the heterogeneous abyss the abyssal seafloor that is ocean depths of 3 000 to 6 000 m is widely considered simply to be vast featureless plains of sediment for example wikipedia asserts that abyssal plains cover more than 50 of the earth s surface and are among the flattest smoothest and least explored regions on earth 1 featureless tracts of mud make intuitive sense since abyssal plains are formed by the deposition of thick blankets of fine grained sediments sinking from the surface ocean or transported as turbidity currents down continental margins in most of the abyss especially on seafloors 10 my old this sediment blanket is tens to thousands of meters thick 2 and seems likely to bury or smoothen most of the irregularities in seafloor crust e g basalt pillows formed at midocean spreading centers riehl et al in pnas 3 help to dispel this notion that the abyssal seafloor is featureless providing evidence of extensive rocky habitats along transform faults in the abyss scientists studying the deep sea have long known that rocky or hard substrates do occur on abyssal plains perhaps the best known are polymetallic manganese nodules that were discovered during the challenger expedition 1872 to 1876 4 nodules are widespread in the pacific abyss and to a much lesser extent the indian and the atlantic oceans 5 in some pacific regions nodules may cover 10 to 50 of the seafloor area providing abundant rocky habitat 6 7 seamounts also provide rocky substrates at abyssal depths where their slopes and outcrops are too steep to hold sediments 8 with as many as 200 000 seamounts in the world ocean seamounts too provide significant habitat area for hard bottom faunas but once again seamounts are concentrated in the pacific ocean 8 surveys with lowered cameras human occupied vehicles remotely operated vehicles and autonomous underwater vehicles 1 1email craigsmi at hawaii edu 1 xref corresp 1 1

attenuation of coda waves in new england abstract seismic wave attenuation was measured in new england from the time domain decay of coda wave amplitudes on narrow bandpass filtered seismograms of local earthquakes the frequency band of interest was 0 75 to 10 hz q c f was found to increase with frequency across this band but there was also a difference between the q c f values for short t t 100 sec lapse times of coda wave propagation for the short lapse time data corresponding to wave paths primarily in the upper crust q c f increases from 400 at 3 hz to 1300 at 10 hz for the large lapse time data corresponding to wave paths in the lower crust and upper mantle q c f was found to vary from 660 at 1 hz to 1500 at 10 hz if we interpret this dataset in terms of a model incorporating both scattering and anelastic attenuation we find that the mean free path of seismic waves over this frequency band is 80 km for short lapse times and 400 km for long lapse times if we assume that scattering is entirely responsible for the observed attenuation we find that the minimum mean free path for short lapse times is about 75 km over all frequencies whereas for long lapse times the minimum mean free path decreases from 400 km at 0 75 hz to 90 km at 10 hz

the relationship between depth age and gravity in the oceans we reassess the applicability of the thermal plate cooling model to the subsidence of the north pacific atlantic and north indian ocean basins we use a new numerical plate model in which the thermophysical parameters of the lithosphere vary with temperature according to the results of laboratory experiments and the ridge temperature structure is consistent with the thickness of the oceanic crust we first attempt to exclude thickened crust from our data set and then to exclude swells and downwellings by masking regions of the data that remains that have significant gravity anomalies when there exists a clear regional correlation between intermediate wavelength gravity and topography we find that the average variation of depth with age is consistent with conventional half space models until about 90 myr thereafter the departure from the half space cooling curve is more rapid than predicted using simple conductive plate cooling models the depth age curves in the pacific and atlantic show 250 m of temporary shallowing between the ages of 90 130 myr a result consistent with the outcome of experiments on the initiation of small scale boundary layer convection the results do not change significantly if the estimated component of the gravity arising from plate cooling is subtracted prior to calculation of the correlation between gravity and topography a 90 km thick conductive plate is nevertheless a reasonable model for the average temperature structure of the oldest part of the pacific ocean lithosphere in the pacific the broad topographic undulations associated with the line island swell the hawaiian swell and surrounding basins have correlated gravity anomalies and an admittance of approximately 30 mgal km 1 and are likely to result from convective circulation in the upper mantle in the northeast atlantic the intermediate wavelength admittance over the cape verde swell is similar in the northwest atlantic over the bermuda swell it is slightly larger but not as well constrained

long term sea level fluctuations driven by ocean basin dynamics earth9s long term sea level history is characterized by widespread continental flooding in the cretaceous period 145 to 65 million years ago followed by gradual regression of inland seas however published estimates of the late cretaceous sea level high differ by half an order of magnitude from 40 to 250 meters above the present level the low estimate is based on the stratigraphy of the new jersey margin by assimilating marine geophysical data into reconstructions of ancient ocean basins we model a late cretaceous sea level that is 170 85 to 270 meters higher than it is today we use a mantle convection model to suggest that new jersey subsided by 105 to 180 meters in the past 70 million years because of north america9s westward passage over the subducted farallon plate this mechanism reconciles new jersey margin based sea level estimates with ocean basin reconstructions

