coherence of seismic body waves from local events as measured by a small aperture array eight local earthquakes were recorded during the operation of a small aperture seismic array at pinyon flat california the site was chosen for its homogeneous granitic geology and its planar topography amplitude spectral ratios for the same signal measured at different stations had average values of less than 2 and maximum values of 7 magnitude squared coherences were estimated for all station pairs these estimates were highest for the p wave arrivals on the vertical component and lowest for the p wave recorded on the transverse component at 500 m station separation the p and s waves were incoherent above 15 hz and 10 hz respectively coherence for both the p and s waves decrease as frequency increases and as distance increases the coherence of signals from borehole sensors located at 300 and 150 m depth displays higher average coherence than equally spaced sites located on the surface the results here suggest that even for sites that appear to be very similar that is those which are located on a planar surface within a few meters of granite bedrock the measured seismic wavefield can be distorted substantially over scale lengths of 500 m coherence properties were calculated from synthetic seismograms which were computed for velocity models with exponential and self similar distribution perturbations standard deviations of 10 are not sufficient for the random velocity distributions to approximate the results from the small aperture array

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

source parameters for small events associated with the 1986 north palm springs california earthquake determined using empirical green functions using small events as empirical green functions which include path site and instrument effects on the p waveforms source parameters were estimated for 25 ml 3 4 to 4 4 events associated with the 1986 north palm springs earthquake the static stress drops ranged from 3 to 80 bars for moments of 0 7 to 11 1021 dyne cm there was a spatial pattern to the stress drops of the aftershocks which showed increasing values along the fault plane toward the northwest compared to relatively low values near the hypocenter of the mainshock the highest values were outside the main area of slip and are believed to reflect a loaded area of the fault that still has an higher level of stress which was not released during the main shock the relatively high stress drop of a preshock in 1983 located close to the hypocenter of the main shock is also interpreted as evidence that stress drops of magnitude 3 and 4 events can be used as indicators of the stress level in a particular area

seismic directional random noise suppression by radial trace time frequency peak filtering using the hurst exponent statistic radial trace time frequency peak filtering filters a seismic record along the radialtrace direction rather than the conventional channel direction it takes the spatial correlation of the reflected events between adjacent channels into account thus radial trace time frequency peak filtering performs well in denoising and enhancing the continuity of reflected events however in the seismic record there is often random noise whose energy is concentrated in certain directions the noise in these directions is correlative we refer to this kind of random noise that is distributed randomly in time but correlative in the space as directional random noise under radial trace time frequency peak filtering the directional random noise will be treated as signal and enhanced when this noise has same direction as the signal therefore we need to identify the directional random noise before the filtering in this paper we test the linearity of signal and directional random noise in time using the hurst exponent the time series of signals with high linearity lead to large hurst exponent value however directional random noise is a random series in time without a fixed waveform and thus its linearity is low therefore we can differentiate the signal and directional random noise by the hurst exponent values the directional random noise can then be suppressed by using a long filtering window length during the radial trace time frequency peak filtering synthetic and real data examples show that the proposed method can remove most directional random noise and can effectively recover the reflected events

thermally induced icequakes detected on blue ice areas of the east antarctic ice sheet over a year of seismic observations 5000 short duration icequakes were detected by a permanent broadband station installed at the princess elisabeth base located 180 km inland in eastern dronning maud land east antarctica icequake detection via seismic waveform pattern recognition indicates the presence of two dominating clusters of events totalizing 1500 icequakes the corresponding icequake locations point towards two distinct zones of outcropping blue ice areas bias located respectively at 4 and 1 km from the seismic station both on the leeward side of a nunatak protruding through the ice sheet the temporal occurrence of these icequakes suggests a close genetic link with thermal contraction of ice caused by significant surface cooling controlled in summer by variations in diurnal solar radiation and in winter by strong cooling during cold katabatic regimes further analysis demonstrates the dependence of these icequakes on the absolute surface temperature and on its temporal change besides providing information on the ice fracture mechanics and rheology investigations of thermal icequakes may be regarded as a ground based proxy for the monitoring of the thermal state of bias and characterization of ice sheet ablation zones

