surface wave tomography of the western united states from ambient seismic noise rayleigh and love wave phase velocity maps summary we present the results of rayleigh wave and love wave phase velocity tomography in the western united states using ambient seismic noise observed at over 250 broad band stations from the earthscope usarray transportable array and regional networks all available threecomponent time series for the 12 month span between 2005 november 1 and 2006 october 31 have been cross correlated to yield estimated empirical rayleigh and love wave green s functions the love wave signals were observed with higher average signal to noise ratio snr than rayleigh wave signals and hence cannot be fully explained by the scattering of rayleigh waves phase velocity dispersion curves for both rayleigh and love waves between 5 and 40 speriod were measured for each interstation path by applying frequency time analysis the average uncertainty and systematic bias of the measurements are estimated using a method based on analysing thousands of nearly linearly aligned station triplets we find that empirical green s functions can be estimated accurately from the negative time derivative of the symmetric component ambient noise cross correlation without explicit knowledge of the source distribution the average traveltime uncertainty is less than 1 s at periods shorter than 24 s we present rayleigh and love wave phase speed maps at periods of 8 12 16 and 20 s the maps show clear correlations with major geological structures and qualitative agreement with previous results based on rayleigh wave group speeds

rayleigh wave tomography beneath intraplate volcanic ridges in the south pacific sources recorded over a 12 month period provides resolution of phase velocities at periods upto100s theaveragephasevelocitiesforthestudyarearevealapronouncedlow velocity zone reaching a minimum shear velocity of 3 95 km s the negative velocity gradient defining the base of the lithosphere observed at 40 15 km abruptly reverses at 70 km depth the underlying positive gradient changes slope at 125 km we attribute these changes in gradient to the onset of incipient partial melting of upwelling mantle in thepresenceofwaterat125km followedbyincreasedmeltproductionat70kmthatleadsto dehydration of the residual matrix and migration of melt to the surface spreading center rayleigh wave tomography shows that there are anomalously low shear velocities extending to at least 50 km depth beneath the sojourn ridge and the hotu matua volcanic complex with relatively high velocities between these volcanic chains these observations are not consistent with passive models for the origin of the volcanic ridges involving lithospheric extension or thermoelastic cracking dynamic models invoking flow in the asthenosphere in the form of small scale convection or viscous fingering instabilities may explain the observed pattern of seismic velocity anomalies

seismic imaging of crust beneath the dharwar craton india from ambient noise and teleseismic receiver function modelling we use cross correlation of continuous 18 months 2009 february to 2010 august ambient noise data recorded over 35 broad band seismographs in the archean dharwar craton and the adjoining granulite terrain to generate rayleigh wave group velocity maps in the period 5 28 s this is supplemented with longer period data 40 70 s from earthquake source combined group velocity measurement was inverted jointly with the teleseismic receiver functions obtained at 50 stations includes 15 stations operated during 1998 2002 to produce shear velocity image of the crust the velocity image reveals thinner crust 34 38 km in the late archean 2 7 ga eastern dharwar craton edc while all other terrains mid archean and proterozoic have crustal thickness from 40 to over 50 km the mid archean 3 36 ga greenstone belt of the western dharwar craton wdc has the thickest crust 50 km the average crustal vs beneath the edc is 3 70 3 78 km s 1 as compared to 3 80 3 95 km s 1 beneath the wdc we observe significant lateral variation in the thickness of lower crust vs 3 8 4 2 km s 1 10 15 km in the edc compared to 20 30 km in the wdc the lowermost part of the crust vs 4 0 km s 1 is thin 5 km beneath the edc in contrast to more thickness 10 27 km beneath the wdc our analysis suggests intermediate composition for the crust beneath the edc similar to those for other cratons in contrast the mid archean exposed wdc crust has more mafic composition and exceptional thickness a scenario at variance with the global observations we interpret this thick mafic crust to represent undeformed geological segment of 3 36 ga the edc with a nearly flat moho felsic to intermediate composition of crust and thin basal layer may represent a reworked terrain during the late archean

continental crust composition constrained by measurements of crustal poisson s ratio deciphering the geological evolution of the earth s continental crust requires knowledge of its bulk composition and global variability the main uncertainties are associated with the composition of the lower crust seismic measurements probe the elastic properties of the crust at depth from which composition can be inferred of particular note is poisson s ratio this elastic parameter can be determined uniquely from the ratio of p to s wave seismic velocity and provides a better diagnostic of crustal composition than either p or s wave velocity alone1 previous attempts to measure have been limited by difficulties in obtaining coincident p and s wave data sampling the entire crust2 here we report 76 new estimates of crustal spanning all of the continents except antarctica we find that on average increases with the age of the crust our results strongly support the presence of a mafic lower crust beneath cratons and suggest either a uniformitarian craton formation process involving delamination of the lower crust during continental collisions followed by magmatic underplating or a model in which crust formation processes have changed since the precambrian era

multiscale finite frequency rayleigh wave tomography of the kaapvaal craton summary we have measured phase delays of fundamental mode rayleigh waves for 12 events recorded by the southern africa seismic experiment at frequencies between 0 005 and 0 035 hz a novel multiscale finite frequency tomographic method based on wavelet decomposition of 3 d sensitivity kernels for the phase of rayleigh waves is used to map the shear velocities in the upper mantle beneath southern africa the kernels are computed by summing coupled normal modes over a very fine grid surrounding the seismic array to estimate and minimize the biases in the model resulting from structures outside the tomographic grid a jackknife inversion method is implemented the contribution of heterogeneities outside the target volume is significant but produces artefacts in the tomographic model that are easily identified and discarded before interpretation with structures on length scales as short as 100 km retrieved beneath the array the deep structure of the kaapvaal craton is revealed with unprecedented detail outside the array the corresponding resolution is 200 km high velocity cratonic roots are confined to the archean craton and extend to depths of at least 250 km confirming earlier surface structural studies we recognize two distinct units in the kaapvaal craton the eastern witwatersrand block and the western kimberley block are separated by a major near vertical translithospheric boundary which coincides with the colesberg lineament lower than average velocities south and east of the kaapvaal craton reveal extensive metasomatism and heating of the lithosphere probably related to the karoo magmatic event and to the opening of the south atlantic ocean

shear wave velocity structure of africa from rayleigh wave analysis the 3d s velocity structure beneath africa is shown by means of a 2d s velocity mapping for depths raging from zero to 500 km determined by the regionalization and inversion of rayleigh wave dispersion the traces of 94 earthquakes occurred from 1990 to 2009 in the study area have been used to obtain the rayleigh wave dispersion these earthquakes were registered by 61 seismic stations located on africa and the surrounding area the dispersion curves were obtained for periods between 5 and 300 s by digital filtering with a combination of mft and tvf filtering techniques after that all seismic events and some stations were grouped to obtain a dispersion curve for each source station path these dispersion curves were regionalized and after inverted according to generalized inversion theory to obtain shear wave velocity models for rectangular blocks with a size of 5 5 the 3d s velocity structure obtained through this procedure is shown in the 2d s velocity maps plotted for several depths these results agree well with the geology and other geophysical results previously obtained the obtained s velocity models suggest the existence of lateral and vertical heterogeneity the zones with consolidated and old structures as cratons present greater s velocity values than the other younger zones nevertheless in the depth range from 20 to 40 km the different moho depths present in the study area generate the principal variation of s velocity a similar behaviour is found for the depth range from 60 to 230 km in which the lithosphere asthenosphere boundary generates the principal variations of s velocity finally it should be highlighted a new and interesting feature obtained in this study the definition of the base of the asthenosphere for depths ranging from 160 to 280 km in the whole african continent

crust and upper mantle structure beneath the pacific northwest from joint inversions of ambient noise and earthquake data 1 we perform a joint inversion of phase velocities from both earthquake and ambient noise induced rayleigh waves to determine shear wave velocity structure in the crust and upper mantle beneath the pacific northwest we focus particularly on the areas affected by mid miocene to present volcanic activity the joint inversion combined with the high density seismic network of the high lava plains seismic experiment and data from the earthscope transportable array provides outstanding resolution for this area in oregon we find that the pattern of low velocities in the crust and uppermost mantle varies between the high lava plains physiographic province and the adjacent northwestern basin and range these patterns may be due to the presence of the brothers fault zone which separates the clockwise rotating northwest basin and range from the relatively undeformed areas further north further to the east the owyhee plateau snake river plain srp and northeastern basin and range are characterized by high crustal velocities though the depth extent of these fast wave speeds varies by province of particular interest is the mid crustal high velocity sill previously only identified within the srp we show this anomaly extends significantly further south into utah and nevada we suggest that one possible explanation is lateral crustal extrusion due to the emplacement of the high density mafic mid crustal sill structures within the srp

