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

joint inversion of source location and focal mechanism of microseismicity abstractthe seismic focal mechanism fm is an effective property to indicate source physics as well as stress and strain distribution in regional local and microscales we have developed an algorithm to jointly invert for the fm and source locations for a given velocity structure all possible combinations of source locations x y and z and fm strike dip and rake were used to compute traveltimes and polarities of waveforms correcting normal moveout times and polarities and stacking all waveforms the x y z strike dip and rake combination that gave the strongest stacking power was identified as the optimal solution compared with the traditional source scanning algorithm ssa that only scanned source locations this algorithm was thereby called the joint source scanning algorithm jssa the jssa method was tested rigorously and it was applied to a hydraulic fracturing data set our work determined several advantages against the ssa method 1 the jssa method could identify many shea

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

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

bar dynamics in a sandy braided river insights from sediment numerical simulations abstract bar dynamics in sandy braided rivers are keys to better understand the morphological processes of braided rivers and sediment distributions limited by insufficient quantitative information and satellite images that only show the larger scale morphology and do not reveal the sand bars in the deeper channels most previous studies have qualitatively assessed bar dynamics but the ways in which the hydraulic parameters of sandy braided rivers control bar dynamics remains poorly understood here we present sediment numerical simulations on sandy braided rivers to investigate the quantitative controls of river parameters on bar dynamics three bar dynamic forms downstream migration lateral variations and bar tail elongation are observed unit bars are prone to downstream migration following formation and the migration rate shows a deceasing trend during braided river evolution this gradually decreasing migration rate is proven to be strongly connected to the decreasing flow velocity of braided channels that confine bar growth the lateral variation in bar dynamics exhibits narrowing migration and widening of sectional morphologies we suggest that braided channel curvature dominantly controls lateral sediment transportation around the bar and thus results in several lateral variation forms of bars the bar tail elongation difference between the two sides of the bar is associated with bar asymmetry strong bar asymmetry can make apparent differences in bar tail elongation

geomorphic effects of wood quantity and characteristics in three italian gravel bed rivers abstract in channel wood is a fundamental component of the riverine system its nature abundance and distribution as well as the role of wood in trapping sediment have been reported by many authors however a lack of knowledge still exists on how the geomorphic effects quantity and characteristics of in channel wood may be altered by different human pressures for this reason in channel wood was surveyed in the brenta piave and tagliamento gravel bed rivers northeastern italy which are altered by different degrees of human pressures both single pieces of wood 0 1 m diameter and or 1 m long and accumulations of large wood were measured on cross sectional transects within the active channels overall 3430 8 4 13 9 and 10 7 elements ha in the brenta piave and tagliamento rivers respectively of isolated pieces and 591 9 8 15 0 and 11 0 wood accumulations ha in the brenta piave and tagliamento rivers respectively accumulations were surveyed in the study sites in the brenta and piave rivers which feature the greater human pressures logs appear in a worse state of conservation in the less disturbed tagliamento river the logs appear to be smaller and in a better state of conservation with higher capacity for resprouting in addition higher geomorphic interactions were found between wood and sediments in the tagliamento river because of its ability to create geomorphic effects in channel wood represents an important source of complexity that can increase habitat diversity in river systems a better knowledge of the role of human disturbances on the characteristics and abundance of large wood in river systems could help in developing better river management and the practical application of river ecology

complex variations in sediment transport at three large river bifurcations during discharge waves in the river rhine river bifurcations strongly control the distribution of water and sediment over a river system a good understanding of this distribution process is crucial for river management in this paper an extensive data set from three large bifurcations in the dutch rhine is presented containing data on bed load transport suspended bed sediment transport dune development and hydrodynamics the data show complex variations in sediment transport during discharge waves the objective of this paper is to examine and explain these measured variations in sediment transport it is found that bend sorting upstream of the bifurcations leads to supply limitation particularly in the downstream branch that originates in the outer bend of the main channel tidal water level variations lead to cyclical variations in the sediment distribution over the downstream branches lags in dune development cause complex hysteresis patterns in flow parameters and sediment transport all bifurcations show evidence of sediment waves which probably are intrinsic bifurcation phenomena the complex transport processes at the three bifurcations cause distinct discontinuities in the downstream fining trend of the river differences among the studied river bifurcations are mainly due to differences in sediment mobility shields value because the variations in sediment transport are complex and poorly correlated with the flow discharge prediction of the sediment distribution with existing relationships for one dimensional models is problematic

morphological perspective on the sedimentary characteristics of a coarse braided reach tagliamento river ne italy abstract in order to understand heterogeneity distribution of hydraulic properties many studies have proposed models of coarse braided river deposits however they often focus either on the surface near surface or on ancient deposit analysis furthermore the link between morphological surface and sedimentological outcrops information has not been fully explored yet this publication aims to characterize the morphodynamics of a braided gravel bed reach of the tagliamento river ne italy and to assess its relationship with the subsurface heterogeneity the morphological analysis is based on a lidar derived dem aerial and satellite photographs from 1998 to 2011 as well as field observations a water stage time series allows the morphological changes to be related to the discharge dynamics the sedimentological knowledge on coarse braided deposits was mainly gained from the observation of analog pleistocene coarse deposits in switzerland the main geomorphological elements are identified in terms of their topographic signature and genesis setting apart the trichotomy water vegetation bar the braidplain is characterized by higher lying zones with dentritic gully drainage networks and active zones where most of the morphology reworking occurs furthermore two morphologies mark the active zones a low discharge morphology low discharge incisions and channels slip face lobes etc superimposed on a high discharge morphology gravel sheets scours etc each morphological element is related to a depositional i e sedimentological element whose preservation potential in the subsurface is assessed as a function of the river bed aggradation dynamic the settings that impact the subsurface flow in terms of fast pathway and connectivity are addressed

