seismic petrophysics and isotropic anisotropic avo methods for unconventional gas exploration exploration and drilling for natural gas in north america has moved radically away from conventional reservoirs to focus on unconventional reservoirs such as tight gas sands and shales these reservoirs have low porosity and near zero permeability with gas stored in natural fractures and within the matrix porosity economic gas production requires hydraulic fracture stimulation to open connections to existing natural fractures or matrix porosity and successful stimulation depends on the formation s geomechanical brittleness being capable of supporting extensive induced fractures however despite adequate stimulation significant variations exist between wells in expected ultimate recovery eur due to the heterogeneity of these resource plays consequently predicting natural fractures or fracture prone sweet spots is essential to optimize development of such plays

bronze age upland settlement decline in southwest england testing the climate change hypothesis abstract the division of land on dartmoor during the bronze age by the construction of moor wide boundaries known as reaves represents a significant development in agricultural practice and land tenure previous research relating to the dartmoor reaves suggests this way of life may have continued for no longer than 200 400 years it has been suggested that their abandonment occurred as the result of a deteriorating climate although there are no published palaeoclimatic reconstructions from the area we therefore test the hypothesis that on dartmoor a marked climatic deterioration occurred in the late bronze age that can be linked to the abandonment of the reaves a palaeoclimatic reconstruction derived from testate amoebae and peat humification analyses is presented from tor royal bog central dartmoor the first such record from southwest england a major shift to a cooler and or wetter climate is inferred from ca 1395 to 1155 cal bc that is coincident with the period hypothesised as encompassing the abandonment this climatic deterioration is replicated in sites in northern britain suggesting it was a widespread event it is concluded that while the evidence supports a climatically forced retreat there are a range of other socio economic factors that must also be taken into consideration

seismic inversion for organic richness and fracture gradient in unconventional reservoirs eagle ford shale texas abstract a method using eagle ford organic shale from texas predicts key unconventional reservoir properties total organic carbon toc and fracture pressure gradient fg applying petrophysical and rock physics models from previous work to the available well log data generates the required logs for calibration i e shear sonic toc organic porosity and saturation prestack seismic data can be evaluated using synthetic forward modeling and can be conditioned further to improve avo response simultaneous prestack inversion to derive acoustic impedance ai and shear impedance si volumes can be run and toc can be derived from those volumes by linear interpolation fracture gradient which also can be thought of as frackability is related directly to poisson9s ratio and effective stress and can be estimated from elastic properties the fracture gradient is related nonlinearly and inversely to toc i e assuming laterally and vertically homogeneous pore pressure distribution inside the spatially limited block of the eagle ford shale higher toc results in lower fg and hence better frackability

an intensity survey of households affected by the northridge california earthquake of 17 january 1994 following the northridge california earthquake of 17 january 1994 the humboldt earthquake education center heec conducted a telephone survey of approximately 6000 adults from within the felt region to study the earthquake s effects on individual households we tabulate human responses to the earthquake and observations of the earthquake s effects on inanimate objects from the heec survey as a function of independently assigned u s geological survey modified mercalli usgs mm intensity for the same communities human responses and subjective judgments about the severity of shaking when averaged over a large number of samples are useful discriminants of the levels of strong ground motion up to those associated with usgs mm intensity vii notwithstanding that individual human responses and subjective judgments are notoriously unreliable a threshold of strong ground motion corresponds to usgs mm intensity of about vii above which over 40 of respondents described the earthquake as violent and most people reported difficulty standing furniture displaced and some damage to their homes even at intensities viii and ix however relatively few people about 15 described their reaction as panic and only about 12 reported major damage to their homes the heec phone survey data show that in communities of low to moderate shaking usgs mm intensities estimated from a single postal questionnaire are quite robust at usgs mm intensity of v and below 88 of usgs mm intensities determined from postal questionnaires are within one intensity unit of intensities determined from the more numerous heec telephone survey data for the same community we introduce the concept of a community decimal intensity scale cdi based on telephone survey data and calibrated to agree on average with the usgs mm intensities the cdis are more regularly distributed than the usgs mm intensities and show much less scatter when plotted as a function of epicentral distance cdis show promise as a tool for comparing regional attenuation for delineating variations in shaking strength within areas mapped as a single mm zone and for rapid preliminary intensity estimates utilizing electronic media

estimating locations and magnitudes of earthquakes in southern california from modified mercalli intensities modified mercalli intensity mmi assignments instrumental moment magnitudes m and epicenter locations of thirteen 5 6 m 7 1 training set events in southern california were used to obtain the attenuation relation mmi 1 64 1 41 m 0 00526 h 2 63 log h where h is the hypocentral distance in kilometers and m is moment magnitude intensity magnitudes m i and locations for five 5 9 m 7 3 independent test events were consistent with the instrumental source parameters fourteen historical earthquakes between 1890 and 1927 were then analyzed of particular interest are the m i 7 2 9 february 1890 and m i 6 6 28 may 1892 earthquakes which were previously assumed to have occurred near the southern san jacinto fault a more likely location is in the eastern california shear zone ecsz these events and the 1992 m 7 3 landers and 1999 m 7 1 hector mine events suggest that the ecsz has been seismically active since at least the end of the nineteenth century the earthquake catalog completeness level in the ecsz is m 6 5 at least until the early twentieth century online material figures and table of empirical mmi site corrections

fracture mapping using seismic amplitude variation with offset and azimuth analysis at the weyburn co2 storage site abstractcap rock integrity is an essential characteristic of any reservoir to be used for long term co2 storage seismic avoa amplitude variation with offset and azimuth techniques have been applied to map hti anisotropy near the cap rock of the weyburn field in southeast saskatchewan canada with the purpose of identifying potential fracture zones that may compromise seal integrity this analysis supported by modeling observes the top of the regional seal watrous formation to have low levels of hti anisotropy whereas the reservoir cap rock composite midale evaporite and ratcliffe beds contains isolated areas of high intensity anisotropy which may be fracture related properties of the fracture fill and hydraulic conductivity within the inferred fracture zones are not constrained using this technique the predominant orientations of the observed anisotropy are parallel and normal to the direction of maximum horizontal stress northeast southwest and agree closely with previous fracture studies

a new exploration tool quantitative core characterization we will describe a new laboratory system which was designed to be highly automated and portable while maintaining quality driving this design was the recognition of the temporal dependence of physical properties it becomes apparent that some sedimentary rocks particularly shales degrade and disaggregate so completely that mechanical or elastic properties cannot be measured this temporal dependence displays a time scale much shorter than normal weathering but greater than the time for stress relief a system was designed to permit field characterization of freshly recovered core material a benefit of automation and portability is a marked increase in measurement efficiency the attributes of this system permit rapid characterization of a large number of fresh cores in remote frontier exploration areas this feature can significantly reduce prospect evaluation time statistically significant rock property databases can be created in a short period of time

modelling elastic properties of impure chalk from south arne field north sea in impure chalk the elastic moduli are not only controlled by porosity but also by contact cementation resulting in relatively large moduli for a given porosity and by admixtures of clay and fine silica which results in relatively small moduli for a given porosity based on a concept of solids suspended in pore fluids as well as composing the rock frame we model p wave and s wave moduli of dry and wet plug samples by an effective medium hashin shtrikman model using chemical mineralogical and textural input for a given porosity the elastic moduli correspond to a part of the solid the iso frame value forming the frame of an upper hashin shtrikman bound whereas the remaining solid is modelled as suspended in the pore fluid the iso frame model is thus a measure of the pore stiffness or degree of cementation of the chalk the textural and mineralogical data may be assessed from logging data on spectral gamma radiation density sonic velocity and water saturation in a hydrocarbon zone whereas the iso frame value of a chalk may be assessed from the density and acoustic p wave logs alone the iso frame concept may thus be directly used in conventional log analysis and is a way of incorporating sonic logging data the rigs 1 and rigs 2 wells in the south arne field penetrate the chalk at the same depth but differ in porosity and in water saturation although almost the entire chalk interval has irreducible water saturation our model combined with petrographic data indicates that the difference in porosity is caused by a higher degree of pore filling cementation in rigs 1 petrographic data indicate that the difference in water saturation is caused by a higher content of smectite in the pores of rigs 1 in both wells we find submicron size diagenetic quartz

valuable lessons from acquiring 3d seismic for coal seam gas coalbed methane cbm or coal seam gas csg is being developed on a basinwide scale primarily as feedstock for three new liquefied natural gas lng facilities on the east coast of australia a recent 3d seismic survey acquired specifically for csg in the surat and bowen basins shows that although structural detail of the reservoir is a valuable tool deriving other information for reservoir characterization from thinly bedded coals requires a thorough investigation of the effects of high reflectivity thin beds although work continues to progress the results so far suggest that 3d seismic surveys can provide information for improved reservoir characterization

