modeling the hydromechanical responses of sandwich structure faults during underground fluid injection injection or withdrawal of fluid at depth may trigger felt seismicity at a site with natural faults or artificial fracturing cracks understanding how to avoid triggering felt earthquakes plays a crucial role in the success of underground anthropogenic activities such as subsurface energy storage and co2 geological sequestration with the application of a hydromechanical coupling finite element model we examine the potential of injection induced pore pressure change and the responding fault slippage along the fault surface in two injection scenarios multi layer injection mli and single layer injection sli the results indicate that fault slippage buildup is mainly located along the portion of the fault intersecting the reservoir mli leads to a relatively lower level of induced seismicity compared with sli in the fault zone the external zone and core of the fault exert a connection effect and barrier effect on the hydraulic connectivity respectively after 20 years of injection the pore pressure in the core presents a smaller change than that in the internal and external zones furthermore an uncertainty analysis was performed to evaluate the statistical significance of permeability in the caprock reservoir and fault core internal zone and external zone and only the permeability in the reservoir significantly affects the level of fault slippage based on the fault zone hydromechanics associated with subsurface energy storage and co2 geological sequestration

broadband extended images by joint inversion of multiple blended wavefields abstractestimation of seismic velocities and subsurface reservoir properties in deep complex geologic environments calls for the coordination of new acquisition technology with novel depth domain inversion methods here we propose a method for inversion of subsurface reflectivity image gathers that jointly relies on broadband data acquired by multimeasurement methods vector acoustic data pressure and its gradients from monopole pressure and dipole e g gradient sources our inversion retrieves depth domain extended images eis which represent the full nonlinear reflectivity operators with pseudosources and pseudoreceivers within the subsurface as a function of time or frequency based on recent advances in interferometry by multidimensional deconvolution mdd we present two mdd based imaging conditions for an ei inversion one imaging condition consists of deconvolving correlation based eis with the so called joint point spread function jpsf these methods can in principle account for

reverse time migration a prospect of seismic imaging methodology abstract reverse time migration rtm is a seismic imaging method to map the subsurface reflectivity using recorded seismic waveforms the practice in exploration seismology has long established a two fold approach of seismic imaging using velocity modeling building to establish the long wavelength reference velocity models and using seismic migration to map the short wavelength reflectivity structures among various seismic migration methods for different situations rtm is the only method that is capable to use all seismic wave types that can be computed numerically being initiated in early 1980 s rtm seeks an image of the subsurface reflectivity as the best match in an image space between the extrapolation of time reversed waveform data and the prediction based on estimated velocity model and source parameters judging the image quality in the same space of forming the images is more advantageous than the approaches of modeling and inversion which seek the solution in the model space but judge its fitness in data space considering that most seismic migration applications today still use primary reflection as the only signal the capability of rtm to use all computable wave types is unique and helpful reducing the imaging artifacts due to mistaking non primary waves as primary reflections hence we refer to those rtm algorithms using only primary reflections as the first generation rtm methods and the rtm algorithms making a full use of primary reflections multiple reflections and other non primary waveform data as the second generation rtm methods this paper reviews the development history of the rtm along with its major challenges current solutions and future perspectives

the role of mineral composition on the frictional and stability properties of powdered reservoir rocks national natural science foundation of china 41672268 41772286 u s department of energy doe de fe0023354

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

triggered earthquakes and deep well activities earthquakes can be triggered by any significant perturbation of the hydrologic regime in areas where potentially active faults are already close to failure the increased pore pressure resulting from fluid injection or alternatively the massive extraction of fluid or gas can induce sufficient stress and or strain changes that with time can lead to sudden catastrophic failure in a major earthquake injection induced earthquakes typically result from the reduction in frictional strength along preexisting nearby faults caused by the increased formation fluid pressure earthquakes associated with production appear to respond to more complex mechanisms of subsidence crustal unloading and poroelastic changes in response to applied strains induced by the massive withdrawal of subsurface material as each of these different types of triggered events can occur up to several years after well activities have begun or even several years after all well activities have stopped this suggests that the actual triggering process may be a very complex combination of effects particularly if both fluid extraction and injection have taken place locally to date more than thirty cases of earthquakes triggered by well activities can be documented throughout the united states and canada based on these case histories it is evident that owing to preexisting stress conditions in the upper crust certain areas tend to have higher probabilities of exhibiting such induced seismicity

