microseismic event location for monitoring co2 injection using double difference tomography increases in pore pressure and volume caused by co2 injection will perturb the ambient stress field and possibly trigger brittle failure on small fractures or faults resulting in microearthquakes monitoring this induced seismicity can help understand the migration of the co2 front and the stress and strain changes in the reservoir miyazawa et al 2008 as part of research efforts of the southwest regional partnership on carbon sequestration supported by the u s department of energy and managed by the national energy technology laboratory a large number of microseismic events have been recorded since early 2008 using a geophone string cemented into a well for monitoring co2 injection at the aneth oil field in utah we use double difference tomography to obtain high precision locations of microseismic events and improve the spatial resolution of the velocity structure simultaneously the double difference seismic tomography method was developed for improving earthquake source locations and tomograph

narrow angle representations of the phase and group velocities and their applications in anisotropic velocity model building for microseismic monitoring it is usually believed that angular aperture of seismic data should be at least 20 to allow estimation of the subsurface anisotropy although this is certainly true for reflection data for which anisotropy parameters are inverted from the stacking velocities or the nonhyperbolic moveout traveltimes of direct p and s waves recorded in typical downhole microseismic geometries make it possible to infer seismic anisotropy in angular apertures as narrow as about 10 to ensure the uniqueness of such an inversion it has to be performed in a local coordinate frame tailored to a particular data set because any narrow fan of vectors is naturally characterized by its average direction we choose the axes of the local frame to coincide with the polarization vectors of three plane waves corresponding to such a direction this choice results in a significant simplification of the conventional equations for the phase and group velocities in anisotropic media and makes it possible to predict which elements of the elastic stiffness tensor are constrained by the available data we illustrate our approach on traveltime synthetics and then apply it to perforation shot data recorded in a shale gas field our case study indicates that isotropic velocity models are inadequate and accounting for seismic anisotropy is a prerequisite for building a physically sound model that explains the recorded traveltimes

tilted ti models in surface microseismic monitoring abstracta recently published analytic technique for computing locations of microseismic events jointly with velocities of homogeneous isotropic media was extended to surface microseismic monitoring and transversely isotropic models with tilted symmetry axes tti the analysis of traveltimes of the direct p sv and sh waves conducted under the assumptions of homogeneity and weak anisotropy indicated that the sv wave data acquired in modern wide azimuth surface microseismic surveys yield uniquely solvable joint inverse problems for an arbitrary symmetry axis tilt whereas the tilts should be close to 90 from the vertical for the p waves propagating in anelliptically anisotropic media and strictly equal to 90 for the sh waves to maintain the uniqueness of the joint inversion these theoretical findings confirmed on ray tracing synthetic were applied to a field microseismic data set the p waves excited by microseismic events were found to exhibit significantly flatter moveouts and better focused st

an efficient algorithm for double difference tomography and location in heterogeneous media with an application to the kilauea volcano 1 improving our understanding of crustal processes requires a better knowledge of the geometry and the position of geological bodies in this study we have designed a method based upon double difference relocation and tomography to image as accurately as possible a heterogeneous medium containing seismogenic objects our approach consisted not only of incorporating double difference in tomography but also partly in revisiting tomographic schemes for choosing accurate and stable numerical strategies adapted to the use of cross spectral time delays we used a finite difference solution to the eikonal equation for travel time computation and a tarantola valette approach for both the classical and double difference three dimensional tomographic inversion to find accurate earthquake locations and seismic velocity estimates we estimated efficiently the square root of the inverse model s covariance matrix in the case of a gaussian correlation function it allows the use of correlation length and a priori model variance criteria to determine the optimal solution double difference relocation of similar earthquakes is performed in the optimal velocity model making absolute and relative locations less biased by the velocity model double difference tomography is achieved by using high accuracy time delay measurements these algorithms have been applied to earthquake data recorded in the vicinity of kilauea and mauna loa volcanoes for imaging the volcanic structures stable and detailed velocity models are obtained the regional tomography unambiguously highlights the structure of the island of hawaii and the double difference tomography shows a detailed image of the southern kilauea caldera upper east rift zone magmatic complex

a new calibration point for the late miocene section of the geomagnetic polarity time scale 40ar 39ar dating of lava flows from akaroa volcano new zealand recent dating of geomagnetic field reversals over the past 2 ma by both the radiometric and astrochronologic techniques indicates that the k ar derived ages for these reversals are too young we report herein on 40ar 39ar incremental heating study of two geomagnetic field reversals trapped in lavas on akaroa volcano new zealand that demonstrate that the k ar derived ages for field reversals at 10 9 ma are too young by about 7 the new age for the termination of chron 5 a critical tie point on the geomagnetic polarity time scale for late miocene time is 9 67 0 11 ma

development and applications of double difference seismic tomography double difference dd tomography is a generalization of dd location it simultaneously solves for the three dimensional velocity structure and seismic event locations dd tomography uses a combination of absolute and more accurate differential arrival times and hierarchically determines the velocity structure from larger scale to smaller scale this method is able to produce more accurate event locations and velocity structure near the source region than standard tomography which uses only absolute arrival times we conduct a stability and uncertainty analysis of dd tomography based on a synthetic data set currently three versions of the dd tomography algorithms exist tomodd tomofdd and tomoadd tomodd assumes a flat earth model and uses a pseudo bending ray tracing algorithm to find rays between events and stations while tomofdd uses a finite difference travel time algorithm and the curvature of the earth is considered both codes are based on a regularly distributed inversion grid with the former for a local scale and the latter for a regional scale in contrast tomoadd adapts the inversion mesh to match with the data distribution based on tetrahedral and voronoi diagrams we discuss examples of applying dd tomography to characterize fault zone structure image high resolution structure of subduction zones and determine the velocity structure of volcanoes

ages of the steens and columbia river flood basalts and their relationship to extension related calc alkalic volcanism in eastern oregon discussion hooper et al 2002 1 present stratigraphic chemical and field relationships for tertiary volcanic rocks of eastern oregon and conclude that 1 the imnaha basalt are 15 5 m y old and 2 the steens basalt ca 16 6 ma represents the earliest eruptions of the columbia river basalt flood

inversion of p wave vsp data for local anisotropy theory and case study we discuss improve and apply the slowness polarization method for estimating local anisotropy from vsp data although the idea of fitting a given anisotropic model to the apparent slownesses measured along a well and polarization vectors recorded by three component downhole geophones is hardly new we extend the area of applicability of the technique and make the anisotropic inversion more robust by eliminating the most operationally difficult and noisy portion of the data the shear waves we show that the shear wave velocity is actually unnecessary for fitting the slowness of polarization dependence of p wave vsp data for the most common geometry of a vertical borehole in a vertically transversely isotropic subsurface such data are governed by the p wave vertical velocity vp0 and two quantities vsp and vsp that describe the influence of anisotropy these quantities depend on conventional anisotropic coefficients and and absorb the s wave velocity we apply the developed theory to a 2d walka

paleomagnetism of miocene east african rift sediments and the calibration of the geomagnetic reversal time scale paleomagnetic stratigraphy and k ar age determinations are reported for the type section of the middle miocene ngorora formation found in the kenya rift valley the magnetostratigraphy is well correlated to the geomagnetic reversal time scale grts and spans from the lower part of chron c5 9 to chron c5ab r 14 k ar dates were determined for euhedral sanidines handpicked from seven tuff horizons within the ngorora formation and the underlying turn phonolite flow these dates can therefore be tied directly to the grts the eight dates fall into three discrete groups averaging 12 5 0 22 ma mean and standard deviation of results from four tuffs 11 6 0 06 ma mean and standard deviation from three tuffs and 10 16 0 38 average of three analyses from one tuff we interpret the age groups as resulting from three successive eruptive episodes the stratigraphic positions of which are well constrained in spite of episodic supply at the eruptive source sediment accumulation is continuous at the resolution of the grts this suggests that accumulation is controlled by basin subsidence rather than sediment supply sanidine dates support an age for the older boundary of marine magnetic anomaly 5 of about 10 ma as opposed to 11 12 ma suggested by the most recent results from icelandic basaltic lava flows