the 1930 santa monica and the 1979 malibu california earthquakes the malibu earthquake m l 5 0 that occurred 1 january 1979 in santa monica bay was located at 33 56 9 n and 118 41 3 w and at a depth of 10 km the focal mechanism of the main shock as determined from first motions recorded by short period high gain seismic stations in southern california shows reverse faulting with one plane dipping 55 to 60 to the north striking 275 to 290 and the second plane dipping 30 to 38 to the south and striking 100 to 120 more than 400 aftershocks were recorded during 1979 focal mechanisms for 20 aftershocks of m 3 0 show similar reverse mechanisms as the main shock the main shock and aftershocks m 2 5 were relocated using a local velocity model and a set of corresponding station delays the aftershocks define a volumetric hypocentral zone 4 km 6 km west trending with depths ranging from 6 to 11 km this 1979 malibu main shock aftershock sequence probably occurred on the eastern end of the anacapa dume fault the santa monica earthquake m l 5 2 that occurred 31 august 1930 was relocated using station delays calculated from the 1979 date set the relocated 1930 epicenter is located near the western end of the santa monica fault the 1979 and 1930 main shocks can be interpreted to define a 8 to 10 km north south sidestep between the anacapa dume and santa monica faults possible segmentation of these two fault systems suggests that they are unlikely to rupture simultaneously in one large earthquake

the selection of sites for paleovegetational studies the judicious selection of sites for paleovegetational and paleoclimatic studies permits paleoecologists to answer specific research questions that go beyond primary descriptions of past vegetation we present a model that describes the relationship between basin size and pollen source area and predicts the proportions of local extralocal and regional pollen sampled by lake basins of different size the distinctive sampling properties of lakes peats and small hollows can be exploited to provide details of pattern in paleovegetation so long as attention is given to the limitations and problems of these types of sites combinations of site types in a single study most fully exploit the information contained in sediments

integrated workflows for shale gas and case study results for the horn river basin british columbia canada the variation in well performance observed between various shale gas plays and indeed within individual basins and on individual pads has gone some way to dispelling myths regarding the perceived homogeneity of shale gas targets with increased quantities of data and more determined analysis we show that understanding the micro and mesoscale heterogeneity can be advanced through interdisciplinary studies that incorporate traditional and advanced geophysical data and methods with geological understanding and engineering measurements this understanding is critical in optimizing well placement the spacing and length of horizontal wells and hydraulic fracturing effort to maximize recovery specifically we illustrate that in the muskwa formation and the otter park klua and evie members of the horn river formation reservoir quality can be predicted using lambda rho and mu rho data extracted from avo inversion studies from log data we show that the most prospective reservoir intervals are characterized by decreasing lambda increasing mu and or a lambda mu ratio less than one

earthquake monitoring in southern california for seventy seven years 1932 2008 the southern california seismic network scsn has produced the scsn earthquake catalog from 1932 to the present a period of more than 77 yrs this catalog consists of phase picks hypocenters and magnitudes we present the history of the scsn and the evolution of the catalog to facilitate user understanding of its limitations and strengths hypocenters and magnitudes have improved in quality with time as the number of stations has increased gradually from 7 to 400 and the data acquisition and measuring procedures have become more sophisticated the magnitude of completeness m c of the network has improved from m c 3 25 in the early years to m c 1 8 at present or better in the most densely instrumented areas mainshock aftershock and swarm sequences and scattered individual background earthquakes characterize the seismicity of more than 470 000 events the earthquake frequency size distribution has an average b value of 1 0 with m 6 0 events occurring approximately every 3 yrs the three largest earthquakes recorded were 1952 m w 7 5 kern county 1992 m w 7 3 landers and 1999 m w 7 1 hector mine sequences and the three most damaging earthquakes were the 1933 m w 6 4 long beach 1971 m w 6 7 san fernando and 1994 m w 6 7 northridge earthquakes all of these events ruptured slow slipping faults located away from the main plate boundary fault the san andreas fault their aftershock sequences constitute about a third of the events in the catalog the fast slipping southern san andreas fault is relatively quiet at the microseismic level and has not had an m 6 earthquake since 1932 in contrast the slower san jacinto fault has the highest level of seismicity including several m 6 events thus the spatial and temporal seismicity patterns exhibit a complex relationship with the plate tectonic crustal deformation

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

experimental mechanical compaction of reconstituted shale and mudstone aggregates investigation of petrophysical and acoustic properties of sw barents sea cap rock sequences abstract this study investigates petrophysical and acoustic properties of experimentally compacted reconstituted samples of seal sequences from the southwestern barents sea the aggregates were collected from drill cuttings of mudstone and shale formations of two exploration wells 7220 10 1 salina discovery and 7122 7 3 goliat field the washed and freeze dried samples were characterized for grain size distributions geochemical analyses and mineralogical compositions a total of 25 compaction tests 12 dry and 13 brine saturated were performed with a maximum effective vertical stress of 50 mpa the laboratory measurements demonstrated that petrophysical and acoustic properties of argillaceous sediments can change within a sedimentary basin and even within a given formation the results show that the collected aggregates from goliat field are compacted more compared to salina discovery the maximum and minimum compaction are measured in samples collected from snadd and fuglen formations respectively the final porosity of brine saturated specimens varies between 5 and 22 the ultrasonic velocity measurements depict that samples with the same porosity values can have a broad range of velocity values the resulting compaction trends in this study were compared to published compaction curves for synthetic mixtures of quartz and clay all compaction trends show higher porosity reduction than the silt fraction with 100 quartz comparison of experimental compaction result of each mudstone and shale aggregate with its corresponding acquired well log data helps to delineate the burial history and exhumation in the study area a net exhumation of 950 m and 800 m is estimated at salina and goliat wells respectively the outcomes of this study can provide insights for hydrocarbon prospect discovery in a pre mature sedimentary basin in terms of exploration and production and also for geological co2 storage sites the experimental results may provide information for well log and seismic interpretation basin modeling and seal integrity of investigated horizons

a method and example of seismically imaging near surface fault zones in geologically complex areas using vp vs and their ratios abstract the determination of near surface vadose zone and slightly below fault locations and geometries is important because assessment of ground rupture strong shaking geologic slip rates and rupture histories occurs at shallow depths however seismic imaging of fault zones at shallow depths can be difficult due to near surface complexities such as weathering groundwater saturation massive nonlayered rocks and vertically layered strata combined p and s wave seismic refraction tomography data can overcome many of the near surface fault zone seismic imaging problems because of differences in the responses of elastic bulk and shear moduli of p and s waves to shallow depth fault zone properties we show that high resolution refraction tomography images of p to s wave velocity ratios v p v s can reliably identify near surface faults we demonstrate this method using tomography images of the san andreas fault saf surface rupture zone associated with the 18 april 1906 m 7 9 san francisco earthquake on the san francisco peninsula in california there the saf cuts through franciscan melange which consists of an incoherent assemblage of greywacke chert greenstone and serpentinite a near vertical zone 75 northeast dip of high p wave velocities up to 3000 m s low s wave velocities 150 600 m s high v p v s ratios 4 8 8 and high poisson s ratios 0 44 0 49 characterizes the main surface rupture zone to a depth of about 20 m and is consistent with nearby trench observations we suggest that the combined v p v s imaging approach can reliably identify most near surface fault zones in locations where many other seismic methods cannot be applied

relationship between the sedimentary microfacies and geomechanical behavior of the asmari formation carbonates southwestern iran abstract the objective of this paper is to address the impact of texture and thus the related sedimentary environments and facies and diagenetic overprint on the geomechanical behavior of the asmari formation carbonates three sets of data were utilized in this study i sedimentological data including thin section petrography porosity density xrf and sem ii rock mechanical data comprising uniaxial compressive strength ucs cohesion c friction angle tensile strength brittleness and drillability index and iii ultrasonic data including s and p wave velocity to study a possible relationship between the sedimentological features and rock mechanical properties a facies index was defined based on the textural and diagenetic features allowing to quantify a sedimentary microfacies based on facies index porosity and ucs five different geomechanical facies gmf were determined for the asmari formation where gmf1 to gmf5 represent very ductile to very brittle material respectively the results showed that mechanical behavior are controlled by the depositional environment open marine to supratidal and diagenetic overprint dissolution cementation dolomitization micritization mechanical and chemical compaction and authigenic clay formation by quantifying the sedimentological and diagenetic features the rock strength may be predicted based on petrographical observations results of this study provide insights for creating a relationship between sedimentological features and rock mechanical behavior based on the gmf concept presented here such studies are helpful for reducing the costs time for acquiring geomechanical datasets

