acoustic survey for marine mammal occurrence and distribution off east antarctica 30 80 e in january february 2006 abstract a large scale systematic acoustic survey for whales and seals in eastern antarctic waters was conducted in january february 2006 during the broke west survey of southern ocean waters between 30 and 80 e longitude an acoustic survey was conducted to complement a traditional visual survey for marine mammal occurrence and distribution as part of the survey 145 difar sonobuoys were deployed every 30 of latitude on north south transects and prior to ctd stations on the initial east west transect underwater sound was analyzed for 70 minute samples from each sonobuoy blue whales were the most commonly recorded species identified at 55 of the sonobuoy deployment sites other species recorded include sperm 46 sites fin 14 humpback 2 and sei 3 whales and leopard 11 and ross 17 seals large numbers of blue and sperm whales and all ross seals were detected on the westernmost two transects which were the only transects of the survey with relatively extensive sea ice remaining off the continental shelf large numbers of blue whales were also detected in the more eastern waters of the survey off the prydz bay region while two detections of pygmy blue whales represent the farthest south these whales have been recorded of the relatively few fin whale detections most occurred in more northerly waters fin whale vocalizations from this region were distinctly different than those recorded elsewhere around antarctica suggesting acoustic recordings may be useful to delineate regional or stock boundaries of this species previously undescribed sounds were attributed to ross seals acoustic detections of these and leopard seal sounds indicate these animals venture further from their traditionally described distributions with vocalizing leopard seals occurring much further north than might be expected overall the results of the sonobuoy survey provide a measure of each species relative spatial distribution over the survey area based on acoustic detections and when combined with the results of the visual survey will provide a comprehensive view of marine mammal distribution throughout the region during the broke west survey

synthesis of earthquake generated t waves t phases excited by earthquakes propagate with low transmission loss along the ocean sound channel and are characterized by long duration wavetrains often having multiple peaks associated with bathymetric highs in the source region although t waves were first identified almost fifty years ago their activation has not been adequately explained in this paper we show that for continental margin earthquakes realistic t phase coda can be computed by expressing the acoustic energy in terms of several low order modes excited by point sources distributed uniformly over the seafloor the conversion of seismic energy to acoustic energy is thus consistent with seafloor scattering

testing low very low frequency acoustic sources for basin wide propagation in the indian ocean low very low frequency acoustic signals were transmitted to distant receivers in the indian ocean the aim was to test methods for characterizing the hydroacoustic capability of the international monitoring system ims that discriminates for nuclear tests in the region several acoustic sources were deployed between seychelles and fremantle australia and the ims receivers comprised a network of hydrophones off diego garcia and australia two of the three acoustic sources tested produced basin scale propagation of impulsive signals single glass spheres imploded within the sound channel produced a clear signal at frequencies above 40 hz at ranges of hundreds to a thousand kilometers five sphere glass implosions were recorded at ranges up to 4400 km near sea surface shots from a large airgun array were recorded in several cases at ranges of hundreds to thousands of kilometers the frequency of the highest signal to noise ratio arrivals varied within the 5 100 hz band high background noise level was

estimates of plume height from infrasound for regional volcano monitoring abstract present efforts in volcano monitoring particularly in southeast asia rely on the combination of local data generally gathered at less than 100 km from the volcano and satellite remote sensing while this combination has its strengths there are still weaknesses that the use of ground based remote sensing data such as distant infrasound measurements could help alleviate infrasound offers tools for detecting and characterizing volcanic plumes independent of cloud cover and time of day larger volcanic eruptions generate infrasound that is related to the plume and offers a unique view into eruption dynamics within the context of monitoring past research has demonstrated that infrasound can be used to estimate source parameters such as the rate at which material is ejected from volcanic vents during eruptions these are key input parameters into empirical and numerical models to estimate the height of volcanic plumes atmospheric ash transport and dispersion here we demonstrate the use of remote infrasound in estimating the height of volcanic plumes including a case study on the may 30 2014 plume from the volcano sangeang api in indonesia we were able to determine the plume height using infrasound gathered from 2000 to over 5000 km distance from the volcano during the january 2020 eruption of taal volcano in the philippines this method was applied to remote infrasound recorded 1650 km to the east we show that our workflow can be implemented in near real time offering an effective tool for rapid plume height measurement including associated uncertainties when volcanic clouds are not visible from the ground or space

ultra long range hydroacoustic observations of submarine volcanic activity at monowai kermadec arc monowai is an active submarine volcanic center in the kermadec arc southwest pacific ocean during may 2011 it erupted over a period of 5 days with explosive activity directly linked to the generation of seismoacoustic t phases we show using cross correlation and time difference of arrival techniques that the eruption is detected as far as ascension island equatorial south atlantic ocean where a bottom moored hydrophone array is operated as part of the international monitoring system of the comprehensive nuclear test ban treaty organization hydroacoustic phases from the volcanic center must therefore have propagated through the sound fixing and ranging channel in the south pacific and south atlantic oceans a source receiver distance of 15 800 km we believe this to be the furthest documented range of a naturally occurring underwater signal above 1 hz our findings which are consistent with observations at regional broadband stations and long range acoustic parabolic equation modeling have implications for submarine volcano monitoring

using hydroacoustic stations as water column seismometers 1 getting seismic data from the deep oceans usually involves ocean bottom seismometers but hydrophone arrays may provide a practical alternative means of obtaining vector data we here explore this possibility using hydrophone stations of the international monitoring system which have been used to study icebergs and t wave propagation among others these stations consist of three hydrophones at about the depth of the deep sound channel in a horizontal triangle array with 2 km sides we use data from these stations in the very low frequency regime 0 01 0 05 hz band to demonstrate that these stations can also be used as water column seismometers by differencing the acoustic pressure we obtain vector quantities analogous to what a seismometer would record comparing processed hydrophone station records of the 2004 great sumatra andaman earthquake with broadband seismograms from a nearby island station we find that the differenced hydrophones are indeed a practical surrogate for seismometers

estimation of the rupture length and velocity of the great sumatra earthquake of dec 26 2004 using hydroacoustic signals 1 unprecedented hydroacoustic observations of the megathrust earthquake of 26 dec 2004 were afforded by a network of 5 small hydroacoustic arrays located in the indian ocean at distances of 2800 to 7000 km from the epicenter each array recorded acoustic waves called t waves generated by this event analysis of a series of short time windows within the t wave coda shows that the receiver to source azimuth varies smoothly as a function of time indicating that the apparent t wave source is not stationary the apparent t wave source moves northward along the sunda trench at an average velocity of 2 km s closely tracking event rupture the hydroacoustic data suggest that the rupture proceeded in two distinct phases initially it progressed northwest along the sunda trench with a velocity of approximately 2 4 km s at 600 km from the epicenter the rupture slowed to approximately 1 5 km s as it continued to propagate to the northwest

tracking submarine volcanic activity at monowai constraints from long range hydroacoustic measurements monowai is a submarine volcanic center in the kermadec arc southwest pacific ocean in the past activity at the volcano had been intermittently observed in the form of fallout at the sea surface discolored water changes in seafloor topography and t phase seismicity but there is no continuous record for more recent years in this study we investigated 3 5 years of recordings at a hydrophone array of the international monitoring system ims located near juan fernandez islands for long range underwater sound waves from monowai results from direction of arrival calculations and density based spatial clustering indicate that 82 discrete episodes of activity occurred between july 2003 and march 2004 and from april 2014 to january 2017 volcanic episodes are typically spaced days to weeks apart range from hours to days in length and amount to a cumulative sum of 137 days of arrivals in total making monowai one of the most active submarine arc volcanoes on earth the resolution of the hydrophone recordings surpasses broadband network data by at least one order of magnitude identifying seismic events as low as 2 2 mb in the kermadec arc region further observations suggest volcanic activity at a location approximately 400 km north of monowai in the tonga arc and at healy or brothers volcano in the southern kermadec arc our findings are consistent with previous studies and highlight the exceptional capabilities of the ims network for the scientific study of active volcanism in the global ocean supporting information

