space geodetic observations of nazca south america convergence across the central andes space geodetic data recorded rates and directions of motion across the convergent boundary zone between the oceanic nazca and continental south american plates in peru and bolivia roughly half of the overall convergence about 30 to 40 millimeters per year accumulated on the locked plate interface and can be released in future earthquakes about 10 to 15 millimeters per year of crustal shortening occurred inland at the sub andean foreland fold and thrust belt indicating that the andes are continuing to build little 5 to 10 millimeters per year along trench motion of coastal forearc slivers was observed despite the oblique convergence

mapping ocean observations in a dynamical framework a 2004 06 ocean atlas abstract this paper exploits a new observational atlas for the near global ocean for the best observed 3 yr period from december 2003 through november 2006 the atlas consists of mapped observations and derived quantities together they form a full representation of the ocean state and its seasonal cycle the mapped observations are primarily altimeter data satellite sst and argo profiles gcm interpolation is used to synthesize these datasets and the resulting atlas is a fairly close fit to each one of them for observed quantities especially the atlas is a practical means to evaluate free running gcm simulations and to put field experiments into a broader context the atlas derived quantities include the middepth dynamic topography as well as ocean fluxes of heat and salt freshwater the atlas is publicly available online www ecco group org this paper provides insight into two oceanographic problems that are the subject of vigorous ongoing research first regarding ocean circulation estimates

confirmation of arabia plate slow motion by new gps data in yemen 1 during the last 10 years a network of about 30 gps sites was measured in djibouti east africa additional points were also measured in yemen oman ethiopia iran and on la reunion island merged with data from the available international gps service permanent stations scattered on the different plates in the area eurasia anatolia africa arabia somalia this unique data set provides new insight on the current deformation in the africa somalia arabia triple junction area and on the arabian plate motion here we show that coherent motions of points in yemen bahrain oman and iran allow us to estimate a geodetically constrained angular velocity for the arabian plate 52 59 n 15 74 w 0 461 myr in itrf2000 this result differs significantly from earlier determinations and is based upon our vectors in yemen they provide new additional data and better geometry for angular velocity determination combined with the african and somalian motions this new angular velocity results in predicted spreading rates in the red sea and the gulf of aden which are 15 20 lower than those measured from oceanic magnetic anomalies and thus averaged over the last 3 myr with respect to eurasia the geodetic motion of arabia is also about 30 slower than predicted by nuvel 1a on the basis of the kinematic results presented here and on other evidence for a similar slower geodetic rate of the indian plate we suggest that the whole collision zone between africa arabia india on one hand and eurasia on the other hand has slowed down in the last 3 myr

geochemistry of archean shales from the pilbara supergroup western australia archean clastic sedimentary rocks are well exposed in the pilbara block of western australia shales from turbidites in the gorge creek group ca 3 4 ae and shales from the whim creek group ca 2 7 ae have been examined the gorge creek group samples characterized by muscovite quartzchlorite mineralogy are enriched in incompatible elements k th u lree by factors of about two when compared to younger archean shales from the yilgarn block alkali and alkaline earth elements are depleted in a systematic fashion according to size when compared with an estimate of archean upper crust abundances this depletion is less notable in the whim creek group such a pattern indicates the source of these rocks underwent a rather severe episode of weathering the gorge creek group also has fairly high b content 85 29 ppm which may indicate normal marine conditions during deposition rare earth element ree patterns for the pilbara samples are characterized by light ree enrichment lanybn 7 5 and no or very slight eu depletion eueu 0 82 0 99 a source comprised of about 80 felsic igneous rocks without large negative eu anomalies felsic volcanics tonalites trondhjemites and 20 mafic ultramafic volcanics is indicated by the trace element data very high abundances of cr and ni cannot be explained by any reasonable provenance model and a secondary enrichment process is called for

on the effects of small scale variability on acoustic propagation in fram strait the tomography forward problem acoustic tomography systems have been deployed in fram strait over the past decade to complement existing observing systems there the observed acoustic arrival patterns are unusual however consisting of a single broad arrival pulse with no discernible repeating patterns or individual ray arrivals the nature of these arrivals is caused by vigorous acoustic scattering from the small scale processes that dominate ocean variability in fram strait simple models for internal wave and mesoscale variability were constructed and tailored to match the variability observed by moored thermisters in fram strait the internal wave contribution to variability is weak acoustic propagation through a simulated ocean consisting of a climatological sound speed plus mesoscale and internal wave scintillations obtains arrival patterns that match the characteristics of those observed i e pulse width and travel time variation the scintillations cause a proliferation of acoustic ray paths however reminiscent of ray chaos this understanding of the acoustic forward problem is prerequisite to designing an inverse scheme for estimating temperature from the observed travel times

wigwam reverberation revisited operation wigwam was a test of a 30 kt nuclear depth charge conducted in deep water 500 miles southwest of san diego on 14 may 1955 its primary purpose was to determine the effectiveness of that device as an antisubmarine weapon the acoustic pulse from the test initially an intense shockwave radiated throughout the north and south pacific oceans acoustic reflections from topographic features were recorded for several hours after the explosion by sound fixing and ranging sofar hydrophones at point sur california and kaneohe hawaii sheehy and halley 1957 identified peaks of the recorded coda with reflections from specific topographic features at great distances e g the hawaiian islands french polynesia or fiji with modern data for seafloor topography and ocean sound speed these coda were computed with surprising accuracy using simple geodesic rays reflected from islands and seamounts the intensity variations of the coda are mostly determined by simple ray geometry together with modest attenuation coda peaks are often obtained from rays arriving simultaneously from multiple but disparate topographic features online material figures of computed and measured coda and associated geodesic paths

geochemistry of banded iron formation of orissa india major and trace element analyses of representative samples of various types of banded iron formation and its various minerals associated sediments iron ores and volcanic tuff from different localities of orissa india are presented in this paper the orissa banded iron formation is classified as precambrian banded iron formation and is similar to the oxide facies iron formation of lake superior type the orissa iron formation consists only of iron oxide and silica with total absence of iron silicate sulfide and carbonate minerals and is devoid of terrigenous material the trace element content suggests the source of the underlying quartzite to be a continental igneous rock mass while the interbedded tuff are of undoubted volcanic origin the overlying iron formation were chemically precipitated as oxidate sediments in which the principal iron mineral magnetite was formed at low temperature in a shallow marine environment from the overwhelming similarity of major and trace element contents of all the samples from the different localities it is postulated that these detached outcrops originated in the same continous basin