the winds of change anisotropic rocks their preferred direction of fluid flow and their associated seismic signatures part 1 editor s note this article is the first of two parts that together form an abbreviated version of the fall 2004 seg aapg distinguished lecture a powerpoint presentation of this material is posted on the seg web site the winds of change refer to much more than just anisotropic rocks whose seismic anisotropy provides insight into horizontal permeability anisotropy the way we view our planet is changing the planet is now being studied as the interaction of four interlocking systems the hydro sphere the atmosphere the lithosphere and the biosphere as all absorb energy from our sun and change the planet and all its subsystems like geology or climate are explicitly evaluated as interdependent and interacting within the context of the local community the heterogeneity at the surface of our planet and the recycling of compounds and elements water nitrogen sulfur etc enable our planet to support life my earth science career has spanned two revolutions the plate tectonic revolution during the 1970s and today s profound reevaluation of how our planet works and our roles as planet dwellers the rocks that are the primary focus of most of our studies are best understood as firstly the result of the interactions of the climate the water conditions the depositional setting the biosphere and the provenance of the sediments and secondly the lithification and geologic history they have undergone the biosphere shows up in our rocks both as fossils a key means of dating rocks and as liquid or solid organic remains we understand any given stratigraphic facies in the context of its spatial neighbors its community and its plate tectonic setting the climate includes the actions of gravity sunlight and atmosphere but it is affected by where the land masses are and how they are linked together oil industry geoscientists are uniquely placed via access to important data and sophisticated tools

influencing factors and fracability of lacustrine shale oil reservoirs abstract shale oil reservoirs need fracturing in order to achieve commercial productivity a key factor influencing the fracturing process is shale fracability which is strictly dependent on rock fabric in this study we focused on the lacustrine shale oil reservoirs located in dongying sag and in the northern jiangsu basin through x ray mineral diffraction rock mechanics and p and s wave velocity tests we analyzed the mineral components and mechanics of different shale lithofacies as well as the influence of these factors on shale fracability based on the results of these analyses we proposed a new method for the evaluation of lake shale oil reservoir fracability the experimental results showed that the macrostructure mineral content lithology and the presence of microfractures in the shale are the main factors affecting its brittleness shales with lamellar and sheet like structures have relatively high young s modulous or lower poisson s ratios under these conditions netted fractures are easily formed during fracturing the fracture toughness of carbonate minerals in shales is strong an appropriate amount of carbonate minerals seemed to increase the shale brittleness however an excessive amount increased its cohesiveness hindering the initiation and propagation of fractures felsic minerals are characterized by high brittleness a characteristic that favors shale fracability on the other hand clay minerals and organic matter are highly plastic a characteristic that hinders fracturing transformations due to their macrostructure and composition lamellar clayey limestones dolomite lamellar clayey siltstones layered calcareous dolomitic siltstones sheet like clay containing siltstones and flaggy carbonate containing siltstones are expected to be easily fractured in addition the presence of microfractures seemed to reduce the overall fracture toughness of the rock they penetrated artificial fractures enhancing rock fracability taking into account the fracture toughness of carbonate minerals and the plastic effect of organic matter we proposed a new formula for the calculation of the brittleness index based on the mineral component method the brittleness indices obtained through the proposed formula were linearly correlated with those calculated through the rock mechanics parameters method overall our results indicate that the silty lithological successions occurring in the study area should be the easiest to fracture followed by the calcareous dolomitic and clayey or organic rich lithological successions this study is of guiding significance for evaluating the fracability of different lithofacies in lacustrine shale oil reservoirs especially the new proposed brittleness index containing the plastic effect of organic matter can correctly evaluate the actual brittleness of organic rich shale

experimental study of ultrasonic rayleigh wave scattering at a thin anisotropic slab in this article we report the results of 3d ultrasonic experiments on rayleigh wave scattering by a narrow vertical anisotropic slab the experimental model was built from two rectangular isotropic blocks with a narrow vertical anisotropic slab embedded between them to provide a welded contact between the blocks and the slab an epoxy glue was applied the slab was made of woodfiber with the fiber oriented horizontally along the surfaces of the slab scattered waves were recorded in the far field zone in the vicinity of the slab and inside the slab the results of the experiments for the far field zone are compared with the results of mathematical modeling using the green9s function technique for thin anisotropic layers welded and nonwelded boundary conditions were used in the mathematical model to take into account the epoxy glue layer the experimental and theoretical results are largely consistent for the welded boundary condition model significant variations of rayleigh wave amplitudes which cannot be explained in the framework of the green9s function method were observed in a wavelength scale zone near the slab

p and s wave velocity measurements of water rich sediments from the nankai trough japan acoustic velocities were measured during triaxial deformation tests of silty clay and clayey silt core samples from the nankai subduction zone integrated ocean drilling program expeditions 315 316 and 333 we provide a new data set continuously measured during pressure increase and subsequent axial deformation a new data processing method was developed using seismic time series analysis compressional wave velocities v p range between about 1450 and 2200 m s and shear wave velocities v s range between about 150 and 800 m s v p slightly increases with rising effective confining pressure and effective axial stress samples from the accretionary prism toe show the highest vp while fore arc slope sediments show lower vp samples from the incoming plate slightly richer in clay minerals have the lowest values for v p v s increases with higher effective confining pressures and effective axial stress irrespective of composition and tectonic setting shear and bulk moduli are between 0 2 and 1 3 gpa and 3 85 and 8 41 gpa respectively elastic moduli of samples from the accretionary prism toe and the footwall of the megasplay fault 1 50 and 3 98 gpa are higher than those from the hanging wall and incoming plate 0 59 and 0 88 gpa this allows differentiation between normal and overconsolidated sediments the data show that in a tectonosedimentary environment of only subtle compositional differences acoustic properties can be used to differentiate between stronger accretionary prism toe and weaker fore arc slope incoming plate sediments especially v p v s ratios may be instrumental in detecting zones of low effective stress and thus high pore fluid pressure

uncertainty in discriminating lithology in different data domains a major goal of geophysical analysis is to predict the lithologic and fluid content of the subsurface of necessity most of the measurements are conducted remotely using seismic or electromagnetic equipment these remote data should be calibrated with the expected properties of the subsurface principally from well control as a result rock physics is a key component of the process to ensure that the appropriate geophysical response is measured and obtained

using avo for fracture detection analytic basis and practical solutions tight low porosity reservoirs can produce significant amounts of hydrocarbons if fracture networks provide the necessary permeability characterization of naturally fractured reservoirs using surface seismic data is an important exploration problem that has attracted much attention in the literature tle for example had an entire issue august 1996 on this subject while the data and modeling in existing publications demonstrate that fracturing causes significant azimuthal variation in recorded seismic signatures the problem is how to infer fracture parameters from these data

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

interpreting seismic data in the presence of azimuthal anisotropy or azimuthal anisotropy in the presence of the seismic interpretation measuring p wave azimuthal anisotropy has been in the recent past an elusive task therefore the interpreter ignored this attribute of the seismic data and left the subject to the research and technology group geophysicists conversely the interpreting geophysicist knew that when measured the anisotropy could yield important reservoir properties related to fractures and stress fields however little did we suspect that p wave azimuthal anisotropy both in velocity and avo would change our perception of data interpretation as is happening now

velocities and quality factors of sedimentary rocks at low and high effective pressures summary techniques for measuring acoustic velocities and quality factors q of sedimentary rocks in the laboratory are sufficiently accurate to establish closely fitting regression curves which represent the variation of these acoustic properties with pressure ultrasonic p and s wave measurements of velocity v v and q q q were made on 16 different water saturated sandstone samples at various effective pressures using an ultrasonic reflection technique and the data were fitted using a simple regression equation containing a constant plus linear and exponential pressure dependent terms the redundancy of the linear term in the regression of q data suggests that microcracks alone govern the pressure variation of q whereas velocities are additionally dependent on another mechanism consistent with the changes in elastic moduli caused by intergranular compression causing small reductions in porosity the implied rates of microcrack closure with increasing effective pressure in all samples were found to be comparable the regression equations describe the data closely enough to enable the extrapolation of acoustic properties to both low and high effective pressures this is of practical use since laboratory techniques can produce uncertain results at low pressures due to coupling problems and low signal strengths whilst high pressures require large confining vessels low pressure and high pressure data are applicable to shallow seismic surveys and hydrocarbon exploration respectively

