correlations of earthquake focal mechanisms summary we performed a statistical analysis of the harvard catalogue of seismic moment tensor solutions we investigated the distribution of hypocentres on focal spheres of earthquakes the hypocentres are concentrated along fault planes the hypocentre distribution does not significantly differ for earthquakes in different depth ranges to study the rotation of focal mechanisms we have solved an inverse problem of a 3 d rotation of double couple earthquake sources i e for each pair of focal mechanisms we find all four 3 d rotations which rotate one mechanism into another the stochastic disorientation of focal mechanisms is well approximated by the rotational cauchy distribution which has previously been identified through theoretical arguments and simulations as the result of stress perturbations caused by random defects in the medium the cauchy distribution is characterized by one parameter k k 0 means no rotations and k 0 5 corresponds to approximately random rotation for earthquake focal mechanisms the value of k is between 0 05 and 0 1 in a fault zone and it increases with distance between pairs of events in directions other than a fault plane k reaches the value 0 5 the cauchy distribution is then close to completely random rotations although k increases slowly with depth in general disorientations of focal mechanisms in various depth ranges display the same dependence therefore we can conclude that deep earthquakes are controlled by the same stress interaction regime as shallow events the results of these measurements made us question the suitability of some terms and models that are commonly used in the theory of an earthquake source for example we argued that tectonic earthquakes rupture rock material which has large scale defects or faults comparable in size with tectonic blocks in which they originate properties of the rocks should be significantly different from those of regular materials where the size of defects is typically much smaller than the scale of interest these properties should strongly depend on the geometry location and orientation of major defects

mesoscale biogeochemical responses to iron fertilization in the upper layers of the southern ocean iron experiment areas 1 during the southern ocean iron experiment sofex january february 2002 two iron fertilization experiments were conducted at the south 66 45 s 171 8 w and north 56 23 s 172 w patches the south patch was replete with all macronutrients whereas the north patch was nearly depleted of silicate using a towed water sampling measurement system high resolution three dimensional observations of temperature salinity co2 partial pressure pco2 and the concentrations of total co2 tco2 nitrate phosphate and silicate in the upper 100 m were obtained 10 and 28 days after initial iron additions in the south and north patches respectively tco2 and nutrient drawdowns observed in the south patch were small due to wind events that limited biological response in the early postfertilization period at the north patch drawdown signals were stronger resulting from the longer time since fertilization the north patch was dispersed along a frontal zone between two distinct waters with the denser subducted under the lighter subduction limited co2 uptake from the air but provided alternative mechanisms for vertical carbon export based on the biogeochemical drawdowns and published estimates of the rate of the entrainment of nonfertilized waters into the patch the mean net community productivity over 28 days was estimated to be 94 12 mmol carbon m 2 day 1 to which the air to sea flux contributed only 2 despite low silicate concentrations and potential limitation of growth of silicifying plankton in the north patch our estimates of the enhanced carbon uptake are similar to estimates from higher silicate environments citation hales b and t takahashi 2012 mesoscale biogeochemical responses to iron fertilization in the upper layers of the southern ocean iron experiment areas j geophys res 117 c01018 doi 10 1029 2011jc006956

air sea exchange of dimethylsulfide in the southern ocean measurements from so gasex compared to temperate and tropical regions 1 in the southern ocean gas exchange experiment so gasex we measured an atmospheric dimethylsulfide dms concentration of 118 54 pptv 1 a dms sea to air flux of 2 9 2 1 mol m 2 d 1 by eddy covariance and a seawater dms concentration of 1 6 0 7 nm dividing flux by the concurrent air sea concentration difference yields the transfer velocity of dms kdms the kdms in the southern ocean was significantly lower than previous measurements in the equatorial east pacific sargasso sea northeast atlantic and southeast pacific normalizing kdms for the temperature dependence in waterside diffusivity and solubility results in better agreement among various field studies and suggests that the low kdms in the southern ocean is primarily due to colder temperatures the higher solubility of dms at a lower temperature results in greater airside control and less transfer of the gas by bubbles formed from breaking waves the final normalized dms transfer velocity is similar to k of less soluble gases such as carbon dioxide in low to moderate winds in high winds dms transfer velocity is significantly lower because of the reduced bubble mediated transfer

two contrasting granite greenstone terranes in the pilbara craton australia evidence for vertical and horizontal tectonic regimes prior to 2900ma abstract major tectono metamorphic differences between two pre 2900 ma granite greenstone terranes of the pilbara craton indicate evolution under fundamentally different tectonic regimes the east pilbara granite greenstone terrane ep contains a typical dome and basin regional structural pattern lacking any preferred orientation of domical granitoid complexes intervening synclinal greenstone belts or faults the ep greenstone succession contains no low angle thrusting is demonstrably autochthonous throughout the ep and most of its stratigraphic components are common to all the greenstone belts the oldest greenstone successions of the ep were deposited between 3515 and 3320 ma by repeated cycles of plume related mafic felsic volcanism onto 3725 3600 ma continental crust intrusion of syn volcanic tonalite trondhjemite granodiorite ttg sheets and subvolcanic laccoliths at ca 3490 3430 ma caused locally significant syn volcanic doming but had only limited penetration into the uppermost greenstone succession a major deformation event at 3315 ma is consistent with gravity driven diapiric doming of the ttg complex and sinking of denser overlying greenstones into adjacent synclines this diapiric deformation established the main features of the present dome and basin pattern subsequent monzogranite intrusion was almost entirely restricted to the cores of the granitoid domes and together with renewed diapirism at 3240 and 2950 ma amplified some of these domes into almost vertical cylindrical structures the crustal evolution of the ep cannot be satisfactorily explained using plate tectonic models the west pilbara granite greenstone terrane wp exhibits a strong northeast oriented structural grain defined by the elongation of granitoid complexes the trend of its two main greenstone belts and by numerous closely spaced east and northeast striking faults unlike the ep the wp is a collage of three separate fault bounded tectono stratigraphic domains each of which contains a unique stratigraphic succession and a separate set of tectonic structures the oldest greenstones of the wp belong to the ca 3280 3250 ma roebourne group that is restricted to the karratha domain the roebourne group is an ultramafic felsic volcanic succession with overlying subordinate clastic metasedimentary rocks isotopic data indicate that the group was deposited on ca 3480 ma crust or was derived from a source region of this age but the basal contact of the group is obscured by intrusive 3270 ma tonalite and granodiorite the roebourne group is interpreted to have formed on ep basement during rifting of the ep after which the ep and wp evolved in different tectonic environments at ca 3160 ma the karratha domain was tectonically over ridden by oceanic type crust of the regal formation indicating collision with an unknown plate to the north the regal formation forms the lower part of the cleaverville domain the upper component being the unconformable post collision ca 3020 ma cleaverville formation the sholl domain containing the 3130 3115 ma whundo group is separated from the karratha and cleaverville domains by a major long lived fault zone the sholl shear zone ssz the whundo group is a juvenile predominantly basaltic pile showing no evidence of contamination by crust older than 3280 ma and is interpreted to have been deposited on oceanic type crust in the post 3240 ma rift four granitoid complexes in the wp were mainly formed between 3015 and 2970 ma and have no age equivalents in the ep no diapiric domes are present in the wp where all deformation is interpreted to be the result of successive episodes of horizontal compression consistent with evolution in phanerozoic style plate tectonic environments

modified frequency wavenumber algorithm for regional seismograms using filon s quadrature modelling of lg waves in eastern north america summary the main focus of this study is to develop an efficient frequency wavenumber code to synthesize high frequency say 10 hz regional seismograms up to a distance of more than 1000 km in a medium consisting of a large number of crustal layers and investigate effects of regional waveguides on lg waves in this newly developed code the frequency wavenumber response is evaluated by using the filon s quadrature at high frequency and the polynomial approximation of bessei s functions implementing trapezoidal integration at low frequency this has reduced the computation time by several folds compared to the time needed for the trapezoidal integration using this algorithm both broad band seismograms at harvard and short period ectn eastern canadian telemetered network seismograms from 1988 november 25 saguenay earthquake were successfully modelled a moment magnitude of 5 9 was used initially an average waveguide was calibrated to successfully excite the regional pnl and snl waves at hrv its near surface structure constrained by matching the recorded frequency content the crust mantle transition zone was constrained by modelling the strength of the broad band snl waves consisting of sn ssmsnsmssms and ssmssms phases relative to the initial pnl waves the model was modified to consist of thin layers with an alternating high and low velocity distribution to match the high frequency ectn lg waves observed from 300 to 600 km away in addition the effect of a near surface irregular receiver structure on the duration of lg waves was also investigated by convolving its response with the regional lg seismograms initial study suggests this method as viable for modelling the entire lg waves including the coda numerical studies suggest that the shapes and peak amplitudes on lg seismograms depend more strongly on the source depth anelasticity and crustal waveguide than do the pnl seismograms

an evaluation of electromagnetic methods in the presence of geologic noise an important element of electromagnetic em prospecting is survey design numerical modeling algorithms may be used to calculate signal to geologic noise s n ratios to compare different survey configurations and measured responses quantitatively our models consist of a prismatic three dimensional 3 d target in a conductive half space which may contain an overburden conductor the models are energized by a time varying current transmitted in a loop of wire the signal is the scattered or anomalous response of the target while the geologic noise is either the response of the half space or the anomalous response of the overburden conductor for typical loop sizes in exploration the coincident loop configuration has a relatively high s n ratio and thus a relatively high capability to resolve the target in the case of half space noise measurements made with the horizontal loop moving coil configuration can be just as effective if the coil separation is one and one half to two times the depth of buria

depth of investigation in electromagnetic sounding methods the time or frequency at which the electromagnetic em response of a buried inhomogeneity can first be measured is determined by its depth of burial and the average conductivity of the overlying section it is relatively independent of the type of source or receiver and their separation the ability to make measurements at this time or frequency however depends on the sensitivity and accuracy of the instrumentation the signal strength and the ambient noise level these factors affect different em sounding systems in surprisingly different ways for the magnetotelluric mt method it is possible to detect a buried half space under about 1 5 skin depths of overburden the maximum depth of investigation is virtually unbounded because of high signal strengths at low frequencies transient electromagnetic tem soundings on the other hand have a limited depth of penetration but are less affected by static shift errors for tem a buried inhomogeneity can be detected under about one diffusion depth of overburden for conventional near zone sounding in which induced voltage is measured impulse response the depth of investigation is proportional to the 1 5 power of the source moment and ground resistivity by contrast if the receiver is a magnetometer step response system the depth of investigation is proportional to the 1 3 power of source moment and is no longer a function of resistivity magnetic field measurements may therefore be superior for exploration in conductive areas such as sedimentary basins far zone or long offset tem soundings are traditionally used for deep exploration the depth of investigation for a voltage receiver is proportional to the 1 4 power of source moment and resistivity and is inversely proportional to the source receiver separation magnetic field measurements are difficult to make at long offsets because instrumental accuracy limits the measurement of the very slow decay of the magnetic field frequency domain controlled source systems are ideally suited for sounding at the very shallow depths needed for engineering archaeological and groundwater applications because of the relative ease of extending the measurements to arbitrarily high frequencies and also because geometric soundings can be made at low induction numbers

