sources sinks and storage of river sediment in the atlantic drainage of the united states the history of sediment and its movement in the atlantic drainage demonstrate some of the difficulties of modeling sediment on a river basin scale soil erosion was accelerated by a factor of at least 10 when european settlers cleared forests and planted crops although increasing soil conservation practice and decreasing crop farming have since reduced the rates of erosion large quantities of eroded material are still stored on hillslopes and in stream valleys where they continue to augment the sediment loads of the rivers the sediment from this episode of erosion that is largely past can be expected to emerge from storage for many decades and perhaps even several centuries to come the reservoirs that have been built on many of the major rivers trap significant portions of the moving sediment which in some places may be remobilized by large floods essentially all the river sediment that reaches the atlantic coastal zone is trapped in estuaries and coastal marshlands probably less than 5 is deposi

timing trace and origin of basaltic migration in eastern australia eastern australian cenozoic volcanism includes a prominent southward migration of activity varied explanations have invoked hotspot or linear magma sources in the asthenosphere the movement of australia over old seafloor spreading zones with direct or delayed response in volcanism or changes in stress fields the present appraisal using new data contradicts some ideas and favours volcanism triggered directly by passage of lithosphere over initial sites of coral sea spreading the conclusions suggest that eastern australia has a major complex hotspot trail established for the past 65 myr it forms an independent and key continental reference to the hawaiian emperor oceanic trail it raises the notion that both continental and oceanic trails can mark the ghosts of former spreading sites

a teleseismic shear wave splitting study to investigate mantle flow around south america and implications for plate driving forces summary closure of the pacific ocean basin by the convergence of its surrounding plates some of which have deep continental roots implies that there is net mass flux out of the mantle under the pacific here we report on a shear wave splitting study designed to test the prediction that there should be flow around its southern margin our results show no evidence for present day flow around the tip of southern south america instead the results suggest present day flow directions in the southern atlantic that parallel the south american absolute plate motion direction even under antarctica the results also provide evidence for absolute plate motion driven by the basal drag of ocean basin scale mantle flow and suggest that 200 km thick flow boundary layers exist under south america and antarctica and also demonstrate that mantle flow directions cannot be reliably inferred from present day plate morphology

empirical estimation of peak pressure level from sound exposure level part ii offshore impact pile driving noise numerical models of underwater sound propagation predict the energy of impulsive signals and its decay with range with a better accuracy than the peak pressure a semi empirical formula is suggested to predict the peak pressure of man made impulsive signals based on numerical predictions of their energy the approach discussed by galindo romero lippert and gavrilov j acoust soc am 138 in press 2015 for airgun signals is modified to predict the peak pressure from offshore pile driving which accounts for impact and pile parameters it is shown that using the modified empirical formula provides more accurate predictions of the peak pressure than direct numerical simulations of the signal waveform

the origin of hotspot traces evidence from eastern australia interpretation of available isotopic ages and of published geologic maps of igneous rocks in eastern australia indicates a north south time transgressive pattern of cessation of igneous activity along a curvilinear trace beginning about 35 ma at 20 sup 0 s and extending to the present near 37 sup 0 s however volcanic activity began 70 60 ma over the length of the highlands and persisted through the early cenozoic until progressive cessation began the latitudinal rate of termination is compatible with that predicted by plate reconstructions relative to the hawaiian hotspot but the trend of the trace is incompatible with that predicted unless the hawaiian emperor bend is somewhat greater than 50 m y in age relative to the labrecque et al 1977 time scale the volcanic pattern appears to be incompatible with a hotspot or plume hypothesis paleostress and contemporary stress indicators as well as the volcanic pattern support a model in which the trace forms due to intraplate extension normal to the trend of the trace resulting in pressure release and melting at the base of the lithosphere beginning in the late cretaceous this stress field persisted until 35 ma when progressive reorientation of the stress field occurred cessation of igneous activity reflectedmore onset of compression normal to the trend of the trace as a consequence a migrating stress node is recorded in the progressive pattern of extinction of volcanic activity along the trace evidence from other hotspot traces suggests that they too represent intraplate stress controls it is not necessary to postulate deep sources mantle plumes for the origin of hotspot traces intraplate stress due to drag plate margin forces thermal contraction and nonsphericity of the earth can also reflect absolute motion less

