combined visual and quantitative techniques in the study of natural turbulent flows an important difficulty in understanding turbulence in natural flows is that one does not see what is being measured by devices recording velocity fluctuations this study shows how visualization of turbulent structures can be effectively implemented in natural river flows in order to match turbulent flow structures with their velocity signatures flow visualization is combined with high frequency 20 hz velocity measurements from electromagnetic current meters two fluvial environments are examined in a river confluence where the difference in turbidity provides a natural tracer very strong negative velocity fluctuations for the streamwise component are concomitant with an upwelling motion a video recording made from a bridge of the passage of turbulent structures delineated by turbid and clear water allowed us to relate the marked fluctuations in velocity to eddies of a duration of 1 2 s in the mixing layer in a gravel bed river we have examined patterns of eddy shedding in the lee of a pebble cluster these patterns were highlighted by dye milk injected in the separation zone downstream black and white images were obtained from an underwater lens linked to a video camera recorder we observed a complex dynamic characterized by two dominant patterns of eddy shedding one with a clear motion of eddies toward the water surface and another with a downward expansion toward the bed of the structures this pattern is related to the passage of intermittent wedges of low speed fluid separated by wedges of fast moving fluid

numerical modeling of flow processes over gravelly surfaces using structured grids and a numerical porosity treatment this article describes the development and validation of a method for representing the complex surface topography of gravel bed rivers in high resolution three dimensional computational fluid dynamic models this is based on a regular structured grid and the application of a porosity modification to the mass conservation equation in which fully blocked cells are assigned a porosity of zero fully unblocked cells are assigned a porosity of one and partly blocked cells are assigned a porosity of between 0 and 1 according to the percentage of the cell volume that is blocked the model retains an equilibrium wall function and an rng type two equation turbulence model the model is combined with a 0 002 m resolution digital elevation model of a flume based water worked gravel bed surface acquired using two media digital photogrammetry and with surface elevations that are precise to 0 001 m the model is validated by comparison with velocity data measured using a three component acoustic doppler velocimeter adv model validation demonstrates a significantly improved level of agreement than in previous studies notably in relation to shear at the bed although the resolution of model predictions was significantly higher than the adv measurements making model assessment in the presence of strong shear especially difficult a series of simulations to assess model sensitivity to bed topographic and roughness representation were undertaken these demonstrated inherent limitations in the prediction of 3 d flow fields in gravel bed rivers without high resolution topographic representation they also showed that model predictions of downstream flux were more sensitive to topographic smoothing that to changes in the roughness parameterization reflecting the importance of both mass conservation i e blockage and momentum conservation effects at the grain and bed form scale model predictions allowed visualization of the structure of form flow interactions at high resolution in particular the most protruding bed particles exerted a critical control on the turbulent kinetic energy maxima typically observed at about 20 of the flow depth above the bed

analyzing earthquake clustering features by using stochastic reconstruction 1 on the basis of the epidemic type aftershock sequence etas model and the thinning procedure this paper gives the method about how to classify the earthquakes in a given catalogue into different clusters stochastically the key points of this method are the probabilities of one event being triggered by another previous event and being a background event making use of these probabilities we can reconstruct the functions associated with the characteristics of earthquake clusters to test a number of important hypotheses about the earthquake clustering phenomena we applied this reconstruction method to the shallow seismic data in japan and also to a simulated catalogue the results show the following assertions 1 the functions for each component in the formulation of the space time etas model are good enough as a first order approximation for describing earthquake clusters 2 a background event triggers less offspring in expectation than a triggered event of the same magnitude 3 the magnitude distribution of the triggered event depends on the magnitude of its direct ancestor 4 the diffusion of the aftershock sequence is mainly caused by cascades of individual triggering processes while no evidence shows that each individual triggering process is diffusive and 5 the scale of the triggering region is still an exponential law as formulated in the model but not the same one for the expected number of offspring

earthquake patterns in diverse tectonic zones of the globe we extend existing branching models for earthquake occurrences by incorporating potentially important estimates of tectonic deformation and by allowing the parameters in the models to vary across different tectonic regimes we partition the earth s surface into five regimes trenches including subduction zones and oceanic convergent boundaries and earthquakes in outer rise or overriding plate fast spreading ridges and oceanic transforms slow spreading ridges and transforms active continental zones and plate interiors everything not included in the previous categories our purpose is to specialize the models to give them the greatest possible predictive power for use in earthquake forecasts we expected the parameters of the branching models to be significantly different in the various tectonic regimes because earlier studies bird and kagan in bull seismol soc am 94 6 2380 2399 2004 found that the magnitude limits and other parameters differed between similar categories we compiled subsets of the cmt and pde earthquake catalogs corresponding to each tectonic regime and optimized the parameters for each and for the whole earth using a maximum likelihood procedure we also analyzed branching models for california and nevada using regional catalogs our estimates of parameters that can be compared to those of other models were consistent with published results examples include the proportion of triggered earthquakes and the exponent describing the temporal decay of triggered earthquakes we also estimated epicentral location uncertainty and rupture zone size and our results are consistent with independent estimates contrary to our expectation we found no dramatic differences in the branching parameters for the various tectonic regimes we did find some modest differences between regimes that were robust under changes in earthquake catalog and lower magnitude threshold subduction zones have the highest earthquake rates the largest upper magnitude limit and the highest proportion of triggered events fast spreading ridges have the smallest upper magnitude limit and the lowest proportion of triggered events the statistical significance of these variations cannot be assessed until methods are developed for estimating confidence limits reliably some results apparently depend on arbitrary decisions adopted in the analysis for example the proportion of triggered events decreases as the lower magnitude limit is increased possibly because our procedure for assigning independence probability favors larger earthquakes in some tests we censored earthquakes occurring near and just after a previous event to account for the fact that most such earthquakes will be missing from the catalog fortunately the branching model parameters were hardly affected suggesting that the inability to measure immediate aftershocks does not cause a serious estimation bias we compare our branching model with the etas model and discuss the differences in the models parametrization and the results of earthquake catalogs analysis

gulf of mexico tectonic history hotspot tracks crustal boundaries and early salt distribution a late jurassic mantle plume may have generated hotspot tracks on the north american plate and the yucatan penninsula tectonic block as the gulf of mexico opened ca 150 ma the tracks are identified from deep basement structural highs that have been mapped by integrating seismic refraction and gravity data they are associated with high amplitude distinctive gravity anomalies that provide the basis for a kinematic reconstruction that restores the western ends of the hotspot tracks with a 20 clockwise rotation of the yucatan block or almost one half the total rotation required to open the gulf of mexico basin the duration of track generation is estimated to have been about 8 10 m y or almost one half the total time required to open the gulf of mexico basin prior to this rotation extension of continental crust over a 10 12 m y interval was the result of approximately 22 of counterclockwise rotation and crustal thinning autochthonous salt appears to be confined to the continental flanks of the hotspot tracks confirming that salt was deposited during continental extension and not after ocean floor had begun to form a prominent gravity anomaly along the western boundary of the basin is interpreted to be produced by a marginal ridge which was created along the ocean continent transform boundary as the basin opened the eastern flank of this marginal ridge and the northernmost easternmost and southernmost terminations of the hotspot tracks are interpreted to coincide with the oceanic continental crustal boundary in the basin dale e bird consults in the oil and gas exploration industry as a potential fields specialist since 1981 his experience in the industry includes acquisition processing interpreting and marketing geophysical data including positions with aerodat world geoscience marathon oil company digicon and aero service he earned a ph d from the university of houston in 2004 and his research interests are regional geology and tectonics and the integration and interpretation of gravity and magnetic data he is a member of several local and international geological and geophysical societies kevin burke has been a professor of geology in the university of houston since 1983 having previously lived and worked in several parts of the world his main research is in tectonics the large scale evolution of planetary lithospheres his current interests include african and asian geology and the derivation of large igneous provinces from the core mantle boundary stuart a hall is a professor of geosciences specializing in the study of gravity and magnetic fields he received a b sc honors degree in physics from the university of birmingham united kingdom 1968 and a ph d in geophysics from the university of newcastle upon tyne united kingdom 1976 his current research interests are mainly focused on the use of geophysical data to investigate the development of small ocean basins and orogenic belts he is a member of the society of exploration geophysicists american geophysical union royal astronomical society and sigma xi research society john f casey is a professor of geology and chair of the department of geosciences at the university of houston specializing in structure tectonics and geochemisty he received a b a degree in geology from the university of pennsylvania in 1975 and a ph d in geology with honors from the state university of new york albany in 1980 his research has focused on the tectonics and geochemistry of midocean ridges transform faults and ophiolite bearing orogenic belts

