analysis of fracture propagation behavior using hydraulically induced acoustic emissions in the bernburg salt mine germany hydraulic fracturing experiments were carried out at the bernburg salt mine in germany the induced acoustic emission ae events were detected by accelerometers surrounding the sources and the observed ae events had a frequency component of over 40 khz many similar waveforms were identified in the detected events and their source locations were determined with an error of less than 6 cm the principal direction of the source distribution changed with depth according to the rotation of the principal stress direction and the shape of the fracture was determined to be elliptical the source locations were distributed as an ellipse with a radius of about 1 m in both fracturing and re fracturing tests at six different levels a theoretical examination of fracture growth showed that macroscopic fractures extend with an aspect ratio which is a function of normal and shear stresses and suggests that shear stress leads to the formation of elliptical fractures and that the elliptical shape of macroscopic fractures is controlled by the ratio of the shear stress to the normal stress

hydraulic conductivity of stratified unsaturated soils effects of random variability and layering for simulating flow in heterogeneous porous media it is computationally more efficient to define an equivalent effective i e upscaled medium rather than considering detailed spatial heterogeneities in this paper the effective unsaturated hydraulic conductivity k of soils exhibiting random variability layering or both is calculated based on numerical simulations of steady state evaporation from a shallow water table it is demonstrated that the effective k of randomly varied coarse textured soils generally falls between the harmonic and geometric means of the unsaturated hydraulic conductivities of the constituting soils layering and random variability when occurring concurrently magnify each other s effects on effective k as a result the higher the degree of heterogeneity the lower the effective k therefore neglecting either random spatial variability or layering in numerical simulations can lead to significant overestimation of water flow in soils

effective unsaturated hydraulic conductivity of layered sands accurate estimates of field scale hydraulic conductivities of unsaturated heterogeneous soils are very difficult to obtain in the present study various approaches to determining effective conductivity values for heterogeneous sands are compared with laboratory measurements the unsaturated hydraulic conductivity k of two homogeneous sands and one layered sand composed of the two homogeneous sands was measured using the steady state flux control method the averaged k curves of the two homogeneous sands using a direct averaging approach were compared with the measured layered sand k data the result shows that the geometric mean of hydraulic conductivity suction curves of the coarse and medium sands approximates the measured hydraulic conductivity suction curve of the layered sand the observed suction variance and effective hydraulic conductivity were compared with expressions developed from a stochastic theory the results support the stochastic approach

utilizing multiplets as an independent assessment of relative microseismic location uncertainty abstract location uncertainty is a key factor affecting interpretation of microseismic data associated with multistage hydraulic fracturing we provide an independent assessment of relative microseismic event location uncertainty using multiplets microseismic events that occur in essentially the same place with the same source characteristics we establish a relationship between waveform similarity and hypocentral separation using synthetic events in a representative velocity model finding an upper bound of 15 m between events in any given multiplet group this implies that greater separation of locations for events within a multiplet reflects relative location error we identified hundreds of multiplet groups in a case study in the barnett with unusually high quality data all stages were recorded with two downhole monitoring arrays although the events within each multiplet group must be within 15 m of each other to produce nearly identical waveforms on the recording arrays the scatter in contractor

post 12 m y rotation of southwest washington paleomagnetic field directions from the basalt of pack sack lookout are compared to those from the pomona member of the saddle mountains basalt of the columbia river basalt group the pomona crops out over a wide region on the columbia plateau east of the cascade range and the basalt of pack sack lookout crops out well to the west of the cascades about 30 to 60 km east of the washington coast our paleomagnetic results support existing geologic and geochemical evidence that both these units are part of a single 12 m y old flow that erupted in western idaho and flowed to the washington coast the magnetic data further indicate that southwest washington has undergone clockwise rotation with respect to the columbia plateau and stable north america the data suggest that both a large scale regional rotation of 16 and locally complex small scale rotations exist the two being present to different degrees in the eastern and western regions of southwest washington the cascade range appears to coincide with the tectonic boundary separating rotated and unrotated regions of washington state rotation of southwest washington appears to have been associated with the rotation of large pieces of western oregon and southern washington possibly as a result of either a ridge push force from the basin and range province or shear along the pacific north america plate boundary

a technique for identifying microseismic multiplets and application to the valhall field north sea a fast fully automatic technique to identify microseismic multiplets in borehole seismic data is developed the technique may be applied in real time to either continuous data or detected event data for a number of three component receivers and does not require prior information such as p or s wave time picks peak crosscorrelation coefficients evaluated in the frequency domain are used as the basis for identifying microseismic doublets the peak crosscorrelation coefficient at each receiver is evaluated with a weighted arithmetic average of the normalized correlation coefficients of each component each component is weighted by the maximum amplitude of the signal for that component to reduce the effect of noise on the calculations the weighted average correlations are averaged over all receivers in a time window centered on a fixed lag time the size of the time window is determined from the dominant period in the signal and the lag time is the time that maximizes the average correlation coefficient the technique is applied to a three component passive seismic data set recorded at the valhall field north sea a large number of microseismic doublets are identified that can be grouped into multiplets reducing the total number of absolute event locations by a factor of two seven large multiplets reflect the repeated multiple rerupturing up to 30 times on a single fault and significant stress release two major faults dominate the seismic activity causing at least one fourth of the observed events

induced microearthquake patterns in hydrocarbon and geothermal reservoirs six case studies the injection or production of fluids can induce microseismic events in hydrocarbon and geothermal reservoirs by deploying sensors downhole data sets have been collected that consist of a few hundred to well over 10 000 induced events we find that most induced events cluster into well defined geometrical patterns in many cases we must apply high precision relative location techniques to observe these patterns at three sedimentary sites thin horizontal strands of activity are commonly found within the location patterns we believe this reflects fracture containment between stratigraphic layers of differing mechanical properties or states of stress at a massive carbonate and two crystalline sites combinations of linear and planar features indicate networks of intersecting fractures and allow us to infer positions of aseismic fractures through their influence on the location patterns in addition the fine scale seismicity patterns often evolve systematically with time at sedimentary sites migration of seismicity toward the injection point has been observed and may result from slip induced stress along fractures that initially have little resolved shear in such cases triggering events may be critical to generate high levels of seismic activity at one crystalline site the early occurrence of linear features that traverse planes of activity indicate permeable zones and possible flow paths within fractures we hope the continued development of microseismic techniques and refinement of conceptual models will further increase our understanding of fluid behavior and lead to improved resource management in fractured reservoirs

magnetostratigraphy and mid palaeolatitude vgp dispersion during the permo carboniferous superchron results from parana basin southern brazil rhythmites summary a detailed magnetostratigraphic and rock magnetism study of two late palaeozoic rhythmite exposures itu and rio do sul from the itarare group parana basin brazil is presented in this paper after stepwise alterning field procedures and thermal cleaning were performed samples from both collections show reversed characteristic magnetization components which is expected for late palaeozoic rocks however the itu rocks presented an odd flat inclination pattern that could not be corrected with mathematical methods based on the virtual geomagnetic pole vgp distributions correlation tests between the maximum anisotropy of the magnetic susceptibility axis k1 and the magnetic declination indicated a possible mechanical influence on the remanence acquisition the rio do sul sequence displayed medium to high inclinations and provided a high quality palaeomagnetic pole after shallowing corrections of f 0 8 of 347 5 e 63 2 s n 119 a95 3 3 k 31 which is in accordance with the palaeozoic apparent wander pole path of south america the angular dispersion sb for the distribution of the vgps calculated on the basis of both the 45 cut off angle and vandamme method was compared to the best fit model g for mid latitudes both of the sb results are in reasonable agreement with the predicted palaeo latitudinal s relationship during the cretaceous normal superchron cns although the sb value after the vandamme cut off has been applied is a little lower than expected this result in addition to those for low palaeolatitudes during the permo carboniferous reversed superchron pcrs previously reported indicates that the low secular variation regime for the geodynamo that has already been discovered in the cns might have also been predominant during the pcrs

elevated paleomagnetic dispersion at saint helena suggests long lived anomalous behavior in the south atlantic earth s magnetic field is presently characterized by a large and growing anomaly in the south atlantic ocean the question of whether this region of earth s surface is preferentially subject to enhanced geomagnetic variability on geological timescales has major implications for core dynamics core mantle interaction and the possibility of an imminent magnetic polarity reversal here we present paleomagnetic data from saint helena a volcanic island ideally suited for testing the hypothesis that geomagnetic field behavior is anomalous in the south atlantic on timescales of millions of years our results supported by positive baked contact and reversal tests produce a mean direction approximating that expected from a geocentric axial dipole for the interval 8 to 11 million years ago but with very large associated directional dispersion these findings indicate that on geological timescales geomagnetic secular variation is persistently enhanced in the vicinity of saint helena this in turn supports the south atlantic as a locus of unusual geomagnetic behavior arising from core mantle interaction while also appearing to reduce the likelihood that the present day regional anomaly is a precursor to a global polarity reversal

