sea level earth s dominant elevation implications for duration and magnitudes of sea level variations abstracthigh resolution digital elevation models of earth s solid fluid interface reveal that earth s bimodal elevation distribution is characterized by a dominant mode at or very close to present day sea level it is hypothesized that sea level is earth s dominant modal elevation because it is the only elevation where two opposing first order surface processes erosion and deposition act to increase the area of a single elevation the observation that sea level is the dominant elevation implies that 1 the time needed for the modal elevation to adjust is very short and or 2 long term 106 107 yr mean sea level has not varied significantly from its present height the mass of material that defines the sea level modal elevation is quite small whether integrated over 1 or 100 m of thickness and could be transported in 104 yr this would suggest that the shoreline at no matter what height relative to the present 0 m elevation was probably always earth s dominant elevation however eurasia north am

foreland shortening and crustal balancing in the andes at 30 s latitude excellent surface exposures known benioff zone geometry a dynamic morphology and the availability of industry seismic reflection data all make the andes at 30 s an excellent transect for investigating crustal scale balanced sections 150 170 km of horizontal shortening has occurred in three major belts located between the trench and the foreland the thin skinned east verging precordillera of western argentina accounts for 60 75 of the total shortening and formed mostly since major volcanism ceased at 10 ma industry seismic reflection data show that the decollement of the precordillera belt is located anomalously deep at 15 km the belt is dominated by fault propagation folds and contains several prominent out of sequence thrust faults seismic stratigraphie analysis shows that miocene strata in the iglesia valley located between the precordillera and the crest of the andes accumulated in a piggy back basin onlap relations on the western side indicate that the high cordillera was uplifted as a major fault bend fold over a buried ramp thrusting in the two western belts both in the high cordillera of chile formed during the waning stages of arc volcanism 11 16 ma and account for 25 40 of the shortening the observed shortening is probably greater than can be accounted for with reasonable crustal thicknesses indicating the possibility of continental truncation or erosion along the plate margin or an anomalously thick root held down by the nearly flat subducted nazca plate our preferred crustal geometry puts the ramp between upper and lower crustal deformation west of the high topography requiring crustal scale tectonic wedging to thicken the crust beneath the crest of the andes this non unique model provides a simple explanation of the first order morphology of the andes at this latitude

the early paleozoic evolution of the argentine recordillera as a laurentian rifted drifted and collided terrane a geodynamic model discussion and reply

zircon and whole rock nd pb isotopic evidence for a grenville age and a laurentian origin for the basement of the precordillera in argentina suggestions that the precordillera of argentina has an early paleozoic connection to the appalachian ouachita rifted margin of the southern u s have been based on cambro ordovician stratigraphy and faunal assemblages further support comes from comparing precambrian grenville appalachian basement with xenoliths brought up in precordil leran miocene volcanic rocks u pb zircon ages and whole rock pb and nd isotopic data from the xenoliths show that precordilleran basement along with some part of the westernmost sierras pampeanas pie de palo range to the east is essentially unique in south america and is best interpreted as being derived from laurentia a grenville age is substantiated by u pb zircon upper intersect ages of 1102 pm 6 ma for a mafic xenolith and near 1100 ma for acidic xenoliths both xenolith types contain pink doubly terminated prismatic igneous zircons with relatively high u and pb concentrations rounded colorless low u and pb zircons with overgrowths produced in a later pre

developing an event tree probabilistic tsunami inundation model for ne atlantic coasts application to a case study this study constitutes a preliminary assessment of probabilistic tsunami inundation in the ne atlantic region we developed an event tree approach to calculate the likelihood of tsunami flood occurrence and exceedance of a specific near shore wave height for a given exposure time only tsunamis of tectonic origin are considered here taking into account local regional and far field sources the approach used here consists of an event tree method that gathers probability models for seismic sources tsunami numerical modeling and statistical methods it also includes a treatment of aleatoric uncertainties related to source location and tidal stage epistemic uncertainties are not addressed in this study the methodology is applied to the coastal test site of sines located in the ne atlantic coast of portugal we derive probabilistic high resolution maximum wave amplitudes and flood distributions for the study test site considering 100 and 500 year exposure times we find that the probability that maximum wave amplitude exceeds 1 m somewhere along the sines coasts reaches about 60 for an exposure time of 100 years and is up to 97 for an exposure time of 500 years the probability of inundation occurrence flow depth 0 m varies between 10 and 57 and from 20 up to 95 for 100 and 500 year exposure times respectively no validation has been performed here with historical tsunamis this paper illustrates a methodology through a case study which is not an operational assessment

the storegga slide tsunami comparing field observations with numerical simulations abstract deposits from the storegga tsunami have been found in coastal areas around the norwegian sea and north sea from the northeast coast of england to beyond the arctic circle in northern norway the tsunami deposits reach onshore elevations of 10 12 m above sea level of their time in western norway 3 6 m in northeast scotland and above 20 m on the shetland islands these elevations are compared with surface wave elevations derived from a numerical simulation of the storegga slide a good agreement is obtained for a retrogressive slide that descends at 25 30 m s and that has short time lags of 15 20 s between each individual slide block

paleozoic laurentia gondwana interaction and the origin of the appalachian andean mountain system laurentia the rift bounded precambrian nucleus of north america may have broken out from a neoproterozoic supercontinent between east and west gondwana several lines of evidence suggest that the appalachian margin of laurentia subsequently collided with the proto andean margin of the amalgamated gondwana supercontinent in different relative positions during early and mid paleozoic time in route to final docking against northwest africa to complete the assembly of pangea hence the appalachian and andean orogens may have originated as a single mountain system the overall hypothesis retains the same paleomagnetic and paleobiogeographic controls as previous global reconstructions for the paleozoic era laurentia gondwana collisions may help to explain contemporaneous unconformities in the paleozoic sedimentary cover of the laurentian gondwanan and baltic cratons

