extracting time domain green s function estimates from ambient seismic noise 1 it has been demonstrated experimentally and theoretically that an estimate of the green s function between two seismic stations can be obtained from the time derivative of the long time average cross correlation of ambient noise between these two stations this tdgf estimate from just the noise field includes all tensor components of the green s function and these green s function estimates can be used to infer earth structure we have computed cross correlations using 1 to 30 continuous days of ambient noise recorded by over 150 broadband seismic stations located in southern california the data processing yielded thousands of cross correlation pairs for receiver separations from 4 500 km which clearly exhibit coherent broadband propagating dispersive wavetrains across frequency band 0 1 2 hz

interferometric seismic imaging around the active lalor mine in the flin flon greenstone belt canada abstract seismic interferometry which recovers the impulse response of the earth by cross correlation of ambient noise recorded at sets of two receivers has found several applications including the generation of virtual shot gathers for use in seismic reflection processing to evaluate the effectiveness of this passive recording technique in mineral exploration in a hard rock environment 336 receivers recorded 300 h of ambient noise over the volcanogenic massive sulphide deposit of the recently discovered lalor mine in the canadian flin flon greenstone belt a novel time domain beamforming algorithm was developed to search for individual source locations demonstrating that the vast majority of noise originated from the mine and ventilation shafts of the lalor mine the results of the beamforming were utilized in conjunction with frequency wavenumber filtering to remove undesirable mostly monochromatic surface wave noise originating from nearby sources virtual shot gathers were generated along three receiver lines each of which was processed as a separate 2 d reflection line two of the resulting unmigrated reflection profiles are compared against coincident dipmoveout stacked data from a larger coincident 3 d dynamite seismic survey that was also acquired over the lalor mine in 2013 using knowledge of the local geology derived from numerous boreholes coherent events recovered in the passive reflection profiles are inferred to be either spurious arrivals or real reflections some of which can be interpreted in terms of geological contacts indicating the future potential of passive recording surveys in hard rock settings

passive seismic reflection interferometry a case study from the aquistore co2 storage site saskatchewan canada abstractseismic reflection interferometry has recently been tested in a few resource exploration applications we have evaluated passive seismic interferometry results for data from the aquistore co2 storage site saskatchewan canada with the objective of testing the method s ability to image the subsurface geology and its potential for time lapse imaging we analyzed passive seismic data recorded along two perpendicular geophone lines for two time periods that include 23 days in june 2014 and 13 days in february 2015 beam forming analysis showed that a nearby power plant is the dominant source of ambient noise we retrieved virtual shot gathers not only by correlating long noise panels 1 h for both recording periods but also by correlating shorter noise panels 10 s from two days of each recording period we applied illumination diagnosis to the noise panels from the two chosen days for each period to help suppress the surface waves comparisons of the common midpoints stacked sections resulting

seismic interferometry reconstructing the earth s reflection response in1968 jonclaerboutshowedthatthereflectionresponseofa 1dacousticmediumcanbereconstructedbyautocorrelatingthe transmission response since then several authors have derived relationships for reconstructing green s functions at the surface using crosscorrelations of noise recordings that were taken at thesurfaceandthatderivedfromsubsurfacesources foracousticmedia wereviewrelationsbetweenthereflection response and the transmission response in 3d inhomogeneous lossless media these relations are derived from a one way wavefield reciprocity theorem we use modeling results to show howtoreconstructthereflectionresponseinthepresenceoftransientsubsurfacesourceswithdistinctexcitationtimes aswellas inthepresenceofsimultaneouslyactingnoisesourcesinthesubsurface weshowthatthequalityofreconstructedreflectionsdepends on the distribution of the subsurface sources for a situation with enough subsurface sources that is for a distribution that illuminates the subsurface area of interest from nearly all directions the reconstructed reflection responses and the migrated depth image exhibit all the reflection events and the subsurface structures of interest respectively with only a few subsurface sources that is with insufficient illumination the reconstructed reflection responses are noisy and can even become kinematically incorrect at the same time however the depth image which was obtained from their migration still shows clearly all the illuminated subsurface structures at their correct positions for the elastic case we review a relationship between the reflection green s functions and the transmission green s functionsderivedfromatwo waywavefieldreciprocitytheorem usingmodelingexamples weshowhowtoreconstructthedifferent components of the particle velocity observed at the surface and resulting from a surface traction source this reconstruciton is achievedusingcrosscorrelationsofparticlevelocitycomponents measured at the surface and resulting from separate p and s wavesourcesinthesubsurface

seismic exploration scale velocities and structure from ambient seismic noise 1 hz the successful surface waves retrieval in solid earth seismology using long time correlations and subsequent tomographic images of the crust have sparked interest in extraction of subsurface information from noise in the exploration seismology subsurface information in exploration seismology is usually derived from body wave reflections 1 hz which is challenging for utilization of ambient noise we use 11 h of noise recorded in the sirte basin libya first we study the characteristics of the noise we show that the bulk of the noise is composed of surface waves at frequencies below 6 hz some noise panels contain nearly vertically traveling events we further characterize these events using a beamforming algorithm from the beamforming we conclude that these events represent body wave arrivals with a fairly rich azimuthal distribution having body wave arrivals in the noise is a prerequisite for body wave reflections retrieval we crosscorrelate and sum the recorded ambient noise panels to retrieve common source gathers following two approaches using all the noise and using only noise panels containing body wave arrivals likely to contribute to the reflections retrieval comparing the retrieved gathers with active seismic data we show that the two way traveltimes at short offsets of several retrieved events coincide with those of reflections in the active data and thus correspond to apexes of reflections we then compare retrieved stacked sections of the subsurface from both approaches with the active data stacked section and show that the reflectors are consistent along a line the results from the second approach exhibit the reflectors better

