quiescent explosive transitions during dome forming volcanic eruptions using seismicity to probe the volcanic processes leading to the 29 july 2008 vulcanian explosion of soufriere hills volcano montserrat

enhanced terrestrial weathering runoff and surface ocean carbonate production during the recovery stages of the paleocene eocene thermal maximum 1 the carbonate saturation profile of the oceans shoaled markedly during a transient global warming event known as the paleocene eocene thermal maximum petm circa 55 ma the rapid release of large quantities of carbon into the ocean atmosphere system is believed to have triggered this intense episode of dissolution along with a negative carbon isotope excursion cie the brevity 120 220 kyr of the petm reflects the rapid enhancement of negative feedback mechanisms within earth s exogenic carbon cycle that served the dual function of buffering ocean ph and reducing atmospheric greenhouse gas levels detailed study of the petm stratigraphy from ocean drilling program site 690 weddell sea reveals that the cie recovery period which postdates the cie onset by 80 kyr is represented by an expanded 2 5 m thick interval containing a unique planktic foraminiferal assemblage strongly diluted by coccolithophore carbonate collectively the micropaleontological and sedimentological changes preserved within the cie recovery interval reflect a transient state when ocean atmosphere chemistry fostered prolific coccolithophore blooms that suppressed the local lysocline to relatively deeper depths a prominent peak in the abundance of the clay mineral kaolinite is associated with the cie recovery interval indicating that continental weathering runoff intensified at this time as well robert and kennett 1994 such parallel stratigraphic changes are generally consonant with the hypothesis that enhanced continental weathering runoff and carbonate precipitation helped sequester carbon during the petm recovery period e g dickens et al 1997 zachos et al 2005

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

repeated fracture and healing of silicic magma generate flow banding and earthquakes textures in an exceptionally preserved effusive rhyolite conduit at torfajokull iceland indicate that rising magma repeatedly fractured and healed at shallow levels in the conduit rfh process anastomosing tuffisite veins filled by fine grained juvenile clasts were generated by shear fracture of highly viscous magma in the glass transition interval welding of the particulate material during subsequent deformation led to thorough healing of veins allowing repeated fracture of the same body of magma we propose that the rfh process is a rechargeable trigger mechanism for hybrid seismicity and show that the time scale of the process and the fractures formed by it are consistent with the repeat time and magnitude of hybrid earthquakes during silicic eruptions the rfh process may also form the flow banding that is nearly ubiquitous in obsidian

water magma interaction some theory and experiments on peperite formation experiments using molten thermite as a magma analog produce peperite when the melt interacts with wet sand these experiments also show explosive behavior developing strombolian and surtseyan like bursts the results demonstrate that the application of fuel coolant interaction fci theory is appropriate for interpretation of peperites the theory described includes discussion of the importance of mass interaction ratios of wet sediment and magma rs which determine thermal equilibrium temperature limits and contact interface dynamics the dynamics of the interface between magma and wet sediments involves heat transfer over a wide range of rates from passive quenching to explosive fragmentation a vapor film layer develops at the interface and acts both as an insulating barrier promoting passive quenching as well as a potential energy reservoir that can cause magma fragmentation mingling of the magma with wet sediments and explosive quenching when the vapor film becomes unstable an important parameter in determining the behavior of the vapor film is the value of rs which controls whether heat can be convectively removed from the layer as more is being added from its contact with magma if rs 1 for fully saturated sediments there is enough water in the sediments to make convective heat flow effective in quenching the magma but below that value there is the potential that the vapor film will be unstable producing highly dynamic phenomena including explosive fragmentation at values of rs 0 1 there is insufficient water to allow the escalation of explosive fragmentation

magnetofossil spike during the paleocene eocene thermal maximum ferromagnetic resonance rock magnetic and electron microscopy evidence from ancora new jersey united states previous workers identified a magnetically anomalous clay layer deposited on the northern united states atlantic coastal plain during the paleocene eocene thermal maximum petm the finding inspired the highly controversial hypothesis that a cometary impact triggered the petm here we present ferromagnetic resonance fmr isothermal and anhysteretic remanent magnetization first order reversal curve and transmission electron microscopy analyses of late paleocene and early eocene sediments in drillcore from ancora new jersey a novel paleogeographic analysis applying a recent paleomagnetic pole from the faeroe islands indicates that new jersey during the initial eocene had a 6 9 degrees lower paleolatitude 27 3 degrees for ancora and a more zonal shoreline trace than in conventional reconstructions our investigations of the petm clay from ancora reveal abundant magnetite nanoparticles bearing signature traits of crystals produced by magnetotactic bacteria this result the first identification of ancient biogenic magnetite using fmr argues that the anomalous magnetic properties of the petm sediments are not produced by an impact they instead reflect environmental changes along the eastern margin of north america during the petm that led to enhanced production and or preservation of magnetofossils

observations of long period earthquakes accompanying hydraulic fracturing waveforms of most seismic events accompanying hydraulic fracturing have been reported to contain clear p and s waves and have fault plane solutions consistent with shear displacement across a fault this observation is surprising since classical hydraulic fracturing theory predicts the creation of a tensile opening of a cavity in response to fluid pressure very small long period events similar to long period earthquakes observed at volcanoes were found to occur during four hydraulic fracturing experiments carried out at fenton hill new mexico since the long period earthquakes occur in the same region as the shear type events it is concluded that the unusual character of the long period earthquake waveforms is due to a source effect and not a path effect the occurrence of long period earthquakes during hydraulic fracturing could indicate tensile fracturing many waveforms of these events are identical which implies that these events represent repeated activation of a given source a proposed source for these long period events is the sudden opening of a channel that connects two cracks filled with fluid at different pressures the sizes of the two cracks differ which causes two or more peaks to appear in the spectra each peak beingmore associated with one physical dimension of each crack from the frequencies at which spectral peaks occur crack lengths are estimated to be between 3 and 20m less

strombolian explosions 1 a large bubble breaking at the surface of a lava column as a source of sound strombolian activity consists of a series of explosions caused by the breaking of large overpressurized bubbles at the surface of the magma column acoustic pressure has been measured for 36 explosions at stromboli we propose that sound is generated by the vibration of the bubble before it bursts oscillations are driven by an initial overpressure inside the bubble assumed to be initially at rest just below the magma air interface inertia effects cause the bubble to overshoot its equilibrium radius then the bubble becomes underpressurized and contracts because of gas compressibility these oscillations are only slightly damped by viscous effects in the magma layer above the bubble the bubble cannot complete more than one cycle of vibration because of instabilities developing on the magma layer that lead to its breaking near the minimum radius assuming a simple geometry we model this vibration and constrain the radius and length of the bubble and the initial overpressure by fitting a synthetic waveform to the measured acoustic pressure the fit between synthetic and observed waveforms is very good both for frequency 60 rad s 1 and amplitude the initial bubble radius is 1 m and the length varies between several and a few tens of meters from the initial overpressure approximately 105 pa we calculate the maximum radial velocity of ejecta 30 m s 1 the generally good agreement between data and predictions of our model leads us to suggest that acoustic measurements are a powerful tool for the understanding of eruption dynamics

