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

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

the characteristics of movable fluid in the triassic lacustrine tight oil reservoir a case study of the chang 7 member of xin anbian block ordos basin china abstract the micropore throat structure of a tight oil reservoir is complex and its movable fluid distribution differs from that of a conventional reservoir by using nuclear magnetic resonance nmr and centrifugation the movable fluid distribution in the chang 7 tight reservoir in the xin anbian block of the ordos basin was quantitatively evaluated combined with the results of the physical property and high pressure mercury intrusion experiments the effects of the porosity permeability pore size distribution and micropore throat structure on the movable fluid distribution in the chang 7 tight reservoir were analyzed the nmr results show that the t2 spectral morphology of the chang 7 tight oil reservoir in the xin anbian block can be characterized by three main patterns with different amplitudes of front and post peaks the front peak corresponds to the scale of small pores and the post peak corresponds to the scale of large pores based on the three t2 spectrum patterns the chang 7 tight reservoir can be divided into three types type 1 reservoir with more small pores and fewer large pores type 2 reservoir with similar amounts of small and large pores and type 3 reservoir with fewer small pores and more large pores thus the characteristics of these three types of reservoirs can be determined the movable fluid parameters were calculated by nmr and centrifugation the movable fluid saturation of the type 1 reservoir is low with an average of 20 38 and the average movable fluid porosity is 1 47 the type 2 and type 3 reservoirs have higher movable fluid contents of 40 79 and 47 04 respectively the average movable fluid porosities of the type 2 and type 3 reservoirs are 3 37 and 3 48 respectively the greater number of small pores and smaller number of large pores in the type 1 reservoir result in weak correlations of the movable fluid with the physical properties and pore throat structure parameters the movable fluid saturation is negatively correlated with the maximum pore radius mainstream throat radius and maximum mercury saturation and is strongly positively correlated only with the porosity of the large pores as the number of large pores increases the movable fluid saturation strongly correlates with the property parameters pore size distribution and pore throat structure parameters in the type 2 and type 3 reservoirs the movable fluid saturations are positively affected by the maximum pore radius median radius mainstream throat radius and effective porosity but are strongly negatively correlated only with the radius mean value these results indicate that the fluid mobility of these two types of reservoirs can be promoted by the pore throat system to obtain favorable seepage characteristics

use of nmr logging to obtain estimates of hydraulic conductivity in the high plains aquifer nebraska usa 1 hydraulic conductivity k is one of the most important parameters of interest in groundwater applications because it quantifies the ease with which water can flow through an aquifer material hydraulic conductivity is typically measured by conducting aquifer tests or wellbore flow wbf logging of interest in our research is the use of proton nuclear magnetic resonance nmr logging to obtain information about water filled porosity and pore space geometry the combination of which can be used to estimate k in this study we acquired a suite of advanced geophysical logs aquifer tests wbf logs and sidewall cores at the field site in lexington nebraska which is underlain by the high plains aquifer we first used two empirical equations developed for petroleum applications to predict k from nmr logging data the schlumberger doll research equation ksdr and the timur coates equation kt c with the standard empirical constants determined for consolidated materials we upscaled our nmr derived k estimates to the scale of the wbf logging k kwbf logging estimates for comparison all the upscaled kt c estimates were within an order of magnitude of kwbf logging and all of the upscaled ksdr estimates were within 2 orders of magnitude of kwbf logging we optimized the fit between the upscaled nmr derived k and kwbf logging estimates to determine a set of site specific empirical constants for the unconsolidated materials at our field site we conclude that reliable estimates of k can be obtained from nmr logging data thus providing an alternate method for obtaining estimates of k at high levels of vertical resolution

hydrological changes in the mediterranean sea over the last 30 000 years sea surface temperatures were reconstructed over the last 30 000 years from alkenone paleothermometry sst alk and planktonic foraminifera assemblages using the modern analog technique mat sst foram along two cores of the mediterranean sea md84 632 levantine basin and md04 2797 siculo tunisian strait oxygen isotope of planktonic foraminifera g bulloides for core md04 2797 and g ruber for core md84 632 were also determined sst alk in the levantine basin indicate colder values at the last glacial maximum lgm 14 c than earlier established from mat and a cooling amplitude of 6 7 c comparable to the central mediterranean sea climatic events such as the younger dryas yd and heinrich events 1 and 2 h1 and h2 were times of significant cooling in the two cores in the eastern basin values of local seawater oxygen isotope w indicate relatively saltier waters during the lgm and deglaciation than today with increasing w values higher salinity in the eastern basin and decreasing ones lower salinity in the central mediterranean sea during cold stadials the observed alterations of surface water properties t and w in the central and eastern mediterranean at the lgm are consistent with model experiments showing slightly lower evaporation in the mediterranean than today except for the eastern basin

