crystallographic fabrics of omphacite rutile and quartz in vendee eclogites armorican massif france consequences for deformation mechanisms and regimes abstract this study aims at further understanding of the mechanisms how lattice preferred orientations lpo develop during deformation in the main eclogite minerals microstructures and textures of deformed eclogites from the les essarts complex western france were investigated using optical microscopy and electron backscatter diffraction ebsd in the scanning electron microscope microfabric analyses of eclogite facies minerals are used to identify their deformation mechanisms which define the rheology at high pressure metamorphic conditions mechanisms of intracrystalline deformation by dislocation movement dislocation creep result usually in a non linear flow law typically power law while diffusive processes diffusion creep correspond to linear flow laws general microstructural observations may suggest intracrystalline deformation dislocation creep of omphacite the omphacite lpo vary between s and l type and correlate with oblate or prolate grain shape fabrics respectively until now these lpo types have not been understood by plasticity models based on dislocation glide on the known slip systems in clinopyroxene an alternative interpretation is given in terms of anisotropic growth and dissolution with grain boundary diffusion as the rate controlling process there are further indications suggesting diffusion creep with concomitant anisotropic growth and dissolution as a main deformation mechanism in omphacite in omphacite around a hollow garnet crystallographic and shape fabrics align with the c 001 axes parallel to the grain elongations defining the mineral lineation which rotates locally with the inferred flow direction in this part the grain sizes of omphacite and rutile are larger than in the surrounding matrix the geometry of both the shape and crystallographic fabrics is interpreted to represent the local stress regime directions and ratios of the principal stresses the lpo of rutile duplicate the lpo of omphacite and a similar distinction between s and l type was used rutile deformation mechanisms probably involve dislocation creep as well as diffusion creep quartz mainly occurs as an interstitial phase with weak lpo patterns interpreted as random no representative obliquity of the lpo in omphacite nor rutile with respect to foliation and lineation was observed to be used as potential shear sense criteria however the rutile lpo was slightly rotated relative to the omphacite lpo consistently in most samples the results suggest that diffusion processes are strongly involved in the deformation of eclogites a linear flow law should be taken into account in tectonic models where eclogites are incorporated

statistical analysis and clustering features of the phlegraean fields earthquake sequence may 1983 may 1984 abstract the seismic activity at the phlegraean fields volcanic area southern italy during the period may 1983 may 1984 5 301 selected events has been analyzed from a statistical point of view the analysis of the time series associated to the microearthquakes shows a high degree of interdependence among the events the main feature being the occurrence of dense swarms the generalized poisson process provides a good fit for the sequence the clustering of the events has not substantially changed during the analyzed period while the mean rate of occurrence of the swarms has generally increased the distribution of the magnitudes within the swarms shows pronounced maxima of energy around the center of the subsequences in agreement with theoretical models of fractures in highly heterogeneous media

late quaternary slip rates on the acireale piedimonte normal faults and tectonic origin of mt etna sicily abstract mt etna is located along the east coast of sicily near the boundary between the continental crust of the hyblean plateau and the mesozoic oceanic crust of the ionian basin the main active faults near mt etna cut the base of its eastern flank forming a 30 km long system of nne and nnw trending ene chelon fault segments the acireale piedimonte system showing dip slip and oblique right lateral motion most segments are associated with shallow depth seismicity and all have late pleistocene to holocene vertical slip rates ranging between 1 and 2 mm yr typical of major active normal faults worldwide eruptive fissures arranged in nne to ne trending zones cut the highest slopes of the volcano on the footwall of the normal fault system structural analysis suggests that current motions along both the active faults and eruptive fissures are kinematically compatible and simply linked with ongoing wnw ese directed regional extension such extension characterizes at a greater scale the active tectonics of southern italy where all large shallow historical earthquakes have remained confined within a narrow normal fault belt or rift zone stretching from the northern calabrian arc to southeastern sicily the southernmost west dipping faults of that rift zone in calabria aspromonte cut across the calabro peloritan thrust belt to join the mostly east dipping acireale piedimonte faults along the western boundary of ionian oceanic lithosphere which continues southwards as the malta escarpment we thus relate magmatism at etna to dilational strain on the footwall of an east facing crustal scale normal fault at the bend where the siculo calabrian rift zone veers 60 eastwards as it begins to cross the calabrian arc leaving the east facing margin of the ionian sea to catch up with the west facing margin of the tyrrhenian sea farther north

very shallow earthquakes and brittle deformation in active volcanic areas the eatnean region as an example abstract some aspects of the stress field acting in active volcanic areas were investigated by studying the relationship between surficial seismicity h 1 2 km and the brittle deformation pattern of the etna volcano the magmatic composition and structural character of mt etna are described together with its geodynamic regional context after a discussion of the problem of the state of stress in active volcanoes and a definition of very shallow seismicity the high level of surficial seismicity the morphology of the sedimentary basement and the kinematic behaviour of the faults suggest that the eastern flank of mt etna is a shallow seismotectonic domain structurally decoupled from the rest of the volcanic body this flank shows a tendency to slide in an eastern direction and is bound to the north by a left lateral oblique slip normal fault trending e w and in the south by an arcuate fault system with right lateral features right lateral oblique slip normal faults

a fractal approach to the temporal distribution of microseismicity at the low eastern flank of mt etna during 1989 1994 abstract seismicity affecting the low eastern flank of mt etna shows clustering in time we analysed a catalog of microearthquakes recorded by the four stations of the osservatorio sismologico di protezione civile di acireale during the period 1989 1994 in general a strong deviation from periodic and random distribution was found the temporal clustering is scale invariant and a fractal dimension can be derived to characterize it fractal dimensions seem to be correlated to the beginning of two major eruptions