broadband seismic background noise at temporary seismic stations observed on a regional scale in the southwestern united states background noise power spectral density psd estimates for 54 pass cal colorado plateau rio grande rift great plains seismic transect la ristra stations were computed using data from 1999 to 2000 at long periods 0 01 0 1 hz typical vertical noise levels are approximately 12 db higher than the nearby global seismic network gsn borehole station anmo but horizontal power spec tral density psd noise levels are approximately 30 db higher long period noise levels exhibit essentially no spatial correlation along the la ristra transect indi cating that local thermal or atmosphere driven local slab tilt is the dominant source of noise in this band between 0 1 and 0 3 hz typical noise levels are dominated by naturally occurring microseismic noise and are essentially identical to those observed at anmo at short periods 0 3 8 hz typical noise levels along the network exceed anmo levels by approximately 15 db with the highest levels corresponding to proximity to cultural noise sources no significant day night variations were observed in the microseismic band however both low and high frequency noise levels show an increase of up to 8 db in median midday versus midnight noise levels we find that the major shortcomings of these shallow passcal style temporary vaults rela tive to a gsn style borehole installation are increased susceptibility to long period horizontal 20 sec noise and to surface noise sources above approximately 2 hz although the high frequency near surface noise field is unavoidable in shallow vaults we suggest that increased understanding and mitigation of local tilt effects in shallow vaults offers the possibility of significantly improving the long period noise environment

seismic waves from elephant vocalizations a possible communication mode 1 we conducted experiments with trained african elephants that show that low frequency elephant vocalizations produce rayleigh waves we model a potential range for these seismic waves under ideal conditions of c 2 km in appropriate conditions surface waves from an elephant s infrasonic vocalizations might propagate further than airborne sound and provide advantages over acoustic communication however if we use the detection capabilities of the human ear as a benchmark for the signal detection thresholds of elephants our estimates of attenuation and ambient seismic noise suggest that the seismic detection range is unlikely to exceed the acoustic detection range under normal atmospheric conditions we conclude that elephants may benefit from seismic detection in circumstances where the range of acoustic communication is limited or in cases where multimodal communication is advantageous given our current understanding elephants are unlikely to rely on seismic waves as their primary mode for long range communication

high frequency seismic noise as a function of depth abstract evidence is presented supporting the view that high frequency seismic noise decreases with increased depth noise amplitudes are higher near the free surface where surface wave noise cultural noise and natural wind induced noise predominate data were gathered at a hard rock site in the northwestern adirondack lowlands of northern new york between 15 and 40 hz noise levels at this site are more than 10 db less at 945 m depth than they are at the surface and from 40 to 100 hz the difference is more than 20 db in addition time variability of the spectra is shown to be greater at the surface than at either 335 or 945 m depths part of the difference between the surface and subsurface noise variability may be related to wind induced noise coherency measurements between orthogonal components of motion show high frequency seismic noise is more highly organized at the surface than it is at depth coherency measurements between the same component of motion at different vertical offsets show a strong low frequency coherence at least up to 945 m vertical offsets as the vertical offset decreases the frequency band of high coherence increases

analysis of anthropogenic and natural noise from multilevel borehole seismometers in an urban environment auckland new zealand abstract two short period seismometers were permanently installed at depths of 26 and 383 m beneath the eden park stadium in central auckland in october 2008 and incorporated into the auckland volcano seismic network in 2011 these borehole seismometers were temporarily augmented by a surface sensor to characterize the site response at this location despite the borehole installations seismic monitoring is challenging in this urban environment due to high anthropogenic noise that superimposes the earth s signal we analyze the power spectral density of continuous noise records over long and short time periods to quantify the reduction in noise with depth and the effect of temporal noise variations on the detection capabilities for earthquakes and volcanic tremor we identify natural and anthropogenic noise sources that temporarily elevate noise levels by 10 15 db using records from the rugby world cup matches held at the eden park stadium and by comparing records of daytime versus nighttime periods and windy versus calm days characterization of these noise sources shows that the frequency ranges of traffic and train noise at this site overlap 1 35 hz and 8 35 hz respectively however they exhibit distinct maxima at peak frequencies of 7 and 26 hz modeling of the structure beneath the stadium shows that the noise spectrum generated by the nearby train excites frequencies within the topmost waitemata sequences that get efficiently trapped in the low velocity waveguide beneath the 20 m thick basalt layer at the surface although the shallow borehole sensor generally shows a noise improvement of 5 db in comparison to the surface sensor it exhibits higher noise levels in the 8 35 hz frequency range due to the trapped noise waves wind causes increased microseismic noise at 0 1 1 hz that is coherent at all depth levels and shows the most pronounced time variation online material figures of earthquake and quarry blast locations spectrogram and coherency

