231pa 230th fractionation by ocean transport biogenic particle flux and particle type 231pa and 230th are removed from the water column by a process of reversible scavenging which quickly removes 230th to the sediment 231pa is less efficiently scavenged onto particles than 230th and is therefore more effectively transported via advection and diffusion before it reaches the ocean sediment this study combines particle fields dust opal caco3 poc derived from observations with the bern3d intermediate complexity ocean model and an equilibrium scavenging model for isotopes the equilibrium partition coefficient for particulate versus dissolved isotope activity is varied with particle type the model can explain many of the features of the global 231pa and 230th distribution the success of such a simple model at representing the global pattern of 231pa 230th activity ratio supports the use of this proxy in paleoceanographic studies we use the model to address the controversy concerning which particle types are dominant in fractionating 231pa 230th in the ocean the lithogenic dust flux is found to be unimportant for 231pa 230th fractionation the ocean fractionation of 231pa 230th is dominated by the distribution of the caco3 and opal flux we also confirm that opal is a weak scavenger of 230th

very long period oscillations of mount erebus volcano as the signal decays vlp scalar moments up to 5 10 11 n m exceed sp moments by an order of magnitude or more suggesting distinct though genetically related sp and vlp source mechanisms we conclude that vlp signals arise from excitation of a quasi linear resonator that is intimately associated with the conduit system and is excited by gravity and inertial forces associated with gas slug ascent eruption and magma recharge vlp signal stability across hundreds of eruptions spanning 5 years the persistence of the lava lake and the rapid posteruptive lava lake recovery indicate a stable near summit magma reservoir and vlp source process index terms 4544 oceanography physical internal and inertial waves 7280 seismology volcano seismology 8419 8414 volcanology eruption mechanisms 8419 volcanology eruption monitoring 7280 keywords strombolian very long period volcano seismology

source mechanism of very long period signals accompanying dome growth activity at merapi volcano indonesia 1 very long period vlp pulses with period of 6 7s displaying similar waveforms were identified in 1998 from broadband seismographs around the summit crater these pulses accompanied most of multiphase mp earthquakes a type of long period event locally defined at merapi volcano source mechanisms for several vlp pulses were examined by applying moment tensor inversion to the waveform data solutions were consistent with a crack striking 70 and dipping 50 sw 100m under the active dome suggest pressurized gas transport involving accumulation and sudden release of 10 60 m3 of gas in the crack over a 6s interval

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

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

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

broadband seismic observation at the sakurajima volcano japan we installed a portable broadband seismometer streckeisen sts 2 at the sakurajima volcano which has been very active in the recent years the recorded seismograms show a wide variety both in temporal and spectral contents of seismic events from explosions to tremors and exhibit the importance of such broadband seismometry at volcanos we present examples of seismograms to show the potential of broadband seismic observation in monitoring volcanic activities

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

highlights from a seismic broadband array on stromboli volcano an array of nine three component broadband seismometers was deployed in two different configurations on stromboli volcano the analysis of the seismic wavefield related to volcanic explosions revealed some observations which offer a completely new insight into the internal dynamics of a volcano these new observations are restricted to the low frequency range below 1 hz and underline therefore the superiority of broadband recordings over conventional short period observations surprisingly simple wavelets indicate an initially contracting source mechanism gas jets that could not be seen in a short period seismic record at all generate a clear dilatational wavelet in a broadband recording suggesting the same contracting source mechanism the analysis of particle motion and seismic array techniques permits a location of the seismic source we find low frequency signals of 3s and 6s period that are not related to eruptions and do not share a common source with the eruption related events a video recording of visible volcanic activity at the crater region allows one to correlate precisely eruptive features with seismic signals

assessing the depth resolution of tomographic models of upper mantle structure beneath iceland 1 earlier inversions of body wave delay time data recorded during the icemelt portable broadband experiment imaged a cylindrical plume like low velocity anomaly extending to at least 400 km depth beneath iceland but the depth extent of the anomaly resolvable by tomography has recently been called into question we have performed several additional resolution tests to evaluate the depth resolution of tomographic models of the icelandic upper mantle the distribution of paths of body waves recorded by icemelt can distinguish among three different types of models a a wide and shallow anomaly b a narrow and deep anomaly and c a narrow and shallow anomaly while tomographic models contain an element of nonuniqueness these tests illustrate that the depth resolution of passive seismic experiments spanning subaerial iceland is adequate for distinguishing among alternative geodynamic models

