s velocity variations beneath north america 1 we investigate s velocity variation in the upper mantle beneath north american to better understand the effects of data heterogeneity model parameterization and regularization to this end we analyzed and fit regional s and rayleigh wave trains generated by earthquakes around north america that occurred between the years 2000 through 2006 including waveforms from the transportable array stations of earthscope s usarray these new data were combined with constraints used for the 3 d s velocity model na04 in order to create a new model na07 another model was created from a suite of good fit models to provide a useful guide for model velocities and uncertainties by estimating ranges of probable velocity variations throughout the upper mantle we find that the southern and eastern edges of the north american craton appear to be defined by paleozoic orogens rather than proterozoic ones on average the archean portion of the craton is 200 km thick while the paleozoic part averages 175 km thick with an 80 m s lower s velocity the horizontal gradients in velocity are over 1 0 100 km at the western margin of the craton 0 5 100 km in the south and 1 100 km at the eastern margin

deep mantle forces and the uplift of the colorado plateau 1 we introduce a quantitative model of global mantle convection that reconstructs the detailed motion of a warm mantle upwelling over the last 30 ma towards the interior of the southwestern usa from observed present day mantle heterogeneity the onset and evolution of uplift in the central basin and range province and colorado plateau during this time is determined by tracking the topographic swell due to this mantle upwelling we show that 1 the extension and basaltic volcanism post 25 ma in the central basin and range coincides with the arrival and eastward progression of this upwelling and 2 dynamic uplift of the southern colorado plateau totaling about 1 km transpired in the last 20 ma since 10 ma the center of uplift continued northeastward from the southwestern rim of the plateau consistent with a young grand canyon model and eastward sweep of magmatism in the western colorado plateau

high resolution receiver function imaging reveals colorado plateau lithospheric architecture and mantle supported topography 1 after maintaining elevations near sea level for over 500 million years the colorado plateau cp has a present average elevation of 2 km we compute new receiver function images from the first dense seismic transect to cross the plateau that reveal a central cp crustal thickness of 42 50 km thinning to 30 35 km at the cp margins isostatic calculations show that only approximately 20 of central cp elevations can be explained by thickened crust alone with the cp edges requiring nearly total mantle compensation we calculate an uplift budget showing that cp buoyancy arises from a combination of crustal thickening heating and alteration of the lithospheric root dynamic support from mantle upwelling and significant buoyant edge effects produced by small scale convecting asthenosphere at its margins

cocorp deep reflections moho at 50 km 16 s beneath the colorado plateau cocorp deep reflection data on the colorado plateau reveal complex reflections to about 16 s two way travel time 50 km beyond which there is an abrupt decrease of reflectivity this boundary is interpreted to represent the moho an inference consistent with the existing but limited refraction data sets when they are reconciled with the recent independent determination of an 8 10 8 15 km s pn velocity beneath the colorado plateau this 50 km depth to moho and 8 10 8 15 km s pn velocity for the colorado plateau closely resembles that of the high plains just east of the rocky mountains the absence of continuous strong reflections at the moho suggests that the moho beneath the colorado plateau is a transition not a velocity step function on the scale of the reflection experiment the reflection boundary may represent the base of complex and discontinuous reflectors of the crust and crust mantle transition below which the mantle may be largely peridotite with a velocity of 8 1 km s these results strongly reinforce the suggestion that the moho on deep reflection data in relatively stable continental regions is represented by an abrupt decrease in reflectivity below which the mantle is relatively seismically transparent

broadband seismic background noise at temporary seismic stations observed on a regional scale in the southwestern united states background noise power spectral density psd estimates for 54 pass cal colorado plateau rio grande rift great plains seismic transect la ristra stations were computed using data from 1999 to 2000 at long periods 0 01 0 1 hz typical vertical noise levels are approximately 12 db higher than the nearby global seismic network gsn borehole station anmo but horizontal power spec tral density psd noise levels are approximately 30 db higher long period noise levels exhibit essentially no spatial correlation along the la ristra transect indi cating that local thermal or atmosphere driven local slab tilt is the dominant source of noise in this band between 0 1 and 0 3 hz typical noise levels are dominated by naturally occurring microseismic noise and are essentially identical to those observed at anmo at short periods 0 3 8 hz typical noise levels along the network exceed anmo levels by approximately 15 db with the highest levels corresponding to proximity to cultural noise sources no significant day night variations were observed in the microseismic band however both low and high frequency noise levels show an increase of up to 8 db in median midday versus midnight noise levels we find that the major shortcomings of these shallow passcal style temporary vaults rela tive to a gsn style borehole installation are increased susceptibility to long period horizontal 20 sec noise and to surface noise sources above approximately 2 hz although the high frequency near surface noise field is unavoidable in shallow vaults we suggest that increased understanding and mitigation of local tilt effects in shallow vaults offers the possibility of significantly improving the long period noise environment

numerical simulation of barotropic jets over a sloping bottom comparison to a laboratory model of the northern current 1 in order to study the role of a sloping bottom on the mesoscale variability of the northern current a series of barotropic laboratory experiments was performed on a rotating table setup the present work is devoted to a numerical model which aims to simulate these laboratory conditions in order to further investigate aspects which are difficult to treat in the laboratory the onset of instabilities the influence of the velocity profile the relative position of the jet over the slope and the influence of the jet width on the resulting instabilities are discussed the robustness and the origin of a shelf break topographic rossby wave detected in our westward laboratory flows is also discussed the barotropic model for westward currents such as the northern current with rossby numbers in the range ro 0 1 0 2 predicts wavelengths of 50 75 km similar to those observed in sst images the periods associated with the model instabilities 3 3 3 8 days would be close to a 3 5 day band of mesoscale activity recorded from current meter devices in the gulf of lions which lies out of the traditionally considered baroclinic instability theory other particularities such as the up slope migration of the northern current and the increasing mesoscale activity for increasing jet velocities can also be explained through the present model these results would point out barotropic instability as a factor to consider apart from the traditional idea of baroclinic instability in order to partially explain the northern current mesoscale variability

