character and distribution of borehole breakouts and their relationship to in situ stresses in deep columbia river basalts the character and distribution of borehole breakouts in deeply buried basalts at the hanford site in south central washington state are examined in light of stress indicator data and hydraulic fracturing stress data by means of acoustic televiewer and acoustic waveform logging systems a series of boreholes penetrating the grande ronde basalt of the columbia river basalt group were logged to examine the extent of breakouts at depths near 1000 m breakouts occur discontinuously throughout the interiors of most flows in some boreholes the distribution of borehole wall breakouts closely correlates with the incidence of core disking differences in the distribution of breakouts and disking are attributed to differences in failure mechanisms a thin interval of breakout free basalt occurs near the upper and lower limits of flow interiors with many intervals of breakouts terminating at the intersection of oblique fractures with the borehole hydraulic fracturing stress measurement results obtained from four deep boreholes indicate anisotropic horizontal principal stresses with maximum principal stress along an approximate north trending axis consistent with the east trending orientation of breakouts acoustic waveform logs indicate that there is no measurable difference between the seismic properties of breakout free flow tops and flow interiors the highly coherent waveforms obtained in almost all flow interiors indicate that damage to the borehole wall associated with breakout formation remains confined to the thin annulus of stress concentration

stress strain paradox plate coupling and forearc seismicity at the cascadia and nankai subduction zones abstract in the continental forearcs of the cascadia and nankai subduction zones geodetic strain measurements indicate crustal contraction in the direction of plate convergence nearly margin normal but earthquake focal mechanisms and other stress indicators show maximum compression along strike margin parallel it is evident that the geodetic strain signals reflect the temporal fluctuations of elastic stress associated with subduction earthquake cycles not the absolute stresses the absolute margin normal stress is not only much less than the margin parallel stress but also no greater than the lithostatic value indicating a very weak subduction thrust fault weak subduction faults are also consistent with geothermal data which require very low frictional heating along the faults great subduction earthquakes occur at very low shear stresses and cause small perturbations to the forearc stress regime because these small elastic stress perturbations are relatively fast they give large strain rates that are detected by geodetic measurements the present nearly margin normal contraction in both places is due to the locking of the subduction fault and the consequent increase in elastic stress in the direction of plate convergence with the margin parallel compression being dominant the small increase in margin normal stress may change the forearc seismicity in cascadia from a mixture of thrust and strike slip types into mainly thrust before the next great subduction earthquake in nankai the change should be from strike slip to quiescence as observed in the nankai forearc prior to the 1944 1946 great subduction earthquakes

stress directions in eastern north america determined to 4 5 km from borehole elongation measurements stress directions have been determined to depths of 4 5 km in eastern north america from borehole elongation measured by dipmeter calipers in 47 wells the average maximum horizontal stress directions are eastern canada n54 e 7 appalachian basin n58 e 8 and the illinois basin n89 w 5 stress directions determined for the illinois and appalachian basins are in agreement with published interpretations from hydraulic fractures and earthquake fault plane solutions new results from eastern canada and the appalachian basin show that stress directions are everywhere consistent with the midcontinent stress province these data suggest that the maximum horizontal stress does not rotate from the ene midcontinent trend to nw near the atlantic coast a directional analysis of hydraulic fractures petal centerline fractures and natural fractures from the appalachian basin shows that borehole elongation is systematically aligned perpendicular to the directions of hydraulic fractures centerline fractures and northeast striking natural fractures but is not systematically aligned with northwest striking natural fractures these observations indicate that borehole elongations provide reliable stress orientations

flow patterns of magma in dikes makhtesh ramon israel directions of magma flow were measured in a system of radial dikes in makhtesh ramon israel the flow directions were determined from field observations of segments fingers grooves and groove molds of the dikes the study indicates that the mean axis of magma flow is subhorizontal toward the north in agreement with the direction of divergence of the radial dike system two modes of flow were observed 1 regular bedding parallel flow in the well stratified rock units and 2 irregular meandering flow in the massive rock units it is suggested that corrugated dike walls in well stratified host rocks cause magma channelization and random or self generated restrictions in massive host rocks cause the apparent meanders furthermore the major lithologic boundaries in the host units strongly affect segmentation of the dikes

optimal estimation of spatially variable recharge and transmissivity fields under steady state groundwater flow part 2 case study abstract the first order analytical solution of the inverse problem for estimating spatially variable recharge and transmissivity under steady state groundwater flow developed in part 1 is applied to the upper floridan aquifer in ne florida parameters characterizing the statistical structure of the log transmissivity and head fields are estimated from 152 measurements of transmissivity and 146 measurements of hydraulic head available in the study region optimal estimates of the recharge transmissivity and head fields are produced throughout the study region by conditioning on the nearest 10 available transmissivity measurements and the nearest 10 available head measurements head observations are shown to provide valuable information for estimating both the transmissivity and the recharge fields accurate numerical groundwater model predictions of the aquifer flow system are obtained using the optimal transmissivity and recharge fields as input parameters and the optimal head field to define boundary conditions for this case study both the transmissivity field and the uncertainty of the transmissivity field prediction are poorly estimated when the effects of random recharge are neglected

dyke intrusion into a pre existing joint network the aiguablava lamprophyre dyke swarm catalan coastal ranges abstract a structural analysis has been performed in the upper permian lamprophyric dyke swarm of aiguablava costa brava ne iberia emplacement of sub vertical dykes is related to the presence of a widespread joint network mostly developed during the cooling and decompression of the late variscan leucogranitic host rocks the joint pattern consists on multiple sub vertical joint sets among which two orthogonal sets at n23 and n113 are predominant a sub horizontal set is also prominent the sub vertical dykes have a mean n100 n125 trend which corresponds to the trend of one of the main joint sets however dyke segmentation is noticeable at the dm to cm scale and this is inferred to be related to dyke propagation and emplacement along the variably oriented pre existing joints a mean robust sub horizontal nne ssw net dilation direction was measured from matching dyke jogs markers in the host rock and analysis of maximum dyke thicknesses and this is in line with the minimum principal stress axis 3 derived from a three dimensional paleostress analysis from dyke orientations the inferred maximum principal stress axis 1 is sub vertical indicating that dykes intruded under conditions of tectonic extension furthermore a mohr construction allowed calculation of the stress ratio 0 29 close to a prolate stress ellipsoid and a driving pressure ratio r 0 27 which corresponds to a magmatic pressure almost equal to the intermediate principal stress axis 2 it is inferred that many of the pre existing joint sets were exploited by the magma the wnw ese joint set normal to 3 being the most favorable for dyke emplacement the present study highlights the structural control of a pre existing fracture network on emplacement of the aiguablava lamprophyres in the upper crust during late permian nne ssw brittle extension

in situ stress natural fracture distribution and borehole elongation in the auburn geothermal well auburn new york hydraulic fracturing stress measurements and a borehole televiewer survey were conducted in a 1 6 km deep well at auburn new york this well which was drilled at the outer margin of the appalachian fold and thrust belt in the appalachian plateau penetrates approximately 1540 m of lower paleozoic sedimentary rocks and terminates 60 m into the precambrian marble basement analysis of the hydraulic fracturing tests indicates that the minimum horizontal principal stress increases in a nearly linear fashion from 9 9 0 2 mpa at 593 m to 30 6 0 4 mpa at 1482 m the magnitude of the maximum horizontal principal stress increases in a less regular fashion from 13 8 1 2 mpa to 49 0 2 0 mpa over the same depth range the magnitudes of the horizontal principal stresses relative to the calculated overburden stress are somewhat lower than is the norm for this region and are indicative of a strike slip faulting regime that at some depths is transitional to normal faulting as expected from the relative aseismicity of central new york state however analysis of the magnitudes of the horizontal principal stresses indicates at least to a depth of 1 5 km that frictional failure on favorably oriented preexisting fault planes is unlikely orientations of the hydraulic fractures at 593 and 919 m indicate that the azimuth of the maximum horizontal principal stress at auburn is n83 e 15 in agreement with other stress field indicators for this region the borehole televiewer log revealed a considerable number of planar features in the auburn well the great majority of which are subhorizontal dips 5 and are thought to be bedding plane washouts or drill bit scour marks in addition a smaller number of distinct natural fractures were observed on the borehole televiewer log of these the distinct steeply dipping natural fractures in the lower half of the sedimentary section at auburn tend to strike approximately east west while those in the upper part of the well and in the precambrian basement exhibit no strong preferred orientation the origin of this east west striking fracture set is uncertain as it is parallel both to the contemporary direction of maximum horizontal compression and to a late paleozoic fracture set that has been mapped to the south of auburn in addition to these planar features the borehole televiewer log indicates paired dark bands on diametrically opposite sides of the borehole throughout the auburn well processing of the borehole televiewer data in the time domain revealed these features to be irregular depressions in the borehole wall as these depressions were consistently oriented in a direction at right angles to the direction of maximum horizontal compression we interpret them to be the result of stress induced spalling of the borehole wall breakouts

effect of temporally correlated recharge on fluctuations of groundwater levels 1 the effect of temporally correlated groundwater recharge r t on fluctuations of the hydraulic head h t was investigated with theoretical analyses and numerical simulations under an exponentially correlated recharge ecr process analytical solutions for the hydraulic head covariance chh and variance h2 were derived with a linear reservoir model it was found that chh and h2 are time dependent or nonstationary and reduce to those derived in a previous study for a white noise recharge wnr when the correlation timescale of the recharge process approaches zero it is also found that h2 for ecr is proportional to t2 while that for wnr is proportional to t for a substantial period of time indicating that h t under ecr may vary as a smooth curve with no fractal characteristics d 1 0 while h t under wnr fluctuates as a brownian motion d 1 5 the theoretical findings were verified by numerical simulations the power spectra of the simulated heads with a one dimensional transient groundwater flow model under ecr were shown to have distinct slopes in the log log plot with d 1 02 it was emphasized that the effect of temporal correlation in groundwater recharge is to dampen the fluctuations of the head and base flow and that daily groundwater recharge rates may have little temporal correlation in the hydrogeological conditions similar to the walnut creek site

