geodynamic control on carbonate diagenesis petrographic and isotopic investigation of the upper jurassic formations of the paris basin france abstract the oxfordian and kimmeridgian carbonates of the eastern edge of the paris basin display poor reservoir properties stable isotope investigation of these non recrystallized cements through both microdrilling sampling and in situ sims secondary ion mass spectrometry analysis shows that they originated from slightly buffered meteoric fluids 3 smow to 8 smow flowing through the malm carbonate aquifers of the eastern edge of the paris basin after a review of the post upper jurassic history of the paris basin it appears that meteoric water supplies leading to such cementations were associated with the evolution of the basin s geodynamic setting and notably with the lcu late cimmerian unconformity major event which corresponds to the uplift of the london brabant massif denudation of the oxfordian and kimmeridgian carbonates on the southern flank of the london brabant massif to the north of the study area then lead to lateral recharging of the associated aquifers with meteoric fluids this scenario is similar to the one proposed to explain cementations of the jurassic carbonates in the wessex weald basins which emphasizes the main role played by the cretaceous unconformities over carbonate diagenesis at the scale of the northwestern tethys margin

the deep seismicity of the tyrrhenian sea summary l he study reappraises the deep seismicity of the tyrrhenian sea careful examination of the quality of reported hypocentres shows that the earthquakes define a zone dipping nw about 200 km along strike 50 km thick and reaching a depth of about 500 km the zone is slightly concave to the nw at a depth of 300 km but contrary to many previous reports is not tightly concave nor are there significant spatial gaps in the seismicity which is effectively continuous with depth seismicity is however concentrated in the depth interval 250 300 km where the dip of the seismic zone changes from 70 above 250 km to a more gentle dip of 45 at greater depths seven fault plane solutions are available for the largest earthquakes in this depth interval all of them consistent with a p axis down the dip of the seismic zone and all of them requiring movement on faults out of the plane of the subducting slab two deep earthquakes near naples lie well outside the main zone of activity for one of which a fault plane solution is available that has ap axis not aligned with the dip of the seismic zone the tightly concave slabgeometry favoured by other reports is supported mainly by the location of these events near naples which we think may represent deformation in a separate probably shallower dipping piece of subducted lithosphere the lack of shallow seismicity and particularly of thrust faulting earthquakes at the surface projection of the benioff zone suggests that active subduction has ceased estimates of the convergence rate responsible for subduction in the last 10 myr far exceed the present convergence rate of africa and eurasia suggesting that the subduction was related instead to the stretching and thinning of the crust in the tyrrhenian sea

early diagenetic microporosity in the cotton valley limestone of east texas abstract the upper jurassic cotton valley limestone was deposited on a mature ramp where monotonous regional slopes were punctuated by salt generated structures and basement topography the strandline and the crests of paleobathymetric highs were blanketed by oolitic and palletoidal grainstones the ratio of grainstones to mudstones increases in the upper cotton valley reflecting a regional shallowing phase thinner shoaling upward sequences are present but they do not correlate easily especially from basement highs to salt domes probably because salt movement occurred during deposition of cotton valley rocks the complex diagenetic history of the cotton valley inferred from cross cutting features observed in thin section and from trace element and stable isotope content includes the origin of chalky microporosity especially in ooids this intraparticle intercrystalline porosity occurs in a fabric of equant subhedral to euhedral low mg calcite micro rhombs which appear to have developed at the expense of an acicular precursor such microporous ooids are present mainly on the crests of paleobathymetric highs nearby offstructure ooids contain a mixture of micritic and well preserved ooids however these micritic ooids are different from the micro rhombic microporous ones on the highs the well preserved low mg calcite ooids from offstructure positions exhibit relict acicular microstructures in some of their lamellae the chalky microporosity is crosscut by virtually every other diagenetic feature in the cotton valley limestone the 13c values from individual microporous ooids range from 1 65 to 2 76 pdb which is not in the range of values associated with precipitation in a hydrocarbon rich environment the formation of microporosity was followed by the formation of embayed grain contacts pore filling cementation grain compaction stylolite formation replacements by quartz and rhombic dolomite fracturing fracture filling cementation saddle dolomite late leaching and formation of authigenic sulfides the microporosity is interpreted to have been formed in the near surface diagenetic environment early in the burial history of the cotton valley as there is no evidence of vadose diagenesis the ooids on the crests of calcarenite shoals must have been placed is disequilibrium with their surroundings by a change in water chemistry probably as a consequence of regression and an influx of fresh water the introduction of hydrocarbons appears to be contemporaneous with such late diagenetic features as saddle dolomite and authigenic sulfides however the extent to which those fluids affected the micro rhombic calcite crystals appears to be negligible

monte carlo simulation of stress associated scattering attenuation from laboratory ultrasonic measurements abstract seismic coda waves scattered by small scale heterogeneities contain information on stress changes of the medium because of changes in the physical state of materials based on the ultrasonic measurements under different stresses for a cylindrical sandstone sample we investigate the influence of stress changes on ultrasonic s coda attenuation and aim to characterize its stress frequency dependent pattern considering the complexity of ultrasonic coda waveforms measured from finite size rock samples in laboratory experiments the monte carlo simulation is employed to synthesize ultrasonic envelopes which act by incorporating the effect of multiple scatterings and boundary reflections on coda waves the optimal simulation parameters estimated by minimizing the residual between the observed and synthesized envelopes indicate that the rock sample under study presents moderate heterogeneities the relationship between attenuation and stress is similar for direct and coda s waves and remains stable in the range of high effective stresses around 30 60 mpa with less stress sensitivity enhanced attenuation for both types of waves occurs at lower effective stresses but with coda attenuation much faster and stronger presenting a quite different nonlinear behavior with respect to stress coda attenuation increases drastically at extremely low effective stresses below 15 mpa because of the increase in rock compliance showing much greater sensitivity to high pore pressure than intrinsic attenuation this study improves our understanding of the mechanism of ultrasonic coda attenuation and its scaling dependence on stress and frequency

a possible seismic gap within a highly seismogenic belt crossing calabria and eastern sicily italy a review of the seismic geologic and geodynamic information available for the calabro sicilian region of southern italy leads us to suggest a unifying view of the larger m 7 earthquakes that have occurred there in the last millennium coincidentally concentrated in the last 3 7 centuries the seismicity coincides with a narrow curvilinear extensional belt that passes through western calabria and eastern sicily wces belt and which includes a nearly continuous north south succession of primarily east dipping normal faults in our reconstruction of the seismotectonic process the faulting is activated by west northwest east southeast extension induced by residual rollback of the ionian subduction slab our analysis of the space time distribution of strong earthquakes indicates a zone of conspicuous aseismicity m 4 5 since 1700 m 7 since 1000 along the belt corresponding to the 30 km long scaletta fiumefreddo segment of the messina fiumefreddo fault in eastern sicily moreover because estimated recurrence times are on the order of a millennium for m 7 earthquakes along different parts of the wces belt and because historical data for destructive earthquakes in the first millennium a d are not detailed enough to allow reliable identification of the source zones we cannot definitely state whether or not there is a late stage seismic gap for a large earthquake in eastern sicily by applying standard relationships the potential for a magnitude 7 earthquake can be estimated for the scaletta fiumefreddo 30 km long normal fault segment the level of seismic activity has been low in the possible gap area in the past two decades when the upgraded local network has detected tens of events above magnitude 2 5 with values up to 3 7 hypocenter locations of these events seem to delineate the deep geometry of two faults reported in the surface geologic maps one of which is the scaletta fiumefreddo silent fault coulomb stress changes not larger than 0 6 bar produced on the silent fault by the most recent m 7 regional earthquake 1908 and the substantially nil coulomb stress change on the same fault by m 7 earthquakes of 1693 and 1783 imply relatively small perturbation by previous earthquakes to the silent fault compared with the coulomb stress perturbation of 2 2 5 bars estimated by other investigators on the 1908 earthquake source caused by major earthquakes of the previous centuries

spatio temporal evolution of volcano seismicity a laboratory study we report a laboratory and microstructural study of a suite of deformation experiments in which basalt from mount etna volcano is deformed and fractured at an effective confining pressure representative of conditions under a volcanic edifice 40 mpa particular attention was paid to the formation of a fracture and damage zone with which to stimulate coupled hydro mechanical interactions that create the various types of seismicity recorded on volcanic edifices and which usually precede eruption location of ae events through time shows the formation of a fault plane during which waveforms exhibit the typical high frequency characteristics of volcano tectonic vt earthquakes we found that these vt earthquakes were particularly pronounced when generated using dry samples compared to samples saturated with a pore fluid water vt events generated during deformation of water saturated sample are characterised by a distinctive high frequency onset and a longer low frequency coda exhibiting properties often seen in the field as hybrid events we present evidence that hybrid events are in fact the common type of volcanic seismic event with either vt or low frequency lf events representing end members and whose proportion depend on pore fluid being present in the rock type being deformed as well as how close the rock is to failure we find a notable trend of reducing instances of hybrid events leading up to the failure stage in our experiments suggesting that during this stage the pore fluid present in the rock moves sufficiently quickly to provide a resonance seen as a lf coda our data supports recent modeling and field studies that postulate that hybrid events generated in volcanic areas are likely to be generated through the interaction of hydrothermal fluids moving through a combination of pre existing microcrack networks and larger faults such as those we observe in forensic post test examination

late quaternary deformation history of the volcanic edifice of panarea aeolian arc italy a series of raised palaeoshorelines is documented along the emergent coastal slopes of panarea and surrounding islets at elevations of 115 palaeoshoreline ia and 100 m a s l ib 62 5 m ii 35 m iii 12 m iv 10 12 va and 5 m vb according to stratigraphic constraints and cross cutting relationships these palaeoshorelines are correlated with discrete high sea level stillstands during marine oxygen isotope stages mis 5e 5c 5a and 3 coastal elevation changes suggest the occurrence of a long term sustained uplift trend of the volcanic edifice since the last interglacial last 124 ka the uplift rates are not constant but display a progressive deceleration from maximum values of 1 5 1 58 m ka in the period between 124 and 100 ka down to the lowest values of 0 66 0 69 m ka which tend to be constant starting from 81 ka bp the long term deformation pattern of panarea suggests that a transitory volcano related component of uplift interplayed with the regional tectonic component affecting the sub volcanic basement which has undergone a persistent and widespread uplift since the mid pleistocene the volcano related component of uplift prevailing between 124 and 100 81 ka is interpreted as the result of visco elastic deformation mechanisms which characterize the progressive re equilibration of the shallow magmatic system following the incoming quiescence of the volcanic edifice the long term uplift values at panarea are higher than in the main portion of the western central aeolian arc where a mean uplift rate of 0 34 m ka was estimated since the last interglacial last 124 ka such a pattern of deformation on a regional scale may be a response to active deformation processes connected with the southeastward rollback of the subducting ionian slab which is still active only in correspondence with the eastern sector of the aeolian arc including panarea in the short term a localized submergence trend has been documented at the nearby islet of basiluzzo for the last 2 000 years likely connected to neo tectonic movements along main ne sw trending faults

thermo mechanical modeling of the tyrrhenian sea lithospheric necking and kinematics of rifting we present the results of quantitative forward modeling of the sardinian rifted margin of the tyrrhenian sea the purpose of this study is to investigate the thermo mechanical structure that affects the thinning of the lithosphere across the margin the role of lithospheric necking during basin formation constrained by basement topography moho depth and gravity anomalies is modeled for different compensation models independent constraints are obtained from the analysis of the predicted thermal structure a deep level of necking 25 km is required to explain the observed crustal geometries and gravity anomaly signature the model predicts spatial and temporal variations in rheology during extension with important implications for kinematics of lithospheric thinning prerift lithospheric conditions strain rate and temperature during extension appear to be the key controls on the style of lithospheric rifting and necking in the tyrrhenian sea a forward model for basin stratigraphy is presented for the polyphase history of the tyrrhenian rifting this model provides quantitative estimates of time space dependent crustal thinning and rates of extension

stress associated intrinsic and scattering attenuation from laboratory ultrasonic measurements on shales seismic attenuation is sensitive to stress induced subtle changes in the physical state of rocks in this study the stress and frequency associated attenuation is quantified through ultrasonic measurements on three differently oriented cylindrical shale samples under various axial stresses as an improvement to the single scattering model the elastic monte carlo method is employed to investigate multiple scattering attenuations by incorporating the boundary reflections and wave conversions our results show that as the axial stress increases the intrinsic attenuation decreases in all directions while the scattering attenuation decreases slightly in the direction perpendicular to the bedding but increases largely and nonlinearly in other directions these discrepancies result from different attenuation mechanisms both the intrinsic and scattering attenuation are found to be largest in the direction 45 to the bedding but least in the perpendicular direction the s wave attenuation is larger and more sensitive to stress changes than p wave attenuation due to its shorter wavelength as expected from sandstone examples the scattering attenuation in shales is significantly larger and more sensitive to stress changes than the intrinsic attenuation the frequency dependence of scattering attenuation suggests that the peak frequency with the maximum scattering attenuation is independent of axial stresses but varies in different directions of an individual rock with different heterogeneity and anisotropy scales the peak frequency of s coda is smaller and its peak scattering attenuation is larger than p coda in conclusion the stress and frequency dependence of ultrasonic attenuations in shales differ largely in various directions indicating significant anisotropy and heterogeneity