crustal structure and evolution beneath the colorado plateau and the southern basin and range province results from receiver function and gravity studies over the past several decades contrasting models have been proposed for the physical and chemical processes responsible for the uplift and long term stability of the colorado plateau cp and crustal thinning beneath the basin and range province brp in the southwestern united states here we provide new constraints on the models by modeling gravity anomalies and by systematically analyzing over 15 500 p to s receiver functions recorded at 72 usarray and other broadband seismic stations on the southwestern cp and the southern brp our results reveal that the brp is characterized by a thin crust 28 2 0 5 km a mean vp vs of 1 761 0 014 and a mean amplitude r of p to s converted wave relative to that of the direct p wave of 0 181 0 014 that are similar to a typical continental crust consistent with the model that the thin crust was the consequence of lithospheric stretching during the cenozoic the cp is characterized by the thickest crust 42 3 0 8 km largest vp vs 1 825 0 009 and smallest r 0 105 0 007 values in the study area in addition many stations on the cp exhibit a clear arrival before the p to s converted phase from the moho corresponding to a lower crustal layer of about 12 km thick with a mafic composition we hypothesize that the lower crustal layer which has an anomalously large density as revealed by gravity modeling and high velocities in seismic refraction lines contributed to the long term stability and preuplift low elevation of the colorado plateau

dating crust mantle separation re os isotopic study of mafic xenoliths from central arizona mafic deep crustal and shallow upper mantle xenoliths hosted in the chino valley and camp creek latites of central arizona have 187os 188os 0 216 to 1 51 ratios dramatically higher than values typical of mantle peridotite 0 13 re os model ages for the xenoliths range from 0 57 to 2 3 ga with a mean of 1 1 0 6 ga consistent with the possibility that the xenoliths sample proterozoic lower crust and upper mantle underplated to the ca 1 6 1 8 ga basement combined os and sr nd pb data indicate that these xenoliths were not formed by crustal contamination of cenozoic asthenospheric melts but allow for recent interaction between old mafic materials in the lithosphere and high 87sr 86sr low 143nd 144nd melts of proterozoic lithospheric mantle the potassic latite hosts to the xenoliths also have radiogenic os indicating that they are melts of a mafic rather than a peridotitic source in the old lithosphere these data demonstrate the utility of the re os system in defining mantle separation ages or the initial time of melt extraction from a peridotitic mantle even in cases where the lithospheric mantle is remelted long after its formation

xenolithic evidence for proterozoic crustal evolution beneath the colorado plateau tertiary diatremes of the navajo volcanic field brought a wide variety of proterozoic xenoliths to the surface of the colorado plateau examination of crustal xenoliths from the navajo volcanic field diatremes permits reconstruction of proterozoic pressure temperature p t histories beneath the colorado plateau diatremes from the northwest part of the navajo volcanic field carry the greatest variety of xenoliths including metasedimentary rocks amphibolites felsic gneisses mafic granulites and crustally derived eclogites these rock types show variable degrees of hydrous alteration and evidence for complex reaction histories in contrast diatremes from the southeast part of the navajo volcanic field contain primarily mafic and felsic granulites that show fewer reaction textures and less alteration metasedimentary and eclogitic xenoliths are absent in these diatremes the p t paths from the northwest xenoliths are counterclockwise and reach temperatures as high as 850 c and pressures equal to or greater than 10 kbar later hydrous alteration occurred around 500 c and 8 12 kbar xenoliths from the southeast diatremes preserve little evidence of their p t evolution but paths involve heating and or decompression the differing rock types p t paths and alteration histories of the northwest and southeast populations suggest that proterozoic tectonism juxtaposed two distinct crustal blocks beneath the colorado plateau previous workers have postulated that the boundary between the proterozoic yavapai and mazatzal provinces occurs in the region our data support the existence of a northeast trending boundary beneath the four corners area if the eclogitic metamorphism and hydrous alteration are proterozoic in age their restricted occurrence beneath the northwest part of the plateau suggests that subduction was northwest dipping during proterozoic accretion of the mazatzal province onto north america

geophysical evidence for hydration of the crust and mantle of the nazca plate during bending at the north chile trench water transported in subducting oceanic plates plays a key role in a number of phenomena including intraslab seismicity and arc magmatism however the locus of plate hydration and water distribution in crust and mantle of plates entering subduction zones is debated we present evidence for anomalously low seismic velocities and densities of the crust and upper mantle of the nazca plate at the north chile trench crustal seismic velocities at the trench are lower than velocities of mature fast spreading crust and even lower than velocities of highly extended slow spreading crust in addition the nazca plate at the north chile trench may contain an 20 km thick upper mantle layer with 17 serpentine which implies 2 5 wt water these results document pervasive rock alteration by water percolation linked to bending related extensional faulting

raising the colorado plateau shallow marine rocks exposed on the 2 km high 45 km thick colorado plateau in the western united states indicate that it was near sea level during much of the phanerozoic isostatic calculations however illuminate the difficulty in maintaining a 45 km thick crust at or near sea level we propose that an isostatically balanced 30 km thick proto colorado plateau crust was thickened during the late cretaceous to early tertiary by intracrustal flow out of an overthickened sevier orogenic hinterland this plateau would have been supported by a thick 70 km crustal root which is proposed to have been the source region for hot and weak mid crustal material that flowed eastward from the plateau toward the low elevation proto colorado plateau

timing of colorado plateau uplift initial constraints from vesicular basalt derived paleoelevations we have developed a technique for measuring paleoelevation on the basis of the vesicularity of basaltic lava flows we are currently applying this technique to determine the timing and extent of cenozoic uplift of the colorado plateau because the technique measures paleoatmospheric pressure it is not subject to uncertainties stemming from the use of proxies that depend on environmental factors other than elevation alone vesicular lavas preserve a record of paleopressure at the time and place of lava emplacement because the difference in internal pressure in bubbles at the base and top of a lava flow depends on atmospheric pressure and lava flow thickness the modal size of the vesicle bubble population is larger at the top than at the bottom this leads directly to paleoatmospheric pressure and thus elevation because the thickness of the flow can easily be measured in the field and the vesicle sizes can be measured in the laboratory on the colorado plateau volcanic fields are generally found around the margins of the plateau basaltic lavas range in age from 0 to 23 ma present elevations range from 1 7 km to 3 3 km samples were collected from lava flows in the areas of marysvale springerville grand mesa and the san juan mountains and analyzed to determine the timing and extent of uplift the analysis of the samples using x ray computed tomography imaging and our numerical techniques for determining vesicle population statistics indicate uplift of 350 2200 m depending on age there is a clear relationship between age and amount of uplift original elevation subtracted from present elevation the results indicate slow uplift of 40 m m y between 25 ma and 5 ma only 800 m of uplift during that time and rapid uplift of 220 m m y since 5 ma 1100 m during that time these results reconcile the long standing controversy between interpretations of ancient versus recent uplift by providing an uplift history curve for the colorado plateau