theory of the airborne sound field generated in a resonant magma conduit abstract explosive sources triggered inside a magma conduit may excite the conduit into acoustic resonance the acoustic field in the conduit can propagate into the atmosphere through an open vent and ensonify the overlying atmosphere the character of the airborne sound field is determined by a combination of propagation and source effects the resonance of the magmatic conduit and the diffraction of the sound field at the volcanic vent are acoustic propagation effects whereas the explosion pressure signature and the firing rate of the explosions define the source characteristics for wavelengths larger than the conduit radius only the longitudinal resonances of the magmatic conduit are relevant and the open vent radiates like a piston surrounded by an infinite baffle in this case the fluid particle velocities are directed along the axis of the conduit and the sound field may propagate into the surrounding bedrock through the conduit wall displacement induced by the fluid overpressure this coupling may produce seismic signals with banded spectra such as volcanic tremor and long period events the airborne pressure field retains the modal structure of the sound field in the magmatic conduit which contains information on the conduit geometry and geo acoustic properties of the magma the seismic wavefield is driven by the acoustic field in the magma and also contains this information although it may be filtered by propagation effects in the bedrock the theoretical sound field in the magma conduit is used to interpret seismic tremor signals recorded at mt spurr volcano alaska rapid variations in the acoustic impedance of the magma conduit terminations can create systematic changes in the tremor spectra which can be used to monitor changes in the magmatic system the results of the modelling illustrate the difference between source effects and conduit resonance as well as the value of seismoacoustic measurements in volcanic environments

perth bermuda sound propagation 1960 adiabatic mode interpretation a 1960 experiment is examined in which sound from three underwater explosions near perth australia was detected near bermuda a recent attempt munk et al j phys ocean 18 1876 1988 to calculate propagation paths for this event included rotational flattening of the earth and horizontal refraction determined from the vertical sound speed minimum that calculation left bermuda in a shadow zone the current work invokes adiabatic mode theory to include refraction due to horizontal variations in the vertical mode structure these results include separate horizontal rays for each of the first few vertical modes using an archival data set of 230 ocean sound profiles to generate the modes numerically where appropriate interaction with bathymetry is included this solution possesses two eigenray groups group a passes just south of the cape of good hope at which point group b is almost 1000 km to the south intermediate rays are blocked by islands group a proceeds unimpeded to bermuda for a total t

on the mechanism of conversion of seismic waves to and from t waves in the vicinity of island shores high frequency seismic records from the polynesian seismic network are used to investigate in detail the processes of conversion of acoustic t wave energy from and to seismic waves at island shores on the source side we study the seismic to acoustic conversion based on t phases from hawaiian events recorded at polynesian stations located on the coral platter on the receiver side we study the acoustic to seismic conversion based on t phases from marine sources recorded across the polynesian islands in both instances our results underline the importance of steep slopes typically 50 in allowing an efficient conversion between p waves in the island structure and t waves in the water column these slopes can be coral reefs or the heads of young presumably unconsolidated basalt flows under this geometry modeling based on raytracing indicates that the seismic record of the t phase consists of a p wave at distances from the conversion point greater than 9 km at shorter distances s waves and surface waves are generated in the absence of a steep slope only surface waves are present these models can be used to compute precise and predictable travel time station corrections allowing the use of seismometers located inland to exploit the superb detection and location capabilities of t waves

seismic velocities of upper oceanic crust new measurements are reported for the seismic velocities in upper oceanic crust layer 2a at off axis sites along a track at 34 n in the pacific where the sediments were thin 33m and the crustal age increased from 42 to 63 m y the data were obtained in experiments designed to measure the reflection coefficient at each site using a horizontal line array the reflection coefficient versus angle information was inverted for the seismic velocities using a nonlinear inversion technique based on a simulated annealing search algorithm the p wave velocity increased from 2 7 to 3 1 km s along the track and the shear velocity in creased from about 1 0 to 1 6 km s these results suggest that the aging process controlled by passive hydrothermal circulation is continuing at these sites

tidally controlled stick slip discharge of a west antarctic ice a major west antarctic ice stream discharges by sudden and brief periods of very rapid motion paced by oceanic tidal oscillations of about 1 meter acceleration to speeds greater than 1 meter per hour and deceleration back to a stationary state occur in minutes or less slip propagates at approximately 88 meters per second suggestive of a shear wave traveling within the subglacial till a model of an episodically slipping friction locked fault reproduces the observed quasi periodic event timing demonstrating an ice stream s ability to change speed rapidly and its extreme sensitivity to subglacial conditions and variations in sea level

a comparative study of slope stability methods and mitigative design of a highway embankment landslide with a potential for deep seated sliding abstract during the very exceptional 1991 1992 winter of heavy rainfall in jordan slope stability problems were encountered at an embankment at station 47 300 along irbid amman highway geological and geotechnical investigations were conducted at the landslide area parametric slope stability analysis and back analysis were carried out for the embankment at the time of instability using both modified bishop and modified janbu limiting state equilibrium methods incorporated in the computer program pcstabl5m achilleos e 1988 user guide for pcstabl5m joint highway research project report jhrp 88 19 school of civil engineering purdue university west lafayette in usa in order to determine with confidence the most representative values of regional shear strength parameters explain the failure mechanism assess the condition at the time of failure and investigate all possible failure mechanisms through different foundation layers furthermore slope stability analysis was carried out for mitigative design options in the analysis different conditions of piezometric water level were considered moreover circular and sliding block failure surfaces at shallow and deep seated levels were investigated analysis showed that the main causes of instability were excessive load of the embankment constructing the embankment on colluvial deposits and the ingress of water into the embankment and the underlying colluvial material resulting in its softening the landslide movement occurred mainly within the colluvial deposits the most likely location of the slip surface was at the embankment colluvium contact analysis also showed a potential for a deep seated sliding along a marl layer that governed the remediation procedures which should be implemented to stabilize the area the best estimates of effective shear strength parameters of the materials encountered at the landslide area were as follows for colluvium cohesion c 0 0 and angle of friction gft 25 0 and for marl c 25 kpa and gft 13 0 the most appropriate remedial measure for road design and stabilization of the sliding area was found to be a combination of vertical reduction in embankment height and horizontal realignment this remediation was implemented in the field successfully

a study on the ambient noise field at a hydroacoustic array near robinson crusoe island continuous long term sound sources are recorded at hydroacoustic station h03s a threeelement hydrophone array south of robinson crusoe island between 2014 april 23 and 2017 august 20 the origin of the signal between 3 and 20 hz is investigated by using cross correlation array processing using plane wave beamforming and spectral analysis onebit normalization is successfully applied as a cross correlation pre processing step in order to suppress undesired earthquake events in the data traveltimes retrieved from averaged cross correlations do not yield a coherent array direction of arrival averaged envelopes of the cross correlations however indicate a coherent signal approaching h03s from a south southwest direction beamforming indicates two dominant backazimuth directions 172 224 antarctica and 242 monowai volcanic seamount this continuous source field creates possibilities to investigate the applicability of acoustic thermometry at hydrophones h03 s1 s2 cross correlation and array processing indicate significant directional variation in local propagation most likely related to the steep slope in the bathymetry near h03s in addition it is demonstrated that the ambient noise field is not sufficiently equipartitioned it is shown that this causes a large error in the estimated temperature primarily due to the short receiver spacing these large errors have not been addressed in previous studies on deep ocean acoustic thermometry hence it is shown that acoustic thermometry does not perform well on small arrays such as h03s the power spectral density yields a strong broadband signal in january march most likely related to iceberg noise a narrow banded signal around 17 hz between april and september corresponds to whale calls the best beam sound pressure levels towards antarctica are compared to era5 climatologies for sea ice cover and normalized stress into the ocean supporting the hypothesis of iceberg noise

hydroacoustic detection of volcanic activity on the gorda ridge february march 1996 abstract beginning at 0700 gmt on 28 february 1996 intense seismicity was detected in the northeast pacific ocean using the t phase monitoring system developed by noaa pmel to access the u s navy s sound surveillance system sosus in the north pacific the event was preliminarily located on the northernmost segment of the gorda ridge near 42 67 n and 126 8 w in the vicinity of the ridge segment high narrowgate the nature of the seismicity was similar to that observed in june 1993 at the coaxial segment of the juan de fuca ridge which was later documented to be a lateral magma injection with subsequent eruption due to several gaps in the data the detection information was not as comprehensive as during the coaxial event but an initial migration of epicenters from the narrowgate area down rift is inferred based on arrival bearings from a single array there is evidence for an additional diking event on the second and third day of activity there is also indication of a concentration of epicenters located near 42 6 n as occurred during the coaxial episode at what was later determined to be an eruption site examination of t wave rise times generally supports this interpretation based on the nature and duration of the activity a response effort was initiated which later confirmed hot water plumes and fresh lava flows at the site based on both hydroacoustic information and field observations it is proposed that the episode began with a lateral dike injection possibly with eruptive activity in the summit region followed by multiple magma pulses and eventual focusing of the seismic activity and extrusion near 42 6 n

structural and tectonic setting of the permo triassic basins of northwest europe abstract the permo triassic basins of nw europe formed by i late orogenic spreading of the variscan mountain belt eventually leading to ocean floor formation in the mid atlantic ii continental rifting propagating south from the arctic and iii thermal subsidence following carboniferous volcanic activity in the north sea spreading values in the northernmost north sea west of shetland and west and southwest of britain are relatively high but the sediments are dominantly continental the permo triassic rifting affected lithosphere thickened during caledonian and variscan orogenesis however subsidence associated with the arctic rifting together with global sea level changes allowed marine incursions into the north sea producing the large zechstein salt basins interference of the different basin formation mechanisms led to a complex three dimensional fault pattern and multidirectional extension across britain and the north sea this fault pattern formed the basic framework for subsequent jurassic and cretaceous basin formation

