the shallow magma chamber of stromboli volcano italy in this work we integrate artificial and natural seismic sources data to obtain high resolution images of the shallow inner structure of stromboli volcano overall we used a total of 21 953 p readings from an active seismic experiment and an additional 2731 p and 992 s readings deriving from 269 local events the well defined vp vs and vp vs tomograms have highlighted the following i the region where magma cumulates at shallow depths 2 4 km below sea level bsl forming an elongated ne sw high velocity body vp 6 0 km s and vs 3 5 km s with a very fast velocity core 6 5 vp 7 0 km s of 2 km3 ii the presence of some near vertical pipe like structures characterized by relatively high p velocities values mainly linked to past activity e g strombolicchio and iii a near vertical pipe like volume with high vp vs 1 78 1 85 located beneath to the craters down to 1 0 km bsl overlying a deeper region 1 0 to 3 0 km bsl with low vp vs 1 64 1 69 interpreted as the actual and preferential pathway of magma toward the surface our results demonstrate the importance of combining passive and active seismic data to improve in a tomographic inversion the resolution of the volcanic structures and to discover where magma may be stored

seismic features of the june 1999 tectonic swarm in the stromboli volcano region italy abstract crustal tectonic seismicity in the southern tyrrhenian sea is characterized by the high occurrence rates of earthquakes to the west of the alignment of salina lipari and vulcano islands in the aeolian archipelago only a few earthquakes affect the crustal region east of these islands whereas intermediate and deep seismicity plays a relevant role based on this evidence two aspects of the seismic swarm recorded at the aeolian island seismic network between june 6 and 17 1999 looked anomalous the first aspect concerned the number of earthquakes 78 that affected the stromboli submarine edifice in a short time interval secondly despite the low maximum magnitude md 3 2 reached the cumulative strain release was conspicuous in comparison with previous swarms in this region we localized the swarm about 6 km northeast of stromboli at a depth between 8 and 12 km the source region was identified using standard methods of hypocentral location as well as azimuth analysis it is worth noting that the volcanic activity at stromboli did not change significantly during the swarm nor throughout the following months therefore the seismic swarm had no link with volcanic activity observed at the surface most of the earthquakes shared similar waveform and frequency content and can be divided into families we identified some earthquakes with magnitude up to md 3 having relatively low frequency content at different seismic stations this anomalous feature leads us to hypothesize the presence of fluid circulation and or propagation of seismic waves in a ductile medium our hypothesis is in agreement with studies on marine geology which highlight various forms of submarine volcanism in the southern basin of the tyrrhenian sea

quantitative application of poststack acoustic impedance inversion to subsalt reservoir development the cost and complexity of deep water subsalt development wells is so great that a very limited spatial sampling of the target reservoir is achievable with well data thus the quantitative use of seismic data becomes of paramount importance poststack seismic amplitude inversion and poststack seismic attribute analysis and modeling are frequently employed to perform quantitative prediction of reservoir properties from surface seismic data several authors have shown that both absolute and relative acoustic impedance aai and rai respectively derived from poststack seismic amplitude inversion can be useful for quantitative estimates of summary reservoir properties such as average porosity net to gross and others this includes suprasalt and minibasin clastic reservoirs typically encountered in the middle and lower tertiary plays in the deep water gulf of mexico several of which are also encountered subsalt where depth to target can exceed 9000 m and highest frequencies at target are often rather l