reply to comment on probabilistic tsunami hazard in the northeast atlantic from near and far field tectonic sources by fonseca pure and applied geophysics 2016

disentangling the control of tectonics eustasy trophic conditions and climate on shallow marine carbonate production during the aalenian oxfordian interval from the western france platform to the western tethyan domain the objective of this work is to improve our understanding of the processes controlling changes in the architecture and facies of intracontinental carbonate platforms we examined the facies and sequence stratigraphy of aalenian to oxfordian limestones of western france seventy seven outcrop sections were studied and thirty one sedimentary facies identified in five depositional environments ranging from lower offshore to backshore platform evolution was reconstructed along a 500 km cross section twenty two depositional sequences were identified on the entire western france platform and correlated with european third order sequences at the biozone level demonstrating that eustasy was the major factor controlling the cyclic trend of accommodation the tectonic subsidence rate was computed from accommodation measurements from the aalenian to the oxfordian in key localities tectonism controlled the sedimentation rate and platform architecture at a longer time scale tectonic subsidence triggered the demise of carbonate production at the bathonian callovian boundary while the uplift made possible the recovery of carbonate platform from caen to le mans during the mid oxfordian topography of the paleozoic basement mainly controlled lateral variations of paleodepth within the western france platform until the mid bathonian a synthesis of carbonate production in the western tethyan domain at that time was conducted stages of high carbonate production during the bajocian bathonian and the middle to late oxfordian are synchronous with low 13c high eccentricity intervals and rather dry climate promoting 1 evaporation and carbonate supersaturation and 2 oligotrophic conditions periods of low carbonate production during the aalenian and from the middle callovian to early oxfordian correlate with high 13c and low eccentricity intervals characterized by wet climate and less oligotrophic conditions such conditions tend to diminish growth potential of carbonate platforms this work highlights the importance of climate control on carbonate growth and demise at large scale in western tethyan epicontinental seas

analysis of geological hiatus surfaces across africa in the cenozoic and implications for the timescales of convectively maintained topography geological maps are a powerful but underutilized tool for constraining geodynamic processes and models unraveling the cenozoic elevation history of africa and distinguishing between competing upli

the use of scenarios to evaluate the tsunami impact in southern italy this paper outlines the main contributions to the definition and evaluation of tsunami hazard and risk resulting from studies undertaken in italy in recent years and emphasises that adopting characteristic cases or scenarios is a very useful and advantageous technique three main cases are given as valuable examples that is the 1627 gargano tsunami the 1693 eastern sicily tsunami and the 1908 messina straits tsunami since 1 they characterise three distinct tsunamigenic regions 2 they are instances of destructive events and 3 they have been extensively studied in the last decade the paper elucidates the state of the art of the research on these events clarifies the chief points of agreement and disagreement among scientists and illustrates the main issues that are to be addressed by future research to provide reliable assessment of tsunami risk and to implement efficient countermeasures to defend the life of people coastal structures and the coastal environment against the attacks of tsunamis

modeling tsunamis from earthquake sources near gorringe bank southwest of portugal the azores gibraltar fracture zone with the huge bathymetric reliefs in the area southwest of portugal is believed to have been the source of large historic tsunami events this report describes simulations of tsunami generation and propagation from sources near the gorringe bank the well documented 1969 tsunami event is examined both with a ray tracing technique and with finite difference models based on various shallow water equations both methods show that the most likely source location is southeast of the gorringe bank near the epicenter location determined from seismic data the tsunami source is calculated by formulas given by okada 1985 for surface deformation of an elastic half space caused by faulting observed wave amplitude and travel time and values computed from an initial wave field according to okada 1985 formulas show acceptable agreement for most stations along the coast of portugal and spain however in order to explain a large primary wave with downward displacement observed on the coast of morocco an alternative source model with a larger area of downward displacement has been introduced this also leads to a better overall fit with observed travel time implications for disastrous events as the one in 1755 are also discussed linear hydrostatic shallow water models are used for most of the simulations but the importance of nonlinearity and dispersion is examined with the boussinesq equations the sensitivity of the solution to changes in the location and the strength of the source is discussed and a series of grid refinement studies are performed in order to assess the accuracy of the simulations

joint seismic geodynamic mineral physical modelling of african geodynamics a reconciliation of deep mantle convection with surface geophysical constraints recent progress in seismic tomography provides the first complete 3 d images of the combined thermal and chemical anomalies that characterise the unique deep mantle structure below the african continent we present a tomography based model of mantle convection that provides an excellent match to fundamental surface geodynamic constraints on internal density heterogeneity that includes both compositional and thermal contributions where the latter are constrained by mineral physics the application of this thermochemical convection model to the problem of african mantle dynamics yields a reconciliation of both surface gravity and topography anomalies to deep seated mantle flow under the african plate over a wider range of wavelengths than has been possible to date on the basis of these results we predict flow in the african asthenosphere characterised by a clear pattern of focussed upwellings below the major centres of late cenozoic volcanism including the kenya domes hoggar massif cameroon volcanicline cape verde and canary islands the flow predictions also reveal a deep seated large scale active hot upwelling below the western margin of africa under the cape verde islands that extends down to the core mantle boundary the scale and dynamical intensity of this west african superplume is comparable to the south african superplume that has long been assumed to dominate the large scale flow dynamics in the deep mantle under africa we evaluate the plausibility of the predicted asthenospheric flow patterns through a comparison with seismic azimuthal anisotropy derived from independent analyses of african shear wave splitting data

