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

broadband seismic experiment at merapi volcano java indonesia very long period pulses embedded in multiphase earthquakes abstract multiphase mp and low frequency lf earthquakes with spectral peak amplitudes at 3 4 and 1 hz respectively are two common types of shallow volcanic earthquakes previously recognized at merapi volcano their mechanisms are poorly understood but mps have been temporally associated with lava dome growth we conducted a seismic experiment in january february 1998 using four broadband seismographs to investigate the nature of seismic activity associated with dome growth during our experiment merapi experienced mild dome growth with low level seismic activity we compare our data to that recorded on a local short period sp network with the following preliminary results mp and lf events as recorded and classified on the short period network instruments were recognized on the broadband network frequency spectrograms revealed similar patterns in the near summit region at widely separated broadband stations higher frequency spectra than previously recognized were identified for both mp and lf events and were strongly attenuated as a function of radial distance from the source thus the spectral characteristics of these events as recorded on far field stations are not fully indicative of the source processes in particular many events classified as lf type appear to have much high frequency energy near the source this aspect of these so called lf earthquakes and their association with very long period vlp pulses suggests that many events identified in the far field as lf events are in actuality a variety of the mp event and involve similar source processes broadband records indicated that simple large amplitude vlp pulses were embedded in mp and lf wavetrains from event to event these pulses were similar in their waveforms and had periods of 4 s vlp events embedded in lf and mp earthquakes were located using particle motions the epicenters were clustered in a central region of the dome complex and preliminary source depths were within about 100 m of the dome surface suggesting a source region deep within the dome or the uppermost conduit a similar source location was established by study of mp high frequency onsets our broadband data suggests that we have recorded both elastic seismic waves and a simple embedded pulse that is interpreted to represent a surface tilt at the seismometer site the inferred tilt indicates an inflation and subsequent deflation possibly caused by a gas pressure pulse or episodic shallow magma transport with stick slip movement of the conduit wall

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

seismic and infrasonic signals associated with an unusual collapse event at the soufriere hills volcano montserrat 1 in march 2004 during a period of no magma extrusion at soufriere hills volcano montserrat an explosive event occurred with little precursory activity recorded broadband seismic signals ranged from an ultra long period signal with a dominant period of 120 s to impulsive short duration events containing frequencies up to 30 hz synthetic displacement functions were fit to the long period data after application of the seismometer response these indicate a shallow collapse of the volcanic edifice occurred initiated 300 m below the surface lasting 100 s infrasonic tremor and pulses were also recorded in the 1 20 hz range the high frequency seismicity and infrasound are interpreted as the subsequent collapse of a gravitationally unstable buttress of remnant dome material which impacted upon the edifice surface this unique dataset demonstrates the benefits of deploying multi parameter stations equipped with broadband instruments

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

on the relation between infrasound seismicity and small pyroclastic explosions at karymsky volcano 1 ground and atmospheric propagating elastic waves are integrated with digitized video to reconstruct important parameters during the onset of eruptions at karymsky volcano in 1999 muzzle velocities which range from 10 to 55 m s for 34 analyzed explosive events are found to be very well correlated with eruption velocities synthesized from infrasonic trace data acoustic modeling proposed here invokes a linear acoustic source consistent with a 3 m piston that accelerates upwards timing of acoustic arrivals relative to video records of material emission is used to constrain fragmentation sources depths which are assumed to be coincident with infrasound generation these sources are generally shallow with an observed vertical range of about 15 m systematic changes in source depth are observed during two nights of data collection and are attributed to variations in the depth of the magma free surface relative timing of acoustic and seismic arrivals is used to identify the presence of seismicity prior to fragmentation this seismicity is emergent and low intensity but significant because it precedes the presumed fragmentation events by variable amounts up to 4 s the primary short period seismic phases appear coincident with the initiation of fragmentation and infrasound generation because of the complexity of the seismic green s function it is not possible to correlate amplitude from a specific seismic pulse with observed eruption intensity