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

precursory characteristics of the seismicity before the 6 august 2012 eruption of tongariro volcano north island new zealand abstract the 6 august 2012 eruption from the upper te maari crater of tongariro volcano followed approximately three weeks of precursory seismic activity earthquake relocations including data from extra temporary stations indicated that nearly all events were in a small area very close to upper te maari most of these relocated events were very shallow with nearly all events being between 1000 and 1500 m below the ground surface the pre eruption seismicity occurred in three main swarms during the first swarm on 12 13 july 2012 all the earthquakes had consistent inter event times of 71 8 min while in the later swarms 17 20 and 29 30 july many events had a similar pattern of consistent inter event times the stationary quasi periodic clockwork earthquake process suggests that a single fracture point was excited by a nearly constant rate flux process the dominant type of earthquake observed in these swarms had a sharp onset and a broad spectrum with strong energy from 2 to 10 hz most events seen had a local magnitude of 1 5 to 2 5 with virtually no smaller events most of these earthquakes appeared to belong to a main earthquake family whose characteristics included a strong spectral component at about 2 hz and three bursts of energy spaced at intervals of about 1 5 s of the 116 located earthquakes 75 had a correlation coefficient greater than 0 70 with a master event the spectra of these events did not change with size with matching frequency peaks for all the events with a high correlation the last event of this type was the day before the 6 august 2012 eruption none have been seen since and there has been very little seismicity under tongariro this seismicity alerted gns science and other organisations to the unrest of tongariro and the volcanic alert level and aviation colour code were raised to publicise this gns science also increased its monitoring of tongariro and discovered that the magmatic gas concentrations had increased compared to previous measurements in may 2012 however the seismicity did not show any accelerating trend that suggested an immediate eruption threat indicating the difficulty of predicting small eruptions in tongariro and similar volcanoes

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

seismicity accompanying the 1999 eruptive episode at telica volcano nicaragua abstract telica volcano nicaragua is a persistently restless basaltic andesite stratovolcano located in the central american volcanic front a high rate of low frequency seismic events lfs has been recorded at telica since the installation of a single vertical component 1 hz seismic sensor teln near its summit in 1993 due to the high rate of lfs at telica traditional methods of forecasting volcanic activity based on increases in the overall rate of seismicity are not applicable therefore an understanding of the nature of precursory changes in telica s seismicity is necessary to forecast future volcanic activity in may 1999 a nine month eruptive episode started at telica consisting of phreatic to phreatomagmatic explosions here we analyse over 29 000 seismic events recorded during a fifteen month period of seismicity bracketing this eruptive episode in an attempt to retrospectively identify precursory changes in seismicity seismic event rates between january 1999 and march 2000 show a reduction in the lf event rate three months before the onset of eruptive activity closely followed by a short lived swarm of high frequency hf 5 hz events after a three month data gap a second reduction in the lf event rate started in august 1999 directly following eruptive activity in august and approximately two months before a series of explosions in october 1999 this reduction in the lf event rate was closely followed by a short lived swarm of hf events that was coincident with the onset of numerous 22 short lived but populous lf multiplets a further reduction in event rate for both lfs and hfs is evident in the months between the october 1999 explosions and explosions on the 29th of december 1999 we suggest that these changes in seismicity reflect a transition from open system degassing to closed system degassing at telica and could signify a change in the volcanic system preceding future episodes of phreatic to phreatomagmatic activity at telica and similar persistently restless volcanic systems worldwide we note that these signals are for phreatic to phreatomagmatic activity and thus may not pertain to magmatic volcanism or to other persistently restless volcanoes prior to their magmatic activity

spatial extent of a hydrothermal system at kilauea volcano hawaii determined from array analyses of shallow long period seismicity 2 results we present a probabilistic method to locate the source of seismic events using seismic antennas the method is based on a comparison of the event azimuths and slownesses derived from frequency slowness analyses of array data with a slowness vector model several slowness vector models are considered including both homogeneous and horizontally layered half spaces and also a more complex medium representing the actual topography and three dimensional velocity structure of the region under study in this latter model the slowness vector is obtained from frequency slowness analyses of synthetic signals these signals are generated using the finite difference method and include the effects of topography and velocity structure to reproduce as closely as possible the behavior of the observed wave fields a comparison of these results with those obtained with a homogeneous half space demonstrates the importance of structural and topographic effects which if ignored lead to a bias in the source location we use synthetic seismograms to test the accuracy and stability of the method and to investigate the effect of our choice of probability distributions we conclude that this location method can provide the source position of shallow events within a complex volcanic structure such as kilauea volcano with an error of 200 m

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

anisotropy repeating earthquakes and seismicity associated with the 2008 eruption of okmok volcano alaska 1 we use shear wave splitting sws analysis and double difference relocation to examine temporal variations in seismic properties prior to and accompanying magmatic activity associated with the 2008 eruption of okmok volcano alaska using bispectrum cross correlation a multiplet of 25 earthquakes is identified spanning five years leading up to the eruption each event having first motions compatible with a normal fault striking ne sw cross correlation differential times are used to relocate earthquakes occurring between january 2003 and february 2009 the bulk of the seismicity prior to the onset of the eruption on 12 july 2008 occurred southwest of the caldera beneath a geothermal field earthquakes associated with the onset of the eruption occurred beneath the northern portion of the caldera and started as deep as 13 km subsequent earthquakes occurred predominantly at 3 km depth coinciding with the depth at which the magma body has been modeled using geodetic data automated sws analysis of the okmok catalog reveals radial polarization outside the caldera and a northwest southeast polarization within we interpret these polarizations in terms of a magma reservoir near the center of the caldera which we model with a mogi point source sws analysis using the same input processing parameters for each event in the multiplet reveals no temporal changes in anisotropy over the duration of the multiplet suggesting either a short term or small increase in stress just before the eruption that was not detected by gps or eruption triggering by a mechanism other than a change of stress in the system