fault parameters in the messina strait southern italy and relations with the seismogenic source abstract the messina strait is characterized by strong deformations in pliocene and pleistocene times but considering the historical seismicity significant uncertainity exists as to whether any of the surface fault systems reflects the location geometry and mechanisms of the seismogenic source based on field data and structural analyses the parameters length l displacement d age of activity t minimum slip rate min and total geological moment m g have been derived for all the faults exposed on the sicilian and calabrian sides of the strait the analysis of these parameters shows that the highest rates of activity pertain to interconnected faults of different orientation and length which bound the uplifted crystalline basement relative to the pliocene pleistocene foundered zones of the calabrian side the comparison between the fault slip rates and the regional uplift rates shows that each single fault contributes for a limited fraction only to the whole deformation release in the area the contribution of the whole fault population expressed as cumulative m g release is still one order of magnitude less than the seismic moment release taking into account the underestimation of the geological parameters the lack of information on the offshore faults and the role of anelastic deformation by aseismic creep the data suggest that the long term recurrence of seismic breaks is partitioned at the surface in a complex array of interconnected faults some of these faults might represent basement inherited structures repeatedly and preferentially reactivated over geological time

statistical physics seismogenesis and seismic hazard the scaling properties of earthquake populations show remarkable similarities to those observed at or near the critical point of other composite systems in statistical physics this has led to the development of a variety of different physical models of seismogenesis as a critical phenomenon involving locally nonlinear dynamics with simplified rheologies exhibiting instability or avalanche type behavior in a material composed of a large number of discrete elements in particular it has been suggested that earthquakes are an example of a self organized critical phenomenon analogous to a sandpile that spontaneously evolves to a critical angle of repose in response to the steady supply of new grains at the summit in this stationary state of marginal stability the distribution of avalanche energies is a power law equivalent to the gutenberg richter frequency magnitude law and the behavior is relatively insensitive to the details of the dynamics here we review the results of some of the composite physical models that have been developed to simulate seismogenesis on different scales during 1 dynamic slip on a preexisting fault 2 fault growth and 3 fault nucleation the individual physical models share some generic features such as a dynamic energy flux applied by tectonic loading at a constant strain rate strong local interactions and fluctuations generated either dynamically or by fixed material heterogeneity but they differ significantly in the details of the assumed dynamics and in the methods of numerical solution however all exhibit critical or near critical behavior with behavior quantitatively consistent with many of the observed fractal or multifractal scaling laws of brittle faulting and earthquakes including the gutenberg richter law some of the results are sensitive to the details of the dynamics and hence are not strict examples of self organized criticality nevertheless the results of these different physical models share some generic statistical properties similar to the universal behavior seen in a wide variety of critical phenomena with significant implications for practical problems in probabilistic seismic hazard evaluation in particular the notion of self organized criticality or near criticality gives a scientific rationale for the a priori assumption of stationarity used as a first step in the prediction of the future level of hazard the gutenberg richter law a power law in energy or seismic moment is found to apply only within a finite scale range both in model and natural seismicity accordingly the frequency magnitude distribution can be generalized to a gamma distribution in energy or seismic moment a power law with an exponential tail this allows extrapolations of the frequency magnitude distribution and the maximum credible magnitude to be constrained by observed seismic or tectonic moment release rates the answers to other questions raised are less clear for example the effect of the a priori assumption of a poisson process in a system with strong local interactions and the impact of zoning a potentially multifractal distribution of epicentres with smooth polygons the results of some models show premonitory patterns of seismicity which could in principle be used as mainshock precursors however there remains no consensus on both theoretical and practical grounds on the possibility or otherwise of reliable intermediate term earthquake prediction

omphacite textures in eclogites of the tauern window implications for the exhumation of the eclogite zone eastern alps abstract we discuss the relationship of omphacite lattice preferred orientation lpo patterns in eclogite and kinematic indicators in the matrix surrounding the eclogite during the very rapid exhumation of the deeply buried eclogite zone in the tauern window of the eastern alps lpo patterns are presented from profiles parallel to the eclogite stretching lineation across the eclogite zone the omphacite textures show symmetric patterns across the entire eclogite zone only in few cases slight asymmetries are observed the patterns are characterized by an alignment of 110 with the foliation and a maximum of 001 close to the lineation and are indicative of deformation by intracrystalline glide on the 010 001 and 110 001 slip systems the patterns have close resemblance to s type lpo patterns and probably developed during the burial and accretion of the eclogites we argue that the lpo patterns are not related to deformation associated with the very rapid exhumation of the eclogite zone we conclude that exhumation related deformation was concentrated in the metasedimentary rocks that surround the eclogites allowing the eclogites to preserve their burial lpo signature during the exhumation process kinematic indicators show top n thrusting at the base of the eclogite zone and sinistral strike slip faulting at the top most of the kinematic indicators record blueschist and greenschist facies metamorphic conditions however because of the very rapid exhumation of the eclogite zone with rates exceeding 36 km myr 1 the kinematic indicators are interpreted to reflect the entire exhumation process from eclogite facies conditions we discuss a model according to which the eclogite zone was exhumed in an oblique extrusion wedge

earthquake activity during the 1983 etna eruption seismic stations with automatic p picking and satellite retransmission were set up on mount etna following the eruption started on march 1983 positions of the stations were chosen in order to complement the permanent telemetered network of catania university

structural development and petrofabrics of eclogite facies shear zones bergen arcs western norway implications for deep crustal deformational processes caledonian eclogite facies shear zones developed from grenvillian garnet granulite facies anorthosites and gabbros in the bergen arcs of western norway allow direct investigation of the relations between macroscopic structures and crystallographic preferred orientation cpo in lower continental crust field relations on the island of holsnoy show that the eclogites formed locally from granulite facies rocks by progressive development of 1 eclogite adjacent to fractures 2 eclogite in discrete shear zones 2 m thick 3 eclogite breccia consisting of 80 well foliated eclogite that wraps around rotated granulite blocks and 4 anastomosing subparallel eclogite facies shear zones 30 100 m thick continuous over distances 1 km within the granulite terrane these shear zones deformed under eclogite facies conditions at an estimated temperature of 670 50 c and a minimum pressure of 1460 mpa which corresponds to depths of 55 km in the continental crust detailed investigation of the major shear zones shows the development of a strong foliation defined by the shape preferred orientation of omphacite and by alternating segregations of omphacite garnet rich and kyanite zoisite rich layers a consistent lineation throughout the shear zones is defined by elongate aggregates of garnet and omphacite the cpo of omphacite determined from five axis universal stage measurements shows a strong b axis maximum normal to foliation and a c axis girdle within the foliation plane with weak maxima parallel to the lineation direction these patterns are consistent with deformation of omphacite by slip parallel to 001 and suggest glide along 010 the lineation and cpo data reveal a consistent sense of shear zone movement although the displacement was small localized faulting of high grade rocks accompanied by fluid infiltration can be an important mode of failure in the lower continental crust field relations show that granulite facies rocks can exist in a metastable state under eclogite facies conditions and imply that the lower crust can host differing metamorphic facies at the same depth deformation of granulite and partial conversion to eclogite such as is exposed on holsnoy island may be an orogenic scale process in the lowermost crust of collisional orogens