frictional properties of sedimentary rocks and natural fault gouge from the longmen shan fault zone sichuan china in this paper we report friction experiments performed on samples collected from the region hit by the 2008 wenchuan earthquake in the longmen shan fault zone lfz of sichuan southwestern china the materials tested consisted of simulated gouges prepared from intact clay rich mudstone and sandstone a calcite limestone plus a natural fault gouge from a trenched surface rupture cutting the mudstone and sandstone the clay rich samples including the natural gouge were dominated by illite and quartz in our experiments we sheared 1 mm thick gouge layers between saw cut driver blocks using a triaxial testing machine at conditions corresponding to 2 km depth in the lfz temperature was varied from 25 c to 150 c and to investigate the velocity dependence of friction we stepped the shear displacement rate between 1 22 and 0 122 m s our results show that the natural gouge was more illite rich and much weaker than the protolith mudstone and sandstone and showed a steady state friction coefficient of 0 4 compared with 0 6 for the latter the limestone gouge displayed values of 0 6 0 7 all samples except the limestone showed stable velocity strengthening slip the limestone showed velocity strengthening at 25 c 50 c but quasi static oscillations at 100 c 150 c along with velocity weakening behavior at 150 c we apply our results to discuss the role of the sedimentary rocks studied during events such as the wenchuan earthquake and argue that the clay rich sediments of the region may have a damping effect upon ruptures propagating from depth whereas the limestone may accelerate propagation producing significant stress drops

isrm suggested methods for rock stress estimation part 3 hydraulic fracturing hf and or hydraulic testing of pre existing fractures htpf contents1 introduction 10112 summaryoftestmethods 10123 assumptionsandlimitations 10123 1 hydraulicfracturing hf 10123 2 hydraulictestsonpre existingfractures htpf 10124 apparatus 10134 1 fractureorientationdetectiondevices 10145 personnelquali cation 10146 equipmentperformance 10147 hydraulicfracturingtestprocedure 10148 hydraulic fracturedelineation 10168 1 impressionpackertechnique 10168 2 geophysicalimagingtechnique 10179 obtainingcriticalpressureparametersfromthepressure timerecords 101710 stresscalculations 101810 1 hydraulicfracturing hf 101810 2 hydraulictestsonpre existingfractures 101911 reportingofresults 1019references 1020

on the relation between seismic interferometry and the migration resolution function seismic interferometry refers to the process of retrieving new seismic responses by crosscorrelating seismic observations at different receiver locations seismic migration is the process of forming an image of the subsurface by wavefield extrapolation comparing the expressions for backward propagation known from migration literature with the green s function representations for seismic interferometry reveals that these seemingly distinct concepts are mathematically equivalent the frequency domain representation for the resolution function of migration is identical to that for the green s function retrieved by seismic interferometry or its square in the case of double focusing in practice they differ because the involved green s functions in seismic interferometry are all defined in the actual medium whereas in migration one of the green s functions is defined in a background medium

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

unloading induced rock fracture activation and maximum seismic moment prediction abstract hundreds of anthropogenic earthquakes have recently occurred worldwide due to underground space creation and energy extraction the mechanism behind the human induced geohazards is most likely associated with the reduction of normal stress on pre existing fractures and faults this study reports a series of laboratory experiments to investigate the mechanism of unloading induced fracture activation and proposes a simple approach to predict the maximum seismic moment for a critically stressed fracture the unloading driven shear test results exhibit that the unloading process induces the stress states of the sawcut and natural fractures to approach the mohr coulomb failure envelope and the normal stress unloading rate influences the peak slip rate the fracture instability is dependent on the relationship between the stiffness of the system and the slip weakening rate of the fracture and the shear dilation mainly occurs after the fracture activation the test results also show that the critical shear stress of the sawcut fracture during the unloading driven shear test is approximately equal to the residual shear strength after the displacement driven fracture slip this relationship inspires us to develop a new approach to estimate the maximum seismic moment our data demonstrate that the maximum seismic moments for both the fractures obtained from the unloading driven shear tests are all below the upper limit lines indicating that the proposed approach is reasonable the uncertainty analysis shows that the accurate estimation of fault size can improve the maximum seismic moment prediction

postseismic relaxation driven by brittle creep a possible mechanism to reconcile geodetic measurements and the decay rate of aftershocks application to the chi chi earthquake taiwan we evaluate the effect of coseismic stress changes on the fault slip at midcrustal depth assuming a velocity strengthening brittle creep rheology we show that this model can help reconcile the time evolution of afterslip as measured from geodesy with aftershocks decay we propose an analytical expression for slip of the brittle creeping fault zone bcfz that applies to any dynamic or static stress perturbation including shear stress and normal stress changes the model predicts an initial logarithmic increase of slip with time postseismic slip rate decays over a characteristic time t r a that does not depend on the amplitude of the stress perturbation and it asymptotically joins the long term creep imposed by interseismic stress buildup given that the seismicity rate might be considered proportional to the sliding velocity of the bcfz the model predicts a decay rate of aftershocks that follows omori s law with a mathematical formalism identical to that of dieterich 1994 although based on a different mechanical rationale our model also differs from dieterich s model in that it requires that aftershock sequences and deep afterslip as constrained from geodetic measurements should follow the same temporal evolution we test this for the 1999 chi chi earthquake m w 7 6 and find that both sets of data are consistent with a model of afterslip due to the response of the bcfz the inferred relaxation time t r 8 5 years requires a value for a log v being the coefficient of friction in the range between 1 3 10 3 and 10 2

