the q structure of the upper mantle constraints from rayleigh wave amplitudes 1 the three dimensional shear attenuation or q structure of the upper mantle is still poorly understood despite the increasing accuracy and sophistication of velocity models of the same part of the earth here we present a set of three dimensional q models of the upper mantle based on amplitude measurement of minor and major arc rayleigh waves in the period range 70 170 s the models show that areas of low attenuation underlie continents to a depth of around 300 km and areas of high attenuation are associated with oceans and plate boundaries particularly in the top 200 km below 350 km the sensitivity of the data to attenuation structure decreases rapidly it is well known that the amplitudes of surface waves can be strongly influenced by factors other than attenuation in particular focusing due to elastic structure and errors in source mechanisms we consider the effects of focusing by discussing the implications of the results of selby and woodhouse 2000 comparisons with focusing predictions using phase velocity maps allow us to identify features due to focusing in maps of attenuation distribution the influence of the source on the observed attenuation distribution is investigated by including a source term in the model inversion we find that successfully combining the data at each frequency into one three dimensional model requires that this source term must vary with frequency suggesting that a simple correction to the scalar moment of each event cannot explain the observations although the effects of focusing and the source can be significant we find that the observed attenuation pattern is robust up to degree 8 however shorter wavelength structure can be strongly influenced by other controls finally we use one of the models to predict the degree 2 attenuation pattern for 250 s rayleigh waves the observed pattern suggests that existing normal mode observations may be explainable in terms of structure above 350 km depth

a 500 year long record of tephra falls from redoubt volcano and other volcanoes in upper cook inlet alaska abstract volcanic ash layers preserved in glacial lacustrine sediments at skilak lake on the kenai peninsula of southcentral alaska constitute a record of eruptions at redoubt volcano and other alaskan volcanoes which affected the upper cook inlet area during the last 500 years high resolution magnetic susceptibility profiling delineates similar sequences of tephra layers in several 1 m long lake sediment cores electron microprobe analyses of glass shards from the tephras indicate correlation of some ash layers with known reference tephras from the source volcanoes while other ash layers record previously unknown prehistoric eruptions skilak lake cores contain ash from the historic 1912 katmai eruption the 1902 redoubt eruption and the 1883 mount st augustine eruption as well as prehistoric ash layers erupted from crater peak at mt spurr ca 250 350 years ago from redoubt volcano at ca 300 400 years ago and again at ca 350 450 years ago and a 500 year old ash from mount st augustine still older tephras from redoubt volcano and crater peak at mt spurr are found lower in the cores the cores indicate that volcanoes in the cook inlet area have erupted every 10 35 years during the 20th century and ash falls have occurred at skilak lake at least once every 50 100 years for the last 500 years with redoubt spurr and augustine volcanoes being the most important sources of tephra

an empirical relationship between seismic attenuation and velocity anomalies in the upper mantle we use recent p wave attenuation q 1 and velocity vp tomographic models of the tonga fiji region to obtain an empirical relation between attenuation and velocity for the upper mantle the attenuation and velocity anomalies show a strong inverse correlation allowing the determination of an empirical relationship the relationship is similar to a predicted relation derived from laboratory experiments on peridotite and dunite assuming the observed anomalies result from temperature variations the results here suggest that the observed anomalies are generally consistent with the effect of temperature and demonstrate that the combination of velocity and attenuation data provides powerful constraints on the physical state of upper mantle materials we find that the chosen geotherm and activation energy has a strong effect on the position of the solidus within the seismic data

upper mantle attenuation and velocity structure from measurements of differential s phases summary although much progress has been made in determining the 3 d distribution of seismic wave velocities in the earth substantially less is known about the 3 d distribution of intrinsic attenuation in this study variations in attenuation and shear velocity of the earth s mantle are constrained using measurements of differential traveltime and attenuation the data are broad band displacement sh seismograms filtered to have energy in the period range 8 20 s the seismograms are obtained from over 600 globally distributed earthquakes of magnitude mw 5 5 or greater differential traveltimes and differential t values from multiple s phases are estimated by a waveform fitting method resulting in approximately 4300 measurements for ss s in the distance range 50u 105u and 1000 measurements for sss ss in the distance range 90u 179u each measurement consists of a differential traveltime and a corresponding differential t the differential traveltimes and t values are inverted to obtain models of the lateral variation of shear velocity and lateral variation of qm where qm 1 qm the models explain the data well but have limited depth resolution the velocity models show good correlation with previous studies in particular low velocities are observed underlying mid oceanic ridges and convergent margins and high velocities are found for continental regions the qm models show shield regions to be less attenuating than prem with ridges appearing as highly attenuating features the models have limited depth resolution and to address this problem we also present a shear velocity model obtained from the combination of body wave and surface wave data sets