identifying seismicity patterns leading flank eruptions at mt etna volcano during 1981 1996 seismicity time properties of the etna volcano italy are investigated through a systematic pattern recognition analysis mean hypothesis testing mht has been applied to a long time database of instrumental data recorded from 1981 to 1996 to identify relevant correlation among seismic patterns main seismogenic volumes and the eight flank eruptions occured in the same period time evolution of the test statistic t ratio calculated on a temporal window starting 75 days prior to a volcanic eruption and extending 25 days after reveals that there is a pattern of seismic activity prior to the eruptions that can be used as a diagnostic tool as well as a physical modeling support in eruption forecasting

changing in crust mechanical behaviour due to raising magma a fracturing model of se flank of mt etna sicily abstract associated with the remarkable flank eruption which started in late october 2002 a series of earthquakes occurred on the lower eastern flank of mt etna the m d 4 4 bongiardo s venerina earthquake at 10 02 am gmt 29th october affected a large nnw sse area severely damaging nearby villages the faulting model proposed in this paper seeks to justify the two causes of the fracturing process as well as its spatiotemporal development for this purpose a preliminary analysis of the morphotectonic framework and the detected fractures linked to october 2002 earthquakes has been carried out we will therefore consider the seismic activity which affected the volcano in 2001 and 2002 additionally we will review previous scientific studies of seismic tomography and macroseismic data in particular the fracturing mechanisms appear to be linked to the volcanic area uplift as a consequence of rising magma the consequent change in the rheology beneath this sector of the volcano explains the differing reaction of the crust at different levels

early detection of eruptive dykes revealed by normalized difference vegetation index ndvi on mt etna and mt nyiragongo abstract flank fissure eruptions involve lateral injection and propagation of magma in a volcanic edifice along pre existing fractures in the direction of the rift zones where magma intrusion and lava flow production are concentrated over time thus the identification and mapping of active fractures and faults is a fundamental aspect of studies of active volcanic systems however gradual dyke wedge emplacement at depth in well fractured zones on volcano flanks and in volcanic rift zones does not necessarily trigger large amplitude deformation signals susceptible to be recorded months or even years before the actual eruption here we show that active and potentially eruptive areas can be detected up to 2 yrs before the arrival to the surface of the final eruptive dyke and venting of lava flows by processing satellite images applying a normalized difference vegetation index ndvi algorithm a posteriori analysis of satellite images indeed reveals that the surficial effects of dyke wedge injection and ascent on plant growth were apparent for mt etna from 2000 to 2002 and for mt nyiragongo in 2001 thus months to years before they erupted

long term record of co2 degassing along mt etna s flanks and its relationship with magma dynamics and eastern flank instability a record of soil co2 flux data on the lower flanks of mt etna measured from 1989 to 2008 is discussed in the framework of multidisciplinary observations including seismicity ground deformations and flank instability a huge increase in soil co2 fluxes appears to be related to the dynamics of magma ascent in the upper portions of the volcano 0 3 km and the intrusion of dykes along the southern rift as mainly observed before the 1991 93 eruption even after the 1991 93 eruption the recharge of the shallow central reservoir was accompanied by a long term increase in soil co2 degassing mainly in the southwestern area the 2001 eruption marked dramatic changes in the areal distribution of seismicity the deformation pattern and the soil co2 degassing indeed while the soil co2 degassing showed background values in the southwestern area it progressively increased in the eastern sector and along the pernicana fault this has been related to the marked sliding of the eastern flank since the 2002 03 eruption and the associated seismicity this study provides evidence that the extent of soil co2 degassing on the lower flanks of mt etna is controlled by 1 the volume of involved magma 2 the intrusion of dykes in the upper parts of the volcano and 3 fault movement and seismicity this implies that different degassing structures must be monitored simultaneously when attempting to understand the behavior of the volcano as a whole

coeval high pressure metamorphism thrusting strike slip and extensional shearing in the tauern window eastern alps 1 recent findings for a young 31 5 0 7 ma age of high pressure metamorphism at 90 km depths in the eclogite zone of the tauern window eastern alps prompt the question about the timing of the structural development of the tauern window and its relation to high pressure metamorphism we show that all major structures in the tauern window resulting from strong n s lithospheric shortening and simultaneous minor e w extension began developing coevally with high pressure metamorphism in the eclogite zone large scale strike slip shear zones started to form at 32 30 ma and facilitated the spatial accommodation of simultaneous shortening and extension at least some of the strike slip and extensional shear zones operated into the middle miocene either continuously or intermittently with pronounced activity at 21 15 ma the considerable exhumation of the eclogite zone from 90 km depths into the middle crust and the tectonic development of its framework occurred within only 1 2 ma after eclogitization this is evidenced by almost identical ages for eclogite facies metamorphism and for the development of the major structures that bound the eclogite zone under blueschist and greenschist facies metamorphic conditions we discuss a tectonic model in which considerable transpressional shortening and thickening took place in the present central southern part of the tauern window we propose that the tauern window nucleated here and that most of the regional deformation at 32 30 ma is today found at the periphery of the window and in the adjacent austroalpine units afterward transpression continued the window grew to the e w and n and deformation progressed to those parts of the window ductile deformation in the present day surface level ceased at 15 ma

