tomography of core mantle boundary and lowermost mantle coupled by geodynamics summary we propose an innovative approach to mapping cmb topography from seismic p wave traveltime inversions instead of treating mantle velocity and cmb topography as independent parameters as has been done so far we account for their coupling by mantle flow as formulated by forte peltier this approach rests on the assumption that p data are sufficiently sensitive to thermal heterogeneity and that compositional heterogeneity albeit important in localized regions of the mantle e g within the d region is not sufficiently strong to govern the pattern of mantle wide convection and hence the cmb topography the resulting tomographic maps of cmb topography are physically sound and they resolve the known discrepancy between images obtained from classic tomography on the basis of core reflected and core refracted seismic phases since the coefficients of mantle velocity structure are the only free parameters of the inversion this joint tomography geodynamics approach reduces the number of parameters nevertheless the corresponding mantle models fit the seismic data as well as the purely seismic ones

a three dimensional microgeodynamic model of melt geometry in the earth s deep interior 1 this article presents a three dimensional microgeodynamic model of grain melt geometry in partially molten rocks the isotropic unit cell of the partially molten rock is characterized by a face centered cubic symmetry consisting of rhombic dodecahedral grains the variation of surface tension between grain grain and grain melt contacts excites a coupled viscous flow within grains and the interstitial melt leading to a steady state grain melt geometry we obtain the fractional area of intergranular contact contiguity from these models as a function of melt volume fraction between melt fractions of 0 05 and 0 25 comparison with previous results indicates that the contiguity in three dimensional models is lower than in two dimensional models the contrast between two and three dimensional values of contiguity increases at high melt volume fractions we apply our model to the ultralow velocity zones ulvzs and the very low velocity province vlvp in the earth s core mantle boundary the observed seismic signature of the ulvz and vlvp can be explained by peridotite melt volume fractions between 0 08 and 0 12 and between 0 01 and 0 05 respectively in a matrix of elastic properties similar to the preliminary earth reference model

double beam analysis of anomalies in the core mantle boundary region seismic p waves from nuclear explosions at the kazakhstan test site in eastern kazakhstan kts observed at the yellowknife array yka canada are used to analyze the structure at the base of the mantle under severnaya zemlya arctic sea 18 events at the degelen subsite and 9 events at the shagan river subsite of kts are studied the simple waveforms and well controlled source parameters of nuclear explosions allow the use of the events as source arrays in addition to the usual receiver array configuration a new method double beamforming integrating both concepts is presented this method increases the resolution considerably for the degelen yka path one anomalous arrival 1 9 s before pcp slowness between p and pcp slowness is observed smaller anomalous arrivals are found 6 5 s degelen yka and 8 1 s before pcp shagan river yka these anomalous phases cannot be explained with standard earth models they are produced by reflections from an inhomogeneity in the lowermost mantle at 82 3n 107 5e under the area north of severnaya zemlya the strong variations between the wavefields for the two source receiver combinations indicate a heterogeneous structure in the lower mantle the anomaly found here is located close to an anomaly in the lowermost mantle beneath the nansen basin

accuracy of the lightning mapping array 1 the location accuracy of the new mexico tech lightning mapping array lma has been investigated experimentally using sounding balloon measurements airplane tracks and observations of distant storms we have also developed simple geometric models for estimating the location uncertainty of sources both over and outside the network the model results are found to be a good estimator of the observed errors and also agree with covariance estimates of the location uncertainties obtained from the least squares solution technique sources over the network are located with an uncertainty of 6 12 m rms in the horizontal and 20 30 m rms in the vertical this corresponds well with the uncertainties of the arrival time measurements determined from the distribution of chi square values to be 40 50 ns rms outside the network the location uncertainties increase with distance the geometric model shows that the range and altitude errors increase as the range squared r2 while the azimuthal error increases linearly with r for the 13 station 70 km diameter network deployed during steps the range and height errors of distant sources were comparable to each other while the azimuthal errors were much smaller the difference in the range and azimuth errors causes distant storms to be elongated radially in plan views of the observations the overall results are shown to agree well with hyperbolic formulations of time of arrival measurements e g proctor 1971 two appendices describe 1 the basic operation of the lma and the detailed manner in which its measurements are processed and 2 the effect of systematic errors on lightning observations the latter provides an alternative explanation for the systematic height errors found by boccippio et al 2001 in distant storm data from the lightning detection and ranging system at kennedy space center

a doubling of the post perovskite phase boundary and structure of the earth s lowermost mantle a new model of the deep earth allows geophysicists to measure variations in earth s temperature near the boundary between the rocky mantle and core using a recently discovered phase change in the lowest part of the earth s mantle where atoms rearrange themselves in crystals under extreme pressure and temperature the model also explains odd features of this part of the mantle such as patchy regions that reflect seismic waves generated by large earthquakes and inferences of dense partial melting combined with observations the results imply very large variations in temperature providing further evidence for circulation of material throughout the earth s mantle the thermal structure of the earth s lowermost mantle the d layer spanning depths of 2 600 2 900 kilometres1 is key to understanding the dynamical state and history of our planet earth s temperature profile the geotherm is mostly constrained by phase transitions such as freezing at the inner core boundary or changes in crystal structure within the solid mantle that are detected as discontinuities in seismic wave speed and for which the pressure and temperature conditions can be constrained by experiment and theory a recently discovered phase transition at pressures of the d layer2 3 4 is ideally situated to reveal the thermal structure of the lowermost mantle where no phase transitions were previously known to exist here we show that a pair of seismic discontinuities observed in some regions of d can be explained by the same phase transition as the result of a double crossing of the phase boundary by the geotherm at two different depths this simple model can also explain why a seismic discontinuity is not observed in some other regions and provides new constraints for the magnitude of temperature variations within d

strong seismic scatterers near the core mantle boundary west of mexico pkpphasesobservedinjapan showstrongpre cursors with clear onsets for earthquakes that occurred in south america the onset times of the pkp precursors can allbeexplainedbyexistenceofseismicscatterersinthelow ermost 100 kmof themantlewest of mexico withinan area of 200 km300 km forward modeling of pkp precursor amplitudes indicates that a p wave velocity variation of at least 6 is required to explain the large amplitudes of the observed pkp precursors suggesting that the core mantle boundary region beneath west of mexico is a highly anoma lous region characterized by strong seismic scatterers

scattered p p waves observed at short distances we detect previously unreported 1 hz scattered waves at epicentral dis tances between 30 and 50 and at times between 2300 and 2450 s after the earthquake origin these waves likely result from off azimuth scattering of pkpbc to pkpbc in the upper mantle and crust and provide a new tool for mapping variations in fine scale 10 km mantle heterogeneity array beams from the large aperture seismic array lasa clearly image the scattered energy gradually emerging from the noise and reaching its peak amplitude about 80 s later and returning to the noise level after 150 s stacks of transverse versus radial slowness t r show two peaks at about 2 2 and 2 2 s indicating the waves arrive along the major arc path 180 to 360 and significantly off azimuth we propose a mantle and surface pkpbc to pkpbc scattering mechanism for these observations because 1 it agrees with the initiation time and distinctive slowness signature of the scattered waves and 2 it follows a scattering path analogous to previously observed deep mantle pkkpscat tering chang and cleary 1981 the observed upper mantle scattered waves and pkkp waves fit into a broader set of scattered waves that we call p 0 dp 0 which can scatter from any depth d in the mantle

thermodynamics of silicate liquids in the deep earth article i nfo we discuss the geophysical implications of recent first principles molecular dynamics simulations of mgsio3 liquid in particular the findings that the gruneisen parameter increases by a factor of three on two fold compression and the predicted melting curve the predicted melting temperature of mgsio3 perovskite at 136 gpa is 5400 600 k which if lowered by freezing point depression by 1300 k yields a mantle solidus temperature of 4100 k identical to recent estimates of the temperature at the base of the mantle we argue on this basis that partial melting at the base of the mantle is plausible while mgsio3 perovskite is denser than the isochemical liquid reasonable values of iron partitioning and bulk iron contents leads to the conclusion that a melt at the base of the multi component mantle would be denser than its surroundings and therefore buoyantly stable we predict the bulk sound velocity of this melt to be 10 9 km s 1 less than that of ultra low velocity zones and consistent with the explanation of these regions as being due to partial melting the increase on compression of the gruneisen parameter in the liquid state yields isentropes that are much hotter than previously thought a potential temperature of only 2450 k is sufficient to melt the entire mantle and a magma ocean will begin crystallization at mid mantle depths rather than at the base of the mantle

