theory of acoustic propagation in a multi phase stratified liquid flowing within an elastic walled conduit of varying cross sectional area abstract a theoretical solution is derived for the sound field in an arbitrarily layered viscous fluid moving with the non negligible mach number within a duct with elastic walls and varying cross sectional area the solution is applied to the interpretation of infrasonic and seismic signals preceding and accompanying volcanic eruptions and can be used to study the acoustic response of various types of volcanic fluids including magma gas mixtures ash gas mixtures and bubble rich liquids the acoustic field in a magma conduit can be propagated into the atmosphere through an open vent and coupled into the ground through the displacement of the magma conduit walls the theoretical solutions predict that fluids moving with the non negligible mach number will exhibit significant attenuation in the upstream direction thereby reducing the quality factor of the conduit resonance thus acoustic energy generated during an eruption may be preferentially radiated downstream exacerbating the acoustic decoupling between the upper and lower parts of a stratified magma column a source model for a repeated cavitation process is introduced as a possible excitation mechanism for tremor signals

fractal properties of tremor and gas piston events observed at kilauea volcano hawaii we study the fractal properties of shallow volcanic tremor and gas piston events associated with magma degassing at kilauea volcano hawaii using data from two dense short baseline arrays of seismographs deployed near the active crater of puu oo on the east rift of the volcano we found an upper bound on the fractal dimension of a strange attractor common to phase portraits of both tremor and gas piston activities in the range of 3 1 4 5 with a mean of 3 75 over a scale length of the wave field of the order of 100 m the dimension of the attractor fluctuates over the course of tremor and gas piston episodes within a range comparable to the spatial variations of fractal dimensions found in the wave field the existence of a categorically stable attractor characterizing both types of activities strongly suggests that the excitation mechanism of tremor is similar to that of gas piston events which in turn are correlated with visual observations at the volcanic vent the low value derived for the dimension of the attractor in phase space points to significant self organization in the process of generation of tremor and offers general constraints on the dimensionality of attractors derived from models of acoustic emission associated with magma flow vesiculation and degassing

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

scaling behavior and source mechanism of tremor recorded at erebus volcano ross island antarctica abstract erebus is an intraplate stratovolcano of phonolitic composition located at the southern end of terror rift within the west antarctica rift system the volcanic edifice of erebus exhibits a summit plateau that hosts the main crater and a smaller inner crater that contains a persistent lava lake volcano seismic signals are recorded at erebus by a permanent network of short period and broadband seismometers installed around the volcano edifice we investigate the duration amplitude scaling of tremor recorded by the closest 0 6 2 km broadband stations to the inner crater during may 2002 april 2004 in order to elucidate the physical processes taking place at its source after screening the data for signals related to non volcanic sources such as iceberg calving we obtained 72 tremor events spectral analysis reveals that these events were either harmonic exhibiting several overtones or broadband but there were also mixed events that contained both of these two states all tremor episodes considered in this study follow an exponential duration amplitude distribution that implies a scale bound source process this precludes the possibility that any of these signals is related to iceberg calving near ross island or that rock fracturing processes play any role in tremor generation the large viscosity of phonolitic magma 105 3 pa s suggests that source mechanisms which require high flow speeds in order to excite tremor are unlikely to operate at erebus on the other hand oscillations of co2 bubble clouds formed at localized asperities within the magma chamber represent a scale bound source that is also consistent with the observed oxidation state of ascending gas and with the deep 5 7 km location of the tremor source these results are important for understanding tremor processes at volcanoes which similar to erebus exhibit vigorous convection in their shallow plumbing system

