very long period volcanic tremor at stromboli italy we analyze a long time space series of stromboli volcanic tremors a very low frequency content in the range of 0 02 0 5 hz has been found by using spectral analysis and independent component analysis independent component analysis is an entropy based technique we observe the occurrence of a component having a period of 30 sec polarization analysis shows that the wave field comes mainly from the crater area well evidenced by seismometers located around the summit ring whereas the radiation becomes increasingly scattered at stations located around the base of this volcano based on its apparent velocity the 30 sec component appears to be a slow wave related to inhomogeneities of the source and or gas pressure fluctuations inside the shallow plumbing system

broadband recording of strombolian explosions and associated very long period seismic signals on mount erebus volcano ross island antarctica in december 1996 and january 1997 broadband seismometers were deployed on the summit plateau of mount erebus at radial distances of 0 7 1 4 and 1 9 km from the central crater and lava lake strombolian explosions at erebus previously have been observed to produce seismic and acoustic energy between 1 and 6 hz new observations document significant energy with spectral peaks as grave as 20 s nearly identical very long period vlp signals begin 1 5 s prior to explosions have dilatational onsets and persist for up to 150 s similar vlp waveforms were recorded at all three stations indicating that the seismograms are essentially source dominated particle motions suggest an initial depth for the vlp source of up to several hundred meters migrating deeper in the course of 15 s such explosion associated vlp signals may indicate a nondestructive lossy resonance or nonlinear fluid flow excitation within the shallow magmatic system

source process of very long period events accompanying long period signals at cotopaxi volcano ecuador abstract renewed seismic activity of cotopaxi ecuador began in january 2001 with the increased number of long period lp events followed by a swarm of volcano tectonic vt earthquakes in november 2001 in late june 2002 the activity of very long period vlp 2 s events accompanying lp 0 5 1 s signals began beneath the volcano the vlp waveform was characterized by an impulsive signature which was accompanied by the lp signal showing non harmonic oscillations we observed temporal changes of both the vlp and lp signals from the beginning until september 2003 the vlp signal gradually disappeared and the lp signal characterized by decaying harmonic oscillations became dominant assuming possible source geometries we applied a waveform inversion method to the observed waveforms of the largest vlp event our inversion and particle motion analyses point to volumetric changes of a sub vertical crack as the vlp source which is located at a depth of 2 3 km beneath the northeastern flank the spectral analysis of the decaying harmonic oscillations of lp events shows frequencies between 2 0 and 3 5 hz with quality factors significantly above 100 the increased vt activity and deformation data suggest an intrusion of magma beneath the volcano a release of gases with small magma particles may have repetitively occurred due to the pressurization which was caused by sustained bubble growth at the magma ceiling the released particle laden gases opened a crack above the magma system and triggered the resonance of the crack we interpret the vlp and lp events as the gas release process and the resonance of the crack respectively

crustal structure of the sheared southwestern barents sea continental margin abstract eighteen expanding spread profiles from the southwestern barents sea continental margin were studied with a variety of seismic interpretation techniques and in conjunction with seismic reflection data the velocity depth profiles from the slope intercept herglotz wiechert and sum methods were compared and contrasted to the velocity depth curve calculated from the iterative forward modelling of the amplitudes the velocity depth profiles derived from the sum and forward modelling of the amplitudes were used to produce synthetics in both the x t and p domains to choose the technique that most accurately represented the data the results showed the oceanic crust at the senja fracture zone to be different from standard oceanic crust with a higher than average velocity for layer 2 of 5 7 6 4 km s 1 and slightly smaller crystalline crustal thickness the continent ocean transition at crustal depths was shown to be narrow in the range of 10 20 km our results were consistent with two different crustal provinces east of the senja fracture zone the tertiary marginal basin and the cretaceous basin region the velocity depth curves enabled us in a gross sense to suggest the depths to deep sedimentary interfaces and the top of the crystalline crust that were normally not observed in the reflection profiles depths down to 20 km were inferred for the base of the sedimentary section in the southwestern barents sea the crust thinned gently towards the continent ocean boundary at the senja fracture zone whereas the crustal thickness changed abruptly below the hornsund fault zone at the margin farther north we associated the change in crustal structure with cenozoic in the thick crust beneath the svalbard platform in the north the depths to mantle determined on the shelf were consistent with that observed on a deep multichannel seismic line that crosses the area

broadband measurements of the sources of explosions at stromboli volcano italy during september october 1997 21 three component broadband seismometers were deployed on stromboli volcano at radial distances of 0 3 2 2 km from the active crater to investigate the source mechanisms of strombolian explosions in the 2 50 s band the very long period vlp signals associated with explosions are consistent with two stationary sources repeatedly activated in time vlp particle motions are essentially linear and analyses of semblance and particle motions are consistent with a source centroid offset 300 m beneath and 300 m northwest of the active vents similar vlp waveforms are observed at all 21 stations indicating that the seismograms are source dominated the vlp ground displacement response to each explosion may be qualitatively interpreted as 1 pressurization of the conduit associated with the ascent of a slug of gas 2 depressurization of the conduit in response to mass withdrawal during the eruption and 3 repressurization of the conduit associated with the replenishment of the source with fluid

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

modeling strombolian eruptions of karymsky volcano kamchatka russia a model is proposed to explain temporal patterns of activity in a class of periodically exploding strombolian type andesite volcanoes these patterns include major events explosions which occur every 3 30 min and subsequent tremor with a typical period of 1 s this two periodic activity is thought to be caused by two distinct mechanisms of accumulation of the elastic energy in the moving magma column compressibility of the magma in the conduit and viscoelastic response of the almost solid magma plug on the top a release of the elastic energy occurs during a stick slip dynamic phase transition in a boundary layer along the walls of the conduit this phase transition is driven by the shear stress accumulated in the boundary layer the intrinsic hysteresis of this first order phase transition explains the long periods of inactivity in the explosion cycle temporal characteristics of the model are found to be qualitatively similar to the acoustic and seismic signals recorded at karymsky volcano in kamchatka

a crustal study off lofoten n norway by use of 3 component ocean bottom seismographs abstract twenty four 3 component ocean bottom seismographs obs were used in august 1988 in a combined seismic refraction and reflection study off lofoten n norway the purpose of the experiment was to map the crustal structure from the continental shelf to the oceanic crust off lofoten the very high data quality is demonstrated by the strong p wave and shear wave reflections as well as converted waves from the moho observed on the continental shelf these arrivals are observed continuously from near vertical to wide angle incidence very high seismic sea floor velocities in this area 3 1 km s to 5 1 km s indicates absence or very thin sequences of mesozoic sediments the 5 1 km s refractor coincides with the base cretaceous reflection interpreted from the multichannel reflection data the crystalline continental crust is here divided in layers with velocities of 6 0 km s 6 4 km s and 6 8 km s respectively on the seaward side of the escarpment tertiary sediments varying in thickness from 1 0 1 5 km are situated on top of a 1 5 2 0 km thick layer of flood basalt containing seaward dipping reflectors a layer with velocity of 6 7 km s is observed above the lower crust which in this area is found to have a velocity as high as 7 3 km s these high velocities indicate that the crust in this area is of oceanic origin or alternatively the high velocity layer in the lower crust might represent a magmatic body underplating highly thinned and intruded continental crust seven obss were deployed in the area that was covered by landward flowing basalt deposited during the early eocene breakup between norway and greenland the survey was partly performed to investigate whether this method can be used to map structures below the basalt which is impenetrable with conventional seismic reflection techniques the obs data contain considerable information about structures below the flood basalt pre opening sediments up to 4 0 km thick are indicated below the 1 0 2 5 km thick landward flowing basalt the velocities of the crystalline portion of the crust are found to be similar to those observed under the continental shelf 6 0 6 8 km s which implies that the crust east of the escarpment is of continental origin the crystalline crust is strongly thinned in this area showing a minimum thickness of about 6 km the depth to the moho increases from about 15 km in the western part of the area to about 26 km on the continental shelf the success of the obs survey indicates that such measurements can become an important tool in investigations on passive volcanic margins and potentially in other areas where highly reflective surfaces make the reflection technique inefficient

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

identifying elements of the plumbing system beneath kilauea volcano hawaii from the source locations of very long period signals location of vlp signals at kilauea

vesiculation in magmas from stromboli and implications for normal strombolian activity and paroxysmal explosions in basaltic systems 1 we performed a series of x ray tomographic experiments and lattice boltzmann permeability simulations on pyroclastic products from explosive activity at stromboli between december 2004 and may 2006 we reconstructed the 3 d textures of vesicles to investigate the relationship between the nature of vesiculation in the erupted products and the dynamics of gas transport in the shallow conduit in order to derive implications for the eruptive behavior of basaltic volcanoes scoriae from normal strombolian explosions display remarkably consistent vesicle volume distributions fit by power laws with an exponent of 1 0 2 we ascribe the origin of such distributions to the combined effect of coalescence and continuous nucleation events in the steady state shallow magma system that supplies normal strombolian activity volume distributions and textures of vesicles in pumice clasts from the 5 april 2003 and 15 march 2007 paroxysmal activity are markedly different from those in the scoriae besides a power law function with a higher exponent portions of these distributions can be also fit by an exponential function suggesting the attempt of the system to reach near equilibrium conditions the investigated pumice clasts also lack the large connecting vesicles responsible for the development of degassing pathways in the stromboli magma that erupts the scoriae this testifies to a decreased degassing efficiency of the magma associated with paroxysmal explosions and potential overpressure buildup at depth by comparison with degassing experiments on basaltic melts we derive a time constraint on the order of minutes to hours for the incubation of paroxysms at stromboli

