monte carlo estimation and resolution analysis of seismic background velocities the complete solution to an inverse problem including information on accuracy and resolution is given by the a posteriori probability density in the model space by running a modified simulated annealing samples from the model space can be drawn in such a way that their frequencies of occurrence approximate their a posteriori likelihoods using this method maximum likelihood estimation and uncertainty analysis of seismic background velocity models are performed on multioffset seismic data the misfit between observed and synthetic waveforms within the time windows along computed multioffset travel times is used as an objective function for the simulated annealing approach the real medium is modeled as a series of layers separated by curved interfaces lateral velocity variations within the layers are determined by interpolation from specified values at a number of sampling points the input data consists of multioffset seismic data additionally zero offset times are used to migrate the reflectors in time to the depth domain the multioffset times are calculated by an efficient ray tracing algorithm which allows inversion of a large number of seismograms the a posteriori probability density for this problem is highly multidimensional and highly multimodal therefore the information contained in this distribution cannot be adequately represented by standard deviations and covariances however by sequentially displaying a large number of images computed from the a posteriori background velocity samples and the data it is possible to convey to the spectator a better understanding of what information we really have on the subsurface

multicomponent magnetizations from the mississippian mauch chunk formation of the central appalachians and their tectonic implications previous paleomagnetic study of mississippian red beds of the mauch chunk formation from the central appalachians reported shallow inclination directions a positive fold test was obtained after thermal demagnetization typically to only 550 c the near equatorial position for north america indicated by these results has been used to support the idea of a circa 15 latitudinal tectonic offset of the acadia displaced terrain in the northern appalachians the present study of 153 samples from 29 sites occupied in the mauch chunk formation of eastern and southern pennsylvania reveals multicomponent magnetizations a characteristic component declination d 161 0 inclination i 27 8 alpha95 a95 7 9 with unblocking temperatures usually concentrated above 650 c and with dual polarity 10 sites normal 13 sites reversed is isolated in 23 sites and passes a fold test at the 99 confidence level it is interpreted as an early acquired hematitic detrital or chemical magnetization of pre alleghanian orogeny and pre kiaman reverse polarity interval age a southern hemisphere paleolatitude of 15 for the sampling area is indicated another component has generally lower unblocking temperatures which however can extend up to 650 c or more and therefore is also likely to be carried by hematite this secondary magnetization d 170 6 i 5 3 a95 5 0 isolated in 25 sites is of uniform reverse polarity and application of fold tests suggests that it is of synfolding origin a near equatorial paleolatitude 3 n at the time of acquisition is obtained consistent with permo carboniferous kiaman directions from north america incomplete removal of the secondary component can explain the previous results from the mauch chunk comparison of the present paleomagnetic results with those from similar age rocks in the canadian maritimes does not support a latitudinal offset of acadia with respect to interior north america in the early carboniferous in fact according to these and other paleomagnetic data thought to be representative of this age the atlantic bordering continents already were near to a pangea configuration the alleghanian and particularly the hercynian orogenies therefore may not be associated with the closure of a large latitudinal ocean later in the carboniferous and permian alleghanian deformation however may have resulted in the partial bending of the pennsylvanian salient on the basis of apparently systematic deviations in paleomagnetic declinations

plate and intraplate processes of hercynian europe during the late paleozoic abstract it is speculated that until late carboniferous time the region of hercynian europe was occupied by an elongated island arc system underlain by a segment of continental crust in the upper carboniferous two subduction zones are assumed to have extended from the north and south beneath hercynian europe an extensive zone of hot partially molten upper mantle lay above and between these and diapiric uprise of portions of this material led to separation of mafic magmas widespread partial melting in the lower and middle crust high temperature low pressure metamorphism in crustal rocks and regional uplift and extension of the crust as indicated by intermontane troughs and their associated volcanic rocks in visean to westphalian time hercynian europe collided with both the large neighbouring plates north america europe and africa during these diachronous collisions and owing to reduced rigidity of the relatively hot island arc crust the irregular continental margins of the larger and thicker continental plates induced oroclinal bending of hercynian europe after the collision processes had been terminated processes of upper mantle activity continued causing further crustal uplift and even enhanced crustal extension for several tens of million years into the lower permian decline of the upper mantle activity beneath hercynian europe is indicated by crustal subsidence and formation of a peneplain in permian time followed by the upper permian transgression of both the zechstein sea and the tethys sea which mark the end of the hercynian geodynamic cycle

