using fractal crustal magnetization models in magnetic interpretation1 evidence from borehole susceptibility logs and the spectral analysis of aeromagnetic data suggests that the three dimensional distribution of magnetization within the crust can be described as fractal this property can be exploited in magnetic interpretation methods which explicitly require statistical information on the spatial variation of magnetization specifically we address the problem of magnetic source depth estimation through downward continuation and gridding aeromagnetic survey data using the method of kriging when magnetic data are continued downwards the depth at which the power spectrum flattens out the white depth can be taken to be an estimate of the top of the source distribution this procedure assumes that individual sources are uncorrelated with each other taking into account the correlation of the magnetization using a fractal description leads to a reduction in this depth estimate gridding of randomly distributed magnetic measurements using kriging requires an estimate of the covariance of the data compared with the assumption of a white uncorrelated magnetization distribution using fractal covariances for kriging produces gridded estimates which more closely reflect the statistics of the underlying magnetization process and produce maps with a justifiable degree of smoothness

modelling of magnetic data for scaling geology interpretation of magnetic data can be carried out either in the space or frequency domain the interpretation in the frequency domain is computationally convenient because convolution becomes multiplication the frequency domain approach assumes that the magnetic sources distribution has a random and uncorrelated distribution this approach is modified to include random and fractal distribution of sources on the basis of borehole data the physical properties of the rocks exhibit scaling behaviour which can be defined as p k ak where p k is the power spectrum as a function of wave number k and a and are the constant and scaling exponent respectively a white noise distribution corresponds to 0 the high resolution methods of power spectral estimation e g maximum entropy method and multi taper method produce smooth spectra therefore estimation of scaling exponents is more reliable the values of are found to be related to the lithology and heterogeneities in the crust the modelling of magnetic data for scaling distribution of sources leads to an improved method of interpreting the magnetic data known as the scaling spectral method the method has found applicability in estimating the basement depth curie depth and filtering of magnetic data

quantifying lateral heterogeneities in fluvio deltaic sediments using three dimensional reflection seismic data offshore gulf of mexico scale invariant statistics and strong anisotropy in rock properties are documented from well log and three dimensional seismic data in pleistocene fluvial and deltaic deposits in the eugene island 330 field gulf of mexico systematic quantification of lateral lithologic heterogeneity within a stratigraphic framework using reflection seismic data reveals that fluvial and deltaic depositional systems exhibit statistical behavior related to stratigraphic fabric well log and seismic data profiles show a decay in power spectra with wavenumber k according to k with between 1 and 2 3 vertical and horizontal well log data exhibit power law scaling behavior with between 1 and 2 horizontal seismic horizon slices were extracted from within fluvial and deltaic deposits seismic data from fluvial and deltaic deposits exhibit distinct differences in variance and each depositional system reveals directional anisotropy in one dimensional seismic data profiles from the fluvial deposit reveal anisotropy along depositional strike 1 1 and dip 2 2 the higher correlation observed in the direction of stratigraphic dip for the fluvial deposit may reflect the depositional fabric associated with channel systems correlation parameters obtained in specific depositional environments can potentially be used to quantify rock fabric and provide constraints in the modeling of sedimentary processes

deformation and metamorphism associated with crustal rifting the permian to liassic evolution of the lake lugano lake como area southern alps abstract in connection with movements between europe and adria the southern alps underwent extension leading to the formation of the middle jurassic south alpine passive continental margin as a result of mainly s vergent alpine thrusting and folding a substantially preserved mesozoic crustal section ranging from the surface to a paleo depth of ca 15 km is exposed in the lugano lake como area tectonic processes associated with permo mesozoic extension can thus be investigated at different crustal levels rifting began with a thermal anomaly during which rocks at middle crustal levels were sheared at ca 650 750 c deformation was distributed on a several km wide zone and late kinematic pegmatites were emplaced at this stage temperatures then decreased and beginning in the norian extension was accommodated by a major e dipping normal fault the lugano val grande normal fault the fault which can be followed down to a paleo depth of ca 12 km was listric and flattened to 20 at ca 7 9 km depth in the upper 8 10 km deformation was only brittle whereas at deeper crustal levels greenschist mylonites were formed with continued normal faulting the colder hanging wall cooled the fault zone and greenschist mylonites were progressively replaced by lower temperature ultramylonites and cataclasites the thickness of the fault zone varies from some tens of meters in the upper 5 6 km to several hundred meters at deeper levels deformation was thus discrete at a crustal scale

imaging and interpreting the shallow crystalline crust abstract in the past many tests of high resolution seismic imaging methods utilizing off the shelf technology from hydrocarbon exploration have had only limited success some problems associated with the application of seismic profiling in the shallow crystalline crust differ from those encountered in sedimentary basins perhaps the most fundamental distinction stems from differences in statistical properties of the reflection coefficient time series analysis of power spectra derived from borehole data indicates that the reflection coefficients in the crystalline crust are depleted in the seismic bandwidth relative to sedimentary basins this fundamental difference must be considered in the design of shallow crustal seismic surveys in order to achieve success to a first approximation acoustic impedance variations in sedimentary basins are controlled by velocity changes whereas velocity and density can vary independently in the crystalline crust and changes in density may be relatively more important in controlling reflectivity in certain instances density fluctuations outweigh velocity fluctuations for example physical rock property data from mining districts in the canadian shield suggest that massive fe oxide or sulphide bodies will generate strong seismic reflections

from granulites to eclogites in the sesia zone italian western alps a record of the opening and closure of the piedmont ocean the sesia zone italian western alps offers one of the best preserved examples of pre alpine basement reactivated under eclogite facies conditions during the alpine orogenesis a detailed mineralogical study of eclogitized acid and basic granulites and related amphibolites is presented in these rare weak to undeformed rocks microstructural investigations allow three main metamorphic stages to be distinguished a a medium to low p granulite stage giving rise to the development of orthopyroxene garnet plagioclase brown amphibole ilmenite biotite in basic granulites and garnet k feldspar plagioclase cordierite sillimanite biotite ilmenite in acid granulites b a post granulite re equilibration associated with the development of shear zones producing discrete amphibolitization of the basic granulites and widespread development of biotite sillimanite cordierite spinel in the acid rocks c an eo alpine eclogite stage giving rise to the crystallization of high p and low t assemblages in an effort to quantify this evolution independent well calibrated thermobarometers were applied to basic and acid rocks for the granulite event p t estimates are 7 9 kbar and 700 800 c and for subsequent retrograde evolution p t was 4 5 kbar and 600 c for the eo alpine eclogite metamorphism pressure and temperature conditions were 14 16 kbar and 550 c the inferred p t path is consistent with an uplift of continental crust produced by crustal thinning prior to the subduction of the continental rocks in the light of the available geochronological constraints we propose to relate the pre alpine granulite and post granulite retrograde evolution to the permo jurassic extensional regime the complex granulite eclogite transition is thus regarded as a record of the opening and of the closure of the piedmont ocean

