m 7 2 it was found that a seismic quiescence had taken place during a period of three years before these earthquakes and been followed by foreshock activation the dimensions of the quiescence areas reached the first hundreds of kilometers whereas the epicenters of strong events were located on the edge of quiescence anomalies the areas of foreshock activation were about 50 100 km and strong events occurred in the region of maximum anomalies the number of clusters increased comparatively to the background events during the stages of foreshock activation in epicenter areas of strong earthquakes the results strengthen the physical basis of earthquake prediction

numerical investigation of geometrical and hydraulic properties in a single rock fracture during shear displacement with the navier stokes equations extensive research has shown that fluid flow through rock fractures is greatly influenced by surface roughness for a single rock fracture the roughness of the upper and bottom surfaces is the same in the initial condition and then its deformation occurs with normal stress and shear stress imposed on the natural rock previous researchers have paid considerable attention to describing the roughness of the single fracture and its effects on fluid flow however few studies have explained the fluid flow with shear displacement and the direction of the fluid flow velocity field in this work a more detailed 2d numerical model was developed using a laser scanner system with a spacing grid of 0 1 mm to investigate the influence of shear displacement accurately the comsol multiphase codes were applied by applying the navier stokes equations the results of the procedure for shear displacement simulation illustrate the distribution of the absolute velocity and pressure drop under the constant pressure gradient the velocities predicted at the vertical profiles of the inlet were similar to the parabolic velocity curve defined by the cubic laws the mean mechanical aperture was usually larger than the hydraulic aperture from the measured flow rates and a devised empirical equation was proposed to describe the relationship between the mechanical aperture and the hydraulic aperture values the recirculation zones observed in directional fluid flow during shear explain the anisotropy of roughness of a single fracture and the phenomenon argues the applicability of local cubic laws which overestimate the total fluid flow rate

characterization and analysis of a translational rockslide on a stepped planar slip surface abstract in 2014 a small stepped planar rockslide blocked a road near the town of san germano chisone in northwest italy photographs of the rock cut that failed above the road were taken before and after the rockslide occurred some photos were acquired with the assistance of a uav these photos were used to conduct a forensic analysis of the rockslide with the aid of photogrammetry software it was possible to characterize the slope geometry and the larger geological structures that influenced the slope behaviour a stepped planar slip surface and the shape of the slabs of rock that failed were defined by discontinuities and these were well documented in the 3d photogrammetry models the effective dilation angle was estimated from an assessment of the roughness of the discontinuity surfaces forming the slip surface the stability of the rockslide was analysed as a stepped translational failure mechanism a two block force equilibrium model of the rockslide was developed with this analytic model both deterministic and probabilistic methods were used to study the influence of water pressure as well as time dependent shear strength degradation along the discontinuities and corrosion of rockbolts the analysis suggests that the rockslide was caused by a combination of inadequate rock support time dependent shear strength degradation and water pressure in the joints resulting from above average rainfall

stochastic modeling of seafloor morphology inversion of sea beam data for second order statistics at scale lengths less than 100 km or so statistical descriptions of seafloor morphology can be usefully employed to characterize ridge crest processes off ridge tectonics and vulcanism sedimentation and postdepositional transport we seek to develop methods for the estimation of seafloor statistics that take into account the finite precision resolution and sampling obtained by actual echo sounding systems in this initial paper we restrict our attention to the problem of recovering second order statistics from data sets collected by multibeam devices such as sea beam the seafloor is modeled as a stationary zero mean gaussian random field completely specified by its two point covariance function we introduce an anisotropic two point covariance function that has five free parameters describing the amplitude orientation characteristic wave numbers and hausdorff fractal dimension of seafloor topography we formulate the general forward problem relating this model to the statistics of an ideal multibeam echo sounder in particular the along track autocovariance functions of individual beams and the cross covariance functions between beams of arbitrary separation using these second moments as data functionals we then pose the inverse problem of estimating the seafloor parameters from realistic noisy data sets with finite sampling and beamwidth and we solve this inverse problem by an iterative linearized least squares method the inversion method is applied to sea beam transit data from both the pacific and atlantic oceans sea beam system noise stands out as a sharp spike on the along track autocovariance function and can be modeled as a white noise process whose amplitude generally increases with beam angle the five parameters in our second order model can be estimated from the inversion of data sets comprising 100 200 km of track length in general the cross track wave number is the most poorly determined although uncertainties in the assumed sea beam response may bias the values of the fractal dimension using the assumed beamwidth the measured noise values and the seafloor parameters recovered from the inversion we generate sea beam synthetics whose statistical character can be directly compared with raw sea beam data for most of the track segments we have processed thus far the synthetics are similar to the data in the case of one atlantic profile however the comparison clearly indicates the necessity of incorporating higher order statistics the space domain procedures described in this paper can be extended for this purpose

