non parametric seismic hazard in mines seismic hazard analysis methods in mines are reviewed for the purpose of selecting the best technique to achieve this goal the most often used hazard analysis procedure which is based on the classical frequency magnitude gutenberg richter relation as well as alternative procedures are investigated since the maximum regional seismic event magnitude m max is of paramount importance in seismic hazard analysis this work provides a generic formula for the evaluation of this important parameter the formula is capable of generating solutions in different forms depending on the assumptions of the model of the magnitude distribution and or the available information regarding past seismicity it includes the cases i in which seismic event magnitudes are distributed according to the truncated frequency magnitude gutenberg richter relation and ii in which no specific model of the magnitude distribution is assumed both synthetic monte carlo simulated seismic event catalogues and actual data from the copper mine in poland and gold mine in south africa are used to demonstrate the discussed hazard analysis techniques our studies show that the non parametric technique which is independent of the assumed model of the distribution of magnitude provides an appropriate tool for seismic hazard assessment in mines where the magnitude distribution can be very complex

nontrivial clustering of microseismicity induced by hydraulic fracturing for induced microseismicity associated with hydraulic fracturing the frequency magnitude distribution is typically characterized by a falloff with increasing magnitude that is significantly faster than for seismicity along active fault systems this characteristic may arise from a break in scale invariance possibly due to mechanical layering that typifies fine grained sedimentary rocks in many shale gas and tight oil reservoirs the latter would imply the presence of spatio temporal magnitude correlations using three microseismic catalogs for well stimulations in widely separated locations with varying hydraulic fracturing methods we show that events with similar magnitudes indeed tend to cluster in space and time in addition we show that the inter event time distribution can be described by a universal functional form characterized by two power laws one exponent can be related to the presence of inter event triggering as in aftershock sequences and is a consequence of the omori utsu law the other one is a reflection of the intrinsic spatial variation in the microseismic response rates taken together these features are indicative of non trivial spatio temporal clustering of induced microseismicity and hence of direct relevance for time dependent seismic hazard assessment

effects of long term fluid injection on induced seismicity parameters and maximum magnitude in northwestern part of the geysers geothermal field the long term temporal and spatial changes in statistical source and stress characteristics of one cluster of induced seismicity recorded at the geysers geothermal field u s are analyzed in relation to the field operations fluid migration and constraints on the maximum likely magnitude two injection wells prati 9 and prati 29 located in the northwestern part of the field and their associated seismicity composed of 1776 events recorded throughout a 7 year period were analyzed the seismicity catalog was relocated and the source characteristics including focal mechanisms and static source parameters were refined using first motion polarity spectral fitting and mesh spectral ratio analysis techniques the source characteristics together with statistical parameters b value and cluster dynamics were used to investigate and understand the details of fluid migration scheme in the vicinity of injection wells the observed temporal spatial and source characteristics were clearly attributed to fluid injection and fluid migration toward greater depths involving increasing pore pressure in the reservoir the seasonal changes of injection rates were found to directly impact the shape and spatial extent of the seismic cloud a tendency of larger seismic events to occur closer to injection wells and a correlation between the spatial extent of the seismic cloud and source sizes of the largest events was observed suggesting geometrical constraints on the maximum likely magnitude and its correlation to the average injection rate and volume of fluids present in the reservoir

mineralization controls in island arc settings insights from philippine metallic deposits abstract a review of the gold copper volcanogenic massive sulfide and ultramafic hosted i e chromitite nickel sulfide platinum group minerals deposits in the philippines is presented it is critical that a thorough understanding of the spatial and temporal relationship among magmatism structures and mineralization must be gained if the correct evaluation of the economic potential of a particular deposit is to be done structural features conducive to precious and base metal mineralizations are associated with shear zones extensional jogs and collision zones in northern luzon alkali and adakitic magmatism are considered good markers for gold copper mineralization volcanogenic massive sulfide deposits are hosted by either ophiolites of marginal basin origin or metamorphic terranes exploration works on these deposits have been geared in determining the gold content of the massive sulfides chromitite deposits are related with ultramafic rock hosted deposits their occurrence is attributed to crystallization magma mixing and mantle melt interaction processes in subduction related settings the multiple stages of partial melting responsible for the formation of supra subduction zone ophiolites result in the generation of second to third stage melts that are enriched in nickel sulfides and platinum group minerals on the basis of structural geochemical and tectonic controls panay mindoro and central mindanao and the sierra madre leyte and samar are good exploration targets for precious and base metal deposition in the western and eastern sides of the philippines respectively

