segmented lateral dyke growth in a rifting event at barðarbunga volcanic system iceland crust at many divergent plate boundaries forms primarily by the injection of vertical sheet like dykes some tens of kilometres long1 previous models of rifting events indicate either lateral dyke growth away from a feeding source with propagation rates decreasing as the dyke lengthens2 3 4 or magma flowing vertically into dykes from an underlying source5 6 with the role of topography on the evolution of lateral dykes not clear here we show how a recent segmented dyke intrusion in the bar arbunga volcanic system grew laterally for more than 45 kilometres at a variable rate with topography influencing the direction of propagation barriers at the ends of each segment were overcome by the build up of pressure in the dyke end then a new segment formed and dyke lengthening temporarily peaked the dyke evolution which occurred primarily over 14 days was revealed by propagating seismicity ground deformation mapped by global positioning system gps interferometric analysis of satellite radar images insar and graben formation the strike of the dyke segments varies from an initially radial direction away from the bar arbunga caldera towards alignment with that expected from regional stress at the distal end a model minimizing the combined strain and gravitational potential energy explains the propagation path dyke opening and seismicity focused at the most distal segment at any given time and were simultaneous with magma source deflation and slow collapse at the bar arbunga caldera accompanied by a series of magnitude m 5 earthquakes dyke growth was slowed down by an effusive fissure eruption near the end of the dyke lateral dyke growth with segment barrier breaking by pressure build up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries

the magmatic plumbing system of the askja central volcano iceland as imaged by seismic tomography the magmatic plumbing system beneath askja a volcano in the central icelandic highlands is imaged using local earthquake tomography we use a catalog of more than 1300 earthquakes widely distributed in location and depth to invert for the p wave velocity vp and the vp vs ratio extensive synthetic tests show that the minimum size of any velocity anomaly recovered by the model is 4 km in the upper crust depth 8 km below sea level bsl increasing to 10 km in the lower crust at a depth of 20 km bsl the plumbing system of askja is revealed as a series of high vp vs ratio bodies situated at discrete depths throughout the crust to depths of over 20 km we interpret these to be regions of the crust which currently store melt with melt fractions of 10 the lower crustal bodies are all seismically active suggesting that melt is being actively transported in these regions the main melt storage regions lie beneath askja volcano concentrated at depths of 5 km bsl with a smaller region at 9 km bsl their total volume is 100 km3 using the recorded waveforms we show that there is also likely to be a small highly attenuating magmatic body at a shallower depth of about 2 km bsl

minas fault zone late paleozoic history of an intra continental orogenic transform fault in the canadian appalachians abstract the minas fault zone mfz defines the boundary between the avalon and meguma terranes in the canadian appalachians and is exposed in mainland nova scotia and southern new brunswick these terranes originated along the gondwanan margin but had accreted to laurentia by the middle devonian the surface trace of the mfz is adjacent to the southern margin of the latedevonian permian maritimes basin the late devonian late carboniferous evolution of the mfz involves several episodes of oblique dextral shear that resulted in basin formation and inversion and at various times the zone was the focus of magmatism regional fluid flow and mineralization in the late devonian early carboniferous asymmetric rifting accompanied by dextral shear produced two coeval sequences the horton group which is dominated by continental clastic strata and the fountain lake group which consists predominantly of bimodal volcanic rocks that overlie high level plutons emplaced along active shear zones the overall tectonic environment may have been dominated by dextral transtension along the southern margin of laurentia which corresponded with the northern flank of the rheic ocean a major change in the evolution of the minas fault zone occurred in the late mississippian early pennsylvanian and produced the e w chedabucto fault clockwise rotation of pre existing structures local zones of transtension and transpression as well as regional fluid flow and extensive mineralization this major change may reflect the onset of laurentia gondwana oblique collision the effects of which continued into the latest carboniferous with coeval development of flower structures and pull apart basins in zones of local transpression and transtension

stress sensitivity of fault seismicity a comparison between limited offset oblique and major strike slip faults we present a new three dimensional inventory of the southern san francisco bay area faults and use it to calculate stress applied principally by the 1989 m 7 1 loma prieta earthquake and to compare fault seismicity rates before and after 1989 the major high angle right lateral faults exhibit a different response to the stress change than do minor oblique right lateral thrust faults seismicity on oblique slip faults in the southern santa clara valley thrust belt increased where the faults were unclamped the strong dependence of seismicity change on normal stress change implies a high coefficient of static friction in contrast we observe that faults with significant offset 50 100 km behave differently microseismicity on the hayward fault diminished where right lateral shear stress was reduced and where it was unclamped by the loma prieta earthquake we observe a similar response on the san andreas fault zone in southern california after the landers earthquake sequence additionally the offshore san gregorio fault shows a seismicity rate increase where right lateral oblique shear stress was increased by the loma prieta earthquake despite also being clamped by it these responses are consistent with either a low coefficient of static friction or high pore fluid pressures within the fault zones we can explain the different behavior of the two styles of faults if those with large cumulative offset become impermeable through gouge buildup coseismically pressurized pore fluids could be trapped and negate imposed normal stress changes whereas in more limited offset faults fluids could rapidly escape the difference in behavior between minor and major faults may explain why frictional failure criteria that apply intermediate coefficients of static friction can be effective in describing the broad distributions of aftershocks that follow large earthquakes since many of these events occur both inside and outside major fault zones

structural geology of the penobsquis salt structure late bashkirian inversion tectonics in the moncton basin new brunswick eastern canada this study uses new information acquired from field mapping mineral exploration boreholes and seismic reflection profiles to constrain the structural geology deformation mechanisms and timing of the penobsquis salt structure this information is used to place the development of the salt structure into the context of the tectonic evolution of the moncton basin the penobsquis salt structure is an elongate salt wall separated from underlying rocks by a mylonitic detachment horizon it may be divided into two segments a southwestern asymmetric southeast verging structure and a northeastern strongly asymmetric to overturned southeast verging structure associated with the penobsquis fault an initial low amplitude salt anticline formed during deposition of the mabou group serpukhovian time the salt anticline was modified into a high amplitude salt wall after deposition of cumberland group sediments early bashkirian or later the sense of asymmetry of the penobsquis salt structure the presence of thrust faults within the structure the spatial association of the structure with a major reverse fault in the salt cover and the temporal association of salt movement and compressional tectonic events suggest that the salt structure developed in response to tectonic contraction during inversion of the moncton basin

intense seismicity during the 2014 2015 barðarbunga holuhraun rifting event iceland reveals the nature of dike induced earthquakes and caldera collapse mechanisms

seismicity of the askja and barðarbunga volcanic systems of iceland 2009 2015 abstract a large seismic network deployed in the icelandic highlands recorded 100 000 earthquakes from 2009 to 2015 we develop a local magnitude scale appropriate for use in central iceland which is similar to the scale used by the iceland meteorological office using this large catalogue of earthquakes we analyze the spatial and temporal changes in seismicity rates and b values in microearthquakes recorded from the usually ductile lower crust we find that b values are high reflecting the presence of high thermal gradients and low stresses driving seismicity associated with the movement of melt in contrast b values in the upper crust are variable low b values indicative of a high stress environment are observed during seismic swarms such as those around mt her ubrei and around bar arbunga caldera a persistently seismically active area around a geothermal area within askja caldera has a b value around 1 but has a strong annual cycle of seismicity we attribute the annual cycle to varying load from the snow cover modulating the seismicity seismicity driven by the intrusion of a large dyke has a b value well above 1 driven by the high pore fluid pressures and thermal gradients around the dyke

time dependent dike propagation from joint inversion of seismicity and deformation data dike intrusions both deform earth s surface and induce propagating earthquake swarms we develop methods to utilize both deformation and seismicity from brittle volcano tectonic earthquakes to image time dependent dike propagation dieterich s 1994 seismicity rate theory is used to relate dike induced stress changes to seismicity rate and is combined with elastic green s functions relating dike opening to deformation different space time patterns of seismicity develop if earthquakes occur at the same depth as the dike compared to above below the dike in the former seismicity initiates near the dike s leading edges but shuts off as the dike tips pass and seismogenic volumes fall into stress shadows in the latter seismicity continues at a decaying rate after the tips pass we focus on lateral propagation and develop a nonlinear inversion method that estimates dike length and pressure as a function of time the method is applied to the 2007 father s day intrusion in kilauea volcano seismicity is concentrated at 3 km depth comparable to geodetic estimates of dike depth and decays rapidly in time with lateral propagation only and a vertical dike tip line it is difficult to fit both gps data and the rapid down rift jump in seismicity suggesting significant vertical propagation for the events to have occurred below the dike requires a very short aftershock decay time hence unreasonably high background stressing rate the rapid decay is better explained if the dike extends somewhat below the seismicity we suggest that joint inversion is useful for studying the diking process and may allow for improved short term eruption forecasts

seismic amplitude ratio analysis of the 2014 2015 bar arbunga holuhraun dike propagation and eruption magma is transported in brittle rock through dikes and sills this movement may be accompanied by the release of seismic energy that can be tracked from the earth s surface locating dikes and deciphering their dynamics is therefore of prime importance in understanding and potentially forecasting volcanic eruptions the seismic amplitude ratio analysis sara method aims to track melt propagation using the amplitudes recorded across a seismic network without picking the arrival times of individual earthquake phases this study validates this methodology by comparing sara locations filtered between 2 and 16hz with the earthquake locations same frequency band recorded during the 2014 2015 bar arbunga holuhraun dike intrusion and eruption in iceland integrating both approaches also provides the opportunity to investigate the spatiotemporal characteristics of magma migration during the dike intrusion and ensuing eruption during the intrusion sara locations correspond remarkably well to the locations of earthquakes several exceptions are however observed 1 a low frequency signal was possibly associated with a subglacial eruption on 23 august 2 a systematic retreat of the seismicity was also observed to the back of each active segment during stalled phases and was associated with a larger spatial extent of the seismic energy source this behavior may be controlled by the dike s shape and or by dike inflation 3 during the eruption sara locations consistently focused at the eruptive site 4 tremor rich signal close to ice cauldrons occurred on 3 september this study demonstrates the power of the sara methodology provided robust site amplification quality factors and seismic velocities are available plain language summary locating earthquakes usually implies picking phase arrivals p and s waves another technique called seismic amplitude ratio analysis sara was recently introduced to locate them only by using the amplitude recorded at different pairs of seismic stations however this technique was never proven to be true this study shows that the earthquake locations derived by sara compares remarkably well with the locations of 30 000 seismic events triggered when magma migrated in the icelandic crust prior to the 2014 2015 holuhraun eruption but the results also provide new insight into the magma dynamics that led to the largest eruption of the last two centuries in europe we show that ground vibration was continuously triggered during the 2week period preceding the eruption when magma forced its way toward the eruption site but also during the eruption itself several intriguing features were observed including low frequency vibrations possibly associated with eruption below the ice or large patches of seismic activity when the magma stopped propagating toward the eruption site this methodology performs very well provided some parameters are available and allows to gain insights into the complex dynamics associated with magma movements