fractal analysis applied to characteristic segments of the san andreas fault fractal theory is applied in a quantitative analysis of the san andreas fault saf geometry the method which directly measures the increase in total fault length with a decrease in ruler size gives the fractal dimension d and scaling properties for the chosen length band 0 5 1000 km a physical interpretation of d is that it measures the irregularity of the fault trace in the selected band the fault is subdivided into six segments of distinctive seismic behavior a main fault trace which shows either maximum coseismic slip or creeping was selected for analysis with three alternative branches examined for the saf system south of san bernardino branches of the fault trace are not considered in this work fractal dimensions calculated for the different segments range from 1 0008 to 1 0191 and are different from 1 0 to the 95 confidence interval these small changes reflect the overall smoothness of the main fault trace significant variations in d among segments indicate heterogeneities in the fault smoothness along strike d also changes significantly from the short length band to the long length band where the demarcation point ranges from 1 to 2 km the short length band has larger d values a slight correlation is obtained between the fractal dimension of the main trace and the extent of subparallel faulting this indicates some correspondence between the main fault trace irregularity and the complexity of subsidiary fault traces in plan view

a comparison of cross hole electrical and seismic data in fractured rock cross hole anisotropic electrical and seismic tomograms of fractured metamorphic rock have been obtained at a test site where extensive hydrological data were available a strong correlation between electrical resistivity anisotropy and seismic compressional wave velocity anisotropy has been observed analysis of core samples from the site reveal that the shale rich rocks have fabric related average velocity anisotropy of between 10 and 30 the cross hole seismic data are consistent with these values indicating that observed anisotropy might be principally due to the inherent rock fabric rather than to the aligned sets of open fractures one region with velocity anisotropy greater than 30 has been modelled as aligned open fractures within an anisotropic rock matrix and this model is consistent with available fracture density and hydraulic transmissivity data from the boreholes and the cross hole resistivity tomography data however in general the study highlights the uncertainties that can arise due to the relative influence of rock fabric and fluid filled fractures when using geophysical techniques for hydrological investigations

stratosphere to troposphere transport revealed by ground based lidar and ozonesonde at a midlatitude site 1 this paper presents ozone structures measured by a ground based ozone lidar and ozonesonde at huntsville alabama on 27 29 april 2010 originating from a stratosphere to troposphere transport event associated with a cutoff cyclone and tropopause fold in this case the tropopause reached 6 km and the stratospheric intrusion resulted in a 2 km thick elevated ozone layer with values between 70 and 85 ppbv descending from the 306 k to 298 k isentropic surface at a rate of 5 km day 1 the potential temperature was provided by a collocated microwave profiling radiometer we examine the corresponding meteorological fields and potential vorticity pv structures derived from the analysis data from the north american mesoscale model the 2 pvu pv unit surface defined as the dynamic tropopause is able to capture the variations of the ozone tropopause estimated from the ozonesonde and lidar measurements the estimated ozone pv ratio from the measured ozone and model derived pv for the mixing layer between the troposphere and stratosphere is 41 ppbv pvu with an uncertainty of 33 within two days the estimated mass of ozone irreversibly transported from the stratospheric into the troposphere is between 0 07 tg 0 9 1033 molecules and 0 11 tg 1 3 1033molecules with an estimated uncertainty of 59 tropospheric ozone exhibited enormous variability due to the complicated mixing processes low ozone and large variability were observed in the mid troposphere after the stratospheric intrusion due to the westerly advection including the transition from a cyclonic system to an anticyclonic system this study using high temporal and vertical resolution measurements suggests that in this case stratospheric air quickly lost its stratospheric characteristics once it is irreversibly mixed down into the troposphere