shallow velocity structure of stromboli volcano italy derived from small aperture array measurements of strombolian tremor abstract the properties of the tremor wave field at stromboli are analyzed using data from small aperture arrays of short period seismometers deployed on the north flank of the volcano the seismometers are configured in two semi circular arrays with radii of 60 and 150 m and a linear array with length of 600 m the data are analyzed using a spatiotemporal correlation technique specifically designed for the study of the stationary stochastic wave field of rayleigh and love waves generated by volcanic activity and by scattering sources distributed within the island the correlation coefficients derived as a function of frequency for the three components of motion clearly define the dispersion characteristics for both rayleigh and love waves love and rayleigh waves contribute 70 and 30 respectively of the surface wave power the phase velocities of rayleigh waves range from 1000 m sec at 2 hz to 350 m sec at 9 hz and those for love waves range from 800 to 400 m sec over the same frequency band these velocities are similar to those measured near puu oo on the east rift of kilauea volcano hawaii although the dispersion characteristics of rayleigh waves at stromboli show a stronger dependence on frequency such low velocities are consistent with values expected for densely cracked solidified basalt the dispersion curves are inverted for a velocity model beneath the arrays assuming those dispersions represent the fundamental modes of rayleigh and love waves

hidden dykes detected on ultra long period seismic signals at piton de la fournaise volcano broadband seismic data enable us to test whether ultra long period ulp signals can be used to investigate magma chamber pressure state and to monitor volcanic eruptions by systematically investigating seismic signals at geoscope station rer we find ulp signals associated with volcanic events during the last 2 decades we tentatively propose to interpret these signals as events highlighting the activity of the upper magma feeding system of the piton de la fournaise volcano and as being related to the deep magma chamber some of these unusual signals were previously detected and usually interpreted in term of tilt battaglia j aki k montagner j j p tilt signals derived from a geoscope vbb station on the piton de la fournaise volcano geophys res lett 27 5 2000 605 608 they are detected using sts1 seismometers sensitive in the bandwidth 10 3 to 10 2 hz this alternative model enables to quantify each event in terms of a pressure drop in the upper magma reservoir of the volcano two kinds of seismic waveforms can be associated with two types of fracturing events the first one is related to the fast rise of a magma batch coming from the deep magma chamber and the second is the result of a slow rise in pressure inside a shallow reservoir in both cases we are able to detect these events on very long period seismic data the interpretation of these signals supports the idea of a single magma source at the sea level thus we propose to classify all the eruptions occurring during the last two decades into two groups corresponding to the two primary pressure states of the magma chamber 2007 elsevier b v all rights reserved

long period events and tremor at popocatepetl volcano 1994 2000 and their broadband characteristics following an initial phreatic eruption on 21 december 1994 activity at popocatepetl has been dominated by fumarolic emissions interspersed with more energetic emissions of ashes and gases a phase of repetitive dome building and dome destroying episodes began in march 1996 and is still ongoing at present we describe the long period lp seismicity accompanying eruptive activity at popocatepetl from december 1994 through may 2000 using data from a three component broadband seismometer located 5 km from the summit crater the broadband records display a variety of signals with periods ranging in the band 0 04 90 s long period events and tremor with typical dominant periods in the range 0 3 2 0 s are the most characteristic signals observed at popocatepetl these signals appear to reflect volumetric sources driven by pressure fluctuations associated with the unsteady transport of gases beneath the crater very long period vlp signals are also observed in association with lp events and tremor the vlp signals which accompany lp events display ricker like wavelets with periods near 36 s whereas vlp signals associated with tremor waveforms typically show sustained oscillations at periods ranging up to 90 s the spectra and particle motion patterns remain similar from event to event for the majority of lp and tremor signals analyzed during the time span of this study suggesting a repeated non destructive activation of a common source hypocenters determined by phase pick analyses of selected lp events recorded by the seven station permanent popocatepetl short period network suggest that the majority of these events are confined to a source region in the top 1 5 km below the crater floor the repetitive occurrences of vlp signals with closely matched waveform characteristics are consistent with a non destructive reactivation of at least two sources one source appears to coincide with the main source region of lp seismicity whereas the second is a deeper source whose activity appears to be intimately linked with episodes of monochromatic tremor

seismoacoustic measurements during the july august 2001 eruption of mt etna volcano italy abstract on july 18 2001 two main eruptive vents opened on the southern flank of mount etna volcano italy at 2100 m and 2550 m a s l respectively the former vent fed mild strombolian activity and lava flows while the latter represented the main explosive vent producing strong phreato magmatic explosions explosions at this latter vent however shifted to a strombolian style in the following days before switching back to phreato magmatic activity towards the end of the eruption which ended on august 9 2001 on august 3 a small seismoacoustic array was deployed close to the eruptive vents the array was composed of three stations which recorded seismic and infrasonic waves coming from both of the eruptive vents a further seismoacoustic station equipped with a thermal infrared sensor was also installed several kilometers north of the first array seismic signals relating to the strombolian activity at the 2100 m vent were characterized by a strong decompression at the source analysis of the time delays between seismic infrasonic and infrared event onsets also revealed that ejection velocities during explosions from both vents were subsonic time delays between the onset of explosive events apparent in the infrared and infrasound data indicated that the explosion source at the 2550 m vent was located 220 250 m below the crater rim in comparison the depth of the seismic source was estimated to be between 230 and 335 m below the rim this converts to 120 150 and 130 235 m below the preexisting ground surface in addition time delays between seismic and infrasonic signals recorded for the lower 2100 m vent also revealed a seismic source that was no more than a few tens of meters deeper than the fragmentation surface

thermal seismic and infrasound observations of persistent explosive activity and conduit dynamics at santiaguito lava dome guatemala abstract in january 2003 we deployed a seismo acoustic array along with thermal sensors to define the dynamics and source characteristics of persistent intermittent explosive activity at the santiaguito lava dome guatemala seismic and acoustic waveforms accompanying thermal transients i e the thermal signature produced by the vertical ash plumes allowed discrimination of 35 explosions from minor degassing events during the 15 5 h observation period characteristics of thermal transients along with elastic and thermal energy flux from the explosive ash emissions allowed for a standardized measurement of eruption intensity duration frequency and repose interval using the thermal data we calculated a range of minimum exit velocities of 16 76 m s and convective rise rates of 9 26 m s to heights of 100 and 600 m above the vent source depths for the explosions were calculated using the thermo acoustic delay indicating a source 100 620 m below the vent the intensity of the explosions based on thermal amplitude and proxies for elastic energy released is not dependent on repose interval or depth the data support the notion for shear induced fragmentation at the conduit walls due to stick slip movement of the upper degassed part of the magma column as a source mechanism loci of explosion depths suggest that this operates within a 500 m thick dacite plug in the uppermost portion of the conduit

crustal structure across the southwest newfoundland transform margin a seismic refraction survey providing deep crustal structure information of the continent ocean boundary across the south west newfoundland transform margin was carried out using large air gun sources and ocean bottom seismometer receivers continental crust 30 km thick beneath the southern grand banks p wave velocity 6 2 6 5 km s thins oceanward to a 25 km wide transition zone in the transition zone paleozoic basement of the grand banks 5 5 5 7 km s is replaced by a basement of oceanic volcanics and synrift sediments 4 5 5 5 km s seaward of the transition zone the crust is oceanic in character with a velocity gradient from 4 7 to 6 5 km s and a thickness of 7 8 km oceanic layer 3 is absent no significant thickness of intermediate velocity 7 km s material is present at the continent ocean transition indicating that no under plating of continental crust has taken place the continent ocean transition across the transform margin is much narrower than across rifted margins supporting the

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

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

analysis of sustained long period activity at etna volcano italy abstract following the installation of a broadband network on mt etna sustained long period lp activity was recorded accompanying a period of total quiescence and the subsequent onset of the 2004 2005 effusive episode from about 56000 events detected by an automatic classification procedure we analyse a subset of about 3000 signals spanning the december 17th 2003 september 25th 2004 time interval lp spectra are characterised by several unevenly spaced narrow peaks spanning the 0 5 10 hz frequency band these peaks are common to all the recording sites of the network and different from those associated with tremor signals throughout the analysed time interval lp spectra and waveforms maintain significant similarity thus indicating the involvement of a non destructive source process that we interpret in terms of the resonance of a fluid filled buried cavity polarisation analysis indicates radiation from a non isotropic source involving large amounts of shear concurrently with lp signals recordings from the summit station also depict very long period vlp pulses whose rectilinear motion points to a region located beneath the summit craters at depths ranging between 800 and 1100 m beneath the surface based on a refined repicking of similar waveforms we obtain robust locations for a selected subset of the most energetic lp events from probabilistic inversion of travel times calculated for a 3d heterogenous structure lp sources cluster in a narrow volume located beneath the summit craters and extending to a maximum depth of 800 m beneath the surface no causal relationships are observed between lp vlp and tremor activities and the onset of the 2004 2005 lava effusions thus indicating that magmatic overpressure played a limited role in triggering this eruption these data represent the very first observation of lp and vlp activity at etna during non eruptive periods and open the way to the quantitative modelling of the geometry and dynamics of the shallow plumbing system