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

4d velocity of strombolian eruptions and man made explosions derived from multiple doppler radar instruments abstract we used a novel system of three continuous wave doppler radars to successfully record the directivity of i strombolian explosions from the active lava lake of erebus volcano antarctica ii eruptions at stromboli volcano italy and iii a man made explosion in a quarry erebus volcano contains a convecting phonolite lava lake presumably connected to a magma chamber at depth it is one of the few open vent volcanoes that allow a direct observation of source processes during explosions its lava lake is the source of frequent violent strombolian explosions caused by large gas bubbles bursting at the lake surface the exact mechanism of these bubble bursts is unclear as is the mechanism of the creation of the infrasound signal accompanying the explosions we use the doppler radar data to calculate the directivity of strombolian eruptions at erebus this allows us to derive information about the expected type of infrasound source pattern i e the role of a dipole in addition to the monopole signature and the physical structure of the volcano we recorded 10 large explosions simultaneously with three radars enabling us to calculate time series of 3d directivity vectors i e effectively 4d which describe the direction of preferred expansion of the gas bubble during an explosion such directivity information allows a comparison to dipole infrasound radiation patterns recorded during similar explosions only a few weeks later video observations of explosions support our interpretation of the measurements we conclude that at erebus the directivity of explosions is mainly controlled by random processes since the geometry of the uppermost conduit is assumed to have a large effect on the directivity of explosions the results suggest a largely symmetrical uppermost conduit with a vertical axis of symmetry for infrasound recordings a significant dipole signature can be expected in addition to the predominant monopole signature

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

infrasonic harmonic tremor and degassing bursts from halema uma u crater kilauea volcano hawaii 1 the formation evolution collapse and subsequent resurrection of a vent within halema uma u crater kilauea volcano produced energetic and varied degassing signals recorded by a nearby infrasound array between 2008 and early 2009 after 25 years of quiescence a vent clearing explosive burst on 19 march 2008 produced a clear complex acoustic signal near continuous harmonic infrasonic tremor followed this burst until 4 december 2008 when a period of decreased degassing occurred the tremor spectra suggest volume oscillation and reverberation of a shallow gas filled cavity beneath the vent the dominant tremor peak can be sustained through helmholtz oscillations of the cavity while the secondary tremor peak and overtones are interpreted assuming acoustic resonance the dominant tremor frequency matches the oscillation frequency of the gas emanating from the vent observed by video tremor spectra and power are also correlated with cavity geometry and dynamics with the cavity depth estimated at 219 m and volume 3 106 m3 in november 2008 over 21 varied degassing bursts were observed with extended burst durations and frequency content consistent with a transient release of gas exciting the cavity into resonance correlation of infrasound with seismicity suggests an open system connecting the atmosphere to the seismic excitation process at depth numerous degassing bursts produced very long period 0 03 0 1 hz infrasound the first recorded at kilauea indicative of long duration atmospheric accelerations kilauea infrasound appears controlled by the exsolution of gas from the magma and the interaction of this gas with the conduits and cavities confining it

comparison of rate constants for some molecular tracers generated during artificial maturation of kerogens influence of kerogen type abstract the purpose of this work is to carry out artificial maturation of various kerogens under isothermal conditions in open and closed systems and to derive kinetic parameters for specific molecular tracers such as n c 12 and n c 24 alkanes results show that individual normal alkane generation from type i and type ii kerogens follows first order kinetics in both open and closed pyrolysis systems however the normal alkanes generated from type iii samples do not follow a first order mechanism for type i and type ii kerogens slightly different rate constants are obtained for n c 12 and n c 24 generation whereas for the two type iii kerogens n c 24 is produced much faster than n c 12 combining the rate constants derived from open and closed system pyrolysis arrhenius plots were obtained for the four samples under study from which accurate sets of kinetic parameters were calculated

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

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

propagation of acoustic waves in a visco elastic two phase system influences of the liquid viscosity and the internal diffusion abstract the main purpose of the present paper is to present the mathematical expression for the frequency dependent effective acoustic properties of a liquid bubble mixture effects of the bubble resonance the heat and mass transfer between the liquid and bubbles and the viscoelasticity of the liquid are included in the expression several characteristic frequencies associated with these internal processes are represented by simple functions of the material and condition parameters using these expressions the acoustic properties of bubbly magmas are calculated and analyzed it is shown that the dispersion and attenuation of the pressure wave are particularly considerable in the frequency range lower than the characteristic frequency of the mass transfer and in the range near the characteristic frequency of the viscous response of the bubble radius in the frequency range bounded by these two frequencies the bubbly magma can be regarded as an elastic medium with the slow sound speed the significance of such acoustic properties on resonance of a body of bubbly magma is demonstrated in a simple one dimensional system