a co2 rich gas trigger of explosive paroxysms at stromboli basaltic volcano italy in addition to rhythmic slug driven strombolian activity stromboli volcano occasionally produces discrete explosive paroxysms 2 per year on average for the most frequent ones that constitute a major hazard and whose origin remains poorly elucidated partial extrusion of the volatile rich feeding basalt as aphyric pumice during these events has led to consider their triggering by the fast ascent of primitive magma blobs from possibly great depth here i examine and discuss the alternative hypothesis that most of the paroxysms could be triggered and driven by the fast upraise of co2 rich gas pockets generated by bubble foam growth and collapse in the sub volcano plumbing system data for the so2 and co2 crater plume emissions are used to show that stromboli s feeding magma may originally contain as much as 2 wt of carbon dioxide and early coexists with an abundant co2 rich gas phase with high co2 so2 molar ratio 60 at 10 km depth below the vents compared to 7 in time averaged crater emissions pressure related modelling indicates that the time averaged crater gas composition and output are well accounted for by closed system decompression of the basalt gas mixture until the volcano crust interface 3 km depth followed by open degassing and crystallization in the volcano conduits however both the low viscosity and high vesicularity of the basaltic magma permit bubble segregation and bubble foam growth at deep sill like feeder discontinuities and at shallower physical boundaries such as the volcano crust interface where the gas rich aphyric basalt interacts with the unerupted crystal rich and viscous magma drained back from the volcano conduits gas pressure build up and bubble foam collapse at these boundaries will intermittently trigger the sudden upraise of co2 rich gas blobs that constitute the main driving force of the paroxysms deeper sourced gas blobs driving the most powerful explosions will be the richest in co2 and have highest co2 so2 ratios this mechanism is shown to account well for the dynamic seismic and petrologic features of stromboli s paroxysms and hence to provide a potential alternative interpretation for their genesis and their forecasting enhanced bubble foam leakage prior to a paroxysm or foam emptying in several steps should lead indeed to precursory upstream of co2 rich gas and increasing co2 so2 ratio in crater plume emissions the recent detection of such signals prior to two explosions in december 2006 and march 2007 strongly supports this expectation and the model proposed in this study

magma dynamics during the 2007 stromboli eruption aeolian islands italy mineralogical geochemical and isotopic data abstract after the 6 month long effusive event of 2002 2003 a new lava effusion occurred at stromboli between 27 february and 2 april 2007 despite the different durations approximately the same volume of magma was emitted in both eruptions in the order of 107 m3 a paroxysmal eruption occurred at the summit craters in both the 2002 2003 and 2007 episodes during which a significant amount of low porphyritic lp volatile rich magma was erupted in both cases the paroxysm did not interrupt the lava emission here we present compositional data including texture mineralogy chemistry and sr and nd isotope ratios of bulk rock groundmass and separated minerals of lavas erupted in 2007 together with chemistry and sr and nd isotope composition of the pumices emitted during the 15 march paroxysm as a whole the lavas have the same texture and chemistry that characterize the highly porphyritic hp products usually erupted at stromboli during normal strombolian activity and effusive events compared to the previous hp products the 2007 lavas show minor but systematic mineralogical and isotopic variations which are consistent with a modest increase of the magma supply rate of the volcano compositional variations during the entire duration of the event are very modest glass chemistry changes in lavas erupted in the second half of march can be explained by the minor mixing between the volatile rich lp magma rising through the shallow magmatic system during the 15 march paroxysm and the degassed residing hp magma a first conclusion of this study is that there is no compositional evidence supporting major changes in the magma dynamics of the volcano accompanying the effusive activity as also suggested for the 2002 2003 event the activity of stromboli is controlled by a steady state feeding system in which refilling mixing degassing and crystallization at shallow level continuously operate with modest oscillations in the magma supply rate switching between normal strombolian and effusive activity is related to periods of relatively more vigorous refilling of the shallow system leading to progressive pressure increase in the upper conduits associated with only minor compositional variations in the erupted products

insights into the dynamic processes of the 2007 stromboli eruption and possible meteorological influences on the magmatic system 1 the unrest of stromboli volcano leading to the february 27 april 2 2007 eruptive period and to the march 15 paroxysm is constrained by combining broad band seismic data and 1 hz gps high rate gps hereinafter hrgps measurements during the pre eruptive stage the simultaneous examination of seismic and hrgps data together with weather parameters suggests the possible influence of external perturbations on the magmatic system which evolved toward a critical state after january 2007 some days after the onset of the eruption a sudden change of the seismic and eruptive behaviour was recognized while ground deformation began to show a deflation the march 15 paroxysm was preceded about two days before by a peak of the hrgps spectral power densities a small inflation and by the occurrence of a few vt earthquakes located at depths down to 3 5 km b s l these findings constrain for the first time at stromboli volcano the deep origin of a fast rising magma batch rich in gas that led to a strong explosive event

