systematic analysis of crustal anisotropy along the karadere duzce branch of the north anatolian fault s u m m a r y we perform a systematic analysis of crustal anisotropy along and around the karadere duzce branch of the north anatolian fault naf which ruptured during the 1999 mw 7 4 izmit and mw 7 1 duzce earthquakes a method consisting of an iterative grid search for the best shear wave splitting parameters in sliding time windows is applied to 22 000 measurements recorded in the 6 month period after the izmit main shock based on objective criteria 6600 measurements are assigned high quality and used for further detailed analysis most stations near the rupture zone have fast polarization directions that are parallel to and change with the nearby fault strike the average delay times for ray paths that propagate along the rupture zone are larger than for the other paths these results suggest the existence of an approximately 1 km broad zone around the karadere duzce branch with fault parallel cracks or shear fabric however some fault zone fz stations record bimodal or scattered polarization directions while stations near large structural complexities e g branching and offsets show average fast polarization directions that are almost perpendicular to the local fault strike the average fast polarization directions from ray paths that propagate inside the almacik block south of the karadere duzce branch are neither parallel to the local fault strike nor to the expected regional maximum compressive stress direction the large overall spatial variations of the results imply that multiple structures and mechanisms contribute to the observed crustal anisotropy in our study area most stations do not exhibit a clear dependency of shear wave splitting delay time with increasing depth and hypocentral distance indicating that the anisotropy is confined primarily to the top 3 4 km of the crust using the observed average delay time at fz stations and assumed propagation distance of 3 5 km we estimate the apparent crack density in the damaged shallow fz rock to be approximately 7 per cent

passive monitoring of anisotropy change associated with the parkfield 2004 earthquake 1 we investigate temporal variations in the polarization of surface waves determined using ambient seismic noise cross correlations between station pairs at the time of the mw 6 0 parkfield earthquake of september 28 2004 we use data recorded by the high resolution seismic network s 3 component seismometers located along the san andreas fault our results show strong variations in azimuthal surface wave polarizations for the paths containing station varb one of the closest stations to the san andreas fault synchronous with the parkfield earthquake concerning the other station pair only smooth temporal variations of are observed two principal contributions to these changes in are identified and separated they are 1 slow and weak variations due to seasonal changes in the incident direction of seismic noise and 2 strong and rapid rotations synchronous with the parkfield earthquake for paths containing station varb strong shifts in are interpreted in terms of changes in crack induced anisotropy due to the co seismic rotation of the stress field because these changes are only observed on paths containing station varb the anisotropic layer responsible for the changes is most likely localized around varb in the shallow crust these results suggest that the polarization of surface waves may be very sensitive to changes in the orientations of distributed cracks and that implementation of our technique on a routine basis may prove useful for monitoring stress changes deep within seismogenic zones

geological and industrial implications of extensive dilatancy anisotropy extensive dilatancy anisotropy is the hypothesized distribution of stress aligned fluid filled microcracks pervading most rocks in the earth s crust the geometry of the cracks and the aligning stress field can be monitored by analysing the waveforms of shear waves propagating through the rockmass the ability to estimate some of the parameters of the crack and stress geometry by analysing shear wave particle displacements has widespread implications

seasonality in particle motion of microseisms summary microseisms are a continuous source of seismic signal which mainly consist of rayleigh waves but are known to contain some other types of seismic waves we developed a simple processing procedure for single station three component seismic data which allows us to select rayleigh wave dominated portions application of this procedure to data from southern california led us to confirm that excitation of the secondary peak microseisms the predominant energy at about 0 15 hz occurs in coastal regions the source directions viewed at each station do not change very much throughout the year we also discovered that the ratio of the horizontal to vertical amplitudes in rayleigh waves termed h z in this paper is shown to have seasonal variations the h z estimates typically reach their maximum in winter and their minimum in summer seasonal variations are observed at most stations but peak to peak amplitudes of seasonal variations vary greatly from station to station ranging between 0 and 40 per cent two hypotheses were examined to explain this phenomenon the first hypothesis is that it is caused by seasonal changes in seismic velocities in a layer between the surface and the groundwater level the second hypothesis is that it is caused by seasonal changes in relative excitation of higher modes compared to dominant fundamental mode rayleigh waves the first hypothesis is not likely because predicted amplitudes of seasonal variations in h z are too small to explain observed variations the second hypothesis seems quite plausible if source regions move seasonally among regions with different ocean depths the technique developed in this paper however is not sufficient to answer this question conclusively

