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

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

seismicity of the aegean and surrounding area abstract seismicity parameters based on instrumental and historical data are given for 36 seismic sources of shallow earthquakes and for 6 seismic sources of intermediate depth earthquakes in the aegean and surrounding area 34 n 43 n 18 e 30 e these parameters are of two categories parameters of the first category are useful for seismic hazard evaluation a and b values of the frequency magnitude relation maximum earthquake magnitude number of shocks larger than certain magnitude per year while parameters of the second category are proper for describing the spatial distribution of seismicity mean return period most probable magnitude in a certain time period moment rate shallow seismicity is highest along the convex side of the hellenic arc but close to the coast ionian islands south peloponnesus south of crete south of karpathos and rhodos in central greece patraikos corinthiakos evoikos gulfs thessalia and along a seismic belt which includes the northwestern anatolia fault zone the northernmost part of the aegean sea and the serbomacedonia zone the intermediate depth seismic activity is distributed in two parts of the benioff zone which dips from the convex side eastern mediterranean to the concave side aegean sea of the hellenic arc the one part shows a low dip angle and includes earthquakes with focal depths between 70 km and 100 km this part has a high seismicity earthquake magnitudes up to 8 0 and is situated below the inner slope of the sedimentary part of the hellenic arc eastern peloponnesus north of crete rhodos based on the fact that this part of the benioff zone is a continuation of the seismic zone of shallow earthquakes along the hellenic arc and that both zones have the same seismicity it is concluded that they constitute a continuous seismic belt on which coupling occurs between the subducted eastern mediterranean lithosphere and the overthrusted aegean lithosphere the other inner part of the benioff zone shows low seismicity maximum earthquake magnitude up to 7 1 with earthquakes of focal depths between 100 km and 180 km it dips at a mean angle of 38 below the volcanic arc of the southern aegean sea and is the result of the subduction of the front part of the eastern mediterranean lithosphere without coupling with the aegean lithosphere

temporal and spectral characteristics of seismicity observed at popocatepetl volcano central mexico abstract popocatepetl volcano entered an eruptive phase from december 21 1994 to march 30 1995 which was characterized by ash and fumarolic emissions during this eruptive episode the observed seismicity consisted of volcano tectonic vt events long period lp events and sustained tremor before the initial eruption on december 21 vt seismicity exhibited no increase in number until a swarm of vt earthquakes was observed at 01 31 hours local time visual observations of the eruption occurred at dawn the next morning lp activity increased from an average of 7 events a day in october 1994 to 22 events per day in december 1994 at the onset of the eruption lp activity peaked at 49 events per day lp activity declined until mid january 1995 when no events were observed tremor was first observed about one day after the initial eruption and averaged 10 h per episode by late february 1995 tremor episodes became more intermittent lasting less than 5 min and the number of lp events returned to pre eruption levels 7 events per day using a spectral ratio technique low frequency oceanic microseismic noise with a predominant peak around 7 s was removed from the broadband seismic signal of tremor and lp events stacks of corrected tremor episodes and lp events show that both tremor and lp events contain similar frequency features with major peaks around 1 4 hz frequency analyses of lp events and tremor suggest a shallow extended source with similar radiation pattern characteristics the distribution of vt events between 2 5 and 10 km also points to a shallow source of the tremor and lp events located in the first 2500 m beneath the crater under the assumption that the frequency characteristics of the signals are representative of an oscillator we used a fluid filled crack model to infer the length of the resonator

automatic detection of long period events at campi flegrei caldera italy 1 we propose a novel approach to analyze continuous seismic signal and separate the sources from background noise a specific application to the seismicity recorded at campi flegrei caldera during the 2006 ground uplift is presented the fundamental objective is to improve the standard procedures of picking the emergent onset arrivals of the seismic signals often buried in the high level ambient noise in order to obtain an appropriate catalogue for monitoring the activity of this densely populated volcanic area this is particularly useful in order to estimate the release of the seismic energy and to put constraints on the source dynamics an independent component analysis based approach for the blind source separation of convolutive mixtures is adopted to obtain a clear separation of long period events from the ambient noise the approach presents good performance and it is suitable for real time implementation in seismic monitoring its application to the continuous seismic signal recorded at campi flegrei has allowed the extraction of high quality waveforms considerably improving the detection of low energy events

models of tremor and low frequency earthquake swarms on montserrat recent observations from soufriere hills volcano in montserrat reveal a wide variety of low frequency seismic signals we discuss similarities and differences between hybrid earthquakes and long period events and their role in explosions and rockfall events these events occur usually in swarms and occasionally merge into tremor an observation that can shed further light on the generation and composition of harmonic tremor we use a 2d finite difference method to model major features of low frequency seismic signatures and compare them with the observations a depth dependent velocity model for a fluid filled conduit is introduced which accounts for the varying gas content in the magma and the impact on the seismic signals is discussed we carefully analyse episodes of tremor that show shifting spectral lines and model those in terms of changes in the gas content of the magma as well as in terms of a time dependent triggering mechanism of low frequency resonances in this way we explain the simultaneous occurrence of low frequency events and tremor with a spectral content comprising integer harmonics

study on the long period source mechanism at campi flegrei italy by a multi parametric analysis abstract the source properties of the long period events that occurred at campi flegrei caldera italy during the 2004 2006 ground uplift episode are investigated by analyzing the temporal release of seismic energy amplitude distribution and inter event occurrence time moreover an entropy based decomposition method is applied to identify the simpler waveforms thought to be representative of the source mechanism of long period events on the basis of the outcomes we propose that the main part of these events is the result of a source process triggered by a mechanism of fluid charge discharge which causes pressure drop in a main branch of a dentritic network of the hydrothermal system in this model the rate of the poissonian process about 15 min which drives the occurrence of the long period events provides the average recharge time of the system up to the critical condition a partial shunting of the fluid flow away from the main conduit activates the resonance of a second branch spatially separated from the first one this is a process that occurs whenever the fluid pressure exceeds a critical value and produces less energetic long period events the mechanism of pressure variation in the two conduits generates signals with preferred amplitude scales described by a bi lognormal distribution from a dynamical point of view long period events result well described by a low dimensional dynamical system finally the time pattern of the energy release and its correlation with the diurnal solid earth tide suggest that the whole mechanism of fluid charge discharge is likely modulated by tidal stress variation