constraints on present day shortening rate across the central eastern andes from gps data two years of continuous gps data from several sites in south america indicate that arequipa in the southern peruvian andes has a velocity of 13 3 mm yr two standard errors to the northeast with respect to stable south america we interpret these data as reflecting a combination of elastic strain accumulation associated with a locked nazca south america subduction zone and a small amount of crustal shortening across the fold and thrust belt on the eastern margin of the andes models of elastic strain accumulation for fully locked and partly locked subduction zones constrain shortening in the eastern andes to 0 3 mm yr fully locked and 0 12 mm yr partly locked slower than some geologic estimates averaged over millions of years

long range propagation of sound through oceanic mesoscale structures assumptions related to the feasibility of ocean acoustic tomography are investigated utilizing range dependent sound speed profiles the models include a warm midocean eddy and a cold core gulf stream ring superposed on a latitudinal geographic variation covering 1000 km the results show that changes in the acoustic travel times produced by mesoscale features can be nonlinear that the ray paths are substantially displaced by a mesoscale eddy and that information from a single source and receiver can be used to infer the distance to a mesoscale disturbance

alumina rich rocks from the early precambrian of the kaapvaal craton as indicators of paleosols and as products of other decompositional reactions within early archaean to early proterozoic pelites and volcanics of the kaapvaal craton rocks with above 20 al2o3 are widely distributed the alumina rich nature of these rocks is ascribed to decompositional reactions during which up to about 60 of the original material was leached out of the source rock and removed in solution many of these rocks also show diagenetic enrichment in k2o of up to 10 the decomposition reactions in many cases affected the source rocks without disturbing fine structures such as perlitic devitrification cracks in volcanic glass granules the origin of the majority of these rocks can be ascribed to decomposition during subaerial weathering they represent paleosols for other occurrences the stratigraphic context rules out an explanation as paleosols the origin of this type is ascribed to subaqueous decomposition of lavas or tuffs assisted by hydrothermal exhalations it is shown that alumina rich rocks in greenschist belts almost exclusively formed subaqueously whereas the younger occurrences mostly are of weathering origin geotectonic differences are invoked to explain this contrast rocks of similar chemical composition are described from the canadian shield zimbabwe western australia india and the baltic shield they illustrate that the preservation potential of these rocks is high only the study of the stratigraphic context will allow a conclusion on whether a particular occurrence is the product of weathering or subaqueous decomposition

turning point filters analysis of sound propagation on a gyre scale acoustic transmissions from pioneer seamount off california to a vertical array near hawaii are analyzed using a technique which we call a turning point filter the observables travel time and axial inclination are interpreted in terms of the ocean sound speed field the method permits a uniform treatment of the arrival pattern from the early ray like arrivals to the late mode like arrivals including peak arrivals which cannot be identified as either rays or modes an adiabatic range dependence is assumed and wentzel kramers brillouin jeffreys formalism is applied

three dimensional parabolic equation modeling of mesoscale eddy deflection the impact of mesoscale oceanography including ocean fronts and eddies on global scale low frequency acoustics is examined using a fully three dimensional parabolic equation model the narrowband acoustic signal for frequencies from 2 to 16 hz is simulated from a seismic event on the kerguellen plateau in the south indian ocean to an array of receivers south of ascension island in the south atlantic a distance of 9100 km the path was chosen for its relevance to seismic detections from the ha10 ascension island station of the international monitoring system for its lack of bathymetric interaction and for the dynamic oceanography encountered as the sound passes the cape of good hope the acoustic field was propagated through two years 1992 and 1993 of the eddy permitting ocean state estimation ecco2 estimating the circulation and climate of the ocean phase ii system the range of deflection of the back azimuth was 1 8 with a root mean square of 0 34 the refraction due to mesoscale oceanography could therefore have significant impacts upon localization of distant low frequency sources such as seismic or nuclear test events

uplift of the central andean plateau and bending of the bolivian orocline the topography of the central andes can be considered the primary tectonic signal of late cenozoic mountain building in an arid region where the effects of uplift and magmatism are little obscured by denudation the spatial coverage of the topographic signal is more complete than that for sparsely sampled geological and geophysical data a color coded image of digitized topography between 12 s and 37 s highlights the altiplano puna one of the world s most remarkable plateaus and reveals important physiographic clues about the formation of that major feature the topographic data combined with information on structure magmatism seismicity and paleomagnetism support a simple kinematical model for the late cenozoic evolution of the central andes the model does not require collisional effects or enormous volumes of intrusive additions to the crust but instead calls upon plausible amounts of crustal shortening and lithospheric thinning the model interrelates andean uplift a changing geometry of the subducted nazca plate and a changing outline in map view of the leading edge of the south american plate crustal shortening has accommodated convergence between the chilean peruvian forearc and the south american foreland the altiplano puna plateau can be constructed by a combination of crustal shortening and thickening and lithospheric thinning above a shallow dipping 20 30 subducted plate the seawardly concave bend of western south america the bolivian orocline was enhanced but not completely produced by an along strike variation in the amount of late cenozoic shortening maximum shortening in bolivia both produced the widest part of the plateau and increased the seaward concavity of the bolivian orocline the along strike variations of shortening are hypothesized to result from corresponding along strike variations in the width of a weakened zone in the overriding plate weakening occurs above the wedge of asthenosphere located between the subducted and overriding plates hence the width of the zone of weakening depends upon the dip of the subducted plate two types of shortening are recognized 1 a widespread basin and range laramide like shortening that characterizes modem activity in the sierras pampeanas and late miocene deformation of the altiplano puna and 2 on the eastern side of the cordilleras and plateau an east verging foreland fold thrust belt in which the underthrust foreland compresses and thickens the ductile lower crust and produces a plateau uplift of the upper crust the second type of shortening can be applied to plio quaternary deformations throughout the central andes but with a substantial narrowing of the region of plateau uplift in peru and south of 28 s a proposed monoclinal flexure of the upper crust on the western side of the plateau uplift explains the remarkably simple and regular morphology of the main western slope of the central andes the monocline is located above the tip of the asthenospheric wedge between the converging plates it is postulated to occur above the western limit of lower crustal thickening in the regions of horizontal subduction the monocline can be associated with a late miocene asthenospheric wedge tip

