seismic tomography a window into deep earth abstract the goal of this paper is to provide an overview of the current state of the art in seismic tomography and trace its origins from pioneering work in the early 1970s to its present status as the pre eminent tool for imaging the earth s interior at a variety of scales due to length limitations we cannot hope to cover every aspect of this diverse topic or include mathematical derivations of the underlying principles rather we will provide a largely descriptive coverage of the methodology that is targeted at readers not intimately familiar with the topic the relative merits of local versus global parameterization ray tracing versus wavefront tracking backprojection versus gradient based inversion and synthetic testing versus model covariance are explored a variety of key application areas are also discussed including body wave traveltime tomography surface wave tomography attenuation tomography and ambient noise tomography established and emerging trends many of which are driven by the ongoing rapid increases in available computing power will also be examined including finite frequency tomography full waveform tomography and joint tomography using multiple datasets several practical applications of seismic tomography including body wave traveltime attenuation and surface waveform are presented in order to reinforce prior discussion of theory

using surface waves recorded by a large mesh of three element arrays to detect and locate disparate seismic sources author posting the authors 2018 this article is posted here by permission of the royal astronomical society for personal use not for redistribution the definitive version was published in geophysical journal international 215 2018 942 958 doi 10 1093 gji ggy316

shear wave model of southern africa from regional rayleigh wave tomography with 2 d sensitivity kernels summary rayleigh wave phase velocities are computed at the period range of 20 167 s in southern africa from a two plane wave tpw tomography method using 2 d born approximation sensitivity kernels these phase velocities are compared with the results of the tpw method using gaussian sensitivity functions and the correlation between the two methods is good up to 100 s the correlation coefficient becomes less than 0 5 at periods greater than 111 s indicating significant finite frequency effects at long periods the correlation of phase velocity between adjacent frequencies increases with period for inversions using the 2 d sensitivity kernels while such a systematic trend is not observed for inversions using gaussian sensitivity functions in addition low phase velocity anomalies at long periods 111 167 s are better and more consistently imaged from inversions using 2 d sensitivity kernels to account for finite frequency effects and improve resolution the 2 d sensitivity kernels are therefore recommended in regional tpw tomography a 3 d shear wave model is developed from the phase velocities obtained in southern africa the new model confirms the existence of a fast mantle lid underlain by a low velocity zone revealed in a previous model constrained from the tpw method using gaussian sensitivity functions one new feature in this model is the vertical alignment of a shallow low velocity anomaly with a deep high velocity anomaly at the western bushveld province the alignment provides new evidence to support the interpretation of the slow anomaly as the result of high iron content from the bushveld intrusion and the fast as a more depleted residual mantle a low velocity channel at the depths of 220 310 km from the namaqua natal belt to the northwest of the kaapvaal craton is also imaged it suggests that the hot asthenosphere beneath the mobile belt can migrate into the craton area through a weak channel and produce thermal disturbance at the base of the craton further more low velocity anomalies from 100 to 140 km in the 3 d model agree well with the localities of kimberlites erupted at 65 104 ma in the kaapvaal craton this observation supports that kimberlites are generated in the lithosphere by thermal disturbance and provides additional evidence for the depth extent of mantle xenoliths

wave theoretical inversion of teleseismic surface waves in a regional network phase velocity maps and a three dimensional upper mantle shear wave velocity model for southern germany summary using teleseimic surface wave data from 110 selected earthquakes recorded at 10broad band stations in southern germany we construct phase velocity maps of rayleigh waves for southern germany in a further step these maps are inverted for a three dimensional model of the sv velocity of the upper 200 km of the mantle we attempt to take into account the effect of heterogeneous structure outside the study region by jointly inverting the data for heterogeneous phase velocity inside the study region and the distortion of the incoming wavefields by the surrounding structure the total wavefield in the study region is computed with a scattering formalism which includes multiple forward scattering and single backscattering since in principle the data can be perfectly fit by the incoming wavefields without any heterogeneous structure inside the study area we impose additional constraints on the incoming wavefields to reduce the non uniqueness the most important constraint is an energy criterion which states that the energy of the modelled wavefield in the study area averaged over many events should be equal to the energy sampled by the stations we demonstrate that enforcing this criterion generates phase velocity maps with heterogeneous structure nevertheless we are able to satisfy the energy criterion without any heterogeneous structure at the price of an only slightly increased data misfit hence it must be concluded that a seismic network of size and station density such as the one used in this study is still insufficient to demonstrate convincingly the existence of heterogeneities in the network area using teleseismic surface waves any reasonable structure combined with the appropriate incoming wavefields would allow an acceptable fit of our data this frustrating conclusion of course applies to all other comparable studies which use teleseismic surface waves although we cannot convincingly show that any phase velocity map we find should be preferred over others we are able to obtain good reconstructions of test structures from realistic synthetic data with the same station and event distribution as the real data moreover we find that the geometric pattern of the phase velocity maps obtained from real data depends only weakly on the constraints applied in the inversion while the amplitude of the phase velocity perturbations is almost completely determined by the constraints for all periods considered the fit to the data is extremely good the reduction of the quadratic misfit relative to the case of plane incoming waves and no structure is dramatic for the shorter periods the 3 d model of vertical shear wave velocity down to a depth of 200 km exhibits a basic division into four quadrants separated by a vertical plane intersecting the surface along a nearly west east line and a horizontal plane at about 130 km depth the northern rants show high velocities in the top 120 km and low velocities below 140 km the opposite is the case for the southern quadrants an exception to this general feature is a pronounced low velocity zone in the northwestern corner of the region

seismic structure of the central us crust and shallow upper mantle uniqueness of the reelfoot rift abstract using seismic surface waves recorded with earthscope s transportable array we apply surface wave imaging to determine 3d seismic velocity in the crust and uppermost mantle our images span several proterozoic and early cambrian rift zones mid continent rift rough creek graben rome trough birmingham trough southern oklahoma aulacogen and reelfoot rift while ancient rifts are generally associated with low crustal velocity because of the presence of thick sedimentary sequences the reelfoot rift is unique in its association with low mantle seismic velocity its mantle low velocity zone lvz is exceptionally pronounced and extends down to at least 200 km depth this lvz is of variable width being relatively narrow 50 km wide within the northern reelfoot rift which hosts the new madrid seismic zone nmsz we hypothesize that this mantle volume is weaker than its surroundings and that the reelfoot rift consequently has relatively low elastic plate thickness which would tend to concentrate tectonic stress within this zone no other intraplate ancient rift zone is known to be associated with such a deep mantle low velocity anomaly which suggests that the nmsz is more susceptible to external stress perturbations than other ancient rift zones