multidisciplinary observations of the 2011 explosive eruption of telica volcano nicaragua implications for the dynamics of low explosivity ash eruptions we present multidisciplinary observations of the march june 2011 vei 2 eruptive episode of the basalticandesite telica volcano nicaragua which allow for a comprehensive study of the eruption mechanics of low explosivity eruptions at persistently active volcanoes the observations are from a dense network of seismic and gps instrumentation augmented by visual observations of the eruptive episode geochemical and petrologic analysis of eruptive products plume so2 measurements and temperature measurements of fumaroles inside and outside the active vent the 2011 eruptive episode was telica s most explosive since 1999 and consisted of numerous vulcanian explosions with maximum column heights of 1 5 2 km above the crater rim depositing a low volume of dominantly hydrothermally altered ash based on observed variations in seismicity temperature and so2 flux the lack of deformation of the edifice the non juvenile origin of and predominance of accretionary lapilli in the ash we propose that temporary sealing of the hydrothermal system between similar to 0 5 and 2 km depth allowed pressure to build up prior to vulcanian explosions making this a phreatic eruptive episode

multiplets their behavior and utility at dacitic and andesitic volcanic centers 1 multiplets or groups of earthquakes with similar waveforms are commonly observed at volcanoes particularly those exhibiting unrest using triggered seismic data from the 1980 1986 mount st helens msh eruption we have constructed a catalog of multiplet occurrence our analysis reveals that the occurrence of multiplets is related at least in part to the viscosity of the magma we also constructed catalogs of multiplet occurrence using continuous seismic data from the 2004 eruption at msh and 2007 eruption at bezymianny volcano russia prior to explosions at msh in 2004 and bezymianny in 2007 the multiplet proportion of total seismicity mpts declined while the average amplitudes and standard deviations of the average amplitude increased the life spans of multiplets time between the first and last event were also shorter prior to explosions than during passive lava extrusion dome forming eruptions that include a partially solidified plug like msh 1983 1986 and 2004 2008 often possess multiplets with longer life spans and mpts values exceeding 50 conceptually the relatively unstable environment prior to explosions is characterized by large and variable stress gradients brought about by rapidly changing overpressures within the conduit we infer that such complex stress fields affect the number of concurrent families mpts average amplitude and standard deviation of the amplitude of the multiplets we also argue that multiplet detection may be an important new monitoring tool for determining the timing of explosions and in forecasting the type of eruption

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

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

observations of hybrid seismic events at soufriere hills volcano montserrat july 1995 to september 1996 swarms of small repetitive events with similar waveforms and magnitudes are often observed during the emplacement of lava domes over 300 000 such events were recorded in association with the emplacement of the lava dome at soufriere hills volcano montserrat from august 1995 through august 1996 these events originated 2 3 km deep they exhibited energy ranging over 1 5 4 5 hz and were broader band than typical long period events we term the events hybrid between long period and volcano tectonic the events were more impulsive and broader band prior to compared with during and after periods of inferred increased magma flux rate individual swarms contained up to 10 000 events often exhibiting very similar magnitudes and waveforms throughout the swarm swarms lasted hours to weeks during which inter event intervals generally increased then decreased often several times long duration swarms began about every two months starting in late september 1995 we speculate that the events were produced as the magma column degassed into adjacent cracks

long period seismicity during magma movement at volcan de colima during the period from february to september 2005 volcan de colima produced 30 vulcanian explosions of sufficient magnitude to produce pyroclastic flows of variable size with a total volume of at least 2 5 106 m3 swarms of long period events were associated with each event their duration ranging from about 6 h to 3 days and each swarm containing up to 886 events the characteristics of the swarms have been studied to understand the source mechanism and their relationship with the vulcanian explosions in total 12 548 long period events were analysed using various comparative and statistical methods patterns were not apparent in the data with no correlation between different properties of the swarms duration magnitude or frequency of occurrence of lp events and the magnitude of the associated vulcanian explosion whether recorded by seismicity volume of pyroclastics or altitude of the eruption column this along with other characteristics of the swarms such as the continuation of the swarm after the explosion with an increase in long period event amplitude in some cases suggests that the mechanism is not merely associated with the pressurization under an impermeable cap and resulting pressure differentials between adjacent volumes within the system it is more likely that the production of long period events is dominated by brittle fracturing on the margins of an ascending magma body a model is proposed whereby the unloading above the ascending magma column produced by a vulcanian explosion resulted in an increase in ascent rate reflected in the increasing amplitude of long period events the results reflect the complexity of non linear processes involved during magma ascent degassing crystallization and rupture of the impermeable plug during the vulcanian process at volcan de colima as at many volcanoes long period events represent a useful precursor for eruptive activity for monitoring this paper highlights some useful analyses that can be carried out which could illustrate certain characteristics of an eruptive episode a preliminary model is presented of the conduit processes at work during the cyclic extrusive and explosive activity during 2005

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

origin of the sound generated by strombolian explosions during strombolian eruptions large bubbles break at the surface of the lava column and produce sound acoustic pressure recorded during several explosions on the eastern vent of stromboli volcano shows a pattern consistent between explosions the well marked oscillation contains only very low frequencies around 7 hz and is followed by a signal containing now both higher frequencies and lower frequency less than 4 hz the generation of sound is explained by the vibration 7 hz and bursting higher frequencies of large bubbles followed by the drainage of magma down in the conduit less than 4 hz the interpretation suggests that 1 the bubble vibrates before bursting and 2 the vibration prior to bursting yields more energy than the bursting itself the radius of bubbles responsible for explosions is determined to be close to 1 meter in agreement with observations of a few conduit sizes

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

infrasound from the 2012 2013 plosky tolbachik kamchatka fissure eruption abstract we use both regional and local infrasound data to investigate the dynamics of the 2012 2013 eruption of tolbachik volcano kamchatka russia during select periods of time analysis of regional data recorded at the ims array is44 in southern kamchatka 384 km from the vent focuses on the eruption onset in november 2012 while analysis of local data focuses on activity in february and august 2013 signals recorded from tolbachik suggest a change in eruptive intensity possibly occurred from november 27 30 2012 local infrasound data recorded at distances of 100 950 m from the vent are characterized primarily by repeated transient explosion signals indicative of gas slug bursts three methods are employed to pick slug burst events in february and august the nature of slug bursts makes a monopole acoustic source model particularly fitting permitting volume outflux and slug radius calculations for individual events volume outfluxes and slug radii distributions provide three possible explanations for the eruption style of tolbachik volcano from mid february to late august cumulative outflux for slug bursts i e mass of emissions from individual bursts derived by infrasound for both february and august range from