regional change of coda q in the oceanic lithosphere coda q of 22 local earthquakes recorded on islands located in young and old oceanic lithosphere areas has been measured we found that the q values at periods of from 1 to 2 seconds increase from young to old ocean lithosphere in the same way as for the continent where the intensity of current tectonic activity shows a strong negative correlation with the coda q the q values increase with frequency proportional to fn where n was found to be 0 46 0 61 with the higher values for younger oceanic lithosphere which is again similar to the continents where the active regions have higher n values

use of seismoscope records to determine ml and peak velocities more information about ground motion can be extracted from seismoscope records than a single point on a response spectrum to demonstrate this the relation between seismoscope response and wood anderson instrument output and peak horizontal ground velocity has been studied by simulating the various responses for a range of distances and magnitudes the simulations show that the relation used by jennings and kanamori 1979 to convert from peak seismoscope readings to the peak response of a wood anderson instrument has a distance and magnitude dependent systematic error the error is negligible however for modern seismoscopes at distances of a few tens of kilometers at several hundred kilometers the relation underestimates the wood anderson response by as much as a factor of two the spread in jennings and kanamori s estimate of ml for the 1906 san francisco earthquake recorded on seismoscopes having relatively low natural frequencies 0 26 and 0 5 hz is reduced by the results in this paper the upper value from a seismoscope in carson city nevada at 290 km from the fault going from ml 7 2 to ml 7 0 and the lower value from yountville california r 60 km going from about 6 3 to 6 4 about 0 3 units of the remaining spread may be due to local geologic site conditions if the 0 3 units is distributed equally between the yountville and carson city recordings the estimates of ml for the san francisco earthquake then become 6 5 and 6 8 somewhat lower than jennings and kanamori s final estimates of 6 3 4 to 7 although the error in using the relation of jennings and kanamori to estimate wood anderson response was at most a factor of 1 6 for the 1906 earthquake the error can be substantially larger for smaller earthquakes recorded on similar low frequency seismoscopes the relation between wood anderson and seismoscope response used by jennings and kanamori can be combined with an empirical relation between peak horizontal velocity and wood anderson response to predict peak velocity from seismocope recordings the simulations show that this relation v max 8 1 awa where v max is the peak horizontal velocity in centimeters second and awa is one half the range of the wood anderson motion in meters forms a lower bound for estimates of peak velocity from seismoscope recordings the relation is good for stations within about 100 km of earthquakes with moment magnitudes of about 4 5 to 6 5 and it underestimates peak velocity by factors up to 2 or 3 for larger earthquakes at distances within 100 km an application of the simulation method to the 1976 guatemala earthquake moment magnitude 7 6 results in 37 cm sec as a lower bound to v max with 66 cm sec as a more likely value from the seismocope recording in guatemala city approximately 25 km from the motagua fault

s wave attenuation in the crust in northern greece abstract the attenuation of shear waves in the crust is estimated for frequencies between 1 5 and 12 0 hz by applying a single station method based on the rate of decay of the s wave to coda wave amplitude ratio with distance the data used come from local earthquakes that occurred in the thessaloniki area northern greece during the period 1983 through 1989 and were recorded by the telemetered network of the geophysical laboratory of the university of thessaloniki the q s values obtained are 115 244 477 and 755 for 1 5 3 0 6 0 and 12 0 hz respectively these values are very close to the coda q values estimated for the same area using the s to s single scattering model for lapse times between 30 and 100 sec but they are higher than the coda q values for lapse times between 10 and 30 sec the estimated q s is found to be strongly frequency dependent proportional to f 0 91 which is very close to the frequency dependence of the coda q

seismic interpretation of pelagic sedimentation regimes in the 18 53 ma eastern equatorial pacific basin scale sedimentation and infilling of abyssal valleys understanding how pelagic sediment has been eroded transported and deposited is critical to evaluating pelagic sediment records for paleoceanography we use digital seismic reflection data from an integrated ocean drilling program site survey amat03 to investigate pelagic sedimentation across the eastern central equatorial pacific which represents the first comprehensive record published covering the 18 53 ma eastern equatorial pacific our goals are to quantify 1 basin hill scale primary deposition regimes and 2 the extent to which seafloor topography has been subdued by abyssal valley filling sediments the eastern pacific seafloor consists of a series of abyssal hills and basins with minor late stage faulting in the basement ocean crust rarely outcrops at the seafloor away from the rise crest both hills and basins are sediment covered the carbonate compensation depth is identified at 4440 m by the appearance of acoustically transparent clay intervals in the seismic data overall we recognized three different sedimentation regimes depositional high sedimentation rate transitional and minimal sedimentation low sedimentation rate regimes in all areas the sedimented seafloor mimics the underlying basement topography although the degree to which topography becomes subdued varies depositional regimes result in symmetric sedimentation within basins and subdued topography whereas minimal sedimentation regimes have more asymmetric distribution of sediments within topographic lows and higher seafloor relief regardless of sedimentation regime enhanced sediment deposition occurs within basins however we observe that basin infill is rarely more than twice as thick as sediment cover over abyssal hills if this variation is due to sediment focusing the focusing factor in the basins as measured by 230th is no more than a factor of 1 3 of the total vertical particulate rain