an automatic seismic event processing for detection and location the p m c c method we present a new method for automatic detection and location of seismic events recorded on a network it is based on a progressive study of the interstation correlation functions which leads to a consistent set of time delays when a seismic phase is present three different examples are processed on networks of different sizes

infrasonic tremor wavefield of the pu u ō ō crater complex and lava tube system hawaii in april 2007 1 long lived effusive volcanism at the pu u crater complex kilauea volcano hawaii produces persistent infrasonic tremor that has been recorded almost continuously for months to years previous studies showed that this infrasonic tremor wavefield can be recorded at a range of 10 km however the low signal power of this tremor relative to ambient noise levels results in significant propagation effects on signal detectability at this range in april 2007 we supplemented a broadband infrasound array at 12 5 km from pu u mene with a similar array at 2 4 km from the source kipu the additional closer range data enable further evaluation of tropospheric propagation effects and provide higher signal to noise ratios for studying volcanic source processes the infrasonic tremor source appears to consist of at least two separate physical processes we suggest that bubble cloud oscillation in a roiling magma conduit beneath the crater complex may produce a broadband component of the tremor low frequency sound sourced in a shallow magma conduit may radiate infrasound efficiently into the atmosphere due to the anomalous transparency of the magma air interface we further propose that more sharply peaked tones with complex temporal evolution may result from oscillatory interactions of a low velocity gas jet with solid vent boundaries in a process analogous to the hole tone or whistler nozzle the infrasonic tremor arrives with a median azimuth of 67 at kipu additional infrasonic signals and audible sounds originating from the extended lava tube system to the south of the crater complex median azimuth 77 coincided with turbulent degassing activity at a new lava tube skylight our observations indicate that acoustic studies may aid in understanding persistent continuous degassing and unsteady flow dynamics at kilauea volcano

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

characteristics of seismic waves composing hawaiian volcanic tremor and gas piston events observed by a near source array a correlation method specifically designed for describing the characteristics of a complex wave field is applied to volcanic tremor and gas piston events recorded by a semicircular array of geos instruments set at the foot of the puu oo crater on the east rift of kilauea volcano hawaii the spatial patterns of correlation coefficients obtained as functions of frequency for the three components of motion over the entire array are similar for gas piston events and tremor and clearly depict dispersive waves propagating across the array from the direction of puu oo the wave fields are composed of comparable amounts of rayleigh and love waves propagating with similar and extremely slow phase velocities ranging from 700 m s at 2 hz to 300 m s at 8 hz the highly cracked solidified lava flow on which the array was deployed and subjacent structure of alternating lava and ash layers formed during repeated eruptions of puu oo since 1983 appear to be responsible for the low velocities observed the results from puu oo stand in sharp contrast to those obtained in an experiment conducted in 1976 on the partially solidified lava lake of kilauea iki rayleigh waves were not observed in kilauea iki but well developed trains of love waves were seen to propagate there with velocities twice as high as those observed near puu oo these differences in the propagation characteristics of surface waves at the two sites may be attributed to the presence of a soft horizontal layer of molten rock in kilauea iki which may have lowered the phase velocity of rayleigh waves more drastically than that of love waves resulting in severe scattering of the rayleigh wave mode on the other hand the thin superficial pahoehoe flow under our array at puu oo may have favored the development of vertical columnar joints more extensively at this location than at kilauea iki which may have reduced the shear moduli controlling the love wave mode the average phase velocities in the frequency band from 2 to 5 hz found at puu oo are roughly similar to those determined for tremor at klyuchevskoy volcano kamchatka but the frequency dependence appears much stronger at puu oo