time clustering properties of seismicity in the etna region between 1874 and 1913 time properties of seismic activity of the etna volcano italy from 1874 to 1913 are investigated by fractal dimension analysis period selection was due to the interesting volcanic and seismic activity which had occurred within this time interval a catalogue was adopted revised by the reexamination of historical sources and with the addition of new material time evolution of the temporal fractal dimension dt calculated on a 40 seismic events moving window revealed the following correlations with the eruptive processes long term fractal dimension variations are due to the magma rise from the depth mid term variations are closely related to stress conditions at the volcano edifice and short term variations are induced by the onset of eruption the spatial localisation of data allowed interpretation of seismic activity in relation to the main structural systems outcropping on the volcano edifice and in the surrounding areas

plate boundary kinematics in the alps motion in the arosa suture zone the arosa zone forms a melange complex along the penninic austroalpine boundary and belongs to the main alpine suture zone accretion and plate collision occurred during cretaceous and lower tertiary time a mixture of ophiolitic rocks and pelagic sediments is imbricated with flysch and blocks of austroalpine continental derivation we present a description of deformation structures an analysis of strain and a kinematic interpretation based on structural work deformation histories of imbricates show a translation path that was west directed between ca 110 and 50 ma and north directed thereafter the kinematics of the arosa zone agrees with the recently deduced displacement history of the austroalpine units in the eastern alps during the cretaceous orogeny this calls for a predominantly top to the west imbrication of austroalpine and penninic units and is in contradiction to what is inferred in most models of the eastern alps a direct relation between the deformation along the austroalpine margin and relative plate motion existed

formation of the haida 1998 oceanic eddy 1 two large mesoscale anticyclonic eddies formed along the west coast of the queen charlotte islands of western canada in early 1998 altimetry measurements from topex poseidon and ers 2 satellites suggest that these eddies first appeared near cape st james at the southern tip of the islands the eddies merged in june to form haida 1998 the highest eddy ever observed in the region currents near cape st james in winter follow complicated patterns attributed to tidal rectification and pressure driven outflow from hecate strait the adjustment of these flows to the bathymetric features likely contributes to the formation of haida eddies eddies that first appear farther north along the west coast of the queen charlotte islands are set up by other processes such as baroclinic instability

omphacite fabric variation in the cabo ortegal eclogite nw spain relationships with strain symmetry during high pressure deformation petrostructural study of cabo ortegal eclogite tectonites provides an insight into the relationships between omphacite lattice preferred orientation and the fundamental deformation parameters in particular strain symmetry microstructural evidence is consistent with a tectonic origin of eclogite fabrics by coeval pyroxene plastic deformation and recrystallization under eclogite facies metamorphic conditions omphacite shape fabrics and garnet spatial distributions are anisotropic and representative of the fields of either apparent flattening or constriction omphacite lattice preferred orientations are dominated by 010 axis maxima normal to the foliation s type or flattening fabrics by 001 axis maxima parallel to the lineation l type or constriction or correspond to other fabric patterns described in the literature omphacite crystallographic fabrics are consistently asymmetric with respect to the structural framework defined by foliation and lineation this suggests that non coaxial deformation components either simple or general shear accompanied eclogite fabric development in addition to any flattening or constriction strain paths and permit shear sense determination these petrostructural features were acquired in the course of eo hercynian ductile deformation probably during deep subduction under 1 5 1 7 gpa confining pressure temperatures above 600 700 c low differential stress 15 20 mpa and slow strain rate 10 12 10 15s 1

origin and mechanical significance of honeycomb garnet in high pressure metasedimentary rocks from the tauern window eastern alps high pressure schists 2 2 5 gpa from the eclogite zone in the tauern window contain honeycomb garnet in which fine webs of garnet surround strain free quartz carbonate grains high resolution x ray computed tomography shows that the garnet webs form a cellular structure that coats all surfaces of the inclusions electron backscatter diffraction analysis shows that the garnet cells are crystallographically continuous with more massive garnet regions and that the quartz carbonate inclusions have random orientations in contrast matrix quartz exhibits a prominent crystallographic preferred orientation cpo high resolution transmission electron microscopy shows few dislocations in either the garnet or the inclusion quartz most honeycomb garnet is chemically homogeneous but some displays asymmetric core rim zoning taken together these observations are most consistent with formation of the garnet sheets via precipitation from a wetting fluid along quartz quartz grain boundaries or possibly via wholesale precipitation of garnet quartz carbonate from a fluid in either case a silicate rich aqueous fluid must have been present the likelihood that a fully wetting fluid existed at high pressure has important implications for rheology during subduction of metasedimentary rocks strain may be accommodated by grain rotation and sliding in an aqueous silicate slurry rather than via dislocation creep mechanisms at high pressures the absence of a cpo in early quartz may thus point to involvement of a pervasive grain boundary fluid rather than requiring low differential stresses during subduction

importance of gravitational spreading in the tectonic and volcanic evolution of mount etna the interaction between gravity and thermal effects largely determines the structural and magmatic evolution of volcanic constructs at scales spanning several orders of magnitude from small cones to the oceanic crust1 3 although gravitational spreading is a direct consequence of this interaction and a fundamental process in volcano growth it is rarely recognized as such here we describe a striking example of this process at etna volcano in italy the volcano and its clay rich substratum are slowly spreading towards the east and south driven by gravity spreading produces extensional structures in the summit region and contpressional structures at the base of the volcano eastward movement of the volcanic edifice over a stationary magma supply may be the cause of an apparent westward migration of volcanic activity as gravitational spreading seems to control the location and magnitude of shallow seismicity and flank eruptions an appreciation of its effects could become an essential element of future volcanic hazard evaluation our model proposed here for etna may also be relevant to a reinterpretation of the geological history of a number of other volcanoes