shear wave velocity structure in the northern basin and range province from the combined analysis of receiver functions and surface waves a new method based on the joint inversion of receiver functions and surface wave phase velocities results in well determined shear velocity structures that are consistent with the compressional wave structure gravity heat flow and elevation data in the northern basin and range this new inversion method takes advantage of average velocity information present in the surface wave method and differential velocity information contained in the receiver function method thus min imizing the nonuniqueness problem that results from the velocity depth trade off an unusually thick 38 kin and relatively faster crust and upper mantle are found in central and eastern nevada compared to the thin 28 to 34 km and slower crust and upper mantle of the western basin and range we interpret the regions of thicker and faster crust and upper mantle as zones that have undergone less cenozoic ex tension relative to the surrounding regions to the west and north the thick crust and consequently greater depth to the dense mantle material is consistent with the gravity low pattern in central and eastern nevada simple gravity modeling shows both local and regional isostatic compensation occur within 40 km of the surface indicating a near classical airy type of compensation in the province we analyze in detail the shear wave s wave velocity model derived from the receiver functions at station bmn and compressional wave p wave velocity models derived from the 1986 passcal experiment in northwestern nevada the most interesting feature of these models is the presence of negative velocity gradients in the s wave model with no corresponding velocity decrease in the p wave models between depths of 10 and 24 km this combined velocity model may be explained by high pore fluid pressures at these depths this model favors a layered fluid porosity model proposed in the literature to explain extensive middle to lower crust conti nental seismic reflections and high electrical conductivity an upper mantle grada tional low velocity zone is present between 32 and 38 km in the s wave model this upper mantle shear wave low velocity zone is consistent with partial melt which may be the source material for magmatic underplating in this region

multistep modelling of teleseismic receiver functions combined with constraints from seismic tomography crustal structure beneath southeast china summary with a growing number of modern broad band seismographic stations in asia the conditions have improved to allow higher resolution structural studies on regional scales here we perform a receiver based study of the lithosphere of southeast china using waveform records ofexcellentqualityfrom14chinesenationaldigitalseismicnetworkandfourglobalseismic network stations calculating the theoretical receiver functions rfs that match the observed rfs from teleseismic waveforms is an established technique for retrieving information about crustalanduppermantlestructurebeneathaseismicreceiver rfs however arepredominantly sensitivetothegradientsinthelithosphericelasticparameters anditisimpossibletodetermine a non unique distribution of seismic parameters such as absolute shear wave speeds as a function of depth unless other geophysical data are combined with rfs thus we combine rfswithindependentinformationfromshearandcompressionalwavespeedsaboveandbelow the mohoroviy discontinuity available from the existing tomographic studies we introduce a statistical approach for automatically selecting only mutually coherent rfs from a large set of observed waveforms furthermore an interactive forward modelling software is introduced and applied to observed rfs to define a prior physically acceptable range of elastic parameters in the lithosphere this is followed by a grid search for a simple crustal structure an initial model for a linearized iterative inversion is constructed from multiple constraints including results from the grid search for shear wave speed the moho depth versus vp vs ratio domain search and tomography the thickness of the crust constrained by our multistep approach appears to be more variable in comparison with tomographic studies with the crust thinning significantly towards the east we observe low values of vp vs ratios across the entire region which indicates the presence of a very silicic crust we do not observe any correlation between the crustal thickness or age of the crust with vp vs ratios which argues against a notion that there is a simple relationship between mineralogical composition and crustal thickness and age on a global scale

automated detection extraction and measurement of regional surface waves our goal is to develop and test an effective method to detect identify extract and quantify surface wave signals for weak events observed at regional stations we describe an automated surface wave detector and extractor designed to work on weak surface wave signals across eurasia at intermediate periods 8 s 40 s the method is based on phase matched filters defined by the rayleigh wave group travel time predictions from the broadband group velocity maps presented by ritzwoller and levshin 1998 and ritzwoller et al 1998 and proceeds in three steps signal compression signal extraction or cleaning and measurement first the dispersed surface wave signals are compressed in time by applying an anti dispersion or phase matched filter defined from the group velocity maps we refer to this as the compressed signal second the surface wave is then extracted by filtering noise temporally isolated from the time compressed signal this filtered signal is then redispersed by applying the inverse of the phase matched filter finally we adaptively estimate spectral amplitude as well as group and phase velocity on the filtered signal the method is naturally used as a detector by allowing origin time to slide along the time axis we describe preliminary results of the application of this method to a set of nuclear explosions and earthquakes that occurred on or near the chinese lop nor test site from 1992 through 1996 and one explosion on the indian rajasthan test site that occurred in may of 1998

review secular tectonic evolution of archean continental crust interplay between horizontal and vertical processes in the formation of the pilbara craton australia the archean pilbara craton contains five geologically distinct terranes the east pilbara karratha sholl regal and kurrana terranes all of which are unconformably overlain by the 3 02 to 2 93 ga de grey superbasin the 3 53 3 17 ga east pilbara terrane ep represents the ancient nucleus of the craton that formed through three distinct mantle plume events at 3 53 3 43 3 35 3 29 and 3 27 3 24 ga each plume event resulted in eruption of thick dominantly basaltic volcanic successions on older crust to 3 72 ga and melting of crust to generate first tonalite trondhjemite granodiorite ttg and then progressively more evolved granitic magmas in each case plume magmatism was accompanied by uplift and crustal extension the combination of conductive heating from below thermal blanketing from above and internal heating of buried granitoids during these events led to episodes of partial convective overturn of upper and middle crust these mantle melting events caused severe depletion of the subcontinental lithospheric mantle making the ep a stable buoyant unsubductable continent by c 3 2 ga extension accompanying the latest event led to rifting of the protocontinent margins at between 3 2 and 3 17 ga after 3 2 ga horizontal tectonic forces dominated over vertical forces as revealed by the geology of the three terranes karratha sholl and regal of the west pilbara superterrane the c 3 12 ga whundo group of the sholl terrane is a fault bounded 10 km thick volcanic succession with geochemical characteristics of modern oceanic arcs including boninites and evidence for flux melting that indicate steep archean subduction at 3 07 ga the 3 12 ga sholl terrane 3 27 ga karratha terrane and c 3 2 ga regal terrane accreted together and onto the ep during the prinsep orogeny this was followed by development of the de grey superbasin an intracontinental sag basin and widespread plutonism 2 99 2 93 ga as a result of orogenic relaxation and slab break off craton wide compressional deformation at 2 95 2 93 ga culminated with 2 91 ga accretion of the 3 18 ga kurrana terrane with the ep this compression caused amplification of the dome and keel structure in the ep final cratonization was effected by emplacement of 2 89 2 83 ga post tectonic granites

tectonic evolution of proterozoic australia proterozoic australia has long been interpreted as a single intact continent in which all tectonic and magmatic activity was intracratonic this paper proposes an alternative hypothesis in which numerous fragments of continental crust were assembled by plate tectonic processes the assembly was completed between 1300 and 1100 ma when the crustal fragments were combined as an early component of the rodinian supercontinent rifting and fragmentation of archaean continents began in the late archaean and continued into the proterozoic passive margin deposits such as those of the hamersley basin accumulated on isolated fragments of archaean crust these numerous fragments were subsequently assembled into three cratons by 1830 ma a west australian craton was established by collision of the archaean pilbara and yilgarn cratons which were joined along the capricorn orogen similarly a south australian craton developed by amalgamation of the proto gawler and proto curnamona cratons along the kimban orogen a north australian craton appears to have formed by accretion of numerous crustal fragments including the kimberley pine creek lucas and altjawarra cratons with sutures marked by the king leopold halls creek tennant creek and proto isan orogens the southern margin of the north australian craton was the site of repeated terrane accretion and orogenic activity between 1880 ma and 1400 ma this included an orogenic event at 1880 1850 ma the strangways 1780 1730 ma argilke 1680 1650 ma and chewings 1620 1580 ma orogenies and the intracratonic anmatjira uplift 1500 1400 ma intracratonic rifting at 1750 to 1710 ma and 1640 to 1600 ma produced the mcarthur basin and related minor basins parts of which were deformed by the isan orogeny at 1600 and 1530 ma rifting along the line of the capricorn orogen led to deposition in the overlying intracratonic bangemall basin between 1630 and 1300 ma along the eastern margin of the south australian craton the 1670 to 1600 ma olarian orogeny marks interaction with now obscured continental crust to the east tectonic activity between 1300 and 1100 ma led to the assembly of proterozoic australia as an early component of the supercontinent of rodinia this first involved the amalgamation of the west australian and north australian cratons followed by collision with the south australian craton the centralian superbasin developed over the junction of the north south and west australian cratons between 830 and 750 ma rifting to the east formed the adelaide geosyncline at 830 ma this was followed by the breakup of rodinia with the rifting apart of laurentia and gondwanaland along the eastern margin of proterozoic australia at 750 ma and the subsequent formation of the palaeo pacific ocean after the breakup of rodinia a series of northeast southwest compressional events followed by periods of relaxation reflect the assembly of a new supercontinent old lines of weakness were reactivated culminating in the intracratonic king leopold paterson petermann ranges and pinjarra orogenies between 620 and 540 ma subsequent reactivation continued into the phanerozoic with the widespread eruption of continental flood basalts and the formation of intracratonic basins 540 530 ma

suspended sediment transport in the deepwater navigation channel yangtze river estuary china in the dry season 2009 2 numerical simulations 1 a three dimensional wave current sediment coupled numerical model with wetting and drying process is developed to understand hydrodynamics and sediment transport dynamics in the deepwater navigation channel dnc the north passage of the yangtze river estuary yre china the model results are in good agreement with observed data and statistics show good model skill scores and correlation coefficients the model well reproduces the spring neap variation between a well mixed estuary and a highly stratified estuary model results indicate that the estuarine gravitational circulation plays the most important role in the estuarine turbidity maximum etm formation in the dnc the upstream nonlocal sediment intrusion through the spillover mechanism is a major source of sediment trapping in the north passage after the morphological changes numerical studies are conducted to show scenarios in the yre under the effects of different forcings river discharges waves and winds between these study cases surface wave breaking relieves the sediment trapping and bottom wave current interaction aggravates the bed erosion and elevates the ssc in the etm the former and the latter have the least and largest influence on the suspended sediment transport in the dnc the wind effects have a greater influence on sediment trapping than the river discharges and the steady northwesterly wind condition favors the siltation in the dnc most the significance of density driven turbidity current is also assessed which can enhance the saline water intrusion and suppress the turbulent mixing in the bottom boundary layer

analysing two dimensional effects in central loop transient electromagnetic sounding data using a semi synthetic tipper approach we present a simple and feasible approach to analyse and identify two dimensional effects in central loop transient electromagnetic sounding data and the correspondingly derived quasi two dimensional conductivity models the proposed strategy is particularly useful in minimising interpretation errors it is based on the calculation of a semi synthetic transient electromagnetic tipper at each sounding and for each observational transient time point the semi synthetic transient electromagnetic tipper is derived from the measured vertical component of the induced voltage and the synthetically calculated horizontal component the approach is computationally inexpensive and involves one two dimensional forward calculation of an obtained quasi two dimensional conductivity section based on a synthetic example we demonstrate that the transient electromagnetic tipper approach is applicable in identifying which transient data points and which corresponding zones in a derived quasi twodimensional subsurface model are affected by two dimensional inhomogeneities the one dimensional inversion of such data leads to false models an application of the semi synthetic transient electromagnetic tipper to field data from the azraq basin in jordan reveals that in total eight of 80 investigated soundings are affected by two dimensional structures although the field data can be fitted optimally using onedimensional inversion techniques the largest semi synthetic tipper response occurs in a 300 m wide region around a strong lateral resistivity contrast the approach is useful for analysing structural features in derived quasi two dimensional sections and for qualitatively investigating how these features affect the transient response to avoid misinterpretation these identified zones corresponding to large tipper values are excluded from the interpretation of a quasi two dimensional conductivity model based on the semi synthetic study we also demonstrate that a quantitative interpretation of the horizontal voltage response e g by inversion is usually not feasible as it requires the exact sensor position to be known although a tipper derived purely from field data is useful as a qualitative tool for identifying two dimensional distortion effects it is only feasible if the sensor setup is sufficiently accurate our proposed semi synthetic transient electromagnetic tipper approach is particularly feasible as an a posteriori approach if no horizontal components are recorded or if the sensor setup in the field is not sufficiently accurate