tree ring reconstructed summer temperature anomalies for temperate east asia since 800 c e we develop a summer temperature reconstruction for temperate east asia based on a network of annual tree ring chronologies covering the period 800 1989 c e the east asia reconstruction is the regional average of 585 individual grid point summer temperature reconstructions produced using an ensemble version of point by point regression statistical calibration and validation tests indicate that the regional average possesses sufficient overall skill to allow it to be used to study the causes of temperature variability and change over the region the reconstruction suggests a moderately warm early medieval epoch ca 850 1050 c e followed by generally cooler little ice age conditions ca 1350 1880 c e and 20th century warming up to the present time since 1990 average temperature has exceeded past warm epochs of comparable duration but it is not statistically unprecedented superposed epoch analysis reveals a volcanic forcing signal in the east asia summer temperature reconstruction resulting in pulses of cooler summer conditions that may persist for several years substantial uncertainties remain however particularly at lower frequencies thus requiring caution and scientific prudence in the interpretation of this record

drought reconstructions for the continental united states abstract the development of a 2 lat 3 long grid of summer drought reconstructions for the continental united states estimated from a dense network of annual tree ring chronologies is described the drought metric used is the palmer drought severity index pdsi the number of grid points is 154 and the reconstructions cover the common period 1700 1978 in producing this grid an automated gridpoint regression method called point by point regression was developed and tested in so doing a near optimal global solution was found for its implementation the reconstructions have been thoroughly tested for validity using pdsi data not used in regression modeling in general most of the gridpoint estimates of drought pass the verification tests used in addition the spatial features of drought in the united states have been faithfully recorded in the reconstructions even though the method of reconstruction is not explicitly spatial in its design the drought reconstructions show that the 1930s dust bow

teleseismic shot profile migration the shot profile migration approach of wave equation migration generates subsurface images using the interferometric principle of crosscorrelating two passive wavefields these wavefields are typically a source wavefield containing energy from an excited source and a receiver wavefield comprised of scattered source wavefield energy by the discontinuous earth structure shot profile migration can be recast as a novel way of imaging the earth s lithosphere using teleseismic wavefield data where the source wavefield is the directly arriving wavefront and the receiver wavefield is the following wavefield coda we demonstrate that the shot profile technique can be tailored to suit teleseismic acquisition geometry and wavefields assuming an acoustic framework and 2 5d experimental geometry we develop procedures that enable kinematic and structural imaging migration using both transmission and free surface reflected passive wavefields experiments with synthetic data demonstrate the method s applicability a

the 1452 or 1453 a d kuwae eruption signal derived from multiple ice core records greatest volcanic sulfate event of the past 700 years 1 we combined 33 ice core records 13 from the northern hemisphere and 20 from the southern hemisphere to determine the timing and magnitude of the great kuwae eruption in the mid 15th century we extracted volcanic deposition signals by applying a high pass loess filter to the time series and examining peaks that exceed twice the 31 year running median absolute deviation by accounting for the dating uncertainties associated with each record these ice core records together reveal a large volcanogenic acid deposition event during 1453 1457 a d the results suggest only one major stratospheric injection from the kuwae eruption and confirm previous findings that the kuwae eruption took place in late 1452 or early 1453 which may serve as a reference to evaluate and improve the dating of ice core records the average total sulfate deposition from the kuwae eruption was 93 kg so4 km 2 in antarctica and 25 kg so4 km 2 in greenland the deposition in greenland was probably underestimated since it was the average value of only two northern greenland sites with very low accumulation rates after taking the spatial variation into consideration the average kuwae deposition in greenland was estimated to be 45 kg so4 km 2 by applying the same technique to the other major eruptions of the past 700 years our result suggests that the kuwae eruption was the largest stratospheric sulfate event of that period probably surpassing the total sulfate deposition of the tambora eruption of 1815 which produced 59 kg so4 km 2 in antarctica and 50 kg so4 km 2 in greenland

climate response to large high latitude and low latitude volcanic eruptions in the community climate system model 1 explosive volcanism is known to be a leading natural cause of climate change the second half of the 13th century was likely the most volcanically perturbed half century of the last 2000 years although none of the major 13th century eruptions have been clearly attributed to specific volcanoes this period was in general a time of transition from the relatively warm medieval period to the colder little ice age but available proxy records are insufficient on their own to clearly assess whether this transition is associated with volcanism this context motivates our investigation of the climate system sensitivity to high and low latitude volcanism using the fully coupled ncar community climate system model ccsm3 we evaluate two sets of ensemble simulations each containing four volcanic pulses with the first set representing them as a sequence of tropical eruptions and the second representing eruptions occurring in the mid high latitudes of both the northern and southern hemispheres the short term direct radiative impacts of tropical and high latitude eruptions include significant cooling over the continents in summer and cooling over regions of increased sea ice concentration in northern hemisphere nh winter a main dynamical impact of moderate tropical eruptions is a winter warming pattern across northern eurasia furthermore both ensembles show significant reductions in global precipitation especially in the summer monsoon regions the most important long term impact is the cooling of the high latitude nh produced by multiple tropical eruptions suggesting that positive feedbacks associated with ice and snow cover could lead to long term climate cooling in the arctic