use of s wave attenuation from perforation shots to map the growth of the stimulated reservoir volume in the marcellus gas shale abstract water filled fractures stimulated by hydraulic fracturing will severely attenuate s waves by comparing the p and s wave amplitudes generated from perforation shots in the marcellus gas shale one can infer the existence and constrain the location of stimulated hydraulic fractures the waveforms of the perforation shots in unstimulated gas shale are first analyzed to define the prestimulation radiation pattern then the change of perforation shot s wave waveform is examined for information about the development of hydraulic fractures s wave attenuation validates the existence of offstage hydraulic fractures and the invasion of treatment fluid from another neighbor stage this method might have potential use in designing an active seismic survey to more effectively monitor hydraulic fracture stimulation beyond the current microseismic mapping techniques

microseismic hydraulic fracture imaging in the marcellus shale using head waves we studied microseismic data acquired from a geophone array deployed in the horizontal section of a well drilled in the marcellus shale near susquehanna county pennsylvania head waves were used to improve event location accuracy as a substitution of the traditional p wave polarization method we identified that resonances due to poor geophone to borehole coupling hinder arrival time picking and contaminate the microseismic data spectrum the traditional method had substantially greater uncertainty in our data due to the large uncertainty in p wave polarization direction estimation we also identified the existence of prominent head waves in some of the data these head waves are refractions from the interface between the marcellus shale and the underlying onondaga formation the source location accuracy of microseismic events can be significantly improved by using both the p s wave direct arrival times and the head wave arrival times based on the improvement we propose a new acquisition geometry and

fine tuning the radiometrically derived geomagnetic polarity time scale gpts for 0 10 ma new 40ar 39ar step heating ages for geomagnetic field reversals at 3 2 and 4 5 ma along with previous data at 1 2 10 and 16 ma are used to derive a geomagnetic polarity time scale for 0 10 ma these ages for chron boundaries are fitted to the relative widths of the polarity intervals on the ocean floor using a cubic spline technique the interpolated ages of chrons for 0 6 ma are in good agreement with the astronomical time scale and differ considerably from earlier attempts based in part on k ar dates significant differences between the interpolated ages and the astronomical time scale are noted for the onset of the olduvai and reunion sub chrons there is better agreement if 40ar 39ar data obtained from direct dating of these chrons is utilized this time scale is estimated to be accurate to 1 for 0 6 ma for 6 10 ma the lack of a tie point limits the accuracy to about 2

new 40ar 39ar dating of the grande ronde lavas columbia river basalts usa implications for duration of flood basalt eruption episodes by discussion abstract barry et al 2010 presented 40 ar 39 ar ages to argue for a very limited duration 0 4 m y for the eruption of the grande ronde lavas critical examination of their data sets shows 1 a number of their plateau ages are statistically invalid and 2 many of their groundmass matrix samples were altered and did not yield valid estimates of the time of crystallization in general their ages err on the young side reflecting partial 40 ar loss due to alteration and there is no compelling evidence therein to argue for very limited duration for the grande ronde basalt the imnaha grande ronde and wanapum basalt erupted within 0 7 m y starting at 16 4 ma by contrast the ages of barry et al 2010 span the interval 16 6 to 14 7 ma and in some instances are out of stratigraphic sequence

extending the astronomical polarity time scale into the miocene an astronomical time scale is presented for the late miocene based on the correlation of characteristic sedimentary cycle patterns in marine sections in the mediterranean to the 65 n summer insolation curve of la90 1 2 with present day values for the dynamical ellipticity of the earth and tidd dissipation by the moon this correlation yields ages for all sedimentary cycles and hence also for the recorded polarity reversals and planktonic foraminiferal and dinoflagellate events the tortonian messinian t m boundary placed at the first regular occurrence of the globorofuliu conomiozea group in the mediterranean is dated at 7 24 ma the duration of the messinian is estimated at 1 91 myr because the miocene pliocene boundary has been dated previously at 5 33 ma 3 the new time scale is confirmed by oar 3gar ages of volcanic beds and by the number of sedimentary cycles in the younger part of the mediterranean messinian

seafloor bioalteration of sulfide minerals results from in situ incubation studies we present results of incubation studies conducted at low temperatures 4 c in the vicinity of a seafloor hydrothermal vent system we reacted fe s cu and zn bearing minerals including pyrite marcasite chalcopyrite sphalerite elemental sulfur and a portion of a natural chimney sulfide structure for 2 months at the main endeavour segment of the juan de fuca ridge in the pacific ocean our study utilizes fluorescent in situ hybridizations fish scanning and transmission electron microscopy sem tem and light microscopic analysis the surfaces of these minerals are solely colonized by bacteria and not by archaea colonization densities vary over an order of magnitude with the following sequence elemental sulfur chimney sulfide marcasite pyrite sphalerite chalcopyrite and correspond well with the abiotic oxidation kinetics of these materials excepting elemental sulfur which is both the least reactive to oxidizing species and the most heavily colonized colonization densities also correspond with apparent degree of reaction dissolution pitting accumulation of secondary alteration products heavy accumulations of secondary fe oxides on fe bearing minerals most notably on the chimney sulfide form in situ as the result of mineral dissolution and the activity of neutrophilic fe oxidizing bacteria results suggest that mineral oxidizing bacteria play a prominent role in weathering of seafloor sulfide deposits and that microbial utilization of mineral substrates contributes to biomass production in seafloor hydrothermal environments

determination of s wave slowness from a linear array of borehole receivers summary locations of seismic events from a linear array of receivers may require determination of slowness vectors of arriving waves in an isotropic medium p waves are polarized along the slowness vector which enables direct determination of backazimuth i e azimuth to a source from a receiver from p wave polarization in contrast s waves usually have much larger signal to noise ratio than p waves but are polarized in a plane perpendicular to their slowness vectors which prevents direct determination of their backazimuth we have developed a novel technique to determine the slowness vector of s waves detected in a linear array of receivers in an isotropic medium we combine the s wave polarization measurement with the derivative of the s wave travel times along the array to obtain the full slowness vector and backazimuth the proposed method allows one to determine direction to sources of seismic events from a single linear array of receivers using only s waves this technique is not affected by sv waves which is shown by a test on a synthetic data set we also test the method on two real microseismic data sets from hydraulic fracturing treatments and show that it outperforms the backazimuth determination from p waves and from horizontal polarization of s waves

inversion of multicomponent multiazimuth walkaway vsp data for the stiffness tensor vertical seismic profiling vsp an established technique can be used for estimating in situ anisotropy that might provide valuable information for characterization of reservoir lithology fractures and fluids the p wave slowness components conventionally measured in multiazimuth walkaway vsp surveys allow one to reconstruct some portion of the corresponding slowness surface a major limitation of this technique is that the p wave slowness surface alone does not constrain a number of stiffness coefficients that may be crucial for inferring certain rock properties those stiffnesses can be obtained only by combining the measurements of p waves with those of s or ps modes here we extend the idea of horne and leaney who proved the feasibility of joint inversion of the slowness and polarization vectors of p and sv waves for parameters of transversely isotropic media with a vertical symmetry axis vti symmetry we show that there is no need to assume a priori vti symmetry or any other specific typ

estimation of effective anisotropy simultaneously with locations of microseismic events passive seismic tomography in which the event locations and the velocity model are inferred simultaneously is seldom used to process microseismic surveys acquired in the oil and gas industry we discuss advantages of applying tomographic ideas to typical microseismic data recorded in a single nearly vertical well to monitor hydraulic stimulation of a shale gas reservoir microseismic events are conventionally located in the energy industry applications using a velocity model derived from sonic logs and perforation shots instead of fixing the model as is normally done we alter it while locating the events this added flexibility not only makes it possible to accurately predict traveltimes of the recorded p and s waves but also provides a convincing evidence for anisotropy of the examined shale formation while we find that velocity heterogeneity does not need to be introduced to explain the data acquired at each stage of hydraulic fracturing the obtained models are suggestive of possible time laps