comment on paper morphology and compositions of spinel in pu u ō ō lava 1996 1998 kilauea volcano hawaii enigmatic discrepancies between lava and gas based fo2 determinations of pu u ō ō lava

subsidence in late paleozoic basins in the northern appalachians during the interval between continental collision in the devonian and continental breakup in the triassic the northern appalachians became the site of a wide plate boundary zone of dominantly right lateral strike slip as is typical of intracontinental transforms tectonism was both diachronous and rapidly variable along strike through regimes of pure strike slip transpressional deformation and rapid subsidence of extensional basins up to 9 km of mainly nonmarine clastic sediments accumulated in these local depocenters which subsided episodically in two stages 1 an initial phase of stretching and thinning of the lithosphere when subsidence was rapid fault controlled and often accompanied by volcanism and 2 a subsequent phase of gradual thermal subsidence during which the depositional basins expanded to bury the earlier border faults and progressively younger sedimentary units onlapped basement the largest depocenter the magdalen basin opened as a pull apart between strike slip faults in newfoundland and new brunswick from late devonian to early carboniferous subsequent thermal subsidence affected a large area during medial and late carboniferous a phenomenon that is well recorded to the north and west where no later tectonism occurred in areas to the south and east of the basin strike slip on other faults continued into the time of thermal subsidence introducing complications such as localized transpressional deformation and rapid subsidence in smaller pull aparts

insar observations and models of crustal deformation due to a glacial surge in iceland surges are common at all the major ice caps in iceland ice masses of gigatons may shift from the upper part of the outlet glacier towards the terminus in a few months advancing the glacier front by up to several kilometres the advancing ice front may be up to 100 m thick increasing the load on crustal rocks correspondingly we use the observed change in crustal loading during a surge of the western part of the vatnajokull ice cap iceland during 1993 1995 and the corresponding elastic crustal deformation surveyed with interferometric synthetic aperture radar to investigate the material properties of the solid earth in this region crustal subsidence due to the surge reaches 75mm at the edge of the si ujokull outlet glacier this signal is mixed with a broad uplift signal of 12 mm yr relative to our reference area caused by the ongoing retreat of vatnajokull in response to climate change we disentangle the two signals by linear inversion finite element modelling is used to investigate the elastic earth response of the surge as well as to confirm that no significant viscoelastic deformation occurred as a consequence of the surge the modelling leads to estimates of the young s modulus and poisson s ratio of the underlying earth comparison between the observed and modelled deformation fields is made using a bayesian approach that yields the estimate of a probability distribution for each of the free parameters residuals indicate a good agreement between models and observations one layer elastic models result in a young s modulus of 43 2 49 7 gpa 95 per cent confidence and poisson s ratio of 0 0 27 after removal of outliers our preferred model with two elastic layers provides a better fit to the whole surge signal this model consists of a 1 km thick upper layer with an average young s modulus of 12 9 15 3 gpa and poisson s ratio of 0 17 overlying a layer with an average young s modulus of 67 3 81 9 gpa and poisson s ratio of 0 25

deformation mechanisms and flow regimes in limestones from the helvetic zone of the swiss alps abstract this paper is based on a combined field transmission electron tem and transmission optical tom microscope study of limestones from the helvetic zone swiss alps and discusses the deformation mechanisms and flow regimes that governed the deformation of these rocks during pre metamorphic regional ductile deformations the limestones deformed by power law dislocation creep with differential stresses probably not exceeding 1 kbar dynamic recrystallization with grain boundary sliding and grain boundary migration allowed the grains to be less elliptical than the strain ellipse a characteristic of the structure is the existence of dislocation free subgrains in the footwall of and approaching the lochseiten calc mylonite along the glarus overthrust grain boundary sliding becomes more important shift to diffusional creep or superplastic flow during a syn and post metamorphic deformation dynamic recovery seems to have become less competitive no dislocation free sub grains and along thrust faults twinning indicates a shift to higher differential stresses at the close of the deformation it was not possible to separate these deformation phases on the basis of the dislocation debris sub grain sizes as observed in tem and tom were identical in limestones that underwent cataclastic deformation the rocks seem to have started breaking up along the grain boundaries the new grain fragments are very small 0 1 0 3 m and are heavily twinned in tem the old large grains show very long straight glide dislocations cleavage and when shattered ring patterns in diffraction

late devonian carboniferous detachment faulting and extensional tectonics in western cape breton island nova scotia canada abstract shallow dipping detachment faults have played a key role in the evolution of the late devonian to carboniferous maritimes basin of western cape breton island the faults are responsible for large scale post orogenic crustal thinning and denudation of mid crustal levels tournaisian and westphalian clastic sedimentation can be related to detachment faulting along the margaree shear zone msz and the ainslie detachment ad respectively the msz consists of thick shallow dipping retrogressive mylonite overprinted by cataclastic horizons brittle detachment faults and chloritic breccia the shear zone crosscuts and transports low grade late devonian bimodal volcanic rocks and redbeds of the fisset brook formation in its hanging wall towards the west and juxtaposes them against exhumed medium to high grade metamorphic rocks and basement in its footwall locally the mylonite is 200 700 m thick and outcrops along strike from north to south for approximately 60 km tournaisian coarse clastic units and debris flow deposits of the horton group unconformably overlie ductile mylonite of the msz due to incision of brittle faults into the msz regional transgression and marine flooding of the extensional complex and exhumed units are marked by the thick visean carbonate and evaporite deposits of the windsor group the carbonates reflect a relatively quiescent tectonic regime and widespread subsidence was likely due to the cessation of extension related thermally induced buoyancy in a tectonically thinned crust the ainslie detachment nucleated as a regional flat lying fault along the carbonate evaporite contact at the top of the macumber formation forming calc mylonite near the base of the windsor group significant stratigraphic omissions in the windsor group above the detachment provide clear evidence of an extensional regime during faulting clastic deposits of the westphalian cumberland group are bounded by the detachment and sedimentation is related to listric normal faults which cut down section towards the west southwest the documentation of detachment faults has widespread implications for the interpretation of the post orogenic evolution of the northern appalachians an extensional regime can now be recognized deep reflection seismic data are interpreted in light of the new findings and can be related to late devonian carboniferous basin formation

development of pull apart basins a comparative study of well mapped active and ancient pull apart basins suggests a qualitative model for their continuous development pull aparts evolve from incipient to extremely developed basins through a sequence of closely related states new and compiled map data from several areas including the northern caribbean and turkey suggests the following stages in pull apart development 1 in rigid intracontinental strike slip plate boundary zones larger pull aparts nucleate at releasing fault bends along segments of the principal displacement strike slip fault zone which are oblique to the theoretical interplate slip lines 2 initial opening across releasing fault bends produces spindle shaped basins defined and often bisected by oblique slip faults connecting the discontinuous ends of the strike slip faults 3 increased strike slip offset produces basin shapes which we colloquially call lazy s shape for basins between sinistral faults and lazy z shape for basins between dextral faults 4

mechanical models for dikes a third school of thought abstract geological and geophysical data from continental volcanic centers and giant radial swarms and from oceanic shield volcanoes and rift zones indicate that dikes propagate laterally for distances that can be 10 to over 100 times their height what traps dikes within the shallow lithosphere and promotes these highly eccentric shapes gravity induced stress gradients in the surrounding rock and pressure gradients in the magma are the primary loading mechanisms pressure gradients due to magma flow are secondary to insignificant because the flow direction is dominantly horizontal this configuration of vertical blade shaped dikes with horizontal dike propagation and magma flow is fundamentally different from the two dike model configurations described in a recent review paper as two schools of thought for mechanical models of dikes in school i a dike is disconnected from its source and ascends under the influence of buoyancy in school ii a dike is connected to a magma reservoir and is driven upward by magma flux from the source we review the geological and geophysical data supporting the vertical dike horizontal flow propagation configuration and suggest the abundance and veracity of these data in many different geological settings and the modeling results that address this physical process warrant adding this as a third school of thought a new analytical solution for the boundary value problem of a homogeneous isotropic and linear elastic solid with a vertical fluid filled crack is used to investigate the effects of gravitationally induced stress and pressure gradients on the aperture distribution dike tip stress intensity and stable height model results indicate that in a homogeneous crust dikes can achieve stable heights greater than a kilometer only if the host rock fracture toughness k ic 100 mpa m 1 2 however density stratification of the crust is an effective mechanism for trapping kilometer scale dikes even if the host rock is very weak k ic 0 this analysis may explain why vertical dikes propagate laterally for great distances but reside within a narrow range of depths in the crust

deep crustal melt plumbing of barðarbunga volcano iceland understanding magmatic plumbing within the earth s crust is important for understanding volcanic systems and improving eruption forecasting we discuss magma plumbing under bar arbunga volcano iceland over a 4 year period encompassing the largest icelandic eruption in 230 years microseismicity extends through the usually ductile region of the earth s crust from 7 to 22 km depth in a subvertical column moment tensor solutions for an example earthquake exhibits opening tensile crack behavior this is consistent with the deep 7 km seismicity being caused by the movement of melt in the normally aseismic crust the seismically inferred melt path from the mantle source is offset laterally from the center of the bar arbunga caldera by 12 km rather than lying directly beneath it it is likely that an aseismic melt feed also exists directly beneath the caldera and is aseismic due to elevated temperatures and pervasive partial melt under the caldera

geochemical evidence of the renewal of volcanic activity inferred from co2 soil and so2 plume fluxes the 2007 stromboli eruption italy on 27 february 2007 a new eruption occurred on stromboli which lasted until 2 april it was characterized by effusive activity on the sciara del fuoco and by a paroxysmal event 15 march this crisis represented an opportunity for us to refine the model that had been developed previously 2002 2003 eruption and to improve our understanding of the relationship between the magmatic dynamics of the volcano and the geochemical variations in the fluids in particular the evaluation of the dynamic equilibrium between the volatiles co2 and so2 released from the magma and the corresponding fluids discharged from the summit area allowed us to evaluate the level of criticality of the volcanic activity one of the major accomplishments of this study is a 4 year database of summit soil co2 flux on the basis of which we define the thresholds low medium high for this parameter that are empirically based on the natural volcanological evolution of stromboli the so2 fluxes of the degassing plume and the co2 fluxes emitted from the soil at pizzo sopra la fossa are also presented it is noteworthy that geochemical signals of volcanic unrest have been clearly identified before during and after the effusive activity these signals were found almost simultaneously in the degassing plume so2 flux and in soil degassing co2 flux at the summit although the two degassing processes are shown to be clearly different the interpretation of the results will be useful for future volcanic surveillance at stromboli

