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

monitoring ash emission episodes at mt etna the 16 november 2006 case study abstract mt etna in sicily italy is one of the best monitored basaltic volcanoes in the world due to the frequent eruptions from its summit and flanks routine monitoring carried out by istituto nazionale di geofisica e vulcanologia sezione di catania for surveillance purposes permits following the evolution of volcanic events in this paper a description of the ash monitoring system as occurred during the august december 2006 summit eruption at the southeast crater sec is shown this eruption was characterized by lava flow effusions and vigorous strombolian activity eighteen paroxysmal episodes occurred up to the end of november forming weak ash plumes accompanied by moderate tephra fallout over etna s slopes during these events we applied a multidisciplinary approach to promptly monitor the paroxysmal activity and the associated tephra fallout through analysis from seismic tremor and observation from live cameras sampling operations mapping and analysis of the deposit during the most significant episodes we carried out textural and grain size analysis on tephra samples and evaluated the total grain size deposit and the erupted volume while numerical simulations of tephra dispersal allowed better understanding eruptive dynamics an example of this methodology is applied to the 16 november episode during which seismic tremor furnished important constraints on the chronology this paroxysmal eruption produced light fallout on the north east sector of the volcano for about ten hours and a number of debris avalanches over the slopes of the sec cone the erupted deposit was composed for the most part of lithic components and characterized by a total size distribution centered on 2 2 while its total mass was evaluated 7 10 6 kg on the whole such integrated studies help to obtain information on magma fragmentation and eruptive mechanisms to characterize the explosive styles shown by etna and finally to better approach the monitoring of imminent eruptions

array analyses of seismic noise at mt vesuvius volcano italy abstract the properties of the seimic noise wavefield at mt vesuvius volcano italy are investigated using a dense array of short period seismometers deployed on the south west flank of the volcano and operated on 1997 1998 the array had an aperture of 500 m and average station spacing of 40 m the main goal of this deployment was to investigate the possible presence of correlated signals which could be attributed to subsurface magmatic and or hydrothermal activity volcanic tremor the spectral properties of the noise wavefield are investigated using data from the arrays and from the summit stations of the permanent seismic network operated by the vesuvius observatory the seismic noise is characterized by three main spectral peaks at frequencies

observations and analysis of b type earthquakes explosions and volcanic tremor at pavlof volcano alaska an eight station network of short period seismometers has been operated near pavlof volcano 55 25 n 161 54 w alaska peninsula since 1976 high quality analog to digital and direct digital data were recorded during eruptions in 1980 through 1983 data are analyzed from explosions with distinct air phases b type volcanic earthquakes shallow low frequency events lacking clear s phases and volcanic tremor to determine source and propagation effects between zero and several hundred b type events and explosions per day are recorded with higher numbers during eruptions magnitudes range between 0 5 and 1 3 and b values range between 1 9 0 1 and 2 6 0 1 with no systematic relation to eruptive activity six results are most important 1 data from a recently installed three component station reveal that the highest amplitude waves of the b type events show retrograde elliptical particle motion and normal dispersion and are hence probably rayleigh waves 2 stacking of the events enhances the p wave which has a velocity of 3 1 0 1 km sec 1 3 the explosions and b type events have similar hypocenters as evidenced by signal characteristics and wave arrival times 4 the b type events contain virtually no high frequency energy even when allowing for attenuation effects in particular we estimate the anelastic attenuation coefficient q to have a value of 45 20 for rayleigh waves in the shallow part of the volcano 5 volcanic tremor spectra exhibit evenly spaced narrow peaks which we model as eigenvalues of organ pipe resonance in the magma conduit we estimate the length of the conduit to be a maximum of 1 6 km 6 the volcano shows evidence of extreme lateral variation of velocity and attenuation in its shallow structure

velocity and spectral characteristics of the volcanic tremor at etna deduced by a small seismometer array abstract a small l shaped short period seismic array was set up at etna volcano to measure the wave velocity and the incoming azimuth of the volcanic tremor generated by the volcanic activity at etna in non eruptive conditions cross correlation techniques were used to measure the phase shifts between the array stations an approximately n s direction of the propagation direction was estimated coincident with the azimuth of the crater area of etna an apparent velocity of less than 500 m s was estimated suggesting a surface propagation of the tremor waves spectral analysis confirming previous results shows velocity spectra peaked at approximately 2 hz a localized source coincident with the crater area agrees with our data and could generate the volcanic tremor at etna in non eruptive stages

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

beach and dune erosion during storm surges this paper presents the set up and results of an extensive research programme concerning the erosion of coastal dunes during storm surges a large number of two dimensional and three dimensional mobile bed model tests has been carried out to investigate the process of dune erosion the state of art after a series of small scale tests is summarized attention is focussed on large scale tests carried out in the delta flume with random waves up to 2 m significant height sediment concentration and orbital velocity measurements are discussed the large scale tests have confirmed the validity of a modelling technique based on the dimensionless fall velocity parameter h tw the model results are being applied to check the safety of existing coastal dunes as a water retaining structure that has to protect the major part of the netherlands from inundation during storm surges

beyond the spac method exploiting the wealth of circular array methods for microtremor exploration we explore the wealth of alternative methods for inferring phase velocities of rayleigh waves using vertical component seismograms of microtremors from a circular array of seismic sensors which are formulable along the extension of the popularly used spatial autocorrelation spac method four such methods are illustrated here the centerless circular array cca method the henstridge methods of the zeroth and first orders the h0 and h1 methods respectively and what we tentatively call the fifth v method different methods of phase velocity estimation have different wavelength ranges of good resolution implementation to field data from two sites reveals that the traditional spac method and the h0 method are both capable of producing reasonable estimates of rayleigh wave phase velocities within a relatively narrow range on the short wavelength side whereas the h1 method is valid in a relatively narrow range on the long wavelength side the cca and v methods both remain valid over a very broad range of wavelengths the upper limit extending as far up as several 10s of times the array radius use of a noise compensation technique can further prolong the maximum resolvable wavelength of the cca method we also illustrate the field performance of circle phase methods which give without recourse to the conventional frequency wavenumber analysis estimates for the principal arrival directions of rayleigh waves on the basis of circular array seismograms of microtremors

