the present day stress field of australia abstract the unusual present day crustal stress pattern of the australian continent has been the subject of scientific debate for over 25 years the orientation of maximum horizontal present day stress s hmax in continental australia is unlike all other major tectonic plates in that the stress pattern shows regional variability and it is not oriented sub parallel to the direction of absolute plate motion previous studies on the stress pattern of australia revealed that the complex stress pattern of the continent is controlled at a first order by the superposition of plate tectonic forces exerted at the plate boundaries however prior analysis of the contemporary australian crustal stress pattern have been unable to model or explain the stress pattern observed in most of eastern australia and has not extensively addressed the numerous smaller scale variations in stress orientation the recent development of unconventional reservoirs in australia has resulted in a greatly increased amount of new data for stress analysis in previously unstudied or poorly constrained areas in eastern australia in addition stress analysis in conventional hydrocarbon mineral and geothermal exploration in all other parts of the continent provides the opportunity to review and update the australian stress map asm this study presents the new release of the asm with a total of 2150 stress data records in australia increased from 594 data records in 2003 the 2016 asm contains 1359 data records determined from the interpretation of drilling related stress indicators 650 from earthquake focal mechanism solutions 139 from shallow engineering measurements and two from geological indicators the results reveal four distinct regional trends for the s hmax orientation in australia including a nne ssw s hmax trend in northern and northwestern australia which rotates to a prevailing e w orientation in most western and south australia the orientation of s hmax in eastern australia is primarily ene wsw and swings to nw se in southeastern australia a comparison between the new asm database and neotectonic features further confirms the role of contemporary stress in recent deformation of the australian crust the 2016 asm reveals significant discrepancies between newly observed s hmax orientations and predictions by published geomechanical numerical models for the australian continent forces generated at the boundary of indo australian plate remain the major control on the regional crustal stress pattern in continental australia however the increased data density particularly in eastern australia reveals numerous local perturbations of the stress field that were not previously clearly captured hence the key findings of the new release are that local intra plate stress sources are more significant than previously recognized particularly in eastern australian basins and cause substantial local scale rotations of the present day crustal stress pattern that have not been factored into existing australian stress models

acceleration source spectra anticipated for large earthquakes in northeastern north america a set of 16 large intraplate earthquakes are considered on the basis of their tectonic settings compressive focal mechanisms and shallow focal depths as possible analogs for large earthquakes that may be anticipated to occur in northeastern north america the earthquakes range in seismic moment from 5 1023 to 3 1026 dyne cm and include the mainshocks and largest aftershocks of the 1982 miramichi canada the 1985 to 1988 nahanni canada and the 1988 tennant creek australia earthquake sequences the teleseismic recordings of these earthquakes are spectrally analyzed by correcting the logarithmically averaged acceleration spectra for the frequency dependent effects of attenuation and interference of the depth and direct phases the resulting acceleration source spectra are generally flat at high frequencies the mainshock spectra exhibit intermediate spectral falloffs that is u where 1 over frequencies that characteristically extend from 0 1 to 0 5 hz in contrast the largest aftershocks of the three sequences named above exhibit 2 spectral shapes the high frequency source spectral levels increase with seismic moment approximately as ru m 1 3 the 1988 saguenay canada earthquake which occurred significantly deeper than the other earthquakes exhibits an anomalous spectral shape combining the teleseismic data with strong motion recordings indicates that the intermediate spectral falloff for this earthquake extends from 0 2 to 3 hz the spectral amplitude at 3 hz is a factor of 3 higher than the amplitude anticipated for an earthquake of this size from the other 15 earthquakes

unusual behavior in atmospheric angular momentum during the 1965 and 1972 el ninos abstract the global atmospheric angular momentum aam is known to increase with tropical eastern pacific sea surface temperature sst anomalies during el nino events using a reanalysis dataset the ratio of the monthly aam anomaly to el nino sst anomaly based on the nino 3 4 index is found to be approximately 1 angular momentum unit 1025 kg m2 s 1 per degree celsius for most post 1975 el ninos this ratio is much smaller however during the 1965 66 and 1972 73 el ninos raising the possibilities that either the early reanalysis data are in error due to sparse observations or the atmospheric response to the two early el ninos was unusual the possibility of a severe data problem in the reanalysis is ruled out by cross validating the aam time series with independent measurements of length of day the latitudinal structures of the zonal wind anomalies in 1965 66 and 1972 73 are examined for both the reanalysis and a set of general circulation model gcm simulations multiple gcm runs with specifie

assessing the reliability of magnesium in foraminiferal calcite as a proxy for water mass temperatures though many studies on the mg contents in the calcitic tests of foraminifers exist the processes controlling its uptake are still a matter of debate laboratory cultures offer an excellent opportunity to reveal these mechanisms the mg concentrations within single chambers of the planktic foraminifer globigerinoides sacculifer brady maintained under controlled laboratory conditions were measured 1 at variable temperatures 19 5 29 5 c and constant salinity and 2 at variable salinity 22 45 and constant temperature the experimental results suggest that under natural conditions temperature is the leading mechanism controlling the mg ca ratio temperature and magnesium are related proportionally a temperature increase of ca 10 c gives rise to an increase of the magnesium concentrations of ca 130 drastic unnatural salinity changes dominate the effects of temperature a 110 change in the mg ca ratio was observed when salinity was elevated or reduced by more than ca 10 specimens which underwent gametogenesis reveal significantly higher mg concentrations than specimens that did not release gametes partition coefficients for mg in foraminiferal calcite are orders of magnitude lower than values from inorganically precipitated calcite when comparing observed mg ca ratios of foraminiferal tests with predicted mg ca ratios calculated according to empirical equations it becomes evident that foraminiferal tests are undersaturated with respect to mg for the water temperature they have experienced apparently foraminifers are capable of controlling their mg concentration the physiological processes presumably responsible for such depressed mg ca ratios appear to be temperature controlled as deduced from the close relationship of the observed mg ca ratios and water temperature this study demonstrates that variations in temperature and salinity are definitely reflected in the mg content of foraminiferal tests magnesium may thus serve as a paleo proxy for past surface water temperatures as long as postdepositional changes and salinity variations are of subordinate importance or can be excluded

the end permian mass extinction a rapid volcanic co2 and ch4 climatic catastrophe abstract the end of the permian was a time of crisis that culminated in the earth s greatest mass extinction there is much speculation as to the cause for this catastrophe here we provide a full suite of high resolution and coeval geochemical results trace and rare earth elements carbon oxygen strontium and clumped isotopes reflecting ambient seawater chemistry and water quality parameters leading up to the end permian crisis preserved brachiopod low mg calcite based seawater chemistry supplemented by data from various localities documents a sequence of interrelated primary events such as coeval flows of siberian trap continental flood basalts and emission of carbon dioxide leading to warm and extreme greenhouse conditions with sea surface temperatures sst of 36 c for the late permian although anoxia has been advanced as a cause for the mass extinction most biotic and geochemical evidence suggest that it was briefly relevant during the early phase of the event and only in areas of upwelling but not a general cause instead we suggest that renewed and increased end permian siberian trap volcanic activity about 2000 years prior to the extinction event released massive amounts of carbon dioxide and coupled with thermogenic methane emissions triggered extreme global warming and increased continental weathering eventually these rapidly discharged greenhouse gas emissions less than 1000 years before the event ushered in a global hothouse period leading to extreme tropical ssts of 39 c and higher based on these sea surface temperatures atmospheric co 2 concentrations were about 1400 ppmv and 3000 ppmv for the late and end permian respectively leading up to the mass extinction there was a brief interruption of the global warming trend when sst dropped concurrent with a slight but significant recovery in biodiversity in the western tethys it is possible that emission of volcanic sulfate aerosols resulted in brief cooling just after the onset of intensified warming during the end of the permian after aerosol deposition global warming resumed and the biotic decline proceeded and was accompanied by suboxia in places of the surface ocean which culminated in the greatest mass extinction in earth history

magnetotelluric evidence for serpentinisation in a cambrian subduction zone beneath the delamerian orogen southeast australia abstract the delamerian orogen in southeast australia represents a proterozoic continental rift margin overprinted by convergent margin andean style subduction in the cambrian a detailed 150 km east west magnetotelluric transect was collected across the orogen to investigate the electrical resistivity structure the magnetotelluric transect follows an existing full crustal reflection seismic transect of which interpretations support a westward dipping cambrian subduction model as derived from field mapping and geochemistry a 2d inversion of the data from the 68 station broadband magnetotelluric transect imaged a heterogeneous crust with lateral changes as large as 10 000 m occurring over 15 km the crust within the western glenelg zone is resistive in contrast to the eastern glenelg zone and the grampians stavely zone above the paleo subduction zone which host three conductive pathways the main low resistivity regions 1 10 m reside at mid lower crustal depths 10 30 km extending up to the surface with a higher resistivity 300 m but still much less than surrounding resistivity mantle 1000 m crust 10 000 m fluids released from the upper mantle during the cambrian west dipping subduction are interpreted to have moved up crustal faults to create the observed low resistivity pathways by serpentinisation and magnetite creation in mafic ultramafic rocks the electrical conductivity of hand samples of serpentinised mafic ultramafic rocks in the region was found to be much greater than most other rock types present in addition to adding insight into the crustal structure the magnetotelluric data also supports geological surface mapping as the major lawloit and yarramyljup faults that bound different geological domains also mark domains of different electrical structure

experimental grain size sensitive flow of hot pressed brazilian quartz aggregates abstract grain size sensitive flow may be of particular importance in the flow of rocks in natural high strain zones hot pressed aggregates of synthetic ultrafine grained brazilian quartz of nominal grain sizes 0 4 1 3 and 4 5 m were deformed at 300 mpa confining pressure and temperatures of 1273 1473 k fully ductile flow at differential stresses below 200 mpa followed 0 4 exp 220000 r t d 2 where is strain rate s 1 is stress mpa d is grain size microns and r is the gas constant grains remained equant and mostly dislocation free without significant crystallographic fabric water pressure 25 50 mpa was estimated from water adsorbed onto grain boundaries during specimen fabrication flow was inferred to be controlled by silicon volume diffusion and to be sensitive to water fugacity at differential stresses 200 mpa non linear flow involved dislocation motion extrapolation to natural strain rates and temperatures that predict grain size sensitive flow in quartz should only be important at 800 k and very small grain sizes 1 m flow law parameters may change over the extrapolation interval e g through a transition to control by silicon grain boundary diffusion but geological evidence suggests that flow of even very fine grained quartzites commonly occurs by recrystallization accommodated dislocation creep rather than by diffusional accommodation