high temperature elasticity of iron bearing olivines the first high temperature data on the nine adiabatic elastic moduli for iron bearing olivine are reported these measurements are on two single crystal specimens of natural olivine at ambient pressure and from room temperature to a maximum of 1500 k the two specimens contain 8 and 9 modal percent fayalite which required the oxygen fugacity be controlled at high temperature to preserve their chemical stability the rectangular parallelepiped resonance apparatus was adapted to buffer the specimens from the atmosphere with a mixture of co and co2 gas a small increase 1 2 gpa in the adiabatic bulk modulus of each specimen over that of end member forsterite was found the data are high quality to extreme temperatures with good agreement found when comparing the temperature derivatives of the elastic moduli of the two specimens neither specimen exhibits measurable nonlinear temperature dependence in the computed isotropic bulk and shear moduli which is in contrast to published forsterite data the temperature derivatives of the isotropic bulk modulus ks are 1 69 1 80 10 2 gpa k 1 for the two olivine specimens and the shear modulus g derivatives are 1 38 1 36 10 2 gpa k 1 these derivatives are only slightly larger in magnitude than ks t p 1 56 10 2 and g t p 1 30 10 2 gpa k 1 found previously for iron bearing olivine over a very small temperature range there are also no significant differences between the temperature derivatives found here and the average derivatives of end member forsterite from data retrieved over a slightly larger temperature range several dimensionless parameters have been calculated from these results and are discussed in view of systematics which bear on high pressure phases in earth s transition zone one result from these systematics related to the seismic velocities in the earth and especially the shear wave velocities is that an olivine content of less than 50 is implied at the 400 km discontinuity if earth s upper mantle is isochemical furthermore the substitution of almost 10 iron for magnesium at the forsterite end of the olivine solid solution series has little effect on the dimensionless parameters or on the temperature derivatives of the elastic moduli at high temperature

effects of a pebble cluster on the turbulent structure of a depth limited flow in a gravel bed river pebble clusters are important morphological features of gravel bed rivers and have a significant effect on the spatial and temporal response of the flow this paper presents original results from measurements of velocity taken at a high spatial and temporal resolution in a turbulent flow upstream and downstream from a pebble cluster three electromagnetic current meters 0 013 m in diameter mounted on a wading rod were deployed upstream and downstream of an isolated pebble cluster along 31 vertical profiles that contained between 7 and 13 points in a 5 m long section the high sampling resolutions in a natural environment permitted characterization of the complex dynamics of the turbulent flow in the vicinity of the cluster the description of these dynamics is based on the interpretation of contour maps of several turbulence statistics including moments of velocity distributions reynolds shear stress quadrant analysis and autocorrelation function downstream from the cluster flow is decelerated the intensity of turbulence increases and zones of strong vertical motions are present the superimposition of the maps allowed us to decompose the field of turbulent flow around a pebble cluster into distinct regions in a downstream direction from the cluster we observed zones of flow acceleration recirculation vortex shedding flow reattachment fluid upwelling and flow recovering results indicate the existence of highly dynamic boundaries between zones where strong intermittent events are generated they also highlight the difference between shedding and upwelling motions of the flow

slab portal beneath the western aleutians tomographic images of the distribution of shear wave speed beneath the northwestern pacific delineate the configuration of the subducted oceanic lithosphere beneath the western aleutian arc at 100 km depth a fast shear wave speed anomaly is beneath the aleutian arc everywhere east of 1738e between 1648e and 1738e however seismic velocities at this depth are slow relative to the surrounding mantle the lateral termination of the fast shear wave speed anomaly at depth coincides with a gap in deep seismicity beneath the aleutians the absence of these two distinctive traits of subducting slabs leads us to conclude that this segment of the aleutian arc overlies a very large window in the otherwise continuous lithospheric slab that we term a slab portal this portal is likely to facilitate the production of distinctive volcanic rocks adakites or high mg andesites by partially melting the adjacent edges of the slab the miocene age of most adakites in the westernmost aleutians where no slab is present may indicate that the portal formed relatively recently the chemistry of western aleutian adakites approximates that of typical continental crust so their genesis and subsequent lateral transport toward kamchatka is a plausible mechanism for new continent formation

space time etas models and an improved extension for sensitive detection of anomalous seismicity such as quiescence and activation in a given region we need a suitable statistical reference model that represents a normal seismic activity in the region the regional occurrence rate of the earthquakes is modeled as a function of previous activity the specific form of which is based on empirical laws in time and space such as the modified omori formula and the utsu seki scaling law of aftershock area against magnitude respectively this manuscript summarizes the development of the epidemic type aftershock sequence etas model and proposes an extended version of the best fitted space time model that was suggested in ogata ogata y 1998 space time point process models for earthquake occurrences ann inst statist math 50 379 402 this model indicates significantly better fit to seismicity in various regions in and around japan d 2005 elsevier b v all rights reserved

suspended sediment concentration and calibre in relation to surface flow structure in squamish river estuary southwestern british columbia surface grabs of suspended sediments from boils and the background flow in squamish estuary revealed strong differences between the two environments boils exhibit higher sediment concentrations and larger particle sizes than the background flow the higher sediment concentrations and larger grain sizes in boils are related to tidal phase with maximum concentrations and sediment sizes occurring in the early decelerating phase of the tidal flow sediment concentrations and grain sizes in the background flow are comparatively invariant with tidal phase boils appear to play an important if not dominant role in suspending and transporting sand sized sediments in squamish estuary

lithospheric structure of the texas gulf of mexico passive margin from surface wave dispersion and migrated ps receiver functions the seismic velocity structure beneath texas gulf coastal plain gcp is imaged by migrating ps receiver functions with a seismic velocity model found by fitting surface wave dispersion we use seismic data from a linear array of 22 broadband stations spaced 16 20 km apart a common conversion point ccp stacking technique is applied to earthquake data to improve the s n ratios of receiver functions using an incorrect velocity model for depth migration of a stacked ccp image may produce an inaccurate image of the subsurface to find sufficiently accurate p and s velocity models we first apply a nonlinear modeling technique to fit rayleigh wave group velocity dispersion via very fast simulated annealing vs ranges from 1 5 km s in shallow layers of the gcp to 4 5 km s beneath the llano uplift and just outboard of the balcones fault zone bfz the bfz is characterized by slow velocities that persist to nearly 100 km depth in the stacked image the largest amplitude positive polarity event ranges from the surface at the llano uplift to a maximum depth of 16 km beneath matagorda island we attribute this event to the sediment basement contact which is expected to produce a large impedance contrast another large amplitude and positive polarity event at 35 km depth which likely marks the moho disappears outboard of the luling fault zone the disappearance of the moho beneath the gcp may be due to serpentinization of the upper mantle which would reduce the impedance contrast between the lower crust and upper mantle dramatically