comments on the paper automatic detection and discrimination of volcanic tremors and tectonic earthquakes an application to ambrym volcano vanuatu by daniel rouland denis legrand mikhail zhizhin and sylvie vergniolle j volcanol geotherm res 181 2009 196 206

evidence of nonextensive statistical physics behavior of the hellenic subduction zone seismicity abstract the hellenic subduction zone hsz is the most seismically active region in europe many destructive earthquakes have taken place along the hsz in the past in this study we investigate the seismicity of the hsz based on the science of complex systems the spatiotemporal distributions of seismicity as well as the magnitude distribution are studied using the concept of nonextensive statistical physics nesp defining five seismic zones and forming an earthquake dataset that covers the period 1976 2009 we apply the nesp ideas to formulate the cumulative distribution functions of the inter event times and distances and the magnitude distribution along the hsz our results indicate that the nonextensive parameter qt which is related with the inter event time distribution presents almost similar values in each of the seismic zones and reflects the long term scale of the seismicity evolution in the hsz the qd parameter which is related with the inter event distance distribution presents a significant variation along the seismic zones this variation is related with the different degree of spatial earthquake clustering in each of the seismic zones of the hsz moreover in the framework of the fragment asperity model the thermostatistical parameter qm which is related with the frequency magnitude distribution could be used as an additional index to inform us about the physical state of each seismic zone along the hsz the variations of the qm parameter are related with the energy release rate in each seismic zone the models used fit rather well to the observed distributions implying the usefulness of nesp in investigating such phenomena exhibiting scale free nature and long range memory effects

effects of three dimensional velocity structure on the seismicity of the 1984 morgan hill california aftershock sequence abstract a three dimensional velocity model for the area surrounding the 24 april 1984 morgan hill earthquake has been developed by simultaneously inverting local earthquake and refraction arrival time data this velocity model corresponds well to the surface geology of the region predominantly showing a low velocity region associated with the sedimentary sequence to the southwest of the madrone springs fault this low velocity sequence extends to a depth of approximately 5 km previously constructed geologic cross sections for this region had suggested that these sediments extended to a depth of less than 2 km relocation of 2 179 hypocenters with the three dimensional velocity model did not show great differences when compared to locations done with a one dimensional velocity model with station corrections in both cases the calaveras fault is steep but has a noticeable dip to the northeast and the seismicity does not intersect the surface along the trace of the calaveras fault in the southern half of the rupture zone the greatest differences between the two sets of locations was that the locations using the three dimensional velocity model were deeper and fewer earthquakes were located within the low velocity region the focal mechanisms were also determined for 946 earthquakes using both the one dimensional and three dimensional earth models both earth models yield similar focal mechanisms for these earthquakes

source process of low frequency earthquakes associated with the 2000 eruption of mt usu abstract we installed five broadband seismometers around mt usu just before the first eruption in 2000 and the observation continued over 8 months among the total of 590 relocated earthquakes that occurred from march 31 12 58 p m to april 5 2000 41 low frequency earthquakes were identified low frequency earthquakes based on waveforms and s wave spectra can be classified into several families we investigated the source process of the low frequency earthquakes classified as type 1 for which the similarity among events was the highest the character of waveforms and s wave spectra of type 1 earthquakes at mt usu are quite similar to the hybrid and lp earthquakes at mt redoubt alaska whose source process was explained well by the resonance of a fluid filled crack assuming that they have similar source processes we estimated several parameters such as crack size by forward modeling we obtained the following parameters that explain main features e g the frequencies of major peaks of the observed s wave spectra at three stations hgsn shnzn and znkji in the frequency range of 0 5 5 hz assuming a vertical crack crack length is 200 m 100 m for its width 0 14 m for its thickness 100 for its stiffness 0 5 for the ratio of bulk modulus and rigidity and 0 07 for viscous damping loss the pressure pulse triggering the crack oscillation has a rise time of 0 25 s from the difference in characteristics of waveforms among stations of various azimuths the strike of the crack was likely to be northeast to southwest the use of the site corrected spectra enables us to pin point the value of viscous damping loss so that we can conclude that water steam mixture was responsible for the low frequency events at mt usu

subsurface structure of the solfatara volcano campi flegrei caldera italy as deduced from joint seismic noise array volcanological and morphostructural analysis 1 the joint application of different seismological techniques for seismic noise analysis and the results of a volcanological and morphostructural survey have allowed us to obtain a detailed and well constrained image of the shallow crustal structure of the solfatara volcano campi flegrei caldera italy horizontal to vertical spectral ratios inversion of surface wave dispersion curves and polarization analysis provided resonance frequencies and peak amplitudes shear wave velocity profiles and polarization pattern of coherent ambient noise these results combined in a unique framework indicate that the volcanic edifice is characterized by lateral and vertical discontinuities and heterogeneities in terms of shear wave velocity lithological contrasts and structural setting the interpretation of the seismological results with the volcanological and morphostructural constraints supports the hypothesis that the volcano has been characterized by a complex and intense activity with the alternation of constructive and destructive phases during which magmatic and phreatomagmatic explosions built a complex tuff cone later reworked by atmospheric agents and altered by hydrothermal activity the differences in the velocity structure between the central and eastern parts of the crater have been interpreted as resulting from a possible eastward migration of the eruptive vent along the deformational features affecting the area and to the presence of viscous lava and lithified tuff bodies within the feeding conduits which are buried under a covering of reworked materials of variable thickness the observed fault and fracture systems partially inherited from regional structural setting and exhumed during volcanism and ground deformation episodes also seems to strongly control wave propagation affecting the noise polarization properties

