thermal state of the taranaki basin new zealand the taranaki basin is an active margin basin that has been significantly affected by miocene subduction tectonics along the pacific australian plate boundary we have analyzed its present day thermal state using 354 bottom hole temperatures bhts from 115 wells distributed throughout the basin the measured temperatures were corrected using an exact solution to bullard s equation rather than the horner approximation thereby allowing for recovery dependence on well diameter and correction for some bhts at early time after circulation had ceased thermal conductivity measurements were completed on 256 samples from eight wells and matrix conductivities were determined for six end member lithologies by inversion formation conductivities are based on the conductivity and relative proportion of each end member component corrected bhts in situ thermal conductivity and estimates of sediment heat production were combined to compute the present day steady state heat flow the average heat flow is 60 mw m 2 but important geographic variations are present heat flow on the western platform is remarkably consistent at 53 60 mw m 2 attesting to its relative stability since the late cretaceous heat flow in the southern part of the basin is 65 70 mw m 2 due to as much as 3 km of late miocene erosion on the southern onshore and to the south of the peninsula heat flow is 50 3 mw m 2 possibly due to the heat sink effects of crustal thickening heat flow is highest at 74 mw m 2 on the northern peninsula adjacent to the taranaki volcanic zone suggesting a causal relationship between quaternary volcanism and high heat flow

test ban treaty verification with regional data a review this paper summarizes the use of regional 30 seismic data in a test ban context for detecting locating identifying and determining the yield of underground nuclear explosions in many areas of the world eastern north america africa eastern ussr lg is the largest amplitude wave recorded on standard seismograph systems and thus is the most appropriate phase for monitoring small magnitude events excellent location capability for near regional events has been demonstrated at the norwegian small aperture array noress using lg and p waves lg and other regional phases may contain information on source depth but such information has not been exploited to date fifteen classes of regional discriminants have been identified including 1 1 first motion 2 2 ms mb 3 3 p2 p1 ratio 4 4 excitation of short period sh waves 5 5 lg rg amplitude ratios 6 6 pn lg pg lg and pmax lg amplitude ratios 7 7 lg group velocity and energy ratios in lg 8 8 excitation of sn 9 9 third moment of frequency 10 10 generation of higher mode surface waves 11 11 peak amplitudes of love and rayleigh waves and long period surface wave energy density 12 12 prevailing period of long period love waves 13 13 spectral ratio long period s waves to rayleigh waves 14 14 spectral ratio long period love waves to rayleigh waves 15 15 frequency of the peak spectral amplitudes and spectral ratios in pn pg s and lg each of these proposed discriminants has with differing degrees of success separated some explosions from some earthquakes however most have been tested only on limited data usually from one geographic region and only one or two recording stations no systematic analyses have been done to determine the best individual discriminant or combination of them preliminary evaluation of the use of lg for yield determination suggests that regional waves hold promise in this application theoretical studies have contributed significantly to the understanding of propagation characteristics of regional waves but further studies are required emphasizing modeling for realistic anisotropic sources the major conclusion of this study is that a systematic and comparative evaluation of all the proposed regional discriminants is now required utilizing a common data base derived from all present day test sites this evaluation would suggest the optimal discrimination procedure using regional waves and would also define areas of needed research without such an integrated evaluation it is still possible to speculate using existing results on the most promising regional discriminants

imaging subduction from the trench to 300 km depth beneath the central north island new zealand with vp and vp vs summary recent dense deployments of portable digital seismographs have provided excellent control on earthquakes beneath the central north island of new zealand here we use a subset of the best recorded earthquakes in an inversion for the 3 d vp and vp vs structure the data set includes 39 123 p observations and 18 331 s observations from 1239 earthquakes and nine explosions the subducted plate is imaged as a high vp low vp vs feature vp within the mantle of the subducted slab is almost always 8 5 km s 1 which requires the ca 120 myr slab to be unusually cold the low vp vs within the subducted plate closely parallels the lower plane of the dipping seismic zone it most likely indicates fluid resulting from dehydration of serpentine in the slab mantle and the earthquakes themselves are likely to be promoted by dehydration embrittlement we identify a region with vp 8 0 km s 1 directly above the dipping seismic zone can be interpreted as sinking entrained with the motion of the subducted slab and forming a viscous blanket that insulates the slab from the high temperature mantle wedge material in the overlying low vp region can be interpreted as rising within a return flow within the wedge the volcanic front appears to be controlled by where this dipping low vp region meets the base of the crust the thickness of the backarc crust also shows significant variation along strike in the central taupo volcanic zone tvz the crust is ca 35 km thick while southwest of mt ruapehu the crust thickens by ca 10 km there is no significant low vp zone in the mantle wedge in this southwestern region suggesting that this thicker crust has choked off mantle return flow the seismic tomography results when combined with constraints on mantle flow from previous shear wave splitting results provide a plausible model for both the distribution of volcanism in the central north island and the exceptional magmatic productivity of the central tvz

characteristics of surface waves generated by events on and near the chinese nuclear test site our goal is to characterize surface waves at intermediate periods 5 30s generated by nuclear explosions and natural earthquakes occurring in and around the chinese nuclear test site at lop nor observed at epicentral distances between 10 and 20 we present observations of rayleigh and love wave group velocities spectral amplitudes and polarizations for eight nuclear explosions and nine earthquakes recorded at iris and geoscope broad band digital stations and at the kirghiz telemetered seismic network knet the wave paths studied cross complex geological regimes waveforms are extremely complicated yet observations made with frequency time analysis are robust and repeatable 1 group velocity and spectral amplitude measurements vary strongly across the studied region but display understandable systematics related to known tectonic features 2 both group velocity and spectral amplitude measurements across the knet array are generally similar at periods above 10s but differences are striking at shorter periods stacking methods dependent on waveform coherence across the network should only succeed at periods above 10 s for this large scale array 3 group velocity measurements for earthquakes and nuclear explosions that share a common wave path agree well but spectral amplitudes differ appreciably especially for rayleigh waves typically earthquake spectra are enriched in longer periods 12 20s relative to explosion spectra for events of the same magnitude 4 higher modes are observed on frequency time diagrams for rayleigh waves generated by earthquakes but are not observed for explosions 5 multipathing is observed in both frequency time diagrams and polarization analyses but again is qualitatively understandable in terms of known structural features in particular the channelling of love waves by the tarim basin is documented 6 large amplitude love waves are generated by nuclear explosions at lop nor indicative of significant tectonic release we discuss the relevance of the differences in spectral amplitudes between earthquakes and explosions and of the appearance of higher modes on earthquake frequency time diagrams to the problem of discriminating nuclear explosions from earthquakes

spectral discrimination between nts explosions and western united states earthquakes at regional distances spectral ratio disciminants are applied to 72 western united states earthquakes and 64 nts explosions recorded at four broadband seismic stations surrounding nts the ratio of the energy in the 1 to 2 and 6 to 8 hz bands for pn pg and lg is calculated and a simple distance correction applied to the data the spectral ratio appears to have potential as a disciminant at relatively small magnitudes 3 0 4 5 to 5 0 this may be due to uncertainties in the apparent source time function for explosions these complications may be due to changes in the dynamic response of the material in the near source region as a function of overburden pressure effects of secondary sources or to variations in regional phase excitation with depth

an investigation of the regional variations and frequency dependence of anelastic attenuation in the mantle under the united states in the 0 5 4 hz band summary studies of teleseismic p and s wave amplitudes and spectra in the 0 5 4 hz band show large variations in the attenuative properties of the upper mantle under the united states the data indicate that attenuation is greatest under the south western united states including but not confined to the basin and range province the lowest attenuation prevails under the north central shield regions the north eastern part of the country consisting of new england and possibly including a larger area along the eastern seaboard is characterized by moderate attenuation in the mantle the level of the high frequency energy in short period seismic waves and the differences between q values derived from short and long period data indicate that q is frequency dependent the form of frequency dependence of t compatible with the data in the 0 5 4 hz range does not allow a rapid decrease of t with increasing frequency rather it supports a gradual decrease covering the broader 0 1 4 hz range the curves of t versus frequency for shield to shield and mixed shield to western united states type paths are parallel with an average difference of 0 2 s in t in the short period band but may diverge towards the long period band for both curves t p is below 1 s for shield to shield paths t p must be below 0 5 s at 1 hz

organic matter characterization and distribution in sediments of the terminal lobes of the congo deep sea fan evidence for the direct influence of the congo river the terminal lobe complex of the congo river submarine fan sits on the abyssal atlantic plain at 5000 m water depth 760 km offshore from the river mouth estuarine area while most rivers deliver particulate material to the continental shelf particulate matter from the congo river largely bypasses the shelf and is transported by turbidity currents through the congo submarine canyon system we determined the quantity and quality of the organic matter reaching the terminal lobe complex at five sites with marked morphological differences that may influence the distribution of organic matter a suite of bulk geochemical oc 13corg 15n c n 137cs and palynofacies analyses were done on cores collected from the terminal lobe area these results were also compared to the composition of sediments collected upstream at the malebo pool congo river distal lobe complex sediments contain high amounts of terrestrial organic carbon 3 5 wt that is homogeneously distributed in surficial 22 cm and deeper sediments 580 cm silty clay facies strongly altered soil derived organic matter with well preserved land plant detritus from the congo river predominates a terrestrial soil origin for the particulate load was confirmed by the elevated 137cs activity in lobe sediments the vertical distribution of the 137cs signal suggests that there has been a massive arrival of terrestrial sediments since 1963 consistent with a turbiditic origin from the locations surveyed we estimate a maximum accumulation of terrestrial organic carbon of ca 1 kg oc m 2 y 1 for the distal lobe however transport modifies the organic matter both in terms of quantity and quality observed differences were attributed to preferential degradation of nitrogenous matter during diagenesis and to the addition of highly remineralized marine organic matter results from our temporal reference site e suggest that organic matter may be preserved in turbidite facies for thousands of years the good preservation state of the accumulated organic matter shows that turbiditic lobe complexes should be considered as a sink for terrestrial organic carbon in the deep ocean

spectral discrimination of nts explosions and earthquakes in the southwestern united states using high frequency regional data a high frequency seismic station has been operating since march 1987 near nelson nv records of earthquakes at regional distances from the station show substantially more energy at frequencies above 10 hz than records of nuclear tests of comparable magnitude on the nevada test site this contradicts the predictions made by investigators who have advocated high frequency monitoring for nuclear test detection and identification measuring the slopes of the pg velocity spectra between 4 and 30 hz successfully discriminates 11 nts explosions from 36 earthquakes recorded in the first seven months of operation the spectral differences may result from the respective source depths with the earthquakes occurring deeper and in faster material than the explosions

an evaluation of seismic decoupling and underground nuclear test monitoring using high frequency seismic data an effective solution to the problem of the detection and identification of low yield coupled and fully decoupled underground nuclear explosions appears available via use of high frequency seismic data ranging up to 30 or 40 hz in order to evaluate detection identification capabilities when using such data it is necessary to estimate 1 spectral characteristics and relative amplitudes of both p and s waves from explosions and earthquakes over the frequency band from 5 to 40 hz 2 signal transmission characteristics over this band through pertinent types of earth structure and 3 recording system and ground noise characteristics over this frequency band in this study each of these topics is considered in turn as they relate to detection and discrimination of the signals from low yield coupled and decoupled explosions in the regional and teleseismic distance ranges estimates of the capabilities of specific hypothetical networks to detect and identify insofar as signal to noise ratio is an important factor in identification explosions within the ussr are then considered these estimates of signal detection capability provide the central focus for the study as they serve to translate diverse and rather complex sets of observational data and theory into concrete predictions of monitoring capability following the assessment of detection capabilities the problem of identification of small events is considered with particular emphasis on discrimination at regional distances where the network is calculated to provide signals of high signal to noise ratio the principal results and conclusions of this study are as follows 1 seismic system noise can be suppressed to levels well below ground noise at quiet sites up to frequencies at least as high as 30 40 hz when using presently available hardware 2 average amplitudes of high frequency noise in a variety of geological environments are very low and change little with time or season 3 transmission of high frequency p and s wave signals in the regional distance range in stable continental areas and shields is nearly as efficient as at 1 hz with effective q factors in shield areas being about 9000 and 4000 for high frequency pn and sn respectively while the effective q for pn waves in tectonic areas is about 1000 4 a properly designed and deployed network of 25 simple three component nonarray stations internal to the ussr and 15 similar stations surrounding the ussr is predicted to be capable of multistation detection at high signal to noise ratio of fully decoupled 1 kt explosions located at all potential decoupling sites within the ussr 5 by inference from the quantitative agreement of empirical observations and theoretical predictions when using lower frequency data over a great range of explosion yields we conclude that procedures based on the use of both detectable p and s waves will serve to identify explosion generated seismic signals at least as small as those expected from a fully decoupled 1 kt explosion