early palaeozoic palaeobiogeography of the variscan regions abstract the palaeobiogeographic method appears to be an attractive alternative for reconstruction of the palaeogeography of the variscan regions during the palaeozoic the evolution of faunal assemblages and climatic characteristics from the cambrian up to the end of the devonian demonstrates that baltica and north gondwana represent two major and independent palaeogeographic entities separated by a mid european rheic ocean which opened as early as the cambrian and closed progressively from the devonian the south armorican ocean whose closure generated the so called ligerian orogen is regarded as a branch of the rheic ocean both a tornquist s sea separating baltica from its western extension avalonia during the ordovician and a proto tethys ocean extending between southwestern europe and north africa during the devonian are excluded from our reconstructions

blocky regularization schemes for full waveform inversion with ill posed inverse problems such as full waveform inversion regularization schemes are needed to constrain the solution whereas many regularization schemes end up smoothing the model an undesirable effect with fwi where high resolution maps are sought blocky regularization does not it identifies and preserves strong velocity contrasts leading to step like functions these models might be needed for imaging with wave equation based techniques such as reverse time migration or for reservoir characterization enforcing blockiness in the model space amounts to enforcing a sparse representation of discontinuities in the model sparseness can be obtained using the 1 norm or cauchy function which are related to long tailed probability density functions detecting these discontinuities with vertical and horizontal gradient operators helps constraining the model in both directions blocky regularization can also help recovering higher wavenumbers that the data used for inversion would allow thus helping controlling the cost of fwi while the cauchy function yields blockier models both 1 and cauchy attenuate illumination and inversion artifacts

strike slip orogens an explanation for the hercynides the nature of oblique plate interactions is not yet well understood the oblique interaction of pacific and n american plates has resulted in large scale migration rotation and accretion of microplates intervening basins are ephemeral individually filled and deformed oblique motion results in zones of both compression and extension the latter may be sufficient to generate new oceanic crust and the former to obduct it both subduction and collision are restricted in time and space the resulting orogen is extraordinarily complex in detail the far more complicated hercynides are the result of dextral interaction between continental plates europe and africa the lateral variability of the orogen the major and long lived strike slip faults the bimodal volcanism and related ore deposits of the european trough the lizard ophiolite and its melanges the nw spanish ophiolites and the iberian pyrite belt are all explained using an oblique collision model in particular the generation deformation and obduction of ophiolites in oblique slip mobile zones is discussed

geophysical and geochemical evidence for a hercynian magmatic arc maryland to georgia the distribution of hercynian granitic plutons in the central and southern appalachians is compatible with their being generated in a continental magmatic arc environment isotopic and geochemical data show a consistent pattern of lesser degree of crustal involvement in the most easterly plutons both gravity and aeromagnetic anomaly data suggest that the plutons were either synchronous with or postdate the development of the geophysical anomalies and are unlikely to be a part of any major allochthon

origin of beach ridges and swales abstract sandy beach ridges occur in four main categories 1 swash built 2 settling lag 3 eolian 4 storm surge ridges in the first two classes are geometrically regular only a few tens of centimeters above adjacent swales and commonly in ridge sets and systems tens to hundreds of ridges each individual sets of 5 25 ridges tend to stand 0 5 m to 2 m above or below adjacent sets ridges in the third and fourth classes do not have these characteristics do not occur in sets and are generally not suitable for detailed historical studies no one of these ridges is the same as the storm built berm which is almost never preserved swash built sandy beach ridges have diagnostic 1 map spacing 2 accretion rate 3 periodicity 4 crossbedding and 5 granulometry the last two indicate fair weather waves on a sandy beach in contrast with settlinglag ridges postma style which have the same external geometry but which were deposited without important wave work and in contrast with storm built berms generally seen on eroding coasts but rarely or never in beach ridge plains the grain size kurtosis of beach sand is an excellent index to near shore wave energy density changes in kurtosis at ridge set boundaries mark changes in long term wave energy density hence in sea level the latter can be deduced also from set height differences and from spacing differences periodicity is typically 30 60 years map spacing 25 50 m and accretion rate fairly close to 1 m yr a few ridge sets with intervals of 3 7 10 12 or 18 19 years have smaller spacings this is not what can be done if each ridge is built by one storm if each ridge had been built by one storm wide beach ridge plains like one in denmark dating from about 11 700 yr b p would have been formed in the last 30 50 years at accretion rates of hundreds of meters per year instead each swash type sandy beach ridge was made by a sea level rise and fall couplet amplitude 5 30 cm the swale marks the lower position this mechanism reflects the fact that the transverse profile from beach to sea is gently concave upward with maximum curvature close to shore this is a shape which is out of adjustment with the shoaling wave system shortly after a small sea level change settling lag ridges were built without waves hence the ridge and swale sequence in this case cannot be attributed to waves either fair weather or storm these ridges show the same historical pattern as do swash built ridges this fact suggests that both were controlled by the same mechanism sea level change