the uplift of the sierra nevada and implications for late cenozoic epeirogeny in the western cordillera tilted cenozoic strata in the eastern great valley california record progressive late cenozoic uplift of the sierra nevada the magnitude of tilting is combined with other geologic data using a technique pioneered by grant and others to infer the rate and timing of post late miocene uplift between the kings river and the feather river angular unconformities of late neogene age have been reported throughout the east central great valley typically stratigraphic units of late oligocene through miocene pliocene age beneath the unconformities dip approximately 1 2 1 6 southwest middle to late pliocene units above the unconformities dip approximately 0 6 0 9 southwest and progressively overlap younger units from east to west these angular unconformities are interpreted to represent the onset of late cenozoic uplift of the sierra nevada due to westward tilting dated volcaniclastic units in the east central sacramento valley bracket the onset of tilting there between 3 4 and 8 4 ma stratigraphic and geologic relations from the stanislaus river area eastern san joa quin valley suggest that the late cenozoic tilting probably began approximately 5 ma previously published tilt data from the san joaquin valley combined with new work in the eastern sacramento valley indicate that the rate of post late miocene tilting has been approximately uniform in the east central great valley early to middle pleistocene units typically dip 0 5 0 7 southwest middle pleistocene units dip 0 2 0 4 middle to late pleistocene units dip 0 1 0 15 late pleistocene units dip 0 05 0 1 if it is assumed that major westward tilting began 5 ma these data indicate an approximately uniform tilting rate of 0 28 per million years these data have important implications for models of the uplift simultaneous inception of tilting in the east central great valley at approximately 5 ma does not support models that link uplift of the sierra nevada to the migration of the mendocino triple junction late cenozoic tilting of the sierra nevada block does not appear to coincide temporally with the onset of major basin and range extension the uplift may be due to thinning of the mantle lithosphere beneath the sierra nevada but the tilt data do not afford a direct test of this hypothesis post late miocene tilting of the sierra nevada is temporally associated with late cenozoic uplift of the northern basin and range uplift of the cascades uplift of the colorado plateau and uplift of the southern rocky mountains supporting the contention that tilting of the sierra nevada may have occurred as part of a cordillera wide uplift event

patterns and timing of late quaternary faulting in the great basin province and relation to some regional tectonic features large scale surface faulting events each tens of kilometers long and involving more than a meter of displacement of late quaternary age have not been uniformly distributed but have been concentrated in subprovincial and smaller belts and areas within the great basin province furthermore faulting apparently has not been uniformly distributed over time the average recurrence interval of large scale faulting events on individual faults in the province is measured in thousands or tens of thousands of years in contrast to such long recurrence intervals in the central nevada and eastern california seismic belts large scale faulting events have occurred during the last 111 years in an apparently coherent sequential belt filling pulse of activity in which events were separated by only a few years or a few decades the questions are where are other pulses of large scale faulting likely to occur and what controls the localization of such belts and areas characterized by higher rates of faulting two examples of tectonic subprovinces that may play a role in delimiting smaller zones of faulting are the black rock carson sink zone of extension and the central nevada downwarp the central nevada seismic belt lies along the dividing line between these two subprovinces and the northwest margin of the black rock carson sink zone of extension coincides with the margin of a fingerlike belt of dense faulting in northwestern nevada

effect of sampling time in the laboratory investigation of braided rivers we focus on the measurement of the bed elevation of braided networks in flume experiments in particular the effect of the survey frequency on the measurement accuracy is studied to this aim an innovative measurement system is adopted it consists of a laser ultrasonic sensor and can survey the bed elevation under owing water this measurement system was used to profile a flume transect with a frequency of 4 minutes without stopping the water discharge by this technique the topography of a single transect was continuously acquired during the evolution of a braided river model twelve braided rivers generated with different experimental conditions were studied the main results are i there exists a threshold survey frequency 4 8 minutes in our analysis which guarantees that the morphological evolution of the braiding channels is fully measured ii if this threshold frequency of survey is exceeded significant errors occur in the balance of the eroded deposited sediments and in the evaluation of the bed elevation dynamics and iii these errors depend on the river stream power

assembling an ignimbrite mechanical and thermal building blocks in the bishop tuff california abstract the building blocks that control ignimbrite physical characteristics are here defined as mechanical flow units and flow packages and thermal cooling units ignimbrite construction from these mechanical and thermal building blocks is illustrated by a longitudinal profile of the bishop tuff in the owens river gorge california in the bishop ignimbrite flow unit boundaries can be defined only locally but known or inferred multiple flow units combine to form eruptive packages showing imbricate offlapping relationships such that each package is thickest successively farther from the source in these packages the presence or absence of flow unit boundaries does not necessarily reflect directly the presence or absence respectively of time breaks thus massive ignimbrite need not be the product of continuous accumulation progressive aggradation the intrinsic thermal properties of each package or parts thereof have combined with local thicknesses of accumulated material to control the weld

morphological effects of different channel forming discharges in a gravel bed river the study analyses the morphological response of a gravel bed river to discharges of different magnitude from moderate events that occur several times a year to a 12 year flood and so defines the range of formative discharges for single morphological units channels bars islands and a range of magnitude of morphological activity from the threshold discharges for gravel transport and minor bar modification up to flows causing major morphological changes the study was conducted on the tagliamento river a large gravel bed river in north eastern italy using two different methods analysis of aerial photographs and field observation of painted gravel particles the available photographs five flights from august 1997 to november 2002 and the two commissioned flights june 2006 and april 2007 do not define periods with a single flood event but the intervals are short enough 11 to 22 months to have a limited number of flood events in each case the fieldwork which involved cross section survey grain size analysis and observation of painted sediments complemented the aerial surveys by allowing analysis of channel response to single flood events substantial morphological changes e g bank erosion of several tens of metres up to more than 100 m associated with flood events with a recurrence interval between 1 1 year and 12 years have been documented multiple forming discharges were defined based on the activity of different morphological units discharges equal to 20 50 of the bankfull discharge are formative for the channels whereas the bankfull discharge 1 1 year flood in this case of the tagliamento river is formative for low bars larger floods but still relatively frequent with a recurrence interval less than five years are required for full gravel transport on high bars and significant morphological changes of islands copyright 2009 john wiley sons ltd