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

low frequency waves in the ligurian sea during december 1977 observations of low frequency waves in the ligurian sea in december 1977 are presented from time series of thermal infrared images obtained by satellite noaa 5 the mean wavelength and phase velocity are estimated they are respectively 38 km and 18 cm s 1 these waves are analyzed as large amplitude baroclinic waves fairly good agreement is found with a two layer model

source parameters of earthquakes in and around the korean peninsula deduced from spectral analysis abstract spectral analysis of 200 seismograms from seven moderate magnitude earthquakes in the southwestern sea of japan the korean peninsula and the yellow sea is performed to determine their source parameters and to discuss their tectonic implications short and long period records of body and rayleigh waves are employed the deduced seismic moments vary from 5 9 1023 to 2 9 1025 dyn cm and the stress drops vary from 8 to 56 bar generally rather low stress drop values are obtained which suggests that materials beneath the studied region are highly fractured and softened by the high heat flow related to the opening of the sea of japan and the rise of the north china basin

the behavior of jet currents over a continental slope topography with a possible application to the northern current abstract the northern current is a slope current in the northwest mediterranean that shows high mesoscale variability generally associated with meander and eddy formation a barotropic laboratory model of this current is used here to study the role of the bottom topography on the current variability for this purpose a source sink setup in a cylindrical tank placed on a rotating table is used to generate an axisymmetric barotropic current to study inviscid topographic effects experiments are performed over a topographic slope and also over a constant depth setup the latter being used as a reference for the former with the aim of obtaining a fully comprehensive view of the vorticity balance at play the flow may be forced in either azimuthal direction leading to a westward prograde current similar to the northern current or an eastward retrograde current for slow flows eastward and westward currents showed similar patterns dominated by kelvin helmholtz type instabilities for high speed flo

paleobotanical evidence of eocene and oligocene paleoaltitudes in midlatitude western north america comparisons of the physiognomy of leaves from modern vegetation of known climates with that of eocene and oligocene fossil leaf assemblages from middle latitudes of western north america indicate paleoaltitudes comparable or higher than those at present using canonical correspondence analysis a multivariate statistical approach that includes nonlinear relationships between characters and environmental parameters we relate leaf physiognomy of fossil samples to modern vegetation of known environmental parameters including moist enthalpy of the atmosphere a thermodynamically conserved quantity of the atmosphere that varies with altitude by estimating enthalpy values for both lowland leaf assemblages and coeval interior leaf assemblages altitudes for the interior assemblages can be estimated to 890 m in northeastern washington and southern british columbia the high eocene altitudes indicate subsidence or collapse of an area undergoing crustal extension and may reflect an immediately preceding period of uplift that triggered the extension similarly other areas that have undergone cenozoic crustal extension appear to have been at least as high as they are at present three sites from the rocky mountains also indicate elevations at least as high as at present and therefore suggest subsidence either resulting from cooling of a hot upper mantle or erosion and isostatic compensation of surrounding terrain high altitudes during eocene and oligocene time in western north america appear to have been normal even in areas such as the green river basin and therefore cast doubt on the commonly inferred late cenozoic uplift of that region

circulation over a submarine canyon in the nw mediterranean 1 the circulation in blanes canyon an interruption in the nw mediterranean continental shelf north of barcelona was investigated the study employs data from oceanographic surveys carried out in the summer and fall of 2003 velocity data show that in the vicinity of the shelf break the flow is deflected along the canyon walls a cyclonic mean flow can be seen over the canyon mouth owing to vortex stretching of fluid parcels advected across the shelf break field observations are in qualitative agreement with fundamental fluid dynamic considerations based on potential vorticity conservation and friction effects at lateral boundaries evidence is given that upwelling is found near the shelf break inside the canyon in the two field experiments this upwelling extends vertically from the seasonal thermocline at about 100 m to the shelf slope front at about 200 m there is no evidence that upwelled water can reach the continental shelf

deep flow variability in a deeply incised mediterranean submarine valley blanes canyon abstract deep flow variability in blanes canyon is analyzed by means of a unique dataset in which the canyon was instrumented at its axis and at the two canyon walls from march 2003 to july 2004 the mean intensity of deep currents range between 3 5 cm s 1 at the canyon axis 1500 m and 5 4 cm s 1 upstream canyon wall 900 m a wavelet analysis shows that the energy is concentrated in the 2 30 day band and it is mainly associated to single not periodical not wave related events uncoupled at the different canyon sites an empirical orthogonal function analysis shows two main patterns of current variability explaining 65 of the total variance the first mode represents intensifications of the typical along bathymetry pattern of currents over the canyon the second mode corresponds to near bottom upwelling events along the canyon axis with water exiting the canyon through the canyon head after discussing possible forcing mechanisms it is here suggested that such deep upwelling events are associated to offshore displacements of the northern current namely the interaction of the current with the particular shape of the canyon topography at large depths 1800 m would be responsible for the observed deep upwelling events

evidence of a several day propagating wave abstract a large 8 day oscillation was recorded during several months by current meters moored at several depths and places on the continental slope off the gulf of lions in the northwestern mediterranean sea this signal is clearly associated with a propagating wave the location of the moorings the space and time scale and specific features of the signal account for a relationship between the characteristics of the wave and the mean bottom slope as supported by the results of a simple analytical model it is suggested that the bottom slope acts like a wave guide for the wave