free energy minimization by simulated annealing with applications to lithospheric slabs and mantle plumes an optimization algorithm based upon the method of simulated annealing is of utility in calculating equilibrium phase assemblages as functions of pressure temperature and chemical composition operating by analogy to the statistical mechanics of the chemical system it is applicable both to problems of strict chemical equilibrium and to problems involving metastability the method reproduces known phase diagrams and illustrates the expected thermal deflection of phase transitions in thermal models of subducting lithospheric slabs and buoyant mantle plumes it reveals temperature induced changes in phase transition sharpness and the stability of fe rich phase within an field in cold slab thermal models and it suggests that transitions such as the possible breakdown of silicate perovskite to mixed oxides can amplify velocity anomalies

an interpretation of the variscan structures in sw england the variscan structures in sw england apart from the high level structures in the culm synclinorium of n devon are recumbent with an overall gentle southward dip of cleavages thrusts and recumbent folds translation was towards the nnw the structures are interpreted on a thin skinned model with a basal decollement dipping gently s related to a s dipping subduction zone s of the lizard the granites are thought to have been generated to the s of their present position and injected northwards above the decollement zone

joint traveltime inversion of wide angle seismic data and a deep reflection profile from the central north sea we report results from the seismic wide angle and broadband survey carried out over the mid north sea high this paper focuses on integrating the information from a conventional deep multichannel reflection profile and a coincident wide angle profile obtained by recording the same shots on a set of ocean bottom hydrophones obh to achieve this integration a new traveltime inversion scheme was developed reported elsewhere that was used to invert traveltime information from both the wide angle obh records and the reflection profile simultaneously results from the inversion were evaluated by producing synthetic seismograms from the final inversion model and comparing them with the observed wide angle data and an excellent match was obtained it was possible to fine tune velocities in less well resolved parts of the model by considering the critical distance for the moho reflection the seismic velocity model was checked for compatibility with the gravity field and used to migrate and depth convert the reflection profile the unreflective upper crust is characterized by a high velocity gradient whilst the highly reflective lower crust is associated with a low velocity gradient at the base of the crust there are several subhorizontal reflectors a few kilometres apart in depth and correlatable laterally for several tens of kilometres these reflectors are interpreted as representing a strike section through northward dipping reflectors at the base of the crust identified on orthogonal profiles by freeman et al 1988 as being slivers of subducted and imbricated oceanic crust relics of the mid palaeozoic iapetus ocean

louisiana cheniers settling from high water abstract there are two kinds of cheniers in louisiana one made largely of shell debris the other mostly quartz sand this report deals with the second in other study areas where swash built beach ridges are made of quartz sand suite mean values of grain size kurtosis show near shore wave energy level and the extent to which settling from water was important kurtosis close to 3 3 5 indicates moderate to high wave energy density and little or no settling kurtosis about 4 indicates low energy as k rises above 4 the settling component increases louisiana cheniers have a very high kurtosis 10 and a standard deviation of kurtosis 9 5 far higher than any other sandy beach ridges now known nothing else 6 these numbers put the cheniers in a class with settling deposits from waning stages of storms just seaward of the surf zone a plot of kurtosis against standard deviation of the grain diameter places the louisiana examples with other known products of settling such as the horizontally bedded settling lag not swash built beach ridges on mesa del gavilan near the mouth of the rio grande texas one narrow sandy swash built beach ridge does not represent a single storm but decades of slow deposition by the swash each ridge indicates a small slow rise and fall pair in sea level perhaps 5 40 cm beach ridges commonly occur in sets of 5 to 20 or more differences in the heights of ridge sets mark larger changes in sea level high ridge sets represent a century or more of high sea level low ridge sets indicate a century or more of low sea level the vertical difference between set elevations is typically less to much less than three meters the louisiana cheniers except where splayed are like beach ridge sets rather than like the individual swash built beach ridges that are seen in other study areas

origin of beach ridges reply abstract the important difference here is whether or not sea level can change by the right amounts and on the right schedule curray says no however various reports in the recent literature cited below show that he is mistaken likewise his concept of uniform global change is not supported by the published data sea level does change at relatively short intervals years decades by amounts that are adequate to produce individual sandy beach ridges and this change is not uniform at all places my citation of curray and others for an 18 6 year period in one sandy beach ridge plain was an inadvertent error and i apologize for it my caveat that we do not know that his study area in a well known modern deformational belt was completely stable throughout the holocene is still valid the corollary data obtained from such areas may not be as useful as information from other areas therefore the presumed 18 6 yr cycle is suspect ab initio curray s hypothesis that beach ridges are initiated by what is basically the suggestion of de beaumont does not provide a suitable model as is discussed below finally curray disregards the detailed granulometric analysis which was the basis for most of my work this modern analysis can stand alone if necessary and is not affected in any significant way by warping or other small deformation however the present availability of records of small modern sea level changes confirms the reasonableness of the timing and magnitudes which were deduced as part of the granulometric work