stability morphology and surface grain size patterns of channel bifurcation in gravel cobble bedded anabranching rivers this study presents the first detailed field based analysis of the morphology of bifurcations within anabranching cobble gravel rivers bifurcations divide the flow of water and sediment into downstream anabranches thereby influencing the characteristics of the anabranches and the longevity of river islands the history morphology bed grain size and flow vectors at five bifurcations on the renous river new brunswick canada were studied in detail the angles of bifurcations within five anabranching rivers in the miramichi basin were investigated the average bifurcation angle was 47 within the range of values cited for braided river bifurcations bifurcation angle decreased when anabranches were of similar length shields stresses in channels upstream of bifurcations were lower than reported values for braided rivers stable bifurcations displayed lower shields stresses than unstable bifurcations contrary to experimental results from braided river bifurcations bifurcations in anabranching rivers are stabilized by vegetation that slows channel migration and helps to maintain a uniform upstream flow field the morphology of stable bifurcations enhances their stability a large bar shaped like a shallow ramp that increases in elevation to floodplain level forms at stable bifurcations floodplains at stable bifurcations accrete upstream at rates between 0 9 and 2 5 m a 1 bars may also form within the entrance of an anabranch downstream of the bifurcation node these bars are associated with bifurcation instability forming after a period of stability or an avulsion channel abandonment occurs when a bar completely blocks the entrance to one anabranch the stability of channels upstream of bifurcations and the location of bars at bifurcations influence bifurcation stability and the maintenance of river anabranching in the long term copyright 2006 john wiley sons ltd

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

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

bifurcation dynamics and avulsion duration in meandering rivers by one dimensional and three dimensional models at river bifurcations water and sediment are divided over two branches the dynamics of the bifurcation determine the long term evolution centuries of the downstream branches potentially leading to avulsion but the dynamics are poorly understood the long term evolution can only be studied by one dimensional models because of computational costs for such models a relation describing the sediment division is necessary but only few relations are available and these remain poorly tested so far we study the division of sediment and the morphodynamics on a timescale of decades to centuries by idealized three dimensional modeling of bifurcations with upstream meanders and dominantly bed load transport an upstream meander favors one bifurcate with more sediment and the other with more water leading to destabilization the bifurcations commonly attain a highly asymmetrical division of discharge and sediment after a few decades to a few centuries depending on combinations of the relevant parameters although past work on avulsions focused on slope advantage we found that bifurcations can be quasibalanced by opposing factors such as a bifurcate connected to the inner bend with a downstream slope advantage nearly balanced bifurcations develop much slower than unbalanced bifurcations which explains the observed variation in avulsion duration in natural systems which branch becomes dominant and the timescale to attain model equilibrium are determined by the length of the downstream bifurcates the radius of the upstream bend a possible gradient advantage for one bifurcate and notably the width depth ratio the latter determines the character of the bars which may result in overdeepening and unstable bars the distance between the beginning of the upstream bend and the bifurcation determines the location of such bars and pools which may switch the dominant bifurcate in fact when the bifurcation is quasibalanced by opposing factors any minor disturbance or a different choice of roughness or sediment transport predictor may switch the dominant bifurcate the division of sediment is nearly the same as the division of flow discharge in most runs until the discharge division becomes very asymmetrical so that a bifurcate does not close off entirely this partly explains the sustained existence of residual channels and existence of anastomosing rivers and the potential for reoccupation of old channel courses we develop a new relation for sediment division at bifurcations in one dimensional models incorporating the effect of meandering the flow and sediment divisions predicted by two existing relations and the new relation for one dimensional models are in qualitative agreement with the three dimensional model these one dimensional relations are however of limited value for wider rivers because they lack the highly three dimensional bar dynamics that may switch the direction of bifurcation evolution the potential effects of bed sediment sorting bank erosion and levee formation on bifurcation stability and avulsion duration are discussed

seismic anisotropy in sedimentary rocks part 2 laboratory data part one of this paper presents a method for measuring seismic velocities and transverse isotropy in rocks using a single core plug this method saves at least two thirds of the time for preparing core samples and measuring velocities in transversely isotropic ti rocks using this method we have measured velocity and anisotropy of many shale and reservoir rocks from oil and gas fields around the world we present some of the data in this paper which include seismic velocity and anisotropy in 17 brine saturated shale samples 1 gas and brine saturated coal sample 8 brine saturated sands 12 gas saturated sands 32 gas saturated carbonate samples and 25 brine saturated carbonate samples the results show that clays and fine layering in sedimentary rocks are the main causes of seismic anisotropy very little intrinsic anisotropy exists in unfractured reservoir rocks such as sands sandstones and carbonates under reservoir conditions in contrast all shales were found seismically anisotropic anisotr

absorption and scattering in ground penetrating radar analysis of the bishop tuff 1 ground penetrating radar gpr signals are attenuated by both absorption and scattering we performed low frequency 100 mhz gpr surveys at the volcanic tableland of the bishop california tuff to evaluate the factors that control gpr depth of investigation and to develop insight into the capabilities of such radars for mars the subsurface reflection character was very different for two different commercial systems used together they revealed both internal welding contacts in the tuff and an abundance of discrete scatterers attenuation coefficients were computed from profiles that showed distributed scattering the semilogarithmic signal decay is directly analogous to seismic coda the absorption intrinsic loss was determined to be 1 db m from low frequency vertical electric soundings the residual attenuation that is the attenuation in the absence of absorption is attributed to scattering scattering attenuation of 1 db m at 25 50 mhz corresponds to mean free paths as short as 4 m a fraction of the two way propagation distances of 20 40 m therefore the bishop tuff is formally a strong scatterer to gpr the mean free path is also comparable to the subsurface radar wavelength in this case maximizing scattering loss the scatterers themselves likely originate as welding heterogeneities contrasts in dielectric constant due to density differences may be supplemented by moisture variations on mars scattering is likely to contribute significant losses to gpr signals in all but the most uniform materials and unfrozen thin films of water in the lower cryosphere could influence both absorption and scattering