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

s wave velocity images of the dead sea basin provided by ambient seismic noise abstract based on passive seismic interferometry applied to ambient seismic noise recordings between station pairs belonging to a small scale array we have obtained shear wave velocity images of the uppermost materials that make up the dead sea basin we extracted empirical green s functions from cross correlations of long term recordings of continuous data and measured inter station rayleigh wave group velocities from the daily correlation functions for positive and negative correlation time lags in the 0 1 0 5 hz bandwidth a tomographic inversion of the travel times estimated for each frequency is performed allowing the laterally varying 3 d surface wave velocity structure below the array to be retrieved subsequently the velocity frequency curves are inverted to obtain s wave velocity images of the study area as horizontal depth sections and longitude and latitude depth sections the results which are consistent with other previous ones provide clear images of the local seismic velocity structure of the basin low shear velocities are dominant at shallow depths above 3 5 km but even so a spit of land with a depth that does not exceed 4 km is identified as a salt diapir separating the low velocities associated with sedimentary infill on both sides of the lisan peninsula the lack of low speeds at the sampling depth of 11 5 km implies that there are no sediments and therefore that the basement is near 10 11 km depth but gradually decreasing from south to north the results also highlight the bowl shaped basin with poorly consolidated sedimentary materials accumulated in the central part of the basin the structure of the western margin of the basin evidences a certain asymmetry both whether it is compared to the eastern margin and it is observed in north south direction infill materials down to 8 km depth are observed in the hollow of the basin unlike what happens in the north and south where they are spread beyond the western dead sea shore

crustal structure and dynamics of botswana we present the first nationwide crustal thickness and vp vs maps for botswana based on the analysis of new p wave receiver functions of nars botswana network integrated with previous receiver function results in botswana using h k analysis we found crustal thickness values ranging from 34 km for the okavango rift zone to 49 km at the border between the magondi belt and the zimbabwe craton for stations with significant sediment cover a sediment correction was applied based on sequential h k stacking we observed distinct differences for the kaapvaal craton the eastern part has a high vp vs ratio typical of a predominantly mafic composition suggesting lateral extension of the bushveld mafic complex on the other hand the western part with a vp vs ratio of 1 67 is felsic probably as a result of delamination caused by proterozoic rifting processes further to the west of the kaapvaal craton we found a crustal thickness of 42 km and a vp vs ratio of 1 76 for the nosop basin these values are similar to other cratonic regions in botswana suggesting the presence of a buried craton as proposed by previous studies we confirm a relatively thin crust 34 39 km compared to the rest of botswana and high vp vs ratio 1 84 underneath the okavango rift zone found by previous receiver function studies notably we also found a relatively thin crust 37 km and high vp vs ratio 1 84 in central botswana underneath the passarge basin

quantitative relations of seismic source parameters and a classification of earthquakes abstract relations between earthquake parameters moment m0 fault area s fault length l and width w stress drop time characteristics and magnitudes and faulting type dip slip ds and strike slip ss are quantitatively analyzed using a dataset of 240 events m 5 the analysis is carried further toward an earthquake systematization by introducing earthquake classes the results are 1 1 l w 2 1 for ds l w 2 30 for ss and l w 3 7 for giant m0 1029 dyne cm earthquakes respectively 2 2 log m0 1 5 log s 22 2 s in km2 and tentatively log m0 2 45 log s 17 49 for ds and ss and giant earthquakes respectively 3 3 the large scatter of data in m0 s dependences is the result of the combined effect of the variation in and l w 4 4 the concept of constant is replaced by variable to explain the large variations in relations between m0 s l and w for both ds and ss earthquakes and partly between body and surface wave magnitudes low intermediate and high stress drop gd 30 30 60 and 60 bar respectively earthquakes are defined 5 5 a relation of reciprocity exists between seismic slip fault length and width and stress drop 6 6 a saturation of s for some very large earthquakes is suggested from the interpretation of actual data on m0 s l w etc 7 7 the total source duration tsd increases with m0 in relation with earthquake type and tentatively log m0 2 16 log tsd 24 50 holds for ds earthquakes 8 8 log m0 1 5 mm 16 1 holds for mm brune engen mantle wave magnitude 8 5 8 75 9 9 more magnitudes of shorter or longer period on both body and surface wave basis are useful in constraining significant earthquake features 10 10 low and high frequency earthquakes can be distinguished using the gutenberg richter relation ms mb as a reference relation or a relation between ms and mmaxb 11 11 aki s similarity conditions are extended by adding two more conditions as to express more specifically four basic features geometry deformation frequency and time of the earthquake source 12 12 a reference earthquake is defined by criteria consistent with the similarity conditions 13 13 on this basis and in view of nonsimilarity of earthquakes in their totality a scheme for earthquake classification is proposed

a seismic refraction investigation of the archaean kaapvaal craton south africa using mine tremors as the energy source summary the structure of the central kaapvaal craton of southern africa has been investigated by deep seismic sounding using mine tremors as energy sources seismometers were deployed at approximately 10 km intervals on two profiles stretching between major mine tremor source regions mine tremors are rich in shear energy enabling joint interpretation of p and s waves and produce substantial energy at frequencies as low as 1 hz record sections are presented for both p and s waves and the traveltimes and amplitudes interpreted using 2 d ray tracing techniques synthetic seismograms computed for a 1 d velocity model by the reflectivity method compare well with the observed data a generalized seismic model of the kaapvaal craton has the following features supracrustal strata 0 10 km thick upper crystalline basement with p wave velocities of 6 0 6 2 km s the boundary between upper and lower crust at a depth of 14 18 km a lower crust with a relatively uniform seismic velocity in the range 6 4 6 7 kms and the crust mantle transition over 1 3 km with the moho at a depth of about 35 km the lower crust is found to be seismically attenuating and has a poisson s ratio of about 0 28 it is also known to be electrically conductive these observations are in accord with the presence of hydrated mantle rock at the base of the crust the velocity depth model of the kaapvaal craton is similar to models derived for other archaean cratons the proterozoic provinces adjacent to the kaapvaal craton are significantly thicker and have an intermediate to high velocity layer developed at the base of the crust this is interpreted to indicate a change in the process of crustal growth with basaltic underplating becoming more important since the archaean this change is attributed to a change in the composition of the upper mantle the higher temperatures in the archaean mantle led to the eruption of komatiitic lavas resulting in an ultradepleted mantle unable to produce significant volumes of basaltic melt proterozoic crust developed above fertile mantle and subsequent partial melting resulted in basaltic underplating and crustal inflation

