self similar rupture implied by scaling properties of volcanic earthquakes occurring during the 2004 2008 eruption of mount st helens washington we analyze a group of 6073 low frequency earthquakes recorded during a week long temporary deployment of broadband seismometers at distances of less than 3 km from the crater at mount st helens in september of 2006 we estimate the seismic moment m0 and spectral corner frequency f0 using a spectral ratio approach for events with a high signal to noise snr ratio that have a cross correlation coefficient of 0 8 or greater with at least five other events a cluster analysis of cross correlation values indicates that the group of 421 events meeting the snr and cross correlation criteria forms eight event families that exhibit largely self similar scaling we estimate the m0 and f0 values of the 421 events and calculate their static stress drop and scaled energy er m0 values the estimated values suggest self similar scaling within families as well as between five of eight families i e m0 f0 3 and er m0 constant we speculate that differences in scaled energy values for the two families with variable scaling may result from a lack of resolution in the velocity model the observation of self similar scaling is the first of its kind for such a large group of low frequency volcanic tectonic events occurring during a single active dome extrusion eruption

waveform classification of volcanic low frequency earthquake swarms and its implication at soufriere hills volcano montserrat low frequency volcanic earthquakes are indicators of magma transport and activity within shallow conduit systems at a number of volcanoes these events exhibit a high degree of waveform similarity providing a criterion for classification using cross correlation techniques to quantify the degree of similarity we develop a method to sort events into families containing comparable waveforms events within a family have been triggered within one small source volume from which the seismic wave has then travelled along an identical path to the receiver this method was applied to a series of 16 low frequency earthquake swarms well correlated with cyclic deformation recorded by tiltmeters at soufriere hills volcano montserrat in june 1997 nine waveform groups were identified containing more than 45 events each the families are repeated across swarms with only small changes in waveform indicating that the seismic source location is stable with time the low frequency seismic swarms begin prior to the point at which inflation starts to decelerate suggesting that the seismicity indicates or even initiates a depressurisation process a major dome collapse occurred within the time window considered removing the top 100 m of the dome this event caused activity within some families to pause for several cycles before reappearing this shows that the collapse did not permanently disrupt the source mechanism or the path of the seismic waves

infrasonic tremor in the diffraction zone 1 volcanic tremor signals recorded by an infrasound array 12 5 km from the active vent of k lauea volcano show clear diurnal amplitude variations and originate from a well defined direction pointing to the active pu u crater complex spectral amplitudes between 0 02 0 3 hz a proxy for wind speed increase when the wind speeds increase during the daytime spectral amplitudes between 0 5 3 hz where infrasonic tremor is concentrated increase when the wind speeds decrease at night power spectrum analysis shows that when ambient noise levels drop infrasonic tremor amplitudes rise array processing confirms this relationship and reveals tremor detections and amplitudes decrease during the day these changes in infrasonic tremor spectral amplitude and coherence are most likely due to diurnal variations in atmospheric boundary layers affecting infrasonic propagation within the diffraction zone recognition of these regional atmospheric patterns is necessary to permit robust infrasonic remote sensing of volcanic processes

time dependent spatial amplitude patterns of harmonic tremor at arenal volcano costa rica seismic wave interferences seismograms recorded at the receivers of a small aperture seismic array usually display very similar waveforms and amplitudes as a consequence of their close proximity during the analysis of the volcanic tremor wave field at arenal volcano costa rica we detected significant differences in the amplitudes of harmonic tremor recorded at the stations of a small aperture 210 m seismic array the amplitude distributions are geometrically complex and characterized by strong gradients they occur just for harmonic tremors any other type of seismic event produces nearly uniform amplitudes across the array this suggests some relation with harmonic frequency content moreover the spatial amplitude patterns change with time some of these observations could be explained by an extreme combination of source path and site effects but they also could be produced by interference of different components of the seismic wave field we use numerical calculations to investigate the amplitude pattern generated by two interfering plane waves and are able to reproduce the main features of the observed amplitude patterns we propose mechanisms that might generate seismic wave fields with multiple components and conclude that interference can explain the complexity and variability of the harmonic tremor wave field at arenal volcano online material wave field animation

capturing the acoustic radiation pattern of strombolian eruptions using infrasound sensors aboard a tethered aerostat yasur volcano vanuatu we obtained an unprecedented view of the acoustic radiation from persistent strombolian volcanic explosions at yasur volcano vanuatu from the deployment of infrasound sensors attached to a tethered aerostat while traditional ground based infrasound arrays may sample only a small portion of the eruption pressure wavefield we were able to densely sample angular ranges of 200o in azimuth and 50o in take off angle by placing the aerostat at 38 tethered loiter positions around the active vent the airborne data joined contemporaneously collected ground based infrasound and video recordings over the period 29 july to 1 august 2016 we observe a persistent variation in the acoustic radiation pattern with average eastward directed root mean squared pressures more than 2 times larger than in other directions the observed radiation pattern may be related to both path effects from the crater walls and source directionality

swarms of repeating long period earthquakes at shishaldin volcano alaska 2001 2004 abstract during 2001 2004 a series of four periods of elevated long period seismic activity each lasting about 1 2 months occurred at shishaldin volcano aleutian islands alaska the time periods are termed swarms of repeating events reflecting an abundance of earthquakes with highly similar waveforms that indicate stable non destructive sources these swarms are characterized by increased earthquake amplitudes although the seismicity rate of one event every 0 5 5 min has remained more or less constant since shishaldin last erupted in 1999 a method based on waveform cross correlation is used to identify highly repetitive events suggestive of spatially distinct source locations the waveform analysis shows that several different families of similar events co exist during a given swarm day but generally only one large family dominates a network of hydrothermal fractures may explain the events that do not belong to a dominant repeating event group i e multiple sources at different locations exist next to a dominant source the dominant waveforms exhibit systematic changes throughout each swarm but some of these waveforms do reappear over the course of 4 years indicating repeatedly activated source locations the choked flow model provides a plausible trigger mechanism for the repeating events observed at shishaldin explaining the gradual changes in waveforms over time by changes in pressure gradient across a constriction within the uppermost part of the conduit the sustained generation of shishaldin s long period events may be attributed to complex dynamics of a multi fractured hydrothermal system the pressure gradient within the main conduit may be regulated by temporarily sealing and reopening of parallel flow pathways by the amount of debris within the main conduit and or by changing gas influx into the hydrothermal system the observations suggest that shishaldin s swarms of repeating events represent time periods during which a dominant source is activated

source mechanisms of explosions at stromboli volcano italy determined from moment tensor inversions of very long period data 1 seismic data recorded in the 2 30 s band at stromboli volcano italy are analyzed to quantify the source mechanisms of strombolian explosions during september 1997 to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous elastic medium that takes topography into account two source centroids are identified each representative of the distinct event types associated with explosive eruptions from two different vents the observed waveforms are well reproduced by our inversion and the two source centroids that best fit the data are offset 220 and 260 m beneath and 160 m northwest of the active vents the source mechanisms include both moment tensor and single force components the principal axes of the moment tensor have amplitude ratios 1 1 2 which can be interpreted as representative of a crack if one assumes the rock matrix at the source to have a poisson ratio n 1 3 a value appropriate for hot rock both imaged cracks dip 60 to the northwest and strike northeast southwest along a direction parallel to the elongation of the volcanic edifice and a prominent zone of structural weakness as expressed by lineaments dikes and brittle structures for our data set the volume changes estimated from the moments are 200 m 3 for the largest explosion from each vent together with the volumetric source is a dominantly vertical force with a magnitude of 10 8 n consistent with the inferred movement of the magma column perched above the source centroid in response to the piston like rise of a slug of gas in the conduit index terms 7215 seismology earthquake parameters 7280 seismology volcano seismology 8419 8414 volcanology eruption mechanisms keywords very long period seismicity moment tensor inversions eruption mehanics

long period events the most characteristic seismicity accompanying the emplacement and extrusion of a lava dome in galeras volcano colombia in 1991 abstract since its reactivation in 1988 the principal eruptions of galeras volcano occurred on may 4 9 1989 july 16 1992 and january 14 march 23 april 3 april 14 and june 7 1993 the initial eruption was a phreatic event which clearly marked a new period of activity a lava dome was extruded within the main crater in october 1991 and subsequently destroyed in an explosive eruption on july 16 1992 the eruptions that followed were all vulcanian type explosions the seismicity accompanying the emplacement extrusion and destruction of the lava dome was dominated by a mix of long period lp events and tremor displaying a variety of waveforms repetitive lp events with dominant periods in the range 0 2 1 s were observed in october and november 1991 and visually correlated with short energetic pulses of gas venting through a crack bisecting the dome surface each lp event was characterized by a weak precursory signal with dominant periods in the range 0 05 0 1 s lasting roughly 7 s using the fluid driven crack model of chouet 1988 1992 we infer that two distinct cracks may have acted as sources for the lp and precursor signals spectral analyses of the data yield the following parameters for the lp source crack length 240 360 m crack width 130 150 m crack aperture 0 5 3 4 mm crack stiffness 100 500 sound speed of fluid 880 m s and excess pressure 0 01 0 19 mpa similar analyses yield the parameters of the precursor source crack length 20 30 m crack width 15 25 m crack aperture 2 3 8 7 mm crack stiffness 5 15 sound speed of fluid 140 m s and excess pressure 0 06 0 15 mpa combined with geologic and thermodynamic constraints obtained from field observations these seismic parameters suggest a gas release mechanism in which the episodic collapse of a foam layer trapped at the top of the magma column subjacent to the dome releases a slug of pressurized gas which escapes to the surface while dilating a preexisting system of cracks in the dome structure accordingly the fracture observed on the crystallized dome body is the surface extension of the lp source crack where lp activity is induced by the rapid emission and expansion of gas flowing through this conduit the width and aperture of the crack estimated in the model are in good agreement with the length and aperture of the fracture estimated from visual observations the source parameters of the precursor signal are suggestive of a nozzle like conduit connecting the lp source crack to the underlying magma reservoir excitation of this conduit segment is attributed to the rapid emission and acceleration of the frothy fluid resulting from the collapse of the foam layer at the top of the reservoir the calculated periodicity of foam collapse events is in agreement with the observed average rate of thirteen lp events per hour

