viscosity of microlite bearing rhyolitic obsidians an experimental study to investigate the influence of microlites on lava flow rheology the viscosity of natural microlite bearing rhyolitic obsidians of calc alkaline and peralkaline compositions containing 0 1 0 4 wt water was measured at volcanologically relevant temperatures 650 950 c stresses 103 105 pa and strain rates 10 5 to 10 7 s 1 the glass transition temperatures t g were determined from scanning calorimetric measurements on the melts for a range of cooling heating rates based on the equivalence of enthalpic calorimetric and shear viscosity relaxation we calculated the viscosity of the melt in crystal bearing samples from the t g data the difference between the calculated viscosity of the melt phase and the measured viscosity for the crystal bearing samples is interpreted to be the physical effect of microlites on the measured viscosity the effect of 45 vol crystals for both of these samples a connectivity factor is apparent with for the latter a close packing framework of crystals which is interpreted to influence the apparent viscosity

a compositional tipping point governing the mobilization and eruption style of rhyolitic magma measurements of the composition dependent viscosity of rhyolitic magma reveal a tipping point that changes the physical properties of the melt and controls the transition between effusive and explosive eruptions calcalkaline rhyolites produce the largest explosive volcanic eruptions but these eruptions can switch repeatedly between being effusive and explosive this is difficult to attribute to the rheological effects of magma water content or crystallinity danilo di genova and co authors report the viscosity of a series of melts spanning the compositional range of the yellowstone rhyolitic volcanic system they find that within a narrow compositional zone melt viscosity increases by up to two orders of magnitude which they propose to be the consequence of melt structure reorganization the authors confirm that such a compositional tipping point exists in the global geochemical record of rhyolites which separates effusive from explosive deposits they conclude that the anhydrous water free composition of calcalkaline rhyolites is decisive in determining mobilization and eruption dynamics of the earth s largest volcanic systems the most viscous volcanic melts and the largest explosive eruptions1 on our planet consist of calcalkaline rhyolites2 3 these eruptions have the potential to influence global climate4 the eruptive products are commonly very crystal poor and highly degassed yet the magma is mostly stored as crystal mushes containing small amounts of interstitial melt with elevated water content5 it is unclear how magma mushes are mobilized to create large batches of eruptible crystal free magma further rhyolitic eruptions6 7 8 can switch repeatedly between effusive and explosive eruption styles and this transition is difficult to attribute to the rheological effects of water content or crystallinity9 10 here we measure the viscosity of a series of melts spanning the compositional range of the yellowstone volcanic system and find that in a narrow compositional zone melt viscosity increases by up to two orders of magnitude these viscosity variations are not predicted by current viscosity models11 12 and result from melt structure reorganization as confirmed by raman spectroscopy we identify a critical compositional tipping point independently documented in the global geochemical record of rhyolites at which rhyolitic melts fluidize or stiffen and that clearly separates effusive from explosive deposits worldwide this correlation between melt structure viscosity and eruptive behaviour holds despite the variable water content and other parameters such as temperature that are inherent in natural eruptions thermodynamic modelling demonstrates how the observed subtle compositional changes that result in fluidization or stiffening of the melt can be induced by crystal growth from the melt or variation in oxygen fugacity however the rheological effects of water and crystal content alone cannot explain the correlation between composition and eruptive style we conclude that the composition of calcalkaline rhyolites is decisive in determining the mobilization and eruption dynamics of earth s largest volcanic systems resulting in a better understanding of how the melt structure controls volcanic processes

the proportionality between relative plate velocity and seismicity in subduction zones the magnitude and rate of seismicity differ between subduction zones calculations of background seismicity rates based on a global model of subduction zone seismicity reveal a positive correlation between relative plate velocity and background seismicity yet only the seismically quieter zones seem capable of generating magnitude 9 earthquakes

slow diffusive fault slip propagation following the 6 april 2009 l aquila earthquake italy 1 two laser strainmeters that operate at 1400 m depth about 20 km ne of the epicenter of the 6 april 2009 magnitude 6 3 l aquila italy earthquake have produced a clear record of postseismic strain here we show the results from the analysis of the data related to the first few days after the event strain after about 1 5 days is fully consistent with afterslip on a stationary region of the earthquake causative fault the preceding few hour long transient whose seismic moment history is quasi exponential is fully consistent with unilateral diffusive slip propagation toward the shallower part of the same fault the propagation path ends where later afterslip probably occurred slip propagation similar to heat diffusion has been suggested to explain the observed scaling law between amplitude and duration of slow earthquakes here we give the first observational evidence of the role and details of slow rupture propagation

the cooling of frontal flow ramps a calorimetric study on the rocche rosse rhyolite flow lipari aeolian islands italy relaxation geospeedometry using differential scanning calorimetry dsc has been applied to quantify the cooling history across the glass transition of flow ramps at the front of the calcalkaline rhyolite rocche rosse flow of lipari aeolian islands italy modelled cooling rates for the obsidian retrieved from two profiles range between 0 2 and 0 03 k min 1 cooling at the flow front appears to be dominated by conductive heat loss of individual flow ramps forming individual cooling units cooling rates of tens of kelvins per day appear to have controlled the last stage of viscous deformation before the entire flow came to rest it is inferred that cooling rates slower than those modelled are required to sustain flow in highly viscous rhyolitic lavas

lapse time dependence of coda q anisotropic multiple scattering models and application to the pyrenees abstract the coda quality factor of short period s waves q c excited by local earthquakes in the pyrenees has been measured as a function of the length of the coda window l w for different choices of the onset time of the coda t w in the 2 16 hz frequency band we observe a transient regime characterized by an increase of q c with l w followed by a stabilization around a plateau the value of which depends on the central frequency of the signal using monte carlo simulations of wave transport in a variety of random media 1200 models we demonstrate that the lapse time dependence of q c in the pyrenees may be modeled by multiple anisotropic scattering of seismic waves without invoking any depth dependence of the attenuation properties in the crust in our model anisotropic scattering is quantified by the ratio between the transport mean free path and the mean path l l at 6 hz the data require an anisotropy factor l l 5 a transport mean free path l 400 km and an intrinsic quality factor q i 800 from the frequency dependent plateau of q c at large lapse time we infer an intrinsic quality factor of the form q i 400 f 0 4 in the pyrenees we also show how the rapid increase of the lapse time dependence of q c with frequency may be exploited to put constraints on the power spectrum of heterogeneities in the crust

columbia river flood basalts from a centralized crustal magmatic system the columbia river basalt group in the northwestern united states derived from flood basalt eruptions that occurred 16 million years ago exhibits variability in geography and trace element geochemistry that has led to a number of proposed magma origins however the geochemical variability can be explained by a relatively simple model in which magma is derived from a mantle plume that assimilated continental crust in a centralized magma system the columbia river basalt group in the northwestern united states1 comprising about 230 000 cubic kilometres of rock exhibits unusual patterns in lava distribution geochemistry and its apparent relationship to regional tectonics consequently there is little consensus on the origin of its magmas2 3 4 5 6 7 8 9 10 11 12 here we examine the isotopic ratios of sr nd pb and os and trace element abundances in columbia river basalts the results suggest that most of the lava was produced when magma derived from a mantle plume assimilated continental crust in a central magma chamber system located at the boundary between the north american craton and the accreted terranes of idaho and oregon other related basalts are the product of mixing between the mantle plume and different types of regional upper mantle magma was then transported over a wide region by an extensive network of dykes a process that has been identified in other flood basalt provinces as well13 interactions of the plume with surrounding upper mantle and of mantle derived magmas with regional crust provide a relatively simple6 7 9 14 15 model to explain the more unusual features of the main phase columbia river basalts

intrinsic and scattering seismic wave attenuation in the central apennines italy abstract recently an earthquake sequence formed by a series of subsequences characterized by large earthquakes three events m 6 0 and five events m 5 0 occurred in the central apennines in 6 7 months during 2016 2017 several studies interpreted this cascading type of earthquake occurrence as associated with fluid movements through an interconnected network of cracks around the active faults that triggered the subsequences in different time and location in the present study we aim to verify if the presence of fluids is confirmed by the pattern of seismic wave attenuation to do so we separately estimate the space averaged parameters intrinsic qi 1 and scattering qs 1 proportional to the correspondent attenuation parameters by applying a modified multiple lapse time window analysis mltwa in order to establish reference background values for the study region mltwa measures the decay of s wave energy with distance and lapse time and fit it to the energy transport equation solution for scattering yielding the seismic albedo b0 qs 1 qt 1 and the extinction length le qt 1 parameters as a function of frequency the knowledge of the separated attenuation parameters allows determining which process of seismic energy dissipation dominates in the region in the present study b0 results to be around0 6 at 1 5 hz and decreases with increasing frequency down to 0 2 indicating that the attenuation of the seismic energy carried by s wave is controlled by intrinsic dissipation rather than by scattering moreover the intrinsic attenuation is frequency dependent f 0 9 for the uniform model and f 0 4 for the crust moho model this behavior well matches with the presence of fluids in the faults and fracture zones in the central apennines in agreement with results from other independent studies in the region finally a comparison among the attenuation parameters estimated for this area and those measured in several areas of italy and other parts of the world is presented together with a discussion on the comparison between the present mltwa attenuation estimates and homologous results obtained for the same area with different approaches

