locating non volcanic tremor along the san andreas fault using a multiple array source imaging technique summary non volcanic tremor nvt has been observed at several subduction zones and at the san andreas fault saf tremor locations are commonly derived by cross correlating envelope transformed seismic traces in combination with source scanning techniques recently they have also been located by using relative relocations with master events that is low frequency earthquakes that are part of the tremor locations are derived by conventional traveltime based methods here we present a method to locate the sources of nvt using an imaging approach for multiple array data the performance of the method is checked with synthetic tests and the relocation of earthquakes we also applied the method to tremor occurring near cholame california a set of small aperture arrays i e an array consisting of arrays installed around cholame provided the data set for this study we observed several tremor episodes and located tremor sources in the vicinity of saf during individual tremor episodes we observed a systematic change of source location indicating rapid migration of the tremor source along saf

inherent anisotropic stiffness of weathered geomaterial and its influence on ground deformations around deep excavations the shear modulus g0 at very small strain 0 001 or less is an important parameter for predicting ground movements of many geotechnical structures recent advances in laboratory testing enable th

drained and undrained anisotropic elastic stiffness parameters equations that map drained to undrained elastic stiffness parameters in a cross anisotropic material are presented graphs of various anisotropic stiffness ratios are used to illustrate the important trends a new 2 d graph showing the elastic bound enables measured elastic parameters to be plotted which all lie well within it the 2 d graph enables uncoupled and incompressible materials to be shown plus materials with particular initial effective stress path slopes in an undrained triaxial test bounds more restrictive than the elastic one are also discussed and the likely ranges of various anisotropic stiffness ratios are presented in general undrained anisotropy is much less than drained that is closer to isotropic in undrained plane strain conditions vertical and horizontal moduli are found to be the same in drained plane strain conditions the ratios of the moduli are almost the same as the young s moduli

seismic insight into explosive paroxysms at stromboli volcano italy abstract at stromboli volcano italy continuous seismic monitoring and periodic visual observations of volcanic activity for surveillance purposes began in the mid 1980s since 1985 two eruptions have occurred one lasting from december 1985 until april 1986 and one in may 1993 there have also been two small overflows in 1990 and 1994 since these episodes of lava effusion the persistent strombolian activity of the volcano has had several fluctuations during the past 15 years some episodes climaxed in powerful explosions according to seismic records these paroxysms consisted of a variable number of explosion quakes in rapid succession i e from tens of seconds to a few minutes associated with a notable increment in the amplitude of volcanic tremor throughout these episodes which are called explosive sequences lapilli fragments of old rock and bombs of varying dimensions were ejected affecting an area greater than the crater terrace where the active craters are located in this article we describe the explosive sequences recorded at stromboli between 1985 and 1999 we provide a characterization in terms of reduced displacement and duration for nine episodes occurring in 1998 and 1999 their reduced displacements range from 15 to 124 cm 2 their durations are between 6 and 18 min we find no change in the frequency content of the seismic signal several minutes before and during the sequences considering medium to long term behavior the spectral amplitude of the seismic signal decreases or has low values over several months preceding the occurrence of the paroxysms this feature is common to 20 of the 22 explosive sequences and is indicative of internal conditions that periodically characterize the feeder we surmise that the paroxysms are the result of the partial obstruction of the volcanic conduit when the magma column is low or dropping the onset of the explosive sequence causing the sudden removal of the material which forms the obstruction would trigger a sudden depressurization of the conduit and the rapid rise of magma from depth

s rich apatite hosted glass inclusions in xenoliths from la palma constraints on the volatile partitioning in evolved alkaline magmas the composition of s rich apatite of volatile rich glass inclusions in apatite and of interstitial glasses in alkaline xenoliths from the 1949 basanite eruption in la palma has been investigated to constrain the partitioning of volatiles between apatite and alkali rich melts the xenoliths are interpreted as cumulates from alkaline la palma magmas apatite contains up to 0 89 wt so3 3560 ppm s 0 31 wt cl and 0 66 wt ce2o3 sulfur is incorporated in apatite via several independent exchange reactions involving p5 ca2 vs s6 si4 na and ce3 the concentration of halogens in phonolitic to trachytic glasses ranges from 0 15 to 0 44 wt for cl and from 0 2 wt so3 dsapatite glass is only slightly dependent on the melt composition and can be expressed as so3 apatite wt 0 157 ln so3 glass wt 0 9834 the phonolitic compositions of glass inclusions in amphibole and hauyne are very similar to evolved melts erupted on la palma the lower sulfur content and the higher cl content in the phonolitic melt compared to basaltic magmas erupted in la palma suggest that during magma evolution the crystallization of hauyne and pyrrhotite probably buffered the sulfur content of the melt whereas the evolution of cl concentration reflects an incompatible behavior trachytic compositions similar to those of the water rich glass inclusions analyzed in apatite and clinopyroxene are not found as erupted products these compositions are interpreted to be formed by the reaction between water rich phonolitic melt and peridotite wall rock

dynamics of mild strombolian activity on mt etna abstract here we report the first measurements of gas masses released during a rare period of strombolian activity at the bocca nuova crater mt etna sicily uv camera data acquired for 195 events over an 27 minute period 27th july 2012 indicate erupted so2 masses ranging from 0 1 to 14 kg per event with corresponding total gas masses of 0 1 to 74 kg thus the activity was characterised by more frequent and smaller events than typically associated with strombolian activity on volcanoes such as stromboli events releasing larger measured gas masses were followed by relatively long repose periods before the following burst a feature not previously reported on from gas measurement data if we assume that gas transport within the magma can be represented by a train of rising gas pockets or slugs then the high frequency of events indicates that these slugs must have been in close proximity in this case the longer repose durations associated with the larger slugs would be consistent with interactions between adjacent slugs leading to coalescence a process expedited close to the surface by rapid slug expansion we apply basic modelling considerations to the measured gas masses in order to investigate potential slug characteristics governing the observed activity we also cross correlated the acquired gas fluxes with contemporaneously obtained seismic data but found no relationship between the series in line with the mild form of manifest explosivity