precise microearthquake locations and fluid flow in the geothermal reservoir at soultz sous forets france i relocated two microearthquake clusters induced by hydraulic stimulation of a hot dry rock geothermal reservoir in the rhine graben near soultz sous forets france the two clusters were chosen from a collection of clusters identified within a 16 000 event data set obtained in 1993 i determined p and s wave arrival times manually choosing distinctive peaks if waveforms were similar at a given station or first breaks if waveforms were emergent or nodal judging weights accordingly requiring a minimum of five arrival times yielded populous clusters of 226 and 355 events in both cases relocation revealed two distinct planar patches of activity 100 to 200 m across intersecting and truncating one another along a common edge linear segments traverse the planar patches and may mark intersections with seismically inactive fractures the earliest activity occurred along these segments these segments may therefore mark permeable zones that could be important components of the fluid flow network the interpretation of linear segments as flow paths is supported by path dimension constraints derived from fluid flow modeling studies and by the expected confining effects of hydrothermal sealing found in cored fractures orientations of the planar features are verified through consistency with orientations found in core and logging studies in addition focal mechanisms obtained by constraining slip planes parallel to active planes indicate normal to right lateral strike slip consistent with the measured stress field focal mechanisms indicate mass deficits at inside corners implying that the concentrations of activity at fracture intersections may result from slip on one fracture causing extension and a resulting permeability increase in the other the improved location precision results from a ten fold improvement in the precision of arrival time estimation for phases that were similar as estimated from the standard deviation of residuals grouped by station and phase before and after repicking only a two fold improvement was noted for poorly correlated or nodal phases for this data set the manual phase picking yielded more interpretable detail in the location patterns compared to results of an automatic cross correlation technique the manual results could be used to guide improvements to automatic techniques to obtain precise locations of the entire data set

a comparison of detailed equatorial red bed records of secular variation during the permo carboniferous reversed superchron eve basin southern france also deposited at low latitudes additionally we critically review published data from low latitude permian red beds from the same basins we focus on records with a sufficient number of samples and acquire whenever possible the original data or as a second choice parametrically sampled published site means we test the distributions of these directions using a statistical secular variation field model tk03 gad the angular standard deviation asd of the virtual geomagnetic pole vgp distribution is a measure of palaeo secular variation and we compare our values of asd from the permian red beds to those from lavas erupted in the last 5 myr contrary to our previous studies we now conclude that secular variation during the permo carboniferous reversed superchron is slightly but significantly reduced at low latitudes compared with the recent field as based on a latest compilation that supercedes earlier compilations it also agrees with a new study which found that psv at low palaeolatitudes during the cretaceous normal superchron was also significantly lower than in periods with frequent reversals

palaeosecular variation over the past 5 myr based on a new generalized database summary a generalized database of global palaeomagnetic data from 3719 lava flows and thin dykes of age 0 5 ma has been constructed for use with a relational database management system the database includes all data whose virtual geomagnetic poles vgp lie within 45 of the spin axis and can be used for studies of palaeosecular variation and for geomagnetic field modelling because many of these data were collected and processed more than 15 20 years ago each result has been characterized according to the demagnetization procedures carried out analysis of these data in terms of the latitude variation of the angular dispersion of vgps palaeosecular variation from lavas strongly suggests that careful data selection is required and that many of the older studies may need to be redone using more modern methods differences between the angular dispersions for separate normal and reverse polarity data sets confirm that many older studies have not been adequately cleaned magnetically therefore the use of the database for geomagnetic field modelling should be carried out with some caution using a vgp cut off angle that varies with latitude the best data set consists of 2636 results that show a smooth increase of vgp angular dispersion with latitude model g for palaeosecular variation which is based on modelling of the antisymmetric dipole and symmetric quadrupole dynamo families provides a good fit to these results

navigational infrastructure at the east pacific rise 9 50 n area following the 2005 2006 eruption seafloor benchmarks and near bottom multibeam surveys 1 four seafloor benchmarks were deployed with rov jason2 at frequently visited areas along the northern east pacific rise nepr ridge crest near 9 50 n within the ridge2000 epr integrated study site iss bull s eye when used in concert with established deep ocean acoustic positioning techniques these benchmarks provide navigational infrastructure to facilitate the integration of near bottom data at this site by allowing efficient and quantitative coregistration of data and observations collected on multiple dives and over multiple cruises high resolution near bottom multibeam bathymetric surveys also were conducted along and across the ridge crest to provide a morphological and geological context for the benchmark areas we describe the navigation and data processing techniques used to constrain the benchmark positions and outline operational details to effectively use benchmarks at this and other deep ocean sites where multidisciplinary time series studies are conducted the well constrained positions of the benchmarks provide a consistent geospatial framework that can be used to limit navigational uncertainties during seafloor sampling and mapping programs and enable accurate spatial coregistration and integration of observations these data are important to test a range of multidisciplinary hypotheses that seek to link geological chemical and biological processes associated with crustal accretion and energy transfer from the mantle to the hydrosphere at mid ocean ridges

dominant directions of epicenter distribution of regional mining induced seismicity series in upper silesian coal basin in poland the regional mining induced seismicity of the upper silesian coal basin poland forms two major and two minor spatial clusters the directional patterns of seismic series from the major clusters were studied with the use of the analysis of deflections the seismic series is parameterized by the deflection angle of the straight line connecting epicenters of every two consecutive events measured from ns direction the trends of epicenter migration are characterized by modes of distribution of the deflection angle estimated by the nonparametric kernel method the distribution of deflection angles for the studied seismic series is not random altogether four trends of epicenter migration have been identified two are connected with the subseries of events that belong to the same cluster and are related to the shape of the clusters whereas the other two linked to the subseries of events that alternate between the clusters indicate that mutual positions of events in such series are not random the results support recent hypotheses pertaining to low tectonic instability of this region

precise source location of ae doublets by spectral matrix analysis of triaxial hodogram we have developed a precise relative source location technique using acoustic emission doublets ae doublets in the triaxial hodogram method to evaluate the direction and distance of subsurface extension cracks an ae doublet is a pair of acoustic emissions with similar waveforms and adjacent locations on the same crack but which occur at different times the relative source location is estimated by an analysis in the frequency domain the relative distance between two ae sources is determined from the difference of p s arrival time delays by cross spectrum analysis the relative direction is derived using a spectral matrix from the difference in p wave polarization directions we also propose a method to optimize the estimated relative location by using a group of ae doublets the accuracy of the estimated source location was confirmed by performing field experiments the relative locations of artificial wave sources about 150 m from a triaxial detector can be estimated with distance errors of less than 1 m and direction errors of less than 3 8 degrees in both azimuth and inclination results of the application of this analysis on ae doublets in a geothermal field demonstrate its ability to evaluate deeper subsurface fractures

geomagnetic secular variation recorded by sediments deposited during the cretaceous normal superchron at low latitude abstract paleosecular variation of the earth s magnetic field reflects the convective vigor of the geodynamo to investigate the energy regime of the geodynamo during the cretaceous normal superchron we collected 534 samples for a paleosecular variation study from a 1400 m long paleontologically well described section in northern peru thermal demagnetization isolates stable magnetization directions carried by greigite arguments are equivocal whether this remanence is syn diagenetic acquired during the cretaceous normal superchron or a secondary overprint acquired during a chron of solely normal polarity in the upper cenozoic yet pre bruhnes 800 kyr we explore the ramifications on the s value which quantifies paleosecular variation that arises from directional analysis sun compass correction bedding correction sampling frequency outlying directions and different recording media the sum of these affects can readily raise the s value by more than 20 s values from northern peru are indistinguishable from other s values for the cretaceous normal superchron as well as those for the last 5 ma summing over all the potential uncertainties we come to the pessimistic conclusion that the s value is an unsuitable parameter to constrain geodynamo models alternatively no statistical difference in paleosecular variation exists during much of the cretaceous normal superchron and during the last 5 ma