high resolution strontium isotope stratigraphy across the cambrian ordovician transition we have analyzed 214 fossil apatite samples from nine stratigraphic sections worldwide that cover the lower cambrian to lower ordovician for their strontium isotope ratios of these samples 180 from six sections that cover the cambrian ordovician transition 5 ma reveal how the extent of isotopic alteration can differ greatly according to lithology and sample type from three limestone sections 126 euconodont samples yield the most consistent 87sr 86sr ratios and are used in this article to constrain seawater 87sr 86sr across the cambrian ordovician boundary by contrast protoconodonts paraconodonts and inarticulate brachiopods are far less likely to retain a primary 87sr 86sr signature and appear to be of only limited value for chemostratigraphy seawater 87sr 86sr fell from maximum values for the phanerozoic of more than 0 7092 during the early late cambrian to 0 7090 by the earliest ordovician high resolution sampling has permitted the recognition of sinusoidal variations with a wavelength on the order of 1 ma that are superimposed on the overall fall in 87sr 86sr these variations may be caused by high order cycles in seawater 87sr 86sr or diagenetic alteration

geochemistry of modern brachiopods applications and implications for oceanography and paleoceanography abstract modern rhynchonellida terebratulida thecideida and a few inarticulated brachiopods were collected live or soon after death at 30 locations from depths of 2 3940 m from the equator to high latitudes covering the atlantic pacific indian caribbean and mediterranean oceans seas well preserved fibers of the secondary layer combined with sr 450 1928 mg kg mn 1 199 mg kg and fe 1 610 mg kg contents confirm with few exceptions the excellent preservation of the modern brachiopod material evaluation of the stable isotope compositions was conducted on 276 specimens and on 374 published samples for a total database of 650 samples from 80 locations it revealed that oxygen isotope incorporation into shell calcite secondary layer of modern articulated brachiopods in most cases occurs in equilibrium with the ambient water and as such reflects surrounding environmental conditions thecideida as a group shallow water and low latitude incorporate oxygen isotopes 3 04 to 0 35 into shell calcite in equilibrium with their ambient water a large majority of genera and species of the terebratulida shallow water and low mid latitude also incorporate oxygen 2 30 to 3 48 into shell calcite in isotopic equilibrium with their surrounding water in contrast equilibrium incorporation of oxygen isotopes into shell calcite by the rhynchonellida is uncertain but a vital effect probably applies to the craniida the question of equilibrium disequilibrium incorporation of carbon isotopes into shell calcite of modern brachiopods remains unresolved at this time isotope compositions range up to 4 5 5 6 and 1 5 for 13 c and up to 5 5 5 9 and 0 3 for 18 o for shallow water low mid and high latitude brachiopods respectively strontium isotopes of modern brachiopods as expected show no significant variation with location latitude water depth temperature salinity and general water conditions once local habitat and ecological influences of fossil brachiopods from similar latitudes are considered their isotopic elemental values should be valuable diagenetic indicators and important oceanographic chemostratigraphic proxies

75 plus years of anisotropy in exploration and reservoir seismics a historical review of concepts and methods the idea that the propagation of elastic waves can be anisotropic i e that the velocity may depend on the direction is about 175 years old the first steps are connected with the top scientists of that time people such as cauchy fresnel green and kelvin for most of the 19th century anisotropic wave propagation was studied mainly by mathematical physicists and the only applications were in crystal optics and crystal elasticity during these years important steps in the formal description of the subject were made at the turn of the 20th century rudzki stressed the significance of seismic anisotropy he studied many of its aspects but his ideas were not applied research in seismic anisotropy became stagnant after his death in 1916 beginning about 1950 the significance of seismic anisotropy for exploration seismics was studied mainly in connection with thinly layered media and the resulting transverse isotropy very soon it became clear that the effect of layer induced anisotropy on data ac

