integrated seismic and cone penetration test observations at a distressed earthen levee marrero louisiana u s a abstract seismic refraction velocity versus depth models can complement our understanding of natural soils beneath flood protection levees at locations between geotechnical sites levee failures in new orleans in 2005 are attributable in part to poor understanding of sediments between geotechnical sites to a first order subsurface fluvial deltaic facies in the lower mississippi delta plain correlate with general geotechnical properties of water content and cohesive strength but are too laterally variable to be easily predicted from geotechnical sites spaced 100 m apart an artificial earthen levee suitable for seismic investigation lies 15 km s of the city of new orleans louisiana values of shear wave velocity vsh versus depth 0 20 m are derived by forward ray trace models of seismic refraction arrivals which match key boundaries identified at geotechnical cone penetration testing sites spaced at 300 m apart in particular a 100 m section along the levee crest shows continuous cracks which are as much as 10 cm wide and 30 cm deep at their northern end cracking may relate to high strain induced by variable near surface subsidence of organic rich sediments topographic cross sections across the levee show variable differential subsidence of 1 2 m based on effective medium theory vp and vsh versus depth profiles indicate unexpectedly greater saturation and lower shear moduli on the unprotected levee side adjacent to the cracks integration of geophysical sedimentary and topographic data even if only at a few locations can help locate anomalous zones in sub levee soil between geotechnical boring sites future preventive monitoring of flood protection barriers stands to benefit greatly from integrated data sets ground truthed to geotechnical data

fluid inclusion petrography of sw england granites and its potential in mineral exploration fluid inclusions in granite quartz from sw england provide a record of the complex and protracted hydrothermal history of this important metallogenic province regional variations in terms of the different types of inclusions can be correlated on an inter pluton scale with both the texture of the host granite and the extent to which it is mineralized on an intra granite scale those areas where mineralization is particularly pronounced show a higher overall inclusion abundance than areas where little or no mineralization is known to occur the types of fluid inclusion most commonly related to sn w cu mineralization are halite free moderate temperature inclusions inclusions containing visible co2 at room temperature are restricted to two localities in sw england both of these contain stockwork vein swarm tungsten mineralization these regional fluid inclusion anomalies show that fluid inclusion petrography using a simple petrographic microscope has potential application in the field of mineral exploration

tourmalinite from northern guangxi china the extensive development of tourmalinite is a feature that distinguishes the northern guangxi polymetallic tin province of china from similar metallogenic provinces elsewhere two types of tourmalinite occur in the province the first type in the lower part of the early proterozoic sibao group is bedded stratiform or lenticular tourmalinite that shows well developed laminated gel and degelatinized structures its mineral assemblage is very simple and the grain size ranges from 2 to 8 m this tourmaline is relatively rich in mg with an fe fe mg ratio of 0 25 0 50 the second type of tourmalinite occurs as lodes distributed in the exocontact zone of late proterozoic biotite granite intrusions its mineral assemblage is relatively complex the tourmaline is present as euhedral or subhedral crystals ranging from 0 1 to 3 5 mm mostly from 0 5 to 1 mm this tourmaline commonly exhibits a radiating zoned structure with fe fe mg ratios of 0 64 0 79 it is suggested that the bedded tourmalinite formed by exhalation in an early proterozoic spreading ridge environment whereas the vein tourmalinite formed in a plate convergence setting genetically associated with emplacement of late proterozoic biotite granite as the tourmalinites themselves are related to mineralized rocks and orebodies their origin and the related boron cycle of the region reflect to some extent the formation and evolution of the associated polymetallic tin deposits of the region

shear velocity structure from regionalized surface wave dispersion in the basin and range lateral variations of shear velocity structure in the western united states are studied using observations of rayleigh and love wave phase velocity dispersion we measured rayleigh wave dispersion in the 6 60 sec period range on over 80 paths using both single and two station methods love wave dispersion was also measured on about 50 paths a pure path regionalization method employing a block province grid is used to determine lateral variations of dispersion in the basin and range and adjacent geologic regions structural inversions of the regionalized rayleigh wave dispersion curves indicate significant lateral variations in the crust and upper mantle structure of the basin and range and transition areas a pronounced low velocity zone in the upper mantle is found under the eureka heat flow province in the central basin and range the lithospheric thickness in this province is 45 km in contrast to the great basin model of priestley and brune 1978 approx 65 km regionalization of love wave data together with the rayleigh wave results suggest the existence of polarization anisotropy in many areas of the basin and range if verified anisotropy must be accounted for in phase velocity inversions for the structure of the basin and range

in situ measurements of velocity dispersion and attenuation in new jersey shelf sediments the existence of acoustic velocity dispersion and frequency dependence of attenuation in marine sediments is investigated using in situ measurements from a wideband acoustic probe system during the shallow water 2006 experiment direct path pulse propagation measurements show evidence of velocity dispersion within the 10 80khz frequency band at two silty sand sites on the new jersey shelf the measured attenuation in db m shows linear frequency dependency within the 10 80khz frequency band the measured velocity dispersion and attenuation curves are in good agreement with those predicted by an extended biot theory yamamoto and turgut j acoust soc am 83 1744 1751 1988 for sediments with a distribution of pore sizes

seismic source modeling seismic source modeling is taken to mean the modeling of seismograms to investigate kinematic properties of the earthquake source current trends such as the use of other data types e g geodetic measurements of coseismic deformation and the explicit consideration of source dynamics when modeling seismograms are beginning to blur this definition but i will adhere to it in this review i have divided seismic source modeling into teleseismic regional and near source modeling teleseismic modeling has the advantage of global coverage for earthquakes of magnitude 5 5 and larger but does not provide much more than point source parameters regional distance modeling has the advantage of a more rapid assessment of earthquake source properties but is complicated by relatively complex wave propagation the coverage is also limited to areas of broadband regional networks typically continental areas of developed countries near source modeling has the potential for detailed imaging of source properties but very few earthquakes occur in regions with sufficient instrumentation to allow this i have also included a section on historical earthquakes because of the additional issues that seismologists face in working with pre wwssn data and because of the important issues such as earthquake recurrence that require historical data in addition to reviewing the progress in seismic source modeling during the last four years i have also briefly reviewed some of the progress in understanding earthquake physics and hazards that has come about because of basic research in earthquake source modeling

tidal height and frequency dependence of acoustic velocity and attenuation in shallow gassy marine sediments remote prediction of gassy marine sediment properties is important for geohazard assessment gas bubble resonance theory suggests that gassy sediments exhibit acoustic wave velocity frequency and attenuation frequency relationships that depend on gas bubble size gas content and sediment elastic properties an acoustic monitoring experiment to investigate gas bubble resonance effects was undertaken at an intertidal site at dibden bay southampton united kingdom a vertical hydrophone array was positioned to straddle the top of the gassy zone identified on acoustic reflection profiles at about 1 m below the seabed a miniboomer in the seabed above the array was used to generate broadband 600 hz to 3000 hz acoustic signals every 10 min during a 24 hour period with water depths varying between 0 m subaerial exposure at low tide and 2 35 m at high tide the calculated frequency spectra of compressional wave attenuation coefficient show an attenuation maximum over 200 db m that shifts in frequency from 1050 hz at low tide to 1250 hz at high tide thus for the first time providing direct evidence of in situ gas bubble resonance in marine sediments modeling suggests that effective gas bubble radii of 11 mm to 13 mm are responsible for the attenuation maximum supported by x ray computed tomography scan observations on a pressure core which also indicate that bubble shape depends on sediment type modeling of bubble size fluctuations due to pressure equilibration cannot reproduce the observed frequency shift of the attenuation maximum implying that gas diffusion and nonspherical bubbles are significant

long period regional wave moment tensor inversion for earthquakes in the western united states source parameters of moderate to large size mw 4 5 earthquakes in the western united states from 1992 to 1994 are determined by point source moment tensor inversion of complete long period t 35 50 s ground motions recorded at regional distances 1 12 stable long period signals are obtained by low pass filtering records from the very broadband seismometers recently deployed in several networks in the western united states these signals are dominated by fundamental mode rayleigh and love waves which have very simple waveforms due to the limited dispersion on the short paths to regional stations since long period motions are relatively insensitive to the attenuation model and crustal structure used in the inversion they provide robust constraints on the seismic moment and faulting geometry as long as adequate azimuthal coverage is available comparisons of solutions for 21 events with results of other regional and teleseismic wave inversions are made to assess the model dependence and uncertainties of our regional centroid moment tensor rcmt solutions rcmt inversion has limited source depth resolution for shallow crustal events but the focal mechanism and seismic moment determinations prove quite stable over a range of source depths in the crust as well as over a range of crustal propagation models simultaneous waveform inversion of shorter period body wave signals can improve the source depth resolution by applying path corrections for heterogeneous crustal structure shorter period surface wave energy can also be inverted allowing the methodology to be extended to lower magnitude regional events as well the rcmt procedure requires minimal signal processing only a sparse broadband network and a simple laterally homogeneous propagation model thus it can readily be automated and applied in near real time to events in the magnitude range from 4 5 to 7 5 distributed over an area as large as the western united states