seismic strain and seismogenic stress regimes in the crust of the southern tyrrhenian region abstract an investigation has been performed to identify and characterize the seismic deformation zones active over the last decades in the region of italy that has experienced the strongest seismicity during the last centuries the study is based on the estimate of hypocenter locations fault plane solutions seismogenic stress and seismic strain tensor orientations carried out using the entire dataset of the national and local seismic networks and the recently improved three dimensional 3d crustal velocity model of the study area a series of simulation tests have been performed to evaluate the significance of the earthquake space distribution obtained and whether it was influenced by network geometry problems related to the sea and the lack of ocean bottom seismometers in the sectors where hypocentral location was synthetically proved to be reliable space distributions of earthquakes located with epicenter and focal depth errors less than 3 and 4 km respectively have been compared with local geology in order to identify seismogenic faults the dataset of 32 fault plane solutions estimated with fault parameter errors less than 20 has been used to investigate space variations of seismogenic stress and seismic strain orientations over the study area stress was found to be uniform in the messina strait and southern calabria where inversion of the available set of 11 fault plane solutions showed clear evidence of an extensional regime the different orientations of the minimum compressive stress and strain found in this sector together with the information available on local geology and tectonics lead us to propose that the seismicity occurring over the last decades in the messina strait and southern calabria was not in general produced at the main faults but at minor faults activated by the main tectonic stress field acting in the area to the west in the sector including western etna the nebrodi chain and the western aeolian islands analysis of the available set of 16 fault plane solutions revealed a certain degree of stress heterogeneity with an apparent prevalence of north south compression this east to west change of stress strain regimes is evaluated in the light of current hypotheses regarding the geodynamics of the study region

meteoric diagenesis marine diagenesis and microporosity in pleistocene and oligocene limestones enewetak atoll marshall islands abstract microporosity occurs in pleistocene and oligocene limestones cored on enewetak atoll in cores of pleistocene limestone 10 80 m deep mi microporosity is present in aragonitic skeletal grains that underwent partial intrafabric dissolution chalkification leaving a porous meshwork of aragonite needles microporous aragonite is most abundant in 5 10 m thick intervals below zones of intense diagenesis associated with paleo freshwater lenses extensive microporosity was apparently generated by slow intrafabric dissolution of aragonite in mixing zones below freshwater lenses microporous aragonite is an intermediate step in the calcitization or dissolution of aragonite most calcitized aragonite neomorphic calcite formed by precipitation of sparry calcite in over microporous aragonite aragonitic fossils were not converted to microporous microcrystalline calcite therefore data from the pleistocene of enewetak suggest that widespread microporous microcrystalline calcite does not form directly from pure aragonite at least not in open meteoric systems or mixing zones microporous micrite occurs in oligocene wackestones 930 m deep deposited in a slope environment the microporous micrite is characterized by equant and prismatic crystals of low magnesium calcite lmc equant crystals are anhedral to euhedral and 2 10 m in diameter prismatic calcite crystals are subhedral 5 10 m wide and 20 50 m long stable isotopic and trace element geochemistry suggest that microporous micrite formed by diagenetic alteration of high magnesium calcite hmc micrite in deep seawater undersaturated with respect to hmc but supersaturated with respect to lmc probably near the sediment water interface mineralogy and crystal morphology of the microporous aragonite is very different from microporous shelf limestones in the thamama group cretaceous persian gulf see moshier 1989 equant microcrystals of calcite in the oligocene micrites are similar to those in microporous parts of the thamama group widespread microporosity in lmc limestones could form by alteration of hmc micrite in mixing zones or in seawater undersaturated with respect to hmc but supersaturated with respect to lmc

modern tectonic stress field in the mediterranean region evidence for variation in stress directions at different scales summary a compilation of more than one thousand stress indicators which include in situ stress measurements focal mechanisms microtectonic and other geological data allowed us to reconstruct the modern stress field in the mediterranean region and the surrounding area average stress directions at different scales have been reconstructed by means of a linear interpolation method this method takes into account the distribution scale and quality of stress data the results of the interpolation at plate scale allow us to recognize slightly deformed regions such as the northwestern european platform where average maximum horizontal stress direction is oriented roughly nnw sse subparallel to absolute and relative plate velocity directions other regions such as the caucasus alps and pyrenees where recent tectonic deformation and seismicity are present display important variations of stress directions the reconstruction of the average stress directions at different scales within the french alps pointed out that the average stress field pattern may vary from one scale to another nevertheless variations of stress directions at a given scale are consistent with the kinematics of faults of the same scale

relation between stratigraphic architecture and multi scale heterogeneities in carbonate platforms the barremian lower aptian of the monts de vaucluse se france abstract understanding the relationship between multi scale sedimentary heterogeneities and the stratigraphic architectures of carbonate platforms improves the interpretation of paleoenvironmental evolution in time and space such an approach improves the prediction of the spatial distribution of reservoir properties within carbonate stratigraphic units the reservoir scale stratigraphic anatomy and the growth history of a barremian aptian carbonate platform monts de vaucluse se france was based on 1 high resolution measured sections on outcrops 2 detailed microfacies analyses 3 paleoenvironmental interpretations 4 biostratigraphy using rudist bivalves foraminifera calcareous algae and locally echinoderm and ammonites and 5 sequence stratigraphic interpretations with a special focus on the identification of discontinuity surfaces with a significant stratigraphic correlation potential and critical environmental meaning the platform succession consists of subtidal mainly infralittoral with rare inter to supratidal deposits thirty types of elementary facies grouped in 12 facies associations have been defined the vertical and lateral changes in paleoenvironments together with the development of remarkable stratigraphic surfaces such as subaerial exposures marine erosional surfaces and drowning surfaces allow the definition of five stratigraphic sequences ranging from the late barremian to the earliest aptian these depositional sequences can be grouped into two distinct carbonate sedimentary systems characterized by specific sedimentary profiles and skeletal and non skeletal components 1 a carbonate platform with stronger hydrodynamic gradients rimmed by a narrow belt of high energy deposits with corals and rudistid rudstone facies and 2 a carbonate ramp dominated by orbitolinids fine grained facies including an elongated high energy oolitic shoal the two dimension architecture of the depositional sequences dimensioned geometries thickness and facies variations and the morphology of the shelf reflect a strong interaction between tectonic differential subsidence sediment production and global environmental conditions at the km scale the gorges de la nesque stratigraphic motif could represent a nested stratigraphic structure within the large scale model which could be implemented for up scaling petrophysical properties from the well to a full field model the association of coral facies to the rudist dominated system in the provence platform is a very clear proxy of the polarity of the carbonate platform and is critical for subsurface facies property modeling based on well data finally at the global scale the stratigraphic architecture and the step wise drowning events of the provence platform confirm and document the precursor events associated with environmental perturbations that affected the carbonate factory prior the oceanic anoxic event 1a oae1a

isotope signatures associated with early meteoric diagenesis the environments in which carbonate diagenesis proceeds have been documented in previous studies of holocene and late pleistocene sediments and limestones on barbados west indies variations in the carbon and oxygen isotopic composition of limestones produced during early freshwater diagenesis have been observed in this study to occur in specific patterns six potentially useful patterns emerge when one views stable isotope data within a stratigraphic framework 1 the subaerial exposure surface is characterized by strongly 12c enriched limestones 13c compositions of underlying limestones grow progressively heavier with increasing depth 2 the subaerial exposure surface may also be marked by slight 18o enrichment 3 an abrupt shift in 18o values may differentiate sediments above the exposure surface from those below 4 sediments altered in the marine meteoric mixing zone may be characterized by positive covariance between their 18o and 13c compositions 5 the vadose phreatic boundary may be marked by a sharp increase in 13c values in the seaward portions of a fresh groundwater system and 6 samples contemporaneously altered in a single fresh groundwater system within an areally restricted region should display a narrow range of 18o and a wide range of 13c compositions analysis of samples from five palaeozoic and mesozoic formations which contained petrographic evidence of early freshwater diagenesis showed that isotope patterns similar to those observed in barbados limestones have been preserved in rocks as old as mississippian these isotope patterns could prove to be useful for identifying diagenetically induced porosity trends in carbonate rocks they might be used to identify limestones diagenetically altered in meteoric environments to identify mixing zone cements and dolomites and to trace the regional and vertical distributions of early meteoric groundwater systems in ancient carbonate formations

contribution of numeric dynamic modelling to the understanding of the seismotectonic regime of the northern apennines abstract in this paper we investigate the forces possibly active in the area of the northern apennines by means of two dimensional finite element modelling assuming a viscoelastic rheology the forces included in the models are related to continental convergence between africa and eurasia to negative buoyancy of the subducted adriatic lithosphere and to positive buoyancy of anomalously hot mantle material underneath tuscany model predicted stress distribution is compared with seismotectonic data available for the area of the northern apennines and with earthquakes distribution our results indicate that continental convergence cannot be the only mechanism acting in the study area since it causes insignificant subcrustal stresses in disagreement with intermediate seismicity observed under the apennines asthenospheric upwelling under tuscany back arc region is shown to play a crucial role in the present day dynamics of the tyrrhenian apennines positive buoyancy causes an upwards and eastwards flow that generates extensional bending stresses in tuscany and at the top of the slab under the apennines horizontal pushing of the slab is proposed as an alternative mechanism to slab pull to generate subcrustal stresses activation of slab pull does not result in a significant change in orientation of the principal stress axes at shallow depths with respect to the model in which only asthenospheric diapirism is active therefore the existence of a continuous gravitationally sinking slab cannot be ruled out on the basis of comparison with seismotectonic observations both models successfully reproduce extension in tuscany and compression in the outer margin of the apenninic belt but fail to reproduce extension along the inner portion of the chain our modelling highlights the importance of better constraining the lateral extent of the asthenospheric diapir in order to find out whether the extension and tectonic uplift in the apennines is caused by asthenospheric upwelling as in the area of tuscany

palaeomagnetic study of cretaceous red beds from the eastern hindukush ranges northern pakistan palaeoreconstruction of the kohistan karakoram composite unit before the india asia collision we report palaeomagnetic results obtained from cretaceous red bed samples collected from the eastern hindukush mountains northern pakistan rock magnetic studies revealed specular haematite as the dominant remanence carrier while pigmentary haematite magnetite and goethite are responsible for the acquisition of secondary magnetizations thermal treatment generally revealed three components of magnetization the most unstable component a was removed between 200 c and 500 c which corresponds to the local present field direction the intermediate component b was generally separated between 200 c and 660 c the omnipresence of this complex secondary component across the northern suture zone suggests that movement of chemically active orogenic fluids at or slightly before the time of the india asia collision was probably responsible for the authigenic remagnetization processes the characteristic component c was generally unblocked between 600 c and 685 c the characteristic directions from 12 sites fall into two groups the sites from the purit formation give a tilt corrected mean direction of d 311 2 i 4 4 k 12 4 95 17 8 indicating a counter clockwise rotation of about 66 and 15 relative to eurasia and india respectively the tilt corrected mean direction for the reshun and drosh formations is d 263 0 i 2 2 k 52 7 95 10 6 which indicates that the sampling area experienced a counter clockwise rotation of about 114 and 63 with respect to eurasia and india respectively in both cases the palaeomagnetic rotation is consistent with the regional superstructure of the hindukush pamir karakoram syntaxial bend the difference in rotation between these two groups is probably due to local tectonic movement caused by the net rotation of thrust sheets along the northern suture zone the palaeolatitudes calculated for purit and reshun drosh formations are 2 2 s and 1 1 n respectively this indicates that about 4000 km of convergence has taken place since the mid cretaceous of which about 90 per cent post dates the india asia collision the late cretaceous inclination values across the northern suture zone are almost identical which indicates that suturing had been completed at the time of chrm acquisition

seismic codas on the earth and the moon a comparison the phenomenon of the seismic coda which is composed of seismic energy delayed by scattering is seen on both the earth and the moon on the moon the scattered coda is very large relative to body wave arrivals with a delay of the time of maximum energy whereas on earth scattered codas are relatively small and show no delay of the energy maximum in both cases the form of the coda is controlled by three distance scales the mean free path l which is the average distance seismic energy travels before it is scattered the attenuation distance x which is the average distance seismic energy travels before it is attenuated and the source receiver distance r two coda models are discussed based on these parameters a strong scattering diffusion model and a weak scattering single scattering model a discussion of the diffusion scattering model indicates that if x l 1 diffusion scattering is an appropriate model but if x l 1 single scattering is the appropriate model within the appropriate range of r a survey of the literature indicates that for the frequency range 0 5 10 hz diffusion scattering is important in lunar codas but for the frequency range 1 25 hz single scattering is important in terrestrial codas another important effect of attenuation is the elimination of scattering paths much longer than x on the moon this means that seismic energy in the coda can only propagate directly in the near surface strong scattering zone between surface sources and the seismometer for source seismometer separations of the order of x l 12 otherwise scattering is limited to regions near the source and the receiver on earth this effect probably prevents multiple scattering