breakup between australia and antarctica a brief review in the light of new data abstract the arguments justifying the revised timing of breakup between australia and antarctica cande and mutter 1982 and the reconstruction of broken ridge and kerguelen plateau mutter and cande 1983 are reviewed and considered with respect to new subsidence data the age of breakup was revised from anomaly 22 time 55 my b p to anomaly 34 time 85 my b p the rough topography of the diamantina zone can be attributed to very slow spreading 5 mm yr beginning between the times of anomaly 34 and anomaly 19 the reconstruction of broken ridge and kerguelen plateau at anomaly 34 time shows overlap of these two features but the overlap problem is nearly resolved by anomaly 18 time 42 my b p normal seafloor spreading rates 22 mm yr commenced at anomaly 19 time 43 my b p subsidence patterns calculated from biostratigraphic data from wells drilled along australia s southern margin are interpreted as more consistent with the revised age of australia antarctic breakup subsidence curves systematically show rapid subsidence associated with the rift phase of margin development followed by much slower thermally controlled subsidence during the drift phase the timing of the rift to drift transition is believed to coincide with the age of breakup 60 to 110 my b p in addition the subsidence curves indicate a west to east propagation of breakup along the southern margin magnetic anomaly patterns and stratigraphie observations are consistent with this hypothesis

the role of catastrophic geomorphic events in central appalachian landscape evolution abstract catastrophic geomorphic events are taken as those that are large sudden and rare on human timescales in the nonglaciated low seismicity central appalachians these are dominantly floods and landslides evaluation of the role of catastrophic events in landscape evolution includes assessment of their contributions to denudation and formation of prominent landscape features and how they vary through space and time tropical storm paths and topographic barriers at the blue ridge and allegheny front create significant climatic variability across the appalachians for moderate floods the influence of basin geology is apparent in modifying severity of flooding but for the most extreme events flood discharges relate mainly to rainfall characteristics such as intensity duration storm size and location landslide susceptibility relates more directly to geologic controls that determine what intensity and duration of rainfall will trigger slope instability large floods and landslides are not necessarily effective in producing prominent geomorphic features large historic floods in the piedmont have been minimally effective in producing prominent and persistent geomorphic features in contrast smaller floods in the valley and ridge produced erosional and depositional features that probably will require thousands of years to efface scars and deposits of debris slide avalanches triggered on sandstone ridges recover slowly and persist much longer than scars and deposits of smaller landslides triggered on finer grained regolith even though the smaller landslides may have eroded greater aggregate volume the surficial stratigraphic record can be used to extend the spatial and temporal limits of our knowledge of catastrophic events many prominent alluvial and colluvial landforms in the central appalachians are composed of sediments that were deposited by processes similar to those observed in historic catastrophic events available stratigraphic evidence shows two scales of temporal variation one related to quaternary climate changes and a more recent higher frequency variation due to rare events during the holocene in much of the central appalachians landforms related to quaternary climate changes persist as the most prominent features despite the modifying effects of late holocene catastrophic events

three dimensional spherical models of convection in the earth s mantle three dimensional spherical models of mantle convection in the earth reveal that upwelling cylindrical plumes and downwelling planar sheets are the primary features of mantle circulation thus subduction zones and descending sheetlike slabs in the mantle are fundamental characteristics of thermal convection in a spherical shell and are not merely the consequences of the rigidity of the slabs which are cooler than the surrounding mantle cylindrical mantle plumes that cause hotspots such as hawaii are probably the only form of active upwelling and are therefore not just secondary convective currents separate from the large scale mantle circulation active sheetlike upwellings that could be associated with mid ocean ridges did not develop in the model simulations a result that is in agreement with evidence suggesting that ridges are passive phenomena resulting from the tearing of surface plates by the pull of descending slabs