paleomagnetism and dating of a thick lava pile in the permian bakaly formation of eastern kazakhstan regularities and singularities of the paleomagnetic record in thick lava series abstract paleomagnetic results on thick lava series are among the most important sources of information on the characteristics of ancient geomagnetic fields most paleo secular variation data from lavas psvl are of late cenozoic age there are far fewer results from lavas older than 5 ma the central asia orogenic belt that occupies several million square kilometers in asia is probably the world s largest area of paleozoic volcanism and is thus an attractive target for psvl studies we studied a ca 1700 m thick lava pile in eastern kazakhstan of early permian age magmatic zircons successfully separated from an acid flow in this predominantly basaltic sequence yielded an early permian age of 286 3 3 5 ma oriented samples were collected from 125 flows resulting in 88 acceptable quality flow means n 4 samples radius of confidence circle 95 15 of the high temperature magnetization component the uniformly reversed component is pre tilting and arguably of a primary origin the overall mean direction has a declination 242 0 and an inclination 56 2 k 71 5 95 1 8 n 88 sites pole at 44 1 n 160 6 e a95 2 2 our pole agrees well with the early permian reference data for baltica in accord with the radiometric age of the lava pile and geological views on evolution of the western part of the central asia orogenic belt the new early permian result indicates a comparatively low level of secular variation especially when compared to psvl data from intervals with frequent reversals still the overall scatter of dispersion estimates that are used as proxies for sv magnitudes elongation values and elongation orientations for psvl data is high and cannot be fitted into any particular field model with fixed parameters both observed values and numerical simulations indicate that the main cause for the scatter of form parameters elongation values and elongation orientations is the too small size of collections dispersion estimates concentration parameter and standard angular deviation are more robust and their scatter stems from other sources which may include non stochastic features of datasets like clusters loops etc or non stationary behavior of secular variation magnitude over time intervals of many million years

improved relative locations of clustered earthquakes using constrained multiple event location a new method for improving relative locations of clustered earthquakes is presented and applied to a suite of microearthquakes induced by hydraulic fracturing the method is based on the assumption that clustering of earthquake hypocenters is obscured by the uncorrelated scatter of individual hypocenters the method is implemented as an additional constraint in a joint hypocenter determination jhd scheme the method shifts event hypocenters toward the center of mass of the events within some volume surrounding the event location if the rms misfit between predicted and measured arrival times does not increase significantly the method uses the same basic assumption of jones and stewart 1997 which is that there is greater clustering in actual earthquake locations than there is in locations determined using conventional techniques our method differs in that it is implemented as part of the jhd process so it operates on raw travel time data rather than on derived hypocenters the method produces hypocenters from a demonstration field dataset that are similar to those obtained by phillips et al 1997 from time consuming precise manual repicking of relative arrival times of events the clustering constraint can easily be incorporated as an additional constraint in earthquake location velocity tomography codes and may lead to improved velocity structure determination and earthquake location pattern identification and interpretation

geomagnetic reversal frequency since the late cretaceous models of geomagnetic reversals as a stochastic or gamma renewal process have generally been tested for the heirtzler et al 1 magnetic polarity time scale which has subsequently been superseded examination of newer time scales shows that the mean reversal frequency is dominated in the cenozoic and late cretaceous by a linearly increasing trend on which a rhythmic fluctuation is superposed subdivision into two periods of stationary behavior is no longer warranted the distribution of polarity intervals is visibly not poissonian but lacks short intervals the labrecque et al 2 polarity time scale shows the positions of 57 small wavelength marine magnetic anomalies which may represent short polarity chrons after adding these short events the distribution of all polarity intervals in the age range 0 40 myr is stationary and does not differ significantly from a poisson distribution a strong asymmetry develops in which normal polarity chrons are poisson distributed but reversed polarity chrons are gamma distributed with indexk 2 this asymmetry is of opposite sense to previous suggestions and results from the unequal distribution of the short polarity chrons which are predominantly of positive polarity and concentrated in the late cenozoic if short wavelength anomalies arise from polarity chrons the geomagnetic field may be more stable in one polarity than the other alternative explanations of the origin of short wavelength marine magnetic anomalies cast doubt on the inclusion of them as polarity chrons however the observed behavior of reversal frequency suggests that core processes governing geomagnetic reversals possess a long term memory

the foam drainage equation for unsaturated flow in porous media 1 a class of capillary flows in unsaturated porous media is characterized by quasi steady viscous flow confined behind curved air water interfaces and within liquid bodies held by capillary forces along crevices and grain contacts the geometry of the connected capillary liquid network within the pore space resembles channels that form between adjacent bubbles in foam plateau borders with solid grains representing gas bubbles in foam for simplified channel geometry we combine expressions for viscous flow with continuity considerations to describe the evolution of the channels cross sectional area during gravity drainage this formulation enables modeling of unsaturated flow without invoking the richards equation and associated hydraulic functions we adapt a formalism originally developed for foam free drainage drainage under gravity or forced drainage infiltration front motion to a class of unsaturated flows in porous media that require a few input parameters only mean channel corner angle air entry value and porosity for certain initial and boundary conditions we demonstrate that the reduction in capillary channel cross section yields a consistent description of self regulating internal fluxes toward attainment of the so called field capacity in soil and provides an alternative method for interpretation of outflow experiments for prescribed pressure boundary conditions additionally the geometrically explicit formulation provides a more intuitive picture of capillary flows across textural boundaries changes in channel cross section and number of channels the foam drainage methodology expands the range of tools available for analyses of unsaturated flow processes and offers more realistic links between liquid configuration and flow dynamics in unsaturated porous media

evidence for a very long term trend in geomagnetic secular variation reconstructions of palaeosecular variation suggest that the earth s magnetic field reversed less frequently 2 82 to 2 45 billion years ago relative to the cenozoic era this suggests a long term trend of decreasing geodynamo stability since the archaean eon the earth s inner core is believed to inhibit rapid fluctuations in the geomagnetic field from developing into full polarity reversals1 2 consequently during the precambrian the smaller size of the inner core might suggest that polarity reversals could occur more readily it is therefore surprising that there are indications that reversals were rare during this period3 4 here we use new and existing palaeomagnetic data from three continents to examine the stability of the earth s magnetic field from 2 82 to 2 45 billion years ago we show that on average geomagnetic secular variation the field variations produced by normal geodynamo action during the late archaean and early proterozoic was different from that of the past 200 million years specifically the apparent variability of the geomagnetic pole as viewed at low and mid latitudes was reduced relative to the past 200 million years according to both dynamo simulations4 and more recent palaeomagnetic field observations5 the observed pattern of secular variation suggests a lower frequency of polarity reversals 2 5 billion years ago this may imply that the geodynamo is becoming progressively less stable over long timescales consistent with some numerical simulations6 7 possibly as a result of changing outer core geometry that has accompanied inner core growth

lead isotopes and the sources of the columbia river basalt group a detailed study of 208pb 204pb 207pb 204pb and 206pb 204pb ratios suggests that the number of pb isotopic reservoirs required for the columbia river basalt group crbg as currently defined must be increased from the presently accepted four to at least six the identities of the six reservoirs are two of mid ocean ridge basalt morb slightly contaminated with sediment rl and r2 rl being cascades pb one a probable plume component r3 two of unspecified mantle material but probably of rl type contaminated with local crustal pb r4 and r5 and the sixth a complex enriched reservoir of 2150 ma age r6 rl is an end member for all crbg except the saddle mountains basalts r2 is a second end member for the picture gorge basalt and appears to be unique to it both rl and r2 are related to the juan de fuca subduction zone and the back arc spreading associated with it r3 is the principal source for most of the wanapum basalt as well as for most of the chemically evolved portions of the grande ronde basalt volumetric and tectonic considerations require that one source of the crbg be a plume or at least a nonlocal crustal or uppermost mantle source and r3 is the ideal candidate for that role r4 is the second source for the imnaha basalt and r5 is the source for the 206pb rich varieties of the grande ronde basalt r4 and r5 are identified with contamination by local phanerozoic crust because of their similarity to local crustal pb and because the rocks which contain them also have cu contents correlated with their pb isotopic compositions r6 is the parent for pb in all the saddle mountain basalts this last source appears to have been homogeneous 2150 m y ago but has since split into a number of separate discrete pockets each with its own characteristic pb isotopic signature some of these appear in individual saddle mountain basalt flows while other sources have mixed with r4 to produce individual saddle mountain basalt flows of the ice harbor set r6 is similar in all its isotopic properties to the precambrian basement that is exposed to the immediate north of the columbia river basalt group the overall model for columbia river basalt group genesis is termed plume reinforced back arc magmatism