source levels of shallow explosive charges experimental measurements are reported in this article for the source levels of 0 82 kg signals underwater sound sus charges detonated at nominal depths of 18 3 91 and 183 m the data were recorded in the farfield using a high resolution digital data acquisition system that provided good reproduction of both the high and low frequency components of the signal from the explosion the results are presented in 1 3 octave bands from 5 630 hz and represent the mean values of samples of at least 30 charges for each depth group the standard deviations were within 1 db for most frequency bands analysis of the distribution of explosion depths indicated that the average detonation depths were consistently deeper than the nominal depths this result was attributed to the effect of the relatively cold water temperatures at the experimental site in addition to the measured source levels estimates for 0 82 kg sus charges at 244 m were scaled from the experimental data using a method suggested by hughes r hu

excitation of t phases by seafloor scattering t phases excited by suboceanic earthquakes are classified into two types abyssal phases which are excited near the earthquake epicenter at seafloor depths far below the sofar velocity channel and slope t phases which are excited at continental or ocean island slopes and ridges at distances up to several hundreds of kilometers from the epicenter in this article it is demonstrated that approximate time frequency characteristics of both classes of t phase can be synthesized under the assumption that t phases are excited by scattering from a rough seafloor seafloor scattering at shallow depths preferentially excites low order acoustic modes that propagate efficiently within the ocean sound channel minimum at greater depths scattering excites higher order modes which interact weakly with the seafloor along much of the propagation path using known variations in near source bathymetry t phase envelopes are synthesized at several frequencies for several events south of the fox islands that excited both

hydroacoustic signals generated by parked and drifting icebergs in the southern indian and pacific oceans summary we report the detection principally by the french polynesian seismic network of hydroacoustic signals generated inside large icebergs either parked along the wilkes coast of antarctica in the indian ocean or drifting in the southern pacific ocean between latitudes of 55 and 65 s during the years 2002 2004 the signals can be classified into two very broad families based on the nature of their spectra a first group features prominently monochromatic signals whose frequency can however fluctuate with time during a single sequence of emission typically lasting a few to a few tens of minutes such signals are generally reminiscent of those detected in 2000 in the ross sea and are generated principally in the indian ocean iceberg parking lot between longitudes 144 e and 156 e a new family of signals features a much broader spectrum superimposed on a number of preferential frequencies suggesting the background activation of a number of resonators these signals occur both in the parking lot and in the southern pacific further variations in spectra are documented inside each family on the basis of similar in situ observations on ross sea icebergs under project southberg the first family is generally interpreted as expressing a stick and slip process during collisions between large iceberg masses the second family of signals are observed during exceptional episodes of the otherwise silent drift of the icebergs in the deep pacific basin some of which correlate with their passage over the various fronts defining the oceanographic southern convergence zone finally a most recent episode of activity generally similar to the above first family was detected on 2004 december 3 4 at the ocean entry of the dibble ice tongue 600 km west of the parking lot along the coast of antarctica it is interpreted as resulting from collisions between large drifting icebergs and fragments of the ice tongue calved off during its disintegration as documented by satellite imagery

deep seafloor arrivals an unexplained set of arrivals in long range ocean acoustic propagation receptions from a ship suspended source in the band 50 100 hz to an ocean bottom seismometer about 5000 m depth and the deepest element on a vertical hydrophone array about 750 m above the seafloor that were acquired on the 2004 long range ocean acoustic propagation experiment in the north pacific ocean are described the ranges varied from 50 to 3200 km in addition to predicted ocean acoustic arrivals and deep shadow zone arrivals leaking below turning points deep seafloor arrivals that are dominant on the seafloor geophone but are absent or very weak on the hydrophone array are observed these deep seafloor arrivals are an unexplained set of arrivals in ocean acoustics possibly associated with seafloor interface waves

evidence of harmonic tremor from a submarine volcano detected across the pacific ocean basin 1 since the 1950s seismic activity associated with submarine volcanic eruptions has been detected throughout the pacific ocean basin using hydroacoustic methods however narrowband harmonic tremor with multiple overtones typically associated with subaerial volcanic eruptions has not commonly been observed this paper presents a series of recently recorded hydroacoustic signals that originated in the volcano islands arc south of japan a region that frequently experiences submarine eruptions the signals are characterized by a narrowband long duration high amplitude fundamental centered at 10 hz with three harmonics at 20 30 and 40 hz and are consistent with harmonic tremor signals observed using traditional seismic methods at active subaerial volcanoes throughout the world these hydroacoustic signals were detected 21 different times over the period from april 1998 through december 1999 typically lasting from several days to several weeks after a 6 month hiatus the signals were detected 26 more times from june 2000 through august 2001 the signals are qualitatively interpreted as a result of resonance of a magma gas mixture within a large chamber conduit near the surface of a shallow 1 km submarine volcanic edifice allowing for efficient release of acoustic energy into the ocean sound channel during periods of peak energy radiation the tremor could be clearly detected on hydrophones in the western aleutians hawaii west coast of the united states and eastern equatorial pacific and was detected by the french polynesian seismic network covering a maximum distance of 14 000 km

remote hydroacoustic sensing of large icebergs in the southern indian ocean implications for iceberg monitoring hydroacoustic signals generated by drifting icebergs that crack disintegrate and collide were identified on two hydrophone arrays in the indian ocean these hydrophone arrays are deployed in the sound fixing and ranging channel enabling the detection of small sources over ranges of several thousand kilometers due to the low attenuation source locations estimated from the signal bearings at the arrays are used to monitor two very large icebergs c20 and b17b spatial and temporal correlation of the location estimates with satellite observations confirm that the icebergs can be hydroacoustically resolved hydroacoustic generation rates at both c20 and b17b are highest at times of observed breakup for c20 which underwent continuous breakup clusters of events to the southeast of the main iceberg show that hydroacoustic observations can identify trails of icebergs that calved from the main berg whose dimensions are less than that easily resolved by moderate resolution satellite monitoring

mode coherence at megameter ranges in the north pacific ocean this article analyzes the coherence of low mode signals at ranges of 3515 and 5171 km using data from the acoustic thermometry of ocean climate atoc and alternate source test ast experiments vertical line arrays at hawaii and kiritimati received m sequences transmitted from two sources the 75 hz bottom mounted atoc source on pioneer seamount and the near axial dual frequency 28 84 hz ast source deployed nearby this study demonstrates that the characteristics of the mode signals at 5171 km range are quite similar to those at 3515 km range at 75 hz the mode time spreads are on the order of 1 5 s implying a coherence bandwidth of 0 67 hz the time spread of the 28 hz signals is somewhat lower but these signals show significantly less frequency selective fading than the 75 hz signals suggesting that at the lower frequency the multipaths are temporally resolvable coherence times for mode 1 at 75 hz are on the order of 8 min for the 3515 km range and 6 min for 5171 km range at 28 hz mode 1 is much more stable with a magnitude squared coherence of greater than 0 6 for the 20 min transmission period

csees an expert system for analysis and design of cut slopes and embankments an expert system is developed for evaluating failure potential of cut slopes and embankments the fuzzy sets theory is used with the modified monte carlo simulation technique to obtain the slope failure potential index sfpi incorporating factors affecting slope stability such as geology topography geomorphology precipitation vegetation and drainage conditions the developed cut slopes and embankments expert system csees includes a classification system for evaluating failure potential of cut slopes and embankments and a data bank on landslides in jordan the proposed classification system and slope failure potential method proved to be successful for the areas that experienced landslides in the past the expert system can be used directly for areas with the same geological formations as those areas in which landslides occurred in the past and can be used for areas with other geological formations by modifying the rock type or foundation material type factor incorporated in the expert system

ctbto s data and analysis pertaining to the search for the missing argentine submarine ara san juan the argentine submarine ara armada de la republica argentina san juan went missing on november 15th 2017 with its last confirmed contact location around 600 kilometres east of comodoro rivadavia chubut argentina in the days following the initiation of the multi national search and rescue mission the comprehensive nuclear test ban treaty organization ctbto analysed data recorded by its international monitoring system ims sensor network for any signals that could support this effort two of the ims hydrophone stations ha10 in the central atlantic ocean and ha04 in the southern indian ocean were found to have recorded an unusual hydroacoustic signal of unknown nature a hydroacoustic anomaly which originated from the vicinity of the last known location of the ara san juan on december 1st 2017 confirmation of the detection and localization capability of the ims network was made possible by a calibration test involving a depth charge deployed by the argentine navy also this signal was detected by the two ims hydrophone stations and its origin located to within 39 km of the announced deployment location after extended search operations on november 17th 2018 the ara san juan was found on the seabed at approximately 900 metres depth less than 20 km from the location of the hydroacoustic anomaly provided by ctbto this paper presents the methodologies applied by ctbto within months after the loss of the submarine aimed at detecting locating and characterizing the november 15th signal of unknown origin and the december 1st calibration explosion