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

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

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

multiparametric approach in investigating volcano hydrothermal systems the case study of vulcano aeolian islands italy seismic activity ground deformation and soil and fumarole temperatures acquired during 2004 2007 at vulcano aeolian islands are analysed and the time relations among the different time series are discussed changes in temperature of fumarolic gases took place during four anomalous periods november 2004 march 2005 october 2005 february 2006 august october 2006 july december 2007 at the same time as an increasing number of volcano seismic events in particular the temperatures at high temperature vents and at steam heated soil ranged in time from 180 to 440 c and from 20 to 90 c respectively the maximum daily number of volcano seismic events was 57 reached during the second anomalous period this seismicity characterised by focal depth generally lower than 1 km below sea level b s l and composed of different kinds of events associated to both resonance and shear failure processes is related to the shallow dynamics of the hydrothermal system during the analysed period very few volcano tectonic earthquakes took place and tilt recordings showed no sharp or important changes in light of such observations the increases in both temperature and volcano seismic events number were associated to increases in the release of gas from a deep and stable magma body without magma intrusions within the shallow hydrothermal system indeed a greater release of gas from depth leads to increased fluid circulation that can promote increases in volcano seismic events number by both fracturing processes and resonance and vibration in cracks and conduits the different trends observed in the measured geochemical and geophysical series during the anomalous periods can be due to either time changes in the medium permeability or a changing speed of gas release from a deep magma body finally all the observed variations together with the changing temporal distribution of the different seismic event kinds suggest that the hydrothermal system at vulcano can be considered unsteady and dynamic

monitoring rapid temporal change in a volcano with coda wave interferometry 1 multiply scattered waves typically dominate the late part of the seismic coda in local earthquake seismograms small medium changes that have no detectable influence on the first arrivals are amplified by multiple scattering and may thus be readily observed in the coda we exploit this idea using coda wave interferometry to monitor temporal changes at mount erebus volcano antarctica erebus is one of the few volcanoes on earth with a long lived convecting lava lake large exsolved gas bubbles generate impulsive strombolian explosions that provide a repeating seismic source of seismic energy propagating through the strongly scattering geology of the volcano we examined these signals during a particularly active eruptive two month period between december 1999 and february 2000 early seismograms are highly reproducible throughout this period during the first month this is also the case for the coda approximately midway through this period however the seismic coda decorrelates rapidly over a period of several days this indicates a rapid change in the scattering properties of the volcano likely reflecting subtle changes in the near summit magma conduit system that would not be discernible using direct or single scattered seismic wave methods

source mechanism of long period events at kusatsu shirane volcano japan inferred from waveform inversion of the effective excitation functions abstract we investigate the source mechanism of long period lp events observed at kusatsu shirane volcano japan based on waveform inversions of their effective excitation functions the effective excitation function which represents the apparent excitation observed at individual receivers is estimated by applying an autoregressive filter to the lp waveform assuming a point source we apply this method to seven lp events the waveforms of which are characterized by simple decaying and nearly monochromatic oscillations with frequency in the range 1 3 hz the results of the waveform inversions show dominant volumetric change components accompanied by single force components common to all the events analyzed and suggesting a repeated activation of a sub horizontal crack located 300 m beneath the summit crater lakes based on these results we propose a model of the source process of lp seismicity in which a gradual buildup of steam pressure in a hydrothermal crack in response to magmatic heat causes repeated discharges of steam from the crack the rapid discharge of fluid causes the collapse of the fluid filled crack and excites acoustic oscillations of the crack which produce the characteristic waveforms observed in the lp events the presence of a single force synchronous with the collapse of the crack is interpreted as the release of gravitational energy that occurs as the slug of steam ejected from the crack ascends toward the surface and is replaced by cooler water flowing downward in a fluid filled conduit linking the crack and the base of the crater lake

an efficient repeating signal detector to investigate earthquake swarms repetitive earthquake swarms have been recognized as key signatures in fluid injection induced seismicity precursors to volcanic eruptions and slow slip events preceding megathrust earthquakes we investigate earthquake swarms by developing a repeating signal detector rsd a computationally efficient algorithm utilizing agglomerative clustering to identify similar waveforms buried in years of seismic recordings using a single seismometer instead of relying on existing earthquake catalogs of larger earthquakes rsd identifies characteristic repetitive waveforms by rapidly identifying signals of interest above a low signal to noise ratio and then grouping based on spectral and time domain characteristics resulting in dramatically shorter processing time than more exhaustive autocorrelation approaches we investigate seismicity in four regions using rsd 1 volcanic seismicity at mammoth mountain california 2 subduction related seismicity in oaxaca mexico 3 induced seismicity in central alberta canada and 4 induced seismicity in harrison county ohio in each case rsd detects a similar or larger number of earthquakes than existing catalogs created using more time intensive methods in harrison county rsd identifies 18 seismic sequences that correlate temporally and spatially to separate hydraulic fracturing operations 15 of which were previously unreported rsd utilizes a single seismometer for earthquake detection which enables seismicity to be quickly identified in poorly instrumented regions at the expense of relying on another method to locate the new detections due to the smaller computation overhead and success at distances up to 50 km rsd is well suited for real time detection of low magnitude earthquake swarms with permanent regional networks

seismic characterization of the fall 2007 eruptive sequence at bezymianny volcano russia we examine an eruptive sequence in late 2007 at bezymianny volcano to characterize the magmatic plumbing system and eruption related seismicity earthquake locations reveal seismicity below and offset to the north of the volcano along a tectonic fault based on historical seismicity the magma chamber is postulated to have a top at about 6 km depth minor dome explosions large sub plinian eruptions and dome collapses are analyzed using an automated event classification scheme low frequency tremor interpreted as gas escape and low frequency earthquakes are a dominant proportion of the energy released we also examine multiplet earthquakes whose behavior during the study period changed significantly and systematically before the largest eruption demonstrating the potential of tracking multiplets to assess changing conditions with the conduit

