significant sink of ocean eddy energy near western boundaries ocean eddies generated through instability of the mean flow are a vital component of the energy budget of the global ocean modelling combined with satellite altimetry data suggests that the energy from westward propagating eddies is scattered and eventually dispersed when they reach the western boundary of an ocean basin

probability of a given magnitude earthquake induced by a fluid injection 1 fluid injections in geothermic and hydrocarbon reservoirs induce small earthquakes 3 m 2 occasionally however earthquakes with larger magnitudes m 4 occur we investigate magnitude distributions and show that for a constant injection pressure the probability to induce an earthquake with a magnitude larger than a given value increases with injection time corresponding to a bi logarithmical law with a proportionality coefficient close to one we find that the process of pressure diffusion in a poroelastic medium with randomly distributed sub critical cracks obeying a gutenberg richter relation well explains our observations the magnitude distribution is mainly inherited from the statistics of pre existing fracture systems the number of earthquakes greater than a given magnitude also increases with the strength of the injection source and the tectonic activity of the injection site our formulation provides a way to estimate expected magnitudes of induced earthquakes it can be used to avoid significant earthquakes by correspondingly planning fluid injections

mesoscale air sea interaction and its role in eddy energy dissipation in the kuroshio extension abstractusing the high resolution community earth system model cesm output this study investigates air sea interaction and its role in eddy energy dissipation in the kuroshio extension ke regi

role of fluid injection on earthquake size in dynamic rupture simulations on rough faults an outstanding question for induced seismicity is whether the volume of injected fluid and or the spatial extent of the resulting pore pressure and stress perturbations limit rupture size we simul

characterization of hydraulic properties of rocks using probability of fluid induced microearthquakes the use of borehole fluid injections is typical for exploration and development of hydrocarbon or geothermal reservoirs such injections often induce small magnitude earthquakes the nature of processes leading to triggering of such microseismicity is still not completely understood here we consider induced microseismicity using as examples two case studies of geothermal reservoirs in crystalline rocks and one case study of a tight gas sandstone reservoir in all three cases we found that the probability of induced earthquakes occurring is very well described by the relaxation law of pressure perturbation in fluids filling the pore space in rocks this strongly supports the hypothesis of seismicity triggered by pore pressure moreover this opens additional possibilities of using passive seismic monitoring to characterize hydraulic properties of rocks on the reservoir scale with high precision

geomechanical analysis of fluid injection and seismic fault slip for the mw4 8 timpson texas earthquake sequence an earthquake sequence that culminated in a mw4 8 strike slip event near timpson east texas the largest reported earthquake to date in that region had previously been attributed to wastewater injection starting 17 months before the onset of recorded seismic activity to test if this earthquake sequence can be attributed to wastewater injection we conducted coupled poroelastic finite element simulations to assess the spatial and temporal evolution of pore pressure and stress field in the vicinity of the injection wells and to calculate the coulomb failure stress on the seismogenic fault as a function of the permeability of the injection layer fault orientation fault permeability and orientation and magnitude of the in situ stress we find that injection induced fault slip is plausible within the range of selected model input parameters with slip favored by low reservoir permeability low fault permeability and a favorable orientation of the fault relative to the in situ stress state other combinations of equally plausible input parameters predict no slip within 96 months of simulated injection under most favorable boundary conditions for fault slip fault slip occurs 7 months after the start of injection our results highlight the importance of detailed geomechanical site characterization for robust fault stability assessment prior to wastewater injection

islands as eddy transformation and generation hotspots cabo verde case study abstract deep ocean islands have long been associated with the generation of oceanic eddies in their wakes however their interaction with incoming eddies has seldom been considered this study focuses on the characterization of background and locally generated mesoscale eddies in the cabo verde archipelago between 2003 and 2014 special attention is given to the interaction of incoming eddies with the bathymetry of the islands along with their impacts on the local generation of eddies island induced wind shear effects are also considered in addition some examples of the biological response to background and locally generated eddies are discussed this is achieved by combining remote sensing satellite observations for wind sea surface height and chlorophyll a chla surface concentrations the results show that the interaction between incoming background eddies and the archipelago is a recurrent phenomenon which results in eddy deflection splitting merging intensification and termination sorted by highest to lowest number of occurrences local island induced disturbances are also significant mainly due to atmospheric effects such processes result in the generation of island induced eddies and in wind mediated eddy intensification and confinement more often observed in the leeward group nonetheless it is strongly suggested that many of the locally generated eddies are a direct product or by product of the interaction of background eddies with the islands with respect to the biological realm a locally generated cyclonic eddy is observed to originate a pronounced phytoplankton bloom in the vicinity of the tallest island nonetheless background eddies generated off the african coast are often associated with enhanced chla concentrations when they intersect the archipelago such observations challenge the idea that local biological productivity in deep oceanic islands is exclusively driven by island induced mechanisms