vertical fluxes of sediment in oscillatory sheet flow time series of vertical sediment fluxes are derived from concentration time series in sheet flow under waves while the concentrations c z t vary very little with time for z 10d50 the measured vertical sediment fluxes qzs z t vary strongly with time in this vertical band and their time variation follows to some extent the variation of the grain roughness shields parameter 2 5 t thus sediment distribution models based on the pickup function boundary condition are in some qualitative agreement with the measurements however the pickup function models are only able to model the upward bursts of sediment during the accelerating phases of the flow they are so far unable to model the following strong downward sediment fluxes which are observed during the periods of flow deceleration classical pickup functions which essentially depend on the shields parameter are also incapable of modelling the secondary entrainment fluxes which sometimes occur at free stream velocity reversal the measured vertical fluxes indicate that the effective sediment settling velocity in the high 0 3 c z t 0 4 concentration area is typically only a few percent of the clear water settling velocity while the measurements of richardson and jeronimo chem eng sci 34 1979 1419 from a different physical setting lead to estimates of the order 20 the data does not support gradient diffusion as a model for sediment entrainment from the bed that is detailed modelling of the observed near bed fluxes would require diffusivities that go negative during periods of flow deceleration an observed general trend for concentration variability to increase with elevation close to the bed is also irreconcilable with diffusion models driven by a bottom boundary condition

finite difference synthesis of infrasound propagation through a windy viscous atmosphere application to a bolide explosion detected by seismic networks summary a finite difference time domain fdtd algorithm has been developed to model linear infrasound propagation through a windy viscous medium the algorithm has been used to model signals from a large bolide that burst above a dense seismic network in the us pacific northwest on 2008 february 19 we compare synthetics that have been computed using a g2s ecmwf atmospheric model to signals recorded at the seismic networks located along an azimuth of 210 from the source the results show that the timing and the range extent of the direct stratospherically ducted and thermospherically ducted acoustic branches are accurately predicted however estimates of absorption obtained from standard attenuation models sutherland bass predict much greater attenuation for thermospheric returns at frequencies greaterthan0 1hzthanisobserved weconcludethateitherthestandardabsorptionmodelfor the thermospheric is incorrect or that thermospheric returns undergo non linear propagation at very high altitude in the former case a better understanding of atmospheric absorption at high altitudes is required in the latter a fully non linear numerical method is needed to test our hypothesis that higher frequency arrivals from the thermosphere result from non linear propagation at thermospheric altitudes

saturated and subcooled hydrothermal boiling in groundwater flow channels as a source of harmonic tremor the potential of hydrothermal boiling in groundwater flow channels for generating harmonic tremor a relatively monochromatic ground vibration associated with volcanic activity is examined we use simple organ pipe theory of normal mode fluid vibration and fundamental energy considerations to develop a first order analytical model of a hydrothermal boiling source of harmonic tremor we use this model to estimate order of magnitude groundwater flow channel lengths and boiling heat transfer rates required to produce harmonic tremor with dominant frequencies in the range 0 5 5 hz and surface wave reduced displacements of up to 100 cm2 depending on groundwater sound speed flow channel lengths of the order of 1 1000 m are required to produce fluid vibration eigenfrequencies in the range 0 5 5 hz the boiling heat transfer rate required to produce tremor with a given surface wave reduced displacement depends on the tremor frequency and on whether saturated boiling or subcooled boiling is the cause of the tremor saturated boiling produces groundwater vibration via steam bubble growth whereas subcooled boiling produces groundwater vibration via steam bubble collapse we find that subcooled hydrothermal boiling is from 102 to 104 times more efficient than saturated boiling in converting boiling thermal power to seismic power for example the boiling heat transfer rates required to produce 1 hz tremor with reduced displacements of up to 100 cm2 via subcooled boiling are generally less than a few thousand megawatts for saturated boiling the required boiling heat transfer rates are several orders of magnitude larger than this the highest values of heat flow reported in the literature for volcanic crater lakes and terrestrial and ocean floor geothermal areas are of the order of 1000 mw taking this value as a first order estimate of an upper limit on possible boiling heat transfer rates in volcanic hydrothermal systems our results suggest that saturated hydrothermal boiling is capable of generating only low amplitude harmonic tremor with surface wave reduced displacements no higher than a few square centimeters however subcooled hydrothermal boiling could potentially generate high amplitude harmonic tremor with reduced displacements as large as several hundred square centimeters as a specific application of our model we evaluate the potential of hydrothermal boiling for generating harmonic tremor at recently active mount st helens and nevado del ruiz volcanoes we conclude that subcooled boiling likely could have produced the tremor episodes considered at both volcanoes saturated boiling also could explain the nevado del ruiz tremor but probably not the more powerful mount st helens tremor

faulting within the mount st helens conduit and implications for volcanic earthquakes the 2004 2008 eruption of mount st helens produced seven dacite spines mantled by cataclastic fault rocks comprising an outer fault core and an inner damage zone these fault rocks provide remarkable insights into the mechanical processes that accompany extrusion of degassed magma insights that are useful in forecasting dome forming eruptions the outermost part of the fault core consists of finely comminuted fault gouge that is host to 1 to 3 mm thick layers of extremely fine grained slickenside bearing ultracataclasite interior to the fault core there is an 2 m thick damage zone composed of cataclastic breccia and sheared dacite and interior to the damage zone there is massive to flow banded dacite lava of the spine interior structures and microtextures indicate entirely brittle deformation including rock breakage tensional dilation shearing grain flow and microfaulting as well as gas and fluid migration through intergranular pores and fractures in the damage zone slickenside lineations and consistent orientations of riedel shears indicate upward shear of the extruding spines against adjacent conduit wall rocks paleomagnetic directions demagnetization paths oxide mineralogy and petrology indicate that cataclasis took place within dacite in a solidified steeply dipping volcanic conduit at temperatures above 500 c low water content of matrix glass is consistent with brittle behavior at these relatively high temperatures and the presence of tridymite indicates solidification depths of more than a million small and low frequency drumbeat earthquakes with coda magnitudes m d 2 slip patches possibly along observed extensive principal shear zones within the fault core but probably not along the smaller riedel shears although our field and structural data are compatible with stick slip models they do not rule out seismic and infrasound models that call on resonance of steam filled fractures to generate the drumbeat earthquakes we suggest that stick slip and gas release processes may be coupled and that regardless of the source mechanism the distinctive drumbeat earthquakes are proving to be an effective precursor for dome forming eruptions our data document a continuous cycle of deformation along the conduit margins beginning with episodes of fracture in the damage zone and followed by transfer of motion to the fault core we illustrate the cycle of deformation using a hypothetical cross section of the mount st helens conduit extending from the surface to the depth of magmatic solidification

ground coupled air waves and diffracted infrasound from the arequipa earthquake of june 23 2001 1 on june 23 2001 a strong earthquake measuring mw 8 4 occurred along the coast of south central peru coherent infrasonic waves were detected over a period of one hour by the is08 infrasound station in bolivia analysis of the ground coupled air waves shows that the rupture propagated from the northwestern to the southeastern part of the fault with a rupture velocity of 3 3 km s the azimuth variation of the infrasonic waves is attributed to a distribution of secondary sources along the highest mountain ranges which excite infrasonic waves that are diffracted to the ground the predominant source of infrasound is likely distributed along the andean cordillera using the azimuth and arrival time determination the horizontal scale size of the distant source regions of infrasonic waves is reconstructed over distances greater than 400 km

utilizing the solution of sound diffraction by a thin screen to evaluate infrasound waves attenuated around volcano topography abstract the observation of infrasound signals in the vicinity of volcanoes is a powerful tool to understand the source of explosive volcanic activity although the propagation of infrasound signals is affected by the local topography such effects are often ignored in the analysis leading to potential misinterpretation of the source parameters in this study we propose a simple low cost method of evaluating the attenuation of infrasound signals by topographical barriers in this method the first step approximates the elevation profile between the source and station into one thin screen like barrier then a mathematically exact solution of a sound diffraction problem is adopted to evaluate the attenuation of the infrasound amplitudes to assess the validity of this method the obtained estimates are compared with actual infrasound data observed at sakurajima volcano japan the results show that the estimates of relative amplitude to a reference station are more accurate than those considering only geometrical spreading suggesting that the proposed method provides a useful first order investigation of the attenuation of infrasound signals the spatial distribution of the attenuation in the entire area of the volcano was also estimated revealing a significant contrast between the eastern and western sides of the study area variations in signal attenuation also depend on the radial distance from the crater and were mainly attributed to variations of the relative screen height to the incident wavelength

