superplastic nanofibrous slip zones control seismogenic fault friction understanding the internal mechanisms controlling fault friction is crucial for understanding seismogenic slip on active faults displacement in such fault zones is frequently localized on highly reflective mirrorlike slip surfaces coated with thin films of nanogranular fault rock we show that mirror slip surfaces developed in experimentally simulated calcite faults consist of aligned nanogranular chains or fibers that are ductile at room conditions these microstructures and associated frictional data suggest a fault slip mechanism resembling classical ashby verrall superplasticity capable of producing unstable fault slip diffusive mass transfer in nanocrystalline calcite gouge is shown to be fast enough for this mechanism to control seismogenesis in limestone terrains with nanogranular fault surfaces becoming increasingly recognized in crustal faults the proposed mechanism may be generally relevant to crustal seismogenesis

response of large scale ionospheric convection to substorm expansion onsets a case study 1 we have studied the response of large scale ionospheric convection to substorm expansion onsets on the basis of two weak substorms of 1 may 2001 during which a large part of the dawn cell of the two cell ionospheric convection pattern was monitored by the superdarn radars ionospheric convection began to enhance first in a localized region of the equatorward part of the dawn cell 2 minutes before the expansion onsets of both substorms and then enhanced in the entire dawn cell successively the enhanced convection persisted throughout their expansion phase possibly even near the footprint of a plasma sheet region without fast flows observed by geotail these observations suggest that ionospheric convection begins to enhance just before substorm expansion onset and then enhances in the entire cell possibly regardless of the presence of fast earthward flows in the corresponding plasma sheet region of the magnetotail the global enhancement of ionospheric convection is consistent with that of magnetotail convection which also begins just before onset

brittle and semibrittle creep of tavel limestone deformed at room temperature deformation and failure mode of carbonate rocks depend on the confining pressure in this study the mechanical behaviour of a limestone with an initial porosity of 14 7 is investigated at constant stress at confining pressures below 55 mpa dilatancy associated with micro fracturing occurs during constant stress steps ultimately leading to failure similar to creep in other brittle media at confining pressures higher than 55 mpa depending on applied differential stress inelastic compaction occurs accommodated by crystal plasticity and characterized by constant ultrasonic wave velocities or dilatancy resulting from nucleation and propagation of cracks due to local stress concentrations associated with dislocation pile ups ultimately causing failure strain rates during secondary creep preceding dilative brittle failure are sensitive to stress while rates during compactive creep exhibit an insensitivity to stress indicative of the operation of crystal plasticity in agreement with elastic wave velocity evolution and microstructural observations

a proposed production model of rapid subauroral ion drifts and their relationship to substorm evolution multisatellite data are used to examine the temporal relationship between subauroral ion drifts said and the phases of an auroral substorm utilizing images of auroral luminosities taken by the dynamics explorer 1 de 1 spacecraft and observations of particle injection at geosynchronous orbit we identify the time of expansive phase onset and estimate the time at which recovery begins noting the times at which said are observed simultaneously by the de 2 spacecraft we find that said typically occur well after substorm onset more than 30 min during the substorm recovery phase substantial westward ion drifts and field aligned currents are observed well equatorward of the auroral oval during the expansion phase of a substorm but the drifts lack the narrow spike signature associated with said prior to substorm onset and after substorm recovery field aligned currents are absent equatorward of the auroral oval and the ionosphere is very nearly corotating a phenomenological model of said production is proposed that qualitatively agrees with the observed ionospheric signatures and substorm temporal relationship in this model substorm generated subauroral field aligned currents close via pedersen currents with the outward flowing region 1 currents at higher latitudes these pedersen currents flow in the region of low conductivity equatorward of the auroral oval and are associated with relatively large poleward directed electric fields the frictional heating of the ions caused by collisions with the corotating neutral atmosphere substantially increases the rate of ion atom interchange between o and n2 subsequent fast recombination of no with electrons further reduces the subauroral f region conductivities with a corresponding increase in the electric field and the frictional heating this heating leads to thermal expansion substantial field aligned plasma flow and very large depletions in the f peak concentration thus additionally reducing the height integrated pedersen conductivity

dynamic rupture processes inferred from laboratory microearthquakes we report macroscopic stick slip events in saw cut westerly granite samples deformed under controlled upper crustal stress conditions in the laboratory experiments were conducted under triaxial loading 1 2 3 at confining pressures 3 ranging from 10 to 100 mpa a high frequency acoustic monitoring array recorded particle acceleration during macroscopic stick slip events allowing us to estimate rupture speed in addition we record the stress drop dynamically and we show that the dynamic stress drop measured locally close to the fault plane is almost total in the breakdown zone for normal stress 75 mpa while the friction f recovers to values of f 0 4 within only a few hundred microseconds enhanced dynamic weakening is observed to be linked to the melting of asperities which can be well explained by flash heating theory in agreement with our post mortem microstructural analysis relationships between initial state of stress rupture velocities stress drop and energy budget suggest that at high normal stress leading to supershear rupture velocities the rupture processes are more dissipative our observations question the current dichotomy between the fracture energy and the frictional energy in terms of rupture processes a power law scaling of the fracture energy with final slip is observed over eight orders of magnitude in slip from a few microns to tens of meters

the lac troilus gold copper deposit northwestern quebec a possible archean porphyry system the lac troilus gold copper deposit is located approximately 120 km north of chibougamau quebec within the northeastern part of the evans frotet greenstone belt an archean bimodal supracrustal sequence of mafic to felsic volcanic flows and tuffs volcanic rocks in the vicinity of the deposit form an overturned sequence of porphyritic intermediate tuffs and flows and mafic lapilli tuffs these rocks were intruded post tilting by syn to late tectonic felsite and feldspar porphyry dikes and sills the bulk of the copper gold mineralization is hosted within a zone of in situ breccia along the contact between the intermediate and mafic volcanic rocks the lac troilus deposit has a drill indicated geologic resource totaling approximately 60 million metric tons containing over 2 5 million oz gold 3 million oz silver and 60 000 metric tons copper mineralization consists of 2 to 3 percent sulfides with localized areas of up to 7 percent sulfides the sulfides are principally chalcopyrite pyrite and pyrrhotite with rare sphalerite the sulfides form disseminations tiny veinlets and narrow semimassive seams and are controlled by both foliation and fractures gold generally occurs as electrum although native gold and calaverite have been recognized the electrum occurs as discrete grains generally from 20 to 100 mu m in diameter along sulfide grain boundaries and along fractures within the sulfides the lac troilus deposit shows strong mineral and chemical zonation the core area of wall rock alteration characterized by a zone of strong biotite alteration is centered on a large felsic dike situated in the immediate structural footwall to the deposit moving outward there is a decrease in the intensity of biotite alteration and an increase in plagioclase epidote and calcite alteration data currently available indicate that the zonation is asymmetric and is best developed upward into the hanging wall chemical zonation is indicated by strong potassium enrichment in the footwall which grades into a more sodium enriched zone in the hanging wall calcium is depleted in all altered rocks adjacent to the copper gold mineralization the copper and iron sulfide minerals and gold show similar zoning patterns the core area is characterized by a chalcopyrite pyrrhotite rich assemblage proceeding toward the structural hanging wall there is a gradual decrease in chalcopyrite and pyrrhotite contents and a relative increase in pyrite the potassic footwall rocks are primarily copper bearing whereas the hanging wall sodium enriched rocks tend to be gold rich and copper poor the zone of brecciation which has both sodium and potassium enrichment is both gold and copper rich considering the size and nature of the wall rock alteration zones the metal zoning grades and characteristics of the host rocks the lac troilus deposit is similar to and may have formed in a manner analogous to porphyry copper gold deposits in the phanerozoic such as island copper in british columbia

shallow slip deficit due to large strike slip earthquakes in dynamic rupture simulations with elasto plastic off fault response summary slip inversions of geodetic data from several large magnitude 7 strike slip earthquakes point to coseismic slip deficit at shallow depths 3 4 km that is coseismic slip appears to decrease towards the earth surface while the inferred slip distribution may be consistent with laboratory derived rate and state friction laws suggesting that the uppermost brittle crust may be velocity strengthening there remains a question of how the coseismic slip deficit is accommodated throughout the earthquake cycle the consequence of velocity strengthening fault friction at shallow depths is that the deficit of coseismic slip is relieved by post seismic afterslip and interseismic creep however many seismic events with inferred shallow slip deficit were not associated with either resolvable shallow interseismic creep or robust shallow afterslip hence the origin of shallow slip deficit remains uncertain in this study we investigate whether inelastic failure in the shallow crust due to dynamic earthquake rupture can explain the inferred deficit of shallow slip evidence for such failure is emerging from geologic seismic and geodetic observations we find that the amount of shallow slip deficit is proportional to the amount of inelastic deformation near the earth surface such deformation occurs under a wide range of parameters that characterize rock strength in the upper crust however the largest magnitude of slip deficit in models accounting for off fault yielding is 2 4 times smaller than that inferred from kinematic inversions of geodetic data to explain this discrepancy we further explore to what extent assumptions in the kinematic inversions may bias the inferred slip distributions inelastic deformation in the shallow crust reduces coseismic strain near the fault introducing an additional artificial deficit of up to 10 per cent of the maximum slip in inversions of geodetic data that are based on purely elastic models the largest magnitude of slip deficit in our models combined with the bias in inversions accounts for up to 25 per cent of shallow slip deficit which is comparable but still smaller than 30 60 per cent deficit inferred from kinematic inversions we discuss potential mechanisms that may account for the remaining discrepancy between slip deficit predicted by elasto plastic rupture models and that inferred from inversions of space geodetic data

