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

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

explosive origin of silicic lava textural and δd h2o evidence for pyroclastic degassing during rhyolite effusion a long standing challenge in volcanology is to explain why explosive eruptions of silicic magma give way to lava a widely cited idea is that the explosive to effusive transition manifests a two stage degassing history whereby lava is the product of non explosive open system gas release following initial explosive closed system degassing direct observations of rhyolite eruptions indicate that effusive rhyolites are in fact highly explosive as they erupt simultaneously with violent volcanic blasts and pyroclastic fountains for months from a common vent this explosive and effusive overlap suggests that pyroclastic processes play a key role in rendering silicic magma sufficiently degassed to generate lava here we use precise h isotope and magmatic h2o measurements and textural evidence to demonstrate that effusion results from explosion s lavas are the direct product of brittle deformation that fosters batched degassing into transient pyroclastic channels tuffisites that repetitively and explosively vent from effusing lava our measurements show specifically that d h ratios and h2o contents of a broad suite of explosive and effusive samples from chaiten volcano hydrous bombs plinian pyroclasts tuffisite veins and lava define a single and continuous degassing trend that links wet explosive pyroclasts 1 6 wt h2o d 76 4 to dry obsidian lavas 0 13 wt h2o d 145 7 this geochemical pattern is best fit with batched degassing model that comprises small repeated closed system degassing steps followed by pulses of vapour extraction this degassing mechanism is made possible by the action of tuffisite veins which by tapping already vesicular or brecciated magma allow batches of exsolved gas to rapidly and explosively escape from relatively isolated closed system domains and large tracts of conduit magma by giving them long range connectivity even though tuffisite veins render magma degassed and capable of effusing they are nonetheless the avenues of violent gas and particle transport and thus have the potential to drive explosions when they become blocked or welded shut thus the effusion of silicic lava traditionally thought to be relatively benign process presents a particularly hazardous form of explosive volcanism

tornillos at vulcano clues to the dynamics of the hydrothermal system abstract the number of tornillo events has recently increased at the vulcano island italy while only 15 tornillos were recorded during 2004 2006 584 events occurred in 2007 2008 they were located just below la fossa crater at depths ranging between 0 1 and 1 km b s l during two intervals in 2007 2008 increases in the number of tornillos took place at the same time as temperature and geochemical anomalies were observed the spectral content of the tornillos generally characterized by one two dominant spectral peaks near 6 and 10 hz varied over time with changes also noted in the quality factors the simplest source mechanism proposed for tornillos is the free eigenvibration of a fluid volume within a crack or a conduit based on this model we propose a causal relationship between the temperature and geochemical anomalies and the increases in numbers of tornillos as the amount of hydrothermal fluids increases during the anomalies the upward flux of fluids grows the consequent changes in the pressure temperature and dynamics of the system of cracks and conduits result in the generation of tornillos based on the fluid filled crack conduit model the shallow depths of the sources and the values of the quality factors the fluid within the resonant crack conduit was inferred to be an ash gas or water droplet gas mixture moreover the observed variations in the wavefield can be caused by small changes in the location of the source in the source mechanism or in the medium in between the source and the seismic station finally another peculiar feature of tornillos is the amplitude modulation that can be explained as a result of a beating phenomenon

