strength and anisotropy of foliated rocks with varied mica contents abstract we have shortened 15 schists and gneisses with varying compositions 15 75 mica by volume at angles of 45 and 90 to foliation s to investigate the influence of micas on the strength and anisotropy of foliated rocks at the conditions tested t 25 c p c 200 mpa and e 10 5 s 1 compressive strengths vary by a factor 4 in the 45 and 90 orientations and individual rock types exhibit directional responses ranging from isotropic to strongly anisotropic trends of decreasing strength decreasing anisotropy and increasing ductility are observed with increasing mica content strains in all samples were localized within inclined shear zones accommodated by dislocation slip and grain scale microkinking in micas and microcracking in all other silicates stress strain response and grain scale deformation microstructures both indicate that mechanical behavior is strongly influenced by the concentration and spatial arrangement of micas shear zone formation is associated either with discrete brittle fracture transitional strain softening or steady strength ductile shear in both brittle and transitional samples extensive microcracking of strong quartzo feldspathic bridges occurs and stress drop magnitudes decrease with decreasing spacing and increasing overlap of adjacent critically oriented micas steady strength ductile shear zones develop in samples containing domains of interconnected micas and isotropic mechanical response is observed in those in which micas are contiguous in nearly all directions

the preparatory phase of the mw 6 1 2009 l aquila italy normal faulting earthquake traced by foreshock time lapse tomography

assessment of earthquake locations in 3 d deterministic velocity models a case study from the altotiberina near fault observatory italy the accuracy of earthquake locations and their correspondence with subsurface geology depends strongly on the accuracy of the available seismic velocity model most modern methods to construct a velocity model for earthquake location are based on the inversion of passive source seismological data another approach is the integration of high resolution geological and geophysical data to construct deterministic velocity models in which earthquake locations can be directly correlated to the geological structures such models have to be kinematically consistent with independent seismological data in order to provide precise hypocenter solutions we present the altotiberina at seismic model a three dimensional velocity model for the upper tiber valley region northern apennines italy constructed by combining 300 km of seismic reflection profiles 6 deep boreholes down to 5 km depth detailed data from geological surveys and direct measurements of p and s wave velocities performed in situ and in laboratory we assess the robustness of the at seismic model by locating 11 713 earthquakes with a non linear global search inversion method and comparing the probabilistic hypocenter solutions to those calculated in three previously published velocity models constructed by inverting passive seismological data only our results demonstrate that the at seismic model is able to provide higher quality hypocenter locations than the previous velocity models earthquake locations are consistent with the subsurface geological structures and show a high degree of spatial correlation with specific lithostratigraphic units suggesting a lithological control on the seismic activity evolution

microfracturing paleostress and the growth of faults abstract we have analyzed the microfractures in samples taken near one thrust fault and five normal faults of known displacement to test the dependence of microfracture density and distribution on fault slip we have also recorded the orientation of microfractures as a function of distance from the associated fault surface in order to control as many parameters as possible shallow faults with similar lithologies were chosen they showed the same kind of deformation namely microfracturing without block rotation recrystallization extensive granulation or crystal plasticity the results of over 8000 microfracture measurements suggest that maximum microfracture density is independent of net slip we interpret this relationship as indicating that the preponderance of microfracturing occurs in proximity to the propagating fault tip the angular relationship between the shear plane and microfractures was commonly found to be between 5 and 20 significantly less than the 30 expected between the far field maximum principal stress and the shear surface this low angle between microfracture orientation and shear plane orientation is predicted for a local stress field associated with a propagating mode ii fault tip other possible explanations for the small angle for tensional microfractures and the shear surface are 1 the effective confining pressure was very low or 2 shear strength at failure was much larger than expected

