inflation deflation cycles revealed by tilt and seismic records at stromboli volcano 1 strombolian activity is driven by gas dynamic where large quantities of volatiles are first exsolved and then suddenly released ejecting fragmented lava at 100 300 m height with exit velocities of 20 70 m s this conduit process is detected as vlp seismicity only in the final stage 10 s before the explosion when the rising gas slug interacts with the shallower part last 200 300 m of the feeding conduits we present new ground deformation recorded with high resolution tiltmeters 1 nrad sampled at 1 hz and detected by broad band seismometers that extends the perception of this explosive process tiltmeters and seismometers reveal that the explosive process is accompanied by a persistent deformation of the ground detected as small 100 nrad inflation deflation cycles 250 s long and associated with the constant process of gas recharge and discharge of the magma conduit

a stratigraphic case history using three dimensional seismic data in the gulf of thailand a three dimensional marine seismic survey was conducted in the gulf of thailand to aid in the development of a gas field indicated by three wildcat wells the results and interpretation reported previously demonstrated improved fault resolution and better structural definition five successful appraisal wells have now been drilled and these show that most of the sands have limited extent widespread character changes in the seismic data also support stratigraphic variations in many of the sands several new methods of 3d stratigraphic interpretation have been developed while investigating the depositional history of this area anomalous seismic amplitudes tied to sands penetrated by wells and mapped from seiscroptm horizontal sections in time and depth have indicated the distribution of bars and channels horizon seiscrop sections each sliced through a single bed have been used to delineate these depositional features directly g logtm sections displaying seismic logs derived by rigorous wave equation inversion confirm the existence of these features sands greater than 10 m thick have proved mappable

source mechanism of vulcanian degassing at popocatepetl volcano mexico determined from waveform inversions of very long period signals 1 the source mechanism of very long period vlp signals accompanying volcanic degassing bursts at popocatepetl is analyzed in the 15 70 s band by minimizing the residual error between data and synthetics calculated for a point source embedded in a homogeneous medium the waveforms of two eruptions 23 april and 23 may 2000 representative of mild vulcanian activity are well reproduced by our inversion which takes into account volcano topography the source centroid is positioned 1500 m below the western perimeter of the summit crater and the modeled source is composed of a shallow dipping crack sill with easterly dip of 10 intersecting a steeply dipping crack northeast striking dike dipping 83 northwest whose surface extension bisects the vent both cracks undergo a similar sequence of inflation deflation and reinflation reflecting a cycle of pressurization depressurization and repressurization within a time interval of 3 5 min the largest moment release occurs in the sill showing a maximum volume change of 500 1000 m3 pressure drop of 3 5 mpa and amplitude of recovered pressure equal to 1 2 times the amplitude of the pressure drop in contrast the maximum volume change in the dike is less 200 300 m3 with a corresponding pressure drop of 1 2 mpa and pressure recovery equal to the pressure drop accompanying these volumetric sources are single force components with magnitudes of 108 n consistent with melt advection in response to pressure transients the source time histories of the volumetric components of the source indicate that significant mass movement starts within the sill and triggers a mass movement response in the dike within a few seconds such source behavior is consistent with the opening of a pathway for escape of pent up gases from slow pressurization of the sill driven by magma crystallization the opening of this pathway and associated rapid evacuation of volcanic gases induces the pressure drop pressure recovery in the magma filling the sill is driven by diffusion of gases from the resulting supersaturated melt into bubbles assuming a penny shaped crack at ambient pressure of 40 mpa the observed pressure and volume variations can be modeled with the following attributes crack radius 100 m crack aperture 5 m bubble number density 1010 1012 m 3 initial bubble radius 10 6 m final bubble radius 10 5 m and net decrease of gas concentration in the melt 0 01 wt