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

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

tungurahua volcano ecuador structure eruptive history and hazards abstract tungurahua one of ecuador s most active volcanoes is made up of three volcanic edifices tungurahua i was a 14 km wide andesitic stratocone which experienced at least one sector collapse followed by the extrusion of a dacite lava series tungurahua ii mainly composed of acid andesite lava flows younger than 14 000 years bp was partly destroyed by the last collapse event 2955 90 years ago which left a large amphitheater and produced a 8 km3 debris deposit the avalanche collided with the high ridge immediately to the west of the cone and was diverted to the northwest and southwest for 15 km a large lahar formed during this event which was followed in turn by dacite extrusion southwestward the damming of the chambo valley by the avalanche deposit resulted in a 10 km long lake which was subsequently breached generating another catastrophic debris flow the eruptive activity of the present volcano tungurahua iii has rebuilt the cone to about 50 of its pre collapse size by the emission of 3 km3 of volcanic products two periods of construction are recognized in tungurahua s iii history from 2300 to 1400 years bp high rates of lava extrusion and pyroclastic flows occurred during this period the magma composition did not evolve significantly remaining essentially basic andesite during the last 1300 years eruptive episodes take place roughly once per century and generally begin with lapilli fall and pyroclastic flow activity of varied composition andesite dacite and end with more basic andesite lava flows or crater plugs this pattern is observed in the three historic eruptions of 1773 1886 and 1916 1918 given good age control and volumetric considerations tungurahua iii growth s rate is estimated at 1 5 106 m3 year over the last 2300 years although an infrequent event a sector collapse and associated lahars constitute a strong hazard of this volcano given the 3000 m relief and steep slopes of the present cone a future collapse even of small volume could cover an area similar to that affected by the 3000 year old avalanche the more frequent eruptive episodes of each century characterized by pyroclastic flows lavas lahars as well as tephra falls directly threaten 25 000 people and the agoyan hydroelectric dam located at the foot of the volcano

geochemical evidence for relict degassing pathways preserved in andesite andesitic arc volcanoes degas large quantities of volatiles evidence for vapour transport in the erupted lavas is rarely preserved and poorly understood but is crucial for understanding eruption style we present geochemical evidence for the transport of metal bearing vapour in shear zones preserved in lavas erupted from soufriere hills volcano montserrat textural evidence suggests that shear induced brittle failure occurred in a narrow zone at the conduit wall or in the lava dome elevated metal concentrations cu au ag pb zn within the zones indicate that the fractures acted as a transient pathway for metal bearing magmatic gases during slip frictional heating to temperatures of 1000 c caused partial melting at the slip surface resorption of volatiles and metals into the partial melt preserved the geochemical signature of magmatic vapour in the shear zone cordierite which is highly unusual in volcanic rocks crystallised from the peraluminous partial melt with metal bearing sulphides and oxides the shear zones provide the first geochemical evidence for vapour segregation and transport through viscous andesite magmas and provide an insight into controls on eruption style

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

the rise and fall of periodic drumbeat seismicity at tungurahua volcano ecuador abstract highly periodic drumbeat long period lp earthquakes have been described from several andesitic and dacitic volcanoes commonly accompanying incremental ascent and effusion of viscous magma however the processes controlling the occurrence and characteristics of drumbeat and lp earthquakes more generally remain contested here we use new quantitative tools to describe the emergence evolution and degradation of drumbeat lp seismicity at the andesitic tungurahua volcano ecuador in april 2015 the signals were recorded during an episode of minor explosive activity and ash emission without lava effusion and are the first to be reported at tungurahua during the ongoing 17 yrs of eruption following four days of high levels of continuous and pulsed tremor highly periodic lp earthquakes first appear on 10 april over the next four days inter event times and event amplitudes evolve through a series of step wise transitions between stable behaviors each involving a decrease in the degree of periodicity families of similar waveforms persist before during and after drumbeat activity but the activity levels of different families change coincidentally with transitions in event rate amplitude and periodicity a complex micro seismicity initiation sequence shows pulse like and stepwise changes in inter event times and amplitudes in the hours preceding the onset of drumbeat activity that indicate a partial de coupling between event size and rate the observations increase the phenomenology of drumbeat lp earthquakes and suggest that at tungurahua they result from gas flux and rapid depressurization controlled by shear failure of the margins of the ascending magma column