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

constraints on explosive sources with spall from near source waveforms spall the tensile failure of a material due to high stress loading has been observed in a number of contained and surface explosions the phenomenon results in a repartition of the initial spherical explosion energy source yielding a second energy source which is cylindrical and delayed in time recent spall models by day et al 1983 demanding conservation of momentum have shown the phenomenon to have little contribution to 20 sec surface waves these models are extended to include the effect of the process on near source seismograms the spall model is constrained by observations within the nonlinear regime of the source which bound the mass momentum and timing of the process comparison of these forward models with the inverse vertical point force source inferred from seismic recordings of a bermed surface explosion yields excellent agreement the spall model developed from the contained explosion cheat is used to create synthetic seismograms comparisons of these waveforms with those from a mueller murphy contained explosion indicate that the waveform contribution from spall is similar in size to the spherical explosion waveform the complete synthetic composed of the spall and explosion contribution compares favorably with observational data from the cheat experiment in both amplitude and energy distribution

models of tremor and low frequency earthquake swarms on montserrat recent observations from soufriere hills volcano in montserrat reveal a wide variety of low frequency seismic signals we discuss similarities and differences between hybrid earthquakes and long period events and their role in explosions and rockfall events these events occur usually in swarms and occasionally merge into tremor an observation that can shed further light on the generation and composition of harmonic tremor we use a 2d finite difference method to model major features of low frequency seismic signatures and compare them with the observations a depth dependent velocity model for a fluid filled conduit is introduced which accounts for the varying gas content in the magma and the impact on the seismic signals is discussed we carefully analyse episodes of tremor that show shifting spectral lines and model those in terms of changes in the gas content of the magma as well as in terms of a time dependent triggering mechanism of low frequency resonances in this way we explain the simultaneous occurrence of low frequency events and tremor with a spectral content comprising integer harmonics

temperature dependence of elastic p and s wave velocities in porous mt unzen dacite laboratory measurements of elastic properties of volcanic rocks are crucial for the modelling of volcano seismic activity compared to the large database reported in the literature for sedimentary igneous and metamorphic rocks the data set for volcanic rocks is limited and mostly restricted to basalts data for more silica rich rocks are sparse in particular velocity data for silica rich volcanic rocks measured at elevated temperature are lacking we measured the elastic p and s wave velocities and the velocity anisotropy of porous dacitic rocks from unzen volcano japan exhibiting an open porosity of 3 3 to 24 3 vol the measurements were done at temperatures of up to 600 c and confining pressures of 100 mpa corresponding to depths of 3000 4000 m samples with even higher porosities failed at the required pressures the measurements were carried out in a cubic multi anvil pressure apparatus using the pulse transmission technique in contrast to low porosity magmatic and metamorphic rocks the seismic velocities of the investigated volcanic rocks increased and the velocity anisotropies decreased with increasing temperature due to further sample compaction there is a close relationship between velocity density and porosity the higher the density and the lower the porosity the higher are the p and s wave velocities these results can contribute to a better understanding of the propagation of seismic energy through the volcanic edifice

source location of the 19 february 2008 oregon bolide using seismic networks and infrasound arrays 1 on 19 february 2008 a bolide traveled across the sky along a southern trajectory ending in a terminal burst above oregon the event was well recorded by the usarray other seismic networks four infrasound arrays and several video cameras we compare the results of locating the burst using these different sensor networks specifically we reverse time migrate acoustic to seismic coupled signals recorded by the usarray out to 800 km range to image the source in 2 d space and time we also apply a grid search over source altitude and time minimizing the misfit between observed and predicted arrival times using 3 d ray tracing with a high resolution atmospheric velocity model our seismic and video results suggest a point source rather than a line source associated with a hypersonic trajectory we compare the seismic source locations to those obtained by using different combinations of observed infrasound array signal back azimuths and arrival times we find that all locations are consistent however the seismic location is more accurate than the infrasound locations due to the larger number of seismic sensors a more favorable seismic source receiver geometry and shorter ranges to the seismometers for the infrasound array locations correcting for the wind improved the accuracy but implementing arrival times while increasing the precision reduced the accuracy presumably due to limitations of the source location method and or atmospheric velocity model we show that despite known complexities associated with acoustic to seismic coupling aboveground infrasound sources can be located with dense seismic networks with remarkably high accuracy and precision

measurements of two types of dilatational waves in an air filled unconsolidated sand this study consists of laboratory measurements of dilatational waves propagating through an air filled unconsolidated sand one excitation technique consists of a loudspeaker suspended in the air above the packing of sand a second excitation technique uses a mechanical shaker in contact with the sand the transmitted signals are received using microphones and geophones located at various depths within the sand an interpretation based on measured phase speeds indicates that the transmitted energy from the suspended loudspeaker source is partitioned primarily but not exclusively into the type ii dilatational wave this wave attenuates rapidly and is only detected at depths of less than about 15 cm for this particular sample at the deeper depths the detected signal is associated with the type i dilatational wave the mechanical shaker produces only a type i dilatational wave both the geophone and microphone sensors can detect both types of dilatational waves

dynamics of seismogenic volcanic extrusion at mount st helens in 2004 05 the 2004 05 eruption of mount st helens exhibited sustained near equilibrium behaviour characterized by relatively steady extrusion of a solid dacite plug and nearly periodic shallow earthquakes here we present a diverse data set to support our hypothesis that these earthquakes resulted from stick slip motion along the margins of the plug as it was forced incrementally upwards by ascending solidifying gas poor magma we formalize this hypothesis with a dynamical model that reveals a strong analogy between behaviour of the magma plug system and that of a variably damped oscillator modelled stick slip oscillations have properties that help constrain the balance of forces governing the earthquakes and eruption and they imply that magma pressure never deviated much from the steady equilibrium pressure we infer that the volcano was probably poised in a near eruptive equilibrium state long before the onset of the 2004 05 eruption

repeating coupled earthquakes at shishaldin volcano alaska since it last erupted in 1999 shishaldin volcano aleutian islands alaska has produced hundreds to thousands of longperiod 1 2 hz lp earthquakes every day with no other sign of volcanic unrest in 2002 the earthquakes also exhibited a short period 4 7 hz sp signal occurring between 3 and 15 s before the lp phase although the sp phase contains higher frequencies than the lp phase its spectral content is still well below that expected of brittle failure events the sp phase was never observed without the lp phase although lp events continued to occur in the absence of the precursory signal the twophased events are termed bcoupled eventsq reflecting a triggered relationship between two discrete event types both phases are highly repetitive in time series suggestive of stable non destructive sources waveform cross correlation and spectral coherence are used to extract waveforms from the continuous record and determine precise p wave arrivals for the sp phase although depths are poorly constrained the sp phase is believed to lie at shallow b4 km depths just west of shishaldin s summit the variable timing between the sp and lp arrivals indicates that the trigger mechanism between the phases itself moves at variable speeds a model is proposed in which the sp phase results from fluid moving within the conduit possibly around an obstruction and the lp phase results from the coalescence of a shallow gas bubble the variable timing is attributed to changes in gas content within the conduit the destruction of the conduit obstacle on november 21 2002 resulted in the abrupt disappearance of the sp phase published by elsevier b v

criteria for discretization of seafloor bathymetry when using a stairstep approximation application to computation of t phase seismograms acoustic solutions for numerical models in which an overly coarse discretization of a stairstep boundary is employed to simulate smoothly varying bathymetry are degraded in a way that simulates scattering geometrical optics approximations are used to derive discretization criteria for simulating a smoothly sloping interface for the case of a source embedded in either an acoustic or an elastic seafloor and applied to modeling t phases a finite difference time domain modeling approach is used to synthesize t phases for both smoothly sloping and rough seafloor boundaries it is shown that scattering at a rough seafloor boundary yields ocean borne acoustic phases with velocities near those of observed t phase while smooth seafloor models yield t phases with slower horizontal velocities the long duration of the computed t phases for both the rough acoustic and elastic models is consistent with energy being scattered into the sound channel both as it transits the ocean crust boundary as well as at several subsequent seafloor reflections however comparison between the elastic and acoustic modeling solutions indicates that the t phase wavetrain duration decreases with decreasing impedence contrast between the ocean and seafloor

investigating spectral distortion of local volcano infrasound by nonlinear propagation at sakurajima volcano japan author s maher s p matoza r s de groot hedlin c d gee k l fee d yokoo a

the source of infrasound associated with long period events at mount st helens 1 during the early stages of the 2004 2008 mount st helens eruption the source process that produced a sustained sequence of repetitive long period lp seismic events also produced impulsive broadband infrasonic signals in the atmosphere to assess whether the signals could be generated simply by seismic acoustic coupling from the shallow lp events we perform finite difference simulation of the seismo acoustic wavefield using a single numerical scheme for the elastic ground and atmosphere the effects of topography velocity structure wind and source configuration are considered the simulations show that a shallow source buried in a homogeneous elastic solid produces a complex wave train in the atmosphere consisting of p sv and rayleigh wave energy converted locally along the propagation path and acoustic energy originating from the source epicenter although the horizontal acoustic velocity of the latter is consistent with our data the modeled amplitude ratios of pressure to vertical seismic velocity are too low in comparison with observations and the characteristic differences in seismic and acoustic waveforms and spectra cannot be reproduced from a common point source the observations therefore require a more complex source process in which the infrasonic signals are a record of only the broadband pressure excitation mechanism of the seismic lp events the observations and numerical results can be explained by a model involving the repeated rapid pressure loss from a hydrothermal crack by venting into a shallow layer of loosely consolidated highly permeable material heating by magmatic activity causes pressure to rise periodically reaching the pressure threshold for rupture of the valve sealing the crack sudden opening of the valve generates the broadband infrasonic signal and simultaneously triggers the collapse of the crack initiating resonance of the remaining fluid subtle waveform and amplitude variability of the infrasonic signals as recorded at an array 13 4 km to the nw of the volcano are attributed primarily to atmospheric boundary layer propagation effects superimposed upon amplitude changes at the source

varying seismic acoustic properties of the fluctuating lava lake at villarrica volcano chile villarrica volcano outgasses through an open lava lake with bubbles ranging in size from submillimeter to several meters the largest of which produce strombolian bursting events that are visible from the crater rim thousands of shallow strombolian events identified through seismic waveform cross correlation were found to produce discrete and repetitive long period seismic and infrasonic signals we identified variations of up to 0 7 s in seismic acoustic arrival delay times between april and july 2010 at a station 750 m from the vent which we interpret as due to fluctuations in the level of lava lake during time periods interpreted as having high lava lake levels based on reduced time delays interevent times were also reduced and average seismic amplitude measurements seismic and acoustic event energies and volcano acoustic seismic ratios were all high as compared to times when the lava lake was lower the crater is also a source of nearly continuous monotonic infrasonic tremor we found that the peak frequency of this infrasonic tremor typically around 0 5 1 0 hz was inversely correlated with seismic acoustic delay times and therefore an indicator of lava lake level we use this correlation to propose a new model for infrasonic tremor generation namely using crater geometry to approximate a bessel horn we interpret the two clearest cycles of elevated seismicity and lava lake level as due to an increase in exsolved gas resulting from an injection of volatile rich magma or an overturn in a deeper magma reservoir