seismic anisotropy of fractured rock a simple method for including the effects of geologically realistic fractures on the seismic propagation through fractured rocks can be obtained by writing the effective compliance tensor of the fractured rock as the sum of the compliance tensor of the unfractured background rock and the compliance tensors for each set of parallel fractures or aligned fractures the compliance tensor of each fracture set is derivable from a second rank fracture compliance tensor for a rotationally symmetric set of fractures the fracture compliance tensor depends on only two fracture compliances one controlling fracture compliance normal the other tangential to the plane of the fractures the stiffness tensor which is more useful in the consideration of elastic wave propagation through rocks can then be obtained by inversion the components of the excess fracture compliance tensor represent the maximum amount of information that can be obtained from seismic data if the background rock is isotropic and the normal a

effects of sand shale anisotropy on amplitude variation with angle ava modelling the sawan gas field pakistan as a key case study for south asia s sedimentary basins amplitude variation with angle ava is a technique widely used in the characterisation of hydrocarbon reservoirs and assumes the earth s crust to be an isotropic medium yet anisotropy is ubiquitous in stratigraphic sequences and has first order effects on seismic ava responses when investigating subsurface prospects this work analyses the effects of anisotropic strata on ava responses using the lower goru formation middle indus basin pakistan as a case study in the study area shale intervals are interbedded with reservoir sands of the sawan gas field shales in this field form laminae or are dispersed within reservoir sands making the lower goru formation an example of a vertically transversely isotropic vti medium in this work we calculate the effective saturated mechanical properties of the lower goru formation based on rock physics templates the backus 1962 average typically designed for layered media combined with the empirical relations of brown and korringa 1975 and wood 1955 the input data used in our rock physics modelling is based on detailed petrophysical analyses of well data using the saturated effective mechanical properties of the lower goru formation we generate angle dependent reflection coefficient curves and seismic ava responses based on exact and approximate solutions for both isotropic and anisotropic reservoir scenarios our results suggest that the effects of lithological anisotropy are more pronounced in places with thick shale beds within reservoir sands conversely angle dependent reflection curves and seismic ava responses based on isotropic or anisotropic cases give similar solutions in the presence of thin shale beds as a corollary of this work we present a bayesian inversion method for the estimation of porosity in vti media

a model for induced seismicity caused by hydrocarbon production in the western canada sedimentary basin over the past three decades a significant number of small magnitude and shallow earthquakes have occurred in the western canada sedimentary basin and are located along its western flank near areas of oil and gas production one of the better documented examples is the swarm of earthquakes associated with the strachan field in the alberta foothills a model based on segall s poroelastic theory is developed to account for the occurrence of earthquakes below the strachan reservoir using this methodology we show that the earthquake of 19 october 1996 underneath the strachan field was most probably triggered by gas extraction the numerical model also implies that gas extraction would cause subsidence and localized changes in in situ stress magnitudes there is a strong correlation between rates of production and the number of seismic events but the onset of major seismic activity postdates the commencement of production by approximately 5 years poroelastic modelling can account neatly for this observe

earthquake hazard after a mainshock in california after a strong earthquake the possibility of the occurrence of either significant aftershocks or an even stronger mainshock is a continuing hazard that threatens the resumption of critical services and reoccupation of essential but partially damaged structures a stochastic parametric model allows determination of probabilities for aftershocks and larger mainshocks during intervals following the mainshock the probabilities depend strongly on the model parameters which are estimated with bayesian statistics from both the ongoing aftershock sequence and from a suite of historic california aftershock sequences probabilities for damaging aftershocks and greater mainshocks are typically well constrained after the first day of the sequence with accuracy increasing with time

a new velocity model for clay sand mixtu res1 none of the standard porosity velocity models e g the time average equation raymer s equations is satisfactory for interpreting well logging data over a broad depth range clays in the section are the usual source of the difficulty through the bias and scatter that they introduce into the relationship between porosity and p wave transit time because clays are composed of fine sheet like particles they normally form pores with much smaller aspect ratios than those associated with sand grains this difference in pore geometry provides the key to obtaining more consistent resistivity and sonic log interpretations a velocity model for clay sand mixtures has been developed in terms of the kuster and toksoz effective medium and gassmann theories in this model the total pore space is assumed to consist of two parts 1 pores associated with sand grains and 2 pores associated with clays including bound water the essential feature of the model is the assumption that the geometry of pores associated with sand grains is significantly different from that associated with clays because of this porosity in shales affects elastic compliance differently from porosity in sand stones the predictive power of the model is demonstrated by the agreement between its predictions and laboratory measurements and by its ability to predict sonic logs from other logs over large depth intervals where formations vary from unconsolidated to consolidated sandstones and shales

a pollen based pseudobiomisation approach to anthropogenic land cover change the degree of anthropogenic modification of land cover through the mid to late holocene is of significant interest for archaeologists climate modellers and conservation ecologists amongst others spatially extensive pollen data provide an appropriate resource for the reconstruction of land cover change however traditional simple methods e g the ap nap ratio do not provide the degree of detail required for these user groups a range of more sophisticated methods have been developed e g mechanistic model based methods but they require a high degree of understanding of the pollen vegetation relationship which is resource and time consuming this paper proposes a method of intermediate complexity by which major land cover changes can be assessed for individual sites and regions a pseudobiomisation approach is used in which pollen taxa are assigned to different land cover classes lcc and the sum of adjusted pollen proportions for each class used to determine an lcc affinity score for individu

potentially induced earthquakes during the early twentieth century in the los angeles basin recent studies have presented evidence that early to mid twentieth century earthquakes in oklahoma and texas were likely induced by fossil fuel production and or injection of wastewater hough and page 2015 frohlich et al 2016 considering seismicity from 1935 onward hauksson et al 2015 concluded that there is no evidence for significant induced activity in the greater los angeles region between 1935 and the present to explore a possible association between earthquakes prior to 1935 and oil and gas production we first revisit the historical catalog and then review contemporary oil industry activities although early industry activities did not induce large numbers of earthquakes we present evidence for an association between the initial oil boom in the greater los angeles area and earthquakes between 1915 and 1932 including the damaging 22 june 1920 inglewood and 8 july 1929 whittier earthquakes we further consider whether the 1933 m w 6 4 long beach earthquake might have been induced and show some evidence that points to a causative relationship between the earthquake and activities in the huntington beach oil field the hypothesis that the long beach earthquake was either induced or triggered by an foreshock cannot be ruled out our results suggest that significant earthquakes in southern california during the early twentieth century might have been associated with industry practices that are no longer employed i e production without water reinjection and do not necessarily imply a high likelihood of induced earthquakes at the present time online material summary of background information about the wilmington oil field information about revisited earthquakes between 1900 and 1935 tables of felt events and accounts of three earthquakes

source parameters of the 1933 long beach earthquake regional seismographic network and teleseismic data for the 1933 m l 6 3 long beach earthquake sequence have been analyzed both the teleseismic focal mechanism of the main shock and the distribution of the aftershocks are consistent with the event having occurred on the newport inglewood fault the focal mechanism had a strike of 315 dip of 80 to the northeast and rake of 170 relocation of the foreshock main shock aftershock sequence using modern events as fixed reference events shows that the rupture initiated near the huntington beach newport beach city boundary and extended unilaterally to the northwest to a distance of 13 to 16 km the centroidal depth was 10 2 km the total source duration was 5 sec and the seismic moment was 5 10 25 dyne cm which corresponds to an energy magnitude of m w 6 4 the source radius is estimated to have been 6 6 to 7 9 km which corresponds to a brune stress drop of 44 to 76 bars both the spatial distribution of aftershocks and inversion for the source time function suggest that the earthquake may have consisted of at least two subevents when the slip estimate from the seismic moment of 85 to 120 cm is compared with the long term geological slip rate of 0 1 to 1 0 mm yr along the newport inglewood fault the 1933 earthquake has a repeat time on the order of a few thousand years

geomechanical lithology based analysis of microseismicity in organic shale sequences a pennsylvania marcellus shale example abstract using an innovative workflow incorporating microseismic attributes and geomechanical well logs we have defined major geomechanical drivers of microseismic expression to understand reservoir stimulation response in an engineering geologic context microseismic data from a hydraulically fractured marcellus well in the appalachian basin central pennsylvania were sampled vertically through the event cloud crossing shale limestone sandstone and chert we focused our analysis on the devonian organic shale and created pseudologs of moment magnitude mw b value and event count the vertical moving average sampling of microseismic data was completed such that the sample interval matched that of the geophysical well logs this technique creates robust high resolution microseismic logs that show subtle changes in microseismic properties and allow direct crossplotting of microseismic versus geophysical logs we chose five geomechanical properties to form the framework against which to interrogate