active deformation of the pacific northwest continental margin tilted and uplifted marine terraces in southern oregon show progressive landward tilting of the coastal ranges at about 5 16 10 8 rad yr 1 for the last 0 25 m y tide gauges in washington and british columbia and ten resurveyed leveling lines running inland from the coast indicate contemporary landward down to the east tilt rates of about 1 12 10 8 rad yr 1 averaged over periods of from 10 to 50 years the leveling lines traverse and the terraces cut across dipping cenozoic strata pleistocene dips to 3 mio pliocene dips to 30 and eocene dips to 60 southern oregon from cape blanco to the siletz river shows geodetic or terrace tilting in the same direction as the underlying stratal dips hence present day deformation continues past deformation of the coastal ranges and is most likely related to active subduction of the juan de fuca plate the steep stratal dips lack of major active faults and historic earthquakes and presence of very young bedding plane faults suggest that much of the onshore deformation and shortening within the overlying north american plate is taken up by folding rather than thrust faulting present shortening rates across north trending folds near the coast are between 0 02 and 1 9 10 7 yr 1 the rate of shortening decreases rapidly eastwards from the juan de fuca north american plate boundary a total of about 25 mm yr 1 of permanent shortening could be occurring within the north american plate most of it in the westernmost 40 km the landward tilt and shortening rates are similar to those above many other subduction zones that have experienced great thrust earthquakes while a high strain rate measured near seattle washington has been interpreted as elastic strain accumulation before a thrust earthquake the low level of historic seismicity and the similarity of short and long term deformation rates suggest alternatively that the subduction beneath washington is aseismic the issue has considerable implications for seismic hazard evaluation in the pacific northwest and could be resolved by a search for the effects or lack of effects of prehistoric great earthquakes

transient dike propagation and arrest near the level of neutral buoyancy abstract we present a finite difference perturbation method to investigate transient dike propagation from a magma chamber 1 2 km below the level of neutral buoyancy in oceanic crust and explore the role of density gradation in dike propagation arrest the dike is modeled as a magma filled blade crack and the host rock is assumed to be a linear elastic medium with graded mass density an integral equation approach is used to obtain the dike propagation velocity and stress intensity factor at the propagating dike tip the finite difference perturbation method is applicable generally to mafic dikes with v less than 50 pa m where is the magma viscosity and v the dike propagation velocity numerical results show that dike propagation velocity initially increases with dike length reaches a peak value when the dike tip reaches a position well above the level of neutral buoyancy and then rapidly decreases to zero after the dike propagates further into the region above the level of neutral buoyancy which indicates that density gradation is an effective mechanism for dike arrest the effects of host rock fracture toughness and magma chamber depth relative to the level of neutral buoyancy are also discussed

mechanics of emplacement and tectonic implications of the ramon dike systems israel a radial system comprising more than 200 basaltic and trachytic dikes and two minor systems of parallel dikes intruded the ramon area southern israel during the early cretaceous field relations between dikes and fractures in the radial system indicate that the dikes intruded self generated fractures and thus indicate the directions of the tectonic stresses other field observations indicate that the dikes propagated in subhorizontal directions up to distances of 15 km from their source our analysis of the emplacement mechanics of these dikes shows that the horizontal propagation is best explained by the density differences between the intruding magma and the host rocks the measured mean density for basement rocks at depths greater than 2 4 km is 2 55 0 07 g cm3 and it is 2 36 0 21 g cm3 for the sedimentary cover above for the magma to be propagating horizontally at its neutral buoyancy level requires a mean magma density of about 2 5 g cm3 the large distance of horizontal propagation requires a low viscous pressure drop below 0 1 mpa km within the dike and an overpressure of about 1 mpa in the magma chamber we computed stress trajectories using a two dimensional elastic model for a pressurized hole in a regional stress field and compared it to the ramon radial system the model reveals that the dikes originated at a central intrusion of about 3 km diameter and intruded under a predominantly radial state of stress with negligible regional stress field this period of weak tectonic stresses and intensive magmatism falls between the early mesozoic extensional regime and the late mesozoic cenozoic compressional regime in israel the calculated center of the radial system is offset from a large magnetic anomaly south of the ramon area suggesting a 3 km right lateral displacement along the ramon fault after the intrusion of the radial system

the effects of recharge on flow nonuniformity and macrodispersion the spatial statistical structure of the fluid velocity field in the case of uniformly recharged heterogeneous aquifers is investigated and the spatial covariances of the velocity field are derived this information is necesary for an investigation of flow and macrodispersion using the lagrangian formalism proposed by dagan 1984 the resulting first two moments of the velocity are nonstationary they are functions of a parameter which characterizes the degree of flow nonuniformity and is related to the recharge the displacement variances are computed and tested favorably using numerical simulations simple relations are developed which relate the transport parameters found for the case of uniform in the average flows to nonuniform flows using a simple nonlinear transformation of the travel time based on

mechanisms of dike propagation in layered rocks and in massive porous sedimentary rocks the mechanisms of dike propagation are analyzed through detailed examination of small structures associated with the dike intrusion exposures in the ramon area israel offer an opportunity to evaluate theoretical models of tensile fracture propagation and to better understand the factors governing the dike geometry dike related structures are studied in two jurassic units the ardon formation a well stratified sequence of shales and dolomites and the inmar formation which is composed of porous massive sandstones with a few shale lenses it is shown that for the different host rocks the propagation mechanisms and structures differ significantly dikes in the ardon formation are dominated by 1 20 m wide segments confined to distinct layers the mechanisms of segment containment are determined by calculating the stress intensity factor for an extension crack approaching a mechanical interface it is apparent that dike segmentation and containment is controlled mainly by in situ stress and shear moduli differences between adjacent layers and partly by bedding plane slippage dikes in the inmar formation are dominated by smaller segments and by 1 10 cm wide and 10 100 cm long fingers with intermittent smooth patches and slickensides opposite dike walls display exact mirror images of these features dikes propagate in alternating stages of viscous flow and brittle deformation the viscous stages include fluidization of the sandstone by the dike related fluids and increase of the pore pressure in the rock a viscous instability develops between the highly viscous fluidized sandstone and the less viscous dike related fluids forming a zone of viscous fingering in front of the dike stages of brittle fracturing occur when the pore pressure is released and the flux of fluids is insufficient to fluidize the rock

dike surface lineations as magma flow indicators within the sheeted dike complex of the troodos ophiolite cyprus mesoscopic flow lineations and anisotropy of magnetic susceptibility ams have been measured for dikes within the cretaceous age troodos ophiolite with the goal of comparing the direction of initial magma flow through dike conduits immediately following crack propagation with that of flow of subsequent magma emplaced during later stages of dike growth dike margin indicators of flow include cusp axes and elongate vesicles found high in the ophiolite pseudostratigraphy and ridge and groove structures termed hot slickenlines found throughout the complex a unique flow direction is determined where elongate vesicles near dike margins display imbrication with respect to the margin significant changes in vesicle elongation directions across dikes likely indicate either changes in magma flow direction after dike propagation or back flow of magma during the waning stages of intrusion surface lineations generally lie subparallel to the direction of flow inferred from ams determinations on cores within 5 cm of dike margins surface lineations also lie subparallel to the long axis e1 of the orientation ellipsoid defined by long axes of groundmass plagioclase phenocrysts measured in sections from ams cores correlation of surface lineations with interior indicators of flow ams plagioclase trachytic texture indicate that the surface features are good proxies for grain scale magma flow directions during dike propagation in troodos dikes orientations of surface flow features in the dikes of the troodos ophiolite indicate an approximately equal mix of subhorizontal to near vertical magma flow contradicting the paradigm of primarily vertical flow of magma beneath continuous axial magma chambers at oceanic spreading centers our data are consistent with a model of magma emplacement both vertically and horizontally away from isolated magma chambers beneath axial volcanoes spaced along a ridge crest

topographic meteorologic and canopy controls on the scaling characteristics of the spatial distribution of snow depth fields 1 in this study lidar snow depths bare ground elevations topography and elevations filtered to the top of vegetation topography vegetation in five 1 km 2 areas are used to determine whether the spatial distribution of snow depth exhibits scale invariance and the control that vegetation topography and winds exert on such behavior the one dimensional and mean two dimensional power spectra of snow depth exhibit power law behavior in two frequency intervals separated by a scale break located between 7 m and 45 m the spectral exponents for the low frequency range vary between 0 1 and 1 2 for the one dimensional spectra and between 1 3 and 2 2 for the mean twodimensional power spectra the spectral exponents for the high frequency range vary between 3 3 and 3 6 for the one dimensional spectra and between 4 0 and 4 5 for the mean two dimensional spectra such spectral exponents indicate the existence of two distinct scaling regimes with significantly larger variations occurring in the larger scale regime similar bilinear power law spectra were obtained for the fields of vegetation height with crossover wavelengths between 7 m and 14 m further analysis of the snow depth and vegetation fields together with wind data support the conclusion that the break in the scaling behavior of snow depth is controlled by the scaling characteristics of the spatial distribution of vegetation height when snow redistribution by wind is minimal and canopy interception is dominant and by the interaction of winds with features such as surface concavities and vegetation when snow redistribution by wind is dominant

local crustal extension at mount st helens washington seismicity and the orientation of fault planes from focal mechanisms indicate that mount st helens is located at a dextral offset along the st helens seismic zone shz earthquake swarms occurring in this offset are related to volcanic eruptions because motion on the shz is in a right lateral strike slip sense this dextral offset creates extension within a volume of the crust between the offset fault segments this offset geometry is similar to that of geothermal areas along the san andreas fault system we apply a model derived from these geothermal areas to mount st helens and find that the major differences between mount st helens and the geothermal areas can be related to the ratio of the width of the offset between fault segments l to the seismogenic depth h at mount st helens this ratio is 1 whereas in the geothermal areas the ratio is 1 we propose that when l h 1 as at mount st helens the regional minimum principal stress does not completely dominate the small volume under extension and as a consequence the opening geometry is poory established compared to the oblique crustal spreading that characterizes the geothermal areas where l h 1 late quaternary volcanic vents near mount st helens strike northeast similar to the strike of a set of pre quaternary faults and intrusive rocks that are mapped north of the volcano in addition the deepest earthquakes occurring within the extensional volume are aligned along a northeast striking fault since these northeast striking features are aligned approximately prependicular to the regional minimum principal stress we infer that the spatial position of mount st helens is controlled by the junction of the right stepping offset of the shz with the older set of fractures and that these fractures are favorably aligned with respect to the contemporary regional tectonic stress directions for the transport of magma through the brittle crust the sense of fault motions predicted by our model for local crustal extension is consistent with an apparent component of right lateral shear measured from geodetic lines around mount st helens during june and july 1980

late quaternary deformation of marine terraces on the cascadia subduction zone near cape blanco oregon the cape blanco region of south coastal oregon sits on the upper plate of the cascadia subduction zone about 60 70 km east of the base of the continental slope though the region has no historic coseismic deformation late quaternary deposits and landforms show abundant evidence of uplift folding and faulting a set of five late quaternary marine terraces and one uplifted holocene beach berm are preserved in the cape blanco region stratigraphic and altitudinal surveys of these physiographic features combined with several numerical and correlation age determinations permit a reconstruction of tectonic deformation near cape blanco in approximately the last 200 000 years the most cogent aspects of the neotectonics in this part of the cascadia subduction zone are that an east west trending anticline deforms the lower three terraces 80 125 ka as well as accounting for uplift of the holocene storm berm latest movement on the anticline was no more than 2 000 years ago but the anticline also deforms sediments as old as middle miocene the anticline is consistent with a north south principal contraction axis at cape blanco in about the last 100 000 years an older terrace at cape blanco approximately 200 ka is offset by two reactivated faults whose movements prior to the eocene served to suture several terranes to the north american continent tectonic tilting in the older terrace is not consistent with a north south principle axis of contraction but the axis of tilt is parallel to north northwest striking structures developed in the quaternary fold belt offshore on the continental shelf the observed deformation indicates that regional stress in the vicinity of cape blanco in the late quaternary has been accommodated by a variable pattern of strain