infrasonic waves and volcanic tremor at stromboli the origin of the volcanic tremor is still under debate many theories have been proposed in the last years but none has yet been completely accepted in 1993 highly sensitive pressure sensors 2 175 pa volt used to monitor the explosive activity at stromboli have revealed unexpected correlation between small spike shaped pressure signals 1 2 pa and volcanic tremor these pressure pulses repeat regularly in time with a recurrent period of ca 1 s video camera images allowed us to correlate the pressure pulses with small gas bursts occurring at one of the active vents the striking correlation 0 971 between infrasonic and seismic energy fluctuations is particularly meaningful in the frequency domain infrasonic and seismic signal share the same spectral content 3 hz for every station within a range of 700 m around the craters correlations in time and frequency domain remained unaltered during the 1994 field experiments moreover during 1994 the increased degassing activity has been followed by an increase in pressure release 7 8 pa and by a shift towards higher frequencies 8 hz both in the infrasonic and seismic records infrasonic waves and volcanic tremor show similar energy fluctuations and frequency contents appearing therefore to be produced by the same dynamical process on this basis we claim that volcanic tremor at stromboli originates by continuous outbursting of small gas bubbles in the upper part of the magmatic column

source mechanisms of explosions at stromboli volcano italy determined from moment tensor inversions of very long period data 1 seismic data recorded in the 2 30 s band at stromboli volcano italy are analyzed to quantify the source mechanisms of strombolian explosions during september 1997 to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous elastic medium that takes topography into account two source centroids are identified each representative of the distinct event types associated with explosive eruptions from two different vents the observed waveforms are well reproduced by our inversion and the two source centroids that best fit the data are offset 220 and 260 m beneath and 160 m northwest of the active vents the source mechanisms include both moment tensor and single force components the principal axes of the moment tensor have amplitude ratios 1 1 2 which can be interpreted as representative of a crack if one assumes the rock matrix at the source to have a poisson ratio n 1 3 a value appropriate for hot rock both imaged cracks dip 60 to the northwest and strike northeast southwest along a direction parallel to the elongation of the volcanic edifice and a prominent zone of structural weakness as expressed by lineaments dikes and brittle structures for our data set the volume changes estimated from the moments are 200 m 3 for the largest explosion from each vent together with the volumetric source is a dominantly vertical force with a magnitude of 10 8 n consistent with the inferred movement of the magma column perched above the source centroid in response to the piston like rise of a slug of gas in the conduit index terms 7215 seismology earthquake parameters 7280 seismology volcano seismology 8419 8414 volcanology eruption mechanisms keywords very long period seismicity moment tensor inversions eruption mehanics

identifying elements of the plumbing system beneath kilauea volcano hawaii from the source locations of very long period signals location of vlp signals at kilauea

hidden dykes detected on ultra long period seismic signals at piton de la fournaise volcano broadband seismic data enable us to test whether ultra long period ulp signals can be used to investigate magma chamber pressure state and to monitor volcanic eruptions by systematically investigating seismic signals at geoscope station rer we find ulp signals associated with volcanic events during the last 2 decades we tentatively propose to interpret these signals as events highlighting the activity of the upper magma feeding system of the piton de la fournaise volcano and as being related to the deep magma chamber some of these unusual signals were previously detected and usually interpreted in term of tilt battaglia j aki k montagner j j p tilt signals derived from a geoscope vbb station on the piton de la fournaise volcano geophys res lett 27 5 2000 605 608 they are detected using sts1 seismometers sensitive in the bandwidth 10 3 to 10 2 hz this alternative model enables to quantify each event in terms of a pressure drop in the upper magma reservoir of the volcano two kinds of seismic waveforms can be associated with two types of fracturing events the first one is related to the fast rise of a magma batch coming from the deep magma chamber and the second is the result of a slow rise in pressure inside a shallow reservoir in both cases we are able to detect these events on very long period seismic data the interpretation of these signals supports the idea of a single magma source at the sea level thus we propose to classify all the eruptions occurring during the last two decades into two groups corresponding to the two primary pressure states of the magma chamber 2007 elsevier b v all rights reserved

subband decomposition and reconstruction of continuous volcanic tremor abstract a new method of analyzing volcanic tremor is presented which uses properties of undecimated wavelet packet transforms to filter decompose and recover signals from continuous multichannel data the method preserves many standard properties that are used to characterize tremor such as wavefield polarization and seismic energy in this way we can better understand the potentially many seismic sources that combine to form continuous volcanic tremor and we can specifically address the problem of what causes changing tremor spectral content tests on synthetic data suggest that sdr can recover multiple quasi continuous signals that differ from one another by an order of magnitude even in noisy environments tests on real data recorded at erta ale in 2002 suggest that sdr can recover signals with geophysically meaningful interpretations and corroborates existing seismic and multiparametric work by harris et al 2005 jones et al 2006 and harris 2008 we suggest that this algorithm could effectively detect subtle changes in the time frequency content of volcanic tremor and recover signals from real seismic sources that appear buried in background noise and or partly masked by one another such an algorithm could allow volcanologists much greater insight into the dynamics of volcanic systems and could detect subtle signals that might help address the possibility of unrest