the development and behaviour of low angle normal faults during cenozoic asymmetric extension in the northern apennines italy abstract movements on low angle normal faults lanf are not predicted by traditional anderson byerlee frictional fault mechanics our investigations centre on three normal fault systems active at distinct times during the regional extension of the northern apennines with each showing different degrees of crustal exhumation these are from e to w the altotiberina fault system umbria the radicofani fault system tuscan mainland and the zuccale fault system isle of elba regional extension has been a continuous process since middle miocene migrating progressively from west to east with deformation accommodated by a set of e to ne dipping lanf and more steeply sw dipping antithetic structures the lanf acted as regional detachments accommodating a majority of the extension in the northern apennines with individual faults exhibiting several kilometres of displacement regionally the stress field has been characterised by a vertical 1 and a ne sw tuscan mainland and umbria to e w elba trending 3 where exposed at the surface the main lanf detachments possess a well developed fault core of foliated fault rocks in which fluids have played a key role in weakening due to reaction softening and the onset of stress induced solution precipitation mechanisms we speculate that the e dipping normal faults initiated with relatively low angles of dip due to differential drag generated by mantle flow following slab retreat and roll back beneath the apennine chain

fault zone architecture and deformation processes within evaporitic rocks in the upper crust 1 recently in the northern apennines geophysical data have identified the triassic evaporites te anhydrites and dolomites as the source region of the major extensional earthquakes of the area m 6 in order to characterize fault zone architecture and deformation processes within the te we have studied exhumed evaporite bearing normal faults within the upper crust the structure of large displacement 100 m normal faults is given by 1 a zoned fault core with a wider portion of fault parallel foliated ca sulphates ductile deformation overprinted by an inner fault core ifc of localized brittle deformation and 2 wide dolostones to absent ca sulphates damage zones of fault fracture patterns fault rock assemblage within the ifc is characterized by fault breccia gouge and cataclasites of different grain size most of the deformation within the ifc is localized along thin and fault parallel principal slip surfaces pss made of dolomite rich fine grained cataclasite sem analyses show an evolution from ca to st to gypsum rich mineralization due to episodic fluid flow events channeled along the fault zones during different stages of fault exhumation the development of the observed fault geometry can be explained by a mechanical fault evolution model where initial faulting occurs along broad and ductile shear zones within the anhydrites and causes fracturing within the dolostones progressive deformation within the fault core leads to the development of fault parallel dolomite rich cataclastic layers their reactivation coupled with transient fluid overpressures can produce embrittlement and localization of brittle deformation within the ifc

α β phase transition in quartz monitored using acoustic emissions summary it is usually suggested that thermal cracking in a quartz bearing rock results from the anomalously high volumetric expansion coefficients of quartz e g simmons cooper 1978 it has also been recognized that thermal expansion mismatch and mineral anisotropy contribute to thermal cracking in materials that consist of a polycrystalline aggregate composed of several anisotropic minerals even in the absence of a temperature gradient friedrich wong 1986 experiments investigating thermal cracking in rocks commonly involve imaging and quantitative stereology of crack populations induced in rocks treated to various peak temperatures e g friedrich johnson 1978 homand etienne troalan 1984 atkinson mcdonald meredith 1984 meredith atkinson 1985 here we report on acoustic emission experiments that monitor the process of thermal cracking as it occurs during heating supported by measurements of crack surface area pore fluid permeability porosity and surface conductivity carried out on rock samples treated to various peak temperatures the acoustic emission measurements show a strong peak of microcracking at the phase transition temperature for quartz 573 c superimposed upon a background of microcracking due to thermal expansion there is also a clear peak of microcracking at higher temperatures 800 c that can be attributed to oxidation dehydroxylation reactions of hornblende and chlorite measurements of fluid permeability pore surface area porosity and electrical conductivity made on samples that have been heat treated to various maximum temperatures show increases associated with a major episode of cracking in the 500 600 c temperature range indicating that the new cracks form a well interconnected network this has been confirmed by sem and optical microscopy these results have implications for the electrical conductivity of the continental crust providing a mechanism enabling the high pore fluid connectivity needed to explain zones of high electrical conductivity at depth providing that cracks opened in this way remain open at the high pressures existing at depth it should be recognized however that th se measurements are limited in their direct application since they were obtained under initially dry conditions at laboratory pressures