ambient noise rayleigh wave tomography of new zealand summary we present the first new zealand wide study of surface wave dispersion using ambient noise observed at 42 broad band stations in the national seismic network geonet and the global seismic network gsn year long vertical component time series recorded between 2005 april 1 and 2006 march 31 have been correlated with one another to yield estimated fundamental mode rayleigh wave green s functions we filter these green s functions to compute rayleigh wave group dispersion curves at periods of 5 50 s using a phase matched filter frequency time analysis technique the uncertainties of the measurements are estimated based on the temporal variation of the dispersion curves revealed by 12 overlapping 3 month stacks after selecting the highest quality dispersion curve measurements we compute group velocity maps from 7 to 25 s period these maps and 1 d shear wave velocity models at four selected locations exhibit clear correlations with major geological structures including the taranaki and canterbury basins the hikurangi accretionary prism and previously reported basement terrane boundaries

dead sea basin imaged by ambient seismic noise tomography in the framework of the dead sea integrated research project desire 59 seismological stations were deployed in the region of the dead sea basin twenty of these stations recorded data of sufficiently high quality between may and september 2007 to be used for ambient seismic noise analysis empirical green s functions are extracted from cross correlations of long term recordings these functions are dominated by rayleigh waves whose group velocities can be measured in the frequency range from 0 1 to 0 5 hz analysis of positive and negative correlation lags of the green s functions makes it possible to identify the direction of the source of the incoming energy signals with frequencies higher than 0 2 hz originate from the mediterranean sea while low frequencies arrive from the direction of the red sea travel times of the extracted rayleigh waves were measured between station pairs for different frequencies and tomographically inverted to provide independent velocity models four such 2d models were computed for a set of frequencies all corresponding to different sampling depths and thus together giving an indication of the velocity variations in 3d extending to a depth of 10 km the results show low velocities in the dead sea basin consistent with previous studies suggesting up to 8 km of recent sedimentary infill in the basin the complex structure of the western margin of the basin is also observed with sedimentary infill present to depths not exceeding 5 km west of the southern part of the dead sea the high velocities associated with the lisan salt diapir are also observed down to a depth of 5 km the reliability of the results is confirmed by checkerboard recovery tests

the 14 november 2001 kokoxili kunlunshan tibet earthquake rupture transfer through a large extensional step over the 14 november 2001 kokoxili tibet earthquake m w 7 8 ruptured 400 km of the western kunlun fault in northern tibet we apply two inversion methods to p and sh waves recorded by the global seismographic network to recover the spatial and temporal history of the rupture process the observed surface rupture consists of two strike slip segments offset by an extensional step over little surface rupture was observed in the graben system in this step over which is approximately 45 km long and over 10 km wide our results imply that the rupture did not jump this large gap but that the rupture was continuous through the graben the earthquake began with a small strike slip subevent presumably along the westernmost of the two segments this was followed 5 sec later by a subevent of about the same magnitude but having an oblique mechanism with a large normal faulting component the likely location for this subevent is within the graben this oblique slip event probably enabled transfer of the rupture onto the main kunlun fault the main moment release began 18 sec after rupture initiation and propagated over 350 km eastward along the kunlun fault slip on this segment was very heterogeneous averaging 2 m for the first 200 km followed by a sharp increase to a maximum of 7 5 m within the next 50 km and then a rapid decline the average rupture velocity along the main segment was high 3 6 km sec 1 and probably exceeded the local shear wave velocity the m w 7 8 kokoxili earthquake had a longer surface rupture and faster average rupture velocity radiated more energy and probably had a lower average fracture energy than the november 2002 m w 7 9 denali fault alaska earthquake evidence suggests that the velocity of the rupture front dropped significantly after passing the point of maximum slip implying a large difference in frictional strength between the two ends of the fault online material waveform fits to teleseismic body waves

ambient noise tomography of the greater geneva basin in a geothermal exploration context the greater geneva basin is one of the key targets for geothermal exploration in switzerland until recently information about the subsurface structure of this region was mostly composed of well logs seismic reflection lines and gravity measurements as part of the current effort to further reduce subsurface uncertainty and to test passive seismic methods for exploration purposes we performed an ambient noise tomography of the greater geneva basin we used 1 5 years of continuous data collected on a temporary seismic network composed of 28 broadband stations deployed within and around the basin from the vertical component of the continuous noise recordings we computed cross correlation functions and retrieved rayleigh wave group velocity dispersion curves we then inverted the dispersion curves to obtain 2d group velocity maps and proceeded to a subsequent inversion step to retrieve a large scale 3d shear wave velocity model of the basin we discuss the retrieved features of the basin in the light of local geology previously acquired geophysical datasets and ongoing geothermal exploration the greater geneva basin is an ideal natural laboratory to test innovative geothermal exploration methods because of the substantial geophysical datasets available for comparison while we point out the limits of ambient noise exploration with sparse networks and current methodology we also discuss possible ways to develop ambient noise tomography as an affordable and efficient subsurface exploration method

moho depth and crustal composition in southern africa abstract we present new results on structure thickness and composition of the crust in southern africa based on 6300 seismic receiver functions at 85 stations application of hk stacking to the entire sase dataset and use of multi frequency bands improve resolution substantially we observe a highly heterogeneous crustal structure with short wavelength variations in thickness h vp vs ratio composition and moho sharpness which defines 20 blocks that do not everywhere coincide with surface tectonic features in the zimbabwe craton the tokwe block has h 35 38 km and vp vs 1 74 1 79 whereas the thicker crust in the tati block h 47 51 km may be related to deformation of the archean crust along the cratonic margin two distinct crustal blocks with similar crustal thickness 42 46 km but significantly different vp vs ratios are recognized in the limpopo belt extreme values of 1 90 1 94 at the dyke swarms in eastern limpopo and 1 84 at the olifants river dyke swarm and easternmost bushveld intrusion complex bic indicate voluminous magmatic intrusions in the whole crust we find no evidence for magmatic intrusions in the central inferred part of bic where the crust is thick 45 50 km and vp vs is low 1 68 1 70 this thick crustal root may have deflected rising magmas to form the two bic lobes most of central kaapvaal has thin 35 40 km crust and vp vs 1 74 these characteristics are similar to the tokwe block in zimbabwe craton and may indicate delamination of pre existing lower crust which is further supported by a very sharp moho transition the exposed cross section in the vredefort impact crater is non representative of cratonic crust due to shallow moho 34 km and high vp vs 1 80 attributed to shock metamorphism high vp vs 1 76 is typical of the witwatersrand basin and anomalously low vp vs 1 66 1 67 marks the kaapvaal kheis namaqua transition highly heterogeneous crust both in thickness and vp vs ratio is typical of the namaqua natal and cape fold belts

new seismic model of the upper mantle beneath africa we present a seismic model of the upper 400 km of the mantle beneath africa and surrounding regions this model is constructed by inverse modeling of fundamental mode rayleigh wave phase velocities 40 200 s for about 8000 propagation paths among the most pronounced anomalies are high shear velocity structures as much as 6 higher than in the preliminary reference earth model beneath the west african congo and kalahari cratons that extend to about 250 km depth these structures have near vertical margins across which the shear velocity changes by as much as 6 over 500 km distance anomalous low shear velocities 3 4 lower than in the preliminary reference earth model structures are observed beneath the east african red sea and gulf of aden rifts and beneath the northwestern indian ocean these structures extend to a depth of at least 250 km our model cannot be reconciled with models that invoke a large number of plumes that have impinged on the base of the lithosphere nor does our seismic model indicate that high temperature low density material beneath the lithosphere is responsible for the uplift of southern africa