eastbound sublithosphere mantle flow through the caribbean gap and its relevance to the continental undertow hypothesis recent evidence indicates that beneath the caribbean a tongue of sublithosphere mantle is flowing from the pacific to the atlantic dragging the overlying lithosphere eastward i shear wave splitting results from beneath the andean subduction zone and venezuela suggest mantle flow eastward through the caribbean ii volcanic chemistry in central america indicates a slab source beneath nicaragua but a different source in costa rica above the proposed pacific outflow iii an extinct volcanic arc accreted to the margins of the caribbean swept eastward through the caribbean gap between north south america the 1982 continental undertow model requires shallow mantle flow through the caribbean gap from the pacific to the atlantic if continents have deep roots and if shallow mantle flow beneath oceans is decoupled from convection at deeper levels the new evidence from the caribbean is thus compatible with the continental undertow model and perhaps with other models involving decoupled shallow flow

mantle conveyor beneath the tethyan collisional belt abstract collisional belts are generated by the arrival of continental lithosphere into a subduction zone the tethyan suture from the bitlis to the himalayas is a prime example where the arabian and indian plates collided with eurasia during the cenozoic while the kinematics of this process are well established its dynamics are more uncertain india and arabia intriguingly keep advancing in spite of large collisional resisting forces and in the absence of a substantial upper mantle slab driving force at present day we perform global mantle circulation computations to test the role of deep mantle flow as a driving force for the kinematics of the tethyan collisional belt evaluating different boundary conditions and mantle density distributions as inferred from seismic tomography or slab models our results show that mantle drag exerted on the base of the lithosphere by a large scale convective conveyor belt with an active upwelling component is likely the main cause for the ongoing indentation of the indian and arabian plates into eurasia

bridging onshore and offshore present day kinematics of central and eastern mediterranean implications for crustal dynamics and mantle flow we present a new kinematic and strain model of an area encompassing the calabrian and hellenic subduction zones western anatolia and the balkans using haines and holt s 1993 method we derive continuous velocity and strain rate fields by interpolating geodetic velocities including recent gps data in the balkans relative motion between stable eurasia and the western aegean sea is gradually accommodated by distributed n s extension from southern balkans to the eastern corinth gulf so that the westward propagation of the north anatolian fault naf throughout continental greece or peloponnesus is not required we thus propose that the naf terminates in north aegean and that n s extension localized in the corinth gulf and distributed in southern balkans is due to the retreat of the hellenic slab the motion of the hyblean plateau apulia peninsula south adriatic sea ionian basin and sirte plain can be minimized by a single rigid rotation around a pole located in the sirte plain compatible with the opening the pelagian rifts 2 2 5 mm yr and seismotectonics in libya we interpret the trenchward ultraslow motion of the calabrian arc 2 2 5 mm yr as pure collapse the calabrian subduction being now inactive in the absolute plate motion reference frame our modeled velocity field depicts two toroidal crustal patterns located at both ends of the hellenic subduction zone clockwise in nw greece and counter clockwise in western anatolia we suggest the nw greece toroidal pattern is the surface expression of a slab tear and consequent toroidal asthenospheric flow

geologic evidence for the plate driving mechanism the continental undertow hypothesis and the australian antarctic discordance investigations of the pattern of flow in the mantle have been carried out almost exclusively by theoretical geophysicists mainly fluid dynamicists because mantle flow has been considered too deep and too disconnected to leave direct traces in surface tectonic geology this geophysical approach has not yet provided a detailed understanding of mantle flow the assumption of invisibility of mantle flow from the surface should be reassessed the tectonic history of gaps in the circum pacific ring of continents caribbean scotia sea australian antarctic discordance suggests that upper mantle return flow is escaping from the pacific hemisphere as the pacific ocean contracts and is avoiding the regions beneath continents major continental masses may thus have the deep roots suggested by some seismologists if these roots are coupled to the lower mantle plates that include continents may be driven by continental undertow in this case continental motions may tell us the pattern of lower mantle flow and the resulting four celled lower mantle picture is remarkably simple a key area for testing the continental undertow hypothesis is the australian antarctic discordance a low saddle on the spreading ridge between these two continents in the continental undertow view upper mantle flow escaping the pacific is met in the discordance by upper mantle flow originating at the java sumatra trench with the bathymetric low representing the sink toward which this converging flow is moving two new lines of evidence support this interpretation 1 isotope geochemistry of ridge basalts from the discordance shows that mantle sources with distinctive pacific ocean and indian ocean characters meet precisely at the discordance 2 seismic tomography reveals cool upper mantle under the discordance which argues for feeding of this ridge segment laterally rather than from beneath hot spot tracks in and just east of australia appear to argue against the continental undertow hypothesis but do not allow an unambiguous test of the continental undertow hypothesis mantle flow patterns may in fact be partly visible from the surface and careful evaluation of key regions by tectonic geologists may provide a fruitful approach to understanding mantle dynamics

