noise based monitoring and imaging of aseismic transient deformation induced by the 2006 basel reservoir stimulation abstractwe have analyzed the time dependent properties of the ambient seismic wavefield between 0 1 and 8 hz to detect resolve monitor and image the deformation induced by the water injection associated with the stimulation of the 2006 deep heat mining project in the city of basel switzerland the application of passive methods allowed the detection of an aseismic transient of approximately 35 days duration that began with the onset of the reservoir stimulation peak deformation was reached some 15 days after the bleed off and after the induced seismicity ceased we resolved a significant increase in seismic velocities and a simultaneous decorrelation of the noise correlation coda waveforms the wavefield properties implied that the material response was monitored mainly in the sedimentary layer 2 5 km above the stimulated volume that was approximately 4 5 km deep we inverted the velocity change and decorrelation data to estimate the spatial distribution of the medium changes the resulting imag

sea ice growth and water mass modification in the mertz glacier polynya east antarctica during winter in july september 1999 an extensive oceanographic survey 87 conductivity temperature and depth measuring stations was conducted in the mertz glacier polynya over the adelie depression off the antarctic coast between 145 and 150 e we identify and describe four key water masses in this polynya highly modified circumpolar deep water hmcdw winter water ww ice shelf water isw and high salinity shelf water hssw combining surface velocity data from an acoustic doppler current profiler with three hydrographic sections we found the hmcdw to be flowing westward along the shelf break 0 7 sv the ww and hssw flowing eastwards underneath mertz glacier 2 0 sv and that there was a westward return flow of isw against the continent 1 2 sv using a simple box model for the exchanges of heat and fresh water between the principal water masses we find that the polynya was primarily a latent heat polynya with 95 of the total heat flux caused by sea ice formation this heat flux results from a fresh water equivalent sea ice growth rate of 4 9 7 7 cm d 1 and a mass exchange between hmcdw and ww of 1 45 sv the inferred ocean heat flux is 8 14 w m 2 and compares well with other indirect estimates

the importance of earthquake interactions for injection induced seismicity retrospective modeling of the basel enhanced geothermal system author s catalli f rinaldi ap gischig v nespoli m wiemer s abstract 2016 american geophysical union all rights reserved we explore the role of earthquake interactions during an injection induced seismic sequence we propose a model which considers both a transient pressure and static stress redistribution due to event interactions as triggering mechanisms by calibrating the model against observations at the enhanced geothermal system of basel switzerland we are able to reproduce the time behavior of the seismicity rate we observe that considering earthquake interactions in the modeling leads to a larger number of expected seismic events 24 more if compared to a pressure induced seismicity only the increase of the number of events is particularly evident after the end of the injection we conclude that implementing a model for estimating the static stress changes due to mutual event interactions increases significantly the understanding of the process and the behavior of induced seismicity

seismicity triggered by fluid injection induced aseismic slip anthropogenic fluid injections are known to induce earthquakes the mechanisms involved are poorly understood and our ability to assess the seismic hazard associated with geothermal energy or unconventional hydrocarbon production remains limited we directly measure fault slip and seismicity induced by fluid injection into a natural fault we observe highly dilatant and slow 4 micrometers per second m s aseismic slip associated with a 20 fold increase of permeability which transitions to faster slip 10 m s associated with reduced dilatancy and micro earthquakes most aseismic slip occurs within the fluid pressurized zone and obeys a rate strengthening friction law 0 67 0 045ln v v with v 0 1 m s fluid injection primarily triggers aseismic slip in this experiment with micro earthquakes being an indirect effect mediated by aseismic creep