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

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

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

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

on the spectral peaks of volcanic tremor at stromboli abstract seismic activity at stromboli volcano is characterized by a variety of signals emanating from three vents for a long time the northwest vent has been in constant activity periodically large explosions occur and material is ejected beyond the crater walls these large explosions are accompanied by sonic and infrasonic pressure waves in the atmosphere and explosion quakes apart from large explosions there is constant activity in the form of continuous gas bursts which are related to low infrasonic pulses in the atmosphere and volcanic tremor we assume that volcanic tremor and low pressure infrasonics are generated by gas bubbles inside the volcanic conduit and accordingly we compute synthetic tremor by modeling the source function as a pressure variation in a spherical cavity that propagates through a finely layered medium by means of haskell s formalism to simulate a tremor we superpose in time domain a large number of such pulses of varying amplitudes and time delays according to the observed infrasonic series in addition to the spectral similarity the observed and synthetic tremor display the same autocorrelation and hurst exponents implying similar long term correlation we present strong evidence in favour of an interpretation of the spectral peaks of the volcanic tremor at stromboli in terms of resonances of the layered structure hence as a path effect rather than a source effect

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

evidence for remotely triggered microearthquakes during salt cavern collapse summary microseismicity is a good indicator of spatio temporal evolution of physical properties of rocks prior to catastrophic events like volcanic eruptions or landslides and may be triggered by a number of causes including dynamic characteristics of processes in play or and external forces we show evidence of triggered microseismicity observed in the vicinity of an underground salt cavern prone to collapse by a remote m 7 2 earthquake which occurred 12 000 km away high dynamic range broad band records reveal the strong time correlation between a dramatic change in the rate of local high frequency microseismicity and the passage of low frequency seismic waves including body love and rayleigh surface waves pressure was lowered in the cavern by pumping operations of brine out of the cavern we demonstrate the near critical state of the cavern before the collapse by means of 2 d axisymmetric elastic finite element simulations on this basis we show that the increment of stress necessary for the failure of the dolomite layer which ensures the stability of the whole system is of the same order of magnitude as the maximum dynamic stress magnitude observed during the passage of the earthquakes waves this suggests that the stress oscillations due to the seismic waves correlated with the recorded microearthquakes induced damage of the overburden which eventually led to the collapse of the salt cavern we show that the contribution of rayleigh waves is the most efficient to trigger microseismicity at periods close to the natural fundamental frequency of the cavern system found at about 10 20 s by investigating the impulse response of the cavern overburden brine system

self potential variations associated with ultra long period seismic signals at merapi volcano 1 we report about self potential sp anomalies registered 150 m from the active lava dome of merapi volcano which are associated with ultra long period ulp seismic signals periods 100 s during a 5 month period of simultaneous sp and seismological measurements 50 ulp events were detected seismologically if sp time series corresponding to ulp events are aligned to the onset times of ulp events and stacked the resulting traces show anomalous sp with an amplitude of 5 20 mv km and 40 60 min duration in contrast the anomalous signals were not present in ground temperature data nor in sp data recorded 1 km from the summit sp anomalies associated with ulp seismicity might be caused by electro kinetic effect of fluid flow in subsurface this result is consistent with the ulp generation model based on seismological observations and adds new information towards the understanding of ulp seismicity

canonical model of volcano acoustics a full wave theoretical model is developed for the acoustic field generated by an explosive point source embedded in a magma column that is open to the atmosphere the green s functions for the field in the magma and the atmosphere are derived on the basis of several simplifying assumptions concerning the geometry of the conduit the boundary conditions and the geoacoustic properties of the magma a kinematic model for the acoustic signature of the explosive source is proposed which when combined with the green s functions provides full analytical expressions for the acoustic field in the magma and in the atmosphere as complex functions of frequency by fourier inversion the airborne pressure spectrum is transformed into a pressure time series the predicted sound pulse in the atmosphere and its energy spectrum are highly dispersive showing complicated structure that arises from the coherent addition of many normal modes of oscillation i e depth and radial resonances in the magma column at high frequencies for which the aperture of the vent is many wavelengths across each mode is launched into the atmosphere as a parallel sided beam of sound with a characteristic angle of elevation which through snell s law is determined by the speed of sound in the magma relative to that in air at somewhat lower frequencies the modal beams of sound undergo angular spreading due to diffraction at the edge of the vent in the lowest frequency regime where the wavelength is comparable with the aperture the airborne field shows little angular structure a comparison between airborne acoustic data that we recorded in july 1994 at the western vent of stromboli volcano and the predictions of the theory using parameters that are characteristic of stromboli show compelling agreement the theoretical and observed power spectra both display the following features 1 a concentration of energy below 20 hz associated with the first four longitudinal resonances 2 radial resonances between 35 and 65 hz and 3 a broad minimum around 30 hz arising because the source lies near nulls in longitudinal modes that would otherwise be excited the conclusion is that the airborne sound signature from an explosive volcanic event may be inverted to provide estimates of the depth and radius of the magma conduit the depth spectral shape and peak shock wave pressure of the source and the viscosity of the magma