seismic fault zone trapped noise systematic velocity contrasts across and within fault zones can lead to head and trapped waves that provide direct information on structural units that are important for many aspects of earthquake and fault mechanics here we construct trapped waves from the scattered seismic wavefield recorded by a fault zone array the frequency dependent interaction between the ambient wavefield and the fault zone environment is studied using properties of the noise correlation field a critical frequency fc 0 5 hz defines a threshold above which the in fault scattered wavefield has increased isotropy and coherency compared to the ambient noise the increased randomization of in fault propagation directions produces a wavefield that is trapped in a waveguide cavity like structure associated with the low velocity damage zone dense spatial sampling allows the resolution of a near field focal spot which emerges from the superposition of a collapsing time reversed wavefront the shape of the focal spot depends on local medium properties and a focal spot based fault normal distribution of wave speeds indicates a 50 velocity reduction consistent with estimates from a far field travel time inversion the arrival time pattern of a synthetic correlation field can be tuned to match properties of an observed pattern providing a noise based imaging tool that can complement analyses of trapped ballistic waves the results can have wide applicability for investigating the internal properties of fault damage zones because mechanisms controlling the emergence of trapped noise have less limitations compared to trapped ballistic waves

determination of pore size distribution in sedimentary rocks by proton nuclear magnetic resonance abstract the distribution of pore sizes in sedimentary rocks can be determined from laboratory measurements of proton nuclear magnetic resonance nmr longitudinal relaxation t 1 in water saturated rocks the details of the longitudinal relaxation curve are converted into a t 1 distribution curve by approximating the data with a sum of single exponential decays the non linear least squares minimization procedure includes a regularization term that reduces excursions in the computed density function thus producing smooth and robust results the t 1 distribution curve is scaled to pore size distributions by a phenomenological parameter that describes the strength of the proton interaction between the fluid and the pore wall this parameter is relatively constant in sandstones but is an order of magnitude less with greater variability in carbonates there is excellent qualitative and quantitative agreement between pore size distributions determined by nmr and independently determined information on pore sizes for a variety of sedimentary rocks the laboratory derived t 1 distributions are used to estimate the irreducible water saturation in sandstones by identifying the fraction of pores less than 4 m in diameter

seismic interferometry with antipodal station pairs in this study we analyze continuous data from all global seismographic network stations between year 2000 and 2009 and demonstrate that several body wave phases e g pp pcppkp sksp and pps propagating between nearly antipodal station pairs can be clearly observed without array stacking using the noise coda cross correlation method based on temporal correlations with global seismicity we show that the observed body waves are clearly earthquake related moreover based on single earthquake analysis we show that the earthquake coda energy observed between 10 000 and 30 000 s after a large earthquake contributes the majority of the signal we refine our method based on these observations and show that the signal can be significantly improved by selecting only earthquake coda times with our improved processing the pkikp phase which does not benefit from the focusing effect near the antipode can now also clearly be observed for long distance station pairs

application of nmr logging to reservoir characterization of low resistivity sands in the gulf of mexico1 nuclear magnetic resonance nmr technology from laboratory data and well logs is rapidly gaining acceptance as a petrophysical tool for evaluating reservoir quality the evaluation of laboratory nmr data as a core analysis technique shows that nmr relaxation time distributions match independent estimates of pore size distributions these other pore size estimates come from grain size analyses pore throat distributions from mercury porosimetry thin section petrography and permeability values irreducible water saturation estimates from nmr based pore size distributions also correspond well with independent measures of irreducible water from special core flood tests in this study we look at the relaxation time distributions extracted from laboratory and downhole nmr measurements to determine pore geometry and volumetrics within a reservoir this understanding leads to a better overall reservoir characterization both core and log nmr data are used to demonstrate that there is a direct connection between nmr relaxation time distributions and the fundamental property of pore size in sandstones this description of pore size distributions allows us to estimate permeability and irreducible water saturation additionally the nmr logs accurately characterize the nmr core lab measurements and provide important information that enhances the description of low resistivity pay

