carbon isotope systematics of archean au ag vein deposits in the superior province abundant carbonate is a characteristic feature of most archean mesothermal au ag vein deposits but the source of the c is controversial for superior province deposits collectively the maximum variation of average 13c values is from 9 0 0 7 1 n 19 darius to 0 6 1 6 1 n 7 cochenour willians and limiting 13c values are 13 6 and 1 3 at the deposit scale fe dolomites in nongraphitic lithologies are for the most part isotopically uniform where 13c 3 4 0 4 1 hollinger 3 2 0 3 mcintyre 4 7 1 7 dome 2 8 0 6 buffalo ankerite 3 6 0 5 macassa 3 2 0 3 bousquet 5 4 0 9 lamaque and 5 3 0 5 hasaga the restricted individual ranges of 13c values imply a corresponding uniformity to the ambient temperature and 13c c of the ore forming fluids within individual deposits small systematic variations of 13c carbonate arise from i interaction of hydrothermal fluids with carbonaceous rocks ii immiscible separation of co2 ch4 or iii

earthquake clusters in southern california i identification and stability 1 we use recent results on statistical analysis of seismicity to present a robust method for comprehensive detection and analysis of earthquake clusters the method is based on nearest neighbor distances of events in space time energy domain the method is applied to a 1981 2011 relocated seismicity catalog of southern california having 111 981 events with magnitudes m 2 and corresponding synthetic catalogs produced by the epidemic type aftershock sequence etas model analysis of the etas model demonstrates that the cluster detection results are accurate and stable with respect to 1 three numerical parameters of the method 2 variations of the minimal reported magnitude 3 catalog incompleteness and 4 location errors application of the method to the observed catalog separates the 111 981 examined earthquakes into 41 393 statistically significant clusters comprised of foreshocks mainshocks and aftershocks the results reproduce the essential known statistical properties of earthquake clusters which provide overall support for the proposed technique in addition systematic analysis with our method allows us to detect several new features of seismicity that include 1 existence of a significant population of single event clusters 2 existence of foreshock activity in natural seismicity that exceeds expectation based on the etas model and 3 dependence of all cluster properties except area on the magnitude difference of events from mainshocks but not on their absolute values the classification of detected clusters into several major types generally corresponding to singles burst like and swarm like sequences and correlations between different cluster types and geographic locations is addressed in a companion paper

seasonal dynamics of elemental sulfur in two coastal sediments a spectrophotometric method for elemental sulfur s0 analysis without interference from other reduced sulfur compounds was adapted for the use in reducing sediments the s0 distribution in two coastal sediments was studied regularly from summer to winter and compared to factors regulating the s0 accumulation such as redox potentials the rate of bacterial sulfide production and the general sulfur chemistry dense coatings of sulfur bacteria developed on the sediment surface of a sulfuretum which had an s0 concentration of up to 41 mol s cm 3 the 2 5 mm thick bacterial coating contained 40 of all s0 in the sediment a more typical marine sediment with a few cm thick oxidized surface layer had an s0 maximum of 1 3 mol s cm 3 at 2 4 cm depth the s0 maximum in both sediments increased from summer to winter as the sediments gradually became more oxidized the deeper layers maintained a low s0 concentration most of the s0 in the upper few mm of a laboratory sulfuretum was present inside sulfur bacteria and actively migrated up and down with the bacteria depending upon the changing light and oxygen conditions

a seismological model for earthquakes induced by fluid extraction from a subsurface reservoir a seismological model is developed for earthquakes induced by subsurface reservoir volume changes the approach is based on the work of kostrov 1974 and mcgarr 1976 linking total strain to the summed seismic moment in an earthquake catalog we refer to the fraction of the total strain expressed as seismic moment as the strain partitioning function a probability distribution for total seismic moment as a function of time is derived from an evolving earthquake catalog the moment distribution is taken to be a pareto sum distribution with confidence bounds estimated using approximations given by zaliapin et al 2005 in this way available seismic moment is expressed in terms of reservoir volume change and hence compaction in the case of a depleting reservoir the pareto sum distribution for moment and the pareto distribution underpinning the gutenberg richter law are sampled using monte carlo methods to simulate synthetic earthquake catalogs for subsequent estimation of seismic ground motion hazard we demonstrate the method by applying it to the groningen gas field a compaction model for the field calibrated using various geodetic data allows reservoir strain due to gas extraction to be expressed as a function of both spatial position and time since the start of production fitting with a generalized logistic function gives an empirical expression for the dependence of on reservoir compaction probability density maps for earthquake event locations can then be calculated from the compaction maps predicted seismic moment is shown to be strongly dependent on planned gas production