core mantle boundary shape constraints inferred from the pressure torque acting between the core and the mantle summary in the last few years models of the flow at the top of the earth s core and of the related pressure field have been calculated from the secular variation of the geomagnetic field and core mantle topographies have been computed by seismologists a pressure torque results from the action of the pressure field on the core topography which can theoretically be computed from models of both the pressure field and the core mantle interface small scale features of the flow and of the topography are shown to be capable of contributing strongly to the pressure torque it is thus impossible to calculate the exact value of the torque from the knowledge of only the long wavelength components of the models but the interaction between the large scale components generates by itself torques two orders of magnitude larger than the torques inferred from the irregularities of the length of the day it is nevertheless possible to reconcile the topographic coupling mechanism with the length of the day observations keeping the amplitude of the core topography proposed by seismologists if an orthogonality relation between the geometry of the fluid upwellings and downwellings at the top of the core and the topography is satisfied it is shown how to compute such a topography for a given flow and close to an original topography provided by seismic tomography some consequences of the so inferred link between the fluid flow at the top of the core and the core mantle boundary topography are discussed

siderite clumped isotope thermometry a new paleoclimate proxy for humid continental environments abstract clumped isotope measurements can be used to exploit the paleoclimatic potential of pedogenic siderite feco3 however the applicability of this method is held back by the lack of clumped isotope calibrations of mineralogies other than calcite and aragonite here we present an inorganic calibration of siderites grown in the laboratory between 21 and 51 c linear regression of 47 values and temperature 106 t2 k yields the following relationship r2 0 997 47 rf 0 0356 0 0018 10 6 t 2 0 172 0 019 we demonstrate that this calibration is indistinguishable from calcite at current levels of analytical precision our observations suggest that there is likely no large systematic bias in the clumped isotope acid fractionation factors between the two different carbonate minerals we also present clumped isotope measurements of a natural siderite collected from holocene sediments of the mississippi river delta we find that siderites record warm season marsh water temperatures instead of mean annual temperatures as it has long been presumed this finding has important implications for the accuracy of siderite stable isotope and clumped isotope based climate reconstructions

hyperextension serpentinization and weakening a new paradigm for rifted margin compressional deformation the early eocene magma rich northeast atlantic rifted margins contain a large number of pre breakup and post breakup compressional structures located in abandoned early cretaceous hyperextended basins with crustal stretching factors of 3 4 or more the deformation both predates and postdates the magma rich breakup the hyperextended basins are often underlain by high velocity lower crustal bodies which we argue represent partially serpentinized upper mantle long lived lithospheric weakening and proneness to deformation is proposed to relate to crustal hyperextension probably enhanced by mantle hydration

modes of active intraplate deformation flinders ranges australia 1 the flinders ranges form one of the most seismically active zones within the australian continent with seismogenic strain rates over the last 30 years of 10 16 s 1 active deformation in the region reflects late neogene increases in stress levels in the indo australian plate as a response to increased plate boundary forcing from collision zones with the neighboring asian and pacific plates geological and geophysical observations suggest two modes of active deformation in operation in the flinders ranges over the last several million years 1 low amplitude 200 500 m long wavelength 200 km lithospheric flexure and 2 active reverse faulting along the range front with fault slip rates of up to 50 m myr 1 numerical models are developed to explore the contribution of each of these deformation modes to the observed geophysical signals an elastic mode of deformation is suggested by a distinctive long wavelength positive correlation between gravity and topography in which the flinders ranges are bordered by anomalous topographic and gravity lows now occupied by playa lake systems centered some 50 km outboard of range bounding faults numerical models show that flexural instabilities localized by vertical loads arising from older tectonic structuring produce a first order match with observed topography and gravity numerical models are also used to illustrate how the localized failure evident in the contemporary seismicity and quaternary faulting record within the flinders ranges reflects thermal weakening associated with extraordinary concentrations of heat producing elements in the crust as reflected in modern day heat flows of 90 mw m 2

geochemistry of modern brachiopods applications and implications for oceanography and paleoceanography abstract modern rhynchonellida terebratulida thecideida and a few inarticulated brachiopods were collected live or soon after death at 30 locations from depths of 2 3940 m from the equator to high latitudes covering the atlantic pacific indian caribbean and mediterranean oceans seas well preserved fibers of the secondary layer combined with sr 450 1928 mg kg mn 1 199 mg kg and fe 1 610 mg kg contents confirm with few exceptions the excellent preservation of the modern brachiopod material evaluation of the stable isotope compositions was conducted on 276 specimens and on 374 published samples for a total database of 650 samples from 80 locations it revealed that oxygen isotope incorporation into shell calcite secondary layer of modern articulated brachiopods in most cases occurs in equilibrium with the ambient water and as such reflects surrounding environmental conditions thecideida as a group shallow water and low latitude incorporate oxygen isotopes 3 04 to 0 35 into shell calcite in equilibrium with their ambient water a large majority of genera and species of the terebratulida shallow water and low mid latitude also incorporate oxygen 2 30 to 3 48 into shell calcite in isotopic equilibrium with their surrounding water in contrast equilibrium incorporation of oxygen isotopes into shell calcite by the rhynchonellida is uncertain but a vital effect probably applies to the craniida the question of equilibrium disequilibrium incorporation of carbon isotopes into shell calcite of modern brachiopods remains unresolved at this time isotope compositions range up to 4 5 5 6 and 1 5 for 13 c and up to 5 5 5 9 and 0 3 for 18 o for shallow water low mid and high latitude brachiopods respectively strontium isotopes of modern brachiopods as expected show no significant variation with location latitude water depth temperature salinity and general water conditions once local habitat and ecological influences of fossil brachiopods from similar latitudes are considered their isotopic elemental values should be valuable diagenetic indicators and important oceanographic chemostratigraphic proxies

an ancient rift complex and its relation to contemporary seismicity in the new madrid seismic zone gravity magnetic geologic and seismicity data have been combined in a seismotectonic analysis of the new madrid seismic zone previous studies have presented evidence for several rift zones in this area upper mississippi embayment including the reelfoot rift a late precambrian early paleozoic failed arm which extends n ne from the ancient continental margin in this study we propose that the northern terminus of the reelfoot rift forms a rift complex which appears to correlate well with the seismicity in the area this correlation suggests that faults associated with this rift complex are being reactivated in the contemporary stress field ene compression if this interpretation is valid it represents a seismotectonic model which can be used to predict the extent of future seismicity in the new madrid seismic zone the proposed rift complex also provides a coherent model for the tectonic development of this region of the north american midcontinent

earth s variable rotation recent improvements in geodetic data and practical meteorology have advanced research on fluctuations in the earth9s rotation theinterpretation of these fluctuations is inextricably linked with studies of the dynamics of the earth moon system and dynamical processes in the liquid metallic core of the earth where the geomagnetic field originates other parts of the earth9s interior and the hydrosphere and atmosphere fluctuations in the length of the day occurring on decadal time scales have implications for the topography of the core mantle boundary and the electrical magnetic and other properties of the core and lower mantle investigations of more rapid fluctuations bear on meteorological studies of interannual seasonal and intraseasonal variations in the general circulation of the atmosphere and the response of the oceans to such variations

δ18o and δ13c values of modern brachiopod shells abstract researchers have not rigorously tested the hypothesis that calcite from modern brachiopod shells is precipitated in oxygen isotope equilibrium with ambient seawater isotopic variability at the intraspecimen and intertaxon levels has not been examined without such data for modern brachiopods similar data from ancient brachiopods cannot be accurately interpreted in this study a survey is made of 18 o and 13 c values of terebratulid rhynchonellid thecideidine and craniacean brachiopods from antarctica the bay of fundy curacao japan new zealand norway puget sound palau sicily and south africa this suite of samples provides a wide range of taxonomic levels temperatures salinities and depositional environments for evaluating the degree of isotopic equilibrium attained during precipitation of brachiopod calcite new data indicate that modem brachiopod calcite is not always precipitated in oxygen and carbon isotope equilibrium with ambient seawater calcite from the primary layer and specialized shell structures hinge brachidium foramen interarea muscle scars are depleted in both 18 o and 13 c a characteristic of biological fractionation or vital effects often found in other calcerous marine organisms our findings suggest that these portions of the brachiopod shell should be avoided during sampling of ancient brachiopods secondary layer calcite the material most often analyzed in ancient brachiopods has higher 18 o and 13 c values which approach and sometimes correspond with predicted equilibrium values therefore secondary layer calcite is the most suitable portion of the brachiopod shell for use as an ancient seawater proxy although near equilibrium precipitation in secondary layer calcite is encouraging to those studying the isotopic composition of ancient oceans these data come with caveats large intraspecimen variability in the 18 o values of secondary layer calcite 1 in some samples limits the use of brachiopods as precise indicators of the 18 o value or temperature of ancient seawater the 18 o and 13 c values of secondary layer calcite deviate from predicted equilibrium values toward the lower values of the primary layer and specialized shell structures indicating a measurable vital effect in most cases measured 18 o values are lower than the calculated equilibrium values dictated by seasonal variations in the 18 o value and temperature of seawater ontogenetic variations in the 13 c values of secondary layer calcite have also been measured and must be assessed when interpreting ancient data modern brachiopods occur in a wide range of seawater salinities and temperatures therefore the relation between salinity and the 18 o value of seawater must be known to correctly calculate the temperature of calcite precipitation from secondary layer 18 o values errors of up to 15 c are found if ambient seawater is assumed to have a constant 18 o value e g 0 smow and the 18 o values of secondary layer calcite are used to calculate temperature coupled with vital effects and intraspecimen variability these errors can obscure the resolution of secular variations in the rock record

high temperature environments of human evolution in east africa based on bond ordering in paleosol carbonates many important hominid bearing fossil localities in east africa are in regions that are extremely hot and dry although humans are well adapted to such conditions it has been inferred that east african environments were cooler or more wooded during the pliocene and pleistocene when this region was a central stage of human evolution here we show that the turkana basin kenya today one of the hottest places on earth has been continually hot during the past 4 million years the distribution of 13c 18o bonds in paleosol carbonates indicates that soil temperatures during periods of carbonate formation were typically above 30 c and often in excess of 35 c similar soil temperatures are observed today in the turkana basin and reflect high air temperatures combined with solar heating of the soil surface these results are specific to periods of soil carbonate formation and we suggest that such periods composed a large fraction of integrated time in the turkana basin if correct this interpretation has implications for human thermophysiology and implies a long standing human association with marginal environments