the 2012 brawley swarm triggered by injection induced aseismic slip it has long been known that fluid injection or withdrawal can induce earthquakes but the underlying mechanisms remain elusive for example the 2012 brawley swarm which produced two strike slip shocks with magnitudes larger than 5 3 and surface ruptures in the close vicinity of a geothermal field started with earthquakes about 5 km deeper than the injection depth 1 5 km this makes the causality between the injection and seismicity unclear here we jointly analyze broadband and strong motion waveforms uavsar leveling measurements and field observations to reveal the detailed seismic and aseismic faulting behaviors associated with the 2012 brawley swarm in particular path calibration established from smaller events in the swarm allows waveform inversion to be conducted up to 3 hz to resolve finite rupture process of the mw 4 7 normal event our results show that the 2012 earthquake sequence was preceded by aseismic slip on a shallow normal fault beneath the geothermal field aseismic slip initiated in 2010 when injection rate rapidly increased and triggered the following earthquakes subsequently including unusually shallow and relatively high frequency seismic excitations on the normal fault in this example seismicity is induced indirectly by fluid injection a result of mediation by aseismic creep rather than directly by a pore pressure increase at the location of the earthquakes

a numerical model for fluid injection induced seismicity at soultz sous forets abstract during fluid injection experiments at the geothermal site of soultz sous forets france more than 114 000 induced seismic events with magnitudes between 2 0 and 2 9 were detected by a local downhole monitoring network of these 35 039 events are sufficiently constrained to be located hypocenters align along a sub vertical planar structure with the apparent width being dominated by data scattering indicating that seismic activity predominantly occurs along a pre existing larger scale fault structure for this scenario we present a numerical model to simulate hydraulic overpressures and induced seismicity during hydraulic injection the numerical model is based on the physical processes of fluid pressure and stress diffusion with triggering of the induced seismicity being controlled by coulomb friction even in its simplest form of a fault zone without any structural heterogeneity the numerical model reproduces typical observations at soultz sous forets such as number and magnitude of induced events hypocenter locations including the kaiser effect occurrence of post injection seismicity and the largest magnitude event occurring several days after shut in

role of basement in epithermal deposits the kushikino and hishikari gold deposits southwestern japan abstract the magma ore deposit relationship of most low sulfidation epithermal ore deposits is still unclear partly because many stable isotopic studies of such deposits have indicated the predominance of meteoric waters within hydrothermal fluids however it is certainly true that hydrothermal systems are ultimately driven by magmatic intrusions and epithermal gold deposits might therefore be produced by magmatic activity even in deposits having has no obvious links to a magma we re examine the genesis of two typical low sulfidation epithermal gold deposits the kushikino and hishikari deposits using structural simulations and isotope data many epithermal gold deposits including the kushikino and hishikari deposits have been discovered in kyushu southwestern japan the kushikino deposit comprises fissure filling veins within neogene andesitic volcanics that overlie unconformably cretaceous sedimentary basement the veins consist of gold and silver bearing quartz and calcite with minor amounts of adularia sericite and sulfides although carbon and oxygen isotopic data for the veins indicate a meteoric origin of the ore fluid finite element simulations suggest that the vein system might have formed in direct response to magma intrusion in particular geophysical data suggest that intruding magma has uplifted the basement rocks thereby producing fractures and veins and a positive bouguer anomaly and providing the heat necessary to drive an ore forming hydrothermal system the second component of this study has been to investigate the nature and evolution of the kushikino and hishikari epithermal systems isotope data document the geochemical evolution of the hydrothermal fluids we conclude that the existence of sedimentary basement rocks at depth might have affected the strontium and carbon isotopic ratios of the kushikino and hishikari ore fluids the 87 sr 86 sr ratios and 13 c 18 o trend reveal that major ore veins in the hishikari deposit can be distinguished from shallow barren veins it was suggested isotopically that fluids responsible for the barren veins in nearby shallow and barren circulation systems were only controlled by the shallow host rocks such multi isotope systematics provide a powerful tool with which to determine the center of hydrothermal activity and thereby document the evolution of hydrothermal fluids