robust evidence for random fractal scaling of groundwater levels in unconfined aquifers this study introduces new approaches to improve the statistical robustness of techniques for quantifying the fractal scaling of groundwater levels and uses these techniques to investigate scaling of groundwater levels from a consolidated permeable carbonate aquifer six groundwater level time series and an associated river stage time series from the unconfined chalk aquifer a dual porosity fractured limestone aquifer in the pang lambourn catchment uk have been analysed surrogate data of time series with known scaling properties have been used to estimate the probability distribution of the spectral and geometric scaling exponents determined by detrended fluctuation analysis dfa and power spectral density psd respectively robust regression techniques have been used to improve estimates of the scaling exponents and robust non parametric techniques have been used to correlate scaling exponents with features of the boreholes and catchments strong statistical support has been found for temporal scaling of groundwater levels over a wide range of time scales however bootstrap estimates of the scaling exponents indicate a much larger range of exponents than found by previous studies suggesting that the uncertainty in existing estimates of scaling exponents may be too small there is robust evidence that geometrical scaling properties at each borehole can be related to the depth of the observation boreholes and distance of those boreholes from the river in the catchment but no such correlations were found for the spectral scaling exponents the results build on the body of evidence that groundwater levels as with many hydrogeological phenomena may be well modelled with mathematical concepts from statistical mechanics that do not attempt to capture every detail of these highly heterogeneous and complex systems

features of spatiotemporal groundwater head variation using independent component analysis abstract the effect of external stimuli on a groundwater system can be understood by examining the features of spatiotemporal head variations however the head variations caused by various external stimuli are mixed signals to identify the stimuli features of head variations we propose a systematic approach based on independent component analysis ica frequency analysis cross correlation analysis well selection strategy and hourly average head analysis we also removed the head variations caused by regional stimuli e g rainfall and river stage from the original head variations of all the wells to better characterize the local stimuli features e g pumping and tide in the synthetic case study the derived independent component ic features are more consistent with the features of the given recharge and pumping than the features derived from principle component analysis in a real case study the ics associated with regional stimuli highly correlated with field observations and the effect of regional stimuli on the head variation of all the wells was quantified in addition the tide agricultural industrial and spring pumping features were characterized therefore the developed method can facilitate understanding of the features of the spatiotemporal head variation and quantification of the effects of external stimuli on a groundwater system

the tectonic significance of dikes of irregular fold like shape the effects of postemplacement deformation on originally nonplanar dikes were tested experimentally and compared to field data from the rainy lake zone ontario canada where irregular fold like structures are observed the analyses reveal that two processes are responsible for the irregular dike geometries first dikes intrude with varying orientations as they propagate across layers with rheology contrasts thus developing nonplanar profiles second with postemplacement ductile deformation dikes that are more competent than the host rocks are folded and refracted in variable amounts with the amount depending on the initial dike geometry the heterogeneities in the host and the regional strain deformed dikes and veins are often used as kinematic markers to evaluate regional tectonics using methods that generally assume that veins had planar walls prior to deformation the experimental results indicate that caution should be taken when using this approach and they provide criteria to distinguish between intrusive and deformation structures in intensely deformed areas where distinction between the two is not readily apparent

temporal scaling of hydraulic head and river base flow and its implication for groundwater recharge 1 spectral analyses were conducted for hourly hydraulic head h data observed over a 4 year period at seven monitoring wells in the walnut creek watershed iowa the log power spectral density of the hydraulic head fluctuations versus log frequency f at all seven wells is shown to have a distinct slope or fractal dimension d indicating temporal scaling in the time series of water level fluctuations the fractal dimension of the time series varies from well to well and the spectrum for the average h over all seven wells has a fractal dimension of 1 46 and hurst coefficient of 0 54 the log power spectral density of estimated base flow in the walnut creek and four other watersheds versus log f is shown to have two distinct slopes with a break in scaling at about 30 days it is shown that the groundwater recharge process in a basin can be estimated from a head spectrum based on existing theoretical results hydraulic head in an aquifer may fluctuate as a fractal in time in response to either a white noise or fractal recharge process depending on physical parameters i e transmissivity and specific yield of the aquifer the recharge process at the walnut creek watershed is shown to have a white noise spectrum based on the observed head spectrum

the relative contribution of accretion shear and extension to cenozoic tectonic rotation in the pacific northwest large cenozoic clockwise rotations defined by paleomagnetic data are an established fact in the pacific northwest and many tectonic models have been proposed to explain them including 1 rotation of accreted oceanic microplates during docking 2 dextral shear between north america and northward moving oceanic plates to the west and 3 microplate rotation in front of an expanding basin and range province stratigraphic onlap relations and local structure indicate that microplate rotation during docking was not a major contributor to the observed rotations coast range structures basin and range extension and paleomagnetic data from middle miocene 15 ma coast range rocks indicate that dextral shear is responsible for at least 40 of the post 15 ma rotation of the coast range and that basin and range extension is responsible for the remainder reconstructions based on extrapolation of this ratio back to 37 and 50 ma are consistent with reconstructions based on paleomagnetic and stratigraphic relations in older rocks and suggest that dextral shear has been a significant contributor to rotation during most of tertiary time changes in the dextral shear rotation rate over the past 50 m y correlate directly with changes in the velocity of the farallon plate parallel to the coast and provide a strong argument for oblique subduction as the driving mechanism continental reconstructions incorporating shear may provide constraints on the rate of extension in the northernmost basin and range region and suggest 17 extension since 15 ma 39 since 37 ma and 72 since 50 ma near latitude 42 n

multifractal analysis and modeling of rainfall and river flows and scaling causal transfer functions river flows have been known to be scaling for over 40 years and scaling notions have developed rapidly since the 1980s using the framework of universal multifractals and time series of rainfall and river runoff for 30 french catchments basin sizes of 40 km 2 to 200 km 2 from 1 day to 30 years we quantify types and extent of the scaling regimes for both flow and rain series we observed a scale break at roughly 16 days which we associate with the synoptic maximum the time scale of structures of planetary spatial extent for the two scaling regimes in both series we estimate the universal multifractal parameters as well as the critical exponents associated with multifractal phase transitions using these exponents we perform causal multifractal time series simulations and show how a simple linear scaling transfer function can be used to relate the low frequency rainfall series to the corresponding river flow series the highfrequency regime requires nonlinear transforms

stress orientations from well bore breakouts in the coalinga region borehole breakouts are caused by unequal stress concentrations around a borehole resulting in shear failure of the borehole wall and creating hole elongation perpendicular to the maximum horizontal in situ stress breakouts in tertiary sedimentary rocks were identified in 10 holes in the west coalinga cantua creek and west haven oil fields in the western san joaquin valley the deeper and more reliable 1 5 to 3 7 km breakouts were oriented northwest indicating northeast compressive stress perpendicular to the major fold axes in the san joaquin valley and at a 70 90 angle to the major strike slip faults in the coast ranges this stress direction is consistent with a reverse slip component on northwest trending faults in the region and with the focal mechanisms reported for the may 1983 coalinga earthquake the existing literature on stress measurements in central and southern california indicates that on a regional scale the stress regime is transitional between thrust and strike slip faulting a hydraulic fracture test in the kettleman hills oil field at 3 km depth indicates that this stress regime exists in the upper crust near coalinga as well

recent movements of the juan de fuca plate system analysis of the magnetic anomalies of the juan de fuca plate system allows instantaneous poles of rotation relative to the pacific plate to be calculated from 7 ma to the present by combining these with global solutions for pacific america and absolute relative to hot spot motions a plate motion sequence can be constructed this sequence shows that both absolute motions and motions relative to america are characterized by slower velocities where younger and more buoyant material enters the convergence zone pivoting subduction the resistance provided by the youngest portion of the juan de fuca plate apparently resulted in its detachment at 4 ma as the independent explorer plate in relation to the hot spot framework this plate almost immediately began to rotate clockwise around a pole close to itself such that its translational movement into the mantle virtually ceased after 4 ma the remainder of the juan de fuca plate adjusted its motion in response to the fact that the youngest material entering the subduction zone was now to the south differences in seismicity and recent uplift between northern and southern vancouver island may reflect a distinction in tectonic style between the normal subduction of the juan de fuca plate to the south and a complex underplating occurring as the explorer plate is overridden by the continent the history of the explorer plate may exemplify the conditions under which the self driving forces of small subducting plates are overcome by the influence of larger adjacent plates the recent rapid migration of the absolute pole of rotation of the juan de fuca plate toward the plate suggests that it too may be nearing this condition

patterns of magma flow in segmented silicic dikes at summer coon volcano colorado ams and thin section analysis abstract a complex pattern of magma flow is found in two silicic dikes of a radial swarm at summer coon an eroded stratovolcano in southern colorado the two intrusions are broken into multiple segments that suggest vertical dike propagation however anisotropy of magnetic susceptibility ams measurements and thin section observations suggest that magma flow was often subhorizontal and away from the center of the volcano segments that are proximal to the central intrusion are characterized by magma that flowed steeply upward at the proximal segment extremity then laterally along the segment and finally downward at the distal end of the segment magma flow in offset segment tips located far from the volcano center was subhorizontal towards the adjacent segment implying lateral propagation of segment tips towards one another this observation suggests relatively high driving pressure in distal dike segments as supported by dike thickening with radial distance from the center of the volcano the present study indicates that radial dike evolution at stratovolcanoes is dominated by lateral flow of magma and dike segmentation is a poor magma flow indicator a horizontally propagating radial dike has the potential to cause an eruption low on the flank of a composite cone which poses a significant yet largely unrecognized hazard to population centers and infrastructure that may surround the volcano

