broadband recording of strombolian explosions and associated very long period seismic signals on mount erebus volcano ross island antarctica in december 1996 and january 1997 broadband seismometers were deployed on the summit plateau of mount erebus at radial distances of 0 7 1 4 and 1 9 km from the central crater and lava lake strombolian explosions at erebus previously have been observed to produce seismic and acoustic energy between 1 and 6 hz new observations document significant energy with spectral peaks as grave as 20 s nearly identical very long period vlp signals begin 1 5 s prior to explosions have dilatational onsets and persist for up to 150 s similar vlp waveforms were recorded at all three stations indicating that the seismograms are essentially source dominated particle motions suggest an initial depth for the vlp source of up to several hundred meters migrating deeper in the course of 15 s such explosion associated vlp signals may indicate a nondestructive lossy resonance or nonlinear fluid flow excitation within the shallow magmatic system

the 2018 2019 seismo volcanic crisis east of mayotte comoros islands seismicity and ground deformation markers of an exceptional submarine eruption on may 10th 2018 an unprecedented long and intense seismic crisis started offshore east of mayotte the easternmost of the comoros volcanic islands the population felt hundreds of events over the course of one year 32 earthquakes with magnitude greater than 5 occurred including the largest event ever recorded in the comoros mw 5 9 on may 15th 2018 earthquakes are clustered in space and time unusual intense long lasting monochromatic very long period events were also registered from early july 2018 global navigation satellite system stations and interferometric synthetic aperture radar registered a large drift testimony of a large offshore deflation we describe the onset and the evolution of a large magmatic event thanks to the analysis of the seismicity from the initiation of the crisis through its first year compared to the ground deformation observation gnss and insar and modelling we discriminate and characterise the initial fracturing phase the phase of magma intrusion and dike propagation from depth to the sub surface and the eruptive phase that starts on july 3rd 2018 around fifty days after the first seismic events the eruption is not terminated two years after its initiation with the persistence of an unusual seismicity whose pattern has been similar since summer 2018 including episodic very low frequency events presenting a harmonic oscillation with a period of 16 s from july 2018 the whole mayotte island drifted eastward and downward at a slightly increasing rate until reaching a peak in late 2018 at the apex the mean deformation rate was 224 mm yr 1 eastward and 186 mm yr 1 downward during 2019 the deformation smoothly decreased and in january 2020 it was less than 20 of its peak value a deflation model of a magma reservoir buried in a homogenous half space fits well the data the modelled reservoir is located 45 5 km east of mayotte at a depth of 28 3 km and the inferred magma extraction at the apex was 94 m3 s 1 the introduction of a small secondary source located beneath mayotte island at the same depth as the main one improves the fit by 20 while the rate of the main source drops by a factor of 5 during 2019 the rate of the secondary source remains stable this might be a clue of the occurrence of relaxation at depth that may continue for some time after the end of the eruption according to our model the total volume extracted from the deep reservoir was 2 65 km3 in january 2020 this is the largest offshore volcanic event ever quantitatively documented this seismo volcanic crisis is consistent with the trans tensional regime along comoros archipelago

source process of very long period events accompanying long period signals at cotopaxi volcano ecuador abstract renewed seismic activity of cotopaxi ecuador began in january 2001 with the increased number of long period lp events followed by a swarm of volcano tectonic vt earthquakes in november 2001 in late june 2002 the activity of very long period vlp 2 s events accompanying lp 0 5 1 s signals began beneath the volcano the vlp waveform was characterized by an impulsive signature which was accompanied by the lp signal showing non harmonic oscillations we observed temporal changes of both the vlp and lp signals from the beginning until september 2003 the vlp signal gradually disappeared and the lp signal characterized by decaying harmonic oscillations became dominant assuming possible source geometries we applied a waveform inversion method to the observed waveforms of the largest vlp event our inversion and particle motion analyses point to volumetric changes of a sub vertical crack as the vlp source which is located at a depth of 2 3 km beneath the northeastern flank the spectral analysis of the decaying harmonic oscillations of lp events shows frequencies between 2 0 and 3 5 hz with quality factors significantly above 100 the increased vt activity and deformation data suggest an intrusion of magma beneath the volcano a release of gases with small magma particles may have repetitively occurred due to the pressurization which was caused by sustained bubble growth at the magma ceiling the released particle laden gases opened a crack above the magma system and triggered the resonance of the crack we interpret the vlp and lp events as the gas release process and the resonance of the crack respectively

