spine growth and seismogenic faulting at mt unzen japan the concluding episode of activity during the recent eruption of mt unzen october 1994 to february 1995 was characterized by incremental spine extrusion accompanied by seismicity analysis of the seismic record reveals the occurrence of two dominant long period event families associated with a repeating nondestructive source mechanism which we attribute to magma failure and fault controlled ascent we obtain constraints on the slip rate and distance of faulting events within these families that analysis is complemented by an experimental thermomechanical investigation of fault friction in mt unzen dacitic dome rock using a rotary shear apparatus at variable slip rates and normal stresses a power density threshold is found at 0 3 mw m 2 above which frictional melt forms and controls the shear resistance to slip inducing a deviation from byerlee s frictional law homogenized experimentally generated pseudotachylytes have a similar final chemistry thickness and crystal content facilitating the construction of a rheological model for particle suspensions this is compared to the viscosity constrained from the experimental data to assess the viscous control on fault dynamics the onset of frictional melt formation during spine growth is constrained to depths below 300 m for an average slip event this combination of experimental data viscosity modeling and seismic analysis offers a new description of material response during conduit plug flow and spine growth showing that volcanic pseudotachylyte may commonly form and modify fault friction during faulting of dome rock this model furthers our understanding of faulting and seismicity during lava dome formation and is applicable to other eruption modes

burrows dug by large vertebrates into rain moistened middle jurassic sand dunes abstract in south central utah eolian cross strata of the escalante member of the entrada sandstone contain inclined cylindrical burrows up to 63 cm in diameter and 305 cm long of the 14 large tunnels located during this study 12 descend from second and third order bounding surfaces that formed on the lee slopes of large dune ridges well above the water table the tunnels are inclined 15 22 one tunnel ends in an expanded chamber eolian cross strata fill proximal portions of four of the tunnels and indicate that after abandonment sand drifts migrated as much as a meter into the open shafts structureless sand and breccia blocks that were generated by roof collapse fill other tunnels animals dug the tunnels in rain moistened cohesive sand the burrows may have served as temporary shelters from severe diurnal conditions in the shadeless subtropical entrada dune field

large reemergence of anthropogenic carbon into the ocean s surface mixed layer sustained by the ocean s overturning circulation abstractwe evaluate the output from a widely used ocean carbon cycle model to identify the subduction and obduction reemergence rates of anthropogenic carbon cant for climatological conditions during the world ocean circulation experiment woce era in 1995 using a new set of lagrangian diagnostic tools the principal scientific value of the lagrangian diagnostics is in providing a new means to connect cant reemergence pathways to the relatively rapid renewal time scales of mode waters through the overturning circulation our main finding is that for this model with 2 04 pgc yr 1 of uptake of cant via gas exchange the subduction and obduction rates across the base of the mixed layer mlbase are 4 96 and 4 50 pgc yr 1 respectively which are twice as large as the gas exchange at the surface given that there is net accumulation of 0 17 pgc yr 1 in the mixed layer itself this implies the residual downward cant transport of 1 40 pgc yr 1 across the mlbase is associated with diffusion importantly th

viscosity of hydrous etna basalt implications for plinian style basaltic eruptions water dissolved in a silicate melt can strongly influence its physical properties and thus magma behavior during crystallization degassing foaming and fragmentation etna is a basaltic volcano whose activity is dominated by effusive eruptions which have long represented a threat to the densely populated surrounding area recently recognition of the products of a plinian eruption 122 b c has raised further issues for hazard assessment at etna and other basaltic volcanoes constraining the behavior of etna magma under conditions relevant to both effusive and explosive hazards requires viscosity data under conditions near the glass transition here we have investigated the viscosity of hydrous etna lava in order to better understand eruptive processes which characterize this volcano the experimental methods which have been used include piston cylinder synthesis of the hydrated melts micropenetration viscometry for low temperature viscosity measurements and near infrared spectroscopy for the evaluation of sample homogeneity and measurements of water content additionally scanning calorimetric determinations were performed to check whether incipient crystallization had occurred sample compositions were determined using electron microprobe analysis and 57fe mossbauer spectroscopy results from this study are compared with previous reports of trachytic phonolitic and model calc alkaline rhyolite hpg8 compositions the viscosity of the basaltic melt dry and wet has been parameterized in terms of temperature and water content via the non arrhenian equation log10 4 643 5 812 44 427 04 h2o t k 499 31 28 74 ln h2o where is the viscosity in pa s h2o is the water content in wt and t is the temperature in kelvin we observe that the viscosity of alkali basalt at more than 0 5 wt h2o is similar to that of an alkaline trachyte agnano monte spina eruption phlegrean fields and much higher than that of a peralkaline phonolite teide tenerife at similar silica contents and nbo t for water contents above 1 5 wt the viscosity of the basalt is similar to that of rhyolitic melts with similar water contents at temperatures ranging from 1 050 to 1 150 c and with water contents between 0 5 and 2 3 wt eruptive conditions the viscosities calculated using the equation defined in this study are 1 in reasonable agreement with those calculated using shaw s model and 2 much lower than those experimentally determined in a previous study however outside these temperature and water content ranges the agreement with shaw s model 1972 breaks down

high density bioturbated sandstones in the mississippian mauch chunk formation eastern pennsylvania usa implications for continental ecospace exploitation abstract continental communities represented by complex rapidly evolving invertebrate ecosystems first appeared during the early palaeozoic era and are recorded in surface and subsurface bioturbation the mississippian age mauch chunk formation contains several high density bioturbated fine grained sandstones that are preserved as erosively based fluvial channel fills several of these channel sandstone bodies are almost completely homogenized by subsequent bioturbation throughout their entire thickness up to a maximum depth of 1 6 m the mauch chunk ichnofossil record demonstrates that high density bioturbation occurred at least 30 my prior to the permian and well before its widespread distribution in the triassic hence the late mississippian high density bioturbated sandstones demonstrate a much earlier high density exploitation of the continental subsurface ecospace than previously known

late magmatic healed fractures in granitoids and their influence on subsequent solid state deformation abstract late magmatic fractures developed during final stages of magma crystallization are recorded in many granitoid plutons by planar trails of magmatic biotite and or leucocratic veins but have not been previously described such biotite rich trails with lengths of a few centimetres to several tens of centimetres widths of a few millimetres and a variable orientation are ubiquitous in meta granitoids of the neves area tauern window eastern alps italy these pre alpine granitoids were metamorphosed to upper amphibolite facies and deformed during the alpine orogeny allowing the effect of planar healed magmatic fractures on the nucleation of subsequent solid state ductile shear zones to be directly assessed numerical models considering power law viscous materials predict that planar arrays of a weaker mineral e g biotite oriented at around 45 to the shortening direction should nucleate and localize viscous deformation however no discernible localization on the natural small scale biotite trails is observed even when they delineate planes that were well oriented for shear reactivation in contrast heterogeneous shear zones nucleated on larger scale 1 10 m long planar compositional or structural boundaries such as joints dykes quartz veins alteration layers surrounding veins and zones of magma mingling outlined by densely packed clusters of basic enclaves irrespective of their orientation relative to the imposed shortening direction clearly some crucial aspect is missing from purely viscous numerical models we propose that this missing aspect is the observed interplay between fracture and flow with new fractures developing and localizing shear at bulk strains too low for discernible localization to occur on the pre existing healed magmatic fractures natural granitoids have a truly elasto plasto viscous rheology even at low differential stress as in the neves example and for high grade metamorphic conditions considered as typical of wet ductile middle crust