high rate injection is associated with the increase in u s mid continent seismicity an unprecedented increase in earthquakes in the u s mid continent began in 2009 many of these earthquakes have been documented as induced by wastewater injection we examine the relationship between wastewater injection and u s mid continent seismicity using a newly assembled injection well database for the central and eastern united states we find that the entire increase in earthquake rate is associated with fluid injection wells high rate injection wells 300 000 barrels per month are much more likely to be associated with earthquakes than lower rate wells at the scale of our study a well s cumulative injected volume monthly wellhead pressure depth and proximity to crystalline basement do not strongly correlate with earthquake association managing injection rates may be a useful tool to minimize the likelihood of induced earthquakes

depth migration of seasonally induced seismicity at the geysers geothermal field seismicity from injected fluids provides insight into the hydraulically conductive fracture network at the geysers tg california geothermal reservoir induced earthquakes at tg result from both thermoelastic and poroelastic stresses as injected fluids cool the rocks and increase pore pressure the spatiotemporal evolution of m 1 5 seismicity is characterized as a function of depth in the northwest and southeast regions of tg to develop time dependent earthquake rates using an epidemic type aftershock sequence model the seismicity and injection follow an annual cycle that peaks in the winter months and is correlated by depth the results indicate a time lag of 6 months for fluids to migrate 3 km below the injection depth water injection is the main cause of seismicity as fluids penetrate into the reservoir our results suggest that a steeply dipping fracture network of hydraulically conductive faults allows fluid migration to a few kilometers below the point of injection

fault activation by hydraulic fracturing in western canada hydraulic fracturing has been inferred to trigger the majority of injection induced earthquakes in western canada in contrast to the midwestern united states where massive saltwater disposal is the dominant triggering mechanism a template based earthquake catalog from a seismically active canadian shale play combined with comprehensive injection data during a 4 month interval shows that earthquakes are tightly clustered in space and time near hydraulic fracturing sites the largest event moment magnitude mw 3 9 occurred several weeks after injection along a fault that appears to extend from the injection zone into crystalline basement patterns of seismicity indicate that stress changes during operations can activate fault slip to an offset distance of 1 km whereas pressurization by hydraulic fracturing into a fault yields episodic seismicity that can persist for months

characterizing potentially induced earthquake rate changes in the brawley seismic zone southern california the brawley seismic zone bsz in the salton trough of southern california has a history of earthquake swarms and geothermal energy exploitation some earthquake rate changes may have been induced by fluid extraction and injection activity at local geothermal fields particularly at the north brawley geothermal field nbgf and at the salton sea geothermal field ssgf we explore this issue by examining earthquake rate changes and interevent distance distributions in these fields in oklahoma and arkansas where considerable wastewater injection occurs increases in background seismicity rate and aftershock productivity and decreases in interevent distance were indicative of fluid injection induced seismicity here we test if similar changes occur that may be associated with fluid injection and extraction in geothermal areas we use stochastic epidemic type aftershock sequence models to detect changes in the underlying seismogenic processes shown by statistically significant changes in the model parameters the most robust model changes in the ssgf roughly occur when large changes in net fluid production occur but a similar correlation is not seen in the nbgf also although both background seismicity rate and aftershock productivity increased for fluid injection induced earthquake rate changes in oklahoma and arkansas the background rate increases significantly in the bsz only roughly corresponding with net fluid production rate increases moreover in both fields the interevent spacing does not change significantly during active energy projects this suggests that although geothermal field activities in a tectonically active region may not significantly change the physics of earthquake interactions earthquake rates may still be driven by fluid injection or extraction rates particularly in the ssgf