broadband seismic experiment at merapi volcano java indonesia very long period pulses embedded in multiphase earthquakes abstract multiphase mp and low frequency lf earthquakes with spectral peak amplitudes at 3 4 and 1 hz respectively are two common types of shallow volcanic earthquakes previously recognized at merapi volcano their mechanisms are poorly understood but mps have been temporally associated with lava dome growth we conducted a seismic experiment in january february 1998 using four broadband seismographs to investigate the nature of seismic activity associated with dome growth during our experiment merapi experienced mild dome growth with low level seismic activity we compare our data to that recorded on a local short period sp network with the following preliminary results mp and lf events as recorded and classified on the short period network instruments were recognized on the broadband network frequency spectrograms revealed similar patterns in the near summit region at widely separated broadband stations higher frequency spectra than previously recognized were identified for both mp and lf events and were strongly attenuated as a function of radial distance from the source thus the spectral characteristics of these events as recorded on far field stations are not fully indicative of the source processes in particular many events classified as lf type appear to have much high frequency energy near the source this aspect of these so called lf earthquakes and their association with very long period vlp pulses suggests that many events identified in the far field as lf events are in actuality a variety of the mp event and involve similar source processes broadband records indicated that simple large amplitude vlp pulses were embedded in mp and lf wavetrains from event to event these pulses were similar in their waveforms and had periods of 4 s vlp events embedded in lf and mp earthquakes were located using particle motions the epicenters were clustered in a central region of the dome complex and preliminary source depths were within about 100 m of the dome surface suggesting a source region deep within the dome or the uppermost conduit a similar source location was established by study of mp high frequency onsets our broadband data suggests that we have recorded both elastic seismic waves and a simple embedded pulse that is interpreted to represent a surface tilt at the seismometer site the inferred tilt indicates an inflation and subsequent deflation possibly caused by a gas pressure pulse or episodic shallow magma transport with stick slip movement of the conduit wall

dyke intrusion model for the 1989 seismovolcanic activity off ito central japan in the last 10 years extensive earthquake swarms have occurred intermittently in the region east of izu peninsula central japan in july 1989 an active swarm again took place off ito city and among all past activities it was nearest to land and shallowest this activity eventually became a weak submarine eruption the first of its kind in this region associated with this event a borehole tiltmeter at 92 m depth installed several kilometers from the source area detected distinct continuous tilt change with the following features 1 tilt of 20 rad was observed within 1 week preceding the eruption 2 tilt change showed a good correlation to swarm activity 3 no obvious coeruption tilt change was observed on the basis of the tilt record and swarm distribution we constructed a dislocation model to interpret the seismovolcanic activity the model consists of two tensile faults each of which corresponds to magma intrusions in may and july and a right lateral reverse fault representing the largest earthquake m5 5 at 1109 lt on july 9 this model can simulate not only the above tilt data but also the record of a nearby dilatometer the results from daily laser distance measurements and daily global positioning system monitoring as well as results from other conventional distance surveys and leveling surveys in the surrounding region from this model we conclude that the intersection of the shear fault with the tensile fault caused magma to come up into soft sedimentary layers at the seabottom creating a lava dome later an instability brought about a magma phreatic explosion which did not generate any substantial crustal deformations at deeper levels

long period 12 sec volcanic tremor observed at usu 2000 eruption seismological detection of a deep magma plumbing system 1 from a temporal deployment of a broadband seismic network at usu volcano japan we observed long period 12 sec volcanic tremors during the first few weeks of the eruptive activity which started in the end of march 2000 the source of these long period tremors are located relatively deep at a depth of 5 km and their amplitude variation well correlates with the uplift rate of the eruption area we thus attribute these long period tremors to the flow induced vibration of a magma chamber and its outlet located around the source region of the long period tremors this may be the first seismological detection of long period 10 sec vibrations of a deep magma plumbing system