anisotropic shear wave velocity structure of the earth s mantle a global model 1 we combine a new large data set of surface wave phase anomalies long period waveforms and body wave travel times to construct a three dimensional model of the anisotropic shear wave velocity in the earth s mantle our modeling approach is improved and more comprehensive compared to our earlier studies and involves the development and implementation of a new spherically symmetric reference model simultaneous inversion for velocity and anisotropy as well as discontinuity topographies and implementation of nonlinear crustal corrections for waveforms a comparison of our new three dimensional model s362ani with two other models derived from comparable data sets but using different techniques reveals persistent features 1 strong 200 km thick high velocity anomalies beneath cratons likely representing the continental lithosphere underlain by weaker fast anomalies extending below 250 km which may represent continental roots 2 weak velocity heterogeneity between 250 and 400 km depths 3 fast anomalies extending horizontally up to 2000 3000 km in the mantle transition zone beneath subduction zones 4 lack of strong long wavelength heterogeneity below 650 km suggesting inhibiting character of the upper mantle lower mantle boundary and 5 slow velocity superplumes beneath the pacific and africa the shear wave radial anisotropy is strongest at 120 km depth in particular beneath the central pacific lateral anisotropic variations appreciably improve the fit to data that are predominantly sensitive to the uppermost and lowermost mantle but not to the waveforms that control the transition zone and midmantle depths tradeoffs between lateral variations in velocity and anisotropy are negligible in the uppermost mantle but noticeable at the bottom of the mantle

global models of surface wave attenuation 1 a large data set of fundamental mode rayleigh wave amplitudes is analyzed to derive global models of surface wave attenuation 1 q the data set consists of measurements of rayleigh wave amplitude anomalies in the period range 50 250 s for 347 earthquakes observed at 179 seismic stations the amplitude anomalies are considered to depend on four factors intrinsic attenuation along the ray path elastic focusing effects along the ray path a source factor accounting for uncertainties in the strength of excitation and a receiver factor accounting for uncertainties in the response at the station the amplitude data are inverted simultaneously for global maps of attenuation expanded in spherical harmonics up to degree 12 global maps of phase velocity expanded to degree 20 and source and receiver correction factors all four variable types are shown to be important in explaining the amplitude anomalies a data set of phase delay measurements provides additional constraints on velocity structure the maps of attenuation obtained by simultaneous inversion for elastic and anelastic models contain important features that are not robustly imaged when the effect of focusing on wave amplitude is ignored these include high attenuation along western north america and along the east pacific rise and other ridge systems and low attenuation associated with stable continental interiors the global attenuation maps exhibit a strong correlation with phase velocity maps corrected for the effect of the crust particularly for periods 200 s the correlation suggests that the variability in both q and velocity in the shallow upper mantle is primarily thermal in origin

on the robustness of attenuation measurements on teleseismic p waves insights from micro array analysis of the 2017 north korean nuclear test author s bezada mj byrnes j eilon z abstract summary despite their importance as a fundamental constraint on earth properties regional scale measurements of body wave seismic attenuation are scarce this is partially a result of the difficulty in producing robust estimates of attenuation in this paper we focus on measuring differential attenuation on records of teleseismic p waves we examine a unique data set of five records of the north korean nuclear test of 2017 measured at five broad band seismic stations deployed within a few metres of each other but using different installation procedures given their extreme proximity we expect zero differential intrinsic attenuation between the different records however we find that different attenuation measurement methods and implementation parameters in fact produce significant apparent differential attenuation t frequency domain methods yield a wide range of t estimates between stations depending on measurement bandwidth and nuances of signal processing this measurement instability increases for longer time windows time domain methods are largely insensitive to the frequency band being considered but are sensitive to the time window that is chosen we determine that signal generated noise can affect measurements in both the frequency and time domain in some cases the range of results amounts to a significant fraction of the range of differential attenuation across the conterminous united states as determined by a recent study we suggest some approaches to manage the inherent instability in these measurements and recommend best practices to confidently estimate body wave attenuation

