reply to comments by h bjornsson et al on iceland as a heat island 1 bjornsson et al 2005 hereinafter referred to as bjj make two critical points about our paper on iceland douglass et al 2005 the first is that bjj s own analysis of temperature trends in iceland does not support our conclusions that recent temperature increases in iceland are due to variations in thermal heating the second is that one of bjj s maps is not the same as our corresponding map despite having originated in the same data set the authors first point is moot because they only reinforce our actual findings below we briefly discuss but do not immediately resolve the map problem 2 in the paper we note that iceland s considerable geothermal activity suggests a connection to the observed data but after pointing out the quantitative inadequacy of the geothermal hypothesis we state the temperature trends we observe must be due to complex persistent microclimate effects that do not conform to simple forcing theory and which involve quite large positive feedbacks even in our introduction we point out the quantitative results and refer to them as an unresolved puzzle bjj also refer to our observation of the extended nature of the warming trend as a contention that the geothermally enhanced warming extends over an area far larger than iceland emphasis ours this was neither said nor implied in our paper the large extent of the warming trend was presented as observed fact not contention and with no specific claim that the warming was geothermally enhanced the mapping discrepancy may be related to different methods of data conversions from the original gaussian grid to a 2 5 2 5 grid our published map was produced by a bilinear interpolation program gg2ll which is found at the web site containing the ncep data kistler et al 2001 data available at http dss ucar edu datasets ds090 2 data monthly we are looking into the discrepancy further and at this time can remark only that either version of the 2 m map under discussion is generally consistent with both our higher altitude maps and our conclusions 3 we welcome bjj s alternative hypothesis that changes in sea ice cover may have caused the large observed warming trend indeed one of the purposes of our paper was to call attention to this interesting anomaly one hopes that the extensive literature quoted by the authors can produce a quantitative explanation we are not ready to accept the authors hypothesis that the local anomaly is simply part of a global warming trend especially as it applies to the time period we studied as shown by douglass et al s 2005 figures 1a and 1b the anomaly in question is unique to latitudes at and above that of iceland 4 we take this opportunity to remind readers that the observed anomalies are not simply at the surface a finding that tends to be obscured by this discussion was that the 1979 1996 anomaly has an altitude effect whose existence implies a strong long term correlation in warming and cooling processes at different altitudes the sea ice hypothesis may be consistent with this but a quantitative explanation remains to be found

effects of meteorological and hydrogeological factors on gross recharge percentage at unconfined sandy aquifers with an equatorial climate a thorough understanding of rainfall recharge processes and their controlling factors is essential for management of groundwater systems this study investigates the effects of various meteorological and hydrogeological factors on the gross recharge percentages the rainfall recharge relationships and the recharge threshold values for unconfined sandy aquifers under an equatorial climate among the meteorological factors investigated rainfall intensity was found to have the most significant impact on the gross recharge rate the effects of potential evaporation rate relative humidity and air temperature on the gross recharge percentage were significant when the vadose zone thickness is larger than 2 5 m the recharge threshold values were found to depend strongly on the vadose zone thickness the rainfall recharge relationships could generally be well defined by a normal log relationship the rainfall recharge relationships derived here are applicable to yield estimates of gross recharge percentages for unconfined sandy aquifers under an equatorial climate using rainfall intensity and vadose zone thickness as input variables in this study a theory was developed and validated to provide physical explanations for the observations based on the residence time of the percolated rainwater within the vadose zone among the soil hydraulic parameters tested porosity and saturated hydraulic conductivity were found to have the most pronounced effects on the gross recharge percentage utilizing the sensitivity results and the theory derived an approach was developed for extending the application of the derived rainfall recharge relationships to other sand textures the approach was found to be capable of producing rough and fast estimations of gross recharge percentage for other sand textures copyright 2007 john wiley sons ltd

a comparison of modeling approaches for steady state unconfined flow abstract the dupuit forchheimer the fully saturated flow and the variably saturated flow models are compared for problems involving steady state unconfined flow through porous media the variably saturated flow model is the most comprehensive of the three and requires more parameters the performances of the three models are compared for different soil properties problem dimensions and flow geometries there are certain types of problems where the simpler models may yield satisfactory results for soils with large pores and or broad pore size density functions the variably saturated flow model solutions to steady state problems approach those of the fully flow model owing to the manner in which the soil water retention curve and relative permeability function respectively affect the variably saturated flow model solutions for problems of significant size the fully saturated flow model may be sufficient as the effects of the vadose zone are relatively diminished for problems with radial symmetry e g steady flow to a well the fully saturated flow model performs well because the variably saturated flow model is relatively insensitive to the parameters describing the soil properties as the amount of vadose zone flow compared with the total flow is relatively insignificant in such problems