sediments at the top of earth s core unusual physical properties at the core mantle boundary have been inferred from seismic and geodetic observations in recent years we show how both types of observations can be explained by a layer of silicate sediments which accumulate at the top of the core as earth cools compaction of the sediments expels most of the liquid iron but leaves behind a small amount of core material which is entrained in mantle convection and may account for the isotopic signatures of core material in some hot spot plumes extraction of light elements from the liquid core also enhances the vigor of convection in the core and may increase the power available to the geodynamo

seismic evidence of partial melt within a possibly ubiquitous low velocity layer at the base of the mantle three source regions show evidence of a low velocity layer that is less than 15 kilometers thick on top of the core mantle boundary and require about a 3 1 ratio of shear to compressional velocity reduction which is consistent with partial melt layer thickness is correlated with travel time residuals of the seismic phases that are most sensitive to the lowermost mantle velocity these observations suggest that the layer is thinned beneath downwellings but is present everywhere along the core mantle boundary low viscosity accompanying partial melt can localize the upwelling of warmed mantle making the low velocity layer a plausible source of mantle plumes

structural features and shear velocity structure of the pacific anomaly 1 we constrain structural features and shear velocity structure of a low velocity anomaly in the lower mantle beneath the pacific we term it the pacific anomaly on the basis of forward travel time and waveform modeling of the observed direct s sdiff scs sks and skks phases sampling a great arc across the anomaly from eastern eurasia to southern south america after correction for the effects of earthquake mislocation and the seismic heterogeneities outside the pacific anomaly seismic observations suggest that the pacific anomaly along the great arc consists of at least two separated portions with a 740 km wide gap between them the western portion of the anomaly is about 1050 km wide extends at least 740 km above the core mantle boundary cmb and exhibits a trapezoidal shape with lateral dimensions increasing slightly with depth the velocity structure of the western portion varies from 3 0 at the top 740 km above the cmb to 3 5 at 100 km above the cmb and an average shear velocity reduction of 5 in the bottom 100 km of the mantle the eastern portion of the anomaly reaches at least 340 km above the cmb beneath the mid pacific with an 1800 km wide base and has a uniform velocity reduction of 3 waveform modeling further suggests a very low velocity layer with a shear velocity reduction of 10 located at the edge of the western portion of the anomaly combining the latest results from others we present a general picture of structural and velocity structures of the pacific anomaly the structural and velocity features suggest that the anomaly represents a cluster of metastable thermo chemical piles

a two dimensional p sv hybrid method and its application to modeling localized structures near the core mantle boundary a p sv hybrid method is developed for calculating synthetic seismograms involving two dimensional localized heterogeneous structures the finite difference technique is applied in the heterogeneous region and generalized ray theory solutions from a seismic source are used in the finite difference initiation process the seismic motions after interacting with the heterogeneous structures are propagated back to the earth s surface analytically with the aid of the kirchhoff method anomalous long period sks spdks observations sampling a region near the core mantle boundary beneath the southwest pacific are modeled with the hybrid method localized structures just above the core mantle boundary with lateral dimensions of 250 to 400 km can explain even the most anomalous data observed to date if s velocity drops up to 30 are allowed for a p velocity drop of 10 structural shapes and seismic properties of those anomalies are constrained from the data since synthetic waveforms are sensitive to the location and lateral dimension of seismic anomalies near the core mantle boundary some important issues such as the density change and roughness of the structures and the sharpness of the transition from the structures to the surrounding mantle however remain unresolved due to the nature of the data

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

probing the core mantle boundary beneath europe and western eurasia a detailed study using pcp summary we use pcp the core reflected p phase recordings of deep earthquakes and nuclear explosions from the grafenberg germany and norsar norway arrays to investigate the core mantle boundary region beneath europe and western eurasia we find evidence for a previously unknown ultra low velocity zone 600 km south east of moscow located at the edge of a middle size low shear velocity region imaged in seismic tomography that is located beneath the volga river region the observed amplitude variations of pcp can be modelled by velocity reductions of p and s waves of 5 and 15 respectively with a density increase of 15 travel time delays of pre and postcursors are indicating a thickness of about 13 km for this ultra low velocity region ulvz however our modelling also reveals highly ambiguous amplitude variations of pcp and a reflection off the top of the anomaly for various ulvzs and topography models accordingly large velocity contrasts of up to 10 in vp and 20 in vs cannot be excluded in general the whole volga river region shows a complex pattern of pcp amplitudes caused most likely by cmb undulations further pcp probes beneath paris kiev and northern italy indicate likely normal cmb conditions whereas the samples below finland and the hungary slovakia border yield strongly amplified pcp signals suggesting strong cmb topography effects we evaluate the amplitude behaviour of pcp as a function of distance and several ulvz models using the 1d reflectivity and the 2d gauss beam method the influence of the velocity and density perturbations is analysed as well as the anomaly thickness the dominant period of the source wavelet and interface topographies strong variation of the pcp amplitude are obtained as a function of distance and of the impedance contrast we also consider two types of topographies undulations atop the cmb in the presence of flat ulvzs and vice versa where a broad range of cmb topography dimensions lead to large pcp amplitude variations only large ulvz undulations generate significant amplitude scattering consequently this indicates that topography effects of anomalies may mask the true medium parameters as well as the ulvz thickness moreover there might be a possibility of misinterpreting the precursor as pcp in particular for thin ulvzs

comparison of nighttime zonal neutral winds and equatorial plasma bubble drift velocities over brazil 1 we present results from the first extended period of coincident observations of thermospheric zonal neutral winds and equatorial plasma bubble epb zonal drift velocities over northeastern brazil during the october to december months of 2009 and 2010 the epb zonal drift velocities are estimated utilizing images of the o i 630 0 nm emissions recorded by a wide angle imaging system at cajazeiras thermospheric neutral wind estimates are based upon common volume observations made by a bistatic fabry perot interferometer fpi experiment using fpis located at cajazeiras and cariri in brazil observing the doppler shift of the o i 630 0 nm emission the results illustrate a similar pattern of nighttime and night to night variations in the zonal neutral winds and epb zonal drift velocities in general the geomagnetic zonal neutral winds and the epb velocities show an excellent agreement illustrating that the f region dynamo is fully developed however in the early evening hours the epb zonal speed is slower than that of the background winds on several occasions we conclude that this indicates that during the bubble evolution period in the early evening the f region dynamo is not fully activated

small scale changes of core mantle boundary reflectivity studied using core reflected pcp abstract short period pcp phases from earthquakes in the western aleutians recorded at the canadian yellowknife array yka sample the core mantle boundary cmb beneath the alaskan kenai peninsula and the cook inlet the pcp to p amplitude ratios for these events show large variability with some amplitude ratios more than an order of magnitude larger than predicted by radial earth models such as iasp91 or prem the amplitude ratios vary laterally with pcp core mantle boundary reflection points showing a 1 region with exceptionally large amplitude ratios it is likely that the variability in relative pcp amplitudes is due in large part to cmb topography other mechanisms such as radiation pattern mantle attenuation focusing and defocusing and core mantle boundary velocity and density perturbations could cause variations on scale lengths of less than a degree as found in this study but are unable to produce variations as large as those we observe

constraints on core mantle boundary topography from normal mode splitting 1 the frequencies of earth s normal modes are split by rotation ellipticity and internal structure of the earth thus models of mantle heterogeneity and discontinuity topography generate splitting that may be tested against observations we insert maps of core mantle boundary cmb topography which are derived via either a purely seismic or a joint tomographic geodynamic inversion of body waves data on top of tomographic model s20rts we then calculate synthetic splitting functions for normal modes that have been shown to be sensitive to cmb topography and compare these to observed normal mode splitting data the cmb topography maps obtained via geodynamically constrained tomography fit normal mode data better than purely seismic maps in particular when the geodynamic constraint also accounts for the presence of post perovskite in the d 00 region we test the significance of the reduction in misfit using the concept of observability which suggests that normal modes are able to observe the difference between the different cmb topography maps in addition we find that the statistical significance assessed by checking what fraction of 1000 randomly generated cmb models achieve a comparatively good fit as the desired model is higher than 92 for degree 2 and 98 for all degrees in summary we have identified a model of cmb topography that fits body wave data and improves at least to some extent the fit to normal mode data and is coherent with the large scale pattern of deep mantle heterogeneity expected on the basis of convection modeling

