the thickness of faults from laboratory experiments to field scale observations to assess the role of the fault thickness on its mechanical behavior we first present the results of an experimental modeling of a thick fault core our laboratory setup consists in an annular simple shear apparatus in which we can apply very large shear displacements 50 m to 100 particle thick granular samples thanks to a window in the apparatus pictures of the microstructures can be continuously taken during shear we observe from a correlation image velocimetry technique that a significant strain field exists outside of the observable shear band this strain field though of small magnitude compared to that existing inside the shear band is very structured and extends in a region much wider than expected from individual static observations i e wider than the directly observable shear band moreover this strain field controls most of the evolution of the shear strength of the fault we then propose plausible comparisons of our experimental results to geological observations of fault cores in the region of aigion corinth gulf greece the studied faults indeed display spectacular indurated fault planes lying on weakly cohesive material signatures of cementation clay mineral distribution and porosity profile of one of the studied fault cores are included and discussed in the light of the experimental results our observations suggest that the maximum shear strain during earthquakes might occur not in the center but on the border of the fault cores it is presumably localized in a transition zone which exhibits a significant cementation owing to a process of mechanical smearing by fine particles this zone may also act as a very low permeability layer responsible for a channeling of the fluid flow such a scheme of progressive multi sub localizations is different from classical descriptions of faults and consistent with a layering of the core consisting of separated zones of high strains or large cataclastic flows

ultracataclasite structure and friction processes of the punchbowl fault san andreas system california abstract the punchbowl fault is an exhumed 40 km displacement fault of the san andreas system in the devil s punchbowl the fault contains a continuous ultracataclasite layer along which the punchbowl formation sandstone and an igneous and metamorphic basement complex are juxtaposed the fabric of the ultracataclasite layer and surrounding rock indicate that nearly all of the fault displacement occurred in the layer by analogy with nearby active faults we assume that the punchbowl fault was seismogenic and that the ultracataclasite structure records the passage of numerous earthquake ruptures we have mapped the ultracataclasite layer at 1 1 and 1 10 to determine the mode of failure and to constrain the processes of seismic slip on the basis of color cohesion fracture and vein fabric and porphyroclast lithology two main types of ultracataclasite are distinguished in the layer an olive black ultracataclasite in contact with the basement and a dark yellowish brown ultracataclasite in contact with the sandstone the two are juxtaposed along a continuous contact that is often coincident with a single continuous nearly planar prominent fracture surface pfs that extends the length of the ultracataclasite layer in all exposures no significant mixing of the brown and black ultracataclasites occurred by offset on anastomosing shear surfaces that cut the contact or by mobilization and injection of one ultracataclasite into the other the ultracataclasites are cohesive throughout except for thin accumulations of less cohesive reworked ultracataclasite along the pfs structural relations suggest that 1 the black and brown ultracataclasite were derived from the basement and sandstone respectively 2 the black and brown ultracataclasites were juxtaposed along the pfs 3 the subsequent final several kilometers of slip on the punchbowl fault occurred along the pfs and 4 earthquake ruptures followed the pfs without significant branching or jumping to other locations in the ultracataclasite by comparison with rock friction experiments the slip localization along the pfs in the ultracataclasite implies rate weakening behavior with a critical slip distance similar to laboratory values and thus relatively small nucleation and breakdown dimensions for earthquake ruptures of the various mechanisms proposed to explain the low strength of the san andreas and to produce dynamic weakening of faults those that require or assume extreme localization of slip are most compatible with our observations

inversion for seismic slip rate history and distribution with stabilizing constraints application to the 1986 andreanof islands earthquake we develop and present a method of inverting seismograms including their absolute amplitudes to obtain the complete seismic slip time history and distribution using the method of linear programming a rectangular fault is discretized into cells and the source duration into time steps the inversion for the slip rate distribution on the fault as a function of time reduces to the solution of a system of linear equations the influence on the solution of constraining different source parameters such as the sign of the slip rate and the seismic moment is investigated it is found that the constraint of positiveness of slip rate and the constraint that the seismic moment determined from the solution should be close to that obtained from the centroid moment tensor cmt solution are very strong constraints and are essential to obtaining a physically reasonable solution since the inverse problem is unstable instead of presenting only one particular solution we examine several solutions equally well fitting the data for all practical purposes we find that when both constraints are applied the solution becomes quite stable the method is applied to a data set consisting of the vertical component of available digitally recorded teleseismic p waves at stations within a chosen distance window for the 1986 andreanof islands earthquake mw 8 0 the preferred solution is the one in which the slip rate is constrained to be positive and the moment is set to the cmt value the average rupture speed in the 90 km segment to the east of the hypocenter was 3 2 km s and in the 190 km section to the west was 2 km s the maximum slip in the area of large moment release to the west was 5 m and the maximum slip rate which occurs in the same place as the maximum slip was 6 5 m s the slip distribution on the fault shows a corrugated pattern with the long axis in the direction of the plate convergence rather than normal to the arc which was the slip vector direction for the earthquake with most of the slip occurring pn a region of the fault to the west of the rupture nucleation zone this region continued to slip for about 55 s the total source duration being about 80 s the results of this analysis suggest that the long term motion on this portion of the aleutian arc is indeed in the direction of plate convergence

shear and normal load perturbations on a two dimensional continuous fault 2 dynamic triggering 1 the influence of normal and shear stress static perturbations on a strike slip fault is addressed on the basis of a two dimensional continuous and quasi dynamic model friction along the fault plane is described using a rate and state friction law with depth variable properties normal and shear stress perturbations result in similar effects in terms of earthquake triggering iftm s is constant t ands being the amplitude of the shear and normal stress fluctuations respectively and m being a constant which can be interpreted as the static friction coefficient on the fault in a coulomb failure model therefore the coulomb stress changecff tm s is a useful tool to account simultaneously for normal and shear stress variations in our model we also show that when estimating the clock advance or clock delay of an earthquake the simple coulomb failure model is at first order in good agreement with our results during the first 90 of the earthquake cycle however it differs significantly during the last 10 due to the sharp velocity increase predicted by the rate and state friction law before rupture this suggests that as long as static variations of stress are concerned realistic fault models using rich laboratory based friction laws like rate and state friction laws may lead topredictions fairly close to the ones made using one of the simplest failure model i e the coulomb failure model this may explain why coulomb stress change computations although often based on drastic approximations have been able in many occasions to explain earthquake triggering sequences index terms 7209 seismology earthquake dynamics and mechanics 7215 seismology earthquake parameters 7260 seismology theory and modeling keywords earthquake triggering static triggering coulomb stress change rate and state friction laws clock advance delay

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

laboratory gouge friction seismic like slip weakening and secondary rate and state effects 1 we investigate experimentally the frictional response of a thick sample of simulated fault gouge submitted to very high shear displacements up to 40 m in an annular simple shear apparatus acsa the frictional strength of our granular material exhibits velocity weakening consistent with classical rate and state dependent friction laws the length scale involved in the latter phenomenon is dc 100 m however the evolution of friction is largely dominated by a significant slip weakening active over decimetric distances l 0 5 m interestingly these decimetric frictional length scales are quantitatively compatible with those estimated for natural faults during shearing a thin and highly sheared layer emerges from the thick and slowly deforming bulk of the sample because of the intermittent and non local coupling observed between these two zones we relate the large frictional length scales in our data to the slow structuring of the thick interface

scaling of the critical slip distance for seismic faulting with shear strain in fault zones theoretical and experimentally based laws for seismic faulting contain a critical slip distance1 5 dc which is the slip over which strength breaks down during earthquake nucleation on an earthquake generating fault this distance plays a key role in determining the rupture nucleation dimension6 the amount of premonitory and post seismic slip7 10 and the maximum seismic ground acceleration1 11 in laboratory friction experiments d c has been related to the size of surface contact junctions2 5 12 thus the discrepancy between laboratory measurements of dc 10 5m and values obtained from modelling earthquakes 10 2m has been attributed to differences in roughness between laboratory surfaces and natural faults5 this interpretation predicts a dependence of dc on the particle size of fault gouge2 breccia and wear material but not on shear strain here we present experimental results showing that dc scales with shear strain in simulated fault gouge our data suggest a new physical interpretation for the critical slip distance in which dc is controlled by the thickness of the zone of localized shear strain as gouge zones of mature faults are commonly 102 103 m thick12 17 whereas laboratory gouge layers are 1 10 mm thick our data offer an alternative interpretation of the discrepancy between laboratory and field based estimates of dc

control of rupture by fault geometry during the 1966 parkfield earthquake a reanalysis of the available data for the 1966 parkfleld california earthquake mr 5 suggests that although the ground breakage and aftershocks extended about 40 km along the san andreas fault the initial dynamic rupture was only 20 to 25 km in length the foreshocks and the point of initiation of the main event locate at a small bend in the mapped trace of the fault detailed analysis of the p wave first motions from these events at the gold hill station 20 km southeast indicates that the bend in the fault extends to depth and apparently represents a physical discontinuity on the fault plane other evidence suggests that this discontinuity plays an important part in the recurrence of similar magnitude 5 to 6 earthquakes at parkfield analysis of the strong motion records suggests that the rupture stopped at another discontinuity in the fault plane an en echeion offset near gold hill that lies at the boundary on the san andreas fault between the zone of aseismic slip and the locked zone on which the great 1857 earthquake occurred foreshocks to the 1857 earthquake occurred in this area sieh 1978 and the epicenter of the main shock may have coincided with the offset zone if it did a detailed study of the geological and geophysical character of the region might be rewarding in terms of understanding how and why great earthquakes initiate where they do