3d seismic traveltime tomography imaging of the shallow subsurface at the c o2 sink project site ketzin germany a 3d reflection seismic survey was performed in 2005 at the ketzin carbon dioxide c o2 pilot geological storage site the c o2 sink project near berlin germany to image the geological structure of the site to depths of about 1 km because of the acquisition geometry frequency limitations of the source and artefacts of the data processing detailed structures shallower than about 150 m were unclear to obtain structural images of the shallow subsurface we applied 3d traveltime tomography to data near the top of the ketzin anticline where faulting is present understanding the shallow subsurface structure is important for long term monitoring aspects of the project after c o2 has been injected into a saline aquifer at about 650 m depth we used a 3d traveltime tomography algorithm based on a combination ofsolving for 3d velocity structure and static corrections in the inversion process to account for artefacts in the velocity structure because of smearing effects from the unconsolidated cover th

hydroclimatic changes in china and surroundings during the medieval climate anomaly and little ice age spatial patterns and possible mechanisms abstract investigating hydroclimatic changes during key periods such as the medieval climate anomaly mca 1000 1300 ad and the little ice age lia 1400 1900 ad is of fundamental importance for quantifying the responses of precipitation to greenhouse gas induced warming on regional and global scales this study synthesizes the most up to date and comprehensive proxy moisture precipitation records during the past 1000 years in china and surroundings the proxy data collected include 34 records from arid central asia aca and 37 records from monsoonal asia our results demonstrate a pattern of generally coherent regional moisture variations during the mca and lia in mid latitude asia north of 30 n monsoonal northern china north china and northeast china was generally wetter while aca northwest china and central asia was generally drier during the mca than in the lia a west east mode the boundary between wetter northern china and drier aca was roughly consistent with the modern summer monsoon boundary in monsoonal china to the east of 105 e the northern part was generally wetter while the southern part was generally drier during the mca than in the lia a north south mode with a boundary roughly along the huai river at about 34 n these spatial patterns of moisture precipitation variations are also identified by instrumental data during the past 50 years in order to understand the possible mechanisms related to the moisture variations during the mca and lia we investigate the major sst and atmospheric modes e g the el nino southern oscillation enso the atlantic multidecadal oscillation amo and the north atlantic oscillation nao which affect the moisture precipitation variations in the study region using both the instrumental data and the reconstructed time series it is found that the enso may play an important role in determining hydroclimatic variability over china and surroundings on a multi centennial time scale and that the foregoing spatial patterns could be attributed to the la nina like el nino like condition during the mca lia in addition amo and nao may also have their own contributions

retrieving virtual reflection responses at drill bit positions using seismic interferometry with drill bit noise in the field of seismic interferometry researchers have retrieved surface waves and body waves by cross correlating recordings of uncorrelated noise sources to extract useful subsurface information the retrieved wavefields in most applications are between receivers when the positions of the noise sources are known inter source interferometry can be applied to retrieve the wavefields between sources thus turning sources into virtual receivers previous applications of this form of interferometry assume impulsive point sources or transient sources with similar signatures we investigate the requirements of applying inter source seismic interferometry using non transient noise sources with known positions to retrieve reflection responses at those positions and show the results using synthetic drilling noise as source we show that if pilot signals estimates of the drill bit signals are not available it is required that the drill bit signals are the same and that the phases of the virtual reflections at drill bit positions can be retrieved by deconvolution interferometry or by cross coherence interferometry further for this case classic interferometry by cross correlation can be used if the source power spectrum can be estimated if pilot signals are available virtual reflection responses can be obtained by first using standard seismic while drilling processing techniques such as pilot cross correlation and pilot deconvolution to remove the drill bit signatures in the data and then applying cross correlation interferometry therefore provided that pilot signals are reliable drill bit data can be redatumed from surface to borehole depths using this inter source interferometry approach without any velocity information of the medium and we show that a well positioned image below the borehole can be obtained using interferometrically redatumed reflection responses with just a simple velocity model we discuss some of the practical hurdles that restrict the application of the proposed method offshore

seismic imaging of the site response using microearthquake recordings part i method abstract microearthquake signals from widely distributed geographical regions have been noticed repeatedly to be strongly affected by local site effects the corresponding seismograms contain important information on the individual propagation path a single station inversion method is presented which allows the imaging of the subsurface impedance structure from locally recorded sh waves records the technique is based on the kunetz claerbout equation which in its original form states the relationship between the transmission response and the reflection response for p waves in a horizontally layered medium and vertical incidence claerbout 1968 by adapting claerbout9s formulation to the transmission problem for sh waves under oblique incidence microearthquake recordings can be used to calculate corresponding pseudo reflection seismograms which in turn can be inverted for the impedance structure by exploiting levinson recursion limitations in the high frequency content of the signals due to the combined effects of absorption recording system and bandlimited source signals as well as the influence of noise drastically reduce the resolutional power of the inversion procedure a number of different deconvolution techniques have been tested with synthetic seismograms for the applicability to reduce these effects good results have been obtained with the blind deconvolution technique of scherbaum and stoll 1985 utilizing the minimum phase property of the green9s function from the analysis of synthetic data it can be expected that for realistic source receiver situations and short period recording systems the main reflectors down to a depth of several hundreds of meters could be resolved