sea level variations global sedimentation rates and the hypsographic curve sea level changes during the neozoic have been estimated by two different methods the first involves measuring the amount of present day land area which was flooded during the past and using the present day hypsographic curve to estimate the amount of sea level rise necessary to produce this flooding the second involves the estimation of the changing volume of mid oceanic ridges through time and estimating sea level changes after having allowed for isostatic adjustment a difference in sea level of 170 m is obtained from the two methods for the cretaceous 80 100 m y b p this is equivalent to a difference in continental flooding of 24 mm 2 using the present day hypsographic curve we attempt to explain this difference firstly by allowing for the fact that the present day ocean basins have more sediment in them than did the cretaceous ocean basins this produces a sea level change in the opposite direction to that produced by the reduction in mid ocean ridge volume since the cretaceous secondly we suggest another large factor in producing the difference is that the present day hypsographic curve is not the correct one to use when studying sea level stands in the cretaceous present day average continental heights are closely related to continental areas accepting this principle if continents are joined together in the past their average height must be greater and so their hypsographic curve must be steeper a given sea level rise would produce less continental flooding during times of continental aggregation than it would today

sedimentary record of a tsunami during roman times bay of cadiz spain abstract historical data show that the gulf of cadiz has been exposed to destructive tsunamisduring at least the past 2000 yr the last tsunami was generated by the ad 1755 lisbon earthquake which affected the atlantic coasts of spain portugal and morocco today these littoral areas areintensely populated and the expected damage could be much greater tsunami studies are of greatimportance in helping to determine the recurrence interval of these events the presence of washover fan deposits on the inland margin of the valdelagrana spit bar cadiz spain indicates the occurrence of a high energy marine event ca 2300 cal yr bp historical geomorphological sedimentological palaeontological and geochronological data suggest that atsunami could have affected the area during roman times copyright 2002 john wiley sons ltd journal of quaternary science keywords tsunami deposits grain size palaeontology gulf of cadiz south spain introduction investigations of the geological records of past tsunamis arean important tool in helping to determine the recurrenceinterval of such events in a region these investigations arealso the only way of determining the prehistoric occurrenceand tsunami hazard in areas of infrequent seismic activity however at present it is dif cult to distinguish betweentsunami deposits and those laid down by other high energyevents such as a storm surge or hurricane recent work bygoff et al 2001 has helped to identify a series of diagnosticcriteria for tsunami deposits and research is underway tohighlight the differences between these and other high energyevents goff and chagu e goff in preparation j goff personalcommunication 2002 wave hydrodynamics the speci ccoastal setting morphology orientation availability and typeof sediments depositional environments tsunami magnitudeand tidal range are all factors that help to de ne the type andpreservation of tsunami deposits furthermore the ability todetermine the tsunamigenic source largely depends upon thepalaeoseismic and historical record e g goff et al 2001

tsunami induced morphological change a model based impact assessment of the 1755 tsunami in ne atlantic from the morocco coast abstract tsunamis can be responsible for coastal geomorphic crises extensively inundated coasts can suffer widespread and dramatic changes in their morphology due to sediment erosion transport and deposition processes in this paper we investigate the tsunami induced morphological changes on coasts prone to inundation and how sediment transport is controlled by both tsunami and sediment characteristics we focus on a tsunami prone coast in the ne atlantic tangier morocco that experienced the 1755 lisbon tsunami we use a coupled hydrodynamic and morphodynamic numerical model together with high resolution digital elevation and sedimentary models to simulate the impact of tsunamis on the morphology and sediment distribution of tangier bay due to the uncertainty on the source and effects of the 1755 event we consider two 1755 like tsunamigenic scenarios that have the potential to cause different levels of inundation results show that the coastal zone of tangier can undergo substantial changes in morphology and sediment distribution following the tsunami impact for the selected scenarios the volume of sediments mobilized at both the offshore and onshore zones of the tangier site ranges from 30 000 to 200 000 m3 moreover the presence of mobile sediments and conditions favoring tsunami shoaling lead to an increase in wave impact on the coastal configuration conversely the presence of the breakwaters helps to protect the tangier coast by limiting the extent of the affected area the results of this study suggest that the assessment of tsunami induced coastal impact should include the effect on morphology

paleozoic terranes of eastern australia and the drift history of gondwana abstract critical assessment of paleozoic paleomagnetic results from australia shows that paleopoles from locations on the main craton and in the various terranes of the tasman fold belt of eastern australia follow the same path since 400 ma for the lachlan and thomson superterranes but not until 250 ma or younger for the new england superterrane most of the paleopoles from the tasman fold belt are derived from the lolworth ravenswood terrane of the thomson superterrane and the molong monaro terrane of the lachlan superterrane consideration of the paleomagnetic data and geological constraints suggests that these terranes were amalgamated with cratonic australia by the late early devonian the lolworth ravenswood terrane is interpreted to have undergone a 90 clockwise rotation between 425 and 380 ma although the tamworth terrane of the western new england superterrane is thought to have amalgamated with the lachlan superterrane by the late carboniferous geological syntheses suggest that movements between these regions may have persisted until the middle triassic this view is supported by the available paleomagnetic data with these constraints an apparent polar wander path for gondwana during the paleozoic has been constructed after review of the gondwana paleomagnetic data the drift history of gondwana with respect to laurentia and baltica during the paleozoic is shown in a series of paleogeographic maps