permeability evolution during non isothermal compaction in volcanic conduits and tuffisite veins implications for pressure monitoring of volcanic edifices abstract explosive volcanic eruptions are destructive geological phenomena that pose hazards of significant socioeconomic impact and potential loss of life effective risk mitigation and decision making prior to and during volcanic crises require real time monitoring of gas overpressure the single most important driving force for explosive eruptions development and release of gas overpressure are regulated by gas loss through permeable pathways that are inherently transient here we use geometry dependent conductive cooling models in concert with the most up to date welding and permeability models to assess the potential for freezing in permeability within 1 conduit filling pyroclastic deposits and 2 tuffisite veins within the edifice we find that both geometry and dimension of each deposit dictate its thermal evolution and with that its transient outgassing capacity rapid cooling of thin sheet like tuffisite veins preserves high porosities and permeabilities in contrast wide cylindrical conduit filling deposits cool slowly and permeability is annihilated over a period of minutes to hours this highlights that conduit filling deposits lose their outgassing capacity through welding while tuffisite veins previously thought to rapidly seal can form long lived outgassing features we use the model results to calculate the time dependent gas flow partitioning between both degassing lithologies based on the reconstructed outgassing pattern we outline the potential to use the gas flow balance between the central conduit and distal fumaroles fed by tuffisite veins as a simple tool to monitor gas overpressure within a volcanic edifice

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

the climate in western europe during the last glacial interglacial cycle derived from pollen and insect remains using the pollen sequence of la grande pile xx france we review problems with the application of transfer functions in paleoclimatic reconstructions one of them is to find modern analogues for the herbaceous vegetation of the cold periods we propose a method to distinguish between steppes and tundra vegetations for which the moderns are only partial analogues of the glacial periods another method to solve these problems is based on constraining by insect remains the two methods provide coherent reconstructions the results are also compared with other paleodata there is a good correlation with the six cold heinrich events between 70 and 15 ka b p a cooling event during the eemian period marked by high percentages of taxas at about 125 ka b p needs still to be correlated with high resolution ocean and ice cores

rapid localized flank inflation and implications for potential slope instability at tungurahua volcano ecuador abstract high rates of volcano surface deformation can be indicative of a forthcoming eruption but can also relate to slope instability and possible flank collapse tungurahua volcano ecuador has been persistently active since 1999 and has previously experienced catastrophic flank failures during the ongoing eruptive activity significant surface deformation has been observed with the highest rates contained within the amphitheatre shaped scar from the 3000 year old failure on the west flank however the cause of this asymmetric deformation and how it might relate to slope stability has not been assessed here for the first time we present a range of models to test physical processes that might produce asymmetric deformation which are then applied to slope stability our models are informed by insar measurements of a deformation episode in november 2015 which show a maximum displacement of 3 5 cm over a period of 3 weeks during which time the volcano also experienced multiple explosions and heightened seismicity asymmetric flank material properties from the rebuilding of the cone cannot explain the full magnitude and spatial footprint of the observed west flank deformation the inflation is inferred to be primarily caused by shallow short term pre eruptive magma storage that preferentially exploits the 3 ka flank collapse surface shallow and rapid pressurization from this inclined deformation source can generate shear stress along the collapse surface which increases with greater volumes of magma this may contribute to slope instability during future unrest episodes and promote flank failure with general application to other volcanoes worldwide displaying asymmetric deformation patterns

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

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

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

high resolution paleoclimatic trends for the holocene identified using magnetic susceptibility data from archaeological excavations in caves abstract a proxy paleoclimatic curve has been produced for the holocene c 9000 3500 bp from magnetic susceptibility ms measurements of sediment samples collected from two dated archaeological excavation trenches in konispol cave albania the resulting ms data provide paleoclimate estimates that are in excellent agreement with independently published paleoclimatic trends for early middle holocene time basically ms variations are attributed to variations in climate controlled pedogenesis and the production of magnetic mineral phases including maghemite outside the cave these soils are then washed blown or tracked into the cave where they accumulate creating the ms changes observed in the samples recovered low ms magnitudes indicate times of cooler drier climate resulting from reduced pedogenesis while warmer wetter times yield higher pedogenetic rates and thus higher ms magnitudes it is clear from the konispol cave results that some caves provide ideal protected environments from which high resolution paleoclimatic records can be extracted composite sections from excavations within a single region can yield a relatively continuous long term climatic proxy that can be routinely correlated to artefacts recovered from these or other protected excavations within the same region