carbon and oxygen isotope halo in carbonates related to the mcarthur river hyc zn pb ag deposit north australia implications for sedimentation ore genesis and mineral exploration a study of carbon and oxygen isotope ratios in fine grained sedimentary dolomite in the barney creek formation of the mcarthur basin demonstrates the presence of an extensive isotope halo surrounding the giant stratiform hyc zn pb ag deposit dolomite within the halo shows an 18o enriched and 13c depleted isotope signature 18o 23 to 26 smow 13c 2 to 3 5 pdb relative to normal proterozoic sedimentary dolomite beyond the halo 18o 20 23 and 13c 0 to 2 the c o isotope halo within the dolomitic siltstones extends at least 15 km southwest of the hyc deposit and approximately coincides with a previously defined lithogeochemical halo of elevated fe mn zn pb and tl dolomitic siltstone lamellae within the stratiform zn pb ag ores at hyc exhibit an isotopic range similar to that of the halo dolomites suggesting that the ore and halo equilibrated with the same hydrothermal fluid modeling of isotopic exchange accompanying fluid rock interaction suggests that the halo dolomites equilibrated with low temperature fluids 50 120 c which were enriched in 18o 18o 5 5 but with an average crustal carbon isotope signature 13c 6 1 our preferred interpretation is that the oxygen and carbon isotope halo at hyc is related to the development of an extensive brine pool this pool was deepest in the vicinity of the hyc deposit adjacent to the emu fault and it became shallower to the southwest away from the fault using the carbon isotope fractionation equation between dolomite and hc batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document o 3 mbox end document it is possible to estimate the temperature variation at the base of the brine pool during the accumulation of the barney creek formation brine pool temperatures were highest in and adjacent to the hyc deposit 40 70 c and decreased to values of 17 to 30 c remote from the deposit these temperatures are similar to those recorded in the red sea brine pool associated with the atlantis ii metalliferous sediment deposit based on our work at hyc and lady loretta strata bound 18o enriched carbonate lithogeochemical halos may be a characteristic of the proterozoic stratiform zn pb ag deposits of northern australia these halos are more extensive than the narrow 18o depletion halos recorded in dolomites surrounding skarn mississippi valley type and irish style zn pb deposits this fundamental difference in the isotopic halo characteristics of these groups of zinc deposits is probably related to the low temperature synsedimentary brine pool origin of the north australian sedex deposits in contrast to the various replacement and open space fill origins of skarn mississippi valley type and irish style deposits

a permeability model for naturally fractured carbonate reservoirs abstract based on a detailed structural study performed on a reservoir surface analogue a fracture permeability model for carbonate reservoirs is proposed this involves four hierarchical systems each one assumed to convey fluids exclusively to that of immediately higher order new basic equations are then provided simulating hydrodynamic reservoir response the large scale first order structures consist of faults to which high permeability structures damage zones are associated at the meter scale stratabound joint systems together with bedding joints bounding the mechanical layers form a connected network transporting fluids to the fault system at a lower scale down to crystal size non stratabound joints constitute a pervasive and capillary fracture network which conveys fluids within the rock mass the non fractured host rock constitutes the lower permeability system at the crystal scale as no published works include an effective integration of detailed structural and numerical models the present study aims at covering a significant gap in the literature also providing appropriate theoretical basis for subsequent studies on fracture network modeling and reservoir simulation besides its application in the field of reservoir development and management the illustrated model may also be useful in environmental studies involving ground fluids such as e g in the field of special toxic nuclear waste management