wavelet coherence analysis of broadband array data recorded at stromboli volcano italy we present a wavelet coherence method that is capable of displaying local coherence information between two seismic stations in the sense of a spectrogram we have analyzed the vertical components of a 20 min long time series from four stations that were situated in the seismic near field of stromboli volcano typical volcanic seismic signals recorded in the near field of stromboli volcano consist of continuous volcanic tremor superimposed on frequent strombolian explosion signals the tremor exhibits a banded and frequency stable structure whereas the broadband explosion signals span two or three frequency decades we demonstrate that signals related to explosion earthquakes are strongly correlated within the network over 1 5 frequency decades using synthetic data we show how coherent signal portions can be extracted out of noisy data using a coherence filtering method a time delay analysis using coherence information results in a coarse source location estimation that lies within the crater region with the exception of randomly fluctuating coherence peaks low correlations have been observed in the characteristic bands that are assumed to be generated by continuous tremor in the low frequency band that is related to the ocean microseisms period 4 8 sec we observe mostly high correlation that breaks down during the appearance of explosion earthquake signals based on further analysis using the inverse wavelet transformation we propose a model that describes the breakdown phenomenon as a superposition of two independent events

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

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

tilt signals derived from a geoscope vbb station on the piton de la fournaise volcano we report some very long period transients observed on a very broadband seismic station of the geoscope network which is situated 8 km away from the summit of the piton de la fournaise volcano we transform the ground velocity measured by the seismic station into tilt and test the result by comparing with data from blum type classical pendulum tiltmeters located in the same vault the comparison validates the use of the horizontal seismometers for measuring tilt for periods shorter than 25 hours the method is applied to the transients observed prior to several eruptions and magmatic intrusions since 1991 because of the moderate distance between geoscope station and the summit of the volcano the obtained tilt measurements provide information about eruptions and intrusions which complement the information on the geometry and location of the magmatic source provided by the summit tilt network

interaction of seismic and air waves recorded at stromboli volcano explosion quake seismograms recorded at stromboli show that seismic phases with a high amplitude and high frequency content propagate with a velocity of approximately 330 m s the sound speed the analysis of seismograms recorded at a distance of 500 m from one of the three active vents shows for the first onset a low frequency and particle motion characteristic of a p wave which loses its longitudinal polarization with the onset of the air wave recording the explosion quakes simultaneously with a microphone we could ascertain that the high frequency onset coincided with the air wave s in order to better understand the seismic wavefield generated by the atmospheric pressure we performed a controlled source experiment at stromboli using a seismic gun seismograms with the same two phases and particle motions comparable with the volcano seismic data were obtained a second experiment demonstrated that the air wave propagates at least in the uppermost 1 m of the ground we suggest that the seismic source of the corresponding seismograms is an explosion at the top of the magma column and conclude that the p and air waves are both generated in the same point and at the same time

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

marine carbonate systems in the sarmatian middle miocene of the central paratethys the zsambek basin of hungary the study of eight stratigraphic sections at the margin of the semi enclosed zsa mbe k basin hungary allows the sedimentary anatomy of oolitic bioclastic systems in the sarmatian of the central paratethys to be reconstructed the mollusc foraminiferal and ostracod associations indicate that the carbonate systems are latest badenian to late sarmatian in age the lower upper sarmatian deposits are organized in superimposed subaqueous dunes prograding towards the basin on a low angle ramp during the late sarmatian the ramp underwent subaerial erosion linked to a moderate relative fall in sea level lagoonal deposits were later formed and microbial nubeculariid bryozoan serpulid buildups were emplaced the abnormal marine conditions of the sarmatian conducive to the development of a poorly diversified flora and fauna and dominant non skeletal grains are linked to fluctuating salinities mesotrophic to eutrophic conditions and perhaps high alkalinity

magmatic dike resonances inferred from very long period seismic signals very long period vlp signals showing simple decaying harmonic oscillations with periods near 10 seconds and lasting for about 300 seconds were observed in association with an earthquake swarm that occurred beneath hachijo island japan results from the source mechanism analysis and waveform simulation based on a fluid filled crack model consistently point to the resonance of a dike filled with a basaltic magma as the source of the vlp signals thus vlp signals can be used to probe the state of the fluid and dynamic processes within a volcanic system