secular variation of the middle and late miocene geomagnetic field recorded by the columbia river basalt group in oregon idaho and washington usa

behavior of the paleosecular variation during the permian carboniferous reversed superchron and comparisons to the low reversal frequency intervals since precambrian times we investigated the paleo latitudinal dependence of angular dispersion sets of virtual geomagnetic poles vgps for the permian carboniferous reversed superchron pcrs 262 318 ma in order to analyze the paleosecular variation during this period we prepared different paleomagnetic datasets from scientific databases and recent literature based on selection criteria which provided high degree of refinement model g of mcfadden et al 1988 was fitted to the vgp dispersion data providing the shape parameters a and b which were further compared with similar results for the cretaceous normal superchron cns and other periods of different geomagnetic reversal rates throughout the last 3 ga our results indicate high similarity between the angular vgp dispersion from the pcrs and cns a low vgp dispersion at low paleolatitudes and strong paleolatitudinal dependence in contrasting difference for periods of higher reversal rates the last 5 ma despite the geodynamic differences related to both phanerozoic superchrons such evidence could point out similar heat flux conditions in the cmb which may favor compatible stability conditions throughout these magnetozones notably two additional observations which arose from the shape parameters relations for both phanerozoic superchrons and precambrian datasets demand further investigation i a pattern of increase for the b a ratio throughout the 0 5 1 6 ga interval was observed which could be partially explained by the maya superchron recently proposed by gallet et al 2012 ii the b a relationship for both phanerozoic superchrons and the 2 45 2 82 ga interval pointed to the presence of one or more long term magnetozones throughout the paleoproterozoic

effective parameters for multiphase flow in layered soils abstract this paper examines whether practical and useful effective parameters can be developed and used in the complex case of multiphase flow in heterogeneous porous formations strong nonlinearities in the governing flow equations make exact evaluation of effective parameters difficult and several shortcomings in the published work to date are identified in particular an important multiphase flow phenomenon fingering has yet to be properly treated this may be a severe limitation because as demonstrated in two dimensional laboratory experiments the presence of heterogeneities will provide conditions suitable for the generation of fingers the development of fingers introduces a new length scale into the hierarchy of heterogeneity scales exhibited by natural porous formations the finger diameter experimentally it is observed that finger development allows fluid to by pass a significant fraction of the porous media increasing the front velocity and reducing the degree of large scale entrapment as explicit consideration of fingering has yet to be included in the evaluation of effective parameters for multiphase flow including unsaturated flow such phenomena may not be accurately represented in the approaches developed thus far the experimental observations suggest that when the scale of an oil plume is much larger than the heterogeneity length scale then a large scale flow model based on the local flow equations should describe the overall flow even in the presence of local fingering nevertheless the challenging problem of deriving the appropriate effective properties remains

geomagnetic secular variation in the cretaceous normal superchron and in the jurassic abstract it is now widely thought that geomagnetic polarity reversals occur spontaneously as a result of normal dynamo action rather than being externally triggered if this is the case then it may well be that periods of time in which the geomagnetic reversal frequency was dramatically different were characterised by different styles of secular variation two such periods were the cretaceous normal superchron cns 84 125 ma when the field was dominantly of a single polarity for 40 myr and the jurassic period 145 200 ma when reversals occurred at an average rate of as much as 4 6 myr 1 here we analyse a database of new and published palaeomagnetic directions from lavas emplaced during these periods in order to obtain first order descriptions of the palaeosecular variation psv during these times we then compare these records with one another and with that produced for the period 0 5 ma with average reversal frequency of 4 0 myr 1 our results are more equivocal than those obtained in a previous similar study mcfadden p l merrill r t mcelhinny m w lee s h 1991 reversals of the earths magnetic field and temporal variations of the dynamo families journal of geophysical research solid earth and planets 96 3923 3933 we demonstrate that this is probably a result of the previous study being affected by an artefact of their correction for within site scatter the usefulness of our jurassic record is severely limited by the restricted palaeolatitudinal span of the available data however our record for the cns is sufficient to allow us to conclude that it was likely that secular variation then was different from that in the 0 5 ma period this supports the hypothesis of a link between psv and reversal frequency and therefore endorses psv analysis as a first order tool for determining geomagnetic stability in the past

new 40ar 39ar dating of the grande ronde lavas columbia river basalts usa implications for duration of flood basalt eruption episodes abstract grande ronde basalt grb lavas represent the most voluminous eruptive pulse of the columbia river snake river yellowstone hotspot volcanism with an estimated eruptive volume of 150 000 km 3 grb lavas form at least 66 of the total volume of the columbia river basalt group new 40 ar 39 ar dates for grb lavas reveal they were emplaced within a maximum period of 0 42 0 18 my a well documented stratigraphy indicates at least 110 grb flow fields or individual eruptions and on this basis suggests an average inter eruption hiatus of less than 4000 years isotopic age dating cannot resolve time gaps between grb eruptions and it is difficult to otherwise form a picture of the durations of eruptions because of non uniform weathering in the top of flow fields and a general paucity of sediments between gr lavas where sediment has formed on top of grb lavas it varies in thickness from zero to 20 30 cm of silty to fine sandy material with occasional diatomaceous sediment individual grb eruptions varied considerably in volume but many were greater than 1000 km 3 in size most probably eruptive events were not equally spaced in time some eruptions may have followed short periods of volcanic repose perhaps 10 2 to 10 3 of years whilst others could have been considerably longer many 1000 s to 10 4 years recent improvements in age dating for other continental flood basalt cfb lava sequences have yielded estimates of total eruptive durations of less than 1 my for high volume pulses of lava production the grb appears to be a similar example where the main pulse occupied a brief period even allowing for moderate to long duration pahoehoe flow field production the amount of time the system spends in active lava producing mode is small less than c 2 6 based on eruption durations of approximately 10 000 years compared to the duration of the entire eruptive pulse of c 420 000 years a review of available 40 ar 39 ar data for the major voluminous phases of the columbia river basalt group suggests that activity of the steens basalt imnaha basalt grb may have at times been simultaneous with obvious implications for climatic effects resolving intervals between successive eruptions during cfb province construction and durations of main eruptive pulses remains vital to determining the environmental impact of these huge eruptions

possible links between long term geomagnetic variations and whole mantle convection processes the earth s internal magnetic field varies on timescales of months to billions of years the field is generated by convection in the liquid outer core which in turn is influenced by the heat flowing from the core into the base of the overlying mantle much of the magnetic field s variation is thought to be stochastic but over very long timescales this variability may be related to changes in heat flow associated with mantle convection processes over the past 500 myr correlations between palaeomagnetic behaviour and surface processes were particularly striking during the middle to late mesozoic era beginning about 180 myr ago simulations of the geodynamo suggest that transitions from periods of rapid polarity reversals to periods of prolonged stability such as occurred between the middle jurassic and middle cretaceous periods may have been triggered by a decrease in core mantle boundary heat flow either globally or in equatorial regions this decrease in heat flow could have been linked to reduced mantle plume head production at the core mantle boundary an episode of true polar wander or a combination of the two

geologic and hydrologic controls on the movement of water through a thick heterogeneous unsaturated zone underlying an intermittent stream in the western mojave desert southern california 1 a two dimensional axially symmetric unsaturated flow model was developed to test hypotheses about geologic and hydrologic controls on the movement of water through the thick heterogeneous unsaturated zone underlying oro grande wash in the mojave desert california heterogeneity within the unsaturated zone was simulated with multiple realizations of subsurface geology estimated on the basis of transition probability markov chain statistics model results show lateral spreading of water away from the wash was best approximated by realizations that include thin horizontally extensive clay layers that impede the downward movement of water there was a wide range in model responses for these realizations and the movement of water through unsaturated zones containing thin horizontally extensive clay layers may be more difficult to predict than water movement through unsaturated zones where clay layers are less extensive for realizations having less extensive clay layers the range of model responses decreased with time and model results became increasingly similar as water encountered larger volumes of material