geological evidence for the geographical pattern of mantle return flow and the driving mechanism of plate tectonics tectonic features at the earth s surface can be used to test models for mantle return flow and to determine the geographic pattern of this flow a model with shallow return flow and deep continental roots places the strongest constraints on the geographical pattern of return flow and predicts recognizable surface manifestations because of the progressive shrinkage of the pacific averaging 0 5 km2 yr over the last 180 m y this model predicts upper mantle outflow through the three gaps in the chain of continents rimming the pacific caribbean drake passage australian antarctic gap in this model upper mantle return flow streams originating at the western pacific trenches and at the java trench meet south of australia filling in behind this rapidly northward moving continent and providing an explanation for the negative bathymetric and gravity anomalies of the australian antarctic discordance the long continued tectonic movements toward the east that characterize the caribbean and the easternmost scotia sea may be produced by viscous coupling to the predicted pacific outflow through the gaps and the caribbean floor slopes in the predicted direction if mantle outflow does pass through the gaps in the pacific perimeter it must pass beneath three seismic zones central america lesser antilles scotia sea none of these seismic zones shows foci below 200 km mantle material flowing through the caribbean and drake passage gaps would supply the mid atlantic ridge while the java trench supplies the indian ocean ridges so that deep mantle upwellings need not be centered under spreading ridges and therefore are not required to move laterally to follow ridge migrations the analysis up to this point suggests that upper mantle return flow is a response to the motion of the continents the second part of the paper suggests a possible driving mechanism for the plate tectonic process which may explain why the continents move this hypothetical driving mechanism has four aspects 1 the lower mantle convects 2 this convection drives the continents by drag on their deep roots 3 return flow in the upper mantle provides a volumetric balance for the motion of the continental masses without passing under them and 4 oceanic plates are effectively decoupled from the asthenosphere and are driven largely by slab pull this mechanism accounts for the opening of the atlantic the ability of spreading ridges to stay on the midlines of oceans and the penetration of india into asia following their collision continental motions strongly imply lower mantle upwelling and divergence beneath the atlantic and southeast indian oceans and convergence and subsidence along the tethyan belt this picture disagrees with the concept derived from hot spot studies of an undeforming absolute reference framework at depth but weaknesses in current hot spot theory would make a rejection of the present model on this ground premature if the present model is generally correct a fairly simple pattern of lower mantle convection with as few as four cells may explain much of the tectonic complexity of the earth

sound radiation from impact driven raked piles sound emissions from impact pile driving of raked piles present a significant azimuthal dependence in the radiated sound field due to the non axisymmetric orientation of the pile in this work the sound radiation from raked piles is modeled using a finite element method fem model of the pile and near field region the near field model of the sound field is then used as input into a normal mode model to predict the sound radiation in the far field the azimuthal dependence of the radiated sound field is shown to be accurately predicted using an equivalent axisymmetric fem model of the pile configuration thus negating the need to construct a fully three dimensional model 3d of the raked pile this is achieved by matching the radiated field from the equivalent axisymmetric pile model to a vertical array of phased point sources and then horizontally offsetting the source locations to match the incline of the raked pile the resulting sound field closely matches the numerical predictions from a fully 3d fem model of the raked pile the results of numerical modeling are compared to corresponding acoustic measurements taken on the north west shelf of western australia