the brittle plastic transition in experimentally deformed quartz aggregates deformation experiments have been conducted to provide constraints on the processes responsible for the brittle plastic transition in quartz aggregates a correlation between mechanical behavior and distinctive microstructural characteristics indicates that the brittle plastic transition in nonporous quartzite involves at least three transitions in deformation mechanism that occur with increasing temperature and or pressure first there is a transition from cataclastic faulting to semibrittle faulting microstructural observations indicate that this transition occurs due to the activation of dislocations in addition faulting is more stable in the semibrittle faulting regime due to the blunting of the stresses at the advancing fault tip by dislocation glide second there is a transition from semibrittle faulting to semibrittle flow this transition corresponds to a change from localized to distributed deformation microstructural observations indicate that microcracks nucleate in response to stress concentrations at dislocation pileups in the semibrittle flow regime we conclude that the transition to semibrittle flow occurs when the stress intensity at crack tips is insufficient to allow propagation across grain boundaries third there is a transition from semibrittle flow to dislocation creep microstructural observations suggest that this transition occurs as a result of an increase in grain boundary mobility with increasing temperature in addition microstructural observations indicate that a transition from dominantly mode i axial to mode ii shear microcracking occurs with an increase in confining pressure from 0 4 to 0 8 gpa regardless of temperature the differential stresses supported by the experimentally deformed samples are higher than those expected under geologic conditions however a comparison of the experimentally produced microstructures to those reported from natural fault zones suggests that similar processes are operative in the laboratory and in the earth the results of this study provide further evidence to indicate that the brittle plastic transition in the continental crust occurs over a relatively wide range of conditions

fault roughness at seismogenic depths from lidar and photogrammetric analysis fault surface roughness is a principal factor influencing earthquake mechanics and particularly rupture initiation propagation and arrest however little data currently exist on fault surfaces at seismogenic depths here we investigate the roughness of slip surfaces from the seismogenic strike slip gole larghe fault zone exhumed from ca 10 km depth the fault zone exploited pre existing joints and is hosted in granitoid rocks of the adamello batholith italian alps individual seismogenic slip surfaces generally show a first phase of cataclasite production and a second phase with beautifully preserved pseudotachylytes of variable thickness we determined the geometry of fault traces over almost five orders of magnitude using terrestrial laser scanning lidar ca 500 to 1 10 m is not anisotropic and less evolved than at smaller scales these observations are consistent with an evolution of roughness due to fault surface processes that takes place only at scales smaller or comparable to the observed net slip differences in roughness evolution between shallow and deeper faults the latter showing evidences of seismic activity are interpreted as the result of different weakening versus induration processes which also result in localization versus delocalization of deformation in the fault zone from a methodological point of view the technique used here is advantageous over direct measurements of exposed fault surfaces in that it preserves in cross section all of the structures which contribute to fault roughness and removes any subjectivity introduced by the need to distinguish roughness of original slip surfaces from roughness induced by secondary weathering processes moreover offsets can be measured by means of suitable markers and fault rocks are preserved hence their thickness composition and structural features can be characterised providing an integrated dataset which sheds new light on mechanisms of roughness evolution with slip and concomitant fault rock production

strength characteristics of the r f and c slip systems in calcite abstract numerical modelling of crystallographic preferred orientation or texture development in plastically deformed materials requires specification of all potential slip and twinning systems and their relative strengths or critical resolved shear stresses crrs it is widely believed that the most important intracrystalline deformation systems in calcite are twinning on e 1 018 40 4 1 slip on r 10 1 4 2 021 and slip on f 1 012 2 2 01 the superscripted signs indicating slip sense it is these systems which have been used in modelling texture development in calcite polycrystals to date however modelling has been limited by insufficient and partly conflicting data on the relative strengths of the various slip and twinning systems in calcite deformation experiments on calcite single crystals performed by us in recent years taken together provide new data for a more complete and consistent quantification of the strength properties of the calcite glide systems in our experiments single crystals of calcite were compressed in both the 4041 and 2243 orientations at temperatures and constant strain rates in the range 300 800 c and 3 10 4 3 10 8 s 1 respectively the stress strain curves obtained mostly show two yield points slip line analysis shows that these yield points are related to the onset of macroscopically observable slip first on an r 2 021 system and then on an f 10 1 1 or c a system the latter two systems dominate at higher temperature 600 c at strain rate 3 10 5 s 1 and have not been taken into account in any texture modelling so far with increasing absolute temperature tabs calculated crss values c for the r f and c systems decrease in a manner which can be described by empirical power law functions of the type c a tabs b where b r 2 021 and f 10 1 1 systems the yield stresses for r 2 021 and f 10 1 1 slip were found to be rather insensitive to strain rate with conventional power law stress exponents 12 comparing the present results with previous data we conclude that two regimes of slip system activity exist namely a low temperature regime involving e twinning slip on r 2 021 and on f 2 2 01 positive direction not reported and a high temperature regime with r 2 021 f 10 1 1 and c a slip this slip system transition occurs at t 400 c at strain rate 10 4 10 5 s 1 and is expected to be associated with one or more texture transitions the results point to a clear need for renewed texture modelling of calcite polycrystals

westward plasma drift in the midlatitude ionospheric f region in the midnight dawn sector in this paper we report the observations of a sharp ionospheric plasma velocity reversal boundary at subauroral latitudes during magnetic storms in the midnight dawn sector the zonal plasma drift was eastward poleward of the velocity boundary and became westward equatorward of the boundary the latitudinal extent of the westward drifts was 20 a local maximum of the drift occurred only 2 5 below the boundary the magnitude of the maximum velocity was 200 400 m s 1 between 2100 and 0300 local time lt and as high as 780 m s 1 near midnight the large westward plasma drift immediately equatorward of the velocity boundary first occurred at 2100 lt and continuously extended across midnight to the dawn sector the location of the maximum velocity coincided with the minimum density within the midlatitude ionospheric trough the latitude of the velocity boundary decreased from geographic latitude 53 to 43 corresponding to geomagnetic latitude 65 to 55 between 2100 and 0800 lt we propose that the large westward drift at subauroral latitudes is driven by the polarization jet electric fields in the ring current and that the lower latitude westward drift with moderate magnitude is caused by the disturbance wind dynamo

the effects of porosity on the brittle ductile transition in sandstones sandstones with porosities of 6 0 13 9 19 9 20 9 22 and 27 6 were deformed under triaxial conditions either as whole core samples or 35 sawcut samples at confining pressure conditions of 0 1 5 10 30 50 70 90 110 and 130 mpa whole cores exhibited three types of deformational behavior 1 thoroughgoing shear fractures 2 brittle ductile transitional behavior characterized by cataclastic shear zones and 3 pervasive ductile cataclastic flow sawcut cores exhibited either 1 brittle behavior accomplished by reactivation of the sawcut or by the development of a crosscutting shear fracture or 2 penetrative ductile cataclastic flow which obliterated the sawcut the 35 sawcut cores lack the development of multiple shear zones associated with transitional brittle ductile behavior in whole cores the brittle ductile boundary in both sawcut and whole cores occurs at similar confining pressures and is dependent upon initial porosity of the sandstone increasing the confining pressure has the effect of shifting the brittle ductile boundary to lower porosities a comparison of frictional strengths and fracture strengths confirms byerlee s 1968 observation that the change from brittle to ductile behavior is related to frictional properties of the material

characterization of nucleation during laboratory earthquakes 1 we observe the nucleation phase of in plane ruptures in the laboratory we show that the nucleation is composed of two distinct phases a quasi static and an acceleration stage followed by dynamic propagation we propose an empirical model which describes the rupture length evolution the quasi static phase is described by an exponential growth while the acceleration phase is described by an inverse power law of time the transition from quasi static to accelerating rupture is related to the critical nucleation length which scales inversely with normal stress in accordance with theoretical predictions and to a critical surfacic power which may be an intrinsic property of the interface finally we discuss these results in the frame of previous studies and propose a scaling up to natural earthquake dimensions

identification of substorm expansive phase onsets 1 over the years many different particle and electromagnetic signatures have been invoked to identify the onset of what is called a substorm in this paper i shall first clarify what is generally meant by the term substorm onset and i shall show that some disturbances identified as substorm onsets should be treated with care i shall review the substorm in terms of its two recognized characteristic components directly driven and storage release i shall then discuss the importance of pseudobreakups in deciding what constitutes a legitimate substorm onset and in doing so will illustrate the subjective nature of present substorm onset identification techniques i shall stress that substorm like disturbances can take place both near the equatorward edge of the midnight sector oval mapping to the near earth magnetotail inside 12 re and near the poleward edge of the evening sector oval mapping to regions much farther downtail i shall present case studies that illustrate that some poleward edge disturbances have magnetic and auroral signatures that may be incorrectly interpreted as legitimate expansive phase onsets on the basis of this study i suggest that what may appear to be a lengthy series of closely spaced expansive phases may in fact be a single expansive phase followed by an arbitrarily long period of poleward border activity