generation of vulcanian activity and long period seismicity at volcan de colima mexico abstract during the current episode which commenced in 1998 activity at volcan de colima has been characterised by daily vulcanian events several effusive phases and a number of larger dome destroying explosions the upper edifice comprises of an intricate array of fractures and within this system variations in the magma ascent rate rheology and volatile contents complete a complexity which controls the style of activity subtle variations in one or more of these factors can trigger a transition a model is presented of the vulcanian explosion mechanism which is reflected in the associated seismicity first the breaching of an impermeable cap and the initial gas loss after the rupture low frequency signal followed by fragmentation high frequency signal in 2005 a series of larger vulcanian explosions associated with ascending magma represent the period of activity with the highest production rate in recent years pyroclastic flows were produced by column collapse with the absence of vesicularity amongst the products pointing to a deep source of gas driving the eruption the appearance of swarms of long period lp events associated with the explosions provided a great opportunity for analysis and an insight into the processes within the fracture system which control the eruptive style cross correlation of the lp waveforms produced a series of ten families which reappeared in subsequent swarms suggesting a consistent source brittle fracture associated with the enhanced stain rate found along the conduit margins is suggested as the source of this seismicity this is supported by a linear relationship between log event rate and relative amplitude of the events within each swarm an analysis of the temporal distribution of lp events revealed a variation in conditions between swarms for some swarms the conditions within the fracture system meant that a conflict between the processes associated with magma ascent was revealed whilst for others it was a situation of failure and backup which can be interpreted as the failing and activation of different fractures within the upper edifice

swarms of similar long period earthquakes in the mantle beneath mauna loa volcano abstract we present analyses of two swarms of long period lp earthquakes at 30 km depth that accompanied the geodetically observed 2002 2005 mauna loa intrusion the first lp earthquake swarm in 2002 consisted of 31 events that were precursory and preceded the start of mauna loa inflation the second lp swarm of two thousand events occurred from 2004 2005 the rate of lp earthquakes slowed significantly coincident with the occurrence of the december 26 2004 m w 9 3 sumatra earthquake suggesting that the seismic waves from this great earthquake may have had a dynamic triggering effect on the behavior of mauna loa s deep magma system using waveform cross correlation and double difference relocation we find that a large number of earthquakes in each swarm are weakly similar and can be classified into two families the relocated hypocenters for each family collapse to compact point source regions almost directly beneath the mauna loa intrusion we suggest that the observed waveform characteristics are compatible with each family being associated with the resonance of a single fluid filled vertical crack of fixed geometry with differences in waveforms between events being produced by slight variations in the trigger mechanism if these lp earthquakes are part of the primary magma system that fed the 2002 2005 intrusion as indicated by the spatial and temporal associations between mantle seismicity and surface deformation then our results raise the possibility that this magma system may be quite focused at these depths as opposed to being a diffuse network it is likely that only a few locations of mauna loa s deep magma system met the geometric and fluid dynamic conditions for generating lp earthquakes that were large enough to be recorded at the surface and that much of the deep magma transfer associated with the 2002 2005 intrusion occurred aseismically

shallow repeating seismic events under an alpine glacier at mount rainier washington usa we observed several swarms of repeating low frequency 1 5 hz seismic events during a 3 week period in may june 2010 near the summit of mount rainier washington usa that likely were a result of stick slip motion at the base of alpine glaciers the dominant set of repeating events multiplets featured 4000 individual events and did not exhibit daytime variations in recurrence interval or amplitude volcanoes and glaciers around the world are known to produce seismic signals with great variability in both frequency content and size the low frequency character and periodic recurrence of the mount rainier multiplets mimic long period seismicity often seen at volcanoes particularly during periods of unrest however their near surface location lack of common spectral peaks across the recording network rapid attenuation of amplitudes with distance and temporal correlation with weather systems all indicate that ice related source mechanisms are the most likely explanation we interpret the low frequency character of these multiplets to be the result of trapping of seismic energy under glacial ice as it propagates through the highly heterogeneous and attenuating volcanic material the mount rainier multiplet sequences underscore the difficulties in differentiating low frequency signals due to glacial processes from those caused by volcanic processes on glacier clad volcanoes

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

a numerical investigation of choked flow dynamics and its application to the triggering mechanism of long period events at redoubt volcano alaska we use numerical simulations of transonic flow through a crack to study the dynamics of the formation of shock waves downstream from a nozzle like constriction inside the crack the model solves the full set of navier stokes equations in two dimensions via an explicit multifield finite difference representation the crack walls are assumed to be perfectly rigid and elastic coupling to the solid is not considered the simulations demonstrate how the behavior of unsteady shock waves near the walls can produce recurring step like pressure transients in the flow which in turn induce resonance of the fluid filled crack the motion of the shock waves is governed primarily by smooth low amplitude pressure fluctuations at the outlet of the crack the force induced on the walls scales with the amplitude of the shock which is a function of the magnitude of the inlet pressure aperture of the constriction and thickness of the boundary layer the applied force also scales in proportion to the spatial extent of the shock excursion which depends on the fluctuation rate of outlet pressure using the source parameters of long period lp events at redoubt volcano alaska as a guide for our simulations we infer that coupling of the shock to the walls occurs for crack inlet to outlet pressure ratios pi po 2 31 and that the position of the shock front becomes most sensitive to outlet pressure fluctuations for flow regimes with pi po 2 48 for such regimes fluctuations of outlet pressure of up to 0 5 mpa at rates up to 3 mpa s are sufficient to induce pressure transients with magnitudes up to 12 5 mpa over 0 1 2 5 m of the walls within 0 5 s these flow parameters may be adequate for triggering the lp events in the precursory swarm to the december 14 1989 eruption of redoubt according to the flow model the recurrence rate and amplitudes of l p events are inferred to be a manifestation of the response of a shallow hydrothermal reservoir to the sustained injection of superheated steam from a magma column roofing below this reservoir