a subsurface flow of material from the sun s equator to its poles gas on the sun s surface has been observed1 2 3 4 to flow away from the equator towards both poles if the same flow persists to great depths it could play an important dynamical role in the eleven year sunspot cycle by carrying the magnetic remnants of the sunspots to high latitudes5 an even deeper counterflow which would be required to maintain mass balance could explain why new sunspots form at lower latitudes as the cycle progresses6 these deep flows would also redistribute angular momentum within the sun and therefore help to maintain the faster rotation of the equator relative to the poles7 here we report the detection using helioseismic tomography of the longitude averaged subsurface flow in the outer 4 of the sun we find that the subsurface flow is approximately constant in this depth range and that the speed is similar to that seen on the surface this demonstrates that the surface flow penetrates deeply so that it is likely to be an important factor in solar dynamics

using supervirtual first arrivals in controlled source hardrock seismic imaging well worth the effort varied applications of seismic interferometry have arisen in the last decade however the potential of the method to improve reflection seismic processing in hardrock environments has not explicitly been regarded therefore in this paper we investigate the potential of retrieving the first arrivals originally hindered by high noise level in the exploitation of controlled source data acquired over the iron oxide apatite rich deposit at grangesberg sweden and its mining induced structures the supervirtual first arrivals retrieved using interferometry methodologies allowed first breaks to be picked more extensively than in the original data revised static corrections significantly improved the linearity of the first arrivals and continuity of reflections in the source gathers especially reflections considerably enhanced in the source gathers stacked constructively in the final section comparison with geological data supported by traveltime forward modelling indicates that these reflections represent the unmined part of the deposit other reflections at shallower depth are interpreted as anthropogenic faults possibly located at lithological contacts tomographic inversion was also run using the augmented traveltime data the greater resolution and penetration of this new tomographic image allowed better bridging with the results of the reflection seismic section velocity anomalies depict the presence of mining induced structures and a potential brewery fault which is believed to put at risks an urban area even though the potential of first arrival retrieval seems to be case dependent this study illustrates that interferometry may substantially improve the accuracy of static corrections and subsequent stack for hardrock imaging as well as in the penetration and resolution of traveltime tomograms

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

studying co2 storage with ambient noise seismic interferometry a combined numerical feasibility study and field data example for ketzin germany seismic interferometry applied to ambient noise measurements allows the retrieval of the seismic response between pairs of receivers we studied ambient noise seismic interferometry ansi to retrieve time lapse reflection responses from a reservoir during co2 geologic sequestration using the case of the experimental site of ketzin germany we applied ansi to numerically modeled data to retrieve base and repeat reflection responses characterizing the impedances occurring at the reservoir both with and without the injection of co2 the modeled data represented global transmission responses from band limited noise sources randomly triggered in space and time we found that strong constraints on the spatial distribution of the passive sources were not required to retrieve the time lapse signal as long as sufficient source location repeatability was observed between the base and the repeat passive survey to illustrate the potential of the technique ansi was applied to three days of passive field data recorded in 2012 at ketzin comparison with the modeled results illustrated the potential to retrieve key reflection events using ansi on field data from ketzin this study supports the idea that the geologic setting and characteristics of ambient noise at ketzin may be opportune to monitor co2 sequestration

reconstruction of subsurface structure from ambient seismic noise an example from ketzin germany summary passive seismic interferometry is a new promising methodology for seismic exploration interferometry allows information about the subsurface structure to be extracted from ambient seismic noise in this study we apply the cross correlation technique to approximately 25 hr of recordings of ambient seismic noise at the ketzin experimental co2 storage site germany common source gathers were generated from the ambient noise for all available receivers along two seismic lines by cross correlation of noise records this methodology isolates the interstation green s functions that can be directly compared to active source gathers we show that the retrieved response includes surface waves refracted waves and reflected waves we use the dispersive behaviour of the retrieved surface waves to infer geological properties in the shallow subsurface and perform passive seismic imaging of the subsurface structure by processing the retrieved reflected waves

imaging the active faults with ambient noise passive seismics and its application to characterize the huangzhuang gaoliying fault in beijing area northern china abstract most serious geotechnical problems related to rock engineering are generated by the existence of faults detection of fault especially active faults is the first step to conduct any further in depth studies in faulted rock mass or rock blocks in this paper we investigated the plausibility to image fault zones by passive seismic surveys using recorded ambient noise the test site is in the north suburb of beijing northern china along the south bank of the northwest southeast running wenyuhe river where the nne striking huangzhuang gaoliying fault hgf active in the holocene is crossing in general the results are in good agreement with previous studies using active source seismics conducted in this area along the hgf and existing borehole drillings in the vicinity undoubtedly active source seismic reflection technique is the best technique to image fault in depth with high resolution the drawback is its high cost and the necessity of using explosives a practice usually prohibited in urban settings in contrast passive seismic surveys take the advantage of the ever existing ambient noise source and provide a low cost technique and fast deployment that can locate the fault effectively though the imaging resolution is lower compared to those obtained by active source seismic surveys our passive seismic experiment at the wenyuhe river site demonstrated that this approach is effective especially for those faults with significant normal faulting component and the stratigraphy is significantly different on the two sides crossing the fault line