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

velocity models and site effects at kawah ijen volcano and ijen caldera indonesia determined from ambient noise cross correlations and directional energy density spectral ratios abstract two different ambient seismic noise techniques allow the determination of velocity models at ijen caldera and kawah ijen volcano at ijen caldera two average velocity models are constrained down to a depth of 3 km by inverting the stacked dispersion curve obtained by ambient noise cross correlation in addition four local velocity models were obtained by inverting the horizontal to vertical spectral ratio of the directional energy densities of ambient noise dedhvr i e computed through auto correlation of ambient noise this set of velocity models is then compared to the geology of the caldera and the local discontinuities are evidenced at kawah ijen volcano a map of local dominant frequencies is provided by the dedhvr measurements recorded at 87 sites around kawah ijen volcano the horizontality of the shallow layers and the great outcrop of the crater rim facilitate the interpretation of the dedhvrs furthermore the inversion of several juxtaposed dedhvrs provided a complete 2 d velocity model of the flank of the crater unlike other stratovolcanoes the kawah ijen appears to have a remarkably homogeneous structure the dedhvr technique is used for the first time in a volcanic environment and shows a great potential for an accurate and fast computation of the velocity model on volcanoes

evidence for gas influence on volcanic seismic signals recorded at stromboli abstract the meaning of the large variety of seismic waveforms showing different frequencies associated with volcanic activity is still uncertain no definitive model for source dynamics has been proposed yet at present seismic models explaining the origin of the spectral content of the seismic signal are mainly linked to geometrical features of the volcanic conduit and to resonant effects induced by pressure fluctuations in a fluid filled conduit such models assume the physical system to be in a steady state over a long interval of time at stromboli the seismicity produced by each of the three active vents is not stable and can suddenly change in time therefore the application of stable resonator models appears to be unwarranted on the basis of infrared image analyses atmospheric pressure and seismic wavefield signals we show that different frequency contents and different explosive styles occur at stromboli at the same time at different vents moreover we give evidence to support the idea that seismicity and explosivity are both controlled by a variable gas flow regime released during explosions at the top of the magma column we have recognized two main pressure regimes controlling the explositivity at stromboli one is impulsive short and possibly produced by a gas accumulation beneath a cap rock the other has an intermittent regime feature and lasts longer we demonstrate how the first one generates a monochromatic low frequency wavefield while the second shows a high frequency spectrum where the frequency content depends on pressure fluctuations and on pressure gradient we suggest different pressure growth and gas flow in the magma as the common source for both explosive style and seismic wavefield

a two radius circular array method inferring phase velocities of love waves using microtremor records 1 we present a new method to estimate phase velocities of love waves from horizontal motion seismograms of microtremors obtained with seismic sensors placed around two circumferences of different radii under the assumption that the fundamental mode dominates we applied our new method to field data acquired at a test site where the shallow underground seismic velocity profile is known and have confirmed that the phase velocities of the fundamental mode love waves could be inferred with sufficient precision within certain wavelength ranges outside the wavelength ranges suitable for analysis the spectral ratio an intermediary quantity calculated from measurement records prior to phase velocity evaluation deviated from theoretical expectations the pattern of deviations could satisfactorily be accounted for by considering three factors theoretically the presence of higher mode surface waves directional aliasing related to the finite number of sensors and the presence of incoherent noise

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

temporal and spatial characteristics of volcanic tremor wave fields abstract detailed volcanic tremor studies were carried out with portable seismic stations installed both in the near and distant zones at klyuchevskoy volcano in 1984 1986 and 1987 it has been determined that the coherence of wave field decreases with distance to 0 5 km and does not change at greater distances based on coherence and phase spectra the frequency dependence of the phase velocities has been determined the dispersion of phase velocity points to the surface character of the wave field the behaviour of volcanic tremor characteristics through time is stationary which implies stability of the parameters of the volcanic tremor source a detailed spectral study has demonstrated that when the intensity of volcanic tremor varies by a few orders of magnitude parts of the low frequency and high frequency spectra change which is likely due to the variations in source dimensions the detailed spectral characteristics of tremor may be used for both determining the source parameters and studying the structure of the medium

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

long period seismicity in the shallow volcanic edifice formed from slow rupture earthquakes volcanic eruptions are often preceded by long period seismic events that were thought to be generated by the resonance of cracks filled with magmatic fluid analysis and modelling of long period seismicity at volcanoes in italy costa rica and peru shows that it could instead be caused by slow rupture along faults in the upper volcanic edifice

near surface velocity structure of pacaya volcano guatemala derived from small aperture array analysis of seismic tremor knowledge of the typically complicated near surface structure on volcanoes is critical for determining accurate seismic event locations and seismic source mechanisms associated with precursory and eruptive activity to generate a near surface velocity model for the active cone of pacaya volcano guatemala we recorded seismic tremor and ambient noise with a small aperture array of 11 short period seismometers in january 2011 the diffuse wavefield was investigated using the spatial autocorrelation spac method and we computed rayleigh and love dispersion curves at the array location the phase velocities for rayleigh waves range from 1000 m s at 2 hz to 230 m s at 10 hz those for love waves range from 600 to 250 m s over the same frequency band such low velocities are consistent with the presence of unconsolidated tephra on the surface of the volcano interspersed with lava flows assuming they represent the fundamental modes of rayleigh and love waves we inverted the dispersion curves to produce a shear wave velocity model of the upper 500 m beneath the array online material s wave velocity models obtained from inversion and love and rayleigh wave dispersion curves

