a self regulating model of bedrock river channel geometry 1 the evolution of many mountain landscapes is controlled by the incision of bedrock river channels while the rate of incision is set by channel shape through its mediation of flow the channel shape is itself set by the history of bedrock erosion this feedback between channel geometry and incision determines the speed of landscape response to tectonic or climatic forcing here a model for the dynamics of bedrock channel shape is derived from geometric arguments a normal flow approximation for channel flow and a threshold bed shear stress assumption for bedrock abrasion the model dynamics describe the competing effects of channel widening tilting bending and variable flow depth transient solutions suggest that channels may take 1 10 ky to adapt to changes in discharge implying that channel disequilibrium is commonplace if so landscape evolution models will need to include bedrock channel dynamics if they are to probe the effects of climate change

boundary shear in circular pipes running partially full the distribution of boundary shear stress in circular conduits flowing partially full with and without a smooth flat bed simulating deposited sediments has been examined experimentally ranging from 0 375 f 1 96 f froude number and 65 000 r 342 000 r hydraulic radius using the preston tube technique the invert level of the flat bed and the water depth have been varied to simulate a wide range of possible flow conditions that may occur in culverts sewers and hydropower tunnels the distribution of boundary shear stress around the wetted perimeter is shown to be highly sensitive to changes in cross sectional shape the results have been analyzed in terms of the variation of local global shear stress versus perimetric distance and the percentage of the total shear force acting on the wall or bed of the conduit the sfw results sfw the percentage of the average wall shear force of the overall shear force have been shown to agree well with knight s empirical formula for prismatic channels the influence of secondary flows on the distribution of boundary shear stress and the implications of this for sediment transport have also been examined

hydraulic geometry river sediment and the definition of bedrock channels a growing literature deals with bedrock channels erosion processes within them and their role in landscape evolution formal definitions currently in use classify channels as bedrock when alluvial cover is discontinuous or thin this is equated with a physical property of the flow using up to date erosion laws and descriptions of channel dynamics we show that existing definitions are difficult to apply and may lead to conflicting classifications we propose the definition a bedrock channel cannot substantially widen lower or shift its bed without eroding bedrock applied to channels in taiwan this leads to a different classification than previous definitions by analysing at a station hydraulic geometry of these channels we show that the classification exposes different controls of sediment effects on dynamics of channels classified as alluvial and bedrock

quantifying measurement uncertainty of thirty meter shear wave velocity thirty meter shear wave velocity v s 30 is commonly used to estimate near surface conditions for site classification seismic site response liquefaction analysis and other geotechnical earthquake engineering application quantifying the uncertainty in v s 30 measurements is important for determining the accuracy and precision of this geophysical test this study gathers existing available comparative and blind shear wave velocity tests to evaluate the apparent or observable intra and intermethod variability presented in this article are estimates of v s 30 uncertainty for the invasive methods of downhole suspension logging and seismic cone penetration testing the noninvasive method of spectral analysis of surface waves and the method of shear wave velocity correlated geologic units discussed is the issue of soil disturbance with respect to invasive methods and how this may result in measurement bias results of this study indicate that uncertainty of shear wave velocity measurements are on the order of 1 3 coefficient of variation standard deviation mean for downhole suspension logging and seismic cone penetration testing 5 6 coefficient of variation for spectral analysis of surface waves and 20 35 coefficient of variation for shear wave velocity correlated geologic units presented here are procedures for propagating the uncertainty and or bias in forward analyses

regression analysis of vs30 using topographic attributes from a 50 m dem abstract the average shear wave velocity for the top 30 m v s30 is one of the simple predictors of earthquake ground motion amplification we performed a multiple linear regression analysis of the logarithm of observed v s30 at 1646 locations in japan with three topographic attributes slope gradient surface texture and the logarithm of elevation calculated from a 50 m dem a v s30 map was created using the partial regression coefficients the determination coefficient was 0 318 the development of the estimation method of v s30 from a dem will be useful for earthquake vulnerability assessment

early to mid tertiary inverted metamorphic gradient under the colorado plateau evidence from eclogite xenoliths in ultramafic microbreccias navajo volcanic field mid tertiary ultramafic microbreccia diatremes from the navajo volcanic field in the four corners area of the colorado plateau contain an ultramafic xenoliths suite in which lower temperature prograde metamorphic eclogites are associated with higher temperature garnet clinopyroxenites that were retrograded and hydrated to chlorite eclogite assemblages and directions of metamorphic reactions are consistent with the model of a laramide age inverted metamorphic gradient established as prograde reactions in a dehydrating oceanic slab caused hydration and cooling in the overlying subcontinental upper mantle wedge comparison with an inverse metamorphic gradient in the pelona schists inferred to represent an exposed part of the same subduction system in southwestern arizona and southern california confirms the shallow dip of the laramide subduction zone predicted by the regional distribution of subduction related volcanic rocks

distribution of erosion across bedrock channels lateral erosion in bedrock rivers is an important control on the shape of channel crosssections and the coupling of channels and hillslopes recent observations link lateral erosionto the variability of flow we propose two mechanisms to explain this one is based on changing shear stress distributions within the channel with varying flood level the other on the competition between cover and tool effects in fluvial bedrock erosion we assess these processes for the liwu river taiwan and conclude that cover and tool effects dominate the partitioning of lateral and vertical erosion in this case

controls on the strength of coupling among climate erosion and deformation in two sided frictional orogenic wedges at steady state 1 many important insights regarding the coupling among climate erosion and tectonics have come from numerical simulations using coupled tectonic and surface process models however analyses to date have left the strength of the coupling between climate and tectonics uncertain and many questions unanswered we present an approximate analytical solution for two sided orogenic wedges obeying a frictional rheology and in a condition of flux steady state that makes explicit the nature and sensitivity of the coupling between climate and deformation we make the simplifying assumption that the wedge grows in a self similar fashion consistent with airy isostasy such that topographic taper is invariant with orogen width tectonic influx rate and climate we illustrate first how and why the form of the erosion rule matters to orogen evolution and then derive a physically based orogen scale erosion rule we show that steady state orogen width crest elevation and crustal thickness are controlled by the ratio of accretionary flux to erosional efficiency to a power dictated by the erosion process remarkably we show that for most combinations of parameters in the erosion law rock uplift rate is more strongly controlled by erosional efficiency than it is by the accretionary flux further assuming frontal accretion with no underplating the spatial distribution of erosional efficiency dictates the relative rock uplift rates on the pro wedge and retro wedge and the time averaged trajectories of rocks through the orogen the restriction to invariant frictional properties is conservative in these respects systems subject to positive feedback between erosion and rheology will exhibit even stronger coupling among climate erosion and deformation than shown here

direct observation of immiscibility in pyrope almandine grossular garnet although recent thermodynamic models predict a low temperature miscibility gap in the pyrope almandine grossular garnet solid solution series coexistence of two immiscible garnets consistent with the calculated miscibility gap has not been demonstrated previously here we report the discovery of such a coexistence in nature which provides direct evidence for immiscibility in the pyrope almandine grossular system garnet inclusions were found near solidified fluid melt inclusions in a single pyrope crystal collected from the ultramafic diatreme at garnet ridge arizona microprobe analyses close to the contact between the pyrope host and one garnet inclusion yield formulae of mg 1 98 ca 0 52 fe 0 50 mn 0 02 al 1 89 cr 0 09 si 3 o 12 for the host and mg 1 28 ca 1 31 fe 0 41 mn 0 02 al 1 93 cr 0 07 si 3 o 12 for the inclusion high resolution analytical traverses across the two garnet boundary reveal that the compositional difference between the inclusion and the host increases as the contact is approached implying that the two garnet grains represent an immiscible pair rather than a disequilibrium coexistence the compositions of the coexisting garnets are in good agreement with those predicted from recent thermodynamic mixing models for pyrope almandine grossular garnet

a mechanistic model for river incision into bedrock by saltating bed load 1 abrasion by bed load is a ubiquitous and sometimes dominant erosional mechanism for fluvial incision into bedrock here we develop a model for bedrock abrasion by saltating bed load wherein the wear rate depends linearly on the flux of impact kinetic energy normal to the bed and on the fraction of the bed that is not armored by transient deposits of alluvium we assume that the extent of alluvial bed cover depends on the ratio of coarse sediment supply to bed load transport capacity particle impact velocity and impact frequency depend on saltation trajectories which can be predicted using empirical functions of excess shear stress the model predicts a nonlinear dependence of bedrock abrasion rate on both sediment supply and transport capacity maximum wear rates occur at moderate relative supply rates due to the tradeoff between the availability of abrasive tools and the partial alluviation of the bedrock bed maximum wear rates also occur at intermediate levels of excess shear stress due to the reduction in impact frequency as grain motion approaches the threshold of suspension measurements of bedrock wear in a laboratory abrasion mill agree well with model predictions and allow calibration of the one free model parameter which relates rock strength to rock resistance to abrasive wear the model results suggest that grain size and sediment supply are fundamental controls on bedrock incision rates not only by bed load abrasion but also by all other mechanisms that require bedrock to be exposed in the channel bed

dynamic equilibrium between an active uplift and the sevier river utah in a zone of active tectonic uplift one expects a river to change morphology simply because valley slope deforms but by cutting through a transverse uplift the sevier river in southern utah also adapts to the tectonics by eroding and depositing these localized changes of transport are caused by varying channel geometry pattern sedimentology and slope in the uplift the river is narrow efficiently shaped coarser grained and expends a greater proportion of energy on bed particles it deposits sediments downstream in exaggerated meandering reaches with wider less efficient channels localized erosion and deposition create a dynamic equilibrium with the structural growth but this equilibrium includes nonlinear responses like knickpoints and depositional lobes in response to the required erosion and deposition the river so dramatically alters channel grain size and channel geometry that the increase of sinuosity expected in the tectonically steepened valley does not occur