basaltic thermals and subplinian plumes constraints from acoustic measurements at shishaldin volcano alaska the 1999 basaltic eruption of shishaldin vol cano alaska usa included both strombolian and sub plinian activity as well as a pre subplinian phase inter preted as the local coalescence within a long foam in the conduit although few visual observations were made of the eruption a great deal of information regarding gas ve locity gas flux at the vent and plume height may be inferred by using acoustic recordings of the eruption by relating acoustic power to gas velocity a time series of gas velocity is calculated for the subplinian and pre subplinian phases these time series show trends in gas velocity that are inter preted as plumes or for those signals lasting only a short time thermals the subplinian phase is shown to be com posed of a thermal followed by five plumes with a total expelled gas volume of 1 5 10 7 m 3 the initiation of the subplinian activity is probably related to the arrival of a large overpressurised bubble close to the top of the magma column a gradual increase in low frequency 0 01 0 5 hz signal prior to this trigger bubble may be due to the rise of the bubble in the conduit this delay corresponds to a reservoir located at 3 9 km below the surface in good agreement with studies on other volcanoes the presence of two thermal phases is also identified in the middle of the pre subplinian phase with a total gas release of 4 3 10 6 m 3 and 3 6 10 6 m 3 gas veloc ity at the vent is found to be 82 m s 1 and 90 m s 1 for the subplinian plumes and the pre subplinian thermals respectively the agreement is very good between estimates of the gas flux from modelling the plume height and those obtained from acoustic measurements leading to a new method by which eruption physical parameters may be quantified fur thermore direct measurements of gas velocity can be used for better estimates of the so2 flux released during the eruption

static and dynamic pressure sensitivity anisotropy of a calcareous shale optimizing the productivity of nonconventional low permeability shale reservoirs requires detailed knowledge of the mechanical properties of such materials these rocks elastic anisotropy is acknowledged but usually ignored due to difficulties in obtaining such information here we study in detail the dynamic and static elastic properties of a suite of calcareous mudstones from the nonconventional duvernay reservoir of alberta canada the complete set of transversely isotropic elastic constants is obtained from strategically oriented ultrasonic transducers to confining pressures of 90 mpa wave speed anisotropies of up to 35 are observed at even the highest confining pressures furthermore the stress sensitivity of the wave speeds and hence moduli is itself highly dependent on direction with speeds taken perpendicular to the bedding plane being highly nonlinearly dependent on pressure whereas those along the bedding plane show unexpectedly nearly no pressure dependence these observations are in qualitative agreement with the preferentially oriented porosity and minerals seen in scanning electron microscope images these results may be significant to the interpretation of sonic logs and azimuthal amplitude versus offset for principal stress directions for the concentration of stress within such formations and for estimation of static engineering moduli from sonic log wave speeds

automatic hypocenter determination of volcano induced seismic transients based on wavefield coherence an application to the 1998 eruption of mt merapi indonesia in order to monitor the seismic activity of mt merapi indonesia over a long period of time we installed a permanent array of both broadband and short period seismometers during the summer of 1997 considering the requirements of an automatic classification and localization system for seismic monitoring and surveillance at active volcanoes we split this network into three small aperture arrays distributed around the volcano we introduce here a newly developed method to determine the hypocenters in an automatic non linear manner using the coherence of seismic waves observed at the different arrays to test this method we analyze a swarm of vt b events recorded by the network the first step in this algorithm is based on a modified smoothed coherence transform in the second step we perform a semblance analysis applied to the 3d problem evaluating the quality of the estimated relative onset times after more than one year of dormancy mt merapi renewed its activity at the end of june 1998 this gave us the opportunity to analyze all stages of dome growth collapse and new intrusion of magma using the associated seismicity in a post processing sense this also allowed us to calibrate and test our newly developed automatic monitoring system using the more pronounced waveforms of vt b events by detecting and classifying different event types automatically we are able to localize a large number of vt b events which occurred just before the initial eruption we are also able to resolve some properties of the wavefield at mt merapi which are essential for further interpretations finally the results show that the source region of the vt b type seismicity just before the 1998 eruption is closely related to the region of subsequent high volcanic activity and therefore may represent a promising tool to forecast future eruptions

highlights from a seismic broadband array on stromboli volcano an array of nine three component broadband seismometers was deployed in two different configurations on stromboli volcano the analysis of the seismic wavefield related to volcanic explosions revealed some observations which offer a completely new insight into the internal dynamics of a volcano these new observations are restricted to the low frequency range below 1 hz and underline therefore the superiority of broadband recordings over conventional short period observations surprisingly simple wavelets indicate an initially contracting source mechanism gas jets that could not be seen in a short period seismic record at all generate a clear dilatational wavelet in a broadband recording suggesting the same contracting source mechanism the analysis of particle motion and seismic array techniques permits a location of the seismic source we find low frequency signals of 3s and 6s period that are not related to eruptions and do not share a common source with the eruption related events a video recording of visible volcanic activity at the crater region allows one to correlate precisely eruptive features with seismic signals

strength and post peak response of colorado shale at high pressure and temperature abstract the paper presents the thermo mechanical strength characterization of colorado shale which serves as a cap rock to underlying oil rich formations in cold lake area east central alberta canada samples from the westgate and joli fou formations were tested at high temperatures along triaxial compression stress paths with effective consolidation pressures and temperatures consistent with in situ stresses and operative conditions these lab tests were complemented with indirect tensile strength unconfined compression and triaxial constant effective mean stress tests at ambient temperature for a more comprehensive knowledge of the material strength particularly at low confining pressures the lab experimental results revealed brittle behavior of the tested shales with considerable strain softening both peak and post peak strength envelopes of the tested material were observed to be nonlinear with a pronounced curvature at low mean stresses and to decrease at high temperatures a simple thermo mechanical failure criterion is proposed to capture the aforementioned constitutive features this provides a modeling framework for determining the material strength close to the zone of tensile failure at different temperatures which is of utmost relevance to cap rock integrity assessments finally measured axial and radial deformations as well as x ray tomography images were used to verify that the observed constant rate of dilation in the post peak response of the samples was a reflection of the morphology of the virtually smooth shear plane and not representative of the material behavior