interpretation of resonance frequencies recorded during hydraulic fracturing treatments hydraulic fracturing treatments are often monitored by strings of geophones deployed in boreholes instead of picking discrete events only we here use time frequency representations of continuous recordings to identify resonances in two case studies this paper outlines an interpretational procedure to identify their cause using a subdivision into source path and receiver side effects for the first case study two main resonances are observed both at depth by the downhole geophones and on the surface by two broadband arrays the two acquisition networks have different receiver and path effects yet recorded the same resonances these resonances are therefore likely generated by source effects the amplitude pattern at the surface arrays indicates that these resonances are probably due to pumping operations in the second case study selective resonances are detected by the downhole geophones resonances coming from receiver effects are either lower or higher frequency and wave propagation modeling shows that path effects are not significant we identify two possible causes within the source area namely eigenvibrations of fractures or non darcian flow within the hydraulic fractures in the first situation 15 10 m long fluid filled cracks could generate the observed resonances an interconnected fracture network would then be required corresponding to mesoscale deformation of the reservoir alternatively systematic patterns in non darcian fluid flow within the hydraulic fracture could also be their leading cause resonances can be used to gain a better understanding of reservoir deformations or dynamic fluid flow perturbations during fluid injection into hydrocarbon and geothermal reservoirs co2 sequestration or volcanic eruptions

source mechanism of vulcanian degassing at popocatepetl volcano mexico determined from waveform inversions of very long period signals 1 the source mechanism of very long period vlp signals accompanying volcanic degassing bursts at popocatepetl is analyzed in the 15 70 s band by minimizing the residual error between data and synthetics calculated for a point source embedded in a homogeneous medium the waveforms of two eruptions 23 april and 23 may 2000 representative of mild vulcanian activity are well reproduced by our inversion which takes into account volcano topography the source centroid is positioned 1500 m below the western perimeter of the summit crater and the modeled source is composed of a shallow dipping crack sill with easterly dip of 10 intersecting a steeply dipping crack northeast striking dike dipping 83 northwest whose surface extension bisects the vent both cracks undergo a similar sequence of inflation deflation and reinflation reflecting a cycle of pressurization depressurization and repressurization within a time interval of 3 5 min the largest moment release occurs in the sill showing a maximum volume change of 500 1000 m3 pressure drop of 3 5 mpa and amplitude of recovered pressure equal to 1 2 times the amplitude of the pressure drop in contrast the maximum volume change in the dike is less 200 300 m3 with a corresponding pressure drop of 1 2 mpa and pressure recovery equal to the pressure drop accompanying these volumetric sources are single force components with magnitudes of 108 n consistent with melt advection in response to pressure transients the source time histories of the volumetric components of the source indicate that significant mass movement starts within the sill and triggers a mass movement response in the dike within a few seconds such source behavior is consistent with the opening of a pathway for escape of pent up gases from slow pressurization of the sill driven by magma crystallization the opening of this pathway and associated rapid evacuation of volcanic gases induces the pressure drop pressure recovery in the magma filling the sill is driven by diffusion of gases from the resulting supersaturated melt into bubbles assuming a penny shaped crack at ambient pressure of 40 mpa the observed pressure and volume variations can be modeled with the following attributes crack radius 100 m crack aperture 5 m bubble number density 1010 1012 m 3 initial bubble radius 10 6 m final bubble radius 10 5 m and net decrease of gas concentration in the melt 0 01 wt

evaluating trace elements as paleoclimate indicators multivariate statistical analysis of late mississippian pennington formation paleosols kentucky u s a abstract the temporal and spatial distributions of trace elements in paleosols in relation to soil forming processes and climate have received little attention primarily due to their generally low concentrations 100 ppm and a fundamental lack of knowledge of their behavior in soil systems trace element concentrations of pennington formation paleosols spanning an 8 ma interval in the late mississippian chesterian were analyzed using linear and multivariate statistics of whole rock elemental data linear statistics of the elemental data set show that ti zr nb cs la hf ta w ce and th have the highest correlation through time with r values 0 75 nb served as the proxy trace element for comparison temporal trends in nb closely match trends in lessivage clay formation and accumulation by feldspar weathering mean annual precipitation map and chemical weathering map effectively controls soil hydrology and the accumulation of organic matter and clay map in conjunction with chemical we

the propagation and seismicity of dyke injection new experimental evidence to reach the surface dykes must overcome the inherent tensile strength of the country rock as they do they generate swarms of seismic signals frequently used for forecasting in this study we pressurize and inject molten acrylic into an encapsulating host rocks of 1 etna basalt and 2 comiso limestone at 30 mpa of confining pressure fracture was achieved at 12 mpa for etna basalt 7 2 mpa for comiso limestone the generation of radial fractures was accompanied by acoustic emissions ae at a dominant frequency of 600 khz during magma movement in the dykes ae events of approximately 150 khz dominant frequency were recorded we interpret our data using ae location and dominant frequency analysis concluding that the seismicity associated with magma transport in dykes peaks during initial dyke creation but remains significant as long as magma movement continues these results have important implications for seismic monitoring of active volcanoes

deep volcanic tremor and magma ascent mechanism under kilauea hawaii deep harmonic tremor originating at depths around 40 km under kilauea was studied using records accumulated since 1962 at the hawaii volcano observatory of the u s geological survey the deep source of the tremor was determined by onset times and confirmed by the relative amplitude across the island wide network of seismometers the period of tremor was conclusively shown to be determined by the source effect and not by the path or station site effect because the period would change considerably in time but maintained uniformity across the seismic net during the tremor episode the tremor appeared to be primarily composed of p waves we interpret the observed period and amplitude in terms of the stationary crack model of aki et al 1977 and find that the seismic moment rates for deep tremors are considerably larger than those for shallow tremors suggesting more vigorous transport for the former we propose a kinematic source model which may be more appropriate for deep tremor according to this model a measurable quantity called reduced displacement is directly proportional to the rate of magma flow a systematic search for deep tremor episodes was made for the period from 1962 through 1979 and the amplitude period and duration of the tremor were tabulated we then constructed a cumulative reduced displacement plot over the 18 year period the result shows a generally steady process which does not seem to be significantly affected by major eruptions and large earthquakes near the surface the total magma flow estimated from the reduced displacement is however one order of magnitude smaller than that estimated by swanson 1972 it may be that most channels transport magma aseismically and only those with strong barriers generate tremor

seismic tremor in subduction zones rock physics evidence 1 episodic tremor and slip ets have been correlated with rupture phenomena in subducting oceanic lithosphere at 30 45 km depth where high vp vs ratios which suggest high fluid pressures have been observed ets by accommodating slip in the down dip portion of the subduction zone may trigger megathrust earthquakes up dip in the locked section during dehydration experiments on serpentinite typical rock of the oceanic lithosphere at temperatures found in nature at 30 45 km depth 400 550 c we observe seismic signals in the form of acoustic emissions that closely resemble low frequency earthquakes seismic tremor and regular earthquakes our findings support the concept that water released during dehydration reactions increases the pore pressures and can trigger ets and regular earthquakes by reducing slip resistance