high definition analysis of fluid induced seismicity related to the mesoscale hydromechanical properties of a fault zone interactions between pore pressure strain and seismicity were analyzed in a 30 m thick shallow fault zone that was subjected to a small overpressure of 80 kpa to produce small changes in effective stress simultaneous pressure strain and seismic measurements taken in the fractured damage zone during the pressurization indicated that seismicity is triggered along low permeable highly rigid low dip angle mesoscale inherited fractures where deformation is controlled by the hydromechanical behavior of the surrounding high permeability not so rigid aseismic sub vertical fault related fractures using a three dimensional distinct element representation of the fractures network we show that the seismicity observed is mainly due to shear slip along inherited planes in response to the mechanical loading induced by the opening by a few microns of the surrounding subfaults

seismic velocity changes associated with aseismic deformations of a fault stimulated by fluid injection fluid pressure plays an important role in the stability of tectonic faults however the in situ mechanical response of faults to fluid pressure variations is still poorly known to address this question we performed a fluid injection experiment in a fault zone in shales while monitoring fault movements at the injection source and seismic velocity variations from a near distance 10 meters monitoring network we measured and located the p and s wave velocity perturbations in and around the fault using repetitive active sources we observed that seismic velocity perturbations dramatically increase above 1 5 mpa of injection pressure this is consistent with an increase of fluid flow associated with an aseismic dilatant shearing of the fault as shown by numerical modelling we find that seismic velocity changes are sensitive both to fault opening by fluid invasion and effective stress variations and can be an efficient measurement for monitoring fluid driven aseismic deformations of faults

the 2016 mw5 1 fairview oklahoma earthquakes evidence for long range poroelastic triggering at 40 km from fluid disposal wells abstract wastewater disposal in the central u s is likely responsible for an unprecedented surge in earthquake activity much of this activity is thought to be driven by induced pore pressure changes and slip on pre stressed faults which requires a hydraulic connection between faults and injection wells however direct pressure effects and hydraulic connectivity are questionable for earthquakes located at large distances and depths from the injectors here we examine triggering mechanisms of induced earthquakes which occurred at more than 40 km from wastewater disposal wells in the greater fairview region northwest oklahoma employing numerical and semi analytical poroelastic models the region exhibited few earthquakes before 2013 when background seismicity started to accelerate rapidly culminating in the mw5 1 fairview earthquake in february 2016 injection rates in the 2 2 5 km deep arbuckle formation started to increase rapidly in 2012 about two years before the start of seismicity increase most of the injection activity was concentrated toward the northeast of the study region generating a relatively cohesive zone of pressure perturbations between 0 1 and 1 mpa much of the near injection seismicity was likely triggered by pressure effects and fault assisted pressure diffusion to seismogenic depth outside of the high pressure zone we observed two remarkably detached linear seismicity clusters which occurred at 20 to 50 km distance from the initial seismicity and 10 to 40 km from the nearest high rate injector semi analytical models reveal that poroelastically induced coulomb stress changes surpass pore pressure changes at these distances providing a plausible triggering mechanism in the far field of injection wells these results indicate that both pore pressures and poroelastic stresses can play a significant role in triggering deep and distant earthquakes by fluid injection and should be considered for seismic hazard assessment beyond the targeted reservoir

magnitudes of induced earthquakes and geometric scales of fluid stimulated rock volumes sometimes rock stimulations by fluid injections into geothermal boreholes are able to trigger perceptible or even potentially damaging earthquakes this does not seem to be the case for hydraulic fracturing of hydrocarbon reservoirs reasons for such a difference and factors defining magnitudes of induced earthquakes triggered tectonicly as well as induced artificially remain unclear we analyzed microseismic data obtained by fluid stimulations at different geothermal and hydrocarbon sites this analysis indicates that a rupture corresponding to a fluid induced earthquake seems to be only probable along a surface located mainly inside a stimulated rock volume we approximated the stimulated volume by an ellipsoid and compared the statistics of induced events with the statistics of randomly distributed thin flat disks modeling rupture surfaces we found that one of the main factors limiting the probability to induce a large magnitude event is the minimum principal axis of a fluid stimulated rock volume