scaling nature of crustal susceptibilities scale invariant or self similar properties have been demonstrated for a wide range of geophysical processes and rock properties evidence from well logs and inferences from aeromagnetic field power spectra suggest that crustal susceptibility also shows this behaviour with a power spectrum proportional to the 4 power of the spatial frequency we examine two large susceptibility measurement data sets and find that they both support the scaling hypothesis

the nature of the non gaussianity of primary reflection coefficients and its significance for deconvolution one of the important properties of a series of primary reflection coefficients is its amplitude distribution this paper examines the amplitude distribution of primary reflection coefficients generated from a number of block averaged well logs with block thicknesses corresponding to 1 ms two way time the distribution is always essentially symmetric but has a sharper central peak and larger tails than a gaussian distribution thus any attempt to estimate phase using the bi spectrum third order spectrum is unlikely to be successful since the third order moment is almost identically zero complicated tri spectrum fourth order spectrum calculations are thus required minimum entropy deconvolution med schemes should be able to exploit this form of non gaussianity however both these methods assume a white reflectivity sequence they would therefore mix up the contributions to the trace s spectral shape that are due to the wavelet and those that are due to non white reflectivity unless corrections are introduced a mixture of two laplace distributions provides a good fit to the empirical amplitude distributions such a mixture distribution fits nicely with sedimentological observations namely that clear distinctions can be made between sedimentary beds and lithological units that comprise one or more such beds with the same basic lithology and that lithological units can be expected to display larger reflection coefficients at their boundaries than sedimentary beds the geological processes that engender major lithological changes are not the same as those for truncation of bedding analyses of sub sequences of the reflection series are seen to support this idea the variation of the mixing proportion parameter allows for scale and shape changes in different segments of the series and hence provides a more flexible description of the series than the generalized gaussian distribution which is shown to also provide a good fit to the series both the mixture of two laplace distributions and the generalized gaussian distribution can be expressed as scale mixtures of the ordinary gaussian distribution this result provides a link with the ordinary gaussian distribution which might have been expected to be the distribution of a natural series such as reflection coefficients it is also important in the consideration of the solution of med type methods it is shown that real coloured primary reflection series do not seem to be obtainable as the deconvolution result from med type deconvolution schemes

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

permian deposits of the southern alps as product of initial alpidic taphrogenesis sedimentological and morphotectonic investigations of permian deposits between the val camonica and the karawanken mountains indicate the development of a complex rift system which initiated the alpidic sedimentation phase

crustal structure of eastern nevada from cocorp deep seismic reflection data the western nevada segments of the cocorp 40 n deep seismic reflection survey of the north american cordillera reveal the geometry of structures of cenozoic and possibly earlier ages to travel times of 10 s corresponding to depths of 30 km the most striking feature of the data is a band of prominent reflections typically at traveltimes of 9 5 to 10 5 s that are present discontinuously across the entire data set few reflections are observed from beneath the base of this reflective zone which is interpreted as the crust mantle transition this reflection mono is inferred to be continuous across the survey area varying gradually in depth but without resolvable offsets it appears to have taken its present form or position during basin range crustal extension the middle to lower crust in much of the survey area is characterized by discontinuous reflections that are typically subhorizontal and locally dip gently west these reflections may represent intrusions or shear zones related to basin range or pre basin range extension but some are likely to be inherited from earlier compressional deformation reflections from the upper crust are interpreted as images of basin fill strata basin range normal faults and mesozoic and paleozoic thrusts related to back arc thrusting and accretion of oceanic and arc related rocks

the broad band fractal nature of heterogeneity in the upper crust from petrophysical logs in situ measurements of petrophysical properties of the upper crust from wire line logs provide a direct means of assessing fluctuations in these properties with depth and thus allow for the statistical characterization of crustal heterogeneity wire line logs from a cluster of nine boreholes 1000 1500 m deep have been analysed using four different techniques autocorrelation semi variogram rescaled range and power spectra six of the boreholes are vertical the remainder inclined all penetrate clastic and pyroclastic rock the analysis techniques have been tested on synthetic data for which we have precise control on the scaling in order to assess their robustness the results for the borehole data show broad band fractal scaling with a fractal dimension of 1 62 to 1 97 autocorrelation 1 59 to 1 79 rescaled range and 1 61 to 2 0 power spectra the use of different techniques to estimate the fractal dimension provides an excellent constraint on the results furthermore it allows us to determine which model for crustal heterogeneity best describes the data a band limited von karman function or unbounded fractal scaling in order to test the possible anisotropy in the scaling parameters the horizontal scaling properties for this area have been calculated by correlation spectra analysis of neighbouring wells this suggests that upper crustal correlation lengths are of the order of kilometres and anisotropic being over four times greater in the horizontal direction the origins of the observed power law scaling are complex analysis of long term correlations between logs and televiewer data points towards the influence of fracture porosity within the pyroclastics but a fractal distribution of pore spaces within the clastics also controls the log fluctuations separating the logs into clastic and pyroclastic subsets reveals slight differences in fractal scaling as determined by autocorrelation and semi variogram these differences are attributed to the dominance of either primary or fracture porosity within each geological unit

the tectonic and rheological evolution of an attenuated cross section of the continental crust ivrea crustal section southern alps northwestern italy and southern switzerland the tectonic and rheological evolution of the southern alpine continental crust is reconstructed from structural petrological and radiometric studies in the ivrea and strona ceneri basement units the deep crust of the southern alps acquired its present compositional and metamorphic zonation during paleozoic magmatism and amphibolite to granulite facies regional metamorphism inferred strength contrasts between lower crustal and upper mantle rocks in the ivrea zone are low at the high temperatures of regional metamorphism late paleozoic transtension and basic to intermediate magmatism in all crustal levels preceded extensional faulting associated with the formation of a passive continental margin during early mesozoic time extensional uplift and cooling of the basement section is coupled with crustal scale trends of increasing rheological stratification grain size reduction and strain localization mylonitic shear zones in the lower crust and a broad zone of noncoaxial shear at the base of the intermediate crust in the ivrea zone are inferred to have controlled the high strain rheology of the attenuating southern alpine crust the deep crust in the thinned ivrea crustal cross section transferred noncoaxial strain from the upper mantle to the intermediate and upper crust final uplift and exposure of the deep southern alpine crust occurred during late cretaceous to tertiary alpine thrusting

a critical assessment of the tectono thermal memory of rocks and definition of tectono metamorphic units evidence from fabric and degree of metamorphic transformations

eoalpine and mesoalpine tectonics in the southern alps according to structural and stratigraphic data eoalpine and mesoalpine tectonics can be clearly recognized in the southern alps and distinguished from the better known neoalpine deformation