ecology of earliest reptiles inferred from basal pennsylvanian trackways trackways representing the earliest evidence for the origin of reptiles amniotes are reported from the basal pennsylvanian grande anse formation new brunswick canada amniote characters include pentadactyl manus and pes slender digits whose relative lengths approximate a phalangeal formula of 23453 manus and 23454 pes narrow digit splay 40 63 putative transverse scale impressions on digit pads and straight tail drag the trackways occur in the deposits of a seasonally active dryland river channel sedimentological context suggests for the first time that early amniotes existed in water stressed environments where the cleidoic egg would have presumably conferred reproductive advantage

long period seismicity in the shallow volcanic edifice formed from slow rupture earthquakes volcanic eruptions are often preceded by long period seismic events that were thought to be generated by the resonance of cracks filled with magmatic fluid analysis and modelling of long period seismicity at volcanoes in italy costa rica and peru shows that it could instead be caused by slow rupture along faults in the upper volcanic edifice

brittle creep in basalt and its application to time dependent volcano deformation time dependent brittle deformation is a fundamental and pervasive process operating in the earth s upper crust its characterization is a pre requisite to understanding and unraveling the complexities of crustal evolution and dynamics the preferential chemical interaction between pore fluids and strained atomic bonds at crack tips a mechanism known as stress corrosion allows rock to fail under a constant stress that is well below its short term strength over an extended period of time a process known as brittle creep here we present the first experimental measurements of brittle creep in a basic igneous rock a basalt from mt etna volcano under triaxial stress conditions results from conventional creep experiments show that creep strain rates are highly dependent on the level of applied stress and can be equally well fit by a power law or an exponential law with a 20 increase in stress producing close to three orders of magnitude increase in creep strain rate results from stress stepping creep experiments show that creep strain rates are also influenced by the imposed effective confining pressure we show that only part of this change can be attributed to the purely mechanical influence of an increase in effective pressure with the remainder interpreted as due to a reduction in stress corrosion reactions the result of a reduction in crack aperture that restricts the rate of transport of reactive species to crack tips overall our results also suggest that a critical level of crack damage is required before the deformation starts to accelerate to failure regardless of the level of applied stress and the time taken to reach this point the experimental results are discussed in terms of microstructural observations and fits to a macroscopic creep law and compared with the observed deformation history at mt etna volcano c 2011 elsevier b v all rights reserved

eruption dynamics at mount st helens imaged from broadband seismic waveforms interaction of the shallow magmatic and hydrothermal systems 1 the current eruption at mount st helens is characterized by dome building and shallow repetitive long period lp earthquakes waveform cross correlation reveals remarkable similarity for a majority of the earthquakes over periods of several weeks stacked spectra of these events display multiple peaks between 0 5 and 2 hz that are common to most stations lower amplitude very long period vlp events commonly accompany the lp events we model the source mechanisms of lp and vlp events in the 0 5 4 s and 8 40 s bands respectively using data recorded in july 2005 with a 19 station temporary broadband network the source mechanism of the lp events includes 1 a volumetric component modeled as resonance of a gently nnw dipping steam filled crack located directly beneath the actively extruding part of the new dome and within 100 m of the crater floor and 2 a vertical single force attributed to movement of the overlying dome the vlp source which also includes volumetric and single force components is 250 m deeper and nnw of the lp source at the sw edge of the 1980s lava dome the volumetric component points to the compression and expansion of a shallow magma filled sill which is subparallel to the hydrothermal crack imaged at the lp source coupled with a smaller component of expansion and compression of a dike the single force components are due to mass advection in the magma conduit the location geometry and timing of the sources suggest the vlp and lp events are caused by perturbations of a common crack system

small earthquakes tectonic forces earthquake scaling and frequency of occurrence relations require that small earthquakes be just as important as larger ones in redistributing the forces that drive relative displacements across active faults of any dimension including plate boundaries

tetrapod trackways from the early middle devonian period of poland the fossil record of the earliest tetrapods vertebrates with limbs rather than paired fins consists of body fossils and trackways the earliest body fossils of tetrapods date to the late devonian period late frasnian stage and are preceded by transitional elpistostegids such as panderichthys and tiktaalik that still have paired fins claims of tetrapod trackways predating these body fossils have remained controversial with regard to both age and the identity of the track makers here we present well preserved and securely dated tetrapod tracks from polish marine tidal flat sediments of early middle devonian eifelian stage age that are approximately 18 million years older than the earliest tetrapod body fossils and 10 million years earlier than the oldest elpistostegids they force a radical reassessment of the timing ecology and environmental setting of the fish tetrapod transition as well as the completeness of the body fossil record

climate of the supercontinent pangea numerous climate models predict that the geography of the supercontinent pangea was conducive to the establishment of a megamonsoonal circulation in general geologic evidence supports the hypothesis of a megamonsoon that reached maximum strength in the triassic pangea in the late carboniferous had widespread peat formation in what is now central and eastern north america and europe and relatively dry conditions on the colorado plateau the equatorial region of the continent became drier through the end of the carboniferous by the permian the equatorial region of pangea was dry and indicators of aridity and rainfall seasonality became more widespread wind directions from colorado plateau eolian sandstones are consistent with an increasing influence of monsoonal circulation at this time in the triassic climate in the colorado plateau region became relatively wet though still seasonal and the few eolian sandstones indicate a major shift in wind direction at that time in addition sedimentation

discrimination of local and global effects on upper mississippian stratigraphy illinois basin u s a abstract interpretive cross sections based on detailed descriptions of 33 outcrops and cores are used to better understand the relative effects of tectonics eustasy tides and climate on upper mississippian middle chesterian stratigraphy in the tectonically active tide dominated illinois basin the cross sections show that five mixed carbonate siliciclastic high frequency sequences in the bethel through glen dean formations can be correlated around the outcrop belt through areas with very different subsidence histories the sequence boundaries are marked by paleosols and incised valleys and can be correlated basin wide within a framework of distinctive marker beds because of its updip position lowstand systems tracts are not preserved in the illinois basin the transgressive systems tracts generally consist of one or two parasequences that are typically composed of tidally influenced quartz sandstone filling incised valleys at the base overlain by open marine skeletal limestone shallow marine shale and heterolithic siliciclastic tidal flat deposits the maximum flooding surface mfs for the sequences is picked at the base of the deepest water limestone facies highstand systems tracts are composed of 1 to 6 regressive parasequences that consist of basal offshore skeletal limestone capped by laterally extensive shale and heterolithic siliciclastic tidal flat facies the basin wide extent of the sequence boundaries and maximum flooding surfaces across tectonic highs and lows suggests that the sequences were produced by eustatic sea level changes rather than local tectonics or autogenic processes the sequences were likely produced by moderate to high amplitude 30 100 m fourth order 400 ky glacio eustatic sea level changes driven by the transition from the greenhouse conditions of the early mississippian to the icehouse conditions of the late paleozoic the lateral extent and frequency of component parasequences suggests that they were likely produced by fifth order sea level changes 10 100 ky the sequences may be bundled into third order composite sequences but the third order signal is obscured by the magnitude of the fourth order sea level changes a feature typical of ice house stratigraphies the sequences can be used as time slices to identify spatial and temporal variations in differential subsidence between the cincinnati arch and the more rapidly subsiding basin interior episodes of high and low differential subsidence occurred every two to three sequences these subsidence variations had a major impact on lithofacies distribution and onlap and offlap geometries in sequences and parasequences the occurrence of some widespread seismically disturbed beds suggests that active faulting occurred during deposition normal faulting appears to have occurred during periods of high differential subsidence and reverse faulting during periods of low differential subsidence differential subsidence and related normal and reverse faulting may have occurred in response to phases of thrust loading and quiescence in the appalachian orogenic belt to the east even in this tectonically active setting however it is the eustatic signal that generates basin wide mappable stratigraphic sequences