strombolian explosions 2 eruption dynamics determined from acoustic measurements strombolian activity consists of a series of explosions due to the breaking of a large overpressurized bubble at the surface of the magma column acoustic pressure due to sound waves has been measured and analyzed at stromboli for more than 50 explosions three parts can be distinguished in the acoustic pressure waveform which are related to the behavior of the bubble before during and after its bursting before the sharp rise in acoustic pressure the signal is dominated by waves with a frequency of 2 hz which develop on the nose of the bubble they produce sound in air by imposing a rapid motion to the interface and one could detect a bubble travelling in the uppermost 30 m of the magma column when the bubble reaches the air magma interface its strong vibration driven by a large overpressure inside the gas generates the main event with a frequency around 9 hz after the bubble has burst kinematic waves of frequency around 4 5 hz are the main source of sound they develop at the surface of the magma left on the conduit side the three types of motion although determined independently give consistent results furthermore combining the results obtained for the two types of kinematic waves the magma viscosity is estimated to be of 300 65 pa s which is in good agreement with petrological constraints and corroborates the validity of our analysis this suggests that acoustic measurements constitute a powerful tool in the understanding of eruption dynamics

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

radiative heat power at stromboli volcano during 2000 2011 twelve years of modis observations abstract twelve years of night time modis moderate resolution imaging spectroradiometer observations has been analysed to detect and quantify the radiative heat power emitted by stromboli volcano from march 2000 to september 2011 using an accurate background subtraction of the modis signal at 4 m we were able to discriminate two main regimes of thermal radiation related to different levels of volcanic activity effusive eruptions occurred on december 28 2002 and february 27 2007 radiated at an average of 186 mw with a frequency of alert detection of 50 95 conversely during the typical strombolian activity an average of 9 mw is radiated with a frequency of alert detection of 0 45 although during the effusive eruptions the radiative power is basically controlled by the lava discharge rate our results suggest that during non effusive periods strombolian regime both the intensity and the frequency of modis alerts are controlled by the height of the magmatic column feeding the activity at the surface in particular we found that a radiative power of 50 mw corresponds to a high magma column which is exposed in the vent area at the same rate in which the deeper gas rich magma is typically supplied within the feeding system of stromboli 0 3 m3 s 1 in this condition the magmatic system approaches steady state regimes above this threshold a transition from strombolian to effusive regimes may occur as shown by the detection of 50 mw 8 10 days before the onset of both the last two major flank eruptions these values were reached after 1 2 months of gradual increase of the radiative power which was likely associated the rising of the magma column within the shallowest portion of the conduit in addition our data suggest that over the years 2000 2011 several cycles of rise and fall of the magma column have occurred which however did not culminate into an effusive eruption but only into recurrent episodes of sustained spattering or fountaining and summit overflows these fluctuations has substantially increased in frequency and intensity after the 2007 eruption thus suggesting that this event has perturbed in some way the shallow plumbing system of stromboli we stress that the detection of a radiative power higher than 50 mw is a clear evidence of a very high magma column which may prelude the onset of an effusive eruption and or periods of sustained vent activity in conclusion we suggest that systematic analysis of modis data can be used to detect variations in the intensity of strombolian activity and may considerably improve volcano surveillance at stromboli as well as at other open system volcanoes

multipath variability due to the gulf stream a phase coded signal with 64 ms resolution was transmitted at 10 min intervals for a 19 day period over two 300 km ranges the acoustic source was moored at 2000 m depth northwest of bermuda one receiver was moored at 2000 m depth to the northeast of the source and the other receiver was bottom mounted at 1000 m depth near bermuda the large 0 6 s travel time change at the bermuda receiver is probably due in large part to motion of the source mooring in the presence of currents the multipath arrival pattern at the moored receiver undergoes significant modification due to the presence of a southern meander of the gulf stream which intersects this transmission path

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

anatomy of a strombolian eruption inferences from particle data recorded with thermal video over the past decade a proliferation of new technologies has pushed forward our ability to measure the dynamics of volcanic emissions as they exit and ascend above the vent measuring parameters of all particles as they exit the vent during an explosive eruption is the best way to gather parameters such as size shape velocity and mass for the solid particulate fraction of the plume in our case this being the lapilli and bomb component we compute particle velocities and size distributions using high spatial resolution centimeter sized pixel thermal infrared imagery collected at 200 hz for small explosive eruptions at stromboli italy our study covers 13 eruptions from stromboli s southwest crater that occured in october 2012 plus 13 eruptions from the southwest crater and 5 eruptions from the northeast crater in may 2014 we obtain a statistically robust database for size mass and velocity of 83 000 particles most particles have sizes of 5 to 15 cm so that the majority of individual particle masses are below 0 4 kg however 4950 6 of the particles are heavier than 5 kg and represent 59 of the total mass erupted we also show that the smallest particles detected have the highest velocities with the maximum recorded vent leaving velocity being 240 m s while the thermal data provide insights into particle emission and launch dynamics correlation with seismic data sheds light on the source mechanism our results lead us to suggest that pyroclast dominated explosions are a consequence of the presence of a viscous degassed cap at the head of the magma column whereas gas dominated events are a consequence of slug bursting in a cleaner conduit the cap having been lost by convective overturn