estimates of upper crustal heterogeneity in the baltic shield from seismic scattering and borehole logs abstract constraints on small scale heterogeneity in the upper crust of the baltic shield were obtained from stochastic modelling of a variety of seismic data from the babel and siljan ring surveys a non linear least squares inversion scheme was applied to wavefield fluctuations in seismic reflections to obtain statistical parameters of the medium through which the wave energy propagated the reflections are from dolerite sills intruded at depths of 6 12 km into the palaeoproterozoic upper crust of the central baltic shield analysis of the babel data set reveals that the upper crust is a weakly scattering stochastic medium with velocities characterised by an exponential autocorrelation function with a correlation length of 150 50 m and rms velocity perturbation of 1 5 0 5 further inversions show that most of the scattering occurs within the upper few kilometres of the crust analysis of the sijan seismic data set reveals heterogeneity with length scales of 210 50 m and a velocity perturbation of about 1 0 the autocovariance and power spectrum of the sonic log and studies of frequency dependent q in vsp data from the gravberg 1 borehole give consistent estimates of basement heterogeneity the upper crust in this region is characterised by a correlation distance of 35 5 m and rms velocity perturbation of 4 6 in the uppermost 1 2 km of crust associated with near surface fracturing and a correlation distance of 140 50 m and rms velocity perturbation of 1 5 0 5 in the uppermost 6 8 km associated with compositional heterogeneity

pre alpine and alpine evolution of the south alpine basement of the orobic alps new k ar age determinations on the gneisses and schists of the south alpine basement of the orobic alps and their separated minerals have been carried out to supplement and support the previous study ofbocchio et al 1981

eocene ultra high temperature uht metamorphism in the gruf complex central alps constraints by la icpms zircon and monazite dating in petrographic context the gruf complex in the lepontine alps is one of the rare occurrences of phanerozoic uht metamorphism in the world but its age is still a matter of debate here we present la icpms dating in petrographic context of zircon and monazite from an uht restitic granulite zircons and monazites are both included in large crystals and in retrograde symplectites in such restitic rocks partial melting or fluid interactions are unlikely precluding resetting of the monazite chronometers zircon cores yield permian ages interpreted as age of charnockitisation they are sometimes surrounded by a narrow rim at 32 ma monazites are strongly zoned but all yield a 31 8 0 3 ma 15 age interpreted as the time of complete re crystallisation during the uht paragenesis we propose that the zircons dated a post hercynian metamorphism which is responsible of the widespread formation of granulites in the southern alps and the crust differentiation this fluid absent melting event produced refractory lithologies such as restites in charnockites we suggest that gruf uht paragenesis is alpine in age and cristallised from these refractory lithologies we conclude that the lower restitic crust produced at the permian time had the ability to achieve uht conditions during the fast exhumation and heating related to lithospheric thinning in alpine time

synthetic stratigraphy with a stochastic diffusion model of fluvial sedimentation abstract models of stratigraphic completeness and bed formation in fluvial depositional environments have most often assumed that successive depositional and erosional events deposit or erode amounts of sediment independently this results in a random walk model for the total amount of deposited sediment locally as a function of time we consider an extension of the random walk model of sedimentation in an alluvial plain in which deposition or erosion is concentrated in randomly avulsing channels and sediment transport is modeled by the diffusion equation culling s model in contrast to the random walk model this model results in an anticorrelated sequence locally as a function of time i e after an area has aggraded it has a higher elevation and a lower rate of future aggradation in a p evious paper we analyzed the topography generated by the model and argued that porosity variations could be associated with topographic variations the power spectrum s the square of the coefficients in a fourier series of one dimensional transects of topography and porosity horizontally and vertically in this model have a power law dependence on wave number k s k k s with values of s close to those observed in this paper we show that the model deposits sediment with a rate depending on time interval as a power law with exponent 3 4 more consistent with observations than the random walk model the model produces an exponential bed thickness distribution with a skew depen ent on the sedimentation rate of the basin in accordance with observations we also examine the persistence in the series of bed thicknesses as a function of depth for the stochastic diffusion model of sedimentation no persistence is observed if the model fully characterizes the autocyclic dynamics in fluvial sedimentary basins the lack of persistence in the synthetic bed sequences suggests that observed persistence and cyclicity in real bed thickness sequences must be the result of allocyclic processes

from permo triassic lithospheric thinning to jurassic rifting at the adriatic margin petrological and geochronological record in valtournenche western italian alps abstract slices of polycyclic metasediments marbles and meta cherts are tectonically amalgamated with the polydeformed basement of the dent blanche tectonic system along a major alpine shear zone in the western alps becca di sale area valtournenche valley a combination of techniques structural analysis at various scales metamorphic petrology geochronology and trace element geochemistry was applied to determine the age and composition of accessory phases titanite allanite and zircon and their relation to major minerals the results are used to reconstruct the polyphase structural and metamorphic histories comprising both pre alpine and alpine cycles the pre alpine evolution is associated with low pressure high temperature metamorphism related to permo triassic lithospheric thinning in meta cherts microtextural relations indicate coeval growth of allanite and garnet during this stage at 300 ma textures of zircon also indicate crystallisation at ht conditions ages scatter from 263 to 294 ma with a major cluster of data at 276 ma in impure marble u pb analyses of titanite domains with variable al and f contents yield apparent 206pb 238u dates range from permian to jurassic chemical and isotopic data suggest that titanite formed at permian times and was then affected by extension related fluid circulation during the triassic and jurassic which redistributed major elements al and f and partially opened the u pb system the alpine cycle lead to early blueschist facies assemblages which were partly overprinted under greenschist facies conditions the strong alpine compressional overprint disrupted the pre alpine structural imprint and or reactivated earlier structures the pre alpine metamorphic record preserved in these slices of metasediments reflects the onset of the permo triassic lithospheric extension to jurassic rifting

syn contractional overprinting between extension and shortening along the montagna dei fiori fault during plio pleistocene antiformal stacking at the central apennines thrust wedge toe

phase transformations earthquakes and the descending lithosphere abstract the energy dissipated from metastable phase transformations is investigated in this paper in addition to the kinetic energy envisaged by randall at least two other major forms of energy latent heat and metastability energy are involved in a metastable phase transformation the seismic energy density for metastable phase transformation is of the order of 10 24 10 25 erg km 3 for most mantle silicates as an example an earthquake of magnitude m 7 5 would require only 0 01 0 03 or 0 04 km 3 of basalt olivine or pyroxene respectively undergoing metastable phase transformation earthquakes caused by both faulting and phase transformation mechanisms have been observed in high pressure laboratory experiments the energy density associated with a faulting mechanism appears to be four to five orders of magnitude less than that associated with metastable phase transformations of mantle silicates confirming theoretical expectations according to all of the thermal models for the descending lithosphere available in the literature metastable phase transformations almost certainly occur in the descending lithosphere enormous energies would be released suddenly in association with these metastable phase transformations thus earthquakes within the descending lithosphere at depths greater than 100 km may be induced by metastable phase transformations however metastable phase transformations in the descending lithosphere have little or an opposing effect on the tectonic engine driving the motion of plates into the mantle