the early paleozoic evolution of the argentine precordillera as a laurentian rifted drifted and collided terrane a geodynamic model paleontologic and stratigraphic evidence points to the early paleozoic precordilleran terrane of western argentina as being the conjugate rift pair of the appalachians stratigraphic similarities of the cambrian and early arenig carbonate series and very strong affinities among trilobite conodont and brachiopod faunas show their close relationship the most probable provenance areas are the appalachian ouachita rifted margin and the newfoundland appalachians although the former fits better with geometric and drifting paths suggested by faunal affinities increasing celtic and baltic brachiopod genera and divergent stratigraphy since the arenig indicate the drifting of the precordilleran terrane collisional foredeeps developed on collapsed former platform carbonates as flexural subsidence progressed the collision of the precordillera with western gondwana occurred during the mid llanvirn to llandeilo a magmatic arc related to eastward subduction present coordinates was active in the famatina range east of the precordillera this region of celtic affinity shows faunal exchange with the precordilleran terrane since the late arenig and may represent accreted intra iapetus volcanic island arc complexes the rifting and drifting stages are consistent with paleoclimatic and paleomagnetic data that show the migration of the precordilleran terrane from periequatorial to peripolar latitudes between the cambrian and latest ordovician the deep ocean to the west of the precordillera started to close by the late ordovician with the eastward drift of the chilenian terrane absence of volcanic or pyroclastic arc derived rocks in the precordillera indicate west dipping subduction as chilenia approached the continental margin a new forebulge was established on the former collided precordilleran terrane developing an erosional unconformity in central precordillera talacasto tambolar arch a gondwanic signature was fully developed by the middle silurian when the malvinokaffric clarkeia fauna flourished before then the late ordovician glacial record and associated hirnantia fauna were the first clear tie to gondwana during the silurian the marginal basin behaved as a foreland with lithosphere rheology and eustasy governing the sequence stratigraphy wrench faulting along its eastern boundary displaced the precordillera toward the south continued shortening during closure with the chilenian terrane in the mid devonian produced thrust loading of the basin and generated a thick graywacke succession final accretion of chilenia late devonian generated a regional angular unconformity between the lower and upper paleozoic new eastward subduction was initiated west of the accreted chilenian terrane during the late permian triassic as indicated by the choiyoi volcanic complex which presently outcrops in the frontal cordillera

runup of solitary waves on a circular island this is a study of the interactions of solitary waves climbing up a circular island a series of large scale laboratory experiments with waves of different incident height to depth ratios and different crest lengths is described detailed two dimensional run up height measurements and time histories of surface elevations around the island are presented a numerical model based on the two dimensional shallow water wave equations including runup calculations was developed numerical model predictions agreed very well with the laboratory data and the model was used to study wave trapping and the effect of slope under certain conditions enhanced runup and wave trapping on the lee side of the island were observed suggesting a possible explanation for the devastation reported by field surveys in babi island off flores indonesia and in okushiri island japan

probabilistic tsunami hazard in the northeast atlantic from near and far field tectonic sources in this article we present the first study on probabilistic tsunami hazard assessment for the northeast ne atlantic region related to earthquake sources the methodology combines the probabilistic seismic hazard assessment tsunami numerical modeling and statistical approaches we consider three main tsunamigenic areas namely the southwest iberian margin the gloria and the caribbean for each tsunamigenic zone we derive the annual recurrence rate for each magnitude range from mw 8 0 up to mw 9 0 with a regular interval using the bayesian method which incorporates seismic information from historical and instrumental catalogs a numerical code solving the shallow water equations is employed to simulate the tsunami propagation and compute near shore wave heights the probability of exceeding a specific tsunami hazard level during a given time period is calculated using the poisson distribution the results are presented in terms of the probability of exceedance of a given tsunami amplitude for 100 and 500 year return periods the hazard level varies along the ne atlantic coast being maximum along the northern segment of the morocco atlantic coast the southern portuguese coast and the spanish coast of the gulf of cadiz we find that the probability that a maximum wave height exceeds 1 m somewhere in the ne atlantic region reaches 60 and 100 for 100 and 500 year return periods respectively these probability values decrease respectively to about 15 and 50 when considering the exceedance threshold of 5 m for the same return periods of 100 and 500 years

topographic growth around the orange river valley southern africa a cenozoic record of crustal deformation and climatic change we reconstruct the history of topographic growth in southern africa on both sides of the orange river valley from an integrated analysis of erosion surfaces crustal deformation and climate change first we propose an inventory of erosion surfaces observed in the study area and classify them according to their most likely formative process i e chemical weathering or mechanical erosion among the various land units observed we define a new class of landform the pedivalley which corresponds to a wide valley with a flat erosional floor in the orange river valley we mapped three low relief erosion surfaces each bevelling a variety of lithologies the oldest and most elevated is 1 a stripped etchplain evolving laterally into 2 a stepped pediplain bearing residual inselbergs 3 a younger pediplain later formed in response to a more recent event of crustal deformation these are all cenozoic landforms the etchplain is associated with a late palaeocene to middle eocene weathering event and the two pediplains are older than the middle miocene alluvial terraces of the orange river landscape evolution was first driven by slow uplift 10 m ma followed by a second interval of uplift involving a cumulative magnitude of at least 200 m this event shaped the transition between the two pediplains and modified the drainage pattern a final phase of uplift magnitude 60 m occurred after the middle miocene and drove the incision of the lower terraces of the orange river climate exerted a major control over the denudation process and involved very humid conditions responsible for lateritic weathering followed by more arid conditions which promoted the formation of pedivalleys collectively these produce pediplains