analysis of near source contributions to early p wave coda for underground explosions iii inversion for isotropic scatterers a systematic array processing analysis is applied to 916 teleseismic shortperiod p wave signals from 25 underground explosions at pahute mesa in order to establish whether coherent arrivals scattered from near source velocity heterogeneity can be identified the signal coherence is measured using semblance which can be statistically evaluated using the noncentral f distribution if the noise properties are suitable the effects of unsuitable correlated noise due to common path and receiver contributions are suppressed by applying station weighting functions obtained by stacking all observations at a given receiver similar corrections for individual events are applied to reduce biases due to variations in surface reflection times and spall effects the characteristics of the spatial and phase velocity resolution of the semblance analysis are established by a series of synthetic calculations including cases with random arrivals in the p wave coda the procedure is applied to the actual data under the assumption that any scattering structures present radiate isotropically although this constraint could be relaxed given independent knowledge of a particular scatterer s nature the pahute mesa data show some evidence for enhanced scattering contributions to the first 15 sec of the p wave signals from the western edge of the silent canyon caldera the overall confidence level in this interpretation is fairly low because simulations with random scattering in the p coda successfully match many features observed in the stacked data

an automatic phase picker for local and teleseismic events an automatic detection algorithm has been developed which is capable of time p phase arrivals of both local and teleseismic earthquakes but rejects noise bursts and transient events for each signal trace the envelope function is calculated and passed through a nonlinear amplifier the resulting signal is then subjected to a statistical analysis to yield arrival time first motion and a measure of reliability to be placed on the p arrival pick an incorporated dynamic threshold lets the algorithm become very sensitive thus even weak signals are timed precisely during an extended performance evaluation on a data set comprising 789 p phases of local events and 1857 p phases of teleseismic events picked by an analyst the automatic picker selected 66 per cent of the local phases and 90 per cent of the teleseismic phases the accuracy of the automatic picks was ideal i e could not be improved by the analyst for 60 per cent of the local events and 63 per cent of the teleseismic events

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

modeling the failure of magmatic foams with application to stromboli volcano italy abstract the failure of magmatic foams has been implicated as a fundamental process in eruptions occurring at open conduit basaltic volcanoes in order to investigate the failure of magmatic foams we applied the fiber bundle model using global load sharing the strengths of the fibers for the model were taken from bubble wall widths measured in four computer simulated foams of low porosity and from one very low porosity and two high porosity foams produced in the laboratory by heating hydrated basaltic glasses to 1200 c the relative strength of an individual fiber in the model was calculated from the square of a bubble wall s average width and absolute strengths of the foams were calculated based upon the correlation of the strength of one modeled foam with experimental data the fiber bundle model is shown to successfully reproduce measured tensile strengths of porous volcanic rocks studied by other researchers and confirms previous findings of the primary importance of foam porosity as well as the secondary importance of structural details that affect the number and size of bubble walls and permeability because of the success of the fiber bundle model in reproducing experimental foam failure its results are compared to infrasonic measurements associated with bubbles at stromboli italy and demonstrate that within uncertainty the power law exponents of the infrasonic energies and of the fiber bundle model energies are in agreement both show a crossover from an exponent of 5 2 associated with the bursting of small bubbles in the infrasonic measurements to an exponent of 3 2 for normal strombolian eruptions associated with infrasonic signals from meter scale bubbles the infrasonic signals for major explosions and a paroxysmal eruption at stromboli fall near the extrapolation of the power law defined by the low amplitude bubble bursting events and are interpreted to reflect the bursting of multitudes of small bubbles rather than a few large bubbles the measurement of small amplitude infrasonic events at stromboli appears useful in predicting the recurrence interval of paroxysmal eruptions at this volcano and may also provide a tool that uses common small amplitude infrasonic events to constrain the frequency of larger eruptions at other volcanoes

locating the sources of volcanic explosions and volcanic tremor at stromboli volcano italy using beam forming on diffraction hyperboloids abstract the wave field of volcano induced seismic signals at stromboli volcano italy was observed using a network of four broadband seismometers in addition to the standard spectral analysis of the recorded signals new spectral techniques such as wavelet transform and wavelet coherence analysis were also used in order to discriminate between signals related to volcanic tremor and volcanic explosions the common features of these two types of signals are characterised by the maximum of the power spectral density values located in the frequency band 2 0 hz and the main orientation of the principal axes of the particle motion ellipsoids in the frequency bands analysed the seismic signals of the volcanic explosions at stromboli cover the total frequency band whereas the spectral content of the volcanic tremor is restricted to narrow frequency bands ranging from 0 3 5 0 hz in order to localize both types of signals a modified inversion technique was used the result of this beam forming on diffraction hyperboloids of both types of signals reveal a surprisingly shallow source location ranging from 0 2 km 0 7 km above sea level suggesting that the sources of the volcanic explosions as well as of the volcanic tremor are restricted to the uppermost parts of the volcano this is in agreement with several nonseismological observations of this volcano the combination of spectral analysis of volcanic tremor and volcanic explosions with the analysis of ground displacement implies a mechanism which can be described by an ascending bubble of volcanic gas in a nearly closed volcanic system and finally the forced ejection of the material through a narrow channel at the top of the magma column

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

elastic properties of anisotropic synthetic calcite muscovite aggregates 1 a set of synthetic aggregates containing mixtures of calcite and muscovite were compacted with varying uniaxial loads ranging from 20 mpa up to 400 mpa their elastic properties have been measured using compressional and shear waves in confining hydrostatic pressures up to 475 mpa measured seismic velocities are shown to depend on 1 the ratio of calcite to muscovite 2 the uniaxial load used during sample manufacturing and 3 the porosity amount prior to velocity measurements the matrix framework may also affect the seismic velocities but this effect is not easily quantifiable in general measured seismic velocities decrease with increasing muscovite content and porosity elastic properties have been calculated based on texture measurements which were obtained by neutron diffraction the calculated velocities are based on the calcite and muscovite single crystal elastic tensors their orientation distribution functions and their modal fractions a large discrepancy is apparent between calculated and measured velocities where the former always overestimate the actual velocities shear waves display less of a difference between calculated and measured values than do compressional waves indicating that waves propagating by shearing are less affected by sample porosity and matrix framework a better agreement between measured and calculated seismic velocities arises when the initial porosity is taken into account using a differential effective medium model seismic anisotropy is evident from both measured and calculated velocities and is low for samples containing pure calcite but becomes prominent as the muscovite concentration increases the intensity of anisotropy further depends on the uniaxial load used during sample compaction and the initial porosity