work done by atmospheric winds on mesoscale ocean eddies mesoscale eddies are ubiquitous in the ocean and dominate the ocean s kinetic energy however physical processes influencing ocean eddy energy remains poorly understood mesoscale ocean eddy wind interaction potentially provides an energy flux into or out of the eddy field but its effect on ocean eddies has not yet been determined here we examine work done by atmospheric winds on more than 1 200 000 mesoscale eddies identified from satellite altimetry data and show that atmospheric winds significantly damp mesoscale ocean eddies particularly in the energetic western boundary current regions and the southern ocean furthermore the large scale wind stress curl is found to on average systematically inject kinetic energy into anticyclonic cyclonic eddies in the subtropical subpolar gyres while mechanically damps anticyclonic cyclonic eddies in the subpolar subtropical gyres

a statistical model for seismic hazard assessment of hydraulic fracturing induced seismicity we analyze the interevent time distribution of hydraulic fracturing induced seismicity collected during 18 stages at four different regions we identify a universal statistical process describing the distribution of hydraulic fracturing induced events in time the distribution of waiting times between subsequently occurring events is given by the exponential probability density function of the homogeneous poisson process our findings suggest that hydraulic fracturing induced seismicity is directly triggered by the relaxation of stress and pore pressure perturbation initially created by the injection therefore compared to this relaxation the stress transfer caused by the occurrence of preceding seismic events is mainly insignificant for the seismogenesis of subsequently occurring events we develop a statistical model to compute the occurrence probability of hydraulic fracturing induced seismicity this model can be used to assess the seismic hazard associated with hydraulic fracturing operations no aftershock triggering has to be included in the statistical model

scaling of seismicity induced by nonlinear fluid rock interaction 1 fluid injections into geothermal systems sometimes can produce significant seismic events with magnitudes of up to 4 however in the case of hydraulic fracturing of hydrocarbon reservoirs such events occur extremely seldom in the last case in contrast to the former one the structure of rocks is being actively destroyed e g opening of tensile fractures and the fluid rock interaction is strongly nonlinear e g a strong increase of permeability what is the role of this nonlinearity we consider nonlinear pore pressure diffusion to explain features of seismicity we formulate seismicity triggering front its propagation is sensitive to a grade of nonlinearity to spatial dimension of diffusion and to the injection rate we show that a probability of an event with a magnitude larger than a given one increases proportionally to the injected mass an increase of this probability with time is insensitive to the nonlinearity we compare different borehole experiments in some cases the injection produces clearly nonlinear impact on rocks in others this impact is approximately linear we find a well agreement with our theory we observe an insensitivity of temporal increments of magnitude probability to the grade of nonlinearity these increments are controlled by injection rate increments in contrast nonlinear fluid rock interactions are characterized by a strong dominance of small earthquakes defects activated by a nonlinear diffusion possibly obey gutenberg richter statistics with anomalous high b values in the case of a linear diffusion magnitude distributions of events are probably inherited from pre existing fracture systems

discrimination between induced triggered and natural earthquakes close to hydrocarbon reservoirs a probabilistic approach based on the modeling of depletion induced stress changes and seismological source parameters earthquakes occurring close to hydrocarbon fields under production are often under critical view of being induced or triggered however clear and testable rules to discriminate the different events have rarely been developed and tested the unresolved scientific problem may lead to lengthy public disputes with unpredictable impact on the local acceptance of the exploitation and field operations we propose a quantitative approach to discriminate induced triggered and natural earthquakes which is based on testable input parameters maxima of occurrence probabilities are compared for the cases under question and a single probability of being triggered or induced is reported the uncertainties of earthquake location and other input parameters are considered in terms of the integration over probability density functions the probability that events have been human triggered induced is derived from the modeling of coulomb stress changes and a rate and state dependent seismicity model in our case a 3 d boundary element method has been adapted for the nuclei of strain approach to estimate the stress changes outside the reservoir which are related to pore pressure changes in the field formation the predicted rate of natural earthquakes is either derived from the background seismicity or in case of rare events from an estimate of the tectonic stress rate instrumentally derived seismological information on the event location source mechanism and the size of the rupture plane is of advantage for the method if the rupture plane has been estimated the discrimination between induced or only triggered events is theoretically possible if probability functions are convolved with a rupture fault filter we apply the approach to three recent main shock events 1 the m w 4 3 ekofisk 2001 north sea earthquake close to the ekofisk oil field 2 the m w 4 4 rotenburg 2004 northern germany earthquake in the vicinity of the sohlingen gas field and 3 the m w 6 1 emilia 2012 northern italy earthquake in the vicinity of a hydrocarbon reservoir the three test cases cover the complete range of possible causes clearly human induced not even human triggered and a third case in between both extremes