dynamic topography and long term sea level variations there is no such thing as a stable continental platform abstract globally uniform i e eustatic sea level trends with time scales approaching 100 myr have been inferred from both seismic and backstripping stratigraphic analysis at a small set of geographic sites that are presumed to lie on stable continental platforms and passive continental margins characterized by simple thermal subsidence histories e g the new jersey margin the western african margin we demonstrate using mantle flow simulations based on high resolution seismic tomography that both the new jersey margin and the conjugate western african margin have been subject to orders of 100 m of dynamic i e flow induced topography change over the last 30 myr we also show that the changing pattern of downwelling mantle flow associated with plate subduction is a significant contributor to the background eustatic sea level trend which is also of order 100 m during the 30 myr time window therefore late cenozoic variations of dynamic topography on these passive margin sites are comparable to the eustatic sea level changes and can partially mask the latter furthermore even if the observed trend could be accurately corrected for local dynamic topography variation the residual eustatic signal does not merely reflect changes in mean spreading rates at mid ocean ridges we conclude that the observed long term sea level variations at so called stable sites cannot be interpreted as eustatic moreover previous analyses that have used long term sea level trends as a proxy for spreading rates and geochemical fluxes must be revisited

post rift stratigraphic evolution of the atlantic margin of namibia and south africa implications for the vertical movements of the margin and the uplift history of the south african plateau abstract the aim of this study is to constrain the post rift deformations of the atlantic passive margin of namibia and south africa using an extensive industrial 2d reflection seismic dataset calibrated by wells and onshore outcrops that have been revaluated in age biostratigraphy in order to discuss the evolution of the south african plateau uplift the first order evolution of the margin is tectonically driven and can be divided into three principal phases the first 131 93 5 ma comprises an overall retrogradational trend that results from a rate of accommodation created by the thermal flexure of the margin that is higher than the sediment supply the second 93 5 66 ma comprises an overall aggradational progradational trend that results from a relative increase in sediment supply due to an uplift and subsequent erosion of the margin and the inland domain the third 66 0 ma is retrogradational again in response to a decrease in sediment supply induced by a relative stability of the margin and climate conditions this study demonstrates that the present day configuration of the margin is acquired during the late cretaceous from 81 to 66 ma with a strike long wavelength and seaward tilt of the margin which could be related to the growth of the onshore main escarpment we also characterize a regional oligocene unconformity marked by a significant downward shift of the shoreline which suggests a moderate uplift of the inland domain and could be associated with a reactivation of the relic late cretaceous relief

ocean temperature induced change in lithospheric thermal structure a mechanism for long term eustatic sea level change eustatic sea level change can be produced by a change in ocean bottom water temperature through an alteration of the upper thermal boundary condition of oceanic lithosphere the consequent evolution of lithospheric thermal structure can cause thermal expansion or contraction of the lithosphere if continental lithosphere remains unaffected by the change in ocean temperatures eustatic sea level will change as measured in the continental frame of reference a two dimensional finite difference model has been formulated and shows that if ocean bottom water temperature were to change rapidly by 14 c as it may have during the tertiary sea level would change by 8 m in 8 m y and 17 m in 40 m y this result is in agreement with the one dimensional error function solution for a heating or cooling halfspace however the changes in lateral heat flow between ocean water and the continental slope and between oceanic and continental lithosphere can produce epeirogenic motions of the continental margins and th

local tsunamis and distributed slip at the source variations in the local tsunami wave field are examined in relation to heterogeneous slip distributions that are characteristic of many shallow subduction zone earthquakes assumptions inherent in calculating the coseismic vertical displacement field that defines the initial condition for tsunami propagation are examined by comparing the seafloor displacement from uniform slip to that from an ideal static crack we demonstrate that dip directed slip variations significantly affect the initial cross sectional wave profile because of the hydrodynamic stability of tsunami wave forms these effects directly impact estimates of maximum runup from the local tsunami in most cases an assumption of uniform slip in the dip direction significantly underestimates the maximum amplitude and leading wave steepness of the local tsunami whereas dip directed slip variations affect the initial wave profile strike directed slip variations result in wavefront parallel changes in amplitude that are largely preserved during propagation from the source region toward shore owing to the effects of refraction tests of discretizing slip distributions indicate that small fault surface elements of dimensions similar to the source depth can acceptably approximate the vertical displacement field in comparison to continuous slip distributions crack models for tsunamis generated by shallow subduction zone earthquakes indicate that a rupture intersecting the free surface results in approximately twice the average slip therefore the observation of higher slip associated with tsunami earthquakes relative to typical subduction zone earthquakes of the same magnitude suggests that tsunami earthquakes involve rupture of the seafloor whereas rupture of deeper subduction zone earthquakes may be imbedded and not reach the seafloor

boulder deposition during major tsunami events a remarkable accumulation of marine boulders located above the present spring tide level has occurred in two coastal lowlands of the algarve portugal the size interval of the particles studied here is seldom reported in the literature in association with extreme events of coastal inundation thus making this study of relevance to many other coasts worldwide the spreads of boulders extend several hundred meters inland and well beyond the present landward limit of storm activity the marine origin of the boulders is demonstrated by well developed macro bioerosion sculpturing and in situ skeletal remains of endolithic shallow marine bivalves the good state preservation of the fossils within the boulders indicates that abrasion during transport and redeposition was not significant we envisage boulder deposition as having taken place during the lisbon tsunami of ad 1755 through the simultaneous landward entrainment of coarse particles from nearshore followed by rapid shoreward suspended dominated transport and non graded redeposition that excluded significant sorting by weight or boulder dimensions we use numerical hydrodynamic modeling of tsunami and storm waves to test the observational data on boulder dimensions density size distribution on the most likely processes of sediment deposition this work demonstrates the effectiveness of the study of boulder deposits in tsunami reconstruction copyright 2011 john wiley sons ltd