anatomy of a buried thrust belt activated during hydraulic fracturing abstract tectonically active fault networks are often inter connected but in the case of injection induced seismicity prior knowledge of fault architecture tends to be severely limited in most cases reactivated faults due to fluid injection are inferred after the fact by the spatial distribution of induced seismicity hypocenters such reliance on post injection seismicity impedes any pre operational risk analysis as well as development of a more holistic understanding of fault system models by combining high resolution depth migrated 3 d seismic data with a new focal depth estimation method that reduces spatial uncertainty of hypocenters this study pinpoints microearthquake fault activation within a buried thrust belt in the montney formation in western canada british columbia during hydraulic fracturing operations rupture nucleation occurred on seismically imaged thrust ramps that cut through the debolt formation a massive carbonate layer that underlies the stimulated zone high resolution seismic images reveal transverse structures interpreted as basement controlled fold hinges or tear faults that transferred displacement between thrust faults during late cretaceous paleogene compressional shortening the spatio temporal pattern of induced seismicity suggests that these transverse structures provide permeable pathways for aseismic pore pressure diffusion thus connecting distinct thrust faults and enabling earthquake triggering on a timescale of days and at distances of up to 2 km from the injection wells inferred relationships highlight how the fault system is connected including apparent stress concentrations at the intersections of transverse structures and orogen parallel thrust ramps

seismic responses to fluid pressure perturbations in a slipping fault seismicity induced by fluid injection in a natural fault is investigated in situ in the near field of the source we present synchronous seismic and hydromechanical measurements directly recorded in the decametric injection zone the three main types of seismic events were recorded during injection and shut in high amplitude and short duration seismic events se i e microearthquakes low to constant amplitude and 5 to 17 s long tremor like signals tls and long period events lp with a narrow frequency band content seismicity first initiates with a sequence of se and tls when pressure is high 3 5 mpa slip is activated on the fault which experiences a twentyfold increase of permeability then lp events appear to be associated to fluid leakage in the fault caused by dilation during slip during shut in residual pressures as low as 0 6 mpa still trigger se events we show that the initial tls sequence triggers when a progressive transition occurs from rupture controlled by effective stress variations close to the injection source to a large friction weakening dominated slip on the fault we conclude that the combination of these different seismic signal types may be a proxy to monitor fault instability associated to fluid pressure perturbations

porphyry mo and epithermal au ag pb zn mineralization in the zhilingtou polymetallic deposit south china the zhilingtou polymetallic deposit south china provides an excellent opportunity to investigate the magmatic hydrothermal evolution of the porphyry mo to epithermal au ag pb zn ore spectrum new zircon u pb sphalerite 40ar 39ar and pyrite rb sr ages together with previous molybdenite re os ages indicate that the granitic magmatism and mo au ag pb zn mineralization were coeval and cogenetic in the early cretaceous 113 ma fluid inclusions and h o isotope results have established the evolution from an early high temperature h2o nacl magmatic fluid system mo mineralization to a medium temperature mixed fluid system of magmatic and meteoric water au ag mineralization to a peripheral late stage low temperature h2o nacl meteoric water fluid system epithermal au ag pb zn mineralization moreover the sulfur isotopic compositions 34s 2 1 7 8 of the sulfide minerals confirm a genetic link to the granitic magma lead isotope data from pyrite and the granite rhyolite porphyries are similar indicating that they share a common pb source the geochronological geochemical and isotopic lines of evidences consistently suggest that the porphyry mo and epithermal au ag pb zn mineralization formed in one magmatic hydrothermal system the porphyry epithermal mineralization model for zhilingtou has significant importance for prospecting work in south china where mo and associated pb zn ag resources are abundant