a record of appalachian denudation in postrift mesozoic and cenozoic sedimentary deposits of the u s middle atlantic continental margin abstract the complex interplay between source terrain uplift basin subsidence paleoclimatic shifts and sea level change left an extensive sedimentary record in the contiguous offshore basins of the u s middle atlantic margin salisbury embayment baltimore canyon trough and hatteras basin isopach maps of 23 postrift lower jurassic to quaternary a allostratigraphic units coupled with a revised stratigraphic framework reveal that tectonism by regulating sediment supply accumulation rate dominated the interplay of forcing mechanisms tectonic pulses are evidenced by abruptly accelerated sediment accumulation marked latitudinal shifts in the location of depocenters and regional changes in lithofacies relatively rapid tectonic subsidence during the early and middle jurassic history of the basins may have enhanced sediment accumulation rates beginning in the late jurassic however subsidence rates decreased significantly though occasional short pulses of subsidence may have effected relative sea level rises sea level change heavily influenced the distribution and redistribution of sediments one they reached the basins and paleoclimate regulated the relative abundance of carbonates and evaporites in the basins we conclude that source terrains of the central appalachian highlands were tectonically uplifted intensely weathered and rapidly eroded three times since the late triassic 1 early to middle jurassic aalenian to callovian 2 mid early cretaceous barremian and 3 late cenozoic middle miocene intervals of tectonic quiescence following these three tectonic pulses provided conditions suitable for the formation of regional erosion surfaces geomorphic features commonly reported to characterize the central appalachian highlands this series of three irregularly spaced tectonic quiescent cycles does not however match the traditional four cycle concept of post triassic appalachian peneplanation

role of debris flows in long term landscape denudation in the central appalachians of virginia four major storms that triggered debris flows in the virginia west virginia appalachians provide new insights into the role of high magnitude low frequency floods in longterm denudation and landscape evolution in mountainous terrain storm denudation in the blue ridge mountain drainage basins is approximately an order of magnitude greater compared to basins located in the mountains of the valley and ridge province this difference is probably the result of higher storm rainfall from the blue ridge storms radiocarbon dating of debris flow deposits in the blue ridge indicates a debris flow return interval of not more than 2 4 k y in mountainous river basins this finding combined with measurements of basin denudation suggests that approximately half of the long term denudation from mechanical load occurs episodically by debris flow processes although floods of moderate magnitude are largely responsible for mobilizing sediment in lowgradient streams our data suggest that high magnitude low frequency events are the most significant component in delivering coarse grained regolith from mountainous hollows and channels to the lowland floodplains

hotspots in the southern oceans an absolute frame of reference for motion of the gondwana continents abstract the geometry and geochronology of aseismic ridges and oceanic islands in the southern oceans provide a good test of the proposition that hotspots remain fixed over long periods of time that is motion of an order of magnitude less than the relative motion between plate pairs in most cases it is concluded that inter hotspot movement cannot be discerned for the period 100 m y to present and that widely distributed hotspots in the atlantic and indian oceans provide a frame of reference for plate motions following the disintegration of gondwanaland which is independent of paleomagnetism this frame of reference is absolute in that it gives the motion of the lithosphere with respect to the mantle hotspots the absolute motion model indicates that africa and antarctica are now moving only very slowly that there has been significant relative movement between east and west antarctica since the cretaceous and prescribes the relative motion between the somali and african plates

impact of regional mantle flow on subducting plate geometry and interplate stress insights from physical modelling summary physical models of subduction investigate the impact of regional mantle flow on the structure of the subducted slab and deformation of the downgoing and overriding plates the initial mantle flow direction beneath the overriding plate can be horizontal or vertical depending on its location with respect to the asthenospheric flow field imposed mantle flow produces either over or underpressure on the lower surface of the slab depending on the initial mantle flow pattern horizontal or vertical respectively overpressure promotes shallow dip subduction while underpressure tends to steepen the slab horizontal mantle flow with rates of 1 10 cm yr 1 provides sufficient overpressure on a dense subducting lithosphere to obtain a subduction angle of 60 while the same lithospheric slab sinks vertically when no flow is imposed vertical drag force due to downward mantle flow exerted on a slab can result in steep subduction if the slab is neutrally buoyant but fails to produce steep subduction of buoyant oceanic lithosphere the strain regime in the overriding plate due to the asthenospheric drag force depends largely on slab geometry when the slab dip is steeper than the interplate zone the drag force produces negative additional normal stress on the interplate zone and tensile horizontal stress in the overriding plate when the slab dip is shallower than the interplate zone an additional positive normal stress is produced on the interplate zone and the overriding plate experiences additional horizontal compressive stress however the impact of the mantle drag force on interplate pressure is small compared to the influence of the slab pull force since these stress variations can only be observed when the slab is dense and interplate pressure is low

