sequence age and source of silicic fallout tuffs in middle to late miocene basins of the northern basin and range province the latest cenozoic 6 ma ash beds in the western united states have been intensively studied for several decades the more widespread of these ash beds are well documented event horizons that are of great value in studies of the timing and pace of geological climatological and biological events throughout the region because explosive volcanism was not restricted to latest neogene time in this region many older ash beds are likely to prove as useful as younger beds as event horizons once they are located characterized and dated as a first step in developing a useful chronology of older cenozoic ash beds in the western united states we have sampled and analyzed silicic fallout tuffs in middle to late miocene sedimentary basins across the northern basin and range province the northern basin and range basins ideally situated in the vicinity of major coeval silicic volcanic centers contain numerous relatively unaltered silicic fallout tuffs we have correlated tuffs between all sampled sections on the basis of glass shard composition the composite stratigraphic sequence established by the correlations contains more than 200 individual tuffs including 59 widely distributed tuffs termed correlative tuffs the tuffs vary widely in composition but most are in one of two compositional groups gray metaluminous vitric tuffs gm tuffs or white metaluminous vitric tuffs wm tuffs distribution patterns compositional characteristics and correlation with ash flow tuffs show that the source for most gm tuffs was the snake river plain volcanic province along the northern edge of the northern basin and range and the source for most wm tuffs was the southwestern nevada volcanic field in the southern part of the northern basin and range the northern basin and range tuffs range in age from ca 16 6 ma the ages of individual tuffs are determined variously by direct isotopic dating by correlation to previously dated fallout and ash flow tuffs or by interpolation age estimation ages for most tuffs are known to within 0 25 m y 1 or less and for many tuffs to within 0 1 m y or less the sequence and ages of tuffs established in this study provide insights into the evolution of the northern basin and range basins and patterns of explosive volcanism in coeval volcanic centers and contribute to the development of a high resolution stratigraphy and chronology of coeval sedimentary deposits throughout the western united states

rhyolitic globular peperites from the aznalcollar mining district iberian pyrite belt spain physical and chemical controls abstract globular peperites are exposed along the aznalcollar mining district iberian pyrite belt ipb spain these rocks originated by mingling of a low viscosity rhyolitic sill with unlithified wet sediments highly amygdaloidal up to 80 vol millimeters to centimeters across rhyolite globules extend from the upper contact of the sill for several centimeters into fine grained volcaniclastic host rocks the sill is very similar to other rhyolites in the ipb in terms of petrography and chemistry it is aphyric to very sparsely quartz phyric with small quartz phenocrysts vesicularity has been measured in the sill as vesicle area fraction determined by point counting over a rectangular grid and number density per unit area determined by counting every vesicle within the grid area amygdale distribution measured within the sill indicates a process by which vesicles migrated vertically from the lower portions of the sill to the roof zone we suggest that this migration process caused local density changes large enough to allow the rhyolitic magma to become buoyant enough to move through the overlying sediments producing globular peperites globular structures are preserved when rhyolite globules entered the wet sediment

practical equivalent continuum characterization of jointed rock masses a simple practical method to characterize the strength and stiffness of jointed rock masses is presented in this paper the empirical relations for the strength and stiffness of rock masses have been arrived based on the statistical analysis of a large amount of experimental data which are used for representing the jointed rock mass as an equivalent continuum the effect of joints in the rock mass is taken into account by a joint factor these obtained relations are incorporated in a non linear fem code to represent the equivalent continuum analysis the equivalent continuum model has been validated against experimental results for jointed rock masses with different joint fabric and joint orientation and also with the results from explicit modeling of joints using fem the developed model has also been applied to calculate the deformation around a large power station cavern in rhyolite rock at 200 m depth

back analysis of a rock landslide to infer rheological parameters abstract on 30 january 2009 a rock slide involving approximately 0 23 mm 3 of highly jointed gneiss from the local ercinic substratum was recorded in southern italy the landslide occurred after exceptional autumnal rainfalls and involved a quarry whose activity has been documented over the past 10 years by aerial images an engineering geology model of the slope involved in the landslide was developed based on the geomechanical classification of the outcropping rock masses the isrm 2007 indexes ib the block size index and jv the volumetric joint count and the observed geological setting of the slope an equivalent continuum approach was adopted to attribute strength and stiffness parameter values to the different classes of jointed rock masses a simplified evolutionary model of the slope was developed starting from 300 ka i e from the erosional phase following the deposition of the 300 m a s l marine terrace deposits overlaying the gneiss substratum to 30 january 2009 the model took into account the main depositional phases as indicated by the pleistocene marine terrace deposits and the documented stages of quarry activity time dependent stress strain numerical modelling was performed by the fdm software flac 6 0 a visco plastic burger model was used to back analyse the landslide event and to define the values of the rheological parameters for the jointed gneiss the results which were strongly constrained by the geomorphological evidences and by the displacement field observed before and after the landslide demonstrated a combination of i time dependent gravitational slope deformation and ii anthropogenic release due to quarry activity which induced a progressive failure process and an increase in the jointing within the gneissic rock mass located behind the cut wall of the quarry failure was ultimately triggered by intense rainfalls that occurred in the 3 months before the landslide the stress strain numerical modelling demonstrated the reliability of visco plastic rheology for simulating the rock mass creep in this case history viscosity values in the range of 10 19 10 23 pa s were derived

magma composition and viscosity as controls on peperite texture an example from passamaquoddy bay southeastern canada silurian mafic lava flows and rhyolite sills in the passamaquoddy bay area southeastern canada interacted with wet sediment to produce peperitic breccia the pahoehoe type mafic flows flowed over and bulldozed into wet unconsolidated silt and sand to produce both blocky and fluidal peperite at their lower contacts soft sediment deformation structures in the siltstone adjacent to the flows irregularly shaped vesicles in the siltstone and siltstone filled vesicles in the mafic lava all indicate the sediment was wet at the time of flow emplacement sills of rhyolite emplaced into the same sedimentary sequence also interacted with the wet sediment and produced peperite at both the upper and lower contacts evidence for the rhyolitic magma interacting with wet sediment includes sediment filled vesicles in rhyolite quartz filled vesicles in siltstone and angular non vesicular shards of rhyolite in clastic dykes peperite formed by this process is exclusively blocky the rhyolitic magma in the passamaquoddy bay sequence and other examples of high viscosity magma producing only blocky peperite suggest that in contrast to low viscosity magmas which produce a combination of blocky and fluidal peperite only blocky peperite will form associated with highly viscous rhyolite magma the sediment that interacted with both the mafic and rhyolitic lavas is of similar texture indicating that in this case sediment texture did not control peperite type the change from fluidal to blocky peperite texture may also be controlled in part by the magma temperature and or confining pressure and the generation and maintenance of a steam film at the magma wet sediment interface

seismic mountain building landslides associated with the 2008 wenchuan earthquake in the context of a generalized model for earthquake volume balance here we assess earthquake volume balance and the growth of mountains in the context of a new landslide inventory for the mw 7 9 wenchuan earthquake in central china coseismic landslides were mapped from high resolution remote imagery using an automated algorithm and manual delineation which allow us to distinguish clustered landslides that can bias landslide volume calculations employing a power law landslide area volume relation we find that the volume of landslide associated mass wasting 2 8 0 9 0 7 km3 is lower than previously estimated 5 7 15 2 km3 and comparable to the volume of rock uplift 2 6 1 2 km3 during the wenchuan earthquake if fluvial evacuation removes landslide debris within the earthquake cycle then the volume addition from coseismic uplift will be effectively offset by landslide erosion if all earthquakes in the region followed this volume budget pattern the efficient counteraction of coseismic rock uplift raises a fundamental question about how earthquakes build mountainous topography to provide a framework for addressing this question we explore a group of scaling relations to assess earthquake volume balance we predict coseismic uplift volumes for thrust fault earthquakes based on geophysical models for coseismic surface deformation and relations between fault rupture parameters and moment magnitude mw by coupling this scaling relation with landslide volume mw scaling we obtain an earthquake volume balance relation in terms of moment magnitude mw which is consistent with the revised wenchuan landslide volumes and observations from the 1999 chi chi earthquake in taiwan incorporating the gutenburg richter frequency mw relation we use this volume balance to derive an analytical expression for crustal thickening from coseismic deformation based on an index of seismic intensity over a defined area this model yields reasonable rates of crustal thickening from coseismic deformation e g 0 1 0 5 km ma 1 in tectonically active convergent settings and implies that moderate magnitude earthquakes mw 6 7 are likely responsible for most of the coseismic contribution to rock uplift because of their smaller landslide associated volume reduction our first order model does not consider a range of factors e g lithology climate conditions epicentral depth and tectonic setting nor does it account for viscoelastic effects or isostatic responses to erosion and there are important large uncertainties on the scaling relationships used to quantify coseismic deformation nevertheless our study provides a conceptual framework and invites more rigorous modeling of seismic mountain building

evidence for sea level oscillations by the characteristic thickness of marine deposits from raised terraces of southern calabria italy abstract clastic deposits associated with marine terraces can provide evidence for detecting eustatic oscillations the method is based on the characteristic thickness ct of beach formations which are generally deposited on a wave cut platform between the breakpoint and the swash upper limit on any present day coast ct reflects equilibrium related to current shore processes with a constant sea level it represents a local threshold t cr as when sea level rises ct increases by a value equal to the rise amplitude this amount is reduced in uplifted areas by the magnitude of coeval uplifting the amplitude of sea level variations detected by ct can be calculated knowing ct t cr uplift rate and the duration of an oscillation the method is applied to the clastic deposits of 23 marine terraces stepped between 52 and 172 m and shaped over the mis 5 mis 4 period along the calabria coast of the messina strait not only the great orbital oscillations mis 5 5 mis 5 3 mis 5 1 and mis 3 are recorded but also several rapid and low amplitude events are detected into each substage the most surprising result is the ten small oscillations during mis 5 5 the duration of which ranges between 2 ka and less than 1 ka while sea level oscillates from 0 5 to 12 m in amplitude by calculating initial relative sea level highstands and also lowstands preceding them detailed eustatic oscillations of the curve are drawn

large scale rhyolite peperites jurassic southern chile development of a jurassic volcano tectonic rift basin in the southern andes created a setting in which thick rhyolitic volcaniclastic sequences accumulated in submarine environments and were penetrated by hypabyssal intrusions during or shortly after deposition in the ultima esperanza district of southern chile extensive masses of peperite were produced when rhyolite magma underwent quenching disruption and commingling with wet unconsolidated sediments during intrusion at shallow levels beneath the sea floor the peperite forms discordant intrusive masses with volumes of up to several cubic kilometers in which large widely spaced coherent rhyolite feeder pods are surrounded by and grade into closely packed and dispersed peperite closely packed peperite consists of tightly fitting clasts separated by sediment filled fractures in dispersed peperite the sediment forms a matrix surrounding large masses of fractured rhyolite and smaller more widely separated rhyolite clasts evidence of in situ quench fragmentation is well preserved on both outcrop and thin section scales thin sections show that clast margins and in some cases entire small clasts underwent cooling contraction granulation releasing shards of quenched rhyolite and fragments of phenocrysts into the adjacent sediment interaction between magma and wet sediment was non explosive and involved fluidization of the host sediments creating space for the intruding magma and causing pervasive injection of highly mobile sediment along thermal contraction cracks in quench fragmented rhyolite the ability of the magma to undergo complex intermixing with large volumes of sediment with widespread preservation of in situ fragmentation textures is interpreted to reflect a relatively low magma viscosity presumably caused by retention of volatiles in the magma at the ambient pressures involved beds of redeposited peperite within the rift basin fill indicate that some of the intrusive peperite masses reached the sea floor undergoing slumping and mass flow the peperites were thus an important local source of coarse grained debris during the evolution of the basin