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

automatic detection and discrimination of volcanic tremors and tectonic earthquakes an application to ambrym volcano vanuatu abstract an algorithm of automatic detection and discrimination of volcanic tremors defined as events containing only p type wave and tectonic earthquakes containing both p and s waves is applied on data recorded on a 3 component sts 2 broad band seismometer installed from july to november 2000 at ambrym volcano vanuatu the algorithm consists in detecting p waves and if any s waves according to a modified version zhizhin m rouland d bonnin j gvishiani a burtsev a 2006 rapid estimation of earthquake source parameters from pattern analysis of waveforms recorded at a single 3 component station bull seism soc am 96 6 2329 2347 of the component energy comparison method cecm proposed by nagano et al nagano k niitsuma h chubachi n 1989 automatic algorithm for triaxial hodogram source location in downhole acoustic emission measurement geophysics 54 4 508 513 the duration and maximum amplitude are automatically measured for each volcanic tremor and for each tectonic earthquake with corresponding duration and amplitude magnitudes during the four and half months of observation 1959 local and regional tectonic earthquakes with epicentral distances estimated from s p interval time ranging from a few kilometres to about 800 km and 14942 volcanic tremors with duration ranging from 10 to 2000 s have been detected the gutenberg and richter laws of tectonic earthquakes and volcanic tremors are examined according to their duration and amplitude magnitudes and completeness of the corresponding catalogues is studied the observations on the coherence of some long duration volcanic tremors which display four different intermittencies 77 17 min 165 10 min 565 50 min 1065 50 min are interpreted as different types of degassing

dynamics of strombolian explosions inferences from field and laboratory studies of erupted bombs from stromboli volcano strombolian activity is characterized by repeated low energy explosions and is named after the volcano where such activity has persisted for around 2000 years i e stromboli aeolian islands italy stromboli represents an excellent laboratory where measurements of such explosions can be made from safe but close distances during a field campaign in 2008 two 15 cm diameter bombs were quenched and collected shortly after a normal explosion the bombs were characterized in terms of their textural chemical rheological and geophysical signatures the vesicle and crystal size distribution of the samples coupled with the glass chemistry enabled us to quantify variations in the degassing history and rheology of the magma resident in the shallow i e in last 250 m of conduit length the different textural facies observed in these bombs showed that fresh magma was mingled with batches of partially to completely degassed oxidized high crystallinity high viscosity evolved magma this magma sat at the top of the conduit and played only a passive role in the explosive process the fresh microlite poor vesiculated batch however experienced a response to the explosive event by undergoing rapid decompression integration of geophysical measurements with sample analyses indicates that popular bubble bursting models may not fit this case we suggest that the degassed magma forms a plug or rheological layer at the top of the conduit through which the fresh magma bursts in this model we need to consider the paradox of a slug ascending too fast through a magma of varying viscosity and yield strength

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

predicting volcanic eruptions in recent years some major volcanic eruptions have been forecast successfully but others have claimed many lives in his perspective scarpa charts recent efforts to improve predictions of volcanic eruptions broadband seismic studies such as those of kumagai et al are a powerful tool for modeling the magma dynamics this and other techniques such as strain meters in boreholes will lead to a more quantitative approach in physical volcanology

performance of the radial semblance method for the location of very long period volcanic signals we investigate the performance of a source location method that com bines multichannel semblance and particle motions and is being increasingly used to obtain estimates of the source locations of very long period vlp seismic signals recorded on volcanoes the method makes use of the radial particle motions and large wavelengths that characterize the vlp events to assess the capabilities of this radial semblance method and to better understand its limitations we quantify the effects of window length noise contents of the signal inaccurate velocity models receiver coverage and orientation errors in the horizontal components of the receiv ers our results show that the semblance method performs best when 1 the noise level is low enough to allow a good characterization of the waveforms 2 the sources are located at distances between one half of the average receiver spacing and about two times the network aperture and 3 the orientations of the horizontal components of the seismometers are known with relative accuracy when these requirements are met the radial semblance method constitutes an adequate tool to obtain preliminary locations of vlp volcanic signals recorded by broadband networks moreover we provide a formula to determine the radial semblance level that should be used to define error regions associated to the estimated source locations

locating sources of volcanic tremor and emergent events by seismic triangulation application to arenal volcano costa rica 1 we address the issue of locating the sources of volcanic tremor and emergent events with a method requiring a limited amount of equipment a network of several triangular seismic antennas made of vertical sensors is used the slowness vectors are estimated at each array on a sliding window by inverting the time delays between the sensors calculated with the cross spectral method a probabilistic approach is adopted whereby each measure and its error are represented by a probability density function pdf a weighted summation of the pdfs is carried out in which the stable directions of propagation are enhanced the effects of the structural heterogeneities are taken into account by introducing an additional error associated to a robust hyperbolic secant sech type pdf the resulting pdfs of the back azimuth are combined to calculate a pdf of the source location the maximum likelihood of this pdf is taken as an estimate of the source position and its spread is characterized by a covariance analysis data from an experiment carried out at arenal volcano costa rica with four arrays are analyzed the precision and robustness of the method are tested by exploring the influence of the array configuration and other parameters the mean standard deviation on the position of the sources is 600 m for the tremor and 400 m for the explosions and long period lp events several tremors explosions and lp events are analyzed and their sources located the seismogenic zone is located in a 600 m radius area centered on the active crater

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

radar doppler velocimetry of volcanic eruptions theoretical considerations and quantitative documentation of changes in eruptive behaviour at stromboli volcano italy summary the use of radar doppler velocimetry for the observation of volcanic activity is new we used this method to continuously observe the activity of one vent of stromboli volcano italy from the end of 2000 april until early may during this period we recorded 702 eruptions 132 of which occurred before a strong rain storm passed over the island on april 29 in order to interpret the recorded doppler data we developed a program that simulates different strombolian eruption scenarios for which we then calculate the theoretical doppler spectra comparing our theoretical data with the observed data we are able to show that most of the eruptions are nearly vertical although we did observe only one component of the eruption vector with our doppler radar one of the most interesting features of the data set is a significant change in eruptive behaviour that correlates with the occurrence of the rain storm we find that on average the eruption duration increased by a factor of 2 eruptive velocities were much higher and indirect evidence indicates that the average particle diameter of the erupted material decreased this change may have several causes but the coincidence with the rain storm may be evidence of magma water interaction and feedback on the volcanic activity if the fluid source rain changing the eruptive style is at the surface and in near surface layers then the main control on final eruption dynamics at stromboli volcano must also be in rather shallow regions

vent discrimination at stromboli volcano italy eruptive activity at stromboli volcano was significantly elevated over background levels in may 2001 during 63 h of observation eight vents produced on average 17 explosions h with an average repose interval of 3 min during this period the stromboli vents exhibited consistent seismic and acoustic signatures based on cross correlation cluster analysis dendrogram clustering based on waveform cross correlation was used to illustrate the complexity of the near surface plumbing system of stromboli s multi vent edifice cross correlations of displacement seismograms produced by explosions at specific craters such as the northeast crater nec form dense waveform clusters with correlation coefficients between 0 96 and 0 99 while displacement waveforms from other craters such as the southwest crater swc exhibit loose clusters with correlations between 0 88 and 0 96 the inconsistency of swc events as compared to the nec suggests that the vent system there is more heterogeneous cluster linkage distance between the nec cluster and the central crater cc cluster is shorter than the linkage distance between the nec and swc clusters indicating that nec and cc are more closely related infrasonic observations were used to locate vent explosions confirming that the clusters of events are associated with specific vents or craters qualitative analyses of acoustic waveforms from approximately 500 explosions reveal that impulsive acoustic signals were associated with short mechanically simple ground displacement responses these events may correspond to the bursting of an individual gas slug similar degassing mechanisms from vents in the nec and the cc show common characteristics in their displacement waveforms

chronology of tertiary fan deposits off the western barents sea implications for the uplift and erosion history of the barents shelf abstract a combined biostratigraphic and seismic study was performed on three holes drilled in the western barents sea two holes penetrate the thick sedimentary wedge which forms a large fan located off a trough on the barents sea shelf the bjornoyrenna fan the study shows that the fan was built over a short time span in the late pliocene pleistocene mainly due to glacial erosion of the barents shelf region this contrasts earlier age assignments which concluded that fan deposition started in the oligocene the results have a major impact on the understanding of trough mouth fan formation and has important bearing on the history of the sedimentary basins of the barents shelf

broadband seismic observations at satsuma iwojima volcano japan this paper reports the results of preliminary analysis of broadband seismic observations conducted at satsuma iwojima volcano japan the recorded broadband data show a wide variety of seismic features small m 0 short period volcanic earthquakes characterized by a long 5 s emergent phase and by nearly identical waveforms are located at the very shallow part of the summit crater long period seismic pulses synchronized with a regular amplitude modulation of volcanic tremor have an interval of approximately 46 to 50 min each of the long period pulses has almost identical waveform polarization of the long period events suggests a very shallow source which can be interpreted as a result of a volume expansion mechanism the correlation between the long period seismic pulses and volcanic tremor seems to be associated with magma convection and the degassing process inside the conduit of the volcano

crustal structure and transform margin development south of svalbard based on ocean bottom seismometer data abstract the barents sea is located in the northwestern corner of the eurasian continent where the crustal terrain was assembled in the caledonian orogeny during late ordovician and silurian times the western barents sea margin developed primarily as a transform margin during the early tertiary in the northwestern part south of svalbard multichannel reflection seismic lines have poor resolution below the permian sequence and the early post orogenic development is not well known here in 1998 an ocean bottom seismometer obs survey was collected southwest to southeast of the svalbard archipelago one profile was shot across the continental transform margin south of svalbard which is presented here p wave modeling of the obs profile indicates a caledonian suture in the continental basement south of svalbard also proposed previously based on a deep seismic reflection line coincident with the obs profile the suture zone is associated with a small crustal root and westward dipping mantle reflectivity and it marks a boundary between two different crystalline basement terrains the western terrain has low 6 2 6 45 km s 1 p wave velocities while the eastern has higher 6 3 6 9 km s 1 velocities gravity modeling agrees with this as an increased density is needed in the eastern block the s wave data predict a quartz rich lithology compatible with felsic gneiss to granite within and west of the suture zone and an intermediate lithological composition to the east a geological model assuming westward dipping caledonian subduction and collision can explain the missing lower crust in the western block by subduction erosion of the lower crust as well as the observed structuring due to the transform margin setting the tectonic thinning of the continental block during opening of the norwegian greenland sea is restricted to the outer 35 km of the continental block and the continent ocean boundary cob can be located to within 5 km in our data distinct from the outer high commonly observed on transform margins the upper part of the continental crust at the margin is dominated by two large rotated down faulted blocks with throws of 2 3 km on each fault apparently formed during the transform margin development analysis of the gravity field shows that these faults probably merge to one single fault to the south of our profile and that the downfaulting dominates the whole margin segment from spitsbergen to bjornoya south of bjornoya the faulting leaves the continental margin to terminate as a graben 75 km south of the island adjacent to the continental margin there is no clear oceanic layer 2 seismic signature however the top basement velocity of 6 55 km s 1 is significantly lower than the high 7 km s 1 velocity reported earlier from expanding spread profiles esps and we interpret the velocity structure of the oceanic crust to be a result of a development induced by the 7 8 km thick sedimentary overburden