fluctuations in the earth s rotation since 1830 from high resolution astronomical data summary fluctuations in the earth s rotation since 1830 as evidenced by changes in the length of the day are derived from astronomical data having subannual resolution before 1955 5 timings of linar occultations are used after 1955 5 the data are taken from the time series tai ut1 although the data in the earliest period 1830 90 display decade fluctuations in the length of the day they are not accurate enough to reveal interannual variations in this regard also the results from 1890 1925 are somewhat dubious the quality of the data after 1925 though is such that the temporal behaviour of the interannual fluctuations in the length of the day can be traced with confidence we present plots of the interannual fluctuations in the period 1890 1987 and the longer term decade fluctuations in the period 1830 1983 the interannual fluctuations in the length of the day since 1925 are compared with an index of the el nino southern oscillation enso phenomenon in the ocean atmosphere system and are subjected to spectral analysis the results support the conclusions reached by other authors that these fluctuations are linked to circulation changes in the atmosphere associated with enso and in part to the quasi biennial oscillation in the equatorial stratosphere s zonal winds a spectral analysis of our 62 yr series of length of day values since 1925 reveals two significant peaks in the interannual range 2 4 yr one is roughly biennial and the other is about twice this period broadly supporting results obtained previously from shorter records our analysis of high resolution data therefore contributes to ongoing efforts to establish a close relationship between the length of the day and aspects of the global climate system in the period before modern data became available in 1955 5

13c 18o isotope signatures and clumped isotope thermometry in foraminifera and coccoliths accurate constraints on past ocean temperatures and compositions are critical for documenting climate change and resolving its causes most proxies for temperature are not thermodynamically based appear to be subject to biological processes require regional calibrations and or are influenced by fluid composition as a result their interpretation becomes uncertain when they are applied in settings not necessarily resembling those in which they were empirically calibrated independent proxies for past temperature could provide an important means of testing and or expanding on existing reconstructions here we report measurements of abundances of stable isotopologues of calcitic and aragonitic benthic and planktic foraminifera and coccoliths relate those abundances to independently estimated growth temperatures and discuss the possible scope of equilibrium and kinetic isotope effects the proportions of 13c 18o bonds in these samples exhibits a temperature dependence that is generally similar to that previously been reported for inorganic calcite and other biologically precipitated carbonate containing minerals apatite from fish reptile and mammal teeth calcitic brachiopods and molluscs aragonitic coral and mollusks most species that exhibit non equilibrium 18o 16o 18o and 13c 12c 13c ratios are characterized by 13c 18o bond abundances that are similar to inorganic calcite and are generally indistinguishable from apparent equilibrium with possible exceptions among benthic foraminiferal samples from the arctic ocean where temperatures are near freezing observed isotope ratios in biogenic carbonates can be explained if carbonate minerals generally preserve a state of ordering that reflects the extent of isotopic equilibration of the dissolved inorganic carbon species

geophysical analysis of zonal tidal signals in length of day summary the earth s zonal response coefficient k is estimated from the tidal signals in the observed length of day lod data its magnitude and phase are functionals of the earth s internal structure and dynamics in this paper an analysis of 13 years of precise lod data 1980 1992 reveals strong signals for nine zonal tidal groups ranging from 5 to 35 days in period numerical estimates of k for 27 major tides are thus obtained 11 among which are considered sufficiently high in signal to noise ratio to provide meaningful geophysical constraints on the earth s rotational dynamics the results favour a k magnitude close to but somewhat smaller than 0 315 which is the theoretical value for an elastic mantle completely decoupled from the fluid core plus equilibrium oceans a small amount of dispersion is also detectable where shorter periods tend to have lower k magnitude and larger phase lag our k magnitude estimates are consistent with two recently published non equilibrium ocean tide models and an anelastic response in the mantle although an equilibrium response in the ocean and a purely elastic response in the mantle is not disallowed phase lags of a few degrees are required by both ocean tide models and by our data

interannual atmospheric torque and el nino southern oscillation where is the polar motion signal 1 in this paper we investigate the atmospheric excitation of polar motion pm associated with the el nino southern oscillation enso phenomenon enso effects on length of day due to changes in the axial component of atmospheric angular momentum aam have long been recognized but identification of pm excitation with enso induced equatorial aam anomalies has proved more elusive here we use an appropriately modified form of the inverted barometer ib assumption to study enso related atmospheric torques arising from pressure loading on the earth s ellipsoidal bulge and mountains and from frictional wind stress over the earth s land and ocean covered surface the resulting dissipation torques which accommodate adjustment of the oceanic mass distribution to time variable atmospheric loading are found to be small the ellipsoidal torques have the largest amplitude reflecting the order of magnitude discrepancy between the height departures of the earth s bulge 20 km and its surface orography 2 km because of relatively uniform pressure covariances with the southern oscillation index over the continents for the largely land based x component and the uniform ib response for the largely ocean based y component however the enso related pm excitation arising from the ellipsoidal torques is reduced to an amplitude comparable with the sum of regional mountain torques from the individual continents the largest of these are generated over asia and antarctica arising from efficient coupling of enso related surface pressure anomalies with large scale orographic features the geometrical mitigation of the ellipsoidal torques classically expected to dominate equatorial aam forcing accounts for the lack of a detectable atmosphere driven polar motion response to enso

sr mg ratios of modern marine calcite empirical indicators of ocean chemistry and precipitation rate holocene biotic and abiotic marine calcite have a similar range of mg contents 0 to 22 and 4 to 21 mol mgco3 respectively yet biotic calcite has sr2 concentrations that are consistently 1250 ppm higher than those of abiotic calcite as in laboratory experiments a positive linear relation is observed between dsr and calcite mg content this produces two distinct linear trends on a plot of sr2 vs mg2 concentrations principal axes of variation for both trends have similar slopes yet distinctly different sr2 concentration intercepts biotic y 0 024x 1298 r2 0 70 abiotic y 0 027x 47 r2 0 77 the similar slopes of these trends reflect the constancy of mgca and srca ratios of modern seawater equations describing the dependence of dsr on calcite mg content are derived from both trends biotic dsr 3 16 x 10t 6 ppm mg 0 169 abiotic dsr 3 52 x 10 6 ppm mg 0 0062 characterization of sr mg trends for holocene materials allows comparison with analogous trends from ancient samples to estimate relative changes in seawater mgca and srca ratios the relatively high sr contents of biotic calcite result from rapid precipitation rates associated with shell accretion in marine organisms calcites precipitated from seawater in laboratory experiments have dsr values that are similar to those of biotic marine calcite suggesting that both precipitate at approximately the same rate our estimates of surface area normalized precipitation rates in planktonic and benthonic foraminifera are comparable to those of seeded ph stat experiments we conclude that the dsr values for biotic and experimental marine calcite are kinetically controlled whereas the lower precipitation rates of abiotic marine calcite yield dsr values that approximate equilibrium conditions experimentally derived equations describing the relation between dsr and calcite precipitation rate indicate that the offset in sr content between biotic and abiotic calcite is the result of abiotic precipitation rates that are two to five orders of magnitude lower than those of biotic precipitates however observations of naturally occurring marine cements suggest that the five order of magnitude offset best represents natural system processes

inner core rotation and its variability from nonparametric modeling 1 we present a new approach for studying the inner core rotation and its variability by separating the underlying structure from its time evolution this is achieved by fitting a large set of existing seismic bc df traveltime data with a smoothing spline analysis which is implemented in the statistics package r this method allows us to separate the time independent mantle contribution from the time dependent core contribution without any a priori constraints and to also estimate the error of the fit we add our newly acquired seismic data from the passcal experiment arctic in northern alaska to pkp differential traveltime measurements previously obtained from south sandwich islands earthquakes and recorded at college col and the alaskan seismic network this nearly doubles the number of measurements to a total of 1165 and increases the data coverage of the inner core structure and our time coverage to about 55 years the large number of measurements allows us to use the standard statistical method of bootstrapping to derive the rotation rate and thus to further separate the core structure from its time evolution this approach has been successfully tested with synthetic data sets that feature both a nonlinear structure and variable rotation rates while sharing the same earthquakes and stations geometry as our real data applying this method to the real data yields an average rotation rate of 0 39 0 090 22 yr 1 at 68 confidence level our results also suggest a nonzero acceleration of the inner core with an apparent change in the rotation rate from 0 24 to 0 56 yr 1 within the last 55 years the minimum torque acting on the inner core is estimated 1 19 1016 n m which could result from the imbalance of the electromagnetic and gravitational torques

glacial surface temperatures of the southeast atlantic ocean a detailed record of sea surface temperature from sediments of the cape basin in the subtropical south atlantic indicates a previously undocumented progression of marine climate change between 41 and 18 thousand years before the present ky b p during the last glacial period whereas marine records typically indicate a long term cooling into the last glacial maximum around 21 ky b p consistent with gradually increasing global ice volume the cape basin record documents an interval of substantial temperate ocean warming from 41 to 25 ky b p the pattern is similar to that expected in response to changes in insolation owing to variations in earth s tilt

earth s rotation variations a wavelet analysis historical to up to date data of the minute variations in the solid earth s rotation are subjected to a comprehensive time frequency wavelet analysis the length of day for the period 1962 2012 confirms the presence of a prominent robust 6 year periodicity and reveals an anomalously strong 18 6 year tidal oscillation as well as a 13 year quasi periodic signal the polar motion excitation for the period 1900 2012 validates the existence of the 26 year markowitz wobble and shows an 8 year quasi periodic signal but no appreciable 18 6 year periodicity although it is known that exchanges of angular momentum with the geophysical fluids are responsible for the rotational variations of the solid earth the exact physical mechanisms involved on interannual to decadal timescales are still far from understood