stress induced borehole elongation a comparison between the four arm dipmeter and the borehole televiewer in the auburn geothermal well the nature and origin of borehole elongation recorded by the four arm dipmeter calipers is studied utilizing information obtained from hydraulic fracturing stress measurements and borehole televiewer data taken in a well located in auburn new york a preferred orientation n10 w s10 e 10 and a less prominant e w orientation of borehole elongation was observed on two runs of the dipmeter comparisons of borehole geometry determined using the televiewer and the dipmeter show that both tools give the same orientation of borehole elongtion provided that the zone of elongation is longer than 30 cm comparisons of dipmeter caliper data with orientation of in situ stress and natural fractures obtained from hydrofracturing tests and televiewer data show that the n10 w s10 e borehole elongations 1 are axisymmetric 2 are aligned with the minimum horizontal stress sh and 3 are not associated with natural fractures intersecting the well these elongations are interpreted as stress induced well bore breakouts the e w elongation direction is characterized by an asymmetric borehole cross section in thinly bedded rocks and is not caused by breakouts this asymmetric geometry can be discriminated from breakouts using the oriented electric measurements provided by the dipmeter this study demonstrates that the dipmeter can be used to determine the orientation of sh by mapping breakouts confirming the results of earlier less detailed studies and provides a firm basis for mapping regional stress patterns using existing dipmeter data

fracture propagation and coalescence at bedding plane in layered rocks abstract fracture propagation fracture coalescence and their interactions with the bedding plane in layered rocks are of great significance when conducting a stability analysis of structures on or within the layered rock mass in this work we developed a numerical model by the inserted cohesive element ce method to simulate the evolution of fracture paths in layered rocks then validated it with modified wedge splitting tests the results indicate that the fracture penetration deflection behaviour at the bedding plane is controlled by two strength thresholds of the bedding plane 1 if the bedding plane strength threshold i the fracture directly penetrates the bedding plane and 2 if threshold i bedding plane strength threshold ii first the fracture deflects along the bedding plane without any daughter fractures or penetration and then one or two daughter fractures can form a two flawed model is used to simulate the fracture coalescence the fracture coalescence is first determined by the bedding plane s strength thresholds if bedding plane strength threshold i fracture coalescence can occur only if the second flaw is located within a certain range no coalescence occurs if the bedding plane strength

crustal structure beneath the central oregon convergent margin from potential field modeling evidence for a buried basement ridge in local contact with a seaward dipping backstop models of magnetic and gravity anomalies along two e w transects offshore central oregon one of which is coincident with a detailed velocity model provide quantitative limits on the structure of the subducting oceanic crust and the crystalline backstop the models indicate that the backstop forming western edge of the siletz terrane an oceanic plateau that was accreted to north america 50 million years ago has a seaward dip of less than 60o3 seismic magnetic and gravity data are compatible with no more than 2 km of subducted sediments between the siletz terrane and the underlying crystalline crust of the juan de fuca plate the data also suggest the presence of a n s trending 200 km long basaltic ridge buried beneath the accretionary com plex from about 43on to 45on although the height and width of this ridge probably vary along strike it may be up to 4 km high and several kilometers wide in places and appears to be locally in contact with the siletz terrane beneath heceta bank several models for the origin of this ridge are discussed these include a sliver of siletz terrane detached from the main siletz terrane dur ing a late eocene episode of strike slip faulting imbrication and thickening of subducted oceanic crust in place an aseismic ridge rafted in on the subducting oceanic crust during the past 1 2 mil lion years and a series of ridges and or seamounts rafted in over a longer period of time and trans ferred from the subducting plate to the overlying plate the last model is the most consistent with the complicated history of local uplift subsidence and slope instability recorded in the ridges basins and banks of this part of the margin we speculate that the massive seaward dip ping western edge of the siletz terrane in this region inhibits subduction of seamounts and sedi ments resulting in fomation of buried ridge as the accumulated flotsam and jetsom of subduction this process may also be responsible for thickening of lower accretionary complex material over steepening of slopes leading to massive slumping and north south extension through strike slip faulting in the accretionary complex to the west of the buried ridge regardless of its origin the ridge may currently be acting as an asperity inhibiting subduction

physical processes of shallow mafic dike emplacement near the san rafael swell utah some 200 shonkinite dikes sills and breccia bodies on the western colorado plateau of south central utah were intruded from approximately 3 7 to 4 6 ma contemporaneous with mafic volcanism along the nearby plateau margin thicknesses of dikes range to about 6 m the log normal mean thickness is 85 cm despite the excellent exposures of essentially all dikes in strata of the jurassic san rafael group their number is indeterminate from their outcrop and spacing because they are everywhere greatly segmented by our grouping of almost 2000 dike segments most dikes are less than 2 km in outcrop length the longest is 9 km because the san rafael magmas were primitive and probably ascended directly from the mantle dike lengths in outcrop are much less than their heights the present exposures probably lie along the irregular upper peripheries of dikes that lengthen and merge with depth orientations of steps on dike contacts record local directions of dike fracture propagation about half of the measurements plunge less than 30 showing that lateral propagation at dike peripheries is as important as the vertical propagation ultimately responsible for ascent the san rafael dikes now exposed after erosion of about 0 5 1 5 km appear to thicken and shorten upward probably because near surface vesiculation enhanced magmatic driving pressures propagation likely ceased soon after the first dike segments began to feed nearby sills or vented to initiate small volume eruptions most of the dikes are exposed in clastic strata of the jurassic san rafael group they probably acquired their strikes however while ascending along well developed joints in massive sandstones of the underlying glen canyon group rotation of far field stresses during the emplacement interval cannot account for disparate strikes of the dikes which vary through 110 most lying between north and n25 w rather the two regional horizontal principal stresses were probably nearly equal and so the dominant n75 e direction of dike opening was not strongly favored across the center of the swarm about 10 to 15 dikes overlap and produce 15 20 m of dilation many are in sufficient proximity that later dikes should be thinner than earlier ones if neither the magma pressures nor regional stresses were changing during the emplacement interval however dike thicknesses vary systematically neither along the length of the swarm nor in proportion to the number of neighboring dikes it appears that crustal extension during the magmatic interval relieved compressive stresses localized by intrusion

intrusion of lamprophyre dyke and related deformation effects in the host rock salt a case study from the loule diapir portugal abstract a rock salt lamprophyre dyke contact zone sub vertical ne sw strike was investigated for its petrographic mechanic and physical properties by means of anisotropy of magnetic susceptibility ams and rock magnetic properties coupled with quantitative microstructural analysis and thermal mathematical modelling the quantitative microstructural analysis of halite texture and solid inclusions revealed good spatial correlation with ams and halite fabrics the fabrics of both lamprophyre and rock salt record the magmatic intrusion plastic flow and regional deformation characterized by a nw se trending steep foliation ams and microstructural analysis revealed two deformation fabrics in the rock salt 1 the deformation fabrics in rock salt on the nw side of the dyke are associated with high temperature and high fluid activity attributed to the dyke emplacement 2 on the opposite side of the dyke the emplacement related fabric is reworked by localized tectonic deformation the paleomagnetic results suggest significant rotation of the whole dyke probably during the diapir ascent and or the regional tertiary to quaternary deformation

stochastic analysis of solute transport in heterogeneous aquifers subject to spatially random recharge this paper derives and solves approximate unconditional moment equations for a concentration plume in a two dimensional spatially random transmissivity field subject to spatially random recharge and non uniform linear trending velocity closed form expressions are derived for the unconditional non stationary auto covariances for head and velocity and the cross covariances between velocity head recharge and log transmissivity based on a system of coupled first order partial differential moment equations and assumed hole type input covariance functions for log transmissivity and recharge the unconditional flow related moment equations are incorporated into a system of solute transport moment equations which is solved using a galerkin finite element algorithm a constant positive mean recharge yields a mean velocity gradient which enhances the ensemble mean plume spreading in the longitudinal direction similar to results found by rubin and bellin 1994 water resour res 30 4 939 948 spatial variability in recharge further enhances the spreading of the ensemble mean plume especially in the lateral direction uncertainty in the spatial distribution of recharge also increases the extent of the ensemble standard deviation plume particularly in the lateral direction and increases the coefficient of variation of solute concentration the uncertainty in the prediction of solute transport increases with increasing recharge variance and spatial correlation scale

simplified analysis of horizontal stresses in a buttressed forearc sliver at an oblique subduction zone forearc slivers are commonly present at obliquely convergent margins such slivers are often buttressed at their leading edges but no quantitative model of the buttress effect exists i consider the horizontal stresses in a buttressed sliver using a simple plan view two dimensional elastic model the driving force created by the subducting plate is approximated by a body force in the direction of plate convergence an airy stress function solution relates the stress field to the boundary and body forces that allows the relative importance of different forces driving and resisting the sliver to be evaluated oblique subduction can easily cause arc parallel compression in the buttressed sliver especially near the leading edge because the arc parallel component of the driving force by the subducting plate is integrated over a much larger distance than its arc normal component for the southwest kuril arc the stress field predicted by the simple model agrees with that inferred from geological structures it is possible that the model can also explain the stress field of the cascadia forearc as constrained by earthquake focal mechanisms and in situ stress measurements

geology of the mount st helens area record of discontinuous volcanic and plutonic activity in the cascade arc of southern washington the quaternary edifice of mount st helens volcano was built upon a deeply eroded terrane of gently folded and altered volcanic and plutonic rocks that represent the core of the tertiary cascade magmatic arc these rocks constitute an east dipping homoclinal sequence several kilometers thick of subaerially erupted mafic to silicic flows and volcaniclastic strata k ar ages from this section range from about 28 to 23 ma late oligocene and earliest miocene which corresponds to an apparent lull in cascade volcanism to the north of mount rainier volcanism was essentially continuous during this period of time and neither a well defined base nor top of the section is exposed within the mapped area basalt and basaltic andesite dominate the lower part of the mid tertiary section whereas andesitic and dacitic rocks comprise most of the upper part this section was intruded by numerous mafic to silicic dikes sills and irregular plutonic bodies most no more than a few million years younger than their host rocks and subjected to pervasive burial metamorphism and widespread hydrothermal alteration large areas of hornfelsed rock surrounding even relatively small intrusions indicate that the proportion of plutonic rock becomes significantly greater at shallow depth beneath the existing erosion surface a large granitic pluton intruded the mid tertiary section north of spirit lake at about 21 ma the earl porphyry copper deposit occurs within the pluton but appears too young 17 ma to be genetically related to it in contrast to the rather continuous and voluminous oligocene to early miocene activity volcanism since then in the mount st helens area has been localized and volumetrically minor products of three younger eruptive periods have been recognized a sequence of 15 m y old pyroxene andesite flows resting unconformably on mid tertiary strata south of mount st helens widespread shallow dikes and sills of pyroxene andesite between 10 and 8 m y old and compositionally diverse rocks erupted during the past 3 m y the quaternary lavas are more potassic than the tertiary lavas and typically contain phenocrysts of hornblende and biotite which are absent from the older rocks a number of tertiary structures define a broad nne trending zone that may reflect a deep seated lithospheric flaw that has controlled the locus of cascade magmatism in southern washington for the past 25 m y mount st helens lies within this zone at the intersection of the nnw striking st helens seismic zone shz and an ene trending alignment of pleistocene silicic plug domes no surface breakage has been detected along the shz which is apparently very young the linear zone of silicic vents is probably controlled by a fault that has been interpreted from seismic records to occur directly beneath the volcano this zone parallels the directions of regional maximum horizontal compressive stress and north america juan de fuca plate convergence mount st helens is an example of a low volume tectonically controlled magmatic system in an early stage of development