the 2010 granada spain deep earthquake the deep earthquake h 650 km that occurred on 11 april 2010 south of granada spain has been studied using the inversion of body waves at teleseismic and regional distances we have obtained a solution of dip slip motion on either a vertical plane or a nearly horizontal plane with the pressure axis dipping 45 to the east the horizontal plane is chosen as the rupture plane with rupture propagating from east to west on the basis of directivity effects at teleseismic distances and differences of the waveforms at regional distances the comparison of these results with the focal mechanisms of four other deep earthquakes that occurred in the same area shows similar rupture processes the origin of this deep seismic activity remains an open question tomographic studies have shown the existence of an anomalous body in this region that extends from 200 to 700 km depth the olivine spinel phase transitions or shear melting along horizontal planes inside of this body may be an explanation for the occurrence of these earthquakes

a three dimensional radially anisotropic model of shear velocity in the whole mantle summary we present a 3 d radially anisotropic s velocity model of the whole mantle saw642an obtained using a large three component surface and body waveform data set and an iterative inversion for structure and source parameters based on non linear asymptotic coupling theory nact the model is parametrized in level 4 spherical splines which have a spacing of 8 the model shows a link between mantle flow and anisotropy in a variety of depth ranges in the uppermost mantle we confirm observations of regions with vsh vsv starting at 80 km under oceanic regions and 200 km under stable continental lithosphere suggesting horizontal flow beneath the lithosphere we also observe a vsv vsh signature at 150 300 km depth beneath major ridge systems with amplitude correlated with spreading rate for fast spreading segments in the transition zone 400 700 km depth regions of subducted slab material are associated with vsv vsh while the ridge signal decreases whilethemid mantlehasloweramplitudeanisotropy vsv in the lowermost 300 km which appears to be a robust conclusion despite an error in our previous paper which has been corrected here the 3 d deviations from this signature are associated with the large scale low velocity superplumes underthecentralpacificandafrica suggestingthatvsh vsv isgeneratedinthepredominant horizontal flow of a mechanical boundary layer with a change in signature related to transition to upwelling at the superplumes

scp a probe of ultralow velocity zones at the base of the mantle the core reflected phase scp is a sensitive probe of the properties of an ultralow velocity zone ulvz at the base of the mantle in synthetic experiments a ulvz with large depressions in p and s velocities results in scp having two diagnostic precursors and one later arrival whose timing depends on ulvz vp vs and thickness amplitudes of the additional arrivals can be large if ulvz shear velocity has extreme reductions such as 30 and greater some data examples are presented for southwest pacific events recorded at short period and broadband arrays in hawaii which show evidence for a ulvz resolving all three additional arrivals will help in addressing the strength and ratio of vs and vp reductions in ulvz and thus the issue of partial melt

new seismic and tomography data in the southern part of the harghita mountains romania southeastern carpathians connection with recent volcanic activity the southern part of the southeastern carpathians represents the site of the most recent volcanic eruptions of the entire carpathian pannonian region the products of these eruptions range from 42 to 10 ka radiocarbon ages in the south harghita mountains high k calc alkaline rocks with adakite like features and at 1 2 0 6 ma k ar ages in the persani mountains alkali basalts they were emplaced in a post collisional regime ciomadul volcano is located at the southernmost part of the nw se oriented c limani gurghiu harghita range crossing the inner part of the southeastern carpathians and in the rough proximity of the vrancea seismic zone at ca 60 km toward nw its magma generation is attributed to geodynamic events closely related to the seismogenic area a number of particular geophysical and geochemical features located in the study region including 1 the abrupt attenuation of the seismic waves originating from the vrancea intermediate depth foci 2 the most intense heat flow anomaly in romania 3 the most prominent 3he 4he anomaly measured in natural postvolcanic gas emanations are all in favor of the hypothesis of a still existing hot local magma chamber data acquired during recent seismic monitoring of the vrancea zone and its neighborhoods suggest an enhancement of the local seismicity beneath the southern edge of the south harghita mts both at crustal and subcrustal levels at the same time recent tomography images obtained using local earthquake data correlate well with the presence of a vertically extended low velocity zone coming from the upper mantle to the assumed magmatic chambers located in the crust the present data supporting the presence of an active crustal magma chamber beneath ciomadul allow us to consider that future volcanic activity at this volcano cannot be discarded

core mantle boundary topography from short period pcp pkp and pkkp data abstract we use a total of 839 369 pcp pkpab pkpbc pkpdf pkkpab and pkkpbc residual travel times from bull seism soc am 88 1998 722 grouped in 29 837 summary rays to constrain lateral variation in the depth to the core mantle boundary cmb we assumed a homogeneous outer core and the data were corrected for mantle structure and inner core anisotropy inversions of separate data sets yield amplitude variations of up to 5 km for pcp pkpab pkpbc and pkkp and 13 km for pkpdf this is larger than the cmb undulations inferred in geodetic studies and moreover the pcp results are not readily consistent with the inferences from pkp and pkkp although the source receiver ambiguity for the core refracted phases can explain some of it this discrepancy suggest that the travel time residuals cannot be explained by topography alone the wavespeed perturbations in the tomographic model used for the mantle corrections might be too small to fully account for the trade off between volumetric heterogeneity and cmb topography in a second experiment we therefore re applied corrections for mantle structure outside a basal 290 km thick layer and inverted all data jointly for both cmb topography and volumetric heterogeneity within this layer the resultant cmb model can explain pcp pkp and pkkp residuals and has approximately 0 2 km excess core ellipticity which is in good agreement with inferences from free core nutation observations joint inversion yields a peak to peak amplitude of cmb topography of about 3 km and the inversion yields velocity variations of 5 in the basal layer the latter suggests a strong trade off between topography and volumetric heterogeneity but uncertainty analyses suggest that the variation in core radius can be resolved the spherical averages of all inverted topographic models suggest that the data are best fit if the actual cmb radius is 1 5 km less than in the earth reference model used i e the average outer core radius would be 3478 km

fine scale ultralow velocity zone structure from high frequency seismic array data 1 variability of core mantle boundary cmb structure is imaged at the kilometer to tens of kilometers scale by intensive waveform modeling of the scp phase recordings of earthquakes in the tonga fiji subduction zone from the small aperture 10 km high frequency 2 4 hz alice springs array in central australia are used to document anomalous scp waveform variations due to the presence of an ultralow velocity zone ulvz at the cmb these data expand coverage from previous results using the warramunga array which is located slightly to the north and indicate the existence of a geographically confined ulvz at the cmb roughly 100 km in lateral extent south of new caledonia and east of australia synthetic modeling indicates seismic velocity reductions of 8 and 24 for p wave and s waves respectively and a well constrained density increase of 10 in a 8 5 km thick layer above the cmb this ulvz patch is well explained by an elevated iron content of partially molten mantle material likely present as divalent oxidized iron in the low spin state the properties of such an iron enriched assemblage are consistent with both an elevated density and bulk modulus of this region as are dictated from our best fit seismic results furthermore a positive velocity gradient within the ulvz may be present which need not be associated with a decrease in melt content within this region but could rather be associated with a shift in the textural distribution of melt within the ulvz

core mantle boundary topography as a possible constraint on lower mantle chemistry and dynamics article i nfo the origin of large low shear wave velocity provinces llsvps in the lowermost mantle beneath the central pacific and africa is not well constrained we explore numerical convection calculations for two proposed hypotheses for these anomalies namely thermal upwellings e g plume clusters and large intrinsically dense piles of mantle material e g thermochemical piles each of which uniquely affects the topography on earth s core mantle boundary cmb the thermochemical pile models predict a relatively flat but elevated cmb beneath piles presumed llsvps with strong upwarping along llsvp margins the plume cluster models predict cmb upwarping beneath upwellings that are less geographically organized both models display cmb depressions beneath subduction related downwelling while each of the two models produces a unique characteristic style of cmb topography we find that seismic models will require shorter length scales than are currently being employed in order to distinguish between the end member dynamic models presented here

scp constraints on ultralow velocity zone density and gradient thickness beneath the pacific short period teleseismic recordings of scp from events in the tonga fiji tf and marianas mar subduction complexes made by the u s geological survey hawaiian volcano observatory seismograph network are examined for evidence of pre and post scp phases such arrivals would be caused by interaction of scp with ultralow velocity zone ulvz structures at the base of the mantle and can therefore be used to constrain the properties and occurrence of ulvzs the relative timings and amplitudes of scp two pre scp phases and one post scp phase potentially provide very good constraints on ulvz compressional and shear velocities density and thickness for example the amplitude of the topside s to p conversion sdp is very strongly density contrast dependent while the amplitude of the last arriving scsp a core reflection that converts to p upon emergence from the ulvz is very strongly dependent on the shear velocity contrast previous data largely consisting of diffracted spdiffks arrivals and reflected pcp precursors have been unable to provide good constraints on these two properties in our data set though we find very little evidence for pre and post scp arrivals even for tf paths where abundant evidence for the presence of ulvz exists for the tf data distance range 43 48 precursor amplitudes are at or below the data noise level if the density contrast ln is 10 km thick which lower scsp amplitudes below detectable levels taken together these properties favor ulvz material composed dominantly of partial melt but a contribution from core mantle reaction products cannot be ruled out for the mar distance range 55 58 pre and post scp arrival amplitudes are predicted to be higher although such arrivals are absent from the mar recordings however the quality of our data is not sufficiently good to rule out the presence of thinner and or more subdued ulvz in that region