evolution and thickness of the lithosphere beneath coastal california many of the tectonic features of the california coast ranges are directly related to the northward migration of the mendocino triple junction along the western edge of north america during the past 20 to 30 m y at the triple junction the western edge of the north american plate slides off the relative northward moving and subducting gorda plate leaving the thin western edge in direct contact with asthenosphere upwelling to fill the space vacated by the underlying gorda plate two dimensional time dependent thermal modeling of this process constrained by teleseismic delay studies is used to construct a map of lithospheric thickness of coastal california among the implications of this map are that 1 the high heat flow in the coast ranges can be almost entirely accounted for by the asthenospheric upwelling associated with the migrating mendocino triple junction 2 the general elevation and the late cenozoic volcanism in the california coast ranges are responses to a zone of unusually thin 20 to 45 km lithosphere that extends southward behind the mendocino triple junction and 3 the course of some segments of the san andreas fault in both central and southern california appear to deviate from a deeper more fundamental transform boundary separating the pacific and north american plates

tide induced seawater groundwater circulation in shallow beach aquifers summary in this paper we investigated the tide induced seawater groundwater circulation in shallow beach aquifers using the finite element model marun the numerical solutions were generalized using a dimensionless formulation from a dimensionless tidal period and a dimensionless beach slope of 10 we obtained results that apply to a wide range of beach permeabilities from 10 4 m s to 10 3 m s beach slopes from 3 16 to 31 6 tidal amplitude 0 3 m 2 m and period diurnal or semidiurnal the numerical simulations demonstrated the following the maximum darcy velocity always occurs at the intersection of the watertable and the beach surface the offshore beach groundwater is almost stagnant compared with the onshore groundwater flow which may explain the previous observations that the major portion of the seaward groundwater seepage usually occurs in the shallow part of the submerged beach the outflow from the seepage face accounts for 41 97 average 55 of the outflow from the intertidal zone the amount of seawater infiltrating into the intertidal zone in a tidal cycle increases with the beach permeability and decreases when the inland recharge increases and ranges from 35 5 m 3 yr 1 m 1 to 505 8 m 3 yr 1 m 1 for all the cases considered smaller beach slopes smaller inland freshwater recharges and or greater beach permeability lead to larger saltwater plumes in the intertidal zone of the beach the results are in line with the existing results of field observations and numerical simulations by previous researchers a 2008 elsevier b v all rights reserved

lithospheric and upper mantle structure of southern tibet from a seismological passive source experiment fifteen seismic stations were operated with about 20 km spacing in southern tibet across the zangbo suture the collision zone between india and asia between may and october 1994 as part of the international deep profiling of tibet and the himalaya project indepth ii for wide angle recording of the controlled source experiment and for passive earthquake recording in addition a dense deployment 4 km spacing of stations within the german depth profiling of tibet and the himalayas gedepth project also recorded a number of teleseismic earthquakes the third data source used in this study is the records of the permanent broadband station at lhasa teleseismic records have been obtained in sufficient quantity and quality to derive an image of the structure of the lithosphere and upper mantle from p to s converted phases important results are as follows the moho at 70 80 km and a second discontinuity at 50 60 km depth are observed over the entire profile south and north of the zangbo suture the data from the gedepth dense array enable the detection of inclined structures penetrating the crust at the zangbo suture a pronounced low velocity zone exists north of the zangbo suture at about 10 20 km depth the locations of the upper mantle discontinuities at 410 and 660 km depth are in agreement with the global reference model iasp91 kennett 1991 over a large region of the himalaya and southern tibet