passive seismic imaging using microearthquakes we have developed a method of processing seismic signals generated by microearthquakes to image local subsurface structure beneath a recording station this technique uses the autocorrelation of the vertically traveling earthquake signals to generate pseudoreflection seismograms that can be interpreted for subsurface structure processed pseudoreflection data from microearthquakes recorded in the island of hawaii show consistent reflectivity patterns that are interpreted as near surface horizontal features forward modeling of the pseudoreflection data results in a p wave velocity model that shows reasonable agreement with the velocity model derived from a refraction study in the region usable signal to noise ratio is obtained down to 2 s a shear wave velocity model was also generated by applying this technique to horizontal component data

underestimation of body waves and feasibility of surface wave reconstruction by seismic interferometry interferometry is an approach to extract the green s function between two receivers as if the virtual source is at one of the receiver locations the green s function which is the response to an impulsive source accounts for the wave propagation in the medium between the two receivers it is commonly thought that green s function estimates obtained from interferometry accurately represent the full green s function but this is not always the case in fact the accuracy of the retrieved green s function which consists of the surface and body waves is in practice restricted by the limited distribution of the sources of field fluctuations we demonstrate the importance of adequate source distribution for the accuracy of the retrieved green s function using examples from interferometry applications in these examples sources are controlled as in exploration seismology or uncontrolled as in crustal seismology

feasibility of utilizing wavelet phase to map the co2 plume at the ketzin pilot site germany spectral decomposition is a powerful tool that can provide geological details dependent upon discrete frequencies complex spectral decomposition using inversion strategies differs from conventional spectral decomposition methods in that it produces not only frequency information but also wavelet phase information this method was applied to a time lapse three dimensional seismic dataset in order to test the feasibility of using wavelet phase changes to detect and map injected carbon dioxide within the reservoir at the ketzin carbon dioxide storage site germany simplified zero offset forward modelling was used to help verify the effectiveness of this technique and to better understand the wavelet phase response from the highly heterogeneous storage reservoir and carbon dioxide plume ambient noise and signal to noise ratios were calculated from the raw data to determine the extracted wavelet phase strong noise caused by rainfall and the assumed spatial distribution of sandstone channels in the reservoir could be correlated with phase anomalies qualitative and quantitative results indicate that the wavelet phase extracted by the complex spectral decomposition technique has great potential as a practical and feasible tool for carbon dioxide detection at the ketzin pilot site

3d baseline seismics at ketzin germany the co2sink project a 3d 25 fold seismic survey with a bin size of 12 by 12 m and about 12 km 2 of subsurface coverage was acquired in 2005 near a former natural gas storage site west of berlin as part of the fiv

summer cooling driven by large volcanic eruptions over the tibetan plateau abstractlarge volcanic eruptions may cause abrupt summer cooling over large parts of the globe however no comparable imprint has been found on the tibetan plateau tp here we introduce a 400 y

extracting coherent wave fronts from acoustic ambient noise in the ocean a method to obtain coherent acoustic wave fronts by measuring the space time correlation function of ocean noise between two hydrophones is experimentally demonstrated though the sources of ocean noise are uncorrelated the time averaged noise correlation function exhibits deterministic waveguide arrival structure embedded in the time domain green s function a theoretical approach is derived for both volume and surface noise sources shipping noise is also investigated and simulated results are presented in deep or shallow water configurations the data of opportunity used to demonstrate the extraction of wave fronts from ocean noise were taken from the synchronized vertical receive arrays used in the frame of the north pacific laboratory npal during time intervals when no source was transmitting

seismic imaging of the site response using microearthquake recordings part ii application to the swabian jura southwest germany seismic network the subsurface site structure of the swabian jura southwest germany seismic network has been modeled from the inversion of locally recorded sh wave microearthquake seismograms the observed records have been deconvolved from the effects of apparent source pulse broadening due to the combined influence of frequency bandlimited source signals absorption peg leg multiple reflections and the recording system following the procedure of scherbaum and stoll 1985 corresponding pseudo reflection seismograms were calculated based on the kunetz claerbout relation for sh waves and inverted using a levison recursion algorithm the final structural models have been optimized in terms of numbers of layers and depth resolution using ferber s 1985 noise stabilization technique the resulting impedance models for the swabian jura southwest germany seismic network show some strongly correlated reflectors in the uppermost layers which are well understood in terms of the local stratigraphy the comparison of the inverted impedance model hsn with the p wave velocity log from a nearby exploration drilling trochtelfingen beb shows a high degree of similarity of the dominating reflectors down to a depth of several hundred meters as a consequence the coda generating process for the early part of the coda of the observed swabian jura microearthquake seismograms wood anderson magnitude mwa 3 0 can be completely interpreted as an effect of the local subsurface structure

finite difference elastic wave propagation in 2d heterogeneous transversely isotropic media1 the velocity stress formulation for propagation of elastic seismic waves through 2d heterogeneous transversely isotropic media of arbitrary orientation is presented the equations are recast into a finite difference scheme and solved numerically using fourth order spatial operators and a second order temporal operator on a staggered grid absorbing free surface and symmetry boundary conditions have been implemented test cases compare well with other published solutions synthetic seismograms are calculated over two idealized models i vertical fractures in granite with a dolerite sill reflector and ii a dipping anisotropic shale comparisons with the isotropic counterparts show significant differences which may have to be accounted for in seismic processing in the future