detailed analysis of acoustic emission activity during catastrophic fracture of faults in rock abstract the detailed time space distribution of acoustic emission ae events during the catastrophic fracture of rock samples containing a pre existing joint or potential fracture plane is obtained under triaxial compression using a high speed 32 channel waveform recording system and the results are discussed with respect to the prediction and characterization of catastrophic fault failure ae activity is modeled quantitatively in terms of the seismic b value of the magnitude frequency relation the self excitation strength of the ae time series and the fractal dimension of ae hypocenters consistent with previous studies on rock samples containing a fracture plane with several asperities the present analyses reveal three long term phases of ae activity associated with damage creation on heterogeneous faults each clearly identifiable based on the above parameters a long term decreasing trend and short term fluctuation of the b value in the phase immediately preceding dynamic fracture are identified as characteristic features of the failure of heterogeneous faults based on the experimental results it is suggested that precursory anomalies related to earthquakes and other events associated with rock failure are strongly dependent on the heterogeneity of the fault or rock mass a homogeneous fault or rock mass appears to fracture unpredictably without a consistent trend in precursory statistics while inhomogeneous faults fracture with clear precursors related to the nature of the heterogeneity

seismo mechanical response of anisotropic rocks under hydraulic fracture conditions new experimental insights unconventional hydrocarbon resources found across the world are driving a renewed interest in mudrock hydraulic fracturing methods however given the difficulty in safely measuring the various controlling factors in a natural environment considerable challenges remain in understanding the fracture process to investigate we report a new laboratory study that simulates hydraulic fracturing using a conventional triaxial apparatus we show that fracture orientation is primarily controlled by external stress conditions and the inherent rock anisotropy and fabric are critical in governing fracture initiation propagation and geometry we use anisotropic nash point shale nps from the early jurassic with high elastic p wave anisotropy 56 and mechanical tensile anisotropy 60 and highly anisotropic cemented crab orchard sandstone with p wave tensile anisotropies of 12 and 14 respectively initiation of tensile fracture requires 36 mpa for nps at 1 km simulated depth and 32 mpa for crab orchard sandstone in both cases with cross bedding favorable orientated when unfavorably orientated this increases to 58 mpa for nps at 800 m simulated depth far higher as fractures must now traverse cross bedding we record a swarm of acoustic emission activity which exhibits spectral power peaks at 600 and 100 khz suggesting primary fracture and fluid rock resonance respectively the onset of the acoustic emission data precedes the dynamic instability of the fracture by 0 02 s which scales to 20 s for 100 m size fractures we conclude that a monitoring system could become not only a forecasting tool but also a means to control the fracking process to prevent avoidable seismic events

role of pore fluids in the generation of seismic precursors to shear fracture a systematic study of temporal changes in seismic b values defined as the log linear slope of the earthquake frequency magnitude distribution has shown that large earthquakes are often preceded by an intermediate term increase in b followed by a decrease in the months to weeks before the earthquake1 the onset of the b value increase can precede earthquake occurrence by as much as 7 years a recently proposed fracture mechanics model of the earthquake source2 explains these temporal fluctuations in b in terms of the underlying physical processes of time varying applied stress and crack growth the model predicts two minima in b separated by a short lived maximum here we report the results of controlled laboratory deformation experiments done in simulated upper crustal conditions on both air dried and water saturated rock specimens as found in previous experiments3 5 shear fracture in dry specimens is characterized by a decline in b during anelastic deformation to a single minimum reached just before failure but in water saturated specimens when pore fluid volume is kept constant by servo control we also observe a second intermediate term b value minimum so reproducing the double b value anomaly predicted by the model2

cooling dominated cracking in thermally stressed volcanic rocks most studies of thermally induced cracking in rocks have focused on the generation of cracks formed during heating and thermal expansion both the nature and the mechanism of crack formation during cooling are hypothesized to be different from those formed during heating we present in situ acoustic emission data recorded as a proxy for crack damage evolution in a series of heating and cooling experiments on samples of basalt and dacite results show that both the rate and the energy of acoustic emission are consistently much higher during cooling than during heating seismic velocity comparisons and crack morphology analysis of our heated and cooled samples support the contemporaneous acoustic emission data and also indicate that thermal cracking is largely isotropic these new data are important for assessing the contribution of cooling induced damage within volcanic structures and layers such as dikes sills and lava flows

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

source process of a long period event at kilauea volcano hawaii summary we analyse a long period lp event observed by a dense seismic network temporarily operated at kilauea volcano hawaii in 1996 we systematically perform spectral analyses waveform inversions and forward modeling of the lp event to quantify its source process spectral analyses identify two dominant spectral frequencies at 0 6 and 1 3 hz with associated q values in the range 10 20 results from waveform inversions assuming six moment tensor and three single force components point to the resonance of a horizontal crack located at a depth of approximately 150 m near the northeastern rim of the halemaumau pit crater waveform simulations based on a fluid filled crack model suggest that the observed frequencies and q values can be explained by a crack filled with a hydrothermal fluid in the form of either bubbly water or steam the shallow hydrothermal crack located directly above the magma conduit may have been heated by volcanic gases leaking from the conduit the enhanced flux of heat raised the overall pressure of the hydrothermal fluid in the crack and induced a rapid discharge of fluid from the crack which triggered the acoustic vibrations of the resonator generating the lp waveform the present study provides further support to the idea that lp events originate in the resonance of a crack

real time and in situ assessment of conduit permeability through diverse long period tremors beneath aso volcano japan abstract long period signal lps 0 2 2 s and very long period signal vlp 2 100 s observed in the shallow volcanic plumbing system are typically repetitive and time invariant in their location and source mechanism offering in situ probes of hot fluid transport over the eruption cycles while the amplitude and activity of volcanic tectonic earthquakes and lp events have been commonly used to infer overpressure within their source region one missing link is an observable that may permit inference on the change in the permeability of the conduit plug wall which can regulate the degree of pressurization affect the mechanical strength of the surrounding rock and consequently the likelihood of an upcoming eruption here we show that during the 2011 2016 eruption cycle at aso volcano in japan long period tremor events a vlp of 15 s period with opposite waveform polarity can be systematically detected and categorized as pressurization and depressurization events in the same crack like conduit we suggest that depending on the strength of the surrounding rock and the permeability of the crack like conduit wall plug pressurization due to magmatic heat and vaporization is more likely to occur when a less permeable conduit plug wall can effectively keep the gas inside the crack like conduit on the other hand depressurization is prone to occur if the conduit wall plug permeability is sufficiently high to allow gas to escape from the conduit considering the amplitude of lpt proportional to the conduit overpressure contrasting energetics of these diverse lpt events allows us to define whether the conduit is prone to pressurization or depressurization providing a framework to infer how the permeability of the conduit wall plug may evolve over an eruption cycle