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

natural and man induced stress evolution of slopes the monte mario hill in rome the paper deals with stress release effects induced by man made cuts or excavations into natural stiff clay slopes that experienced erosion in response to valley deepening the study was focused on the monte mario hill in rome italy which formed part of an area of recent urban expansion the methodology of the study relied on a reference engineering geology model which was developed on the basis of site and laboratory data and stress strain analyses the latter analyses were carried out with the finite difference code flac 4 0 numerical modelling was based on a sequential approach taking into account the main evolutionary stages of the tiber river valley in rome 9s urban area and then making cuts at the bottom of the slope located south of the monte mario astronomical observatory the simulation revealed the stress release effects that fluvial erosion and excavation fronts have caused on the investigated slopes and their consequent gravitational instabilities these processes appear with metre scale displacements followed by stress release cracks actually observed on the slopes under review in quantifying stress release deformations the simulation took into account the possible role of creep in the observed retardation of stress release effects

long term gravitational deformation of rocks by mass rock creep abstract subsurface rocks beneath slopes are deformed to various degrees in various ways by mass rock creep mrc when they are subjected to a gravitationally unstable state for a long period mrc forms folds faults and numerous kinds of fractures such deformation is one of the main factors for deteriorating rock masses on slopes and also precursors of many landslides mrc deformations which have often been ascribed to tectonic origins can be distinguished from tectonic ones by their deformational features landforms and relationships between slope morphology and subsurface structures mrc folds are flexural slip folds that have the following mesoscopic to microscopic characteristics their axial surfaces are not smooth but are jagged and many visible openings or open fractures develop in association with the folds the jagged axial surfaces become smoother at depth and openings decrease in width with increasing overburden at the deformation site macroscopic types of mrc folds change according to the relationship between foliations and slopes buckling folds form in consequent slopes drag folds form in a deeper part of obsequent slopes and bending folds form in slopes with steep dipping foliations consequent or obsequent by downslope bowing of foliations shear fractures and tension fractures are the main deformational structures formed by mrc in massive rocks among shear fractures those of listric origin are remarkable tension fractures in general occur either in networks dividing rocks into fragments that slip and rotate irregularly in relation to each other or in parallel arrays of steeply dipping fractures an mrc fault has a shear zone consisting of a pulverized zone with gouge and a phyllitic or brecciated zone in a densely foliated rock the phyllitic zone is formed by microscopic slip along foliations in a sparsely foliated rock the brecciated zone is formed by random crushing except for the faults made through the shear fractures in massive rocks landforms due to mrc are gentle slopes bounded by horseshoe knicklines upslope convex slopes ridge top depressions multiple ridges uphill facing scarps and ridge crossing depressions

numerical study on deep seated gravitational slope deformation in a shale dominated dip slope due to river incision abstract based on numerical simulation this study investigates the triggering factors and evolution of deep seated gravitational deformation in a dip slope consisting of a shale dominated sequence of sediments results from continuum based finite difference numerical modeling demonstrate that long term strength degradation of a rock mass is a prerequisite for the development of gravitational slope deformation and that river incision resulting in change of slope geometry and corresponding stress concentration and redistribution is a major driving mechanism for the progressive evolution of deep seated gravitational slope deformation dsgsd numerical simulation considering the influence of weak planes indicates that the bedding planes control the strength of rock mass and form a structural constraint on the development of gravitational slope deformation a satisfactory correlation between the distribution of numerically simulated plastic shear bands and weak zones in drill cores demonstrates that the weak zones within the slope are formed due to gravitational slope deformation furthermore numerical simulation shows a link between geomorphological development and internal deformation of the slope which aids in the understanding of relationships between interior deformation of the slope the exterior geomorphology and related effect factors including river incision and strength degradation

landslide erosion coupled to tectonics and river incision the steep topography of mountain landscapes arises from interactions between tectonic rock uplift valley incision and landslide erosion on hillslopes an analysis of more than 15 000 landslides in the eastern himalaya mapped from satellite images shows that steep uplands primarily respond to uplift and river incision by increases in landslide erosion rates rather than by steepened hillslope angles

how voluminous rhyolite lavas mimic rheomorphic ignimbrites eruptive style emplacement conditions and formation of tuff like textures silicic lavas of large volume and relatively great areal extent are not uncommon in association with the tracks of mantle plume hotspots across the continents these units are commonly eroded and or poorly exposed and their interpretation as lavas has been controversial the morphology of a 15 km 3 calc alkalic rhyolitic unit 75 to 77 wt sio 2 on the owyhee plateau of southwestern idaho shows that it is a true lava flow emplaced by effusion the eruption tapped a zoned magma chamber with a small volume of nearly aphyric magma underlain by a much larger volume of less evolved crystal rich magma magmatic temperatures were about 830 c and h 2 o contents were about 2 to 2 75 wt eruptive activity first involved explosive venting of the nearly aphyric magma followed by effusion of the crystal rich magma movement of the lava over and around the tephra deposits formed large discrete lava lobes one flow lobe reached 9 km from the vent though the unit is a true lava flow a diverse suite of fragmental textures including rock that closely resembles welded tuff formed by lava flow processes during the time the flow was active

genesis and diagnostic value of soft sediment deformation structures a review abstract soft sediment deformation structures are recognized as important diagnostic features in the rock record for determination of depositional environments and slope processes the diagnostic value of these structures is reevaluated by analysis of the parameters controlling sediment deformation soft sediment deformation is contemporaneous with deposition and occurs dominantly in course silt to fine sand the high depositional rate low permeability and low shear strength of grains within this sediment range maximize the occurrence of deformation the dominant mechanisms responsible for sediment deformation include 1 liquefaction or fluidization 2 reverse density gradation 3 slumping or slope failure and 4 shear stress in most cases a combination of these mechanisms occurs the processes function in a continuum producing features that are microscopic to megascopic in scale it is shown that the processes and thus the structures are not environment specific the true diagnostic value of the structures may be in defining hydrodynamic conditions and in interpreting paleocurrents and paleoclimatic and paleoseismic events ultimately for the best diagnostic results soft sediment deformation structures should be studied in association with all other available lithologic structural and paleontological information

time dependent modelling of a mountain front retreat due to a fold to fault controlled lateral spreading abstract the eastern betic cordillera spain exemplifies at the sierra de aitana an impressive case of lateral spreading which involves a mountain anticline ridge dislodged by a post orogenic extensional tectonic the deep trenches testify the ongoing gravitational slope deformation featured by a rock mass lateral spreading the sierra de aitana anticline ridge was dislodged along a normal fault zone which generated a scarp with a kilometric lateral continuity the lateral spreading originated because eocene limestone overlays eocene marls inducing a continuous evolution over time due to visco plastic deformations and isolating huge prismatic blocks to quantify the creep driven stress strain effects at sierra de aitana ridge the mechanical and rheological parameter values of the involved rocks were quantified through field and laboratory tests which allowed to constrain an engineering geological model based on equivalent continuum approach a stress strain numerical modelling aimed at back analysing the sequential morpho structural evolution of the sierra de aitana anticline ridge was performed by reproducing the retreat of the ridge front and the time succession of faults re activations a time dependent solution was approached by assuming a time dependent creep configuration of the modelling and a parametric solution adopted to calibrate rock mass rheology also taking into account tectonic displacement due to the aitana normal fault system by simulating these element as interface in the discretized domain influence of pre existing joint sets by assuming a main anisotropy in the elasto plastic failure solution admissible variations of the regional stress field related to compressive and extensional phases and a generalised visco plastic behaviour representing the ductile marls the numerical modelling outputs that the lateral spreading mainly evolved as a creep driven process while stress release induced by tectonic activity is not sufficient to justify the observed landforms the obtained results highlight a not negligible role of inherited structural elements for regulating the time evolution of the ongoing gravitational process at the sierra the aitana anticline

long term behaviour of the late quaternary normal faults in the straits of messina area calabrian arc structural and morphological constraints abstract the calabrian arc is located in the peri tyrrhenian orogenic belt of southern italy and is characterised by intense post collision dynamics this consists of rapid regional uplifting combined with active normal faulting affecting the tyrrhenian side of calabria and the ionian coast of sicily the siculo calabrian rift zone the effects of the two combined processes are well exposed in the straits of messina area that represent a major transfer zone located between two opposing sets of normal faults characterising the southern calabria and the northeastern sicily branches of the rift in the straits of messina region the distribution and elevation of the upper quaternary marine terraces suggest a southward propagation of the normal fault belt from calabria to sicily it occurred at about 125 ka after a long period of tectonic quiescence and was triggered by huge elastic releases in southern calabria the long term behaviour recorded on the distinct fault segments of the rift is to relate to the presence of a crustal barrier that influenced both the geometry and the fault propagation along the rift zone

volcanic avalanche fault zone with pseudotachylite and gouge in french massif central abstract structures and textures with sedimentological variations at different scales of the lithofacies assemblage help us to constrain the basal kinematic transition from non depositional to depositional conditions during volcanic avalanche emplacement in the well exposed impact sheared contact along volcanic avalanche fault zone in the french massif central we observe how the granular textures of the pseudotachylite and fault gouge have recorded the propagation of shock wave with granular oscillatory stress sequential events of basal aggradation along avalanche fault zone have been established related to fractal d values temperature pressure regime and oscillatory stress during slow wave velocity a typical lithofacies assemblage with a reverse grading shows the pseudotachylite and fault gouge a cataclastic gradient is characterised by the fractal d values from 2 7 in jigsaw breccias with pseudotachylite partial melt to 2 6 in the polymodal gouge shock brecciation and comminution produce cataclastic shear bands in the pseudotachylite and quartz microstructures along the basal contact of the volcanic debris avalanche deposit gouge microstructures show granular segregation cataclasis with antithetic rotational riedel shear and an arching effect between the riedel shear bands x ray microtomography provided 3d microfabrics along the clastic vein in the sandy gouge from the available statistical dataset a few equations have been developed implicating the same cataclastic origin with a co genetic evolution of lithofacies an impact wave during primary shear propagation may contribute to produce hydroclastic matrix pseudotachylite partial melt and proximal gouge thixotropy with v 50m s and a t