empirical garnet muscovite geothermometry in low grade metapelites selwyn range canadian rockies partitioning of fe and mg between garnet and phengitic muscovite was calibrated as a geothermometer by green hellman 1982 using experimental data at 25 30 kbar when the thermometer is applied to pelites regionally metamorphosed at pressures of between 3 and 7 kbar it yields temperatures much higher than those from the garnet biotite thermometer a new empirical calibration is proposed for use with such rocks with particular application where garnet occurs at lower grades than biotite the new calibration is where k is given by in k in kd and xii are mole fractions in the garnets the calibration was derived from comparison with the garnet biotite thermometer of ferry spear 1978 assuming no pressure dependence for the partitioning between garnet and muscovite no ferric iron partitioning ideal mixing in muscovite and the garnet mixing model of ganguly saxena 1984 modified for a non linear ca effect this latter garnet mixing model was selected because it gave the geologically most reasonable results it has not proved possible to distinguish a pressure effect from a ferric iron effect despite the simplifying assumptions used to derive the calibration it yields temperatures generally within 15 c of those given by the garnet biotite thermometer and has been used to supply thermometric data in a low grade region of the canadian rockies

prograde metamorphism of metapelites garnet biotite thermometry and prograde changes of biotite chemistry in high grade rocks of west uusimaa southwest finland abstract the metamorphic grade in west uusimaa sw finland increases from low to intermediate amphibolite facies in the west island of kemio up to granulite facies in the middle and eastern parts mineral assemblages in metapelitic rocks indicate metamorphic conditions of 700 825 c 3 5 kbar for the high amphibolite and granulite facies region which is in agreement with independent estimates these metamorphic conditions are used to evaluate garnet biotite thermometry zoning in garnet fe enrichment and mg depletion towards rims bordered by biotite or cordierite and a distinct fe depletion mg enrichment of biotites in contact with garnet are caused by fe mg exchange of these minerals during retrogression 550 c the general prograde metamorphic trend from medium to high grade in west uusimaa is reflected by a systematic change in the composition of biotites thermometry and biotite chemistry are used to indicate that the granulite facies metamorphism in west uusimaa is probably caused by a thermal event

quantitative integration of hydrogeophysical data conditional geostatistical simulation for characterizing heterogeneous alluvial aquifers high resolution geophysical parameter information as it can be provided for example by crosshole georadar and seismic tomography has proven to provide useful spatial information to complement traditional hydrological methods such as core analyses logging techniques and tracer or pumping tests quantitative integration of these diverse database components is one of the major challenges in the field of high resolution hydrogeophysics because of their different scales of measurement and the usually weak petrophysical relations among the measurements in this study we systematically explore the usefulness of a conditional stochastic simulation approach based on simulated annealing for this purpose first we generate a realistic model of an alluvial aquifer consisting of a 2d scale invariant porosity field on the basis of this model we generate synthetic neutron porosity logs and crosshole georadar tomographic surveys we then use the proposed geostatistical simulation approach to integrate this hydr

variations of sulfur isotopes trace element compositions and cathodoluminescence of mississippi valley type pb zn ores from the drau range eastern alps slovenia austria implications for ore deposition on a regional versus microscale the sulfur isotope composition of sulfide ore minerals of the drau range varies considerably down to centimeter scale variations both on a regional and a local scale broadly scattering 34s values ranging between 2 and 25 per mil with a mean around 17 per mil are probably related to both local bacteriogenic and thermal reduction of late triassic marine sulfate the 34s is typically more depleted in ore deposited in subtidal carbonate rocks than in the economic zn and pb ore preferably deposited within intratidal carbonate host rock the 34s 32s ratio increases on the order of fes2 pbs zns which reflects disequilibrium and low temperature formation the strong depletion of 34s in botryoidal sphalerite ranging between 24 and 32 per mil appears to be correlated with the crystal mode wurtzite sphalerite fibers and the enrichment of the trace elements fe as tl and ge sphalerite generations of specific cathodoluminescense color and closely related trace element composition are correlated district wide a decrease of the trace elements fe as tl and ge in the sphalerite generations is coeval with a minor depletion of 34s in the range of 3 and 12 per mil for 34s values in several hand specimens variations in 34s values and trace element zonation on a regional to local scale indicates mixing of local sulfur sources with a regional metal rich brine however distinct peaks in some ore deposits and more positive 34s values of between 5 and 10 per mil are also compatible with derivation of the sulfur from basement rocks the enrichment of the trace element cu in orange luminescing sphalerite negatively correlated with fe as tl and ge and therefore strongly suggests leaching of copper from late permian to early triassic continental red beds frequent evaporites in this stratigraphic section might have supplied sulfur of relatively heavy isotopic composition to the brine hence some sulfur may also have been transported with a metal rich brine

seismic wavelet estimation a frequency domain solution to a geophysical noisy input output problem in seismic reflection prospecting for oil and gas a key step is the ability to estimate the seismic wavelet impulse response traveling through the earth such estimation enables filters to be designed to deblur the recorded seismic time series and allows the integration of downhole and surface seismic data for seismic interpretation purposes an appropriate model for the seismic time series is a noisy input noisy output linear model the authors tackle the estimation of the impulse response in the frequency domain by estimating its frequency response function they use a novel approach where multiple coherence analysis is applied to the replicated observed output series to estimate the output signal to noise ratio snr at each frequency this combined with an estimate of the ordinary coherence between observed input and observed output and with the spectrum of the observed input and cross spectrum of the observed input and output enables estimation of the frequency response function the methodology is seen to work well on real and synthetic data

extensional detachment faulting in the evolution of a tethys passive continental margin eastern alps switzerland the austroalpine nappes of switzerland represent an exhumed and tectonically imbricated segment of the passive continental margin of the jurassic tethys within one of these nappes err nappe part of an upper crustal extensional detachment is preserved indicating that the thinning of the crust was achieved by non uniform extension the mesozoic age of the detachment is shown by comparison between its associated cataclasites and identical cataclasites that are found as redeposited components in middle jurassic sedimentary breccias this low angle detachment within the basement was kinematically linked to synsedimentary high angle normal faults at the surface the area of the err nappe belongs in terms of jurassic paleogeography to the most distal part of the continental margin where both low and high angle normal faults dipped oceanward that is west to northwest in present day coordinates in the more proximal part of the margin however the high angle normal faults dipped eastward toward the continent ammonite stratigraphy within the sediment prisms adjacent to the faults gives evidence for an early jurassic age of the faulting in the proximal part of the margin whereas in the distal part faulting occurred during latest early to middle jurassic time we therefore propose that the jurassic extension of the crust which finally led to the opening of the piemont ligurian ocean was achieved by two fault systems which differ in geometry fault orientation and age these fault systems were composed of a basal low angle detachment with high angle normal faults above the orientation of the older eastward dipping detachment was prone for reactivation during early alpine crustal shortening the present day thrust contact between the two major tectonic units of the area the lower austroalpine and the central austroalpine nappe complex therefore might correspond to an eastward dipping jurassic low angle normal fault