on the time scale of thermal cycles associated with open vent degassing thermal imagery obtained with portable infrared cameras is widely used to track and measure volcanic phenomena in the case of explosive eruptions both air and ground based thermal monitoring have enabled collection of data streams from relatively safe distances analysis of these data have enabled the characterisation of different explosive regimes parameterisation of eruptive plumes and assessment on the dynamics occurring in the shallow system here we explore the suitability of infrared imagers for investigating the short time scale eruptive behaviour of three basaltic volcanoes we present high time resolution thermal image data sets recorded at etna stromboli and k lauea volcano at the time of observations all three exhibited pulsed degassing signal processing of the mean apparent temperature time series highlights four broad classes of cyclic temperature changes at the three volcanoes based on characteristic time scales revealed in the periodograms 1 15 s 2 20 50 s 3 1 10 min and 4 12 90 min based on previous studies and integrating time series results with qualitative visible and thermal observations and in case of k lauea also with so2 column amounts in the plume we hypothesise that short cycles relate mainly to bursting of overpressured gas bubbles at the magma surface while long cycles might be associated with mechanisms of gas slug formation and ascent and to the emplacement and drainage of a lava lake at k lauea slow fluctuations may reflect periodic variations of the lava lake surface level the data from all three volcanoes reveal superimposition of degassing cycles of different frequencies suggesting link through common magmatic processes and physical properties

radon surveys and real time monitoring at stromboli volcano influence of soil temperature atmospheric pressure and tidal forces on 222rn degassing abstract we used a network of stations to perform systematic radon surveys at stromboli volcano the time series of periodic measurements show that monthly average 222rn emissions reflect changes in volcanic activity and exhibit increasing trends prior and during the last major eruptive cycles maps of radon emissions indicate that diffuse degassing is operative at stromboli volcano concentrated degassing essentially occurs in the summit area and within a sector proximal to the two major ne trending faults these sites were chosen for deploying the two real time stations that are currently operating at stromboli in these devices the 222rn electronic dosimeters are connected to a radiomodem for wireless data transfer to a receiving station at the volcano observatory radon activity soil temperature and atmospheric pressure data are sampled and instantaneously transferred via web so that they can be checked remotely collected time series reveal an overall inverse correlation between radon emissions and seasonal temperature variations radon emissions in sectors of diffuse degassing are modulated by tidal forces as well radon activities recorded at the summit station located along the fracture zone where the gas flux is concentrated are positively correlated with changes in atmospheric pressure and confirm the occurrence of the atmospheric stack effect we finally emphasize that real time radon monitoring is an innovative technique that may be systematically applied in volcano surveillance

statistical analysis of the volcano seismicity during the 2007 crisis of stromboli italy 1 we analyze the volcano seismicity recorded during the pre and co eruptive regimes of the 2007 effusive crisis at stromboli volcano italy data set is composed of the continuous recordings of a three component broad band seismometer and of a sacks evertson strainmeter starting from the characterization of the non effusive phase as a stationary state of equilibrium we investigate the effusive phase as a non equilibrium state a statistical analysis reveals that the explosion occurrence is always driven by a nearly poissonian process as for the standard activity even during the effusive phase with the only difference in shortening the inter times explosion quake amplitudes are lognormally distributed until the effusive phase becoming then broader this indicates that many scales are involved a slightly different process can be advocated for the swarms of the explosions occurring during the effusive phase this suggests that the dynamics of the exsolution and or aggregation of the gas slugs should differ from the nucleation mechanism responsible of the standard strombolian activity the pre eruptive regime is characterized by a very long deformative signal that appears as a transient oscillating signal with a period of about three days that modulates the explosion amplitudes in a conceptual vibrating cavities model it is related to a chocking phenomenon induced by magma injection which in turn leads to the effusion