traveltime and amplitude anomalies at the seismic broad band may grf summary traveltime and amplitude residuals of p waves from teleseismic events show a positive correlation at the stations of the german seismic broad band array grf fast arrivals consistently have reduced amplitudes in the four frequency ranges considered short period bandpass wwssn sp filter broad band velocity and wwssn lp filter with the exception of the wwssn lp filter 40 60 per cent of the average of the relative traveltime and almost 100 per cent of the average of the amplitude residuals at individual stations with respect to the reference station a1 can be explained by near surface sediment layers these shallow structures are known from local and regional geology and are documented in borehole local refraction and polarization studies this aximuthal and distance independent term station average reaches values of up to 0 55 s and 0 15 units in log amplitude magnitude even after the removal of these station averages which also contain a trend of increasing crustal and uppermost mantle velocity from north to south large azimuthal and distance dependent relative traveltime and magnitude residuals can be observed across the array these residuals vary between 0 8 and 1 1 s and 0 54 and 0 72 magnitude units negative fast traveltime residuals are again related to negative magnitude residuals small amplitudes the azimuthal and distance dependent patterns of these residuals are identical within three distinct clusters of stations the main features of the residual patterns correlate well with the main fault systems and inhomogeneities near the array some of which have been postulated previously the velocity anomalies causing the azimuthal and distance dependent residuals are located in crust and uppermost mantle under the array and its vicinity the fact that local effects like sedimentary covers are responsible for 40 per cent or more of the station average residuals demonstrates again that site effects should be removed before tomographic methods are employed the simple stations corrections usually applied in global tomography might severely underestimate the influence of local and regional velocity anomalies since even after the removal of the station average residual large azimuthal and distance dependent traveltime and amplitude anomalies remain between stations less than 100 km apart these anomalies due to shallow inhomogeneities might then erroneously be mapped into features at greater depth

iron rich perovskite in the earth s lower mantle the equations of state of perovskite with mg sub 0 75 fe sub 0 25 sio sub 3 and mgsio sub 3 compositions have been investigated by synchrotron x ray diffraction up to 130 gpa at 300 k in diamond anvil cells here we show that the addition of 25 fe in mgsio sub 3 perovskite increases its density and bulk sound velocity v phi by 4 6 and 6 7 respectively at lower mantle pressures based on concurrent synchrotron x ray emission and moessbauer spectroscopic studies of the samples the increase in v phi and density can be explained by the occurrence of the low spin fe3 and the extremely high quadrupole component of fe sup 2 combining these experimental results with thermodynamic modeling our results indicate that iron rich perovskite can produce an increase in density and a value of v phi that is compatible with seismic observations of reduced shear wave velocity in regions interpreted as dense stiff piles in the lower mantle therefore the existence of the fe rich perovskite in the lower mantle may help elucidate the cause of the lower mantle large low shear velocity provinces llsvps where enhanced density and v phi are seismically observed to anti correlate with the reduced shear wave velocity

localized double array stacking analysis of pcp d and ulvz structure beneath the cocos plate mexico central pacific and north pacific abstract a large high quality p wave data set comprising short period and broadband signals sampling four separate regions in the lowermost mantle beneath the cocos plate mexico the central pacific and the north pacific is analyzed using regional one dimensional double array stacking and modelling with reflectivity synthetics a data screening criterion retains only events with stable pcp energy in the final data stacks used for modelling and interpretation this significantly improves the signal stacks relative to including unscreened observations allows confident alignment on the pcp arrival and allows tight bounds to be placed on p wave velocity structure above the core mantle boundary cmb the pcp reflections under the cocos plate are well modelled without any ultra low velocity zone from 5 to 20 n at latitudes from 15 to 20 n we find evidence for two p wave velocity discontinuities in the d region the first is 182 km above the cmb with a ln vp of 1 5 near the same depth as a weaker discontinuity

whole earth tomography from delay times of p pcp and pkp phases lateral heterogeneities in the outer core or radial anisotropy in the mantle we perform tomographic inversions of compressional wave travel time measurements in order to image the laterally varying radial anisotropy of p wave velocity in the entire mantle in order to achieve an adequate sensitivity to both horizontal and vertical p velocity throughout the mantle we include in our data set travel time measurements corresponding to ray paths of very different geometries specifically we use data associated with the phases p pcp core reflected and pkpbc pkp df core refracted all extracted from the bulletins of the international seismological centre 1964 1993 pcp pkpbc and pkpdf data are also sensitive to the topography of the core mantle boundary cmb and pkp only to the velocity structure of the earth s core these circumstances require that we also allow for cmb topographic anomalies as free parameters in our inversions and investigate the possibility of the existence of lateral heterogeneities in the outer core e g ritzwoller et al 1986 stevenson 1987 wahr and de vries 1989 vasco and johnson 1998 the solution models that we propose include alternatively a laterally heterogeneous outer core a radially anisotropic mantle or both so that trade offs between those features can also be evaluated we conclude that only minor and very localized radially anisotropic anomalies are present in the middle and lower mantle the most prominent being located in the deepest 400 km under the western pacific we find a discrepancy particularly evident by a comparison between different models of the cmb topography between the travel time measurements that are sensitive to the earth s core and those that are not we show that it is not possible to explain this discrepancy only in terms of radial anisotropy of the mantle and or lateral heterogeneity of the outer core

a lower mantle s wave triplication and the shear velocity structure of d summary a lower mantle s wave triplication detected with short and longperiod wwssn and csn recordings indicates a substantial shear velocity discontinuity near 280 km above the core mantle boundary the triplication can be observed in rotated sh seismograms from intermediate and deep focus events throughout the distance range from 70 to 95 three distinct source region receiver array combinations that have been investigated in detail demonstrate consistent travel time and relative amplitude behaviour of the triplication with slight systematic shifts in the triplication indicating up to 40km variations in the depth of the discontinuity modelling of the observations with synthetic seismograms produced with the cagniard de hoop and reflectivity methods constrains the shear velocity increase to be 2 75 k 0 25 per cent comparable to upper mantle discontinuities short period observations indicate that the velocity increase may be a sharp first order discontinuity or may extend over a transition zone no more than 50 km thick the shear velocity gradient below the discontinuity within the d layer is not well constrained by the sh data but slightly positive or near zero velocity gradients are consistent with the long period amplitude ratios of scsh sh

shear and compressional velocity models of the mantle from cluster analysis of long period waveforms summary we present a new technique for the efficient measurement of the traveltimes of long period body wave phases the technique is based on the fact that all arrivals of a particular seismic phase are remarkably similar in shape for a single event this allows the application of cross correlation techniques that are usually used in a regional context to measure precise global differential times the analysis is enhanced by the inclusion of a clustering algorithm that automatically clusters waveforms by their degree of similarity this allows the algorithm to discriminate against unusual or distorted waveforms and makes for an extremely efficient measurement technique this technique can be applied to any seismic phase that is observed over a reasonably large distance range here we present the results of applying the algorithm to the long period channels of all data archived at the iris dmc from 1976 to 2005 for the seismic phases s and p from 23 to 100 and ss and pp from 50 to 170 the resulting large data sets are inverted along with existing surface wave and updated differential traveltime measurements for new mantle models of s and p velocity the resolution of the new model is enhanced particularly in the mid mantle where ss and pp turn we find that slow anomalies in the central pacific and africa extend from the core mantle boundary to the upper mantle but their direct connection to surface hotspots is beyond our resolution furthermore we find that fast anomalies that are likely associated with subducting slabs disappear between 1700 and 2500 km and thus are not continuous features from the upper to lower mantle despite our extensive coverage and high resolution of the mid mantle