subsurface cyclic magma sill expansions in the 2000 miyakejima volcano eruption possibility of two phase flow oscillation 1 step like tilt changes were observed at intervals of dozens of hours during the caldera formation stage occurred during the 2000 miyakejima volcano eruption our analysis suggests that these tilt steps were caused by the cyclic expansion of a subsurface sill like magma plumbing system trending from se to nw of the volcano in the same period a caldera gradually grew at the summit area to a very large 1 6 km in diameter and 450 m in depth the source mechanism of these tilt steps is fairly well explained by a two phase flow instability called a pressure drop oscillation this model indicates that the gas phase capacity in the upper part of the conduit acts as a pump that controls the flux of two phase magma in the sill like reservoir caldera formation as well as magma uplift and descent in the conduit may reflect temporal changes in the intervals between tilt steps which are themselves proportional to the volume of this gas capacity

complex behavior and source model of the tremor at arenal volcano costa rica typical records of volcanic tremor and explosion quakes at arenal volcano are analyzed with a high resolution time frequency method the main characteristics of these seismic signals are 1 numerous regularly spaced spectral peaks including both odd and even overtones 2 frequency gliding in the range 0 9 2 hz of the fundamental peak 3 frequency jumps with either positive or negative increments 4 tremor episodes with two simultaneous systems of spectral peaks affected by independent frequency gliding 5 progressive transitions between spasmodic tremor and harmonic tremor 6 lack of clear and systematic relationship between the occurrence of explosions and tremor some examples of alternation between two states of oscillation characterized by different fundamental frequencies are also observed some tremor and explosion codas are characterized by acoustic and seismic waves with identical spectral content and frequency gliding which suggests a common excitation process we propose a source model for the tremor at arenal in which intermittent gas flow through fractures produces repetitive pressure pulses the repeating period of the pulses is stabilized by a feedback mechanism associated with standing or traveling waves in the magmatic conduit the pressure pulses generate acoustic waves in the atmosphere and act as excitation of the interface waves in the conduit when the repeating period of the pulses is stable enough they produce regularly spaced spectral peaks by the dirac comb effect and hence harmonic tremor when the period stability is lost because of failures in the feedback mechanism the tremor becomes spasmodic the proposed source model of tremor is similar to the sound emission process of a clarinet fractures in the solid or viscous layer capping the lava pool in the crater act as the clarinet reed and the conduit filled with low velocity bubbly magma is equivalent to the pipe of the musical instrument the frequency gliding is related to variations of the pressure in the conduit which modify the gas fraction the wave velocity and possibly the length of the resonator moreover several observations suggest that two seismic sources associated with two magmatic conduits are active in arenal volcano they could explain in particular the apparent independence of tremor and explosions and the episodes of tremor displaying two simultaneous systems of spectral peaks

instability in flow through elastic conduits and volcanic tremor the stability of fluid flow through a narrow conduit with elastic walls is explored treating the fluid as incompressible and viscous and the walls as semi infinite linear hookean solids instabilities analogous to roll waves occur in this system we map out the physical regime in which they are excited for elastic wave speeds much higher than the fluid speed a critical reynolds number is required for instability however that critical value depends linearly on wavenumber and so can be made arbitrarily small for long waves for smaller elastic wave speeds the critical reynolds number is reduced still further and rayleigh waves can be destabilized by the fluid even at zero reynolds number a brief discussion is given of the nonlinear dynamics of the instabilities for large elastic wave speed and the significance of the results to the phenomenon of volcanic tremor is presented although magma itself seems unlikely to generate flow induced vibrations the rapid flow through fractured rock of low viscosity fluids exsolved from magma appears to be a viable mechanism for volcanic tremor

deterministic non linear source processes of volcanic tremor signals accompanying the 1996 vatnajokull eruption central iceland summary observations and theoretical considerations have cast doubt on the suggestion that volcanic tremor source processes may be modelled by a linear oscillator that is set into resonance by a sustained disturbance volcanic tremor signals that accompanied the 1996 vatnajokull subglacial eruption central iceland have been analysed using methods from the discipline of non linear dynamics in order to investigate the possibility that they originated from a non linear source the volcano seismic phenomena associated with the eruption were recorded by a permanent network equipped with broad band seismometers hotspot using a sampling rate of 20 samples s 1 the eruption was preceded by increased seismic activity for a period of 2 days which also included a large earthquake with a moment magnitude of 5 6 the tremor during the first 2 days of the eruption has a high signal to noise ratio at the nearest station to the eruption site and starts as a continuous signal later evolving to low amplitude background tremor interrupted by high amplitude cigar shaped bursts having an average duration of 250 s the phase space which describes the evolution of the behaviour of a non linear system was reconstructed from the original tremor seismograms using the delay embedding theorem suggested by takens the delay time used for the reconstruction was selected after examining the autocorrelation function which showed a first zero crossing at a timelag of 4 samples and the average mutual information that showed no minimum indicating that the tremor process may have been undersampled based also on phase space portraits for different delay times a delay time of one sample interval 0 05 s was used the sufficient embedding dimension for phase space reconstruction was selected by applying the false nearest neighbours method which revealed complete unfolding of the tremor attractor at dimensions 7 8 implying upper bounds of its fractal dimension in the range 3 5 4 0 the phase space prediction errors of different segments of the tremor time series were compared in order to check whether the attractor dynamics change substantially with time it was found that for continuous tremor there was almost no dynamic variation in contrast to the background tremor and the superposed bursts that gave a maximum prediction error when the former was used to predict the latter this difference in dynamics also had an effect on their spectra the amplitude spectrum of a burst or continuous tremor has a much sharper decay at high frequencies than that of the background tremor a possible physical mechanism that may explain these observed characteristics involves turbulent slug flow of magma in a narrow cylindrical conduit generating the different dynamic regimes as the reynolds number varies

