natural gas hydrates on the southeast u s margin constraints from full waveform and travel time inversions of wide angle seismic data strong bottom simulating reflectors bsr have been mapped over a region of approximately 50 000 km2 on the southeastern u s margin and have been associated with possible abundance of natural gas hydrates in june 1992 coincident single channel seismic and wide angle ocean bottom seismic data were acquired in the region focusing on the blake ridge and the carolina rise wide angle reflections from the bsrs were clearly observed at offsets up to 6 km joint travel time inversion was conducted with wide angle and vertical incidence data in order to explore possible regional variation and the resultant two dimensional average velocity models imply higher background velocities on the carolina rise full waveform inversion was then performed to determine the seismic origin of the bsrs the best fit model shows a similar low velocity 1 4 km s beneath the bsr at both sites indicating trapped free gas with low saturation 10 the inversion results also indicate that a thin high velocity wedge with a maximum velocity of 2 3 km s is present just above the blake ridge bsr sediment reflectivities were also calculated and higher reflectivities are observed on the carolina rise an increase in reflectivity below the bsr seems to correspond to the gas bearing zone at both sites concentration of hydrates were estimated based on these velocity models whereas average hydrate concentration of 3 of the total sediment volume is suggested for the lower half of the hydrate stability zone at the blake ridge only a very low average concentration of hydrate can be expected at the carolina rise the hydrates seem to be concentrated near the base of the hydrate stability zone and the maximum hydrate concentration is estimated as 20 at the blake ridge and 7 at the carolina rise both of which are too high to be explained by in situ biogenic activity only and require some secondary accumulation mechanism it is suggested that hydrate recycling caused by the stability field migration may have effectively condensed hydrates at both sites additional enhancement by upward fluid expulsion may also be viable for the blake ridge

palaeoclimate aptian mystery solved the volcanic eruption that created the ontong java plateau released large quantities of carbon dioxide a reconstruction of co2 concentrations suggests that the eruption promoted climate change and the expansion of ocean anoxia

modelling the macroscopic behavior of strombolian explosions at erebus volcano abstract we analyze seismic signals associated with the strombolian explosion quakes at erebus volcano antarctica examining the high frequency 0 5 hz portion of the spectrum we consider recordings relative to two time periods during the years 2005 and 2006 cross correlation analysis allows us to distinguish three classes of events spectral properties and polarization analysis provide evidence of a very complex volcanic structure we conduct analyses to elucidate the macroscopic dynamic system associated with the explosions the distribution of the times between successive explosion quakes is exponential implying a poissonian process as observed at stromboli volcano but on a different time scale the sequence of the occurrence of the explosions can be described by classical intermittency a coalescence chandrasekar landau mean field model reproduces gas bubble sizes comparable with those observed at the lava lake surface finally the classical equation for the ascent of gas bubbles is generalized by adding a diffusive process this model provides ascent velocities depending on the bubble radius for gas bubbles greater than a few centimeters variation in ascent velocity due to diffusion becomes negligible and the ascent velocity appears to be governed primarily by buoyancy

source constraints of tungurahua volcano explosion events the most recent eruptive cycle of tungurahua volcano began in may 2004 and reached its highest level of activity in july 2004 this activity cycle is the last one of a series of four cycles that followed the reawakening and major eruption of tungurahua in 1999 between june 30 and august 12 2004 three temporary seismic and infrasonic stations were installed on the flanks of the volcano and recorded over 2 000 degassing events the events are classified by waveform character and include explosion events the vast majority spanning three orders of pressure amplitudes at 3 5 km from the vent 0 1 180 pa jetting events and sequences of repetitive infrasonic pulses called chugging events travel time analysis of seismic first arrivals and infrasonic waves indicates that explosions start with a seismic event at a shallow depth 200 m followed 1 s later by an out flux of gas ash and solid material through the vent cluster analysis of infrasonic signals from explosion events was used to isolate four groups of similar waveforms without apparent correlation to event size location or time the clustering is thus associated with source mechanism and probably spatial distribution explosion clusters do not exhibit temporal dependence

infrasonic tremor in the diffraction zone 1 volcanic tremor signals recorded by an infrasound array 12 5 km from the active vent of k lauea volcano show clear diurnal amplitude variations and originate from a well defined direction pointing to the active pu u crater complex spectral amplitudes between 0 02 0 3 hz a proxy for wind speed increase when the wind speeds increase during the daytime spectral amplitudes between 0 5 3 hz where infrasonic tremor is concentrated increase when the wind speeds decrease at night power spectrum analysis shows that when ambient noise levels drop infrasonic tremor amplitudes rise array processing confirms this relationship and reveals tremor detections and amplitudes decrease during the day these changes in infrasonic tremor spectral amplitude and coherence are most likely due to diurnal variations in atmospheric boundary layers affecting infrasonic propagation within the diffraction zone recognition of these regional atmospheric patterns is necessary to permit robust infrasonic remote sensing of volcanic processes

propagation of acoustic waves in a viscoelastic two phase system influence of gas bubble concentration abstract volcanic explosions generate pressure perturbations in the atmosphere and a seismic wavefield in the ground the source is therefore well coupled with the atmosphere and the ground the acoustic and elastic wavefields reflect dynamical processes at the source and the viscoelastic properties of the magma gas medium at low pressure 70 strongly affect the propagation properties of the acoustic wavefield we found that the amplitude of the infrasonic wavefield in the atmosphere typically recorded in case of strombolian explosions 2 105 pa can be explained by a deep 50 m source embedded in the magma conduit only if a very large unrealistic pressure drop 1013 pa is assumed the strong damping linked to the poor elastic properties of the shallow magma gas mixture prevents the efficient propagation of the acoustic waves in the magma gas mixture and resonance of body waves cannot occur infrasonic waves can be transmitted from the magma to the atmosphere only when the source is very shallow

attenuation of seismic waves in methane gas hydrate bearing sand compressional wave p wave and shear wave s wave velocities vp and vs respectively from remote seismic methods have been used to infer the distribution and volume of gas hydrate within marine sediments recent advances in seismic methods now allow compressional and shear wave attenuations q1p and q1s respectively to be measured however the interpretation of these data is problematic due to our limited understanding of the effects of gas hydrate on physical properties therefore a laboratory gas hydrate resonant column was developed to simulate pressure and temperature conditions suitable for methane gas hydrate formation in sand specimens and the subsequent measurement of both q1p and q1s at frequencies and strains relevant to marine seismic surveys 13 dry gas saturated sand specimens were investigated with different amounts of methane gas hydrate evenly dispersed throughout each specimen the results show that for these dry specimens both q1p and q1s are highly sensitive to hydrate saturation with unexpected peaks observed between 3 and 5 per cent hydrate saturation it is thought that viscous squirt flow of absorbed water or free gas within the pore space is enhanced by hydrate cement at grain contacts and by the nanoporosity of the hydrate itself these results show for the first time the dramatic effect methane gas hydrate can have on seismic wave attenuation in sand and provide insight into wave propagation mechanisms these results will aid the interpretation of elastic wave attenuation data obtained using marine seismic prospecting methods

lithium isotope evidence for enhanced silicate weathering during oae 1a early aptian selli event an abrupt rise in temperature forced by a massive input of co2 into the atmosphere is commonly invoked as the main trigger for oceanic anoxic events oaes global warming initiated a cascade of palaeoenvironmental perturbations starting with increased continental weathering and an accelerated hydrological cycle that delivered higher loads of nutrients to coastal areas stimulating biological productivity the end result was widespread anoxia and deposition of black shales the hallmarks of oaes in order to assess the role of weathering as both an oae initiator and terminator via co2 sequestration during the early aptian oae 1a selli event 120 ma the isotopic ratio of lithium isotopes was analysed in three sections of shallow marine carbonates from the pacific and tethyan realms and one basinal pelagic section from the tethyan domain because the isotopic composition of lithium in seawater is largely controlled by continental silicate weathering and high and low temperature alteration of basaltic material a shift to lighter 7li values is expected to characterize oaes the studied sections illustrate this phenomenon 7li values decrease to a minimum coincident with the negative carbon isotope excursion that effectively records the onset of oae 1a a second negative 7li excursion occurs coeval with the minimum in strontium isotopes after the event the striking similarity to the strontium isotope record argues for a common driver the formation and destruction weathering of an oceanic lip could account for the parallel trend in both isotope systems the double spike in lithium isotopes is probably related to a change in weathering congruencies such a chemostratigraphy is consistent with the hypothesis that an increase in silicate weathering in conjunction with organic carbon burial led to drawdown of atmospheric co2 during the early aptian oae 1a