reply to comment on paper morphology and composition of spinel in pu u o o lava 1996 1998 kilauea volcano hawaii enigmatic discrepancies between lava and gas based fo2 determinations of pu u o o lava

review of the evolution of geochemical monitoring networks and methodologies applied to the volcanoes of the aeolian arc italy abstract fluids discharged from volcanic systems are the direct surface manifestation of magma degassing at depth and provide primary insights for evaluating the state of volcanic activity we review the geochemical best practice in volcanic surveillance based to a huge amount of monitoring data collected at different active volcanoes using both continuous and discontinuous approaches the targeted volcanoes belong to the aeolian arc located in the tyrrhenian sea italy and they have exhibited different activity states during the monitoring activities reported here la fossa cone on vulcano island has been in an uninterrupted quiescent stage characterized by variable solfataric activity in contrast stromboli island has shown a persistent mild explosive activity episodically interrupted by effusive eruptions in 1985 2002 2007 and 2014 panarea island which is the summit of a seamount rising from the seafloor of the southern tyrrhenian sea showed only undersea fluid release the only observable clues of active volcanism at panarea island have been impulsive changes in the undersea fluid release with the last submarine gas burst event being observed in november 2002 the geochemical monitoring and observations at each of these volcanoes has directly involved the volcanic plume and or the fumarole vents thermal waters and diffuse soil degassing depending on the type of manifestations and the level of activity encountered through direct access to the magmatic samples when possible and the collection of as much observable data related to the fluid release as possible the aim has been i to verify the thermodynamic equilibrium condition ii to discern among the possible hydrothermal magmatic marine and meteoric sources in the fluid mixtures iii to develop models of the fluid circulation supported by data iv to follow the evolution of these natural systems by long term monitoring and v to support surveillance actions related to defining the volcanic risk and the evaluation and possible mitigation of related hazards the examples provided in this review article show the close relationships among data analysis interpretation and modeling we particularly focus on describing the fieldwork procedures since any theoretical approach must always be verified and supported by field data rather than just by experiments controlled in laboratory indeed the natural systems involve many variables producing effects that cannot be neglected the monitored volcanic systems have been regarded as natural laboratories and all of the activities have focused on both volcanological research and surveillance purposes in order to ensure that these two goals have overlapped an appendix is also included that explains the scientific approach to the systematic activities regarding geochemical monitoring of volcanic activity

effects of source model variations on coulomb stress analyses of a multi fault intraplate earthquake sequence abstract fault models are quickly produced and iteratively improved over weeks to years following a major earthquake to characterise the dynamics of rupture evaluate the role of stress transfer and contribute to earthquake forecasting we model coulomb stress transfer cfs between the largest foreshock mw 5 4 1 year prior to first mainshock and three mw 6 1 to 6 5 earthquakes that occurred in a 12 hour period on january 22 1988 in central australia tennant creek earthquake sequence to investigate the role of static stress transfer in earthquake triggering relative to progressive source model development the effects of fault model variance are studied using cfs modelling of five different fault source model sequences 27 total models using different inputs from seismic and geospatial data some initial models do not yield positive cfs changes proximal to hypocentres but in all models preceding earthquakes generate positive cfs 0 1 bar on 10 to 30 of the forthcoming receiver fault rupture areas the most refined and data integrative model reveals cfs 0 7 to 13 bars within 2 km of impending hypocentres and large 30 to 99 areas of positive cfs when compared to global compilations of threshold cfs prior to impending ruptures average 3 71 bar median 1 bar this suggests that coulomb stress change theory adequately explains the tennant creek rupture sequence in the most refined model earthquake inter event times decrease as cfs increases suggesting that higher stress magnitudes may have more rapidly within hours triggered successive events thus accounting for some temporal aspects of this sequence cfs analyses provide a useful framework for understanding the spatiotemporal aspects of some intraplate earthquakes the progressive refinement of source models using emergent data may reduce epistemic uncertainties in the role of stress transfer that result from different model inputs approaches and results

triggering of earthquake aftershocks by dynamic stresses it is thought that small static stress changes due to permanent fault displacement can alter the likelihood of or trigger earthquakes on nearby faults many studies of triggering in the near field particularly of aftershocks rely on these static changes as the triggering agent and consider them only in terms of equivalent changes in the applied load on the fault here we report a comparison of the aftershock pattern of the moment magnitude mw 7 3 landers earthquake not only with static stress changes but also with transient oscillatory stress changes transmitted as seismic waves that is dynamic stresses dynamic stresses do not permanently change the applied load and thus can trigger earthquakes only by altering the mechanical state or properties of the fault zone these dynamically weakened faults may fail after the seismic waves have passed by and might even cause earthquakes that would not otherwise have occurred we find similar asymmetries in the aftershock and dynamic stress patterns the latter being due to rupture propagation whereas the static stress changes lack this asymmetry previous studies have shown that dynamic stresses can promote failure at remote distances but here we show that they can also do so nearby

driving magma to the surface the 2011 2012 el hierro volcanic eruption we reanalyzed the seismic and deformation data corresponding to the pre eruptive unrest on el hierro canary islands in 2011 we considered new information about the internal structure of the island we updated the seismic catalogue to estimate the full evolution of the released seismic energy and demonstrate the importance of non located earthquakes using seismic data and gps displacements we characterized the shear tensile type of the predominant fracturing and modelled the strain and stress fields for different time periods this enabled us to identify a prolonged first phase characterized by hydraulic tensile fracturing which we interpret as being related to the emplacement of new magma below the volcanic edifice on el hierro this was followed by post injection unidirectional migration probably controlled by the stress field and the distribution of the structural discontinuities we identified the effects of energetic magmatic pulses occurring a few days before the eruption that induced shear seismicity on pre existing faults within the volcano and raised the coulomb stress over the whole crust we suggest that these magmatic pulses reflect the crossing of the moho discontinuity as well as changes in the path geometry of the dyke migration towards the surface the final phase involved magma ascent through a pre fractured crust

geological correlations between cape breton island and newfoundland northern appalachian orogen geological correlations between cape breton island and newfoundland are apparent both in surface geology and at deeper crustal levels based on similarities in sm nd isotopic signatures the mira terrane of southeastern cape breton island is part of the avalon terrane sensu stricto and is composed of neoproterozoic volcanic sedimentary plutonic belts and overlying cambrian rocks directly comparable to those in the western part of the newfoundland avalon terrane the bras d or terrane is also mainly of neoproterozoic age but shows lithological and isotopic contrasts with the mira terrane small areas of similar neoproterozoic rocks occur in southern newfoundland and to the north as inliers in the exploits terrane the bras d or terrane and similar rocks in newfoundland are interpreted to represent a peri gondwanan terrane where rocks of the gander terrane were later formed hence this area is part of the central mobile belt and distinct from avalon terrane sensu stricto the aspy terrane is a complex area

evolution of a lateral dike intrusion revealed by relatively relocated dike induced earthquakes the 2014 15 barðarbunga holuhraun rifting event iceland abstract understanding dikes is vital as they serve both as bodies that build the crust and as conduits that feed eruptions and must be monitored to evaluate volcanic hazard during the 2014 15 bar arbunga rifting event iceland intense seismicity accompanied the intrusion of a 50 km lateral dike which culminated in a 6 month long eruption we here present relocations of earthquakes induced by the lateral dike intrusion using cross correlated sub sample relative travel times the 100 m spatial resolution achieved reveals the complexity of the dike propagation pathway and dynamics jerky segmented and allows us to address the precise relationship between the dike and seismicity with direct implications for hazard monitoring the spatio temporal characteristics of the induced seismicity can be directly linked in the first instance to propagation of the tip and opening of the dike and following this after dike opening indicate a relationship with magma pressure changes i e dike inflation deflation followed by a general post opening decay seismicity occurs only at the base of the dike where dike imposed stresses combined with the background tectonic stress from regional extension over 200 yr since last rifting are sufficient to induce failure of pre existing weaknesses in the crust while the greatest opening is at shallower depths emplacement oblique to the spreading ridge resulted in left lateral shear motion along the distal dike section studied here and a prevalence of left lateral shear failure fault plane strikes are predominately independent of the orientation of lineations delineated by the hypocenters indicating that they are controlled by the underlying host rock fabric this high resolution study provides unprecedented opportunity for comparison with both geodetic and field frozen dike observations and development and consolidation of analytical and analogue models with implications for rifting processes and real time monitoring of magma intrusion

magma supply and storage at kilauea volcano hawaii 1956 1983 abstract shallow crustal magma reservoirs beneath the summit of kilauea volcano and within its rift zones are linked in such a way that the magma supply to each can be estimated from the rate of ground deformation at the volcano s summit our model builds on the well documented pattern of summit inflation as magma accumulates in a shallow summit reservoir followed by deflation as magma is discharged to the surface or into the rift zones magma supply to the summit reservoir is thus proportional to summit uplift and supply to the rift zones is proportional to summit subsidence the average proportionality constant is 0 33 10 6 m 3 rad this model yields minimum supply estimates because it does not account for magma which escapes detection by moving passively through the summit reservoir or directly into the rift zones calculations suggest that magma was supplied to kilauea during july 1956 april 1983 at a minimum average rate of 7 2 10 6 m3 month roughly 35 of the net supply was extruded the rest remains stored within the volcano s east rift zone 55 and southwest rift zone 10 periods of relatively rapid supply were associated with the large kapoho eruption in 1960 and the sustained mauna ulu eruptions in 1969 1971 and 1972 1974 bursts of harmonic tremor from the mantle beneath kilauea were also unusually energetic during 1968 1975 suggesting a close link between kilauea s deep magma supply region and shallow storage reservoirs it remains unclear whether pulses in magma supply from depth give rise to corresponding increases in shallow supply or if instead unloading of a delicately balanced magma transport system during large eruptions or intrusions triggers more rapid ascent from a relatively constant mantle source

modeling stress changes induced by earthquakes in the southern marlborough region south island new zealand between 1888 and 1994 a series of seven earthquakes of m w 5 9 7 2 occurred within a 150 km by 150 km area southern marlborough region directly east of the alpine fault major strike slip faults in this region including the hope kakapo and clarence faults serve to transfer plate motion from the alpine fault northeastward to the hikurangi subduction zone we have modeled induced changes in coulomb failure stress cfs to determine whether stress triggering could have occurred during this sequence and to determine how the earthquakes have affected stress along the north westland segment of the alpine fault which appears to have last ruptured in this region in a d 1717 we included the effects of secular stress accumulation on the four most rapidly slipping faults in the region alpine awatere clarence and hope but neglected the effects of viscoelastic relaxation our results suggest that at least six of seven earthquakes and possibly all seven events when uncertainties in earthquake location and focal mechanism are considered occurred in regions where cfs exceeded 10 kpa indicating stress triggering may have occurred although cfs exceeds 10 kpa along most of the north westland segment of the alpine fault at depths of 10 km or less cfs is less than 10 kpa at depths of 10 km or more if rupture for large alpine fault events initiates at depths of 10 km or more then this result implies that the induced stress since 1848 has not brought this segment significantly closer to failure manuscript received 1 february 2001