measuring surface wave phase velocities beneath small broad band arrays tests of an improved algorithm and application to the french alps the local measurement of dispersion curves of intermediate period surface waves is particularly difficult because of the long wavelengths involved we suggest an improved procedure for measuring dispersion curves using small aperture broad band arrays the method is based on the hypotheses of plane incoming waves and that averaging over a set of events with a good backazimuth distribution will suppress the effects of diffraction outside the array none of the elements of the processing are new in themselves but each step is optimized so we can obtain a reliable dispersion curve with a well defined uncertainty the method is based on the inversion for the slowness vector at each event and frequency using time delays between pairs of stations where the time delays deltat are obtained by frequency domain wiener filtering the interstation distance projected on to the slowness vector d is then calculated the final dispersion curve is found by at each frequency calculating the inverse of the slope of the best fitting line of all d deltat points to test the algorithm it is applied to synthetic seismograms of fundamental mode rayleigh waves in different configurations 1 the sum of several incident waves 2 an array located next to or above a crustal thickening and 3 added white noise using regular and irregular backazimuth distributions in each case a circular array of 23 km diameter and composed of six stations is used the algorithm is stable over a large range of wavelengths between half and a tenth of the array size depending on the configuration the situations of several simultaneously incoming waves or neighbouring heterogeneities are well handled and the inferred dispersion curve corresponds to that of the underlying medium above a strong lateral heterogeneity the inferred dispersion curve corresponds to that of the underlying medium up to wavelengths of eight times the array size in the configuration considered but further work is needed to better understand the limits under which the obtained dispersion curve is not biased in the case of 5 per cent spectral amplitude white noise the dispersion curve is also stable for wavelengths up to approximately eight times the array size but this limit depends of course strongly on the noise level the method is finally applied to data from two arrays in the french alps located 50 km apart it is possible to measure the dispersion curves up to wavelengths approximately ten times bigger than the array diameter the difference in the dispersion curves is compatible with a crustal and lithospheric thickening under the alps however the observed errors are large which result in severe limits on the interpretation in terms of lithospheric structure longer recording periods may help to reduce the errors otherwise the algorithm is likely to be of use mainly in areas where the lateral variations outside the array are smaller than those of the french alps

gld100 the near global lunar 100 m raster dtm from lroc wac stereo image data 1 we derived near global lunar topography from stereo image data acquired by the wide angle camera wac of the lunar reconnaissance orbiter camera lroc system from polar orbit tracks the lroc wac provides image data with a mean ground resolution at nadir of 75 m pixel with substantial cross track stereo overlap wac stereo images from the one year nominal mission and the first months of the science mission phase are combined to produce a near global digital terrain model dtm with a pixel spacing of 100 m the global lunar dtm 100 m or gld100 it covers 79 s to 79 n latitudes 98 2 of the entire lunar surface we compare the gld100 with results from previous stereo and altimetry based products particularly with the lunar orbiter laser altimeter lola altimetry which is the current topographic reference for the moon we describe typical characteristics of the gld100 and based upon the comparison to the lola data set assess its vertical and lateral resolution and accuracy we conclude that the introduced first version of the stereo based gld100 is a valuable topographic representation of the lunar surface complementary to the lola altimetry data set further improvements can be expected from continuative investigations

finite frequency traveltime tomography of san francisco bay region crustal velocity structure summary seismic velocity structure of the san francisco bay region crust is derived using measurements of finite frequency traveltimes a total of 57 801 relative traveltimes are measured by cross correlation over the frequency range 0 5 1 5 hz from these are derived 4862 summary traveltimes which are used to derive 3 d p wave velocity structure over a 341 140 km2 area from the surface to 25 km depth the seismic tomography is based on sensitivity kernels calculated on a spherically symmetric reference model robust elements of the derived p wave velocity structure are a pronounced velocity contrast across the san andreas fault in the south bay region west side faster a moderate velocity contrast across the hayward fault west side faster moderately low velocity crust around the quien sabe volcanic field and the sacramento river delta very low velocity crust around lake berryessa these features are generally explicable with surface rock types being extrapolated to depth 10 km in the upper crust generally high mid lower crust velocity and high inferred poisson s ratio suggest a mafic lower crust

interhemispheric atlantic seesaw response during the last deglaciation the asynchronous relationship between millennial scale temperature changes over greenland and antarctica during the last glacial period has led to the notion of a bipolar seesaw which acts to redistribute heat depending on the state of meridional overturning circulation within the atlantic ocean here we present new records from the south atlantic that show rapid changes during the last deglaciation that were instantaneous within dating uncertainty and of opposite sign to those observed in the north atlantic our results demonstrate a direct link between the abrupt changes associated with variations in the atlantic meridional overturning circulation and the more gradual adjustments characteristic of the southern ocean these results emphasize the importance of the southern ocean for the development and transmission of millennial scale climate variability and highlight its role in deglacial climate change and the associated rise in atmospheric carbon dioxide

mid latitude interhemispheric hydrologic seesaw over the past 550 000 years an interhemispheric hydrologic seesaw in which latitudinal migrations of the intertropical convergence zone itcz produce simultaneous wetting increased precipitation in one hemisphere and drying in the other has been discovered in some tropical and subtropical regions for instance chinese and brazilian subtropical speleothem cave formations such as stalactites and stalagmites records show opposite trends in time series of oxygen isotopes a proxy for precipitation variability at millennial to orbital timescales suggesting that hydrologic cycles were antiphased in the northerly versus southerly subtropics this tropical to subtropical hydrologic phenomenon is likely to be an initial and important climatic response to orbital forcing the impacts of such an interhemispheric hydrologic seesaw on higher latitude regions and the global climate system however are unknown here we show that the antiphasing seen in the tropical records is also present in both hemispheres of the mid latitude western pacific ocean our results are based on a new 550 000 year record of the growth frequency of speleothems from the korean peninsula which we compare to southern hemisphere equivalents the korean data are discontinuous and derived from 24 separate speleothems but still allow the identification of periods of peak speleothem growth and thus precipitation the clear hemispheric antiphasing indicates that the sphere of influence of the interhemispheric hydrologic seesaw over the past 550 000 years extended at least to the mid latitudes such as northeast asia and that orbital timescale itcz shifts can have serious effects on temperate climate systems furthermore our result implies that insolation driven itcz dynamics may provoke water vapour and vegetation feedbacks in northern mid latitude regions and could have regulated global climate conditions throughout the late quaternary ice age cycles

shear velocity structure and azimuthal anisotropy beneath eastern north america from rayleigh wave inversion 1 we have obtained shear velocity structure beneath the northeastern united states and southeastern canada using rayleigh wave phases and amplitudes thin crust 36 42 km is observed along the atlantic coast and in the eastern appalachian orogen and thick crust 42 46 km is imaged in the western appalachians and in the western new york portion of the grenville province the variation of crustal thickness correlates well with the observed bouguer gravity anomalies in the upper mantle the high velocity continental keel of cratonic north america is present in the western part of the study area while a broad low velocity region is imaged in new england from the hudson river valley to the white mountains this low velocity anomaly is probably the consequence of past heating of the lithospheric mantle associated with the monteregian hotspot and may represent intrusion of asthenosphere into the edge of the keel in addition to lateral variations in velocity we estimate the azimuthal dependence of phase velocity strong and relatively uniform shear wave splitting is observed in the study region but at periods of 100 s or less the average azimuthal anisotropy of rayleigh waves is less than 1 and is not significantly different from zero at any individual period this small degree of azimuthal anisotropy is not consistent with a substantial contribution to shear wave splitting from fossil anisotropy in the lithosphere much of the source of the shear wave splitting must lie deeper than 200 km