timing of the permian triassic biotic crisis implications from new zircon u pb age data and their limitations abstract the most profound biotic crisis in the earth s history causing the near extinction of both terrestrial and marine life occurred at the end of the permian period about 253 myr ago and marks the paleozoic mesozoic era boundary the cause of this event is still a matter of vigorous debate with both brief and catastrophic as well as gradual mechanisms having been proposed similar to a recent landmark study this study uses the u pb method on zircons from the uppermost permian lowermost triassic ash fall deposits at meishan zhejiang province se china in order to examine time and rate constraints for these events the results of both this study and previous work show that for these ash layers the effects of pb loss are combined with varying amounts and sources of inheritance resulting in an age scatter which prohibits the extraction of a statistically robust age in many cases though the effects of pb loss on the zircons analyzed in this study were reduced by leaching the grains in hydrofluoric acid as opposed to commonly applied air abrasion prior to analysis the presence within a single ash layer of multiple generations of older xenocrysts in many cases only slightly older than the depositional age has made quantitative interpretation even more difficult when these combined phenomena bias individual zircon ages by less than a percent they are extremely difficult to deconvolute and if multi grain analyses are used can become impossible to recognize because of the resulting age averaging monte carlo simulations using actual measurements of individual zircon crystals show that age excursions due to pb loss and xenocrystic contamination for the meishan bentonites are easily homogenized to the point of undetectability when replicate analyses of multi grain zircon samples are compared thus this study uses only high precision analyses of single crystals whether from our work or that of previous studies three main conclusions have emerged first our data require a significant increase in the age of the permian triassic boundary by more than 2 myr compared to the previous study which shifts the age to a value older than 253 ma second neither our data nor those from previous work can confirm or negate the possibility of a very abrupt biotic crisis third even large suites of very high quality single zircon u pb analyses for these tuffs cannot in most cases yield objective reliable and robust dates with accuracies at the sub myr level though the temptation to perform arbitrary selection of subsets of the analyses for that purpose is almost irresistible the last conclusion is not an indictment of zircon u pb dating in general other rocks and other zircon populations can and do behave very differently and further technical advances will likely improve our ability to prepare grains or sub grains of adequately enhanced quality for analysis consequently the results of the present study strongly suggest that for problems requiring time scale accuracy inferences from zircon u pb dating must be based on sufficiently large suites of single crystal or crystal domain high precision analyses

array estimators and the use of microseisms for reconnaissance of sedimentary basins a natural field seismic technique is possible to attain by observing microseisms with a suitably designed array and by digitally processing the data to obtain estimates of the phase velocities of rayleigh waves wavelengths of interest in detecting depth to the basement of sedimentary basins are in the range 2 to 20 km and correspond to wave periods from 1 to 7 s an array of five or seven seismometers deployed as an expanding cross configuration simplifies field procedures and is adequate for phase velocity measurements of rayleigh waves in the required wavelength range provided high resolution frequency wavenumber spectral analysis is used this analysis can be implemented on a minicomputer in the field results obtained from observation in a sedimentary basin of known structure show predominantly fundamental mode rayleigh wave propagation the scatter of velocity estimates is small enough to allow inversion by curve matching and depth to the basement can be computed to an accuracy of 30 percent w

the cenozoic evolution of the strontium and carbon cycles relative importance of continental erosion and mantle exchanges the past variations of the seawater 87sr86sr isotopic ratio are related to changes in the relative contribution of the mantle sr input to the ocean and the sr supply from continental weathering recently it has been postulated that the cenozoic increase in the seawater 87sr86sr isotopic ratio was associated with the uplift of the himalayan and andean mountains at that time these orogenies may have changed the sr isotopic ratio of the continental rocks undergoing weathering as a result of extensive metamorphism increased the river flux of sr through enhanced weathering in these regions and possibly caused the global climatic cooling trend of the cenozoic a model of the major geochemical cycles coupled to an energy balance climate model is used to explore the possible causes of the mesozoic cenozoic fluctuations in the seawater 87sr86sr isotopic ratio the contribution of the mantle exchanges at mid ocean ridges of the recycling of seafloor carbonates through plate margin volcanism and of the alteration of seafloor basalts to the fluctuations of the seawater 87sr86sr isotopic ratio are studied finally this model tentatively describes the impact of the himalayan orogeny on the geochemical cycles of sr and c some possible effects of the extensive metamorphism associated with the india asia collision and of the himalayan uplift are modelled the model reproduces the cenozoic increase of the seawater 87sr86sr isotopic ratio however the impact of the himalayan orogeny on the c cycle appears to be limited and insufficient to generate the global climatic cooling of the cenozoic rather in the model the cenozoic cooling is mostly due to the reduction of the co2 emission from mid ocean ridge volcanism and to changes in the chemical weathering rates in the rest of the world excluding the himalayas