dynamic modelling of stress accumulation in central italy role of structural heterogeneities and rheology summary recent efforts to relate the style of seismicity in the central apennines to the stress build up induced by active geodynamic processes by means of simple viscoelastic dynamic models have shown that seismicity in this region is likely to be controlled by two major processes the westward underthrusting of the adriatic plate under the apennines and the asthenospheric upwelling underneath tuscany in this work using these results as a starting point we evaluate by means of 2 d dynamic models the effects of structural heterogeneities major crustal scale faults this improvement is made possible by the recent publication of the results of the crop 03 seismic line and of temperature dependent rheologies within the crust and the lithospheric mantle on the stress field induced by the two processes mentioned above modelling results are compared with detailed seismicity data we show that for all models the predicted stress fields are controlled at large wavelengths by an upward state of flexure in tuscany and a downward state of flexure in the apenninic foredeep in agreement with previous studies when activating crustal scale discontinuities however strong local rotations of the major axes of the stress tensor occur in the proximity of the faults generating complex local stress fields characterized by the coexistence of compressive and tensional styles this could explain the coexistence as observed within certain regions of central italy of compressive and extensional events when detailing the rheology using plastic behaviour for the lithospheric portions of the models a complex profile of yield stresses is considered the materials characterized by higher strength being the sedimentary cover and the lithospheric mantle model predicted stress concentrates in these materials the lateral variability of the thickness of the sedimentary cover induces strong local rotations at shallow depths of the stress eigenvectors all of the models predict a stress field roughly compatible with the distribution and style of seismicity of the region the use of progressively more realistic rheologies and geometries however gives slightly better results when compared to seismicity data this paper shows that sensible results may be obtained by combining active and natural source seismicity with finite element modelling

horizontal crustal motion in the central and eastern mediterranean inferred from satellite laser ranging measurements four campaigns to acquire satellite laser ranging slr measurements at sites in the mediterranean region have been completed these measurements to the lageos satellite made largely by mobile systems cover a time span beginning in november 1985 and ending in june 1993 the range data from 18 sites in the central and eastern mediterranean have been simultaneously analyzed with data acquired by the remainder of the global laser tracking network estimates of horizontal motion were placed into a regional northern europe fixed kinematic reference frame uncertainties are on the order of 5 mm yr for sites having at least four occupations by mobile systems and approach 1 mm yr for permanently located sites with long histories of tracking the resulting relative motion between sites in the aegean exhibit characteristics of broadly distributed pattern of radial extension but at rates that are about 50 larger than those implied from studies of seismic strain rates based on seismicity of magnitude 6 or greater or across the region the motion estimated for sites in turkey exhibit velocity components associated with the westward motion of the anatolian block relative to eurasia these results provide a present day snapshot of ongoing deformational processes as experienced by the locations occupiedmore by slr systems less

earthquakes as beacons of stress change aftershocks occurring on faults in the far field of a large earthquake rupture can generally be accounted for by changes in static stress on these faults caused by the rupture1 2 this implies that faults interact and that the timing of an earthquake can be affected by previous nearby ruptures3 4 5 6 here we explore the potential of small earthquakes to act as beacons for the mechanical state of the crust we investigate the static stress changes resulting from the 1992 landers earthquake in southern california which occurred in an area of high seismic activity stemming from many faults we first gauge the response of the regional seismicity to the landers event with a new technique and then apply the same method to the inverse problem of determining the slip distribution on the main rupture from the seismicity assuming justifiable parameters we derive credible matches to slip profiles obtained directly from the landers mainshock7 8 our results provide a way to monitor mechanical conditions in the upper crust and to investigate processes leading to fault failure

seismotectonics of the calabrian arc abstract relocation of intermediate and deep earthquakes of tyrrhenian sea area through joint hypocenter determination for the period 1962 1979 has allowed a more detailed definition of the geometry of this peculiar benioff zone earthquakes dip along a quasi vertical plane to 250 km depth there is a 50 dip in the 250 340 km depth range and a low dip angle to 480 km depth the structure sketched from the hypocenters is almost continuous but most energy has been released in the 230 340 km depth interval an evaluation of fault plane solutions of intermediate earthquakes in this area indicates predominance of down dip compressions in the central part of the slab at the border strike slip motion occurs independent of depth some earthquakes that occurred at intermediate depth less than 100 km along the ionian margin of calabria show predominance of reverse faulting with the p axis oriented se nw however shallow earthquakes in the calabria sicily region indicate a more complex motion with predominance of normal faulting a possible interpretation of these features according to the available geological history which involves subduction of continental lithosphere is discussed

diagenetic patterns and pore space distribution along a platform to outer shelf transect urgonian limestone barremian aptian se france abstract the urgonian limestones of late barremian early aptian from provence se france are characterized by the occurrence of microporous limestones at regional scale alternating with tight carbonates this study based on petrographical sediment texture facies and diagenetical analyses cement stratigraphy porosity and isotope geochemistry of more than 800 limestone samples provides insight into the parameters controlling the genesis preservation or occlusion of microporosity along an inner platform to outer shelf transect the tight and microporous urgonian limestones from provence can be grouped into 5 rock types based on textures associated depositional environments porosity and pore type being 1 tight inner platform tip 2 porous inner platform pip 3 tight outer platform top 4 porous outer platform pop and 5 tight outer shelf tos in tight tip top and tos types limestones intergranular and intragranular pore spaces were entirely occluded by early marine and or early meteoric cementation whereas in microporous pip pop limestones a significant fraction of the intergranular macroporosity was preserved during early and shallow burial diagenesis micrite neomorphism hybrid ostwald ripening process occurred during meteoric shallow burial diagenesis in pip and pop limestones during the regional durancian uplift event albian lower cenomanian this process resulted in microporosity enhancement and preservation circulation of meteoric fluids during exhumation produces intercrystalline microporosity enhancement and moldic porosity development the present study documents the important role that both early diagenetic and depositional cycles and long term tectonic processes have on pore space evolution and distribution in mesozoic platform carbonates

dynamic models of subduction geophysical and geological evidence in the tyrrhenian sea summary predictions based on a 2 d finite element model for subduction underneath the calabrian arc in southern italy are compared with a variety of geophysical and geological data such as the present day stress pattern within the slab uplift from the elevation of marine terraces in calabria and subsidence in the tyrrhenian marsili basin from odp leg 107 we model the behaviour of the slab driven by slab pull in agreement with the present tectonic style in this part of the mediterranean as suggested by several investigators the model accounts for the crustal lithospheric and mantle structures in a vertical cross section perpendicular to the calabrian subduction zone the shape of the slab is constrained on the basis of new tomographic images in the southern tyrrhenian sea which were obtained from the regional seismic stations of the istituto nazionale di geofisica while the rheological properties of the mantle are taken from global dynamic models density contrasts between the subducted slab and the surrounding mantle based on petrological models drive the flow in our viscoelastic model stress values displacements and vertical velocities at the surface are sampled at different times after loading until dynamic equilibrium is reached our estimates are appropriate for a time window of 100 kyr the validity of our comparison with the geological record is based on the assumption that the tectonic configuration in the past was not substantially different from that of the present day two families of models with unlocked and locked subduction faults are considered the unlocked models allow for roll back of the trench of about 20 mm yr in agreement with some geological estimates the same family of models predicts uplift of the calabrian arc of about 1 mm yr l and subsidence in the marsili basin of 1 2 mm yr in agreement with geological surveys the deviatoric stress obtained from the unlocked model is consistent with the continuous distribution of deep seismicity in the southern tyrrhenian sea with minor concentration within the lithospheric wedge locked models fail to reproduce these geophysical and geological observations predictions derived from a detached slab model are not consistent with the continuous hypocentral distribution of deep seismicity in the southern tyrrhenian sea deformation at the surface and the stress patterns at depth for a detached slab differ substantially from those of a continuous plate dynamic topography and horizontal motions are reduced when compared with the continuous plate with deviatoric stresses concentrated within the relict slab our results indicate that subduction is a major tectonic process in the southern tyrrhenian sea

laboratory study on scattering characteristics of shear waves in rock samples to understand the scattering characteristics of seismic shear waves in the earth a laboratory physical model experiment in ultrasonic frequency range was performed by analyzing waveform envelopes and particle motions of shear waves in media with different correlation distance and fluctuation intensity we studied the strength of scattered wave excitation and the distortion of shear wave polarization as a function of ka wavenumber times the correlation distance we used gabbro and granite as media having different small scale random heterogeneities the granite we used contained preferred oriented thin microcracks the correlation distance a and the standard deviation of the fractional fluctuation of the shear wave velocity were estimated by fitting exponential type autocorrelation functions the estimated values were a 0 84 mm and 8 1 for the gabbro and a 0 39 mm and 17 0 for the granite waveform measurements were performed in the frequency range 0 25 1 mhz which roughly corresponds to ka as 0 25 1 envelope broadening appeared when ka exceeds 0 4 for the granite and 1 4 for the gabbro shear wave polarizations were distorted by scattering when ka exceeds 0 2 for the granite and 0 7 for the gabbro the results on envelope broadening suggest the importance of large angle scattering due to small scale random heterogeneities and cracks in the envelope broadening in addition to diffraction effects due to large scale heterogeneities the effect of aligned microcracks on scattering was also examined it was found that scattering was prominent when shear wave propagates perpendicular to the aligned crack plane manuscript received 1 march 2002

subduction related intermediate depth and deep seismicity in italy insights from thermal and rheological modelling geological data suggest that after a period of oceanic lithosphere subduction about 170 km of continental lithosphere were subducted under the northern apennines since about 23 myear at rates of ca 1 cm year whereas more than 700 km of mesozoic oceanic lithosphere ionian lithosphere have been subducted under the calabrian arc at rates of about 3 cm year however a well developed wadati benioff zone can be only recognised below the calabrian arc down to depths of 450 500 km whereas intermediate depth seismicity reaches maximum depths of about 90 km under the northern apennines we model the thermal state of these two subduction zones and apply temperature dependent non linear rheological laws to evaluate the down dip extent of brittle regions in the two subduction zones we show that differences in subduction rate and in slab composition continental vs oceanic produce a far deeper down to 290 380 km brittle field in the colder calabrian slab than in the warmer northern apenninic slab 70 120 km thus explaining differences in the maximum depth of seismicity in both regions concerning deep earthquakes in the calabrian subduction zone models predict that metastable olivine persists down to depths of 430 km this could possibly explain the maximum depth of earthquakes in the area the small extent of the metastable olivine wedge produces a small density anomaly that cannot explain the pervasive down dip compression observed in the ionian slab 2004 elsevier b v all rights reserved

microporous and tight limestones in the urgonian formation late hauterivian to early aptian of the french jura mountains focus on the factors controlling the formation of microporous facies microporous and tight limestones with contrasting porosity and permeability values directly related to the microfabric of the micritic matrix outcrop in the urgonian formation of the french jura mountains this study investigates the factors controlling the differentiation between the microporous and tight facies and proposes a diagenetic model for the development and preservation of the microporosity in these limestones the petrophysical properties are not related to the depositional texture the petrographical content or the mineralogical composition however the tight layers contain indications of emersion e g bird eyes keystone vugs and desiccation cracks the sedimentation in very shallow conditions up to emersion is confirmed by the covariant more positive values of oxygen and carbon isotopes the microporous intervals systematically occur a few meters below the tight layers affected by emersion this position strongly suggests the importance of meteoric water input rapidly after sedimentation in the differentiation between tight and microporous limestones the diagenetic model proposed for the development and preservation of the microporous facies involves partial early cementation of the interstitial mud mainly composed of low mg calcite crystals sedimentation during a calcite sea period inside a meteoric phreatic lens by in situ dissolution reprecipitation processes hybrid ostwald ripening this early cementation partly preserves the original microfabric and intercrystalline microporosity and allows the carbonate sediment to resist compaction during burial the identification of the conditions favorable to the development of microporosity in these urgonian limestones may improve the knowledge and modeling of some microporous carbonate reservoir rocks

the importance of subduction for the modern stress field in the tyrrhenian area the tyrrhenian sea was formed by lithospheric extension in a context of continental convergence between africa and eurasia at present a compilation of strain and stress indicators in this region by rebai et al 1992 shows that an extensive regime is still predominant in the tyrrhenian sea while northern italy and southern sicily are undergoing compression this tectonic configuration is the result of two major contributions which act on a very heterogeneous lithosphere the africa eurasia collision on the one hand and the subduction along the calabrian arc on the other the latter is expected to create a trench suction force on the overriding tyrrhenian plate the objective of this paper is to investigate the relative importance of these contributions using a numerical model developed by p bird 1989 based on an improved version of the thin plate approach which models lithospheric deformation in an horizontal plane the results of this model demonstrate the necessity of considering the forces related to subduction to understand the modern stress and strain field an extrusion mechanism alone cannot explain present day observations the salient features of the current tectonic regime are reproduced by the model which however predicts more limited extension than expected further work will be needed to find a better tuning of the parameters and ascertain the quality of available data