control of hazard due to seismicity induced by a hot fractured rock geothermal project in 2003 hydraulic stimulations were carried out in a geothermal field in eastern el salvador central america as part of a project to explore the feasibility of commercial hot fractured rock energy generation a key requisite for this environmentally friendly energy source is that the fracturing of the hot rocks at depths of 1 2 km must not produce levels of ground shaking at the surface that would present a serious disturbance or threat to the local population thresholds of tolerable ground motion were inferred from guidelines and regulations on tolerable levels of vibration and from correlations between instrumental strong motion parameters and intensity considering the vulnerability of the exposed housing stock the thresholds were defined in terms of peak ground velocity pgv and incorporated into a traffic light system that also took account of the frequency of occurrence of the induced earthquakes the system was implemented through a dedicated seismograph array and locally derived predictive equations for pgv the traffic light was used as a decision making tool regarding the duration and intensity of pumping levels during the hydraulic stimulations the system was supplemented by a small number of accelerographs and re calibrated using records obtained during the rock fracturing

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

on the seasonal eddy variability in the kuroshio extension abstractusing a recently developed tool multiscale window transform mwt and the mwt based canonical energy transfer theory this study investigates the seasonal eddy variability in the kuroshio

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

satellite observations of mesoscale eddy induced ekman pumping abstractthree mechanisms for self induced ekman pumping in the interiors of mesoscale ocean eddies are investigated the first arises from the surface stress that occurs because of differences between surface wind and ocean velocities resulting in ekman upwelling and downwelling in the cores of anticyclones and cyclones respectively the second mechanism arises from the interaction of the surface stress with the surface current vorticity gradient resulting in dipoles of ekman upwelling and downwelling the third mechanism arises from eddy induced spatial variability of sea surface temperature sst which generates a curl of the stress and therefore ekman pumping in regions of crosswind sst gradients the spatial structures and relative magnitudes of the three contributions to eddy induced ekman pumping are investigated by collocating satellite based measurements of sst geostrophic velocity and surface winds to the interiors of eddies identified from their sea surface height signatures on average e

enhanced vertical propagation of storm induced near inertial energy in an eddying ocean channel model the interaction between inertial oscillations generated by a storm and a mesoscale eddy field is studied using a southern ocean channel model it is shown that the leakage of near inertial energy out of the surface layer is strongly enhanced by the presence of the eddies with the anticyclonic eddies acting as a conduit to the deep ocean given the ubiquity of the atmospheric storm tracks a source of near inertial energy for the ocean and regions of strong ocean mesoscale variability we argue that this effect could be important for understanding pathways by which near inertial energy enters the ocean and is ultimately available for mixing

faults strengthening and seismicity induced by geothermal exploitation on a spreading volcano mt amiata italia abstract seismogenic structures such as faults play a primary role in geothermal system generation recharge and output they are also the most susceptible to release seismic energy over fluid injection extraction operations during anthropic exploitation we describe the microseismic activity recorded in 2000 2001 in the piancastagnaio geothermal field on the se flank of mt amiata volcano southern tuscany italy from our field observations we find that a relatively high percentage i e about 5 of the recorded events are of hydro fracturing origin and have a distinct waveform seismic signature when compared to the recorded events of tectonic shear fracturing origin while hydrofracturing events are mostly concentrated around the geothermal fields the spatial distribution of hypocenters shows a deepening and a density increase of the micro seismic activity from the volcanic axis toward the exploited geothermal reservoir suggesting that volcanic spreading at amiata is still active the study of different data sets from different time periods together with the knowledge from terzaghi s law that production of large quantity of pore fluid with the associated fluid pressure reduction could augment the stress normal to faults surfaces and thus their resistance to slip make us argue that the process of volcanic spreading affecting the edifice of amiata may allow augmented accumulation of stresses on faults eventually leading to the release of higher stress drops once ruptures occur the gutenberg richter magnitude frequency distribution shows that the strongest events on record have a local magnitude in the 5 5 5 m l range for 100 year recurrence time in conclusions we infer that geothermal exploitation at mt amiata should be closely monitored in order to understand how fluid injection production is responsible for the hydrofracturing seismic activity and affects stress accumulation on and rupture of faults within and in the neighborhood of the geothermal fields this understanding may allow a geothermal field management that will hopefully reduce the risk for inducing larger seismic events in the area