delamination or slab detachment beneath vrancea new arguments from local earthquake tomography 1 vrancea located at the southeastern carpathians arc bend is one of the areas in the alpine himalayan belt that features strong earthquakes occurring at intermediate depths 60 200 km in this study we investigated the crustal and lithospheric structure beneath the vrancea seismic area using a local earthquake tomography approach we used an updated and revised catalog spanning from 1982 to 2006 that uses data from both permanent and temporary networks in the target area simultaneous tomographic inversion for the vp and vs anomalies and the vp vs ratio and source locations was done using the lotos code the reliability and robustness of the results were rigorously checked using various tests e g by studying the role of different parameters on the results of the inversion performing the inversion using random data subsets and synthetic modeling the tomography results clearly indicate the presence of a high velocity material beneath vrancea at a depth interval of about 60 200 km that coincides with the distribution of intermediate depth seismicity this result agrees generally with previous tomographic studies we compare two scenarios leading to this structure 1 subduction and slab detachment and 2 drop forming or delamination the latter mechanism presumes that the thickening of the crust due to continent continent collision causes transformation of the mafic lower crust into denser eclogite this material accumulates until it reaches a critical mass at which point it forms a large drop that begins to fall down we propose that the high velocity anomaly we observe in our tomogram might represent the descending eclogitic lower crust material enveloped by the entrained lithosphere it is possible that a similar delamination process can be observed in other parts of the alpine himalayan belt such as in the pamir hindu kush area

the effect of large scale shear velocity heterogeneity on ss precursor amplitudes 1 precursors to the ss wave have been analyzed extensively to characterize seismic discontinuities in the upper mantle we examine the influence of shear velocity heterogeneity on the amplitude of underside shear wave reflections off the 410 i e s410s and 660 i e s660s discontinuities using waveform data from global seismic networks and spectral element method synthetics for four tomographic models of the crust and mantle on average the s660s ss amplitude ratio is smaller than values predicted for the preliminary reference earth model prem and tomographic models of shear velocity perturbations from prem the variation of s410s ss and s660s ss ratios determined for the 3 d models is significant its amplitude depends on the amplitude of shear velocty heterogeneity in the mantle and on the incorporated model for the crust the s410s ss and s660s ss amplitude variations are stronger in the data and do not correlate spatially with the simulated ratios it is therefore not certain that the spatial variation of s410s ss and s660s ss as expressed by cap averaging can be related to compositional heterogeneity in the mantle given the profound influence of the heterogeneous crust and mantle

intense seismic scattering near the earth s core mantle boundary beneath the comoros hotspot i report strong seismic pkp precursors recorded in the seismic stations in tanzania for earthquakes occurred in the fiji subduction zone the observed pkp precursors show clear onsets and rapid variations of amplitude for different events and stations i develop a technique to use the precursor onset times to determine the location of seismic scatterers and apply forward modeling of precursor amplitudes to place constraints on the magnitude of seismic anomalies the travel time analysis indicates that these recorded pkp precursors are caused by the seismic scattering in the lowermost 360 km of the mantle beneath the comoros hotspot the amplitudes of the observed pkp precursors suggest a rather complex seismic structure with a p velocity variation of at least 8 likely associated with partial melt

localized boundary layer below the mid pacific velocity anomaly identified from a pcp precursor dense record sections from deep earthquakes in fiji and argentina recorded on hundreds of short period stations in california at distances of 81 to 85 are used to investigate the detailed p wave velocity structure above the core mantle boundary cmb in the fiji data a secondary phase arriving 2 to 4 s after the direct p is identified as a precursor to pcp this phase provides good evidence for a reflection off the top of a thin low velocity layer above the cmb comparisons to synthetic seismograms indicate a layer thickness of 10 km and a velocity reduction of 5 10 compared to the overlying mantle a record section from an argentina event does not show the pcp precursor indicating that the low velocity layer is not a global feature this thin low velocity layer is in the same place as a much larger s wave velocity anomaly in the lower mantle and is probably indicative of a boundary layer just above the cmb under the mid pacific

p and pcp travel time tomography for the core mantle boundary pcp arrival times reported to the international seismological centre isc are inverted for vertical travel time anomaly at the core mantle boundary cmb we first invert about 2 106 isc first p arrival data for the three dimensional 3 d structure of the mantle and hypocenter locations iteratively the pcp data are corrected for the relocated hypocenters and the 3 d structure this correction has reduced the observed pcp residuals the corrected pcp data are then inverted for the vertical travel time anomalies at the cmb which are due either to velocity anomaly or topographic anomaly the spherical average of the inverted structure requires either a velocity reduction in the boundary layer just above the cmb by 3 if the layer is 20 km thick or a lowering of the cmb by 3 km the heterogeneity pattern of the cmb is drastically different from that of the overlying d layer negative vertical travel time anomalies appear in the northern high latitude region and positive anomalies appear under southeast asia and middle to south america the lateral dimensions of these anomalies are of the order of 40 the anomalies can be interpreted as either a velocity perturbation in the boundary layer 7 if the layer is 20 km thick or an undulation of the cmb 7 km various tests including the error and resolution estimations indicate that these three anomalies are the significant resolvable features of the cmb these anomalies are also corroborated by the result of the joint inversion of p and pcp for both the 3 d mantle and the 2 d cmb assuming that the layer is laterally heterogeneous in iron content and deforms at the base in isostatic equilibrium with the outer core the pcp data are also inverted for the isostatic figure of the boundary layer the velocity perturbation in this case is 5 6 if the layer is 20 km thick and the cmb undulation is only 1 2 km regardless whether the cmb heterogeneity is due to velocity and or topographic perturbations it is dominant in the zonal component of degree 2 while the degree 2 pattern in the lower mantle including the d is dominant in sectorial component

statistical approach of the influence of petrography in mechanical properties and durability of granitic stones the influence of petrographic features on the strength of granitic stones is a wide studied topic which finds different correlations depending on the research and the granite type the aim of this article was to provide an accurate statistical analysis in which the amount of analysed data did not imply any doubt about the representativity of the samples and the accuracy of the results the focused principal component analysis was used because it allows to explain a determinate property in relation to several variables in addition the expression of the results was done as a simple and graphical representation that allowed to interpret the results in a global way data of texture mineralogy and strength of 12 granites were obtained in this study and were completed by those of more than 100 granites obtained from the literature the durability of the twelve granite characterized was also assessed a thermal fatigue test was carried out in 5 5 5 cm cubes revealing that the thermal expansion experimented by the different minerals was enough to produce variations in the crack network even if temperature was lower than the microfissuration threshold

seismic anisotropy in the core mantle transition zone split s waves observed at hockley texas from events in the tonga fiji region of the southwest pacific show predominantly vertically polarized shear wave sv energy arriving earlier than horizontally polarized sh energy for rays propagating horizontally through d after corrections are made for the effects of upper mantle anisotropy beneath hockley a time lag of 1 5 to 2 0 s remains for the furthest events 93 9 100 6 while the time lags of the nearer observations 90 5 92 9 nearly disappear at closer distances the s waves from these same events do not penetrate as deeply into the lower mantle and are not split these observations suggest that a patch of d beneath the central pacific is anisotropic while the mantle immediately above the patch is isotropic the thickness of the anisotropic zone appears to be of the order of 100 200 km observations of shear wave splitting have previously been made for paths that traverse d under the caribbean and under alaska sh leads sv the reverse of the hockley observations but in these areas the fact that sv leads sh in the hkt data shown here suggests a different sort of anisotropy under the central pacific from that under alaska and the caribbean the case of sh travelling faster than sv is consistent with transverse isotropy with a vertical axis of symmetry vti and does not require variations with azimuth the case of sv leading sh is consistent with transverse isotropy with a horizontal axis of symmetry hti an azimuthally anisotropic medium and with a vti medium formed by a hexagonal crystal given that mg fe sio3 perovskite appears unlikely to form anisotropic fabrics on a large scale the presence of anisotropy may point to chemical heterogeneity in the lowermost mantle possibly due to mantle core interactions

on the absence of an ultralow velocity zone in the north pacific 1 using an unusually large earthquake near the big island of hawaii we study the core mantle boundary cmb beneath the north northeastern pacific between hawaii and north america a dense sampling of the cmb is achieved using the core reflected phase pcp recorded at a large number of high quality stations in north america including networks in california oregon washington and alaska as well as at earthscope s usarray stations we apply an adaptive stacking technique for optimal record alignment on specific phases namely p and pcp and subsequently stack seismograms to obtain summation traces possessing relatively high signal to noise ratios of pcp and p anomalous ultralow velocity zone ulvz layering at the cmb has been noted to exist in various parts of the pacific beneath the lowermost mantle large low shear velocity province imaged by tomography ulvz structure produces anomalous pcp waveform variations in the form of precursors to pcp these pcp data however lack precursory energy indicating either that 1 ulvz layering is lacking or 2 that a ulvz is present and thinner than our detection threshold i e less than a few kilometers thick we use synthetic waveform modeling to establish the sensitivity and utility of investigating the time window ahead of pcp for precursors generated from fine scale cmb layering these results combined with evidence for ulvz structure in other parts of the pacific suggest that ulvzs are intermittent and possibly only detectable in regions where mantle currents collect ulvz material whether or not partially molten presumably beneath or near upwellings or plumes