integration of hydraulically induced microseismic event locations with active seismic attributes a north texas barnett shale case study abstracthydraulic fractures are delineated by induced microseismic event distributions and typically propagate perpendicular to the regional minimum stress direction however at a smaller scale varying mineralogical composition and existing fault and fracture networks can influence developing fracture networks we integrated microseismic event locations with seismic attributes from multichannel seismic reflection data including inversion results for impedance and lame parameters and seismic curvature attributes we found that microseismic event locations consistently correlate to zones of low seismic impedance and low and values describing characteristic material properties of fracture prone zones within the north texas lower and upper barnett shale additionally event locations showed a weak correlation with anticlinal structures as defined by volumetric curvature attributes we suggest that the low impedance low and zones were related to the boundary between calcite filled fractures a

assessing preferential seepage and monitoring mortar injection through an earthen dam settled over a gypsiferous substrate using combined geophysical methods abstract for several decades the sant llorenc de montgai reservoir has experienced different problems that could affect the safety of the engineering structure for this reason several corrective actions have been taken over the years here we present a study involving complementary geophysical methods including electrical resistivity tomography seismic refraction tomography and frequency domain electromagnetic surveys the analysis of the inverted electrical resistivity tomography cross sections combined with the seismic refraction results and land subsidence monitoring data show the likely mechanism of abnormal seepage the areas where mortar injections were applied as a corrective measure are also clearly delineated in addition the evolution of the state of the embankment has been established from two successive electrical resistivity tomography surveys in the last two decades the results show areas where corrective mortar injections have been effective while in other areas new abnormal seepage has been detected the lithological heterogeneity of the bedrock especially the dissolution of gypsum rich rocks induced subsidence effects and caused abnormal seepage in different areas along the embankment our results indicate how corrective solutions can be optimized to reduce the cost of corrective engineering interventions

lake sediments erosion and landscape change during the holocene in britain and ireland abstract lakes are excellent repositories of air borne and especially stream borne materials it has long been recognised that lake sediments contain a strong record of catchment soils via the inputs of minerogenic and chemical erosional products to these may be added a variety of palaeoecological indicators including pollen fungi sphagnum leaves and faunal remains pollen analysis in particular enables land use change to be assessed over many millennia and demonstrates the landscape impacts of woodland clearance grazing and crop cultivation radiocarbon dating provides a chronology for environmental and agricultural change and acts as an indicator of erosion in its own right the use of such indicators to reconstruct past instances and patterns of erosion is demonstrated with reference mainly to 50 british and irish lake sites and especially those which have produced signals of erosion in the form of accelerated sediment accumulation and inversed or reversed sequences of radiocarbon dates during the mid and late holocene sites displaying even or decreased sedimentation through time are concentrated in northern and northwestern scotland and have either no clear signs of human impact or only so towards the latter part of the holocene this pattern probably reflects a combination of factors including low population densities thin soils and the sealing effect of blanket peat in contrast all sites with accelerated erosion have indications of anthropogenic impact this is often prior to levels of increased sedimentation showing a delay in system response while the spread of dates for the start of the rise in sediment accumulation spans 6200 940 bp three clusters are evident at 5295 4970 4530 4235 and 2980 2810 bp radiocarbon inversions mostly reversals are evident for 18 sites no obvious causal patterning is indicated and they probably demonstrate no more than the fact that catchment soils including peats around a particular site were pushed beyond an erosional threshold sufficient to age the sediments deposited within the lakes it is hoped that improvements in data quality will allow the refinement of such exercises in the future and that lakes will be valued as repositories of long term landscape sensitivity

geophysical properties within the san andreas fault zone at the san andreas fault observatory at depth and their relationships to rock properties and fault zone structure 1 we examine the relationships between borehole geophysical data and physical properties of fault related rocks within the san andreas fault as determined from data from the san andreas fault observatory at depth borehole geophysical logs cuttings data and drilling data from the region 3 to 4 km measured depth of the borehole encompass the active part of the san andreas fault the fault zone lies in a sequence of deformed sandstones siltstone shale serpentinite bearing block in matrix rocks and sheared phyllitic siltstone the borehole geophysical logs reveal the presence of a low velocity zone from 3190 to 3410 m measured depth with vp and vs values 10 30 lower than the surrounding rocks and a 1 2 m thick zone of active shearing at 3301 3303 m measured depth seven low velocity excursions with increased porosity decreased density and mud gas kick signatures are present in the fault zone geologic data on grain scale deformation and alteration are compared to borehole data and reveal weak correlations and inverse relationships to the geophysical data in places vp and vs increase with grain scale deformation and alteration and decrease with porosity in the fault zone the low velocity zone is associated with a significant lithologic and structural transition to low velocity rocks dominated by phyllosilicates and penetratively foliated sheared rocks the zone of active shearing and the regions of low sonic velocity appear to be associated with clay rich rocks that exhibit fine scale foliation and higher porosities that may be a consequence of the fault related shearing of foliated and fine grained sedimentary rocks

new evaluation methods using conventional logging data for gas shale in southern china abstract because of characteristics of compactness rich in organic matter and gas adsorption the parameters that decide shale quality are not only porosity and permeability but also the abundance of organic matter mineral composition crack and mechanical properties logging evaluation methods of conventional reservoirs are not valid in gas shale advanced technology of core measurements can obtain more accurate parameters of gas shale however because it is restricted by heterogeneity and the high price of core this method cannot be used widely to develop a continuous section based on conventional wireline logging data the natural properties of rocks underground are calculated using the improved evaluation model including mineral composition clay constituents total organic carbon toc content porosity permeability crack porosity and mineral brittleness index moreover based on the rock physics model with rich organic matter elastic properties are achieved to calculate mechanical propert

effects of porosity and clay content on wave velocities in sandstones the ultrasonic compressional vp and shear vs velocities and first arrival peak amplitude ap were measured as functions of differential pressure to 50 mpa and to a state of saturation on 75 different sandstone samples with porosities ranging from 2 to 30 percent and volume clay content c ranging from 0 to 50 percent respectively both vp and vs were found to correlate linearly with porosity and clay content in shaly sandstones at confining pressure of 40 mpa and pore pressure of 1 0 mpa the best least squares fits to the velocity data are vp km s 5 59 6 93 2 18c and vs km s 3 52 4 91 1 89c deviations from these equations are less than 3 percent and 5 percent for vp and vs respectively the velocities of clean sandstones are significantly higher than those predicted by the above linear fits about 7 percent for vp and 11 percent for vs which indicates that a very small amount of clay 1 or a few percent of volume fraction significantly reduces the elastic moduli of sandstones for shaly

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

measurement of the normal tangential fracture compliance ratio zn zt during hydraulic fracture stimulation using s wave splitting data we develop a method to invert s wave splitting sws observations measured on microseismic event data for the ratio of normal to tangential compliance zn zt of sets of aligned fractures we demonstrate this method by inverting for zn zt using sws measurements made during hydraulic fracture stimulation of the cotton valley tight gas reservoir texas when the full sws data set is inverted we find that zn zt 0 74 0 04 windowing the data by time we were able to observe variations in zn zt as the fracture stimulation progresses most notably we observe an increase in zn zt contemporaneous with proppant injection rock physics models and laboratory observations have shown that zn zt can be sensitive to 1 the stiffness of the fluid filling the fracture 2 the extent to which this fluid can flow in and out of the fracture during the passage of a seismic wave and 3 the internal architecture of the fracture including the roughness of the fracture surfaces the number and size of any asperities and the presence of material filling the fracture these factors have direct implications for modelling the fluid flow properties of fractures consequently the ability to image zn zt using sws will provide useful information about fractured rocks and allow additional constraints to be placed on reservoir behaviour

a proposed rupture scenario for the 1925 mw 6 5 santa barbara california earthquake abstract the 29 june 1925 santa barbara earthquake is among the largest 20th century earthquakes in southern california the earthquake also predated the installation of strong motion and local monitoring instruments in southern california some instrumental data are however available from long period instruments at regional and teleseismic distances the current catalog moment magnitude is mw 6 8 initial intensity magnitudes mi estimated from original coast and geodetic survey intensity assignments were lower mi 6 3 in this study we assign modified mercalli intensity values at 239 locations including 144 specific locations within the city of santa barbara for which detailed damage information is available comparing the reinterpreted intensities with did you feel it intensities for recent events in california we estimate mw 6 5 with a plausible range of 6 3 6 6 we further consider reported instrumental amplitudes to estimate an instrumental moment magnitude of mw 6 6 0 5 our preferred final estimate is mw 6 5 based on available constraints including aftershock locations inferred from data recorded on portable instruments we propose that the earthquake nucleated east of the city of santa barbara closer to the coast than previously estimated and ruptured unilaterally 30 km to the west possibly along the south dipping mesa rincon creek and the more ranch fault systems contrary to suggestions made in earlier studies e g willis 1925a relatively high intensities 50 km west of santa barbara can then be explained by directivity rather than involvement of the santa ynez fault finally we discuss the possibility that the earthquake was triggered by the larger mw 6 6 clarkston montana earthquake the previous day or induced by oil production in the summerland oil field