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

capturing the acoustic radiation pattern of strombolian eruptions using infrasound sensors aboard a tethered aerostat yasur volcano vanuatu we obtained an unprecedented view of the acoustic radiation from persistent strombolian volcanic explosions at yasur volcano vanuatu from the deployment of infrasound sensors attached to a tethered aerostat while traditional ground based infrasound arrays may sample only a small portion of the eruption pressure wavefield we were able to densely sample angular ranges of 200o in azimuth and 50o in take off angle by placing the aerostat at 38 tethered loiter positions around the active vent the airborne data joined contemporaneously collected ground based infrasound and video recordings over the period 29 july to 1 august 2016 we observe a persistent variation in the acoustic radiation pattern with average eastward directed root mean squared pressures more than 2 times larger than in other directions the observed radiation pattern may be related to both path effects from the crater walls and source directionality

theory of the airborne sound field generated in a resonant magma conduit abstract explosive sources triggered inside a magma conduit may excite the conduit into acoustic resonance the acoustic field in the conduit can propagate into the atmosphere through an open vent and ensonify the overlying atmosphere the character of the airborne sound field is determined by a combination of propagation and source effects the resonance of the magmatic conduit and the diffraction of the sound field at the volcanic vent are acoustic propagation effects whereas the explosion pressure signature and the firing rate of the explosions define the source characteristics for wavelengths larger than the conduit radius only the longitudinal resonances of the magmatic conduit are relevant and the open vent radiates like a piston surrounded by an infinite baffle in this case the fluid particle velocities are directed along the axis of the conduit and the sound field may propagate into the surrounding bedrock through the conduit wall displacement induced by the fluid overpressure this coupling may produce seismic signals with banded spectra such as volcanic tremor and long period events the airborne pressure field retains the modal structure of the sound field in the magmatic conduit which contains information on the conduit geometry and geo acoustic properties of the magma the seismic wavefield is driven by the acoustic field in the magma and also contains this information although it may be filtered by propagation effects in the bedrock the theoretical sound field in the magma conduit is used to interpret seismic tremor signals recorded at mt spurr volcano alaska rapid variations in the acoustic impedance of the magma conduit terminations can create systematic changes in the tremor spectra which can be used to monitor changes in the magmatic system the results of the modelling illustrate the difference between source effects and conduit resonance as well as the value of seismoacoustic measurements in volcanic environments

the roar of yasur handheld audio recorder monitoring of vanuatu volcanic vent activity abstract we describe how near field audio recording using a pocket digital sound recorder can usefully document volcanic activity demonstrating the approach at yasur vanuatu in may 2014 prominent emissions peak at 263 hz interpreted as an organ pipe mode high pass filtering was found to usefully discriminate volcano vent noise from wind noise and autocorrelation of the high pass acoustic power reveals a prominent peak in exhalation intervals of 2 5 4 and 8 s with a number of larger explosive events at 200 s intervals we suggest that this compact and inexpensive audio instrumentation can usefully supplement other field monitoring such as seismic or infrasound a simple estimate of acoustic power interpreted with a dipole jet noise model yielded vent velocities too low to be compatible with pyroclast emission suggesting difficulties with this approach at audio frequencies perhaps due to acoustic absorption by volcanic gases

relative partitioning of acoustic and seismic energy during strombolian eruptions the relative elastic energy partitioning during strombolian eruptions can be estimated from acoustic pressure and seismic velocity records we outline methods for determining acoustic and seismic energies for sensors deployed within several kilometers of erupting vents we use these energies to introduce the concept of the volcano acoustic seismic ratio g or vasr which is the ratio of elastic energy propagated through the atmosphere and into the earth eruption vasr is a physical diagnostic of explosive degassing that is appropriate for comparing eruption mechanisms at individual and between various volcanoes here we assess acoustic and seismic energies and corresponding vasr for discrete strombolian explosive events at karymsky and erebus volcanoes we attribute the relatively high and stable vasr at erebus g 8 standard deviation 41 to repeatable source conditions occurring at the surface of a persistent lava lake with accompanying strong coupling to the atmosphere lower and more variable vasr at karymsky g 0 18 in 1998 to g 1 51 in 1991 with standard deviations of 93 and 313 respectively is attributed to changing conditions within a narrow partially choked conduit variable seismoacoustic energy partitioning for karymsky as manifested by the large vasr standard deviation suggests that conduit conditions affecting vasr which include magma properties conduit obstruction or fragmentation depths can evolve both during the course of an explosion and between successive events d 2005 elsevier b v all rights reserved

high sea surface temperatures during the early aptian oceanic anoxic event 1a in the boreal realm the early aptian was characterized by the widespread occurrence of anoxia in the oceans known as oceanic anoxic event oae 1a intense degassing from submarine volcanic plateaus presumably resulted in high atmospheric co2 concentrations culminating in greenhouse conditions oae 1a can therefore be considered as a past natural experiment important to understand the future evolution of our climate paleotemperature estimates for oae 1a are however predominantly based on bulk oxygen isotopes which are susceptible to diagenetic overprinting while tex86 paleotemperature estimates are limited in number or derived from stratigraphically poorly constrained sections here we reconstructed for the first time sea surface water temperatures ssts based on the tex86 paleothermometer from an oae 1a section from the middle northern latitudes 39 n paleolatitude we find a sst rise starting prior to oae 1a and reaching a maximum during the event with ssts of 31 34 c 4 9 c higher than those of older hauterivian lower aptian sediments from the same sedimentary basin the end of oae 1a is marked by relatively lower ssts of 30 c these observations are supported by belemnite based oxygen isotope d18obel data and calcareous nannofossils our integrated data set clearly indicates that super greenhouse conditions prevailed during oae 1a at northern latitudes ssts are similar to those estimated for coeval low latitudinal sites suggesting that an equable warm climate with reduced latitudinal gradients characterized the early aptian

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

explosion dynamics of pyroclastic eruptions at santiaguito volcano 1 in jan 2003 we monitored explosions at santiaguito volcano guatemala with thermal infrasonic and seismic sensors thermal data from 2 infrared thermometers allowed computation of plume rise speeds which ranged from 8 to 20 m s rise rates correlated with cumulative thermal radiance indicating that faster rising plumes correspond to explosions with greater thermal flux the relationship between rise speeds and elastic energy is less clear seismic radiation may not scale well with thermal output and or rise speed because some of the thermal component may be associated with passive degassing which does not induce significant seismicity but non impulsive gas release is still able to produce a high thermal flux which is the primary control on buoyant rise speed

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

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

eruption dynamics of the sw crater of stromboli volcano italy an interdisciplinary approach abstract we report on the evaluation of in situ measurements of eruption velocities and relative mass flux collected by doppler radar as well as acoustic and infrared data that were recorded at stromboli volcano doppler radar observations were made alongside thermal acoustic and seismic measurements to 1 further investigate the complex waveforms of the sw crater by combining infrasonic infrared and doppler radar measurements 2 establish a relationship between infrared acoustic and doppler radar measurements and 3 verify that all instruments observe the same behavior in terms of relative mass eruption rate we also explore the relationship between kinetic and acoustic energy released during an eruption comparing the different methods to each other we are able to show that the mass erupted can be estimated either from the total reflected doppler radar energy or from infrared observations however neither thermal nor reflected energy can provide a value in terms of absolute mass in kg the erupted masses of different eruptions can only be evaluated relative to each other using the combined three data sets we especially focus on the eruption dynamics of the sw crater of stromboli namely its fluctuations in eruption strength these pulses in one eruptive event so called pulsations dominate more than 40 of the eruptions of sw crater previous models that explain pulsations to be generated by multiple consecutively exploding bubbles are supported by our combined analysis of infrasound thermal data particle velocities and the reflected energy

a seismically constrained mass discharge rate for the initiation of the may 18 1980 mount st helens eruption we calculate the vertical mass discharge rate from mount st helens for the first few minutes of the may 18 1980 cataclysmic eruption using a new method based on seismic constraints the observed seismic waves indicate that the seismic source is a series of single forces we model these forces as thrusts due to a combination of the momentum flux of the erupted products and the pressure of the eruptive jet the momentum discharge rate is converted to a mass discharge rate based on estimates of the velocity and jet pressure as constrained by a simple fluid dynamical model only two parameters are necessary for the calculation mach number and sound velocity the calculated mass ejected in the first 100 s is 1 6 10 11 4 6 10 11 kg since the total blast deposit is 3 2 10 11 4 1 10 11 kg one possible interpretation is that the directed blast had a significant 30 vertical component