models of the upper mantle beneath the central north island new zealand from speeds and anisotropy of subhorizontal p waves pn 1 the central north island of new zealand shows significant variations in pn wave speeds over small distances ranging from 8 5 0 2 km s to 7 4 0 1 km s over a distance of 150 km a combination of national network seismometers local volcanic seismic monitoring networks and temporary deployments are used to collect arrival times from local events during the period of 1990 2006 the data set consists of approximately 11 200 pn observations from 3000 local earthquakes at 91 seismograph sites we have created a method that allows us to model the predominant wavelength features of p wave speeds in the uppermost mantle as well as estimating values of mantle anisotropy and irregularities in the crust beneath stations using least squares collocation the resulting model shows distinct variations in uppermost mantle pn velocities velocities of less than 7 5 km s are found beneath the back arc extension region of the central volcanic region and under the taranaki volcanic region indicating the presence of water and partial melt the region to the east shows extremely high velocities of 8 3 8 5 km s where the p waves are traveling within the subducting pacific slab slightly lower than normal mantle velocities of 7 8 8 1 km s are found in the western north island suggesting a soft mantle pn anisotropy estimates throughout the north island show predominately trench parallel fast directions ceasing to nulls in the west anisotropy measurements indicate the strain history of the mantle null anisotropy measurements suggest an undisturbed mantle suggesting that mantle beneath the western north island is young

roughness at the base of the seismogenic zone contributing factors the cutout depth of microseismic activity in continental fault zones appears to correspond to the onset of greenschist metamorphic conditions at about 300 c it can generally be modeled as the transition from frictional to quasi plastic behavior in quartzofeldspathic crust shear resistance increases with depth through the frictional regime to peak at the transition beneath which it falls off exponentially with increasing temperature larger earthquake ruptures ml 5 5 nucleate around this transition depth where the highest concentrations of strain energy may accumulate varying depth and amplitude of the peak shear resistance along strike induce fluctuations in strain energy concentration at the base of the seismogenic zone factors affecting the depth of the transition include crustal composition geometry and mode of faulting fluid pressure levels in the frictional regime and water content in the quasi plastic regime quasi plastic strain rate and geothermal gradient evaluation of their relative importance is complicated because several are interdependent however compositional change may cause abrupt irregularities in seismogenic depth and peak shear resistance while regional variations in heat flow look to be particularly effective in creating long wavelength heterogeneities in strain energy concentration affecting faulting style

spatial and temporal patterns of benthic macrofaunal communities on the deep continental margin in the gulf of guinea abstract density taxonomic composition at higher taxon level and vertical distribution of benthic macrofaunal communities and sediment characteristics pore water nitrogen organic carbon sulfur c n ratio n alcohol biomarkers were examined at three deep sites on the congo gabon continental margin this study was part of the multidisciplinary biozaire project that aimed at studying the deep benthic ecosystems in the gulf of guinea sampling of macrofaunal communities and of sediment was conducted during three cruises january 2001 december 2001 and december 2003 at two downslope sites 4000 m depth one located near the congo submarine channel 15 km in the south and the other one far from the channel 150 km in the south the third area located 8 km north of the congo channel in the surroundings of a giant pockmark at 3160 m depth was sampled during one cruise in december 2003 at these three locations the macrofaunal communities presented relatively high densities 327 987 ind 0 25 m 2 compared with macrofaunal communities at similar depths that is due to high levels of food input related to the congo river and submarine system activities that affect the whole study area the communities were different from each other in terms of taxonomic composition at higher taxon level phylum class order for all the groups except for the polychaetes classified into families the polychaetes dominated the communities and were responsible for the increase in densities observed at both deep sites 4000 m between january 2001 and december 2003 whereas the tanaidaceans the isopods and the bivalves were the other most abundant taxa responsible for the spatial differences between these sites the community at 3150 m differed from the two deep communities by higher abundances in bivalves nemerteans and holothuroids the composition of the polychaete community also differed among sites in the vicinity of the congo channel the expected positive effect of the additional organic matter transported through the turbiditic currents on to the surrounding benthic communities was not observed as the increase in densities during the study period was higher at the site located away from the congo channel than near the channel 80 vs 30 that may be due to the low food value of the organic matter of terrestrial origin carried through the turbidites and or to the disturbance caused by these turbidites conversely far from the channel the macrofaunal communities benefit from organic matter of higher energetic value originating mainly from marine sources but also from continental sources carried by the congo plume or by near bed currents across or along the continental slope spatial and temporal variability in trophic and physical characteristics of the sediment habitat at both deep sites also affected the vertical distribution of the macrofaunal communities the activities of the very active congo system structure the deep macrofaunal communities on a large area in terms of densities composition and vertical distribution the food input is enhanced at regional scale as well as the heterogeneity of the sediment characteristics mainly in terms of organic matter quality marine vs terrigenous in turn the densities are enhanced as well as the regional diversity of the macrofaunal communities in terms of taxonomic composition and distribution

analysis of seismic discrimination capabilities using regional data from western united states events additional studies have been conducted to help verify the findings of previous investigations cf murphy and bennett 1982 which indicated that spectral differences in short period regional phases may be diagnostic of source type for nevada test site nts explosions and nearby earthquakes recorded at tonto forest observatory in arizona regional phase signals from two additional stations the uinta basin observatory array in utah and the blue mountains observatory array in oregon and from supplemental events including aftershocks of the 1966 caliente nevada earthquake have been analyzed these stations are at epicentral distances of 430 to 530 km for tonto forest observatory 520 to 670 km for uinta basin observatory and 870 to 880 km for blue mountains observatory with the near ranges representing the distances to the caliente source area and the far ranges to the average nts source receiver distances this enhanced data base included 50 earthquakes within about 150 km of nts and 35 nts explosions recorded at one or more stations the events cover a magnitude range from about 2 8 to 5 2 mb with the majority of earthquakes concentrated in the lower half of that range the current investigation essentially corroborated our previous findings that comparison of simple peak amplitude measurements of regional p and lg phases did not consistently discriminate between earthquakes and explosions this discriminant breakdown appears to be related to variability in excitation of regional phases from similar sources which has been dramatically illustrated by observations from the 1966 caliente aftershocks these events produced large variations in the relative amplitudes of pg and lg signals even though the events were spatially restricted to a small zone in contrast the lg spectral ratio discriminant measure defined in the previous study continued to provide reliable distinction between the earthquake and explosion sources for data observed at all three stations the discrimination capability of the spectral ratio prevails in spite of the evident mechanism variability between earthquakes and shifts in the discrimination threshold between stations apparently related to attenuation differences along the propagation paths

attenuation in western nevada preliminary results from earthquake and explosion sources we present preliminary results from a study of the attenuation of regional seismic waves at frequencies between 1 and 15 hz and distances up to 250 km in western nevada following the methods of anderson and hough 1984 and hough et al 1988 we parameterize the asymptote of the high frequency acceleration spectrum by a two parameter model we relate the model parameters to a two layer model for qi and qd the frequency independent and the frequency dependent components of the quality factor we comparing our results to previously published q studies in the basin and range and find that our estimate of total q qt in the shallow crust is consistent with shear wave q at close distances as determined by chavez and priestley 1985 for depths greater than 5 km we obtain a qt which is consistent with previous estimates of coda q singh and herrmann 1983 and lgq chavez and priestley 1986 suggesting that both coda q and lgq are insensitive to near surface contributions to attenuation in addition to our attenuation results we compare the high frequency content of explosions with that of earthquakes our results from s waves are similar to results for pg waves by chael et al 1987 and chael 1988 who find that the pg wave spectra from explosions are depleted in high frequency energy with respect to earthquake spectra taylor et al 1988 look at spectral energy at 1 2 hz compared to energy at 6 8 hz for earthquakes and explosions and find especially for lg waves relative depletion of the higher frequencies for explosion sources this result is also consistent with the results from this study

slopes of p to s wave spectral ratios a broadband regional seismic discriminant and a physical model concerns about nuclear proliferation and negotiations toward a comprehensive test ban treaty ctbt emphasize the need for robust seismic monitoring and regional discrimination capabilities especially at low magnitudes standard regional discrimination techniques have many shortcomings for example they cannot always discriminate shallow low magnitude earthquakes or mining related events i show that slopes of p to s wave spectral ratios can be used to discriminate shallow and normal depth earthquakes from explosions and possibly to discriminate explosions from mining related rockburst or collapse events p to s wave slopes and conventional high frequency p to s wave spectral amplitude ratios discriminate even better in combination than alone a comparison of pn and lg spectra from nevada test site nts explosions and earthquakes shows that this method discriminates concentrated explosions from earthquakes and other shallow seismic events such as mine collapses because s waves from explosions decay more rapidly at high frequencies than do s waves from earthquakes spectra of one dimensional reflectivity synthetic seismograms show that frequency dependent attenuation of explosion generated p to s wave converted phases in the near surface layers may be responsible for the differences in lg s wave spectral falloff these simulations also show that absolute amplitudes of earthquake p to s wave spectral ratios are very sensitive to mechanism and depth which may help explain the variable performance of conventional methods

early diagenesis in the congo deep sea fan sediments dominated by massive terrigenous deposits part i oxygen consumption and organic carbon mineralization using a micro electrode approach abstract organic matter om transfer from the continent to the ocean occurs across margins which constitute a major area of om recycling and burial the lobe complex of the congo deep sea fan is connected to the river mouth by a canyon and alimented by recurrent turbidity currents containing a large proportion of labile terrigenous om and producing high sedimentation rates these inputs support the development of ecosystems harboring rich assemblages of vesicomyid bivalves and bacterial mats called habitats here we present o2 microprofiles and diffusive oxygen uptake rates dous obtained during the congolobe project at six sites of this active lobe complex by in situ and on board methods based on micro electrode profiling the dataset is used to determine remineralization rates and study the biogeochemical dynamics of different ecosystems of the lobe area in order to compare levee and background sediments to the habitats developed on the flanks of the main turbiditic channel levee and background sediments are characterized by significantly higher dous than abyssal sediments at 5000 m meters depth 2 5 mmol o2 m 2 d 1 versus 1 5 2 5 mmol o2 m 2 d 1 and the habitats are hotspots of om remineralization with dou values ranging between 8 and 40 mmol o2 m 2 d 1 by comparing sites near the active channel to a site located 50 km away we show that the lobe connection to the main turbiditic channel is vital to the dense benthic communities

stress and strain from earthquakes at the southern termination of the taupo volcanic zone new zealand abstract we use first motion polarity data from small earthquakes recorded by a recent dense seismograph deployment to determine 16 new focal mechanisms at the southern termination of the taupo volcanic zone tvz these crustal earthquakes are between 11 km and 41 km deep and have focal mechanisms which range from normal to strike slip we then combine these focal mechanism data with previously determined focal mechanisms to investigate earthquake strain directions a prominent feature of the combined data is the consistency of the t axes which indicates that subhorizontal nnw extensional strain predominates at all depths in the crust at the southern termination of the tvz we then use all currently available first motion data to invert for the stress tensor orientation first motion data from earthquakes throughout the crust show a consistent minimum principal stress 3 orientation which is subhorizontal and oriented nw the 3 azimuth that we observe 316 is perpendicular to the strike of recent aligned vents in the southern tvz very similar to the extension direction in the ruapehu segment of the tvz determined from structural data and consistent with the 3 direction determined from a stress inversion using crustal earthquakes in the central tvz north of lake taupo this suggests that the stresses driving the opening of the tvz continue to be active at its southern termination the stress and strain results combined with the earthquake distribution are consistent with a model where the tvz is only the present day surface expression of an extensive region of active mantle corner flow that is progressively eroding thicker crust to the south we also investigate the temporal evolution of stress around mt ruapehu the southernmost large andesitic volcano in the tvz given previous suggestions that this may change during the eruption cycle we find no major change in the stress tensor orientation at the time of the 1995 eruption using first motion data from earthquakes 15 20 km from the volcano

early diagenesis in the sediments of the congo deep sea fan dominated by massive terrigenous deposits part ii iron sulfur coupling abstract deep sea fans are well known depot centers for organic carbon that should promote sulfate reduction at the same time the high rates of deposition of unconsolidated metal oxides from terrigenous origin may also promote metal reducing microbial activity to investigate the eventual coupling between the iron and sulfur cycles in these environments shallow sediment cores

