analysis of the completeness magnitude and seismic network coverage of japan abstract a reliable estimate of completeness magnitude m c above which all earthquakes are considered to be detected by a seismic network is vital for seismicity related studies we show a comprehensive analysis of m c in japan we use the catalog maintained by the japan meteorological agency jma and also available information on seismic stations that report to jma for computing m c we adopt a commonly used method based on the gutenberg richter frequency magnitude law presently m c 1 0 might be typical in the mainland but to have a complete catalog one needs to use earthquakes with magnitudes of 1 9 or larger comparison with the southern california seismic network scsn suggests that the recent event detectability in the mainland generally shows similar completeness levels to that in the authoritative region of scsn we argue that the current m c of japan is due to the success of network modernization over time particularly we show that the spatiotemporal change of m c closely matches the addition of the hi net borehole stations to enhancing seismic station density it started in october 1997 in southwestern japan continuing to northeastern japan until 2002 as suggested from this matching we confirm that m c inversely correlates with station density further we find that irrespective of the network change after 1997 this correlation is unchanged in time demonstrating that the influence on m c from factors beyond station density does not vary in time contrary to alaska and california wiemer and wyss 2000 our results do not attribute such factors simply to anthropogenic noise because this is due to the borehole stations that reduce ambient noise we conclude that in japan the anthropogenic noise has an insignificant effect on m c

mechanism of deep low frequency earthquakes further evidence that deep non volcanic tremor is generated by shear slip on the plate interface 1 we study the mechanism of low frequency earthquakes lfes in the nankai trough in western shikoku japan precise locations have previously suggested that they represent shear slip on the plate boundary in this paper we examine the mechanism of these events due to the low signal to noise ratio we analyze stacked lfe waveforms and compare them with the waveforms of nearby earthquakes of known mechanism within the subducting philippine sea plate analysis of both the focal mechanism using p wave first motions and the moment tensor using s waveforms indicates that lfes represent shear slip on a low angle thrust fault dipping to the northwest namely the plate interface together with reports that deep tremor consists of a swarm of lfes our results suggest that deep tremor is generated directly by shear slip on the plate interface and as such represents a seismic signature of the accompanying slow slip events

the lami pyroclastic succession lipari aeolian islands a clue for unravelling the eruptive dynamics of the monte pilato rhyolitic pumice cone abstract the lami succession piled up during the explosive activity of the monte pilato on lipari island central aeolian arc italy it comprises a repetitive alternation of fall and pyroclastic density current beds which define 13 units separated by fine ash beds despite the homogeneous rhyolitic composition the juveniles fragments show strong textural heterogeneities from highly vesicular pumice to dense black obsidians the pumice types are termed i tube which shows elongated tubular vesicles ii frothy highly vesicular with large sub rounded vesicles and iii agglomerated and welded two types of obsidian pyroclasts are recognized i aphyric black obsidian and ii grey obsidian showing spherulitic texture all these pyroclastic types occur throughout the stratigraphic succession and mixed in the same bed they account for changing physical conditions along the conduit which is hypothesised to be filled by a melt plug during the eruption of 12 out of 13 units the strong textural heterogeneities of the juvenile fragments testify for the existence of differential shear rates which can be explained though two shear mechanism i simple shear producing horizontal zonation of texture in the conduit with black obsidians along the conduit walls passing to tube and frothy pumice to the centre and ii pure shear producing a vertical zonation in the conduit with black obsidians at the top overlying frothy pumice agglomerated and welded pumice of unit 13 is thought to represent the portion of magma heated by a batch of hotter melt that entered the magma chamber and triggered the eruption the deposits of unit 13 represent a unique case of spatter accretion due to accumulation of hot low viscous rhyolitic pumice fragments emplaced from pyroclastic fountaining

incorporating seismic observations into 2d conduit flow modeling conduit flow modeling aims to understand the conditions of magma at depth and to provide insight into the physical processes that occur inside the volcano low frequency events characteristic to many volcanoes are thought to contain information on the state of magma at depth therefore by incorporating information from low frequency seismic analysis into conduit flow modeling a greater understanding of magma ascent and its interdependence on magma conditions and physical processes is possible the 2d conduit flow model developed in this study demonstrates the importance of lateral pressure and parameter variations on overall magma flow dynamics and the substantial effect bubbles have on magma shear viscosity and on magma ascent the 2d nature of the conduit flow model developed here allows in depth investigation into processes which occur at or close to the wall such as magma cooling and brittle failure of melt these processes are shown to have a significant effect on magma properties and therefore on flow dynamics by incorporating low frequency seismic information an advanced conduit flow model is developed including the consequences of brittle failure of melt namely friction controlled slip and gas loss this model focuses on the properties and behaviour of magma at depth within the volcano and their interaction with the formation of seismic events by brittle failure of melt

size distribution of parkfield s microearthquakes reflects changes in surface creep rate s u m m a r y the nucleation area of the series of m6 events in parkfield has been shown to be characterized by low b values throughout the seismic cycle since low b values represent high differential stresses the asperity structure seems to be always stably stressed and even unaffected by the latest main shock in 2004 however because fault loading rates and applied shear stress vary with time some degree of temporal variability of the b value within stable blocks is to be expected we discuss in this study adequate techniques and uncertainty treatment for a detailed analysis of the temporal evolution of b values we show that the derived signal for the parkfield asperity correlates with changes in surface creep suggesting a sensitive time resolution of the b value stress meter and confirming near critical loading conditions within the parkfield asperity

formation process of the kuroshio large meander in 2004 1 formation process of the 2004 kuroshio large meander has been examined using a data assimilation and prediction system the small meander southeast of kyushu that occurred in december 2003 remains stationary until the next spring the vorticity analysis indicates that this small meander is maintained by a balance between the advection and the bottom pressure torque on the continental slope this balance is achieved as a result of reducing the advection by a westward propagating negative temperature anomaly originating in the wind stress field the small meander starts moving eastward around may 2004 when an anticyclonic eddy east of the tokara strait is intensified by coalescing of two anticyclonic eddies at that time a deep anticyclonic eddy is generated below the kuroshio by a cross frontal flow the deep anticyclonic eddy grows up during its eastward propagation then a southward flow in the eastern part of the eddy carries the kuroshio path offshore bringing about the large meander the eddy energetic analysis indicates that baroclinic instability is essentially responsible for this large meander formation the sensitivity analysis reveals that the small meander and the intensified anticyclonic eddy significantly affect the phase speed and the amplitude of the meander respectively it is also revealed that a slow phase speed and a large amplitude of the meander are regarded as conditions for the stationary large meander which is also applicable to the past large meanders in the 2004 large meander these conditions coexist by the stationary small meander staying until the intensified anticyclonic eddy triggers baroclinic instability