measurements with an automatically recording inverted echo sounder aries and the bubble clouds abstract we report here analysis of the first observations with a new instrument aries designed to record the acoustic backscatter from bubble clouds at several levels below the surface of the ocean the instrument is deployed on a subsurface mooring and records internally data has been analysed from deployments of aries for one week in the irish sea and for periods of 4 and 9 weeks near the edge of the uk continental shelf during periods in which meteorological data waves and near surface temperatures and on occasion currents were being recorded by other instruments the results while being generally similar to earlier measurements in coastal waters show that the bubble clouds are more intense having greater acoustic scattering cross per unit volume mv and extend on average deeper into the water column a simple model accounting for the shape of the clouds their advection through the sonar beam and their decay through bubbles returning to the surface or through their gas dissolving int

transient electromagnetic sounding for groundwater the feasibility of using the transient electromagnetic sounding ts or tdem method for groundwater exploration can be studied by means of numerical models as examples of its applicability to groundwater exploration we study four groundwater exploration problems 1 mapping of alluvial fill and gravel zones over bedrock 2 mapping of sand and gravel lenses in till 3 detection of salt or brackish water interfaces in freshwater aquifers and 4 determination of hydrostratigraphy these groundwater problems require determination of the depth to bedrock location of resistive high porosity zones associated with fresh water determination of formation resistivity to assess water quality and determination of lithology and geometry respectively the ts method is best suited for locating conductive targets and has very good vertical resolution unlike other sounding techniques where the receiver transmitter array must be expanded to sound more deeply the depth of investigation for the ts method is a

australia s large earthquakes and recent fault scarps abstract nineteen large earthquakes up to magnitude ms 6 8 have occurred within continental australia this century and at least seven recent prehistoric fault scarps have been discovered the magnitude of the earthquake causing each of these prehistoric fault scarps has been estimated from the observed fault length and maximum scarp height and none exeeds magnitude 7 0 their occurrence demonstrates that the australian plate is undergoing significant internal deformation but as yet there is no model to explain their cause nor the likely site of the next large earthquake the absence of earthquake epicentres on the current tectonic map of australia is a regrettable omission

coherent structures at the ocean surface in convectively unstable conditions the turbulent boundary layer at the ocean surface has some dynamical similarities to the atmospheric boundary layer1 4 the atmospheric turbulent boundary layer may exhibit not only random fluctuations but also spatially coherent organized motion5 6 thorpe1 conjectured that such organized motion should also be found in the upper ocean boundary layer in convectively unstable conditions here i report on observations made in the tropical atlantic ocean which confirm this view horizontal temperature profiles obtained at a depth of 2 m at night revealed ramp like structures vertical velocity profiles in the upper few metres of the ocean was determined using a free rising profiler and exhibited abrupt changes corresponding to sudden changes in temperature these features are known5 6 to be characteristic of spatially coherent organized motions in turbulent boundary layers

non double couple earthquake mechanisms at the hengill grensdalur volcanic complex southwest iceland the hengill grensdalur area in iceland generates frequent small non double couple earthquakes with explosive volumetric components we collected high quality three component digital recordings of 4 000 earthquakes on a purpose designed 32 station network in 1991 and determined focal mechanisms for 100 of the best recorded earthquakes by inverting amplitude ratios many of the mechanisms are consistent within the errors with simultaneous shear and tensile faulting with tensile faults parallel to the local spreading ridge and shear faulting similar to that in the south iceland transform fault zone some events cannot be explained by this model however and require other processes such as crack closing and partial compensation of tensile cracks by fluid flow

a multistep approach for joint modeling of surface wave dispersion and teleseismic receiver functions implications for lithospheric structure of the arabian peninsula 1 we present a multiple step procedure for joint modeling of surface wave group velocity dispersion curves and teleseismic receiver functions for lithospheric velocity structure the method relies on an initial grid search for a simple crustal structure followed by a formal iterative inversion an additional grid search for shear wave velocity in the mantle and finally forward modeling of transverse isotropy to resolve love rayleigh surface wave dispersion discrepancy it considers longer period surface wave group velocity swgv dispersion allowing for the resolution of deeper structure compared to previous joint inversions the grid search for simple crustal structure is facilitated using a library of precomputed receiver functions and swgv dispersion curves the iterative inversion improves fit to the data by increasing the number of layers in the crust when necessary in order to fit the swgv for periods greater than about 50 s we perform a grid search over mantle velocities including the mantle lid and low velocity zone keeping the crustal structure fixed to the values from the previous step in some cases a clear love rayleigh discrepancy prevents a simultaneous fit of the group velocities with an isotropic model the love rayleigh discrepancy can be resolved by allowing shear wave transverse isotropy with a vertical symmetry axis vsh vsv differences in the uppermost mantle the method is applied to 10 stations in the arabian peninsula sampling various tectonic environments including active continental rifting and stable regions the resulting shear velocity models confirm rapid crustal thinning of the arabian shield toward the red sea however we do not find strong evidence for crustal thickening toward the arabian platform our results suggest that the mantle lithosphere thickness varies regionally but that the mantle shear velocities beneath the arabian shield and red sea coast are generally anomalously low furthermore our results indicate the presence of strong polarization anisotropy up to about 10 in the lithospheric upper mantle in the vicinity of as well as farther away from the red sea our modeling yields vsv vsh in the southwestern part of the arabian peninsula consistent with vertical flow and vsh vsv in the northwestern part of the arabian peninsula and the continental interior consistent with horizontal flow indicating that the mantle flow pattern is not uniform along the axis of the red sea

wave turbulence interactions in the upper ocean part ii statistical characteristics of wave and turbulent components of the random velocity field in the marine surface layer abstract we present the results of an analysis of field data collected by donelan who used a miniature drag sphere to measure velocities beneath wind waves on lake ontario linear statistical techniques are used to separate the velocity into wave and turbulent parts while we mostly aim at demonstrating the effects of surface wind waves on the statistical characteristics of the turbulent field in the upper mixed layer we also interpret several features of the data on the hags of recent theoretical results one of the most intriguing features of the turbulent velocity spectra so obtained is a large peak near the dominant wave frequency we review various possible explanation for this behavior although we prefer a model in which the turbulence is assumed frozen on the timescale of the waves this model requires no new dynamics and gives explicit formulae relating the dissipation rate to the magnitude of the spectral densities for high and low frequencies on this basis we have determined a dissipation leng

the optical volume scattering function in a surf zone inverted to derive sediment and bubble particle subpopulations 1 the effects of particle fields including bubbles on the optical volume scattering function vsf were investigated in the surf zone off scripps pier as part of an ongoing effort to better understand the underlying dynamics in the vsf in the subsurface ocean vsfs were measured at 20 hz at angles spanning 10 170 in 10 increments with a device called the multiangle scattering optical tool mascot modification of the phase function was observed in passing suspended sediment plumes wave injected bubble plumes and combinations of these particle populations relative to the background phase function enhancement in the 60 80 range was observed in association with bubble plumes consistent with theoretical predictions vsfs were inverted to infer size distributions and composition using a least squares minimization fitting procedure applied to a library of phase functions each representing a lognormally distributed subpopulation with refractive index and coating where applicable phase functions representative of nonspherical mineral particle subpopulations were computed using discrete dipole approximation dda and improved geometric optics method igom techniques for randomly oriented asymmetric hexahedra phase functions for coated bubbles were computed with the lorenz mie theory inversion results exhibited stable solutions that qualitatively agreed with concurrent acoustical measurements of bubbles aggregate particle size distribution expectations and anecdotal videography evidence from the field although a comparable inversion with a library that assumed spherical shaped particles alone provided less stable results with some incorrectly assigned subpopulations several dominant subpopulation trends were consistent with the results obtained using nonspherical representations of mineral particles

the energy flux from the wind to near inertial motions in the surface mixed layer abstract time series of wind stress computed from long term meteorological buoy data off north america are used to examine the forcing of surface inertial currents by the wind a simple damped slab model of the mixed layer is used to compute h the average flux of energy from the wind to mixed layer inertial currents in a mixed layer of fixed depth h the forcing of mixed layer inertial motions is highly intermittent most of the forcing occurs during the winter months with a few dozen events accounting for typically over half the total energy flux major forcing events are usually associated with translating cold fronts or small lows with scales of about 100 km the larger synoptic scale features have little energy at the inertial frequency and thus result in only weak forcing of inertial currents a strong seasonal signal exists in the inertial forcing at ows p 50 n 145 w 50 m is largest from october to february and is a factor of 12 above the june and july values if seasonally varying

nw australian intraplate seismicity and stress regime 1 the interrelations between stress orientation regional deformation and seismic activity in the context of intraplate seismicity continue to pose difficult questions stress models of the australian continent are largely based on nonseismic information our study of 26 microearthquakes in nw australia shows that they are good indicators of the seismogenic stress field by inverting focal mechanisms calculated from the events we obtained deviatoric stress tensors in full agreement with the known in situ stress field the stress tensors corroborate the elastic modeling of the continent the methods used here have widespread applicability in determining crustal stress field parameters in regions where in situ stress data are sparse or absent

air sea gas transfer in the southern ocean 1 gas transfer velocities were determined in the southern ocean during the southern ocean iron fertilization experiment sofex using the dual deliberate tracer technique the decrease of the purposefully injected tracers sulfur hexafluoride and helium 3 could be well described by gas exchange parameterizations with wind speed that satisfy global constraints based on bomb 14c uptake the concentration decrease of tracers could be predicted slightly better with established relationships if gas transfer was modeled as a function of the cube rather than the square of the wind speed particularly over a time interval with high and variable winds however both fits can model the concentration decrease within the uncertainty of the observations this suggests that it will be singularly difficult to definitively determine if a quadratic or cubic dependence of gas exchange with wind is more appropriate based on deliberate tracer measurements however these results show that gas exchange rates in the southern ocean are not anomalous when compared with the rest of the ocean thus this cannot account for discrepancy between observational and model based estimates of uptake of co2 in the southern ocean using a high quality wind speed field obtained from the quikscat satellite seawinds scatterometer and an established surface water pco2 climatology the co2 uptake in the southern ocean 34 s is reassessed the total uptake rates are similar to previous observation based estimates but the analysis shows that the uptake rate is sensitive to wind speed product used and the wind speed distribution

investigation of surge derived pyroclastic flow formation by numerical modelling of the 25 june 1997 dome collapse at soufriere hills volcano montserrat deposits from ash cloud surges associated with dome collapse can under certain conditions be remobilised to form surge derived pyroclastic flows sdpfs using numerical modelling we reproduce the emplacement of these flows and investigate the conditions that favour their genesis we use the new version of the numerical model volcflow which simulates the two components of a pyroclastic flow the basal avalanche and the overriding ash cloud surge the basal avalanche primary block and ash flows and sdpfs are simulated using three previously published rheological laws plastic frictional and frictional velocity weakening rheologies applied to the 25 june 1997 dome collapse at soufriere hills volcano the models reproduce to different degrees the deposit footprints formed by the block and ash flows the ash cloud surges and the sdpfs in the plastic model sdpfs occur if the ash cloud surge deposit exceeds a threshold thickness that allows it to remobilise and flow in the frictional models sdpfs occur only if ash cloud surge deposition takes place on a slope exceeding the friction angle of the ash results also highlight that sdpfs appeared so clearly in 1997 at montserrat due to a combination of topographic factors i a bend in the mosquito ghaut drainage that allowed the ash cloud surges to detach ii a depositional area on the watershed between the eastern and western drainage channels and iii a network of tributaries that drained all the remobilised mass into dyer s river to form a single large sdpf our model could be a promising tool for the future forecasting of hazards posed by surge derived pyroclastic flows