ni in chrome pyrope garnets a new geothermometer proton microprobe analyses of the minerals in garnet peridotite xenoliths from kimberlites show that the partitioning of ni between chrome pyrope garnet and olivine is strongly temperature t dependent the range of ni contents in olivines is small relative to that in the analyzed garnets a geothermometer therefore can be derived based only on the ni content of garnet this allows estimation of t for single cr pyrope grains such as the inclusions in diamonds if these can be assumed to have equilibrated with olivine

stable channels with mobile bed formulation and numerical solution natural rivers and streams are observed to maintain stable banks while transporting sediment over a central bed region the development of a numerical model that accounts for this essential feature of natural rivers and streams is discussed in this paper the model considers the concept of momentum diffusion and assumes a channel comprising a flat bed region and two curving bank regions the resulting boundary stress distribution is such that boundary particles in the flat bed region are subjected to stresses great enough to put them in motion while particles in the bank regions are only in a state of incipient motion it is the combination of this channel geometry and the phenomenon of momentum diffusion that allows for the successful simulation of the stable bank mobile bed condition experienced by rivers while this paper emphasizes the theoretical and numerical aspects of the problem a companion paper deals with the application and verification of the model it presents design equations and grap

topographic slope as a proxy for seismic site conditions and amplification we describe a technique to derive first order site condition maps directly from topographic data for calibration we use global 30 arc sec topographic data and v s 30 measurements here v s 30 refers to the average shear velocity down to 30 m aggregated from several studies in the u s as well as in taiwan italy and australia v s 30 values are correlated against topographic slope to develop two sets of parameters for deriving v s 30 one for active tectonic regions where topographic relief is high and one for stable shields where topography is more subdued by taking the gradient of the topography and choosing ranges of slope that maximize the correlation with shallow shear velocity observations we can recover to first order many of the spatially varying features of sitecondition maps developed for california our site condition map for the low relief mississippi embayment also predicts the bulk of the v s 30 observations in that region despite rather low slope ranges we find that maps derived from the slope of the topography is often well correlated with other independently derived regional scale site condition maps but the latter maps vary in quality and continuity and subsequently also in their ability to match observed v s 30 measurements contained therein alternatively the slope based method provides a simple approach to uniform site condition mapping

garnetite xenoliths and mantle water interactions below the colorado plateau southwestern united states garnetite xenoliths from ultramafic diatremes in northeastern arizona provide insights into hydration and metasomatism in the mantle the garnetites contain more than 95 garnet some of which has complex compositional zonation related to growth in fractures within grains accessory minerals include rutile ilmenite chlorite clinopyroxene and zircon zircon grains in one rock were analyzed in situ to determine u pb ages and hf isotopic compositions most u pb analyses plot on or near concordia in the range 60 85ma but a few are discordant the range in 176 hf 177 hf is about 0 2818 0 2828 with grains zoned to more radiogenic hf from interiors to rims the garnetite protolith contained zircons at least 1 8ga in age and garnet and additional zircon crystallized episodically during the interval 85 60ma the garnetites are interpreted as mantle analogues of rodingites formed in metasomatic reaction zones caused by water rock interactions in proterozoic mantle during late cretaceous and cenozoic subduction of the farallon plate associated eclogite xenoliths may have been parts of these same reaction zones the rodingite hypothesis requires serpentinization in the mantle wedge 700km from the trench beginning 5 10myr before tectonism related to low angle subduction

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

site characterization using integrated imaging analysis methods on satellite data of the islamabad pakistan region we develop an integrated digital imaging analysis approach to produce a first approximation site characterization map for islamabad pakistan based on remote sensing data we apply both pixel based and object oriented digital imaging analysis methods to characterize detailed 1 50 000 geomorphology and geology from advanced spaceborne thermal emission and reflection radiometer aster satellite imagery we use stereo correlated relative digital elevation models rdems derived from aster data as well as spectra in the visible near infrared vnir to thermal infrared tir domains the resulting geomorphic units in the study area are classified as mountain including the margala hills and the khairi murat ridge piedmont and basin terrain units the local geologic units are classified as limestone in the margala hills and the khairi murat ridge and sandstone rock types for the piedmonts and basins shear wave velocities for these units are assigned in ranges based on established correlations in california these ranges include vs30 values to be greater than 500 m sec for mountain units 200 600 m sec for piedmont units and less than 300 m sec for basin units while the resulting map provides the basis for incorporating site response in an assessment of seismic hazard for islamabad it also demonstrates the potential use of remote sensing data for site characterization in regions where only limited conventional mapping has been done

comments on tectonic implications of the age composition and orientation of lamprophyre dikes navajo volcanic field arizona by a w laughlin m j aldrich jr m shafiqullah and j husler commentaire sur l article de a w laughlin m j aldrich jr m shifiqullah et j husler paru dans earth planet sci le hers nld 1979 43 279 284

knickpoint initiation and distribution within fluvial networks 236 waterfalls in the waipaoa river north island new zealand if knickpoints transmit signals of base level fall in river networks then improvements in our understanding of their retreat rate and basin wide distribution helps constrain the transient response following perturbation many studies of knickpoint retreat focus on the response of trunk streams to base level fall here we examine the response of an entire fluvial network as recorded by 236 active knickpoints distributed within the waipaoa river on the north island of new zealand base level fall within the waipaoa catchment initiated 18 000 years ago in response to a climatically triggered and tectonically exacerbated pulse of incision using observations from field work aerial photo analysis and a digital elevation model dem we study the knickpoint positions within the network we find that 70 of the knickpoints are located at drainage areas between 1 10 5 m 2 and 1 10 6 m 2 and more than half are b1 km upstream of a large change in drainage area for the knickpoints b1 km upstream of large tributary junctions we find that the retreat distances were well correlated with the tributaries drainage areas in order to determine how a pulse of incision distributes itself throughout a fluvial network we develop two simple end member models and compare their behavior to the observed knickpoint distribution in the waipaoa in the first model we propose that a knickpoint initiated at the basin outlet retreats upstream and distributes the signal throughout the network at a rate that is a power law function of drainage area in the second model we propose that knickpoints form near a threshold drainage area below which channels cannot incise with the same efficiency as possible in downstream reaches though neither model addresses the along stream variability in substrate or knickpoint form the misfit between the modeled and the observed knickpoints along stream positions are surprisingly low b1 km 1 25 of the total stream length for knickpoints with drainage areas b1 10 6 m 2 large misfits up to 3 5 km are observed for knickpoints with present day drainage areas greater than 1 10 6 m 2 the large single step in channel elevation that characterizes knickpoints presently observed in tributaries of the waipaoa river may not characterize the base level fall signal that propagated through the trunk streams evidence for progressive rather than instantaneous incision in the trunk streams the knickpoints vicinities to tributary junctions and the equivalent success of the two end member models lead us to conclude that the present positions of the 236 observed knickpoints are largely a consequence of thresholds in channel incision at low drainage areas

a simplified analysis of the total seismic hazard in italy abstract total seismic hazard assessment i e the base hazard modified by local site conditions plays a key role in seismic risk prevention and mitigation this is an important topic due to the impact of a reliable hazard assessment on the resilience of local communities in the case of an earthquake this paper presents a study that evaluates the total seismic hazard for the entire italy excluding the island of sardinia the results are expressed in terms of amplification factors and total hazard parameters to this end soil characterisation was performed firstly using italian seismic network data for 259 sites uniformly distributed across italy and secondly using the mean value of the shear wave velocity available from a global dataset produced by the united states geological survey the amplification effects were quantified according to i an approach consistent with the italian building code and ii one dimensional site response analyses these two procedures are referred to as parsimonious and rigorous here respectively the results indicate a generally satisfactory match between the estimates obtained by means of these two procedures for periods lower than 0 5 s while parsimonious procedures at periods longer than 0 5 s provide an upper limit on the total seismic hazard finally a seismic classification in terms of the classes of total hazard parameters is proposed for the italian peninsula area

controls on the channel width of rivers implications for modeling fluvial incision of bedrock on the basis of the manning equation and basic mass conser vation principles we derive an expression for scaling the steady state width w of river channels as a function of discharge q channel slope s roughness n and width to depth ratio a w 5 a a1 2 2 3 3 8 q 3 8 s 23 16 n 3 8 we propose that channel width to depth ratio in addition to roughness is a function of the material in which the channel is developed and that where a river is con fined to a given material width to depth ratio and roughness can be assumed constant given these simplifications the expression emulates traditional width discharge relationships for rivers incis ing bedrock with uniformly concave fluvial long profiles more sig nificantly this relationship describes river width trends in terrain with spatially nonuniform rock uplift rates where conventional discharge based width scaling laws are inadequate we suggest that much of observed channel width variability in river channels confined by bedrock is a simple consequence of the tendency for water to flow faster in steeper reaches and therefore occupy smaller channel cross sections we demonstrate that using conventional scaling relationships for channel width can result in underestima tion of stream power variability in channels incising bedrock and that our model improves estimates of spatial patterns of bedrock incision rates