reconstructing frequency magnitude statistics from detection limited microseismic data microseismic monitoring particularly the monitoring of hydraulic fracturing in gas and oil bearing shales has developed significantly over the last ten years early work focused on the location of microseismic events but more recently there have been attempts to extract more of the information afforded by this rich data source in particular the recovery of the frequency magnitude distribution which is expected to follow a gutenberg richter distribution may provide insights into the prevailing effective stress regime in the vicinity of the events this stress regime varies with distance from the hydraulic fracturing at the propagating fracture one expects conditions for tensile or shear failure away from the fracture one may broadly expect microseismicity associated with pre existing weakness in the rock occurring at effective stress conditions close to the conditions existing prior to the treatment all geophysical experiments are detection limited and the microseismic monitoring case does not differ in this regard in constructing a statistical indicator such as the distribution of moment magnitudes we would like the estimate to be robust and use as much of the data as possible in analysing earthquake catalogues the predominant practise is to determine a magnitude of completeness denoting the detection limit of the catalogue this approach defines a minimum magnitude above which all events are thought to have been reliably recorded in effect this imposes an artificial conservative detection limit to replace the unknown detection limit of the catalogue we present the case of an arbitrary detection limit and introduce an approach from astronomy that is particularly suited to the single well observing geometry most prevalent in hydraulic fracture monitoring we calculate b values for a set of event magnitudes from the barnett shale formation where multiple stimulation treatments were applied in a pair of wells zipper frac followed by a four stage treatment in a third well and find significant variations in the b value between the pumped stages

how fracture systems affect permeability development in shallow water carbonate rocks an example from the gargano peninsula italy abstract fracture networks control the permeability of many reservoirs since the fracture patterns of petroleum reservoirs in situ are difficult to study in detail field analogues are very important for understanding their fracture related permeability here we present the results of a study of the fracture system of carbonate rocks of lower cretaceous age in a quarry associated with the damage zone and fault core of a major fault zone on the gargano peninsula in south italy we measured the attitude of 1541 fractures and faults along several vertical and horizontal scan lines there are two main fracture sets one strikes between e w and ese wnw the other nne ssw a total of 675 fracture spacing measurements indicate log normal spacing distributions with an arithmetic mean fracture spacing of 0 29 m and a median of 0 15 m the data plotted on a log log plot suggest three main spacing subpopulations each of which follows approximately a power law with different fractal dimensions subpopulation 1 where the spacing ranges from 1 to 10 cm and the straight line slope d fractal dimension is 0 20 represents fractures confined to laminated carbonate mudstones multilayers that form the microbial mat deposits of a peritidal cycle subpopulation 2 where the spacing ranges from 11 to 55 cm and d is 0 77 represents fractures confined to thicker layers forming a part of a peritidal cycle the contacts of which are marked by stylolites subpopulation 3 where the spacing ranges from 56 to 243 cm and d is 2 81 represents fractures that dissect comparatively thick units of an entire peritidal cycle for the spacing the minimum coefficient of variation c v defined as standard deviation divided by the mean is 1 00 essentially randomly spaced fractures while its maximum c v is 1 62 suggesting that some fractures form clusters some clusters being denser than others the clusters composed of fractures with varying attitudes and therefore commonly intersecting are likely to contribute significantly to the overall permeability of the carbonate rock fracture aperture opening data n 324 also show a log normal size distribution with a mean opening of 1 01 cm and median of 0 29 cm log log plots indicate that a part of this data groups into two subpopulations i and ii each of which follows approximately a power law the straight line slope d the fractal dimension of subpopulation i is 0 46 whereas that of subpopulation ii is 1 49 we present boundary element models showing that laminated carbonate mudstones and their contacts modify the local stress fields so as to encourage fracture offset and commonly arrest our results also show that when a fluid driven subpopulation 2 fracture approaches subpopulation 1 fractures the induced tensile stresses may result in the opening up of many of the subpopulation 1 fractures directly above the tip of the subpopulation 2 fractures if in addition the contacts between the multilayers are weak they also tend to open up thus generating a large interconnected cluster of vertical fractures and horizontal contacts the results suggest that the tensile stresses induced by a comparatively large fluid driven subpopulation 2 fracture may contribute to the formation of an interconnected cluster of subpopulation 1 fractures and associated contacts thereby significantly increasing the permeability of the carbonate rock