crustal volumes of the continents and of oceanic and continental submarine plateaus global topographic data and the assumption of airy isostasy have been used to estimate the crustal volumes of the continents and the oceanic and continental submarine plateaus the calculated crustal volumes are 7182 x lo6 km3 for the continents 242 x lo6 km3 for continental submarine plateaus and 369 x lo6 km3 for oceanic plateaus the falkland plateau and the lord howe rise are the two largest continental submarine plateaus with volumes of 48 x lo6 km3 and 47 x lo6 km3 respectively total continental crustal volume is 7581 x lo6 km3 including the volume of continental sediments on the ocean floor 160 x lo6 km3 in good agreement with previous estimates continental submarine plateaus on the seafloor comprise 3 2 of the total continental crustal volume the largest oceanic plateaus in order of decreasing size are the ontong java plateau the kerguelen plateau the caribbean the chagos laccadive ridge the ninetyeast ridge and the mid pacific mountains together they comprise 54 of the total anomalous crustal volume in oceanic plateaus an upper bound to the continental crust addition rate by the accretion of oceanic plateaus is 3 7 km3 yr a value that assumes accretion of all oceanic plateaus with a total volume of 4 9 of the continental crustal volume on a 100 myr time scale even if a substantial fraction of the crustal volume in oceanic plateaus is subducted accretion of oceanic plateaus could make a contribution to continental growth since the upper bound to the addition rate exceeds recent estimates of the island arc addition rate subduction of continental submarine plateaus with the oceanic lithosphere on a 100 myr time scale gives an upper bound to the continental crustal subtraction rate of 2 4 km3 yr much larger than recent estimates of crustal subtraction by subduction of seafloor sediments effective subduction of all oceanic plateaus implies equally effective subduction of continental submarine plateaus a potentially important way to recycle continental crust back into the mantle may be the break off of small fragments from the continents entrapment of the continental fragments in the seafloor and subduction of the fragments with the oceanic lithosphere this process may be occurring in the mediterranean for corsica and sardinia

azimuthal velocity variations caused by borehole stress concentrations in laboratory experiments borehole stress concentrations caused by far field uniaxial stress produce measurable variations in compressional wave velocities near the borehole uniaxial stress was applied perpendicular to the axis of a borehole drilled through a sandstone block inside the fluid filled borehole refracted compressional waves were propagated in the rock parallel to the borehole axis at discrete azimuths producing a scan of velocity versus azimuth as uniaxial stress increased significant variations of compressional wave velocity with azimuth developed of the order of 10 variation the azimuth of velocity minima provides an excellent indicator of the direction of maximum far field uniaxial stress accurate to 5 the detailed variation of velocity with azimuth while approximately sinusoidal has sufficient character to provide new information about the rock one interpretation yields the curvature of the velocity versus stress curve of the rock

the objective determination of the instantaneous predominant frequency of seismic signals and inferences on q of coda waves a technique to detect spectrum variations versus time along seismic signals is applied to coda waves of local earthquakes friuli northern italy the technique consists of an autoregressive modeling and utilizes nonlinear spectral analysis where the spectrum of stochastic processes is estimated as the transfer function of the filter that whitens the process under analysis this approach appears to be particularly well suited to those investigations where automatic measurements of the instantaneous frequency have to be carried out on digital data

globsed updated total sediment thickness in the world s oceans we present globsed a new global 5 arc minute total sediment thickness grid for the world s oceans and marginal seas globsed covers a larger area than previously published global grids and incorporates updates for the ne atlantic arctic southern ocean and mediterranean regions which results in a 29 7 increase in estimated total oceanic sediment volume we use this new global grid and a revised global oceanic lithospheric age grid to assess the relationship between the total sediment thickness and age of the underlying oceanic lithosphere and its latitude an analytical approximation model is used to mathematically describe sedimentation trends in major oceanic basins and to allow paleobathymetric reconstructions at any given geological time this study provides a much needed update of the sediment thickness distribution of the world oceans and delivers a model for sedimentation rates on oceanic crust through time that agrees well with selected drill data used for comparison