origin of coexisting minette and ultramafic breccia navajo volcanic field trace element evidence indicates that at the buell park diatreme navajo volcanic field the felsic minette can be best explained by crystal fractionation from a potassic magma similar in composition to the mafic minettes compatible trace element cr ni sc abundances decrease while concentrations of most incompatible elements ce yb rb ba sr remain constant or increase from mafic to felsic minette in particular the nearly constant ce yb ratio of the minettes combined with the decrease in cr ni and sc abundances from mafic to felsic minette is inconsistent with a model of varying amounts of partial melting as the process to explain minette compositions the uniformity of rare earth element ree abundances in all the minettes requires that an accessory mineral apatite dominated the geochemistry of the ree during fractionation a decrease in p2o5 from mafic to felsic minette and the presence of apatite in cognate inclusions are also consistent with apatite fractionation higher initial87sr 86sr ratios in the felsic minettes relative to the proposed parental mafic minettes however is inconsistent with a simple fractionation model also a separated phlogopite has a higher initial87sr 86sr ratio than host minette these anomalous isotopic features probably reflect interaction of minette magma with crust the associated ultramafic breccia at buell park is one of the navajo kimberlites but ree concentrations of the matrix do not support the kimberlite classification although the matrix of the breccia is enriched in the light ree relative to chondrites and has high la rb ba and sr concentrations relative to peridotites the concentrations of these elements are significantly lower than in south african kimberlites a high initial87sr 86sr ratio combined with petrographic evidence of ubiquitous crustal xenoliths in the navajo kimberlites suggests that the relatively high incompatible element concentrations are due to a crustal component apparently navajo kimberlites are most likely a mixture of comminuted mantle wall rock and crustal material there is no evidence for an incompatible element rich magma which is characteristic of south african kimberlites if the mafic minettes are primary magmas derived from a garnet peridotite source with chondritic ree abundances then ree geochemistry requires very small less than 1 degrees of melting to explain the minettes alternatively the minettes could have formed by a larger degree of melting of a metasomatized relatively light ree enriched garnet peridotite the important role of phlogopite and apatite in the differentiation of the minettes supports this latter hypothesis

shear wave velocity model of the santiago de chile basin derived from ambient noise measurements a comparison of proxies for seismic site conditions and amplification summary we determined a high resolution 3 d s wave velocity model for a 26 km 12 km area in the northern part of the basin of santiago de chile to reach this goal we used microtremor recordings at 125 sites for deriving the horizontal to vertical h v spectral ratios that we inverted to retrieve local s wave velocity profiles in the inversion procedure we used additional geological and geophysical constraints and values of the thickness of the sedimentary cover already determined by gravimetric measurements which were found to vary substantially over short distances in the investigated area the resulting model was derived by interpolation with a kriging technique between the single s wave velocity profiles and shows locally good agreement with the few existing velocity profile data but allows the entire area as well as deeper parts of the basin to be represented in greater detail the wealth of available data allowed us to check if any correlation between the s wave velocity in the uppermost 30 m v30s and the slope of topography a new technique recently proposed by wald and allen exists on a local scale we observed that while one lithology might provide a greater scatter in the velocity values for the investigated area almost no correlation between topographic gradient and calculated v30s exists whereas a better link is found between v30s and the local geology finally we compared the v30s distribution with the msk intensities for the 1985 valparaiso event pointing out that high intensities are found where the expected v30s values are low and over a thick sedimentary cover although this evidence cannot be generalized for all possible earthquakes it indicates the influence of site effects modifying the ground motion when earthquakes occur well outside of the santiago basin

a numerical study of mineral zoning formed during the cooling of finite volume grains a numerical model is used to study compositional profiles formed by cation exchange and diffusion at constant cooling rates in spherical mineral grains fe mg zoning in garnet olivine pairs is used as an example zoned concentration profiles can be described by an exponential function changes in the parameters of the function can be used to evaluate the effects of changes in inclusion size cooling history diffusion parameters and exchange enthalpy the composition of an olivine inclusion within garnet depends strongly on inclusion size due to finite volume effects as does zoning in the garnet surrounding the inclusion thus estimates of equilibration temperatures obtained from small inclusions of one phase within another require a size correction however for a spherical garnet within an olivine matrix the effect is small for garnet radii greater than 1000 m the shapes of zoned concentration profiles are useful for bounding both the rate of cooling and the final temperature in addition the concentration ratios fe garnet fe olivine may be used to estimate the cooling rate once the final temperature is bounded

mesoscale fluvial erosion parameters deduced from modeling the mediterranean sea level drop during the messinian late miocene 1 after a base level drop rivers are the first components of the landscape to respond by incising into topography a base level drop results in a knickpoint in the downstream part of river longitudinal profiles whether knickpoints are preserved or erased during the upstream propagation of incision is still debated preservation and erasure of knickpoints are two end member processes that work in natural systems at different timescales different length scales and different places the huge 1500 m and fast tens of kiloyears sea level drop in the mediterranean during the messinian resulted in the fast propagation of incision far inland this is especially the case in the rhone valley southern france where the knickpoint is 300 km from the mediterranean coast numerical modeling of this event has been performed using the ros model which simulates both erosional and depositional processes in rivers the best fit between numerical results and geological data is obtained for a nonlinear relation between incision and drainage area and for a small transport length of sediment this small transport length at least 2 orders of magnitude lower than the length of the rhone suggests that the longitudinal profile relaxed in a diffusive way so that the initial knickpoint was not preserved finally after a base level fall the propagation of fluvial incision is very fast at geological timescales hundreds of kiloyears despite this the diffusive response implies that the time required for restoration of an equilibrium profile is very long

lower crustal evolution under central arizona sr nd and pb isotopic and geochemical evidence from the mafic xenoliths of camp creek abstract oligocene potassic volcanism at the camp creek area arizona has sampled the lower crust by bringing mafic granulite amphibolite and garnet bearing pyroxenite eclogite xenoliths to the surface xenolith geobarometry records metamorphic pressures of approximately 10 kbar and temperatures of 650 900 c whole rock sr and nd isotopic compositions correlate roughly with xenolith metamorphic mineral assemblages higher temperature eclogites have 87sr 86sr ranging from 0 7066 to 0 7080 and end of 2 to 5 8 while lower temperature amphibolites have 87sr 86sr of 0 7074 to 0 7082 and end of 6 to 9 sr and nd isotopic compositions of mineral separates reflect in some xenoliths intermineral diffusion up to the time of latite eruption and limited exchange with the host latite pb isotopic compositions of the xenoliths show little mineralogical dependence and overlap the field for normal morb these data suggest that lower crustal metamorphism has significantly affected the sr and nd isotope evolution of the eclogites but has had little effect on their pb isotope systematics for xenoliths closer to igneous bulk compositions i e not enriched in metamorphic garnet and pyroxene nd depleted mantle model ages range from 1 2 to 1 9 ga in agreement with the pb pb array age of 1 1 0 6ga this is interpreted as dating the separation of the lower crust from the mantle during the proterozoic crust building event in this area similar nd model ages for nearby cenozoic and mesozoic granitoids suggest that the type of mafic lower crust represented by the camp creek xenoliths may be a suitable source for younger plutonics in the area

channel width response to differential uplift 1 the role of channel width and slope adjustments to differential uplift in rivers within actively deforming terrains remains contentious here high resolution topographic surveying of formerly antecedent outwash channels demonstrates marked changes in channel width as a primary response to differential uplift for five late quaternary alluvial paleochannels crossing small folds along the active ostler fault zone of southern new zealand nearly continuous measurements of paleochannel width and concomitant incision reveal abrupt narrowing of widths toward minimum values at channel positions coincident with the initial uplift when the magnitude of differential uplift is sufficiently small narrowing alone permits these channels to remain antecedent in the context of a unit stream power model for fluvial erosion observed limits on the magnitude of channel narrowing suggest that above some threshold amount of differential uplift continued incision requires concomitant changes in channel gradient thus when crossing small growing folds alluvial rivers simply narrow their channels whereas larger folds that demand greater incision prompt an initial narrowing followed by channel steepening

experiments and observations bearing on the solubility and diffusivity of carbon in olivine the solubility and diffusivity of c in olivine at 0 1 2 0 and 3 0 gpa have been constrained by annealing single crystals of san carlos olivine in 14c labelled co2 co2 h2o and graphite at 1200 1450 c in nearly all annealed specimens carbonaceous material was observed at the diffusion interface that consisted of either 1 graphite used as a c source 2 elemental c probably graphite formed by reduction of the c o h fluid phase present or 3 carbon rich surface films interpreted as silicate dissolved in the fluid phase at high pressure quenched onto the crystal surface the significant range of 14c beta particles in olivine and photographic emulsion coupled with the presence of carbonaceous material at the diffusion interface gives rise to apparent concentration profiles after removal of the carbonaceous material we retained no unambiguous evidence for c diffusion into olivine the sensitivity and spatial resolution of the beta track method constrain either the solubility to be less than 30 ppmw parts per million by weight c or the diffusivity to be less than 10 12 cm2 s observations and geochemical data on natural rocks bearing on the nature and distribution of c in the earth s upper mantle are discussed in light of these constraints

abundance and distribution of ultramafic microbreccia in moses rock dike quantitative application of mapping spectroscopy moses rock dike is a tertiary diatreme containing serpentinized ultramafic microbreccia sum located on the colorado plateau in utah field evidence indicates that sum was emplaced first followed by breccias derived from the permian strata exposed in the walls of the diatreme and finally by complex breccias containing basement and mantle derived rocks sum is primarily found dispersed throughout the matrix of the diatreme we examined the nature of sum abundance and spatial distribution using data collected remotely by the airborne imaging spectometer ais the minerals serpentine gypsum and illite as well as desert varnish and the lithologies sum and various sandstones were identified from the ais data six end members sum two types of sandstone gypsiferous soil clay rich soil desert varnish were chosen to represent the dominant lithologies of the surface in moses rock dike region spectra of these end members were used in an intimate mixing model to deconvolve the ais spectral data into surface abundance coefficients for each component using a nonnegative least squares inverse algorithm the results of this calculation of surface composition are consistent with field observations and investigations sum distribution and abundance in the matrix of the diatreme were examined in detail and two distinct styles of sum dispersion were observed one style is characterized by high to moderate sum abundance surrounded by halos of lesser sum abundance the dispersion halos grade steeply into regions of the matrix with little to no sum the second style is characterized by moderate sum abundances and broad dispersion halos with sum distributed across the entire width of the diatreme these dispersion styles are consistent with emplacement of the dike as a fluidized solid volatile system where sum which is emplaced early becomes reincorporated into the turbulent flow of the diatreme by abrasion and comminution by paniculate matter carried along in the eruption this eroded material is then dispersed throughout the matrix by eddy diffusion the first style represents an early arrested phase of the eruption sequence while the second style represents a more mature phase distributions of the second style probably indicate the location of channels where flow was concentrated during later stages of eruption since both styles are observed at the same level of erosion this indicates that the duration of eruption varied along strike at moses rock dike