coherent flow structures in a depth limited flow over a gravel surface the role of near bed turbulence and influence of reynolds number 1 in gravel bed rivers the microtopography of the bed exerts a significant effect on the generation of turbulent flow structures although field and laboratory measurements have indicated that flows over gravel beds contain coherent macroturbulent flow structures the origin of these phenomena and their relationship to the ensemble of individual roughness elements forming the bed is not quantitatively well understood here we report upon a flume experiment in which flow over a gravel surface is quantified through the application of digital particle imaging velocimetry which allows study of the downstream and vertical components of velocity over the entire flow field the results indicate that as the reynolds number increases 1 the visual distinctiveness of the coherent flow structures becomes more defined 2 the upstream slope of the structures increases and 3 the turbulence intensity of the structures increases analysis of the mean velocity components the turbulence intensity and the flow structure using quadrant analysis demonstrates that these large scale turbulent structures originate from flow interactions with the bed topography detection of the dominant temporal length scales through wavelet analysis enables calculation of mean separation zone lengths associated with the gravel roughness through standard scaling laws the calculated separation zone lengths demonstrate that wake flapping is a dominant mechanism in the production of large scale coherent flow structures in gravel bed rivers thus we show that coherent flow structures over gravels owe their origin to bed generated turbulence and that large scale outer layer structures are the result of flow topography interactions in the near bed region associated with wake flapping

potential field evidence for a volcanic rifted margin along the texas gulf coast potential fi eld data along the texas portion of the gulf of mexico indicate a large amplitude coast parallel magnetic maximum and a smaller bouguer gravity high models constrained by seismic refraction data indicate that these maxima manifest a deeply buried volcanic rifted passive margin or other magnetic high in the outer transitional crust buried 12 15 km the source is 220 km wide similar to the voring plateau in norway and the u s east coast this margin which formed during the opening of the gulf of mexico differs in origin from the transform boundary of the northeast mexico margin tehuantepec transform and we infer a jurassic triple junction related to the borderland rift system which is traceable as far as southeast california

seismic vp vs tomography of texas oklahoma with a focus on the gulf coast margin abstract the northwestern gulf of mexico passive margin contains an extensive record of continental collision and rifting as well as deformation associated with orogenic events and heavy sedimentation seismic traveltime tomography that incorporates new data from 328 broadband seismic stations deployed throughout the region reveals features that correlate well with expected mantle structures as well as features that have no obvious expression at the surface among the former are a large fast anomaly that corresponds to the southern extent of the laurentia craton and a large slow anomaly associated with the southern oklahoma aulacogen among the latter are a slow layer that we interpret to be a shear zone at the base of the cratonic and transitional continental lithosphere a zone that is bounded at its top and bottom by discontinuities and high levels of seismic anisotropy identified in companion receiver function and shear wave splitting studies respectively a high velocity body underlying the gulf coastal plain may mark delaminating lower crust if this is true it could provide indirect evidence for an elevated geotherm during the rifting process that created the gulf of mexico

reconciling surface plate motions with rapid three dimensional mantle flow around a slab edge a central axiom of the theory of plate tectonics is that the surface plates are coupled to and carried along by convection in the earth s mantle the situation is rather different at subduction zones however margarete jadamec and magali billen now present calculations that quantify this variance they use three dimensional numerical models of buoyancy driven deformation with realistic slab geometry for the alaska subduction transform system to determine the surrounding mantle flow field they show that near a subduction zone edge mantle flow velocities can have magnitudes of greater than ten times the surface plate motions and that the complex mantle flow field is consistent with observations from seismic anisotropy these results imply local rapid transport of geochemical signatures through subduction zones the direction of tectonic plate motion at the earth s surface and the flow field of the mantle inferred from seismic anisotropy are well correlated globally implying large scale coupling between the mantle and surface plates but the fit is poor at subduction zones here three dimensional numerical models of buoyancy driven deformation for the alaska subduction transform system are used to find the origin of the regional decoupling of flow the results imply local rapid transport of geochemical signatures through subduction zones the direction of tectonic plate motion at the earth s surface and the flow field of the mantle inferred from seismic anisotropy are well correlated globally suggesting large scale coupling between the mantle and the surface plates1 2 the fit is typically poor at subduction zones however where regional observations of seismic anisotropy suggest that the direction of mantle flow is not parallel to3 4 5 6 7 and may be several times faster than6 plate motions here we present three dimensional numerical models of buoyancy driven deformation with realistic slab geometry for the alaska subduction transform system and use them to determine the origin of this regional decoupling of flow we find that near a subduction zone edge mantle flow velocities can have magnitudes of more than ten times the surface plate motions whereas surface plate velocities are consistent with plate motions8 and the complex mantle flow field is consistent with observations from seismic anisotropy5 the seismic anisotropy observations constrain the shape of the eastern slab edge and require non newtonian mantle rheology the incorporation of the non newtonian viscosity9 10 results in mantle viscosities of 1017 to 1018 pa s in regions of high strain rate 10 12 s 1 and this low viscosity enables the mantle flow field to decouple partially from the motion of the surface plates these results imply local rapid transport of geochemical signatures through subduction zones and that the internal deformation of slabs decreases the slab pull force available to drive subducting plates

coherent flow structures in a depth limited flow over a gravel surface the influence of surface roughness 1 turbulent flows moving over a gravel bed develop large scale macroturbulent flow structures that are initiated at anchor clasts in the bed and grow and dissipate as they move upward through the flow depth this paper extends previous research in which we investigated the influence of the reynolds number on coherent flow structures generated over a gravel bed by assessing the importance of effective bed roughness here we report on flume experiments in which flows over beds of decreasing surface roughness have been quantified through the application of digital particle imaging velocimetry which allows study of the downstream and vertical components of velocity over the entire flow field these results indicate that as the effective roughness increases 1 the visual distinctiveness of the coherent flow structures becomes more defined throughout the flow depth 2 the upstream angle of slope of the coherent flow structure increases and 3 the reduction in streamwise flow velocity and turbulence intensity toward the upstream side of the structure becomes greater applying standard scaling laws these structures appear shear generated and form through a combination of both wake flapping and the reattachment of localized shear layers associated with flow separation around individual topographic protrusions as the effective protrusion decreases the scale of these coherent flow structures also decreases

on the relationship between lower magnitude thresholds and bias in epidemic type aftershock sequence parameter estimates 1 modern earthquake catalogs are often described using spatial temporal point process models such as the epidemic type aftershock sequence etas models of ogata 1998 earthquake catalogs often have issues of incompleteness and other inaccuracies for earthquakes of magnitude below a certain threshold and such earthquakes are typically removed prior to fitting a point process model this paper investigates the bias in the parameters in etas models introduced by the removal of the smallest events it is shown that in the case of most of the etas parameters the bias increases approximately exponentially as a function of the lower magnitude cutoff