attenuation parameters for friuli region from strong motion accelerogram spectra abstract by using the accelerometric data obtained during the heaviest earthquakes that occurred in friuli in 1976 an attempt was made to obtain a law of attenuation in the northeastern po river area as dependence on the frequency the study was carried out by comparison of power spectra of entire accelerograms at different distances in the frequency range of 0 1 to 10 hz a q value was found which was proportionally dependent on the frequency as f n with n 1 1 this result can be considered valid for that region and for distances of up to about 200 km from the epicentral area

evidence for the variation of stress drop between normal and thrust faulting earthquakes in italy the horizontal components of 45 strong motion accelerograms recorded in friuli italy from may to september 1976 have been analyzed in order to estimate the stress drop of eight thrust faulting earthquakes two different stress parameters the brune stress drop and the apparent stress a have been considered the friuli main shock has a strong stress drop 800 bars while the aftershocks have stress drops which range from 250 to 400 bars five accelerograms written by the montenegro yugoslavia earthquake of april 1979 have also been analyzed this thrust faulting earthquake had a stress drop of 900 bars the stress drops of these thrust faulting earthquakes are compared to the stress drops determined by rovelli et al 1988a for nine normal faulting earthquakes which occurred in the apennines region from 1979 to 1984 the radiated energies and apparent stresses have also been calculated for the set of apennine earthquakes the thrust faulting earthquakes in the alpine dynaride region exhibit higher values for both the brune and the apparent stress than the normal faulting earthquakes in the apennines region excluding the friuli and montenegro main shocks the brune stress drops of the thrust faults are approximately 3 times those of the normal faults while the apparent stresses are twice as large this difference is statistically significant at a confidence level of 95 the same difference also emerges from the scaling of the peak ground motions recorded in these two regions suggesting an enhanced severity of the seismic input in the alpine dynaride environment compared with the apennines

global sediment thickness data set updated for the australian antarctic southern ocean we present a new 5 min sediment thickness grid for the australian antarctic region 60 e 155 e 30 s 70 s new seismic reflection and refraction data have been used to add detail to the conjugate australian and antarctic margins and intervening ocean floor where regional sediment thickness patterns were poorly known previously on the margins sediment thickness estimates were computed from velocity depth functions from sonobuoy refraction velocity solutions ground truthed against seismic reflection data for the southeast indian ridge abyssal plains sediment thickness contours from geli et al 2007 were used the new regional minimum sediment thickness grid was combined with the global national geophysical data center ngdc sediment grid to create an updated global grid even using the minimum estimates sediment accumulations on the extended australian and antarctic continental margins are 2 km thicker across large regions and up to 9 km thicker in the ceduna basin compared to the global ngdc compilation of sediment thickness data

evolution of deep water rifted margins testing depth dependent extensional models 1 a general understanding of rifted margins which form by thinning of the continental lithosphere exists nevertheless the exact form of thinning is unclear this debate has been stimulated by acquisition of dense seismic wide angle and deep reflection surveys from atlantic ocean margins a central issue concerns the way in which thinning changes with depth we have tackled this issue by developing a generalized inverse model this model attempts to fit subsidence and crustal thinning observations by varying strain rate as a function of time and space depth dependent thinning is permitted but we do not prescribe its existence or form here the algorithm is applied to six margins including two of the most contentious conjugate margins newfoundland iberia and brazil angola calculated strain rate histories predict thinning estimates which broadly match estimates inferred from normal faulting the eastern indian and beaufort sea margins formed by largely uniform lithospheric thinning in contrast the newfoundland iberian conjugate margins formed by a pattern of strongly depth dependent strain rate to account for the paucity of syn rift decompression melting of the underlying asthenosphere the lithospheric mantle close to oceanic continent transition must thin more slowly than the overlying crust this form of depth dependency is not common for example the brazil angolan conjugate margin could have formed by uniform lithospheric thinning provided thick layers of salt were deposited in a preexisting 400 m deep topographic depression depth dependent thinning is not required to account for rapid subsidence of presalt strata

body wave crustal attenuation characteristics in the garhwal himalaya india we estimate frequency dependent attenuation of p and s waves in garhwal himalaya using the extended coda normalization method for the central frequencies 1 5 2 3 4 6 8 10 12 and 16 hz with earthquake hypocentral distance ranging from 27 to 200 km forty well located local earthquake waveforms were used to study the seismic attenuation characteristics of the garhwal himalaya india as recorded by eight stations operated by wadia institute of himalayan geology dehradun india from 2007 to 2012 we find frequency dependent p and s wave quality factors as defined by the relations q p 56 8f 0 91 0 002 and q s 151 8f 0 84 0 002 by fitting a power law frequency dependence model for the estimated values over the whole region both the q p and q s values indicate strong attenuation in the crust of garhwal himalaya the ratio of q s q p 1 obtained for the entire analyzed frequency range suggests that the scattering loss is due to a random and high degree of heterogeneities in the earth medium playing an important role in seismic wave attenuation in the himalayan crust