drainage basin responses to climate change recent investigations have shown that the extent of the channel network in some drainage basins is controlled by a threshold for overland flow erosion the sensitivity of such basins to climate change is analyzed using a physically based model of drainage basin evolution the golem model simulates basin evolution under the action of weathering processes hillslope transport and fluvial bedrock erosion and sediment transport results from perturbation analyses reveal that the nature and timescale of basin response depends on the direction of change an increase in runoff intensity or a decrease in vegetation cover will lead to a rapid expansion of the channel network with the resulting increase in sediment supply initially generating aggradation along the main network followed by downcutting as the sediment supply tapers off by contrast a decrease in runoff intensity or an increase in the erosion threshold will lead to a retraction of the active channel network and a much more gradual geomorphic response cyclic changes in runoff intensity are shown to produce aggradational degradational cycles that resemble those observed in the field cyclic variations in runoff also lead to highly punctuated denudation rates with denudation concentrated during periods of increasing runoff intensity and or decreasing vegetation cover the sediment yield from threshold dominated basins may therefore exhibit significant variability in response to relatively subtle environmental changes a finding which underscores the need for caution in interpreting modern sediment yield data

petrological evolution of the crust and mantle in its simplest form crust mantle evolution can be thought of as a study of the processes by which material is lost from the mantle and forms new crust the overall goal is achievement of mass balance between the average composition of material known to have been added to the crust and the estimated average composition of the entire crust attainment of this goal for the earth has been elusive primarily because the materials available for study have generally been involved in several stages of evolution including fractionation within both the crust and mantle and recycling of material from crust to mantle thereby complicating the interpretation of available data although the overall composition of the continental crust generally has been modelled as andesitic taylor and mclennan 1981a the present upper continental crust is granodioritic and requires a more mafic lower crust it has been proposed taylor and mclennan 1981a that originally the archean crust had an andesitic composition throughout its volume and that partial melting in the lower crust developed more felsic melts that rose to enrich the upper crust leaving a more mafic residuum of lower crust this concept has been challenged by weaver and tarney 1981a who argue that the granulites of presumed lower crustal origin do not have the correct compositions for this model if one considers more recent additions to the crust from the mantle over the past several hundred million years it appears that these latest additions are basaltic with very little if any granitic additions in fact barker 1981 in his introduction to a special issue of jgr on granites and rhyolites states to date no one has demonstrated that such magmas may form in the mantle indeed much experimental and geochemical work indicates that such siliceous liquids cannot originate there therefore such magmas must be generated in the crust in island arc environments where the average composition of added material normally is thought to be andesitic a anderson 1982 has shown that the parent melt is basaltic not andesitic in addition kay 1980 has shown that the k content of the newly added material is less than the average k content of the previously existing crust in the oceanic crust the additions from the mantle are basaltic and according to o hara 1982 probably are derived from very mafic picritic melts as parents continental flood basalts which have also added material from mantle to crust also are clearly derived from basaltic parental melts basaltic volcanism study project 1981 thus the evidence for the nature of material subtracted from the mantle and added to the crust for the past several hundred million or perhaps a billion years points to very mafic melts this contrasts significantly with the overall andesitic composition of continental crust it implies furthermore that if the overall archean crustal composition was andesitic as estimated by taylor and mclennan 1981a then additions to the crust have become more mafic with time a concept in direct conflict with most models in which secular trends are from mafic to felsic with time veizer and jansen 1979 and mclennan et al 198o a question which is beginning to appear either explicitly or implicitly is whether crustal volcanic rocks or the crust as a whole really represents the parent melt that formed in the mantle a anderson 1982 o hara 1982 and nisbet and walker 1982

geomorphic limits to climate induced increases in topographic relief recognition of the potential for strong dynamic coupling between atmospheric and tectonic processes has sparked intense cross disciplinary investigation and debate on the question of whether tectonics have driven long term climate change or vice versa it has been proposed that climate change might have driven the uplift of mountain summits through an isostatic response to valley incision because isostasy acts to compensate mean elevations the debate hinges on the question of whether climate change can significantly increase topographic relief or more precisely increase the volume of missing mass between summits and ridges here we show that in tectonically active mountain ranges geomorphic constraints allow only a relatively small increase in topographic relief in response to climate change thus although climate change may cause significant increases in denudation rates potentially establishing an important feedback between surficial and crustal processes neither fluvial nor glacial erosion is likely to induce significant isostatic peak uplift

generation and verification of theoretical rating curves in the whitewater river basin kansas 1 a new method for generating stage discharge relations rating curves for geomorphically stable channels is presented and applied to two streams in the whitewater river basin kansas the approach converts measurements of stage into discharge using a fluid mechanically based model the model does not use empirical roughness coefficients such as manning coefficients but rather determines channel roughness from field measurements of the 1 channel geometry 2 the physical roughness of the bed banks and floodplain and 3 the vegetation density on the banks and floodplain these measurements are used to calculate explicitly the drag on the small scale topographic features on the boundary the drag on the stems and branches of woody vegetation and the friction on the bed banks and floodplain the theoretical rating curves produced by the model for two study reaches which are near u s geological survey usgs streamflow gauging stations are in good agreement with direct measurements of discharge made by the usgs our method has the potential of providing accurate estimates of stream flows less expensively than conventional gauging methods in addition the method can be used to obtain more accurate discharge estimates than conventional indirect methods for determining discharge which are based on estimates of manning s coefficient

thessaloniki s detailed microzoning subsurface structure as basis for site response analysis the city of thessaloniki is located in northern greece close to a large seismogenic area and it has experienced several destructive earthquakes during the present century in this paper we focus on the definition of the subsurface structure of the city from a site response analysis perspective the paper presents together with a summary of geology and seismicity the results of a large scale geophysical and geotechnical survey in order to determine and validate geometry and dynamic properties of the main soil formations the synthesis and combination of recent results regarding the dynamic properties with those obtained from the elaboration of a large database of classical geotechnical tests led to the design of a detail geotechnical map and of various 1 d profiles 2 d cross sections and 3 d thematic maps for the main soil formations these soil profiles and maps are oriented to site effect studies and provide a comprehensive picture easily adapted to geographic information systems gis for planning and design purposes moreover the results of this study were correlated with macroseismic observations reported in many earlier published microzonation studies of thessaloniki these comparative observations revealed the complexity of surface geology of the urban area a fact which is expected to provoke additional amplification with respect to 1 d resonance

long river profiles tectonism and eustasy a guide to interpreting fluvial terraces along three rivers at the mendocino triple junction northern california strath cut and fill terraces have formed in response to tectonic and eustatic processes detailed surveying and radiometric dating at multiple sites indicate that lower reaches of the rivers are dominated by the effects of oscillating sea level primarily aggradation and formation of fill terraces during sea level high stands alternating with deep incision during low stands a eustasy driven deposi tional wedge extends tens of kilometers upstream on all rivers tapering to zero thickness this distance is greater than expected from studies of the effects of check dams on much smaller streams elsewhere due in part to the large size of these rivers however the change in gradient is nearly identical to other base level rise studies the depositional gradient is about half that of the original channel middle to upper reaches of each fiver are dominated by the effects of long term uplift primarily lateral and vertical erosion and formation of steep unpaired strath terraces exposed only upstream of the depositional wedge vertical incision at a rate similar to that of uplift has occurred even during the present sea level high stand along rivers with highest uplift rates strath terraces have steeper gradients than the modem channel bed and do not merge with marine terraces at the river mouth consequently they cannot be used to determine altitudes of sea level high stands strath formation is a continuous process of response to long term uplift and its occurrence varies spatially along a river depending on stream power and hence position upstream strath terraces are found only along certain parts of a coastal stream upstream of the aggradational effects of oscillating sea level and far enough downstream that stream power is in excess of that needed to transport the prevailing sediment load for a given size fiver the greater the uplift rate the greater the rate of vertical incision and consequently the less the like lihood of strath terrace formation and preservation

regional correlations of vs30 and velocities averaged over depths less than and greater than 30 meters using velocity profiles from sites in japan california turkey and europe we find that the time averaged shear wave velocity to 30 m vs30 used as a proxy for site amplification in recent ground motion prediction equations gmpes and building codes is strongly correlated with average velocities to depths less than 30 m vsz with z being the averaging depth the correlations for sites in japan corresponding to the kik net network show that vs30 is systematically larger for ag ivenvsz than for profiles from the other regions the difference largely results from the placement of the kik net station locations on rock and rocklike sites whereas stations in the other regions are generally placed in urban areas underlain by sediments using the kik net velocity profiles we provide equations relating vs30 to vsz for z ranging from 5 to 29 m in 1 m increments these equations and those for california velocity profiles given in boore 2004b can be used to estimate vs30 from vsz for sites in which velocity profiles do not extend to 30 m the scatter of the residuals decreases with depth but even for an averaging depth of 5 m a variation in logvs30 of 1 standard deviation maps into less than a 20 uncertainty in ground motions given by recent gmpes at short periods the sensitivity of the ground motions to vs30 uncertainty is considerably larger at long periods but is less than a factor of 1 2 for averaging depths greater than about 20 m we also find that vs30 is correlated with vsz for z as great as 400 m for sites of the kik net network providing some justification for using vs30 as a site response variable for predicting ground motions at periods for which the wavelengths far exceed 30 m online material estimates of vs30 at k net stations