earthquake nucleation on rough faults earthquake nucleation is currently explained using rate and state stability analysis which successfully models the behavior of laboratory simulated faults with constant thickness gouge layers however roughness is widely observed on natural faults and its influence on earthquake nucleation is little explored here we conduct frictional sliding experiments with different roughness on granite samples at upper crustal conditions 30 200 mpa we observe a wide range of behaviors from stable sliding to stick slip depending on the combination of roughness parameters and normal stress stick slip is repeatedly observed in velocity strengthening regimes and increases in normal stress stabilize slip these features are not fully predicted by current stability analysis we derive a new instability criterion that matches our observations based on fracture energy considerations and the size of weak patches created by fault roughness

large scale porphyry type mineralization in the central asian metallogenic domain a review abstract a series of porphyry type cu mo au deposits including some giant world class deposits such as kounrad aktogai kal makyr oyu tolgoi and chalukou occur in the central asian metallogenic domain camd the outline of the camd almost overlaps with that of the central asian orogenic belt caob which is located between the east europe siberia tarim and north china cratons the camd comprises sparsely exposed tectonic slices of precambrian high grade metamorphic basement rocks that are sandwiched between phanerozoic accretionary complexes and arc rocks according to geological metallogenic geochronological and tectonic setting characteristics the camd comprises three metallogenic provinces 1 the kazakhstan cu au mo 2 the mongolia cu au and 3 the northeast china mo cu metallogenic provinces early paleozoic 490 to 440 ma and late paleozoic 330 to 295 ma large scale porphyry type mineralization in the kazakhstan metallogenic province is intimately associated with the evolution of the central tianshan yili northern tianshan kokchetav chingiz paleozoic arc system which was terminated by the late permian closure of the western segment of the paleo asian ocean in contrast the 370 ma and 240 ma porphyry type mineralization of the mongolia metallogenic province is related to the tuva mongolia arc collage system that was formed during the evolution of the paleo asian ocean in the paleozoic and the mongol okhotsk ocean in the early mesozoic furthermore the northeast china metallogenic province was affected by three distinct geodynamic processes that were associated with the paleo asian mongol okhotsk and paleo pacific oceans during the paleozoic 250 ma the early mesozoic 200 ma and the late mesozoic 200 90 ma respectively except for the early paleozoic cu mineralization at duobaoshan 480 ma and bainaimiao 440 ma the porphyry type mineralization of this metallogenic province is predominantly characterized by widespread mesozoic mo mineralization in general porphyry type deposits of the camd have geological structural metallogenic alteration and fluid characteristics which are consistent either with those related to the oceanic subductional arc settings of the circum pacific metallogenic domain or with those of the continental collisional environment in the tethyan metallogenic domain the involvement of highly oxidized intermediate to felsic magmas is fundamental for the formation of porphyry deposits even though the prevalent mash and slab melting models can be employed to interpret the genesis of some porphyry cu deposits in the camd a here newly suggested model which is based on pre enriched mafic lower crust and the subduction of a relictic mid oceanic ridge is thought to explain the large scale copper mineralization in the balkhash west junggar metallogenic belt of the kazakhstan metallogenic province nevertheless most of the porphyritic suites associated with the mo deposits in the northeast china metallogenic province have relatively depleted mantle like neodymium and hafnium isotopic compositions suggesting that the ore forming granitic magma may have predominantly been derived from juvenile lower crust upwelling of asthenosphere may have triggered the melting of the lower crust during post collisional extension subsequent to the closure of the paleo asian ocean in the triassic the subduction of the paleo pacific ocean in the jurassic and the thinning of the lithosphere caused by rollback of the paleo pacific plate in the cretaceous ancient crustal components were only locally found to have been involved in the magma source of several medium large mo deposits

prospectivity of mesoproterozoic magmatism in the northern karbi hills ne india for porphyry copper mineralization abstract the kuthori porphyry copper prospect in the mesoproterozoic kaziranga magmato sedimentary domain of the northern karbi hills of shillong plateau ne india is a recently discovered granitoid hosted cu fe s occurrence we present here a preliminary geological account to appraise the petrography geochronology and bulk geochemistry of the occurrence and propose a geological model for copper mineralization in the precambrian granitiods of karbi hills these largely anorogenic a type granitoids show evidences of multiple injections of magma of varying compositions ranging from granite granodiorite quartz monzonite the granitoids have undergone hydrothermal alteration resulting in the development of alteration mineral zones characterized by a central zone of potassic alteration containing quartz k feldspar biotite sericite followed by phyllic and argillic alteration showing typomorphic mineral growth away from the central alteration zone the granitoids have wide range of silica contents 54 69 73 07 are dominantly metaluminous and calc alkaline contain high total alkalis and fe rich biotite and show high abundances of y nb zr high feo feo mgo ratios and low cao mgo and sr abundances the incompatible trace element distribution pattern positive zircon ehf t 3 2 to 9 7 initial whole rock 87sr 86sr ratio 0 703 and sulphide minerals with 34s 32s ratio 4 5 0 05 indicate magma and sulphide derivation from an enriched mantle source at varying temperatures 828 c 688 c the overall evidence suggests that granitoid magma production and emplacement took place in postcollision back arc basin creating avenues for ore deposition due to a rapid diapiric rise of magma sudden decrease in pressure and temperature resurgent boiling marked by crackle brecciation and increase in the oxidation state of magma

plastic instabilities implications for the origin of intermediate and deep focus earthquakes adiabatic or catastrophic plastic shear has been reported in metals polymers and metallic glasses the phenomenon is associated with rapid stress drops and audible pings or clicks as the material deforms in a plastic manner the driving force for the plastic instability is the stored elastic strain energy of the loading system and in many respects the behavior is reminiscent of the shear stress response arising from stick slip events during unstable frictional sliding although the precise mechanism is different it is shown here that adiabatic plastic shear is capable of explaining the detailed distribution of intermediate and deep focus earthquakes within subduction zones the earthquake events being the result of instabilities in material undergoing plastic flow it is argued that for a particular strain rate there exists a critical temperature tc which is depth dependent for temperatures below tc the material is strain rate softening and for a soft enough loading system may undergo catastrophic plastic shear for temperatures above tc the material is strain rate hardening and is always stable during plastic shear the cutoff depth for deep focus earthquakes then corresponds to the transition from strain rate softening to strain rate hardening material and for commonly accepted geothermal gradients within the slab corresponds to approximately 800 km the precise distribution of earthquakes within the slab is a function of the subtle interplay between the geothermal gradient and the tc gradient in particular a decrease in seismic activity is to be expected below about 300 km in the slab with total stress drops decreasing from a maximum of 700 mpa above 300 km to a maximum of 50 mpa below 300 km the differences in foci distribution between subduction zones such as tonga new hebrides and peru result from minor differences in the geothermal gradients within the slabs the model predicts the development of triple seismic zones high in the slab double seismic zones down to approximately 300 km and single seismic zones down to 800 km such a distribution is to be expected of relatively young cool slabs as the slab heats up the seismic activity retreats up the slab the paper only proposes a deformation mechanism for earthquake generation it does not address the stress field within the slab but only the distribution of strength thus the distribution of focal plane mechanisms is not considered only the locations where earthquakes due to plastic instabilities are possible the absence of earthquakes does not necessarily mean that the slab does not exist it only means that the slab is too hot to undergo plastic instability this means that aseismic subduction is a distinct possibility in many regions of high geothermal gradient within the slab i e circa 3 c km 1

effects of load point velocity on frictional instability behavior abstract triaxial experiments were conducted on sawcut westerly granite specimens sandwiched with a simulated gouge layer of ultrafine quartz over a wide range of normal stresses from 25 to 250 mpa tens and sometimes hundreds of repeated stick slip events were observed to persist over a total slip displacement up to 10 mm a transition from stick slip to stable sliding was observed as the result of cumulative slip displacement the total slip displacement over which repeated stick slip instabilities occurred before the transition to stable sliding decreases with increasing normal stress the stress drop amplitude decreases with increasing load point velocity the experimentally determined stress drop amplitude was also found to increase as a function of the time of stationary contact the dependence of stress drop amplitude on load point velocity and on time of stationary contact can be characterized empirically by a power law preliminary data suggest that the two effects are coupled the seismological implications of the experimental data are discussed at relatively high normal stresses above 250 mpa no systematic dependence of stress drop amplitude on load point velocity was observed an increase in gouge particle size stabilizes the frictional instability behavior a mixed mode of velocity weakening and velocity strengthening behavior was occasionally observed