new isotopic evidence bearing on bonanza au ag epithermal ore forming processes new cu s and pb isotope data provide evidence for a magmatic source of metal loid s and sulfur in epithermal au ag deposits even though their ore forming solutions are composed primarily of heated meteoric ground waters the apparent isotopic discrepancy between ore metals and ore forming solutions and even between the ore and associated gangue minerals indicates two different sources of epithermal ore forming constituents 1 a shallow geothermal system that not only provides the bulk of water for the ore forming solutions but also major chemical constituents leached from host rocks silica aluminum potassium sodium calcium to make gangue minerals and 2 metals and metalloids as te sb etc and sulfur se derived from deeper magma bodies isotopic data are consistent with either vapor phase transport of metal loids and sulfur and their subsequent absorption by shallow geothermal waters or formation of metallic au ag cu phases nanoparticles at depth from magmatic fluids prior to encountering the geothermal system the latter is most consistent with ore textures that indicate physical transport and aggregation of nanoparticles were significant ore forming processes the recognition that epithermal au ag ores form in tectonic settings that produce magmas capable of releasing metal rich fluids necessary to form these deposits can refine exploration strategies that previously often have focused on locating fossil geothermal systems

aseismic motions drive a sparse seismicity during fluid injections into a fractured zone in a carbonate reservoir author s duboeuf l de barros l cappa f guglielmi y deschamps a seguy s abstract 2017 american geophysical union all rights reserved an increase in fluid pressure in faults can trigger seismicity and large aseismic motions understanding how fluid and faults interact is an essential goal for seismic hazard and reservoir monitoring but this key relation remains unclear we developed an in situ experiment of fluid injections at a 10 meter scale water was injected at high pressure in different geological structures inside a fault damaged zone in limestone at 280 m depth in the low noise underground laboratory france induced seismicity as well as strains pressure and flow rate was continuously monitored during the injections although nonreversible deformations related to fracture reactivations were observed for all injections only a few tests generated seismicity events are characterized by a 0 5 to 4 khz content and a small magnitude approximately 3 5 they are located within 1 5 m accuracy between 1 and 12 m from the injections comparing strain measurements and seismicity shows that more than 96 of the deformation is aseismic the seismic moment is also small compared to the one expected from the injected volume moreover a dual seismic behavior is observed as 1 the spatiotemporal distribution of some cluster of events is clearly independent from the fluid diffusion 2 while a diffusion type pattern can be observed for some others clusters the seismicity might therefore appear as an indirect effect to the fluid pressure driven by aseismic motion and related stress perturbation transferred through failure

seismicity related to the hydraulic stimulation of grt1 rittershoffen france the rittershoffen deep geothermal reservoir in northeastern france is well characterized and has been extensively studied by a multidisciplinary approach a hydraulic stimulation for the development of the geothermal reservoir was performed in june 2013 this injection of fluid led to seismic activity which was closely monitored by a dedicated set of seismic stations the seismic sequence started during the injection but showed an unusual long quiet period of 4 d after shut in before the occurrence of a second swarm of events here we take the opportunity of this well monitored activity to gain insight into the geomechanical factors favouring the development of induced earthquakes we apply a template matching approach and a relative relocation procedure to obtain a precise estimate of the geometries of the activated structures our approach shows that the induced events during the injection took place on two parallel planar structures it shows that details of the seismicity generally obtained from borehole seismic network are achievable from surface network when an appropriate analysis is performed the development of this induced seismicity is in good agreement with the known stress field and failure criterion proposed for the reservoir in particular the orientation of the activated structure associated focal mechanisms and the overpressure needed to initiate the seismic activity are all in line with the geomechanical model of the area the swarm of delayed events 4 d after shut in can be well explained by considering an aseismic slip on the imaged fault and the related static stress transfer we therefore suggest that the ability to monitor local slow aseismic movements at depth in conjunction with precise tracking of the seismicity is of primary importance to understand induced earthquake activity