preservation of proterozoic terrane boundaries within the colorado plateau and implications for its tectonic evolution abstract during the proterozoic the north american continent grew by the accretion of arcs onto the archean craton subsequent tectonic events affected much of the lithosphere of western north american resulting in the destruction of many of the features that reflect continental growth the colorado plateau which is centrally located within the tectonically active western portion of north america experienced only minor amounts of volcanism during subsequent magmatic events and has undergone comparatively little internal deformation during the remainder of the precambrian and phanerozic despite the occurrence of some significant tectonic events because the lithosphere of the plateau has not been significantly reworked by tectonic events it may have retained structures since accretion that give insight into processes of continental growth the crust of the southeastern portion of the colorado plateau revealed here through seismic data recorded by the temporary spe and la ristra arrays is greater than 40 km thick and possesses distinct changes in intercrustal layering and the character of the moho the moho appears quite dim towards the center of the plateau and much brighter along its southeastern margins connecting changes in crustal features that are common between the two arrays indicates a northeastern structural trend that matches the pattern of gravity anomalies in the region differences in crustal structures between terranes extend across much of the crust suggesting that entire distinct crustal columns align with terrane boundaries it is unlikely that extensive crustal flow as required by some models of plateau evolution could have traversed across the entire colorado plateau without producing features that cross cut these boundaries

northern current variability and its impact on the blanes canyon circulation a numerical study a high resolution 1 2 km 3d numerical model was used to analyze the interaction of the northern current a right bounded flow with the blanes submarine canyon bc nw mediterranean although it refers to a climatological simulation the model properly suites our purpose since it simulates the northern current nc mesoscale variability as well as its seasonal variability model results were validated with satellite sea surface temperature and current meter data the simulated nc tends to be faster and deeper in winter and slower and shallower in summer according to our results nc meanders and eddies are recurrent in the bc area and produce highly fluctuating three dimensional circulation patterns within the canyon we found that nc meanders and anticyclonic eddies propagating along the current pathway tend to be deep and consequently their effects extend down to the deeper part of the bc we also found that the meandering of the nc plays a key role in enhancing vertical motions inside the bc upwelling and downwelling events occurring on timescales of 4 20 days are associated with nc meanders crests and troughs passing over the bc net upwelling downwelling events are accordingly influenced by the nc seasonality they are more predominant in winter while damped in summer our results show the importance of nc meanders in creating local net upwelling downwelling and strengthen the evidence that continuous right bounded downwelling favorable flows can also produce net upwelling inside submarine canyons

cocorp arizona transect strong crustal reflections and offset moho beneath the transition zone the consortium for continental reflection profiling cocorp transect across the southwest margin of the colorado plateau in arizona reveals prominent subhorizontal zones of reflections here termed the bagdad reflection sequence brs which dominate the upper and middle crust in the transition zone tz between the colorado plateau and the basin and range province a cenozoic origin for the brs is considered most likely it may represent fragmented or sheared zones related to detachment faulting or a series of intrusions possibly emplaced along preexisting zones of weakness moho reflections observed beneath the tz and the basin and range province contrast with the nonreflective moho beneath the colorado plateau suggesting that extension and its associated igneous processes probably played a key role in the development of reflectors at the moho the moho and a prominent midcrustal reflector are offset by about 3 km in a normal sense in at least one place this is the best example of offset moho yet found by cocorp and contrasts sharply with cocorp observations of a smooth moho elsewhere this offset is probably a late tectonic expression of crustal extension and thinning across the tz

early proterozoic assembly of tectonostratigraphic terranes in southwestern north america a 500 km wide early proterozoic orogenic belt in arizona and adjacent areas is divided into lithotectonic blocks by northeast and north trending shear zones structural and u pb zircon studies suggest that these blocks may have experienced different tectonic histories prior to their juxtaposition by thrust and strike slip movements on shear zones a northwestern province here called the yavapai province is composed of at least five tectonic blocks and was assembled at about 1700 ma a southeastern province here called the mazatzal province is composed of at least three blocks and was assembled and juxtaposed with the northwestern province during the mazatzal orogeny between 1695 and 1630 ma the diversity of seemingly incompatible 1700 ma tectonic regimes now in close proximity to each other and the absence of systematic cross strike changes in age and character of deformation plutonism and metamorphism suggest a model whereby the orogenic belt developed and north america grew by assembly of d

colorado plateau magmatism and uplift by warming of heterogeneous lithosphere the forces that drove rock uplift of the low relief high elevation tectonically stable colorado plateau are the subject of long standing debate while the adjacent basin and range province and rio grande rift province underwent cenozoic shortening followed by extension the plateau experienced approximately 2 km of rock uplift without significant internal deformation here we propose that warming of the thicker more iron depleted colorado plateau lithosphere over 35 40 myr following mid cenozoic removal of the farallon plate from beneath north america is the primary mechanism driving rock uplift in our model conductive re equilibration not only explains the rock uplift of the plateau but also provides a robust geodynamic interpretation of observed contrasts between the colorado plateau margins and the plateau interior in particular the model matches the encroachment of cenozoic magmatism from the margins towards the plateau interior at rates of 3 6 km myr 1 and is consistent with lower seismic velocities and more negative bouguer gravity at the margins than in the plateau interior we suggest that warming of heterogeneous lithosphere is a powerful mechanism for driving epeirogenic rock uplift of the colorado plateau and may be of general importance in plate interior settings

a 3 d shear velocity model of the crust and uppermost mantle beneath the united states from ambient seismic noise summary in an earlier study bensen et al measured surface wave dispersion curves from ambient noise using 203 stations across north america which resulted in rayleigh and love wave dispersion maps from 8 70 s period and 8 20 s period respectively we invert these maps in a two step procedure to determine a 3 d shear wave velocity model v s of the crust and uppermost mantle beneath much of the contiguous us the two steps are a linearized inversion for a best fitting model beneath each grid node followed by a monte carlo inversion to estimate model uncertainties in general a simple model parametrization is sufficient to achieve acceptable data fit but a rayleigh love discrepancy at periods from 10 to 20 s is observed in which simple isotropic models systematically misfit rayleigh and love waves in some regions crustal features observed in the model include sedimentary basins such as the anadarko green river williston basins as well as california s great valley and the mississippi embayment the east west velocity dichotomy between the stable eastern us and the tectonically deformed western us is shown to be abrupt in the crust and uppermost mantle but is not coincident in these regions crustal high velocity material tends to lap over the high velocities of the uppermost mantle the rayleigh love discrepancy between 10 and 20 s period is crustal in origin and is observed in a number of regions particularly in extensional provinces such as the basin and range it can be resolved by introducing radial anisotropy in the lower or middle crust with v sh v sh by about 1 per cent