a 25 000 year record of earthquakes on the owens valley fault near lone pine california implications for recurrence intervals slip rates and segmentation models seven trenches in eastern california across the owens valley fault near lone pine expose two episodes of faulting since early holocene time in the form of 1 m throw in lacustrine beds with liquefaction that were buried and then faulted again 1 m by the m 7 5 to 7 75 a d 1872 owens valley earthquake geomorphic maps applications of sequence stratigraphy and analyses of radiocarbon from charcoal and tufa deposits indicate that the paleoearthquake the penultimate event here occurred between 10 200 200 and 8800 200 cal yr b p the cumulative vertical displacement from these last two earthquakes in three trenches averages 2 4 0 3 m 2 and the penultimate event has slightly larger displacements a synthesis of available data indicates that the antepenultimate event was probably as large and occurred between ca 24 000 and 14 000 cal yr b p 2 thus the two interseismic intervals between the last three surface faulting earthquakes on the southern owens valley fault are each 10 000 yr this 25 000 year record indicates that the two event normal oblique slip rate on the owens valley fault near lone pine is 1 0 0 5 m k y this result is similar to that of several previous geological studies here yet it is still slower than slip rates on the northern owens valley fault and several factors slower than contemporary geodetic measurements this study attempts to account for different dating methods and interpretational uncertainties to acknowledge how little is known about the slip history of the owens valley fault and adjacent faults and to consider the role of segmentation as well as splay and distributed faulting in comparisons of displacement data among different sites along the entire 100 10 km length of the owens valley fault

source mechanisms of three moderate california earthquakes of july 1986 abstract we studied the source processes of three moderate size earthquakes in california the m s 6 0 event of july 8 1986 near palm springs the m s 5 8 shock of july 13 1986 offshore of oceanside and the m s 6 2 event of july 21 1986 in the chalfant valley on the east side of the sierra nevada the centroidal source parameters are estimated by inversion of long period p and sh waves recorded at teleseismic distances by seismographs of worldwide networks a more detailed description of the source is then obtained by analyzing broadband seismograms the north palm springs earthquake had a simple rupture process most of the seismic moment was released in the first 3 sec in a single step the strike of the source fault plane follows the average trend of the banning fault and its dip agrees with the dip of the fault plane delineated by the aftershocks the faulting mechanism of the main shock is right lateral strike slip with a sizable reverse component that is consistent with uplift north of the banning fault the earthquake offshore of oceanside had a slightly more complex rupture process the far field source time function consists of two pulses that represent the release of most of the moment in the first 3 sec the source mechanism indicates reverse faulting with the compressional axis trending northeast almost perpendicular to the trend of mapped faults offshore the event does not appear to be associated with major mapped faults in the area but the strike of one of the nodal planes agrees with the trend of the major mapped faults offshore and its mechanism is consistent with the missing component of plate convergence not taken up by the onshore strike slip fault systems and the idea of a weak san andreas fault system the rupture process of the chalfant valley earthquake was yet more complicated the source time function indicates that in a 4 sec time window three asperities were broken the source mechanism indicates right lateral strike slip faulting with a small normal faulting component on a fault that dips approximately 50 southwest earthquake activity suggests that presently the deformation in the northern part of the owens valley which includes the chalfant valley is dominated by conjugate strike slip faults which strike obliquely to the main range bounding normal faults the waveforms indicate the presence of a low velocity zone at a depth of about 20 km in the crust in the chalfant valley a synthesis of information from waveform modeling first motion fault plane solutions and aftershock distributions indicates that the nucleation and or termination of rupture for the north palm springs and the chalfant valley events were controlled by preexisting fault geometry

cross double difference inversion for simultaneous velocity model update and microseismic event location microseismic monitoring is an approach for mapping hydraulic fracturing detecting the accurate locations of microseismic events relies on an accurate velocity model the 1d layered velocity model is generally obtained by model calibration from inverting perforation data however perforation shots may only illuminate the layers between the perforation shots and the recording receivers with limited raypath coverage in a downhole monitoring problem some of the microseismic events may occur outside of the depth range of these layers to derive an accurate velocity model covering all of the microseismic events and locating events at the same time we apply the cross double difference cdd method for the simultaneous inversion of a velocity model and event locations using both perforation shots and microseismic data the cdd method could provide accurate locations in both the relative and absolute sense utilizing cross traveltime differences between p and s phases over different events at the downhole monitoring scale the number of cross traveltime differences is sufficiently large to constrain events locations and velocity model as well in this study we assume that the layer thickness is known velocities of p and s wave are inverted different simultaneous inversion methods based on the geiger s dd and cdd algorithms have been compared with the same input data synthetic and field data experiments suggest that combining both perforation shots and microseismic data for the simultaneous cdd inversion of the velocity model and event locations is available for overcoming the trade offs in solutions and producing reliable results this article is protected by copyright all rights reserved

how do gravel bed rivers braid sedimentary processes and bed forms leading to the onset of braiding were observed in small scale hydraulic models of gravel bed streams the laboratory streams had a variety of combinations of constant discharge and slope but identical bed material particle size distributions from initially straight channels braiding occurred by four different processes deposition and accumulation of a central bar chute cutoff of point bars conversion of single transverse unit bars to mid channel braid bars and dissection of multiple bars in these experiments the chute cutoff mechanism was the most common but the predominant braiding mechanism depends upon sediment mobility excess bed shear stress and the bed form regime at very low excess bed shear stress the central bar process dominates but at higher excess bed shear stress slip face unit bars are more common bed scour at confluences is more pronounced and propogation of alternate convergence scour and divergence deposition is more likely thus chu

modelling bedload yield in braided gravel bed rivers abstract this paper outlines an approach for estimating the annual bedload yield of a braided channel this procedure is based on the extension of theory of flow and sediment transport in braided rivers recently presented by paola 1996 the revised approach accounts explicitly for the relationship between increasing discharge and varying channel hydraulics and is suitable for use in obtaining bedload transport rate estimates over a range of discharges integration of such estimates using flow duration data allows annual bedload yield to be determined model parameterisation is achieved using topographic survey data for the waimakariri river new zealand comparison of modelled bedload yield with values estimated from repeated topographic surveys indicates that the model is able to accurately predict both the medium term c 30 years mean annual bedload yield of the waimakariri at crossbank the section 17 8 km upstream of the river mouth and also short term fluctuations in bedload yield associated with varying annual flow statistics streamwise patterns of volumetric erosion and deposition determined for a 45 km length of the waimakariri using the model are also in broad agreement with trends identified in topographic survey data for the period 1961 1997 however significant deviations between modelled and surveyed volumes of cut and fill are evident at some locations comparison of model performance with conventional applications of bedload transport equations which tend to underestimate transport rates for braided channels suggests that the approach presented here may represent a significant improvement this is the case because the model quantifies the relationship between braid intensity and spatial variability in flow hydraulics at a cross section output from the model suggests that braided rivers may transport a significant proportion of their annual bedload at lower discharges than those indicated by earlier theoretical approaches results also provide quantitative support for the argument that increased intensity of braiding may promote higher rates of bedload transport in gravel bed rivers