evidence for non constant energy moment scaling from coda derived source spectra 1 we present two lines of evidence showing the ratio of seismically radiated energy er to seismic moment mo increases with increasing moment for crustal events spanning 5 orders in seismic moment this ratio often referred to as the scaled energy er m0 has been elusive and the subject of recent debate within the seismological community because significant frequency dependent corrections must be made to account for source and path heterogeneity it is not uncommon that energy estimates of the same event by different researchers have significantly different values to minimize some of the potential problems we used the regional coda methodology outlined by mayeda et al 2003 on 4 large earthquake sequences mw 7 4 and 7 2 izmit duzce mw 7 2 gulf of aqaba mw 7 3 landers and mw 7 2 hector mine this methodology has been shown to provide the lowest variance estimate of the source spectrum when compared against traditional direct wave estimates in our first approach we made energy estimates from coda derived spectra and observed that increases with increasing moment for 3 7 mw 7 4 in our second approach we used the simple idea outlined by prieto et al 2004 to directly test for self similarity under self similarity earthquake source spectra scaled by 3 should have the same shape to test this one needs very stable spectra either through spectral stacking of direct wave spectra or by the use of stable coda derived spectra for all sequences we found that the mainshocks and larger aftershocks had significantly different spectral shapes than the smaller events the scaled 3 spectra of the larger events represented an upper bound having larger amplitudes near the corner frequency in fact an 3 5 scaling moved the larger events closer to the mean of the spectral population though the spectral shape differences persisted these results strongly suggest that earthquakes are not scaling self similarly and that complexities in the rupture process such as variable slip velocity exist between small and large events

rheomorphic ignimbrites of the rogerson formation central snake river plain usa record of mid miocene rhyolitic explosive eruptions and associated crustal subsidence along the yellowstone hotspot track rogerson graben usa is critically placed at the intersection between the yellowstone hotspot track and the southern projection of the west snake river rift eleven rhyolitic members of the re defined 420 m thick rogerson formation record voluminous high temperature explosive eruptions emplacing extensive ashfall and rheomorphic ignimbrite sheets yet each member has subtly distinct field chemical and palaeomagnetic characteristics new regional correlations reveal that the brown s view ignimbrite covers 3300 km2 and the wooden shoe ignimbrite covers 4400 km2 and extends into nevada between 11 9 and 8 ma the average frequency of large explosive eruptions in this region was 1 per 354 ky about twice that at yellowstone the chemistry and mineralogy of the early rhyolites show increasing maturity with time possibly by progressive fractional crystallisation this was followed by a trend towards less evolved rhyolites that may record melting and hybridisation of a mid crustal source region contemporaneous magmatism induced crustal subsidence of the central snake river basin is recorded by successive ignimbrites offlapping and thinning up the n facing limb of a regional basin margin monocline which developed between 10 59 and 8 ma the syn volcanic basin topography contrasted significantly with the present day elevated yellowstone hotspot plateau concurrent basin and range extension produced the n trending rogerson graben early uplift of the shoshone hills 10 34 ma was followed by initiation of the shoshone fault and an e sloping half graben 10 3 10 1 ma the graben asymmetry then reversed with initiation of the brown s bench fault 8 ma which remained intermittently active until the pliocene

on the hydrography of puyuhuapi channel chilean patagonia abstract this work describes the hydrographic conditions found in puyuhuapi channel northern chilean patagonia during recent years on a seasonal scale puyuhuapi channel was once a glacial valley but the retreating ice allowed the inflow of marine waters five surveys were conducted between 2008 and 2012 historical data from 1995 to 2007 were included a meteorological oceanographic buoy was also installed in the northern section of puyuhuapi channel and was operational beginning on april 12th 2011 puyuhuapi channel s surface characteristics highlight a fresher northern part and a more haline southern part except during winter when the pattern can reverse due to the intrusion of oceanic water via jacaf channel the channel exhibits a highly variable meridional and seasonal vertical stratification especially in its northern part where during spring and summer the water column is highly stratified but partially mixed during winter puyuhuapi channel is the only fjord channel with severe hypoxic conditions in all of chilean patagonia

compositional gradients surrounding spherulites in obsidian and their relationship to spherulite growth and lava cooling spherical masses of crystal fibers spherulites crystalize from rhyolitic melt glass mainly in response to significant undercooling while lava cools spherulite growth should induce compositional gradients in the surrounding glass from expulsion of incompatible constituents and diffusion of those constituents away from the spherulite finite difference numerical modeling of one dimensional diffusion in which diffusivities are allowed to vary with temperature is used to investigate how compositional gradients reflect spherulite growth and lava cooling overall three forms of gradients are identified elements that diffuse quickly are expelled from the spherulite but then migrate away too quickly to become enriched at the boundary of the spherulite elements that diffuse slowly are trapped within the growing spherulite between those endmembers are elements that are not trapped yet diffuse slow enough that they become enriched at the contact their slow diffusion away then elevates their concentrations in the surrounding glass how enriched those elements are at the spherulite matrix interface and how far their enrichments extend outwards into the glass reflect how spherulites grow and thermal conditions during growth concentrations of h2o rb f li cl na k sr cs ba and be were measured in and around spherulites in obsidian from a 4 7 1 km3 rhyolite lava dome erupted from tequila volcano mexico measurable concentration gradients are found for h2o rb and f attributes of those gradients and the behaviors of the other elements are in accord with their experimentally constrained diffusivities spherulites appear to have grown following radial rather than volumetric growth the observed gradients and lack of others are more consistent with growth mainly below the glass transition which would necessitate the dome cooling at ca 10 5 to 10 7 c s 1 such slow cooling is consistent with the relatively large volume of the dome

viscous heating in silicate melts an experimental and numerical comparison 1 the transition from newtonian to non newtonian flow of silicate melts is commonly manifested as shear thinning at conditions of high stress and strain rate shear thinning may strongly influence the dynamics of magmatic flows but the details of its microscopic origins are not fully understood here we consider viscous heating and thermomechanical coupling as a potential cause of shear thinning we compare the results of laboratory uniaxial compression experiments of a silicate melt with the results of thermomechanical numerical simulations corresponding to the experimental setup both the experimental and numerical results concord and indicate that the reduction of the temperature dependent viscosity in flowing silicate melts is a result of viscous heating viscous heating was quantified for glasses with viscosities ranging from 108 to 1011 pa s and strain rates from 10 5 to 100 s 1 the results of 48 compression experiments indicate that the transition from newtonian to non newtonian flow in the silicate melt occurs at a brinkmann number i e ratio of heat gained to heat lost around 1 whereas brittle behavior dominates the melt deformation when the deborah number i e ratio of viscoelastic relaxation time to characteristic deformation time is larger than around 0 01 the observed viscous heating significantly contributes to the viscosity decrease observed in high stress strain rate experiments and questions our current understanding of the non newtonian deformation behavior of silicate melts

a simple model of fjord and coastal circulation interaction abstract the dynamical interaction of a narrow fjord with a wind driven coastal regime is investigated using a linear two layer numerical model the coriolis acceleration is important in the coastal regime but assumed to he unimportant in the fjord dynamical because v 0 for a wide variety of wind conditions bottom topography and model parameters the wind forced coastal circulation with its geostrophic alongshore currants has a strong effect on the circulation within the fjord these geostrophic currents control the free surface and pycnocline displacement at the fjord mouth thereby strongly affecting fjord circulation this mechanism is an alternative to the classical idea of hydraulic control at the mouth by sills or constrictions model simulators also show that the free surface slope is a baroclinic effect and that alongshore and across shore winds affect the fjord differently alongshore winds produce flooding while up and down fjord winds simply sat up the surface we find that offshore win

deposition of rheomorphic ignimbrite d mogan formation gran canaria canary islands spain rheomorphic ignimbrite d 13 4 ma upper mogan formation on gran canaria a multiple flow single cooling unit is divided into four major structural zones that differ in fabric and finite strain of deformed pyroclasts their structural characteristics indicate contrasting deformation mechanisms during rheomorphic flow the zones are a a basal zone vitrophyre with pure uniaxial flattening perpendicular to the foliation b an overlying shear zone characterized by asymmetric fabrics and a significantly higher finite strain with an ellipsoid geometry similar to stretched oblate bodies c a central zone with a finite strain geometry similar to that of the underlying shear zone but without evidence of a rotational strain component and d a slightly deformed to non deformed top zone where the almost random orientation of subspherical pyroclasts suggests preservation of original syn depositional clast shapes rheomorphic flow in d is the result of syn to post depositional remobilization of a hot pyroclastic flow as shown by kinematic modeling based on a the overall vertical structural zonation suggested by finite strain and fabric analysis b the relation of shear sense to topography c the interrelationship of the calculated vertical cooling progression at the base of the flow formation of vitrophyre and the related vertical changes in strain geometry d the complex lithification history and e the consequent mechanisms of deformational flow rheomorphic flow was caused by load pressure due to an increase in the vertical accumulation of pyroclastic material on a slope of generally 6 8 we suggest that every level of newly deposited pyroclastic flow material of d first passed through a welding process that was dominated by compaction pure flattening before rheomorphic deformation started