contrasting thermomechanical evolutions in the southalpine metamorphic basement of the orobic alps central alps italy in the southern alps a progressive metamorphic zonation with an increase in the geothermal gradient from ne to sw has been widely proposed however recent investigations have shown that the greenschist metamorphic imprint of the low grade zone corresponds to a metamorphic retrogression following amphibolite facies conditions on the other hand in the medium grade zone a later low pressure high temperature lpht metamorphic event has also been proposed in an attempt to resolve these different interpretations new petrological and partly new structural data have been obtained for two sectors of the orobic alps traditionally attributed to different metamorphic zones thermo barometric determinations supported by microstructural analysis indicate the following different pressure retrograde paths in each sector 1 in the val vedello basement wb rocks a first metamorphic imprint characterized by p 7 9 kbar and t 570 610 c was followed by a greenschist retrogression p 4 kbar and t 500 c 2 in the lario basement lb rocks the first detectable metamorphic stage characterized by mineral assemblages indicating p 7 9 kbar and t 550 630 c was followed by a lpht event synkinematic with f2 extensional deformation a greenschist retrogression marks the final uplift of these rocks reinterpretation of the available geochronological data indicates a diachronism for the two thermo mechanical evolutions in the light of these data we interpret the retrograde p t t path of the vvb rocks as a pre permian post thickening uplift and the retrograde p t t evolution of the lb rocks as a permo mesozoic uplift related to the extensional tectonic regime of the tethyan rifting

fractal heterogeneities in sonic logs and low frequency scattering attenuation cycles in sedimentary strata exist at different scales and can be described by fractal statistics we use von karman s autocorrelation function to model heterogeneities in sonic logs from a clastic reservoir and propose a nonlinear parameter estimation our method is validated using synthetic signals when applied to real sonic logs it extracts the fractal properties of high spatial frequencies and one dominant cycle between 2 5 and 7 m results demonstrate non gaussian and antipersistent statistics of sedimentary layers we have derived an analytical formula for the scattering attenuation of scalar waves by 3d isotropic fractal heterogeneities using the mean field theory penetration of waves exhibits a high frequency cutoff sensitive to heterogeneity size therefore shear waves can be attenuated more than compressional waves because of their shorter wavelength

gaussian scaling noise model of seismic reflection sequences evidence from well logs a simple model for reflection series is desirable for two reasons first to have a means of generating model reflection sequences on which to test geophysical data processing techniques specifically methods of predictive deconvolution and second to suggest a way of parameterizing real reflection sequences for classification and further geologic study in this note we wish to discuss a model suggested by hosken 1980 our discussion is founded upon the powerful ideas of self similarity and scaling developed by mandelbrot 1983 and on the paucity of typical lengths in geology typical lengths are common in physics problems for example the length of an organ pipe governs the wavelengths of the notes played when taking photographs geologists include some manmade object to give scale to the photo otherwise it is very hard to tell if say folds are of centimeter size or form whole mountains

the theoretical seismic reflection response of sedimentary sequences a sedimentary sequence can quite often be considered very fruitfully as a discrete markov chain and thus can be described by a stochastic matrix knowing this matrix and the thickness probability distributions of the layers of the various participating lithologies while assuming that their densities and velocities are normally distributed an expression is derived for the autocorrelation or power spectrum of the seismic reflection response this expression can bring out essential characteristics of the power spectra i e the low frequency droop and its slope this then leads to the possible estimation of some physical and sedimentary parameters of the sequence such as the scatter of the reflection coefficients and the sand shale ratio or sedimentary cycle thickness the case of a binary sequence as the predominant sequence of the sediments of the gulf coast area and nigeria is analyzed in detail the theoretical results conform well with field data and lead to the interesting conclusion that indee

well tie fluid substitution and avo modelling a north sea example accurate well ties are essential to practical seismic lithological interpretation as long as the geology in the vicinity of the reservoir is not unduly complex the main factors controlling this accuracy are the processing of the seismic data and the construction of the seismic model from well logs this case study illustrates how seismic data processing to a near offset stack quality control of logs and petrophysical modelling improved a well tie at an oil reservoir we demonstrate the application of a predictive petrophysical model in the preparation and integration of the logs before building the seismic model and we quantify our improvements in well tie accuracy the data for the study consisted of seismic field data from a 3d sail line through a well in a north sea oilfield and a suite of standard logs at the well a swathe of fully processed 3d data through the well was available for comparison the well tie in the shallow section from first pass seismic data processing and a routinely edited sonic log was excellent the tie in a deeper interval containing the reservoir was less satisfactory the phase errors within the bandwidth of the seismic wavelet were of the order of 20 which we consider too large for subsequent transformation of the data to seismic impedance reprocessing the seismic data and revision of the well log model reduced these phase errors to less than 10 and improved the consistency of the deep and shallow well ties the reprocessing included densely picked iterative velocity analysis prestack migration beam forming multiple attenuation stacking the near offset traces and demigration and remigration of the near offset data the petrophysical model was used to monitor and where necessary replace the p wave sonic log with predictions consistent with other logs and to correct the sonic log for mud filtrate invasion in the hydrocarbon bearing sand this editing and correction of the p wave transit times improved the normal incidence well tie significantly the recordings from a monopole source severely underestimated the s wave transit times in soft shale formations including the reservoir seal where the s wave velocity was lower than the p wave velocity in the drilling mud the petrophysical model predicted an s wave log that matched the valid recordings and interpolated between them the subsequent seismic modelling from the predicted s wave log produced a class ii avo anomaly seen on the cdp gathers around the well

random scattering in magnetotellurics typical well logs show substantial variations of formation electrical resistivity over small spatial scales down to the resolution of the logging tool using a plane stratified earth model we examine the effects of this fine scale microstructure on scattering of the naturally occurring electromagnetic em waves used in magnetotellurics we show how 1 d magnetotelluric mt data may be viewed as arising statistically from a smoothed effective medium version of the resistivity depth profile the difference between the data produced by the true medium and the effective medium is attributable to random scattering noise this noise is fundamental to magnetotellurics and other diffusive wave em exploration methods since it arises from the very small spatial scales that are usually ignored the noise has unique statistical properties which we characterize we show that if scattering is the dominant noise source a thin layer of increased resistivity at depth can be reliably detected only if the noise statist

resolution in seismic imaging is it all a matter of perspective classical wave equation migration of seismic data combines both acoustic wave propagation and an imaging condition to produce a subsurface section integral methods implicitly combine high frequency ray asymptotics of the wave equation with a ray dependent imaging condition the inherent limits on subsurface resolution imposed by acoustic wave generation e g source bandwidth subsurface propagation e g attenuation and recording e g receiver arrays and aperture have been studied extensively this article studies how or whether the choice of imaging condition affects resolution we will see in particular that the phenomenon of migration wavelet stretch wherein the vertical resolution of steeply dipping reflectors is preferentially lowered by migration is neither an artifact of an imaging condition nor a reduction of resolution on steeply dipping reflectors in fact we will discover that in seismic imaging of prestack data steeply dipping reflectors are ultimately better resolved than hori