dike propagation through layered rocks 1 dike penetration through a succession of upper crustal layers with different densities is studied with a new numerical code for an individual layer to significantly affect dike ascent its thickness must be of order 1 when scaled to the characteristic length scale for the inflated nose region that develops below the dike tip this characteristic length is l q 1 6 g 1 1 2 g 2 3 where and are the viscosity and buoyancy of magma g and are elastic moduli for the encasing rocks q is the magma flow rate and g gravity for basaltic dikes l is 1 km which is of the same order of magnitude as the typical thickness of sedimentary strata and volcanic deposits in such conditions dike ascent proceeds irregularly with large changes of velocity and width at an interface scaling laws for the ascent rate and dike width are derived penetration through low density layers is determined by a local buoyancy balance in the inflated nose region of the dike independently of the total buoyancy of the magma column between source and tip in such conditions a dike develops an internal overpressure that may be large enough to generate a horizontally propagating sill for this to occur the thickness of the low density layers must exceed a threshold value which depends only on the rock strength and on the average negative buoyancy of magma for basaltic melt we estimate that this threshold thickness cannot be less than about 700 m and is 2 km on average

case for very low coupling stress on the cascadia ssubduction fault a fundamental problem in plate tectonics is the shear strength of major plate boundary faults this translates to the question whether the generally observed small earthquake stress drops of 3 10 mpa on major faults release most of the accumulated stress or only a small fraction of it there is strong evidence that the san andreas fault a major transform plate boundary is weak 20 mpa shear resistance it is not yet clear whether subduction thrust faults are also weak we present two types of evidence from the northern cascadia subduction zone that indicate very low coupling shear stress on that plate interface and hence very low strength of the subduction thrust fault comparable to that estimated for the san andreas fault first the well defined surface heat flow and heat generation allow negligible frictional heating on the plate interface the average shear stress on the fault must thus be very low over a time scale of a few million years second focal mechanism solutions for small crustal earthquakes in the southern vancouver island area indicate that the horizontal stress in the direction of plate convergence has a similar magnitude to the vertical stress this inferred stress state requires the present tectonic stress coupled across the subduction thrust fault to be very low one explanation for the weakness of the fault is the presence of near lithostatic pore fluid pressure in the region of the fault zone for which there is independent evidence the conclusion of a weak subduction thrust fault does not conflict with geodetic observations of contemporary surface deformation which indicate that the fault is currently locked accumulating strain energy toward a future great earthquake the surface deformation responds to the small 20 mpa temporal changes of the stress field associated with the subduction earthquake cycle this transient stress is superimposed on the larger background regional stress field in which the maximum compression is parallel to the margin the weakness of the cascadia subduction thrust fault and the unusual stress state of the forearc region have important implications for earthquake hazards for example a subduction earthquake may induce large strike slip earthquakes in the forearc that affect a large area

seismicity of mount hood and structure as determined from teleseismic p wave delay studies a 16 station seismic network was established in the mount hood area of oregon in 1977 as part of a multidisciplinary study to evaluate the geothermal potential of a typical cascade volcano the immediate objective was to monitor local seismicity and to study the p wave velocity structure of the crust and upper mantle during the 13 months the network was in operation 10 local earthquakes were recorded all these events are spatially associated with the volcano and occurred at shallow depths roughly defining a zone striking north northwest the largest earthquake a magnitude 3 4 event was preceded by a single foreshock and followed by three locatable aftershocks these and the five other located earthquakes were of magnitude less than 2 0 fifty five teleseisms were recorded by the network and used in a teleseismic p wave delay study the residuals from the p delay study indicate that there is no significant velocity anomaly associated with the mount hood volcano and only small velocity variations in the mount hood region

late pleistocene and holocene tectonics of the portland basin oregon and washington from high resolution seismic profiling high resolution seismic reflection profiles were acquired to aid earthquake hazard assessment in the portland vancouver urban area of oregon and washington western north america the profiles show 1 a strong reflector at the base of unconsolidated deposits 2 the ancestral columbia river channel where it has eroded into the unconformity at the base of the unconsolidated deposits and 3 evidence consistent with late pleistocene or holocene faulting the seismic data consist of marine profiles along 40 km segments of the columbia and willamette rivers and two 1 5 km long land profiles across the east bank and portland hills fault zones the marine profiles show a strong reflector as deep as 85 m that correlates with the unconformity at the base of unconsolidated late pleistocene and holocene sediments penetrated in nearby drillholes a 1 5 km wide up to 85 m deep paleochannel filled by unconsolidated sediments marks the course of the ancestral columbia river apparent vertical displacements of late pleistocene or holocene reflectors at the east bank fault are consistent with recent faulting the portland hills fault zone also shows what could be late pleistocene to holocene deformation but other interpretations of these features are possible no obvious faulting of the late pleistocene unconformity is observed on our profiles across the inferred location of the frontal fault zone the strong reflection from the unconformity and a large contrast in measured s wave velocities between the unconsolidated sediments 250 m sec and the underlying strata 477 to 817 m sec indicates the shallow layer could amplify and trap seismic energy during an earthquake these results indicate the east bank and portland hills faults may represent significant seismic hazards to the portland vancouver urban area and emphasize that further characterization of the shallow strata is crucial to estimating the shaking potential at sites above the portland basin manuscript received 17 june 1999

patterns of temporal scaling of groundwater level fluctuation summary we studied the fractal scaling behavior of groundwater level fluctuation for various types of aquifers in puerto rico using the methods of 1 detrended fluctuation analysis dfa to examine the monofractality and 2 wavelet transform maximum modulus wtmm to analyze the multifractality the dfa results show that fractals exist in groundwater fluctuations of all the aquifers with scaling patterns that are anti persistent 1 1 5 1 62 0 07 4 wells the multifractal analysis confirmed the need to characterize these highly complex processes with multifractality which originated from the stochastic distribution of the irregularly shaped fluctuations the singularity spectra of the fluctuation processes in each well were site specific we found a general elevational effect with smaller fractal scaling coefficients in the shallower wells except for the northern karst aquifer upper system high spatial variability of fractal scaling of groundwater level fluctuations in the karst aquifer is due to the coupled effects of anthropogenic perturbations precipitation elevation and particularly the high heterogeneous hydrogeological conditions

basin architecture and density structure beneath the strait of georgia british columbia georgia basin is located within one of the most seismically active and populated areas on canada s west coast over the last decade geological investigations have resolved important details concerning the basin s shallow structure and composition yet until recently relatively little was known about deeper portions of the basin in this study new seismic velocity information is employed to develop a 3 dimensional density model of the basin comparison of the calculated gravity response of this model with the observed gravity field validates the velocity model at large scales at smaller scales several differences between model and observed gravity fields are recognized analysis of these differences and correlation with independent geoscience data provide new insights into the structure and composition of the basin fill and underlying basement specifically four regions with thick accumulations of unconsolidated pleistocene and younger sediments which were not resolved in the velocity model are id

regional tectonic and earthquake hazard implications of a crustal fault zone in southwestern washington the st helens seismic zone shz is a crustal earthquake zone in southwestern washington that is defined by small to moderate magnitude 2 5 to 5 5 earthquakes and focal mechanisms this zone seismically active along a distance of 90 km is interpreted as a fault zone capable of generating a moderate to large magnitude shallow earthquake at the northern end of this seismic zone about 15 km north of the cowlitz river a large area of seismic quiescence for earthquakes above magnitude 3 0 has predominated since 1977 this quiescence leaves open the question whether the shz continues northward into southern puget sound earthquake focal mechanisms along the shz indicating nearly vertical strike slip faulting with the preferred fault planes striking north south from these focal mechanisms we infer that the direction of maximum compression is northeast approximately parallel with the direction of plate convergence between the north american and juan de fuca plates we interpret the focal mechanism data as evidence for locked subduction this tectonic model raises the possibility of a large magnitude subduction earthquake neither the possibility of a moderate to large shallow crustal earthquake nor a major subduction event is part of the current earthquake hazard assessment for washington

early cenozoic saucer shaped sills of the faroe islands an example of intrusive styles in basaltic lava piles abstract the early cenozoic igneous activity of the north atlantic igneous province that generated widespread sill complexes in sedimentary basins at the nw european margins also generated various intrusive systems in the contemporaneous basaltic lava pile of the faroe islands the faroe island basalt group comprises seven formations with a total thickness of about 6 5 km of which four major formations are built up of tholeiitic lava flows each being several hundred metres thick and three thinner formations are mostly built up of volcaniclastic lithologies each being a few metres to a few tens of metres thick the largest sills are exposed as partly saucer shaped bodies in the three uppermost formations where inner gently dipping basal sill sections gradually give way to more steeply inclined discordant outer rims that commonly cut several hundred metres into overlying lava flows numerous subvertical and moderately inclined dykes ranging in thickness from c 0 5 to c 4 0 m intersect the areas affected by sill intrusion but only inclined dykes or sheets have been positively identified as sill feeders locally controlled rotations of least principal stress axes 3 during initial sill intrusion or propagation may have been an important contributing factor in determining the overall geometry of the investigated intrusions

a model for radial dike emplacement in composite cones based on observations from summer coon volcano colorado usa we mapped the geometry of 13 silicic dikes at summer coon an eroded oligocene stratovolcano in southern colorado to investigate various characteristics of radial dike emplacement in composite volcanoes exposed dikes are up to about 7 km in length and have numerous offset segments along their upper peripheries surprisingly most dikes at summer coon increase in thickness with distance from the center of the volcano magma pressure in a dike is expected to lessen away from the pressurized source region which would encourage a blade like dike to decrease in thickness with distance from the center of the volcano we attribute the observed thickness pattern as evidence of a driving pressure gradient which is caused by decreasing host rock shear modulus and horizontal stress both due to decreasing emplacement depths beneath the sloping flanks of the volcano based on data from summer coon we propose that radial dikes originate at depth below the summit of a host volcano and follow steeply inclined paths towards the surface near the interface between volcanic cone and basement which may represent a neutral buoyancy surface or stress barrier magma is transported subhorizontally and radially away from the center of the volcano in blade like dikes the dikes thicken with increasing radial distance and offset segments and fingers form along the upper peripheries of the intrusions eruptions may occur anywhere along the length of the dikes but the erupted volume will generally be greater for dike fed eruptions far from the center of the host volcano owing to the increase in driving pressure with distance from the source observed eruptive volumes vent locations and vent area intrusions from inferred post glacial dike fed eruptions at mount adams washington usa support the proposed model hazards associated with radial dike emplacement are therefore greater for longer dikes that propagate to the outer flanks of a volcano