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

satellite observations of chlorophyll phytoplankton biomass and ekman pumping in nonlinear mesoscale eddies nonlinear mesoscale eddies can influence biogeochemical cycles in the upper ocean through vertical and horizontal advection of nutrients and marine organisms the relative importance of these two processes depends on the polarity of an eddy cyclones versus anticyclones and the initial biological conditions of the fluid trapped in the core of the eddy at the time of formation eddies originating in the eastern south indian ocean are unique in that anticyclones typically associated with downwelling contain elevated levels of chlorophyll a enhanced primary production and phytoplankton communities generally associated with nutrient replete environments from analysis of 9 years of concurrent satellite measurements of sea surface height chlorophyll phytoplankton carbon and surface stress we present observations that suggest eddy induced ekman upwelling as a mechanism that is at least partly responsible for sustaining positive phytoplankton anomalies in anticyclones of the south indian ocean the biological response to this eddyinduced ekman upwelling is evident only during the austral winter during the austral summer the biological response to eddy induced ekman pumping occurs deep in the euphotic zone beyond the reach of satellite observations of ocean color

detailed joint structure in a geothermal reservoir from studies of induced microearthquake clusters microearthquake clusters form distinct planar patterns within five study regions of a geothermal reservoir undergoing hydraulic fracturing at fenton hill new mexico the patterns define individual slipping joint surfaces of dimension 40 120 m containing 80 150 events each sharp straight edges truncate the clusters we interpret these as marking intersections with aseismic joints each edge orientation is consistent with an intersection between the active joint and a plane oriented parallel to one of the other clusters we identify therefore it appears that cluster shapes constrain the geometry of seismic and aseismic joints both could be important components of the fluid flow network the distribution of inferred slip plane orientations is consistent with but fails to provide sufficient constraint to differentiate conclusively between two very different stress field estimates one measured using pressurization and wellbore breakouts the other using focal mechanisms of the largest microearthquakes an impermeable joint model requiring pore pressure in excess of the normal stress on a joint before slip can occur was inconsistent with many of the inferred slip plane orientations the high quality locations were possible because events from the same cluster generated nearly similar waveforms permitting the precise determination of relative arrival times standard deviations of arrival time residuals fall between 0 1 and 1 1 ms for these clusters major axes and aspect ratios of the 90 confidence ellipsoids range from 6 to 28 m and 1 5 to 8 respectively small events dominate the seismic energy release and thoroughly populate the identified active joints allowing the hypocenters to reflect details of the joint structure to further investigate the reservoir structure we applied a source array slant stack technique to waveforms from the well located clusters yielding directions that scattered energy left each cluster by studying paths of scattered waves we expected to pinpoint impedance contrasts that might have indicated concentrations of fluid filled joints however results show that scattered energy in the s wave coda left the source region in the same direction as the direct s wave direct waves may have excited borehole tube waves that became trapped in the vicinity of the geophone tool overwhelming any energy scattered from the reservoir

deep injection and closely monitored induced seismicity at paradox valley colorado the u s bureau of reclamation s paradox valley unit pvu extracts aquifer brine from nine shallow wells along the dolores river paradox valley in southwestern colorado and after treating high pressure injects the brine 4 3 4 8 km below the surface pvu injects at rates between 800 and 1300 l min since 1991 pvu has emplaced over 4 106 m3 of fluid and induced more than 4000 surface recorded seismic events the events are recorded on the local 15 station paradox valley seismic network the induced seismicity at paradox separates into two distinct source zones a principle zone 95 of the events asymmetrically surrounding the injection well to a maximum radial distance of 3 km and a secondary ellipsoidal zone 2 5 km long and centered 8 km northwest of the injection well the expansion of these zones has stabilized since mid 1999 about three years after the onset of continuous injection within the principal zone hypocenters align in distinct linear patterns showing at depth stratigraphy and the local wray mesa fracture and fault system the primary faults of the wray mesa system are aseismic striking subparallel to the inferred maximum principal stress direction with one or more faults probably acting as fluid conduits to the secondary seismic zone individual seismic events in both zones do not discernibly correlate with short term injection parameters however a 0 5 km2 region immediately northwest of the injection well responds to long term large scale changes in injection rate and the surpassing of a threshold injection pressure focal mechanisms of the induced events are consistent with simple double couple strike slip moments and subhorizontal extension to the northeast in addition the fault planes are consistent with principal stress directions determined from borehole breakouts more than 99 9 of the pvu seismicity is below human detection m 2 5 however approximately 15 events have been felt locally with the largest being a magnitude m 4 3 because of the m 4 3 and two earlier felt m 3 5 events and injection economics pvu changed injection strategies three times since 1996 these changes reduced seismicity from 1100 events year to as low as 60 events year