roots of etna volcano in faults of great earthquakes abstract results from several seismic methods allow us to sketch the deep structure of etna and its ionian margin under etna a volume of high velocity material is found in a structurally high position the emplacement of this suggests spreading of the surrounding medium just offshore down to the east normal faults penetrate through the upper crust the deeper crustal structure beneath appears upwarped from the basin towards etna juxtaposed with the crust of sicily a thinner crust reaches from the ionian basin under etna and the mantle is upwarped in such a structure magma can then be viewed as a melted lens capping a mantle upwarp at shallow depth rather than in an intracrustal chamber this reduces the conflict between estimates of its volume from excess output of volatiles and short residence times a link in time is indicated between volcanic and seismic activity at a large scale over the millennium the reported ends of episodes of high output rates of magma are followed by the reported occurrences of magnitude 7 earthquakes which caused destruction in southeastern sicily several steep active normal fault have been imaged to a depth of 10 km the crust up to 30 km offshore of the cities of catania and augusta which may be fault planes for such large earthquakes they expand and prolongate the system of the timpe faults on the eastern flank of etna thus linking large scale tectonics offshore with the volcano etna developed together with normal faulting upwarp and spreading during the recent evolution of the former ionian subduction activation of the material at depth at the lateral edge of the slab by vertical motion with extension above could produce the peculiar type of etna magmatism

location and orientation of eruptive fissures and feederdykes at mount etna influence of gravitational and regional tectonic stress regimes abstract lava extrusion from fissures on the flanks of the etna volcano is a common feature of recent activity as evidenced by the eruptions of 1971 1981 1983 and 1985 and was of similar importance during prehistoric times we propose here a model within which the location and orientations of the large majority of historic eruptive fissures on etna s flanks together with their feeder dykes are explained within the framework of a gravitational stress regime stress orientations within this regime are controlled largely by the gross morphology of the volcano but are significantly modified by local topographic anomalies we propose that the gravitational stress regime largely supercedes an earlier developed regional tectonic stress regime which still operates in the sub volcanic basement and may remain the dominant control of eruptive fissure and feeder dyke disposition at lower altitudes on the flanks the proposed model is supported by 1 detailed examination of fissure locations and orientations and the relationship between fissure azimuths and topography 2 precise horizontal distance measurement and vertical ground deformation studies of a recent eruption and 3 qualitative physical modelling experiments in which coloured water is injected into solidified gelatine solutions representing variously shaped volcanic constructs a cautious approach is advocated when extrapolating trends of spatially limited fissure segments for the purpose of locating potential sites of magma ascent and implications of the model for hazard analysis are outlined

contribution of ductile flow to exhumation of low temperature high pressure metamorphic rocks san juan cascade nappes nw washington state the san juan cascade sjc nappes were subducted to a depth of 18 km metamorphosed under low temperature high pressure conditions and then exhumed all within 16 m y during exhumation penetrative deformation by solution mass transfer smt resulted in a widespread spaced cleavage strain directions were determined for 27 sandstone samples and absolute strain measurements for a subset of 19 samples z directions generally plunge moderately to the ne and x and y directions are scattered in the plane perpendicular to z smt deformation is constrictional at the local scale but the tensor average indicates plane strain uniaxial shortening at the regional scale with sx sy and sz equaling 1 01 0 91 and 0 58 respectively the average flattening plane xy dips 30 to the ne and the average x direction plunges 20 to the north the large shortening in z was compensated by a mass loss volume strain of 47 we present a simple one dimensional model that illustrates the relationship between finite strain and ductile exhumation for a steady state convergent wedge assuming depth dependent ductile flow and no reversal of principal strain rates with depth this model indicates that ductile thinning of the sjc nappes accomplished only 13 of the total exhumation despite a vertical shortening strain of 36 there is no evidence that normal faulting contributed significantly to exhumation we conclude that erosion operating at an average rate of 1 1 km m y 1 was the dominant exhumation process

recent deep earthquake occurrence at mt etna sicily italy abstract the seismic activity of mt etna from april 1988 until the december 1991 eruption was monitored by means of permanent and temporary seismic networks volcanic activity that occurred during this period tremor increase with lava fountains at the summit craters and eruptions was preceded and accompanied by the occurrence of deep z 15 km seismicity this deep seismic activity occurring a few days up to some weeks before the volcanic phases was characterized by typical mainshock aftershocks sequences focal mechanisms of the more energetic events which preceded the eruptions show that the compression axis was nearly north south parallel to the direction of the compressive stress field acting in the area at regional scale both the observation of deep seismicity occurrence also before or during previous eruptions and the role played by tectonics as controller of the magma uprise suggest the hypothesis of a relation between the seismic energy released in the volcanic basement and the recharge mechanisms of the volcanic system in this hypothesis the deep seismicity located in the etnean area could be considered as a possible forerunner of volcanic activity

plastic flow of omphacite in eclogites at temperatures below 500 c implications for interplate coupling in subduction zones in subduction zones oceanic crust of the downgoing plate presumably forms a continuous interlayer between the upper and the lower plate during subduction the basaltic material is transformed to eclogite thus the flow strength of eclogite must pose an upper bound to shear stresses across the plate boundary for the deeper levels of subduction zones up to now experimental flow laws for wet diopside have been applied to predict the strength of eclogites however based on experimental calibration the material would be essentially undeformable by dislocation creep at 650 c even at 700 c a strain rate of 10 14 s 1 would still imply a differential stress of ca 150 mpa omphacite microstructures in eclogites from the piemonte zone western alps reveal shape preferred orientation subgrains and sutured high angle grain boundaries due to migration recrystallization and a pronounced crystallographic preferred orientation these textures indicate that the omphacite was deformed by dislocation creep in contrast garnet forms rigid inclusions within the weaker pyroxene matrix fe mg exchange thermometry for garnet omphacite pairs indicates temperatures of 465 50 c valle di locana and 475 50 c vallone di saint marcel for a pressure of 1 5 gpa these results are not consistent with the predictions based on experimental flow laws for diopside our data suggest that the flow strength of sodic pyroxene is significantly lower than that of diopside this finding is consistent with the homologous temperature concept with the melting temperature of jadeite at 3 gpa being approximately 350 c lower than that of diopside in addition dynamic migration recrystallization of omphacite in the investigated samples can be linked to small chemical changes this indicates that mobile grain boundaries formed an effective pathway for the exchange of ions and that this exchange was fast compared to the rate of boundary migration thus the combined reduction of stored strain energy and chemical free energy provided the driving force for recrystallization the potential effects of these chemical changes on flow strength remain to be explored