variability in eruption style and associated very long period events at fuego volcano guatemala 1 repeated short term deployments of seismic infrasound video and gas emission instruments at fuego volcano guatemala have revealed three types of very long period vlp events associated with conduit sealing pressure accumulation and release in 2008 ash rich explosions issued from a vent on the western flank and produced one type of vlp type 1 impulsive bomb rich explosions from the summit vent in 2009 produced a shorter period vlp type 2 but also generated ash release type 3 vlp events occurred during ash free exhalations from the summit in 2008 and had waveform shapes similar to type 2 events weak infrasound records for type 1 explosions compared to type 2 suggest lower pressures and higher magma porosity for type 1 type 3 events correlate with spikes in so2 emission rate and are driven by partial sealing and rapid release of ash free gas at the summit vent variations in the vlp period may provide a new tool for monitoring conditions within the conduit

explosive dome eruptions modulated by periodic gas driven inflation volcan santiaguito guatemala breathes with extraordinary regularity as the edifice s conduit system accumulates free gas which periodically vents to the atmosphere periodic pressurization controls explosion timing which nearly always occurs at peak inflation as detected with tiltmeters tilt cycles in january 2012 reveal regular 26 6 min inflation deflation cycles corresponding to at least 101 kg s of gas fluxing the system very long period vlp earthquakes presage explosions and occur during cycles when inflation rates are most rapid vlps locate 300 m below the vent and indicate mobilization of volatiles which ascend at 50 m s rapid gas ascent feeds pyroclast laden eruptions lasting several minutes and rising to 1 km vlps are not observed during less rapid inflation episodes instead gas vents passively through the conduit producing no infrasound and no explosion these observations intimate that steady gas exsolution and accumulation in shallow reservoirs may drive inflation cycles at open vent silicic volcanoes

tilt prior to explosions and the effect of topography on ultra long period seismic records at fuego volcano guatemala 1 ground tilt is measured from broadband seismic records prior to frequent explosions at fuego volcano guatemala we are able to resolve tilt beginning 20 30 minutes prior to explosions followed by a rapid reversal in deformation coincident with explosion onsets the tilt amplitude and polarity recorded on the horizontal channels vary from station to station such that the steep and unusual topography of the upper cone of fuego appears to affect the ultra long period signals we account for the effect of topography and attempt to constrain the tilt source depth and geometry through finite difference modeling the results indicate a shallow spherical pressure source and that topography must be considered when attempting to model tilt sources at volcanoes with steep topography the tilt signals are interpreted as pressurization of the shallow conduit beneath a crystallized plug followed by elastic deflation concurrent with explosive pressure release

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

temporal trends in lava dome extrusion at santiaguito 1922 2000 we present a means of extracting lava dome extrusion rates from data provided by the thematic mapper and enhanced thematic mapper plus instruments flown on the landsat satellites extrusion rates derived from the landsat data for santiaguito dome complex guatemala during november 1987 and january 2000 of 0 72 0 08 and 0 48 0 09 m3 s 1 compare favorably with ground based estimates of 0 63 0 28 and 0 48 0 17 m3 s 1 a satellite data derived set of 18 extrusion rate estimates between 1987 and 2000 along with ground based volume estimates prior to 1987 allow us to infer volumes of magma erupted since 1922 these data reveal cyclic extrusion at santiaguito each cycle begins with a 3 6 year long phase of high extrusion rate 0 5 2 1 m3 s 1 followed by a longer 3 11 years phase of low extrusion rate 0 2 m3 s 1 the 8th cycle began in 1996 and was still in its high extrusion rate phase during january 2000 with time however the durations of the low extrusion rate phases have increased peak extrusion and time averaged extrusion rates for each cycle have decreased and the difference between extrusion rates during the high and low extrusion rate phases of each cycle has decreased these trends may be the result of depressurization and exhaustion of the source in this case the current eruption may be expected to end around 2020 alternatively santiaguito may be entering a period of persistent activity maintained by a stable magma supply in this case we may expect extrusion to become less cyclic and to stabilize at 0 2 0 4 m3 s 1 however a 2 wt decrease in sio2 content of erupted products since 1970 appears to be consistent with chamber exhaustion as well as an increase in block lava flow lengths during 1970 2000