the san andreas fault revisited through seismic noise and surface wave tomography 1 we present here surface wave tomography results for the san andreas fault in the parkfield area california usa that were extracted from microseismic noise in the 0 15 hz to 0 35 hz frequency band using passive seismic correlation techniques using directive noise incoming from the pacific ocean passive seismic noise tomography was performed using three component sensors from a dense seismic network a rotation algorithm was applied to the nine component noise correlation tensor that optimally forced each station pair to re align in the noise direction a necessary condition to extract unbiased travel times from passive seismic processing after the rotation was performed an optimal surface wave tensor is obtained from which love waves were extracted for tomography inversion dispersion curves were then inverted to obtain a three dimensional shear velocity map showing vertical geological structures and a 1 3 km wide low seismic velocity dip which are in agreement with previous tomography studies in the same area

near surface seismic anisotropy attenuation and dispersion in the aftershock region of the 1999 chi chi earthquake summary seismograms from local aftershocks of the 1999 chi chi taiwan earthquake recorded at a 200 m deep downhole station chy of the taiwan central weather bureau seismic network cwbsn have clear direct upgoing shear waves and their surface reflected downgoing phases measurements of time difference between the direct and reflected phases of the fast and slow components of split shear waves show approximately 8 per cent velocity anisotropy in the top 200 m of the crust the phase velocities extracted from the direct and reflected waveforms display clear evidence of attenuation related dispersion taking the dispersion and geometrical spreading factor into account we estimate the q value of the shear waves by fitting calculated results to the observed reflected waveforms the amplitude spectral density ratios between the direct and reflected phases are approximately linear within the frequency range 2 15 hz this allows us also to estimate the q value from the slope of the amplitude spectral ratio in db hz 1 i nthis range the estimated q values with both methods based on a set of similar waveforms and additional 156 high quality records are 61 68 for the fast components and 43 52 for the slow components the observed attenuation anisotropy may be similarly to velocity anisotropy a manifestation of microcracks alignment and their response to in situ stress strong attenuation anisotropy 23 30 per cent in this study along with attenuationrelated dispersion in the shallow crust can affect significantly the properties of shear waves and should be taken into account in studies employing surface and shallow borehole records of shear waveforms

87sr 86sr record of permian seawater abstract a population of 169 permian articulate brachiopod shells was analysed for their 87 sr 86 sr ratios 51 of these characterised as well preserved and stratigraphically well defined are utilized for delineation of the permian seawater strontium isotope trend the 87 sr 86 sr curve shows values of about 0 7080 in the lowermost permian asselian followed by a gradual decline to 0 70685 in the capitanian and a minor rise in the dzhulfian and lower dorashamian to values of 0 70715 just below the permian triassic boundary the early permian decrease in the strontium isotope curve that commences in the early sakmarian is coincident with the advancing deglaciation of the gondwana and with the increased aridity in large parts of the pangaea these factors may have led to a reduced continental weathering of rb rich silicate rocks and thus to the decline in seawater 87 sr 86 sr starting with the artinskian the opening of the neotethys and the associated widespread basaltic volcanism supplied low radiogenic strontium to seawater from an enhanced hydrothermal flux in the capitanian basaltic volcanism in the entire palaeotethys ceased and this may have been the reason for a slightly more radiogenic seawater isotopic composition during the lopingian higher input of riverine sr due to expansion of humid areas may have been a contributory factor