enhanced density estimation from prestack inversion of multicomponent seismic data using 3c 2d seismic data in the albacora block campos basin brazil we analyzed the potential of multicomponent data for density esti mation by simultaneously inverting prestack compressional and mode converted seismic data initial forward modeling using the available well logs shows that small changes in density at the reservoir level affect the ps reflectivity more than pp the inversion engine uses a global optimization algorithm with a nonlinear cost function to simultaneously invert a number of in put stacks to an earth model inverting solely pp data has shown a lower cor relation between the estimated density and the measured log in comparison to jointly inverting both pp and ps data the results also show that adding ps information in the inversion pro cess improves the density inversion bandwidth and consequently inversion resolution

data driven adaptive decomposition of multicomponent seabed recordings dual sensor hydrophone and three component geophone data recorded on the seafloor allow the elastic wavefield to be decomposed into its upgoing and downgoing p and s wave components most decomposition algorithms require accurate knowledge of the elastic properties of the seafloor in the vicinity of the receivers and properly calibrated sensors in order for the data to be a faithful vector representation of the ground motion we present a multistep adaptive decomposition scheme that provides the necessary information directly from the data by imposing constraints on intermediate decomposition results the proposed scheme requires no a priori information and only a minimal amount of user defined input thus allowing multicomponent data to be decomposed in an automated data driven fashion the performance of the technique is illustrated using seabed data acquired in the north sea with prototype single sensors multicomponent geophones individually sampled realistic seafloor properties and sensor calibration operators are obtained and elastic decomposition of the calibrated data generally yields good results dominant water layer reverberations are successfully attenuated and primary reflections are substantially enhanced in the computed upgoing p wave potential just below the seafloor in contrast the result for the upgoing s wave potential is somewhat less convincing although the energy of water layer multiples is substantially reduced notable amounts of undesired multiple energy remain in this section after decomposition particularly at high offsets these imperfections may point to inaccuracies in the parametrization of the seafloor or remaining inaccuracies in the vector fidelity of the horizontal geophone recordings nevertheless the results obtained with the extended data driven decomposition scheme are at least comparable to previously published results

fault s hydraulic diffusivity enhancement during injection induced fault reactivation application of pore pressure diffusion inversions to laboratory injection experiments in situ observations of fluid induced fault slip reactivation as well as the analysis of induced seismicity have demonstrated the complexity of fluid fault interactions under geological conditions if fluid flow commonly reactivates faults in the form of aseismic slip or earthquakes the resulting shear deformation causes strong modifications of the hydraulic properties in this context the relationship between slip front and fluid front on deep faults remains not fully understood in this study we investigate shear induced fluid flow and hydraulic diffusivity enhancement during fracture shearing in the laboratory we use a series of injection reactivation tests conducted under triaxial conditions at different confining pressures 30 60 and 95 mpa the evolution of the fluid pressure along the saw cut andesite rock sample was monitored by two pressure sensors at two opposite locations of the experimental fault we estimate the history of the effective hydraulic diffusivity and its associated uncertainties governing the experimental fault using the pressure history at two points on the fault for this we develop a deterministic and a probabilistic inversion procedure which is able to reproduce the experimental data for a wide time range of the different experiments in this study the hydraulic diffusivity increases by one order of magnitude through the injection experiment hydraulic diffusivity changes are mainly governed by the reduction of the effective normal stress acting on the fault plane with a second order effect of the shear slip

mega earthquakes rupture flat megathrusts the 2004 sumatra andaman and 2011 tohoku oki earthquakes highlighted gaps in our understanding of mega earthquake rupture processes and the factors controlling their global distribution a fast convergence rate and young buoyant lithosphere are not required to produce mega earthquakes we calculated the curvature along the major subduction zones of the world showing that mega earthquakes preferentially rupture flat low curvature interfaces a simplified analytic model demonstrates that heterogeneity in shear strength increases with curvature shear strength on flat megathrusts is more homogeneous and hence more likely to be exceeded simultaneously over large areas than on highly curved faults

fault slip controlled by stress path and fluid pressurization rate the practice of injecting fluids into the crust is linked to regional increases in seismicity increasing fluid pressure along preexisting faults is believed to enhance seismicity rates by reducing the shear stress required for slip but the processes that cause faults to slip under conditions of fluid pressurization are poorly constrained we use experimental rock deformation to investigate the controls of fluid pressurization and pressurization rates on fault slip style we show that pore fluid pressurization is less effective that mechanical changes in fault normal stress at initiating accelerated slip events fluid pressurization enhances the total slip slip velocity and shear stress drop of events initiated by mechanical changes in normal stress and these parameters are correlated with pressurization rate but not the magnitude of fluid pressure this result is consistent with field scale observations and indicates that processes active at the pore network scale affect induced seismicity