observations on attenuation and shear wave velocity in fine grained marine sediments compressional p wave attenuation shear s wave attenuation and shear s wave velocity measurements compiled for fine grained unconsolidated sediments show trends that do not support empirical relationships hamilton j acoust soc am 68 1313 1340 1980 in acoustics and ocean bottom f a s e specialize conf madrid 1987 commonly used for geoacoustic modeling the exception is compressional wave attenuation data from 10 hz to 500 khz that essentially follow a frequency dependence of f1 2 standard deviations p wave attenuation with depth is difficult if not impossible to predict given the variability in the data examination of several attenuation depth profiles indicates that those of mitchell and focke j acoust soc am 67 1582 1589 1980 may be the best choice for predicting p wave attenuation with depth at the present time the assumption that s wave and p wave attenuations are proportional hamilton j acoust soc am 60 334 338 1976c in acoustics and ocean bottom

inversion of regional pn1 and surface wave data for source parameters of a borah peak aftershock we present results of a comparative source study on one of the largest aftershocks of the borah peak idaho earthquake series the mechanism of this event had been previously studied using first motions and teleseismic p wave data and we report here our results from analysis of regional pn1 and surface waves the pn1 waves gave an estimate of the source duration near 5 sec in agreement with the teleseismic p waves both the source duration and the effect of surface wave dispersion through laterally heterogeneous crustal structures must be accounted for in the moment tensor inversions of intermediate period surface waves all data sources both long period and short gave consistent source mechanisms and the long periods also yield three independent and consistent estimates of the seismic moment the results demonstrate the promise of formal source parameter retrieval techniques applied to regional data for the study of earthquakes with magnitudes below the magnitude threshold of teleseismic source determinations

geotechnical and geophysical characteristics of muskeg samples from alberta canada abstract a series of laboratory tests have been performed to explore the geotechnical and geophysical characteristics of fibrous muskeg i e grassy bog using undisturbed block samples obtained from alberta canada the basic index properties of muskeg show similar values to the reference data for other organic soils and they significantly differ from those of typical inorganic soils due to high organic content muskeg has high water content high compressibility and high initial permeability the effective stress and porosity play a major role in controlling the stress dependent geophysical properties of shear wave velocity real permittivity and electrical conductivity the values of peak drained friction angle obtained in the direct shear tests are in the range of 26 to 51

analysis of shear wave attenuation in unconsolidated sands and glass beads chotiros and isakson j acoust soc am 135 3264 3279 2014 contend that the physics based grain shearing gs theories of wave propagation in granular materials are not consistent with one particular shear attenuation data set for water saturated angular sand that has appeared in the literature this provides them with the rationale for developing their own model an extension of the empirical biot stoll model which they designate the extended biot eb model in this article the eb model and the grain shearing theories are briefly reviewed and it is demonstrated that in fact the original gs theory accurately matches the frequency dependent trends of all the shear attenuation data sets that are currently available including those for saturated angular sands after random fluctuations are suppressed by averaging over several realizations of the medium it is also pointed out that chotiros and isakson s treatment of the available shear attenuation data is highly selective and that the format in which they present the selected data makes their comparisons with theoretical models difficult to interpret thus their attempts at validating the eb model and their conclusions concerning alternative theories should be treated with caution

1 5d inversion of lateral variation of scholte wave dispersion reliable models of in situ shear wave velocities of shallow water marine sediments are important for geotechnical applications lithological sediment characterization and seismic exploration studies we infer the 2d shear wave velocity structure of shallow water marine sediments from the lateral variation of scholte wave dispersion scholte waves are recorded in a common receiver gather generated by an air gun towed behind a ship away from a single stationary ocean bottom seismometer an offset window moves along the common receiver gather to pick up a local wavefield a slant stack produces a slowness frequency spectrum of the local wavefield which contains all modes excited by the air gun amplitude maxima dispersion curves in the local spectrum are picked and inverted for the shear wave velocity depth profile located at the center of the window as the window continuously moves along the common receiver gather a 2d shear wave velocity section is generated in a synthetic example the smooth lateral variation of surficial shear wave velocity is well reconstructed the method is applied to two orthogonal common receiver gathers acquired in the baltic sea northern germany the inverted 2d models show a strong vertical gradient of shear wave velocity at the sea floor along one profile significant lateral variation near the sea floor is observed

characterisation of collapsing loess by seismic dilatometer abstract structural collapse and sudden volume changes represent a major geotechnical issue particularly in loess soils there are different criteria for assessing collapse potential based on laboratory test results which require the collection of undisturbed samples from test pits this can be a complicated and costly procedure often financially unjustified for smaller projects this paper presents the results of seismic dilatometer tests sdmt performed at a single location in a loess soil in belgrade in addition to the results of single oedometer collapse tests performed on high quality samples from test pits after comparing laboratory test results it was possible to determine that in samples collected from boreholes dry unit weight is approximately 20 higher than in block samples taken from test pits while moisture content is between 1 and 4 higher unit weight estimated from dmt is on average 15 higher than the unit weight obtained from block samples the constrained modulus mdmt determined by dmt are highly compatible with oedometer modulus eoed obtained from samples at natural moisture content this paper presents two possible ways of identifying collapsing loess based on intermediate dmt parameters and the ratio of g0 mdmt the tests results indicate that if the ratio between the material index id and the horizontal stress index kd is greater than 5 the danger of collapse is imminent simultaneous observation of the changes of id and kd with depth on a semi log graph in the same scale is recommended in this way the relative distance between them may be clearly noticed the larger the distance becomes the greater the risk of collapse in the collapsing loess ratio g0 mdmt is found to be higher than 21 for kd less than 0 6 while in non collapsing loess g0 mdmt is less than 21 for higher values of kd in terms of dmt loess is considered as underconsolidated soil which is one of the most common definitions of loess

normalized undrained shear strength of clay shales this paper examines the possibility of normalizing the undrained shear strength behavior of clay shales shales are formed in sedimentary basins by diagenetic processes which turn young clay sediments into compacted and lithified shales cementation at grain contacts affects many properties of shales including the apparent preconsolidation and shear strength based on a study of 25 different types of materials the normalized undrained shear strength of clay shales was found to correlate satisfactorily with overconsolidation ratio following the shansep stress history and normalized soil engineering properties normalization procedure for clays the normalized undrained shear strength correlation appears valid regardless of the cause of the apparent preconsolidation correlations of the apparent preconsolidation stress with unconfined compressive strength and compressional wave velocity are proposed to predict the normalized undrained shear strength of clay shales

underwater masw to evaluate stiffness of water bottom sediments stiffness measurements are often necessary for geotechnical characterization of an underwater site seismically these measurements can be made through the dispersion analysis of the rayleigh type surface waves successful terrestrial application of this method has been reported by many investigators using spectral analysis of surface waves sasw and more recently using multichannel analysis of surface waves masw the masw method was originally developed as a land survey method to investigate the near surface materials for their elastic properties for example the shear wave velocity vs by recording and analyzing rayleigh type surface waves using a vertical impulsive seismic source and receivers the acquired data are first analyzed for dispersion characteristics and from these the shear wave velocity is estimated using an inversion technique

characterisation and engineering properties of tiller clay abstract a detailed characterisation of the quick clay underlying the ntnu research site at tiller trondheim is presented the objective of the work is to provide guidance on quick clay parameters to engineers and researchers working with similar clays in scandinavia and north america especially on landslide hazard assessment the material is lightly overconsolidated and is characterised by its high degree of structure and very high sensitivity quick clay clay and water contents are both about 40 the plasticity index is low 5 this relates to the low active minerals of the clay and silt fractions illite chlorite and quartz feldspars respectively undrained shear strength is of the order of 30 kpa to 50 kpa medium stiff and increases with depth the deposit is consistent across the site and its properties are similar to other norwegian quick clays significant efforts have been made into examining sample disturbance effects on the material it was found that thin walled steel fixed piston samples can yield results similar to those of block samples provided the work is carried out with extreme care and storage time is minimised the piezocone cptu test proved very useful in characterising the material