intrusion of horizontal dikes tectonic significance of middle proterozoic diabase sheets widespread in the upper crust of the southwestern united states initially horizontal sheet intrusions of middle proterozoic diabase are abundant in a region 650 by 300 km across in arizona and california the diabase forms discordant sheets in basement granite and gneiss and sills in overlying shelf sedimentary sequences massive granite is the most common basement host for the sheets probably because it fractured more easily than foliated hosts during sheet emplacement steep feeder dikes are rare compared to the sheets the diabase in many places is exposed in fault blocks that were tilted during tertiary tectonic extension structure sections restored from the map patterns of upended blocks show that the sheets were intruded at levels throughout the upper crust to depths of at least 13 km sheet intrusion implies a vertical orientation of the least compressive stress so i conclude that the crust was under tectonic compression or in an isotropic state of stress at the time of diabase intrusion about 1 1 ga magma overpressures water encountered by rising magma vertical changes in the crustal stress regime and flotation of low density granite all may be important factors for sheet intrusion the stress conditions suggested by the presence of the sheets argue against an extensional tectonic regime earlier proposed for the diabase event the diabase province contrasts structurally with similar age provinces of basaltic magmatism elsewhere in north america that show evidence of tectonic extension such as the midcontinent rift the consistent orientations of the sheets commonly allow them to be used as structural markers for postdiabase deformation of basement blocks sheet intrusions in the geologic record may be seriously underreported their recognition is important for the interpretation of seismic reflection profiles of continental crust sheets in arizona may be responsible for the bagdad reflection sequence which extends to depths of at least 15 km

pn tomography of the western united states using usarray 1 usarray has now provided several years of high quality seismic data and improved ray coverage for much of the western united states which will enable increased resolution for studies of the lithospheric and deeper structure of the north american continent here we analyze pn arrival times from the transportable stations of usarray to resolve crustal thickness and uppermost mantle structure we use 123 008 pn picks from april 2004 to october 2009 as measured by the array network facility at epicentral distances from 180 to 1450 km these picks are derived from 778 stations at 70 km spacing and 7903 earthquakes and quarry blasts applying the classic time term method we use a regularized least squares inversion to estimate crustal thickness variations and image velocity perturbations in the uppermost mantle just below the moho we also consider upper mantle anisotropy and describe the velocity perturbations with a cos 2 azimuthal variation our crustal thickness map generally agrees with receiver function results from other researchers but differs in some details we obtain an average upper mantle velocity of 7 93 km s with higher velocities beneath eastern washington and northern idaho and lower velocities near the california mexico border the sierra nevada the northern coastal california region and the greater yellowstone area we observe large anisotropic anomalies in southern california as well as in the snake river plain area these results should complement other seismic studies e g body and surface wave tomography and shear wave splitting to provide information about composition temperature and tectonic processes in the western united states

poisson s ratio behaviour in various crystalline rocks application to the study of the earth s interior the study of poisson s ratio behaviour in various crystalline rocks under different temperatures and pressures shows this parameter to depend upon the rock composition rather than upon p t conditions the results of this study are presented in the form of a comparison of z distributions within the consolidated crust and continental upper mantle and the specific variations of in crust and mantle rocks underlying the voronezh crystalline massif vcm these investigations which are based upon seismic and seismological data as well as high pressure experiments should clarify in particular the composition and petrology of the earth s interior

through thick and thin a new model for the colorado plateau from seismic refraction data from pacific to arizona crustal experiment we have constructed a model for the crust and uppermost mantle beneath the colorado plateau by combining newly acquired seismic refraction wide angle reflection data from the 1989 pacific to arizona crustal experiment pace cross profile with data collected by roller 1965 a combination of forward modeling methods was used to model travel times and relative amplitudes of crustal and upper mantle phases the salient features of the model for the colorado plateau hereafter referred to as the plateau are 1 an upper crust having an average velocity of 6 1 km s with a low vertical velocity gradient 2 midcrustal discontinuities at depths of 30 to 38 km beneath the plateau 3 a lower crust that varies in thickness 5 to 16 km and has an average velocity of 6 8 km s 4 a transitional lower crust upper mantle boundary and 5 a crustal thickness of 45 3 km a comparison of our new model for the colorado plateau with recent models for the basin and range shows that the upper crusts of the two provinces are similar but that the lower crust of the plateau is thicker particularly in the plateau s central region these observations are consistent with the idea that the basin and range could have formed from crust like that of the colorado plateau

western united states extension how the west was widened abstract cenozoic extension in the western united states presents a complex interrelation of extension volcanism and plate boundary tectonics that defeats simple notions of active or passive rifting forces driving extension can originate at plate boundaries through basal traction basal normal forces or from buoyancy forces internal to the crust and lithospheric mantle the latter two are most responsible for driving extension where it is observed in the basin and range the complex evolution of the northern basin and range probably represents removal or alteration of mantle lithosphere interacting with buoyancy stored in the crust in contrast crustal buoyancy forces combined with a divergent plate boundary between about 28 and 16 ma to drive extension in the southern basin and range the central basin and range most likely extended as a result of boundary forces external to itself but arising from buoyancy forces elsewhere in the western united states

dynamic subsidence and uplift of the colorado plateau we use inverse models of mantle convection to explore the vertical evolution of the colorado plateau by satisfying multiple constraints seismic tomography stratigraphy in the western united states and great plains and other structural and volcanic data adjacent to the plateau the model provides predictions on the continuous history of colorado plateau vertical motion since 100 ma with the arrival of the flat lying farallon slab dynamic subsidence swept from west to east over the plateau and reached a maximum ca 86 ma two stages of uplift followed the removal of the farallon slab below the plateau one in the latest cretaceous and the other in the eocene with a cumulative uplift of 1 2 km both the descent of the slab and buoyant upwellings raised the plateau to its current elevation during the oligocene a locally thick plateau lithosphere enhances the coupling to the upper mantle so that the plateau has a higher topography with sharp edges the models predict that the plateau tilted downward to the northeast before the oligocene caused by northeast trending subduction of the farallon slab and that this northeast tilting diminished and reversed to the southwest during the miocene in response to buoyant upwellings