analysis of high frequency pg lg ratios from nts explosions and western u s earthquakes the high frequency pg lg discriminant is studied between frequencies of 0 5 and 10 hz using 294 nts explosions and 114 western u s earthquakes recorded at four broadband seismic stations operated by lawrence livermore national laboratory the stations are located at distances of about 200 to 400 km from the nevada test site nts event magnitudes ranged from about 2 5 to 6 5 and propagation paths for the earthquakes range from approximately 175 to 1300 km the discriminant is shown to be very effective and displays improved separation between earthquakes and explosions as frequency is increased because of propagation effects it is important to apply distance corrections directly to the amplitude ratios or to the magnitude corrected amplitudes prior to computing the ratios multivariate discrimination analysis using both maximum likelihood gaussian classifiers and a backpropagation neural network show that approximately 95 of the events can be correctly identified both classification procedures were designed to handle missing data filled in using a nearest neighbor algorithm except for a few notable exceptions most of the earthquake misclassifications occur for mb 4 which is expected for events having reduced signal to noise ratios all of the explosion misclassifications occur for mb 4 suggesting a source or near source effect rather than an effect of poor signal to noise ratio the explosions that were misclassified were typically of magnitude large enough to be classified correctly by mb ms or love wave energy the main drawback of the pg lg discriminant is that because of signal to noise considerations and propagation effects the number of measurements are reduced considerably at higher frequencies it is expected that the problem will be amplified as magnitudes are reduced and event receiver distances are increased

in situ fluxes and zonation of microbial activity in surface sediments of the hakon mosby mud volcano from the hakon mosby mud volcano hmmv on the southwest barents sea shelf gas and fluids are expelled by active mud volcanism we studied the mass transfer phenomena and microbial conversions in the surface layers using in situ microsensor measurements and on retrieved cores the hmmv consists of three concentric habitats a central area with gray mud a surrounding area covered by white mats of big sulfide oxidizing filamentous bacteria beggiatoa and a peripheral area colonized by symbiontic tube worms pogonophora a fourth habitat comprised gray microbial mats near gas seeps the differences between these four methane fueled habitats are best explained by different transport rates of sulfate into the sediments and pore water upflow rates the upflow velocities were estimated by two independent methods at 3 6 m yr21 in the central area and 0 3 1 m yr21 in beggiatoa mats in the central area no sulfide was found indicating that the rapidly rising sulfate free fluids caused sulfate limitation that inhibited anaerobic oxidation of methane aom under beggiatoa mats a steep sulfide peak was found at 2 to 3 cm below the seafloor bsf most likely due to aom all sulfide was oxidized anaerobically possibly through nitrate reduction by beggiatoa the beggiatoa mats were dominated by a single filamentous morphotype with a diameter of 10 mm and abundant sulfur inclusions a high diversity of sulfide oxidizer morphotypes was observed in a grayish microbial mat near gas vents where aerobic sulfide oxidation was important the sediments colonized by pogonophora were influenced by bioventilation allowing sulfate penetration and aom to 70 cm bsf the hmmv is a unique and diverse ecosystem the structure and functioning of which is mainly controlled by pore water flow

distinguishing between stress induced and structural anisotropy at mount ruapehu volcano new zealand 1 we have created a benchmark of spatial variations in shear wave anisotropy around mount ruapehu new zealand against which to measure future temporal changes anisotropy in the crust is often assumed to be caused by stress aligned microcracks and the polarization of the fast quasi shear wave is thus interpreted to indicate the direction of maximum horizontal stress but can also be due to aligned minerals or macroscopic fractures changes in seismic anisotropy have been observed following a major eruption in 1995 96 and were attributed to changes in stress from the depressurization of the magmatic system three component broadband seismometers have been deployed to complement the permanent stations that surround ruapehu creating a combined network of 34 three component seismometers this denser observational network improves the resolution with which spatial variations in seismic anisotropy can be examined using an automated shear wave splitting analysis we examine local earthquakes in 2008 we observe a strong azimuthal dependence of and so introduce a spatial averaging technique and two dimensional tomography of recorded delay times the anisotropy can be divided into regions in which agrees with stress estimations from focal mechanism inversions suggesting stress induced anisotropy and those in which is aligned with structural features such as faults suggesting structural anisotropy the pattern of anisotropy that is inferred to be stress related cannot be modeled adequately using coulomb modeling with a dike like inflation source we suggest that the stress induced anisotropy is affected by loading of the volcano and a lithospheric discontinuity

crustal seismicity in taranaki new zealand using accurate hypocentres from a dense network a large dense network of three component broad band seismographs was used to determine accurate hypocentres for earthquakes in taranaki new zealand they allow us to characterize seismicity around mt taranaki a large dormant andesite cone volcano and to map precisely two major lineations of crustal seismicity a minimum 1 d velocity model was used to locate 389 local earthquakes using the probabilistic non linear earthquake location program nonlinloc there are few earthquakes beneath mt taranaki itself and all are relatively small and shallow 10 km deep the shallow seismogenic zone can be explained by the crust being unusually hot thus causing the base of the brittle ductile transition to be shallower than normal beneath mt taranaki this is supported by a high heat flow anomaly in this area the absence of any volcanic earthquakes beneath mt taranaki suggests that active volcanic processes are currently unlikely and the shallow brittle ductile transition depth means that precursory volcano tectonic seismicity from any future magmatic intrusion is unlikely to occur below 10 km depth the permanent seismic network can locate earthquakes in taranaki reasonably accurately and can reproduce most of the details seen by the temporary seismograph deployment provided that only the best hypocentres are considered however beneath mt taranaki which is the most important area for volcano monitoring hypocentres determined by the permanent network are too deep by 4 12 km the active cape egmont fault zone cefz west of mt taranaki is the most seismically active area with earthquakes in the upper crust to about 22 km depth spatial and temporal clustering earthquakes with similar waveforms and an absence of obvious main shocks imply that earthquake swarms make up a significant proportion of the seismicity in this area earthquakes in eastern taranaki occur primarily along the taranaki ruapehu line trl thought to be a major boundary across which the crustal thickness changes by about 10 km these earthquakes are less clustered have a b value typical of tectonic earthquakes and occur in the lower crust to a depth of 35 km with the upper crust almost aseismic the abrupt cessation of seismicity at 35 km depth is consistent with this boundary marking the moho with no earthquakes in the mantle the concentration of earthquakes in the lower crust requires it to be drier and more mafic than the wet quartzo feldspathic composition often used to model crustal rheology there is no change in maximum earthquake depth across the currently accepted location of the trl but there is a 10 km decrease in maximum earthquake depth some 25 km to the north of the currently accepted location this suggests that the true position of the trl is 25 km north of the hitherto accepted position

three dimensional tomographic imaging of the taranaki volcanoes new zealand 3 d models of the p wave velocity vp the ratio of p to s wave velocity vp vs and the p wave quality factor qp are determined for the crust in taranaki new zealand using local tomography and data from a dense network average spacing 5 km of 68 three component broad band seismographs vp and vp vs models were determined by jointly inverting p traveltimes and s p traveltime intervals and a qp model by inverting t t qp observations derived from modelling the velocity amplitude spectrum of p wave arrivals an approximately 5 km diameter region of high vp and low vp vs beneath the taranaki volcanoes extends from the surface to a depth of about 10 km and images the roots of the volcanoes formed by successive magmatic intrusions at mt taranaki this will probably be the path through which future magma intrusions will reach the surface we are unable to image any magma storage within the upper 16 km of the crust as the volumes involved are probably smaller than the 5 km resolution of our models the volcanoes sit in the taranaki basin a large sedimentary basin characterized by low vp c 4 km s 1 and high vp vs 1 9 attributed to unconsolidated water saturated sediments and these are underlain by basement rocks with vp 5 km s 1 and vp vs 1 7 there is a c 20 per cent contrast in vp across the taranaki fault at the eastern boundary of the taranaki basin and a small shallow high vp vs 2 0 anomaly above the seismically active cape egmont fault zone west of the taranaki volcanoes although the qp model is of significantly lower resolution than the vp and vp vs models it shows a low qp anomaly c 100 between 4 and 10 km depth that corresponds to the deepest onshore part of the taranaki basin

contemporary horizontal velocity and strain rate fields of the pacific australian plate boundary zone through new zealand we have inverted velocity solutions from nine geodetic networks distributed across new zealand to derive present day continuous horizontal velocity and strain rate fields at the earth s surface throughout the country the nine networks contain a total of 362 global positioning system gps stations that have been observed at least twice and at least a year apart between 1991 and 1998 the model velocity field is expanded as bicubic spline interpolation functions defined within a curvilinear grid that covers the country and extends into the assumed rigid australian and pacific plates to west and east the inversion jointly minimizes the magnitudes of fitted strain rates and the misfit to the observed velocity data the spline technique allows high spatial resolution of strain rate variations especially in regions with spatially dense gps data expansion of the model velocity field on the surface of a sphere allows arbitrarily large areas to be studied previously known aspects of new zealand plate boundary deformation are highlighted with improved resolution including back arc extension in the taupo volcanic zone rotation of the hikurangi forearc away from this zone in the north island and a band of high shear strain rate under the southern alps to the southeast of the alpine fault our results reveal several new features including a region of enhanced shear straining apparently associated with strike slip faults in the southern north island and a band of contractional straining subparallel and well east of the alpine fault that is similar to features found in numerical and sandbox models of continental collision

geochemical and biological recovery of the disturbed seafloor in polymetallic nodule fields of the clipperton clarion fracture zone ccfz at 5 000 m depth environmental data were obtained on the nodule fields of the clipperton clarion fracture zone at 5 000 m depth in june 2004 during the nodinaut cruise the long term effects of physical disturbance made by a dredge 26 yr ago on the sediment were investigated we focused our study on its track which is still visible on the bottom the first major consequence of the passage of this equipment was to remove 4 cm 6 0 5 cm of superficial sediment the physical and chemical properties of this disturbed sediment sampled in the track did not change significantly over time and has not shown any recovery since the disturbance however an exception was observed for depth variations of manganese concentration in the sediment which were similar in the track to those in the surrounding undisturbed sediment and can be explained by the diffusion over time of oxygen from the sea water on the other hand the biological activity measured in the track with the respirometer rap2 carried by the submersible nautile did not differ from the unperturbed site which suggests that the benthic fauna has completely recovered as have nutrient fluxes at the water sediment interface

discrimination of earthquakes and explosions in the eastern united states using regional high frequency data high frequency regional records from small earthquakes 1 3 magnitude 4 and comparable magnitude explosions are analyzed to find a reliable seismic discriminant in the eastern u s over 500 digital vertical component seismograms recorded by the new york state seismic network in the distance ranges 10 to 610 km are used mean p lg spectral ratios in the band 1 25 hz are about 0 5 and 1 25 for earthquakes and explosions respectively in the eastern united states we find that the high frequency p lg spectral amplitude ratio in the frequency band 5 25 hz is a reliable and robust discriminant for classifying these events a linear discriminant function analysis indicates that the p lg spectral amplitude ratio method provides discrimination power with a total misclassification probability of about 1 single hole instantaneous explosions and ripple fired quarry blasts have somewhat different p lg spectral ratios but as a group are distinctly different from earthquakes

cold seep like macrofaunal communities in organic and sulfide rich sediments of the congo deep sea fan methane rich fluids arising from organic matter diagenesis in deep sediment layers sustain chemosynthesis based ecosystems along continental margins this type of cold seep develops on pockmarks along the congo margin where fluids migrate from deep buried paleo channels of the congo river acting as reservoirs similar ecosystems based on shallow methane production occur in the terminal lobes of the present day congo deep sea fan which is supplied by huge quantities of primarily terrestrial material carried by turbiditic currents along the 800 km channel and deposited at depths of up to nearly 5000 m in this paper we explore the effect of this carbon enrichment of deep sea sediments on benthic macrofauna along the prograding lobes fed by the current active channel and on older lobes receiving less turbiditic inputs macrofaunal communities were sampled using either usnel cores on the channel levees or rov blade cores in the chemosynthesis based habitats patchily distributed in the active lobe complex the exceptionally high organic content of the surface sediment in the active lobe complex was correlated with unusual densitiesof macrofauna for this depth enhanced by a factor 7 to 8 compared with those of the older abandoned lobe whose sediment carbon content is still higher than in angola basin at same depth macrofaunal communities dominated by cossurid polychaetes and tanaids were also more closely related to those colonizing low flow cold seeps than those of typical deep sea sediment in reduced sediments microbial mats and vesicomyid bivalve beds displayed macrofaunal community patterns that were similar to their cold seep counterparts with high densities low diversity and dominance of sulfide tolerant polychaetes and gastropods in the most sulfidic habitats in addition diversity was higher in vesicomyid bivalve beds which appeared to bio irrigate the upper sediment layers high beta diversity is underscored by the variability of geochemical gradients in vesicomyid assemblages and by the vesicomyid population characteristics that vary in density size and composition by modifying the sediment geochemistry differently according to their morphology and physiology the different vesicomyid species play an important role structuring macrofauna composition and vertical distribution dynamics of turbiditic deposits at a longer temporal scale thousands of years and their spatial distribution in the lobe area also resulted in high heterogeneity of the cold seep like communities dynamics of chemosynthetic habitats and associated macrofauna in the active lobe area 2 please note that this is an author produced pdf of an article accepted for publication following peer review the definitive publisher authenticated version is available on the publisher web site resembled those previously observed at the regab pockmark along the congo margin and rapid succession is expected to cope with high physical disturbance by frequent turbiditic events and huge sedimentation rates finally we propose a model of the temporal evolution of these peculiar habitats and communities on longer timescales in response to changes in distributary channels within the lobe complex