early cambrian continental reconstructions climatically related sedimentary facies and faunal distributions have been combined with palaeomagnetic data to make provisional reconstructions of the early cambrian world laurentia baltica and siberia appear to have formed a continental group which rifted apart from each other prior to 600 ma the consolidation of much of gondwana probably occurred in the pan african orogeny well before the cambrian though the assembly of several east asian terranes is still speculative the archaeocyathan reefs of siberia southern europe and morocco with their bigotinid trilobite fauna suggest that these areas were adjacent to each other and at low latitudes avalonia had close faunal links with western gondwana but lacked bigotinids and archaeocyathans and may have been situated off west africa and florida during the early cambrian there was a northward migration of laurentia towards the equator as its separation from baltica and siberia increased and a southward movement of gondwana

earth s constant mean elevation implication for long term sea level controlled by oceanic lithosphere dynamics in a pitman world abstracton a spherical earth the mean elevation approximately 2440 m would be everywhere at a mean earth radius from the center this directly links an elevation at the surface to physical dimensions of earth including surface area and volume which are at most very slowly evolving components of the earth system earth s mean elevation thus provides a framework within which to consider changes in height of earth s solid surface as a function of time in this article the focus will be on long term nonglacially controlled sea level long term sea level has long been argued to be largely controlled by changes in ocean basin volume related to changes in the area age distribution of oceanic lithosphere as generally modeled by walter pitman and subsequent workers the age depth relationship of oceanic lithosphere including both the ridge depth and the coefficients describing the age depth relationship are assumed constant this article examines the consequences of adhering to these assumptions when pl

the impact of humans on continental erosion and sedimentation rock uplift and erosional denudation of orogenic belts have long been the most impor tant geologic processes that serve to shape continental surfaces but the rate of geomor phic change resulting from these natural phe nomena has now been outstripped by human activities associated with agriculture con struction and mining although humans are now the most important geomorphic agent on the planet s surface natural and anthro pogenic processes serve to modify quite dif ferent parts of earth s landscape in order to better understand the impact of humans on continental erosion we have examined both long term and short term data on rates of sediment transfer in response to glacio fl u vial and anthropogenic processes phanerozoic rates of subaerial denuda tion inferred from preserved volumes of sedimentary rock require a mean conti nental erosion rate on the order of 16 m per million years m m y resulting in the accumulation of 5 gigatons of sediment per year gt yr erosion irregularly increased over the 542 m y span of phanerozoic time to a pliocene value of 53 m m y 16 gt yr current estimates of large river sediment loads are similar to this late neogene value and require net denudation of ice free land surfaces at a rate of 62 m m y 21 gt yr consideration of the variation in large river sediment loads and the geomorphology of respective river basin catchments suggests that natural erosion is primarily confi ned to drainage headwaters 83 of the global river sediment fl ux is derived from the high est 10 of earth s surface subaerial erosion as a result of human activity primarily through agricultural practices has resulted in a sharp increase in net rates of continental denudation although less well constrained than estimates based on surviving rock volumes or current river loads available data suggest that present farmland denudation is proceeding at a rate of 600 m m y 75 gt yr and is largely confi ned to the lower elevations of earth s land surface primarily along passive continental margins 83 of cropland erosion occurs over the lower 65 of earth s surface the conspicuous disparity between natu ral sediment fl uxes suggested by data on rock volumes and river loads 21 gt yr and anthropogenic fl uxes inferred from measured and modeled cropland soil losses 75 gt yr is readily resolved by data on thicknesses and ages of alluvial sediment that has been deposited immediately downslope from erod ing croplands over the history of human agriculture accumulation of postsettlement alluvium on higher order tributary channels and fl oodplains mean rate 12 600 m m y is the most important geomorphic process in terms of the erosion and deposition of sedi ment that is currently shaping the landscape of earth it far exceeds even the impact of pleistocene continental glaciers or the cur rent impact of alpine erosion by glacial and or fl uvial processes conversely available data suggest that since 1961 global cropland area has increased by 11 while the global population has approximately doubled the net effect of both changes is that per capita cropland area has decreased by 44 over this same time interval 1 per year this is 25 times the rate of soil area loss antici pated from human denudation of cropland surfaces in a context of per capita food pro duction soil loss through cropland erosion is largely insignifi cant when compared to the impact of population growth

evaluating tsunami impact on the gulf of cadiz coast northeast atlantic the gulf of cadiz coasts are exposed to tsunamis emergency planning tools are now taking into account this fact especially because a series of historical occurrences were strikingly significant having left strong evidence behind in the mareographic records the geological evidence or simply the memory of the populations the study area is a strip along the algarve coast south portugal an area known to have been heavily impacted by the 1 november 1755 event in this study we use two different tsunami scenarios generated by the rupture of two thrust faults identified in the area corresponding to 8 1 8 3 magnitude earthquakes tsunami propagation and inundation computation is performed using a non linear shallow water code with bottom friction numerical modeling results are presented in terms of flow depth and current velocity with maximum values of 7 m and 8 m s for inundation depth and flow speed respectively these results constitute a valuable tool for local authorities emergency and decision planners to define the priority zones where tsunami mitigation measures must be implemented and to develop tsunami resilient communities

multiple magnetizations in the cambrian ordovician carbonate platform of the argentine precordillera and their tectonic implications abstract cambrian to early ordovician carbonate deposits from the eastern and central areas of the argentine precordillera have been studied palaeomagnetically in six different localities 21 sites three localities 11 sites in the central precordillera show two post tectonic magnetic components a shallow up and northward directed component removed by intermediate af up to 20 mt and at temperatures up to 450 c component a and a steeper down and southward directed component with higher coercivities and unblocking temperatures component b component a is interpreted as a recent or possibly neogene secondary magnetization and component b as permian irm studies show that the magnetization is carried by probably sd or psd magnetite the geographical distribution of the permian remagnetization in the limestones and the occurrence of other formations remagnetized syntectonically at approximately the same time in the western precordillera indicate a regional remagnetization event during the early permian probably associated with the san rafaelic tectonic phase that affected the central chilean argentine andes in the late palaeozoic 290 265 ma aprox eastern areas of the precordillera not affected by this event do not show evidence of this permian remagnetization and a probably primary albeit ill defined magnetization component c could be isolated in three sites vgps computed from these sites are broadly consistent with early palaeozoic poles of gondwana