characterizing spatial variability in velocity and turbulence intensity using 3 d acoustic doppler velocimeter data in a plane bed reach of east st louis creek colorado usa abstract we investigated the influence on flow resistance of flow structure and turbulence at the reach scale in a mountain channel using 3 d velocity measurements and geostatistical analysis to understand the complexity of the flow structure in a reach with limited bed irregularities the increase in flow resistance at low flows in a plane bed reach was not fully explained by grain resistance therefore detailed 3 d velocity measurements were made to investigate spatial variability in velocity and turbulence components and potential controls on flow resistance one plane bed reach was surveyed over two stages in fraser experimental forest colorado using a combination of a total station lidar light detection and ranging and a sontek flowtracker handheld adv acoustic doppler velocimeter lidar was used to capture bank and channel geometry at low flows whereas the water surface and bed data were collected with the total station at all flows we used the standard deviation of bed elevation b within a moving window as an index of roughness height ks and calculated the relative submergence of the bed at different stages as h ks where h is the local flow depth adv measurements were collected on a grid with a 0 3 m to 0 5 m spacing geostatistical analysis of the velocity data indicated that the flow was highly three dimensional and varied based on stage demonstrating that even small irregularities in the bed have a significant influence on the flow characteristics the streamwise component was the largest at both low and high flow but varied more throughout the reach at low flow at high flow the greatest streamwise velocities were located within the thalweg areas of upwelling and downwelling also varied based on stage with this component being strongly influenced by small changes in the morphology at high flow and by protuberant grains at low flows the cross stream velocity and turbulence components were controlled by the flow structure and less by the roughness of the bed the turbulence intensity is significant when considering hydraulics for predicting sediment transport and for habitat assessment the plane bed flow patterns were compared to results from a pool riffle reach in the north fork cache la poudre river a step pool reach in east st louis creek and a step pool reach in italy on the rio cordon the comparison of the 3 d velocities among channel types showed that the plane bed reach has higher streamwise velocities but similar values of cross stream and transverse velocities streamwise turbulence intensities were similar in both the plane bed and step pool reach in east st louis creek the analysis revealed that the connection between the flow characteristics and the channel was not only related to the gross morphology and location of larger clasts but also to the development of shear layers from the convergence of flow therefore it is essential to understand how water moving in one direction can alter the characteristics of another component of flow and how this interaction is connected to the bed morphology

macroturbulent structure of open channel flow over gravel beds the turbulent structure of open channel flow over a mobile gravel bed was investigated in an 8 m long 0 3 m wide and 0 3 m deep tilting flume a flow visualization technique was used and complemented by measurements of flow velocity fluctuations near the bed the experiments reveal that turbulent flow consists of a sequence of large scale eddies with a vertical size close to the flow depth an average length equal to four to five depths and a width of about two depths the downstream motion of these eddies causes quasiperiodic fluctuations of the local flow velocity components the development of longitudinal troughs and ridges on the mobile bed and preferential transport of bed particles along troughs are related to the effect of the eddies the experimental results indicate that the depth scale eddies are an important turbulence mechanism contributing to sediment transport

robust classification for the joint velocity intermittency structure of turbulent flow over fixed and mobile bedforms two datasets of turbulence velocities collected over different bedform types under contrasting experimental conditions show similarity in terms of velocity intermittency characteristics and suggest a universality to the velocity intermittency structure for flow over bedforms one dataset was obtained by sampling flow over static bedforms in different locations and the other was based on a static position but mobile bedforms a flow classification based on the velocity intermittency behaviour is shown to reveal some differences from that based on an analysis of reynolds stresses boundary layer correlation and turbulent kinetic energy this may be attributed to the intermittency variable which captures the local effect of individual turbulent flow structures locations in the wake region or the outer layer of the flow are both shown to have a velocity intermittency behaviour that departs from that for idealized wakes or outer layer flow because of the superposition of localized flow structures generated by bedforms the combined effect of this yields a velocity intermittency structure unique to bedform flow the use of a time series of a single velocity component highlights the potential power of our approach for field numerical and laboratory studies the further validation of the velocity intermittency method for non idealized flows undertaken here suggests that this technique can be used for flow classification purposes in geomorphology hydraulics meteorology and environmental fluid mechanics 2014 the authors earth surface processes and landforms published by john wiley sons ltd

on the evolution and form of coherent flow structures over a gravel bed insights from whole flow field visualization and measurement the microtopography of a gravel bed river has been shown to generate turbulent flow structures that originate from shear flow generated in the near bed region although field and laboratory measurements have shown that such flows contain a range of coherent flow structures cfs the origin evolution and characteristics of the turbulent structures are poorly understood here we apply a combined experimental methodology using planar laser induced fluorescence and particle imaging velocimetry lif piv to measure simultaneously the geometric kinematic and dynamic characteristics of these cfs the flow structures were analyzed by applying standard reynolds decomposition and lagrangian vortex detection methods to understand their evolution propagation and growth in the boundary layer and characterize their internal dynamical complexity the lif results identify large individual fluid packets that are initiated at the bed through shear that generate a bursting mechanism when these large individual fluid packets are analyzed through direct flow measurement they are found to contain several smaller scales of fluid motion within the one larger individual fluid parcel flow measurements demonstrate that near bed shear controls the initiation and evolution of these cfs through merging with vortex chains that originate at the bed the vortex chains show both the coalescence in the formation of the larger structures and also the shedding of vortices from the edges of these packets which may influence the life span and mixing of cfs in open channels the life span and geometric characteristics of such cfs are critical in influencing the duration and intensity of near bed stresses that are responsible for the entrainment of sediment

accuracy of modern global earthquake catalogs we compare several modem 1977 present worldwide earthquake catalogs to infer their completeness earthquake origin time and hypocenter location accuracy magnitude scalar seismic moment errors and difference between individual focal mechanism moment tensor solutions the harvard centroid moment tensor cmt us geological survey usgs mt usgs first motion fm focal mechanism pde and isc catalogs have been analyzed and compared the catalogs completeness and accuracy vary in time and depend on earthquake depth and tectonic environment we propose a new statistical method for evaluating catalog completeness and show the results for the cmt dataset a difference in frequency range of seismic waves used in earthquake processing leads to varying degrees of catalog completeness for foreshocks and aftershocks close in time earthquake origin time versus centroid time as well as hypocenter location versus centroid location can be explained well by earthquake scaling relations comparing moment magnitudes and regular earthquake magnitudes yields estimated magnitude uncertainties and shows that latter magnitudes poorly estimate earthquake size for large events moment errors reported in the cmt solutions are well correlated with the cmt gs mt magnitude difference and hence indicate magnitude uncertainty well a normalized seismic moment tensor has 4 d f and its accuracy can be represented as the non double couple non dc component value the 3 d angle phi of dc source rotation and a position of the rotation pole our results suggest that a routinely determined non dc component is in most cases only an artifact the distribution of the phi value varies over catalog time earthquake depth focal mechanism and magnitude the seismic moment errors and the value of the non dc component are indicative of the phi value for the best solutions the 3 d angle in the cmt catalog is on the order of 5 7degrees the cmt catalog is obviously the best dataset in completeness and accuracy of its detailed solutions our results specifying uncertainties and completeness of global earthquake catalogs can be used in studies of geodynamic processes tectonic deformation associated with earthquakes earthquake stress analysis and in many other applications of earthquake catalog data seismogram interpretation techniques can be reviewed and possibly revised in light of these results c 2002 elsevier science b v all rights reserved