global azimuthal anisotropy in the transition zone surface wave dispersion measurements for love wave overtones carry evidence of azimuthal anisotropy in the transition zone of earth s mantle 400 to 660 kilometers deep a backus gilbert inversion of anisotropic phase velocity maps with resolution kernels mainly sensitive to the transition zone shows a robust long wavelength azimuthally anisotropic velocity structure this observation puts new constraints on the mineralogy and dynamics of the transition zone because this anisotropy may result from aligned minerals tilted laminated structures or even organized pockets of fluid inclusions

q tomography of the upper mantle using three component long period waveforms summary we present a degree 8 3 d q model qrlw8 of the upper mantle derived from three component surface waveform data in the period range 60 400 s the inversion procedure involves two steps in the first step 3 d whole mantle velocity models are derived separately for elastic sh transverse component and sv vertical and longitudinal component velocity models using both surface and body waveforms and the non linear asymptotic coupling theory nact approach in the second step the surface waveforms thus aligned in phase are inverted to obtain a 3 d q model in the depth range 80 670 km various stability tests are performed to assess the quality of the resulting q model and in particular to assess possible contamination from focusing effects we find that the 3 d patterns obtained are stable but the amplitude of the lateral variations in q is not well constrained because large damping is necessary to extract the weak q signal from data the model obtained agrees with previous results in that a strong correlation of q with tectonics is observed in the first 250 km of the upper mantle with high attenuation under oceanic regions and low attenuation under continental shields it is gradually replaced by a simpler pattern at larger depth at the depths below 400 km the q distribution is generally dominated by two strong minima one under the southern pacific and one under africa yielding a strong degree 2 pattern most hotspots are located above regions of low q at this depth ridges are shallow features in both velocity and q models

global lateral variations of shear wave attenuation in the upper mantle we analyze several thousand high quality globally recorded ss s differential waveforms to constrain the lateral variation of shear wave attenuation q in the upper mantle we use a multitaper frequency domain technique to measure attenuation parameterized by a t operator and implement a robust estimation technique to compute t and its variance the differential waveform technique minimizes the effect of factors such as finite source duration and structural complexity near the source and receiver so the differential ss s waveforms are mainly sensitive to the shear attenuation in the upper mantle under the ss bounce point we use seismograms recorded at ranges of 45 to 100 and compute the ss s differential t from the broadening of the ss waveform relative to the hilbert transform of the s waveform a careful choice of fitting windows allows us to reduce the biasing effects of interfering phases which can affect t by up to 0 5 s the t residuals with respect to preliminary reference earth model prem vary by 1 5 s with an average of 0 24 s our study suggests an average q value of 112 most of the lateral variations of q are within 30 of this value in the top 400 km of the mantle slightly lower than the prem value of 128 there is a qualitative correlation of t residual with tectonic region with distinctly higher attenuation observed under young oceans compared to platforms and shields also the lateral variations of the residuals are similar in trend to those observed in studies of the attenuation of scs multiples at long wavelengths the qp map shows a modest correlation with shear wave attenuation maps computed from surface wave analyses and with the patterns of lateral variations of shear velocities at certain upper mantle depths predicted by the model s16b30 the correlation with the velocity model is highest at 300 500 km depth indicating that there may be a contribution to long wavelength attenuation from relatively deep regions formal inversion for an upper mantle q model shows that while lateral resolution is quite good depth resolution is poor as might be expected better depth resolution must await combined body wave and surface wave inversions