quantification of vertical movement of low elevation topography combining a new compilation of global sea level curves and scattered marine deposits armorican massif western france a wide range of methods are available to quantify earth s surface vertical movements but most of these methods cannot track low amplitude 5 ma e g cosmogenic isotope studies vertical movements characteristic of plate interiors the difference between the present day elevation of ancient sea level markers deduced from well dated marine deposits corrected from their bathymetry of deposition and a global sea level gsl curve are sometimes used to estimate these intraplate vertical movements here we formalized this method by re assessing the reliability of published gsl curves to build a composite curve that combines the most reliable ones at each stage based on the potential bias and uncertainties inherent to each curve we suggest i that curves which reflect ocean basin volume changes are suitable for the ca 100 to 35 ma greenhouse period ii whereas curves that reflects ocean water volume changes are better suited for the ca 35 to 0 ma icehouse interval and iii that for these respective periods the fit is best when using curves that accounts for both volume changes we used this composite gsl curve to investigate the poorly constrained paleogene to neogene vertical motions of the armorican massif western france it is characterized by a low elevation topography a variscan basement with numerous well dated cenozoic marine deposits scattered upon it using our method we identify low amplitude vertical movements ranging from 66 m of subsidence to 89 m of uplift over that time period their spatial distribution argues for a preferred scale of deformation at medium wavelengths i e order 100 km which we relate to the deformation history of northwestern european lithosphere in three distinct episodes i a phase of no deformation between 38 and 34 ma that has been previously recognized at the scale of northwestern europe ii a phase of low subsidence between 30 and 3 6 ma possibly related to buckling of the lithosphere and iii a phase of more pronounced uplift between 2 6 ma and present which we relate to the acceleration of the africa apulia convergence or to enhanced erosion in the rapidly cooling climate of the pleistocene

reconciling cretaceous paleomagnetic and marine magnetic data for iberia new iberian paleomagnetic poles 1 the cretaceous paleogeography and the kinematic evolution of the iberian plate are poorly constrained especially problematic is to reconcile iberian paleomagnetic data with paleomagnetic data of the neighboring plates and with euler poles derived from seafloor magnetic anomalies the first limitation arises from the cretaceous normal polarity superchron where paleogeographic reconstruction using marine magnetic anomalies is handicapped the second arises from the paucity of reliable paleomagnetic poles with satisfactory statistical criteria and age in order to address these shortcomings and provide new high quality paleomagnetic poles for iberia we conducted a detailed rock magnetic and paleomagnetic study of two cretaceous magmatic sills the paco de ilhas pi and foz da fonte ff sills from the lusitanian basin portugal recently dated at about 88 and 94 ma respectively our results show that the magnetic mineralogy of the sills is primary i e acquired during magma cooling and essentially represented by titanomagnetite the corresponding paleomagnetic poles match the synthetic apwp from the african plate at 80 and 100 ma on the basis of a rigorous selection of iberian cretaceous poles we then calculated mean paleomagnetic poles for different time intervals and found that iberian paleomagnetic data fit well the global apwp between 70 and 120 ma but move far away from the apwp at pre rift times our approach shows that new and better constrained paleomagnetic poles can aide in solving part of the contradiction between iberian and african apwps

seismicity source mechanisms and tectonics of the azores gibraltar plate boundary abstract a study and partial revision of the seismicity and source mechanisms of earthquakes are presented for the oceanic plate boundary of eurasia and africa from the azores islands to the strait of gibraltar focal mechanisms of 36 earthquakes wave form modelling of 4 and seismic moments and dimensions of 28 have been calculated these results indicate that the boundary is divided into three sections with different characteristics the azores the central section and the east section the azores section has high seismicity of moderate magnitude and a low slip rate 0 76 cm yr the predominant mechanism is normal or transform faulting with horizontal tensions on average in a n25 e direction in the central section large earthquakes occur with strike slip right lateral motion along faults in an e w direction there is a high slip rate 3 39 cm yr the east section is of more complex nature large earthquakes also occur but the predominant mechanism is reverse faulting with a horizontal pressure axis in the n30 w direction resulting in underthrusting of africa from the slip vectors the pole of rotation for the african plate is located at 28 2 n 21 1 w nearer to the boundary than previous locations close to the continent there is a continuation in the ocean crust of some structural features of the iberian peninsula

early paleozoic orogenic belt of the andes in southwestern south america result of laurentia gondwana collision the late precambrian to early paleozoic age rock units of the pampean ranges the puna and the north patagonian massif of southwestern south america constitute the famatinian orogenic belt they are interpreted as an ordovician collisional belt between the occidentalia terrane and the gondwana craton they include mafic and ultramafic belts of neoproterozoic to early paleozoic age an intense tectonothermal event resulted from the collision syntectonic granitoids represent crustal melting in that collision syntectonic to late tectonic foreland basins developed the recently proposed juxtaposition of laurentia and east antarctica australia in the neoproterozoic raises the possibility that laurentia and western south america were close together in the early paleozoic and therefore that the famatinian belt resulted from laurentia gondwana collision occidentalia which is bordered by a cambrian carbonate platform similar to that of eastern north america may be a sliver detached from laurentia during late ordovician time

