reservoir structure and wastewater induced seismicity at the val d agri oilfield italy shown by three dimensional vp and vp vs local earthquake tomography wastewater injection into a high rate well in the val d agri oilfield the largest in onshore europe has induced swarm microseismicity since the initiation of disposal in 2006 to investigate the reservoir structure and to track seismicity we performed a high spatial resolution local earthquake tomography using 1281 natural and induced earthquakes recorded by local networks the properties of the carbonate reservoir rock fracturing pore fluid pressure and inherited faults control the occurrence and spatiotemporal distribution of seismicity a low vp high vp vs region under the well represents a fluid saturated fault zone ruptured by induced seismicity high vp high vp vs bumps match reservoir culminations indicating saturated liquid bearing zones whereas a very low vp low vp vs anomaly might represent a strongly fractured and depleted zone characterized by significant fluid withdrawal the comprehensive picture of the injection linked seismicity obtained by integrating reservoir scale tomography high precision earthquake locations geophysical and injection data suggests that the driving mechanism is the channelling of pore pressure perturbations through a high permeable fault damage zone within the reservoir the damage zone surrounds a pliocene reverse fault optimally oriented in the current extensional stress field the ruptured damage zone measures 2 km along strike 3 km along dip and is confined between low permeability ductile formations injection pressure is the primary parameter controlling seismicity rate our study underlines that local earthquake tomography also using wastewater induced seismicity can give useful insights into the physical mechanism leading to these earthquakes

the denver earthquakes of 1967 1968 abstract a detailed study of the earthquakes associated with the rocky mountain arsenal disposal well is presented long period surface wave studies are used together with p wave first motions to show that the 10 april 9 august and 27 november 1967 earthquakes occurred at depths of 3 to 5 km and were characterized by normal faulting along a northwest striking fault plane a joint hypocenter relocation of 103 microearthquakes of a data set of 279 recorded between 1967 and 1968 shows a hypocenter pattern striking n50 w with most of the events located about 5 km northwest of the disposal well at depths between 3 to 8 km a fault plane dipping southwest is tenuously suggested by those earthquakes with depths less than 5 km modeling of near field seismoscope observations lend support to the focal mechanisms derived

the stress dependence of olivine creep rate implications for extrapolation of lab data and interpretation of recrystallized grain size abstract based on measured values for the stress exponent n 3 5 combined with the empirically determined relationship between dislocation density and stress 1 37 and an analysis of diffusion kinetics in olivine we conclude that silicon pipe diffusion limits strain rate in the dislocation creep regime furthermore assuming that steady state recrystallized grain size is set by a dynamic balance between strain energy density associated with dislocations and surface energy density associated with grain boundaries the resulting dependence of recrystallized grain size on stress accurately describes experimental observations when the empirical dislocation density versus stress relationship is accounted for d 1 1 37 the improved physical understanding of the stress dependence of creep rate provides justification for incorporation of experimentally derived flow laws into models of geodynamical process and grain size evolution these lab constraints combined with independent analyses of the stress dependence of mantle viscosity based on geophysical data provide bounds on rheological properties such as the yield stress of the lithosphere

dislocations and slip systems of mantle minerals this chapter focuses on dislocations and slip systems that are responsible for the plastic flow of high pressure mantle minerals after briefly introducing some basic concepts on crystal plasticity we describe some recent experimental advances of the last decade that have contributed to our understanding of the rheology of mantle minerals among them we describe some progress in the achievement of deformation experiments under high pressure a more detailed review is presented by durham et al this volume we present then a novel transmission electron microscopy tem technique large angle convergent beam electron diffraction lacbed which is very well adapted to the characterization of dislocations in beam sensitive materials as well as the determination of dislocation burgers vectors and characters from the fine analysis of x ray diffraction peak broadening the present review is in the continuity of the paper entitled plastic rheology of crystals by poirier published in 1995 in mineral physics crystallography a handbook of physical constants agu reference shelf 2 poirier s paper reviewed the plasticity of some important minerals including olivine and pyroxenes concerning these two minerals the reader is invited to refer to poirier s contribution in 1995 poirier stated about high pressure mantle minerals despite their importance for the rheology of the transition zone and the lower mantle there is no information on the plasticity of the high pressure mantle minerals in the relevant conditions of temperature and pressure seven years later the situation has significantly evolved and is still rapidly changing it is the aim of this paper to highlight these recent advances plastic flow is basically a transport phenomenon controlled by the motion of defects point defects dislocations or grain boundaries the driving force is provided by the applied shear stress in many cases deformation is produced by the motion of dislocations and the present paper

experimental grain size sensitive flow of hot pressed brazilian quartz aggregates abstract grain size sensitive flow may be of particular importance in the flow of rocks in natural high strain zones hot pressed aggregates of synthetic ultrafine grained brazilian quartz of nominal grain sizes 0 4 1 3 and 4 5 m were deformed at 300 mpa confining pressure and temperatures of 1273 1473 k fully ductile flow at differential stresses below 200 mpa followed 0 4 exp 220000 r t d 2 where is strain rate s 1 is stress mpa d is grain size microns and r is the gas constant grains remained equant and mostly dislocation free without significant crystallographic fabric water pressure 25 50 mpa was estimated from water adsorbed onto grain boundaries during specimen fabrication flow was inferred to be controlled by silicon volume diffusion and to be sensitive to water fugacity at differential stresses 200 mpa non linear flow involved dislocation motion extrapolation to natural strain rates and temperatures that predict grain size sensitive flow in quartz should only be important at 800 k and very small grain sizes 1 m flow law parameters may change over the extrapolation interval e g through a transition to control by silicon grain boundary diffusion but geological evidence suggests that flow of even very fine grained quartzites commonly occurs by recrystallization accommodated dislocation creep rather than by diffusional accommodation

creep mechanisms in the lithospheric mantle inferred from deformation of iron free forsterite aggregates at 900 1200 c abstract to further constrain the plasticity of rocks in the uppermost lithospheric mantle deformation experiments were carried out on forsterite aggregates using a gas medium apparatus paterson press at 300 mpa 900 1200 c and nearly constant strain rates of 10 5 s 1 the starting material was a synthetic iron free forsterite aggregate with an average grain size of 2 8 m and 2 3 of iron free enstatite eight deformation experiments were performed as well as an additional static annealing to characterize grain growth the maximum stresses obtained range from 480 to 1870 mpa below 1000 c where stress significantly exceeds confining pressure and based on microstructural observations grain boundary mediated creep is observed with evidences of sliding and cavitation gaping at grain boundaries at 1050 1200 c where pseudo steady state could be achieved the microstructures are very different and show evidences of dislocation activity resulting from the activation of several dislocation slip systems with increasing temperature when compared to rheology laws previously obtained from similar experiments the temperature dependence of iron free olivine creep is similar to the one of its iron bearing counterpart at high temperature 1200 c at temperatures 1000 c however the strength of iron free olivine is higher than for iron bearing olivine the deformation induced textures obtained show that grain boundary sliding gbs lead to cavitation which was activated in response to large differential stresses i e beyond the goetze criterion given these high stress conditions our results cannot be directly applied to deformation of the earth s mantle at large scale nevertheless they highlight the key role played by grain boundaries in producing strain at lithospheric temperatures when crystal plastic mechanisms remain inefficient

ground motion prediction equation for small to moderate events at short hypocentral distances with application to induced seismicity hazards abstract the evaluation of seismic hazard from induced seismicity requires the development of ground motion prediction equations gmpes that are tuned to the key magnitude distance range for such applications i use events of m 3 6 at hypocentral distances less than 40 km drawn from the next generation attenuation west 2 nga west 2 database to develop a gmpe that accounts correctly for point source scaling in both magnitude and distance space for such events the developed gmpe is in demonstrable agreement with the nga west 2 database and with the predictions of a stochastic point source simulation model the database is sparse at close distances implying epistemic uncertainty of as much as a factor of 2 in ground motion amplitudes within 10 km of the hypocenter an important conclusion from this study is that the ground motion amplitudes for moderate induced events could be much larger near the epicenter than predicted by most of the nga west 2 gmpes the potential for large motions is a consequence of the shallow depth of induced events which places the earthquake fault only a short distance beneath the epicenter

stress drop estimates of potentially induced earthquakes in the guy greenbrier sequence we calculate corner frequencies and stress drops for 25 potentially induced earthquakes mw 2 17 2 57 in the guy greenbrier sequence in the central arkansas we use the spectral ratio method employing highly similar earthquakes as empirical green s functions egfs we show that multiple egfs give consistent corner frequency estimates for the same earthquake and find a range of stress drops of 1 02 mpa to 42 50 mpa with a median of 10 57 mpa by using the brune spectral model and the source parameters given by sato and hirasawa 1973 we also analyze stress drop dependence on the assumed spectral models and source parameters and use a bootstrapping analysis to calculate the uncertainty in corner frequency and stress drop estimates the boatwright spectral model leads to lower stress drop estimates than the brune spectral model due to the limited bandwidth and fixed fall off rates we find that the uncertainty in the stress drop of each earthquake is generally much smaller than the range of stress drop estimates the value and range of these stress drops of the potentially induced earthquakes are similar to tectonic earthquakes in california reported by other spectral ratio studies our results highlight the value of spectral ratio analyses of earthquakes in the central united states

global models of ridge push force geoid and lithospheric strength of oceanic plates an understanding of the transmission of ridge push related stresses in the interior of oceanic plates is important because ridge push force is one of the principal forces driving plate motion here i assess the transmission of ridge push related stresses in oceanic plates by comparing the magnitude of the ridge push force to the integrated strength of oceanic plates the strength is determined based on plate cooling and rheological models the strength analysis includes low temperature plasticity ltp in the upper mantle and assumes a range of possible tectonic conditions and rheology in the plates the ridge push force has been derived from the thermal state of oceanic lithosphere seafloor depth and crustal age data the results of modeling show that the transmission of ridge push related stresses in oceanic plates mainly depends on rheology and predominant tectonic conditions if a lithosphere has dry rheology the estimated strength is higher than the ridge push force at all ages for compressional tectonics and at old ages 75 ma for extension therefore under such conditions oceanic plates may not respond to ridge push force by intraplate deformation instead the plates may transmit the ridge push related stress in their interior for a wet rheology however the strength of young lithosphere 75 ma is much less than the ridge push force for both compressional and extensional tectonics in this case the ridge push related stress may dissipate in the interior of oceanic plates and diffuses by intraplate deformation the state of stress within a plate depends on the balance of far field and intraplate forces

