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

significant effect of grain size distribution on compaction rates in granular aggregates we investigate the role of pressure solution in deformation of upper to mid crustal rocks using aggregates of halite as a room temperature analog for fluid assisted deformation processes in the earth s crust experiments evaluate the effects of initial grain size distribution on macroscopic pressure solution rate of the aggregate and compare the results to theoretical models for pressure solution we find that the grain size exponent deviates significantly from the theoretical value of 3 for diffusion controlled pressure solution models typically assume mono dispersed spherical particles in pseudo regular packing we infer that the discrepancy between experimentally determined grain size exponents and the theoretical values are a result of deviation of experimental and natural samples from regular packs of mono dispersed spherical particles moreover we find that compaction rates can vary by up to one order of magnitude as a function of the width of the grain size distribution for a given mean grain size wider size distributions allow for higher initial compaction rates increasing the macroscopic compaction rate with respect to more narrow grain size distributions grain sizes in rocks fault gouges and hydrocarbon reservoirs are typically log normal or power law distributed and therefore pressure solution rates may significantly exceed theoretical predictions spatiotemporal variations in pressure solution rates due to variations in grain size may cause the formation of low porosity zones which could potentially focus deformation in these zones and produce pockets of high pore pressures promoting nucleation of frictional instability and earthquake rupture

tracing the transition of gold from source to sponge to sink the late timing of gold is a characteristic feature of orogenic gold deposits for many of these deposits gold and other metals were liberated from the host greenstone belt and or early sulfides concomitant with the syndeformational and fluid assisted metamorphic transition of pyrite to pyrrhotite and remobilized into late high grade ore shoots however this metamorphic driven gold upgrading model is usually inferred at least in part from mineral textures which can be equivocal in the absence of geochemical and or isotopic constraints herein we report new bulk mineral separate and in situ pb isotope results for minerals in key textures in the paleoproterozoic meliadine gold district arsenopyrite and pyrite porphyroblasts occur in paleoproterozoic quartz ankerite veins and are enveloped by remobilized pyrrhotite chalcopyrite and galena crystals that accompany gold in late microtextural sites a texture that forms the basis for the gold upgrading model early sieve textured arsenopyrite and pyrite are gold rich and tend to yield the least radiogenic pb isotope compositions high 207 pb 206 pb and 208 pb 206 pb ratios suggesting these relict domains escaped complete recrystallization during later reworking late inclusion free arsenopyrite and pyrite overgrowths scatter to more radiogenic pb isotope compositions low 207 pb 206 pb and 208 pb 206 pb ratios and are typically gold poor which we attribute to reworking and precipitation from a younger and more radiogenic fluid prior to and or during the precipitation of free gold in variably plunging high grade ore shoots at 1 90 to 1 85 ga remobilized sulfides are the youngest sulfide phases but locally yield low 206 pb 204 pb and 207 pb 204 pb ratios and thus spurious old model ages which overlap with the least radiogenic sieve textured arsenopyrite pyrite domains the isotopic signature of these remobilized sulfides was likely inherited from pb liberated during reworking of early arsenopyrite and pyrite and a second crustal pb source that was introduced during late remobilization our results highlight the importance of element recycling from early sulfides and or the neoarchean deposit host rocks during significantly younger paleoproterozoic reworking and gold remobilization the in situ pb isotope results of early and remobilized sulfides document the transition of gold from source to sponge to sink which is likely a feature that occurred during the formation of other orogenic style gold deposits

hydrologic segmentation of high temperature shear zones structural geochemical and isotopic evidence from auriferous mylonites of the renco mine zimbabwe abstract combined structural mineralogical and geochemical observations in auriferous mylonites of the renco mine hosted by late archaean high grade metamorphic granitoids in southern zimbabwe are used to describe the spatially heterogeneous fluid flow and metasomatism that occurred synchronous with deformation at mid to upper amphibolite facies metamorphic conditions significantly the narrow on average 1m wide mylonitic shear zones are internally zoned reflecting a pronounced hydrologic segmentation during deformation shear zones typically consist of two distinct domains i anastomosing quartz feldspar biotite hornblende mylonites and or quartz mylonites and ii tabular shaped pods referred to as lithons that are enveloped by mylonites and that exhibit evidence of transient episodes of brittle fracturing and ductile creep whole rock geochemistry and mass balance calculations indicate dramatic element volume up to 100 and associated mass gains for the brittle ductile lithons that are mineralogically reflected in a volumetrically abundant sulphide mineralisation and the formation of a pervasively developed silicate alteration paragenesis in contrast mylonites have experienced only minor element and volumetric changes and minor alteration 18 o values for whole rocks and quartz are enriched in lithons compared to wall rocks and enveloping mylonites which implies the influence of externally derived fluids these results indicate a strongly domainal fluid flow and mass transfer fluid advection was dominated by microscopic and macroscopic fracture permeabilities related to periods of coseismic dilatancy in lithons the patchy but partly interconnected distribution of lithons enveloped by mylonites indicates that deformation in the high temperature shear zones was characterised by transient periods of seismic slip rather than continuous aseismic creep based on the well preserved internal mineralogical and textural development of the renco shear zones a more general model applicable for fluid advection coupled with the rheological behaviour of mid crustal shear zones is presented

nonlinear dynamics granular media and dynamic earthquake triggering the landers earthquake of 1992 triggered a series of earthquakes in other parts of california focusing attention on the mechanism of remote triggering laboratory experiments on granular material under pressure suggest that triggering is a result of seismic waves impinging on a fault and inducing elastic nonlinear behaviour of the fault core accompanied by instantaneous weakening and failure the resulting softening to weakening model fits in well with field observations of real earthquakes the 1992 magnitude 7 3 landers earthquake triggered an exceptional number of additional earthquakes within california and as far north as yellowstone and montana1 2 3 since this observation other large earthquakes have been shown to induce dynamic triggering at remote distances for example after the 1999 magnitude 7 1 hector mine1 and the 2002 magnitude 7 9 denali4 earthquakes and in the near field as aftershocks5 the physical origin of dynamic triggering however remains one of the least understood aspects of earthquake nucleation1 2 3 4 5 the dynamic strain amplitudes from a large earthquake are exceedingly small once the waves have propagated more than several fault radii for example a strain wave amplitude of 10 6 and wavelength 1 m corresponds to a displacement amplitude of about 10 7 m here we show that the dynamic elastic nonlinear behaviour of fault gouge perturbed by a seismic wave may trigger earthquakes even with such small strains we base our hypothesis on recent laboratory dynamic experiments conducted in granular media a fault gouge surrogate6 7 from these we infer that if the fault is weak8 9 10 seismic waves cause the fault core modulus to decrease abruptly and weaken further if the fault is already near failure this process could therefore induce fault slip

in situ pb isotope analysis of pyrite by laser ablation multi collector and quadrupole icpms pb isotope ratios measured in the mineral pyrite provide a valuable petrogenetic tool with widespread applicability in order to interpret complex structural and mineralogical textures however a method of in situ analysis is essential while laser ablation icpms is ideally suited to this task the low melting point of sulfide the highly variable and often high pb contents and the potential presence of relatively radiogenic inclusions introduce a number of analytical problems unique to pyrite pb isotope analysis here we address these issues using results obtained on two very different analytical systems based around multi collector and quadrupole icpms instruments respectively we suggest that controlled ablation of pyrite is only achieved at low laser fluence and that under these conditions standardisation using silicate reference materials is inappropriate and natural pyrite standards are to be preferred the inherent variability in pb and sometimes u concentrations in pyrite requires careful selection of detector systems for optimal analysis and in this regard both quadrupole and multi collector icpms instruments can play important and complimentary roles multi collector instruments provide higher precision analyses but detector configurations can prohibit simultaneous measurement of u th and pb furthermore the micrometer scale variability in pb concentrations can cause problems for both faraday cup and ion counting detection systems in contrast quadrupole icpms systems allow simultaneous measurement of u th and pb and have more flexible detection systems with many orders of magnitude dynamic range but are unable to produce high precision data results are presented for two different analytical systems and demonstrate a very strong dependence of data quality upon signal size in addition they allow some estimation of the limiting precision obtainable by these methods finally a geological example is provided from the giant sukhoi log sedimentary au deposit of russia

direct simulations of the stress redistribution in the scaling organization of fracture tectonics soft model summary a time dependent stochastic process with three states solid broken and moving is considered in a hierarchical system made of embedded cells of increasing levels an earthquake of a given scale k is associated with the moving state of a cell of level k and results from the coherent self organization of fractures of lower scales a direct cascade of stress redistribution generates small scale stress heterogeneities in the neighbourhood of the active fracture an interesting feature of the model is that the size of the domain where stress redistribution takes place grows proportional to the length of the fracture in the framework of the general model inspired by the progress in the use of the renormalization techniques in approaching critical point phenomena we independently study a fracturing submodel and a friction submodel these submodels are two state models that act on diierent timescales in the friction submodel which comprises broken and moving states the transitions between these two states are associated with stick slip behaviour in a completely fractured fault zone in the fracturing submodel which comprises solid and broken states we model the brittle behaviour of rock material in both models we obtain a spatio temporal clustering of earthquakes realistic aftershock sequences whose frequency decreases respect the modi ed omori law and a frequency magnitude relationship that respects the gutenberg richter law we show that the model behaviour is controlled by the stress heterogeneity in the fault zone we nd evidence for a relationship between the periodicity of the largest earthquakes and the b value and we indicate how the diierent physical ingredients underlying each submodel can be gathered together in a more general model

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

genetic significance of fluid inclusions in the csa cu pb zn deposit cobar australia csa mine exploits a cobar type cu pb zn au ag deposit within a cleaved and metamorphosed portion of the cobar supergroup central new south wales the deposit comprises systems of lenses that encompass veins disseminations and semi massive to massive cu pb zn ores the systems and contained lenses truncate bedding are approximately coplanar with regional cleavage and similarly oriented shear zones and plunge parallel to the elongation lineation systems have extreme vertical continuity 1000 m short strike length 400 m and narrow width 100 m exhibit vertical and lateral ore type variation and have alteration haloes models of ore formation include classical hydrothermalism structurally controlled remobilisation and polymodal concepts syntectonic emplacement now holds sway fluid inclusions were examined from quartz sulphide veins adjacent to now extracted ore from coexisting quartz sulphide within ore and from vughs in barren quartz veins lack of early primary inclusions precluded direct determination of fluids associated with d2 d3 ore and vein emplacement similarly decrepitation by near isobaric heating of the two oldest secondary populations precluded direct determination of fluid phases immediately following d2 d3 ore and vein emplacement post decrepitation outflow late d3 to early post d3 is recorded by monophase ch4 inclusions entrained outflow of deeply circulated meteoric fluid modified the ch4 system modification is recorded by h2o ch4 and h2o trace ch4 secondary populations and by an h2o trace ch4 primary population the contractional tectonics d2 d3 of ore emplacement was superseded by relaxational tectonics d4p that facilitated meteoric water penetration and return flow under d2 prograde metamorphism entrapment temperatures tt and pressures pt for pre decrepitation secondary inclusions are estimated as tt 300 330 c and pt 1 5 2 kbar plith the lithostatic pressure decrepitation accompanied peak metamorphism t 350 380 c in mid to late d3 while in late d3 to early post d3 essentially monophase ch4 secondary inclusions were entrapped at tt 350 c and pt 1 5 2 kbar plith subsequently abundant ch4 and entrained meteoric water were entrapped as h2o ch4 secondaries under slowly decreasing temperature tt 330 350 c and constant pressure pt 1 5 2 kbar finally with increasingly dominant meteoric outflow h2o trace ch4 populations record decreasing temperatures tt 300 to 350 down to 275 300 c at pressures of phydrostatic pt 1 kbar plith 1 5 kbar the populations of inclusions provide insight into fluid types flow regimes and p t conditions during parts of the deposit s evolution they indirectly support the role of basin derived ch4 fluids in ore formation but provide no insight into a basement sourced ore forming fluid they fully support post ore involvement of meteoric water the poorly constrained entrapment history is believed to span 10 ma from 395 to 385 ma