spectro temporal features applied to the automatic classification of volcanic seismic events abstract feature extraction and selection are very relevant processes in the design of automatic classifiers in the context of volcanic seismic signal classification most of the features presented in the literature have been extracted separately from a single domain such as time or frequency however spectrograms which combine time and frequency information are widely used by experts during the classification of manual seismic events this paper proposes to evaluate the performance of classifiers trained with features extracted from the spectro temporal domain individually or combined with other conventional features the parameters were extracted from the spectrogram based on a curve which combines the high energy components and the frequency bandwidth information through the duration of the event the tests were performed at the llaima volcano and seismic events were classified into four classes long period tremor volcano tectonic and tectonic using a database of signals recorded between the years 2009 and 2017 the main achievements of this study were the reduction of more than 70 of the error and false positive rates and also a reduction of approximately 30 of the number of features compared with a baseline established in previous studies thus the inclusion of spectro temporal information was considered relevant to complement the conventional features and to support classification

time space variation of volcano seismic events at la fossa vulcano aeolian islands italy new insights into seismic sources in a hydrothermal system we investigated the relationship between volcano seismic events recorded at la fossa crater of vulcano aeolian islands italy during 2004 2006 and the dynamics of the hydrothermal system during the period of study three episodes of increasing numbers of volcano seismic events took place at the same time as geothermal and geochemical anomalies were observed these geothermal and geochemical anomalies have been interpreted as resulting from an increasing deep magmatic component of the hydrothermal fluids three classes of seismic events long period high frequency and monochromatic events characterised by different spectral content and various similarity of the waveforms have been recognised these events clustered mainly below la fossa crater area at depths of 0 5 1 1 km b s l were space distributed according to the classes based on their features we can infer that such events at vulcano are related to two different source mechanisms 1 fracturing processes of rocks and 2 resonance of cracks or conduits filled with hydrothermal fluid in the light of these source mechanisms the increase in the number of events at the same time as geochemical and geothermal anomalies were observed was interpreted as the result of an increasing magmatic component of the hydrothermal fluids implying an increase of their flux indeed such variation caused an increase of both the pore pressure within the rocks of the volcanic system and the amount of ascending fluids increased pore pressures gave rise to fracturing processes while the increased fluid flux favoured resonance and vibration processes in cracks and conduits finally a gradual temporal variation of the waveform of the hybrid events one of the subclasses of long period events was observed likely caused by heating and drying of the hydrothermal system

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

tornillos modeled as self oscillations of fluid filling a cavity application to the 1992 1993 activity at galeras volcano colombia abstract tornillos are quasi monochromatic seismic signals with a slowly decaying coda that are observed near active volcanoes and geothermal areas worldwide in this work a lumped parameter model describing the tornillo source process as the self oscillations of fluid filling a cavity is investigated a nonlinear ordinary differential equation is derived that governs the behavior of the model taking into account viscous and nonlinear damping as well as the reaction force of the fluid inside the cavity this equation is numerically integrated both for different cavity sizes and different fluids of volcanological interest such as gas h2o co2 h2o so2 and gas particle mixtures ash so2 water droplets h2o this cavity model predicts that when the filling fluid is a mixture of ash and so2 the signal duration will increase until the mixture becomes enriched in ash and then the duration exhibits a decrease additionally the damping coefficients 1 2q of the synthetic signals are estimated in the range between 0 002 and 0 014 both results agree well with the temporal variation of tornillos duration and the estimated q quality factors damping coefficients observed at galeras volcano in the context of the cavity model tornillo frequency variations from 4 hz to 1 hz observed prior to eruptions can be interpreted as the result of fluid composition changes as more ash particles are added this is in agreement with the observation that gas accumulation at galeras was a steady rather than an episodic process and that tornillos were most likely triggered after a fluid pressure threshold had been exceeded