new insights into banded tremor from the 2008 2009 mount etna eruption 1 we investigated the banded tremor activity occurring at mt etna volcano between august october 2008 during the 2008 2009 eruption the banded tremor occurred in episodes lasting 25 30 min with intervals in between the episodes of about 25 min seismic signal analyses showed that the banded tremor was characterized by spectral contents wavefields and source locations that differed from the ordinary volcanic tremor the infrasound recordings exhibited an intermittent infrasonic tremor alternating with the banded tremor episodes finally nonlinear analyses suggested that a banded tremor system can be considered chaotic implying 1 sensitive dependence on initial conditions suggesting not only that a banded tremor system requires particular conditions to generate but also that slight variations of these conditions are able to greatly change the features of the banded tremor or even to stop it and 2 long term unpredictability that is the impossibility to forecast the long term evolution of the banded tremor on the basis of all these results and analogies with geyser models we suggest a model of banded tremor that invokes alternating recharge discharge phases banded tremor is due to perturbations in shallow aquifers such as fluid movement and bubble growth or collapse due to hydrothermal boiling triggered by the heat and hot fluid transfer from the underlying magma bodies this heat fluid transfer also causes an increasing pressure in the aquifer leading to fluid discharge during this process the seismic radiation decreases and if the fluid discharge is well coupled with the atmosphere acoustic signals are generated

seismic and acoustic recordings of an unusually large rockfall at mount st helens washington 1 on 29 may 2006 a large rockfall off the mount st helens lava dome produced an atmospheric plume that was reported by airplane pilots to have risen to 6 000 m above sea level and interpreted to be a result of an explosive event however subsequent field reconnaissance found no evidence of a ballistic field indicating that there was no explosive component the rockfall produced complex seismic and infrasonic signals with the latter recorded at sites 0 6 and 13 4 km from the source an unusual very long period 50 s infrasonic signal was recorded a signal we model as the result of air displacement two high frequency infrasonic signals are inferred to result from the initial contact of a rock slab with the ground and from interaction of displaced air with a depression at the base of the active lava dome

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

three dimensional p and s wave velocity structure of redoubt volcano alaska the three dimensional p and s wave structure of redoubt volcano alaska and the underlying crust to depths of 7 8 km is determined from 6219 p wave and 4008 s wave first arrival times recorded by a 30 station seismograph network deployed on and around the volcano first arrival times are calculated using a finite difference technique which allows for flexible parameterization of the slowness model and easy inclusion of topography and source receiver geometry the three dimensional p wave velocity structure and hypocenters are determined simultaneously while the three dimensional s wave velocity model is determined using the relocated seismicity and an initial s wave velocity model derived from the p wave velocity model assuming an average vp vs ratio of 1 78 convergence is steady with approximately 73 and 52 reduction in p and s wave arrival time rms respectively after 10 iterations the most prominent feature observed in the three dimensional velocity models derived for both p and s waves is a relative low velocity near vertical pipelike structure approximately 1 km in diameter that extends from 1 to 6 km beneath sea level this feature aligns axially with the bulk of seismicity and is interpreted as a highly fractured and altered zone encompassing a magma conduit the velocity structure beneath the north flank of the volcano between depths of 1 and 6 km is characterized by large lateral velocity variations high velocities within this region are interpreted as remnant dikes and sills and low velocities as regions along which magma migrates no large low velocity body suggestive of a magma chamber is resolved in the upper 7 8 km of the crust

comparing near regional and local measurements of infrasound from mount erebus antarctica implications for monitoring abstract local 100 s of metres from vent monitoring of volcanic infrasound is a common tool at volcanoes characterized by frequent low magnitude eruptions but it is generally not safe or practical to have sensors so close to the vent during more intense eruptions to investigate the potential and limitations of monitoring at near regional ranges 10 s of km we studied infrasound detection and propagation at mount erebus antarctica this site has both a good local monitoring network and an additional international monitoring system infrasound array is55 located 25 km away we compared data recorded at is55 with a set of 117 known strombolian events that were recorded with the local network in january 2006 75 of these events were identified at is55 by an analyst looking for a pressure transient coincident with an f statistic detection which identifies coherent infrasound signals with the data from january 2006 we developed and calibrated an automated signal detection algorithm based on threshold values of both the f statistic and the correlation coefficient application of the algorithm across is55 data for all of 2006 identified infrasonic signals expected to be strombolian explosions and proved reliable for indicating trends in eruption frequency however detectability at is55 of known strombolian events depended strongly on the local signal amplitude 90 of events with local amplitudes 25 pa were identified at is55 compared to only 26 of events with local amplitudes

volcanic tremor masks its seismogenic source results from a study of noneruptive tremor recorded at mount st helens washington on 2 october 2004 a significant noneruptive tremor episode occurred during the buildup to the 2004 2008 eruption of mount st helens washington this episode was remarkable both because no explosion followed and because seismicity abruptly stopped following the episode this sequence motivated us to consider a model for volcanic tremor that does not involve energetic gas release from magma but does involve movement of conduit magma through extension on its way toward the surface we found that the tremor signal was composed entirely of love and rayleigh waves and that its spectral bandwidth increased and decreased with signal amplitude with broader bandwidth signals containing both higher and lower frequencies our modeling results demonstrate that the forces giving rise to this tremor were largely normal to conduit walls generating hybrid head waves along conduit walls that are coupled to internally reflected waves together these form a crucial part of conduit resonance giving tremor wavefields that are largely a function of waveguide geometry and velocity we find that the mechanism of tremor generation fundamentally masks the nature of the seismogenic source giving rise to resonance thus multiple models can be invoked to explain volcanic tremor requiring that information from other sources such as visual observations geodesy geology and gas geochemistry be used to constrain source models with concurrent gps and field data supporting rapid rise of magma we infer that tremor resulted from drag of nearly solid magma along rough conduit walls as magma was forced toward the surface

an automatic seismic event processing for detection and location the p m c c method we present a new method for automatic detection and location of seismic events recorded on a network it is based on a progressive study of the interstation correlation functions which leads to a consistent set of time delays when a seismic phase is present three different examples are processed on networks of different sizes

infrasound from earthquakes 1 infrasonic signals have been observed from 31 earthquakes by arrays of microphones operated by the los alamos national laboratory between 1983 and 2003 the properties of the signals are presented signal amplitudes corrected for propagation and distance show a relation with seismic magnitude the variance in the relation is understood primarily in terms of the uncertainties or errors in the ground motion deduced from an independent data set and the stratospheric winds which strongly influence signal propagation signal durations can extend over many minutes a relation is found between signal duration and magnitude to understand this we propose a model in which regions distant from the epicenter are excited by seismic surface waves the surface motion of these regions in turn produces signals which precede or follow the signals from the epicenter analysis failed to detect signals from 56 earthquakes during the observation period predicted signal to noise ratios for these earthquakes indicated that the signals would have been too weak for detection

global morphology of infrasound propagation i atmospheric sound waves in the 0 02 10 hz region also known as infrasound exhibit long range global propagation characteristics measurable infrasound is produced around the globe on a daily basis by a variety of natural and man made sources as a result of weak classical attenuation 0 01 db km 1 at 0 1 hz these acoustic signals can propagate thousands of kilometers in tropospheric stratospheric and lower thermospheric ducts to model this propagation accurately detailed knowledge of the background atmospheric state variables the global winds and temperature fields from the ground to 170 km is required for infrasound propagation calculations we have developed a unique atmospheric specification system g2s that is capable of providing this information using acoustic ray tracing methods and detailed g2s atmospheric specifications we investigate the major aspects of the spatiotemporal variability of infrasound propagation characteristics

seismo acoustic signals associated with degassing explosions recorded at shishaldin volcano alaska 2003 2004 in summer 2003 a chaparral model 2 microphone was deployed at shishaldin volcano aleutian islands alaska the pressure sensor was co located with a short period seismometer on the volcano s north flank at a distance of 6 62 km from the active summit vent the seismo acoustic data exhibit a correlation between impulsive acoustic signals 1 2 pa and long period lp 1 2 hz earthquakes since it last erupted in 1999 shishaldin has been characterized by sustained seismicity consisting of many hundreds to two thousand lp events per day the activity is accompanied by up to 200 m high discrete gas puffs exiting the small summit vent but no significant eruptive activity has been confirmed the acoustic waveforms possess similarity throughout the data set july 2003 november 2004 indicating a repetitive source mechanism the simplicity of the acoustic waveforms the impulsive onsets with relatively short 10 20 s gradually decaying codas and the waveform similarities suggest that the acoustic pulses are generated at the fluid air interface within an open vent system so2 measurements have revealed a low so2 flux suggesting a hydrothermal system with magmatic gases leaking through this hypothesis is supported by the steady state nature of shishaldin s volcanic system since 1999 time delays between the seismic lp and infrasound onsets were acquired from a representative day of seismo acoustic data a simple model was used to estimate source depths the short seismo acoustic delay times have revealed that the seismic and acoustic sources are co located at a depth of 240 200 m below the crater rim this shallow depth is confirmed by resonance of the upper portion of the open conduit which produces standing waves with f 0 3 hz in the acoustic waveform codas the infrasound data has allowed us to relate shishaldin s lp earthquakes to degassing explosions created by gas volume ruptures from a fluid air interface

changes in seismic velocity during the first 14 months of the 2004 2008 eruption of mount st helens washington mount st helens began erupting in late 2004 following an 18 year quiescence swarms of repeating earthquakes accompanied the extrusion of a mostly solid dacite dome over the next four years in some cases the waveforms from these earthquakes evolved slowly likely reflecting changes in the properties of the volcano that affect seismic wave propagation we use coda wave interferometry to quantify small changes in seismic velocity structure usually 1 between two similar earthquakes and employed waveforms from several hundred families of repeating earthquakes together to create a continuous function of velocity change observed at permanent stations operated within 20 km of the volcano the high rate of earthquakes allowed tracking of velocity changes on an hourly time scale changes in velocity were largest near the newly extruding dome and likely related to shallow deformation as magma first worked its way to the surface we found strong correlation between velocity changes and the inverse of real time seismic amplitude measurements during the first three weeks of activity suggesting fluctuations of pressure in the shallow subsurface may have driven both seismicity and velocity change velocity changes during the remainder of the eruption likely result from a complex interplay of multiple effects and are not well explained by any single factor alone highlighting the need for complementary geophysical data when interpreting velocity changes