physical and transport property variations within carbonate bearing fault zones insights from the monte maggio fault central italy the physical characterization of carbonate bearing normal faults is fundamental for resource development and seismic hazard here we report laboratory measurements of density porosity vp vs elastic moduli and permeability for a range of effective confining pressures 0 1 100 mpa conducted on samples representing different structural domains of a carbonate bearing fault we find a reduction in porosity from the fault breccia 11 7 total and 6 2 connected to the main fault plane 9 total and 3 5 connected with both domains showing higher porosity compared to the protolith 6 8 total and 1 1 connected with increasing confining pressure p wave velocity evolves from 4 5 km s to 5 9 km s in the fault breccia is constant at 5 9 km s approaching the fault plane and is low 4 9 km s in clay rich fault domains we find that while the fault breccia shows pressure sensitive behaviour a reduction in permeability from 2 10 16 m2 to 2 10 17 m2 the cemented cataclasite close to the fault plane is characterized by pressure independent behaviour permeability 4 10 17 m2 our results indicate that the deformation processes occurring within the different fault structural domains influence the physical and transport properties of the fault zone in situ vp profiles match well the laboratory measurements demonstrating that laboratory data are valuable for implications at larger scale combining the experimental values of elastic moduli and frictional properties it results that at shallow crustal levels m 1 earthquakes are less favoured in agreement with earthquake depth distribution during the l aquila 2009 seismic sequence that occurred on carbonates

multistage sedimentary and metamorphic origin of pyrite and gold in the giant sukhoi log deposit lena gold province russia gold mineralization at sukhoi log in eastern siberia is hosted in a deformed neoproterozoic organic bearing and pyritic black shale and siltstone sequence that is folded into a tight overturned anticline the deposit contains about 30 million ounces of gold at an average grade of 2 0 g t au and is one of the largest known undeveloped gold resources the high grade gold zone forms a gently dipping tabular body in the core of the anticline the best gold grades occur in narrow bedding parallel pyrite quartz veinlets that have been folded during the main deformation event lower grade gold is associated with disseminated pyrite developed in and around the high grade core of the deposit detailed paragenetic studies of the mineralization and host rocks have defined six stages of pyrite development in the carbonaceous sediments the two earliest forms of pyrite termed py1 and py2 are commonly developed in stratiform layers of micron sized crystals framboids and fine euhedra which are interpreted as synsedimentary to early diagenetic in origin coarser grained bedding parallel aggregates of inclusion rich pyrite termed py3 contain inclusions of arsenopyrite native gold and gold tellurides and are interpreted to form during late diagenesis and earliest deformation coarse euhedral pyrite py4 overgrows the earlier pyrite py1 py2 and py3 and the slaty cleavage developed in the host rocks indicating a syndeformation timing late stage inclusion free pyrite py5 overgrows and replaces earlier sulfides and is considered to be syn to late deformation laser ablation inductively coupled plasma mass spectrometry la icpms analyses of the various pyrite types indicate that the synsedimentary py1 contains the highest levels of invisible gold varying from 0 4 to 12 1 ppm with a mean of 3 22 ppm au and 1 900 ppm as py1 is also enriched in a suite of trace elements mo sb ni co se te ag cu pb zn mn ba cr u v which are similar to those concentrated by organic processes in euxinic sedimentary environments later generations of pyrite from py2 to py5 including pyrite in bedding parallel pyrite quartz veinlets contain progressively lower contents of invisible gold and most other trace elements however this metamorphic and postmetamorphic pyrite contains microinclusions of free gold arsenopyrite pyrrhotite sphalerite and chalcopyrite the paragenetic textural and chemical relationships at sukhoi log suggest that gold was clearly initially introduced prior to cleavage development accompanying sedimentation of the organic rich shales and fixed during diagenesis within the structure of diagenetic arsenian pyrite subsequently accompanying deformation gold was liberated from recrystallized diagenetic pyrite to become concentrated as free gold and gold tellurides within metamorphic pyrite and folded bedding parallel pyrite quartz veinlets two key processes are considered vital to the formation of the sukhoi log deposit original synsedimentary and early diagenetic concentration of gold dissolved within arsenian pyrite in organic rich black shales and metamorphic processes that liberated gold from the early forms of arsenian pyrite to be concentrated as free gold and gold tellurides within late diagenetic and metamorphic pyrite and associated pyrite quartz veinlets in the core of an overturned anticline these ore forming processes are unlikely to be unique to sukhoi log other black shale and turbidite hosted deposits that occur in rifted continental margin environments which have undergone collision and basin inversion may form by similar processes

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

seismic evidence for rock damage and healing on the san andreas fault associated with the 2004 m 6 0 parkfield earthquake we deployed a dense linear array of 45 seismometers across and along the san andreas fault near parkfield a week after the m 6 0 parkfield earthquake on 28 september 2004 to record fault zone seismic waves generated by aftershocks and explosions seismic stations and explosions were co sited with our previous exper iment conducted in 2002 the data from repeated shots detonated in the fall of 2002 and 3 months after the 2004 m 6 0 mainshock show 1 0 1 5 decreases in seismic wave velocity within an 200 m wide zone along the fault strike and smaller changes 0 2 0 5 beyond this zone most likely due to the coseismic damage of rocks during dynamic rupture in the 2004 m 6 0 earthquake the width of the damage zone characterized by larger velocity changes is consistent with the low velocity waveguide model on the san andreas fault near parkfield that we derived from fault zone trapped waves li et al 2004 the damage zone is not symmetric but extends farther on the southwest side of the main fault trace waveform cross correlations for repeated aftershocks in 21 clusters with a total of 130 events located at different depths and distances from the array site show 0 7 1 1 increases in s wave velocity within the fault zone in 3 months starting a week after the earthquake the velocity recovery indicates that the damaged rock has been healing and regaining the strength through rigidity recovery with time most likely due to the closure of cracks opened during the mainshock we estimate that the net decrease in seismic velocities within the fault zone was at least 2 5 caused by the 2004 m 6 0 parkfield earthquake the healing rate was largest in the earlier stage of the postmainshock healing process the magnitude of fault healing varies along the rupture zone being slightly larger for the healing beneath middle mountain correlating well with an area of large mapped slip the fault healing is most promi nent at depths above 7 km

dynamic response of a rock fracture filled with viscoelastic materials rock fractures filled with viscoelastic materials such as sand usually contribute to rock mass instability under the influence of seismic waves and dynamic loads the purpose of this study is to verify that the specific fracture stiffness and the specific initial mass of the filling sand are two key fracture parameters in interrelating the physical mechanical and seismic properties of a rock fracture filled with dry sand a series of dynamic tests using a split hopkinson rock bar was conducted on a simulated sand filled fracture the experimental results show that stress wave attenuation across the filled fracture is strongly affected by wave reflection and transmission at the fracture interfaces and the dynamic compaction of the filling sand with the comparison between the analytical predictions by the displacement discontinuity model and the displacement and stress discontinuity model and the experimental results from the laboratory tests it is found that both models can predict a filled fracture with a smaller thickness i e less than 10 mm the displacement and stress discontinuity model may be used to predict a fracture with a larger thickness by considering the specific initial mass of filling materials the wave transmission coefficient for a filled fracture generally increases with increasing specific fracture stiffness

pyrite compositions from vhms and orogenic au deposits in the yilgarn craton western australia implications for gold and copper exploration abstract the archaean yilgarn craton western australia is a world class metallogenic province hosting considerable resources of au ag ni cu zn and fe here we present trace element compositions of pyrite from 30 orogenic au and 5 volcanic hosted massive sulphide vhms deposits across the yilgarn pyrites from vhms deposits tend to have higher sn se cu pb bi and lower ni relative to orogenic deposits vhms deposit pyrites commonly have co ni as 100au te au se te orogenic gold deposits could be subdivided based on association of au with as or te pyrites from au as ores generally have pb bi 5 se te 5 pb sb 100 and the majority of au is refractory in pyrite structure at the same time au te association pyrites are characterised by lower values of pb bi se te and tl te higher values of ag au pb sb and au generally resides in inclusions of different compositions our data can be used at the exploration stage to distinguish between vhms vs orogenic au signatures for all studied deposits inclusion populations are summarised with implications for au and ag deportment orogenic au deposits from the yilgarn mostly have multistage formation histories reflected in the presence of multiple generations of pyrites however only some deposits record multiple high au mineralisation events

pb isotope compositions of pyrite from the c quartz tourmaline vein of the siscoe gold deposit val d or quebec constraints on the origin and age of the gold mineralization the siscoe mine was one of the richest in the val d or mining camp producing 27 5 tonnes t of gold and 9 5 t of silver from 1929 to 1949 the c quartz tourmaline vein at the siscoe mine which is the youngest auriferous vein on the property is an excellent example of a high grade archean lode gold deposit it contains an average of 45 g t au and locally up to 221 g t au this vein cuts all dikes the main regional foliation s2 and several auriferous quartz carbonate veins and is interpreted to be a shear structure that formed during the development of a late to post d2 reverse fault the vein comprises mainly alternating tourmaline and quartz rich layers and gold occurs commonly in late fractures cutting the vein the visible wall rock alteration is characterized by the occurrence of tourmaline pyrite and calcite in this study we report the pb isotope compositions of hydrothermal pyrite separates taken from the c quartz tourmaline vein and its wall rock pyrite is abundant in the wall rock where it occurs as grains with inclusions of chalcopyrite gold tetradymite pyrrhotite rutile silicates and carbonates in the vein it forms euhedra generally devoid of inclusions locally the euhedra are fractured and the fractures are filled with native gold calcite and tetradymite textural relationships suggest that pyrite precipitated synchronously with and or after gold in the wall rock but predated gold in the vein pyrite separates from the vein and its wall rock yielded similar 206pb 204pb 207pb 204pb and 208pb 204pb ratios 13 63 13 83 14 58 14 62 and 33 42 33 76 respectively which are more radiogenic than those reported for volcanic supracrustal and syntectonic plutonic rocks of the southern abitibi subprovince but are very similar to those of the late to posttectonic s type granites in the pontiac subprovince and lacorne block this suggests that the pb originated from a reservoir similar to that of the magmas which produced these granites or alternatively that it was leached from the latter the pb ratios yield a model age of 2 57 0 07 ga which is interpreted to date the cooling of the hydrothermal system that introduced and or remobilized gold into the c quartz tourmaline vein these results when considered in the context of the evolution of the southern abitibi indicate that widespread hydrothermal circulation occurred between 2 64 and 2 55 ga after the collision of the pontiac and abitibi subprovinces and was caused by dewatering and s type magmatism in the thickened unstable continental crust this long lived hydrothermal system promoted remobilization of gold from earlier veins and possibly introduction of gold from deeper zones enhancing gold resources in the siscoe deposit

the coupled geochemistry of au and as in pyrite from hydrothermal ore deposits the ubiquity of au bearing arsenian pyrite in hydrothermal ore deposits suggests that the coupled geochemical behaviour of au and as in this sulfide occurs under a wide range of physico chemical conditions despite significant advances in the last 20years fundamental factors controlling au and as ratios in pyrite from ore deposits remain poorly known here we explore these constraints using new and previously published empa la icp ms sims and pixe analyses of as and au in pyrite from carlin type au epithermal au porphyry cu cu au and orogenic au deposits volcanogenic massive sulfide vhms witwatersrand au iron oxide copper gold iocg and coal deposits pyrite included in the data compilation formed under temperatures from 30 to 600 c and in a wide variety of geological environments the pyrite au as data form a wedge shaped zone in compositional space and the fact that most data points plot below the solid solubility limit defined by reich et al 2005 indicate that au1 is the dominant form of au in arsenian pyrite and that au bearing ore fluids that deposit this sulfide are mostly undersaturated with respect to native au the analytical data also show that the solid solubility limit of au in arsenian pyrite defined by an au as ratio of 0 02 is independent of the geochemical environment of pyrite formation and rather depends on the crystal chemical properties of pyrite and post depositional alteration compilation of au as concentrations and formation temperatures for pyrite indicates that au and as solubility in pyrite is retrograde au and as contents decrease as a function of increasing temperature from 200 to 500 c based on these results two major au as trends for au bearing arsenian pyrite from ore deposits are defined one trend is formed by pyrites from carlin type and orogenic au deposits where compositions are largely controlled by fluid rock interactions and or can be highly perturbed by changes in temperature and alteration by hydrothermal fluids the second trend consists of pyrites from porphyry cu and epithermal au deposits which are characterised by compositions that preserve the au as signature of mineralizing magmatic hydrothermal fluids confirming the role of this sulfide in controlling metal ratios in ore systems