a 6 year westward rotary motion in the earth detection and possible micg coupling mechanism abstract seeking geophysical explanations for the periodic six year oscillation syo previously found in the earth s length of day variation lod we analyze the global gps displacement and geomagnetic data using the array processing technique of ose optimal sequence estimation and find clear evidences of the 6 yr signals which manifest as a westward rotary propagating wave of the sectoral spherical harmonic pattern of degree 2 order 2 y 22 based on the period the spatial pattern and the amplitudes and the estimated phases that exhibit consistent synchronicity among the three datasets we propose the following scenario the mantle inner core gravitational micg coupling gives rise to a 6 yr axial torsional libration of the inner core controlled by the sectoral y 22 density anomalies or the equatorial ellipticities in the inner core and the lower mantle the angular momentum exchange between which manifests as the syo in lod it forces into action a pressure wave 2 cyclic in 6 yr through the fluid outer core which in turn produces the corresponding gps and geomagnetic variations our findings provide insight into the dynamics of the deep earth and corroborate a positive density anomaly for the lower mantle large low shear velocity provinces

structural controls on localized intraplate deformation and seismicity in southern australia insights from local earthquake tomography of the flinders ranges data from an array of 24 seismometers are used to image the crust beneath the flinders ranges southeast australia with the goal of improving our understanding of crustal structure rheology and the mechanism responsible for the localized intraplate deformation that characterizes this region a subset of p and s wave traveltimes is inverted to jointly recover earthquake hypocenters p wave velocity structure and v p v s anomalies the p wave velocity model reveals a spatial correlation between major negative velocity perturbations and concentrations of seismicity in particular a cluster of seismicity is observed within a distinct low velocity region between the archean mesoproterozoic gawler craton and the palaeo mesoproterozoic curnamona province from 7 to 20km depth we postulate that this may be associated with a pre existing structural weakness in the crust that arises primarily from rifting between the curnamona province and the gawler craton another area characterized by a high level of seismicity overlies a major sequence of n s trending ross delamerian thrust faults which correspond to a band of low v p and particularly v p v s the lack of evidence for elevated heat flows in both of these seismogenic regions suggests that thermally induced weakness is unlikely to play a dominant role instead the dynamic behavior of this intraplate region appears to be caused by a serendipitously oriented regional stress field provided by far field forces that originate from the boundary between the pacific and australian plates which acts upon preexisting structural weaknesses in the lithosphere

high regional climate sensitivity over continental china constrained by glacial recent changes in temperature and the hydrological cycle the east asian monsoon is one of earth s most significant climatic phenomena and numerous paleoclimate archives have revealed that it exhibits variations on orbital and suborbital time scales quantitative constraints on the climate changes associated with these past variations are limited yet are needed to constrain sensitivity of the region to changes in greenhouse gas levels here we show central china is a region that experienced a much larger temperature change since the last glacial maximum than typically simulated by climate models we applied clumped isotope thermometry to carbonates from the central chinese loess plateau to reconstruct temperature and water isotope shifts from the last glacial maximum to present we find a summertime temperature change of 6 7 c that is reproduced by climate model simulations presented here proxy data reveal evidence for a shift to lighter isotopic composition of meteoric waters in glacial times which is also captured by our model analysis of model outputs suggests that glacial cooling over continental china is significantly amplified by the influence of stationary waves which in turn are enhanced by continental ice sheets these results not only support high regional climate sensitivity in central china but highlight the fundamental role of planetary scale atmospheric dynamics in the sensitivity of regional climates to continental glaciation changing greenhouse gas levels and insolation

a revised calibration of the clumped isotope thermometer abstract a growing number of materials and environmental settings are studied using the carbonate clumped isotope 47 thermometer the method has been applied in both biogenic and non biogenic carbonate systems in marine and terrestrial settings over a wide range of geological timescales the current 47 temperature calibration gives good temperature estimates for most biogenic materials however systematic biases are commonly observed at low temperatures in this study we report additional calibration data that covers a wider temperature range at more evenly distributed temperatures and are measured at higher analytical precision than the original calibration combining these data with the original calibration yields a 47 t relationship that is similar to the original calibration though slightly less steep 47 0 0526 0 0025 10 6 t 2 0 0520 0 0284 this revised calibration is in better agreement with biogenic carbonates including those grown at low temperatures the difference between the original and revised calibrations is significant for carbonates forming below 16 c or above 49 c 47 values of 0 68 and 0 56 additionally we include a comprehensive analysis of the sources of error associated with 47 measurements and estimated temperatures and recommend measurement strategies for obtaining the desired precision as an illustration we apply the revised calibration and uncertainty analysis to 3 previously published studies at low temperatures the revised calibration results in significant differences from the original calibration and hence affects the interpretation of the environmental signal recorded in light of our 47 errors analysis in cases where the temperature signals are small we find that replicate analyses are critical to identify a temperature signal

on the fidelity of shell derived δ18oseawater estimates article i nfo 18 oseawater a robustproxyforsurfacesalinity we assessthe fidelity of shell derived 18 oseawater estimates for the surface dwelling foraminifer globigerinoides ruber white using an atlantic meridional coretop transect spanning basin scale temperature and salinity gradients shell derived and observed 18 oseawater values are well correlated r 2 0 77 but a large systematic bias is observed shell mg ca ratios are significantly elevated above values expected from observed and isotopic calcification temperatures in the saline subtropical gyres of both hemispheres this temperature independent shell mg ca ratio variability termed excess mg ca i s highly correlated with surface salinity r 2 0 77 and the observed salinity dependence 27 4 is much higher than indicated by culture studies 6 2 our coretop data are used to develop new atlantic basin temperature and salinity calibration equations that are accurate 1 1 c and 0 20 respectively precise r 2 0 82 and 0 81 respectively and verifiable using previously published data these results are valid for the relatively high salinities of the subtropical atlantic 35 5 37 3 we discover that inclusion of other published data from lower salinity regions b35 indicates little or no excess mg ca taken together these results point to a strongly non linear positive salinity effect on shell mg ca ratios that significantly affects the accuracy of sst and 18

clumped isotope signatures in modern brachiopod carbonate abstract we present a temperature to 47 relationship for naturally occurring modern brachiopods which was established using a suite of thirteen brachiopod specimens from twelve sampling localities that span a mean annual seawater temperature range of 0 8 to 29 0 c sample locations and depths were selected to maximize the range of temperatures covered by the calibration while minimizing the seasonal temperature variability impacting the samples linear least squares regression analysis yields the following relationship expressed using the ghosh et al 2006 reference frame 47 0 0478 0 0099 10 6 t 2 0 1164 0 1203 n 13 r 2 0 91 95 ci this equation lies within the 95 confidence interval of the original relationship determined using synthetic calcite ghosh et al 2006 but is in better agreement with the newly revised calibration of zaarur et al 2013 however despite this broad agreement our equation has a shallower slope than the equations for synthetic calcites and yields temperatures at the warm end of the calibration temperature range 47 0 640 that are as much as 3 1 c offset from those predicted using the equation of zaarur et al 2013 on the other hand our new equation has a steeper slope than the henkes et al 2013 equation for modern brachiopods and mollusks this finding is consistent with the hypothesis that differences in the protocols employed by laboratories that use different temperatures of phosphoric acid digestion cause the observed discrepancies between the 47 values reported by various laboratories

deciphering kinetic metabolic and environmental controls on stable isotope fractionations between seawater and the shell of terebratalia transversa brachiopoda this study presents carbon and oxygen stable isotope data obtained from high resolution sampling 500 m of the brachiopod terebratalia transversa from the san juan islands washington state usa the aim of this study is to unravel the respective effects of physiological and environmental controls on the stable isotopic composition of brachiopod shell calcite based on an sem study of the shell a three dimensional sampling was performed in order to investigate carbon and oxygen isotope variations along isochrons and ontogenetic transects the primary as well as the outer part of the secondary shell layer display large and variable isotopic offsets as high as 7 for 13c and 6 for 18o relative to expected equilibrium values the significant positive correlations between 18o and 13c values indicate that the isotopic compositions of these shell domains are mainly controlled by kinetic isotope fractionation effects the ontogenetic 13c and 18o variations can be used to establish a growth curve of the studied specimen whose age is estimated close to 8 years the extent of apparent o 18 disequilibrium observed in this study is about as large as any yet measured in any organism which makes this brachiopod an interesting and important case the carbon and oxygen isotope compositions increase from the outer towards the inner part of the secondary layer where they reach values of 0 0 8 and 0 8 to 0 2 respectively corresponding calculated temperatures are between 12 and 13 8 c and fall in the range of seawater temperatures recorded off the san juan islands 7 13 c these results suggest that the calcite fibres were secreted more and more slowly during the thickening of the shell throughout the animal s life finally approximating isotopic equilibrium this study illustrates that the stable isotopic composition of the modern brachiopod t transversa is predominantly influenced by kinetic fractionation and to a minor degree by metabolic effects except for the innermost part of the shell the measured isotope ratios do not reflect environmental conditions during shell precipitation it remains to be tested by comparable studies whether other modern brachiopod species or even fossil brachiopods reflect comparable fractionation effects these results point out the need for re examination of paleozoic oceanographic conditions

the rotation of the earth earth rotation studies are reviewed for the 1987 1990 time period it is noted that the emphasis in these studies has shifted from improvements in the observational techniques to interpreting and gaining greater understanding of the variations of the earth rotations there have been progressive improvements in the accuracy and the temporal resolution of earth rotation measurements

decadal sea surface temperature variability in the subtropical south pacific from 1726 to 1997 a d we present a 271 year record of sr ca variability in a coral from rarotonga in the south pacific gyre calibration with monthly sea surface temperature sst from satellite and ship measurements made in a grid measuring 1 degrees by 1 degrees over the period from 1981 to 1997 indicates that this sr ca record is an excellent proxy for sst comparison with sst from ship measurements made since 1950 in a grid measuring 5 degrees by 5 degrees also shows that the sr ca data accurately record decadal changes in sst the entire sr ca record back to 1726 shows a distinct pattern of decadal variability with repeated decadal and interdecadal sst regime shifts greater than 0 75 degrees c comparison with decadal climate variability in the north pacific as represented by the pacific decadal oscillation index 1900 1997 indicates that several of the largest decadal scale sst variations at rarotonga are coherent with sst regime shifts in the north pacific this hemispheric symmetry suggests that tropical forcing may be an important factor in at least some of the decadal variability observed in the pacific ocean

amplitude and timing of temperature and salinity variability in the subpolar north atlantic over the past 10 k y paired planktic foraminiferal 18 o and mg ca data reveal trends of increasing temperatures 3 c and salinities in the subpolar north atlantic over the course of the holocene which were punctuated by abrupt events the trends likely refl ect an insolation forced northward retreat of the boundary between polar and north atlantic subsurface waters the superimposed variability does not appear to be periodic but tends to recur within a broad millennial band the records provide convincing evidence of open ocean cooling nearly 2 c and freshening during the 8 2 ka event and suggest similar conditions at 9 3 ka however the two largest temperature oscillations in our record 2 c occurred during the past 4 k y suggesting a recent increase in temperature variability relative to the mid holocene perhaps in response to neoglaciation which began at about this time