near synchronous interhemispheric termination of the last glacial maximum in mid latitudes isotopic records from polar ice cores imply globally asynchronous warming at the end of the last glaciation however 10be exposure dates show that large scale retreat of mid latitude last glacial maximum glaciers commenced at about the same time in both hemispheres the timing of retreat is consistent with the onset of temperature and atmospheric co2 increases in antarctic ice cores we suggest that a global trend of rising summer temperatures at the end of the last glacial maximum was obscured in north atlantic regions by hypercold winters associated with unusually extensive winter sea ice

fault textures in volcanic conduits evidence for seismic trigger mechanisms during silicic eruptions it is proposed that fault textures in two dissected rhyolitic conduits in iceland preserve evidence for shallow seismogenic faulting within rising magma during the emplacement of highly viscous lava flows detailed field and petrographic analysis of such textures may shed light on the origin of long period and hybrid volcanic earthquakes at active volcanoes there is evidence at each conduit investigated for multiple seismogenic cycles each of which involved four distinct evolutionary phases in phase 1 shear fracture of unrelaxed magma was triggered by shear stress accumulation during viscous flow forming the angular fracture networks that initiated faulting cycles transient pressure gradients were generated as the fractures opened which led to fluidisation and clastic deposition of fine grained particles that were derived from the fracture walls by abrasion fracture networks then progressively coalesced and rotated during subsequent slip phase 2 developing into cataclasite zones with evidence for multiple localised slip events fluidisation and grain size reduction phase 2 textures closely resemble those formed on seismogenic tectonic faults characterised by friction controlled stick slip behaviour increasing cohesion of cataclasites then led to aseismic distributed ductile deformation phase 3 and generated deformed cataclasite zones which are enriched in metallic oxide microlites and resemble glassy pseudotachylite continued annealing and deformation eventually erased all structures in the cataclasite and formed microlite rich flow bands in obsidian phase 4 overall the mixed brittle ductile textures formed in the magma appear similar to those formed in lower crustal rocks close to the brittle ductile transition with the rheological response mediated by strain rate variations and frictional heating fault processes in highly viscous magma are compared with those elsewhere in the crust and this comparison is used to appraise existing models of volcano seismic activity based on the textures observed it is suggested that patterns of long period and hybrid earthquakes at silicic lava domes reflect friction controlled stick slip movement and eventual healing of fault zones in magma which are an accelerated and smaller scale analogue of tectonic faults

seismic and acoustic signatures of surficial mass movements at volcanoes abstract surficial mass movements such as debris avalanches rock falls lahars pyroclastic flows and outburst floods are a dominant hazard at many volcanoes worldwide understanding these processes cataloging their spatio temporal occurrence and detecting tracking and characterizing these events would advance the science of volcano monitoring and help mitigate hazards seismic and acoustic methods show promise for achieving these objectives many surficial mass movements generate observable seismic and acoustic signals and many volcanoes are already monitored significant progress has been made toward understanding modeling and extracting quantitative information from seismic and infrasonic signals generated by surficial mass movements however much work remains in this paper we review the state of the art of the topic covering a range of scales and event types from individual rock falls to sector collapses we consider a full variety of volcanic settings from submarine to subaerial shield volcano to stratovolcano finally we discuss future directions toward operational seismo acoustic monitoring of surficial mass movements at volcanoes

an overview of volcano infrasound from hawaiian to plinian local to global abstract volcano infrasound is an increasingly useful technique for detecting locating characterizing and quantifying eruptive activity and can be used to constrain eruption source parameters in recent years studies of infrasound data from active volcanoes have shown clear progress towards mitigating volcanic hazards and understanding volcanic source processes volcano acoustic sources are shallow or aerial thus volcano infrasound data provide valuable information on eruption dynamics and are readily combined with direct and remote observations of gas ash and other eruptive phenomena the infrasound signals produced by volcanoes are indicative of the eruption style and dynamics here we review the diversity of infrasound signals generated by a wide variety of volcanic eruptions from hawaiian to plinian and the physical processes inferred to produce them we place particular emphasis on regional 15 250 km distance and global 250 km distance volcano infrasound studies as recent work in this area has made significant advances in monitoring and characterizing remote and difficult to monitor eruptions long range infrasonic detection of explosive volcanic eruptions is possible due to the energetic source mechanisms involved minor atmospheric attenuation at low frequencies and the existence of waveguides in the atmosphere however accurate characterization of the atmosphere and its spatiotemporal variability is required for reliable long range sound propagation modeling and correct interpretation of global infrasound recordings conversely because volcanic explosions are energetic and sometimes repetitive infrasound sources they can be used to validate atmospheric and acoustic propagation models

subevents of long period seismicity implications for hydrothermal dynamics during the 2004 2008 eruption of mount st helens 1 one of the most striking aspects of seismicity during the 2004 2008 eruption of mount st helens msh was the precise regularity in occurrence of repetitive long period lp or drumbeat events over sustained time periods however this precise regularity was not always observed and at times the temporal occurrence of lp events became more random in addition accompanying the dominant lp class of events during the 2004 2008 msh eruption there was a near continuous randomly occurring series of smaller seismic events these subevents are not always simply small amplitude versions of the dominant lp class of events but appear instead to result from a separate random process only loosely coupled to the main lp source mechanism we present an analysis of the interevent time and amplitude distributions of the subevents using waveform cross correlation to separate lp events from the subevents we also discuss seismic tremor that accompanied the 8 march 2005 phreatic explosion event at msh this tremor consists of a rapid succession of lps and subevents triggered during the explosion in addition to broadband noise from the sustained degassing immediately afterward seismicity returned to the pre explosion occurrence pattern this triggering in relation to the rapid ejection of steam from the system and subsequent return to pre explosion seismicity suggests that both seismic event types originated in a region of the subsurface hydrothermal system that was 1 in contact with the reservoir feeding the 8 march 2005 phreatic explosion but 2 not destroyed or drained by the explosion event finally we discuss possible thermodynamic conditions in a pressurized hydrothermal crack that could give rise to seismicity pressure drop estimates for typical lp events are not generally large enough to perturb pure water in a shallow hydrothermal crack into an unstable state however dissolved volatiles such as co2 may lead to a more unstable system increasing the seismogenic potential of a hydrothermal crack subject to rapid heat flux the interaction of hydrothermal and magmatic systems beneath msh in 2004 2008 thus appears able to explain a wide range of observed phenomena including subevents lp events larger md 2 events and phreatic explosions

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

volcanic hybrid earthquakes that are brittle failure events 1 volcanoes generate a variety of pre eruptive low frequency seismic signals hybrid earthquakes comprise a class of these signals having high frequency onsets followed by low frequency ringing they are used empirically to predict eruptions but their ambiguous physical origin limits their diagnostic use the short duration near field hybrid seismograms associated with the 2004 mount st helens eruption indicate that much of the prolonged signal is due to path rather than resonating fluids we show using seismic source spectra that the hybrids have a corner frequency seismic moment relationship that scales consistently with brittle failure the unusually low frequency of these earthquakes can result from low rupture velocities combined with strong path effects due to their shallow sources this new application of near field instrumentation provides the first seismological evidence for brittle failure as a major process in dome building and suggests that hybrids should not be used as direct indicators of fluids

evolution of the december 14 1989 precursory long period event swarm at redoubt volcano alaska abstract the intermittency pattern and evolution in waveforms of long period lp seismic events during the intense 23 h swarm that preceded the december 14 1989 eruption of redoubt volcano are investigated utilizing cross correlation to exploit the high degree of similarity among waveforms a substantially more complete event catalog is generated than was available from near realtime detection based on short term long term amplitude ratios which was saturated by the high rate of activity the temporal magnitude distribution of the predominant lp events is found to have an unusual banded structure in which the average magnitude of each band slowly increases and then decreases through time a bifurcation that appears in the uppermost band shortly after the peak in magnitudes is characterized by a quasi periodicity in intermittency and magnitude that is reminiscent of one of the classic routes to chaotic behavior in some non linear systems the waveforms of the predominant events evolve slowly but unsteadily through time these gradual changes appear to result from variations in the relative amplitudes of spectral peaks that remain stable in frequency which suggests that they are due to differential excitation of a single resonant source two other previously unrecognized repetitive waveforms are also identified but the signals from these secondary events are not clearly recorded at distances beyond the closest station similarities among the spectra of the predominant and secondary events suggest that the signals from these events also could represent different modes of exciting the same source significant changes in the rates and the sizes of the largest of these secondary events appear to coincide with the peak in the size distribution of the predominant lps at least some of the non repetitive lp waveforms in the swarm appear to be the result of the superposition of signals from the rapid repetition of predominant lp source thus placing a constraint on the repeat time of the triggering mechanism for this source a lone hybrid event which has a waveform character intermediate between the predominant lp events and high frequency volcano tectonic events was also identified in the swarm the occurrence of this event provides important evidence that the low frequency character of the lp events is a source rather than a path or site effect

investigation of possibility of damage from acoustically coupled seismic waveform from blast and artillery noise from artillary fire causes complaints around military installations cracked house foundations are often included in these complaints for the moderate size explosives involved and the minimum distances 2 km to homes it is improbable that directly induced seismic vibrations would have high enough amplitudes to cause this kind of damage a possibility that has not been previously investigated is that the acoustically induced seismic wave might have a high enough amplitude to damage foundations measurements of the acoustic wave and the acoustically induced seismic wave were made for 8 in artillery shells and 500 lb bombs with peak levels up to 145 db and it was found that the induced seismic wave was much smaller than the minimum criteria for damage in addition an acoustic to seismic steady state plane wave model was modified to predict the acoustic coupled seismic wave comparison between predicted and measured results will be presented work supported by wes cerl