delineation and interpretation of seismotectonic domains in western north america indicators of crustal stress and regional seismicity are used to delineate six seismotectonic domains in western north america the san andreas east central california ecc mendocino triple junction mtj and pacific northwest pnw domains are found to have similar stress fields although the style and rate of deformation in each is different we propose that all of these domains are generated by shear between the pacific and north american plates in the mtj and pnw domains this shear may be evidence for the initiation of a transform fault connection between the san andreas and the queen charlotte island fault systems the ecc a region including much of the sierra nevada appears to result from the relatively stiff nature of the san andreas fault system the big bend and region of relatively new faulting in northern california act to make the san andreas fault system appear stiff on a regional scale two other domains the northern basin and range nbr and the intermountain seismic belt isb show evidence of being controlled by more local forces the nbr has been heated and uplifted in the past and is presently extending to the northwest because of a release of tectonic compression at the juan de fuca north america plate boundary the isb can be explained by readjustments between the colorado plateau and the basin and range province which may be caused by the lowering of the basin and range due to extension

the state of stress near the mendocino triple junction from inversion of earthquake focal mechanisms focal mechanisms of 70 earthquakes occurring in the region of the mendocino triple junction between 1977 and 1995 are inverted to obtain the regional stress orientations and relative magnitudes in this technically complex area a diverse set of earthquake geometries is consistent with a single stress field characterized by north northwest horizontal maximum principal compressive stress although this stress direction is almost perpendicular to convergence between the north american and gorda plates it is consistent with the stress direction inferred within the gorda plate northwest of the triple junction a maximum compressive stress direction nearly parallel to strike of the cascadia subduction zone implies very low resolved shear stress across this plate boundary evidence for failure along the southernmost section of the cascadia subduction zone comes from the occurrence of the recent 1992 ms 7 1 cape mendocino underthrusting earthquake as well as from measurements of holocene surface uplift consistent with the 1992 coseismic uplift pattern rupture of the cascadia subduction zone under this stress regime requires that the southernmost region of the gorda north american plate boundary is weak

geologic evidence for a magma chamber beneath newberry volcano oregon at newberry volcano central oregon more than 0 5 m y of magmatic activity including caldera collapse and renewed caldera filling volcanism has created a structural and thermal chimney that channels magma ascent holocene rhyolitic eruptions 1 have been confined mainly within the caldera in an area 5 km in diameter 2 have been very similar in chemical composition phenocryst mineralogy and eruptive style and 3 have occurred as recently as 1300 years ago with repose periods of 2000 3000 years between eruptions holocene basaltic andesite eruptions are widespread on the flanks but are excluded from the area of rhyolitic volcanism basaltic andesite in fissures at the edge of the rhyolite area has silicic inclusions and shows mixed basalt rhyolite magma relations these geologic relations and the high geothermal gradient that characterizes the lower part of a drill hole in the caldera u s geological survey newberry 2 indicate that a rhyolitic magma chamber has existed beneath the caldera throughout the holocene its longevity probably is a result of intermittent underplating by basaltic magma

structural characterization of deep water deposits in a foreland basin silla syncline chilean patagonia with applications to depositional processes abstract based on our detailed structural characterization we examine possible relationships between thrust faults and strike slip faults and thrust cored folds and depositional units in the silla syncline a 4 km wide fold composed of fine grained mudstone coarse sandstone and conglomerate deposits of the cerro toro formation in the magallanes foreland basin chilean patagonia the syncline is bounded on its western flank by an asymmetric anticline and on its eastern flank by a broad zone of thrust faults and associated folds which are oriented sub parallel to the syncline axis deposition of the coarse grained units of the silla syncline appears to have taken place in this structurally defined trough controlled primarily by thrust fault related growth structures flanking the syncline the syncline and surrounding area have also been deformed by two sets of strike slip faults one right lateral and one left lateral the strike slip and thrust faulting operated contemporaneously for much of their active periods although it appears that thrust faulting confined within the fine grained units initiated slightly earlier than strike slip faulting in addition younger igneous intrusions at high angle to bedding generally localize along the strike slip faults the cross cutting relationships among the intrusions strike slip faults and flexural slip faults show that all these structures were active during the same period which extends beyond mid miocene these conclusions support the premise that structures in deep water sediments are important for understanding not only the deformation of a foreland basin but also its depositional architecture

late quaternary tectonic deformation in the cape arago bandon region of coastal oregon as deduced from wave cut platforms the cape arago region of south central oregon sits on the upper plate of the cascadia subduction zone about 80 km east of the base of the continental slope the style of late pleistocene deformation along the cascadia forearc near cape arago is well expressed by the altitudinal variation of a set of five uplifted wave cut platforms these platforms record open folding with a half wavelength of about 6 7 km as well as late quaternary offset on flexural slip reverse faults that parallel bedding in the underlying bedrock the folds have produced both landward and seaward tilts to the uplifted wave cut platforms because the folds cut obliquely across the coastline the magnitude of coastal uplift is variable in the case of the lowest 80 ka wave cut platform this variable uplift has resulted in coastal deformation ranging from subsidence to a maximum uplift of 0 8 m kyr quantitative analysis of the mechanism of flexural slip folding for the south slough syncline near cape arago indicates that the late quaternary strain rate has decreased in the last 200 kyr evidence of past great subduction style earthquakes such as regional uplift and regional landward tilting of wave cut platforms or regional submergence of coastlands is lacking inmore the cape arago region instead the deformational style is controlled by folding though localized folding is dominant the occurrence of great subduction style earthquakes is not precluded because localized folding could occur concurrently with regional coseismic deformation less

role of shale thickness on vertical connectivity of fractures application of crack bridging theory to the austin chalk texas abstract contrasting material properties of alternating chalk and shale layers control vertical connectivity of fractures our field observations within the austin chalk texas indicate that 1 the majority of vertical fractures occur in chalk layers and abut against contacts with shale layers 2 thicker shale layers have greater resistance to fracture propagation than thinner shale layers from these observations we hypothesize both the resistance of shale to fracturing and the thickness of shale layers may inhibit fracture propagation across the shale and into the next chalk layer we model crack propagation within a three layered system brittle chalk fracture resistant shale brittle chalk the modeled crack extends across the shale but closing tractions applied to the crack segment within the shale layer simulate resistance of shale to fracturing the crack tip lies a short distance within the unfractured chalk layer simulating a coplanar flaw with potential to propagate if the stress intensity factor at the flaw exceeds the chalk fracture toughness the crack propagates thereby bridging and eventually rupturing the shale layer for any chalk thickness there is a critical shale thickness above which fractures cross the shale layer and below which fractures arrest at shale finite element method fem analysis evaluates the influence of shale ductility within the chalk shale chalk system although remote and fluid pressure driven fractures produce identical stress intensity factors in elastic chalk shale systems lower driving stresses are required to propagate fluid pressure driven fractures through a system ductile shale layers than fractures under remote tension

rock interface strength influences fluid filled fracture propagation pathways in the crust abstract rock interface strengths have often been assumed to be zero in numerical and analogue models of fracture propagation and magma intrusion in the crust rock strength tests were performed to explore the role that rock interfaces have on the geometry and propagation dynamics of fluid filled fractures in the crust we used a 1 kn test machine to study 5 mm thick cuboidal specimens cut from a sandstone siltstone rock core where the strata were known to host magma intrusions and the rock interface between the units was intact by measuring the load required to grow a crack running along the lithological contact between the layers we calculate its fracture toughness k c the siltstone had an average k c of 0 56 0 03 mpa m 1 2 compared to the sandstone at 0 42 0 02 mpa m 1 2 the rock interface had intermediate average fracture toughness to the parent units at 0 45 0 03 mpa m 1 2 these results have important implications on fracture propagation pathways through rocks as well as for the geometry and propagation dynamics of magma intrusions in the crust

the 25 march 1993 scotts mills oregon earthquake and aftershock sequence spatial distribution focal mechanisms and the mount angel fault abstract the 25 march 1993 m l 5 7 crustal earthquake near scotts mills oregon was the largest earthquake to occur in the pacific northwest in over a decade the mainshock was located at 45 033 n 122 586 w and at a depth of about 15 1 km based on arrival time data from the short period pacific northwest seismograph network beginning about 12 h after the mainshock investigators from the u s geological survey deployed 22 digital seismographs to record aftershocks using data from the temporary and permanent stations we analyzed a subset of 50 aftershocks with quality locations hypocenters of these aftershocks lie on a northwest trending steeply dipping plane strike 290 10 dipping 60 5 to the north northeast in agreement with the preferred slip plane of the mainshock focal mechanism solution strike 294 dipping 58 to the north northeast the planar structure defined by the aftershock locations may be a southeast continuation of the mount angel fault a reverse fault identified from both surface and subsurface evidence the mapped southeast extent of the mount angel fault is located less than 10 km west of the scotts mills epicentral region in addition the mainshock focal mechanism solution with a combination of reverse motion and right lateral strike slip has a geometry and sense of motion consistent with the mount angel fault while aftershock focal mechanisms are varied p axes are consistently oriented in a subhorizontal north south direction this earthquake sequence together with the geological and geophysical evidence for the mount angel fault suggests a significant crustal earthquake hazard for this region of northwest oregon