long period seismicity at shishaldin volcano alaska in 2003 2004 indications of an upward migration of the source before a minor eruption abstract we have analyzed the long period lp seismic activity at shishaldin volcano aleutians islands alaska in the period october 2003 july 2004 during which a minor eruption took place in may 2004 with ash and steam emissions thermal anomalies volcanic tremor and small explosions we have focused the attention on the time evolution of lp rate size spectra and polarization dip angle along the dataset we find an evolution toward more shallow dip angles in the polarization of the waveforms during the sequence the dip angle is a manifestation of the source location because the lp seismic sources are presumed to reflect the aggregation of gas slug or pockets within the melt we use the polarization dip at the lp onset as a proxy for the nucleation depth of the seismic events within the conduit we refer to this parameter as the nucleation dip and the position along the conduit of the gas aggregation as nucleation depth the nucleation dip changes throughout the dataset it shows a sharp decrease between the end of december 2003 and the end of january 2004 followed by a gradual increase until the onset of the eruption at the same time a general increase of the lp rate occurs we have associated the dip evolution with a sinking and a subsequent decrease of the nucleation depth which would quickly migrate up to about 8 km below the crater rim followed by a slow depth decrease which culminates in the eruption the change in the nucleation depth reflects either a pressure variation within the plumbing system which would affect the confining pressure experienced by the gas aggregations we have imputed such a pressure change to the intrusion of batches of magma from a deeper magma chamber 5 km for a cylindric conduit with rigid walls this leads to a volume of the injected new magma of 10 5 10 7 m 3 compatible with estimates in other areas suggesting that the lp process can be considered a good proxy of the thermodynamical conditions of the shallow plumbing system

precursory swarms of long period events at redoubt volcano 1989 1990 alaska their origin and use as a forecasting tool abstract during the eruption of redoubt volcano from december 1989 through april 1990 the alaska volcano observatory issued advance warnings of several tephra eruptions based on changes in seismic activity related to the occurrence of precursory swarms of long period lp seismic events dominant period of about 0 5 s the initial eruption on december 14 occurred after 23 years of quiescence and was heralded by a 23 hour swarm of lp events that ended abruptly with the eruption after a series of vent clearing explosions over the next few days dome growth began on december 21 another swarm with lp events similar to those of the first began on the 26th and ended in a major tephra eruption on january 2 eruptions continued over the next two weeks and then ceased until february 15 when a large eruption initiated a long phase of repetitive dome building and dome destroying episodes that continued into april warnings were issued before the major events on december 14 and january 2 but as the eruptive sequence continued after january 2 the energy of the swarms decreased and forecasting became more difficult a significant but less intense swarm preceded the february 15 eruption which was not forecast this eruption destroyed the only seismograph on the volcanic edifice and stymied forecasting until march 4 when the first of three new stations was installed within 3 km of the active vent from march 4 to the end of the sequence on april 21 there were eight eruptions six of which were preceded by detectable swarms of lp events although weak these swarms provided the basis for warnings issued before the eruptions on march 23 and april 6 the initial swarm on december 13 had the following features 1 short duration 23 hours 2 a rapidly accelerating rate of seismic energy release over the first 18 hours of the swarm followed by a decline of activity during the 5 hours preceding the eruption 3 a magnitude range from 0 4 to 1 6 4 nearly identical lp signatures with a dominant period near 0 5 s 5 dilatational first motions everywhere and 6 a stationary source location at a depth of 1 4 km beneath the crater this occurrence of long period events suggests a model involving the interaction of magma with groundwater in which magmatic gases steam and water drive a fixed conduit at a stationary point throughout the swarm the initiation of that sequence of events is analogous to the failure of a pressure relief valve connecting a lower supercharged magma dominated reservoir to a shallow hydrothermal system a three dimensional model of a vibrating fluid filled crack recently developed by chouet is found to be compatible with the seismic data and yields the following parameters for the lp source crack length 280 380 m crack width 140 190 m crack thickness 0 05 0 20 m crack stiffness 100 200 sound speed of fluid 0 8 1 3 km s compressional wave speed of rock 5 1 km s density ratio of fluid to rock 0 4 and ratio of bulk modulus of fluid to rigidity of rock 0 03 0 07 the fluid filled crack is excited intermittently by an impulsive pressure drop that varies in magnitude within the range of 0 4 to 40 bar such disturbance appears to be consistent with a triggering mechanism associated with choked flow conditions in the crack

a biogenic origin for anomalous fine grained magnetic material at the paleocene eocene boundary at wilson lake new jersey 1 the paleocene eocene thermal maximum which occurred 55 5 ma was caused by a massive release of carbon as indicated by an 3 negative carbon isotope excursion recorded in the marine atmospheric and terrestrial reservoirs one suggested source for the carbon a cometary impactor is based on the sudden appearance and high concentration of single domain sd magnetite in paleocene eocene p e boundary cores from the north atlantic continental margin we evaluate the potential sources of sd magnetite at the p e boundary by presenting new magnetic hysteresis low temperature magnetic remanence and transmission electron microscopy data from the north atlantic coastal ocean our results show a similar increase in sd material but demonstrate that the magnetic material has a biogenic origin these findings indicate that the high concentrations of sd magnetite immediately above the p e boundary are the result of unusual accumulations and or preservation of magnetotactic bacteria such bacteria typically occupy the oxic anoxic transition zone near the sediment water interface or in the water column the high abundances of sd magnetite in sediments from across the shelf may be an artifact of nonsteady state redox conditions and exceptional preservation of sd magnetite it may also indicate that the oxic anoxic redox boundary shifted into the water column the latter explanation implies transient eutrophy of the coastal ocean in this region most likely due to seasonally enhanced runoff and increased stratification and nutrient loading

a new source process for evolving repetitious earthquakes at ngauruhoe volcano new zealand abstract since early 2005 ngauruhoe volcano has produced repeating low frequency earthquakes with evolving waveforms and spectral features which become progressively enriched in higher frequency energy during the period 2005 to 2009 with the trend reversing after that time the earthquakes also show a seasonal cycle since january 2006 with peak numbers of events occurring in the spring and summer period and lower numbers of events at other times we explain these patterns by the excitation of a shallow two phase water gas or water steam cavity having temporal variations in volume fraction of bubbles such variations in two phase systems are known to produce a large range of acoustic velocities 2 300 m s and corresponding changes in impedance contrast we suggest that an increasing bubble volume fraction is caused by progressive heating of melt water in the resonant cavity system which in turn promotes the scattering excitation of higher frequencies explaining both spectral shift and seasonal dependence we have conducted a constrained waveform inversion and grid search for moment position and source geometry for the onset of two example earthquakes occurring 17 and 19 january 2008 a time when events showed a frequency enrichment episode occurring over a period of a few days the inversion and associated error analysis in conjunction with an earthquake phase analysis show that the two earthquakes represent an excitation of a single source position and geometry the observed spectral changes from a stationary earthquake source and geometry suggest that an evolution in both near source resonance and scattering is occurring over periods from days to months