investigation of fault mechanisms during geothermal reservoir stimulation experiments in the cooper basin australia abstract subsequent to an initial reservoir stimulation in 2003 a second long term fluid injection experiment was conducted in the cooper basin australia in 2005 to further enhance and enlarge the existent geothermal reservoir approximately 25 000 m 3 of water were injected into the granitic crust at 4250 m depth thereby inducing about 16 000 seismic events which were recorded by a local eight station network event magnitudes calibrated by recordings of the permanent network of geosciences australia are in the range between m l 1 2 and 2 9 with seismic moments between 10 9 and 10 13 n m hypocenter locations could be determined for 8886 events the spatial hypocenter distribution indicates that the seismicity occurred on the same subhorizontal layer structure identified for the initial reservoir stimulation which is further extended in the course of restimulation early seismicity is located near the outer rim of the previous zone of seismic activity and subsequently migrates both toward and away from the injection well the immediate vicinity of the injection well remains seismically quiet during restimulation these effects can be explained by a simple kaiser effect model where the induced seismicity is controlled by the in situ fluid pressure increase compound fault plane solutions based on p phase polarities indicate a similar fault mechanism for nearly all events the dominating fault mechanism is consistent with the regional stress field acting on a larger scale fracture zone with an orientation as outlined by the hypocenter distribution a small number of events with reverse mechanisms might indicate the existence of conjugated fractures locally intersecting the main fracture zone cumulative slip determined by mapping the slip contribution of individual events onto the fracture zone indicates that most fracture patches in the reservoir slipped repeatedly accumulating up to several centimeters of shear displacement

earthquakes triggered by silent slip events on kīlauea volcano hawaii silent earthquakes or slow slip events happen so slowly that they cannot be detected by conventional seismographs but now the availability of gps data means that they can be followed in detail segall et al report on a series of small earthquakes on k lauea volcano hawaii the earthquakes at depths of 7 to 8 km appear to be triggered by otherwise silent slow slips though small triggered earthquakes of this type can be used to help quantify the increased hazard due to slow slip events slow slip events or silent earthquakes have recently been discovered in a number of subduction zones including the nankai trough1 2 3 in japan cascadia4 5 and guerrero6 in mexico but the depths of these events have been difficult to determine from surface deformation measurements although it is assumed that these silent earthquakes are located along the plate megathrust this has not been proved slow slip in some subduction zones is associated with non volcanic tremor7 8 but tremor is difficult to locate and may be distributed over a broad depth range9 except for some events on the san andreas fault10 slow slip events have not yet been associated with high frequency earthquakes which are easily located here we report on swarms of high frequency earthquakes that accompany otherwise silent slips on k lauea volcano hawaii for the most energetic event in january 2005 the slow slip began before the increase in seismicity the temporal evolution of earthquakes is well explained by increased stressing caused by slow slip implying that the earthquakes are triggered the earthquakes located at depths of 7 8 km constrain the slow slip to be at comparable depths because they must fall in zones of positive coulomb stress change triggered earthquakes accompanying slow slip events elsewhere might go undetected if background seismicity rates are low detection of such events would help constrain the depth of slow slip and could lead to a method for quantifying the increased hazard during slow slip events because triggered events have the potential to grow into destructive earthquakes

decadal mean impact of including ocean surface currents in bulk formulas on surface air sea fluxes and ocean general circulation abstractthe decadal mean impact of including ocean surface currents in the bulk formulas on surface air sea fluxes and the ocean general circulation is investigated for the first time using a global eddy permitting coupled ocean sea ice model although including ocean surface currents in air sea flux calculations only weakens the surface wind stress by a few percent it significantly reduces wind power input to both geostrophic and ageostrophic motions and damps the eddy and mean kinetic energy throughout the water column furthermore the strength of the horizontal gyre circulations and the atlantic meridional overturning circulation are found to decrease considerably by 10 15 and 13 respectively as a result of the weakened ocean general circulation the maximum northward global ocean heat transport decreases by about 0 2 pw resulting in a lower sea surface temperature and reduced surface heat loss in the northern north atlantic additional sensitivity model experiments further demonstrate that

the small effect of poroelastic pressure transients on triggering of production induced earthquakes in the groningen natural gas field over the past decade a steep increase in the number of seismic events has been observed in the groningen gas field the netherlands it is generally accepted that these are induced by compaction of the reservoir rock due to extensive depletion causing a buildup of strain energy in faults that may be released seismically we address the possible triggering of fault slip by the transient pressure field surrounding a well that has undergone a sudden rate change assuming a unilateral decoupling between displacement and pressure numerical experiments are conducted using a sequential finite volume finite element solution strategy that fully incorporates second order terms in the radial flow equation we investigate an idealized groningen like geometry to discover whether the hypothesized possibility of triggering induced seismicity exists explore how some controllable and uncontrollable variables influence its severity and possibly provide clues on how production strategy might be able to avoid its occurrence the results demonstrate that sudden production changes can indeed trigger near well seismic events but that the effect is very small compared to other potential causes changing from sudden to gradual changes in well rates is therefore not expected to lead to a significant reduction in the number or magnitude of production induced earthquakes in the groningen field