40ar 39ar dating of the brunhes matuyama geomagnetic field reversal magnetostratigraphic studies are widely used in conjunction with the geomagnetic polarity time scale gpts to date events in the range 0 to 5 million years ago a critical tie point on the gpts is the potassium argon age of the most recent brunhes matuyama geomagnetic field reversal astronomical values for the forcing frequencies observed in the oxygen isotope record in ocean drilling project site 677 suggest that the age of this last reversal is 780 ka thousand years ago whereas the potassium argon based estimate is 730 ka results from 4039 ar incremental heating studies on a series of lavas from maui that straddle the brunhes matuyama reversal give an age of 783 11 ka in agreement with the astronomically derived value the astronomically based technique appears to be a viable tool for dating young sedimentary sequences

importance of borehole deviation surveys for monitoring of hydraulic fracturing treatments during seismic monitoring of hydraulic fracturing treatment it is very common to ignore the deviations of the monitoring or treatment wells from their assumed positions for example a well is assumed to be perfectly vertical but in fact it deviates from verticality this can lead to significant errors in the observed azimuth and other parameters of the monitored fracture system geometry derived from microseismic event locations for common hydraulic fracturing geometries a 2 deviation uncertainty on the positions of the monitoring or treatment well survey can cause a more than 20 uncertainty of the inverted fracture azimuths furthermore if the positions of both the injection point and the receiver array are not known accurately and the velocity model is adjusted to locate perforations on the assumed positions several millisecond discrepancies between measured and modeled sh p traveltime differences may appear along the receiver array these traveltime discrepancies may then be misinterpreted as an effect of anisotropy and the use of such anisotropic model may lead to the mislocation of the detected fracture system the uncertainty of the relative positions between the monitoring and treatment wells can have a cumulative nonlinear effect on inverted fracture parameters we show that incorporation of borehole deviation surveys allows reasonably accurate positioning of the microseismic events in this study we concentrate on the effects of horizontal uncertainties of receiver and perforation positions understanding them is sufficient for treatment of vertical wells and also necessary for horizontal wells

on the feasibility of inversion of single well microseismic data for full moment tensor the existing paradigm widely accepted in the microseismic community asserts the impossibility of unambiguous estimation of full seismic moment tensor from three component data recorded in a single straight borehole the statement of inversion nonuniqueness related to the lack of illumination of the off plane moment component in the zero solid angle ray apertures tacitly assumes the slowness vectors normal to the relevant wave fronts to be confined to the plane containing the ray trajectories although such arrangements of the rays and slownesses do take place for vertical wells drilled in horizontally layered isotropic and vti transversely isotropic with a vertical symmetry axis formations azimuthal anisotropy commonly expected for hydraulically fractured hydrocarbon bearing shales makes the slowness vectors deviate from a plane arrange themselves into nonzero solid angle apertures and yield theoretically unique inverse problems for seismic moment tensors this paper examines those problems for the anisotropy parameters characterizing fractured shales and siltstones in the bakken their strong azimuthal anisotropy entails not only formally unique but importantly for practical applications well posed inverse problems resulting in robust estimates of the complete moment tensors from single borehole data

full waveform based complete moment tensor inversion and source parameter estimation from downhole microseismic data for hydrofracture monitoring downhole microseismic monitoring is a valuable tool in understanding the efficacy of hydraulic fracturing inverting for the moment tensor has gained increasing popularity in recent years as a way to understand the fracturing process previous studies utilize only part of the information in the waveforms such as direct p and s wave amplitudes and make far field assumptions to determine the source mechanisms the method is hindered in downhole monitoring when only limited azimuthal coverage is available in this study we develop an approach to invert for complete moment tensor using full waveform data recorded at a vertical borehole we use the discrete wavenumber integration method to calculate full wavefields in the layered medium by using synthetic data we find that at the near field range a stable complete moment tensor can be retrieved by matching the waveforms without additional constraints at the far field range we discover that the off plane moment tensor component is poorly constrained

feasibility of joint 1d velocity model and event location inversion by the neighbourhood algorithm using a set of synthetic p and s wave onsets computed in a 1d medium model from sources that mimic a distribution of microseismic events induced by hydrofrac treatment to a monitoring geophone array s we test the possibility to invert back jointly the model and events location we use the neighbourhood algorithm for data inversion to account for non linear effects of velocity model and grid search for event location the velocity model used is composed of homogeneous layers derived from sonic logging results for the case of one and two monitoring wells are compared these results show that the velocity model can be obtained in the case of two monitoring wells if they have optimal relative position the use of one monitoring well fails due to the trade off between the velocity model and event locations

a geomagnetic polarity time scale for the period 0 17 ma based on 40ar 39ar plateau ages for selected field reversals utilizing 40ar 39ar plateau ages for selected field reversals at 1 2 10 16 and 34 ma a geomagnetic polarity time scale gpts is constructed following the technique of cande and kent 1992 this differs markedly from previous gpts especially in middle late miocene time the ages for the chrons in post miocene time are in agreement with values derived by the astrochronological technique refinements in this gpts await acquisition of 40ar 39ar plateau ages for field reversals in the time frames 3 8 ma and 11 15 ma

recalibration of the geomagnetic polarity timescale the quest for improved time control to estimate rates of geologic and paleoenvironmental processes is central to the earth sciences until the middle of this century geochronology was based solely on macrofossil evolution providing the largely unmodified definition of geologic stages in the last few decades with impetus from the deep sea drilling project dsdp and the ocean drilling program odp microfossil biostratigraphy has become increasingly important although new radiometric techniques have resulted in improved absolute age precision the direct correlation of absolute ages to biozonations and hence to geologic stage boundaries remains poor this is due to the difficulty of finding materials suitable for radiometric dating which can be directly correlated to biozonations the bridge between biozonations and absolute ages and the interpolation between absolute ages are best accomplished particularly for cenozoic and late mesozoic time through the geomagnetic polarity timescale gpts the template for late jurassic to quaternary geomagnetic polarity is derived from oceanic magnetic anomalies as demonstrated by heirtzler et al 1968 the gpts can be constructed using oceanic magnetic anomaly record s assuming constant seafloor spreading rate s and interpolating between available radiometric ages in the last quadrennium there have been outstanding developments in radiometric dating and astrochronology which have greatly improved the absolute age control of the gpts