tomographic reconstruction of near borehole slowness using refracted borehole sonic arrivals two dimensional 2 d reconstructions of the near borehole slowness field are computed using arrival times of refracted borehole sonic arrivals first arrival traveltimes derived from both computer simulations and field data from full waveform sonic tools were inverted for the near borehole formation slowness both axially along the borehole and radially away from the borehole the inversion is nonlinear the solution is obtained by means of a series of linear inversions followed by provisional ray tracings each iteration involves the application of a tomographic reconstruction algorithm similar to those used in seismic crosswell tomography or medical imaging applications the technique was demonstrated using ray theoretic examples to simulate radial variations in slowness in addition full waveforms were generated using two and a half dimensional 2 5 d fdm computer models the finite difference method fdm computer models were used to test the validity of the ray theoretic approximation used in the

high resolution velocity field imaging around a borehole excavation damaged zone characterization the excavation of a deep underground structure induces stress field redistribution that creates an excavation damaged zone edz the study of edz physical properties is of prime importance in the framework of nuclear waste geologic storage where edz constitutes a preferential pathway for storage materials toward the biosphere a probe for measuring the ultrasonic velocity field around a cylindrical excavation zone has been developed the probe uses pzt transducers operating at 150 khz to collect all required data with high accuracy and minimum effort the probe is fully monitored for automatic data acquisition also a numerical inversion method reconstructs a stress field using the measured velocity field this method was partially validated in the laboratory on a multilayer test bed following laboratory tests and probe development an in situ experiment was performed in the meuse haute marne underground research laboratory france to assess the safety of nuclear waste storage in the callovo oxfordian argillaceous layer the damaged zone extends up to 0 175 diameter of depth with an anisotropic damage pattern oriented according to the regional stress field the results show the potential of the method to forecast damage of similar larger structures

ground motion waveforms and source spectral scaling from close distance accelerograms in a compressional regime area friuli northeastern italy abstract an aftershock sequence was recorded by an sma 1 instrument installed at gemona del friuli on a massive limestone site during the period from may to october 1976 the sequence consisted of small to moderately large 10 21 m 0 10 25 dyne cm dominant thrust earthquakes that occurred within 15 km of the station the instrument was triggered by p waves for 24 events the resulting records are particularly suitable to the investigation of source properties for the friuli earthquakes acceleration velocity and displacement waveforms have been analyzed in order to investigate source properties durations t and areas 0 of the shear wave pulses have been measured from the displacement time histories and compared with the values of corner frequency f c and seismic moment m 0 estimated in the frequency domain from the acceleration spectra of the same events the comparison between these two set of data reveals that attenuation correction is important also for correct estimations of source parameters from ground motions at close focal distance and moderate magnitudes after correcting for attenuation stress drops are approximately constant 300 bars on the average in the investigated seismic moment range for this sequence the behavior of peak ground motions versus earthquakes size is consistent with the trend obtained from stochastic simulations assuming an omega squared spectral model with a constant stress drop of 300 bars the good results obtained by applying to friuli earthquakes an omega squared model with a constant stress drop of 300 bars are further confirmed by the analysis of spectral ratios for different size earthquakes of the sequence this analysis demonstrates that the finding of this spectral scaling model is not biased to first order by whole path or near site propagation properties whose effect can be significant when data from a single station are investigated

a correction for sediment load upon the ocean floor uniform versus varying sediment density estimations implications for isostatic correction abstract the isostatic correction for the sediment load on oceanic basement has often been calculated using a uniform sediment density irrespective of either water depth or total sediment thickness an alternative method is proposed here in which the sediment density is calculated using the density depth equations of hamilton 1976 for calcareous clay and terrigenous sediment sequences this alternative method takes into account the water depth and total sediment thickness when estimating the sediment density for example deep water 4000 m sediment sequences are likely to be clay rich thick sediment sequences 2000 m usually have a high terrigenous component and shallow sequences are likely to be calcareous rich sediment thicknesses in excess of 1500 m are generally close to a continental margin these density estimations are compared with measurements from 9 ocean drilling program drill sites 1 deep sea drilling project drill site and from densities derived from seismic interval velocities the most commonly used estimates of uniform sediment density were used to calculate isostatic corrections for a 12 km thick sediment sequence these results were then compared with the results determined using the proposed alternative method of estimating sediment densities the proposed method produces isostatic corrections similar to those derived by published methods for sediment sequences