luminescence chronology of pleistocene marine terraces of capo vaticano peninsula calabria southern italy abstract quaternary terrace deposits exposed on the capo vaticano peninsula calabria southern italy have been investigated in order to obtain new osl age estimates six samples were collected from unconsolidated sediments associated with the major marine terraces these form a flight of seven distinct levels distributed between about 600 m and 30 m of altitude the samples were analysed by optically stimulated luminescence osl technique the obtained results provided reliable age estimates showing numerical ages ranging between 214 25 ka and 62 6 ka age determinations combined with geological and morphological information provide new constraints for correlating the distinct orders of marine terraces with the last seven interglacial stages of the eustatic curve this correlation indicates that in the middle late pleistocene this portion of the southern calabrian arc was affected by a vigorous uplift characterized by rates up to 2 mm y

stress strain time numerical modelling of a deep seated gravitational slope deformation preliminary results abstract an analysis of the effects of creep on the development of a deep seated gravitational slope deformation dsgsd carried out by numerical modelling is described the slope rock mass evolution has been simulated applying different creep rheological models the studied dsgsd is located in the central italian alps val s giacomo it is characterised by three main scarps different sets of tensile trenches and counterscarps mapped during a detailed geomorphological survey the mechanical behaviour of the rock masses in terms of elasto plastic parameters has been defined on the base of laboratory and in situ tests in order to simulate this instability process a stress strain time numerical modelling has been performed by a finite difference numerical code fast lagrangian analysis of continua flac the effects of different constitutive model laws have been considered the visco elastic maxwell model the visco elastic burger model and the elasto visco plastic burger model the modelling has been performed simulating the melting of the ancient glacier starting from its maximum load because of the difficulty to determine rock mass creep parameters for each of the rheological models a sensitivity analysis has been performed varying the physical mechanical properties the visco elasto plastic model allows to underline the formation of shear surface showing a depth and a shape in good agreement with the morphologic features of the slope the only action of unloading due to glacier melting seems to be insufficient to generate deep critical surfaces which can be related with the formation of the dsgsd

the importance of earthquake induced landslides to long term slope erosion and slope failure hazards in seismically active regions abstract this paper describes a general method for determining the amount of earthquake induced landsliding that occurs in a seismically active region over time this determination can be used as a quantitative measure of the long term hazard from seismically triggered landslides as well as a measure of the importance of this process to regional slope erosion rates and landscape evolution the method uses data from historical earthquakes to relate total volume of landslide material dislodged by an earthquake to the magnitude m and seismic moment m0 of the earthquake from worldwide data a linear regression relation between landslide volume v and m0 is determined as v m0 1018 9 0 13 where v is measured in m3 and m0 is in dyn cm to determine the amount of earthquake generated landsliding over time this relation is combined with data on seismic moment release for a particular region which may be derived from either earthquake history or fault slip data the form of the m0 v relation allows the rate of production of earthquake induced landslides over time to be determined from total rate of seismic moment release without regard to the distribution of individual events thus simplifying and generalizing the determination application of the method to twelve seismically active regions with areas ranging from 13 275 to 2 308 000 km2 shows that erosion rates from earthquake induced landslides vary significantly from region to region of the regions studied the highest rates were determined for the island of hawaii new zealand western new guinea and the san francisco bay region of california significantly lower rates were determined for iran tibet the sierra nevada great basin region of california and central japan for the time period from 715 ad to the present intermediate rates were determined for peru southern california onshore california turkey and central japan for the time period from 1586 ad to the present to determine the relative long term importance of seismically triggered landslides these erosion rates are compared to erosion rates calculated for other slope processes and to rates calculated from fluvial sediment discharge comparisons with other slope processes indicate that earthquake induced landslides are the predominant agents of slope erosion on the island of hawaii in the san francisco bay region and in western new guinea for hawaii the san francisco bay region and sierra nevada great basin region of california the erosion rates calculated for earthquake induced landslides also exceed the regional erosion rates calculated from fluvial sediment discharge

landslides triggered by the 8 october 2005 kashmir earthquake abstract the 8 october 2005 kashmir earthquake triggered several thousand landslides these were mainly rock falls and debris falls although translational rock and debris slides also occurred in addition a sturzstrom debris avalanche comprising 80 million m3 buried four villages and blocked streams to create two lakes although landsliding occurred throughout the region covering an area of 7500 km2 the failures were highly concentrated associated with six geomorphic geologic anthropogenic settings including natural failures in 1 highly fractured carbonate rocks comprising the lowest beds in the hanging wall of the likely earthquake fault 2 tertiary siliciclastic rocks along antecedent drainages that traverse the hazara kashmir syntaxis 3 steep 50 slopes comprising precambrian and lower paleozoic rocks 4 very steep 50 lower slopes of fluvially undercut quaternary valley fills and 5 ridges and spur crests the sixth setting was associated with road construction extensive fissuring in many of the valley slopes together with the freshly mobilized landslide debris constitutes a potential hazard in the coming snowmelt and monsoon seasons this study supports the view that earthquake triggered landslides are highly concentrated in specific zones associated with the lithology structure geomorphology topography and human presence

a facies based depositional model for ancient and modern tectonically confined tidal straits modern and ancient tidal straits are the least well understood of all tide dominated depositional systems to provide an increased understanding of these systems a facies based depositional model is assessed by comparing multibeam surveys of three present day tidally dominated seaways with a number of superbly exposed neogene to quaternary strait fill successions of calabria south italy the model points out the existence of four depositional zones laterally adjacent from the narrowest strait centre to its terminations distributed along symmetrical or asymmetrical seaways these zones whose signature is recorded in four facies associations in the calabrian tidal straits are as follows i the strait centre zone associated with the tidal current maxima and where sediments are scarce or absent ii the dune bedded zone where sediments form dune complexes due to tidal flow expansion iii the strait end zone where currents decelerate accumulating thinly bedded fine grained deposits and iv the strait margin zone where sediment massflows descend tectonically active steep margins towards the strait axis in ancient tectonically confined narrow seaways these facies generate a distinctive deepening upward vertical succession where tidal currents are the dominant process in the sediment distribution

a 125 kyr long geological record of seismic source repeatability the messina straits southern italy and the 1908 earthquake ms7 2 the occurrence of characteristic earthquakes along segments of major active belts has been described as early as the beginning of the century the large 1908 messina straits blind normal faulting earthquake provides an opportunity to investigate the repetition of characteristic earthquakes and the persistency of the main features of the fault zone over a time scale in the order of 100 kyr we have compared seismological and geodetic descriptions of the 1908 rupture process with long term crustal deformation recorded at different stratigraphic levels by marine terraces marine sedimentary units and landscape features the wealth of elevated coastal features in and around a region affected by large normal faulting earthquakes indicates that coseismic strain is superimposed on much faster uplift on a regional scale we investigated in detail the pattern of deformation of the 125 kyr old lowest emergent terrace and found that it mimics the pattern of elevation changes observed following the earthquake this suggests 1 that the 1908 earthquake is characteristic 2 that its segment boundaries have been stationary during the past 125 kyr and 3 that even the locations of the regions of largest coseismic release do not change through many seismic cycles based on a comparison between observed heights of the 125 kyr terrace and 1908 displacements we estimated an average repeat time of 1000 yr for a 1908 type earthquake we also investigated the height position age and state of deformation of older terraces and found 1 that uplift of the region started about 1 ma and has since continued rather uniformly at 0 9 1 4 mm yr 1 2 that during this time the straits have narrowed at a rate of 10 20 mm yr 1 and 3 that all the main geomorphic features of the messina straits result from the interaction of fast regional uplift 1908 type coseismic subsidence and global sea level fluctuations

variation in peperite textures associated with differing host sediment properties peperites formed by mixing of magma and wet sediment are well exposed along punta china baja california mexico where two sills intrude a section of lava flows limestones and volcaniclastic rocks irregular lobes and dikes extend from the sills several meters into host sediments including highly comminuted flow top breccias lithic lapilli tuff breccias and shelly micrites whereas intrusive contacts with lava flows are sharp and planar where one sill intruded both coarse grained volcaniclastic rock and fine grained limestone textural differences between the hosts produced strikingly different styles of peperite blocky masses of the basaltic intrusions up to 1 m in size were dispersed for distances up to 3 m into host lithic lapilli tuff breccias the blocks consequently underwent in situ fragmentation as they were rapidly quenched the high degree of dispersion resulted from steam explosions as the magma enveloped pockets of water in the coarse grained permeable host elutriation of fine grained material from vertical pipes in tuff breccia above the lower sill provides evidence for meter scale fluidization of the host the contact zone between the basaltic magma and the shelly micrite host resembles a mixture of two viscous immiscible fluids fluidal peperite intrusion occurred behind a stable vapor film which entrained lime mud particles and carried them off grain by grain as magma advanced into the host thin section scale elutriation pipes formed microglobular peperite represents a frozen example of a fuel coolant interaction fci between basaltic magma and fluidized micrite host the intimate intermixing of magma and host at the submillimeter level is attributed to fluid instabilities developed along the magma vapor host interface such intimate intermixing of magma and water bearing fragmental debris is commonly a precursory step toward explosive hydrovolcanism

lithospheric topography tilted plumes and the track of the snake river yellowstone hot spot 1 the trace of the snake river yellowstone hot spot is the world s best example of a mantle plume that has been overridden by continental lithosphere the standard model calls for the plume head to rise under northern nevada and be forced northward to form basalts of the columbia plateau subsequent movement of north america to the southwest over the plume tail created a hot spot trace on the surface we present a new conceptual model for the origin of this feature that resolves inconsistencies in the current standard model and explains the recent documentation of a thermal anomaly in the mantle below yellowstone today that plunges 65 wnw our model implies that the plume tail was forced beneath thinned cratonic lithosphere to the se along with part of the plume head and has remained in this orientation for the last 12 ma we infer that almost all of the volcanism in se oregon and sw idaho prior to 12 ma results from overriding the southern extension of the plume head not the plume tail and that a distinct plume tail hot spot track was not established until formation of the bruneau jarbidge eruptive center around 12 ma the plume tail track may also be controlled by a preexisting structural boundary in lithosphere that is thinner than adjacent lithosphere this model demonstrates the potential importance of lithospheric topography on controlling the surface manifestation of plume volcanism and the complexity that may arise when lithospheric thickness is nonuniform