seismic and hydroacoustic effects of the may 29 2010 submarine south sarigan volcanic explosion energy release and interpretation abstract the may 2010 submarine volcanic crisis of the shallow south sarigan seamount marianas arc ended on may 29 by a violent explosion that emitted a 12 km high atmospheric plume and created a crater 350 m in diameter the application of the multiphase localization method to the pg p t phases of this explosion allows us to refine considerably mainly based on the intense and impulsive t phases the location of their source that fits the position of the newly formed south sarigan crater we highlight the numerous similarities of this final explosion with artificial underwater explosions conventional or nuclear tests of known energy especially the explosive nature of the source in the volcanic basement is confirmed by the similarity of the p phases with those of underground nuclear tests and the application of discriminating criteria ms mb the explosive nature of the source in the water is also confirmedby the application of the identification criteria for hydroacoustic sources and the t phases exceptionally impulsive and of short durations these similarities allow us to provide a rough evaluation of the energy released by the south sarigan final explosion using the methods commonly applied to man generated explosions we estimate a minimal released energy of 1 kt 4 2 1012 j for the seismic effects of the shock and ca 1 t of equivalent tnt i e 4 2 109 j for the hydroacoustic effects of the explosive source in the water the processes leading to this final explosion are discussed on the basis of the sequence of the earlier seismic and eruptive events within the comprehensive nuclear test ban treaty framework this explosion that affected concomitantly the solid liquid and subaerial media is the first well documented one having generated intense waves p hydroacoustic t acoustic infrasounds and tsunamis

thin sediment shear induced effects on low frequency broadband acoustic propagation in a shallow continental sea low frequency 6 3 630 hz acoustic broadband propagation loss data collected in areas of a shallow continental sea where the seabed is composed of hard substrates covered by thin less than 40 m deposits of unconsolidated sediment are presented data are shown to exhibit characteristics consistent with loss due to coupling to interface waves at the sediment substrate interface k e hawker j acoust soc am 65 682 686 1979 in instances of a physically thin sediment cover loss is also attributed to coupling to guided elastic waves in the sediment s j hughes et al j acoust soc am 88 283 397 1990 interpretations are supported by numerical modeling of propagation loss using a recently developed wave number integration code for horizontally layered fluid solid media and geoacoustic models consistent with geophysical data from the sites of acoustic experiments

passive probing of the sound fixing and ranging channel with hydro acoustic observations from ridge earthquakes the international monitoring system includes a hydro acoustic part to verify the comprehensive nuclear test ban treaty besides explosive signals monitoring stations also detect acoustic waves from earthquakes that travel through the sound fixing and ranging sofar channel the travel times of such detections are listed in the reviewed event bulletin which is statistically evaluated for the stations located in the pacific indian and atlantic oceans the celerities of ridge earthquakes are calculated to build up a homogeneous data set based on similar source mechanisms the celerity is defined as the epicentral distance divided by the travel time the global characteristics of these celerities can be well understood in terms of temperature variations in the sofar channel a detailed velocity profile has been retrieved for the atlantic ocean where large differences 14 m s are found between the southern and northern parts of the basin propagation modeling with normal modes supports these findings which shows that the celerity gives an estimate of the sound speed in the sofar channel these results compare remarkably well with those from active experiments showing the ability of passively probing the sofar channel with hydro acoustic waves from earthquake sources

acoustic signals of underwater explosions near surfaces underwater explosions are conventionally identified and characterized by their seismic and or acoustic signature based on spherical models of explosion bubbles these models can be misleading in cases where the bubble is distorted by proximity to the free surface the bottom or to a solid object an experimental and numerical study of the effects of various nearby surfaces on the bubble s acoustic signature is presented measurements from high speed movie visualizations and acoustic signals are presented which show that the effect of proximity to a rigid surface is to increase the first period weaken the first bubble pulse and affect significantly the second period resulting in a peak value at standoffs of the same order as the maximum bubble radius these results are compared to results under a free surface over a bed of sand and over a cavity in a rigid surface in all cases the first period is increasingly lengthened or shortened as the motion of fluid around the bubble is increasingly or decrea

variability of the coherent arrivals extracted from low frequency deep ocean ambient noise correlations correlation processing of ocean noise can be used to develop totally passive ocean monitoring methods using various hydrophone pair orientations this study investigates the frequency dependence seasonal variability and emergence rate of coherent arrivals from cross correlations of low frequency ambient noise f 40 hz recorded on triangular hydrophones arrays these arrays are located at five existing hydroacoustic stations of the international monitoring system ims situated in the deep sound channel and distributed across the atlantic pacific and indian ocean basins for the majority of studied sites persistent and fast emerging coherent arrivals are reliably obtained if the axis connecting the selected hydrophone pair has a direct line of sight with regions of the globe containing stable and diffuse noise sources e g polar ice or seismic noise furthermore for this favorable orientation the emergence rate of coherent arrivals extracted between hydrophone pairs separated by long ranges here 130 km can be approximated based on measurements made between hydrophone pairs separated by short ranges 2 km in the atlantic ocean hence results from this study obtained using existing hydrophone configurations of the ims hydroacoustic stations could be used to guide the placement of other hydrophone arrays over the globe for future long range passive ocean monitoring experiments

on the coherent components of low frequency ambient noise in the indian ocean this letter demonstrates that the dominant coherent component of low frequency 1 hz f 20 hz ambient noise propagating between hydrophone pairs of the same hydroacoustic station deployed in the deep sound channel of the indian ocean is directional and mainly originates from antarctica however the amplitude of the peak coherent noise arrivals obtained using a 4 month long averaging interval was relatively low given the small hydrophones spacing hydrophones 2 km hence extracting similar coherent arrivals between two distinct hydroacoustic stations separated instead by thousands of kilometers for noise based acoustic thermometry purposes seems unlikely even using a year long averaging

source levels for shallow underwater sound charges this paper presents a simple method for removing the surface reflected component from the explosion waveform of signal underwater sound sus charges detonated at shallow depths in order to obtain accurate estimates of the source levels the method is based on the repeated subtraction of time shifted segments of portions of the source waveform that are uncontaminated by the surface reflection the technique provides a method for an accurate estimation of the source levels for charges detonated at depths shallower than 90 m the method is evaluated by comparing the source levels from the processed waveforms with results obtained by scaling source levels for deeper charges to depths of 58 and 18 3 m

residual strength of clays in landslides folded strata and the laboratory the post peak drop in drained shear strength of an overconsolidated clay may be considered as taking place in two stages first at relatively small displacements the strength decreases to the fully softened or critical state value owing to an increase in water content dilatancy second after much larger displacements the strength falls to the residual value owing to reorientation of platy clay minerals parallel to the direction of shearing if the clay fraction is less than about 25 the second stage scarcely comes into operation the clay behaves much like a sand or silt with angles of residual shearing resistance typically greater than 20 degrees conversely when the clay fraction is about 50 residual strength is controlled almost entirely by sliding friction of the clay minerals and further increase in clay fraction has little effect the angles of residual shearing resistance of the three most commonly occurring clay minerals are approximately 15 degrees for kaolinite 10 degrees for illite or clay mica and 5 degrees for montmorillonite when the clay fraction lies between 25 and 50 there is a transitional type of behaviour residual strength being dependent on the percentage of clay particles as well as on their nature the post peak drop in strength of a normally consolidated clay is due only to particle reorientation measurements of strength on natural shear surfaces agree within practical limits of variation with values derived from back analysis of reactivated landslides this field residual strength can be recovered by multiple reversal shear box tests on cut plane samples but in high clay fraction materials it is typically somewhat higher than the strength measured in ring shear tests residual strength is little affected by variation in the slow rates of displacement encountered in reactivated landslides and in the usual laboratory tests but at rates faster than about 100 mm min qualitative changes take place in the pattern of behaviour a substantial gain in strength is followed with increasing displacement by a fall to a minimum value in clays and low clay fraction silts this minimum is not less than the slow or static residual but in clayey silts with clay fractions around 15 25 according to tests currently in progress the minimum can be as low as one half of the static value author trrl