fracture roughness and gouge distribution of a granite shear band 1 localization of deformation during fracture mechanical tests leads to the development of shear bands we performed triaxial tests using sidobre granite at four different confining pressures from 20 to 80 mpa we compared two sets of tests one set was stopped immediately after the formation of the shear band a second one included additional shear deformation from the analysis of thin sections of these laboratory samples we characterize the typical microstructures in the shear band mode i and ii cracks riedel cracks cataclastic flow statistical properties of rupture surface roughness and gouge grain size reveals scaling invariance using a mechanical profiler the fracture roughness is measured along parallel profiles and shown to be correctly described over up to 3 orders of magnitude by self affine geometry with a roughness exponent close to 0 80 this property is very similar to tensile crack even if local processes are different the influence of the slip is observed fracture surfaces are rougher along the slip direction 0 74 than perpendicular to it 0 80 the confining pressure is shown to have a weak effect on the fracture roughness it smoothes the surface slight increase of the roughness exponent gouge particles extracted from the shear band present a power law distribution with an exponent ranging from 1 44 to 1 91 this exponent appears to increase with the shearing displacement and the confining pressure when a significant shear of the band is combined with a high confining pressure i e impeded dilation of the band the hallmark of fragmentation is observed for the particle distribution and related to a smoothing of the band boundary

evolution of feldspars at the amphibolite granulite facies transition in augen gneisses sw norway geochemistry and sr isotopes the sveconorwegian augen orthogneisses of rogaland vest agder sw norway were emplaced as amphibole and biotite bearing granodiorites at 1040 ma concordant rb sr and zircon u pb ages they underwent prograde metamorphism which increased from lower amphibolite facies in the eastern zone to granulite facies in the western zone close to the rogaland anorthosite complex k feldspar megacrysts initially crystallised as phenocrysts and were chemically equilibrated during metamorphism as shown by the flat ba concentration profiles and the increase of the anorthite content from an1 1 in the amphibolitefacies to an2 6 in the granulite facies this increase of the an content suggests an increase in metamorphic temperature the ree content of the megacrysts is related to the associated accessory minerals which depend upon the metamorphic grade sphene allanite apatite zircon and rarely thorite in amphibolite facies and apatite zircon monazite thorite in lower amphibolite and granulite facies amphibole and biotite inclusions in megacrysts were also equilibrated during metamorphism groundmass k feldspar and plagioclase experienced late metamorphic changes during uplift an internal rb sr mineral isochron plagioclase apatite k feldspar defines an age of 870 ma which represents the closure of the rb sr isotopic system in minerals of the augen gneisses this age also represents a k feldspar cooling age in regionally distributed augen gneiss samples the k feldspar cooling age appears to be similar to or slightly older than the biotite cooling age

a new mechanism of slip weakening and strength recovery of friction associated with the mechanical consolidation of gouge i present results of a series of slide hold slide tests on granite surfaces separated by a layer of simulated granite gouge the shear stress during the hold period hold was controlled and used as a major control parameter of the experiments in addition to the time of hold time dependent fault healing which has been observed in many previous similar experiments was observed only at very high hold above 90 of the sliding friction a time independent strengthening termed consolidation strengthening occurred at all hold with a magnitude proportional to the reduction of hold the magnitude of this strengthening was as large as 25 of the residual friction the consolidation strengthening was found to be erased by subsequent slip in quite a different manner than is time dependent healing the friction decreased linearly with slip displacement at a rate independent of the magnitude of the strengthening and hence larger slip displacement is required to erase larger consolidation strengthening on the basis of these results together with earlier authors results of the measurements of porosity change under similar conditions i conclude that the time independent strengthening is due to the occurrence of gouge particle rearrangement to tighter packing enabled by decreased shear stress under a constant normal stress and that the subsequent slip weakening is due to unconsolidation of gouge enabled by particle rearrangement dilatancy during shearing the rate and state dependent friction rsf law was extended to incorporate the present findings

slip correlations on a creeping fault using a quasi static three dimensional fault model which accounts for long range elastic interactions we examine the influence of spatial heterogeneities of frictional strength on the slip distribution along a creeping fault slip fluctuates spatially because of pinning on local asperities we show that three regimes of slip correlations exist the first regime results in a uniform slip as in an homogeneous medium on the contrary slip in the second regime highly fluctuates and is controlled by heterogeneities of frictional strength the third regime is intermediate and develops areas of high slip that are much bigger than the local asperity size self affine properties of the slip distribution this particular regime illustrates the possible misinterpretation of low frequency slip data e g interferometric and gps data in terms of structural or compositional properties along the fault

effective normal stress alteration due to pore pressure changes induced by dynamic slip propagation on a plane between dissimilar materials 1 recent detailed examinations of fault zones show that walls of faults are often bordered by materials that are different from each other and from the more uniform material farther away in addition they show that the ultracataclastic core of mature fault zones where slip is concentrated is less permeable to flow across it than the adjoining material of the damage zone inhomogeneous slip at the interface between materials with different poroelastic properties and permeabilities causes a change in pore pressure there because slip causes compression on one side of the fault wall and extension on the other the pore pressure on the fault increases substantially when the compressed side is significantly more permeable and decreases when instead the extended side is more permeable this change in pore pressure alters the effective normal stress on the slip plane in a way that is analogous to the normal stress alteration in sliding between elastically dissimilar solids the magnitude of the effect due to induced pore pressure can be comparable to or larger than that induced by sliding between elastic solids with a dissimilarity of properties consistent with seismic observations the induced pore pressure effect is increased by increasing contrast in permeability but the normal stress alteration due to elastic contrast increases rapidly as the rupture velocity approaches the generalized rayleigh velocity because the alteration in effective normal stress due to either effect can be positive or negative depending on the contrast in properties the two effects can augment or offset each other

routine characterization and interpretation of complex alkali feldspar intergrowths almost all alkali feldspar crystals contain a rich inventory of exsolution twin and domain microtextures that form subsequent to crystal growth and provide a record of the thermal history of the crystal and often of its involvement in replacement reactions sometimes multiple microtextures strongly influence the subsequent behavior of feldspars at low temperatures during diagenesis and weathering they are central to the retention or exchange of trace elements and of radiogenic and stable isotopes this review is aimed at petrologists and geochemists who wish to use alkali feldspar microtextures to solve geological problems or who need to understand how microtextures influence a particular process we suggest a systematic approach that employs methods available in most well founded laboratories the crystallographic relationships of complex feldspar intergrowths were established by the 1970s mainly using single crystal x ray diffraction but such methods give limited information on the spatial relationships of the different elements of the microtexture or of the mode and chronology of their formation which require the use of microscopy we suggest a combination of techniques with a range of spatial resolution and strongly recommend the use of orientated sections sections cut parallel to the perfect 001 and 010 cleavages are the easiest to locate and most informative techniques described are light microscopy scanning electron microscopy using both backscattered and secondary electrons including the use of surfaces etched in the laboratory electron probe microanalysis and analysis by energy dispersive spectrometry in a scanning electron microscope transmission electron microscopy we discuss the use of cathodoluminescence as an auxiliary technique but do not recommend electron backscattered diffraction for feldspar work we review recent publications that provide examples of the need for great care and attention to pre existing work in microtextural studies and suggest several topics for future work

micromechanics of shear rupture and the control of normal stress abstract conjugate microfault zones and distributed tensile microcracks were observed in low porosity sandstone samples deformed by shear box rupture at different normal stresses statistical data collected from scanning electron microscopic mapping show that tensile microcracks and microfaults are more frequent in the higher normal stress cases the average thickness of the cataclastic microfault zones increases proportionally to rupture normal stress the density of tensile microcracks increases locally in microfault relay and intersection zones where their formation is an important mode of microfault zone cataclasis concentration of longer en echelon tensile microcracks occurs in process zones ahead of the microfault tips connected by cross cracks in an incipient breakdown zone to further propagate the fault fracture densities are much lower in calcite cement grains whose compliancy serves to arrest microfault growth temporarily yet also aid intragranular microcracking in adjacent stiff grains and at grain boundaries tensile microcrack and microfault average dips from the sample rupture surface increase with rupture normal stress with conjugate microfault orientation variability at higher normal stresses aiding their connectivity results of this investigation demonstrate how the fracture porosity and connectivity around rupture zones increase dramatically at increased rupture normal stress impacting on hydrodynamic properties of rupture zones

crystallization paths of leucite bearing lavas examples from italy the salic phases found in leucite basanites trachytes and phonolites may be used to portray crystallization in the system naalsio 4 kalsio 4 caal 2si 2o 8 sio 2 the phonolite pentahedron only two lavas have been found that contain the assemblage leucite nepheline plagioclase sanidine and liquid a natural pseudo invariant assemblage at 900 c 100 equivalent to the isobaric invariant point of the four component system the diversity of phases in this group of lavas illustrates the role of halogens in controlling their crystallization paths thus the presence of f in the leucite basanites has stabilized magnesian biotite and suppressed sanidine as has been found in other basanitic lavas brown and carmichael 1969 the presence of cl in these same lavas has induced the crystallization of sodalite which takes the place of nepheline in the groundmass however in the leucite trachytes biotite has suppressed olivine and coexists with sanidine and leucite the presence of s may produce hauyne at the expense of nepheline and in general sulphate minerals which include apatite have the role in lavas of low silica activity that pyrrhotite plays in liquids of high silica activity both pyroxenes and titaniferous magnetites in this suite of lavas are very aluminous groundmass crystals of pyroxene may have one fifth of si replaced by al other phases which occur occasionally are melanite garnet and a potassium rich hastingsite but neither ilmenite nor a sulphide mineral has been found phenocryst equilibration temperatures derived from olivine and sr rich plagioclase are generally in the range from 1 050 c to 1 150 c the high content of incompatible elements e g k ba rb f sr p in these lavas suggests that they represent a small liquid fraction from a mantle source which possibly contains phlogopite

low frictional strength of quartz rocks at subseismic slip rates 1 laboratory experiments on rocks at low sliding velocity typically yield values of the friction coefficient of 0 6 0 85 here we demonstrate that an extraordinary decrease in friction coefficient accompanies sliding of room dry quartz rocks at rates faster than in most laboratory experiments but slower than seismic slip rates in some cases the friction coefficient decreases from low speed values by more than a factor of 3 this extraordinary weakening likely results from the formation of finely comminuted amorphous wet material on the sliding surface