barotropic and baroclinic tides in the central north pacific ocean determined from long range reciprocal acoustic transmissions abstract travel times of reciprocal 1000 km range acoustic transmissions determined from the 1987 reciprocal tomography experiment are used to study barotropic tidal currents and a large scale coherent baroclinic tide in the central north pacific ocean the difference in reciprocal travel times determines the tidal currents while the sum of reciprocal travel times determines the baroclinic tide displacement of isotachs or equivalently isotherms the barotropic tidal current accounts for 90 of the observed differential travel time variance the measured harmonic constants of the eight major tidal constituents of the barotropic tide and the constants determined from current meter measurements agree well with the empirical numerical tidal models of schwiderski and cartwright et al the amplitudes and phases of the first mode baroclinic tide determined from sum travel times agree with those determined from moored thermistors and current meters the baroclinic tidal signals are consistent with a large

earthquake recurrence and magnitude and seismic deformation of the northwestern okhotsk plate northeast russia 1 recorded seismicity from the northwestern okhotsk plate northeast asia is currently insufficient to account for the predicted slip rates along its boundaries due to plate tectonics however the magnitude frequency relationship for earthquakes from the region suggests that larger earthquakes are possible in the future and that events of mw 7 5 which should occur every 100 350 years would account for almost all the slip of the plate along its boundaries due to eurasia north america convergence we use models for seismic slip distribution along the bounding faults of okhotsk to conclude that relatively little aseismic strain release is occurring and that larger future earthquakes are likely in the region our models broadly support the idea of a single okhotsk plate with the large majority of tectonic strain released along its boundaries

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

a comparison of measured and predicted broadband acoustic arrival patterns in travel time depth coordinates at 1000 km range broadband acoustic signals were transmitted from a moored 250 hz source to a 3 km long vertical line array of hydrophones 1000 km distant in the eastern north pacific ocean during july 1989 the sound speed field along the great circle path connecting the source and receiver was measured directly by nearly 300 expendable bathythermograph xbt conductivity temperature depth ctd and air launched expendable bathythermograph axbt casts while the transmissions were in progress this experiment is unique in combining a vertical receiving array that extends over much of the water column extensive concurrent environmental measurements and broadband signals designed to measure acoustic travel times with 1 ms precision the time mean travel times of the early raylike arrivals which are evident as wave fronts sweeping across the receiving array and the time mean of the times at which the acoustic reception ends the final cutoffs for hydrophones near the sound channel axis are consistent with ray predictions based on the direct measurements of temperature and salinity within measurement uncertainty the comparisons show that subinertial oceanic variability with horizontal wavelengths shorter than 50 km which is not resolved by the direct measurements significantly 25 ms peak to peak affects the time mean ray travel times the final cutoffs occur significantly later than predicted using ray theory for hydrophones more than 100 200 m off the sound channel axis nongeometric effects such as diffraction at caustics partially account for this observation

space geodetic estimation of the nazca south america euler vector abstract gps data from four sites in the nazca plate easter island galapagos robinson crusoe and san felix islands and from five sites in the stable core of the south american plate enabled us to estimate the euler vector of the nazca plate with respect to south america the observed velocities of easter island 6 6 cm yr at 102 3 galapagos 5 1 cm yr at 90 0 robinson crusoe 6 6 cm yr at 80 1 and san felix 6 0 cm yr at 82 1 are significantly slower than the global plate model nuvel 1a velocites for those four sites our estimated euler pole is located at 48 8 n 91 7 w with a rate of 0 59 m y the nuvel 1a and earlier space geodetic studies give rotation rates that are 20 faster

on equations for the speed of sound in seawater long range acoustic transmissions made in conjunction with extensive environmental measurements and accurate mooring position determinations have been used to test the accuracy of equations used to calculate sound speed from pressure temperature and salinity the sound speed field computed using the del grosso equation v a del grosso j acoust soc am 56 1084 1091 1974 give predictions of acoustic arrival patterns which agree significantly better with the long range measurements than those computed using the chen and millero equation c chen and f j millero j acoust soc am 62 1129 1135 1977 the predicted ray travel times and travel time error have been calculated using objectively mapped sound speed fields computed from ctd and xbt data using the measured and predicted ray travel times a negligible correction to del grosso s equation of 0 05 0 05 m s at 4000 m depth is calculated small errors of about 50 m in the gps determination of mooring positions lends a depth independent error of 0 1 m s to the sound speed equation correction work supported by nsf and onr

a theoretical and simulation study of acoustic normal mode coupling effects due to the barents sea polar front with applications to acoustic tomography and matched field processing normal mode coupling due to a shallow water coastal front is considered using oceanographic data from the 1992 barents sea polar front bspf experiment as input to normal mode and parabolic equation pe acoustic propagation models criteria for the sensitivity of mode coupling to coastal front widths are derived and applied to the bspf as a representative example the effects of coastal fronts on tomographic schemes are considered particularly in terms of travel time based tomography the effects of frontal mode coupling on matched field processing schemes are also considered using both the maximum likelihood and variable coefficient likelihood methods which show differing sensitivities to mismatch finally directions for future research are discussed