effects of variability associated with the antarctic circumpolar current on sound propagation in the ocean a series of small depth charges was detonated along a transect from new zealand to antarctica over a period of three days in late december of 2006 signals were recorded by hydrophones deployed near the source and at a sparse network of permanent hydrophone stations operated by the international monitoring system ims at distances up to 9 600 km our purpose was to determine how well signal characteristics could be predicted by the world ocean atlas 2005 woa05 climatological database for sources within the antarctic circumpolar current acc where recorded signal to noise ratios are high travel times and signal dispersion are predicted to within two seconds under the assumption that propagation is adiabatic and follows a geodesic path the deflection of the transmission path by abrupt spatial variations in sound speed at the northern acc boundary is predicted to decrease travel times to the ims stations by several seconds depending on the path the accuracy of source locations estimates based only on travel times depends on the monthly or seasonal database used to predict velocities and on whether we account for path deflection the configuration of the ims hydrophones limits source location accuracy within the acc comparison of signal spectra for recordings near the source and at distance show that transmission loss is nearly uniform as a function of frequency

monitoring pacific ocean seismicity from an autonomous hydrophone array since may 1996 an array of autonomous hydrophone moorings has been continuously deployed in the eastern equatorial pacific to provide long term monitoring of seismic activity including low level volcanic signals along the east pacific rise between 20 n and 20 s and the galapagos ridge the instruments and moorings were designed to continuously record low frequency acoustic energy in the sofar channel for extended periods and produce results comparable to those previously derived by using the u s navy sound surveillance system sosus in the northeast pacific the technology and methodology developed for this experiment including instrument design mooring configuration analysis software location algorithms with an analysis of errors and a predicted error field are described in detail volcanic activity is observed throughout the pacific along with seismicity along transform faults subduction zones and intraplate regions comparison data sets indicate detection thresholds and accuracy better than the land networks for open ocean areas and results comparable to or better than sosus volcanic seismicity along the fast spreading east pacific rise appears similar to documented examples in the northeast pacific but with much shorter durations one example from the intermediate spreading galapagos ridge is comparable to northeast pacific examples and several episodes of activity were observed in the wilkes transform fault zone a site of continuing off axis seismicity is located near 18 s and 116 w isolated intraplate earthquakes are observed throughout the study area earthquake information from this experiment and future observations will be provided through the world wide web and earthquake data centers

localization of antarctic ice breaking events by frequency dispersion of the signals received at a single hydroacoustic station in the indian ocean transient acoustic signals from antarctic ice cracking and breaking events featuring significant frequency dispersion were observed at the hydroacoustic stations deployed in the indian ocean as part of the international monitoring system ims of the comprehensive nuclear test ban treaty based on a comparison with numerical predictions the measured dispersion characteristics were used to estimate the range between ice events and the receiver combined with the bearing capability of the ims stations these estimates allow us to locate ice events from a single hydroacoustic station an analysis of range estimation errors due to uncertainty of the measured time frequency structure of signal arrivals and due to variations of the sound speed profiles was also conducted the analysis showed that the location accuracy from a single hydroacoustic station for the typical ice events was of the same order as that determined from an intersection of bearings from two remote stations if the signal frequency bandw

head wave data inversion for geoacoustic parameters of the ocean bottom off vancouver island head wave signals from small explosive charges have been analyzed to determine a geoacoustic profile for a shallow water site off the west coast of vancouver island the experimental design contained a vertical aperture provided by a vertical line array and a synthetic horizontal aperture from shots at different ranges from the vertical line array the simultaneous use of travel time and amplitude data for both apertures provided improved accuracy and vertical resolution of the estimated geoacoustic profile travel time vs range data from head waves from three distinct sub bottom interfaces were used to measure compressional speeds in the layers below the interfaces and estimate the layers thicknesses spatial filtering of the vertical line array data was necessary to resolve the head wave arrival from the shallowest layers analysis of the interference structure of the head wave power spectra at the vertical line array provided the means to measure the travel time of the head wave from the deepest layer in addition the head wave power spectra were used to estimate the compressional wave attenuation using a method based on the variation with range of the logarithmic derivative with respect to frequency of the head wave spectrum

new seismic evidence for a major geological boundary at shallow depth n devon recently acquired marine reflection data provide evidence for a major geological boundary at shallow depth under the southern bristol channel in the hangingwall block of the bristol channel thrust the boundary is recognized to equate with the top surface of a high velocity layer previously identified along refraction wide angle reflection seismic lines in the north devon area depth estimates from the reflection data and from a new interpretation of the earlier refraction data are combined to produce a contour map of the shallow boundary in the south central bristol channel and north devon areas the boundary has a wsw ene regional trend and lies at a depth of less than 2 km immediately north of the devon coast it is truncated to the north by the bristol channel thrust and deepens southwards across north devon and west somerset the boundary is interpreted as the top surface of a major litho stratigraphic unit older than the outcropping devonian sequence and in normal stratigraphic contact with it however in the absence of regional geological control the nature and age of the underlying high velocity layer remain uncertain

numerical methods in rock mechanics the purpose of this civilzone review paper is to present the techniques advances problems and likely future development directions in numerical modelling for rock mechanics and rock engineering

long range acoustic scattering from a shallow water mud volcano cluster analysis of reverberation measurements in the straits of sicily shows high intensity discrete scattered returns 10 20db above background reverberation these returns are due to scattering from mud volcanoes the reverberation from the mud volcanoes at ranges of 15 22km is reasonably consistent over these spatial scales i e kilometers and temporal scales of several hours measurements separated by 4years are also similar statistical characterization indicates that the reverberation associated with a mud volcano cluster is strongly non rayleigh and that the reverberation can be characterized by a single shape parameter roughly independent of frequency the non rayleigh statistics with a concomitant increase in the probability of false alarm indicate that mud volcanoes are a likely source of clutter mean target strengths were estimated at 1 11db over 160 1400hz and are consistent with target strengths measured during a different year at short direct path ranges accumulated evidence points to

thrust tectonics of s devon the tectonics of the area from start point to chudleigh sw england are shown to be dominated by northward verging thrust nappes two major thrusts are postulated the dartmouth antiform is considered to be a major thrust structure not a fold structure as previously interpreted the torquay limestones are allochthonous and part of a klippe of a major thrust nappe with a minimum displacement of 13 km northwards a progressive and diachronous sequence of deformation has been established with deformation starting in the s and moving n many of the folds and cleavages are probably related to the strains developed locally in thrust tips and may have no regional correlation more intense and complex deformation is found in the s compared to the n the diachroneity is also reflected in the k ar mineral ages in the s at start point southward verging backfolding is the last significant hercynian deformation phase folding the thrust nappes

passive underwater acoustic evolution of a calving event direct measurements of processes occurring at the ice ocean boundary are difficult to acquire because of the dangerous and dynamic nature of the boundary yet these processes are among the least well understood in glaciology because sound travels well through water passive underwater acoustics offers a method to remotely sense activity at this boundary here we present passive acoustic measurements and spectral analysis of the evolution of a subaerial calving event and the subsequent mini tsunami and seiche at meares glacier alaska usa using two hydrophones to record sound from 1 to 40 000 hz we find that each phase of a calving event has distinctive spectral characteristics an event begins with an infrasound rumble 1 20 hz then the ice fractures 20 100 hz falls and impacts the water 200 600 hz high frequency 10 000 hz sound increases in intensity quickly as the iceberg oscillates creating turbulence spray and waves within 10 s the low frequency audible sound dissipates and the mini tsunami and seiche sounds dominate infrasound plus high frequencies and continue for over 10 min the specific frequencies and duration of each phase of a calving event depend on its size and location and the glacier and fjord characteristics

accurate azimuth estimates from a large aperture hydrophone array using t phase waveforms a simple method is described whereby station to source azimuths are estimated by fitting a plane wave to envelope functions of t phases observed on a 5 element hydrophone array around ascension island south atlantic ocean when applied to a data set of 55 earthquakes of known location ranging between 2 and 45 degrees distance from ascension island estimated azimuths have a standard deviation of 3 3 degrees from reference azimuths when 3 or more hydrophone elements are used the standard deviation decreases to 1 8 degrees if t phase data from all 5 hydrophone elements are used we also investigate variations in predicted errors for different array geometries and arrival azimuths this simple method is amenable to automation and can easily be incorporated into a global monitoring system

antarctic icebergs a significant natural ocean sound source in the southern hemisphere in late 2007 two massive icebergs c19a and b15a drifted into open water and slowly disintegrated in the southernmost pacific ocean archived acoustic records show that the high intensity underwater sounds accompanying this breakup increased ocean noise levels at mid to equatorial latitudes over a period of 1 5 years more typically seasonal variations in ocean noise which are characterized by austral summer highs and winter lows appear to be modulated by the annual cycle of antarctic iceberg drift and subsequent disintegration this seasonal pattern is observed in all three oceans of the southern hemisphere the life cycle of antarctic icebergs affects not only marine ecosystem but also the sound environment in far reaching areas and must be accounted for in any effort to isolate anthropogenic or climate induced noise contributions to the ocean soundscape