australian antarctic depression from the mid ocean ridge to adjacent continents a morphotectonic depression some 15 106 km2 in area and centred on the australia antarctic discordance1 extends across the southern half of australia through the south east indian ocean to wilkes land in antarctica fig 1a b the depression is co extensive with a negative satellite free air gravity anomaly2 which suggests that the region is underlain by downward convecting asthenosphere here i outline the depression and explore its age in a pre breakup 55 myr reconstruction fig 1c the eastern highlands of australia and the transantarctic mountains are colinear because the eastern highlands were notably high during the late cretaceous and shared with the transantarctic mountains a history of volcanism in the jurassic both highlands probably constituted the eastern flank of the past depression in the centre of which thick 8 km late cretaceous sediment in the ceduna saddle3 and a possible mirror image in offshore antarctica mark its depocentre a broad area of late carboniferous marine sediments in southern australia4 may represent the earliest sign of the depression

major unconformities termination of extension events and associated surfaces in the south china seas review and implications for tectonic development abstract the distribution of unconformities and end of cenozoic rifting events in the south china seas scs reflects both the modes of rift development and the effects of driving mechanisms continental rifting began in the eastern basins during the paleocene and propagated westwards to the vietnam basin margin in the late eocene continental breakup around 32 28 ma caused a regional reduction or cessation in extensional activity particularly affecting basins furthest from the spreading centre basins in the slope and deepwater area north of the spreading centre exhibit reduced fault activity until 21 20 ma propagation of oceanic crust westwards between 25 and 23 ma and termination of seafloor spreading sometime between 20 5 and 16 ma affected fault activity in the qiongdongnan and nam con song basins in the phu khanh basin and south in the dangerous grounds area extension continued until about 16 ma ending at the red unconformity the end of seafloor spreading around 20 5 ma reflects loss of extensional driving force as thinned continental crust entered the nw borneo subduction zone controversially a key component of the driving force maybe attributed to slab pull a transitional period of about 5 7 my between the onset of subduction of continental crust and final jamming of the subduction zone deep regional unconformity dru is inferred the last pulse of extension was focussed in the western scs and terminated around 10 5 ma detailed understanding of proto south china seas development remains uncertain and controversial

underwater mach wave radiation from impact pile driving theory and observation the underwater noise from impact pile driving is studied using a finite element model for the sound generation and parabolic equation model for propagation results are compared with measurements using a vertical line array deployed at a marine construction site in puget sound it is shown that the dominant underwater noise from impact driving is from the mach wave associated with the radial expansion of the pile that propagates down the pile after impact at supersonic speed the predictions of vertical arrival angle associated with the mach cone peak pressure level as function of depth and dominant features of the pressure time series compare well with corresponding field observations

a revised identification of the oldest sea floor spreading anomalies between australia and antarctica we propose that magnetic anomalies south of australia and along the conjugate margin of antarctica that were originally identified as anomalies 19 to 22 may be anomalies 20 to 34 the original anomaly identification has two troublesome aspects 1 it does not account for an extra anomaly between anomalies 20 and 21 and 2 it provides no explanation for the rough topography comprising the diamantina zone with our revised identification there is no extra anomaly and the diamantina zone is attributed to a period of very slow spreading 4 5mm yr half rate between 90 and 43 m y the ages bounding the interval of slow spreading 90 and 43 m y correspond to times of global plate reorganizations our revised identification opens up the possibility that part of the magnetic quiet zone south of australia formed during the cretaceous long normal polarity interval breakup of australia and antarctica probably occurred sometime between 110 and 90 m y b p the breakup unconformity identified by falvey in the otway basin may correspond to a eustastic sea level change

chaotic topography mantle flow and mantle migration in the australian antarctic discordance oceanic crust formed over the past 30 million years at the australian antarctic discordance aad is characterized by chaotic sea floor topography reflecting a weak magma supply from an unusually cold underlying mantle during the past 3 4 million years however a source of increased magma supply coinciding with the known indian pacific mantle isotopic boundary has propagated into the eastern aad displacing the chaotic terrain and replacing it with normal sea floor pacific mantle reached the eastern boundary of the aad at least 7 million years ago but it was not until 3 4 million years ago that lavas derived from pacific mantle were first erupted within the aad this long hiatus combined with the ridge transform geometry across the aad boundary constrains the locus of mantle migration to a narrow relatively shallow region directly beneath the spreading axis of the southeast indian ridge