passive seismic imaging with directive ambient noise application to surface waves and the san andreas fault in parkfield ca summary this study deals with surface waves extracted from microseismic noise in the 0 1 0 2 hz frequency band with passive seismic correlation techniques for directive noise we explore the concept of passive seismic noise tomography performed on three component sensors from a dense seismic network from the nine component correlation tensor a rotation algorithm is introduced that forces each station pair to re align in the noise direction a necessary condition to extract unbiased traveltime from passive seismic processing after rotation is performed the new correlation tensor exhibits a surface wave tensor from which rayleigh and love waves can be separately extracted for tomography inversion methodological aspects are presented and illustrated with group speed maps for rayleigh and love waves and ellipticity measurements made on the san andreas fault in the parkfield area california usa

analysis of three component ambient vibration array measurements summary both synthetic and observed ambient vibration array data are analysed using high resolution beam forming in addition to a classical analysis of the vertical component this paper presents results derived from processing horizontal components we analyse phase velocities of fundamental and higher mode rayleigh and love waves and particle motions ellipticity retrieved from h v spectral ratios a combined inversion with a genetic algorithm and a strategy for selecting possible model parameters allow us to define structural models explaining the data the results from synthetic data for simple models with one or two layers of sediments suggest that in most cases the number of layers has to be reduced to a few sediment strata to find the original structure generally reducing the number of soft sediment layers in the inversion process with genetic algorithms leads to a class of models that are less smooth they have a stronger impedance contrast between sediments and bedrock combining love and rayleigh wave dispersion curves with the ellipticity of the fundamental mode rayleigh waves has some advantages scatter is reduced when compared to using structural models obtained only from rayleigh wave phase velocity curves by adding information from love waves some structures can be excluded another possibility for constraining inversion results is to include supplementary geological or borehole information analysing radial components also can provide segments of rayleigh wave dispersion curves for modes not seen on the vertical component finally using ellipticity information allows us to confine the total depth of the soft sediments for real sites considerable variability in the measured phase velocity curves is observed this comes from lateral changes in the structure or seismic sources within the array constraining the inversion by combining love and rayleigh wave information can help reduce such problems frequency bands in which the rayleigh wave dispersion curves show considerable scatter are often better resolved by love waves information from the horizontal component can be used to correctly assign the mode number to the different phase velocity curve segments especially when two modes seem to merge at osculation points such merging of modes is usually observed for rayleigh waves and thus can be partly solved if additional information from the love waves and the horizontal component of rayleigh waves is considered whenever a site presents a velocity inversion below the top layer love wave data clearly helps to better constrain the solution

systematic analysis of shear wave splitting in the aftershock zone of the 1999 chi chi taiwan earthquake shallow crustal anisotropy and lack of precursory variations we analyze shear wave splitting sws in a high quality waveform data set recorded at surface and downhole 0 2 km seismometers in a region around the 20 september 1999 m w 7 6 chi chi taiwan earthquake sequence the data set was generated by events in a 5 year period before during and after the mainshock the purpose is to investigate the depth extent of the crustal anisotropy and its possible temporal evolution in relation to the occurrence of large earthquakes results from downhole records show a stable polarization direction of the fast shear wave that matches well the local global positioning system gps velocity field a slightly different polarization direction of the fast shear wave is obtained from surface data this suggests a possible anisotropy change between the top 0 2 km structure and the deeper section of the crust measured time delays below the downhole station have an average value of 0 16 sec without systematic changes for sources from about 8 km to 20 km in depth estimates of time delays in the top 0 2 km of the crust based on shear waves reflected from the free surface give a constant 0 04 sec a likely depth distribution inferred from these two types of measurements and an s velocity model indicates that the crustal anisotropy in the region is dominated by the top 2 to 3 km the measured polarization directions and time delays give essentially constant values over the 2 7 year premainshock and 2 3 year postmainshock periods in the region adjacent to the chi chi rupture and within 10 km from the epicentral region of its two large m 6 0 aftershocks analysis of sws in waveforms produced by earthquake multiplets confirms further the lack of precursory temporal variations of crustal anisotropy in the immediate neighborhood of the chi chi earthquake sequence the results raise doubts on the general usefulness of sws measurements for earthquake forecasting an apparent coseismic increase in anisotropy time delay of approximately 10 is observed for depths 0 2 km however this value is clearly affected by spatial changes associated with different event locations before and after the chi chi mainshock