evolution of the elastic moduli of seismogenic triassic evaporites subjected to cyclic stressing seismic cycles lead to variations in rock physical properties quantifying these changes is of key importance in building reliable crustal deformation models here we report laboratory measurements of the uniaxial compressive strength ucs young s modulus and poisson s ratio both static es s and dynamic ed d of the seismogenic triassic evaporites of the northern apennines triassic evaporites are composed of dolostones anhydrites and gypsum gypsum was the weakest lithology with ucs values ranging from 10 to 26 mpa anhydrite exhibited intermediate values from 52 to 144 mpa and dolostones were the strongest with a maximum ucs of 228 mpa during uniaxial cyclic stressing experiments we observed complex variations in es and s with large increases are observed in the early cycles stage 1 followed by essentially constant values stage 2 before es decreases and s increases approaching failure stage 3 complementary microseismicity acoustic emission ae data show no significant ae during stage 1 then the stress needed to induce ae remained essentially constant stages 2 and 3 integration of mechanical data with microstructural observations suggests a first stage dominated by compaction and strengthening a second stage characterised by quasi elastic behaviour associated with the development of randomly oriented microfractures and a third stage of weakening due to the growth of macrofractures parallel to the direction of the load laboratory dynamic elastic moduli are on average in agreement with dynamic elastic moduli used in crustal modelling however static values of young s modulus are about 50 lower than dynamic ones and static values of poisson s ratio are about 40 higher with respect to dynamic values these observations suggest that the frequency effect on the difference between laboratory and crustal scale dynamic moduli values is rather small and that static values of modulus are more appropriate for crustal deformation modelling than seismically derived values

elastic modeling of the alto tiberina normal fault central italy geometry and lithological stratification influences on the local stress field abstract two dimensional elastic plane strain finite element models fems are generated to study the state of stress and failure induced by a low angle normal fault the alto tiberina fault of the northern apennines central italy it is beyond the scope of the present work to show that slip can occur on such a fault the numerical study was performed to evaluate the influences on the local stress field of the litho mechanical stratification of formations surrounding the fault and those induced by the geometry of the fault the performed models have shown the important role played by evaporites and basement formations of the umbria marche succession as seismogenetic layers the model results have also underlined that the flat ramp geometry of the fault induces high relative concentration of stresses in correspondence with the low angle east dipping synthetic normal faults observed today in shallow depth near the alto tiberina surface trace the stress regime predicted by the final model in which the behavior of the alto tiberina together with the antithetic normal fault of gubbio was simulated reconciles available geological and geophysical observable to a greater extent the numerical results can assist interpretation of the tectonic evolution of the region

physical and transport property variations within carbonate bearing fault zones insights from the monte maggio fault central italy the physical characterization of carbonate bearing normal faults is fundamental for resource development and seismic hazard here we report laboratory measurements of density porosity vp vs elastic moduli and permeability for a range of effective confining pressures 0 1 100 mpa conducted on samples representing different structural domains of a carbonate bearing fault we find a reduction in porosity from the fault breccia 11 7 total and 6 2 connected to the main fault plane 9 total and 3 5 connected with both domains showing higher porosity compared to the protolith 6 8 total and 1 1 connected with increasing confining pressure p wave velocity evolves from 4 5 km s to 5 9 km s in the fault breccia is constant at 5 9 km s approaching the fault plane and is low 4 9 km s in clay rich fault domains we find that while the fault breccia shows pressure sensitive behaviour a reduction in permeability from 2 10 16 m2 to 2 10 17 m2 the cemented cataclasite close to the fault plane is characterized by pressure independent behaviour permeability 4 10 17 m2 our results indicate that the deformation processes occurring within the different fault structural domains influence the physical and transport properties of the fault zone in situ vp profiles match well the laboratory measurements demonstrating that laboratory data are valuable for implications at larger scale combining the experimental values of elastic moduli and frictional properties it results that at shallow crustal levels m 1 earthquakes are less favoured in agreement with earthquake depth distribution during the l aquila 2009 seismic sequence that occurred on carbonates