geochemistry of the granitic rocks and their minerals from serra da estrela central portugal abstract several types of hercynian peraluminous granitic rocks ranging from biotite muscovite granodiorite to muscovite granite occur in the horst of serra da estrela variation diagrams of most major and trace elements of the rocks and biotites and cr and v of muscovites show fractionation trends however nb li rb k rb li mg variation diagrams of the rocks and muscovites and also of sn cs cs k of the muscovites indicate that the muscovite granite probably originated by another mechanism least squares analysis of major elements and modelling of trace elements indicate that the coarse grained porphyritic biotite muscovite granite granite porphyry and fine to medium grained muscovite biotite granite were derived from the granodiorite magma by fractional crystallization of plagioclase quartz and biotite emplacement of granodiorite magma took place at 3 5 3 kb and 720 c granites and granite porphyry probably originated about 690 c but were completely crystallized about 520 c o2 was about 10 17 for the granodiorite and hcl hf was higher whereas log h2o hcl was lower in the granodiorite than in the other granitic rocks of the fractionated series the coarse grained porphyritic biotite muscovite granite was hydrothermally altered between 400 350 c and 260 230 c at about 1 5 1 kb the hydrothermal fluids were probably mainly meteoric in origin but some fluids released during the late stage of granite solidification might also have been involved

some characteristics of the stress field of the 1995 hyogo ken nanbu kobe earthquake we investigate the characteristics of the stress field associated with the 1995 hyogo ken nanbu kobe earthquake we use for the study a tomographic model of the fault slip inferred from the numerous near field recordings and we calculate the space and time evolution of shear stress on the fault during the earthquake we show that the spatial distribution of stress drop is very heterogeneous the apparent strength of the fault at the onset of the earthquake is low of the order of 1 mpa or less which indicates that the pre earthquake tectonic shear stress was close to the static friction over most of the fault at many locations the stress drop rotates significantly during sliding as was originally proposed by spudich 1992 we use the requirement of colinearity between the directions of maximum shear stress and instantaneous slip to determine the initial stress on the fault at the onset of the earthquake the pre earthquake tectonic stress varies greatly over the fault and ranges from about 1 to 10 mpa average values of the initial and final shear stresses over the fault are 3 3 and 1 6 mpa respectively indicating that about half of the pre earthquake tectonic stress was released during the earthquake there is a relatively strong correlation between the initial and final stress distributions which suggests that intrinsic fault properties not modified by the earthquake control the spatial distribution of tectonic stress over the fault we show that on average over the fault the dynamic friction coefficient is equal to about 40 of the static friction coefficient diagrams depicting the evolution of shear stress as a function of slip are consistent with slip weakening behavior but their interpretation is questionable because of the poor resolution of the data at high frequency and because of the constraints imposed on the model to perform the inversion

complexity of seismicity due to highly rate dependent friction we study a simple antiplane fault of finite length embedded in a homogeneous isotropic elastic solid in order to understand the origin of seismic source heterogeneity in the presence of nonlinear rate dependent friction all the mechanical properties of the medium and friction are assumed to be homogeneous starting from a heterogeneous initial stress distribution we apply a slowly increasing uniform stress load far from the fault and we simulate the seismicity for more than 20 000 events in some cases the style of seismicity produced by this model is determined by a control parameter which measures the degree of rate dependence of friction for classical friction models with rate independent friction no complexity appears and seismicity is perfectly periodic for weakly rate dependent friction seismicity becomes slightly nonperiodic but most events are still characteristic earthquakes when friction is highly rate dependent seismicity is completely irregular and ruptures of all sizes occur inside the fault highly rate dependent friction destabilizes the healing process producing premature healing of slip and partial stress drop premature healing causes rupture to take the form of narrow propagating slip episodes the so called heaton s 1990 pulses partial stress drop produces large variations in the state of stress which in turn produce earthquakes of different sizes we make the conjecture that all models in which static stress drop is only a fraction of the dynamic stress drop produce stress heterogeneity

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

geochemistry of the granites and their minerals from paredes da beira penedono northern portugal abstract seven types of hercynian peraluminous muscovite biotite granites t 1 t 5 and muscovite granites t 6 and t 7 occur in the paredes da beira penedono area microscopically they show some small metasomatic effects e g microclinization of plagioclase sericitization of feldspars small chloritization of biotite small amounts of late stage white mica and kaolinization of microcline three different types of white mica muscovite sericite and late stage white mica can be chemically distinguished in a ti mg na diagram variation diagrams of major and trace elements and elemental ratios of granites and muscovites show trends of fractionation from the muscovite biotite granites to the muscovite granites least squares analysis of major elements and modelling of trace elements indicate that the muscovite granite t 7 might have been derived from the muscovite biotite granite magma t 1 by fractional crystallization of quartz k feldspar plagioclase muscovite biotite and ilmenite elemental variation diagrams of granites biotites and muscovites also suggest trends of fractionation a from the muscovite biotite granite t 1 to the muscovite biotite granite t 4 b in the muscovite biotite granite t 5 c in the muscovite granite t 6 however the small metasomatic effects make it difficult to test fractional crystallization the granite t 5 has a large range of composition from the least to the most silicic samples similar to the variation of compositions of the granites in the sequence t 1 t 4 the granite t 1 and the least silicic samples of the granite t 5 would have their origin in two distinct pulses of granite magma and probably have originated by partial melting of metasedimentary materials emplacement of granite magmas took place at 700 c and 4 kbar they were completely crystallized at 450 c and slightly metasomatically altered at 370 c log f h 2 o f hf is smaller in the muscovite granites than in the muscovite biotite granites log f h 2 o f hcl increases and log f hcl f hf and log f h 2 o f hf decrease in the sequence t 1 t 4 of muscovite biotite granites

breaking of a single asperity rupture process and seismic radiation the problem of spontaneous shear rupture of a single circular asperity on an infinite fault plane is studied initially the fault plane is broken everywhere except at a circular asperity an applied displacement at infinity results in a stress concentration along the bounding edge of the asperity the frictional stress on the broken part of the fault plane is taken to be a constant once a point on the asperity breaks the stress there drops to the same value as on the main fault surface the rupture is started by relaxing the shear stress at a point on the asperity edge and is then allowed to propagate spontaneously using a critical stress level fracture criterion the rupture process is calculated numerically it is found that for asperities of constant strength the rupture first propagates around the edge of the asperity and then inward a phenomenon best described by the well known term of classic military maneuver the double encircling pincer movement in the appendix the expressions for the far field seismic radiation due to the rupture of such an asperity are derived it is shown that the nth cartesian component of the far field displacement at x t for p sv and sh waves using the notation of aki and richards 1980 is given by un x t dni 4 c2r s0 i3 t r c ds thus the far field pulses can be directly found from the stress drops on the fault plane this formula is also true for crack or dislocation problems the directivity function dni for displacement for the asperity problem is found to be that for the double couple modified by some factor in particular the fault plane is a nodal plane for sv waves for the rupturing of asperities on a finite fault these directivity functions are applicable only to the initial part of observed pulses at a receiver provided the receiver is not located on the fault plane outside the broken part of the main crack edge in which case it is inapplicable for all time

hydrodynamic aquifer or reservoir compartmentalization changes in oil water contact owc depth across a field are often a signature of reservoir compartmentalization as a result of faulting or stratigraphic barriers such as shales but may equally well be caused by an underlying hydrodynamic aquifer in particular the pressure depth data obtained from an aquifer whose flow is changing over time can look very similar to that obtained from a compartmentalized reservoir misunderstanding which of these mechanisms causes the observed changes in owc across the field may result in poor estimates of oil in place and reduced recovery to address this problem an analytic expression is presented to estimate the time taken for a steady state tilted owc to be established once an aquifer starts flowing a comparison with simulations of hydrodynamic aquifers in homogeneous compartmentalized and heterogeneous reservoir models shows that this expression can be used in combination with the one derived by m k hubbert for the steady state tilt of the owc to clarify whether a reservoir contains barriers or baffles to flow or may simply have not yet reached equilibrium

dynamic faulting under rate dependent friction we discuss the effects of rate dependent friction on the propagation of seismic rupture on active faults several physicists using burridge and knopoff s box and spring model of faulting have proposed that fault complexity may arise from the spontaneous development of a self similar stress distribution on the fault plane if this model proves to be correct it has important consequences for the origin of the complexity of seismic sources in order to test these ideas on a more realistic earthquake model we developed a new boundary integral equation method for studying rupture propagation along an antiplane fault in the presence of nonlinear rate dependent friction we study rupture dynamics of models with single and twin asperities in our models asperities are places on the fault with a higher value of prestress othewise all fault parameters are homogeneous we show that for models with such asperities a slip velocity weakening friction leads to the propagation of supersonic healing phases and to the spontaneous arrest of fracture if the prestress outside the asperities is low enough for models with asperities we can also observe narrow slip velocity pulses qualitatively similar to the so called heaton pulses observed in some earthquake accelerograms we also observe a complex distribution of stress after the rupture that depends on details of the initial distribution of asperities and on the details of the friction law

slickenline orientations as a record of fault rock rheology abstract contact of geometric asperities across rough faults causes perturbations to the shear traction resolved on a fault surface that could potentially deflect the local slip direction slickenlines which record the relative displacement of opposing sides of a fault may therefore be sensitive to fault surface geometry to investigate the relationship between fault geometry shear traction and slip we use ground based lidar to measure the orientations of slickenlines defined by centimeter amplitude corrugations on three fault surfaces slickenline rakes measured in the mean plane of each fault rarely vary by more than a few degrees deviations from the mean rake do not correlate with the fault surface topography at scales up to a few meters but a weak correlation may be present at larger scales slip directions are therefore insensitive to any shear traction perturbations from the contact of geometric asperities at small scales this observation is consistent with scale dependent deformation we show that the roughness of fault surfaces implies that short wavelength asperities fail inelastically because of flattening during fault slip a crossover to elastic deformation occurs at lengths of 10 2 to 10 0 m which defines the minimum dimension of a strength asperity that influences the displacement field the roughness at the crossover length scale corresponds to the typical thickness of fault rocks in the fault core suggesting that fault rock thickness is related to the crossover length scale the data requires that multiple processes combine to produce the fault surface geometry we reconcile the variety of processes with the consistent surface roughness scaling by noting that all of the processes are governed in different ways by the elastic limit of rock