review of the evolution of geochemical monitoring networks and methodologies applied to the volcanoes of the aeolian arc italy abstract fluids discharged from volcanic systems are the direct surface manifestation of magma degassing at depth and provide primary insights for evaluating the state of volcanic activity we review the geochemical best practice in volcanic surveillance based to a huge amount of monitoring data collected at different active volcanoes using both continuous and discontinuous approaches the targeted volcanoes belong to the aeolian arc located in the tyrrhenian sea italy and they have exhibited different activity states during the monitoring activities reported here la fossa cone on vulcano island has been in an uninterrupted quiescent stage characterized by variable solfataric activity in contrast stromboli island has shown a persistent mild explosive activity episodically interrupted by effusive eruptions in 1985 2002 2007 and 2014 panarea island which is the summit of a seamount rising from the seafloor of the southern tyrrhenian sea showed only undersea fluid release the only observable clues of active volcanism at panarea island have been impulsive changes in the undersea fluid release with the last submarine gas burst event being observed in november 2002 the geochemical monitoring and observations at each of these volcanoes has directly involved the volcanic plume and or the fumarole vents thermal waters and diffuse soil degassing depending on the type of manifestations and the level of activity encountered through direct access to the magmatic samples when possible and the collection of as much observable data related to the fluid release as possible the aim has been i to verify the thermodynamic equilibrium condition ii to discern among the possible hydrothermal magmatic marine and meteoric sources in the fluid mixtures iii to develop models of the fluid circulation supported by data iv to follow the evolution of these natural systems by long term monitoring and v to support surveillance actions related to defining the volcanic risk and the evaluation and possible mitigation of related hazards the examples provided in this review article show the close relationships among data analysis interpretation and modeling we particularly focus on describing the fieldwork procedures since any theoretical approach must always be verified and supported by field data rather than just by experiments controlled in laboratory indeed the natural systems involve many variables producing effects that cannot be neglected the monitored volcanic systems have been regarded as natural laboratories and all of the activities have focused on both volcanological research and surveillance purposes in order to ensure that these two goals have overlapped an appendix is also included that explains the scientific approach to the systematic activities regarding geochemical monitoring of volcanic activity

evidence of a partial melt zone beneath stromboli volcano italy from inversion of teleseismic receiver functions teleseismic body waves from broadband seismic stations are used to investigate the crustal and uppermost mantle structure of stromboli volcano through inversion of the receiver functions rfs first we computed rfs in the frequency domain using a multiple taper spectral correlation technique then the non linear neighbourhood algorithm was applied to estimate the seismic shear wave velocity of the crust and uppermost mantle and to define the main seismic velocity discontinuities the stability of the inversion solution was tested using a range of initial random seeds and model parameterizations a shallow moho present at depth of 14 8 km is evidence of a thinned crust beneath stromboli volcano however the most intriguing and innovative result is a low s velocity layer in the uppermost mantle below 32 km the low s velocity layer suggests a possible partial melt region associated with the volcanism as also recently supported by tomographic studies and petrological estimations

dynamics of magma mixing and degassing recorded in plagioclase at stromboli aeolian archipelago italy crystal rich materials scoriae and lava flows emitted during the 1985 2000 activity of stromboli were taken into consideration for systematic study of bulk rock matrix glass chemistry and in particular for the study of chemical and textural zoning of plagioclase the most abundant mineral phase over the considered time period bulk rock composition remained fairly constant in both major sio2 49 2 50 9 wt and k2o 1 96 2 18 wt and trace elements the quite constant chemistry of matrix glasses also indicates that the degree of crystallization of magma was maintained at around 50 vol plagioclase ranges in composition between an62 and an88 and is characterized by alternating 10 100 m thick bytownitic and labradoritic concentric layers although the dominant and representative plagioclase of scoriae is an68 the labradoritic layers an62 70 show small scale 1 5 m oscillatory zoning are free of inclusions and appear to record episodes of slow crystal growth in equilibrium with a degassed liquid having the composition of the matrix glass in contrast the bytownitic layers an70 an88 are patchy zoned show sieve structure with abundant micrometric glass inclusions and voids and are attributed to rapid crystal growth

double difference tomography the method and its application to the hayward fault california we have developed a double difference dd seismic tomography method that makes use of both absolute and relative arrival times by reducing systematic errors using the more accurate relative arrival times the method produces an improved velocity model simultaneously it yields event locations of a quality equivalent to those of the dd location method while avoiding simplifying assumptions of that method we test this method on a synthetic dataset and find that it produces a more accurate velocity model and event locations than standard tomography we also test this method on a hayward fault california earthquake dataset spanning 1984 1998 the earthquakes relocated by this method collapse to a thin line along the fault trace consistent with previous results the dd velocity model has sharper velocity contrasts near the source region than the standard tomography model