volcano tectonic earthquakes a new tool for estimating intrusive volumes and forecasting eruptions abstract we present data on 136 high frequency earthquakes and swarms termed volcano tectonic vt seismicity which preceded 111 eruptions at 83 volcanoes plus data on vt swarms that preceded intrusions at 21 other volcanoes we find that vt seismicity is usually the earliest reported seismic precursor for eruptions at volcanoes that have been dormant for decades or more and precedes eruptions of all magma types from basaltic to rhyolitic and all explosivities from vei 0 to ultraplinian vei 6 at such previously long dormant volcanoes because large eruptions occur most commonly during resumption of activity at long dormant volcanoes vt seismicity is an important precursor for the earth s most dangerous eruptions vt seismicity precedes all explosive eruptions of vei 5 and most if not all vei 4 eruptions in our data set surprisingly we find that the vt seismicity originates at distal locations on tectonic fault structures at distances of one or two to tens of kilometers laterally from the site of the eventual eruption and rarely if ever starts beneath the eruption site itself the distal vt swarms generally occur at depths almost equal to the horizontal distance of the swarm from the summit out to about 15 km distance beyond which hypocenter depths level out we summarize several important characteristics of this distal vt seismicity including swarm like nature onset days to years prior to the beginning of magmatic eruptions peaking of activity at the time of the initial eruption whether phreatic or magmatic and large non double couple component to focal mechanisms most importantly we show that the intruded magma volume can be simply estimated from the cumulative seismic moment of the vt seismicity from log10 v 0 77 log moment 5 32 with volume v in cubic meters and seismic moment in newton meters because the cumulative seismic moment can be approximated from the size of just the few largest events and is quite insensitive to precise locations the intruded magma volume can be quickly and easily estimated with few short period seismic stations notable cases in which distal vt events preceded eruptions at long dormant volcanoes include nevado del ruiz 1984 1985 pinatubo 1991 unzen 1989 1995 soufriere hills 1995 shishaldin 1989 1999 tacana 1985 1986 pacaya 1980 1984 rabaul 1994 and cotopaxi 2001 additional cases are recognized at frequently active volcanoes including popocateptl 2001 2003 and mauna loa 1984 we present four case studies pinatubo soufriere hills unzen and tacana in which we demonstrate the above mentioned vt characteristics prior to eruptions using regional data recorded by neic we recognized in near real time that a huge distal vt swarm was occurring deduced that a proportionately huge magmatic intrusion was taking place beneath the long dormant sulu range new britain island papua new guinea that it was likely to lead to eruptive activity and warned rabaul volcano observatory days before a phreatic eruption occurred this confirms the value of this technique for eruption forecasting we also present a counter example where we deduced that a vt swarm at volcan cosiguina nicaragua indicated a small intrusion insufficient to reach the surface and erupt finally we discuss limitations of the method and propose a mechanism by which this distal vt seismicity is triggered by magmatic intrusion

tilt change recorded by broadband seismometer prior to small phreatic explosion of meakan dake volcano hokkaido japan 1 we discovered an anomalous very long period vlp signal duration about 60 s in the broadband seismic record of the precursory swarm of a small phreatic explosion at the meakan dake volcano hokkaido japan in 2006 this signal was masked by a short period tremor in the original velocity waveform but a considerable dc step appeared in the displacement trace since such a step results from a tilt change we interpreted the observed trace as being a combination of rotational tilt and translational displacement motions the apparent displacement step in the vlp signal indicates subsidence of the summit crater owing to limited data we attempted deflating the mogi source and simulating the seismic record including both motions when only rotational motion is considered the simulated waveform explains well the general features of the observed trace however the combined trace has incompatible phases suggesting that a more complicated source process should be considered