enhancing seismic data resolution using the prestack blueing technique an example from the ketzin co2 injection site germany restricted resolution imposes limits on the detection of subsurface geologic features using surface seismic data despite great improvements in acquisition and processing techniques in recent years seismic data still suffer from limited resolution detailed subsurface information on the geologic conditions at depth cannot always be attained from conventional surface seismic data for the area of this study the carbon dioxide c o2 storage site at ketzin germany high seismic resolution is required for mapping the internal structure of the main target reservoir processing of the 3d surface seismic data using conventional methods did not provide optimum resolution the spectral blueing technique attempts to enhance the surface seismic data resolution well log data generally show a blue spectrum with higher amplitudes at the higher frequencies than the commonly assumed white reflection series by designing and applying one or several operators to poststack data it has been possible to better match th

crustal thermal regime prior to during and after rifting a geochronological and modeling study of the mesozoic south alpine rifted margin an approximately 15 km thick segment of the mesozoic passive continental margin of adria was involved in alpine shortening and is now exposed in the lake como lake lugano area southern alps northern italy and southern swit zerland the segment comprises the monte generoso basin a deep 9 km extensional basin controlled by the activity of the lugano val grande normal fault the paleosurface and mesozoic geometric relations are well preserved so that the kinematics of fault blocks prior to during and after extension are well constrained rb sr 4oar 39ar and zircon fission track data from basement rocks underlying at various the generoso basin depths provide independent estimates on the thermal evolution of the crustal segment during and after rifting most rb sr and 4oar 39ar ages are contemporaneous with the initial stages of rifting late triassic to early jurassic documenting 1 strongly altered thermal conditions before the onset of ex tension and 2 cooling throughout rifting thermal gradients decreased from 60oc km at the onset of extension to 20oc km 4 shortly after breakup zircon fission track ages are juras sic to early cretaceous providing evidence for continued cooling until the beginning of alpine shortening thermoki nematic numerical modeling of the considered crustal segment provides a full two dimensional description of synrift and postrift evolution synthetic time versus temperature curves are extracted from the model and compared with those derived from absolute ages

from rifting to drifting tectonic evolution of the south alpine upper crust from the triassic to the early cretaceous abstract the tectonic evolution of the south alpine rifted margin is discussed on the base of four palinspastic upper crustal profiles extension related to the movements between adria and europe began in the norian after variscan orogeny late carboniferous to middle permian orogenic collapse and continental scale wrenching from the late triassic to the early liassic stretching was mostly limited to the lombardian basin during this time extension was mainly controlled by four major listric faults symmetrically centred around the late carboniferous early permian collio grabens smaller faults which also started in the norian were progressively de activated during the late triassic after the middle liassic faulting in the lombardian basin gradually ceased and the site of extension shifted westwards i e towards the future site of crustal separation extension was then controlled by a set of west dipping normal faults oceanic crust was formed not later than 157 ma the overall extension along the profile which had a final length of 290 km was 52 km which corresponds to a stretching factor of 1 22 for the whole length of the preserved margin the strain rate is ca 1 10 16 s the sedimentation history suggests that the extension of the south alpine margin was a continuous process from the norian to the middle jurassic the changes in tectonic pattern are related to progressive hardening of the lithospheric segment undergoing slow extension

the whiteness hypothesis reflectivity inversion chaos and enders the earth s reflectivity is one of the principal targets of seismic exploration for oil and gas it exhibits some fascinating properties it is blue it is fractal in all probability it reflects the output of a chaotic generator i examine some of these characteristics here specifically i look at the statistical properties of a canonical chaotic model and i examine the effect of multiples on the statistical properties of seismograms generated from primary reflectivities this article is a tribute to enders robinson he is a pioneer who has inspired many he inspires many to this day i am one of them

an investigation of the spectral properties of primary reflection coefficients this paper investigates the form of the nonwhiteness found in the reflection coefficients from a wide variety of rock sequences around the world in all but one case densities are taken as constant due to the paucity of suitable density data the reflection sequences are pseudo white only above a corner frequency below which their power spectrum falls away according to a power law f where is between 0 5 and 1 5 this spectrum can be adequately modelled in practice very simply with an arma 1 1 process which acts on a white innovation sequence the corollary of this is that before wavelet estimation methods are applied all of which except those based on synthetic seismograms presuppose white reflection sequences or deconvolution filters estimated seismic traces should be filtered with the inverse of this process interestingly the estimated arma processes group themselves into two clearly differentiated categories having very different indices of predictability or strictly indices of linear determinism the two categories apparently correlate precisely with two kinds of sedimentation one which consists largely of sequences of rocks with repeating properties called repetitive in this paper but perhaps loosely describable as cyclic and the other which is randomly bedded with no apparent pattern of components the former has indices of predictability which are two to four times as great as those of the latter another probably related property is that for the repetitive sequences tends to be greater than that for non repetitive rock columns the observed power spectra are shown to be consistent with a simple model for the logarithm of acoustic impedance consisting of a mixture of processes where the distribution of time scale parameters is reciprocal detailed effects of block averaging and sampling the logs are shown to depend on the type of sequence under examination

stochastic analysis of sonic logs from the upper crystalline crust methodology to relate local fluctuations observed in sonic logs to small scale velocity fabric along boreholes both filtering effects and noise introduced by the logging procedure must be taken into account sonic log velocities are represented as a time series consisting of a large scale deterministic and a small scale stochastic component the deterministic trend approximated by a low order polynomial best fit contains information on the average velocity structure whereas the small scale stochastic variations consist of noise plus in situ velocity variations convolved with the logging system response the velocity fluctuations of the sonic data considered here are zero mean and have quasi gaussian probability density functions therefore they are well characterised by their second statistical moment i e their autocovariance function tests on synthetic data indicate that the autocovariance function corresponding to this data model may be used to extract information on the second order statistics of the in situ velocity variations along the borehole and to constrain the level of white noise in sonic logs ignoring the presence of filtering effects and noise in sonic logs may result in seriously flawed estimates of the second order statistics of the actual velocity structure assuming a von karman autocovariance function for the in situ velocity variations this model provides a good match to the autocovariance functions of sonic log data from the siljan ring sweden and sudbury areas canada although differing significantly in their noise content these two data sets yield similar results for the small scale velocity structure which is modelled as a bandlimited self affine time series for the siljan ring borehole we found a close relation between small scale variations of the borehole diameter as determined from caliper logs and the level of uncorrelated noise present in the sonic log data

depth to the bottom of magnetic sources dbms from aeromagnetic data of central india using modified centroid method for fractal distribution of sources abstract the depth to the bottom of the magnetic sources dbms has been estimated from the aeromagnetic data of central india the conventional centroid method of dbms estimation assumes random uniform uncorrelated distribution of sources and to overcome this limitation a modified centroid method based on scaling distribution has been proposed shallower values of the dbms are found for the south western region the dbms values are found as low as 22 km in the south west deccan trap covered regions and as deep as 43 km in the chhattisgarh basin in most of the places dbms are much shallower than the moho depth earlier found from the seismic study and may be representing the thermal compositional petrological boundaries the large variation in the dbms indicates the complex nature of the indian crust