observations on the role of lithology in strath terrace formation and bedrock channel width field observations from western washington and eastern tibet indicate a strong lithologic influence on strath terrace formation and highlight the response of bedrock channel width to spatial gradients in bedrock erodibility and or rock uplift rates measurements of local bedrock bed and bank erosion rates together with observations of the role of weathering processes on erosion of siltstones and sandstones illustrate a mechanism that underlies a conceptual model that predicts a strong lithological control on strath terrace formation direct measurements of bedrock erosion rates in lithologies susceptible to accelerated erosion upon sub aerial exposure show that lateral rates of bedrock bank erosion can substantially exceed vertical incision below the perennial flow level due to an asymmetry in erodibility between perennially submerged rock and rock exposed to cyclic wetting and drying on bedrock channel walls under such conditions the rapid weathering mediated lowering of bedrock exposed above baseflow promotes development of a beveled bedrock platform that could become a strath terrace upon abandonment in contrast to previous studies channel widths measured across a substantial gradient in lithology slope and long term erosion rates in eastern tibet do not follow conventional relations where channel width scales as a power law function of drainage area instead as they flow across a zone of rapid uplift these channels systematically narrow relative to the predicted width extrapolated from traditional power law relations field studies from a wide range of geological settings and lithologies support the interpretation that in general strath terraces tend to be more extensive in rivers flowing over weak sedimentary rock and tend to be poorly developed and or preserved where rivers flow over hard erosion resistant rock

knickpoint recession rate and catchment area the case of uplifted rivers in eastern scotland knickpoint behaviour is a key to understanding both the landscape responses to a base level fall and the corresponding sediment fluxes from rejuvenated catchments and must be accommodated in numerical models of large scale landscape evolution knickpoint recession in streams draining to glacio isostatically uplifted shorelines in eastern scotland is used to assess whether knickpoint recession is a function of discharge here represented by its surrogate catchment area knickpoints are identified using ds plots log slope versus log downstream distance a statistically significant power relationship is found between distance of headward recession and catchment area such knickpoint recession data may be used to determine the values of m and n in the stream power law e kamsn the data have too many uncertainties however to judge definitively whether they are consistent with m n 1 bedrock erosion is proportional to stream power and kps should be maintained and propagate headwards or m 0 3 n 0 7 bedrock incision is proportional to shear stress and kps do not propagate but degrade in place by rotation or replacement nonetheless the e scotland m and n values point to the dominance of catchment area discharge in determining knickpoint retreat rates and are therefore more consistent with the stream power law formulation in which bedrock erosion is proportional to stream power copyright 2005 john wiley sons ltd

an updated probabilistic seismic hazard assessment for romania and comparison with the approach and outcomes of the share project the probabilistic seismic hazard analysis for romania is revisited within the framework of the bigsees national research project http infp infp ro bigsees default htm financed by the romanian ministry of education and scientific research in the period 2012 2016 the scope of this project is to provide a refined description of the seismic action for romanian sites according to the requirements of eurocode 8 to this aim the seismicity of all the sources influencing the romanian territory is updated based on new data acquired in recent years the ground motion models used in the analysis as well as their corresponding weights are selected based on the results from several recent papers also published within the framework of the bigsees project the seismic hazard analysis for romania performed in this study are based on the traditional cornell mcguire approach finally the results are discussed and compared with the values obtained in the recently completed share research project the bigsees and share results are not directly comparable since the considered soil conditions are different actual soil classes for bigsees and rock for share nevertheless the analyses of the seismic hazard results for 200 sites in romania reveal considerable differences between the seismic hazard levels obtained in the present study and the share results and point out the need for further analyses and thorough discussions related to the two seismic hazard models especially in the light of a possible future harmonized hazard map for europe

rare earth element geochemistry of garnet lherzolite and megacrystalline nodules from minette of the colorado plateau province abstract mineral and whole rock ree abundances in garnet lherzolite and megacrystalline nodules from the thumb display broad correlations with major element compositions lherzolites with 12 modal clinopyroxene plus garnet high ca al lherzolites have relatively flat chondrite normalized whole rock ree patterns lherzolites poor in clinopyroxene and garnet low ca al lherzolites have lower hree in clinopyroxenes and garnets and higher whole rock lree hree it is concluded that the low ca al lherzolites may have undergone lree metasomatism after depletion of the major element compositions by partial melting and that much of the garnet now present was originally dissolved in aluminous orthopyroxene the high ca al lherzolites may be interpreted either as primordial mantle samples or as products of equilibration with very lree enriched liquids the megacrystalline nodules are medium to ultracoarse grained intergrowths and megacrysts with mineral compositions similar to discrete nodule suites in kimberlites the ree abundances of the megacrystalline minerals are consistent with an origin as cumulates from magma with extremely fractionated ree similar to minette or kimberlite the patterns of correlation of ree and major elements in this inclusion suite are similar to the patterns observed in the garnet lherzolite and discrete nodule suites of southern african kimberlites both of the subcontinental mantle provinces represented by these suites contain three distinct petrogenetic components refractory garnet lherzolite enriched in lree and depleted in hree fertile garnet lherzolite with generally chondritic ree abundances and a suite of ultracoarse minerals precipitated from magma with extremely fractionated ree generally similar to the host magmas

modeling effects of bank friction and woody bank vegetation on channel flow and boundary shear stress in the rio puerco new mexico 1 we have applied a physically based model for steady horizontally uniform flow to calculate reach averaged velocity and boundary shear stress distributions in a natural stream with woody vegetation on the channel banks the model calculates explicitly the form drag on woody plant stems and includes the effects of vegetation on the boundary shear stress velocity and turbulence fields average channel shapes bed gradients and shrub characteristics were determined for four long internally similar reaches covering an 81 km segment of the lower rio puerco in north central new mexico hydraulic geometries for each of three flow events were determined from reach average channel shapes slopes and measured silt line heights above the bed model results show that friction on the lateral boundaries reduced the boundary shear stress in the center of the rio puerco channel by as much as 20 in reaches with moderate to dense bank shrubs perimeter averaged boundary shear stresses were reduced by almost 40 during near bankfull flows model calculated discharges for all three flow events indicate there was a loss of about 40 of the upstream discharge through the 81 km river segment infiltration rates estimated from discharge losses during the quasi steady peak flows and areas of the bed and banks suggest rates of flow loss into the silty sand of the upper banks are about 8 times greater than rates of loss into the clayey silt covered bed and lower banks

computational fluid dynamics and the physical modelling of an upland urban river this paper describes the application of a commercially available three dimensional computational fluid dynamic cfd model to simulate the flow structure in an upland river that is prone to flooding simulations use a rectangular channel geometry smooth sidewalls and a bed topography obtained from the field site that contains a subdued pool riffle sequence the cfd model uses the rng var epsilon turbulence closure scheme of yakhot and orszag j sci comput 1 1986 1 as implemented in fluent 4 4 4 with a free surface results are shown for numerical runs simulating a 1 100 year return interval flood output from the numerical model is compared to a physical model experiment that uses a 1 35 scale fibreglass mould of the field study reach and measures velocity using ultrasonic doppler velocity profiling udvp results are presented from the numerical and flume models for the water surface and streamwise velocity pattern and for the secondary flows simulated in the numerical model a good agreement is achieved between the cfd model output and the physical model results for the downstream velocities results suggest that the streamwise velocity is the main influence on the flow structure at the discharge and channel configuration studied secondary flows are in general very weak being below the resolution of measurement in the physical model and less than 10 of the streamwise velocity in the numerical model consequently there is no evidence for a velocity dip it is suggested that the subdued topography or inlet morphology may inhibit the development of secondary flows that have been recorded in previous flat bed rectangular open channel flows a significant corollary of these results is that the morphological evolution of the pool riffle sequence at high discharges may be controlled primarily by the downstream distribution of velocity and sediment transport with little role for lateral sorting and sediment routing by secondary flows this paper also raises a number of issues that may be of use in future cfd modelling of three dimensional flow in open channels within the geomorphological community

climate driven bedrock incision in an active mountain belt measurements of fluvial bedrock incision were made with submillimeter precision in the east central range of taiwan where long term exhumation rates and precipitation driven river discharge are independently known they indicate that valley lowering is driven by relatively frequent flows of moderate intensity abrasion by suspended sediment is an important fluvial wear process and channel bed geometry and the presence of widely spaced planes of weakness in the rock mass influence erosion rate and style

modeling the evolution of channel shape balancing computational efficiency with hydraulic fidelity 1 the cross sectional shape of a natural river channel controls the capacity of the system to carry water off a landscape to convey sediment derived from hillslopes and to erode its bed and banks numerical models that describe the response of a landscape to changes in climate or tectonics therefore require formulations that can accommodate evolution of channel cross sectional geometry however fully two dimensional 2 d flow models are too computationally expensive to implement in large scale landscape evolution models while available simple empirical relationships between width and discharge do not adequately capture the dynamics of channel adjustment we have developed a simplified 2 d numerical model of channel evolution in a cohesive detachment limited substrate subject to steady unidirectional flow erosion is assumed to be proportional to boundary shear stress which is calculated using an approximation of the flow field in which log velocity profiles are assumed to apply along vectors that are perpendicular to the local channel bed model predictions of the velocity structure peak boundary shear stress and equilibrium channel shape compare well with predictions of a more sophisticated but more computationally demanding ray isovel model for example the mean velocities computed by the two models are consistent to within 3 and the predicted peak shear stress is consistent to within 7 furthermore the shear stress distributions predicted by our model compare favorably with available laboratory measurements for prescribed channel shapes a modification to our simplified code in which the flow includes a high velocity core allows the model to be extended to estimate shear stress distributions in channels with large width to depth ratios our model is efficient enough to incorporate into large scale landscape evolution codes and can be used to examine how channels adjust both cross sectional shape and slope in response to tectonic and climatic forcing