simulating field scale moisture flow using a combined power averaging and tensorial connectivity tortuosity approach 1 various methods have been developed over the past 3 decades to estimate effective unsaturated hydraulic properties we developed an alternative practical approach to estimate three dimensional effective unsaturated hydraulic conductivity via a combined power averaging and tensorial connectivity tortuosity pa tct model an application of the pa tct model to data collected at a field injection site suggests that the model provides a reasonable framework for upscaling core scale measurements as well as an accurate simulation of moisture flow in a heterogeneous vadose zone the heterogeneous media at the injection site are composed of multiple geologic units each of which is represented by an anisotropic equivalent homogeneous medium ehm the directional effective hydraulic conductivity for each anisotropic ehm was determined by upscaling the laboratory measured hydraulic properties with the combined pa tct approach a larger difference between the power values in the horizontal and vertical directions indicates a larger macroscopic anisotropy in unsaturated hydraulic conductivity a moment analysis was used to quantify the center of mass and the spread of the injected water numerical simulations showed that if the flow domain was treated as being isotropic the vertical migration was significantly overestimated while the lateral movement was underestimated to the contrary if the media were treated as layered the lateral moisture movement was considerably overestimated while the vertical movement was underestimated however when the flow domain was modeled as being mildly anisotropic with the pa tct based parameters the model could successfully predict the moisture flow and the simulated plume matched best the center of mass and the spread of the injected water of the observed moisture plume

stratigraphy and petrogenesis of the grande ronde basalt from the deep canyon country of washington oregon and idaho deep canyons cut by the snake salmon grande ronde and imnaha rivers near the point where washington oregon and idaho join expose 800 m of grande ronde basalt flows the grande ronde basalt erupted 16 5 to 14 5 m y b p makes up 85 vol of the columbia river basalt group an area enclosing 1 000 km 2 of the deep canyon country dominated by this basalt was mapped and samples from 16 measured sections in the grande ronde basalt were analyzed for major minor and trace elements three magnetostratigraphic units r 1 n 1 and r 2 were helpful in mapping the area using physically distinct flows the magnetostratigraphic units and certain chemical variations a detailed flow by flow stratigraphy was developed and the lateral extent of many individual flows was traced the number of flows and thickness of each stratigraphic unit decrease from west to east these tholeiitic flows are fine grained and aphyric clinopyroxene and plagioclase are the predominant minerals but olivine orthopyroxene pigeonite and accessory minerals are minor but important phases the flows are primarily of the low mg chemical type with lesser amounts of the high mg chemical type a cyclical trend in the over all major and trace element chemistry through the stratigraphic section is dominated by a ca rich clinopyroxene chemistry rare earth elements show significant light over heavy enrichment but overall patterns remain similar from flow to flow a small negative eu anomaly is present in many flows three models employing fractional crystallization schemes and one combining fractional crystallization and partial melting were tested using least squares modeling a petrogenetic model is proposed wherein partial melting of a heterogeneous clinopyroxene dominated mantle supplied magma that ascended to the crust was temporarily stored and recurrently erupted during storage new basaltic melt with slightly different isotopic and trace element abundances was added and mixed into the liquid that remained after previous eruptions orthopyroxene plagioclase and to a lesser extent olivine fractionated from these temporarily stored liquids upon eruption clinopyroxene and plagioclase with accessory minerals crystallized at the surface

seismic monitoring of the growth of a hydraulic fracture zone at fenton hill new mexico the hydraulic fracturing technique is an important method for enhancing hydrocarbon recovery geothermal energy extraction and solid waste disposal determination of the geometry and growth process of a hydraulic fracture zone is important for monitoring and assessing subsurface fractures a relative source location approach based on a waveform correlation and a grid search method has been developed to estimate relative hypocenter locations for a cluster of 157 microearthquakes induced by hydraulic fracturing at the los alamos hot dry rock hdr geothermal site among the 157 events 147 microearthquakes occurred in a tight cluster with a dimension of 40 m roughly defining a vertical hydraulic fracture zone with an orientation of n40 w the length height and width of the hydraulic fracture zone are estimated to be 40 35 and 5 m respectively analysis of the spatial temporal pattern of the induced microearthquakes reveals that the fracture zone grew significantly averaging 0 2 m minute in a two h

patterns in seismic anisotropy driven by rollback subduction beneath the high lava plains received 24 march 2011 revised 25 may 2011 accepted 31 may 2011 published 8 july 2011 1 we present three dimensional laboratory modeling of the evolution of finite strain and compare these to shear wave splitting observations in the northwest u s under the high lava plains hlp we show that relationships between mantle flow and anisotropy are complicated in subduction zones and factors such as initial orientation of the olivine fast axis style of subduction and time evolving flow are important due to increased horizontal shear systems with a component of rollback subduction have simple trench normal strain alignment within the central region of the backarc mantle wedge while those with more simple longitudinal sinking are often variable and complex in the hlp splitting observations are consistent with rollback driven laboratory results citation druken k a m d long and c kincaid 2011 patterns in seismic anisotropy driven by rollback subduction beneath the high lava plains geophys res lett 38 l13310 doi 10 1029 2011gl047541

evolving core conditions ca 2 billion years ago detected by paleosecular variation abstract paleomagnetic data provide one of the few probes available to interrogate early evolution of the core here we apply this probe by examining the latitudinal dependence of paleosecular variation psv data derived from high quality paleomagnetic data collected from proterozoic and neoarchean rocks these data define a neoarchean geomagnetic field that was more dipolar than that during proterozoic times indicating a change in core conditions the signals observed may reflect a change in forcing of the dynamo and an early onset of inner core growth we propose a model that links evolution of the core mantle and crust in three principal phases i before approximately 3 5 ga an entirely liquid core may not have hosted a geodynamo if heat transport was sufficient across the core mantle boundary however a geodynamo could have been generated if so sources in the shallow outer core could have been more important for generating the dynamo relative to deeper convection resulting in a field that was less dipolar than that generated in later times ii cooling of the lower mantle between ca 2 and 3 5 billion years ago was promoted by deep subduction and possibly coincided with inner core growth the geodynamo during this episode was deeply seated producing a highly dipolar surface magnetic field iii after ca 2 billion years ago continued subduction led to large scale core mantle boundary compositional and heat flux heterogeneity with these changes shallow core contributions to the geomagnetic field grew in importance resulting in a less dipolar field

multiplet clustering analysis reveals structural details within the seismic cloud at the soultz geothermal field france multiplet clustering analysis is a method for precise determination of microseismic event locations and is used to identify subsurface fractures and fracture networks a multiplet is a group of microseismic events with very similar waveforms despite different origin times and it is likely the expression of stress release on the same structure the relative source locations of similar events can be determined with high resolution and accuracy by using the moving window cross spectrum analysis technique deduced seismic clusters called multiplet clusters are indicative of seismically activated structures and the orientations of these structures can be estimated using the seismic clusters even though the absolute locations of the multiplet clusters cannot themselves be determined we examine methods of determining the relative locations of multiplet clusters and introduce the concept of clustering analysis the clustering analysis method is used to estimate the relative location of multiplet clusters by detecting phase differences between similar stacked events we describe the procedure for multiplet clustering analysis estimate relative locations of multiplet clusters and apply the method to induced microseismic data from the soultz hot dry rock field france we show that a fracture network can be delineated through multiplet clustering analysis whereas it is difficult to identify detailed structures on the basis of source locations estimated by the joint hypocenter determination method manuscript received 1 march 2002

stress estimated using microseismic clusters and its relationship to the fracture system of the hijiori hot dry rock reservoir a method for estimating the in situ stress state by analyzing microseismic clusters induced by hydraulic injections is proposed the method is based on focal mechanism analysis supplemented with microseismic doublet analysis the latter is used to discriminate between the fault plane and the auxiliary planes of the focal mechanism solution the method was applied to estimate the stress field within the hijiori hot dry rock geothermal reservoir and yielded results which were consistent with other estimates the mechanics of permeability creation within the reservoir during major hydraulic injections was then examined by evaluating the interaction of the inferred stress field with the natural fracture system the characteristics of the latter were determined by integrating information obtained from core samples acoustic borehole televiewer images and pressure temperature and spinner logs the results indicated that the observed microseismicity and orientation dependent permeability characteristics of the fracture population are well explained by shear failure inferred from coulomb s friction theory it is also shown that the growth direction of the reservoir is strongly controlled by the distribution of favorably oriented pre existing fractures and their interaction with the stress field