sea surface temperature variations in the western mediterranean sea over the last 20 kyr a dual organic proxy uk 37 and ldi approach a high resolution sea surface temperature sst reconstruction of the western mediterranean was accomplished using two independent algae based molecular organic proxies i e the u 37 k index based on long chain unsaturated ketones and the novel long chain diol index ldi based on the relative abundances of c 28 and c 30 1 13 and 1 15 diols two marine records from the western and eastern alboran sea basin spanning the last 14 and 20kyr respectively were studied results from the surface sediments suggest that the two proxies presently reflect seasons with similar sst or simply annual mean sst both proxy records reveal the transition from the last glacial maximum to the holocene in the eastern alboran sea with an sst increase of approximately 7 degrees c for u 37 k and 9 degrees c for ldi minimum ssts 10 12 degrees c are reached at the end of the last glacial maximum and during the last heinrich event with a subsequent rapid sst increase in ldi sst toward the beginning of the bolling period 20 degrees c while u 37 k sst remains constantly low similar to 12 degrees c the bolling allerod period is characterized by a rapid increase and subsequent decrease in u 37 k sst while the ldi sst decrease continuously short term fluctuations in u 37 k sst are probably related to the availability of nutrients and seasonal changes the younger dryas is recorded as a short cold interval followed by progressively warmer temperatures during the holocene the general lower u 37 k derived temperature values in the eastern alboran by approximately 1 5 2 degrees c suggest a southeastward cold water migration by the western alboran gyre and divergence in the haptophyte blooming season between both basins key points high resolution sst reconstruction is performed in the westernmost mediterranean two algae based proxies show the temperature evolution for the last 20 kyr derived ssts suggest different growth seasons of alkenone and diol producers

body wave imaging of earth s mantle discontinuities from ambient seismic noise ambient seismic noise correlations are widely used for high resolution surface wave imaging of earth s lithosphere similar observations of the seismic body waves that propagate through the interior of earth would provide a window into the deep earth we report the observation of the mantle transition zone through noise correlations of p waves as they are reflected by the discontinuities associated with the top 410 kliometers km and the bottom 660 km of this zone our data demonstrate that high resolution mapping of the mantle transition zone is possible without using earthquake sources

extracting seismic attenuation coefficients from cross correlations of ambient noise at linear triplets of stations s u m m a r y we develop and apply an algorithm for deriving interstation seismic attenuation from crosscorrelations of ambient noise recorded by linear arrays theoretical results on amplitude decay due to attenuation are used to form a linear least square inversion for interstation qr values of rayleigh surface waves propagating along linear arrays having three or more stations the noise wave field is assumed stationary within each day and the interstation distances should be greater than the employed wavelength the inversion uses differences of logarithmic amplitude decay curves measured at different stations from cross correlation functions within a given frequency band the background attenuation between noise sources and receivers is effectively cancelled with this method the site amplification factors are assumed constant or following similar patterns in the frequency band of interest the inversion scheme is validated with synthetic tests using ambient noise generated by ray theory based calculations with heterogeneous attenuation and homogenous velocity structure the interstation attenuation and phase velocity dispersion curves are inverted from cross correlations of the synthetic data the method is then applied to triplets of stations from the regional southern california seismic network crossing themojave section of the san andreas fault and a dense linear array crossing the southern san jacinto fault zone bootstrap technique is used to derive empirical mean and confidence interval for the obtained inverse q values the results for the regional stations yield qr values around 25 for a frequency band 0 2 0 36 hz the results for the san jacinto fault zone array give qr values of about 6 30 for frequencies in the range 15 25 hz

the lack of equipartitioning in global body wave coda correlation of the coda of large earthquakes can be used to retrieve body waves at teleseismic distances this retrieval depends on waves propagating with equal energy in all directions equipartitioning we carry out a beamforming analysis of body waves at periods of 10 and 40 s recorded at usarray and show that the late coda up to 10 h after the okhotsk earthquake is dominated by waves propagating in the great circle direction late coda waves are not equipartitioned this implies for seismic interferometry that teleseismic body waves can only be extracted from the coda when the earthquake and the receivers are located on a great circle this happens automatically when the employed stations are antipodal or when the autocorrelation of waves is used the use of long period ambient seismic noise relies on the distribution of sources because scattering only marginally randomizes directions this provides insight into recent observations of core phases extracted from seismic interferometry

seismic tomography of the southern california plate boundary region from noise based rayleigh and love waves we use cross correlations of ambient seismic noise between pairs of 158 broadband and short period sensors to investigate velocity structure over the top 5 10 km of the crust in the southern california plate boundary region around the san jacinto fault zone sjfz from the 9 component correlation tensors associated with all station pairs we derive dispersion curves of rayleigh and love wave group velocities the dispersion results are inverted first for rayleigh and love waves group velocity maps on a 1 5 1 5 km2 grid that includes portions of the sjfz the san andreas fault saf and the elsinore fault we then invert these maps to 3d shear wave velocities in the top 7 km of the crust the distributions of the rayleigh and love group velocities exhibit 2 azimuthal anisotropy with fast directions parallel to the main faults and rotations in complex areas the reconstructed 3d shear velocity model reveals complex shallow structures correlated with the main geological units and strong velocity contrasts across various fault sections along with low velocity damage zones and basins the sjfz is marked by a clear velocity contrast with higher v s values on the ne block for the section se of the san jacinto basin and a reversed contrast across the section between the san jacinto basin and the saf velocity contrasts are also observed along the southern parts on the saf and the elsinore fault with a faster southwest block in both cases the region around the salton trough is associated with a significant low velocity zone strong velocity reductions following flower shape with depth are observed extensively around both the sjfz and the saf and are especially prominent in areas of geometrical complexity in particular the area between the sjfz and the saf is associated with an extensive low velocity zone correlated with diffuse seismicity at depth and a similar pattern including correlation with deep diffuse seismicity is observed on a smaller scale in the trifurcation area of the sjfz these results augment local earthquake tomography images that have low resolution in the top few km of the crust and provide important constraints for studies concerned with behavior of earthquake ruptures generation of rock damage and seismic shaking hazard in the region