partitioned waveform inversion and two dimensional structure under the network of autonomously recording seismographs nonlinear optimization methods are very effective in finding models that predict optimal waveform fits to observed seismograms provided the number of model parameters is small to reduce the size of the large scale two or three dimensional seismic modelling problem path integrals over seismic velocities may be defined as model parameters instead of the seismic velocities themselves this partitions the large scale optimization problem into a number of independent small scale problems and reduces the computational effort by several orders of magnitude the path integral parameters are transformed such that their correlation matrix becomes diagonal a linear inversion performs the mapping from the space of path integral parameters into the model space of seismic velocities and makes backus gilbert resolution analysis possible the method has been applied to body wave and surface wave data from the broadband portable network of autonomously recording seismographs nars in western europe using a surface wave ray approximation to generate synthetics by mode summation waveforms were fitted for frequencies as high as 50 mhz variations in s velocity as large as 6 1 have been established with a vertical resolution of 100 150 km and a horizontal resolution as small as 400 km in parts of the model although a low velocity layer is present under the southern part of the nars array such layer is very weak or absent north of the paris basin horizontal velocity gradients are well resolved down to 400 km depth

rayleigh wave phase velocities small scale convection and azimuthal anisotropy beneath southern california 1 we use rayleigh waves to invert for shear velocities in the upper mantle beneath southern california a one dimensional shear velocity model reveals a pronounced low velocity zone lvz from 90 to 210 km the pattern of velocity anomalies indicates that there is active small scale convection in the asthenosphere and that the dominant form of convection is three dimensional 3 d lithospheric drips and asthenospheric upwellings rather than 2 d sheets or slabs several of the features that we observe have been previously detected by body wave tomography these anomalies have been interpreted as delaminated lithosphere and consequent upwelling of the asthenosphere beneath the eastern edge of the southern sierra nevada and walker lane region sinking lithosphere beneath the southern central valley upwelling beneath the salton trough and downwelling beneath the transverse ranges our new observations provide better constraints on the lateral and vertical extent of these anomalies in addition we detect two previously undetected features a high velocity anomaly beneath the northern peninsular range and a low velocity anomaly beneath the northeastern mojave block we also estimate the azimuthal anisotropy from rayleigh wave data the strength is 1 7 at periods shorter than 100 s and decreases to below 1 at longer periods the fast direction is nearly e w the anisotropic layer is more than 300 km thick the e w fast directions in the lithosphere and sublithosphere mantle may be caused by distinct deformation mechanisms pure shear in the lithosphere due to n s tectonic shortening and simple shear in sublithosphere mantle due to mantle flow

the m chi decomposition of hybrid dual polarimetric radar data with application to lunar craters 1 we introduce a new technique derived from the classical stokes parameters for analysis of polarimetric radar astronomical data this decomposition is based on m the degree of polarization and chi the poincare ellipticity parameter analysis of the crater byrgius a demonstrates how m chi can more easily differentiate materials within ejecta deposits and their relative thicknesses we use goldschmidt crater to demonstrate how m chi can differentiate coherent deposits of water ice goldschmidt crater floor is found to be consistent with single bounce bragg scattering suggesting the absence of water ice and further corroborating adsorbed h to mineral grains or an h2o frost as plausible explanations for a h2o oh detection by near infrared instruments

a new framework for modeling sediment fining during transport with fragmentation and abrasion 1 a new framework for modeling sediment fining during transport is proposed the model is based on a physical description of both abrasion and fragmentation processes it attempts to describe and explain the changes in the grain size distribution of sediments during their transport in a water flow abrasion and fragmentation are modeled through the use of breakage frequency functions and daughter size distributions these functions are determined experimentally for the specific case study which is presented comparison between the predictions from the model and experimental data from the case study show that 1 both abrasion and fragmentation are involved in the degradation 2 fragmentation efficiency decreases during the experiment and 3 the shape of the pebbles provides feedback between abrasion and fragmentation this type of model is therefore appropriate for explaining degradation mechanisms which is promising for a future application to rivers

rayleigh wave tomography of the northeastern margin of the tibetan plateau abstract the convergence between the indian continent and the southern margin of eurasia has eventually led to the growth of the tibetan plateau eastward various models have suggested that a large scale flow in the lower crust or and the asthenosphere is responsible for the uplift of eastern tibet it has also been suggested that the continental flow may move around the thick lithosphere of the ordos plateau and the sichuan basin in order to investigate the validity of the crust mantle flow and its possible path we have used rayleigh wave tomography with sensitivity kernels to estimate both the phase velocity structure 20 143 s and the shear wave velocity structure 0 200 km across the northeastern margin of the tibetan plateau from the surface to 100 km our shear wave velocity model shows a prominent low velocity anomaly beneath northeastern tibet suggestive of a warm lithosphere its boundary lies at 105 e longitude which borders the western ordos plateau and sichuan basin from 125 km to 200 km our shear wave velocity model shows a low velocity channel beneath the qilian qinling orogen that lies between the ordos and sichuan blocks this channel may represent the asthenosphere given the fact that the lithosphere is 120 150 km thick in northeastern tibet and the qinling orogen we also inverted for the anisotropy parameters in the study area simultaneously with the velocity parameters the dominant fast direction is nww see generally consistent with the sks splitting results the calculated shear strain from gps and the fault slip rate measurements furthermore the fast directions in our anisotropic model vary only slightly with periods and the anisotropy magnitudes at long periods 100 143 s are large and exceed those at short medium periods 20 80 s indicating potentially although not necessarily vertically coherent deformation from the crust to the asthenosphere and possibly large deformation in the asthenosphere the deformation seems to be linked to the southeastward extrusion tectonics caused by the collision boundary force

resolving the lithosphere asthenosphere boundary with seismic rayleigh waves summary seismic surface wave measurements offer tight constraints on shear wave speed values within the lithosphere and asthenosphere it is still a matter of debate however how accurately and under what conditions surface waves can resolve the depth and thickness of the lithosphere asthenosphere boundary lab we investigate the sensitivity of rayleigh waves to lab properties and find that if the lab is associated with a 2 3 per cent shear speed reduction at a depth less than 100 km then 10 20 km variations in its depth translate into phase velocity changes of up to 1 per cent variations in the thickness of the lab from zero to a few tens of kilometres cause much smaller phase velocity changes 0 1 per cent although the signal of the lab thickness variations is enhanced by a distinct frequency dependent pattern of phase velocity increases and decreases for lab depths increasing beyond 100 km larger absolute variations in the lab depth and thickness are needed to generate response of the same amplitude in phase velocities we introduce a grid search inversion of phase velocity curves for the lab depth and thickness defining them as the middle and the width respectively of a depth interval with a linear shear speed decrease in it the inversion comprises dense sampling of the lab depthlab thickness parameter plane and non linear gradient search inversions at every point it accountsforanytrade offsofthelabparameterswithshearspeedvariationsaboveandbelow the lab inversions of phase velocity curves for the lab depth and thickness show that the two parameters have uncorrelated uncertainties with the lab depth constrained better than the lab thickness random errors in phase velocity measurements have a limited effect on lab depth measurements causing errors of only a few kilometres measurements of the lab thickness are less robust and are not possible in the presence of large 1 per cent random errors substantial systematic biases in the measurements errors that persist over broad period ranges of tens of seconds can affect both lab depth and lab thickness estimates phasevelocity curves with such biases are not suitable for inversions for lab properties resolving the lab however in particular the lab depth should already be possible with some of the accurate broad band phase velocity measurements available today applying our method to phase velocity data measured in phanerozoic west central germany we find best fitting lab depths in the 60 80 km range the lab depth always understood to be the middle of the shear speed reduction depth range with minimum misfits achieved near the 70 km lab depth beneath the archean guyana shield we determine a 140 175 km lab depth range with a 160 km best fitting mid lab depth