a sharp and flat section of the core mantle boundary the transition zone between the earth s core and mantle plays an important role as a boundary layer for mantle and core convection1 this zone conducts a large amount of heat from the core to the mantle and contains at least one thermal boundary layer2 3 the proximity of reactive silicates and molten iron leads to the possibility of zones of intermediate composition4 here we investigate one region of the core mantle boundary using seismic waves that are converted from shear to compressional waves by reflection at the boundary the use of this phase known as scp the large number of receiving stations and the large aperture of our array all provide higher resolution than has previously been possible5 7 for the 350 km long section of the core mantle boundary under the northeast pacific sampled by the reflections the local boundary topography has an amplitude of less than 500 m no sharp radial gradients exist in the 400 km above the boundary and the mantle to core transition occurs over less than 1 km the simplicity of the structure near and above the core mantle boundary argues against chemical heterogeneity at the base of the mantle in this location

surface waves from underground explosions with spall analysis of elastic and nonlinear source models anomalous surface wave observations from underground explosions have been widely attributed to the phenomenon of spall i e the detachment and subsequent slapdown of near surface layers in response to explosion induced tensile stresses we argue on the basis of a simple equivalent force model that while spall can enhance explosion surface waves at very short periods it cannot contribute significantly to the teleseismic surface waves radiated by underground explosions at periods exceeding about 10 sec previous theoretical results to the contrary are in error having been based on source models which do not conserve momentum a nonlinear two dimensional axisymmetric finite difference simulation of a buried explosion in granite further supports the conclusion that spall cannot contribute to long period surface waves the simulation exhibits extensive spall nonetheless predicted fundamental mode rayleigh wave spectra are nearly identical to those obtained from a spherically symmetric simulation which does not include spall at periods exceeding about 10 sec at shorter periods the two dimensional simulation predicts some rayleigh wave enhancement compared to the one dimensional simulation the maximum enhancement about a factor of 2 occurs at a period of approximately 2 5 sec synthetic long period rayleigh wave seismograms at 3000 km range show no perceptible phase or amplitude anomalies due to spall these results are in excellent agreement with the predictions of our equivalent force model

seismic yield determination of soviet underground nuclear explosions at the shagan river test site summary a study of p and lg based source size estimators has been conducted for 101 presumed underground nuclear explosions at the shagan river test site near semipalatinsk ussr a systematic variation in the relative patterns across the test site has been observed when comparing the p wave estimators world wide mb and ulm and the lg based observations rms lg determined from norsar and grafenberg array recordings these variations correlate well with geological features determined from satellite imagery and suggest in particular that the northeast and southwest portions of the test site divided by the chinrau fault are characterized by distinct geophysical properties a difference in m p mlg bias of as much as 0 15 magnitude units exists between these two subareas available data indicate that the mlg observations are very consistent with published yields and suggest that the magnitude yield relationship for p wave based estimators can be significantly improved by introducing regional bias corrections we have determined such corrections for three subareas of the test site and used the corrected mh and ym observations in combination with the lg data in a weighted averaging scheme to arrive at yield estimates for all events in the database for the explosion of 1988 september 14 we obtain yield estimates from the three estimators ranging from 106 to 118 kt which is consistent with the independently derived estimates of 115 122 kt quoted by sykes ekstrom 1989 a further assessment of the validity of our results would require access to independently measured yields of additional explosions

seismic evidence for small scale heterogeneity throughout the earth s mantle details in the amplitude structure of short period precursors to the seismic core phase pkp can be used to constrain the depth extent of mantle scattering the simplest model consistent with the observations invokes small 8 km weak r m s velocity perturbations of 1 random heterogeneities uniformly distributed throughout the mantle the data do not support previously proposed models that place an increase in the concentration of scattering sites near the base of the mantle and instead place an upper limit on the amplitude of any short wavelength topography at the core mantle boundary

reflection seismic profiles of the core mantle boundary 1 high amplitude high frequency and laterally coherent seismic phases from the core mantle boundary cmb are observed on data from peaceful nuclear explosions in siberia these arrivals are observed at 2600 4000 km offset with travel times and move outs consistent with cmb reflections pcp and are readily correlated because of the small station interval of 10 km the duration and complexity of the arrivals are inconsistent with a simple reflection from a single cmb interface they require the combination of pcp and a complex precursor phase pdp from the top of an ultralow velocity zone ulvz despite the fact that earthquake recordings indicate that there is no ulvz present beneath this part of siberia lateral variations in the waveform imply that the thickness and physical properties of the ulvz change with a wavelength of 150 200 km and an amplitude of up to 8 km we find at least one location where there is no ulvz present at another well sampled location the precursor has higher frequency content than the primary arrival reflectivity modeling of these pcp pdp phases shows that kilometer scale layering may be required in the ulvz to explain the seismic waveform and the frequency split the modeling shows very low velocity in the ulvz with reductions of 25 and 40 for p and s waves respectively this indicates higher percentages of partial melt in the ulvz than hitherto interpreted our observations indicate that the ulvz may be present over wide areas of the earth with a thickness below the resolution limit of seismological data with a lower frequency content

simultaneous inversion of steep angle observations of pcp and scp in europe what can we learn about the core mantle boundary summary at epicentral distances less than 30 the steep angle reflections pcp and scp from the core mantle boundary cmb are normally difficult to identify and rarely reported the reason is that the reflection coefficient at the cmb for these phases is relatively small and pcp and scp onsets are often disturbed by interference with other more prominent phases however the absolute traveltimes of pcp and scp in the steep angle range are the most sensitive seismic phases for depth undulations of the cmb and in addition of all cmb reflections these phases are influenced least by lateral heterogeneities along their ray paths during this study a set of more than 200 such reflections from the earth s core observed at european stations with reflection points below europe was collected and analysed starting from observations at the geres array in germany pcp and scp could also be identified at other european seismic stations the stations used for this study were the fennoscandian arrays norsar nores and fines the grafenberg array in germany and the stations of the german regional seismic network grsn with the combined investigation of pcp and scp a map of reflection points of the cmb below europe could be constructed to reduce the influence of location and other errors traveltime differences were measured between the onsets of p or pn pcp and scp these traveltime differences show positive and negative deviations from theoretical values of up to several seconds cmb undulations of up to 6 km as discussed in the literature change the absolute traveltimes of pcp or scp only by about 0 9 or 1 2 s for an epicentral distance of 20 the observed residuals can be explained by several factors still unresolved location errors lateral heterogeneities along the whole ray paths of all investigated phases or undulations of the depth of the cmb all observed traveltime effects must be known at least one order of magnitude better than the expected effects to resolve statistically reliable cmb undulations inverting the residuals for possible cmb undulations shows that if there is any cmb signal in the data it is very small most of the observed residuals can easily be explained by smaller changes in event depth lateral heterogeneities in the source region and along the whole ray paths and or station corrections but the observations do not require any cmb topography if such undulations of up to 6 km exist all other traveltime effects will mask them coming to this disillusioning result by using the most sensitive data to resolve a cmb topography can only lead to this conclusion all models of cmb undulations derived from traveltime data must be taken as very unsure and any far reaching interpretations of such models should be avoided

seismic anisotropy in the lowermost mantle beneath the pacific onset time differences of up to 3 s are observed between transverse ssh and longitudinal ssv components of broadband s waves at distances of 85 to 120 for paths traversing the lowermost mantle d beneath the pacific after correction for upper mantle anisotropy ssh usually arrives earlier than ssv with the splitting increasing with distance from 100 to 120 the data yield two possible models of anisotropy 1 anisotropy may vary laterally with transverse isotropy existing in higher than average shear velocity regions beneath the northeastern pacific or 2 anisotropy may vary with depth with transverse isotropy concentrated in a thin 100 km thermal boundary layer at the base of d a few recordings at distances less than 105 show that ssv arrives earlier than ssh indicating that general anisotropy likely exists in shallower regions of d