seismogenesis in the stable continental interiors an appraisal based on two examples from india characteristics of two recent moderate earthquakes from india 1993 killari mw 6 1 and 1997 jabalpur mw 5 8 are presented in this paper to illustrate the influence of geologic and tectonic setting on the nature of seismicity in stable continental regions scrs the killari event which occurred in the middle of a cratonic region of low background seismicity long recurrence interval and poorly developed neotectonic features may be qualified as a common type of scr event this earthquake is also characterized by a shallow focal depth and a long sequence of aftershocks in contrast the jabalpur earthquake shows a spatial association with a well defined tectonic structure with significant background seismicity a remarkable feature of this earthquake is its deep focus not commonly observed in scr seismicity this event was associated with fewer aftershocks unlike most other scr earthquakes analogous events are found in other shield regions as well based on their general characteristics a broad classification of moderate scr earthquakes is attempted here two broad groups have been identified in this study 1 a set of deep focus earthquakes that are related to intracratonic paleorifts and 2 shallow focus earthquakes associated with discrete faults in the less deformed precambrian terrains a synthesis of earthquake data from different geologic environments will improve our understanding of the seismogenesis in the shield regions 1999 elsevier science b v all rights reserved

tectonic geomorphology of australia the australian continent is actively deforming in response to far field stresses generated by plate boundary interactions and buoyancy forces associated with mantle dynamics on the largest scale several 10 3 km the submergence of the northern continental shelf is driven by dynamic topography caused by mantle downwelling along the indo pacific subduction system and accentuated by a regionally elevated geoid the emergence of the southern shelf is attributed to the progressive movement of australia away from a dynamic topography low on the intermediate scale several 10 2 km low amplitude c 100 200 m long wavelength c 100 300 km topographic undulations are driven by 1 anomalous smaller scale upper mantle convection and or 2 lithospheric scale buckling associated with plate boundary tectonic forcing on the smallest scale 10 1 km fault related deformation driven by partitioning of far field stresses has modified surface topography at rates of up to c 170 m ma 21 generated more than 30 50 of the contemporary topographic relief between some of australia s highlands and adjacent piedmonts and exerted a first order control on long term 10 4 10 6 a bedrock erosion although australia is often regarded as tectonically and geomorphologically quiescent neogene to recent tectonically induced landscape evolution has occurred across the continent with geomor phological expressions ranging from mild to dramatic australia is one of the lowest flattest most arid and most slowly eroding continents on earth the average elevation of the continent is only c 330 m above sea level asl maximum local topographic relief is everywhere 1500 m defined by elevation ranges with 100 km radii and two thirds of the con tinent is semi arid to arid with the exception of localized upland areas in the flinders and mt lofty ranges and the eastern highlands bedrock

clumped isotope geochemistry the study of naturally occurring multiply substituted isotopologues clumped isotope geochemistry is concerned with the state of ordering of rare isotopes in natural materials that is it examines the extent to which rare isotopes d 13 c 15 n 18 o etc bond with or near each other rather than with the sea of light isotopes in which they swim abundances of isotopic clumps in natural materials are influenced by a wide variety of factors in most cases their concentrations approach within ca 1 relative the amount expected for a random distribution of isotopes deviations from this stochastic distribution result from enhanced thermodynamic stability of heavy isotope clumps slower kinetics of reactions requiring the breakage of bonds between heavy isotopes the mass dependence of diffusive and thermo gravitational fractionations mixing between components that differ from one another in bulk isotopic composition biochemical and photochemical fractionations that may reflect combinations of these simpler physical mechanisms and in some cases other processes we do not yet understand although clumped isotope geochemistry is a young field several seemingly promising applications have already emerged most importantly it appears that proportions of 13 c 18 o bonds in carbonate minerals are sensitive to their growth temperatures independent of bulk isotopic composition thus clumped isotope analysis of ancient carbonates can be used as a quantitative paleothermometer that requires no assumptions about the 18 o of waters from which carbonates grew this approach has been used to reconstruct marine temperatures across the phanerozoic reaching back to the silurian terrestrial ground temperatures across the cenozoic thermal histories of aqueously altered meteorites among other applications clumped isotope geochemistry is also placing new constraints on the atmospheric budget and stratospheric photochemistry of co 2 and should be capable of placing analogous new constraints on the budgets of other atmospheric gases finally this field could be extended to encompass sulfates volatile hydrocarbons organic moieties and other materials

calibration and application of the clumped isotope thermometer to foraminifera for high resolution climate reconstructions the reconstruction of past ocean temperatures is fundamental to the study of past climate changes therefore considerable effort has been invested in developing proxies for seawater temperatures one of the most recent and promising new proxy is carbonate clumped isotope thermometry in particular because it is based on thermodynamic equilibrium and not on biogeochemical proxies here we present a new calibration of the clumped isotope thermometer to foraminifera based on seven species of planktic and benthic foraminifera spanning a growth temperature range of 2 28 c we used a newly developed technique for the measurements of small samples to improve the applicability of this method to paleoceanography our data have a comparable precision 0 005 0 013 and confirm previous calibration studies based on biogenic and inorganic calcite we discuss possible sources of uncertainty such as over underestimation of the calcification temperatures species specific vital effects ph variations between the seawater and the vacuole water of the species and possible kinetic effects on the clumped isotope calibration to validate our calibration study and test the applicability of our measuring technique to paleoclimate and paleoceanographic studies we measured the isotope composition of globigerinoides ruber white at high resolution in a sediment core covering the last 700 years in the gulf of taranto mediterranean sea the results show that it is necessary to average a relatively large number of analyses to achieve a consistent temperature signal for the detection of small sea surface temperature changes although with the current analytical system clumped isotope thermometry is only applicable to the analysis of relatively large sst changes in marine sediments further technical improvements may make this a very powerful technique for paleoceanographic studies

conductivity response to intraplate deformation evidence for metamorphic devolatilization and crustal scale fluid focusing we present two dimensional electrical resistivity models of two 40km magnetotelluric mt profiles across the frome embayment to the east of the northern flinders ranges south australia the lower crust shows low resistivity of 10 m at around 30km depth the middle crust is dominated by resistive 1000 m basement rocks underlying the flinders ranges adjacent to the ranges conductive lower crust is connected to vertical zones of higher conductivity extending to just below the brittle ductile transition bdt at 10 km depth the conductive zones narrow in the brittle upper crust and dip at roughly 45 beneath the surface zones of enhanced conductivity coincide with higher strain due to topographic loading and sparse seismicity we propose that fluids are generated through neotectonic metamorphic devolatilization low resistivity zones display areas of fluid pathways along either pre existing faults or an effect of crustal compression leading to metamorphic fluid generation the lower crustal conductors are responding to long wavelength flexure induced strain while the upper crustal conductors are responding to short wavelength faulting in the brittle regime mt is a useful tool for imaging crustal strain in response to far field stresses in an intraplate setting and provides important constraints for geodynamic modeling and crustal rheology

earthquake environmental effects produced by the mw 6 1 20th may 2016 petermann earthquake australia abstract earthquake environmental effects eees identified in the source region of the 20th may 2016 intraplate moment magnitude mw 6 1 petermann earthquake in central australia are described and classified using the environmental seismic intensity esi 07 scale eees include surface rupture ground fissures and cracks vegetation damage rockfalls and displaced jumped bedrock fragments the maximum esi intensity derived from eees is x consistent with previous observations from some moderate mw crustal earthquakes maximum esi isoseismals correlate with the location of the surface rupture rather than epicentre area due to the dipping geometry of the reverse source fault esi isoseismals encompass a larger area of the hanging wall than the footwall indicating stronger ground motions on the hanging wall due to increased proximity to the rupture source and ground motion amplification effects the maximum areal extent of secondary seismic shaking induced eees 300 km2 is significantly smaller than expected using the published esi 07 scale approx 5000 km2 this relates to the low topographic relief and relatively homogeneous bedrock geology of the study region which i reduced the potential for site response amplification of strong ground motions and ii reduced the susceptibility of the landscape to eee such as landsliding and liquefaction erosional degradation of the observed eee features and decreasing confidence with which they can be uniquely attributed to a seismic origin with increasing time since the earthquake highlight challenges in using many of the natural features observed herein to characterise the locations and attributes of paleo earthquakes

paleoclimate reconstruction using carbonate clumped isotope thermometry carbonate clumped isotope thermometry is a relatively new paleotemperature proxy based on measurements of the degree of ordering of 13 c and 18 o into bonds with each other making the 13 c 18 o 16 o 2 2 ion group in lattices of carbonate minerals this technique has several unusual properties that complement existing methods of paleoclimate reconstruction most importantly it is based on a homogeneous isotope exchange equilibrium and thus constrains temperature independent of the isotopic composition of waters from which carbonates grew this method also appears to be generally insensitive to vital effects that compromise many other paleothermometers based on the chemical properties of biominerals or organic matter at least for those organisms that have been subjected to systematic study to date corals and foraminifera however discrepancies among some calibrations particularly at low temperatures may point toward the existence of vital effects in mollusks and other organisms this review discusses the principles and calibrations of the technique its uses in combination with conventional stable isotope measurements to constrain the 18 o of past waters preservation of paleotemperatures in ancient materials as well as current problems in our understanding of calibrations and interlaboratory data comparisons