arrival angles of teleseismic fundamental mode rayleigh waves across the alparray the dense alparray network allows studying seismic wave propagation with high spatial resolution here we introduce an array approach to measure arrival angles of teleseismic rayleigh waves the approach combines the advantages of phase correlation as in the two station method with array beamforming to obtain the phase velocity vector 20 earthquakes from the first two years of the alparray project are selected and spatial patterns of arrival angle deviations across the alparray are shown in maps depending on period and earthquake location the cause of these intriguing spatial patterns is discussed a simple wave propagation modelling example using an isolated anomaly and a gaussian beam solution suggests that much of the complexity can be explained as a result of wave interference after passing a structural anomaly along the wave paths this indicates that arrival angle information constitutes useful additional information on the earth structure beyond what is currently used in inversions

coseismic slip distribution of the 1923 kanto earthquake japan 1 the slip distribution associated with the 1923 m 7 9 kanto japan earthquake is reexamined in light of new data and modeling we utilize a combination of first order triangulation second order triangulation and leveling data in order to constrain the coseismic deformation the second order triangulation data which have not been utilized in previous studies of 1923 coseismic deformation are associated with only slightly smaller errors than the first order triangulation data and expand the available triangulation data set by about a factor of 10 interpretation of these data in terms of uniform slip models in a companion study by nyst et al shows that a model involving uniform coseismic slip on two distinct rupture planes explains the data very well and matches or exceeds the fit obtained by previous studies even one which involved distributed slip using the geometry of the nyst et al two plane slip model we perform inversions of the same geodetic data set for distributed slip our preferred model of distributed slip on the philippine sea plate interface has a moment magnitude of 7 86 we find slip maxima of 8 9 m beneath odawara and 7 8 m beneath the miura peninsula with a roughly 2 1 ratio of strike slip to dip slip motion in agreement with a previous study however the miura slip maximum is imaged as a more broadly extended feature in our study with the high slip region continuing from the miura peninsula to the southern boso peninsula region the second order triangulation data provide good evidence for 3 m right lateral strike slip on a 35 km long splay structure occupying the volume between the upper surface of the descending philippine sea plate and the southern boso peninsula

regional velocity structure in northern california from inversion of scattered seismic surface waves seismic surface waves recorded by the berkeley digital seismic network have been analyzed in order to constrain three dimensional lateral heterogeneity of the upper mantle under northern california a total of 2164 seismograms from 173 teleseismic events were windowed for the fundamental mode rayleigh wave followed by estimation of complex amplitude spectra over the period range 16 to 100 s using a multiple taper method since rayleigh waves at shorter periods particularly below 35 s suffer from serious multipathing or non plane wave arrivals these amplitude spectra have been interpreted as the product of wavefront distortion along the teleseismic propagation path and seismic structure beneath the network the amplitude spectra are first modeled in terms of non plane incoming wavefields and structural phase velocity perturbations period by period after corrections for moho and surface topography the phase velocity maps are inverted for three dimensional shear velocity perturbations s down to a depth of 200 km the s maps are in good agreement with the results of body studies over a broad spatial scale the dominant signals are associated with the thermal effects of the active gorda and fossil farallon subducted slab stretching from mount shasta through the western sierran foothills to the southern great valley and asthenospheric upwelling beneath the northern coast ranges the southern sierra nevada range is characterized by fast s down to 50 km and slow velocities between 60 and 120 km depth in agreement with independent inferences of a cold crust and warm upper mantle which may provide the buoyancy forces necessary to support the elevation of the range

lithosphere asthenosphere interaction beneath the western united states from the joint inversion of body wave traveltimes and surface wave phase velocities summary the relation between the complex geological history of the western margin of the north american plate and the processes in the mantle is still not fully documented and understood several pre usarray local seismic studies showed how the characteristics of key geological features such as the colorado plateau and the yellowstone snake river plains are linked to their deep mantle structure recent body wave models based on the deployment of the high density large aperture usarray have provided far more details on the mantle structure while surface wave tomography ballistic waves and noise correlations informs us on the shallow structure here we combine constraints from these two data sets to image and study the link between the geology of the western united states the shallow structure of the earth and the convective processes in mantle our multiphase dna10 s model provides new constraints on the extent of the archean lithosphere imaged as a large deeply rooted fast body that encompasses the stable great plains and a large portion of the northern and central rocky mountains widespread slow anomalies are found in the lower crust and upper mantle suggesting that low density rocks isostatically sustain part of the high topography of the western united states the yellowstone anomaly is imaged as a large slow body rising from the lower mantle intruding the overlying lithosphere and controlling locally the seismicity and the topography the large e w extent of the usarray used in this study allows imaging the slab graveyard a sequence of farallon fragments aligned with the currently subducting juan de fuca slab north of the mendocino triple junction the lithospheric root of the colorado plateau has apparently been weakened and partly removed through dripping the distribution of the slower regions around the colorado plateau and other rigid blocks follows closely the trend of cenozoic volcanic fields and ancient lithospheric sutures suggesting that the later exert a control on the locus of magmato tectonic activity today the dna velocity models are available for download and slicing at http dna berkeley edu

new zealand and uk holocene flooding demonstrates interhemispheric climate asynchrony the timing and controls of interhemispheric holocene climate change have remained poorly understood primarily because of the absence of well dated and continuous climatic records in terrestrial environments here we report a new probability based meta analysis of 1185 14 c dates from fluvial sedimentary sequences in new zealand and the uk which provides a robust means of identifying centennial and multicentennial length episodes of holocene river flooding statistical analysis shows that prior to large scale human impact which began at ca 1000 cal yr b p the incidence of extreme floods in new zealand and the uk has been largely asynchronous during the holocene major periods of flooding are controlled by large scale shifts in atmospheric circulation which alter the frequency of extreme precipitation events our novel synthesis demonstrates that short term climate change of sufficient magnitude to modify flooding regimes was out of phase in the temperate maritime regions of the northern and southern hemispheres during much of the holocene this supports recent evidence from both glacial and marine records that holocene climate changes may have been antiphased between the polar regions and that this could have been related to variation in the strength of deep water formation

dynamic strains at regional and teleseismic distances abstract we develop formulas for the size of dynamic strains caused by seismic waves from an earthquake of given magnitude and distance these formulas include peak strain peak dissipated power and total dissipated energy and they are applicable at regional and teleseismic distances the formulas are fits to data from 89 large 6 5 m w 9 0 shallow earthquakes with source distances between 500 and 16 000 km recorded between 1977 and 2013 by three long base laser strainmeters at pinon flat observatory in southern california these strainmeters provide uniquely well calibrated measurements of tensor strain the residuals to the fits suggest that strain values can usually be predicted to within a factor of 2 these data also show that the strain tensor can be substantially different from that expected for plane waves in particular the extension perpendicular to the back azimuth which should be zero is always 20 or more of the extension along that azimuth how much the strains resemble those for plane waves depends on their path perhaps because inhomogeneities along different paths produce different amounts of multipathing the observed strains are systematically 10 30 larger at nearby laser strainmeter sites in the salton trough suggesting local amplification from inhomogeneous crustal structure online material tables of earthquake catalogs and dynamic strain analysis and figures of earthquake magnitude distance distributions and time delays of maximum strain