faulting induced by forced fluid injection and fluid flow forced by faulting an interpretation of hydraulic fracture microseismicity carthage cotton valley gas field texas we analyzed precisely located microearthquake data detected during five hydraulic fracture treatments in the carthage gas field of east texas the treat ments were conducted in two adjacent boreholes within interbedded sands and shales of the upper cotton valley formation the microearthquakes were induced within narrow horizontal bands that correspond to the targeted sandstone layers events throughout all the treatments show strike slip faulting occurring uniformly along vertical fractures trending close to maximum horizontal stress direction these events are consistent with the reservoir s prevalent natural fractures known to be isolated within the sands and trending subparallel to the expected hydraulic fracture orien tation when this uniform fracture system was activated exclusively the detected shear deformation measured as the moment release per unit volume of fluid injected was constant independent of various fluid viscosities and flow rates used within the base of the upper cotton valley formation anomalous event counts and moment release occurred within dense clusters that delineate bends or jogs in the fracture zones the mechanisms are also strike slip but the fault planes are more favorably oriented for failure the dense clusters show location patterns diverging in time suggesting the expulsion of fluids from compressive fault jogs fluid flow forced by the adjacent slip induced loading appears to initially extend the treatments but the loading also tends to lock up and concentrate stress at the jogs as evident by fewer but larger events populating the structures as treatments progress as a result effec tive drainage lengths from the boreholes may be shorter than would be inferred from the seismicity extending past the jogs these high moment asperities are similar to dense patches of seismicity observed along creeping sections of the san andreas fault where they have been attributed to localized zones of strength or stress con centration surrounded by larger regions undergoing stable aseismic slip this sim ilarity plus large moment deficits in terms of volume injected suggests a large component of aseismic slip is induced by the cotton valley treatments

maturity of nearby faults influences seismic hazard from hydraulic fracturing understanding the causes of human induced earthquakes is paramount to reducing societal risk we investigated five cases of seismicity associated with hydraulic fracturing hf in ohio since 2013 that because of their isolation from other injection activities provide an ideal setting for studying the relations between high pressure injection and earthquakes our analysis revealed two distinct groups i deeper earthquakes in the precambrian basement with larger magnitudes m 2 b values 1 5 and few post shut in earthquakes based on geologic history laboratory experiments and fault modeling we interpret the deep seismicity as slip on more mature faults in older crystalline rocks and the shallow seismicity as slip on immature faults in younger sedimentary rocks this suggests that hf inducing deeper seismicity may pose higher seismic hazards wells inducing deeper seismicity produced more water than wells with shallow seismicity indicating more extensive hydrologic connections outside the target formation consistent with pore pressure diffusion influencing seismicity however for both groups the 2 to 3 h between onset of hf and seismicity is too short for typical fluid pressure diffusion rates across distances of 1 km and argues for poroelastic stress transfer also having a primary influence on seismicity

from crucible to graben in 2 3 ma a high resolution geochronological study of porphyry life cycles boyongan bayugo copper gold deposits philippines the boyongan and bayugo porphyry copper gold deposits are part of a belt of gold rich copper deposits in the surigao district of northeast mindanao philippines the detailed age relationships described in this study provide insight into the geologically short life cycles that characterize porphyry formation in dynamic arc environments since their late pliocene emplacement 2 3 2 1 ma shrimp sensitive highresolution ion microprobe u pb zircon dating at depths of 1 2 2 0 km these deposits were exhumed deeply weathered and buried weathering of these deposits led to the development of the world s deepest known porphyry oxidation profile 600 m thick at boyongan and a modest 30 70 m oxidation profile at adjacent bayugo this earlymiddle pleistocene supergene event followed a period of rapid uplift and exhumation in northeast mindanao 2 5 km ma u th he apatite age elevation spectrum subsequent rapid subsidence 0 34 km ma radiocarbon age elevation spectrum and burial of these deposits are attributed to a mid pleistocene shift from transpressional tectonics to the present day transtensional setting in northeast mindanao during this period debris flows volcanic material and fluviolacustrine sediments accumulating in the actively extending mainit graben covered the weathered deposits preserving the supergene profiles beneath 50 500 m of cover this detailed geochronological study documents the geologically short 2 3 ma time scales over which these major intrusion centered mineral deposits evolved from emplacement exhumation deep oxidation and burial highlighting the dynamism of tectonic processes in environments such as the philippine mobile belt 2012 geological society of america

variations in earthquake size distribution across different stress regimes the earthquake size distribution follows in most instances a power law1 2 with the slope of this power law the b value commonly used to describe the relative occurrence of large and small events a high b value indicates a larger proportion of small earthquakes and vice versa statistically significant variations of b values have been measured in laboratory experiments mines and various tectonic regimes such as subducting slabs near magma chambers along fault zones and in aftershock zones3 however it has remained uncertain whether these differences are due to differing stress regimes as it was questionable that samples in small volumes such as in laboratory specimens mines and the shallow earth s crust are representative of earthquakes in general given the lack of physical understanding of these differences the observation that b values approach the constant 1 if large volumes are sampled4 was interpreted to indicate that b 1 is a universal constant for earthquakes in general5 here we show that the b value varies systematically for different styles of faulting we find that normal faulting events have the highest b values thrust events the lowest and strike slip events intermediate values given that thrust faults tend to be under higher stress than normal faults we infer that the b value acts as a stress meter that depends inversely on differential stress