the effect of pressure on ultrasonic velocity and attenuation in near surface sedimentary rocks accurate laboratory ultrasonic measurements of velocity and attenuation were made on water saturated samples of limestone sandstone and siltstone as a function of effective pressure 5 60 mpa using the pulse echo method core samples were taken from carboniferous sediments at the whitchester shallow borehole test site they were cut perpendicular to the horizontal bedding planes the compressional and shear wave velocities and quality factors of the limestones generally showed negligible increases with pressure while those of the siltstones and sandstones showed intermediate and significant increases with pressure respectively at 60 mpa the sandstone samples generally showed a range of quality factors attributed to their differing porosities and differing proportions of rigid skeletal minerals quartz grains and compliant matrix materials clay kerogenic organic matter at 5 mpa they generally showed similar quality factors attributed to the presence of microcracks which occur predominantly at grain contacts the results show that kerogenic organic matter behaves in a similar way to other compliant matrix minerals in causing high attenuation at ultrasonic frequencies and that caution must be exercised when applying high pressure geostatistical relationships to reservoir rocks at low effective pressures the results indicate the presence of two types of squirt flow loss mechanisms clay squirt flowmore dominates at high pressures while microcrack squirt flow dominates at low pressures clean sandstones and limestones can be distinguished from those with significant amounts of compliant minerals and sandstones with cracks can be distinguished from those without cracks less

direct video and hydrophone observations of submarine explosive eruptions at nw rota 1 volcano mariana arc 1 extraordinary video and hydrophone observations of a submarine explosive eruption were made with a remotely operated vehicle in april 2006 at a depth of 550 560 m on nw rota 1 volcano in the mariana arc the observed eruption evolved from effusive to explosive while the eruption rate increased from near zero to 10 100 m3 h during the peak in activity cyclic explosive bursts 2 6 min long were separated by shorter non eruptive pauses lasting 10 100 s the size of the ejecta increased with the vigor of the explosions a portable hydrophone deployed near the vent recorded sounds correlated with the explosive bursts the highest amplitudes were 50 db higher than ambient noise at frequencies between 10 and 50 hz the acoustic data allow us to quantify the durations amplitudes and evolution of the eruptive events over time the low eruption rate high gas lava ratio and rhythmic eruptive behavior at nw rota 1 are most consistent with a strombolian eruptive style we interpret that the eruption was primarily driven by the venting of magmatic gases which was also the primary source of the sound recorded during the explosive bursts the rhythmic nature of the bursts can be explained by partial gas segregation in the conduit and upward migration in a transitional regime between bubbly flow and fully developed slug flow the strongest explosive bursts were accompanied by flashes of red glow and oscillating eruption plumes in the vent apparently caused by magma seawater interaction and rapid steam formation and condensation this is the first time submarine explosive eruptions have been witnessed with simultaneous near field acoustic recordings

using infrasound waves to monitor tropospheric weather and crater morphology changes at volcan tungurahua ecuador abstract we use infrasound waves generated during eruptions of volcan tungurahua ecuador to study both changing atmospheric conditions and volcanic source characteristics analyzed infrasound data were recorded for a 32 month period by a five station network located within 6 5 km from the vent we use cross network correlation to quantify the recurrent eruptive behavior of tungurahua and results are corroborated by reports from the ecuadorian monitoring agency cross network lag times vary over short time periods minutes to days when vent location is stable and attribute these variations to changes in atmospheric structure assuming a fixed source location we invert for average air temperatures and winds in tungurahua s vicinity

seismicity associated with eruptive activity at langila volcano papua new guinea abstract during periods of eruptive activity at langila volcano various combinations of low frequency earthquakes and high frequency air waves have been recorded ranging from earthquakes alone to air waves alone it is shown that these different types of events are part of a continuous range of events which are all interpreted to be explosions at or near the summit continuous tremor is also often recorded for durations of several minutes to hours and is classified into two types harmonic and non harmonic spectral analysis shows that the non harmonic tremor resembles a string of low frequency events in contrast the spectra of harmonic tremor show simple modal characteristics which indicate some type of resonating source this source is thought to include a gas filled cavity above the magma body within the volcano

characterization of in situ elastic properties of gas hydrate bearing sediments on the blake ridge during ocean drilling program leg 164 shear sonic velocity and other geophysical logs were acquired in gas hydrate bearing sediments on the blake ridge to characterize the very distinct seismic signature of such formations anomalous low amplitudes overlying a strong bottom simulating reflector bsr a comparison of the bulk moduli derived from the logs to standard elastic consolidation models shows that the sediments are overconsolidated above the bsr at 440 meters below seafloor mbsf because of the presence of hydrates below the bottom of the thermodynamic hydrate stability zone at 520 mbsf the high compressibility of the formation and the attenuation of the monopole sonic waveforms are typical of sediments partially saturated with free gas between these two depths gas hydrate and free gas seem to coexist within the gas hydrate stability zone we estimate the amount of gas hydrates using different models based on theories for wave scattering in multiphase media and for grain cementation in close agreement with measurements made on discrete in situ samples the latter describes most accurately the interactions between the matrix the pore fluids and the hydrates this model indicates that 5 to 10 of the pore space is occupied by hydrates deposited uniformly on the surface of the grains the comparison with gassmann s model also show that the amount of free gas below the bsr never exceeds 5 of the pore space but is high enough to generate the bsr the coexistence of free gas and gas hydrates below the bsr may be explained by capillary effects in the smaller pores or by remaining crystalline structures after partial hydrate decomposition

sonic waveform attenuation in gas hydrate bearing sediments from the mallik 2l 38 research well mackenzie delta canada 1 the mallik 2l 38 research well was drilled to 1150 m under the mackenzie delta canada and penetrated a subpermafrost interval where methane hydrate occupies up to 80 of the pore space a suite of high quality downhole logs was acquired to measure in situ the physical properties of these hydrate bearing sediments similar to other hydrate deposits resistivity and compressional and shear sonic velocity data increase with higher hydrate saturation owing to electrical insulation of the pore space and stiffening of the sediment framework in addition sonic waveforms show strong amplitude losses of both compressional and shear waves in intervals where methane hydrate is observed we use monopole and dipole waveforms to estimate compressional and shear attenuation comparing with hydrate saturation values derived from the resistivity log we observe a linear increase in both attenuation measurements with increasing hydrate saturation which is not intuitive for stiffening sediments numerical modeling of the waveforms allows us to reproduce the recorded waveforms and illustrate these results we also use a model for wave propagation in frozen porous media to explain qualitatively the loss of sonic waveform amplitude in hydrate bearing sediments we suggest that this model can be improved and extended allowing hydrate saturation to be quantified from attenuation measurements in similar environments and providing new insight into how hydrate and its sediment host interact

deep volcanic tremor and magma ascent mechanism under kilauea hawaii deep harmonic tremor originating at depths around 40 km under kilauea was studied using records accumulated since 1962 at the hawaii volcano observatory of the u s geological survey the deep source of the tremor was determined by onset times and confirmed by the relative amplitude across the island wide network of seismometers the period of tremor was conclusively shown to be determined by the source effect and not by the path or station site effect because the period would change considerably in time but maintained uniformity across the seismic net during the tremor episode the tremor appeared to be primarily composed of p waves we interpret the observed period and amplitude in terms of the stationary crack model of aki et al 1977 and find that the seismic moment rates for deep tremors are considerably larger than those for shallow tremors suggesting more vigorous transport for the former we propose a kinematic source model which may be more appropriate for deep tremor according to this model a measurable quantity called reduced displacement is directly proportional to the rate of magma flow a systematic search for deep tremor episodes was made for the period from 1962 through 1979 and the amplitude period and duration of the tremor were tabulated we then constructed a cumulative reduced displacement plot over the 18 year period the result shows a generally steady process which does not seem to be significantly affected by major eruptions and large earthquakes near the surface the total magma flow estimated from the reduced displacement is however one order of magnitude smaller than that estimated by swanson 1972 it may be that most channels transport magma aseismically and only those with strong barriers generate tremor

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

sangay volcano ecuador structural development present activity and petrology abstract sangay 5230 m the southernmost active volcano of the andean northern volcanic zone nvz sits 130 km above a 32 ma old slab close to a major tear that separates two distinct subducting oceanic crusts southwards quaternary volcanism is absent along a 1600 km long segment of the andes three successive edifices of decreasing volume have formed the sangay volcanic complex during the last 500 ka two former cones sangay i and ii have been largely destroyed by sector collapses that resulted in large debris avalanches that flowed out upon the amazon plain sangay iii being constructed within the last avalanche amphitheater has been active at least since 14 ka bp only the largest eruptions with unusually high plinian columns are likely to represent a major hazard for the inhabited areas located 30 to 100 km west of the volcano however given the volcano s relief and unbuttressed eastern side a future collapse must be considered that would seriously affect an area of present day colonization in the amazon plain 30 km east of the summit andesites greatly predominate at sangay there being few dacites and basalts in order to explain the unusual characteristics of the sangay suite highest content of incompatible elements except y and hree of any nvz suite low y and hree values in the andesites and dacites and high nb la of the only basalt found a preliminary five step model is proposed 1 an enriched mantle in comparison with an morb source or maybe a variably enriched mantle at the site of the sangay prior to quaternary volcanism 2 metasomatism of this mantle by important volumes of slab derived fluids enriched in soluble incompatible elements due to the subduction of major oceanic fracture zones 3 partial melting of this metasomatized mantle and generation of primitive basaltic melts with nb la values typical of the nvz which are parental to the entire sangay suite but apparently never reach the surface and subordinate production of high nb la basaltic melts maybe by lower degrees of melting at the periphery of the main site of magma formation that only infrequently reach the surface 4 afc processes at the base of a 50 km thick crust where parental melts pond and fractionate while assimilating remelts of similar basaltic material previously underplated producing andesites with low y and hree contents due to garnet stability at this depth 5 low pressure fractionation and mixing processes higher in the crust both an enriched mantle under sangay prior to volcanism and an important slab derived input of fluids enriched in soluble incompatible elements two parameters certainly related to the unique setting of the volcano at the southern termination of the nvz apparently account for the exceptionally high contents of incompatible elements of the sangay suite in addition the low cr ni values of the entire suite another unique characteristic of the nvz also requires unusual fractionation processes involving cr spinel and or clinopyroxene either in the upper mantle or at the base of the crust