stromboli 2007 eruption deflation modeling to infer shallow intermediate plumbing system 1 during the effusive phase of the stromboli 2007 eruption the gps and tilt stations recorded small but significant changes which for the first time at this volcano clearly indicated a deflation we modeled the deflation inferring a depressurizing vertically elongated source with centre under the volcano edifice about 2 8 km below sea level the model whose position is above the magma source region inferred by petrological studies and the associated rapid deflation suggest a near free pathway for magma ascent from this source to the upper shallow conduit

response of mount etna to dynamic stresses from distant earthquakes 1 influences of distant earthquakes on volcanic systems by dynamic stress transfer are well documented we analyzed seismic signals and volcanic activity at mount etna during two periods january 2006 and may 2008 that clearly showed variations coincident with distant earthquakes in the first period characterized by mild volcano activity the effect of the dynamic stress transfer caused by an earthquake in greece m 6 8 was twofold 1 banded tremor activity changed its features and almost disappeared 2 a swarm of volcano tectonic vt earthquakes took place the changes of the banded tremor were likely due to variations in rock permeability caused by fluid flows driven by dynamic strain the vt earthquake swarm probably developed as a secondary process promoted by the dynamically triggered activation of magmatic fluids the second period may 2008 showed an intense explosive activity during this interval the dynamic stress transfer associated with the arrival of the seismic waves of the sichuan earthquake m 7 9 affected the character of the seismo volcanic signals and on the following day triggered an eruption in particular we observed changes in volcanic tremor and increases of both occurrence rate and energy of long period events in this case we suggest that dynamic stress transfer caused nucleation of new bubbles in volatile rich magma bodies with consequent buildup of pressure highlighted by the increase of long period activity followed by the occurrence of an eruption we conclude that stresses from distant earthquakes are capable of modifying the state of the volcano

impact of environmental parameters on coral reef development and drowning forward modelling of the last deglacial reefs from tahiti french polynesia iodp expedition 310 the sedimentological and chronological analysis of the last deglacial reef sequences of tahiti french polynesia drilled during the integrated ocean drilling program expedition 310 provide a high resolution data set allowing a well constrained forward modelling study this study represents the first attempt to model in three dimensions the coral reef development of tahiti during the last deglacial sea level rise 23 000 to 6000 cal yr bp using the software dionisos developed by ifp energies nouvelles it allows the testing of the reconstructed last deglacial sea level curve and the different environmental parameters for example wave energy and sediment fluxes that could have influenced the reef development these last deglacial reef sequences form two prominent ridges occurring seaward of the living barrier reef that consist of successive submerged reefs these reefs have been prone to drowning because the window of maximum carbonate production rate is inhibited by high water turbidity sediment supply from a nearby river shallow depth of wave action and substrate availability these factors combined with rapid sea level rise have driven the growth of retrograding reef pinnacles local factors substratum nature sediment supply and wave energy were the main processes that induced the drowning of the inner ridge whereas interplay of local and global factors acceleration of the sea level rise was responsible for the drowning of the outer ridge this particular acceleration of sea level rise of 16 m between 14 6 ka and 14 ka bp corresponds to meltwater pulse 1a

the shallow plumbing system of stromboli island as imaged from 1 hz instantaneous gps positions 1 the stromboli volcano aeolian islands italy erupted suddenly on 28 december 2002 after a 17 year period of typically persistent but moderate eruptive activity followed two days later by a tsunamigenic landslide on its nw flank sciara del fuoco felt in the coastal areas of southern italy three continuous gps stations were quickly deployed near the volcano s rim sampling at 1 hz with instantaneous positions computed relative to a fourth station on its flank we report on two deformation episodes a vent migration on 16 17 february 2003 caused significant displacements at only one site and contributed to the decision not to issue a warning of an impending tsunamigenic landslide the second episode on 5 april 2003 a paroxystic explosion from the summit crater allowed us to model for the first time with geodetic data the shallow magma chambers that give rise to strombolian explosive activity