three dimensional vp and vp vs structure at loma prieta california from local earthquake tomography p and s p times from local earthquakes and p times from explosions at seismic stations in the vicinity of the 1989 loma prieta earthquake are inverted simultaneously to produce three dimensional images of vp and vp vs structure along the rupture zone the results confirm the presence of the major heterogeneities identified in previous studies using p waves only including high vp along the rupture in areas of significant slip and a low velocity wedge along the san andreas at the se edge of the rupture a change in rock properties evidenced by a significant vp vs increase equal to a 30 poisson s ratio increase from the middle crust to the upper crust may have been responsible for the upward termination of the main shock rupture we speculate that the deep high vp body that lies along the se portion of the rupture zone consists of two bodies based on model results indicating that the sw part of the body has relatively high vp vs while the ne part has relatively low vp vs

stress induced temporal variations in seismic anisotropy observed in microseismic data summary in situ stress monitoring of crustal rocks is desirable as it yields insights into earthquake mechanisms volcanic eruptions and changes in hydrocarbon reservoirs shear wave splitting induced by stress controlled cracks in the shallow crust provides a way to infer this stress temporal variations in these observations can be difficult to quantify due to scatter in the data and discontinuous observations here we present evidence of temporal variations in shear wave splitting from a continuous time series with a high occurrence of microseismic events recorded in a borehole we interpret these observations in terms of stress controlled cracks and are able to infer changes in stress and via modelling suggest the cause of the anisotropy possible origins of the temporal variation in per cent anisotropy are tidal or oil field production processes our results suggest that shear wave splitting is a viable probe for inferring changes in crustal stress in cracked rock

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

40ar 39ar age constraints for the jaramillo normal subchron and the matuyama brunhes geomagnetic boundary our mid pleistocene 4oar 39ar age recalibration of the geomagnetic polarity timescale is nearly in accord with the oxygen isotope climate record calibration of the astronomical timescale proposed by johnson 1982 and shackleton et al 1990 4oar 39ar ages of a normally magnetized rhyolite dome in the valles caldera northern mexico yielded a weighted mean age of 1 004 0 019 ma a k ar age of 0 909 0 019 ma for this rock by doell and dalrymple 1966 was the linchpin for the recognition and calibration of the jaramillo normal subchron jns other 4oar 39ar ages from the vailes caldera and 4oar 39ar ages of ivory coast tektites indicate that the jns began at about 1 11 ma and ended before 0 92 ma probably near 0 97 ma the matuyama brunhes boundary occurred between 0 79 ma and 0 76 ma on the basis of 4oar 39ar sanidine ages from 1 three reversely magnetized rhyolite domes of the valles caldera 0 793 0 018 ma 0 794 0 007 ma and 0 812 0 023 ma and pumice 0 789 0 006 ma from the reversely magnetized oldest toba tuff of sumatra and 2 pumice 0 764 0 005 ma and 0 757 0 009 ma from the lower and upper units of the normally magnetized bishop tuff the age of the boundary may be close to 0 77 ma as deduced from rates of sedimentation in ancient lake bonneville utah increasingly aware that the polarity of earth s magnetic field has changed repeatedly through geologic time and isotopic dating of these polarity reversals resulted in a geomagnetic polarity time scale gpts for the late cenozoic this combined paleomagnetic and isotopic research played a pivotal role in confirming plate tectonic theory glen 19821 which revolutionized the earth sciences continual refinement of isotopic ages which define the gpts has increased the usefulness of geomagnetic polarity reversals as marker hori zons in many types of geologic studies we present 4oar 39ar data and ages for some key volcanic units that support changes in the isotopic age chronology of the gpts using volcanic rocks erupted near the time of the geologically youngest two geomagnetic polarity reversals figure 1 the older of the two reversals originally called by doell and dalrymple 1966 the jaramillo event is now named the jaramillo normal subchron jns it is recorded in middle pleistocene rocks as a brief episode of normal polar ity within the late matuyama chron the younger of the two called the matuyama brunhes boundary mbb is regis tered in middle pleistocene rocks worldwide and consists of

the response of braided planform configuration to flow variations bed reworking and vegetation the case of the tagliamento river italy morphological features of braided rivers bars channels and pools experience major changes in area shape and spatial distribution as a response to i the pulsation of discharge during a flood and ii the bed evolution induced by floods in this work at a station relationships between water level and planform configuration were investigated on the tagliamento river a large gravel bed braided river in northeast italy over a 2 year study period comprising three bankfull events and several small to medium floods the analysis was performed on two 1 km long reaches characterized by different riparian vegetation cover ground based images with an hourly temporal resolution were acquired using software controlled digital cameras bars channels pools and vegetated patches were manually digitized on more than 100 rectified images sequences of constant level images spanning the study period were used to quantify the impact of floods on the stability of at a station relationships and on the turnover rate of water bodies the analysis shows that wetted area increased almost linearly with water level in both reaches the average number of branches per cross section peaked at intermediate flow levels increasing from 2 at low flow up to 6 7 the number of branches displayed the largest fluctuations over time with significant changes produced also by moderate floods turnover rates were high in both reaches with more than 30 of wetted areas at low flow converting into bare gravel in less than 2 months vegetation colonization was found to limit the mobility of the low flow channels over time by concentrating the flow in fewer deeper anabranches the number of channels per cross section was 30 40 less in the vegetated reach and the proportion of low flow water bodies in the same position after 12 months increased from 3 to 14 copyright 2012 john wiley sons ltd

active width of gravel bed braided rivers previous analyses have identified the active width of braided rivers the bed area over which bed load flux and short term morphological change occurs as an important element of braiding dynamics and predictions of bed load flux here we compare theoretical predictions of active width in gravel bed braided rivers with observations from sunwapta river and from a generic physical model of gravel braided rivers to provide general observations of the variation in active width and to develop an understanding of the causes of variation bed topography was surveyed daily along a 150 m reach of the pro glacial sunwapta river for a total of four weeks during summer when flow was above threshold for morphological activity in the laboratory detailed digital elevation models dems were derived from photogrammetric survey at regular intervals during a constant discharge run from the field and flume observations there is considerable local and circumstantial variation in active width but also a general trend in average active width with increasing discharge there is also a clear relationship of active width with active braiding index number of active branches in the braided channel network and with dimensionless stream power which appears to be consistent across the range of data from field and physical models thus there is a link between active width and the river morphology and dynamics and the possibility of a general relationship for estimating active width from channel pattern properties or reach scale stream power values from which approximate bedload flux calculations may be made the analysis also raises questions about differences between hydraulically based numerical model computations of instantaneous active width and observation of time integrated morphological active width understanding these differences can give insight into the nature of bedload transport in braided rivers and the relationship to morphological processes of braiding copyright 2011 john wiley sons ltd