the dynamics of the onset of frictional slip the way in which a frictional interface fails is critical to our fundamental understanding of failure processes in fields ranging from engineering to the study of earthquakes frictional motion is initiated by rupture fronts that propagate within the thin interface that separates two sheared bodies by measuring the shear and normal stresses along the interface together with the subsequent rapid real contact area dynamics we find that the ratio of shear stress to normal stress can locally far exceed the static friction coefficient without precipitating slip moreover different modes of rupture selected by the system correspond to distinct regimes of the local stress ratio these results indicate the key role of nonuniformity to frictional stability and dynamics with implications for the prediction selection and arrest of different modes of earthquakes

development of framboidal pyrite during diagenesis low grade regional metamorphism and hydrothermal alteration distribution patterns microstructural relationships and compositional variations for framboidal pyrite in the paleozoic sedimentary host rocks to gold deposits on the northern carlin trend nevada and at fosterville in central victoria collectively demonstrate that it is not all of synsedimentary early diagenetic origin framboidal pyrite also nucleated in hydrothermal veins formed at several kilometers depth and along dissolution surfaces stylolites and crenulation cleavages formed during metamorphism at up to anchizonal grade i e prehnitepumpellyite facies there are no obvious differences in either the size range or internal morphology of framboids formed in these various settings suggesting that a single relatively simple crystallization path may operate over a wide depth range in the upper crust at fosterville anomalously metal rich including au framboidal pyrite is most abundant adjacent to laminated shear veins that developed by slip along bedding surfaces during folding of the sedimentary host rocks microstructural relationships and pb isotope compositions for the framboidal pyrite and other similarly distributed early formed sulfides support development in response to the localized episodic influx of metal enriched h 2s bearing hydrothermal fluids during regional deformation between 440 and 400 ma these findings may have implications for other similarly deformed metasedimentary successions where the discovery of au bearing framboidal pyrite has recently been cited as evidence for significant au enrichment during sedimentation 2009 society of economic geologists inc

global positioning system measurements of present day crustal movements in the arabia africa eurasia plate collision zone we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1994 at 54 sites extending east west from the caucasus mountains of southern russia georgia and armenia to the aegean coast of turkey and north south from the southern edge of the eurasian plate pontus block to the northern edge of the arabian platform viewed from a eurasia fixed reference frame sites on the northern arabian platform move n38 13 w at 20 3 mm yr roughly consistent with the velocity implied by nuvel 1a circuit closure n23 7 w at 24 2 mm yr the motion of arabia appears to be transferred directly to the region of turkey north of the suture however eastern turkey is characterized by distributed deformation while central western turkey is characterized by coherent plate motion involving westward displacement and counterclockwise rotation of the anatolian plate internal deformation within the central part of the anatolian plate is less than 2 mm yr the anatolian plate is decoupled from eurasia along the right lateral strike slip north anatolian fault naf this different response in eastern and western turkey to the collision of arabia may result from the different boundary conditions the hellenic arc forming a free boundary to the west and the asian continent and oceanic lithosphere of the black and caspian seas forming a resistant boundary to the north and east we derive a best fitting euler vector for anatolia eurasia motion of 29 2 0 8 n 32 9 0 4 1 3 0 1 m y the mapped surface trace of the naf corresponds well to a small circle about this pole the new euler vector implies an upper bound for naf slip rate of 30 2 mm yr i e assuming all relative motion is accommodated along the naf using the nuvel 1a euler vector for arabia eurasia and the gps euler vector for anatolia eurasia we determine an arabia anatolia euler vector of 31 2 n 45 2 e 0 9 0 1 m y and an upper bound on the east anatolian fault slip rate of 15 3 mm yr the aegean trough region of western turkey deviates significantly from coherent plate rotation in addition to rotating with anatolia this region shows roughly n s extension at a rate of 14 5 mm yr taken together with satellite laser ranging results along the hellenic arc the contemporary pattern of deformation indicates increasing motions toward the arc suggesting that the westward displacement and counterclockwise rotation of anatolia is driven both by pushing from the arabian plate and by pulling or basal drag associated with the foundering african plate along the hellenic subduction zone

the western ailaoshan volcanic belts and their se asia connection a new tectonic model for the eastern indochina block the western ailaoshan wal volcanic belts mark the western boundary of the south china indochina suture zone along the ailaoshan fold belt geochronological and geochemical evidence suggests that the wal volcanic belts vary in ages and origins and includes 1 l carboniferous earliest m permian ca 300 270 ma incipient backarc basin magmatism 2 m permian ca 265 ma island arc mature backarc basin magmatism 3 early l permian ca 260 255 ma wal indochina arc continent collision and the associated syn collisional granitic magmatism as well as subsequent 4 e triassic ca 250 245 ma post collisional magmatism regional geological comparison indicates that the post l carboniferous wal tectonic evolution was closely related to the eastern indochina block we present a new g plate geodynamic evolution model for the ailaoshan fold belt and its surrounding south china indochina region based on new and published u pb zircon ages together with whole rock and pb isotope geochemical data

micromechanics of the velocity and normal stress dependence of rock friction among the second order effects on friction the most important are those of variable normal stress and of slip velocity velocity weakening which is usually considered the source of the stick slip instability in rock friction has been observed in velocity stepping experiments with westerly granite the friction change was 0 01 to 0 008 for a tenfold velocity increase using normal closure measurements we observed dilation upon each increase in sliding rate we also observed for the first time time dependent closure between surfaces during static loading the dilation that occurred during the velocity stepping experiment was found to be that expected from the static time dependent closure phenomenon this change in closure was used to predict friction change with an elastic contact model the calculated friction change which results from a change in contact area and asperity interlocking is in good agreement with the observed velocity dependence of steady state friction variable normal stress during sliding has two effects first in creating new partial slip contacts and locking some existing fully sliding contacts and second in increasing interlocking for instance when normal load is suddenly increased as a result a transient change in friction occurs upon a sudden change in normal load

frictional strength rate dependence and healing in dfdp 1 borehole samples from the alpine fault new zealand abstract the alpine fault in southern new zealand is a major plate boundary fault zone that according to various lines of evidence may be nearing the end of its seismic cycle and approaching earthquake failure in order to better characterize this fault and obtain a better understanding of its seismic potential two pilot boreholes have been completed as part of a larger drilling project samples representative of the major lithologic subdivisions of the fault zone at shallow 100 m depths were recovered and investigated in laboratory friction experiments we show here that materials from within and very near the principal slip zone psz tend to exhibit velocity strengthening frictional behavior and restrengthen heal rapidly compared to samples of the wall rock recovered near the psz fluid saturation causes the psz to be noticeably weaker than the surrounding cataclasites 0 45 and eliminates the velocity weakening behavior in these cataclasites that is observed in dry tests our results indicate that the psz has the ability to regain its strength in a manner required for repeated rupture but its ability to nucleate a seismic event is limited by its velocity strengthening nature we suggest that seismogenic behavior at depth would require alteration of the psz material to become velocity weakening or that earthquake nucleation occurs either within the wall rock or at the interface between the wall rock and the psz coseismic ruptures which propagate to the surface have been inferred for previous earthquakes on the alpine fault and may be facilitated by the slightly weaker psz material and or high rates of healing in the psz which support fault locking and eventual stress drops

critical behaviour and the evolution of fault strength during earthquake cycles the problem of how fault rheology and heterogeneity interact to produce the observed scaling of earthquakes such as the power law moment frequency relationship remains largely unsolved rock friction experiments have elucidated the properties of smooth faults1 2 3 but seem insufficient to explain the observed complexity of real fault dynamics4 5 the recognition of a connection between fault related processes and critical phenomena in other physical systems together with numerical models of repeated earthquakes have resulted in significant progress in the theoretical interpretation of earthquake scaling4 5 6 7 8 9 10 11 12 13 14 but fault rheology and heterogeneity have so far been treated separately here i attempt to unify the requirements of fault rheology and heterogeneity using numerical calculations of quantized slip in an elastic continuum i show that cyclical fault strength evolves naturally by means of a statistical selection for high strength fault patches asperities resulting in the accumulation and eventual failure of those asperities the applicability of these results to real fault systems is supported by a recent analysis of time dependent earthquake statistics15 these results imply that self similarity and criticality on a fault emerge during an earthquake cycle and suggest that the character of local seismicity can be useful in earthquake forecasting by revealing how advanced a fault is within its cycle

strain rate effect on frictional strength and the slip nucleation process abstract kato n yamamoto k yamamoto h and hirasawa t 1992 strain rate effect on frictional strength and the slip nucleation process in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 269 282 the strain rate dependence of frictional strength is investigated in relation to sliding behaviour by biaxial compression tests of large scale granite samples frictional sliding is generated by increasing shear strain at a constant rate under a constant normal stress on the fault the ram displacement is held constant for a prescribed time interval between two successive sliding events so as to have the same time effect of stationary contact between sliding surfaces we obtained the following results as the strain rate increases 1 sliding becomes more unstable 2 the nucleation zone size of stick slip decreases and 3 frictional strength logarithmically increases result 3 is consistent with the previous study by dieterich 1979a and 1 and 3 are similar to the strain rate effects on failure characteristics of intact rocks reported in the literature result 3 can be explained by a rate and state dependent friction law our results suggest that the strain rate dependence of the fault strength plays an important role in controlling the nucleation process of faulting

experimental evidence of contact loss during stick slip possible implications for seismic behaviour abstract we present results of an experimental study on the stick slip phenomenon focused on detailed measurements of the relative normal displacement this was done mainly to determine whether or not the sliding surfaces become separated during the slip phase as suggested in previous works experiments were performed on pmma as it has mechanical properties comparable to those of brittle rocks and has proved to be a good analogue for rocks in rupture mechanics experiments results show clearly that normal displacement occurs during and after the slip phase the characterisation of the sliding surface enables us to compare the maximum relative normal displacement during the slip phase with asperity height in most cases the maximum relative normal displacement was found to be higher than the average value of the peak to trough relief of the surface showing that sliding surfaces were at least partially separated the phenomenon generally consists of a monotonous slip opening phase followed by a monotonous slip closure phase in some cases the slip closure phase shows oscillations which have been interpreted as elastic bounces this last phenomenon was observed irrespective of the experimental conditions with a probability ranging from 0 1 to 0 3 but no clear variations of this probability have been found as a function of normal stress and roughness these observations may give insights for the explanations of earthquake related problems such as the heat flow paradox anomalous p wave radiation or the inferred low average friction coefficients in subduction zones

fluid inclusions s isotopes and pb isotopes characteristics of the kuh e surmeh carbonate hosted zn pb deposit in the zagros fold belt southwest iran implications for the source of metals and sulfur and mvt genetic model abstract the kuh e surmeh zn pb deposit is hosted by upper permian carbonate platform in the zagros fold belt of southwestern iran the orebody is characterized by massive vein and banded textures it is mostly composed of sphalerite galena and pyrite accompanied with minor barite homogenization temperatures of fluid inclusions in sphalerite and barite range from 94 7 to 200 0 c and 93 6 to 198 0 c respectively fluid salinities of sphalerite and barite hosted inclusions vary from 8 1 to 21 3 wt nacl equiv and 10 5 to 22 6 wt nacl equiv respectively the 34s values of barite range from 11 2 to 11 9 similar to those of gypsum of the nar member 10 9 to 11 7 in the upper permian sedimentary strata and different from the 34s values of jahani salt dome gypsum 29 1 to 30 5 indicating that sulfur was derived from the upper permian evaporites the 34s values of galena and sphalerite range from 1 7 to 15 4 compatible with bacterial sulfate reduction bsr of the upper permian evaporites the pb isotopic compositions of galena yield 206pb 204pb ratios from 17 942 to 18 340 207pb 204pb ratios from 15 649 to 15 744 and 208pb 204pb ratios from 38 186 to 38 458 indicating an upper crustal lead source based on ore textures fluid inclusions isotope data and geochemical compositions of sulfide minerals the kuh e surmeh sulfide mineralization is believed to have precipitated from low temperature sedimentary basin brines and should be classified as a mississippi valley type deposit in a salt diapir environment mineralization is the result of mixing of hypogene metalliferous fluids with more dilute h2s rich fluids during miocene pliocene compression associated with the zagros orogeny