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

high pressure high temperature deformation of dunite eclogite clinopyroxenite and garnetite using in situ x ray diffraction abstract the rheology of eclogite garnetite and clinopyroxenite in the peridotitic upper mantle was experimentally investigated in a large volume press combined with in situ synchrotron x ray diffraction techniques to study the impact on mantle convection resulting from the subduction of oceanic lithosphere experiments were carried out over a range of constant strain rates 2 10 6 3 10 5 s 1 pressures 4 3 to 6 7 gpa and temperatures 1050 to 1470 k results show substantial strength variations among eclogitic garnet and clinopyroxene and peridotitic olivine at low temperatures 1400 k eclogite is weaker than dunite by 0 2 gpa or more garnetite and clinopyroxenite exhibit higher strength than dunite at approximately 1200 k however at higher temperature 1370 k clinopyroxenite is significantly weaker than garnetite and dunite by more than a factor of five we explain these observations by transitions in deformation mechanisms among the mineral phases in clinopyroxene high temperature dislocation creep resulting in a strength reduction replaces low temperature twinning whereas garnet remains very rigid at all experimental conditions when nominally anhydrous dry microstructural observations show phase segregation of clinopyroxene and garnet development of a crystallographic and shape preferred orientation in the former but not in the latter suggesting an overall weak seismic anisotropy detection of eclogite bodies in the peridotite dominated mantle may only be possible via observation of high v p v s 1 ratios a comparable or weaker rheology of eclogite to dunite suggests effective stirring and mixing of eclogite in the convecting mantle

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

viscoplasticity of polycrystalline olivine experimentally deformed at high pressure and 900 c abstract we have performed tri axial compression experiments on olivine aggregates at 900 c and at a confining pressure of 300 mpa in a high resolution gas medium mechanical testing apparatus deformation at two different constant strain rates 1 1 10 5 s 1 and 3 4 10 4 s 1 yields continuous hardening reaching maximal differential stresses of 930 and 1076 mpa respectively before sample failure at ca 10 strain the deformed samples were characterized by electron backscatter diffraction ebsd and transmission electron microscopy tem crystallographic preferred orientations cpo are weak but reveal an alignment of the 010 axes around the compression direction and some concentration of 001 and 100 axes normal to it tem observations confirm plastic deformation by dislocation glide with both 001 and 100 burgers vectors electron tomography performed for the first time on deformed fined grained olivine shows that 001 dislocations glide extensively on 110 and 130 planes in complement to the 010 and 100 glide planes often reported at high temperatures 100 dislocations glide mostly on 010 but 011 and 041 planes are also activated the experimental cpo and relative activity of slip systems are well reproduced by viscoplastic self consistent simulations in which all 100 and 001 slip systems have similar strengths they are also consistent with olivine cpo from natural samples deformed at low temperature comparison of the present mechanical results to those obtained for olivine single crystals at similar conditions shows that at low temperature below 1100 c and high stress 300 mpa polycrystalline olivine has a more complex mechanical behavior than single crystals however both datasets advocate for a much weaker dry mantle lithosphere than previously thought

the role of recrystallisation on the deformation behaviour of calcite rocks large strain torsion experiments on carrara marble abstract the rheological microstructural and textural evolution of carrara marble was studied during experimental deformation in torsion up to very large shear strains 0 4 50 experiments were performed at constant angular displacement rates corresponding to shear strain rates of 6 10 5 3 10 3 s 1 a confining pressure of 300 mpa and temperatures of 500 600 and 727 c microstructures and crystallographic preferred orientations cpo were analysed using light microscopy and electron backscatter diffraction ebsd at all conditions deformation occurred dominantly by dislocation creep even up to very large shear strains after peak stresses 2 recrystallisation mostly by subgrain rotation caused weakening 5 20 grain size reduction and a change in the cpo a monoclinic cpo that formed at small strains at all temperatures evolved into two different large strain cpos at different temperatures at large strains even after complete recrystallisation the cpo continued to strengthen and a secondary foliation was formed at a steep angle to the shear zone boundary this secondary foliation was continuously reset by both subgrain rotation and grain boundary migration recrystallisation and eventually overprinted the primary foliation misidentifying the primary and secondary foliations could result in misinterpretation of the applied strain field more generally information about the amount of strain is lacking for microstructures and cpos of highly deformed ultramylonites

relationships between dynamically recrystallized grain size and deformation conditions in experimentally deformed olivine rocks new microstructural data on experimentally deformed wet and dry natural olivine rocks anita bay and aheim dunite together with the other reliable experimental data indicate that the experimental stress recrystallized grain size relationship in olivine rocks is largely independent of water content and temperature and is only slightly dependent on the flow properties of the material the experimental data cover a stress range of 30 300 mpa water contents from 30 ppm to 300 ppm and temperatures in the range 1100 1650 c local melt contents of up to 10 volume cannot be demonstrated to have a significant effect on the stress grain size relationship

low strength of earth s uppermost mantle inferred from tri axial deformation experiments on dry olivine crystals abstract we have performed tri axial compression experiments on single crystals of san carlos olivine with various orientations at temperatures relevant for the uppermost mantle between 800 and 1090 c the experiments were carried out at a confining pressure of 300 mpa in a high resolution gas medium mechanical testing apparatus at various constant strain rates from 7 10 6 s 1 to 1 10 4 s 1 they yield differential stresses ranging from 88 to 754 mpa unpolarized infrared spectroscopy analyses indicate that hydrogen concentration in the olivine lattice is very low e 1 0 2 10 6 exp 450 60 10 3 rt 1 15 4 1 2 2 where t is the absolute temperature r is the gas constant and is the differential stress in gpa subsequently small fractions of melt or incorporation of hydrogen in olivine may not be required to reconcile natural observations indicating a limited strength of earth s uppermost mantle lithosphere

rheological contrast at the continental moho effects of composition temperature deformation mechanism and tectonic regime abstract the rheological contrast at the moho is an important factor in continental tectonics this paper explores systematically the effects of composition temperature deformation mechanism and tectonic regime on the strength contrast considering four compositions for the lower crust felsic granulite mafic granulite wet diabase dry diabase and two for the lithospheric mantle dry and wet peridotite the strength contrast of the resulting eight compositional layerings is estimated as a function of moho temperature which is varied from 600 to 1500 k the moho temperature can be converted to surface heat flow if the thickness and composition of the crust are known besides a standard case crustal thickness 35 km the cases of a thick 50 km and thin 20 km crust are also considered with wet quartzite crustal rheology in the latter case results show a great variety of strength contrasts according to different conditions excluding the case of very low moho temperature tm 600 k when the behaviour of both lower crust and upper mantle is frictional brittle and therefore the strength contrast vanishes the strength contrast at a given strain rate is a strong function of composition temperature and tectonic conditions weak compositional stratification e g soft lower crust soft lithospheric mantle or hard lower crust hard lithospheric mantle results in lower contrasts than strong compositional stratification for any given compositional combination the absolute value of the strength contrast is higher in compressional as compared to extensional tectonic environments and tends to decrease with increasing temperature from a maximum of hundreds of mpa at low to intermediate moho temperatures 600 1200 k therefore rheological layering is favoured by strong intrinsic i e compositional strength contrasts between lower crust and upper mantle and relatively low moho temperatures

diffusion creep of dry melt free olivine 1 deformation experiments were conducted on fine grained 3 6 m fully synthetic fo90 olivine aggregates in a gas medium apparatus at 300 mpa confining pressure and temperatures of 1150 1360 c the strain rates of the solution gelation derived and therefore genuinely melt free dry samples are about two orders of magnitude lower than the strain rates for nominally melt free aggregates at the same pressure and temperature conditions and grain size benchmark deformation tests with anita bay dunite and mild steel reproduce published data the creep strength of melt added sol gel olivine is similar to the published creep strength of dry melt bearing olivine derived from natural rocks nonlinear least squares fits to the melt free deformation data give an activation energy of 484 kj mol a stress exponent of 1 4 and a grain size exponent of 3 over a range of stresses from 15 to 210 mpa these results suggest that small amounts of melt may be similarly effective in reducing the creep strength of upper mantle rocks as small amounts of water however a possible contribution of grain boundary composition to the observed differences in rheology in the absence of melt cannot be conclusively ruled out by the current experiments

dislocation damping and anisotropic seismic wave attenuation in earth s upper mantle crystal defects form during tectonic deformation and are reactivated by the shear stress associated with passing seismic waves although these defects known as dislocations potentially contribute to the attenuation of seismic waves in earth s upper mantle evidence for dislocation damping from laboratory studies has been circumstantial we experimentally determined the shear modulus and associated strain energy dissipation in pre deformed synthetic olivine aggregates under high pressures and temperatures enhanced high temperature background dissipation occurred in specimens pre deformed by dislocation creep in either compression or torsion the enhancement being greater for prior deformation in torsion these observations suggest the possibility of anisotropic attenuation in relatively coarse grained rocks where olivine is or was deformed at relatively high stress by dislocation creep in earth s upper mantle

mechanisms for the generation of plate tectonics by two phase grain damage and pinning abstract weakening and shear localization in the lithosphere are essential ingredients for understanding how and whether plate tectonics is generated from mantle convection on terrestrial planets we present a new theoretical model for the mechanism of lithospheric weakening and shear localization and hence plate generation through damage grain evolution and zener pinning in two phase polycrystalline lithospheric rocks grain size evolves through the competition of coarsening which drives grain growth with damage which drives grain reduction however in a two phase medium the interface between phases induces zener pinning which impedes grain growth and facilitates damage the size of the pinning surfaces is given by the roughness of the interface and damage to the interface causes smaller pinning surfaces which in turn drive down the grain size forcing the rheology into the grain size dependent diffusion creep regime this process allows damage and rheological weakening to co exist which is normally considered impossible in single phase assemblages moreover pinning greatly inhibits grain growth and shear zone healing which is much faster in single phase materials hence the resulting shear localization is rapid less than 1 myr but the healing time for a dormant weak zone is very slow greater than 100 myrs these effects therefore permit rapidly forming and long lived plate boundaries the model therefore provides a key ingredient and predictive theory for the generation of plate tectonics on earth and other planets