a crustal seismic refraction study in west central arizona a reversed seismic refraction profile was recorded in the southern basin and range province between parker and globe arizona interpretation of both refracted and reflected phases indicates a two layered crust 23 25 km thick and a low pn velocity 7 67 km s pmp pn amplitude analysis on individual traces and synthetic seismogram modeling indicate that a positive velocity gradient may exist in the upper mantle the low pn velocity is indicative of partial melting in the upper mantle and implies that the crust is identical with the lithosphere the heat flow data suggest that the lithosphere was about 40 km thick approximately 5 m y ago on the basis of this and a negative free air gravity anomaly we propose that the lithosphere has been thinned from about 40 to 24 km over the past 5 m y and will probably thin and uplift further in the southern basin and range in arizona

regional gravity studies in southeastern california western arizona and southern nevada bouguer gravity anomaly low pass and band pass maps of southeastern california western arizona and southern nevada are analyzed to determine regional crustal structure based on 100 250 km band pass wavelength filtering of the bouguer anomaly map a low amplitude gravity maximum is associated with the highly extended terrane along the colorado river region of california arizona and nevada two crustal models constructed using bouguer gravity anomaly data and constrained by geological mapping aeromagnetic data and seismic refraction data are consistent with the dome shaped midcrustal lens of probable dioritic composition centered under the whipple mountains proposed by mccarthy et al 1989 although other models are not precluded this midcrustal lens extends from the western edge of the colorado river extensional corridor to east of the buckskin and hualapai mountains in arizona dioritic material is exposed in various mountain ranges in the colorado river extensional corridor and may be part of the source of the gravity maximum that is associated with each range

seismic evidence for widespread western us deep crustal deformation caused by extension morgan moschetti and colleagues use ambient noise tomography data from the western united states to show that strong radial seismic anisotropy exists in the deep crust confined mainly to the geological provinces that have undergone significant extension during the cenozoic era since about 65 million years ago the coincidence of crustal radial anisotropy with these extensional provinces supports the hypothesis that the deep crust within these regions has undergone widespread and relatively uniform strain in response to crustal thinning and extension here a method of seismic wave imaging known as ambient noise tomography is used to generate high resolution images of seismic wave speeds in the crust and uppermost mantle the observations reveal strong and uniform anisotropy where waves travel through rock at different speeds depending on direction in the deep crust in areas of the western united states that have undergone significant extension during the past 65 million years laboratory experiments have established that many of the materials comprising the earth are strongly anisotropic in terms of seismic wave speeds1 observations of azimuthal2 3 and radial4 5 anisotropy in the upper mantle are attributed to the lattice preferred orientation of olivine caused by the shear strains associated with deformation and provide some of the most direct evidence for deformation and flow within the earth s interior although observations of crustal radial anisotropy would improve our understanding of crustal deformation and flow patterns resulting from tectonic processes large scale observations have been limited to regions of particularly thick crust6 here we show that observations from ambient noise tomography in the western united states reveal strong deep middle to lower crustal radial anisotropy that is confined mainly to the geological provinces that have undergone significant extension during the cenozoic era since 65 myr ago 7 8 the coincidence of crustal radial anisotropy with the extensional provinces of the western united states suggests that the radial anisotropy results from the lattice preferred orientation of anisotropic crustal minerals caused by extensional deformation these observations also provide support for the hypothesis that the deep crust within these regions has undergone widespread and relatively uniform strain in response to crustal thinning and extension9 10 11

anatomy of a metamorphic core complex seismic refraction wide angle reflection profiling in southeastern california and western arizona the metamorphic core complex belt in southeastern california and western arizona is a nw se trending zone of unusually large tertiary extension and uplift midcrustal rocks exposed in this belt raise questions about the crustal thickness crustal structure and the tectonic evolution of the region three seismic refraction wide angle reflection profiles acquired and analyzed as a part of the u s geological survey s pacific to arizona crustal experiment were collected to address these issues the results presented here which focus on the whipple and buckskin rawhide mountains yield a consistent three dimensional image of this part of the metamorphic core complex belt the seismic refraction wide angle reflection data are of excellent quality and are characterized by six principal phases that can be observed on all three profiles these phases include refractions from the near surface and crystalline basement reflections from boundaries in the middle and lower crust and reflections and refractions from the upper mantle the final model consists of a thin veneer 2 km of upper plate and fractured lower plate rocks 1 5 5 5 kms 1 overlying a fairly homogeneous basement 6 0 km s 1 and a localized high velocity 6 4 km s 1 body situated beneath the western whipple mountains a prominent midcrustal reflection is identified beneath the whipple and buckskin rawhide mountains between 10 and 20 km depth this reflector has an arch like shape and is centered beneath or just west of the metamorphic core complex belt this event is underlain by a weaker approximately subhorizontal reflection at 24 km depth together these two discontinuities define a lens shaped midcrustal layer with a velocity of 6 35 6 5 km s 1 the apex of this midcrustal layer corresponds roughly to a region of major tectonic denudation and uplift 10 km defined by surface geologic mapping and petrologic barometry studies the layer thins to the northeast and is absent in the transition zone the 6 35 6 5 km s 1 velocities are compatible with a diorite composition or a mixture of mafic and silicic rocks this midcrustal layer is underlain by a higher velocity lower crustal layer that is modeled as only 3 6 km thick beneath the metamorphic core complex belt and regions to the southwest to the northeast however this layer thickens to 8 10 km as the midcrustal layer pinches out above it the velocity of the lower crust is constrained by traveltime modeling and is 6 6 0 15 kms 1 beneath the western transition zone and the metamorphic core complex belt higher velocities may be present farther to the southwest where the layer is thin the velocity of the lower crust is too low to accommodate significant amount of mafic underplating at the base of the crust instead we interpret the velocities to indicate that the lower crust is passively thinned beneath these regions without significant addition of mafic mantle derived intrusions the crust mantle boundary does not dome up beneath the core complexes but remains approximately subhorizontal at a depth of 26 28 km or in the case of the whipple mountains actually deepens a 3 km crustal root is modeled this lack of upward doming of the moho together with the vertical alignment of the metamorphic core complex belt over what are believed to be extension related structures in the middle and lower crust suggest that there is no lateral offset of upper crustal deformation from deeper zones of extension as one would expect if extension occurred along crust penetrating shear zones wernicke 1981 wernicke et al 1985 instead domed and inflated middle crust and thinned lower crust directly underlie the region of greatest thinning of the upper crust