thermal seismic and infrasonic evidences of variable degassing rates at stromboli volcano abstract during june 1999 we measured the amplitude and rate number of events per second at which gas exited the vent at stromboli volcano as discrete gas bursts or puffs this allowed us to identify two styles of gas burst puffing activity the first is characterized by frequent rapidly rising puffs the second by less frequent slowly rising puffs each style persisted over 5 40 min long durations and was associated with a high and low number of strombolian explosions per hour respectively each period was also associated with characteristic delay times between the arrival of the infrasonic and thermal signals during strombolian explosions the delays were longer during vigorous puffing periods to explain our observations we propose a model in which the degassing process cycles between vigorous and weak degassing phases during vigorous degassing phases bubble layers ascend the conduit at a frequency of 0 5 1 0 s 1 this high degassing level reflects a gas rich magma column and leads to an increased rate in the formation of shallow foams and hence an increase in puffing and explosive activity as well as a higher free surface level and or gas jet velocity during weak phases bubble layers ascend the conduit at a reduced frequency of 0 2 0 3 s 1 during such times the magma column is poor in gas this leads to a decreased rate of foam layer formation and hence a reduction in puffing and explosive activity as well as a lower free surface level and or gas jet velocity variations in puffing activity can thus be used to track changes in the rate at which the shallow system is supplied by fresh gas rich magma our observations indicate that the two degassing styles last from 5 to 40 min and that the switch from one to the other occurs over a matter of minutes

complex polarization analysis of particle motion knowledge of particle motion polarization aids in identifying phases on three component seismograms the scheme of montalbetti and kanasewich 1970 is extended to analytic three component seismograms where the imaginary part of the signal is the hilbert transform of the real part this scheme has only one free parameter the length of the time window over which the polarization parameters are estimated so it can be applied in a routine way to three component data the azimuth and dip of the direction of maximum polarization and the degree of elliptical polarization as a function of time for the seismograms are obtained polarization analysis of strong motion data from the 1971 san fernando earthquake aids in the discrimination between wave types which is important for the understanding of the complicated earthquake induced shaking observed in basins most arrivals are incident on the receivers in the direction of the back azimuth to the epicenter which suggests that despite the complicated motions two dimensional finite difference methods are sufficient to understand the effect on seismic waves of the los angeles and san fernando basins vidale and helmberger 1986b

the july august 2000 seismic swarms at campi flegrei volcanic complex italy two swarms of microearthquakes ml 2 2 occurred on july 2 7 and august 22 2000 at campi flegrei accompained by a ground uplift episode 4 cm which interrupted on early march 2000 the descending trend started on 1985 spectral analysis indicates a direct involvement of magmatic hydrothermal fluids in the source process of the july swarm while the august events are typical of shear failure similar to most of the earthquakes that occurred during the last 1982 1984 bradyseismic crisis precise 3 d relative location applied to similar earthquakes allows for the recognition of two parallel alignments trending ne sw at depths of 1 7 and 3 2 km this trend is consistent with the direction of the main focal plane obtained from fault plane solutions and evidences tensile failure in close proximity to the zone of maximum uplift as depicted by geodetic measurements a fault weakening mechanism triggered by increasing pore pressure is invoked as the cause of these earthquakes

nonlinear time series analysis of volcanic tremor events recorded at sangay volcano ecuador the assumption that volcanic tremor may be generated by deterministic nonlinear source processes is now supported by a number of studies at different volcanoes worldwide that clearly demonstrate the low dimensional nature of the phenomenon we applied methods based on the theory of nonlinear dynamics to volcanic tremor events recorded at sangay volcano ecuador in order to obtain more information regarding the physics of their source mechanism the data were acquired during 21 26 april 1998 and were recorded using a sampling interval of 125 samples s 1 by two broadband seismometers installed near the active vent of the volcano in a previous study johnson and lees 2000 classified the signals into three groups 1 short duration 1 min impulses generated by degassing explosions at the vent 2 extended degassing chugging events with a duration 2 5 min containing well defined integer overtones 1 5 hz and variable higher frequency content 3 extended degassing events that contain significant energy above 5 hz we selected 12 events from groups 2 and 3 for our analysis that had a duration of at least 90 s and high signal to noise ratios the phase space which describes the evolution of the behavior of a nonlinear system was reconstructed using the delay embedding theorem suggested by takens the delay time used for the reconstruction was chosen after examining the first zero crossing of the autocorrelation function and the first minimum of the average mutual information ami of the data in most cases it was found that both methods yielded a delay time of 14 18 samples 0 112 0 144 s for group 2 and 5 samples 0 04 s for group 3 events the sufficient embedding dimension was estimated using the false nearest neighbors method which had a value of 4 for events in group 2 and was in the range 5 7 for events in group 3 based on these embedding parameters it was possible to calculate the correlation dimension of the resulting attractor as well as the average divergence rate of nearby orbits given by the largest lyapunov exponent events in group 2 exhibited lower values of both the correlation dimension 1 8 2 6 and largest lyapunov exponent 0 013 0 022 in comparison with the events in group 3 where the values of these quantities were in the range 2 4 3 5 and 0 029 0 043 respectively theoretically a nonlinear oscillation described by the equation g x fcos t can generate deterministic signals with characteristics similar to those observed in groups 2 and 3 as the values of the parameters f are drifting causing instability of orbits in the phase space

seismicity of the hellenic subduction zone in the area of western and central crete observed by temporary local seismic networks temporary local seismic networks were installed in western crete in central crete and on the island gavdos south of western crete respectively in order to image shallow seismically active zones of the hellenic subduction zone more than 4000 events in the magnitude range between 0 5 and 4 8 were detected and localized the resulting three dimensional hypocenter distribution allows the localization of seismically active zones in the area of western and central crete from the mediterranean ridge to the cretan sea furthermore a three dimensional structural model of the studied region was compiled based on results of wide angle seismics surface wave analysis and receiver function studies the comparison of the hypocenter distribution and the structure has allowed intraplate and interplate seismicity to be distinguished high interplate seismicity along the interface between the subducting african lithosphere and the aegean lithosphere was found south of western crete where the interface is located at about 20 to 40 km depth an offset between the southern border of the aegean lithosphere and the southern border of active interplate seismicity is observed in the area of crete the offset varies laterally along the hellenic arc between about 50 and 70 km a southwards dipping zone of high seismicity within the aegean lithosphere is found south of central crete in the region of the ptolemy trench it reaches from the interface between the plates at about 30 km depth towards the surface in comparison the aegean lithosphere south of western crete is seismically much less active including the region of the ionian trench intraplate seismicity within the aegean plate beneath crete and north of crete is confined to the upper about 20 km between 20 and 40 km depth beneath crete the aegean lithosphere appears to be seismically inactive in western crete the southern and western borders of this aseismic zone correlate strongly with the coastline of crete