thermal decomposition of carbonates in fault zones slip weakening and temperature limiting effects 1 during an earthquake the heat generated by fault friction may be large enough to activate the devolatilization of minerals forming the fault rocks in this paper we model the mechanical effects of calcite thermal decomposition on the slip behavior of a fault zone during an earthquake to do so we introduce the coupled effects of calcite volume loss heat consumption and co2 production in the theoretical analysis of shear heating and thermal pressurization of pore fluids we consider a rapidly deforming shear band consisting of a fluid saturated carbonate rock the equations that govern the evolution of pore pressure and temperature inside the band and the mass of emitted co2 are deduced from the mass and energy balance of the multiphase saturated medium and from the kinetics of the chemical decomposition of calcite numerical simulation of seismic slip at depths of 5 to 8 km show that decarbonation has two critical consequences on fault slip first the endothermic reaction of calcite decomposition limits the coseismic temperature increase to less than 800 c corresponding to the initiation of the chemical reaction inside the shear band second the rapid emission of co2 by decarbonation significantly increases the slip weakening effect of thermal pressurization the pore pressure reaches a maximum and then decreases due to the reduction of solid volume causing a restrengthening of shear stress our theoretical study shows on the example of decarbonation that the thermal decomposition of minerals is an important slip weakening process and that a large part of the frictional heat of earthquakes may go into endothermic devolatilization reactions

frictional properties of simulated anhydrite dolomite fault gouge and implications for seismogenic potential the frictional properties of anhydrite dolomite fault gouges and the effects of co2 upon them are of key importance in assessing the risks associated with co2 storage in reservoir formations capped by anhydrite dolomite sequences and in understanding seismicity occurring in such formations such as the italian apennines therefore we performed velocity stepping direct shear experiments on simulated dolomite anhydrite and 50 50 anhydrite dolomite gouges at representative in situ conditions 120 c and ne 25 mpa they were conducted under vacuum or else using water or co2 saturated water as pore fluid pf 15 mpa friction coefficients varied between 0 55 and 0 7 all dry samples exhibited velocity weakening behavior whereas all wet samples exhibited velocity strengthening behavior without or with co2 this is consistent with trends previously reported for such gouges a compilation of literature data shows that the transition from velocity strengthening to velocity weakening occurs in these materials between 80 and 120 c when dry and between 100 and 150 c when wet this implies little seismogenic potential for wet dolomite anhydrite and mixed gouges under co2 storage conditions at 2 4 km depth seismic slip in the italian apennines at depths of 6 km and beyond may be explained by the velocity weakening behavior expected in anhydrite and especially dolomite at temperatures above 150 c

structural controls on the archean troilus gold copper deposit quebec canada the troilus gold copper deposit is a low grade high tonnage resource hosted in archean calc alkaline intrusive rocks in the superior province of quebec it is best known for being one of the few archean analogues of a porphyry cu au deposit an interpretation with significant implications for both mineral exploration and theories of archean plate tectonics recent research presented here has called into question the prevalent genetic model and proposes instead a two stage history of mineralization controlled by contrasting structural regimes developed as part of an orogen disseminated gold copper mineralization and associated potassic alteration occur in a deformation corridor between two felsic dikes emplaced prior to the peak of regional metamorphism postpeak metamorphic high strain sericitic zones with silicified envelopes host quartz veins and a second phase of gold the present size grade and disposition of the orebody is the result of the superposition of these two events an interpretation that impacts on the genetic model as well as exploration exploitation and grade control

why large earthquakes do not nucleate at shallow depths although by definition tectonic earthquakes may nucleate anywhere within the seismogenic layer in almost all cases those earthquakes that become large nucleate near the base of the seismogenic layer because frictional strength and stress drop should increase with depth and in situ stress measurements suggest that the ambient stress increases with depth we have examined spontaneous rupture models with gradients of both average stress drop and average strength relative to ambient stress to determine whether this explains the observed phenomena we report here that ruptures that are nucleated with in the low stress drop shallow regions of the model are inhibited from propagating but those that are nucleated within the high stress drop regions can propagate over the entire fault plane

earthquakes in the ductile regime pseudotachylytes from a crustal scale shear zone in central australia have developed in a cyclical manner once developed an individual pseudotachylyte is deformed in a ductile manner only to be overprinted at a later stage by a new generation of pseudotachylytes such cyclic generation and deformation of pseudotachylyte has been interpreted in the past as representing conditions at the brittleductile transition a different interpretation however is presented here it is proposed that psuedotachylytes and associated ultramylonites can develop entirely within the ductile regime as ductile instabilities such instabilities are different in nature to those previously discussed at length in the geophysical literature but are identical in principle with the instabilities that develop for velocity weakening frictional behavior in spring slider systems at a given strain rate a critical temperature tc is defined at which the transient work hardening equals the product of stress relaxation due to a thermal fluctuation and the heat generated by shearing a necessary condition for ductile instability at a given strain rate is that the temperature is belowtc then the rate of change of stress with respect to strain is negative an additional requirement is that this rate of change exceeds in magnitude the effective elastic stiffness of the loading system ductile instabilities are marginally possible at geological strain rates in quartzites but are possible at mid crustal temperatures in other rock types on the basis of these observations a new interpretation is presented for the base of the seismogenic zone in crustal regions

damage and recovery of calcite rocks deformed in the cataclastic regime compressional and shear wave velocities have been measured during the experimental deformation of carrara marble and solnhofen limestone in the cataclastic regime both in dry and wet conditions at room temperature measurements were performed under hydrostatic conditions up to 260 mpa confining pressure and 10 mpa pore pressure during triaxial loading at the constant strain rate of 10 s as well as during differential stress relaxation during a full cycle our results show that the seismic velocities first increase as effective mean stress increases however when the stress onset of cataclastic deformation was reached elastic velocities showed rapid decrease due to stress induced damage in the rock during stress relaxation tests we observed an increase of elastic velocities with time which suggested a fast recovery of the microstructure a substantial and rapid drop in the velocities occurred when reloading suggesting that the previous recovery was only transient subsequent relaxation tests showed other marked increases in velocities these experimental results suggest that during the deformation of low porosity calcite rich rocks dilatant crack opening and frictional sliding and compaction micromechanism pore closure compete evolutions of elastic properties mainly sensitive to crack density and macroscopic volumetric strain more sensitive to porosity are therefore not systematically correlated and depend on the strain rate the solid stress conditions and the

first observations of the temporal spatial variation of the sub auroral polarization stream from the superdarn wallops hf radar 1 in this letter we present the first two dimensional observations of sub auroral ion drift said variability within the sub auroral polarization stream saps using a new mid latitude superdarn radar located at wallops island va the radar data are complemented with observations from the dmsp f15 timed and noaa 18 spacecraft to confirm that a backscatter feature observed at the equatorward edge of the auroral oval is a manifestation of saps said during a several hour long period on august 6 2005 the velocity data indicate that significant changes in the saps flow occurred on time scales of a few minutes the wallops hf radar observations demonstrate that the saps phenomenon is a source of small scale irregularities extending over many hours of mlt and that the electric fields associated with said in particular are highly variable

a statistical study of the subauroral polarization stream over north american sector using the millstone hill incoherent scatter radar 1979 2019 measurements this work conducts a statistical study of the subauroral polarization stream saps feature in the north american sector using millstone hill incoherent scatter radar measurements from 1979 to 2019

strong velocity weakening and powder lubrication of simulated carbonate faults at seismic slip rates 1 high velocity friction tests were conducted on solid and hollow cylinders of carrara calcite marble dolomite marble silicate bearing calcite marble and calcite gouge to investigate the strength of carbonate faults during seismic slip the experiments performed at normal stresses of 0 6 14 7 mpa slip rates of 0 03 1 60 m s and room temperature in a rotary shear friction testing machine yielded an extraordinarily low steady state friction coefficient 0 1 at slip rates of 1 1 1 2 m s the slip weakening distance of 4 28 m became shorter at higher normal stress or frictional work rate strong velocity weakening was observed not only in steady state but also in nonsteady state friction while the slip rate was changing thus slip deceleration was accompanied by fault strength recovery large rapid temperature rises in narrow shear localization zones less than a few micrometers induced carbonate decomposition such as the breakdown of calcite into aggregates of cao nanograins and co2 in carrara marble scanning electron microscope observation revealed that the shear localization zone in the highly porous decomposition product was a layer of scattered small grains mostly 1 m in diameter these microstructures and the measured high permeability 10 14 m2 of the decomposed marble indicate that the dominant weakening mechanism in our experiments was possibly powder lubrication powder rheology at high slip rates is not yet well understood but the frictional behavior of nanograins appears to be strongly velocity dependent if decarbonation occurs during seismic slip in natural carbonate faults powder lubrication may make the faults slippery even under fluid drained conditions