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

concordant sea floor spreading rates obtained from geochronology astrochronology and space geodesy reversals of the earth s magnetic field allied to sea floor spreading have left their imprint in the form of a magnetic tape recorder on the sea floor it is demonstrated that the geomagnetic polarity time scale for the past few million years derived utilizing a radiometric dates of magnetic field reversals trapped in subareal igneous rocks and b as derived from the milankovitch forcing frequencies and their imprint in the sedimentary environment are in good agreement further sea floor spreading rates calculated from these results are in substantial agreement with the rate of plate movement averaged over the last decade as obtained by space geodetic measurements since the principles underlying these dating techniques are entirely different it lends credence to the results obtained for sea floor spreading arguably the most fundamental process in plate tectonics

passive seismic tomography using induced seismicity at a petroleum field in oman a borehole network consisting of five monitoring wells monitored the induced seismicity at a producing petroleum field for about 11 months nearly 5400 microseismic events were analyzed and used to image the reservoir based on a new double difference dd seismic tomography the dd tomography method simultaneously solved for event locations and vp vs and vp vs models using absolute and differential p s and s p arrival times microseismicity in the field was caused primarily by compaction of the reservoir in and above the gas bearing formation and was distributed along the two major northeast southwest faults in the field the model resolution analysis based on the checkerboard test and the resolution matrix showed that the central part of the model was resolved relatively well for the depth range of 0 7 to 1 1 km clear velocity contrasts were imaged across most parts of the two northeast southwest faults the vp vs ratio estimates from the tomographic inversion were low 1 75 in the shallow

double difference tomography the method and its application to the hayward fault california we have developed a double difference dd seismic tomography method that makes use of both absolute and relative arrival times by reducing systematic errors using the more accurate relative arrival times the method produces an improved velocity model simultaneously it yields event locations of a quality equivalent to those of the dd location method while avoiding simplifying assumptions of that method we test this method on a synthetic dataset and find that it produces a more accurate velocity model and event locations than standard tomography we also test this method on a hayward fault california earthquake dataset spanning 1984 1998 the earthquakes relocated by this method collapse to a thin line along the fault trace consistent with previous results the dd velocity model has sharper velocity contrasts near the source region than the standard tomography model

geochemistry and morphology of metalliferous sediments and oxyhydroxides from the endeavour segment juan de fuca ridge abstract we present first data on the geochemistry mineralogy and morphology of near vent sediments 35 and 200 m from active vent and ridge flank sediments approximately 3 km from the vent field as well as oxyhydroxide deposits from the endeavour segment juan de fuca ridge the purpose of the study was to understand better the origin and characteristic features of metalliferous sediments associated with base and precious metal massive sulfides in volcanic terrains hydrothermal components in sediments are fe si s rich and mn fe si rich phases sulfides and barite which were exclusively derived from plume fallout sulfides are only a minor constituent of near vent sediments 2 4 wt and were not detected in ridge flank sediments the study suggests that the distribution of hydrothermal phases and associated elements in near vent and ridge flank sediments is affected mainly by processes of agglomeration dissolution absorption and settling that take place within a plume and to a lesser extent post depositional processes rapid deposition of sulfides in the vicinity of the vents is reflected in a sharp drop of the cu concentrations in sediments with increasing distance from the vents besides sulfides important carriers of pb cu zn and co in near vent sediments are fe mn oxyhydroxides that occur together with silica as aggregates of gel like material and flaky particles and as coatings on filaments away from the vents trace metals are mostly in fe mn oxyhydroxides and authigenic fe rich montmorillonite oxyhydroxides at the main endeavour field are interpreted to have originated from oxidation of mound sulfides accompanied by precipitation of primary fe oxyhydroxide silica from low temperature fluids at the mothra field seafloor deposits and chimney crusts composed of fe oxyhydroxide mn silica are considered to be direct precipitates from hydrothermal fluids that have been less diluted with seawater oxyhydroxide deposits exhibit unique microtextures that resemble mineralized microorganisms and may indicate existence of diverse microbial communities

extension of the astronomically calibrated polarity time scale to the miocene pliocene boundary the early pleistocene to late pliocene astronomically calibrated time scale of shackleton et al 1 and hilgen 2 is extended to the miocene pliocene boundary this is done by correlating the detailed record of caco3 cycles in the trubi and the lower part of the overlying narbone formation rossello composite section sicily to the astronomical record using 1 inferred phase relations between these caco3 cycles and the corresponding orbital cycles of precession and eccentricity and 2 calibration points provided by the previously established astronomical calibration of sapropelitic layers which occur in the topmost part of the caco3 record 2 this correlation allows all small scale caco3 cycles in the rossello composite section to be coded after the correlative precession peak and to be dated astronomically with an accuracy of 1 ky in combination with the available high resolution magnetostratigraphy it further allows the construction of an astronomically calibrated geomagnetic polarity time scale for the major part of the gilbert and gauss chrons this new time scale gives ages for the reversal boundaries of the kaena 3 04 3 11 ma and mammoth 3 22 3 33 ma the gilbert gauss chron boundary 3 58 ma and the reversal boundaries of the cochiti 4 18 4 29 ma nunivak 4 48 4 62 ma sidufjall 4 80 4 89 ma and thvera 4 98 5 23 ma these ages are significantly older than the ages given by conventional time scales age discrepancies gradually increase with increasing age the age of 5 32 ma for the miocene pliocene boundary as defined by the base of the trubi on sicily is almost 0 5 m y 9 5 older than the presently accepted age of 4 86 ma 3 these considerable discrepancies with the conventional time scale can either be explained by an consistent error in the decay constants used in k ar radiometric dating or more likely by diffusional loss of radiogenic argon

the changing vision of marine minerals abstract non fuel marine minerals are reviewed from the perspective of resources and their value as active analogs that can advance understanding of types of ancient ore deposits that formed in marine settings the theory of plate tectonics is the largest influence in expanding our vision of marine minerals and in developing our understanding of geologic controls of mineralization in space and time prior to the advent of plate tectonics we viewed the ocean basins as passive sinks that served as containers for particulate and dissolved material eroded from land this view adequately explained marine placer deposits heavy minerals and gems aggregates sand and gravel and precipitates phosphorites and manganese nodules although numerous sites of placer mineral deposits are known on continental shelves worldwide current activity pertains to diamond mining off southwestern africa tin mining off southeastern asia and intermittent gold mining off northwestern north america which are all surpassed economically by worldwide recovery of marine sand and gravel in turn dwarfed by offshore oil and gas with the advent of plate tectonics plate boundaries in ocean basins are recognized as active sources of mineralization in the form of hydrothermal massive sulfide deposits and proximal lower temperature deposits hosted in oceanic crust mafic at ocean ridges and felsic at volcanic island arcs and of magmatic ni cu sulfide chromite and pge deposits inferred to be present in the oceanic upper mantle lower crust based on their occurrence in ophiolites some 300 sites of hydrothermal active and relict mineralization most of them minor are known at this early stage of seafloor exploration on ocean ridges in fore arc volcanoes at back arc spreading axes and in arc rifts deposits formed at spreading axes and transported off axis by spreading are present in oceanic lithosphere but are virtually unknown the tag trans atlantic geotraverse hydrothermal field in the axial valley of the mid atlantic ridge latitude 26 n is considered to exemplify a major volcanogenic massive sulfide vms deposit forming at a spreading axis the most prospective of these occurrences lie within the 200 nautical mile 370 km wide exclusive economic zone eez of the nations of the volcanic island arcs of the western pacific where metal content of massive sulfides ag au ba cu pb sb zn exceeds that at ocean ridges plate tectonics early provided a framework for mineralization on the scale of global plate boundaries and is providing guidance to gradually converge on sites of mineralization through regional scales of plate reorganization with the potential to elucidate the occurrence of individual deposits e g eocene carlin type gold deposits investigation of the spectrum of marine minerals as active analogs of types of ancient mineral deposits is contributing to this convergence consideration of questions posed by brian skinner 1997 of what we do and do not know about ancient hydrothermal mineral deposits demonstrates the ongoing advances in understanding driven by investigation of marine minerals