infrasonic tracking of large bubble bursts and ash venting at erebus volcano antarctica abstract explosive degassing at erebus volcano produces infrasound that can be used to locate characterize and quantify eruptive activity from multiple vents we use a three element distributed microphone network to pinpoint eruption sources and track the activity at the prominent vents through time eruptive mechanisms for both source types are analyzed in conjunction with the telemetered time synced video imagery we identify two commonly active vents corresponding to the large often 10 m diameter bubble bursts at the free surface of a persistent phonolitic lava lake ray lake and the less frequent ash rich eruptions from a constricted vent active vent located 80 m from the lava lake during a 3 month study interval from 6 january to 13 april 2006 we identified and mapped more than 350 eruptive sources from the lava lake and 20 sources from the ash vent lava lake events are characterized by high amplitude infrasonic transients that reflect rapid less than a few s acceleration and rupture of magma bubble films followed by an explosion of pressurized gases precise infrasonic localization of the lava lake events to accuracies of a few m indicates variable bubble source locations across a 40 by 50 m region spanning the lava lake spatial variability is corroborated by the video data in contrast degassing from the ash vent produces longer duration tens of s lower amplitude transients that reflect diminished impulsivity and an extended degassing duration features that are corroborated by video because infrasound networks can operate continuously in all weather conditions and during both diurnal and seasonal polar darkness and are easily incorporated into automatic processing they significantly contribute to the completeness and quantification of eruption catalogues for erebus

degassing explosions at karymsky volcano kamchatka during the summer of 1997 karymsky vol cano produced summit explosions about six times each hour typical explosive episodes lasted between 30 seconds and three minutes produced gas and ash columns several hun dred meters high and ejected some incandescent material to better understand the physical source mechanisms re sponsible we recorded hundreds of explosions with a three component broad band seismometer and microphone lo cated 1650 meters from the active vent nearly every explo sion is recorded as an emergent yet identical seismic wavelet which is followed 4 15 s later by an impulsive acoustic ar rival we interpret the signals as a near surface gas volume burst which fractures the vent plug lowers the lithostatic pressure within the magma column and often induces fur ther degassing when degassing continues it is generally manifested as either a series of regular one second chug ging 1 explosions steady higher frequency jetting or a hy brid combination we believe that the seismic signature for chugs short duration harmonic tremor with integer over tones is the result of repeated gas volume bursts at the vent in contrast seismograms for jetting are non harmonic and contain higher frequencies we believe that the competing degassing behaviors are influenced by the gas flux as well as the plug conduit characteristics we propose that a plug exists due to a viscosity gradient caused by volatile depletion in the upper conduit

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

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

volcanic eruptions lightning and a waterfall differentiating the menagerie of infrasound in the ecuadorian jungle 1 in northeastern ecuador near reventador volcano the airwaves are filled with infrasound here we identify the locations and characterize three distinct sources of local infrasound including two types of infrasonic sources which are not commonly discussed in the literature the first of these novel sources is an intense and continuous radiator with a fixed location corresponding to san rafael waterfall the signal from the river exhibits a tremor like envelope that is well correlated across the 3 element infrasound network beyond the river we also observe and map spatially variable sources corresponding to thunder these transient signals have impulsive onsets but are not well correlated across the network and are attributable to spatially distributed source regions finally we identify plentiful infrasound corresponding to reventador s volcanic vent that is associated with unrest this study demonstrates the utility of dispersed infrasound networks for distinguishing variable sources and improving interpretation of mechanisms of infrasound radiators

seismic velocity structure at a gas hydrate reflector offshore western colombia from full waveform inversion seismic reflection profiles across many continental margins have imaged bottom simulating reflectors bsrs which have been interpreted as being formed at the base of a methane hydrate stability field such reflectors might arise either from an impedance contrast between high velocity partially hydrated sediments and water saturated sediments or from a contrast with partially gas saturated sediments these alternatives may be hard to distinguish by conventional amplitude versus offset or waveform modeling approaches here we investigate the origin of a high amplitude bsr in the accretionary wedge offshore of western colombia by seismic waveform inversion the inversion procedure consists of three steps firstly determination of root mean square velocities and hence estimates of the interval velocities between major reflectors by a global grid search for maximum normalized energy along elliptical trajectories in the intercept time slowness domain secondly determination of accurate interval velocities between these reflectors by a monte carlo search for maximum energy and thirdly a waveform fit in the frequency slowness domain using differential reflectivity seismograms and a conjugate gradient optimization algorithm to minimize the sample by sample waveform misfit between data and synthetic at two locations near a structural high we find a 30 m thick low velocity zone beneath the bsr with the properties of a partially gas saturated zone while at a third location where the bsr amplitude is lower we find no evidence for anomalously low velocities the preferential development of the bsr in structures that would tend to intercept fluid flow or migrating gas and the presence of free gas beneath the bsr indicate a mechanism of bsr formation in which free methane gas migrates upward into the hydrate stability field or is carried there in advecting pore water

flux measurements of explosive degassing using a yearlong hydroacoustic record at an erupting submarine volcano at nw rota 1 are primarily h2o so2 and co2 instantaneous fluxes varied by a factor of 100 over the deployment using melt inclusion information to estimate the concentration of co2 in the explosive gases as 6 9 0 7 wt we calculate an annual co2 eruption flux of 0 4 0 1 tg a 1 this result is within the range of measured co2 fluxes at continuously erupting subaerial volcanoes and represents 0 2 0 6 of the annual estimated output of co2 from all subaerial arc volcanoes and 0 4 0 6 of the mid ocean ridge flux the multiyear eruptive history of nw rota 1 demonstrates that submarine volcanoes can be significant and sustained sources of co2 to the shallow ocean

generation and propagation of infrasonic airwaves from volcanic explosions abstract analysis of infrasonic pressure waves generated by active volcanoes is essential to the understanding of volcanic explosion dynamics unlike seismic waves propagating in the earth infrasonic airwaves offer a relatively unfiltered representation of source motions at the vent during an eruption time varying acoustic propagation filters caused by changeable atmospheric conditions are minimal for microphones deployed at intermediate distances johnson et al j volcanol geotherm res in press

an overview of volcano infrasound from hawaiian to plinian local to global abstract volcano infrasound is an increasingly useful technique for detecting locating characterizing and quantifying eruptive activity and can be used to constrain eruption source parameters in recent years studies of infrasound data from active volcanoes have shown clear progress towards mitigating volcanic hazards and understanding volcanic source processes volcano acoustic sources are shallow or aerial thus volcano infrasound data provide valuable information on eruption dynamics and are readily combined with direct and remote observations of gas ash and other eruptive phenomena the infrasound signals produced by volcanoes are indicative of the eruption style and dynamics here we review the diversity of infrasound signals generated by a wide variety of volcanic eruptions from hawaiian to plinian and the physical processes inferred to produce them we place particular emphasis on regional 15 250 km distance and global 250 km distance volcano infrasound studies as recent work in this area has made significant advances in monitoring and characterizing remote and difficult to monitor eruptions long range infrasonic detection of explosive volcanic eruptions is possible due to the energetic source mechanisms involved minor atmospheric attenuation at low frequencies and the existence of waveguides in the atmosphere however accurate characterization of the atmosphere and its spatiotemporal variability is required for reliable long range sound propagation modeling and correct interpretation of global infrasound recordings conversely because volcanic explosions are energetic and sometimes repetitive infrasound sources they can be used to validate atmospheric and acoustic propagation models

infrasonic tremor observed at kīlauea volcano hawai i 1 infrasonic array data collected at k lauea volcano hawai i during november 12 21 2002 indicate that the active vents and lava tube system near the pu u vent complex emit almost continuous infrasound in the 0 3 10 hz frequency band the spectral content of these infrasonic signals matches well that of synchronous seismic tremor in sites protected from wind noise significant signal to noise ratios were recorded as far as 13 km from the crater of pu u the infrasonic recordings suggest that one or more tremor sources may be close to the surface in addition these results demonstrate that adequate site and instrument selections for infrasonic arrays are essential in order to obtain consistent and reliable infrasonic detections