hypocentre estimation of induced earthquakes in groningen induced earthquakes due to gas production have taken place in the province of groningen in the northeast of the netherlands since 1986 in the first years of seismicity a sparse seismological network with large station distances from the seismogenic area in groningen was used the location of induced earthquakes was limited by the few and wide spread stations recently the station network has been extended significantly and the location of induced earthquakes in groningen has become routine work except for the depth estimation of the events in the hypocentre method used for source location by the royal netherlands meteorological institute knmi the depth of the induced earthquakes is by default set to 3 km which is the average depth of the gas reservoir alternatively a differential traveltime for p waves approach for source location is applied on recorded data from the extended network the epicentre and depth of 87 induced earthquakes from 2014 to july 2016 have been estimated the newly estimated epicentres are close to the induced earthquake locations from the current method applied by the knmi it is observed that most induced earthquakes take place at reservoir level several events in the same magnitude order are found near a brittle anhydrite layer in the overburden of mainly rock salt evaporites

morphological development of the florida escarpment observations on the generation of time transgressive unconformities in carbonate terrains abstract an unconformity of 100 m yr magnitude continues to form on the western edge of the florida bahama platform near 26 n where distal mississippi fan sediments are progressively burying the florida escarpment multiple perspectives of the developing unconformity s morphology are revealed using available technologies including gloria images of the entire platform s edge seabeam bathymetric contours and deep tow s high resolution side scan data calibrated with bottom photographs the structure and stratigraphy of the buried escarpment and the associated unconformity are resolved by airgun sparker and deep tow s 4 khz seismic reflection data we summarize the morphological data on the exposed part of the unconformity and the sedimentary deposits accumulating in the basin above the unconformity the exposed cliff face is composed of a staircase of bedding plane terraces which are developed along joint planes the terraces extend 100 1000 m along the escarpment s face and the intervening vertical walls are up to 100 m high the jointed morphology of this mesozoic limestone cliff apparently reflects erosional exposure of its interior anatomy rather than its accretionary shape the change in slope between the platform face and the abyssal plain is very abrupt in places along the contact between the escarpment and fan sediments reduced chemical charged brine seeps occur which locally cause carbonate dissolution and precipitation sulfide mineralization and the deposition of a fossiliferous and organic carbon rich lens associated with chemosynthetic communities these seep deposits and escarpment derived megabreccias intercalate with basinal sediments that overlie the unconformity because surface seismic reflection data do not produce images of the escarpment s face that closely reflect the exposed escarpment s morphology they must also be of limited value in characterizing the surface of similar steeply dipping buried escarpments thus the downslope extent of the heavily eroded platform edge is unclear

correlation between hydrocarbon reservoir properties and induced seismicity in the netherlands earthquakes induced by gas production are a social concern in the netherlands over the last two decades a total of about 350 such earthquakes have been recorded with magnitudes ranging up to 3 5 on richter s scale the new dutch mining law prescribes the operators to give a quantitative estimation of the likelihood of future seismic activity hazard and the associated damage risk this estimation has to be given for every onshore field producing or to be produced a traditional probabilistic seismic hazard analysis psha can not give an estimation of the hazard for a field before the occurrence of seismic activity we have therefore investigated the correlation between parameters related to reservoir and production properties and the occurrence of induced seismicity in a hydrocarbon field statistically using bayes theorem and the rule of succession three key parameters have been identified that show a good correlation with the occurrence of earthquakes pressure drop fault density of the reservoir and stiffness ratio between seal and reservoir rock based on the observed correlation a probability for the occurrence of earthquakes in fields that have no historical earthquake record has been calculated this has resulted in the definition of four groups of hydrocarbon fields having all a different probability 2006