maximum magnitude of injection induced earthquakes a criterion to assess the influence of pressure migration along faults abstract the maximum expected earthquake magnitude is an important parameter in seismic hazard and risk analysis because of its strong influence on ground motion in the context of injection induced seismicity the processes that control how large an earthquake will grow may be influenced by operational factors under engineering control as well as natural tectonic factors determining the relative influence of these effects on maximum magnitude will impact the design and implementation of induced seismicity management strategies in this work we apply a numerical model that considers the coupled interactions of fluid flow in faulted porous media and quasidynamic elasticity to investigate the earthquake nucleation rupture and arrest processes for cases of induced seismicity we find that under certain conditions earthquake ruptures are confined to a pressurized region along the fault with a length scale that is set by injection operations however earthquakes are sometimes able to propagate as sustained ruptures outside of the zone that experienced a pressure perturbation we propose a faulting criterion that depends primarily on the state of stress and the earthquake stress drop to characterize the transition between pressure constrained and runaway rupture behavior

vector acoustic reverse time migration of volve ocean bottom cable data set without up down decomposed wavefields abstractmethods for wavefield injection are commonly used to extrapolate seismic data in reverse time migration rtm injecting a single component of the acoustic field for example pressure leads to ambiguity in the direction of propagation each recorded wavefront is propagated both upward and downward and spurious or ghost reflectors are created alongside real reflectors in the subsurface image thus wavefield separation based on the combination of pressure and particle velocity data is generally performed prior to imaging to extract only the upgoing field from multicomponent seabed or towed marine seismic recordings by instead combining vector acoustic va data with monopole and dipole type propagators in the extrapolation of shot or receiver gathers we show that wavefield separation or deghosting can instead be performed on the fly at limited additional cost this strategy was successfully applied to a line of a north sea ocean bottom cable data set acquired over the volve field we t

prestack depth migration of primary and surface related multiple reflections part i imaging surface related multiples i e all seismic waves reflected at the free surface at least once often severely contaminate seismic recordings because conventional imaging techniques require input data that consist of primary reflections only significant processing effort is commonly dedicated to attenuating multiples prior to migration on the other hand surface related multiples provide additional illumination of the subsurface and therefore should not be considered as noise we present a prestack depth migration method that allows primary and multiple reflections to be imaged simultaneously depth imaging using primary and multiple reflections dipmr involves decomposing the datainto upgoing and downgoing wave constituents followed by downward extrapolation artifacts generated by interference of upgoing and downgoing events not associated with the same subsurface reflection points crosstalk are attenuated by using a 2d deconvolution imaging condition in contrast to existing methods dipmr doe

offset and angle domain common image point gathers for shot profile migration prestack depth migration of shot profiles by downward continuation is a practical imaging algorithm that is especially cost effective for sparse shot wide azimuth geometries the interpretation of offset as the displacement between the downward propagating shot wavefield and upward propagating receiver wavefield enables us to extract offset domain common image point cip gathers during shot profile migration the offset domain gathers can then be transformed to the angle domain with a radial trace mapping originally introduced for shot geophone migration the computational implications of this procedure include both the additional cost of multioffset imaging and an implicit transformation from shot geophone to midpoint offset coordinates although this algorithm provides a mechanism for imaging angle dependent reflectivity via shot profile migration for sparse shot geometries the fundamental problem of shot aliasing may severely impact the quality of cip gathers

evidence for coupled seismic and aseismic fault slip during water injection in the geothermal site of soultz france and implications for seismogenic transients summary we analysed the triggered seismicity recorded near 3 km in depth within granite during the 1993 water injection experiment at soultz france we selected all large multiplets associated with the largest dislocated fault identified on the borehole logging 4 3 cm slip and showed that each one consisted of the repeated rupture of a single asperity these asperities were forced to rupture due to fault creep around them so that their growing cumulative slip history reveals the creep history on the fault with a mean slip rate and a seismicity rate both decaying approximately as 1 t this is consistent with a rate strengthening friction law on the creeping faults and differs from the interpretation of omori type 1 t seismicity rates in terms of a weakening friction control of the unstable fault surfaces this model of asperity rupture forced by relaxation creep is easily generalized in seismogenic regions even for single ruptures of asperities on small creeping faults showing that a significant part of aftershock rates can be controlled by the strengthening friction properties and the creep of faults at all scales this lead us to introduce the concept of a critical asperity density above which dynamic interaction between neighbouring asperities can initiate large seismic ruptures at soultz the asperity density is subcritical but the neighbouring asperities nonetheless interact at distances up to a few source dimensions as revealed by their delayed cross triggering considering the seismic cloud in soultz at a global scale the strain produced by the injection experiment was mostly aseismic related to creep on major faults and causing large permeability changes influencing in turn the pore pressure diffusion and the creeping process our observations demonstrate that the identification and analysis of multiplets can provide accurate images of the geometry and kinematics of transient slip patches and indirectly detect pore pressure changes which should contribute to a better understanding of the coupling between transient fluid flow creep and microseismic activity in seismogenic regions