zones of t wave excitation in the ne indian ocean mapped using variations in backazimuth over time obtained from multi channel correlation of ims hydrophone triplet data summary ground coupled hydro acoustic waves so called t waves observed at international monitoring system ims hydrophone triplet stations in the indian ocean were analysed for backazimuth and apparent wave speed by applying a progressive multi channel correlation method pmcc for t waves which propagate along topographically unblocked geodesic paths the three triplet channels generally show good signal correlation over sliding windows and various frequency bands a characteristic change in backazimuth over time in some cases combined with signs of dispersion is observed for many t waves generated by earthquakes from the margin of the indo australian plate between the sunda islands to the southeast and the andaman islands to the northwest backazimuths and arrival times of those pmcc detections are used to map point by point the areas where ground to water coupling takes place such areas are mostly linked to large gradients in the bathymetry predominantly at approximately the depth of the axis of the sound fixing and ranging sofar channel along island arcs edges of continental shelves and at comparatively small features like isolated islands or sea mountains six examples are discussed in this paper for the strongest events the area of detectable groundto water coupling often spans distances of more than 15 in one case even more than 26 and a range in backazimuths of up to 35 information on the accuracy of backazimuth determination on the average hydro acoustic wave speed along the wave path and on topographic blockage of waves can also be inferred from the results owing to the consistency and great detail of the mapped coupling zones for the study area it can be shown that it is predominantly seismic energy from p and or pn waves that couples efficiently into the sofar channel particularly for deep focus events the backazimuths determined for the highest amplitude segments of the signals can deviate considerably from the great circle azimuth between source and receiver and may therefore lead to inaccurate epicentre locations based on backazimuth measurements of t waves in some cases laterally reflected t waves are observed

spectral analysis of underwater explosions in the dead sea the present study utilizes the israel seismic network isn as a spatially distributed multichannel system for the discrimination of low magnitude events ml 2 5 namely earthquakes and underwater explosions in the dead sea in order to achieve this we began with the application of conventional single station methods such as spectral short period ratios we then applied a newly developed network oriented algorithm based on different spectral features of the seismic radiation from underwater explosions and earthquakes i e spectral semblance statistics twenty eight single shot underwater explosions uwes and 16 earthquakes in the magnitude range ml 1 6 2 8 within distances of 10 150 km recorded by the isn were selected for the analysis the analysis is based on a smoothed 0 5 hz window fourier spectrum of the whole signal defined by the signal to noise criterion without picking separate wave phases it was found that the classical discriminant of the seismic energy ratio between the relatively low frequency 1 6 hz and high frequency 6 11 hz bands averaged over an isn subnetwork showed an overlap between uwes and earthquakes and cannot itself provide reliable identification we developed and tested a new multistation discriminant based on the low frequency spectral modulation lfsm method in our case the lfsm is associated with the bubbling effect in underwater explosions the method demonstrates a distinct azimuth invariant coherency of spectral shapes in the low frequency range 1 12 hz of short period seismometer systems the coherency of the modulated spectra for different isn stations was measured by semblance statistics commonly used in seismic prospecting for phase correlation in the time domain the modified statistics provided an almost complete separation between earthquakes and underwater explosions

seismic refraction investigation of the structural setting of the lizard and start complexes sw england a long refraction line was established between the lizard and start peninsulas during a large scale seismic experiment carried out in sw england during 1979 interpretation of first arrival data indicates a shallow crustal structure consisting of two layers of regional extent the upper layer of average velocity 5 15 km s is interpreted as devonian metasediments the underlying layer with a velocity of about 6 10 km s lies at a depth of several kilometres beneath the lizard complex but rises eastwards to occur at or near surface in the eddystone and start areas the lower layer is believed to represent a pre devonian crystalline basement of which the metamorphic rocks of start and eddystone are constituent parts by contrast the lizard complex is interpreted as a thin surface sheet overlying devonian metasediments

saretl an expert system for probabilistic displacement based dynamic 3 d slope stability analysis and remediation of earthquake triggered landslides different models were developed for evaluating the probabilistic three dimensional 3 d stability analysis of earth slopes and embankments under earthquake loading using both the safety factor and the displacement criteria of slope failure in the 3 d analysis the critical and total slope widths become two new and important parameters the probabilistic models evaluate the probability of failure under seismic loading and consider the different sources of uncertainties involved in the problem i e uncertainties stemming from the discrepancies between laboratory measured and in situ values of shear strength parameters randomness of earthquake occurrence and earthquake induced acceleration the models also take into consideration the spatial variabilities and correlations of soil properties the developed models are incorporated in a computer program ptddssa probabilistic three dimensional dynamic slope stability analysis these developed analysis design procedures are incorporated within a code named saretl stability analysis and remediation of earthquake triggered landslides that was developed in this study for stability analysis and remediation of earthquake triggered landslides in addition to the dynamic inertia forces the developed system takes into consideration the local site effects the code is capable of 1 prediction of permanent deformations that result from landslides under seismic loading using both probabilistic and deterministic approaches 2 the assessment of landslide hazard that affects major transportation routes in the event of earthquakes and the preparation of earthquake induced landslide hazard maps i e maps that show expected displacements and probability of slope embankments failure for different earthquakes magnitudes and environmental conditions 3 proposing a mitigation strategy against landslides and suggesting guidelines for remedial measures the developed expert system is applied to a major highway case study design maps are developed for the highway under seismic loading

internal deformation of the gorda plate observed by hydroacoustic monitoring on august 29 1991 the national oceanic and atmospheric administration vents program began monitoring the northeast pacific ocean plate boundaries using continuously recorded data from the u s navy s sound surveillance system sosus hydrophone arrays routine detection and location of small 2 4 m 3 5 earthquakes revealed a nne ssw trending band of seismicity through the center of the gorda plate the majority of the earthquakes in the band were not detected by land based seismic networks this band of microearthquakes was active from the initiation of sosus monitoring in august 1991 through july 1992 at a rate of 20 events per week since august 1992 however the activity has effectively ceased some of the microearthquakes in the band are likely aftershocks to three large mw 6 mid gorda plate earthquakes that occurred 1 2 months prior to the beginning of sosus monitoring the hydroacoustically detected events in the band however do not occur in the proximity of the mw 6 events and the activity level increased several months afterward suggesting the microseismicity band represents a more general pattern of deformation within the gorda plate the cessation of the midplate activity follows the occurrence of a large earthquake sequence in the adjacent cascadia subduction zone in april 1992 it is proposed that the band of microseismicity and the three large midplate events reflect an accumulation of stress in the gorda plate with the eventual termination of this pattern due to stress reduction associated with movement in the adjacent subduction zone stress field modeling of the region yields results consistent with this interpretation

methods for monitoring hydroacoustic events using direct and reflected t waves in the indian ocean 1 the recent installation of permanent three element hydrophone arrays in the indian ocean offshore diego garcia and cape leeuwin australia provides an opportunity to study hydroacoustic sources in more detail than previously possible we developed and applied methods for coherent processing of the array data for automated association of signals detected at more than one array and for source location using only direct arrivals and using signals reflected from coastlines and other bathymetric features during the 286 day study 4725 hydroacoustic events were defined and located in the indian and southern oceans events fall into two classes tectonic earthquakes and ice related noise the tectonic earthquakes consist of mid ocean ridge trench and intraplate earthquakes mid ocean ridge earthquakes are the most common tectonic events and often occur in clusters along transform offsets hydroacoustic signal levels for earthquakes in a standard catalog suggest that the hydroacoustic processing threshold for ridge events is one magnitude below the seismic network fewer earthquakes are observed along the java trench than expected because the large bathymetric relief of the source region complicates coupling between seismic and hydroacoustic signals leading to divergent signal characteristics at different stations we located 1843 events along the antarctic coast resulting from various ice noises most likely thermal fracturing and ice ridge forming events reflectors of signals from earthquakes are observed along coastlines the mid indian ocean and ninety east ridges and other bathymetric features reflected signals are used as synthetic stations to reduce location uncertainty and to enable event location with a single station