archean and proterozoic crustal evolution evidence from crustal seismology seismic velocity models for archean and proterozoic provinces throughout the world are analyzed the thickness of the crust in archean provinces is generally found to be about 35 km except at collisional boundaries whereas proterozoic crust has a significantly greater thickness of about 45 km and has a substantially thicker high velocity 7 0 km s layer at the base we consider two models that may explain these differences the first model attributes the difference to a change in the composition of the upper mantle the higher temperatures in the archean mantle led to the eruption of komatiitic lavas resulting in an ultradepleted lithosphere unable to produce significant volumes of basaltic melt proterozoic crust developed above fertile mantle and subsequent partial melting resulted in basaltic underplating and crustal inflation in the second model convection in the hot archean mantle is considered to have been too turbulent to sustain stable long lived subduction zones by the proterozoic the mantle had cooled sufficiently for substantial island and continental arcs to be constructed and the high velocity basal layer was formed by basaltic underplating

evolution of the lithosphere in the indian ocean from combined earthquake and ambient noise tomography rayleigh wave dispersion extracted from ambient seismic noise has been widely used to image crustal and uppermost mantle structure applications of this approach in continental settings are abundant but there have been relatively few studies within ocean basins by cross correlating ambient noise recorded at broadband seismic stations around the indian ocean we demonstrate the feasibility of extracting high quality long period 10 30 mhz rayleigh waves that traverse the entire ocean basin high quality rayleigh wave cross correlation functions can be obtained from stacking waveforms over less than two years at land stations and less than four years at island stations we show that adding the dispersion information extracted from ambient noise to a global earthquake data set can improve the resolution of phase velocity maps by about 20 in the northern indian ocean where the station distribution is the best we find that a plate cooling model with a potential temperature of 1450 c and plate thickness of 125 km can fit both the seismic observations and seafloor topography the seychelles mascarene plateau is characterized by anomalously slow velocity at 30 mhz the inclusion of ambient noise data in the tomographic inversion shifts the slow velocity anomaly into better agreement with the topographic relief allowing us to estimate its crustal thickness and confirm that the plateau s elevation is supported by thick crust the 10 and 20 mhz phase velocity maps show a strong asymmetry across the central indian ridge that is best explained by eastward asthenospheric flow emanating from nearby hotspots

seismic evidence of on going sublithosphere upper mantle convection for intra plate volcanism in northeast china abstract a 3 d crustal and upper mantle s wave velocity model of ne china is constructed by inversion of phase velocity dispersion curves at 6 140 s periods from ambient noise tomography and two plane surface wave tomography the seismic data used in this study are collected from 120 china earthquake administration cea permanent stations and 127 portable stations of necessarray we observe strong low s wave velocity beneath the changbaishan volcano in the upper mantle to at least 200 km depth which is interpreted as a mantle upwelling beneath the changbaishan volcano that is consistent with the body wave tomographic image the songliao basin is dominated by a high velocity extending to at least 200 km depth built upon the observed velocity anomalies we propose a sub lithosphere mantle convection model for ne china in which the upwelling of upper mantle materials from the mantle transition zone to the changbaishan volcano could induce a local sub lithosphere convection in the upper mantle and the strong high velocity of the upper mantle beneath the songliao basin corresponds to the downwelling limb of this convection cell the downwelling beneath the songliao basin could also induce secondary local convection in the asthenosphere to the west leading to local asthenospheric upwelling beneath the abaga and halaha volcanoes in the xing an mongolia orogenic belt

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

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

a seismic refraction investigation of the namaqualand metamorphic complex south africa the namaqualand metamorphic complex forms part of the precambrian shield of southern africa and hosts several major base metal deposits a long line seismic refraction experiment traversing the complex was conducted in order to complement geological and geophysical studies of the structure and evolution of this region seismograms were obtained at approximately 10 km intervals along the 290 km profile seismic ray tracing techniques were used to model the travel time and amplitude data it was found that the namaqualand lower crust is comprised of a substantial proportion of intermediate velocity 6 2 to 6 9 km s rocks these intermediate velocity rocks approach the surface near the midpoint of the profile moho was found to be at a depth of 42 km no correlation was found between the seismic and electrical resistivity models of the crust when the seismic velocity structure of the middle proterozoic namaqualand metamorphic complex is compared with that of adjacent geological provinces it is found to differ significantly from the archaean kaapvaal province but resemble the late proterozoic damara province these differences might be attributed to variations in the principal mechanisms of crustal growth between archaean and proterozoic times

crustal and uppermost mantle structure in southern africa revealed from ambient noise and teleseismic tomography summary rayleigh wave phase velocity maps in southern africa are obtained at periods from 6 to 40 s using seismic ambient noise tomography applied to data from the southern africa seismic experiment sase deployed between 1997 and 1999 these phase velocity maps are combined with those from 45 to 143 s period which were determined previously using a two planewave method by li burke in the period range of overlap 25 40 s the ambient noise and two plane wave methods yield similar phase velocity maps dispersion curves from 6 to 143 s period were used to estimate the 3 d shear wave structure of the crust and uppermost mantle on an 1 1 grid beneath southern africa to a depth of about 100 km average shear wave velocity in the crust is found to vary from 3 6 km s 1 at 0 10 km depths to 3 86 km s 1 from 20 to 40 km and velocity anomalies in these layers correlate with known tectonic features shear wave velocity in the lower crust is on average low in the kaapvaal and zimbabwe cratons and higher in the surrounding proterozoic terranes such as the limpopo and the namaquanatal belts which suggests that the lower crust underlying the archean cratons is probably less mafic than beneath the proterozoic terranes crustal thickness estimates agree well with a previous receiver function study of nair et al archean crust is relatively thin and light and underlain by a fast uppermost mantle whereas the proterozoic crust is thick and dense with a slower underlying mantle these observations are consistent with the southern african archean cratons having been formed by the accretion of island arcs with the convective removal of the dense lower crust if the foundering process became less vigorous in arc environments during the proterozoic

surface wave array tomography in se tibet from ambient seismic noise and two station analysis i phase velocity maps summary empirical green s functions egfs between pairs of seismographs can be estimated from the time derivative of the long time cross correlation of ambient seismic noise these egfs reveal velocity dispersion at relatively short periods which can be used to resolve structures in the crust and uppermost mantle better than with traditional surface wave tomography we combine rayleigh wave dispersion estimates from egfs and from traditional two station ts analysis into a new approach to surface wave array tomography with data from dense receiver arrays we illustrate the methodology with continuous broad band recordings from a temporary seismographic network on the southeastern part of the tibetan plateau in sichuan and yunnan provinces sw china the egfs are robust under temporal changes in regional seismicity and the use of either ambient noise approximated by records without signal from events with magnitude mb 5 or 4 or surface wave coda produces similar results the egfs do not strongly depend on the presence of large earthquakes but they are not reciprocal for stations aligned in the n s direction this directionality reflects the paucity of seismicity to the north of the array using a far field representation of the surface wave green s function and an image transformation technique we infer from the egfs the rayleigh wave phase velocity dispersion in the period band from 10 30 s a classical ts approach is used to determine rayleigh wave phase velocity dispersion between 20 120 s together they constrain phase velocity variations for t 10 120 s which can be used to study the structure from the crust to the upper mantle beneath se tibet short and intermediate period 10 80 s phase velocities are prominently low suggesting that the crust and upper mantle beneath se tibet is characterized by slow shear wave propagation