age spreading rates and spreading asymmetry of the world s ocean crust we present four companion digital models of the age age uncertainty spreading rates and spreading asymmetries of the world s ocean basins as geographic and mercator grids with 2 arc min resolution the grids include data from all the major ocean basins as well as detailed reconstructions of back arc basins the age spreading rate and asymmetry at each grid node are determined by linear interpolation between adjacent seafloor isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust are interpolated by geological estimates of the ages of passive continental margin segments the age uncertainties for grid cells coinciding with marine magnetic anomaly identifications observed or rotated to their conjugate ridge flanks are based on the difference between gridded age and observed age the uncertainties are also a function of the distance of a given grid cell to the nearest age observation and the proximity to fracture zones or other age discontinuities asymmetries in crustal accretion appear to be frequently related to asthenospheric flow from mantle plumes to spreading ridges resulting in ridge jumps toward hot spots we also use the new age grid to compute global residual basement depth grids from the difference between observed oceanic basement depth and predicted depth using three alternative age depth relationships the new set of grids helps to investigate prominent negative depth anomalies which may be alternatively related to subducted slab material descending in the mantle or to asthenospheric flow a combination of our digital grids and the associated relative and absolute plate motion model with seismic tomography and mantle convection model outputs represents a valuable set of tools to investigate geodynamic problems

ecology of a polymetallic nodule occurrence gradient implications for deep sea mining abyssal polymetallic nodule fields constitute an unusual deep sea habitat the mix of soft sediment and the hard substratum provided by nodules increases the complexity of these environments hard substrata typically support a very distinct fauna to that of seabed sediments and its presence can play a major role in the structuring of benthic assemblages we assessed the influence of seafloor nodule cover on the megabenthos of a marine conservation area area of particular environmental interest 6 in the clarion clipperton zone 3950 4250 m water depth using extensive photographic surveys from an autonomous underwater vehicle variations in nodule cover 1 20 appeared to exert statistically significant differences in faunal standing stocks some biological diversity attributes faunal composition functional group composition and the distribution of individual species the standing stock of both the metazoan fauna and the giant protists xenophyophores doubled with a very modest initial increase in nodule cover from 1 to 3 perhaps contrary to expectation we detected little if any substantive variation in biological diversity along the nodule cover gradient faunal composition varied continuously along the nodule cover gradient we discuss these results in the context of potential seabed mining operations and the associated sustainable management and conservation plans we note in particular that successful conservation actions will likely require the preservation of areas comprising the full range of nodule cover and not just the low cover areas that are least attractive to mining

time frequency analysis of seismic excitation and estimates of attenuation parameters for the friuli italy local earthquakes abstract stochastic modelling is applied to the analysis of local earthquake recordings which are usually extremely rich in random incident wave trains that are chaotically superimposed because of scattering effects in the earth s crust the presence in the seismic signal of effects connected with the scale of inhomogeneity in the lithosphere cannot be deterministically described in detail the application of a stochastic second order autoregressive model to accelerometric records for the higher magnitude m l 6 friuli earthquakes and to short period seismometric records for the aftershocks of the strong earthquake of 6 may 1976 has allowed inferences to be drawn about the spectral properties of seismic signals and the propagation mechanisms of seismic waves these inferences are based on an extremely small number of parameters of a mathematical model suitable for simultaneously describing the random sequence of scattered wave trains in the time and frequency domains useful physical information has been obtained about the dynamic characteristic correlation times and the predominant frequency of the seismic signals moreover the strength 2 e t of the innovation of the stochastic process fitting the real digital data set has been estimated from the envelopes of 2 e t the quantity heuristically used in the stochastic approach to describe seismic excitation the mean free path between successive scatterings l or the equivalent diffusivity coefficient d and turbidity g and their dependence on seismic wave frequency have been investigated for friuli using seismometric data at an epicentral distance of 20 km and earthquakes with a magnitude just under 2 mean free path estimates obtained by means of autoregressive parameters vary from 5 km for the strong interaction model to 30 km for the single scattering model furthermore by means of accelerometric records for the strongest earthquakes in friuli during may and september 1976 the dependence for the maximum of the seismic excitation on the epicentral distance r was estimated as 2 e max r with 1 94 0 13 which is in good agreement with results obtained for the same region using standard methods by means of acceleration peaks versus r lastly stochastic modelling provides a method of estimating change versus time for the predominant frequency and characteristic correlation time of narrow band digital recordings these two parameters were computed by means of autoregressive parameters in different physical situations and were found to be functions of the earthquake source the instrumentation frequency response and the earth s filtering effects

spectral analyses of the ktb sonic and density logs using robust nonparametric methods we use robust techniques to estimate power spectra coherences and transfer functions of the german continental deep drilling program ktb sonic and density logs and lithologically defined subsets thereof our results confirm the overall 1 wavelength decay of the power spectra inferred by parametric analyses but provide superior resolution and nonparametric estimates of errors and statistical significance we demonstrate the absence of any statistically meaningful coherence between the velocity logs from the main and pilot holes suggesting a spatially quasi isotropic upper crustal velocity structure also there is little coherence between the physical and caliper logs indicating that disturbances introduced by breakouts and uneven relief of the borehole wall mostly contribute to the uncorrelated portions of the velocity logs coherence between the gamma and physical logs is weak to absent indicating that the observed velocity and density fluctuations are dominated by the physical state of the rocks rather than by their petrological composition attempts to derive poisson s ratio and its variation with wavelength from the relationship between the shear and compressional velocity logs met with limited success but imply that caution should be exercised when comparing poisson s ratio derived from laboratory studies on samples representative of a region to crustal scale seismic determinations our preferred interpretation is that fluctuations in the physical logs in the intermediate wavelength range 10 150 m are dominated by cracks and their level of fluid saturation at larger wavelengths 50 150 m the effects of the petrology becomes more significant as shown by changes in slope of the power spectra and the emerging coherence between the vp and the gamma logs