source location variability and volcanic vent mapping with a small aperture infrasound array at stromboli volcano italy stromboli volcano in italy is a persistently active complex volcanic system in may 2002 activity was confined to 3 major summit craters within which several active vents hosted multiple explosions each hour during a 5 day field campaign an array of 3 low frequency microphones was installed to investigate the coherent infrasound produced by degassing from these vents consistent phase lags across the 3 stations indicate distinct sources that are subsequently investigated to determine the associated vent location apparent depth and origin time the cross correlation routine allows for variations in comparison window length waveform filtering bandwidth and correlation and consistency thresholds allowing for improved detection of certain types of degassing sources identification of activity at the various vents could be subsequently corroborated with 3 channels of synchronously acquired thermal data and video during the may 2002 experiment persistent energetic infrasound was observed from a passive degassing source within the central crater cc and transient infrasound produced by discrete strombolian explosions was identified at 4 additional vents the continuous infrasound produced by the cc exhibits variable frequency dependent correlation lag times that are interpreted as a diffraction effect due to the acoustic radiator s recessed location within a steep walled crater such dispersion has important implications for accurate eruption source modeling because it indicates that infrasonic waveforms may be significantly filtered during propagation transient explosion signals from the northeast crater nec and southwest crater swc vents also exhibit dynamic correlation lag times but this scatter may be more reasonably attributed to variable epicentral locations explosions from the nec west vent for instance appear to emanate from a diffuse zone with a lateral extent in excess of 10 m

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

experimental and analytical modeling of basaltic ash explosions at mount etna italy 2001 1 the summer 2001 flank eruption of mount etna ended with repeated basaltic ash explosions the explosions were similar to small scale vulcanian blasts and probably originated when a plug of magma at the top of the conduit became overpressurized we use three independent methods to estimate the overpressure in the plug 1 to determine the pressure differential required to fragment the plug we use a shock tube apparatus to heat and pressurize ballistic blocks at temperature t up to 900 c and pressure p up to 25 mpa and rapidly decompress them to ambient conditions 2 we apply a model to determine the overpressure generated by microlite growth at depth because pyroclasts from the explosions have 35 vol more microlites than preceding strombolian product and 3 we relate the range of ballistic blocks to their exit velocity and with models for vulcanian eruptions the exit velocity to pressure in the conduit experiments and ejecta range bracket the overpressure driving the explosions between 3 and 5 mpa below 2 5 mpa the blocks would not reach the observed range but above 5 mpa the existing blocks with 20 porosity would not survive the explosions crystallization of 35 vol microlites at a depth of 100 m increases the pressure in the plug to 6 mpa above atmospheric enough to drive the explosions with a possible contribution from deeper volatiles combining the different methods we also constrain the exsolved water at fragmentation at 0 05 wt and provide inferences on how the explosions came to an end

seismic and acoustic observations at mount erebus volcano ross island antarctica 1994 1998 volcanic activity at mount erebus is dominated by eruptive activity within a phonolitic summit lava lake common eruption styles range from passive degassing to strombolian explosions which typically occur several times daily and occasionally in swarms of up to 900 per day shallow explosions although generally the result of steady exsolution of volatiles from depth can be triggered by surficial input of h 2o through mass wasting of rock snow and ice from the crater walls broadband observations of strombolian explosions document very long period vlp signals with strong spectral peaks near 20 12 and 7 s which are polarized in the vertical radial plane these signals precede lava lake surface explosions by 1 5 s are highly repeatable and persist for up to 200 s first motions indicate a deflationary source with any precursory inflation being below the 30 s passband of our instruments particle motions suggest a vlp source residing up to 800 m below the lava lake surface however this depth could be exaggerated by near field radial tilt seismic and acoustic signals associated with lava lake explosions commonly show evidence for multiple bubble bursts in corresponding complexity features resulting from varying time delays and relative sizes of superimposed bursts a systematic decrease in seismic acoustic ratio for smaller surface explosions suggests that either the seismic energy from the smallest shallowest bubble bursts experiences much greater seismic attenuation than energy arising from larger events which may involve a deeper less attenuative portion of the magma column and or that the shallowest layer is seismically isolated from deeper parts of a stratified magma column which are not excited by the smallest explosions due to sharp impedance contrasts across distinct layers tremor at erebus is uncommon with only a few isolated instances identified in five years of monitoring some tremor events are nearly monochromatic and some exhibit numerous gliding harmonic spectral lines q 2000 elsevier science b v all rights reserved

characterizing complex eruptive activity at santiaguito guatemala using infrasound semblance in networked arrays abstract we implement an infrasound semblance technique to identify acoustic sources originating from volcanic vents and apply the technique to the generally low amplitude infrasound

infrasound connecting the solid earth oceans and atmosphere the recently reinvigorated field of infrasonics is poised to provide insight into atmospheric structure and the physics of large atmospheric phenomena just as seismology has shed considerable light on the workings and structure of earth s solid interior although a natural tool to monitor the atmosphere and shallow earth for nuclear explosions it is becoming increasingly apparent that infrasound also provides another means to monitor a suite of natural hazards the frequent observation of geophysical sources such as the unsteady sea surface volcanoes and earthquakes that radiate energy both up into the atmosphere and down into the liquid or solid earth and transmission of energy across earth s boundaries reminds us that earth is an interconnected system this review details the rich history of the unheard sound in the atmosphere and the role that infrasonics plays in helping us understand the earth system

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

a laboratory investigation into the seismic velocities of methane gas hydrate bearing sand remote seismic methods which measure the compressional wave p wave velocity vp and shear wave s wave velocity vs can be used to assess the distribution and concentration of marine gas hydrates in situ however interpreting seismic data requires an understanding of the seismic properties of hydrate bearing sediments which has proved problematic because of difficulties in recovering intact hydrate bearing sediment samples and in performing valid laboratory tests therefore a dedicated gas hydrate resonant column ghrc was developed to allow pressure and temperature conditions suitable for hydrate formation to be applied to a specimen with subsequent measurement of both vp and vs made at frequencies and strains relevant to marine seismic investigations thirteen sand specimens containing differing amounts of evenly dispersed hydrate were tested the results show a bipartite relationship between velocities and hydrate pore saturation with a marked transition between 3 and 5 hydrate pore saturation for both vp and vs this suggests that methane hydrate initially cements sand grain contacts then infills the pore space these results show in detail for the first time using a resonant column how hydrate cementation affects elastic wave properties in quartz sand this information is valuable for validating theoretical models relating seismic wave propagation in marine sediments to hydrate pore saturation

influence of near source volcano topography on the acoustic wavefield and implication for source modeling in near source conditions 5 km the atmosphere is often assumed to be fully transparent to acoustic waves and to have a small effect on the acoustic wavefield as a consequence the propagation of the acoustic waves in the atmosphere near the source is often neglected and waveform is compensated only in amplitude by the inverse of the distance from the source however the amplitude distribution at five infrasonic stations deployed around the active craters of the stromboli volcano reveals anomalous decay up to 11 db larger than expected which cannot be explained in terms of energy loss for geometrical spreading the distribution of amplitude decay changes for different source positions suggesting a strong relationship with the source to receiver path geometry by using 2d fdtd modeling we show that the anomalous amplitude distribution of the acoustic waves at stromboli is not necessarily due to the source radiation pattern but it is strongly influenced by the topography of the ground atmosphere interface diffraction and reflection of topography contaminate the acoustic wavefield and have a strong effect in reducing the amplitude and altering the waveform our work demonstrates that line of sight conditions are quite difficult to be achieved in acoustic experiments and that a detailed knowledge of the topography along the crater receiver path is necessary whenever infrasound waveforms are used to invert for the source process

monitoring seismo volcanic and infrasonic signals at volcanoes mt etna case study volcanoes generate a broad range of seismo volcanic and infrasonic signals whose features and variations are often closely related to volcanic activity the study of these signals is hence very useful in the monitoring and investigation of volcano dynamics the analysis of seismo volcanic and infrasonic signals requires specifically developed techniques due to their unique characteristics which are generally quite distinct compared with tectonic and volcano tectonic earthquakes in this work we describe analysis methods used to detect and locate seismo volcanic and infrasonic signals at mt etna volcanic tremor sources are located using a method based on spatial seismic amplitude distribution assuming propagation in a homogeneous medium the tremor source is found by calculating the goodness of the linear regression fit r 2 of the log linearized equation of the seismic amplitude decay with distance the location method for long period events is based on the joint computation of semblance and r 2 values and the location method of very long period events is based on the application of radial semblance infrasonic events and tremor are located by semblance brightness and semblance based methods respectively the techniques described here can also be applied to other volcanoes and do not require particular network geometries such as arrays but rather simple sparse networks using the source locations of all the considered signals we were able to reconstruct the shallow plumbing system above sea level during 2011