nucleation of rupture under slip dependent friction law simple models of fault zone the initiation of frictional instability is investigated for simple models of fault zone using a linearized perturbation analysis the fault interface is assumed to obey a linear slip weakening law the fault is initially prestressed uniformly at the sliding threshold in the case of antiplane shear between two homogeneous linearly elastic media space time and spectral solutions are obtained and shown to be consistent the nucleation is characterized by 1 a long wavelength unstable spectrum bounded by a critical wave number 2 an exponential growth of the unstable modes and 3 an induced off fault deformation that remains trapped within a bounded zone in the vicinity of the fault these phenomena are characterized in terms of the elastic parameters of the surrounding medium and a nucleation length that results from the coupling between the frictional interface and the bulk elasticity these results are extended to other geometries within the same formalism and implications for three dimensional rupture are discussed finally internal fault structures are investigated in terms of a fault parallel damaged zone spectral solutions are obtained for both a smooth and a layered distribution of damage for natural faults the nucleation is shown to depend strongly on the existence of a internal damaged layer this nucleation can be described in terms of an effective homogeneous model in all cases frictional trapping of the deformation out of the fault can lead to the property that arbitrarily long wavelengths remain sensitive to the existence of a fault zone

felsic mineral crystallization trends in differentiating alkaline basic magmas mineral compositional relationships have been studied in a variety of alkaline basic rocks from small highlevel intrusions these small intrusions must have cooled quickly as the phases are all zoned especially those forming the matrix of some of the rocks which seem to have formed under conditions of almost perfect fractional crystallization

towards a more practical two feldspar geothermometer the thermodynamic basis of several recent attempts to formulate a simple two feldspar geothermometer is discussed together with a review of earlier empirical geothermometers and ones based on experimental studies in the ternary feldspar system it is shown that double binary thermometers which involve the combination of regular solution mixing models for the binary alkali feldspar system with ideal mixing in plagioclases do not give a satisfactory representation of two feldspar relations especially for albite rich compositions where a critical point exists thermometers based on mixing parameters for ordered alkali feldspar frameworks are even more unjustified both because low plagioclases are certainly non ideal and because of uncertainty in knowing the degree of al si order in the alkali feldspar when exchange equilibrium was achieved a thermodynamic thermometer requires knowledge of ternary activities which are at present unknown experimental determinations of relationships in the ternary feldspar system are reviewed and the correct general form of the thermometer constructed using mainly the experimental data of seck 1971a and smith and parsons 1974 chemographic tests for equilibrium between feldspar pairs are suggested and petrographie features discussed in an appendix new values are given of margules parameters calculated for binary disordered alkali feldspars from recent solvus data up to 15 kbars and their physico chemical basis examined we suggest that accurate representations of the mixing properties of disordered alkali feldspars using margules parameters are at present premature

revised two feldspar geothermometry applied to sri lankan feldspars abstract two feldspar geothermometry is applied to granulite and amphibolite facies feldspars from sri lanka a procedure is suggested to correct for compositional changes due to retrograde resetting the feldspars derive from different geological units from different rocks involved in different acts of deformation and to feldspars which grew at different times in the temperature time deformation history of the parent rock string perthites from granulite facies rocks in the eastern highland complex hc which are the deepest in the pile yield highest temperatures of c 890 c 850 c feldspars that unmixed during or after f 4 give temperatures around 800 c 750 c in the south but 870 c 830 c in the north in the north near peak temperatures outlasted formation of the big late f 4 folds in the south temperature started to drop before f 4 temperatures obtained from mesoperthites of monzonitic to pegmatitic metamagmatic rocks from the west of the hc give 780 c 770 c interpreted as the minimum temperature of growth during f 4 and reflecting metamorphic equilibration a large metagranite in the nw vijayan nwv contains coarse string perthites yielding a temperature of metamorphic equilibration for phenocrysts and a temperature of metamorphic formation for coarse recrystallized grains of 880 c 840 c this proves that the nwv went through the same granulite facies deformation and metamorphism as the hc before it was swamped by strong migmatization at 751 c 710 c at a late stage whenever string perthites are deformed and recrystallize once or several times during falling temperature the original grains and first recrystallizates yield the highest the younger and younger generations of recrystallized grains successively lower temperatures of formation in the same sequence grains and plagioclase domains unmixed from them become successively less and finer thus there is a very good correlation between string perthite morphology and temperature of growth or equilibration preceding unmixing

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

two feldspar geothermometry a review and revision for slowly cooled rocks recent improvements in the experimental and thermodynamic basis of two feldspar geothermometry allow one to recover temperatures of coexistence more reliably some problems however persist 1 the experimental solvi by seck 1971a and elkins and grove 1990 differ from each other 2 it is not known to what extent na k ca exchange equilibrium is approached 3 both solvi are probably metastable with regard to al si order 4 it is difficult to judge how closely high temperature natural feldspars compare to this situation 5 the thermodynamic treatment neglects phase transformations 6 the temperature dependence of the margules parameters used to model non ideal mixing behaviour may not be linear 7 it is not clear which expressions should be used to describe ideal activities with these caveats in mind we treat the problem of retrograde resetting in high grade metamorphic rocks that were slowly cooled under essentially dry conditions coexisting feldspars from such rocks commonly do not plot on a common isotherm thus temperatures derived from such pairs using any of the proposed two feldspar geothermometers will necessarily be in error we suggest that the non equilibrium compositions result from retrograde intercrystalline k na exchange this exchange continues after the plagioclase and alkali feldspar have already become essentially closed systems with respect to al si exchange which is a prerequisite for na k ca exchange we use a modified version of the fuhrman and lindsley 1988 programme to reverse the k na exchange and derive concordant temperatures

dynamic simulations of slip on a smooth fault in an elastic solid we report on numerical simulations of slip evolution along a two dimensional slip varies only with depth vertical strike slip fault in an elastic half space using a framework incorporating full inertial elastodynamics the model is a follow up on earlier quasi static and quasi dynamic simulations of deformations along smooth fault systems in elastic continua the fault is driven below a crustal depth of 24 km by a constant plate velocity of 35 mm yr deformation at each fault location in the crustal zone is the sum of slip rate contributions from rate and state dependent friction and power law creep where both processes have temperature dependent and hence depth varying coefficients and both take place locally under the same stress the simulations employ two versions of rate and state dependent friction a slip law which requires nonzero velocity for state evolution and an ageing slowness law which incorporates state evolution and restrengthening in stationary contact the assumed constitutive laws and distribution of frictional parameters are compatible with laboratory experiments the elastodynamic calculations are based on spectral representations of variables and a new algorithm providing a unified computational framework for calculations of long deformational histories containing short periods of rapid instabilities the simulations show dynamic rupture propagation and wave phenomena not accounted for in the previous quasi static and quasi dynamic works however the results are qualitatively similar to those obtained by corresponding quasi static and quasi dynamic calculations slip histories along a smooth fault simulated here with full elastodynamics for various constitutive laws and model parameters consist mostly of quasi periodic large events this finding indicates that inertial dynamics does not provide a generic mechanism for generating spatio temporal complexities of slip on the other hand calculations done for cases representing approximately strongly disordered systems do show rich slip histories with a range of event sizes this result is compatible with our previous conclusions that the origin of observed broad distributions of earthquake sizes is strong fault zone heterogeneities the fully dynamic calculations illustrate the evolution of nucleation phases of instabilities associated with accelerating and expanding creep final slip values of model earthquakes in full elastodynamic calculations are larger than those of corresponding quasi static and quasi dynamic events the dynamic overshoot in simulations with the slip version of friction is larger than in those employing the ageing slowness law

particle dynamics simulations of rate and state dependent frictional sliding of granular fault gouge recent simulations using the particle dynamics method pdm have successfully captured many features of natural faults zones as illuminated in laboratory studies however 2 d simulations conducted on idealized assemblages of particles using simple elastic frictional contact laws yield friction values considerably lower than natural materials and lack time and velocity dependent changes in strength that influence dynamic fault slip here preliminary results of new pdm simulations are described in which particle motions are restricted as a proxy for particle interlocking and out of plane contacts and time dependent contact healing is introduced to capture temporal strengthening of granular assemblages frictional strength is increased and in the absence of interparticle rolling can attain values observed in the laboratory the resulting mechanical behavior is qualitatively similar to that described by empirically based rate state friction laws providing new physical insight into the discrete mechanics of natural faults

review of the physical basis of laboratory derived relations for brittle failure and their implications for earthquake occurrence and earthquake nucleation a laboratory derived crack growth based constitutive relation for brittle faulting is developed the relation consists of two rheologic components a nonlinear arrhenius dependence of strain rate on temperature and stress corresponding to subcritical crack growth and a linear slip weakening behavior associated with dilatancy crack coalescence and supercritical crack growth the implications of this general behavior for the onset of rapid slip earthquake nucleation are considered laboratory observations of static fatigue and time dependent failure from rock fracture and rock friction experiments are consistent with this simple constitutive description as are the predictions of rate and state dependent equations for the onset of rapid frictional slip between bare rock surfaces i argue that crack growth is the physical process that controls time dependent rock fracture and the time dependent onset of unstable frictional sliding some similar and related arguments made in the past 1 2 century in the fields of rock mechanics and earthquake seismology are reviewed for stressing rates appropriate for the san andreas fault system the simple constitutive relation with lab derived constants predicts a minimum time for nucleation of 1 yr general predictions are a minimum nucleation patch radius of 0 06 to 0 2 m and a minimum earthquake moment of 8 5 x 107nm