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

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

changes in braided river morphology resulting from aggradation and degradation forty three experiments were completed in a large flume 1 8 x 18 3 m to examine the effects of sediment load sediment size and channel gradient on braided river morphology the laboratory results were supported by field research and analogs from the published literature subaerially exposed braid bars were formed by the dissection and further accretion of stalled linguoid dunes which are actively migrating bedforms bar forming processes and channel dynamics were the same in both sand and gravel bed channels however linguoid dunes stalled and were transformed into braid bars more frequently in gravel bed channels and therefore gravel bed channels were more intensely braided aggradation resulted in the development of more bars rather than in an increase in the size of preexisting braid bars the number of actively migrating linguoid dunes also increased with sediment load in the highly mobile sand bed channels conversely in degrading channels the number of braid bars decreased and average bar

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

property changes of oil shale during artificial maturation the irati formation from the parana basin brazil abstractacquiring elastic property information from oil shale during pyrolysis remains a difficult endeavor we subject oil shale samples from the irati formation in the parana basin brazil to high temperature high pressure hydrous and anhydrous pyrolysis while simultaneously acquiring p and s waveform data we present elastic properties as a function of temperature at constant differential pressure using samples cored in three different directions relative to the bedding plane hydrous pyrolysis decreased total organic carbon toc in samples from 25 wt to 20 wt whereas anhydrous pyrolysis had no significant change in toc the cores experienced higher strain hysteresis up to 0 094 residual axial strain after hydrous pyrolysis compared to after anhydrous pyrolysis 0 56 residual axial strain the larger residual strain was accompanied by a larger increase in shear velocity up to 35 after hydrous pyrolysis as compared to the 3 shear velocity increase after anhydrous pyrolysis the change coul

faulting on the volcanic tableland owens valley california the volcanic tableland brittle surface of the 764 000 yr old bishop tuff documents extensive faulting in the northern owens valley california during the late quaternary the tableland surface is cut by at least 226 fault scarps with a total of 328 km of surface rupture scarps are lens shaped rips in the surface of the bishop tuff with vertical offsets of a few meters to 140 m and lengths up to several kilometers the scarps have an average trend of n10 20 w and dip steeply both to the east and west the tableland records at least 290 m of cross valley extension in the last 764 000 yrs at an average rate of at least 400 m m y and a cumulative seismic moment of at least 2 8 cdot 10 28 dyne cm the volcanic tableland lies astride what has been called the white mountain seismic gap of the eastern california central nevada seismic zone seismic moment recorded on the tableland can be used to estimate average recurrence interval of surface rupturing earthquakes on the floor of the owens valley

life of a bifurcation in a gravel bed braided river channel bifurcation is a key element in braided rivers determining the water and sediment distribution and hence controlling the morphological evolution recent theoretical and experimental findings as well as field observations showed that bifurcations in gravel bed braided rivers are often asymmetrical and highly unstable in this paper field data are presented on a bifurcation in the tagliamento river northeast italy the planform configuration of the bifurcation and its temporal evolution was monitored by an automatic digital camera during a series of seven floods with different magnitudes this remote sensing technique allowed a high temporal resolution pictures were acquired every hour that was proved to be essential in a highly dynamic system as the one considered here digitized maps of the channels provided information on the location of the bifurcation the width of the anabranches the angle between them along with the occurrence and migration of sediment bars data were acquired at two different water levels giving the possibility to compare low and high flow conditions the monitored bifurcation is largely unstable and shows sudden changes in the water distribution mainly driven by the bar migrating in the upstream channel and entering the distributaries a relationship between width asymmetry and flood magnitude was observed confirming previous analyses moreover recent theoretical findings were applied in order to test the possibility to estimate general trends in bifurcation evolution the analysis pointed out the relevance of a correct assessment of the characteristic temporal scales as the bifurcation evolves on a timescale similar to that of bar migration and flood duration understanding the interactions between these processes is therefore crucial in order to increase the ability to model and predict the morphological evolution of a braided network copyright 2012 john wiley sons ltd

cerberus fossae elysium mars a source for lava and water cerberus fossae a long fracture system in the southeastern part of elysium has acted as a conduit for the release of both lava and water onto the surface the southeastern portion of the fracture system localized volcanic vents having varying morphology in addition low shields occur elsewhere on the cerberus plains three locations where the release of water has occurred have been identified along the northwest athabasca and grjota vallis and southeast rahway vallis portions of the fossae water was released both catastrophically and noncatastrophically from these locations a fluvial system that extends more than 2500 km has formed beginning at the lower flank of the elysium rise across the cerberus plains and out through marte vallis into amazonis planitia the timing of the events is late amazonian

the missing dimension effects of lateral variation on 1 d calculations of fluvial bedload transport most calculations of bedload transport in rivers including those in numerical models of aggradation and degradation are 1 d all hydraulic and transport rate calculations are averaged over the channel width because bedload transport laws are nonlinear width averaged calculations will underestimate the true bedload flux if there is any local spatial variation in either the bed or the flow this paper analyses the effects on bedload transport capacity of spatial variation in applied and critical c shear stress separately and in combination a simple but versatile statistical model is used to represent variability in with allowance for differences between sand and gravel bed rivers and for below bankfull flow bedload flux is shown to increase greatly with the variance of especially in gravel bed rivers variability in c through bed patchiness may increase reduce or make little difference to bedload flux depending on the correlation between and c simple width averaging leads to severe underestimation of bedload transport in most conditions some alternatives are considered the findings have implications for sediment routing models srms but further research is needed to explore the issue fully

estimates of strain due to brittle faulting sampling of fault populations abstract the geometry of sampling domains is a first order consideration in the characterization of brittle fault populations in most cases descriptions of fault size distributions based on map cross section traverse or borehole data systematically underestimate the number of small faults present in a volume the geometry of sampling domains may be accounted for using an empirical proportionality between fault displacement and trace length estimates of strain in which the sampling geometry is considered suggest that small faults accommodate a significant portion of the total strain due to the brittle faulting process

