low p wave velocity at the base of the mantle a tool for investigating p wave vp structure at the base of the mantle is presented sks waves at distances around 107 are incident upon the core mantle boundary cmb with a slowness that allows for coupling with diffracted p waves pd at the base of the mantle the p wave diffraction occurs at both the sks entrance and exit locations of the outer core the resulting phase spdks arrives slightly later in time than sks having a wave path through the mantle and core very close to sks the difference time between sks and spdks most strongly depends on vp at the base of the mantle near sks core entrance and exit points digitized long period 5 15s observations from deep focus tonga events recorded by north american wwssn and canadian seismographic network stations and south american events recorded by european and eurasian wwssn stations exhibit anomalously large spdks sks difference times sks and the later arriving spdks are separated by several seconds more than predictions made by the global average prem model models having a pronounced low velocity zone in vp at the base of the mantle best predict the observations these models are perturbations of the prem model whereby the lowermost 50 100 km of the d layer has a negative vp gradient with the mantle side cmb vp reduced from prem by 5 to 13 0 km s at the base of the mantle

sks and spdks sensitivity to two dimensional ultralow velocity zones 1 seismic wave propagation through two dimensional core mantle boundary cmb ultralow velocity zones ulvzs is modeled using a global pseudospectral algorithm seismograms are synthesized for several types of ulvz models to investigate the effect of these structures on sks and spdks phases one dimensional models and two dimensional models with different quasi 1 d velocity structures on the source and receiver sides of the cmb provide a baseline for comparison with other 2 d models models with finite length ulvzs are used to test the sensitivity of the spdks travel time and waveform to different portions of the p diffracted wave path this test shows that spdks waves are only sensitive to ulvzs with lengths 100 km our results give three tools for identifying and characterizing 2 d ulvz structures first dual spdks pulses indicate exposure to at least two separate cmb velocity structures either different source and receiver side cmb velocities or different adjacent velocity regions for which pdiff inception occurs outside of and propagates into a ulvz second high amplitude sks precursors indicate a very strong i e thick and or large velocity perturbations ulvz hence the absence of sks precursors in most previous ulvz studies indicates that very strong sharp ulvzs are not common third mean spdks delays relative to prem constrain the minimum ulvz strength and length combinations required to produce a given travel time delay

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

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

in situ observations of phase transition between perovskite and cairo 3 type phase in mgsio 3 and pyrolitic mantle composition abstract in situ observations of the perovskite cairo3 phase transition in mgsio3 and in pyrolitic compositions were carried out using a laser heated diamond anvil cell interfaced with a synchrotron radiation source for pure mgsio3 the phase boundary between the orthorhombic mg perovskite and cairo3 type phases in the temperature range of 1300 3100 k was determined to be p gpa 130 3 0 0070 0 0030 t 2500 k using platinum as a pressure calibrant we confirmed that the cairo3 type phase remained stable up to pressures of at least 156 gpa and temperatures of 2600 k the consistency of our results with previous theoretical calculations leads us to conclude that the 2700 km seismic discontinuity at the bottom of the lower mantle can be attributed to a phase transition to the cairo3 type phase the phase change from an orthorhombic mg perovskite to a cairo3 type bearing assemblage in a pyrolitic mantle composition was also observed at p 125 gpa which corresponds to the same mantle depth as the seismic discontinuity the phase boundary between the orthorhombic mg perovskite and cairo3 type bearing assemblage was determined to be p gpa 124 4 0 008 0 005 t 2500 k using gold as a pressure calibrant this transition boundary indicates that the temperature at a depth of 2700 km is about 2600 k and the adiabatic temperature gradient in the lower mantle is estimated to be 0 31 k km the partition coefficients and the effect of some elements on the phase equilibrium between the orthorhombic mgsio3 perovskite and cairo3 type mgsio3 were estimated from ab initio calculations our experimental and theoretical results indicate that the d layer consists of a cairo3 type bearing assemblage which is likely to have significant effect on the chemical and thermal evolution of the earth s mantle