infrasonic precursors to a vulcanian eruption at sakurajima volcano japan the may 1998 eruption sequence of sakurajima volcano was monitored by ten infrasonic stations ten seismometers and a video camera during this seismo acoustic experiment we recorded hundreds of infrasonic tremor and long period events associated with seismic signals and observed a progression from relative quiescence to a vulcanian eruption the number of infrasonic events increased with escalating volcanic activity and the dominant character of the infrasonic signals changed from impulsive to emergent at 22 17 of may 19 sakurajima released ash and gases to a height of 2 km above the vent an event that was recorded continuously by one infrasonic and two seismic stations we present the experimental setup as well as a procedure through which infrasonic signals may be incorporated into future eruption monitoring and forecasting algorithms for open vent volcanic systems in addition our recordings suggest that infrasonic signals are more representative of processes occurring within the volcanic interior than are seismic signals which are strongly altered by diffraction and scattering in the volcanic edifice

volcano infrasound a review abstract exploding volcanoes which produce intense infrasound are reminiscent of the veritable explosion of volcano infrasound papers published during the last decade volcano infrasound is effective for tracking and quantifying eruptive phenomena because it corresponds to activity occurring near and around the volcanic vent as opposed to seismic signals which are generated by both surface and internal volcanic processes as with seismology infrasound can be recorded remotely during inclement weather or in the dark to provide a continuous record of a volcano s unrest moreover it can also be exploited at regional or global distances where seismic monitoring has limited efficacy this paper provides a literature overview of the current state of the field and summarizes applications of infrasound as a tool for better understanding volcanic activity many infrasound studies have focused on integration with other geophysical data including seismic thermal electromagnetic radiation and gas spectroscopy and they have generally improved our understanding of eruption dynamics other work has incorporated infrasound into volcano surveillance to enhance capabilities for monitoring hazardous volcanoes and reducing risk this paper aims to provide an overview of volcano airwave studies from analog microbarometer to modern pressure transducer and summarizes how infrasound is currently used to infer eruption dynamics it also outlines the relative merits of local and regional infrasound surveillance highlights differences between array and network sensor topologies and concludes with mention of sensor technologies appropriate for volcano infrasound study

calcareous nannoplankton response to surface water acidification around oceanic anoxic event 1a ocean acidification induced by atmospheric co2 may be a major threat to marine ecosystems particularly to calcareous nannoplankton we show that during the aptian 120 million years ago oceanic anoxic event 1a which resulted from a massive addition of volcanic co2 the morphological features of calcareous nannofossils traced the biological response to acidified surface waters we observe the demise of heavily calcified nannoconids and reduced calcite paleofluxes at the beginning of a pre anoxia calcification crisis ephemeral coccolith dwarfism and malformation represent species specific adjustments to survive lower ph whereas later abundance peaks indicate intermittent alkalinity recovery deepwater acidification occurred with a delay of 25 000 to 30 000 years after the dissolution climax nannoplankton and carbonate recovery developed over 160 000 years under persisting global dysoxia anoxia

combined vertical incidence and wide angle seismic study of a gas hydrate zone blake ridge wide angle ocean bottom seismic data and single channel seismic reflection data were collected in june 1992 over an area where gas hydrates are thought to be extensive on blake ridge offshore south carolina wide angle reflections were observed on four woods hole oceanographic institution ocean bottom hydrophones at offsets up to 15 km results from traveltime inversion show that the bottom simulating reflector bsr that marks the base of the hydrate stability field lies 400 500 m below the seafloor and is overlain by a 200 to 300 m thick layer of average velocity 1 9 km s 1 there is no evidence for significant lateral velocity variation associated with lateral changes in bsr character ray tracing calculations show that the observation of the bsr out to large offsets 7 km constrains the maximum vertical velocity gradient to about 0 5 s 1 amplitude versus offset avo analysis was performed for ranges up to about 6 km and incidence angles of more than 70 the high amplitude of the bsr in the normal incidence data can be explained by two models both of which include a strong negative impedance contrast the hydrate wedge model and the free gas layer model synthetic seismogram calculation for the wedge model using the reflectivity method shows a strong increase in the bsr amplitudes at offsets between 3 and 5 km because of postcritical reflections and diving waves within the wedge this amplitude increase is clearly not observed in the data which shows only a relatively modest increase in amplitude with offset this observation agrees better with the calculated avo for the gas layer model the lack of a distinct reflection from the base of the gas layer implies that the gas layer is not thicker than 25 m and or that the base of the gas layer is a gradational boundary

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

ground coupled airwaves at pavlof volcano alaska and their potential for eruption monitoring an abnormally high number of explosion quakes were noted during the monitoring effort for the 2007 eruption of pavlof volcano on the alaska peninsula in this study we manually cataloged the explosion quakes from their characteristic ground coupled airwaves this study investigates how the ground coupled airwaves might be used in a monitoring or analysis effort by estimating energy release and gas mass release over 3 104 quakes were recorded the energy release from the explosions is approximated to be 3 1011 j and the total gas mass assuming 100 water released was 450 t the tracking of explosion quakes has the potential to estimate relative eruption intensity as a function of time and is thus a useful component of a seismic monitoring program

interpretation and utility of infrasonic records from erupting volcanoes abstract in the most basic seismo acoustic studies at volcanoes infrasound monitoring enables differentiation between sub surface seismicity and the seismicity associated with gas release under optimal conditions complicated degassing signals can be understood relative explosion size can be assessed and variable seismo acoustic energy partitioning can be interpreted the extent to which these points may be investigated depends upon the quality of the infrasonic records a function of background wind noise microphone sensitivity and microphone array geometry and the type of activity generated by the volcano frequency of explosions bandwidth of the signals and coupling efficiency of the explosion to elastic energy to illustrate the features benefits and limitations of infrasonic recordings at volcanoes we showcase acoustic and seismic records from five volcanoes characterized by explosive degassing these five volcanoes erebus in antarctica karymsky in russia and sangay tungurahua and pichincha in ecuador were the focus of seismo acoustic experiments between 1997 and 2000 each case study provides background information about the volcanic activity an overview of visual observations during the period of monitoring and examples of seismo acoustic data we discuss the benefits and utility of the infrasound study at each respective volcano finally we compare the infrasound records and eruptive activity from these volcanoes with other volcanoes that have been the focus of previous seismo acoustic experiments

airwaves generated by an underwater explosion implications for volcanic infrasound 1 a shallow explosion in a fluid is one of the fundamental processes of airwave generation in volcanic eruptions to better understand the mechanism of the airwave generation underwater explosion experiments were conducted although the underwater explosions have been intensely studied over the last century airwaves have received little attention in this study pressure waves were measured in air and under water and the corresponding motion of the water surface was captured by a high speed video camera airwaves and associated styles of the surface motion show similarities determined by the scaled depth defined as the depth divided by the cubic root of the explosion energy the air waveforms are quite different from the pressure waves measured in the water and cannot be completely explained by linear transmission of pressure waves from water to air the mechanism of airwave generation is a combination of wave transmission and dynamics of the interface boundary the first mechanism directly reflects the explosion source and the same source is also observed as the underwater pressure waves on the other hand the second is not necessarily visible in the underwater pressure waves but will provide information on the mechanical properties and behavior of the material above the explosion source each mechanism is analyzed in the experiments

three dimensional volcano acoustic source localization at karymsky volcano kamchatka russia abstract we test two methods of 3 d acoustic source localization on volcanic explosions and small scale jetting events at karymsky volcano kamchatka russia recent infrasound studies have provided evidence that volcanic jets produce low frequency aerodynamic sound jet noise similar to that from man made jet engines for man made jet noise noise sources localize along the turbulent jet flow downstream of the nozzle discrimination of jet noise sources along the axis of a volcanic jet requires high resolution in the vertical dimension which is very difficult to achieve with typical volcano acoustic network geometries at karymsky volcano an eroded edifice dvor caldera adjacent to the active cone provided a platform for the deployment of five infrasound sensors in july 2012 with intra network relief of 600 m the network was designed to target large scale jetting but unfortunately only small scale jetting and explosions were recorded during the 12 day experiment a novel 3 d inverse localization method srcloc is tested and compared against a more common grid search semblance technique simulations using synthetic signals show that srcloc is capable of determining vertical solutions to within 150 m or better for signal to noise ratios 1 for this network configuration however srcloc locations for explosions and small scale jetting at karymsky volcano show a persistent overestimation of source elevation and underestimation of sound speed the semblance method provides more realistic source locations likely because it uses a fixed realistic sound speed of 340 m s explosion waveforms exhibit amplitude relationships and waveform distortion strikingly similar to those theorized by modeling studies of wave diffraction around the crater rim we suggest that the delay of acoustic signals and apparent elevated source locations are due to raypaths altered by topography and or crater diffraction effects implying that topography in the vent region must be accounted for when attempting 3 d volcano acoustic source localization though the data presented here are insufficient to resolve small scale jet noise sources similar techniques may be successfully applied to large volcanic jets in the future