frictional properties of olivine at high temperature with applications to the strength and dynamics of the oceanic lithosphere 1 faulting and brittle deformation of mantle rocks occurs in many tectonic settings such as oceanic transform faults oceanic detachment faults subduction zones and continental rifts however few data exist that directly explore the frictional properties of peridotite rocks improved constraints on the brittle deformation of peridotite is important for a more complete understanding of the rheological properties of the lithosphere furthermore our comparatively detailed understanding of plastic deformation in olivine allows us to explore the possible role of thermally activated intracrystalline deformation mechanisms in macroscopically brittle processes it has been hypothesized and some experimental data indicate that plastic yielding by dislocation glide low temperature plasticity determines the direct effect in the rate and state frictional constitutive formulation plastic flow may also have important implications for the blunting or necking at asperity contacts that influences the time and or displacement dependent friction evolution effect and frictional healing we present results from saw cut experiments on fine grained synthetic olivine fault gouge conducted in a gas medium deformation apparatus in the temperature range of 400 1000 c with 100 mpa confining pressure we conducted velocity stepping tests to explore the rate and temperature dependence of sliding stability we also conducted slide hold slide experiments to investigate the time and temperature dependence of fault zone restrengthening frictional healing the mechanical data and microstructural observations allow us to explore the role of thermally activated processes in frictional sliding the data indicate systematic temperature dependenceof rate and state variables that can be attributed to plastic yielding at grain to grain contacts we explore the implications of such temperature dependent behavior for controlling the base of the seismogenic zone in the oceanic lithosphere and we seek insight into possible mechanistic models for the interactions between fracture and flow that could lead to improved constraints on the strength of the lithosphere

laboratory study of fault healing and lithification in simulated fault gouge under hydrothermal conditions abstract seismic data geologic observations and laboratory friction studies suggest that faults lithify and strengthen heal during the interseismic period of the earthquake cycle we report on experiments to investigate the influence of healing duration and temperature on the strength and healing rate of simulated faults layers of m sized quartz powder were used to simulate granular fault gouge gouge layers were sheared within sioux quartzite in a triaxial pressure vessel at elevated pressures p c 250 mpa elevated temperatures 230 636 c and in the presence of water p h 2 o 75 mpa we performed hold slide experiments in which samples were subjected to a period of healing under hydrostatic load followed by shear deformation healing times ranged from a few hundred s to 10 5 s to isolate the effects of lithification and temperature on friction we ran two types of hold slide experiments 1 samples were subjected to healing and shear deformation at elevated temperature and 2 following healing at elevated temperature temperature was reduced prior to shear we also ran slide hold slide experiments in which samples were healed under shear load at elevated temperature 636 c experiments in which deformation was carried out at a lower temperature than healing show that both the static and sliding coefficient of friction increase with heal time samples healed and deformed at higher temperature showed lower peak strengths and within the scatter of our data did not exhibit time dependent strengthening these data are interpreted to result from enhanced lithification rates at elevated temperature samples healed under shear load exhibited a log linear decrease in friction with hold time modeling using rate and state dependent friction laws indicates velocity strengthening behavior with friction a b values of 0 05 to 0 08 our data indicate that at high temperature the effective state evolution term b is negative moreover the data indicate the rate of frictional strengthening varies significantly for hydrostatic and non hydrostatic load conditions our measurements of healing are consistent with seismic estimates of fault healing rates if stress drop is a fraction of the total shear stress and effective fault normal stress is 60 to 100 mpa

clustering and periodic recurrence of microearthquakes on the san andreas fault at parkfield california the san andreas fault at parkfield california apparently late in an interval between repeating magnitude 6 earthquakes is yielding to tectonic loading partly by seismic slip concentrated in a relatively sparse distribution of small clusters 20 meter radius of microearthquakes within these clusters which account for 63 of the earthquakes in a 1987 92 study interval virtually identical small earthquakes occurred with a regularity that can be described by the statistical model used previously in forecasting large characteristic earthquakes sympathetic occurrence of microearthquakes in nearby clusters was observed within a range of about 200 meters at communication speeds of 10 to 100 centimeters per second the rate of earthquake occurrence particularly at depth increased significantly during the study period but the fraction of earthquakes that were cluster members decreased

variable initial pb isotopic compositions of rocks associated with the ug2 chromitite eastern bushveld complex abstract an investigation of the pb isotopic compositions of plagioclase and sulfide in a stratigraphic interval including the ug2 chromitite of the eastern bushveld complex has been conducted to determine the pb isotopic composition s of the magma s that crystallized to form this part of the intrusion gain a better understanding of why coexisting plagioclase and sulfide commonly exhibit widely different pb isotopic compositions and explore the use of pb isotopes in deducing post accumulation history analyses were obtained in situ with a nuplasma multicollector icp ms coupled with 193 nm excimer or 213 nm lasers most plagioclase compositions fall on the 207pb 204pb vs 206pb 204pb geochron of 2 06 ga which is the solidification age of the intrusion the measured ratios have not been affected by radiogenic ingrowth and plagioclase generally remained closed to pb exchange after initial cooling the array of plagioclase compositions on the geochron is significantly larger than that defined by analytical error this indicates that in terms of pb at least two different magma compositions were present the composition of the least radiogenic magma was approximated by that of the contemporaneous bse with 238u 204pb and 232th 204pb values of 9 0 and 35 respectively suggesting a mantle derivation with little or no involvement of the continental crust while the second magma possessed a pb isotopic composition similar to the upper crust with 9 6 compared to plagioclase sulfides generally possess slightly higher 206pb 204pb ratios for equivalent 207pb 204pb ratios such that their compositions fall between the 2 06 and 1 86 ga geochrons the latter age is much younger than the cooling age the data are interpreted to mean that the bushveld complex remained buried in the crust at temperatures of several hundred c for about 200 ma after solidification and that any sulfides accessible to fluid continued to re equilibrated during this time with more radiogenic pb the sulfide pb may have been transported into the bushveld complex by fluids from an external reservoir when the rocks were still partially molten and thus permeable alternatively the sulfide pb may have originated mainly from radiogenic decay of u and th present in minerals other than the sulfides in the immediately surrounding bushveld rocks followed by local redistribution of pb by whatever fluid was present indeed some sulfides are characterized by 208pb 204pb ratios sufficiently high that an external source is unlikely this observation and the fact that the sulfides display small scale heterogeneity suggest that most if not all of the radiogenic sulfide pb was locally derived it also implies that during the post solidification re equilibration period there was no large scale fluid flow through the microfracture network because otherwise the isotopic heterogeneities would not have been preserved the minerals in 2 of the 19 samples studied contain young pb presumably introduced by meteoric waters that permeated the macrofracture network

pb isotope composition of ni cu pb ore deposits in an archean greenstone belt evidence for proterozoic remobilization in the pontiac subprovince of canada

dynamics of earthquake normal faulting two dimensional lattice particle model a 2d lattice particle model is used to simulate the dynamic rupture process of a normal fault the system equations for the particle motions are solved numerically by the finite difference method under a given block boundary condition the flexibility of the implementation of a 2d lattice particle model to simulate an earthquake dynamic process was demonstrated in previous modeling of a shallow angle thrust fault shi et al 1998 numerical results indicate that the particle motions displacement velocity and acceleration along the fault are discontinuous both in the fault parallel and fault normal directions with a localized slip rupture and localized fault separation in the vicinity of the fault outcrop the position at which the fault intersects with the free surface the particle velocity and acceleration increase rapidly both on the hanging wall and the footwall the particle motions on the hanging wall are larger than those on the footwall these motions are amplified as the fault scarp develops rupture breaks out at the surface with strong asymmetry between the hanging wall and the footwall along the free surface as the distance from the fault outcrop increases the particle velocity and acceleration decrease rapidly on the footwall and less rapidly on the hanging wall the asymmetrical particle motion results from the geometrical effect of the dip of the fault the free surface and the dynamic source rupture the combination of all of these effects causes a strong asymmetry in stress when the rupture pulse approaches the free surface the dynamically propagating rupture is characterized by a ramp slip time function accompanied with fault opening the slip pulse becomes sharper when the rupture approaches the free surface consequentially the hanging wall in the vicinity of the fault exhibits a large vibration which generates a strong surface wave propagating along the free surface away from the fault scarp on the hanging wall side this result is similar but significantly different from the numerical simulation of a normal fault with a moving double couple dislocation source benz and smith 1988 in addition the numerical result is qualitatively in agreement with recent foam rubber experiments brune and anooshehpoor 1999 and similar to results from a finite element simulation oglesby et al 1998 oglesby 1999 comparing with a 2d strike slip fault and thrust fault the particle motions in the vicinity of the normal fault on the free surface are smaller for a same size rupture pulse

stochastic strong ground motion simulation of the 12 november 1999 duzce turkey earthquake using a dynamic corner frequency approach on 12 november 1999 only three months after the 17 august 1999 kocaeli earthquake mw 7 4 an earthquake of mw 7 1 occurred immediately to the east of the kocaeli rupture in northwestern turkey resulting in extensive structural damage in the city of duzce and its surrounding area it was reported to be a right lateral strike slip event on the previously unbroken segment of the north anatolian fault zone with a north dipping fault plane this paper presents stochastic finite fault simulation of near field ground motions from this earthquake at selected near fault stations based on a dynamic corner frequency approach using the computer program exsim motazedian and atkinson 2005 the method requires region specific source path and site characterizations as input model parameters the source mech anism of the 1999 duzce event and regional path effects are well constrained from previous studies of the earthquake the local site effects at the selected stations are studied as a combination of the kappa operator and frequency dependent soil ampli fication the model parameters are validated against recordings and a stress drop value of 100 bars is estimated for the 1999 duzce earthquake the validated model is then used to compute synthetic records around the fault distribution of peak ground motion parameters is observed to be consistent with the building damage dis tribution in the near fault region most affected by the seismic shaking the attenuation of synthetic ground motion parameters is compared with recent ground motion pre diction equations proposed for the region by gulkan and kalkan 2002 ulusay et al 2004 and akkar and bommer 2007 as well as two next generation attenuation models by boore and atkinson 2007 and campbell and bozorgnia 2007 despite discrepancies at several stations stochastic finite fault modeling based on a dynamic corner frequency approach confirms to be a practical tool to reproduce the ground motions of large earthquakes

scaling differences between large interplate and intraplate earthquakes a study of large intraplate earthquakes with well determined source parameters shows that these earthquakes obey a scaling law similar to large interplate earthquakes in which m 0 l 2 or u l where l is rupture length and u is slip in contrast to interplate earthquakes for which 1 10 5 for for the intraplate events 6 10 5 which implies that these earthquakes have stress drops about 6 times higher than interplate events this result is independent of focal mechanism type this implies that intraplate faults have a higher frictional strength than do plate boundaries and hence that faults are velocity or slip weakening in their behavior this factor may be important in producing the concentrated deformation that creates and maintains plate boundaries

age and paragenesis of mineralisation at coronation hill uranium deposit northern territory australia coronation hill is a u au platinum group elements deposit in the south alligator valley sav field in northern australia south of the better known unconformity style u east alligator rivers ear field the sav field differs from the ear by having a more complex basin basement architecture a volcanically active fault trough jawoyn sub basin developed on older basement and then was disrupted by renewed faulting before being buried beneath regional mcarthur basin sandstones that are also the main hanging wall to the ear deposits primary mineralisation at coronation hill formed at 1607 26 ma rather than 600 900 ma as previously thought and so it is likely that the sav was part of a single west mcarthur basin dilational event most ore is hosted in sub vertical faults and breccias in the competent volcanic cover sequence this favoured fluid mixing acid buffering forming illite and oxidation of fe2 and reduced c rich assemblages as important uranium depositional mechanisms however reduction of u in fractured older pyrite pb model age of 1833 67 ma is an important trap in diorite some primary ore was remobilised at 675 21 ma to form coarse uraninite ni co pyrite networks containing radiogenic pb coronation hill is polymetallic and in this respect resembles the egress style u deposits in the athabascan basin canada however these are all cover hosted a hypothesis for further testing is that coronation hill is also egress style with ores formed by fluids rising through basement hosted fault networks u reduction by diorite pyrite and carbonaceous shale and into veins and breccias in the overlying jawoyn sub basin volcano sedimentary succession