frequency dependent rheology of vesicular rhyolite frequency dependent rheology of magmas may result from the presence of inclusions bubbles crystals in the melt and or from viscoelastic behavior of the melt itself with the addition of deformable inclusions to a melt possessing viscoelastic properties one might expect changes in the relaxation spectrum of the shear stresses of the material e g broadening of the relaxation spectrum resulting from the viscously deformable geometry of the second phase we have begun to investigate the effect of bubbles on the frequency dependent rheology of rhyolite melt the present study deals with the rheology of bubble free and vesicular rhyolite melts containing spherical voids of 10 and 30 vol we used a sinusoidal torsion deformation device vesicular rhyolite melts were generated by the melting at 1 bar of an armenian obsidian dry fountain erevan armenia and little glass mountain obsidian california the real and imaginary parts of shear viscosity and shear modulus have been determined in a frequency range of 0 005 10 hz and temperature range of 600 900 c the relaxed shear viscosities of samples obtained at low frequencies and high temperatures compare well with data previously obtained by parallel plate viscometry the relaxed shear viscosity of vesicular rhyolites decreases progressively with increasing bubble content the relaxation spectrum for rhyolite melt without bubbles has an asymmetric form and fits an extended exponent relaxation the presence of deformable bubbles results in an imaginary component of the shear modulus that becomes more symmetrical and extends into the low frequency high temperature range the internal friction q 1 is unaffected in the high frequency low temperature range by the presence of bubbles and depends on the bubble content in the high temperature low frequency range the present work in combination with the previous study of stein and spera 1992 illustrates that magma viscosity can either increase or decrease with bubble content depending upon the rate of style of strain during magmatic flow

flow and fracturing of viscoelastic media under diffusion driven bubble growth an analogue experiment for eruptive volcanic conduits abstract to visualize the behavior of erupting magma in volcanic conduits we performed shock tube experiments on the ductile brittle response of a viscoelastic medium to diffusion driven bubble expansion a sample of shear thinning magma analogue is saturated by gas ar under high pressure on rapid decompression ar supersaturation causes bubbles to nucleate grow and coalesce in the sample forcing it to expand flow and fracture experimental variables include saturation pressure and duration and shape and lubrication of the flow path bubble growth in the experiments controls both flow and fracturing and is consistent with physical models of magma vesiculation two types of fractures are observed i sharp fractures along the uppermost rim of the sample and ii fractures pervasively diffused throughout the sample rim fractures open when shear stress accumulates and strain rate is highest at the margin of the flow a process already inferred from observations and models to occur in magma pervasive fractures originate when wall friction retards expansion of the sample causing pressure to build up in the bubbles when bubble pressure overcomes wall friction and the tensile strength of the porous sample fractures open with a range of morphologies both types of fracture open normally to flow direction and both may heal as the flow proceeds these experiments also illustrate how the development of pervasive fractures allows exsolving gas to escape from the sample before the generation of a permeable network via other processes e g bubble coalescence this is an observation that potentially impact the degassing of magma and the transition between explosive and effusive eruptions

mapping the b value anomaly at 100 km depth in the alaska and new zealand subduction zones a positive anomaly in the frequency magnitude distribution b value is detected at approximately 90 100 km depth in two subduction zones the b value in this anomalous zone is 40 higher than in adjacent volumes we use regional catalogs with a magnitude of completeness of 2 6 central alaska and cook inlet 2 0 shumagin islands and 3 5 new zealand to resolve the b value as a function of space in more detail we project all earthquakes onto planes perpendicular to the strike of the slab these cross section views of the b value distribution locate the high b value anomalies at a depth of 90 100 km on the upper surface of the wadati benioff zone at these depths slab dehydration may increase pore pressure thus lowering the effective stress and increasing the b value increased pore pressure would also lower the liquidus in the overlying asthenosphere giving rise to the volcanism that occurs directly above this zone

a rheological investigation of vesicular rhyolite abstract the rheology of vesiculating rhyolitic systems exerts a strong control on the transport of silicic magmas in the subvolcanic to volcanic environments we present here an investigation of vesiculating and vesiculated rhyolites using dilatometric methods this study examines the effect of vesicle content on the viscosity of a natural supercooled rhyolitic liquid with 0 70 vesicles the experimental samples of rhyolitic glass are derived from fusion of a natural obsidian from little glass butte oregon crystal free rhyolite glasses of varying porosity were prepared by fusing obsidian powder in a pt crucible differing porosities were obtained by varying the temperature 1300 1650 c and duration 0 5 6 h of the fusions cylindrical samples of the resulting vesiculated rhyolites were cored from the crucible using diamond tools and their ends were ground flat and parallel for dilatometry the porosity of each sample was determined from archimedean buoyancy density determinations and comparison with bubble free rhyolite 2 331 g cm 3 porosity 1 p p o the density of foamed samples was determined using their mass volume and regular geometry viscosities were determined in the parallel plate mode at stresses of 5 10 3 to 10 5 pa the viscosimeter was calibrated using nbs 711 glass the bubble contents were microscopically investigated using a video reflected light system and image analysis software distribution functions of the size orientation aspect ratio and surface porosity were obtained the viscosity of rhyolite decreases with increasing bubble content a general relationship of the form 0 1 c describes the effect of porosity in volume fraction on the viscosity where c is a dimensionless constant 22 4 2 9 and log 10 0 10 94 0 04 pa s at 850 c

on the stress dependence of the earthquake b value laboratory experiments have shown that the b value in the size distribution of acoustic emission events decreases linearly with differential stress there have been a number of observations that indicate that this relation may also hold for earthquakes here using a simple frictional strength model for stresses in the continental lithosphere combined with earthquake b values measured as a function of depth in a wide variety of tectonic regions we verify and calibrate that relation finding b 1 23 0 06 0 0012 0 0003 1 3 where the stress difference 1 3 is in megapascal for subduction zones we find that b value correlates linearly with the slab pull force and with the net reduction of plate interface normal force both of which also indicate a negative linear relation between b value and differential stress

earth science microseismicity data forecast rupture area on 28 september 2004 there was an earthquake of magnitude 6 0 at parkfield california here we show that the size distribution of the micro earthquakes recorded in the decades before the main shock occurred allowed an accurate forecast of its eventual rupture area applying this approach to other well monitored faults should improve earthquake hazard assessment in future