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

assessment of morphological changes induced by flow and flood pulses in a gravel bed braided river the tagliamento river italy large gravel bed braided rivers show a highly dynamic evolution where even moderate flow pulses can produce significant morphological adjustment an estimation of network variations is needed by river authorities as well as by ecologists for better managing river ecosystems however few field investigations have been performed to measure the effect of unsteady discharges in braided rivers in this paper we report on the morphological changes induced by six different floods in a 1 km long reach of the tagliamento river italy topographic surveys were performed after each significant flood and an automatic digital camera continuously monitored the planimetric configuration repeated measurements of cross section profiles allowed the quantification of the transported sediments volume and in particular provided a basis to estimate the percentage of the floodplain subject to morphological evolution data analysis showed a good relationship between peak flow level active width and mean bed level changes similarly lateral channel shifting is likely to increase for larger floods monitoring of a range of discharges up to bankfull conditions revealed a fundamental difference between flow pulses events on the average occurring one or more times per year and flood pulses with a return period larger than two years the morphological evolution in the former case is mainly limited to a few active branches and is locally driven by bank erosion at the bend apex on the other hand larger floods induce a complete reworking of the network configuration where bifurcations and confluences play a crucial role single morphological units like branches nodes bars are no longer recognizable after this type of event braided rivers are therefore characterized by the occurrence of two different spatial and temporal scales that force the ecosystem dynamics

image domain velocity inversion and event location for microseismic monitoring abstractmicroseismic event locations obtained from seismic monitoring data sets are often a primary means of determining the success of fluid injection programs such as hydraulic fracturing for oil and gas extraction geothermal projects and wastewater injection event locations help the decision makers to evaluate whether operations conform to expectations or parameters need to be changed and may be used to help assess and reduce the risk of induced seismicity however obtaining accurate event location estimates requires an accurate velocity model which is not available at most injection sites common velocity updating techniques require picking arrivals on individual seismograms this can be problematic in microseismic monitoring particularly for surface acquisition due to the low signal to noise ratio of the arrivals we have developed a full wavefield adjoint state method for locating seismic events while inverting for p and s wave velocity models that optimally focus multiple complementary ima

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

mechanics of river mouth bar formation implications for the morphodynamics of delta distributary networks 1 in this paper we use observational data and numerical modeling to present a new explanation for the formation of river dominated delta networks observational data from deltas throughout the world show that distributary channel widths depths and lengths decrease nonlinearly with successive bifurcations trends in width and depth are an outcome of hydraulic geometry scaling the trend in channel length is a consequence of delta growth analyses of serial maps show that the positions of bifurcations are the fossilized locations of river mouth bars also called middle ground and distributary mouth bar in front of old delta channel mouths therefore the trend in channel length can be explained through the mechanics of river mouth bar formation and evolution we use delft3d a coupled hydrodynamic and morphodynamic model to simulate the process of river mouth bar formation within an expanding turbulent jet in front of distributary channel mouths our results describe in detail the formation and evolution of a river mouth bar system and demonstrate that the distance to the river mouth bar is proportional to jet momentum flux and inversely proportional to grain size therefore channel length decreases down delta because with each successive bifurcation the jet momentum flux decreases these results can be used to predict the future evolution of river dominated deltas and can be used to aid in hydrocarbon exploration of these depositional environments

a method for estimating the mean bed load flux in braided rivers prediction of bed load flux remains a significant problem in understanding braided river morphodynamics for geomorphic and engineering applications two sets of data from laboratory experiments on braided networks performed at the university of trento italy and at the university of alberta canada provide the basis for development of a dimensionless bed load function and for testing a simple predictive model measured total sediment transport rates time averaged at equilibrium channel configuration collapse to a single dimensionless relationship based on dimensionless stream power bed load fluxes predicted by the parker and bagnold functions and cross section average hydraulic parameters under predict the bed load flux particularly at low shear stress this is consistent with previous observation and theory demonstrating the significant influence of transverse variability of the hydraulic parameters in controlling and predicting bed load flux a simple method for adjusting for this lateral variation is proposed for computing the sediment transport rate using topographic cross sections of braided rivers results show good agreement with the measured values suggesting that simple assumptions combined with the mean morphology of the channel may be sufficient to estimate mean bed load flux model predictions also highlight the significance of active bed width rather than bed shear stress as a fundamental ingredient in the prediction of the bed load rate and therefore as an important morphological property to be modelled the model also predicts similar behaviour in the at a station variability of bed load and in the importance of variation of active width relative to bed shear stress in the transport process

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

kinematics of the eastern california shear zone evidence for slip transfer from owens and saline valley fault zones to fish lake valley fault zone late quaternary slip rates and satellite based geodetic data for the western great basin constrain regional fault slip distribution and evolution the geologic slip rate on the fish lake valley fault zone the northwest extension of the furnace creek fault zone increases northward from about 3 to 5 mm yr in agreement with modeled geodetic data the increase coincides with the intersections of the deep springs fault connected to the owens valley fault zone and of other faults connected to the saline valley fault the combined geologic and geodetic data suggest that 1 the northwest striking faults of the eastern california shear zone north of the garlock fault are connected by north to northeast striking normal faults that transfer slip in a series of right steps and 2 the amount and distribution of slip among the many faults of this broad complex plate boundary have changed through time