experimental investigation into the microstructural and mechanical evolution of phyllosilicate bearing fault rock under conditions favouring pressure solution abstract mature crustal fault zones are known to be zones of persistent weakness this weakness is believed to result from microstructural modifications during deformation such as grain size reduction and foliation development around the brittle ductile transition phyllosilicates are expected to have a significant effect on fault strength in particular under conditions favouring pressure solution to study such effects we performed rotary shear experiments on brine saturated halite kaolinite mixtures aimed at investigating the relation between microstructural and mechanical evolution in a system where pressure solution and cataclasis dominate the results show significant strain weakening and a transition with progressive strain towards more rate sensitive and less normal stress sensitive behaviour this was accompanied by a microstructural evolution from a purely cataclastic microstructure to a mylonitic microstructure consisting of elongate asymmetric clasts in a fine grained foliated matrix the results demonstrate that strain weakening and the development of a typical mylonitic microstructure can occur as a consequence of grain size reduction by cataclasis and a transition to pressure solution accommodated deformation even in the absence of dislocation creep the data raise questions regarding the reliability of microstructures as rheology indicators as well as on the use of low strain monomineralic flow laws for modelling crustal dynamics

fracture analysis in the south western corinth rift greece and implications on fault hydraulic behavior this paper reviews the data concerning the fracture network and the hydraulic characteristics of faults in an active zone of the gulf of corinth pressure gap measured through fault planes shows that in this area the active normal faults aigion helike act at least temporarily and locally as transversal seal the analysis of the carbonate cements in the fractures on both the hangingwall and the footwall of the faults also suggests that they have acted as local seals during the whole fault zone evolution however the pressure and the characteristics of the water samples measured in the wells indicate that meteoric water circulates from the highest part of the relief to the coast which means it goes through the fault zones field quantitative analysis and core studies from the aig 10 well have been performed to define both regional and fault related fracture networks then laboratory thin section observations have been done to recognize the different fault rocks characterizing the fault zone components these two kinds of approach give information on the permeability characteristics of the fault zone to synthesize the data a schematic conceptual 3d fluid flow modeling has been performed taking into account fault zone permeability architecture sedimentation fluid flow fault vertical offset and meteoric water influx as well as compaction water flow this modeling allows us to fit all the data with a model where the fault segments act as a seal whereas the relays between these segments allow for the regional flow from the peloponnese topographic highs to the coast

reactivation of an oceanic fracture by the macquarie ridge earthquake of 1989 theoretical calculations show1 that the occurrence of an earthquake leads to regions of increased shear stress on both sides of the ruptured fault if this stress increase is sufficiently large or if neighbouring faults are close to their failure stress the result may be triggering of earthquakes on pre existing faults in the region a search for this effect2 produced only a few examples all in continental areas where clusters of aftershocks were located in the regions of increased stress the linear dimensions of these clusters were generally less than 20 km and less than one half of the fault length that ruptured in the main shock here i report an example of this phenomenon in which the fault that is reactivated is a nearly 175 km long segment of an oceanic fracture and its length is comparable to that of the main shock the 1989 macquarie ridge earthquake

a tem and microprobe study of a two perthite alkali gabbro implications for the ternary feldspar system an unusual magmatic three feldspar syenogabbro occurs 3 m inside the contact of the klokken gabbro syenite stock it contains plagioclase mesoperthite and cryptoperthite together with a low temperature symplectite intergrowth textural relationships have been investigated by cathodoluminescence bulk chemistry by microprobe and exsolution microtextures and intracrystalline boundaries by tem the mesoperthite has a bulk composition around or26ab52an22 well outside accepted limits of ternary feldspar solid solution it is a mainly coherent lamellar intergrowth of sodic andesine and orthoclase with incipient mtwinning the cryptoperthite bulk composition around or61ab33an6 is a coherent lamellar intergrowth of orthoclase and sodic low oligoclase the compositions of the exsolved phases have been estimated the meso and cryptoperthite crystals have sharp boundaries with each other

dynamic rupture activation of backthrust fault branching we perform dynamic rupture simulations to investigate the possible reactivation of backthrust branches triggered by ruptures along a main thrust fault simulations with slip weakening fault friction and uniform initial stress show that fast propagation speed or long propagation distance of the main rupture promotes reactivation of backthrust over a range of branch angles the latter condition may occur separately from the former if rupture speed is limited by an increasing slip weakening distance towards the junction direction the results suggest a trade off between the amplitude and duration of the dynamic stress near the main rupture front for backthrust reactivation termination of the main rupture by a barrier can provide enhanced loading amplitude and duration along a backthrust rooted near the barrier facilitating its reactivation especially with a high frictional resistance the free surface and depth dependent initial stress can have several additional effects the sign of the triggered motion along the backthrust can be reversed from thrust to normal if a deeply nucleated main rupture breaks the free surface while it is preserved as thrust if the main rupture is terminated by a barrier at depth the numerical results are discussed in relation to several recent megathrust earthquakes in sumatra chile and japan and related topics such as branch feedbacks to the main fault the dynamic view on backthrust fault branching provided by the study fills a gap not covered by quasi static models or observations a specific examined case of antithetic fault branching may be useful for indicating a barrier like behavior along the main fault

origin and residence time of salinity in the aspo groundwater system abstract the origin of salinity within the aspo groundwater system is investigated by combining interpretations of conservative dissolved ions and of stable isotope ratios in water the interpretation concludes that the groundwater salinity results from a mixing between baltic sea water intrusion and a deep seated saline groundwater of marine origin this conclusion supports the geochemical model developed for the aspo site the residence time of the deep salinity is assessed by comparing the 36 cl content of dissolved salt at different depths and the secular equilibrium value of the host rock the 36 cl of deepest levels corresponding to the highest salinity is in equilibrium with rock suggesting a penetration of the deep salinity into the host rock more than 1 5 ma ago

spatial variability in microscopic deformation and composition of the punchbowl fault southern california implications for mechanisms fluid rock interaction and fault morphology abstract we examine the distribution and nature of microstructures geochemistry and mineralogy along two traverses across the punchbowl fault southern california to determine the morphology and deformation mechanisms of the fault zone in schistose rocks the punchbowl fault is an exhumed fault that has two main strands of slip localization and has a total of 44 km of right slip protolith in the study area consists of the pelona schist which is primarily a quartz albite muscovite actinolite schist with thin to medium banding and rare metabasalts the traverses are 1 3 km apart and were conducted at a site with a single fault strand and a site where both principal strands of the fault are exposed the fault zone thickness is a function of the type of measurement that is used to define it for the single strand site analysis of the distribution of microfractures shows that the fault zone consists of a roughly 40 m thick damaged zone adjacent to the fault core the damaged zone is marked by an increase in veins thin cataclasite bands inter and intragranular fracturing and alteration relative to the country rock brittle grain size reduction occurs in a zone 10 m thick as measured from the fault core which consists of a continuous 10 cm thick very fine grained cataclasite that experienced repeated alteration vein injection and grain size reduction whole rock geochemical analyses of the fault related rocks suggest that the geochemically defined fault zone is less than 10 m thick volume loss at the site with one fault strand appears to have been small the dominant alteration reactions associated with the fault core are the hydration of hornblende and actinolite accompanied by the alteration of muscovite to produce a quartz chlorite albite epidote ultracataclasite the composition of the fault core is variable and locally influenced by one of the adjacent protoliths the examination of the two fault strand sites shows that two damaged zone fault core structures are present the region between the two strands experienced a greater degree of deformation than the protolith but the total deformation is much less than immediately adjacent to the fault cores the total thickness of the damaged zone around the two strands is less than 200 m the fault core enveloped by a damaged zone morphology as well as the textures of the fault core rocks are similar to rocks associated with the north branch san gabriel fault which formed in crystalline rocks with a total displacement of 22 km fault thickness is less in the pelona schist than in the crystalline rocks perhaps owing to more efficient strain localization in the schists thus the faults of the san andreas system may be thinner in regions where schists or franciscan rocks are the protolith but the main fault core may be a constant feature of the fault zone transformation induced weakening is less important in this part of the punchbowl fault since the protolith has a large amount of mica the structure of the fault zone with two principal slip surfaces is marked by both chemical changes and microstructures and indicates that some parts of the san andreas fault system may consist of multiple slip surfaces each with a damaged zone that together may create a fault zone 100 m thick and in which slip is localized to zones meters to decimeters thick

the great march 25 1998 antarctic plate earthquake moment tensor and rupture history we use broadband body and mantle wave data to study the 1998 antarctic intraplate earthquake the centroid moment tensor cmt has a large non double couple component there exist two pure double couple constrained solutions that fit the data almost equally well the frequent practice of taking the best double couple gives a far from optimal solution we use p and sh body waves to determine the rupture parameters of the first and larger of the two observed subevents the best rupture plane with strike 96 dip 69 and rake 18 is compatible with only one of the two cmt solutions strike 96 dip 64 rake 23 centroid location 63 1 s 148 4 e 10 km depth centroid time 0313 02 ut and m0 1 3 1021 n m mw 8 0 the first subevent is a simple primarily westward propagating 140 km rupture of 45 s duration with average velocity 3 km s 1 it has a seismic moment of 1 2 1021 n m mw 8 0 with 75 of its moment released between 10 and 27 s and a stress drop of 240 bars the rupture is physically bounded by two fracture zones at 147 5 e and 150 e the second subevent lasted from 70 to 90 s on a fault extending from 210 to 270 km west of the epicenter with a moment of 0 3 0 6 1021 n m mw 7 6 7 8 this is a spectacular example of dynamic stress triggering over a 100 km separation distance with a time delay of 40 s the complex pattern of aftershocks is primarily controlled by preexisting fracture zones on the ocean floor