temporal variations of repeating low frequency volcanic earthquakes at ngauruhoe volcano new zealand abstract a persistent swarm of micro earthquakes was observed at ngauruhoe volcano new zealand from 2005 to 2010 marking the first unrest episode at the volcano since 1975 detailed waveform and spectral analysis of the continuous seismic record revealed eight earthquake families f1 f8 within a sequence of 8561 low frequency earthquakes an analysis of stacked waveforms of each family allowed the families to be linked systematically into four super families that may indicate four different mechanisms and or source locations or geometries the first super family mostly occurred in 2005 and showed stable waveforms and no significant evolution the second super family was dominant over a two year period starting in mid 2006 and displayed a slow evolution with progressively higher frequency the third super family emerged from early 2008 with intermittent occurrence and high seismicity and progressed to higher peak frequency in 2010 the fourth super family was mainly observed from late 2008 to mid 2009 and had the highest peak frequency in 2009 the observed evolutionary pattern may be driven by a modest multi year input of gas and heat from a deeper relict magmatic zone into the shallow volcano hydrothermal system the interplay of gas from below and seasonal meltwater from above may have modulated the seismic activity and may relate to repeated over pressurization and failure of constricted evolving pathways within a pervasive crack system

long period seismicity reveals magma pathways above a laterally propagating dyke during the 2014 15 barðarbunga rifting event iceland abstract the 2014 15 bar arbunga holuhraun rifting event comprised the best monitored dyke intrusion to date and the largest eruption in iceland in 230 years a huge variety of seismicity was produced including over 30 000 volcano tectonic earthquakes vts associated with the dyke propagation at 6 km depth below sea level and large magnitude earthquakes accompanying the collapse of bar arbunga caldera we here study the long period seismicity associated with the rifting event we systematically detect and locate both long period events lps and tremor during the dyke propagation phase and the first week of the eruption we identify clusters of highly similar repetitive lps which have a peak frequency of 1 hz and clear p and s phases followed by a long duration coda the source mechanisms are remarkably consistent between clusters and also fundamentally different to those of the vts we accurately locate lp clusters near each of three ice cauldrons depressions formed by basal melting that were observed on the surface of dyngjujokull glacier above the path of the dyke most events are in the vicinity of the northernmost cauldron at shallower depth than the vts associated with lateral dyke propagation at the two northerly cauldrons periods of shallow seismic tremor following the clusters of lps are also observed given that the lps occur at 4 km depth and in swarms during times of dyke stalling we infer that they result from excitation of magmatic fluid filled cavities and indicate magma ascent we suggest that the tremor is the climax of the vertical melt movement arising from either rapid repeated excitation of the same lp cavities or sub glacial eruption processes this long period seismicity therefore represents magma pathways between the depth of the dyke vt earthquakes and the surface notably we do not detect tremor associated with each cauldron despite melt reaching the base of the overlying ice cap a concern for hazard monitoring

resonances of a volcanic conduit triggered by repetitive injections of an ash laden gas 1 a swarm of long period lp seismic events was recorded in december 2001 before heightened eruptive activity of tungurahua volcano an andesitic stratovolcano in ecuador the lp events showed simple decaying harmonic oscillations with frequencies ranging from 2 to 3 5 hz and quality factors q significantly larger than 100 our spectral analysis of the lp events identified systematic temporal variations in both frequency and q of the lp events assuming a crack resonator at the source of lp events the temporal variations can be consistently explained by increasing the ash content within the resonator which may be caused by repetitive injections of an ash laden gas into a pre existing crack in the conduit as a preparatory process for eruptions

seismic evolution of the 1989 1990 eruption sequence of redoubt volcano alaska abstract redoubt volcano in south central alaska erupted between december 1989 and june 1990 in a sequence of events characterized by large tephra eruptions pyroclastic flows lahars and debris flows and episodes of dome growth the eruption was monitored by a network of five to nine seismic stations located 1 to 22 km from the summit crater notable features of the eruption seismicity include 1 small long period events beginning in september 1989 which increased slowly in number during november and early december 2 an intense swarm of long period events which preceded the initial eruptions on december 14 by 23 hours 3 shallow swarms 0 to 3 km of volcano tectonic events following each eruption on december 15 4 a persistent cluster of deep 6 to 10 km volcano tectonic earthquakes initiated by the eruptions on december 15 which continued throughout and beyond the eruption 5 an intense swarm of long period events which preceded the eruptions on january 2 and 6 nine additional intervals of increased long period seismicity each of which preceded a tephra eruption hypocenters of volcano tectonic earthquakes suggest the presence of a magma source region at 6 10 km depth earthquakes at these depths were initiated by the tephra eruptions on december 15 and likely represent the readjustment of stresses in the country rock associated with the removal of magma from these depths the locations and time history of these earthquakes coupled with the eruptive behavior of the volcano suggest this region was the source of most of the erupted material during the 1989 1990 eruption this source region appears to be connected to the surface by a narrow pipe like conduit as inferred from the hypocenters of volcano tectonic earthquakes concentrations of shallow volcano tectonic earthquakes followed each of the tephra eruptions on december 15 these shocks may represent stress readjustment in the wall rock related to the removal of magma and volatiles at these depths this shallow zone was the source area of the majority of long period seismicity through the remainder of the eruption the long period seismicity likely reflects the pressurization of the shallow portions of the magmatic system

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

micro mechanics of drained and undrained shearing of compacted and overconsolidated crushable sand a numerical crushable soil sample has been created using the previously published mcdowell and de bono 2013 model and subjected to a range of stress paths compacted sand simulations are performed using conventional triaxial stress paths constant mean stress and constant volume conditions and a critical state line established overconsolidated samples have been created by crushing the soil down the isotropic normal compression line unloading and shearing at constant radial stress constant mean stress or constant volume and a critical state line is again established the critical state line is unique at high stresses for the simulated compacted and overconsolidated sands and is parallel to the isotropic normal compression line in agreement with available data and a previously published theory the critical state line at low stress levels is non unique and a function of the particle size distribution in agreement with available data constant volume tests exhibit the well known phenomena of phase transformation points and peak strengths are observed for drained soils on the dense side of critical the numerical soil produces a state boundary surface that compares well to available data