sedimentary architecture depositional facies and diagenetic response to intracratonic deformation and climate change inferred from outcrops for a pivotal period jurassic cretaceous boundary paris basin france abstract the aim of this study is to decipher the respective influences of geodynamic and climate disturbances at the jurassic cretaceous boundary on sedimentary facies and carbonate diagenesis in a stable intracratonic basin using isotopic geochemistry and subsidence quantification fourteen lithofacies were deposited in a 1 carbonate platform and 2 a delta plain environment climate change from cool and wet to warm and semi arid conditions during the early tithonian influenced the syn sedimentary dolomitization process within the carbonate platform during the mid tithonian architecture and facies reconstructions well constrained the jurassic cretaceous unconformity jcu which was an important local structural episode marked by 1 an 80 m uplift in the eastern paris basin and by 2 the formation of a nw se low wavelength 15 km wide and 30 km long flexure this first tectonic event tended to maintain brine ponds and supratidal marsh environments in the platform during the late tithonian and early berriasian forming purbeckian facies and associated dolomitic facies a major depositional change occurred between the early and late berriasian from shallow carbonate platform environments to fluviatile deltaic clastic deposits wealden facies this facies change is underlain by a major unconformity corresponding to the ryazanian unconformity it is marked 1 by erosion processes karstification of the carbonate substrate and the development of ferruginous weathering products goethite followed by 2 incision processes in a fluvial deltaic environment this unconformity is consecutive to a 40 m uplift in the eastern paris basin the rifting phase in the bay of biscay in the pyrenean zone and in the artic north atlantic together with the opening of the ligurian sea had a major influence on the northern part of france by causing uplifts 120 m from the tithonian and flexuring geodynamics played a major role in carbonate demise in the paris basin leading to exposure and karstification of the carbonate platform added to the generalized uplift western tethyan cool and humid conditions from the late berriasian caused terrigenous influx into large scale marine domains which was detrimental and unfavorable to carbonate growth

andean tectonics related to geometry of subducted nazca plate seismological and geological data show that tectonic segmentation of the andes coincides with segmentation of the subducted nazca plate which has nearly horizontal segments and 30 east dipping segments andean tectonics above a flat subducting segment between 28 s to 33 s are characterized by from west to east 1 a steady topographic rise from the coast to the crest of the andes 2 no significant quaternary and possibly neogene magmatism 3 a narrow belt of eastward migrating apparently thin skinned neogene to quaternary shortening of the andes and 4 plio pleistocene uplift of the crystalline basement on reverse faults in the pampeanas ranges from about 15 to 24 s over a 30 dipping subducted plate a west to east andes cross section includes 1 a longitudinal valley east of coastal mountains 2 an active neogene and holocene andesitic volcanic axis 3 the altiplano puna high plateau 4 a high neogene but inactive thrust belt eastern cordillera and 5 an active eastward migrating subandean thin skinned thrust belt tectonics above a steeply subducting segment south of 33 s are similar west of the volcanic axis but quite different to the east early cenozoic tectonics of western north america were quite similar to the neogene andes however duration of segmentation was longer and the width of deformation was greater in the western united states patterns of crustal seismicity are systematically related to plio quaternary structural provinces implying that current deformational processes have persisted since at least the pliocene horizontal compression parallel to the plate convergence direction is indicated to a distance of 800 km from the trench above flat subducting segments crustal seismicity occurs over a broad region whereas over steep segments it is confined to the narrow thrust belt strain patterns in the forearc region are complex and perhaps extensional and a broad region of the altiplano puna and eastern cordillera appears to be aseismic

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

paleomagnetic confirmation of the laurentian origin of the argentine precordillera abstract several recent tectonic models have portrayed the argentine precordillera has been recently portrayed as an early paleozoic laurentian derived exotic terrane now found in southwestern south america these models have primarily been based on strong biogeographic and stratigraphic evidence however no paleomagnetic data have previously been available to independently test them a paleomagnetic study was therefore carried out on the early cambrian cerro totora formation exposed in the northern reaches of the argentine precordillera after stepwise thermal demagnetization a pre folding remanence was identified in ten sites of this formation yielding a paleomagnetic pole ct at 37 0 n 314 1 e a95 5 8 this pole is not consistent with the latest proterozoic early paleozoic apparent polar wander path for gondwana but it agrees with the early cambrian section of the laurentian path if the argentine precordillera is positioned as the conjugate margin of the ouachita embayment in southeast laurentia this result confirms that the precordillera is an allochthonous terrane derived from laurentia in cambrian times that was later accreted to gondwana probably in middle ordovician times

rapid erosion of the southern african plateau as it climbs over a mantle superswell we present new sedimentary flux data confirming that a large pulse of erosion affected the southern african plateau in the late cretaceous and is likely to be related to a major uplift episode of the plateau this short phase of erosion i e less than 30 myr in duration has commonly been difficult to reconcile with a mantle origin for the plateau anomalous uplift given its size the rise of the african superplume is likely to have lasted much longer here we demonstrate by using a simple model for fluvial erosion that tilting of the continent as it rides over a wide dynamic topography high cannot only cause rapid uplift of the plateau but also trigger continent wide drainage reorganization leading to substantial denudation in a relatively short amount of time the amplitude and short duration of the sedimentary pulse are best reproduced by assuming a strong erodibility contrast between the karoo sedimentary and volcanic rocks and the underlying basement we also present a new compilation of paleoclimate indicators that shows a transition from arid to very humid conditions approximately at the onset of the documented erosional pulse suggesting that climate may have also played a role in triggering the denudation the diachronism of the sedimentary flux between the eastern and western margins of the plateau and the temporal and geographic coincidence between the uplift and kimberlite eruptions are however better explained by our tilt hypothesis driven by the migration of the continent over a fixed source of mantle upwelling