shallow magma mingling driven strombolian eruptions at mt yasur volcano vanuatu 1 mt yasur volcano vanuatu has been increasingly recognized for its high frequency strombolian eruptions strombolian activity is often regarded as a product of the rapid ascent of gas slugs originating from a deep magma which mingle with a batch of shallow magma upon eruption heterogeneous crystal distribution as well as bimodal bubble size distributions in the eruptive products generally supports this view here the strombolian activity at mt yasur is analyzed a rheological investigation indicates that the basaltic andesitic eruptive products contain an apparently homogeneous glass phase and yet exhibit evidence of a distinct range of glass transition temperatures with multiple peaks occurring in individual samples such anomalous behavior is proposed to result from the mingling of magmas with contrasting oxidation states the unstable nature of the measured glass transition behavior leads us to the inference that mingling is located in the shallow parts of the eruptive conduits partly driven by rejuvenation of material slumped from the crater walls into an open conduit system the dynamics of this process may expose the periodicity of the eruptions themselves

the role of large bubbles detected from acoustic measurements on the dynamics of erta ale lava lake ethiopia the activity at the surface of the lava lake on erta ale volcano ethiopia shows that large bubbles are regularly breaking at a fixed position on the lava lake this is also where the small lava fountains are sometimes produced since this location is likely to be directly above the volcanic conduit feeding the lava lake we have done continuous measurements between march 22 and 26 2003 to understand the degassing of a volcano in permanent activity the bubble size has been first estimated from videos which once combined with the acoustic pressure can constrain the source of the sound the gas volume and overpressure stayed roughly constant between 36 700 m3 and 4 103 1 8 104 pa respectively simultaneous thermal measurements showed regular peaks which occurred when the crust was broken by a large bubble hence gave a direct indication on the typical return time between the bubbles 1 h these spherical cap bubbles had a high reynolds number 4600 20000 therefore a wake periodically unstable formed and detached from the bubble bottom the bubbly wake if the detachment occurs close to the surface can explain the duration of lava fountains measured on the videos the periodic arrival of bubbly wakes which mostly detach from the driving spherical cap within the lava lake could explain the absence of cooling at erta ale erebus antartica villarica chile and nyiragongo democratic republic of congo without invoking a convective downflow of magma in the conduit as previously done

studies of the seismic coda using an earthquake cluster as a deeply buried seismograph array loosely speaking the principle of green s function reciprocity means that the source and receiver positions in a seismic experiment can be exchanged without affecting the observed seismograms consequently the seismograms observed at a single observation location o and caused by a cluster of microearthquakes at locations ei are identical to the time series that would be measured by an array of stress meters emplaced at positions ei recording waves generated by a source acting at o by applying array analysis techniques like slant stacking and frequency wave number analysis to these seismograms we can determine the directions and velocities of the component waves as they travel in the earthquake focal region rather than at the surface we have developed a computationally rapid plane wave decomposition which we have applied to single station recordings of aftershocks of the 1984 morgan hill california earthquake the analysis is applied to data from three seismic stations having considerably different site geologies one is a relatively hard rock station situated on franciscan metamorphics one is within the calaveras fault zone and one is on semiconsolidated sand and gravels we define the early coda to be the part of the coda initiating immediately after the direct s wave and ending at twice the s wave lapse time the character of the s wave and early coda varies from being impulsive at the first station to highly reverberative at the last we examine waves in sequential time windows starting at the s wave and continuing through the early part of the coda at all seismic stations the early coda is dominated by a persistent signal that must be caused by multiple scattering probably within 2 km of each seismic station despite clear station to station differences in the character of the early coda coda q values measured in the late coda greater than twice the s lapse time agree well among stations implying that the mechanisms causing the varying behavior of the early coda do not control the coda decay rate at the stations we have considered coda q values measured on horizontal components of motion agree within a factor of 2 with those measured on vertical components we have not been able to determine the composition of the late coda because of a low signal to noise ratio our analysis technique however is quite appropriate for such a task

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

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

quantifying structural states of soft mudrocks in this paper a cm model is proposed to quantify structural states of soft mudrocks which are dependent on clay fractions and porosities physical properties of natural and reconstituted soft mudrock samples are used to derive two parameters in the cm model with the cm model a simplified homogenization approach is proposed to estimate geomechanical properties and fabric orientation distributions of soft mudrocks based on the mixture theory soft mudrocks are treated as a mixture of nonclay minerals and clay water composites nonclay minerals have a high stiffness and serve as a structural framework of mudrocks when they have a high volume fraction clay water composites occupy the void space among nonclay minerals and serve as an in fill matrix with the increase of volume fraction of clay water composites there is a transition in the structural state from the state of framework supported to the state of matrix supported the decreases in shear strength and pore size as well as increases in compressibility and anisotropy in fabric are quantitatively related to such transition the new homogenization approach based on the proposed cm model yields better performance evaluation than common effective medium modeling approaches because the interactions among nonclay minerals and clay water composites are considered with wireline logging data the cm model is applied to quantify the structural states of colorado shale formations at different depths in the cold lake area alberta canada key geomechancial parameters are estimated based on the proposed homogenization approach and the critical intervals with low strength shale formations are identified