numerical modeling of fluvial strath terrace formation in response to oscillating climate many river systems in western north america retain a fluvial strath terrace rec ord of discontinuous downcutting into bedrock through the quaternary their importance lies in their use to interpret climatic events in the headwaters and to determine long term incision rates terrace formation has been ascribed to changes in sediment supply and or water discharge produced by late quaternary climatic fluctuations we use a one dimensional channel evolution model to explore whether temporal variations in sediment and water discharge can generate terrace sequences the model includes sediment transport vertical bedrock erosion limited by alluvial cover and lateral valley wall erosion we set limits on our modeling by using data collected from the terraced wind river basin two types of experiments were performed constant period sinusoidal input histories and variable period inputs scaled by the marine 18 o rec ord our simulations indicate that strath terrace formation requires input variability that produces a changing ratio of vertical to lateral erosion rates straths are cut when the channel floor is protected from erosion by sediment and are abandoned and terraces formed when incision can resume following sediment cover thinning high sediment supply promotes wide valley floors that are abandoned as sediment supply decreases in contrast wide valleys are promoted by low effective water discharge and are abandoned as discharge increases widening of the valley floors that become terraces occurs over many thousands of years the transition from valley widening to downcutting and terrace creation occurs in response to subtle input changes affecting local divergence of sediment transport capacity formation of terraces lags by several thousand years the input changes that cause their formation our results suggest that use of terrace ages to set limits on the timing of a specific event must be done with the knowledge that the system can take thousands of years to respond to a perturbation the incision rate calculated in the field from the lowest terrace in these systems will likely be higher than the rate calculated by using older terraces because the most recent fluvial response in the field is commonly downcutting associated with declining sediment input since the last glacial maximum this apparent increase in incision rates is observed in many river systems and should not necessarily be interpreted as a response to an increase in rock uplift rate

experimental simulation of channel incision into a cohesive substrate at varying gradients six flume runs using a substrate of 30 bentonite and 70 fine sand were used to examine channel incision into a cohesive homogeneous substrate gradients for the various runs were 1 2 5 10 and 20 other variables remained constant discharge 2 l s sediment discharge averages 3 g s run time 15 with increasing flume gradient bed forms change from parallel longitudinal grooves to a broad shallow channel with weakly undulating bed and walls and then to a progressively deeper and more undulating inner channel downstream changes in reach scale several channel widths gradient may thus be responsible for downstream variability of erosional bed forms in the absence of changes in other controlling variables for bedrock channels it is not necessary to invoke substrate variability to explain the presence of erosional bed forms and associated variations in cross sectional area erosional bed forms may approximate an equilibrium state in which negligible change occurs in bed form dimensions or shape with time downstream alternations between solely erosion and deposition of an alluvial veneer over incisional features occur along channel reaches of constant gradient the downstream length of these alternations is inversely proportional to gradient

determination of geomechanical site effects in france from macroseismic intensities and reliability of macroseismic magnitude of historical events results from a detailed analysis of the french macroseismic database sirene96 show that geomechanical site effects i e site effects due to superficial geology can be statistically detected and quantified from macroseismic data our results are used to derive a predictive map of potential site effects in france and to check if site effects induce a significant overestimation of macroseismic magnitude of historical events the key hypothesis of our work is that geological formations of similar age produce similar site effects because one expects the younger sediments to be less compacted and therefore more prone to cause site effects a geological formation is associated with each intensity using a geographic information system gis and the digital geological map of france two approaches are developed in order to characterise the intensity increase associated with geological formations having the same age the first approach is based on the intensities that differ significantly from the average pattern intensities which are labelled as anomalies in the second approach a theoretical intensity attenuation law is computed for each selected event only from observations located on formations older than 2 my according to the results of the first approach these formations are unlikely to cause site effects and for the sake of simplicity they are labelled as rocks younger formations are defined as sediments the derived attenuation laws are then used to compute the residuals for each observation residuals are classified as a function of the age of the formations on which they are located the results of the two approaches are in good agreement no intensity amplification is detected for formations older than 1 my for younger formations the younger the formations the larger the average intensity increase the average intensity increase reaches 0 6 0 2 degree on the msk scale for 0 my sediments the results are better expressed in terms of probability for 0 my sediments there is an estimated 83 probability of observing an intensity increase for 0 01 my and 0 75 my sediments this probability is about 52 the magnitude of the intensity increase is variable but it is generally small it has a 26 probability to reach 1 degree or above on the msk scale for 0 my sediments and this probability falls to about 5 for 0 01 and 0 75 my formations a predictive map of geomechanical site effects is produced by extrapolating the characteristics of intensity increases to all geologic formations of similar age in france glacial and fluvial valleys already known as being subject to site effects clearly appear on this map as well as less expected areas such as the south atlantic coast lastly new estimations of macroseismic magnitude that exclude intensities potentially affected by geomechanical site effects are realised a magnitude overestimation due to site effects can possibly exist but it remains limited 0 2 this result tends to demonstrate that geomechanical site effects in france do not significantly distort our knowledge of historical seismicity

empirical model for basin effects accounts for basin depth and source location empirical relationships are developed to predict amplification factors for 5 damped response spectral acceleration that incorporate basin response effects the parameters considered are depth to the 1 5 km sec shear wave isosurface z 1 5 as well as the location of the source beneath or outside the perimeter of the basin in which the site is located sites located in a basin overlying the source are denoted as having coincident source and site basin locations cbl and are differentiated from distinct source and site basin locations dbl amplification factors for cbl and dbl sites are evaluated from simulated data developed by others and strong motion data amplification factors derived from strong motion recordings are taken as residuals of rock attenuation relations coupled with amplification factors for shallow site conditions models relating amplification to z 1 5 were developed separately for the cbl and dbl data groups the results indicate that the use of basin models is generally worthwhile for periods t 0 75 sec at those long periods residuals are significantly sensitive to z 1 5 for cbl but not for dbl the standard deviation is also reduced for long periods to an extent that the standard deviations for long and short periods are similar

geothermometry and kinetics in a two spinel peridotite nodule colorado plateau compositions and zoning of minerals in a two spinel peridotite from minette in the navajo volcanic field on the colorado plateau provide unusual opportunities to compare geothermometers at low mantle temperature and to study equilibration rates the xenolith contains pleonaste mg sub 55 fe sub 45 al sub 1 62 fe sub 10 cr sub 28 o sub 4 and magnetite mg sub 16 fe sub 89 mn sub 01 al sub 18 fe sub 1 38 cr sub 32 ti sub 06 o sub 4 related by granule exsolution together with olivine foyv orthopyroxene 3 5 al sub 2 o sub 3 and clinopyroxene both two spinel equilibria and several olivine pleonaste geothermometers indicate equilibration near or below 700 sup 0 c confirming the general accuracy and continued equilibration of these geothermometers at low temperatures calculated olivine magnetite temperatures are much too high two pyroxene temperatures are near 800 sup 0 c olivine is zoned in ca fe and mg within 50 mu m of spinel by exchange with local grain boundary melts gradients at pleonaste magnetite contacts were caused by multicomponent diffusion after heating by minette effects include slight uphill diffusion of cr effective binary diffusion coefficients near 1100 sup 0 c estimated by comparison with gradients in olivine are near 10kaa cm sup 2 sec for al in magnetite and 10kab cm sup 2 sec for al in pleonaste an average mg value is in the same range the time interval between plucking of the inclusionmore and minette solidification is calculated as about 60 hours consistent with ascent times calculated assuming newtonian viscosity for the minette magmas less

automated procedure for estimating vs30 utilizing p wave seismograms and its application to japan abstract we develop an automated procedure to estimate time averaged shear wave velocities in the upper 30 m of soil deposits vs30 rapidly and objectively based on initial p wave seismogram amplitudes in the radial and vertical directions we apply this procedure to 630 kiban kyoshin network stations in japan utilizing 9207 records it is clear that the estimates are in good agreement with real world measurements filtering records based on signal to noise ratio snr thresholds slightly improves vs30 estimation but a decrease in the number of records results in an inability to estimate vs30 at certain sites we propose bias correction models based on snrs and take off angles to facilitate vs30 estimation at numerous sites while maintaining suitable prediction performance we observe that the performance of the proposed method is similar to that of methods utilizing different types of proxies for various regions we successfully apply the proposed method to 989 kyoshin network stations utilizing 18 454 records and create a vs30 map for the entire area of japan

cover effect in bedrock abrasion a new derivation and its implications for the modeling of bedrock channel morphology the sediment load of a bedrock river plays an important role in the fluvial incision process by providing tools for abrasion the tools effect and by covering and thereby protecting the bed the cover effect we derive a new formulation for the cover effect in which the fraction of exposed bed area falls exponentially with increasing sediment flux or decreasing transport capacity and explore its consequences for the model of bedrock abrasion by saltating bed load erosion rates predicted by the model are higher than those predicted by earlier models in a closed system the maximum erosion rate is predicted to occur when sediment supply is equal to transport capacity for a flat bed by optimizing the channel geometry to minimize the potential energy of the stream and using representative values for both discharge and grain size we derive equations for the geometry of a bedrock river and explore how predictions for width slope and bed cover vary as functions of drainage area rock uplift rate and rock strength the equations predict a dependence of channel width on drainage area similar to the relations using a simple shear stress incision law the slope area relationship is predicted to be concave up in a log log regime with a curvature dependent on uplift rate however this curvature does not deviate sufficiently from a straight line to allow discrimination between models using empirical data dependence of channel width and slope on rock uplift rate can be separated into two domains for low uplift rates channel geometry is largely insensitive to uplift rate due to a threshold effect at high uplift rates there is a power law dependence bed cover is predicted to increase progressively downstream and to increase with increasing uplift rate in our model the width to depth ratio is a function of both tectonic and climatic forcing this indicates that the scaling between channel width and bed slope is neither a unique indicator of tectonic forcing at steady state nor a signature of transience or steady state we conclude that sediment effects need to be taken into account when modeling bedrock channel morphology