the 2009 l aquila central italy mw6 3 earthquake main shock and aftershocks 1 a m w 6 3 earthquake struck on april 6 2009 the abruzzi region central italy producing vast damage in the l aquila town and surroundings in this paper we present the location and geometry of the fault system as obtained by the analysis of main shock and aftershocks recorded by permanent and temporary networks the distribution of aftershocks 712 selected events with m l 2 3 and 20 with m l 4 0 defines a complex 40 km long nw trending extensional structure the main shock fault segment extends for 15 18 km and dips at 45 to the sw between 10 and 2 km depth the extent of aftershocks coincides with the surface trace of the paganica fault a poorly known normal fault that after the event has been quoted to accommodate the extension of the area we observe a migration of seismicity to the north on an echelon fault that can rupture in future large earthquakes

earthquake nucleation on rate and state faults aging and slip laws we compare 2 d quasi static earthquake nucleation on rate and state faults under both aging and slip versions of the state evolution law for both versions mature nucleation zones exhibit 2 primary regimes of growth well above and slightly above steady state corresponding respectively to larger and smaller fault weakening rates well above steady state aging law nucleation takes the form of accelerating slip on a patch of fixed length this length is proportional to b 1 and independent of a where a and b are the constitutive parameters relating changes in slip speed and state to frictional strength under the slip law the nucleation zone is smaller and continually shrinks as slip accelerates the nucleation zone is guaranteed to remain well above steady state only for values of a b that are low by laboratory standards near steady state for both laws the nucleation zone expands the propagating front remains well above steady state giving rise to a simple expression for its effective fracture energy g c this fracture energy controls the propagation style for the aging law g c increases approximately as the square of the logarithm of the velocity jump this causes the nucleation zone to undergo quasi static crack like expansion to a size asymptotically proportional to b b a 2 for the slip law g c increases only as the logarithm of the velocity jump and crack like expansion is not an option instead the nucleation zone grows as an accelerating unidirectional slip pulse under both laws the nucleation front propagates at a velocity larger than the slip speed by roughly b divided by the logarithm of the velocity jump where is the effective elastic shear modulus for this prediction to be consistent with observed propagation speeds of slow slip events in subduction zones appears to require effective normal stresses as low as 1 mpa

spherical cap harmonic analysis of super dual auroral radar network superdarn observations for generating maps of ionospheric convection 1 a spherical cap harmonic analysis scha technique is introduced for mapping the 2 d high latitude ionospheric convection pattern based on super dual auroral radar network superdarn velocity measurements the current method for generating such maps is the fit technique which generates global scale maps over the entire convection region this is accomplished by combining observations with a statistical model to prevent unphysical solutions in areas away from the observation points and by forcing the plasma flow to zero at the low latitude boundary of the convection zone both constraints distort the mapped convection and require a preconception of where the plasma flow lines should close by focusing on mapping the convection over a region well covered by velocity observations the scha technique is freed of these constraints and more accurately reproduces local convection we generate large scale convection maps from superdarn data for various interplanetary magnetic field imf conditions during periods of widespread radar coverage to show the patterns are consistent with expectations for various imf configurations we validate the scha maps by comparing them with the 2 d ion drifts measured by the dmsp satellites and with the 2 d convection vectors obtained by merging superdarn measurements at beam crossings the scha technique is shown to perform comparably to the fit technique over regions of good data coverage for limited data coverage and over regions of highly variable flow particularly near the equatorward edge of the mapping region the scha technique provides a better solution for mapping ionospheric convection based on superdarn radar observations

pseudotachylyte generated in the semi brittle and brittle regimes bench canyon shear zone central sierra nevada pseudotachylyte cuts cretaceous plutonic and volcanic rocks in the bench canyon shear zone central sierra nevada california as documented by optical and scanning electron microscopy the pseudotachylyte displays evidence for a friction melt origin including vesicles amygdules crystallites flow fabrics and embayed crystal fragments based on fault related rock association vein morphology and inferred crustal level of generation two distinct types of pseudotachylyte are documented in the shear zone pseudotachylyte associated with cataclasite was generated at shallow crustal levels 1 10 km via unstable velocity weakening abrasive wear friction pseudotachylyte associated and interlayered with mylonite was generated at deeper crustal levels 10 15 km most likely via stable velocity strengthening adhesive wear friction this pseudotachylyte underwent ductile deformation in the solid state interlayered pseudotachylyte and mylonite records cyclic aseismic seismic slip at a transitional crustal level between the semi brittle field of quartzofeldspathic rocks and the base of the seismogenic zone the cyclicity is attributed to strain rate fluctuation effected by strain resistant phacoids pore fluid pressure variation ductile instabilities or downward fault propagation the mode of deformation within the shear zone progressed from i production of mylonite during amphibolite to greenschist facies conditions to ii generation of pseudotachylyte by intermittent seismic faulting within a background of aseismic shear in the upper realm of the semi brittle field 300 400 c to iii generation of pseudotachylyte through seismic events in the brittle 300 c during uplift exhumation and cooling some of the latter may have been generated at shallow enough crustal levels 4 km to allow vesicle formation the exhumation of a crustal level exposing such an assemblage provides a rare opportunity to study the enigmatic nature of the transitional change from semi brittle flow to seismogenic rupturing

spatio temporal evolution of aseismic slip along the haiyuan fault china implications for fault frictional properties article history we use 20 years of synthetic aperture radar acquisitions by the ers and envisat satellites to investigate the spatial and temporal variations of strain rates along the 35 km long creeping section of the haiyuan fault at the north eastern boundary of the tibetan plateau we then use the derived displacements to infer the fault s frictional properties and discuss the relationship between creep and the seismic behavior of the fault located in between a millennial seismic gap and the 1920 m8 surface rupture trace this section has an average creep rate of 5 1m m yr about the interseismic loading rate the comparison of average surface velocity profiles derived from sar interferometry across the creeping section reveals a creep rate increase and or a creep migration to shallower depth between the 1990s and the 2000s we apply a smoothed time series analysis scheme on envisat insar data to investigate the creep rate variations during the 2004 2009 time period our analysis reveals that the creep rate accelerated in 2007 although data resolution does not allow to better constrain the onset of creep acceleration and its amplitude both decadal and short term transient behaviors are coeval with the largest earthquakes m 4 5 along the fault segment in recent years from the precise mapping of the surface fault trace we use the fault strike variations and the mohr circle construction to compute the along strike distribution of the friction coefficient along the creeping segment and compare it with the observed distribution of the creep rate we find that the creep rate scales logarithmically with the friction coefficient in agreement with the rate and state friction law in a rate strengthening regime the estimated value of log v 2 10 3 indicates that the earthquakes occurring along the creeping section cannot be the cause for a significant change in the overall segment s creep rate and that the recorded micro seismicity is most likely creep driven finally given the size and frictional properties of the creeping section we estimate based on previous models of dynamic rupture simulations a 0 20 probability for a rupture to break through this section together with the geometrical configuration of the haiyuan fault these results suggest that the creeping segment may act as a persistent barrier to earthquake propagation

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

large earthquake nucleation associated with stress exchange between middle and upper crust earthquake nucleation and propagation can be explained using two basic concepts crustal strength and fault rheology despite numerous experimental and modeling studies the way in which a faulted crust generates a seismic cycle under loading is still controversial we discuss earthquake generation using a 2 d finite element model which includes relevant features of geodynamical problems such as rheological layering dynamic coulomb faulting and relative plate velocity the occurrence of a deep nucleation is explained by the strong viscosity drop at the base of the seismogenic layer without any transition of frictional properties of the fault rather viscosity contrast causes a stress transfer around the fault that reloads the fault plane during the postseismic phase we argue that this mechanism may explain the seismic cycle for large faults in the continental crust

slow rupture of an aseismic fault in a seismogenic region of central italy 1 slow earthquakes and afterslips prove that the earth does not have just two response time scales i e that of tectonic loading and that of regular earthquakes a swarm of slow earthquakes with time constants of the order of hundreds of seconds has been detected by a laser interferometer below the gran sasso massif italy we analyse and model these observations to identify a very plausible source in a local fault with no historic seismic behavior while slow earthquakes occurring in subduction zones and at the transition between locked and stably sliding segments of the san andreas fault are often associated with seismic events in the case of the apennines there is no correlation between local seismicity and slow earthquakes slow earthquakes therefore may also represent a specific failure behavior for a seismically locked fault adding further complexity to the interpretation of geologic data for seismic hazard estimates

off fault plasticity favors the arrest of dynamic ruptures on strength heterogeneity two dimensional cases we study the effects of a plastic behavior of the volume around the fault on in plane and anti plane 2d rupture dynamics both rupture modes exhibit similar answer to off fault yielding in terms of modification of the kinematics of the rupture front and in terms of energy lost outside the fault plane we then compare the ability of the rupture to propagate through a barrier on the interface the plastic behavior responsible for a linear increase of the global fracture energy during dynamic crack growth enhances the rupture front sensitivity to a static resistance increase on the fault consequently the rupture arrest is more easily provoked in heterogeneous models that include a plastic yielding even with relatively small variations of frictional resistance along the fault plane