global positioning system measurements from eastern tibet and their implications for india eurasia intercontinental deformation we present and interpret global positioning system gps measurements of crustal motions for the period 1991 1998 for a network encompassing the eastern part of the tibetan plateau and its foreland relative to a eurasian frame defined by minimizing the velocities of 16 gps stations in europe central asia and siberia stations within all parts of the plateau foreland in south china move 6 10 mm yr east southeast indicating that the eastward movement within the plateau is part of a broader eastward movement that involves the plateau and its eastern and northern foreland north of the plateau foreland stations move northeastward at 10 mm yr indicating that the northern boundary of the deformation zone lies north of the plateau with this realization of a eurasian frame the velocity of the gps station at bangalore in southern india implies that the northward motion of india is 5 12 mm yr slower than that predicted from the nuvel 1a plate reconstruction viewed relative to the south china block stations of the northeast plateau bounded on the north by the qilian shan and the altyn tagh fault move nne to ne with velocities ranging from 19 mm yr within the plateau to 5 11 mm yr in its foreland the altyn tagh fault shows left lateral slip of 10 mm yr at 95 e and shortening across the fault of 5 mm yr stations south and west of the xianshuihe xiaojiang fault system define a crustal fragment rotating clockwise at 10 mm yr relative to the south china block around the eastern himalayan syntaxis the gps measurements indicate no significant shortening 3 mm yr within the longmen shan of the central eastern plateau and its adjacent foreland although the longmen shan rise over 6 km in 100 km horizontal distance geological studies indicate that the deformational field was established diachronously in late miocene to pliocene time was characterized by no east west shortening of tibetan crust and has an inhomogeneous style of deformation resulting from a balance of different tectonic processes

geochemical evolution of archean shales from south africa i the swaziland and pongola supergroups abstract the fig tree group and moodies group part of the swaziland supergroup are exposed in the barberton mountain land and are 3 3 3 5 ga old shales from the fig tree group are characterized by variable rare earth element ree patterns with lan ybn 5 5 1 8 95 confidence and eu eu 0 97 0 18 shales from the moodies group have more fractionated ree patterns lan ybn 8 7 2 0 and less variable eu anomalies eu eu 0 92 0 02 both groups are characterized by very high abundances of cr and ni modelling of those trace elements which are relatively unfractionated during sedimentary processes ree th sc is consistent with the derivation of these sedimentary rocks from a mixture of the archean bimodal igneous suite mafic volcanics tonalites trondhjemites felsic volcanics with the moodies group requiring a larger percentage of the felsic end member the data for shales from the swaziland supergroup support models suggesting that the archean exposed crust was of more mafic composition than the post archean upper crust and that intracrustal melting was relatively unimportant in differentiating the archean crust the pongola supergroup is younger than the swaziland supergroup but older than 2 9 ga shales and mudstones from the nsuze and mozaan groups show ree characteristics intermediate between the older shales of the swaziland supergroup and typical post archean shales one quartzite sample from the witwatersrand supergroup ca 2 6 ga has a ree pattern virtually parallel to average post archean shales but with much lower abundances the change from typical archean to post archean sedimentary trace element patterns has been documented in early proterozoic successions from canada and australia this change has been related to a short interval of intense growth and chemical differentiation of the continental crust during the late archean 2 7 2 5 ga in southern africa this change appears to have taken place much earlier 3 2 2 9 ga but can be related to similar processes thus the period of crustal evolution related to the archean proterozoic boundary while virtually episodic regionally occurred over a protracted period world wide during the period ca 3 2 2 5 ga

a decade of acoustic thermometry in the north pacific ocean 1 over the decade 1996 2006 acoustic sources located off central california 1996 1999 and north of kauai 1997 1999 2002 2006 transmitted to receivers distributed throughout the northeast and north central pacific the acoustic travel times are inherently spatially integrating which suppresses mesoscale variability and provides a precise measure of ray averaged temperature daily average travel times at 4 day intervals provide excellent temporal resolution of the large scale thermal field the interannual seasonal and shorter period variability is large with substantial changes sometimes occurring in only a few weeks linear trends estimated over the decade are small compared to the interannual variability and inconsistent from path to path with some acoustic paths warming slightly and others cooling slightly the measured travel times are compared with travel times derived from four independent estimates of the north pacific 1 climatology as represented by the world ocean atlas 2005 woa05 2 objective analysis of the upper ocean temperature field derived from satellite altimetry and in situ profiles 3 an analysis provided by the estimating the circulation and climate of the ocean project as implemented at the jet propulsion laboratory jpl ecco and 4 simulation results from a high resolution configuration of the parallel ocean program pop model the acoustic data show that woa05 is a better estimate of the time mean hydrography than either the jpl ecco or the pop estimates both of which proved incapable of reproducing the observed acoustic arrival patterns the comparisons of time series provide a stringent test of the large scale temperature variability in the models the differences are sometimes substantial indicating that acoustic thermometry data can provide significant additional constraints for numerical ocean models

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

horizontal refraction of acoustic signals retrieved from north pacific acoustic laboratory billboard array data in 1998 1999 a comprehensive low frequency long range sound propagation experiment was carried out by the north pacific acoustic laboratory npal in this paper the data recorded during the experiment by a billboard acoustic array were used to compute the horizontal refraction of the arriving acoustic signals using both ray and mode based approaches the results obtained by these two approaches are consistent the acoustic signals exhibited weak if any regular horizontal refraction throughut most of the experiment however it increased up to 0 4 deg the sound rays were bent towards the south at the beginning and the end of the experiment these increases occurred during midspring to midsummer time and seemed to reflect seasonal trends in the horizontal gradients of the sound speed the measured standard deviation of the horizontal refraction angles was about 0 37 deg which is close to an estimate of this standard deviation calculated using 3d modal theory of low frequency sound propagation throu