periodic behavior of soil co2 emissions in diffuse degassing areas of the azores archipelago application to seismovolcanic monitoring time series of soil co2 efflux recorded in the azores archipelago volcanic hydrothermal areas feature daily and seasonal variations the recorded co2 efflux values were lower during summer than in the winter season the diurnal co2 efflux values were higher at dawn and lower in the early afternoon contrary to that observed in biogenic environments co2 efflux cycles correlated well with the environmental variables such as air temperature wind speed and barometric pressure which also showed low and high frequency periodicities several simulations were performed here using the transport of unsaturated groundwater and heat 2 tough2 geothermal simulator to complement the study of rinaldi et al 2012 the effects of the water table depth air temperature perturbation amplitude and soil thermal gradient contributed to an explanation of the contrasts observed in the diurnal s1 and semidiurnal s2 soil co2 efflux peaks for the different monitoring sites and seasons filtering techniques multivariate regression analysis and fast fourier transform filters were also applied to the recorded time series to remove effects of external variables on the soil co2 efflux the resulting time series the residuals correspond to the best approach to the deep seated volcanic hydrothermal co2 emissions and thus should be used in seismovolcanic monitoring programs even if no evident correlation can be established yet between the soil co2 residuals and seismicity over the monitored time a seismic swarm that occurred around the end of 2008 might have triggered some deviations from the observed daily cycles

the 2007 eruption of stromboli volcano insights from real time measurement of the volcanic gas plume co2 so2 ratio abstract the recent eruption of stromboli in february april 2007 offered a unique chance to test our current understanding of processes driving the transition from ordinary persistent strombolian to effusive activity and the ability of instrumental geophysical and geochemical networks to interpret and predict these events here we report on the results of two years of in situ sensing of the co 2 so 2 ratio in stromboli s volcanic gas plume in the attempt to put constraints on the trigger mechanisms and dynamics of the eruption we show that large variations of the plume co 2 so 2 ratio range 0 9 26 preceded the onset of the eruption since december 2007 interrupting a period of relatively steady and low ratios time averaged ratio 4 3 lasting from at least may to november 2006 by contrasting our observations with numerical simulations of volcanic degassing at stromboli derived by use of an equilibrium saturation model we suggest that the pre eruptive increase of the ratio reflected an enhanced supply of deeply derived co 2 rich gas bubbles to the shallow plumbing system this larger than normal ascent of gas bubbles was likely sourced by a 1 3 km deep gas melt separation region probably a magma storage zone and caused faster convective overturning of magmas in the shallow conduit an increase in the explosive rate and in seismic tremor and finally the collapse of the la sciara del fuoco sector triggering the effusive phase the high co 2 so 2 ratios up to 21 observed during the effusive phase and particularly in the days and hours before a paroxysmal explosion on march 15 2007 indicate the persistence of the same gas source and suggest that de pressurization of the same 1 3 km deep magma storage zone could have been the trigger mechanism for the paroxysm itself

evidence of tectonic control on active arc volcanism the panarea stromboli tectonic link inferred by submarine hydrothermal vents monitoring aeolian arc italy 1 the combination of the latest geophysical instruments and geochemical methods applied to the arc volcanism aeolian islands italy has given new insights on the role of active tectonics on fluids migration a continuous monitoring of the hydrothermal system off the island of panarea has shown contemporaneous modifications of the vented fluids and the seismic activity of the nearby stromboli volcano the almost contemporary start of the last volcanic crisis at panarea and stromboli in 2002 besides the contemporary variation of the 3 he 4 he ratios at both the islands and the large number of submarine crater shaped structures at panarea bears testimony to interconnections between the volcanic edifices to confirm a tectonic drive of magmatic fluids over volcanic arcs implies that episodes of volcanic unrest can be triggered by the tectonic activity increasing the volcanic risk for the whole area and this might be the case of the stromboli panarea volcanic complex