mid pleistocene cave fills megafaunal remains and climate change at naracoorte south australia towards a predictive model using u th dating of speleothems abstract the limestone caves of the naracoorte region in south australia contain extensive deposits of megafauna rich sediments and intercalated cave formation speleothems high precision thermal ionisation mass spectrometry tims u th dating of flowstones directly associated with several large deposits reveals a distinct cyclicity in the timing of sediment and flowstone depositional events in the naracoorte caves this pattern parallels a cyclical alternation of wet phases and intervening periods with a water deficit over the last 500 ka ayliffe et al 1998 geology 26 147 dates from flowstone interlayers in the fossil deposits coincide with the massive speleothem growth events which characterise wet phases hiatuses in flowstone deposition correlatable through several cave systems imply that water deficits were initiated by regional aridity during full glacial and then extended into the succeeding warmer wetter interglacials clastic deposits in caverns with restricted entrance shafts correlate with hiatuses suggesting many of these deposits contain fauna representative of full glacial and interglacial climates caverns with small openings have often been sealed from the surface and dating has constrained the length of accumulation episodes in several fossil deposits one to less than 20 ka the hydrological regimes and environmental conditions inferred from the timing of speleothem deposition have been used to develop a model for cyclic sediment and bone accumulation in the caverns at naracoorte over the last 400 ka the giant victoria fossil chamber deposit accumulated prior to 200 ka and because its entrance is large it may contain faunas representative of all climatic phases there has been no apparent change in faunal diversity at naracoorte over at least three glacial interglacial cycles of the middle pleistocene

500 ka precipitation record from southeastern australia evidence for interglacial relative aridity 230 th 234 u dating of speleothems from southeastern australia documents changes in effective precipitation over the past 500 k y at a temporal resolution not previously achieved results show that the highest effective precipitation for the southeastern interior of australia occurred during stadials and cool interstadials of the past four glacial cycles interglacials and warm interstadials as well as glacial maxima are comparatively arid we suggest that lower regional temperatures over the continent and changes in atmospheric circulation stronger walker circulation produced the observed periods of increased effective precipitation

a review of new zealand palaeoclimate from the last interglacial to the global last glacial maximum abstract results from terrestrial and marine palaeoclimate proxies are integrated to reconstruct palaeoclimate variations in new zealand from the last interglacial to the global last glacial maximum glgm by combining data from 21 speleothems we have constructed composite o c stable isotope sequences from 0 to 88 5 ka bp and from 107 8 to 128 2 ka bp the gaps in the sequence a 19 3 ka break in coverage in mis 5b c and a 2 97 ka gap in mis 5a preclude the construct of a continuous record so data were referenced to a common scale by normalising individual records subtracting means and dividing by standard deviation overlapping records were then merged chronologically these records were compared to integrated summer insolation for 45 s and to terrestrial and marine environmental proxies available for the new zealand region the mis 5e thermal maximum in new zealand was around 128 122 kiloyears bp ka bp and therefore similar in timing to the last interglacial in australia southern europe and greenland temperatures in parts of the north island may have been 2 3 c warmer than present and the sea rose 3 6 m above modern level in mis 5d and 5b cool conditions with glacial advances occurred in the south island but from about 87 to 73 ka in mis 5a warmth within 2 c of present characterised most of the interstadial locally termed the otamangakau interstadial conditions then cooled rapidly and culminated in a mis 4 glacial advance that was the greatest of the new zealand last glacial cycle nzlgm the climate was cool to cold and while wet in westerly windward locations may have been dry in the east combined australian and new zealand evidence suggests glacial culmination around 67 62 ka this regional lgm coincided with severe cooling in europe during mis 3 conditions were very variable the climate in eastern north island hawke bay and the bay of plenty at the start of mis 3 was similar to the holocene and the period 61 43 ka was relatively mild overall and is termed the aurora interstadial although it contained a short interval of mountain glacier expansion around 49 47 ka after 43 ka conditions cooled again with a glacial advance from 42 to 38 ka before a return to milder but still cool conditions during the moerangi interstadial from 37 to 31 ka after this conditions deteriorated at the lead in to the glgm the maximum glacial advance occurred in late mis 3 between 31 and 29 ka the glacial onset was abrupt with te anau glacier in fiordland one of the largest in the southern alps taking only about 2000 years to achieve its maximum glgm depth probably because conditions were wet as well as cold but stable isotope data suggest that the climate then became drier while remaining cold and the glacier progressively ablated such that its surface had lowered 390 m by the start of mis 2 and by 600 m by ca 18 ka the glgm maximum in new zealand may have led the terrestrial ice sheet lgm in the northern hemisphere by a few thousand years possibly because alpine glaciers respond more rapidly to climate change than continental ice sheets the culmination of the glgm in nz occurred in mis 3 about 12 000 years before global ice volume reached its peak as determined by the marine stable isotope record the marine glgm by the time global ice volume was at a maximum 19 ka glaciers had almost disappeared from major fiordland valleys in new zealand whereas polar ice sheet records have revealed a bi polar see saw this is not so evident in the mid latitudes because some temperate zone inter hemispheric climate events coincide closely in time perhaps the see saw effect diminishes with distance from the poles

high resolution surface wave tomography beneath the aegean anatolia region constraints on upper mantle structure summary this study provides new constraints on the upper mantle structure from western greece to central anatolia using seismic data of permanent broad band networks recently installed in greece and turkey and from a two year temporary array simbaad experiment we used 200 seismic events recorded at 146 broad band stations with a typical interstation distance of 60 100 km across the study area the high resolution 3 d shear wave velocity model of the mantle is obtained by inversion of fundamental mode rayleigh wave phase velocity maps for periods between 20 and 195 s the tomography is based on ray tracing in heterogeneous media taking into account external propagation effects the horizontal resolution is approximately 100 km however small heterogeneities may suffer from some horizontal smearing and damping the vertical resolution is approximately 100 km the vertical smoothing is necessary to avoid unresolved spurious shear wave velocity oscillations in the upper mantle the errors on shear wave velocities in our 3 d model 0 02 0 1 km s 1 are significantly smaller than the amplitude of vs variations 0 3 0 5 km s 1 in spite of the vertical and horizontal smoothing our model shows details in the upper mantle structure never reached at regional scale in the area the overall structure is characterized by a low velocity zone 80 200 km depth reflecting a slow and warm asthenosphere underlying a thin lithosphere the southwesternmost termination of the low velocity anomaly corresponds to the northward dipping hellenic slab the detailed shear velocity structure of the upper mantle beneath anatolia appears to be far more geometrically complex than revealed in previous tomographic studies of the area at depths larger than or equal to 160 km velocities are overall high beneath anatolia partly due to the presence of dipping high velocity anomalies which we tentatively interpret as remnant slabs the southernmost high velocity anomaly beneath anatolia is separated from the eastern edge of the hellenic slab by a major low velocity anomaly which we interpret as the trace of asthenospheric mantle material rising inside a vertical slab tear beneath southwestern anatolia

the mairan domes silicic volcanic constructs on the moon 1 the mairan domes are four features located in northern oceanus procellarum at 312 3e 41 4n on the moon high resolution visible imagery visible to mid ir spectra and lunar prospector th abundance data all indicate that these four domes have a composition that is consistent with derivation from a si rich highly evolved magma