do calcite rocks obey the power law creep equation abstract the power law creep equation e n exp q rt is commonly used to relate strain rate e stress and temperature t for thermally activated dislocation creep in rocks when triaxial deformation experiments on marble and limestone samples are performed at temperatures of 400 1050 c to strains 3 and 10 7 s 1 the variations in strength among different rocks at nominally identical conditions are much larger than the experimental uncertainty during dislocation creep the strengths of various limestones and marbles decrease with increasing grain size similar to the hall petch effect in metals the stress sensitivity of strain rate n ln e ln and the temperature sensitivity of strain rate q r ln e 1 t differ greatly for the various calcite aggregates there is a systematic dependence of n and q on stress grain size and perhaps temperature and there is no interval in stress where n is constant thus the steady state power law equation is an inadequate description of dislocation creep in calcite rocks to improve the constitutive law it may be necessary to include at least one additional state variable that scales with grain size

a century of induced earthquakes in oklahoma seismicity rates have increased sharply since 2009 in the central and eastern united states with especially high rates of activity in the state of oklahoma growing evidence indicates that many of these events are induced primarily by injection of wastewater in deep disposal wells the upsurge in activity has raised two questions what is the background rate of tectonic earthquakes in oklahoma how much has the rate varied throughout historical and early instrumental times in this article we show that 1 seismicity rates since 2009 surpass previously observed rates throughout the twentieth century 2 several lines of evidence suggest that most of the significant earthquakes in oklahoma during the twentieth century were likely induced by oil production activities as they exhibit statistically significant temporal and spatial correspondence with disposal wells and intensity measurements for the 1952 el reno earthquake and possibly the 1956 tulsa county earthquake follow the pattern observed in other induced earthquakes and 3 there is evidence for a low level of tectonic seismicity in southeastern oklahoma associated with the ouachita structural belt the 22 october 1882 choctaw nation earthquake for which we estimate m w 4 8 occurred in this zone online material a discussion of historical earthquakes and populations in oklahoma figures of intensity and earthquake location maps and a cumulative count of earthquakes in oklahoma and tables of accounts and felt reports

effect of water and stress on the lattice preferred orientation of olivine the influence of water and stress on the lattice preferred orientation lpo of olivine aggregates was investigated through large strain shear deformation experiments at high pressures and temperatures p 0 5 2 1 gpa t 1470 1570 k under both waterpoor and water rich conditions the specimens are hot pressed synthetic olivine aggregates or single crystals of olivine water was supplied to the sample by decomposition of a mixture of talc and brucite deformation experiments were conducted up to shear strain 6 using the griggs apparatus where water fugacity was up to 13 gpa at the pressure of 2 gpa the water content in olivine saturated with water increases with increasing pressure and the solubility of water in olivine at p 0 5 2 gpa was 400 1200 ppm h si several new types of lpo in olivine are found depending on water content and stress samples deformed in waterpoor conditions show a conventional lpo of olivine where the olivine 100 axis is subparallel to the shear direction the 010 plane subparallel to the shear plane type a however we identified three new types type b c and e of lpo of olivine depending on the water content and stress the type b lpo of olivine which was found at relatively high stress and or under moderate to high water content conditions is characterized by the olivine 001 axis subparallel to the shear direction the 010 plane subparallel to the shear plane the type c lpo which was found at low stress and under water rich conditions is characterized by the olivine 001 axis subparallel to the shear direction the 100 plane subparallel to the shear plane the type e lpo which was found under low stress and moderate water content is characterized by the olivine 100 axis subparallel to the shear direction the 001 plane subparallel to the shear plane observations by transmission electron microscopy tem and scanning electron microscopy sem show that the dislocations in water poor samples type a are curved and both b 100 and b 001 dislocations have a similar population numerous subgrains are seen in water poor samples in backscattered electron images in contrast water rich samples both type b and type c contain mostly b 001 dislocations and dislocations are straight and sub grain boundaries are rare compared to those in water poor samples these observations suggest that 1 dominant slip systems in olivine change with water fugacity and stress and 2 grain boundary migration is enhanced in the presence of water seismic anisotropy corresponding to the fabrics under water rich condition is significantly different from that under water poor condition consequently the relationship between seismic anisotropy and flow geometry in water rich regions is expected to be

induced seismicity associated with fluid injection into a deep well in youngstown ohio 1 over 109 small earthquakes mw 0 4 3 9 were detected during january 2011 to february 2012 in the youngstown ohio area where there were no known earthquakes in the past these shocks were close to a deep fluid injection well the 14 month seismicity included six felt earthquakes and culminated with a mw 3 9 shock on 31 december 2011 among the 109 shocks 12 events greater than mw 1 8 were detected by regional network and accurately relocated whereas 97 small earthquakes 0 4 mw 1 8 were detected by the waveform correlation detector accurately located earthquakes were along a subsurface fault trending ene wsw consistent with the focal mechanism of the main shock and occurred at depths 3 5 4 0 km in the precambrian basement we conclude that the recent earthquakes in youngstown ohio were induced by the fluid injection at a deep injection well due to increased pore pressure along the preexisting subsurface faults located close to the wellbore we found that the seismicity initiated at the eastern end of the subsurface fault close to the injection point and migrated toward the west away from the wellbore indicating that the expanding high fluid pressure front increased the pore pressure along its path and progressively triggered the earthquakes we observe that several periods of quiescence of seismicity follow the minima in injection volumes and pressure which may indicate that the earthquakes were directly caused by the pressure buildup and stopped when pressure dropped

the experimental deformation of dunite deformation experiments have been carried out on two dunites anita bay of 100 m grain size and aheim of 900 m grain size at strain rates from 10 3 to 10 6 s 1 and temperatures from 1000 c to 1300 c in a gas medium deformation apparatus at 300 mpa confining pressure most of the tests were under wet conditions defined by the presence of small amounts of water from hydrous minerals initially present constant strain rate and relaxation experiments covering ranges of flow stress down to about 70 mpa and 7 mpa respectively show that there is a change in flow law in going below about 100 mpa differential stress and that the coarser grained rock is stronger than the finer grained one power law parameters above the transition are n 4 48 0 31 and q 498 38 kj mol 1 for aheim dunite and n 3 35 0 17 and q 444 24 kj mol 1 for anita bay dunite while below the transition relaxation tests on anita bay dunite give n 2 44 0 18 and q 386 27 kj mol 1 it is concluded that there is a weakening effect of water that this effect is mainly in the grain boundaries and that grain boundary sliding is probably a significant deformation mechanism at the lower stresses under wet conditions

elasticity of single crystal olivine at high pressures and temperatures abstract elasticity of single crystal san carlos olivine has been derived from sound velocity and density measurements at simultaneous high pressure temperature conditions up to 20 gpa and 900 k using in situ brillouin spectroscopy and single crystal x ray diffraction in externally heated diamond anvil cells these experimental results are used to evaluate the combined effect of pressure and temperature on full elastic constants of single crystal olivine to better understand its velocity profiles and anisotropies in the deep mantle analysis of the results shows that the shear moduli display strong concave behaviors as a function of pressure at a given high temperature while the longitudinal modulus c 11 and the off diagonal moduli c 12 and c 13 exhibit greater temperature dependence at higher pressures than at relatively lower pressures using a finite strain theory and thermal equation of state modeling for a pyrolitic mantle composition along an expected mantle geotherm our results show that the magnitude of the v p and v s jumps at the 410 km depth are 6 and 6 4 respectively which are greater than that found in seismic observations suggesting a mantle olivine content of 40 50 vol which is less than what is expected for the pyrolite model our modeled velocity profiles for a metastable olivine wedge in the subduction slabs along a representative cold slab geotherm are 6 and 10 lower than those of wadsleyite and ringwoodite respectively at corresponding depths of the normal mantle our modeled results also show that metastable olivine in the cold slabs could have strong v p and v s anisotropies the maximum v p anisotropy is estimated to be 19 22 at transition zone depth whereas the maximum v s splitting is 13 23 and increases with depth as a result the presence of a metastable olivine wedge at the transition zone depth would exhibit a seismic signature of low velocity and strong seismic anisotropy which are consistent with recent seismic observations for various locations of the slabs and can be used as mineral physics constraints for future seismic detections of the metastable olivine wedges in the deep mantle

hydraulic properties of injection formations constrained by surface deformation author s shirzaei m manga m zhai g abstract 2019 the author s wastewater injection over the past decade has increased seismicity in the central usa in some cases accompanied by detectable surface uplift here we use this uplift to constrain subsurface properties and pore pressure evolution we apply an advanced multitemporal interferometric algorithm to 35 synthetic aperture radar images acquired by alos satellite over four years before the 2012 earthquake sequence in east texas where large volumes of wastewater are disposed at depths of 800 m and 1800 m to solve for the hydraulic diffusivity of the injection layers we jointly inverted the injected volume and uplift data considering a poroelastic layered half space we find diffusivity values of 0 3 0 1 m 2 s and 0 7 0 15 m 2 s for shallow and deep injection layers respectively which combined with seismically derived bulk moduli yields permeability values of 5 5 2 6 10 14 m 2 and 1 9 0 25 10 13 m 2 for these layers consistent with permeability range reported for rodessa formation and well test values hydraulic conductivity determines the evolution of pore pressure and thus the origin and location of induced seismicity this study highlights the value of geodetic observations to constrain key hydrogeological properties of injection layers and to monitor the evolution of the subsurface pressure change

regional fractures ii fracturing of mesaverde reservoirs in the piceance basin colorado 1 cretaceous strata in the east central piceance basin of northwestern colorado were subjected to several phases of stress due to horizontal tectonic compression burial and uplift these rocks contain a regional set of west northwest extension fractures observed in abundant vertical and deviated core from the u s department of energy s multiwell experiment and slant hole completion test wells time depth relationships fracture orientation and fluid inclusion analyses indicate that the fractures formed at about 36 40 ma during a phase of increased laramide west northwest compression and in a pressure temperature regime compatible with the geologically reconstructed maximum burial depths this regional fracturing is an example of load parallel extension fracturing and basinwide dilatancy at depth under conditions of high pore pressure and anisotropic tectonically created horizontal stress