subduction evolution and mantle dynamics at a continental margin central north island new zealand 1 central north island new zealand provides an unusually complete geological and geophysical record of the onset and evolution of subduction at a continental margin whereas most subduction zones are innately two dimensional north island of new zealand displays a distinct three dimensional character in the back arc regions specifically we observe mariana type subduction in the back arc areas of central north island in the sense of back arc extension high heat flow prolific volcanism geothermal activity and active doming and exhumation of the solid surface evidence for emplacement of a significant percent of new lithosphere beneath the central north island comes from heat flux of 25 mw km of strike of volcanic zone and thinned crust underlain by rocks with a seismic wave speed consistent with underplated new crust seismic attenuation qp 1 is high 240 and rhyolitic and andesitic volcanism are widespread almost complete removal of mantle lithosphere is inferred here in pliocene times on the basis of the rock uplift history and upper mantle seismic velocities as low as 7 4 0 1 km s in contrast southwestern north island exhibits chilean type back arc activity in the sense of compressive tectonics reverse faulting low heat flow thickened lithosphere and strong coupling between the subducted and overriding plates this rapid switch from mariana type to chilean type subduction occurs despite the age of the subducted plate being constant under north island moreover stratigraphic evidence shows that processes that define the extensional back arc area the central volcanic region are advancing southward into the compressional system wanganui basin at about 10 mm yr we link the progression from one system to another to a gradual and viscous removal of thickened mantle lithosphere in the back arc regions thickening occurred during the miocene within the taranaki fault zone the process of thickening and convective removal is time and temperature dependent and has left an imprint in both the geological record and geophysical properties of central north island which we document and describe

fault slip accumulation in an active rift over thousands to millions of years and the importance of paleoearthquake sampling abstract the catastrophic earthquakes that recently september 4th 2010 and february 22nd 2011 hit christchurch new zealand show that active faults capable of generating large magnitude earthquakes can be hidden beneath the earth s surface in this article we combine near surface paleoseismic data with deep 1 ma timescales in the taranaki rift new zealand our analysis shows that the integration of different timescale datasets provides a basis for identifying active faults not observed at the ground surface estimating maximum fault rupture lengths inferring maximum short term displacement rates and improving earthquake hazard assessment we find that fault displacement rates become increasingly irregular both faster and slower on shorter timescales leading to incomplete sampling of the active fault population surface traces have been recognised for

organic carbon turnover time in deep sea benthos abstract the ratio of organic carbon supply to the deep sea floor estimated with sediment traps to total benthic biomass in terms of organic carbon concentration was used to calculate average turnover or residence times for the benthic community over a broad depth interval in the western north atlantic ratios indicate that the biomass carbon turns over on average time scales of months with little predictable variation over the depth interval 70m to 5300m detrital organic carbon in sediments at the same stations turned over on scales of years to centuries the shortest detrital carbon turnover was just over 8 years in a sandy continental shelf environment versus 609 years at 5 3km depth on the hatteras abyssal plain the turnover time estimates calculated with poc fluxes were assessed by comparing poc fluxes with estimates of total community respiration at each location the poc flux rates were greater than the sediment oxygen demand flux rates in mg carbon m 2d 1 and the disparity was much greater in the deep sea than on the continental margin we suggest that this difference is primarily the result of a decline in the quality of the organic compounds in the rain of sinking poc rather than physiological responses to cold or pressure this implies that caution must be used when interpreting the relationships between the total organic carbon fluxes measured with sediment traps at great depths and rates of metabolic processes

spectral evidence for source multiplicity in explosions application to regional discrimination of earthquakes and explosions abstract spectral and cepstral analysis were performed on regional array noress recordings of mining explosions in scandinavia and russia in order to detect the effects of delayed explosions or ripple firing commonly used in mine blasting practice noress array stacked spectra corrected for instrument and noise were computed in windows on pn pg sn and lg waves from the mine blasts by averaging individual channel spectra frequency by frequency across the array for comparison spectra were also computed for six western norway earthquakes located near the blasjo and titania norwegian mines also stack spectra of p coda sn and lg were computed using norsar seismograms for presumed peaceful nuclear explosions pnes located at near regional distances 10 in western russia the norsar spectra were determined in the same manner as the noress spectra except that an individual source correction was applied to the spectra comparison of western norway mine blast spectra and nearby earthquakes shows that the earthquake pn spectra are peaked in the 8 to 16 hz band with little energy below 6 hz whereas the explosion spectra have flatter spectra from 3 to 16 hz this difference in the pn spectra may be caused by the earthquakes occurring at greater depths than the explosions differences in the near source media or source mechanism effects in the earthquake spectra the main difference between earthquake and explosion spectra is that the explosion spectra exhibit marked scalloping or modulation patterns not observed in the earthquake spectra the modulation patterns are identical in spectra of all phases indicating that they are caused by multiple shot sequences or ripple firing simulated multiple source spectra determined using the noress seismograms for one of the western norway earthquakes resulted in spectra that resembled many of the explosion modulation patterns based on the simulation studies and cepstral analysis of the spectra the mine explosions appear to be composed of two to three separate explosions delayed by between 80 to 150 msec moreover the norsar spectra of pnes indicate that these signals are also produced by multiple explosions although they have larger delay times of between 0 9 to 1 5 sec these results show that spectral modulations in seismogram spectra of economic explosions including mine explosions and nuclear explosions fired for peaceful economic purposes can be used to distinguish them from earthquakes and nuclear explosion weapons tests

probabilistic earthquake location in complex three dimensional velocity models application to switzerland 1 we present a new approach to determine precise and reliable hypocenter locations in the tectonically complex region of switzerland a three dimensional 3 d p wave velocity model to be used for earthquake relocation is obtained by simultaneously inverting arrival times of local earthquakes for hypocenter locations and 3 d p wave velocity structure a 3 d p wave velocity model derived from controlled source seismology css is used as an initial reference model the final 3 d model thus combines all available information from both css and local earthquake data the probabilistic nonlinear formulation of the earthquake location problem includes a complete description of location uncertainties and can be used with any kind of velocity model in particular the combination of nonlinear global search algorithms such as the oct tree importance sampling with probabilistic earthquake location provides a fast and reliable tool for earthquake location the comparison of hypocenter locations obtained routinely by the swiss seismological service sed to those relocated in the new 3 d velocity model using a probabilistic approach reveals no systematic shifts but does exhibit large individual shifts in some epicenter locations and focal depths we can attribute these large shifts in part to large uncertainties in the hypocenter location events with a low number of observations 8 and no observation within the critical focal depth distance typically show large location uncertainties improved hypocentral locations particularly for mine blasts and earthquakes whose routine hypocenter locations had been questionable confirm that improved velocity model and probabilistic earthquake location yield more precise and reliable hypocenter locations and associated location uncertainties for switzerland

fundamental and higher mode rayleigh wave characteristics of ambient seismic noise in new zealand 1 in order to use ambient seismic noise for mapping earth s structure it is important to understand the spatiotemporal characteristics of the noise field this study uses data collected during four austral winter months of 2002 to investigate new zealand s ambient seismic noise field in the double ocean wave frequency range 0 1 0 3 hz it is shown via beamforming analysis that there are two distinct dispersive waves in the data these waves can be separated their estimated phase velocities 2 5 2 and 4 3 km s in the frequency range 0 14 0 25 hz match well with fundamental and higher mode rayleigh dispersion curves studies of double wave frequency microseisms elsewhere generally show the rayleigh noise fields to be dominated by fundamental mode waves the reason why higher mode signals are observed here may reflect a combination of long ocean wave periods large waveheights the direct deep water approach to narrow continental margins and the proximity of the seismograph array to the source regions citation brooks l a j townend p gerstoft s bannister and l carter 2009 fundamental and higher mode rayleigh wave characteristics of ambient seismic noise in new zealand geophys res lett 36 l23303 doi 10 1029 2009gl040434

new gastropods from deep sea hydrocarbon seeps off west africa thirteen new species of gastropods are described from the zairov 1 2 and biozaire 1 3 cruises to the methane seeps off the congo river patellogastropoda paralepetopsis sasakii sp nov neolepetopsidae cocculiniformia pyropelta oluae sp nov and p sibuetae sp nov pyropeltidae tentaoculus granulatus sp nov pseudococculinidae neomphalina leptogyra costellata sp nov family uncertain vetigastropoda puncturella similis sp nov fissurellidae lepetodrilus shannonae sp nov lepetodrilidae caenogastropoda provanna reticulata sp nov and p chevalieri sp nov cordesia provannoides gen et sp nov provannidae phymorhynchus coseli sp nov and p cingulata sp nov conidae heterobranchia hyalogyrina rissoella sp nov hyalogyrinidae all species except t granulatus from a settlement trap belong to groups known from cold seeps and the entire seep fauna here is new to science biogeographical affinity of this gastropod fauna is to the west atlantic seeps not to the mediterranean seeps or mid atlantic vents fragments of the autecology of the species are presented the evolution of the seep gastropod fauna is briefly discussed and a continuous immigration of taxa is supported the oldest verified occurrences of modern taxa in the seeps date back to cenomanian cretaceous time while some taxa seem not to appear until very late tertiary

carbon and silica megasink in deep sea sediments of the congo terminal lobes carbon and silicon cycles at the earth surface are linked to long term variations of atmospheric co2 and oceanic primary production in these cycles the river sea interface is considered a biogeochemical hotspot and deltas presently receive and preserve a major fraction of riverine particles in shallow water sediments in contrast periods of glacial maximum lowstand were characterized by massive exports of sediments to the deep sea via submarine canyons and accumulation in deep sea fans here we calculate present day mass balances for organic carbon oc and amorphous silica asi in the terminal lobe complex of the congo river deep sea fan as an analogue for glacial periods we show that this lobe complex constitutes a megasink with the current accumulation of 18 and 35 of the oc and asi river input respectively this increases the estimates of organic carbon burial by 19 in the south atlantic ocean in a zone representing less than 0 01 of the basin these megasinks might have played a role in carbon trapping in oceanic sediments during glacial times

continental fault structure and the shallow earthquake source plate boundaries in continental crust are generally less sharply defined than in the oceans with seismicity spread over broad areas interplate displacements appear to be largely accommodated by networks of major fault zones a simple 2 level model for these important structures accounts for the depth distribution of most continental earthquakes and for the observed range of faulting styles and associated rock deformation textures the model consists of a seismogenic frictional slip regime overlying quasi plastic mylonite belts wherein shearing is largely accommodated aseismically due mainly to the changing response of quartz to deformation with increasing temperature shear resistance increases with depth to a peak value in the vicinity of the frictiona1 quasi plastic transition and then decreases rapidly the depth to which microseismic activity extends appears inversely related to regional heat flow and can be satisfactorily modelled as the frictional quasi plastic transition for different geotherms using laboratory determined flow laws for quartz bearing rocks larger earthquake ruptures m 5 5 tend to nucleate near the base of the seismogenic regime in the region inferred to have the highest shear resistance and concentration of distortional strain energy consideration is also given to the depression of isotherms and seismic activity in regions of thrusting and to the question of the downward continuation of major fault zones through the lithosphere decoupling of the upper crust on flat lying shear zones may accompany higher level dip slip and perhaps in some circumstances strike slip faulting being favoured by above average continental heat flow and a high quartz content in the middle or deep crust the average level of deviatoric stress within the seismogenic regime remains an outstanding problem

seafloor oxygen consumption fuelled by methane from cold seeps the leakage of cold methane rich fluids from subsurface reservoirs to the sea floor sustains some of the richest ecosystems on the sea bed these cold seep communities consume around two orders of magnitude more oxygen than the surrounding sea floor as a result of the microbial consumption of seep methane