seasonal variations of seismic velocities in the san jacinto fault area observed with ambient seismic noise s u m m a r y we observe seasonal seismic wave speed changes dv v in the san jacinto fault area and investigate several likely source mechanisms velocity variations are obtained from analysis of 6 yr data of vertical component seismic noise recorded by 10 surface and six borehole stations we study the interrelation between dv v records frequency dependent seismic noise properties and nearby environmental data of wind speed rain ground water level barometric pressure and atmospheric temperature the results indicate peak to peak seasonal velocity variations of 0 2 per cent in the 0 5 2 hz frequency range likely associated with genuine changes of rock properties rather than changes in the noise field phase measurements between dv v and the various environmental data imply that the dominant source mechanism in the arid study area is thermoelastic strain induced by atmospheric temperature variations the other considered environmental effects produce secondary variations that are superimposed on the thermal based changes more detailed work with longer data on the response of rocks to various known external loadings can help tracking the evolving stress and effective rheology at depth

anelastic earth structure from the coherency of the ambient seismic field 1 cross correlation of the ambient seismic field is now routinely used to measure seismic wave travel times however relatively little attention has been paid to other information that could be extracted from these signals in this paper we demonstrate the relationship between the spatial coherency of the ambient field and the elastodynamic green s function in both time and frequency domains through measurement of the frequency domain coherency as a function of distance we sequentially recover phase velocities and attenuation coefficients from these measurements we generate 1 d shear wave velocity and attenuation models for southern california the ambient field measurements of attenuation and the exceptional path coverage that results from the many possible interstation measurements allow us to extend q estimates over a range of frequencies that has previously been difficult to analyze using earthquake data measurements from paths that cross major sedimentary basins show both lower wave speeds and lower quality factors than other paths as expected our results indicate that there is a wealth of information available in the spatial coherency of the ambient seismic field

mapping pressurized volcanic fluids from induced crustal seismic velocity drops volcanic eruptions are caused by the release of pressure that has accumulated due to hot volcanic fluids at depth here we show that the extent of the regions affected by pressurized fluids can be imaged through the measurement of their response to transient stress perturbations we used records of seismic noise from the japanese hi net seismic network to measure the crustal seismic velocity changes below volcanic regions caused by the 2011 moment magnitude m w 9 0 tohoku oki earthquake we interpret coseismic crustal seismic velocity reductions as related to the mechanical weakening of the pressurized crust by the dynamic stress associated with the seismic waves we suggest therefore that mapping seismic velocity susceptibility to dynamic stress perturbations can be used for the imaging and characterization of volcanic systems

integrated petrophysical evaluation of the lower middle bakken member in the viewfield pool southeastern saskatchewan canada abstract the viewfield pool of the lower middle bakken member the largest light oil pool in saskatchewan canada has been described as an unconventional resource play reservoir evaluation in this pool has been challenging because of low permeability complex lithology and reservoir heterogeneity to address the difficulties this study employed an integrated approach to derive reservoir parameters and provided a detailed petrophysical characterization of the viewfield middle bakken play which led to a division of unit a the lower middle bakken member into two subunits a1 for the lower interval and a2 for the upper interval petrophysical models were developed based on thorough analyses of core measurements conventional well logs and available advanced nuclear magnetic resonance nmr well log data the proposed models were applied to determine reservoir properties including shale content porosity permeability and water saturation for the two subunits in 163 vertical wells among which three have nmr logs the results reveal that subunits a1 and a2 differ significantly in petrophysical properties and reservoir quality a2 the very fine grained dolomitic sandstone subunit has larger pore size higher porosity and permeability lower shale content and water saturation and thus represents the preferred interval for oil production across the viewfield bakken pool area and has greater resource potential than the siltstone subunit a1 the mapped petrophysical properties show spatial trends that align well with the previously recognized regional geological features favourable potential high productivity zones can be outlined by the areas of intersection of all essential reservoir parameters above defined threshold values

quantifying the effects of nondiffuse noise on ballistic and coda wave amplitude from variances of seismic noise interferometry in southern california we develop a new approach based on the variance of noise cross correlation to characterize the noise source and wave propagation under the influence of a non diffuse noise field based on the rando