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

fluidization of wet sediments during the emplacement and cooling of various igneous bodies during the emplacement and cooling of igneous bodies fluidization of wet sediment by water vapour may occur by heating or by pressure relief during the opening of fractures momentary fluidization causes sediment reconstitution and local transport continuous fluidization can result in substantial sediment displacement theoretical considerations show that fluidization due to heating is not likely to occur at depths where pressure is much greater than 312 bars studies of the emplacement of sills of andesite ayrshire fluid rhyolite ramsey island and viscous rhyolite moelwyn hills recognize a wide range of phenomena attributable to wet sediment fluidization and in places modify existing interpretations the transgressive bases of the subaqueously welded ash flow tuffs of the capel curig volcanic formation are consistent with emplacement attended by fluidization of the subjacent sediment evidently fluidization is a means by which large volumes of wet sediment can be replaced by igneous material with minimal disturbance of the remaining host also fluidization can result in exceptionally complex contact relationships between sedimentary host and intrusive rocks and can cause fractures formed during cooling to be thoroughly pervaded by sediment fluidization is commonly associated with the formation of peperites

the statistical structure and filter characteristics of tritium fluctuations in fractured basalt the statistical structure and spectral covariance characteristics of tritium fluctuations are examined from injection of low level radioactive waste in a fractured basalt aquifer the tritium fluctuations are the result of a time varying injection well concentration the integral scale of the fluctuations increases with distance from the source and the observation well spectra are characteristic of a dispersive type filter on the basis of these qualitative attenuation characteristics a theoretical filter is constructed and transport parameters are estimated the analysis indicates that environmental tracers may provide a useful extension to controlled tests over large length scales 100 m although current research has concentrated on the importance of intrinsic variability such as porous media heterogeneities the present study addresses the control exerted by extrinsic variability as exhibited by source strength fluctuations

synrift magmatism in a cenozoic rift basin from 3d seismic data wichianburi sub basin phetchabun basin thailand part 1 distribution and timing of intrusions and forced folds the late oligocene pliocene wichianburi sub basin phetchabun rift thailand has undergone three phases of development late oligocene early miocene c 16 ma east west extension on predominantly nnw sse to north south striking faults 16 ma c 3 ma ne extension on nnw sse north south and ne sw trending faults and 3 ma to present post rift subsidence the basin was also affected by intrusive and extrusive igneous activity from 24 to 2 ma the relationships among the structure rift basin stratigraphy and sheet intrusions are unusually well documented as a result of extensive hydrocarbon exploration drilling and 3d seismic data together with the production of hydrocarbons from igneous sills the oldest igneous activity c 24 13 ma lies sw of the wichianburi sub basin where extrusive rocks exposed at the surface have been dated by k ar and 40ar 39ar methods the overall igneous activity youngs from the south of the basin to the north 11 9 ma numerous domal folds occur across the basin the sill and laccolith dimensions the rate of fold development the variable timing of fold formation and the fold geometry all indicate that the folds are related to magma emplacement not tectonic inversion fold formation occurred at c 16 15 and 12 11 ma in single or multiple stages the timing of folding coupled with the radiometric dating of some sills k ar 39ar 40ar indicates that the greatest amount of intrusive activity occurred between 16 and 11 ma the 16 ma date coincides with the switch from east west to nw se extension which promoted dilatancy within the upper crust along a range of synrift fault orientations and some pre rift trends the burial history of the main depocentre shows that miocene sill emplacement occurred at depths

statistical analyses and modeling approaches to hydrodynamic characteristics in alluvial aquifer this study is aimed at quantifying the difference in aquifer s response to recharge between some different locations in a fan aquifer and a delta aquifer for a preliminary study of revealing mechanisms of water transport in alluvial aquifer the aquifer s response to recharge is statistically quantified with the two viewpoints 1 timing and volume of recharge and 2 time length of aquifer s holding water for the first point a statistical model that links precipitation and groundwater level is introduced and its parameters are identified using correlation analysis our results show that the recharge rate at the toe is higher than that at the apex and at the delta for the second point the concept of memory effect of aquifer is adopted and quantified using the autocorrelation and spectral analyses our results show that the memory effect is longer at the toe of fan than at the apex and thus a temporary increase of water level has about five times as long term influence on subsequent water levels at the toe of the fan as at the apex this study demonstrates that the statistical analyses and modeling of hydrological data are useful for characterizing aquifer s hydrodynamics copyright 2012 john wiley sons ltd

well bore breakouts and in situ stress the detailed cross sectional shape of stress induced well bore breakouts has been studied using specially processed ultrasonic borehole televiewer data we show breakout shapes for a variety of rock types and introduce a simple elastic failure model which explains many features of the observations both the observations and calculations indicate that the breakouts define relatively broad and flat curvilinear surfaces which enlarge the borehole in the direction of minimum horizontal compression this work supports the hypothesis that breakouts result from shear failure of the rock where the compressive stress concentration around the well bore is greatest and that breakouts can be used to determine the orientation of the horizontal principal stresses in situ

near surface in situ stress introduction from plots of in situ stress versus depth it is apparent that horizontal stress is several times the vertical stress at depths of 100 m within the earth s crust hast 1958 herget 1973 haimson 1978 brown and hoek s 1978 compilation of earth stress shows that the average of principal horizontal stresses at zero depth varies between 2 7 and 40 5 mpa the literature contains no consensus on why the horizontal stresses should be so high at shallow depths possible mechanisms include plastic yield and subsequent elastic deformation accompanying unloading on removal of overburden seagar 1964 topography voight 1966 and creep under tectonic forces hast 1969

costerfield antimony gold deposit southeast australia coupling between brittle deformation and dissolution precipitation reactions in the melbourne zone abstract the antimony gold deposits at costerfield are a swarm of dyke like antimony gold lodes within a brittle transpressional fault system they are hosted in the lower silurian sedimentary rocks of the melbourne zone of the lachlan orogen individual lodes are dominated by stibnite or stibnite gold and widths vary from 1 cm to 200 cm averaging 30 cm and lengths can exceed 1 km lodes occur as fault parallel layers or lenses mantled by deformed quartz rich margins or overgrowths of hydrothermal quartz and carbonate inclusions in the stibnite rich lodes include vuggy randomly oriented prismatic crystals crack sealed and stretched quartz with sugary mosaics of equant quartz grains and quartz breccias randomly oriented quartz and stibnite textures common in the centre of the lodes indicate free growth from a fluid throughout the mineralized system the hydrothermal stibnite has replaced and overgrown the earlier quartz deformed lode margins preserve sub horizontal lineations and evidence of oblique crack seal re opening that reflect emplacement associated with late sinistral strike slip movements in bounding faults crystallographic orientation data collected from the marginal quartz using neutron diffraction and supported by microstructural observations reveal that lode emplacement also involved dissolution precipitation creep and pressure solution both the marginal quartz and the lodes are overprinted by later microfractures within which there has been precipitation of stibnite pyrite arsenopyrite sphalerite and minor gold 3 d neutron tomography revealed individual gold crystals with gold voxel sizes ranging from 140 m to 580 m were located in late arsenopyrite gold domains that overprint the stibnite the mechanical evolution of the lodes involved short lived brittle processes in combination with dissolution precipitation crystallization in active fault zones these ore bodies provide insights about the dynamics of fluid flow and flow velocities when faults breach over pressured reservoirs of hydrothermal fluid our results also suggest that the costerfield deposit was formed directly from metal rich metamorphic fluids produced during tabberabberan 375 ma prograde metamorphism of sedimentary rocks near the base of the lower paleozoic melbourne zone which lie above the proterozoic selwyn block from a reinterpretation of seismic reflection data the deformation in the melbourne zone sedimentary wedge is characterized by thrusts isolating relatively undeformed packages of sedimentary units which were moved in a piggyback manner up west dipping faults the ore bearing fluids migrated upwards at least in part along these footwall thrusts from the base of the heathcote fault zone in the upper levels of the sedimentary package out of sequence strike slip sub vertical splays from these second order faults carried the mineralizing fluids to the orebodies east west compression during the tabberabberan orogeny preceded a northwest southeast oriented stress field which reflects the collision of vandieland against the gondwanan margin this produced the sinistral strike slip faults which in turn controlled the overall permeability of the hydrothermal system

earthquakes near swift reservoir washington 1958 1963 seismicity along the southern st helens seismic zone abstract five earthquakes m 4 0 that occurred near swift reservoir on the southern st helens seismic zone shz in southwestern washington in 1960 and 1961 were located using a master event technique these five earthquakes include the 17 september 1961 siouxon peak earthquake of magnitude 5 1 m l as well as the swift creek earthquake on 11 october 1960 m coda 4 4 the siouxon peak earthquake focal mechanism exhibits right lateral strike slip faulting on a north south fault plane and is very similar to focal mechanisms calculated for recent earthquakes along the shz the sense of motion for the more poorly determined swift creek earthquake focal mechanism is consistent with either left lateral strike slip on a northerly striking fault plane or thrust both of which are anomalous for southwestern washington based on first motion differences in polarity which results in a different focal mechanism and the temporal separation between the swift creek earthquake and a swarm that preceded the siouxon peak earthquake we have divided the earthquakes near swift reservoir into two sequences the swift creek earthquake sequence beginning in early 1959 and culminating in the october 1960 swift creek earthquake and the siouxon peak sequence that began in january 1961 and included the siouxon peak main shock 8 months later the temporal and spatial pattern for the 1961 siouxon peak sequence agrees well both with that predicted by an asperity model and that observed for the 1980 to 1981 elk lake earthquake sequence along the shz about 35 km to the north the temporal similarities of these two sequences coupled with their similar moment release suggest an empirical model which may permit forecasting the next moderate earthquake along the shz the swift creek activity with its unusual for southwestern washington focal mechanism may have been induced by the impounding of the nearby swift reservoir

dike intrusion into unconsolidated sandstone and the development of quartzite contact zones abstract shallow near surface magma emplacement into a porous unlithified sandstone occurred by forceful dike dilation and was accompanied by a localized hydrothermal event petrographic fabric authigenic mineralogy and petrophysical data grade smoothly through the quartzite contact zone outward into the friable inmar sandstone of makhtesh ramon israel quartz grain deformation fracturing and rehealing of grains and pressure solution constitute overwhelming evidence of a compressive environment adjacent to dike margins albeit with temperatures and pressures insufficient to fully recrystallize detrital grains dikes were accommodated primarily by the repacking of the sandstone with both brittle and elastic grain interaction post emplacement heating together with elastic compressive stress dissipation lead to fracture healing and pressure solution the occasional columnar jointing must be related to thermal contraction of the quartzite during later cooling and resulting mode i cracks the alteration of both contact zone and dike material occurred via a transitory and confined hydrothermal seepage up dike margins elsewhere around the world highly altered intrusions bordered by indurated sometimes uniformly jointed sediments may also be the result of forceful magma emplacement and hydrothermal alteration at near surface levels

entrainment of country rock during basaltic eruptions of the lucero volcanic field new mexico as magma rises through the lithosphere it may entrain wall rock debris the entrainment process depends on the local hydrodynamic regime of the magma e g velocity temperature bulk density the extent of interaction of magma with groundwater and the mechanical properties of the wall rocks wall rock entrainment results in local flaring of dikes and conduits which in turn affects the hydrodynamics of magma ascent and eruption we studied upper crustal xenoliths erupted from small volume basaltic volcanoes of the lucero volcanic field west central new mexico in order to assess the relative importance of various entrainment mechanisms during a range of eruptive styles including strongly hydrovolcanic strombolian and effusive processes total xenolith volume fractions ranged from 0 3 0 9 in hydrovolcanic facies to 10 4 10 2 in strombolian facies the volcanoes erupted through a thick well characterized sequence of paleozoic and lower mesozoic sedimentary rocks so that erupted xenolith