analysis of infrasonic and seismic events related to the 1998 vulcanian eruption at sakurajima abstract we present results from a detailed analysis of seismic and infrasonic data recorded over a four day period prior to the vulcanian eruptive event at sakurajima volcano on may 19 1998 nearly one hundred seismic and infrasonic events were recorded on at least one of the nine seismic infrasonic stations located within 3 km of the crater four unique seismic event types are recognized based on the spectral features of seismograms including weak seismic tremor characterized by a 5 6 hz peak mode that later shifted to 4 5 hz long period events are characterized by a short duration wide spectral band signal with an emergent high frequency onset followed by a wave coda lasting 15 20 s and a fundamental mode of 4 2 4 4 hz values of q for long period events range between 10 and 22 suggesting that a gas rich fluid was involved explosive events are the third seismic type characterized by a narrow spectral band signal with an impulsive high frequency onset followed by a 20 30 second wave coda and a peak mode of 4 0 4 4 hz volcano tectonic earthquakes are the fourth seismic type prior to may 19 1998 only the tremor and explosion seismic events are found to have an infrasonic component like seismic tremor infrasonic tremor is typically observed as a weak background signal explosive infrasonic events were recorded 10 15 s after the explosive seismic events and with audible explosions prior to may 19 on may 19 high frequency impulsive infrasonic events occurred sporadically and as swarms within hours of the eruption these infrasonic events are observed to be coincident with swarms of long period seismic events video coverage during the seismic infrasonic experiment recorded intermittent releases of gases and ash during times when seismic and acoustic events were recorded the sequence of seismic and infrasonic events is interpreted as representing a gas rich fluid moving through a series of cracks and conduits beneath the active summit crater

seismoacoustic investigations of paroxysmal activity at mt etna volcano new insights into the 16 november 2006 eruption 1 on 16 november 2006 a 1 day long paroxysmal eruption occurred at the summit craters of mt etna volcano a multiparametric approach consisting of analyzing infrasonic seismic and video camera recordings was carried out to follow its evolution volcanological and geophysical observations identified three eruptive phases in the first phase infrasonic and seismic characteristics reflected the highly explosive nature of the activity waveform characterization of infrasound events confirmed the activity of the several explosive vents at the summit of southeast crater sec during the second phase results highlighted the decoupling between seismic and infrasonic sources which was due to the decrease in explosive activity and the reactivation of effusive vents located south of bocca nuova and on the saddle between bocca nuova and sec the third phase was the most intense and was characterized by various volcanic phenomena pyroclastic flows jets of dark ash and white steam the very high radiated infrasonic energy together with infrasound event features led us to infer a gas enrichment of the shallow magma column preceding by a few minutes and likely related to the pyroclastic flows in the sec area after the eruption at sec variations in infrasound events related to the activity of northeast crater nec were found the observed spectral changes and the source mechanism modeling of the nec infrasound events suggest the existence of a link in the plumbing system feeding the two craters

non linear explosion tremor at sangay volcano ecuador a detailed analysis of discrete degassing pulses chugs at sangay volcano was performed on seismic and infrasonic records to determine the physics of the conduit infrasonic chugging signals appear as repetitive pulses with small variations in amplitude and time lag an automated time domain analysis was developed to measure with high precision time intervals and amplitudes at different wave arrivals reducing the possibility error associated with hand picking using this automated method a strong positive correlation of acoustic amplitude with repose time between individual pulses on chugging signals of sangay was found on numerous oscillating sequences frequency gliding of apparent harmonic frequencies generally trends from high to low frequency at sangay in contrast to trends at karymsky volcano russia a new description of chugging events using wavelet transform methods appropriate for non stationary signals shows subtle changes in the waveforms relate to physical processes in the volcano a system of non linear feedback based on choked flow at the vent is postulated as the most likely source of this volcanic tremor

acoustic source characterization of impulsive strombolian eruptions from the mount erebus lava lake abstract we invert for acoustic source volume outflux and momentum imparted to the atmosphere using an infrasonic network distributed about the erupting lava lake at mount erebus ross island antarctica by modeling these relatively simple eruptions as monopole point sources we estimate explosively ejected gas volumes that range from 1 000 m 3 to 24 000 m 3 for 312 lava lake eruptions recorded between january 6 and april 13 2006 though these volumes are compatible with bubble volumes at rupture as estimated from explosion video records departures from isotropic radiation are evident in the recorded acoustic wavefield for many eruptions a point source acoustic dipole component with arbitrary axis orientation and strength provides precise fit to the recorded infrasound this dipole source axis corresponding to the axis of inferred short duration material jetting varies significantly between events physical interpretation of dipole orientation as being indicative of eruptive directivity is corroborated by directional emissions of ejecta observed in erebus eruption video footage although three azimuthally distributed stations are insufficient to fully characterize the eruptive acoustic source we speculate that a monopole with a minor amount of oriented dipole radiation may reasonably model the primary features of the recorded infrasound for these eruptions

infrasonic monitoring at stromboli volcano during the 2003 effusive eruption insights on the explosive and degassing process of an open conduit system 1 stromboli is an open conduit volcano characterized by persistent conduit degassing and explosive dynamics during the 2003 effusive eruption we monitored this activity with a five element array deployed at 450 m from the active craters the array allows us to track in real time changes of explosive activity in terms of source position and excess pressure release infrasonic monitoring located the new active vents in the same preeruptive position revealing that the collapse of the crater terrace has not changed the geometry of the shallow feeding system elevation of the infrasonic source is stable at 750 m above sea level coincident with the elevation of the crater terrace this suggests a shallow position of the magma column or if the source is embedded in the conduit diffraction at the crater rim at the end of the eruption back azimuth analysis indicates that explosive activity was progressively reestablished at all of the craters following a ne toward sw direction along the collapsed trench the array detected significant small amplitude 1 pa infrasonic activity occurring at a rate of approximately one pulse every 2 s and generally located in only one vent at a time this persistent activity is not related to strombolian explosion but we infer it is reflecting the overpressurized degassing of the magma column amplitude distribution of 7 million infrasonic signals shows that this degassing is 1 order of magnitude more energetic than the explosions besides infrasonic amplitude distribution presents a decay with a double slope indicating that explosions and degassing are driven by conduit dynamics acting at two different rates

finite difference time domain modeling of transient infrasonic wavefields excited by volcanic explosions 1 numerical modeling of waveform diffractions along the rim of a volcano vent shows high correlation to observed explosion signals at karymsky volcano kamchatka russia the finite difference modeling assumed a gaussian source time function and an axisymmetric geometry a clear demonstration of the significant distortion of infrasonic wavefronts was caused by diffraction at the vent rim edge data collected at karymsky in 1997 and 1998 were compared to synthetic waveforms and variations of vent geometry were determined via grid search karymsky exhibited a wide range of variation in infrasonic waveforms well explained by the diffraction and modeled as changing vent geometry rim diffraction of volcanic infrasound is shown to be significant and must be accounted for when interpreting source physics from acoustic observations

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

an 11 million year long record of astronomically forced fluvial alluvial deposition and paleoclimate change in the early cretaceous songliao synrift basin china abstract in the cretaceous songliao basin northeastern china boreholes have recovered detailed geologic data from sub basins that developed during the early rifting of the basin among these the lower cretaceous shahezi formation k1s in the songshen 4 ss4 well is represented by an 836 m thick succession of fluvial alluvial deposits with coals distributed throughout the upper part of the formation gamma ray gr logging data are quantitatively related to grain size defined litho facies that recur throughout the succession with high gr values in mudstones and low gr values in sandstones cyclostratigraphic analysis of the gr log reveals depositional cycling at frequencies that are consistent with those of the earth s astronomical parameters the results also indicate that occurrence of coal beds occur every 100 kyr when development of vegetation at the depositional site was promoted by humid climate we propose a model of astronomically forced hydroclimate change to explain the cycling of depositional environments between fluvial and alluvial conditions the model describes a principally fluvial environment that episodically experienced at one extreme advancing alluvial conditions involving a drop in base level lake recession and increased aridity conglomerates and coarse sands and at the other extreme an advancing lakeshore with a rise in base level and increased humidity fine sands silts muds and coal a floating astronomical time scale was established by calibrating long orbital eccentricity 405 kyr cycles interpreted along the gr series the results indicate that the duration of the k1s is 11 14 myr 27 5405 kyr long orbital eccentricity cycles corresponding to an average sedimentation rate of 6 55 cm kyr the recognition of astronomical forcing in this early cretaceous fluvial alluvial dominated depositional setting offers a new framework for interpreting the sedimentary cyclicity and dynamics of early rift basins and for developing time scales