causal fracture prediction curvature stress and geomechanics we propose scaling volume curvature measurements with material property estimates to produce a superior prediction of natural fractures curvature is one of many indirect fracture inferring attributes it does not detect fractures but is causally related to them through the assumption that increasing curvature relates to increasing strain there are many other variables that are causally related to fractures we propose that it would be advantageous to create combinations of these causal variables with curvature some of the most well known and important causes of variations in natural fracture density are material properties relating to brittleness material properties are critical geologically at all scales from large scale regional studies to prospect level inquiries because the properties may vary significantly within individual formations and between formations these vertical and lateral changes in material properties may be important and should be considered in fracture estimation along with c

earthquakes induced by hydraulic fracturing in poland township ohio felt seismicity induced by hydraulic fracturing is very rare with only a handful of reported cases worldwide using an optimized multistation cross correlation template matching routine 77 earthquakes were identified in poland township mahoning county ohio that were closely related spatially and temporally to active hydraulic fracturing operations we identified earthquakes as small as local magnitudes m l 1 up to 3 potentially one of the largest earthquakes induced by hydraulic fracturing in the united states these events all occurred from 4 to 12 march 2014 and the rate decayed once the ohio department of natural resources issued a shutdown of hydraulic fracturing at a nearby well on 10 march using a locally derived velocity model and double difference relocation the earthquakes occurred during six stimulation stages along two horizontal well legs that were located 0 8 km away nearly 100 stimulation stages in nearby wells at greater distances from the earthquake source region did not coincide with detected seismicity during the sequence hypocenters migrated 600 m along an azimuth of 083 defining a vertically oriented plane of seismicity close to the top of the precambrian basement the focal mechanism determined for the m l 3 event had a vertically oriented left lateral fault plane consistent with the earthquake distribution and the regional stress field the focal mechanism orientation and depth of hypocenters were similar to those of the 2011 youngstown earthquake sequence that occurred 18 km to the northwest and was correlated with wastewater injection instead of hydraulic fracturing considering the relatively large magnitude of the poland township events and the b value of 0 89 it appears the hydraulic fracturing induced slip along a pre existing fault fracture zone optimally oriented in the regional stress field

common features of the excitation and propagation of strong ground motion for north american earthquakes the central matter of this investigation is the commonly held belief that eastern north america ena earthquakes are felt to much greater distances at all levels of intensity than their western u s wus counterparts of the same source strength by comparing the areas enclosed by modified mercalli intensities i to iii felt iv v vi and vii for ena and wus earthquakes at the same source strength we find that this proposition is mostly false at damaging levels of ground motion intensities vi to vii and greater for m 7 neither should such differences exist if strong ground motion is confined to r 150 km and arrives principally as body waves and if ena and wus earthquakes share the same average stress drop in fact observable differences in the areas enclosed by intensity vi a vi for ena and wus earthquakes at the same m point to slight but significant differences in stress drop the ena earthquakes having stress drops a factor of about 2 higher only for the largest earthquakes m 7 as the 1811 to 1812 new madrid and 1886 charleston earthquakes seem to be can strong ground motion propagate to much greater distances as low loss higher mode surface waves in ena relative to wus the strong dependence of high frequency strong ground motion on stress drop and its weak dependence on m admit the possibility that the 1811 to 1812 events and the 1886 charleston earthquakes are no larger than m 6 to 7 provided that their stress drops are higher than average by a factor of 2 or so

elastic anisotropy due to aligned cracks in porous rock all theoretical expressions which relate the characteristics of saturated aligned cracks to the associated elastic anisotropy are restricted in some important way for example to the case of stiff pore fluids or of the absence of equant porosity or of a moderately high frequency band because of these restrictions previous theory is not suitable for application to the upper crust where the pore fluid is brine kf k820 the equant porosity is often substantial p 0 1 and the frequency band is sonic to seismic this work removes these particular restrictions recognizing in the process an important mechanism of dispersion a notable feature of these more general expressions is their insensitivity at low frequency to the aspect ratio of the cracks only the crack density is critical an important conclusion of this more general model is that many insights previously achieved concerning the shear wave splitting due to vertical aligned saturated cracks are sustained however conclusions on crack orientation or crack aspect ratio which were derived from p wave data or from shear wave critical angles may need to be reconsidered further the non linear coupling between pores and cracks due to pressure equalization effects means that the linear schoenberg muir calculus may not be applied to such systems the theory receives strong support from recent data by rathore et al on artificial samples with controlled crack geometry

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

nucleation and arrest of dynamic rupture induced by reservoir depletion seismic events induced by the depletion of hydrocarbon reservoirs can cause damage to housing and cause societal and economic unrest however the factors controlling the nucleation and size of production induced seismic events are not well understood here we used geomechanical modeling of production induced stresses and dynamic rupture modeling to assess the conditions controlling down dip rupture size a generic model of offset depleting reservoir compartments separated by a fault was modeled in 2 d using the finite element package diana fea linear slip weakening was used to control fault friction behavior fault reactivation was computed in a quasi static analysis simulating stresses during reservoir depletion followed by a fully dynamic analysis simulating seismic rupture the sensitivity of reactivation and rupture size to in situ stress dynamic friction critical slip distance and reservoir offset was evaluated after reactivation a critical fault length was required to slip before seismic instability could occur in a subsequent fully dynamic analysis the propagation and arrest of dynamic rupture was simulated rupture remained mostly confined to the reservoir interval but could also propagate into the overburden and underburden or sometimes transition into a run away rupture propagation outside the reservoir interval was promoted by a critical in situ stress a large stress drop a small fracture energy and no or little reservoir offset with increasing offset up to the reservoir thickness reactivation was promoted but dynamic rupture size decreased 2019 the authors

a century of oil field operations and earthquakes in the greater los angeles basin southern california abstract most of the seismicity in the los angeles basin la basin occurs at depth below the sediments and is caused by transpressional tectonics related to the big bend in the san andreas fault however some of the seismicity could be associated with fluid extraction or injection in oil fields that have been in production for almost a century and cover 17 of the basin in a recent study first the influence of industry operations was evaluated by analyzing seismicity characteristics including normalized seismicity rates focal depths and b values but no significant difference was found in seismicity characteristics inside and outside the oil fields in addition to identify possible temporal correlations the seismicity and available monthly fluid extraction and injection volumes since 1977 were analyzed second the production and deformation history of the wilmington oil field were used to evaluate whether other oil fields are likely to experience similar surface deformation in the future thir

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

estimation of rock physics properties from seismic attributes part 1 strategy and sensitivity analysis abstractthe quantitative estimation of rock physics properties is of great importance in any reservoir characterization we have studied the sensitivity of such poroelastic rock physics properties to various seismic viscoelastic attributes velocities quality factors and density because we considered a generalized dynamic poroelastic model our analysis was applicable to most kinds of rocks over a wide range of frequencies the viscoelastic attributes computed by poroelastic forward modeling were used as input to a semiglobal optimization inversion code to estimate poroelastic properties porosity solid frame moduli fluid phase properties and saturation the sensitivity studies that we used showed that it was best to consider an inversion system with enough input data to obtain accurate estimates however simultaneous inversion for the whole set of poroelastic parameters was problematic due to the large number of parameters and their trade off consequently we restricted the sensitivity tests to

observations of static coulomb stress triggering of the november 2011 m5 7 oklahoma earthquake sequence in november 2011 a m5 0 earthquake occurred less than a day before a m5 7 earthquake near prague oklahoma which may have promoted failure of the mainshock and thousands of aftershocks along the wilzetta fault including a m5 0 aftershock the m5 0 foreshock occurred in close proximity to active fluid injection wells fluid injection can cause a buildup of pore fluid pressure decrease the fault strength and may induce earthquakes keranen et al 2013 links the m5 0 foreshock with fluid injection but the relationship between the foreshock and successive events has not been investigated here we examine the role of coseismic coulomb stress transfer on earthquakes that follow the m5 0 foreshock including the m5 7 mainshock we resolve the static coulomb stress change onto the focal mechanism nodal plane that is most consistent with the rupture geometry of the three m 5 0 earthquakes as well as specified receiver fault planes that reflect the regional stress orientation we find that coulomb stress is increased e g fault failure is promoted on the nodal planes of 60 of the events that have focal mechanism solutions and more specifically that the m5 0 foreshock promoted failure on the rupture plane of the m5 7 mainshock we test our results over a range of effective coefficient of friction values hence we argue that the m5 0 foreshock induced by fluid injection potentially triggered a cascading failure of earthquakes along the complex wilzetta fault system