stable creeping fault segments can become destructive as a result of dynamic weakening faults in earth s crust accommodate slow relative motion between tectonic plates through either similarly slow slip or fast seismic wave producing rupture events perceived as earthquakes these types of behaviour are often assumed to be separated in space and to occur on two different types of fault segment one with stable rate strengthening friction and the other with rate weakening friction that leads to stick slip the 2011 tohoku oki earthquake with moment magnitude m w 9 0 challenged such assumptions by accumulating its largest seismic slip in the area that had been assumed to be creeping here we propose a model in which stable rate strengthening behaviour at low slip rates is combined with coseismic weakening due to rapid shear heating of pore fluids allowing unstable slip to occur in segments that can creep between events the model parameters are based on laboratory measurements on samples from the fault of the m w 7 6 1999 chi chi earthquake the long term slip behaviour of the model which we examine using a unique numerical approach that includes all wave effects reproduces and explains a number of both long term and coseismic observations some of them seemingly contradictory about the faults at which the tohoku oki and chi chi earthquakes occurred including there being more high frequency radiation from areas of lower slip the largest seismic slip in the tohoku oki earthquake having occurred in a potentially creeping segment the overall pattern of previous events in the area and the complexity of the tohoku oki rupture the implication that earthquake rupture may break through large portions of creeping segments which are at present considered to be barriers requires a re evaluation of seismic hazard in many areas

laboratory micro seismic signature of shear faulting and fault slip in shale this article reports the results of a triaxial deformation experiment conducted on a transversely isotropic shale specimen this specimen was instrumented with ultrasonic transducers to monitor the evolution of the micro seismic activity induced by shear faulting triaxial failure and subsequent fault slip at two different rates the strain data demonstrate the anisotropy of the mechanical quasi static compliance of the shale the p wave velocity data demonstrate the anisotropy of the elastic dynamic compliance of the shale the spatio temporal evolution of the micro seismic activity suggests the development of two distinct but overlapping shear faults a feature similar to relay ramps observed in large scale structural geology the shear faulting of the shale specimen appears quasi aseismic at least in the 0 5 mhz range of sensitivity of the ultrasonic transducers used in the experiment concomitantly the rate of micro seismic activity is strongly correlated with the imposed slip rate and the evolution of the axial stress the moment tensor inversion of the focal mechanism of the high quality micro seismic events recorded suggests a transition from a non shear dominated to a shear dominated micro seismic activity when the rock evolves from initial failure to larger and faster slip along the fault the frictional behaviour of the shear faults highlights the possible interactions between small asperities and slow slip of a velocity strengthening fault which could be considered as a realistic experimental analogue of natural observations of non volcanic tremors and very low frequency earthquakes triggered by slow slip events

intermittent slip along the alto tiberina low angle normal fault in central italy the alto tiberina normal fault atf in central italy is a 50 km long crustal structure that deepens at a low angle 15 20 events on the fault plane are about ten times less than those located i

on the use of multicomponent streamer recordings for reconstruction of pressure wavefields in the crossline direction three component measurements of particle motion would bring significant benefits to towed marine seismic data if processed in conjunction with the pressure data we show that particle velocity measurements can increase the effective nyquist wavenumber by a factor of two or three depending on how they are used a true multicomponent streamer would enable accurate data reconstruction in the crossline direction with cable separations for which pressure only data would be irrecoverably aliased we also show that conventional workflows aimed at reducing these aliasing effects such as moveout correction applied before interpolation are compatible with multicomponent measurements some benefits of velocity measurements for deghosting data are well known we outline how the new measurements might be used to address some long standing deghosting challenges of particular interest specifically we propose methods for recovering de ghosted data between streamers and for 3d deghosting of seismic data at the stream

long period long duration seismic events during hydraulic fracture stimulation of a shale gas reservoir we report here a series of long period and long duration lpld seismic events observed during hydraulic fracturing in a shale gas reservoir these unusual events 10 100 s in duration are observed most clearly in the frequency band of 10 80 hz and are remarkably similar in appearance to tectonic tremor sequences first observed in subduction zones these complex but coherent wave trains have finite moveouts obtained from cross correlation the moveout direction of the events confirms that they originate in the reservoir from the area where the fracturing is going on clear p and s wave arrivals cannot be resolved within the lpld episodes but in some cases small micro earthquakes occur in the sequences whether these micro earthquakes are causal or coincidental is not known it has also been observed that in three contiguous frac stages all lpld events appear to come from two distinct places along one of two hypothetical fracture planes interestingly the stages which have the largest number of lpld