the 1998 valhall microseismic data set an integrated study of relocated sources seismic multiplets and s wave splitting werelocate303microseismiceventsrecordedin1998bysensorsinasingleboreholeinthenorthseavalhalloilfield asemiautomated array analysis method repicks the p and s wave arrival times and p wave polarizations which are needed to locate these events the relocated sources are confined predominantly toa50 m thickzonejustabovethereservoir andlocationuncertaintiesarehalfthoseofpreviousefforts multipletanalysisidentifies 40 multiplet groups which include 208 of the 303 events the largest group contains 24 events and five groups contain 10 or more events within each multiplet group we further improve arrival time picking through crosscorrelation which enhances the relative accuracy of the relocated events and reveals that more than 99 of the seismic activity lies spatially in three distinct clusters the spatial distribution of events and waveform similarities reveal two faultlike structures that match well with north northwest south southeast trending fault planes interpreted from 3d surface seismic data most waveform differencesbetweenmultipletgroupslocatedonthesefaultscanbeattributed to s wave phase content and polarity or p to s amplitude ratio the range in p to s amplitude ratios observed on the faults is explained best in terms of varying source mechanisms wealsofindacorrelationbetweenmultipletgroupsandtemporal variations in seismic anisotropy as revealed by s wave splitting analysis we explain these findings in the context of a cyclic rechargeanddissipationofcap rockstressesinresponsetoproduction driven compaction of the underlying oil reservoir the cyclic nature of this mechanism drives the short term variations in seismic anisotropy and the reactivation of microseismic source mechanismsovertime

estimation of effective unsaturated hydraulic conductivity tensor using spatial moments of observed moisture plume 1 knowledge of unsaturated zone hydraulic properties is critical for many environmental and engineering applications various stochastic methods have been developed during the past 2 decades to estimate the effective unsaturated hydraulic properties independent of these stochastic methods we develop in this paper a practical approach to estimate the three dimensional 3 d effective unsaturated hydraulic conductivity tensor using spatial moments of 3 d snapshots of a moisture plume under transient flow conditions an application of the new approach to data collected at the hanford site in southeastern washington state yields an effective unsaturated hydraulic conductivity tensor that exhibits moisture dependent anisotropy the effective hydraulic conductivities compare well with laboratory measured unsaturated hydraulic conductivity data from small core samples they also reproduce the general behavior of the observed moisture plume at the site we also define a moisture diffusivity length concept which we use in conjunction with estimated correlation scales of the geologic media at the field site to explain deviations between the observed and simulated plumes based on the derived effective hydraulic properties

spatial and temporal variability of water percolation and movement in a system of longitudinal dunes western negev israel subsurface lateral flow has previously been identified in dune areas where the average annual rainfall exceeds 200 mm very little is known about subsurface flow in sandy deserts with less than 100 mm of rainfall per year the present study deals with the water regime in a system of longitudinal dunes in the negev desert sixteen boreholes were dug down to a depth of 6 m across a sandy ridge and the adjacent corridor soil moisture and water movement were monitored with a neutron probe during two consecutive years the first year had been relatively wet and in the following year the rainfall was slightly lower than the long term average the data obtained show that in an average year water percolation is limited to 60 cm with no lateral water movement deeper percolation in the range 180 400 cm occurs in response to rainy spells with about 100 mm of cumulative rain within two months the process involves subsurface lateral flow and water movement by the piston effect the lateral flow on the flanks of the dune is explained by differences in hydraulic conductivities within the sloping layers 1997 by john wiley sons ltd

a revisit of drawdown behavior during pumping in unconfined aquifers received 16 march 2010 revised 7 february 2011 accepted 7 march 2011 published 6 may 2011 1 in this study the s shaped log log drawdown time curve typical of pumping tests in unconfined aquifers is reinvestigated via numerical experiments like previous investigations this study attributes the departure of the s shape from the drawdown time behavior of the confined aquifer to the presence of an additional source of water unlike previous studies this sourceof water isreinvestigated byexaminingthetemporal and spatial evolution of the rate of change in storage in an unconfined aquifer during pumping this evolution is then related to the transition of water release mechanisms from the expansion of water and compaction of the porous medium to the drainage of water from the unsaturated zone above the initial water table and initially saturated pores as the water table falls during the pumping of the aquifer afterward the 1 d vertical drainage process in a soil column is simulated results of the simulation show that the transition of the water release mechanisms in the 1 d vertical flow without an initial unsaturated zone can also yield the s shaped drawdown time curve as in an unconfined aquifer we therefore conclude that thetransitionofthewaterreleasemechanismsandverticalflowintheaquiferarethecauseof the s shaped drawdown time curve observed during pumping in an unconfined aquifer we also find that the moisture retention characteristics of the aquifer material have greater impact than its relative permeability characteristics on the drawdown time curve furthermore influences of the spatial variability of saturated hydraulic conductivity specific storage and saturated moisture content on the drawdown curve in the saturated zone are found to be more significant than those of other unsaturated properties finally a cross correlation analysis reveals that the drawdown at a location in a heterogeneous unconfined aquifer is mainly affected by local heterogeneity near the pumping and observation wells applications of a model assuming homogeneity to the estimation of aquifer parameters as such may require a large number of observation wells to obtain representative parameter values in conclusion we advocate that the governing equation for variably saturated flow through heterogeneous media is a more appropriate and realistic model that explains the s shaped drawdown time curves observed in the field

effective hydraulic conductivities of transient unsaturated flow in stratified soils the effective hydraulic conductivities of transient unsaturated flow in stratified soils are evaluated using a three dimensional stochastic approach because of the disparity of the correlation scales in a stratified soil the general stochastic equations are simplified and this allows analytical evaluation and derivation of generic expressions for the effective hydraulic conductivities simple asymptotic expressions valid at particular ranges of the soil property and the mean flow characteristics are also derived several examples illustrating the results using data from two real soils are also presented it was found that the effective hydraulic conductivities show significant hysteresis and are anisotropic with a degree of anisotropy depending on the mean flow conditions wetting or drying such hysteresis and anisotropy are produced by the spatial variability of the hydraulic soil properties rather than hysteresis or anisotropy of the local parameters a physical interpretation of the results is given along with a qualitative comparison with field observations the ramifications of this study need to be further investigated and be considered in field applications such as waste disposal control

absolute and relative locations of similar events with application to microearthquakes in southern iceland it is well known that similar earthquakes i e earthquakes having almost identical waveforms allow extremely accurate relative timing of the seismic arrivals this has traditionally been used for

quickly erupted volcanic sections of the steens basalt columbia river basalt group secular variation tectonic rotation and the steens mountain reversal 1 the steens basalt now considered part of the columbia river basalt group crbg contains the earliest eruptions of this magmatic episode lava flows of the steens basalt cover about 50 000 km2 of the oregon plateau in sections up to 1000 m thick the large number of continuously exposed quickly erupted lava flows some sections contain over 200 flows allows for small loops in the magnetic field direction paths to be detected for volcanic rocks this detail and fidelity are rarely found outside of the holocene and yield estimates of eruption durations at our four sections of 2 5 ka for 260 m at pueblo mountains 0 5 to 1 5 ka for 190 m at summit springs 1 3 ka for 170 m at north mickey and 3 ka for 160 m at guano rim that only one reversal of the geomagnetic field occurred during the eruption of the steens basalt the steens reversal at approximately 16 6 ma is supported by comparing 40ar 39ar ages and magnetic polarities to the geomagnetic polarity timescale at summit springs two 40ar 39ar ages from normal polarity flows 16 72 0 29 ma 16 61 and 16 92 0 52 ma 16 82 equals 2 error place their eruptions after the steens reversal while at pueblo mountains an 40ar 39ar age of 16 72 0 21 ma 16 61 from a reverse polarity flow places its eruption before the steens reversal paleomagnetic field directions yielded 50 nontransitional directional group poles which combined with 26 from steens mountain provide a paleomagnetic pole for the oregon plateau of 85 7 n 318 4 e k 15 1 a95 4 3 comparison of this new pole with a reference pole derived from crbg flows from eastern washington and a synthetic reference pole for north america derived from global data implies relative clockwise rotation of the oregon plateau of 7 4 5 0 or 14 5 5 4 respectively probably due to northward decreasing extension of the basin and range

fracture mapping in the soultz sous forets geothermal field using microearthquake locations 1 in 2003 a massive hydraulic fracturing experiment was carried out at the european geothermal hot dry rock site at soultz sous forets france the 2 week injection of water generated a high level of microseismic activity triggering about 90 000 microearthquakes during and after the fluid injection of these 21 000 events detected at all stations were located individually with a grid search algorithm to characterize the extent of the seismic zones and ultimately of the fracture network the accuracy of these initial locations was around 70 m not sufficient to map detailed fracture patterns a precise relocation effort was undertaken to reduce the location uncertainties using three different techniques joint hypocenter determination jhd collapsing and multiplet analysis the collapsing method was added to the jhd results to further consolidate the hypocenters on the other hand a multiplet analysis was performed on the initial data set for identifying microearthquakes with similar waveforms and hence relocating relatively the correlated events the delays in traveltime were computed by wavelet analysis and the events were relocated using a grid search algorithm we found 7463 events whose seismograms correlated with a correlation coefficient of 0 8 or higher most of which were doublets multiplets are horizontal tube like structures with lengths from a hundred to several hundred meters striking along the direction of the maximum compressive horizontal stress we interpret these structures as the preferential paths where fluid flow is largely confined this hypothesis is reinforced by the good correlation in depth between the events and the fluid outflows observed in the well therefore we believe that these relocated events highlight the zones where the permeability of the reservoir is increased