clustering characteristics of gas extraction induced seismicity in the groningen gas field the groningen gas field in the north of the netherlands is one of the largest gas fields in the world since the early 1990s induced seismicity has been recorded the largest magnitude event observed so far was a mw 3 6 event at the town of huizinge in 2012 the risk posed by the induced events urged the necessity to build comprehensive seismological models capable of explaining the spatial temporal distribution of the recorded seismicity and evaluating the regional seismic hazard and risk the link between the occurrence of the seismicity and pressure depletion due to the production of the gas has been firmly established however the construction of comprehensive seismological models as well as hazard assessment is complicated by the fact that it is difficult to distinguish between induced and clustered events events triggered by stress transfer of preceding neighbouring events this paper explores the contribution of clustered populations i e aftershocks to the groningen induced seismic catalogue based on a statistical methodology in the time space magnitude domain specifically the distributions of space time distances between pairs of nearest neighbour earthquakes referred to as cluster style is analysed the cluster style of the groningen induced seismicity is found to be very diffuse and characterized by a very low proportion of fore aftershock sequences and swarms 5 per cent and a large proportion of repeater events 10 per cent in contrast to human induced seismicity in other regions the background seismicity rate of groningen is very low temporal variations in background seismicity rates can be related to changes in fault loading rates induced by gas production furthermore a significant amount of independent coincidental events events occurring very close in time but long distances apart are observed as the large gas field is fully connected loading of the faults occurs roughly simultaneously throughout the field hence the statistical probability of events occurring very close in time but spatially far apart is significantly larger than in areas of fluid injection induced seismicity the significant amount of repeaters and coincidental events cause an overabundance of events at intermediate time and space distances this is further enhanced by the larger location errors in the catalogue increasing the estimated space distance for non relocated events the diffusivity due to this overabundance of events at intermediate time and space distances and the low proportion of true fore aftershocks renders the statistical method used incapable of deriving a proper mode separation value however this is not unique to this method any statistical method aimed at resolving two populations will break down if one of the populations analysed is too small hence it is advisable to use caution when distinguishing fore aftershocks sequences or swarms for induced seismicity where the relative proportion of clustered events may be significantly lower than for tectonic events in addition given the small proportion of clustering and the general uncertainty in earthquake statistics the results of this paper indicate that a distinction for earthquake risk modelling in groningen is unnecessary

differentiating induced and natural seismicity using space time magnitude statistics applied to the coso geothermal field a remarkable characteristic of earthquakes is their clustering in time and space displaying their self similarity it remains to be tested if natural and induced earthquakes share the same behavior we study natural and induced earthquakes comparatively in the same tectonic setting at the coso geothermal field covering the preproduction and coproduction periods from 1981 to 2013 we analyze interevent times spatial dimension and frequency size distributions for natural and induced earthquakes individually these distributions are statistically indistinguishable determining the distribution of nearest neighbor distances in a combined space time magnitude metric lets us identify clear differences between both kinds of seismicity compared to natural earthquakes induced earthquakes feature a larger population of background seismicity and nearest neighbors at large magnitude rescaled times and small magnitude rescaled distances local stress perturbations induced by field operations appear to be strong enough to drive local faults through several seismic cycles and reactivate them after time periods on the order of a year

stable isotope evidence for chemosynthesis in an abyssal seep community communities of abundant organisms similar to those which surround the hydrothermal vents of the east pacific rise epr occur in 3 266 m of water in the gulf of mexico they were discovered with the alvin at 26 02 n 84 55 w in an area where pore waters seep from the cretaceous limestones of the adjacent platform at the contact between the florida escarpment and the holocene hemipelagic sediments of the abyssal gulf because of the unusual abundance of organisms in this deep sea environment and the taxonomic similarities to the chemosynthetically based communities which surround the hydrothermal vents on the epr the seep communities are suspected to exist on a local non photosynthetic food source1 we have now measured isotope ratios in tissues of organisms which surround these saline seeps to determine the origin of the local food chain the tissues have extremely negative 13c 42 to 77 pdb and 15n 2 72 to 9 34 air values such highly fractionated carbon and nitrogen isotopes are unknown in food chains based on photosynthesis suggesting that these communities are chemosynthetic the cause of this extreme fractionation is attributed either to assimilation from local supplies of isotopically depleted methane and ammonium or to biochemical fractionation the tissues of these animals contain significant amounts of 14c 60 modern so the source of this fractionated carbon is not predominantly fossil methane

continental margin brine seeps their geological consequences local dissolution observed at the base of the florida escarpment appears to result from acid generated by sea floor oxidation of dissolved sulfide species carried in brines that seep from the base of the escarpment the extent of seep corrosion depends upon the amount of sulfide that has exited the platform and the efficiency with which the acid attacks the limestones of the escarpment calculations suggest that brine seepage influences the shape of these escarpments by undercutting and steepening the carbonate continental margin edges other processes competing for the dissolved sulfides are bacterial chemosynthesis and sulfide mineralization which produces organic carbon and sulfide mineral rich deposits along the unconformity that separates the buried escarpment from onlapping abyssal sediments