effect of flood basalt stratigraphy on the phase of seismic waveforms recorded offshore faroe islands abstractthe generation of short period multiples between highly heterogeneous layers of basalt flows can strongly alter transmitted seismic wavefields these layers filter and modify penetrating waves producing apparent attenuation and phase changes in the observed waveforms we investigated the waveform and apparent phase changes of the primary seismic signal using mainly the maximum kurtosis approach we compared the seismic recordings from two short offset vertical seismic profiles vsps with synthetic seismograms generated from sonic logs in the same wells and we found that short period multiples cause a rapid broadening of the primary arrivals and strong apparent phase changes within a short depth interval below the top of the basalt flows relatively large uncertainties were associated with estimating constant phase shifts of the seismic arrivals within the topmost 250 m of the basalt sequences where complex scattering occurred within this interval of the brugdan i well a phase only compensat

thermal modeling of carboniferous to triassic sediments of the karawanken range southern alps as a tool for paleogeographic reconstructions in the alpine dinaridic pannonian realm vitrinite reflectance was measured in late carboniferous to triassic shales siltstones and marls of the karawanken range thermal models of the central south karawanken range were calibrated on the basis of these data they suggest an eroded overburden of more than 3 200 m of jurassic to cretaceous sediments and a heat flow in the range of 42 to 60 mw m 2 during the time of maximum subsidence because the reconstructed thermal history of the south karawanken range is very similar to the thermal history of the generoso basin western southern alps these data provide strong evidence for a deep basinal position of the southern karawanken range during jurassic to cretaceous times a vitrinite reflectance anomaly at the northern margin of the south karawanken range is explained by advective heat transport during the oligocene the heat source for the anomalies at the western margin of the seeberg rise and in the area between the periadriatic lineament and the donat fault zone is unknown vitrinite reflectance in late triassic sediments indicates the south karawanken range and the south zala unit of the pannonian basement as exotic blocks in the sava composite unit this is explained by miocene displacement of structural units which were derived from different paleogeographical segments of the permo mesozoic western tethyan margin

spectral analyses of the ktb sonic and density logs using robust nonparametric methods we use robust techniques to estimate power spectra coherences and transfer functions of the german continental deep drilling program ktb sonic and density logs and lithologically defined subsets thereof our results confirm the overall 1 wavelength decay of the power spectra inferred by parametric analyses but provide superior resolution and nonparametric estimates of errors and statistical significance we demonstrate the absence of any statistically meaningful coherence between the velocity logs from the main and pilot holes suggesting a spatially quasi isotropic upper crustal velocity structure also there is little coherence between the physical and caliper logs indicating that disturbances introduced by breakouts and uneven relief of the borehole wall mostly contribute to the uncorrelated portions of the velocity logs coherence between the gamma and physical logs is weak to absent indicating that the observed velocity and density fluctuations are dominated by the physical state of the rocks rather than by their petrological composition attempts to derive poisson s ratio and its variation with wavelength from the relationship between the shear and compressional velocity logs met with limited success but imply that caution should be exercised when comparing poisson s ratio derived from laboratory studies on samples representative of a region to crustal scale seismic determinations our preferred interpretation is that fluctuations in the physical logs in the intermediate wavelength range 10 150 m are dominated by cracks and their level of fluid saturation at larger wavelengths 50 150 m the effects of the petrology becomes more significant as shown by changes in slope of the power spectra and the emerging coherence between the vp and the gamma logs

principles and application of maximum kurtosis phase estimation1 methods of minimum entropy deconvolution med try to take advantage of the non gaussian distribution of primary reflectivities in the design of deconvolution operators of these wiggins 1978 original method performs as well as any in practice however we present examples to show that it does not provide a reliable means of deconvolving seismic data its operators are not stable and instead of whitening the data they often band pass filter it severely the method could be more appropriately called maximum kurtosis deconvolution since the varimax norm it employs is really an estimate of kurtosis its poor performance is explained in terms of the relation between the kurtosis of a noisy band limited seismic trace and the kurtosis of the underlying reflectivity sequence and between the estimation errors in a maximum kurtosis operator and the data and design parameters the scheme put forward by fourmann in 1984 whereby the data are corrected by the phase rotation that maximizes their kurtosis is a more practical method this preserves the main attraction of med its potential for phase control and leaves trace whitening and noise control to proven conventional methods the correction can be determined without actually applying a whole series of phase shifts to the data the application of the method is illustrated by means of practical and synthetic examples and summarized by rules derived from theory in particular the signal dominated bandwidth must exceed a threshold for the method to work at all and estimation of the phase correction requires a considerable amount of data kurtosis can estimate phase better than other norms that are misleadingly declared to be more efficient by theory based on full band noise free data

upper crustal seismic velocity heterogeneity as derived from a variety of p wave sonic logs sonic log measurements provide detailed 1 d information on the distribution of elastic properties within the upper crystalline crust at scales from about one metre to several kilometres 10 p wave sonic logs from six upper crustal drill sites in europe and north america have been analysed for their second order statistics the penetrated lithological sequences comprise archean volcanic sequences proterozoic mafic layered intrusions and precambrian to phanerozoic gneisses and granites despite this variability in geological setting tectonic history and petrological composition there are notable similarities between the various data sets after removing a large scale deterministic component from the observed velocity depth function the residual velocity fluctuations of all data sets can be described by autocovariance functions corresponding to band limited self affine stochastic processes with quasi gaussian probability density functions depending on the maximum spatial wavelength present in the stochastic part of the data the deterministic trend can be approximated either by a low order polynomial best fit or by a moving average of the original sonic log data the choice of the trend has a significant impact on the correlation length and on the standard deviation of the residual stochastic component but does not affect the hurst number for trends defined by low order polynomial best fits correlation lengths were found to range from 60 to 160 m whereas for trends defined by a moving average the correlation lengths are dominated by the upper cut off wavenumber of the corresponding filter regardless of the trend removed the autocovariance functions of all data sets are characterised by low hurst numbers of around 0 1 0 2 or equivalently by power spectra decaying as 1 k a possible explanation of this statistical uniformity is that sonic log fluctuations are more sensitive to the physical state in particular to the distribution of cracks than to the petrological composition of the probed rocks