earthquake failure sequences along a cellular fault zone in a three dimensional elastic solid containing asperity and nonasperity regions numerical simulations of earthquake failure sequences along a discrete cellular fault zone are performed for a three dimensional 3 d model representing approximately the central san andreas fault the model consists of an upper crust overlying a lower crust and mantle region together defining an elastic half space with a vertical half plane fault the fault contains a region where slip is calculated on a uniform grid of cells governed by a static kinetic friction law and regions where slip is prescribed so as to represent tectonic loading aseismic fault creep and adjacent great earthquakes the computational region models a 70 km long and 17 5 km deep section of the san andreas fault to the nw of the great 1857 rupture zone different distributions of stress drops on failing computational cells are used to model asperity parkfield asperity and nonasperity fault regions the model is inherently discrete and corresponds to a situation in which a characteristic size of geometric disorder within the fault i e cell size here a few hundreds of meters is much larger than the nucleation size of the order of tens of centimeters to tens of meters based on slip weakening or state evolution slip distances the computational grid is loaded by a constant plate motion imposed at the lower crust upper mantle and creeping fault regions and by a staircase slip history imposed at the 1857 and 1906 rupture zones stress transfer along and outside the fault due to the imposed loadings and failure episodes along the computational grid is calculated using 3 d elastic dislocation theory the resulting displacement field in the computational region is compatible with geodetic and seismological observations only when the asperity and nonasperity regions are characterized by significantly different average stress drops the frequency magnitude statistics of the simulated failure episodes are approximately self similar for small events with b 1 2 the b value of statistics based on rupture area ba is about 1 but are strongly enhanced with respect to self similarity for events larger than a critical size this is interpreted as a direct manifestation of our 3 d elastic stress transfer calculations beyond certain rupture area and potency seismic moment divided by rigidity release values the event is usually unstoppable and it continues to grow to a size limited by a characteristic model dimension this effect is not accounted for by cellular automata and block spring models in which the adopted simplified stress transfer laws fail to scale properly with increasing rupture size the simulations suggest that local maxima in observed frequency magnitude statistics correspond to dimensions of coherent brittle zones such as the width of the seismogenic layer or the length of a fault segment bounded by barriers the analysis indicates that a single cell size representing approximately a single scale of geometric disorder cannot induce self similarity in a 3 d elastic model over a broad range of magnitudes a representation of geometric disorder covering a range of scales may thus be required to generate a wide domain of self similar gutenberg richter statistics our simulations show a great diversity in the mode of failure of the parkfield asperity the earthquakes themselves define an irregular sequence of events the modeling like many other discrete fault models suggests that expectations for periodic parkfield earthquakes and or simple precursory patterns repeating from one event to the other are unrealistic

a morphologic characterisation of the 1963 vajont slide italy using long range terrestrial photogrammetry abstract the 1963 vajont slide in northeast italy is an important engineering and geological event although the landslide has been extensively studied new insights can be derived by applying modern techniques such as remote sensing and numerical modelling this paper presents the first digital terrestrial photogrammetric analyses of the failure scar landslide deposits and the area surrounding the failure with a focus on the scar we processed photogrammetric models to produce discontinuity stereonets residual maps and profiles and slope and aspect maps all of which provide information on the failure scar morphology our analyses enabled the creation of a preliminary semi quantitative morphologic classification of the vajont failure scar based on the large scale tectonic folds and step paths that define it the analyses and morphologic classification have implications for the kinematics dynamics and mechanism of the slide metre and decametre scale features affected the initiation direction and displacement rate of sliding the most complexly folded and stepped areas occur close to the intersection of orthogonal synclinal features related to the dinaric and neoalpine deformation events our analyses also highlight for the first time the evolution of the vajont failure scar from 1963 to the present

structural diagnostics of the tropopause inversion layer and its evolution the tropopause inversion layer til is marked by a peak in static stability directly above the tropopause the til is quantitatively defined with new diagnostics using global positioning system radio occultation temperature soundings and reanalysis data a climatology of the til is developed from reanalysis data 1980 2011 using diagnostics for the position depth and strength of the til based on the til peak in static stability til diagnostics have defined relationships to the synoptic situation in the upper troposphere and lower stratosphere the til is present nearly all the time the til becomes hard to define in the subtropics where tropical air overlies midlatitude air in a region of complex static stability profiles the mean position of the subtropical til gradient is sharp and is co located with the subtropical tropopause break over the period 1980 2011 the til depth below the tropopause has decreased by 5 per decade and increased above the tropical tropopause by a similar percentage furthermore the latitude of the abrupt change in the til from tropical to extratropical in the lower stratosphere appears to have shifted poleward in each hemisphere by 1 latitude per decade depending on the diagnostic examined reanalysis trends should be treated with caution

inversion for seismic anisotropy using genetic algorithms1 a general inversion scheme based on a genetic algorithm is developed to invert seismic observations for anisotropic parameters the technique is applied to the inversion of shear wave observations from two azimuthal vsp data sets from the conoco test site in oklahoma horizontal polarizations and time delays are inverted for hexagonal and orthorhombic symmetries the model solutions are consistent with previous studies using trial and error matching of full waveform synthetics the shear wave splitting observations suggest the presence of a shear wave line singularity and are consistent with a dipping fracture system which is known to exist at the test site application of the inversion scheme prior to full waveform modelling demonstrates that a considerable saving in time is possible whilst retaining the same degree of accuracy