plastic deformation and development of clinopyroxene lattice preferred orientations in eclogites abstract we use an anisotropic viscoplastic self consistent vpsc model to simulate the development of omphacite lattice preferred orientations lpos in response to deformation by dislocation glide in these simulations we consider slip systems identified either in naturally deformed omphacite or in experimentally deformed diopside simulated lpos reproduce very well the characteristic omphacite lpo pattern in naturally deformed eclogites a strong concentration of 001 axes sub parallel to the lineation and of 010 poles sub perpendicular to the foliation these models reconcile the interpretation of omphacite lpos in eclogites and tem observations of naturally deformed omphacite since they show that omphacite lpos in naturally deformed eclogites may develop by dislocation glide on 1 2 110 110 001 110 and 001 100 we also investigate the effect of the strain regime on the omphacite lpo development the simulations show that changes in deformation regime lead to second order variations in omphacite lpo patterns similar to those observed in eclogites such as an asymmetry of the lpo relative to the structural frame a stronger concentration of the 001 axes relative to the 010 pole concentration or a dispersion of 001 axes in the foliation plane this suggests that omphacite lpo patterns may carry information on the deformation regime simple shear transtension active during the high pressure events

long term earthquake clustering summary we analyse statistically the long term properties of several instrumental earthquake catalogues complete catalogues exhibit both short and long term clustering for earthquakes of all depth ranges after accounting for the effect of short term clustering we find that in residual declustered catalogues long term clustering not periodicity characterizes the occurrence of all earthquakes shallow intermediate and deep the degree of clustering in residual catalogues is the same for earthquakes in different depth ranges circumstantial evidence indicates that the long term v ariation of seismicity is governed by a power law temporal distribution as in short term clustering it is scale invariant the fractal dimension of an earthquake set on the time axis is of the order of 0 8 0 9 therefore mainshock occurrence is closer to a stationary poisson process than standard aftershock sequences of shallow earthquakes

time correlation analysis of the microseismicity of the low eastern flank of mt etna volcano italy an analysis in terms of time correlation functions has been applied to the time distribution of microseismicity we considered the single station detections m 2 recorded by each one of the four working stations of the network of the osservatorio sismologico di protezione civile acireale catania located on the active faults systems timpe of the low eastern flank of mt etna information obtained on the time regularity of seismic crisis and on the time correlation between the activities recorded by different stations allowed a better understanding of the role of the two main structures the timpa di santa tecla is the most seismogenic structure in the area and probably played a role in the magma transfer process for the 1989 eruption modifications of the local stress field by actions of this feature may have produced gravitational instability along a second structural system the timpa di s leonardello with a time delay of about 100 days by contrast magma penetration associated with the larger eruption of 1991 1993 had a deeper rise system and had no effect on local stress conditions consequently there was no correlation between volcanism and seismicity

ebsd measured lattice preferred orientations and seismic properties of eclogites we investigated the deformation mechanisms and the seismic properties of 10 eclogite samples from different localities alps norway mali and eastern china through the analysis of their microstructures and lattice preferred orientations lpo these samples are representative of various types and intensity of deformation under eclogitic metamorphic conditions omphacite and garnet lpo were determined from electron backscatter diffraction ebsd technique garnet appears to be almost randomly oriented whereas omphacite develops strong lpo characterized by the 001 axes concentrated sub parallel to the lineation and the 010 poles concentrated sub perpendicular to the foliation in order to analyze the deformation mechanisms that produced such omphacite lpo we compare our observations to lpo simulated by viscoplastic self consistent numerical models a good fit to the measured lpo is obtained for models in which the dominant slip systems are 1 2h110i 11 0 001 110 and 001 100 dominant activation of these slip systems is in agreement with tem studies of naturally deformed omphacite seismic properties of eclogite are calculated by combining the measured lpo and the single crystal elastic constants of omphacite and garnet although eclogite seismic anisotropies are very weak less than 3 for both p and s wave they are generally characterized by a maximum p wave velocity sub parallel to the lineation and by a minimum velocity approximately normal to foliation the mean p and s wave velocities are high respectively 8 6 and 4 9 km s the s wave anisotropy pattern displays complex relationships with the structural frame but the fast polarization plane generally tends to be parallel to the foliation calculated reflection coefficients show that an eclogite crust interface is generally a good reflector rc 0 1 whereas an eclogite body embedded in the upper mantle would be hardly detectable

indentation model of the eastern alps and the origin of the tauern window a lithospheric model scaled for density and viscosity was shortened obliquely in front of an indenter whose shape and orientation match those of the south alpine indenter deformation was initially localized into subparallel sets of conjugate transpressive thrusts these structures evolved into folds which were strongly amplified and converged closer together during ongoing shortening finally forming a series of tight antiforms at the same time this tightly folded structure locally accommodated significant orogen parallel extension attaining 100 in front of the leading edge of the indenter but only 15 on the scale of the entire model the internal architecture and fault pattern of the model in map view are very similar to those of the tauern window in the eastern alps emphasizing the importance of localization of folding and shortening rather than orogen parallel extension for its formation