introduction to aapg bulletin thematic issue on fault seals russell davies is the united states operations manager and consulting structural geologist for rock deformation research dallas texas he received a ph d in structural geology from texas a m university he has worked in the oil and gas industry for more than 10 years in exploration and production with shell and in research on topics including fault interpretation methods structural styles and seal analysis with arco jim handschy received a ph d in geology and geophysics from rice university he has worked in the oil and gas industry for 17 years on exploration development research and technology services projects for phillips petroleum shell oil and el paso natural gas he has experience in prospect development and evaluation complex structural interpretation and trap analysis from around the world he has served as team leader and project manager for various groups as chief geologist and is currently manager of global geology for upstream at conocophillips this volume of the aapg bulletin presents a review of the processes calibration and prediction of fault seal mechanisms and their capacity to support hydrocarbon columns geological seals are commonly low permeability rocks that retard the flow of hydrocarbons top seals for example are low permeability strata such as shales that overlie hydrocarbon reservoirs and stall the upward migration of hydrocarbons fault seals also trap hydrocarbons but by mechanisms that reduce the permeability along a fault mechanisms controlling fault seals in unlithified sediments have been identified primarily as 1 shale gouge or smear in the fault zone or 2 juxtaposition of reservoir against nonreservoir lithologies the low permeability lithology along the fault surface is the fault rock early studies of fault sealing mechanisms proposed that the smearing of clay rich layers such as shale along a fault plane created a lower permeability fault rock or seal between two reservoirs smith 1966 1980 weber et

fault slicing a new approach to the interpretation of fault detail the manner in which a fault intersects a hydrocarbon reservoir affects production characteristics and thus must be understood in great detail a 3 d seismic data volume can be sliced interactively to yield seismic sections parallel to a fault plane these fault slices can then be used in several ways for the study of faults tracking of correlative horizons on fault slices provides a map of fault throw and permits study of the throw as a function of vertical traveltime and horizontal position because a fault slice remains within one major fault block the study of growth relationships in that block is facilitated splinter faults which are also significant in development and production can be studied effectively on fault slices because of the uniform proximity of these sections to the parent fault we conclude that there is some uniformity in azimuth between splinter faults and their parent

an examination of the continuous wavelet transform for volcano seismic spectral analysis abstract volcanoes produce widely varying seismic signals due to the presence of complex and non linear physical processes the temporal distribution of seismicity at volcanoes ranges from individual transients to swarms of many small events and protracted volcanic tremor the spectral range of volcanic signals is unequivocally broadband with coincident high 20 hz and very low down to periods of hundreds of seconds frequency signals frequently observed at many volcanic systems as such interpretations of volcano seismic source and process require suitable characterisation in the time frequency t f domain the adoption of automated approaches to routine seismic processing at volcanoes also creates the need to evaluate how we suitably extract discriminatory features of interest from such diverse volcano seismic signals here we assess the performance of the continuous wavelet transform cwt for spectral representations of volcano seismic signals the localisation property of wavelet transforms gives the cwt a distinct advantage over commonly used moving window fourier transforms enabling it to capture sharp changes in signal and represent signals over a wide range of timescales examination of seismic data for typical volcano seismic phenomena such as volcano tectonic earthquakes vts shows that cwt scalograms have better t f resolution across broader frequency ranges than fourier transform spectrograms which suffer from greater spectral smearing in the time domain at higher frequencies the inherent log scale representation of cwt scalograms is also better suited for detection and representation of very long period vlp signals and for distinguishing volcanic signals from ambient microseismic noise when applied to seismic data from santiaguito volcano in guatemala cwt analysis reveals pre and syn eruptive signals across a wide range of frequency bands ranging from 600 s to 50 hz with ultra long period signals ulps 30 to 600 s detected on instruments up to 1 9 km from the active vent which is beyond the range of previously detected ulps at this volcanic system the cwt scalogram conveniently represents these simultaneous syn eruptive spectral features in a single plot which can aid exploratory analysis and inform source models furthermore the edge detection capabilities of the cwt accurately identify sharp changes in the raw signal over the vlp ulp frequency range 5 to 600 s thought to represent sudden deflation associated with eruption providing a useful tool for picking explosive eruptions the addition of an average wavelet energy distribution to cwt scalograms which reveals the average energy across the whole signal at each wavelet scale is also useful for characterising spectral content and identifying spectral peaks as its smooth appearance is easier to interpret than fft spectral amplitude plots we conclude that wavelet transform methods are underutilised in volcano seismology where their t f localisation properties would be particularly well suited and suggest potential applications in terms of automated event detection and classification