the palaeoenvironment and deformation of beaconites like burrows in the old red sandstone at gortnabinna sw ireland the gortnabinna area contains a number of well preserved deformed burrows within the fluviatile old red sandstone of s ireland detailed logging of the local succession enables subdivision into four facies facies 1 represents sheet flood deposits facies 2 ephemeral stream channels facies 3 marginal sheet flood deposits and facies 4 low energy settling of fines the burrows occur in facies 1 and 4 the sediments are now folded into a large upright westward plunging anticline the fold has a well developed axial planar cleavage and is extended along strike by listric normal faults the burrows in facies 1 were originally circular and orthogonal to bedding and reveal a n s layer parallel shortening strain of 2 1 followed by a shear strain of 1 48 during folding these burrows have a bimodal distribution of diameters with peaks in the ranges 50 80 and 110 170 mm the burrows of facies 4 are sub parallel to the bedding plane and are generally curved with a maximum width of 180 mm and lengths of up to 2 3 m these burrows display passive infill following abandonment the burrows are morphologically similar though distinct from beaconites barratti which has been described from elsewhere in the old red sandstone and are tentatively interpreted as lungfish burrows

woodland hypothesis for devonian tetrapod evolution abstractthe rarity of devonian tetrapods and the absence of tetrapods during the first 14 million years of the mississippian romer s gap have inspired hypotheses of fish tetrapod evolutionary transition as an escape from difficult habitats such as deserts or stagnant waters these hypotheses and romer s gap are tested here using depth to calcic horizon in paleosols of the northern appalachians as a proxy for precipitation and vegetation changes during the devonian and mississippian all tetrapod bones and trackways in this region as well as fossil tree remains were found at times of high precipitation indicated by deep calcic paleosols when subhumid woodlands expanded at the expense of semiarid shrublands in alluvial lowlands no tetrapods or tree fossils were found in abundant paleosols with the shallow calcic horizons of aridland soils the mean annual precipitation requirement of devonian mississippian tetrapods and trees was at least mm global distribution of prototetrapods and aquatic tetrapo

waveform inversion of oscillatory signatures in long period events beneath volcanoes 1 the source mechanism of long period lp events is examined using synthetic waveforms generated by the acoustic resonance of a fluid filled crack we perform a series of numerical tests in which the oscillatory signatures of synthetic lp waveforms are used to determine the source time functions of the six moment tensor components from waveform inversions assuming a point source the results indicate that the moment tensor representation is valid for the odd modes of crack resonance with wavelengths 2l n 2w n n 3 5 7 where l and w are the crack length and width respectively for the even modes with wavelengths 2l n 2w n n 2 4 6 a generalized source representation using higher order tensors is required although the efficiency of seismic waves radiated by the even modes is expected to be small we apply the moment tensor inversion to the oscillatory signatures of an lp event observed at kusatsu shirane volcano central japan our results point to the resonance of a subhorizontal crack located a few hundred meters beneath the summit crater lakes the present approach may be useful to quantify the source location geometry and force system of lp events and opens the way for moment tensor inversions of tremor

source analysis of acoustic emissions in aue granite cores under symmetric and asymmetric compressive loads the effect of stress anisotropy on the brittle failure of granite is investigated under uniaxial compression non standard asymmetric compression tests are performed on cores of aue granite diameter 52 mm length 100 mm in which 20 per cent of the core top surface remains unloaded the edge of the asymmetric steel loading plate acts as a stress concentrator from where a shear rupture is initiated the propagation of the fracture related process zone from top to bottom of the core is mapped by microcrack induced acoustic emissions compared to standard uniaxial tests with symmetric loading in the asymmetric tests both a greater quantity and more localized distributions of emission event hypocentres are observed the maximum event density doubles for asymmetric 20 events per 10 6 m3 compared to symmetric tests the cluster correlation coefficient a measure of strain localization in the faulting process reaches 0 15 for symmetric and 0 30 for asymmetric tests the clustering of events however is found post failure only three different amplitudes are used to determine b values discussed as a possible failure precursor focal amplitudes determined at a 10 mm source distance and maximum amplitudes measured at eight piezoceramic sensors lead to b values that drop before rock failure first pulse amplitudes automatically picked from emission wavelets show no anomaly first motion polarity statistics of amplitudes indicate that a shear crack type radiation pattern is responsible for 70 per cent of the failure of granite irrespective of stress boundary conditions for type s events with an equal percentage of dilatational and compressional first motions focal mechanisms are determined by fitting measured first pulse amplitudes to an assumed double couple radiation pattern while hypocentres of large type s events align parallel to the later fracture plane their fault plane solutions show no coherent pattern spatial views of fracture planes reconstructed from x ray computed tomograms reveal local small scale changes in fracture plane orientation nodal planes from average fault plane solutions of the microscopic acoustic emission events coincide with the overall orientation of the macroscopic fracture plane azimuth strike angle determined from thin sections and tomograms

invertebrate trace fossils in semi arid to arid braided ephemeral river deposits of the mississippian middle member of the mauch chunk formation eastern pennsylvania usa abstract the rapid diversification of terrestrial ecosystems was initiated in the silurian and subsequently continued through the mississippian detailed collecting of the middle member of the mississippian mauch chunk formation in eastern pennsylvania has yielded a number of important vertebrate and invertebrate trace fossils indicating the presence of a significant terrestrial biotic diversity during the early carboniferous this report illustrates the diverse invertebrate trace fossil assemblage associated with the ephemeral river systems of the mauch chunk the mauch chunk invertebrate ichnoassemblage consists of backfilled burrows of deposit feeders both meniscate taenidium and non meniscate planolites that typically cross cut bedding arthropod trackways diplichnites diplopodichnus stiaria kouphichnium and stialla striated trails cruziana and resting traces rusophycus and surface or shallow subsurface grazing trails or burrows gordia tetrapod footprints mostly made by temnospondyl amphibians are also part of this ichnoassemblage the mauch chunk invertebrate ichnoassemblage corresponds well to the scoyenia ichnofacies in consisting of simple burrows trackways striate and bilobate trails and pits and simple meniscate burrows typically trace fossils of the scoyenia ichnofacies indicate opportunistic behaviors in subaerial environments that are temporarily or periodically inundated indeed the palaeoenvironmental setting of these traces is a semi arid to possibly arid braided ephemeral river system with extensive overbank deposits the invertebrate traces were developed both as infaunal burrows in the tops and within channel sandstones and as surface and grazing traces on in channel mudstone draped bedforms and in proximal overbank deposits the in channel mudstone draped bedforms display both vertebrate and invertebrate trace fossils the mauch chunk invertebrate ichnofossil assemblage resembles other devonian through triassic ichnoassemblages from ephemeral fluvial red beds confirming that the terrestrial invertebrate fauna had already fully colonized fluvial environments by mississippian time furthermore the development of the scoyenia ichnoguild in the mauch chunk formation in the form of abundant traces of deposit feeders of a shallow to intermediate depth infauna esp taenidium is unusually early when compared to the previously known palaeozoic record