crust mantle coupling mechanism in cameroon west africa revealed by 3d s wave velocity and azimuthal anisotropy abstract to understand the depth variation of deformation beneath cameroon west africa we developed a new 3d model of s wave isotropic velocity and azimuthal anisotropy from joint analysis of ambient seismic noise and earthquake surface wave dispersion we found that the cameroon volcanic line cvl is well delineated by slow phase velocities in contrast with the neighboring congo craton in agreement with previous studies apart from the congo craton and the oubanguides belt the uppermost mantle revealed a relatively slow velocity indicating a thinned or thermally altered lithosphere the direction of fast axis in the upper crust is mostly ne sw but trending approximately n s around mt oku and the southern cvl the observed crustal azimuthal anisotropy is attributed to alignment of cracks and crustal deformation related to magmatic activities a widespread zone of weak to zero azimuthal anisotropy in the mid lower crust shows evidence for vertical mantle flow or isotropic mid lower crust in the uppermost mantle the fast axis direction changed from ne sw to nw se around mt oku and northern cameroon this suggests a layered mechanism of deformation and revealed that the mantle lithosphere has been deformed ne sw fast azimuths are observed beneath the congo craton and are consistent with the absolute motion of the african plate suggesting a mantle origin for the observed azimuthal anisotropy our tomographically derived fast directions are consistent with the local sks splitting results in some locations and depths enabling us to constrain the origin of the observed splitting the different feature of azimuthal anisotropy in the upper crust and the uppermost mantle implies decoupling between deformation of crust and mantle in cameroon

rayleigh wave phase velocity maps of tibet and the surrounding regions from ambient seismic noise tomography ambient noise tomography is applied to the significant data resources now available across tibet and surrounding regions to produce rayleigh wave phase speed maps at periods between 6 and 50 s data resources include the permanent federation of digital seismographic networks five temporary u s program for array seismic studies of the continental lithosphere passcal experiments in and around tibet and chinese provincial networks surrounding tibet from 2003 to 2009 totaling 600 stations and 150 000 interstation paths with such a heterogeneous data set data quality control is of utmost importance we apply conservative data quality control criteria to accept between 5000 and 45 000 measurements as a function of period which produce a lateral resolution between 100 and 200 km across most of the tibetan plateau and adjacent regions to the east misfits to the accepted measurements among passcal stations and among chinese stations are similar with a standard deviation of 1 7 s which indicates that the final dispersion measurements from chinese and passcal stations are of similar quality phase velocities across the tibetan plateau are lower on average than those in the surrounding nonbasin regions phase velocities in northern tibet are lower than those in southern tibet perhaps implying different spatial and temporal variations in the way the high elevations of the plateau are created and maintained at short periods 20 s very high velocities are imaged in the tarim basin the ordos block and the sichuan basin these phase velocity dispersion maps provide information needed to construct a 3 d shear velocity model of the crust across the tibetan plateau and surrounding regions

two receiver measurements of phase velocity cross validation of ambient noise and earthquake based observations phase velocities derived from ambient noise cross correlation are compared with phase velocities calculated from cross correlations of waveform recordings of teleseismic earthquakes whose epicentres are approximately on the station station great circle the comparison is conducted both for rayleigh and love waves using over 1000 station pairs in central europe we describe in detail our signal processing method which allows for automated processing of large amounts of data ambient noise data are collected in the 5 80 s period range whereas teleseismic data are available between about 8 and 250 s resulting in a broad common period range between 8 and 80 s at intermediate periods around 30 s and for shorter interstation distances phase velocities measured from ambient noise are on average between 0 5 per cent and 1 5 per cent lower than those observed via the earthquake based method this discrepancy is small compared to typical phase velocity heterogeneities 10 per cent peak to peak or more observed in this period range we nevertheless conduct a suite of synthetic tests to evaluate whether known biases in ambient noise cross correlation measurements could account for this discrepancy we specifically evaluate the effects of heterogeneities in source distribution of azimuthal anisotropy in surface wave velocity and of the presence of near field rather than far field only sources of seismic noise we find that these effects can be quite important comparing individual station pairs the systematic discrepancy is presumably due to a combination of factors related to differences in sensitivity of earthquake versus noise data to lateral heterogeneity the data sets from both methods are used to create some preliminary tomographic maps that are characterized by velocity heterogeneities of similar amplitude and pattern confirming the overall agreement between the two measurement methods

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

seismic structure of the crust and uppermost mantle of the capricorn and paterson orogens and adjacent cratons western australia from passive seismic transects abstract the seismic structure of the proterozoic capricorn and paterson orogens and adjacent archaean yilgarn and pilbara cratons western australia is determined using a passive seismic approach we use recordings of distant earthquakes made along two transects of 3 component broadband stations the stations were deployed for approximately 1 year mid 2006 2007 during which time 70 earthquakes were recorded at each station with a suitable signal to noise ratio for receiver function analysis and hence the s wavespeed profiles of the crust and uppermost mantle beneath each recording station are determined we investigate the deep crustal constraints on terrane boundary locations the patterns of seismic discontinuities in the crust and the variations in the depth and character of the moho this broad scale information regarding the present day crustal architecture and hence the crustal evolution of western australia complements previous surface geological and other geophysical studies western australia is an exceptionally large well preserved region of ancient crust and hence this work also adds to the body of knowledge regarding proterozoic orogenic processes in general the new passive seismic work shows a region of double crust or upper mantle discontinuities beneath the glenburgh terrane adjacent to the northwest yilgarn craton the upper crust of the orogens is always layered whereas the cratons have a simple upper crust both the capricorn and paterson orogens are characterised by deeper moho discontinuities with a lesser wavespeed contrast than the very sharp discontinuity observed beneath the adjacent pilbara and yilgarn cratons this is consistent with the weaker orogenic crust of the capricorn and paterson orogens accommodating most of the horizontal deformation during assembly and reworking of the west australian craton while the pilbara and yilgarn cratons acted as rigid crustal blocks

offshore rayleigh group velocity observations of the south island new zealand from ambient noise data we thank captain and crew of the r v thomas g thompson cruise tn229 the r v roger revelle cruise rr1002 and the sio obsip facility for expert assistance at sea the obs instruments used in this field program were provided by the u s national ocean bottom seismic instrumentation pool http www obsip org moana seismic data are archived at the iris data management center the collection of ocean bottom seismic data was funded by the national science foundation under grants ear 0409564 ear 0409609 and ear 0409835 new zealand onshore seismic data made available by the geonet project sponsored by eqc gns science and linz j stachnik acknowledges support from the cires postdoctoral fellowship program f c lin was supported by nsf grant cybersees 1442665 and the king abdullah university of science and technology kaust under award ocrf 2014 crg3 2300 we thank martha savage dan zietlow justin ball craig jones bill fry and peter molnar for valuable comments and discussion and john collins for leading the moana obs experiment we thank two anonymous reviewers and editor mike ritzwoller for their constructive comments

thinning and flow of tibetan crust constrained by seismic anisotropy intermediate period rayleigh and love waves propagating across tibet indicate marked radial anisotropy within the middle to lower crust consistent with a thinning of the middle crust by about 30 the anisotropy is largest in the western part of the plateau where moment tensors of earthquakes indicate active crustal thinning the preferred orientation of mica crystals resulting from the crustal thinning can account for the observed anisotropy the middle to lower crust of tibet appears to have thinned more than the upper crust consistent with deformation of a mechanically weak layer that flows as if confined to a channel

surface wave tomography from ambient seismic noise of accelerograph networks in southern korea 1 an efficient and robust cross correlation technique for estimation of surface wave green s function between two locations is applied to a set of ambient noise data recorded by accelerograph networks in the southern korea we have estimated 1843 group velocities of rayleigh waves in the period band of 2 4 seconds from correlation pairs of 91 accelerograph stations relatively dense and uniform coverage of the pairs provides us with high resolution tomographic image of surface wave group velocities in the region the resulting group velocity distribution correlates well with the characteristic features of geological map of the region displaying low velocities for the sedimentary basins and regions of volcanic and metasedimentary rocks and high velocities for the regions where granitoid basement rocks outcrop the short period information from the accelerograph network can enhance resolution of the subsurface structures at depths within a few kilometers which may be predominantly responsible for simulation results of strong ground motions