detailed investigation of long period activity at campi flegrei by convolutive independent component analysis abstract this work is devoted to the analysis of seismic signals continuously recorded at campi flegrei caldera italy during the entire year 2006 the radiation pattern associated with the long period energy release is investigated we adopt an innovative independent component analysis algorithm for convolutive seismic series adapted and improved to give automatic procedures for detecting seismic events often buried in the high level ambient noise the extracted waveforms characterized by an improved signal to noise ratio allows the recognition of long period precursors evidencing that the seismic activity accompanying the mini uplift crisis in 2006 which climaxed in the three days from 26 28 october had already started at the beginning of the month of october and lasted until mid of november hence a more complete seismic catalog is then provided which can be used to properly quantify the seismic energy release to better ground our results we first check the robustness of the method by comparing it with other blind source separation methods based on higher order statistics secondly we reconstruct the radiation patterns of the extracted long period events in order to link the individuated signals directly to the sources we take advantage from convolutive independent component analysis that provides basic signals along the three directions of motion so that a direct polarization analysis can be performed with no other filtering procedures we show that the extracted signals are mainly composed of p waves with radial polarization pointing to the seismic source of the main lp swarm i e a small area in the solfatara also in the case of the small events that both precede and follow the main activity from a dynamical point of view they can be described by two degrees of freedom indicating a low level of complexity associated with the vibrations from a superficial hydrothermal system our results allow us to move towards a full description of the complexity of the source which can be used by means of the small intensity precursors for hazard model development and forecast model testing showing an illustrative example of the applicability of the cica method to regions with low seismicity in high ambient noise

seismic characteristics of variable convection at erta ʻale lava lake ethiopia abstract the active summit lava lake of erta ale volcano ethiopia offers a unique opportunity to study magma convection in february 2002 we collected a multiparametric set of seismic thermal and video data these data indicate that the lake cycled between periods characterized by low 0 01 0 08 m s 1 and high 0 1 0 4 m s 1 convection rates typically lasting tens to hundreds of minutes three seismometers placed around the active crater recorded continuous tremor with a dominant frequency of 2 hz and energy at frequencies from 0 8 to 12 hz here we characterize the seismic signature of each regime by its spectral content wavefield polarization and tremor source location for both regimes the wavefield is mostly rectilinear azimuths and incidence angles are consistent with p waves originating in one of two locations the north edge of the active lava lake or a region 100 150 m ene of the lava lake because both regimes are dominated by a low frequency rectilinearly polarized wavefield we investigate the source location using a method that solves for location and isotropic source power by a weighted least squares amplitude based inversion of seismic data we find that tremor source regions are unique to each convective regime although some location overlap exists when tremor is located in short time windows wavefield composition suggests that the convective phases may share a common source process but their differing locations indicate that either the source region is non stationary or a second source skews the location during the high convective phase tremor polarization and location suggests that the low frequency tremor is caused by bubble coalescence and bursting in a conduit whose surface is the lava lake the higher frequency signal associated with the high convective regime is associated with a scattered more complex wavefield superimposed on the low frequency background tremor caused by bubble bursting and cracking of cooled crust at the lava lake surface

seismicity associated with the 2004 2006 renewed ground uplift at campi flegrei caldera italy abstract following the significant ground uplift 1 8 m of the 1982 1984 bradyseismic crisis the recent history of campi flegrei volcanic complex italy has been dominated by a subsidence phase recent geodetic data demonstrate that the subsidence has terminated and that positive ground deformation renewed in november 2004 at a low but accelerating rate leading to about 4 cm of uplift by the end of october 2006 as in previous episodes ground uplift has been accompanied by swarms of micro earthquakes m 1 4 in three distinct episodes october 2005 october 2006 and december 2006 hypocenters of these earthquakes are mainly located beneath the solfatara volcano at depths ranging between 0 5 and 4 km inversion of s wave spectra indicates source radius and stress drop on the order of 30 60 m and 104 9 105 pa respectively fault plane solutions indicate predominantly normal mechanisms accompanying the october 2006 swarm we detected intense long period lp activity for about 1 week these signals consist of weak monochromatic oscillations whose spectra exhibit a main peak at frequency 0 8 hz this peak is common to all the stations of the network and not present in the noise spectra suggesting that it is a source effect about 75 of the detected lps cluster into three groups of mutually similar events adjustment of waveforms using cross correlation allows for precise alignment and stacking which enhances signal onsets and permits accurate absolute arrival picks and thus better absolute as well as relative locations locations associated with the three different clusters are very similar and appear to delineate the se rim of the solfatara volcano at a depth of about 500 m the most likely source process for the lp events involves the resonance of a fluid filled buried cavity quality factors of the resonator cluster in a narrow interval around 4 which is consistent with the vibration of a buried cavity filled with a water vapour mixture at poor gas volume fractions we propose a conceptual model to interpret the temporal and spatial patterns of the observed seismicity

seismovolcanic signals at deception island volcano antarctica wave field analysis and source modeling the seismovolcanic signals associated with the volcanic activity of deception island antarctica recorded during three antarctic summers 1994 1995 1995 1996 and 1996 1997 are analyzed using a dense small aperture 500 m seismic array the visual and spectral classification of the seismic events shows the existence of long period and hybrid isolated seismic events and of low frequency quasi monochromatic and spasmodic continuous tremors all spectra have the highest amplitudes in the frequency band between 1 and 4 hz while hybrids and spasmodic tremors have also significant amplitudes in the high frequency band 4 10 hz the array analysis indicates that almost all the well correlated low frequency signals share similar array parameters slowness and back azimuth and have the same source area close to the array site the polarization analysis shows that phases at high frequency are mostly composed of p waves and those phases dominated by low frequencies can be interpreted as surface waves no clear shear waves are evidenced from the energy evaluation we have found that the reduced displacement values for surface and body waves are confined in a narrow interval volcano tectonic seismicity is located close to the array at a depth shallower than 1 km the wave field properties of the seismovolcanic signals allow us to assume a unique source model a shallow resonating fluid filled crack system at a depth of some hundreds of meters all of the seismic activity is interpreted as the response of a reasonably stable stationary geothermal process the differences observed in the back azimuth between low and high frequencies are a near field effect a few episodes of the degassification process in an open conduit were observed and modeled with a simple organ pipe