the gas transfer through polar sea ice experiment insights into the rates and pathways that determine geochemical fluxes sea ice is a defining feature of the polar marine environment it is a critical domain for marine biota and it regulates ocean atmosphere exchange including the exchange of greenhouse gases such as co2 and ch4 in this study we determined the rates and pathways that govern gas transport through a mixed sea ice cover n2o sf6 3he 4he and ne were used as gas tracers of the exchange processes that take place at the ice water and air water interfaces in a laboratory sea ice experiment observation of the changes in gas concentrations during freezing revealed that he is indeed more soluble in ice than in water ne is less soluble in ice and the larger gases n2o and sf6 are mostly excluded during the freezing process model estimates of gas diffusion through ice were calibrated using measurements of bulk gas content in ice cores yielding gas transfer velocity through ice kice of 5 10 4 m d 1 in comparison the effective air sea gas transfer velocities keff ranged up to 0 33 m d 1 providing further evidence that very little mixed layer ventilation takes place via gas diffusion through columnar sea ice however this ventilation is distinct from air ice gas fluxes driven by sea ice biogeochemistry the magnitude of keff showed a clear increasing trend with wind speed and current velocity beneath the ice as well as the combination of the two this result indicates that gas transfer cannot be uniquely predicted by wind speed alone in the presence of sea ice

new insight into cainozoic sedimentary basins and palaeozoic suture zones in southeast australia from ambient noise surface wave tomography 1 detailed images of rayleigh wave group velocity are derived from ambient seismic noise recorded by wombat a large rolling seismic array project in southeast australia group velocity maps sensitive to crustal structure exhibit low velocity anomalies in the presence of sedimentary basins and recent hot spot volcanism and high velocities in regions of out cropping metamorphic and igneous rocks distinct and well constrained patches of low velocity within the murray basin provide new insight into the spatial extent and possible composition of pre tertiary infra basins in a broader tectonic context our results show little evidence for the palaeozoic building blocks of the southeast australian continent that have been inferred from geological mapping and potential field data this may mean that apparent changes in basement terrane near the surface are not associated with major changes in composition at depth

exploiting seismic signal and noise in an intracratonic environment to constrain crustal structure and source parameters of infrequent earthquakes in many regions of the world characterized by a relatively low rate of seismicity the determination of local and regional seismic source parameters is often restricted to an analysis of the first onsets of p waves or first motion analysis due to incomplete information about earth structure and the small size of the events when rare large earthquakes occur in these regions their waveforms can be used to model earth structure this however makes the nature of the earthquake source determination problem circular as source information is mapped as structure presented here is one possible remedy to this situation where through a two step approach we first constrain earth structure using data independent of the earthquake of interest in this study we focus on a region in western australia with low seismicity and minimal instrument coverage and use the capra lp temporary deployment to demonstrate that reliable structural models of the upper lithosphere can be obtained from an independent collection of teleseismic and ambient noise datasets apart from teleseismic receiver functions rfs we obtain group velocities from the cross correlation of ambient noise and phase velocities from the traditional two station method using carefully selected teleseismic earthquakes and station pairs crustal models are then developed through the joint inversion of dispersion data and rfs and structural green s functions are computed from a layered composite model in the second step of this comprehensive approach we apply full waveform inversion three component body and surface waves to the 2007 ml 5 3 shark bay western australia earthquake to estimate its source parameters seismic moment focal mechanism and depth we conclude that the full waveform inversion analysis provides constraints on the orientation of fault planes superior to a first motion interpretation

measurements of air sea gas transfer during an open ocean algal bloom measurements of air sea gas transfer were made during the development of a large algal bloom that immediately followed in situ iron enrichment in the equatorial pacific ocean gas transfer rates were determined from changes in the ratio of the deliberately released tracers sulphur hexafluoride and helium 3 this first application of the dual tracer technique in the open ocean produced estimates of the gas transfer rate that were similar in magnitude to those obtained previously from measurements in shelf seas we found no evidence that gas transfer rates declined during the development of the algal bloom incorporation of the new open ocean measurements with other published dual tracer data gives a relationship between transfer velocity and wind speed that explains 82 of the total variance in the dataset

convectively driven turbulent mixing in the upper ocean abstract two experiments were performed to study the characteristics of turbulence in convective mixed layers in the upper ocean in the first a diurnal convective mixed layer developed in the bahamas under the influence of the cycle of daytime solar heating and nighttime evaporative cooling the mixed layer reached as deep as 100 m each night and restratified each day in the second the mixed layer of a warm core gulf stream ring deepened from less than 50 m to more than 150 m in a little more than a day when subjected to rapid cooling during a cold air outbreak although individual profiles of the rate of viscous dissipation of turbulent kinetic energy had considerable spatial and temporal variability the mean dissipation profiles were similar to those in convecting atmospheric boundary layers the is established by the surface buoyancy flux jb0 jb0 0 61 and 0 72 in the bahamas and ring data respectively compared with 0 64 in convecting atmospheric mixed layers the mean profiles decre

a regional comparison of particle size distributions and the power law approximation in oceanic and estuarine surface waters 1 the particle size distribution psd is commonly used in studies of sediment fluxes phytoplankton dynamics and optical scattering from particulates but little is known about the spatial and temporal variability of this parameter here we analyze in situ laser diffraction measurements of the psd from a variety of estuarine and open ocean systems the power law or junge type distribution provided a good fit to surface ocean particle size distributions measured from 6 to 250 m psd slopes ranged from 2 7 to 4 7 with a mean of 3 63 consistent with theory high particle slopes 3 78 and low particle concentrations characterized the open ocean waters of the atlantic and the southern ocean lower psd slopes 3 63 and high concentrations were characteristic of estuarine waters river plumes consistently showed the lowest psd slopes 3 30 and highest particle concentrations characteristic of larger bloom forming phytoplankton and production of particle aggregates in the north atlantic an inverse relationship was found between psd slope and chlorophyll concentration such results follow the biological paradigm that larger phytoplankton are prevalent in bloom conditions and smaller phytoplankton dominate in oligotrophic water large temporal variability in psd was observed in near coastal regions prone to sediment resuspension from storms and tidal flow dense sea grass beds consistently had lower particle concentrations compared to surrounding waters due to reductions in current flow and sediment resuspension simple power law approximations of particle size distributions can be successfully used to describe and assess particle distributions in a wide array of oceanic and estuarine water types

the application of tem to cyprus type massive sulfide exploration in cyprus cyprus type massive sulfide mineral deposits are difficult geophysical targets with small physical parameter contrasts between the silicically altered mineralization and the altered conductive pillow lavas in which they occur during the period 1988 1991 two research projects studied the application of the transient electromagnetic tem sounding method to exploration for such deposits initially we tested the method over three mapped mineral deposits at klirou philani and strongyli using sirotem mki and iise instruments surveys using both coincident and central loop configurations failed to detect the mineralization at all three sites conductive anomalies seen beneath two of the deposits might be related to groundwater contamination by the mineral ions and may represent an exploration target based on this work we implemented a new exploration strategy using tem for structural mapping to identify possible mineral bearing structures initial results from the mathiatis sha prospect resolved some int

earthquake mechanisms from linear programming inversion of seismic wave amplitude ratios the amplitudes of radiated seismic waves contain far more information about earthquake source mechanisms than do first motion polarities but amplitudes are severely distorted by the effects of heterogeneity in the earth this distortion can be reduced greatly by using the ratios of amplitudes of appropriately chosen seismic phases rather than simple amplitudes but existing methods for inverting amplitude ratios are severely nonlinear and require computationally intensive searching methods to ensure that solutions are globally optimal searching methods are particularly costly if general moment tensor mechanisms are allowed efficient linear programming methods which do not suffer from these problems have previously been applied to inverting polarities and wave amplitudes we extend these methods to amplitude ratios in which formulation on inequality constraint for an amplitude ratio takes the same mathematical form as a polarity observation three component digital data for an earthquake at the hengill grensdalur geothermal area in southwestern iceland illustrate the power of the method polarities of p sh and sv waves unusually well distributed on the focal sphere cannot distinguish between diverse mechanisms including a double couple amplitude ratios on the other hand clearly rule out the double couple solution and require a large explosive isotropic component

quasi 3d modeling of airborne tem data by spatially constrained inversion we present a new methodology spatially constrained inversion sci that produces quasi 3d conductivity modeling of electromagnetic em data using a 1d forward solution spatial constraints are set between the model parameters of nearest neighboring soundings data sets models and spatial constraints are inverted as one system the constraints are built using delaunay triangulation which ensures automatic adaptation to data density variations model parameter information migrates horizontally through spatial constraints increasing the resolution of layers that would be poorly resolved locally sci produces laterally smooth results with sharp layer boundaries that respect the 3d geological variations of sedimentary settings sci also suppresses the elongated artifacts commonly seen in interpretation results of profile oriented data sets in this study sci is applied to airborne time domain em data but it can also be implemented with other ground based or airborne data types

application of an unstructured mesh model to the determination of the baroclinic circulation of the irish sea 1 a three dimensional finite volume model with horizontally varying but fixed in time mesh is used to compute the baroclinic circulation of the irish sea during 1995 tidal forcing was applied along the model s open boundary with meteorological forcing taken from observations initial calculations were performed with a mesh that had high resolution in the well mixed near coastal region a necessary requirement in order to reproduce tides in the region although offshore in the stratified area the mesh was slightly coarser than that used in earlier finite difference models subsequent calculations were performed using an enhanced resolution which is significantly finer than earlier finite difference models in the offshore region which is thermally stratified in summer due to solar heating and low tidal mixing this produces a cold water bottom dome separated from the well mixed shallow water regions by strong tidal fronts calculations show that both model meshes can reproduce the observed major features of the baroclinic circulation of the western irish sea with the coarse mesh model giving comparable results to earlier finite difference models in the case of the finer mesh model there are sharper horizontal density gradients in the region of the fronts which show the presence of baroclinic instability and associated small scale variability as observed in satellite images but not found in the coarser mesh model due to lack of resolution results from the fine mesh model show significantly more spatial variability comparable to that found in the measurements

coastal aquifer assessment based on geological and geophysical survey northwestern crete greece groundwater preservation comprises a major problem in water policy the comprehension of the groundwater hydraulic systems can provide the means to approach this problem generally drilling is expensive and time consuming on the other hand new techniques have been applied during the last few decades that provide useful information on the depth and quality of aquifers among them transient electromagnetic method tem is an appealing method that provides fast results with minimum field crew and solves several hydrogeological problems many portable systems for single site measurements are commercially available the tem fast 48hpc was used for acquiring 106 soundings in the northwestern crete in greece for defining the hydrogeological characteristics of the study area since there were no available data from boreholes detailed geological hydrolithological and tectonic survey was applied prior to the geophysical measurements all the data were integrated to produce a secure and reliable hydrogeological model for the study area prior to any future hydrowell specifically geometrical and hydraulic data of the study area groundwater were acquired two unconnected aquifers were detected and their possible contamination due to saltwater intrusion was analyzed and eliminated moreover a location for borehole construction and groundwater pumping based on the potential of the aquifer system was proposed finally the contribution of tem and electrical resistivity tomography geophysical methods in studying complex coastal aquifers is shown by this work