crustal structure beneath southern africa and its implications for the formation and evolution of the kaapvaal and zimbabwe cratons the formation of archean crust appears to in volve processes unique to early earth history initial results from receiver function analysis of crustal structure beneath 81 broadband stations deployed across southern africa re vealsignicantdierences inthenatureof thecrustandthe crust mantle boundary between archean and post archean geologic terranes with the notable exception of the colli sional limpopo belt where the crust is thick and the moho complex the crust beneath undisturbed archean craton is typically thin 35 40 km unlayered and characterized byastrongvelocitycontrastacrossarelativelysharpmoho thiscrustalstructurecontrastsmarkedlywiththatbeneath post archeanterranesandbeneatharcheanregionsaected bylarge scaleproterozoicevents thebushveldcomplexand the okwa magondi belts where the crust tends to be rel atively thick 45 50 km and the moho is complex

transdimensional inversion of ambient seismic noise for 3d shear velocity structure of the tasmanian crust abstractambient seismic noise tomography has proven to be a valuable tool for imaging 3d crustal shear velocity using surface waves however conventional two stage inversion schemes are severely limited in their ability to properly quantify solution uncertainty and account for inhomogeneous data coverage in response to these challenges we developed a two stage hierarchical transdimensional bayesian scheme for inverting surface wave dispersion information for a 3d shear velocity structure and apply it to ambient seismic noise data recorded in tasmania southeast australia the key advantages of our bayesian approach are that the number and distribution of model parameters are implicitly controlled by the data and that the standard deviation of the data noise is treated as an unknown in the inversion furthermore the use of bayesian inference which combines prior model information and observed data to quantify the a posteriori probability distribution means that model uncertainty information can b

azimuthal anisotropy beneath southern africa from very broad band surface wave dispersion measurements summary seismic anisotropy within the lithosphere of cratons preserves an important record of their ancient assembly in southern africa anisotropy across the archean kaapvaal craton and limpopo belt has been detected previously by observations of sks wave splitting because sks splitting measurements lack vertical resolution however the depth distribution of anisotropy has remained uncertain end member interpretations invoked the dominance of either anisotropy in the lithosphere due to the fabric formed by deformation in archean or palaeoproterozoic orogenies or that in the asthenosphere due to the fabric formed by the recent plate motion each with significant geodynamic implications to determine the distribution of anisotropy with depth we measured phase velocities of seismic surface waves between stations of the southern african seismic experiment we applied two complementary measurement approaches very broad band cross correlation and multimode waveform inversion robust rayleigh and love wave dispersion curves were derived for four different subregions of the archean southern africa in a period range from 5 s to 250 400 s rayleigh and 5 s to 100 250 s love depending on the region rayleigh wave anisotropy was determined in each region at periods from 5 s to 150 200 s sampling from the upper crust down to the asthenosphere the jackknife method was used to estimate uncertainties and the f test to verify the statistical significance of anisotropy we detected strong anisotropy with a n s fast propagation azimuth in the upper crust of the limpopo belt we attribute it to aligned cracks formed by the regional e w extensional stress associated with the southward propagation of the east african rift our results show that it is possible to estimate regional stress from short period surface wave anisotropy measured in this study using broad band array recordings of teleseismic surface waves rayleigh wave anisotropy at 70 120 s periods shows that the fabric within the deep mantle lithosphere of the limpopo belt and northern kaapvaal craton is aligned parallel to the archean palaeoproterozoic sutures at block boundaries this confirms that the fabric within the lithosphere created by pervasive ancient deformation is preserved to this day suture parallel fabric is absent however in the deep lithosphere of the western kaapvaal craton suggesting that it was not reworked in the collision with the craton s core either due to its mechanical strength or because the deformation mechanism was different from those that operated in the north anisotropy at periods greater than 120 130 s shows fast directions parallel to the plate motion and indicates shear wave anisotropy in the asthenosphere the depth distribution of anisotropy revealed by surface wave measurements comprises elements of both end member models proposed previously anisotropy in the asthenosphere shows fast propagation directions parallel to the plate motion anisotropy in the limpopo and northern kaapvaal lithosphere shows fast directions parallel to the archean palaeoproterozoic sutures the distribution of sks splitting orientations across southern africa reflects anisotropic fabric both within the lithosphere dominating the splitting beneath the limpopo belt and northern kaapvaal craton and within the asthenosphere dominating beneath the western kaapvaal craton

electrical lithosphere beneath the kaapvaal craton southern africa 1 a regional scale magnetotelluric mt experiment across the southern african kaapvaal craton and surrounding terranes called the southern african magnetotelluric experiment samtex has revealed complex structure in the lithospheric mantle large variations in maximum resistivity at depths to 200 250 km relate directly to age and tectonic provenance of surface structures within the central portions of the kaapvaal craton are regions of resistive lithosphere about 230 km thick in agreement with estimates from xenolith thermobarometry and seismic surface wave tomography but thinner than inferred from seismic body wave tomography the mt data are unable to discriminate between a completely dry or slightly damp a few hundred parts per million of water structure within the transitional region at the base of the lithosphere however the structure of the uppermost 150 km of lithosphere is consistent with enhanced but still low conductivities reported for hydrous olivine and orthopyroxene at levels of water reported for kaapvaal xenoliths the electrical lithosphere around the kimberley and premier diamond mines is thinner than the maximum craton thickness found between kimberley and johannesburg pretoria the mantle beneath the bushveld complex is highly conducting at depths around 60 km possible explanations for these high conductivities include graphite or sulphide and or iron metals associated with the bushveld magmatic event we suggest that one of these conductive phases most likely melt related sulphides could electrically connect iron rich garnets in a garnet rich eclogitic composition associated with a relict subduction slab

shallow crustal structure of the tanlu fault zone near chao lake in eastern china by direct surface wave tomography from local dense array ambient noise analysis ambient noise tomography ant has been used successfully to image shallow earth structure here we perform ant on a local dense seismic array around the tanlu fault zone tfz to the southeast of hefei city anhui province in eastern china the array consists of 53 stations with average spacing close to 5 km cross correlations of vertical component ambient noise data of different station pairs are computed in 1 h segments and stacked over 1 month from 17 march to 26 april 2017 clear fundamental mode rayleigh waves are observed between 0 2 and 5 s period we then use the direct surface wave tomographic method with period dependent ray tracing to invert group and phase dispersion travel time data simultaneously for three dimensional 3d shear wave velocity vs structure the vs model shows clear correlation with the known geologic features the tfz is associated with a high velocity anomaly zone in the shallow crust corresponding to metamorphic rocks due to magma intrusion low velocity anomaly zones are mainly located to the west of the tfz caused by thick sedimentary layers in the hefei basin our study shows that with ambient noise data recorded on a dense array and an advanced surface wave inversion method we can image detailed structure around the fault zone

estimates of fracture parameters of earthquakes a new estimate of the fracture parameters of earthquakes is provided in this paper by themuskhelishvili method 1953 a number of basic relations among fracture mechanics parameters are derived a scheme is proposed to evaluate the slip weakening parameters in terms of fault dimension average slip and rise time and the new results are applied to 49 events compiled in the earthquake catalogue ofpurcaru andberckhemer 1982

formation of an archaean continent about 30 of the earth is covered by continents but only about 10 small kernels of these continentsae known as archaean cratonsae are continental fragments formed before 2 5 gyr ago the kaapvaal craton of south africa which formed and stabilized between 3 7 and 2 7 gyr ago is one of the oldest reasonably sized examples of these continental fragments it consists of a mosaic of subdomains that have been welded together by processes similar to those of modern day plate tectonics the earliest subdomains may have owed their origin to the onset of efficient recycling from the earth s hydrosphere into the mantle