the structural setting and tectonic significance of the glen dessary syenite inverness shire the glen dessary syenite crops out in the steep belt of the northern highland moine it is enclosed within a psammite envelope which was previously assigned to the glenfinnan division but which is here correlated with the psammites of the loch eil division exposed to the e of the loch quoich line three episodes of deformation have been identified in the moine metasediments of the glen dessary area but only the latest d 3 is thought to have deformed the syenite imposing on it a strong steeply plunging mineral lineation the syenite is thought to occupy the core of a large intensely curvilinear d 3 synform the d 3 structures which deform the syenite can be correlated with upright structures which reworked previously flat lying already crystalline rocks recognized at loch quoich upright reworking must be younger than the glen dessary syenite dated by u pb methods at 456 5 ma two hitherto unrecorded small bodies of granitic gneiss similar to the c 1020 ma ardgour gneiss have been identified in psammites of the loch eil division near the w end of loch arkaig their presence suggests that the loch eil division has a grenville history and is part of the 9old moine9

the evolution of the avalonian plate abstract the avalon platform of newfoundland is the type locality of the avalonian plate that is characterized by late precambrian volcanic and clastic rocks marine at the bottom and terrestrial at the top all are intruded by 650 550 ma granites late precambrian rocks in the southern british isles are similar in both areas northeastern parts of the belt are affected by deformation and metamorphism that have orogenic aspects the orogeny is referred to as the avalonian in newfoundland and monian in britain to the southeast of the avalonian rocks in europe lies another late precambrian cadomian orogenic belt of rocks as a part of the pan african orogenic belt the cadomian and avalonian belts extend into north africa morocco since these belts are ophiolite bearing it is suggested that the plate was bordered by oceanic domains it is therefore proposed that a microcontinental volcanic arc that was generated in the late precambrian was orogenically deformed by collision with north america europe and africa and survived as a coherent terrain until the late carboniferous

pre mesozoic paleomagnetism and plate tectonics although the arguments perhaps did not convince everyone at the time the paleomagnetic polar wander paths for europe and north america plotted by runcom 1956 certainly convinced me as a young graduate student that continental drift as we called it in those pre plate tectonic days deserved serious attention then throughout the 1960s the geoscience world seemed busy documenting and refining the models of seafloor spreading and plate tectonics that governed the opening of today s oceans as the number of publications espousing plate tectonics seemed to grow exponentially an often tacit assumption was that the continental breakup was a unique event and that pangea was a quasi primordial continental configuration ahead of his time however j tuzo wilson 1966 queried in a now classical paper did the atlantic close and then re open the 1973 penrose conference in vail colorado on pre mesozoic plate tectonics dewey spall 1975 showed that by then many earth scientists were preoccupied with proving that the tacit assumption was wrong and that wilson was right but compared to mesozoic and later plate tectonics the task of quantifying pre mesozoic continental movements is much more difficult since there are no seafloor magnetic anomalies to work with and much of the potential evidence e g ophiolites diagnostic supracrustal sequences high pressure low temperature metamorphic rocks has been destroyed by that ultimate plate tectonic process the continent continent collision and by sub sequent uplift and erosion nevertheless a multitude of observations facts interpretations reinterpretations proposals and hypotheses can now be found in the literature for virtually any pre mesozoic period and any geographic

automatic 1 d waveform inversion of marine seismic refraction data summary full waveform synthetic seismograms are now used as standard in the interpretation of marine refraction data but only with a laborious trial and error fitting procedure we show how the matching of observed waveforms with wkbj synthetic seismograms can be efficiently and automatically performed for 1 d earth models automation of the inversion is difficult because of the multi modal irregular form of the misfit of data and synthetics a sequence of three steps is required for a complete inversion location of the deepest valley of the misfit function descent to the global minimum and description of the neighbourhood of the minimum for error analysis the first step is accomplished with a monte carlo search through a very large model space defined by poor prior knowledge of velocities and gradients of the solution weak traveltime constraints are used to eliminate poorly fitting models from waveform calculations a comparison of the traveltime and waveform misfits of the monte carlo models clearly illustrates that waveforms are providing more information than traveltimes alone bayesian statistics are used to construct marginal probability distributions and the covariance matrix which give a rough preliminary error analysis in the second step damped least squares linearized inversion makes small adjustments to the best fitting monte carlo model as it descends to the global minimum finally the immediate neighbourhood of the global minimum is explored with constrained least squares inversion realistic error bounds on each parameter are defined from the resulting slices through the misfit function these bounds are much narrower than traveltime inversion provides correlations between parameters are obtained from the covariance matrix constructed from models examined during this error analysis the inversion methods are illustrated on the ff2 refraction data set of the scripps institution of oceanography the monte carlo search successfully locates the valley of the global minimum as well as a nearby secondary minimum the error analysis puts realistic error bounds on the detailed inversion of this data set by spudich orcutt