broadband measurements of the sources of explosions at stromboli volcano italy during september october 1997 21 three component broadband seismometers were deployed on stromboli volcano at radial distances of 0 3 2 2 km from the active crater to investigate the source mechanisms of strombolian explosions in the 2 50 s band the very long period vlp signals associated with explosions are consistent with two stationary sources repeatedly activated in time vlp particle motions are essentially linear and analyses of semblance and particle motions are consistent with a source centroid offset 300 m beneath and 300 m northwest of the active vents similar vlp waveforms are observed at all 21 stations indicating that the seismograms are source dominated the vlp ground displacement response to each explosion may be qualitatively interpreted as 1 pressurization of the conduit associated with the ascent of a slug of gas 2 depressurization of the conduit in response to mass withdrawal during the eruption and 3 repressurization of the conduit associated with the replenishment of the source with fluid

very long period oscillations of mount erebus volcano as the signal decays vlp scalar moments up to 5 10 11 n m exceed sp moments by an order of magnitude or more suggesting distinct though genetically related sp and vlp source mechanisms we conclude that vlp signals arise from excitation of a quasi linear resonator that is intimately associated with the conduit system and is excited by gravity and inertial forces associated with gas slug ascent eruption and magma recharge vlp signal stability across hundreds of eruptions spanning 5 years the persistence of the lava lake and the rapid posteruptive lava lake recovery indicate a stable near summit magma reservoir and vlp source process index terms 4544 oceanography physical internal and inertial waves 7280 seismology volcano seismology 8419 8414 volcanology eruption mechanisms 8419 volcanology eruption monitoring 7280 keywords strombolian very long period volcano seismology

a reinterpretation of seismicity associated with the january 1983 dike intrusion at kilauea volcano hawaii in january 1983 a dike intrusion fissure eruption generated a swarm of 375 magnitude 1 to 3 earthquakes along a 16 km segment of kilauea s middle east rift zone we searched the hawaiian volcano observatory catalog for multiplets of similar events from this region from 1980 through 1985 and obtained precise relative locations by waveform cross correlation over 150 of the intrusion earthquakes could be grouped into 14 multiplets of five or more events with sufficient similarity for accurate relocation some multiplets were active for only a few minutes during the downrift migration phase of the seismic swarm consistent with generation near the propagating dike tip while others were active for several days the two multiplets nearest the origin of the seismic swarm include events from the preceding days and months most multiplets span only 50 to 100 m following relocation are located at about 3 to 4 km depth and appear to deepen downrift the catalog depths of those earthquakes in multiplets and those not in multiplets are similar suggesting that most of the recorded seismicity may have come from a very limited depth interval despite the fact that the dike breached the surface by analogy with a mechanical model used to explain a similar clustering of background seismicity in the upper east rift in 1991 we infer that the earthquakes are generated in regions of high stress concentration immediately above kilauea s deforming deep rift body this conclusion is consistent with the depth of the top of the deep rift body inferred from geodetic data and with numerical calculations suggesting that a significant ambient differential stress is required for dikes to produce earthquakes larger than magnitude 1

source mechanism of very long period signals accompanying dome growth activity at merapi volcano indonesia 1 very long period vlp pulses with period of 6 7s displaying similar waveforms were identified in 1998 from broadband seismographs around the summit crater these pulses accompanied most of multiphase mp earthquakes a type of long period event locally defined at merapi volcano source mechanisms for several vlp pulses were examined by applying moment tensor inversion to the waveform data solutions were consistent with a crack striking 70 and dipping 50 sw 100m under the active dome suggest pressurized gas transport involving accumulation and sudden release of 10 60 m3 of gas in the crack over a 6s interval