detection of gas in sandstone reservoirs using avo analysis a 3 d seismic case history using the geostack technique the geostack technique is a method of analyzing seismic amplitude variation with offset avo information one of the outputs of the analysis is a set of direct hydrocarbon indicator traces called fluid factor traces the fluid factor trace is designed to be low amplitude for all reflectors in a clastic sedimentary sequence except for rocks that lie off the mudrock line the mudrock line is the line on a crossplot of p wave velocity against s wave velocity on which water saturated sandstones shales and siltstones lie some of the rock types that lie off the mudrock line are gas saturated sandstones carbonates and igneous rocks in the absence of carbonates and igneous rocks high amplitude reflections on fluid factor traces would be expected to represent gas saturated sandstones of course this relationship does not apply exactly in nature and the extent to which the mudrock line model applies varies from area to area however it is a useful model in many basins of the world including the one

earthquake hypocenters and focal mechanisms in central oklahoma reveal a complex system of reactivated subsurface strike slip faulting the sharp increase in seismicity over a broad region of central oklahoma has raised concern regarding the source of the activity and its potential hazard to local communities and energy industry infrastructure since early 2010 numerous organizations have deployed temporary portable seismic stations in central oklahoma in order to record the evolving seismicity in this study we apply a multiple event relocation method to produce a catalog of 3639 central oklahoma earthquakes from late 2009 through 2014 regional moment tensor rmt source parameters were determined for 195 of the largest and best recorded earthquakes combining rmt results with relocated seismicity enabled us to determine the length depth and style of faulting occurring on reactivated subsurface fault systems results show that the majority of earthquakes occur on near vertical optimally oriented ne sw and nw se strike slip faults in the shallow crystalline basement these are necessary first order observations required to assess the potential hazards of individual faults in oklahoma

poroelastic stress changes associated with primary oil production in the los angeles basin california abstract while recent investigations of induced earthquakes have focused on earthquakes associated with wastewater injection and unconventional recovery methods the potential for earthquakes to be induced by primary production has long been recognized we use boundary element methods to quantify the predicted geometry and amplitude of stress and strain changes associated with removal of large volumes of fluids in poroelastic reservoirs focusing on the los angeles basin la basin in california we show that significant stress perturbations upward of 0 1 mpa while localized typically extended several kilometers away from production horizons by the early 1940s by this time production horizons in the southwestern la basin were 2 4 km deep models thus predict that stress conditions would have been perturbed significantly on faults at the upper edge of the seismogenic brittle crust typically around 6 km predicted stress and strain changes associated with oil fields in the southwestern la basin durin

acoustic and petrophysical relationships in low shale sandstone reservoir rocks this paper describes the measurements of the acoustic and petrophysical properties of two suites of low shale sandstone samples from north sea hydrocarbon reservoirs under simulated reservoir conditions the acoustic velocities and quality factors of the samples saturated with different pore fluids brine dead oil and kerosene were measured at a frequency of about 0 8 mhz and over a range of pressures from 5 mpa to 40 mpa the compressional wave velocity is strongly correlated with the shear wave velocity in this suite of rocks the ratio v p v s varies significantly with change of both pore fluid type and differential pressure confirming the usefulness of this parameter for seismic monitoring of producing reservoirs the results of quality factor measurements were compared with predictions from biot flow and squirt flow loss mechanisms the results suggested that the dominating loss in these samples is due to squirt flow of fluid between the pores of various geometries the contribution of the biot flow loss mechanism to the total loss is negligible the compressional wave quality factor was shown to be inversely correlated with rock permeability suggesting the possibility of using attenuation as a permeability indicator tool in low shale high porosity sandstone reservoirs

palaeoecological evidence for the prehistoric settlement of bodmin moor cornwall southwest england part ii land use changes from the neolithic to the present abstract radiocarbon dated pollen sequences from two areas of bodmin moor rough tor in the north west and the east moor are presented and the evidence for settlement in the prehistoric period on the moor considered the nature and extent of human impact in the two areas are compared and the evidence for anthropogenic activity in the environmental record is related to that deduced from the archaeology a tentative model of settlement and land use from the neolithic to the iron age is proposed with early activity in the neolithic leading to a peak of settlement in the bronze age and continuing activity on the moor during the iron age and into the romano british period human activity may have begun in the earliest neolithic and was possibly associated with construction of the hill top enclosure at rough tor the bronze age peak of activity that is apparent in the archaeology is also represented in the palynological record activity in the iron age and later shows that the moorland was intensively used for grazing and probably hay production until settlement expanded back onto the uplands in the medieval period this last phase resulted in the impoverishment of the soils and development of the current acid grassland and heath dominated vegetation of the moor finally various suggestions are made for future research into the palaeoecology of bodmin moor

estimating earthquake location and magnitude from seismic intensity data analysis of modified mercalli intensity mmi observations for a training set of 22 california earthquakes suggests a strategy for bounding the epicentral region and moment magnitude m from mmi observations only we define an intensity magnitude m i that is calibrated to be equal in the mean to m m i mean m i where m i mmi i 3 29 0 0206 i 1 68 and i is the epicentral distance km of observation mmi i the epicentral region is bounded by contours of rms m i rms m i m i rms m i m i where rms is the root mean square rms m i m i is the minimum rms over a grid of assumed epicenters and empirical site corrections and a distance weighting function are used empirical contour values for bounding the epicenter location and empirical bounds for m estimated from m i appropriate for different levels of confidence and different quantities of intensity observations are tabulated the epicentral region bounds and m i obtained for an independent test set of western california earthquakes are consistent with the instrumental epicenters and moment magnitudes of these earthquakes the analysis strategy is particularly appropriate for the evaluation of pre 1900 earthquakes for which the only available data are a sparse set of intensity observations

later holocene vegetation history of the isles of scilly uk coastal influence and human land use in a small island context small islands tend to experience exacerbated environmental social vulnerabilities due to isolation size and a small resource base the response of social communities to environmental stress can be addressed by compiling palaeoecological proxies for land management alongside archaeological records this paper presents pollen data from four new late holocene sequences that lie around sea level on the isles of scilly south west england to understand the impact of coastal change on island communities interpretation of sequences near the coastal zone can be confounded by problems in disentangling human impact from maritime and wetland influence multivariate analysis is used to separate samples influenced by maritime conditions and wetland development from inland human land management practices during the bronze age clearance of woodland resulted in an intensively managed pastoral system and archaeological datasets indicate that maritime resources formed an important part of the subsistence economy despite coastal change that resulted in loss of land area and reduced the extent of the intertidal zone the pollen data and evidence from existing archaeological data show continuity through later prehistory and into the medieval period the archaeological data and pollen evidence point towards a highly resilient community that employed a mixed and varied subsistence base copyright c 2015 john wiley sons ltd

piping and pipeflow in a deep peat catchment abstract natural pipes are common in many upland blanket peats yet little is known about pipe network morphology or pipeflow processes most information on soil piping comes from the shallow peaty podzols of the welsh uplands where monitoring suggests that pipes may be important contributors to streamflow this paper presents information on piping and pipeflow from a deep upland blanket peat catchment in the pennine hills of northern england pipe outlets are found throughout the soil profile ranging from the underlying substrate at 3 m depth to pipes which are within a few centimetres of the surface mean pipe diameters range from 3 to 70 cm some pipes are over 150 m long slopes in the catchment are less steep than those usually associated with soil piping continuous flow records were obtained from 15 gauging sites on 8 separate pipes the pipeflow response from deep blanket peat was found to be different to that reported in the shallow peaty podzols of the welsh uplands the distinction between ephemeral and perennial pipe types does not appear to be useful within the deep pennine blanket peat response times from all of the pipes are short even from pipes deep within the peat at the same time pipes have a prolonged recession limb such that they maintain low flow for longer periods than most other runoff production processes within the catchment pipeflow contributes around 10 of the streamflow volume but can at times contribute up to 30 soil pipes may therefore be far more important in some upland peat catchments than previous work has hitherto suggested