the sources of ore forming material in the low sulfidation epithermal wulaga gold deposit ne china constraints from s pb isotopes and ree pattern abstract the wulaga gold deposit located in heilongjiang province ne china is a subvolcanic rock hosted low sulfidation epithermal gold deposit and has an au reserve of about 84 tons the gold mineralization occurs in a crypto explosive breccia and is spatially and temporally associated with an early cretaceous granodioritic porphyry three individual stages of mineralization have been identified in the wulaga gold deposit an early white quartz euhedral vein stage a fine grained pyrite marcasite stibnite chalcedony stage and a late calcite pyrite stage the sulfur isotopic values of sulfide minerals vary in a wide range from 4 to 4 9 but are concentrated in the range of 3 to 0 implying that sulfur in the hydrothermal fluids was derived from magmatic volatiles lead isotopic results of the granodioritic porphyry 206pb 204pb 18 341 18 395 207pb 204pb 15 507 15 523 208pb 204pb 38 174 38 251 and sulfide minerals 206pb 204pb 18 172 18 378 207pb 204pb 15 536 15 600 208pb 204pb 38 172 38 339 are comparatively consistent and clustered together between the orogenic and upper mantle lines indicating the lead in the ores is closely related to the parent magma of the granodioritic porphyry the ree patterns of fluid inclusions trapped in sulfides are similar to those of the granodioritic porphyry which confirms the magmatic origin of the ree in the hydrothermal fluids the characteristics of s and pb isotopes and ree suggest that the ore forming materials of the wulaga gold deposit are partly magmatic in origin and related to a high level hydrous granodioritic magma

mechanisms of mid to outer shelf transport of shoreline released tracers abstracttransport of shoreline released tracer from the surfzone across the shelf can be affected by a variety of physical processes from wind driven to submesoscale with implications for shorelin

nucleation and arrest of dynamic slip on a pressurized fault 1 elevated pore pressure can lead to reactivation of slip on pre existing fractures and faults when the static coulomb failure is reached locally as the pressurized region spreads diffusively slip can accumulate quasi statically paced by the pore fluid diffusion or dynamically in this work we consider a prestressed fault with a locally peaked diffusively spreading pore pressure field to study 1 conditions leading to the escalation of slip and nucleation of dynamic rupture and 2 rupture run out distance before it is arrested nucleation appears in this model when the fault friction decreases from its peak value with slip while arrest of dynamic propagation is imminent on aseismic faults i e such that prestress b is less than the residual fault strength rat ambient conditions when fluid overpressure is a small to moderate fraction of the ambient value of normal effective stress and prestress is large enough for fault slip to be activated by overpressure dynamic rupture always nucleates and the nucleation length increases with decreasing prestress practically independently of the overpressure value transition from the ultimately unstable b r to the ultimately stable b r fault loading is marked by a strong increase of the nucleation length 1 b r 2 as b approaches r from above for aseismic faults b r no dynamic rupture is nucleated at large fluid overpressures for all but the smallest values of prestress the largest run out distances of dynamic slip on aseismic faults correspond to overpressure prestress just sufficient for slip activation in such cases the dynamically accumulated slip can lead to enhanced dynamic fault weakening resulting in a sustained dynamic rupture and generating a large earthquake this is consistent with field observations when the largest injection induced seismicity occurred after fluid injection ended