seismic tracking of lahars using tremor signals debris flows or lahars frequently occur in volcanic regions and cause serious disasters to nearby communities lahars are commonly observed as long lasting high frequency tremor in seismic records we propose a seismic technique to locate the source of tremor originating from lahars by using waveform data from a seismic network in this method we fit the surface wave amplitudes from point sources positioned over the surface of a volcano to the observed tremor amplitudes and estimate the spatial distributions of the normalized residuals in successive time windows the observed tremor amplitudes at individual stations are corrected by site amplification factors independently estimated from coda waves of tectonic earthquakes the positions of time windows applied to the observed tremor signals are corrected for the travel times of individual source and receiver pairs we track the source of tremor or lahars as temporal changes of the best fit locations in the residual distributions this method is an extension of the existing methods used to locate seismic events and tremor associated with volcanic eruptions we applied this technique to tremor signals of lahars observed by a seismic network at cotopaxi volcano ecuador our analysis showed regions with small residuals on the ne flank of the volcano this suggests that lahars descended on this flank which is consistent with the result of a field survey that found fresh lahar deposits on the ne flank our method which can be easily automated may be useful for the rapid detection and monitoring of lahars

echo resonance and hydraulic perturbations in magma cavities application to the volcanic tremor of etna italy in relation to its eruptive activity a study is presented of spectral features of volcanic tremor recorded at mount etna sicily italy following the methods of analysis suggested by the resonant scattering formalism of gaunaurd and uberall 1978 1979a 1979b and the model for hydraulic origin of seidl et al 1981 the periods investigated include summit and flank eruptions that occurred between 1984 and 1993 recordings from a permanent station located near the top of the volcano were used and the temporal patterns associated with a the average spacing bar delta between consecutive spectral peaks in the frequency range 1 6 hz b the spectral shape and c the overall spectral amplitude were analyzed bar delta values are thought to depend on the physical properties of magma such as its density which in turn is controlled by the degree of gas exsolution variations in the spectral shape are tentatively attributed to changes in the geometrical scattering from the boundary of resonant conduits and magma batches finally the overall amplitude at the station should essentially reflect the state of turbulence of magma within the superficial ascending path a limit in the application of the resonant scattering formalism to the study of volcanic tremor is given by the fact that the fundamental modes and integer harmonics are difficult to identify in the frequency spectra as tremor sources are likely within cavities of very complex geometry rather than in spherical or cylindrical chambers as expected by theory this study gives evidence of some correlations between the analyzed temporal patterns and the major events in the volcanic activity related to both lava flow and explosions at the summit vents in particular relatively high values of bar delta have been attained during the se crater eruption of 1984 the complex eruptive phases of september october 1989 and the 1991 1993 flank eruption suggesting the presence of a relatively dense magma for all of these events conversely very low values have been recorded in coincidence with the december 1985 activity and the paroxysmal explosions at the summit craters of early 1990 which are interpreted here as fed by fluid vesiculated magma appreciable modifications in the spectral shape have been observed in relation to changes of the volcanic activity that probably preceded the opening and disactivation of shallow dykes or magma batches finally the overall amplitude seems to be a sensitive indicator of the state of gas turbulence within the shallow conduits as is suggested by the high values attained during phases of intense volcanic activity

a double seismic antenna experiment at teide volcano existence of local seismicity and lack of evidences of volcanic tremor data analyzed in the present work correspond to a 40 days field experiment carried out in teide volcano canary islands spain with two short period small aperture dense seismic antennas in 1994 the objective of this experiment was to detect analyze and locate the local seismicity we analyzed also the background seismic noise to investigate the possible presence of volcanic tremor from a set of 76 events we selected 21 of them in base of their good signal to noise ratio and their possibility to locate their seismic source by using the seismic antennas a visual classification based on the s p time and seismogram shape has permitted to establish three groups of events local seismicity s p time between 3 and 5 s very local earthquakes s p time smaller than 3 s and artificial explosions these earthquakes have been located by applying the zero lag crosscorrelation technique and the inverse ray tracing procedure those earthquakes that were recorded simultaneously by both seismic antennas were also located by intersecting both back azimuths the analysis of the seismicity has revealed that the amount of seismicity in teide volcano is moderate this seismicity could be distributed in three main areas inside the caldera edifice below the teide pico viejo complex in the eastern border of the caldera edifice and offshore of the island at present this activity is the only indicator of the volcano dynamics the analysis of the back ground seismic noise has revealed that at frequencies lower than 2 hz the oceanic load signal is predominant over other signals even over local earthquakes with a magnitude of 2 0 due to this although if in the teide area were present a weak volcanic tremor or other volcanic signals with predominant peaks below 2 hz to observe them would be a very difficult task q 2000 elsevier science b v all rights reserved

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

shallow structure of mt vesuvius volcano italy from seismic array analysis data from a portable dense seismic array deployed on mt vesuvius in may 1994 during a 2d seismic tomography experiment are analyzed in the present paper the array consisted of two groups of short period geophones 4 5 hz natural frequency formed by 16 and 25 vertical components plus two horizontal components distributed along an arc like shape along the summit crater stacks of later arrivals interpreted as reflected phases provide a significant constraint to a boundary layer located in the depth range 1 5 2 2 km beneath the summit crater with average velocity v 1 8 2 2 km s interpreted as the top of the limestone basement the correlation methods applied on microtremor records allowed to infer the shallow velocity structure up to 400 m beneath the crater rim

using so 2 camera imagery and seismicity to examine degassing and gas accumulation at kīlauea volcano may 2010 abstract so 2 camera measurements at k lauea volcano hawaii in may of 2010 captured two occurrences of lava lake rise and fall within the halema um au crater summit vent during high lava stands we observed diminished so 2 emission rates and decreased seismic tremor similar events at k lauea have been described as the result of sporadic degassing following gas accumulation beneath a mostly impermeable lava lake surface incorporation of so 2 camera data into a multi parameter dataset gives credence to the likelihood of shallow gas accumulation as the cause of these high stand events with accumulated gas release upon lake level drop compensating for the gas deficit reached during accumulation