mining induced seismicity seismic measurement using multiplet approach and numerical modeling the volume of influence of mining works is essentially determined from in situ observations field measurements particularly surface subsidence measurements as well as from numerical investigations seismic monitoring is the primary requirement for mining in rock burst environment a micro seismic network is systematically used to monitor coal extraction in the provence colliery south eastern france a significant database of seismic events is now available a further advancement in this sequence was added by the development of doublets technique or multiplet selections the technique uses with the database to identify families of seismic events and to work out the relative locations of these events the analysis of location of these multiplet families showed a particular spatial distribution locations of the epicentre follow the direction in which the coalface is advancing numerical models are used in the paper to show the overstress distribution by comparing the seismic activity and results of the numerical modeling of the advancing coalface with observations a close correlation can be established between the location of seismic activity and induced stresses in the ground surface of the working areas by combining micro seismic monitoring with the numerical modeling the volume of influence of long wall mines is determined results show that such a coupling can be an efficient way for detecting areas subjected to rock burst hazards this can also prove to be a powerful tool for assisting the planning of underground workings in complex geological and mining conditions

chemical discrimination of columbia river basalt flows 1 the homogeneity and distinctive chemical composition of individual columbia river basalt flows are illustrated in a series of chemical plots and the procedure for flow identification is outlined the unique characterization of many individual eruptions permits units to be mapped from feeder dike to flow margins across the columbia plateau for hundreds of kilometers and so provides critical constraints on the physical and chemical evolution of this continental flood basalt province

regional correlation of grande ronde basalt flows columbia river basalt group washington oregon and idaho the tholeiitic flood basalts of the columbia river basalt group of middle and late miocene age cover more than 200 000 km2 in washington oregon and idaho the most voluminous formation of the group the grande ronde basalt erupted for 2 m y from north northwest trending fissure systems concentrated in southeast washington and adjacent oregon and idaho four magnetostratigraphic units designated r1 n1 r2 and n2 from oldest to youngest are recognized on the basis of polarity in the grande ronde and provide the broad stratigraphic framework for the formation in this study major element chemistry and relative stratigraphic position within the polarity intervals are used to identify and correlate individual flows and sequences of flows within the grande ronde basalt on a regional scale systematic examination of more than 350 analyses from 47 stratigraphic sections show that most flows fall into one of five major chemical groupings which are distinguished primarily by small but significant variations in mgo tio2 and p2o5 content in addition four minor chemical types local to the eastern part of the province have been identified feeder dikes of each chemical type have also been located flows or packets of flows of each chemical type can be correlated between field sections to define specific chemical stratigraphic subunits these subunits consist of several flows collectively 30 150 m thick subunits of most chemical types are repeated at irregular intervals throughout the formation no progressive chemical trend occurs within the grande ronde many of the chemical stratigraphic subunits extend to the margins of the province although most are confined to the source region in eastern washington although the total number of subunits is less in the west away from the fissure systems the total thicknesses of the n2 and r2 magnetostratigraphic units are each as thick or thicker than the corresponding units in eastern washington the greatest thicknesses occur in the central part of the province within the pasco basin the distribution of basalt relative to the location of vents as well as the relative east west thicknesses suggests that basalt flowed hundreds of kilometres westward during the most voluminous grande ronde eruptions ponding against the irregular margin of the cascade range and being diverted through the ancestral columbia gorge toward the washington oregon coast between these huge sheetflood events smaller eruptions blanketed areas within the source region and ongoing regional subsidence created a shallow westward draining basin in the center of the province

groundwater resources and quality variations caused by gravel mining in coastal streams abstract we study the effects of gravel mining on the aquifer river system in the baix fluvia area ne spain field data show that instream mining has caused a decline of the water table head of the unconfined aquifer along the fluvia river further dredging in its lowermost reaches reduces its stage and decreases its slope to zero which facilitates mixing with sea water and thus salty water intrusion from the river into the aquifer a dimensionless solution of the boussinesq s equation is derived to estimate the water table shape and the amount of groundwater lost as runoff for any given decline of the river stage a flow and solute transport finite element model is also used to calculate groundwater loses for the fluvia case we find that results of the general analytical solution are consistent with those of the numerical model which reproduces the actual layered aquifer and a more appropriate domain geometry finally the observed chloride distribution and time evolution are broadly reproduced using the numerical model it shows that significant chloride plumes develop after the cone of depression of the nearby wells reaches the river however a natural clean up takes place in the absence of pumping when the natural water gradient turns completely towards the river

large scale infiltration experiments into unsaturated stratified loess sediments monitoring and modeling summary two large scale field experiments were conducted to track water flow through unsaturated stratified loess deposits in the experiments a trench was flooded with water and water infiltration was allowed until full saturation of the sediment column to a depth of 20 m was achieved the water penetrated through a sequence of alternating silty sand and sandy clay loess deposits the changes in water content over time were monitored at 28 points beneath the trench using time domain reflectometry tdr probes placed in four boreholes detailed records were obtained from a 21 day period of wetting followed by a 3 month period of drying and finally followed by a second 14 day period of re wetting these processes were simulated using a two dimensional numerical code that solves the flow equation the model was calibrated using pest the simulations demonstrate that the propagation of the wetting front is hampered due to alternating silty sand and sandy clay loess layers moreover wetting front propagation is further hampered by the extremely low values of the initial unsaturated hydraulic conductivity thereby increasing the water content within the onion shaped wetted zone up to full saturation numerical simulations indicate that above hydrostatic pressure is developed within intermediate saturated layers enhancing wetting front propagation

reflection technique in time frequency domain using multicomponent acoustic emission signals and application to geothermal reservoirs we have developed a reflection technique for estimating deep geothermal reservoir structures using acoustic emission signals as a source which is useful when there is no proper estimating technique because of high temperature high pressure and great depth because its resolution is not high enough for comparison with methods such as well logging we have enhanced the technique by developing a time frequency domain analysis of multicomponent acoustic emission signals using a wavelet transform the reflected wave is separated from an incoherent coda by analyzing the shape of a 3 d hodogram a linear shape indicates the arrival of a coherent signal such as a reflected wave and an incoherent signal such as a coda makes a spherical shape we construct a spectral matrix of 3 d particle motion using a wavelet transform as is done in a time frequency domain we evaluate the linearity of the 3 d hodogram for each time and frequency by using the eigenvalues of the spectral matrix three dimensional inversion o

effects of hydraulic conductivity heterogeneity on vadose zone response to pumping in an unconfined aquifer summary it is of great importance to be able to properly simulate flow mechanisms within the vadose zone as they are controlling factors for solute transport to groundwater bodies the highly detailed pumping test data set collected by bevan et al 2005 at the borden aquifer provides a unique opportunity to investigate the controlling factors for fluid flow and moisture distribution in the vadose zone in response to pumping the field results show capillary fringe thicknesses that increased with duration of pumping and decreased with distance from the well this increased thickness was persistent for the duration of the 7 day test previous numerical analysis of the pumping test has been able to replicate the observed moisture contents at discrete time intervals moench 2008 but the physical mechanisms controlling the moisture content observations are poorly understood hydraulic conductivity heterogeneity has been proposed as a potential mechanism for the capillary fringe extension observed in the field using stochastic hydraulic conductivity fields moisture content distributions observed during the bevan et al 2005 pumping test were simulated using a variably saturated numerical model a monte carlo analysis was performed and ensemble results are presented the ensemble mean hydraulic head drawdown was an adequate match to the field data although there was a small but consistent over prediction of drawdown the ensemble mean thickness of the capillary fringe was not significantly different from the result of a homogeneous simulation and did not replicate the increasing thickness observed in the field the ensemble mean capillary fringe extension was not found to be dependent upon distance from the pumping well or duration of pumping zones of perched water were formed in many of the heterogeneous realizations however neutron probe data collected during the field experiment does not support the presence of these perched zones