unified multi depth level field decomposition wavefield decomposition forms an important ingredient of various geophysical methods an example of wavefield decomposition is the decomposition into upgoing and downgoing wavefields and simultaneous decomposition into different wave field types the multi component field decomposition scheme makes use of the recordings of different field quantities such as particle velocity and pressure in practice different recordings can be obscured by different sensor characteristics requiring calibration with an unknown calibration factor not all field quantities required for multi component field decomposition might be available or they can suffer from different noise levels the multi depth level decomposition approach makes use of field quantities recorded at multiple depth levels e g two horizontal boreholes closely separated from each other a combination of a single receiver array combined with free surface boundary conditions or acquisition geometries with a high density of vertical boreholes we theoretically describe the multi depth level decomposition approach in a unified form showing that it can be applied to different kinds of fields in dissipative inhomogeneous anisotropic media e g acoustic electromagnetic elastodynamic poroelastic and seismoelectric fields we express the one way fields at one depth level in terms of the observed fields at multiple depth levels using extrapolation operators that are dependent on the medium parameters between the two depth levels lateral invariance at the depth level of decomposition allows us to carry out the multi depth level decomposition in the horizontal wavenumber frequency domain we illustrate the multi depth level decomposition scheme using two synthetic elastodynamic examples the first example uses particle velocity recordings at two depth levels whereas the second example combines recordings at one depth level with the dirichlet free surface boundary condition of zero traction comparison with multicomponent decomposed fields shows a perfect match in both amplitude and phase for both cases the multi depth level decomposition scheme is fully customizable to the desired acquisition geometry the decomposition problem is in principle an inverse problem notches may occur at certain frequencies causing the multi depth level composition matrix to become uninvertible requiring additional notch filters we can add multi depth level free surface boundary conditions as extra equations to the multi component composition matrix thereby overdetermining this inverse problem the combined multi component multi depth level decomposition on a land data set clearly shows improvements in the decomposition results compared with the performance of the multi component decomposition scheme

s waves profiles from noise cross correlation at small scale abstract cross correlations of ambient seismic noise recordings are studied to infer shear wave velocities vs profiles versus depth experiments are performed over inter station distances ranging from 60 m to about 400 m in the crowded and noisy historical centre of napoli where the conditions for the use of active controlled source seismic spreadings are prohibitive even for just one receiver from the noise cross correlation group velocity dispersion curves are extracted with ftan method and their non linear inversion supplies vs profiles versus depth the information of nearby stratigraphies and the range of vs variability for samples of neapolitan soils and rocks confirms the validity and reliability of the results obtained with our expeditious procedure if successfully tested in other geological settings the proposed approach is a low cost methodology to get reliable vs velocity profiles versus depth

reflection images from ambient seismic noise one application of seismic interferometry is to retrieve the impulse response green s function from crosscorrelation of ambient seismic noise various researchers show results for retrieving the surface wave part of the green s function however reflection retrieval has proven more challenging we crosscorrelate ambient seismic noise recorded along eight parallel lines in the sirte basin east of ajdabeya libya to obtain shot gathers that contain reflections we take advantage of geophone groups to suppress part of the undesired surface wave noise and apply frequency wavenumber filtering before crosscorrelation to suppress surface waves further after comparing the retrieved results with data from an active seismic exploration survey along the same lines we use the retrieved reflection data to obtain a migrated reflection image of the subsurface

application of the virtual refraction to near surface characterization at the boise hydrogeophysical research site seismic interferometry is a relatively new technique to estimate the green s function between receivers spurious energy not part of the true green s function is produced because assumptions are commonly violated when applying seismic interferometry to field data instead of attempting to suppress all spurious energy we show how spurious energy associated with refractions contains information about the subsurface in field data collected at the boise hydrogeophysical research site by forming a virtual shot record we suppress uncorrelated noise and produce a virtual refraction that intercepts zero offset at zero time these two features make the virtual refraction easy to pick providing an estimate of refractor velocity to obtain the physical parameters of the layer above the refractor we analyse the cross correlation of wavefields recorded at two receivers for all sources a stationary phase point associated with the correlation between the reflected wave and refracted wave from the interface identifies the critical offset by combining information from the virtual shot record the correlation gather and the real shot record we determine the seismic velocities of the unsaturated and saturated sands as well as the variable relative depth to the water table finally we discuss how this method can be extended to more complex geologic models