p wave tomography of the mantle under the alpine mediterranean area 1 we study the upper mantle p wave velocity structure below the euro mediterranean area down to 1000 km depth by seismic travel time tomography we invert summary residuals constructed with both regional and teleseismic first arrival data reported by the international seismological centre isc 1964 1995 introducing some alternative strategies in the travel time tomographic approach and a new scheme to correct teleseismic data for global mantle structure our high resolution model pm0 5 is parameterized with three dimensional 3 d linear splines on a grid of nodes with 0 5 spacing in both horizontal directions and 50 km vertical spacing we obtain about 26 root mean square rms reduction of residuals by inversion in addition to roughly 31 reduction after summary rays formation and selection sensitivity analyses are performed through several test inversions to explore the resolution characteristics of the model at different spatial scales the distribution of large scale fast anomalies suggests that two different stages of a convection process presently coexist in very close regions the mantle dynamics of western central europe is dominated by blockage of subducted slabs at the 660 km discontinuity and ponding of seismically fast material in the transition zone contrarily in the eastern mediterranean fast velocity material sinks into the lower mantle suggesting that the flow of the cold downwelling here is not blocked by the 660 km discontinuity on a smaller scale the existence of tears in the subducted slab lithospheric detachment all along both margins of the adriatic plate as proposed by some authors is not supported by our tomographic images

the evolution of the calabrian arc evidence from paleomagnetic and gps observations abstract the present day arcuate shape of the calabrian arc has been accomplished during neogene and early pleistocene by large and opposite vertical axis rotations along the two arms of the arc clockwise cw rotations have been systematically registered in sicily and calabria whereas counterclockwise ccw rotations were measured in southern apennines such opposite vertical axis rotations ceased in the uppermost part of the lower pleistocene about 1 ma ago along almost the entire calabrian arc and are not observed in the present day gps velocity field the end of the calabrian arc bending during the quaternary marks a decrease in the efficiency of the tectonic processes related to the long lived subduction of the ionian slab which caused the halting of the back arc opening in the southern tyrrhenian sea

towards establishing criteria for identifying trigger mechanisms for soft sediment deformation a case study of late pleistocene lacustrine sands and clays onikobe and nakayamadaira basins northeastern japan five main deformation units discrete sheets of deformed sediments that lie between a significant thickness of undeformed sediment were selected for study within late pleistocene lacustrine sands and clays in the onikobe and nakayamadaira basins northeastern japan the deformed units show evidence of deformation by a variety of mechanisms including fluidization liquefaction brittle failure and cohesive flow driving forces are thought to be primarily reverse density gradient systems but also include gravitational body force shear stress and unequal loading the main trigger mechanisms are firstly earthquakes secondly overloading from volcanic sands and thirdly to a lesser extent subaqueous currents consideration is given to criteria that allow the trigger mechanism to be identified this study shows that the following criteria can be used to identify a seismic triggering agent i setting ii the extent of the deformation units iii absence of evidence relating to other potential trigger mechanisms and iv evidence relating to other potential trigger mechanisms is present but can be seen elsewhere in the stratigraphic section associated with undeformed sediment conversely the following criteria while they are important in interpreting the driving force and deformation mechanism have no relevance to the trigger mechanism i sediment composition ii deformation structures being restricted to a single stratigraphic interval 1 m thick not necessarily correlatable over large areas and iii similarity to structures in the literature

morphometric analysis and amino acid geochronology of uplifted shorelines in a tectonic region near reggio calambria south italy the tectonic coastline of the calabrian peninsula provides an opportunity to study the morphology and history of elevated marine shorelines near capo dell armi eleven shorelines are preserved between sea level and 256 m with some correlation difficulties posed by the dissection of the area by intermittent streams we are able to correlate several of the shorelines across the entire study area with the support of correlations provided by amino acid geochronology we have identified four shorelines dating from the last interglacial period isotope stage 5 the oldest two both contain the strombus bubonius fauna and are of indistinguishable early last interglacial ages stage 5e aminozone e ca 125 ka the highest terrace vii is associated with a shoreline at 157 m and the lower with a shoreline around 125 105 m a s l of the two younger stage 5 without strombus bubonius the higher v lies at about 90 100 m and produces amino acid ratios slightly younger than but statistically indistinguishable from those of aminozone e however the youngest last interglacial shoreline deposits iv have produced amino acid ratios correlated to late stage 5 5a elsewhere in the mediterranean basin amino acid and geomorphic data have shown that uplift varies the study area from 0 85 to 1 03 m ka and suggeststhat constant uplift along any one traverse is unlikely

thermoluminescence dating tests of pleistocene sediments from uplifted marine shorelines along the southwest coastline of the calabrian peninsula southern italy abstract this paper presents tl age estimates of pleistocene raised marine terraces from southern calabria southern italy it focuses on the dating of last interglacial shallow marine sand deposits including several tyrrhenian key reference deposits whose stratigraphic assignment is based on biostratigraphic evidence presence of a strombus bubonius fauna and geochronometric data amino acid data calibrated with u th dates on coral the tl age estimates are obtained on alkali feldspar coarse grains using their blue tl emission they are in good agreement with the ir osl age estimates obtained on the same feldspar samples our feldspar tl method is tested on two tyrrhenian key reference sites ravagnese and bovetto in the reggio di calabria area their measured tl age estimates 97 11 ka and 100 10 ka are lower than their estimated geological age i e oxygen isotope substage 5e the correction for long term fading suggested by mejdahl 1988 is tested on these two samples using a lifetime of 446 ka as estimated from both calabrian and miocene sand collected within the same area this correction would yield preliminary tl ages 116 13 ka and 116 12 ka that are in better agreement with the expected geological age the application of our tl method to paleoshorelines lying below the tyrrhenian reference shoreline of ravagnese bovetto yields stratigraphically consistent tl age estimates the tl method is also applied to two supposedly pre last interglacial paleoshorelines which are geomorphologically older than the tyrrhenian reference shorelines they remain however chronologically undifferentiated both by the tl and the amino acid methods finally the preliminary feldspar tl results obtained on the miocene and the calabrian sand deposits 1 ma suggest that our feldspar tl method is limited in the sw calabrian area to about 200 ka

history of subduction and back arc extension in the central mediterranean summary geological and geophysical constraints to reconstruct the evolution of the central mediterranean subduction zone are presented geological observations such as upper plate stratigraphy hp lt metamorphic assemblages foredeep trench stratigraphy arc volcanism and the back arc extension process are used to define the infant stage of the subduction zone and its latest back arc phase based on this data set the time dependence of the amount of subducted material in comparison with the tomographic images of the upper mantle along two cross sections from the northern apennines and from calabria to the gulf of lyon can be derived further the reconstruction is used to unravel the main evolutionary trends of the subduction process results of this analysis indicate that 1 subduction in the central mediterranean is as old as 80 myr 2 the slab descended slowly into the mantle during the first 20 30 myr subduction speeds were probably less than 1 cm year x1 3 subduction accelerated afterwards producing arc volcanism and back arc extension and 4 the slab reached the 660 km transition zone after 60 70 myr this time dependent scenario where a slow initiation is followed by a roughly exponential increase in the subduction speed can be modelled by equating the viscous dissipation per unit length due to the bending of oceanic lithosphere to the rate of change of potential energy by slab pull finally the third stage is controlled by the interaction between the slab and the 660 km transition zone in the southern region this results in an important re shaping of the slab and intermittent pulses of back arc extension in the northern region the decrease in the trench retreat can be explained by the entrance of light continental material at the trench

the origins of glacially related soft sediment deformation structures in upper ordovician glaciogenic rocks implication for ice sheet dynamics in the upper ordovician glaciogenic rocks of west gondwana many soft sediment deformation structures are attributed to glaciotectonic processes however little is known about the subglacial and ice marginal processes associated with this ice sheet a systematic description and interpretation of these soft sediment deformation structures is supplemented by a comparison with late quaternary and modern glacial settings to provide qualitative constraints on the character of ancient subglacial thermal regimes soft sediment striations were formed by discontinuous shear induced deformation beneath an ice sheet that oscillated between warm and cold based thermal regimes beneath warm based ice coupling across the ice bed interface was poor with sliding and loading occurring at this surface loading of soft waterlogged sediments allowed the development of fluted surfaces which are also associated with the formation of truncated folded zones during times of cold thermal regimes coupling across the ice bed interface was enhanced by freezing which caused changes in the position of the freezing front these discontinuous changes coupled with sustained subglacial shearing resulted in the development of stacked soft sediment striated surfaces in areas where the subglacial substrate had an irregular topography complex shear zones formed that comprised stacked duplex systems interlayered with highly strained units preserving pervasive folded lineations at the ice front large glaciotectonic deformation structures comparable with push moraines developed during sustained periods of re advance that created composite thrust and fold systems deformation was transmitted for up to 1 km from the ice front and reduced in intensity with distance other deformation structures include dome like folds that consist of central anticlines 30 to 70 m in width with tight rim synclines that formed by the load induced diapiric intrusion of muds an ice sheet surging mechanism is inferred for the development of composite thrust and fold systems and the coeval sediment diapirs these surges potentially caused the widespread reorganisation of a glacial load resulting in the pro to subglacial extrusion of soft sediments

snake river sr type volcanism at the yellowstone hotspot track distinctive products from unusual high temperature silicic super eruptions a new category of large scale volcanism here termed snake river sr type volcanism is defined with reference to a distinctive volcanic facies association displayed by miocene rocks in the central snake river plain area of southern idaho and northern nevada usa the facies association contrasts with those typical of silicic volcanism elsewhere and records unusual voluminous and particularly environmentally devastating styles of eruption that remain poorly understood it includes 1 large volume lithic poor rhyolitic ignimbrites with scarce pumice lapilli 2 extensive parallel laminated medium to coarse grained ashfall deposits with large cuspate shards crystals and a paucity of pumice lapilli many are fused to black vitrophyre 3 unusually extensive large volume rhyolite lavas 4 unusually intense welding rheomorphism and widespread development of lava like facies in the ignimbrites 5 extensive fines rich ash deposits with abundant ash aggregates pellets and accretionary lapilli 6 the ashfall layers and ignimbrites contain abundant clasts of dense obsidian and vitrophyre 7 a bimodal association between the rhyolitic rocks and numerous coalescing low profile basalt lava shields and 8 widespread evidence of emplacement in lacustrine alluvial environments as revealed by intercalated lake sediments ignimbrite peperites rhyolitic and basaltic hyaloclastites basalt pillow lava deltas rhyolitic and basaltic phreatomagmatic tuffs alluvial sands and palaeosols many rhyolitic eruptions were high mass flux large volume and explosive vei 6 8 and involved h2o poor low 18o metaluminous rhyolite magmas with unusually low viscosities partly due to high magmatic temperatures 900 1 050 c sr type volcanism contrasts with silicic volcanism at many other volcanic fields where the fall deposits are typically plinian with pumice lapilli the ignimbrites are low to medium grade non welded to eutaxitic with abundant pumice lapilli or fiamme and the rhyolite extrusions are small volume silicic domes and coulees sr type volcanism seems to have occurred at numerous times in earth history because elements of the facies association occur within some other volcanic fields including trans pecos texas etendeka parana lebombo the english lake district the proterozoic keewanawan volcanics of minnesota and the yardea dacite of australia