a mechanism governing the estuarine circulation in deep strongly stratified fjords the estuarine circulation in deep strongly stratified fjords is discussed it is argued that a two layer description of the stratification in the fjord is correct in very wide fjords wide compared to the width of the mouth and possibly also in narrow fjords with high runoff and or weak mixing a theory for the thickness and the salinity of the brackish layer in a wide fjord was earlier developed by the present author and published in swedish 1975 and it is presented here among other findings in that theory we may mention that the thickness of the brackish layer is primarily determined by the internal hydraulic control for high specific runoff runoff unit horizontal surface area of the fjord and weak mixing in the other extreme with low specific runoff and strong mixing the thickness of the brackish layer is found to be proportional to the monin obukhov length the circulation in not very wide fjords is also discussed it is found that recirculation in the brackish layer may be expected whereby a two layer description of the flow field breaks down at least locally a critical rayleigh number that seems to control the recirculation of brackish water within the fjord is found a theory for the density difference between the mouth and the head in the brackish layer in the fjord is developed from the critical rayleigh number condition it is found that this density difference normally is proportional to the density difference between the brackish water at the mouth and the underlying sea water provided that the river runoff is not too heavy and or the mixing is not too weak this prediction is confirmed by extensive measurements from the nordfjord

semidiurnal internal tides in a patagonian fjord abstract the fjords of central chilean patagonia 47 s receive fresh water from both precipitation and the baker river this buoyancy input generates a two layer hydrographic system characterized by strong salinity stratification 30 g kg 1 over a depth range of 7 15 m which favors baroclinic conditions in the fjord hourly current velocity profiles were collected with an acoustic doppler current profiler adcp moored at a depth of 40 m during march april 2009 and complemented by 11 ctd profiles and hourly sea level time series these data allowed the detection of semidiurnal internal tidal waves for the first time in this region wavelength and horizontal phase speeds were determined by the dynamical mode 1 for internal waves maximum wavelength was 52 km travelling at a horizontal phase speed of 1 16 m s 1 wavelet spectral and empirical orthogonal function eof analysis techniques applied to the echo anomaly signal and to the baroclinic velocity showed largest semidiurnal amplitudes near the pycnocline out of three modes obtained from the eof analysis two modes displayed a two or three layer flow structure with flow direction reversing at the pycnocline the semidiurnal internal waves were found as fluctuations near the pycnocline in sporadic packets correlated to high discharge pulses of the baker river r2 0 77 additionally internal froude number calculations at the mouth of the baker river indicated critical flow conditions which allowed for generation of internal waves at the plume front these waves are separated from the river plume after internal wave phase speeds surpassed frontal speeds this suggests that the internal waves were modulated by pulses in high river discharge rather than the interaction of barotropic tide with bathymetry a sill an implication of these internal waves would be to increase vertical mixing of nutrients toward the surface through shear instabilities which would favor primary production

preliminary experimental determination of the partitioning of lithium between plagioclase crystals of different anorthite contents abstract the role of plagioclase anorthite content in controlling the partitioning of li has been investigated experimentally plagioclase crystals of different anorthite contents were equilibrated with a single plagioclase powder at 1000 c the results show that the partition coefficient of lithium is a strong function of the anorthite content of the plagioclase decreasing by a factor of 3 5 from an 60 to an 80 this has important implications for the interpretation of the distribution of li in plagioclase in natural samples an example of the importance of considering the change in partition coefficient with plagioclase anorthite content is given using published plagioclase li contents in the products of the soufriere hills volcano it is shown that the distribution of li in these plagioclase phenocrysts can be reproduced using a model in which li diffuses into and out of the plagioclase crystals if the change in partition coefficient with an content is accounted for because li diffusion in plagioclase is very rapid the distribution of li in plagioclase crystal rims can record changing conditions during eruption and pyroclastic flow emplacement second to minute timescales

origin of the columbia plateau and snake river plain deflection of the yellowstone plume previous models relating the snake river plain and columbia river basalt northwest united states to the yellowstone plume have not taken into account the effects of the subducted farallon and juan de fuca plates not only did subduction shield the surface from mantle plume activity but it deflected the plume in the direction of plate motion a variety of geophysical and geologic evidence suggests that the plume penetrated the subducted slab at 17 5 ma causing eruption of the columbia river basalt the plate boundary then migrated over the plume and the yellowstone plume has recovered to a more nearly vertical conduit forming the snake river plain and yellowstone plateau

diffusion controlled spherulite growth in obsidian inferred from h2o concentration profiles spherulites are spherical clusters of radiating crystals that occur naturally in rhyolitic obsidian the growth of spherulites requires diffusion and uptake of crystal forming components from the host rhyolite melt or glass and rejection of non crystal forming components from the crystallizing region water concentration profiles measured by synchrotron source fourier transform spectroscopy reveal that water is expelled into the surrounding matrix during spherulite growth and that it diffuses outward ahead of the advancing crystalline front we compare these profiles to models of water diffusion in rhyolite to estimate timescales for spherulite growth using a diffusion controlled growth law we find that spherulites can grow on the order of days to months at temperatures above the glass transition the diffusion controlled growth law also accounts for spherulite size distribution spherulite growth below the glass transition and why spherulitic glasses are not completely devitrified

effective diffusivities within oceanic thermohaline staircases a scale for the thickness of layers in regular diffusive type thermohaline staircases derived from dimensional analysis is found to collapse oceanic data combining this scale with laboratory derived double diffusive flux laws we formulate effective diffusivities for salt heat and density the diffusivities depend on the turner number r but are independent of the brunt vaisala frequency for r near 1 the diffusivities for salt and heat are approximately equal 10 4 m2 s 1 they decrease roughly as r 4 and r 2 respectively over the oceanic range 1 r 10

thermal diffusivity of rhyolitic glasses and melts effects of temperature crystals and dissolved water thermal diffusivity d was measured using laser flash analysis on pristine and remelted obsidian sam ples from mono craters california these high silica rhyo lites contain between 0 013 and 1 10 wt h2o and 0 to 2 vol crystallites at room temperature dglass varies from 0 63 to 0 68 mm 2 s 1 with more crystalline samples having higher d a st increases dglass decreases approaching a constant value of 0 55 mm 2 s 1 near 700 k the glass data are fit with a simple model as an exponential function of temperature and a linear function of crystallinity dissolved water contents up to 1 1 wt have no statistically significant effect on the thermal diffusivity of the glass upon crossing the glass transition d decreases rapidly near 1 000 k for the hydrous melts and 1 200 k for anhydrous melts rhy olitic melts have a dmelt of 0 51 mm 2 s 1 thermal conduc tivity k0d cp of rhyolitic glass and melt increases slightly with t because heat capacity cp increases with t more strongly than density and d decrease the thermal conductivity of rhyolitic melts is 1 5 wm 1 k 1 a nd should vary little over the likely range of magmatic temperatures and water contents these values of d and k are similar to those of major crustal rock types and granitic protoliths at magmatic temperatures suggesting that changes in thermal properties accompanying partial melting of the crust should be relatively minor numerical models of shallow rhyolite intrusions indicate that the key difference in thermal history between bodies that quench to obsidian and those that crystallize results from the release of latent heat of crystallization latent heat release enables bodies that crystallize to remain at high temperatures for much longer times and cool more slowly than glassy bodies the time to solidification is similar in both cases however because solidification requires cooling through the glass transition in the first case and cooling only to the solidus in the second

vapor transfer prior to the october 2004 eruption of mount st helens washington dome lavas from the 2004 eruption of mount st helens show elevated li contents in plagioclase phenocrysts at the onset of dome growth in october 2004 these cannot be explained by variations in plagioclase melt partitioning but require elevated li contents in coexisting melt a fact confirmed by measurements of li contents as high as 207 g g in coexisting melt inclusions similar li enrichment has been observed in material erupted prior to and during the climactic may 1980 eruption and is likewise best explained via pre eruptive transfer of an exsolved alkali rich vapor phase derived from deeper within the magma transport system unlike 1980 however high li samples from 2004 show no evidence of excess 210pb 226ra implying that measurable li enrichments may occur despite significant differences in the timing and or extent of magmatic degassing diffusion modeling shows that li enrichment occurred within 1 yr before eruption and that magma remained li enriched until immediately before eruption and cooling this short flux time and the very high li contents in ash produced by phreatomagmatic activity prior to the onset of dome extrusion suggest that vapor transfer and accumulation were associated with initiation of the current eruption overall observation of a high li signature in both 1980 and 2004 dacites indicates that li enrichment may be a relatively common phenomenon and may prove useful for petrologic monitoring of mount st helens and other silicic volcanoes lithium diffusion is also sufficiently rapid to constrain vapor transfer on similar time scales to short lived radionuclides

double diffusive layering and mixing in patagonian fjords abstract double diffusive layering was quantified for the first time in the chilean patagonian fjords region 41 5 56 s approximately 600 temperature and salinity profiles collected during 1995 2012 were used to study water masses quantify diffusive layering and compute the vertical diffusivity of heat development of diffusive layering or simply layering was favored by relatively fresh cold waters overlying salty warm waters fresh waters are frequently derived from glacial melting that influences the fjord either directly or through rivers salty waters are associated with modified subantarctic msaaw and subantarctic water saaw double diffusive convection occurred as layering in 40 of the year round data and as salt fingering in 5 m 2 s 1 diffusive layering events presented a meridional gradient with less layering within the 41 47 s northern region relative to the southern region between 47 and 56 s layering occupied on average 27 and 56 of the water column in the northern and southern regions respectively thermohaline staircases were detected with microprofile measurements in martinez and baker channels 48 s showing homogeneous layers 2 4 m thick below the pycnocline 10 40 m also in this area increased vertical mixing coincided with the increased layering events high values of thorpe scale l t 7 m dissipation rate of tke e 10 5 10 3 w kg 1 and diapycnal eddy diffusivity k 10 6 10 3 m 2 s 1 were associated with diffusive layering implications of these results are that diffusive layering should be taken into account together with other mixing processes such as shear instabilities and wind driven flows in biological and geochemical studies