shear viscosity of rhyolite vapor emulsions at magmatic temperatures by concentric cylinder rheometry abstract the viscosity of natural rhyolitic melt from lipari aeolian islands and melt bubble emulsions 30 50 vol porosity generated from lipari rhyolite have been measured in a concentric cylinder rheometer at temperatures and shear rates in the range 925 1150 c and 10 3 10 1 2 s 1 respectively in order to better understand the dependence of emulsion shear viscosity on temperature and shear rate in natural systems bubble free melt exhibits newtonian arrhenian behavior in the temperature range 950 1150 c with an activation energy of 395 30 kj mol the shear viscosity is given by log m 8 320 20624 t suspensions were prepared from natural rhyolite glass to which small amounts of na2so4 were added as a foaming agent reasonably homogeneous magmatic mixtures with an approximate log normal distribution of bubbles were generated by this technique suspension viscosity varied from 106 1 to 108 37 pa s and systematically correlates with temperature and porosity in the shear stress range 104 26 105 46 pa of the experiments the viscosity of melt bubble emulsions is described in terms of the relative viscosity r e m where e is the emulsion viscosity and m is the viscosity of melt of the same composition and temperature the dependence of relative viscosity on porosity for magmatic emulsions depends on the magnitude of the capillary number ca g rb 1 m 1 the ratio of viscous forces acting to deform bubbles to interfacial forces resisting bubble deformation for inviscid bubbles in magmatic flows three regimes may be identified for ca 10 an asymptotic regime is reached in which relative viscosity decreases with increasing porosity and is independent of ca our experiments were carried out for 30

rheological tests of polyurethane foam undergoing vesiculation deformation solidification as a magma analogue abstract in this study we examined the rheology of polyurethane foam puf as an analogue system of magma undergoing vesiculation deformation and solidification solid puf was formed by mixing two polymeric liquids followed by chemical reactions of foaming and curing the transient rheology during the processes was investigated using an instrument based on a stress controlled rheometer first the oscillatory rheology was measured applying small amplitude oscillations with cyclic frequency sweeps in the foaming stage the frequency dependence of the rheology depends on the dynamic capillary number in a similar way to the existing bubbly flow model in the curing stage the viscoelasticity of the liquid becomes dominant and the rheology of puf shows maxwell type viscoelasticity with relaxation time exponentially increasing with time when the reaction is rapid because of high temperature the viscoelasticity during curing is not scaled by the single relaxation time instead puf passes through a condition called gelation which is characterized by a power law relaxation spectrum next we examined the relationship between the dynamic viscosity measured by the small strain oscillation and the shear viscosity measured with a fixed shear rate at a large strain we found that puf obeys the cox merz rule which states that the two viscosities are equivalent when the shear rate and the angular frequency are equal specifically the shear viscosity tends to be smaller than the dynamic viscosity by a few tens of percent the difference was shown to be in the range expected for bubbly fluid in the foaming stage while it went beyond what can be explained by the bubbly fluid model when the viscoelasticity of the liquid becomes significant x ray computed tomography analyses revealed that samples in these cases contained large bubbles indicating bubble coalescence we infer that the difference is caused by bubble coalescence as well as non newtonian rheology during solidification including gelation all these processes might occur in actual magma during eruptions we show that the ranges of the capillary number comparing the deformation time and the bubble shape relaxation time and deborah number comparing the deformation time and the viscoelastic relaxation time in our experiments are comparable with their ranges expected for magma ascending in an eruptive conduit the characteristic time of viscosity increase of puf was also shown to be realizable for magma in natural volcanoes we conclude that puf is useful for simulating magma processes in eruptive conduits

the effects of co2 brine rheology on leakage processes in geologic carbon sequestration 1 leakage from geologic carbon sequestration gcs sites is inherently challenging to study because co2 driven by buoyant forces travels over long distances undergoing phase changes and encountering numerous connate brine and formation chemistries as it rises to the surface this work explores the effect that co2has on the rheological properties of brine solutions over a range of gcs relevant temperature pressure ionic strength and shear conditions under the fluid liquid equilibrium conditions that prevail in the deep subsurface viscosity of co2 brine mixtures was found to be a function of temperature and pressure alone once leakage conditions ensue discrete co2bubbles form in brine resulting in the vapor liquid equilibrium vle and these mixtures exhibit complex linear viscoelastic time dependent and thixotropic behavior the presence of co2 g bubbles on the flow of the bulk fluid could have important impacts on impeding via shear drag force leakage depending on the geometrical geochemical and geophysical characteristics of a storage site under vle conditions the effective viscosity of co2 brine mixtures was found to be up to five times higher than brine alone but the microstructure was easily destroyed and not readily regained under high shear conditions at higher temperatures and higher ionic strength the effect is less pronounced these results were considered in the context of flow through porous media and the effect on buoyancy driven flow is significant understanding this effect is important for developing an accurate constitutive relationship for leaking co2 which will lead to better capacity to select and monitor gcs sites

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

non newtonian flow of bubbly magma in volcanic conduits the dynamics of magma ascent along volcanic conduits toward the earth s surface affects eruptive styles and contributes to volcanic hazard the rheology of ascending magmatic mixtures is known to play a major role on mass flow rate as well as on pressure and exit velocity at the vent even determining effusive versus explosive eruptive behavior in this work we explore the effects of bubble induced non newtonian rheology on the dynamics of magma flow in volcanic conduits we develop a quasi 2 d model of magma ascent that incorporates a rheological constitutive equation describing the strain dependent effect of gas bubbles on the viscosity of the multiphase magma non newtonian magma flow is investigated through a parametric study where the viscosity of the melt and the water content are varied over natural ranges our results show that non newtonian rheology leads to greater exit velocity mass flow and density the pressure distribution along the conduit remains very similar to the newtonian case deviating only at the conduit exit plug like velocity profiles develop approaching the conduit exit when mixture velocity is high and are favored by smaller liquid viscosity since the mass flow rate the density and the velocity of the mixture exiting from the conduit are fundamental for quantifying and assessing the transport and emplacement dynamics neglecting that the non newtonian effect of bubble bearing magmas may result in misinterpretation of the deposit and consequently eruptive behavior