scales of structural heterogeneity within neotectonic normal fault zones in the aegean region abstract structural heterogeneities within neotectonic normal fault zones in the aegean region are important controls on the geomorphic expression of their uplifted footwall blocks contrasting fault rocks and slip plane phenomena corrugations comb fractures slip parallel fractures and pluck holes are responsible for mesoscopic inhomogeneities within fault scarps along strike disruptions in the continuity of fault scarps step over zones step up zones step down zones footwall cross faults and hangingwall cross faults are products of perturbations in slip plane geometry or intersections with transverse faults large scale variations in range front morphology reflect contrasting patterns of deformation within fault zones some major fault zones and many minor fault zones are characterized by a migration of the active slip plane towards the hangingwall resulting in a distributed network of high angle faults and a range front which is stepped in profile the presence of a localized mass of uneroded bedrock hangingwall salients protruding from the hangingwall of some major fault zones results in intense deformation along a principal slip plane and a range front which is ramp like in profile as a consequence of structural heterogeneities within neotectonic normal fault zones fault scarps and range fronts in the aegean region are subject to a temporally and spatially variable pattern of degradation

spatial separation of large earthquakes aftershocks and background seismicity analysis of interseismic and coseismic seismicity patterns in southern california we associate waveform relocated background seismicity and aftershocks with the 3 d shapes of late quaternary fault zones in southern california major earthquakes that can slip more than several meters aftershocks and near fault background seismicity mostly rupture different surfaces within these fault zones major earthquakes rupture along the mapped traces of the late quaternary faults called the principal slip zones pszs aftershocks occur either on or in the immediate vicinity of the pszs typically within zones that are 2 km wide in contrast the near fault background seismicity is mostly accommodated on a secondary heterogeneous network of small slip surfaces and forms spatially decaying distributions extending out to distances of 10 km from the pszs we call the regions where the enhanced rate of background seismicity occurs the seismic damage zones one possible explanation for the presence of the seismic damage zones and associated seismicity is that the damage develops as faults accommodate bends and geometrical irregularities in the pszs the seismic damage zones mature and reach their finite width early in the history of a fault during the first few kilometers of cumulative offset alternatively the similarity in width of seismic damage zones suggests that most fault zones are of almost equal strength although the amount of cumulative offset varies widely it may also depend on the strength of the fault zone the time since the last major earthquake as well as other parameters in addition the seismic productivity appears to be influenced by the crustal structure and heat flow with more extensive fault networks in regions of thin crust and high heat flow

stylolites a review abstract stylolites are ubiquitous geo patterns observed in rocks in the upper crust from geological reservoirs in sedimentary rocks to deformation zones in folds faults and shear zones these rough surfaces play a major role in the dissolution of rocks around stressed contacts the transport of dissolved material and the precipitation in surrounding pores consequently they play an active role in the evolution of rock microstructures and rheological properties in the earth s crust they are observed individually or in networks in proximity to fractures and joints and in numerous geological settings this review article deals with their geometrical and compositional characteristics and the factors leading to their genesis the main questions this review focuses on are the following how do they form how can they be used to measure strain and formation stress how do they control fluid flow in the upper crust geometrically stylolites have fractal roughness with fractal geometrical properties exhibiting typically three scaling regimes a self affine scaling with hurst exponent 1 1 0 1 at small scale up to tens or hundreds of microns another one with hurst exponent around 0 5 to 0 6 at intermediate scale up to millimeters or centimeters and in the case of sedimentary stylolites a flat scaling at large scale more complicated anisotropic scaling scaling laws depending of the direction of the profile considered is found in the case of tectonic stylolites we report models based on first principles from physical chemistry and statistical physics including a mechanical component for the free energy associated with stress concentrations and a precise tracking of the influence of grain scale heterogeneities and disorder on the resulting micro structures experimental efforts to reproduce stylolites in the laboratory are also reviewed we show that although micrometer size stylolite teeth are obtained in laboratory experiments teeth deforming numerous grains have not yet been obtained experimentally which is understandable given the very long formation time of such geometries finally the applications of stylolites as strain and stress markers to determine paleostress magnitude are reviewed we show that the scalings in stylolite heights and the crossover scale between these scalings can be used to determine the stress magnitude its scalar value perpendicular to the stylolite surface during the stylolite formation and that the stress anisotropy in the stylolite plane can be determined for the case of tectonic stylolites we also show that the crossover between medium millimetric scales and large pluricentimetric scales in the case of sedimentary stylolites provides a good marker for the total amount of dissolution which is still valid even when the largest teeth start to dissolve which leads to the loss of information since the total deformation is not anymore recorded in a single marker structure we discuss the impact of the stylolites on the evolution of the transport properties of the hosting rock and show that they promote a permeability increase parallel to the stylolites whereas their effect on the permeability transverse to the stylolite can be negligible or may reduce the permeability depending on the development of the stylolite

zoned ternary feldspars in the klokken intrusion exsolution microtextures and mechanisms the microtextures developed during relatively slow cooling as a function of bulk composition in zoned ternary feldspars from syenodiorites and syenites in the klokken intrusion described in the preceding paper were determined by tem and their origin and evolution deduced the feldspars normally have a plagioclase core and an alkali feldspar rim cores become smaller and rims larger and the an content of both decrease with distance from the contact of the intrusion the following microtextural sequence was observed the inner plagioclase cores are homogeneous oligoclase andesine with albite growth twins only but are crypto antiperthitic towards the outer core at first small platelets of low sanidine a few nanometres thick and up to 10 nm long occur sporadically only on albite twin composition planes with further increase in bulk or they are homogeneously distributed in the plagioclase thicker through going plates in platelet free areas are found which induce albite twins in the surrounding plagioclase the microtextures in the rims are regular cryptomesoperthitic with 601 lenses or lamellae depending on the bulk or content of low sanidine in albite twinned low oligoclase andesine albite and pericline twins in plagioclase in an m twin relationship together with lenticular low sanidine were found in only one small area the overall diffraction symmetry of the mesoperthites is monoclinic showing that exsolution started in a monoclinic feldspar whereas that of the antiperthites is triclinic the intermediate zone between the core and rim is more complex and microtextures vary over distances of a few micrometres the cryptomesoperthites are very regular where or rich and probably arose by spinodal decomposition the platelets in the outer cores arose by heterogeneous nucleation on twin composition planes and by homogeneous nucleation elsewhere near the intermediate zone they coarsened to give larger plates which induced albite twins in the plagioclase because of the zoning microtextures that were initiated in areas of given composition can propagate laterally into zones of different composition a diagram is given showing the relationship between ternary bulk composition and the microtexture developed in coherent perthitic alkali feldspars and plagioclases from slowly cooled rocks

numerical simulation of afterslips and slow slip events that occurred in the same area in hyuga nada of southwest japan summary we propose a model of numerical simulation for the coexistence of afterslip for m7 earthquake and slow slip events in the hyuga nada region of japan that incorporates 3 d geometry of the philippine sea plate coseismic slip events recurrence of slow slip events and afterslip are qualitatively reproduced using the composite law which is a type of rate and state dependent friction law with higher cut off velocity in addition characteristic slip distances in the area are larger than those in other seismic source areas in our simulation afterslip which occurred at the velocity weakening regime triggered an aseismic transient event after the termination of this event spontaneous slow slip events repeatedly occurred in the same area after a similar event sequence was repeated another afterslip occurrence triggered a larger coseismic slip in a wide area including that of the slow slip events following this coseismic slip the aseismic slip area was locked until the next afterslip propagation which triggered an aseismic transient event these results suggest that detailed observation of spatial and temporal distribution within the area of aseismic slip may indicate the potential of recurring slow slip events and future large earthquakes

the macquarie ridge earthquake of 1989 summary a study of the seismicity on the central portion of the macquarie ridge before and after the 1989 may 23 macquarie ridge earthquake mw 8 2 and the solution of the inverse problem to obtain the moment release time history during the earthquake are presented the aftershock study shows that there were remarkably few and small aftershocks on the main fault the aftershocks were distributed along a 220 km portion of the india australia pacific plate boundary and indicate that the motion was bilateral on a vertical fault in addition the earthquake reactivated a 175 km section of a fault to its west which had been dormant since at least 1964 and 44 per cent of the aftershocks occurred on this feature moreover the largest aftershocks in the five month period following the event occurred not on the main fault plane but on the reactivated one based on available bathymetry gravity and magnetic anomaly data from the region this reactivated feature is interpreted as being an old oceanic fracture zone and hence a pre existing zone of weakness the aftershock distribution and their focal mechanisms are interpreted in terms of the tectonics of the region and suggest that a triangular piece of crust to the west of the macquarie ridge is being squeezed to the north and west the centroid moment tensor solution was obtained using both gdsn and geoscope data simultaneously it shows that the motion was primarily strike slip on a vertical fault with a moment of mo 1 5 x lo2 n m and a centroid depth of 19 5 km the moment release distribution and time history were obtained by inversion of broad band body waves recorded digitally by the gdsn and geoscope networks the rupture is found to be bilateral with the propagation first starting towards the north east and a few seconds later towards the south west the moment release was low in the hypocentral area with the higher areas of moment located towards the north east and south west of this the average rupture speed was approximately the shear wave speed no simple relation between the moment release pattern and the distribution of aftershocks on the fault plane was found instead the aftershock distribution is seen to be dominated by the intersection of the reactivated fault and the main fault plane with most aftershocks occurring to the north of this intersection

carbon isotope records from extant caribbean and south pacific sponges evolution of δ13c in surface water dic stable isotope records of demosponges from the caribbean and coral sea are described for the purpose of studying the influence of fossil fuel co2 on the carbon isotopic composition of dissolved inorganic carbon dic in surface water the slow growing sponges precipitate calcium carbonate in isotopic equilibrium with ambient sea water and are used to detect changes in 13cdic from pre industrial times early 19th century to the present we observed similar shapes and ranges in 13c curves measured on caribbean specimens collected from water depths of 25 84 and 91 m as well as a specimen collected in shallow waters off new caledonia the records reveal a highly significant correlation with atmospheric 13cco2 13cdic values for caribbean and coral sea surface waters were calculated using the 13c sponge records while 13c of atmospheric co2 decreased by about 1 4 from the early 19th century to 1990 13cdic of caribbean and coral sea surface waters decreased by 0 9 0 2 and 0 7 0 3 respectively no isotopic equilibrium between surface water dic and atmospheric co2 was observed either during the pre industrial steady state or during the last 100 years the lower amount of depletion in the surface water 13cdic with respect to the atmospheric anthropogenic signal is explained by the dilution of the surface waters by biologically altered subsurface water dic the lower 13c decrease in the coral sea points to a stronger influence of the subsurface water source compared to the caribbean