reappraisal of a 2200 ma old paleosol near waterval onder south africa abstract a fossil soil paleosol about 2200 ma old in a deep roadcut between the towns of waterval boven and waterval onder transvaal here called the waterval onder clay paleosol was formerly reported to have formed on the hekpoort basalt it is here thought to have developed on a thick formerly at least 5 5 m upward fining and thinning sequence of sandstone siltstone and shale derived from pre existing soils on hekpoort basalt within the basal portion of the fluvial dwaal heuvel formation in contrast to paleosols developed on hekpoort basalt the waterval onder clay paleosol is little deformed lacks corestones and shows compositional variation and berthierine rich laminae interpreted as relict bedding the paleosol has a ridge and swale topography linear or wavy gilgai and a subsurface structure mukkara typical of modern vertisols since there is considerable relict bedding it probably formed over a short period of time less than 7000 years and was not self plowing to the extent seen in modern vertisols clastic dikes filled with sandstone from the overlying rocks are evidence that the profile was periodically dry to depths of at least 2 m more drab colored rocks below that may represent the level of permanent water table iron and manganese stain of layers and claystone granules within the surface horizon of the profile have some characteristics of modern rock varnish and could be taken as evidence for life in the soil the high ratio of ferric to ferrous iron near the surface of the paleosol together with evidence from clastic dikes that this horizon was not waterlogged is an indication of an oxidizing atmosphere although probably one in which oxygen was much less abundant than it is today the very low amounts of acid titratable bases in the shaly parent material of this paleosol and surficial loss of these bases within the paleosol appear to have been produced by decarbonation reactions comparable to those found today in soils of vascular land plants a likely source of weathering acid during the precambrian is an elevated abundance of atmospheric carbon dioxide considering these likely atmospheric differences together with the distribution of comparable modern vertisols and other geological evidence the climate under which this soil formed was probably semiarid to subhumid seasonally dry and temperate

early archean silicate spherules of probable impact origin south africa and western australia layers of sand sized silicate spherules in 3 2 to 3 5 ga archean greenstone belts in south africa and western australia formed by the accumulation of quenched liquid silicate droplets having primary compositions resembling those of immediately underlying rock sequences the layers and particles appear to be unrelated to volcanic activity and we suggest that both occurrences may represent melt droplets formed during meteorite or comet impacts if so these spherules are the oldest known terrestrial impact products if these objects are representative of a larger population of early archean impact features it may be possible to directly estimate the meteorite flux on the early archean earth

global plate velocities from the global positioning system we have analyzed 204 days of global positioning system gps data from the global gps network spanning january 1991 through march 1996 on the basis of these gps coordinate solutions we have estimated velocities for 38 sites mostly located on the interiors of the africa antarctica australia eurasia nazca north america pacific and south america plates the uncertainties of the horizontal velocity components range from 1 2 to 5 0 mm yr with the exception of sites on the pacific and nazca plates the gps velocities agree with absolute plate model predictions within 95 confidence for most of the sites in north america antarctica and eurasia the agreement is better than 2 mm yr we find no persuasive evidence for significant vertical motions 3 standard deviations except at four sites three of these four were sites constrained to geodetic reference frame velocities the gps velocities were then used to estimate angular velocities for eight tectonic plates absolute angular velocities derived from the gps data agree with the no net rotation nnr nuvel 1a model within 95 confidence except for the pacific plate our pole of rotation for the pacific plate lies 11 5 west of the nnr nuvel 1a pole with an angular speed 10 faster our relative angular velocities agree with nuvel 1a except for some involving the pacific plate while our pacific north america angular velocity differs significantly from nuvel 1a our model and nuvel 1a predict very small differences in relative motion along the pacific north america plate boundary itself our pacific australia and pacific eurasia angular velocities are significantly faster than nuvel 1a predicting more rapid convergence at these two plate boundaries along the east pacific rise our pacific nazca angular velocity agrees in both rate and azimuth with nuvel 1a

deformation of convergent plates evidence from discrepancies between gps velocities and rigid plate motions 1 systematic discrepancies between the global positioning system gps site velocities and those predicted by plate motion models across the andes the himalayan tibetan plateau and the taiwan orogen delineate diffuse plate boundary deformation and significant intraplate deformation even in the presumably rigid oceanic plates the relationship between the gps velocities and the predictions of plate motion models is illustrated using a simple timescale dependent mechanical model of plate convergence a simple stiffness number based on the difference between the predictions of plate motion models and the gps velocity near plate boundaries provides a convenient measure of the plate like behavior of convergent plates and strain partitioning between intraplate and interplate deformation

the kauai near source test knst modeling and measurements of downslope propagation near the north pacific acoustics laboratory npal kauai source in april 2002 a series of recordings were taken near the north pacific acoustic laboratory npal kauai source this source transmits broadband low frequency signals to receivers in various locations across the pacific travel time calculations based upon the nonbottom interacting pe or ray trace modeling for the kauai source lagged the actual first arrival by 1 second or so a disturbing discrepancy that needed answering the kauai near source test knst was designed to take measurements near the kauai source to examine the effect of the local bathymetry on the signal transmitted into the ocean six receptions using a 100 m vla at ranges from 0 2 to 52 km were taken parabolic equation pe simulations of the channel impulse response for the measurement ranges are in good agreement with the observations pe simulations using an exposed basalt seafloor match the data much better than those with a silty sand cover a primary result of this test was the indication that there may be significant energy in the first bottom bounce comparable to the direct path purely refracted ray this implies that the seafloor near the source influences the arrival times and patterns of the field at long distances and should be taken into account

a test of basin scale acoustic thermometry using a large aperture vertical array at 3250 km range in the eastern north pacific ocean broadband acoustic signals were transmitted during november 1994 from a 75 hz source suspended near the depth of the sound channel axis to a 700 m long vertical receiving array approximately 3250 km distant in the eastern north pacific ocean the early part of the arrival pattern consists of raylike wave fronts that are resolvable identifiable and stable the later part of the arrival pattern does not contain identifiable raylike arrivals due to scattering from internal wave induced sound speed fluctuations the observed ray travel times differ from ray predictions based on the sound speed field constructed using nearly concurrent temperature and salinity measurements by more than a priori variability estimates suggesting that the equation used to compute sound speed requires refinement the range averaged ocean sound speed can be determined with an uncertainty of about 0 05 m s from the observed ray travel times together with the time at which the near axial acoustic reception ends used as a surroga

resonant diurnal internal tides in the north atlantic using a large acoustical array located midway between puerto rico and bermuda we have observed enhanced diurnal tidal signals associated with the lowest internal wave mode these signals result from a diurnal internal wave resonantly trapped between the shelf just north of puerto rico and the turning latitude a distance of about 1100 km the data obtained using the large acoustical array are consistent with the predicted airy function variation with latitude of diurnal internal waves near the turning latitude the existence of this wave is a striking demonstration of the long spatial and temporal coherence of oceanic internal tides in general the energy radiated by such waves is a loss of energy from the earth moon system and a source of energy for mixing in the deep ocean