a global tomographic model of shear attenuation in the upper mantle we present a global three dimensional model of shear attenuation in the upper mantle based on the measurement of amplitudes of low frequency 100 300s rayleigh waves observed at stations of the geoscope and iris networks attenuation coefficients are measured on r1 and r2 paths using a method which minimizes the effects of focussing due to propagation in a three dimensional elastic earth through a series of tests which in particular involve the computation of synthetic models of attenuation and focussing we demonstrate that long wavelength lateral variations in attenuation in the first 400 500 km of the mantle can indeed be resolved the model is obtained in a two step procedure the first step consists in the computation of maps of rayleigh wave attenuation at different periods using an inversion method without a priori parametrisation which involves the introduction of a correlation length chosen here at 3000 km to optimize the trade off between resolution and variance in the model in the second step after corrections for shallow structure an inversion with depth is performed assuming lateral heterogeneity is confined to depths between 80 and 650 km the resulting model presents lateral variations in qp that are correlated with tectonic features in particular ridges and shields in the first 250 km of the upper mantle below that depth the pattern shifts and becomes correlated with the hotspot distribution particularly so if the buoyancy strength of hotspots is taken into account two major low velocity zones appear to be located in the central pacific and beneath northern africa in the depth range 300 500 km this pattern seems to continue at greater depth but resolution becomes insufficient below 500 km to draw definitive conclusions the smooth lateral variations retrieved are on the order of 50 down to 400 km we propose an interpretation in terms of plume lithosphere ridge interaction in the upper mantle arguing for deflection of the bulk of hot upwelling material from plumes towards ridges which may be occurring between 200 and 300 km depth

reconciling mantle attenuation temperature relationships from seismology petrology and laboratory measurements seismic attenuation measurements provide a powerful tool for sampling mantle properties laboratory experiments provide calibrations at seismic frequencies and mantle temperatures for dry melt free rocks but require 102 103 extrapolations in grain size to mantle conditions also the effects of water and melt are not well understood at the same time body wave attenuation measured from dense broadband arrays provides reliable estimates of shear wave attenuation qs 1 affording an opportunity for calibration we reanalyze seismic data sets that sample arc and back arc mantle in central america the marianas and the lau basin confirming very high attenuation qs 25 80 at 1 hz and depths of 50 100 km at each of these sites independent petrological studies constrain the temperature and water content where basaltic magmas last equilibrated with the mantle 1300 1450 c the qs measurements correlate inversely with the petrologically inferred temperatures as expected however dry attenuation models predict qs too high by a factor of 1 5 5 modifying models to include effects of h2o and rheology dependent grain size shows that the effects of water enhanced dissipation and water enhanced grain growth nearly cancel so h2o effects are modest therefore high h2o in the arc source region cannot explain the low qs nor in the back arc where lavas show modest water content most likely the high attenuation reflects the presence of melt and some models of melt effects come close to reproducing observations overall body wave qs can be reconciled with petrologic and laboratory inferences of mantle conditions if melt has a strong influence beneath arcs and back arcs

seismic attenuation near the east pacific rise and the origin of the low velocity zone abstract low shear wave velocities beneath mid ocean ridges and in the low velocity zone beneath oceanic plates commonly have been attributed to the presence of melt or dissolved water but several recent studies have challenged that interpretation the alternative is that the anelastic effects of increasing temperature may cause the observed drop in velocity along with a predicted increase in attenuation we report the first measurements of surface wave attenuation within regional arrays of seismometers on the seafloor near the east pacific rise there is much less attenuation than is predicted by models in which the velocity is controlled solely by the direct elastic and anelastic effects of changing temperature suggesting that melt and water concentration do play an important role there also is somewhat less attenuation than is found in global studies we speculate that scattering from unresolved velocity heterogeneities contribute to the apparent attenuation in global studies