a very slow basal layer underlying large scale low velocity anomalies in the lower mantle beneath the pacific evidence from core phases a multi phase analysis using long period world wide standardized seismograph network and canadian network data has been conducted using core phases for deep focus events from the southwest pacific these include sks s2ks svd iff and sp dks the last phase emerges from sks near 106 and is associated with a p wave diffracting along the bottom of the mantle patterns in s2ks sks differential travel times t s2ks sks correlate with those in sp dks sks t spdks sks t s2ks sks values strongly depend on variations in v s structure in the lower third of the mantle whereas t spdks sks values mainly depend on v p structure and variations in a thin zone 100 km or less at the very base of the mantle anomalously large t s2ks sks and t spdks sks values relative to the preliminary reference earth model prem are present for fiji tonga and kermadec events recorded in north and south america along with anomalously large sv diff amplitudes well into the core s shadow more northerly paths beneath the pacific to north america for indonesian and solomon events display both prem like and anomalous times a model compatible with the observations is presented and contains a thin very low velocity layer at the base of the mantle that underlies the large volumetric lower mantle low velocity regions in the southwest pacific a low velocity layer of 20 100 km thickness with reductions of up to 5 10 relative to prem can reproduce t spdks sks as well as sv diff amplitudes large scale more than 1000 km lower mantle v s heterogeneity 2 4 can explain long wavelength trends in t s2ks sks the exact thickness and velocity reduction in the basal layer is uncertain owing to difficulties in resolving whether anomalous structure occurs on the source and or receiver side of wavepaths at the cmb

solid liquid iron partitioning in earth s deep mantle iron in partially molten rocks under deep mantle conditions partitions into the melt phase less than previously reported suggesting that melt generated near the core mantle boundary should segregate upwards denis andrault et al investigate phase relationships in partially molten rocks under deep mantle conditions and find that iron in the rocks partitions into the melt phase to a lesser extent than has previously been reported the calculated densities of the solid and melt phases suggest that melt generated near the core mantle boundary should be buoyant and hence should segregate upwards melting processes in the deep mantle have important implications for the origin of the deep derived plumes believed to feed hotspot volcanoes such as those in hawaii1 they also provide insight into how the mantle has evolved geochemically and dynamically since the formation of earth2 melt production in the shallow mantle is quite well understood but deeper melting near the core mantle boundary remains controversial modelling the dynamic behaviour of deep partially molten mantle requires knowledge of the density contrast between solid and melt fractions although both positive and negative melt buoyancies can produce major chemical segregation between different geochemical reservoirs each type of buoyancy yields drastically different geodynamical models ascent or descent of liquids in a partially molten deep mantle should contribute to surface volcanism or production of a deep magma ocean respectively we investigated phase relations in a partially molten chondritic type material under deep mantle conditions here we show that the iron partition coefficient between aluminium bearing mg fe sio3 perovskite and liquid is between 0 45 and 0 6 so iron is not as incompatible with deep mantle minerals as has been reported previously3 calculated solid and melt density contrasts suggest that melt generated at the core mantle boundary should be buoyant and hence should segregate upwards in the framework of the magma oceans induced by large meteoritic impacts on early earth our results imply that the magma crystallization should push the liquids towards the surface and form a deep solid residue depleted in incompatible elements

regional waveform calibration in the pamir hindu kush region twelve moderate magnitude earthquakes m b 4 5 5 in the pamir hindu kush region are investigated to determine their focal mechanisms and to relocate them using their regional waveform records at two broadband arrays the kyrgyzstan regional network knet and the 1992 pakistan himalayas seismic experiment array pakh in northern pakistan we use the cut and paste source estimation technique to invert the whole broadband waveforms for mechanisms and depths assuming a one dimensional velocity model developed for the adjacent tibetan plateau for several large events the source mechanisms obtained agree with those available from the harvard centroid moment tensor cmt solutions an advantage of using regional broadband waveforms is that focal depths can be better constrained either from amplitude ratios of pnl to surface waves for crustal events or from time separation between the direct p and the shear coupled p wave spn spmp for mantle events all the crustal events are relocated at shallower depths compared with their international seismological centre bulletin or harvard cmt depths after the focal depths are established the events are then relocated horizontally using their first arrival times only minor offsets in epicentral location are found for all mantle events and the bigger crustal events while rather large offsets up to 30 km occur for the smaller crustal events we also tested the performance of waveform inversion using only two broadband stations one from the knet array in the north of the region and one from the pakh array in the south we found that this geometry is adequate for determining focal depths and mechanisms of moderate size earthquakes in the pamir hindu kush region

p and s wave reflections from anomalies in the lowermost mantle summary seismic p and s waves recorded at the grf array in germany are used to study the inhomogeneous structure of the boundary layer d at the base of the mantle the use of the seismic array allows the detection of small scale anomalies in the lowermost mantle the lateral resolution attainable is about 100 to 400 km i e more than 10 times better than with tomographic methods the analysis of 13 years of grf broad band array data yields 255 events with high signal to noise ratio which are used to map the lowermost mantle 74 of these events show anomalous p waves pdp which arrive 3 6 s after the direct p wave and have a slowness 0 7 0 8 s smaller than the slowness of direct p other events close to the events with pdp do not have such an anomalous phase using slowness traveltime amplitude and waveform information it is demonstrated that pdp is caused by an anomalous lower mantle velocity structure below the turning point of the p wave if the pp phase i e a p wave first reflected at the free surface near the source is used together with the p phase distinct and well sepaarted p velocity anomalies can be determined under the nansen basin the kara sea and northern siberia the areas of the bounce points of pdp in the lower mantle have a lateral extension of about 100 by 200 km but this is not the size of the anomaly since the resolution of p waves at 1 hz in this depth is 130 km by 260 km fresnel zone the accuracy to which the depth of the reflector 2612 km under the nansen basin and 2605 km under northern siberia respectively can be determined for 1 d models is 10 to 20 km the velocity contrast at the lower mantle discontinuity is about 3 per cent 1 to 1 5 per cent areas which have velocity fluctuations smaller than about 1 per cent can not be detected as anomalous areas 2 d models of the anomalies reveal the range of adequate models and possible trade offs if the lateral extension of the anomaly is about 7 the reflector has to be 40 km deeper than in the 1 d model if the dip of the reflector in the lowermost mantle is only about 1 5 it is difficult to resolve if the reflector is tilted towards the source or towards the receiver for the anomaly under the nansen basin deviations from the great circle path are observed for pdp indicating 3 d effects below the three anomalies the core mantle boundary cmb can be located by pcp with a depth in agreement with standard earth models under northern siberia has a region where p and s velocity anomalies coincide but also a region where only an s velocity anomaly but no p velocity anomaly is observed this results in changes of the poisson ratio from 5 9 per cent to 4 8 per cent 1 5 per cent across the discontinuity in the lowermost mantle for the regions studied the analysis of the s waves s sds and scs reveals two s velocity anomalies in the lowermost mantle under northern siberia the first anomaly coincides with the p velocity anomaly under northern siberia and can be explained by a 1 d model with a reflector depth of 2610 km 15 km and a velocity contrast of 2 3 per cent the second s velocity anomaly is in an area where no p velocity anomaly can be detected the corresponding 1 d s velocity model has a reflector depth of 2575 km 15 km and an s velocity contrast of 2 6 per cent the smallest structures that can be resolved with the s waves in this depth are about twice as large as for the p waves i e 230 km by 460 km fresnel zone the joint analysis of p and s waves therefore shows a region with a p velocity anomaly together with weak indications for an s velocity anomaly nansen basin and a second region with a p but no s anomaly kara sea the lowermost mantle

evidence for normal and inhomogeneous lowermost mantle and core mantle boundary structure under the arctic and northern canada summary seismic p waves from a total of about 200 nuclear explosions in the usa the former ussr and china observed at 10 arrays and four networks in europe canada and the usa are used to analyse the structure at the base of the mantle and the core mantle boundary cmb the simple waveforms and well controlled source parameters of nuclear explosions allow one to use the events as source arrays in addition to the usual receiver array configuration a new array technique double beamforming kruger et al 1993 integrating both concepts is applied which increases the slowness resolution considerably a total of 56 source receiver combinations i e reflection points in the lower mantle or on the cmb could be analysed in five regions anomalous arrivals pdp with slowness and arrival times between those of p and pcp are observed one of these five areas svalbard region shows short period pcp p amplitude ratios which are about three times higher than those predicted by standard earth models in the severnaya zemlya region where pdp and pcp precursors were observed previously kruger et al 1993 pcp shows azimuth deviations of up to 10 for some other regions deviations of the pcp waveform from the direct p waveform are also observed these anomalous phases and the pcp waveform distortions cannot be explained with standard 1 d earth models they are probably produced by inhomogeneities in the lowermost mantle the observed variations in the waveforms are strong indications of a laterally heterogeneous structure in two depth ranges the first is the cmb and its immediate vicinity of a few tens of kilometres the second region is the depth range between about 200 and 300 km above the cmb maps of the north pole region giving the distributions of inhomogeneities in the lower mantle and on the cmb are presented these maps show evidence of strong heterogeneity of the d boundary layer and possibly also of the cmb in the same area