seismic structure of the lithosphere from teleseismic converted arrivals observed at small arrays in the southern sierra nevada and vicinity california 21 well distributed teleseisms 30 to 100 distance were recorded by mixed broad band bb and short period sp seismic arrays at mineral king mk and horseshoe meadow hm in the southern sierra nevada and at darwin plateau dp between the inyo and argus ranges these arrays permit identification and separation of direct p and s arrivals reflections from topography scattered energy and arrivals from different back azimuths multipath arrivals p to s conversions can be identified from beamed bb or sp seismograms least squares time domain processing recovered single event receiver functions from these beamed seismograms converted phases attributable to the moho are clear and uncomplicated at dp ps p times of 3 9 4 2 s correspond to crustal thicknesses of 31 33 km assuming a mean p crustal velocity of 6 2 km s and a poisson s ratio of 0 255 ps p times at hm eastern sierra are 3 9 4 6 s 32 37 km excepting some unusual seismograms from events at back azimuths of 225 239 mk western sierra times for ps p show a strong e w asymmetry 3 9 4 1 s 31 33 km from the east and 4 8 5 3 s 39 42 km from the west the mk arrivals from the east are multiple and substantially weaker by comparison with hm and dp these results confirm the absence of a thick crust under the southern high sierra inferred from both a refraction experiment coincident with this experiment and some earlier studies at dp the moho event follows an intracrustal negative polarity event defining the top of an s wave low velocity zone this feature dips west under the sierran crest at hm but is absent farther west at mk this feature appears to be a manifestation of extensional strain and thus indicates that the surficially undeformed sierra overlies a tectonized lower crust sub moho energy is absent under the basin and range dp but is conspicuous under the high sierra at positive arrivals 7 3 s mk and 9 s hm after the p these arrivals might be from the base of a low velocity low density upper mantle body supporting the sierra

experimental and numerical assessment of transient stream aquifer exchange during disconnection understanding the state of connection processes of stream aquifer systems is of great interest for water resources management particularly in semi arid regions and where groundwater is extracted in the vicinity of a river bank here we present a combined experimental numerical study to explain physical processes involved in disconnected stream aquifer systems a stream aquifer sand box was built to measure the infiltration rate through the stream bed during aquifer drainage the pressures in the saturated zone of the aquifer and the infiltration rate were measured in order to quantify the fluid flow in this system the transient transitional stage between connected and disconnected flow regimes which was obtained experimentally is characterised by a maximum infiltration rate across the stream bed before a decrease towards a constant value this behaviour is analysed by means of transient numerical simulations using relevant hydrodynamic parameters the importance of the drainage kinematics and unsaturated zone parameters for the temporal variation of the infiltration rate is demonstrated the possible occurrence of a maximum infiltration rate value during the transitional stage is characterised into a general view of the stream aquifer disconnection with direct implications for pumping near a stream

rainfall infiltration derived submarine groundwater discharge from multi layered aquifer system terminating at the coastline this article investigates the quantity of submarine groundwater discharge sgd from a coastal multi layered aquifer system in response to constant rainfall infiltration the system comprises an unconfined aquifer a leaky confined aquifer and an aquitard between them and terminates at the coastline an approximate analytical solution is derived based on the following assumptions i flow is horizontal in the aquifers and vertical in the aquitard and ii flow in the unconfined aquifer is described by nonlinear boussinesq equation the analytical solution is compared with numerical solutions of the strictly two dimensional nonlinear model to validate the model assumptions used for the analytical solution the sgd from the leaky confined aquifer increases with the inland rainfall infiltration recharge and the specific leakage of aquitard the maximum sgd ranges from 1 87 to 10 37 m3 per day per meter of shoreline when rainfall infiltration ranges from 18 2 to 182 mm year and the specific leakage of aquitard varies from 10 9 to 10 1 l day copyright 2011 john wiley sons ltd

seismic images of the deep structure of the san andreas fault system central coast ranges california three dimensional inversion of teleseimic p wave travel time residuals recorded at the u s geological survey central california array has resolved small scale approx tens of kilometers crustal and upper mantle heterogeneity down to depths of 90 km beneath the california coast ranges upper crustal lateral velocity variations of 8 correlate closely with surface geology lower than average velocities are associated with thick tertiary sedimentary fill and higher than average velocities with basement exposures lower crustal velocity heterogeneity of 4 appear to reflect crustal thickness variations a thinner crust is indicated southwest of the san andreas fault and northwest of san pablo bay a linear zone of low velocities 0 to 40 subparallel to the san andreas fault was resolved in the upper mantle the preferred interpretation is that the low velocities indicate a narrow upwarp of asthenosphere to unusually shallow depths approx 45 km beneath the coast ranges such an unusual upper mantle structure may have been produced by the northwestward migration along the california coast of a transiently unstable mendocino triple junction the inversion results also indicate the possibility of partial decoupling of the crust from the upper mantle