temporal evolution of flow conditions in sustained magmatic explosive eruptions abstract the temporal evolution of fundamental flow conditions in the magma chamber plus conduit system such as pressure velocity mass flow rate erupted mass etc during sustained magmatic explosive eruptions was investigated to this aim simplified one dimensional and isothermal models of magma chamber emptying and conduit flow were developed and coupled together the chamber model assumed an homogeneous composition of magma and a vertical profile of water content the chamber could have a cylindrical elliptical or spherical rigid geometry inside the chamber magma was assumed to be in hydrostatic equilibrium both before and during the eruption since the time scale of pressure variations at the conduit inlet of the order of hours is much longer than the travel time of magma in the conduit of the order of a few minutes the flow in the conduit was assumed as at steady state the one dimensional mass and momentum balance equations were solved along a circular conduit with constant diameter assuming choked flow conditions at the exit bubble nucleation was considered when the homogeneous flow pressure dropped below the nucleation pressure given the total water content and the solubility law above the nucleation level bubbles and liquid magma were considered in mechanical equilibrium the same equilibrium assumption was made above the fragmentation level between gas and pyroclasts due to the hydrostatic hypothesis the integration of the density distribution in the chamber allowed to obtain the total mass in the chamber as a function of pressure at the chamber top and through the conduit model as a function of time simulation results pertaining to rhyolitic and basaltic magmas defined at the volcanic eruption mechanism modeling workshops durham nh 2002 nice france 2003 are presented important flow variables such as pressure density velocity shear stress in the chamber and conduit are discussed as a function of time and magma chamber and conduit properties results indicate that vent variables react in different ways to the pressure variation of the chamber pressure density and mass flow rate show relative variations of the same order of magnitude as the conduit inlet pressure whereas velocity is more constant in time sill like chambers produce also significantly longer and more voluminous eruptions than dike like chambers water content stratification in the chamber and the increase of chamber depth significantly reduce the eruption duration and volume maximum erupted mass fractions of about 0 2 are computed for small water saturated and shallow chambers

the rheology of two phase magmas a review and analysis abstract we consider the current state of our understanding of the rheology of two phase magmas that is suspensions of either bubbles or crystals in a viscous silicate melt the discussion is restricted to strain rates at which the suspending melt can be considered newtonian we start by considering the range of textures found in magmas and the bubble deformation and particle motions caused by shearing we then review proposed models for suspensions focussing on those functions of the form r f or f that have been most widely used to describe magmatic systems r is the relative apparent viscosity of the suspension is the volume fraction of the suspended phase is the driving stress and is the strain rate both theoretical and empirical methods are presented and then compared against the available analogue i e non magmatic and magmatic data the paper contains new data and significant re analysis of previously published data we present a new semi empirical constitutive model for bubble bearing magmas that is valid for steady and unsteady flow and large strains and strain rates this equation utilises a new parameter the capillarity cx that encapsulates the combined effect of shearing and unsteadiness on bubble suspensions we also present a new scheme for dealing with polydispersivity of bubble suspensions new data on the rheology of particle suspensions undergoing forced oscillations are presented these data show that the cox merz rule only holds for dilute particle suspensions 0 25 a re analysis of all available experimental data that relate rheology to particle aspect ratio provides distinct curves of maximum packing as a function of aspect ratio for smooth and rough particles with magmatic data lying on the curve appropriate for rough particles we analyse several rheological datasets of crystal bearing basaltic magmas and find that they are in good agreement with the constitutive equations derived from analogue data by contrast the same equations do not agree well with data for high viscosity haplogranitic melts this may be an effect of fracturing or viscous dissipation within these samples the paper concludes with a practical rheological recipes section giving a step by step method for calculating a constitutive equation for a two phase magmatic suspension and assessing its likely accuracy

interface locking along the subduction megathrust from b value mapping near nicoya peninsula costa rica 1 to understand controlling factors for seismogenesis and strain accumulation in subduction megathrusts we examine seismicity patterns across nicoya costa rica to determine the overall and spatial variability in the earthquake frequency magnitude distribution along the interface the mean reduction in earthquake activity with magnitude b value is higher 1 06 than global subduction zone averages 0 6 0 8 suggesting the interface here is weakly coupled strong spatial variations in b are anticorrelated 0 53 with geodetic estimates of interface locking of e norabuena et al 2004 high b prevails in two regions including the subducted fisher seamount chain a broad zone of reduced b is observed at and offshore the central nicoya coast extending towards an imaged locked patch these results suggest b value studies may be useful in identifying regions of increased interface locking in subduction zones which may indicate regions capable of large slip in future large earthquakes

a study on the variations of recent seismicity in and around the central anatolian region of turkey abstract variations of the recent seismicity in and around the central anatolian region of turkey were evaluated based on the seismic b value standard normal deviate z value genas modelling annual probabilities and return periods of the earthquakes the catalog includes 16 702 earthquakes between 1974 and 2019 with magnitudes from 1 0 to 6 3 time distribution of b value shows that there is a tendency to decrease after the year of 2002 and b value decreased from 1 58 0 03 to 1 25 0 05 at the beginning of 2019 annual probabilities for magnitude ranges of 3 0 4 0 have the values between 3 and 30 return periods for magnitude levels of 5 0 5 5 have the values from 5 to 20 years and a value of 80 years for magnitude level of 6 0 the genas results show the significant temporal variations in the number of earthquakes smaller and larger than specific magnitude intervals by supplying the beginning periods of increases and decreases in the earthquake activity rate remarkable reductions in region time distribution of b value at the beginning of 2019 were detected in the regions covering nigde fault and its vicinity along the south west northwest and southwest directions among the mut fault zone karsanti karaisali fault zone and karatas osmaniye fault zone in and around surgu fault and along its northwest direction between surgu fault and east anatolian fault zone significant seismic quiescence areas in z value distribution include the northwest ends of the tuzgolu fault zone and study area including akpinar fault the northeast of salanda fault between salanda fault and the central anatolian fault zone the northeast parts of the central anatolian fault zone the west of malatya fault between surgu fault and the east anatolian fault zone the southeast end of the tuzgolu fault zone karsanti karaisali fault zone and its vicinity the southwest of tuzgolu thus these anomaly areas observed in the central anatolian region and its vicinity at the beginning of 2019 may be one of the most likely zones for the next strong large earthquake occurrences

further evidence of hemispheric differences in the mlt mean wind climatology simultaneous mf radar observations at poker flat 65 n 147 w and davis 69 s 78 e 1 results of a comparative study of the wind fields in the mesosphere and lower thermosphere over poker flat 65 n 147 w and davis 69 s 78 e are presented the study utilized the mf radar wind data collected simultaneously during the period 1999 2000 mean winds during this period are examined to study the hemispheric features emphasis has been given to the climatological variations over these two high latitude stations the results suggest large hemispheric differences in the mean circulation further the observed mean wind characteristics are compared with results obtained from other high latitude stations