analysis of long period seismic waves excited by the may 18 1980 eruption of mount st helens a terrestrial monopole long period 100 to 260 s love and rayleigh waves excited by the eruption of mount st helens on may 18 1980 and recorded by ida sro and asro stations were analyzed to determine the mechanism of the eruption the amplitude radiation patterns of both rayleigh and love waves are two lobed with a nodal direction in e5 s for rayleigh waves and in n5 e for love waves these radiation patterns preclude any double couple mechanism the radiation pattern the initial phase the relatively large amplitude ratio of love to rayleigh waves and the existence of clear nodes in the radiation patterns of fundamental mode and higher mode rayleigh waves suggest that the source is represented by an almost horizontal less than 15 from the horizontal single force pointed toward s5 w the surface wave spectra fall off very rapidly at periods shorter than 75 s suggesting a very slow source process although the details of the source time history could not be determined a smooth bell shaped time function f o s t 1 2 f o l cos t for 0 t 2 and f o s t 0 for t 2 with 75 s is considered appropriate on the basis of comparison between synthetic and observed seismograms and of the shape of the source spectrum the peak value of the force f 0 is about 10 18 dynes the tailing end of the source time function could not be resolved and some overshoot may be added the magnitude and the time history of the force can be explained by a northward landslide followed by a lateral blast observed at the time of the eruption two distinct events about 110 s apart can be identified on body wave and short period surface wave records the first event may correspond to the earthquake which triggered the landslide and the lateral blast the second event appears to correspond to a second large earthquake and explosion which took place about 2 minutes after the first earthquake

mechanism of phreatic eruptions at aso volcano inferred from near field broadband seismic observations broadband seismometers deployed at aso volcano in japan have detected a hydrothermal reservoir 1 to 1 5 kilometers beneath the crater that is continually resonating with periods as long as 15 seconds when phreatic eruptions are observed broadband seismograms elucidate a dynamic interplay between the reservoir and discharging flow along the conduit gradual pressurization and long period 20 seconds pulsations of the reservoir during the 100 to 200 seconds before the initiation of the discharge followed by gradual deflation of the reservoir concurrent with the discharging flow the hydrothermal reservoir where water and heat from the deeper magma chamber probably interact appears to help control the surface activity at aso volcano

very long period signals associated with vulcanian explosions at popocatepetl volcano mexico very long period vlp seismic signals associated with large summit eruptions of popocatepetl volcano in the last four years are investigated using data from a broadband seismometer 0 04 120 s deployed on the north flank of the volcano at a radial distance of 5 km from the active crater the vlp signals associated with individual eruptions share similar waveforms discrete vlp signals accompanying long period lp events also share similar signatures and have dominant periods that are nearly identical to those observed in the vlp waveforms of explosions the vlp particle motions for eruption onsets consistently point to a source located a few km beneath the crater the vlp ground displacement response to each explosion is marked by a compression followed by a dilatation and terminating with another compression suggesting a sequence of pressurization depressurization repressurization of the conduit the repetitive nature of the waveforms points to a non destructive source process which has remained active in the magmatic system of popocatepetl at least since april 1997

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

gas slug ascent through changes in conduit diameter laboratory insights into a volcano seismic source process in low viscosity magmas seismic signals generated during the flow and degassing of low viscosity magmas include long period lp and very long period vlp events whose sources are often attributed to dynamic fluid processes within the conduit we present the results of laboratory experiments designed to investigate whether the passage of a gas slug through regions of changing conduit diameter could act as a suitable source mechanism a vertical liquid filled glass tube featuring a concentric diameter change was used to provide canonical insights into potentially deep or shallow seismic sources as gas slugs ascend the tube we observe systematic pressure changes varying with slug size liquid depth tube diameter and liquid viscosity gas slugs undergoing an abrupt flow pattern change upon entering a section of significantly increased tube diameter induce a transient pressure decrease in and above the flare and an associated pressure increase below it which stimulates acoustic and inertial resonant oscillations when the liquid flow is not dominantly controlled by viscosity net vertical forces on the apparatus are also detected the net force is a function of the magnitude of the pressure transients generated and the tube geometry which dictates where and hence when the traveling pressure pulses can couple into the tube in contrast to interpretations of related volcano seismic data where a single downward force is assumed to result from an upward acceleration of the center of mass in the conduit our experiments suggest that significant downward forces can result from the rapid deceleration of relatively small volumes of downward moving liquid