terminal settling velocity of commonly occurring sand grains published measurements of terminal settling velocity for commonly occurring sands are used to develop three equations which join into a single segmented curve of dimensionless form results are noticeably different from those for spheres of similar diameter and permit calculation of the settling velocity for usual sand grains without specification of exact grain shape for quartz in water the three equations of different settling regimes correspond approximately to very fine sand fine to coarse sand and very coarse sand

the morphodynamic effects of incident wave groupiness and tide range on an energetic beach abstract the roles played by daily tide range and incident wave groupiness in affecting the short term morphodynamic responses of an energetic beach are examined demodulation of original tide and wave time series from the moderate energy narrabeen beach australia resulted in new time series of daily tide range and a daily grouping factor which expresses the relative amplitude of the alternation between groups of high and low waves using these new time series together with time series of daily beach state and changing breaker conditions statistical analyses were performed aimed at determining the contributions made by tide and groupiness in explaining time varying beach state additional to those made by time varying wave conditions eigenvector analyses of monthly surveyed beach and surf zone profiles provided a set of time series on modes of profile configuration change which were also analyzed to determine the relative effects of waves and tide range on profile shape both tide range and groupiness are significant determinants of beach state the six beach states are reflective low tide terrace transverse bar and rip rhythmic bar and beach longshore bar trough and dissipative wright and short 1984 provided that wave conditions are within the appropriate range to favor beach states at the reflective end of the sequence spring tides will tend to favor the low tide terrace over the transverse bar and rip state higher tide ranges are also associated with more subdued bar trough topography the more accentuated bar trough profiles are developed when tide range is minimal overall higher relative incident wave groupiness favors the more dissipative states incident wave groupiness is the dominant factor determining whether the low tide terrace state or transverse bar and rip state prevails provided incident wave steepnesses permit one or the other of these states groupiness is also important in discriminating between the transverse bar and rip and rhythmic bar and beach states

array analysis using circular wave front geometry an application to locate the nearby seismo volcanic source summary the zero lag cross correlation technique used for array analysis in the hypothesis of plane waves has been modified to allow the wave front to be circular synthetic tests have been performed to check the capability of the method which returns the input test data when the source array distances are not greater than two or three times the array aperture for this distance range the method furnishes an estimate of the apparent velocity and the epicentral coordinates of the source for more distant sources the method becomes equivalent to that based on the planar wave approximation which gives an estimate of the backazimuth to the source and the apparent velocity the method has been applied to seismic data recorded at the active volcano located at deception island antarctica 35 volcanic long period events occurring in a small swarm were selected results show that the epicentres are close to the array between 0 4 and 2 km and aligned in a sw direction in agreement with one of the main directions of the fracture system of deception volcano

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

the correlation of microtremors empirical limits and relations between results in frequency and time domains summary the use of the correlation of microtremor records is on its way to develop into a common tool to estimate local shear wave velocity structure for this reason the establishment of the conditions for the correct use of this method and its limitations when applied to real data is becoming increasingly important in addition to the use of frequency domain spatial correlation technique the spatial autocorrelation spac method the use of time domain correlation to obtain the green s function of the medium is rapidly gaining presence we explore the use of microtremor correlation techniques in the time domain to determine local velocity structure and compare with previous results obtained with the same data using spac our data come from three experiments carried out in parkway and wainuiomata valleys in new zealand using broad band portable stations interstation distances range from 5 m to 2 1 km and our results are useful in the frequency band from 0 1 to 7 hz frequency domain correlation requires an isotropic microtremor field a condition that need not be satisfied in the time domain two station correlations provide useful results due to the temporal stationarity and isotropy in average of the microtremor wavefield this manifests itself in the symmetry of the temporal correlation functions with respect to zero time our results show that the local velocity structure and the interstation distance are the key factors conditioning the frequency range where surface wave dispersion can be correctly measured either in frequency or time domains we confirm that when the interstation distance becomes much larger than the dominant wavelengths only the correlation in time domain is useful all our results indicate that the signal obtained in the correlation of vertical component microtremors is due to the fundamental mode of rayleigh waves which appears as the most stable propagation mode without any indication of body waves

seismic patterns and fluid dynamic features preceding and accompanying the january 15 1990 eruptive paroxysm on mt etna italy abstract on the basis of data collected during a seismological investigation carried out on mt etna italy during a phase of the volcanic activity marked by progressive transition from strombolian bursts to effusive paroxysms at the se crater january 1990 three types of seismic regime have been recognized they are interpreted to be linked to modifications in the regimes of volcanic gases and vapours within the upper levels of the magma column as suggested by recent studies on the dynamics of magmatic fluids our analysis also reveals that the use of usual seismic parameters such as the temporal patterns associated with the occurrence of discrete low frequency events spindles and the coefficient m of the ishimoto iida law can furnish information about variations in the behaviour of the system before the irreversible evolution of the volcanic activity toward eruptive paroxysms

site specific issues for strong ground motions during the kocaeli turkey earthquake of 17 august 1999 as inferred from array observations of microtremors and aftershocks array observations of microtremors and aftershocks were carried out near the permanent strong motion observation sites and the damaged areas after the kocaeli turkey earthquake of 17 august 1999 the major objectives were to determine s wave velocity structures at the sites and to understand the site effects on strong motion or damage array observation of microtremors is a useful method for determining the s wave velocity structures in a sedimentary basin with less practical restriction than the other geotechnical methods the spatial autocorrelation method spac was applied to array data of microtremors for determining s wave velocity structures the spac method generally provides an equivalent result with that of the frequency wavenumber method using fewer array sites and a smaller array size most strong motion sites near the fault are classified into stiff and or very hard soils the records cannot directly be used for interpreting damage to buildings in the sedimentary basin records of long durations of strong motion at ats near avcilar west of istanbul are closely related to the low velocity v s 200 m sec of the surface layers the s wave velocity structure at avcilar where there was severe damage during the mainshock is similar to that of the lowland ats and it differs significantly from that of cna located 4 km northeast of avcilar where the strong motion record was obtained from the mainshock the strong ground motion at avcilar during the mainshock is estimated to be similar to that at ats of the strong motion sites sakarya skr is located on very hard soil whereas thick and soft sediments cover downtown adapazari it is plausible that strong ground motions during the mainshock in the damaged area adc were significantly different from those of skr a large difference between the strong motions of a hillside and the lzmit bay area in and around golcuk is also indicated by a comparison of aftershock records