seismicity rate immediately before and after main shock rupture from high frequency waveforms in japan 1 we analyze seismicity rate immediately before and after 82 main shocks with the magnitudes ranging from 3 to 5 using waveforms recorded by the hi net borehole array in japan by scrutinizing high frequency signals we detect 5 times as many aftershocks in the first 200 s as in the japan meteorological agency catalogue after correcting for the changing completeness level immediately after the main shock the aftershock rate shows a crossover from a slower decay with an omori s law exponent p 0 58 0 08 between 20 and 900 s after the main shock to a faster decay with p 0 92 0 04 after 900 s the foreshock seismicity rate follows an inverse omori s law with p 0 73 0 08 from several tens of days up to several hundred seconds before the main shock the seismicity rate in the 200 s immediately before the main shock appears steady with p 0 35 0 50 these observations can be explained by the epidemic type aftershock sequence etas model and the rate and state model for a heterogeneous stress field on the main shock rupture plane alternatively nonseismic stress changes near the source region such as episodic aseismic slip or pore fluid pressure fluctuations may be invoked to explain the observation of small p values immediately before and after the main shock

estimation of high frequency wave radiation areas on the fault plane by the envelope inversion of acceleration seismograms we have developed an inversion method to estimate high frequency wave radiation areas on the fault plane it is very difficult to perform a source inversion for seismic waveforms whose frequencies are higher than 1 hz because of two problems one is the difficulty in obtaining green s functions that are accurate enough for such high frequencies and the other is that involved in doing a waveform inversion for such oscillatory data we overcame these problems by using aftershock records as empirical green s functions and by using the envelopes of acceleration seismograms as the inversion data instead of waveforms envelopes were calculated by smoothing the acceleration seismograms with a running root mean square time window we applied this method to the 1993 kushiro oki japan earthquake mw 7 6 which occurred on a horizontal fault plane inside the pacific plate subducting beneath the north american plate we adopted the mjma 4 9 aftershock as the empirical green s function event we bandpass filtered 2 0 10 0 hz the strong motion acceleration seismograms at three stations and calculated the envelopes by smoothing with a 5 0 s window length the 40 km 60 km fault plane was divided into 4 6 meshes and the acceleration radiation intensity and rupture time of each mesh were obtained by the inversion the results are as follows 1 high frequency waves radiated weakly around the rupture starting point but radiated mainly near the periphery of the fault plane an area with particularly strong radiation intensity of high frequency waves is seen at the edge of the fault plane about 30 km southwest of the rupture starting point its size is about 20 km 20 km 2 the distribution of high frequency radiation intensity and slip distribution are complementary to each other that is the radiation of high frequency waves was strong in those areas where that of low frequency waves was weak

double diffusive convection in this paper we present a rather personal view of the important developments in double diffusive convection a subject whose evolution has been the result of a close interaction between theoreticians laboratory experimenters and sea going oceano graphers more recently applications in astrophysics engineering and geology have become apparent in the final section we attempt to draw some general conclusions and suggest that further progress will again depend on a close collaboration between fluid dynamicists and other scientists

contribution of the patagonia icefields of south america to sea level rise digital elevation models of the northern and southern patagonia icefields of south america generated from the 2000 shuttle radar topography mission were compared with earlier cartography to estimate the volume change of the largest 63 glaciers during the period 1968 1975 2000 these glaciers lost ice at a rate equivalent to a sea level rise of 0 042 0 002 millimeters per year in the more recent years 1995 2000 average ice thinning rates have more than doubled to an equivalent sea level rise of 0 105 0 011 millimeters per year the glaciers are thinning more quickly than can be explained by warmer air temperatures and decreased precipitation and their contribution to sea level per unit area is larger than that of alaska glaciers

emplacement and rheomorphic deformation of a large lava like rhyolitic ignimbrite grey s landing southern idaho the miocene grey9s landing ignimbrite reaches 70 m thick and covers at least 400 km 2 in the central region of the snake river plain it shows particularly intense welding and rheomorphic deformation and although parts are eutaxitic most is lava like with flow banding and no fiamme a near ubiquitous penetrative flow lamination associated with a well developed elongation lineation is folded into small intrafolial tight to isoclinal oblique and sheath folds which are refolded by larger folds in the upper parts structural and kinematic analysis reveals that welding and early deformation occurred rapidly during deposition from a very hot 1000 c high mass flux pyroclastic density current that flowed westward across a graben faulted landscape as hot particles were deposited they rapidly agglutinated and coalesced and underwent noncoaxial shear in a subhorizontal ductile shear zone close to the current deposit interface the shear zone is interpreted to have been less than 2 m thick it produced and deformed the rheomorphic fabric and it migrated upward with the rising current deposit interface during aggradation so that it transiently affected all levels of the resultant thick ignimbrite deformation was progressive and after the density current had dissipated viscous spreading and downslope flow continued and involved an increasingly thick portion of the sheet this folded the flow banding and f 1 intrafolial isoclines into larger sheath folds and into more upright periclines near the top of the ignimbrite we demonstrate that structural and kinematic analysis can elucidate the emplacement history of rheomorphic ignimbrites

influence of extrusion rate and magma rheology on the growth of lava domes insights from particle dynamics modeling abstract lava domes are structures that grow by the extrusion of viscous silicic or intermediate composition magma from a central volcanic conduit repeated cycles of growth are punctuated by collapse as the structure becomes oversized for the strength of the composite magma that rheologically stiffens and strengthens at its surface here we explore lava dome growth and failure mechanics using a two dimensional particle dynamics model the model follows the evolution of fractured lava with solidification driven by degassing induced crystallization of magma the particle dynamics model emulates the natural development of dome growth and rearrangement of the lava dome which is difficult in mesh based analyses due to mesh entanglement effects the deformable talus evolves naturally as a frictional carapace that caps a ductile magma core extrusion rate and magma rheology together with crystallization temperature and volatile content govern the distribution of strength in the composite structure this new model is calibrated against existing observational models of lava dome growth results show that the shape and extent of the ductile core and the overall structure of the lava dome are strongly controlled by the infusion rate the effects of extrusion rate on magma rheology are sensitive to material stiffness which in turn is a function of volatile content and crystallinity material stiffness and material strength are key model parameters which govern magma rheology and subsequently the morphological character of the lava dome and in turn stability degassing induced crystallization causes material stiffening and enhances material strength reflected in non newtonian magma behavior the increase in stiffness and strength of the injected magma causes a transition in the style of dome growth from endogenous expansion of a ductile core to stiffer and stronger intruding material capable of punching through the overlying material and resulting in the development of a spine or possibly inducing dome collapse simulation results mimic development of a megaspine upon the influx of fresh magma which leads to the re direction of magma flow creating a new shear zone and the switching of dome growth from one side to the other our model shows similar dome growth dynamics as observed at soufriere hills volcano montserrat indicating a strong correlation between extrusion rate and its subsequent effect on mechanical properties and variations in magma rheology

relation between mainshock rupture process and omori s law for aftershock moment release rate summary we compare the source time functions i e moment release rates of three large california mainshocks with the seismic moment release rates during their aftershock sequences aftershock moment release rates computed by summing aftershock moments in time intervals follow a power law time dependence similar to omori s law from minutes to months after the mainshock furthermore in contrast to the previously observed saturation in numbers of aftershocks shortly after the mainshock rupture no such saturation is seen in the aftershock moment release rates which are dominated by the largest aftershocks we argue that the observed saturation in aftershock numbers described by the time offset parameter c in omori s law is likely an artefact due to the underreporting of small aftershocks which is related to the difficulty of detecting large numbers of small aftershocks in the mainshock coda we further propose that it is more natural for c to be negative i e singularity follows the onset of mainshock rupture than positive singularity precedes onset of rupture to make a more general comparison of mainshock rupture process and aftershock moment rates we then scale mainshock time functions to equalize the effects of the varied seismic moments for the three california mainshocks we compare the scaled time functions with similarly scaled aftershock moment rates finally we compare global averages of scaled time functions of many shallow events to the average scaled aftershock moment release rate for six california mainshocks in each of these comparisons the extrapolation using omori s law of the aftershock moment rates back in time to the onset of the mainshock rupture indicates that the temporal intensity of the aftershock moment release is about 1 5 orders of magnitude less than the maximum reached by the mainshock rupture this may be due to the differing amplitudes and relative importance of static and dynamic stresses in aftershock initiation compared to mainshock rupture propagation

controls on lithium concentration and diffusion in zircon abstract thermal annealing of zircons prior to uranium lead dating by laser ablation inductively coupled plasma mass spectrometry is a commonly implemented procedure which improves data accuracy and precision by partially repairing radiation damage from the decay of uranium and thorium however it also leads to significantly higher concentrations of lithium in the zircon lattice which become positively correlated with trivalent yttrium and rare earth elements prior to such treatments zircons typically contain lithium below detection limits typically