geologic analysis of the upper jurassic haynesville shale in east texas and west louisiana the upper jurassic haynesville shale is currently regarded as one of the most prolific emerging shale gas plays in the continental united states it has estimated play resources of several hundred trillion cubic feet and per well reserves estimated as much as 7 5 bcf the reservoir spans more than 16 counties along the boundary of eastern texas and western louisiana although this basin has a long history of exploration and analysis of its mesozoic section a comprehensive subsurface study characterizing the haynesville shale has not been conducted this article is the first to address the structural setting stratigraphy depositional environment and facies fracturing and production challenges of the haynesville shale gas play basement structures and salt movement influenced carbonate and siliciclastic sedimentation associated with the opening of the gulf of mexico the haynesville shale is an organic and carbonate rich mudrock that was deposited in a deep partly euxinic and anoxic basin during the kimmeridgian to the early tithonian related to a second order transgression that deposited organic rich black shales worldwide the haynesville basin was surrounded by carbonate shelves of the smackover and haynesville lime louark sequence in the north and west several rivers supplied sand and mud from the northwest north and northeast into the basin haynesville mudrocks contain a spectrum of facies ranging from bioturbated calcareous mudstone laminated calcareous mudstone and silty peloidal siliceous mudstone to unlaminated siliceous organic rich mudstone framboidal to colloidal pyrite is variably present in the form of concretions laminae and individual framboids and replaces calcite cement and mollusk shells haynesville reservoirs are characterized by overpressuring porosity averaging 8 to 12 sw of 20 to 30 nanodarcy permeabilities reservoir thickness of 200 to 300 ft 70 to100 m and initial production of as much as 30 mmcf day reservoir depth ranges from 9000 to 14 000 ft 3000 to 4700 m and lateral drilling distances are 3000 to 5000 ft 1000 to 1700 m typical haynesville wells exhibit a steeper decline curve 80 in the first year than other shale gas plays which is attributed to a very high overpressure

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

experimental deformation of olivine single crystals at mantle pressures and temperatures abstract deformation experiments were carried out in a deformation dia high pressure apparatus d dia on oriented san carlos olivine single crystals at pressure p ranging from 3 5 to 8 5 gpa temperature t from 1373 to 1673 k and in poor water condition oxygen fugacity fo2 was maintained within the olivine stability field and contact with enstatite powder ensured an orthopyroxene activity aopx 1 two compression directions were tested promoting either 1 0 0 slip alone or 0 0 1 slip alone in 0 1 0 crystallographic plane here called respectively a slip and c slip constant applied stress and specimen strain rates e were monitored in situ using time resolved x ray synchrotron diffraction and radiography respectively transmission electron microscopy tem investigation of run products revealed that dislocation creep was responsible for sample deformation comparison of the obtained high p deformation data with the data obtained at room p by bai et al bai q mackwell s l kohlstedt d l 1991 high temperature creep of olivine single crystals 1 mechanical results for buffered samples journal of geophysical research 96 2441 2463 on identical materials deformed at comparable t fo2 aopx conditions allowed quantifying the p effect on a slip and c slip rheological laws a slip transition with increasing pressure from dominant a slip to dominant c slip is documented a slip appears sensitive to pressure which translates into the high activation volume v a 12 4 c m 3 mol in the corresponding rheological law while pressure has little effect on c slip with v c 3 4 c m 3 mol these results may explain the discrepancy between olivine low p and high p deformation data which has been debated in the literature for more than a decade

late laramide thrust related and evaporite domed anticlines in the southern piceance basin northeastern colorado plateau new seismic and gravity data across the hydrocarbon producing divide creek and wolf creek anticlines in the southern piceance basin reveal contrasting styles of deformation within two widely separated time frames seismic data indicate that prebasin paleozoic deformation resulted in block faulting of the precambrian crystalline basement rocks and overlying cambrian through middle pennsylvanian strata movement along these block faults throughout much of pennsylvanian time during northeast southwest crustal extension likely influenced distribution of the middle pennsylvanian desmoinesian evaporite rich facies younger rocks including the thick succession of cenozoic basin strata then buried the paleozoic structures tectonic reconfiguration of the basin s eastern margin occurred during late laramide northeast southwest compression when a basement involved thrust block whose surface expression is the grand hogback monocline moved into the piceance basin a decollement developed in front of the thrust block within the mechanically weak desmoinesian evaporites and splayed out basinward as small scale imbricate thrusts in the upper cretaceous mancos shale the divide creek anticline formed above these splays as thrusting locally overthickened the shale and repeated the sandstone units between it and the evaporites the wolf creek anticline to the east however is due to both depositional and tectonic thickening of the evaporite section along the decollement gravity data confirm that excess mater al of relatively low density exists beneath the wolf creek structure whereas material of relatively higher density overthickened shale is found beneath the divide creek anticline thrust related basin margins and intrabasin folds structurally analogous to the divide creek and wolf creek anticlines may be more common than presently recognized in the rocky mountain foreland one well documented example is the pinedale anticline in the northern green river basin wyoming which like the divide creek anticline developed above a zone of splay faults from a decollement in front of a large thrust block

modifications to existing ground motion prediction equations in light of new data we compare our recent ground motion prediction equations gmpes for western north america wna boore and atkinson 2008 ba08 and eastern north america ena atkinson and boore 2006 ab06 atkinson 2008 a08 to newly available ground motion data based on these comparisons we suggest revisions to our gmpes for both wna and ena the revisions for wna affect only those events with m 5 75 while those for ena affect all magnitudes these are simple modi fications to the existing gmpes that bring them into significantly better agreement with data the wealth of new data clearly demonstrates that these modifications are warranted we therefore recommend the use of the updated equations for seismic hazard analyses and other applications more detailed studies are under way by many investigators including ourselves to develop a new generation of ground motion models in both wna and ena from scratch through a comprehensive reevaluation of source path site and modeling issues in time those more complete models will replace those proposed in this study however as the new models will be several years in development we recommend using the modified models proposed herein labeled ba08 for wna ab06 for ena and a08 for ena to replace a08 as interim updates to our existing models the proposed models are in demonstrable agreement with a rich database of ground motions for moderate magnitude earthquakes in both wna and ena and are constrained at larger magnitudes by the ba08 magnitude and distance scaling

inversion for crustal structure using reflections from the passcal ouachita experiment an interface inversion has been tested and applied to wide angle reflection data from the 1986 passcal ouachita experiment an interface corrugation with a relief of 10 km and a width of 30 km was successfully imaged in a test of the interface inversion velocity depth curves derived for shot points 14 19 using the tail sum method are similar to an average one dimensional velocity model from forward modeling using travel time correlations from southern profiles 14 19 the similarity of these velocity depth curves positioned over the southern half of the passcal experiment suggests that crustal structure in this region is approximately laterally homogeneous lower crustal velocities are not well resolved due to the recording on most profiles of only small segments of the travel time triplications a two dimensional velocity structure was derived by using the average one dimensional velocities for the deeper crustal layers and formally inverting for depth to interfaces the final inversion model is found to be consistent with previous refraction interpretations south of the ouachita orogenic trend and concurrent interpretations of the passcal data set inversion results for the central and southern portion of the passcal profile indicate a depth of 10 12 km for a midcrustal layer which thins southward from approximately 10 km to about 4 km a lower crustal layer with an average thickness of 12 km and a moho depth of approximately 29 5 km are also determined interface depths are in agreement with a normal moveout stack of the passcal data set in particular the shallowing of the moho to a depth of 30 km over the northern 50 km of the profile matches previous interpretations of the data set and has been interpreted here and in previous studies as the location of the paleozoic continental margin geophysical studies of the modern atlantic continental passive margin provide the simplest comparison to the crustal structure derived here the lower crustal layer found south of the shallowing of the moho to 30 km beneath the passcal profile is analogous in thickness and position to rift stage lower crust however other tectonic interpretations are possible given the uncertainties in velocity and lithology relationships

earthquake ground motion prediction equations for eastern north america new earthquake ground motion relations for hard rock and soil sites in eastern north america ena including estimates of their aleatory uncertainty vari ability have been developed based on a stochastic finite fault model the model incorporates new information obtained from ena seismographic data gathered over the past 10 years including three component broadband data that provide new in formation on ena source and path effects our new prediction equations are similar to the previous ground motion prediction equations of atkinson and boore 1995 which were based on a stochastic point source model the main difference is that high frequency amplitudes f 5 hz are less than previously predicted by about a factor of 1 6 within 100 km because of a slightly lower average stress parameter 140 bars versus 180 bars and a steeper near source attenuation at frequencies less than 5 hz the predicted ground motions from the new equations are generally within 25 of those predicted by atkinson and boore 1995 the prediction equations agree well with available ena ground motion data as evidenced by near zero average residuals within a factor of 1 2 for all frequencies and the lack of any significant residual trends with distance however there is a tendency to positive residuals for moderate events at high frequencies in the distance range from 30 to 100 km by as much as a factor of 2 this indicates epistemic uncertainty in the prediction model the positive residuals for moderate events at 100 km could be eliminated by an increased stress parameter at the cost of producing negative residuals in other magnitude distance ranges adjustment factors to the equations are provided that may be used to model this effect