the constitutive equation and flow dynamics of bubbly magmas 1 a generalized constitutive equation for bubbly liquids is presented which successfully reproduces the expected viscosity response for both steady flows with varying capillary number ca a measure of the bubble deformation and unsteady flows with varying dynamic capillary number cd a measure of the steadiness of the flow previously given in separate studies the constitutive equation is given in terms of observable material and flow parameters and is

quasi periodic slow slip events in the afterslip area of the 1996 hyuga nada earthquakes japan 1 the time evolution of afterslip on a plate boundary experiencing interplate earthquakes is expected to show logarithmic decay the global positioning system network in japan has been monitoring transient deformation since the occurrence of two large interplate earthquakes with moment magnitudes of 6 8 and 6 7 in the hyuga nada area southwest japan in 1996 the spatial and temporal evolution of aseismic interplate slip based on crustal deformation data indicates that afterslip followed the two earthquakes and gradually declined to background rates by around 2004 with total moment magnitude of 7 3 however quasi periodic slow slip events suddenly began within the afterslip area in 2005 with approximately one year duration and two year recurrence interval the moment magnitudes of the three slow slip events since january 2005 range from 6 7 to 6 8 this differs greatly from the expected behavior of logarithmic decay over time both velocity strengthening and velocity weakening rate and state modes have been implicated as the cause of afterslip whose location is complementary to the main shock area of velocity weakening while a slow slip event occurs in the velocity weakening area with different frictional properties from those of an afterslip area in light of the seemingly different frictional properties the coexistence of afterslip and slow slip events in the same area would provide additional information about precisely how the plate interface is behaving the monitoring of these slow slip events should give the clues to understanding the coexistence of long term afterslip and slow slip events and the increasing risk of earthquakes in neighboring areas

correlating seismicity parameters and subsidence in the tokai region central japan 1 we demonstrate that transients in subsidence rate in the tokai area of central japan correlate with changes in the rate and size distribution of earthquakes three largely independent seismic catalogs cover this region national research institute for earth science and disaster prevention nied japanese meteorological agency jma and japan university network catalog junec comparing seismicity patterns between these three data sets offers a unique opportunity to verify seismicity anomalies based on independent sources a study of data quality magnitude reporting consistency and consistency across the three data sources reveals that the nied data for the period 1981 2002 are best suited for seismicity analysis we spatially and temporally map seismicity rates finding that a significant decrease in the earthquake rate of m 2 0 events coincides with an accelerated subsidence period however this anomaly disappears when including smaller magnitudes in the analysis this relative quiescence of larger events can readily be explained when interpreting the transient in seismicity in the framework of a change in the earthquake size distribution or b value the background b value of about 0 8 increased in the period 1987 5 1989 5 to a value of b 1 2 a highly significant change that can be confirmed in all three data sets the correlation between subsidence and b value change is significant stress tensor inversions of focal mechanism data for the anomalous period show an increase in thrusting type earthquakes while a unique interpretation of the relationship between subsidence and b value is not possible we propose that an increase in the locking stress a slow stick event is consistent with all observations

strain induced outgassing of three phase magmas during simple shear a major factor determining the explosivity of silicic eruptions is the removal of volatiles from magma through permeability controlled outgassing we studied the microstructural development of permeability during deformation of highly viscous magma by performing simple shear experiments on bubble 0 12 0 36 volume fraction and crystal bearing 0 0 42 volume fraction silicate melts experiments were performed under torsion at high temperature and pressure 723 873 k and 150 200 mpa in a paterson deformation apparatus at bulk shear strains between 0 and 10 the experimental setup allows for gas escape if bubble connectivity is reached on the sample periphery three dimensional imaging and analysis of deformed bubbles was performed using x ray tomography the development of localized deformation in all samples enhanced by crystal content leads to brittle fracture at bulk strains 2 and sample wide fracturing in samples deformed to strains 5 a decrease in both bubble fraction and dissolved volatile content with increasing strain along with strain hardening rheological behavior suggests significant shear induced outgassing through the fracture networks applicable to shallow conduit degassing in magmas containing crystal fractions of 0 0 42 this study contributes to our understanding of highly viscous magma outgassing and processes governing the effusive explosive transition

viscous dissipation in explosive volcanic flows 1 most models for magma flow in volcanic conduits during explosive eruptions assume isothermal ascent conditions due to the high heat capacity of the magma here we present a non isothermal axisymmetrical flow model that accounts for the temperature dependent viscosity of magma and viscous dissipation of heat significant changes in velocity and temperature profiles result in strong reduction of the conduit friction leading to an order of magnitude increase in discharge rate in comparison with the isothermal case this allows high intensity eruptions to occur from significantly narrower volcanic conduits and so helps to resolve inconsistencies between conduit dimensions inferred from models and observations for a given conduit diameter fragmentation can occur at much shallow depths than for an isothermal model

spatial and temporal distributions of b values related to long term slow slip and low frequency earthquakes in the bungo channel and hyuga nada regions japan abstract long term slow slip events sses and low frequency earthquakes lfes repeatedly occur in the area encompassing the bungo channel and hyuga nada region in japan sses are slow earthquake events with a duration of months to years characterized by a type of slip that is considered transitional between the fast rupture of regular earthquakes and stable sliding along a plate interface and have characteristics sensitive to stress states near the plate interface in addition since lfes are also thought to occur at the plate interface it would be useful to infer the stress state in this region this study focuses on the stress dependent characteristics of the b values of regular earthquakes sses and lfes as well as the spatio temporal relationships between b values and these events in this area using the japan unified high resolution relocated catalog for earthquakes juice the b value which represents the relative proportion of large to small earthquakes is inversely related to differential stress or effective stress the b values are moderate to low b 0 6 1 1 in regions with a high incidence of long term sses this spatial b value anomaly is attributed to the partial release of accumulated stress in regions with a relatively high differential stress due to sse activity furthermore the b value distributions estimated in this study provide constraints on the mechanisms that generate lfes on the other hand the b values increase and decrease before and during periods of enhanced lfe activity in the bungo channel respectively the increase and following decrease in b values are thought to reflect episodes of low and high shear strength along the plate interface which were caused by the presence of abundant slab derived fluids under undrained conditions above the plate interface and decreased pore pressure related to fluid depletion via lfe generation respectively