joint inversion for effective anisotropic velocity model and event locations using s wave splitting measurements from downhole microseismic data abstractan accurate velocity model is essential in microseismic imaging layered sediments and subvertical cracks from tectonic stress and hydraulic fracturing make velocity models more complicated than isotropy or simple anisotropy such as vertical transverse isotropy downhole microseismic acquisition usually cannot achieve sufficient ray coverage that is required to develop a low symmetry anisotropic model from traveltimes alone to solve this problem we have developed a new type of data s wave splitting parameters the delay time of the slow s wave and fast s wave polarization direction to determine anisotropic models a genetic algorithm inversion is adopted to solve for the locations of events and the stiffness tensor of an anisotropic medium simultaneously we applied this method to synthetic waveforms from numerical modeling and successfully recovered the input event locations and the velocity model the effectiveness of this method is further demonstrated by using real microseismic data acqu

kinetics of sulfide mineral oxidation in seawater implications for acid generation during in situ mining of seafloor hydrothermal vent deposits abstract growth in global metal demand has fostered a new age of unconventional mining on the seafloor in situ pulverization and extraction of seafloor massive sulfide sms deposits is economically attractive due to minimal overburden and high ore grades however important environmental questions remain on the significance of localized acid generation via irreversible sulfide mineral oxidation data on the reaction kinetics are necessary to estimate anthropogenic acid production during seafloor mining laboratory experiments were performed to evaluate the effects of ph temperature dissolved oxygen and surface area on the oxidation rate of pyrrhotite and chalcopyrite in seawater these minerals were chosen to constrain the range of reaction rates because pyrrhotite oxidizes relatively quickly while chalcopyrite is kinetically slow the rate laws for the abiotic oxidation of pyrrhotite and chalcopyrite in seawater at 22 c are given in the form r sp k m o 2 a m h b where rsp is the specific rate moles m 2 sec 1 k is the rate constant oxygen and proton concentrations are expressed in molalities m and their reaction orders as a and b respectively the specific rate laws obtained for each sulfide studied are r sp pyrrhotite 10 7 27 m o 2 aq 0 51 0 08 m h 0 08 0 03 r sp chalcopyrite 10 9 38 m o 2 aq 1 16 0 03 m h 0 36 0 09 when used to quantitatively predict maximum acid generation rates these rate laws indicate that acid production from in situ sms mining is insufficient to exceed the buffering capacity of advecting seawater we also calculated the residence times of crushed sulfides in seawater with low po2 0 10 atm ph of 8 23 c and find that depending on grain size mining waste may persist near the seafloor for years the implications are positive in terms of slow acid production but potentially problematic considering the potential ecological effects of an unnatural influx of particulates

microseismic joint location and anisotropic velocity inversion for hydraulic fracturing in a tight bakken reservoir abstractto improve the accuracy of microseismic event locations we developed a new inversion method with double difference constraints for determining the hypocenters and the anisotropic velocity model for unconventional reservoirs we applied this method to a microseismic data set monitoring a middle bakken completion in the beaver lodge area of north dakota geophone arrays in four observation wells improved the ray coverage for the velocity inversion using an accurate anisotropic velocity model is important to correctly assess the height growth of the hydraulically induced fractures in the middle bakken our results showed that 1 moderate to strong anisotropy exists in all studied sedimentary layers especially in the upper and lower bakken shale formations where the thomsen parameters and can be greater than 0 4 2 all the events selected for high signal to noise ratio and used for the joint velocity inversion are located in the bakken and overlying lodgepole formations i e no events a

joint location of microseismic events in the presence of velocity uncertainty the locations of seismic events are used to infer reservoir properties and to guide future production activity as well as to determine and understand the stress field thus locating seismic events with uncertainty quantification remains an important problem using bayesian analysis a joint probability density function of all event locations was constructed from prior information about picking errors in kinematic data and explicitly quantified velocity model uncertainty simultaneous location of all seismic events captured the absolute event locations and the relative locations of some events with respect to others along with their associated uncertainties we found that the influence of an uncertain velocity model on location uncertainty under many realistic scenarios can be significantly reduced by jointly locating events many quantities of interest that are estimated from multiple event locations such as fault sizes and fracture spacing or orientation can be better estimated in practice using the proposed approach

oxidative dissolution of hydrothermal mixed sulphide ore an assessment of current knowledge in relation to seafloor massive sulphide mining highlights seafloor massive sulphides vary in mineralogy and oxidise at different rates galvanic cells play a role in increasing dissolution rates sms deposits that have been inactive for some time may have lost economic value the geochemistry of oxidation products has potential to be an exploration tool potential for anthropogenic release of heavy metals during seafloor mining any risk needs addressing by the isa prior to the formation of mining regulations the weathering process of seafloor massive sulphide sms deposits can be considered analogous to weathering of terrestrial volcanogenic massive sulphides vms deposits however in the context of sms deposits the process occurs in chemically buffered waters of near neutral ph resulting in the formation of insoluble fe oxy hydroxide minerals including goethite and hematite as well as sulphates such as jarosite as a result of this precipitation it is commonly assumed that any sms deposit is unlikely to exhibit a significant loss of metals dissolution and release of heavy metals into the water column however galvanic interactions have never been considered in this seafloor context whilst they have already been shown to have the ability to increase dissolution significantly in terrestrial deposits if heavy metal release is not temporally balanced by precipitation of oxide phases there is the potential that these metal occurrences lose economic value this is specifically significant if there is an industrial focus on exploiting deposits associated with hydrothermal vents that have been inactive for some time not only this but the geochemistry of weathering products gossans that are formed have the potential to be used as tools for exploration furthermore it is unknown what impact galvanic coupling may have with regards to anthropogenic release of heavy metals during seafloor mining of deposits associated with either active or inactive vents disturbance of sediment plume generation and dewatering process this environmental impact needs to be addressed prior to the formulation of regulations for deep sea mining by the international seabed authority the present review examines our current understanding of oxidation and dissolution of a mixed sulphide ore bringing together lines of evidence from a range of literature sources based on this review different seafloor sulphide ore deposits will dissolve by oxidation and release a variety of different metals economic and or toxic all at different rates with galvanic cells playing a role by increasing dissolution rates while precipitation of oxide and oxy hydroxide phases will occur it is unknown in both a natural weathering and anthropogenic mining context whether heavy metal release including economic and toxic metals is temporally balanced by this precipitation and any subsequent adsorption based on our current understanding certain sites will be more predisposed to oxidation as a result of their mineralogy those containing significant pyrrhotite marcasite galena and secondary copper sulphides and or environment higher temperatures and oxygen concentrations lower ph s furthermore certain sites pose more of an environmental risk in terms of toxicity than others with arc related sms deposits associated with higher concentrations of as pb sb cd and hg and ultra mafic hosted sms deposits associated with high concentrations of co and ni the review highlights the need for subsequent studies that investigate the natural weathering process of seafloor sulphide ore deposits including how this process impacts their economic value and consequent geochemical signature of oxides that are produced over time moreover this review underlines the necessity for experiments to elucidate the oxidative dissolution of ore throughout any mining process

estimation of lava extrusion and magma production rates for two flood basalt provinces utilizing the statistical approach of cox and dairymple 1967 it is shown that the geomagnetic polarity time scale of harland et al 1982 may contain errors of 0 85 1 0 m y for middle late miocene times a revised time scale based on the work of mcdougall et al 1984 is correlated with the magnetostratigarphic units of the columbia river basalts united states lava extrusion rates reached a peak of 275 km3 kyr for a period of 0 5 m y around 15 8 ma during the columbia volcanic episode it is suggested that even higher rates of lava extrusion may have occurred in the deccan province central india 65 ma a simple energy budget calculation indicates that the reunion hotspot could provide enough heat to melt the total volume of rock needed to produce the deccan traps during the 5 m y it would have taken the subcontinent to traverse the hotspot