diverse sclerozoan assemblages encrusting large bivalve shells from the callovian middle jurassic of southern poland a diverse sclerozoan assemblages consisting of both encrusting and boring biota are described from the large limid bivalves ctenostreon from the callovian hardground setting of zalas in southern poland at least 27 encrusting and seven bioerosion taxa are reported here which makes this assemblage not only one of the most diverse in the middle jurassic but the richest in encrusting taxa from the callovian the encrusters consist of cryptic biota of which sedentary polychaetes and cyclostome bryozoans dominate with respect to both species number and abundance the bioerosion traces are dominated by tiny pits referred to the ichnogenus oichnus probably made by some soft bodied biota in the present case followed by the borings of acrothoracican barnacles rogerella the first colonizers of the bivalve shells probably were borers as they only occur in the host shells the encrusting pioneers presumably were oysters and oyster like bivalves followed by opportunistic serpulid sabellid polychaetes and cyclostome bryozoans the last colonizers were calcisponges and thecideide brachiopods in comparison to the only known late callovian shallow and reef associated tropical sclerozoans of israel the assemblage from the open marine deeper setting of poland is much richer in encrusting taxa such a surprising high encruster diversity in the marine northern paleo latitude may have resulted from the deeper and calmer environment with a both reduced sedimentation rate and algal cover and without any significant salinity changes the factors that are thought to have impacted the tropical and shallow marine sclerozoans from israel

windshield and sound barrier for seismic sensors a system and method for reducing acoustic wind or other background noise that may interfere with sensing of a seismic signal is provided more specifically a shield is provided to enclose a geophone and thereby protect it from harmful noise the shield may comprise a rigid shell a structural damping material an acoustically absorptive material and a compliant seal for coupling the shield to the ground or reference surface

studies of high frequency seismic noise in eastern kazakhstan abstract three seismographic stations have been established in the region of the principal underground nuclear weapons test site in the republic of kazakhstan in the soviet union instrumentation includes both surface and borehole seismometers with a bandwidth of 100 hz and a system dynamic range of 180 db power spectra of the regional ambient ground acceleration peak between 4 and 6 hz and are on average frequency independent above 10 hz where levels are approximately equal to 10 15 to 10 16 m sec 2 2 hz 1 kazakh noise levels are roughly equivalent to those observed by the regional seismic test network between 1 and 20 hz and about 10 to 20 db higher than the very low noise model for lajitas texas in the same band noise observed by the borehole sensors is about 10 db less than that observed by the surface instruments above about 20 hz under low wind conditions at two of the three kazakh sites borehole improvement is greater under high winds the third kazakh site karasu is characterized by much higher surface noise levels 15 to 20 db higher than the borehole levels from 4 to 40 hz under both low or high wind conditions which is attributed to amplification by local site conditions and the exposed terrain power spectra of individual runs of ambient vertical ground acceleration measured down the borehole show that high frequency slopes between 10 and 80 hz vary between f 0 60 and f 0 22 depending on wind and site conditions

a comparison of the high frequency 1 hz surface and subsurface noise environment at three sites in the united states abstract surface and subsurface high frequency 1 hz noise data were recorded using nearly identical instrumentation at three widely separated sites in the united states amarillo texas datil new mexico and pinedale wyoming for extended periods of time under varying wind conditions while the sites are geologically distinct the near surface noise environments have many common features that we believe may be due in large part to the presence of a surficial layer of highly attenuative unconsolidated material at each site noise levels seen at or near the surface 5 m or less are much higher up to 30 db and much more variable power range up to 44 db than those seen at depth the smallest range was 9 db for 1951 m at amarillo the greatest gains in noise level reduction are realized within the first 100 m and probably much shallower

western extension of the iberian european plate boundary during the early cenozoic pyrenean convergence a new model abstract a dense seismic net work allows of drawing the western prolongation of the northern boundary of the iberian plate this early cenozoic deformed boundary is disrupted by two prominent nw se transform faults a kinematic reconstruction with a nw late cretaceous lower eocene motion of the iberian plate is proposed the azores biscay rise is interpreted as a short lived subduction zone whereas king s trough could be a transform fault

high frequency analysis of seismic background noise as a function of wind speed and shallow depth we used a deep 1500 m cased borehole near the town of datil in west central new mexico to study high frequency 1 hz seismic noise characteristics the remote site had very low levels of cultural noise but strong winds winter and spring made the site an excellent candidate to study the effects of wind noise on seismograms along with a three component set of surface sensors teledyne geotech gs 13 a vertical borehole seismometer gs 28 was deployed at a variety of depths 5 43 and 85 m to investigate signal and noise variations wind speed was measured with an anemometer event triggered and time triggered data streams were recorded on a reftek 72 02 data acquisition system located at the site our data show little cultural noise and a strong correlation between wind speed and seismic background noise the minimum wind speed at which the seismic background noise appears to be influenced varies with depth 3 m sec at the surface 3 5 m sec at 43 m in depth and 4 m sec at 85 m in depth for wind speed below 3 to 4 m sec we observe omni directional background noise that is coherent at frequencies below 15 hz this coherence is destroyed when wind speeds exceed 3 to 4 m sec we use a test event md 1 6 and superimposed noise to investigate signal to noise ratio snr improvement with sensor depth for the low q valley fill of the datil borehole dbh site we have found that snr can be improved by as much as 20 to 40 db between 23 and 55 hz and 10 to 20 db between 10 and 20 hz by deploying at a 43 m depth rather than at the surface at the surface there is little signal above noise in the 23 to 55 hz frequency band for wind speeds greater than 8 m sec thus high frequency signal information that is lost at the surface can be recorded by deploying at the relatively shallow depth of 40 m because we observe only minor further reductions in seismic background noise sbn at deeper depths 40 m is likely to be a reasonable deployment depth for other high frequency monitoring sites in similar environmental and geologic conditions