one hundred years of earthquake recording in australia abstract a comprehensive new catalog of australian earthquakes has been compiled and used to review the seismicity of australia the catalog contains 27 000 events of which 17 000 are considered to be mainshocks the catalog is complete for all australian events with a magnitude greater than m l 5 5 since 1910 m l 5 since 1960 m l 4 since 1970 and m l 3 5 since 1980 it is complete for events in southern australia above m l 3 5 since 1965 and m l 2 since 1980 before the development of local magnitude scales for australia around 1990 the richter magnitude scale was generally used at 600 km a typical hypocentral distance for much of australia the richter formula overestimates magnitude by around 0 5 units thus the results in the catalogs before and after the early 1990s are potentially discrepant most well located australian earthquakes are in the southern areas of the continent where the seismometer density is greatest in general the location uncertainty of australian earthquakes is high only 60 of events are located with an uncertainty of 10 km or less this percentage is smaller for earthquakes before 1980 and before 1960 very few events were located to within 10 km the hypocentral depths of australian earthquakes range mostly between 8 and 18 km except for the southwest corner of the continent where they are typically shallower than 5 km the seismicity in some areas of australia has been steady for at least 100 yr including the southeast corner the flinders ranges and the northwest corner in contrast seismicity in the southwest corner jumped by at least a factor of 6 in the 1940s and has been steady since then much of the rest of australia is characterized by episodic seismicity these episodes begin with a period of high activity lasting 1 10 yr and they are normally associated with a large m 6 earthquake following the large earthquake there is often a period of moderate activity lasting from a few years to several decades before and after each episode is a quiescent period of low activity lasting 0 1 10 ka during which the seismicity is more than an order of magnitude lower than during the period of high activity frequency magnitude relations were calculated using events since 1970 from the new catalog gutenberg richter a and b values were calculated on an 85 km grid and maps of the probability of an earthquake of m 4 9 occurring per year were derived these results are very similar to the global seismic hazard assessment program gshap map for australia the results were used to define four large 20 000 km 2 seismogenic zones fig 1 there are also several other small zones some of which appear to reflect recent episodes while others appear to be long lived the expected number of earthquakes m 5 and m 6 strain rate and deformation rate is given for the four large zones the remainder of australia and the whole australian continent the combined estimates of strain using seismic global positioning system gps and satellite laser ranging slr data suggest east west compressive deformation across southern australia of 0 65 2 0 mm per year likely to be in the 0 5 1 0 mm per year range

an updated global earthquake catalogue for stable continental regions reassessing the correlation with ancient rifts summary we present an updated global earthquake catalogue for stable continental regions scrs i e intraplate earthquakes that is available on the internet our database contains information on location magnitude seismic moment and focal mechanisms for over 1300 m moment magnitude 4 5 historic and instrumentally recorded crustal events using this updated earthquake database in combination with a recently published global catalogue of rifts we assess the correlation of intraplate seismicity with ancient rifts on a global scale each tectonic event is put into one of five categories based on location i interior rifts taphrogens ii rifted continental margins iii non rifted crust iv possible interior rifts and v possible rifted margins we find that approximately 27 per cent of all events are classified as interior rifts i 25 per cent are rifted continental margins ii 36 per cent are within non rifted crust iii and 12 per cent iv and v remain uncertain thus over half 52 per cent of all events are associated with rifted crust although within the continental interiors i e away from continental margins non rifted crust has experienced more earthquakes than interior rifts no major change in distribution is found if only large m 6 0 earthquakes are considered the largest events m 7 0 however have occurred predominantly within rifts 50 per cent and continental margins 43 per cent intraplate seismicity is not distributed evenly instead several zones of concentrated seismicity seem to exist this is especially true for interior rifts taphrogens where a total of only 12 regions are responsible for 74 per cent of all events and as much as 98 per cent of all seismic moment released in that category of the four rifts taphrogens that have experienced the largest earthquakes seismicity within the kutch rift india and the east china rift system may be controlled by diffuse plate boundary deformation more than by the presence of the ancient rifts themselves the st lawrence depression canada besides being an ancient rift is also the site of a major collisional suture thus only at the reelfoot rift new madrid seismic zone nmsz usa is the presence of features associated with rifting itself the sole candidate for causing seismicity our results suggest that on a global scale the correlation of seismicity within scrs and ancient rifts has been overestimated in the past because the majority of models used to explain intraplate seismicity have focused on seismicity within rifts we conclude that a shift in attention more towards non rifted as well as rifted crust is in order

stress perturbation associated with the amazonas and other ancient continental rifts the state of stress in the vicinity of old continental rifts is examined to investigate the possibility that crustal structure associated with ancient rifts specifically a dense rift pillow in the lower crust may modify substantially the regional stress field both shallow 2 0 2 6 km depth breakout data and deep 20 45 km depth crustal earthquake focal mechanisms indicate a n to nne maximum horizontal compression in the vicinity of the paleozoic amazonas rift in central brazil this compressive stress direction is nearly perpendicular to the rift structure and represents a 75 rotation relative to a regional e w compressive stress direction in the south american plate elastic two dimensional finite element models of the density structure associated with the amazonas rift as inferred from independent gravity modeling indicate that elastic support of this dense feature would generate horizontal rift normal compressional stresses between 60 and 120 mpa with values of 80 100 mpa probably most representative of the overall structure the observed 75 stress rotation constrains the ratio of the regional horizontal stress difference to the rift normal compressive stress to be between 0 25 and 1 0 suggesting that this rift normal stress may be from 1 to 4 times larger than the regional horizontal stress difference a general expression for the modification of the normalized local horizontal shear stress relative to the regional horizontal shear stress shows that the same ratio of the rift normal compression relative to the regional horizontal stress difference which controls the amount of stress rotation also determines whether the superposed stress increases or decreases the local maximum horizontal shear stress the potential for fault reactivation of ancient continental rifts in general is analyzed considering both the local stress rotation and modification of horizontal shear stress for both thrust and strike slip stress regimes in the amazonas rift case because the observed stress rotation only weakly constrains the ratio of the regional horizontal stress difference to the rift normal compression to be between 0 25 and 1 0 our analysis is inconclusive because the resultant normalized horizontal shear stress may be reduced for ratios 0 5 or enhanced for ratios 0 5 additional information is needed on all three stress magnitudes to predict how a change in horizontal shear stress directly influences the likelihood of faulting in the thrust faulting stress regime in the vicinity of the amazonas rift a rift normal stress associated with the seismically active new madrid ancient rift may be sufficient to rotate the horizontal stress field consistent with strike slip faults parallel to the axis of the rift although this results in a 20 40 reduction in the local horizontal shear stress within the seismic zone sparse stress data in the vicinity of the seismically quiescent midcontinent rift of the central united states suggest a stress state similar to that of new madrid with the local horizontal shear stress potentially reduced by as much as 60 thus the markedly different levels of seismic activity associated with these two subparallel ancient rifts is probably due to other factors than stress perturbations due to dense rift pillows the modeling and analysis here demonstrate that rift normal compressive stresses are a significant source of stress acting on the lithosphere and that in some cases may be a contributing factor to the association of intraplate seismicity with old zones of continental extension

stable isotopes in late pennsylvanian brachiopods from the united states implications for carboniferous paleoceanography stable isotopic analyses have been performed on nearly 500 nonluminescent brachiopod shells from kansas new mexico and texas to evaluate temporal and geographic variability in the carbon and oxygen isotopic record for late pennsylvanian time brachiopod specimens were collected from missourian and virgilian shales and examined in thin section for preservation of microstructure and absence of cathodoluminescence as a primary test for shell preservation regional variations are observed in the 18o and 13c values of nonluminescent brachiopod shells of the same genera average 18o values for the three genera analyzed crurithyris composita and neospirifer are highest in kansas 1 9 intermediate in texas 2 3 and lowest in new mexico 3 6 vital effect on the 18o of these genera appears minimal 18o data and other evidence suggest warmer temperatures for the shallow new mexico localities and slightly higher salinity for the kansas sea relative to the texas sea the 13c values of composita average about 1 higher than those of co occurring crurithyris and neospirifer suggesting microhabitat differences or vital effects preservation of this species effect argues for preservation of original 13c values average 13c values are highest in texas intermediate in kansas and lowest in new mexico although these values range from 2 6 to 4 9 for individual genera the regional variation in 13c averages less than 1 data for nonluminescent brachiopods and marine cements reveal a mid carboniferous 13c increase of 2 in paleotethyan sea water this increase is not seen in samples from the north american epicontinental seas which opened to the panthalassa ocean this regional difference in 13c appears to be due to changes in ocean circulation associated with the closing of the equatorial seaway and formation of pangea

direct inversion of earthquake first motions for both the stress tensor and focal mechanisms and application to southern california in inverting populations of focal mechanisms to estimate stress misfits may arise owing to 1 errors in determining the fault plane solutions and 2 real variations in the state of stress among a number of techniques that invert for stress most effectively regard only the latter and only indirectly describe the former through statistical means so make it difficult to differentiate real stress variations from noisy data ambiguity arises because realistic methods for determining focal mechanisms for small earthquakes depend on p wave first motions in a highly nonlinear manner which is difficult to propagate into stress inversions to address these issues we present a new method for constraining stress tensors in which first motion observations are directly inverted for stress without assuming that focal mechanisms are known the technique produces estimates of four stress parameters a suite of focal mechanisms consistent with both the stress tensor and the first motions and estimates of the uncertainty in stress it also provides a natural test of the stress homogeneity hypothesis and a means to identify those earthquakes whose first motions are not consistent with a homogeneous stress tensor when tested against artificial data the method correctly recovers input stresses and yields uncertainties that depend upon both data distribution and reliability of first motion picks as expected utilizing first motions from the southern california catalog the method is applied to several clusters and aftershock sets from 1981 to 1992 typical uncertainties in stress orientation exceed 20 30 at the 95 confidence level resulting from 5 mispick rates typical of even the cleanest data these uncertainties exceed some previous estimates for similar populations presumably because they account for focal mechanism un certainties and perhaps indicating that some previously reported stress variations are not statistically significant most populations are found to be internally consistent with a homogeneous stress field the most significant exceptions being aftershock sequences of some major earthquakes in at least one case the 1992 landers sequence aftershocks at the north end of the rupture zone appear to reflect exceedingly heterogeneous stresses overall the method provides a useful and robust approach for evaluating stress constraints provided by p wave first motions