pore system characterisation in heterogeneous carbonates an alternative approach to widely used rock typing methodologies abstract rock typing is used in carbonate reservoir characterisation to group petrophysically similar rocks for reservoir modelling purposes the focus is often upon bringing together samples with similar porosity permeability and capillary pressure to achieve this rock typing studies are usually conducted primarily on core plugs using routine core analysis data and thin sections however such an approach results in a tendency to focus on grouping samples with consistent petrophysical properties ignoring the geological controls on pore evolution this means that modelling rock types predicatively using 3d geocellular models is not easily accomplished furthermore where geological observations are made they tend to consider only depositional rock properties and not the effects of diagenesis in doing so a key control on the evolution of the carbonate pore network is ignored this paper addresses these issues using a giant carbonate reservoir in northern oman rock types were defined on the basis of pore geometry whilst retaining distinct geological descriptors the aim was to ensure that each rock type could be defined on the basis of both its petrophysical properties and behaviour during hydrocarbon recovery the results show that characterisation of pore heterogeneity is critical to the prediction of flow behaviour under reservoir conditions and that routine petrophysical parameters are often not good indicators of sweep efficiency

phase transformations in a harzburgite composition to 26 gpa implications for dynamical behaviour of the subducting slab abstract the mineralogy adopted by a depleted harzburgite composition has been studied over the pressure interval 5 26 gpa at temperatures of 1300 1400 c the pyroxene garnet component of the harzburgite composition harzburgite minus 82 wt olivine transforms to majorite garnet by 18 19 gpa and further disproportionates to the assemblage of garnet stishovite mg 2 sio 4 spinel above 20 gpa at still higher pressures first ilmenite 22 24 gpa and then perovskite mgsio 3 24 26 gpa are found to coexist with garnet garnet disappears at 26 gpa and almost complete transition to perovskite is achieved at this pressure the mineral proportions and density profiles in the subducting oceanic lithosphere modelled by a combination of 80 harzburgite 20 primitive morb compositions are calculated as a function of depth under conditions isothermal with surrounding pyrolite mantle and also for a temperature distribution in which the slab is substantially cooler than surrounding mantle to below 700 km under isothermal conditions the slab has a density similar to surrounding mantle to a depth of 600 km however between 600 and 700 km the slab is up to 0 08 g cm 3 denser than surrounding mantle this is caused primarily by the higher alumina content in pyrolite as compared to harzburgite which causes the transition to perovskite in pyrolite to occur at substantially higher pressures than in harzburgite the presence of alumina also smears out the garnet perovskite transition in pyrolite over a depth interval of 50 km whereas this transformation is much sharper in the harzburgite composition calculations based on the observed phase equilibria also show that a subducted cool slab remains much denser by 0 1 0 3 g cm 3 than surrounding mantle to a depth of 700 km but possesses a density similar to surrounding mantle below this depth these results have important implications for the dynamical behaviour of slabs possessing different thermal regimes when they encounter the 670 km discontinuity and also for the nature of this discontinuity

free surface formulation of mantle convection ii implication for subduction zone observables summary viscous and viscoelastic models for a subduction zone with a faulted lithosphere and internal buoyancy can self consistently and simultaneously predict long wavelength geoid highs over slabs short wavelength gravity lows over trenches trench forebulge morphology and explain the high apparent strength of oceanic lithosphere in trench environments the models use two different free surface formulations of buoyancydriven flows see for example part i lagrangian viscoelastic and pseudo free surface viscous formulations the lower mantle must be stronger than the upper in order to obtain geoid highs at long wavelengths trenches are a simple consequence of the negative buoyancy of slabs and a large thrust fault decoupling the overriding from underthrusting plates the lower oceanic lithosphere must have a viscosity of less than pa s in order to be consistent with the flexural wavelength of forebulges forebulges are dynamically maintained by viscous flow in the lower lithosphere and mantle and give rise to apparently stiffer oceanic lithosphere at trenches with purely viscous models using a pseudo free surface formulation we find that viscous relaxation of oceanic lithosphere in the presence of rapid trench rollback leads to wider and shallower back arc basins when compared to cases without viscous relaxation moreover in agreement with earlier studies the stresses necessary to generate forebulges are small 100 bars compared to the unrealistically high stresses needed in classic thin elastic plate models

ultrasonic properties of sedimentary rocks effect of pressure saturation frequency and microcracks seismic velocities and attenuations are influenced by lithology porosity and permeability as well as the kind and quantity of the pore fluids the microstructure of rocks is another important factor influencing seismic properties this influence can be used to investigate the pressure dependent closure of microcracks for this purpose velocities and attenuations of p and s waves have been determined at ultrasonic frequencies in three different rocks vacuum dry and partially saturated with water as a function of hydrostatic pressure up to 200 mpa a new combined model has been developed with this model an explicit description of the microstructure local fluid flow lf and macrostructure gassmann effect global fluid flow is possible assuming a patchy saturation i e inhomogeneous distribution of the fluid in the pores and modulus reduction both the saturation dependent measurements and the pressure dependent data can be explained the modelling and the phenomenological interpretation of the data gained under increasing hydrostatic pressure yields consistent results concerning the amount of crack closure as well as the range in which crack closure appears in high porosity sandstones bentheimer and obernkirchner sandstone a strong closure of cracks already with a small increase of pressure must be concluded in a low porosity harzer greywacke a significantly lower closure of cracks can be concluded within the pressure range of 0 100 mpa it is shown however that there must be open cracks in all rocks even under elevated hydrostatic pressure resulting in a measurable effect due to lf

closure of the africa eurasia north america plate motion circuit and tectonics of the gloria fault we examine the closure of the current plate motion circuit between the african north american and eurasian plates to test whether these plates are rigid and whether the gloria fault is an active transform fault we also investigate the possible existence of microplates that have been previously proposed to lie along these plate boundaries and compare the predicted direction of motion along the african eurasian plate boundary in the mediterranean with the direction of slip observed in earthquakes from marine geophysical data we obtain 13 transform fault azimuths and 40 3 m y average spreading rates 34 of which are determined from comparison of synthetic magnetic anomaly profiles to 140 observed profiles slip vectors from 32 earthquake focal mechanisms further describe plate motion detailed magnetic surveys north of iceland provide 11 rates in a region where prior plate motion models had few data magnetic profiles north of the azores triple junction record a rate of 24 mm yr 4 mm yr slower than used by prior models gloria and sea beam surveys accurately measure the azimuths of seven transform faults our plate motion model fits six of the seven within 2 two transform faults surveyed by gloria side scan sonar lie near famous area transform faults a and b and give azimuths 13 clockwise of them because recent studies show that short offset transforms such as transforms a and b are in many places oblique to the direction of plate motion we exclude azimuths from transforms with less than 35 km offset the best fitting and closure enforced vectors fit the data well except for a small systematic misfit to the slip vectors on right lateral slipping transforms slip vectors tend to be a few degrees clockwise of plate motion and mapped fault azimuths whereas on left lateral slipping transforms slip vectors tend to be a few degrees counterclockwise of plate motion and mapped fault azimuths we search the long eurasia north america boundary for evidence of an additional plate but find no systematic misfits to the data in particular if a spitsbergen plate exists and moves relative to eurasia its motion is less than 3 mm yr an africa eurasia euler vector determined by adding the eurasia north america and africa north america euler vectors is consistent with the gloria fault trend and with slip vectors from eastern azores gibraltar ridge focal mechanisms a small circle centered at the africa eurasia closure enforced pole fits the trace of the gloria fault the model in which closure was enforced predicts 4 mm yr slip across the azores gibraltar ridge and west northwest convergence near gibraltar 45 more oblique than suggested by a recent model based on compressive axes of focal mechanisms moreover our model predicts directions of plate motion that agree well with northwest trending slip vectors from thrust earthquakes between gibraltar and sicily because closure enforced vectors fit the data nearly as well as the best fitting vectors we conclude that the data are consistent with a rigid plate model and with the gloria fault being a transform fault

the interplay between global tectonic processes and the seismic cycle in the umbria marche seismogenic region summary for the central apennines peninsular italy a series of tectonic mechanisms are reproduced by means of finite element models in order to study the effects of active tectonics on the seismic cycle in the umbria marche seismogenic zone continental extension and rift push effects induced by small scale convection are modelled within 2 d viscoelastic models of the crust lithosphere system in vertical cross sections perpendicular to the strike of the major tectonic structures under study namely the apennines and the colfiorito fault zone where the 1997 seismic sequence took place with the aim of constraining the active tectonic mechanisms at the regional scale and the behaviour of the fault in the seismogenic zone at the local scale modelled baseline rate of change are compared with newly acquired gps data retrieved from the two permanent gps receivers of camerino came and elba elba deliberately installed along the modelled transect these receivers are located at both edges of the continental extension in the front of the apennines close to the adriatic plate in the east and in the rear of the chain in the tyrrhenian domain the deformation pattern inferred from seismicity and from the geodetic data is consistent with small scale convection in the tyrrhenian domain which reproduces extension in the rear of the apennines and compression in the front of the chain a convective mechanism associated with backarc opening and doming of the asthenosphere provides an extensional rate along a baseline connecting two sites in the front of the chain camerino and in its rear elba comparable to the observed baseline rate of change the viscosity of the lower crust plays a fundamental role in determining the style of stress in the crust lithosphere system once constrained by means of the extensional baseline rate inferred from gps the modelled slip across the colfiorito fault and the modelled earthquake recurrence time are consistent with the 1997 normal fault event and with palaeoseismicity respectively

when did sardinia stop rotating new palaeomagnetic results previous palaeomagnetic results from tertiary volcanic rocks of sardinia suggest that the island underwent a quick counterclockwise rotation between 20 5 and 19 ma in order to test this hypothesis a new palaeomagnetic study was carried out on sediments and volcanic rocks with well controlled biostratigraphic or radiometric ages younger than the suggested age for the end of the rotation unrotated palaeomagnetic directions obtained from the upper ignimbrites radiometric age 18 5 19 7 myr and the aquitanian tuffs collected in the anglona region n sardinia would suggest that the rotation ended earlier than 20 5 myr the directions found in the volcanics are perhaps the result of secular variation rather than differential rotation of the anglona region with respect to surrounding regions two sites belonging to the upper ignimbritic unit si2 in the monte traessu monte rispisu area logudoro region exhibited a large amount of rotation d 320 4 i 60 which may be age related radiometric age 19 9 myr four dikes radiometric age 18 3 16 7 myr in the arcuentu volcanic complex arburese region yield results d 348 4 i 33 8 that indicate a further amount of rotation after their emplacement stable end point directions were successfully isolated from three upper burdigalian langhian sedimentary sites biostratigraphic age 18 15ma from the marmilla and logudoro regions consistent paleomagnetic directions obtained from these sites d 352 i 49 indicate that a small amount of rotation was still to be completed in the langhian time this result is consistent with the history of sardinian volcanism which did not end until 13 ma

spatial variations of seismogenic stress orientations in sicily south italy abstract seismogenic stress orientations are estimated in the lithosphere of sicily by inversion of 131 local earthquake focal mechanisms fms selected from the literature an average misfit f 14 5 between stress tensor and fms indicates that the entire set of earthquakes is generated by a highly heterogeneous stress field detailed analysis of stress tensors and related earthquake misfits obtained for tens of subsets based on spatial separation of data allowed us to identify two main stress domains in the study region i a compressional domain including etna western sicily and the southern tyrrhenian sea offshore sicily where the 1 orientation roughly changes from nw se in the etna area and western sicily to nne ssw at the northeastern edge of the domain eolian islands and ii an extensional domain in northeastern sicily between the eolian islands and etna where 3 is oriented analogously to previously estimated in the easterly confining extensional area of the messina straits general agreement is found between this stress pattern and the gps crustal displacement vectors reported in the most recent literature for the study region moreover stress inversion enables us to locate the extensional domain more accurately than the presently available gps data finally the stress orientations estimated in the southern and western sectors of the study area etna and western sicily on and offshore match well with the displacement fields predicted for sicily by large scale models of plate motion conversely a mismatch is observed in the northeastern sector eolian islands and northeastern sicily we suggest that the joint action of africa eurasia convergence and ionian subduction trench retreat rollback of the subducting slab may explain the stress pattern detected in sicily in the present study work for computation of a finite element regional geodynamic model based on geophysical and geological data collected over the last few years has recently started with the purpose of quantitatively checking this hypothesis

dynamic and static moduli static and dynamic bulk moduli ks and kd are measured as continuous functions of pressure from zero to 2 3 kilobars for two sandstones a tuff limestone granite and oil shale results for the sandstones and granite are in good agreement with previously reported data with ks kd varying from about 0 5 at atmospheric pressure to close to unity at pressures 2 kilobars and above for rocks behaving elastically under static loading the ks kd ratio is inversely related to the microcrack density for the limestone time dependent deformation associated with pore collapse results in ks kd ratios approaching 0 1 at high pressure upon unloading while initially high 1 0 at high pressures ks kd becomes lower than values obtained during loading at low pressures 1 kilobar due to opening of microcracks generated during pore collapse for the oil shale in which few microcracks exist ks kd remains relatively constant with pressure at a value of about 0 7