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

numerical modeling of seismicity induced by fluid injection in naturally fractured reservoirs the interaction between hydraulic and natural fractures is of great interest for the energy resource industry because natural fractures can significantly influence the overall geometry and effectiveness of hydraulic fractures microseismic monitoring provides a unique tool to monitor the evolution of fracturing around the treated rock reservoir and seismic source mechanisms can yield information about the nature of deformation we performed a numerical modeling study using a 2d distinct element particle flow code pfc2d to simulate realistic conditions and increase understanding of fracturing mechanisms in naturally fractured reservoirs through comparisons with results of the geometry of hydraulic fractures and seismic source information locations magnitudes and mechanisms from both laboratory experiments and field observations a suite of numerical models with fully dynamic and hydromechanical coupling was used to examine the interaction between natural and induced fractures the effect of orienta

a 2d model of hydraulic fracturing damage and microseismicity we present a model for hydraulic fracturing and damage of low permeable rock it computes the intermittent propagation of rock damage microseismic event locations microseismic frequency magnitude distributions stimulated rock volume and the injection pressure the model uses a regular 2d grid and is based on ideas from invasion percolation all damaged and connected cells during a time step constitute a microseismic event where the size of the event is the number of cells in the cluster the magnitude of the event is the log 10 of the event size the model produces events with a magnitude frequency distribution having a b value that is approximately 0 8 the model is studied with respect to the physical parameters permeability of damaged rock and the rock strength high permeabilities of the damaged rock give the same b value approx 0 8 but moderate permeabilities give higher b values another difference is that high permeabilities produce a percolation like fracture network while moderate permeabilities result in damage zones that expand circularly away from the injection point in the latter case of moderate permeabilities the injection pressure increases substantially beyond the fracturing level the rock strength and the time step do not change the observed b value of the model for moderate changes

mesozoic porphyry cu au mineralization and associated adakite like magmatism in the philippines insights from the giant atlas deposit the atlas porphyry cu au deposit is located in central cebu island in the philippines with a proven mineral reserve of 1420 mt at 0 45 cu 0 24 g t au 0 018 g t mo and 1 8 g t ag it is associated with the lutopan quartz diorite porphyry stock that was emplaced into the cretaceous volcano sedimentary sequences of the cansi formation two stages of hypogene alteration have been identified at atlas stage i quartz magnetite chalcopyrite pyrite veins associated with potassic and propylitic alteration and stage ii anhydrite pyrite chalcopyrite specularite veins associated with phyllic alteration supergene gypsum veins are also present mineralization is mainly associated with the stage i and stage ii veins the lutopan quartz diorite porphyry yielded a zircon u pb age of 108 5 1 6 ma and is characterized by high sr y 54 69 with the corresponding magma having high oxygen fugacity avg fmq 2 7 avg ce4 ce3 of zircon 439 and h2o concentrations presence of amphibole and biotite phenocrysts and low magmatic temperatures avg ti in zircon thermometry 706 c the relatively low la yb ratios 9 11 listric shaped normalized ree patterns with weak or absent eu anomalies together with zircon ehf t values of 3 4 to 10 0 whole rock isr values of 0 70373 0 70382 end t values of 2 4 3 4 and mg numbers of 49 53 suggest that the lutopan quartz diorite porphyry was likely derived from partial melting of young lower continental crust or interaction between asthenospheric melts and lower crust melts that evolved to adakite like trace element compositions through amphibole fractionation stage i veins yielded a pyrite re os isochron age of 110 2 5 6 ma making atlas the only mesozoic porphyry deposit discovered in the philippines

combined microseismic and 4d to calibrate and confirm surface 3d azimuthal avo lmr predictions of completions performance and well production in the horn river gas shales of nebc the ability to high grade gas shales is essential to optimizing completions and maximizing stimulated rock volume srv in the capital intensive development of the horn river resource play in northeast british columbia nebc to assist in optimizing stimulation efforts seismic data are used to estimate and map four parameters that influence hydraulic fracture effectiveness rock properties in situ stress natural fractures and reservoir geometry