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

anisotropy correction for deviated well sonic logs application to seismic well tie borehole sonic logs acquired in deviated wells penetrating the hrz and colville shales in the niakuk field in alaska s north slope are seen to be significantly faster than vertical well logs these differences are attributed to shale anisotropy an iterative inversion scheme was created to invert for shale anisotropy parameters using multiple wells penetrating shale sections at different angles the inversion involves fitting the sonic log data at a range of borehole angles to the compressional wave group velocity surface the result is an estimate of the anisotropy parameters e and and the vertical p wave velocity the results show that the shales are strongly anisotropic with compressional wave anisotropy thomsen s parameter e on the order of 40 and the anisotropy parameter relates vertical velocity to short offset nmo velocity around 10 this large anisotropy can affect seismic imaging avo and time depth calculations a procedure was created to estimate the anisotropy corrected vertical s

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

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

interaction between migrating bars and bifurcations in gravel bed rivers 1 in the present work we investigate the interaction between migrating alternate bars and the dynamics of river bifurcations laboratory experiments are carried out to study a y shaped bifurcation with fixed banks and erodible bed composed of well sorted sand the problem is also analyzed by developing a theoretical one dimensional model results show the occurrence of regular fluctuations in the discharge distribution at the bifurcation node which are strictly related to bar migration the effectiveness of bars in conditioning the bifurcation behavior increases with bar amplitude and decreases with bar migration speed four qualitatively different behaviors of the system are observed as the controlling parameters of the flow are varied within a range significant for gravel bed rivers the theoretical predictions are in good qualitative agreement with the experimental observations

the role of vegetation and large wood on the topographic characteristics of braided river systems riparian vegetation and large wood play a crucial role in shaping rivers on the one hand vegetation tends to increase bank stability reduce channel width and reduce the braiding index in gravel bed rivers conversely large wood tends to increase channel dynamics and promote avulsions the effects of vegetation and large wood have been rarely simulated together in flume experiments in this paper we present a series of experimental runs conducted in a large flume facility using cylindrical wooden dowels and alfalfa seedlings to represent logs and vegetation respectively in order to investigate their role on determining the topographical nature of braided river systems a terrestrial laser scanner was used to measure in detail the topography of the channels and bars and distribution of the elevations and second order structure functions were used to explore the topography that large wood and vegetation imposed on the braided pattern in the flumes results show that vegetation reduced the braiding index and produced wider and deeper channels the standard deviation of the bed elevations was higher than in flumes without vegetation large wood alone was not effective in changing the braiding index or the standard deviation of the elevations when vegetation and large wood acted together in the flume the braiding index reached a minimum value and the skewness of the distribution of elevation increased revealing shallower pools if compared with runs conducted with only vegetation

velocity anisotropy in shales a petrophysical study using ultrasonic velocity and anisotropy measurements on a variety of shales with different clay and kerogen content clay mineralogy and porosity at a wide range of effective pressure we find that elastic anisotropy of shales increases substantially with compaction the effect is attributed to both porosity reduction and smectite to illite transformation with diagenesis a means of kerogen content mapping using velocity versus porosity crossplot for shales is shown matrix anisotropy of shales dramatically increases with kerogen reaching the maximum values of about 0 4 at total organic carbon toc 15 20 a strong chemical softening effect was found in shales containing even minor amounts of swelling smectite clay when saturated with aqueous solution this effect results in a significant p wave anisotropy reduction as compared to dry and oil saturated shales since mature black shales are normally oil wet this effect can only have a local significance restricted to the wellbore wall accurate measurements of phase velocities including velocities at a 45 direction to the bedding plane allow us to immediately calculate elastic stiffnesses and anisotropic parameters intrinsic high pressure properties of shales display an e 0 relation introduction of the bedding parallel microcracks in overpressured shales results in a decrease when fully fluid saturated and a increase when partially gas saturated with a characteristic effect on the shape of the p wave velocity surface at small angles of incidence filtering the contribution of the intrinsic anisotropy of shales it is possible to estimate the pore fluid phase microcrack density and aspect ratio parameters using seismic anisotropy measurements

microseismic image domain velocity inversion marcellus shale case study abstractseismic monitoring at injection wells relies on generating accurate location estimates of detected micro seismicity event location estimates assist in optimizing well and stage spacings assessing potential hazards and establishing causation of larger events the largest impediment to generating accurate location estimates is an accurate velocity model for surface based monitoring the model should capture 3d velocity variation yet rarely is the laterally heterogeneous nature of the velocity field captured another complication for surface monitoring is that the data often suffer from low signal to noise levels making velocity updating with established techniques difficult due to uncertainties in the arrival picks we use surface monitored field data to demonstrate that a new method requiring no arrival picking can improve microseismic locations by jointly locating events and updating 3d p and s wave velocity models through image domain adjoint state tomography this approach creates a co

data acquisition design for microseismic monitoring microseismic monitoring of hydraulic well treatments is one of the most useful seismic techniques that can aid the development of tight gas and shale gas fields the main challenge in these fields is an extremely low formation permeability which lies in the microdarcy or even nanodarcy range and requires thousands of closely spaced wells to drain the reservoir for example the barnett field in texas usa has more than 12 000 producing wells depending on the specifics of a given reservoir it might be developed via vertical or slanted or horizontal wells or any combination thereof such varied well geometries and relatively small well spacing provide ample opportunities for microseismic surveys

measurements in a braided river chute and lobe 1 flow pattern sediment transport and channel change this paper and its companion ashworth et al this issue discuss measurements of channel change and associated flow and sediment transport processes in a representative chute and bar reach within a proglacial gravel bed river the sunwapta river in the canadian rockies during a week in which water discharge through the reach increased then decreased a sediment wave passed into and partly along the reach at first the chute aggraded then sediment was eroded from the chute and deposited in a prograding lobe to one side of the original bar head between two distributaries measurements of velocity shear stress and gravel transport rate revealed day to day changes in the divergent pattern of flow and sediment transport the off center location of the lobe reflected an initial asymmetry in the pattern of flow and sediment transport but as the lobe grew the flow and transport gradually switched away to the other distributary width averaged bed load transport rates do not agree well with average rates inferred from bar head deposition or from volumes and spatial patterns of scour and fill the indirect estimates are considered more reliable than those based on direct sampling for necessarily brief durations by the end of the study the new lobe had almost accreted onto the original bar head supporting the idea that most braid bars are of compound origin temporal and spatial patterns in grain size distributions of the bed bed load and deposited sediment are discussed in the companion paper

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