monte carlo simulation of seismogram envelopes in scattering media the analysis of the seismogram coda envelopes of local and regional earthquakes is one of the most effective strategies for investigating the heterogeneous lithospheric structure characterized by the seismic scattering and attenuation in order to synthesize the coda envelope we introduce a numerical scheme called the direct simulation monte carlo method which has been used in the field of the kinetic theory of gases because of the simplicity of the algorithm the method has several advantages over previous methods in terms of the flexibility of the numerical calculation to incorporate various factors required to construct realistic seismogram envelopes on the basis of coda envelope simulations including multiple scattering we show that an increase of seismic velocity with depth severely affects the shape of the coda envelope the effects of ray bending due to the velocity increase at the moho and the reflection at the free surface are clearly found in the synthesized envelope for a shallow earthquake our simulation demonstrates that the amplitude of the envelope is magnified by stagnation of seismic energy at shallow depths due to the positive velocity gradient with depth because of this effect for an a priori assumption of a homogeneous velocity model the measurement of the scattering coefficient by conventional methods may be overestimated

diagenesis of barremian aptian platform carbonates the urgonian limestone formation of se france near surface and shallow burial diagenesis the diagenesis of carbonate platform sediments is controlled by the original facies and mineralogy climate sea level changes and burial history these controls are clearly seen in the diagenesis of the urgonian platform carbonates of se france early diagenesis in the urgonian platform included the precipitation of marine cements dissolution of rudist shells and minor karstification diagenetic features produced during this phase were controlled by several falls in relative sea level during the barremian to mid aptian punctuating platform sedimentation the original mineralogy of the sediment and the prevailing semi arid arid climate in the region at this time following a relative sea level rise and further sedimentation progressive burial of the platform led to minor compaction followed by precipitation of coarse equant zoned to non luminescent calcite cement this cement was cut by later stylolites suggesting a relatively shallow burial origin stable isotope mean values 7 94 18o and 0 36 13c and trace element mean values of fe 334 ppm mn 92 ppm and sr 213 ppm data suggest that these cements precipitated from meteoric fluids at temperatures slightly elevated relative to depositional temperatures a variable thickness of replacive dolomite which occurs preferentially within the shelf margin facies of the lower part of the urgonian post dates mechanical fracturing and chemical compaction but pre dates the main phase of stylolitization it is probable that the dolomitizing fluid was sourced by the early compaction driven release of connate fluids held within the underlying muddy units the burial history of these rocks suggests that calcite cementation and dolomitization took place at relatively shallow burial depths 1 1 5 km the overall diagenetic history of the urgonian limestone formation is a reflection of the pre conditioning of the platform limestones by climate sea level tectonics and the shallow burial depths experienced by the platform during the later mesozoic

seismic deformation in the mediterranean area estimated by moment tensor summation summary theoretical relationships allow the distributed deformation due to seismic activity to be quantified on the basis of the analysis of moment tensors we apply this method to a data set consisting of seismic events that have occurred in the past 85 yr 1908 1992 along the most important seismogenic zones of the mediterranean region we use the centroid moment tensor cmt catalog prepared at harvard university covering the last 16yr and older data from jackson mckenzie 1988 we determine the seismic deformation and compare it to estimates of the overall deformation as obtained from global plate motion and geological studies we generally find that the geometry of seismic deformation is similar to tectonic predictions even though spanning a shorter time interval the cmt catalog often gives a better estimate of deformation geometry than the whole data set 85yr seismic deformation generally ranges from less than 10 per cent to more than 90 per cent of the total deformation uncertainties arise because data sets may not be representative of the long term seismic behaviour of each zone more reliable estimates for comparison with geodynamic processes should result from analysis of a longer time period for which no instrumental data are available the similarity of the deformation geometry using cmt data with tectonic expectations suggests for several zones the possibility of using historical data to infer longer term deformation rates based on current deformation geometry

the role of subduction on the horizontal motions in the tyrrhenian basin a numerical model the horizontal motions in the tyrrhenian basin and surrounding chains induced by subduction along the calabrian arc and northern apennines are analyzed by means of numerical models based on finite element techniques the driving mechanism in 2 dimensional vertical cross sections perpendicular to the trench is the slab pull due to the negative buoyancy of a stratified viscoelastic plate that models the ionic oceanic lithosphere or adriatic plate sinking in the upper mantle for the modern tectonic setting of the area we test the sensitivity of extension in the back arc and of roll back of the overriding plate to variations in the viscosity structure and in the geometry of subduction our results are compared with extensional velocities inferred from geology and slr vlbi data

interplay between subduction and continental convergence a three dimensional dynamic model for the central mediterranean summary the mediterranean region is attracting considerable attention due to the complexities of its tectonic setting which is considered worldwide a unique natural laboratory for studying the occurrence of extensional tectonics in a general context of continental convergence the tyrrhenian apennine system is controlled by the west dipping subduction of the adria ionian lithosphere and by the near north south convergence between the african and eurasian plates we provide the first 3 d dynamic model of the central mediterranean that quantifies the effects of subduction and convergence on surface deformation in simplified geometry the axis of the model extends from sicily to the alps along the subduction hinge line a convergence rate of 1 cm yr 1parallel to the subduction hinge has been applied to the tyrrhenian block in agreement with global plate motion models density contrasts within the slab cause the gravitational sinking and roll back of the slab in the southern tyrrhenian domain modelling results show a gradual decrease of hinge retreat from south to north with values ranging between 8 and 2 mm yr 1 indicating that the arculate geometry of the hinge line along the italian peninsula is ultimately controlled by the interplay between subduction and convergence the pattern of vertical velocity along directions perpendicular to the hinge with subsidence in the foredeeps and uplift at the eastern border of the tyrrhenian domain is maintained along the whole italian peninsula with higher values in the southern areas

rudists and carbonate platforms in the aptian a case study on biotic interactions with ocean chemistry and climate variations in aptian carbonate platform growth and associated turnover among rudists are reviewed and the results synthesized with evidence for climate change to yield an explanatory model extensive platform growth throughout the atlantic tethys low palaeolatitude pacific seamount belt in the earliest aptian was accompanied by prolific rudist diversification especially among the predominantly aragonitic caprinids occupying platform margins it was ubiquitously interrupted in the mid early aptian in tandem with major perturbations of the global carbon cycle that culminated in oceanic anoxic event 1a although the causal linkages remain contentious platform growth terminated along most of the northern tethyan margin and maybe also in the new world meanwhile lithocodium bacinella or similar microbial encrustations became widespread in lower palaeolatitudes recovery of tethyan platforms in the late early aptian was limited to lower palaeolatitudes caprinid rich platform margin facies again prevailed in central and southern tethyan areas but gave way to those dominated by rudists with a thickened calcitic outer shell layer polyconitids and requieniids in marly successions around iberia the end of the early aptian saw the lazarus style disappearance of caprinids and renewed tethyan platform growth in the late aptian was dominated by calcite rich rudists although rudists remained scarce in the new world until the terminal aptian this study postulates that sea water acidification influenced both the mid early aptian platform debacle and the subsequent late early aptian geographical restriction of platform recovery although in contrasting atmospheric regimes at first it was forced by the increasing atmospheric levels of volcanically derived co2 with mitigation in low latitudes from thermal expulsion of aqueous co2 here termed the kettle effect due to greenhouse warming however subsequent cooling due to drawdown of atmospheric co2 by organic carbon burial could have sustained acidification of platform waters in higher latitudes by reducing the protective kettle effect there caprinid susceptibility to such assaults may have been as much due to exposure on their preferred outer platform habitats as to their mineralogy the increased calcite aragonite ratio among rudists through the aptian resulted largely from this taxonomic turnover

subcrustal earthquakes in the northern apennines italy evidence for a still active subduction previously unreported subcrustal earthquakes have been located up to 90 km depth beneath the northern apennines italy these earthquakes occur beneath a zone of abundant upper crustal seismicity mostly confined to the upper 20 km of the crust although there are relatively few well located subcrustal earthquakes there appears to be a general southwestward deepening of the hypocenters from the adriatic to the tyrrhenian sea consistent with other geophysical data which suggest that the adriatic lithosphere is presently subducting beneath the northern apennines

shear wave attenuation in the lithosphere beneath italy and surrounding regions tectonic implications more than 700 waveforms produced by 51 shallow earthquakes and recorded at regional distances 250 1400 km by the italian seismic network have been analyzed to characterize the amplitude and frequency contents of the crustal and uppermost mantle shear waves lg and sn respectively the crustal phase lg efficiently propagates through the relatively stable adriatic continental crust while it is not observed along propagation paths crossing major physiographic features like the apennine chain and the basinal domain of the tyrrhenian and ionian seas similar to lg efficient sn propagation is observed in the uppermost mantle beneath the po plain and the adriatic sea efficient sn transmission is also observed across the northern ionian sea and sicily and in the area between sardinia and the northern coasts of africa sn are efficiently transmitted across the sicily channel and rather efficient sn propagate beneath the ligurian sea on the contrary inefficient sn transmission characterizes the uppermost mantle beneath the apennines the western margin of the italian peninsula and the southern tyrrhenian sea shear wave attenuation suggests the presence of asthenospheric material in the uppermost mantle probably related to the present day extension along the apennine chain and in the tyrrhenian basin this interpretation is consistent with the presence of extensive neogene and quaternary volcanic activity in these areas and related high heat flow proposed lithospheric delaminatioh processes beneath the apennines and subduction beneath the tyrrhenian sea can reasonably explain the observed high attenuation zones in the uppermost mantle in contrast a high strength mantle lid is inferred to underlay the po plain the adriatic sea and the northern ionian sea the available waveforms also indicate that a continuous mantle lid is present beneath sicily and the extensional domain of the sicily channel as well as in the marine area south of sardinia

coastal sea level trends from topex poseidon satellite altimetry and tide gauge data in the mediterranean sea during the 1990s a joint analysis of topex poseidon satellite altimetry and tide gauge data is used to estimate sea level trends along the mediterranean sea coast from 1993 january to 2002 february a generalized least squares gls method allows us to take into account the space time distribution of the data and their respective error budgets nearly optimal parameters of the covariance functions involved in the gls method are estimated at different scales of analysis using a trial and error method combined data time series are then reconstructed at 153 locations along the coast the basin wide averaged linear trend for the coastal area shows a sea level rise of 4 54 0 30 mm yr 1 compared to 4 28 0 30 mm yr 1 for the open ocean only i e a 0 26 0 16 mm yr 1 difference the error is smaller because the systematic error does not take part in the error budget which is quite significant at local scales the coastal linear trends ranges from 8 5 to 13 5 mm yr 1 which is much narrower than ranges found by other open sea studies 24 0 to 10 0 16 0 to 29 0 mm yr 1 however a detailed error budget shows that the largest estimation errors come from the spatial extrapolation of the sea level signal required when tide gauge and altimeter data are merged the second error source is the instrumental noise and the random noise generated by the littoral contamination on altimeter measurements and from the crustal motions that are contaminating the tide gauge signal at local scale it is estimated that 85 percent of the error on linear trends does not exceed 2 mm yr 1

variations in stratigraphic and reservoir properties adjacent to the mid paleocene sequence boundary campo section pyrenees spain abstract the paleocene of the campo section spain has different sedimentological characteristics above and below the mid paleocene unconformity beneath the unconformity sediments are dominated by evaporitic carbonates and collapse breccias above it they are characterized by continental detrital beds alternating with paleosols different subaerial features are observed and correspond to different porosity values pore throat sizes and micrite morphologies unexposed or intertidal facies have low porosity low throat pore size mesoporosity and well preserved rhombic crystals intermediate exposed facies paleosols possess medium porosity medium pore throat size microporosity and mainly micro rhombic crystals finally the facies corresponding to high exposure intensity and to evaporitic original facies presents high porosity permeability large pore throat size and rounded micritic crystals these observations show that the emersion phase caused important dissolution especially when associated with an easily dissolved original lithofacies

stress associated coda attenuation from ultrasonic waveform measurements 1 the theoretical and practical exploration of stress changes from seismic waves has been the focus of recent debate within the scientific community because of its direct implications on earthquake forecasts and seismic hazards propagating in underground structures wave velocity and attenuation contain information on stress changes of the earth s interior as a result of changes in the physical state of materials seismic coda which consists of a superposition of incoherent scattered waves is known to reflect small scale random heterogeneities in the earth medium in this article we investigate the coda attenuation under different effective stresses using laboratory measurements to increase our understanding of the dependence of acoustic coda attenuation on stress variations in rocks