physics based forecasting of induced seismicity at groningen gas field the netherlands earthquakes induced by natural gas extraction from the groningen reservoir the netherlands put local communities at risk responsible operation of a reservoir whose gas reserves are of strategic importance to the country requires understanding of the link between extraction and earthquakes we synthesize observations and a model for groningen seismicity to produce forecasts for felt seismicity m 2 5 in the period february 2017 to 2024 our model accounts for poroelastic earthquake triggering and rupture on the 325 largest reservoir faults using an ensemble approach to model unknown heterogeneity and replicate earthquake statistics we calculate probability distributions for key model parameters using a bayesian method that incorporates the earthquake observations with a nonhomogeneous poisson process our analysis indicates that the groningen reservoir was not critically stressed prior to the start of production epistemic uncertainty and aleatoric uncertainty are incorporated into forecasts for three different future extraction scenarios the largest expected earthquake was similar for all scenarios with a 5 likelihood of exceeding m 4 0

extreme threshold failures within a heterogeneous elastic thin sheet and the spatial temporal development of induced seismicity within the groningen gas field measurements of the strains and earthquakes induced by fluid extraction from a subsurface reservoir reveal a transient exponential like increase in seismicity relative to the volume of fluids extracted if the frictional strength of these re activating faults is heterogeneously and randomly distributed then progressive failures of the weakest fault patches account in a general manner for this initial exponential like trend allowing for the observable elastic and geometric heterogeneity of the reservoir the spatio temporal evolution of induced seismicity over 5 years is predictable without significant bias using a statistical physics model of poro elastic reservoir deformations inducing extreme threshold frictional failures of previously inactive faults this model is used to forecast the temporal and spatial probability density of earthquakes within the groningen natural gas reservoir conditional on future gas production plans probabilistic seismic hazard and risk assessments based on these forecasts inform the current gas production policy and building strengthening plans

the origin and isotopic composition of dissolved sulfide in groundwater from carbonate aquifers in florida and texas the 34s values of dissolved sulfide and the sulfur isotope fractionations between dissolved sulfide and sulfate species in floridan ground water generally correlate with dissolved sulfate concentrations which are related to flow patterns and residence time within the aquifer the dissolved sulfide derives from the slow in situ biogenic reduction of sulfate dissolved from sedimentary gypsum in the aquifer in areas where the water is oldest the dissolved sulfide has apparently attained isotopic equilibrium with the dissolved sulfate 34s 65 per mil at the temperature 28 c of the system this approach to equilibrium reflects an extremely slow reduction rate of the dissolved sulfate by bacteria this slow rate probably results from very low concentrations of organic matter in the aquifer in the reducing part of the edwards aquifer texas there is a general down gradient increase in both dissolved sulfide and sulfate concentrations but neither the 34s values of sulfide nor the sulfide sulfate isotope fractionation correlates with the ground water flow pattern the dissolved sulfide species appear to be derived primarily from biogenic reduction of sulfate ions whose source is gypsum dissolution although upgradient diffusion of h2s gas from deeper oil field brines may be important in places the sulfur isotope fractionation for sulfide sulfate about 38 per mil is similar to that observed for modern oceanic sediments and probably reflects moderate sulfate reduction in the reducing part of the aquifer owing to the higher temperature and significant amount of organic matter present contributions of isotopically heavy h2s from oil field brines are also possible

discriminating characteristics of tectonic and human induced seismicity we analyze statistical features of background and clustered subpopulations of earthquakes in different regions in an effort to distinguish between human induced and natural seismicity analysis of end member areas known to be dominated by human induced earthquakes the geyser geothermal field in northern california and tautona gold mine in south africa and regular tectonic activity the san jacinto fault zone in southern california and the coso region excluding the coso geothermal field in eastern central california reveals several distinguishing characteristics induced seismicity is shown to have 1 higher rate of background events both absolute and relative to the total rate 2 faster temporal offspring decay 3 higher rate of repeating events 4 larger proportion of small clusters and 5 larger spatial separation between parent and offspring compared to regular tectonic activity these differences also successfully discriminate seismicity within the coso and salton sea geothermal fields in california before and after the expansion of geothermal production during the 1980s online material figures of examined regions earthquake epicenters and joint distributions of the time and space components of the nearest neighbor distance