cocorp seismic reflection profiling in the ouachita mountains of western arkansas geometry and geologic interpretation cocorp seismic reflection profiling in the ouachita mountains of western arkansas indicates that 1 carboniferous foreland basin deposits within the arkoma basin thicken dramatically toward the south reaching an aggregate thickness in excess of 12 km 4 5 s two way travel time beneath the southern edge of the frontal thrust zone 2 evidence for northward directed low angle thrusting within this clastic sequence is prominent with a probable decollement surface lying at or near the contact with underlying early paleozoic shelf carbonates 3 beneath the benton uplift a sequence of discontinuous events defines a broad antiform cresting at approximately 7 km 2 8 s this structure appears to mimic the anticlinorial shape of the benton uplift indicated by the surface outcrop pattern 4 beneath the southern ouachitas south dipping stratified events are observed to depths in excess of 14 km 5 0 s 5 deeper in the section a prominent gently north dipping reflection occurs at approximately 22 km depth 7 6 s beneath the northern coastal plain southern ouachitas extrapolation of data along strike in the ouachita belt and consideration of large scale structure observed in other collisional orogenic belts suggest that the reflection events observed beneath the benton uplift represent early paleozoic shelf carbonates correlative with those that floor the arkoma basin to the north this interpretation requires that the early paleozoic deep water sediments exposed in the core of the ouachitas be allochthonous and also implies significant basement uplift beneath the core zone to the south the prominent package of layered reflections occurring beneath the southern ouachitas and northern coastal plain indicates that a significant portion of the crust in that region is composed of imbricate sedimentary and or metasedimentary strata at relatively shallow levels these strata are correlative with the carboniferous flysch cropping out in the southern ouachitas and at somewhat deeper levels they are correlative with the early to middle paleozoic deep water sediments exposed on the benton uplift

multi scale seismicity model for seismic risk for a general use of the frequency magnitude fm relation in seismic risk assessment we formulate a multi scale approach that relies on the hypothesis that only the ensemble of events that are geometrically small compared with the elements of the seismotectonic regionalization can be described by a log linear fm relation it follows that the seismic zonation must be performed at several scales depending upon the self similarity conditions of the seismic events and the linearity of the log fm relation in the magnitude range of interest the analysis of worldwide seismicity using the harvard catalog where the seismic moment is recorded as the earthquake size corroborates the idea that a single fm relation is not universally applicable the multi scale model of the fm relation is tested in the italian region

upper mantle seismic wave velocity effects of realistic partial melt geometries we investigate seismic wave velocity reduction resulting from the presence of partial melt in the upper mantle the amount of shear and bulk modulus reduction produced by the presence of a connected network of realistically shaped and naturally organized melt inclusions is found using finite element calculations the geometries of the inclusions are taken directly from laboratory experiments of mantle melting with finite element meshes constructed to conform to these shapes the shear and bulk moduli of the composite material are found for both the unrelaxed isolated inclusions and relaxed pressure equalized inclusions cases by assigning appropriate material properties to the fluid modulus reduction from deformation simulations of a solid containing realistically shaped and ellipse shaped melt inclusions quantify the effect of melt pocket cuspateness and melt pocket organization on seismic velocity reduction the three dimensional response is estimated from two dimensional distributions of the melt phase by determining the mode ii and mode iii components of elastic modulus reduction separately and summing their effects in general cuspate and naturally organized melt inclusions cause greater velocity reduction it is shown that v and vs reduction per percent partial melt are at least 3 6 and 7 9 respectively even higher values for velocity reduction are possible above 1 melt fraction if melt exists only in tubules below 1 melt fraction the lower more conservative values of velocity reduction are 070 greater for vp and 84 greater for vs than the analytically determined values for ellipsoidal inclusions somewhat greater effects are possible if nonrandom organization of melt occurs on scales greater than our model

evolution of coarse gravel bed forms field measurements at flood stage field measurements to investigate the origin and growth of mesoscale gravel bed forms in deep flows were made in the north fork toutle river washington sonar observations of the gravel streambed at a stationary point were recorded during two storm flows in december 1989 and january 1990 with concurrent bed load sampling and continuous velocity measurements mean diameter of bed load was about 3 cm flow depths were 1 4 2 4 m and bed shear stresses were 2 5 times the critical stress of mean bed load diameter as computed from the depth slope product these records document the hydrodynamic conditions under which dunelike coarse gravel bed forms were observed coarse gravel dunes height 20 cm length 6 15 m evolved more than 24 hours after peak stage primarily by accretion as inferred from bed form changes revealed in dual sonar records dune heights increased to 40 cm as mean trough elevation rose about 50 cm over several hours smaller dunes wavelength 1 3 m transitional from bed load sheets migrated on the backs of the large dunes the superposed dunes finally became indistinguishable from the large dunes which diminished in height by increasing the mean level of troughs gravel deposition occurred at the observation point in conjunction with migration of gravel dunes the direct comparison of known bed form regimes and gravel bar facies provides alternative interpretations of gravelly deposits

seismicity and geodetic anomalies in a wide area preceding the niigata ken chuetsu earthquake of 23 october 2004 central japan 1 the ordinary short term occurrence rate of earthquakes in a region is predicted using the epidemic type aftershock sequence etas model of triggering seismicity any anomalous seismic activity such as quiescence and activation can be quantified by identifying significant deviation from the predicted rate such anomalies are revealed to have occurred during the three year period leading up to the 2004 chuetsu earthquake of m6 8 mw6 6 central japan the quiescence and activation which took place in the zone of negative and positive increments of the coulomb failure stress respectively were possibly caused by aseismic slip on or near the focal fault plane such slip is further supported by transient crustal movement around the rupture source time series records of the baseline distances between permanent gps stations deviated from the predicted trends with the deviations mostly consistent with the coseismic horizontal displacements of the stations due to the chuetsu earthquake the cumulated preceding slip is estimated to be roughly equivalent to mw6

crustal and upper mantle structure of southeast tibet from rayleigh wave tomography 1 we have applied the two plane wave inversion technique to fundamental mode rayleigh waves in southeast tibet phase velocity variations are obtained at 15 periods from 20 to 143 s and are used to construct three dimensional shear wave velocity structure a low velocity zone is imaged in the middle crust of southeast tibet in which velocity perturbation varies from 4 to 3 the slow area might be associated with high temperature and partial melt and can flow ductilely while the high velocity region could be relatively cold and mechanically strong enough to pass crustal strain implying that coherent lithospheric deformation is possible with the presence of complicated crustal flow strong negative anomalies in the shallow crust are imaged at 92 e correlating with the location of a north south rift zone a fast mantle lid to a depth of 120 km is present beneath most of the study area the lithosphere is significantly slower in the central part of the study area than in the west and east to the east of 96 e a subvertical high velocity zone is imaged at 120 240 km depths under the bangong nujiang suture bns which is more like the subduction of the asian lithosphere we interpret the high velocity anomalies to the south of the bns as the subducted indian lithosphere and those to the north as the asian lithosphere a vertical low velocity column is observed in the central part of the region from the lower crust to the midupper mantle which is probably in part responsible for the rift at 92 e the slow anomaly is likely associated with asthenosphere upwelling following the opening of a slab window that could have developed when the slab was torn apart vertically because of the significant change of subducting direction at the eastern syntaxis