strontium isotope stratigraphy of the middle devonian brachiopods and conodonts a set of 145 strontium isotope ratios based on skeletal components of emsian to frasnian age reveals a detailed structure of the seawater 87sr 86sr curve that can ultimately serve as a tool for high resolution isotope stratigraphy in the devonian brachiopod and conodont samples were collected in the eifel region of germany the area around the global stratotype for the middle devonian with an apparent average temporal resolution in the 105 y range preservation of the brachiopod shell material has been assessed by optical microscopy sem and cathodoluminescence and only the better preserved internal secondary layer of the shell has been utilized for strontium isotope measurements the 87sr 86sr curve shows a short decline from 0 7081 to 0 7078 through the late emsian followed by short term fluctuations with an amplitude of up to 10 4 around a mean of 0 7078 during the eifelian and givetian and a rise from late givetian into the late devonian the above high frequency oscillations and spikes are likely a reflection of condensed sedimentary records due to erosional and nondepositional events but a direct confirmation for such a scenario can be claimed only for the latest eifelian otomari event insufficient stratigraphic resolution precludes testing for the other events and isotopic spikes conodont skeletal elements even if well preserved at cai 2 5 yielded results that are mostly enriched in radiogenic 87sr if compared to coeval brachiopods although this enrichment is usually within the 10 5 range conodonts despite their superior stratigraphic resolution should be utilized only as a material of second choice in cases where brachiopods are rare or absent

variations in the strontium isotopic composition of seawater during the neogene the authors report 261 strontium isotopic analyses of well preserved planktonic foraminifers from three deep sea drilling project sites 519 588 and 607 these samples cover the period from 24 ma to present with an average of approximately one sample per 100 ka the combination of high sample density and uniformity of analytical procedures has produced a well defined record of changes in the sup 87 sr sup 86 sr of seawater during the neogene the record can be viewed as a series of essentially linear segments with slopes ranging from as high as 6 times 10 sup minus 5 m y to as low as 0 m y the times associated with major inflections in the curve do not appear to correspond to simple geologic phenomena such as eustatic cycles but are probably controlled by a combination of tectonic and climatic factors that influenced the abundance and isotopic composition of terrestrial strontium input to the oceans the strontium isotopic data are consistent with a progressive increase in the chemical weathering rates of the continents during the neogene probably related to repeated glaciations increased exposure of continents by lowered sea level and increased continental relief resulting from high rates of tectonic uplift

shear wave anisotropy in the crust around the san andreas fault near parkfield spatial and temporal analysis summary we systematically analysed shear wave splitting sws for seismic data observed at a temporary array and two permanent networks around the san andreas fault saf observatory at depth the purpose was to investigate the spatial distribution of crustal shear wave anisotropy around the saf in this segment and its temporal behaviour in relation to the occurrence of the 2004 parkfield m 6 0 earthquake the dense coverage of the networks the accurate locations of earthquakes and the high resolution velocity model provide a unique opportunity to investigate anisotropy in detail around the saf zone the results show that the primary fast polarization directions pds in the region including the saf zone and the northeast side of the fault are nw se nearly parallel or subparallel to the saf strike some measurements on the southwest side of the fault are oriented to the nne ssw direction approximately parallel to the direction of local maximum horizontal compressive stress there are also a few areas in which the observed fast pds do not fit into this general pattern the strong spatial variations in both the measured fast pds and time delays reveal the extreme complexity of shear wave anisotropy in the area the top 2 3 km of the crust appears to contribute the most to the observed time delays however substantial anisotropy could extend to as deep as 7 8 km in the region the average time delay in the region is about 0 06 s we also analysed temporal patterns of sws parameters in a nearly 4 yr period around the 2004 parkfield main shock based on similar events the results show that there are no appreciable precursory coseismic or post seismic temporal changes of sws in a region near the rupture of an m 6 0 earthquake about 15 km away from its epicentre