discovery of widely available abyssal rock patches reveals overlooked habitat type and prompts rethinking deep sea biodiversity habitat heterogeneity and species diversity are often linked on the deep seafloor sediment variability and hard substrate availability influence geographic patterns of species richness and turnover the assumption of a generally homogeneous sedimented abyssal seafloor is at odds with the fact that the faunal diversity in some abyssal regions exceeds that of shallow water environments here we show using a ground truthed analysis of multibeam sonar data that the deep seafloor may be much rockier than previously assumed a combination of bathymetry data ruggedness and backscatter from a trans atlantic corridor along the vema fracture zone covering crustal ages from 0 to 100 ma show rock exposures occurring at all crustal ages extrapolating to the whole atlantic over 260 000 km2 of rock habitats potentially occur along atlantic fracture zones alone significantly increasing our knowledge about abyssal habitat heterogeneity this implies that sampling campaigns need to be considerably more sophisticated than at present to capture the full deep sea habitat heterogeneity and biodiversity

study of the montenegro earthquake sequence march july 1979 abstract data from more than 80 european seismic stations concerning foreshocks the main shock and aftershocks of the earthquake which occurred near the coast of montenegro on 15 april 1979 have been collected and analyzed the data have allowed the focal mechanism of the two strongest shocks to be estimated the hypocentral coordinates of more than 180 aftershocks and some foreshocks have been also computed giving the time space distribution of the sequence the shocks are mostly contained in an area about 100 km long and 30 km wide almost corresponding to the adriatic coast line of the yugoslavia albania border region the hypocentral depths although determined approximately appear to be in the order of 15 to 20 km the results have been compared with previous knowledge of the tectonics of the zone

patchy deposits of cenozoic pelagic sediments in the central pacific export of pelagic carbonate tests from surface waters and their deposition at the seafloor plays a significant role in the co 2 cycle and ability of the oceans to absorb atmospheric co 2 sediment 2 3 0 th and 3 he measurements have been interpreted as evidence that significant lateral advection of pelagic material occurs in the water column leading to marked spatial variations in deposition rates and in particular to significant focusing of deposits on the pacific equator we report spatially continuous stratigraphy from two 1000 km seismic lines that show evidence of depositional anomalies near the equator accumulation rates were apparently enhanced locally by a factor of two similar to the proposed modern sediment focusing factors but the anomalies are surprisingly patchy over the 20 m y period analyzed they are not confined to an equatorial region and they are not necessarily found on adjacent seismic profiles these intermediate scale anomalies are 100 km across and represent areas of seafloor that received more deposits for one period less in following periods and vice versa variogram analysis was used to determine how the spatial scales of deposition changed over the neogene the period when the spatial scale of depositional variability was largest correlates with hiatuses in drill cores a correlation that we interpret as caused by enhanced and spatially heterogeneous carbonate dissolution at that time the study suggests that seismic stratigraphy has the potential to reveal spatial patterns related to unsteady bottom water flow and chemistry

elastic wave evaluation of downhole hydraulic fracturing modeling and field applications abstractwe numerically simulate elastic wave propagation along a fluid filled borehole with a hydraulically fractured formation the numerical model is based on the results of hydraulic fracturing on laboratory specimens two typical models are simulated a main fracture crossing the borehole and a fracture network extending from the borehole in addition both models contain small secondary fractures surrounding the borehole our result indicates that wave propagation in the main fracture model is characterized by significant s wave anisotropy for polarization along and normal to the fracture orientation with the magnitude of anisotropy depending on the fracture aperture and filling material in contrast no significant anisotropy is observed for the fracture network model in both models wave propagation is significantly affected by small fracture induced near borehole velocity variation our modeling results provide a theoretical foundation for evaluating hydraulic fracturing using the borehole acou