an analysis of spectral differences between nevada test site and shagan river nuclear explosions spectral ratio discrimination studies carried out on events located in the western united states and soviet union s u illustrate that pronounced differences in radiated explosion source spectra relative to nearby earthquakes exist between the two regions nevada test site nts explosions are characterized by the existence of more low frequency and or less high frequency energy greater low to high frequency spectral ratios than western u s earthquakes the opposite pattern is observed in the s u with nuclear explosions appearing to have more high frequency and or less low frequency energy than earthquakes these observations may be caused by at least two principal effects that are probably acting in parallel 1 variations in depth dependent effects of attenuation acting between the shallow explosions and deeper earthquakes and 2 differences in the dynamic response of the near source geology to the passing explosion shock wave anelastic synthetic seismogram calculations illustrate that depth dependent attenuation effects may explain the spectral observations however a number of observations using near and far field data from nts explosions suggest that near source effects are the dominant factor a quasi empirical explosion source model is proposed that simultaneously fits the spectral ratio data from both the u s and s u relative to earthquakes in each of the respective regions additionally the model fits the trends of the spectral ratios observed as a function of magnitude the key to the model is the shape of the pressure time history acting at the elastic radius for explosions detonated in weak porous rock the radiated shock wave divides into a two wave system consisting of an elastic precursor followed by a plastic wave the generation of this two wave system introduces a rise time into the pressure time history in the frequency domain a second corner frequency is established in a third order model with an 3 high frequency decay whose value is inversely proportional to the time separation of the two waves in higher strength saturated rocks or for overburied explosions the effective rise time is short and a second order model is appropriate with an 2 high frequency decay the second order model provides a good fit to the s u data in contrast a hybrid model is required to fit the nts data with an 3 high frequency decay for shallow explosions detonated in unsaturated tuff that evolves to an 2 decay as depth of burials reach higher strength saturated rocks below the water table

fauna and habitat types driven by turbidity currents in the lobe complex of the congo deep sea fan abstract this study characterizes the habitats and megafaunal community of the congo distal lobe complex driven by turbidity currents through the use of remotely operated vehicle rov still imagery transects covering distances in the order of kilometers in this sedimentary abyssal area about 5000 m deep and 750 km offshore from western africa large quantities of deposited organic material supplied by the congo river canyon and channel support aggregations of large sized foraminifers bathysiphon sp and vesicomyid clams christineconcha regab abyssogena southwardae often associated with methane cold seeps as well as opportunistic deep sea scavengers additionally bacterial mats assumed to be formed by large sulfur oxidizing filamentous bacteria beggiatoa type and black patches of presumably reduced sediment were seen which are together with sulfur oxidizing symbiont bearing vesicomyids indicators of sulfide rich sediments habitat and faunal distribution were analyzed in relation to the microtopography obtained with the rov multibeam echosounder at three sites from the entrance of the lobe complex where the channel is still deep to the main flatter area of turbidite deposition specific characteristics of the system influence animal distributions both the forams and the vesicomyid clams tended to avoid the channels characterized by high speed currents and are therefore preferentially located along channel flanks affected by sliding and on levees formed by channel overspill foram fields are found in flat areas and form large fields whereas the vesicomyids have a patchy distribution and appear to show a preference for regions of local topographical relief such as slide scars or collapsed blocks of sediments which likely facilitate sulfide exhumation the colonization of sulfide rich sediments by vesicomyids is limited but nonetheless was seen to occur in the main deposition area where they have to cope with very high sedimentation rates up to 20 cm yr and frequent turbidity currents other biological adaptations to the local conditions likely determine the presence and survival of animals in the system large agglutinated forams are known to be adept at quickly colonizing disturbed sediment and capitalizing on abundant but irregular food sources and vesicomyid clams have a mobile lifestyle that enables them to maintain their population in the ever changing landscape of sulfide rich sediment outcrops turbiditic systems appear to be intermediate between other energy rich habitats sustaining chemosynthesis in the deep sea being locally less stable in terms of energy supply than cold seeps limiting the number of cold seep specialists able to colonize but constituting a longer lived habitat than food falls turbidite fans therefore represent distinct deep sea habitats that contribute to sustaining populations of both chemosynthesis based and opportunistic taxa in the deep sea

three dimensional attenuation structure of the hikurangi subduction zone in the central north island new zealand summary we use waveform data from 2708 earthquakes recorded by dense seismograph deployments in the central north island of new zealand to image the 3 d attenuation structure of the hikurangi subduction zone down to ca 300 km depth attenuation images are obtained by determining the quality factor of p waves qp using a t inversion with a previously determined 3 d seismic velocity model we have included limited frequency dependence for qp with qp being frequency independent above 10 hz and having a frequency dependence of f 10 0 5 below 10 hz the qp images provide further constraint on the large scale features associated with subduction and magmatism beneath the central north island and serve to refine interpretations of crust and upper mantle structure from vp and vp vs the subducted plate is the most prominent feature in the qp images its high qp 900 1200 is consistent with the ca 120 myr old slab being relatively cold qp is better at resolving the slab than vp the coincidence of a strong gradient in qp with the upper plane of the dipping seismic zone indicates that even below 75 km depth the upper envelope of seismicity provides a good estimate of the location of the plate interface the mantle wedge is generally imaged as a relatively low qp 400 feature below 50 km depth however there are significant changes evident in the wedge along the strike of the subduction zone the most pronounced low qp in the mantle wedge occurs from ca 50 to 85 km depth beneath the productive rhyolite dominated central segment of the taupo volcanic zone suggesting a close link between volcanism and low qp in the shallow mantle wedge there is a strong correlation between low qp l owvp and high vp vs in this part of the mantle wedge suggesting that high temperature is the controlling influence on qp there within 30 km of the surface of the slab there is a large change in qp but only a modest change in vp our results are consistent with a fluid rich viscous blanket being entrained with the motion of the subducted slab down to ca 140 km depth where hydrous melting of mantle peridotite initiates trenchward of the volcanic front a strong horizontal gradient to higher qp is imaged in the mantle wedge we interpret this as a stagnant mantle nose not involved in the corner flow of the adjacent mantle the distribution of qp within both the slab and the overlying plate provides support for dehydration embrittlement being important in promoting seismicity in the mantle of the slab where qp is high at shallow depth in the forearc it is usually underlain by low qp near the plate interface this suggests that competent terranes in the forearc may act as aquicludes increasing fluid content in the rocks below and hence might control the distribution of coupling at the plate interface

evidence and age estimation of mass wasting at the distal lobe of the congo deep sea fan on continental margins sulfate reduction occurs within the sedimentary column it is coupled with the degradation of organic matter and the anaerobic oxidation of methane these processes may be significantly disturbed by sedimentary events leading to transient state profiles for the involved chemical species yet little is known about the impact of turbidity currents and mass wasting on the migration of chemical species and the redox reactions in which they are involved due to its connection to the river the congo deep sea fan continuously receives huge amount of organic matter rich sediments primarily transported by turbidity currents which impact on the development of the associated ecosystems rabouille et al 2016 thus it is well suited to better understand causal relationships between sedimentary events and fluid flow path with consequences on the zonation of early diagenesis sequences here we combined sedimentological observations with geochemical analyses of pore water and sediment samples to explore how sedimentary instabilities affected the migration of methane and the distribution of organic matter within the sedimentary column the results unveiled mass wasting processes affecting recent turbiditic and pelagic deposits and are interpreted as being slides slumps and debrites two slides were responsible for the exhumation of an organic matter rich sedimentary block of more than 5 m thick and the movement of a methane rich sedimentary block while turbidity currents enable the intercalation of sandy intervals within a pelagic clay layer the youngest slide promoted the development of two sulfate methane transition zones smtz and may have possibly triggered a lateral migration of methane numerical simulation of the sulfate profile indicates that the youngest sedimentary event has occurred around a century ago our study emphasizes that turbidity currents and sedimentary instabilities can significantly affect the transport paths and the distribution of both methane and organic matter in the terminal lobe complex with consequences on geochemical zonation of the sequential early diagenetic processes within the sedimentary column

a major step in the continental moho and its geodynamic consequences the taranaki ruapehu line new zealand summary receiver function analysis reveals a 7 km step like change in crustal thickness across the taranaki ruapehu line tr line of north island new zealand the tr line runs east west between the active andesite volcanoes of mt taranaki and ruapehu and marks the southernmost extent of subduction zone volcanism in new zealand north of the tr line receiver functions show a strong and sharp p to s ps conversion at 25 1 5 km depth which is interpreted as a shallow moho at the tr line the moho ps conversion deepens across a step to 32 km depth and weakens further south the moho deepens to 35 km most of the 7 km step change in crustal thickness occurs over a lateral distance of 8 km yet there is little surface or topographic manifestation of the line given fresnel zone considerations the dip of the moho offset could vary between 90 and 45 gravity seismic attenuation and electrical data all show that the tr line is not only a step in crustal thickness but also a profound lithospheric boundary as mantle properties such as attenuation qp 1 implied density and electrical resistivity change abruptly across the line an east west oriented cluster of earthquakes with hypocentral depths of 20 40 km is centred on the moho step we propose that the moho step the earthquakes and the rapid change in mantle properties across the tr boundary are causally related processes that could be responsible for the phenomena described here include the rapid removal of mantle lithosphere and lower crust to the north of the tr line

subcrustal earthquakes in the central south island new zealand and the root of the southern alps the pukaki microearthquake network has revealed significant earthquake activity deeper than 15 km in the central south island new zealand extending to a depth of 73 km beneath the crest of the southern alps events deeper than 25 km define a planar seismic zone that has a strike of 41 and dips northwest at 19 gravity models suggest that earthquakes in this zone are occurring in a seismogenic uppermost mantle underlying an aseismic lower crustal root to the southern alps the 17 difference in strike of the dipping seismic zone and the alpine fault provides an explanation for the pattern of uplift and crustal thickening seen in the central south island

single station spectral discrimination using coda waves spectral discrimination methods applied at regional distances are based on the observation that there is a difference in the frequency content of the seismic waves radiated from the source region of earthquakes and explosions we have investigated a spectral discrimination method that exploits the scattered energy contained in the event codas of seismograms to measure the relative source excitation of earthquakes and explosions as a function of frequency key strengths of the coda method include the following 1 it is not affected by source radiation pattern because the scattering process averages the radiation over the focal sphere 2 path corrections are not required with the coda method because coda waves are scattered throughout a common crustal volume 3 it can be successfully applied using data from only a single station and 4 it can be successfully applied using data with clipped direct arrivals to implement the coda method we first estimate a type curve which represents the average shape of all the individual coda decay curves for a particular frequency band the shape of the type curve as well as the shape of all individual coda decay curves is controlled by the scattering and attenuation properties of the crustal volume sampled by the coda waves a common path effect the amplitude of the type curve is not defined and we arbitrarily adjust it to have a zero mean the amplitude difference between an individual event coda decay curve and the type curve provides a relative measure of the event s source size within the particular frequency band we define this amplitude difference as the relative source factor our approach exploits all of an event s usable coda for each spectral measurement thus providing a more stable measure of relative source size than could be obtained from using a predefined fixed length time window analysis of 27 nevada test site explosions and 15 southern great basin earthquakes 3 1 m 4 7 shows that the source factor difference between the 0 5 to 1 and 2 to 4 hz bands plotted against the 1 to 2 hz source factor is a stable event discriminant the method reliably distinguishes small explosions from small earthquakes 3 0 m 3 5 even if the explosions are overburied because the coda method requires only one seismic station we believe that it would be especially useful in identifying small clandestine underground nuclear tests that occur far from established networks

geological controls on focused fluid flow associated with seafloor seeps in the lower congo basin a synthesis of backscatter imagery coupled with a large 3d seismic dataset in the lower congo basin lcb reveals a patchy distribution of features interpreted to be associated with fluid seepage from 300 m to 2500 m water depth with the exception of one region of anomalous backscatter positive relief mounds all inferred seep sites occur in negative relief pockmarks the extensive 3d seismic dataset in the lcb offers a unique opportunity to study the plumbing system that is feeding surface cold seep systems and in general to reconstruct the relationship between tectonics and fluid flow in continental margins the fluid seeps in the lcb are associated with morphologically stratigraphically or tectonically controlled focused fluid flow the integration of the geophysical datasets backscatter imagery coupled to 3d seismic clearly indicates that fluid seeps are not randomly distributed but their seabed organization reflects 1 the location of the underlying structure reservoir or trap where the fluids are coming from 2 the geometry and morphology of the reservoir trap and 3 the discontinuities in the sedimentary column along which fluids have migrated in the lcb seafloor pockmarks are always associated with underlying tectonic structures fault zones salt diapirs polygonal faults or buried sedimentary bodies turbiditic channels erosional surfaces whereas they never occur above sub horizontal parallel stratified fine grained sediments even if triggering processes can not be clearly defined here we propose a model of seafloor fluid seep organization which represents a new tool for identifying the geometry of flow pathways and the underlying buried bodies where the fluids are originating from this qualitative 3d model provides insight into the geohydrologic processes of continental margins

metastability mechanical strength and the support of mountain belts exhumed high pressure rocks from the caledonian root zone in norway provide analogues for processes occurring today under southern tibet allowing large scale geophysical observations from gravity and earthquakes to be linked with the mechanical properties of metastable rocks under high mountains metastability is essential for the survival of thick mountain roots and hence of high mountains and is in turn controlled by water if water is absent dry granulite formed from earlier melting episodes is both stable and strong and likely to survive in the eclogite stability field of deep root zones for hundreds of million years but if hydrous fluid is introduced the transformation of granulite to eclogite is relatively rapid and accompanied by a dramatic loss of strength in norway this transformation was initiated by water infiltration along fractures formed by earthquakes the same process as marked by deep earthquakes may be occurring today beneath southern tibet