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

using a cross correlation technique to refine the accuracy of the failure forecast method application to soufriere hills volcano montserrat prior to many volcanic eruptions an acceleration in seismicity has been observed suggesting the potential for this as a forecasting tool the failure forecast method ffm relates an accelerating precursor to the timing of failure by an empirical power law with failure being defined in this context as the onset of an eruption previous applications of the ffm have used a wide variety of accelerating time series often generating questionable forecasts with large misfits between data and the forecast as well as the generation of a number of different forecasts from the same data series here we show an alternative approach applying the ffm in combination with a cross correlation technique which identifies seismicity from a single active source mechanism and location at depth isolating a single system at depth avoids additional uncertainties introduced by averaging data over a number of different accelerating phenomena and consequently reduces the misfit between the data and the forecast similar seismic waveforms were identified in the precursory accelerating seismicity to dome collapses at soufriere hills volcano montserrat in june 1997 july 2003 and february 2010 these events were specifically chosen since they represent a spectrum of collapse scenarios at this volcano the cross correlation technique generates a five fold increase in the number of seismic events which could be identified from continuous seismic data rather than using triggered data thus providing a more holistic understanding of the ongoing seismicity at the time the use of similar seismicity as a forecasting tool for collapses in 1997 and 2003 greatly improved the forecasted timing of the dome collapse as well as improving the confidence in the forecast thereby outperforming the classical application of the ffm we suggest that focusing on a single active seismic system at depth allows a more accurate forecast of some of the major dome collapses from the ongoing eruption at soufriere hills volcano and provides a simple addition to the well used methodology of the ffm

seismicity during the initial stages of the guy greenbrier arkansas earthquake sequence we analyze the background seismicity initiation and earliest stages of the guy greenbrier arkansas earthquake sequence which was potentially induced by wastewater injection starting in july 2010 during the 3 month time period 2010 06 01 to 2010 09 01 high resolution observations of low magnitude seismicity and the high quality arkansas public well database facilitate detailed analysis of spatial and temporal correlations between earthquakes wastewater injection and hydraulic fracturing we detected 14 604 earthquakes with magnitudes 1 5 ml 2 9 using two sensitive waveform similarity based event detection methods in parallel fingerprint and similarity thresholding fast and template matching we located the 1 740 largest earthquakes that form 16 spatially compact clusters using p and s phases from 3 stations with the double difference relocation algorithm and an improved velocity model constrained by the location of quarry blasts we enhanced the temporal resolution of these event clusters by assigning smaller unlocated events to a cluster based on waveform similarity most clustered earthquakes during this time were both spatially and temporally correlated with hydraulic fracturing stimulation at several production wells for one cluster microseismicity was correlated with individual stages of stimulation many other wells had no detectable nearby seismicity during stimulation we found a smaller number of events located on the guy greenbrier fault that were likely induced by wastewater injection the concurrent presence of seismicity induced by hydraulic fracturing and wastewater injection presents a challenge for attribution and seismic hazard characterization but the combination of precision seismology and high quality well information allows us to disentangle the effects of these two processes

families of similar events and modes of oscillation of the conduit at yasur volcano vanuatu abstract we examined one year of seismic recordings collected in 2008 during a temporary experiment at yasur volcano vanuatu the volcano has a permanent strombolian activity that was at a relatively high level during most of our experiment with commonly at least one explosion per minute associated with this activity the network recorded intense seismicicity with hundreds of transients per day video recordings indicate that most of the high frequency transients are directly related to the strombolian explosions they also outline the presence of fewer signals which are not accompanied by any surface activity the classification of transient events recorded at a station close to the summit indicates that a significant part of the events exhibit waveform similarity this technique allows the identification of characteristic repeating events among the hundreds of thousands of transients recorded during the experiment most of the families of similar events are groups of explosion quakes eqs but a few are groups of long period events related to deeper processes by scanning the 9 months of continuous data available at the summit station with master events extracted from these families we reconstruct their temporal evolution our results show that several families dominate the activity with a few of them lasting for several months we show that their temporal evolutions can be used to probe changes in the structure or activity of the volcano we observe that a major change was induced by a m 7 3 subduction earthquake which occurred on april 9 2008 about 80 km from the volcano while this event did not change significantly the surface morphology of the volcano nor the intensity of the eruptive activity it interrupted the families as none of them is present both before and after the event this change in the waveforms can be explained by a drop in the seismic velocity of the volcano caused by the distal event numerous other transitions between families are observed sudden or progressive these can be interpreted as representative of changes in the eruptive dynamics the presence of similar eqs especially for impulsive explosions indicates that the source mechanism is reproducible and has a stable location for some periods this favors a source process based on the oscillation of the conduit or oscillation of the edifice in response to the explosive decompression of gas slugs at the free surface of the conduit our results suggest that the seismic activity of yasur is characterized by the presence of dominant modes of resonance of the conduit which may be influenced both by external and internal factors

the effect of scale on rock fracture toughness a fractal approach this paper assesses the applicability of fractal geometry concepts to the formulation of a law of rock toughness parameter variation as a function of specimen size different diameter marble and sandstone specimens were subjected to short rod tests and the results obtained which showed a marked scale effect were analysed using the multifractal scaling law developed for concrete to determine whether or not the basic hypothesis underlying this theory can be applied to rock the fractal nature of the fracture surfaces of the two lithotypes considered was investigated to this end surface profiles were determined using a high precision laser technique and their degree of fractality was assessed by three different methods cet expose examine dans quelle mesure les concepts de la geometrie fractale peuvent servir a formuler une loi de la variation des parametres de resistance des roches en fonction des dimensions des eprouvettes on a soumis du marbre et du gres a des essais sur eprouvettes a entaille a v et

sustained long period seismicity at shishaldin volcano alaska abstract from september 1999 through april 2004 shishaldin volcano aleutian islands alaska exhibited a continuous and extremely high level of background seismicity this activity consisted of many hundreds to thousands of long period lp 1 2 hz earthquakes per day recorded by a 6 station monitoring network around shishaldin the lp events originate beneath the summit at shallow depths 0 3 km volcano tectonic events and tremor have rarely been observed in the summit region such a high rate of lp events with no eruption suggests that a steady state process has been occurring ever since shishaldin last erupted in april may 1999 following the eruption the only other signs of volcanic unrest have been occasional weak thermal anomalies and an omnipresent puffing volcanic plume the lp waveforms are nearly identical for time spans of days to months but vary over longer time scales the observations imply that the spatially close source processes are repeating stable and non destructive event sizes vary but the rate of occurrence remains roughly constant the events range from magnitude 0 1 to 1 8 with most events having magnitudes