acoustic tomography in the canary basin meddies and tides an acoustic propagation experiment over 308 km range conducted in the canary basin in 1997 1998 was used to assess the ability of ocean acoustic tomography to measure the flux of mediterranean water and meddies instruments on a mooring adjacent to the acoustic path measured the southwestward passage of a strong meddy in temperature salinity and current over nine months of transmissions the acoustic arrival pattern was an initial broad stochastic pulse varying in duration by 250 to 500 ms followed eight stable identified ray arrivals small scale sound speed fluctuations from mediterranean water parcels littered around the sound channel axis caused acoustic scattering internal waves contributed more modest acoustic scattering based on simulations the main effect of a meddy passing across the acoustic path is the formation of many early arriving near axis rays but these rays are thoroughly scattered by the small scale mediterranean water fluctuations a meddy decreases the deep turning ray travel times by 10 30 ms the dominant acoustic signature of a meddy is therefore the expansion of the width of the initial stochastic pulse while this signature appears inseparable from the other effects of mediterranean water in this region the acoustic time series indicates the steady passage of mediterranean water across the acoustic path tidal variations caused by the mode 1 internal tides were measured by the acoustic travel times the observed internal tides were partly predicted using a recent global model for such tides derived from satellite altimetry

the effect of bottom interaction on transmissions from the north pacific acoustic laboratory kauai source acoustic signals transmitted from a 75 hz broadband source near kauai as part of the north pacific acoustic laboratory npal experiment were recorded on an array of receivers near california at a range of 3890 km and on a vertical line array at a range of 3336 km in the gulf of alaska because the source is approximately 2 m above the seafloor and the bottom depth at the receivers near california is approximately 1800 m acoustic interaction with the bathymetry complicates the identification of the recorded arrivals with those present in numerical simulations of the experiment ray methods were used to categorize acoustic energy according to interactions with the sea bottom and surface and to examine the significance of seafloor geometry a modal decomposition was also used to examine the role of range dependent bathymetry and to associate the effects on the acoustic field with seafloor features at specific ranges parabolic equation simulations were performed in order to investigate the sensitivity of

three dimensional observations of a deep convective chimney in the greenland sea during winter 1988 89 abstract all available temperature data including moored thermistor hydrographic and tomographic measurements have been combined using least squares inverse methods to study the evolution of the three dimensional temperature field in the greenland sea during winter 1988 89 the data are adequate to resolve features with spatial scales of about 40 km and larger a chimney structure reaching depths in excess of 1000 m is observed to the southwest of the gyre center during march 1989 the chimney has a spatial scale of about 50 km near the limit of the spatial resolution of the data and a timescale of about 10 days the chimney structure breaks up and disappears in only 3 6 days a one dimensional vertical heat balance adequately describes changes in total heat content in the chimney region from autumn 1988 until the time of chimney breakup when horizontal advection becomes important a simple one dimensional mixed layer model is surprisingly successful in reproducing autumn to winter bulk temperatur

no net rotation model of current plate velocities incorporating plate motion model nuvel 1 we present nnr nuvel1 a model of plate velocities relative to the unique reference frame defined by requiring no net rotation of the lithosphere while constraining relative plate velocities to equal those in global plate motion model nuvel 1 demets et al 1990 differences between nnr nuvel1 and no net rotation plate motion model am0 2 minster and jordan 1978 are as large as 15 mm yr in nnr nuvel1 the pacific plate rotates in a right handed sense relative to the no net rotation reference frame at 0 67 m y about 63 s 107 e this rotation nearly parallels but is 32 slower than the pacific hotspot euler vector of hs2 nuvel1 which is a global model of plate hotspot velocities constrained to consistency with nuvel 1 gripp and gordon 1990 at hawaii the pacific plate moves relative to the no net rotation reference frame at 70 mm yr which is 25 mm yr slower than the pacific plate moves relative to the hotspots differences between nnr nuvel1 and hs2 nuvel1 are described completely by a right handed rotation of 0 33 m y about 49 s 65 e the 99 confidence ellipsoids for plate hotspot motion in model hs2 nuvel1 exclude the corresponding euler vectors from model nnr nuvell thus the no net rotation reference frame differs significantly from the hotspot reference frame if the difference between reference frames is caused by motion of the hotspots relative to a mean mantle reference frame then hotspots beneath the pacific plate move with coherent motion towards the east southeast alternatively the difference between reference frames may show that the uniform drag no net torque reference frame which is kinematically equivalent to the no net rotation reference frame is based on a dynamically incorrect premise possible exceptions to the assumption of uniform drag include a net torque on the lithosphere due to attached subducting slabs and greater resistance to plate motion beneath continents than beneath oceans

decelerating nazca south america and nazca pacific plate motions space geodetic estimates of the rate of nazca south america convergence and nazca pacific spreading averaging over several years show that present day rates are significantly slower than the 3 million year average nuvel 1a model the implied rates of deceleration are consistent with longer term trends extending back to at least 20 ma about the time of initiation of andes growth and may reflect consequences of ongoing subduction and construction of the andes e g increased friction and viscous drag on the subducted slab as the leading edge of south america thickens

assessing the horizontal refraction of ocean acoustic tomography signals using high resolution ocean state estimates the analysis of signals for acoustic tomography sent between a source and a receiver most often uses the unrefracted geodesic path an approximation that is justified from theoretical considerations relying on estimates of horizontal gradients of sound speed or on simple theoretical models to quantify the effects of horizontal refraction caused by a realistic ocean environment horizontal refractions of long range signals were computed using global ocean state estimates for 2004 from the estimating the circulation and climate of the ocean ecco2 project basin scale paths in the eastern north pacific ocean and regional scale paths in the philippine sea were used as examples at o 5 mm basin scales refracted geodesic and geodesic paths differed by only about 5 km gyre scale features had the greatest refractive influence but the precise refractive effects depended on the path geometry with respect to oceanographic features refraction decreased travel times by 5 10 ms and changed azimuthal angles by about 0 2 at o 500 km regional scales paths deviated from the geodesic by only 250 m and travel times deviated by less than 0 5 ms such effects are of little consequence in the analysis of tomographic data refraction details depend only slightly on mode number and frequency