sulfur isotope and porewater geochemistry of florida escarpment seep sediments abstract distributions of porewater constituents so 4 nh 4 cl co 2 and h 2 s solid phase iron and sulfur concentrations and the sulfur isotopic composition of dissolved and solid phases were investigated in sediments from abyssal seeps at the base of the florida escarpment despite the apparent similarity of seep sediment porewater chemistry to that of typical marine sediments undergoing early diagenesis relationships between chemical distributions and isotopic measurements revealed that the distribution of pore fluid constituents was dominated by processes occurring within the platform rather than by in situ microbial processes ammonium and sulfate concentrations were linearly correlated with chloride concentrations indicating that variations in porewater chemistry were controlled by the admixture of seawater and a sulfate depleted brine with a chlorinity of 27 5 1 9 and 2 2 1 3 mm ammonium concentration at sites dominated by seepage dissolved sulfate isotopic composition remained near seawater values despite depletion in porewater concentrations porewater co 2 concentrations were found to be elevated relative to seawater but not to the extent predicted from the observed sulfate depletion sediment solid phase sulfur was predominantly pyrite at concentrations as high as 20 s by weight in contrast to typical marine deposits pyrite concentrations were not related to the quantity of sedimentary organic matter pyrite 34 s values ranged from 29 to 21 cdt however only positive 34 s values were observed at sites associated with high pyrite concentrations isotopically heavy pyrite was observed at sites with porewater sulfate of seawater like isotopic composition isotopically light pyrite was associated with sites where porewater sulfate exhibited 34 s values greater than those in seawater indicating the activity of in situ microbial sulfate reduction thus dual sulfide sources are suggested to explain the range in sediment pyrite isotopic composition a 34 s enriched 10 to 20 source adverted from within the florida platform and a lighter 34 s depleted component generated in situ from microbial reduction of seawater sulfate the degree of pyritization of seep sediments was as high as 0 9 and was controlled by pyrite concentrations which varied over a wider range than did the non pyrite solid phase iron concentrations the highest non sulfide solid phase iron concentrations were observed in sediments that are believed to be at the front of the advancing seep fluids i e hemipelagic sediments newly exposed to the seep fluids indicating that dissolution of hemipelagic background sediment may be the source of at least half of the iron to the highly pyritized seep sediments porewater sulfide concentrations were variable reaching a maximum of 5 7 mm and were not correlated with the degree of pyritization of the sediments suggesting that iron was not particularly limiting to pyrite formation

organic carbon sulphur and iron in recent semi euxinic sediments of kau bay indonesia kau bay island of halmahera eastern indonesia is a 470 m deep basin separated from the pacific ocean by a sill that is at present only 40 m below sea level during weichselian time the sea level dropped below the depth of the sill and freshwater sediments were deposited these sediments are rich in organic matter corg 2 6 wt with terrigenous isotope characteristics 13corg 28 to 30 and are also rich in sulphur s 4 wt this sulphur enrichment is interpreted to be a late diagenetic feature related to diffusion of dissolved sulphate and sulphide from the marine sediments into the freshwater sediments the sulphur in these sediments has a 34s value of 15 the overlying holocene sediments consist of marine muds deposited in alternating low oxygen and h2s bearing bottom waters the marine sediments are also rich in organic matter corg 2 6 wt but of mixed terrigenous and marine origin 13c 25 to 19 moreover the sulphur content of these holocene sediments is lower s 1 2 wt and isotopically lighter 34s 20 in addition to pyrite large amounts of acid volatile sulphur avs compounds accumulate in kau bay the reactive iron content of the sediment limits the amount of iron that is sulphidized while the supply of oxidants controls the limited conversion of avs to pyrite total and reactive iron contents are strongly correlated with the amount of terrigenous organic matter as a consequence of their common provenance and depositional histories the marine sediments in kau bay show no simple relation between organic carbon and sulphur