crustal structure of the northern part of the voring basin mid norway margin from wide angle seismic and gravity data abstract three regional ocean bottom seismograph obs profiles with a total of fifteen recovered obss were acquired in the northern part of the voring basin mid norway margin in 1996 the data have been modelled by inversion and forward modelling of the obs vertical components p waves the velocity is found to increase downwards within the sedimentary layers due to increasing depth of burial confining pressure within the two deepest sedimentary layers there seems to be an increase of 0 5 1 km s in velocity northwestwards this increase is most likely caused by high velocity sill intrusions in the sedimentary rocks emplaced during the rift episode leading to early eocene opening of the ne atlantic the presence of significant amounts of sills seems to terminate close to the nyk high along profile 5 dip profile and close to a dome northwest of the shelf edge along profile 6 dip profile the velocity in the top of this dome is anomalously high 3 4 km s at only 1 km depth beneath the seafloor suggesting that the high consists of volcanic rocks or heavily intruded sedimentary rocks the relatively low velocities derived from within the upper crystalline crust 5 9 6 2 km s confirms that the crust is of continental origin within the lower crust there seems to be a clear increase in velocity northwestwards from about 7 0 km s to about 7 4 km s suggesting that the amount of high velocity intrusions underplating in the lower crust decreases landwards the modelling of the strike profile profile 7 suggests that the transition from a lower crust dominated by magmatic intrusions to a more undisturbed continental lower crust is located approximately beneath this profile the model for profile 7 ties closely southwestwards to the models derived from obs data acquired in 1992 and northeastwards to lofoten obs data acquired in 1988 the models indicate that the thick magmatic intrusions in the sedimentary rocks and lower crust extend further landwards in the area of the 1992 survey and that the transition zone is related to the surt lineament the distribution of magmatic rocks thus seems to correlate strongly with pre breakup structures in addition to the p wave modelling gravity modelling has been performed along all profiles the gravity modelling confirmed all main aspects of the obs models and provided constraints on the crustal structures towards the ends of the profiles

the classification of seismo volcanic signals using hidden markov models as applied to the stromboli and etna volcanoes the aim of this work is to apply the hidden markov model hmm method to recognise seismic signals belonging to different active volcanoes we use data obtained from two field surveys carried out in 1997 and 1999 at stromboli and etna respectively for stromboli we used two types of seismic signals for recognition purposes strombolian explosions and background seismic noise whilst for etna we used volcanic tremors and tremor bursts we initially proceeded to visually identify the signals and to segment the data to obtain a model for each event class we then applied these models separately to each volcano dataset finally combining both datasets as a test of the portability of the system the method analyses the seismograms and compares the characteristics of the data to a number of pre defined event classes if a signal is present the method detects its occurrence and produces a classification we observed that to obtain reliable results a careful and adequate segmentation process is crucial and that each signal type must be represented by its own specific model once we had built this model the success level of the system was high the success rates obtained indicated that the method was fully able to detect isolate and identify signals from raw seismic data these results imply that once an adequate training process has been used this method is particularly appropriate for work in real time as well as concurrently with the data acquisition system

amplitude and recurrence time analysis of lp activity at mount etna italy the aim of this work is to improve our understanding of the long period lp source mechanism at mt etna italy through a statistical analysis of detailed lp catalogues the behaviour of lp activity is compared with the empirical laws governing earthquakes recurrence in order to investigate whether any relationships exist between these two apparently different earthquake classes we analysed a family of 8894 events detected during a temporary experiment in august 2005 for that time interval the lp activity is sustained in time and the volcano did not exhibit any evident sign of unrest the completeness threshold of the catalogue is established through a detection test based on synthetic waveforms the retrieved amplitude distribution differs significantly from the gutenberg richter law and the inter event times distribution does not follow the typical law expected for tectonic activity in order to compare these results with a catalogue for which the source mechanism is well established we applied the same procedure to a dataset from stromboli volcano where recurrent lp activity is closely related to very long period pulses in turn associated with the summit explosions our results indicate that the two catalogues exhibit similar behaviour in terms of amplitude and inter event time distributions this suggests that the etna s lp signals are most likely driven by stress changes caused by an intermittent degassing process occurring at depth similar to that which drives the summit explosions at stromboli volcano

the effects of seismic rotations on inertial sensors summary with the important increase in the number of instruments especially in the near field of quite significant earthquakes unsaturated traces have led seismologists to question what they are really measuring we have performed a review of previous studies related to the effects of rotations on both horizontal and vertical components of various sensors illustrations of near field records show that the recovering static displacement requires an accurate rotation estimation that present day seismometers cannot achieve estimations of coseismic tilts rotation around an horizontal axis using seismometers cannot be achieved independently of translational motion therefore for specific configurations such as near field or long period far field reconstruction of the ground motion requires specific rotation measurements effects of the chi chi earthquake 1999 on accelerograms make the static displacement estimation unreliable for long period background noise far field horizontal seismic signals present unexpected n45 polarization which is explained by the similar influence of the rotation around the vertical axis on the two horizontal components for the geoscope network this feature has been seen for stations with a streckeisen sts 1 sensor while those with a streckeisen sts 2 sensor do not show this polarization feature this study suggests that sensor installation should follow a protocol that will better guarantee the verticality of the sensors moreover rotational recordings with ad hoc sensors are necessary and by adequately correcting the traces they will enable us to reconstruct the translational motion from recorded seismic signals

geochemical monitoring of the 2002 2003 eruption at stromboli volcano italy precursory changes in the carbon and helium isotopic composition of fumarole gases and thermal waters significant changes in the helium and carbon isotopic composition of shallow thermal waters vs gas and a crater fumarolic gas have been recorded at stromboli prior and during the 2002 2003 eruption the3he 4he ratios corrected for air contamination rc ra and 13c of fumarolic gases gradually increased from may to november 2002 before the eruption onset these variations imply early degassing of a gas rich magma at depth that likely fed both the intense strombolian activity and small lava overflows recorded during that period the lava effusion of late december 2002 was shortly preceded by a marked rc ra decrease both in water and fumarolic gases comparison of he co2 and ch4 co2 ratios in dissolved gas and with rm delta 13 rm c rm co 2 values rules out the rc ra decrease due to an increasing input of radiogenic4he the rc ra decrease is attributed to the he isotope fractionation during rapid magma ascent and degassing a new uprising of 3he rich magma probably occurred in january to february 2003 when rc ra ratios displayed the highest values in dissolved gases ever measured before 4 56 rc ra the increase in he co2 and ch4 co2 ratios and decrease in 13c of dissolved co2 was recorded after the 5 april 2003 explosive paroxysm likely caused by enhanced gas water interaction inducing co2 dissolution no anomalous rc ra values were recorded in the same period when usual strombolian activity gradually resumed

pyroclast tracking velocimetry illuminates bomb ejection and explosion dynamics at stromboli italy and yasur vanuatu volcanoes a new image processing technique pyroclast tracking velocimetry was used to analyze a set of 30 high speed videos of strombolian explosions from different vents at stromboli italy and yasur vanuatu volcanoes the studied explosions invariably appear to result from the concatenation of up to a hundred individual pyroclast ejection pulses all these pulses share a common evolution over time including 1 a non linear decrease of the pyroclast ejection velocity 2 an increasing spread of ejection angle and 3 an increasing size of the ejected pyroclasts these features reflect the dynamic burst of short lived gas pockets in which the rupture area enlarges while pressure differential decreases we estimated depth of pyroclast release to be approximately 1 and 8 m below the surface at stromboli and yasur respectively in addition explosions featuring more frequent pulses also have higher average ejection velocities and larger total masses of pyroclasts these explosions release a larger overall amount of energy stored in the pressurized gas by a combination of more frequent and stronger ejection pulses in this context the associated kinetic energy per explosion ranging 103 109 j appears to be a good proxy for the explosion magnitude differences in the pulse defining parameters among the different vents suggest that this general process is modulated by geometrical factors in the shallow conduit as well as magma specific rheology indeed the more viscous melt of yasur compared to stromboli is associated with larger vents producing fewer pulses but larger pyroclasts

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

seismic precursors of a basaltic paroxysmal explosion track deep gas accumulation and slug upraise 1 basaltic volcanoes though fed with low viscosity magma occasionally produce sudden paroxysmal explosions that are unforecasted and whose triggering mechanism remains poorly elucidated here we report on the first detection of seismic signals precursory to such an explosion on 5 april 2003 at stromboli volcano italy this strongest event in the past 73 years was preceded by 25 h of seismic tremor variation broadly coincident with strong geochemical anomalies in crater plume emissions followed by 15 h of tilt related long period inflation pulses of increasing amplitude these precursory signals are best explained by accelerating growth and leakage of a bubble melt foam layer formed at 10 km depth whose collapse triggered the fast ascent of co2 rich gas slugs and then the explosion our results open new perspectives for the forecasting of such paroxysmal explosions and associated hazards

identifying elements of the plumbing system beneath kilauea volcano hawaii from the source locations of very long period signals summary we analyzed 16 seismic events recorded by the hawaiian broad band seismic network at kilauea volcano during the period september 9 26 1999 two distinct types of event are identified based on their spectral content very long period vlp waveform amplitude decay pattern and particle motion we locate the vlp signals with a method based on analyses of semblance and particle motion different source regions are identified for the two event types one source region is located at depths of 1 km beneath the northeast edge of the halemaumau pit crater a second region is located at depths of 8 km below the northwest quadrant of kilauea caldera our study represents the first time that such deep sources have been identified in vlp data at kilauea this discovery opens the possibility of obtaining a detailed image of the location and geometry of the magma plumbing system beneath this volcano based on source locations and moment tensor inversions of vlp signals recorded by a permanent large aperture broad band network