organic matter budget in the southeast atlantic continental margin close to the congo canyon in situ measurements of sediment oxygen consumption abstract a study of organic carbon mineralization from the congo continental shelf to the abyssal plain through the congo submarine channel and angola margin was undertaken using in situ measurements of sediment oxygen demand as a tracer of benthic carbon recycling two measurement techniques were coupled on a single autonomous platform in situ benthic chambers and microelectrodes which provided total and diffusive oxygen uptake as well as oxygen microdistributions in porewaters in addition sediment trap fluxes sediment composition org c tot n caco3 porosity and radionuclide profiles provided measurements of respectively input fluxes and burial rate of organic and inorganic compounds the in situ results show that the oxygen consumption on this margin close to the congo river is high with values of total oxygen uptake tou of 4 0 6 3 6 0 5 mmol m 2 d 1 at 1300 and 3100 m depth respectively and between 1 9 0 3 and 2 4 0 2 mmol m 2 d 1 at 4000 m depth diffusive oxygen uptakes dou were 2 8 1 1 2 3 0 8 0 8 0 3 and 1 2 0 1 mmol m 2 d 1 respectively at the same depths the magnitude of the oxygen demands on the slope is correlated with water depth but is not correlated with the proximity of the submarine channel levee system which indicates that cross slope transport processes are active over the entire margin comparison of the vertical flux of organic carbon with its mineralization and burial reveal that this lateral input is very important since the sum of recycling and burial in the sediments is 5 8 times larger than the vertical flux recorded in traps transfer of material from the congo river occurs through turbidity currents channelled in the congo valley which are subsequently deposited in the lobe zone in the congo fan below 4800 m ship board measurements of oxygen profiles indicate large mineralization rates of organic carbon in this zone which agrees with the high organic carbon content 3 and the large sedimentation rate 19 mm y 1 found on this site the lobe region could receive as high as 19 mol c m 2 y 1 1 3 being mineralized and 2 3 being buried and could constitute the largest depocenter of organic carbon in the south atlantic

surface seismic and electrical methods to detect fluids related to faulting in the absence of drilling surface based geophysical methods are necessary to observe fault zones and fault zone physical properties at seismogenic depths these in situ physical properties can then be used to infer the presence and distribution of fluids along faults although such observations are by nature indirect and become less exact with greater depth multiple observations of a range of such geophysical properties as compressional and shear seismic velocity vp and vs vp v5 ratio related to poisson s ratio resistivity and attenuation in and adjacent to fault zones offer the greatest hope of making inferences of the fault zone geometry fluids in the fault zone and fluid reservoirs in the surrounding crust for simple geometries fault zone guided waves can provide information on fault zone width and velocities for faults of the order of 200 m wide to address the question of whether a narrow fault zone can be imaged well enough at depths of seismic rupture to infer the presence of anomalously high fluid rock ratios we present synthetic seismic tomography and magnetotelluric examples for an ideal case of a narrow fault zone with a simple geometry large changes in material properties and numerous earthquakes within the fault zone a synthetic 0 5 km wide fault zone with 20 velocity reduction is well imaged using local earthquake tomography when sequential velocity inversions are done the true fault width is found even to 9 km depth although the calculated amplitude of the velocity reduction is lower than the actual amplitude vp vs is as well determined as vp magnetotelluric imaging of a synthetic fault zone shows that a conductive fault zone can be well imaged within the upper 10 km further a narrow 1 km very low resistivity 3 ohm m fault core can be imaged within a broad 5 km low resistivity 10 ohm m fault zone illustrating that regions of a fault containing large quantities of interconnected fluids within a broader conductive fault zone should be detectable thus variations in fluid content and fluid pressure can be inferred from electrical and seismic methods but there will always be uncertainty in these inferences due to the trade off with other factors such as intrinsic variations in porosity mineralogy and pore geometry the best approach is combined modeling of varied seismic and electrical data

macrofaunal communities within and adjacent to a detritus rich submarine canyon system abstract macrofaunal abundance biomass diversity and species assemblages within scripps and la jolla submarine canyons are compared with those on the nearby continental shelf and slope our primary objective was to examine the effect of detrital aggregates on infaunal communities within canyons two submarines a remotely operated vehicle rov and a soutar box corer were used to collect samples within the canyons organic enrichment by macrophyte detritus was evident from canyon heads down to 550 m and evidence of strong currents coarse sediment was found down to 700 m infaunal density and biomass were higher in the canyons than outside at all depths where comparative data were available 100 500 m infaunal assemblages in canyons were distinct from those at reference stations both the canyon and non canyons samples showed community differentiation with depth species diversity was generally high but decreased with depth outside of canyons and increased with depth within the canyons low diversity at shallow depths within the canyon is attributed to a combination of organic enrichment and physical disturbance submarine canyons are commonly found to contain distinct species assemblages or higher faunal densities and or biomass than nearby non canyon regions at similar depths canyons are regular features along most ocean margins and appear to be important as sites of enhanced secondary production provide diverse habitats and act as conduits of coastal detritus to the deep sea

a discrimination analysis of short period regional seismic data recorded at tonto forest observatory abstract a new seismic discriminant based on spectral differences of regional phases from earthquakes and explosions recorded at a single station has been tested and found to work remarkably well the test data consisted of a well constrained set of 30 nevada test site nts explosions and 21 earthquakes located within about 100 km of nts which were recorded on short period seismographs at the tonto forest observatory in central arizona at an epicentral distance averaging 530 km the events in the data set cover a magnitude range from 3 3 to 4 8 m b for which p n p g and l g phases have been analyzed we found that although l g phases from earthquakes are typically more prominent than for explosions with comparable p wave amplitude levels simple time domain l g p amplitude ratios do not result in a separation of the earthquake and explosion samples consistent enough to provide reliable discrimination however spectral analyses of the data over the frequency band from 0 5 to 5 0 hz revealed significant differences in the spectra of certain regional phases which proved to be a quite reliable discriminant in particular both the p g and l g spectra from earthquakes have been found to be richer in high frequency content than corresponding explosion spectra a discriminant measure defined as the ratio of average l g spectral amplitude level in the 0 5 to 1 0 hz passband to that in the 2 0 to 4 0 hz passband provides good separation of earthquake and explosion populations

spectral characteristics of regional phases recorded at noress abstract the spectral characteristics of pn and lg are studied for regional events recorded at the noress array in norway the emphasis is on the potential value of spectral ratios for identifying events as earthquake chemical explosions and nuclear explosions the events studied include a suite of explosions from the titania mine in southwest norway a suite of events of unknown source type from a site offshore about 90 km from this mine suites of explosions from several mines in the soviet union about 1000 km from noress events from several locations along the 90 azimuth from noress an apparent earthquake in the north atlantic and a nuclear explosion pne at a range of 1560 km the event identification issues addressed are as follows 1 can earthquakes and explosions be identified based on the ratio of high and low frequency energy in their signal spectra 2 do spectral ratios separate mine blasts from earthquakes for all source areas 3 will spectral ratio discriminants be effective for identifying decoupled underground nuclear explosions we conclude that spectral ratios can sometimes separate events an example is separation of the titania mine blasts from the events at the nearby offshore locations although we cannot be sure how much this is due to path differences however in general spectral ratios vary as much within classes of events as they do among different classes the pne in our data set allows the simulation of spectra from a decoupled nuclear explosion by simply applying the frequency dependent decoupling factor to the observed pn spectrum for this event after applying a distance correction the spectrum for this simulated decoupled nuclear explosion is similar to those for the soviet union mine blasts in our data set

storm induced sediment gravity flows at the head of the eel submarine canyon northern california margin 1 as part of the strataform program a bottom boundary layer bbl tripod was deployed at 120 m depth in the northern thalweg of the eel canyon during winter 2000 increases of the near bottom suspended sediment concentrations ssc recorded at the canyon head were not directly related to the eel river discharge but were clearly linked to the occurrence of storms bbl measurements revealed that during intensifications of the wave orbital velocity sediment transport at the head of the canyon occurred as sediment gravity flows directed down canyon observational evidence for near bed sediment gravity flow transport included an increase toward the bed of the down canyon component of wave averaged velocity and high estimated ssc at higher sampling frequencies 1 hz the current components during these events fluctuated at the same periodicity as the pressure reflecting a clear influence of the surface wave activity on the generation and maintenance of the sediment gravity flows the origin of such flows is not related to the formation of fluid muds on the shelf or to intense wave current sediment resuspension around the canyon head region rather liquefaction of sediment deposited at the head of the canyon induced by wave load excess pore water pressures during storms combined with elevated slopes around the canyon head appear to be the mechanisms initiating sediment transport the resulting fluidized sediment layer can easily be eroded entrained into the water column and transported down canyon as a sediment gravity flow results from this study reveal that storm induced sediment gravity flows occur periodically in the eel canyon head and suggest that this kind of sediment transport process can occur in other submarine canyons more frequently than previously expected

the congolobe project a multidisciplinary study of congo deep sea fan lobe complex overview of methods strategies observations and sampling the presently active region of the congo deep sea fan around 330 000 km2 called the terminal lobes or lobe complex covers an area of 2500 km2 at 4700 5100 m water depth and 750 800 km offshore it is a unique sedimentary area in the world ocean fed by a submarine canyon and a channel levee system which presently deliver large amounts of organic carbon originating from the congo river by turbidity currents this particularity is due to the deep incision of the shelf by the congo canyon up to 30 km into the estuary which funnels the congo river sediments into the deep sea the connection between the river and the canyon is unique for major world rivers

contemporary tectonic stress pattern of the taranaki basin new zealand the present day stress state is a key parameter in numerous geoscientific research fields including geodynamics seismic hazard assessment and geomechanics of georeservoirs the taranaki basin of new zealand is located on the australian plate and forms the western boundary of tectonic deformation due to pacific plate subduction along the hikurangi margin this paper presents the first comprehensive wellbore derived basin scale in situ stress analysis in new zealand we analyze borehole image and oriented caliper data from 129 petroleum wells in the taranaki basin to interpret the shape of boreholes and determine the orientation of maximum horizontal stress s hmax we combine these data 151 s hmax data records with 40 stress data records derived from individual earthquake focal mechanism solutions 6 from stress inversions of focal mechanisms and 1 data record using the average of several focal mechanism solutions the resulting data set has 198 data records for the taranaki basin and suggests a regional s hmax orientation of n068 degrees e 22 degrees which is in agreement with nw se extension suggested by geological data furthermore this ene wsw average s hmax orientation is subparallel to the subduction trench and strike of the subducting slab n50 degrees e beneath the central western north island hence we suggest that the slab geometry and the associated forces due to slab rollback are the key control of crustal stress in the taranaki basin in addition we find stress perturbations with depth in the vicinity of faults in some of the studied wells which highlight the impact of local stress sources on the present day stress rotation

terrestrial and marine n alcohol inputs and degradation processes relating to a sudden turbidity current in the zaire canyon abstract n alcohol biomarkers from sediment trap samples collected during a turbiditic event and surficial sediments on a levee of the zaire canyon equatorial west african margin one of the world s largest and still very active deep sea fans were examined the initial goal was to study the benthic ecosystem in relation to organic matter inputs as the quantity and quality might influence its development two criteria were used the relative abundance of short 20 and long chain c 22 n alcohols derived from marine organisms and higher plants respectively and the ratio of odd to even carbon numbered 20 n alcohols to assess the extent of alteration the material collected in the trap 30 m above the bottom when the turbiditic current occurred exhibited a high abundance of terrigenous n alcohols this trap did collect the turbidity material in contrast to the one located at 400 m the influence of the turbidity current was also revealed in the surficial sediment sampled nine months after the event the initial turbiditic material from the 30 m trap settled on to the sediment and extensive degradation was apparent upon this settling assuming a first order degradation rate the degradation rate constants were 3 4 and 0 9 y 1 for 19 and c 22 n alcohols respectively

discrimination of chemical explosions and earthquakes in central europe a case study both natural and artificial seismicity is observed in the vogtland area at near regional distance 180 km from the geress array this setting offers the opportunity to test various discrimination criteria using a uniform data set of 39 earthquakes and 22 chemical explosions strip mine and quarry blasts from a single epicentral region mostly eliminating wave path and distance effects discriminants used include lg pg and lg rg maximum amplitude ratios spectral peaks and slopes extracted by autoregressive moving average arma modeling master event correlation and the search for time independent frequency structures in sonograms although no single discrimi nant achieves a perfect separation of the two populations a joint discrimination scheme employing simple majority voting reduces misclassifications to 2 future research will focus on possible generalization and the physical basis of the discriminants