beyond receiver functions passive source reverse time migration and inverse scattering of converted waves 1 we present a wave equation prestack depth migration to image crust and mantle structures using multi component earthquake data recorded at dense seismograph arrays transmittedp and swaves recorded on the surface are back propagated using an elastic wave equation solver the wave modes are separated after the reverse time continuation of the wavefield from the surface and subjected to a cross correlation type imaging condition forming an inverse scattering transform reverse time migration rtm does not make assumptions about the presence or properties of interfaces notably it does not assume that interfaces are locally horizontal with synthetic experiments and different background models we show that passive source rtm can reconstruct dipping and vertically offset interfaces even in the presence of complex wave phenomena such as caustics and point diffraction and that its performance is superior to traditional receiver function analysis e g common conversion point ccp stacking in complex geological environments

lithospheric assembly and modification of the se canadian shield abitibi grenville teleseismic experiment this paper presents the results of a joint lithoprobe incorporated research institutions for seismology iris program for array seismic studies of the continental lithosphere passcal teleseismic experiment that investigates portions of the grenville and superior provinces of the canadian shield along the quebec ontario border data from a 600 km long n s array of 28 broadband seismographs deployed between may and october 1996 have been supplemented with additional recordings from an earlier 1994 deployment and from stations of the canadian national seismograph network and the southern ontario seismic network relative delay times of p and s waves from 123 and 40 teleseismic events respectively have been inverted for velocity perturbations in the upper mantle and reveal a low velocity nw se striking corridor that crosses the southern portion of the line at latitude 46 n and lies between 50 and 300 km depth multievent s k s splitting results yield an average delay time of 0 57 0 22 s and a direction of fast polarization of n93 e 18 which is consistent with an earlier interpretation as being due to fossil strain fields related to the last major regional tectonic event subtle variations in splitting parameters over the low velocity corridor may suggest an associated disruption in mantle fabric profiling of radial receiver functions reveals large and abrupt variations in moho topography specifically a gradual thickening in crust from 40 to 45 km between latitudes 45 n and 46 n which is followed by an abrupt thinning to 35 km at 46 6 n some 65 km southeast of the grenville front this structure is interpreted as a subduction suture extending the full length of the front and punctuating a major pre grenvillian archean proterozoic episode of lithospheric assembly in the southeast canadian shield the low velocity mantle corridor by contrast is better explained as the extension of the monteregian white mountain new england seamount hotspot track below the craton and is here postulated to represent interaction of the great meteor plume with zones of weakness within the craton developed during earlier rifting episodes

imaging of structure at and near the core mantle boundary using a generalized radon transform 1 construction of image gathers 1 we introduce a method for imaging heterogeneity at and near interfaces in earth s lowermost mantle with broadband three component seismograms from global seismograph networks our approach is based on inverse scattering and allows the extraction of pertinent signal from large data sets and requires few a priori assumptions about the heterogeneity under study which makes it complementary to the forward modeling of selected waveforms here we construct a generalized radon transform for heterogeneous anisotropic elastic media to map broadband seismogram windows comprising main arrivals with their coda and precursors into multiple images of a target structure the common image point gathers thus produced reveal multiscale variations in elastic properties near deep interfaces the grt can be applied to narrow and wide angle data and the automated extraction of signal from data over a wide range of epicentral distances enables exploration of core mantle boundary cmb regions that cannot with present day data coverage be imaged with the triplicated waveforms used in forward modeling studies tests with synthetic data produced both with idealized and actual source receiver distributions illustrate pertinent aspects of the theory and show that multiple weak interfaces can be detected and located correctly with a radial resolution of 15 km for the frequencies used even in the presence of random noise that would prohibit visual inspection and modeling of the subtle signals we transformed the transverse component scs waveforms into image gathers of a cmb patch beneath central america juxtaposition of stacks of these gathers involving 35 000 seismograms produces a two dimensional 2 d image profile revealing contrasts in elastic properties near the target depth of the cmb and 280 340 km above it the latter may mark the top of the so called d region the images also reveal a richness of structures in between these depths combined with a statistical analysis of these singularities described in paper 2 the approach to imaging presented here paves the way to large scale seismic exploration of the lowermost mantle