predicting eruptions from precursory activity using remote sensing data hybridization abstract many volcanoes produce some level of precursory activity prior to an eruption this activity may or may not be detected depending on the available monitoring technology in certain cases precursors such as thermal output can be interpreted to make forecasts about the time and magnitude of the impending eruption kamchatka russia provides an ideal natural laboratory to study a wide variety of eruption styles and precursory activity prior to an eruption at bezymianny volcano for example a clear increase in thermal activity commonly occurs before an eruption which has allowed predictions to be made months ahead of time conversely the eruption of tolbachik volcano in 2012 produced no discernable thermal precursors before the large scale effusive eruption however most volcanoes fall between the extremes of consistently behaved and completely undetectable which is the case with neighboring kliuchevskoi volcano this study tests the effectiveness of using thermal infrared tir remote sensing to track volcanic thermal precursors using data from both the advanced spaceborne thermal emission and reflection radiometer aster and advanced very high resolution radiometer avhrr sensors it focuses on three large eruptions that produced different levels and durations of effusive and explosive behavior at kliuchevskoi before each of these eruptions tir spaceborne sensors detected thermal anomalies i e pixels with brightness temperatures 2 c above the background temperature high temporal low spatial resolution i e hours and 1 km avhrr data are ideal for detecting large thermal events occurring over shorter time scales such as the hot material ejected following strombolian eruptions in contrast high spatial low temporal resolution i e days to weeks and 90 m aster data enables the detection of much lower thermal activity however activity with a shorter duration will commonly be missed aster and avhrr data are combined to track low level anomalies months prior to an eruption and higher energy events prior to large eruptions to develop a monitoring approach for this eruption style results show that strombolian eruptions produce enough energy in the pre eruptive phase to trigger an avhrr detection paired with aster data the results can be extended back in time to develop a precursory timeline which captures subtle changes in volcanic activity that would commonly go unnoticed in a single data set although these precursors may be volcano and eruption specific the now sixteen year old database from aster allows this methodology to be repeatable at other volcanoes to establish a quantitative precursory baseline which would be an improvement over current eruption classifications

unsupervised neural analysis of very long period events at stromboli volcano using the self organizing maps we have implemented a method based on an unsupervised neural network to cluster the waveforms of very long period vlp events associated with explosive activity at the stromboli volcano southern italy stromboli has several active vents in the summit area producing together more than 200 explosions day we applied this method to investigate the relationship between each vent and its associated vlp explosive waveform we selected 147 vlp events recorded between november and december 2005 when digital infrared camera recordings were available from a visual inspection of the infrared camera images we classified the vlps on the basis of which vent produced each explosion we then applied the self organizing map som an unsupervised neural technique widely applied in data exploratory analysis to cluster the vlps on the basis of their waveform similarity our analysis demonstrates that the most recurrent vlp waveforms are usually generated by the same vent some exceptions occurred however in which different waveforms are associated with the same vent as well as different vents generating similar waveforms this suggests that the geometry of the upper conduit vent system plays a role in shaping the recurring vlp events whereas occasional modest changes in the source process dynamics produce the observed exceptions

eruptive sequence and seismic activity of llaima volcano chile during the 2007 2009 eruptive period inferences of the magmatic feeding system abstract llaima volcano one of the most active volcanoes in south america has experienced intense activity during the last 100 years the most recent eruptive activity occurred during the period 2007 2009 with at least six energetic eruptions the january 1st 2008 vei 3 being the strongest episode most of the paroxysmal activity was characterized by a rapid increase in seismic energy minutes to hours and the absence of precursory signals as well as by an accelerated drop of the seismic energy and eruption intensity at the end moreover subtle changes in the increase of low energy long period lp seismicity and the occurrence of minor explosive activity six months before the onset of the eruptive cycle were the only remarkable changes observed in advance this is the first study that includes a detailed description of the 2007 2009 eruptive period and is based on a temporal analysis of the seismic records technical reports from the monitoring network and 2000 photos this set allows a characterization of the coeval eruptive styles including strombolian and hawaiian activity morphological changes of the active vents inside the main crater and two fractures located in the sw and se flanks ten phases were identified based on the eruptive style volcanic explosivity index vei and the salient features of the seismic events the seismicity that accompanied the eruptive phases was characterized by the predominance of a continuous tremor tr and discrete lp events and a remarkable absence of volcano tectonics vt earthquakes a waveform cross correlation analysis of lp events showed an overall low similarity between them which suggests multiple sources our observations and analysis suggest that the plumbing system is composed of multiple independent structures some of which reached the surface during this eruptive period indicating that the upper part of the cone could be an unstable and essentially weak zone the activity and seismicity observed are characteristic of an open vent system in which the magma can ascend rapidly from several km depth with little to no clear precursory activity these results are in agreement with petrological studies of the products of these eruptions

linking variable explosion style and magma textures during 2002 at stromboli volcano italy microtextural characteristics of fresh ejecta from stromboli volcano were examined from three periods of differing eruption style and intensity in 2002 activity shifted from relatively weak and infrequent ash charged explosions during january through may into two broad cycles of waxing activity in june through late september and late september through december followed by the onset on 28 december of the 2002 2003 effusive eruption analyzed sets of lapilli from may september october and 28 december show contrasts in the physical properties of magma resident in the shallow conduit during this range of activity three distinct textures are observed among the analyzed pyroclasts low density ld with an abundance of subspherical bubbles the presence of large irregularly shaped bubbles and a light to transparent glass matrix transitional texture tt with an intermediate number of subspherical bubbles a high frequency of large irregularly shaped bubbles and a honey colored glass matrix and high density hd with sparse relatively small bubbles conspicuous large irregular bubbles and a dark glass matrix observational and quantitative data density vesicle size indicate that these textures are linked through variable residence time in stromboli s shallow conduit with an ongoing evolution from ld to hd magma calculations suggest that residual ld magma will evolve to hd texture in a period of hours to days contrasting amounts of the ld tt and hd magmas are present in each sample with the most tt in may the most ld in september october and the most hd in december this implies that the shallow magma had a different rheology at each collection period the viscosity of ld and hd magmas are calculated to be in the range of 2 000 to 2 600 and 3 000 to 5 000 pa s respectively which with their changing proportions must have implications for rates of bubble slug ascent and processes of fragmentation this study suggests that an increasing maturity of magma in stromboli s shallow conduit with resultant increase in viscosity feeds back to reduce the intensity of explosions whereas a steady flux of ld magma favors more powerful explosions

evidence of vlp volcanic tremor in the band 0 2 0 5 hz at stromboli volcano italy 1 we analyze time series of strombolian volcanic tremor recorded with a network of broadband seismic stations we evidence the occurrence of a significant component of volcanic tremor in the range 0 2 0 5 hz by using linear and nonlinear methods the polarization and zlcc analysis show that the wave field is characterized by high apparent velocity 2 km s it comes mainly from the crater area with a clear amplitude decay towards the sea level the previous properties are loosed when the tremor level is higher suggesting that in this case the wave field is more affected by oceanic noise the waveform extracted by independent component analysis ica shows a behaviour like nonlinear beats as in the case of high frequency waveforms we conclude that this component displays a behaviour like the wave field at higher frequencies in spite of its low frequency and it is produced by the vibrations of the volcanic conduit

response of a hydrothermal system to magmatic heat inferred from temporal variations in the complex frequencies of long period events at kusatsu shirane volcano japan we investigate temporal variations in the complex frequencies frequency and quality factor q of long period lp events that occurred at kusatsu shirane volcano central japan we analyze lp waveforms observed at this volcano in the period between 1988 and 1995 which covers a seismically active period between 1989 and 1993 systematic temporal variations in the complex frequencies are observed in october november 1989 july october 1991 and september 1992 january 1993 we use acoustic properties of a crack filled with hydrothermal fluids to interpret the observed temporal variations in the complex frequencies the temporal variations in october november 1989 can be divided into two periods which are explained by a gradual decrease and increase of a gas volume fraction in a water steam mixture in a crack respectively the temporal variations in july october 1991 can be also divided into two periods these variations in the first and second periods are similar to those observed in november 1989 and in september november 1992 respectively and are interpreted as drying of a water steam mixture and misty gas in a crack respectively the repeated nature of the temporal variations observed in similar seasons between july and november suggests the existence of seasonality in the occurrence of lp events this may be caused by a seasonally variable meteoritic water supply to a hydrothermal system which may have been heated by the flux of volcanic gases from magma beneath this volcano

broadband seismic monitoring of active volcanoes using deterministic and stochastic approaches 1 we systematically used two approaches to analyze broadband seismic signals for monitoring active volcanoes one is waveform inversion of very long period vlp signals assuming possible source mechanisms the other is a source location method of long period lp events and tremor using their amplitudes the deterministic approach of the waveform inversion is useful to constrain the source mechanism and location but is basically only applicable to vlp signals with periods longer than a few seconds the source location method assumes isotropic radiation of s waves and uses seismic amplitudes corrected for site amplifications this simple approach provides reasonable source locations for various seismic signals such as a vlp event accompanying lp signals an explosion event and tremor associated with lahars and pyroclastic flows observed at five or fewer stations our results indicate that a frequency band of about 5 12 hz and a q factor of about 60 are appropriate for the determination of the source locations in this frequency band the assumption of isotropic radiation may become valid because of the path effect caused by the scattering of seismic waves the source location method may be categorized as a stochastic approach based on the nature of scattering waves systematic use of these two approaches provides a way to better utilize broadband seismic signals observed at a limited number of stations for improved monitoring of active volcanoes