mapping high pn velocity beneath the colorado plateau constrains uplift models the massive international seismological centre data set of the past 20 years and the two station method are used to determine pn velocities in the mantle lid beneath the colorado plateau in this method the event is located at distances where pn is the first arrival 2 16 and the path is in or very near the azimuth of the two station pair and crosses the plateau this technique to a large extent minimizes the hypocenter mislocation effect and possible errors due to variations in the crustal structure near the source since only the difference in travel times at the two stations is used however this technique has a few underlying assumptions and possible sources of errors such as the quality of the pn data base and station delays caused by varying crustal structure that require an extremely careful application of the method a detailed study of the source of errors and a methodology of selection of the data are presented application of this method to the colorado plateau using all possible two station pairs from 53 stations located within or along the margin of the plateau yields an average high pn velocity of 8 12 0 09 km s this value is considerably larger than the average value of 7 83 km s based on available but very limited seismic refraction profiles but is remarkably similar to the average value of 8 1 km s for the relatively stable midcontinent region our new pn velocity for the colorado plateau eliminates the paradox in the literature that emphasizes the rather close similarity between average pn velocities beneath the colorado plateau and the basin and range province while their tectonic and magmatic cenozoic history is dramatically different previous models for the structure and evolution of the plateau have used the low pn velocity as an important constraint on density and thermal state of the lithosphere hence such models should be reexamined on the basis of this new uppermost mantle pn velocity determination there are two main models that have been proposed to explain the 2 km uplift of the colorado plateau one is based on a combination of thermal thinning of the lithosphere and crustal thickening and the other involves a combination of the delamination of the subducted subhorizontal farallon oceanic plate from the overriding north american plate and crustal thickening we show that the delamination model is more readily consistent not only with our velocity determination and the elevation of the plateau but also with varied geological observations reported in the literature that concern the cenozoic evolution of western north america

contrasting lithospheric structure between the colorado plateau and great basin initial results from colorado plateau great basin passcal experiment the colorado plateau great basin cpgb passcal experiment provides broadband seismic data that allow us to determine crustal and upper mantle structure in the colorado plateau and eastern great basin twelve portable broadband seismometers throughout utah and nevada are supplemented by permanent broadband stations in the region receiver functions indicate an average crustal thickness of 35 5 km in the great basin gb with a strong p to s ps conversion from the moho the crust in the transition between the great basin and colorado plateau cp produces a strong intracrustal conversion the cp has somewhat thicker crust 42 5 km and weaker moho conversion br surface wave phase velocities are 3 4 higher than cp phase velocities in the 20 35 s range consistent with a thinner crust under the gb the phase velocities at periods greater than 40 s are indistinguishable between the two provinces indicating that differences between upper mantle velocities are minor shear wave splitting yields fast polarizations that parallel the western and northern boundaries of the cp with delay times decreasing towards the center of the plateau

nd and sr isotope chronostratigraphy of colorado plateau lithosphere implications for magmatic and tectonic underplating of the continental crust nd sr isotopes and major and trace element abundances were measured in lower and upper crustal xenoliths carried in tertiary minettes and kimberlitic diatremes of the colorado plateau the objective was to establish the vertical distribution of mantle extraction ages for an undisturbed precambrian crustal province characterized by normal thickness and low cratonic heat flow and to thereby evaluate the importance of magmatic or tectonic underplating in crustal growth mid proterozoic age 1 7 2 0 ga material is found at all levels of the crust although mafic granulites and amphibolites have major and trace element compositions compatible with an origin as magmatically underplated material nd model ages do not indicate that there has been significant mantle contribution to the lower crust by igneous processes such as magmatic underplating since the main crust forming event ca 1 85 ga ago the meta igneous lower crustal xenoliths have relatively radiogenic nd isotopic compositions and unradiogenic sr compositions there is little variability in nd model ages in spite of large variability in sm nd high and variable sm nd ratios were therefore established early in the history of the protolith during igneous or metamorphic processes coincident with or shortly after extraction from the mantle metapelitic xenoliths tectonically emplaced into the lower crust have the same proterozoic model ages as meta igneous parts of the lower crust these paragneisses are probably arc associated sediments that were underthrust during terrane accretion in the proterozoic the isotopic data indicate that eclogite xenoliths are likely to represent proterozoic lithosphere rather than subducted mesozoic morb as previously proposed a number of the eclogite xenoliths have experienced a metasomatic event which introduced lree sio2 and na2o and shifted the nd and sr isotopic compositions the least altered eclogite xenoliths have major and trace element and radiogenic nd isotopic compositions similar to those of other proterozoic mafic lower crustal xenoliths a more plausible protolith for the eclogites is proterozoic lithosphere that was metamorphosed to eclogite facies conditions either during precambrian continental assembly or in more recent times

laramide crustal thickening event in the rocky mountain foreland and great plains the rocky mountain foreland and great plains of the western united states were formerly part of a continental platform adjusted by erosion and deposition in cambrian through jurassic time to near mean sea level and therefore to a near uniform crustal thickness of approximately 33 km today the region stands at regional elevations up to 2 km isostatically supported by a crust exceeding 50 km in thickness reasonable estimates of tertiary sedimentation and laramide strain do not account for more than 15 of the implied thickening however from approximately 70 40 m y b p this region was underlain by a horizontally subducting slab of farallon plate lithosphere moving northeast this slab could have been the cause of the thickening finite difference thermal models with specified kinematics show only a temporary cooling of the base of the north american lithosphere by this slab the excess weight of the slab would have depressed the region plate bending calculations show a quantitative agreement of predicted depression with upper cretaceous isopachs since depression by this slab lasted until the eocene at least the latest cretaceous regression was probably caused by a laramide crustal thickening event the farallon slab might have caused crustal thickening in two ways its excess weight would have drawn in ductile lower crust from surrounding regions however calculations show that this effect is too slow too local and too reversible to explain most of the crustal thickening therefore it seems likely that ductile lower crust was transported from sw to ne by shear stresses which the farallon plate exerted on the base of the north american lithosphere a preliminary finite element calculation based on this hypothesis shows the correct general pattern of crustal thickening an unexpected but encouraging result is that predicted principal compression directions are orthogonal to many laramide basement uplifts