infrasound connecting the solid earth oceans and atmosphere the recently reinvigorated field of infrasonics is poised to provide insight into atmospheric structure and the physics of large atmospheric phenomena just as seismology has shed considerable light on the workings and structure of earth s solid interior although a natural tool to monitor the atmosphere and shallow earth for nuclear explosions it is becoming increasingly apparent that infrasound also provides another means to monitor a suite of natural hazards the frequent observation of geophysical sources such as the unsteady sea surface volcanoes and earthquakes that radiate energy both up into the atmosphere and down into the liquid or solid earth and transmission of energy across earth s boundaries reminds us that earth is an interconnected system this review details the rich history of the unheard sound in the atmosphere and the role that infrasonics plays in helping us understand the earth system

a theoretical treatment of the long range propagation of impulsive signals under strongly ducted nocturnal conditions on clear nights over flat land a sound duct develops in which sound can carry to great distances as is the case with all ducted propagation there is strong dispersion so that a broadband signal undergoes severe distortion as it propagates the signal received at long ranges from an impulsive source is a wave train of much greater duration than the initial impulse consisting of a series of arrivals the long range ground to ground propagation of an impulsive signal in a typical nocturnal duct is studied and the natures of the various arrivals are explained a direct connection is drawn between the meteorological and ground conditions and the structure of the propagated signal

infrasonic imaging of the kunlun mountains for the great 2001 china earthquake 1 on november 14 2001 a strong earthquake occurred on the high plateau of western china at a distance of 1800 km from the epicenter coherent infrasonic waves were detected for more than one hour using both an inverse location procedure and a complete simulation of the radiated pressure field distant source regions are accurately located the seismo acoustic coupling along a mountain belt is clearly demonstrated such an event offers an opportunity to validate velocity models in the atmosphere as well as to improve the understanding of the amplification of ground displacement caused by the topography

characteristics of seismic and acoustic signals produced by calving bering glacier alaska 1 we recorded 126 calving and iceberg breakup events from the terminus of the bering glacier during five days in august 2008 using seismometers and three small aperture arrays of infrasound sensors the seismic signals were typically emergent narrow band and lower frequency similar to records at other glaciers the acoustic records were characterized by shorter duration higher frequency signals with more impulsive onsets we demonstrate that triangular infrasound arrays permit improved locations of calving events over seismic arrivals that rely on a relatively complicated poorly known velocity model twenty six of 35 well located events occurred on icebergs in vitus lake rather than the glacier face while our data do not permit a complete description of the source process the distinctive frequency contents and durations in the seismic and infrasound data suggest that the two data types record different aspects of the same process

tutorial on sound propagation outdoors concerns about noise in the community date back to the dawn of recorded history then after centuries of relatively little activity scientific interest grew during the 17th century and social concerns were again voiced during the 19th century many of the wave propagation mechanisms relevant outdoors were understood at least qualitatively by the late 1800s today knowledge of sound propagation phenomena is of great economic and social importance because of environmental and other concerns reality is more complicated than geometrical spreading above flat ground some grounds are acoustically hard like concrete and others soft as snow corresponding reflection coefficients are complex and vary with angle grounds may not be flat leading to shadow zones or alternatively multiple reflections at the ground gradients of wind or temperature refract waves either upwards upwind or in a temperature lapse or downwards downwind or in a temperature inversion atmospheric turbulence causes fluctuations in the acoustical effects many of these features mutually interact measured sound pressure levels owe as much to near surface weather and to ground shape and impedance as to acoustical factors such as source and receiver heights and their separation this tutorial paper emphasizes field measurements and simple physical interpretations

influence of near source volcano topography on the acoustic wavefield and implication for source modeling in near source conditions 5 km the atmosphere is often assumed to be fully transparent to acoustic waves and to have a small effect on the acoustic wavefield as a consequence the propagation of the acoustic waves in the atmosphere near the source is often neglected and waveform is compensated only in amplitude by the inverse of the distance from the source however the amplitude distribution at five infrasonic stations deployed around the active craters of the stromboli volcano reveals anomalous decay up to 11 db larger than expected which cannot be explained in terms of energy loss for geometrical spreading the distribution of amplitude decay changes for different source positions suggesting a strong relationship with the source to receiver path geometry by using 2d fdtd modeling we show that the anomalous amplitude distribution of the acoustic waves at stromboli is not necessarily due to the source radiation pattern but it is strongly influenced by the topography of the ground atmosphere interface diffraction and reflection of topography contaminate the acoustic wavefield and have a strong effect in reducing the amplitude and altering the waveform our work demonstrates that line of sight conditions are quite difficult to be achieved in acoustic experiments and that a detailed knowledge of the topography along the crater receiver path is necessary whenever infrasound waveforms are used to invert for the source process

insights into explosive activity at closely spaced eruptive vents using infrasound signals example of mt etna 2008 eruption abstract on 13 may 2008 an eruptive fissure opened on mount etna s eastern flank feeding both explosive activity and lava effusion from multiple vents for about 14 months during the investigated may september 2008 eruptive period infrasound recordings from a 4 station sparse network allowed tracking of the explosive activity in terms of location and dynamics in order to focus on activity from the eruptive fissure the infrasonic events generated by the summit craters were selected by using both spectral features and time delays between pairs of stations and excluded from our analysis then to accurately locate events from the fissure we used a composite method based on the semblance and brightness functions this enabled the study of the co existence of more than one infrasound source and or its migration along the eruptive fissure hence results permitted us to discriminate the number of active vents and their location along the fissure even when due to poor weather conditions it was not possible to access the vents or carry out direct observations the eruptive activity was characterised by variations in the number of active vents according to the overall intensity of the eruptive event variability of the infrasound waveforms highlighted either that distinct vents produced signals with different waveforms or that single vents generated different events during distinct periods of time or finally both the previous phenomena we applied the strombolian bubble vibration model to model waveform differences and attributed the signal variations to bubble radius changes

infrasonic precursors to a vulcanian eruption at sakurajima volcano japan the may 1998 eruption sequence of sakurajima volcano was monitored by ten infrasonic stations ten seismometers and a video camera during this seismo acoustic experiment we recorded hundreds of infrasonic tremor and long period events associated with seismic signals and observed a progression from relative quiescence to a vulcanian eruption the number of infrasonic events increased with escalating volcanic activity and the dominant character of the infrasonic signals changed from impulsive to emergent at 22 17 of may 19 sakurajima released ash and gases to a height of 2 km above the vent an event that was recorded continuously by one infrasonic and two seismic stations we present the experimental setup as well as a procedure through which infrasonic signals may be incorporated into future eruption monitoring and forecasting algorithms for open vent volcanic systems in addition our recordings suggest that infrasonic signals are more representative of processes occurring within the volcanic interior than are seismic signals which are strongly altered by diffraction and scattering in the volcanic edifice

volcano infrasound a review abstract exploding volcanoes which produce intense infrasound are reminiscent of the veritable explosion of volcano infrasound papers published during the last decade volcano infrasound is effective for tracking and quantifying eruptive phenomena because it corresponds to activity occurring near and around the volcanic vent as opposed to seismic signals which are generated by both surface and internal volcanic processes as with seismology infrasound can be recorded remotely during inclement weather or in the dark to provide a continuous record of a volcano s unrest moreover it can also be exploited at regional or global distances where seismic monitoring has limited efficacy this paper provides a literature overview of the current state of the field and summarizes applications of infrasound as a tool for better understanding volcanic activity many infrasound studies have focused on integration with other geophysical data including seismic thermal electromagnetic radiation and gas spectroscopy and they have generally improved our understanding of eruption dynamics other work has incorporated infrasound into volcano surveillance to enhance capabilities for monitoring hazardous volcanoes and reducing risk this paper aims to provide an overview of volcano airwave studies from analog microbarometer to modern pressure transducer and summarizes how infrasound is currently used to infer eruption dynamics it also outlines the relative merits of local and regional infrasound surveillance highlights differences between array and network sensor topologies and concludes with mention of sensor technologies appropriate for volcano infrasound study

characteristics and source modeling of broadband seismic signals associated with the hydrothermal system at satsuma iwojima volcano japan abstract the broadband seismic data observed at satsuma iwojima volcanic island in southwestern japan show a wide variety of interesting features one of them is the periodic and frequency dependent amplitude modulation of volcanic tremors another interesting feature is the occurrence of very long period vlp seismic pulses synchronized with the tremor amplitude modulation both the tremor amplitude modulation and the vlp pulses have fairly regular intervals of 46 50 min suggesting a spatially fixed non destructive repetitive source we performed waveform inversions to reveal the source mechanism of the vlp pulses assuming a point source embedded in a medium that realistically represented the topography of the island numerical tests showed that the green s functions used in the inversion were significantly affected by the topography the observed vlp pulses were well explained by the rapid expansion of an inclined crack 100 m beneath the floor of the summit crater which had a seismic moment of 3 10 10 nm both the characteristic amplitude modulation and the vlp pulses are explained systematically by a model consisting of a water filled crack and a network of gas paths the water filled crack was heated above the boiling temperature of the water in it a sudden break of the unstable superheated state caused sudden vaporization and a pressure increase which was observed as the vlp pulse the network of gas paths consisted of swollen portions and constricted portions which worked as tremor generators when vapor from the water filled crack passed through

seismic and infrasound signals at mt etna modeling the north east crater conduit and its relation with the 2008 2009 eruption feeding system abstract on 13 may 2008 an eruption began at mt etna from an eruptive fissure that opened on the upper eastern flank of the volcano during 12 13 may 157 infrasonic events together with the related seismic transients were collected we carried out several analyses to obtain dominant frequencies pseudospectrograms peak to peak amplitudes source locations and time lags between infrasonic and seismic events spectra of the infrasonic events show two main spectral peaks in the frequency bands 0 4 0 7 hz and 1 5 2 0 hz respectively both infrasonic and seismic events were separately located below the north east crater where no eruptive activity was observed moreover significant changes in infrasound spectral content as well as in the infrasonic seismic lags were found a few hours before the beginning of the eruption on the basis of the collected information the infrasound source mechanism was modeled as a superposition of pipe and helmholtz resonance also leading to outline the geometry of the shallower portion of the north east crater plumbing system the occurrence of these seismo infrasonic events together with other geological and geophysical evidences led us to inferring a direct link between north east crater activity and the eruptive fissure further based on variations over time of both spectral features and seismic infrasonic time lag shallowing phenomena of the free magma column inside north east crater conduit were hypothesized such an uprise of magma was likely caused by a pressure increase inside the plumbing system occurring before the beginning of the 2008 2009 eruption