the african plate a history of oceanic crust accretion and subduction since the jurassic we present a model for the jurassic to present evolution of plate boundaries and oceanic crust of the african plate based on updated interpretation of magnetic gravity and other geological and geophysical data sets location of continent ocean boundaries and age and geometry of old oceanic crust jurassic and cretaceous are updated in the light of new data and models of passive margin formation a new set of oceanic palaeo age grid models constitutes the basis for estimating the dynamics of oceanic crust through time and can be used as input for quantifying the plate boundary forces that contributed to the african plate palaeo stresses and may have influenced the evolution of intracontinental sedimentary basins as a case study we compute a simple model of palaeo stress for the late cretaceous time in order to assess how ridge push slab pull and horizontal mantle drag might have influenced the continental african plate we note that the changes in length of various plate boundaries especially trenches do not correlate well with absolute plate motion but variations in the mean oceanic crust age seem to be reflected in acceleration or deceleration of the mean absolute plate velocity

upper crustal seismic velocity heterogeneity as derived from a variety of p wave sonic logs sonic log measurements provide detailed 1 d information on the distribution of elastic properties within the upper crystalline crust at scales from about one metre to several kilometres 10 p wave sonic logs from six upper crustal drill sites in europe and north america have been analysed for their second order statistics the penetrated lithological sequences comprise archean volcanic sequences proterozoic mafic layered intrusions and precambrian to phanerozoic gneisses and granites despite this variability in geological setting tectonic history and petrological composition there are notable similarities between the various data sets after removing a large scale deterministic component from the observed velocity depth function the residual velocity fluctuations of all data sets can be described by autocovariance functions corresponding to band limited self affine stochastic processes with quasi gaussian probability density functions depending on the maximum spatial wavelength present in the stochastic part of the data the deterministic trend can be approximated either by a low order polynomial best fit or by a moving average of the original sonic log data the choice of the trend has a significant impact on the correlation length and on the standard deviation of the residual stochastic component but does not affect the hurst number for trends defined by low order polynomial best fits correlation lengths were found to range from 60 to 160 m whereas for trends defined by a moving average the correlation lengths are dominated by the upper cut off wavenumber of the corresponding filter regardless of the trend removed the autocovariance functions of all data sets are characterised by low hurst numbers of around 0 1 0 2 or equivalently by power spectra decaying as 1 k a possible explanation of this statistical uniformity is that sonic log fluctuations are more sensitive to the physical state in particular to the distribution of cracks than to the petrological composition of the probed rocks

a scattering model to explain seismic q observations in the lithosphere between 1 and 30 hz observations of lithospheric q for shear waves in the range 1 30 hz reported in the literature are examined using a scattering model consisting of randomly distributed spheres for the single scattering approximation i have assumed 1 q 1 q sub i gv omega where q sub i is the intrinsic q due to anelasticity v is the velocity of shear waves omega is angular frequency and g is the turbidity g is taken as a constant in this paper since g integral n a sigmada where n a da is the number of scattering spheres of radius a unit volume and sigma is the scattering cross section for a sphere this suggests that geometrical scattering dominates this will be true for ka 1 where k is wavenumber based on this criterion and the observation that q is large i e g small at a frequency of 0 05 hz a is of the order of magnitude 1 10 km fits of observations of shear wave q from japan and central asia indicate that q sub i 2000 500 for the lithosphere of both regions g 0 01 km for the japan observations and g 0 005 km sup 1 for central asia

assessing rock brittleness and fracability from radial variation of elastic wave velocities from borehole acoustic logging rock brittleness and fracability of subsurface formations are two important parameters for hydraulic fracturing in hydrocarbon reservoir production this paper presents an effective technique to assess these parameters using the radial variation of compressional and shear velocities from borehole acoustic logging our technique is based on a rock mechanic phenomenon that a brittle rock with high fracability tends to leave a significant amount of drilling induced cracks at the borehole wall resulting in radial elastic wave velocity variation away from borehole by determining the velocity variation the combined effects of brittleness and fracability of formation rocks can be assessed the compressional wave travel time tomography and flexural shear wave inversion methods are respectively used to obtain compressional and shear velocity variations well log data analysis examples demonstrate the practicability and effectiveness of this technique

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

the deep western boundary current at the bounty trough east of new zealand indications for its activity already before the opening of the tasmanian gateway abstract the eastern new zealand oceanic sedimentary system is influenced by the main deep cold water inflow to the pacific ocean the deep western boundary current dwbc odp leg 181 targeted this region the two northern sites odp 1123 and 1124 are mainly used for interpretation of dwbc flow newly acquired high resolution seismic reflection profiles directly cross odp site 1122 in the outer bounty trough area we can decipher the first appearance of a branch of the dwbc meandering into the bounty trough as early as 20 to 16 7 ma we identified four different drift deposits of the dwbc in the outer bounty trough area the deepest two drifts were formed before the opening of the tasmanian gateway and thus provide the first evidence of a pre oligocene deep circulation at the eastern new zealand margin additionally migration of the drift crests to the west and to the east is interpreted to indicate modifications in core flow pathway of the dwbc due to response to climate changes eocene cooling cooling due to west antarctic ice shield build up tectonic influence opening of tasmanian gateway and enhanced sediment input first turbiditic deposits of bounty channel