the lithosphere asthenosphere boundary in the tien shan karakoram region from s receiver functions evidence for continental subduction 1 significant s to p converted wave energy from the crust mantle and lithosphere asthenosphere boundaries the moho and the lab respectively has been observed in the tien shan and karakoram orogenic belts and used for the determination of the thickness of the crust and the mantle lithosphere the moho lies at depths of 45 65 km in the tien shan and adjacent regions and deepens to 70 km depth in pamir and karakoram the thickness of the lithosphere varies between 90 and 120 km underneath the tien shan and increases to a value of 160 km beneath the tarim basin to the south of the tarim basin the lower boundary of the asian lithosphere can be clearly followed to a depth of 270 km beneath central pamir and karakoram while the indian lithosphere is observed beneath the karakoram dipping from 130 km to 170 km towards the north the observations indicate a scenario of continental collision and subduction consistent with seismicity and the surface wave tomography results

numerical modeling of water flow below dry salt lakes effect of capillarity and viscosity abstract we investigate numerically the effects of capillarity and viscosity on density dependent flows below dry salt lakes the numerical model marun boufadel m c suidan m t venosa a d 1999a a numerical model for density and viscosity dependent flows in two dimensional variably saturated media j contam hydrol 37 1 20 is used to assess the combined and separate effects of capillarity and concentration engendered viscosity on the groundwater dynamics of a two dimensional system simulating a dry lake we found that accounting for concentration engendered viscosity effects under saturated water flow conditions gives totally different groundwater dynamics from the case where these effects are neglected however concentration dependent viscosity effects were minor when unsaturated water flow conditions were present under variably saturated flow conditions capillarity effects gave totally different hydraulics in the porous domain from the saturated flow case upwelling regions observed under saturated flow conditions were downwelling when capillarity effects were present a mesh orientation study revealed that density dependent flows were susceptible to the orientation of the diagonals of the triangular elements a discussion on the accuracy and the efficiency of the marun model in the context of density and viscosity dependent flows in two dimensional variably saturated media is also provided

crust and mantle structure across the basin and range colorado plateau boundary at 37 n latitude and implications for cenozoic extensional mechanism we present new evidence on the seismic velocity and density of the crust and upper mantle along a 200 km long transect across the eastern basin and range and western colorado plateau at 37 n latitude receiver functions computed from the p waveforms recorded with 10 portable broadband stations deployed along the transect were used to estimate crustal thickness variations the crust is 30 35 km thick within the eastern basin and range and increases over a distance of 100 km at the western edge of the colorado plateau reaching a maximum of approximately 45 km east of the hurricane fault the timing of crustal multiples within the reciever functions were used to estimate the v p v s of the crust along the profile and we found that the western colorado plateau crust is characterized by a high poisson s ratio 0 28 0 29 indicative of a crust with an average mafic composition we estimated the upper mantle lid thickness along our profile based on teleseismic p wave travel times and constraints provided by gravity data our data and available geophysical constraints are most consistent with a lithosphere that thickens from an average thickness of 60 km beneath the basin and range to 100 km beneath the western colorado plateau although the basin and range lithosphere may have significant thickness variations the thick strong mafic crust and thicker mantle lid under the colorado plateau can account for the relative geologic stability and subdued magmatism of the plateau during laramide compression and cenozoic extension compared to surrounding regions the crustal and lithospheric thinning across the tectonic boundary occurs over a short distance 100 km suggesting it is a geologically young feature produced by a predominantly mechanical response to late cenozoic extension our new lithosphere model at 37 n latitude is consistent with the existence in early cenozoic time of a flat subducted slab at 100 km depth and a relict sevier laramide 50 60 km thick crustal welt and 60 100 pure shear extension values of 1 6 2 0 during the late cenozoic

lithospheric structure of northern california from teleseismic images of the upper mantle teleseismic p wave travel time residuals from 120 earthquakes recorded across the u s geological survey california seismic network were used to determine the lithosphere p wave velocity structure beneath northern california a region characterized by complex interactions between the pacific north american and gorda plates lateral p wave velocity variations beneath the array were determined by inversion of 9383 travel time residuals inversion results for the crust show strong correlations to volcanic features the active volcanic fields shasta medicine lake lassen and clear lake are characterized by crustal low velocity anomalies that average approximately 6 possibly identifying partially molten magma bodies cooled solidified magma bodies beneath the extinct volcanic fields sonoma southern clear lake and sutler buttes are denoted by relative velocity highs averaging 3 the largest upper mantle velocity variations occur in the depth range 30 110 km where velocities vary from 5 5 to 9 5 these velocity variations reflect changes in the thickness and geometry of the pacific north american and gorda plates where they interact at the mendocino triple junction north of the mendocino triple junction the steep 70 east dipping portion of the gorda plate is imaged as a 5 velocity high to depths near 270 km a presumed segment of the gorda plate observed beneath the northern great valley and south of the inferred edge of the plate is characterized by a 9 velocity high in the depth range 30 70 km beneath the northern coast ranges shallow asthenosphere is imaged in the depth range 30 100 km as a pronounced southward tapering 4 low velocity zone which we interpret as the slab window results from this study provide improved constraints on gorda plate subduction evolution of the san andreas fault system and development of the lithosphere beneath western north america