trampoline effect in extreme ground motion in earthquake hazard assessment studies the focus is usually on horizontal ground motion however records from the 14 june 2008 iwate miyagi earthquake in japan a crustal event with a moment magnitude of 6 9 revealed an unprecedented vertical surface acceleration of nearly four times gravity more than twice its horizontal counterpart the vertical acceleration was distinctly asymmetric the waveform envelope was about 1 6 times as large in the upward direction as in the downward direction which is not explained by existing models of the soil response we present a simple model of a mass bouncing on a trampoline to account for this asymmetry and the large vertical amplitude the finding of a hitherto unknown mode of strong ground motion may prompt major progress in near source shaking assessments

site amplification of coda waves from local earthquakes in central california the goals of this study are two fold 1 to examine the site effect of coda waves believed to be the average site effect of shear waves in order to understand its spatial and frequency dependent behavior and 2 to learn what we can about the processes that generate the coda itself we use digital data from over 90 earthquakes each recorded by a subset of some 150 stations in the coast ranges of central california between san francisco and san luis obispo results from the band 1 5 to 24 hz indicate that site amplification depends strongly on surface geology and frequency at low frequencies 1 5 to 3 0 hz changes in amplification up to a factor of 20 are observed amplification generally varies inversely with deposit age at sediment sites and is lowest at granite and franciscan basement sites at high frequencies 6 to 24 hz the pattern changes many granite sites the majority in the gabilan range exhibit increasing amplification with frequency relative to the average station this behavior differs strikingly from that observed at sediment and franciscan sites which roll off at an intermediate rate and many sediment sites adjacent to the san andreas fault zone which decay away even more rapidly with frequency these results can be explained qualitatively by appealing to variable near site impedance and attenuation however complicating phenomena such as mode excitation in valley sediments must exist at low frequencies peaked behavior at a few hard rock sites at high frequency 12 hz currently lacks explanation at a few sediment sites the low frequency excitation is so strong that the coda envelopes begin to take on different shapes this contradicts the assumption based on previous observations that the coda shape is independent of source receiver location thus some site measurements may be artificially high the working model of coda waves as body wave energy backscattered from randomly distributed inhomogeneities must be modified to include the possibility of efficient near site resonance excited by incident direct and coda wave energy

quantifying early aftershock activity of the 2004 mid niigata prefecture earthquake mw6 6 1 we analyze the early aftershock activity of the 2004 mid niigata earthquake using both earthquake catalog data and continuous waveform recordings the frequency magnitude distribution analysis of the japan meteorological agency jma catalog shows that the magnitude of completeness of the aftershocks changes from values around 5 0 immediately after the main shock to about 1 8 12 hours later such a large incompleteness of early events can bias significantly the estimation of aftershock rates to better determine the temporal pattern of aftershocks in the first minutes after the niigata earthquake we analyze the continuous seismograms recorded at six high sensitivity seismograph network hi net stations located close to the aftershock distribution clear aftershocks can be seen from about 35 s after the main shock we estimate that the events we picked on the waveforms recorded at two seismic stations ngoh and ynth situated on opposite sides of the aftershock distribution are complete above a threshold magnitude of 3 4 the c value determined by taking these events into account is about 0 003 days 4 3 min statistical tests demonstrate that a small but nonzero c value is a reliable result we also analyze the decay with time of the moment release rates of the aftershocks in the jma catalog since these rates should be much less influenced by the missing small events the moment rates follow a power law time dependence from few minutes to months after the main shock we finally show that the rate and state dependent friction law or stress corrosion could explain well our findings

broadening of seismogram envelopes in the randomly inhomogeneous lithosphere based on the parabolic approximation southeastern honshu japan analyzing horizontal component seismograms of small earthquakes with intermediate hypocentral distances in southeastern honshu japan we found that time widths of seismogram envelopes around direct s waves are much longer than source duration times estimated from their magnitudes the time lags of the maximum amplitude and the half maximum after the peak were measured from the onset of the direct s wave arrival from band pass filtered seismograms from 2 to 32 hz even though there is considerable scatter both the time lags are found to increase with increasing hypocentral distance up to 305 km we hypothesize that pulse shape broadens and the maximum amplitude is reduced after propagating through the random structure of the lithosphere the parabolic approximation theoretically predicts that the long wavelength component of velocity inhomogeneities compared with the wavelength of seismic waves produces diffraction fluctuations and makes seismogram envelopes broaden with increasing travel distance in the saturated regime supposing a gaussian autocorrelation function for the randomness and an empirical frequency dependent attenuation we propose a formula for the temporal change in the power spectral density of seismic waves applying this formula to the observed data we statistically evaluated the scale of random inhomogeneities the mean square fractional velocity fluctuation was estimated to be 10 3 times the correlation distance a in kilometers

seasonal mixing processes in an arctic fjord system abstract studies of water movement in the aafardlikavs qaumarujuk fjord system in west greenland have barn carried out in order to understand the movement of mine tailings discharged into agfardlikavs fjord observations are explained in terms of resonance of the internal tide deep convection associated with sea ice growth and basin water exchange occurring at the time of ice breakup in early summer mixing processes are dominated by these events illustrating the limitations of any seasonal description based on conventional diffusive processes

evaluation of models for the origin of miocene low δ18o rhyolites of the yellowstone columbia river large igneous province two models have been proposed for the origin of the low 18o rhyolites of the snake river plain yellowstone hotspot trend the first involves a single multicyclic caldera system or multiple nested or overlapping systems in which the early erupted products become hydrothermally altered and are subsequently melted to form low 18o rhyolites bindeman and valley 2001 watts et al 2011 the second model appeals to a crustal magma source which was hydrothermally altered in a thermal event prior to the onset of miocene magmatism boroughs et al 2005 we critically evaluate the plausibility of each and provide thermal temporal and volume constraints which must be included in any model for the petrogenesis of low 18o rhyolites of the central snake river plain although the models are not mutually exclusive we conclude that a component of pre existing low 18o crust is required in the central snake river plain where the greatest volumes of strongly 18o depleted rhyolite occur this component could be provided by meteoric hydrothermally altered granites of the idaho batholith which are cut by the central snake river plain

vertical heat transfer in the arctic ocean the role of double diffusive mixing 1 microstructure profiles collected in the central amundsen basin are analyzed in order to quantify the role of double diffusive mixing for vertical heat transfer from the atlantic layer in the profiles a persistent but laterally incoherent thermohaline staircase structure is identified in the 200 260 m depth range the staircase contains homogeneous layers with average height of 1 3 m and thin high gradient interfaces with average temperature and salinity jumps of about 0 065 c and 0 015 respectively when inferred from a commonly used diffusive convection parameterization the average vertical heat flux within the staircase is 0 6 w m 2 this is one order of magnitude larger than the molecular diffusion alone and of the same order as the overall heat loss from the atlantic layer in the deep basins of the arctic ocean the parameterization is evaluated using observed turbulent heat fluxes and is found to overestimate diffusive convective fluxes with up to an order of magnitude especially for weak thermal forcing small temperature jumps in staircase staircases coexist with thermohaline intrusions in the vertical temperature and salinity profiles lomonosov ridge is identified as a potential region for formation of intrusions it is found that salt fingering is the dominant process during intrusion growth whereas diffusive convection is the dominant process in maintaining the intrusions at steady state in the deep basins

spatial and frequency dependent properties of site amplification factors in japan derived by the coda normalization method we have estimated broadband f 0 5 8 hz site amplification factors at 1800 sites in japan based on the coda normalization method using 4001 seismograms obtained from 48 events the results show that in the low frequency band f 0 5 1 hz the site amplification factor varies over a wide range from 4 to 24 db with larger site amplification factors 8 db in such major basins as kushiro rumoi sapporo aomori sendai niigata tokyo toyama nagoya osaka oita and kagoshima on the other hand the site amplification factor in the high frequency band f 4 8 hz varies over a relatively narrow range from 0 to 18 db at each station and has no clear correlation with the surface geology of each station we then examined the contribution of the site amplification at each station to the anomalous distribution of the intensity pattern during large earthquakes by correcting the observed ground accelerations at each k net and kik net station with their corresponding estimated site amplification factors the corrected pattern of intensity shows simple concentric isoseismal intensity contours around the hypocenter indicating the applicability of our estimates to strong motion predictions we confirmed that our estimates are superior to those derived from geology such as those based on the regression of the averaged s wave velocity from the surface to a depth of 30 m graphic 1 with a smaller standard deviation of intensity variations based on a standard decay function of intensity versus hypocentral distance 1 embed inline graphic 1 gif

variability in earthquake stress drop and apparent stress 1 we apply empirical green s function coda based analysis to four earthquake sequences in japan that span a magnitude range of 1 8 to 6 9 to measure radiated energy corner frequency and stress drop we find no systematic dependence of apparent stress or stress drop on seismic moment for these sequences and find they both are log normally distributed however we identify several anomalous events both energetic and enervated that show sharply different spectral signatures from the rest of the population these events indicate that much of the variation in apparent stress and stress drop is statistically significant which may have important implications for seismic hazard analysis