inverting the source mechanism of strombolian explosions at mt yasur vanuatu using a multi parameter dataset abstract the source mechanism of strombolian explosions at mt yasur vanuatu is analyzed using a unique data set which enables us to combine different methodologies the novelty of the approach presented here lies in the combination of seismic acoustic and doppler radar data thus using infrasound and doppler radar observations we are able to provide independent estimates of the volume of the eruptive source in the following we show that a correlation exists between source volume and the maximum particle velocity of the expelled volcanic products in order to determine the source location and the associated mechanism and to compare those two methods we use time reversal imaging and moment tensor inversion while the first method also applies to extended sources the latter might be biased by its intrinsic point source approximation we show that time reversal imaging can deliver an estimate of the source depth without any a priori assumptions even in an unfavorable scenario in terms of topography and receiver setup the inverted source mechanism retrieved from moment tensor inversion is found to be largely isotropic with minor deviatoric components the inverted source location points towards an area to the north west of the active craters indicative of a common feeder system of the activity at mt yasur however it is also evident that to fully locate the source of strombolian activity at yasur location precision must be enhanced

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

shallow degassing events as a trigger for very long period seismicity at kīlauea volcano hawai i the first eruptive activity at k lauea volcano s summit in 25 years began in march 2008 with the opening of a 35 m wide vent in halema uma u crater the new activity has produced prominent very long period vlp signals corresponding with two new behaviors episodic tremor bursts and small explosive events both of which represent degassing events from the top of the lava column previous work has shown that vlp seismicity has long been present at k lauea s summit and is sourced approximately 1 km below halema uma u by integrating video observations infrasound and seismic data we show that the onset of the large vlp signals occurs within several seconds of the onset of the degassing events this timing indicates that the vlp is caused by forces sourced at or very near the lava free surface due to degassing transmitted down the magma column and coupling to the surrounding rock at 1 km depth

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

seismicity on volcanoes generated by gas slug ascent 1 very long period vlp signals provide a unique insight into the source process of seismic signals recorded on active or restless volcanoes this is due to the large wavelengths that may allow the structural heterogeneity to be ignored hence source inversions can be calculated the source process involved in such events is thought to be related to magma transport gas slug ascent or dike resonance initiated by a fluid driven process numerical modelling of gas slug ascent constrained by results from published laboratory experiments shows that this process is capable of generating long period and vlp like signals inputting the fluid dynamic derived forces into an elastic medium with volcano like topography vlp signals are reproduced a moment tensor inversion is performed on these synthetic vlp signals retrieving the correct input source mechanism a pipe structure

long period and very long period events at mt etna volcano characteristics variability and causality and implications for their sources abstract almost 50 000 long period lp events were recorded at mt etna from november 2003 to may 2006 we analysed these events as well as very long period vlp events which were associated with some of them during some intervals the spectral and wavefield features of lp events remained steady with significant changes occurring between the intervals based on the times of the changes we distinguish five different sub periods in particular during sub period iii june november 2005 the wavefield at the stations nearest to the summit area was composed of p waves locations for 150 lp events occurring in sub period iii determined using radial semblance changed at the same time as the events spectral features changed it was during this sub period that many of the lp events were associated with vlp events based on similarity of the waveforms we distinguished two families of vlp events with gradually evolving waveforms the two families are located in slightly different places but near the sources of the lp events the change between the families occurred at the same time as the spectra of the lp events changed finally the source of the vlp events was investigated by performing complete waveform moment tensor inversion of stacks of the two families synthetic green s functions for the full moment tensor were calculated for a homogeneous half space for both families the source region with the highest variance reduction lies approximately beneath the active craters at 500 m below the altitudes of the stations the solutions for both families are very similar with sources that are between 60 and 70 isotropic attempts to determine deviatoric moment tensors produced consistently poorer fits the remaining energy is poorly constrained and is likely to be noise in conclusion these results highlight changes in the lp and vlp events at mt etna over time and the causal relationship between them