crustal structure of the outer voring plateau offshore norway from ocean bottom seismic and gravity data four ocean bottom seismograph obs profiles acquired across the continent ocean transition zone of the outer voring plateau have been modeled by inversion and forward modeling of the obs vertical component traces p waves the thickness of the sedimentary layers deposited since the early eocene continental breakup varies from up to 2 2 km above the basaltic inner flows if to a minimum of 0 2 km about 20 km seaward of the voring escarpment ve with a velocity of 1 6 2 55 km s the thickness of the uppermost layer of basalt varies from 0 5 to 4 5 km and its velocity ranges from 3 4 to 5 km s the modeling of the two dip profiles suggests that strongly intruded preopening sedimentary rocks extend 40 km seaward of the ve farther seaward another layer of extrusives intrusives is found beneath the uppermost layer of basalt the lateral variations in velocity in the main crustal layer along the dip profiles indicate that the continent ocean transition extends over a 30 50 km wide zone in between strike profile 3 oceanic 6 6 7 35 km s and strike profile 4 continental 6 1 7 0 km s an up to 7 km thick lower crustal high velocity body 7 1 7 4 km s is interpreted in terms of intrusions in the lower crust beneath and landward of the continent ocean transition the total thickness of the normal oceanic crust is estimated to be 7 9 km the anomalously thick oceanic crust reaches a maximum thickness of about 25 km and the crustal thickness is estimated to be 17 22 km beneath the if gravity modeling of the profiles confirmed all main aspects of the velocity models and provided constraints on the crustal structures toward the ends of the profiles where the ray coverage was low

array tracking of infrasonic sources at stromboli volcano 1 infrasonic arrays are a powerful tool for volcanic monitoring and hazard assessment explosions were recorded at stromboli using a small aperture array of 4 infrasonic stations allowing precise vent location the acoustic signals were delayed and summed revealing the existence of two main groups of infrasonic waves the ne crater produces short 3 s high amplitude 20 80 pa pressure waves while the sw crater produces small acoustic pressure 10 30 pa with long 5 15 s coda the two groups reflect different in explosive styles and similar spectral content centered on 5 6 hz when stacked together acoustic waveforms for each crater reveal the same pressure pulse which indicates a common source process we infer that the acoustic onset at both craters is generated by the burst of a large gas bubble while the acoustic coda is controlled by a sustained pressure release

a numerical simulation of magma motion crustal deformation and seismic radiation associated with volcanic eruptions summary the finite difference method is used to calculate the magma dynamics seismic radiation and crustal deformation associated with a volcanic eruption the model geometry consists of a cylindrical reservoir and narrow cylindrical conduit embedded in a homogeneous crust we consider two models of eruption in the first model a lid caps the vent and the magma is overpressurized prior to the eruption the eruption is triggered by the instantaneous removal of the lid at which point the exit pressure becomes equal to the atmospheric pressure in the second model a plug at the reservoir outlet allows pressurization of only the magmatic fluid in the reservoir before the eruption magma transfer between the reservoir and conduit is triggered by the instantaneous removal of the plug and the eruption occurs when the pressure at the conduit orifice exceeds the material strength of the lid capping the vent in both models magma dynamics are expressed by the equations of mass and momentum conservation in a compressible fluid in which fluid expansion associated with depressurization is accounted for by a constitutive law relating pressure and density crustal motions are calculated from the equations of elastodynamics the fluid and solid are dynamically coupled by applying the continuity of wall velocities and normal stresses across the conduit and reservoir boundaries free slip is allowed at the fluid solid boundary both models predict the gradual depletion of the magma reservoir which causes crustal deformation observed as a long duration dilatational signal superimposed on this very long period vlp signal generated by mass transport are long period lp oscillations of the magma reservoir and conduit excited by the acoustic resonance of the reservoir conduit system during the eruption the volume of the reservoir vent size and magma properties control the duration of vlp waves and dominant periods of lp oscillations the second model predicts that when the magmatic fluid reaches the vent a high pressure pulse occurs at this location in accordance with the basic theory of compressible fluid dynamics this abrupt pressure increase just beneath the vent is consistent with observed seismograms in which pulse like rayleigh waves excited by a shallow source are dominant the strength of the lid plays an important role in the character of the seismograms and in defining the type of eruption observed

interpretation of very long period tremors at ambrym volcano vanuatu as quasi static displacement field related to two distinct magmatic sources 1 a 3 component broadband seismometer sts 2 has been deployed on the sw slope of ambrym vanuatu a large caldera volcano with two persistent lava lakes from july to november 2000 well polarized very long period tremors 18 22s vlpts occurred quite continuously whereas other seismic signal with periods of 9s 6 7s 5s 2 3 2 7s 1 95s and 1s were intermittent vlpts signals show two clearly distinct directions pointing towards the caldera polarization orientations suggest two sources the first one and the most active fits with the zone from which silicic lava flows erupted in 1986 in the central to eastern part of the caldera the second one corresponds to the active zone formed by the complex marum volcanic center and the benbow cone in the western part of the depression structure the depths are estimated between 2 7 2 9 km with respect to sea level vlpts are interpreted as the quasi static displacement field of two nondestructive sources they indicate the persistent continuing magmatic activity beneath the eastern floor of the caldera although no volcanic activity is observed in this area and the more obvious but less active corresponding to the lava lakes these data also corroborate the complex internal structure of the ambrym caldera suggested by geological data and bimodal magmatism basaltic 50 sio2 and silicic 60 sio2

moment tensor inversion of very long period seismic signals from strombolian eruptions of erebus volcano article i nfo strombolian eruptions from the long lived lava lake of erebus volcano ross island antarctica generate repeating very long period vlp signals containing energy between approximately 30 and 5 s that persist for several minutes and through the post eruptive refilling of the lava lake the initial approximately 10 s of this signal is moderately variable particularly with respect to its initial polarity while the following vlp coda has been observed to be stable since the earliest vlp observations were made 1996 to estimate forces and force couples consistent with the erebus vlp signature we perform moment tensor inversions for point sources using high signal to noise data stacks from the six station 18 component broadband seismographic network and green s function forward calculations that incorporate topography we infer a shallow approximate depth of less than 400 m below the lava lake surface source centroid that underlies the center to the northwestern rim of the main crater east and north of the lava lake integrated mii functions over the predominant 180 s signal duration of vlp events show that the net scalar moments for these events are on the order of 4 10 13 n m corresponding to a moment magnitude mw 3 for typical sized vlp events moment rate tensors which characterize force couple components are dominated 85 97 of variance by dilatational components approximately 25 of the data variance is attributable to single forces that are attributable to oscillatory reaction forces caused by fluid transport however the relative contributions of vertical forces and couples with this sparse network is poorly resolved for these shallow sources the generally high degree of repeatability in the vlp signal across thousands of eruptions over the past decade indicates that the response of the conduit system to gas slug ascent and subsequent gravitational disequilibrium is stable consistent with the generally unchanging surface manifestation of the convecting lava lake system and arguing for a thermally and dynamically stable conduit system beneath the lava lake

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 attenuation and shallow velocity structures at stromboli volcano italy the surface wave field associated with the explosive activity at stromboli volcano is investigated using data recorded by two short period seismic arrays deployed on the north and west flanks of the volcano the group velocity dispersion curves for rayleigh waves are derived using the multiple filter technique the phase velocity dispersion curves are recovered using a phase match filter and compared with that inferred from zero lag cross correlation analysis applied to the array data these analyses indicate rayleigh wave group velocities ranging from 0 29 to 0 24 km sec in the 1 5 to 8 0 hz frequency band and phase velocities ranging from 1 km sec at 1 5 hz to about 0 3 km sec at frequencies above 5 hz in addition the dispersive properties of the attenuation coefficient for rayleigh waves are inferred from application of the multiple filter technique to seismograms recorded at different distances from the source these results are validated through examination of the spectral amplitude decay with distance for both body and rayleigh waves the values of the body wave quality factor thus obtained are q 20 and q 6 for the north and west side of the island respectively the velocity and attenuation dispersion curves are inverted for the shear wave velocity and q structures down to a depth of about 200 m shear wave velocities for the west flank range from about 0 3 km sec for the uppermost 17 m thick layer to 1 9 km sec at depths greater than 200 m comparison with previous studies indicates a similar velocity structure for the north and west flanks the attenuation structure for the west flank is described by a shallower 36 m thick layer with q 9 underlain by a half space with q 50 on the north flank q 40 for the shallower 30 m thick layer and q 44 for the underlying half space residuals from analysis of the spectral decay with distance are used to quantify site effects affecting the different array elements on the west flank local amplifications at that array are interpreted in terms of an edge effect associated with concave topography velocity similarities observed at the north and west flanks are compatible with surface geologic data discrepancies in attenuation properties at the two sites are interpreted in terms of different degrees of heterogeneity and crack density controlling the scattering quality factor q s manuscript received 15 april 2001

acoustic measurements of the 1999 basaltic eruption of shishaldin volcano alaska 2 precursor to the subplinian phase the 1999 eruption of shishaldin volcano alaska usa displayed both strombolian and subplinian basaltic activity the subplinian phase was preceded by a signal of low amplitude and constant frequency c2 hz lasting 13 h this bhumming signalq is interpreted as the coalescence of the very shallow part of a foam building up in the conduit which produces large gas bubbles before bursting the acoustic waveform of the hum event is modelled by a helmholtz resonator gas is trapped into a rigid cavity and can only escape through a tiny upper hole producing sound waves at shishaldin the radius of the hole c 5m is close to that of the conduit c6 m the cavity has a length of c60 m and gas presents only a small overpressure between c1 2 10 3 and 4 5 10 3 mpa such an overpressure is obtained by the partial coalescence of a foam formed by bubbles with a diameter from c2 3 mm at the beginning of the episode towards c0 64 mm very close to the end of the phase the intermittency between hum events is explained by the ripening of the foam induced by the h2o diffusion through the liquid films the two extreme values from 600 to 10 s correspond to a bubble diameter from 2 2 to 0 3 mm at the beginning and end of the pre subplinian phase respectively the extremely good agreement between two independent estimates of bubble diameters in the shallow foam reinforces the validity of such an interpretation the total gas volume lost at the surface during the humming events is at most 5 9 10 6 m 3 at the very end of the presubplinian phase there is a single large bubble with an overpressure of c0 42 mpa the large overpressure suggests that it comes from significant depth unlike other bubbles in the pre subplinian phase this deep bubble may be responsible for the entire foam collapse resulting in the subplinian phase d 2004 elsevier b v all rights reserved