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

ramifications of high in situ temperatures for laboratory testing and inferred stress states of unlithified sediments a case study from the nankai margin abstract the recovery of drill cores involves changes in pressure and temperature conditions which inevitably alter the mechanical properties of unlithified sediments while expansion from unloading after core recovery is well studied the effects from cooling on standard geotechnical tests are commonly neglected along the central portion of the nankai margin sediments were recovered from high in situ temperatures of up to 110 c during iodp leg 190 so far the interpretation of the consolidation state of the lower shikoku basin facies lsb entering the accretionary nankai margin is ambiguous results from laboratory consolidation tests at room temperature show high pre consolidation stresses these were interpreted as hardening caused by cementation while the field based porosity vs depth trend points towards normal consolidation as an explanation for this discrepancy the change of the mechanical properties by cooling from in situ to laboratory conditions is proposed in this paper the results of a thermo mechanical model are compared to published field data this comparison suggests that the observed hardening is at least partially an artefact from cooling during core recovery and that the strata may be considered normally consolidated to slightly overconsolidated the latter can be explained by minor cementation or the influence of secondary consolidation the results suggest that cooling from high in situ temperatures may be important for the interpretation of the consolidation state of other sedimentary successions elsewhere

site identification and correlation using geoarchaeological methods at the cabeco do porto marinho cpm locality rio maior portugal abstract several geoarchaeological techniques have been employed in evaluating an open air site within a uniform sand matrix near rio maior portugal electrical resistivity data acquired at the upper palaeolithic site complex of cabeco do porto marinho cpm delineated an important new occupational locus this result was confirmed first by auger testing which recovered subsurface artefacts and then by direct excavation in addition 107 samples were recovered at the site for magnetic susceptibility measurements comparisons between magnetic susceptibility profiles from two loci including the new area at cpm show distinctive patterns which allow direct correlation between the occupation areas these methods provide quick and inexpensive means for investigators to evaluate new sites or to correlate between and within sites without resorting to other more time consuming and expensive techniques

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

fluid dynamics inside a wet volcano inferred from the complex frequencies of long period lp events an example from papandayan volcano west java indonesia during the 2011 seismic unrest abstract we present results of our study aimed at understanding the dynamics of fluids inside a wet volcano through the analysis of swarms of long period lp events accompanying the 2011 seismic unrest at papandayan volcano west java indonesia prior to this unrest we measured an extremely high percentage 100 of co2 in the ground at the summit crater however with a very low value of so2 flux 6 tons day increase in volcanic activity was also observed from the records of a tiltmeter a long term inflation was followed by an abrupt deflation that took place concurrently with the swarms of lp events thereafter swarms of local tectonic lt and volcano tectonic vt earthquakes started we focus here on analyzing the lp events in the following manner first we estimate the source location of lp events by applying a 3 d non linear hypocenter localization algorithm which includes topography we then study the waveforms and spectral characteristics of lp events recorded at different stations and investigate whether or not these characteristics are due to source effects subsequently we compute the oscillation frequencies f and the decay characteristics q factor in the complex frequency domain of the coda part of the lp events by using the sompi method which is based on a homogeneous auto regressive ar equation the rectangular fluid filled crack model is used to estimate the physical processes related to the observed temporal variations in the complex frequencies we divide the swarms of lp events into two intervals the first interval occurred between june and july 2011 48 lp events while the second interval extended from september to october 2011 36 lp events the frequencies of lp events observed during these intervals range between 1 1 and 6 2 hz while the q factors are widely scattered between 20 and 400 we estimate the compositions of fluids inside the crack during both intervals as either water foam mixtures of water and h2o gas steam or misty gas mixtures of water droplets and h2o gas steam we finally suggest that if an eruption were to have taken place following the 2011 unrest it would have been in phreatic style rather than magmatic style the results of our study therefore contribute to the effort in the prediction of the behavior of future eruptions and to volcanic hazards assessment and therefore to volcanic risk mitigation