observations of the transition layer abstract the transition layer is the poorly understood interface between the stratified weakly turbulent interior and the strongly turbulent surface mixed layer the transition layer displays elevated thermohaline variance compared to the interior and maxima in current shear vertical stratification and potential vorticity a database of 91 916 km or 25 426 vertical profiles of temperature and salinity from seasoar a towed vehicle is used to define the transition layer thickness acoustic doppler current measurements are also used when available statistics of the transition layer thickness are compared for 232 straight seasoar sections which range in length from 65 to 1129 km with typical horizontal resolution of 4 km and vertical resolution of 8 m transition layer thicknesses are calculated in three groups from 1 vertical displacements of the mixed layer base and of interior isopycnals into the mixed layer 2 the depths below the mixed layer depth of peaks in shear stratification and potenti

multistep modelling of receiver based seismic and ambient noise data from wombat array crustal structure beneath southeast australia summary a limitation of most forms of passive seismic tomography using distant earthquakes lies in the fact that crustal structure is poorly resolved an attempt is made here to address this issue by modelling teleseismic receiver functions rfs and dispersion curves derived from ambient noise through a multistep approach the seal3 experiment in central and southern new south wales nsw used here represents one of 13 array deployments that so far comprise the large wombat project which aims to cover a significant portion of the australian continent with a rolling array of seismometers an interactive forward modelling software package irffm2 is introduced and applied to the observed rfs and surface wave dispersion curves to define a prior physically acceptable range of elastic parameters in the lithosphere which is combined with a grid search and a linearized inversion our results emphasize the importance of a joint treatment of rfs and dispersion data as the predictions from 1 d velocity models at individual stations derived from only rfs display large departures from the observed ambient noise dispersion curves in total 27 jointly constrained 1 d shear wave models are produced which provide sufficient sampling of the crust beneath seal3 to permit detailed inferences about lateral variations in structure to be made of particular note is the observation that the moho deepens towards the mountainous southeast where it exceeds 50 km in depth beneath the southern highlands of nsw thus marking out some of the thickest crust in australia the complex lateral variations in mid lower crustal velocity that we observe probably reflect the manifold interactions of a thinning lithosphere associated igneous underplating recent hot spot related volcanism and uplift our results image an important part of the lithosphere that is poorly constrained by regional and teleseismic tomography and contribute to the understanding of the formation of the southern highlands and the palaeozoic lachlan orogen

stirring up the biological pump vertical mixing and carbon export in the southern ocean the biological carbon pump bcp transports organic carbon from the surface to the ocean s interior via sinking particles vertically migrating organisms and passive transport of organic matter by advection and diffusion while many studies have quantified sinking particles the magnitude of passive transport remains poorly constrained in the southern ocean weak thermal stratification strong vertical gradients in particulate organic matter and weak vertical nitrate gradients suggest that passive transport from the euphotic zone may be particularly important we compile data from seasonal time series at a coastal site near palmer station annual regional cruises in the western antarctic peninsula wap cruises throughout the broader southern ocean and soccom autonomous profiling floats to estimate spatial and temporal patterns in vertical gradients of nitrate particulate nitrogen pn and dissolved organic carbon doc under a steady state approximation the ratio of pn z to no3 z suggests that passive transport of pn may be responsible for removing 46 37 58 of the nitrate introduced into the surface ocean of the wap with dom contributing an additional 3 6 and for 23 19 28 of the bcp in the broader southern ocean a simple model parameterized with in situ nitrate pn and primary production data suggested that passive transport was responsible for 54 of the magnitude of the bcp in the wap our results highlight the potential importance of passive transport by advection and diffusion of organic matter in the southern ocean but should only be considered indicative of high passive transport rather than conclusive evidence due to our steady state assumptions

southern ocean gas exchange experiment setting the stage 1 the southern ocean gas exchange experiment so gasex is the third in a series of u s led open ocean process studies aimed at improving the quantification of gas transfer velocities and air sea co2 fluxes two deliberate 3he sf6 tracer releases into relatively stable water masses selected for large dpco2 took place in the southwest atlantic sector of the southern ocean in austral fall of 2008 the tracer patches were sampled in a lagrangian manner using observations from discrete ctd rosette casts continuous surface ocean and atmospheric monitoring and autonomous drifting instruments to study the evolution of chemical and biological properties over the course of the experiment co2 and dms fluxes were directly measured in the marine air boundary layer with micrometeorological techniques and physical chemical and biological processes controlling air sea fluxes were quantified with measurements in the upper ocean and marine air average wind speeds of 9 m s 1 to a maximum of 16 m s 1 were encountered during the tracer patch observations providing additional data to constrain wind speed gas exchange parameterizations in this paper we set the stage for the experiment by detailing the hydrographic observations during the site surveys and tracer patch occupations that form the underpinning of observations presented in the so gasex special section particular consideration is given to the mixed layer depth as this is a critical variable for estimates of fluxes and biogeochemical transformations based on mixed layer budgets

assembling and reactivating the proterozoic capricorn orogen lithotectonic elements orogenies and significance abstract the capricorn orogen was initiated during palaeoproterozoic suturing events that brought together the archaean yilgarn and pilbara cratons to form the west australian craton the orogen comprises palaeoproterozoic plutonic and medium to high grade metamorphic rocks of the gascoyne complex a series of palaeoproterozoic volcano sedimentary and sedimentary basins including the ashburton blair yerrida bryah padbury and earaheedy basins and the deformed margins of the pilbara and yilgarn cratons major pulses of deformation and metamorphism took place during the ca 2200 ma ophthalmian orogeny the 2000 1960 ma glenburgh orogeny the 1830 1780 ma capricorn orogeny and a more localized unnamed event at the end of the palaeoproterozoic 1670 1620 ma the orogen has been the site of repeated intracratonic reactivation with renewed basin formation magmatism and orogeny during the mesoproterozoic and the neoproterozoic the exhumed palaeoproterozoic components of the orogen are unconformably overlain by the intracratonic mesoproterozoic edmund and collier basins bangemall supergroup which have been deformed during the neoproterozoic edmundian orogeny the ophthalmian and glenburgh orogenies affected the northern and southern margins of the orogen respectively the former resulted in the development of a foreland basin along the pilbara craton margin whereas the latter is associated with accretion of an allochthonous element the glenburgh terrane of the gascoyne complex to the northwestern margin of the yilgarn craton effects of the capricorn orogeny extended across the entire orogen and provide a younger limit for amalgamation of the yilgarn and pilbara cratons a number of basins developed along both the northern and southern margin of the orogen during this event and were filled with sediment eroded from the yilgarn craton the gascoyne complex and a presently unexposed early palaeoproterozoic terrane the capricorn orogeny corresponds with a major phase of continental collision both in australia and world wide which appears to mark a major phase of supercontinent assembly mineralization within the orogen includes a wide variety of deposit types that can be related to collisional settings including the world class iron orebodies of the hamersley basin

instruments for particle size and settling velocity observations in sediment transport in this paper we describe two sensors for measurement of particle size distribution and settling velocity distribution these measurements are critical to the correct estimation of the true sediment concentration in the field as well as to evaluating models for transport rates of sediments a multi angle measurement of laser scattering is made and inverted to obtain the particle size distribution since small angle scattering is relatively insensitive to particle composition the size distribution measurements are robust and do not require particle refractive index it is shown that with a knowledge of the size distribution true particulate volume concentration can be obtained unaffected in calibration by changes in particle size distribution the data from bottom boundary layer experiments using the instrument show the presence of temporal variability in size distribution associated with the strength of forcing of the boundary layer the importance of these observations lies in the implication that historical data acquired with single parameter optical or other sensors needs to be revisited in the second instrument analyzing the observation of size distributions during settling in a settling column produces settling velocity estimates in this case the history of concentration of each size class is examined to determine the settling velocity without invoking any assumptions of settling regime settling velocity data from a field experiment off the new jersey coast fit the model wf na 0 45 10 23 a 1 2 n

time domain electromagnetic soundings at the nevada test site nevada structural discontinuities and variations in the resistivity of near surface rocks often seriously distort dc resistivity and frequency domain electromagnetic fdem depth sounding curves reliable interpretation of such curves using one dimensional 1 d models is difficult or impossible short offset time domain electromagnetic tdem sounding methods offer a number of advantages over other common geoelectrical sounding methods when working in laterally heterogeneous areas in order to test the tdem method in a geologically complex region measurements were made on the east flank of yucca mountain at the nevada test site nts coincident offset coincident single and central loop configurations with square transmitting loops either 305 or 152 m on a side were used measured transient voltages were transformed into apparent resistivity values and then inverted in terms of 1 d models good fits to all of the offset coincident and single loop data were obtained using three layer models in most of the area two well defined interfaces were mapped one which corresponds closely to a contact between stratigraphic units at a depth of about 400 m and another which corresponds to a transition from relatively unaltered to altered volcanic rocks at a depth of about 1000 m in comparison with the results of a dipole dipole resistivity survey more the results of the tdem survey emphasize changes in the geoelectrical section with depth nonetheless discontinuities in the layering mapped with the tdem method delineated major faults or fault zones along the survey traverse 5 refs 10 figs 1 tab less

upper ocean inertial currents forced by a strong storm part i data and comparisons with linear theory abstract a strong isolated october storm generated 0 35 0 7 m s 1 inertia frequency currents in the 40 m deep mixed layer of a 300 km 300 km region of the northeast pacific ocean the authors describe the evolution of these currents and the background flow in which they evolve for nearly a month following the storm instruments included ctd profilers 36 surface drifters an array of 7 moorings and air deployed velocity profilers the authors then test whether the theory of linear internal waves propagating in a homogeneous ocean can explain the observed evolution of the inertial frequency currents the subinertial frequency flow is weak with typical currents of 5 cm s 1 and steady over the period of interest the storm generates inertial frequency currents in and somewhat below the mixed layer with a horizontal scale much larger than the rossby radius of deformation reflecting the large scale and rapid translation speed of the storm this scale is too large for significant linear propagation of the

interpretation of long offset transient electromagnetic data from the odenwald area germany using two dimensional modelling summary the standard 1 d inversion approach for the interpretation of transient electromagnetic tem data usually fails in the presence of near surface conductivity anomalies since multidimensional inversion codes are not routinely available the only alternative to discarding the data may be trial and error forward modelling we interpret data from a long ovset transient electromagnetic lotem survey which was carried out in 1995 in the odenwald area using 2 d finite diverence modelling we focus on a subsegment of the lotem profile which was shot with two diverent electric dipole transmitters a model is found which consistently explains the electric and magnetic field data at eight locations for both transmitters first we introduce a conductive dyke under the receiver spread to explain sign reversals in the magnetic field transients a conductive slab under one of the transmitters is required to obtain a reasonable quantitative fit for that transmitter consideration of the electric field data then requires a modification of the layered earth background finally we study the response of a crustal conductor which was the original target of the survey the data are sensitive to the conductor and for the investigated subset of the data the fits are slightly better without the conductive layer