mean flow and turbulence structure over fixed two dimensional dunes implications for sediment transport and bedform stability detailed measurements of flow velocity and its turbulent fluctuation were obtained over fixed two dimensional dunes in a laboratory channel laser doppler anemometry was used to measure the downstream and vertical components of velocity at more than 1800 points over one dune wavelength the density of the sampling grid allowed construction of a unique set of contour maps for all mean flow and turbulence parameters which are assessed using higher moment measures and quadrant analysis these flow field maps illustrate that 1 the time averaged downstream and vertical velocities agree well with previous studies of quasi equilibrium flow over fixed and mobile bedforms and show a remarkable symmetry from crest to crest 2 the maximum root mean square rms of the downstream velocity values occur at and just downstream of flow reattachment and within the flow separation cell 3 the maximum vertical rms values occur within and above the zone of flow separation along the shear layer and this zone advects and diffuses downstream extending almost to the next crest 4 positive downstream skewness values occur within the separation cell whereas positive vertical skewness values are restricted to the shear layer 5 the highest reynolds stresses are located within the zone of flow separation and along the shear layer 6 high magnitude high frequency quadrant 2 events ejections are concentrated along the shear layer kelvin helmholtz instabilities and dominate the contribution to the local reynolds stress and 7 high magnitude high frequency quadrant 4 events occur bounding the separation zone near reattachment and close to the dune crest and are significant contributors to the local reynolds stress at each location these data demonstrate that the turbulence structure associated with dunes is controlled intrinsically by the formation magnitude and downstream extent of the flow separation zone and resultant shear layer furthermore the origin of dune related macroturbulence lies in the dynamics of the shear layer rather than classical turbulent boundary layer bursting the fluid dynamic distinction between dunes and ripples is reasoned to be linked to the velocity differential across the shear layer and hence the magnitude of the kelvin helmholtz instabilities which are both greater for dunes than ripples these instabilities control the local flow and turbulence structure and dictate the modes of sediment entrainment and their transport rates

constraints on the size of the smallest triggering earthquake from the epidemic type aftershock sequence model bath s law and observed aftershock sequences 1 the physics of earthquake triggering together with simple assumptions of self similarity imply the existence of a minimum magnitude m0 below which earthquakes do not trigger other earthquakes noting that the magnitude md of completeness of a seismic catalog is not in general the same as the magnitude m0 of the smallest triggering earthquake we compare observed aftershock sequence parameters with the predictions made by the epidemic type aftershock sequence model to constrain the value of m0 in particular we use quantitative fits to observed aftershock sequences from three previous studies as well as bath s law to obtain four estimates of m0 we show that the branching ratio n average number of triggered earthquakes per earthquake also equal to the fraction of aftershocks in a seismic catalog is the key parameter controlling the estimate of the minimum triggering magnitude m0 conversely physical upper bounds for m0 estimated from rate and state friction indicate that at the very least 55 of all earthquakes are aftershocks

emergence of coherent flow structures over a gravel surface a numerical experiment 1 gravel bed rivers have complex porous and irregular surfaces characterized by a range of morphological forms these topographical structures determine the flow structures that develop over the river bed primarily by the shedding of vortices in the downstream wake of protruding clasts previous research into these flow structures has come from experimental studies which have used either flow visualization or single point measurements techniques here we present a numerical experiment where large eddy simulation les is used to study the generation evolution and destruction of these flow structures over a naturally water worked gravel surface the numerical simulations reported in this paper show that there are two distinct scales of boundary influence upon the shallow flow and emphasize that the measured flow variability at any one point in a natural river will contain both locally derived and upstream inherited flow structures according to the range of scales of bed topography present

changes in velocity profiles at roughness transitions in coarse grained channels heterogeneous coarse grained channels are often characterized by local transitions in bed surface roughness distinct spatial zones in terms of grain size have been reported for example sand ribbons and bedload sheets the transition from areas of finer to coarser grained surface sediment is often abrupt however the effects of these transitions on the shape of the velocity profile and associated shear velocity and roughness length estimates have not been investigated in detail in coarse grained channels this paper therefore examines the combined effects of a sudden change in surface roughness and of superimposed scales of resistance on the structure of the turbulent boundary layer measurements along roughness transitions from smooth to rough beds were conducted in a flume using artificial roughness features and in a natural gravel bed river immediately at the transition from a zone of close packed roughness to a rougher section dominated by obstacles superimposed on the more or less uniform roughness surface boundary shear stress and roughness length increase considerably downstream from this transition velocity profiles become concave upwards downstream and upstream sections show significant differences in terms of near bed velocities deceleration downstream of the transition velocity gradient and turbulence intensity of the streamwise velocity component comparing the mean velocity profiles corresponding to these two different roughness surfaces gives some indication of the proportion of total shear velocity or shear stress associated with the pressure drag produced by large and isolated obstacles

sp receiver function imaging of a passive margin transect across texas s gulf coastal plain abstract the gulf coast of texas has been the subject of intensive geological and geophysical investigation in pursuit of hydrocarbons but studies that penetrate beyond the upper crust are limited to a few refraction profiles and regional surface wave investigations the passing of earthscope s transportable array has facilitated regional investigations of the lithosphere but its 70 km station spacing does not allow many important tectonic features to be imaged a broadband seismic transect across the texas gulf coastal plain was therefore performed in order to image deep structure beneath this passive margin and the transition to the neighboring craton a 2d sp receiver function common conversion point ccp stacked image produced for this transect reveals several discontinuities in the sub crustal lithosphere the region nearest the shoreline is underlain by an anomalous 18 km thick low velocity layer that produces a strong negative pulse in the sp receiver functions the drop in velocity is too large to be due to any reasonable change in fe or mg content but could be produced by partial melt or mantle hydration it is unlikely that partial melt would still be found in a 160 180 year old passive margin such as the gulf coast but hydration possibly introduced by a through going balcones fault system and resulting serpentinization could produce the observed anomaly an event with negative polarity appears at a depth of 110 km which we interpret to be the lithosphere asthenosphere boundary lab thermal variations alone would not produce a sufficiently sharp discontinuity to be imaged by sp converted phases recent shear wave splitting studies revealed unusually large delay times in this region along with fast polarization directions that differ from measurements on the laurentian craton large delay times may imply significant flow which could also produce frictional heating due to shearing and partial melt which would steepen the velocity gradients an additional layer is bounded by discontinuities at 145 165 km depth with negative polarity and 185 205 km depth with positive polarity the appearance of these discontinuities suggests that the mantle beneath the lab is more complicated here than elsewhere and that the transition from lithosphere to asthenosphere occurs over a broad 85 100 km thick depth interval

seismic velocity structure and anisotropy of the alaska subduction zone based on surface wave tomography southcentral alaska is a complex tectonic region that transitions from subduction of pacific crust to flat slab subduction and collision of overthickened yakutat crust because much of the yakutat crust has been subducted seismic imaging is needed in order to understand the crustal and upper mantle structural framework for this active tectonic setting here we use teleseismic rayleigh waves to image large scale variations in shear wave structure our imaging technique employs a two plane wave representation with finite frequency sensitivity kernels our 3 d isotropic model reveals several features the subducting pacific yakutat slab slow wave speeds characterizing the onshore yakutat collision zone slow wave speeds of the wrangell subduction zone and a deep tomographic contrast at the eastern edge of the pacific yakutat slab we produce anisotropic phase velocity maps that exhibit variations in the fast direction of azimuthal anisotropy these maps show the dominance of the yakutat slab on the observed pattern of anisotropy west of the yakutat slab the fast directions are approximately aligned with the plate convergence direction in the region of the yakutat slab the pattern is more complicated along the margins of the slab the fast directions are roughly parallel to the margins we identify notable differences and similarities with published sks splitting measurements integrative modeling using 3 d anisotropy models and different seismic measurements will be needed in order to establish a detailed 3 d anisotropic velocity model for alaska this study provides a large scale starting point for such an effort