subsoil structure using spac measurements along a line the spac spatial autocorrelation method was proposed almost 50 years ago by aki 1957 this method allows a phase velocity dispersion curve to be obtained from microtremor measurements using an array of stations arranged in a circle the subsoil structure is subsequently derived from the inversion of that dispersion curve in this article we show that it is possible to get similar results using microtremors recorded along a line we use microtremor records obtained by using four broadband seismographs disposed along a line with different interstation spacings 5 10 20 and 40 m our data are precessed by using the standard spac procedure with the exception of the azimuthal average the final subsoil structure as determined from the inversion of the phase velocity dispersion curve shows excellent agreement with previous results at the site of our measurements our results suggest that the use of the spac method is not restricted to a particular geometry of the array provided that the basic requirement of stationarity is fulfilled

shallow velocity models at the kilauea volcano hawaii determined from array analyses of tremor wavefields the properties of the surface wavefield at kilauea volcano are analysed using data from small aperture arrays of short period seismometers deployed in and around the kilauea caldera tremor recordings were obtained during two japan us cooperative experiments conducted in 1996 and 1997 the seismometers were deployed in three semi circular arrays with apertures of 300 300 and 400 m and a linear array with length of 1680 m data are analysed using a spatio temporal correlation technique well suited for the study of the stationary stochastic wavefields of rayleigh and love waves associated with volcanic activity and scattering sources distributed in and around the summit caldera spatial autocorrelation coefficients are obtained as a function of frequency and are inverted for the dispersion characteristics of rayleigh and love waves using a grid search that seeks phase velocities for which the l 2 norm between data and forward modelling operators is minimized within the caldera the phase velocities of rayleigh waves range from 1400 to 1800 m s 1 at 1 hz down to 300 400 m s 1 at 10 hz and the phase velocities of love waves range from 2600 to 400 m s 1 within the same frequency band outside the caldera rayleigh wave velocities range from 1800 to 1600 m s 1 at 1 hz down to 260 360 m s 1 at 10 hz and love wave velocities range from 600 to 150 m s 1 within the same frequency band the dispersion curves are inverted for velocity structure beneath each array assuming these dispersions represent the fundamental modes of rayleigh and love waves the velocity structures observed at different array sites are consistent with results from a recent 3 d traveltime tomography of the caldera region and point to a marked velocity discontinuity associated with the southern caldera boundary

lateral heterogeneities and microtremors limitations of hvsr and spac based studies for site response abstract we report a site effect study carried out in a small alluvial valley nari basin in ulleung island republic of korea in that small valley a permanent broad band array of five stations records ground motion continuously in addition we performed microtremor measurements using two arrays of stations a small aperture array 60 m and a medium aperture one 500 m ambient vibration was also recorded at 38 points inside the basin the records were analyzed using horizontal to vertical spectral ratios hvsr to estimate dominant frequency and maximum amplification and the spatial autocorrelation spac method to estimate the subsoil structure via phase velocity dispersion curves nari basin is clearly a 3d structure but it was expected that a laterally irregular model might be built from the interpolation of several 1d models dominant frequency maps based on results from hvsr suggest a simple sedimentary structure with mostly smooth lateral variations in contrast maximum amplification distribution is very irregular and shows no correlation with dominant frequency in the case of nari it seems that the complexity of the basin structure cancels the usefulness of hvsr we could estimate a phase velocity dispersion curve for 81 of the station pairs recording simultaneously ambient vibration in our arrays in all the cases the resulting dispersion curve had a simple shape suggesting that the subsoil structure consists of a single layer over a half space however the dispersion curves are incompatible among them even for different station pairs covering the same path something impossible if the subsoil structure were 1d it seems that the passive methods we have used in nari basin are not adapted to its structure this makes a tomography unfeasible and we are unable to propose a subsoil structure for nari basin our results show that surface wave dispersion may be estimated using the spac method even when the medium is far from 1d we believe that this problem is enhanced by the small size of this basin which amplifies the effect of lateral heterogeneities

seismic source dynamics of gas piston activity at kilauea volcano hawai i since 2008 eruptive activity at the summit of kilauea volcano hawai i has been confined to the new overlook pit crater within the halema uma u crater among the broad range of magmatic processes observed in the new pit are recurring episodes of gas pistoning the gas piston activity is accompanied by seismic signals that are recorded by a broadband network deployed in the summit caldera we use raw data recorded with this network to model the source mechanism of representative gas piston events in a sequence that occurred on 20 25 august 2011 during a gentle inflation of the kilauea summit 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 medium that takes topography into account we apply a new waveform inversion method that accounts for the contributions from both translation and tilt in horizontal seismograms through the use of green s functions representing the seismometer response to translation and tilt ground motions this method enables a robust description of the source mechanism over the period range 1 10 000 s most of the seismic wavefield produced by gas pistoning originates in a source region 1 km below the eastern perimeter of the halema uma u pit crater the observed waveforms are well explained by a simple volumetric source with geometry composed of two intersecting cracks featuring an east striking crack dike dipping 80 to the north intersecting a north striking crack another dike dipping 65 to the east each gas piston event is marked by a similar rapid inflation lasting a few minutes trailed by a slower deflation ramp extending up to 15 min attributed to the efficient coupling at the source centroid location of the pressure and momentum changes accompanying the growth and collapse of a layer of foam at the top of the lava column assuming a simple lumped parameter representation of the shallow magmatic system the observed pressure and volume variations can be modeled with the following attributes foam thickness 10 50 m foam cell diameter 0 04 0 10 m and gas injection velocity 0 01 0 06 m s 1 gas piston activity occurs in a narrow pipe with diameter of 6 m connecting the halema uma u pit crater to the subjacent dike system the height of the magma column is estimated at 104 m at the start of the sequence based on the period of very long period vlp oscillations accompanying the onset of the gas piston signal based on the change in the period of vlp oscillations and tilt evidence the height of the magma column is inferred to have risen by up to 23 m by the end of the 5 day long sequence a penny shaped crack model of the dike geometry yields effective diameters of 1 2 2 9 km for the east dike and 0 7 km for the north dike the shallower north dike segment is embedded in a relatively weak medium compatible with expected mechanical properties in the hydrothermal environment of this dike