temporal change in coda q before the tangshan earthquake of 1976 and the haicheng earthquake of 1975 a new earthquake precursor called coda q is demonstrated for the tangshan earthquake of 1976 and for the haicheng earthquake of 1975 the precursor is based on the measurement of coda decay rate for small local earthquakes in the general area that is preparing for a major earthquake during the 3 year period preceding the tangshan earthquake the coda q was about 3 times lower than it was before or after this period a comparable change also occured at the time of the haicheng earthquake the observed change cannot be due to the change in the source parameters such as the focal depth or the source spectrum the coda q precursor appears to detect the same physical process detected by other precursors such as b value quiescence radon water quality vp vs and animal behavior but has advantages over them in its clearer physical mechanism easier sampling and better defined anomalous region

development of microporosity in a micritic limestone reservoir lower cretaceous middle east abstract abundant intercrystalline microporosity is developed within the matrix of micritic limestones over several hundreds of meters of section in the thamama group lower cretaceous at sajaa field eastern u a e sediments in the upper shuaiba formation uppermost tamama group include muddy rudist algal coralgal and orbitolina dominated lithofacies matrix is composed of euhedral to subhedral micro rhombic low mg calcite crystals with average diameters of about 5 m microporosity development was not related to leaching chalkification of lithified micrite during post depositional emergence of the shuaiba formation features diagnostic of emergence are lacking in core below the upper contact of the unit matrix microporosity is believed to have been an early developed property of micritic limestones trace element compositions of matrix reflect a diagenetic process that involved conversion of a calcitic lime mud into micro rhombic micrite and microspar using a closed system geochemical model the observed matrix oxygen isotope compositions 18 o of 4 to 5 pdb are compatible with dissolution of aptian lime mud 18 o of 2 pdb and reprecipitation of calcite in fluids of marine composition under conditions corresponding to burial depths of 550 800 m porosity of 30 50 at 40 50 c closed system conditions are consistent with textural constraints for limited or arrested cementation in the matrix chemical compaction was responsible for partial occlusion of matrix microporosity as microporosity is decreased in zones of intense stylolitization slight corrosion of matrix crystals and leaching of peloids and orbitolina postdated cementation and chemical compaction during deep burial

the dynamics of back arc extension an experimental approach to the opening of the tyrrhenian sea the e w opening tyrrhenian sea developed after the cretaceous palaeogene alpine collision nearly perpendicular to the motion of the african plate as a back arc of the adria ionian westward subduction three driving mechanisms have been proposed to explain the dynamic evolution of the tyrrhenian apennine system 1 the northward indentation of the african plate 2 the retreating subduction of the adria ionian lithosphere and 3 the gravitational collapse of the alpine post collisional wedge in order to define the relative contribution of each of these mechanisms in the neogene dynamic of the tyrrhenian apennine system we performed 3 d laboratory experiments in which we simulated a retreating subduction process in a compressional regime oriented perpendicularly to the direction of subduction in this framework we also tested the influence of the gravitational collapse of the overriding plate experiments were constructed using dry sand and silicone putties to simulate brittle upper crust and ductile lower crust upper mantle respectively these layers floated on a high density low viscosity glucose syrup which simulated the asthenosphere the main conclusion of our experiments is that large scale continental extension similar to that observed in the tyrrhenian area could be reproduced perpendicular to the shortening direction induced by the indentation of the african plate in this framework extensional processes are indeed possible if the trench retreat velocity is higher than the rate of shortening induced by the advancing african plate our experimental results indicate that this high trench retreat velocity could be explained by the coexistence of the gravitational collapse of the post alpine wedge with a slab pull process linked to the retreating subduction of the adria ionian plate while the first mechanism is predominant in the northern tyrrhenian area the second one seems to be important in the latest stage of extension and oceanic accretion of the southern tyrrhenian area

three dimensional modelling of crustal motions caused by subduction and continental convergence in the central mediterranean summary crustal deformation in the central mediterranean is modelled by means of 3 d finite element models assuming a viscoelastic rheology the tectonic mechanisms under investigation are subduction of the ionian oceanic lithosphere beneath the calabrian arc and continental convergence between the african and eurasian blocks very long baseline interferometry vlbi data at the station noto in sicily and the results from global models of plate motions are taken as representative of the motion of the african plate with respect to eurasia while vlbi solutions at matera and medicina in the southern and northern parts of the italian peninsula are geodetic observations that must be compared with modelling results vertical deformation rates are taken from geological and tide gauge records the model that best fits the observations includes the effects of subduction in the southern tyrrhenian and convergence between africa and europe the overthrusting of the tyrrhenian domain onto the adriatic domain results in an eastward component of the velocity at the eastern border of the tyrrhenian domain in agreement with vlbi data from the matera and medicina stations and gps data from northeastern sicily and the eolian islands the highest subsidence rates are obtainedinthe southern tyrrhenian and are of the order of 1 2 1 4 mm yr 1 along the whole adriatic coast of the italian peninsula subsidence in the foredeeps is of the order of 0 2 0 5 mm yr 1 the apenninic chain is rising with rates of the order of 0 2 0 4 mm yr 1 subduction beneath the calabrian arc is responsible for a roll back velocity higher than in the northern areas 2 d models built for the geological past indicate the possibility of roll back velocities of several centimetres per year in particular active rifting in the tyrrhenian and softening of the crust in the back arc basin result in a trench retreat velocity in agreement with geological estimates our results show that numerical modelling can be used to estimate present day deformation rates and the contribution of active tectonics to sea level changes along coastal areas

burial dissolution of micrite in middle east carbonate reservoirs jurassic cretaceous keys for recognition and timing abstract this paper discusses burial diagenesis and especially a burial dissolution phase and its effects on micrite microtexture in reservoirs in the middle east three microporous reservoirs were selected the cenomanian mishrif formation in iraq the kimmeridgian tithonian arab d and the barremian kharaib formations both in abu dhabi staining cathodoluminescence and scanning electron microscopy were used for petrographic observations in the selected reservoirs three typical micrite microtextures are distinguished micro rhombic compact anhedral and rounded the chronology of diagenesis based on petrographic observations shows that mineralogical stabilisation through high magnesian calcite replacement by low magnesian calcite led to the formation of micro rhombic micrites non reservoir facies such as seals present compact anhedral micrites correlation between these micrites and high aluminium content suggests alumino silicate minerals clays as a catalyst for pressure dissolution and thus for reservoir degradation through cementation micrites from the upper part of oil reservoirs are dissolved during burial diagenesis dissolution is responsible for rounded shape and for reduction of crystal size it also implies pore diameter and pore throat size enlargement comparison of porosity and permeability with scanning electron microscope data confirms that rounded micrites are better reservoirs than micro rhombic micrites

differences between static and dynamic elastic moduli of a typical seismogenic rock summary static and dynamic elastic moduli of calcare massiccio mudstone limestone the typical seismogenic rock in the italian apennines are measured using a standard uniaxial static compression test a dual cantilever forced oscillation test and ultrasonic measurement of elastic wave velocities these measurements cover nine decades in frequency including the seismic domain neither a significant frequency dependence nor a pronounced strain amplitude dependence was observed providing a young s modulus of 75 7 gpa and a poisson s ratio of 0 28 0 02 these values are characteristic of calcare massiccio in undamaged condition

quantitative stratigraphy of rudist limestones and its bearing on spatial organisation of rudist communities the late barremian urgonian sequences of provence s e france abstract rudist beds in platform carbonates of late barremian age early cretaceous cropping out in the marseille region provence se france possess a substantial lateral continuity 40 km whereas associated rudist bodies tend to be less continuous transition probabilities markov chain analysis are used at a regional scale to test the lateral continuity of rudist bodies and their four associated rudist assemblages each rudist assemblage has a specific probability to be adjacent to itself or to any one at a local scale analysing the variations of transition probabilities as a function of distance using various proxies shows a periodic spatial trend the style of which depends on the type of rudist assemblage i e community type the foregoing documents two groups with different properties group 1 includes two communities characterised by small forms restricted to very shallow and muddy settings organised spatially into small patches c 1000 1500 m with moderate spacing c 1500 2000 m group 2 includes two communities characterised by mixed size or large forms typical of deeper water and more sandy settings organised spatially into large patches c 3000 m with a larger spacing c 3000 4000 m the internal architecture and the dimensions of these rudist bodies argue against a reefal nature quantitative estimates of lateral continuity and spatial variations of rudist bodies have a significant potential for reservoir modelling of hydrocarbon bearing rudist rich platform carbonates

stresses and plate boundary forces associated with subduction plate margins primary tectonic stress in the lithosphere is predominantly caused by lateral density variations within the earth and associated topographical loading when such a stress system caused by major sublithospheric density anomalies is intersected by a weak zone which cuts across the lithosphere plate boundary forces develop and modify the plate interior stresses in this paper unite element analysis is used to model the stresses and plate boundary forces associated with subduction plate boundaries with dipping and vertical slabs extending to about 270 and 400 km depths having the subduction fault both locked and unlocked in such regions several types of horizontal deviatoric stress may occur including 1 local compression in the trench arc region caused by the dense sinking slab and the associated surface downflexure 2 plate interior tension which occurs when this compression is intersected by a weak subduction fault 3 local tension associated with thickening of the crust at the arc and elsewhere 4 local tension in the back arc region produced by the underlying low density upper mantle and 5 downbending stresses in the subducting slab thermal stresses and transmitted ridge push which are not included in the modelling here a gradient from compression in the forearc to tension in the back arc can be modelled in terms of these stresses when the fault is partially locked it is however the intersection of the local compression 1 by an unlocked or partially locked subduction fault that modifies the plate interior stresses and gives rise to the slab pull and trench suction plate boundary forces the state of stress in the interior of the overriding plate is also crucially influenced by back arc spreading where this occurs plate boundary forces have been evaluated for each of the models it is shown that slab pull and trench suction may be of comparable magnitude

modern tectonic regime in the tyrrhenian area observations and models summary the rapid opening since 10 ma of the tyrrhenian sea in a context of convergence between eurasia and africa remains a puzzling geodynamic problem one of the most plausible scenarios proposed by malinverno ryan 1986 attributes extension to southward and eastward migration of the trench resulting from subduction of the african adriatic lithosphere below the european lithosphere at present subduction only continues along the calabrian arc a compilation of recent strain and stress indicators by rebai philip taboada 1992 indicates that an extensional regime still prevails in the tyrrhenian sea whereas compression dominates north and south of this area in an earlier paper bassi sabadini 1994 used a numerical model to demonstrate the necessity of a trench suction force acting along the subduction trench to produce the present extension in the tyrrhenian domain this study however did not discuss in detail the tectonic regime in the different areas composing the domain nor the match between the observations and the model in this paper we first review the constraints provided by the observations compiled by rebaiet al 1992 and by more recent measurements we then investigate how much of the observed tectonic regime can be understood in terms of plate interaction forces using thin plate models bird 1989 the geometry and heterogeneous lithospheric properties of the models are constrained by observations the best constrained boundary conditions are held constant the remaining are regarded as parameters that we tune in order to fit the observations our results indicate that the present day tectonic regime in the tyrrhenian area can be explained as a consequence of trench retreat associated with the subduction of ionian oceanic lithosphere under the calabrian arc combined with a rotation of the apennines possibly related to a rotation of the adriatic microplate this study supports therefore the model of malinverno ryan 1986 and suggests moreover that rotation of the apennines is an ongoing process which is supported by seismological and geodetic data but remains to be understood in terms of geodynamics a discrepancy between observations and models is observed in western sicily which can be attributed to modelling limitations the weak extensional activity of the corsica sardinia block however is not explained by this model

localization of seismic coda at merapi volcano indonesia 1 the energy of the seismic coda generated by multiple scattering at small scale heterogeneities in the earth is generally uniformly distributed in space at some late lapse time 3 component seismogram envelopes of volcano tectonic b type earthquakes recorded at merapi volcano on the contrary show a systematic decrease of the coda amplitude with distance from the summit of the volcano we present two different models to explain this observation in the first model seismic energy transport is described as a diffusion process and the observed coda localization is explained by an inhomogeneous distribution of the diffusion coefficient d d r as a simple analytical model we use a strongly scattering cylinder representing the volcano embedded in a homogeneous half space representing the surrounding crust in the second model we assume the disorder within the strato volcano to be so large that diffusion theory breaks down and a transition to the so called anderson localization regime occurs this model predicts a concentration of seismic energy near the source region and can thus also explain the observed coda localization

numerical simulation of the biot slow wave in water saturated nivelsteiner sandstone the development of rock acoustic models is important for interpreting seismic data these models should relate seismic properties such as wave velocity and attenuation to the production and lithological properties of reservoir rocks such as porosity permeability fluid type and fluid saturation