waveform inversion of marine reflection seismograms for p impedance and poisson s ratio summary the estimation of the elastic properties o the crust from surface seismic recordings is of great importance for an understanding of the lithology and the detection of mineral resources although in marine reflection experiments only p waves are recorded information on shear properties o the medium si contained in the reflection amplitudes recorded at different distances from the source being able to estimate both dialatational and shear properties gives stronger constraints on the lithology it is therefore desirable to recover both types of elastic parameters from multi offset seismograms in the real data example presented here the amplitude of the reflections cannot be explained by one parameter related to the dilatational properties p impedance only when trying to minimize the least squares fit between synthetic and real multi offset seismograms when adding an additional parameter related to the shear properties poisson s ratio the fit between synthetic and real seismograms improves synthetic wavefrom fitting experiments underline the possibility of recovering poisson s ration when the p impedance model is well known from fitting waeveforms recorded at small offsetts in the real data example the resulting models for p impedance and poisson s ratio are anticorrelated in most depth regions but are correlated in particular depth region indicating a sudden change in lithology

suspect terranes and accretionary history of the appalachian orogen the north american connection or the grenvillian continental crust that separated from eastern north america during the initiation of the appalachian orogenic cycle is poorly defined within the present orogen a variety of terranes occur outboard of the north american miogeocline all structurally uncoupled and therefore suspect stratigraphic analysis indicates that appalachian accretion progressed from the miogeocline outward the boundaries of the earliest accreted western terranes are marked by melange and ophiolite complexes later boundaries between eastern terranes are steep mylonitic zones and brittle faults accretionary events defined by stratigraphic analysis correspond to times of major deformation plutonism and metamorphism in the history of the orogen

a kinematic model for the collision and complete suturing between gondwanaland and laurussia in the carboniferous maps of middle to late carboniferous strike slip faults in western europe northern africa and eastern north america have been compiled from geological gravity and magnetic onshore and offshore data a large majority of these faults can be interpreted in terms of a logical syn to post collisional pattern superimposed on the initial suture between the african i e gondwana and north american european laurussian continental margins the pre collision positions of the major continents are derived from paleomagnetic data and when combined with the general distribution of the strike slip faults lead to a kinematic model of the complex middle late carboniferous collision in this model the west african precambrian craton acted as a rigid promontory or die with respect to the partially rigid plastic zones between it and the large north american craton these partially rigid plastic zones comprise the external appalachian and canadian maritime margins the mauritanide and hercynian margins of north

40 ar 39 ar mineral age record of early caledonian tectonothermal activity in the baltoscandian miogeocline central scandinavia in central portions of the scandinavian caledonides greenschist facies volcanosedimentary successions within the koeli nappe complex have been thrust several hundred kilometers eastward onto the baltoscandian platform these were derived from eugeoclinal terranes situated outboard west of the baltica continent during the early paleozoic the koeli nappe complex is tectonically underlain by higher grade units within the seve nappe complex these are composed of amphibolite and granulite facies rocks and locally contain eclogites the seve nappes tectonically separate koeli units from structurally lower allochthons derived from more inboard environments along the baltoscandian miogeocline previous mineral isotopic age determinations from seve and koeli units have been in the 430 to 390 ma range and have been interpreted to presumably date cooling following scandian middle silurian to early devonian metamorphism however incremental release sup 40 ar sup 39 ar dates recorded by minerals within some of the koeli and seve nappes exposed in jaemtland sweden taennforsen and are districts provide evidence of earlier tectonothermal activity hornblendes from the seve and koeli nappe complexes display variably discordant age spectra as a result of low temperature experimental evolution of loosely bound extraneous argon components however in most analyses plateau ages of 510 to 475 ma koeli and 465 to 455more ma seve are defined in contrast muscovite and biotite from all tectonic units record scandian cooling ages between 245 and 410 ma the older events recorded by hornblende within these seve and koeli units are evidence of early caledonian tectonothermal activity and subsequent diachronous cooling during the early middle ordovician less