status of co2 storage in deep saline aquifers with emphasis on modeling approaches and practical simulations carbon capture and storage ccs is the only viable technology to mitigate carbon emissions while allowing continued large scale use of fossil fuels the storage part of ccs involves injection of carbon dioxide captured from large stationary sources into deep geological formations deep saline aquifers have the largest identified storage potential with estimated storage capacity sufficient to store emissions from large stationary sources for at least a century this makes ccs a potentially important bridging technology in the transition to carbon free energy sources injection of co2 into deep saline aquifers leads to a multicomponent multiphase flow system in which geomechanics geochemistry and nonisothermal effects may be important while the general system can be highly complex and involve many coupled nonlinear partial differential equations the underlying physics can sometimes lead to important simplifications for example the large density difference between injected co2 and brine may lead to relatively fast buoyant segregation making an assumption of vertical equilibrium reasonable such simplifying assumptions lead to a range of simplified governing equations whose solutions have provided significant practical insights into system behavior including improved estimates of storage capacity easy to compute estimates of co2 spatial migration and pressure response and quantitative estimates of leakage risk when these modeling studies are coupled with observations from well characterized injection operations understanding of the overall system behavior is enhanced significantly this improved understanding shows that while economic and policy challenges remain co2 storage in deep saline aquifers appears to be a viable technology and can contribute substantially to climate change solutions

wide area imaging from obs multiples the subseafloor structure offshore western canada was imaged using first order water layer multiples from oceanbottom seismometer obs data and the results were compared to conventional imaging using primary reflections this multiple migration mirror imaging method uses the downgoingpressurewavefieldjustabovetheseafloor which is devoid of any primary reflections but consists of receiverside ghosts of these primary reflections the mirror imaging method employs a primaries only kirchhoff prestack depth migration algorithm to image the receiver ghosts the additional travel path of the multiples through the water layer is accountedforbyasimplemanipulationofthevelocitymodel and processing datum the receivers lie not on the seabed but on a sea surface twice as high as the true water column migration results show that the multiple migrated image provides a much broader illumination of the subsurface than is possible for conventional imaging using the primaries especially for the very shallow reflections and sparse obs spacing the resulting image from mirror imaging has illumination comparable to the vertical incidence surface streamer single channelreflectiondata

on the evolution of elastic properties during laboratory stick slip experiments spanning the transition from slow slip to dynamic rupture the physical mechanisms governing slow earthquakes remain unknown as does the relationship between slow and regular earthquakes to investigate the mechanism s of slow earthquakes and related quasi dynamic modes of fault slip we performed laboratory experiments on simulated fault gouge in the double direct shear configuration we reproduced the full spectrum of slip behavior from slow to fast stick slip by altering the elastic stiffness of the loading apparatus k to match the critical rheologic stiffness of fault gouge kc our experiments show an evolution from stable sliding when k kc to quasi dynamic transients when k kc to dynamic instabilities when k kc to evaluate the microphysical processes of fault weakening we monitored variations of elastic properties we find systematic changes in p wave velocity vp for laboratory seismic cycles during the coseismic stress drop seismic velocity drops abruptly consistent with observations on natural faults in the preparatory phase preceding failure we find that accelerated fault creep causes a vp reduction for the complete spectrum of slip behaviors our results suggest that the mechanics of slow and fast ruptures share key features and that they can occur on same faults depending on frictional properties in agreement with seismic surveys on tectonic faults our data show that their state of stress can be monitored by vp changes during the seismic cycle the observed reduction in vp during the earthquake preparatory phase suggests that if similar mechanisms are confirmed in nature high resolution monitoring of fault zone properties may be a promising avenue for reliable detection of earthquake precursors

fault structure stress or pressure control of the seismicity in shale insights from a controlled experiment of fluid induced fault reactivation clay formations are present in reservoirs and earthquake faults but questions remain on their mechanical behavior as they can vary from ductile aseismic to brittle seismic an experiment at a scale of 10 m aims to reactivate a natural fault by fluid pressure in shale materials the injection area was surrounded by a dense monitoring network comprising pressure deformation and seismicity sensors in a well characterized geological setting thirty two microseismic events were recorded during several injection phases in five different locations within the fault zone their computed magnitude ranged between 4 3 and 3 7 their spatiotemporal distribution compared with the measured displacement at the injection points shows that most of the deformation induced by the injection is aseismic whether the seismicity is controlled by the fault architecture mineralogy of fracture filling fluid and or stress state is then discussed the fault damage zone architecture and mineralogy are of crucial importance as seismic slip mainly localizes on the sealed with calcite fractures which predominate in the fault damage zone as no seismicity is observed in the close vicinity of the injection areas the presence of fluid seems to prevent seismic slips the fault core acts as an impermeable hydraulic barrier that favors fluid confinement and pressurization therefore the seismic behavior seems to be strongly sensitive to the structural heterogeneity including permeability of the fault zone which leads to a heterogeneous stress response to the pressurized volume