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

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

diffraction enhancement in prestack seismic data seismic diffractions are often considered noise and are intentionally or implicitly suppressed during processing diffraction like events include true diffractions wave conversions or fracture waves which may contain valuable information about the subsurface and could be used for interpretation or imaging using synthetic and field data we examine workflows to separate diffractions from reflections that allow enhancement of diffraction like signals and suppression of reflections the workflows consist of combinations of standard processing modules most workflows apply normal moveout corrections to flatten reflection hyperbolas which eases their removal we observe that the most effective techniques are the decomposition of seismic gathers into eigensections and flows based on radon transformations

short term precursors of strombolian explosions at yasur volcano vanuatu the seismic wavefield associated with strombolian activity is usually dominated by explosion quakes eqs tremor and various signals generated by surface phenomena looking at the seismicity recorded at yasur volcano in 2008 we found that beside the transient events which occur simultaneously with surface explosions the seismicity includes events related to a deeper process these long period lp events form a family of similar events located below the southeastern part of the crater rim at a depth of about 700 1200 m below the summit they are commonly followed by eqs with a variable delay the examination of about 20 000 lp eq sequences at several stations near the summit shows that interevent delays follow distributions peaked around 11 12 s this short delay compared to the relatively great source depth of the lps favors a causal relationship linked to pressure transfer rather than gas slug propagation after nucleation at the lp source

identifying elements of the plumbing system beneath kilauea volcano hawaii from the source locations of very long period signals summary we analyzed 16 seismic events recorded by the hawaiian broad band seismic network at kilauea volcano during the period september 9 26 1999 two distinct types of event are identified based on their spectral content very long period vlp waveform amplitude decay pattern and particle motion we locate the vlp signals with a method based on analyses of semblance and particle motion different source regions are identified for the two event types one source region is located at depths of 1 km beneath the northeast edge of the halemaumau pit crater a second region is located at depths of 8 km below the northwest quadrant of kilauea caldera our study represents the first time that such deep sources have been identified in vlp data at kilauea this discovery opens the possibility of obtaining a detailed image of the location and geometry of the magma plumbing system beneath this volcano based on source locations and moment tensor inversions of vlp signals recorded by a permanent large aperture broad band network

bushveld symplectic and sieve textured chromite is a result of coupled dissolution reprecipitation a comparison with xenocrystic chromite reactions in arc basalt textures of bushveld chromite from thin seams and accessory disseminations in the platreef and the northernmost waterberg project area were compared with textures of xenocrystic chromite from mantle xenoliths found in neogene basalt in the kurile island arc the sieve textured to symplectic rims around the resorbed chromite in the kurile samples resulted from the reaction between chromite and chromite undersaturated basaltic melt with the inclusions in chromite being entrapped during episodes of chromite primary growth chemical dissolution and reprecipitation or secondary growth the relics of the lattice oriented etch tunnels suggest that the dissolution preferentially developed along the crystallographic planes and defects the bushveld chromites exhibiting similar textures are interpreted as reaction textured chromites by analogy with the kurile samples the bushveld sieve textured fish hook to symplectic and amoeboidal to atoll like chromites are believed to have been formed due to coupled dissolution reprecipitation of the earlier cumulus or xenocrystic chromite during interaction with chromite undersaturated evolved melt the electron backscattered diffraction data confirm the same single crystal crystallographic orientation of all domains of the reaction textured chromites as well as their clustered semi dissolved relics therefore bushveld inclusion rich chromite might have captured different populations of melt inclusions during its discontinuous out of equilibrium growth with fast episodic resorption and regeneration the occurrence of reaction textured chromites indicates a zone of interaction between dynamic magmatic influxes where chemical equilibrium was not achieved whereas a complete re equilibration between chromite and the stagnant and sequestered interstitial liquid was attained during the formation of the massive chromitites

acoustic sounder measurements of the vertical velocity of volcanic jets at stromboli volcano we have used a sodar acoustic doppler sounder to characterize the behavior of volcanoes and in particular to measure the vertical velocities of volcanic jets we have analyzed more than 100 explosions on stromboli volcano eolian islands first results show vertical speeds close to the vent ranging from 20 m s to 80 m s the uncertainty in the measurements is close to 10 due mainly to the inaccurate knowledge of the sound speed in volcanic jets this is small compared to other volcanological methods this method is well suited for monitoring temporal variations during an eruption and should be particularly interesting for the study of the eruptive dynamics of lava fountains the doppler spectrum in explosions appears to be related to different types of echoes and contains information on particle sizes in the jet

experimental peridotite melt reaction at one atmosphere a textural and chemical study sieve textured clinopyroxene and spinel are common in mantle xenoliths and have been interpreted to be the result of partial melting mantle metasomatism and host magma xenolith reaction during transport in this paper we test the latter hypothesis with a series of reduced and oxidized experiments at 1 200 and 1 156 c at one atmosphere using a synthetic leucitite melt and discs of natural peridotite our results show that sieve texture development on clinopyroxene and spinel in mantle xenoliths is the result of a multistage reaction process in the first step orthopyroxene undergoes incongruent dissolution to produce a silica and alkali rich melt together with olivine as this melt migrates along grain boundaries it causes incongruent dissolution of clinopyroxene and spinel the incongruent dissolution mechanism involves complete dissolution of the clinopyroxene or spinel followed by nucleation and growth of a secondary clinopyroxene or spinel once the reacting melt is saturated the reaction of orthopyroxene clinopyroxene and spinel with infiltrated host magma results in a range of melt compositions that are very similar to those interpreted to be due to very small degrees of partial melting

polarization analyses of broadband seismic data recorded on stromboli volcano italy from 1996 to 1999 1 we analyze broadband seismic data recorded at a single station deployed on stromboli island from 1996 to 1999 in order to determine basic parameters of the seismic wavefield and study their relationship with volcanic activity in addition to a characterization in the frequency domain we apply polarization analysis and study long term variations of these parameters possibly reflecting also changes in source properties our analysis is twofold first we focus on a meaningful reduction of the data to selected parameters i e azimuth and incidence angle which can be correlated with volcanic activity secondly we investigate if there is maintenance of the correlations over long time spans we observe statistically significant long term changes from several months to year in the wavefield parameters considered we interpret such changes as possibly being caused by the enhanced strength of a deep source potentially by supply of fluids from a low part of the magma feeder between the end of 1997 and the first months of 1998