temporal scaling of groundwater discharge in dual and multicontinuum catchment models this paper presents a multicontinuum approach to model fractal temporal scaling of catchment response in hydrological systems the temporal scaling of discharge is quantified in frequency domain by the transfer function h x which is defined as the ratio between the spectra of catchment response and recharge time series the transfer function may scale with frequency x as h x x2b while the classical linear and dupuit models predict exponents of b52 and b51 observations indicate scalings with noninteger exponents b such behaviors have been described by multifractal models which however often lack a relation to the medium characteristics we revisit and extend the classical linear dupuit aquifer models and discuss their physical meanings in the light of the resulting aquifer dynamics on the basis of these classical models we derive a multicontinuum approach that provides physical recharge models which are able to explain fractal behaviors with exponents 1 2 b 2 furthermore this approach allows to link the fractal dynamics of the discharge process to the physical aquifer characteristics as reflected in the distribution of storage time scales we systematically analyze the catchment responses in the proposed multicontinuum models and identify and quantify the time scales which characterize the dynamics of the catchment response to recharge

stress origins and earthquake potentials in cascadia focal mechanism solutions for shallow earthquakes throughout the cascadia plate system indicate that the primary regional stress is northerly compression even though the juan de fuca plate generally is thought to be subducting n50 e this compressional stress is pervasive throughout the gorda juan de fuca explorer plate system and much of the adjoining section of north american plate modeling using a discrete element code shows that this stress primarily is due to the pacific plate being driven into the gorda block and juan de fuca plate at the mendocino and blanco fracture zones this plate collision causes compression of the offshore plate system northward through the 45 w trending vancouver island and leads to transfer of northerly compression into the overriding plate the northerly compression in the cascadia plate system has caused large crustal earthquakes in the regions of vancouver and northern california and may be capable of causing large earthquakes also in and offshore of washington and oregon several independent lines of evidence confirm that the cascadia subduction interface is coupled strongly and that subduction primarily must be accompanied by significant earthquakes rather than occurring aseismically for numerous earthquakes within the subducted plate focal mechanisms indicate extensional stresses that trend downdip these earthquakes reflect plate extension that is due to sinking of the more deeply subducted plate and to plate motion being resisted at the shallow subduction interface the slab pull force of the sinking plate also can lead to earthquakes at the shallow subduction interface and the potential exists for m 7 5 8 0 subduction earthquakes to occur at segments of the subduction boundary at washington and vancouver and less frequently so at segments of the subduction boundary at oregon the in plate driving forces of the offshore cascadia plate system do not appear to contribute significantly to regional stresses stresses and earthquakes at the cascadia province primarily result from the action of the pacific plate on the gorda juan de fuca explorer plate system a transfer of this action into the overriding north american plate and the independent sinking and slab pull force of the subducted oceanic lithosphere

source characteristics of hypothetical subduction earthquakes in the northwestern united states historic earthquake sequences on subduction zones that are similar to the cascadia subduction zone are used to hypothesize the nature of shallow subduction earthquakes that might occur in the northwestern united states based on systematic comparisons of several physical characteristics including physiography and seismicity subduction zones that are deemed most similar to the cascadia subduction zone are those in southern chile southwestern japan and colombia these zones have all experienced very large earthquake sequences and if the cascadia subduction zone is also capable of storing elastic strain energy along its greater than 1000 km length then earthquakes of very large size m w 8 1 2 must be considered circumstantial evidence is presented that suggests but does not prove that large subduction earthquakes along the cascadia subduction zone may have an average repeat time of 400 to 500 yr

a seismic reflection profile across the cascadia subduction zone offshore central oregon new constraints on methane distribution and crustal structure in 1989 we conducted an onshore offshore seismic experiment to image the crustal structure of the cascadia forearc in this paper we discuss the processing and interpretation of a multichannel seismic reflection profile across the continental margin that was collected as part of this effort this profile reveals several features of the forearc that were not apparent in an earlier coincident reflection profile one of the most important of these features is a very strong bottom simulating reflection bsr beneath the midslope region that is nearly continuous from water depths of about 1500 m to 600 m where it appears to crop out on the seafloor the pressure and temperature conditions at the bsr derived from our observations are remarkably consistent with the experimentally determined phase diagram for a methane hydrate seawater system over a broad range of temperatures and pressures assuming hydrostatic pressure and the temperature gradiant measured near the base of the continental slope during ocean drilling program odp leg 146 interval velocities and reflection coefficients derived from the data indicate that the bsr represents a contrast between sediment with a small amount of hydrate overlying sediment containing free gas consistent with results obtained during leg 146 although the regional distribution of the anomalously strong bsr beneath the midslope is poorly known we speculate that it may be related to apparent slope instability the data also provide constraints on the thickness and geometry of the siletz terrane which is the basement beneath the shelf and acts as the subduction zone backstop a deep reflection which might mistakenly be interpreted to be moho if coincident large aperture data were not available is interpreted to be the base of the siletz terrane a recently active strike slip fault zone that overlies the seaward edge of the siletz terrane suggests that the siletz terrane controls the location of decoupling of the subduc tion complex from the rest of the forearc

direction of maximum horizontal compression in western oregon determined by borehole breakouts elliptical borehole enlargements or breakouts caused by systematic spalling of a borehole wall were identified in 18 wells drilled in the coast range and willamette valley of western oregon the breakouts generally indicate a nnw to nne orientation of maximum horizontal compression hmax that agrees with the predominant direction of hmax determined from earthquake focal mechanisms from post middle miocene structural features and from alignments of holocene volcanic centers in the pacific northwest however this orientation is inconsistent with the n50 e convergence between the juan de fuca and north american plates determined by riddihough 1984 from juan de fuca plate magnetic lineations as young as 730 ka the brunhes matuyama boundary the predominant nnw to nne orientation of hmax may be due to the complex interaction of a northwestward moving pacific plate driving into the gorda and juan de fuca plates and indirectly transmitting n s compression across the strongly coupled cascadia subduction zone into the overriding north american plate spence 1989 alternatively the predominant nnw to nne orientation of hmax may be due to a landward counterclockwise rotation of the direction of hmax from n50 e compression offshore to n s compression in the coast range

spectral analysis of river resistance and aquifer diffusivity in a river confined aquifer system hydraulic connections between a river and an adjacent aquifer are controlled by the river resistance and aquifer diffusivity in this paper we derive a spectral solution linking the power spectrum

stress orientations from borehole wall fractures with examples from colorado east texas and northern canada azimuthally aligned breakouts in oil wells are explained as shear fractures in the zone of amplified stress difference near the borehole in a stress field having unequal horizontal principal stres

transform push oblique subduction resistance and intraplate stress of the juan de fuca plate the juan de fuca plate is a small oceanic plate between the pacific and north america plates in the southernmost region referred to as the gorda deformation zone the maximum compressive stress 1 constrained by earthquake focal mechanisms is n s off oregon and possibly off washington nw trending left lateral faults cutting the juan de fuca plate indicate a 1 in a ne sw to e w direction the magnitude of differential stress increases from north to south this is inferred from the plastic yielding and distribution of earthquakes throughout the gorda deformation zone to understand how tectonic forces determine the stress field of the juan de fuca plate we have modeled the intraplate stress using both elastic and elastic perfectly plastic plane stress finite element models we conclude that the right lateral shear motion of the pacific and north america plates is primarily responsible for the stress pattern of the juan de fuca plate the most important roles are played by a compressional force normal to the mendocino transform fault a result of the northward push by the pacific plate and a horizontal resistance operating against the northward or margin parallel component of oblique subduction margin parallel subduction resistance results in large n s compression in the gorda deformation zone because the force is integrated over the full length of the cascadia subduction zone the mendocino transform fault serves as a strong buttress that is very weak in shear but capable of transmitting large strike normal compressive stresses internal failure of the gorda deformation zone potentially places limits on the magnitude of the fault normal stresses being transmitted and correspondingly on the magnitude of strike parallel subduction resistance transform faults and oblique subduction zones in other parts of the world can be expected to transmit and create stresses in the same manner

reinitiation or termination of fluid driven fractures at frictional bedding interfaces 1 a two dimensional numerical model for coupled elastic deformation and fluid flow has been developed to examine reinitiation or termination of a vertical fluid driven fracture in bedded rocks the rocks on both sides of the bedding interface are assumed to be impermeable and a newtonian fluid whose viscous dissipation cannot be neglected is injected at a constant rate crack nucleation on the frictional interface is controlled by a tensile stress criterion a fracture approaching the interface or terminating on it can generate a large bed parallel tensile stress in the uncracked layer in excess of the local tensile strength to initiate a new fracture the propagation of the nucleated fracture is assisted by interface sliding and pressurized fluid the bedding interface can provide a conductive channel to connect the parent and the new fractures fluid partitioning among fracture branches depends on local stress states and triggers their competition to become the main fracture the three types of fracture patterns generated numerically by the model are crosscutting through terminating at and offsetting at the interface a large modulus or toughness contrast across the interface can lead to containment of the hydraulic fracture on the interface for offsetting fractures the presence of the bedding plane can reduce fracture permeability and any associated high stress barrier acts to slow or arrest further fluid driven fracture growth propagating the new fracture results in high excess pressure consistent with measured abnormal pressure in commercial fracture treatments the predicted offset distances are on the order of centimeters and their continued growth is perpendicular to the bedding contacts

temporal and spatial scaling of hydraulic response to recharge in fractured aquifers insights from a frequency domain analysis quantification of the recharge in fractured aquifers is particularly challenging because of the multiscale heterogeneity and the range of temporal scales involved here we investigate the hydraulic response to recharge of a fractured aquifer using a frequency domain approach transfer functions are calculated in a range of temporal scales from 1 day up to a few years for a fractured crystalline rock aquifer located in ploemeur s brittany france using recharge and groundwater level fluctuations as input and output respectively the spatial variability of the response to recharge characteristic response time amplitude temporal scaling is analyzed for 10 wells sampling the different compartments of the aquifer some of the transfer functions follow the linear reservoir model behavior on the contrary others display a temporal scaling at high frequency that cannot be represented by classic models large scale hydraulic parameters estimated from the low frequency response are compared with those estimated from hydraulic tests at different scales the variability of transmissivity and storage coefficient tends to decrease with scale and the average estimates converge toward the highest values at large scale the small scale variability of diffusivities which implies the existence of a range of characteristic temporal scales associated with different pathways is suggested to be at the origin of the unconventional temporal scaling of the hydraulic response to recharge at high frequency

intrusion of basalt into frozen sediments and generation of coherent margined volcaniclastic dikes cmvds coherent margined volcaniclastic dikes cmvds are described for the first time from askja dyngjufjoll iceland these dikes display continuous coherent glassy margins 5 cm thick and have a variety of clastic interiors comprising vitric tephra pillow and pillow fragment bearing lapilli tuffs cmvds are interpreted to form when basaltic dikes interact with subglacial ice cemented volcaniclastic sediments formation requires chilling of dike margins drainage of the dike interior and flooding of the cavity by meltwater followed by non explosive mingling of magma clastics and water evidence for ice cementation includes minimal interaction with the host 3 mm peperite local pillowed dike margins and the preservation of continuous glassy coherent margins along the edge of a drained dike cavity cmvds should be present at other volcanic centers with ice cemented sediments including the martian cryosphere