age origin and significance of nodular sulfides in 2680 ma carbonaceous black shale of the eastern goldfields superterrane yilgarn craton western australia abstract sulfide nodules composed of pyrite occur within black shales in the lucky bay area of the bulong domain eastern goldfields superterrane yilgarn craton western australia that correlate with the neoarchean black flag group detailed petrography reveals a variety of shapes and textures from spherical to ovoid and zoned to uniform some nodules have recrystallized resulting in a later generation of pyrite all have been affected by post depositional metamorphism as evidenced by pressure shadows containing quartz mica carbonate assemblages la icp ms analyses show that these nodules are enriched in a range of trace elements including co ni cu ag sb te au tl pb and bi gold and te concentrations range from 0 3 to 1 ppm and 10 to 50 ppm respectively the black flag group equivalents stratigraphically and structurally underlie a younger basin east of lucky bay that contains turbidites sandy debris flows and bif the latter of which hosts several gold deposits at randalls 60 km se of kalgoorlie it is likely that the lateral equivalents of the nodular sulfide bearing black shale originally occurred stratigraphically beneath what is now the ore horizon at randalls given its anomalous au and te content this lithology is a potential contributor of gold to the bif hosted gold deposits of the randalls goldfield as well as other similar gold resources elsewhere in the eastern goldfields superterrane

laboratory observation of acoustic fluidization in granular fault gouge and implications for dynamic weakening of earthquake faults 1 several lines of evidence including remote triggering of earthquakes and modulation of seismic tremor by earth tides suggest that faults weaken when subject to shaking and dynamic stresses associated with the passage of seismic waves however the origin of such dynamic weakening is poorly understood here we explore the role of acoustic resonance for dynamic fault weakening using laboratory measurements experiments were conducted using a split hopkinson pressure bar assembly with dynamic stressing via impact loading samples were composed of crushed rock particles from mine tailings with a particle size distribution similar to that found in a natural fault gouge we used pulse shaper techniques and carefully evaluated dynamic stresses recorded at the front and rear of the sample to ensure that dynamic force balance was satisfied our experiments document acoustic induced fluidization and dramatic dynamic weakening frictional strength and elastic modulus of a simulated fault gouge are reduced by a factor of 5 10 via acoustic fluidization we find a threshold acoustic pressure for fluidization that varies systematically with gouge zone properties our observations could help explain dynamic fault weakening and triggering of earthquake fault slip by dynamic stressing

the evolution of authigenic zn pb fe bearing phases in the grieves siding peat western tasmania a thick peat profile overlying mineralized metasediments possesses exceptionally high base metal contents up to 28 6 wt zn and up to 3 8 wt pb in the form of abundant detrital and authigenic minerals this metal rich peat was examined using x ray diffraction scanning electron microscopy and raman spectroscopy to determine the characteristics mineral associations phase evolution and conditions of formation of zn pb fe bearing minerals within the peat mineral assemblages consisting of sulfides silicates sulfates oxides carbonates and phosphates could be classified as follows 1 detrital minerals supplied by the surrounding rocks i e cambrian volcanics and sediments ordovician carbonates and 2 authigenic phases that are precipitated in situ including the predominant zn pb fe bearing phases detrital minerals are characterized by weathering related morphologies e g round smooth surfaces and angular edges and dissolution pits whereas authigenic phases are recognized by their delicate microparticle textures e g bladed framboidal and botryoidal textures zinc bearing phases are represented by non stoichiometric phases also containing s c o and al sphalerite baileychlore and fe zn pb carbonate authigenic pb and fe bearing phases are also present in the peat such as galena anglesite plumbojarosite magnetite and pyrite a line of descent of authigenic sulfides has been established suggesting that a non stoichiometric possibly amorphous zn rich phase is a precursor to the sphalerite stages of pyrite formation where massive polycrystalline pyrite is produced via disseminated and framboidal pyrite have also been hypothesized in this study the assemblages of authigenic minerals in the peat reflect dynamic physical and chemical conditions including biological processes and are not necessarily in equilibrium with each other

region specific key seismic parameters for earthquakes in northern iran strong motion accelerograms recorded within northern iran are used to examine the propagation characteristics of shear wave including geometric spreading behavior q value j 0 and horizontal to vertical h v ratio these region specific key seismic parameters are estimated from 259 three component records of 22 earth quakes with magnitude ranging from m 4 9 to m 7 4 in northern iran the geometric spreading follows a trilinear behavior with a strong postcritical reflection from the moho the first and second hinges of the trilinear behavior are at 75 and 150 km respectively the associated q value based on the vertical component is q 87 f 1 46 j0 value for vertical and horizontal components are 0 03 and 0 05 respec tively because of lack of station specific site information the h v ratio is considered to be a rough estimation of generic site amplification the obtained region specific parameters are used to estimate the average stress drop based on three stochastic modeling approaches stochastic point source modeling suggests a brune stress drop of 125 bars whereas stochastic finite fault modeling based on static and dynamic corner frequency approaches suggests a stress drop of 68 bars

southern san andreas fault seismicity is consistent with the gutenberg richter magnitude frequency distribution the magnitudes of any collection of earthquakes nucleating in a region are generally observed to follow the gutenberg richter gr distribution on some major faults however paleoseismic rates are higher than a gr extrapolation from the modern rate of small earthquakes would predict this along with other observations led to the formulation of the characteristic earthquake hypothesis which holds that the rate of small to moderate earthquakes is permanently low on large faults relative to the large earthquake rate wesnousky et al 1983 schwartz and coppersmith 1984 we examine the rate difference between recent small to moderate earthquakes on the southern san andreas fault ssaf and the paleoseismic record hypothesizing that the discrepancy can be explained as a rate change in time rather than a deviation from gr statistics we find that with reasonable assumptions the rate changes necessary to bring the small and large earthquake rates into alignment agree with the size of rate changes seen in epidemic type aftershock sequence modeling where aftershock triggering of large earthquakes drives strong fluctuations in the seismicity rates for earthquakes of all magnitudes the necessary rate changes are also comparable to rate changes observed for other faults worldwide these results are consistent with paleoseismic observations of temporally clustered bursts of large earthquakes on the ssaf and the absence of m 7 earthquakes on the ssaf since 1857

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

study of weak and strong ground motion including nonlinearity from the northridge california earthquake sequence abstract this article presents a new method to estimate s wave site response relative to a regional layered crustal model the method is useful for site specific strong motion prediction because the estimated site response functions are referenced to an idealized regional layered model for which we know the ground response exactly we applied this method to the northridge earthquake sequence we determined the site amplifications from aftershocks with magnitudes 2 6 to 4 3 at 21 stations that were colocated with strong motion stations these site response functions were then used to modify synthetic seismogram calculated for the northridge mainshock in the same regional layered crustal model and thus obtain site specific ground motion estimates these site specific synthetic seismograms have higher correlation to observations in comparison to the synthetic seismograms without weak motion site correction they have similar amplitude and frequency content to the observations especially at sites with recorded peak ground accelerations below 0 3 g at sites with larger ground motions however this approach overestimates the strong motion the differences are made clear when we estimate site response functions from the strong motion records and compare them with those from weak motion records we express the differences as the average ratio of the weak to strong motion site response aws ratio when the ground motion is low the aws ratio is near unity indicating that the weak and strong motion site responses agree with each other within the uncertainty however the aws ratio increases as the ground motion amplitude increses the difference in weak and strong motion site responses becomes significant at stations where peak acceleration was above 0 3 g peak velocity was above 20 cm sec or peak strain was above 0 06 during the mainshock this result demonstrates directly from the ground motion observations the relationship between nonlinear site response and peak ground motion parameters the nonlinearity is present on soft rock sites as well as on sediment sites

the 1 october 1995 dinar earthquake sw turkey the dinar earthquake ms 6 1 usgs pde of 1 october 1995 occurred on the nwse trending dinar fault the earthquake is associated with a 10 km long surface rupture with predominantly normal faulting the mainshock was preceded by a series of foreshocks that started 6 days before the mainshock and included two md 4 5 events the mainshock source mechanism derived from the inversion of broad band p waves revealed that two sub events occurred on a nw se trending normal fault with a small strike slip component according to the source model estimated in this study the first rupture started at a depth of about 8 km and reached to a depth of about 12 km propagating north west the total seismic moment found from the inversion of p waveforms is 2 0 times 10 18 nm the seismic moment of the second sub event was about four times larger than the first one field observations gps measurements and slip vector obtained from the inversion of broad band p waveforms suggest that the nw se trending dinar fault is due to the internal deformation of sw anatolia moving south westwards

testing for pb isotopic differences between minerals in the kiglapait layered intrusion by la icp ms abstract mineral scale pb isotopic variations in cumulates of the kiglapait intrusion the largest troctolitic intrusion of the proterozoic nain plutonic suite in labrador canada are evaluated directly in thin section by single spot la icp ms analysis of minerals with low pb concentrations e g plagioclase 0 31 3 3 ppm clinopyroxene 0 06 1 1 ppm at high spatial resolution

on the mechanics of earthquake afterslip we propose a model for earthquake afterslip based on rate and state variable friction laws in the model afterslip is attributed to the interaction of a velocity weakening region at depth within which earthquakes nucleate with an upper region of velocity strengthening frictional behavior the existence of this upper region is supported by independent seismologic observations and the results of laboratory friction experiments in our model afterslip is the result of relaxation of a stress perturbation within the velocity strengthening region which arises when an earthquake propagates into that region from below we derive the stress perturbation and its decay from the friction constitutive law using a simple 1 degree of freedom approximation for the elastic interaction between the fault and its surroundings this approximation is based on thickness averaged displacements and slip velocities within the velocity strengthening region which is assumed to slip as a rigid block coseismic and postseismic slip are coupled through the thickness averaged stiffness k of the velocity strengthening region we assume k to be inversely proportional to the thickness of this region which means that thicker velocity strengthening regions have a greater tendency to arrest coseismic slip we model the afterslip time histories of the 1966 parkfield and 1987 superstition hills earthquakes and relate the model parameters to physical parameters which may govern the rheologic behavior of the faults in accord with field observations our model predicts 1 that afterslip on some faults scales with the thickness of the unconsolidated sedimentary cover and 2 that proportionally more afterslip occurs for earthquakes in which coseismic surface slip is small compared with coseismic slip at depth velocity strengthening frictional behavior is to be expected for faults within poorly consolidated sediments and for those that contain significant gouge zones about 500 m within their shallow regions 3 5 km combining our results with those of recent laboratory friction studies indicates that relatively young faults with little accumulated fault gouge should exhibit little afterslip

simultaneous measurement of sulfur and lead isotopes in sulfides using nanosecond laser ablation coupled with two multi collector inductively coupled plasma mass spectrometers abstract we herein report the coupling of a nanosecond laser ablation system with a large scale multi collector inductively coupled plasma mass spectrometer nu1700 mc icpms np 1700 and a conventional nu plasma ii mc icpms np ii for the simultaneous laser ablation and determination of in situ s and pb isotopic compositions of sulfide minerals we found that the required aerosol distribution between the two spectrometers depended on the pb content of the sample for example for a sulfide containing 100 3000 ppm pb the aerosol was distributed between the np 1700 and the np ii spectrometers in a 1 1 ratio while for lead contents 3000 and

late interseismic state of a continental plate bounding fault petrophysical results from dfdp 1 wireline logging and core analysis alpine fault new zealand 1 we present a geophysical characterization at 0 1 100 m scales of a major plate bounding continental fault in a late interseismic state the alpine fault produces mw 8 earthquakes every 200 400 years and last ruptured in 1717 ad wireline geophysical logs and rock cores extending from one side of the alpine fault to the other were acquired in two boreholes drilled in 2011 at gaunt creek during the first phase of the deep fault drilling project dfdp 1 these data document ambient conditions under which the next alpine fault earthquake will occur principal component analysis of the wireline logging data reveals that 80 of the variance is accounted for by electrical acoustic and natural gamma properties and preliminary multivariate classification enables the lithologies of sections of missing core to be reconstructed from geophysical measurements the fault zone exhibits systematic variations in properties consistent with common processes of progressive alteration and comminution near the principal slip zone superimposed on different protolith compositions our observations imply that the fault zone has the opposite sense of elastic asymmetry at 0 1 100 m scales to that of the crustal scale orogen imaged by remote geophysical methods on the basis of the fault zone scale asymmetry the bimaterial interface model of preferred earthquake rupture directions implies a northeastward direction of preferred alpine fault rupture on going characterization of the structural and hydraulic architecture of the alpine fault will improve our understanding of the relationship between in situ conditions earthquake rupture processes and the hazards posed by future earthquakes