amphibian burrows and ephemeral ponds of the lower permian speiser shale kansas evidence for seasonality in the midcontinent abstract burrows attributed to the lysorophid brachydectes elongatus occur within a green mudstone lens in the lower permian wolfcampian speiser shale council grove group of eastern kansas the burrow bearing unit consists of a 100 m long lens of massive calcareous silty mudstone with a maximum thickness of 35 cm the lens also contains the fossils of fish amphibians reptiles charophytes stomachara and ostracodes carbonita the mudstone lens pinches out laterally into red pedogenically modified mudstone the burrows occur in three layers at the top of each layer is a subaerial exposure surface indicated by rhizoliths mudcracks and coarse grained lags the mudstone lens is interpreted as the deposit of a shallow ephemeral pond the burrows occur in three vertically and temporally separated clusters with concentrations up to 20 m2 the burrows show two types of architecture type i burrows are elongate elliptical tubes 4 32 cm long and 2 7 cm in width type ii burrows are short elliptical tubes 1 5 3 5 cm in length and 2 5 5 cm in width the burrow fill consists of a mudstone capped by sandy siltstone each burrow layer contains a varying number of articulated and disarticulated lysorophid skeletons within the burrows and surrounding matrix while similar to permian lungfish burrows the architecture and surficial morphology of the lysorophid burrows permits their distinction even in the absence of body fossils the occurrence of burrow layers capped by subaerial exposure surfaces and separated by layers of non burrowed massive mudstone indicates that burrowing occurred in response to episodic perhaps seasonal droughts on the permian coastal plain the lysorophid burrowing behavior is analogous to that of the extant amphibians amphiuma sp and siren intermedia which inhabit rivers and ponds in the southeastern usa

large vertebrate burrow from the upper mississippian mauch chunk formation eastern pennsylvania usa abstract a burrow of probable amphibian origin was discovered in the upper member of the mississippian mauch chunk formation in eastern pennsylvania facies analysis of the upper member indicates that deposition occurred in an ephemeral braided stream setting the burrow is housed in a mudstone and is filled by two graded beds of conglomerate to sandstone it is characterized by a flared opening leading into a narrower slightly helical tunnel that ends in an inflated ovate chamber approximately 51 to 60 cm in diameter with a maximum height of 20 cm the flared opening is stratigraphically higher than the elevation at the base of the chamber the tunnel has a semicircular base the geometries abrupt angle changes inflated termination width to height ratios of the terminal chamber and graded fill indicate that the structure was an open void prior to sedimentation the geometry and size of this structure are incompatible with known invertebrate burrows and erosional features palaeosauropus primaevus an amphibian footprint ichnotaxon recovered from the mauch chunk formation was made by an amphibian of sufficient size to create such a large burrow this type of burrowing was most likely a response to seasonal droughts as local water sources evaporated

imaging slow failure in triaxially deformed etna basalt using 3d acoustic emission location and x ray computed tomography we have deformed basalt from mount etna italy in triaxial compression tests under an effective confining pressure representative of conditions under a volcanic edifice 40 mpa and at a constant strain rate of 5 similar to 10 6 s 1 despite containing a high level of pre existing microcrack damage etna basalt retains a high strength of 475 mpa we have monitored the complete deformation cycle through contemporaneous measurements of axial strain pore volume change compressional wave velocity change and acoustic emission ae output we have been able to follow the complete evolution of the throughgoing shear fault without recourse to any artificial means of slowing the deformation locations of ae events over time yields an estimate of the fault propagation velocity of between 2 and 4 mm s 1 we also find excellent agreement between ae locations and post test images from x ray microtomography scanning that delineates deformation zone architecture

evolution of the mechanics of the 2004 2008 mt st helens lava dome with time and temperature the 2004 2008 eruption of mount st helens washington usa formed a typical example of a pelean spiny lava dome with solid spines of crystalline silicic lava extruded along shear zones bounded by fault gouge cashman et al 2008 iverson et al 2006 creation of and movement along shear zones in this erupting lava recorded as shallow micro earthquakes were thus key controls on eruption style and rate in addition to dome stability as eruption style and lava dome stability often change within individual eruptions it is important to identify how the strength of dome rocks changes with temperature time texture and extrusion rate however critical values of the shear strength of dome lava at eruptive temperatures have never been measured we have found in controlled laboratory experiments simulating eruption conditions that dome lava strength increased during the course of the 2004 2008 eruption of mount st helens as the textures became more crystalline and less porous increasing lava strength during the eruption would lead to deformation becoming increasingly localised to shear zones explaining why the extrusion style and centre were so consistent acoustic emissions and microstructure analysis indicate that fracturing was more localised at higher temperatures resulting in higher strengths at eruptive temperature compared to ambient temperatures for later erupted samples the strength of these later erupted samples at eruptive temperatures increased markedly with strain rate this would damp any increases in effusion rate that may result from changes in magma pressure explaining the steady effusion rate at mount st helens from 2004 to 2008

seismological analysis of conduit dynamics in fragmentation experiments we simulate gas burst and volcanic explosions under controlled laboratory conditions inducing fragmentation of volcanic rocks by rapid depressurization a series of experiments were performed in a shock tube apparatus at room temperature and a pressure range of 4 to 20 mpa using argon ar gas and particles or pumice samples of different porosities the instrumentation of this system with high precision piezoelectric sensors enabled us to capture elastic waves and to recognize their characteristic signatures by relating these signals to physical processes in the wave field we have been able to characterize the conduit mechanism and the source dynamics we compare and discuss conspicuous features of the waveforms and frequency spectra of these experimental signals with those of volcanic origin despite the fact that these signals are different in amplitude resulting from different scale conditions our observations indicate that the physical processes that occur during simulated explosions and those that occur during volcanic eruptions yield comparable signatures in their respective records the effects of the source receiver configuration and resonance also have significant implications all this suggests that the physical processes e g pressurization and depressurization of a system involve a system response that causes similar distinctive effects independent of the system size reflecting its intrinsic dynamics these similarities imply that powerful constraints on the source mechanisms of volcanic seismicity can emerge from seismic investigations of experimental simulations of volumetric sources such constraints may yield significant advances in the understanding of volcanic conduit dynamics and in the interpretation of seismic unrest at volcanic centers

helical burrow casts of therapsid origin from the beaufort group permian of south africa abstract large helical burrow casts of vertebrate origin have been discovered at several localities in the lowermost strata of the teekloof formation of the beaufort group permian in the southwestern karoo basin south africa they are not only the oldest but also the first vertebrate burrows of helical geometry to be found in rocks of pre mammalian age the burrow casts are vertically disposed spiralling tubes filled with fine grained sandstone or siltstone often with a calcareous cement tube diameters gradually increase from 60 mm in the upper entrance decline through two non contacting dextral coils to about 160 mm at the base of the spiral whereupon the tube straightens and widens into a horizontal terminal chamber burrow depths range from 0 5 0 75 m and the ramp angle ranges from 10 to 32 although within any single spiral it is constant articulated skeletons of the small dicynodont diictodon have been found within the terminal chambers and spirals of three sand filled burrows linear ridges preserved on the outer walls and floor of some of the terminal chambers resemble scratch marks possibly made by the claws and beak of diictodon during burrow excavation the sedimentary sequences at two separate localities are interpreted as having been deposited by episodic sheet floods and distributary splay fans in the proximal floodbasin areas flanking an aggrading meanderbelt rise comparison is drawn between helical burrow casts in the lower beaufort and other recorded occurrences in particular daimonelix a beaver burrow from the miocene of nebraska fundamental similarities far outweigh differences to the extent that the beaufort helical burrows may be grouped with the daimonelices it is concluded that the excavation of large helical burrows an activity usually attributed to rodents was pre empted by mammal like reptiles some 50 million years before the first anatomical mammals evolved