imaging the colliding indian and asian lithospheric plates beneath tibet 1 a high resolution image of the base of the lithosphere from s to p converted seismic waves revealed the collision architecture of the indian and asian continental plates beneath the tibetan plateau the base of the indian lithosphere dips northward from a depth of 160 km beneath the himalayas to a depth of 220 km just south of the bangong suture the base of the asian lithosphere is nearly horizontal at the depth of 160 180 km from central to northern tibet there is a vertical gap of about 50 km between indian and asian lithospheres our observation of a well defined thick lithosphere throughout the entire plateau is not consistent with models of wholesale convective instability of a thickened mantle lithosphere which would predict a very thin asian lithosphere the hypothesized sequential southward subduction of tibetan and asian continental lithospheres leading to the growth of the tibetan plateau if correct cannot be occurring below 180 km depth our results along with available geological and geophysical data strongly support that the plateau is predominantly formed by a relatively coherent north dipping subducted indian continental lithosphere in the south which presently can be traced to the middle of the plateau and a south dipping subducted asian lithosphere in the north at a shallower depth

the lithosphere asthenosphere boundary beneath the western united states summary s receiver functions from 67 broad band seismic stations in the western united states clearly reveal the existence of a mantle discontinuity with velocity reduction downward which we interpret as the lithosphere asthenosphere boundary lab the average depth of the lab is 70 km the boundary is relatively sharp with an overall sharpness of less than 20 km the boundary is more prominent south of the mendocino triple junction where the farallon plate has completely subducted this may indicate partial melts at the base of the lithosphere caused by the upwelling of the asthenospheric flow through the slab window a double low velocity zone is observed at base of the lithosphere beneath southern sierra nevada implying a second melting zone at a depth of 100 km well correlated with previous studies of lithospheric delamination in the area

comparative study of green and ampt analysis for a falling water table in a homogeneous sand profile equations are developed for a green and ampt type analysis for a falling water table regime in an initially saturated homogeneous profile of porous material both with and without the presence of an applied surface flux of constant magnitude the predictive capability of these green and ampt equations for a homogeneous medium sand is then tested against results obtained from a computer based numerical analysis of the differential equation describing water movement in unsaturated porous media three simulations with different rates of water table fall are described for the zero surface flux case with one of these rates also being used when an applied surface infiltration flux is included in the system comparisons with green and ampt results are then made for these simulations in terms of the discharge time relationship the position of the draining front with time and the thickness of the draining capillary fringe with time in certain cases the approximate analysis is shown to agree with the numerical simulations quite satisfactorily while in others notably those involving a more rapid water table fall the differences are significant

seismic evidence for asthenospheric updoming beneath the western bohemian massif central europe 1 detailed images of the lithosphere beneath the western bohemian massif were obtained by analysis of more than 8500 p receiver functions at the intersection of regensburg leipzig rostock zone and eger rift crustal thickness decreases to 26 km from approx 31 km in the surroundings the receiver functions display a positive phase at about 6 s delay time and a strong negative phase at 7 to 8 s which coincides with an area of moho updoming co2 mantle derived degassing and earthquake swarm activity these phases can be modeled by a velocity increase at 50 km and a velocity decrease at 65 km depth the velocity decrease observed over an area of 5300 km2 gives evidence for local asthenospheric updoming and or a confined body of partial melt which might be the cause for high co2 mantle fluid flow and earthquake swarm activity in this recently nonvolcanic intracontinental rift area

iceland as a heat island 1 iceland is a strong localized source of non eruptive volcanic warming and cooling temperature trend maps show that this phenomenon is localized to an area of about twice that of iceland with altitude the area remains constant but the phenomenon weakens and changes sign upon passing through the tropopause the effect s magnitude implies a large positive feedback according to a conventional climate forcing estimate this phenomenon is unique in that it is not observed for the other major volcanic islands