geotechnical properties of bentonite seams its effects on casing integrity under steam injection in cold lake alberta bentonite seams of varying thicknesses from a few millimetres to about 30 cm are found at depths of 200 300 m within the belle fourche formation and second white specks unit in the cretaceous col

it takes three to tango 2 bubble dynamics in basaltic volcanoes and ramifications for modeling normal strombolian activity this is the second paper in a two part series examining numerical simula tions of buoyancy driven ow in the presence of large viscosity contrasts in the rst pa per we demonstrated that a combination of three numerical tools an extended ghost uid type method the level set approach and the extension velocity technique accurately simulate complex interface dynamics in the presence of large viscosity contrasts in this paper we use this three fold numerical method to investigate bubble dynamics in the conduits of basaltic volcanos with a focus on normal strombolian eruptions strombolian type activity named after the famously episodic eruptions at stromboli volcano is char acterized by temporally discrete fountains of incandescent clasts the mildly explosive nature of normal strombolian activity as compared to more eusive variants of basaltic volcanism is related to the presence of dissolved gas in the magma yielding a complex two phase ow problem we present a detailed scaling analysis allowing identication of the pertinent regime for a given ow problem the dynamic interactions between gas and magma can be clas sied into three non dimensional regimes based on bubble sizes and magma viscosity re solving the uid dynamics at the scale of individual bubbles is not equally important in all three regimes as long as bubbles remain small enough to be spherical their dy namic interactions are limited compared to the rich spectrum of coalescence and breakup processes observed for deformable bubbles in particular once inertia ceases to be neg ligible one key nding in our simulations is that both large gas bubbles and large conduit lling gas pockets slugs are prone to dynamic instabilities that lead to their rapid breakup during buoyancy driven ascent we provide upper bound estimates for the maximum sta ble bubble size in a given magmatic system and discuss the ramications of our results for two commonly used models of normal strombolian type activity the rise speed dependent rsd model and the collapsing foam cf model

estimates of eruption velocity and plume height from infrasonic recordings of the 2006 eruption of augustine volcano alaska abstract the 2006 eruption of augustine volcano alaska began with an explosive phase comprising 13 discrete vulcanian blasts these events generated ash plumes reaching heights of 3 14 km the eruption was recorded by a dense geophysical network including a pressure sensor located 3 2 km from the vent infrasonic signals recorded in association with the eruptions have maximum pressures ranging from 13 111 pa eruption durations are estimated to range from 55 350 s neither of these parameters however correlates with eruption plume height the pressure record however can be used to estimate the velocity and flux of material erupting from the vent assuming that the sound is generated as a dipole source eruptive flux in turn is used to estimate plume height assuming that the plume rises as a buoyant thermal plume heights estimated in this way correlate well with observations events that exhibit strongly impulsive waveforms are underestimated by the model suggesting that flow may have been supersonic

fifteen days of continuous activity survey at stromboli volcano italy in late september 2000 doppler radar seismicity infrared soil humidity and mapping of the crater region the intention of our study was to gain new insight into the complex interplay between different types of eruption of the stromboli volcano by combining detailed field observation with different geophysical methods we recorded more than 600 eruptions by use of continuous doppler radar measurements we detected the onset of the seismic precursor and the beginning of the visible eruption by use of seismic and infrared data two soil samples per day were used to monitor the effect of humidity on the eruptive style we mapped the crater region as a reference base for the long term morphological changes of the active region and for the exact positions of our measurement systems two distinct types of eruption were distinguished from each other on the basis of seismic and radar data short wide angle strombolian explosions and pulsating sharp angle fountain like eruptions data and visual observations imply that weather conditions significantly effect volcanic activity we also interpret the intensification of eruptive activity during our field study as replenishment of the reservoir with a new batch of magma in late september 2000

transversely isotropic stiffness parameters and their measurement in colorado shale drained stress path triaxial tests and confined torsion tests were conducted on colorado shale core samples to investigate transversely isotropic stiffness parameters at small strain deformation nonlinear plastic behaviour occurred along the primary loading path even at strains less than 0 01 nonlinear hysteric behaviour was only observed during the loading unloading path however the shale material displayed transverse isotropy in deformation and very small or nondetectable poisson s ratios in vertical and horizontal directions this special response alludes to the postulate that the colorado shale could be approximated by a transversely isotropic elasticity model at small strain levels with negligible yielding key words anisotropy elasticity stiffness triaxial test torsion test shale

the general and congruent effects of structure in natural soils and weak rocks the engineering properties of naturally occurring sedimentary and residual deposits which are usually treated in geotechnical engineering as soils are reviewed and it is shown that usually they have characteristics due to bonded structure which are similar to those of porous weak rock while this structure can arise from many causes its effects follow a simple general pattern that involves stiff behaviour followed by yield this yield can be described in a similar way to that occurring due to overconsolidation although it is a separate phenomenon the effects of structure are as important in determining engineering behaviour as are the effects of initial porosity and stress history which are the basic concepts of soil mechanics as it can be described in a general way it is concluded that structure and its effects should be treated as a further basic concept of equal importance l article passe en revue les proprietes des depots sedimentaires et residuels naturels qui sont nor malement traites comm

understanding the textures and origin of shock melt pockets in martian meteorites from petrographic studies comparisons with terrestrial mantle xenoliths and experimental studies we present a textural comparison of localized shock melt pockets in martian meteorites and glass pockets in terrestrial mantle derived peridotites specific textures such as the development of sieve texture on spinel and pyroxene and melt migration and reaction with the host rock are identical between these two apparently disparate sample sets based on petrographic and compositional observations it is concluded that void collapse variable shock impedance is able to account for the occurrence of pre terrestrial sulfate bearing secondary minerals in the melts high gas emplacement efficiencies and s al ca and na enrichments and fe and mg depletion of shock melt compositions compared to the host rock previously used as arguments against such a formation mechanism recent experimental studies of xenoliths are also reviewed to show how these data further our understanding of texture development and can be used to shed light on the petrogenesis of shock melts in martian meteorites