rayleigh wave tomography of the british isles from ambient seismic noise we present the first rayleigh wave group speed maps of the british isles constructed from ambient seismic noise the maps also constitute the first surface wave tomography study of the crust under the british isles at a relatively high resolution we computed interferometric interstation rayleigh waves from vertical component records of ambient seismic noise recorded on 63 broad band and short period stations across the uk and ireland group velocity measurements were made from the resulting surface wave dispersion curves between 5 and 25 s using a multiple phase matched filter method uncertainties in the group velocities were computed by calculating the standard deviation of four dispersion curves constructed by stacking a random selection of daily cross correlations where an uncertainty could not be obtained for a ray path using this method we estimated it as a function of the interreceiver distance group velocity maps were computed for 5 25 s period using the fast marching forward solution of the eikonal equation and iterative linearized inversion at short and intermediate periods the maps show remarkable agreement with the major geological features of the british isles including terrane boundaries in scotland regions of late palaeozoic basement uplift areas of exposed late proterozoic early palaeozoic rocks in southwest scotland northern england and northwest wales and sedimentary basins formed during the mesozoic such as the irish sea basin the chester basin the worcester graben and the wessex basin the maps also show a consistent low velocity anomaly in the region of the midlands platform a proterozoic crustal block in the english midlands at longer periods which are sensitive velocities in the lower crustal upper mantle the maps suggest that the depth of moho beneath the british isles decreases towards the north and west areas of fast velocity in the lower crust also coincide with areas thought to be associated with underplating of the lower crust such as northern ireland the eastern irish sea and northwest wales

microfracture processes in the breakdown zone during dynamic shear rupture inferred from laboratory observation of near fault high frequency strong motion high frequency velocities are measured during stick slip motion in the immediate vicinity of a fault in a granite sample to reveal the microscopic process taking place in the breakdown zone defined in the slip weakening model it is found that 1 the onset time of the observed strong motion approximately coincides with the local rupture onset time 2 the observed near fault high frequency strong motion duration is approximately proportional to the local breakdown time and 3 the power spectra of strong motions exhibit significant amplitudes at frequencies above the value offmax wherefmax is a cut off frequency relevant to rupturing the breakdown zone these observations suggest that the high frequency motion would be due to the incoherent brittle microfracture whose characteristic scale is much shorter than the breakdown zone size we present a stochastic fault model to synthesize the near fault high frequency velocity waveforms in the model a number of small circular subfaults are distributed randomly on the fault and the rupture onset time of an individual subfault is assumed to be random the main features of the observed velocity waveforms are well explained by this numerical modeling it is concluded that approximately half of the total energy of high frequency elastic waves observed at a point is radiated from the propagating breakdown zone we emphasize the importance of the observation of near fault high frequency strong motions for large shallow earthquakes

ambient noise surface wave tomography of the iberian peninsula implications for shallow seismic structure 1 we have obtained high resolution group velocity maps of rayleigh waves at periods from 8 to 25 seconds across the iberian peninsula by cross correlating four months of ambient noise data recorded by 40 permanent broadband stations group velocity maps accurately image the main structural elements of the iberian upper crust including the iberian massif alpine orogens and major sedimentary basins the pyrenees and the iberian chain are imaged as relatively high group velocities in contrast with the betic cordillera which is characterized by low velocities we explain these low velocities in the betics by the presence of widespread intramontane basins created in an extensional episode simultaneous with north south convergence between the african and eurasian plates the most prominent low velocity anomalies in the iberian peninsula are related to the guadalquivir basin the flysch units of the campo de gibraltar and the sediments of the gulf of cadiz

crustal and uppermost mantle velocity structure and its relationship with the formation of ore districts in the middle lower yangtze river region abstract in this study we conduct ambient noise tomography and teleseismic two plane wave tomography to probe the crustal and uppermost mantle structures in the middle lower yangtze river region the data used include 14 months from july 2012 to august 2013 of continuous vertical component ambient noise data and 219 teleseismic earthquakes recorded at 138 broadband seismic stations from chinese provincial networks and 19 temporary seismic stations deployed by china university of geosciences beijing first we apply ambient noise tomography to the collected ambient noise data to generate rayleigh wave group and phase velocity maps at 5 42 s periods and two plane wave tomography method to earthquake data to generate intermediate to long period phase velocity maps at 20 143 s periods we then combine the short to intermediate period velocity maps from ambient noise and the intermediate to long period phase velocity maps from earthquake data to generate broadband phase velocity maps at periods from 5 to 143 s by inverting these 5 143 s rayleigh wave velocity maps we construct a 3 d shear wave velocity model from the surface to 250 km depth in the middle lower yangtze river region the 3 d model shows that in the upper crust the basin regions including the jianghan hehuai subei hefei and nanyang basins are all featured with low velocities and the mountain regions with high velocities in the uppermost mantle a low velocity zone at 100 200 km depth is observed beneath the middle lower yangtze river metallogenic belt moreover our tomographic results show that the ningwu and ningzhen ore districts are clearly characterized by the strongest low velocity anomaly in the uppermost mantle at 70 200 km depth the depth extent of the low velocity zone becomes shallower and the amplitude of low velocity anomaly becomes larger from the southwest jiurui ore district to northeast ningwu ore districts the change pattern of the low velocity zone in the depth extent and the amplitude is consistent with the fact that peak ages of magmatic events along the middle lower yangtze river metallogenic belt progressively become younger and younger from 148 ma in the southwest to 125 ma in the northeast the observed low velocity zone may represent the cooling hot upper mantle which was partially molten in the past resulting from partial melting of the paleo pacific plate or of an enriched mantle source induced by the westward subduction of the paleo pacific plate the upwelling of the mantle derived magmas may result in the formation of these granitic rocks and coeval ores deposits along the middle lower yangtze river metallogenic belt

shear wave velocity structure of the bushveld complex south africa the structure of the crust in the environs of the bushveld complex has been investigated by jointly inverting high frequency teleseismic receiver functions and 2 60 s period rayleigh wave group velocities for 16 broadband seismic stations located across the bushveld complex group velocities for 2 15 s periods were obtained from surface wave tomography using local and regional events while group velocities for 20 60 s periods were taken from a published model 1 d shear wave velocity models obtained for each station show the presence of thickened crust in the center of the bushveld complex and a region at the base of the crust where shear wave velocities exceed 4 0 km s the shear wave velocity models also suggest that velocities in some upper crustal layers may be as high as 3 7 3 8 km s consistent with the presence of mafic lithologies these results favor a continuous sheet model for the bushveld complex in which the outcropping mafic layers of the western and eastern limbs are continuous at depth beneath the center of the complex however detailed modeling of receiver functions at one station within the center of the complex indicates that the mafic layering may be locally disrupted due to thermal diapirism triggered by the emplacement of the bushveld complex or thermal and tectonic reactivation at a later time