an inverted continental moho and serpentinization of the forearc mantle volatiles that are transported by subducting lithospheric plates to depths greater than 100 km are thought to induce partial melting in the overlying mantle wedge resulting in arc magmatism and the addition of significant quantities of material to the overlying lithosphere asthenospheric flow and upwelling within the wedge produce increased lithospheric temperatures in this back arc region but the forearc mantle in the corner of the wedge is thought to be significantly cooler here we explore the structure of the mantle wedge in the southern cascadia subduction zone using scattered teleseismic waves recorded on a dense portable array of broadband seismometers we find very low shear wave velocities in the cold forearc mantle indicated by the exceptional occurrence of an inverted continental moho which reverts to normal polarity seaward of the cascade arc this observation provides compelling evidence for a highly hydrated and serpentinized forearc region consistent with thermal and petrological models of the forearc mantle wedge this serpentinized material is thought to have low strength and may therefore control the down dip rupture limit of great thrust earthquakes as well as the nature of large scale flow in the mantle wedge

southern african crustal evolution and composition constraints from receiver function studies 1 stacking of approximately 1500 radial receiver functions recorded at about 80 broadband seismic stations deployed in southern africa reveals systematic spatial variations in the ratio of crustal p and s wave velocities crustal thickness h and the amplitude of the converted moho phases r the eastern zimbabwe and the southern kaapvaal cratons are characterized by small h 38 km small 1 73 and large r 0 15 values suggesting that the relatively undisturbed archean crust beneath southern africa is separated from the mantle by a sharp moho and is felsic in composition the limpopo belt which was created by a collisional event at 2 7 ga displays large h 43 km but similar and r values relative to the cratonic areas the bushveld mafic intrusion complex and its surrounding areas show large 1 78 large h 43 km and small r 0 11 values reflecting the intrusion of mafic material into the original crust as a result of the bushveld event at 2 05 ga excluding the bushveld the spatially consistent and age independent low accentuate the difference between felsic crustal composition and more mafic island arcs that are thought to be the likely source of continental material within such an island arc model our data combined with xenolith data excluding mantle delamination in cratonic environments suggest that the modification to a felsic composition e g by the partial melting of basalt and removal of residue by delamination is restricted to have occurred during the collision between the arcs and the continent

na sws 1 1 a uniform database of teleseismic shear wave splitting measurements for north america 1 this version of shear wave splitting sws database db for north america na contains 6224 pairs of splitting parameters fast polarization directions and splitting times measured using all the available data recorded by digital broadband seismic stations over the period of 1980 2007 and archived at the incorporated research institutions for seismology data management center the measurements were produced using a set of robust procedures that involve automated batch processing and manual screening and were ranked quantitatively on the basis of a uniform criterion the result is a homogeneous database of individual rather than station averaged splitting parameters that can be used by a variety of geoscientists for the understanding of the structure and dynamics of the earth s deep interior beneath na this data brief describes the seismic data and techniques used to generate the sws results the spatial and azimuthal coverage and the limitations of the db the db will be periodically updated and enhanced by adding newly recorded data and by measuring splitting parameters using the pks and skks phases in addition to sks the database can be accessed at http www mst edu liukh sws

formation of the rocky mountains western united states a continuum computer model one hypothesis for the information of the rocky mountain structures in late cretaceous through eocene time is that plate of oceanic lithosphere was underthrust horizontally along the base of the north american lithosphere the horizontal components of the motion of this plate are known from paleomagnetism and the edge of the region of flat slab can estimated from reconstructed patterns of volcanism new techniques of finite element modeling allow prediction of the thermal and mechanical effects of horizontal subduction on the north american plate a model that has a realistic temperature dependent rheology and a simple plane layered initial condition is used to compute the consequences of horizontal underthrusting in the time interval 75 million to 30 million years before present successful prediction of this model include i the location amount and direction of horizontal shortening that has been inferred from laramide structures ii massive transport of lower crust from southwest to northeast iii the location and timing of the subsequent extension in metamorphic core complexes and the rio grande rift and iv the total area eventually involved in basin and range style extension in a broad sense this model has predicted the belt of laramide structures the transport of crust from the coastal region to the continental interior the subsequent extension in metamorphic core complexes and the rio grande rift and the geographic region of late tertiary basin and range extension its principal defects are that i many events are predicted about 5 million to 10 million years too late and ii the wave of crustal thickening does not travel far enough to the east reasonable modifications to the oceanic plate kinematics and rheologies that were assumed may correct these defects the correspondence of model predictions to actual geology is already sufficiently close to show that the hypothesis that horizontal subduction caused the laramide orogeny is probably correct the rocky mountain thrust and reverse faults formed in an environment of east west to northeast southwest compressive stress that was caused by the viscous coupling between the oceanic plate and the base of the north american crust nonuniform crustal thickening by simple shear transport also caused relative uplifts therefore this model is consistent with both of the range forming mechanisms that have been inferred 1 a new proposal that arises from this simulation is that horizontal subduction also caused the subsequent extensional basin and range taphrogeny by stripping away the mantle lithosphere so that the crust was exposed to hot asthenosphere after the oceanic slab dropped away

spatial variations of crustal characteristics beneath the hoggar swell algeria revealed by systematic analyses of receiver functions from a single seismic station the hoggar swell in algeria is one of the significant massifs of northwest africa the paucity of high resolution geophysical studies of the crust and mantle beneath the massifs is mostly responsible for the heated debates about the depth of the source region of the cenozoic volcanism and the closely related uncertainty about the mechanism that formed and maintains the high elevation of the swells here we report results from a systematic study of 1386 high quality receiver functions rfs recorded by station tam the only permanent broadband seismic station on the hoggar swell the resulting crustal thickness is about 34 km and the vp vs is 1 77 when all the rfs from the station are stacked our study reveals a sharp contrast in the amplitude of the p to s converted phases between the volcanic highly fractured tefedest terrane and the non volcanic less fractured laouni terrane the former has a stacking amplitude that is comparable to typical cratonic areas and the latter has an amplitude that is only about 25 as large spatially consistent crustal thickness and an intermediate mafic crust are inferred on the tefedest terrane while spatially variable crustal thickness and a felsic crust is inferred beneath the laouni terrane the observations can be best explained by a mantle derived underplated magmatic layer beneath the mechanically stronger laouni terrane and magmatic diking and resultant volcanism associated with the mechanically weaker tefedest crust the study demonstrated the significance of a long running station in the investigation of spatial variations of crustal characteristics