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

effect of recent stress history on the stiffness of overconsolidated soil the stress strain behaviour of overconsolidated soil is non linear and the stiffiiess depends on the current state and stress history in addition to the overall stress history which is best described by the overconsolidation ratio the recent stress history either a sudden change in the direction of the stress path or a period of time at a constant stress state has a major effect on subsequent stiffiiess the effects of a change in the direction of the loading path on the stiffness of overconsolidated soil were examined in laboratory stress path tests on reconstituted samples of london clay further tests were carried out on reconstituted samples of other soils with a range of plasticities the test results showed that the behaviour of over consolidated soil is largely inelastic and highly nonlinear and that the recent history has a major effect on the subsequent stiffiiess particularly for relatively small changes of stress or strain for reconstituted samples of london clay the stiffiiess near the s

polarisation analysis of the independent components of low frequency events at stromboli volcano eolian islands italy abstract independent component analysis ica applied on low frequency lf events recorded at stromboli volcano reveals that these signals are composed of three independent components in three different frequency bands approximately 0 8 1 2 2 4 3 0 3 2 4 5 hz respectively the first two frequency ranges are mainly composed of body waves coming from a direction in a range of 30 30 around the crater area this result is a clear indication that the entire signal in these frequency bands comes from the source area in fact any scattered wave should have different back azimuth propagation due to the random distribution of scatterers location however the last independent component is dominated by other kinds of waves coming from many different directions

sliding episodes during the 2002 2003 stromboli lava effusion insights from seismic volcanic and statistical data analysis 1 repeated phenomena of flank instability accompanied the 28 december 2002 to 21 july 2003 eruption of stromboli volcano the major episodes were two tsunamigenic landslides on 30 december 2002 2 d after the volcano unrest after 30 december sliding processes remodeled the area affected by slope instability we propose analyses of 565 sliding episodes taking place from december 2002 to february 2003 we try to shed light on their main seismic features and links with the ongoing seismic and volcanic activity using variogram analysis as well a characterization of the seismic signals in the time and frequency domains is presented for 185 sliding episodes their frequency content is between 1 hz and 7 hz on the basis of the dominant peaks and shape of the spectrum we identify three subclasses of signals one of which has significant energy below 2 hz low frequency signatures were also found in the seismic records of the landslides of 30 december which affected the aerial and submarine northwestern flank of the volcano accordingly we surmise that spectral analysis might provide evidence of sliding phenomena with submarine runouts we find no evidence of sliding processes induced by earthquakes additionally a negative statistical correlation between sliding episodes and explosion quakes is highlighted by variogram analysis variograms indicate a persistent behavior memory of the flank instability from 5 to 10 d we interpret the climax in the occurrence rate of the sliding processes between 24 and 29 january 2003 as the result of favorable conditions to slope instability due to the emplacement of nw se aligned dike fed vents located near the scarp of the landslide area afterward the stabilizing effect of the lava flows over the northwestern flank of the volcano limited erosive phenomena to the unstable loose slope not covered by lava

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

toward a single station approach for microzonation using vertical rotation rate to estimate love wave dispersion curves and direction finding abstract microzonation the estimation of shear wave velocity profiles of the upper few 100 m in dense 2d profiles is one of the key methods for understanding the variation in seismic damage caused by ground shaking events and thus for mitigating the risk of damage in the future in this article we present a novel method for estimating the love wave phase velocity dispersion using ambient noise recordings we use the vertical component of rotational motions inherently present in ambient noise and the established relation to simultaneous recordings of transverse acceleration in which the phase velocity of a plane sh or love type wave acts as a proportionality factor we demonstrate that the developed inversion technique shows comparable results to more classical array based methods furthermore we demonstrate that if portable weak motion rotational motion sensors are available and the installation of a seismic network or array is not possible a single point multicomponent approach for estimating the dominant direction of the incident wavefield and the local velocity structure will be feasible with similar performance compared to more classical techniques

a comparative study of the anisotropic dynamic and static elastic moduli of unconventional reservoir shales implication for geomechanical investigations abstractwe obtained the complete set of dynamic elastic stiffnesses for a suite of shales representative of unconventional reservoirs from simultaneously measured p and s wave speeds on single prisms specially machined from cores static linear compressibilities were concurrently obtained using strain gauges attached to the prism regardless of being from static or dynamic measurements the pressure sensitivity varies strongly with the direction of measurement furthermore the static and dynamic linear compressibilities measured parallel to the bedding are nearly the same whereas those perpendicular to the bedding can differ by as much as 100 compliant cracklike porosity seen in scanning electron microscope images controls the elastic properties measured perpendicular to the rock s bedding plane and results in highly nonlinear pressure sensitivity in contrast those properties measured parallel to the bedding are nearly insensitive to stress this anisotropy to the pressure dependency of the stra

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

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

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

probabilistic source location of explosion quakes at stromboli volcano estimated with double array data data from two dense arrays of short period seismometers are used to retrieve source locations of the explosion quakes at stromboli volcano slowness vectors estimated at both arrays with the zero lag cross correlation technique constitute the experimental data set a probabilistic approach based on a grid search spanning the volcano interior is used to calculate the probability of the source location results depict a shallow source located beneath the crater area at depths not greater than 500 m below the surface results are slightly different from but comparable to those obtained in a companion experiment carried out in the same time period using a broad band seismometer network which show a source shifted some hundreds of meters northwest of the crater area the method is revealed to be effective and useful for future studies having the purpose of real time tracking of the explosion quakes and tremor