seismic wave attenuation energy dissipation in viscoelastic crystalline solids seismic imaging as a tool to understand the structure and perhaps the dynamics of the planet at depth involves the spatially resolved combined study of wave velocities and velocity dispersion wave birefringence and wave attenuation mechanical absorption when integrated with insights from petrology plus or minus input from magneto tellurics specific hypotheses concerning structure at depth can be formulated cf karato 1993 karato and karki 2001 the recent advances in tomography have allowed significant improvements in spatial resolution which also have allowed ever more exacting hypotheses of structure to be articulated nevertheless as is nicely illustrated by the relatively recent seismic analyses of an accreting plate margin the east pacific rise e g toomey et al 1998 webb and forsyth 1998 the structures inferred at depth can vary significantly clearly the interpretation of seismic data is limited specifically by a lack of understanding of the physical processes by which low frequency wave absorption occurs particularly in the cases a where melt is present and or b where the material is being actively plastically deformed this chapter emphasizes the mineral physics materials science of mechanical absorption specifically in dense materials at elevated temperature the interest then is in employing the physical study of mechanical absorption to understand natural phenomena such as those mentioned above beyond questions of the basic mineral physics of absorption the guiding interest the community of scholars pursuing the ideas is in isolating actual absorption mechanisms operative in the geological setting thereby allowing for a greater discrimination in the interpretation of seismic data at the outset i note that this contribution does not seek to be a comprehensive review of the ideas and work involved in the physics of mechanical absorption there are marvelous reviews in the literature that are both authoritative and current i refer to these frequently in contemplating my own

estimating local bed shear stress from velocity observations replicate velocity observations using conventional equipment under typical field conditions are used to evaluate the precision of different methods for estimating local boundary shear stress from velocity measurements the bed shear velocity u can be estimated within 3 using the depth averaged velocity in the vertically averaged logarithmic velocity profile to be accurate this method is limited to relatively simple flow geometries which may be expected to have the appropriate velocity structure estimates of u made using a single near bed velocity observation are less precise by a factor of 3 because of the larger uncertainty associated with a single observation accuracy of this method requires appropriate flow conditions only near the bed so it may be applied in a wider range of flow conditions including spatially variable flow estimates of u from the slope of the near bed velocity profile are the least precise and require the most restrictive flow conditions for accuracy but offer the advantage that they may be made without independent knowledge of the bed roughness different methods for estimating roe should be useful in judging the precision of estimates made under similar conditions these estimates of precision together with considerations of convenience and model accuracy provide the basis for select ing the most appropriate or advantageous method for different conditions and purposes

seismic attenuation and mantle wedge temperatures in the alaska subduction zone 1 anelastic loss of seismic wave energy or seismic attenuation 1 q provides a proxy for temperature under certain conditions the q structure of the upper mantle beneath central alaska is imaged here at high resolution an active subduction zone where arc volcanism is absent to investigate mantle thermal structure the recent broadband experiment across the alaska range beaar provides the first dense broadband seismic coverage of this region the spectra of p and sh waves for regional earthquakes are inverted for path averaged attenuation operators between 0 5 and 20 hz along with earthquake source parameters these measurements fit waveforms significantly better when the frequency dependence of q is taken into account and in the mantle frequency dependence lies close to laboratory values inverting these measurements for spatial variations in q reveals a highly attenuating wedge with q 500 assuming frequency dependence comparison with p results shows that attenuation in bulk modulus is negligible within the low q wedge as expected for thermally activated attenuation mechanisms bulk attenuation is significant in the overlying crust and subducting plate indicating that q must be controlled by other processes the shallowest part of the wedge shows little attenuation as expected for a cold viscous nose that is not involved in wedge corner flow overall the spatial pattern of q beneath alaska is qualitatively similar to other subduction zones although the highest wedge attenuation is about a factor of 2 lower the q values imply that temperatures exceed 1200 c in the wedge on the basis of recent laboratory based calibrations for dry peridotite these temperatures are 100 150 c colder than we infer beneath japan or the andes possibly explaining the absence of arc volcanism in central alaska