diversity of solutions of the problem of earthquake faulting inversion application to sh waves for the great 1989 macquarie ridge earthquake abstract we use the sh waves generated by the great 1989 macquarie ridge earthquake to investigate the non uniqueness of the inverse problem of earthquake faulting the details of the method of linear programming developed for this problem of solution of a constrained set of equations is described protective measures necessary to remove loss of accuracy when solving the problem for large numbers of unknowns and constraints are developed it is shown that solutions which look very different fit the data almost equally well a method is presented for choosing solutions with desirable properties e g with the most uniformly distributed moment along the fault or with the most concentrated moment release on the fault from among available solutions the results show that the data may equally well be interpreted as representing an asperity model of faulting or a propagating crack model of faulting the common feature of all the models is that the hypocentral region is a region of low moment release with regions of higher release being located to its northeast and its southwest along the fault clearly this earthquake did not initiate by the rupture of an asperity

thickness of the seismic slip zone this article reviews geologic and other evidence constraining the thickness of the principal slip zone psz that accommodates the bulk of coseismic shear displacement during an individual rupture event surface deformation from rupturing may occupy swaths tens of meters or more in width but trenches across active faults generally reveal that incremental slip is accommodated by a psz that is tens of centimeters or less in thickness geomorphic evidence coupled with the observations from trenching suggest a psz may stay well localized for distances of several kilometers through many rupture episodes mine exposures and exhumed fault zones demonstrate that pszs separating different lithologies within the fault core although contained within damage zones of variably fractured rock ranging up to hundreds of meters in thickness often comprise just a few centimeters of gouge ultracataclasite that have accommodated large finite displacements 1 km microstructural studies demonstrate incremental slip localized still further down to 1 10 mm as do other fault rock assemblages slickensides and slickenfibers fault veins of pseudotachylyte friction melt intravein septa in hydrothermal fault infills the accumulated evidence indicates that localization of coseismic shearing to less than 10 cm on planar faults is widespread throughout the crustal seismogenic zone with extreme localization to less than 1 cm not uncommon however some distributed coseismic shear may also develop especially at rupture irregularities coseismic reduction of shear resistance from friction melting t 1000 c or from transient thermal pressurization of aqueous fluids t 100 c requires slip during moderate to large earthquakes u 1 m to be restricted to narrow zones respectively a few centimeters or tens of centimeters in thickness given the evidence for slip localization the apparent scarcity of pseudotachylyte suggests either that seismic friction melting is a rare phenomenon or that pseudotachylyte is only rarely preserved in recognizable form within mature hydrated fault zones

scaling of the shear rupture process from nucleation to dynamic propagation implications of geometric irregularity of the rupturing surfaces a series of systematic high resolution laboratory experiments have been performed on the nucleation of propagating slip failure on preexisting faults having different surface roughnesses to demonstrate how the size scale and duration of shear rupture nucleation are affected by geometric irregularity of the rupturing surfaces on the basis of the experimental results it has been discussed theoretically how consistently scale dependent physical quantities inherent in shear rupture are scaled the experiments led to conclusive results that the nucleation process consists of two phases phase i an initial quasi static phase and phase ii a subsequent accelerating phase and that the nucleation process is greatly affected by geometric irregularities on the rupturing surfaces in phase i the rupture grows at a slow steady speed which is independent of the rupture growth length l in contrast during phase ii the rupture develops at accelerating speeds v which increase with an increase in l obeying a power law v vs l c n where vs is the shear wave velocity c is the characteristic length representing the geometric irregularity of the fault surfaces and and n are constants 8 87 10 29 and n 7 31 scale dependency of scale dependent physical quantities including the nucleation zone size and its duration is commonly ascribed to scale dependency of the slip dependent constitutive law parameter dc which is in turn governed by c it has been discussed that a unified comprehension can be provided for shear rupture of any size scale if the constitutive law for shear rupture is formulated as a slip dependent law

sidewall crystallization in the klokken intrusion zoned ternary feldspars and coexisting minerals the syenitic layered series in the klokken intrusion is surrounded by a zone 500 m thick of nearly structureless unlaminated syenite followed outwards by a zone of vertically banded gabbro 200 m thick at the outer rim the unlaminated syenite is intrusive into the gabbro and develops a thin 2 m transition zone of syenodiorite at the contact a traverse across the vertical transition zone and inwards towards the layered series was sampled with a portable drill mafic silicates olivine clinopyroxene biotite show inward evolution in fe fe mg across the syenodiorite unlaminated syenite zones feldspars change rapidly across the syenodiorite zone from rocks dominated by plagioclase in some cases together with two alkali feldspars one a mesoperthite or cryptomesoperthite the other a cryptoperthite to rocks in which plagioclase is seen only rarely as cores to cryptomesoperthitic alkali feldspar crystals plagioclase is absent from the layered series

the seismic cycle and the difference between foreshocks and aftershocks in a mechanical fault model 1 we examine the evolution of and the exchange between two forms of elastic energies stored in the quasi static fault model of ziv and rubin 2003 the first etect is due to the integrated slip deficit accumulated between the plate boundaries and the fault surface and the second efault is the result of differential slip along the fault surface the results of our analysis reveal cyclic exchange between the two energies on a efault versus etect plot the seismic cycle has a triangular shape with the large earthquakes occurring at the top corner of the triangle where efault is maximum and the foreshocks and the aftershocks occupying the right side and left side respectively while both foreshocks and aftershocks dissipate tectonic energies the cumulative effect of the foreshocks is to increase the potential elastic energy along the fault plane and the cumulative effect of the aftershocks is to reduce it

elastodynamic analysis for slow tectonic loading with spontaneous rupture episodes on faults with rate and state dependent friction we present an efficient and rigorous numerical procedure for calculating the elastodynamic response of a fault subjected to slow tectonic loading processes of long duration within which there are episodes of rapid earthquake failure this is done for a general class of rate and state dependent friction laws with positive direct velocity effect the algorithm allows us to treat accurately within a single computational procedure loading intervals of thousands of years and to calculate for each earthquake episode initially aseismic accelerating slip prior to dynamic rupture the rupture propagation itself rapid post seismic deformation which follows and also ongoing creep slippage throughout the loading period in velocity strengthening fault regions the methodology is presented using the two dimensional 2 d antiplane spectral formulation and can be readily extended to the 2 d in plane and 3 d spectral formulations and with certain modifications to the space time boundary integral formulations as well as to their discretized development using finite difference or finite element methods the methodology can be used to address a number of important issues such as fault operation under low overall stress interaction of dynamic rupture propagation with pore pressure development patterns of rupture propagation in events nucleated naturally as a part of a sequence the earthquake nucleation process earthquake sequences on faults with heterogeneous frictional properties and or normal stress and others the procedure is illustrated for a 2 d crustal strike slip fault model with depth variable properties for lower values of the state evolution distance of the friction law small events appear the nucleation phases of the small and large events are very similar suggesting that the size of an event is determined by the conditions on the fault segments the event is propagating into rather than by the nucleation process itself we demonstrate the importance of incorporating slow tectonic loading with elastodynamics by evaluating two simplified approaches one with the slow tectonic loading but no wave effects and the other with all dynamic effects included but much higher loading rate

can observations of earthquake scaling constrain slip weakening summary we use observations of earthquake source parameters over a wide magnitude range m w 0 7 to place constraints on constitutive fault weakening the data suggest a scale dependence of apparent stress and stress drop both may increase slightly with earthquake size we show that this scale dependence need not imply any difference in fault zone properties for different sized earthquakes we select 30 earthquakes well recorded at 2 5 km depth at cajon pass california we use individual and empirical green s function spectral analysis to improve the resolution of source parameters including static stress drop and total slip s we also measure radiated energy e s w ecompare the cajon pass results with those from larger california earthquakes including aftershocks of the 1994 northridge earthquake and confirm the results of abercrombie 1995 e s m 0 where rigidity and both e s m 0 and increase as m 0 and s increases uncertainties remain large due to model assumptions and variations between possible models and earthquake scale independence is possible within the resolution assuming that the average trends are real we define a quantity g 2 es m 0 s 2w hich is the total energy dissipation in friction and fracture minus 1 s w here 1 is the final static stress if 1 d the dynamic shear strength during the last increments of seismic slip then g g the fracture energy in a slip weakening interpretation of dissipation

shear heating induced thermal pressurization during earthquake nucleation 1 we model earthquake nucleation in 2d on narrow faults with coupled rate state friction and shear heating induced thermal pressurization including diffusive transport of heat and pore pressure thermal pressurization increases pore pressure p decreasing frictional resistance observed fault core permeability is generally too low to mitigate thermal pressurization at subseismic slip speeds under drained isothermal conditions nucleation with the aging law is crack like with the interior of the slip zone always near maximum slip speed when thermal pressurization is included it can dominate weakening at speeds of 0 02 20 mm s for hydraulic diffusivities chyd from 10 8 to 10 3 m2 s and nominal material parameters well before seismic radiation occurs dramatic along strike localization of slip occurs due to feedback in which the area of maximum slip experiences the greatest weakening which in turn favors more slip with the slip law however nucleation is pulse like with slip speed decaying behind the pulse tip thermal pressurization is diminished relative to the aging law case since most weakening occurs in locations with limited slip yet we find that it can overwhelm frictional weakening at slip speeds in the range of 1 100 mm s for chyd from 10 8 to 3 10 5 m2 s at higher slip speeds the finite thickness of the shear zone becomes significant reducing thermal pressurization even if not the dominant weakening mechanism thermal pressurization is likely to be significant at or before the onset of seismic radiation