wind induced ground motion wind noise is a problem in seismic surveys and can mask the seismic signals at low frequency this research investigates ground motions caused by wind pressure and shear stress perturbations on the ground surface a prediction of the ground displacement spectra using the measured ground properties and predicted pressure and shear stress at the ground surface is developed field measurements are conducted at a site having a flat terrain and low ambient seismic noise triaxial geophones are deployed at different depths to study the wind induced ground vibrations as a function of depth and wind velocity comparison of the predicted to the measured wind induced ground displacement spectra shows good agreement for the vertical component but significant underprediction for the horizontal components to validate the theoretical model a test experiment is designed to exert controlled normal pressure and shear stress on the ground using a vertical and a horizontal mass spring apparatus this experiment verifies the linear elastic rheology and the quasi static displacements assumptions of the model the results indicate that the existing surface shear stress models significantly underestimate the wind shear stress at the ground surface and the amplitude of the fluctuation shear stress must be of the same order of magnitude as the normal pressure measurement results show that mounting the geophones flush with the ground provides a significant reduction in wind noise on all three components of the geophone further reduction in wind noise with depth of burial is small for depths up to 40 cm

coastal cliff top ground motions as proxies for environmental processes 1 a two year dataset of coastal cliff microseismic ground motions is used to explore energy transfer to a cliff the long term dataset enables us to characterise cliff motion responses to a wide range of environmental processes and examine whether short term characteristics are representative of the long term we examine whether cliff top motions are reliable proxies for environmental processes to inform future investigations into the drivers of erosion the study is based at an actively eroding macrotidal hard rock cliffed coast where considerable intra annual variability in wave tide and storm conditions permit the examination of a full range of environmental permutations three frequency bands of ground motion are identified that represent wind and wave processes that transfer energy to the cliff examining mean energy transfer by aggregating the frequency bands by sea water elevation reveals a notable departure from tidal inundation duration alone of relevance to understanding the timing duration and intensity of effective processes of erosion peak energy transfer to the cliff face occurs during the largest storms where water levels significantly exceed those of tidal inundation rather than at locations most frequently inundated by tides we anticipate it is therefore these conditions that are likely to be most effective in eroding hard rock coasts rather than periods which accrue energy transfer associated with still or calm waters and hence tidally modulated inundation may not relate well to coastal erosion promisingly despite signal overlap and noise cliff top motions can be used as proxies for the processes that transfer energy to the coast

anatomy of the high frequency ambient seismic wave field at the tcdp borehole 1 the taiwan chelungpu fault drilling project tcdp installed a vertical seismic array between 950 and 1270 m depth in an active thrust fault environment in this paper we analyze continuous noise records of the tcdp array between 1 and 16 hz we apply multiple array processing and noise correlation techniques to study the noise source process properties of the propagation medium and the ambient seismic wave field diurnal amplitude and slowness patterns suggest that noise is generated by cultural activity the vicinity of the recording site to the excitation region indicated by a narrow azimuthal distribution of propagation directions leads to a predominant ballistic propagation regime this is evident from the compatibility of the data with an incident plane wave model polarized direct arrivals of noise correlation functions and the asymmetric arrival shape evidence for contributions from scattering comes from equilibrated earthquake coda energy ratios the frequency dependent randomization of propagation directions and the existence of correlation coda waves we conclude that the ballistic and scattered propagation regime coexist where the first regime dominates the records but the second is weaker yet not negligible consequently the wave field is not equipartitioned correlation signal to noise ratios indicate a frequency dependent noise intensity iterations of the correlation procedure enhance the signature of the scattered regime discrepancies between phase velocities estimated from correlation functions and in situ measurements are associated with the array geometry and its relative orientation to the predominant energy flux the stability of correlation functions suggests their applicability in future monitoring efforts