the use of earthquake rate changes as a stress meter at kilauea volcano stress changes in the earth s crust are generally estimated from model calculations that use near surface deformation as an observational constraint but the widespread correlation of changes of earthquake activity with stress has led to suggestions that stress changes might be calculated from earthquake occurrence rates obtained from seismicity catalogues although this possibility has considerable appeal because seismicity data are routinely collected and have good spatial and temporal resolution the method has not yet proven successful owing to the non linearity of earthquake rate changes with respect to both stress and time here however we present two methods for inverting earthquake rate data to infer stress changes using a formulation for the stress and time dependence of earthquake rates application of these methods at kilauea volcano in hawaii yields good agreement with independent estimates indicating that earthquake rates can provide a practical remote sensing stress meter

toggling of seismicity by the 1997 kagoshima earthquake couplet a demonstration of time dependent stress transfer 1 two m 6 well recorded strike slip earthquakes struck just 4 km and 48 days apart in kagoshima prefecture japan in 1997 providing an opportunity to study earthquake interaction aftershocks are abundant where the coulomb stress is calculated to have been increased by the first event and they abruptly stop where the stress is dropped by the second event this ability of the main shocks to toggle seismicity on and off argues that static stress changes play a major role in exciting aftershocks whereas the dynamic coulomb stresses which should only promote seismicity appear to play a secondary role if true the net stress changes from a sequence of earthquakes might be expected to govern the subsequent seismicity distribution however adding the stress changes from the two kagoshima events does not fully capture the ensuing seismicity such as its rate change temporal decay or migration away from the ends of the ruptures we therefore implement a stress transfer model that incorporates rate state friction in which seismicity is treated as a sequence of independent nucleation events that are dependent on the fault slip slip rate and elapsed time since the last event the model reproduces the temporal response of seismicity to successive stress changes including toggling decay and aftershock migration nevertheless the match of observed to predicted seismicity is quite imperfect due perhaps to inadequate knowledge of several model parameters however to demonstrate the potential of this approach we build a probabilistic forecast of larger earthquakes on the expected rate of small aftershocks taking advantage of the large statistical sample the small shocks afford not surprisingly such probabilities are highly time and location dependent during the first decade after the main shocks the seismicity rate and the chance of successive large shocks are about an order of magnitude higher than the background rate and are concentrated exclusively in the stress triggering zones

volcanic tremor at mt vesuvius associated with low frequency shear failures abstract mt vesuvius has been dormant since the eruption occurred in 1944 after which the conduit closed and the volcano entered a quiescent state only a minor seismic activity characterized by low magnitude volcano tectonic vt earthquakes testifies that the magmatic system is still active in this paper we report the fist quantitative analysis of volcanic tremor discovered at vesuvius through the analysis of array data a seismic array installed in 2012 improved the monitoring performance of the local network permitting the identification of low amplitude coherent signals many of such coherent signals recorded during the last few years have been classified as volcanic tremor we selected 22 tremor events based on their amplitude and on the number of available stations and performed detailed analysis aimed at location and characterization of the source they are characterized by low frequency duration of a few minutes and the strongest episodes are recorded at distance up to 90 km from the volcano in many cases we could identify p s wave pairs in the seismograms that allowed a precise location of the source depth which is in the range between 5 km and 6 5 km below the crater waveform features spectral analysis and comparison with vt earthquakes located at the same depth indicate that the source mechanism of the vesuvius non eruptive tremor is a sequence of low frequency shear failures

modeling the three dimensional structure of macroscopic magma transport systems application to kilauea volcano hawaii we report the results of modeling the three dimensional internal structure of kilauea s magmatic passageways the approach uses a clear plexiglass model containing equally spaced levels upon which well located seismic hypocenters are plotted application of constraining geologic and geophysical criteria to this distributed volume of earthquakes permits the interpretation of seismic structures produced by fracturing in response to locally high fluid pressures four magma transport and storage structures have been identified within and beneath kilauea 1 primary conduit the conduit transporting magma into kilauea s summit storage reservoir rises from the model base 14 6 km to the 6 5 km depth level it is a zone of intense fracturing and inferred intrusion whose horizontal sections are elliptical in planform over its height the average major axis of the component horizontal sections is 3 3 km with an average minor axis of 1 7 km this yields an aspect ratio of 0 52 at the 14 6 km level the strike of the major axis is n67 e during passage from the upper mantle through the oceanic crust this axis rotates in a right handed sense until the strike is n41 w at the 6 5 km level 2 magma chamber complex floor the interval from 6 5 to 5 7 km immediately over the primary conduit is aseismic this suggests differentially high fluid to rock ratios and relatively weak pathways for further vertical transport into higher levels of the storage complex as well as lateral leakage eastward into the mauna ulu staging area for later vertical ascent beneath the upper east rift zone seismicity within the immediately subjacent rocks that form the top of the primary conduit at 6 5 km suggests that this inferred magma rich horizon forms the effective floor of the summit storage complex 3 magma chamber crown intense seismicity over the 1 1 1 9 km depth interval defines an elliptical region in plan view the top of this region has a broad apex with an average major axis of 1 5 km and an average minor axis of 1 1 km producing an aspect ratio of 0 73 this region coincides with the epicentral position of summit vertical displacement maxima during inflationary deformation and is interpreted as a region of intense diking crowning the summit storage complex 4 upper east rift zone pipe from a depth of 5 7 km a cylindrical region of seismicity rises beneath the upper east rift zone to the 1 9 km level where it merges with the subhorizontal upper east rift zone duct this pipe like zone has a mean diameter of 1 4 km and a vertical axis that pierces the surface of the volcano at the intersection of the koae fracture system and the upper east rift zone we suggest this pipe forms a principal connection between the base of the summit storage reservoir and near surface storage compartments and ducts in the upper east rift zone in this role the pipe is suggested to have contributed heavily to mauna ulu s magma supply during 1969 1974 the model of magma transport and storage thus constructed provides a context in which other types of data e g ground deformation and electrical conductivity may be interpreted as well as a means of refining petrological inferences based on lava chemistry

gas analyses from the pu u o o eruption in 1985 kilauea volcano hawaii volcanic gas samples were collected from july to november 1985 from a lava pond in the main eruptive conduit of pu u o o from a 2 week long fissure eruption and from a minor flank eruption of pu u o o the molecular composition of these gases is consistent with thermodynamic equilibrium at a temperature slightly less than measured lava temperatures comparison of these samples with previous gas samples shows that the composition of volatiles in the magma has remained constant over the 3 year course of this episodic east rift eruption of kilauea volcano the uniformly carbon depleted nature of these gases is consistent with previous suggestions that all east rift eruptive magmas degas during prior storage in the shallow summit reservoir of kilauea minor compositional variations within these gas collections are attributed to the kinetics of the magma degassing process

the ainslie detachment a regional flat lying extensional fault in the carboniferous evaporitic maritimes basin of nova scotia canada the ainslie detachment occurs near the base of the carboniferous windsor group forming a regional flat lying extensional fault distributed across 10 000 km 2 new mapping has delineated the structure through southwestern cape breton island and into central nova scotia shearing is concentrated at the top of the basal macumber limestone along its contact with overlying evaporites and younger allochthonous units the highly contrasting rheologies of the formations created an anisotropic zone of weakness which acted as an upper crustal stress guide stratigraphically controlling the trajectory of the detachment through the basin the detachment is characterized by an approximately 3 10 m thick calc mylonite zone with an intense planar fabric featuring alternating very fine grained shear planes and coarser annealed layers coarser layers are boudinaged into pinch and swell structures locally producing segmented augen highly strained intraclasts ooids and peloids recrystallized carbonate boudins and carbonate vein segments are included in the calc mylonite as semirigid inclusions and rotated porphyroclasts thick zones of fault breccia straddle portions of the detachment and overprint the mylonite demonstrating an evolution to brittle conditions during progressive shear listric faults in the hanging wall of the detachment feature a ramp and flat geometry with an upper detachment occurring along the upper contact of the windsor group with the overlying namurian mabou group locally up to 2 km of the stratigraphic succession has been removed with faults cutting downsection in a westerly direction producing rollover in the hanging wall

volcano geodesy recent developments and future challenges abstract ascent of magma through earth s crust is normally associated with among other effects ground deformation and gravity changes geodesy is thus a valuable tool for monitoring and hazards assessment during volcanic unrest and it provides valuable data for exploring the geometry and volume of magma plumbing systems recent decades have seen an explosion in the quality and quantity of volcano geodetic data new datasets some made possible by regional and global scientific initiatives as well as new analysis methods and modeling practices have resulted in important changes to our understanding of the geodetic characteristics of active volcanism and magmatic processes from the scale of individual eruptive vents to global compilations of volcano deformation here we describe some of the recent developments in volcano geodesy both in terms of data and interpretive tools and discuss the role of international initiatives in meeting future challenges for the field

aftershocks halted by static stress shadows the role of permanent versus transient crustal stress changes in triggering earthquakes is debated analysis of the stress imparted by the joshua tree and nearby landers earthquakes in california in 1992 implies that a permanent drop in stress can halt aftershocks so such static stress changes should be incorporated into seismic hazard assessments

triggered earthquakes suppressed by an evolving stress shadow from a propagating dyke the role of static versus dynamic stresses in earthquake clusters is unclear analysis of earthquakes triggered by a dyke intrusion at an icelandic volcano unambiguously demonstrates that static stresses are important for earthquake clustering large earthquakes can generate small changes in static stress increases that trigger aftershock swarms or reductions that create a region of reduced seismicity a stress shadow1 2 however seismic waves from large earthquakes also cause transient dynamic stresses that may trigger seismicity3 4 this makes it difficult to separate the relative influence of static and dynamic stress changes on aftershocks dyke intrusions do not generate dynamic stresses so provide an unambiguous test of the stress shadow hypothesis here we use gps and seismic data to reconstruct the intrusion of an igneous dyke that is 46 km long and 5 m wide beneath bar arbunga volcano central iceland in august 2014 we find that during dyke emplacement bursts of seismicity at a distance of 5 to 15 km were first triggered and then abruptly switched off as the dyke tip propagated away from the volcano we calculate the evolving static stress changes during dyke propagation and show that the stressing rate controls both the triggering and then suppression of earthquake rates in three separate areas adjacent to the dyke our results imply that static stress changes help control earthquake clustering similar small static stress changes may be important for triggering seismicity near geothermal areas regions being hydrofractured and deflating oil and gas fields