source process of very long period seismic events associated with the 1998 activity of iwate volcano northeastern japan we observed very long period seismic events that are associated with the 1998 activity of iwate volcano northeast japan the events show a dominant period of 10 s and duration of 30 60 s often with accompanying short period waves at the beginning and at the end of the long period signals by analyzing the broadband seismograms we find that the source elongates in the east west direction for 4 km at a depth of 2 km beneath the western part of iwate volcano results of moment tensor inversions show a source mechanism of mutual deflation and inflation of two chambers located at the western and eastern edges of the source region the source region coincides with the low seismic velocity zone detected by seismic tomography and is very close to the locations of pressure sources estimated from crustal deformation data on the basis of these results we infer that the very long period seismic events are generated by transportation and movement of magmatic fluid hot water and or magma in a shallow part of the volcano we further present a simple source model of very long period seismic events based on one dimensional flow dynamics and propose a new parameter to characterize the size of very long period event the energy flow rate which is obtained by dividing the seismic moment by the dominant period the energy flow rate was estimated as 3 1 1012 j s for the event on july 29 1998

limited fluid rock interaction at marble gneiss contacts during cretaceous granulite facies metamorphism seward peninsula alaska stable isotope profiles show that flat lying marble units acted as impermeable barriers to upward fluid flow in transitional amphibolite granulite grade rocks of the kigluaik mountains seward peninsula alaska the degree of permeability is related to the composition of the marble the margin of a thick pure dolomite marble chemically reacted with underlying metasyenite ah2o 0 2 to form a 2 cm boundary layer of calcite forsterite by introduction of sio2 no fluid penetrated past this reaction front although the high temperature of metamorphism 800 c allowed transport of carbon and oxygen isotopes for an additional 2 cm by diffusion through the solid dolomite a second marble with a higher silica content underwent more decarbonation which enhanced porosity and lead to a greater extent of isotope transport 2 3 m in contact with quartzo feld spathic gneiss below an estimate of total fluid flux across the bottom of this marble layer based on the shape of the isotope profile is 1 cm3 cm2 directed down out of the marble at two other marble gneiss contacts steep isotopic gradients coincide with lithologic contacts indicating very little cross lithology fluid flow the extent of diffusional transport of isotopes in the marbles is limited and interpreted as indicating the transient presence of a pore fluid generated by thermally driven devolatilization reactions no wholesale pervasive advection of c o h fluid occurred across the thick continuous marble units near the exposed base of the kigluaik group section during the entire regional metamorphic cycle activities of pore fluid species were controlled by internal processes movement of volatiles and stable isotopes between contrasting rock types was dominantly diffusive channelized fluid pathways through the marble units developed during uplift and cooling but were not present during peak metamorphism heating of the section occurred by conduction probably from an underlying magma source and not by advection of a c o h fluid

very long period seismic signals and caldera formation at miyake island japan over a period of roughly 40 days starting on 8 july 2000 a caldera structure 1 7 kilometers in diameter developed by means of gradual depression and expansion of the summit crater at miyake island japan at the same time very long period vlp seismic signals were observed once or twice a day source mechanism analyses of the vlp signals show that the moment tensor solutions are smooth step functions over a time scale of 50 seconds with dominant volumetric change components we developed a model to explain the caldera and the vlp signals in which a vertical piston of solid materials in the conduit is intermittently sucked into the magma chamber by lateral magma outflow this model offers potential for making quantitative estimations of the characteristic physical properties of magma systems

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

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

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

real time monitoring and massive inversion of source parameters of very long period seismic signals an application to stromboli volcano italy 1 we present a comprehensive processing tool for the real time analysis of the source mechanism of very long period vlp seismic data based on waveform inversions performed in the frequency domain for a point source a search for the source providing the best fitting solution is conducted over a three dimensional grid of assumed source locations in which the green s functions associated with each point source are calculated by finite differences using the reciprocal relation between source and receiver tests performed on 62 nodes of a linux cluster indicate that the waveform inversion and search for the best fitting signal over 100 000 point sources require roughly 30 s of processing time for a 2 min long record the procedure is applied to post processing of a data archive and to continuous automatic inversion of real time data at stromboli providing insights into different modes of degassing at this volcano