bryozoans in transition the depauperate and patchy jurassic biota bryozoans were profoundly affected by the end permian and probably also by the end triassic mass extinction events their recovery in terms of diversity and disparity during the jurassic was slow and geographically patchy critical compilation of data from the published literature reveals only 172 valid species 160 cyclostomes 10 ctenostomes and 2 cheilostomes some as yet not formally named however the rate of description of new jurassic bryozoan species during the last two hundred years implies that many more species remain to be discovered and described the jurassic is the only geological period during which cyclostomes were the dominant order and is also important in having the oldest cheilostome bryozoan the first representative of the order that dominates the modern bryozoan biota species diversity peaked in the bathonian where local assemblages may contain up to 33 species encrusters account for 124 73 of the 172 jurassic species among which small sheet like forms especially those assigned to the form genus berenicea are the most numerous the overwhelming predominance in the jurassic of weeds with runner ribbon or sheet colony forms is striking unlike the triassic and cretaceous large tree like or frondose erect colonies are uncommon and species with fenestrate articulated and free living colonies are unknown of 92 geographically categorized entries for jurassic bryozoans in the zoological record 1937 2003 80 87 are european records outside europe diversity appears to have remained low throughout the jurassic and non weedy species are particularly scarce compared with the cretaceous jurassic bryozoans show no adaptations that can be interpreted as related to the increased predation pressure associated with the mesozoic marine revolution the jurassic bryozoan biota shares characteristics with both the stenolaemate dominated palaeozoic triassic biota and the cheilostome dominated cretaceous recent biotas

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

continuous catchment scale monitoring of geomorphic processes with a 2 d seismological array 1 distributed activity of geomorphic processes with different spatiotemporal scales is hard to monitor in detail with conventional methods but might be detected with seismometers from july to september 2010 we deployed 14 seismometers to evaluate the ability of a two dimensional array with small interstation distances 11 km to continuously monitor geomorphic processes in a mountain catchment 370 km2 in taiwan spectral analysis of seismic records highlights different sources with high frequency content 1 hz consistent with hillslope and river processes using a common detection algorithm and a location technique based on the timing of seismic amplitude we have located 314 near surface events most of which 69 occurred during daily convective storms event activity was positively correlated with the precipitation intensity but this relation was not uniform in the catchment high resolution satellite images and air photos did not show geomorphic change during the study which did not have any episodes of extreme precipitation a majority of events 61 were collocated with preexisting geomorphic features landslide scars gullies within the uncertainty on location 9 of interstation distance the combination of event location and timing suggests a geomorphic source of recorded signals and most events had the seismic characteristics of rockfall debris avalanches or slides reactivation of prior erosion sites by such processes is difficult to detect with imagery but can possibly be resolved by seismic monitoring when proven this approach will allow a spatially comprehensive survey of geomorphic activity at the catchment scale with temporal detail sufficient to evaluate the exact meteorological conditions under which process events occur

epibiont shadowing a hitherto unrecognized way of preserving soft bodied fossils outlines of soft bodied sessile epibionts that grew attached to the surfaces of calcareous shells in ancient seas are sometimes preserved by a process termed epibiont shadowing processes that altered the surface of the shell were prevented from happening immediately beneath the attached epibiont leaving a shadow of its attachment site following its death and decay microboring around the perimeter of the epibiont by presumed endolithic cyanobacteria gave rise to endolithic shadows and dissolution of the calcareous substrate maybe beneath larger smothering organisms produced solution shadows of smaller organisms that protected their sites of attachment from such etching effects recognition of this type of preservation allows the stratigraphic range of certain soft bodied groups to be extended details of the shadows may yield information about the morphological construction of the groups in question

vertical seismic profiling of oroville microearthquakes velocity spectra and particle motion as a function of depth direct evidence of site distortion of p and s wave microearthquake source spectra at oroville california is presented the data were gathered by placing vertical and three component seismometers at 90 m intervals in a 500 m borehole through the cleveland hill normal fault on which the 1975 ml 5 7 oroville earthquake took place high pressure hydraulic locking mechanisms were used to firmly lock the seismometer packages against the borehole wall digital event triggering geos recorders were used to receive the data some 30 seismic events including 12 microearthquakes were recorded during the 4 months the seismometers were deployed by comparing the velocity spectra of microearthquake waves at the different depths it can be seen that scattering and attenuation in the shallow crust around the borehole dominantly affect high frequency s waves above 15 hz the value of the apparent s wave quality factor qas for the upper 500 m of crust at this site is 9 one feature of this low qas is a gross difference between s wave corner frequencies observed at ground level and 500 m downhole for example the uphole and downhole s wave corner frequencies for the mcoda 0 4 microearthquake of julian day 259 differ by a factor of 2 or more low quality factors and depth dependent corner frequencies were also observed for p waves but these data are less definitive due to lower signal to noise ratios based on their three component particle motions and polarizations the direct s waves of the microearthquakes appear to be composed of two phases which have similar amplitudes but different apparent velocities it is possible that the velocity differences are a result of anisotropy in the underlying rock