array tracking of the volcanic tremor source at deception island antarctica we have found experimental evidence which shows that the volcanic tremor recorded at deception island south shetland islands antarctica is a superposition in time of overlapping hybrid events we studied data from a small aperture seismic array data analysis for tremor and hybrids included 1 spectral analysis 2 apparent slowness and back azimuth determination by using the zero lag cross correlation method and 3 polarization analysis both types of events share these common features a two dominant spectral bands at frequencies 1 3 hz the most energetic and 4 8 hz b several coherent phases with the same back azimuth to the source and apparent slowness along the whole signal c in the high frequency band the apparent slowness is very low around 0 17 s km indicating the propagation of body waves d in the low frequency band the apparent slowness is high around 1 6 s km consistent with the presence of surface waves and e clear p wave onset followed by a complex pattern of rayleigh waves therefore both types of events are strongly related because they share the same source region the same wave propagation properties and the same wave composition moreover several arrivals that resemble a single hybrid event have been found along the tremor signals due to these reasons we hypothesize that volcanic tremor of deception island is a superposition of hybrid type events the source of both types could be the interaction between thaw water and hot materials in a shallow aquifer

seismic attenuation and shallow velocity structures at stromboli volcano italy the surface wave field associated with the explosive activity at stromboli volcano is investigated using data recorded by two short period seismic arrays deployed on the north and west flanks of the volcano the group velocity dispersion curves for rayleigh waves are derived using the multiple filter technique the phase velocity dispersion curves are recovered using a phase match filter and compared with that inferred from zero lag cross correlation analysis applied to the array data these analyses indicate rayleigh wave group velocities ranging from 0 29 to 0 24 km sec in the 1 5 to 8 0 hz frequency band and phase velocities ranging from 1 km sec at 1 5 hz to about 0 3 km sec at frequencies above 5 hz in addition the dispersive properties of the attenuation coefficient for rayleigh waves are inferred from application of the multiple filter technique to seismograms recorded at different distances from the source these results are validated through examination of the spectral amplitude decay with distance for both body and rayleigh waves the values of the body wave quality factor thus obtained are q 20 and q 6 for the north and west side of the island respectively the velocity and attenuation dispersion curves are inverted for the shear wave velocity and q structures down to a depth of about 200 m shear wave velocities for the west flank range from about 0 3 km sec for the uppermost 17 m thick layer to 1 9 km sec at depths greater than 200 m comparison with previous studies indicates a similar velocity structure for the north and west flanks the attenuation structure for the west flank is described by a shallower 36 m thick layer with q 9 underlain by a half space with q 50 on the north flank q 40 for the shallower 30 m thick layer and q 44 for the underlying half space residuals from analysis of the spectral decay with distance are used to quantify site effects affecting the different array elements on the west flank local amplifications at that array are interpreted in terms of an edge effect associated with concave topography velocity similarities observed at the north and west flanks are compatible with surface geologic data discrepancies in attenuation properties at the two sites are interpreted in terms of different degrees of heterogeneity and crack density controlling the scattering quality factor q s manuscript received 15 april 2001

estimation of the near surface velocity structure of the yasur yenkahe volcanic complex vanuatu small aperture array measurements of seismic noise at seven sites around yasur volcano vanuatu are performed to estimate the vp and vs velocities of the shallow structure the spatial autocorrelation spac and the frequency wavenumber f k methods are used to determine rayleigh phase velocity dispersion curves phase velocities computed with the spac method vary between 580 m s and 960 m s at 1 hz and between 270 m s and 420 m s at 15 hz f k dispersion curves show velocities of 300 340 m s and 800 940 m s at 1 hz and 200 230 m s at 15 hz an inversion technique based on the use of the neighbourhood algorithm has been used to calculate the one dimensional velocity model at each site velocity models reach 200 m deep and mainly contain two layers and a half space for sites close to the siwi caldera rims comparisons with geology and hydrothermal system studies suggest that the two layers highlighted in models may correspond to two large pyroclastic sequences related to caldera collapses based on the flank of an old volcano results obtained for the other three sites located inside the caldera show the influence of the hydrothermal system on p and s wave velocities for these sites fluid circulation inside the volcanic deposits causes lower velocities at depth to obtain a near surface velocity model of the volcanic structure each 1d velocity model is spatially extrapolated according to the surface geology results highlight four distinct areas the siwi caldera edges with high velocities and the resurgent block the ash plain and the yasur edifice with lower velocities at depth

cyclic spattering seismic tremor and surface fluctuation within a perched lava channel kīlauea volcano in late 2007 a perched lava channel built up to 45 m above the preexisting surface developed during the ongoing eruption near pu u cone on k lauea volcano s east rift zone the lava channel was segmented into four pools extending over a total of 1 4 km from late october to mid december a cyclic behavior consisting of steady lava level rise terminated by vigorous spattering and an abrupt drop in lava level was commonly observed in pool 1 we use geologic observations video time lapse camera images and seismicity to characterize and understand this cyclic behavior spattering episodes occurred at intervals of 40 100 min during peak activity and involved small 5 10 m high fountains limited to the margins of the pool most spattering episodes had fountains which migrated downchannel each spattering episode was associated with a rapid lava level drop of about 1 m which was concurrent with a conspicuous cigar shaped tremor burst with peak frequencies of 4 5 hz we interpret this cyclic behavior to be gas pistoning and this is the first documented instance of gas pistoning in lava well away from the deeper conduit our observations and data indicate that the gas pistoning was driven by gas accumulation beneath the visco elastic component of the surface crust contrary to other studies which attribute similar behavior to the periodic rise of gas slugs the gas piston events typically had a gas mass of about 2 500 kg similar to the explosions at stromboli with gas accumulation and release rates of about 1 1 and 5 7 kg s 1 respectively the time averaged gas output rate of the gas pistoning events accounted for about 1 2 of the total gas output rate of the east rift zone eruption