explosions and periodic tremor at karymsky volcano kamchatka russia summary the explosions of karymsky volcano often produce signals containing a sequence of repeating pulses recorded on acoustic and seismic sensors known as chugging the amplitudes of these pulses correlate with the time interval between pulses for a given measured acoustic pressure seismic amplitudes take on arbitrary values up to a specific empirically determined threshold conversely events with a small seismic amplitude yielded acoustic waves with large variations and large amplitude seismic events corresponded to large acoustic waves these observations are not consistent with a source modelled by a resonating conduit rather a model consisting of a sequence of discrete pulses explains the data and provides a framework for understanding the dynamics of degassing at the vent the physical model for chugging involves a time varying narrowing vent where gasses are released in a series of oscillations which appear to be harmonic but instead are modelled as short term transients or discrete pulses suggestive of choked flow

spectral analysis of harmonic tremor signals at mt semeru volcano indonesia a detailed spectral analysis of tremor signals recorded at mt semeru volcano indonesia in october 1992 by the german indonesian volcano expedition give 92 reveals clearly harmonic spectra containing up to 11 integer harmonics the spectral features can be explained by any rhythmically pulsating source producing a temporarily stable source signal as one realisation of this concept we model the source as a resonating gas volume generating seismic signals similar to the sound generated in a recorder

volcanic eruptions observed with infrasound 1 infrasonic airwaves produced by active volcanoes provide valuable insight into the eruption dynamics because the infrasonic pressure field may be directly associated with the flux rate of gas released at a volcanic vent infrasound also enhances the efficacy of volcanic hazard monitoring and continuous studies of conduit processes here we present new results from erebus fuego and villarrica volcanoes highlighting uses of infrasound for constraining quantitative eruption parameters such as eruption duration source mechanism and explosive gas flux

an infrasound array study of mount st helens the ongoing activity of mount st helens provides an opportunity to study the infrasonic wavefield produced by an active silica rich volcano in late october 2004 as a pilot experiment for the acoustic surveillance for hazardous eruptions ashe project we deployed two infrasound arrays each co located with a broadband seismometer and weather station to continuously record seismo acoustic signals from mount st helens the nearest array coldwater was deployed on the northern flank of the volcano 13 km from the summit the second array sacajawea was deployed 250 km east of the volcano at a distance where stratospherically ducted acoustic waves may be expected during the winter this paper presents an overview of the experimental setup and preliminary results from this unique data set eruptions on january 16th 2005 and march 9th 2005 produced strong infrasonic signals the aseismic january 16th eruption signal lasted 9 4 min beginning at 11 20 44 01 16 05 utc while the march 9th eruption signal lasted 52 8 min beginning at 01 26 17 03 09 05 utc with the main steam and ash venting stage probably lasting 7 2 min the march 9th signal was an order of magnitude larger than the january 16th signal and was clearly recorded 250 km east at the sacajawea array infrasonic expressions of long period lp seismic events drumbeats have also been intermittently observed and are recorded as acoustic waves mimicking the waveform and temporal sequence of their seismic counterparts these acoustic observations provide important constraints for source models of long period events and eruptions

timing and magnitude of early aptian extreme warming unraveling primary δ18o variation in indurated pelagic carbonates at deep sea drilling project site 463 central pacific ocean abstract in order to elucidate early aptian marine paleotemperature evolution across the period of enhanced organic carbon corg burial oceanic anoxic event oae 1a stable isotope analyses were performed on pelagic limestones at deep sea drilling project site 463 central pacific ocean the 18o data exhibit a distinct anomaly by 2 spanning the oae 1a interval i e a 6 m thick phytoplanktonic corg rich unit constrained by magneto bio and 13c stratigraphy elucidation of paleotemperature significance of the 18o shift is made by taking account of recent sr ca evidence at the same section which revealed that geochemical signals in carbonate poor lithologies are relatively unaltered against burial diagenesis by discriminating 18o values from carbonate poor samples caco3 contents 5 30 wt it appears that an abrupt rise in sea surface temperatures ssts by 8 c 1 7 shift in 18o occurred immediately before oae 1a whereas a cooling mode likely prevailed during the peak corg burial in terms of its stratigraphic relationship as to the corg rich interval and to a pronounced negative 13c excursion as well as its timescale the observed sst rise resembles those associated with the paleocene eocene thermal maximum and more strikingly jurassic toarcian oae this observation is consistent with the hypothesis that these paleoenvironmental events were driven by a common causal mechanism which was likely initiated by the greenhouse effect via massive release of ch4 or co2 from the isotopically light carbon reservoir and terminated by a negative productivity feedback

nannofossils and superplumes the early aptian nannoconid crisis a group of calcareous nannoplankton named nannoconids experienced a crisis in the early aptian and recovered only later in the late aptian after a period of virtual absence although no extinctions occurred the widespread nature of the nannoconid crisis suggests a global causal factor this crisis is recorded within the chiastozygus litterarius nannofossil and globigerinelloides blowi planktonic foraminiferal zones postdates magnetic chronozone m0 by approximately 300 kyr and precedes the oceanic anoxic subevent 1a and associated 13c anomaly by some 40 100 kyr selective dissolution and anoxia cannot explain the crisis because nannoconids are dissolution resistant forms and their crisis clearly precedes the deposition of anoxic sediments at least 1 m y prior to the nannoconid crisis the onset of a nannoplankton speciation event may be the response of nannofloras to a major rise in relative sea level the nannoconid crisis seems to be synchronous with the early aptian volcanic eruptions in the pacific ocean hence calcareous nannoplankton were severely affected by the superplume volcanic episode the coccolithophorid bloom nannoconid crisis was possibly induced by the excessive co2 levels in the atmosphere and or caused by changes in nutrient content of oceanic surface waters fertility was enhanced by rapid turnover of nutrients due to the abnormal volcanic activity and accelerated transfer of nutrients from the continents into the oceans under warm and humid conditions of the mid cretaceous greenhouse climate the nannoconid crisis may represent a competition between phytoplankton groups for nutrients or more likely competition between different calcareous nannoplankton the biologic affinity and mode of life of nannoconus are unknown because there is no modern analog of this genus however comparison of lower cretaceous nannofossil assemblages with modern nannoplankton cummunities suggests that nannoconids like extant florisphaera profunda possibly inhabited the lower photic zone concentrations of nutrients in the upper euphotic zone may have triggered blooms of coccolithophorids and nannoconid depletion this model implies that the nannoconid crisis is the result of an abrupt major change in the structure of surface waters caused directly or indirectly by the superplume the adjustments of the biosphere to the new paleoceanographic and climatic conditions required some 40 100 kyr before changing into abnormally high primary productivity and deposition of organic carbon rich sediments with dinoflagellates outcompeting nannoplankton

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

the effect of hydrate content on seismic attenuation a case study for mallik 2l 38 well data mackenzie delta canada 1 observations of velocities in sediments containing gas hydrates show that the strength of sediments increases with hydrate saturation hence it is expected that the attenuation of these sediments will decrease with increasing hydrate saturation however sonic log measurements in the mallik 2l 38 well and cross hole tomography measurements in the mallik field have shown that attenuation increases with hydrate saturation we studied a range of mechanisms by which increasing hydrate saturation could cause increased attenuation we found that a difference in permeability between the host sediment and the newly formed hydrate can produce the observed effect we modelled attenuation in terms of biot and squirt flow mechanisms in composite media we have used our model to predict observed attenuations in the mallik 2l 38 well mackenzie delta canada

a global study of volcanic infrasound characteristics and the potential for long range monitoring abstract volcanic infrasound from explosive eruptions is detectable at distances up to 1000 s of km and is often recorded on the international monitoring system ims infrasound network though infrasound produced by individual volcanoes has previously been studied more general relationships between infrasound characteristics and eruption parameters remain unclear therefore using a dataset comprising 110 events at 39 globally distributed volcanoes we assess the ability of the ims to monitor remote volcanoes and investigate whether volcanic infrasound exhibits consistent trends across a range of eruption styles and intensities acoustic pressure amplitude and frequency content of the volcanic infrasound were measured and acoustic energy was also calculated these were compared along with the maximum distance of detection for each event to the maximum plume height reported for the event which was used as a proxy for event intensity of the events investigated 62 were detected by at least one infrasound station the maximum distance at which an event was detected generally increased with the plume height and infrasound produced during the eruption of manam png in january 2005 which produced a plume which rose over 20 km above the summit was detected at a distance of 10 671 km total acoustic energy and acoustic pressure amplitude corrected for geometrical spreading increased with plume height whilst the lowest frequency present in the volcanic infrasound decreased additionally relationships seen between infrasound characteristics and eruption plume height indicate that analyses of this data alone could constrain vital estimates of plume heights for otherwise un observed eruptions taken together these findings indicate that if made available for this purpose in the future the ims infrasound network could complement existing monitoring techniques by detecting and characterising eruptions at remote volcanoes which often have no local monitoring networks