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

the 2012 emilia seismic sequence northern italy imaging the thrust fault system by accurate aftershock location abstract starting from late may 2012 the emilia region northern italy was severely shaken by an intense seismic sequence originated from a m l 5 9 earthquake on may 20th at a hypocentral depth of 6 3 km with thrust type focal mechanism in the following days the seismic rate remained high counting 50 m l 2 0 earthquakes a day on average seismicity spreads along a 30 km east west elongated area in the po river alluvial plain in the nearby of the cities ferrara and modena nine days after the first shock another destructive thrust type earthquake m l 5 8 hit the area to the west causing further damage and fatalities aftershocks following this second destructive event extended along the same east westerly trend for further 20 km to the west thus illuminating an area of about 50 km in length on the whole after the first shock struck on may 20th a dense network of temporary seismic stations in addition to the permanent ones was deployed in the meizoseismal area leading to a sensible improvement of the earthquake monitoring capability there a combined dataset including three component seismic waveforms recorded by both permanent and temporary stations has been analyzed in order to obtain an appropriate 1 d velocity model for earthquake location in the study area here we describe the main seismological characteristics of this seismic sequence and relying on refined earthquakes location we make inferences on the geometry of the thrust system responsible for the two strongest shocks

rheological characterization of a sedimentary formation from a stress profile inversion summary detailed stress measurements have been carried out within a sedimentary sequence composed of a hard clay formation laying horizontally between two limestone units in the eastern paris basin france orientations of the minor and major horizontal principal stresses are found to be in good agreement with the direction of major shortening that prevailed during the last tectonic stage however their magnitudes exhibit an intriguing evolution with depth while the magnitude of the maximum horizontal stress slowly but regularly increases with depth the magnitude of the minimum horizontal one is larger in the hard clay formation than in the surrounding limestone units contrary to expectation from simple elastic considerations an analytical calculation demonstrates that the genesis of the current stress state may be reproduced by taking into account horizontal strains in two different directions and simulating erosion of part of the overburden with a viscoelastic model for the hard clay and an elastic behaviour for the limestone however the elastic constants that are derived for the limestone in order to fit the measured stress field correspond to a material that is more deformable and has a lower poisson s ratio than predicted by laboratory tests this discrepancy may be explained by a slow long term deformation process in the limestone possibly associated with pressure solution

stress strength relationship in the lithosphere during continental collision lithospheric strength profiles generated for a shortening continental lithosphere generally predict excessively high differential stresses in the sub moho continental mantle this seems inconsistent with the relative scarcity of earthquakes at this depth this inconsistency was put forward as evidence for weak mantle rheology however this argument implicitly assumes that strength envelopes are valid in actively deforming regions we test this assumption on two end member model lithospheres having identical upper crustal rheologies but with 1 a weak lower crust and strong mantle and 2 a strong lower crust and weak mantle for this purpose we compare one dimensional 1 d with 2 d visco elastoplastic numerical models of continental shortening the 2 d models show that strongly heterogeneous deformation typically follows initially homogeneous deformation lithospheric scale buckle folds and shear zones result in strain rate variations of as much as three orders of magnitude differential stresses in the upper crust are close to yield as predicted by 1 d models stresses in deeper lithospheric regions however are significantly smaller than in 1 d models especially in actively deforming regions systematic numerical simulations as a function of temperature and deformation rate reveal that 1 d models are reliable in hot and or slowly deforming lithospheres only the relative scarcity of earthquakes at mantle levels should thus be interpreted as an intrinsic consequence of strong lithospheric deformation rather than as evidence for a weak upper mantle

investigating fault reactivation during multiple tectonic inversions through mechanical and numerical modeling an application to the central northern apennines of italy abstract within inversion tectonic contexts the reactivation of pre existing discontinuities depends upon many structural stratigraphic and mechanical factors among these a fundamental aspect is represented by the orientation and attitude of pre existing discontinuities with respect to the new stress field the aim of this work is to evaluate the stress regimes and the mechanical conditions that controlled the reactivation of segmented pre thrusting normal faults in the central northern apennines of italy these faults were involved both in positive and negative inversion tectonic events during tertiary quaternary times mechanical slip tendency analysis and numerical using coulomb 3 3 software models allowed us to reconstruct a 3d stress field for both inversion events and to evaluate the effect of many parameters orientation of faults fault dip angle and mechanical parameters on fault reactivation our results highlighted that the orientation of pre existing faults with respect to the stress axes represents the main factor controlling inversion tectonic phenomena where other mechanical and geometric variables exert a subordinate role the models well reproduce the neogene quaternary deformation history reconstructed from detailed geological and structural analyses for the central northern apennines of italy and could be applied to other regions that have experienced inversion tectonic processes