aftershock slip behavior of the 1989 loma prieta california earthquake an analysis of 745 aftershocks of the m7 1 loma prieta earthquake of 17 october 1989 reveals a wide variety of focal mechanisms at the northwestern end of the aftershock zone earthquakes that apparently occurred off the main rupture plane exhibit mechanisms with predominantly reverse slip on planes nearly parallel to the san andreas fault at the southeastern end the mechanisms exhibit right lateral motion on near vertical planes suggesting that these aftershocks involve slip on the san andreas fault few of the aftershock mechanisms in the central zone resemble the main shock mechanism strike n130 degree e dip 70 degree sw rake 104 degree but instead exhibit reverse right lateral left lateral and normal motion on planes subparallel to the main shock rupture plane the dip of the aftershock zone is parallel to the main shock slip plane and includes the main shock hypocenter however the lack of agreement between the main shock and the aftershock mechanisms suggests that few of the aftershocks occurred on the main shock slip plane this behavior is consistent with observations of aftershock sequences for other dip slip events and also with studies indicating that main shock rupture zones are at all other times mostly aseismic if the stress drop for the main shock relievedmore most of the tectonic stress the mechanisms could reflect the heterogeneity of the near field stress redistribution alternatively the variety of the aftershock mechanisms may reflect deformation by block motion within a narrow zone adjacent to the main shock rupture plane less

integration of detrital gold microchemistry heavy mineral distribution and sediment geochemistry to clarify regional metallogeny in glaciated terrains application in the caledonides of southeast ireland regional exploration for rare and precious metal enrichment traditionally uses multielement geochemical analysis of the fines 150 m fraction of stream sediments however these data can be misleading in glaciated regions with complex geology here we compare the spatial distributions of data from sediment fines with distributions of heavy mineral concentrates including detrital gold in the same region gold grains are characterized according to abundance and morphology plus a microchemical signature from the combination of alloy analysis and systematic identification of mineral inclusions revealed in polished sections these inclusions survive indefinitely and are indicative of hypogene mineralogy whereas the metal loadings of fines may be affected by weathering or anthropogenic activity all three approaches are mutually supportive sediment fines analyses provide a basis for more labor intensive targeted gold grain studies which in turn highlight specific gold element associations useful for interpretation of geochemical data sets spatial distributions of resistate heavy mineral suites constrain the directions and extents of glacial transport which facilitates more confident interpretations of placer lode relationships from gold grain studies characterization of 2 160 gold grains from 40 localities in the auriferous region of southeast ireland provided a clear indication of proximity of gold to source and identified gold derived from different episodes of mineralization a distinction is apparent between gold in the south of the region wexford likely derived from widespread stratabound au as fe s mineralization and that in the north wicklow where the historical placer mining district of the goldmines river yielded gold with inclusions exhibiting a distinctive pb bi as association the goldmines river placers formed by the efficient accumulation and preservation of detrital gold derived from several discrete intravalley sources we recommend that a combination of classic stream sediment geochemistry heavy mineral analysis and gold grain studies is used more widely to provide additional insights on the location and nature of gold mineralization and regional metallogeny in regions of poor exposure and complex geology

geotechnical site characterization in the greater memphis area using cone penetration tests abstract the determination of seismic ground hazards in memphis and shelby county tennessee is facilitated by the use of electronic cone penetration tests that can provide up to four independent readings with depth from a single sounding one series of soundings is being performed for site specific mapping to determine the presence and extent of potentially liquefiable sediments in situ soil resistance to liquefaction and initial soil stiffness for ground motion amplification studies another series of soundings is being conducted in conjunction with field paleoliquefaction mapping in the new madrid seismic zone to better define the intensity magnitude and geographic extent of ground failures caused by large past earthquake events as well as information about the source sands in this paper an overview is given on the types of multi channeled penetrometer data that are being collected including vertical profiles of cone tip stress qt sleeve friction fs penetration porewater pressure u1 or u2 downhole shear wave velocity vs and or electrical conductivity ke representative soundings are presented from select sites to illustrate repeatability data post processing methods and that derived downhole vs profiles are generally in good agreement with non invasive surface techniques at two memphis test sites cyclic stress based procedures for liquefaction are discussed with relation to data from a paleoliquefaction site in germantown tennessee and estimates of the minimum magnitude of the historic event are discussed while estimates of the earthquake magnitude are preliminary pending additional study on attenuation relationships and site response in the deep soils of the mississippi embayment it is inferred from evaluation of in situ test data using cyclic stress based techniques that the december 1811 new madrid earthquake was likely larger than a mw 7 5 event

multichannel analysis of surface waves masw for offshore geotechnical investigations abstract multichannel analysis of surface wave masw surveys are commonly used onshore to produce shear wave velocity vs profiles this paper describes its use in offshore geotechnical investigations underwater masw umasw where the focus was on the upper 15 m of the sediment profile to aid the design of structures such as marine pipelines cable routes and shallow anchor systems umasw was shown to provide reliable data in irish offshore conditions in water depths of up to 50 m the receiver spacing and array length rather than the characteristics of the air gun seismic energy source were the primary control on signal penetration and resolution of individual sediment layers good resolution of the properties of the upper 5 m of sediment was found by reducing the receiver spacing to as low as 0 3 m a test site with a broad intertidal zone allowed coincident land marine and direct measurements to be compared and vs profiles obtained from umasw onshore masw and by seismic cone testing scptu were in good agreement vs profiles estimated from published correlations with cptu data in sandy sediments agreed well with the measured values inversion of data using different software packages showed only a minor variation in results

manganiferous garnet underlying the bousquet gold orebody quebec metamorphosed manganese sediment as a guide to gold ore garnet quartz muscovite rock stratigraphically underlies a volcanogenic pyritic gold orebody within bousquet township abitibi greenstone belt quebec garnet constitutes only 3 of the rock within muscovite rich layers near its east and west ends whereas the rock contains 12 of garnet near its center trails of quartz carbonate and sulphide inclusions and parallel bands of an ultrafine black opaque mineral produce a layered appearance in the garnet garnet consists of 25 mno and is zoned with maximum mno content at its center furthermore mno content is greatest in garnet near the center and stratigraphic top of the rock and decreases systematically to the east west and stratigraphic base pb zn and ba exhibit similar enrichment trends from stratigraphic base to top of the rock however ba remains abundant in the overlying orebody the interpretation is that the garnet rock was a primary mn rich sediment that accumulated near a sea floor hydrothermal vent by analogy with modern hydrothermal mn d

near surface geophysical techniques for geohazards investigations some canadian examples over the last 40 years there has been an expansion of activity in applications of near surface geophysical techniques for various types of geohazards investigations in canada numerous national and international research groups have been working with the near surface geophysics section of the geological survey of canada to develop techniques for specific canadian engineering and environmental geohazards problems a few of the more interesting examples from widespread parts of the country are discussed in this paper

the seismic source parameters of the 1991 costa rica aftershock sequence evidence for a transcurrent plate boundary the april 22 1991 valle de la estrella costa rica earthquake ms 7 6 was a back arc thrusting event associated with the underthrusting of the caribbean plate beneath central america a network of three passcal type portable instruments was deployed to monitor the aftershock activity in southern costa rica 2 to 6 weeks after the main shock the waveforms recorded on three component midperiod seismometers were used to recover source information for 15 small aftershocks magnitudes between 3 2 and 4 4 with a linear moment tensor inversion method we conducted several tests to investigate the effects of unknown structure and event mislocation on source parameter recovery the longer period waveforms in general are less sensitive to the effects of the structural details so that the essential source information can be successfully extracted from the waveform data the earlier part of the seismic wave forms has proven to be the most important carrier of the source information a gross crustal model can be used to describe the structure for the source study the small changes in the waveform character resulting from the mislocation of the events or inexact green s functions generated from the oversimplified crustal model do not prohibit us from the recovery of the source orientation at local distances in contrast the determination of the focal depth is subject to uncertainty because of the lack of detailed structural information our focal mechanisms are generally in good agreement with p wave first motion fault plane solutions determined from a local short period network the aftershocks show a clear spatial segmentation based on focal mechanism type most aftershocks near or southeast of the main shock were thrusting events with focal mechanisms similar to the main shock in contrast a cluster of aftershocks northwest of the main shock showed dominantly left lateral strike slip motion on a northeasterly striking nodal plane this suggests that a diffuse deformation zone exists in central costa rica and is characterized by left lateral strike slip motion this diffuse transcurrent deformation zone coincides with several geologic and geophysical features and perhaps is a result of the slower subduction rate of the buoyant cocos ridge than its adjacent segments along the middle america trench mat the diffuse transcurrent boundary may intersect with the north panama deformed belt npdb near limon costa rica and is very likely a plate boundary for the proposed panama block