seismic detection of rigid zones at the top of the core data from earthquakes in the tonga fiji region recorded at a seismic array in northern australia show evidence for rigid zones at the top of the outer core the scp waveforms can be modeled by thin 0 12 to 0 18 kilometer zones of molten iron mixed with solid material with a small but positive s wave velocity 0 6 to 0 8 kilometer per second that enables the propagation of s waves in the outermost core the zones may be topographic highs of the core mantle boundary filled by light core sediments and might be important for variation of earth s nutation and for convection of the outer core

modeling the ratios of skks and sks amplitudes with ultra low velocity zones at the core mantle boundary 1 between 105 115 degrees the sks waveform is complicated by the formation of spdks a wave that has segments of p diffraction along the core mantle boundary while previous studies have primarily focused on the move out of spdks from sks we analyze the concomitant reduction of the sks amplitude long period skks sks amplitude ratios present a coherent global pattern skks sks is relatively large in north and south american recordings of deep tonga fiji earthquakes but prem like in european recordings of earthquakes in south america and north american recordings of earthquakes in indonesia modeling of skks sks indicate that ultra low velocity zones ulvzs layers at the base of the mantle with a thickness of about 10 20 km and a shear velocity reduction between 20 30 are required to explain high skks sks ratios and the early move out of spdks

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

constraints on localized core mantle boundary structure from multichannel broadband sks coda analysis 1 in recent years a wide range of geophysical results have offered evidence that earth s lowermost mantle is characterized by strong lateral variations in material properties among the structures of particular interest are intermittent ultralow velocity zones ulvzs located directly above the core mantle boundary cmb which were originally inferred from the distortion of teleseismic spdks phases ulvzs have been modeled as layers with sharp boundaries and seismic velocity reductions 10 and interpreted as regions of partial melt in this study we further constrain local ulvz structure beneath north america by signal processing and waveform modeling of the sks coda recorded at broadband seismic arrays secondary phases in the sks coda are effectively isolated by eigenimage processing residual i e sks less data sections from various western pacific events display clear spdks arrivals followed by a secondary phase whose timing and slowness are consistent with cmb origins one dimensional modeling of these phases by reflectivity and generalized ray synthetics favors an asymmetric model with ulvz present at only one of the cmb intercepts the preferred ulvz is characterized by reductions in p and s velocities of 18 and 50 respectively and a diffuse upper boundary these characteristics are consistent with local production and gravitational sinking of dense e g iron rich partial melt above the cmb we postulate that a gradational ulvz beneath north america may mark a lateral transition domain between regions of mantle upwelling where more uniform ulvzs exist and regions of downwelling where ulvzs are either nonexistent or imperceptibly thin

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

ultralow velocity zone geometries resolved by multidimensional waveform modelling ultra low velocity zones ulvzs are thin patches of material with strongly reduced seismic wave speeds situated on top of the core mantle boundary cmb a common phase used to detect ulvzs is spdks skpds an sks wave with a short diffracted p leg along the cmb most previous efforts have examined ulvz properties using 1d waveform modeling approaches we present waveform modeling results using the 2 5d finite difference algorithm psvaxi allowing us better insight into ulvz structure and location we characterize ulvz waveforms based on ulvz elastic properties shape and position along the spdks raypath in particular we vary the ulvz location e g source or receiver side ulvz topographical profiles e g boxcar trapezoidal or gaussian and ulvz lateral scale along great circle path 2 5o 5o 10o we observe several waveform effects absent in 1d ulvz models and show evidence for waveform effects allowing the differentiation between source and receiver side ulvzs early inception of the spdks skpds phase is difficult to detect for receiver side ulvzs with maximum shifts in skpds initiation of 3o in epicentral distance whereas source side ulvzs produce maximum shifts of spdks initiation of 5o allowing clear separation of source versus receiver side structure we present a case study using data from up to 300 broadband stations in turkey recorded between 2005 and 2010 we observe a previously undetected ulvz in the southern atlantic ocean region centered near 45o s 12 5ow with a lateral scale of 3 vp reduction of 10 vs reduction of 30 and density increase of 10 relative to prem