local regional and plate scale sources for the stress field in the adriatic and periadriatic region abstract the stress field at a specific location is the sum of regional stress controlled by plate scale tectonic processes with local sources here we evaluate and discuss the different sources from geodynamic to local scale and the controlling factors including the jurassic paleogeography of the adriatic passive margin of present day stress in the adriatic sea and periadriatic regions of italy using two kinds of numerical models 3d mantle scale viscoelastic models and 2 5d lithosphere scale thin shell models the subcrustal stress field of the slabs in the dinarides hellenic and apennines calabrian subduction zones are characterized by downdip extension and compression respectively this difference is explained by the velocity of the adriatic slab with respect to the upper mantle in the hotspot reference frame the slab in the calabrian subduction zone is encroached and down pushed whereas the slab in the hellenic subduction zone is sustained by the mantle flow at the plate scale the upper crustal stress field at the apennines front is governed by the different nature of the lithosphere probably oceanic in the ionian sea and continental elsewhere which in turn determines first order rotations of the stress axes second order rotations of the stress axes depend on the jurassic paleogeography and consequent differential advancement of the thrust fronts with recesses and salient occurring in correspondence with jurassic structural highs and lows respectively the eastward relative motion of the mantle with respect of the lithosphere enhances the onset of nw se oriented compression within the adriatic plate consistent with observations finally 2 5d thin shell models demonstrate that present day stress does not simply follow the long wavelength pattern 500 1000 km due to plate tectonics and mantle interaction but is greatly affected by the presence of second and third order sources like crustal structure faults and topography most importantly these factors give an observable effect in data

micro rhombic calcite and microporosity in limestones a geochemical study of the lower cretaceous thamama group u a e abstract euhedral micro rhombic calcite forms a microporosity network in limestones of the lower cretaceous thamama group u a e isotopic and trace element data indicate that micro rhomb formation was a two step process associated with diagenesis in meteoric waters the micro rhombic calcite and the micropores are both products of the second event sr fe mn and mg contents of the micro rhombs are all relatively low ranging from 108 to 310 ppm 34 to 308 ppm 3 to 32 ppm and 0 42 to 0 68 mole respectively the low sr and mg contents indicate extensive flushing of these constituents from the rock the low fe and mn contents are probably inherited from the original sediments and indicate the lack of any fe or mn in the pore fluids during micro rhomb formation the 13c of the micro rhombs 3 1 to 4 5 pdm are also primary unaltered by diagenesis the 13o of the micro rhombs 4 5 to 6 0 pdb reflect alteration by mateoric waters a large number of pore volumes and an open water buffered system would be necessary to flush sr and mg yet decreasing 18o with increasing porosity indicates that 18o values in non porous intervals are partially rock buffered two diagenetic events are thus implicated the first flushing sr and mg and lowering 18o in all rocks and the second event actually forming the micro rhombs and further altering 18o as a function of porosity the first diagenetic event was most likely mineralogical stabilization in an unconfined meteoric aquifer immediately after shuaiba deposition if mineralogical stabilization was completed in the first event then calcite to calcite recrystallization is implicated for the second event the second event may have occurred in the unconfined meteoric aquifer or it may have occurred in a confined meteoric aquifer during the early late cretaceous

carbonate platform stratal geometries and the question of subaerial exposure abstract integrated petrographic geochemical and fluid inclusion analyses indicate that the most prominent exposure unconformity at the southern margin of the vercors carbonate platform in southeastern france does not coincide with the major break in depositional geometry therefore changes in sediment supply and dispersal strongly influenced the resulting stratal geometries and prevent direct reconstructions of sea level from the stratal patterns platform to basin transects exposed in the cirque d archiane contain two prograding grainstone tongues separated by a wedge of finer grained slope sediments that thin toward the platform diagenetic analyses have been done at several strategic platform top bedding planes to determine the extent to which these sedimentologic breaks represent subaerial exposure while many bedding planes contain some evidence of meteoric alteration one of these bedding surfaces is unique in that it exhibits several generations of overprinted meteoric calcite cements bladed to blocky morphology precipitation in biomolds extinct to zoned cathodoluminescence low mg and 18 o variable 13 c freshwater fluid inclusions that are cross cut by marine borings eroded dolomitized clasts derived from this exposure surface occur in the uppermost portion of the finer grained wedge this combined evidence indicates that a significant episode of subaerial exposure took place at this horizon prior to deposition of the overlying platform top sediments the most significant change in depositional style and therefore the most likely position for a sequence boundary defined by stratal geometry is the top of the lower grainstone tongue however the intensely altered exposure surface and its basinward equivalent in the wedge lie 50 m above the top of the lower grainstone tongue therefore the surface containing the most extensive record of meteoric diagenesis does not stratigraphically coincide with the surface representing the most significant lateral shift in depositional facies

constraints on the seismotectonics of the central mediterranean from very long baseline interferometry summary very long baseline interferometry vlbi determined site velocities from seven stations in western europe reveal a stable continental platform north of the alps deformations between sweden germany and spain can not exceed 2 mm yr south of the alps significant motions are occurring with respect to stable europe two sites east of the apennine mountains on peninsular italy have north easttrending velocities which increase from 2 mm yr l in the north at medicina to 6 mm yr l in the south at matera in contrast the vlbi site in the south eastern corner of sicily is moving 7 mm yr i to the north north west these velocities are largely explained if southern sicily is attached to a north westerly moving african plate and the eastern portion of the italian peninsula forms part of a hypothesized adriatic sea crustal block which is rotating counter clockwise with respect to europe about a pole near the alps such an explanation is consistent with the styles of the larger historical earthquakes of the region which show ne sw extension across the apennines north south convergence across the alps and ne sw compression in coastal yugoslavia the adria plate model generates 1 5 2 2 x 10l8 nm yr l of potential earthquake moment along the northern and central apennines historical records suggest that 30 60 per cent of this moment is released seismically based on a direct strain rate measurement recurrence intervals for italian earthquakes south of medicina are estimated to be 12 46 yr for m6 5 quakes and 35 143 years for m7 0 quakes

interaction of seismic waves with a viscous liquid layer abstract the interaction of seismic waves with a layer filled with a viscous fluid is studied this study is intended to provide the basis for designing active seismic experiments to detect the existence of hydraulically induced fractures in a hot dry rock geothermal energy system we compute transmission and reflection coefficients for p sv and sh waves incident at arbitrary angles onto a fluid layer embedded between two homogeneous half spaces we find that coefficients for sh waves at normal incidence can be written in terms of two dimensionless parameters one of these parameters i is the ratio of acoustic impedance of the fluid to the acoustic impedance of the solid the other dimensionless parameter d is a measure of the amount of energy the sh wave loses during one pass through the fluid layer we find that the amplitude of the sh wave transmitted through the fluid layer is equal to the amplitude of the incident sh wave if i is nearly 1 and d is small as d increases energy is lost due to viscous dissipation in the fluid and transmitted wave amplitude diminishes if i is not nearly 1 some energy is reflected by the fluid layer three dimensionless parameters are required for solution for the case of p waves normally incident on the fluid layer one parameter r is the ratio of the bulk modulus to effective shear modulus of the fluid the second parameter is the ratio of elastic impedance of the solid to the shear impedance of the fluid and the third is d we find that the value of r is a good measure of the importance of fluid viscosity on the propagation of p waves through the fluid detailed studies of the effects of fluid and solid physical properties on the amplitudes of transmitted and reflected waves when waves are normally incident provide valuable insight into the importance of physical properties in the calculations for non normal incidence finally reflection and transmission coefficients are computed for p and sv waves incident at arbitrary angle on a viscous fluid layer physical properties of fluid and rock are chosen to be those thought appropriate for the los alamos national laboratory hot dry rock geothermal test site located at fenton hill new mexico

morphometry of micrite particles in cretaceous microporous limestones of the middle east influence on reservoir properties abstract microporosity may account for a significant part of the total porosity of cretaceous limestone reservoirs of the middle east in these microporous facies porosity is moderate to excellent up to 35 while permeability is poor to moderate up to 190 md micritic limestones also may form dense layers with very low porosity and permeability values micritic samples were collected from three fields of the habshan and mishrif formations to examine the spatial relationship with their porosity permeability and pore throat radius distributions two key parameters of the micritic particles are studied using scanning electron microscopy their morphology shape and inter crystal contacts and their crystallometry results reveal that micrite matrixes can be subdivided into three petrophysical classes class c strictly microporous limestones with coarse punctic to partially coalescent micrites is made up of coarse 2 m polyhedral to rounded micritic crystals it has good to excellent porosity 8 28 poor to moderate permeability 0 2 190 md and a mean pore threshold radius of more than 0 5 m the class c is usually observed in rudist shoal facies where relatively high hydrodynamic energy disfavoured deposition of the finer micritic crystals it also developed within meteoric leaching intervals below exposure surfaces class f strictly microporous limestones with fine punctic to partially coalescent micrites is composed of fine

carbonate production by rudist bivalves the record of late barremian requieniid communities from provence se france abstract rudist bearing sediments from platform carbonates of late barremian age early cretaceous cropping out in the marseille region provence se france were investigated on a 46 km wide transect after seven stratigraphic sections to quantify the role of rudists in the corresponding stratigraphic system by using various proxies the regional stratigraphic contribution of total thickness of rudist beds is relatively high 43 1 each rudist community type possesses a specific skeletal contribution of skeletal content in the range of 19 2 to 31 5 at a stratigraphic scale including rudist rich and rudist free beds the skeletal contribution drops to 13 8 this value is derived from the standard skeletal contribution obtained for each community type combined with the stratigraphic contribution of rudist beds in vertical successions and horizontal stratigraphic units a closely related value 12 8 is obtained from calculations using specific lateral dimensions of rudist bodies and their spacing i e modules depending on community types each community has a particular potential quantitative contribution to the overall regional stratigraphic system rudist production is deduced from the cyclostratigraphic approach of accumulation rates for each community type estimates of caco 3 net production are in the range of 19 to 50 kg m 2 ka 1 these values are very low when compared with those obtained at a biological scale for modern bivalves late cretaceous rudists and recent coral reefs the geological scale used for our estimates may partly account for this difference whereas low accommodation rates linked to cretaceous greenhouse conditions appear a potential important factor in this respect the low net production of requieniid dominated communities sediment dwellers not framework builders also reflects their limited sedimentogenetic power

geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy abstract serri g innocenti f and manetti p 1993 geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 117 147 the neogene quaternary magmatism of the northern apenninic arc took place in four phases separated in space and time which become progressively younger from west to east phase i 14 ma phase ii 7 3 6 0 ma phase iii 5 1 2 2 ma phase iv 1 3 0 1 ma this magmatism is the result of the activation of three physically separate sources 1 the adriatic continental crust extracted from the mantle in the late proterozoic 2 a strongly refractory recently k enriched harzburgitic mantle located in the mechanical boundary layer mbl of the lithosphere and 3 a recently metasomatized cpx rich mantle compositionally variable from iherzolite to wehrlite clinopyroxenite interpreted as an ephemerally k enriched asthenosphere the adriatic continental crust is the dominant source of the acid plutonic and volcanic rocks of the tuscan region the acid magmatism is mostly found inside an ellipsoidal area about 150 300 km centred on giglio island here defined as the tuscan crustal dome within this area mantle derived magmas unaffected by important crustal contamination processes and mixing with crustal anatectic melts have so far not been found pure crustal magmas are rare but are represented for example by some of the san vincenzo and roccastrada rhyolites virtually all the tuscan acid centres show evidence of mixing with potassic mantle derived magmas major and trace elements as well as 87 sr 86 sr and 143 nd 144 nd data on primitive rocks mg 65 reveal two groups of mantle derived magmas these define two distinct mantle enrichment trends both essentially due to the additions of k rich components which metasomatized separate compositionally diverse upper mantle sectors in both cases the most remarkable mineralogical effect of these enrichment processes is the production of variable amount of phlogopite through reaction between fluids and or melts with the mantle the rocks of group i ol hy and q normative lamproites ultrapotassic high mg latites ultrapotassic shoshonites and shoshonites saturated trend are considered to be derived by partial melting at low pressure 87 sr 86 sr 0 717 ce sr 0 3 and k 2 o na 2 o 6 7 and low ratios of 143 nd 144 nd 0 5121 0 5120 and ba la 87 sr 86 sr 0 712 and k 2 o na 2 o 8 9 values and low 143 nd 144 nd ba la 0 10 ratios these constraints do not allow to exclude a complete identity between the k rich components which metasomatized the mantle sources of the saturated and undersaturated trend magmas the geochemical and isotopic features of the components that metasomatized the mantle sources of the northern apenninic arc magmatism can be explained by a geodynamic process which causes a large amount of crustal materials to be incorporated within the upper mantle we propose that the delamination and subduction of the adriatic continental lithosphere related to the still ongoing northern apennine continental collision provide a viable mechanism to explain the genesis and eastward discontinuous migration of the magmatism in central italy the subduction of delaminated lithospheric mantle with lower crustal slivers would have exposed uppermost mantle adriatic mbl and crustal units previously imbricated in the apennine chain to the heating advected by the upwelling of a recently and ephemerally k enriched asthenospheric mantle wedge and by the underplating of magmas derived from it we consider that the diapiric uprising of a hot crustally contaminated asthenosphere occurs in the wake left above the sinking of the adriatic delaminated subducting continental lithosphere the delamination subduction process of the adriatic lithosphere has probably started in the early middle miocene but earlier than 15 14 ma ago as indicated by the age and petrologic characteristics of the first magmatic episode sisco lamproite of the northern apennine orogenesis