measuring lateral variability of sediment geoacoustic properties dispersion analysis of interface waves scholte stoneley rayleigh has been used extensively to determine geoacoustic models of near bottom ocean sediments in the traditional approach a single seismic trace is analyzed to obtain group velocity dispersion using the multiple filter technique a dispersion curve obtained in this manner reflects the averaged influence of the sediment acoustic properties over the entire path from source to receiver thus a geoacoustic model derived from this dispersion curve is not a true vertical section in the vicinity of the receiver unless the sediment properties do not change over the entire propagation path however when a linear array of receivers is used to obtain data simultaneously at a number of different ranges it is possible to derive both group and phase velocity dispersion curves that correspond to propagation over a short portion typically 5 m of the total path at many different ranges with this kind of data the range dependent variation of geoacoustic properties in the sediment may be assessed results are presented based on data obtained with a 24 receiver array and an explosive source both deployed on the seafloor analysis of data from a number of shallow water sites suggests that there is a considerable amount of lateral inhomogeneity even over very short ranges

tourmalinization related to late proterozoic early palaeozoic lode gold mineralization in the bin yauri area nigeria three types of tourmaline occurrence have been identified in the area of bin yauri nigeria mesothermal lode gold mineralization these are 1 stratabound tourmalinites in pelitic metasediments 2 tourmaline in a hydrothermal alteration assemblage within hornfelsed wall rocks 3 tourmaline in auriferous quartz and quartz carbonate veins although the tourmaline occurrences are all within or close to the contact aureole of a granodiorite intrusion geochemical characteristics of the tourmalines are broadly similar and reflect a common metasedimentary source two stages of tourmalinization are envisaged the earlier ca 1100 ma involved syngenetic diagenetic formation of tourmalinites while the later ca 500 ma involved epigenetic hydrothermal tourmaline gold mineralization possibly derived by dehydration and devolatilization of metasedimentary sequences containing tourmaline rich rocks or tourmalinites electron microprobe analyses indicate that the tourmalines are intermediate members of the schorl dravite solid solution series plots involving feo mgo and or al2o3 from these analyses are used to constrain the sources and processes of tourmalinization two metallogenic implications are derived from this study one is that although the tourmalinites are barren of gold and base metal mineralization their occurrences nevertheless encourages exploration for syngenetic exhalative massive sulphide deposits in the region the other implication applies to the potential use of tourmaline in deciphering the physico chemical conditions of gold mineralizing fluids in the bin yauri area

inversion of regional surface wave spectra for source parameters of aftershocks from the loma prieta earthquake abstract surface waves recorded at regional distances are used to study the source parameters for three of the larger aftershocks of the 18 october 1989 loma prieta california earthquake the short period p wave first motion focal mechanisms indicate a complex aftershock sequence with a wide variety of mechanisms many of these events are too small for teleseismic body wave analysis therefore the regional surface waves provide important long period information on the source parameters intermediate period rayleigh and love wave spectra are inverted for the seismic moment tensor elements at a fixed depth and repeated for different depths to find the source depth that gives the best fit to the observed spectra for the aftershock on 19 october at 10 14 35 m d 4 2 we find a strike slip focal mechanism with right lateral motion on a nw trending vertical fault consistent with the mapped trace of the local faults for the aftershock on 18 october at 10 22 04 m d 4 4 the surface waves indicate a pure reverse fault with the nodal planes striking wnw for the aftershock on 19 october at 09 53 50 m d 4 4 the surface waves indicate a strike slip focal mechanism with a nw trending vertical nodal plane consistent with the local strike of the san andreas fault differences between the surface wave focal mechanisms and the short period p wave first motion mechanisms are observed for the aftershocks analyzed this discrepancy may reflect the real variations due to differences in the band width of the two observations however the differences may also be due to 1 errors in the first motion mechanism due to incorrect near source velocity structure and 2 errors in the surface wave mechanisms due to inadequate propagation path corrections

measurements of acoustic wave velocities and attenuation in marine sediments propagation and attenuation of acoustic waves in fluid saturated sediments have been studied theoretically and experimentally in situ acoustic transmission tests in saturated beach sand show that compressional waves are dispersive within a certain frequency band where the intrinsic attenuation is maximum this indicates that low frequency wave velocities in marine sediments are at least 5 to 10 less than the velocities obtained from high frequency measurements and viscous damping due to the relative motion between solid skeleton and fluid is the main damping mechanism in the frequency range of 1 30 khz the agreement between the experimental results and biot s theory enables the remote determination of porosity and permeability of marine sediments by using measured compressional and shear wave characteristics approximate relations are used to determine the porosity and permeability of the marine sediments using the measured acoustic wave velocities and attenuation

regional seismic phases across the ligurian sea lg blockage and oceanic propagation abstract the ligurian sea west mediterranean is an example of a narrow oceanic basin which stops lg wave propagation locating the exact point of lg extinction was one of the goals of the sisbalig ii seismological experiment which deployed both inland stations in provence and corsica and ocean bottom seismometers obs in the ligurian sea a precise analysis of all available regional seismological data using energy diagrams reveals the role of the provence margin in the lg phase extinction for seismic events occurring in the southwestern alps the extinction is not a progressive phenomenon along oceanic travel path but occurs in a narrow zone of about 20 km width in the vicinity of the provence margin the extinction is accompanied by the generation of two types of diffracted waves the mantle phase sn v s 3 5 km s 1 and very low velocity s waves appearing both near the provence margin and in the middle of the ligurian basin we performed numerical simulation of sh wave propagation in two dimensional 2d media to investigate the mechanisms of lg extinction the simulations confirm that simple crustal thinning at the continent ocean boundary alone cannot cause the observed extinction of lg waves although the change in moho depth does induce the diffraction of a part of the incident lg wavetrain into mantle waves giving rise to the sn phase on the other side of the basin the existence of soft oceanic sediments is a very important factor in explaining the extinction as a large part of the lg energy is transferred into slow s waves trapped in the sediments moreover comparison of synthetic seismograms and observed data shows that the observed two packets of low velocity waves are an indication of the asymmetry of the ligurian basin with the existence of two shallow basins with very low s velocity 1 0 km s 1 near the provence margin and in the middle of the ligurian sea however the attenuation of lg waves in the vicinity of the provence margin is more abrupt in the data than in the simulations this discrepancy could result from the complex geometry of the continent ocean transition zone and its possibly very diffractive nature two factors that could add to lg extinction at the margin and are impossible to take into account in models

deformational and stratigraphic influences on mineralization in se ireland the evidence that has accumulated to date to support the thesis that deformational and stratigraphic controls are reflected in the occurrence and siting of metal deposits in se ireland is evaluated in the case of an important tungsten deposit stratigraphic influences can be seen in the geochemical and mineralogical development of wallrocks prior to crystallization of granite hosted mineralization tourmalinites confined to a definable stratigraphic interval are associated with pegmatite hosted lithium deposits though the stratigraphic control is important the tungsten and lithium deposits are in addition confined to the trace of a major deformation zone

relationship between shear wave velocity and geotechnical parameters for norwegian clays abstracta database of shear wave velocity vs measurements using a variety of techniques and soil properties measured on high quality samples for 28 norwegian sites has been established the purpo

shear wave velocity as function of cone penetration test measurements in sand and silt mixtures abstract a database of research quality piezocone test cptu results and shear wave velocity v s measurements assembled in the context of an ambitious research project carried out at the treporti test site venice italy has been interpreted in order to study the seismic response of the predominantly silty sediments forming the venetian lagoon basin as well as to explore potential correlations for such intermediate soils the experience gained so far with the treporti database and other field data collected in the lagoon area has shown that the mechanical behavior of venetian soils cannot be easily interpreted using the existing and well established cptu based approaches hence the interest in examining whether or not the seismic response of these sediments expressed in terms of shear wave velocity follows the framework published for other soils the applicability to the available data of a number of existing correlations originally developed either for sands or fine sediments has been first investigated and updated relationships have been then suggested furthermore the small strain stiffness calculated from v s measurements has been compared with the field stiffness derived from the observed performance of a full scale test embankment built in the treporti site so as to verify common design assumptions the verification and calibration of existing approaches are likely to constitute a useful contribution to the practice of geotechnics not only in the venetian lagoon area but also in the silty deposits usually present in the surrounding alluvial plain and other similar depositional environments allowing rapid estimates of seismic soil classification as well as small strain stiffness properties for preliminary design or at sites where only cone penetration data are available