processing of crust in the root of the caledonian continental collision zone the role of eclogitization segments of the root to the caledonian collision zone are exposed along the west coast of norway allowing the study of processes and petrophysical conditions at the deepest crustal levels p t conditions prevailing in these crustal root zones correspond to eclogite facies eclogitization is associated with marked changes in petrophysical properties notably a density 10 15 and vp increase which may give a mantle signature to an eclogitized crust the observed ductility enhancement may be caused by transformation plasticity reduction in grain size formation of new mineral assemblages and presence of fluid in the western gneiss region and the bergen arcs eclogites form along shear zones interpreted as fluid pathways with sharp boundaries to their metastable protolith this makes eclogite shear zones potential deep crustal reflectors dry crust subducted into roots of continental collision zones will undergo eclogitization only if hydrous fluids are available timing of metamorphic reactions does not depend on crossing of equilibrium boundaries in the p t space but rather on the introduction of fluids into the system eclogites are not only passive recorders of p t t paths illustrating very deep subduction of crust 100 km rapid changes in petrophysical properties make fluid induced eclogitization a dynamic process that influences geodynamics stresses set up by the volume changes or by tectonic forces are released by ductile deformation along shear zones and by seismic faulting as evidenced by syn eclogitic pseudotachylytes in the metastable protolith deformation including seismicity enhances fluid infiltration and further eclogitization dense and rheologically weak eclogites may delaminate and sink into the mantle in the absence of fluids crustal doubling may occur without metamorphic re equilibration the evolution of a collision zone depends on the fluid regime which should be considered in geodynamic modelling in addition to p and t

large scale ground deformation of etna observed by gps between 1994 and 2001 we have processed thirty global positioning system gps campaigns carried out at etna from 1994 to early 2001 between the last two main flank eruptions of the mt etna sicily italy this rest period allowed us to investigate the deep magma plumbing system of the mt etna the temporal dynamics of twenty three points observed three times or more were analyzed all the time series show a first order linear trend during the five years period it suggests that the volcano was continuously deformed by the action of a deep source while a discrete activity of the volcano was observed at the summit we have interpreted the residual deformation field as the result of an major eastward motion of the eastern flank of the volcano

time seismicity patterns affecting local and regional fault systems in the etna region preliminary results for the period 1874 1913 an analysis of time correlation function and fractal dimension has been performed on the seismic activity that affected mt etna volcano italy during 1874 1913 in order to investigate the behaviour of some suspected magma controlling regional fault systems the time span considered has been characterized by intense seismic and volcanic activity with eight flank eruptions mainly occurring along the same north south fissure system the analysis of historical sources has been used to revise and improve the seismic catalogue all macroseismic information has been reinterpreted using the new european macroseismic scale 1998 ems the results contribute to the definition of the seismic behaviour of some regional fault systems relevant to the geodynamics of the area and provide some insights into the dynamic processes of mt etna volcano

upwards migration of seismic focii a forerunner of the 1989 eruption of mt etna italy data from a portable array of three component digital stations run at mt etna from 1988 to early 1990 highlight the seismic behaviour of the volcano before the 1989 eruption one of the most significant in terms of energy of the last two decades after a two year period of weak and discotinuous seismicity the depth of the seismically active volumes was observed to become shallower a few months before the volcanic event the overall migration of the events inferred by hypocentral locations and decreases of s p time differences at two stations agrees with other geophysical forerunners and allows further insights into the changes in the stress field leading to the eruption

archimedes revisited a structural test of eclogite emplacement models in the austrian alps high pressure rocks of the eclogite zone tauern window eastern alps formed at 20 kb 600 c uplift was fast without post burial heating extensive near field and far field deformation of the eclogite zone and its surroundings provide evidence for a tectonic uplift mechanism published emplacement models buoyant rise underplating and extension wrench faulting create distinct patterns of crustal deformation and are therefore testable by structural analysis we show that emplacement related deformation and its kinematics are consistent with underplating and extension extension is two phased the first phase may be driven by changes in rate or direction of plate convergence the second phase is due to large scale underplating of continental crust

development of shape and lattice preferred orientations application to the seismic anisotropy of the lower crust abstract we review the physical basis of the development of fabrics in plastic and viscous flow and illustrate the typical fabrics formed by these processes in the main rock forming silicates of the lower crust feldspar quartz pyroxene and amphibole the orientation process in plastic deformation where a single slip is dominant is recalled and the role of the constraint of neighbouring grains is emphasized the fabric development of anisometric crystals in viscous flow is discussed as a function of the main controlling parameters shear strain aspect ratio and interference between crystals the same sense of fabric asymmetry is introduced by plastic and viscous flow between the flow plane and the shape preferred orientation and hence coherent kinematic analysis can be undertaken in both modes of flow in order to assess the role of such fabrics in the seismic laminations of the lower continental crust we have calculated the seismic p wave properties of typical fabrics for hypothetical monomineralic and polymineralic rocks the calculations show that the strongest anisotropies develop in monomineralic rock with values between 5 and 16 compared with 5 and 8 for typical rock compositions the strongest anisotropies for layered monomineralic rocks generated by fabrics is only 6 compared to the 14 suggested by model studies of the observed seismic laminations we suggest that other effects such as compositional layering and or constructive interference of seismic waves are responsible for augmenting the apparent anisotropy

the nappe rule why does it work the nappe rule stresses that imbrication emplaces nappes with higher metamorphic grade above those with lower grade this means that the overriding nappes must be exhuming during nappe stacking otherwise metamorphic grade would increase structurally downwards the high grade metamorphic internides of many orogens are characterized by a pervasive nappe emplacement related subhorizontal foliation indicative of vertical ductile shortening thinning by quantifying finite strain in the gran paradiso massif italian alps we show that vertical ductile thinning associated with a nappe emplacement related subhorizontal foliation caused sufficient exhumation of the overriding nappes and can thus explain the occurrence of higher grade rocks above lower grade ones

deformation induced clinopyroxene fabrics from eclogites abstract clinopyroxene omphacite microfabric studies in eclogites are useful in characterizing the deformation that has affected deeper parts of subduction zones we present the microfabrics and tem structures of four samples representative of the various deformation types known in eclogites the 001 axis tends to be parallel to the lineation while the 010 plane is close to the foliation but these general features undergo strong variations in relation to the shape fabric in strongly lineated samples 010 tends to be spread out in a great circle normal to the lineation whereas 001 is dispersed in the foliation in the case of strongly foliated samples the slip systems identified by tem are 001 100 001 110 and 1 2 110 110 operation of dislocation creep is testified by the presence of dislocations and dislocation walls but this process alone cannot explain all the observed features particularly some aspects of the crystallographic preferred orientation hence other deformation mechanisms must be involved these may be dynamic migration recrystallization by grain boundary migration as well as mass transfer processes this study illustrates that not every crystallographic mineral preferred orientation can be explained by dislocation glide and or twinning processes alone in addition it also demonstrates that eclogite microfabrics can be used to unravel deformation parameters in subduction and or collision zones