influence of near surface volcanic structure on long period seismic signals and on moment tensor inversions simulated examples from mount etna 1 long period lp seismicity on volcanoes is thought to be associated with moving fluids or resonating fluid filled conduits hence lp moment tensor mt source inversions might have a direct bearing on our understanding of the plumbing system using 3 d full wavefield simulations and 2 d sensitivity kernels in a digital elevation model of mount etna we investigate the influence of near surface volcanic structure on lp signals and on moment tensor inversions contrary to common wisdom in crustal seismology we find that despite their relatively long wavelengths lps are severely distorted by near surface structures including layering and topographic features in particular near surface low velocity structures which are commonly observed on volcanoes play a critical role in controlling the nature of lp signals if not accounted for these path effects leak into the source solution leading to the emergence of erroneous source geometries spurious forces and incorrect source time functions this is particularly problematic if one adopts an unconstrained solution space for the source with many free parameters hence there is a fine balance in the trade off between the velocity model and the source in the absence of high resolution near surface velocity control we demonstrate the importance of employing a priori source information from other fields e g structural geology for shallow lps constraining the number of free parameters in the inversion a probabilistic approach should then be taken as the model with the best fit is not necessarily the true solution

shallow degassing events as a trigger for very long period seismicity at kīlauea volcano hawai i the first eruptive activity at k lauea volcano s summit in 25 years began in march 2008 with the opening of a 35 m wide vent in halema uma u crater the new activity has produced prominent very long period vlp signals corresponding with two new behaviors episodic tremor bursts and small explosive events both of which represent degassing events from the top of the lava column previous work has shown that vlp seismicity has long been present at k lauea s summit and is sourced approximately 1 km below halema uma u by integrating video observations infrasound and seismic data we show that the onset of the large vlp signals occurs within several seconds of the onset of the degassing events this timing indicates that the vlp is caused by forces sourced at or very near the lava free surface due to degassing transmitted down the magma column and coupling to the surrounding rock at 1 km depth

the low frequency earthquake swarms at mount pinatubo philippines implications for magma dynamics abstract mount pinatubo s intense low frequency lf earthquake swarms in 1992 provide insight into the volcano s shallow plumbing system and into the possible magmatic process that generate these unusual earthquakes lf waveforms are remarkably uniform with spectral peaks at about 1 hz recorded at pinatubo 1 week prior to the june 1991 cataclysmic eruption lf events reappeared 1 year later and a day before a new dome began to grow in the volcano s freshly formed caldera seismicity with at least 23 000 lf events accompanied the 1992 dome growth and both simultaneously ceased after 4 months the magnitude range of the thousands of lf events is narrow at only 1 6 units and show a more restricted range in size during any particular period within the crisis defining a group magnitude during two lf earthquake swarms the group magnitude gradually varied indicating a pervasive process affecting the mechanism of lf earthquake generation hypocenters of pinatubo s lf earthquakes define a vertical pipe extending from the crater floor to 4 2 km below sea level coinciding with the column formed by high frequency hf earthquakes prior to the 1991 cataclysmic eruption a dike intrusion along the nw trending maraunot fault is also suggested by the hypocenters the temporal amplitude and waveform features and hypocenter location of pinatubo s lf earthquakes are distinctly different from those of hf events and indicate a close affinity of lf earthquakes to one another lf events appear to be caused by interactions between more fluid magma intruding semi ductile materials confined within the volcano s shallow plumbing system this source mechanism can account for the occurrence of lf earthquakes as swarms and multiplets the limited magnitude range of the events the temporally changing group magnitudes the obscurity of s phase the existence of hybrid lf hf earthquakes and the close relationship of lf earthquakes with dome extrusions the 1992 lf seismicity at pinatubo trails the 1991 paroxysmal eruption residual melt left in the shallow conduit following the 1991 eruption may have reached density and viscosity contrasts that allowed fluid fractions to intrude more viscous but still ductile part of the magma this process may have produced the small sized 1992 dome by analogy we suggest that the 1991 pre eruptive dome and lf events may have involved viscous materials left by the 500 year bp eruption and intruded by the then ascending melt

mapping the sources of the seismic wave field at kilauea volcano hawaii using data recorded on multiple seismic antennas seismic antennas constitute a powerful tool for the analysis of complex wave fields well designed antennas can identify and separate components of a complex wave field based on their distinct propagation properties the combination of several antennas provides the basis for a more complete understanding of volcanic wave fields including an estimate of the location of each individual wave field component identified simultaneously by at least two antennas we used frequency slowness analyses of data from three antennas to identify and locate the different components contributing to the wave fields recorded at kilauea volcano hawaii in february 1997 the wave field components identified are 1 a sustained background volcanic tremor in the form of body waves generated in a shallow hydrothermal system located below the northeastern edge of the halemaumau pit crater 2 surface waves generated along the path between this hydrothermal source and the antennas 3 back scattered surface wave energy from a shallow reflector located near the southeastern rim of kilauea caldera 4 evidence for diffracted wave components originating at the southeastern edge of halemaumau and 5 body waves reflecting the activation of a deeper tremor source between 02 hr 00 min and 16 hr 00 min hawaii standard time on 11 february

intermittent behaviour of volcanic tremor at mt etna harmonic tremor is widely studied and modelled in a very narrow frequency band 1 5 hz which represents the eigenfrequencies of a resonator assumed as the source of the phenomenon minimal effort was dedicated towards understanding its behaviour in larger temporal scales here we characterise the dynamic behaviour of volcanic tremor while evaluating the complete spectrum of the generalised dimension of the phase space the starting time series constitutes the tremor amplitude picked every 10 minutes the choice of this lag time is made on the basis of a qualitative analysis of the properties of the tremor the results show intermittent behaviour of the dynamics which requires an 8 dimensional map to be completely described an interesting result is that the maximum clustering of point density in phase space occurs in a monodimensional space which implies a periodicity sometimes observed experimentally an appropriate predictive model needs more constraints on the nature of the eight variables involved in the process