feasibility of virtual source reflection seismology using interferometry for mineral exploration a test study in the lalor lake volcanogenic massive sulphide mining area manitoba canada approximately 300 hours of ambient noise data were recorded on a grid of receivers covering an area of 4 km2 over the lalor mine canada to test the capability of seismic interferometry to image ore deposits in the crystalline rock environment underground mining activities create the main source of ambient noise in the area alongside the ambient noise survey a larger three dimensional active source seismic survey was also acquired and used to evaluate the interferometry results power spectral density calculations show random ambient noise with a frequency range of 2 hz 35 hz a beamforming analysis identified body waves arriving from the west northwest pointing towards the mine and surface waves propagating from the northeast the calculated virtual shot gathers retrieved by cross correlating ambient noise at all receivers were processed following both two dimensional and three dimensional approaches using a sequence similar to the one applied to the activesource three dimensional data the dip moveout stacked section reveals a number of events similar to those observed on the processed active seismic sections in particular the passive seismic interferometry method is capable to partly image shallowly dipping reflections but did not produce convincing images of steeply dipping reflections dip moveout stacked sections obtained with different cross correlation time windows indicate that the strength and number of reflections generally increase with longer noise records however a few reflections at depth show reduced coherency with longer noise time windows the passive seismic interferometry results over the lalor mining area are encouraging but image quality of the passive survey is lower than the acquired active three dimensional survey at the area future ambient noise surveys with longer offsets shorter receiver spacing and wider azimuth distribution are needed in crystalline rock environment to address the potential of the method for mineral exploration

time distance helioseismology the application of seismology to the study of the solar interior1 2 helioseismology has advanced almost solely by the prediction and measurement of the sun s frequencies of free oscillation or normal modes direct measurement of the travel times and distances of individual acoustic waves the predominant approach in terrestrial seismology3 would appear to be more difficult in view of the number and stochastic nature of solar seismic sources here however we show that it is possible to extract time distance information from temporal cross correlations of the intensity fluctuations on the solar surface this approach opens the way for seismic studies of local solar phenomena such as subsurface in homogeneities near sunspots and should help to refine global models of the internal velocity stratification in the sun

general characteristics of temperature variation in china during the last two millennia three alternate china wide temperature composites covering the last 2000 years were established by combining multiple paleoclimate proxy records obtained from ice cores tree rings lake sediments and historical documents five periods of temperature variation can be identified a warm stage in ad 0 240 a cold interval between ad 240 and 800 a return to warm conditions from ad 800 1400 including the medieval warm period between ad 800 1100 the cool little ice age period between 1400 1920 and the present warm stage since 1920 regional temperature variation is found during ad 800 1100 when warm conditions occurred in eastern china and in the northeastern tibetan plateau and in ad 1150 1380 when the southern tibetan plateau experienced a warm interval in contrast evidence for cool conditions during the lia is more consistent among the proxy records the temperature reconstructions for china and the northern hemisphere show good agreement over the past millennium

rayleigh wave group velocity of the icelandic crust from correlation of ambient seismic noise 1 by cross correlating 2 years of ambient seismic noise from 31 broadband stations distributed across iceland we have been able to measure rayleigh wave group velocity in three discrete frequency bands centered on 4 7 and 17 s sensitive to approximately the top 6 10 and 25 km of the crust for 289 420 and 139 station to station paths respectively these are inverted to yield tomographic group velocity maps of the icelandic crust the results correlate with the major tectonic features on iceland and agree well with earlier seismic studies based on traditional methods active source and earthquake specifically we obtain low velocities in the central parts of iceland coinciding with the rift zones and young crust in contrast the parts of iceland covered with older tertiary volcanics reveal relatively higher velocities at the shorter periods 4 and 7 s this correlation reflects porosity degree of fracturing and alteration at the longest period 17 s i e at greater depth this correlation may reflect the thermal state of the crust with warm and seismically slow material near the rifts and cooler and seismically faster material beneath the tertiary formations to the east and west

solar and volcanic fingerprints in tree ring chronologies over the past 2000 years abstract the sun is the main driver of earth s climate yet the sun s role in forcing decadal to centennial climate variations has remained controversial especially in the context of understanding contributions of natural climate forcings to continuing global warming to properly address long term fingerprints of solar forcing on climate long term very high resolution globally distributed climate proxy records are necessary in this study we compile and evaluate a near global collection of annually resolved tree ring based climate proxies spanning the past two millennia we statistically assess these records in both the time and frequency domains for solar forcing i e total solar irradiance tsi and climate variability with emphasis on centennial time scales analyses in the frequency domain indicate significant periodicities in the 208 year frequency band corresponding to the devries cycle of solar activity additionally results from superposed epoch analysis sea point toward a possible solar contribution in the temperature and precipitation series however solar climate associations remain weak with for example no clear linkage distinguishable in the southwestern united states drought records at centennial time scales other forcing factors namely volcanic activity appear to mask the solar signal in space and time to investigate this hypothesis we attempted to extract volcanic signals from the temperature proxies using a statistical modelling approach wavelet analysis of the volcanic contribution reveals significant periodicities near the devries frequency during the little ice age lia this remarkable and coincidental superposition of the signals makes it very difficult to separate volcanic and solar forcing during the lia nevertheless the volcano free temperature records show significant periodicities near the devries periodicity during the entire past 1500 years further pointing to solar mechanisms and emphasising the need for solar related studies in the absence of strong multi decadal volcanic forcing