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

non newtonian behavior of plagioclase bearing basaltic magma subliquidus viscosity measurement of the 1707 basalt of fuji volcano japan abstract laboratory measurements of viscosity were done for basalt erupted in 1707 ad from fuji volcano japan using a concentric cylinder rotational viscometer at temperatures of 1297 1157 c 1 atm pressure and fo 2 near the ni nio buffer on cooling elongated plagioclase crystals with a mean length width ratio of ca 8 5 appeared at 1237 c followed by olivine at 1157 c at progressively lower temperatures the total crystal volume fraction increased monotonously to ca 0 25 viscosity increased from 38 9 to 765 pa s at a shear strain rate of 1 s 1 this basalt magma behaves as a newtonian fluid at temperatures greater than 1217 c but shear thinning behavior occurs at temperatures less than 1197 c because of the suspended plagioclase crystals this behavior is well approximated as a power law fluid at the onset of shear thinning the crystal volume fraction was between 0 06 and 0 13 which is attributed to the pronounced lath shape of plagioclase crystals the relative viscosity increases monotonously with increase of crystal volume fraction at a constant shear strain rate and with decrease of shear strain rate at a constant crystal volume fraction a modified form of the krieger dougherty equation is introduced herein it enables us to describe the dependencies of relative viscosity on both the crystal volume fraction and shear strain rate and consequently the onset of shear thinning behavior

earthquake statistics at parkfield 1 stationarity of b values 1 in this paper paper 1 we quantitatively show that the heterogeneous pattern of b values of the gutenberg richter relation in the parkfield segment of the san andreas fault is to a high degree stationary for the past 35 years this prepares the grounds for paper 2 where we test the hypothesis that our model of spatially varying b values forecasts future seismicity more accurately than the approach in which one assumes a constant b value equal to the average regional value the method we develop to measure stationarity in the presence of spatial heterogeneity consists of the following steps 1 determine the optimal dimensions of the sampling volume by mapping b values with a wide range of radii and selecting the largest radius that gives the most detailed resolution of the b value heterogeneity along the selected fault segment the high data density permits the definition of the dominant dimensions of the seismotectonic fabric which is about 8 10 km 2 map the difference in b value between two periods selecting numerous possible catalog divisions 3 identify significant changes of b values by the utsu test utsu 1992 along the studied fault segment of 110 km length only one patch of radius 5 km showed a significant increase in b from below average to above as a function of time this change in b initiates around 1993 and thus correlates in space and time with a well documented episode of creep at depth using the derived spatial variable b value distributions we find that the highest probability for earthquakes with magnitude m 6 is in the middle mountain asperity where the 1966 parkfield earthquake nucleated and where all m 4 5 events in the data set occurred in contrast if only the regional average b value of 0 92 is used to predict future seismicity the creeping segment north of parkfield should produce major earthquakes most frequently a conclusion that contradicts the observations

a global search for triggered tremor following the 2011 mw 9 0 tohoku earthquake abstract the 2011 m w 9 0 tohoku japan earthquake triggered deep tectonic tremor and shallow microearthquakes in numerous places worldwide here we conduct a systematic survey of triggered tremor in regions where ambient or triggered tremor has been previously identified tremor was triggered in the following regions south central alaska the aleutian arc shikoku in southwest japan the north island of new zealand southern oregon the parkfield cholame section of the san andreas fault in central california the san jacinto fault in southern california taiwan and vancouver island we find no evidence of triggered tremor in the calaveras fault in northern california one of the most important factors in controlling the triggering potential is the amplitude of the surface waves data examined in this study suggest that the threshold amplitude for triggering tremor is 0 1 cm s which is equivalent to a dynamic stress threshold of 10 kilopascals the incidence angles of the teleseismic surface waves also affect the triggering potentials of love and rayleigh waves the results of this study confirm that both love and rayleigh waves contribute to triggering tremor in many regions in regions where both ambient and triggered tremor are known to occur tremor triggered by the tohoku event generally occurred at similar locations with previously identified ambient and or triggered tremor further supporting the notion that although the driving forces of triggered and ambient tremor differ they share similar mechanisms we find a positive relationship between the amplitudes of the triggering waves and those of the triggered tremor which is consistent with the prediction of the clock advance model online material table of measured parameters and other information related to triggering nontriggering information and figures of observed seismograms

extrusion cycles during dome building eruptions abstract we identify and quantify controls on the timescales and magnitudes of cyclic periodic volcanic eruptions using the numerical model domeflow de michieli vitturi et al 2010 which was developed by the authors for magma systems of intermediate composition domeflow treats the magma mixture as a liquid continuum with dispersed gas bubbles and crystals in thermodynamic equilibrium with the melt and assumes a modified poiseuille form of the viscous term for fully developed laminar flow in a conduit of cylindrical cross section during ascent magma pressure decreases and water vapor exsolves and partially degasses from the melt as the melt simultaneously crystallizes causing changes in mixture density and viscosity two mechanisms previously proposed to cause periodic eruption behavior have been implemented in the model and their corresponding timescales explored the first applies a stick slip model in which motion of a shallow solid plug is resisted by static dynamic friction as described in iverson et al 2006 for a constant magma supply rate at depth this mechanism yields cyclic extrusion with timescales of seconds to tens of seconds with values generally depending on assumed friction coefficients the second mechanism does not consider friction but treats the plug as a high viscosity newtonian fluid during viscous resistance pressure beneath the degassed plug can increase sufficiently to overcome dome overburden plug weight and viscous forces and ultimately drive the plug from the conduit in this second model cycle periods are on the order of hours and decrease with increasing magma supply rate until a threshold is reached at which point periodicity disappears and extrusion rate becomes steady vanishingly short periods magma volatile content for fixed chamber pressure has little effect on cycle timescales but increasing volatile content increases mass flow rate and cycle magnitude as defined by the difference between maximum and minimum extrusion rates increasing mass flow rate also increases the magnitude of predicted deformation cycles both models have been applied to dome building eruptions using conditions appropriate for the soufriere hills volcano montserrat results suggest that the modeled stick slip mechanism cannot explain the cycles of extrusion and explosion well documented at montserrat timescales of hours however a subset of the simulations for the viscous plug model are consistent with the montserrat data and therefore demonstrate the feasibility of this second formulation

rheological properties of magma from the 1538 eruption of monte nuovo phlegrean fields italy an experimental study abstract the rheology of natural partially crystallized samples from monte nuovo 1538 ad eruption have been investigated using a high temperature high pressure internally heated pressure vessel within the temperature interval of investigation the samples exhibited newtonian rheology at deformation strain rates up to 10 4 s 1 at higher strain rates a decrease of viscosity with increasing strain rate shear thinning eventually terminating in a sudden viscosity drop stress weakening was observed stress weakening occurred at higher applied strain rates and stresses with increasing temperature the microstructural analyses of the samples revealed that stress weakening resulted from strain localization which occurred in brittle and viscous regimes at the lowest and highest temperatures investigated respectively the different rheological behaviors of the investigated material is likely responsible for the changes in the dynamics of magma ascent within the volcanic conduit during the eruption of monte nuovo volcano we infer that the occurrence of syn eruptive decompression driven crystallization observed in previous studies induced strong variations in the rheological properties of magma which in turn was responsible for the changes of eruptive style observed during the monte nuovo eruption