temperature and carbonate ion effects on mg ca and sr ca ratios in benthic foraminifera aragonitic species hoeglundina elegans received 16 march 2005 revised 20 june 2005 accepted 3 november 2005 published 21 february 2006 1 core top samples from atlantic little bahama banks lbb and pacific hawaii and indonesia depth transects have been analyzed in order to assess the influence of bottom water temperature bwt and aragonite saturation levels on mg ca and sr ca ratios in the aragonitic benthic foraminifer hoeglundina elegans both the mg ca and sr ca ratios in h elegans tests show a general decrease with increasing water depth although at each site the decreasing trends are consistent with the in situ temperature profile mg ca and sr ca ratios in lbb are substantially higher than in indonesia and hawaii at comparable water depths with a greater difference observed with increasing water depth because we find no significant difference between results obtained on live and dead specimens we propose that these differences are due to primary effects on the metal uptake during test formation evaluation of the water column properties at each site suggests that in situ co3 ion concentrations play an important role in determining the h elegans mg ca and sr ca ratios the co3 ion effect is limited however only to aragonite saturation levels dco3 aragonite below 15 mmol kg 1 above this level temperature exerts a dominant effect accordingly we propose that mg ca and sr ca in h elegans tests can be used to reconstruct thermocline temperatures only in waters oversaturated with respect to the mineral aragonite using the following relationships mg ca 0 034 0 002 bwt 0 96 0 03 and sr ca 0 060 0 002 bwt 1 53 0 03 for dco3 aragonite 1 5mmol kg 1 the standard error associated with these equations is about 1 1 c reconstruction of deeper water temperatures is complicated because in undersaturated waters changes in mg ca and sr ca ratios reflect a combination of changes in co3 and bwt overall we find that sr ca rather than mg ca in h elegans may be a more accurate proxy for reconstructing paleotemperatures

length of day variations caused by el nino southern oscillation and quasi biennial oscillation two prominent interannual atmospheric fluctuations the el nino southern oscillation in the troposphere ocean system and the quasi biennial oscillation in the equatorial stratosphere account for most of the observed interannual length of day lod variation from 1964 through 1987 with a relative contribution of about 2 to 1 thus the atmosphere lod connection extends from seasonal and shorter periods to interannual periods up to about 10 years

time variable gravity signal of an anomalous redistribution of water mass in the extratropic pacific during 1998 2002 1 cox and chao 2002 reported the detection of a large anomaly in the time series of earth s dynamic oblateness j2 the lowest degree gravity spatial harmonic in the form of a positive jump since 1998 overshadowing the decreasing secular trend in j2 caused primarily by the postglacial rebound pgr here we report that recent data show that j2 has been rapidly returning toward normal with pgr considered since early 2001 in search of the geophysical and climatic causes for this 1998 2002 j2 anomaly we report an oceanographic event that took place in the extratropic north and south pacific basins that was found to match remarkably well with the time evolution of the anomaly we examine the leading nonseasonal extratropic pacific empirical orthogonal function principal component modes in the sea surface height ssh data from topex poseidon sea surface temperature sst data from the national center for environmental predictions and output fields of the estimating the circulation and the climate of the ocean ecco ocean general circulation model ogcm including ocean bottom pressure obp and temperature and salinity profiles the phenomenon appears to be part of the pacific decadal oscillation and temporal correlations are made however quantitatively the obp field of the ecco model predicts a j2 anomaly that is smaller in magnitude than the observed by a factor of about 3 we discuss various possibilities for reconciling this discrepancy in terms of inadequacies of present ogcms and considering other geophysical contributions a complete resolution of the j2 enigma awaits further studies

earth s spin and volcanic eruptions evidence for mutual cause and effect interactions the angular velocity of earth s rotation shows decadal oscillations due to the lunisolar gravitational torque as well as inter or intra annual changes arising from the angular momentum exchange between the atmosphere and the solid earth the energies involved in the length of day lod variations may affect the crustal deformation rate and seismic energy release on a global scale we found significant correlation between the occurrences of major volcanic eruptions and the lod pattern since ad 1750 on a multiyear scale eruption frequency worldwide increases with lod changes moreover the injection of sulphur gases into the atmosphere during major eruptions is accompanied by significant inter annual lod variations this provides evidence of complex mutual cause and effect interactions stress changes induced by multiyear variations in earth s spin may affect climactic volcanic activity also the atmosphere s dynamic response to volcanic plumes may result in global changes of wind circulation and climate with consequent lod variations

a secondary ionization mass spectrometry calibration of cibicidoides pachyderma mg ca with temperature an evaluation of c pachyderma mg ca using a new suite of warm water multicores from the florida straits shows that the slope of mg ca with temperature is shallower than previously thought using secondary ionization mass spectrometry we have documented that the distribution of magnesium within the polished walls of foraminiferal tests is gaussian suggesting that the mg ca in these samples is not affected by the addition of a secondary high magnesium calcite in the walls the mg ca within a typical c pachyderma test varies by about 20 1 100 and the variability increases slightly in tests with higher mg ca the regression of c pachyderma mg ca with temperature has a slope of 0 13 0 05 mmol mol 1 per c indistinguishable from the slope observed in inductively coupled plasma mass spectrometry measurements from a different subset of the same multicores but about one half the slope of previously published calibrations the largest differences between the calibrations comes at the warm water end of the regression where previously published c pachyderma mg ca values from little bahama bank are at least 3 mmol mol 1 higher than observed in these new cores the reasons for this difference are not fully known but are most likely related to diagenesis at little bahama bank

tex86 and stable δ18o paleothermometry of early cretaceous sediments implications for belemnite ecology and paleotemperature proxy application abstract recent studies have cast doubt on the unadjusted usage of jurassic and cretaceous 18 o paleotemperature data derived from belemnites since the latter data often reflect cooler paleotemperature estimates than would be expected in this study we address this problem by analysing rocks of barremian to early aptian age from two outcrops in northern germany using tex 86 paleothermometry along with 142 belemnite guards studied for their stable isotope 13 c 18 o and trace element composition magnesium strontium iron and manganese both tex 86 and 18 o bel indicate very warm water temperatures for a distinctive black shale sequence of late early barremian age hauptblatterton with temperatures of up to 29 c and 23 c respectively we observe a constant offset of tex 86 temperatures versus the 4 to 5 c cooler 18 o belemnite signal for this interval the late barremian sequence shows an increase of the 18 o bel values from 1 to 0 reflecting temperatures around 16 to 12 c while the contemporaneous tex 86 temperatures vary between 26 and 32 c the common occurrence of belemnites in the anoxic sediments of the early barremian implies however clearly a nektonic way of life similar to that of recent teuthids rather than a nektobenthic one like sepia this in turn suggests that the belemnites investigated here genera praeoxyteuthis aulacoteuthis oxyteuthis and neohibolites were active swimmers which inhabited a deeper habitat below the thermocline in an epicontinental sea of perhaps 100 to 250 m water depth the offset of the tex 86 and 18 o bel data is therefore interpreted to reflect temperature signals from two different depth habitats i e the tex 86 is selectively derived from warm sea surface waters and the belemnites likely occupied deeper and cooler waters with relative increasing salinities in the late barremian this study stresses the importance that the taxonomy paleobiology and ecology of the belemnite taxa genera species used for paleotemperature reconstructions must be considered before the 18 o bel signal can be further interpreted the variation of the 18 o signature gained from one belemnite population of 22 specimens by 1 1 suggests that the 18 o data of individual belemnites should be used with caution for reconstructing long termed paleotemperature trends

localization of intraplate deformation through fluid assisted faulting in the lower crust the flinders ranges south australia abstract in this paper we present a hypothesis for localized intraplate deformation in the continental crust of south central australia that involves fluid assisted reactivation of faults in the mid to lower crust using data from a temporary seismometer deployment in the flinders ranges we show that earthquakes relocated in a 3d velocity model cluster in elongated low vp vs anomalies that extend to depths exceeding 20 km and are aligned with the axis of the flinders ranges in the northern flinders ranges these low vp vs anomalies can be interpreted as fractured neoproterozoic to cambrian sediments that separate two cratonic blocks the gawler craton to the west and the curnamona province in the east previous studies of helium isotopes in springs to the north of the area provide evidence of mantle derived fluids that may influence faulting at depth our focal mechanism and stress inversion results show a regionally compressive stress field that provides no evidence for stress concentration we also argue that mechanisms for localized faulting such as thermal weakening and isostatic rebound also fail to account for the occurrence of earthquakes at mid to lower crustal depth in this area of high heat flow and that the focused seismicity can only be explained by high pore fluid pressure in the lower crust

comparison of earth rotation excitation in data constrained and unconstrained atmosphere models changes in earth rotation are strongly related to fluctuations in the angular momentum of the atmosphere and therefore contain integral information about the atmospheric state here we investigate the extent to which observed earth rotation parameters can be used to evaluate and potentially constrain atmospheric models this is done by comparing the atmospheric excitation function computed geophysically from reanalysis data and climate model simulations constrained only by boundary forcings to the excitation functions inferred from geodetic monitoring data model differences are assessed for subseasonal variations the annual and semiannual cycles interannual variations and decadal scale variations observed length of day anomalies on the subseasonal timescale are simulated well by the simulations that are constrained by meteorological data only whereas the annual cycle in length of day is simulated well by all models interannual length of day variations are captured fairly well as long as a model has realistic time varying sst boundary conditions and qbo forcing observations of polar motion are most clearly relatable to atmospheric dynamics on subseasonal to annual timescales though angular momentum budget closure is difficult to achieve even for data constrained atmospheric simulations closure of the angular momentum budget on decadal timescales is difficult and strongly dependent on estimates of angular momentum fluctuations due to core mantle interactions in the solid earth key points earth rotation parameters contain global information about atmospheric dynamics length of day observations can constrain modeled winds in tropical regions polar motion observations can constrain modeled mass movements in midlatitudes

cause and evolution of intraplate orogeny in australia abstractintraplate orogeny remains an enigmatic process in terms of plate tectonics regional continental stress elds agree well with stress orientations predicted by the main forces driv ing and resisting plate motion however regional continental stress elds fail to explain major localized compressive plate deformation in continental interiors far away from plate bound aries global or plate wide intraplate stress models typically assume a laterally homogeneous plate rheology and are con ned to modeling the present without addressing the antiquity of the current stress eld an understanding of intraplate stress and deformation requires the linking of spatial variations in continental rheology with time dependent plate geometry and driving forces here we demonstrate how the complex interplay between juxtaposed weak and strong geological provinces and changes in far eld plate boundary forces has caused intra plate orogenesis and tectonic reactivation in southeastern australia during the tertiary our ndings are contrary to the opinion that continental interiors are insensitive to compression at plate margins and help to explain the mechanisms causing intraplate orogenesis keywords