hyaloclastites peperites and soft sediment deformation textures of a shallow subaqueous miocene rhyolitic dome cryptodome complex palhaza hungary abstract the ne tokaj mountains at palhaza in ne hungary are made up of a complex association of miocene rhyolitic shallow intrusions cryptodomes and endogenous lava domes emplaced into and onto soft wet pelitic sediment in a shallow submarine environment the intrusive extrusive complex shows a range of interaction textures with the host muddy sediment ranging from blocky peperites formed on a 0 1 m scale through to irregular contacts closely resembling globular mega peperites on a 10 m scale the over 200 m thick igneous succession is interpreted to result from the pulsatory growth of shallow cryptodomes through muddy saturated host sediment the intrusions eventually breached the sedimentary cover to build up thick in situ hyaloclastite piles in the shallow subaqueous environment the coherent rhyolitic cryptodome facies is surrounded by intrusive hyaloclastite in the contact zone to the pelitic host sediment in the upper level of the complex rhyolitic dome rock is capped and surrounded by hyaloclastite formed due to quench fragmentation upon contact of the lava surface with sea water

the impact of confining stress on the rock mass deformation modulus the paper presents the results of a literature review combined with additional laboratory testing to determine the significance of confining stress on the true stiffness properties of rocks classical elasticity theory is introduced to set the scene for what is precisely meant by stiffness increase with confining stress previous laboratory based stiffness testing on both intact and jointed rock specimens is reviewed and the experimental results and leading equations and theories are summarised the authors then introduce their own laboratory testing results concerning the same phenomena and present a new expression which is directly compared with both the previous and the newly conducted test data in conclusion it is seen that the rock types tested display significant increase in stiffness under confinement commonly up to 3 times for typical intact rocks and up to 20 times for weak specimens and that the implications for property definitions for numerical modelling are significant and relevant

earthquake triggering of landslides in highly jointed rock masses reconstruction of the 1783 scilla rock avalanche italy abstract the scilla rock avalanche occurred on 6 february 1783 along the coast of the calabria region southern italy close to the messina strait it was triggered by a mainshock of the terremoto delle calabrie seismic sequence and it induced a tsunami wave responsible for more than 1500 casualties along the neighbouring marina grande beach based on subaerial and submarine surveys a 5 106 m3 subaerial landslide was identified together with a 3 106 m3 submarine scar area whereas block deposits are present in both the subaerial and submerged regions a detailed geological reconstruction of the slope was obtained and a geomechanical characterisation of the metamorphic rocks involved in the landslide was performed based on this reconstruction intense jointing conditions of the rock mass can be related to main fault zones parallel and normally oriented to the actual coastline an engineering geology model of the landslide was devised according to an equivalent continuum approach to evaluate both stiffness and strength of the rock mass within the slope a finite difference stress strain numerical modelling of the scilla landslide was performed under dynamic conditions to back analyse the landslide trigger as well as local seismic amplifications this modelling gave new insights into the physical interactions between seismic inputs and slopes as it demonstrated the fundamental role played by i the interaction between the seismic input and geological setting of unsheared rock slopes i e without preexisting landslide masses ii cumulated strain effects due to seismic sequences and iii jointing conditions of the involved rock masses responsible for the seismic amplification of the landslide prone volume driving it toward failure conditions

tectonic evolution of arcuate mountain belts on top of a retreating subduction slab the example of the calabrian arc 1 in this paper new paleomagnetic results from the calabrian arc are presented together with a critical review of all paleomagnetic data collected in the last decades in southern italy our study is focused on the upper miocene to middle pleistocene deposits of the crati extensional basin a sector of the arc where an abrupt change in the sense of paleomagnetic rotations is observed paleomagnetic data indicate that the crati basin underwent a uniform clockwise cw rotation of about 15 20 in its central and southern part whereas the northern sector is organized in small scale fault bounded blocks which rotated independently we interpret this pattern of deformation as the evidence of the complex nature of this area which represents the boundary between two domains characterized by opposite rotations the southern apennines which rotated counterclockwise and the calabria and sicily which rotated cw integrating these new paleomagnetic data with paleomagnetic data from southern italy we reconstruct the history of paleomagnetic rotations through time paleomagnetic rotations highlight the peculiarity of the formation of the calabrian arc curvature and imply that either an oroclinal bending model or a progressive arc model cannot be simply applied to the calabrian arc formation we describe a realistic tectonic geodynamic model where the progressive curvature of the calabrian arc is framed within the space time evolution of the ionian subduction system

peperite a review of magma sediment mingling the study of peperite is important for understanding magma water interaction and explosive hydrovolcanic hazards this paper reviews the processes and products of peperite genesis peperite is common in arc related and other volcano sedimentary sequences where it can be voluminous and dispersed widely from the parent intrusions it also occurs in phreatomagmatic vent filling deposits and along contacts between sediment and intrusions lavas and hot volcaniclastic deposits in many environments peperite can often be described on the basis of juvenile clast morphology as blocky or fluidal but other shapes occur and mixtures of different clast shapes are also found magma is dominantly fragmented by quenching hydromagmatic explosions magma sediment density contrasts and mechanical stress as a consequence of inflation or movement of magma or lava magma fragmentation by fluid fluid shearing and surface tension effects is probably also important in fluidal peperite fluidisation of host sediment hydromagmatic explosions forceful intrusion of magma and sediment liquefaction and shear liquification are probably the most important mechanisms by which juvenile clasts and host sediment are mingled and dispersed factors which could influence fragmentation and mingling processes include magma host sediment and peperite rheologies magma injection velocity volatile content of magma total volumes of magma and sediment involved total volume of pore water heated presence or absence of shock waves confining pressure and the nature of local and regional stress fields sediment rheology may be affected by dewatering compaction cementation vesiculation fracturing fragmentation fluidisation liquefaction shear liquification and melting during magma intrusion and peperite formation the presence of peperite intraclasts within peperite and single juvenile clasts with both sub planar and fluidal margins imply that peperite formation can be a multi stage process that varies both spatially and temporally mingling of juvenile clast populations formed under different thermal and mechanical conditions complicates the interpretation of magma fragmentation and mingling mechanisms

experimental soft sediment deformation structures formed by the liquefaction of unconsolidated sands and some ancient examples the effects of liquefaction in saturated sand bodies under a variety of driving forces are described from shaking table experiments and structures from the geological record are presented which are analogous to the experimental structures the collapse of sloping heaps of cross bedded sand under a gravitational body force generates low angle essentially uncontorted stratification a basal zone of shearing may be present with steepened and folded foresets stretching of foresets may be accommodated on normal faults and bottomsets may be contorted into inclined folds in natural systems the substrate may also liquefy causing deformation driven by an unevenly distributed confining load stratification in the surface bedform is flattened and stratification in the substratum contorted experiments failed to produce relative displacement at the interface between stacked sand bodies liquefaction of gravitationally unstable systems in sands generates load structures comparable to those from sand mud systems recumbent folded deformed cross bedding is formed by current shear over a liquefied bed as has been inferred from field and theoretical analyses shear of nonliquefied sand forms angular folds other deformation mechanisms such as fluidization or seepage may generate structures similar to all of these local water escape structures driven by fluidization occur in the upper parts of some liquefied sand bodies they include cusps sand volcanoes and clastic dykes transient cavities formed in some experiments and seemed to be preserved as breached cusps although the experiments tried to isolate individual driving forces driving forces may operate together and there may be a continuum between deformation driven by water escape and deformation driven by loading different structures from those described here may form where liquefaction develops in a buried layer as opposed to at the sediment surface

products of an effusive subglacial rhyolite eruption blahnukur torfajokull iceland we present field observations from blahnukur a small volume 400 m thick lithofacies associations attest to complex patterns of volcano ice interaction erosive channels at the base of the subglacial sequence are filled by both eruption derived material and subglacial till which show evidence for deposition by flowing meltwater this suggests that meltwater was able to drain away from the vent area during the eruption much of the subglacial volcanic deposits consist of conical to irregularly shaped lava lobes typically 5 10 m long set in poorly sorted breccias with an ash grade matrix a gradational lavabreccia contact at the base of lava lobes represents a fossilised fragmentation interface driven by magma water interaction as the lava flowed over poorly consolidated waterlogged debris sets of columnar joints on the upper surfaces of lobes are interpreted as ice contact features the morphology of the lobes suggests that they chilled within conically shaped subglacial cavities 2 5 m high avalanche deposits mantling the flanks of blahnukur appear to have been generated by the collapse of lava lobes and surrounding breccia a variety of deposit characteristics suggests that this occurred both prior to and after quenching of the lava lobes collapse events may have occurred when the supporting ice walls were melted back from around the cooling lava lobes and breccias much larger lava flows were emplaced in the latter stages of the eruption columnar joint patterns suggest that these flowed and chilled within subglacial cavities 20 m high and 100 200 m in length there is little evidence for magma water interaction at lava flow margins which suggests that these larger cavities were drained of meltwater as rhyolite magma rose to the base of the glacier the nature of the subglacial cavity system played an important role in governing the style of eruption and the volcanic facies generated we present evidence that the cavity system evolved during the eruption reflecting variations in both melting rate and edifice growth that are best explained by a fluctuating eruption rate

quaternary transfer faulting and belt front deformation at pakuashan western taiwan the arcuate pakuashan anticline is located in the outermost front units of the western foothills of taiwan this oblique feature of the deformation front is investigated in terms of combined morphostructural analysis based on imagery and digital elevation model as well as microtectonic analysis of fault slip data a subsurface structural study based on available seismic and well data was also carried out resulting in improved mapping of the neogene series and associated structures this mapping allowed construction of several along strike cross sections such combined analyses revealed that the transverse pakuashan fold is located above a major transfer fault zone this active fault zone accommodates differential westward propagation of thrust units its kinematic evolution is principally controlled by the geometry of the foreland peikang high behaving as a buttress for the west verging thrust sheets a preliminary analytical model of the oblique thrusting at pakuashan is based on similar cases studied by apotria et al 1992 it involves quaternary transfer faulting accommodating the motion of connected thrust sheets moving over oblique ramps linked to a preexisting major basement boundary the hinge fault of the peikang high this analytical modeling accounts for the occurrence of local extension at the intersection of oblique ramps in the southern pakuashan numerous complementary structural and tectonic evidences led us to establish a complete deformation model involving local rotation in southern pakuashan which caused differential slips in northern pakuashan resulting in tear faulting these evidences include large extension at the intersection of oblique ramps distributed extension in the transverse zone regional wrench deformation absence of major reorientation of local stress inside the transverse zone along strike variation of structural styles coupled with low to high uplift rate from the northern to the southern part of the pakuashan fold thus a synthetic reconstruction of the pakua transfer fault zone evolution is proposed as a typical example of active transfer faulting evolving gradually from a primary tear fault with a slight curvature to the left lateral tear fault or transfer fault that offsets two distinct frontal thrust and fold sheets