discrimination using spectral slopes at frequencies up to 50 hz abstract the spectral characteristics of regional pn waves recorded at the high frequency seismic element hfse at the noress array in southern norway are investigated to determine if spectral slope can be used to discriminate between earthquakes and chemical explosions displacement spectra are calculated for 134 events in southern norway that include 36 known earthquakes and 36 known chemical explosions events range in distance from 230 to 620 km and most have signal above the noise at frequencies over 30 hz the average frequency at the peak signal to noise ratio snr is 15 5 hz spectral slopes are measured on a displacement spectrum calculated with a 2 sec window the slopes range between 1 8 and 5 1 and there is no strong evidence that the slope steepens with distance for this data set according to one theory earthquakes should have steeper slopes than explosions but when this data set is separated into earthquakes and explosions we do not see separation between sources with respect to the slope of the spectrum both source types have events with the same range of spectral slopes and the mean slopes and standard deviations are similar spectra of events at the same locations are often similar however explosions from the blasjo mine in western norway show variability in the spectral slope since the path and distance to hfse are the same for these events the variability must be due to differences in the source mechanism for a set of small earthquakes however the observed variability in spectral slopes appears to be more related to distance and path effects therefore we observe as much variation in spectral slope for one source type as there is between source types the time window over which the spectrum is calculated is varied from 1 to 8 sec to determine if a time window consisting of a pure pn wave was required to discriminate between source types spectral slope usually decreases as the window extends deeper into the coda and the energy content of the signal changes the slopes also become more stable and more reliable as longer windows are used however source discrimination is not possible with any time window

early diagenesis in the sediments of the congo deep sea fan dominated by massive terrigenous deposits part iii sulfate and methane based microbial processes abstract geochemical profiles so 4 2 h 2 s ch 4 13 ch 4 and phylogenetic diversity of archaea and bacteria from two oceanographic cruises dedicated to the lobes sediments of the congo deep sea fan are presented in this paper in this area organic rich turbidites reach 5000 m and allow the establishment of patchy cold seep like habitats including microbial mats reduced sediments and vesicomyid bivalves assemblages these bivalves live in endosymbiosis with sulfur oxidizing bacteria and use sulfides to perform chemosynthesis in these habitats unlike classical abyssal sediments anoxic processes are dominant total oxygen uptake fluxes and methane fluxes measured with benthic chambers are in the same range as those of active cold seep environments and oxygen is mainly used for reoxidation of reduced compounds especially in bacterial mats and reduced sediments high concentrations of methane and sulfate co exist in the upper 20 cm of sediments and evidence indicates that sulfate reducing microorganisms and methanogens co occur in the shallow layers of these sediments simultaneously anaerobic oxidation of methane aom with sulfate as the electron acceptor is evidenced by the presence of anmes anaerobic methanotroph dissolved sulfide produced through the reduction of sulfate is reoxidized through several pathways depending on the habitat these pathways include vesicomyid bivalves uptake adults or juveniles in the bacterial mats habitats reoxidation by oxygen or iron phases within the reduced sediment or reoxidation by microbial mats sulfide uptake rates by vesicomyids measured in sulfide rich sea water 90 18 mmol s m 2 d 1 were similar to sulfide production rates obtained by modelling the sulfate profile with different bioirrigation constants highlighting the major control of vesicomyids on sulfur cycle in their habitats

comparison of ground motion from tremors and explosions in deep gold mines seismic body waves from tamped chemical explosions two with yields of 50 and one of 150 kg were compared with corresponding data from three mining induced tremors with a view to testing methods of discriminating between the two types of events detonated at depths of about 2 km all three explosions generated p waves for which the low frequency spectral asymptotes agree well with corresponding results scaled down from nuclear shots at the nevada test site for the two smaller explosions recorded underground at hypocentral distances ranging from 234 to 871 m the p wave corner frequencies defined by the intersections of the low and high frequency asymptotes are also in fine agreement with scaled down results from the nevada test site for the 150 kg explosion which was recorded only at the surface it appears that 2 39 km of upward propagation caused the corner frequency to be at least a factor of 4 lower than anticipated due to attenuation all three explosions generated s waves that appear to be a consequence of deviatoric stress release in the immediate environs of the explosions the three tremors analyzed here generated p and s waves whose spectra and source parameters agree well with standard earthquake source models with regard to discrimination based on p wave spectra we conclude that for events of fixed low frequency spectral asymptotes the explosions typically have higher corner frequencies than tremors or earthquakes although counterexamples certainly exist interestingly the 150 kg explosion was identified as such on the basis of p and s wave polarities that are incompatible with the normally expected double couple source model instead these initial motions are consistent with an explosion in conjunction with normal faulting the body wave spectra of this explosion and those of a nearby tremor however were indistinguishable

deep sea habitat heterogeneity influence on meiofaunal communities in the gulf of guinea to estimate the degree of spatial heterogeneity of benthic deep sea communities we carried out a multiple scale from m s to 200 km investigation in the congo angola margins equatorial west african margin 3150 4800 m in which we examined the metazoan meiofauna at a variety of habitats along the congo channel system and in the associated cold seep we investigate the structure density vertical distribution patterns in the sediment and biomass of meiofaunal communities in the gulf of guinea and how they are controlled by hydrologic and biogeochemical processes the meiofaunal communities in the gulf of guinea were shaped by heterogeneous conditions on the margin and reflect the multiple scale spatial variability that corresponds with the different identified habitats the two control sites located at 100 km away from the canyon were inhabited by very dense and the most diverse meiobenthic communities similar meiobenthic communities inhabited the transition zone between the canyon and the cold seep sites located along the congo channel were obviously affected by the local high velocity bottom currents and unstable sedimentary conditions in this active submarine system extremely low meiobenthic densities and very low proportions in the most surficial sediment layers provided evidence for recently highly disturbed sediments at these sites the remote operated vehicle rov victor 6000 provided images of the cold seep showing a patchy distribution of several types of patchy distributed megafaunal communities dominated by three key symbiotic taxa mytilidae vesicomyidae and siboglinidae these cold seep sediments were colonised by a unique meiobenthic community characterised by a high small scale m s patchiness low species richness and the prominent dominance of two large sized nematode species sabatieria mortenseni which is a cosmopolitan nematode known from littoral habitats and an undescribed desmodora species the high individual body weight of s mortenseni and its dominance at the cold seep site resulted in a significantly higher nematode biomass at the seep compared to the surrounding sites in addition the vertical nematode profiles with maximum proportions in subsurficial layers points to a chemosynthesis based meiobenthic community in this cold seep in contrast to the phytodetritus based communities at the control sites and at the transition zone

discrimination of earthquakes and explosions in southern russia using regional high frequency three component data from the iris jsp caucasus network high frequency regional records from small earthquakes magnitude 4 5 and comparable magnitude chemical explosions are analyzed to find a reliable seismic discriminant in southern russia near kislovodsk the digital three compo nent seismograms recorded during 1992 by the caucasus network operated by la mont doherty earth observatory since 1991 in the distance ranges 15 to 233 km are used mean vertical component pg lg spectral amplitude ratios in the band 8 to 18 hz are about 1 3 and 3 2 for earthquakes and explosions respectively in this region we find that the vertical component pg lg spectral ratio in the frequency band 8 to 18 hz serves quite well for classifying these events a linear discriminant function analysis indicates that the pg lg spectral ratio method provides discrimination power with a total misclassification probability of about 7 the pg lg spectral ratios of rotated three component regional records improve the discrimination power of the spectral ratio method over the vertical component pg lg ratios preliminary analysis indicates that distance corrected vertical component pg lg ratios improve the dis crimination power by about 4 over uncorrected ratios but we find that an even better discriminant is the pg lg spectral ratio of the three component regional records corrected for the free surface effect in the frequency band 8 to 18 hz the free surface corrected three component pg lg spectral ratio provides discrimination power with a total misclassification probability of only 2 6 free surface corrected and network averaged pg lg spectral ratios provide transportability of the spectral ratio method to various regions worldwide

measurement of frequency dependent lg attenuation in the great basin measurement of the spatial decay of spectral amplitudes of the higher mode seismic surface wave train lg indicates that in the great basin the apparent seismic quality factor q is a function of frequency observations along a 300 km profile recording of a nuclear explosion yield the function q 206 0 68 over the band 0 3 10 0 hz similar analysis using numerous recordings of earthquakes along paths which provide a good average sampling of the great basin crust gives q 214 15 0 54 0 09 for 0 3 5 0 hz if the crustal sampling by lg energy from nuclear explosions surface sources is primarily in the shallow crust as has been suggested then these results indicate a greater frequency dependence of apparent q there than at depth

turbidity events observed in situ along the congo submarine channel abstract as part of the multidisciplinary programme biozaire devoted to studying deep sea benthic ecosystems in the gulf of guinea particulate input and its relationship with near bottom hydrodynamics were monitored using long term moorings from 2000 to early 2005 particular attention was given to material input through the congo ex zaire submarine channel that extends 760 km from the congo river mouth to the abyssal plain 5100 m near 6 s due to its direct connection to the congo river the congo canyon and channel system are characterised by particularly active recent sediment transport during this first in situ long term monitoring along the channel an energetic turbidity event was observed in january 2004 at three locations along the channel from 3420 to 4790 m in depth this event tilted and displaced the moorings installed at 3420 m site zr and 4070 m site zd and resulted in high sediment deposition at all three mooring sites the event moved at an average velocity of 3 5 m s 1 along the numerous channel meanders between 3420 and 4070 m then at 0 7 m s 1 between 4070 m and the end of the channel at 4790 m the particle cloud rose above the top of the valley at 4070 m site zd but not at 3420 m site zr where the channel was too deep lastly the mooring line broke at site zd in october 2004 probably due to a strong event like that of 2001 previously described by khripounoff et al khripounoff a vangriesheim a babonneau n crassous p denniellou b savoye b 2003 direct observation of intense turbidity activity in the zaire submarine valley at 4000 m water depth marine geology 194 151 158 between these strong events several peaks of high turbidity and particle flux occurred but without noticeable current increases these events were probably due to local sliding of sediment accumulated on the walls or terraces on the side of the channel the area near 4000 m depth and the lobe appear to be the main depocentres of particulate input rich in organic matter derived from the congo river

spatial and temporal variability of downward particle fluxes on a continental slope lessons from an 8 yr experiment in the gulf of lions nw mediterranean abstract a long term experiment of downward particle fluxes and currents has been initiated in 1993 on the continental slope of the gulf of lions nw mediterranean and pursued within the frame of several french and european projects pnec euromarge nb mtp ii mater eurostrataform sediment traps and current meters were deployed at several locations on this slope deeply incised by numerous canyons with an extensive spatial coverage for the first 2 years canyons at the entrance middle and exit of the gulf with respect to the general along slope circulation head and mid canyon depths adjacent open slope from late 1995 onwards this design was reduced to the two mid canyon moorings at the entrance and exit of the gulf monthly fluxes and hourly temperatures and currents were recorded at 500 m 30 m above bottom mab in the canyon heads at 500 and 1000 m respectively 530 and 30 mab nominal depths at the mid canyon sites and at 750 m 30 mab open slope this study aims at describing the spatial seasonal and interannual variability of flux intensity and composition of settling particles and at analyzing the role of diverse forcings in the control of particle exchange across the margin results from the first 8 years 1993 2001 show that total mass fluxes in the 101 104 mg m 2 d 1 range increase along slope particularly for the near bottom traps between the ne planier canyon and the sw lacaze duthiers canyon limits of the gulf of lions indicating an increased shelf export of particulate matter in the western part of the system bulk chemical composition organic matter carbonate opal and lithogenic fraction remained rather stable during the course of the experiment tending towards values typical of superficial shelf sediments at higher mass fluxes first order calculations using a simple two component mixing model suggest a decreasing contribution of primary particles settling out of the overlying waters to the total flux from the entrance towards the exit of the system particulate material transferred to the deeper slope in the southwestern part of the gulf of lions appears therefore to predominantly originate in resuspended shelf and or upper slope sediment downward particle fluxes and potential forcing parameters exhibit a high seasonal variability with higher values from late autumn to early spring furthermore unprecedented winter flux peaks observed in 1999 dominated the interannual differences which otherwise were quite limited correlations between sources of particulate material on the shelf i e river and atmospheric inputs phytoplankton biomass and sediment resuspension cross slope exchange mechanisms derived from in situ temperature and current records and flux data indicate a predominant effect of dense cold water cascading on the exchange of particulate matter between the shelf and the slope