deformation of olivine under mantle conditions an in situ high pressure high temperature study using monochromatic synchrotron radiation polycrystalline samples of san carlos olivine were deformed at high pressure 2 8 7 8 gpa high temperature 1153 to 1670 k and strain rates between 7 10 sup 6 and 3 10 sup 5 s sup 1 using the d dia apparatus stress and strain were measured in situ using monochromatic x rays diffraction and imaging respectively based on the evolution of lattice strains with total bulk strain and texture development we identified three deformation regimes one at confining pressures below 3 4 gpa one above 4 gpa both below 1600 k and one involving growth of diffracting domains associated with mechanical softening above approx 1600 k the softening is interpreted as enhanced grain boundary migration and recovery below 1600 k elasto plastic self consistent analysis suggests that below 3 4 gpa deformation in olivine occurs with large contribution from the so called a slip system 100 010 above approx 4 gpa the contribution of the a slip decreases relative to that of the c slip 001 010 this conclusion is further supported by texture refinements thus for polycrystalline olivine the evolution in slip systems found by previous studies may be progressive starting from as low as 3 4 gpa and up to 8 gpa during such a gradual change activation volumes measured on polycrystalline olivine cannot be linked to a particular slip systemmore straightforwardly the quest for the activation volume of olivine at high pressure should cease at the expense of detailed work on the flow mechanisms implied such evolution in slip systems should also affect the interpretation of seismic anisotropy data in terms of upper mantle flow between 120 and 300 km depth less

the role of pre existing mechanical anisotropy on shear zone development within oceanic mantle lithosphere an example from the oman ophiolite structural and fabric analysis of the well exposed hilti mantle section oman ophiolite suggests that shear zone development which may have resulted from oceanic plate fragmentation was influenced by pre existing mantle fabric present at the paleoridge detailed structural mapping in the mantle section revealed a gently undulating structure with an east west flow direction a nw se strike slip shear zone cuts across this horizontal structure the crystal preferred orientation cpo of olivine within the foliation is dominated by 010 axial patterns rather than more commonly observed 010 100 patterns suggesting that the horizontal flow close to the moho involved non coaxial flow olivine cpo within the shear zone formed at low temperature is characterized by 001 100 patterns and a sinistral sense of shear the olivine cpo becomes weaker with progressive mylonitization and accompanying grain size reduction and ultimately develops into an ultra mylonite with a random cpo pattern the olivine 010 axis is consistently sub vertical even where the horizontal foliation has been rotated to a sub vertical orientation within the shear zone these observations suggest that the primary mechanical anisotropy mantle fabric has been readily transformed into a secondary structure shear zone with minimum modification this occurred as a result of a change of the olivine slip systems during oceanic detachment and related tectonics during cooling we propose that primary olivine cpo fabrics may play a significant role in the subsequent structural development of the mantle thus the structural behavior of oceanic mantle lithosphere during subduction and obduction may be strongly influenced by initial mechanical anisotropy developed at an oceanic spreading center

detecting seismic anisotropy above the 410 km discontinuity using reflection coefficients of underside reflections abstract we investigate the effect of various types of deformation mechanisms on the reflection coefficients of p and s waves underside reflections off the 410 km discontinuity to develop a diagnostic tool to detect the style of deformation at boundary layers we calculate the reflection coefficient for p and sh underside reflections using velocity perturbations resulting from aligned minerals above the 410 km discontinuity for different deformation scenarios the results show that in the case of an anisotropic olivine layer above an isotropic wadsleyite layer the p wave reflection coefficient amplitudes are only slightly influenced by the joint effect of angle of incidence and the strength of imposed deformation without any polarity reversal and for all deformation styles for the sh wave underside reflections the incidence angle for which a polarity reversal occurs changes with distance for all scenarios and in addition changes with azimuth for shear deformation scenarios these differences in amplitude and polarity patterns of reflection coefficients of different deformation geometries especially for s wave at shorter distances potentially provide a possibility to distinguish between different styles of deformation at a boundary layer we also show a first test using currently available elastic constants of anisotropic wadsleyite beneath anisotropic olivine

revisiting the timpson induced earthquake sequence a system of two parallel faults the 17 may 2012 m4 8 timpson earthquake is the largest known earthquake in eastern texas it is suspected to have been induced by wastewater injection from two nearby high volume wells its catalo

viscoplastic self consistent and equilibrium based modeling of olivine lattice preferred orientations implications for the upper mantle seismic anisotropy anisotropy of upper mantle physical properties results from lattice preferred orientation lpo of upper mantle minerals in particular olivine we use an anisotropic viscoplastic self consistent vpsc and an equilibrium based model to simulate the development of olivine lpo and hence of seismic anisotropy during deformation comparison of model predictions with olivine lpo of naturally and experimentally deformed peridotites shows that the best fit is obtained for vpsc models with relaxed strain compatibility slight differences between modeled and measured lpo may be ascribed to activation of dynamic recrystallization during experimental and natural deformation in simple shear for instance experimental results suggest that dynamic re crystallization results in further reorientation of the lpo leading to parallelism between the main 010 100 slip system and the macroscopic shear thus modeled simple shear lpos are slightly misoriented relative to lpos measured in natural and experimentally sheared peridotites this misorientation is higher for equilibrium based models yet seismic properties calculated using lpo simulated using either anisotropic vpsc or equilibrium based models are similar to those of naturally deformed peridotites errors in the prediction of the polarization direction of the fast s wave and of the fast propagation direction for p waves are usually 15 moreover overestimation of lpo intensities in equilibrium based and vpsc simulations at high strains does not affect seismic anisotropy estimates because these latter are weakly dependent on the lpo intensity once a distinct lpo pattern has been developed thus both methods yield good predictions of development of upper mantle seismic anisotropy in response to plastic flow two notes of caution have nevertheless to be observed in using these results 1 the dilution effect of other upper mantle mineral phases in particular enstatite has to be taken into account in quantitative predictions of upper mantle seismic anisotropy and 2 lpo patterns from a few naturally deformed peridotites cannot be reproduced in simulations these abnormal lpos represent a small percent of the measured natural lpos but the present sampling may not be representative of their abundance in the earth s upper mantle

monitoring the earthquake source process in north america with the implementation of the usgs national earthquake information center prompt assessment of global earthquakes for response system pager rapid determination of earthquake moment magnitude is essential especially for earthquakes that are felt within the contiguous united states we report an implementation of moment tensor processing for application to broad seismically active areas of north america this effort focuses on the selection of regional crustal velocity models codification of data quality tests and the development of procedures for rapid computation of the seismic moment tensor we systematically apply these techniques to earthquakes with reported magnitude greater than 3 5 in continental north america that are not associated with a tectonic plate boundary using the 0 02 0 10 hz passband we can usually determine with few exceptions moment tensor solutions for earthquakes with m w as small as 3 7 the threshold is significantly influenced by the density of stations the location of the earthquake relative to the seismic stations and of course the signal to noise ratio with the existing permanent broadband stations in north america operated for rapid earthquake response the seismic moment tensor of most earthquakes that are m w 4 or larger can be routinely computed as expected the nonuniform spatial pattern of these solutions reflects the seismicity pattern however the orientation of the direction of maximum compressive stress and the predominant style of faulting is spatially coherent across large regions of the continent

analysis of the cleburne texas earthquake sequence from june 2009 to june 2010 on 9 june 2009 an graphic 1 2 8 earthquake shook cleburne texas a community not known to have previously experienced earthquakes over 50 small earthquakes followed by the end of december 2009 a temporary network of four and then five iris passcal broadband systems was deployed from june 2009 to june 2010 recording data that were used to locate 38 events with the most confident p and s arrival picks event locations were distributed along a 2 km long north northeast trend the location centroid was at 32 298 n 97 372 w and at 3 6 km depth this location is approximately 1 3 km from a saltwater disposal well that began injection in october 2007 and 3 2 km away from a second injection well that was active from september 2005 to late july 2009 focal mechanisms estimated for the best recorded events suggest a north northeast south southwest trending normal fault with a dip of 50 and a component of oblique motion rake of 80 this average solution is generally consistent with the north northeast trending extensional faults that are prevalent across parts of texas oklahoma louisiana and arkansas stress drops calculated from p and s spectra for seven different events ranged from 3 9 to 90 bars with most estimates between 40 and 50 bars typical values for intraplate earthquakes because there were no known previous earthquakes and the located events were close to the two injection wells and near the injection depth the possibility exists that earthquakes may be related to fluid injection online material tables of absolute and relative earthquake locations and a figure summarizing focal mechanism solutions 1 embed inline graphic 1 gif

pressure sensitivity of olivine slip systems and seismic anisotropy of earth s upper mantle the mineral olivine dominates the composition of the earth s upper mantle and hence controls its mechanical behaviour and seismic anisotropy experiments at high temperature and moderate pressure and extensive data on naturally deformed mantle rocks have led to the conclusion that olivine at upper mantle conditions deforms essentially by dislocation creep with dominant 100 slip the resulting crystal preferred orientation has been used extensively to explain the strong seismic anisotropy observed down to 250 km depth the rapid decrease of anisotropy below this depth has been interpreted as marking the transition from dislocation to diffusion creep in the upper mantle but new high pressure experiments suggest that dislocation creep also dominates in the lower part of the upper mantle but with a different slip direction here we show that this high pressure dislocation creep produces crystal preferred orientations resulting in extremely low seismic anisotropy consistent with seismological observations below 250 km depth these results raise new questions about the mechanical state of the lower part of the upper mantle and its coupling with layers both above and below

new type of olivine fabric from deformation experiments at modest water content and low stress a new type of olivine fabric was found by high strain simple shear deformation experiments in the presence of trace amounts of water at 0 5 2 2 gpa and 1470 1570 k in this fabric called e type fabric the olivine 100 axis is subparallel to the shear direction and the 001 plane is parallel to the shear plane this geometry suggests that the 100 001 slip system makes the dominant contribution to total strain this fabric is dominant at a modest water content 200 coh 1000 h 10 6 si at low stresses and high temperatures some mylonites from peridotite massifs show this type of olivine fabric which suggests the presence of water during the shear localization the seismic anisotropy caused by this fabric is qualitatively similar to that by dry fabric a type but the magnitudes of anisotropy are different between the two types for horizontal flow the amplitude of vsh vsv anisotropy is weaker but the amplitude of shear wave splitting is stronger for the e type fabric than for the a type dry fabric seismic anisotropy in the oceanic upper mantle may be due to the olivine e type fabric