the extratropical tropopause inversion layer global observations with gps data and a radiative forcing mechanism global characteristics of the extratropical tropopause inversion layer identified in radiosonde observations by birner are studied using high vertical resolution temperature profiles from gps radio occultation measurements the gps data are organized according to the height of the thermal tropopause in each profile and a temperature inversion layer above the tropopause with an average magnitude of 3 5 k is found to be a ubiquitous climatological feature the gps data show that the inversion layer is present for all seasons in both hemispheres spanning the subtropics to the pole and there is not strong longitudinal structure dependence of the inversion layer on upper troposphere vorticity is studied while anticyclones exhibit a substantially stronger inversion than cyclones as expected from balanced dynamics the inversion is evident for all circulation types radiative transfer calculations indicate that strong gradients in both ozone and water vapor near the tropopause contribute to the inversion significant absorption of both longwave and shortwave radiation by ozone occurs warming the region above the tropopause water vapor near and immediately above the tropopause contributes to cooling effectively enhancing the inversion

a diagnostic equation for tendency of lapse rate tropopause heights and its application abstractthe tropopause is the boundary between the troposphere and stratosphere and is normally defined by the temperature lapse rate previous studies have noted that synoptic scale and planetary

sheared rock joints dependence of damage zones on morphological anisotropy abstract the objective of this work is to determine the 3d structural morphological factors such as position elevation extension and dipping of asperities and relative position of asperities that are essential to analyze the shear behavior of rock joints a series of shear test was performed at three normal stresses 7 14 and 21 mpa with identical cement mortar replicas of a natural fracture for each normal stress under the same shear rate shear displacement was stopped at five different values the shear tests were performed at four different directions after each shear test grey level images of both upper and lower walls of the replicas were acquired using a ccd camera then using a segmentation method we have developed the damaged areas are identified in such a way that damaged contours can be superposed on a topographic map results of the investigation include a set of images showing both the morphology of the joint and the specific position of each damaged asperity numerical data are also available

description and classification of rock surfaces by means of laser profilometry and mathematical morphology the evaluation of surface roughness is crucial to the hydrochemical and mechanical description of fractured rock masses surface roughness contains information on rock strength deformability permeability etc recent years have witnessed a rapid development of new methods for measuring the surface of rock fracture using state of the art technologies currently available measuring instruments such as profilometers and confocal microscopes provide information about hundreds of thousands of even millions measurement points which represent the investigated surface the key problem therefore is to work out methods to adequately interpret such large packets of data this study attempts a thorough analysis of this type of data using image processing and mathematical morphology methods the paper presents the results received from morphological gradients analyses of the results obtained from the watershed as well as the analyses of variograms furthermore it proposes the application of morphological filtering for selecting the roughness component of a rock fracture these results have been used in classifying the investigated rock this classification was based on pattern recognition methods by the definition of the 6d features space and the definition of learning sets a successful classification of investigated rocks has been obtained with up to ca 95 correct recognitions

improvement of photogrammetric jrc data distributions based on parabolic error models this research describes the influences of the focal length of lenses as well as camera to object distances that control the accuracy and precision of 3d photogrammetry models used for assessing joint roughness coefficients jrc a parabolic error model which is developed by a series of photogrammetric laboratory tests is used to improve the jrc data distributions obtained from the photogrammetry 3d models the influences of camera to object distances and focal lengths on the accuracy of jrc values are investigated in laboratory conditions a series of photogrammetry tests are performed under different conditions by varying the camera to object distances and the camera lens focal lengths the camera positions are controlled on a sliding device to increase the accuracy of geo referencing the results suggest the allowable photographic distances for the employed photogrammetry equipment e g camera and focal lengths of lenses to estimate jrc values through comparison with the manually measured values the root mean square error rmse of jrc functions which are correlated with the camera distances and the normalized jrc values are depicted as different size parabolic curves according to the employed focal lengths these models successfully improve on the accuracy of the originally obtained jrc distributions

synthetic rough fractures in rocks natural fractures serve a very important function in the transport of fluid through rocks as well as in the flow of electrical charge and heat the creation of numerically synthesized fractures can aid the study of the physical processes connected with fractures synthetic fracture is the term used to describe fractures that are created numerically in such a way that they share the same mean geometrical characteristics as specific natural fractures measured by profiling by a process known as tuning we have modified methods for producing synthetic rough surfaces whose geometric properties are tuned to mimic natural fracture surfaces in rocks in order to create synthetic fractures that are statistically identical to those found in rocks one important such modification has been the incorporation of a method that allows the surfaces to be matched at long wavelengths and unmatched at short wavelengths with the degree of matching varying smoothly in between as it does for real fractures we have compared numerically synthetic fractures created using the new method with fractures created using an existing technique that uses a mismatch wavelength as a sudden discontinuity between matched and unmatched behavior as well as data from fractures in real rocks this comparison has shown that the new technique provides much more realistic numerically synthesized fractures than previous methods synthetic fractures created with the new method have been used in normal closure and fluid flow modeling and the results are reported in a companion paper