the aurora volcanic field california nevada oxygen fugacity constraints on the development of andesitic magma the aurora volcanic field located along the northeastern margin of mono lake in the western great basin has erupted a diverse suite of high k and shoshonitic lava types with 48 to 76 wt sio2 o ver the last 3 6 million years there is no correlation between the age and composition of the lavas three quarters of the volcanic field consists of evolved 4 wt mgo basaltic andesite and andesite lava cones and flows the majority of which contain sparse euhedral phenocrysts that are normally zoned there is no evidence of mixed hybrid magmas the average eruption rate over this time period was 200 m 3 ykm 2 yyear which is typical of con tinental arcs and an order of magnitude lower than that for the slow spreading mid atlantic ridge all of the au rora lavas display a trace element signature common to subduction related magmas as exemplified by baynb ratios between 52 and 151 pre eruptive water contents ranged from 1 5 wt in plagioclase rich two pyroxene andesites to 6 wt in a single hornblende lamprophyre and several biotite hornblende andesites calculated oxygen fugacities fall within 0 4 and 12 4 log units of the ni nio buffer the aurora potassic suite follows a classic calc alkaline trend in a plot of feo t ymgo vs sio 2 and displays linear decreasing trends in feo t and tio2 with sio2 content suggesting a prominent role for fe ti oxides during differentiation however develop ment of the calc alkaline trend through fractional crys tallization of titanomagnetite would have caused the residual liquid to become so depleted in ferric iron that its oxygen fugacity would have fallen several log units below that of the ni nio buffer nor can fractionation of hornblende be invoked since it has the same effect as titanomagnetite in depleting the residual liquid in ferric iron together with a thermal stability limit that is lower than the eruption temperatures of several andesites 1040 10808c derived from two pyroxene ther mometry unless some progressive oxidation process occurs fractionation of titanomagnetite or hornblende cannot explain a calc alkaline trend in which all erupted lavas have oxygen fugacites the ni nio buffer in con trast to fractional crystallization closed system equi librium crystallization will produce residual liquids with an oxygen fugacity that is similar to that of the initial melt however the eruption of nearly aphryic lavas ar gues against tapping from a magma chamber during equilibrium crystallization a process that requires crys tals to remain in contact with the liquid a preferred model involves the accumulation of basaltic magmas at the mantle crust interface which solidify and are later remelted during repeated intrusion of basalt as an end member case closed system equilibrium crystallization of a basalt followed by equilibrium partial melting of the gabbro will produce a calc alkaline evolved liquid namely high sio 2 and low feo t ymgo with a relative fo2 corrected for the effect of changing temperature that is similar to that of the initial basalt differentiation of the aurora magmas by repeated partial melting of previous underplates in the lower crust rather than by crystal fractionation in large stable magma chambers is consistent with the low eruption rate at the aurora vol canic field

tertiary extensional tectonics in tuscany northern apennines italy abstract two extensional events have been recognized in the tertiary evolution of tuscany the first event occurred in the period between the late oligocene and late tortonian and caused a stretching of 120 or greater the second event occurred between the late tortonian and quaternary periods and caused a stretching not greater than 10 the first event is characterized by the exhumation of middle crust rocks and therefore by the development of core complexes the most significant structures of the first event are low angle normal faults which characterize the upper plate of the core complexes and ductile shear zones which characterize the lower plate the low angle normal faults tend to die out in the late triassic evaporite level which constitutes the main detachment of the core complexes the main structures of the second extensional event are high angle normal faults which dissect all the previous tectonic features these faults border tectonic depressions which were the site of clastic sedimentation from late tortonian to quaternary time these normal faults may tend to flatten in a seismic lozenge shaped band explained as an active extensional shear zone which is located at the brittle ductile boundary a similar explanation is given for the detachment located in the late triassic evaporite level during the first extensional event while the first extensional event is in the framework of the northern apennine post collisional evolution the second extensional event because it affects an already stretched crust could be attributed to the southern tyrrhenian opening which began during late tortonian

evidence from the ad 2000 izu islands earthquake swarm that stressing rate governs seismicity magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat such swarm seismicity also migrates with time and often exhibits a dog bone shaped distribution the largest earthquakes in swarms produce aftershocks that obey an omori type exponential temporal decay but the duration of the aftershock sequences is drastically reduced relative to normal earthquake activity here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion a 1 000 fold increase in seismicity rate and a 1 000 fold decrease in aftershock duration occurred during the two month long dyke intrusion we find that the seismicity rate is proportional to the calculated stressing rate and that the duration of aftershock sequences is inversely proportional to the stressing rate this behaviour is in accord with a laboratory based rate state constitutive law suggesting an explanation for the occurrence of earthquake swarms any sustained increase in stressing rate whether due to an intrusion extrusion or creep event should produce such seismological behaviour

stress triggering in thrust and subduction earthquakes and stress interaction between the southern san andreas and nearby thrust and strike slip faults 1 we argue that key features of thrust earthquake triggering inhibition and clustering can be explained by coulomb stress changes which we illustrate by a suite of representative models and by detailed examples whereas slip on surface cutting thrust faults drops the stress in most of the adjacent crust slip on blind thrust faults increases the stress on some nearby zones particularly above the source fault blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults we calculate that during a progressive thrust sequence in central california the 1983 mw 6 7 coalinga earthquake brought the subsequent 1983 mw 6 0 nunez and 1985 mw 6 0 kettleman hills ruptures 10 bars and 1 bar closer to coulomb failure the idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events in agreement with findings of prior investigations subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust faulting events on the periphery of the seismic rupture and its downdip extension these features are evident in aftershocks of the 1957 mw 9 1 aleutian and other large subduction earthquakes we further examine stress changes on the rupture surface imparted by the 1960 mw 9 5 and 1995 mw 8 1 chile earthquakes for which detailed slip models are available calculated coulomb stress increases of 2 20 bars correspond closely to sites of aftershocks and postseismic slip whereas aftershocks are absent where the stress drops by more than 10 bars we also argue that slip on major strike slip systems modulates the stress acting on nearby thrust and strike slip faults we calculate that the 1857 mw 7 9 fort tejon earthquake on the san andreas fault and subsequent interseismic slip brought the coalinga fault 1 bar closer to failure but inhibited failure elsewhere on the coast ranges thrust faults the 1857 earthquake also promoted failure on the white wolf reverse fault by 8 bars which ruptured in the 1952 mw 7 3 kern county shock but inhibited slip on the left lateral garlock fault which has not ruptured since 1857 we thus contend that stress transfer exerts a control on the seismicity of thrust faults across a broad spectrum of spatial and temporal scales

gas composition of the january 1983 eruption of kilauea volcano hawaii abstract gas collections were made from a 900 c vent both by conventional evacuated bottle wet chemical techniques and by manual pumping of flowthrough bottles the complete analyses suggest an equilibrium assemblage quenched at 1 010 c about midway between fountain and vent temperatures i suggest that the very low c s ratio is due to degassing of co2 during storage of the magma in a shallow reservoir before eruption the two sampling techniques yielded analytical data in mutual agreement

h2s fluxes from mt etna stromboli and vulcano italy and implications for the sulfur budget at volcanoes abstract we present here new measurements of sulfur dioxide and hydrogen sulfide emissions from vulcano etna and stromboli italy made by direct sampling at vents and by filter pack and ultraviolet spectroscopy in downwind plumes measurements at the f0 and fa fumaroles on vulcano yielded so 2 h 2 s molar ratios of 0 38 and 1 4 respectively from which we estimate an h 2 s flux of 6 to 9 t d 1 for the summit crater for mt etna and stromboli we found so 2 h 2 s molar ratios of 20 and 15 respectively which combined with so 2 flux measurements suggest h 2 s emission rates of 50 to 113 t d 1 and 4 to 8 t d 1 respectively we observe that source and plume so 2 h 2 s ratios at vulcano are similar suggesting that hydrogen sulfide is essentially inert on timescales of seconds to minutes this finding has important implications for estimates of volcanic total sulfur budget at volcanoes since most existing measurements do not account for h 2 s emission

thinning of the upper mantle during late paleozoic appalachian orogenesis across the appalachian orogen of new england the splitting of core refracted shear waves from a wide range of arrival directions indicates the presence of two nearly uniform horizontal layers of anisotropic upper mantle the anisotropy in the lower layer has a fast axis nearly parallel to the absolute motion of the north american plate and thus is attributed to basal shear as the plate plows through asthenospheric mantle the anisotropy of the upper layer is inferred to be a fossil fabric residing in lithospheric mantle the finite extension direction of the upper fabric is subhorizontal and oriented normal to the local trend of the appalachian orogen the upper fabric is consistent over a broad region beneath and west of the new england appalachians which indicates that it formed after devonian closure of the iapetus ocean probably during or after the paleozoic acadian and alleghany orogenies tectonic scenarios for synconvergent or postconvergent extension developed for tibet predict rapid surface uplift and increased heat flow due to lithospheric thinning consistent with coeval late orogenic mantlederived magmatism in both the northern appalachians and morocco

probing coulomb stress triggering effects for a mw 6 0 earthquake sequence from 1997 to 2014 along the periphery of the bayan har block on the tibetan plateau abstract recently there have occurred the manyi kangding earthquake sequence including the 1997 manyi 2001 kokoxili 2008 yutian 2008 wenchuan 2010 yushu 2013 lushan 2014 yutian and 2014 kangding earthquakes along the periphery of the bayan har block on the northern tibetan plateau we employ the coulomb failure model to probe the stress triggering effects on this sequence in terms of coseismic postseismic and interseismic coulomb stress changes we examine the coulomb stress changes from both the manyi kangding sequence and other large earthquakes from 1411 to 2012 around the bayan har block and interseismic tectonic stressing we use a stratified spherical postseismic relaxation model to compute postseismic coulomb stress changes we develop an explicit spherical least squares collocation model to calculate interseismic coulomb stress changes our results indicate that when merely considering triggering effects because of earthquakes from the manyi kangding sequence the compounded coulomb stress changes of the coseismic and postseismic coulomb stress changes are generally insignificant except for the 2013 lushan earthquake 0 14 bar this general insignificance of coulomb stress changes imparted by the manyi kangding sequence agrees with previous studies although interseismic coulomb stress changes always load each hypocenter on the other hand when surrounding prior m 6 0 earthquakes are considered we found that the compounded coulomb stress changes become significant ranging from 0 14 to 10 4 bars according to the constant apparent friction coulomb failure model with an intermediate coefficient of 0 4 therefore all eight earthquakes are well explained by coulomb stress changes when thoroughly considering large earthquakes around the bayan har block our findings indicate the importance of considering a broader group of neighboring large earthquakes for coulomb stress analysis