dislocation creep of fine grained olivine 1 deformation experiments conducted in a gas medium apparatus at temperatures from 1200 to 1350 c with a fine grained solution gelation derived fe bearing olivine show a stress dependence of the strain rate at stresses above 150 mpa which is much stronger than previously reported for polycrystalline samples the data can be fit by a power law with n with n 7 8 or equally well by a peierls creep law with exponential stress dependence due to the observed strong stress dependence the samples deform at significantly higher strain rates at a given stress than single crystals or coarse grained polycrystals with n 3 5 tem observations indicate the presence of dislocations with at least two different burgers vectors with free dislocations predominantly of screw character subgrain walls are present but are only weakly developed and have small misorientation angles both the rheology and dislocation structures are consistent with creep rate limited by dislocation glide or cross slip for aggregates with grain sizes smaller than or approaching the recrystallized grain size deformation mechanism maps extrapolated to lithospheric temperatures using the melt free diffusion creep rheology of faul and jackson 2007 the dislocation creep rheology of hirth and kohlstedt 2003 and the results described here indicate that deformation conditions of ultramylonitic shear zones fall near the triple point of peierls dislocation and diffusion creep

the dallas fort worth earthquake sequence october 2008 through may 2009 this paper describes a sequence of small earthquakes m b 3 3 that occurred at the dallas fort worth airport texas between 30 october 2008 and 31 may 2009 analysis of records at regional station wmok identified more than 180 earthquakes in the sequence about 90 percent occurred in four clusters on 30 october 1 november 20 november 26 december and 15 17 may after the sequence began a six station temporary local network obtained high quality three component records for 11 earthquakes occurring between 20 november and 1 december analysis of these data demonstrated that all 11 earthquakes originated from a focus near 32 855 n 97 051 w with an estimated depth 4 4 km this location is less than 0 5 km from a well completed in august 2008 that extends to a depth of 4 2 km drilled to dispose of brines collected during flowback of hydraulic fracturing fluids associated with the production of natural gas brine disposal commenced at the well on 12 september 2008 seismograms and s p intervals for the earthquakes are similar though not identical and relative locations indicate they occurred along a north northeast south southwest trend with horizontal and vertical dimensions of 1 1 km and 0 2 km respectively this trend is approximately coincident with that of a mapped normal fault in the subsurface and consistent with the maximum horizontal in situ stress direction because of the absence of previous historical earthquakes the proximity of the brine disposal well and the similarity with other documented cases of induced seismicity it seems likely that fluid injection induced the 2008 2009 sequence

a scanning electron microscope study of the effects of dynamic recrystallization on lattice preferred orientation in olivine effects of dynamic recrystallization on lattice preferred orientation lpo in olivine were investigated through the combination of two sem based techniques electron backscattered diffraction ebsd technique for crystallographic orientation measurement and backscattered electron imaging bei for dislocation observation samples are experimentally deformed olivine aggregates in simple shear geometry in the sample deformed at t 1473 k and high stresses 480 mpa only incipient dynamic recrystallization is observed along grain boundaries orientations of these small recrystallized grains are more random than that of relict grains suggesting an important role of grain boundary sliding at this stage of recrystallization in the sample deformed at t 1573 k and low stress 160 mpa dynamic recrystallization is nearly complete and the lpo is characterized by two 100 peaks one peak is located at the orientation subparallel to the shear direction and is dominated by grains with high schmid factor the other occurs at high angles to the shear direction and is due to the contribution from grains with low schmid factor grains with high schmid factor tend to have higher dislocation densities than those with low schmid factor based on these observations we identify two mechanisms by which dynamic recrystallization affects lpo 1 enhancement of grain boundary sliding due to grain size reduction leading to the modification of lpo caused by the relaxation of constraint for deformation 2 grain boundary migration by which grains with lower dislocation densities grow at the expense of grains with higher dislocation densities based on the deformation mechanism maps and stress versus recrystallized grain size relation we suggest that the first mechanism always plays an important role whereas the second mechanism has an important effect only under limited conditions

two year survey of earthquakes and injection production wells in the eagle ford shale texas prior to the mw4 8 20 october 2011 earthquake abstract between november 2009 and september 2011 the earthscope usarray program deployed 25 temporary seismograph stations on a 70 km grid in south central texas between 27 n 31 n and 96 w 101 w this area includes the eagle ford shale for decades this geographic region has produced gas and oil from other strata using conventional methods but recent developments in hydrofracturing technology has allowed extensive development of natural gas resources from within the eagle ford our study surveys small magnitude seismic events and evaluates their correlation with fluid extraction and injection in the eagle ford identifying and locating 62 probable earthquakes including 58 not reported by the u s geological survey the 62 probable earthquakes occur singly or in clusters at 14 foci of these foci two were situated near wells injecting recently increased volumes of water eight were situated near wells extracting recently increased volumes of oil and or water and four were not situated near wells reporting significant injection extraction increases thus in this region while the majority of small earthquakes may be triggered induced by human activity they are more often associated with fluid extraction than with injection we also investigated the m w 4 8 20 october 2011 fashing earthquake the largest historically reported earthquake in south central texas that occurred two weeks after the removal of the temporary usarray stations a field study indicated that the highest intensity mmi vi region was about 10 km south of 2010 2011 foreshock activity and that there were no high volume injection wells within 20 km of the mmi v vi region or the foreshocks however the 20 october 2011 earthquake did coincide with a significant increase in oil water extraction volumes at wells within the mmi v vi region and this was also true for previous earthquakes felt at fashing in 1973 and 1983 in contrast our study found significant increases in injection prior to an mblg3 6 20 july 1991 earthquake near falls city texas thus the eagle ford geographic region with seismic activity associated both with extraction and injection appears to be more complex than the barnett shale of northeast texas where a similar survey found possible correlations only with fluid injection

the evolution of seismic barriers and asperities caused by the depressuring of fault planes in oil and gas fields of south texas fluid pressures within some oil and gas fields of south texas have dropped to less than 20 per cent of their original values producing earthquakes with magnitudes up to 3 9 in recent years differential compaction of the depressurized region may be sufficient to result in the number and size of earthquakes generated or the faults may have been creeping prior to depressurization in either model the depressuring of fluids strengthens a fault and at first produces a barrier to slip as strain accumulates due to compaction or the continued aseismic slip of nearby portions of the fault stress builds up along the locked portions eventually forming high stress regions or asperities the asperities ultimately fail and earthquakes occur the process is repeated as long as the faults are active as the fluid pressures continue to decrease the barriers and subsequent asperities may increase in size and strength resulting in increasingly large and frequent earthquakes

induced earthquake magnitudes are as large as statistically expected a major question for the hazard posed by injection induced seismicity is how large induced earthquakes can be are their maximum magnitudes determined by injection parameters or by tectonics deterministic limits on induced earthquake magnitudes have been proposed based on the size of the reservoir or the volume of fluid injected however if induced earthquakes occur on tectonic faults oriented favorably with respect to the tectonic stress field then they may be limited only by the regional tectonics and connectivity of the fault network in this study we show that the largest magnitudes observed at fluid injection sites are consistent with the sampling statistics of the gutenberg richter distribution for tectonic earthquakes assuming no upper magnitude bound the data pass three specific tests 1 the largest observed earthquake at each site scales with the log of the total number of induced earthquakes 2 the order of occurrence of the largest event is random within the induced sequence and 3 the injected volume controls the total number of earthquakes rather than the total seismic moment all three tests point to an injection control on earthquake nucleation but a tectonic control on earthquake magnitude given that the largest observed earthquakes are exactly as large as expected from the sampling statistics we should not conclude that these are the largest earthquakes possible instead the results imply that induced earthquake magnitudes should be treated with the same maximum magnitude bound that is currently used to treat seismic hazard from tectonic earthquakes

effects of water on dynamically recrystallized grain size of olivine abstract recrystallized grain size versus stress relationship for olivine has been determined under water poor and water rich conditions we found that when the water content in olivine exceeds 800 ppm h si the size of recrystallized grains is about two to three times larger than under water poor conditions compared at the same stress level microstructural observations of deformed samples show that the ratio of recrystallized grain size to that of subgrains increases significantly with water content and that the volume fraction of grains containing subgrain boundaries is smaller under water rich conditions than under water poor conditions these observations suggest that the enhancement of grain boundary mobility by water is more significant than that of dislocation recovery leading to a larger size of recrystallized grains under water rich conditions

human induced seismicity and large scale hydrocarbon production in the usa and canada we compare current and historic seismicity rates in six states in the usa and three provinces in canada to past and present hydrocarbon production all states provinces are major hydrocarbon producers our analyses span three to five decades depending on data availability total hydrocarbon production has significantly increased in the past few years in these regions increased production in most areas is due to large scale hydraulic fracturing and thus underground fluid injection furthermore increased hydrocarbon production generally leads to increased water production which must be treated recycled or disposed of underground increased fluid injection enhances the likelihood of fault reactivation which may affect current seismicity rates we find that increased seismicity in oklahoma likely due to salt water disposal has an 85 correlation with oil production yet the other areas do not display state province wide correlations between increased seismicity and production despite 8 16 fold increases in production in some states however in various cases seismicity has locally increased multiple factors play an important role in determining the likelihood of anthropogenic activities influencing earthquake rates including i the near surface tectonic background rate ii the existence of critically stressed and favorably oriented faults which must be hydraulically connected to injection wells iii the orientation and magnitudes of the in situ stress field combined with iv the injection volumes and implemented depletion strategies a comparison with the seismic hazard maps for the usa and canada shows that induced seismicity is less likely in areas with a lower hazard the opposite however is not necessarily true

shaking from injection induced earthquakes in the central and eastern united states abstract in this study i consider the ground motions generated by 11 moderate m w 4 0 5 6 earthquakes in the central and eastern united states that are thought or suspected to be induced by fluid injection using spatially rich intensity data from the u s geological survey did you feel it system i show the distance decay of intensities for all events is consistent with that observed for tectonic earthquakes in the region but for all of the events intensities are lower than the values predicted from an intensity prediction equation that successfully characterizes intensities for regional tectonic events i introduce an effective intensity magnitude m ie defined as the magnitude that on average would generate a given intensity distribution for all 11 events m ie is lower than the event magnitude by 0 4 1 3 magnitude units with an average difference of 0 82 units this suggests stress drops of injection induced earthquakes are systematically lower than tectonic earthquakes by an estimated factor of 2 10 however relatively limited data suggest intensities for epicentral distances less than 10 km are more commensurate with expectations for the event magnitude which can be reasonably explained by the shallow focal depth of the events the results suggest damage from injection induced earthquakes will be especially concentrated in the immediate epicentral region