frictional heterogeneities on carbonate bearing normal faults insights from the monte maggio fault italy observations of heterogeneous and complex fault slip are often attributed to the complexity of fault structure and or spatial heterogeneity of fault frictional behavior such complex slip patterns have been observed for earthquakes on normal faults throughout central italy where many of the mw 6 to 7 earthquakes in the apennines nucleate at depths where the lithology is dominated by carbonate rocks to explore the relationship between fault structure and heterogeneous frictional properties we studied the exhumed monte maggio fault located in the northern apennines we collected intact specimens of the fault zone including the principal slip surface and hanging wall cataclasite and performed experiments at a normal stress of 10 mpa under saturated conditions experiments designed to reactivate slip between the cemented principal slip surface and cataclasite show a 3 mpa stress drop as the fault surface fails then velocity neutral frictional behavior and significant frictional healing overall our results suggest that 1 earthquakes may readily nucleate in areas of the fault where the slip surface separates massive limestone and are likely to propagate in areas where fault gouge is in contact with the slip surface 2 postseismic slip is more likely to occur in areas of the fault where gouge is present and 3 high rates of frictional healing and low creep relaxation observed between solid fault surfaces could lead to significant aftershocks in areas of low stress drop

on the relationship between fault permeability increases induced stress perturbation and the growth of aseismic slip during fluid injection author s cappa f guglielmi y nussbaum c birkholzer j abstract 2018 american geophysical union all rights reserved fluid injections into the deep subsurface can at times generate earthquakes but often they only produce aseismic deformations here we analyze the influence of fault hydromechanical properties on the growth of injection induced aseismic slip using hydromechanical modeling we show how permeability enhancement in addition to the background stress and frictional weakening has an important effect on the pressure diffusion and slip growth during injection we find that the more pronounced the fault permeability enhancement the stronger is the growth of the aseismic slip zone the effect of enhanced permeability is more pronounced when the fault is initially close to failure our results show that aseismic slip grows beyond the pressurized zone when the fault permeability increases while slip remains behind the pressurized zone when permeability does not vary from its initial preslip value thus fault permeability increases should be considered as complementary mechanism to current models of fluid induced aseismic slip

investigation of injection induced seismicity using a coupled fluid flow and rate state friction model we describe a numerical investigation of seismicity induced by injection into a single isolated fracture injection into a single isolated fracture is a simple analog for shear stimulation in enhanced geothermal systems egs during which water is injected into fractured low permeability rock triggering slip on preexisting large scale fracture zones a model was developed and used that couples 1 fluid flow 2 rate and state friction and 3 mechanical stress interaction between fracture elements based on the results of this model we propose a mechanism to describe the process by which the stimulated region grows during shear stimulation which we refer to as the sequential stimulation ss mechanism if the ss mechanism is realistic it would undermine assumptions that are made for the estimation of the minimum principal stress and unstimulated hydraulic diffusivity we investigated the effect of injection pressure on induced seismicity for injection at constant pressure there was not a signifi

precipitation of gold in a low sulfidation epithermal gold deposit insights from a submillimeter scale oxygen isotope analysis of vein quartz sir we welcome the opportunity to respond to bogie and lawless discussion of our paper on the submillimeter scale oxygen isotope variation of vein quartz from the low sulfidation style gold deposit at the hishikari mine the disputed point is whether or not the bladed and fine grained quartz precipitated initially as chalcedony and recrystallized to quartz in a subsequent stage similarity of texture between chalcedony e g typically found in agate and flaky or acicular bladed quartz suggests that there is some truth in bogie and lawless idea the texture of bladed quartz suggests rapid crystallization from solutions supersaturated with respect to quartz however it is difficult to define only from the texture whether

rupture propagation behavior and the largest possible earthquake induced by fluid injection into deep reservoirs earthquakes caused by fluid injection into deep underground reservoirs constitute an increasingly recognized risk to populations and infrastructure quantitative assessment of induced seismic hazard however requires estimating the maximum possible magnitude earthquake that may be induced during fluid injection here i seek constraints on an upper limit for the largest possible earthquake using source physics simulations that consider rate and state friction and hydro mechanical interaction along a straight homogeneous fault depending on the orientation of the pressurized fault in the ambient stress field different rupture behavior can occur 1 uncontrolled rupture front propagation beyond the pressure front or 2 rupture front propagation arresting at the pressure front in the first case fault properties determine the earthquake magnitude and the upper magnitude limit may be similar to natural earthquakes in the second case the maximum magnitude can be controlled by carefully designing and monitoring injection and thus restricting the pressurized fault area