image processing of explosive activity at stromboli abstract a new way to study the dynamics of explosive behaviour at different vents of stromboli volcano is proposed the method is based on computer processing of images taken by an infrared film camera at a rate of 4 pictures per second each picture has been digitized by use of an image scanner with a 75 d p i dots per inch resolution and 256 levels of gray then processed and the total mass of the ejected material has been calculated for each photograph with this procedure the flux of ejected matter throughout every single explosive event has been reconstructed the analysis of trajectories made on adequate samples of ejecta has allowed us to evaluate the ejection velocity the mode of the mass flux distribution and the mean value of the velocities calculated for individual particles quantify the kinetic energy of an explosion vents nos 1 and 3 which remained active after the last effusive eruption of 1985 1986 show several explosive patterns the energy of which is measured the observed flux distributions have been checked both numerically and experimentally by modelling impulsive events the computer simulations of the mass distributions have allowed us to speculate on the possible explosive dynamisms two different models have been used a single impulse model confirms the behaviour actually shown by one of the two vents while the behaviour of the other is better depicted by a cumulative trend of successive impulses in rhythmic sequence moreover through the experimental approach we have had the opportunity to test the overall resolution of the method the observed matter flux distribution has then been associated to the seismic signals in order to correlate the dynamics involved in the explosions with the seismic source mechanisms

effusive to explosive transition during the 2003 eruption of stromboli volcano the persistent explosive activity of stromboli volcano italy ceased in december 2002 and correlated with the onset of a seven month long effusive eruption on the volcano flank from new vents that opened just below the summit craters we intensively monitored this effusive event collecting and interpreting in real time an extensive multiparametric geophysical data set the resulting data synergy allowed detailed insights into the conduit dynamics that drove the eruption and the transition back to the typical strombolian activity we present a direct link between gas flux magma volume flux and seismicity supporting a gas driven model whereby the balance between gas flux and gas overpressure determines whether the system will support effusive or explosive activity this insight enabled us to monitor the migration of the magma column up the conduit and to explain the onset of explosive activity

eruption source processes derived from seismic and acoustic observations of the 25 september 2007 ruapehu eruption north island new zealand abstract mt ruapehu erupted on 25 september 2007 at 20 26 pm nzdt 8 26 ut generating a steam column to about 15 000 ft 4600 m a directed ballistic and surge deposit of coarse blocks and ash to the north of the crater lake and initiated lahars in the whangaehu catchment and whakapapa ski field the eruption was recorded on three broadband seismometers and two acoustic pressure sensors which indicated broadly coherent waveform characteristics across the network the eruption had a duration of less than 1 min as indicated by strong seismic and acoustic pulses the acoustic wave coincided with observed very long period vlp seismic signal 2 25 s period the acoustic pulse had a positive pressure indicating an explosion and travelled at a velocity of 320 m s the syn eruptive vlp was composed of surface waves having strong radial and transverse components the immediate aftermath of the eruption produced about 4 min of continued high amplitude spasmodic tremor signals that probably resulted from post explosion phase associated vent backfill stabilisation the eruption was preceded by minor volcano tectonic earthquakes and tremor bursts which began 10 min before the main eruption two smaller vlp signals were associated with these tremor pulses at 20 17 and 20 25 these pre eruptive vlp signals had particle motions indicating body and surface waves from a sub surface source region modelling of the vlp sources using a 3d finite difference method shows that that the pre eruption vlp signals are consistent with a volume fluctuation at 3 7 km depth from a radially symmetric source the main eruption vlp was consistent with a south and downward directed single force in response to a northward directed jet and northward directed ballistic deposits

low frequency seismic signals recorded by obs at stromboli volcano southern tyrrhenian sea 1 five three component broadband ocean bottom seismometers obss were deployed on the seafloor around the aeolian islands southern tyrrhenian sea by comparing obss digital seismograms we found a low frequency seismicity recorded only at obs05 the nearest seafloor station to stromboli volcano this seismicity appears in the form of a continuous seismic signal tremor like signal as well as a considerable number of shock like events we focused on recordings from obs05 to verify their correlation with stromboli volcanic activity from the spectral analysis we observed low frequency events lp events superposed upon the continuous background noise tremor lp events and tremor showing similar energy fluctuations and frequency content appear to be produced by the same dynamic processes we interpret this low frequency seismicity as probably originating from a continuous uprising of gas bubbles from the deeper part of the stromboli magmatic column this could highlight the existence of a deeper source for low frequency seismicity

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