characterization of induced seismicity patterns derived from internal structure in event clusters seismicity induced by co2 injection at decatur illinois occurs in distinct clusters and shows no obvious correlation with the proceeding pressure front we analyse some of these clusters in more depth by using a waveform cross correlation approach with this approach we can associate about 1400 events from two clusters with moment magnitudes between 1 1 and 1 7 with specific formations of much smaller vertical dimensions 10th of meters than the depth resolution of traveltime based event locations the differentiation of reservoir and basement events and the definition of sub clusters by waveform correlation rather than by location helps to better analyse the spatio temporal evolution of the events within a cluster in the decatur case this is characterized by event migration from the reservoir into the adjacent basement the spatial variation of brune stress drop and gutenberg b value exhibit signs of a fluid driven triggering mechanism at the cluster level revealing a punctual hydraulic connection between reservoir and basement most likely associated with basement faults cutting into the reservoir the observed clustering of seismicity can thus be explained by the lateral heterogeneity of permeability and crustal strength and is overall consistent with a pressure induced triggering mechanism hence proper long term risk mitigation for large scale fluid injection close to the basement requires prior mapping of small sub seismic basement connected faults

violations of gutenberg richter relation in anthropogenic seismicity anthropogenic seismicity as is the undesired dynamic rockmass response to technological processes as environments are shallow hence their heterogeneities have important impact on as moreover as is controlled by complex and changeable technological factors this complicated origin of as explains why models used in tectonic seismicity may be not suitable for as we study here four cases of as testing statistically whether the magnitudes follow the gutenberg richter relation or not the considered cases include the data from mponeng gold mine in south africa the data observed during stimulation of geothermal well basel 1 in switzerland the data from acu water reservoir region in brazil and the data from song tranh 2 hydropower plant region in vietnam the cases differ in inducing technologies in the duration of periods in which they were recorded and in the ranges of magnitudes in all four cases the observed frequency magnitude distributions statistically significantly differ from the gutenberg richter relation although in all cases the gutenberg richter b value changed in time this factor turns out to be not responsible for the discovered deviations from the gutenberg richter born exponential distribution model though the deviations from gutenberg richter law are not big they substantially diminish the accuracy of assessment of seismic hazard parameters it is demonstrated that the use of non parametric kernel estimators of magnitude distribution functions improves significantly the accuracy of hazard estimates and therefore these estimators are recommended to be used in probabilistic analyses of seismic hazard caused by as

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

seismic hazard assessment under complex source size distribution of mining induced seismicity abstract it is well documented that a variety of factors controlling the rockmass fracturing process in mines often results in a complexity of mining event size distribution in such cases the estimation of the probability functions of source size parameterizations with the use of presently known distribution models brings about an unacceptable and systematic over or underestimation of the seismic hazard parameters it is therefore recommended that the non parametric kernel estimators of the event size distribution functions be applied to stationary hazard studies in mining seismicity these data driven estimators adapted to seismic source size characterization accurately fit all kinds of data underlying distributions regardless of their complexity recently the non parametric approach to size characterization was supported by a special method of uncertainty analysis based on resampling techniques at present it is a fully developed method which provides point and interval estimates of size distribution functions and related hazard parameters two examples of its use in studying mining seismic data are presented and discussed in this paper the analyzed data sets were recorded in two different copper mines in poland the smoothed bootstrap test for multimodality which is a specialized tool for investigating the shapes of probability densities provided highly significant proof that in both cases the probability densities of source size parameterization were complex thus implied the superiority of the non parametric estimation to the classic model based approach in the studied cases the data were then used to construct non parametric kernel estimates of the source size cumulative distribution function cdf the exceedance probability and the mean return period furthermore confidence intervals for these quantities were also estimated the intervals for cdf were narrow showing that the procedures of non parametric estimation and resampling based uncertainty analysis were precise due to the fact that the mean return period is very sensitive to values of the cdf in particular for larger events sizes the uncertainty of the return period estimates was not insignificant but remained manageable the point and interval estimates of source size cdf and hazard parameters so obtained were compared with the respective point estimates achieved from the inappropriate in the case of complex magnitude distributions model based approach