peperite formed by lava flows over sediments an example from the central parana continental flood basalts brazil pahoehoe flows interbedded with sediments have been identified in the superior portion of parana continental flood basalts pcfb west portion of parana state southern brazil in the study area peperites are generated by the interaction between lava flows and wet lacustrine sediments silt and clay evidence that the sediments were unconsolidated or poorly consolidated and wet when the lava flowed over them includes vesiculated sediment sediment in vesicles and fractures in lava flow and in juvenile clasts in the peperite and soft sediment deformation hydrodynamic mingling of lava and wet sediments coarse mingling is predominant and volcanic rocks and textures related to explosive phase of molten fuel coolant interaction mfci are not observed in study area locally centimeter sized areas display direct contact between ash sized juvenile clasts and sediments formed by the collapse of a vapor film the textures of fluidal peperites in the central pcfb indicate that the relevant factors that led to a coarse mingling between lava sediment are 1 lava properties low viscosity 2 fine grained unconsolidated or poorly consolidated wet sediment and 3 a single episode of interaction between lava flows and sediment

lateral spreading processes in mountain ranges insights from an analogue modelling experiment abstract the results of a study on gravitational induced lateral spreading phenomena are here reported the lateral spreading processes are widely represented in the italian apennines due to the widespread overlapping of stiff rock masses on more ductile ones the stress strain evolution of these processes was investigated by combining an analogical and a numerical modelling approach the analogue modelling reproduced the evolution of a carbonate ridge thrust over a clayey flysch with reference to the case study of mt roccatagliata mt sant angelo ridge the rock mass juxtaposition was reproduced in a laboratory experiment by overlapping a brittle concrete on a viscous ductile material these materials were selected with rheological properties physically scaled with respect to the natural rock mass prototypes the spreading phenomenon was modelled by opening horizontal panels in sequential stages and monitoring the resulting stresses within the ductile material during the experiment a stress strain modelling was also performed by an fdm numerical solution this modelling replied the laboratory experiment by testing the use of different rheological constitutive laws the resulting stresses and morphological evolutions are comparable with the analogical laboratory experiment only if a time dependent rheological behaviour is assumed for the ductile material the results show that lateral spreading processes can be properly investigated by combining analogue and numerical modelling techniques which take into account the viscous plastic behaviour of the used materials

a numerical analysis of rock creep induced slide a case study from jiweishan mountain china landslides and slope failures are very common phenomena in hilly regions southwestern china these are hazardous because of the accompanying progressive movement of the slope forming material to minimize the landslide effects slope failure analysis and stabilization require in depth understanding of the process that governs the behavior of the slope the present paper first briefly describes a three dimensional numerical brittle creep model for rock the model accounts for material heterogeneity through a stochastic local failure stress field and local material degradation using an exponential material softening law then a case study of the jiweishan rockslide that occurred in china is numerically investigated considering the effect of the mining activity numerical simulations visualize the entire process of the jiweishan rockslide from the fracture initiation propagation and coalescence the distribution and evolution of associated stress and deformation field during the slide are also presented numerical simulations show that the underground mining excavations have remarkably negative effect on the stability of the rock slope which is one of the important triggering factors of the rockslide moreover it is possible to take some precautions for the unstable failure of rock mass by monitoring acoustic emission ae events or microseismicities since the occurrence of clusters of ae events prior to the final unstable rockslide the results are of general interest because they can be applied to the investigation of time dependent instability in rock masses to the mitigation of associated rock hazards in rock engineering and even to a better understanding of the seismic activities in geological and geophysical phenomena occurring in the earth s crust

interpreting quaternary uplift rates at the mendocino triple junction northern california from uplifted marine terraces analysis of the altitudinal spacing of 14 flights of marine terraces indicates a spatial pattern of varying uplift rates that agrees with that determined from previously dated terraces for the past 3 81 ka and temporal changes in uplift rates from 1 m ka to 3 5 m ka that may reflect response to changes in tectonic regime during passage of the mendocino triple junction mtj a possible mechanism for regional uplift is growth of a slab window south of the mtj the region of most rapid uplift is 25 43 km south of the mtj immediately south of the northern boundary of the slab window the coastline is tilted upward to the south in the region directly above the southern edge of the subducted gorda plate at point delgada 55 km south of the present mtj where the northern edge of the slab window passes approximately 300 ka uplift rates have been 1 2 m ka for at least 330 ka more than 1 4 m y after passage of the southern edge of the subducted slab at the mendocino coast uplift rates have been less than 0 4 m ka for at least 330 ka

prolonged seismically induced erosion and the mass balance of a large earthquake large earthquakes deform the earth s surface and drive topographic growth in the frontal zones of mountain belts they also induce widespread mass wasting reducing relief the sum of these two opposing effects is unknown using a time series of landslide maps and suspended sediment transport data we show that the mw7 6 chi chi earthquake in taiwan was followed by a period of enhanced mass wasting and fluvial sediment evacuation peaking at more than five times the background rate and returning progressively to pre earthquake levels in about six years therefore it is now possible to calculate the mass balance and topographic effect of the earthquake the choshui river has removed sediment representing more than 30 of the added rock mass from the epicentral area this has resulted in a reduction of surface uplift by up to 0 25 m or 35 of local elevation change and a reduction of the area where the chi chi earthquake has built topography for other large earthquakes erosion may evolve in similar predictable ways reducing the efficiency of mountain building in fold and thrust belts and the topographic expression of seismogenic faults prolonging the risk of triggered processes and impeding economic regeneration of epicentral areas

late holocene emergence in calabria italy abstract a field survey along the coasts of calabria has found little evidence of holocene emergence the greatest being no more than 1 0 1 5 m in elevation a former shoreline a thick crust of calcareous algae in growth position at about 0 6 m capping an elevated beachrock slab was dated 2990 60 yr b p this emergence is recent if compared to the time of the climatic optimum and relatively slight if late pleistocene uplift rates which in some cases exceed 1 mm yr are considered this apparent discrepancy can be explained by taking into account glacio and hydroisostatic effects of the last glaciation which have produced subsidence at decreasing rates during the late holocene in a wide area around the former scandinavian ice sheet which includes most of the mediterranean according to isostatic modelling the average subsidence rate during the last 6000 5000 years was between 0 4 and 1 mm yr near the coasts of calabria if global sea level changes can be neglected it is only when the subsidence rate of glaciohydro isostatic origin became slower than the local uplift that emergence at a slower rate than that of the tectonic uplift trend could have begun such emergence is therefore a recent phenomenon in the holocene and its rate is still much slower than that of tectonic uplift predominating in calabria over a longer time scale

fluidization of wet sediments during the emplacement and cooling of various igneous bodies during the emplacement and cooling of igneous bodies fluidization of wet sediment by water vapour may occur by heating or by pressure relief during the opening of fractures momentary fluidization causes sediment reconstitution and local transport continuous fluidization can result in substantial sediment displacement theoretical considerations show that fluidization due to heating is not likely to occur at depths where pressure is much greater than 312 bars studies of the emplacement of sills of andesite ayrshire fluid rhyolite ramsey island and viscous rhyolite moelwyn hills recognize a wide range of phenomena attributable to wet sediment fluidization and in places modify existing interpretations the transgressive bases of the subaqueously welded ash flow tuffs of the capel curig volcanic formation are consistent with emplacement attended by fluidization of the subjacent sediment evidently fluidization is a means by which large volumes of wet sediment can be replaced by igneous material with minimal disturbance of the remaining host also fluidization can result in exceptionally complex contact relationships between sedimentary host and intrusive rocks and can cause fractures formed during cooling to be thoroughly pervaded by sediment fluidization is commonly associated with the formation of peperites

extensive soft sediment deformation and peperite formation at the base of a rhyolite lava owyhee mountains sw idaho usa in the northern owyhee mountains sw idaho a 200 m thick flow of the miocene jump creek rhyolite was erupted on to a sequence of tuffs lapilli tuffs breccias and lacustrine siltstones of the sucker creek formation the rhyolite lava flowed over steep palaeotopography resulting in the forceful emplacement of lava into poorly consolidated sediments the lava invaded this sequence liquefying and mobilising the sediment propagating sediment subvertically in large metre scale fluidal diapirs and sediment injectites the heat and the overlying pressure of the thick jump creek rhyolite extensively liquefied and mobilised the sediment resulting in the homogenization of the sucker creek formation units and the formation of metre scale loading structures simple and pendulous load casts detached pseudonodules density contrasts between the semi molten rhyolite and liquefied sediment produced highly fluidal rayleigh taylor structures local fluidisation formed peperite at the margins of the lava and elutriation structures in the disrupted sediment the result is a 30 40 m zone beneath the rhyolite lava of extremely deformed stratigraphy brittle failure and folding is recorded in more consolidated sediments indicating a differential response to loading due to the consolidation state of the sediments the lava sediment interaction is interpreted as being a function of 1 the poorly consolidated nature of the sediments 2 the thickness and heat retention of the rhyolite lava 3 the density contrast between the lava and the sediment and 4 the forceful emplacement of the lava this study demonstrates how large lava bodies have the potential to extensively disrupt sediments and form significant lateral and vertical discontinuities that complicate volcanic facies architecture

deformation of the 125 ka marine terrace in italy tectonic implications in peninsular italy marine terraces and shorelines created during oxygenisotope substage 5e known historically as the tyrrhenian highstand provide a reliable and homogeneous datum of vertical motions during the past 125 000 years published accounts of 121 locations on the tyrrhenian inner edge were reinterpreted and used to calculate both local and regional uplift rates the data show arching of southern italy between the tyrrhenian and the adriatic coasts and of the calabrian arc between the sangineto and the longi taormina tectonic lineaments at rates of up to 1 2 mm yr for the past 125 ka they also suggest that the present configuration of the southern apennines is the product of post early pleistocene regional uplift superimposed on tortonian to early pleistocene thrusting uplift patterns are characterised by different wavelength in different geodynamic settings suggesting a close link with the depth of the causative tectonic sources