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

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

alluvial sediment sources in a glaciated catchment the voidomatis basin northwest greece x ray diffraction xrd of the fine matrix component of four alluvial units and modern channel sediments in the voidomatis river basin of northwest greece shows that fine sediment sources have changed considerably during the late quaternary the matrix fraction of the modern channel sediments is derived predominantly from erosion of local flysch rocks and soils during the last glaciation however the fine sediment load of the voidomatis river was dominated by glacially ground finely comminuted limestone materials limestone derived fine sediment is not produced in significant amounts under modern climatic conditions by combining this xrd work with a detailed programme of clast lithologic 1 analysis we have reconstructed former bedload and fine sediment load composition the lithological properties of both the coarse 8 256 mm and fine 63 m elements of the sediment load have varied markedly during the late quaternary a simple semiquantitative assessment of fine sediment mineralogy using diffractogram peak height data has provided a valuable complement to the information gathered from more traditional clast lithological techniques together in favourable geological settings fine fraction mineralogy and clast lithological analysis can provide a valuable tool for the reconstruction of late quaternary alluvial environments

volcanic seismicity at montserrat a comparison between the 2005 dome growth episode and earlier dome growth in 2005 soufriere hills volcano on montserrat started its third major episode of dome growth since the current eruption started in 1995 the style of seismicity associated with dome growth has changed in particular the events known as hybrid earthquakes have reduced in numbers by an order of magnitude compared to previous dome growth episodes in the past hybrid earthquakes have been associated with magma ascent and so it is surprising to observe prolonged periods of rapid dome growth during which very few hybrid earthquakes are recorded in addition the frequency of the codas of hybrid earthquakes as well as of some of the so called long period events has changed the changes in recorded seismicity have had a marked effect on the techniques used to monitor the state of the volcano and those events that continue to be recorded in large numbers rockfall events have been used to assess the state of activity at the volcano

complex seismic sources in volcanic environments radiation modelling and moment tensor inversions abstract long period lp signals are special seismic events observed at volcanoes which comprise both a high frequency onset due to brittle failure and a more energetic low frequency part due to resonance in a fluid filled conduit they are critical for volcano monitoring since they can be used as a volcanic forecasting tool classic seismology assumes planar faults for seismic sources however there is increasing evidence that suggests different fault shapes such as dyke faults and ring faults we consider in this study narrow dykes and conduits rather than large calderas hence we model these complex sources by superposing vertical single double couple dc sources arranged along narrow fault structures with inner upward movement we calculate seismic radiation patterns and synthetic seismograms for a rupture along a dyke three different partial ring ruptures and a full ring rupture results show that planar faults are the most effective at radiating energy the more the source geometry deviates from a planar fault the smaller become the amplitudes and therefore the moment magnitudes for example the amplitudes decrease to 2 4 of the planar radiation for a full ring rupture and to 0 7 for a dyke rupture the waveforms produced by partial ring ruptures are in accordance to what is expected in the far field representing the derivative of the source displacement and emulating radiation of a dc with different azimuths however the dyke and full ring sources produce waveforms that appear to represent the second derivative of the source displacement and negative first onset polarisations moment tensor inversions support similarities between dc ruptures and partial ring ruptures however they show ambiguous solutions for the other sources this point source assumption can lead to misinterpretations of slip history on the fault and a consistent underestimation of magnitudes which has direct implications for magma ascent estimations derived from seismic amplitudes

magnetic susceptibility applied as an age depth climate relative dating technique using sediments from scladina cave a late pleistocene cave site in belgium abstract here we demonstrate that magnetic susceptibility ms data from scladina cave belgium provide a time depth climate relationship that is correlated to the marine oxygen isotopic record and thus yields a high resolution relative dating method for sediments recovered from many archaeological sites this methodology will help resolve one of the major problems facing archaeologists namely the difficulty of acquiring absolute dates with reasonable precision for the period from 40 000 to 400 000 years or so the problem is that dating techniques applicable to most materials within this age range are subject to significant errors relative dating techniques such as magnetic secular variation or stable isotope methods offer the potential to improve this precision but both methods suffer from problems that make broad application to many sites impossible however for most archaeological cave sites ms measurements of cave sediments offers the potential for intra site correlation and paleoclimate estimation this is possible in protected cave environments because the ms of cave sediments results from climate processes active outside caves which cause variations in magnetic properties of the sediments that ultimately accumulate inside caves once deposited these materials are often preserved and their stratigraphy provides a time depth climate signal that can be identified therefore ms data can be used as an independent methodology alongside conventional methods such as sedimentology and palynology for relative age dates and correlation within and between sites by tracing evidence of paleoclimatic change this correlation has been used to infer an age of 90 000 7000 years for neanderthal skeletal remains recovered from scladina cave an important middle paleolithic archaeological site in belgium