super deep low velocity layer beneath the arabian plate 1 s and p receiver functions reveal indications of a low s velocity layer at 350 410 km depths beneath the arabian plate a similar layer was previously found beneath the kaapvaal craton in southern africa and tunguska basin of the siberian platform we hypothesize that the boundary at 350 km depth may separate dry mantle root of the arabian plate from the underlying wet mantle layer this boundary is not found beneath the gulf of aden where the root is destroyed by sea floor spreading

variably saturated modeling of transient drainage sensitivity to soil properties abstract numerical analysis of a transient two dimensional rectangular symmetry unconfined drainage problem using a variably saturated flow model shows that the location of the phreatic surface and the height of the seepage face are functions of the capillary forces exerted in the vadose zone a sensitivity analysis investigating the effects of independent variations in the saturated hydraulic conductivity and the two van genuchten parameters is compared to one performed where the saturated hydraulic conductivity is functionally related to the van genuchten parameters the relationship between these descriptive soil parameters which may be used to describe the pore size density function of a porous medium and the saturated hydraulic conductivity is surmised based upon limited empirical evidence expressing the permeability as a function of these soil properties reverses the sensitivities of the variably saturated model to the van genuchten parameters from the preliminary work performed herein consideration of the number of degrees of freedom used when performing a sensitivity analysis is shown to warrant great care if the predicted sensitivities are to have meaningful physical interpretations

subcratonic low velocity layer and flood basalts 1 teleseismic recordings of several seismograph stations are processed with the aid of the s receiver function technique farra and vinnik 2000 the data provide evidence of a strong reduction of s velocity at a depth around 360 km station bosa and 280 300 km station lbtb in the east of southern africa a similar feature is found in the tunguska basin of the siberian platform from the recordings of station nril in both regions large volumes of flood basalts have been erupted 190 180 ma and 250 ma ago respectively the coincidence suggests a causal relation between the two phenomena this relation implies that the low velocity anomalies migrate with the plates

steady seepage in trenches and dams effect of capillary flow steady seepage from two dimensional domains is investigated using a dimensionless formulation for variably saturated media that depends on three dimensionless parameters m n and the parameter m is the product of the anisotropy ratio and the squared ratio of the vertical length scale to the horizontal length scale the parameter n increases with the uniformity of the pore sizes and represents the ratio of the domain height to the height of the capillary fringe our modeling results show that the seepage face height in rectangular domains is always larger than the seepage face height computed from saturated flow models the results also show that the seepage face height increases with increasing m increasing n and or decreasing the outflows computed from the present model are always larger than the outflows computed by the dupuit assumption nomographs for rectangular and trapezoidal domains simulating trenches and dams are presented

timing of volcanism in the sierra nevada of california evidence for pliocene delamination of the batholithic root recent seismic experiments across the southern sierra nevada california show that the range lacks a thick crustal root xenolith studies indicate that delamination and loss of much of the lower crust may have occurred between 10 and 3 ma we estimate that delamination occurred ca 3 5 ma on the basis of a sudden pulse of mafic potassic magmatism within and just east of the sierra nevada from 4 to 3 ma this pulse interrupted the low level of volcanism that had prevailed regionally since 13 ma delamination could have promoted magmatism via decompression melting heating of the shallow lithosphere by upwelling asthenosphere and foundering of crustal rocks into the mantle and could have provided dynamic support to the range foundering of the lower crust may have occurred spontaneously owing to negative buoyancy or may have been triggered by extension between the sierra nevada and death valley

crustal thickness map of the western united states by partitioned waveform inversion the partitioned waveform inversion method nolet 1990 was used to obtain a new crustal thickness map of the western united states we fitted 200 seismograms containing higher and fundamental mode rayleigh waves for events and stations in the western united states which provided average crustal thickness constraints between each source receiver pair all these constraints were combined in a linear inversion to obtain a crustal thickness map local crustal thickness estimates from published seismic reflection refraction work were used as additional constraints to overcome deficiencies of path coverage in some areas the resulting crustal thickness map shows thicker 45 km crust beneath the cascades thick 40 km crust beneath the sierra nevada thin 30 km crust beneath the basin and range and thick greater than 45 km crust beneath the colorado plateau the boundary between the colorado plateau and the southern leg of the basin and range is a prominent feature of the model thick crust is seen at the bend of the san andreas fault near los angeles our model is broadly consistent with the crustal thickness map of mooney and weaver 1989 a quantitative comparison with the crustal thickness model 3smac nataf and ricard 1996 was performed by inverting for a model that deviates least from it results show that we are able to retain most of the features of that model while maintaining a good fit to the surface wave and point constraint data