time scale wavelet patterns related to the 1998 1999 eruptions of the colima volcano and their possible implications for eruption forecasting the seismic activity from one of the most active documented periods of the colima volcano from october 1998 to july 1999 was analyzed using the wavelet transform to study the evolution in time of energy content at different scales of seismic signals preceding eruptive episodes time scale analysis shows seismic energy concentrations at particular scales preceding significant eruptions concentrations that do not appear within the same time frame for non eruptive stages quantification of the energy at each scale eases the recognition of characteristic wavelet patterns before the occurrence of significant effusive or explosive eruptions the recognition of precursory wavelet patterns which does not depend on the absolute level of energy release could help to objectively identify precursors to imminent explosive eruptions even in cases where other seismic energy based methods are not conclusive

mechanism of the 1996 97 non eruptive volcano tectonic earthquake swarm at iliamna volcano alaska a significant number of volcano tectonic vt earthquake swarms some of which are accompanied by ground deformation and or volcanic gas emissions do not culminate in an eruption these swarms are often thought to represent stalled intrusions of magma into the mid or shallow level crust real time assessment of the likelihood that a vt swarm will culminate in an eruption is one of the key challenges of volcano monitoring and retrospective analysis of non eruptive swarms provides an important framework for future assessments here we explore models for a non eruptive vt earthquake swarm located beneath iliamna volcano alaska in may 1996 june 1997 through calculation and inversion of fault plane solutions for swarm and background periods and through coulomb stress modeling of faulting types and hypocenter locations observed during the swarm through a comparison of models of deep and shallow intrusions to swarm observations we aim to test the hypothesis that the 1996 97 swarm represented a shallow intrusion or failed eruption observations of the 1996 97 swarm are found to be consistent with several scenarios including both shallow and deep intrusion most likely involving a relatively small volume of intruded magma and or a low degree of magma pressurization corresponding to a relatively low likelihood of eruption

non linear explosion tremor at sangay volcano ecuador a detailed analysis of discrete degassing pulses chugs at sangay volcano was performed on seismic and infrasonic records to determine the physics of the conduit infrasonic chugging signals appear as repetitive pulses with small variations in amplitude and time lag an automated time domain analysis was developed to measure with high precision time intervals and amplitudes at different wave arrivals reducing the possibility error associated with hand picking using this automated method a strong positive correlation of acoustic amplitude with repose time between individual pulses on chugging signals of sangay was found on numerous oscillating sequences frequency gliding of apparent harmonic frequencies generally trends from high to low frequency at sangay in contrast to trends at karymsky volcano russia a new description of chugging events using wavelet transform methods appropriate for non stationary signals shows subtle changes in the waveforms relate to physical processes in the volcano a system of non linear feedback based on choked flow at the vent is postulated as the most likely source of this volcanic tremor

localization of self potential sources in volcano electric effect with complex continuous wavelet transform and electrical tomography methods for an active volcano 1 this study concerns the fluid flow circulation associated with magmatic intrusion during volcanic eruptions from electrical tomography studies the objective is to localize and characterize the sources responsible for electrical disturbances during a time evolution survey between 1993 and 1999 of an active volcano the piton de la fournaise we have applied a dipolar probability tomography and a multi scale analysis on synthetic and experimental sp data we show the advantage of the complex continuous wavelet transform which allows to obtain directional information from the phase without a priori information on sources in both cases we point out a translation of potential sources through the upper depths during periods preceding a volcanic eruption around specific faults or structural features the set of parameters obtained vertical and horizontal localization multipolar degree and inclination could be taken into account as criteria to define volcanic precursors