revised age calibration points for the geomagnetic polarity time scale two of the seven cenozoic age calibration points in the widely used cande and kent s geomagnetic polarity time scale have recently been revised the rest of the five calibration points are revised here based on recently available radioisotopic dates and magnetostratigraphic data ages of the magnetic reversals are recalculated using the revised calibration points differences between the present time scale and cande and kent s revised time scale are generally less than 0 3 m y the largest up to 1 3 m y being in the early miocene

formation of massive sulfide deposits on oceanic ridge crests incremental reaction models for mixing between hydrothermal solutions and seawater equilibrium path calculations have been used to model mixing between hot 350 c hydrothermal solutions and ambient seawater in an attempt to simulate mineral precipitation at seafloor vents these calculations predict temperatures of precipitation paragenetic sequence of minerals and chemical composition of chimney deposits associated with vents on the seafloor at 21 n epr assuming sulfate sulfide disequilibrium during mixing the paragenetic sequence revealed is chalcopyrite anhydrite pyrrhotite pyrite sphalerite graphite and barite when sulfate sulfide equilibria is permitted during mixing however reduction of small amounts of sulfate results in early precipitation of pyrite and a sequence of cu rich sulfide minerals chalcopyrite bornite chalcocite covellite this sequence is analogous to that observed in thin chimney walls the calculations indicate that sulfide mineral precipitation occurs in response to both cooling and change in composition of the hydrothermal solutions as a result of mixing varying the amount of mixing with respect to temperature simulating conductive heating of seawater prior to mixing results in only minor variations in the sequence and abundance of precipitated phases anhydrite precipitation during mixing occurs early which is consistent with formation of an anhydrite leading edge of chimney structures similarly extrapolation of warm spring data from galapagos to zero so4 concentration suggests anhydrite formation due to mixing with seawater beneath the seafloor most likely below the level of reactive calcareous sediments subsequent interaction of the mixed hydrothermal solution with those sediments results in elevated and variable ca concentrations estimated for end member solutions from the galapagos precipitation of mg hydroxide sulfate hydrate in the walls of the vent chimneys at 21 n epr occurs as a result of conductive heating of ambient seawater with only very minor amounts of mixing in contrast precipitation of amorphous silica in the vents must be due to conductive cooling of the hydrothermal solutions thus incremental reaction calculations demonstrate that reactions occurring in and associated with venting ridge crest hydrothermal solutions can be effectively modeled using the thermodynamic data and reaction modeling codes available today departures from equilibrium required to accurately model the mixing process are easily accommodated and consistent with data from the vents and vent forming materials

evidence for errors in the geomagnetic polarity time scale at 17 15 ma 40ar 39ar dating of basalts from the pacific northwest usa 40ar 39ar incremental heating studies have been carried out on whole rock basalt samples from the columbia river basalt crb and the steens basalt to obtain crystallization ages with a standard error 1 these high precision accurate ages are utilized with the known magnetostratigraphy of the crb to test the accuracy of the early to middle miocene section of the geomagnetic polarity time scales currently in use we conclude that these time scales underestimate the ages of various chrons within this time range by 0 9 m y

approximate traveltime inversion in downhole microseismic monitoring abstract in downhole microseismic monitoring accurate event location relies on the accuracy of the velocity model the model can be estimated along with event locations anisotropic models are important to get accurate event locations taking anisotropy into account makes it possible to use additional data two s wave arrivals generated due to shear wave splitting however anisotropic ray tracing requires iterative procedures for computing group velocities which may become unstable around caustics as a result anisotropic kinematic inversion may become time consuming in this paper we explore the idea of using simplified ray tracing to locate events and estimate medium parameters in the simplified ray tracing algorithm the group velocity is assumed to be equal to phase velocity in both magnitude and direction this assumption makes the ray tracing algorithm five times faster compared to ray tracing based on exact equations we present a set of tests showing that given perforation shot data one can use inversion based on simplified ray tracing even for moderate to strong anisotropic models when there are no perforation shots event location errors may become too large for moderately anisotropic media

constrained tomography of realistic velocity models in microseismic monitoring using calibration shots the knowledge of the velocity model in microseismic jobs is critical to achieving statistically reliable microseismic event locations the design of microseismic networks and the limited sources for calibration do not allow for a full tomographic inversion we propose optimizing a priori velocity models using a few active shots and a nonlinear inversion suitable to poorly constrained systems the considered models can be described by several layers with different p and s wave velocities the velocities may be constant or have 3d gradients the layer interfaces may be simple dipping planes or more complex 3d surfaces in this process the p and s wave arrival times and polarizations measured on the seismograms constitute the observed data set they are used to estimate two misfit functions i one based on the measurement residuals and ii one based on the inaccuracy of the source relocation these two functions are minimized thanks to a simulated annealing scheme which decreases the risk of converging to a local solution within the velocity model the case study used to illustrate this methodology highlights the ability of this technique to constrain a velocity model with dipping layers this was performed by jointly using sixteen perforation shots recorded during a multi stage fracturing operation from a single string of 3c receivers this decreased the location inaccuracies and the residuals by a factor of six in addition the retrieved layer dip was consistent with the pseudo horizontal trajectories of the wells and the background information provided by the customer finally the theoretical position of each calibration shot was contained in the uncertainty domain of the relocation of each shot in contrast single stage inversions provided different velocity models that were neither consistent between each other nor with the well trajectories this example showed that it is essential to perform a multi stage inversion to derive a better updated velocity model

40ar 39ar ages of flood basalt provinces in russia and china and their possible link to global faunal extinction events a cautionary tale regarding alteration and loss of 40ar abstract the hypothesis that the permo triassic boundary ptb mass extinctions were caused by flood basalt volcanism in russia siberian traps and or china the emeishan traps is investigated from the point of view of time of occurrence 40 ar 39 ar ages numerous published ages in the literature are rejected as good estimates of the time of crystallization the filters applied in this respect are a statistical reliability of plateau isochron sections of stepheating data and b the alteration state of the material that was dated alteration appears to be ubiquitous unsurprising since most of the material dated was used without acid leaching a procedure that is effective in yielding fresh er samples of 70 ages in the literature for the main pulse of siberian trap volcanism less than ten prove to be reliable ages similar techniques applied to 40 ar 39 ar for the emeishan traps leaves only a single reliable age for the magmatic episode these ages are compared to both published and new 40 ar 39 ar ages for the ptb as based on analysis of minerals from critical ash beds in china there is good overlap in the ages ptb 250 0 0 1 ma siberian trap lavas 250 1 0 4 ma lending credence to a genetic link between the formation of the siberian traps and the faunal extinction event at the ptb a similar link for the formation of the viluy traps russia and the late devonian extinction event is investigated only a single reliable 40 ar 39 ar age is available for the viluy traps and falls close to the interpolated age for the frasnian fammenian boundary the use of the unspiked k ar technique to yield accurate ages for such altered samples is questioned a review of u pb data pertinent to these problems suggests a close temporal link between the formation of the siberian traps and the ptb comparison of u pb and 40 ar 39 ar ages for the ptb raises questions about the accuracy of high precision sanidine ages possibly resulting from very slow leakage of 40 ar from this mineral