high resolution seismic array imaging based on an sem fk hybrid method we demonstrate the feasibility of high resolution seismic array imaging based on teleseismic recordings using full numerical wave simulations we develop a hybrid method that interfaces a frequency wavenumber fk calculation which provides analytical solutions to 1 d layered background models with a spectral element sem numerical solver to calculate synthetic responses of local media to plane wave incidence this hybrid method accurately deals with local heterogeneities and discontinuity undulations and represents an efficient tool for the forward modelling of teleseismic coda including converted and scattered waves we benchmark the accuracy of the sem fk hybrid method against fk solutions for 1 d media we then compute sensitivity kernels for teleseismic coda waves by interacting the forward teleseismic waves with an adjoint wavefield produced by injecting coda waves as adjoint sources based on adjoint techniques these sensitivity kernels provide the basis for mapping variations in subsurface discontinuities density and velocity structures through non linear conjugate gradient methods we illustrate various synthetic imaging experiments including discontinuity characterization volumetric structural inversion for the crust or subduction zones these tests show that using pre conditioners based upon the scaled product of sensitivity kernels for different phases combining finite frequency traveltime and waveform inversion and or adopting hierarchical inversions from longto short period waveforms could reduce the non linearity of the seismic inverse problem and speed up its convergence the encouraging results of these synthetic examples suggest that inversion of teleseismic coda phases based on the sem fk hybrid method and adjoint techniques is a promising tool for structural imaging beneath dense seismic arrays

large scale waveform inversions of surface waves for lateral heterogeneity 2 application to surface waves in europe and the mediterranean linear surface wave scattering theory is used to reconstruct the lateral heterogeneity under europe and the mediterranean using surface wave data recorded with the network of autonomously recording seismographs nars the waveform inversion of the phase and the amplitude of the direct surface wave leads to a variance reduction of approximately 40 and results in phase velocity maps in the period ranges 30 40 s 40 60 s and 60 100 s a resolution analysis is performed in order to establish the lateral resolution of these inversions using the phase velocity perturbations of the three period bands a two layer model for the s velocity under europe and the mediterranean is constructed the s velocity perturbations in the deepest layer 100 200 km are much more pronounced than in the top layer 0 100 km which confirms that the low velocity zone exhibits pronounced lateral variations in both layers the s velocity is low under the western mediterranean while the s velocity is high under the scandinavian shield in the deepest layer a high s velocity region extends from greece under the adriatic to northern italy several interesting smaller features such as the massif central are reconstructed one of the spectacular features of the reconstructed models is a sharp transition in the layer between 100 and 200 km near the tornquist tesseyre zone this would indicate that there is a sharp transition at depth between central europe and the east european platform the waveform inversion of the surface wave coda leads to good waveform fits but the reconstructed models are chaotic this is due both to a lack of sufficient data for a good imaging of the surface wave energy on the heterogeneities and to an appreciable noise component in the surface wave coda

abrupt millennial scale changes in intensity of southern hemisphere westerly winds during marine isotope stages 2 4 the strength of mid southern latitude westerly atmospheric circulation plays an important role in global climate due to a lack of long continuous high resolution paleoclimate archives from mid southern latitudes it remains unclear what factors control changes in its intensity and how past changes affected the climates of landmasses in their path here we show growth rate and stable isotope 18 o 13 c profiles from a south island new zealand stalagmite hw3 that permit centennial scale investigation of southern hemisphere westerly paleointensity between 73 and 11 ka correlation between hw3 growth rate and isotope profiles suggests sensitivity to changes in annual precipitation a factor controlled by westerly intensity low growth rates and relatively enriched isotope ratios define long term trends in hw3 supporting existing evidence that weaker westerlies predominated during the last glacial period abrupt millennial scale events occur frequently such that the hw3 record resembles greenland ice core stable isotope profiles furthermore nearly synchronous timing of nine prominent wet and cool intervals with heinrich events supports studies showing that increased westerly intensity is closely linked to north atlantic cooling as well as heinrich events the hw3 profiles also show an antarctic cold reversal like event during deglaciation advocating for a bipolar seesaw of global climate at that time

lro observations of morphology and surface roughness of volcanic cones and lobate lava flows in the marius hills 1 the volcanic domes cones sinuous rilles and pyroclastic deposits of the marius hills region of the moon 13 4 n 304 6 e represent a significant episode of magmatic activity at or near the lunar surface that is still poorly understood comparisons between lroc nac block populations mini rf data and diviner derived rock abundances confirm that blocky lava flows comprise the domes of the marius hills 8 m features measured by diviner indicate that the domes are not rich in silica and are not significantly different than surrounding mare materials lroc observations indicate that some of the dome building lava flows originated directly from volcanic cones many of the cones are c shaped while others are irregularly shaped and local topography and lava eruptions affect cone shape in general the cones are morphologically similar to terrestrial cinder and lava cones and are composed of varying amounts of cinder spatter and lava many of the cones are found in local groupings or alignments the wide range of volcanic features from broad low domes to steep cones represents a range of variable eruption conditions complex morphologies and variable layering show that eruption conditions were variable over the plateau

the relationship between the instantaneous velocity field and the rate of moment release in the lithosphere summary instantaneous velocity gradients within the continental lithosphere are often related to the tectonic driving forces this relationship is direct if the forces are secular as for the case of loading of a locked section of a subduction interface by the downgoing plate if the forces are static as for the case of lateral variations in gravitational potential energy then velocity gradients can be produced only if the lithosphere has on average zero strength the static force model may be related to the long term velocity field but not the instantaneous velocity field typically measured geodetically over a period of several years because over short time intervals the upper lithosphere behaves elastically in order to describe both the short and long term behaviour of an elastic lithosphere viscoelastic asthenosphere system in a selfconsistent manner i construct a deformation model termed the expected interseismic velocity eiv model assuming that the lithosphere is populated with faults that rupture continually each with a definite mean recurrence time and that the earth is well approximated as a linear elastic viscoelastic coupled system i derive a simple relationship between the instantaneous velocity field and the average rate of moment release in the lithosphere examples with synthetic fault networks demonstrate that velocity gradients in actively deforming regions may to a large extent be the product of compounded viscoelastic relaxation from past earthquakes on hundreds of faults distributed over large 10 6 km 2 areas

waveform tomography of crustal structure in the south san francisco bay region 1 we utilize a scattering based seismic tomography technique to constrain crustal structure around the southern san francisco bay region sfbr this technique is based on coupled traveling wave scattering theory which has usually been applied to the interpretation of surface waves in large regional scale studies using fully three dimensional kernels this technique is here applied to observed p s and surface waves of intermediate period 3 4 s dominant period observed following eight selected regional events we use a total of 73 seismograms recorded by a u s geological survey short period seismic array in the western santa clara valley the berkeley digital seismic network and the northern california seismic network modifications of observed waveforms due to scattering from crustal structure include positive or negative amplification delay and generation of coda waves the derived crustal structure explains many of the observed signals which cannot be explained with a simple layered structure there is sufficient sensitivity to both deep and shallow crustal structure that even with the few sources employed in the present study we obtain shallow velocity structure which is reasonably consistent with previous p wave tomography results we find a depth dependent lateral velocity contrast across the san andreas fault saf with higher velocities southwest of the saf in the shallow crust and higher velocities northeast of the saf in the midcrust the method does not have the resolution to identify very slow sediment velocities in the upper approximately 3 km since the tomographic models are smooth at a vertical scale of about 5 km