balancing reservoir creation and seismic hazard in enhanced geothermal systems summary fractureshear dilatancyisanessentialprocessforenhancingthepermeabilityofdeepgeothermal reservoirs and is usually accompanied by the radiation of seismic waves however the hazard and risk perspective of induced seismicity research typically focuses only on the question of how to reduce the occurrence of induced earthquakes here we present a quantitative analysisofseismichazardasafunctionofthetwokeyfactorsdefininganenhancedgeothermal system the permeability enhancement and the size of the stimulated reservoir our model has two coupled components 1 a pressure diffusion model and 2 a stochastic seismicity model permeability is increased in the source area of each induced earthquake depending on the amount of slip which is determined by the magnitude we show that the few largest earthquakes i e 5 10 events with m 1 5 contribute more than half of the total reservoir stimulation the results further indicate that planning and controlling of reservoir engineering operations may be compromised by the considerable variability of maximum observed magnitude reservoir size the gutenberg richter b value and shapiro s seismogenic index i e a measure of seismic reactivity of a reservoir that arises from the intrinsic stochastic nature of induced seismicity we also find that injection volume has a large impact on both reservoir size and seismic hazard injection rate and injection scheme have a negligible effect the impact of site specific parameters on seismicity and reservoir properties is greater than that of the injected volume in particular conditions that lead to high b values possibly a low differential stress level have a high impact on seismic hazard but also reduce the efficiency of the stimulation in terms of permeability enhancement under such conditions target reservoir permeability can still be achieved without reaching an unacceptable level of seismic hazard if either the initial reservoir permeability is high or if several fractures are stimulated the proposed methodology is a first step towards including induced seismic hazard analysis into the design of reservoir stimulation in a quantitative and robust manner

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

formation of intrathermocline lenses by eddy wind interaction abstractmesoscale intrathermocline lenses are observed throughout the world ocean and are commonly attributed to water mass anomalies advected from a distant origin an alternative mechanism of local generation is offered herein in which eddy wind interaction can create lens shaped disturbances in the thermocline numerical simulations illustrate how eddy wind driven upwelling in anticyclones can yield a convex lens reminiscent of a mode water eddy whereas eddy wind driven downwelling in cyclones produces a concave lens that thins the mode water layer a cyclonic thinny such transformations should be observable with long term time series in the interiors of mesoscale eddies

temporal changes in stress drop frictional strength and earthquake size distribution in the 2011 yamagata fukushima ne japan earthquake swarm caused by fluid migration

routes to energy dissipation for geostrophic flows in the southern ocean wind power inputs at the surface ocean are dissipated through smaller scale processes in the ocean interior and turbulent boundary layer simulations suggest that seafloor topography enhances turbulent mixing and energy dissipation in the ocean interior

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

injection induced seismicity poroelastic and earthquake nucleation effects the standard model of injection induced seismicity considers changes in coulomb strength due solely to changes in pore pressure we consider two additional effects full poroelastic coupling of stress and pore pressure and time dependent earthquake nucleation we model stress and pore pressure due to specified injection rate in a homogeneous poroelastic medium stress and pore pressure are used to compute seismicity rate through the dieterich 1994 model for constant injection rate the time to reach a critical seismicity rate scales with t r2 cfc where r is distance from the injector c is hydraulic diffusivity and fc is a factor that depends on mechanical properties and weakly on r the seismicity rate decays following a peak consistent with some observations during injection poroelastic coupling may increase or decrease the seismicity rate depending on the orientation of the faults relative to the injector if injection induced stresses inhibit slip abrupt shut in can lead to locally sharp increases in seismicity rate tapering the flux mitigates this effect the maximum magnitude event has been observed to occur postinjection we suggest the seismicity rate at a given magnitude depends on the nucleation rate the size distribution of fault segments and if the background shear stress is low the time varying volume of perturbed crust this leads to a rollover in frequency magnitude distribution for larger events with a corner that increases with time larger events are absent at short times but approach the background frequency with time larger events occurring post shut in are thus not unexpected

aftershocks triggered by fluid intrusion evidence for the aftershock sequence occurred 2014 in west bohemia vogtland the west bohemia vogtland region central europe is well known for its repeating swarm activity however the latest activity in 2014 although spatially overlapping with previous swarm activity consisted of three classical aftershock sequences triggered by ml3 5 4 4 and 3 5 events to decode the apparent system change from swarm type to mainshock aftershock characteristics we have analyzed the details of the major ml4 4 sequence based on focal mechanisms and relocated earthquake data our analysis shows that the mainshock occurred with rotated mechanism in a step over region of the fault plane unfavorably oriented to the regional stress field most of its intense aftershock activity occurred in plane with classical characteristics such as i the maximum magnitude of the aftershocks is significantly less than the mainshock magnitude and ii the decay can be well fitted by the omori utsu law however the absolute number of aftershocks and the fitted omori utsu c and p parameters are much larger than for typical sequences by means of the epidemic type aftershock sequence model we show that an additional aseismic source with an exponentially decaying strength triggered a large fraction of the aftershocks corresponding pore pressure simulations with an exponentially decreasing flow rate of the fluid source show a good agreement with the observed spatial migration front of the aftershocks extending approximately with log t thus we conclude that the mainshock opened fluid pathways from a finite fluid source into the fault plane explaining the unusual high rate of aftershocks the migration patterns and the exponential decrease of the aseismic signal