a paleopedologic and ichnologic perspective of the terrestrial pennsylvanian landscape in the distal appalachian basin u s a abstract the conemaugh group of southeastern ohio contains numerous ichnofossil bearing paleosols in both the lower glenshaw and upper casselman formations which were deposited during the kasimovian and gzhelian 305 301 ma along the distal edge of the appalachian basin this study examined the small scale twenty four stratigraphic sections were measured from ten sites in athens county ohio from which thirty paleosols were identified and described detailed field descriptions allowed differentiation of four distinct pedotypes one in the glenshaw formation and three in the casselman formation the glenshaw pedotype gpt is a vertisol that formed on a proximal to distal floodplain the three casselman pedotypes represent entisols inceptisols cpti alfisols cptii and vertisols cptiii all four types contain evidence of alteration by post pedogenic processes such as drowning by migrating river channels or rising sea level or a gradual transition from one alluvial subenvironment to another as a result of channel migration eight morphologically distinct ichnofossils were observed in the conemaugh group paleosols including three types of rhizoliths lined and unlined vertical to subhorizontal shafts chambers sinuous burrows with and without bioglyphs and general burrow mottling these ichnofossils occur in distinct assemblages that form unique ichnocoenoses within each of the four pedotypes they were produced by various plants arthropod detritivores carnivores and herbivores as well as amphibians and early reptiles as temporary to permanent members of complex soil ecosystems pedogenic properties combined with ichnofossil diversity abundance and distribution increase the understanding of the complexity of late pennsylvanian soil ecosystems and provide details on the small scale variations in paleosols due to short term autogenic changes in alluvial environments although broad regional studies across 10 2 10 3 of kilometers are important small scale variations over less than 1 km are needed to understand the effects of localized changes in hydrology topography organisms and sedimentary processes on soil formation and soil biodiversity consideration of these types of localized studies is also vital when attempting to interpret regional to global scale aspects of environment such as climate from paleosols

significance of different modes of rhizolith preservation to interpreting paleoenvironmental and paleohydrologic settings examples from paleogene paleosols bighorn basin wyoming u s a abstract different modes of preservation of root traces rhizoliths provide information on soil moisture regimes in alluvial paleosols in the paleogene fort union and willwood formations of the bighorn basin wyoming u s a this paper links different styles of rhizolith preservation to paleosols whose other pedogenic attributes provide information on ancient soil drainage consequently the paleodrainage significance of different rhizolith preservation patterns is established more confidently rhizoliths consisting of elongate gray mottles rhizohaloes with red rims are common in relatively well drained red paleosols the gray zones are depleted of iron fe whereas the color of the rims indicates hematite accumulation these features are typical of surface water gley processes that caused fe and manganese mn to move from the root channel outward to the soil matrix calcareous rhizocretions either calcareous tubular concretions or micro accumulations of carbonate within gray rhizotubules are also common in moderately well drained red paleosols more poorly drained purple paleosols also have rhizoliths consisting of fe depletion zones however the rhizohaloes are surrounded by yellow brown goethite rims rather than red hematitic rims in many paleosols the red and yellow brown accumulation rims were partly removed by continued depletion producing abundant irregular shaped mottles the nature of the rhizohalo and the color of the fe oxide rim provide information about the intensity of gleying that a paleosol underwent the poorly drained paleosols also show rhizoliths preserved as goethite accumulations contained within gray depletion zones indicating movement of reduced fe from the matrix towards the root channel probably as a result of groundwater gley processes the goethite accumulations are intermingled locally with lignite representing preservation of the root organic material some rhizoliths are preserved as tube shaped concentrations of small 0 1 0 2 mm diameter black spheres whose color indicates a mix of mn and fe oxides these are most common in paleosols with low chroma gray matrix colors indicating very poor drainage the very poorly drained paleosols also show rhizoliths preserved in jarosite which is an oxidation product of pyrite careful observational and geochemical analysis of rhizoliths which are common in continental deposits can help produce a clearer and more thorough interpretation of ancient drainage conditions information about degree of ancient soil wetness or moisture is important for understanding past climatic conditions and for reconstructing terrestrial paleolandscapes

effect of phase transitions on seismic properties of metapelites a new high temperature laboratory calibration we report new measurements of the seismic properties of an upper amphibolite facies metapelite from the serie dei laghi basement southern alps northern italy presenting evidence for the transition using elastic wave velocity methods and under in situ conditions measurements were made using an internally heated gas apparatus under hydrostatic conditions to 500 mpa and temperatures to 1075 k p wave and s wave velocities were measured parallel and normal to both lineation and foliation at room temperature an average v p at 400 mpa of 6 4 km s and v p anisotropy of 15 were found and an average v s1 of 3 6 km s 8 2 anisotropy and v s2 of 3 5 km s 4 1 anisotropy were also measured to observe the effects of the quartz transition under hydrostatic conditions elastic wave velocity was monitored continuously as the sample was heated to 1075 k at 400 mpa v p was seen to decrease monotonically with increasing temperature to 950 k as temperature continued to increase v p rapidly increased until 1075 k the effect was found to be reversible and is interpreted in terms of the transition in quartz in broad agreement with previous studies a simple interpretation of the data taking into account a field case from southern tuscany as well as natural and elevated geothermal gradient suggests that thermal and hydraulically driven fracture is a likely cause of bright spots seen in these areas with knowledge of the depth of such features the transition additionally allows the temperature at depth to be estimated

paleoclimate controls on stratigraphic repetition of chemical and siliciclastic rocks climate is a primary control on sediment flux from continental sources into sedimentary systems in warm climates siliciclastic input is greatest under highly seasonal rainfall nonseasonal conditions favor formation of end member chemical rocks perennially wet climates are conducive to coal formation whereas dry climates produce carbonates and or evaporites stratigraphic repetition of siliciclastic and chemical rocks therefore appears to be related to paleoclimate cycles as well as to transgressive regressive events and tectonics

temporal variations in seismicity during quasi static and dynamic rock failure abstract a comprehensive model is presented which can explain temporal fluctuations in seismic b values in the period leading to mechanical failure in terms of the underlying physical processes of time varying applied stress and stress corrosion enhanced crack growth under conditions of constant strain rate the form of the b value anomaly in the period leading to failure depends on the form of the stress time relationship for the case where dynamic failure occurs at peak stress after a period of strain hardening the model predicts a single cusp like b value anomaly reaching a critically low value of 0 5 at failure for the physically most realistic case where dynamic failure is preceded by a period of precursory strain energy release during strain softening the model predicts two minima in the b value separated by a temporary maximum or inflection point these fluctuations in the b value are consistent with reported intermediate term and short term earthquake precursors separated by a period of seismic quiescence for the case of quasi static cataclastic flow the b value mirrors the stress and never falls to the critical value because there is no critical rupture new results from a series of controlled laboratory experiments are presented in which microseismic event rates and b value were monitored contemporaneously with stress time data for all variants of the stress time relationship recent field observations of temporal changes in seismicity rates and b value preceding major earthquakes are also reported both data sets exhibit b value anomalies which are consistent with the model predictions