archean chemical weathering at three localities on the canadian shield abstract sapropelite developed on a granodiorite basement below the archean steeprock group in the western superior structural province of canada weathered materials from a 3 15 ga granitic basement to the archean yellowknife supergroup in the slave structural province and weathered detritus from contemporaneous komatiites and gneissic basement of the archean prince albert group in northern churchill structural province have been analysed the deviation of the weakly metamorphosed weathered material from the chemical composition of their precursors is comparable to that seen in more recent weathered profiles from similar source materials this includes the enhancement of ferric to ferrous iron ratios and potash to soda lime and magnesia ratios there is also an increase in lighter ree and a depletion of heavier ree quartz rich sediments immediately above the unconformity derived from the basement granitoids may be enriched in aluminum and iron and yield chloritoid under proper metamorphic conditions sediments formed from mixed sources such as weathered gneissic basement and contemporaneous komatiitic volcanics yield anomalous resistate sedimentary mixtures such as chromiferous quartzites based on the data given here there is no need to postulate that different weathering and or ground water systems were operative during the archean compared to more recent times on the other hand the complicated weathering and diagenetic history that altered material undergoes below a subsiding unconformity relies as much or more on the buffering capacity of the enclosed rock mass as on the atmospheric conditions prevalent at the time of weathering hence weathering profiles old and new are more a response to local environmental conditions within the rock than the composition of the atmosphere

on the time mean state of ocean models and the properties of long range acoustic propagation 1 receptions on three vertical hydrophone arrays from basin scale acoustic transmissions in the north pacific during 1996 and 1998 are used to test the time mean sound speed properties of the world ocean atlas 2005 woa05 of an eddying unconstrained simulation of the parallel ocean program pop and of three data constrained solutions provided by the estimating the circulation and climate of the ocean ecco project a solution based on an approximate kalman filter from the jet propulsion laboratory ecco jpl a solution based on the adjoint method from the massachusetts institute of technology ecco mit and an eddying solution based on a green s function approach from ecco phase ii ecco2 predictions for arrival patterns using annual average woa05 fields match observations to within small travel time offsets 0 3 1 0 s predictions for arrival patterns from the models differ substantially from the measured arrival patterns from the woa05 climatology and from each other both in terms of travel time and in the structure of the arrival patterns the acoustic arrival patterns are sensitive to the vertical gradients of sound speed that govern acoustic propagation basin scale acoustic transmissions therefore provide stringent tests of the vertical temperature structure of ocean state estimates this structure ultimately influences the mixing between the surface waters and the ocean interior the relatively good agreement of the acoustic data with the more recent ecco solutions indicates that numerical ocean models have reached a level of accuracy where the acoustic data can provide useful additional constraints for ocean state estimation

estimating range to a vocalizing fin whale using the timing and amplitude of multipath arrivals a semi automated method is described to range to vocalizing fin whales using the timing and amplitude of multipath arrivals measured on seafloor receivers calls are detected and multipath arrivals identified with a matched filter multipath times and relative amplitudes are predicted as a function of range by ray tracing because the direct and first water column multiple arrivals are not always observed different hypotheses for the observed arrival paths must be considered for two arrivals an amplitude threshold is used to determine if the first arrival is the direct path and if not the call is disregarded as distant when three or more arrivals are detected three hypotheses for the paths of arrivals are considered the solution is the hypothesis and range that minimizes the timing and optionally amplitude ratio or absolute amplitude residual the method is tested with data from two ocean bottom seismometers one on the juan de fuca ridge and the other in the cascadia basin solutions obtained by

the role of simulated small scale ocean variability in inverse computations for ocean acoustic tomography ocean acoustic tomography depends on a suitable reference ocean environment with which to set the basic parameters of the inverse problem some inverse problems may require a reference ocean that includes the small scale variations from internal waves small mesoscale or spice tomographic inversions that employ data of stable shadow zone arrivals such as those that have been observed in the north pacific and canary basin are an example estimating temperature from the unique acoustic data that have been obtained in fram strait is another example the addition of small scale variability to augment a smooth reference ocean is essential to understanding the acoustic forward problem in these cases rather than a hindrance the stochastic influences of the small scale can be exploited to obtain accurate inverse estimates inverse solutions are readily obtained and they give computed arrival patterns that matched the observations the approach is not ad hoc but universal and it has allowed inverse estima

crustal shortening in the andes why do gps rates differ from geological rates gps data indicate 30 40 mm yr 1 present day crustal shortening across the andes whereas geological evidence shows crustal shortening concentrated in the sub andean thrust belt at a much lower rate 15 mm yr 1 we reconcile the discrepancy between the geodetic and the geological crustal shortening using geodynamic modeling that includes timescale dependent crustal deformation the gps velocities reflect the instantaneous deformation in the andes that includes both permanent deformation and elastic deformation that will be recovered during future earthquakes whereas the lower geological rates reflect only the permanent deformation the three dimensional viscoelastic model predicts nearly uniform short term velocity gradients across the andes similar to the gps results and concentrated long term crustal shortening in the sub andean thrust zone consistent with geological observations

the elevation history of the tibetan plateau and its implications for the asian monsoon abstract the determination of the evolving palaeoaltitude of the tibetan plateau since the india eurasia collision underpins our understanding of how orography in central asia affects the intensity of the monsoon and hence global climate change palaeoaltitudes however cannot be measured directly and need to be inferred from proxy observations that are usually model dependent differing tectonic models for the behaviour of the lithosphere during continental collision have contrasting implications for the elevation of the plateau however two techniques recently employed for determining palaeo elevation are independent of tectonic models the first involving the variation with altitude of oxygen isotopes in precipitation and the second involving the change of leaf morphology with moist static energy of the atmosphere elevation studies have focused on southern tibet largely due to the relative ease of access to the region there is a remarkable unanimity amongst the diverse techniques applied that the altitude of the southern plateau has not significantly changed since at least the mid miocene ca 15 ma arguing for an onset of the monsoon system during or before the early miocene a range of tectonic studies suggest that the northern and eastern parts of the plateau are younger geomorphological features but there are few quantitative constraints of the timing of elevation from these regions of tibet since both the elevation and the surface area of the plateau impact on atmospheric circulation palaeoaltitude studies need to be extended to chart the increasing areas of elevated land surface through time