lithospheric instability and the source of the cameroon volcanic line evidence from rayleigh wave phase velocity tomography the cameroon volcanic line cvl is a 1800 km long volcanic chain extending sw ne from the gulf of guinea into central africa that lacks the typical age progression exhibited by hot spot related volcanic tracks this study investigates the upper mantle seismic structure beneath the cvl and surrounding regions to constrain the origin of volcanic lines that are poorly described by the classic plume model rayleigh wave phase velocities are measured at periods from 20 to 182 s following the two plane wave methodology using data from the cameroon seismic experiment which consists of 32 broadband stations deployed between 2005 and 2007 these phase velocities are then inverted to build a model of shear wave velocity structure in the upper mantle beneath the cvl results show that phase velocities beneath the cvl are reduced at all periods with average velocities beneath the cvl deviating more than 2 from the regional average and 4 beneath the congo craton this distinction is observed for all periods but is less pronounced for the longest periods measured inversion for shear wave velocity structure indicates a tabular low velocity anomaly directly beneath the cvl at depths of 50 to at least 200 km and a sharp vertical boundary with faster velocities beneath the congo craton these observations demonstrate widespread infiltration or erosion of the continental lithosphere beneath the cvl most likely caused by mantle upwelling associated with edge flow convection driven by the congo craton or by lithospheric instabilities that develop due to the nearby edge of the african continent

northwest european palaeoclimate as indicated by growth frequency variations of secondary calcite deposits a compilationn for the northwest of europe of over 500 uranium series speleothen and travertine dates is presented using a cumulative distributed error frequency approach these secondary carbonate deposits require both significant groundwater supply and a biogenic soil carbon dioxide source for their growth during glacial periods soil co2 production is inhibited and the water supply is ice locked therefore growth is slowed significantly if not stopped thus deposits can be used on a chronological basis to give a signal of glacial and non glacial periods however sensitivity to the groundwater supply modifies this signal with growth also limited in times of high aridity the palaeoclimatic signal is thus complex the compilation presented is used both as a chronology for comparison with the orbitally tuned marine oxygen isotope record and as a palaeoclimatic indicator attention is focused on two periods of the last glacial interglacial cycle where the record provides a significantly different palaeoclimatic record to other terrestrial and oceanic records these are the isotope stages 5 4 transition for which a relatively low cumulative growth frequency indicates an earlier increase in aridity than observed elsewhere and isotope stage 3 the pleniglacial where both statistically significant high 49 62 ka and low 22 35 44 46 ka levels of growth are observed and can be used to constrain the timing of many of the interstadial events within this period

one dimensional models of shear wave velocity for the eastern mediterranean obtained from the inversion of rayleigh wave phase velocities and tectonic implications summary on a sw ne profile from the libyan coast towards central turkey phase velocity curves of the fundamental rayleigh mode were measured using a two station method the inversion of phase velocity curves yields 1 d models of shear wave velocity down to approximately 200 km depths that may be interpreted as estimates of average models between neighbouring stations on the profile strong lateral variations in the shear wave velocity structure are imaged along the profile the subducted oceanic african mantle lithosphere is indicated in 1 d models for the region around crete by significantly enlarged shear wave velocities it is also imaged by an average model of the structure between stations on crete and santorini on a path crossing the libyan sea south of crete the resulting model is slower than a model expected for 110 myr old oceanic lithosphere the passive african margin is thus assumed to extend northwards beneath the libyan sea anomalous low shear wave velocities are found for the uppermost mantle beneath central turkey down to a depth of approximately 130 km using two stations on crete the average depth of the oceanic moho within the subducting slab is estimated to be at approximately 50 km beneath crete for this arc parallel path an enlarged standard deviation of the measured phase velocities of approximately 0 2 km s 1 between 10 and 30 mhz is observed that is probably caused by strong lateral heterogeneity related to the subducting slab in addition in this frequency range an anomalous propagation of the fundamental rayleigh mode is detected that is indicated by measured phase velocities that are approximately one standard deviation faster than phase velocities expected from a great circle approximation an average shear wave velocity of approximately 3 5 km s 1 is observed above the oceanic moho in order to explain the recent lithospheric structure of the hellenic subduction zone a tectonic model is assumed for the ne sw striking profile considered it is based on the calculated 1 d models tectonic reconstructions and on a model derived from the metamorphic history of rocks exposed on crete the suggested model summarizes the tectonic development at a lithospheric scale starting in the late cretaceous accretion of crustal material of two microcontinents to eurasia is assumed while continuous subduction of the oceanic lithosphere of different ocean basins and possibly of the mantle lithosphere of the microcontinents resulted in a single slab the length of the oceanic lithosphere that was subducted south of crete is estimated to be not greater than approximately 550 km

improvements in the knowledge of the anelastic structure of the iberian peninsula from seismic data of the iliha project summary attenuation coefficients of rayleigh waves propagating across the iberian peninsula and quality factor models were obtained for different two station great circle paths the data used were long period wave trains contained in the seismograms provided by the iliha array installed in the peninsula in the 1980s more than 300 seismograms were analysed to obtain 14 sets of similar paths consisting of either paths totally included in one of the four pure tectonic regions or mixed paths crossing several regions we used the two station method to determine attenuation parameters r and then an inversion method to derive q 1 models the attenuation coefficients of seismic energy in the 10 120 s range are in the range 2 8 10 3 0 1 10 3 km 1 and correlate well with both previous results obtained from analogue wwssn and most seismogeotectonic characteristics of iberia the q models obtained also agree with a few models for iberia determined earlier and they show significant variations from one region to another as a general feature the values are higher in the active seismotectonic regions typical maximum of 2 6 10 3 km 1 than in the more stable ones typical maximum of 1 4 10 3 moreover the maximum of q 1 in the active regions 145 10 3 120 10 3 is higher than in the stable ones 40 10 3 100 10 3 in general both the regionalized attenuation coefficients of rayleigh waves and the quality factor models exhibit a good agreement with previously published lg wave attenuation and coda q distribution patterns in iberia

interpretation of seismic surface waves in regional networks joint estimation of wavefield geometry and local phase velocity method and numerical tests summary teleseismic surface waves in general strongly deviate from plane waves as is evident from the analysis of surface wave data recorded with dense networks this causes conventional ray based tomographic techniques to break down if applied to network surface wave data we present a new inversion method based on the acoustic wave equation and applicable to vertical component surface wave data which successfully deals with non plane wavefield geometries the basic idea of the method is a joint estimation of the incoming wavefield and heterogeneous structure within the network region crucial to the success of the method is an adequate parametrization of the incoming wavefield which is realized using hermite gaussian basis functions additionally we apply a constraint on the wavefield parameters that expresses the idea that the samples of the wavefield taken at the station locations should be representative for the wavefield in the whole network region in this way wavefields that show stronger fluctuations in spectral amplitude than observed at the stations are rejected to represent heterogeneous structure within the network region we use an expansion into 2 d hermite gaussian functions provided that the density of stations is sufficient the proposed method retrieves heterogeneous structure in the network region very well it is not sensitive to noise or non uniform azimuthal coverage of earthquakes moreover it yields smoothed versions of the true model if the roughness of the latter has been underestimated in the inversion conversely if the true model is much smoother than anticipated inspection of the trade off between model smoothness and data misfit allows us to find the correct model the limiting factor for the inversion is the density of stations which must allow for a reliable interpolation of the observed wavefield within the network therefore in order to perform regional surface wave studies it is essential to deploy seismic stations in the region of interest itself