subsurface structure at the insight landing site from compliance measurements by seismic and meteorological experiments measurements of ground compliance at the insight landing site describing the surface response to pressure loading are obtained from seismic and meteorological data compliance observations show an increase with frequency indicating the presence of a stiffer rock layer beneath the exposed regolith we performed a markov chain monte carlo inversion to investigate the vertical profile of the elastic parameters down to 20 m below insight compliance was inverted both freely and assuming prior knowledge of compaction in the regolith and the limitations and strengths of the methods were assessed on the basis of theoretical considerations and synthetic tests the inverted young modulus exhibits an increase by a factor of 10 100 over the first 10 15 m compatible with a structural discontinuity between 0 7 and 7 m the proposed scheme can be used for joint inversion of other seismic geological or mechanical constraints to refine the resulting vertical section

the influence of wind on measurements of seismic noise summary the horizontal to vertical spectral ratio hvsr technique of microtremor measurement is widely applied in microzonation and site response studies given the small amplitude of the measured signal unwanted disturbances may adversely affect the results we analysed the influence of local wind on microtremor measurements as follows first we studied variation in hvsr at a permanent three component seismological station under various wind patterns second we conducted an experiment under controlled condition in a wind room equipped with a laser particle image velocimeter analysing the effect of increasing wind speed on various sensor digitizer configurations third we undertook numerical modelling to explain the observed data our main conclusions are that wind increases the amplitude of all components of the microtremor wavefield but does not affect hvsr however certain sensor digitizer configurations can be adversely affected by instrumental noise due to turbulence at the air instrument ground interface

high frequency 1 100 hz noise and signal recorded at different depths in a mine northwest adirondacks ny seismograms of noise recorded simultaneously at the surface and at two subsurface stations 335m and 945m below surface level show that high frequency 1 100 hz background noise is reduced at the subsurface stations seismometers at all three stations are well coupled to hard crystalline bedrock most of the noise reduction occurs between the surface and 335m depth between 1 and 3 hz seismic noise correlates well with wind speed at all levels above 3 hz wind speed up to 8 m sec does not influence high frequency noise levels at 335m or 945m depths at the surface however high frequency noise is associated with wind speeds in excess of 2 m s a site resonance is characteristic of the surface spectra but is not characteristic of the subsurface sites spectral signal to noise s n ratios measured for s waves from a regional earthquake delta 530 km m sub b 4 1 are roughly equal from 1 10 hz at all depths above 10 hz however s n is greater at the subsurface stations with s n greater than 1 up to 30 hz for the surface station approx 50 hz for the 335m station and approx 70 hz for the 945m station results indicate the advantage of employingmore high frequency sensors sufficiently below the surface to reduce the level of noise and to improve the s n ratio in the high frequency range such an advantage could be critically important for nuclear test detection and discrimination less

a study on seismic noise variations at colfiorito central italy implications for the use of h v spectral ratios 1 seismic noise recorded by broad band stations in the middle of and around the colfiorito plain is analyzed in the frequency band 0 1 to 10 hz small daily variations in noise amplitude are found on the order of 2 for f 1 hz in contrast long term amplitude variations due to weather conditions are significant throughout the analyzed frequency band for f 1 hz the amplitude increase can be as large as a factor of 50 in the low frequency band horizontal components vary much more than the vertical at both firm and soft sites however these noise variations at low frequencies do not contaminate significantly the 0 9 hz peak of the h v spectral ratio that fits the fundamental eigenfrequency of the sedimentary fill of the basin resonating during earthquakes correlating the long term variations of noise with different meteorological parameters we find that wind speed best matches the low frequency noise disturbances

crust mantle boundary reflectors in nevada from ambient seismic noise autocorrelations summary the depth of reflector layers in the earth s crust is usually estimated using controlled sources or earthquake signals ambient seismic noise however can also be used for this purpose we develop and apply a new method based on continuous waveform analysis to estimate the two way p wave reflection component of the green s function beneath each station the green s functions are retrieved from continuous record autocorrelation stacks at broad band sensor locations within the usarray earthscope transportable array in the western great basin and the sierra nevada in a region with complex crustal and upper mantle structure in this paper we show evidence of a reflector at the crust mantle boundary moho discontinuity derived for the first time from ambient noise autocorrelations using short period 1 s data our results compare well with earthquake and controlled source investigations and with tomography findings in the region moho depth is difficult to resolve seismically because of the lack of favourable spatial distribution of source and receiver geometries in contrast our method can be applied at any desired sensor spacing to estimate earth reflector depth beneath surface located sensors providing unprecedented resolution

analysis of high frequency seismic noise in the western united states and eastern kazakhstan seismographic stations were operated for several months during 1987 at three sites within 250 km of the kazakh test site in the u s s r and through most of 1988 and early 1989 at three sites within 250 km of the nevada test site in the united states we have analyzed surface and borehole noise levels at these sites as a function of wind speed using nearly 2000 recordings of ambient ground noise collected at the u s stations and several hundred noise measurements from the u s s r sites at the surface wind did not become a noticeable source of noise until a minimum speed of 4 to 5 m sec in the boreholes noise levels were affected by wind conditions to a much smaller degree than at the surface between 3 and 10 hz surface and borehole noise levels were typically comparable and western u s sites were generally quieter than kazakh sites in the 10 to 80 hz band surface noise in the western united states was much higher than in kazakhstan but downhole noise levels in both regions were similar and greatly reduced compared to surface noise we suspect that this is due to differences in surface vault quality between the two sets of stations