evidence for dike emplacement beneath iliamna volcano alaska in 1996 two earthquake swarms comprising 88 and 2833 locatable events occurred beneath iliamna volcano alaska in may and august of 1996 swarm earthquakes ranged in magnitude from 0 9 to 3 3 increases in so2 and co2 emissions detected during the fall of 1996 were coincident with the second swarm no other physical changes were observed in or around the volcano during this time period no eruption occurred and seismicity and measured gas emissions have remained at background levels since mid 1997 earthquake hypocenters recorded during the swarms form a cluster in a previously aseismic volume of crust located to the south of iliamna s summit at a depth of 1 to 4 km below sea level this cluster is elongated to the nnw sse parallel to the trend of the summit and southern vents at iliamna and to the regional axis of maximum compressive stress determined through inversion of fault plane solutions for regional earthquakes fault plane solutions calculated for 24 swarm earthquakes located at the top of the new cluster suggest a heterogeneous stress field acting during the second swarm characterized by normal faulting and strike slip faulting with p axes parallel to the axis of regional maximum compressive stress the increase in earthquake rates the appearance of a new seismic volume and the elevated gas emissions at iliamna volcano indicate that new magma intruded beneath the volcano in 1996 the elongation of the 1996 1997 earthquake cluster parallel to the direction of regional maximum compressive stress and the accelerated occurrence of both normal and strike slip faulting in a small volume of crust at the top of the new seismic volume may be explained by the emplacement and inflation of a subvertical planar dike beneath the summit of iliamna and its southern satellite vents

akaso field nigeria use of integrated 3 d seismic fault slicing clay smearing and rft pressure data on fault trapping and dynamic leakage the akaso field stoiip 78 106 m3 401 million stb of the eastern niger delta is separated from the large cawthorne channel field stoiip 208 106 m3 1307 million stb by a major antithetic counterregional normal fault in 1989 three dimensional 3 d seismic data acquired and interpreted over the field revealed a subtle splinter or backsplit fault off this major antithetic fault west of the main akaso field behind this backsplit fault we observed stacked amplitude anomalies these anomalies extended to the structural spillpoint defined against the akaso backsplit fault fault slicing and clay smear studies of the backsplit and main antithetic fault indicated strong seal potential with possible leak windows along the fault planes in 1989 the sealing potentials of the western end of the akaso boundary fault were fully confirmed by a deviated appraisal well which found a stoiip of 29 106 m3 183 million stb in a series of stacked footwall closures the initial trapping potential of this major antithetic normal fault can be contrasted with its subsequent behavior during depletion by using rft data acquired in a series of development wells drilled in 1990 in the main akaso structure at the eastern end of the antithetic fault here major stacked columns of oil and gas are trapped and sealed by the antithetic fault but we identified evidence of subsequent leakage due to production effects from the adjacent cawthorne channel field depletion of the unproduced akaso g sands was found to be due to production from the juxtaposed e sands of the adjacent cawthorne channel field thus we inferred dynamic fault leakage we observed a dynamic pressure drop of 400 2144 kpa 58 311 psi between the juxtaposed akaso and cawthorne channel sand due to active crossflow the akaso field therefore represents a prime example of the trapping potential of a clay smeared fault and its subsequent leakage during differential depletion our observations methodology and implications described herein may have an important bearing on reservoir management philosophies in similar structural settings

ultra long period seismic signals and cyclic deflation coincident with eruptions at santiaguito volcano guatemala abstract broadband seismic observations made near the active vent at santiaguito provide constraints on changing pressures inside the edifice during january 2009 we recorded episodic ultra long period signals ulps 30 s that were coincident with eruptive activity centered on the active el caliente vent these signals lasted 2 5 min and corresponded to depressurization of a volume beneath the dome coincident shorter period seismic signals 0 5 hz appeared to be associated with shallow level pyroclastic emissions and dome surface motions these shorter period signals varied significantly from event to event unlike the ulp waveforms which were self similar as opposed to the short period signals which were recorded across the network the ulps were only recorded on the horizontal channels of 3 stations that were within 1 1 km of the vent this and other factors suggest that they were a result of long period rotational motion rather than horizontal translation ulp source locations derived from horizontal particle motions point to the northwestern part of el caliente 150 m from the vent axis the general locus of activity from 1967 until flank collapses in 1989 1990 we modeled the ulp signal as a mogi source and solved for three dimensional location and equivalent source strength through analysis of 78 events we identify a mean mogi source that is 200 m west of and 250 m beneath the centre of the vent with the peak volume changes accompanying eruptions ranging from 125 to 1825 m 3 these inferred volume losses coincide with the onset of gas venting and or explosive eruptions at the surface of caliente based upon these observations we develop a model to describe the pre eruptive eruptive and inter eruptive physical processes occurring at the surface and inside santiaguito