what we can and cannot learn about earthquake sources from the spectra of seismic waves earthquake sources are commonly viewed as shear dislocations this imposes distinct limitations on what source parameters can be realistically determined from radiated shear wave spectra first the slip velocity on the fault is the real parameter that controls the strength of the high frequency radiation it can be directly determined from acceleration spectra by fitting their high frequency level second the relationship between corner frequency of the spectrum and the radius of the source is fundamentally unclear as a result the source dimensions cannot be accurately determined from the spectra such an estimate would be as accurate as any other informed guess third the stress drop only serves as a proxy for the source radius in the relationship between the radius and the corner frequency it thus cannot be reliably determined from the spectra the quantity usually obtained from the spectra and referred to as the stress drop is a poorly defined parameter that may bear little relevance to the actual stresses acting on faults this parameter has little meaning unless converted to the maximum slip velocity which is the only quantity that can be accurately determined from the spectra the typical value of stress drop of 100 bars established from the spectra of california events may imply that the typical slip velocities have been on the order of 0 5 m sec although it is more accurate to determine slip velocities directly from the spectra

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

simultaneous inversion for q and source parameters of microearthquakes accompanying hydraulic fracturing in granitic rock an inversion that fits spectra of earthquake waveforms and gives robust estimates of corner frequency and low frequency spectral amplitude has been used to determine source parameters of 223 microearthquakes induced by hydraulic fracturing in granodiorite assuming a 2 source model the inversion fits the p wave spectra of microearthquake waveforms to determine individual values of corner frequency and low frequency spectral amplitude for each event and one average frequency independent q for all source receiver paths we also implemented a constraint that stress drops of all microearthquakes be similar but not equal and found that this constraint did not significantly degrade the quality of the fits to the spectra the waveforms analyzed were recorded by a borehole seismometer the p wave q was found to be 1070 for q values as low as 600 and as high as 3000 the misfit between model and spectra increased by less than 5 per cent and the average corner frequency changed by less than 15 per cent from those obtained with a q of 1070 average stress drop was 3 7 bars seismic moments obtained from spectra ranged from 1013 to 1018 dyne cm the low stress drops are interpreted to result from underestimation of the actual stress drops because of a nonuniform distribution of stress drop and slip along the fault planes spatially varying stress drops and slips result from the strong rock heterogeneity due to the injection of fluid into the rock stress drops were found to be larger near the edges of the seismic zone in regions that had not been seismically active during previous injections the seismic moments determined from spectra were used to obtain a coda length to moment relation then moments were estimated for 1149 events from measurements of coda lengths from events whose moments could not be measured from spectra because of saturation or a low signal to noise ratio the constant of proportionality between cumulative number of events and seismic moment is higher than that found for tectonic regions the slope is so high that the seismic energy release is dominated by the large number of small events in the absence of information about the number of events smaller than we studied we cannot estimate the total seismic energy released by the hydraulic injection

the determination of the seismic quality factor q from vsp data a comparison of different computational methods1 ten methods for the computation of attenuation have been investigated namely amplitude decay analytical signal wavelet modelling phase modelling frequency modelling rise time pulse amplitude matching technique spectral modelling and spectral ratio in particular we have studied the reliability of each of these methods in estimating correct values of q using three synthetic vsp seismograms for plane p waves with different noise contents the investigations proved that no single method is generally superior rather some methods are more suitable than others in specific situations depending on recording noise or geology the analytical signal method has been demonstrated to be superior if true amplitude recordings are available otherwise spectral modelling or in the noise free case the spectral ratio method is optimal finally two field vsps in sediments are investigated only in the case of the highest quality vsp can significant information be deduced from the computed attenuation

fracking in tight shales what is it what does it accomplish and what are its consequences fracking is a popular term referring to hydraulic fracturing when it is used to extract hydrocarbons we distinguish between low volume traditional fracking and the high volume modern fracking used to recover large volumes of hydrocarbons from shales shales are fine grained rocks with low granular permeabilities during the formation of oil and gas large fluid pressures are generated these pressures result in natural fracking and the resulting fracture permeability allows oil and gas to escape reducing the fluid pressures these fractures may subsequently be sealed by mineral deposition resulting in tight shale formations the objective of modern fracking is to reopen these fractures and or create new fractures on a wide range of scales modern fracking has had a major impact on the availability of oil and gas globally however there are serious environmental objections to modern fracking which should be weighed carefully against its benefits