soil liquefaction evaluation using shear wave velocity abstract a reasonably good relationship between shear wave velocity swv and standard penetration resistance spt of granular soils in agreement with previous studies was obtained from field tests a similar correlation between swv and cone penetration resistance of granular soils was also obtained using seed s standard penetration test spt based soil liquefaction charts new charts of soil liquefaction evaluation based on swv data were developed for various magnitude earthquakes

evidence of dispersion in an artificial water saturated sand sediment a laboratory experiment was conducted to measure the speed of sound in an artificial water saturated granular sediment composed of cleaned and sorted medium grained sand and degassed distilled water the experiment was conducted within a range of frequencies where dispersion is predicted by a number of existing models between 2 and 4khz the sound speed was inferred from measurements of the resonance frequencies of a thin walled cylindrical container filled with the material an elastic waveguide model was used to account for the effect of the finite impedance of the walls although this effect was found to be small from 20 to 300khz the sound speed was obtained directly from time of flight measurements within the sediment dispersion in close agreement with the williams effective density fluid model k l williams j acoust soc am 110 2276 2281 2001 was observed

field experiments to study seafloor seismoacoustic response results of a 5 year program to measure the seismoacoustic properties of unlithified sediments in the seafloor are presented a field technique utilizing an impulsive source and a geophone array located on the seafloor was used to obtain detailed travel time curves which permit a number of different kinds of analysis a new signal source powered by electrically detonated 8 gauge shotgun shells was used to focus energy into the bottom and eliminate much of the high frequency water borne noise that accompanies the usual explosive sources both interface waves and wide angle refractions were analyzed a variety of data inversion techniques including slant stacking and cross multiplication were used to obtain dispersion curves and constrained least squares inversion using partial derivatives was used to develop an iterative inversion method to obtain velocity and attenuation as a function of depth examples of data from a wide angle of different kinds of sediment ranging from soft holocene mud to stiff over

a laboratory investigation into the seismic velocities of methane gas hydrate bearing sand remote seismic methods which measure the compressional wave p wave velocity vp and shear wave s wave velocity vs can be used to assess the distribution and concentration of marine gas hydrates in situ however interpreting seismic data requires an understanding of the seismic properties of hydrate bearing sediments which has proved problematic because of difficulties in recovering intact hydrate bearing sediment samples and in performing valid laboratory tests therefore a dedicated gas hydrate resonant column ghrc was developed to allow pressure and temperature conditions suitable for hydrate formation to be applied to a specimen with subsequent measurement of both vp and vs made at frequencies and strains relevant to marine seismic investigations thirteen sand specimens containing differing amounts of evenly dispersed hydrate were tested the results show a bipartite relationship between velocities and hydrate pore saturation with a marked transition between 3 and 5 hydrate pore saturation for both vp and vs this suggests that methane hydrate initially cements sand grain contacts then infills the pore space these results show in detail for the first time using a resonant column how hydrate cementation affects elastic wave properties in quartz sand this information is valuable for validating theoretical models relating seismic wave propagation in marine sediments to hydrate pore saturation

inversion of regional surface wave spectra for source parameters of aftershocks from the 1992 petrolia earthquake sequence abstract regional distance surface waves are used to study the source parameters for moderate size aftershocks of the 25 april 1992 petrolia earthquake sequence the cascadia subduction zone had been relatively seismically inactive until the onset of the mainshock m s 7 1 this underthrusting event establishes that the southern end of the north america gorda plate boundary is seismogenic it was followed by two separate and distinct large aftershocks m s 6 6 for both occurring at 07 41 and 11 41 on 26 april as well as thousands of other small aftershocks many of the aftershocks following the second large aftershock had magnitudes in the range of 4 0 to 5 5 using intermediate period surface wave spectra we estimate focal mechanisms and depths for one foreshock and six of the larger aftershocks m d 4 0 to 5 5 these seven events can be separated into two groups based on temporal spatial and principal stress orientation characteristics within two days of the mainshock four aftershocks m d 4 to 5 occurred within 4 hr of each other that were located offshore and along the mendocino fault these four aftershocks comprise one group they are shallow thrust events with northeast trending p axes we interpret these aftershocks to represent internal compression within the north american accretionary prism as a result of gorda plate subduction the other three events compose the second group the shallow strike slip mechanism determined for the 8 march foreshock m d 5 3 may reflect the right lateral strike slip motion associated with the interaction between the northern terminus of the san andreas fault system and the eastern terminus of the mendocino fault the 10 may aftershock m d 4 1 located on the coast and north of the mendocino triple junction has a thrust fault focal mechanism this event is shallow and probably occurred within the accretionary wedge on an imbricate thrust a normal fault focal mechanism is obtained for the 5 june aftershock m d 4 8 located offshore and just north of the mendocino fault this event exhibits a large component of normal motion representing internal failure within a rebounding accretionary wedge these two aftershocks and the foreshock have dissimilar locations in space and time but they do share a north northwest oriented p axis

historical coseismic surface deformation of fluvial gravel deposits schafberg fault lower rhine graben germany intraplate earthquakes pose a significant seismic hazard in densely populated rift systems like the lower rhine graben in central europe while the locations of most faults in this region are well known constraints on their seismogenic potential and earthquake recurrence are limited in particular the holocene deformation history of active faults remains enigmatic in an exposure excavated across the schafberg fault in the southwestern lower rhine graben south of untermaubach in the epicentral region of the 1756 duren earthquake m l 6 2 we mapped a complex deformation zone in holocene fluvial sediments we document evidence for at least one paleoearthquake that resulted in vertical surface displacement of 1 2 0 2 m the most recent earthquake is constrained to have occurred after 815 ad and we have modeled three possible earthquake scenarios constraining the timing of the latest event coseismic deformation is characterized by vertical offset of sedimentary contacts distributed over a 10 m wide central damage zone faults were identified where they fracture and offset pebbles in the vertically displaced gravel layers and fracture orientation is consistent with the orientation of the schafberg fault this study provides the first constraint on the most recent surface rupturing earthquake on the schafberg fault we cannot rule out that this fault acted as the source of the 1756 duren earthquake our study emphasizes the importance of and the need for paleoseismic studies in this and other intracontinental regions in particular on faults with subtle geomorphic expression that would not typically be recognized as being potentially seismically active our study documents textural features in unconsolidated sediment that formed in response to coseismic rupturing of the underlying bedrock fault we suggest that these features e g abundant oriented transgranular fractures in their context should be added to the list of criteria used to identify a fault as potentially active such information would result in an increase of the number of potentially active faults that contribute to seismic hazards of intracontinental regions

shallow water sediment properties derived from high frequency shear and interface waves low frequency sound propagation in shallow water environments is not restricted to the water column but also involves the subbottom thus as well as being important for geophysical description of the seabed subbottom velocity attenuation structure is essential input for predictive propagation models to estimate this structure bottom mounted sources and receivers were used to make measurements of shear and compressional wave propagation in shallow water sediments of the continental shelf usually where boreholes and high resolution reflection profiles give substantial supporting geologic information about the subsurface this colocation provides an opportunity to compare seismically determined estimates of physical properties of the seabed with the ground truth properties measurements were made in 1986 with source detector offsets up to 200 m producing shear wave velocity versus depth profiles of the upper 30 50 m of the seabed and p wave profiles to lesser depths measurements in 1988 were made with smaller source devices designed to emphasize higher frequencies and recorded by an array of 30 sensors spaced at 1 m intervals to improve spatial sampling and resolution of shallow structure these investigations with shear waves have shown that significant lateral and vertical variations in the physical properties of the shallow seabed are common and are principally created by erosional and depositional processes associated with glacial cycles and sea level oscillations during the quaternary when the seabed structure is relatively uniform over the length of the profiles the shear wave fields are well ordered and the matching of the data with full waveform synthetics has been successful producing velocity attenuation models consistent with the subsurface lithology indicated by coring results both body waves and interface waves have been modeled for velocity attenuation as a function of depth with the aid of synthetic seismograms and other analytical techniques some results give strong evidence of anisotropy and lateral heterogeneity in shear velocity of the upper 5 10 m of sediments and of extremely high velocity gradients in the topmost 1 2 m possibly exceeding 30 s 1