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

on the volcanic waveguide an analytical solution for the sound field in a resonant magma conduit with depth dependent magma properties provides a versatile interpretative tool for the analysis of seismoacoustic signals generated by fluid processes in active volcanoes expressions are given for the acoustic field in the atmosphere and the seismic field in the ground radiated through the magma conduit vent and walls respectively a new source model allows the resonance in the conduit to be excited by the vertical fluid velocity at the bottom of the conduit this source model represents acoustic excitation induced by low frequency fluid oscillations or large volume fluctuations originating at depth the magma conduit is modeled as a three section duct with each section having a different density sound speed viscosity and dimension the modal structure of the coupled resonant system is retained as the sound field in the conduit propagates into the surrounding bedrock and the overlying atmosphere the source time function permits estimates of the total mass injected or removed from the magmatic system and the source spectrum acts as a band pass filter on the resonant modes of the conduit theoretical or empirical source functions can be used to drive the seismoacoustic wave field and the amplitude of the source velocity may be constrained by the ballistics of pyroclasts and the height of ash plumes the acoustic properties of the melt may be predicted from the temperature composition and flow conditions of the magma as a function of depth comparisons of synthetic waveforms and spectra with those of seismic and acoustic signals recorded on active volcanoes permit estimates of the conduit geometry density sound speed and attenuation properties of the melt and characterize the temporal and spectral features of the source function the ability to extract this information accurately and efficiently from seismic and acoustic data streams may permit near real time modeling of fluid driven processes in active volcanoes

infrasonic jet noise from volcanic eruptions 1 the lowermost section of a vulcanian or plinian volcanic eruption column may be thought of as a momentum driven turbulent free shear jet flow we propose that large amplitude and long duration infrasonic 20 hz signals recorded at ranges of tens of kilometers during powerful eruptions at mount st helens usa and tungurahua ecuador represent a low frequency form of jet noise a preliminary test of this hypothesis is made by comparing the observed infrasonic spectra to the empirically derived similarity spectra for pure air jets although the spectral shapes are in approximate agreement the observed volcanic signals have additional complexities not present in the pure air laboratory data these features may result from multiphase flow containing solid particles and liquid droplets very high temperatures and perhaps complex crater morphology however the overall similarity between the volcanic signals and jet noise indicates that broadband infrasound measurements at volcanoes may provide a quantitative link to eruption jet dynamics and would aid substantially in the remote assessment of volcanic hazard

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

earthquakes related to active salt doming near kulyab tadjikistan ussr in the region near kulyab tadjikistan hundreds of shallow earthquakes with magnitudes greater than 2 have been reported in soviet yearly catalogs since 1964 this area appears as a well defined cluster of activity distant from the line of epicenters that defines the gissar kokshal seismic zone to the north of the pamir ranges the geology of this region is dominated by the presence of numerous salt domes surrounded by neogene and quaternary continental deposits the spatial relationship between these earthquakes and the salt domes suggests that the two phenomena may be related moderate earthquakes m 5 occurred in 1972 and 1973 and intensities of surface shaking greater than mm 6 were reported from earthquakes in 1937 1952 1969 1972 1973 and 1978 the earthquake on 2 april 1973 and its aftershocks were located in a region where no salt domes have been mapped at the surface however a buried salt diapir has been mapped at depth by geophysical means these earthquakes may result from active salt diapirism at depth the mechanism for producing this seismicity could be either the active fracturing of the cap rock by the rising diapir or the concentration of tectonic stresses in the thinned section above and adjacent to the diapir the salt related earthquakes may produce lower frequency radiation than other events of the same size

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

array measurements and modeling of sources of shallow volcanic tremor at kilauea volcano hawaii we show that resonances in near surface layers path effects or a combination of near surface resonances and source resonances source effects could be responsible for the sharp spectral peaks found in the records of gas piston activity and volcanic tremor recorded near puu oo crater on kilauea volcano hawaii two types of sources are found to be compatible with observations and can not be distinguished using our data in one model impulsive explosion point sources are embedded in the puu oo structure in the other model impulsive point sources of pressure excite the resonances of a fluid filled crack embedded in that structure both models require shallow sources z 100 m and display a strong dependence of the radiated spectrum on source depth over a depth range comparable to the overall thickness of the surficial layers based on these results it may be possible to track changes in source depth through temporal changes in observed spectra a potentially useful tool for monitoring volcanic activity at this site we estimate the depth and spatial extent of volcanic tremor and gas piston activity using two dense arrays with respective apertures of 800 and 120 m located near puu oo measurements of slowness ray parameter and azimuth as a function of time clearly indicate that the sources of volcanic tremor and gas piston activity are located beneath or in close proximity to the puu oo crater at depths shallower than approximately 1 km based on slowness and particle motion analyses we find that the records of volcanic tremor and gas piston events at puu oo consist of a complex combination of body and surface waves