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

evidence for magma intrusion during the mammoth lakes earthquakes of may 1980 and implications of the absence of volcanic harmonic tremor the compensated linear vector dipole clvd mechanism p wave radiation with conical nodal surfaces found for the mammoth lakes earthquakes of may 1980 has been attributed to dike intrusion by julian and his colleagues there is a concern about this interpretation because magma intrusion through a crack should radiate compressional first motion everywhere chouet s calculation on a magma intrusion model however showed that the main dynamic motion as well as the final static displacement have patterns similar to the clvd mechanism we found an example of observed radiation pattern similar to the clvd mechanism from eruption earthquakes at mount aso obtained by sassa and we interpret the observation as misidentification of the main motion as the initial motion in searching for a similar misidentification for the mammoth lakes earthquakes we found that there are numerous reports of compression for short period p waves at stations where long period p waves show unequivocal dilatation furthermore we found that the compressional short period first motion is systematically earlier than the dilatational one these observations can be explained if the source of magma intrusion generated compressional first motions which were very weak and of high frequency contents in the direction where long period p waves are dilatational the seismic moment of the mammoth lakes earthquakes suggests an involvement of magma volume of the order of 10 2 km3 however we have not yet observed long period events or volcanic harmonic tremors which are often observed at active volcanos we review recent advances in theories and observations on volcanic tremor and conclude that for the volume of magma reservoir suggested for the mammoth lakes area a fluctuation of pressure of the order of 10 2 bar would generate measurable tremor this conclusion is obtained under the assumption that both the viscosity of magma and the radiation loss of the magma reservoir are low enough for the excitation of a harmonic tremor we found that the concept of reduced displacement introduced by aki and koyanagi for body waves and by fehler for surface waves is very useful for estimating the physical parameters of a volcanic tremor source

10s period volcanic tremors observed over a wide area in southwestern japan unusual seismic oscillations with a period of 10 seconds were observed over a wide area of southwestern japan several lines of evidence indicate that the origin of these 10s waves must be around the aso volcano located in the central part of kyushu island japan although a 10s period is unusually long for a volcanic tremor and no corresponding surface activity at the crater was reported by the local observatory the volcanic origin of the tremor is indisputable a further astonishing aspects of the observation is that there exists a strong correlation between the onset of 10s waves observed remotely and cessation of high frequency 1hz volcanic tremors at the aso volcano the aso volcano appears to be trembling with a 10s period without this having been noticed since seismic monitoring of volcanic activity is limited to high frequencies above 1 hz at the most of the volcanoes in the world long period tremors of the type observed here might be a widespread phenomenon that has been overlooked

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

ground motion in the near field of a fluid driven crack and its interpretation in the study of shallow volcanic tremor we present a study of the motion of the ground in the near field of a fluid driven tensile crack embedded in a layered half space the source that we consider is the jerky opening of a channel connecting two fluid filled cracks and the cause of this opening is the excess pressure of fluid in one of the cracks we make a complete representation of the three components of ground motion in the space time and frequency domains and analyze the effects of fluid compressibility source depth and medium structure on the ground response the calculations show the presence of a dominant frequency of motion which depends not only on the source geometry and bulk modulus of the fluid but also on medium characteristics receiver position and the component of motion being considered using this source model we view an episode of volcanic tremor as a continuous sequence produced by numerous jerky openings of channels occurring randomly in time along a chain of cracks our results are applied to the october 5 6 1963 east rift eruption of kilauea volcano hawaii and found to be compatible with available seismic data suggesting that magma is transported through an ensemble of cracks with the area of 1 1 km each pair of cracks constituting an individual dike segment which opens in discrete increments at a rate of 1 s we obtain the following parameters for each dike segment opening increase in cavity volume 40 m3 stress drop 0 004 bar seismic moment 1019 dyn cm and force applied by the fluid to open the dike 1014 dyn the total moment integrated over the entire duration of tremor for the eruption is 0 5 1024 dyn cm roughly equivalent to a single magnitude m 5 earthquake the seismic source parameters and other field observations offer constraints on the process of mass transport and are compatible with the excess pressure and viscosity of magma of about 40 bars and 102 p respectively

moment tensor analysis of near field broadband waveforms observed at aso volcano japan abstract locations and focal mechanisms of long period volcanic events observed at aso volcano japan are determined by waveform inversion near field broadband three component seismograms of four to seven stations are simultaneously inverted in the time domain in order to find the six component seismic moment tensor a linear inversion is performed at each point of a 3d grid located under the volcano in order to constrain the centroid position and the focal mechanism of the source the complete displacements including near field waves in a homogeneous half space for a general point source are taken into account inversions of 43 long period tremors and six phreatic eruptions exhibit mainly an isotropic mechanism with a minor deviatoric component that may originate from a north south trending crack these events are all located in a small region at about 1 3 km depth beneath the active crater the high accuracy both of locations a few hundred meters and of focal mechanisms given by the inversion is partly attributed to the rapid variation of the amplitude of the static displacement seen in the long period part of the near field seismograms