the october 17 1989 loma prieta california earthquake and its aftershocks geometry of the sequence from high resolution locations hypocenters of the loma prieta sequence form a dipping zone that rises from the mainshock hypocenter and is parallel to the mainshock nodal plane most aftershocks cluster around the perimeter of the zone surrounding a relatively aseismic center which approximates the region of mainshock rupture at its southeastern end the dipping aftershock zone warps into a vertical surface that corresponds to the san andreas fault in the central and northwestern parts of the zone at depths above 10 km the aftershocks define numerous disjoint fault structures the large component of reverse slip observed in this event agrees with a simple model for slip on a dipping plane within a compressional fault bend we do not believe that the loma prieta earthquake occurred on the sargent fault however we are unable to conclude whether it ruptured the principal plate boundary fault or a less frequently active fault

field evaluation of deformation characteristics of a lacustrine clay deposit using seismic piezocone tests abstract the use of the seismic piezocone test scptu in geotechnical site investigation offers direct field measurement on stratigraphy and soil behaviour compared with some traditional investigation methods such as drilling sampling and field inspecting method or laboratory test procedures scptu can greatly accelerate the field work and hereby reduce corresponding operation cost this paper presents the methods review to predict the constrained modulus m and to measure small strain shear modulus gmax from scptu data the capacity of current interpretation methods to predict the constrained modulus m was evaluated for lixia river lagoonal soils several sites in lixia river area were selected for this study in each site scptu tests were performed and the soundings of cone tip resistance qc sleeve friction fs pore pressure u2 and shear wave velocity vs were recorded the predicted m values obtained from the scptu interpretation methods were compared with the reference values determined from the laboratory consolidation tests results of this study showed that the sanglerat method was able to predict m better than the other methods two new correlations were also developed to predict m from the corrected cone tip resistance qt and the net cone tip resistance qn small strain shear stiffness can be tentatively estimated in the absence of direct measurement of shear wave velocity the reliable result was obtained using an association between gmax qt and pore pressure parameter bq compared to field downhole wave velocity measurements scptu can lead to a more reliable measurement of maximum stiffness profile with depth the stress strain strength response of the clays was evaluated by the maximum shear stiffness and undrained shear strength

prediction of long term settlement on soft clay using shear wave velocity and damping characteristics this paper presents a method of calculating long term settlement of a loaded pad on soft clay at klang selangor malaysia where the soil model is treated as an anelastic material of viscoelastic property initially an elastic shear modulus g value from shear wave velocity profiles of the seismic tests from spectral analysis of surface wave sasw and continuous surface wave csw tests was obtained a value of damping d at an equivalent elastic strain is then calculated from the hysteresis of the plate load tests corrected to equivalent strain using the damping strain formula the calculated elastic settlement and its equivalent damping are then used to calculate the long term settlement by applying the generalised viscoelastic formula comparisons to traditional methods of settlement predictions were made and the viscoelastic formula has shown better agreement to the observed settlement further modification of the settlement formula is introduced to improve the settlement accuracy to 10

lithogeochemical studies of aureoles around the panasqueira tin tungsten deposit portugal multi element lithogeochemical surveys of aureoles surrounding tin tungsten bearing quartz vein systems have been utilized infrequently in exploring for these deposits at panasqueira beira beixa portugal a wrich quartz vein mineralization occurs in the beira schists surrounding a greisenized cupola and offers a suitable test case for such lithogeochemical studies therefore shale samples were collected at a density of about 6 samples per km2 pronounced anomalies of tin and tungsten have been detected in these samples together with those of other elements coeval with the mineralizing processes

stable isotope studies of sulphide mineralisation on the leinster granite margin and some observations on its relationship to coticule and tourmalinite rocks in the aureole galena and sphalerite occur in brecciated veins along the eastern margin of the caledonian leinster granite in south east ireland this mineralisation is spatially related to the occurrance of spessartine quartzites coticules in the aureole rocks tourmalinites are closely associated with these coticules a decrease in the temperature of mineralisation from about 500 c in the northern unit i to 250 c in the central unit iii to possibly less than 200 c in the southern unit v of the intrusion is suggested by decreasing sulphide 34s values increasing sulphate 34s values and sulphide sulphate fractionation values sulphur carbon and oxygen isotope data suggest the involvement in the vein mineralisation of sulphur carbon and mineralising fluids at least partially derived from the coticule and tourmaline bearing aureole schists

velocity dispersion in water saturated granular sediment recent experiments in the gulf of mexico have yielded a wealth of information on the environmental conditions and geoacoustic response of a uniform sand stratum immediately beneath the seafloor a comparison of p wave velocities measured at low 125 hz and high 11 50 khz frequencies in this layer indicates that there is a significant amount of velocity dispersion that occurs in the interval between these extremes this narrow band dispersion which is not consistent with the often used assumption of a nearly constant q model is in accordance with the predictions of the biot theory it results from viscous damping in the fluid as it moves relative to the skeletal frame other recent field data that support this conclusion are presented

regional magnitude scaling transportability and ms mb discrimination at small magnitudes data sets of mb pn and mb lg measurements are presented for three continental regions in order to investigate scaling relationships with moment magnitude w and event discrimination at small magnitudes compilations of published measurements are provided for eastern north american and central asian earthquakes and new measurements are reported for earthquakes located in western united states statistical tests on w mb relationships show that the mb lg scale of nurru 1973 is transportable between tectonic regions and a single unified w mb lg relationship satisfies observations for m 6 5 in all regions a unified relationship is also developed for nuclear explosions detonated at the nevada test site and test sites of the former soviet union regional mb for explosions scale at higher rates than for earthquakes and of significance is the finding that mb pn for explosions scales at a higher rate than mb lg a model is proposed where differences in scaling rates are related to effects of spectral overshoot and near field rg scattering on the generation of pn and lg waves by explosions for earthquakes mb pn and mb lg scale similarly showing rates near 1 0 or 2 3 log1omo seismic moment

estimating quality factor and mean grain size of sediments from high resolution marine seismic data seismic quality factor has the potential to characterize sediment properties but seldom is used by the industry for offshore siteinvestigationsbecauseofpracticaldifficultieswithreflection seismology e g restricted bandwidth and because of uncertaintiesinrock physicsmodels aspectral ratioanalysisofhighresolution marine seismic data can determine a quality factor to within a 95 confidence of 10 within the uppermost 30 m of unconsolidated marine sediments our spectral ratio technique doesnotrequireassumptionsonhowattenuationscaleswithfrequency emphasis is placed on interpretation of spectral signatures before applying an iteratively reweighted robust leastsquaresregressiontosubduetheeffectsofnoiseandlocalheterogeneities when determining the quality factor of a sediment package we combined data from boomer and chirp sources to examine attenuation over four octaves of frequency 0 5 8 0 khz and to demonstrate that expanding the frequency range improves the precision and accuracy of quality factor fits we obtain frequency independent quality factors with 95 confidence intervals of 13512 10 and 1076 5 for silty clays with mean grain sizes of 7 7 and 6 9 phi respectively and 63 10 7 for a modern sand deposit with mean grain size 2 5 phi from the solent u k sediments with higher quality factorsrequiremoreindependentobservationstoachieveadesirable 95 confidence we required only 45 traces over sands and 1250 traces over the lowest attenuating silty clays by constructing an empirical model of quality factor against mean grain size from published sediment studies the mean grain sizes of our solent sediments can be located and we find that quality factor can beusedtodistinguishbetweencoarsegrain dominatedandclaydominatedsediments

shear wave velocity and attenuation in the upper layer of ocean bottoms from long range acoustic field measurements several physics based seabed geoacoustic models including the biot theory predict that compressional wave attenuation 2 in sandy marine sediments approximately follows quadratic frequency dependence at low frequencies i e 2 kf n db m n 2 a recent paper on broadband geoacoustic inversions from low frequency lf field measurements made at 20 locations around the world has indicated that the frequency exponent of the effective sound attenuation n 1 80 in a frequency band of 50 1000 hz zhou et al j acoust soc am 125 2847 2866 2009 carey and pierce hypothesize that the discrepancy is due to the inversion models neglect of shear wave effects j acoust soc am 124 el271 el277 2008 the broadband geoacoustic inversions assume that the seabottom is an equivalent fluid and sound waves interact with the bottom at small grazing angles the shear wave velocity and attenuation in the upper layer of ocean bottoms are estimated from the lf field inverted effective bottom attenuations using a near grazing bottom reflection expression for the equivalent fluid model derived by zhang and tindle j acoust soc am 98 3391 3396 1995 the resultant shear wave velocity and attenuation are consistent with the sax99 measurement at 25 hz and 1000 hz the results are helpful for the analysis of shear wave effects on long range sound propagation in shallow water