source process of a long period event at kilauea volcano hawaii summary we analyse a long period lp event observed by a dense seismic network temporarily operated at kilauea volcano hawaii in 1996 we systematically perform spectral analyses waveform inversions and forward modeling of the lp event to quantify its source process spectral analyses identify two dominant spectral frequencies at 0 6 and 1 3 hz with associated q values in the range 10 20 results from waveform inversions assuming six moment tensor and three single force components point to the resonance of a horizontal crack located at a depth of approximately 150 m near the northeastern rim of the halemaumau pit crater waveform simulations based on a fluid filled crack model suggest that the observed frequencies and q values can be explained by a crack filled with a hydrothermal fluid in the form of either bubbly water or steam the shallow hydrothermal crack located directly above the magma conduit may have been heated by volcanic gases leaking from the conduit the enhanced flux of heat raised the overall pressure of the hydrothermal fluid in the crack and induced a rapid discharge of fluid from the crack which triggered the acoustic vibrations of the resonator generating the lp waveform the present study provides further support to the idea that lp events originate in the resonance of a crack

numerical simulation of the steam water flow instability as a mechanism of long period ground vibrations at geothermal areas summary we present a model for the excitation of continuous ground vibration at geothermal areas and active volcanoes which is based on the instability of water steam two phase flow through a series of numerical experiments we evaluate the amplitude and period of ground vibrations excited by density wave oscillation called dwo one of the flow instability phenomena which is known in the nuclear reactor engineering to occur under a wide variety of boundary conditions we consider a vertical cylindrical pipe buried underground and 1 d flows through it driven by the lithostatic pressure gradient water flows into the pipe from below and is evaporated by the heat supplied from outside when the heating rate is low after a perturbation such as a change in heating rate is given to the flow system a decaying oscillation of pressure flow velocity and void fraction occurs being followed by a stationary flow on the other hand when the heating rate exceeds a threshold the perturbation grows to a continuous oscillation with a fixed amplitude forming a limit cycle dwo we investigate how various parameters such as pipe length pressure and heating rate affect the stability of the two phase flow we then estimate the amplitudes of seismic waves excited by dwo assuming that the pipe is embedded in a elastic half space we find that a longer pipe can excite a dwo of longer period and of larger maximum amplitude for a pipe of length of 100 m with its bottom at the depth of 150 m the dwo period is nearly 10 s in this case the maximum pipe diameter for the excitation of limit cycle dwo for reasonable rates of stationary conductive heat supply from country rocks to the two phase mixture inside the pipe less than about 35 mw m 3 is 0 02 m the maximum amplitudes of ground displacement due to dwo are of the order of 7 10 8 m and 4 10 9 m at epicentral distances of 200 and 1000 m respectively typical geothermal areas and active volcanoes can supply heat and discharged water mass which are required to excite dwo larger than typical background noises therefore dwo due to a shallow water steam flow could excite ground motions with periods longer than 10 s which is large enough to be observed with suitably designed broadband seismic experiments at geothermal fields

source mechanism of long period events at kusatsu shirane volcano japan inferred from waveform inversion of the effective excitation functions abstract we investigate the source mechanism of long period lp events observed at kusatsu shirane volcano japan based on waveform inversions of their effective excitation functions the effective excitation function which represents the apparent excitation observed at individual receivers is estimated by applying an autoregressive filter to the lp waveform assuming a point source we apply this method to seven lp events the waveforms of which are characterized by simple decaying and nearly monochromatic oscillations with frequency in the range 1 3 hz the results of the waveform inversions show dominant volumetric change components accompanied by single force components common to all the events analyzed and suggesting a repeated activation of a sub horizontal crack located 300 m beneath the summit crater lakes based on these results we propose a model of the source process of lp seismicity in which a gradual buildup of steam pressure in a hydrothermal crack in response to magmatic heat causes repeated discharges of steam from the crack the rapid discharge of fluid causes the collapse of the fluid filled crack and excites acoustic oscillations of the crack which produce the characteristic waveforms observed in the lp events the presence of a single force synchronous with the collapse of the crack is interpreted as the release of gravitational energy that occurs as the slug of steam ejected from the crack ascends toward the surface and is replaced by cooler water flowing downward in a fluid filled conduit linking the crack and the base of the crater lake

fast wavefield decomposition of volcano tectonic earthquakes into polarized p and s waves by independent component analysis abstract in the present work a new approach for the analysis of polarization of seismic signals is proposed the method is based on independent component analysis and allows the identification and separation of the basic sources which are naturally polarized into the vertical and horizontal planes the results from the case study of a swarm of volcano tectonic earthquakes occurred at campi flegrei in october 2015 are impressive a clear separation of the p and s wave seismic phases in the time domain is obtained in addition the efficiency of the method in retrieving the polarization parameters is demonstrated by the comparison with other standard techniques the presented approach provides wavefield decomposition and polarization analysis in a single step thus avoiding a priori cumbersome filtering procedures and segmentation of the signals it is useful for discriminating and analysing different seismic phases and can be applied to a variety of volcanic and tectonic signals therefore it can strongly support all the studies on propagation and source mechanism moreover due to its fastness and robustness this stand alone tool can be routinely used in the volcano monitoring practice

inferences on the source of long period seismicity at campi flegrei from polarization analysis and reconstruction of the asymptotic dynamics in the present paper we analyse long period lp events and seismic noise recorded at campi flegrei during the uplift episode of 2004 2006 the results of a detailed polarization analysis indicate that the large number of lps detected during the seismic crisis were accompanied by a sustained activity consisting of very low energy volcanic signals these weak volcanic signals which are usually absent in ambient noise recorded in the studied area and lp events have similar properties namely they are radially polarized towards the same lp source the large dataset analysed allows us to study the statistics of the polarization leading to the extraction of the average properties of the volcanic signals an estimate of the complexity of the system can be provided by the degrees of freedom necessary to describe the asymptotic dynamics in a reconstructed phase space this analysis shows that both lps and low energy signals can be described by a low dimensional dynamical system while ambient noise unrelated to volcanic activity is higher dimensional based on these observations we interpret the phenomena observed during the seismic crisis in the framework of the theory of self oscillating systems in which lps and low energy signals represent self oscillations generated by a persistent hydrothermal source