crustal scale thrusting and extension in the hercynian schwarzwald and vosges central europe the hercynian outcrop areas in the schwarzwald of sw germany and vosges of easternmost france consist from north to south of three major lithotectonic complexes very low to medium grade metamorphics of the saxothuringian belt the polymetamorphic central gneiss complex and the tectonic melange of the southern complex juxtaposition of these three complexes occurred by oblique convergent motions in early carboniferous time the saxothuringian belt is part of a major se dipping accretionary wedge that consists of lower paleozoic meta sedimentary and metaigneous rocks and superimposed upper devonian to lower carboniferous synorogenic volcanics and elastics the central gneiss complex consists of polymetamorphic paragneisses orthogneisses metabasites and meta ultramafics dipping to the nw the southern complex consists of an imbricated melange of north to nw dipping synorogenic elastics volcanics and blocks of ultramafics and gneissic basement the central gneiss complex cgc experienced pervasive hercynian low pressure high temperature metamorphisrn before it was emplaced against and thrust over the sedimentary and volcanic fill of the adjacent synorogenic basins this convergence 340 330 ma produced mylonitic cataclastic shear zones in the cgc the most significant shear zones are the se verging todtnau fault zone between the cgc and the southern complex and the nw verging lubine fault zone between the central gneiss complex and the rocks of the saxothuringian belt these two fault zones enclose a bivergent pop up of the polymetamorphic basement the todtnau fault zone probably extends for more than 100 km along strike and can be traced to a depth of 10 km by deep seismic reflection studies detachment probably occurred along a mid crustal zone of anatexis expressed by a domain of low seismic reflectivity between about 10 and 15 km crustal thickening during early carboniferous convergence led to an extensional phase of crustal reordering between about 330 and 280 ma that was accompanied by the massive rise of posttectonic granitic plutons from middle to high crustal levels simultaneous creation of a structural lamination in the refractory lower crust neglected the main convergent tectonic boundaries it produced a basin and range type lower crust and mantle crust transition in early permian time and involved a major advective input of heat

on the cause of 1 f power spectral scaling in borehole sonic logs borehole logs provide in situ information about the scaling of fluctuations in the elastic properties of rock a surprising finding has been the widespread 1 f type 0 5 1 5 scaling of borehole sonic log power spectra yielding no clear correlation with geological age type or history raising questions about the reliability and origin of these findings ubiquitous fractures for example have been evoked as the most likely explanation of these results firstly we show that the smoothing effects of the logging tool must be taken into account in order to obtain reliable values of we then investigate the scaling properties of lithology only in perfectly exposed metamorphic rock by explicitly excluding fractures we find clear 1 f scaling for reconstructed velocity data based solely on lithological variations although fractures are certainly important in contributing to 1 f fluctuations in borehole logs intrinsic geology may also play a significant role

scale invariant topography and porosity variations in fluvial sedimentary basins we consider a model offloodplain evolving with channelvulsion deposition nd erosion avulsion is modeled asrndom process in spce and time sediment transport is modeled by the diffusion equation culling s model the power spectrum of vritions in the topographic profiles predicted by the model s k is proportional to k 2 where k is the wvenumber this is the brown noise often observed in topography the power spectrum of wristions in the local elevation in time is proportional to f s where f is the frequency the model prediction of brown noise floodplain topography is roughly consistent with spectralnlyses of microtopography measured with lserltimetry we inferred brown noise pleotopogrphy by comparing the pir correlation function of showing wells in the denvernd powder river basins with a synthetic oil field bsed on caprock with brown noise topography topographic control of variations in the grain size of deposited sediment suggests that porosity vritions my exhibit the scale invrince predicted for the topographic profile to illustrate vertical scale invariance in porosity vritions we computed the power spectrum of vertical porosity well logs in 15 offshore wells in the gulf of mexico at spatial scales bove 3 m we find anverge power spectral exponent of 1 4 close to our model prediction of 1 5

patterns of continental extension along the conjugate margins of the central and north atlantic oceans and labrador sea the anomalously thin crust and subsidence history of passive margins suggest that significant extension occurs within continental lithosphere prior to the onset of seafloor spreading we estimate the amount of continental extension prior to seafloor spreading along the conjugate margins of the central and north atlantic oceans and labrador sea from the total tectonic subsidence of the margins in the central atlantic basin the integrated continental extension varies from 225 km for the break between the southern appalachian segment of the north american margin and africa to over 600 km for the break between the blake plateau region of north america and the cape verde terrace region of africa the original width of the extended zone varies from 240 to 770 km in the north atlantic and labrador basins the integrated extension varies from 60 km for the break between northern labrador and greenland to over 600 km for the break between newfoundland and europe the original width of the extended zones in these basins varies from 100 km to over 1460 km in general continental breakup involves two to three times less extension where it follows the preexisting structural grain than where it crosses the preexisting grain as a result seafloor spreading tends to begin first along segments which follow the structural grain extension tends to be symmetrically distributed between conjugate margins where the break follows the grain and asymmetrically distributed where the break crosses the grain failure parallel to the structural grain exhibits greater variability from margin to margin than failure across the grain this phenomenon appears to result from differences in the nature of preexisting weaknesses within the structural grain we conclude that the distribution of the continental extension along passive margins is to a large extent controlled by the orientation of the break relative to the structural grain and the nature of the preexisting weaknesses within that structural grain

replication of apparent nonlinear seismic response with linear wave propagation models it is necessary to understand ground motion amplification by sediment defined as the ratio of ground motions at sediment sites to those at rock sites to predict seismic loadings for earthquake engineering at sediment sites observed weak motion amplifications from magnitude 3 to 4 aftershocks of the 1994 northridge earthquake were twice as large as magnitude 6 7 mainshock amplifications amplitude dependent nonlinear amplification by sediment is one explanation however earthquake simulations with empirical impulse responses and elastic finite difference calculations with weakly heterogeneous random three dimensional 3d crustal velocity variations show that linear wave propagation can explain observed apparently nonlinear sediment responses random 3d velocity variations also reproduce the observed log normal dispersion of peak ground motions deterministic wave propagation models are not adequate to quantify the scaling and dispersion of near source ground motions

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press

a field study of seismic attenuation in layered sedimentary rocks i vsp data summary a coherence matching technique was used to estimate q from both real and log derived synthetic vsp data to try to determine the relative contributions of apparent and intrinsic attentuation in layered sedimentary rocks the field experiment was carried out at the imperial college borehole test site in northumberland england the holes have been drilled through a cyclical sequence of the namurian upper limestone group the q analysis indicates that for frequencies from 40 to 200 hz scattering attenuation due to interbed multiples within the horizontally layered sequences is the dominant mechanism and any contribution from intrinsic attenuation is relatively insignificant confirmation of this result is obtained from an analysis of the frequency content of scattered energy in the coda of the downgoing compressional wave although uncertainty bounds on the q values are large these vsp data are not consistent with an intrisic q value as low as 20 which has been estimated from 500 hz to 1 5 khz crosshole data at the same site as described in part ii

scaling geology and seismic deconvolution the reflection seismic signal observed at the surface is the convolution of a wavelet with a reflection sequence representing the geology deconvolution of the observations without prior knowledge of the wavelet can be done by making assumptions about the statistics of the reflection sequence in particular the widely used prediction error filter is obtained by assuming that the power spectra of reflection sequences are white however evidence from well logs suggests that the power spectra are in fact proportional to a power of the frequency f that is to f with equal approximately to 1