laboratory simulations of tensile fracture development in a volcanic conduit via cyclic magma pressurisation during volcanic unrest high magma pressure induces cracking and faulting of the country rock providing conduits for the transport of magma and other fluids these conduits known as dykes are fundamental structures for the transport of magma to the surface in volcanically active regions the mechanics of dyke propagation is not yet fully understood but is crucial to better model dyke emplacement and eruption in volcanoes central to this need is a greater understanding of the mechanical properties of the magma country rock interaction as a function of known magmatic pressure temperature and stress here we report data from a series of experiments in which we cyclically compress viscoelastic rhyolitic magma at 828 c 892 c and 918 c inside a cylindrical conduit like shell of basalt from mt etna italy until fracture occurs the compression is performed under strain rates cyclically varying between 5 10 6 and 5 10 5 s 1 the resultant monitored axial loading and relaxation illustrates how the presence of a visco elastic fluid magma controls the stress induced at the conduit margin boundary this is achieved by analysing the viscoelastic relaxation through time to calculate an apparent modulus which is found to decrease with both increasing temperature and time in the 4 cycles before failure we find that the apparent modulus decreases from 180 to 40 gpa 80 to 20 gpa and 8 to 1 gpa for imposed stress cycles at 828 c 892 c and 918 c respectively we theoretically estimate a tensile strength at failure of approximately 7 11 mpa consistent with recent field data and in agreement with a model derived from the sample geometry and basic material parameters post experimental neutron computed tomography and microscopic analyses further reveal the fragmentation of the melt and generation of tuffisite veins inside the conduit due to spontaneous crack nucleation associated with conduit wall fracture the geometry of the rupture area inside the melt is akin to a mach cone associated with supershear fractures we discuss our findings in terms of magma rock interaction leading to dykes tuffisite veins and magma fragmentation

seismicity preceding volcanic eruptions new experimental insights a variety of seismic signals representing different physical mechanisms precedes volcanic eruptions the most meaningful signals are high and low frequency earthquakes and volcanic tremor that have tentatively been related to fracturing and magma transport in the volcanic edifice we provide experimental support for this association by reproducing magma migration while recording seismic signals opening fractures emit high frequency acoustic events while the switch to low frequency and harmonic tremor accompanies the flow of the melt in the fractures discerning between these seismic signals in nature can significantly refine volcanic hazard evaluation

relative source locations of continuous tremor before and after the subplinian events at shinmoe dake in 2011 volcano monitoring systems are not always ready to resolve signals at the onset of eruptive activity this study makes use of stations installed later to calibrate the performance of the stations that had been operated before the eruption seven stations recorded continuous volcanic tremor before and during the subplinian eruptions of shinmoe dake japan in 2011 we estimated the source locations of the tremor using the amplitude distribution the stability of the analysis was obtained by careful selection of time windows in which signals from a single source are dominated the site effects and the regional attenuation factor were evaluated using tremor recorded after the major eruptions by a dense seismic array and a good number of stations a tremor source changed its depth beneath the crater for one week before the major eruption rising from a depth of a few kilometer to the water layer three times each of which occurred following shallow inflation and minor eruptions it is interpreted as migration of gas probably with magma which further transported heat to the water layer and triggered the subplinian eruptions

on the generation mechanisms of fluid driven seismic signals related to volcano tectonics the generation mechanics of fluid driven volcano seismic signals and their evolution with time remains poorly understood we present a laboratory study aiming to better constrain the time evolution of such signals across temperature conditions 25 to 175 c in order to simulate a bubbly liquid simulations used pressures equivalent to volcanic edifices up to 1 6 km in depth using a triaxial deformation apparatus equipped with an array of acoustic emission ae sensors we investigate the origin of fluid driven seismic signals by rapidly venting the pore pressure through a characterized damage zone during the release of water at 25 c broadband signals were generated with frequencies ranging from 50 to 160 khz however the decompression of a water steam phase at 175 c generated a bi modal spectrum of different signals in the range 100 khz and 160 khz these new results are consistent with natural signals from active volcanoes such as mt etna and highlight the role of fluid and gas phases such as bubbly liquids in generating different types of volcano tectonic seismicity

physical modeling of the formation and evolution of seismically active fault zones acoustic emission ae in rocks is studied as a model of natural seismicity a special technique for rock loading has been used to help study the processes that control the development of ae during brittle deformation this technique allows us to extend to hours fault growth which would normally occur very rapidly in this way the period of most intense interaction of acoustic events can be studied in detail characteristics of the acoustic regime ar include the gutenberg richter b value spatial distribution of hypocenters with characteristic fractal correlation dimension d hurst exponent h and crack concentration parameter pc the fractal structure of ar changes with the onset of the drop in differential stress during sample deformation the change results from the active interaction of microcracks this transition of the spatial distribution of ae hypocenters is accompanied by a corresponding change in the temporal correlation of events and in the distribution of event amplitudes as signified by a decrease of b value the characteristic structure that develops in the low energy background ae is similar to the sequence of the strongest microfracture events when the ar fractal structure develops the variations of d and b are synchronous and d 3b this relation which occurs once the fractal structure is formed only holds for average values of d and b time variations of d and b are anticorrelated the degree of temporal correlation of ar has time variations that are similar to d and b variations the observed variations in laboratory ae experiments are compared with natural seismicity parameters the close correspondence between laboratory scale observations and naturally occurring seismicity suggests a possible new approach for understanding the evolution of complex seismicity patterns in nature

possible hydraulic significance of two kinds of potholes examples from the paleo potomac river potholes preserved along abandoned sections of bedrock bounded rivers should provide significant paleohydraulic data if the conditions for pothole formation are understood in a prototype study we recognize two kinds of potholes along the paleo potomac river near great falls virginia vertical potholes drilled into the strath floor are circular in plan and are interpreted to form at sites of small stream depths and high flow velocity lateral potholes noncircular with overhanging roofs are found on flanks of rock obstacles they are interpreted to be eroded by sediment laden vertical flow near the air water interface the vortices circulate water in the horizontal plane and begin to form near the free surface in flow separation zones downstream of the obstacles the geometry of flow separation zones and thus the location of the lateral potholes are scaled by flow reynolds number therefore lateral potholes could be used to reconstruct paleoflow depths and velocities if parts of the channel bed adjacent to the flow obstruction are preserved

laboratory simulation of volcano seismicity the physical processes generating seismicity within volcanic edifices are highly complex and not fully understood we report results from a laboratory experiment in which basalt from mount etna volcano italy was deformed and fractured the experiment was monitored with an array of transducers around the sample to permit full waveform capture location and analysis of microseismic events rapid post failure decompression of the water filled pore volume and damage zone triggered many low frequency events analogous to volcanic long period seismicity the low frequencies were associated with pore fluid decompression and were located in the damage zone in the fractured sample these events exhibited a weak component of shear double couple slip consistent with fluid driven events occurring beneath active volcanoes