seismic attenuation tomography of the mariana subduction system implications for thermal structure volatile distribution and slow spreading dynamics 1 the anelastic structure of a subduction zone can place first order constraints on variations in temperature and volatile content we investigate seismic attenuation across the western pacific mariana subduction system using data from the 2003 2004 mariana subduction factory imaging experiment this 11 month experiment consisted of 20 broadband stations deployed on the arc islands and 58 semibroadband ocean bottom seismographs deployed across the fore arc island arc and back arc spreading center we compute amplitude spectra for p and s arrivals from local earthquakes and invert for the path averaged attenuation for each waveform along with the seismic moment and corner frequency for each earthquake additionally we investigate earthquake source parameter assumptions and frequency dependent exponents ranging from 0 to 0 6 tomographic inversion of nearly 3000 t estimates at 0 27 for 2 d qp 1 and qp qs structure shows a 75 km wide columnar shaped high attenuation anomaly with qp 43 60 beneath the spreading center that extends from the uppermost mantle to 100 km depth a weaker high attenuation region qp 56 70 occurs at depths of 50 100 km beneath the volcanic arc and the high attenuation regions are connected at depths of 75 125 km the subducting pacific plate is characterized by low attenuation at depths greater than 100 km but high attenuation is found in the plate between 50 and 100 km depth the fore arc shows high attenuation near the volcanic arc and beneath the serpentinite seamounts in the outer fore arc qs structure is less well resolved than qp because of a smaller data set but qp qs ratios are significantly less than 2 throughout the study region as temperatures estimated from qs 1 are unusually high we interpret the arc and wedge core anomalies as regions of high temperature with enhanced q 1 due to hydration and or melt the slab and fore arc anomalies as indicative of slab derived fluids and or large scale serpentinization and the columnar shaped high qp 1 anomaly directly beneath the back arc spreading center as indicative of a narrow region of dynamic upwelling and melt production beneath the slow spreading ridge axis

the global attenuation structure of the upper mantle 1 a large data set of fundamental mode rayleigh wave amplitudes is analyzed to derive a new global three dimensional model of shear wave attenuation in the upper mantle the amplitude observations span a range of periods between 50 and 250 s and are derived from earthquakes with mw 6 0 that occurred between 1993 and 2005 four separate factors may influence an amplitude anomaly intrinsic attenuation along the raypath elastic focusing effects along the raypath uncertainties in the strength of excitation and uncertainties in the response at the station in an earlier paper dalton and ekstrom 2006a dependence of the retrieved attenuation structure on these terms was shown to be significant and an approach was developed to invert the amplitudes simultaneously for each term the new three dimensional attenuation model qrfsi12 which is the subject of this paper is derived using this method the model contains large lateral variations in upper mantle attenuation 60 to 100 and exhibits strong agreement with surface tectonic features at depths shallower than 200 km at greater depth qrfsi12 is dominated by high attenuation in the southeastern pacific and eastern africa and low attenuation along many subduction zones in the western pacific resolution tests confirm that the change in pattern of attenuation above and below 200 km depth can be determined with confidence using the fundamental mode data set the new model is highly correlated with global models of shear wave velocity particularly in the uppermost mantle suggesting that the same factors may control both seismic attenuation and velocity in this depth range however forcing the lateral perturbations in attenuation to match those found in global velocity models decreases the data variance reduction which suggests that subtle differences between patterns of attenuation and velocity are robust

grain size sensitive seismic wave attenuation in polycrystalline olivine 1 in order to investigate the processes responsible for the attenuation of seismic shear waves in the earth s upper mantle four olivine polycrystals ranging in mean grain size d from 3 to 23 m have been fabricated characterized and mechanically tested in torsion at high temperatures and seismic frequencies both the shear modulus which governs the shear wave speed vs and the dissipation of shear strain energy q 1 have been measured as functions of oscillation period to temperature t and for the first time grain size at sufficiently high t all four specimens display similar absorption band viscoelastic behavior adequately represented for 1000 t 1200 or 1300 c and 1 to 100 s by the expression q 1 a tod 1 exp e rt with a 7 5 102 s m 0 26 and e 424 kj mol 1 this mildly grain size sensitive viscoelastic behavior of melt free polycrystalline olivine is attributed to a combination of elastically and diffusionally accommodated grain boundary sliding the latter becoming progressively more important with increasing t and or to extrapolation to the larger mm cm grain sizes expected in the earth s upper mantle yields levels of dissipation comparable with those observed seismologically implying that the same grain size sensitive processes might be responsible for much of the observed seismic wave attenuation the temperature sensitivity of vs is increased substantially by the viscoelastic relaxation allowing the lateral variability of wave speeds to be associated with relatively small temperature perturbations