temporal evolution of a hydrothermal system in kusatsu shirane volcano japan inferred from the complex frequencies of long period events 1 we present a detailed description of temporal variations in the complex frequencies of long period lp events observed at kusatsu shirane volcano using the sompi method we analyze 35 lp events that occurred during the period from august 1992 through january 1993 the observed temporal variations in the complex frequencies can be divided into three periods during the first period the dominant frequency rapidly decreases from 5 to 1 hz and q of the dominant spectral peak remains roughly constant with an average value near 100 during the second period the dominant frequency gradually increases up to 3 hz and q gradually decreases from 160 to 30 during the third period the dominant frequency increases more rapidly from 3 to 5 hz and q shows an abrupt increase at the beginning of this period and then remains roughly constant with an average value near 100 such temporal variations can be consistently explained by the dynamic response of a hydrothermal crack to a magmatic heat pulse during the first period crack growth occurs in response to the overall pressure increase in the hydrothermal system caused by the heat pulse once crack formation is complete heat gradually changes the fluid in the crack from a wet misty gas to a dry gas during the second period as heating of the hydrothermal system gradually subsides the overall pressure in this system starts to decrease causing the collapse of the crack during the third period

stability of the seismic source during effusive and explosive activity at stromboli volcano 1 in december 2002 stromboli volcano erupted triggering a sector collapse and a tsunami during the 7 month long effusive eruption the typical persistent and moderate explosive activity of stromboli ceased however very long period vlp seismic events typically associated with the explosions at stromboli were recorded during the effusive eruption these were clustered mainly in two groups with stable waveforms this suggests that strombolian activity never ceased but was confined deep within the magma conduit a location method based on the seismic directivity recorded with an asynchronous seismic deployment positioned the two clusters 60 m apart from each other at 510 m a s l and 180 m nw from the summit craters however seismic polarization reveals a 50 m upward migration of the vlp source at the end of the eruption when volcanic activity moved from the effusive style to more typical strombolian activity

types and mechanisms of strombolian explosions characterization of a gas dominated explosion at stromboli textural and chemical analyses of bombs quenched directly from a normal explosion at stromboli volcano italy were integrated with coincident seismic acoustic and thermal data the data set defines a new gas dominated type of strombolian eruption named type 0 these events are characterized by high velocity emission 150 250 m s 1 of a few relatively small juvenile particles with entrained non juvenile clasts that previously fell back into the vent to be re erupted for the studied event the explosion depth was more than 250 m deep and the particles showed little residence time in the shallow system slug ascent velocities over the final 20 35 m of magma filled conduit and the low viscosity of the resident magma are all consistent with simple bubble burst in a clean conduit this conduit type and eruption style likely fit popular slug ascent and burst models used to explain strombolian eruptions in contrast the ballistic dominated type of explosions type 1 are associated with larger proportions of stagnant material in the shallow system magma mix we argue that the additional volume of this stagnant material pushes the free surface upward because of the larger volume of material available for entrainment into a type 1 slug burst which has to fragment through a thick cap of degassed material type 1 events tend to be rich in particles in contrast the less spectacular gas rich type 0 events have little material to entrain thus being poor in lapilli and bombs

polarisation analysis of the independent components of low frequency events at stromboli volcano eolian islands italy abstract independent component analysis ica applied on low frequency lf events recorded at stromboli volcano reveals that these signals are composed of three independent components in three different frequency bands approximately 0 8 1 2 2 4 3 0 3 2 4 5 hz respectively the first two frequency ranges are mainly composed of body waves coming from a direction in a range of 30 30 around the crater area this result is a clear indication that the entire signal in these frequency bands comes from the source area in fact any scattered wave should have different back azimuth propagation due to the random distribution of scatterers location however the last independent component is dominated by other kinds of waves coming from many different directions

acoustic measurements of the 1999 basaltic eruption of shishaldin volcano alaska 1 origin of strombolian activity the 1999 basaltic eruption of shishaldin volcano alaska usa displayed both classical strombolian activity and an explosive subplinian plume strombolian activity at shishaldin occurred in two major phases following the subplinian activity in this paper we use acoustic measurements to interpret the strombolian activity acoustic measurements of the two strombolian phases show a series of explosions that are modeled by the vibration of a large overpressurised cylindrical bubble at the top of the magma column results show that the bubble does not burst at its maximum radius as expected if the liquid film is stretched beyond its elasticity but bursting occurs after one cycle of vibration as a consequence of an instability of the air magma interface close to the bubble minimum radius during each strombolian period estimates of bubble length and overpressure are calculated using an alternate method based on acoustic power we estimate gas velocity to be 30 60 m s in very good agreement with synthetic waveforms although there is some variation within these parameters bubble length and overpressure for the first strombolian phase are found to be c82f11 m and 0 083 mpa for the second strombolian phase bubble length and overpressure are estimated at 24f12 m and 0 15 mpa for the first 17 h after which bubble overpressure shows a constant increase reaching a peak of 1 4 mpa just prior to the end of the second strombolian phase this peak suggests that at the time the magma in the conduit may contain a relatively large concentration of small bubbles maximum total gas volume and gas fluxes at the surface are estimated to be 3 3 10 7 and 2 9 10 3 m 3 s for the first phase and 1 0 10 8 and 2 2 10 3 m 3 s for the second phase this gives a mass flux of 1 2 10 3 and 8 7 10 2 kg s respectively for the first and the second strombolian phases

temporal evolution of a magmatic dike system inferred from the complex frequencies of very long period seismic signals 1 i present a detailed description of temporal variations in the complex frequencies of very long period vlp events observed in association with an earthquake swarm that occurred beneath hachijo island japan the individual vlp signals show simple decaying harmonic oscillations with periods near 10 s and they last for about 300 s the vlp activity began on 20 august 2002 and continued until 2 april 2003 spectral analysis of the vlp waveforms identifies two spectral peaks of which the complex frequencies show systematic temporal variations at the beginning of the vlp activity the q values of both the peaks show increasing trends from roughly 15 to 35 in the time period between 22 and 26 august the frequency of one peak shows a decreasing trend from 0 1 to 0 09 hz while the frequency of the other peak shows an increasing trend from 0 128 to 0 136 hz during this time after these systematic variations the frequencies and q values of the two peaks remain roughly constant waveform simulations based on a fluid filled crack model indicate that the observed systematic temporal variations can be reasonably explained by gradual expansion of a crack containing a basalt gas mixture the roughly constant frequencies and q values of the two peaks after these systematic variations suggest that the magmatic dike persistently existed beneath hachijo island for more than 6 months mass and heat advection is required to sustain the dike system implying magmatic flow and convection in the dike and magma chamber beneath this island

pressure changes associated with the ascent and bursting of gas slugs in liquid filled vertical and inclined conduits at basaltic volcanoes the sources of long period and very long period seismicity and acoustic signals are frequently described in terms of fluid dynamic processes in particular the formation and ascent of gas slugs within the magma column and their bursting at the surface to investigate pressure changes associated with these processes two phase flow experiments have been carried out in vertical and inclined pipes with both single gas slugs and a continuously supplied gas phase the ascent of individual gas slugs is accompanied by strong dynamic pressure variations resulting from the flow of liquid around the slug these dynamic transients generate sub static pressures below the ascending slug in viscosity controlled systems and produce super static pressures when the slug reaches the surface and motion ceases in inertia dominated systems conduit inclination promotes a change of regime from bubbly to slug flow and favours an increase in size and velocity of the slugs at the expense of their frequency of occurrence during continuously supplied two phase flow the experimental pressure data support previous theoretical analyses of oscillatory sources in ascending slugs as the slugs approach the surface and burst pressure oscillations are also observed during the release of gas slugs and in their wake region

sliding episodes during the 2002 2003 stromboli lava effusion insights from seismic volcanic and statistical data analysis 1 repeated phenomena of flank instability accompanied the 28 december 2002 to 21 july 2003 eruption of stromboli volcano the major episodes were two tsunamigenic landslides on 30 december 2002 2 d after the volcano unrest after 30 december sliding processes remodeled the area affected by slope instability we propose analyses of 565 sliding episodes taking place from december 2002 to february 2003 we try to shed light on their main seismic features and links with the ongoing seismic and volcanic activity using variogram analysis as well a characterization of the seismic signals in the time and frequency domains is presented for 185 sliding episodes their frequency content is between 1 hz and 7 hz on the basis of the dominant peaks and shape of the spectrum we identify three subclasses of signals one of which has significant energy below 2 hz low frequency signatures were also found in the seismic records of the landslides of 30 december which affected the aerial and submarine northwestern flank of the volcano accordingly we surmise that spectral analysis might provide evidence of sliding phenomena with submarine runouts we find no evidence of sliding processes induced by earthquakes additionally a negative statistical correlation between sliding episodes and explosion quakes is highlighted by variogram analysis variograms indicate a persistent behavior memory of the flank instability from 5 to 10 d we interpret the climax in the occurrence rate of the sliding processes between 24 and 29 january 2003 as the result of favorable conditions to slope instability due to the emplacement of nw se aligned dike fed vents located near the scarp of the landslide area afterward the stabilizing effect of the lava flows over the northwestern flank of the volcano limited erosive phenomena to the unstable loose slope not covered by lava

doppler radar sounding of volcanic eruption dynamics at mount etna besides their common use in atmospheric studies doppler radars are promising tools for the active remote sensing of volcanic eruptions but were little applied to this field we present the observations made with a mid power uhf doppler radar voldorad during a 7 h strombolian eruption at the se crater of mount etna on 11 12 october 1998 main characteristics of radar echoes are retrieved from analysis of doppler spectra recorded in the two range gates on either side of the jet axis from the geometry of the sounding the contribution of uprising and falling ejecta to each doppler spectrum can be discriminated the temporal evolution of total power backscattered by uprising targets is quite similar to the temporal evolution of the volcanic tremor and closely reproduces the overall evolution of the eruption before during and after its paroxysm moreover during the sharp decrease of eruptive activity following the paroxysm detailed analysis of video from camera recording radar and seismic measurements reveals that radar and video signals start to decrease simultaneously approximately 2 5 min after the tremor decline this delay is interpreted as the ascent time through a magma conduit of large gas slugs from a shallow source roughly estimated at about 500 m beneath the se crater detailed analysis of eruptive processes has been also made with voldorad operating in a high sampling rate mode signature of individual outburst is clearly identified on the half part of doppler spectra corresponding to rising ejecta temporal variations of the backscattered power exhibit quasi periodic undulations whereas the maximum velocity measured on each spectrum displays a sharp peak at the onset of each outburst followed by a slow decay with time periodicity of power variations between 3 8 and 5 5 s is in agreement with the occurrence of explosions visually observed at the se vent maximum vertical velocities of over 160 m s 1 were measured during the paraoxysmal stage and the renewed activity finally by using a simplified model simulating the radar echoes characteristics we show that when voldorad is operating in high sampling rate mode the power and maximum velocity variations are directly related to the difference in size and velocity of particles crossing the antenna beam