wave properties and focal mechanisms of n type earthquakes at asama volcano abstract n type earthquakes sometimes occur before the eruption of andesitic volcanoes but their source mechanism has not been understood well their waveforms have stationary periods and decay slowly resembling to damped oscillation they have common characteristics of spectra among the different stations these spectral peaks appear at almost equal intervals of 1 0 hz with common sharpness we made detailed analysis on the n type earthquakes observed at asama volcano in july 1995 during 10 days activity the duration of each earthquake increased gradually from 40 s to 3 min while the peak frequency decreased from 2 7 to 0 8 hz hypocenters are distributed slightly west under the summit crater with 0 4 1 7 km above sea level source mechanism of the n type earthquake is determined using a waveform inversion technique synthetic waveforms are calculated using 2d finite difference method surface topography is included in the calculation to incorporate the case that the source region is higher than the stations since the optimum solution has a large volumetric component we approximated the volumetric part as a volume change of fluid filled sphere or cylinder or plane crack and decomposed the solution into volumetric and non volumetric part consequently it is revealed that the optimum solution can be expressed as crack expansion contraction small fault slip because the spectral peak distribution advocates the crack expansion model among these three candidates the frequency change during this activity may be explained by the time variation of the sound speed of inner fluid from 300 to 100 m s the change of the void fraction of water steam phase might have caused the decrease of the sound speed

an efficient method to compute the dynamic response of a fluid filled crack summary the vibration of a fluid filled crack is considered to be one of the most plausible source mechanisms for the long period events and volcanic tremors occurring around volcanoes as a tool for the quantitative interpretation of source process of such volcanic seismic signals we propose a method to numerically simulate the dynamic response of a fluid filled crack in this method we formulate the motions of the fluid inside and the elastic solid outside of the crack using boundary integrals in the frequency domain and solve the dynamic interactions between the fluid and the elastic solid using the point collocation method the present method is more efficient compared with the time domain finite difference method which has been used in simulations of a fluid filled crack and enables us to study the dynamics of a fluid filled crack over a wide range of physical parameters the method also allows us direct calculation of the attenuation quality factor of the crack resonance which is an indispensable parameter for estimating the properties of the fluid inside the crack the method is also designed to be flexible to many applications which may be encountered in volcano seismology and thus extensions of the method to more complicated problems are promising

seismicity characteristics of a potentially active quaternary volcano the tatun volcano group northern taiwan the tatun volcano group tvg is located at the northern tip of taiwan near the capital taipei and close to two nuclear power plants because of lack of any activity in historical times it has been classified as an extinct volcano even though more recent studies suggestthattvgmighthavebeenactiveduringthelast20ka inmay2003aseismicmonitoringprojectatthetvgareawasinitiated by deploying eight three component seismic stations some of them equipped with both short period and broadband sensors during the 18 months observation period local seismicity mainly consisted of high frequency earthquakes either occurring as isolated events or as a continuous sequence in the form of spasmodic bursts mixed and low frequency events were also present during the same period eventhoughtheyoccurredonlyrarely arrivaltimesfromeventswithclearp s wavephaseswereinvertedinordertoobtaina minimum 1dvelocity modelwithstation corrections probabilistic nonlinear earthquakelocationswere calculated for allthese events using the newly derived velocity model most high frequency seismicity appeared to be concentrated near the areas of hydrothermal activity forming tight clusters at depths shallower than 4 km relative locations calculated using the double difference method and utilising catalogue and cross correlation differential traveltimes showed insignificant differences when compared to the nonlinear probabilistic locations in general seismicity in the tvg area seems to be primarily driven by circulation of hydrothermal fluids as indicated by the occurrence of spasmodic bursts mixed low frequency events and a b value 1 17 0 1 higher than in any other part of taiwan these observations that are similar to those reported in other dormant quaternary volcanoes indicate that a magma chamber may still exist beneath tvg and that a future eruption or period of unrest should not be considered unlikely