the work budget of rough faults abstract faults in nature have measurable roughness at many scales and are not planar as generally idealized we utilize the boundary element method to model the geomechanical response of synthetic rough faults in an isotropic linear elastic continuum to external tectonic loading in terms of the work budget faults are generated with known fractal roughness parameters including the root mean square slope a measure of roughness amplitude and the hurst exponent h a measure of geometric self similarity energy within the fault models is partitioned into external work w ext internal elastic strain energy w int gravitational work w grav frictional work w fric and seismic energy w seis results confirm that w ext or work done on the external model boundaries is smallest for a perfectly planar fault and steadily increases with increasing this pattern is also observed in w int the energy expended in deforming the host rock the opposite is true for gravitational work or work done against gravity in uplifting host rock as well as with frictional work or energy dissipated with frictional slip on the fault and w seis or seismic energy released during slip events effects of variation in h are not as large as for but w grav w fric and w seis increase with increasing h with w int and w ext decreasing across the same range remarkably however for a narrow range of roughness amplitudes which are commonly observed along natural faults the total work of the system remains approximately constant while slightly larger than the total work of a planar fault faults evolve toward the most mechanically efficient configuration therefore we argue that this range of roughness amplitudes may represent an energy barrier preventing faults from removing asperities and evolving to smooth planar discontinuities a similar conclusion is drawn from simulations at relatively shallow depths with results showing that shallower faults have larger energy barriers and can be mechanically efficient at higher roughness amplitudes

a novel three dimensional discrete fracture network model for investigating the role of aperture heterogeneity on fluid flow through fractured rock masses abstract effect of anisotropic aperture on the hydraulic properties of single rock fractures has been systematically investigated yet the aperture variability of individual fractures in 3d discrete fracture networks dfns is commonly negligible by using parallel plate fractures the present study proposed a 3d dfn model with fractures having heterogeneous apertures to estimate the influence of fracture variability on fluid flow in total a set of 1280 3d models with increasing fracture densities and fracture lengths are generated and the fluid flow through the models is simulated using a developed numerical code the influences of aperture heterogeneity and network topology on the flow pattern and permeability of 3d dfns are estimated the results show that the network topology provides a first order frame of geometrical connectivity and the heterogeneous aperture further allows the flow to select some most transmissive channels within these connected fractures the dfn model with identical apertures generates a large number of medium flow rate regions whereas the dfn model with fractures having heterogeneous apertures results in extremely low and high flow rate regions the permeability ratio of the two models is widely spread in terms of a small variation in the average mechanical aperture as a result of strong dependence on the aperture distribution the average permeability ratio increases significantly first and then approaches to 1 0 with increasing the average mechanical aperture this allows for the definition of a critical mechanical aperture above which the permeability can be properly predicted using the dfn model with fractures having identical apertures and below which the permeability is much altered by the aperture variability and the dfn model with fractures having heterogeneous apertures should be employed

observed cyclone anticyclone tropopause vortex asymmetries relatively little is known about coherent vortices near the extratropical tropopause even with regard to basic facts about their frequency of occurrence longevity and structure this study addresses these issues through an objective census of observed tropopause vortices the authors test a hypothesis regarding vortex merger asymmetry where cyclone pairs are repelled and anticyclone pairs are attracted by divergent flow due to frontogenesis emphasis is placed on arctic vortices where jet stream influences are weaker in order to facilitate comparisons with earlier idealized numerical simulations results show that arctic cyclones are more numerous persistent and stronger than arctic anticyclones an average of 15 cyclonic vortices and 11 anticyclonic vortices are observed per month with maximum frequency of occurrence for cyclones anticyclones during winter summer there are are about 47 more cyclones than anticyclones that survive at least 4 days and for longer lifetimes 1 day survival probabilities are nearly constant at 65 for cyclones and 55 for anticyclones mean tropopause potential temperature amplitude is 13 k for cyclones and 11 k for anticyclones with cyclones exhibiting a greater tail toward larger values an analysis of close proximity vortex pairs reveals divergence between cyclones and convergence between anticyclones this result agrees qualitatively with previous idealized numerical simulations although it is unclear to what extent the divergent circulations regulate vortex asymmetries