seismic anisotropy in a hydrocarbon field estimated from microseismic data the study of seismic anisotropy in exploration seismology is gaining interest as it provides valuable information about reservoir properties and stress directions in this study we estimate anisotropy in a petroleum field in oman using observations of shear wave splitting from microseismic data the data set was recorded by arrays of borehole geophones deployed in five wells we analyse nearly 3400 microearthquakes yielding around 8500 shear wave splitting measurements stringent quality control reduces the number of reliable measurements to 325 shear wave splitting modelling in a range of rock models is then used to guide the interpretation the difference between the fast and slow shear wave velocities along the raypath in the field ranges between 0 10 and it is controlled both by lithology and proximity to the ne sw trending graben fault system that cuts the field formations the anisotropy is interpreted in terms of aligned fractures or cracks superimposed on an intrinsic vertical transversely isotropic vti rock fabric the highest magnitudes of anisotropy are within the highly fractured uppermost unit of the natih carbonate reservoir anisotropy decreases with depth with the lowest magnitudes found in the deep part of the natih carbonate formation moderate amounts of anisotropy are found in the shale cap rock anisotropy also varies laterally with the highest anisotropy occurring either side of the south eastern graben fault the predominant fracture strikes inferred from the fast shear wave polarizations are consistent with the trends of the main faults ne sw and nw se the majority of observations indicate subvertical fracture dip 70 cumulatively these observations show how studies of shear wave splitting using microseismic data can be used to characterize fractures important information for the exploitation of many reservoirs

inversion of microseismic data for triclinic velocity models modern downhole microseismic surveys often employ geometries in which ray trajectories generated by a collection of locatable events provide full polar and azimuthal coverage making it possible to estimate the in situ seismic anisotropy we show that traveltimes and particle motions of the direct p and shear waves acquired in such geometries can constrain stiffness tensors of triclinic media while obtaining all 21 stiffness coefficients of a homogeneous triclinic space simultaneously with locating pertinent microseismic events from data recorded in a single vertical well is relatively straightforward the same methodology does not necessarily succeed in layered formations because the combination of their vertical heterogeneity and azimuthal anisotropy might invalidate the commonly adopted approximation of the event azimuths by those of the p wave polarization vectors when the event azimuths cannot be derived from the particle motions traveltimes observed in two or more wells are required to locate the events and build layered triclinic or higher symmetry azimuthally anisotropic velocity models as our numerical tests indicate the multi well event location methods are expected to perform better than their single well counterparts because they rely solely on triangulation and eliminate the usually pronounced azimuthal uncertainties in the event locations that stem from noises adversely affecting hodogram analysis

testing the accuracy of the geomagnetic polarity time scale gpts at 2 5 ma utilizing40ar 39ar incremental heating data on whole rock basalts abstract recent40ar 39ar dating and astrochronologic calculations indicate that the k ar derived gpts underestimates the ages of geomagnetic field reversals in the interval 2 0 ma we report tests to check the accuracy of k ar data utilized to date the reunion event 2 1 ma and part of the early pliocene portion 4 6 ma of the gpts 40ar 39ar incremental heating studies on whole rock basalts from the island of reunion yield an age of2 14 0 03 ma for the reunion event somewhat older than the earlier k ar value of2 07 0 02 ma on the same set of lava flows study of a single specimen from the newer volcanics australia indicates that the earlier k ar date was accurate but the new40ar 39ar results yield a plateau age 4 56 ma with a standard error of 0 6 as compared to the k ar value 3 the improved precision and accuracy resulting from such40ar 39ar incremental heating studies will play a key role in calibrating more precisely the gpts for the interval 10 0 ma

transitional field behaviour from southern hemisphere lavas evidence for two stage reversals of the geodynamo palaeomagnetic records from australasian basalts provide a rare view of transitional field behaviour as seen from mid southern latitudes these data suggest that a geomagnetic reversal is accomplished in two steps separated by an interval of relative dynamo quiescence a potentially long lived field configuration developed early is observed to be the stepping stone from which both successful and unsuccessful reversal attempts are made several aborted attempts involving the same intermediate field geometry may precede an actual polarity transition

reservoir characterization using surface microseismic monitoring microseismic monitoring of reservoir processes can be performed using surface or near surface arrays we review the published technical basis for the use of the arrays and the historical development of the method beginning with locating earthquakes through geothermal exploration to the growing field of hydraulic fracture monitoring practical considerations for the array deployment and data processing are presented the road ahead for the technology includes a move toward life of field buried arrays as well as opportunities for extended interpretation of the data particularly inversion for source mechanism estimation and measurement of anisotropy in the monitored subsurface

extended wave equation imaging conditions for passive seismic data abstractthe information obtained from seismic monitoring at injection sites is often limited to seismic event properties e g location origin time moment tensor the accuracy of which greatly depends on the assumed or estimated elastic velocity models current traveltime based methods to calibrate velocity models rely on having distinct arrivals in surface seismic monitoring however the signal to noise ratio of arrivals is often too poor for pick based methods and migration techniques are needed wave equation migration can image microseismic sources without the need for picking or knowledge of the onset time by reconstructing the wavefield through the model space and applying an imaging condition we have devised extended imaging conditions for passive seismic wave equation imaging algorithms and we have found that they represent a key step toward verifying and updating elastic velocity models by extending imaging conditions away from zero lag in time and space we can better evaluate the focu

influence of models on seismic event localization source localization is a fundamental problem in seismology current localization techniques often rely on homogeneous isotropic models even if a survey region is known to be geologically complex or anisotropic we investigated a model s influence on localization using data from a hydraulic injection experiment at the continental deep drilling kontinentale tiefbohrung or ktb site in germany we performed the localization with a grid search algorithm and two additional methods for verification from previous work a homogeneous isotropic model based on a borehole check shot and a heterogeneous 3d isotropic model were available vertical seismic profiling vsp and borehole data as well as laboratory data from rock samples provided homogeneous anisotropic models although localization with the isotropic and anisotropic models led to the same magnitude of residuals and therefore to a comparable quality of fit the distribution of the event cloud differed significantly for isotropic and anisotropic media

the susu knolls hydrothermal field eastern manus basin papua new guinea an active submarine high sulfidation copper gold system susu knolls comprises three steep sided conical volcanic peaks standing on a n nw trending ridge in the eastern manus basin a complex zone of convergence between the major indo australian and pacific plates the knolls consist of three porphyritic andesite to dacite domes each 1 0 to 1 5 km in diameter with crests ranging from 1 150 to 1 520 m below sea level an intense hydrothermal plume with peak transmission anomalies in excess of 40 originates from susu knolls and associated hydrothermal venting with fluid temperatures exceeding 300 c and sulfide mineralization has been detected on the crests of all three edifices the most important of these is the 2 47 million metric ton mt solwara 1 copper gold deposit on suzette knoll slated for mining by nautilus minerals the porphyritic dacite is commonly strongly altered by reaction with acidic fluids fragments of sulfide mineralization collected as part of the seafloor talus surrounding the crest of north su and south su are characterized by an assemblage of pyrite fukuchilite enargite covellite chalcopyrite by contrast there are actively venting chimneys on the crest of suzette that are typically zoned with chalcopyrite pyrite tennantite inner zones and barite dominated outer zones the knolls are covered by black sulfidic sediments that contain up to 2 4 wt cu and 3 2 ppm au primary feldspars have been obliterated by the hydrothermal activity that ranges from incipient to intense and which is characterized by natroalunite alunite north su only cristobalite tridymite and rare quartz and kaolinite most volcanic rocks exhibit a patchy surficial coating of native sulfur which may also fill vesicles no altered rocks were dredged from suzette because of the thick sulfidic sediment cover mass balance calculations for altered and unaltered rock from north and south su show that major and trace lithophile elements are depleted in the altered rocks except for ti al si and zr all near immobile in concert with the destruction of the primary minerals and removal of primary components by acidic fluids sulfur and chalcophile trace elements i e as au ba cd cu mo pb and se typically associated with magmatic cu au mineralization are enriched by orders of magnitude in both leached and mineralized rock sulfide and native sulfur 34s values from all three domes range from 7 4 to 0 4 indicating a magmatic component for the sulfur a small group of ore elements i e ag bi in sb and zn are strongly enriched in mineralized breccias and depleted in the altered dacites suggesting redistribution during alteration the presence of advanced argillic alteration the paragenesis of the fe cu as sulfide assemblage and presence of native sulfur together with the sulfur isotope evidence for magmatic input into the hydrothermal fluid at susu knolls are consistent with a submarine high sulfidation magmatic cu au hydrothermal system furthermore the sulfide assemblage pyrite enargite covellite chalcopyrite observed at north and south su and orders of magnitude enrichment of chalcophile elements in both altered and mineralized volcanic rocks relative to unaltered volcanic rock are also characteristic of subaerial high sulfidation epithermal mineralization the susu knolls hydrothermal field is a good example of a modern high sulfidation cu au submarine hydrothermal system