microbiological processes in banded iron formation deposition banded iron formations have been studied for decades particularly regarding their potential as archives of the precambrian environment in spite of this effort the mechanism of their deposition and specifically the role that microbes played in the precipitation of banded iron formation minerals remains unresolved evidence of an anoxic earth with only localized oxic areas until the great oxidation event ca 2 45 to 2 32 ga makes the investigation of o2 independent mechanisms for banded iron formation deposition relevant recent studies have explored the long standing proposition that archean banded iron formations may have been formed and diagenetically modified by anaerobic microbial metabolisms these efforts encompass a wide array of approaches including isotope ecophysiological and phylogeny studies molecular and mineral marker analysis and sedimentological reconstructions herein the current theories of microbial processes in banded iron formation mineral deposition with particular regard to the mechanisms of chemical sedimentation and post depositional alteration are described the main findings of recent years are summarized and compared here and suggestions are made regarding cross disciplinary information still required to constrain the role of the biosphere in banded iron formation deposition

bayesian statistics applied to the location of the source of explosions at stromboli volcano italy abstract we present a method for determining the location and spatial extent of the source of explosions at stromboli volcano italy based on a bayesian inversion of the slowness vector derived from frequency slowness analyses of array data the method searches for source locations that minimize the error between the expected and observed slowness vectors for a given set of model parameters the conditional probability density function of slowness vectors is approximated by a gaussian distribution of expected errors the method is tested with synthetics using a five layer velocity model derived for the north flank of stromboli and a smoothed velocity model derived from a power law approximation of the layered structure application to data from stromboli allows for a detailed examination of uncertainties in source location due to experimental errors and incomplete knowledge of the earth model although the solutions are not constrained in the radial direction excellent resolution is achieved in both transverse and depth directions under the assumption that the horizontal extent of the source does not exceed the crater dimension the 90 confidence region in the estimate of the explosive source location corresponds to a small volume extending from a depth of about 100 m to a maximum depth of about 300 m beneath the active vents with a maximum likelihood source region located in the 120 to 180 m depth interval

interpretation of data from the monitoring thermal camera of stromboli volcano aeolian islands italy twenty eruptive events from the northeast crater of stromboli volcano recorded by a thermal monitoring camera in early 2004 were analysed in order to understand the eruptive dynamics selected events were chosen to be typical of explosions that characterize the steady activity of stromboli in terms of jet height and duration most of the explosions consisted of clast rich single bursts originating from the same vent inside the northeast crater conspicuous ash emission was scarce eruptions were preceded by the flashing of a perturbation wave characterized by low temperatures and an average propagation velocity of about 35 100 m s 1 this perturbation was thought to be caused by the bursting of the gas slug at the bottom of the crater and is interpreted as an air wave this was immediately followed by the expansion of a jet of hot gas and particles at a velocity of 35 75 m s 1 ejecta coarser than 138 cm appeared 1 6 2 s after the onset of the explosion moving at a variable velocity 30 60 m s 1 eruptive events were either vertical or inclined 7 13 towards the nnw this inclination is thought to be a consequence either of the morphology of the conduit following modest rock falls that partially obstructed the uppermost part of the crater or of the displacement of the internal conduit due to the explosive activity of the volcano the instability of the summit area is a further possible cause of the deformation of the conduit

characteristics of isolated hybrid tremor hbt during a calm activity period at aso volcano isolated type tremors having two events with different dominant frequencies are characteristic seismological phenomena observed during the fumarolic activity stage at aso volcano these isolated tremors are called hybrid tremors hbt and comprise two parts an initial part named the hf part with a dominant frequency in the high frequency region approximately 10 hz and the following part named the lf part with a dominant frequency in the low frequency region approximately 2 hz the lf part is observed after the hf part and the hbt is accompanied by a long period tremor lpt hypocenters and source parameters are estimated using seismograms recorded at 64 stations around nakadake crater the amplitude distributions of all hf parts have almost similar trends similarly the amplitude distributions of all lf parts have almost similar trends however the amplitude distributions of hf and lf parts are not similar from these results we proposed that the hypocenters and source parameters of hf and lf parts are not common but each of them have common hypocenters and source parameters the hypocenter region of hf parts was estimated to be just beneath the fumarole region south of the 1st crater the volume fluctuation is the major source factor the hypocenter region of lf parts is estimated to be at a depth of approximately 300 m beneath the first crater the strike slip component is the major source parameter the hypocentral depth of lf parts is located at the upper end of the crack estimated to be the source of the lpts the lpts and hbts are observed almost simultaneously we consider that volcanic fluid is involved in the source mechanisms of both hbt and lpt

strombolian eruptions and dynamics of magma degassing at yasur volcano vanuatu abstract open vent basaltic volcanoes account for a substantial portion of the global atmospheric outgassing flux largely through passive degassing and mild explosive activity we present volcanic gas flux and composition data from yasur volcano vanuatu collected in july 2018 the average volcanic plume chemistry is characterised by a mean molar co2 so2 ratio of 2 14 h2o so2 of 148 and so2 hcl of 1 02 the measured mean so2 flux in the period of 6th to 9th july is 4 9 kg s 1 therefore the mean fluxes of the other species are 7 5 kg s 1 co2 208 kg s 1 h2o and 4 8 kg s 1 hcl the degassing regime at yasur volcano ranges from passive to active styles with the latter including strombolian activity and spattering gases emitted during active degassing are enriched in so2 over hcl and co2 over so2 relative to passive degassing with co2 so2 ratios of 2 85 0 17 so2 hcl of 1 6 0 22 and h2o so2 of 315 78 8 gases emitted during passive degassing have co2 so2 ratios of 1 96 0 12 so2 hcl of 0 50 0 07 and h2o so2 of 174 43 5 we use a model of volatile degassing derived from melt inclusion studies metrich et al 2011 combined with our observations of chemical variations in the outgassing bubbles to propose a mechanism for magma degassing in the conduit at yasur we envisage a shallow conduit filled with crystal rich magma forming a viscous and mobile plug that develops an effective yield strength from the surface to a depth of at least 2000 m in which bubbles are trapped grow ascend towards the surface and burst in a typical strombolian eruption deeper bubbles released during active degassing are enriched in co2 and so2 compared to bubbles released during passive degassing which are sourced from close to the surface and are consequently hcl rich

coupled thermal oscillations in explosive activity at different craters of stromboli volcano 1 thermal infrared thermometers deployed 250 m from stromboli s active craters can detect thermal emissions during strombolian explosions explosions appear as spikes in thermal time series with variations in the mass erupted during each event revealed by pulses in the time series during may 2001 stromboli s ne and sw craters showed consistently different thermal signatures sw crater events were characterized by long lasting 10 s higher amplitude thermal signals with significant fluctuations whereas the ne crater was characterized by short 5 s impulsive lower amplitude signatures the two craters showed well correlated variations in thermal amplitude evolving over periods of several hours and providing strong evidence for linkage of the craters to a common feeding system affected by cyclic processes that drive steady variations in the style of emission

strombolian surface activity regimes at yasur volcano vanuatu as observed by doppler radar infrared camera and infrasound abstract in late 2008 we recorded a continuous multi parameter data set including doppler radar infrared and infrasound data at yasur volcano vanuatu our recordings cover a transition in explosive style from ash rich to ash free explosions followed again by a phase of high ash discharge to assess the present paradigm of strombolian behavior in this study we investigate the geophysical signature of these different explosive episodes and compare our results to observations at stromboli volcano italy to this end we characterize yasur s surface activity in terms of material movement temperature and excess pressure the joint temporal trend in these data reveals smooth variations of surface activity and regime like persistence of individual explosion forms over days analysis of all data types shows ash free and ash rich explosive styles similar to those found at stromboli volcano during ash free activity low echo powers high explosion velocities and high temperatures result from the movement of isolated hot ballistic clasts in contrast ash rich episodes exhibit high echo powers low explosion velocities and low temperatures linked to the presence of colder ash rich plumes furthermore ash free explosions cause high excess pressure signals exhibiting high frequencies opposed to low amplitude low frequency signals accompanying ash rich activity to corroborate these findings we compare fifteen representative explosions of each explosive episode explosion onset velocities derived from doppler radar and infrared camera data are in excellent agreement and consistent with overall observations in each regime examination of infrasound recordings likewise confirms our observations although a weak coupling between explosion velocity and excess pressure indicates changes in wave propagation the overall trend in explosion velocity and excess pressure however demonstrates a general correlation between explosive style and explosion intensity and points to stability of the uppermost conduit on timescales shorter than at stromboli volcano

probabilistic source location of explosion quakes at stromboli volcano estimated with double array data data from two dense arrays of short period seismometers are used to retrieve source locations of the explosion quakes at stromboli volcano slowness vectors estimated at both arrays with the zero lag cross correlation technique constitute the experimental data set a probabilistic approach based on a grid search spanning the volcano interior is used to calculate the probability of the source location results depict a shallow source located beneath the crater area at depths not greater than 500 m below the surface results are slightly different from but comparable to those obtained in a companion experiment carried out in the same time period using a broad band seismometer network which show a source shifted some hundreds of meters northwest of the crater area the method is revealed to be effective and useful for future studies having the purpose of real time tracking of the explosion quakes and tremor