high frequency spectral falloff of earthquakes fractal dimension of complex rupture b value and the scaling of strength on faults the high frequency falloff omega sup minus gamma of earthquake displacement spectra and the b value of aftershock sequences are attributed to the character of spatially varying strength along fault zones the author assumes that the high frequency energy of a main shock is produced by a self similar distribution of subevents where the number of subevents with radii greated than r is proportional to r sup minus d d being the fractal dimension in this model an earthquake is composed of a hierarchical set of smaller earthquakes the static stress drop is parameterized to be proportional to r sup eta and strength is assumed to be proportional to static stress drop he finds that a distribution of subevents with d 2 and stress drop independent of seismic moment eta 0 produces a main shock with an omega sup minus 2 falloff if the subevent areas fill the rupture area of the main shock by equating subevents to islands of high stress of a random self similar stress field on a fault he relates d to the scaling of strength on a fault such that d 2 minus eta thus d 2 corresponds to constant stress drop scaling eta 0 and scale invariant fault strength amore self similar model of aftershock rupture zones on a fault is used to determine the relationship between the b value the size distribution of aftershock rupture zones and the scaling of strength on a fault the b value for aftershock sequences on a fault is found to equal 3 minus 1 5 eta 3 eta therefore this model indicates that the typically observed spectral falloffs of omega sup minus 2 and b values of 1 can be entirely caused by scale invariant strength eta 0 along fault zones less

laser ablation icp ms analysis of silicate and sulfide melt inclusions in an andesitic complex i analytical approach and data evaluation quantitative microanalysis of entire silicate and sulfide melt inclusions by excimer laser ablation inductively coupled plasma mass spectrometry la icpms has been applied to extrusive and shallow intrusive rocks from the andesitic farallon negro volcanic complex northwestern argentina silicate melts are trapped in pyroxene amphibole plagioclase and quartz and sulfide melts are trapped in amphibole details of the analytical approach and the quantification procedure are given and the results are evaluated to test the accuracy of the technique and the validity of the interpretation of analytical signals similar compositions of silicate melt inclusions trapped in truly co precipitating minerals show that the quantification approach of melt inclusion compositions from la icpms signals through an internal standard is valid this correspondence also shows that melt inclusions investigated in this study are not significantly influenced by the boundary layer around a growing crystal or by post entrapment modifications post entrapment diffusive re equilibration only affected the fe and mg content of melt inclusions in mafic phases thus melt inclusions are representative samples of the melt from which the host mineral crystallized with regard to most major and trace elements sulfide melt inclusions present as pyrrhotite with exsolution of au and cu in phases separated during cooling were analyzed for their bulk fe cu and au content and the abundance of these elements was quantified using a silicate glass as external standard the validity of this calibration was tested by comparing electron microprobe analyses of fe cu ni and co in homogeneous sulfide minerals with la icpms results identical results within calculated uncertainty one standard deviation of five to nine analyses mostly between 1 and 5 wt rsd demonstrate that for these elements measured element ratios are independent of the matrix using our analytical setup

predicting intensity and damage distribution during the 1995 dinar turkey earthquake with generated strong motion accelerograms a source model for the 1995 dinar earthquake that is capable of reproducing reasonably well the statistical characteristics of observed strong motion records is used to generate synthetic ground motion accelerograms at 29 different sites along five east west cross sections in the city each section crosses a distribution of topographical geotechnical and damage characteristics all synthetic stations are located within a circle of approximately 4 km diameter and a segment of the ruptured fault extends into the city four parameters are identified to represent the intensity of strong motion accelerograms two of them are the simplest kinematical parameters namely peak ground acceleration and peak ground velocity and the other two are spectral parameters namely the average over a period range of spectral acceleration and of spectral input energy the distribution of each intensity parameter is compared with the observed damage distribution in the city along the five sections spectral intensity parameters predict the damage distribution better than the two kinematical parameters with spectral input energy slightly outperforming spectral acceleration the results suggest that synthetic seismograms generated by using a realistic source model are capable of producing useful estimates of ground motion intensity and consequent structural damage even within the boundaries of a modestsized city in the near field of the earthquake source

in situ u series dating by laser ablation multi collector icpms new prospects for quaternary geochronology the capabilities and potential applications of in situ dating of quaternary materials using laser ablation mc icpms are explored 234 u 238 u and 230 th 234 u can be measured with precision sufficient for dating at a spatial resolution of 100mm or better in samples that contain as a little as 1 ppm uranium moreover u and th concentrations and u series isotope ratios can be continuously profiled to determine changes in age that occur with sample growth e g in speleothems these capabilities additionally permit the dating of bones teeth and possibly molluscs which are subject to post mortem open system behaviour of useries isotopes and can be employed to elucidate processes of u series migration during weathering and diagenesis a drawback of laser ablation mc icpms is that it cannot in general provide u series age estimates with the high precision and accuracy of conventional tims or solution mc icpms methods however sample preparation is straightforward the amount of sample consumed negligible and it can be used to rapidly characterise or screen and select samples from which more precise and accurate dates can be obtained using conventional methods given further instrumental developments and the establishment of suitable matrix matched standards for carbonates and other materials we foresee that laser ablation mc icpms will play an increasingly important role in quaternary dating research r 2005 published by elsevier ltd

source parameters of the 1 october 1995 dinar turkey earthquake from sar interferometry and seismic bodywave modelling abstract the 1 october 1995 m s 6 1 dinar earthquake ruptured a 10 km section of the nw se dinar civril fault there are discrepancies between the published source parameters from seismic data with seismic moments in disagreement by over a factor of two we use both sar interferometry and seismic bodywave modelling to determine earthquake source parameters an interferogram generated from ers 1 2 sar imagery spanning the event and separated by 5 months is used to derive source parameters by a downhill simplex inversion with multiple monte carlo restarts we model the displacements in the satellite line of sight initially using uniform slip on a rectangular dislocation in an elastic half space the resultant model fault plane agrees in strike and location with the observed surface break but systematic residuals exist in the line of sight deformation field resulting in a r m s residual of 20 mm in the interferogram the residuals are reduced if the depth distribution of slip is allowed to vary spatially in four segments along a continuous fault plane our best fitting solution with a r m s misfit of 8 mm reveals two distinct areas of slip on the fault plane strike 145 dip 49 rake 270 a main rupture slipping by 1 44 m between depths of 1 and 8 km becoming deeper to the se and matching the observed surface rupture and an along strike continuation to the nw of the same fault plane but between depths of 8 and 13 km and not associated with a surface break the total geodetic moment 4 5 0 1 10 18 nm is more than twice as large as published seismic moments based on the inversion of p waveforms alone but close to the harvard cmt moment 4 7 10 18 nm we use sh waveforms in addition to the p waves used previously to determine an alternative seismic source mechanism sh waves constrain the depth to be shallower than solutions based on p waves alone agreeing with the depths from the interferometric inversion and resulting in a larger moment 3 1 0 4 10 18 nm than the previous bodywave estimates 2 2 1 10 18 nm the cmt moment reduces in magnitude to a similar size 3 3 10 18 nm if the centroid depth and fault dip are constrained to the values determined from bodywave modelling and interferometry thus the geodetic moment is 40 bigger than the moment determined from seismology

the effects of entrained debris on the basal sliding stability of a glacier 1 new laboratory experiments exploring likely subglacial conditions reveal controls on the transition between stable sliding and stick slip motion of debris laden ice over rock with implications for glacier behavior friction between a rock substrate and clasts in ice generates heat which melts nearby ice to produce lubricating water an increase in sliding speed or an increase in entrained debris raises heat generation and thus meltwater production unstable sliding is favored by low initial lubrication followed by rapid meltwater production in response to a velocity increase low initial lubrication can result from cold or drained conditions whereas rapid increase in meltwater generation results from strong frictional heating caused by high sliding velocity or high debris loads strengthening of the interface healing during stick intervals between slip events occurs primarily through meltwater refreezing when healing and unstable sliding are taken together the experiments reported here suggest that stick slip behavior is common from motion of debris laden glacier ice over bedrock

the roles of time and displacement in velocity dependent volumetric strain of fault zones the relationship between measured friction a and volumetric strain during frictional sliding was determined using a rate and state variable dependent friction constitutive equation a common work balance relating friction and volume change and two types of experimental faults initially bare surfaces of westerly granite and rock surfaces separated by a 1 mm layer of 90 m westerly granite gouge the constitutive equation is the sum of a constant term representing the nominal resistance to sliding and two smaller terms a rate dependent term representing the shear viscosity of the fault surface direct effect and a term which represents variations in the area of contact evolution effect the work balance relationship requires that a differs from the frictional resistance that leads to shear heating by the derivative of fault normal displacement with respect shear displacement d n d s an implication of this relationship is that the rate dependence of d n d s contributes to the rate dependence of a experiments show changes in sliding velocity lead to changes in both fault strength and volume analysis of data with the rate and state equations combined with the work balance relationship preclude the conventional interpretation of the direct effect in the rate and state variable constitutive equations consideration of a model bare surface fault consisting of an undeformable indentor sliding on a deformable surface reveals a serious flaw in the work balance relationship if volume change is time dependent for the model at zero slip rate indentation creep under the normal load leads to time dependent strengthening of the fault surface but according to the work balance relationship no work is done because compaction or dilatancy can only be induced by shearing additional tests on initially bare surfaces and gouges show that fault normal strain in experiments is time dependent consistent with the model this time dependent fault normal strain which is not accounted for in the work balance relationship explains the inconsistency between the constitutive equations and the work balance for initially bare surface faults all rate dependence of volume change is due to time dependence similar results are found for gouge we conclude that a reflects the frictional resistance that results in shear heating and no correction needs to be made for the volume changes the result that time dependent volume changes do not contribute to a is a general result and extends beyond these experiments the simple indentor model and particular constitutive equations used to illustrate the principle

variations in rupture process with recurrence interval in a repeated small earthquake in theory and in laboratory experiments friction on sliding surfaces such as rock glass and metal increases with time since the previous episode of slip1 this time dependence is a central pillar of the friction laws widely used to model earthquake phenomena2 3 on natural faults other properties such as rupture velocity4 5 porosity and fluid pressure6 11 may also vary with the recurrence interval eighteen repetitions of the same small earthquake separated by intervals ranging from a few days to several years allow us to test these laboratory predictions in situ the events with the longest time since the previous earthquake tend to have about 15 larger seismic moment than those with the shortest intervals although this trend is weak in addition the rupture durations of the events with the longest recurrence intervals are more than a factor of two shorter than for the events with the shortest intervals both decreased duration and increased friction are consistent with progressive fault healing during the time of stationary contact

abyssal serpentinites as gigantic factories of marine salts and oil abstract serpentinites occur worldwide in various geological settings such as in magma starved oceanic basins abyssal serpentinites are long term storage for chlorine and carbon the latter forming dominantly reduced and subordinately oxidized compounds hence serpentinites salts and reduced carbon phases coexist in an abyssal association although huge reservoirs of salts and reduced carbonaceous matter in abyssal serpentinites are thought to be lacking this may be more a reflection of intrinsic limits in research methods than an indication of their absence on the other hand shallow seated hydrocarbon rich mud volcanoes and diapirs consisting of salts hydrocarbons oils and gases and clayey muds including mudded serpentines can provide evidence for such an oceanic association here we search for scientific data in support of the oceanic association and hence we propose a reappraisal of exploitable worldwide salt hydrocarbon reservoirs even gigantic in size abyssal serpentinites are well known source rocks of abiotic gaseous hydrocarbons via fischer tropsch type reaction ftt whereas macromolecular carbonaceous matter mostly bitumen found in serpentinites is postulated to be biogenic this inference is based mainly on three assumptions i ftt in nature does not yield oils ii hydrocarbons derive essentially from the thermal alteration of microbial molecules iii the presence of biomarkers traditionally considered evidence of the biological origin of oils nevertheless some lines of strong evidence disprove these accepted conventions i lab experiments demonstrated that ftt can synthesize significant quantities of liquid hydrocarbons oils under conditions compatible with the deeper and more reduced level of serpentinite hosted hydrothermal systems ii macromolecules generally thought to derive from microbial activity can be abiotically generated as documented in extraterrestrial bodies iii biomarkers are evidence for the proliferation of microbial communities which subsist on serpentinization and ftt products thus they are biological pollutants moreover seawater driven serpentinization consumes water producing huge amounts 11 kg halite m 3 of peridotite of salts that can be stored in the deeper zone of abyssal type hydrothermal systems thus the origin of shallow sited salt deposits even gigantic in size can be related to either the advective upwelling of hot hydrothermal brines due to the dehydration of abyssal serpentinites or to the passive upwelling of buoyant saline geobodies piercement structures are indeed seismically imaged in several localities such as south atlantic the gulf of mexico the serpentinite belt extending from cuba to hispaniola the north sea trench and the zagros orogenic belt similar lines of evidence at the microscopic scale have been found in some hyblean serpentinite xenoliths south eastern sicily being representative of the unmetamorfosed in situ relic of the palaeo tethys ocean upon which sicily and its off shore areas lie in spite of the accepted stereotype of hydrocarbons as fossil fuels and hence finite resources reduced carbon compounds abiotically produced in abyssal serpentinites may be copious protracted over time and thus renewable