timescales of bubble coalescence outgassing and foam collapse in decompressed rhyolitic melts abstract the timescale of degassing and outgassing in hydrous rhyolitic melts is investigated in a wide range of conditions by means of decompression experiments the evolution of vesicularity bubble diameter and number density is characterized as a function of time either of decompression or spent at final pressure in order to determine the effect of final pressure temperature syn versus post decompression degassing melt composition and microlites on the timescale of bubble growth coalescence and outgassing the result suggests that different bubble evolution and degassing outgassing timescale corresponding to explosive and effusive eruption regimes can be cast in bulk viscosity melt bubbles bulk versus decompression time rather than path space the bulk time relationship defines three domains of i bubble nucleation and growth restricted to short durations and high bulk 0 03 h for bulk 10 5 6 pa s ii equilibrium degassing with coalescence increasing from negligible permeability 10 13 m 2 to extensive permeability 10 11 12 m 2 and iii outgassing restricted to long durations and low bulk 10 h for bulk 10 6 pa s permeability 10 10 m 2 that eventually leads to foam collapse these findings are applied to the case studies of mt pelee and mt pinatubo to infer the transition from pumice to dense pyroclasts in volcanic eruptions and the possibility of evolving from an explosive plinian eruption to an effusive dome growth event by giving the vesicular magma enough time to outgas and collapse i e hundreds to tens of hours for bulk 10 5 to 10 4 pa s respectively we also show the drastic effect of microlites on re arranging preexistent bubbles and potentially triggering a late nucleation event

an analytical model for gas overpressure in slug driven explosions insights into strombolian volcanic eruptions strombolian eruptions common at basaltic volcanoes are mildly explosive events that are driven by a large bubble of magmatic gas a slug rising up the conduit and bursting at the surface gas overpressure within the bursting slug governs explosion dynamics and vigor and is the main factor controlling associated acoustic and seismic signals we present a theoretical investigation of slug overpressure based on magma static and geometric considerations and develop a set of equations that can be used to calculate the overpressure in a slug when it bursts slug length at burst and the depth at which the burst process begins we find that burst overpressure is controlled by two dimensionless parameters v which represents the amount of gas in the slug and a which represents the thickness of the film of magma that falls around the rising slug burst overpressure increases nonlinearly as v and a increase we consider two eruptive scenarios 1 the standard model in which magma remains confined to the vent during slug expansion and 2 the overflow model in which slug expansion is associated with lava effusion as occasionally observed in the field we find that slug overpressure is higher for the overflow model by a factor of 1 2 2 4 applying our model to typical strombolian eruptions at stromboli we find that the transition from passive degassing to explosive bursting occurs for slugs with volume 24 230 m 3 depending on magma viscosity and conduit diameter and that at burst a typical strombolian slug with a volume of 100 1000 m 3 has an internal gas pressure of 1 5 bars and a length of 13 120 m we compare model predictions with field data from stromboli for low energy puffers mildly explosive strombolian eruptions and the violently explosive 5 april 2003 paroxysm we find that model predictions are consistent with field observations across this broad spectrum of eruptive styles suggesting a common slug driven mechanism we propose that paroxysms are driven by unusually large slugs large v

rheology of bubble bearing magmas abstract the physical effects of air or argon bubbles on the rheology of a calcium aluminosilicate melt have been measured at temperatures ranging from 830 to 960 c at 1 bar pressure the melt composition is sio 2 64 al 2 o 3 23 and cao 13 wt while bubble volume fractions are 0 0 06 0 13 0 32 0 41 and 0 47 measured newtonian viscosities range from 10 10 to 10 14 dpa s melts with bubble fractions of 0 06 and 0 13 show with increasing temperature t an increasing relative viscosity for t t 850 c for all bubble fractions the viscosity decreases markedly with temperature the observed maximum decrease of the relative viscosity is 75 for a bubble fraction of 0 47 at 907 c at all bubble fractions the viscosity is independent of the applied stress which ranged from 11 to 677 bars no clear indications were observed of non newtonian rheological behavior under our experimental conditions the relative viscosity of the two phase liquid depends primarily on the bubble fraction physical and volcanological implications of these measurements are discussed

seafloor geodetic constraints on interplate coupling of the nankai trough megathrust zone seafloor geodetic data from the nankai trough off southwestern japan show that most offshore sites in this earthquake prone region have high slip deficit rates revealing previously unknown locations that could be important for the mitigation of future earthquake and tsunami associated disasters yusuke yokota et al have used seafloor geodetic observations to visualize the seismogenic zone along the nankai trough off southwestern japan which is thought to be one of the most dangerous megathrust zones in the world they suggest that most offshore sites in this region have positive slip deficit rates revealing previously unknown locations that could be potential sources of future earthquakes and tsunamis low slip deficit rates are observed in other regions consistent with distributions of shallow slow earthquakes and subducting seamounts interplate megathrust earthquakes have inflicted catastrophic damage on human society such an earthquake is predicted to occur in the near future along the nankai trough off southwestern japan an economically active and densely populated area in which megathrust earthquakes have already occurred1 2 3 4 5 megathrust earthquakes are the result of a plate subduction mechanism and occur at slip deficit regions also known as coupling regions 6 7 where friction prevents plates from slipping against each other and the accumulated energy is eventually released forcefully many studies have attempted to capture distributions of slip deficit rates sdrs in order to predict earthquakes8 9 10 however these studies could not obtain a complete view of the earthquake source region because they had no seafloor geodetic data the hydrographic and oceanographic department of the japan coast guard jhod has been developing a precise and sustainable seafloor geodetic observation network11 in this subduction zone to obtain information related to offshore sdrs here we present seafloor geodetic observation data and an offshore interplate sdr distribution model our data suggest that most offshore regions in this subduction zone have positive sdrs specifically our observations indicate previously unknown regions of high sdr that will be important for tsunami disaster mitigation and regions of low sdr that are consistent with distributions of shallow slow earthquakes and subducting seamounts this is the first direct evidence that coupling conditions might be related to these seismological and geological phenomena our findings provide information for inferring megathrust earthquake scenarios and interpreting research on the nankai trough subduction zone