stress drop variations of induced earthquakes at the basel geothermal site 1 we determine stress drops from p wave spectra of about 1000 earthquakes induced by hydraulic stimulation in crystalline rock for a deep heat mining project in basel switzerland we observe an increase in stress drop by about a factor of five with radial distance from 10 m to 300 m which suggests that stress drop correlates with pore pressure perturbations due to the injection we test this hypothesis by calculating the injection related pore pressure perturbation based on a simple linear pore pressure diffusion model and find a good correlation of the expected pore pressure perturbation with the estimated stress drops

hydraulic stimulation of natural fractures as revealed by induced microearthquakes carthage cotton valley gas field east texas we produced a high resolution microseismic image of a hydraulic fracture stimulation in the carthage cotton valley gas field of east texas we improved the precision of microseismic event locations four fold over initial locations by manually repicking the traveltimes in a spatial sequence allowing us to visually correlate waveforms of adjacent sources the new locations show vertical containment within individual targeted sands suggesting little or no hydraulic communication between the discrete perforation intervals simultaneously treated within an 80 m section treatment i e fracture zone lengths inferred from event locations are about 200 m greater at the shallow perforation intervals than at the deeper intervals the highest quality locations indicate fracture zone widths as narrow as 6 m similarity of adjacent source waveforms along with systematic changes of phase amplitude ratios and polarities indicate fairly uniform source mechanisms fracture plane orientation and sense of slip over

statistics of fracture strength and fluid induced microseismicity 1 in this paper we develop an approach for estimating the strength of rocks by analyzing fluid induced microseismicity the strength corresponds to the value of critical pressure in the pore space that must be exceeded in order to activate preexisting fractures i e to trigger earthquakes we assume that during hydraulic injection experiments in boreholes microseismicity is mainly triggered by a diffusive process of pore pressure perturbation an analytical solution can be applied to find time dependent pore pressure perturbations in rocks caused by fluid injections characteristics of the spatiotemporal evolution of microseismic clouds can be then used to estimate minimum and maximum pressures necessary to trigger earthquakes moreover we present a method for reconstruction of the full spectrum of rock strength that is we show how to estimate the probability density function of the critical pressure we verify the approach using numerical data and apply it to real data of injection induced microseismicity from two hot dry rock tests in crystalline rocks and one hydraulic fracturing experiment in a sedimentary rock the results show that such an analysis of microseismicity is able to provide us with a completely new feature of natural fractured rocks in situ namely the statistics of their strength we find that very low critical pressures in the range 0 001 1 mpa characterize the strength of preexisting cracks for all data sets analyzed the range of critical pressures is broadly distributed within 3 to 4 orders of magnitude however the probability density functions of critical pressure change very quickly from the zero level to significant values and from significant values to the zero level at the lower and upper limits of their nonvanishing value ranges respectively the lower bound of critical pressure is possibly defined by the magnitude of tidal induced stresses permanently occurring and relaxing in the earth

anomalous chlorofluorocarbon uptake by mesoscale eddies in the drake passage region the role of mesoscale eddies in the uptake of anthropogenic chlorofluorocarbon 11 cfc 11 gas is investigated with a 1 20 eddy resolving numerical ocean model of a region of the southern ocean with a relatively fast air sea equilibrium time scale about a month the air sea cfc 11 flux quickly responds to the changes in the mixed layer cfc 11 partial pressure pcfc 11 at the mesoscale significant correlations are observed between pcfc 11 anomaly anomalies in sea surface temperature sst net heat flux and mixed layer depth an eddy centric analysis of the simulated cfc 11 field suggests that anticyclonic warm core eddies generate negative pcfc 11 anomalies and cyclonic cold core eddies generate positive anomalies of pcfc 11 surface pcfc 11 is modulated by mixed layer dynamics in addition to cfc 11 air sea fluxes a negative cross correlation between mixed layer depth and surface pcfc 11 anomalies is linked to higher cfc 11 uptake in anticyclones and lower cfc 11 uptake in cyclones especially in winter an almost exact asymmetry in the air sea cfc 11 flux between cyclones and anticyclones is found