the 17 may 2012 m4 8 earthquake near timpson east texas an event possibly triggered by fluid injection this study summarizes our investigation of the 17 may 2012 mw rmt4 8 earthquake near timpson texas the largest earthquake recorded historically in eastern texas to identify preshocks and aftershocks of the 17 may event we examined the arrivals recorded at nacogdoches natx 30 km from the 17 may epicenter at nearby usarray transportable array stations and at eight temporary stations deployed between 26 may 2012 and mid 2013 at natx we identified seven preshocks the earliest occurring in april 2008 reliably located aftershocks recorded by the temporary stations lie along a 6 km long nw se linear trend corresponding to a previously mapped basement fault that extends across the highest intensity mmi vii region of the 17 may main shock earthquakes in this sequence are relatively shallow with focal depths ranging from 1 6 to 4 6 km evidence supporting these depths include hypocentral locations of exceptionally well recorded aftershocks s p intervals at the nearest stations and comparisons of synthetics and observed seismograms within 3 km of the linear trend of aftershock activity there are two class ii injection disposal wells injecting at 1 9 km depth beginning in august 2006 and february 2007 with injection rates averaging 42 750 m3 mo and 15 600 m3 mo respectively several observations support the hypothesis that fluid injection triggered the timpson sequence well located epicenters are situated near a mapped basement fault and near high volume injection wells focal depths are at or below the depths of injection and the earliest preshock april 2008 occurred after the onset of injection in 2006

seismic properties of anita bay dunite an exploratory study of the influence of water as a pilot study of the role of water in the attenuation of seismic waves in the earth s upper mantle we have performed a series of seismic frequency torsional forced oscillation experiments on a natural anita bay dunite containing accessory hydrous phases at high temperatures to 13008c and confining pressure pc o f 200 mpa within a gas medium high pressure apparatus both oven dried and pre fired specimens wrapped in ni fe foil within the poorly vented assembly were recovered essentially dry after 50 100 h of annealing at 13008c followed by slow staged cooling the results for those specimens indicate broadly similar absorptionband viscoelastic behaviour but with systematic differences in the frequency dependence of strain energy dissipation q 1 attributed to differences in the small volume fraction of silicate melt and its spatial distribution in contrast it has been demonstrated that a new assembly involving a welded pt capsule retains aqueous fluid during prolonged exposure to high temperaturescallowing the first high temperature torsional forced oscillation measurements under high aqueous fluid pore pressure pf at temperatures 410008c a marked reduction in shear modulus without concomitant increase in q 1 is attributed to the widespread wetting of grain boundaries resulting from grain scale hydrofracturing and the maintenance of conditions

shear wave attenuation and dispersion in melt bearing olivine polycrystals 2 microstructural interpretation and seismological implications 1 the torsional forced oscillation tests of melt bearing olivine aggregates reported by jackson et al 2004 consistently show a peak in attenuation that is absent from melt free aggregates tested under similar conditions and grain sizes characterization by sem shows that the melt resides in triple junction tubules and larger pockets as previously described tem imaging and eds analysis reveals that olivine olivine grain boundaries are characterized by a region 1 nm wide which is structurally and chemically distinct from olivine grain interiors from the possible mechanisms that can produce an anelastic attenuation peak melt squirt can be eliminated for our samples and experimental conditions we attribute the observed attenuation peak to elastically accommodated grain boundary sliding requiring that the grain boundaries are weak relative to olivine grain interiors but have a significantly higher viscosity than bulk melt while the nanometer scale grain boundary structure in the melt bearing aggregates is essentially the same as for melt free aggregates studied previously elastically accommodated sliding in the latter is apparently inhibited by tight three grain edge intersections the exponentially increasing high temperature background attenuation in both types of aggregate is attributed to diffusionally accommodated grain boundary sliding extrapolation to mantle grain sizes shows that the broad peak may be responsible for nearly frequency independent attenuation in partially molten regions of the upper mantle

mechanics of monoclinal systems in the colorado plateau during the laramide orogeny monoclines developed in the colorado plateau region during the laramide orogeny are divided into western and eastern groups by a broad nnw trending antiform through the central part of the plateau in the western group the major monoclines verge to the east whereas in the eastern group the major monoclines verge to the west paleogeographic reconstruction based on paleocurrent indicators and sedimentary facies distribution suggests that the broad antiform was developed during the laramide orogeny and was coeval with the formation of the monoclines in the plateau this relationship implies that the monoclines were drag folds verging towards the center of the plateau as a response to the antiformal warping of the plateau to simulate the warping of the plateau region and the stress distribution that produced the variable trends of the monoclines an elastic thin plate model considering in plane stress was developed this model assumes that 1 sedimentation in the laramide basins provided vertical loading along the edge of the plateau region 2 frictional sliding was operating along the laramide faults on the northern and eastern boundaries and 3 the greatest regional compressive stress was oriented in the n60 e direction and was applied uniformly along the western and southwestern sides of the plateau buoyancy due to instantaneous isostatic adjustment of crustal thickening or magmatic addition was also considered the result of the model suggests that the frictional strength of the uinta thrust system on the northern side of the plateau is at least 2 times greater than that along the park range and sangre de cristo thrust systems on the eastern side of the plateau in order to explain the observed monoclinal trends and the warping pattern within the plateau during the laramide orogeny

laramide orogeny related controls on coal mine ground instability in cretaceous coal seams southern rocky mountain foreland abstract investigation of ground conditions in nine coal mines located in the structurally complex southern rocky mountain foreland tectonic province suggest that structural compression associated with the late cretaceous eocene laramide orogeny caused deformation of cretaceous aged coal seams structures include low angle bedding plane faults and drag folds that are indicative of bedding plane faulting other structures include high angle joints and faults the pattern of structural geologic features documented during mine mapping is similar to the local trends of regionally extensive thrust faults fold axes and basement cored uplifts that formed during the laramide orogeny this suggests that the observed structural geologic features in mines developed in cretaceous coal seams reflect regional deformation that occurred in response to the laramide orogeny the geologic structures documented in colorado new mexico and utah coal mines were commonly associated with major instances of ground failure the recognition of regional tectonic controls on relatively localized geologic structures has important implications for the prediction of degraded ground conditions in advance of mining because the structural discontinuities observed in coal mine immediate roof strata formed in response to regional stress conditions during orogenic activity they can often be simply characterized as linear zones that are relatively continuous along strike at the mine scale once recognized the structural zones can be projected in advance of mining so that section crews can be forewarned of potentially adverse ground conditions and be prepared to install appropriate supplemental support and local modifications to pillar design can be implemented to enhance long term stability thus geologic hazard mapping that incorporates structural geologic features as part of an integrated geologic characterization should be an appropriate method for ground control planning

the 9 april 1993 earthquake in south central texas was it induced by fluid withdrawal an earthquake that occurred 9 april 1993 about 80 km south of san antonio is the largest earthquake known mblg 4 3 in south central texas in historic times the earthquake was felt over a 4000 km2 area and modified mercalli intensities were as high as vi at a gas production facility near fashing texas similar smaller events have occurred since 1973 at three sites near fashing pleasanton and falls city texas we propose a list of nine yes no questions to assess whether a sequence of earthquakes may have been induced by fluid withdrawal the criteria suggest that at least two sites fashing and pleasanton had earthquakes that were induced by fluid withdrawal related to ongoing oil and gas production an alternative possibility is that these events are the southwesternmost examples in a band of weak natural seismic activity between 135 and 240 km from the coast of the gulf of mexico and extending from this region east to the texas louisiana border in addition some injection occurs at all three sites although the volumes of fluid injected at fashing and pleasanton are low enough as to make injection an unlikely cause

high temperature creep of olivine single crystals 2 dislocation structures dislocation structures and densities in experimentally deformed single crystals of san carlos olivine were examined using the oxidation decoration technique the high temperature deformation experiments were conducted at various temperatures t differential stresses and oxygen fugacities o2 the samples were buffered against either orthopyroxene opx or magnesiowustite mw solid state powders and compressed along one of the three 45 orientations in samples that were deformed and subsequently quenched under load seven distinct dislocation structures were observed a for samples compressed parallel to 110 c at 16 50 mpa and o2 10 6atm two different dislocation arrangements were identified for opx buffered samples at 1400 t 1475 c the dislocation structure was composed of curved screw segments that had usually cross slipped and straight edge segments of comparable length at 1300 t 1350 c for opx buffered samples and at 1350 t 1500 c for mw buffered samples the dislocation structure is dominated by arrays of very long edge or mixed dislocations with only a few screw dislocations b for both opx buffered and mw buffered samples compressed parallel to 101 c at 1340 t 1400 c and 30 60 mpa the dislocation configurations are characterized by zigzag near edge dislocations at o2 10 5atm and by straight cross slipped screw dislocations plus pinned edge dislocations at o2 10 9atm c for samples compressed parallel to 011 c at t 1400 c and 70 150mpa the primary dislocations change from long straight edge dislocations for o2 10 4atm and opx buffer to a combination of straight edge dislocations and polygon shaped half loops for o2 10 4atm and mw buffer to gently curved near edge dislocations for o2 10 9atm for both solid state buffers abundant long straight screw dislocations were present in each case for the 011 c samples all of the above variations in dislocation structure are paralleled by changes in the measured power law equation that describes the behavior of creep mechanisms of olivine thus the different dislocation structures are associated with different rate controlling creep mechanisms for all of the dislocation structures the dislocation density increases with differential stress according to the relation 1 4 dislocation structures in samples that were deformed and then statically annealed have also been studied for both 110 c and 011 c samples deformed over a wide range of experimental conditions the dislocation structures on the slip planes generally consist of short curved edge or mixed dislocation segments in 101 1 samples deformed at low o2 50 mpa and 1400 c the dislocation structure was much less altered by annealing than the dislocation structures in 110 c and 011 c samples the density of dislocations decreased much less for these 101 c samples than for the 110 c and 011 c samples due to climb of the edge segments the straight screw segments found in quenched samples became curved and many low angle 100 tilt boundaries connected by straight 100 screw dislocations developed during the annealing process