three dimensional compressional wavespeed model earthquake relocations and focal mechanisms for the parkfield california region we present a new three dimensional 3d compressional wavespeed v p model for the parkfield region taking advantage of the recent seismicity associated with the 2003 san simeon and 2004 parkfield earthquake sequences to provide increased model resolution compared to the work of eberhart phillips and michael 1993 epm93 taking the epm93 3d model as our starting model we invert the arrival time data from about 2100 earthquakes and 250 shots recorded on both permanent network and temporary stations in a region 130 km northeast southwest by 120 km northwest southeast we include catalog picks and cross correlation and catalog differential times in the inversion using the double difference tomography method of zhang and thurber 2003 the principal v p features reported by epm93 and michelini and mcevilly 1991 are recovered but with locally improved resolution along the san andreas fault saf and near the active source profiles we image the previously identified strong wavespeed contrast faster on the southwest side across most of the length of the saf and we also improve the image of a high v p body on the northeast side of the fault reported by epm93 this narrow body is at about 5 to 12 km depth and extends approximately from the locked section of the saf to the town of parkfield the footwall of the thrust fault responsible for the 1983 coalinga earthquake is imaged as a northeast dipping high wavespeed body in between relatively low wavespeeds 5 km sec extend to as much as 10 km depth we use this model to derive absolute locations for about 16 000 earthquakes from 1966 to 2005 and high precision double difference locations for 9 000 earthquakes from 1984 to 2005 and also to determine focal mechanisms for 446 earthquakes these earthquake locations and mechanisms show that the seismogenic fault is a simple planar structure the aftershock sequence of the 2004 mainshock concentrates into the same structures defined by the pre 2004 seismicity confirming earlier observations waldhauser et al 2004 that the seismicity pattern at parkfield is long lived and persists through multiple cycles of mainshocks online material 3d v p model and earthquake relocations

determination of shallow shear wave velocity profiles in the cologne germany area using ambient vibrations summary we have used both single station and array methods to determine shallow shear velocity site profiles in the vicinity of the city of cologne germany from ambient vibration records based on fk analysis we assume that fundamental mode rayleigh waves dominate the analysed wavefield in the frequency range of 0 7 2 2 hz according to this view a close relation exists between h v spectral ratios and the ellipticity of the contributing rayleigh waves the inversion of the shape of h v spectral ratios then provides quantitative information concerning the local shear wave velocity structure however based on tests with synthetic data believed to represent a typical situation in the lower rhine embayment dispersion curves were found to provide stronger constraints on the absolute values of the velocity depth model than the ellipticities the shape of the ellipticities was found to be subject to a strong trade off between the layer thickness and the average layer velocity we have made use of this observation by combining the inversion schemes for dispersion curves and ellipticities such that the velocity depth dependence is essentially constrained by the dispersion curves while the layer thickness is constrained by the ellipticities in order to test this method in practice we have used array recordings of ambient vibrations from three sites where the subsurface geology is fairly well known and geotechnical information is at least partially available in order to keep the parameter space as simple as possible we attempted to fit only a single layer over a half space model however owing to earlier studies from the region we assume a power law depth dependence for sediment velocities for all three sites investigated the inversion resulted in models for which the shear wave velocity within the sediment layer both in absolute value at the surface and in depth dependence are found to be remarkably similar to the results obtained by budny from downhole measurements this is strong support for the interpretation of h v spectral ratios as rayleigh wave ellipticities for all three sites the predicted sh wave site amplification factors at the fundamental frequency are of the order of 5 6 with a slightly smaller value south of cologne

near real time near surface 3d seismic velocity and uncertainty models by wavefield gradiometry and neural network inversion of ambient seismic noisegradiometric wave equation inversion

variation in 87 sr 86 sr of permian seawater an overview the strontium isotope ratio 87sr s6sr of seawater has changed significantly through time in response to variations in the input of sr to the oceans from various crust and upper mantle sources with differing 87sr 86sr values an important aspect of this temporal variation is the empirical finding that while the 87sr 86sr of seawater may vary through time at any given time the sr isotope ratio of the oceans is everywhere the same isotopic uniformity is achieved because the marine residence time of sr 4 x 106 yr is long e g veizer 1989 compared to the oceanic circulation time 103 yr the oceans therefore are well mixed with respect to both sr and sr isotope ratio and all coeval marine derived carbonates sulfates and phosphates will possess the same initial 87sr s6sr value consequently the temporal changes in the 87sr s6sr of seawater can be used to correlate and date marine strata and can provide insight into the global processes that have shaped our world