global shear speed structure of the upper mantle and transition zone s u m m a r y the rapid expansion of broad band seismic networks over the last decade has paved the way for a new generation of global tomographic models significantly improved resolution of global upper mantle and crustal structure can now be achieved provided that structural information is extracted effectively from both surface and body waves and that the effects of errors in the data are controlled and minimized here we present a new global vertically polarized shear speed model that yields considerable improvements in resolution compared to previous ones for a variety of features in the upper mantle and crust the model sl2013sv is constrained by an unprecedentedly large set of waveform fits 3 4 of a million broad band seismograms computed in seismogram dependent frequency bands up to a maximum period range of 11 450 s automated multimode inversion of surface and s wave forms was used to extract a set of linear equations with uncorrelated uncertainties from each seismogram the equations described perturbations in elastic structure within approximate sensitivity volumes between sources and receivers going beyond ray theory we calculated the phase of every mode at every frequency and its derivative with respect to sand p velocity perturbations by integration over a sensitivity area in a 3 d reference model the normally small perturbations of the 3 d model required to fit the waveforms were then linearized using these accurate derivatives the equations yielded by the waveform inversion of all the seismograms were simultaneously inverted for a 3 d model of shear and compressional speeds and azimuthal anisotropy within the crust and upper mantle elaborate outlier analysis was used to control the propagation of errors in the data source parameters timing at the stations etc the selection of only the most mutually consistent equations exploited the data redundancy provided by our data set and strongly reduced the effect of the errors increasing the resolution of the imaging our new shear speed model is parametrized on a triangular grid with a 280 km spacing in well sampled continental domains lateral resolution approaches or exceeds that of regionalscale studies the close match of known surface expressions of deep structure with the distribution of anomalies in the model provides a useful benchmark in oceanic regions spreading ridges are very well resolved with narrow anomalies in the shallow mantle closely confined near the ridge axis and those deeper down to 100 120 km showing variability in their width and location with respect to the ridge major subduction zones worldwide are well captured extending from shallow depths down to the transition zone the large size of our waveform fit data set also provides a strong statistical foundation to re examine the validity field of the jwkb approximation and surface wave ray theory our analysis shows that the approximations are likely to be valid within certain time frequency portions of most seismograms with high signal to noise ratios and these portions can be identified using a set of consistent criteria that we apply in the course of waveform fitting

strong along arc variations in attenuation in the mantle wedge beneath costa rica and nicaragua attenuation structure in the central american subduction zone was imaged using local events recorded by the tomography under costa rica and nicaragua array a 20 month long deployment july 2004 until march 2006 of 48 seismometers that spanned the fore arc arc and back arc regions of nicaragua and costa rica p and s waveforms were inverted separately for the corner frequency and moment of each event and for the path averaged attenuation operator t of each event station pair assuming attenuation is slightly frequency dependent 0 27 then tomographic inversions were performed for s and p attenuation q s 1 and q p 1 since p wave amplitudes reflect both shear and the bulk moduli tomographic inversions were also performed to determine shear and bulk attenuation q s 1 and q 1 the loss of energy per cycle owing to shearing and uniform compression respectively damping and other inversion tomographic parameters were systematically varied as is typical in subduction zone attenuation studies a less attenuating slab upper plate and wedge corner and a more attenuating mantle wedge were imaged in addition first order differences between the mantles beneath nicaragua and costa rica were observed the slab in nicaragua is more attenuating than the slab in costa rica a larger zone of higher shear attenuation also characterizes the nicaraguan mantle wedge within the wedge maximum attenuation values at 1 hz correspond to qs 38 73 beneath nicaragua and qs 62 84 beneath costa rica and average values are qs 76 78 and qs 84 88 respectively attenuation variations correlate with along arc trends in geochemical indicators that suggest that melting beneath nicaragua occurs at more hydrated conditions and possibly to greater extents and depths relative to northern costa rica shear attenuation dominates over bulk attenuation in the well resolved regions of the wedge the more extensive zones of greater shear attenuation observed in the nicaraguan wedge could be explained by higher temperatures and or greater hydration but comparison with petrological data suggests that hydration variations play a larger role average wedge attenuation values are comparable to estimates for the andes and japan greater than those for alaska and less than those for tonga lau