spontaneous complex earthquake rupture propagation the historical development of spontaneous rupture propagation starting from the landmark paper of griffith in 1920 through to the late 1980s is traced with particular emphasis on the work carried out at mit in the 1970s by k aki and his co workers numerical applications of kostrov s method for planar shear cracks were developed by hamano das and aki simultaneously at mit madariaga considered the radiated field of a dynamic shear crack the further development of these ideas for example three dimensional spontaneous planar faulting models continued through the 1980s major insight into the maximum possible rupture speeds for earthquakes developed with the acceptance of the theoretical possibility of supersonic rupture speeds for faults with cohesion and friction the theoretical developments spurring the search for such observations for earthquake ruptures possible mechanisms by which faults stop were elucidated it was shown that a propagating rupture can jump over barriers for cracks with a cohesive zone at its tip complex faulting models namely the barrier and asperity models and their associated radiated field developed in the late 1980s it was shown that dynamic or transient asperities can develop during the complex rupturing process even seemingly relatively simple physical situations can lead to such complex rupturing processes that the usual idea of rupture velocity needs to be abandoned in those cases some of the work initiated by aki and his co workers such as the details of the transition from sub rayleigh to super shear speeds in inplane shear mode and the behavior of the cohesive zone size as the crack extends still remains the subject of research today

high resistant sand injected marl and low resistant damaged marl to locate and characterize the thenia fault zone in boumerdes city north central algeria the purpose of this study was to locate and characterize the thenia fault zone tfz in the urban area of boumerdes city geological and electrical resistivity tomography surveys have targeted the plaisancian marl and its quaternary cover as a whole data indicate a complex near vertical fault zone with an asymmetric and zoned internal structure of at least 150 m wide and with a straight n120 overall trending the fault zone is traversed with two elongated parallel fault branches fb1 and fb2 generally 70 m distant from each other these fault branches locate two intense damage zones idzs of 10 15 m thick each situated at the margin of two damage zones each having a thickness of several tens of meters downward sand injections into idzs during pleistocene epoch possible pulverization of plaisancian marl rocks systematic deflection of actual stream channels and vertical displacement of at least 30 m affecting quaternary alluvial deposits show that the area would have undergone active tectonic driven by the tfz

an extension of rate and state theory to poromechanics 1 laboratory results on granular media have lead to fundamental theoretical developments such as poroelasticity rate and state variable friction that have found widespread application this paper presents results from laboratory experiments that help constrain and combine these theories data from triaxial deformation experiments on quartz sand aggregates are used to illustrate stress dependent behavior of poroelastic parameters e g the biot willis coefficient the results from both volumetric compaction and frictional shear experiments are well described by poroelasticity as well as rate and state variable friction the combination of these constitutive relations may provide a powerful tool that can be used in numerical models that couple mechanical hydraulic and temporal processes in the descriptions of granular deformation

on the inverse problem for earthquake rupture the haskell type source model in order to gain insight into how to invert seismograms correctly to estimate the details of the earthquake rupturing process we perform numerical experiments using artificial data generated for an idealized faulting model with a very simple rupture and moment release history and solve the inverse problem using standard widely used inversion methods we construct synthetic accelerograms in the vicinity of an earthquake for a discrete analog of the haskell type rupture model with a prescribed rupture velocity in a layered medium a constant level of moment is released as the rupture front passes by we show that using physically based constraints such as not permitting back slip on the fault allows us to reproduce many aspects of the solution correctly whereas the minimum norm solution or the solution with the smallest first differences of moment rates in space and time do not reproduce many aspects for the cases studied here with the positivity of moment rate constraint as long as the rupturing area is allowed to be larger than that in the forward problem it is correctly found for the simple faulting model considered in this paper provided that the rupture velocity and the earth structure are known if however the rupture front is constrained either to propagate more slowly or the rupturing area is taken smaller than that in the forward problem we find that we are unable even to fit the accelerograms well use of incorrect crustal structure in the source region also leads to poor fitting of the data in this case the proper rupture front is not obtained but instead a ghost front is found behind the correct rupture front and demonstrates how the incorrect crustal structure is transformed into an artifact in the solution the positions of the centroids of the moment release in time and space are generally correctly obtained

calorimetric and phase diagram approaches to two feldspar geothermometry a critique two feldspar geothermometers based on the thermodynamic properties of the limiting binaries ab an and ab or are unsatisfactory because the ternary nature of the feldspar pairs cannot be accounted for and critical points are not generated ternary mixing data are mandatory there are also serious shortcomings in the experimental ternary phase relation data available at present and even ambiguities in the interpretation of the thermodynamic properties of the binaries which preclude development of a practical geothermometer recent work on feldspar zoning patterns in rocks allows some deductions to be made concerning the geometry of the ternary system but there are dilliculties in the interpretation of natural feldspar pairs framework order disorder presents problems which may be insuperable

determination of constitutive relations of fault slip based on seismic wave analysis constitutive laws define the boundary conditions on fault plane and govern many aspects of earthquake failure although several constitutive laws have been formulated based on laboratory rock experiments and applied to theoretical studies in various fields no actual relation during a natural earthquake has been determined the 1995 kobe earthquake is suitable for detailed kinematic analysis and this enables the first evaluation of constitutive relations for a natural earthquake in this study we determine spatiotemporal slip distribution on an assumed fault plane of the 1995 kobe earthquake by waveform inversion and then solve elastodynamic equations using a finite difference method to determine the stress distribution and constitutive relations on the fault plane an inversion method based on bayes theorem is employed to obtain a spatiotemporal slip distribution and enables us to ensure the objective uniqueness of the solution with numerous parameters and smoothing constraints this slip distribution is then used as part of the boundary condition in the finite difference calculation the time histories of slip and shear stress obtained then provide a constitutive relation at each point on the fault plane they show slip weakening relations almost everywhere on the fault plane while slip rate dependency is not clear the slip weakening behavior has a clear depth dependency indicating that the slip weakening rate d du is smaller in the shallow crust than that in the deep crust this may be associated with the paucity of shallow seismicity observed in the source region of this earthquake as reported for many mature fault systems

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

fault deformation mechanisms and fault rocks in micritic limestones examples from corinth rift normal faults abstract a multidisciplinary study investigates the influence of different parameters on fault rock architecture development along normal faults affecting non porous carbonates of the corinth rift southern margin here some fault systems cut the same carbonate unit pindus and the gradual and fast uplift since the initiation of the rift led to the exhumation of deep parts of the older faults this exceptional context allows superficial active fault zones and old exhumed fault zones to be compared our approach includes field studies micro structural optical microscope and cathodoluminescence geochemical analyses 13 c 18 o trace elements and fluid inclusions microthermometry of calcite sin kinematic cements our main results in a depth window ranging from 0 m to about 2500 m are i all cements precipitated from meteoric fluids in a close or open circulation system depending on depth ii depth in terms of p t condition determines the development of some structures and their sealing iii lithology marly levels influences the type of structures and its cohesive non cohesive nature iv early distributed rather than final total displacement along the main fault plane is the responsible for the fault zone architecture v petrophysical properties of each fault zone depend on the variable combination of these factors

effects of fault interaction on moment stress drop and strain energy release solutions for collinear shear cracks are used to examine quantitatively the effects of fault slip zone interaction on determinations of moment stress drop and static energy release two models the barrier model and the asperity model are considered in the asperity model the actual distribution of strengths on a fault plane is idealized as a combination of two limiting cases areas which slip freely at a uniform value of a residual friction stress and unbroken ligaments or asperities across which slip occurs only at the time of a seismic event in the barrier model slip zones separated by unbroken ligaments barriers are introduced into a uniformly stressed medium to approximate the nonuniform fault propagation proposed by das and aki the strain energy change due to introducing collinear slip zones or due to breaking the asperities between them is shown to be given by the usual formula for an isolated slip zone with the stress drop replaced by the effective stress significant interaction between slip zones occurs only if the length of the asperity is less than half the length of the slip zones for the case of two collinear slip zones fracture of the asperity between them is shown to cause a large moment primarily because of the additional displacement which is induced on the adjacent slip zones for example if the asperity length is 0 05l where l is the length of each adjacent slip zone then fracture of the asperity causes a moment almost 1 8 times the moment caused by introducing a slip zone of length l for two collinear slip zones the local stress drop due to fracture of the separating asperity is shown to become unbounded as the asperity length goes to zero but in the same limit the stress drop averaged over the entire fault length is approximately equal to the apparent stress drop inferred for an isolated fault of the same moment and total fault length this apparent stress drop is approximately equal within a factor of 2 or 3 to the effective stress and hence can be used in the usual formula to give a good estimate of the strain energy change for the barrier model numerical results are given for the ratio of the stress drop calculated on the assumption of an isolated slip zone to the true stress drop for example in the case of two collinear slip zones of length l separated by a barrier of length 0 2l this ratio is 0 5 whereas for a barrier length equal to that of the adjacent slip zones the ratio is 0 24 stress drop estimates become worse with increasing number of fault segments

extensional fault cores in micritic carbonate case studies from the gulf of corinth greece abstract the major pisia and doumena faults of the corinth rift greece are both hosted by micritic carbonate rock their common fault elements are principal slip surfaces layers of fault rocks fault rock and host rock lenses corrugations and smaller shear and tension fractures along planar fault segments a corrugated slip surface with an associated thin fault rock layer is formed well developed down dip corrugations indicate movement along the same surface over many fault increments bends jogs in the faults are sites of complex structural relations hosting frequent lenses more porous fault rocks and dense networks of fractures major jogs in the slip surfaces have both strike and dip oriented undulating curvature that are associated with higher order fracture networks as well as frequent lenses fault core lens shapes of the doumena fault show relationship of length vs width of 3 2 similarly principal slip surfaces of the two faults show undulations with aspect ratios of amplitude vs wavelength 1 19 and 1 14 in strike direction despite a prominent difference in down dip geometry the intrinsic deformation in fault cores of micritic carbonate supports a model in which fluids entered the core by damage zone fractures that are linked to the principal slip surface flow along the fault core was controlled by the fracture system of lenses and thereby lens connectivity but may have been hampered by flow retarding fault rocks the flow potential is especially well developed in fault bends and breached relays due to frequent lenses and well developed fracture networks