diagenetic compaction experiments on simulated anhydrite fault gouge under static conditions faults that crosscut subsurface co2 storage systems offer potential leakage pathways especially if fault reactivation and dilation occur after reactivation however newly formed fault gouge is expected to gradually compact and seal as a function of time to estimate the time scale on which this occurs the processes that control compaction must be understood we performed uniaxial compaction experiments on simulated anhydrite fault gouge to investigate the deformation mechanisms that operate under postslip conditions in faulted anhydrite caprocks this involved constant stress 5 12 mpa and stress stepping experiments 5 7 5 10 mpa performed at 80 c under dry and wet conditions on fault gouge samples prepared from crushed natural anhydrite sieved into different grain size fractions in the range 20 500 m dry samples showed little to no compaction creep whereas wet samples i e flooded with presaturated caso4 solution showed rapid compaction our mechanical data and microstructural observations on wet samples suggest that for fine grain sizes 50 m and low stresses gouge compaction is controlled by diffusion controlled pressure solution with increasing grain size and stress fluid assisted subcritical microcracking becomes dominant pressurizing solution flooded samples with co2 15 mpa led to no significant effect on compaction rates in fine grained material but it decreased compaction rates in coarse samples since fine grain sizes are expected in reactivated faults we infer that pressure solution will dominate in anhydrite cap rocks with extrapolation of our lab data to reservoir conditions suggesting sealing time scales of a few decades

a mechanical model for complex fault patterns induced by evaporite dehydration and cyclic changes in fluid pressure complex fault patterns i e faults which exhibit a diverse range of strikes may develop under conditions where a regional tectonic stress field is weak or absent e g polygonal faults the present paper considers a complex system of synsedimentary faults in the umbria marche apennines italy geometrically similar to polygonal fault systems developed during an early jurassic extensional episode this particular fault pattern differs from many extensional fault systems as it lacks structures that are developed with a classical bimodal conjugate andersonian geometry a conceptual and mechanical model is proposed to explain the development and evolution of the complex fault pattern in which it is proposed that faulting is primarily controlled by the development of volumetric instability in triassic evaporites due to dehydration processes anhydritisation during burial the lithological architecture of the triassic evaporites comprising interbedded ca sulphate layers and dolostones played a fundamental role in controlling the deformation processes cyclic fluid overpressure build up release and the coexistence of brittle and brittle ductile flow processes led to horizontal isotropic and non plane extensional strain fields within the dehydrating rock mass which favoured the development of complex deformation patterns the mechanical model proposed shows that the studied fault pattern developed under a stress field consistent with almost homogeneous stress intensities within the horizontal plane the data presented show that local strain fields and transient fluid pressure conditions have been dominant over weak regional extensional tectonics the findings are relevant to many other areas where complex faulting patterns including polygonal faults occur in association with evaporite or clay rich sedimentary sequences

on fine sediment transport by long waves in the swash zone of a plane beach we calculate suspended sediment transport erosion and deposition under reflected long waves on a plane beach our method employs the shallow water equations and is based on the calculation of the concentration field in lagrangian coordinates this allows results to be obtained readily throughout the whole domain including the often troublesome shoreline region these results suggest that the tendency of wave dominated muddy shores to export sediment and erode over long time scales is not due to wave forcing at infragravity frequencies since the sediment transport under such waves is localized close to the shoreline and is principally directed shorewards they also provide easily reproduced test cases against which to validate the numerical methods used in more detailed studies of coastal sediment transport and morphodynamics