rupture process of the 2008 iwate miyagi nairiku japan earthquake derived from near source strong motion records abstract we derive the rupture process of the 2008 iwate miyagi nairiku japan earthquake m jma 7 2 during which the largest ground acceleration to date namely 4022 cm sec 2 was recorded at a hanging wall station iwth25 station of kik net just above the hypocenter velocity waveform data 0 1 1 hz at 14 strong motion stations of k net and kik net including the borehole records of iwth25 are inverted using the multi time window linear waveform inversion method we assume a horizontally layered velocity structure model having low velocity subsurface layers for each station in order to calculate the green s functions the waveform inversion indicates that there are two major slip patches one patch extends from the hypocenter to the southern shallower part of the fault a particularly large slip area in this patch is centered approximately 8 km to the south of the hypocenter with a maximum slip of 6 2 m the area ruptured between 4 and 9 sec after the initial break the other patch with smaller slip is located in the northern part which broke after the rupture of the southern slip patch the initial 0 4 sec rupture occurred beneath iwth25 contributing to the synthesis of a distinctive upward velocity pulse at this station examination of the slip contribution to the synthetic velocity waveforms and comparison of the isochrones with the slip distribution suggest that a peak acceleration greater than 4000 cm sec 2 observed at iwth25 was generated from the area that is closest to the hypocenter in the southern particularly large slip area

rheomorphism of welded tuffs abstract peralkaline welded tuffs from the islands of gran canaria canary islands and pantelleria italy show abundant evidence for post depositional flow it is demonstrated that rheomorphism or secondary mass flowage can occur in welded tuffs of ignimbrite and air fall origin the presence of a linear fabric is taken as the diagnostic criterion for the recognition of the process deposition on a slope is an essential condition for the development of rheomorphism after compaction and welding internal structures produced during rheomorphic flow can be studied by the methods of structural geology and show similar dispositions to comparable features in sedimentary slump sheets it is shown that secondary flowage can occur in welded tuffs emplaced on gentle slopes provided that the apparent viscosity of the magma is sufficiently low compositional factors favor the development of rheomorphism in densely welded tuffs of peralkaline type

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

spatial distribution of scattering loss and intrinsic absorption of short period s waves in the lithosphere of japan on the basis of the multiple lapse time window analysis of hi net data summary propagation of short period s waves through the crust is strongly controlled by scattering loss and intrinsic absorption scattering loss controls the shape of the seismic envelope and the spatial distribution of the energy while intrinsic absorption produces an exponential decay as a function of time which is independent of the coordinates since both parameters have a different effect it is possible to compute them by means of the multiple lapse time window analysis mltwa in this paper high resolution maps of japan for both seismic s wave attenuation parameters are obtained by using the mltwa with data provided by the hi net seismic network the maps show strong regional variation of the parameters the variations depend mainly on the tectonic setting of each region and volcanism mechanisms in the scattering loss maps in the 1 2 hz map there is a very different behaviour between the northeast stronger scattering loss and the southwest much weaker scattering loss in the northeast of japan areas with strong scattering loss correspond mainly to the location of the volcanic arcs in southwest japan chugoku region and the west side of kii peninsula show strong scattering levels for the 4 8 hz and higher frequency bands in hokkaido strong scattering loss and intrinsic absorption can be observed for the lower frequency bands in the sendai plain we find strong scattering loss for all the frequency bands under all these areas low velocity anomalies have been detected in previous works in tohoku area the east side shows lower intrinsic attenuation than the west side this characteristic seems to extend to the southern part of hokkaido and to central japan in kanto area the values of intrinsic absorption are lower than in the surrounding areas but in the region around the itoigawa shizuoka tectonic line and in its western side strong absorption areas are observed the behaviour of each area for intrinsic absorption is similar to the behaviour observed in the q 1c maps the mltwa is based on the hypothesis of multiple isotropic scattering in a medium with the homogeneous distribution of scattering mean free path and intrinsic absorption although these hypotheses are very simple the results are very informative on the characteristics of each region and show the usefulness of studying the properties of scattered seismic waves in the understanding of the properties of the crust

geochemical precursors to volcanic activity at mount st helens usa the importance of the interplay between degassing and crystallization before and after the eruption of mount st helens washington usa in 1980 is well established here we show that degassing occurred over a period of decades to days before eruptions and that the manner of degassing as deduced from geochemical signatures within the magma was characteristic of the eruptive style trace element lithium and short lived radioactive isotope lead 210 and radium 226 data show that ascending magma stalled within the conduit leading to the accumulation of volatiles and the formation of lead 210 excesses which signals the presence of degassing magma at depth

decay and expansion of the early aftershock activity following the 2011 mw9 0 tohoku earthquake the 2011 m w9 0 tohoku earthquake was followed by an abundant amount of seismicity providing a unique opportunity to analyze the triggering mechanism of great earthquakes although the tohoku earthquake occurred close to a dense seismic network many aftershocks that occurred in the first few hours after the mainshock are not recorded in the earthquake catalogs here we use a template waveform approach to recover as many as possible missing events in the first 12 hours following the tohoku mainshock our analysis is able to detect about 1 4 times more events than those listed in the high sensitivity seismograph hi net earthquake catalog combining our new dataset with earthquakes that occurred at latter times we are able to observe a continuous decay of the aftershock rate and along strike expansion of aftershock area we relate the latter observation to the occurrence of post seismic slip over the deep interface

imaging the high frequency energy radiation process of a main shock and its early aftershock sequence the case of the 2008 iwate miyagi nairiku earthquake japan to understand the energy release process that operates at the end of the main shock rupture and start of the aftershock activity we propose an inversion method that uses continuous high frequency seismogram envelopes of the main shock and early aftershocks i e events that occur at short times after the main shock in our approach the aftershock sequence is regarded as a continuous energy release process rather than a discrete time series of events to correct for the contribution of coda wave energy excited by multiple scattering we use the theoretical envelope synthesized on the basis of the radiative transfer theory as a green s function the site amplification factors are corrected considering the conservation of energy flux and using the coda normalization method the inverted temporal energy release rate for the 2008 mw 6 9 iwate miyagi nairiku earthquake japan decays following t 1 1 at the lapse time t of 40 900 s after the main shock origin time this exponent of the decay rate is similar to the p value of the modified omori law the amount of estimated energy release is consistent with that calculated from the magnitude listed in the aftershock catalog although the uncertainty is large the location of large energy release at the lapse times of 40 900 s approximately overlaps to that of the aftershocks which surrounds the large energy release area during the main shock faulting the maxima of the energy release rate normalized by the average decay rate distributes following a power law similar to the gutenberg richter law

vertical mixing rates in fjords determined using radon and salinity as tracers excess radon profiles were measured in several washington state and british columbia fjords generally exponential profiels were observed during periods of bottom water stagnation values of the vertical eddy diffusivity were estimated from the exponential excess radon profiles and from salinity changes in the stagnant bottom water these values ranged from 0 16 to 36 cm2 s 1 among fjords and the variation could be explained by different inputs of tidal energy into vertical mixing for the different fjords excess radon was also observed in surface water of several fjords the source of this excess radon was the freshwater runoff entering the fjords values of the vertical eddy diffusivity were estimated for the near surface water of narrows inlet from these profiles to be 0 32 to 0 47 cm2 s 1 across the freshwater saltwater interface and 0 9 to 3 1 cm2 s 1 between 5 and 35 m depth

hidden aftershocks of the 2011 mw 9 0 tohoku japan earthquake imaged with the backprojection method 1 the first 25 h of the aftershock sequence following the 11 march 2011 mw 9 0 tohoku japan earthquake is investigated using a backprojection method in total 600 aftershocks are imaged during this time period these aftershocks are distributed over a 500 by 300 km area and include many events in the outer rise the backprojection events are compared with the japan meteorological agency jma catalogue which is composed of earthquakes recorded by local seismic networks in japan surprisingly half of the backprojection events are not found in the jma catalogue these events cluster near the japan trench and in the outer rise and fill in gaps in the spatial distribution of the early aftershock sequence where large main shock slip is thought to have occurred these results show that the jma magnitude of completeness is very high near the trench following the 2011 tohoku main shock and earthquakes as large as magnitude 6 8 went undetected by local seismic networks

anomalous early aftershock decay rate of the 2004 mw6 0 parkfield california earthquake 1 we analyze the seismicity rate immediately after the 2004 mw6 0 parkfield california earthquake from near source seismograms by scrutinizing high frequency signals we can distinguish mainshock coda from early aftershocks occurring as soon as 30 s after the mainshock we find as expected that a significant fraction of aftershocks in the first few hours after the main shock are missing in the northern california seismic network catalog we observe a steady rate of aftershocks in the first 130 s followed by a power law decay of aftershock activity thus there appears to be a distinct early stage of aftershock activity that does not fit the omori s law with a constant p value a phenomenon that we refer to as early aftershock deficiency ead our observation suggests that mainshock rupture and aftershocks are distinct processes not described by a single omori s law several physical models of aftershocks can explain the ead

omori utsu law c values associated with recent moderate earthquakes in japan we investigate the early aftershock activity associated with four moderate earthquakes m w 6 6 6 7 that occurred recently in japan for each aftershock sequence we examine continuous high pass filtered seismograms recorded at seismic stations nearby the main fault to identify as many early events as possible the magnitude of these events is calibrated using aftershocks that are listed in the earthquake catalog of japan meteorological agency jma the analysis of the aftershock decay rates reveals a power law time dependence with a scaling exponent close to 1 0 that starts from about one minute from the mainshock our results demonstrate that the c value of the omori utsu law is very small although a lower bound is not established due to completeness problems in the first minute after the mainshock and statistical fluctuations