compilation of a local vs profile database and its application for inference of vs30 from geologic and terrain based proxies abstract the time averaged shear wave velocity in the upper 30 m of a site v s 30 is commonly used for ground motion prediction when measured velocities are unavailable v s 30 is estimated from proxy based relationships developed for application on global or local scales we describe the development of a local relationship for greece which begins with compilation of a profile database pdb from published sources and engineering reports the pdb contains 314 sites 238 have profile depths 30 m and 59 are within 100 m of accelerographs we find existing relations for extrapolating a time averaged velocity for depths less than 30 m to v s 30 to overpredict v s 30 we present equations for these extrapolations we then compile proxies for pdb sites including terrain type surface geology and surface gradients at 30 and 3 arcsec resolution from radar derived digital elevation models dems when checked against ground survey data we find ground elevations from 3 arcsec dems to be more accurate relative to survey data than alternative 30 9 and 1 arcsec dems drawing upon expert opinion we develop geologic categories based on age gradation and depositional environment and assign such categories to pdb sites we find an existing 30 arcsec gradient based global model to be biased relative to local v s 30 data for gradients 0 05 m m bias relative to a california model is also found for four of the eight well populated geomorphic categories and new local values are provided we find statistically significant effects of the 3 arcsec gradient on v s 30 for quaternary and tertiary materials but no gradient effect for those from the mesozoic among quaternary sediments holocene mapped quaternary age unspecified and mixed fine gradation materials exhibit consistent v s 30 gradient trends whereas pleistocene and coarse gradation sediments have faster velocities for the study region we recommend use of the modified terrain and geology based methods in combination for proxy based v s 30 estimation online material profile database spreadsheet and figures of elevation residuals

discharge discharge variability and the bedrock channel profile long term bedrock incision is driven by daily discharge events of variable magnitude and frequency with ineffective events below an incision threshold we explore theoretically how this short term stochastic behavior controls long term steady state incision rates and bedrock channel profiles combining a realistic frequency magnitude distribution of discharge with a deterministic detachment limited incision model in which incision rate is a power function of basal shear stress above a critical shear stress our model predicts a power law relationship between steady state slope and drainage area consistent with observations the exponent of this power law is independent of discharge mean and variability while the amplitude factor which controls mountain belt relief is a power law function of mean runoff with an exponent of 0 5 and a complex function of runoff variability in accordance with evidence that incision occurs between 6 and 20 of time in rapidly incising rivers 1 mm yr our model predicts that channel steepness is virtually insensitive to runoff variability runoff variability can only decrease channel steepness for very slow incision rates and or weak lithologies the relationship between channel steepness and incision rate is always a power law whose exponent depends on the channel cross sectional geometry and runoff variability this contradicts models neglecting discharge stochasticity in which the steepness incision scaling is set by the incision law exponent our results suggest that changes in climate variability cannot explain an increase in bedrock incision rates during the late cenozoic within the context of a detachment limited model

garnet peridotite from colorado plateau ultramafic diatremes hydrates carbonates and comparative geothermometry crystal fragments of pyrope from diatremes of ultramafic microbreccia in the navajo province of the colorado plateau contain inclusions of olivine pyroxene spinel chlorite amphibole chlorapatite and dolomite the included suite supports earlier hypotheses that hydrous phases and carbonates were primary parts of some garnet peridotite assemblages in the plateau lithosphere garnets with spinel and orthopyroxene inclusions likely all were sampled at pressures less than 36 kb and perhaps as low as 15 20 kb no evidence was found for inclusions from greater depths temperature estimates are 800 900 c for garnet clinopyroxene equilibration but only 500 700 c for garnetolivine equilibration inherent differences between geothermometry methods account for only part of the discrepancy pronounced fe mg zoning in garnet at olivine contacts and the lack of such zoning at clinopyroxene contacts are evidence that the difference in part relates to relative reequilibration rates with cooling the garnet olivine temperature estimates may be the best approximations to mantle temperatures before eruption our data are compatible both with the hypothesis that the garnet peridotite was emplaced in the mantle by large scale horizontal transport in the lithosphere and with the hypothesis that rocks were sampled from precambrian lithosphere cooled to temperatures like those along a low heat flow geotherm discordances between the geothermometers here and in other lherzolite localities may be keys to evaluating tectonic histories of lherzolite masses

modeling of knickpoint retreat on the roan plateau western colorado 1 the roan plateau in western colorado constitutes a natural experiment for studying landscape response to a drop in base level late cenozoic incision of the upper colorado river led to elevational isolation of the plateau and initiation of a wave of incision into its southern edge knickpoints oversteepened reaches that contain waterfalls 60 110 m in height mark the upstream extent of this headward propagating wave that this incision has occurred in a laterally extensive well stratified and essentially flat lying bedrock and in an area with relatively uniform climate implies that it should serve as a good test of existing knickpoint propagation models we predict the locations of knickpoints by using a stream power based celerity model in which knickpoint recession rate is a power function of drainage area and is proportional to rock susceptibility to erosion models of the parachute and roan drainages 17 and 16 knickpoints respectively show expected rapid initial knickpoint propagation rates which decline as drainage area decreases stepwise at tributary junctions the modeled positions of knickpoints match well with observed features using a single combination of parameters to model retreat in both drainage basins we compare our celerity model results with past studies and explore how longitudinal profile analysis may be used to derive independently the exponent on drainage area in the celerity model

the influence of hydrous phases on the microstructure and seismic properties of a hydrated mantle rock abstract to better understand the microstructural evolution of a serpentinized mantle rock and the influence of various hydrous phases on the seismic properties of the mantle wedge we have conducted the detailed microstructural analyses of a sample of tremolite chlorite antigorite schist collected from the moses rock dike central part of the colorado plateau we performed differential effective media dem modelling to study the effect of three hydrous phases forming two phase aggregates with olivine considering the crystallographic preferred orientation cpo of each phase and the shape ratio of the hydrous phases we have demonstrated that in a partially serpentinized peridotite the olivine cpo characteristic of 100 010 dislocation glide is still preserved and the high temperature asthenospheric flow is preserved with a foliation normal to that of antigorite schist the transformation of olivine into antigorite occurs predominantly 75 by the relationship 100 ol 001 atg with 001 ol 010 atg with the 010 ol 001 atg and 001 ol 010 atg relationship observed in areas of weak antigorite cpo chlorite results from the phase transformation of olivine in a relatively static environment as shown by the correlation between the olivine chlorite cpos with 100 ol 100 ch 010 ol 001 ch and 001 ol 010 ch the fluid percolation that caused the localized metasomatism and partial hydration of the mantle occurred possibly along trans lithospheric shear zones the presence of chlorite induces the most important drop on the p wave velocities and may help to explain some local low velocities in the fore arc mantle wedges but is unlikely to be of global importance due to its very high vp vs ratio 1 9 on the other hand antigorite is the only phase that causes important modification on the propagation directions of p and s waves and the only phase to explain the polarization of the fastest shear waves parallel to the subduction trench

fluvial incision and tectonic uplift across the himalayas of central nepal the pattern of fluvial incision across the himalayas of central nepal is estimated from the distribution of holocene and pleistocene terraces and from the geometry of modern channels along major rivers draining across the range the terraces provide good constraints on incision rates across the himalayan frontal folds sub himalaya or siwaliks hills where rivers are forced to cut down into rising anticlines and have abandoned numerous strath terraces farther north and upstream in the lesser himalaya prominent fill terraces were deposited probably during the late pleistocene and were subsequently incised the amount of bedrock incision beneath the fill deposits is generally small suggesting a slow rate of fluvial incision in the lesser himalaya the terrace record is lost in the high range where the rivers are cutting steep gorges to complement the terrace study fluvial incision was also estimated from the modern channel geometries using an estimate of the shear stress exerted by the flowing water at the bottom of the channel as a proxy for river incision rate this approach allows quantification of the effect of variations in channel slope width and discharge on the incision rate of a river the determination of incision rates requires an additional lithological calibration the two approaches are shown to yield consistent results when applied to the same reach or if incision profiles along nearby parallel reaches are compared in the sub himalaya river incision is rapid with values up to 10 15 mm yr it does not exceed a few millimeters per year in the lesser himalaya and rises abruptly at the front of the high range to reach values of 4 8 mm yr within a 50 km wide zone that coincides with the position of the highest himalayan peaks sediment yield derived from the measurement of suspended load in himalayan rivers suggests that fluvial incision drives hillslope denudation of the landscape at the scale of the whole range the observed pattern of erosion is found to closely mimic uplift as predicted by a mechanical model taking into account erosion and slip along the flat ramp flat geometry of the main himalayan thrust fault the morphology of the range reflects a dynamic equilibrium between present day tectonics and surface processes the sharp relief together with the high uplift rates in the higher himalaya reflects thrusting over the midcrustal ramp rather than the isostatic response to reincision of the tibetan plateau driven by late cenozoic climate change or late miocene reactivation of the main central thrust

on the use of high resolution topographic data as a proxy for seismic site conditions vs30 an alternative method has recently been proposed for evaluating global seismic site conditions or the average shear velocity to 30 m depth v s 30 from the shuttle radar topography mission srtm 30 arcsec digital elevation models dems the basic premise of the method is that the topographic slope can be used as a reliable proxy for v s 30 in the absence of geologically and geotechnically based site condition maps through correlations between v s 30 measurements and topographic gradient here we evaluate the use of higher resolution 3 and 9 arcsec dems to examine whether we are able to resolve v s 30 in more detail than can be achieved using the lower resolution srtm data high quality dems at resolutions greater than 30 arcsec are not uniformly available at the global scale however in many regions where such data exist they may be employed to resolve finer scale variations in topographic gradient and consequently v s 30 we use the u s geological survey earth resources observation and science eros data center s national elevation dataset ned to investigate the use of high resolution dems for estimating v s 30 in several regions across the united states including the san francisco bay area in california los angeles california and st louis missouri we compare these results with an example from taipei taiwan that uses 9 arcsec srtm data which are globally available the use of higher resolution ned data recovers finer scale variations in topographic gradient which better correlate to geological and geomorphic features in particular at the transition between hills and basins warranting their use over 30 arcsec srtm data where available however statistical analyses indicate little to no improvement over lower resolution topography when compared to v s 30 measurements suggesting that some topographic smoothing may provide more stable v s 30 estimates furthermore we find that elevation variability in canopy based srtm measurements at resolutions greater than 30 arcsec are too large to resolve reliable slopes particularly in low gradient sedimentary basins