the evolution of elastic moduli with increasing crack damage during cyclic stressing of a basalt from mt etna volcano article i nfo volcanic edifices such as mt etna italy are commonly subject to repeated cycles of stress over time due to the combination of magma emplacement from deep reservoirs to shallow depths and superimposed tectonic stresses such repeated stress cycles lead to anisotropic deformation and an increase in the level of crack damage within the rocks of the edifice and hence changes to their elastic moduli which are a key parameter for reliable modelling of deformation sources we therefore report results of changes in elastic moduli measured during increasing amplitude cyclic stressing experiments on dry and water saturated samples of etna basalt in all experiments the young s modulus decreased by approximately 30 over the total sequence of loading cycles and the poisson s ratio increased by a factor of approximately 3 0 5 microseismicity in terms of acoustic emission ae output was also recorded throughout each experiment our results demonstrate that ae output only re commences during any loading cycle when the level of stress where ae ceased during the unloading portion of the previous cycle is exceeded a manifestation of the kaiser stress memory effect in cycles where no ae output was generated we also observed no change in elastic moduli this result holds for both mechanical and thermal stressing our results are interpreted in relation to measurements of volcano tectonic seismicity and deformation at mt etna volcano

structural response and rock bolting of a rock mass abstract stability of a discontinuous rock mass represented as a blocky rock mass is examined and defined in terms of stress redistribution and formation of hinges the anisotropic compliance of the rock mass controls the initial stress distribution and as small deformational rotations occur finite deformations with the anisotropic compliances control the stress redistributions these stress redistributions induce and intensify stress gradients which in turn encourage further rotations and stress redistributions mechanistic deformations such as slip and rotation cause the blocky mass to act as a structure with the formation of hinges these hinges localise the resultant force at a hinge the force can change its magnitude and line of action but it cannot change its point of application stability of the blocky rock mass is considered in terms of redundancy and as each hinge is formed the redundancy is reduced beaming and arching as a means of load and stress redistribution are examined control of beaming and arching by using rock bolts is considered in relation to stress redistribution and inhibiting the formation of hinges

experimental investigation of the mechanical properties of synthetic magnesium sulfate hydrates implications for the strength of hydrated deposits on mars 1 we have carried out uniaxial compression experiments to determine the mechanical properties of three crystalline magnesium sulfate hydrates that may be present in the near surface environment of mars our synthetic samples of kieserite mgso4 h 2o epsomite mgso4 7 h2o and meridianiite mgso4 11h2o have mean values of unconfined compressive strength of 6 3 0 7 12 9 1 8 and 30 1 4 5 mpa respectively young s modulus of 0 8 0 1 2 9 0 4 and 5 9 0 8 gpa respectively and mean porosity values of 47 8 0 5 11 1 0 6 and 2 9 0 2 respectively although our tests cannot quantify a systematic relationship between hydration state and mechanical properties the different porosities produced by consistent sample preparation methods suggest that the addition of non cation coordinated water molecules likely reduces the strength of individual sulfate hydrate phases however the bulk mechanical properties of our synthetic specimens are instead controlled predominantly by the sample porosity generally the strength increases as the porosity decreases we expect the mechanical properties of sulfate hydrate deposits on mars to be governed by the bulk porosity rather than the strength of the pure solid phase we have performed cyclic stressing tests replicating possible periodic depositional and erosional periods on mars resulting from obliquity changes a gradual compaction and reduction in sample porosity rather than an increase in crack damage is observed with each loading cycle suggesting that the evolution of mechanical properties will depend on local factors such as bulk density in addition to the overall stress history

effects of geological complexities on coseismic displacement hints from 2d numerical modelling by means of a 2d finite element procedure we tested how heterogeneities at the scale of seismogenic fault affect the displacement we defined one or more slip distributions for two typical normal faulting earthquakes in the central apennines computed the displacement occurred within different structures including lateral heterogeneities and compared the different displacement profiles to isolate the effect of the crustal structure to understand at what magnitude the heterogeneities affect the observation significantly we compared the predicted coseismic displacement with gps and dinsar data for the colfiorito 1997 earthquake we find that heterogeneities significantly affect the observable horizontal coseismic displacement for the larger magnitudes whereas for smaller quakes they affect horizontal displacement close to the fault trace only