nonlinear dynamical triggering of slow slip on simulated earthquake faults with implications to earth 1 among the most fascinating recent discoveries in seismology are the phenomena of dynamically triggered fault slip including earthquakes tremor slow and silent slip during which little seismic energy is radiated and low frequency earthquakes dynamic triggering refers to the initiation of fault slip by a transient deformation perturbation most often in the form of passing seismic waves determining the frictional constitutive laws and the physical mechanism s governing triggered faulting is extremely challenging because slip nucleation depths for tectonic faults cannot be probed directly of the spectrum of slip behaviors triggered slow slip is particularly difficult to characterize due to the absence of significant seismic radiation implying mechanical conditions different from triggered earthquakes slow slip is often accompanied by nonvolcanic tremor in close spatial and temporal proximity the causal relationship between them has implications for the properties and physics governing the fault slip behavior we are characterizing the physical controls of triggered slow slip via laboratory experiments using sheared granular media to simulate fault gouge granular rock and glass beads are sheared under constant normal stress while subjected to transient stress perturbation by acoustic waves here we describe experiments with glass beads showing that slow and silent slip can be dynamically triggered on laboratory faults by ultrasonic waves the laboratory triggering may take place during stable sliding constant friction and slip velocity and or early in the slip cycle during unstable sliding stick slip experimental evidence indicates that the nonlinear dynamical response of the gouge material is responsible for the triggered slow slip

sea99 a revised ground motion prediction relation for use in extensional tectonic regimes we present sea99 a revised predictive relation for geometric mean horizontal peak ground acceleration and 5 damped pseudovelocity response spec trum appropriate for estimating earthquake ground motions in extensional tectonic regimes which we demonstrate to have lower ground motions than other tectonic regimes sea99 replaces sea96 a relation originally derived by spudich et al 1996 1997 the data set used to develop sea99 is larger than that for sea96 and minor errors in the sea96 data set have been corrected in addition a one step regression method described by joyner and boore 1993 1994 was used rather than the two step method of joyner and boore 1981 sea99 has motions that are as much as 20 higher than those of sea96 at short distances 5 30 km and sea99 s motions are about 20 lower than sea96 at longer periods 1 0 2 0 sec and larger distance 40 100 km sea99 dispersions are significantly less than those of sea96 sea99 rock motions are on the average 20 lower than motions predicted by boore et al 1994 except for short distances at periods around 1 0 sec where sea99 motions exceed those predicted by boore et al 1994 by as much as 10 com parison of ground motions from normal faulting and strike slip events in our data set indicates that normal faulting horizontal ground motions are not significantly different from extensional regime strike slip ground motions

effects of shear stress applied to surfaces in stationary contact on rock friction in this paper we show how the applied shear stress affects the frictional strength of granite sliding surfaces initially held in stationary contact we develop an experimental scheme to perform a slide and hold friction test whereby the shear stress is servocontrolled during the hold period of the test a series of experiments conducted at a single normal stress of 5 mpa show the following effects first unloading the shear stress during the hold period increases frictional resistance by up to 10 20 a decrease in shear stress linearly increases the frictional resistance of the interface secondly the static friction coefficient increases with the logarithm of contact time the friction coefficient increases by 0 01 per decade of contact time at near zero shear stress levels and by more than 0 02 at shear stress levels that are greater than half the sliding friction

frictional properties of shale reservoir rocks 1 we performed laboratory friction experiments on shale samples from three hydrocarbon reservoirs to assess compositional controls on fault slip behavior accompanying hydraulic stimulation the samples span a range of clay and total organic content from 10 to 60 by weight and demonstrate fine scale heterogeneity within each reservoir friction measurements demonstrate strong dependence of strength and rate state constitutive properties on shale composition shale samples with clay and organic content above 30 by weight show coefficient of friction 0 4 and consistently velocity strengthening behavior while those below this threshold show increased strength and velocity weakening behavior this transition in frictional strength and stability suggests a change in the shale grain packing framework from rigid clast supported to clay mineral and organic matter supported measurements of gouge dilatancy further support these relationships showing a negative correlation with clay and organic content critical slip evolution distance exhibits similar dependence on composition implying common micromechanical mechanisms for the observed transition in frictional behavior we performed microstructural characterization of the experimental samples and observe changes in the gouge load bearing framework and shear localization features consistent with these mechanical data while these results can be applied generally to infer slip stability on faults in clay bearing sedimentary rock we employ the experimental data to place constraints on microearthquake magnitudes and the occurrence of slow shear slip on preexisting faults during hydraulic stimulation in shale reservoirs

fault damage zones of the m7 1 darfield and m6 3 christchurch earthquakes characterized by fault zone trapped waves abstract to characterize the subsurface structure of the damage zones caused by the 2010 2011 canterbury earthquake sequence in new zealand s south island we installed two short linear seismic arrays array 1 across the greendale fault gf surface rupture and array 2 over the surface projection of the blind port hills fault phf that ruptured in the 2010 m7 1 darfield and 2011 m6 3 christchurch earthquakes respectively we recorded 853 aftershocks for 4 months after the christchurch earthquake fault zone trapped waves fztws identified at array 1 for aftershocks occurring on both the gf and the phf show that the post s durations of these fztws increase as focal depths and epicentral distances from the array increase suggesting an effective low velocity waveguide formed by severely damaged rocks existing along the gf and phf at seismogenic depths locations of aftershocks generating prominent fztws delineates the subsurface gf rupture extending eastward as bifurcating blind fault segments an additional 5 8 km beyond the mapped 30 km surface rupture into a zone with comparably lower seismic moment release west of the phf rupture which extends westward to within 5 3 1 km of the subsurface gf the propagation of fztw through the intervening gap indicates moderate gf phf structural connectivity we interpret this zone as a fracture mesh reflecting the interplay between basement faults and stress aligned microcracks that enable the propagation of phf sourced fztws into the gf damage zone simulations of observed fztws suggest that the gf rupture zone is 200 250 m wide consistent with the surface deformation width velocities within the zone are reduced by 35 55 with the maximum reduction in the 100 m wide damage core zone corresponding with surface and shallow subsurface evidence for discrete fracturing the damage zone extends down to depths of 8 km or deeper consistent with hypocentral locations and geodetically derived fault models

variations in the crustal structure beneath western turkey summary we use teleseismic receiver functions to investigate the crustal structure at two locations in westernturkey using seismic data recorded on small arrays of temporary broad band seismographs the results from these analyses are compared with receiver function results from the gdsn station anto on the anatolian plateau in central turkey the crust is 30 km thick in the region of western turkey where active normal faulting reveals present day extension in the upper crust and alkali basaltic volcanism reveals recent extension within the subcrustal lithosphere the crust is 34 km thick further east where crustal extension is still evident but less pronounced in the anatolian plateau which is not currently extending the crust is 38 km thick the level of extension estimated from these measurements of crustal thickness implies a b factor of 1 2 this value agrees with the amount of extension estimated in the upper crust from the integrated seismic strain rate b factor of 1 3 from surface faulting b factor of 1 25 and from the amount of extension in the subcrustal lithosphere estimated from the volcanism b factor 2 all indicating that the extension is approximately uniformly distributed vertically throughout the lithosphere the moho transition in this region appears to thin slightly as the degree of extension increases westwards

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

a composite source model for computing realistic synthetic strong ground motions a composite source model is presented for convolution with synthetic green s functions in order to synthesize strong ground motions due to a complex rupture process of a large earthquake subevents with a power law distribution of sizes are located randomly on the fault each subevent radiates a displacement pulse with the shape of a brune s pulse in the far field at a time determined by a constant rupture velocity propagating from the hypocenter thus all the input parameters have a physical basis we simulate strong ground motions for event station pairs that correspond to records obtained in mexico by the guerrero accelerograph network the synthetic accelerations velocities and displacements have realistic amplitudes durations and fourier spectra

time dependent friction of granite implications for precursory slip on faults frictional forces were measured during sliding between saw cut cylinders of barre granite deformed in a servo controlled triaxial loading machine two different effects occur depending on the type of loading when steady shortening of a stably sliding sample is halted suddenly slip continues at a diminishing rate which depends on the logarithm of the initial sliding velocity thus the frictional strength of the surface is decreasing with time when shortening at a constant rate resumes after the holding period however the frictional resistance temporarily rises to a peak proportional to the logarithm of time of no driving showing a well known increase in friction with time the subsequent decrease in resistance from this peak is continuous the observed frictional resistance of a surface thus results from the interaction of several processes and is not a constant in general but depends on the immediate and preceding deformation when shortening is resumed after a period of holding slip rate across the friction surface temporarily accelerates above the driving rate the slip rate can then either decrease to the driving rate and remain stable or accelerate further and lead to stick slip motion at stress levels below the peak value there is no apparent difference in the frictional resistance until the unloading rate of the loading machine is exceeded between slip episodes which settle stably to the constant driving rate and those which become unstable and result in stick slip the stick slip failure criterion is not a peak stress but rather loss of strength more rapidly that the unloading rate of the loading machine the evidence that accelerating motion before stick slip is due to the time variable strength of rock suggests that accelerating slip will occur before earthquakes unfortunately for easy observation experiments indicate that slip need not be uniform over a fault surface also to be established is whether slip will be sufficiently large in the earth to be detectable nevertheless a plausible mechanism for generating observable phenomena prior to earthquakes is suggested by the laboratory observations

in situ pb isotope analysis of fe ni cu sulphides by laser ablation multi collector icpms new insights into ore formation in the sudbury impact melt sheet abstract laser ablation la multi collector inductively coupled plasma mass spectrometry mc icpms is ideally suited to in situ determination of isotope ratios in sulphide minerals using samples of magmatic sulphide ore from the sudbury impact structure we test la mc icpms analytical protocols that aim to meet a range of analytical challenges in the analysis of pb isotopes these include potential matrix sensitive isotopic fractionation interferences on pb isotopes low melting points of many sulphide minerals the availability of standards magmatic sulphides of wide ranging mineralogy pyrrhotite pentlandite chalcopyrite pyrite and sphalerite were analysed for pb isotopic composition using the silicate glass nist srm 610 as an external standard to correct for instrumental mass fractionation despite matrix sensitive melting and re deposition around ablation pits several lines of evidence indicate that all analyses are accurate within typical analytical uncertainties of 0 003 2 2 and that the defined approach is insensitive to compositional diversity in sample matrix a laser ablation and dissolution based measurements of sulphide powders are in agreement b analyses from each sample define isochron ages within uncertainty of the known crystallization age 1850 ma c the results of sulphide measurements by laser ablation are consistent with age corrected feldspar analyses from the same samples the results have important implications for ore formation in sudbury the pb isotope data regressions are consistent with age corrected feldspar analyses from each respective sample which together with time integrated th u ratios that match whole rock values 3 1 4 0 and 6 1 for the worthington copper cliff and parkin offset dykes respectively indicate chemical equilibrium between the silicate and sulphide systems during ore formation the sulphides within each respective sample have indistinguishable model initial pb isotope ratios 207 pb 204 pb m irrespective of mineralogy or texture indicating a common origin for ores within each of three different offset dykes furthermore variations between offset dykes e g 207 pb 204 pb m 15 514 0 012 15 399 0 009 and 15 275 0 003 show that the ores have differing crustal sources on previously unrecognized scales mass balance considerations particularly for mgo ni and cu indicate that the spatial distribution of mafic target rocks played a significant role in controlling the mineralization potential in different parts of the melt sheet