a constitutive scaling law and a unified comprehension for frictional slip failure shear fracture of intact rock and earthquake rupture 1 it is widely recognized that some of the physical quantities inherent in a rupture are scale dependent and the scale dependence is one of the most no facts and features of rupture phenomena the paper addresses how such scale dependent shear rupture of a broad range from laboratory scale frictional slip failure and shear fracture of intact rock to field scale rupture as an earthquake source can be unified by a single constitutive law noting that the earthquake rupture is a mixed process between frictional slip failure and the shear fracture of intact rock it is concluded that the constitutive law for the earthquake rupture be formulated as a unifying law that governs both frictional slip failure and shear fracture of intact rock it is demonstrated that the slip dependent constitutive law is such a unifying law and a constitutive scaling law is derived from laboratory data on both frictional slip failure and shear fracture of intact rock this constitutive scaling law enables one to provide a consistent and unified comprehension for scale dependent physical quantities inherent in the rupture over a broad range from small scale frictional slip failure and shear fracture in the laboratory to large scale earthquake rupture in the field

average characteristics and activity dependence of the subauroral polarization stream 1 data from the millstone hill incoherent scatter radar taken over two solar cycles 1979 2000 are examined to determine the average characteristics of the disturbance convection electric field in the midlatitude ionosphere radar azimuth scans provide a regular database of ionospheric plasma convection observations spanning auroral and subauroral latitudes and these scans have been examined for all local times and activity conditions we examine the occurrence and characteristics of a persistent secondary westward convection peak which lies equatorward of the auroral two cell convection individual scans and average patterns of plasma flow identify and characterize this latitudinally broad and persistent subauroral polarization stream saps which spans the nightside from dusk to the early morning sector for all kp greater than 4 premidnight the saps westward convection lies equatorward of l 4 60 invariant latitude spans 3 5 of latitude and has an average peak amplitude of 900 m s in the predawn sector saps is seen as a region of antisunward convection equatorward of l 3 55 spanning 3 of latitude with an average peak amplitude of 400 m s

strain localization and the onset of dynamic weakening in calcite fault gouge abstract to determine the role of strain localization during dynamic weakening of calcite gouge at seismic slip rates single slide and slide hold slide experiments were conducted on 2 3 mm thick layers of calcite gouge at normal stresses up to 26 mpa and slip rates up to 1 m s 1 microstructures were analyzed from short displacement 35 cm experiments stopped prior to and during the transition to dynamic weakening in fresh calcite gouge layers dynamic weakening occurs after a prolonged strengthening phase that becomes shorter with increasing normal stress and decreasing layer thickness strain is initially distributed across the full thickness of the gouge layer but within a few millimeters displacement the strain becomes localized to a boundary parallel high strain shear band c 20 m wide during the strengthening phase which lasts between 3 and 30 cm under the investigated conditions the shear band broadens to become c 100 m wide at peak stress the transition to dynamic weakening in calcite gouges is associated with the nucleation of micro slip surfaces dispersed throughout the c 100 m wide shear band each slip surface is surrounded by aggregates of extremely fine grained and tightly packed calcite interpreted to result from grain welding driven by local frictional heating in the shear band by the end of dynamic weakening strain is localized to a single 2 3 m wide principal slip surface flanked by layers of recrystallized gouge calcite gouge layers re sheared following a hold period weaken nearly instantaneously much like solid cylinders of calcite marble deformed under the same experimental conditions this is due to reactivation of the recrystallized and cohesive principal slip surface that formed during the first slide reducing the effective gouge layer thickness to a few microns our results suggest that formation of a high strain shear band is a critical precursor to dynamic weakening in calcite gouges microstructures are most compatible with dynamic weakening resulting from a thermally triggered mechanism such as flash heating that requires both a high degree of strain localization and a minimum slip velocity to activate the delayed onset of dynamic weakening in fresh calcite gouge layers particularly at low normal stresses may inhibit large coseismic slip at shallow crustal levels in calcite bearing fault zones

mechanical behavior and microstructure of simulated calcite fault gouge sheared at 20 600 c implications for natural faults in limestones we report ring shear experiments on simulated calcite fault gouges performed at fixed temperatures t within the range from 20 to 600 c the experiments were performed wet using pore fluid pressures pf of 10 pf 60 mpa one series of experiments employed a constant effective normal stress neff of 50 mpa while in a second series neff was sequentially stepped from 30 to 100 mpa in all experiments sliding velocity v was stepped in the range from 0 03 to 100 m s the results showed stable velocity strengthening behavior at 20 c but velocity weakening at 100 to 550 c for all v steps to 3 m s which was frequently accompanied by stick slip at 600 c velocity strengthening occurred microstructural observations suggest increasing importance of ductile deformation with increasing temperature as reflected by a localized shear band structure at 20 c giving way to a pervasive shear plane parallel grain shape fabric at 600 c using existing flow equations for dense calcite polycrystals we show that dislocation and or diffusion creep of 10 30 m sized bulk gouge grains likely played a role in experiments performed at t 400 c we suggest that the observed velocity weakening behavior can be explained by a slip mechanism involving dilatant granular flow in competition with creep controlled compaction our results have important implications for the breadth of the seismogenic zone in limestone terrains and for the interpretation of natural fault rock microstructures specifically while samples sheared at 400 550 c exhibited essentially brittle frictional mechanical behavior stick slip the corresponding microstructures resembled that of a mylonite

a special issue devoted to abitibi ore deposits in a modern context preface the abitibi greenstone belt which is part of the larger abitibi subprovince in the superior province of the canadian shield e g card and ciesielski 1986 is the largest known archcan greenstonegranite terrane 300 km n s x 400 450 km mineral production and reserves are significant particularly in relation to volcanogenic massive sulfide deposits and structurally controlled archcan goldbearing quartz vein systems the term au quartz vein being used in the sense of lindgren 1933 e g the gold quartz veins of ontario p 662669 volcanogenie massive sulfide production and reserves to 1989 1990 total 424 million metric tons

large scale observations of a subauroral polarization stream by midlatitude superdarn radars instantaneous longitudinal velocity variations 1 we present simultaneous measurements of flow velocities inside a subauroral polarization stream saps made by six midlatitude high frequency superdarn radars the instantaneous observations cover three hours of universal time and six hours of magnetic local time mlt from velocity variations across the field of view of the radars we infer the local 2d flow direction at three different longitudes we find that the local flow direction inside the saps channel is remarkably constant over the course of the event the flow speed however shows significant temporal and spatial variations after correcting for the radar look direction we are able to accurately determine the dependence of the saps velocity on magnetic local time we find that the saps velocity variation with magnetic local time is best described by an exponential function the average velocity at 00 mlt was 1 2 km s and it decreased with a spatial e folding scale of two hours of mlt toward the dawn sector we speculate that the longitudinal distribution of pressure gradients in the ring current is responsible for this dependence and find these observations in good agreement with results from ring current models using tec measurements we find that the high westward velocities of the saps are as expected located in a region of low tec values indicating low ionospheric conductivities

frictional properties and microstructure of calcite rich fault gouges sheared at sub seismic sliding velocities we report an experimental and microstructural study of the frictional properties of simulated fault gouges prepared from natural limestone 96 caco3 and pure calcite our experiments consisted of direct shear tests performed under dry and wet conditions at an effective normal stress of 50 mpa at 18 150 c and sliding velocities of 0 1 10 m s wet experiments used a pore water pressure of 10 mpa wet gouges typically showed a lower steady state frictional strength 0 6 than dry gouges 0 7 0 8 particularly in the case of the pure calcite samples all runs showed a transition from stable velocity strengthening to potentially unstable velocity weakening slip above 80 100 c all recovered samples showed patchy mirror like surfaces marking boundary shear planes optical study of sections cut normal to the shear plane and parallel to the shear direction showed both boundary and inclined shear bands characterized by extreme grain comminution and a crystallographic preferred orientation cross sections of boundary shears cut normal to the shear direction using focused ion beam sem from pure calcite gouges sheared at 18 and 150 c revealed dense arrays of rounded 0 3 m sized particles in the shear band core transmission electron microscopy showed that these particles consist of 5 20 nm sized calcite nanocrystals all samples showed evidence for cataclasis and crystal plasticity comparing our results with previous models for gouge friction we suggest that frictional behaviour was controlled by competition between crystal plastic and granular flow processes active in the shear bands with water facilitating pressure solution subcritical cracking and intergranular lubrication our data have important implications for the depth of the seismogenic zone in tectonically active limestone terrains contrary to recent claims our data also demonstrate that nanocrystalline mirror like slip surfaces in calcite rich faults are not necessarily indicative of seismic slip rates

synvolcanic gold mineralization within a deformation zone the chevrier deposit chibougamau abitibi subprovince canada the chevrier gold deposit is located in the northeastern part of the abitibi subprovince within the chevrier volcanic centre cvc this calc alkaline volcanic centre evolved from mafic to felsic in a submarine environment and the chevrier deposit is spatially associated with the uppermost unit composed mostly of massive dacite to rhyolite dated at 2730 ma the chevrier deposit is divided in two zones the north zone is composed of high grade discordant quartz carbonate veins and disseminated pyrite mostly within melanocratic gabbro dykes whereas the south zone is within a low grade concordant pyrite envelope associated with quartz carbonate pyrite veinlets both zones are highly deformed and show strong carbonate sericite and chlorite alterations although these zones share many characteristics with orogenic deposits the crosscutting of the chevrier deposit by structures associated with the major deformation events suggests that mineralization was prior to these events furthermore felsic dykes associated with the formation of the cvc crosscut auriferous veins and zones therefore suggesting a synvolcanic timing for the gold mineralization characteristics of the zones such as similar vein composition and alteration mineral assemblages and location within the volcanic pile suggest that they are part of a single hydrothermal event where the south zone represents the shallower part of the deposit the chevrier deposit is classified as a noncarbonate hosted stockwork and disseminated deposit and shows many similarities with strata bound gold deposits of the andacollo mining district of chile dating of mineralization at the chevrier deposit indicates that the emplacement of gold occurred more than 25 ma before the onset of the orogeny affecting this part of the abitibi subprovince it also illustrates how synvolcanic mineralization can be misinterpreted as an orogenic deposit without the presence of crosscutting relationships with dykes faults or other structures