optimized deghosting of over under towed streamer data in the presence of noise seismic exploration is widely used to locate geologic formations for hydrocarbon accumulations in a typical marine seismic survey one or more marine seismic streamers are towed behind a survey vessel as the streamers are towed acoustic signals commonly referred to as shots are produced by the seismic source these travel down through the water column into strata beneath the water bottom surface where they are reflected from the various geologic formations and travel back to the sea surface one well known marine seismic problem is that these upgoing waves are then reflected with inverted polarity at the sea surface because of the air water interface hence the sensors in the seismic streamer cable record not only the desired wavefield i e the upgoing wave reflected signal from various subterranean geologic formations but also their reflections from the sea surface the downgoing wave the undesired downgoing reflected signal is known as the receiver ghost depending on the incidence angl

vector wave based elastic reverse time migration of ocean bottom 4c seismic data the acoustic elastic coupled equation aece has a number of advantages when compared to the conventional scalar wave based elastic reverse time migration ertm methods used to image ocean bottom multicomponent seismic data in particular vector wave based ertm requires vectorial p and s waves on both the source and receiver sides but these cannot be directly obtained from wavefield extrapolation using aece we therefore introduced p and s waves vector decomposition vd approach within aece this approach enables the deduction of a novel vd based aece from which vectorial p and s waves can be obtained directly via wavefield extrapolation we are also able to derive a new formulation suitable for vector wave based ertm of ocean bottom multicomponent seismic data that can generate a phase preserved ps image we provide three synthetic examples to illustrate the validity and effectiveness of our new method

using even terms of the scattering series for deghosting and multiple attenuation of ocean bottom cable data inverse scattering multiple attenuation isma is a method of removing free surface multiple energy while preserving primary energy the other key feature of isma is that no knowledge of the subsurface is required in its application i have adapted this method to multicomponent ocean bottom cable data i e to arrays of sea floor geophones and hydrophones by selecting a subseries made of even terms of the current scattering series used in the free surface multiple attenuation of conventional marine surface seismic data streamer data this subseries approach allows me to remove receiver ghosts receiver side reverberations and free surface multiples source side reverberations in multicomponent obc data i have processed each component separately as for the streamer case my obc version of isma preserves primary energy and does not require any knowledge of the subsurface moreover the preprocessing steps of muting for the direct wave and interpolating for missing near offsets are no longer needed

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

stress and fluid transfer in a fault zone due to overpressures in the seismogenic crust 1 stress and fluid transfers were analyzed on the surface of a 30 m thick dextral strike slip fault zone subjected to an overpressure of 63 kpa pressure strain measurements taken during the pressurization indicated a strain state primarily controlled by the hydromechanical behavior of permeable fractures and then by the fluid diffusion in the matrix using thm modeling we simulated an extension of these hydromechanical effects to a 25 km depth in the seismogenic crust applying a lithostatic pressure at the base of the fault the simulations indicate that a significant strain in the damage zone greater than that in the protolith along with the differences in hydraulic diffusivity between the damage zone and protolith may induce high static stress and fluid accumulations in the core under this stress this core is projected to exhibit deformity as much as a 12 m shear slip distributed over a 175 m long active zone

numerical modelling of fault reactivation in carbonate rocks under fluid depletion conditions 2d generic models with a small isolated fault abstract this generic 2d elastic plastic modelling investigated the reactivation of a small isolated and critically stressed fault in carbonate rocks at a reservoir depth level for fluid depletion and normal faulting stress conditions the model properties and boundary conditions are based on field and laboratory experimental data from a carbonate reservoir the results show that a pore pressure perturbation of 25 mpa by depletion can lead to the reactivation of the fault and parts of the surrounding damage zones producing normal faulting downthrows and strain localization the mechanism triggering fault reactivation in a carbonate field is the increase of shear stresses with pore pressure reduction due to the decrease of the absolute horizontal stress which leads to an expanded mohr s circle and mechanical failure consistent with the predictions of previous poroelastic models two scenarios for fault and damage zone permeability development are explored 1 large permeability enhancement of a sealing fault upon reactivation and 2 fault and damage zone permeability development governed by effective mean stress in the first scenario the fault becomes highly permeable to across and along fault fluid transport removing local pore pressure highs lows arising from the presence of the initially sealing fault in the second scenario reactivation induces small permeability enhancement in the fault and parts of damage zones followed by small post reactivation permeability reduction such permeability changes do not appear to change the original flow capacity of the fault or modify the fluid flow velocity fields dramatically