contrasts in hydrology between regions of basal deformation and sliding beneath rutford ice stream west antarctica mapped using radar and seismic data 1 spatially coincident radar and seismic data collected two weeks apart on rutford ice stream were analyzed to investigate the mechanical and hydrological characteristics of the ice bed interface seismic data allow the differentiation of bed deformation from basal sliding in radar data sliding regions are characterised by highly variable permittivity values we suggest these regions are characterized by small water bodies possibly a cavity system in contrast deforming regions are characterised by consistent low permittivity which suggests intimate ice sediment contact without a distinct interface however in deforming regions we identified three bright radar features similar to 50 m wide consistent in lateral location over distances of 5 10 km up and downstream and comprised of water less than similar to 0 2 m deep we interpret these as part of a water evacuation system most likely canals our results emphasise the great potential of radar and seismic techniques in combination to infer basal conditions beneath ice streams

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

earth s core and the geodynamo earth s magnetic field is generated by fluid motion in the liquid iron core details of how this occurs are now emerging from numerical simulations that achieve a self sustaining magnetic field early results predict a dominant dipole field outside the core and some models even reproduce magnetic reversals the simulations also show how different patterns of flow can produce similar external fields efforts to distinguish between the various possibilities appeal to observations of the time dependent behavior of the field important constraints will come from geological records of the magnetic field in the past

using pkikp coda to determine inner core structure 1 synthesis of coda envelopes using single scattering theories 1 previous seismic studies have reported evidence of scattered seismic energy coming from the inner core ic this implies that the ic has lateral variations in structure or composition with a scale length of tens of kilometers in the present study we focus on synthesizing the coda following precritical pkikp and try to determine the location of the heterogeneities that produce this coda using previously reported observations as a guide using a single scattering approximation and ray theory we generate synthetic pkikp coda envelopes from six distinctive places inside the earth within the lower mantle on the source and receiver side along the core mantle boundary on the source and receiver side along the inner core boundary and within the inner core we use two approaches to generate synthetic coda from topography on a boundary surface and one that is appropriate for volumetric scattering in our computations we calculate the arrival time ray parameter and amplitude of the seismic waves and take into account errors in the back azimuth as well as source and receiver effects we find that previously reported spindle shaped or growing coda can only be produced from volumetric heterogeneities located in the shallowest 350 km of the ic however strong trade offs between the different parameters describing the volumetric heterogeneities i e characteristic wavelengths rms velocity or impedance contrast and total volume preclude the determination of a unique model additionally we find that reasonable models of topography at the core mantle boundary can produce large variations of the pkikp amplitude due to focusing and defocusing effects therefore complexity at the inner core boundary is not necessarily required to account for dramatic amplitude variations in the direct pkikp amplitudes

environmental impact of the abandoned coal mines on the surface water and the groundwater quality in the south of bochum germany surface water and groundwater samples were collected from 20 locations situated in the vicinity of the abandoned coal mine fields south of bochum the main objective of this research is to assess the environmental impacts of these mines on the surface water and groundwater quality as well as to determine the factors controlling these impacts the water samples were collected from stream sources groundwater surface water and engineered channels during april 2011 physicochemical parameters were measured during fieldwork water samples were analysed for major ions and aluminium iron manganese ferrous iron zinc and hydrogen sulphide the hydrochemistry of the surface water and the groundwater of this area is characterized by near neutral to alkaline conditions represented by predominance of calcium bicarbonate and sometimes calcium sulphate water types hence the surface water and the groundwater quality in this region is significantly affected by abandoned coal mines these effects resulted from oxidation of iron disulphide minerals that release iron sulphate and hydrogen the presence of carbonate rich materials which contained within the landfilling materials has led the releasing of calcium magnesium and bicarbonate these materials could be the main source responsible for raising the alkalinity of the affected water the environmental hazard of the abandoned coal mines in this area is related to the high concentration of fe especially in the groundwater that possess the highest fe concentration compared to other water sources the fe is 18 times larger than the allowed value in drinking water significant spatial variations of the water pollution were noted in this study for this reason the environmental hazards of the abandoned coal mines in germany should be considered at closure of coal mines in the near future otherwise these mines will be sources of environmental threats unless all necessary measures are taken to reduce their impact