tourmalinite as a potential host rock for gold in the caledonides of southeast ireland initial investigations designed to test the potential for gold in a series of lithologies associated with tourmalinites and coticules in the neighbourhood of the caledonian leinster granite of southeast ireland are reported the results of geological mapping geochemical analyses and panning of stream sediments indicate that significant levels of gold are associated with some tourmalinite zones the possible exploration implication of this work is that tourmalinites have potential as target indicators although secondary controls on mineralization are also important

the frequency dependence of compressional wave velocity and attenuation coefficient of intertidal marine sediments to advance the present understanding of the frequency dependence of compressional wave velocity and attenuation in marine sediments a series of well constrained in situ acoustic transmission experiments 16 to 100khz were performed on intertidal sediments the processing techniques incorporated in situ spreading losses sediment to transducer coupling and thorough error analyses significant variations in velocity and attenuation were observed over scales of tens of meters within the same sediment type velocity was generally nondispersive in sands while highly variable silt velocities prevented any meaningful dispersion estimates from being determined the attenuation coefficient was proportional to frequency for 75 of the experimental sites the measured compressional wave properties were compared to predictions from the grain shearing model for the sandy sites the phase velocities predicted by the grain shearing model exceed those measured while predicted phase velocities agreed with measured gro

characterization on the correlation between shear wave velocity and piezocone tip resistance of jiangsu clays the small strain shear modulus of a soil is a fundamental parameter related to the mechanical behavior used in evaluation of dynamic behavior and seismic design of geotechnical structures the jiangsu soft clay is a lightly overconsolidated and sensitive clay of high plasticity in nature a research database of piezocone penetration test cptu and shear wave velocity vs information for jiangsu soft clays has been collected to study the small strain shear modulus relationships for these soils and to examine the potential use of cptu and vs data in combination for the purposes of characterizing these soils test data for sites are based on the laboratory testing performed on thin wall tube samples and high quality block samples improvements have been suggested to existing correlations between the small strain shear modulus go or vs and index properties for these soils for better prediction of these soil properties

moment energy stress drop and source spectra of western united states earthquakes from regional coda envelopes we present a new method to estimate stable seismic source parameters such as energy moment and orowan stress drop using regional coda envelopes from as few as one broadband station we use the method to compute path and site corrected seismic moment rate spectra for 117 recent western united states earthquakes empirical green s function corrections were applied to our surface and body wave coda envelope measurements to generate s wave source spectra these source spectra provide stable single station estimates of radiated seismic energy es and seismic moment mo that for common events are in excellent agreement with network averaged estimates obtained using local and regional data teleseismic moment estimates are compatible with our regional results but teleseismic energy estimates appear to be nearly an order of magnitude low we estimated the seismic moment of events ranging between mw 2 2 and 7 3 and energy estimates for which we had measured at least 70 of the total energy generally events above mw 3 3 we use these estimates to examine the behavior of derived parameters such as the orowan stress drop 2 es mo while the earthquakes we studied have a small range in orowan stress drop generally between 0 1 and 20 mpa they show a strong tendency for orowan stress drop to increase with moment approximately as mo0 25 we believe this is a source effect and is not due to inadequate bandwidth or attenuation correction and note that this trend appears to continue for microearthquakes as described in a recent deep borehole study in southern california many of the large high stress drop earthquakes show complexity in their moment rate spectra near the corner frequency and cannot be fit by a simple square model instead above the first corner frequency the spectral decay ranges between f 1 0 and f 1 5 this leads to larger estimates of radiated energy than predicted with a simple square model and has implications for seismic hazard estimation coda envelopes have three main advantages over direct arrivals for estimating seismic moment and energy 1 coda amplitudes vary little with geology and source radiation anisotropy and allow accurate single station applications 2 path corrected coda amplitude measurements can be applied to very large regions allowing a comparison of source parameters throughout the western united states using a common methodology and stations 3 because long period coda can last for hours for large local and regional events it allows the analysis of seismograms with clipped early arrivals

in situ estimation of sediment sound speed and critical angle understanding the basic physics of sound penetration into ocean sediments is essential for the design of sonar systems that can detect localize classify and identify buried objects in this regard the sound speed of the sediment is a crucial parameter as the ratio of sound speed at the water sediment interface determines the critical angle sediment sound speed is typically measured from core samples using high frequency 100 s of khz pulsed travel time measurements earlier experimental work on subcritical penetration into sandy sediments has suggested that the effective sound speed in the 2 20 khz range is significantly lower than the core measurement results simulations using biot theory for propagation in porous media confirmed that sandy sediments may be highly dispersive in the range 1 100 khz for the type of sand in which the experiments were performed here it is shown that a direct and robust estimate of the critical angle and therefore the sediment sound speed at the lower frequencies can be achieved by analyzing the grazing angle dependence of the phase delays observed on a buried array a parametric source with secondary frequencies in the 2 16 khz range was directed toward a sandy bottom similar to the one investigated in the earlier study an array of 14 hydrophones was used to measure penetrated field the critical angle was estimated by analyzing the variations of signal arrival times versus frequency burial depth and grazing angle matching the results with classical transmission theory yielded a sound speed estimate in the sand of 1626 m s in the frequency range 2 5 khz again significantly lower the 1720 m s estimated from the cores at 200 khz however as described here this dispersion is consistent with the predictions of the biot theory for this type of sand

in situ measurements of sediment acoustic properties in currituck sound and comparison to models in situ measurements of compressional and shear wave speed and attenuation were collected 30 cm below the water sediment interface in currituck sound north carolina at two field locations having distinctly different sediment types medium to fine grained sand and fine grained sand with approximately 10 mud content shear wave measurements were performed with bimorph transducers to generate and receive horizontally polarized shear waves in the 300 hz to 1 khz band and compressional wave measurements were performed using hydrophones operated in the 5 khz to 100 khz band sediment samples were collected at both measurement sites and later analyzed in the laboratory to characterize the sediment grain size distribution for each field location compressional and shear wave speed and attenuation were estimated from the acoustic measurements and preliminary comparisons to the extended biot model by chotiros and isakson j acoust soc 135 3264 3279 2014 and the viscous grain shearing theory by buckingham

geological setting and genesis of coticules spessartine metapelites in the lower ordovician of the stavelot massif belgium the lower ordovician in the caledonian stavelot massif belgium contains a coticule member probably arenig in age composed of red hematite rich shales alternating with thin yellowish coticule beds these coticules are fine grained highly manganiferous metamorphic rocks mainly composed of spessartine garnet mica and quartz similar rocks of about the same age occur in several localities along the appalachian and caledonian fold belts the belgian coticules are thought to have originated from marly sediments which had been deposited rapidly probably by density currents and in which caco 3 had been diagenetically replaced by mnco 3 during metamorphism spessartine garnets were formed from this mnco 3 and mica manganese and iron are thought to have originated from volcanic exhalative processes

tourmalinites from the golden dyke dome northern australia tourmalinites occur at five stratigraphic levels within the low metamorphic grade multiply deformed lower proterozoic metasediments and metavolcanics of the golden dyke dome the geological setting exhalite associations sedimentary structures and tourmaline chemistry all preclude a granitic origin tourmalinite derived from the isochemical metamorphism of an exhalite comprising silica and tourmaline tourmalinite and other exhalites are hosted by carbonaceous pelitic metasediments and were deposited in deeper basinal areas the ore fluid was probably dolerite heated seawater which leached a thick pile of argillaceous sediments and acquired metals and boron by leaching the first and second increase in geothermal gradient produced tourmalinite the third produced auriferous tourmalinite and iron formations with tourmalinite and exhalative pb zn deposits forming during the period of maximum geothermal gradient more tourmalinite formed during the subsequent decline in geothermal gradient tourmalinites are regarded as b rich iron formations which can be the host for or associated with exhalative deposits of au and base metals