widespread rheomorphic and lava like silicic ignimbrites overlying flood basalts in the northwestern and northern deccan traps the physical volcanology of widespread rhyolites and dacites overlying flood basalt lavas in the northwestern and northern parts of the 65 5 ma deccan traps india is poorly known we show that these are not lava flows but high grade welded and rheomorphic to extremely high grade lava like ignimbrites deposited by pyroclastic density currents evidence for this interpretation includes the following i flat planar contacts with the underlying basalts and absence of basal brecciated zones ii pervasive millimeter to centimeter scale flow banding iii parataxitic textures indicating very high degrees of compaction and welding iv strong rheomorphic deformation producing folds of diverse geometries and sizes showing overprinting relationships with common tight isoclinal and sheath eye folds that are sometimes refolded into f2 and even f3 folds v curvilinear fold hinges with elongation lineations varying from transverse to subparallel to the fold axes vi local boudinage and autobrecciation in flow banded glassy tuffs vii common and abundant spherulites and lithophysae viii intimate association of tuff and vitrophyre at millimeter to tens of meter scales and ix vitroclastic textures showing highly flattened and stretched glass shards and pumice fiamme wrapping around phenocrysts whereas rheomorphic and lava like ignimbrites dominate some non welded and welded eutaxitic ignimbrites also occur voluminous rhyolites and dacites in many flood basalt provinces of the world are recognized as high grade to extremely high grade ignimbrites and the deccan is no exception this deccan explosive silicic volcanism may have significantly contributed to the k pg boundary mass extinctions if contemporaneity can be established by future geochronological work

the diffusive regime of double diffusive convection the diffusive regime of double diffusive convection is discussed with a particular focus on unresolved issues that are holding up the development of large scale parameterizations some of these issues such as interfacial transports and layer interface interactions may be studied in isolation laboratory work should help with these however we must also face more difficult matters that relate to oceanic phenomena that are not represented easily in the laboratory these lie beneath some fundamental questions about how double diffusive structures are formed in the ocean and how they evolve in the competitive ocean environment

cristobalite in a rhyolitic lava dome evolution of ash hazard prolonged and heavy exposure to particles of respirable crystalline silica rich volcanic ash could potentially cause chronic fibrotic disease such as silicosis in individuals living in areas of frequent ash fall here we show that the rhyolitic ash erupted from chaiten volcano chile in its dome forming phase contains increased levels of the silica polymorph cristobalite compared to its initial plinian eruption ash erupted during the initial explosive phase 2 5 may 2008 contained approximately 2 wt cristobalite whereas ash generated after dome growth began from 21 may 2008 contains 13 19 wt the work suggests that active obsidian domes crystallise substantial quantities of cristobalite on time scales of days to months probably through vapour phase crystallisation on the walls of degassing pathways rather than through spherulitic growth in glassy obsidian the ash is fine grained 9 7 17 7 vol 4 m in diameter the respirable range and the particles are mostly angular sparse fibre like particles were confirmed to be feldspar or glass

rheological controls on the emplacement of extremely high grade ignimbrites extremely high grade lava like welded ignimbrites are produced by many large explosive eruptions with volumes typically 101 103 km3 however understanding of the physical properties of these unusual deposits and their transport and depositional mechanisms is incomplete the lava like and rheomorphic grey s landing ignimbrite idaho western united states provides abundant field evidence supporting the upward migration of a transient 2 m thick sub horizontal ductile shear zone at the interface between the pyroclastic density current and the deposit through which all of the aggrading pyroclastic material passed here we use a combination of rheological experiments and thermo mechanical modeling to test the syndepositional shear zone model we show that syndepositional welding and ductile flow are achievable within a very restricted field of likely temperature strain rate space where rapid deformation is favored by higher emplacement temperatures 850 c the field of ductile deformation is broadened significantly by accounting for strain heating which permits a sustained temperature increase of up to 250 c within the shear zone and helps to explain the enormous extents of lava like lithofacies and the intense rheomorphism recorded in extremely high grade ignimbrites recognition of strain heating within rheomorphic ignimbrites suggests that large pyroclastic density currents may travel over a hot substrate potentially hotter than the density current itself

cristobalite in volcanic ash of the soufriere hills volcano montserrat british west indies crystalline silica mostly cristobalite was produced by vapor phase crystallization and devitrification in the andesite lava dome of the soufriere hills volcano montserrat the sub 10 micrometer fraction of ash generated by pyroclastic flows formed by lava dome collapse contains 10 to 24 weight percent crystalline silica an enrichment of 2 to 5 relative to the magma caused by selective crushing of the groundmass the sub 10 micrometer fraction of ash generated by explosive eruptions has much lower contents 3 to 6 percent of crystalline silica high levels of cristobalite in respirable ash raise concerns about adverse health effects of long term human exposure to ash from lava dome eruptions

seismogram envelope inversion for the spatial distribution of high frequency energy radiation from the earthquake fault application to the 1994 far east off sanriku earthquake japan incoherency of high frequency seismic waves leads to the idea to analyze seismogram envelopes disregarding phase information for the source study we develop an inversion method for estimating high frequency above 1 hz energy radiation from the earthquake fault and site amplification factors from observed mean square s wave seismogram envelopes the inversion is executed by using the s wave envelope green function from the onset to coda for a point shear dislocation source in a scattering medium which is formulated based on an extended version of the radiative transfer theory the use of the envelope green function enables us to estimate the spatial distribution of high frequency energy radiation on a fault plane this has been difficult by conventional waveform inversion methods the rupture velocity and the duration time of energy radiation on each subfault are also estimated by grid search method we apply this new method to the 1994 far east off sanriku northeastern japan earthquake mw 7 7 which ruptured a 90 km segment of the plate boundary along the japan trench inverting observed seismogram envelopes at 10 strong motion stations in japan it is concluded that above 90 of the high frequency energy was radiated from the western half of the fault with the largest energy radiation near the deep side edge the rupture velocity is estimated to be 2 7 km s the estimated site amplification factors ranging between 0 3 and 15 are consistent with those independently estimated by the coda normalization method

migration of early aftershocks following the 2004 parkfield earthquake a significant number of the early aftershocks following large shallow earthquakes are missing in existing earthquake catalogues an analysis of the waveforms of 3 647 relocated earthquakes along the parkfield section of the san andreas fault reveals 11 times more aftershocks within three days of the 2004 parkfield earthquake than listed in a standard catalogue large shallow earthquakes are immediately followed by numerous aftershocks a significant portion of these events is missing in existing earthquake catalogues mainly because seismicity after the mainshock can be masked by overlapping arrivals of waves from the mainshock and aftershocks1 2 3 4 however recovery of the missing early aftershocks is important for understanding the physical mechanisms of earthquake triggering2 3 4 and for tracking postseismic deformation around the rupture zone associated with the mainshock5 6 7 here we use the waveforms of 3 647 relocated earthquakes8 along the parkfield section of the san andreas fault as templates9 10 to detect missing aftershocks within three days of the 2004 magnitude 6 0 parkfield earthquake we identify 11 times more aftershocks than listed in the standard catalogue of the northern california seismic network we find that the newly detected aftershocks migrate in both along strike and down dip directions with logarithmic time since the mainshock consistent with numerical simulations of the expansion of aftershocks caused by propagating afterslip11 12 the cumulative number of early aftershocks increases linearly with postseismic deformation in the first two days supporting the view that aftershocks are driven primarily by afterslip13 14

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

spherulite crystallization induces fe redox redistribution in silicic melt rhyolitic obsidians from krafla volcano iceland record the interaction between mobile hydrous species liberated during crystal growth and the reduction of ferric iron in the silicate melt we performed synchrotron ftir and xanes measurements along a transect extending from a spherulite into optically distinct colorless and brown glass zones measurements show that the colorless glass is enriched in oh groups and depleted in ferric iron while the brown glass shows the opposite relationship the color shift between brown and clear glass is sharp suggesting that the colorless glass zone was produced by a redox front that originated from the spherulite margin and moved through surrounding melt during crystallization we conclude that the most likely reducing agent is hydrogen produced by magnetite crystallization within the spherulite the krafla obsidians dramatically capture redox disequilibrium on the micoscale and highlight the importance of hydrous fluid liberation and late stage crystallization to the redox signature of glassy lavas

short term properties of earthquake catalogs and models of earthquake source i review the short term properties of earthquake catalogs in particular the time and size distributions and the completeness of the early part of aftershock sequences for strong shallow earthquakes i determine the parameters of the omori and gutenberg richter laws for aftershocks close in time to a mainshock aftershock sequences of large earthquakes in southern california 1952 kern county 1992 joshua tree landers big bear sequence 1994 northridge and 1999 hector mine recorded in the caltech catalog are analyzed to demonstrate that at the beginning of these series many small earthquakes are absent from the catalog the number of missing earthquakes increases with the magnitude range of a catalog and for some data sets exceeds the number of aftershocks close to a mainshock listed in a catalog comparing global earthquake catalogs harvard centroid moment tensor and preliminary determination of epicenter with local data sets indicates that the catalogs based on longer period waves miss many early aftershocks even when their magnitudes are well above the stated magnitude threshold such short term incompleteness may introduce significant biases to the statistical analysis of the seismicity pattern in particular for branching models of earthquake occurrence incorporating the omori law for such models the likelihood function strongly depends on close aftershocks i review the techniques to alleviate this problem analyzing the source rupture process of several recent large earthquakes suggests that rupture propagation is highly inhomogeneous in space time and focal mechanism these random variations in the rupture process can be viewed as an extension of the aftershock stochastic generating mechanism toward the origin time of a mainshock i review various models of the earthquake rupture process and suggest that fractal distributions of microevents in time space and focal mechanism constitute the development of an earthquake the final identification of an individual earthquake depends on both objective and subjective factors manuscript received 21 may 2003

seismology dynamic triggering of earthquakes the landers earthquake of 1992 triggered a series of earthquakes in other parts of california focusing attention on the mechanism of remote triggering laboratory experiments on granular material under pressure suggest that triggering is a result of seismic waves impinging on a fault and inducing elastic nonlinear behaviour of the fault core accompanied by instantaneous weakening and failure the resulting softening to weakening model fits in well with field observations of real earthquakes after an earthquake numerous smaller shocks are triggered over distances comparable to the dimensions of the mainshock fault rupture although they are rare at larger distances here we analyse the scaling of dynamic deformations the stresses and strains associated with seismic waves with distance from and magnitude of their triggering earthquake and show that they can cause further earthquakes at any distance if their amplitude exceeds several microstrain regardless of their frequency content these triggering requirements are remarkably similar to those measured in the laboratory for inducing dynamic elastic nonlinear behaviour which suggests that the underlying physics is similar1 2