on the volcanic waveguide an analytical solution for the sound field in a resonant magma conduit with depth dependent magma properties provides a versatile interpretative tool for the analysis of seismoacoustic signals generated by fluid processes in active volcanoes expressions are given for the acoustic field in the atmosphere and the seismic field in the ground radiated through the magma conduit vent and walls respectively a new source model allows the resonance in the conduit to be excited by the vertical fluid velocity at the bottom of the conduit this source model represents acoustic excitation induced by low frequency fluid oscillations or large volume fluctuations originating at depth the magma conduit is modeled as a three section duct with each section having a different density sound speed viscosity and dimension the modal structure of the coupled resonant system is retained as the sound field in the conduit propagates into the surrounding bedrock and the overlying atmosphere the source time function permits estimates of the total mass injected or removed from the magmatic system and the source spectrum acts as a band pass filter on the resonant modes of the conduit theoretical or empirical source functions can be used to drive the seismoacoustic wave field and the amplitude of the source velocity may be constrained by the ballistics of pyroclasts and the height of ash plumes the acoustic properties of the melt may be predicted from the temperature composition and flow conditions of the magma as a function of depth comparisons of synthetic waveforms and spectra with those of seismic and acoustic signals recorded on active volcanoes permit estimates of the conduit geometry density sound speed and attenuation properties of the melt and characterize the temporal and spectral features of the source function the ability to extract this information accurately and efficiently from seismic and acoustic data streams may permit near real time modeling of fluid driven processes in active volcanoes

mapping complex vent eruptive activity at santiaguito guatemala using network infrasound semblance pyroclastic laden explosive eruptions from santiaguito volcano guatemala are vented from the 200 m diameter caliente dome summit and result in a superposition of spatially extensive and temporally sustained tens of seconds to minutes acoustic sources a network of infrasonic microphones distributed on various sides of the volcano record distinct waveforms which are poorly correlated across the network and suggestive of acoustic interference from multiple sources presuming the infrasound wavefield is a linear superposition of spatially and temporally distinct sub events we introduce a semblance mapping technique to recover the time history of the spatially evolving sources during successive time windows coincident high resolution video footage corroborates that both rapid dome uplift and individual explosive pulses are likely sources of high semblance infrasound that are identifiable during short 2 s time windows this study suggests that complex and network variable infrasound waveforms are produced whenever a volcanic vent source dimension is large compared to the wavelength of the sound being produced non compact infrasound radiators are probably commonplace at silicic volcanic systems where venting often occurs across a dome surface

three dimensional volcano acoustic source localization at karymsky volcano kamchatka russia abstract we test two methods of 3 d acoustic source localization on volcanic explosions and small scale jetting events at karymsky volcano kamchatka russia recent infrasound studies have provided evidence that volcanic jets produce low frequency aerodynamic sound jet noise similar to that from man made jet engines for man made jet noise noise sources localize along the turbulent jet flow downstream of the nozzle discrimination of jet noise sources along the axis of a volcanic jet requires high resolution in the vertical dimension which is very difficult to achieve with typical volcano acoustic network geometries at karymsky volcano an eroded edifice dvor caldera adjacent to the active cone provided a platform for the deployment of five infrasound sensors in july 2012 with intra network relief of 600 m the network was designed to target large scale jetting but unfortunately only small scale jetting and explosions were recorded during the 12 day experiment a novel 3 d inverse localization method srcloc is tested and compared against a more common grid search semblance technique simulations using synthetic signals show that srcloc is capable of determining vertical solutions to within 150 m or better for signal to noise ratios 1 for this network configuration however srcloc locations for explosions and small scale jetting at karymsky volcano show a persistent overestimation of source elevation and underestimation of sound speed the semblance method provides more realistic source locations likely because it uses a fixed realistic sound speed of 340 m s explosion waveforms exhibit amplitude relationships and waveform distortion strikingly similar to those theorized by modeling studies of wave diffraction around the crater rim we suggest that the delay of acoustic signals and apparent elevated source locations are due to raypaths altered by topography and or crater diffraction effects implying that topography in the vent region must be accounted for when attempting 3 d volcano acoustic source localization though the data presented here are insufficient to resolve small scale jet noise sources similar techniques may be successfully applied to large volcanic jets in the future

seismoacoustic investigations of paroxysmal activity at mt etna volcano new insights into the 16 november 2006 eruption 1 on 16 november 2006 a 1 day long paroxysmal eruption occurred at the summit craters of mt etna volcano a multiparametric approach consisting of analyzing infrasonic seismic and video camera recordings was carried out to follow its evolution volcanological and geophysical observations identified three eruptive phases in the first phase infrasonic and seismic characteristics reflected the highly explosive nature of the activity waveform characterization of infrasound events confirmed the activity of the several explosive vents at the summit of southeast crater sec during the second phase results highlighted the decoupling between seismic and infrasonic sources which was due to the decrease in explosive activity and the reactivation of effusive vents located south of bocca nuova and on the saddle between bocca nuova and sec the third phase was the most intense and was characterized by various volcanic phenomena pyroclastic flows jets of dark ash and white steam the very high radiated infrasonic energy together with infrasound event features led us to infer a gas enrichment of the shallow magma column preceding by a few minutes and likely related to the pyroclastic flows in the sec area after the eruption at sec variations in infrasound events related to the activity of northeast crater nec were found the observed spectral changes and the source mechanism modeling of the nec infrasound events suggest the existence of a link in the plumbing system feeding the two craters

source process of long period seismic events at taal volcano philippines vapor transportation and condensation in a shallow hydrothermal fissure 1 we analyzed observations of a swarm of more than 40 000 long period lp seismic events at taal volcano philippines in 2010 2011 the event waveforms are strongly correlated to each other consistent with a fixed source location and begin with a dilatational first motion they have a peak frequency around 0 8 hz and a quality factor q of 6 waveform inversion of the events pointed to a tensile crack source dipping 30 60 at a shallow 100 200 m depth a simulation using a fluid filled crack model indicated that the complex frequencies of the waveforms are explained by the fundamental longitudinal mode resonance of a vapor filled crack 188 m long a satellite thermal infrared image acquired during the swarm period suggests that the lp events were not accompanied by surface gas releases we considered a vapor transportation model in which vapor exsolved from magma and rose in a fissure extending to the lp source this model yielded estimates that 105 107 m3 of magma was involved in the lp swarm and that the temperature of vapor in the lp source crack was around 600 k we modeled a triggering mechanism of the crack resonance based on sudden condensation of vapor at the crack tip in a cold aquifer this model explained observed characteristics of the events including the dilatational first motion the total volumetric change and the fixed source location

excitation of a buried magmatic pipe a seismic source model for volcanic tremor recent observations of seismic events at various volcanoes suggest that harmonic tremor results from the sustained occurrence of so called long period or low frequency events accordingly we can view the long period volcanic event as the elementary process of tremor and interpret it as the impulse response of the tremor generating system we present a seismic model in which the source of tremor is the acoustic resonance of a fluid filled volcanic pipe triggered by excess gas pressure the model consists of three elements namely a triggering mechanism a resonator and a radiator for simplicity we assume a hemispherical trigger cylindrial resonator and circular radiator set in a vertical configuration with the trigger capping the top of the pipe and the disk shaped radiator shutting off its bottom considering the simple case of a source buried in a homogeneous half space we then apply the discrete wave number method to obtain a complete representation of the ground motion response at near and intermediate distances the results demonstrate that the displacement attributed to the pipe dominates the near field motion while that due to the disk is representative of the intermediate and far fields the trigger itself has a smaller contribution mainly limited to the field in the proximity of the source the characteristics displayed by the free surface response evolve from a strong impulsive signature in the immediate vicinity of the epicenter to a well developed harmonic wave train dominated by rayleigh waves at larger distances no clear shear arrival can be detected in the synthetic seismograms the displacement spectrum reflects the organ pipe modes of the conduit and the bandwidth associated with the dominant spectral peak of motion is controlled by the combined losses due to viscous attenuation in the fluid and elastic radiation into the solid in the case of the cylindrical magma column considered the radiation loss is proportional to the square of the pipe radius while the loss related to viscous damping is inversely proportional to the same factor indicating that the relative importance of the two loss mechanisms is critically dependent on the geometry of the magma reservoir the relative importance of the pipe and disk elements likewise is a function of the conduit cross section this suggests the possibility of determining the geometry of the source as well as the radiation loss and in situ magma viscosity from a comparison of near and far field observations

influence of atmospheric structure and topography on infrasonic wave propagation the effects of topography and atmospheric structures on infrasonic wave propagation from a volcanic source were investigated using observations and numerical modeling this paper presents the first long term observational data set showing spatiotemporal variations in patterns of infrasound propagation at distances of up to 60 km from a persistently active infrasound source sakurajima volcano japan the data show that the amplitudes of infrasonic waves received at distant stations relative to those received at a reference station close to the source can vary up to an order of magnitude over short time intervals and short distances and that they do not follow the theoretical geometric decay expected for homogeneous media moreover waveforms also change significantly in both time and space numerical simulations were performed using a two dimensional finite difference time domain 2 d fdtd method effects of atmospheric structure and topography are included in a vertical section parallel to the wave propagation direction the simulation successfully reproduced the variations of amplitudes and waveforms results are interpreted in terms of wave refraction due to sound and wind speed gradients and wave diffraction at topographic barriers our numerical results indicate that both atmospheric and topographic propagation effects are nonnegligible to evaluate the propagation effects and determine source processes in spatially and temporally varying infrasound data atmospheric data with a time resolution higher than is currently available are required if the data are available the present results suggest that the propagation effects could be evaluated using 2 d fdtd modeling at realistic calculation times