simultaneous inversion of multiple microseismic data for event locations and velocity model with bayesian inference abstractwe have applied bayesian inference for simultaneous inversion of multiple microseismic data to obtain event locations along with the subsurface velocity model the traditional method of using a predetermined velocity model for event location may be subject to large uncertainties particularly if the prior velocity model is poor our study indicated that microseismic data can help to construct the velocity model which is usually a major source of uncertainty in microseismic event locations the simultaneous inversion eliminates the requirement for an accurate predetermined velocity model in microseismic event location estimation we estimate the posterior probability density of the velocity model and microseismic event locations with the maximum a posteriori estimation and the posterior covariance approximation under the gaussian assumption this provides an efficient and effective way to quantify the uncertainty of the microseismic location estimation and capture the correlation between the velo

uncertainties in passive seismic monitoring the use of passive seismic techniques to monitor oil field completion and production processes is on the rise stress changes induced by such reservoir activities as hydraulic fracturing water injection or fluid extraction will often result in failure of the rocks with a concurrent release of seismic energy in the form of compressional p and shear s waves passive seismic monitoring is based on recording these emitted waves and then using their arrival times to estimate the location of the failure events

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

pinning down the brunhes matuyama and upper jaramillo boundaries a reconciliation of orbital and isotopic time scales until recently the temporal calibration of the plio pleistocene portion of the geomagnetic reversal time scale grts was based exclusively on kar isotopic ages of volcanic rocks the so called chronogram technique estimates the age that minimizes discrepancies between a given age assignment for a reversal boundary and the population of dates of known polarity the most widely quoted date 0 73 ma for the brunhes matuyama boundary was derived in such a manner 1 radioactive decay is not the only source of temporal information in the geologic record however variations in several of the orbital parameters of the earth e g precession obliquity eccentricity can be calculated for the last several million years and the climatic response approximated a recent analysis of the so called astronomical technique on oxygen isotopic data from deep sea sediments suggested an age of 0 78 ma for the brunhes matuyama boundary 2 some 50 000 years older than the chronogram estimate we reconcile the two estimates for the age of the last reversal by first presenting new magnetostratigraphic data tied to high quality40ar39ar dates our date for the upper jaramillo boundary is0 992 0 039 ma considerably older than the estimate of 0 91 ma in the standard chronogram based time scale 3 furthermore an age of0 746 0 009 ma was obtained for sediments immediately overlying the brunhes matuyama boundary these data are consistent with the astronomical estimates of 0 78 ma and 0 99 ma for the brunhes matuyama and upper jaramillo boundaries respectively finally we present a new method for estimating the uncertainties of ages calculated using the chronogram technique that employs a simple bootstrap resampling scheme the 95 confidence region for the chronogram estimate of the brunhes matuyama boundary using an updated compilation of date polarity pairs spans from 0 73 to 0 78 ma we find therefore that the discrepancies between the isotopic data set and the astronomical calibration of the brunhes matuyama boundary disappear when appropriate uncertainties are applied for the most recent compilation of isotopic data

paleomagnetic and structural evidence for localized tectonic rotation associated with fault drag in the northeastern mojave desert implications for the late cenozoic tectonic evolution of the eastern california shear zone abstract paleomagnetic data coupled with detailed geological analysis of the southeastern goldstone lake region indicate that lower miocene volcanic and epiclastic rocks of the pink canyon area have been folded faulted and tectonically rotated 28 4 9 0 clockwise about a vertical axis identical rocks lying to the west across the goldstone lake fault east branch have been rotated 9 6 7 4 the coyote canyon fault is locally folded about a vertical axis 25 in a clockwise sense in the pink canyon area timing relationships indicate that rotation is post early miocene regional relationships imply that deformation is late miocene to holocene in age these relationships imply that tectonic rotation is local rather than regional in extent as proposed by some tectonic models the results of this study are generally consistent with the dokka and travis 1 model and the subsequently revised dokka model 2 of strain partitioning in the northeastern mojave desert block

magnetostratigraphy of neogene andean foreland basin strata lat 33 s mendoza province argentina neogene nonmarine strata in the southernmost part of the precordillera thrust belt of the andes of argentina accumulated during the miocene and pliocene in response to eastward advance of thrust sheets located to the west to link the sequence of deformational events with the sedimentary record five stratigraphic sections in the mendoza province were dated using magnetic polarity stratigraphy calibrated with 40 ar 39 ar dates from interbedded tephras these data establish age control on tectonic activity volcanism and deposition the existence of a backarc foreland basin that developed prior to or ca 16 ma is recorded by the oldest strata the ca 15 7 12 2 ma baksi time scale marino formation deposition of this unit is linked to a major phase of thrust activity in the central part of the aconcagua fold and thrust belt in the principal cordillera initiation of deposition coincides with an eastward shift of the subduction related magmatic foci to the argentine principal cordillera the overlying ca 11 7 9 0 ma la pilona formation is thought to record the initiation of exhumation of the frontal cordillera to the northwest of the study region an extensive ash rich unit the 8 9 locally 9 5 to 8 7 ma tobas angostura formation is correlated with the latest and probably the largest extrusive episode in the principal cordillera chronologic data constrain the timing of oil generation in the cuyo basin and development of prospective closures the new data also require that land mammalian fossils found in the rio de los pozos formation are late miocene rather than pliocene as previously believed

velocity calibration for microseismic monitoring a very fast simulated annealing vfsa approach for joint objective optimization to accurately locate microearthquakes that are genetically related to hydraulic fracture stimulation a thorough knowledge of the velocity structure between monitoring and fracturing treatment wells is essential very fast simulated annealing vfsa is implemented to invert for a flat layered velocity model between wells using perforation or string shot data a two point ray tracing method is used to find the ray parameter p for a ray traveling from a source to a receiver the original traveltime calculation formula is modified to account for the borehole source receiver geometry vfsa is used as a tool to optimize p and s wave velocities simultaneously unlike previous applications of vfsa two improvements result from a new study 1 both p and s wave arrival time misfits are considered in a joint objective function and 2 p and s wave velocities are perturbed simultaneously during annealing the inverted velocities follow the true values closely with a very small root mean square error indicating the inverted model is close to the global minimum solution whose rms error should be zero for synthetic examples data noise contaminates inverted models but not substantially in synthetic test results a comparison of models inverted using vfsa and occam s inversion technique indicates that inverted models using vfsa are superior to those using occam s method in terms of velocity accuracy

simultaneous inversion for microseismic event location and velocity model in vaca muerta formation velocity models play a key role in locating microseismic events however it is usually challenging to construct them reliably traditional model building strategies depend on availability of well logs or perforation shots we simultaneously invert for microseismic event locations and a velocity model under the bayesian inference framework and apply it in a field dataset acquired in the vaca muerta formation at neuquen argentina this methodology enables uncertainty and posterior covariance analysis by matching the moveouts of the p and s wave arrival times we were able to estimate a 1d velocity model to achieve improved event locations various analyses indicate the superiority of this model over a model built with the traditional strategy with this algorithm we can perform microseismic monitoring to fracturing treatments where no perforation data is available in addition we can also apply it for long term passive seismicity reservoir monitoring where changes of reservoir properties are expected