a topex poseidon global tidal model tpxo 2 and barotropic tidal currents determined from long range acoustic transmissions abstract tidal currents derived from the tpxo 2 global tidal model of egbert bennett and foreman are compared with those determined from long range reciprocal acoustic transmissions amplitudes and phases of tidal constituents in the western north atlantic are derived from acoustic data obtained in 1991 1992 using a pentagonal array of transceivers small spatially coherent differences between the measured and modeled tidal harmonic constants mostly result from smoothing assumptions made in the model and errors caused in the model currents by complicated topography to the southwest of the acoustical array acoustically measured harmonic constants amplitude phase of m2 tidal vorticity 3 8 10 9s 1 210 310 agree with those derived from the tpxo 2 model 2 5 10 9s 1 250 300 whereas harmonic constants of about 1 2 10 9s 1 350 360 are theoretically expected from the equations of motion harmonic constants in the north pacific ocean are determined using acoustic data from a triangular transceiver array deployed in 1987 these constants are consistent with those given by the tpxo 2 tidal model within the uncertainties tidal current harmonic constants determined from current meters do not generally provide a critical test of tidal models the tidal currents have been estimated to high accuracy using long range reciprocal acoustic transmissions these estimates will be useful constraints on future global tidal models

a spectral analysis of the 21 may 1997 jabalpur india earthquake mw 5 8 and estimation of ground motion from future earthquakes in the indian shield region the jabalpur earthquake 23 08 n 80 06 e h 36 km is the first event in the indian peninsular shield region to be well recorded by a newly installed 10 station broadband seismographic network using these data we estimate q of lg wave in the indian shield region as q 508 0 48 1 20 hz the corrected source spectrum with m 5 4 1024 dyne cm reported in the harvard cmt catalog and an 2 source model requires a stress parameter p of 420 bar to explain high frequency spectral level the computed seismic energy from the records is 7 4 1020 erg which yields an apparent stress and brune stress drop of 62 and 270 bars respectively the analysis of the jabalpur earthquake provides some elements for the estimation of ground motions during future earthquakes in the indian shield region based on the results of the jabalpur earthquake and on studies of tectonically similar region of eastern north america we assume that 1 the sources follow an 2 model 2 s waves dominate at r 100 km and lg waves dominate at r 100 km 3 q f 508 0 48 4 the ground motion is a bandlimited finite duration gaussian white noise and 5 the effective duration of the ground motion equals 1 c 0 05 r where fc is the corner frequency we apply random vibration theory rvt to compute various measures of ground motion such as a max and v max at near source distances the source finiteness is approximately taken into account the attenuation curves for 5 5 mw 7 and for p of 100 400 bar are presented as expected the predicted values with p 420 bar agree reasonably well with the limited jabalpur data an a max of 150 gal is predicted in the epicentral region of this earthquake the predicted curves imply p 100 bar for the latur earthquake of 1993 mw 6 1 h 2 5 km to explain a max 1 g and the reported isoseismal intensities in the epicentral region for koyna earthquake of 1967 mw 6 3 the inferred a max and v max from isoseismal intensities and the recorded strong motions at the koyna dam site are in agreement with the prediction curves for p 100 bar the rvt predictions seem reasonable but need validation from more strong motion data which is presently lacking

pseudo oolites in rocks of the ulundi formation lower part of the archaean fig tree group south africa abstract the ulundi formation of the lowermost fig tree group in the type area in the barberton mountain land consists of a sequence of quartz sericite schists banded cherts and tuffaceous rocks up to 40 m thick it overlies talc carbonate schists assigned to the upper part of the onverwacht group in the cherts which in parts represent the sulfide facies of a banded iron formation silicified spheroids have been observed which appear to be diagenetically altered locally zeolitized accretionary lapilli portions of the cherts formed through silicification of fine grained felsic tuffs and contain abundant stylolite seams along which 4 of the rock thickness has been removed by intrastratal solution during deformation a supposedly organogenic spheroidal structure ramsaysphera has been previously described from the upper part of the ulundi formation the spheroids with diameters of up to 8 mm occur in a distinct bed of up to at least 1 6 m thickness and can be traced in outcrop over an area which originally covered 17 30 km the bed was deposited in fairly still water of several 100 m depth the spheroids accumulated with only little finer grained detrital material the interstices between them being filled by cherty silica and minor amounts of dolomite up to 65 of the spheroids consist of tectonically elongated originally round fragments of a micro felsitic groundmass with remnants of phenocrysts the majority of the remaining spheroids consists of concentrically banded bodies of siliceous material with minor amounts of chlorite and sericite as well as small dolomite crystals these spheroids represent highly altered granules of volcanic glass deposited from volcanic ash clouds through a body of water the prototype of ramsay sphera also belongs to this group of spheroids and there is little microscopic or macroscopic evidence for its explanation as an organic structure

evidence of tidal processes from the lower part of the witwatersrand supergroup south africa abstract a 1600 m succession of quartz arenites and associated shaley deposits comprising the hospital hill subgroup at the base of the witwatersrand supergroup is considered to have been deposited largely under the influence of tidal processes facies analysis indicates that deposition occurred in the following environments 1 marine shalf 2 shallow subtidal to intertidal 3 intertidal flat and 4 tidal inlet the presence of strong tidal currents implies that the witwatersrand basin was open to an ocean basin at least during the early stages of its evolution palaeocurrent trends and isopach data suggest that this probably lay to the southwest an area now occupied by the high grade natal namaqua metamorphic belt the contrast between the supermature quartz arenites of the hospital hill subgroup and the overlying gold bearing immature subgreywackes feldspathic quartzites and conglomerates of fluvial origin is believed to be a function of tidal reworking of sediments