high resolution cmb imaging from migration of short period core reflected phases abstract the fine scale structure of the core mantle boundary cmb region beneath southern alaska is studied using core reflected p waves pcp recorded at the canadian yellowknife array seismic studies of the lowermost mantle have detected a multitude of structures at this contact zone between iron alloy liquid of the core and the silicates of the mantle these structures offer key constraints for the dynamics of mantle and core high quality waveform information and migrated array data have been used to infer the existence of thin layering at the cmb in the form of ultra low velocity zones the data clearly show the absence of an ultra low velocity zone thicker than about 7 km in this region while there is evidence for a weak p wave reflector about 110 km above the cmb beneath the kenai peninsula these observations are in good agreement with the hypothesis that ultra low velocity zones are related to areas with lower than average seismic velocities in tomographic images and absent in regions of fast seismic velocities likely related to subduction processes such as beneath alaska

the romanian earthquake of august 30 1986 a study based on geoscope very long period and broadband data the romanian earthquake of august 30 1986 is the second largest intermediate depth event in this area since the worldwide deployment of digital instrumentation and the first one since the installation of geoscope network it offers the unique opportunity to document this well known but poorly understood zone of deep continental seismicity using high quality teleseismic data in different frequency bands the source is well constrained both from very long period surface wave data observed on geoscope stations and independently from body wave modelling at various worldwide stations the depth obtained is approximately 140 kilometers the seismic moment 0 8 1027 dyne cm and the mechanism from both data sets is very similar to that of the previous 1940 and 1977 vancrea events indicating that these events although having occurred at noticeably different depths are expressions of the same tectonic process however from the detailed study of the source using broadband data it can be inferred that the source presents much less complexity than the 1977 event

detailed investigation of a spot on the core mantle boundary using digital pcp data abstract a number of deep earthquakes from the fiji tonga region were used to study the properties of the core mantle boundary cmb the investigation was restricted to an area with a diameter of only a few hundred kilometers at the cmb the use of a cluster of neighboring events yielding redundant sampling and rather good resolution the components of the investigation are i a classical stacking procedure to search for additional reflectors near the cmb ii a deconvolution of seismograms and a stack of the inferred reflector series for the same purpose iii a matched filter method to determine pcp travel times and pcp p amplitude ratios precisely and iv a comparison with synthetic seismograms to check the consistency of derived travel time residuals and pcp amplitude variations in the presence of cmb topography while we do not see any additional reflector for epicentral distances around 35 we detect by stacking seismograms recorded at 70 an additional phase which might be caused by a reflection from the top of d we show that pcp travel time residuals must not be interpreted as being caused exclusively by cmb topography an additional investigation of synthetics provides some constraints on dominant wavelengths and corresponding amplitudes of cmb undulations for wavelengths of 50 400 km the elevation cannot exceed 2 3 km if pcp is observed in this particular area

small scale ultralow velocity zone structure imaged by scp 1 short period teleseismic scp phases from events in the tonga fiji region recorded at the short period small aperture warramunga array in australia are used to study structure at the core mantle boundary cmb we examine the data for evidence of precursors and postcursors to scp such additional arrivals are generated by the interaction of scp with structure at the reflection and conversion point at or near the cmb we show precursors and postcursors to scp indicating an ultralow velocity zone ulvz at the cmb in the region between tonga fiji and australia one dimensional forward modeling of the short period data leads to models of the ulvz with thickness varying between 5 and 20 km velocity reductions of 0 10 and 10 30 for p velocity and s velocity respectively and 0 50 density increase many events however show simple waveforms consistent with a locally simple cmb models for proximal events can vary greatly indicating very complex three dimensional structure with scale lengths of a few tens of kilometers these results point to complex chemical and physical processes in the lowermost mantle

anisotropy as cause for polarity reversals of d reflections recordings of seismic events that sample the deep mantle can test different hypotheses of mantle processes and composition seismic reflections from structures in the d region the bottom 200 400 km of the earth s mantle can provide information on the velocity contrasts in this region by studying the waveforms and polarities of the d reflections in p and s waves we can potentially distinguish between different explanations for the observed structures such as phase transitions mineral texture or thermal anomalies here we use source receiver combinations that contain reflections from d in two different regions that are both characterised by fast seismic velocities in tomographic models beneath the caribbean a positive s velocity contrast but negative p wave velocity contrast across the d reflector has been reported previously consistent with a model of a phase change in mgsio3 in the second fast velocity region eurasia we detect positive p and s wave velocity contrasts in two orthogonal paths crossing in the lowermost mantle indicating a different scenario for d a path that crosses this region in 45 to the other two great circle paths shows evidence for a negative p velocity contrast one explanation to reconcile observations in both regions is a phase transition from perovskite to post perovskite with a fraction of 12 preferred crystal alignment in the post perovskite phase depending on the travel direction of the waves with respect to the flow direction in the lower mantle positive or negative velocity jumps can be expected other anisotropic models are considered but cannot fully explain the range of observations we find in the data c 2011 elsevier b v all rights reserved

geodynamics and intermediate depth seismicity in vrancea the south eastern carpathians current state of the art abstract the vrancea region of the south eastern carpathians is a remarkable site of intra continental intermediate depth seismicity a large set of geological geophysical and geodetic observations has been accumulated for the last few decades and utilised to improve our knowledge of the shallow and deep structures beneath vrancea the crustal and mantle dynamics and the linkage between deep and surface processes in the region in this article we review geology and tectonics of the vrancea region including post collisional to recent deformations syn to post collisional magmatism and orogenic exhumation along the east and south carpathians the regional seismicity is analysed and the recent seismic studies including reflection refraction body and surface wave tomography are reviewed we discuss new geodetic measurements of horizontal and vertical movements in the region geoelectric studies density gravity and thermal modelling qualitative and quantitative including retrospective geodynamic models developed for vrancea are analysed the knowledge of regional tectonics geodynamics seismicity lithospheric deformation and stress regime in the vrancea earthquake prone region assists in an assessment of strong ground motion seismic hazard and risk the earthquake simulation seismic hazard and earthquake forecasting models have also been reviewed providing a link between deep geodynamic processes and their manifestation on the surface finally we discuss unresolved problems in vrancea in order to improve our understanding of the regional evolution present tectonics mantle dynamics intermediate depth seismicity and surface manifestations of the lithosphere dynamics and to enhance our ability to forecast strong earthquakes in the vrancea region the problems to be solved include i the origin of the high velocity body revealed by seismic tomography studies oceanic versus continental ii the lithospheric scale mechanism driving the miocene subsidence of the transylvania basin iii sub crustal structure between 40 and 70 km iv contemporary regional horizontal and vertical movements and v a comprehensive seismic hazard assessment in the region

a study of small magnitude seismic events during 1961 1989 on and near the semipalatinsk test site kazakhstan official russian sources in 1996 and 1997 have stated that 340 underground nuclear tests unts were conducted during 1961 1989 at the semipalatinsk test site sts in eastern kazakhstan only 271 of these nuclear tests appear to have been described with well determined origin time coordinates and magnitudes in the openly available technical literature thus good open documentation has been lacking for 69 unts at sts

the upper mantle transition zone discontinuities in the pacific as determined by short period array data short period array recordings from pacific earthquakes show precursors to pp produced by underside reflections of p waves off the discontinuities in the upper mantle we use these events to study the structure of the transition zone discontinuities in the central and northern pacific the discontinuities of the mantle transition zone at depths of 410 km and 660 km are particularly interesting for the interpretation of the chemistry and temperature structure of the mantle transition zone the pp reflections from these discontinuities are too small to be identified in unprocessed seismograms therefore array methods are used to detect and identify the pp underside reflections the data of several events show reflections from the 410 km discontinuity the topography of the reflector can be used to study the olivine to spinel phase transition in the central and northwestern pacific the mean depth of the reflector is 404 16 km with topography near the hawaiian islands and the kuriles forward modeling enables an estimate of the minimum impedance contrast and the maximum thickness of the discontinuity this study shows that the 410 km discontinuity must be sharper than 6 km assuming a simple linear gradient for the kcl phase change with an impedance contrast of 8 9 as in iasp91 to be in agreement with our data the minimum impedance contrast for a first order discontinuity would be 6 5 the 660 km discontinuity cannot be detected in this dataset using pp underside reflections in agreement with previous studies forward modeling shows that the non detection of the 660 can be explained by a discontinuity with a thickness of more than 12 km for the iasp91 impedance contrast or by a first order discontinuity with an impedance contrast of less than v9 5 2002 elsevier science b v all rights reserved