seismicity controlled by a frictional afterslip during a small magnitude seismic sequence m l 5 on the chihshang fault taiwan we report evidence for frictional afterslip at shallow depths about 5 to 7 km during a small magnitude seismic sequence with ml 5 along the chihshang fault a main active structure of the longitudinal valley in southeast taiwan the afterslip which was recorded by a nearby borehole dilatometer lasted about a month with a cumulative geodetic moment magnitude of 4 8 0 2 the afterslip comprised two stages and controlled the aftershock sequence the first postseismic stage which followed a ml 4 6 earthquake lasted about 6 h and mostly controlled the ruptures of neighboring asperities e g multiplets near the hypocenter then a 4 week duration large afterslip event following a ml 4 9 earthquake controlled the rate of aftershocks during its first 2 days through brittle creep the study presents a rare case of simultaneous seismological and geodetic observations for afterslip following earthquakes with magnitude lower than 5 furthermore the geodetic moment of the postseismic phase is at least equivalent to the coseismic moment of the sequence

frictional stability permeability relationships for fractures in shales there is wide concern that fluid injection in the subsurface such as for the stimulation of shale reservoirs or for geological co2 sequestration gcs has the potential to induce seismicity that may change reservoir permeability due to fault slip however the impact of induced seismicity on fracture permeability evolution remains unclear due to the spectrum of modes of fault reactivation e g stable versus unstable as seismicity is controlled by the frictional response of fractures we explore friction stability permeability relationships through the concurrent measurement of frictional and hydraulic properties of artificial fractures in green river shale grs and opalinus shale ops we observe that carbonate rich grs shows higher frictional strength but weak neutral frictional stability the grs fracture permeability declines during shearing while an increased sliding velocity reduces the rate of permeability decline by comparison the phyllosilicate rich ops has lower friction and strong stability while the fracture permeability is reduced due to the swelling behavior that dominates over the shearing induced permeability reduction hence we conclude that the friction stability permeability relationship of a fracture is largely controlled by mineral composition and that shale mineral compositions with strong frictional stability may be particularly subject to permanent permeability reduction during fluid infiltration

imbricated aseismic slip and fluid diffusion drive a seismic swarm in the corinth gulf greece the primary processes driving seismic swarms are still under debate here we study the temporal evolution of a seismic swarm that occurred over a 10 day period in october 2015 in the extensional rift of the corinth gulf greece using high resolution earthquakes relocations the seismicity radially migrates on a normal fault at a fluid diffusion velocity 125 m day however this migration occurs intermittently with periods of fast expansion 2 to 10 km day during short seismic bursts alternating with quiescent periods moreover the growing phases of the swarm illuminates a high number of repeaters the swarm migration is likely the results of a combination of multiple driving processes fluid up flow in the fault may induce aseismic slip episodes separated by phases of fluid pressure build up the stress perturbation due to aseismic slip may activate small asperities that produce bursts of seismicity during the most intense phase of the swarm

neoarchean carbonate associated sulfate records positive δ s anomalies mass independent fractionation of sulfur isotopes reported as 33s recorded in archean sedimentary rocks helps to constrain the composition of earth s early atmosphere and the timing of the rise of oxygen 2 4 billion years ago although current hypotheses predict uniformly negative 33 s for archean seawater sulfate this remains untested through the vast majority of archean time we applied x ray absorption spectroscopy to investigate the low sulfate content of particularly well preserved neoarchean carbonates and mass spectrometry to measure their 33 s signatures we report unexpected large widespread positive 33 s values from stratigraphic sections capturing over 70 million years and diverse depositional environments combined with the pyrite record these results show that sulfate does not carry the expected negative 33 s from sulfur mass independent fractionation in the neoarchean atmosphere

the free surface assumption for marine data driven demultiple methods in the past integral formulations for marine data driven demultiple methods have been derived from reciprocity theorems two fundamental assumptions in these derivations were that the sea surface is flat and has a known reflection coefficient often taken to be minus one in this paper we show that for dual sensor data these assumptions can be relaxed the sea surface has to obey the same conditions as any other reflecting boundary in the subsurface it must be constant in time but shape and reflection strength can vary in space for both surface related multiple elimination and multiple attenuation by multi dimensional deconvolution we derive integral equations that depend only on the measured pressure and particle velocity fields finally we show there is an intimate connection between the integral equations for the methods

adjoint state reverse time migration of 4c data finite frequency map migration for marine seismic imaging abstractrecent advances in marine seismic acquisition allow for the recording of vector acoustic va pressure and particle velocity seismic data from dual source configurations i e using monopole as well as dipole sources va reverse time migration rtm can be custom designed to accurately handle amplitude and directivity information from 4c seismic data we present a method for multicomponent rtm that is based on an adjoint state formulation using the full va wave equations for pressure and corresponding displacement fields this method takes advantage of the directional finite frequency information contained in the 4c acoustic fields by using source and receiver weighting operators in the adjoint state imaging scheme with this adjoint state method the source and receiver radiation properties are tailored by choosing specific weighting operators weighting operators were chosen so that source and receiver side ghost arrivals are jointly migrated with primary energy because the dipole field com