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

the restless resurgent campi flegrei nested caldera italy constraints on its evolution and configuration abstract we have collected new stratigraphic data in the campi flegrei caldera through surface geological mapping and study of cores drilled to various depths we integrate these data with geological geochronological and geophysical constraints available in the literature to reconstruct the volcanic and deformational history of the caldera the caldera is a resurgent nested structure resulting from two main collapses related to the campanian ignimbrite 37 ka and the neapolitan yellow tuff 12 ka eruptions while the structure is affected by a broad subsidence ongoing local resurgence and unrest occur inside the younger nested caldera structure although most of the caldera floor consists of multiple structural blocks due to long term deformations magmas were able to erupt only in one sector of the resurgent part the caldera has shown signs of unrest during the past 25 years with short term deformations that have generated a net uplift of 3 5 m the short term deformations are related to the neapolitan yellow tuff caldera resurgence and interpreted as the net result of brittle and ductile components the long term deformations likely represent the sum of the permanent brittle component of each short term deformational event

wavefield properties of a shallow long period event and tremor at kilauea volcano hawaii the wavefields of tremor and a long period lp event associated with the ongoing eruptive activity at kilauea volcano hawaii are investigated using a combination of dense small aperture 300 m and sparse large aperture 5 km arrays deployed in the vicinity of the summit caldera measurements of azimuth and slowness for tremor recorded on the small aperture array indicate a bimodal nature of the observed wavefield at frequencies below 2 hz the wavefield is dominated by body waves impinging the array with steep incidence these arrivals are attributed to the oceanic microseismic noise in the 2 6 hz band the wavefield is dominated by waves propagating from sources located at shallow depths 1 km beneath the eastern edge of the halemaumau pit crater the hypocenter of the lp event determined from frequency slowness analyses combined with phase picks appears to be located close to the source of tremor but at a shallower depth 0 1 km the wavefields of tremor and lp event are characterized by a complex composition of body and surface waves whose propagation and polarization properties are strongly affected by topographic and structural features in the summit caldera region analyses of the directional properties of the wavefield in the 2 6 hz band point to the directions of main scattering sources which are consistent with pronounced velocity contrasts imaged in a high resolution three dimensional velocity model of the caldera region the frequency and q of the dominant peak observed in the spectra of the lp event may be explained as the dominant oscillation mode of a crack with scale length 20 100 m and aperture of a few centimeters filled with bubbly water the mechanism driving the shallow tremor appears to he consistent with a sustained excitation originating in the oscillations of a bubble cloud resulting from vesiculation and degassing in the magma

slab segmentation and late cenozoic disruption of the hellenic arc the hellenic subduction zone displays well defined temporal and spatial variations in subduction rate and offers an excellent natural laboratory for studying the interaction among slab buoyancy subduction rate and tectonic deformation in space the active hellenic subduction front is dextrally offset by 100 120 km across the kephalonia transform zone coinciding with the junction of a slowly subducting adriatic continental lithosphere in the north 5 10 mm yr and a rapidly subducting ionian oceanic lithosphere in the south 35 mm yr subduction rates can be shown to have decreased from late eocene time onward reaching 5 12 mm yr by late miocene time before increasing again along the southern portion of the subduction system geodynamic modeling demonstrates that the differing rates of subduction and the resultant trench offset arise naturally from subduction of oceanic pindos lithosphere until late eocene time followed by subduction of a broad tract of continental or transitional lithosphere hellenic external carbonate platform and then by miocene entry of high density oceanic ionian lithosphere into the southern hellenic trench model results yield an initiation age for the kephalonia transform of 6 8 ma in good agreement with observations consistency between geodynamic model results and geologic observations suggest that the middle miocene and younger deformation of the hellenic upper plate including formation of the central hellenic shear zone can be quantitatively understood as the result of spatial variations in the buoyancy of the subducting slab using this assumption we make late eocene middle miocene and pliocene reconstructions of the hellenic system that include quantitative constraints from subduction modeling and geologic constraints on the timing and mode of upper plate deformation

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

volcanic tremors at etna a model for hydraulic origin spectral analysis of volcanic tremors at etna reveals 2 characteristic features 1 the escaping vapor and gas streams drive the magma in random turbulent motion generating a seismic wave emission according toa f n exp m f k wherea amplitude f frequency n m k parameters 2 sudden transients in the boundary conditions of the piping system generate hydraulic pressure pulses which in the seismogram appear as wave packages their monochromatic frequency content suggests that their origin is associated with strong resonance phenomena it is conclusive that volcanic eruptions may be distinguished and classified according to different eigenfrequencies of the fissure and pipe network involved in the volcanic activity furthermore positions of active dykes may be traced following the amplitude distributions associated with pronounced spectral lines in the tremor spectra

ambrym vanuatu july august 2000 spectral and dynamical transitions on the hours to days timescale abstract ambrym is a large basaltic volcano with a 12 km wide 1900 year old caldera located in the vanuatu archipelago formerly known as new hebrides two cones are currently active in the caldera marum and benbow each with several active vents that hosted visible lava lakes until 1999 on 26 november 1999 an earthquake m w 7 5 located near the northern part of the island caused important changes to the vent morphology during july 2000 we installed a short period seismic station on the eastern rim of benbow crater in the western side of the caldera the station acquired continuous data for about 1 month during this period volcanic tremor was permanently recorded together with discrete events in this paper first results from these data are discussed focusing attention on the existence of significant transitions in the long term volcano dynamics studied both with spectrally derived dominant and average frequencies and more properly dynamical embedding dimensions and delay time parameters during the observation period on 9 august 2000 another significant earthquake was recorded m b 6 3 about 65 km north of the volcano the influence of this and other regional tectonic events on the volcano dynamics are discussed