a review of crust upper mantle structure in the precambrian areas of australia and implications for precambrian crustal evolution the western two thirds of the australian continent are underlain by precambrian rocks seismically this region is characterised by negative teleseismic travel time residuals indicating a thick cold tectosphere despite extensive platform cover and phanerozoic crustal reworking in a few intracratonic sedimentary basins the precambrian crust can be classified broadly into archaean and proterozoic cratons and proterozoic mobile belts the archaean cratons have a two layered crust 25 35 km thick with observed velocities in the lowermost crust in the range 6 8 7 2 km s 1 the moho is a distinct feature with a velocity contrast of 1 0 km s 1 vertical reflection probes in the southern yilgarn block yielded record sections that have numerous laterally discontinuous but distinct reflections especially in the lower crustal layer that are especially concentrated around the boundary between the two crustal layers and the moho the seismic reflections and velocities are consistent with a predominantly felsic crust with mafic lenses constituting 20 35 of the lowermost crust and with the metamorphic grade ranging from granulite in the upper to middle crust to garnet granulite and even eclogite at the base of the crust the proterozoic mobile belts and cratons a have multi layered crust 45 50 km thick velocities below 25 km depth are almost always 7 0 km s 1 and reach 7 4 7 6 km s 1 in the lowermost crust velocities such as these are characteristic of gabbroic basaltic underplate the velocity contrast is 1 0 km s 1 at the moho which is less distinct than in archaean terranes record sections from vertical reflection probes show a highly reflective crust with no correlation between seismic layers in the refraction models and the distribution of vertical reflections the contrasting character of the crust in archaean and proterozoic provinces favours a tectonic model for the evolution of precambrian crust in which predominantly felsic archaean protocrust was tectonically reworked and underplated to produce proterozoic crust the simple two layered protocrust became more complicated in the process the introduction of vast amounts of underplate especially near the crust mantle boundary thickened the crust and destroyed the character of the moho it overprinted the reflection character of the crust so that the bands of reflections now do not correlate with the boundaries between the crustal layers the velocities in the lower crust are high because of the underplate

dynamical processes of transfer at the sea surface abstract this review describes the dynamical processes of transport from and immediately below the sea surface particularly those which involve convergence and the separation of flow and which result in the renewal of surface water at horizontal scales ranging from millimeters to hundreds of meters turbulence at or near the sea surface derives from several processes breaking waves and the bubbles they may produce precipitation and spray langmuir circulation and thermal convection and turbulence which is internally generated by shear interest in the subject derives from the requirements to predict air sea fluxes of heat momentum and gases to develop climate models to interpret satellite images of the sea surface including those of ship wakes and to predict upper ocean structure including mixing layer depth in models of phytoplankton blooms and acoustic propagation the general effect of subsurface turbulence on the sea surface and the effects of surfactants is described and each process is discussed in turn laboratory experiments and theoretical studies have contributed particularly to the understanding of the interaction of vortices and turbulence with the surface and to the consequences of breaking waves they point to the development of instability in the flow ahead of steep waves carrying parasitic capillary waves which may contribute to the onset of flow separation on the leading face of the waves and the development of a rotor or roller below the wave crest shown most clearly in the pattern of streamlines in a frame of reference moving forward with the wave the conditions near the flow separation line on the wave surface ahead of the rotor may be similar to those produced by vortices approaching a free surface detailed observation of breaking waves at sea is lacking but some progress has been made using acoustics to detect the clouds of subsurface bubbles formed by the larger breakers and the depth to which they penetrate the possible importance of three dimensional effects in breaking waves is discussed and a conjectural sketch of the surface flow field and the surface separation and reattachment pattern following a plunging breaker is described recent observations show elevated levels of turbulence close to the sea surface the depth of the layer in which this occurs is shown to be consistent with information derived from sonar studies of the depth of bubble clouds the observed frequency of breaking waves and laboratory observations of breaking waves rain is known to knock down the sea reducing the frequency and intensity of breaking waves the precise mechanics of the phenomena are uncertain but an enhancement of near surface turbulence and the damping of short surface gravity waves has been observed in laboratory experiments langmuir circulation temperature ramps and convection all associated with coherent structures are processes which mix the upper ocean although their relative importance is unknown connections between studies with quite disparate motivations are found to help provide descriptions of the upper ocean processes and estimates of the time scale of surface renewal associated with each of the processes identified many quantities being transferred across the sea surface appear to be transported by dynamical processes of scale much smaller than that of the dominant surface waves although their subsequent diffusion in the mixing layer may be strongly influenced by the larger scale processes further careful measurements in the laboratory and at sea are required to quantify the fluxes associated with the processes and to relate them to external parameters such as wind speed

the skewness of temperature derivatives in oceanic boundary layers abstract the skewness of the derivative of temperature measured by sensors in the upper ocean boundary layer in convective conditions has been measured and is observed to have a sign opposite to that found in conditions of stable heating this is consistent with observations in the atmospheric boundary layer high resolution measurements in the benthic boundary layer on a continental rise show a variation of skewness during the m2 tidal cycle which dominates the motion with negative skewness consistent with conditions favoring convection occurring during the upslope phase of the motion the observations are compared with laboratory studies of the reflection of internal waves from a slope we suggest that information about the gross features of a turbulent oceanic boundary layer flow may be derived from relatively simple measurements

similarity structure in the convective boundary layer of a lake natural convection influences a variety of geophysical phenomena including daily mixing cycles in the atmosphere and in surface waters the seasonal overturn of lakes and global climate variability conceptual models of convection in water are primitive and based on very limited data particularly at small dissipative scales here i present an analysis of microscale data from the convective boundary layer of a lake indicating a complex depth dependence in the rate at which temperature fluctuations are dissipated suitably scaled this vertical structure is remarkably similar to that found in the atmospheric convective boundary layer1 2 stirred by rising thermals of buoyant air heated at the earth s surface this comparison consistent with recent documentation of similarity in the more uniform vertical structure of energy dissipation3 5 suggests another unifying link in the structure and dynamics of convection in boundary layers of lakes oceans and the atmosphere6

the contribution of coccolithophores to the optical and inorganic carbon budgets during the southern ocean gas exchange experiment new evidence in support of the great calcite belt hypothesis 1 we describe optical observations from the southern ocean so gas exchange experiment gasex during march 2008 designed to test the hypothesis that enhanced reflectance of the southern ocean waters was related to a high abundance of coccolithophorids we present multiple lines of evidence in support of this hypothesis 1 birefringence microscopy 2 along track measurements of acid labile backscattering 3 analytical measurements of particulate inorganic carbon pic and 4 above water radiometry measurements made from both ship and satellite at the so gasex study site 51 s 38 5 w coccolithophores and coccoliths were abundant 300 cells ml 1 and 20 000 coccoliths ml 1 and concentrations were stable over time scales of weeks enhanced concentrations of pic were observed between the subtropical front stf and the northern part of the subantarctic front saf and between the saf region and polar front biogenic silica was elevated with the highest concentrations south of the stf these results along with other recent microscope observations of coccolithophores made by other workers around the southern ocean suggest that the region of enhanced reflectance is at least partially due to coccolithophores however the pic estimated from above water reflectance measurements was 2 3x the pic actually measured in the water one possible reason for this is the presence of other sources of scattering such as microbubbles at least during stormy conditions these observations are consistent with the hypothesis that this region of elevated reflectance and pic is part of a significantly larger region which encircles the entire southern ocean each austral summer a band that we call the great calcite belt

upper ocean state estimation in the southern ocean gas exchange experiment region using the four dimensional variational technique 1 a prototypical ocean circulation model and associated 4 d variational data assimilation system is configured in support of the southern ocean gas exchange experiment southern ocean gasex the regional circulation model has 4 km horizontal resolution and 5 m vertical resolution in the upper ocean in situ temperature and salinity observations and remotely sensed gridded sea surface temperature and sea surface height observations are combined with the circulation model between 6 march and 4 april 2008 the benefits of customized data assimilation in support of a single oceanographic cruise are illustrated using southern ocean gasex as a case study the assimilated fields fit the observations within their respective uncertainties and fit 4 6 times better than the initial guess solution before assimilation the fit of the assimilated fields is up to 100 times closer to observations than various global state estimate products using a cost function variance metric the space time variability in mixed layer depth is consistent with the southern ocean gasex observations and shows a deepening through march 2008 this variability is correlated with sea level height anomalies sea surface temperature and air temperature during the assimilation window the mixed layer depth estimate between 21 march and 4 april 2008 at the location of the southern ocean gasex deliberate tracer release is 41 54 6 m the average zonal volume flux estimate is 16 1 9 sv 1 sv is 106 m3 s 1 for latitudes 50 7 s 51 8 s longitude 38 5 w the zonal volume flux approximately halves during 6 16 march temporal changes in volume flux are associated with geostrophic circulation but not with the ekman circulation

sharp spatially constrained inversion with applications to transient electromagnetic data time domain electromagnetic data are conveniently inverted by using smoothly varying 1d models with fixed vertical discretization the vertical smoothness of the obtained models stems from the application of occam type regularization constraints which are meant to address the ill posedness of the problem an important side effect of such regularization however is that horizontal layer boundaries can no longer be accurately reproduced as the model is required to be smooth this issue can be overcome by inverting for fewer layers with variable thicknesses nevertheless to decide on a particular and constant number of layers for the parameterization of a large survey inversion can be equally problematic here we present a focusing regularization technique to obtain the best of both methodologies the new focusing approach allows for accurate reconstruction of resistivity distributions using a fixed vertical discretization while preserving the capability to reproduce horizontal boundaries the formulation is flexible and can be coupled with traditional lateral spatial smoothness constraints in order to resolve interfaces in stratified soils with no additional hypothesis about the number of layers the method relies on minimizing the number of layers of non vanishing resistivity gradient instead of minimizing the norm of the model variation itself this approach ensures that the results are consistent with the measured data while favouring at the same time the retrieval of horizontal abrupt changes in addition the focusing regularization can also be applied in the horizontal direction in order to promote the reconstruction of lateral boundaries such as faults we present the theoretical framework of our regularization methodology and illustrate its capabilities by means of both synthetic and field data sets we further demonstrate how the concept has been integrated in our existing spatially constrained inversion formalism and show its application to large scale time domain electromagnetic data inversions

lithospheric structure of the arabian shield from the joint inversion of receiver functions and surface wave group velocities abstract we estimate lithospheric velocity structure for the arabian shield by jointly modeling receiver functions and fundamental mode group velocities from events recorded by the 1995 1997 saudi arabian portable broadband deployment receiver functions are primarily sensitive to shear wave velocity contrasts and vertical travel times and surface wave dispersion measurements are sensitive to vertical shear wave velocity averages so that their combination bridge resolution gaps associated with each individual data set our resulting models correlate well with the observed surface geology the asir terrane to the west consists of a 10 km thick upper crust of 3 3 km s overlying a lower crust of 3 7 3 8 km s in the afif terrane to the east the upper crust is 20 km thick and has an average velocity of 3 6 km s and the lower crust is about 3 8 km s separating the terranes the nabitah mobile belt is made of a gradational upper crust up to 3 6 km s at 15 km overlying an also gradational lower crust up to 4 0 km s the crust mantle transition is found to be sharp in terranes of continental affinity east and gradual in terranes of oceanic affinity west the upper mantle shear velocities range from 4 3 to 4 6 km s temperatures around 1000 c are obtained from our velocity models for a thin upper mantle lid observed beneath station taif and suggest that the lithosphere could be as thin as 50 60 km under this station

organized structures in subsurface bubble clouds langmuir circulation in the open ocean observations of the movement and distribution of subsurface bubbles reveal the structure of coherent motions near the ocean surface the measurements were obtained in the open ocean from a freely drifting self contained acoustical instrument equipped with side scan sonar dual frequency echo sounders and ambient sound recording systems the bubble clouds are organized into long narrow plumes aligned with the wind consistent with windrows caused by langmuir circulations they have widths of about 3 to 5 m and lengths up to 100 m with multiple scales coexisting their mean separation depends upon wind speed below 5 m s 1 mean spacings were about 5 m increasing to 10 m when winds exceeded 10 m s 1 the maximum depth to which the plumes were observed to penetrate depended to some extent on wind speed with the greatest penetrations of 12 m occurring at the highest wind speeds 13 m s 1 however the time averaged depth of observed bubble plume penetration bears only a weak dependence on wind speed whenever winds exceeded 5 m s 1 a mean penetration depth of 6 m was observed associated with these bubble plumes were maximum downward velocities of about 0 06 m s 1 these speeds were detected at 8 m depth in the center of the plumes magnitudes decreased to zero near the surface and horizontally toward the boundaries of the plumes