crust and uppermost mantle beneath the north china craton northeastern china and the sea of japan from ambient noise tomography 1 a 3 d shear velocity model of the crust and uppermost mantle to a depth of 100 km is presented beneath the north china craton ncc northeastern china the korean peninsula and the sea of japan ambient noise rayleigh wave tomography is applied to data from more than 300 broadband seismic stations from chinese provincial networks cearray the japanese f net and the iris global seismic network continuous data from 2007 to 2009 are used to produce group and phase velocity maps from 8 s to 45 s periods the model is motivated to constrain the distributed intraplate volcanism crustal extension cratonic rejuvenation and lithospheric thinning that are hypothesized for the study region numerous robust features are observed that impose new constraints on the geometry of these processes but discussion concentrates only on four 1 the north south gravity lineament follows the 40 km contour in crustal thickness and crustal thickness is anticorrelated with water depth beneath the sea of japan consistent with crustal isostasy for a crust with laterally variable composition 2 the lithosphere is thin 70 km beneath the songliao bohai graben but seismically fast 3 even thinner more attenuated lithosphere bounds three sides of the eastern ncc in a horseshoe shape identifying a region of particularly intense tectonothermal modification where lithospheric rejuvenation may have reached nearly to the base of the crust 4 low velocity anomalies reach upward in a y shape in the mantle beneath the eastern and western borders of the sea of japan extending well into continental east asia in the west and are separated by a 60 km thick lithosphere beneath the central sea of japan this anomaly may reflect relatively shallow slab dehydration in the east and in the west may reflect deeper dehydration and convective circulation in the mantle wedge overlying the stagnant slab

testing community velocity models for southern california using the ambient seismic field abstract we correlate the vertical component of ambient seismic noise data recorded on 56 broadband stations with dense coverage in the greater los angeles area to determine station to station green s functions these green s functions provide an important test of community velocity models southern california earthquake center scec cvm 4 0 and cvm h 5 2 used for strong ground motion prediction for future scenario earthquakes in southern california comparisons of the ambient noise green s functions for nearly 300 paths with those calculated by the finite element method in the community velocity models reveal a strong waveform similarity for the dominant surface waves between 0 1 and 0 2 hz we find a mean correlation coefficient between the ambient noise and finite element green s functions of 0 62 for the cvm 4 0 and 0 49 for the cvm h 5 2 indicating stronger waveform similarity for cvm 4 0 we also find that for 77 of the paths the surface waves in the finite element green s functions for cvm 4 0 arrive early suggesting that the cvm 4 0 has velocities in the upper 10 km that are too fast along these paths the same bias is evident for cvm h 5 2 but is substantially smaller with only 61 of the paths too fast for 67 of the paths cvm 4 0 has velocities faster than cvm h 5 2 the time lags we obtain between the ambient noise and finite element green s functions provide key information for improving future community velocity models

velocity conductivity relations for cratonic lithosphere and their application example of southern africa 1 seismic velocity is a function of bulk vibrational properties of the media whereas electrical resistivity is most often a function of transport properties of an interconnected minor phase in the absence of a minor conducting phase then the two should be inter relatable primarily due to their sensitivity to temperature variation we develop expressions between shear wave velocity and resistivity for varying temperature composition and water content based on knowledge from two kimberlite fields jagersfontein kaapvaal craton and gibeon rehoboth terrane we test the expressions through comparison between a new high resolution regional seismic model derived from surface wave inversion of earthquake data from africa and the surrounding regions and a new electrical image from magnetotelluric mt data recorded in samtex southern african magnetotelluric experiment the data defined robust linear regression between the two is found to be statistically identical to the laboratory defined expression for 40 wt ppm water in olivine cluster analysis defines five clusters that are all geographically distinct and tectonically relate to i fast cold and variably wet kaapvaal craton ii fast and wet central botswana iii slow warm and wet rehoboth terrane iv moderately fast cold and very dry southernmost angola craton and v slow warm and somewhat dry damara belt from the linear regression expression and the mt image we obtain predicted seismic velocity at 100 km and compare it with that from seismic observations the differences between the two demonstrate that the linear relationship between vs and resistivity is appropriate for over 80 of southern africa finally using the regressions for varying water content we infer water content in olivine across southern africa

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

surface wave tomography of eastern and central tibet from two plane wave inversion rayleigh wave and love wave phase velocity mapssurface wave tomography of eastern and central tibet from two plane wave inversion rayleigh wave and love wave phase velocity maps

structure of the lithosphere beneath the barotse basin western zambia from magnetotelluric data author posting american geophysical union 2019 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in tectonics 38 2 2019 666 686 doi 10 1029 2018tc005246

crustal structure determined from ambient noise tomography near the magmatic centers of the coso region southeastern california we apply seismic ambient noise tomography to image and investigate the shallow shear velocity structure beneath the coso geothermal field and surrounding areas data from a passcal experiment operated within the coso geothermal field between 1998 and 2000 and surrounding broadband stations from the southern california seismic network are acquired and processed daily cross correlations of ambient noise between all pairs of stations that overlapped in time of deployment were calculated and then stacked over the duration of deployment phase velocities of rayleigh waves between 3 and 10 s periods are measured from the resulting cross correlations depending on the period between about 300 and 600 reliable phase velocity measurements are inverted for phase velocity maps from 3 to 10 s periods which in turn are inverted for a 3 d shear velocity model beneath the region the resulting 3 d model reveals features throughout the region that correlate with surface geology beneath the coso geothermal area shear velocities are generally depressed a prominent low velocity anomaly is resolved clearly within the top 2 km no significant anomaly is seen below about 14 km depth and a weakly resolved anomaly is observed between 6 and 12 km depth the anomaly in the top 2 km probably results from geothermal alteration in the shallow subsurface no magmatic body is imaged beneath 14 km depth but the shear velocity anomaly between 6 and 12 km may be attributable to partial melt the thickness and amplitude of the magma body trade off in the inversion and are ill determined low velocities in the regions surrounding coso at depths near 7 km underlie areas with miocene to recent volcanism suggesting that some magmatic processing of the crust could be focused near this depth

a synoptic view of the distribution and connectivity of the mid crustal low velocity zone beneath tibet 1 based on 1 2 years of continuous observations of seismic ambient noise data obtained at more than 600 stations in and around tibet rayleigh wave phase velocity maps are constructed from 10 s to 60 s period a 3 d vsv model of the crust and uppermost mantle is derived from these maps the 3 d model exhibits significant apparently inter connected low shear velocity features across most of the tibetan middle crust at depths between 20 and 40 km these low velocity zones lvzs do not conform to surface faults and significantly are most prominent near the periphery of tibet the observations support the internal deformation model in which strain is dispersed in the deeper crust into broad ductile shear zones rather than being localized horizontally near the edges of rigid blocks the prominent lvzs are coincident with strong mid crustal radial anisotropy in western and central tibet and probably result at least partially from anisotropic minerals aligned by deformation which mitigates the need to invoke partial melt to explain the observations irrespective of their cause in partial melt or mineral alignment mid crustal lvzs reflect deformation and their amplification near the periphery of tibet provides new information about the mode of deformation across tibet

a topographic fingerprint to distinguish alluvial fan formative processes we demonstrate here a topographic fingerprint derived from a 1 m high resolution elevation model dem developed from airborne laser swath mapping alsm that distinguishes between formative processes from surface form in alluvial fans generated through relatively dry debris flows df and those surfaces formed primarily by fluvial sediment transport mf we selected alluvial fans with primarily holocene age surficial deposits along the eastern side of death valley california fans were initially classified in the field into df and mf types largely on the basis of sedimentological characteristics and surface morphometry trend surface analyses were performed on dems of the individual fans in order to remove the long wavelength trends both profile and planimetric from the residual data we found that high resolution surface data distinguishes process information in two ways 1 local relief increases as a function of length scale especially at length scales less than 40 60 m and 2 local relief is significantly higher for debris flow dominated fans than for fluvially dominated fans this fingerprint which is directly related to the dominant surface processes is unavailable from standard 30 m resolution data providing significant support for the acquisition of high quality high resolution data this fingerprint can be used to help calibrate numerical simulations of alluvial fan development and has the potential for similar applications to distinguish between processes of similar landforms on other planetary bodies within our solar system