winter weather regimes in the northeast united states abstractthe method of k means cluster analysis is applied to u s wintertime daily 850 hpa winds across the northeast the resulting weather patterns are analyzed in terms of duration station gridded precipitation storm tracks and climate teleconnections five distinct weather patterns are identified weather type wt 1 is characterized by a ridge over the western atlantic and positive precipitation anomalies as far north as the great lakes wt2 by a trough along the eastern united states and positive precipitation anomalies into southern new england wt3 by a trough over the western atlantic and negative precipitation anomalies along much of the u s east coast wt4 by a trough east of newfoundland and negative precipitation anomalies along parts of the u s east coast and wt5 by a broad shallow trough over southeastern canada and negative precipitation anomalies over the entire u s east coast wt5 and wt1 are the most persistent while wt2 typically progresses quickly to wt3 and then to wt4

seismological insight into the kinematics of the 5 april 2003 vulcanian explosion at stromboli volcano southern italy 1 on 5 april 2003 at 07 13 gmt 09 13 local time a violent vulcanian explosion occurred at stromboli volcano at the time of the event an eruptive crisis was ongoing at the volcano with a lava flow outpouring along the sciara del fuoco flank the seismic signals related to the event were recorded by 8 permanent broadband stations and gives information about the eruption kinematics an ultra long period signal period 20 s that we interpret as the effect of the ground tilt on the broadband sensors starts about 4 min before and terminates about 1 min after the explosion on the basis of the radial pattern of tilt directions we conclude that this signal is the effect of the deformation of the volcanic edifice due to the rapid rising of a batch of magma its ejection and the magma column readjustment about 1 min before the explosion we observe an high frequency signal period 0 1 s that we believe to be related to the vesiculation of the rising batch of gas rich magma at 07 13 35 gmt a powerful very long period signal period 2 20 s marking the onset of the explosive fragmentation is recorded this is confirmed by a blast wave following few seconds later the remaining seismic signal more than 3 min shows an higher frequency content being related only to the fall of ballistic ejecta and to landslides along sciara del fuoco we propose the implementation of an early warning system for the short term forecast of such explosions based on the real time automatic detection of the tilt signals preceding such events

ground deformation associated with the march 1996 earthquake swarm at akutan volcano alaska revealed by satellite radar interferometry in march 1996 an intense swarm of volcano tectonic earthquakes 3000 felt by local residents mmax 5 1 cumulative moment of 2 7 1018 n m beneath akutan island in the aleutian volcanic arc alaska produced extensive ground cracks but no eruption of akutan volcano synthetic aperture radar interferograms that span the time of the swarm reveal complex island wide deformation the western part of the island including akutan volcano moved upward while the eastern part moved downward the axis of the deformation approximately aligns with new ground cracks on the western part of the island and with holocene normal faults that were reactivated during the swarm on the eastern part of the island the axis is also roughly parallel to the direction of greatest compressional stress in the region no ground movements greater than 2 83 cm were observed outside the volcano s summit caldera for periods of 4 years before or 2 years after the swarm we modeled the deformation primarily as the emplacement of a shallow east west trending north dipping dike plus inflation of a deep mogi type magma body beneath the volcano the pattern of subsidence on the eastern part of the island is poorly constrained it might have been produced by extensional tectonic strain that both reactivated preexisting faults on the eastern part of the island and facilitated magma movement beneath the western part alternatively magma intrusion beneath the volcano might have been the cause of extension and subsidence in the eastern part of the island we attribute localized subsidence in an area of active fumaroles within the akutan caldera by as much as 10 cm during 1992 1993 and 1996 1998 to fluid withdrawal or depressurization of the shallow hydrothermal system