comparison of etas parameter estimates across different global tectonic zones abstract branching point process models such as the epidemic type aftershock sequence etas models introduced by ogata 1988 1998 are often used in the description characterization simulation and declustering of modern earthquake catalogs the present work investigates how the parameters in these models vary across different tectonic zones after considering divisions of the surface of the earth into several zones based on the plate boundary model of bird 2003 etas models are fit to the occurrence times and locations of shallow earthquakes within each zone computationally the expectation maximization em type algorithm of veen and schoenberg 2008 is employed for the purpose of model fitting the fits and variations in parameter estimates for distinct zones are compared and seismological implications are discussed in particular we find that estimated background seismicity rates range by a factor of nearly 500 for interplate and trench events respectively the estimated productivity parameter governing the relationship between the magnitude of an earthquake and its expected number of direct aftershocks ranges by a factor of more than five from events in the slow moving zone to events in active continental areas suggesting a much higher rate of swarming in the ridges than in the trenches and active continental zones despite the pronounced differences between the seismicity patterns and parameter estimates in the different zones the etas model with few parameters and with the same functional form seems to fit reasonably well to the seismicity in each zone

lithospheric structure of the south central united states recent seismic data in the ouachita mountains area and the gulf of mexico make it possible to construct a lithospheric scale cross section transect from the midcontinent region to the gulf the authors constructed a transect in the form of a gravity model but it incorporates all available seismic drill hole and geologic data as constraints the thrust sheets of the ouachita orogenic belt appear as a thin veneer covering the southern part of the arkoma basin and the preserved paleozoic continental margin mesozoic rifting is evident in three areas 1 southern arkansas and northern louisiana where extension was minor 2 the vicinity of the texas louisiana coastline where modification of the lithosphere and subsidence were considerable and 3 the deep gulf of mexico where rifting was successful a significant variation in the average density of the mantle which could delineate the north american craton as a lithospheric feature was detected near the paleozoic continental margin

explanation of temporal clustering of tsunami sources using the epidemic type aftershock sequence model temporal clustering of tsunami sources is examined in terms of a branching process model it previously was observed that there are more short interevent times between consecutive tsunami sources than expected from a stationary poisson process the epidemic type aftershock sequence etas branching process model is fitted to tsunami catalog events using the earthquake magnitude of the causative event from the centennial and global centroid moment tensor cmt catalogs and tsunami sizes above a completeness level as a mark to indicate that a tsunami was generated the etas parameters are estimated using the maximum likelihood method the interevent distribution associated with the etas model provides a better fit to the data than the poisson model or other temporal clustering models when tsunamigenic conditions magnitude threshold submarine location dip slip mechanism are applied to the global cmt catalog etas parameters are obtained that are consistent with those estimated from the tsunami catalog in particular the dip slip condition appears to result in a near zero magnitude effect for triggered tsunami sources the overall consistency between results from the tsunami catalog and that from the earthquake catalog under tsunamigenic conditions indicates that etas models based on seismicity can provide the structure for understanding patterns of tsunami source occurrence the fractional rate of triggered tsunami sources on a global basis is approximately 14 online material figures of residual analysis for tsunami and earthquake catalogs

missing links in earthquake clustering models 1 many clustering models imply two kinds of earthquakes spontaneous ones and those triggered by previous earthquakes the pair wise links from earlier to later earthquakes control the estimates of the clustering parameters however earthquake catalogs are limited in time space and magnitude so that triggers of some cataloged earthquakes may be unknown thus some links are unrecognized and some triggered events appear spontaneous here we present a method for identifying such earthquakes and reducing the bias from missing links we treat earthquakes probably affected by missing links as potential triggers but we exclude them in evaluating modeled effects we use an epidemic type aftershock sequence etas model to examine specifics the most affected parameter is the proportion of spontaneous earthquakes the most important missing links apparently follow earthquakes below the magnitude threshold before the start and outside the spatial boundaries of the catalog in that order

lithospheric velocity model of texas and implications for the ouachita orogeny and the opening of the gulf of mexico a 3 d shear wave velocity model of texas has been developed from rayleigh wave phase velocities by using ambient noise data recorded at the usarray stations in the upper crust the ouachita front separates high velocity in the laurentia to its west from low velocity in the east and south texas basins the ouachita belt is characterized as a high velocity zone with local maximums coinciding with known uplifts which we interpret as accreted island arcs during the ouachita orogeny our model evidences a strong ouachita lithosphere that helped to buffer crust thinning from the mesozoic rifting a significantly low velocity anomaly is present in southeast texas in the lower crust and upper mantle we associate this anomaly with a past asthenosphere upwelling that likely originated from the edge of the subducted slab during the ouachita collision and was potentially responsible for the opening of the gulf of mexico

comparison of turbulent flows over clusters of varying density abstractgravel bed rivers commonly form an armored surface layer within which cluster bedforms develop clusters can form in isolation or develop cluster groups of increasing density flume experiments are presented in which a clustered armored surface was formed on a gravel bed flows were measured over an area without a cluster and areas with an isolated cluster a coupling of two clusters and a group of three clusters turbulent flow parameters reynolds stresses and turbulent kinetic energy were calculated from acoustic doppler velocimeter measured flows and visualizations of the flow patterns around clusters flow separated over the cluster crest creating an increase in the turbulent flow properties and a high turbulence intensity region when flow reattached downstream turbulent kinetic energy increased around the coupled clusters but around the grouped clusters the flow field was distinguished by a high degree of uniformity the net effect of increasing density of cluster grouping was an incr

on determining the geometric and kinematic characteristics of coherent flow structures over a gravel bed a new approach using combined plif piv in gravel bed rivers the microtopography of the bed is known to exert a significant influence on the generation of turbulent flow structures that owe their origin to fluid shear generated near the bed although field and laboratory measurements have indicated that flows over gravel beds contain a range of coherent flow structures the kinematic and dynamic properties of these structures are still poorly understood this paper describes a new experimental methodology to quantify simultaneously both the kinematic and dynamic characteristics of coherent flow structures based upon combined planar laser induced fluorescence and particle imaging velocimetry plif piv the results confirm that the primary generative mechanism of coherent flow structures is at the bed where merging hairpin vortices form around bed clasts and generate larger scale fluid motions that advect downstream copyright 2010 john wiley sons ltd

deep structure of the texas gulf passive margin and its ouachita precambrian basement results of the cocorp san marcos arch survey this cocorp deep seismic survey provides a comprehensive image of the southeast texas part of the gulf passive margin and its accreted ouachita arc foundation beneath the updip limit of the cenozoic sediment wedge a prominent antiformal structure is imaged within the interior zone of the buried late paleozoic ouachita orogen the structure appears to involve precambrian grenville basement the crest of the antiform is coincident with the cretaceous tertiary luling mexia talco fault zone some of these faults dip to the northwest counter to the general regional pattern of down to the basin faulting and appear to sole into the top of the antiform suggesting that the ouachita structure has been reactivated as a hingeline to the subsiding passive margin the antiform may be tied via this fault system and the ouachita gravity gradient to the similar devils river waco and benton uplifts interpreted as precambrian basement cored massifs above the paleozoic sequence a possible rift related graben is imaged near the updip limit of jurassic salt paleoshelf edges of the major tertiary depositional sequences are marked by expanded sections disrupted by growth faults and shale diapirs within the wilcox formation the transect crosses the mouth of the 900 m deep yoakum canyon a principal pathway of sediment delivery from the laramide belt to the gulf beneath the wilcox the comanchean lower cretaceous shelf edge capped by the stuart city reef is imaged as a pronounced topographic break onlapped by several moundy sediment packages because this segment of the line parallels strike the topographic break may be interpreted as a 2000 m deep embayment in the cretaceous shelf edge and possibly a major submarine canyon older and deeper than the yoakum canyon