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

old carbon in living organisms and young cac03 cements from abyssal brine seeps abyssal brine springs at the base of the florida escarpment in the gulf of mexico 3 280 m 26 o2 n 84 55 w are surrounded by communities of abundant heterotrophic organisms1 4 and carbonate cemented crusts5 these organisms are apparently supported by local chemosynthetic primary production because the 13c content of their tissues is lower than that found in typical photosynthetically fixed organic carbon6 and the enzymes associated with chemosynthetic metabolism are present in their tissues7 8 here we report that fossil methane is the dominant source of carbon found in living tissues and recent authigenic carbonate minerals associated with abyssal brine seeps at the base of the florida escarpment most organic carbon and authigenic carbonates adjacent to the seeps contain progressively less modern carbon as their 13c contents approach that of methane carried in the brine incorporation of fossil methane 1 3 modern carbon into living tissues and carbonate cements results in recently formed materials which are depleted in 14c therefore 14c cannot be used to indicate the age of authigenic materials produced at the pore water seepage environments that speckle the continental margins of the world

a comparison of long term changes in seismicity at the geysers salton sea and coso geothermal fields geothermal energy is an important source of renewable energy yet its production is known to induce seismicity here we analyze seismicity at the three largest geothermal fields in california the geysers salton sea and coso we focus on resolving the temporal evolution of seismicity rates which provides important observational constraints on how geothermal fields respond to natural and anthropogenic loading we develop an iterative regularized inversion procedure to partition the observed seismicity rate into two components 1 the interaction rate due to earthquake earthquake triggering and 2 the smoothly varying background rate controlled by other time dependent stresses including anthropogenic forcing we apply our methodology to compare long term changes in seismicity to monthly records of fluid injection and withdrawal at the geysers we find that the background seismicity rate is highly correlated with fluid injection with the mean rate increasing by approximately 50 and exhibiting strong seasonal fluctuations following construction of the santa rosa pipeline in 2003 in contrast at both salton sea and coso the background seismicity rate has remained relatively stable since 1990 though both experience short term rate fluctuations that are not obviously modulated by geothermal plant operation we also observe significant temporal variations in gutenberg richter b value earthquake magnitude distribution and earthquake depth distribution providing further evidence for the dynamic evolution of stresses within these fields the differing field wide responses to fluid injection and withdrawal may reflect differences in in situ reservoir conditions and local tectonics suggesting that a complex interplay of natural and anthropogenic stressing controls seismicity within california s geothermal fields

seawater circulation through the flank of the florida platform evidence and implications dense biological communities at the base of the florida escarpment depend on energy provided by reduced compounds for bacterial chemosynthetic production sharp gradients in the concentrations of ch4 h2s nh4 so42 cl na mg2 sr2 i and seabed 226ra2 exist in the sediments underlying these communities the compositions of this fluid departs from that of normal seawater indicating the importance of microbial and diagenetic reactions within the escarpment before it is advected to the seafloor the 87sr 86sr ratios in the seep fluids range from 0 70920 seawater to 0 70773 which requires addition of light mesozoic strontium 18o values 0 3 to 0 1 smow and d values 2 6 smov of these waters are similar to normal seawater values and do not indicate that either meteoric processes or gas hydrates are involved in the genesis of the seeping fluid concentrations of cl ca2 and na suggest that the fluids which arrive at the seafloor are a mixture of mostly seawater with 4 7 formation brine from within the florida bahama platform mesozoic brines within the florida platform occupy levels above the scarp base a density driven flow system in implied which involves mesozoic platform brines that are greatly diluted by seawater entrained through the flanks of the platform the observed depletion of sulfate in the seeping fluids requires that sulfate reduction must occur in the platform within the zone where the recharging seawater and platform brines mix in order to produce the high concentrations of biogenic methane observed methanogenesis is inferred to be occuring within the platform in a zone where sulfate reduction has gone to completion the zone where the mixing of brine and seawater occurs should be cooled by the flushing seawater and heavily corroded by under saturation occurring as a result of the mixing the platform interior mixing is non conservative because of the addition of light mesozoic sr2 and the relative depletion in mg2 with espect to cl ca2 and na2 concentrations the inferred uptake of mg2 and concurrent depletion of so42 on the flanks of this margin