a bayesian approach to estimating tectonic stress from seismological data summary earthquakes are conspicuous manifestations of tectonic stress but the non linear relationships between the stresses acting on a fault plane its frictional slip and the ensuing seismic radiation are such that a single earthquake by itself provides little information about the ambient state of stress moreover observational uncertainties and inherent ambiguities in the nodal planes of earthquake focal mechanisms preclude straightforward inferences about stress being drawn on the basis of individual focal mechanism observations however by assuming that each earthquake in a small volume of the crust represents a single uniform state of stress the combined constraints imposed on that stress by a suite of focal mechanism observations can be estimated here we outline a probabilistic bayesian technique for estimating tectonic stress directions from primary seismological observations the bayesian formulation combines a geologically motivated prior model of the state of stress with an observation model that implements the physical relationship between the stresses acting on a fault and the resultant seismological observation we show our bayesian formulation to be equivalent to a well known analytical solution for a single errorless focal mechanism observation the new approach has the distinct advantage however of including 1 multiple earthquakes 2 fault plane ambiguities 3 observational errors and 4 any prior knowledge of the stress field our approach while computationally demanding in some cases is intended to yield reliable tectonic stress estimates that can be confidently compared with other tectonic parameters such as seismic anisotropy and geodetic strain rate observations and used to investigate spatial and temporal variations in stress associated with major faults and coseismic stress perturbations

a note on fault reactivation reactivation of existing faults whose normal lies in the 1 3 plane of a stress field with effective principal compressive stresses 1 2 3 is considered for the simplest frictional failure criterion n n p where and n are respectively the shear and normal stresses to the existing fault p is the fluid pressure and is the static friction for a plane oriented at to 1 the stress ratio for reactivation is 1 3 1 cot 1 tan this ratio has a minimum positive value at the optimum angle for reactivation given by 12tan 1 1 but reaches infinity when 2 beyond which 3 0 is a necessary condition for reactivation an important consequence is that for typical rock friction coefficients it is unlikely that normal faults will be reactivated as high angle reverse faults or thrusts as low angle normal faults unless the effective least principal stress is tensile

rupture process of the 26 january 2001 mw 7 6 bhuj india earthquake from teleseismic broadband data we investigate the rupture process of the 26 january 2001 bhuj india m w 7 6 earthquake through inversion of teleseismic broadband body waves this earthquake ranks as one of the most important recent events due to its occurrence within a stable continental interior where such events are rare the bhuj earthquake occurred on a moderately dipping blind thrust fault within an ancient failed rift about 70 of the seismic moment released in the earthquake was confined to a very small area 375 km2 surrounding the hypocenter and at depths below 12 km the static stress drop of the bhuj earthquake is anomalously high 20 mpa the source time history of the event indicates very rapid onset to the moment release and most likely high slip velocities within the deep asperity this suggests that some of the damage near the epicenter may have been caused by anomalously high frequency ground motions the teleseismic data also indicate the presence of a second area of large slip in the shallow part of the bhuj fault although the depth extent of this shallow large slip area is not resolved comparisons of the predicted ground motions with observed intensities suggest that substantial slip occurred in the upper 10 km of the fault in order to explain the distribution of high intensities to the west and northwest of the fault the upper surface layers near the bhuj fault consist of unconsolidated low rigidity sediments and alluvium the upper 10 km of the bhuj fault may therefore be in a conditionally stable region that normally deforms through aseismic creep and can sustain seismic rupture only when dynamically stressed by rupture of the high strength deep asperity we suggest that this deep asperity may be related to a lithologic anomaly of ultramafic composition

lithospheric reworking at the proterozoic phanerozoic transition of australia imaged using auslamp magnetotelluric data abstract seventy four stations from the long period australia wide auslamp australian lithospheric architecture magnetotelluric project dataset were used to image the electrical resistivity beneath the neoproterozoic ikara flinders ranges and adjacent palaeo mesoproterozoic curnamona province results from 3d inversions using modem software show a relatively resistive ikara flinders ranges with two parallel arcuate conductors at 20 to 80 km depth in the nackara arc there is a good correlation of diamondiferous kimberlites occurring over conductors which we interpret as evidence for these conductors to be residing on large lithospheric structures that have been conduits for partial melt and volatile movement in the jurassic the curnamona province is remarkably conductive for a region that is thought to have a cratonic core with delamerian reworking only at its edges the conductor covers most of the province at depths of 10 40 km and its presence at lower crustal depths suggests that conductive sediments can not entirely explain it fluids associated with subduction may have pervasively modified the crust in the past resulting in an enrichment of carbon enhancing the conductivity additionally we conclude that the notion of a single continuous arcuate flinders conductivity anomaly is unlikely and that the anomalous response observed is instead a result of the combined response of three separate anomalies the curnamona province conductor and the two nackara arc conductors

coupling of long oceanic waves in the pacific ocean and the rotating elastic earth during the 1986 1987 el nino we investigate interannual coupling between the rotating elastic earth and the ocean during the 1986 1987 el nino we find the e w component of the ground tilt at the esashi earth tides station up toward the east about 50 milliarc seconds mas a rise of sea level about 5 cm at chichijima and oshima in the northwestern pacific ocean and an increase of 1 cm in the very long baseline interferometry vlbi baseline distance between kashima japan and kauai hawaiian islands as well as the residual length of day lod changes of 50 s during the 1986 1987 el nino the residual lod is derived from elimination of changes in atmospheric angular momentum our discussions are based on the coupling between torsional motions of the elastic earth and reflection of the eastward traveling equatorial kelvin waves at the eastern boundary of the pacific ocean these equatorial waves exchange the momentum and the axial and zonal component of vorticity with the elastic earth during the 1986 1987 el nino reflection of the kelvin wave is expected to excite torsional motions and to couple with differential zonal rotation in the elastic earth and to generate anomalies of 1 6 s in lod the differential zonal rotation due to the torsional motion can produce the same order of the magnitude of changes in the vlbi baseline distance between kashima and kauai variations of the e w component of the tilt cannot be explained by torsional motion we infer that the midlatitude rossby waves are generated in the central pacific ocean this conclusion is consistent with sea level changes at chichijima and oshima and changes of the tilt at esashi

the origins of the intraplate stress field in continental australia the ridge push force acting on the indo australian plate exerts a significant torque 8 5 1025n m about a pole at 30 3 n 34 5 e the angular difference between this torque pole and the observed pole of rotation for the plate 19 2 n 35 6 e is less than 12 and suggests that the ridge push force plays an important role in the dynamics of the indo australian plate we have used an elastic finite element analysis to study the predicted intraplate stress field in continental australia for four models which employ different boundary conditions to balance the ridge push torque acting on the plate the modeling indicates that a number of important features of the observed stress field within the australian continent can be explained in terms of balancing the ridge push torque with resistance imposed along the himalaya papua new guinea and new zealand collisional boundaries segments these features include n s to ne sw oriented compression in the northern australia and e w oriented compression in southern australia our analysis also shows that subduction processes along the northern and eastern boundaries provide only second order controls on the intraplate stress field in continental australia

recent mantle degassing recorded by carbonic spring deposits along sinistral strike slip faults south central australia abstract the interior of the australian continent shows evidence for late quaternary to recent fault controlled mantle 3 he and co 2 degassing a series of interconnected nw striking sinistral faults the norwest fault zone nfz in south central australia are associated with travertine mounds the latter show a regular spacing of 50 70 km u series ages on 26 samples range from 354 7 to 1 19 0 02 ka 2 errors and suggest a clustering every 3 4 ka since 26 ka geochemical data demonstrate a remarkable mantle to groundwater connection isotopic data indicate that the groundwater is circulating to depths 3 km and interacting with neoproterozoic cambrian basement and mantle volatiles 3 he 4 he isotope ratios show that the he comes in part from the mantle this demonstrates that the nfz cuts through the entire crust and provides pathways for mantle degassing scaling relationships suggest that the series of sinistral faults that make up the nfz are interconnected at depths and have a significant strike length of 60 70 km or more the nfz occurs where a major compositional boundary and a significant heat flow anomaly occurs and a major step in lithospheric thickness has been mapped we discuss a tectonic model in which recent stress field heat flow and lithospheric structure in central australia reactivated a set of steeply dipping neoproterozoic faults which may now be growing into a crustal lithospheric scale structure

stressing of the new madrid seismic zone by a lower crust detachment fault a new mechanical model for the cause of the new madrid seismic zone in the central united states is analyzed the model contains a subhorizontal detachment fault which is assumed to be near the domed top surface of locally thickened anomalous lower crust rift pillow regional horizontal compression induces slip on the fault and the slip creates a stress concentration in the upper crust above the rift pillow dome in the coseismic stage of the model earthquake cycle where the three largest magnitude 7 8 earthquakes in 1811 1812 are represented by a single model mainshock on a vertical northeast trending fault the model mainshock has a moment equivalent to a magnitude 8 event during the interseismic stage corresponding to the present time slip on the detachment fault exerts a right lateral shear stress on the locked vertical fault whose failure produces the model mainshock the sense of shear is generally consistent with the overall sense of slip of 1811 1812 and later earthquakes predicted rates of horizontal strain at the ground surface are about 10 7 year 1 and are comparable to some observed rates the model implies that rift pillow geometry is a significant influence on the maximum possible earthquake magnitude

environmental and physiological influences on isotopic and elemental compositions of brachiopod shell calcite implications for the isotopic evolution of paleozoic oceans abstract brachiopods from the demissa bed middle devonian hamilton group biologically regulated the incorporation of mg sr and na into their shell calcite significant taxonomic differences in the elemental contents of three species athyris spiriferoides mediospirifer audacula and mucrospirifer mucronatus may be related to differences in calcification processes in contrast no significant difference or vital effects were observed between the isotopic values of mediospirifer audacula and athyris spiriferoides from erie 18o 0 03 p 0 949 13c 0 76 p 0 083 and genessee counties 18o 0 39 p 0 471 13c 0 06 p 0 854 this suggests that these brachiopods did not exert a biological control over their isotopic compositions and that their shell calcites reflect ambient physicochemical conditions isotopic compositions in unaltered shell calcites of brachiopods from genessee county which was close to the basin depocentre are heavy for carbon 13c x 5 01 pdb and oxygen 18o x 2 85 pdb compared to the species sampled at the basin s edge erie county 13c x 2 79 pdb 18o x 3 83 pdb there is a significant separation in isotopic values between the deeper and shallower water brachiopods of the basin 18o 0 98 p 0 0005 13c 2 22 p 0 0005 the 18o variation suggests a temperature salinity change with water depth whereas the change in 13c composition probably records an enrichment depletion of organic matter with water depth this observation has significant implications for paleozoic ocean isotopic evolution studies because many global changes in marine 18o and 13c are based on isotopic shifts of similar magnitude