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

a superposed epoch study of superdarn convection observations during substorms 1 case studies of flow patterns during substorms have revealed characteristic patterns in the period leading to expansion onset velocities in the premidnight region have been observed to become strongly sheared and the premidnight convection reversal has been observed to extend across the midnight meridian at expansion onset the shear decreases and flow at midnight becomes meridional out of the polar cap the study presented here superposes flow patterns from 10 substorm intervals to determine the average flow patterns the study confirms the findings of the case studies and extends them to additional local time sectors in addition changes to the flow pattern after expansion onset are examined

geology of the archean intrusion hosted la grande sud au cu prospect la grande subprovince james bay region quebec the archean la grande and eastmain domains of the la grande subprovince in the james bay region of northwestern quebec are the focus of renewed and extensive exploration as a result of recent major discoveries made in this region e g 8 moz au roberto deposit a number of significant neoarchean au base metal occurrences are present in the la grande domain including the la grande sud au cu prospect zone 32 inferred resource of 4 2 million metric tons mt at 2 1 g t au and 0 2 wt cu the la grande sud au cu prospect is hosted in the 2734 2 ma synvolcanic la grande sud tonalite in the 2751 to 2732 ma yasinski group volcanic rocks the la grande sud tonalite is a synvolcanic calc alkaline intrusion emplaced in an arc like tectonomagmatic setting timing relationships in mineralized zones as well as associated hydrothermal alteration zones support a pre to early d 1 origin for at least a part of the mineralization in the la grande sud tonalite deformation events were responsible for the overprinting of the early mineralization by auriferous shear zone related systems associated with d 2 evidence for a pre d 2 and pre to early d 1 alteration and mineralization system includes 1 a broadly concentric pattern defined by the hydrothermal alteration assemblages within the la grande sud tonalite which suggests that the hydrothermal alteration was at least in part controlled by the geometry of the intrusion rather than by the d 2 deformation 2 the development of a weak biotite bearing potassic assemblage biotite epidote plagioclase muscovite calcite pyrite that is gradually replaced outward from the center of the intrusion by a chlorite bearing propylitic assemblage chlorite epidote muscovite plagioclase calcite pyrite and locally overprinted by a sericitic alteration assemblage muscovite quartz albite chlorite pyrite carbonate which represents the most intense alteration in the la grande sud tonalite 3 the presence of mineralized hydrothermal breccias along the margins of the intrusion 4 deformed disseminated and stockwork style au cu sulfide mineralization consisting of pyrite chalcopyrite tennantite arsenopyrite pyrrhotite bi sulfosalts and native au bi in the sericite chlorite and biotite facies alteration zones 5 s 1 parallel elongated tonalite clasts and sulfide veinlets in d 2 folded and transposed hydrothermal biotite breccias and 6 pyrite porphyroblasts that are elongated parallel to the s 1 fabric syn d 1 metamorphic recrystallization and that were folded during d 2 d 2 was associated with the development of conjugate auriferous extensional quartz tourmaline veins orogenic style veins that were superimposed on the pre to early d 1 intrusion hosted mineralized system gold in these syn to late d 2 veins could have been remobilized from preexisting mineralization disseminated sulfides or was related to a late syn d 2 auriferous hydrothermal event the intrusion hosted au mineralization of the la grande sud au cu prospect illustrates that archean synvolcanic intrusions regardless of their size can host a range of styles of alteration and mineralization including both early and late mineralizing systems

twenty years of paleoseismology in italy abstract italy has one of the most complete and historically extensive seismic catalogues in the world due to a unique and uninterrupted flow of written sources that have narrated its seismic history since about the end of the iron age seismic hazard studies have therefore always been mainly based upon this huge mass of data nevertheless the italian catalogue probably lacks many m 6 5 events the seismogenetic structures responsible for which are characterized by recurrence times that are longer than the time span covered by our historical sources for these reasons and as in other countries earthquake data that in italy have been derived from paleoseismological studies should finally become a necessary ingredient in seismic risk assessment indeed over the past 20 years some hundred trenches have been excavated supplying reliable and conclusive data on the recent activities of many faults through to many robust datings of surface fault events these studies have provided the ages of several unknown or poorly known m 6 5 earthquakes here we summarize the state of the art of paleoseismology in italy and present a first catalogue of 56 paleoearthquakes pci that occurred mainly in the past 6 kyr the pci integrates the historical instrumental seismic catalogue and extends it beyond the recurrence time of the seismogenetic faults 2000 1000 yr we feel confident that the use of the pci will enhance future probabilistic seismic hazard assessment and thus contribute to more reliable seismic risk mitigation programs

dynamic weakening and amorphization in serpentinite during laboratory earthquakes the mechanical properties of serpentinites are key factors in our understanding of the dynamics of earthquake ruptures in subduction zones especially intermediate depth earthquakes here we performed shear rupture experiments on natural antigorite serpentinite which showed that friction reaches near zero values during spontaneous dynamic rupture propagation rapid coseismic slip 1 m s although it occurs over short distances 1 mm induces significant overheating of microscale asperities along the sliding surface sufficient to produce surface amorphization and likely some melting antigorite dehydration occurs in the fault walls which leaves a partially amorphized material the water generated potentially contributes to the production of a low viscosity pressurized melt explaining the near zero dynamic friction levels observed in some events the rapid and dramatic dynamic weakening in serpentinite might be a key process facilitating the propagation of earthquakes at intermediate depths in subduction zones

dynamic subauroral ionospheric electric fields observed by the falkland islands radar during the course of a geomagnetic storm ion drift said located between 53 and 58 magnetic south and lasting 6 5 hours was observed by the falkland islands radar in the pre midnight sector coincident flow data from the dmsp satellites and the magnetically near conjugate northern hemisphere blackstone hf radar reveal that the said was embedded within the broader subauroral polarization streams saps dmsp particle data indicate that the said location closely followed the equatorward edge of the auroral electron precipitation boundary while remaining generally poleward of the equatorward boundary of the ion precipitation the latitude of the said varied throughout the interval on similar timescales to variations in the interplanetary magnetic field and auroral activity while variations in its velocity were more closely related to ring current dynamics these results are consistent with said electric fields being generated by localized charge separation in the partial ring current but suggest that their location is more strongly governed by solar wind driving and associated large scale magnetospheric dynamics

geology and gold molybdenum porphyry mineralisation of the archean taschereau launay plutons abitibi quebec abstract porphyry gold deposits constitute a new challenge for mineral exploration in archean greenstone belts yet the relationships between intrusive rocks and mineralisation remain poorly understood the messegay gold occurrence is situated in the taschereau launay plutonic complex of the northern volcanic zone of the abitibi greenstone belt the taschereau intrusion 2718 2 ma represents a complex network of sills composed of tonalite with minor amounts of diorite monzonite and gabbro the launay granite which intrudes the taschereau pluton is late orogenic and its emplacement was controlled by an early reverse ductile n s shear zone intrusive rocks have been subjected to four episodes of alteration epidote chlorite carbonate magnetite hematite microcline albite pyrite and sericite quartz shear zone hosted and metasomatic au mo mineralisation is mainly associated with albite pyrite assemblages but also occurs within zones of intense magnetite hematite microcline and sericite quartz alteration the messegay gold occurrence is interpreted as a new type of disseminated gold molybdenum porphyry deposit associated with a zone of magmatic differentiation in a magnetite series pluton

fault lubrication and earthquake propagation in thermally unstable rocks experiments performed on dolomite or mg calcite gouges at seismic slip rates v 1 m s and displacements d 1 m show that the frictional coefficient decays exponentially from peak values m p 0 8 in the byerlee9s range to extremely low steady state values ss 0 1 attained over a weakening distance d w microstructural observations show that discontinuous patches of nanoparticles of dolomite and its decomposition products periclase and lime or portlandite were produced in the slip zone during the transient stage d w these observations integrated with co 2 emissions data recorded during the experiments suggest that particle interaction in the slip zone produces flash temperatures that are large enough to activate chemical and physical processes e g decarbonation reactions t 550 c during steady state d d w shear strength is very low and not dependent upon normal stresses suggesting that pressurized fluids co 2 may have been temporarily trapped within the slip zone at this stage a continuous layer of nanoparticles is developed in the slip zone for d d w a slight but abrupt increase in shear strength is observed and interpreted as due to fluids escaping the slip zone at this stage dynamic weakening appears to be controlled by velocity dependent properties of nanoparticles developed in the slip zone experimentally derived seismic source parameter w b i e breakdown work the energy that controls the dynamics of a propagating fracture 1 matches w b values obtained from seismological data of the a d 1997 m6 colfiorito italy earthquakes which nucleated in the same type of rocks tested in this study and 2 suggests similar earthquake scaling relationships as inferred from existing seismological data sets we conclude that dynamic weakening of experimental faults is controlled by multiple slip weakening mechanisms which are activated or inhibited by physicochemical reactions in the slip zone