dynamics of slab detachment 1 we investigate the dynamics of slab detachment around the detachment zone and evaluate the amount of time necessary for slabs to detach the study combines results of two dimensional 2d state of the art thermomechanical numerical simulations and a 1d analytical solution for viscous necking under gravity we show that the dominant deformation mechanism during slab detachment is viscous necking independent of the depth of slab detachment when the slab dip is moderate 35 70 slab detachment is partly affected by localized simple shearing in the colder parts of the slab brittle fracturing breaking plays a minor role during slab detachment our 2d thermomechanical models indicate that the duration of slab detachment quantified from the onset of slab thinning until the actual detachment i e vanishing of slab pull force is relatively short 250 km can occur within a short time interval 1 ma which has implications for geodynamic interpretations using slab detachment as explanation for processes such as melting exhumation or surface uplift the thinning of the slab during detachment observed in 2d simulations agrees well with predictions from a 1d analytical solution indicating that the 1d solution captures the first order features of the detachment process we also evaluate the impact of shear heating on the duration of slab detachment the predictions of a simple semi analytical solution based on dimensionless parameters agree well with our and previously published results

oklahoma experiences largest earthquake during ongoing regional wastewater injection hazard mitigation efforts the 3 september 2016 mw 5 8 pawnee earthquake was the largest recorded earthquake in the state of oklahoma seismic and geodetic observations of the pawnee sequence including precise hypocenter locations and moment tensor modeling shows that the pawnee earthquake occurred on a previously unknown left lateral strike slip basement fault that intersects the mapped right lateral labette fault zone the pawnee earthquake is part of an unprecedented increase in the earthquake rate in oklahoma that is largely considered the result of the deep injection of waste fluids from oil and gas production if this is indeed the case for the m5 8 pawnee earthquake then this would be the largest event to have been induced by fluid injection since 2015 oklahoma has undergone wide scale mitigation efforts primarily aimed at reducing injection volumes thus far in 2016 the rate of m3 and greater earthquakes has decreased as compared to 2015 while the cumulative moment or energy released from earthquakes has increased this highlights the difficulty in earthquake hazard mitigation efforts given the poorly understood long term diffusive effects of wastewater injection and their connection to seismicity

a decade of induced slip on the causative fault of the 2015 mw 4 0 venus earthquake northeast johnson county texas on 7 may 2015 a mw 4 0 earthquake occurred near venus northeast johnson county texas in an area of the bend arch fort worth basin that reports long term high volume wastewater disposal and that has hosted felt earthquakes since 2009 in the weeks following the mw 4 0 earthquake we deployed a local seismic network and purchased nearby active source seismic reflection data to capture additional events characterize the causative fault and explore potential links between ongoing industry activity and seismicity hypocenter relocations of the resulting local earthquake catalog span 4 6 km depth and indicate a fault striking 230 dipping to the west consistent with a nodal plane of the mw 4 0 regional moment tensor fault plane solutions indicate normal faulting with b axes striking parallel to maximum horizontal compressive stress seismic reflection data image the reactivated basement fault penetrating the ordovician disposal layer and mississippian production layer but not displacing post lower pennsylvanian units template matching at regional seismic stations indicates that low magnitude earthquakes with similar waveforms began in april 2008 with increasing magnitude over time pressure data from five saltwater disposal wells within 5 km of the active fault indicate a disposal formation that is 0 9 4 8 mpa above hydrostatic we suggest that the injection of 28 000 000 m3 of wastewater between 2006 and 2015 at these wells led to an increase in subsurface pore fluid pressure that contributed to inducing this long lived earthquake sequence the 2015 mw 4 0 event represents the largest event in the continuing evolution of slip on the causative fault

sensitivity of induced seismic sequences to rate and state frictional processes it is well established that subsurface injection of fluids increases pore fluid pressures that may lead to shear failure along a pre existing fault surface concern amongst oil and gas geothermal and carbon storage operators has risen dramatically over the past decade due to the increase in the number and magnitude of induced earthquakes efforts to mitigate the risk associated with injection induced earthquakes include modeling of the interaction between fluids and earthquake faults here we investigate this relationship with simulations that couple a geomechanical reservoir model and rsqsim a physics based earthquake simulator rsqsim employs rate and state dependent friction rsf which enables the investigation of the time dependent nature of earthquake sequences we explore the effect of two rsf parameters and normal stress on the spatiotemporal characteristics of injection induced seismicity we perform 200 simulations to systematically investigate the effect of these model components on the evolution of induced seismic sequences and compare spatiotemporal characteristics of our synthetic catalogs to observations of induced earthquakes we find that the rsf parameters control the ability of seismicity to migrate away from the injection well the total number and maximum magnitude of induced events additionally the rsf parameters control the occurrence absence of premonitory events lastly we find that earthquake stress drops can be modulated by the normal stress and or the rsf parameters insight gained from this study can aid in further development of models that address best practice protocols for injection operations site specific models of injection induced earthquakes and probabilistic hazard and risk assessments of induced earthquakes

the role of water in the deformation of dunite specimens of two natural dunites anita bay of 100 m grain size and aheirn of 900 m grain size have been deformed in experiments at temperatures between 1200 and 1400 c and constant strain rates between 10 4 and 10 6 s 1 in a gas medium deformation apparatus at 300 mpa confining pressure prior to these experiments the specimens were given a heat treatment in a controlled oxygen fugacity furnace at 1200 c for 60 hours to dehydrate the trace layer silicate minerals present and drive off adsorbed water the predried specimens are much stronger than specimens tested under wet conditions in an earlier study the predried specimens also do not show the apparent grain size dependence seen under wet conditions infrared absorption measurements on the present specimens and those of the earlier study indicate that for a given rock flow stress can be correlated with the intensity of a residual water related broad absorption the addition of water to a predried specimen results in both a mechanical reweakening and an intensifying of the broadband infrared component the weakening of the dunites under wet conditions is probably strongly influenced by the presence of small amounts of a water related species in the grain boundaries but intragranular weakening may also be contributing it is suggested that the concentration of the water related species in the grain boundaries is governed by its concentration in the small melt fraction present the amounts of water that have been found to be of importance for the strength of these dunites are of the order of 0 01 wt amounts much less than most estimates of the water content of the earth s undepleted upper mantle such water may have an important role in determining upper mantle flow behavior stress strain curves for all experiments are available with entire manuscript on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b84 008 2 50 payment must accompany order

a preliminary statistical model for hydraulic fracture induced seismicity in the western canada sedimentary basin we characterize the statistical relationship between hydraulic fracturing and seismicity in western canada by using the concept of cellular seismicity we determine the regionally averaged probability that hydraulic fracture operations will be associated with m 3 seismicity within a 10 km grid cell this rate is 0 01 to 0 026 at the 95th percentile confidence limit monte carlo simulations confirm that the observed correlations are extremely unlikely 1 to have been obtained by chance proximity to a disposal well and proximity to the swan hills formation which has been suggested as a proxy for basement controlled faults appear to increase the likelihood that hydraulic fracturing will trigger seismicity

evolution of a polymineralic mantle shear zone and the role of second phases in the localization of deformation 1 the influence of second phases e g pyroxenes on olivine grain size was studied by quantitative microfabric analyses of samples of the hilti massif mantle shear zone semail ophiolite oman the microstructures range from porphyroclastic tectonites to ultramylonites from outside to the center of the shear zone starting at conditions of ridge related flow they formed under continuous cooling leading to progressive strain localization the dependence of the average olivine grain size on the second phase content can be split into a second phase controlled and a dynamic recrystallization controlled field in the former the olivine grain size is related to the ratio between the second phase grain size and volume fraction zener parameter in the latter dynamic recrystallization manifested by a balance between grain growth and grain size reduction processes yields a stable olivine grain size in both fields the average olivine and second phase grain size decreases with decreasing temperature combining the microstructural information with deformation mechanism maps suggests that the porphyroclastic tectonites 1100 c and mylonites 800 c formed under the predominance of dislocation creep since olivine rich layers are intercalated with layer parallel polymineralic bands in the mylonites nearly equiviscous conditions can be assumed in the ultramylonites diffusion creep represents the major deformation mechanism in the polymineralic layers it is this switch in deformation mechanism from dislocation creep to diffusion creep that forces strain to localize in the fine grained polymineralic domains at low temperatures 700 c underlining the role of the second phases on strain localization in cooling mantle rocks

rheological and microstructural evolution of carrara marble with high shear strain results from high temperature torsion experiments abstract this study investigated the rheological and microstructural evolution of carrara marble deformed to large shear strain to understand how dynamic recrystallization and lattice preferred orientation lpo are related to strain softening processes solid cylinders of carrara marble were deformed in torsion up to a shear strain of 11 at constant twist rates which correspond to a shear strain rate of 3 10 4 s 1 at the outer surface and at temperatures of 1000 and 1200 k 727 and 927 c respectively for the initial grain size of 150 m these conditions are within the dislocation creep regime substantial changes in both rheology and microstructure were observed as the marble deformed to high shear strain at 1000 k 1200 k a peak stress was reached at about 1 0 5 followed by moderate strain weakening an apparent steady state flow stress was obtained at high shear strain of 5 2 the stress exponent n decreased slowly with strain from 10 1 to 6 9 at 1000 k but it remained approximately constant at 1200 k n around 10 at the maximum reached shear strain of 11 8 5 the marble had almost completely recrystallized to a fine grain size of about 10 m 20 m a secondary foliation developed in the recrystallized matrix which is at a large oblique angle to the shear zone boundary szb lpo was measured by electron backscatter diffraction ebsd for both temperatures the lpo evolved from an oblique deformation texture to a very sharp and symmetric single orientation component with r 1014 parallel to the shear plane and a 1210 parallel to the shear direction it is concluded that strain weakening was associated with the development of a strong lpo during dynamic recrystallization to a finer grain size mechanical and microstructural steady state is only reached at large shear strain the steady state lattice and grain shape fabrics can hardly be used as shear sense indicators in such recrystallized calcite mylonites