structures within large volume rhyolite lava flows of the devonian comerong volcanics southeastern australia and the pleistocene ngongotaha lava dome new zealand abstract many rhyolitic units within the late devonian comerong volcanics erupted as lava flows and domes some up to 18 km long and 350 m thick the textural and structural characteristics that distinguish the flows and domes as lava rather than rheomorphic ignimbrite include unbroken phenocrysts zones of autobrecciation and finely developed flow layering with individual layers continuous for several metres the flow layering is typically contorted into isoclinal folds with forms suggesting fluidal deformation and is interlayered with and gradational into restricted zones of pumice rich lapilli tuff and zones of lenticulite breccia the lenticulite breccia comprises discontinuous lenticular rhyolite fragments the long axes of which define a foliation parallel to flow layering lenticles in the breccia vary from elongate layers up to 1 m long and several millimetres thick to short fragments less than 10 cm long and several centimetres wide similar zones of lenticulite breccia consisting of glassy lenticular clasts in a devitrified spherulitic matrix of cristobalite and albite exist within the late pleistocene ngongotaha dome near rotorua new zealand the lenticulite breccia is considered to form by aqueous diffusion and selective devitrification of the rhyolite along anastomosing fluid paths and to be modified by mechanical fracturing of the lava in a zone of high shear stress geochemically the rhyolites are high si and a type with high zr and y contents indicating that they formed from high temperature relatively anhydrous f rich melts a type granitoids crop out intermittently along the length of and adjacent to the volcanic complex and are comagmatic with the rhyolite the high temperature low bubble and phenocryst content and a high eruptive rate of the rhyolite likely resulted in a low effective viscosity and extensive flow units

extended cooling and viscous flow of large hot rhyolite lavas implications of numerical modeling results abstract a common misconception about rhyolite lava flows is that they cannot advance far from their vents and are constrained to be small due to their high viscosities although a high viscosity lava will indeed flow quite slowly it may advance a great distance if the lava efficiently retains heat and thus mobility and if the available magma supply is large to evaluate this possibility a finite difference numerical model was used to determine the rate of heat loss from units interpreted to be large rhyolite lavas cooling of such 100 300 m thick units is very slow and is further retarded by a vesicular carapace and by evolution of latent heat thermal history alone suggests that large thick lava flows could remain active for several decades to constrain the duration of flow advance of these units their inferred apparent viscosities are compared with those of active lava flows mean flow velocity of some large rhyolites in southwestern idaho usa was estimated based on the observation that the units must still have been advancing by viscous flow at the start of spherulite crystallization indicating perhaps a 10 to 18 year flow duration based on studies of obsidian dome california mean flow velocities would have been roughly 0 59 to 2 5 km yr and calculated average apparent viscosities of the flows ranged from 1 8 to 3 6 orders of magnitude greater than the viscosity of the lava itself this relationship also holds for active andesite and basaltic andesite block lava flows which have apparent viscosities 2 7 to 4 orders of magnitude greater than lava viscosities this implies that large rhyolites may indeed have been emplaced in the same manner as less silicic block lavas and that long distance viscous flow is not unrealistic for rhyolite lavas a good example of a large volume lava is the 15 km 3 rhyolite of the badlands sw idaho where vent relations show that lava effused from a fissure and advanced up to 9 km more extensive rhyolites could also be emplaced solely by effusion extended flow of these lavas may lead to the remelting and removal of basal crumble breccias and to the formation of welded shard textures in their margins both processes tending to obscure the lava flow origin of the units the great dimensions of lava like rhyolitic units with volumes of 10 to at least 200 km 3 are not a sufficient reason to assume they erupted as ignimbrites

topography of the calabria subduction zone southern italy clues for the origin of mt etna 1 calabria represents an ideal site to analyze the topography of a subduction zone as it is located on top of a narrow active wadati benioff zone and shows evidence of rapid uplift we analyzed a pattern of surface deformation using elevation data with different filters and showed the existence of a long wavelength 100 km relatively positive topographic signal at the slab edges the elevation of mis 5 5 stage marine terraces supports this pattern although the record is incomplete and partly masked by the variable denudation rate we performed structural analyses along the major active or recently reactivated normal faults showing that the extensional direction varies along the calabrian arc and laterally switches from arc normal within the active portion of the slab to arc oblique or even arc parallel along the northern and southern slab edges this surface deformation pattern was compared with a recent high resolution p wave tomographic model showing that the high seismic velocity anomaly is continuous only within the active wadati benioff zone whereas the northern and southwestern sides are marked by low velocity anomalies suggesting that large scale topographic bulges volcanism and uplift could have been produced by mantle upwelling we present numerical simulations to visualize the three dimensional mantle circulation around a narrow retreating slab ideally similar to the one presently subducting beneath calabria we emphasize that mantle upwelling and surface deformation are expected at the edges of the slab where return flows may eventually drive decompression melting and the mount etna volcanism

mass wasting triggered by the 2008 wenchuan earthquake is greater than orogenic growth shallow earthquakes lead to the uplift of mountain ranges but also trigger landslides that remove mass an analysis of the 2008 wenshuan earthquake suggests that more material was removed from the orogen by widespread landslides than was added by coseismic uplift

groundmass crystallisation and cooling rates of lava like ignimbrites the grey s landing ignimbrite southern idaho usa constraining magmatic and eruptive processes is key to understanding how volcanoes operate however reconstructing eruptive and pre eruptive processes requires the ability to see through any post eruptive modification of the deposit the well preserved grey s landing ignimbrite from the central snake river plain provides an opportunity to systematically investigate the post eruptive processes occurring through a single deposit sheet despite overall compositional homogeneity in both bulk and glass compositions the grey s landing ignimbrite does preserve differences in the abundance of li in plagioclase crystals which are strongly associated with the host lithology li abundances in plagioclase from the quickly cooled upper and basal vitrophyres are typically low average 5 ppm n 262 while plagioclase from the microcrystalline interior of the deposit has higher li contents average 33 ppm n 773 given that no other trace elemental parameter in plagioclase varies we interpret the variability in li to reflect a post depositional process groundmass crystallisation of a rhyolite like grey s landing requires 50 crystallisation of sanidine and variable amounts of a silica rich phase quartz tridymite cristobalite and plagioclase to satisfy mass balance we suggest the low affinity of li for sanidine causes migration of groundmass li into plagioclase during crystallisation even within the microcrystalline interior of the deposit the morphology of the groundmass varies the more marginal finer grained regions are dominated by cristobalite as the sio2 rich phase while tridymite and quartz are additionally found in the more slowly cooled coarser grained portions of thick sections of the ignimbrite numerical models of cooling and crystallisation tested against field observations indicate that the groundmass crystallisation occurred relatively rapidly following emplacement a maximum of a few years where the ignimbrite is thickest these numerical models also illustrate that the time at which the potential for rheomorphism ceases either the ignimbrite is a solid glass or 50 crystalline is diachronous across the deposit

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

chilling and brecciation of a devonian rhyolite sill intruded into wet sediments northern sierra nevada california localized pockets of peperite breccia occur near the base of a well exposed hypabyssal rhyolite sill within the upper devonian volcanic sequence of the northern sierra nevada the peperites resulted from chilling fragmentation and commingling of rhyolite with wet poorly consolidated sediment zones of hyaloclastite breccia extend into the sill above the peperites and represent areas where chilled rhyolite underwent fragmentation but was not intermixed with sediment a dense spherulitic intergrowth developed rapidly within the chilled rhyolite immediately prior to its fragmentation formation of this quench texture probably reflects a reduction in viscosity of the magma due to retention of volatiles in the melt under conditions of relatively high confining pressure

high resolution morpho bathymetric imaging of the messina strait southern italy new insights on the 1908 earthquake and tsunami the 28 december 1908 reggio calabria and messina earthquake named after the two most damaged cities on the coasts of messina strait was one of the strongest mw 7 1 ever to occur in italy and was also followed by a tsunami that severely impacted the coasts of the strait although there is general agreement that its epicentre is located offshore in the messina strait the source fault has never been detected a century long question is therefore pending on the source of both the 1908 earthquake and tsunami within the ongoing debate on this subject little attention has been given so far to morphological insights from high resolution bathymetric multibeam data particularly as regarding the evidence of faults affecting the seafloor and the question of whether a submarine landslide may had been the cause of the tsunami we aim to address this issue by presenting the results of a morpho bathymetric study in the messina strait and surroundings investigated by means of high resolution swath bathymetry the primary morpho structural feature in this area is the axial channel of the messina canyon towards which flow several tributary canyons that incise the steep continental slope on the calabrian and sicilian margins these canyons carve deeply into a very narrow almost lacking continental shelf and merge laterally forming a continuous erosional margin rimming the messina strait this giant composite canyon environment is the locus of intense erosional and depositional processes that superimpose on active tectonic deformation resulting in a complex geomorphology that hinders the distinction between tectonic and sedimentary features seafloor ruptures that may be linked to fault systems compatible with the source of the 1908 earthquake and tsunami could not be identified based from our morpho bathymetric analysis however we provide evidence of several geomorphic features indicative of tectonic deformation in the messina strait define the presence and distribution of submarine landslides and evaluate their possible role as tsunami sources

processes of magma wet sediment interaction in a large scale jurassic andesitic peperite complex northern sierra nevada california the middle jurassic tuttle lake formation in the northern sierra nevada california comprises a thick volcaniclastic sequence deposited in a submarine island arc setting and penetrated by numerous related hypabyssal intrusions a composite andesite diorite intrusive complex 4 5 km long and 1 5 km thick was emplaced while the host tuttle lake sediments were still wet and unconsolidated large parts of the intrusive complex consist of peperite formed where andesitic magma intruded and intermixed with tuff lapilli tuff and tuff breccia the southern half of the complex consists of augite phyric andesite containing peperite in numerous small isolated pockets and in more extensive laterally continuous zones the peperites comprise three main types recognized previously in other peperite studies fluidal peperite consists of small 30 cm closely spaced at least partly interconnected globular to amoeboid andesite bodies enclosed by tuff this peperite type developed during intrusion of magma into fine grained wet sediment along unstable interfaces and fluidization of the sediment facilitated development of complex intrusive geometries blocky peperite and mixed blocky and fluidal peperite formed where magma intruded coarser sediment and underwent variable degrees of brittle fragmentation by quenching and dynamic stressing of rigid margins possibly aided by small steam explosions the northern half of the intrusive complex consists predominantly of a different type of peperite in which decimetre scale plagioclase phyric andesite clasts with ellipsoidal elongate or angular polyhedral shapes are closely packed to widely dispersed within disrupted host sediment textural features suggest the andesite clasts were derived from conduits through which magma was flowing and preserved remnants of the conduits are represented by elongate sinuous bodies up to 30 m or more in length disruption and dispersal of the andesite clasts are inferred to have occurred at least partly by steam explosions that ripped apart a network of interconnected feeder conduits penetrating the host sediments closely packed peperite is present adjacent to mappable intrusions of coherent andesite and along the margin of a large mass of coarse grained diorite these coherent intrusions are considered to be major feeders for this part of the complex examples of magma wet sediment interaction similar in scale to the extensive peperites described here occur elsewhere in ancient island arc strata in the northern sierra nevada based on these and other published examples large scale peperites probably are more common than generally realized and are likely to be important in settings where thick sediment sequences accumulate during active volcanism careful mapping in well exposed terrains may be required to recognize large scale peperite complexes of this type