postsubduction porphyry cu au and epithermal au deposits products of remelting of subduction modified lithosphere porphyry cu mo au and some epithermal au deposits are formed from hydrothermal fluids exsolved from cooling water rich calc alkaline magmas emplaced in volcanoplutonic arcs above subduction zones these magmas originate by partial melting of the metasomatized asthenospheric mantle wedge however there is increasing evidence for the existence of a suite of porphyry cu au and epithermal au deposits related to magmas generated after subduction beneath the arc has ceased associated magmas tend to be mildly alkaline relatively sulfur poor and emplaced as isolated complexes rather than in voluminous volcanoplutonic arcs they are likely formed by remelting of previously subduction modified arc lithosphere triggered by postsubduction lithospheric thickening lithospheric extension or mantle lithosphere delamination metasomatized mantle lithosphere or hydrous lower crustal cumulates residual from first stage arc magmatism contain small amounts of chalcophile and siderophile element rich sulfides and constitute a fertile source for hydrous au rich but relatively sulfur poor magmas during later remelting the recognition that porphyry cu au and related epithermal au systems can also form in postsubduction and collisional tectonic settings expands the range of geological environments and geographical terranes that are prospective for such deposits

breakdown of the gutenberg richter relation for microearthquakes induced by hydraulic fracturing influence of stratabound fractures hydraulic fracturing a powerful completion technique used to enhance oil or gas production from impermeable strata may trigger unintended earthquake activity the primary basis for assessment of triggered and natural seismic hazard is the classic gutenberg richter g r relation which expresses scale independent behaviour of earthquake magnitudes here we use a stochastic approach to simulate and test magnitude distance trends expressed by microseismic catalogues derived from three hydraulic fracture monitoring programmes in north america we show that a widely observed rapid fall off in large magnitude events almost universally quantified using the g r b value may in our case be an artefact of the strongly laminated character of the stimulated oil and gas reservoirs we also show that for the three reservoirs considered mechanical bed thickness can be approximated by a lognormal distribution for a stratabound fracture network this leads asymptotically to a gaussian decay for induced magnitudes we show that the stratabound model provides a more significant correspondence with our observations if applicable in general this result has important implications for determining the energy balance of hydraulic fracture systems i e radiated seismic energy versus injected energy as well as hazard assessments based on the probability of occurrence of anomalous seismic events key words monitoring passive method reservoir geophysics

integrated microseismic and geomechanical study in the barnett shale formation abstractwe have developed a careful chronological review of multistage stimulation treatments in which microseismic interpretation was supported by fracture simulation and finite element geomechanical simulation the interpretation of a zipper frac stimulation treatment conducted in the barnett shale formation in 2011 progressed from microseismic interpretation from well site observation to a self consistent understanding across multiple stages and multiple wells through this process we have developed a tutorial on practical interpretation of microseismic data in the context of the hydraulic fracture treatment information pump data and regional structural information from interpretation of 3d seismic sections analysis of microseismic data included summarizing groups of events in the form of b value d value and extracted planar geometries we advocate the development of a chronological interpretation the consistency of which is tested using forward modeling the process is iterative and relies o

inferring in situ stress changes by statistical analysis of microseismic event characteristics two commonly estimated fractal dimensions called b and d values represent statistical characteristics in the distribution of magnitude sizes b and spatial hypocenter locations d of microseismic events respectively we establish that the values of these two dimensions are related to specific stress regimes through the case study of a heavy oil field drained using cyclic steam stimulation we infer that the measured temporal variation in fractal dimension b is most likely due to significant changes in the local stress regime over a seven month period ranging from extensional faulting fractures opening via a strike slip regime to finally compressive faulting fractures closing the fracture dimension d indicates predominantly planar to spherical hypocenter spatial distributions in the first and last stages but changes to a more linear to planar spatial pattern in the intermediate strike slip regime when the vertical stress is anticipated to be in between the maximum and minimum horizontal stre

it s a matter of size magnitude and moment estimates for microseismic data microseismic mapping is a valuable tool for assessing hydraulic fracture stimulations during a stimulation treatment borehole near surface or surface geophones record passive seismic data the microseismic events are thought to be shear failures that occur around the opening of a tensile hydraulic fracture as it grows over the past several years there has been a large growth in the number of hydraulic fracture monitoring surveys along with the number of vendors who acquire and process microseismic data here we discuss two attributes of microseismic data which are associated with the size of the passive event seismic moment and magnitude