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

palaeoecological evidence for early aragonite dissolution in ancient calcite seas it has been proposed that shallow carbonate seas of upper ordovician and jurassic ages precipitated calcite as the primary calcium carbonate phase1 3 unlike such settings today it is expected that such seas were undersaturated with respect to the more soluble aragonite so that aragonitic invertebrate skeletons would have tended to dissolve here we describe examples in which this seems to have been the case our evidence consists of submarine cemented horizons in which aragonite fossils have been dissolved out to leave open moulds the walls of the moulds are encrusted by contemporaneous organisms confirming the early timing of the aragonite dissolution

broadband seismic noise attenuation versus depth at the albuquerque seismological laboratory abstract seismic noise induced by atmospheric processes such as wind and pressure changes can be a major contributor to the background noise observed in many seismograph stations especially those installed at or near the surface cultural noise such as vehicle traffic or nearby buildings with air handling equipment also contributes to seismic background noise such noise sources fundamentally limit our ability to resolve earthquake generated signals many previous seismic noise versus depth studies focused separately on either high frequency 1 hz or low frequency

temporal variations of seismic velocity at paradox valley colorado using passive image interferometry in our recent article ugalde et al 2014 we applied the passive image interferometry technique of sens schonfelder and wegler 2006 to monitor seismic velocity changes in paradox valley southwestern colorado for this purpose we computed the autocorrelation

high frequency seismic noise at lajitas texas a preliminary analysis of high frequency 1 to 20 hz ambient seismic noise at a very quiet site in southwest texas is presented at frequencies greater than 1 hz the displacement noise power decreases at a rate between f 4 and f 5 the ambient seismic noise is also characterized by persistent narrow band peaks f 0 2 hz of unknown origin the noise appears to be propagating at phase velocities 2 5 to 4 km sec or greater which suggests higher mode surface or body waves estimates of coherence and degree of polarization of three component array data indicate that the high frequency ambient noise is relatively well organized over distances of at least 600 to 700 m for a single component but is relatively unorganized in a three component sense a principal result of this preliminary analysis is that the use of three component high frequency 1 to 20 hz arrays at very quiet sites coupled with three component processors may result in substantial improvement of the thresholds for detection and discrimination of weak seismic events

neotectonics of coastal jeffara southern tunisia state of the art abstract helped by the studies and results of previous researchers we herein study the neotectonic of the coastal jeffara with the input of numerous 2d reflection seismic profiles onshore combined with digital elevation model analyses issued from srtm and field works acquired and available data were then integrated within a gis geodatabase where jerba zarzis and jorf appear to be part of a n s pull apart basin within a nw se transtensive right lateral major fault zone our structural geologic and geomorphologic analyses confirm and prove the presence of nnw sse right lateral en echelon tension gashes nw se aligned salt diapirs numerous active folds offsets en echelon folds and so on they are associated with this major right lateral nw se transtensive major coastal jeffara fault zone that affect the holocene and the villafranchian deposits we therefore confirm herein a new structural geodynamic jeffara model due to the post lower cretaceous northward migration of northern african to the eurasian plates this nw se transtensive fault zone is interpreted as a part of the southern branch of the eastward sahel block extrusion toward the free mediterranean sea boundary therefore this geodynamic movement may explain the presence offshore of small elongated nw se n s and ne sw transtensive basins and grabens with petroleum interest to conclude at the regional scale the structural geomorphologic approach combined with both field work and 2d reflection seismic profile analyses appear to be an excellent tool to prove and confirm the nw se right lateral transtensive extrusion fault zone of the coastal jeffara

low frequency cultural noise 1 abnormal cultural seismic noise is observed in the frequency range of 0 01 0 05 hz cultural noise generated by human activities is generally observed in frequencies above 1 hz and is greater in the daytime than at night the low frequency noise presented in this paper exhibits a characteristic amplitude variation and can be easily identified from time domain seismograms in the frequency range of interest the amplitude variation is predominantly in the vertical component but the horizontal components also show variations low frequency noise is markedly periodic which reinforces its interpretation as cultural noise such noise is observed world wide but is limited to areas in the vicinity of railways the amplitude variation in seismograms correlates strongly with railway timetables and the waveform shows a wavelength shift associated with the doppler effect which indicates that the origin of seismic background noise in the frequency range 0 01 0 05 hz is railways