unified modeling guidance based on a sedimentation parameter for beach changes abstract review of four available proposals for designing coastal movable bed models demonstrates that each suggested model scaling law contradicts all the others accurate laboratory models providing the separate empirical bases however all appear fairly consistent with the new design guidance developed here this formal development considers sediment excursions under wave action by means of a parameter including bed slope and the threshold of sediment movement the consequent relationship for sedimentation similitude between model and prototype indicates that appropriate model sediment and horizontal scale depend on the selected vertical scale along with wave period and prototype sand characteristics explicit forms derived from the general design guidance recover two expressions resembling those previously reported by e k noda 1972 and by p vellinga 1982 the route towards noda s result indicates that guidance is not appropriate for small models of large situations but the present development yields an independent basis and a needed refinement for vellinga s empirical results considerations of sedimentation similitude are also shown to be supported by successful new laboratory models using sand profiles developed in a large wave tank as prototypes spatial distortion seems to be the advisable strategy for small models but proper distortion is rather modest with prototype materials according to present results

the 2011 unrest at katla volcano characterization and interpretation of the tremor sources abstract a 23 hour tremor burst was recorded on july 8 9th 2011 at the katla subglacial volcano one of the most active and hazardous volcanoes in iceland this was associated with deepening of cauldrons on the ice cap and a glacial flood that caused damage to infrastructure increased earthquake activity within the caldera started a few days before and lasted for months afterwards and new seismic activity started on the southern flank no visible eruption broke the ice and the question arose as to whether this episode relates to a minor subglacial eruption with the tremor being generated by volcanic processes or by the flood the tremor signal consisted of bursts with varying amplitude and duration we have identified and described three different tremor phases based on amplitude and frequency features a tremor phase associated with the flood was recorded only at stations closest to the river that flooded correlating in time with rising water level observed at gauging stations using back projection of double cross correlations two other phases have been located near the active ice cauldrons and are interpreted to be caused by volcanic or hydrothermal processes the greatly increased seismicity and evidence of rapid melting of the glacier may be explained by a minor sub glacial eruption a less plausible interpretation is that the tremor was generated by hydrothermal boiling and or explosions with no magma involved this may have been induced by pressure drop triggered by the release of water when the glacial flood started all interpretations require an increase of heat released by the volcano

toward continuous quantification of lava extrusion rate results from the multidisciplinary analysis of the 2 january 2010 eruption of piton de la fournaise volcano la reunion the dynamics of the 2 12 january 2010 effusive eruption at piton de la fournaise volcano were examined through seismic and infrasound records time lapse photography so2 flux measurements deformation data and direct observations digital elevation models were constructed for four periods of the eruption thus providing an assessment of the temporal evolution of the morphology the volume and the extrusion rate of the lava flow these data were compared to the continuous recording of the seismic and infrasonic waves and a linear relationship was found between the seismic energy of the tremor and the lava extrusion rate this relationship is supported by data from three other summit eruptions of piton de la fournaise and gives total volume and average lava extrusion rate in good agreement with previous studies we can therefore provide an estimate of the lava extrusion rate for the january 2010 eruption with a very high temporal resolution we found an average lava extrusion rate of 2 4 m3s 1 with a peak of 106 6 m3s 1 during the initial lava fountaining phase we use the inferred average lava extrusion rate during the lava fountaining phase 30 23 m3s 1 to estimate the value of the initial overpressure in the magma reservoir which we found to range from 3 7 106 pa to 5 9 106 pa finally based on the estimated initial overpressure the volume of magma expelled during the lava fountaining phase and geodetic data we inferred the volume of the magma reservoir using a simple mogi model between 0 25 km3 and 0 54 km3 which is in good agreement with previous studies

gas bubble dynamics model for shallow volcanic tremor at stromboli volcanic tremor at stromboli aeolian islands italy is correlated to small infrasonic transients ripepe et al 1996 which repeat almost rhythmically in time in a range between 0 8 and 1 2 s we demonstrate that infrasonic transients are associated to small gas bubble 0 5 m burstings which produces no transients in the seismic signal tremor ground displacement attenuates with the inverse of the distance from the craters indicating that the source is shallow short term energy release shows that infrasonic and seismic signals are linked to the same dynamical process while at the long term scale it is evident that the two signals are controlled by two distinctive mechanisms we suggest that the possible physical model acts in two steps first gas coalescence and then gas bursting in our model the seismic signal is related to the coalescence of a gas bubble from a layer of small bubbles while the infrasonic signal is linked to the bursting of the bubble when it reaches the magma surface gas bubbles could form by free coalescence in magma or could be forced to coalesce by a structural barrier we calculate that forced coalescence induces in magma a pressure change 104 pa 2 orders of magnitude higher than free coalescence and it explains best the tremor ground displacement 10 5 m recorded at stromboli moreover forced coalescence evidences the role of a structural barrier such as a dike in volcanic tremor source dynamics in this gas dynamic process the delay time of 1 2 s between infrasonic pulses could reflect the gas nucleation interval of basaltic magma thomas et al 1993 manga 1996 we propose that the source function for the shallow volcanic tremor at stromboli could be the viscoelastic reaction of the magma to the pressure decrease induced by gas bubble growth rate under constant depressurization the spectrum of our source function is controlled by the time duration of the pressure pulse which represents the viscoelastic relaxation time of the magma and gas bubble growth rate the predicted asymptotic decay of the frequency contents fits the spectral behavior of the volcanic tremor ground displacement recorded at stromboli we show that the same spectral behavior can be found in ground displacement spectra of volcanic tremor recorded on different volcanoes