quantification of vesicle characteristics in some diatreme filling deposits and the explosivity levels of magma water interactions within diatremes abstract vesicles within juvenile fragments in mafic pyroclastic deposits contain important information about the state of the magma at the time of fragmentation there have been few vesicle studies of juvenile pyroclasts from mafic phreatomagmatic deposits however and none we can find from maar diatreme volcanoes in this paper we document the vesicularity and vesicle population characteristics of juvenile fragments sampled from non bedded lithified deposits of the coombs hills diatreme complex part of the ferrar large igneous province antarctica the diatreme filling pyroclastic deposits dominated by lapilli tuffs and tuff breccias contain typically abundant lithic clasts derived mostly from the enclosing sedimentary sequence and several types of juvenile clasts ranging from blocky to fluidal or raggy in the samples measured 77 80 of the juvenile pyroclasts ranging in size from 0 5 mm to fine lapilli is in the non vesicular to incipiently vesicular range fluidal or rag shaped juvenile clasts some circular vesicles and the lack of microlites all suggest that the coombs hills magma had a relatively low viscosity prior to fragmentation despite the basaltic andesite composition this low viscosity allowed parts of the magma to be fragmented in a non brittle fashion during phreatomagmatic explosions and to form fluidal clasts phreatomagmatic explosions in diatremes can therefore produce diverse types of juvenile clasts simultaneously and the proportions of each will depend on the explosivity of the magma water slurry interaction and other factors recycling of fragments is also thought to be an important factor in generating mixtures of different types of juvenile fragments in diatremes

influence of volcanic eruptions on the climate of the asian monsoon region 1 several state of the art general circulation models gcms predict that large volcanic eruptions should result in anomalous dry conditions throughout much of monsoon asia here we use long and well validated proxy reconstructions of asian droughts and pluvials to detect the influence of volcanic radiative forcing on the hydroclimate of the region since the late medieval period superposed epoch analysis reveals significantly wetter conditions over mainland southeast asia in the year of an eruption with drier conditions in central asia our proxy and model comparison suggests that gcms may not yet capture all of the important ocean atmosphere dynamics responsible for the influence of explosive volcanism on the climate of asia

the virtual refraction useful spurious energy in seismic interferometry seismic interferometry is rapidly becoming an established technique to recover the green s function between receivers but practical limitations in the source energy distribution inevitably lead to spurious energy in the results instead of attempting to suppress all such energy we use a spurious wave associated with the crosscorrelation of refracted energy at both receivers to infer estimates of subsurface parameters we named this spurious event the virtual refraction illustrated by a numerical two layer example we found that the slope of the virtual refraction defines the velocity of the faster medium and that the stationary phase point in the correlation gather provides the critical offset with the associated critical time derived from the real shot record this approach includes all of the necessary information to estimate wave speeds and interface depth without the need of inferences from other wave types

green s functions extraction and surface wave tomography from microseisms in southern california we use crosscorrelations of seismic noise data from 151 stations in southern california to extract the group velocities of surface waves between the station pairs for the purpose of determining the surface wave velocity structure we developed an automated procedure for estimating the green s functions and subsequent tomographic inversion from the 11 325 station pairs based on the characteristics of the noise field we eliminate specific events by a procedure that does not introduce any spurious spectral distortion in the band of interest 0 05 0 2 hz further we only used the emerging arrival structure above a threshold signal to noise ratio the result is that mostly station pairs with their axes oriented toward the sea are used consistent with the noise having a microseism origin finally it is the time derivative of the correlation function that is actually related to the green s function the emergence of the time domain green s function is proportional to the square root of the recording time and inversely proportional to the square root of the distance between stations the tomographic inversion yields a surface wave velocity map that compares favorably with more conventional and elaborate experimental procedures

retrieval of reflections from ambient noise recorded in the mizil area romania we applied seismic interferometry si by crosscorrelation to ambient noise panels recorded in the mizil area romania aiming to retrieve body wave reflections to achieve this goal surface waves in the noise panels input to si should be suppressed we did this by selecting for input to si only noise panels that are not dominated by surface waves the selection was either after visual inspection in the time domain or after automatic slowness evaluation on crosscorrelated panels the latter used the slowness of arrivals passing through the virtual source position at time 0 s we discovered that the automatic slowness evaluation method allows better retrieval of reflections from the retrieved reflection gathers we obtained stacked images of the subsurface comparing the si images to a stacked image from active source data we concluded that some retrieved events correspond to reflectors in the active seismic section including known geologic markers in a previous application of si to ambient noise the retrieved reflections exhibited frequency content lower than that of active data in our results the frequency content of the si retrieved data was comparable to the one of the active data

a euro mediterranean tree ring reconstruction of the winter nao index since 910 c e we develop a new reconstruction of the winter north atlantic oscillation nao index using a network of 97 euro mediterranean tree ring series the reconstruction covers the period 910 2018 c e making it the longest annually resolved estimate of winter nao variability available we use nested correlation weighted principal components regression and the maximum entropy bootstrap method to generate a 2400 member ensemble of reconstructions for estimating the final reconstruction and its quantile uncertainties extensive validation testing of the new reconstruction against data withheld from the calibration exercise demonstrates its skill the skill level of the new reconstruction is also an improvement over two nao reconstructions published earlier spectral analyses indicate that the new reconstruction behaves like a white noise process with intermittent band limited power suggesting that the winter nao is stochastically forced the white noise properties of our reconstruction are also shown to be consistent with the spectral properties of long instrumental nao indices extending back to 1781 and nao indices extracted from a large number of forced climate model runs covering the last millennium in contrast an annually resolved multi proxy nao reconstruction of comparable length based in part on speleothem data behaves more like externally forced red noise process which is inconsistent with our reconstruction long observations and forced model runs