testing the applicability of correlations between topographic slope and vs30 for europe in the past few years a series of articles have been published concerning the use of topographic slope from digital elevation models dems constructed through remote sensing satellite imaging to give first order estimates of national earthquake hazards reduction program nehrp site classes based on the average shear wave velocity in the top 30 m vs30 wald and allen 2007 we evaluate the potential applicability of these methods taking advantage of a large 706 sites new database of measured and estimated vs30 values and their topographic slopes for locations in europe and the middle east novel statistical tests are performed to evaluate the predictive power of the procedure in this region we evaluate the percentage of sites correctly classified misclassified for each site class for active and stable regimes we also analyze the marginal distributions of the input vs30 and slope values and their impact on the vs30 slope correlations and we evaluate whether the method performs better than does chance we also consider the surface geology of sites and investigate whether differences in geology can help explain why certain sites are poorly classified by the method finally we use the city of thessaloniki greece as a test case for comparison between the results of a recent microzonation and the site classes predicted by vs30 slope correlations our results show that the method does a better job than blind chance for all site classes in active regions but only for class b rock and to a lesser extent class c stiff soil sites located in stable areas although the conclusions for stable areas are based on limited data we recommend that site classifications based on the vs30 slope correlations proposed by wald and allen 2007 be used only for regional or national and not local or site specific first order studies in active parts of europe and only in the absence of other more detailed information excluding sites inside small basins or those with special geological conditions that may affect results e g flat lying volcanic plateaus carbonate rocks continental glaciated terrain or a coastal location if slope is not calculated using bathymetric data

mantle derived guyanaite in a cr omphacitite xenolith from moses rock diatreme utah guyanaite naturally occurring crooh has been identified in a xenolith of cr rich omphacitite from the moses rock diatreme in the navajo volcanic field of the southwestern united states it occurs as the dominant phase in small clusters of accessory minerals intergrown with kosmochlor rich omphacite zincian chromite eskolaite and carmichaelite the assemblage is interpreted as the result of metasomatism of chromite bearing serpentinite by slab derived fluids during subduction of the farallon plate in laramide time at the time of entrainment of the xenolith the rock was undergoing prograde metamorphism with guyanaite dehydrating to eskolaite plus water this reaction and the coeval dehydration of the inferred accompanying host serpentinites which would have been much more volumetrically significant provided water for hydration of the subcontinental upper mantle contributing to uplift of the colorado plateau recognition of guyanaite as a component of a subducted slab supports recent proposals based on laboratory experiments that high pressure polymorphs of other common crustal oxy hydroxide minerals such as boehmite and goethite i e high pressure alooh and feooh can also transport and store water in the mantle

on oriented ilmenite needles in garnet porphyroblasts from deep crustal granulites implications for fluid evolution and cooling history abstract garnet porphyroblasts from a litho assemblage containing aluminous granulite and quartzofeldspathic gneisses of the eastern ghats granulite belt india contain nanometer to micrometer thick ilmenite needles oriented crystallographically petrographic and chemical analyses reveal that garnet was formed by dehydration melting reaction s of titaniferous biotite in an oxidized condition elevated oxygen fugacity might have promoted enrichment of ti bearing andradite component of garnet porphyroblasts formed during pre to peak metamorphic condition in appropriate bulk chemistry during the post peak cooling history ti bearing components in garnet decomposed to rhombohedral oxide solid solution ilmenite hematite detailed transmission electron microscopic study of the host garnet and ilmenite solid solution indicates that though there is an overall parallelism of 011 plane of host garnet and 011 plane of ilmenite structural coherence between the two phases was progressively lost during growth from thin to thick needles appropriate cooling rate from high temperature peak metamorphic condition arguably promoted growth of ilmenite solid solution through reaction exsolution process within garnet porphyroblasts

downstream variations in the width of bedrock channels field surveys of channel width w and drainage area a in bedrock channel reaches reveal relationships where w 5 ca b similar to the classic hydraulic geometry of alluvial channels data from five mountain channel networks support the assumption used in many landscape evolution models that an alluvial hydraulic geometry relationship where b 5 0 3 0 5 holds for bedrock channel systems although there is substantial local variability in channel width in bedrock channel systems there is no systematic difference in width versus drainage area relations for the surveyed bedrock and alluvial reaches in sedimentary lithologies in coastal oregon and washington in contrast bedrock channels were narrower and therefore had deeper flow than alluvial channels with equal drainage areas in the granite and limestone terrain of the yuba river california in addition data from the mokelumne river show that bedrock channel width decreases substantially downstream at the contact between relatively weak limestone and more erosion resistant granite but that channel slope does not change appreciably across contacts between these two lithologies data from coastal oregon drainage basins further show systematic channel widening after flood flows and debris flow impacts we conclude that downstream variations in the width of bedrock channels generally follow traditional hydraulic geometry relations but also reflect the local influence of longitudinal patterns of bedrock erosivity and disturbance history

peridotite xenoliths in silica rich potassic latite from the transition zone of the colorado plateau in north central arizona potassic latite in the transition zone of the colorado plateau near chino valley arizona contains abundant eclogite and amphibolite xenoliths and minor websterite and pyroxenite xenoliths one unit contains peridotite xenoliths analyzed samples have mg ratios of 68 and 71 58 and 63 wt sio2 and are enriched in potassium and other large ion lithophile lil elements rare earth element ree patterns are light ree enriched with la greater than 100 times chondritic abundance the peridotite xenoliths are partly to totally altered but contain remnant olivine orthopyroxene and clinopyroxene one harzburgite nodule also contains spinel mineral compositions from the xenoliths are relatively refractory and similar to those in other spinel peridotite xenoliths from the colorado plateau geothermometry on olivine spinel and two pyroxene pairs indicates equilibration temperatures of less than 800 c for the peridotite nodules the relatively low temperatures calculated from mineral equilibria are consistent with temperature estimates for other mantle nodules from under the colorado plateau

dating fluvial terraces with and profiles application to the wind river wyoming abstract fluvial strath terraces provide a record of river incision and the timing of climatic perturbations to the fluvial system dating depositional surfaces like terraces that are older than the range of 14 c however is difficult we employ a cosmogenic radionuclide crn profile technique that addresses a major problem of crn dating on such surfaces nuclide inheritance by measuring 10 be and 26 al profiles we constrain the exposure age and the mean crn inheritance for the deposit the crn profile also yields a self check on the assumptions underlying the method we report our attempts to date terraces along the wind river wy like many sequences of western north american fluvial terraces these are inferred to reflect oscillation between glacial and interglacial conditions in the headwaters previous dating of some of these terraces and the associated terraces and glacial deposits makes this a unique location to compare dating methods dates from five sites along the bull lake glacial correlative terrace wr 3 are 118 125 ka which agrees with dates on bull lake age moraines and independent age estimates on the terrace and is consistent with the model of terrace glacial relationship crn inheritance is significant and highly variable requiring it be considered despite the additional sampling complexity assuming all inheritance in wr 3 deposits arises during exhumation in the headwaters we obtain minimum mean rates of exhumation of 13 130 m my for the source rocks alternatively assuming the crns are inherited during clast transport the time of fluvial transport from source to terrace is 10 ka it increases downstream and is lower for sand than cobbles the crn ages for older terraces wr 7 300 ka and wr 15 510 ka are lower by 50 than previous estimates based on tephrochronology the most plausible explanation is eolian deflation of a once thicker loess cover on the terrace surfaces mean thicknesses of loess of 0 5 1 5 m are required to reconcile these concentrations of crn with the previous estimates of age difficulty in dating the older terraces emphasizes that geologic caution independent estimates of age and multiple sample sites should still be part of dating depositional surfaces with crns even when employing the inheritance correction technique

the application of computational fluid dynamics to natural river channels three dimensional versus two dimensional approaches this paper addresses the recent trend in fluvial geomorphology towards using computational fluid dynamics to explore the adjustment between flow processes sediment transport and river channel morphology it aims to evaluate the extent to which three dimensional 3d models improve predictive ability and prediction utility compared to two dimensional 2d applications this is achieved through comparing the predictions of both 3d and 2d models with high quality field data identical boundary conditions obtained from a confluence within a gravel bed river system with high relative roughness are defined for each model evaluation of the 3d model suggests that there is a fundamental limitation upon model predictive ability due to problems of specifying topographic complexity however comparison with the 2d model shows that the 3d model has a higher predictive ability particularly if the 2d model is not corrected for the effects on flow structure of secondary circulation further the 3d model provides more reliable estimates of bed shear stress and other more useful information such as the three dimensional flow field important for mixing processes this suggests that there is significant merit in the move towards 3d models but that research is required to incorporate methods developed in other fields for dealing with boundary condition uncertainties

multiscale site response mapping a case study of parkfield california the scale of previously proposed methods for mapping site response ranges from global coverage down to individual urban regions typically spatial coverage and accuracy are inversely related we use the densely spaced strong motion stations in parkfield california to estimate the accuracy of different site response mapping methods and demonstrate a method for integrating multiple site response estimates from the site to the global scale this method is simply a weighted mean of a suite of different estimates where the weights are the inverse of the variance of the individual estimates thus the dominant site response model varies in space as a function of the accuracy of the different models for mapping applications site response models should be judged in terms of both spatial coverage and the degree of correlation with observed amplifications performance varies with period but in general the parkfield data show that 1 where a velocity profile is available the square root of impedance sri method outperforms the measured v s 30 30 m divided by the s wave travel time to 30 m depth and 2 where velocity profiles are unavailable the topographic slope method outperforms surficial geology for short periods but geology outperforms slope at longer periods we develop new equations to estimate site response from topographic slope derived from the next generation attenuation nga database