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

evidence of a dyke sheet intrusion at stromboli volcano inferred through continuous tilt a tiltmeter installed in the northern sector of the island of stromboli aeolian archipelago tyrrhenian sea recorded a co seismic offset at the time of the main shock ml 3 7 of the 7 november 1994 swarm located 5 km north of the island during the three months following this event a transient tilt anomaly which was interpreted as due to a lateral intrusion and modelled through a dyke sheet dislocation was recorded the tilt data were used in an analytical inversion based on a propagating tensile source with length and width increasing in time the final result is consistent with the tectonic and structural framework of the volcano area

volcano monitoring using gps developing data analysis strategies based on the june 2007 kīlauea volcano intrusion and eruption 1 the global positioning system gps is one of the most common techniques and the current state of the art used to monitor volcano deformation in addition to slow several centimeters per year displacement rates gps can be used to study eruptions and intrusions that result in much larger tens of centimeters over hours days displacements it is challenging to resolve precise positions using gps at subdaily time intervals because of error sources such as multipath and atmospheric refraction in this paper the impact of errors due to multipath and atmospheric refraction at subdaily periods is examined using data from the gps network on k lauea volcano hawai i methods for filtering position estimates to enhance precision are both simulated and tested on data collected during the june 2007 intrusion and eruption comparisons with tiltmeter records show that gps instruments can precisely recover the timing of the activity

magma dynamics of 2007 stromboli effusive eruption as revealed by high precision location of seismic events stromboli is considered one of the most active volcanoes in the world and its persistent but moderate explosive activity is only interrupted by occasional episodes of more vigorous activity accompanied by lava flows a new effusive eruption began in late february 2007 and was characterized by intense seismic activity throughout the whole period the accurate seismic signals analysis showed the presence of families of events with similar waveform signatures i e multiplets located beneath the crater region since traditional location techniques do not allow obtaining reliable hypocenters our analysis focused on high precision locations of the seismicity in order to better define the source geometry of the events hypocenters therefore have been relocated considering two steps the first based on a robust probabilistic approach is used to find the absolute position of the clusters and the second exploits a master event concept for the relative location of the events finally the shape of the clusters and the temporal migration of the foci were correlated with the eruptive phases the results show that the occurrence of a cluster of events is related to the opening and closure of a vent opened in the sciara del fuoco slope and in particular to the intrusion of a dike injected by central conduit in a radial direction whereas another cluster lies in a narrow vertical volume positioned under the crater area the geometry of the clusters suggests a source region depicting the shallower feeding system overall the results highlight that the high precision locations method is an efficient and quick tool to obtain a better understanding of the magmatic processes occurring during an ongoing eruption

some dynamical characteristics of microseism time series summary microseism time series are non stationary non linear and stochastic and these characteristics can be reproduced by a forced non linear damped oscillator in the present study we show that such an oscillator is also able to explain other widely observed features such as the variation for a given seismic station of the frequency of the secondary peak the variation of the frequency of the primary peak for different seismic stations relative to the same source the variations of amplitude of the power spectrum for stormy days with respect to quiet days and the incoherent propagation of microseisms numerical simulations with the proposed phenomenological model suggest i that the main spectral peak may be due to a competitive process between the resonant response of the medium and an external harmonic force longuet higgins model ii that the secondary peak may be generated by the process associated with the activity of the coastal waves or as a subharmonic of the resonant frequency and iii that the large amplitude variations between quiet and stormy days refers in fact to variations in the source storm distance from a general point of view we can say microseism activity can be interpreted as the resonant response of the earth to atmospheric cyclonic storms coupled with the oceans microseisms are worldwide phenomena usually understood as strong background noise temporally and spatially varying which strongly influences the detection of transient wave arrivals as described by aki richards 1980 two maxima of the power spectrum at about 0 07 hz the primary peak and 0 14 hz the secondary peak are typical features of almost all the recordings at seismic stations the primary peak is usually less intense than that the secondary one and as proposed first by wiechert in 1904 has been attributed to the direct impact of ocean waves on nearby coasts since it roughly coincides with the primary peak of ocean wave oscillations the most intensive peak was interpreted by longuethiggins 1950 as the result of fluctuations of pressure caused by standing waves along the seabed the existence of the two above mentioned peaks although the primary peak may be absent can be considered as a basic feature of seismic noise which may suffer some shift in the frequency location of the two peaks from place to place although preserving an approximate relation 2 1 and strong amplitude variations up to two orders of magnitude due either to the location of the seismic station in quiet or noise places or if in the same place to the presence or absence of storm waves at sea the above observations can be summarized by saying that the shape of the power spectrum is preserved