p and s wave tomography of the mantle beneath the united states mantle seismic structure beneath the united states spanning from the active western plate margin to the passive eastern margin was imaged with teleseismic p and s wave traveltime tomography including usarray data up to may 2014 to mitigate artifacts from crustal structure 5 40 s rayleigh wave phase velocities were used to create a 3 d starting model major features of the final p and s models include two distinct low velocity anomalies at depths of 60 300 km beneath the central and northern appalachians and passive margin the central appalachian low velocity anomaly coincides with eocene basaltic magmatism and the northern anomaly is located along the cretaceous track of the great meteor hot spot at depths of 300 700 km beneath the central and eastern u s large high velocity anomalies are inferred to be remnants of the farallon slab that subducted prior to 40 ma during the laramide orogeny

size shape and dynamics of large scale turbulent flow structures in a gravel bed river in this paper we present a detailed investigation of the size scale and dynamics of macro turbulent flow structures in gravel bed rivers we used an array of seven electromagnetic current meters with high resolution in both space and time to measure the streamwise velocity fluctuations in a gravel bed river the array was deployed successively in various configurations in order to quantify the vertical lateral and longitudinal extent of the flow structures and to estimate their advecting velocities to depict the spatial and temporal properties of the flow structures we used space time velocity matrices space time correlation analysis and coherent structure detection schemes the results show that the large scale turbulent flow structures in a gravel bed river occupy the entire depth of the flow and that they are elongated and narrow the length of the structures is 3 to 5 times the flow depth while the width is between 0 5 and 1 times flow depth in spite of the high roughness of the bed these values are similar to those reported in the literature for laboratory experiments on large scale turbulent flow structures the dynamics of the large scale turbulent flow structures investigated using flow visualization highlight the interactions between the outer flow region and the near bed region our evidence suggests that large scale flow incursions trigger ejections in the near bed region that can develop into megabursts that can reach the water surface

structure and evolution of the central gulf of mexico continental margin and coastal plain southeast united states as in many continental margins mesozoic rifting in the gulf of mexico trended subparallel to older tectonic structures created by opening and closure of a prior ocean basin unlike the situation in most other margins however extension in the gulf of mexico did not involve widespread reactivation of these older tectonic features this difference may be related to the unusual facts that 1 the antecedent passive continental margin was a transform rather than a rift margin and 2 the prior orogeny did not substantially thicken the crust in order to characterize the interaction between mesozoic rifting and prior tectonic events two geophysical transects were constructed across the central gulf of mexico coastal plain and continental shelf the transects show that the early paleozoic passive continental margin buried beneath the late paleozoic ouachita orogen was little affected by compressional tectonism or mesozoic extension during opening of the gulf of mexico the thickness of the crust on this ancient margin decreases from 35 km to 10 km over a distance of only 50 km consistent with previous interpretations that this was a transform margin the ouachita fold and thrust belt is shown to be a thin skinned doubly vergent orogen that formed above a well preserved southward dipping subduction system relict cambrian oceanic crust may exist beneath the southern part of the orogen but its presence is not required by the data the thin crust and shallow mantle in the ouachita suture created a zone of relatively high strength that acted as a barrier to mesozoic extension which is restricted to regions south of the orogen extension was initially distributed over a broad area that included the mississippi interior salt basin and regions south of the wiggins arch extension became progressively more focused south of the wiggins arch with time culminating in the onset of seafloor spreading beneath the modern continental rise mesozoic extension factors are 1 4 1 9 beneath the mississippi interior salt basin 2 9 immediately south of the wiggins arch and 4 adjacent to the oldest oceanic crust in the central gulf of mexico

scalings for large turbulent flow structures in gravel bed rivers 1 the relations between frequency and duration of large scale turbulent flow structures in gravel bed rivers and the distributions of the time intervals between turbulent events are investigated using flow visualisation and velocity measurements the time of occurrence and the duration and amplitude of large bursting motions were estimated independently from a five minute underwater video and from high resolution velocity time series sampled at 20 hz during 38 minutes at three heights above the bed results from both experiments show that the frequency duration relations of the large scale turbulent flow structures follow a power function with exponents ranging between 1 4 and 1 95 values that are typical of bursting systems e g solar flares the frequency distributions of time intervals between two successive ejections display an exponential tail these findings provide models for simulating sequences of large scale turbulent events in a gravel bed river an important step in linking flow turbulence and sediment transport

modeling complex flow structures and drag around a submerged plant of varied posture although vegetation is present in many rivers the bulk of past work concerned with modeling the influence of vegetation on flow has considered vegetation to be morphologically simple and has generally neglected the complexity of natural plants here we report on a combined flume and numerical model experiment which incorporates time averaged plant posture collected through terrestrial laser scanning into a computational fluid dynamics model to predict flow around a submerged riparian plant for three depth limited flow conditions reynolds number 65 000 110 000 plant dynamics were recorded through high definition video imagery and the numerical model was validated against flow velocities collected with an acoustic doppler velocimeter the plant morphology shows an 18 reduction in plant height and a 14 increase in plant length compressing and reducing the volumetric canopy morphology as the reynolds number increases plant shear layer turbulence is dominated by kelvin helmholtz type vortices generated through shear instability the frequency of which is estimated to be between 0 20 and 0 30 hz increasing with reynolds number these results demonstrate the significant effect that the complex morphology of natural plants has on in stream drag and allows a physically determined species dependent drag coefficient to be calculated given the importance of vegetation in river corridor management the approach developed here demonstrates the necessity to account for plant motion when calculating vegetative resistance

mesoproterozoic plate tectonics a collisional model for the grenville aged orogenic belt in the llano uplift central texas the llano uplift of central texas united states exposes the core of a mesoproterozoic orogenic belt that formed along the southern margin of laurentia during grenville time a new collisional model is proposed that reconciles differences in structural stacking apparent tectonic transport and deformation conditions between the eastern and western portions of the uplift and explains uplift and exhumation of high pressure eclogitic rocks emplacement of ophiolitic rocks and subsequent late stage to postcollisional plutonism our model proposes that subduction with southward polarity resulted in collision of an exotic arc with laurentia emplacement of ophiolitic rocks and telescoping of the intervening basinal sediments followed by overriding of the arc and margin of laurentia by a southern continent with transport toward laurentia the model further proposes that convergence led to subduction of the laurentian margin resulting in high pressure metamorphism but buoyancy forces due to subduction of continental crust under the southern continent resulted in uplift and retrotransport away from laurentia in a manner similar to that proposed for the alpine orogeny slab breakoff resulted in upwelling of the asthenosphere leading to intrusion of juvenile granitic plutons subduction along strike caused continued contraction that waned with time the eastern uplift records continent arc continent collision whereas the western uplift records continent continent collision the two regions also expose different crustal levels in the orogen the striking similarity with phanerozoic orogens including emplacement of ophiolites and formation of high pressure rocks implies that plate tectonic processes including subduction were active prior to the neoproterozoic

a variety of aftershock decays in the rate and state friction model due to the effect of secondary aftershocks implications derived from an analysis of real aftershock sequences the model based on rate and state dependent friction law reproduces the temporal decay of an aftershock sequence with the p value of the omori utsu law equal to 1 if we simply assume a constant stress rate over time however because p values vary in real aftershock sequences this model requires some modification this study examined the effect of secondary aftershocks on the variety of the p value a large aftershock causes a stepwise stress increase in the aftershock area and the expected seismicity rate derived from the friction law also increases abruptly these multiple increases in the seismicity rate during its decay following a mainshock could cause variation in the apparent p value in this study a model incorporating this idea is applied to two aftershock sequences observed in japan and is shown to substantially modify the modeling of aftershock activity