the whisper of the hydrothermal seismic noise at ischia island abstract this work is devoted to the study of the background seismic noise at ischia island we highlight two persistent independent signals with dominant frequency peaks in the range 1 2 hz and 3 4 hz respectively the first signal is the most energetic and persistent and its polarization properties are well defined revealing a shallow propagation likely controlled by both tectonic volcanic structures and morphological features this signal is well correlated at all the stations in the casamicciola area and its group velocity is estimated as 500 600 m s the second signal shows similar polarization properties but the temporal pattern of its amplitude is strongly affected by anthropogenic noise revealing a modulation on a diurnal scale on the investigated spatial scales any clearly correlated signal is not evidenced we interpret the 1 2 hz correlated wave packets as the persistent whisper of the shallow circulation of fluids which are a mixing of sea and meteoric water and thermal fluids of the hydrothermal reservoir in the conceptual scheme of the self sustained musical instruments we hypothesize that the solid structure of the shallow hydrothermal system of ischia is formed by a network of channels continuously excited by the circulating hydrothermal fluids which produce a whispered sound i e the seismic noise this mechanism is able to produce persistent self sustained oscillations that we observe as the 1 2 hz seismic signal and eventually higher modes

the 2003 lefkada earthquake field observations and preliminary microzonation map based on liquefaction potential index for the town of lefkada abstract a strong earthquake mw 6 2 occurred offshore the island of lefkada or lefkas on august 14 2003 the maximum intensity has been evaluated io viii ems at lefkada municipality while vi to vii intensities were evaluated at many other villages of the island the offshore nne ssw oriented strike slip right lateral fault was activated by the main shock this fault is the northern termination of the cephalonia transform fault the most characteristic macroseismic effects were extensive typical ground failures like rock falls soil liquefactions subsidence densification ground cracks and landslides these macroseismic effects are remarkably similar to those reported from some historical lefkada shocks e g 1704 1914 ms 6 3 and 1948 ms 6 5 sand boils and ground fissures with ejection of mud were observed at the seaside of the town of lefkada and in the villages of nydri and vassiliki in situ soil profiles are obtained based mainly on borings after the earthquake boreholes records with spt values standard penetration test are obtained and the simplified procedure originally developed by seed and idriss was employed to evaluate the liquefaction resistance of soils the results indicated that the silty sandy layer which lies beneath the artificial fill in the coastal zone in lefkada town had liquefied during the 14 august earthquake an attempt was also made to establish a preliminary microzonation map for lefkada town using the data from liquefaction potential index analyses our map was validated by the occurrence of liquefaction phenomena inside the town

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

synchronization between tides and sustained oscillations of the hydrothermal system of campi flegrei italy 1 long continuous seismic data recorded at five broadband seismic stations during 2006 at campi flegrei caldera have been analyzed introducing a coarse grained method we evaluate the time evolution of amplitude and polarization of the seismic noise in the frequency band common to long period events the series are modulated on tidal time scales the root mean square is basically dominated by solar contribution while the azimuth of the polarization vector shows lunar diurnal and semidiurnal constituents in addition we find that in the frequency band common to long period events the azimuths are polarized toward a specific area suggesting that these persistent oscillations can be induced by the activity of the shallow geothermal reservoir

evidence for ground motion polarization on fault zones of mount etna volcano 1 during local and regional earthquakes an evident amplification of horizontal ground motion is observed at two seismological stations near the tremestieri fault on the southeastern flank of mount etna volcano rotated component spectral ratios show a narrow spectral peak around 4 hz along a n40 e direction a conventional polarization analysis using the eigenvectors of the covariance matrix confirms the very stable directional effect enhancing the approximately ne sw elongation of the horizontal ground motion in the fault zone the effect is evident during the entire seismogram and independent of source back azimuth as well as distance and depth of earthquakes the same polarization is observed in ambient noise as well this consistency allowed us to use microtremors for checking ground motion polarization along and across the tremestieri fault zone with a high spatial resolution the result is a stable polarization of horizontal motion in the entire area that can be observed in a broad frequency band to check whether this ground motion property is recurrent and to understand a possible relationship with fault strike faulting style or orientation of fractures ambient noise was recorded on other mapped faults of the mount etna area the moscarello acicatena and pernicana faults the latter in particular is characterized by different strike and faulting style a systematic tendency of ambient noise to be polarized is found in all of the faults a picture emerges where normal faults of the eastern flank show an e w to ne sw polarization that changes on the pernicana fault which develops approximately e w and is characterized by a prevailing nw se to n s polarization directions of polarization were never parallel to the fault strike moreover polarization persists too far away from the fault trace excluding an effect limited to a narrow low velocity zone hosted between harder wall rocks both these observations rule out an interpretation in terms of fault trapped waves the cause of observed polarizations will be the subject of future studies however the consistency with recent results of velocity anisotropy in a part of the investigated area suggests a possible role of attenuation anisotropy on horizontal amplitude variations versus azimuth

identification of soil redistribution using 137cs for characterizing landslide prone areas a case study in sarno quindici italy debris flows are among the most hazardous and unpredictable processes whose hazard evaluation requires an understanding of the processes that govern sediment supply sediment bulking flow volume and deposition in line with this challenge we estimate the net soil redistribution rates in an area characterized by recurrent instability phenomena using 137cs as a tracer for monitoring soil dynamics an extension of this method by applying it to the case of major landslides is addressed specifically surveys of soil 137cs content at sites in the pizzo d alvano massif italy where a set of particularly damaging landslides occurred on 5 6 may 1998 are reported being this region prone to debris flows two zero order basins are examined one of which experienced a landslide event in that basin deposition is observed whereas the other shows a net loss of soil these results appear to be relevant particularly because the rate of hollow filling could be correlated with the magnitude and or frequency of debris flow occurrence or with some measure of the hazard presented by individual gullies