variations in noise and signal levels in a pair of deep boreholes near amarillo texas to better understand the depth dependence of improvements in signal to noise ratio for borehole seismic data we have collected and analyzed a data set recorded from a pair of high fidelity broadband 1 to 80 hz seismometers sited in two closely separated deep boreholes near amarillo texas the total decrease surface to 1951 m in minimum noise level is up to 30 db the total decrease in maximum noise level is up to 35 db and the range of noise values maximum to minimum at a given depth decreases from 30 to 10 db the majority of the noise reduction occurs within the first few hundred meters below the surface but the decrease continues with depth and there is no indication that even lower noise levels do not exist below our deepest recording depth 1951 m cultural work day noise prominent during normal working hours from 0 to 40 hz is observed at all depths suggesting a strong body wave component wind generated 15 to 60 hz noise is strongest at the surface and is observed as deep as 367 m without a properly shielded hole with the addition of shielding to reduce the coupling between the borehole casing and or cable with the wind wind generated noise above 40 hz can be eliminated at 367 m events with near vertical propagation paths and signal power above 1 hz show signal strength decreasing uphole with a steady winnowing of high frequencies that can be fit by a simple frequency independent q of 35 5 8 for the material between 1951 and 367 m

single station monitoring of volcanoes using seismic ambient noise seismic ambient noise cross correlation is increasingly used to monitor volcanic activity however this method is usually limited to volcanoes equipped with large and dense networks of broadband stations the single station approach may provide a powerful and reliable alternative to the classical cross station approach when measuring variation of seismic velocities we implemented it on the piton de la fournaise in reunion island a very active volcano with a remarkable multidisciplinary continuous monitoring over the past decade this volcano has been increasingly studied using the traditional cross correlation technique and therefore represents a unique laboratory to validate our approach our results tested on stations located up to 3 5 km from the eruptive site performed as well as the classical approach to detect the volcanic eruption in the 1 2 hz frequency band this opens new perspectives to successfully forecast volcanic activity at volcanoes equipped with a single three component seismometer

spectral analysis of seismic noise induced by rivers a new tool to monitor spatiotemporal changes in stream hydrodynamics to 20 db relative to m s 2 hz for all the stations located along a steep 30 km long narrow and deeply incised channel of the trisuli river a major trans himalayan river the early summer increase in high frequency energy is modulated by a 24 h periodicity where the minimum of seismic noise level is reached around noon and the maximum is reached late in the evening a detailed study of seismic noise amplitude reveals a clear correlation with both regional meteorological and hydrological data along the trisuli river seasonal increase in ambient noise coincides with the strong monsoon rainfall and a period of rapid melting of snow and ice in the high elevations the observed 24 h cyclicity is consistent with the daily fluctuation of the precipitation and river discharge in the region river induced seismic noise is partly generated by stream turbulence but this mechanism fails to explain the observed clockwise hysteresis of seismic noise amplitude versus water level this pattern is better explained if a significant part of the observed seismic noise is caused by ground vibrations generated by bed load transport this points out the potential of using background seismic noise to quantify in continuous river bed load and monitor its spatial variations which remain difficult with classical approaches

high frequency borehole seismograms recorded in the san jcinto fault zone southern california part 2 attenuation and site effects we examine surface and downhole p and s wave spectra from local earthquakes recorded at two borehole seismometer arrays knw bh and pfo bh installed in the southern california batholith region of the san jacinto fault zone by the u s geological survey to assess the influence of the weathered layer on the spectral content of high frequency 2 to 200 hz seismic signals earthquake signals recorded downhole at both sites show significantly improved seismic bandwidth due to both a reduction in ambient noise levels and especially to dramatically increased levels of high frequency signal significant seismic signal is observed up to approximately 190 hz for p waves at knw bh stacked spectral ratios from these signals indicate that the highly weathered near surface between 0 and 150 m at knw bh and pfo bh exerts a much larger influence on seismic signals than deeper between 150 and 300 m material modeling of uphole downhole spectral ratio data suggests q 6 5 and q 9 between 0 and 150 m increasing to q 27 and q 26 between 150 and 300 m an outcrop mounted anza network station deployed approximately 0 4 km from knw bh displays roughly similar high frequency content to the knw bh downhole sensors but it exhibits spectra that are significantly colored by directional resonances low q and low velocity near surface material forms a lossy boundary layer at these borehole sites that is advantageous to the high frequency downhole environment not only are noise levels reduced but reflections from the surface and near surface are greatly attenuated as a result high frequency recordings from below the weathered zone more nearly resemble those recorded in a whole space than would otherwise be expected