regionalization of crustal coda q in the continental united states a contour map of crustal q sub 0 values for the entire united states is presented based on a scattering model to explain the coda waves of local and near regional earthquakes these coda q sub 0 values are in good agreement with q of lg waves data are obtained from over 250 local earthquakes with most magnitudes between 3 0 and 5 0 recorded by 25 wwssn and 27 lrsm stations throughout the continental united states these two sets of data provide a range of frequencies from 0 5 to 3 5 hz a frequency dependence of q is observed in the range of frequencies considered a power law dependence of the form q q sub 0 f f sub 0 sup eta is assumed the value of frequency dependence eta is found to be maximum in the tectonically active western united states and least in the stable regions of the central and south central united states the lowest q sub 0 values are obtained in the western united states with values ranging from 140 to 200 in the coastal plains average crustal q sub 0 values for the basin and range province vary from 200 to 300 increasing gradually to 400 in the colorado plateau region q sub 0 valuesmore in the columbia plateau vary from 200 to 400 q sub 0 values increase very rapidly along the central and southern rocky mountains from 400 to 800 east of the rocky mountains q sub 0 values increase gradually in the interior plains to a maximum value of around 1300 in the mississippi embayment region farther east q sub 0 values decrease gradually to an almost constant value of 1000 along the appalachian mountains coastal regions of eastern and northeastern united states have a crustal q sub 0 value between 900 to 700 regions of north central and gulf coastal plains show low q sub 0 values ranging from 600 to 400 and less the source factor b f sub p a measure of the intensity of scattering was obtained for several different regions of the continental united states regions of high q sub 0 values exhibit low intensity of scattering less

shear wave reflectivity anisotropies poisson s ratios and densities of a southern appalachian paleozoic sedimentary sequence abstract the physical properties of a sequence of paleozoic sedimentary rocks have been examined in detail with an emphasis on laboratory measurements of density shear wave velocity shear wave splitting and vp vs ratios seismic properties of 147 cores from 49 rock samples collected from the thorn hill sedimentary sequence of eastern tennessee are examined in terms of implications for future seismic studies in the southern appalachians the shear wave velocities of these rocks are strongly influenced by the relatively high shear wave velocity of quartz shear wave velocity anisotropy is present in most of the lithologic groups it is highest in the shales while being almost insignificant in the dolostones the related phenomenon of shear wave splitting occurs to some degree in all of the lithologies studied and at high pressures originates from mineral orientation splitting due to preferred mineral orientation is most prominent in the shales but also is significant in some of the carbonates compressional to shear velocity vp vs ratios of approximately 1 82 dolostones and 1 95 limestones effectively characterize the carbonates while other lithologies display wider ranges of vp vs primarily due to the influence of accessory minerals such as quartz densities of the sample suite range from 2 34 g cm3 shale to 2 86 g cm3 dolostone using average data for each lithologic group to calculate normal incidence reflection coefficients significant differences in the shear and compressional reflectivity of hypothetical interfaces are found normal incidence shear and compressional wave synthetic seismograms approximating the subsurface reflectivity of the entire thorn hill section indicate that three zones of high amplitude reflections would be seen on reflection records obtained over this 3327 m thick sequence overall the shear and compressional synthetics are similar in appearance differences are seen at some interfaces in the mississippian devonian interval which are more reflective to shear waves and in the ordovician martinsburg formation which appears more reflective to compressional waves

the role of fluids in lower crustal earthquakes near continental rifts earthquakes in the lower continental crust of the earth are rare as the lower crust is thought to be too hot to allow brittle failure so it is surprising that they occasionally occur where continental crust is rifting apart a study of three dimensional crustal structure and seismicity in the taupo volcanic zone an active continental rift in new zealand has now provided insight into how these earthquakes arise the crustal earthquakes form a continuous band along the rift and often occur in swarms suggesting fluid movement in critically loaded fault zones seismic velocities within the band are consistent with the presence of fluids and the linking of upper and lower crust seismicity to crustal structure point to a common explanation for all of the seismicity probably the weakening of faults on the periphery of an otherwise dry crust by hot fluids a report on three dimensional tomographic imaging of seismic velocities and attenuation in the taupo volcanic zone an active continental rift where earthquakes are known to occur in the lower crust finds that crustal earthquakes form a continuous band along the rift and often occur in swarms suggesting fluid movement in critically loaded fault zones the occurrence of earthquakes in the lower crust near continental rifts has long been puzzling as the lower crust is generally thought to be too hot for brittle failure to occur1 2 such anomalous events have usually been explained in terms of the lower crust being cooler than normal3 4 but if the lower crust is indeed cold enough to produce earthquakes then the uppermost mantle beneath it should also be cold enough2 and yet uppermost mantle earthquakes are not observed5 numerous lower crustal earthquakes occur near the southwestern termination of the taupo volcanic zone tvz an active continental rift in new zealand6 here we present three dimensional tomographic imaging of seismic velocities and seismic attenuation in this region using data from a dense seismograph deployment7 we find that crustal earthquakes accurately relocated with our three dimensional seismic velocity model form a continuous band along the rift deepening from mostly less than 10 km in the central tvz to depths of 30 40 km in the lower crust 30 km southwest of the termination of the volcanic zone these earthquakes often occur in swarms suggesting fluid movement in critically loaded fault zones8 seismic velocities within the band are also consistent with the presence of fluids and the deepening seismicity parallels the boundary between high seismic attenuation interpreted as partial melt within the central tvz and low seismic attenuation in the crust to the southwest this linking of upper and lower crustal seismicity and crustal structure allows us to propose a common explanation for all the seismicity involving the weakening of faults on the periphery of an otherwise dry mafic crust by hot fluids including those exsolved from underlying melt such fluids may generally be an important driver of lower crustal seismicity near continental rifts

origin and distribution of the organic matter in the distal lobe of the congo deep sea fan a rock eval survey the congo river the second largest river in the world is a major source of organic matter for the deep atlantic ocean because of the connection of its estuary to the deep offshore area by a submarine canyon which feeds a vast deep sea fan the lobe zone of this deep sea fan is the final receptacle of the sedimentary inputs presently channelled by the canyon and covers an area of 2500 km the quantity and the source of organic matter preserved in recent turbiditic sediments from the distal lobe of the congo deep sea fan were assessed using rock eval pyrolysis analyses six sites located at approximately 5000 m water depth were investigated the mud rich sediments of the distal lobe contain high amounts of organic matter 3 5 to 4 corg the origin of which is a mixture of terrestrial higher plant debris soil organic matter and deeply oxidized phytoplanktonic material although the respective contribution of terrestrial and marine sources of organic matter cannot be precisely quantified using rock eval analyses the terrestrial fraction is dominant according to similar hydrogen and oxygen indices of both suspended and bedload sediments from the congo river and that deposited in the lobe complex the rock eval signature supports the 70 to 80 of the terrestrial fraction previously estimated using c n and 13corg data in the background sediment the organic matter distribution is homogeneous at different scales from a single turbiditic event to the entire lobe and changes in accumulation rates only have a limited effect on the quantity and quality of the preserved organic matter peculiar areas with chemosynthetic bivalves and or bacterial mats explored using rov victor 6000 show a rock eval signature more or less similar to background sediment this high organic carbon content associated to high sedimentation rates 2 to 20 mm yr 1 in the congo distal lobe complex implies a high burial rate for organic carbon consequently the congo deep sea fan represents an enormous sink of terrestrial organic matter when compared to other turbiditic systems over the world

pockmarks in the northern congo fan area sw africa complex seafloor features shaped by fluid flow abstract three pockmarks named hydrate hole black hole and worm hole were studied in the northern congo fan area at water depths around 3100 m the cross disciplinary investigations include seafloor observations by tv sled sampling by tv guided grab and multicorer as well as gravity coring in addition to hydroacoustic mapping by a swath system a parametric sediment echosounder and a deep towed sidescan sonar the pockmarks are morphologically complex features consisting of one or more up to 1000 m wide and 10 15 m deep depressions revealed by swath mapping high reflection amplitudes in the sediment echosounder records indicate the presence of a 25 30 m thick shallow sediment section with gas hydrates which have been recovered by gravity corer hydrates chemosynthetic communities and authigenic carbonates clearly indicate fluid flow from depths which we propose to be mainly in the form of ascending gas bubbles rather than advection of methane rich porewater evidence for seepage at the seafloor is confined to small areas within the seafloor depressions and was revealed by characteristic backscatter facies small meter scale sized depressions signified as pits exist in or close to the pockmarks but seafloor observations did not reveal evidence for the presence of typical seep organisms or authigenic carbonates areas of intermediate backscatter were inhabited by vesicomyid clams in soft sediments high backscatter was associated with vestimentiferan tubeworms siboglinidae and authigenic carbonates we discuss the three different environments pits vesicomyid clams vestimentifera carbonate in the light of differences in the geochemical setting pits are probably formed by escaping gas bubbles but seepage is too transient to sustain chemosynthetic life vesicomyid clams are present in sediments with gas hydrate deposits however the hydrates occur several meters below the surface indicating a lower flux compared to the vestimentifera carbonate environment in the latter environment accumulated carbonates and clam shells indicate that fine grained particles have been eroded away gas hydrates were found in this environment at depths below about 50 cm suggesting the highest supply with methane compared to the other environments

organic carbon accumulation in modern sediments of the angola basin influenced by the congo deep sea fan geochemical data total organic carbon toc content 13corg c n rock eval analyses were obtained on 150 core tops from the angola basin with a special focus on the congo deep sea fan combined with the previously published data the resulting dataset 322 stations shows a good spatial and bathymetric representativeness toc content and 13corg maps of the angola basin were generated using this enhanced dataset the main difference in our map with previously published ones is the high terrestrial organic matter content observed downslope along the active turbidite channel of the congo deep sea fan till the distal lobe complex near 5000 m of water depth interpretation of downslope trends in toc content and organic matter composition indicates that lateral particle transport by turbidity currents is the primary mechanism controlling supply and burial of organic matter in the bathypelagic depths

isolated deep earthquakes beneath the north island of new zealand seismicity shallows towards the south along the tonga kermadec hikurangi margin deep and intermediate seismicity being absent altogether in the south island of new zealand beneath the taranaki region of the north island the maximum depth of the main seismicity is 250 km but very rare events occur directly below at 600 km these could be associated with a detached slab or a vertical aseismic continuation of the subducted pacific plate six small events that occurred in the 1990s were recorded extensively by digital instruments of the new zealand national network nznn and temporary deployments we relocate these events by a joint hypocentre determination jhd method and find their focal mechanisms using first motions and relative amplitudes of p and s arrivals the earthquakes relocate to a remarkably uniform depth of 603 3 kmrelative error 10 km absolute error in a line 30 km long orientated 40 ne roughly parallel to the strike of the intermediate depth seismicity the only consistent component of the focal mechanisms is the tension axis all lie close to horizontal and tend to align with the line of hypocentres we interpret this deep seismic zone as a detached sliver of plate lying horizontally with the same orientation as the main subducted plate above volume change caused by a phase change controlled by the pressure at 600 km and temperature in the sliver produces a pattern of strain that places the sliver under tension along its length

high frequency spectral scaling of a main shock aftershock sequence near the norwegian coast a high frequency seismic element was recently added to the noress regional array in norway this system can monitor seismic signals at frequencies up to 50 hz in february 1986 the high frequency seismic element recorded an mblg 4 7 main shock and several aftershocks which occurred 420 km northwest of noress off norway s western coast these events produced high frequency signals which were well above the background noise at the station p wave spectra of these events scale in a manner consistent with the square constant stress drop source model the data do not require any change in this scaling to magnitudes mblg below 2 in contrast to previous reports that constant stress drop scaling breaks down at smaller magnitudes

3d crustal structure from local earthquake tomography around the gulf of arta ionian region nw greece during summer of 1995 local seismicity was recorded in the area around the gulf of arta in northwestern greece by a dense temporary seismic network of the 441 local events observed at 37 stations 232 well locatable events with a total of 2776 p phase readings were selected applying the criteria of a minimum of 6 p observations and an azimuthal gap less than 180 this data set is used to compute a minimum 1d velocity model for the region several tests are conducted to estimate model stability and hypocenter uncertainties leading to the conclusion that relative hypocenter location accuracy is about 500 m in latitude and longitude and 1 km in depth the minimum 1d velocity model serves as initial model in the non linear inversion for three dimensional p velocity crustal structure by iteratively solving the coupled hypocenter velocity problem in a least squares sense careful analysis of the resolution capability of our data set outlines the well resolved features for interpretation the resulting 3d velocity model shows generally higher average crustal velocities in the east and the well resolved area of the eastern gulf of arta exhibits a homogeneous velocity around 6 km s for the whole upper crust a pronounced north south trending zone of low velocities in the upper 5 10 km is observed in the area of the katouna fault zone kfz at greater depths below 10 km the kfz is underlain by high velocity material e w profiles suggest a horst graben structure associated with the kfz