low differential stress during high pressure metamorphism the microstructural record of a metapelite from the eclogite zone tauern window eastern alps constraints on the state of stress at deep levels of convergent plate boundaries can be obtained from the microstructural record of high pressure metamorphic rocks provided that this record has remained unchanged during exhumation the inclusion patterns in poikiloblastic garnet of a metapelite from the eclogite zone of the tauern window eastern alps reveal a foam microstructure of quartz controlled by grain boundary free energy the garnet blasts show concentric chemical zonation thermobarometry based on correlation between compositional domains in garnet chloritoid and phengite coexisting with kyanite rutile and quartz shows that garnet growth commenced before peak p t conditions close to 25 kbar and 600 c had been reached and continued during the early stage of decompression this implies that the microstructure of quartz controlled by grain boundary free energy persisted continuously during the latest stage of burial to ca 80 km depth and the early stage of exhumation involving detachment from the downgoing slab and release into the subduction channel the foam structure of the overgrown quartz indicates that the differential stress was too low to drive dislocation creep during that period when the rock crossed the interface between the plates with a high differential stress resulting in tectonic overpressure or significant shear heating being ruled out outside the protective garnet the interfacial free energy controlled quartz microstructure has been destroyed completely due to dynamic recrystallization during deformation by dislocation creep this happened while the crustal slice was exhumed to a depth of about 45 km the preservation of this synkinematic quartz microstructure indicates a tectonic scenario where the final cooling was rapid and no marked stress peak was associated with the brittle plastic transition

a linear intensity model to investigate the causal relation between calabrian and north aegean earthquake sequences summary the intensity process associated with a calabrian southern italy earthquake sequence m 5 is modelled as the sum of three separate effects according to the stochastic processes theory ogata et al 1982 1 poisson occurrence of independent events 2 self excitation i e triggering due to earthquakes of the same sequence 3 external triggering due to the occurrence of earthquakes m 6 in an adjacent north aegean region parameters of the model have been estimated by the maice akaike 1974 criterion applied to the historical earthquake catalogues of the two regions 1600 1984 results show that triggering of the calabrian sequence that is due to earthquake occurrence in the aegean region is the predominant effect on the other hand the occurrence of aegean events appears mainly poissonian the estimated probability for a calabrian earthquake following the occurrence of an aegean event increases with time reaching its maximum after around 13 months this time lag is interpreted as being due to stress wave propagation mechanisms following the occurrence of moderate to large earthquakes in the aegean region

a correlation between earthquakes and eruptive phases at mt etna an example and past occurrences a local array was deployed on mt etna to follow precisely the seismic activity occurring at the end of the eruption of the southeast crater in october 1984 swarm activity at sea level beneath the summit was followed by isolated earthquakes a few kilometres deeper and more distant and eventually by destructive earthquakes on the lower slopes there was no continuous migration between these domains of eruptive and seismic activity but the time relation is striking a revised use of the exceptional record over four centuries of eruptions and destructive earthquakes in the mt etna region documents the statistical significance of this type of occurrence of major earthquakes in relation to the end of eruptions

eclogite facies polyphase deformation of the drosdal eclogite western gneiss complex norway and implications for exhumation abstract exhumation of the deep crust during orogenic extension is accepted as a geological phenomenon but structures formed during burial and the earliest stages of exhumation are often overprinted by deformation events occurring at shallower crustal levels the western gneiss complex wgc of norway comprises variably retrogressed high pressure hp and ultrahigh pressure uhp eclogite bodies enclosed in predominantly felsic amphibolite facies rocks the drosdal body located in the sunnfjord area is one of the largest and best preserved eclogites in the wgc and comprises over ca 3 km2 of exposed eclogite facies rocks it is an excellent example of an eclogite tectonite and displays a wealth of structures formed during deformation at a minimum depth of 50 km and peak temperatures of ca 800 c large volumes of mylonites with the eclogite facies assemblage garnet clinopyroxene quartz amphibole clinozoisite phengite kyanite rutile are preserved structures associated with the eclogite facies metamorphism include e w trending isoclinal folds boudinage hinge parallel lineations and meter scale kyanite dominated veins the drosdal body was tightly folded on the kilometer scale under eclogite facies conditions subsequently the shapes of the drosdal body and other mafic bodies in the sunnfjord area were modified during eclogite to amphibolite facies e w directed stretching to give boudin like lenses the timing of formation of a pervasive eclogite facies lineation eclogite facies folds and kyanite bearing veins overlapped substantially and this portion of the deformation history was dominated by a constrictional strain field partitioning of deformation occurred after a substantial amount of eclogite facies deformation had already taken place and resulted in the relative rotation of linear features in specific zones on the scale of 400 m the eclogite facies lineations and fold hinges within the drosdal body are subparallel to amphibolite and greenschist facies structures throughout the wgc although circumstantial this suggests that structures belonging to each of these three metamorphic facies formed during one progressive deformation event corresponding to extensional exhumation our observations are consistent with models involving inhomogeneous deformation of the lower crust during early orogenic extension we envisage that transtensional noncoaxial deformation dominated the extensional deformation of the wgc but that coaxial deformation must have occurred locally

fabric asymmetry and shear sense in movement zones asymmetry between lattice preferred orientation and shape fabrics is commonly observed in microstructural studies of many deformed mineral aggregates e g ice carbonate rocks peridotites and quartzites theoretical predictions are limited by the nature of the models available and more can be gained by discussion of the mechanisms which give rise to such asymmetry in specific natural and experimental situations