breaks in lithology interpretation problems when handling 2d structures with a 1d approximation most airborne electromagnetic aem data are processed using successive 1d approximations to produce stitched conductivity depthsections becausethecurrentinducedinthenearsurface by an aem system preferentially circulates at some radial distancefromahorizontallooptransmittersometimescalledthe footprint the section plotted directly below a concentric transmitter receiver system actually arises from currents induced in the vicinity rather than directly underneath detection of paleochannels as conduits for groundwater flow is a common geo

aeration due to breaking waves part i bubble populations abstract the population of bubbles produced by breaking waves in 10 m winds of up to 12 m s 1 is analyzed using calibrated images from a vertical pencil beam sonar system placed on the seabed near the dutch coast the structure in the images is parameterized and the volumetric bubble backscatter is inverted to yield bubble concentrations data were obtained at three acoustic frequencies with inversion effected by prescribing a bubble spectrum with two free variables leaving a redundant measurement to test the robustness of the model median concentrations may in this way be obtained up to the sea surface measurements are multiply regressed on wind and dominant wave variables bubbles penetrate to a depth of about a factor of 6 1 times the significant wave height hs where is the wave age or ratio of dominant wave phase speed to wind speed the measured mean bubble radius decreases weakly with depth unless waves are gently sloping at about 5 m 1 at 0 4 m the mean radius ranges from 30 to 80

how well does wind speed predict air sea gas transfer in the sea ice zone a synthesis of radon deficit profiles in the upper water column of the arctic ocean we present 34 profiles of radon deficit from the ice ocean boundary layer of the beaufort sea including these 34 there are presently 58 published radon deficit estimates of k the air sea gas transfer velocity in the arctic ocean 52 of these estimates were derived from water covered by 10 sea ice or more the average value of k collected since 2011 is 4 0 1 2 m d 1 this exceeds the quadratic wind speed prediction of weighted kws 2 85 m d 1 with mean weighted wind speed of 6 4 m s 1 we show how ice cover changes the mixed layer radon budget and yields an effective gas transfer velocity we use these 58 estimates to statistically evaluate the suitability of a wind speed parameterization for k when the ocean surface is ice covered whereas the six profiles taken from the open ocean indicate a statistically good fit to wind speed parameterizations the same parameterizations could not reproduce k from the sea ice zone we conclude that techniques for estimating k in the open ocean cannot be similarly applied to determine k in the presence of sea ice the magnitude of k through gaps in the ice may reach high values as ice cover increases possibly as a result of focused turbulence dissipation at openings in the free surface these 58 profiles are presently the most complete set of estimates of k across seasons and variable ice cover as dissolved tracer budgets they reflect air sea gas exchange with no impact from air ice gas exchange

near surface measurements of quasi lagrangian velocities in open water abstract near surface water velocities have been measured in the coastal zone of lake huron and cape cod bay by tracking drifters and drogues using acoustic travel time and compass sighting techniques the near surface current defined as the velocity of near surface drifters and drogues relative to a drogue set at 1 8 m varied on the depth scale on the order of 1 m and was directed nearly parallel to the wind and to predominant wave propagation velocity velocity profiles were logarithmic with depth to order 1 m depth and realistic values of stress were calculated using a law of the wall formula and a karman s constant of 0 4 inferred roughness lengths were of the order of 30 cm anomalously high values of wind stress were inferred from velocity profiles observed during conditions of light wind and steady swell these may be due to the similarity of stokes drift distribution to turbulent shear flow profiles

the effect of langmuir circulation on the distribution of submerged bubbles caused by breaking wind waves clouds of bubbles are generated at the sea surface by breaking wind waves or by heavy rain rows of subsurface bubble clouds have been detected by a bottom mounted side scan sonar and are possibly formed by the effects of langmuir circulation a simple equation is devised to describe the effects of the turbulent diffusion of bubbles from the free surface bubble rise and dissolution and advection by langmuir circulation the equation is solved analytically using a series expansion in which advection is supposed small in comparison with diffusion the solution provides a quantitative measure of the principal effects produced by the circulation in particular the distortion of the bubble field and estimates of the advective flux a random walk numerical model in which changes occurring in individual bubbles are followed is tested against the analytical model in the range for which the latter is valid there is good agreement the numerical model is useful in extending the solutions to more complex cases which include a broad distribution of bubble sizes and to ranges in which the analytic solution is invalid the model is used to quantify the effect of the circulation on the acoustic scattering cross section of the bubble clouds and to explore differences between the conclusions of earlier models and observations by johnson cooke 1979 in the appendices an estimate is made of the depth to which bubbles can be carried by the vertical velocities observed below wind rows and this is found to agree reasonably well with the maximum depth to which bubbles are observed to penetrate estimates of mean vertical diffusion coefficients based on observations of bubbles are compared with some calculated solely from the advective flux in langmuir circulation the latter are as expected smaller than those representing the sum of all the contributions to the flux but are a significant fraction of the order of 0 2 0 4 a method of deriving the vertical diffusion coefficient from observations of the vertical distribution of the acoustic scattering cross section of bubbles appears not to be very sensitive to circulation and may provide estimates within about 25 of the actual values

turbulence in an oceanic convective mixed layer the first direct measurements of turbulence in an oceanic convective mixed layer were obtained during a cold air outbreak the uniformity of the turbulent dissipation rate and its relation to the surface buoyancy flux are similar to observations of convection in the atmosphere

surface wave array tomography in se tibet from ambient seismic noise and two station analysis i phase velocity maps summary empirical green s functions egfs between pairs of seismographs can be estimated from the time derivative of the long time cross correlation of ambient seismic noise these egfs reveal velocity dispersion at relatively short periods which can be used to resolve structures in the crust and uppermost mantle better than with traditional surface wave tomography we combine rayleigh wave dispersion estimates from egfs and from traditional two station ts analysis into a new approach to surface wave array tomography with data from dense receiver arrays we illustrate the methodology with continuous broad band recordings from a temporary seismographic network on the southeastern part of the tibetan plateau in sichuan and yunnan provinces sw china the egfs are robust under temporal changes in regional seismicity and the use of either ambient noise approximated by records without signal from events with magnitude mb 5 or 4 or surface wave coda produces similar results the egfs do not strongly depend on the presence of large earthquakes but they are not reciprocal for stations aligned in the n s direction this directionality reflects the paucity of seismicity to the north of the array using a far field representation of the surface wave green s function and an image transformation technique we infer from the egfs the rayleigh wave phase velocity dispersion in the period band from 10 30 s a classical ts approach is used to determine rayleigh wave phase velocity dispersion between 20 120 s together they constrain phase velocity variations for t 10 120 s which can be used to study the structure from the crust to the upper mantle beneath se tibet short and intermediate period 10 80 s phase velocities are prominently low suggesting that the crust and upper mantle beneath se tibet is characterized by slow shear wave propagation

bubble clouds and temperature anomalies in the upper ocean the processes of mixing in the upper few metres of the ocean are poorly known and largely unqualified1 but are a vital element in ocean atmosphere interaction playing a key part in the transfer and dispersion of heat gases and nutrients here we report results from a towed instrument used to measure simultaneously water temperature and the sound scattered from bubble clouds produced by breaking waves dominant features in the records are correlated intense sound scattering or bubble clouds being associated with warmer water and large positive temperature gradients with the onset of increased scattering the observations provide a more complete picture of the structure and nature of bubble clouds and establish their assocition with dynamical processes of turbulent diffusion in the upper ocean boundary layer

on the influence of 3 d structures in the interpretation of transient electromagnetic sounding data the limitations of a standard 1 d inversion applied to multidimensional synthetic data are investigated simple correction procedures for interpreting field data distorted by 3 d structures are suggested two different transmitter receiver configurations of the transient electromagnetic tem sounding method are examined a central loop configuration for the near zone sometimes called short offset and a fixed transmitter moving receiver configuration for the far zone long offset the 3 d models are structural depressions and highs in both resistive and conductive basements the fixed transmitter grounded dipole in the long offset tem configuration is located at a distance significantly greater than both the size and depth of the structure in all cases 1 d interpretation of the central loop soundings recovers geoelectric parameters of the section with good reliability although fictitious layers may appear near vertical boundaries the 1 d interpretation of long offset soundings does not in most

measurements of air sea gas exchange at high wind speeds in the southern ocean implications for global parameterizations velocity is proposed which is consistent with previou s 3 he sf 6 dual tracer result sf rom the coastal and open ocean obtained at lower wind speeds this suggests that factors controlling air sea gas exchange in this region are similar to those in other parts of the world ocean and that the parameterization presented here should be applicable to the global ocean citation ho d t c s law m j smith p schlosser m harvey and p hill 2006 measurements of airsea gas exchange at high wind speeds in the southern ocean implications for global parameterizations geophys res lett 33 l16611 doi 10 1029 2006gl026817

seismic structure of the crust and uppermost mantle of the capricorn and paterson orogens and adjacent cratons western australia from passive seismic transects abstract the seismic structure of the proterozoic capricorn and paterson orogens and adjacent archaean yilgarn and pilbara cratons western australia is determined using a passive seismic approach we use recordings of distant earthquakes made along two transects of 3 component broadband stations the stations were deployed for approximately 1 year mid 2006 2007 during which time 70 earthquakes were recorded at each station with a suitable signal to noise ratio for receiver function analysis and hence the s wavespeed profiles of the crust and uppermost mantle beneath each recording station are determined we investigate the deep crustal constraints on terrane boundary locations the patterns of seismic discontinuities in the crust and the variations in the depth and character of the moho this broad scale information regarding the present day crustal architecture and hence the crustal evolution of western australia complements previous surface geological and other geophysical studies western australia is an exceptionally large well preserved region of ancient crust and hence this work also adds to the body of knowledge regarding proterozoic orogenic processes in general the new passive seismic work shows a region of double crust or upper mantle discontinuities beneath the glenburgh terrane adjacent to the northwest yilgarn craton the upper crust of the orogens is always layered whereas the cratons have a simple upper crust both the capricorn and paterson orogens are characterised by deeper moho discontinuities with a lesser wavespeed contrast than the very sharp discontinuity observed beneath the adjacent pilbara and yilgarn cratons this is consistent with the weaker orogenic crust of the capricorn and paterson orogens accommodating most of the horizontal deformation during assembly and reworking of the west australian craton while the pilbara and yilgarn cratons acted as rigid crustal blocks

bubble clouds and the dynamics of the upper ocean this is a review of turbulence in the upper ocean close to the sea surface particularly of the information that has been obtained from sonar observations of bubble clouds produced by breaking wind waves these clouds provide tracers of the turbulent motions and are important especially at high wind speeds in the process of air sea gas transfer the observations of bubble clouds are here related to other measurements of turbulence particularly to direct measurements of currents and temperatures in lakes or at sea and to laboratory studies some novel observations of bubble clouds and breaking waves their frequency and relation to langmuir circulation are presented there is now emerging a pattern of clues that point to the dominance of breaking surface gravity waves as a source of turbulence to a depth below the surface of 0 04 to 0 2 times the wavelength of the dominant breaking waves although the effect of swell has yet to be clarified the relative depth appears to increase with increasing values of w 1 c where w10 is the wind speed and c the phase speed of the dominant waves below this region the generation of turbulence may be dominated by shear stress or convection here turbulence is generally similar to that in the atmospheric boundary layer there are however coherent motions on the scale of the mixing layer that persist for periods of a few minutes to an hour or so to which the transport of a large part of the momentum and heat fluxes can be attributed and which strongly affect the dispersion of buoyant particles or bubbles these motions deserve special study to establish their contribution to heat and momentum transport and hence to determine if or when they should be specifically represented in models of the upper ocean devised for example to describe the dispersion of passive and non passive tracers or the air sea transfer of gases