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

detailed fracture system of the soultz sous forets hdr field evaluated using microseismic multiplet analysis the reservoir structure of the soultz hdr field has been investigated by examining induced microearthquake multiplets microseismic events with similar waveforms have been selected from microseismic data obtained during a 1993 hydraulic fracturing experiment precise relative arrival times and source locations have been determined by cross spectrum analysis the cross spectrum analysis decreased the residual from 0 75 ms to 0 1 ms the estimated orientations of the multiplet planes are consistent with fracture orientations detected in soultz boreholes a comparison between the stress field and the orientation of structural planes suggests that the structural planes were under a critical condition of frictional slip

stochastic analysis of unsaturated flow in heterogeneous soils 3 observations and applications results of stochastic theory for flow in heterogeneous soils are analyzed by comparisons with laboratory experiments and field observations and through applications examples the two key theoretical results are 1 the variability of capillary pressure or moisture content increases when mean capillary pressure increases and 2 the anisotropy ratio horizontal vertical of effective mean unsaturated hydraulic conductivity increases when mean capillary pressure increases or mean moisture content decreases comparisons with the field data on moisture content and capillary pressure variability show trends similar to those predicted by the theory calculations of hydraulic conductivity anisotropy based on two actual soils show that the variations in soil texture produce large changes in anisotropy as the mean capillary pressure changes several previously reported field observations and laboratory experiments support the theoretical finding of a capillary pressure dependent hydraulic anisotropy for unsaturated flow the importance of this anisotropy effect in applications involving groundwater recharge irrigation surface runoff generation and waste isolation is discussed

simulated effect of vadose infiltration on water levels in the northern guam lens aquifer regional scale hydrology of the fresh water lens in the northern guam lens aquifer has been simulated in the past using a finite element sharp interface computer model swig2d systematic differences exist between observed and computed water levels computed seasonal peak water levels are higher and the computed seasonal lows are lower than the respective observed levels it is hypothesized that vadose storage must store a substantial amount of water during the wet season and release it gradually into the lens during the dry season flow through the vadose zone was simulated with a one dimensional finite element unsaturated flow program unsat1d in which the van genuchten model is used to characterize unsaturated diffuse flow through the matrix of the vadose zone an additional parameter sink was added to the van genuchten set to account for rapid infiltration down open pathways fractures associated with the closed depressions of the karst terrain a global optimization technique shuffled complex evolution or sce ua method was used to obtain the parameters that minimized the difference between simulated and observed water levels simulations incorporating the van genuchten model were accomplished by combining the two programs unsat1d and swig2d into a single program the sum of squared errors sse between computed and observed water levels in four observation wells was minimized using sce ua reducing the arithmetically averaged sse of the four wells by 30 compared with the sse obtained when the vadose zone was not modeled these results suggest that vadose storage is significant on the other hand the fact that the best fit obtained with an optimum parameter set was able to reduce the sse by no more than 30 suggests that additional phenomena have yet to be accounted for to more fully explain differences between simulated and observed well water levels

evidence for temporal variation of seismic velocity within the upper continental crust observations of systematic temporal variations of seismic anisotropy are presented for an induced seismicity experiment at 9 km depth these observations were made under particularly well controlled conditions in the german continental deep drilling program ktb borehole using shear wave splitting from similar events recorded at a three component instrument located at 4 km depth from a hydraulic fracturing experiment at 9 km depth in a large set of seismic events recorded during the experiment many can be associated with multiplets exhibiting essentially identical waveforms since they must have approximately the same source location and source radiation pattern these events are particularly useful for testing the hypothesis of time dependent anisotropy anisotropy itself is clearly a very prominent feature in the data a simple approach for waveform matching of split shear waves allows unprecedented resolution of variations in shear wave splitting importantly the variation of shear wave splitting with time is a relative measurement which can be performed with higher accuracy than the associated absolute measurement in particular the relative measurement is not affected by timing errors nor by event distance variations during the experiment the difference between shear wave velocities decreases by 2 within 12 hours after that the medium apparently approaches a state which is stable for at least 5 hours we suggest that the temporal variation is due to the tectonic stress release from seismic events caused by the fluid injection this model requires the presence of fluid filled cracks at depths larger than 4 kin

late devonian palaeomagnetism of the north tien shan kyrgyzstan can secular variation vary on a short timescale summary we studied more than 80 lava flows from a 600 m thick pile of upper devonian frasnian basalts and andesites of the aral formation in the north tien shan kyrgyzstan central asia with the aid of stepwise thermal demagnetization a high temperature dual polarity component was reliably isolated from most flows the primary origin of the high temperature component is demonstrated by positive reversal conglomerate and fold tests the most prominent and intriguing feature of this late devonian data set involves a clear distinction in angular dispersion between the lower and upper parts of the studied section a rather low concentration parameter k 13 and several directional anomalies characterize the lower section in contrast a much better grouping k 46 and a lack of directional outliers is observed for the dual polarity vectors from the upper flow sequence of the formation we analysed different mechanisms to account for this directional pattern and found that it is possible in just two ways one is to assume that secular variation sv in the upper sequence is strongly underrepresented and it is a coincidence that the mean directions of both polarities are statistically antipodal and the corresponding concentration parameters are statistically equal the other explanation is to hypothesize that the magnitude of sv can vary several fold at the same palaeolatitude and over time intervals estimated as 10 5 10 6 yr this is in sharp contrast with other models of sv where this magnitude has been assumed to be rather time independent for a givenlatitude ourhypothesisaccountsfortheobservedirregularitiesinpalaeomagneticdata but makes attempts to establish a correlation between sv and other parameters geographic latitude reversal frequency age etc more difficult we are aware however that more data are needed to refute or confirm it

recent investigations of the 0 5 ma geomagnetic field recorded by lava flows we present a synthesis of 0 5 ma paleomagnetic directional data collected from 17 different locations under the collaborative time averaged geomagnetic field initiative tafi when combined with regional compilations from the northwest united states the southwest united states japan new zealand hawaii mexico south pacific and the indian ocean a data set of over 2000 sites with high quality stable polarity and declination and inclination measurements is obtained this is a more than sevenfold increase over similar quality data in the existing paleosecular variation of recent lavas psvrl data set and has greatly improved spatial sampling the new data set spans 78 s to 53 n and has sufficient temporal and spatial sampling to allow characterization of latitudinal variations in the time averaged field taf and paleosecular variation psv for the brunhes and matuyama chrons and for the 0 5 ma interval combined the brunhes and matuyama chrons exhibit different taf geometries notably smaller departures from a geocentric axial dipole field during the brunhes consistent with higher dipole strength observed from paleointensity data geographical variations in psv are also different for the brunhes and matuyama given the high quality of our data set polarity asymmetries in psv and the taf cannot be attributed to viscous overprints but suggest different underlying field behavior perhaps related to the influence of long lived core mantle boundary conditions on core flow psv as measured by dispersion of virtual geomagnetic poles shows less latitudinal variation than predicted by current statistical psv models or by previous data sets in particular the brunhes data reported here are compatible with a wide range of models from those that predict constant dispersion as a function of latitude to those that predict an increase in dispersion with latitude discriminating among such models could be helped by increased numbers of low latitude data and new high northern latitude sites tests with other data sets and with simulations indicate that some of the latitudinal signature previously observed in vgp dispersion can be attributed to the inclusion of low quality insufficiently cleaned data with too few samples per site our matuyama data show a stronger dependence of dispersion on latitude than the brunhes data the taf is examined using the variation of inclination anomaly with latitude best fit two parameter models have axial quadrupole contributions of 2 4 of the axial dipole term and axial octupole contributions of 1 5 approximately 2 of the octupole signature is likely the result of bias incurred by averaging unit vectors

reflection imaging of deep reservoir structure based on three dimensional hodogram analysis of multicomponent microseismic waveforms 1 we have applied a type of reflection technique in which natural or induced microseismicity is used as a wave source and is processed in the time frequency domain to data from the soultz hot dry rock site to image deep structures within the reservoir that may be associated with flow paths among three wells we selected and analyzed 119 good waveforms observed in 2003 the distribution of these 119 events was not strongly inclined and although the selected number of events was much smaller than the total microseismic events located we still succeeded in applying the reflection analysis the reflection images obtained using waveforms from 2003 are in agreement with those obtained using data from 1993 and 2000 finally detailed three dimensional reflection images were created by an integration of estimates using all available waveform data reflectors appear around the deep geothermal wells and one of the dipping reflectors seems to be an obstacle to flow connection that shows a clear correlation with a microseismic cloud created during hydraulic stimulation in 2004 from these analyses we succeeded in interpreting the roles of preexisting structures in the development of flow connection among wells which is an essential factor in a hot dry rock system