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

effect of glass on the frictional behavior of basalts at seismic slip rates we performed 31 friction experiments on glassy basalts gb and glass free basalts gfb at slip rates up to 6 5 m s 1 and normal stress up to 40 mpa seismic conditions frictional weakening was associated to bulk frictional melting and lubrication the weakening distance dw was about 3 times shorter in gb than in gfb but the steady state friction was systematically higher in gb than in gfb the shorter dw in gb may be explained by the thermal softening occurring at the glass transition temperature tg 500 c which is lower than the bulk melting temperature tm 1250 c of gfb postexperiment microanalyses suggest that the larger crystal fraction measured in gb melts results in the higher steady state friction value compared to the gfb melts the effect of interstitial glass is to facilitate frictional instability and rupture propagation in gb with respect to gfb

japan unified high resolution relocated catalog for earthquakes juice crustal seismicity beneath the japanese islands abstract we have generated a high resolution catalog called the japan unified high resolution relocated catalog for earthquakes juice which can be used to evaluate the geometry and seismogenic depth of active faults in japan we relocated 1 1 million hypocenters from the nied hi net catalog for events which occurred between january 2001 and december 2012 to a depth of 40 km we apply a relative hypocenter determination method to the data in each grid square in which entire japan is divided into 1257 grid squares to parallelize the relocation procedure we used a double difference method incorporating cross correlating differential times as well as catalog differential times this allows us to resolve in detail a seismicity distribution for the entire japanese islands we estimated location uncertainty by a statistical resampling method using jackknife samples and show that the uncertainty can be within 0 37 km in the horizontal and 0 85 km in the vertical direction with a 90 confidence interval for areas with good station coverage our seismogenic depth estimate agrees with the lower limit of the hypocenter distribution for a recent earthquake on the kamishiro fault 2014 mj 6 7 which suggests that the new catalog should be useful for estimating the size of future earthquakes for inland active faults

transient effects of magma ascent dynamics along a geometrically variable dome feeding conduit abstract the transient dynamics of magma ascent during dome forming eruptions were investigated and the effects of magma chamber pressure perturbations on eruption rate are illustrated the numerical model domeflow developed by the authors for this work is applied to the problem domeflow is a transient 1 5d isothermal two phase flow model of magma ascent through an axisymmetric conduit of variable radius which accounts for gas exsolution bubble growth crystallization induced by degassing permeable gas loss through overlying magma and through conduit walls as well as viscosity changes due to crystallization and degassing for runs in which chamber pressure increases the time required to reach the new steady state transition time is a complex function of the pressure perturbation while for decreasing chamber pressure transition time is a monotonic function of the magnitude of the pressure perturbation the transition to the new steady state is mainly controlled by magma compressibility travel time time required for one parcel of magma to travel from chamber to surface and the time over which the pressure perturbation occurs results of many runs 300 were analyzed using dimensional analysis to reveal a general relationship which predicts the temporal evolution of magma effusion rate for a given sudden increase in chamber pressure the product of the change in steady state extrusion rate and the time required to reach the new steady state is linearly proportional to the normalized change in chamber pressure the volume of the conduit and the ratio of top and bottom conduit radii and inversely proportional to the cubic root of volatile fraction this relationship is used to interpret observed variations in two ongoing dome building eruptions the soufriere hills volcano montserrat and merapi volcano indonesia

tube pumices as strain markers of the ductile brittle transition during magma fragmentation magma fragmentation the process by which relatively slow moving magma transforms into a violent gas flow carrying fragments of magma is the defining feature of explosive volcanism yet of all the processes involved in explosively erupting systems fragmentation is possibly the least understood1 2 several theoretical and laboratory studies on magma degassing3 4 5 6 7 and fragmentation8 9 10 11 have produced a general picture of the sequence of events leading to the fragmentation of silicic magma12 13 14 but there remains a debate2 over whether magma fragmentation is a consequence of the textural evolution of magma to a foamed state where disintegration of walls separating bubbles becomes inevitable due to a foam collapse criterion or whether magma is fragmented purely by stresses that exceed its tensile strength here we show that tube pumice where extreme bubble elongation is observed is a well preserved magmatic strain marker of the stress state immediately before and during fragmentation structural elements in the pumice record the evolution of the magma s mechanical response from viscous behaviour foaming and foam elongation through the plastic or viscoelastic stage and finally to brittle behaviour these observations directly support the hypothesis that fragmentation occurs when magma undergoes a ductile brittle transition and stresses exceed the magma s tensile strength

focal zone of a future tokai earthquake inferred from the seismicity pattern around the plate interface abstract a future large tokai earthquake has been considered to be the most urgent problem of impending disasters in the central part of the japanese islands since the first warning was announced in 1976 recent progress in observations has provided a great amount of data thus making a detailed investigation possible in this study based on the seismicity and the focal mechanism patterns of microearthquake data the mechanical situation that governs plate interactions around the tokai district was investigated it was found that the seismicity in the subducting philippine sea slab is composed of three characteristic groups of activities intense activity beneath lake hamana a linear cluster extending from lake hamana toward the northwest and a broad cluster expanding over the inland area in the west of suruga bay we propose that these activities occur inside the subducting oceanic crust and reflect the present stress state acting there the mechanism inducing these activities is assumed to come from two stress sources the lateral stretching of the slab and the partial locking between both plates this interpretation leads to the hypothesis that the broad cluster in the west of suruga bay represents a stress concentration due to locking the activity beneath lake hamana is proposed to represent shearing motion induced there and is interpreted to form the boundary between the rupture zones of the 1944 tonankai earthquake and a future large tokai earthquake these analyses resulted in identifying the wide inland area extending from the west coast of suruga bay to lake hamana to be a focal zone of a future tokai earthquake the zone proposed in this study indicates a significant deviation in its strike from the original model proposed by ishibashi in that the former parallels the nankai trough while the latter parallels the suruga trough

tidal modulation of nonvolcanic tremor episodes of nonvolcanic tremor and accompanying slow slip recently have been observed in the subduction zones of japan and cascadia in cascadia such episodes typically last a few weeks and differ from normal earthquakes in their source location and moment duration scaling the three most recent episodes in the puget sound southern vancouver island portion of the cascadia subduction zone were exceptionally well recorded in each episode we saw clear pulsing of tremor activity with periods of 12 4 and 24 to 25 hours the same as the principal lunar and lunisolar tides this indicates that the small stresses associated with the solid earth and ocean tides influence the genesis of tremor much more effectively than they do the genesis of normal earthquakes because the lithostatic stresses are 10 5 times larger than those associated with the tides we argue that tremor occurs on very weak faults