injection induced slip heterogeneity on faults in shale reservoirs abstract managing fluid stimulation protocols is an effective means to mitigate the risk of injection induced earthquakes during shale gas development the success of these protocols is dependent on our understanding of fluid pressure heterogeneity and the associated inhomogeneous slip on critically stressed faults here we show the evolution of velocity weakening zone on a simulated fault derived from fluid injection and velocity stepped experiments and the corresponding non uniform fluid pressure distribution recovered from coupled hydro mechanical simulations our results indicate that the sharp extension of velocity weakening zone occurs before the nucleation of fault rupture which could be an indicator to avoid the reactivation of other fault patches beyond the stimulated zone the dynamic rupture is estimated to extend much faster than the maximum speed of the velocity weakening zone front we infer that the velocity weakening zone may further expand and fully control the fault behavior after multiple slip events

hydraulic fracture energy budget insights from the laboratory in this paper we present results from a series of laboratory hydraulic fracture experiments designed to investigate various components of the energy budget the experiments involved a cylindrical sample of westerly granite being deformed under various triaxial stress states and fractured with distilled water which was injected at a range of constant rates acoustic emission sensors were absolutely calibrated and the radiated seismic energy was estimated the seismic energy was found to range from 7 02e 8 to 1 24e 4 of the injection energy which is consistent with a range of values for induced seismicity from field scale hydraulic fracture operations the deformation energy crack opening of the sample during hydraulic fracture propagation was measured using displacement sensors and ranged from 18 to 94 of the injection energy our results support the conclusion that aseismic deformation is a significant term in the hydraulic fracture energy budget

the history of vein formation determined by 40ar 39ar dating of adularia in the hosen 1 vein at the hishikari epithermal gold deposit japan the hosen 1 vein has a symmetrical banded structure within the hishikari epithermal gold deposit in japan the vein can be divided into four macroscopic bands we used 40ar 39ar dating of adularia by incremental step heating to determine the duration of mineralization in the individual bands of the vein and the history of vein formation plateau ages were obtained from all adularia samples and no significant excess 40ar is recognized from inverse isochrons the derived age spectra suggest that thermal overprinting of the epithermal system did not affect the plateau ages although early bands must have been reheated by the thermal pulses associated with later bands the 40ar 39ar ages of adularia indicate that vein formation occurred episodically in distinct periods separated by intervals of about 30 000 to 110 000 yr the hosen 1 vein grew in at least six increments at the 20 m level and at least four increments at the 62 5 m level the total duration of mineralization from the margin to the center of the hosen 1 vein was about 260 000 yr during which time the temperature of the hydrothermal fluid decreased from 190 to 210 c to less than 170 c

pb sr isotopic evidence for contribution of deep crustal fluid to the hishikari epithermal gold deposit southwestern japan abstract the gold bearing quartz adularia veins of the world class hishikari mine in southwestern japan occur in a geological regime where the rocks of the upper to middle crust are simple and their chemical and sr nd pb isotopic compositions are well studied detailed comparison of pb and sr isotopic data of the hishikari veins with those of all possible source materials demonstrates that metals in the veins were essentially derived from a mixture of magmatic fluid with a deep crustal fluid that originated near the boundary between the shimanto middle crust and the underlying subcontinental crustal materials we propose that the release of the deep crustal fluid was triggered by intrusion of the shishimano rhyodacite magma related to timing of the mineralization this fluid mixture carried metals to the brittle upper crust along fissures created by extensional stress forming the ore deposits although the deep crustal fluid has not been paid much attention it may be distributed over a large scale in the deep crust from the continent to the arc system and play an important role in the genesis of magmatic hydrothermal ore deposits and in the generation of flow induced deep tremor