diagenesis and porosity preservation in eocene microporous limestones south florida usa abstract microporous limestones may contain immobile capillary bound irreducible water that is only in diffusional contact with mobile pore waters or in some reservoirs may contain producible hydrocarbons the preservation and distribution of microporosity impact both subsurface fluid flow and solute transport the diagenesis of microporous limestones has received relatively little attention because their very fine grains and cements are not amenable to standard analytical methods the ocala limestone upper eocene and upper avon park formation middle eocene in south florida contain microporous micritic limestones mudstones to packstones that are at an intermediate stage of diagenesis the limestones have been exposed to the active near surface environment but have not yet reached a burial depth sufficient for intense chemical compaction and associated porosity reduction nuclear magnetic resonance nmr logging allowed for the quantification of total porosity pore size distribution and permeability the ocala limestone and avon park formation have different predominant microfacies and porosity size distributions but yet both retain total porosities predominantly between 35 and 37 estimated microporosities range mostly between 12 and 45 the mudstones and wackestones of the ocala limestone have significantly lower permeabilities mostly 3 to 12 md than the wackestones to grainstones of the avon park formation commonly in the 100 to 3000 md range which have more mixed and overall coarser pore sizes computer modeling using carbon and oxygen stable data indicates that the studied microporous limestones underwent only a low degree of chemical diagenetic alteration despite likely experiencing episodes of freshwater flushing associated with post depositional sea level lowstands the ocala limestone and avon park formation limestones illustrate the general concept that total porosity is often largely preserved through early diagenesis although may undergo intra formational redistribution and that confined aquifers are diagenetic quiescent environments

plio quaternary vertical motion of the northern apennines insights from dynamic modeling we test the effects of different geodynamic mechanisms on the pliocene to present day dynamics and in particular on the vertical motions of the northern apennines system by means of two dimensional finite element models we show that the pliocene features of the northern apennines exhumation of deep rocks in western italy and fast subsidence rates in the adriatic foredeep can be adequately reproduced by a model slab characterized by the passive sinking of a negatively buoyant adriatic slab and by the upwelling of buoyant asthenosphere beneath western italy model slab is however not able to account for the quaternary and present day pattern of vertical motion of eastern italy and of the adriatic basin a deep configuration of the system characterized by a detached slab model detach may explain the vertical motions of these areas constrained by uplift of the eastern portions of the apenninic chain by an eastward shift of the foredeep depocenter and by lower subsidence rates in the adriatic basin the tectonic and stratigraphic data showing major differences between the tertiary and the quaternary evolution of the northern apennines are discussed

assessing pedogenic calcite stable isotope values can positive linear covariant trends be used to quantify palaeo evaporation rates abstract palaeoclimate models suggest enhanced evaporation rates in subtropical regions 15 30 latitude during greenhouse world conditions however there are no empirical data to support these estimates laboratory evaporation experiments have shown that calcites precipitated from variably saturated solutions yield a positive linear covariant trend plct in 18 o calcite versus 13 c calcite values the goal of the present controlled laboratory experiments is to develop a method to quantify regional palaeo evaporation rates from palaeosol calcrete plcts samples of powdered caco 3 were dissolved in de ionized water in pressure sealed containers with a range of elevated atmospheric p co 2 concentrations for 24 h the solution was then allowed to evaporate completely from an open container within an incubator with the time of calcite crystallization noted and aliquots removed for analysis every 24 h the precipitated calcite produced an array of 18 o calcite versus 13 c calcite values that fall upon a plct projected from a theoretical meteoric calcite line mcl water analyses yielded 18 o water enrichments from an initial value of 4 75 vsmow ranging up to between 10 0 and 14 8 the experimental results show that solutions formed under higher p co 2 conditions precipitated calcite very early on during evaporation and thus have 18 o calcite and 13 c calcite values that are slightly enriched relative to the mcl the solutions that formed under low p co 2 conditions precipitated calcite after much of the fluid had evaporated and thus yield more enriched 18 o calcite and 13 c calcite values repeat trials with varying temperature and relative humidity show that the plct is steeper under both higher temperature and low relative humidity the wide range of p co 2 temperature and relative humidity conditions used simulate meteoric phreatic and meteoric vadose conditions that may affect a calcrete horizon over time during numerous dissolution precipitation reactions the results of these experiments show that a dominant factor in the precipitation of vadose calcite is the saturation state of the fluid with respect to caco 3 while the primary factors affecting the magnitude and steepness of the plct are vadose zone temperature relative humidity the starting 18 o water value and saturation state of the fluid with respect to caco 3 since the p co 2 of the rooting zone is cross controlled by the local soil and surface ecology the magnitude of the plct enrichment may not be a direct proxy for palaeo evaporation rates

excitation of true polar wander by subduction true polar wander the global motion of the mantle relative to the earth s rotation axis is known from the analysis of palaeomagnetic data hotspot tracks and plate motions to have occurred at velocities of up to 0 5 myr 1 since the late cretaceous period1 4 we address here the longstanding question of how fast episodes of true polar wander tpw can be excited5 by analysing the impact of the distribution and activity of subduction zones on polar motion using nonlinear liouville equations which allow us to treat large excursions of the polar axis we show that unrealistically fast tpw is excited by subduction episodes unless the lower mantle has a viscosity at least 10 times that of the upper mantle this need for a viscosity increase with depth in the mantle reinforces the conclusions of previous studies on post glacial rebound and geoid anomalies theoretical creep laws and some preliminary results on tpw induced by density anomalies embedded in the mantle6 10 the lower viscosity in the upper mantle means that upper mantle density anomalies are most effective in exciting tpw changes in the pattern of subduction through time may be responsible for both episodes of fast tpw and times of quiescence in polar motion

spatial variation of present day stress field and tectonic regime in tunisia and surroundings from formal inversion of focal mechanisms geodynamic implications for central mediterranean we compiled 123 focal mechanisms from various sources for tunisia and adjacent regions up to sicily to image the current stress field in the maghrebides chain from tunisia to sicily and its foreland stress inversion of all the available data provides a first order stress field with a n150 e horizontal compression shmax and a transpressional tectonic regime but the obtained stress tensor poorly fit to the data set we separated them into regional subsets boxes in function of their geographical proximity kinematic regime homogeneity of kinematic orientations and tectonic setting their respective inversion evidences second and third order spatial variations in tectonic regime and horizontal stress directions the stress field gradually changes from compression in the maghrebides thrust belt to transpression and strike slip in the atlassic and pelagian foreland respectively where preexisting nw se to e w deep faults system are reactivated this spatial variation of the sismotectonic stress field and tectonic regime is consistent with the neotectonic stress field determined by others from fault slip data the major slab transfer edge propagator faults i e north south axis hammamet relay and malte escarpment which laterally delimit the subducting slabs play an active role in second and third order lateral variations of the tectonic regime and stress field orientations over the tunisian sicilian domain the past and current tectonic deformations and kinematics of the central mediterranean are subordinately guided by the plate convergence i e africa eurasia controlled or influenced by lateral slab migration segmentation and by deep dynamics such as lithosphere mantle interaction

macro anisotropy of the electrical conductivity of the crust a magnetotelluric study of the german continental deep drilling site ktb summary the interpretation of magnetotelluric mt data collected in the vicinity of the german continental drilling project ktb has revealed two major structures in the earth s crust first a large scale mid crustal layer of enhanced conductivity is required to fit the regional observations of the anomalous vertical magnetic field second the mt impedances of the area close to the ktb namely the crustal unit of the zone erbendorf vohenstraus zev support a model with a highly anisotropic upper to middle crust the extremely high values of anisotropy derived from the mt measurements exceed the values of anisotropy observed on rock samples in the laboratory by an order of magnitude and therefore exclude intrinsic features as a source for the observed anisotropy the regional mid crustal conductor is in agreement with central europe wide observations of high conductivity layers in the crust while the proposed model of well conducting subvertical dykes within a resistive host rock explains the mt observations and agrees with the steeply dipping seismic reflectors the downhole and core observations from the drilling and the model of the tectonic development of this area however the superposition of both structures leaves some unanswered questions

energy flux model of seismic coda separation of scattering and intrinsic attenuation a new model of seismic coda is presented based on the balance between the energy scattered from the direct wave and the energy in the seismic coda this energy flux model results in a simple formula for the amplitude and time decay of the seismic coda that explicitly differentiates between the scattering and intrinsic anelastic attenuation of the medium this formula is valid for both weak and strong scattering and implicitly includes multiple scattering the model is tested using synthetic seismograms produced in finite difference simulations of wave propagation through media with random spatial variations in seismic velocity some of the simulations also included intrinsic dissipation the energy flux model explains the coda decay and amplitude observed in the synthetics for random media with a wide range of scattering q in contrast the single scattering model commonly used in the analysis of microearthquake coda does not account for the gradual coda decay observed in the simulations for media with moderate or strong scattering attenuation scattering q less than or equal to 150 the simulations demonstrate that large differences in scattering attenuation cause only small changes in the coda decay rate as predicted by the energy flux model the coda decay rate is sensitive however more to the intrinsic q of the medium the ratio of the coda amplitude to the energy in the direct arrival is a measure of the scattering attenuation thus analysis of the decay rate and amplitude of the coda can in principle produce separate estimates for the scattering and intrinsic q values of the crust we analyze the coda from two earthquakes near anza california intrinsic q values determined from these seismograms using the energy flux model are comparable to coda q values found from the single scattering theory the results demonstrate that coda q values are at best measures of the intrinsic attenuation of the lithosphere and are unrelated to the scatteing q less

tomographic images of the upper mantle below central europe and the mediterranean results from delay time tomography of the european mediterranean upper mantle are discussed and where possible interpreted in terms of geodynamic processes slab like positive velocity anomalies of which the locations correlate well with deeper seismicity are found beneath spain the tyrrhenian basin and the aegean these structures are interpreted as images of subducted slabs large aseismic regions with positive velocity anomalies are found beneath the western mediterranean italy the alps dinarides the pannonian basin northern greece and the aegean these anomalies can also be linked to subducted lithosphere from the anomaly patterns it is deduced that subduction occurred below the western mediterranean and along both sides of the adriatic micro plate beneath the dinarides and northern greece the velocity structures suggest detachment of the slab from the surface

seismicity and p wave velocity image of the southern tyrrhenian subduction zone summary this paper focuses on the deep earth structure and earthquake distribution within the southern tyrrhenian subduction zone we discuss seismological observations which provide insight into the mechanics of subduction processes for an unusual compressional margin the motivation for this work derives from the recognition that little is known about one of the most intriguing geodynamic features of the italian peninsula and the fact that a large amount of information can be extracted from data collected by the istituto nazionale di geofisica national seismic network we show that the hypocentres of intermediate and deep earthquakes that have occurred since 1988 image a nw dipping plane continuous from the ionian sea to the tyrrhenian down to 450 km depth we also present a 3 d model of the deep structure beneath southern italy derived using deep earthquake seismic tomography tomographic images reveal a high velocity body dipping from the apulian and iblean forelands towards the tyrrhenian basin in the crust and upper mantle at least down to 320 km depth this high velocity body may be related to the cold subducted ionian lithosphere earthquake hypocentres are confined within the high velocity body delineating the subduction beneath the calabrian arc

squirt flow in fully saturated rocks we estimate velocity frequency dispersion and attenuation in fully saturated rocks by employing the squirt flow mechanism of solid fluid interaction in this model pore fluid is squeezed from thin soft cracks into the surrounding large pores information about the compliance of these soft cracks at low confining pressures is extracted from high pressure velocity data the frequency dependence of squirt induced pressure in the soft cracks is linked with the porosity and permeability of the soft pore space and the characteristic squirt flow length these unknown parameters are combined into one expression that is assumed to be a fundamental rock property that does not depend on frequency the appropriate value of this expression for a given rock can be found by matching our theoretical predictions with the experimental measurements of attenuation or velocity the low frequency velocity limits as given by our model are identical to those predicted by gassmann s formula the high frequency limits may sign

modelling of seismic energy transport at volcanoes with real topography and complex propagation medium abstract in stratovolcanoes multiple scattering of seismic waves is caused by a strongly heterogeneous propagation medium additionally these waves are scattered by the rough topography of the volcano we devised an algorithm to model seismic energy transport in volcanoes based on a monte carlo simulation of the equation of radiative transfer this algorithm takes into account both the real topography of volcanoes which is described by a digital elevation model and the complex subsurface structure of the volcanic edifice which is treated as a random medium theoretical energy densities of two different models were compared to observed energy densities derived from seismograms of shallow volcano tectonic earthquakes that occurred at merapi volcano indonesia a model consisting of a heterogeneous volcano shaped medium over a homogeneous half space was found to be suitable to explain the observed data for merapi volcano our modelling results in a mean free path of 250 m and a thickness of 1 7 km of the scattering volcanic edifice the systematic decrease of the coda energy with source distance of the observed data referred to as coda localization can be successfully explained by our model