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

diverse mid miocene silicic volcanism associated with the yellowstone newberry thermal anomaly the santa rosa calico volcanic field sc of northern nevada is a complex multi vent mid miocene eruptive complex that formed in response to regional lithospheric extension and flood basalt volcanism santa rosa calico volcanism initiated at 16 7 ma concurrent with regional steens columbia river flood basalt activity and is characterized by a complete compositional spectrum of basalt through high silica rhyolite to better understand the relationships between upwelling mafic magmatism coeval extension and magmatic system development on the oregon plateau we have conducted the first compre hensive study of santa rosa calico silicic volcanism detailed stratigraphic based field sampling and mapping illustrate that silicic activity in this volcanic field was primarily focused along its eastern and western margins at least five texturally distinct silicic units are found in the western santa rosa calico volcanic field including abun dant lava flows near vent deposits and shallow intrusive bodies similar physical features are found in the eastern portion of the volcanic field where four physically distinct units are present the western and eastern santa rosa calico units are characterized by abundant macro and microscopic disequilibrium textures reflecting a complex petrogenetic history additionally unlike other mid mio cene oregon plateau volcanic fields e g mcdermitt the santa rosa calico volcanic field is characterized by a paucity of caldera forming volcanism only the cold springs tuff which crops out across the central portion of the volcanic field was caldera derived major and trace element geochemical variations are present within and between eastern and western santa rosa calico silicic units and these chemical differences coupled with the observed disequilibrium textures illustrate the action of open system petrogenetic processes and melt derivation from heterogeneous source materials the processes and styles of santa rosa calico silicic magmatism are linked to three primary factors local focusing of and thermal and material contributions from the regional flood basalt event lithospheric extension within the northern portion of the northern nevada rift and interaction of mid miocene silicic magmas with pre santa rosa calico lithosphere similar processes and styles of mid miocene silicic volcanism likely occurred across the oregon plateau in regions characterized by both focused lithospheric exten sion and localized mafic magmatism

geomagnetic palaeointensities during the cretaceous normal superchron measured using submarine basaltic glass high quality palaeointensity data have been obtained from thellier thellier experiments on recent and cretaceous submarine basaltic glasses whereas the recent samples faithfully yield today s geomagnetic intensity at the site the palaeointensities for the beginning and end of the cretaceous normal superchron are only 45 and 25 respectively of today s value the data thus extend the mesozoic dipole low into the cretaceous superchron and confirm that submarine basaltic glass is an excellent material for palaeointensity studies

glass transition temperatures of natural hydrous melts a relationship with shear viscosity and implications for the welding process abstract glass transition temperatures tg have been determined for natural multicomponent melts using differential scanning calorimetry trachytic dacitic phonolitic and basaltic base compositions have been analysed over a range of water contents up to 3 75 wt for each sample tg has been obtained over a range of cooling heating rates using the extrapolated onset and the peak temperatures in heat capacity temperature curves tg of all compositions are strongly reduced by increasing water content particularly for the first 1 wt added base composition also has an effect with the lowest tg occurring in the peralkaline phonolite suite for all samples a clear dependence on the cooling heating rate has been recorded these results have been compared with rheological investigations on the same samples on the basis of the equivalence of the shear and enthalpic relaxation process timescales we provide a method to predict the shear viscosity at the glass transition for all the melts investigated in this study both dry and hydrous our determinations of tg provide a lower limit for the time temperature envelope that gives rise to densely welded deposits and constraints on their emplacement temperature furthermore by using the viscosity values predicted at the glass transition we suggest that welding processes may occur over timescales on the order of tens of seconds to tens of minutes at tg

spatial variations of aftershock parameters and their relation to geodetic slip models for the 2010 mw8 8 maule and the 2011 mw9 0 tohoku oki earthquakes recent development in analysis tools and deployments of the geodetic and seismic instruments give an opportunity to investigate aftershock sequences at local scales which is important for the seismic hazard assessment in particular we study the dependencies between aftershock sequences properties and deformational geological data on a scale of the rupture extension of megathrust earthquakes for this goal we use on one hand published models of inter co and postseismic slip and geological information and on the other hand aftershock parameters obtained by fitting a modified epidemic type aftershock sequence etas model the altered etas model takes into account the mainshock rupture extension and it distinguishes between primary and the secondary aftershock triggering involved in the total seismicity rate we estimate the spearman correlation coefficients between the spatially distributed aftershock parameters estimated by the modified etas model and crustal physical properties for the maule 2010 mw8 8 and the tohoku oki 2011 mw9 0 aftershock sequences we find that 1 modified etas model outperforms the classical one when the mainshock rupture extension cannot be neglected and represented as a point source 2 anomalous aftershock parameters occur in the areas of the reactivated fault systems 3 aftershocks regardless of their generation tend to occur in the areas of high coseismic slip gradient afterslip and interseismic coupling 4 aftershock seismic moment releases preferentially in regions of large coseismic slip coseismic slip gradient and interseismically locked areas 5 b value tends to be smaller in interseismically locked regions

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

timescales of spherulite crystallization in obsidian inferred from water concentration profiles we determined the kinetics of spherulite growth in obsidians from krafla volcano iceland we measured water concentration profiles around spherulites in obsidian by synchrotron fourier transform infrared spectroscopy the distribution of oh groups surrounding spherulites decreases exponentially away from the spherulite glass border reflecting expulsion of water during crystallization of an anhydrous paragenesis plagioclase sio2 clinopyroxene magnetite this pattern is controlled by a balance between the growth rate of the spherulites and the diffusivity of hydrous solute in the rhyolitic melt we modeled advective and diffusive transport of the water away from the growing spherulites by numerically solving the diffusion equation with a moving boundary numerical models fit the natural data best when a small amount of post growth diffusion is incorporated in the model comparisons between models and data constrain the average spherulite growth rates for different temperatures and highlight size dependent growth among a small population of spherulites

earthquake scaling characteristics and the scale in dependence of seismic energy to moment ratio insights from kik net data in japan 1 we investigate earthquake source characteristics and scaling properties using the results of a spectral inversion of more than 29 000 accelerometric borehole recordings from 1 826 earthquakes mjma 2 7 8 throughout japan we find that the calculated source spectra can be well characterized by the omega square model and show on average self similar scaling over the entire magnitude range with median stress drops of 1 1 and 9 2 mpa for crustal and subcrustal events respectively the seismic energy to moment ratio as theoretically expected if the omega square model is valid shows a strong dependency on stress drop only which in conjunction with data selection practice in some studies to cope with limited recording bandwidth can explain the often observed apparent scale dependence our observations suggest that there is no significant deviation from similarity of the energy radiation in the investigated magnitude range and that the observed scatter is mainly related to the scatter in stress drop

insights on earthquake triggering processes from early aftershocks of repeating microearthquakes characterizing the evolution of seismicity rate of early aftershocks can yield important information about earthquake nucleation and triggering however this task is challenging because early aftershock seismic signals are obscured by those of the mainshock previous studies of early aftershocks employed high pass filtering and template matching but had limited performance and completeness at very short times here we take advantage of repeating events previously identified on the san andreas fault at parkfield and apply empirical green s function deconvolution techniques both landweber and sparse deconvolution methods reveal the occurrence of aftershocks as early as few tenths of a second after the mainshock these events occur close to their mainshock within one to two rupture lengths away the aftershock rate derived from this enhanced catalog is consistent with omori s law with no flattening of the aftershock rate down to the shortest resolvable timescale 0 3 s the early aftershock rate decay determined here matches seamlessly the decay at later times derived from the original earthquake catalog yielding a continuous aftershock decay over timescales spanning nearly 8 orders of magnitude aftershocks of repeating microearthquakes may hence be governed by the same mechanisms from the earliest time resolved here up to the end of the aftershock sequence our results suggest that these early aftershocks are triggered by relatively large stress perturbations possibly induced by aseismic afterslip with very short characteristic time consistent with previous observations on bimaterial faults the relative location of early aftershocks shows asymmetry along strike persistent over long periods