assessing elastic coulomb stress transfer models using seismicity rates in southern california and southwestern japan 1 we investigated whether observed changes in seismicity rate following the 1992 landers and 1995 kobe earthquakes correspond with predictions from coulomb stress transfer models to quantify the relationship between coulomb stress change and seismicity rate change we compared spatial changes in observed seismicity rates to the modeled changes in coulomb failure stress cfs for the two subject earthquakes we begin with the simplest and most common cfs model which assumes that regional stress orientations are uniform and the stress change is resolved on optimally oriented strike slip planes we then extended the cfs models to include the more geophysically realistic assumptions of spatially varying regional stress orientations and optimally oriented planes in three dimensions for all the tested cfs models we found that virtually everywhere seismicity rate changes could be resolved the rate increased regardless of whether the cfs theoretically promoted or inhibited failure and that we were not able to reliably resolve seismicity rate decreases an improvement in the correlation between the sign of the cfs and where rate increases occur when estimating the cfs on optimally oriented planes in three dimensions rather than two dimensions is a consequence of using optimally oriented planes and the ability to primarily observe rate increases the region of positive cfs increases by allowing more degrees of freedom so the correlation with positive rate change appears to increase the areas of highest seismicity rate following the main shock did not correlate with the sign or the magnitude of the cfs rather the areas most active after the main shock were also the most active before the main shock

low angle faulting in strike slip dominated settings seismic evidence from the maritimes basin canada abstract the maritimes basin is an upper paleozoic sedimentary basin centered in the gulf of st lawrence canada early phases of basin formation included the development of partly connected sub basins bounded by high angle faults in an overall strike slip setting interpretation of reprocessed seismic reflection data indicates that a low angle detachment contributed to the formation of a highly asymmetric sub basin this detachment was rotated toward a lower angle and succeeded by high angle faults that sole into the detachment or cut it this model bears similarities to other highly extended terranes and appears to be applicable to strike slip and or transtensional settings

implications of earthquakes for the slab subduction dynamic process in southeast asia abstract earthquake geohazards that occur throughout the borneo block especially in sw borneo cannot be reconciled within the classical earthquake mechanism and a uniform stress field and unfulfilled earthquake forecast for many years in this paper we present a new inventory of 37 borneo earthquakes and focal mechanisms show that in ne borneo earthquakes and aftershocks are dominated by nw trending normal faults in east borneo earthquakes are controlled by the reactivation of nw trending sinistral strike slip faults and the ne trending thrusts acted as the main seismogenic faults in the se borneo seismicity zone we calculated the coulomb stress and observed the shallow faults exhibiting a high coefficient response to the coulomb stress change and all these earthquakes under the coulomb failure regime have decreased by the stress shadows or are triggered by dynamic stress increase and propagation we performed a research using the horizontal gps velocity displacements and vertical seismic sections and found that the micro blocks convergence occurred here corresponding to the coulomb stress distribution and can best explain the earthquake mechanism within the borneo block additionally the earthquakes in sw borneo showing a concordant focal mechanism along the red river fault tinjar fault sumatra trench are deduced to have formed along the sunda block boundary finally the micro block boundaries determined from the heatflux map can be effective in describing the main and aftershocks distribution in se asia and the deep shallow coupling dynamic model is proposed to solve the stress loading for these crustal scale earthquakes and the responses to plate convergence in se asia

oxygen buffering of kilauea volcanic gases and the oxygen fugacity of kilauea basalt volcanic gases collected during episode 1 of the puu oo eruption along the east rift zone of kilauea volcano hawaii have uniform c o h s cl f compositions that are sharply depleted in co2 the co2 poor gases are typical of type ii volcanic gases gerlach and graeber 1985 and were emitted from evolved magma stored for a prolonged period of time in the east rift zone after releasing co2 rich gases during an earlier period of temporary residence in the summit magma chamber the samples are remarkably free of contamination by atmospheric gases and meteoric water thermodynamic evaluation of the analytical data shows that the episode 1 gases have equilibrium compositions appropriate for temperatures between 935 and 1032 c open and closed system equilibrium models of species distributions for the episode 1 gases show unequivocally that coexisting lavas buffered the gas oxygen fugacities during cooling these models indicate that the fo2 buffering process occurs by transfer of oxygen from the major species in the gas phase h2o co2 so2 to the lava during cooling and that the transfer of oxygen also controls the fugacities of several minor and trace species h2 co h2s s2 cl2 f2 in addition to o2 during cooling gas lava exchanges of other components are apparently insignificant and exert little influence compared to oxygen exchange during cooling oxygen transfer during cooling is variable presumably reflecting short term fluctuations in gas flow rates higher flow rates restrict the time available for gas lava oxygen transfer and result in gases with higher equilibrium temperatures lower flow rates favor fo2 constrained equilibration by oxygen transfer down to lower temperatures thus the chemical equilibrium preserved in these gases is a heterogeneous equilibrium constrained by oxygen fugacity and the equilibrium temperatures implied by the compositions of the gases reflect the temperatures at which gas lava oxygen exchange ceased this conclusion challenges the common assumption that volcanic gases are released from lava in a state of chemical equilibrium and then continue equilibrating homogeneously with falling temperature until reaction rates are unable to keep pace with cooling no evidence is found moreover that certain gas species are kinetically more responsive and able to equilibrate down to lower temperatures than those of the last gas lava oxygen exchange homogeneous reaction rates in the gas phase are apparently slow compared to the time it took for the gases to move from the last site of gas lava equilibration to the site of collection an earlier set of data for higher temperature co2 rich type i volcanic gases which come from sustained summit lava lake eruptions supplied by magma that experienced substantially shorter periods of crustal storage shows fo2 buffering by oxygen transfer up to 1185 c oxygen fugacity measurements in drill holes into ponded lava flows suggest that buffering by oxygen transfer may control the fo2 of residual gases down to several hundred degrees below the solidus in the early stages of cooling although the details of the fo2 buffering mechanisms for oxygen transfer are unknown the fact that fo2 buffering is effective from molten to subsolidus conditions suggests that the reaction mechanisms must change with cooling as the reactants change from predominantly melt to melt plus crystals to glass plus crystals mass balance calculations suggest that redox reactions between the gas and ferrous ferric iron in the lava are plausible mechanisms for the oxygen transfer and that the fo2 of the gases is buffered by sliding ferrous ferric equilibria in the erupting lavas contrary to expectations based on models predicting the oxidation of basalt by h2 and co escape during crustal storage co2 rich type i gases and co2 poor type ii gases have identical oxygen fugacities despite greatly different crustal storage and degassing histories volcanic gas data give a tightly constrained log fo2 of nno 0 5 0 05 for subaerially erupted kilauea basalt from liquidus to solidus temperatures consistent with recent fo2 determinations for the mantle source regions of ocean island basalts because the oxygen fugacities of volcanic gases emitted by subaerial lavas imply that the fo2 of kilauea basalt is unchanged during crustal storage kilauea basalt either arrives in the crust with an oxygen fugacity between nno and fmq or it develops an oxygen fugacity in this range immediately upon arrival in the summit chamber

earthquakes triggered by silent slip events on kīlauea volcano hawaii silent earthquakes or slow slip events happen so slowly that they cannot be detected by conventional seismographs but now the availability of gps data means that they can be followed in detail segall et al report on a series of small earthquakes on k lauea volcano hawaii the earthquakes at depths of 7 to 8 km appear to be triggered by otherwise silent slow slips though small triggered earthquakes of this type can be used to help quantify the increased hazard due to slow slip events slow slip events or silent earthquakes have recently been discovered in a number of subduction zones including the nankai trough1 2 3 in japan cascadia4 5 and guerrero6 in mexico but the depths of these events have been difficult to determine from surface deformation measurements although it is assumed that these silent earthquakes are located along the plate megathrust this has not been proved slow slip in some subduction zones is associated with non volcanic tremor7 8 but tremor is difficult to locate and may be distributed over a broad depth range9 except for some events on the san andreas fault10 slow slip events have not yet been associated with high frequency earthquakes which are easily located here we report on swarms of high frequency earthquakes that accompany otherwise silent slips on k lauea volcano hawaii for the most energetic event in january 2005 the slow slip began before the increase in seismicity the temporal evolution of earthquakes is well explained by increased stressing caused by slow slip implying that the earthquakes are triggered the earthquakes located at depths of 7 8 km constrain the slow slip to be at comparable depths because they must fall in zones of positive coulomb stress change triggered earthquakes accompanying slow slip events elsewhere might go undetected if background seismicity rates are low detection of such events would help constrain the depth of slow slip and could lead to a method for quantifying the increased hazard during slow slip events because triggered events have the potential to grow into destructive earthquakes

evidence for extension at the willimantic dome connecticut implications for the late paleozoic tectonic evolution of the new england appalachians

structural and geochemical interactions between magma and sedimentary host rock the hovedoya case oslo rift norway two end member conceptual models are used to describe deformation of the earth s crust induced by magma intrusion mode i fracturing assumes tensile or opening mode elastic deformation while mode ii fracturing assumes plastic shear mode deformation around a viscous indenter field observations of both mechanisms exist but it remains unclear which mechanism dominates in which conditions we describe intrusion geometries host rock deformation and geochemical magma host rock interactions around 53 exceptionally preserved tephrite basanite permian dike segments of 0 5 to 30 cm thickness these thin dikes that is dikelets intruded late ordovician carbonate rich sedimentary rocks on hovedoya island oslo rift norway dikelets emplaced in preexisting fractures dominantly created cavities ahead of their narrow tapering tips and are associated with bent host rock broken bridges and stepped segmented geometries other tips are blunt with dense brittle fracturing around them also cross sectional intrusion segment opening profiles deviate from parabola shaped profiles typical for elastic media the observations demonstrate that dominant opening mode host rock deformation can coexist with shear mode deformation locally alignment of most dikelet segments along the dominant host rock fracture directions highlights the control of local structural orientations on magma emplacement analysis of bulk major and trace element compositions in situ micro xrf sample analysis and carbon and oxygen stable isotope compositions suggests that thermochemical interactions between magma and the carbonate rich host rock produced a low viscosity mixture of magma pore water and gas we propose that such low viscosity hybrid fluid may assist in the intrusion of magma in sedimentary rocks by filling the cavity ahead of propagating sheet intrusion tips