non plane geometries of seismic surface wavefields and their implications for regional surface wave tomography summary seismic surface waves exhibit much more complicated wavefields than is commonly assumed we are led to this conclusion after analysing 90 teleseismic events recorded at on average eight broad band stations in southern germany large amplitude and phase fluctuations across the network are observed which as we show are definitely not due to instrument response or calibration problems in order to give an impression of how surface wavefields may look in reality we fit wavefields to the observed network data using basis wavefields derived from hermite gaussian functions we show both amplitude and phase distributions of several events synthetic wavefields generated by acoustic finite difference computations in a random medium with realistic correlation length and rms velocity fluctuations support the interpretation that most of the observed wavefield anomalies have accumulated on the path of the wave from the source to the network even if no lateral heterogeneities existed in the region of the network the large scale features of the observed wavefields would remain nearly unaltered we also model the synthetic wavefields using hermite gaussian wavefields and achieve extremely good fits in view of the large anomalies of the wavefields we investigate their implications for the regional surface wave tomography in this method one infers regional structure from a set of measurements of phase traveltime between pairs of stations the basic assumption of the method is that the wavefield incident on the network be plane thus all observed phase traveltime anomalies are interpreted in terms of regional heterogeneous structure the consequence is a seemingly highly inconsistent data set we perform several tomographic experiments with realistic synthetic data sets our experiments indicate that regional surface wave tomography may work if there is an excellent coverage of paths crossing the region and if each path is sampled several times under realistic conditions that is on a sparse network with not much more than one velocity value per path the imaging power of surface wave tomography is very poor owing to the seeming inconsistency of the phase traveltimes variance reduction is generally low with an increasing number of traveltime data it further decreases while at the same time the imaging power increases the opposite behaviour is observed if the number of data is reduced variance reduction increases but imaging power decreases hence in connection with regional surface wave tomography high variance reduction indicates a lack of data rather than the goodness of reconstruction

crustal structure below popocatepetl volcano mexico from analysis of rayleigh waves an array of ten broadband stations was installed on the popocatepetl volcano mexico for five months between october 2002 and february 2003 26 regional and teleseismic earthquakes were selected and filtered in the frequency time domain to extract the fundamental mode of the rayleigh wave the average dispersion curve was obtained in two steps firstly phase velocities were measured in the period range 2 50 s from the phase difference between pairs of stations using wiener filtering secondly the average dispersion curve was calculated by combining observations from all events in order to reduce diffraction effects the inversion of the mean phase velocity yielded a crustal model for the volcano which is consistent with previous models of the mexican volcanic belt the overall crustal structure beneath popocatepetl is therefore not different from the surrounding area and the velocities in the lower crust are confirmed to be relatively low lateral variations of the structure were also investigated by dividing the network into four parts and by applying the same procedure to each sub array no well defined anomalies appeared for the two sub arrays for which it was possible to measure a dispersion curve however dispersion curves associated with individual events reveal important diffraction for 6 s to 12 s periods which could correspond to strong lateral variations at 5 to 10 km depth

non linear surface wave phase velocity inversion based on ray theory summary the development of temporary and permanent broad band seismic arrays reinforces the need for advanced interpretation techniques in surface wave analysis we present a new method based on 2 d paraxial ray theory of inverting teleseismic surface wave phase information and constructing phase velocity maps on a regional scale measurements of local phase velocities and propagation directions of rayleigh waves taken from full waveform synthetic seismograms are used to validate the ray theory for smooth structures on a regional scale curved wavefronts created by heterogeneous structure outside the study area are taken into account through joint inversion for the phase velocity field and the shape of the incoming wavefronts in the forward ray tracing procedure the curved wavefronts are introduced through the boundary conditions by equating the slowness vector of the ray at the edge of the study region with the known gradient of the arrival time of the wave to make the inverse problem non singular we constrain the parameters in the inversion primarily by applying a smoothness criteria on the velocity field and on the incoming wave field inversions of synthetic data sets computed by direct ray tracing and by full waveform modelling show that for 100 km spacing between stations the minimum size of structure that we can image is approximately 150 km heterogeneities with a size approximately equal to the wavelength are reconstructed by the ray based inversion even though velocity variations are underestimated due to the wave field smoothing of the structures a minimum signal to noise ratio of 3 5 is necessary in order to correctly retrieve the phase velocity field inversion of a subset of the svekalapko data for 60 s period demonstrates the applicability of the method on real data

surface wave dispersion and upper mantle structure beneath southern germany from joint inversion of network recorded teleseismic events we have determined the dispersion of fundamental mode rayleigh waves in southern germany in the frequency range 4 50 mhz by simultaneously inverting data from 66 teleseismic events recorded at a network of up to 9 broadband stations three different inversion experiments were performed determination of 1 isotropic phase velocity of 2 azimuthally anisotropic phase velocity assuming a plane wave traveling across the network and 3 isotropic phase velocity but now allowing for non plane properties of the wavefield in experiments 1 and 2 for each event amplitude phase and deviation from the great circle azimuth were estimated as well we have obtained remarkably stable results for phase velocity over the whole frequency range between 7 and 25 mhz azimuthal anisotropy is definitely below 0 5 percent below 7 and above 25 mhz we found up to 3 percent anisotropy but with negligible variance reduction compared to the isotropic inversion experiment 1 admitting non plane wavefields in the inversion still yields nearly identical phase velocities on inversion of the phase velocity curve in terms of shear wave velocity we obtained a rather shallow asthenosphere with minimum s of 4 28 km s at about 130 km depth covered by a thin lid with s of 4 63 km s

joint estimation of afterslip rate and postseismic relaxation following the 1989 loma prieta earthquake global positioning system gps data from campaigns carried out over the 5 years following the 1989 loma prieta earthquake and leveling data measured in 1990 and 1992 define the postseismic velocity field around the loma prieta rupture zone subtraction of a background velocity field yields a residual velocity pattern which we interpret as the product of two physical processes 1 slow afterslip along distinct planes in the upper cru st and 2 viscoelastic relaxation of the lower crust and upper mantle biirgmann et al 1997 previously derived an afterslip model involving uniform afterslip on two optimally determined planes in cluding oblique reverse slip on the coseismic rupture and reverse slip on a shallow thrust fault to the northeast of the san andreas fault we further consider models of distributed slip on these two fault planes plus a viscoelastic relaxation pattern which depends on a suitable cose ismic rupture model and crust and mantle viscosities several fault models from the literature were considered for the 1989 coseismic rupture with nearly identical impact on the results simultaneous maximum likelihood inversion of the gps and leveling data for afterslip distri bution and viscosity yields the following results 1 a good fit to the data is obtained by smooth afterslip distributions without any viscoelastic relaxation being required 2 tangible broad scale viscoelastic relaxation of the lower crust and upper mantle are present in this data set at 97 confidence and a lower crustal viscosity of 1029 pa s is obtained however the viscosity of both the lower crust and upper mantle are poorly constrained 3 for a given misfit 20 less integrated afterslip and smoother afterslip distributions result when viscoelas tic relaxation is included 4 maximum slip rates on the slip distributed models are 3 5 crn yr the dominant patches estimated on the two planes fill in the entire depth range 4 13 km without significant overlap and deeper afterslip is not required the afterslip distribution on the coseismic rupture plane is strongly dominated by reverse slip immediately southeast of the main center of coseismic reverse slip