tectonomagmatic activity and ice dynamics in the bransfield strait back arc basin antarctica 1 an array of moored hydrophones was used to monitor the spatiotemporal distribution of small to moderate sized earthquakes and ice generated sounds within the bransfield strait antarctica during a 2 year period a total of 3900 earthquakes 5925 icequakes and numerous ice tremor events were located throughout the region the seismic activity included eight space time earthquake clusters positioned along the central neovolcanic rift zone of the young bransfield back arc basin these sequences of small magnitude earthquakes or swarms suggest ongoing magmatic activity that becomes localized along isolated volcanic features and fissure like ridges in the southwest portion of the basin a total of 122 earthquakes were located along the south shetland trench indicating continued deformation and possibly ongoing subduction along this margin the large number of icequakes observed show a temporal pattern related to seasonal freeze thaw cycles and a spatial distribution consistent with channeling of sea ice along submarine canyons from glacier fronts several harmonic tremor episodes were sourced from a large 30 km2 iceberg that entered northeast portion of the basin the spectral character of these signals suggests they were produced by either resonance of a small chamber of fluid within the iceberg or more likely due to periodicity of discrete stick slip events caused by contact of the moving iceberg with the seafloor these pressure waves appear to have been excited by abrasion of the iceberg along the seafloor as it passed clarence and elephant islands

major crustal reflectors beneath sw england strong wide angle reflection events were detected during a crustal seismic experiment carried out in sw britain in 1979 three crustal reflectors have been identified referred to as rl r2 and r3 rl lies at a depth of about 8 km and appears to be restricted to the interior of the granite batholith underlying sw england the nature of this reflector is unknown r2 is a mid crustal reflector lying at a depth of 10 15 km and interpreted as rising gradually northwards it coincides locally with the base of the granite as predicted by gravity modeling but extends well beyond the northern limit of the granite body it is suggested that r2 may represent a major thrust of late variscan age r3 is the deepest reflector identified and lies at a depth of 27 30 km r3 is interpreted as the base of the crust and its computed depth is in close agreement with the local depth to the moho derived from an earlier seismic experiment in sw britain

estimation of seismic velocities of upper oceanic crust from ocean bottom reflection loss data this paper describes a bayesian inversion of acoustic reflection loss versus angle measurements to estimate the compressional and shear wave velocities in young uppermost oceanic crust layer 2a the data were obtained in an experiment on the thinly sedimented western flank of the endeavor segment of the juan de fuca ridge using a towed horizontal hydrophone array and small explosive charges as sound sources measurements were made at three sites at increasing distance from the ridge spreading center to determine the effect of age of the crust on seismic velocities the inversion used reflection loss data in a 1 3 octave band centered at 16 hz the compressional and shear wave velocities of the basalt were highly sensitive parameters in the inversion the compressional wave velocity increased from 2547 30 to 2710 18 m s over an age span of 1 4 million years ma from the spreading center an increase of 4 5 1 0 ma the basalt shear wave velocity increased by nearly a factor of 2 from 725 to 1320 m s o

comparative evolution of the iapetus and rheic oceans a north america perspective abstract differences in the origin and evolution of the iapetan and rheic oceans profoundly affected the development of the ouachitan appalachian variscan orogen the iapetus ocean was initiated in the late neoproterozoic early cambrian by the separation of large continental landmasses laurentia baltica gondwana whereas the rheic ocean originated in the late cambrian early ordovician as the result of the separation of several ribbon continents collectively termed peri gondwanan terranes from the northern margin of gondwana compared to the classic passive margin developed along the laurentian margin of iapetus passive margin successions to the rheic ocean are more limited in extent during convergence both margins of the iapetus ocean developed western pacific type arc back arc systems whereas subduction of the rheic ocean was primarily directed beneath laurentia and was andean in style closure of iapetus involved a number of arc back arc accretionary events and had occurred by the middle silurian as a result of laurentia baltica collision to form laurussia and the accretion of the peri gondwanan terranes rheic ocean closure occurred in the carboniferous by way of continent continent collision between laurussia and gondwana with gondwana on the lower plate within iapetus the formation of ophiolites occurred early in the orogenic cycle and was followed soon after by obduction hp lt metamorphism and foreland directed thrusting that is intimately related to accretionary events these features dominate the northern appalachian orogen where ht lp metamorphism is attributed to post accretionary slab break off events in contrast hp lt metamorphism within the rheic ocean reflects a type subduction during laurussia gondwana collision and is rapidly succeeded by ht lp metamorphism attributed to orogenic collapse ophiolites are rare and were formed either very early early ordovician or very late devonian carboniferous in the evolution of the ocean the early ordovician ophiolites were not obducted until the carboniferous at least 100 million years after their protoliths were formed rheic ocean closure resulted in the formation of large scale bivergent structures within the orogen with symmetry changing on either side of the rheic suture comparison of the evolution of the iapetus and rheic oceans suggests that differences in rift configuration passive margin development and subduction zone geometry within the two oceans profoundly influenced the subsequent style of orogenesis within the ouachita appalachian variscan orogen

deep ocean sound speed characteristics passively derived from the ambient acoustic noise field the propagation of acoustic waves in the ocean strongly depends on the temperature lowfrequency acoustic waves can penetrate the ocean down to depths where few in situ measurements are available it is therefore attractive to obtain a measure of the deep ocean temperature from acoustic waves the latter is especially true if the ambient acoustic noise field can be used instead of deterministic transient signals in this study the acoustic velocity and hence the temperature is derived in an interferometric approach from hydrophone array recordings the arrays were separated by over 125 km near ascension island in the atlantic ocean at a depth of 850 m furthermore the dispersive characteristics of the deep ocean sound channel are resolved based on the retrieved lag times for different modes in addition it is shown how the resolution of the interferometric approach can be increased by cross correlating array beams rather than recordings from single sensor pairs the observed acoustic lag times between the arrays corresponds well to modelled values based on full wave modelling through best known oceanic models

seismic detection of underwater volcanism the example of french polynesia we present a review of the principal methods used for the seismic detection and identification of active underwater volcanism based on our experience in french polynesia in particular we descrobe the 5 year activity in the tahiti mehetia area during which more than 32000 earthquakes were detected by the polynesian network we discuss the use of the following three types of seismic waves conventional mostly body waves seismic tremor andt waves propagated in the low velocity acoustic channel of the ocean for each of these waves we discuss the principal characteristics of the signals their spectral content the type of information they provide on the activity of the volcano and the various limitations faced by their use in detection or monitoring of underwater volcanic edifices we present a review of the principal swarms monitored by the polynesian network and discuss their characterization as either volcanic or tectonic

seafloor seismicity antarctic ice sounds cetacean vocalizations and long term ambient sound in the indian ocean basin this paper presents the results from the deflo hydroacoustic experiment in the southern indian ocean using three autonomous underwater hydrophones complemented by two permanent hydroacoustic stations the array monitored for 14 months from november 2006 to december 2007 a 3000 x 3000 km wide area encompassing large segments of the three indian spreading ridges that meet at the indian triple junction a catalogue of 11 105 acoustic events is derived from the recorded data of which 55 per cent are located from three hydrophones 38 per cent from 4 6 per cent from five and less than 1 per cent by six hydrophones from a comparison with land based seismic catalogues the smallest detected earthquakes are m b 2 6 in size the range of recorded magnitudes is about twice that of land based networks and the number of detected events is 5 16 times larger seismicity patterns vary between the three spreading ridges with activity mainly focused on transform faults along the fast spreading southeast indian ridge and more evenly distributed along spreading segments and transforms on the slow spreading central and ultra slow spreading southwest indian ridges the central indian ridge is the most active of the three with an average of 1 9 events 100 km month along the sunda trench acoustic events mostly radiate from the inner wall of the trench and show a 200 km long seismic gap between 2 degrees s and the equator the array also detected more than 3600 cryogenic events with different seasonal trends observed for events from the antarctic margin compared to those from drifting icebergs at lower up to 50 degrees s latitudes vocalizations of five species and subspecies of large baleen whales were also observed and exhibit clear seasonal variability on the three autonomous hydrophones whale vocalizations dominate sound levels in the 20 30 and 100 hz frequency bands whereas earthquakes and ice tremor are a dominant source of ambient sound at frequencies 20 hz

sound channel observations of ice generated tremor in the indian ocean 1 mid to low southern latitude hydrophone stations within the indian ocean have recorded two distinct types of low frequency 100 hz tremor that can be correlated with drifting icebergs and glacial features along the wilkes land coast of eastern antarctica the most common of these signals is a variable harmonic tremor vht with spectral peaks that exhibit frequency fluctuations through time these signals typically display a 4 to 10 hz fundamental frequency and may have as many as ten harmonic bands individual vht signal packets have durations of up to 30 min and occur throughout the year in clusters that continue for hours to days a second less commonly observed signal is characterized by shorter duration 25 to 90 s pulses with a convex upward spectrogram appearance these cusped pulse tremors cpt often exhibit a near uniform pulse spacing with episodes continuing for minutes to hours tremor received levels at hydrophones near 32 s 114 e and 7 s 72 e reach as high as 142 and 133 db re 1 pa peak to peak respectively propagation likely occurs as a sea surface reflected phase at high latitudes and a sound channel phase north of the convergence zone with low frequency transmission loss estimates suggesting maximum acoustic source levels of 245 db re 1 pa at 1 m source locations for a subset of the loudest vht signals correlate with the satellite derived locations of a large iceberg b 15d that migrated westward along the wilkes land shelf region during 2002 and early 2003 most vht sources however cannot be correlated with known iceberg locations suggesting that these signals also may be sourced from smaller unnamed icebergs and or associated with outlet glaciers distributed along the wilkes land coast cpt signals have a more limited spatial distribution originating from five specific regions where ice streams are observed the harmonic nature of both signal types is consistent with the resonance of an ice layer or fluid filled cavity within an ice mass