from collisional to rifted basins an example from the southern calabrian arc italy structural interpretation of available geological and geophysical data carried out along a regional transect extending across the southern calabrian arc from the tyrrhenian margins to the ionian off shore demonstrates that a complex interplay between compressional and extensional processes has controlled the evolution of upper miocene pleistocene sedimentary basins developing in this region our data indicate that an upper miocene lower pliocene succession outcropping in the southern calabrian arc represents the infilling of perched basins developed between crystalline basement thrust sheets a similar tectonic pattern characterises the plio pleistocene basins occurring on the frontal part of the arc in the ionian off shore upper pliocene pleistocene sediments outcropping along the tyrrhenian side of the arc reveal that they in fact represent the infilling of extension related basins time space migration of compressional and extensional related sedimentary basins can be explained as the result of different tectonic processes developing on the upper plate as a result of the underplating of the ionian domain beneath the calabrian block in this framework upper miocene lower pliocene and upper pliocene pleistocene perched basins represent therefore fore arc basins developed on the frontal accretionary wedge and or on the hangingwall buttress of the arc during its southeastwards migration late pliocene early pleistocene extensional tectonics occurring along the tyrrhenian side of the arc may indeed be related to accommodation processes which characterised the rear of the wedge to maintain a stable geometry as a result of the underplating of the ionian crust

stratigraphic and structural evolution of the middle miocene synvolcanic oregon idaho graben the oregon idaho graben is a newly identified north south trending synvolcanic graben in southeastern oregon and southwestern idaho within the middle miocene backarc rift system that extends 1100 km from southern nevada to southeastern washington the graben formed along the western margin of the north american craton shortly after the largest volumes of tholeiitic flood basalt erupted columbia river basalt group steens pueblo basalt basalt of malheur gorge basalt and latite unit of ekren et al 1981 1 rhyolite flows and ash flow tuffs 16 1 14 0 ma erupted from northeastern oregon dooley volcanics to northern nevada mcdermitt volcanic field shortly after the flood basalt was emplaced subsidence of the oregon idaho graben 15 5 15 3 ma coincides with eruption of rhyolite flows and caldera related ash flow tuffs from vents along the margins and within the graben mafic and silicic intragraben volcanism accompanied sedimentation from about 15 3 to 10 5 ma sedimentary and volcanic rocks from extrabasinal sources especially southwestern idaho were introduced periodically after initial subsidence the evolution of the oregon idaho graben is divided into three stages stage 1 15 3 14 3 ma followed intragraben caldera collapse and was marked by deposition of fluvial and lacustrine sediment across the graben stage 2 14 3 12 6 ma movement on intragraben fault zones divided the graben into distinct subbasins and marked the onset of calc alkalic volcanism fine grained tuffaceous sediment derived from glassy rhyolite and pyroclastic deposits and basalt tuff cones interbedded with rhyolite ash and lapilli fall deposits and locally erupted basalt hydrovolcanic deposits predominated during synvolcanic subsidence synsedimentary hot spring alteration and precious metals mineralization of graben fill were controlled by the same intragraben fault zones that served as magmatic conduits during stage 3 12 6 10 5 ma the subbasins were filled and graben wide fluviatile and lacustrine sedimentation resumed at about the same time renewed rhyolitic volcanism occurred on both flanks and tholeiitic volcanism resumed within the oregon idaho graben subsidence in the oregon idaho graben ceased as west northwest striking faults related to the formation of the western snake river plain became active 1 ref 28

recent and active tectonics in the calabrian arc southern italy normal faulting which has developed since the middle pleistocene with an overall ese wnw extension is the dominant mode of deformation which has characterized the calabrian arc up to the present quaternary normal faults extend for a total length of about 180 km along the inner side of the arc the different normal fault segments which during the pleistocene controlled the evolution of the main marine sedimentary basins are varying in length from 10 to 20 km and have fault escarpments showing a very young morphology which define the fronts of the major mountain ranges of the arc the morphological features of the fault escarpments suggest slip rates of 0 8 1 1 mm yr for the last 700 k y and values of 0 6 0 9 mm yr for the last 120 k y indicating a uniform rate of faulting since the middle pleistocene crustal seismicity and the mesoseismic areas of historical large events 6 5 m 7 1 which occurred in the calabrian arc are located within a narrow belt along the hanging walls of the quaternary normal fault segments this suggests that the normal faults which dissect the inner side of the calabrian arc may be seismically active

mountain slope deformations along thrust fronts in jointed limestone an equivalent continuum modelling approach abstract engineering geology studies of natural slope stability have rarely relied on continuum modelling of discontinuous rock mass or the use of conventional constitutive laws in fem or fdm codes the paper proposes the use of numerical modelling based on a practical equivalent continuum approach for analysing the deep seated gravitational slope deformations dsgsd observed in the thrust front area of the lepini mountains italian apennines the dsgsd phenomena affect a carbonate ridge close to the villages of san sebastiano and sgurgola inducing a significant risk this study began with the construction of engineering geology sections by distinguishing lithotechnical units on the basis of both site and geomechanical parameters considering geological and geomorphological field evidence the numerical simulations validated the assumed kinematic model of the slope these simulations aimed at estimating the instability of the affected rock masses by identifying a critical mass beyond which ongoing deformations become morphologically evident on the involved slope a ratio of the weight of a critical mass which is the minimum mass required to produce some geomorphological evidence to the weight of the mass involved in the gravitational slope deformations was calculated in order to quantitatively assess the evolutionary stage of the ongoing deformations the calculated ratio demonstrates a more advanced evolutionary stage for the slope sector near the village of sgurgola due to its particular geological setting than the one near the village of san sebastiano

recent deformations and the seismogenic source in the messina strait southern italy abstract the relationships between mechanisms and mode of faulting in pliocene and pleistocene times and seismic release are the basis for an interpretation of the growth of deformation energy in the messina strait the major fault systems trending in ne sw nw se and e w directions divide blocks subjected to high mobility in concurrence with greater uplifting of the calabrian side with respect to sicily across the two sides of the strait as revealed by structural analyses the tectonic features of the area are dominated by normal faulting many synsedimentary features seem to indicate repeated and intermittent pulses of high velocity fault slippage possibly related to seismic shaking when considering the seismic record it seems that the strongest shocks are generated by preferential strain accumulations along the nne ssw fault systems from a geological standpoint it seems clear that the largest events may be alternately related to either the nne ssw e w or nw se fault systems which dissect an extremely cataclastic upper crust the recent deformations of the messina strait can be related to the large scale processes induced by the overthrusting of the thinned tyrrhenian crust over the thickened african crust as suggested by seismic refraction profiles along the inner margin of the calabrian arc the deep deformation mechanisms are reflected by contrasting vertical movements between a stretched and downfaulted tyrrhenian domain and an uplifted chain with resulting large strain accumulations and seismic failure in the brittle upper crust

time dependent evolution of rock slopes by a multi modelling approach abstract this paper presents a multi modelling approach that incorporates contributions from morpho evolutionary modelling detailed engineering geological modelling and time dependent stress strain numerical modelling to analyse the rheological evolution of a river valley slope over approximately 10 2 kyr the slope is located in a transient tectonically active landscape in southwestern tyrrhenian calabria italy where gravitational processes drive failures in rock slopes constraints on the valley profile development were provided by a morpho evolutionary model based on the correlation of marine and river strath terraces rock mass classes were identified through geomechanical parameters that were derived from engineering geological surveys and outputs of a multi sensor slope monitoring system the rock mass classes were associated to lithotechnical units to obtain a high resolution engineering geological model along a cross section of the valley time dependent stress strain numerical modelling reproduced the main morpho evolutionary stages of the valley slopes the findings demonstrate that a complex combination of eustatism uplift and mass rock creep mrc deformations can lead to first time failures of rock slopes when unstable conditions are encountered up to the generation of stress controlled shear zones the multi modelling approach enabled us to determine that such complex combinations may have been sufficient for the first time failure of the s giovanni slope at approximately 140 ka mis 7 even without invoking any trigger conversely further reactivations of the landslide must be related to triggers such as earthquakes rainfall and anthropogenic activities this failure involved a portion of the slope where a plasticity zone resulted from mass rock creep that evolved with a maximum strain rate of 40 per thousand years after the formation of a river strath terrace this study demonstrates that the multi modelling approach presented herein is a useful tool for estimating the progressive development of slope failures because it can highlight time dependent continuous deformations as the major processes that drive rocky slopes to failure this type of approach can be devoted to the best selection of risk mitigation strategies with respect to both human life and anthropic infrastructure

holocene activity of the scilla fault southern calabria insights from coastal morphological and structural investigations abstract integration of on land and offshore geomorphological and structural investigations coupled to extensive radiometric dating of co seismically uplifted holocene beaches allows characterization of the geometry kinematics and seismotectonics of the scilla fault which borders the eastern side of the messina strait in calabria southern italy this region has been struck by destructive historical earthquakes but knowledge of geologically based source parameters for active faults is relatively poor particularly for those running mostly offshore as the scilla fault does the 30 km long normal fault may be divided into three segments of 10 km individual length with the central and southern segments split in at least two strands the central and northern segments are submerged and in this area marine geophysical data indicate a youthful morphology and locally evidence for active faulting the on land strand of the western segment displaces marine terraces of the last interglacial 124 to 83 ka but seismic reflection profiles suggest a full quaternary activity structural data collected on bedrock faults exposed along the on land segment provide evidence for normal slip and nw se extension which is consistent with focal mechanisms of large earthquakes and gps velocity fields in the region detailed mapping of raised holocene marine deposits exposed at the coastline straddling of the northern and central segments supplies evidence for two co seismic displacements at 1 9 and 3 5 ka and a possible previous event at 5 ka co seismic displacements show a consistent site value and pattern of along strike variation suggestive of characteristic type behaviour for the fault the 1 5 2 0 m average co seismic slips during these events document me 6 9 7 0 earthquakes with 1 6 1 7 ka recurrence time because hanging wall subsidence cannot be included into slip magnitude computation these slips reflect footwall uplift and represent minimum average estimates the palaeoseismological record based on the palaeo shorelines suggests that the last rupture on the scilla fault during the february 6 1783 mw 5 9 6 3 earthquake was at the expected time but it may have not entirely released the loaded stress since the last great event at 1 9 ka comparison of the estimated co seismic extension rate based on the holocene shoreline record with available gps velocities indicates that the scilla fault accounts for at least 15 20 of the contemporary geodetic extension across the messina strait