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

comment on hydraulic fracturing in faulted sedimentary basins numerical simulation of potential contamination of shallow aquifers over long time scales by claire gassiat et al

the frasnian famennian mass extinction insights from high resolution sequence stratigraphy and cyclostratigraphy in south china two sequences sfr sfa each 1 1 2 myr in duration are recognised in the strata across the frasnian famennian f f transition both in carbonate platform and interplatform basinal successions in south china the sequence boundary between the two sequences is placed a little below the top of the frasnian the sequences are basically composed of coarsening upward bed thickness increasing upward cycles and shallowing upward cycles parasequences in basinal and platform deposits respectively which stack into cycle sets typically six to eight cycles 10 and 12 cycle sets are identified in sequences sfr and sfa respectively these cycle sets can be further grouped into larger scale composite cycle sets herein termed mesocycle and megacycle sets with two and four cycle sets respectively this vertical cycle stacking pattern and the hierarchy of cyclicity suggest a milankovitch style of forcing such that the cycles and cycle sets were formed in response to the orbital perturbations of precession 16 18 kyr and eccentricity v100 kyr in duration respectively in the basinal cycles smaller scale rhythmic stratification beds typically six to eight beds in a cycle are extensive and were likely caused by millennial scale climatic forcing in the lower sequence sfr the latest highstand deposits consist of calciturbidites and debrites in deep water strata and fenestral limestones in shallow water strata representing a major third order sea level fall within these deposits four cycle sets are further identified in both coeval deep water and platform successions succeeding deeper water organic rich facies within which three cycles occur are the transgressive deposits of the overlying famennian sequence sfa these cycles represent three higher frequency 16 18 kyr sea level fluctuations and accompanying anoxia superimposed on a major third order sea level rise the f f boundary is placed at the top of the first cycle based on conodont data thus a major sea level fall and then a rise occurred in the f f transitional period faunal and sedimentological data reveal a massive biotic decline in concert with the major sea level fall and a further biotic demise coinciding with the major sea level rise and its three superimposed higher frequency sea level fluctuations and accompanying anoxia the f f biotic crisis was therefore characterised by two episodes of step down extinction on the basis of milankovitch orbital rhythms the first major biotic extinction took place over v400 kyr and the subsequent event was v50 kyr in duration i e v450 kyr for the entire event at the same time as the massive decline of normal marine fossils during the latest frasnian sea level fall there was widespread cyanobacterial growth and a thriving of planktonic calcispheres suggesting eutrophic conditions this situation could have caused a severe biotic loss as a result of the deterioration of surface water clarity and formation of anoxic bottom waters due to over

microseismic imaging of a geothermal reservoir stimulation exploitation of geothermal heat energy from rocks at depths of several km has been the goal of vari ous projects since the mid 1970s to exploit the energy in these deep rocks poses technical challenges in drilling well completion creation of the heat exchange reservoir at depth and control of seismicity in spite of the difficulties what are now known as enhanced engineered geothermal systems egs offer almost limitless clean energy so it is not surprising that this technology continues to attract investors however commercial energy production from the greatest potential resource hot rock at depths 5 km or temperatures 200 c remains elusive

probability of inducing given magnitude earthquakes by perturbing finite volumes of rocks 1 fluid induced seismicity results from an activation of finite rock volumes the finiteness of perturbed volumes influences frequency magnitude statistics previously we observed that induced large magnitude events at geothermal and hydrocarbon reservoirs are frequently underrepresented in comparison with the gutenberg richter law this is an indication that the events are more probable on rupture surfaces contained within the stimulated volume here we theoretically and numerically analyze this effect we consider different possible scenarios of event triggering rupture surfaces located completely within or intersecting only the stimulated volume we approximate the stimulated volume by an ellipsoid or cuboid and derive the statistics of induced events from the statistics of random thin flat discs modeling rupture surfaces we derive lower and upper bounds of the probability to induce a given magnitude event the bounds depend strongly on the minimum principal axis of the stimulated volume we compare the bounds with data on seismicity induced by fluid injections in boreholes fitting the bounds to the frequency magnitude distribution provides estimates of a largest expected induced magnitude and a characteristic stress drop in addition to improved estimates of the gutenberg richter a and b parameters the observed frequency magnitude curves seem to follow mainly the lower bound however in some case studies there are individual large magnitude events clearly deviating from this statistic we propose that such events can be interpreted as triggered ones in contrast to the absolute majority of the induced events following the lower bound

fractal properties of fault systems by scattering of body seismic waves abstract one can obtain the fractal dimension of fault systems from the power frequency dependence of the scattering coefficient of x raying p or s waves this estimation may be based on the use of one of the two alternative models of media a medium with discrete random inclusions or a random continuous medium we have shown that if spectral densities of fluctuations in these models are identical the frequency dependencies of the scattering coefficients of the corresponding body waves are identical too in the weak scattering regime however fractal dimensions of a total surface of inclusions and isosurfaces in a random continuous turbulent medium are different the fractal dimension of the total surface of inclusions estimated by scattering coefficient coincides with the estimations of fractal dimensions of the fault systems in japan and the san andreas fault system we think that the fractal dimension of the total surface of faults in seismic active regions is 2 0 2 5 and in aseismic regions is about 3