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

long period events the most characteristic seismicity accompanying the emplacement and extrusion of a lava dome in galeras volcano colombia in 1991 abstract since its reactivation in 1988 the principal eruptions of galeras volcano occurred on may 4 9 1989 july 16 1992 and january 14 march 23 april 3 april 14 and june 7 1993 the initial eruption was a phreatic event which clearly marked a new period of activity a lava dome was extruded within the main crater in october 1991 and subsequently destroyed in an explosive eruption on july 16 1992 the eruptions that followed were all vulcanian type explosions the seismicity accompanying the emplacement extrusion and destruction of the lava dome was dominated by a mix of long period lp events and tremor displaying a variety of waveforms repetitive lp events with dominant periods in the range 0 2 1 s were observed in october and november 1991 and visually correlated with short energetic pulses of gas venting through a crack bisecting the dome surface each lp event was characterized by a weak precursory signal with dominant periods in the range 0 05 0 1 s lasting roughly 7 s using the fluid driven crack model of chouet 1988 1992 we infer that two distinct cracks may have acted as sources for the lp and precursor signals spectral analyses of the data yield the following parameters for the lp source crack length 240 360 m crack width 130 150 m crack aperture 0 5 3 4 mm crack stiffness 100 500 sound speed of fluid 880 m s and excess pressure 0 01 0 19 mpa similar analyses yield the parameters of the precursor source crack length 20 30 m crack width 15 25 m crack aperture 2 3 8 7 mm crack stiffness 5 15 sound speed of fluid 140 m s and excess pressure 0 06 0 15 mpa combined with geologic and thermodynamic constraints obtained from field observations these seismic parameters suggest a gas release mechanism in which the episodic collapse of a foam layer trapped at the top of the magma column subjacent to the dome releases a slug of pressurized gas which escapes to the surface while dilating a preexisting system of cracks in the dome structure accordingly the fracture observed on the crystallized dome body is the surface extension of the lp source crack where lp activity is induced by the rapid emission and expansion of gas flowing through this conduit the width and aperture of the crack estimated in the model are in good agreement with the length and aperture of the fracture estimated from visual observations the source parameters of the precursor signal are suggestive of a nozzle like conduit connecting the lp source crack to the underlying magma reservoir excitation of this conduit segment is attributed to the rapid emission and acceleration of the frothy fluid resulting from the collapse of the foam layer at the top of the reservoir the calculated periodicity of foam collapse events is in agreement with the observed average rate of thirteen lp events per hour

long period events and tremor at popocatepetl volcano 1994 2000 and their broadband characteristics following an initial phreatic eruption on 21 december 1994 activity at popocatepetl has been dominated by fumarolic emissions interspersed with more energetic emissions of ashes and gases a phase of repetitive dome building and dome destroying episodes began in march 1996 and is still ongoing at present we describe the long period lp seismicity accompanying eruptive activity at popocatepetl from december 1994 through may 2000 using data from a three component broadband seismometer located 5 km from the summit crater the broadband records display a variety of signals with periods ranging in the band 0 04 90 s long period events and tremor with typical dominant periods in the range 0 3 2 0 s are the most characteristic signals observed at popocatepetl these signals appear to reflect volumetric sources driven by pressure fluctuations associated with the unsteady transport of gases beneath the crater very long period vlp signals are also observed in association with lp events and tremor the vlp signals which accompany lp events display ricker like wavelets with periods near 36 s whereas vlp signals associated with tremor waveforms typically show sustained oscillations at periods ranging up to 90 s the spectra and particle motion patterns remain similar from event to event for the majority of lp and tremor signals analyzed during the time span of this study suggesting a repeated non destructive activation of a common source hypocenters determined by phase pick analyses of selected lp events recorded by the seven station permanent popocatepetl short period network suggest that the majority of these events are confined to a source region in the top 1 5 km below the crater floor the repetitive occurrences of vlp signals with closely matched waveform characteristics are consistent with a non destructive reactivation of at least two sources one source appears to coincide with the main source region of lp seismicity whereas the second is a deeper source whose activity appears to be intimately linked with episodes of monochromatic tremor

detection of a crack like conduit beneath the active crater at aso volcano japan to constrain the source of long period tremors lpts we deployed a very dense broadband seismic network consisting of totally twenty four stations around the active crater of aso volcano in kyushu japan the spatial variation of the observed signal amplitudes reveals that the source of lpts consists of an isotropic expansion contraction and an inflation deflation of an inclined tensile crack with a strike almost parallel to the chain of craters the detected crack has a dimension of 1 km and its center is located a few hundred meters southwest of the active crater at a depth of about 1 8 km the extension of the crack plane meets the crater chain including the active fumarole at the surface suggesting that the crack has played an important role in transporting gasses and or lava to the craters from below this work also demonstrates a powerful usage of broadband seismometers as geodetic instruments to constrain subsurface structures at active volcanoes