seismic and hydroacoustic tremor generated by colliding icebergs 1 iceberg harmonic tremor iht emanating from tabular icebergs in the southern ocean and along calving margins of the antarctic ice sheet is a complex evolving signal at frequencies above approximately 0 5 hz iht has been observed as t phases on islands in the equatorial pacific as hydroacoustic signals in the indian ocean and by local and regional antarctic seismic networks to identify the iht source mechanism and to understand its relevance to iceberg calving evolution and breakup we deployed seismometers on a giant 25 by 50 km tabular iceberg called c16 in the ross sea antarctica during a uniquely accessible period austral summer 2003 2004 when it was aground against the northern shore of ross island during the deployment period c16 was in sporadic contact with another giant tabular iceberg b15a that was moving under the influence of local ocean currents this study reveals that the c16 associated iht was a manifestation of extended episodes of discrete repeating stick slip icequakes typically thousands of individual subevents per hour produced when the cliff like edges of the tabular icebergs underwent glancing strike slip collisions the iht signal that we observed is thus not a phenomenon associated with iceberg elastic or fluid resonance modes but is instead the consequence of long sequences of very regularly spaced and similar pulses of seismic radiation from these constituent stick slip subevents iht represents a newly identified glaciogenic source of seismicity that can be used to improve our understanding of iceberg dynamics and possibly of ice shelf disintegration processes

application of the model of small scale convection under the island arc to the ne honshu subduction zone 1 we compare the results of 2 d 3 d time dependent models of small scale convection under the island arc with the geophysical and geologic data observed in the ne honshu subduction zone northeast japan assuming that the temperature anomalies have a close connection with the seismic anomalies we may constrain the geometry of the low viscosity wedge lvw overlying the slab which may be produced by the water dehydrated from the subducting slab our preferred model predicts step like low velocity anomalies above the subducting slab rather than smooth anomalies subparallel to the subducting slab since the shallow nature of the lvw is required for the small scale convection to occur at the back arc end of the lvw a movement of cold plumes generated at the back arc end of the lvw may be related to a possible migration of volcanism from back arc to volcanic front side to be consistent with the observation which may suggest the migration rate of 2 cm yr models require weak viscous couplings between the mantle wedge and the underlying subducting slab whose speed of subduction is 10 cm yr three dimensional models showing 3 d temperature variation consist of fairly continuous and strong temperature anomalies several hundreds of degrees under the volcanic front and weak finger like temperature anomalies several tens of degrees behind them which are similar to the pattern of the seismic tomography the time dependent behavior of the temperature field shows that the pattern of fingers flip flops with a timescale equal to the ratio of the horizontal extent of the lvw to the migration speed of cold plumes this change of pattern of fingers may have an important implication for understanding the past distribution of volcanism further studies related to 1 the detailed morphology of the low velocity zone above the subducting slab 2 the spatial and temporal evolution of volcanism and 3 the dynamic 3 d model studies which self consistently determine the distribution of water volatiles and the resultant weak rheology are important for checking the validity of our model or developing alternative models

long range detection of hydroacoustic signals from large icebergs in the ross sea antarctica abstract hydroacoustic signals detected in late 2000 by seismic stations in polynesia are shown to originate from huge icebergs which at the time were drifting in the ross sea after calving off the ross ice shelf the signals present a broad variety of spectral characteristics most of them featuring prominent eigenfrequencies in the 4 7 hz range often complemented by overtones most epicenters obtained by combining observations of distant hydroacoustic and regional seismic records follow the spatio temporal evolution of the drift of iceberg b 15b most of the signals are generated during a 36 day time window when it is speculated that b 15b collided with smaller icebergs or was scraping the ocean floor on the shallow continental shelf we speculate on the possible physical nature of the resonator generating the signals which could correspond to an elastic mode of the iceberg or to the oscillation of fluid filled cracks in the ice

matched field evaluation of acoustic scattering from arctic ice this paper investigates the three dimensional acoustic scatter from large scale features under the arctic ice cover using field data collected during the cearex experiments in april 1989 the analysis involves the identification and isolation of the features under the ice canopy and the simultaneous evaluation of their spatial scattering characteristics a two step matched field processing mfp algorithm is used to solve this complex multiparameter estimation problem using one large 1200 m and four short 300 m vertical line arrays and a crossed horizontal hydrophone array in a matched field processing scheme beamforming under the ice sheet was performed to obtain an approximate map of the rough interface between ice and water this analysis yields estimates for scattering strengths for frequencies ranging between 25 and 105 hz it is shown that scatter from the elastic ice surface is a frequency selective phenomenon this beamformed map is then used to isolate a single discrete scatterer and s

modelling sound propagation in the southern ocean to estimate the acoustic impact of seismic research surveys on marine mammals summary modelling sound propagation in the ocean is an essential tool to assess the potential risk of air gun shots on marine mammals based on a 2 5 d finite difference code a full waveform modelling approach is presented which determines both sound exposure levels of single shots and cumulative sound exposure levels of multiple shots fired along a seismic line band limited point source approximations of compact air gun clusters deployed by r v polarstern in polar regions are used as sound sources marine mammals are simulated as static receivers applications to deep and shallow water models including constant and depth dependent sound velocity profiles of the southern ocean show dipole like directivities in case of single shots and tubular cumulative sound exposure level fields beneath the seismic line in case of multiple shots compared to a semi infinite model an incorporation of seafloor reflections enhances the seismically induced noise levels close to the sea surface refraction due to sound velocity gradients and sound channelling in near surface ducts are evident but affect only low to moderate levels hence exposure zone radii derived for different hearing thresholds are almost independent of the sound velocity structure with decreasing thresholds radii increase according to a spherical 20 log10 r law in case of single shots and according to a cylindrical 10 log10 r law in case of multiple shots a doubling of the shot interval diminishes the cumulative sound exposure levels by 3 db and halves the radii the ocean bottom properties only slightly affect the radii in shallow waters if the normal incidence reflection coefficient exceeds 0 2

the rb sr isochron age of the kennack gneiss and its bearing on the age of the lizard complex cornwall an acid vein from a borehole in the kennack gneiss has given a whole rock rb sr isochron age of 369 12 ma this is interpreted as a metamorphic age recording the time of emplacement of the lizard complex this emplacement in late devonian times was part of an early phase of the hercynian orogeny which also affected the gramscatho 9series9 of s cornwall

evidence for a common scale o 0 1 m that controls seabed scattering and reverberation in shallow water analysis of the spectral content of long range reverberation yields two observations first there is a remarkably similar scale o 0 1 m between three diverse continental shelf regions this is surprising given the complexity and diversity of geologic processes second there is strong evidence that the scale is associated with heterogeneities within the sediment thus sediment volume scattering not interface scattering controls long range reverberation from a few hundred hertz to several kilohertz this is also unexpected given that at long ranges the vertical grazing angles are less than the critical angle and hence the penetration of the acoustic field into the sub bottom is expected to be modest the consistency of the scale o 0 1 m suggests an underlying feature or mechanism that is consistent across many ostensibly diverse geological settings neither the feature nor mechanism is known at this time

the link between climate warming and break up of ice shelves in the antarctic peninsula a review of in situ and remote sensing data covering the ice shelves of the antarctic peninsula provides a series of characteristics closely associated with rapid shelf retreat deeply embayed ice fronts calving of myriad small elongate bergs in punctuated events increasing flow speed and the presence of melt ponds on the ice shelf surface in the vicinity of the break ups as climate has warmed in the antarctic peninsula region melt season duration and the extent of ponding have increased most break up events have occurred during longer melt seasons suggesting that meltwater itself not just warming is responsible regions that show melting without pond formation are relatively unchanged melt ponds thus appear to be a robust harbinger of ice shelf retreat we use these observations to guide a model of ice shelf flow and the effects of meltwater crevasses present in a region of surface ponding will likely fill to the brim with water we hypothesize building on weertman 1973 hughes 1983 and van der veen 1998 that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat a thermodynamic finite element model is used to evaluate ice flow and the strain field and simple extensions of this model are used to investigate crack propagation by meltwater the model results support the hypothesis