hydrogeophysical exploration of three dimensional salinity anomalies with the time domain electromagnetic method tdem summary the time domain electromagnetic method tdem is widely used in groundwater exploration and geological mapping applications tdem measures subsurface electrical conductivity which is strongly correlated with groundwater salinity tdem offers a cheap and non invasive option for mapping saltwater intrusion and groundwater salinization traditionally tdem data is interpreted using one dimensional layered earth models of the subsurface however most saltwater intrusion and groundwater salinization phenomena are characterized by three dimensional anomalies to fully exploit the information content of tdem data in this context three dimensional modeling of the tdem response is required we present a finite element solution for three dimensional forward modeling of tdem responses from arbitrary subsurface electrical conductivity distributions the solution is benchmarked against standard layered earth models and previously published three dimensional forward tdem modeling results concentration outputs from a groundwater flow and salinity transport model are converted to subsurface electrical conductivity using standard petrophysical relationships tdem responses over the resulting subsurface electrical conductivity distribution are generated using the three dimensional tdem forward model the parameters of the hydrodynamic model are constrained by matching observed and simulated tdem responses as an application example a field dataset of ground based tdem data from an island in the okavango delta is presented evaporative salt enrichment causes a strong salinity anomaly under the island we show that the tdem field data cannot be interpreted in terms of standard one dimensional layered earth tdem models because of the strongly three dimensional nature of the salinity anomaly three dimensional interpretation of the field data allows for detailed and consistent mapping of this anomaly and makes better use of the information contained in the tdem field dataset

the northern margin of the capricorn orogen western australia an example of an early proterozoic collision zone abstract the early proterozoic 2200 1600 ma capricorn orogen is a major zone of deformation metamorphism and granite emplacement between the archaean yilgarn and pilbara cratons of northwest australia capricorn orogen structures are recognized along the southern margin of the pilbara craton deforming the archaean granite greenstone terrain of the sylvania inlier together with rocks of the hamersley ashburton and blair basins in the sylvania inlier deformation is characterized by large scale shear zones interpreted as nne directed thrusts in the hamersley basin orogenic deformation forms the ophthalmia fold belt and can be divided into two groups of structures in the southwest large scale dome and basin folds pre ashburton basin are present in the southeast folds and faults are part of a younger syn ashburton basin n directed foreland fold and thrust belt directly linked to deformation in the sylvania inlier the deformed ashburton basin and adjacent parts of the hamersley basin form the ashburton fold belt two periods of deformation are recognized early recumbent folding d1a post ashburton basin pre blair basin and later dextral wrench faulting and associated folding d2a syn or post blair basin capricorn orogen structures are interpreted as the result of an oblique continent continent collision between the pilbara and yilgarn cratons along the southern pilbara margin collision first occurred in the southeast and migrated northwest with the ashburton basin evolving as a foreland basin late stage dextral wrench faulting was the result of westward extrusion of material caught between the opposing craton margins

upper crust of the pilbara craton australia 3d geometry of a granite greenstone terrain the pilbara craton in northwest australia is a 600 550 km region of early mid archaean granite greenstone terrain dominated by granite domes and in part covered by younger rocks gravity and magnetic anomalies are used to map the granite greenstone surface under cover and infer the depth extent of the granite greenstone structures a published seismic refraction interpretation gives a two layer crust for the pilbara craton with the layers separated by a velocity gradient at about 14 km some magnetic anomalies have a 1000 3600 nt amplitude a width at one half amplitude of 9 km and a strike length of 100 km their causative bodies have a top at 1 2 km an average apparent susceptibility of 0 1 0 2 si and importantly a base about 14 km the magnetic material is thought to be a small proportion of banded iron formation within the greenstone belts gravity anomalies are interpreted to indicate that granite margins are generally steep and many granites have a base at a similar level to one another the shape of the gravity anomalies over the granite greenstone boundaries and the amplitude of the anomalies up to 650 m s 2 together with the inferred granite greenstone density contrast are consistent with both the granites and greenstones extending to a depth of 14 km the domes are therefore vertical cylinders extending to mid crustal depths the great depth of the greenstone belts is consistent with the domal structure being due to convective crustal overturn the pilbara craton may be unusual because greenstone belts elsewhere in the world have smaller amplitude gravity anomalies commonly 200 400 m s 2 a shallower inferred base to the greenstone belt generally 8 km and the base of the greenstone belt is thought to be truncated

precambrian tectonic history of the west australian craton and adjacent orogens this review is a synthesis of the precambrian geology of the west aus tralian craton and its fringing orogens it describes the evidence that has recently been reinvestigated and reinterpreted to reveal a long dynamic history of repeated aggregation and dispersal of crustal fragments cratons are large composite geological units of continental crust that have survived intact for significant periods of geological time they are generally tabular bodies with great areal extent millions of square kilo meters and lithospheric thickness 200 400 km orogens are narrow steep zones of tectonic and metamorphic activity associated with the deposition of sediments and the intrusion of plutonic rocks they occur within or along the margins of continents and are generally a few hundred kilometers wide thousands of kilometers long and extend to the base of the litho sphere most orogens are initially associated with compressive tectonics crustal thickening and the transient formation of mountain belts cratons and orogens may survive for very long periods of time but as part of a thin crust on a dynamic mantle they are inherently mobile and travel as rafts for great distances around the surface of the earth they may be torn apart dispersed and reassembled with other continental fragments the boundaries of these crustal fragments once established remain zones of crustal weakness that may be reactivated as intra continental mobile belts or lines along which cratons are assembled and dismembered cf hoffman 1 988

grounded source transient e field modeling of a shallow resistive layer with 3 d inhomogeneity there is growing interest in the use of transient electromagnetic tem sounding for shallow geotechnical environmental and groundwater investigations two commonly used transmitterreceiver configurations for tem sounding are 1 loop loop or its variation in loop configuration and 2 wire loop configuration the less common configuration of a horizontal electric dipole hed transmitter and receiver is treated in this study and called wire wire configuration

breaking of wind generated waves abstract breaking of wind generated waves was studies in a laboratory tank the critical surface slope and global wave steepness for inception of breaking were evaluated besides the frequency of occurrence two other characteristic quantities height and duration of breaking were measured the frequency of breaking was found to increase rapidly with wind velocity following a power law u2 2 the period of breaking remained about 7 of the wave period at all wind velocities the height of breaking was about 30 of the wave height portions of these results compare favorably with other available measurements

topography boundary forces and the indo australian intraplate stress field the relative contribution of topographic e g ridge push continental margins and elevated continental crust and plate boundary e g subduction and collisional forces to the intraplate stress field in the indo australian plate iap is evaluated through a finite element analysis two important aspects of the iap intraplate stress field are highlighted in the present study 1 if substantial focusing of the ridge push torque occurs along the collisional boundaries i e himalaya new guinea and new zealand many of the first order features of the observed stress field can be explained without appealing to either subduction or basal drag forces and 2 it is possible to fit the observed shmax maximum horizontal stress orientation and stress regime information with a set of boundary conditions that results in low tectonic stress magnitudes e g tens of megapascals averaged over the thickness of the lithosphere throughout the plate this study therefore presents a plausible alternative to previous studies of the iap intraplate stress field which predicted very large tectonic stress magnitudes hundreds of megapascals in some parts of the plate in addition topographic forces due to continental margins and elevated continental material were found to play an important role in the predicted stress fields of continental india and australia and the inclusion of these forces in the modeling produced a significant improvement in the fit of the predicted intraplate stresses to the available observed stress information in these continental regions a central focus of this study is the relative importance of the boundary conditions used to represent forces acting along the northern plate margin we note that a wide range of boundary conditions can be configured to match the large portion of the observed intraplate stress field and this nonuniqueness continues to make modeling the iap stress field problematic while our study is an important step forward in understanding the sources of the iap intraplate stress field a more complete understanding awaits a better understanding of the relative magnitude of the boundary forces acting along the northern plate margin

wave follower field measurements of the wind input spectral function part iii parameterization of the wind input enhancement due to wave breaking abstract this is the third in a series of papers describing wave follower observations of the aerodynamic coupling between wind and waves on a large shallow lake during the australian shallow water experiment auswex it focuses on the long standing problem of the aerodynamic consequences of wave breaking on the wind wave coupling direct field measurements are reported of the influence of wave breaking on the wave induced pressure in the airflow over water waves and hence the energy flux to the waves the level of forcing measured by the ratio of wind speed to the speed of the dominant spectral peak waves covered the range of 3 7 the propagation speeds of the dominant waves were limited by the water depth and the waves were correspondingly steep these measurements allowed an assessment of the magnitude of any breaking induced enhancement operative for these field conditions and provided a basis for parameterizing the effect overall appreciable levels of wave breaking occurred for the strong win

optical measurements of small deeply penetrating bubble populations generated by breaking waves in the southern ocean bubble size distributions ranging from 0 5 to 125 m radius were measured optically during high winds of 13 m s 1 and large scale wave breaking as part of the southern ocean gas exchange experiment very small bubbles with radii less than 60 m were measured at 6 9 m depth using optical measurements of the near forward volume scattering function and critical scattering angle for bubbles 80 the bubble size distributions generally followed a power law distribution with mean slope values ranging from 3 6 to 4 6 the steeper slopes measured here were consistent with what would be expected near the base of the bubble plume bubbles likely stabilized with organic coatings were present for time periods on the order of 10 100 s at depths of 6 9 m here relatively young seas with an inverse wave age of approximately 0 88 and shorter characteristic wave scales produced lower bubble concentrations shallower bubble penetration depths and steep bubble size distribution slopes conversely older seas with an inverse wave age of 0 70 and longer characteristic wave scales produced relatively higher bubble concentrations penetrating to 15 m depth larger bubble sizes and shallower bubble size distribution slopes when extrapolated to 4 m depth using a previously published bubble size distribution our estimates suggest that the deeply penetrating small bubbles measured in the southern ocean supplied 36 of the total void fraction and likely contributed to the transfer and supersaturation of low solubility gases

interpretation of transient electromagnetic soundings over three dimensional structures for the central loop configuration summary an assessment is made of the bias of fitting constrained layeredearth models to transient electromagnetic data obtained over 3 d structures in this assessment we use the central loop configuration and show that accurate estimates of the depth of burial of 3 d structures can be obtained with layered earth model fitting however layered earth interpretations are not reliable for estimating depth extents and resistivities of 3 d structures when layered earths are used for interpretation it is advantageous in some cases to use data based on the magnetic field instead of the voltage a magnetic field definition of apparent resistivity in contrast to a definition based on the voltage eliminates apparent resistivity overshoots and undershoots in the data a resistivity undershoot in the data can produce an extraneous and misleading layer in an interpretation of a 3 d resistive structure due to 3 d effects apparent resistivity soundings magnetic field and voltage may rise so steeply at late times that it may not be possible to fit a sounding to a reasonable layered earth model truncating such a sounding over a buried conductor allows for a reasonable layered earth fit and an accurate estimate of the depth to the conductor however the resistivity of the conductor is overestimated measurements of the horizontal field in the central loop configuration can map 3 d structures provided the sensor is located accurately at the centre of the transmitting loop horizontal field calculations show that the transients peak on the flanks of a 3 d structure but are depressed over the structure s centre weak transient responses flanked by two large transient responses which are opposite in sign locate the structure the sign reversal is caused by a corresponding reversal in the currents that are channelled through or deflected away from conductive or resistive structures respectively