coalescence microseismic mapping earthquakes are commonly located by linearized inversion of discrete arrival time picks made from signals recorded at a network of seismic stations if mis picks are made these will contribute to the location therefore causing potential bias for data recorded by a dense seismic array direct imaging methods can be applied instead we describe the coalescence microseismic mapping method which is a bridge between the two approaches and will operate with seismic data recorded continuously on a sparse array by continuously mapping scalar signals derived from the envelope of seismic arrivals we derive robust estimates of the spatio temporal coordinates of the origins of seismic events noisy data are migrated away from the correct origin so do not contribute to errors in location the method is rooted in a bayesian formulation of event location traveltime inversion allows imaging of source locations and has the capacity to handle errors in modelled traveltimes it has the advantage of working with any 3 d velocity model which therefore may include anisotropy it also automatically incorporates both p and s wave data a multiresolution grid search leads to an efficient implementation with a search over a larger domain including joint inversion for location and velocity structure possible where warranted by the data quality we discuss the theory and implementation of this method and illustrate it with real data from microseismic events in iceland caused by melt intrusion in the crust

newly identified carboniferous units the pointe sawyer and chemin des pecheurs formations in the gaspe peninsula quebec implications regarding the evolution of the northwestern sector of the maritimes basin the upper member of the cannes de roches formation was recently recognized overlying the bonaventure formation in the new carlisle area over 100 km southwest of the previously documented exposures of this unit moreover remnants of the la coulee formation which are unconformably overlain by the bonaventure formation have also been recognized underlying with a similar type of contact the lower member of the cannes de roches for mation from this and from facies similarities the lower and middle members of the cannes de roches formation are now considered to be equivalent to the bonaventure formation it is proposed to abandon these two member designa tions and to only keep the bonaventure formation the remaining upper member of the cannes de roches formation is renamed the pointe sawyer formation a late visean to early namurian age is attributed to this grey clastic forma tion from spore analysis dark reddish brown sandstone conformably overlie the pointe sawyer formation in the mal bay area they correspond to the beginning of sedimentation from more distant sources within the regional carbonifer ous stratigraphic succession which was until then characterized by sedimentation from proximal sources this previ ously unidentified unit is here referred to as the chemin des pecheurs formation

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

alunite and the role of magmatic fluids in the tambo high sulfidation deposit el indio pascua belt chile the tambo high sulfidation deposit located within the el indio pascua belt in chile produced almost 25 t 0 8 m oz of gold from altered tertiary rhyodacitic volcanic rocks episodic magmatic hydrothermal activity in the district occurred over at least 4 my and is characterized by several stages of acid sulfate alteration including magmatic hydrothermal magmatic steam steam heated and apparent supergene assemblages two stages of aufag mineralization are recognized and are hosted in barite and alunite within hydrothermal breccias and veins isotopic compositions of fluid in alunite show a dominant magmatic signature with only a variable 18 o enriched meteoric water component throughout the entire hydrothermal process alunite 40 ar 39 ar ages constrain the timing of alteration and the duration of the hydrothermal system pre ore alteration occurred at about 10 to 11 ma and was contemporaneous with the volcanism of the tambo formation alunite from this stage of alteration occurs in the matrix of barren breccias and as fine intergrowths of alunite quartzfclays that selectively replaced feldspars and pumice fragments the textural relationships combined with stable isotope systematics suggest a magmatic hydrothermal origin for the alunite with a local magmatic steam overprint early ore stage alunite 8 7f0 2 ma occurs with barite and goldfwalthierite within open spaces of the breccia matrix and has d 34 s values 24 27x typical of magmatic hydrothermal alunite reflecting equilibrium between aqueous h2s and so4 fluid inclusion ratios of h2s so2 approximately 6 are consistent with ratios determined from stable isotope data and indicate reduced fluid conditions during ore deposition vaporphase transport of au and deposition from condensed magmatic vapor rising from the brittle ductile transition is inferred late gold coprecipitated with a third stage of alunite 8 2f0 2 ma that is characterized by nearly uniform chemical compositions and d 34 s values 1x similar to those for associated enargite reflecting disequilibrium between h2s and so4 this third stage of alunite is isotopically and chemically similar to that of post ore coarse banded alunitefhematite quartz veins that crosscut the breccias in the tambo area analyses of fluid inclusion gas from alunite in these veins indicate high so2 and disequilibrium co2 co ch4 h2 species consistent with a magmatic steam origin the gases are also depleted in he and the late goldbearing alunite was probably precipitated from rapidly ascending so2 rich vapors that were flashed from condensed magmatic

the impact of degassing on the oxidation state of basaltic magmas a case study of kīlauea volcano volcanic emissions link the oxidation state of the earth s mantle to the composition of the atmosphere whether the oxidation state of an ascending magma follows a redox buffer hence preserving mantle conditions or deviates as a consequence of degassing remains under debate thus further progress is required before erupted basalts can be used to infer the redox state of the upper mantle or the composition of their co emitted gases to the atmosphere here we present the results of x ray absorption near edge structure xanes spectroscopy at the iron k edge carried out for a series of melt inclusions and matrix glasses from ejecta associated with three eruptions of k lauea volcano hawai i we show that the oxidation state of these melts is strongly correlated with their volatile content particularly in respect of water and sulfur contents we argue that sulfur degassing has played a major role in the observed reduction of iron in the melt while the degassing of h2o and co2 appears to have had a negligible effect on the melt oxidation state under the conditions investigated using gas melt equilibrium degassing models we relate the oxidation state of the melt to the composition of the gases emitted at k lauea our measurements and modelling yield a lower constraint on the oxygen fugacity of the mantle source beneath k lauea volcano which we infer to be near the nickel nickel oxide nno buffer our findings should be widely applicable to other basaltic systems and we predict that the oxidation state of the mantle underneath most hotspot volcanoes is more oxidised than that of the associated lavas we also suggest that whether the oxidation states of a basalt in particular morb reflects that of its source is primarily determined by the extent of sulfur degassing

strike slip faulting during the 2014 barðarbunga holuhraun dike intrusion central iceland over a 13 day period magma propagated laterally from the subglacial bar arbunga volcano in the northern rift zone iceland it created 30 000 earthquakes at 5 7 km depth along a 48 km path before erupting on 29 august 2014 the seismicity which tracked the dike propagation advanced in short bursts at 0 3 4 7 km h separated by pauses of up to 81 h during each surge forward seismicity behind the dike tip dropped moment tensor solutions from the leading edge show exclusively left lateral strike slip faulting subparallel to the advancing dike tip releasing accumulated strain deficit in the brittle layer of the rift zone behind the leading edge both left and right lateral strike slip earthquakes are observed the lack of non double couple earthquakes implies that the dike opening was aseismic

testing the stress shadow hypothesis 1 a fundamental question in earthquake physics is whether aftershocks are predominantly triggered by static stress changes permanent stress changes associated with fault displacement or dynamic stresses temporary stress changes associated with earthquake shaking both classes of models provide plausible explanations for earthquake triggering of aftershocks but only the static stress model predicts stress shadows or regions in which activity is decreased by a nearby earthquake to test for whether a main shock has produced a stress shadow we calculate time ratios defined as the ratio of the time between the main shock and the first earthquake to follow it and the time between the last earthquake to precede the main shock and the first earthquake to follow it a single value of the time ratio is calculated for each 10 10 km bin within 1 5 fault lengths of the main shock epicenter large values of the time ratio indicate a long wait for the first earthquake to follow the main shock and thus a potential stress shadow whereas small values indicate the presence of aftershocks simulations indicate that the time ratio test should have sufficient sensitivity to detect stress shadows if they are produced in accordance with the rate and state friction model we evaluate the 1989 mw 7 0 loma prieta 1992 mw 7 3 landers 1994 mw 6 7 northridge and 1999 mw 7 1 hector mine main shocks for each main shock there is a pronounced concentration of small time ratios indicating the presence of aftershocks but the number of large time ratios is less than at other times in the catalog this suggests that stress shadows are not present by comparing our results to simulations we estimate that we can be at least 98 confident that the loma prieta and landers main shocks did not produce stress shadows and 91 and 84 confident that stress shadows were not generated by the hector mine and northridge main shocks respectively we also investigate the long hypothesized existence of a stress shadow following the 1906 san francisco bay area earthquake we find that while bay area catalog seismicity rates are lower in the first half of the twentieth century than in the last half of the nineteenth this seismicity contrast is also true outside of the bay area in regions not expected to contain a stress shadow this suggests that the rate change is due to a more system wide effect such as errors in the historical catalog or the decay of aftershocks of the larger 1857 fort tejon earthquake

evidence for early mesozoic extensional faulting in carboniferous rocks southern new brunswick canada the high grade sylvinite orebody 28 k2o mined by the potacan mining company formerly the denison potacan potash company near sussex new brunswick canada has undergone intense internal folding the folds vary in size from centimetres to hundreds of metres are mostly tight to isoclinal recumbent and asymmetrically overfolded towards the southeast and belong to a single varied style group suggesting one deformation event folds are noncylindrical to sheath like locally and have highly variable cross sectional morphologies slickensides are locally common and penetrative slickenline trends in all parts of the mine are northwest southeast all the evidence is consistent with a southeast directed movement across the top of the evaporite body having caused extensive ductile drag folding within both the sylvinite and halite lithologies the evaporites in fact have all the characteristics of a near horizontal mylonite zone variscan deformation during the late carboniferous is generally cited as bein

the search for active marsquakes using subpixel coregistration and correlation best practice and first results the state of seismic activity on mars is currently unknown on earth coseismic displacement has been observed using visible wavelength images and subpixel coregistration and correlation techniques we apply this method to mars with the cosi corr co registration of optically sensed images and correlation software package using high resolution imaging science experiment hirise images focusing on part of the cerberus fossae fault system we derive best practices for applying this method to the study of coseismic displacements on mars using a time series of eight overlapping hirise images we achieve pixel coregistration with a mean accuracy of about 1 50 of a pixel we see no clear evidence for coseismic displacement in this region during a time period of over 8 years one possible displacement signal 1 2 m of west east displacement over a length scale of about 50 m that has similarities to terrestrial coseismic deformation was dismissed as the result of incomplete correction of steep topography during the coregistration stage ancillary observations of recurring slope lineae rsl activity in the surrounding fault system offer no supporting evidence for the occurrence of coseismic displacement but do seem to suggest rsl activity that does not fit into previous seasonal timescales although it is unlikely that we have observed coseismic displacement in our study area during this time period the best practice method and the accuracy of our results offer encouragement for future studies hirise context camera and color and stereo surface imaging system images can be used to complement and independently verify in situ seismic observations by the insight interior exploration using seismic investigations geodesy and heat transport lander or source location changes from the exomars trace gas orbiter spacecraft