earthquake nucleation on model faults with rate and state dependent friction effects of inertia laboratory studies suggest that earthquake nucleation involves a transition from quasi static slip when inertial effects are negligible to inertia driven dynamic motion this transition occurs via quasi dynamic motion during which the effects of inertia become increasingly important the characteristics of this transition which depend on frictional properties of the fault determine the observability of earthquake nucleation by seismic geodetic or other means by investigating the role of inertia during nucleation we obtain a quantitative definition of the limiting velocity vin which marks the end of quasi dynamic motion and the onset of instability for reasonable friction parameters and fault widths we obtain estimates of vin for crustal faults to study the roles of inertia stiffness and friction parameters on preseismic motion we simulate triggered instabilities in a one dimensional model of a homogeneous fault with rate and state variable friction in most of our simulations triggering is achieved by applying a stress perturbation to an initially creeping fault under steady state friction we also investigate triggering on faults which are initially locked and overstressed compared to their nominal frictional strength due to time dependent healing we study the amount up and duration tp of preseismic slip as a function of system mass m and other model parameters for crustal faults we interpret the relevant mass as a product of density and fault width and find that wider fault zones result in smaller up and larger tp both up and tp are proportional to the system stiffness k the characteristic slip distance dc and the friction constitutive parameter a and inversely proportional to the size of the triggering event we find greater up and tp for constitutive laws which allow strengthening at zero velocity compared to laws that require slip or a combination of slip and aging for state evolution in contrast to quasi static modeling our simulations suggest a minimum stress perturbation criterion for instability which may be interpreted in terms of a strain threshold for triggered seismicity

particle mechanics model for the effects of shear on solute retardation coefficient in rock fractures abstract damage on rock fracture surfaces during shear process changes the mechanical and hydrological properties of the fractures and therefore affects solute migration in fractured rocks laboratory experiments on this issue are rarely reported in the literature due to technical difficulties in measuring asperity damage and gouge generation to conceptually investigate the effects of rock fracture surface damage on solute sorption during shear we present a retardation coefficient model considering the effect of wear the particle mechanics model was employed to investigate the effects of gouge generation abrasive wear and microcrack development in the damaged zones on the solute retardation coefficient in rock fractures the results from demonstration examples show that the shear process significantly increases the retardation coefficients by offering more sorption surfaces in the factures due to gouge generation wear microcracking and crushing of gouge particles conceptually three damage zones are classified to characterize the various wear impacts on the solute transport in single fractures outstanding issues of the present model and suggestions for future study are also presented

fault healing inferred from time dependent variations in source properties of repeating earthquakes we analyze two sets of repeating earthquakes on the calaveras fault to estimate in situ rates of fault strengthening healing earthquake recurrence intervals tr range from 3 to 803 days variations in relative moment and duration are combined to study changes in stress drop rupture dimension rupture veloc ity and particle velocity as a function of t healing rates and source variations are compared with predictions of laboratory derived friction laws two interpretations of event duration z are used one in which is given by the ratio of slip to particle ve locity and one in which it scales as rupture dimension divided by rupture velocity our data indicate that faults strengthen during the interseismic period we infer that source dimension de creases with t r due to aseismic creep within the region surround ing the repeating events stress drop increases 1 3mpa per dec ade increase in twhich represents an increase of a factor of 2 3 relative to events with tbetween 10 and 100 days this rate of fault healing is consistent with extrapolations of laboratory meas urements of healing rates if fault strength is high on order of 60mpa and stress drop is roughly 10 of this value

the effect of loading rate on static friction and the rate of fault healing during the earthquake cycle the seismic cycle requires that faults strengthen heal between earthquakes and the rate of this healing process plays a key role in determining earthquake stress drop1 2 3 4 rupture characteristics5 6 and seismic scaling relations2 3 4 7 frictional healing as evidenced by increasing static friction during quasi stationary contact between two surfaces1 8 9 10 11 12 is considered the mechanism most likely to be responsible for fault strengthening2 3 13 14 previous studies however have shown a large discrepancy between laboratory and seismic field estimates of the healing rate2 3 4 14 15 in the laboratory rock friction changes by only a few per cent per order of magnitude change in slip rate whereas seismic stress drop increases by a factor of 2 to 5 per order of magnitude increase in earthquake recurrence interval but in such comparisons it is assumed that healing and static friction are independent of loading rate here i summarize laboratory measurements showing that static friction and healing vary with loading rate and time as expected from friction theory16 17 18 applying these results to seismic faulting and accounting for differences in laboratory seismic and tectonic slip rates i demonstrate that post seismic healing is expected to be retardedfor a period of several hundred days following an earthquake in agreement with recent findings from repeating earthquakes13 14 19 20

potential for earthquake triggering from transient deformations 1 we report on laboratory experiments in which stick slipping shear surfaces are subject to transient stressing to simulate earthquake triggering by seismic waves granular layers and bare granite surfaces were sheared in a servo controlled deformation apparatus in double direct shear the seismic waves from an earthquake and tectonic load were simulated by superimposing a loading rate sinusoid on a constant shear loading rate the dependence of triggered stick slip failure on fault stress state and architecture was analyzed fault architecture was evaluated by varying gouge layer thickness 2 6 mm and studying bare granite surfaces we compare the shortened recurrence times for faults under transient loading conditions to the consistent recurrence intervals under constant loading rate our results imply that triggering depends on oscillation amplitude and frequency as well as properties of the fault larger amplitude dynamic stresses reduce stick slip recurrence intervals for granular layers whereas failure times for granite surfaces are uncorrelated with oscillation amplitude granular layers have shorter recurrence rates at higher frequency whereas the recurrence intervals of granite surfaces are lengthened or unaffected by high frequency oscillations higher frequencies can inhibit failure when fault slip exceeds a critical distance dc prior to peak velocity and encourages failure if dc is achieved postpeak velocity increasing velocity temporarily strengthens faults whereas velocity reduction further weakens and promotes failure as predicted by the rate and state friction laws our results may explain variations in earthquake triggering thresholds and imply that high frequency thresholds may not be constant as has been previously proposed

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

a composite source model of the 1994 northridge earthquake using genetic algorithms abstract the 17 january 1994 northridge earthquake m w 6 7 occurred on a buried thrust fault in the northwest los angeles metropolitan area we investigate the source process of this earthquake using the csmip strong motion records and a composite source model developed by zeng et al 1994a for realistic earthquake strong ground motion prediction our previous studies demonstrated the realism of the synthetic strong motions generated from the composite source model by comparing them with observed records from earthquakes in many areas of the world this article addresses an inverse study of the problem to find a specific composite source model for the northridge earthquake this is done by adjusting the location of a suite of composite subevents using genetic algorithms holland 1975 to best match the observed waveforms a test run of the genetic algorithm on synthetic data sets finds a very good convergence of the approach we reduce largely the intensive computation time by identifying subevents with major contribution to the waveform fit our result for the 1994 northridge earthquake indicates a complex earthquake rupture process with three large slip zones one at the hypocenter and the other two to the west of the hypocenter we then use this model to compute the high frequency strong motion velocity and acceleration the results show that the composite source model provides a very realistic broadband source description for the northridge earthquake

analysis of accelerations from the 1 october 1995 dinar turkey earthquake the dinar earthquake 1 october 1995 occurred in southwestern turkey and had a moment magnitude of 6 4 and a normal faulting mechanism the earthquake caused 90 deaths over 200 injuries and a large amount of damage it was recorded by seven strong motion accelerographs the strong motion accelerograph at dinar is on the edge of the surface projection of the fault the record from dinar is possibly unique in its proximity to the causative fault for this type of mechanism the dinar strong motion station is in a small stiff building on soft sediments with a shallow water table the peak acceleration was 0 32 g on the horizontal component perpendicular to the fault trace the earthquake was caused by rupture on the dinar fault which is a normal fault trending generally toward the south southeast with the hanging wall on the west there was surface rupture along about a 12 km segment of this fault the dinar strong motion station is at the south end of the fault under 1 km from the nearest surface trace the hypocenter was at the south end beneath dinar with rupture propagating toward the north and away from the strong motion site a specific composite source model was found that reproduces the statistical characteristics of the ground motions and also approximately reproduces the low frequency waveform in the strong motion in this model the fault length l is 12 5 km the width w is 17 3 km and the moment m 0 is 4 72 10 25 dyne cm the fault strikes 130 and dips 45 toward the southwest from the surface to 12 km for the composite parameters the largest subevent r max is 4 0 km the rupture velocity is 1 5 km sec and the subevent stress drop is 60 bars after anderson 1997 the composite source model parameters imply that the static stress drop was 36 bars the radiated seismic energy in this event was 4 3 10 21 ergs the apparent stress was 18 bars and the savage wood ratio was 1 0 most of the seismic energy is released at depths greater than 2 km the major asperity is beneath the location where synthetic aperture radar interferometry found the maximum surface deformation

criteria for determining initial lead isotopic compositions of pyrite in archaean lode gold deposits a case study at victory kambalda western australia abstract the initial pb isotopic compositions of ore associated sulphides are important in isotopic tracer studies studies of archaean lode gold deposits from western australia indicate that the pb isotopic data distribution for ore associated galenas and pyrites is commonly linear and determination of the initial pb ratio relies on selecting the least radiogenic composition this detailed pb isotopic study of sulphides from the 32 ore zone which transects a variety of rocks in the victory mine mineralisation dated at 2627 ma has resolved the origin of the pb isotopic heterogeneities which yield linear arrays it has led to the development of criteria for sample selection which more efficiently and effectively target pyrite samples which best preserve the initial pb ratio of the sulphide and hence the ore fluid the most important controls on the displacement of the measured pb ratio of pyrite from the initial pb ratio are in order of importance 1 pb content of pyrite 2 pyrite abundance 3 proximity of pyrite to ore fluid channelway i e vein and 4 host rock the host rock is important because the th u and pb contents and presence of minor u th bearing phases influence the amount and nature of any post formation pb represented in the pyrite data the first three parameters control the magnitude of that influence a high pb content high pyrite abundance and setting in a vein or at a vein margin produce a pb isotopic composition which is more likely to be dominated or buffered by fluid pb i e more accurately reflects the initial pb isotopic ratio conversely pyrite with a low pb content low abundance and siting distal from veining is likely to be more susceptible to post formation modification by contributions from the host rock resulting in a more radiogenic pb isotopic composition

lead isotopic disequilibrium between sulfide and plagioclase in the bushveld complex and the chemical evolution of large layered intrusions abstract the pb isotopic compositions of coexisting plagioclase and sulfide from the bushveld complex were determined by laser ablation multi collector icpms la mc icpms the samples are of the upper critical zone in the northeast corner of the complex and were collected from drill core and underground mine exposures all the rocks are fresh and exhibit no evidence for alteration weathering or disruption of the pb isotope systematics subsequent to the initial cooling of the intrusion furthermore individual plagioclase and sulfide crystals do not contain enough u to warrant correction for radiogenic in growth for these reasons the measured pb isotope ratios approximate the initial ones for plagioclase 207pb 206pb ranges from 0 98 to 1 02 and 208pb 206pb from 2 26 to 2 35 low 207pb 206pb and 208pb 206pb ratios characterize grain boundaries and partially annealed microcracks some of which contain minute fragments of sulfide and other phases and this accounts for most if not all the heterogeneity exhibited by individual samples real compositional differences exist however in plagioclase from different lithologic layers for example plagioclase 207pb 206pb values vary from 1 004 in norite beneath the merensky pyroxenite to 1 009 in the mineralized pyroxenite and 0 997 in overlying norite in most samples in which sulfide and plagioclase coexist the sulfide 207pb 206pb ratio is lower and 208pb 206pb ratio higher than the corresponding ones in plagioclase for example in a mineralized merensky reef sample average sulfide 207pb 206pb and 208pb 206pb ratios are 0 993 and 2 313 respectively while those in plagioclase are 1 000 and 2 292 in one sample the sulfide is extremely heterogeneous with 207pb 206pb and 208pb 206pb ratios as low as 0 84 and 2 12 in this particular sample the compositions must represent an isolated occurrence of addition of a young pb component the array of sulfide and plagioclase compositions requires multiple sources of pb at the time of crystallization or soon thereafter the disequilibrium between plagioclase and sulfide implies that some of the pb originated from the isotopically distinct country rocks and was introduced at temperatures at which the composition of sulfide but not plagioclase could be modified thus bushveld sulfide and to some extent plagioclase do not reliably record the initial pb isotopic composition s of the parent magma s