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

elastic moduli evolution and accompanying stress changes with increasing crack damage implications for stress changes around fault zones and volcanoes during deformation summary the elastic moduli of rock in areas susceptible to crack damage such as within fault zones or volcanic edifices can be subject to large modifications knowledge of how elastic moduli may vary in such situations is important for both the reliable modelling of volcano deformation and stability and for linear and non linear elastic crack models for earthquake rupture furthermore it has previously been shown that changes in elastic moduli can induce changes in the stress field surrounding faults here we report both uniaxial experimental measurements of changes in elastic moduli during increasing amplitude cyclic stressing experiments on a range of different rock types basalts sandstones and granite and the results of modelled stress modifications the trend in elastic moduli evolution with increasing damage was remarkably similar for each rock type with the exception of essentially crack free intrusive basalt that exhibited very minor changes in general young s modulus decreased by between 11 and 32 per cent and poisson s ratio increased by between 72 and 600 per cent over the total sequence of loading cycles these changes are attributed to an increasing level of anisotropic crack damage within the samples our results also show that acoustic emission ae output during any loading cycle only commenced when new crack damage was generated this corresponded to the level of stress where ae ceased during the unloading portion of the previous cycle using the multilayer elastic model of faulkner et al we demonstrate that the damage induced changes in elastic moduli also result in significant decreases in differential stress increases in mean stress and rotation of the applied greatest principal stress relative to the orientation of the mechanical layering the similar trend in the evolution of the elastic moduli of all the rocks tested suggests that stress modification in the damage zone of faults might take the same form regardless of the lithology through which the fault runs these observations are discussed in terms of their applicability to both fault zones and deformation at volcanoes

tectonic implications of late paleozoic metamorphism in southeastern new england a map showing the distribution of pennsylvanian permian metamorphism in southern new england shows that the center of metamorphism is located substantially south and east of middle devonian acadian high grade metamorphism this suggests that the permian disturbance in southern new england is not related to delayed post acadian uplift the map is based on existing data within the pennsylvania basins and on a combination of published microstructures and apparent mineral ages in the surrounding rocks the distribution of metamorphism is however apparently related to major tectonic boundaries that were active during the late paleozoic and suggests that it may be the result of terrane accretion during the late paleozoic

insights on the seismogenic layer thickness from the upper crust structure of the umbria marche apennines central italy 1 we reconstruct the subsurface geology in a region of the northern apennines central italy where a protracted extensional sequence occurred in 1997 1998 with maximum magnitude m 6 0 our study is mainly based on the interpretation of three reprocessed seismic reflection profiles crossing the epicentral area which constrain the subsurface geometry to a depth of about 12 km where most of the shallow seismicity occurs comparing the subsurface setting with accurately determined earthquake locations we find that the seismicity is located entirely within the sedimentary cover and does not penetrate the underlying basement this is explained by considering that the sedimentary cover is rather thick and composed of relatively strong lithologies platform carbonates and evaporites while the upper part of the basement consists of weak phyllites and siliciclastic rocks this weak horizon is also evidenced by the low vp values measured in deep wells of the region its effect is to decouple the sedimentary cover from the crystalline basement where only microseismicity occurs our study indicates that local structure and stratigraphy can significantly influence the distribution of seismicity within the upper crust particularly in complex geological environments such as thrust and fold belts

mesozoic syn and postrifting evolution of the central apennines italy the role of triassic evaporites abstractjurassic cretaceous syn and postrift successions from the central apennines were backstripped to gain information on the mesozoic evolution of the passive margin of the adriatic plate early jurassic rifting led to the development of a horst and graben paleogeography the latium abruzzi carbonate platform and the sabina umbria marche pelagic basin subsidence curves were built for both carbonate platform and pelagic basin domains from original and literature stratigraphic data the paleodepositional depths of the deepwater sediments were reconstructed from field geology data including new paleontological data it is proposed that after the deposition of lower hettangian shallow water carbonates an abrupt increase in paleowater depth to 600 1000 m occurred during the late hettangian sinemurian synrift stage the postrift stage was characterized by basin filling with decreasing paleowater depths during the jurassic and by a new deepening during the cretaceous our backstripping curves show