p wave fault plane solutions and the generation of surface waves by earthquakes in the western united states surface waves recorded at regional distances are used to study the source mechanisms of seven earthquakes in the western united states with magnitudes between 4 3 and 5 5 the source mechanisms of events in or on the margins of the basin and range show t axis with an azimuth of n85 w 16 and a plunge of 12 16 of the seven events four have p wave solutions that are inconsistent with surface wave observations azimuths of the t axis obtained from the surface wave mechanisms and from the p wave solutions differ by up to 45 these events have dip slip or oblique slip mechanisms and the source depths for three of the events are 5 km or less their source mechanisms and small magnitudes make identification of the p wave first motion difficult due to poor signal to noise ratio of the initial p wave and close arrivals of pp or sp with significant amplitude we suggest that mis identification of the p wave first motion and distortion of the body wave ray paths due to non planar structure were sources of error in determining the nodal planes for these events

source mechanism of the 1992 roermond earthquake from surface wave inversion of regional data summary the dutch german border region near the city of roermond the netherlands was hit by a rather strong crustal earthquake at 1 20 ut 1992 april 13 the epicentre is located within the roer valley graben a region currently undergoing extension the centroidal source mechanism of this event has been retrieved by moment tensor inversion of broad band long period surface waves recorded at regional distances 100 1500 km the double couple contribution of the moment tensor corresponds to almost pure normal faulting rake 262 on a steeply south westward dipping fault dip 58 with a nw se trend strike 138 this result is consistent with local tectonics but violates some first motion p wave polarity data the deduced seismic moment is 9 2 1016 n m corresponding to a moment magnitude of 5 3 a centroidal depth of 18 km fits slightly better than 13 km however the differences are small and other methods are necessary to constrain the depth further it is now possible to access a number of broad band three component seismic stations in europe via phone line e g german regional seismic network and the orfeus data centre i e global digital seismic network this allows retrieval of waveform data immediately after an earthquake in this paper we present a potentially fast and reliable procedure for extracting the moment tensor from low frequency surface waves using the roermond earthquake as an example detailed knowledge of the velocity depth structure along the travel paths seems unnecessary with our procedure further testing is required on all future moderate to strong earthquakes in europe using rapidly accessible stations to investigate the procedure s usefulness and possible limitations as a tool for rapid moment tensor estimation

geophysical and geotechnical studies of geology and sediment properties at a quick clay landslide site at esp trondheim norway abstract increased urbanisation and development in previous marginal areas have led to the need to protect the population the environment and infrastructure from hazards such as quick clay landslides in this paper the opportunity which was presented following the gathering of a large amount of data in the area of the quick clay landslide at esp trondheim norway in 2012 is explored the data is of particular interest given the availability of frequency domain helicopter borne electromagnetic data fhem and extensive lidar imaging as well as a full range of in situ geophysical and geotechnical soundings and samples the ground conditions in the area are shown to be complex and it is clear that a multi disciplinary type approach combining geophysical geomorphological and geotechnical investigations is necessary in order to understand the hazards posed by potential quick clay landslides the investigation shows that very good overview mapping of the area can be obtained from fhem and that the data obtained from local electrical resistivity tomography ert and resistivity cone rcptu are consistent with each other and with the fhem data use of ert immediately after the landslide was particularly useful in delineating further risk areas and as an aid for assessment of evacuation of the local population lidar data is particularly useful in understanding the landslide trigger mechanisms the depth of the landslide the form of the run out and the nature of the material in the run out geotechnical data collected in the area is characteristic of that of soft sensitive norwegian marine clays and the various geotechnical and geophysical parameters correlate well with one another and also follow well established patterns the data shows that no single investigative method is available to accurately define quick clay layers but that a number of complimentary in situ and laboratory techniques are necessary for that purpose

new tools for studying seafloor geotechnical and geoacoustic properties three new tools designed to measure certain geotechnical and geoacoustic properties of the sediments just beneath the seafloor are described one tool is a source receiver system designed to generate and receive sh waves or love waves the source applies a torsional impulse to a small circular area of the seafloor and a linear array of gimballed geophones is used to measure horizontal motion perpendicular to the axis of the array energy to generate the torsional pulse is supplied by a rotating flywheel that is suddenly brought to rest the dispersion of love waves produced by this method is used as the basis for a least squares inversion to obtain shear wave velocity as a function of depth a second source receiver system generates vertically polarized shear waves or scholte waves by applying a vertical impulse to the sediment over a small circular area of the bottom in this case the receiving array utilizes gimballed geophones that respond to the vertical motion of the seafloor and the scholte wave di

on the origin of diverse aftershock mechanisms following the 1989 loma prieta earthquake summary we test the hypothesis that the origin at the diverse suite of aftershock mechanisms following the 1989 m 7 1 loma prieta california earthquake is related to the post main shock static stress field we use a 3 d boundary element algorithm to calculate static stresses combined with a coulomb failure criterion to calculate conjugate failure planes at aftershock locations the post main shock static stress field is taken as the of a sum of a pre existing stress field and changes in stress due to the heterogeneous slip across the loma prieta rupture plane the background stress field is assumed to be either a simple shear parallel to the regional trend of the san andreas fault or approximately fault normal compression a suite of synthetic aftershock mechanisms from the conjugate failure planes is generated and quantitatively compared allowing for uncertainties in both mechanism parameters and earthquake locations to well constrained mechanisms reported in the us geological survey northern california seismic network catalogue we also compare calculated rakes with those observed by resolving the calculated stress tensor onto observed focal mechanism nodal planes assuming either plane to be a likely rupture plane various permutations of the assumed background stress field fractional coefficients of aftershock fault planer methods of comparisons etc explain between 52 and 92 per cent of the aftershock mechanisms we can explain a similar proportion of mechanisms however by comparing a randomly reordered catalogue with the various suites of synthetic aftershocks the inability to duplicate aftershock mechanisms reliably on a one to one basis is probably a function of the combined uncertainties in models of main shock slip distribution the background stress field and aftershock locations in particular we show theoretically that any specific main shock slip distribution and a reasonable background stress field are able lo generate a highly variable suite of failure planes such that quite different aftershock mechanisms may be expected to occur within a kilometre of less of each other this scale of variability is less than the probable location error of aftershock earthquakes in the loma prieta region we successfully duplicate a measure of the variability in the mechanisms of the entire suite of aftershocks if static stress changes are responsible for the generation of aftershock mechanisms we are able to place quantitative constraints on the level of stress that must have existed in the upper crust prior to the loma prieta rupture this stress level appears to be too low to generate the average dip across the main shock rupture plane possible reasons for this result range from incorrect initial assumptions of homogeneity in the background stress field friction and fault geometry to driving stresses that arise from deeper in the crust or upper mantle alternatively aftershock focal mechanisms may be determined by processes other than or in addition to static stress changes such as pore pressure changes or dynamic stresses

from geology to geoacoustics evaluation of biot stoll sound speed and attenuation for shallow water acoustics a procedure for estimating acoustic wave velocity and attenuation in ocean sediment using a minimum amount of geological and geotechnical data is demonstrated first the biot stoll theory is presented next various asymptotic formulae for the attenuation coefficient are derived for high low and intermediate frequencies these expressions clearly isolate the effects of intergranular coulomb friction and fluid viscous dissipation on the attenuation of shear and compressional waves under the constraint of a minimum amount of geological and geotechnical information a sequence of empirical equations is compiled to convert basic data such as blow count number from a standard penetration test or shipboard density into sediment geoacoustic properties as a demonstration two well known field cases the atlantic generating station ags site and the atlantic margin coring amcor 6010 site are examined by incorporating the uncertainty involved in the data collection the estimated geoacoustical parameters are provided with a standard deviation

on the use of the norwegian geotechnical institute s prototype seabed coupled shear wave vibrator for shallow soil characterization ii joint inversion of multimodal love and scholte surface waves summary seismic data generated by a novel seabed coupled shear wave vibrator prototype and recorded by a densely populated multicomponent ocean bottom cable allowed several modes of propagation of love and scholte waves to be retrieved in a relatively wide frequency band both global dispersion curves and local dispersion curves are extracted in the frequency wavenumber f k domain and inverted with a multimodal joint scholte and love wave inversion algorithm monte carlo inversion is used for a estimating the global s wave velocity profile of the seabed sediments whereas laterally constrained inversion is used to detect lateral variations of the layer interface depths the results are in agreement and allowed consistent full waveform simulation to be performed the investigation depth is limited to around 40 m due to the low shear wave velocities within the shallow clay layer