equilibrium temperature and redox state of volcanic gas at unzen volcano japan abstract high temperature volcanic gases were collected from a growing dacitic dome of unzen volcano japan apparent equilibrium temperatures aet were calculated for the following two reactions so2 3h2 h2s 2h2o and co2 h2 co h2o both the aet s are higher than the outlet temperature to two hypotheses are examined as a cause of this disagreement one is a partial advancement in the reaction so2 3h2 h2s 2h2o the other is an addition of external water after a final equilibrium attainment based on these hypotheses the equilibrium compositions temperatures and redox potentials were estimated resulting in similar values the estimated temperatures range from 850 to 911 c which is consistent with a petrological estimation made with the lava however the estimated redox potential is one unit less in logfo2 scale than the petrological estimation

degassing of halogens from basaltic volcanism insights from volcanic gas observations abstract the currently available data set of s cl f abundances in volcanic gas plumes and high temperature fumarolic gas samples from basaltic volcanism is reviewed here in the attempt to derive constraints on the modes of halogen degassing from mafic silicate melts apart from large volcano to volcano variations reflecting remarkable differences in volatile abundances in the source magmas each of the explored volcanoes displays large changes of so2 hcl and so2 hf ratios with the style of volcanic activity with hcl hf staying fairly constant halogen abundances are low and so2 hcl and so2 hf are high when fresh volatile rich magmas sustain degassing as during explosive eruptions at the onset of eruptive cycles or shortly before paroxysmal events low so2 hcl and so2 hf ratios are instead characteristic of late stages of volcanic degassing typically being observed in the concluding stages of basaltic eruptions or during periods of reduced magma supply at persistently degassing volcanoes these observations are taken as evidence of halogens being less keen to enter the gas phase relative to s during degassing of basaltic magmas and quantitatively interpreted in light of a rayleigh type open system degassing model the model though simple quantitatively reproduces the range of volcanic gas compositions observed at basaltic volcanoes worldwide and allows prediction of vapour melt partitioning contrasts of factors 9 and 36 for the volatile couples s cl and s f respectively these predictions require validation from appropriately designed experiments of halogen partitioning between magmatic vapours and silicate melts over a range of p t x conditions

halogens and trace metal emissions from the ongoing 2008 summit eruption of kīlauea volcano hawai i volcanic plume samples taken in 2008 and 2009 from the halema uma u eruption at k lauea provide new insights into k lauea s degassing behaviour the cl f and s gas systematics are consistent with syn eruptive east rift zone measurements suggesting that the new halema uma u activity is fed by a convecting magma reservoir shallower than the main summit storage area comparison with degassing models suggests that plume halogen and s composition is controlled by very shallow 77 as gaseous elemental mercury at the point of emission sulphate is an important aerosol component modal particle diameter 0 44 m aerosol halide ion concentrations are low compared to other systems consistent with the lower proportion of gaseous hydrogen halides plume concentrations of many metallic elements rb cs be b cr ni cu mo cd w re ge as in sn sb te tl pb mg sr sc ti v mn fe co y zr hf ta al p ga th u la ce pr nd sm eu gd tb dy er tm are elevated above background air there is considerable variability in metal to so2 ratios but our ratios generally at the lower end of the range previously measured at k lauea support assertions that k lauea s emissions are metal poor compared to other volcanic settings our aerosol re and cd measurements are complementary to degassing trends observed in hawaiian rock suites although measured aerosol metal s ratios are about an order of magnitude lower than those calculated from degassing trends determined from glass chemistry plume enrichment factors with respect to hawaiian lavas are in broad agreement with those from previous studies allowing similar element classification schemes to be followed i e lithophile elements having lower volatility and chalcophile elements having higher volatility the proportion of metal associated with the largest particle size mode collected 2 5 m and that bound to silicate is significantly higher for lithophiles than chalcophiles many metals show higher solubility in ph 7 buffer solution than deionised water suggesting that acidity is not the sole driver in terms of solubility nonetheless many metals are largely water soluble when compared with the other sequential leachates suggesting that they are delivered to the environment in a bioavailable form preliminary analyses of environmental samples show that concentrations of metals are elevated in rainwater affected by the volcanic plume and even more so in fog however metal levels in grass samples showed no clear enrichment downwind of the active vents

degassing of metals and metalloids from erupting seamount and mid ocean ridge volcanoes observations and predictions recently it has been reported that the element polonium degasses from mid ocean ridge and seamount volcanoes during eruptions published and new observations on other volatile metal and metalloid elements can also be interpreted as indicating significant degassing of magmatic vapors during submarine eruptions this process potentially plays an important role in the net transfer of chemical elements from erupting volcanoes to seawater in addition to that arising from sea floor hydrothermal systems in this paper a framework is constructed for predicting and assessing semiquantitatively the potential magnitude and chemical fingerprints in the water column of metal and metalloid degassing using 1 predictions from a summary of element volatilities during mafic subaerial volcanism worldwide and 2 limited data from submarine volcanic effusives the latter include analyses of polonium and trace metals in near volcano water masses sampled following a submarine eruption at loihi seamount hawaii 1000 m bsl in 1996 the element volatility predictions and observations show good agreement considering the limited dataset some of the highest volatility main group and transition element enrichments in seawater over loihi are predicted by the degassing mass transfer model i present when expanded to cover all submarine volcanic activity it is predicted that exit fluxes of these elements are up to 102 103 greater by degassing than by normal mor hydrothermalism in contrast mor exit fluxes of low volatility alkali and alkaline earth elements are likely 102 106 greater from hydrothermal inputs degassing inputs to the ocean are probably highly episodic occurring almost entirely during eruptions these are times of enhanced and abnormal hydrothermalism as well although major hydrothermal and degassing events may not be chemically recognizable in real water masses as wholly distinct entities it is nevertheless possible to predict to what extent each process flavors the effluents of the other degassing at mid ocean ridges may explain a variety of observations previously ascribed to complexities occurring during hydrothermal venting and or fluid ascent in the buoyant hydrothermal plumes above ridges

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

deformational behavior of shale interlayers in evaporite detachment horizons jura overthrust switzerland shale deformation was studied in a series of naturally strained evaporites and shales deformed at low temperatures 70 high strain rates 10 14s 1 and low pressures overburden 2 km as well as in rock samples and sintered specimens experimentally deformed in coaxial and simple shear configurations at temperatures of 20 350 c strain rates of 10 4 10 6s 1 and confining pressures of 0 1 400 mpa within naturally strained shale sulfate multilayers three deformation regimes can be recognized that are separated by the inversion of relative competence of shale and anhydrite and the onset of gypsification respectively in deeper domains strain is focused on slickensides which are often coated with sulfate that acts as a lubricant in shallower domains and especially in domains with significant access to syntectonic water strain becomes pervasive and very low strength ductile shale gypsum tectonites form experiments reveal that confining pressure and water content have a significant influence on style of deformation pervasive or focused on discrete surfaces whereas temperature and strain rate have virtually no influence on either strength or deformation style except at temperatures 200 c that cause dehydration and embrittlement

enhanced stress and changes to regional seismicity due to the 2015 mw 7 8 gorkha nepal earthquake on the neighbouring segments of the main himalayan thrust abstract in this study we evaluate stress evolution and change in seismic hazard after the 2015 gorkha earthquake sequence we take a methodology usually used in areas with well established seismic monitoring and apply it to an area with a sparse dataset and a limited time observation window our goal is to validate this approach as a rapid response tool for seismic forecasting after large earthquakes we propose a long term seismic forecasting model of the main himalayan thrust using the historical earthquake catalogue and regional paleo seismicity through application of the rate and state friction model we evaluate short term rate evolution after the gorkha earthquake the long elapsed time since the last megathrust event and the mainshock coseismic stress increase on the main himalayan thrust suggest high seismic potential in the lalitpur and lamjung areas along the fault system we also calculate the stress change on optimally oriented planes in the region and model the regional seismicity rate using a smoothing kernel method and seismicity since 1921 the location of the consequent earthquakes coincides with areas of high background seismicity rate and areas where stress was enhanced by the mw 7 8 mainshock and mw 7 3 aftershock we model the change of seismic rate over time and project a fast decrease due to the short aftershock duration assumption we use

40ar 39ar dating in the lochaber mulgrave area northern mainland nova scotia implications for timing of regional metamorphism and sediment provenance in the late devonian early carboniferous horton group 40ar 39ar dating of whole rock samples and muscovite separates using age spectrum analysis and of single muscovite grains using total fusion analysis yields new insights into the timing of regional metamorphism and sediment provenance in the late devonian early carboniferous horton group in the lochaber mulgrave area of nova scotia the time of regional metamorphism is constrained to ca 340 335 ma by whole rock spectra from well cleaved slate and shale samples from the lowermost clam harbour river and overlying tracadie road formations of the horton group this ca 340 335 ma event may have been the result of burial and deformation of the horton group by older volcanic and sedimentary rocks of the guysborough group which were overthrust from the south as the result of development of a positive flower structure at a restraining bend along the cobequid chedabucto fault system the boundary between the meguma and avalon terranes detrital muscovite ages of ca 410 380 and ca 500 ma were obtained from

4d gravity changes associated with the 2005 eruption of sierra negra volcano galapagos sierra negra volcano the most voluminous shield volcano in the galapagos archipelago and one of the largest basaltic calderas in the world erupted on october 22 2005 after more than 25 years of quiescence gps and satellite radar interferometryinsar monitoring of the deformation of the caldera floor in the months prior to the eruption documented extraordinary inflation rates 1c m day the total amount of uplift recorded since monitoring began in 1992 approached 5 m at the center of the caldera over the eight days of the eruption the caldera floor deflated a maximum of 5 m and subsquently renewed its inflation but at a decelerating rate to gain insight into the nature of the subsurface mass density changes associated with the deformation gravity measurements performed in 2005 2006 and 2007 are compared to previous measurements from 2001 2002 when the volcano underwent a period of minor deflation and magma withdrawal the residual gravity decrease between 2001 2002 and 2005 is among the largest ever recorded atan active volcano950 gal and suggests that inflation was accompanied by a relative density decrease in the magmatic system forward modeling of the residual gravity data in 4d from 2002 to 2005 gives an estimate of the amount of vesiculation in the shallow sill required to explain the observed gravity variations geochemical constraints from melt inclusion and satellite remote sensing data allow us to estimate the pre eruptive gas content of the magma and place constraints on the thickness of the gas rich sill necessary to produce the gravity anomalies observed results suggest that reasonable sill thicknesses 700 800 m and bubble contents 10 50 volume can explain the large decrease in residual gravity prior to eruption following the eruption 2006 and 2007 the deformation and gravity patterns suggest re equilibration of the pressure regime in the shallow magma system via a renewed influx of relatively gas poor magma into the shallow parts of the system