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

the effects of sliding velocity on the frictional and physical properties of heated fault gouge the frictional properties of a crushed granite gouge and of gouges rich in montmorillonite illite and serpentine minerals have been investigated at temperatures as high as 600 c confining pressures as high as 2 5 kbar a pore pressure of 30 bar and sliding velocities of 4 8 and 4 8 10 2 m sec the gouges showed nearly identical strength behaviors at the two sliding velocities all four gouges however showed a greater tendency to stick slip movement and somewhat higher stress drops in the experiments at 4 8 10 2 m sec varying the sliding velocity also had an effect on the mineral assemblages and deformation textures developed in the heated gouges the principal mineralogical difference was that at 400 c and 1 kbar confining pressure a serpentine breakdown reaction occurred in the experiments at 4 8 10 2 m sec but not in those at 4 8 m sec the textures developed in the gouge layers were in part functions of the gouge type and the temperature but changes in the sliding velocity affected among other features the degree of mineral deformation and the orientation of some fractures

the chapada cu au deposit mara rosa magmatic arc central brazil constraints on the metallogenesis of a neoproterozoic large porphyry type deposit abstract the large chapada cu au deposit is situated in goias magmatic arc central brazil which is part of an accretionary orogen with tectonic evolution between ca 900 and 600 ma during the brasiliano orogeny with a current reserve proven and probable of 420 94 mt cu 0 29 and 479 84 mt au 0 25 g t or 3 83 moz au the chapada cu au deposit is an important example of a large tonnage low grade porphyry copper gold deposit of precambrian age in which the mineralization is disseminated and hosted mainly by biotite rich schists and gneisses in this work we propose a two stage genetic model for the chapada deposit that includes an early porphyry type cu au event overprinted by a shear zone hosted cu au event the first mineralization event represents a rare case of metamorphosed neoproterozoic porphyry type deposit which preserves distinct hydrothermal alteration mineralization zoning developed at the interface between equigranular 867 8 ma to porphyritic 884 15 ma medium to high kcalc alkaline dioritic rocks and mafic to intermediate metavolcanic and metapyroclastic rocks the e nd values are positive from 2 17 to 5 39 thus indicating the juvenile nature of the original rocks for both metavolcano sedimentary and plutonic rocks in this context kyanite rich rocks are interpreted as products of metamorphosed argillic hydrothermal alteration halo and occur as linear alignments oriented parallel to the mara rosa magmatic arc trend the potassic hydrothermal alteration halo which includes the main host rocks of the chapada deposit is characterized by biotite schist muscovite biotite schist amphibole biotite schist and biotite gneiss the ore is represented predominantly by platy deformed chalcopyrite and pyrite disseminations along foliation plans or axial surfaces of folds and to a lesser extent by small massive concentrations in fold hinges the ore shows a systematic oxide sulfide zonation including the peripheral pyritic shell and the central magnetite rich zone in general the geological context of the deposit lacks preserved stocks dykes and breccias while deformed a type quartz veins veinlets are abundant the second mineralization event represents an epigenetic shear zone hosted cu au mineralization associated with d n 1 and occurred between 630 and 580 ma during the late orogenic to post orogenic stage of the mara rosa magmatic arc which may be interpreted as i a shear zone hosted cu au remobilization ii an orogenic cu au mineralization or iii an intrusion related cu au mineralization in the latter case the mineralization could be related to the ilmenite bearing younger metadiorite 634 8 6 8 ma with disseminations of chalcopyrite pyrite and pyrrhotite the narrow range of pyrite and chalcopyrite 34 s values close to 0 between 2 90 and 0 76 indicates that both the porphyry copper gold mineralization and the epigenetic mineralization were generated by sulfur of magmatic origin

off fault deformations and shallow slip deficit from dynamic rupture simulations with fault zone plasticity kinematic source inversions of major m 7 strike slip earthquakes show that the slip at depth exceeds surface displacements measured in the field and it has been suggested that this shallow slip deficit ssd is caused by distributed plastic deformation near the surface we perform dynamic rupture simulations of m 7 2 7 4 earthquakes in elastoplastic media and analyze the sensitivity of ssd and off fault deformation ofd to rock quality parameters while linear simulations clearly underpredict observed ssd and ofds nonlinear simulations for a moderately fractured fault damage zone predict a ssd of 44 53 and ofds of 39 48 consistent with the 30 60 ssd and 46 10 1 ofd reported for the 1992 m 7 3 landers earthquake both ssd and ofds are sensitive to the quality of the fractured rock mass inside the fault damage zone and surface rupture is almost entirely suppressed in poor quality material

dynamic variations of a convection flow reversal in the subauroral postmidnight sector as seen by the superdarn hokkaido hf radar 1 the superdarn hokkaido hf radar capable of measuring the subauroral ionospheric plasma convection especially during storms has been in continuous operation since the beginning of december 2006 we report the first two dimensional observation of a dynamic variation of convection flow reversal in subauroral postmidnight sector during the storm main phase on 29 january 2007 the flow reversal region is extended over 20 in longitude and 5 in latitude lasting for about 10 15 min and the maximum flow speed is about 0 5 1 0 km s the flow reversal structure is reasonably reproduced by the ring current simulation coupled with the ionosphere suggesting that it is produced by the region 2 field aligned current associated with the ring current enhancement during the storm main phase the dynamic variation of the flow reversal structure is interpreted as a transient eastward extension of the elongated dusk convection cell to the postmidnight and equatorward of the dawn cell associated with the variation of the ring current whose structure is controlled by the interplanetary magnetic field and solar wind dynamic pressure it is suggested that the ring current variation is highly coupled with the interplanetary parameters and is much more complicated than ever thought

time evolution of the subauroral electric fields a case study during a sequence of two substorms 1 the temporal evolution of the subauroral polarization stream saps is investigated using the doppler velocity observations by the unwin hf radar in conjunction with the simultaneously observed auroral luminosity and plasma convection reversal regions the event under study of 14 december 2004 1000 1600 ut occurred during geomagnetically quiet conditions when a sequence of two substorms separated by 2 hours was observed by the image satellite it is shown that the saps appeared shortly after the first substorm onset and continued to dominate the westward plasma convection at subauroral magnetic latitudes 59 63 s for 6 hours an unexpected exception occurred near the second substorm onset time when a narrow channel of weaker saps westward convection became embedded in the slow eastward drifting plasma for a short 25 min period which was attributed to the equatorward expansion of the dawn convection cell during the growth and expansion phases of the second substorm another remarkable plasma convection feature was observed in the same 25 min period 5 poleward of saps this was a narrow mirror channel of the eastward drifting plasma parallel to the main saps channel it is argued that the latter feature may also be caused by the equatorward expanding dawn convection cell whose streamlines become compressed by and aligned with the saps poleward edge a possible relationship between the saps intensity and its position relative to the auroral oval is also investigated the results suggest that the magnetosphere ionosphere feedback processes within saps become more effective as the equatorward edge of the eastward convection region retreats poleward with the saps position much less affected by the auroral dynamics

hf radar observations of the f region ionospheric plasma response to storm sudden commencements 1 performance of the super dual auroral radar network superdarn hf radars during geomagnetic storms is investigated by analyzing the data collected during storm events over a 5 year period changes in the occurrence of f region hf backscatter observed by the 6 most equatorward radars are analyzed statistically using a superposed epoch analysis method with respect to a storm sudden commencement ssc regular diurnal variations of the echo occurrence during geomagnetically quiet days are produced and the amount of detected backscatter during storms is adjusted using quiet time curves all radars considered in this study show a significant decrease in the number of detected echoes approximately 24 hours following ssc unexpected significant changes in occurrence levels are also present within a few hours of ssc with most radars observing an increase in the amount of backscatter detected the typical time evolution of f region echo occurrence is highly reminiscent of that of the electron density reported previously also considered is the ionospheric convection response to ssc observed by the zonally looking superdarn unwin radar in new zealand it is shown that the initial response to ssc is instantaneous within uncertainty and appears to be independent of the magnetic latitude and local time the observed convection response timing and morphology are discussed in the context of possible ionospheric propagation mechanisms

an integrated perspective of the continuum between earthquakes and slow slip phenomena slow slip a mechanism by which faults can relieve stress was thought to be distinct from earthquakes however a global review of slow slip phenomena suggests that instead there is a continuum between the two types of event