validation of finite element computations for the quantitative prediction of underwater noise from impact pile driving the acoustic radiation from a pile being driven into the sediment by a sequence of hammer strikes is studied with a linear axisymmetric structural acoustic frequency domain finite element model each hammer strike results in an impulsive sound that is emitted from the pile and then propagated in the shallow water waveguide measurements from accelerometers mounted on the head of a test pile and from hydrophones deployed in the water are used to validate the model results transfer functions between the force input at the top of the anvil and field quantities such as acceleration components in the structure or pressure in the fluid are computed with the model these transfer functions are validated using accelerometer or hydrophone measurements to infer the structural forcing a modeled hammer forcing pulse is used in the successive step to produce quantitative predictions of sound exposure at the hydrophones the comparison between the model and the measurements shows that although several simplifying assumptions were made useful predictions of noise levels based on linear structural acoustic models are possible in the final part of the paper the model is used to characterize the pile as an acoustic radiator by analyzing the flow of acoustic energy 2013 acoustical society of america

thermally induced phase changes lateral heterogeneity of the mantle continental roots and deep slab anomalies pressure induced solid solid phase changes are responsible for most of the increase of density and seismic velocity with depth in the upper mantle lateral variations in temperature cause a similar effect abrupt changes of density and seismic velocity due to phase changes are superposed on smaller changes associated with thermal expansion temperature induced isobaric phase changes are as important in explaining various recent geophysical data as are the more familar pressure induced phase changes in cold slabs the equilibrium mineral assemblage contains high density high velocity phases which are not stable in hotter mantle in particular the ilmenite form of mgsio 3 and the spinel form of mg 2sio 4 have broad stability fields in cold mantle which increase the density and velocity of deep slabs to values in excess of those which have been used in geoid and seismic travel time modeling recent arguments for slab penetration into the lower mantle and whole mantle convection are based on thermal models of the slab which ignore the large density and seismic velocity anomalies associated with temperature induced phase changes when these effects are taken into account the geoid and seismic anomalies associated with subducted slabs are consistent with slab confinement to the upper mantle and layered models of mantle convection the seismicity cutoff and evidence for slab thickening at 670 km also favor this style of convection mantle seismic velocities between 200 and 400 km depth in tectonic and young oceanic regions are lower than in shield regions and this is due to the presence of a melt phase and lower velocity high temperature phase assemblages deep 200 km long lived continental roots differing in chemistry from normal mantle are not required when isobaric phase changes are taken into account high velocity subshield mantle is closer to normal subsolidus mantle than is suboceanic mantle which is affected by the presence of high temperature phase assemblages the whole mantle convection thick continental root and deep slab penetration hypotheses are not supported by seismic and geoid data when isobaric phase changes are included in the analysis phase changes are more effective in changing density and seismic velocity than are lateral variations in temperature and composition the lack of correlation of the geoid with ridges shields heat flow and upper mantle velocity variations suggests a low geoid sensitivity to the upper mantle consistent with layered convection

migration in relation to possible tectonic and regional controls in eastern australian volcanism abstract the wellman mcdougall model for southward migration of central volcano activity in eastern australia is extended to the basaltic lava provinces latitude age plots of volcanic episodes are related to trails initiated from regions of active volcanism at the commencement of northward drift of australia 53 m y b p from southern ocean spreading these trails intersect at least 75 and possibly up to 95 of basaltic episodes and suggest a migratory control the migration of central volcano felsic activity however consistently exceeds sea floor spreading rates with a relative southward motion of 4 10 mm yr the trails give a mean migration direction of 24 9 w of s before 29 30 m y but 8 12 w of s after 29 m y extrapolation of the central volcano activity back in time places it across the coral sea louisiade spreading system and new guinea collision zone at the beginning of drift this suggests that these structures may provide residual thermo tectonic anomalies in the mantle with potential to initiate volcanism under the moving australian plate kinematic reconstruction of australia s drift relative to these structures shows that the western felsic and k rich ultramafic activity falls on progressive overlaps of the coral sea louisiade anomalies the basaltic volcanism generally overlies the central regions of the anomalies the young basalt fields of victoria south australia correspond with positions of the coral sea louisiade anomalies over the last 5 m y the regions of youngest volcanism conductivity anomaly and high heat flow lie near the present projected position of the anomalies some volcanic episodes are not obviously related to migration trails the young basaltic activity in northern queensland may result from movement of the australian plate towards unstable regions of volcanism and uplift in papua new guinea central volcano province spacings appear to match expected lithospheric thickness spacings of basaltic episodes suggest that other factors such as zonal rotational flow in the asthenosphere may also be involved cessation of much volcanism over the eastern australian highlands about 10 m y ago is attributed to imposition of the present regional compressive stress field probably as a result of changes in the sea floor spreading patterns an apparent change in migration direction of volcanism 29 30 m y ago may be related to changes in east west spreading and continental motions adjacent to the australian plate differences between migration directions of volcanism and absolute motions determined for the australian plate may reflect effects of the earth s rotation and migration of spreading ridges the migratory model developed here predicts future australian volcanism mostly in or south of the present regions of younger volcanics and high heat flow it would be basaltic but may be accompanied by felsic activity in tasmania