towards an automatic monitoring system of infrasonic events at mt etna strategies for source location and modeling active volcanoes characterized by open conduit conditions generate sonic and infrasonic signals whose investigation provides useful information for both monitoring purposes and studying the dynamics of explosive processes in this work we discuss the automatic procedures implemented for a real time application to the data acquired by a permanent network of five infrasound stations running at mt etna volcano the infrasound signals at mt etna consist in amplitude transients called infrasound events the adopted procedure uses a multi algorithm approach for event detection counting characterization and location it is designed for an efficient and accurate processing of infrasound records provided by single site and array stations moreover the source mechanism of these events can be investigated off line or in near real time by using three different models 1 strombolian bubble 2 resonating conduit and 3 helmholtz resonator the infrasound waveforms allow us to choose the most suitable model to get quantitative information about the source and to follow the time evolution of the source parameters

seismoacoustic recordings of small earthquakes in the pyrenees experimental results an experiment was conducted in the lesponne valley central french pyrenees to record the sounds that frequently accompany earthquakes in this region seismic and acoustic signals of a short period seismometer and a condenser microphone were continuously monitored for ten months during this period four small m l p transmission but also sv to p conversion into the atmosphere are identified thus confirming former hypotheses formulated by hill et al 1976 unambiguous quantitative constraints on the seismic to acoustic conversion are provided by the computation of transmission coefficients the dominant audio frequencies are recorded in the 5 to 60 hz band that is at the boundary between sounds and infrasounds and at the lower bound of human audibility high frequency infrasounds about 8 hz are interpreted as the transmission to the atmosphere of rayleigh waves induced locally by a thin soil layer

multistation infrasonic observations of the chilean earthquake of 2005 june 13 summary on 2005 june 13 a major earthquake m7 8 occurred in the tarapaca region north chile within the region of high mountains at large distances from the epicentre this event produced coherent infrasonic waves detected by three infrasound stations that are part of the international monitoring system the observed azimuth variations and the long signal durations suggest that wide regions in the andes mountains radiated infrasonic waves from these observations the main sources regions are reconstructed such an event recorded by multiple stations offers an unique opportunity to evaluate the relative contributions of the different source mechanisms involved in large earthquakes as well as to improve our understanding of the amplification of ground displacement caused by the topography with a review of infrasound signals from past earthquakes extended empirical scaling relations are derived we show that beyond the seismic magnitude both seismic source and topographic features also play a predominant role in the generation of infrasound

long period seismicity and very long period infrasound driven by shallow magmatic degassing at mount pagan mariana islands long period lp seismicity and very long period infrasound ivlp were recorded during continuous degassing from mount pagan mariana islands in july 2013 to january 2014 the frequency content of the lp and ivlp events and delay times between the two arrivals were remarkably stable and indicate nearly co located sources using phase weighted stacking over similar events to dampen noise we find that the lp source centroid is located 60 m below and 180 m west of the summit vent the moment tensor reveals a volumetric source modeled as resonance of a subhorizontal sill intersecting a dike we model the seismoacoustic wavefields with a coupled earth air 3 d finite difference code the ratios of pressure to velocity measured at the infrasound arrays are an order of magnitude larger than the synthetic ratios so the ivlp is not the result of lp energy transmitting into the atmosphere at its epicenter based on crater shape and dimensions determined by structure from motion we model the ivlp as acoustic resonance of an exponential horn the source of the continuous plume from gas analysis is shallow magmatic degassing which repeatedly pressurized the dike sill portion of the conduit over the 7 months of observation periodic gas release caused the geologically controlled sill to partially collapse and resonate while venting of gas at the surface triggered resonance in the crater lp degassing only accounts for 12 of total degassing indicating that most degassing is relatively aseismic and that multiple active pathways exist beneath the vent

earthquake classification location and error analysis in a volcanic environment implications for the magmatic system of the 1989 1990 eruptions at redoubt volcano alaska abstract determination of the precise locations of seismic events associated with the 1989 1990 eruptions of redoubt volcano posed a number of problems including poorly known crustal velocities a sparse station distribution and an abundance of events with emergent phase onsets in addition the high relief of the volcano could not be incorporated into the hypoellipse earthquake location algorithm this algorithm was modified to allow hypocenters to be located above the elevation of the seismic stations the velocity model was calibrated on the basis of a posteruptive seismic survey in which four chemical explosions were recorded by eight stations of the permanent network supplemented with 20 temporary seismographs deployed on and around the volcanic edifice the model consists of a stack of homogeneous horizontal layers setting the top of the model at the summit allows events to be located anywhere within the volcanic edifice detailed analysis of hypocentral errors shows that the long period lp events constituting the vigorous 23 hour swarm that preceded the initial eruption on december 14 could have originated from a point 1 4 km below the crater floor a similar analysis of lp events in the swarm preceding the major eruption on january 2 shows they also could have originated from a point the location of which is shifted 0 8 km northwest and 0 7 km deeper than the source of the initial swarm we suggest this shift in lp activity reflects a northward jump in the pathway for magmatic gases caused by the sealing of the initial pathway by magma extrusion during the last half of december volcano tectonic vt earthquakes did not occur until after the initial 23 hour long swarm they began slowly just below the lp source and their rate of occurrence increased after the eruption of 01 52 ast on december 15 when they shifted to depths of 6 to 10 km after january 2 the vt activity migrated gradually northward this migration suggests northward propagating withdrawal of magma from a plexus of dikes and or sills located in the 6 to 10 km depth range precise relocations of selected events prior to january 2 clearly resolve a narrow steeply dipping pencil shaped concentration of activity in the depth range of 1 7 km which illuminates the conduit along which magma was transported to the surface a third event type named hybrid which blends the characteristics of both vt and lp events originates just below the lp source and may reflect brittle failure along a zone intersecting a fluid filled crack the distribution of hybrid events is elongated 0 2 0 4 km in an east west direction this distribution may offer constraints on the orientation and size of the fluid filled crack inferred to be the source of the lp events

acoustically induced seismic waves when an airborne acoustic wave is incident at the ground surface energy is coupled into the ground as seismic motion in a previous publication sabatier et al j acoust soc am 78 1345 1352 1986 the ground surface was modeled as an air filled poroelastic layer overlying a semi infinite nonporous elastic substrate in this work the model is extended to include calculations of the normal seismic transfer function ratio of the normal soil particle velocity at a depth d to the acoustic pressure at the surface measurements of the seismic transfer function for three sites are considered and compared to the predicted values generally good agreement between theory and experiment is achieved by best fits assuming the soil or seismic attenuation this is accomplished by specifying the ratio of the imaginary to real part of the measured seismic p and s wave speeds the seismic transfer functions quite typically exhibit minima and maxima which are associated with the seismic layering of the ground su

blast waves from violent explosive activity at yasur volcano vanuatu 1 infrasonic and seismic waveforms were collected during violent strombolian activity at yasur volcano vanuatu averaging 3000 seismic events showed stable waveforms evidencing a low frequency 0 1 0 3 hz signal preceding 5 6 s the explosion infrasonic waveforms were mostly asymmetric with a sharp compressive 5 106 pa onset followed by a small long lasting rarefaction phase regardless of the pressure amplitude the ratio between the positive and negative phases was constant these waveform characteristics closely resembled blast waves infrared imagery showed an apparent cold spherical front 20 m thick which moved between 342 and 405 m s before the explosive hot gas fragments cloud we interpret this cold front as that produced by the vapor condensation induced by the passage of the shock front we suggest that violent strombolian activity at yasur was driven by supersonic dynamics with gas expanding at 1 1 mach number inside the conduit

an infrasound array study of mount st helens the ongoing activity of mount st helens provides an opportunity to study the infrasonic wavefield produced by an active silica rich volcano in late october 2004 as a pilot experiment for the acoustic surveillance for hazardous eruptions ashe project we deployed two infrasound arrays each co located with a broadband seismometer and weather station to continuously record seismo acoustic signals from mount st helens the nearest array coldwater was deployed on the northern flank of the volcano 13 km from the summit the second array sacajawea was deployed 250 km east of the volcano at a distance where stratospherically ducted acoustic waves may be expected during the winter this paper presents an overview of the experimental setup and preliminary results from this unique data set eruptions on january 16th 2005 and march 9th 2005 produced strong infrasonic signals the aseismic january 16th eruption signal lasted 9 4 min beginning at 11 20 44 01 16 05 utc while the march 9th eruption signal lasted 52 8 min beginning at 01 26 17 03 09 05 utc with the main steam and ash venting stage probably lasting 7 2 min the march 9th signal was an order of magnitude larger than the january 16th signal and was clearly recorded 250 km east at the sacajawea array infrasonic expressions of long period lp seismic events drumbeats have also been intermittently observed and are recorded as acoustic waves mimicking the waveform and temporal sequence of their seismic counterparts these acoustic observations provide important constraints for source models of long period events and eruptions

effects of volcano topography on seismic broad band waveforms volcano seismology often deals with rather shallow seismic sources and seismic stations deployed in their near field the complex stratigraphy on volcanoes and near field source effects have a strong impact on the seismic wavefield complicating the interpretation techniques that are usually employed in earthquake seismology in addition as most volcanoes have a pronounced topography the interference of the seismic wavefield with the stress free surface results in severe waveform perturbations that affect seismic interpretation methods in this study we deal predominantly with the surface effects but take into account the impact of a typical volcano stratigraphy as well as near field source effects we derive a correction term for plane seismic waves and a plane free surface such that for smooth topographies the effect of the free surface can be totally removed seismo volcanic sources radiate energy in a broad frequency range with a correspondingly wide range of different fresnel zones a 2 d boundary element method is employed to study how the size of the fresnel zone is dependent on source depth dominant wavelength and topography in order to estimate the limits of the plane wave approximation this approximation remains valid if the dominant wavelength does not exceed twice the source depth further aspects of this study concern particle motion analysis to locate point sources and the influence of the stratigraphy on particle motions furthermore the deployment strategy of seismic instruments on volcanoes as well as the direct interpretation of the broad band waveforms in terms of pressure fluctuations in the volcanic plumbing system are discussed