wave propagation effects on amplitude variation with offset measurements a modeling study wave propagation effects can significantly affect amplitude variation with offset avo measurements these effects include spreading losses transmission losses interbed multiples surface multiple reflections p sv mode converted waves and inelastic attenuation examination of prestack elastic synthetic seismograms suggests that spreading losses and the transmission losses plus compressional interbed multiples are manifest mainly as a time and offset effect on the primary reflections the surface related multiples and the p sv mode converted waves interfere with prestack amplitudes inducing distortions in the avo pattern such distortions cause large variances in avo model fitting prestack viscoelastic synthetic seismograms also suggest that inelastic attenuation further complicates the avo response because of the offset and time variant amplitude decay effects and the phase change due to dispersion together all these effects severely alter avo behavior and result in serious errors in avo parameter

historical context and chronology of bronze age land enclosure on dartmoor uk the upland of dartmoor southwest england is one of the flagship prehistoric landscapes within britain owing to the excellent survival of extensive prehistoric coaxial field systems archaeological surveys and rescue excavations during the 1970s and 1980s did much to further the understanding of this landscape however much remains to be explored in particular the chronology of enclosure the nature of the pre enclosure landscape and the relationship between bronze age communities and their environment reconsideration of this landscape is important given the place it holds in our understanding of subdivision of the landscape across northwest europe during prehistory this paper presents new palaeoecological data recovered as part of an integrated archaeological and palaeoecological project on northeast dartmoor the sequences detailed here include the first dated neolithic period palaeoenvironmental data from within the prehistoric enclosed land on the moor providing a longer term context for enclosure neolithic groups are implicated in the first establishment of heathland in the study area at around 3630 3370 cal bc during the early bronze age reestablishment of hazel scrub in the study area implies reduced use of the upland although it is not clear whether this is local or indicative of the wider landscape a combination of pollen and fungal spore data indicates a substantial shift to species rich grassland with grazing animals at c 1480 cal bc in a phase that lasted 400 years the later bronze age and early iron age are characterised by low intensity use of the upland these data provide new chronological data for land cover change on dartmoor and whilst they broadly confirm existing models of upland land use in later prehistory their proximity to the standing archaeology affords a more nuanced interpretation of local change

anisotropy estimate for the horn river basin from sonic logs in vertical and deviated wells abstract shale anisotropy must be quantified to obtain reliable information about reservoir fluids lithology and pore pressure from seismic data failure to account for anisotropy in seismic processing can lead to errors in normal moveout nmo dip moveout dmo migration time to depth conversion and amplitude variation with offset avo analysis kriged estimates of density vertical compressional wave and shear wave velocities were derived from vertical wells in an area of interest in the horn river resource play in northeastern british columbia the kriged predictions were compared with measured logs along the trajectory of a deviated well whereas the density comparison provided a blind test of kriging accuracy because density is scalar and independent of well deviation the same comparison for sonic velocities revealed that they are systematically higher than the kriged vertical velocities this difference was used to estimate anisotropy parameters at the location of the deviated well the fac

on a possible connection between three major earthquakes in california and oil production abstract the 1983 coalinga m 6 5 the 1985 kettleman north dome m 6 1 and the 1987 whittier narrows m 5 9 earthquake sequences each occurred beneath major producing oil fields and caused an aftershock sequence whose epicentral extent coincides approximately with that of the overlying oil field despite this coincidence a causal relationship between these sequences and oil production has been discounted because the earthquakes were located at depths of the order of 10 km whereas oil production is confined to the topmost several km moreover because all three oil fields coalinga kettleman north dome and montebello are situated on anticlines that have undergone recent uplift as a consequence of horizontal tectonic compression of the crust natural earthquakes are not unexpected a mechanical connection between oil production and the earthquake sequence is suggested however by the observation that in each case the total seismic deformation was just that required to offset the force imbalance caused by oil production specifically for each of the three sequences m 0 2 m c where m 0 is the sum of the seismic moments is the modulus of rigidity m is the mass of the fluid removed due to oil production is the fraction of the upper crust that is seismogenic and c is the average upper crustal density in essence net extraction of oil and water reduces slightly the average density of the upper crust causing an isostatic imbalance the ductile lower crust deforms in response to this imbalance thus increasing the load on the seismogenic layer which fails seismically to thicken the crust so as to restore static equilibrium locally accordingly earthquakes near the base of the upper crust may be an expected outcome of major oil production from growing anticlines irrespective of the depths of the producing formations

seismic velocities for hydrate bearing sediments using weighted equation a weighted equation based on the three phase time average and wood equations is applied to derive a relationship between the compressional wave p wave velocity and the amount of hydrates filling the pore space the proposed theory predicts accurate p wave velocities of marine sediments in the porosity range of 40 80 and provides a practical means of estimating the amount of in situ hydrate using seismic velocity the shear s wave velocity is derived under the assumption that the p to s wave velocity ratio of the hydrated sediments is proportional to the weighted average of the p to s wave velocity ratios of the constituent components of the sediment in the case that all constituent components are known a weighted equation using multiphase time average and wood equations is possible however this study showed that a three phase equation with modified matrix velocity compensated for the clay content is sufficient to accurately predict the compressional wave velocities for the marine sediments this theory was applied to the laboratory measurements of the p and s wave velocities in permafrost samples to infer the amount of ice in the unconsolidated sediment the results are comparable to the results obtained by repeatedly applying the two phase wave scattering theory the theory predicts that the poisson s ratio of the hydrated sediments decreases as the hydrate concentration increases and the porosity decreases in consequence the amplitude versus offset avo data for the bottom simulating reflections may reveal positive negative or no avo anomalies depending on the concentration of hydrates in the sediments

the attenuation of seismic intensity in italy a bilinear shape indicates the dominance of deep phases at epicentral distances longer than 45 km the attenuation of seismic intensity with distance in italy is analyzed by using felt intensity report data obtained from two comprehensive historical databases recently made available the observed attenuation pattern that in the past was interpreted as a logarithmic or root square or cubic attenuation law shows quite clearly two different linear trends in the near and in the far field at distances shorter than 45 km the decrease of the intensity with distance is about one degree per 20 km while at longer distances the slope is about one degree per 50 km this is in agreement with some recent findings of realistic modeling of seismic ground motion that has been explained as the transition from upper crust direct sg phases to waves reflected at the moho controlling the energy main release the slope of the curve in the far field shows a regional dependence in agreement with recent works on the attenuation of pn and sn phases in italy if effective this correlation might allow us to discriminate the contribution of crustal and subcrustal paths in seismic intensity attenuation studies manuscript received 31 may 2000

explicit use of the biot coefficient in predicting shear wave velocity of water saturated sediments predicting the shear wave s wave velocity is important in seismic modelling amplitude analysis with offset and other exploration and engineering applications under the low frequency approximation the classical biot gassmann theory relates the biot coefficient to the bulk modulus of water saturated sediments if the biot coefficient under in situ conditions can be estimated the shear modulus or the s wave velocity can be calculated the biot coefficient derived from the compressional wave p wave velocity of water saturated sediments often differs from and is less than that estimated from the s wave velocity owing to the interactions between the pore fluid and the grain contacts by correcting the biot coefficients derived from p wave velocities of water saturated sediments measured at various differential pressures an accurate method of predicting s wave velocities is proposed numerical results indicate that the predicted s wave velocities for consolidated and unconsolidated sediments agree well with measured velocities

paleoseismicity of the north branch of the newport inglewood fault zone in huntington beach california from cone penetrometer test data abstract application of cone penetrometer testing cpt is a promising method for studying subsurface fault zones in stratified unconsolidated sediment where trenching is not feasible analysis of data from 72 cpts spaced 7 5 to 30 0 m apart and 9 borings indicates that the north branch fault the active strand of the newport inglewood fault zone nifz in huntington beach has generated at least three and most likely five recognizable surface ruptures in the past 11 7 0 7 ka additional smaller earthquakes similar to the m w 6 4 1933 long beach earthquake may also have occurred but would not be recognizable with this method the minimum right lateral holocene slip rate of the nifz in the study area is estimated to be 0 34 to 0 55 mm yr the actual slip rate may be significantly higher

amplitude versus offset variations in gas sands seismic reflections from gas sands exhibit a wide range of amplitude versus offset avo characteristics the two factors that most strongly determine the avo behavior of a gas sand reflection are the normal incidence reflection coefficient r0 and the contrast in poisson s ratio at the reflector of these two factors r0 is the least constrained based on their avo characteristics gas sand reflectors can be grouped into three classes defined in terms of r0 at the top of the gas sand class 1 gas sands have higher impedance than the encasing shale with relatively large positive values for r0 class 2 gas sands have nearly the same impedance as the encasing shale and are characterized by values of r0 near zero class 3 sands have lower impedance than the encasing shale with negative large magnitude values for r0 each of these sand classes has a distinct avo characteristic an example of a gas sand from each of the three classes is presented in the paper the class 1 example involves a hartshorn channel s