mountain building and mantle dynamics 1 mountain building at convergent margins requires tectonic forces that can overcome frictional resistance along large scale thrust faults and support the gravitational potential energy stored within the thickened crust of the orogen a general dynamic model for this process is still lacking here we propose that mountain belts can be classified between two end members first those of slab pull type where subduction is mainly confined to the upper mantle and rollback trench motion lead to moderately thick crustal stacks such as in the mediterranean second those of slab suction type where whole mantle convection cells conveyor belts lead to the more extreme expressions of orogeny such as the largely thickened crust and high plateaus of present day tibet and the altiplano for the slab suction type deep mantle convection produces the unique conditions to drag plates toward each other irrespective of their nature and other boundary conditions we support this hypothesis by analyzing the orogenic volcanic and convective history associated with the tertiary formation of the andes after 40 ma and himalayas after collision at 55 ma based on mantle circulation modeling and tectonic reconstructions we surmise that the forces necessary to sustain slab suction mountain building in those orogens derive after transient slab ponding from the mantle drag induced upon slab penetration into the lower mantle and from an associated surge of mantle upwelling beneath africa this process started at 65 55 ma for tibet himalaya when the tethyan slab penetrated into the lower mantle and 10 myr later in the andes when the nazca slab did this surge of mantle convection drags plates against each other generating the necessary compressional forces to create and sustain these two orogenic belts if our model is correct the available geological records of orogeny can be used to decipher time dependent mantle convection with implications for the supercontinental cycle

topographic constraints on deviatoric stress field in the indo eurasian collision region seismo tectonic implications the deviatoric stress field are computed from the inversion of gravitational potential energy gpe for the indo eurasian plate collision region including the himalaya and the tibet plateau the resulting stress pattern in combination with stress and strain rates obtained by inverting respectively the focal mechanism solution of large earthquakes and gps derived plate motions are used to study the nature of the present day deformations a narrow belt bordering the himalayan collision zone from the south is characterized by strong compressive stresses the variations in stress pattern along this belt coincide with arc normal ridges extending into the himalaya and are able to explain arc parallel segmentation of seismicity gravitational collapse seems to play an important role in the southeastern tibet plateau depth sensitivity of the seismic derived stresses and gps derived surface strain rates coupled with evidence of arcuate shaped high electrical conductivity favour strong ductile flow around the eastern himalaya syntaxis ehs at mid crustal depth the deflection of crustal flow indicted by the viscous resistance offered by the rigid sichuan basin adds to the traction stresses to cause clockwise rotation of the block around ehs

protracted continental collisions argue for continental plates driven by basal traction abstract in plate tectonic theory collision between two continents should quickly terminate because of continental buoyancy if convergence is to continue it should do so at a new subduction zone where oceanic crust can be consumed the protracted continental collisions in the alps zagros and himalayas which have continued to deform continental crust since the early or middle cenozoic are therefore anomalies in standard plate tectonic theory it is commonly held that plates are driven by slab pull but this does not account for the continuing tethyan collisions where the descending slab has detached from the subducting continent these protracted continental collisions are better explained by horizontal traction of the mantle on the base of deep continental roots dragging the northern and southern continents together along a tethyan axis of mantle convergence continental undertow thus resolves the collision anomaly in plate tectonics