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

imaging magma transport during the 1997 seismic swarm off the izu peninsula japan the spatio temporal evolution of a propagating magma filled crack was estimated from inversion of global positioning system gps data tiltmeters and leveling the dike opened at a maximum rate of 50 millimeters per day and had a peak magma flux of 2 x 10 6 cubic meters per day although the spatial resolution was limited slow upward propagation was resolved during the 9 day long intrusion in contrast the earthquakes migrated rapidly upward during the first 12 hours of the swarm and nearly all of the seismic energy was released in the first 2 days comparison of inversion results with accurate hypocenter locations will lead to improved understanding of magma transport through the brittle crust and of the causes of volcanic seismicity

nonlinear ground motion amplification by sediments during the 1994 northridge earthquake it has been known since at least 1898 ref 1 that sediments can amplify earthquake ground motion relative to bedrock for the weak ground motion accompanying small earthquakes the amplification due to sediments is well understood in terms of linear elasticity hooke s law 2 but there has been a long standing debate regarding the amplification associated with the strong ground motion produced by large earthquakes the view of geotechnical engineers based largely on laboratory studies is that hooke s law breaks down at larger strains causing a reduced nonlinear amplification seismologists on the other hand have tended to remain sceptical of this nonlinear effect mainly because the relatively few strong motion observations seemed to be consistent with linear elasticity although some recent earthquake studies have demonstrated nonlinear behaviour under certain circumstances3 4 the significance of nonlinearity for the type of stiff soil sites found in the greater los angeles region remains unresolved5 here we report that ground motion amplification due to sediments for the main shock of the 1994 northridge earthquake was up to a factor of two less than the amplification observed for its aftershocks these observations imply significant nonlinearity in such amplification and bring into question the use of measurements of weak ground motion to predict the strong ground motion at sedimentary sites

dilatancy induced p waves as evidence for nonlinear soil behavior a much discussed topic in seismology deals with how and under which loading conditions soil shows nonlinear behavior and how this can be verified from seismograms seismologists have been seriously searching for signatures of nonlinear soil response to earthquakes for about two decades a mechanism explaining the dispersion in the p wave spectra due to the interaction between compressional p and shear s waves is presented shear waves in granular materials induce longitudinal dilatancy waves so called waves with approximately double frequency this can be explained with dilatancy and contractancy which is characteristic of granulates under shear deformations the predicted dispersion is observed in laboratory experiments and verified by comparing accelerograms from hard rock and soil stations from the vrancea region romania the arrival time difference between waves and s waves may theoretically be indicative of the thickness of nonsaturated granular layers these results modeled with nonlinear constitutive relations of the rate type show a specific type of nonlinearity in granular sediments also for earthquakes of moderate magnitudes

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

broadband seismic observation at the sakurajima volcano japan we installed a portable broadband seismometer streckeisen sts 2 at the sakurajima volcano which has been very active in the recent years the recorded seismograms show a wide variety both in temporal and spectral contents of seismic events from explosions to tremors and exhibit the importance of such broadband seismometry at volcanos we present examples of seismograms to show the potential of broadband seismic observation in monitoring volcanic activities

shallow conduit system at kilauea volcano hawaii revealed by seismic signals associated with degassing bursts 1 eruptive activity at the summit of kilauea volcano hawaii beginning in march 2008 and continuing to the present time is characterized by episodic explosive bursts of gas and ash from a vent within halemaumau pit crater these bursts are accompanied by seismic signals that are well recorded by a broadband network deployed in the summit caldera we investigate in detail the dimensions and oscillation modes of the source of a representative burst in the 1 10 s band an extended source is realized by a set of point sources distributed on a grid surrounding the source centroid where the centroid position and source geometry are fixed from previous modeling of very long period vlp data in the 10 50 s band the source time histories of all point sources are obtained simultaneously through waveform inversion carried out in the frequency domain short scale noisy fluctuations of the source time histories between adjacent sources are suppressed with a smoothing constraint whose strength is determined through a minimization of the akaike bayesian information criterion abic waveform inversions carried out for homogeneous and heterogeneous velocity structures both image a dominant source component in the form of an east trending dike with dimensions of 2 9 2 9 km the dike extends 2 km west and 0 9 km east of the vlp centroid and spans the depth range 0 2 3 1 km the source model for a homogeneous velocity structure suggests the dike is hinged at the source centroid where it bends from a strike e 27 n with northern dip of 85 west of the centroid to a strike e 7 n with northern dip of 80 east of the centroid the oscillating behavior of the dike is dominated by simple harmonic modes with frequencies 0 2 hz and 0 5 hz representing the fundamental mode 11 and first degenerate mode 12 21 of the dike although not strongly supported by data in the 1 10 s band a north striking dike segment is required for enhanced compatibility with the model elaborated in the 10 50 s band this dike provides connectivity between the east trending dike and the new vent within halemaumau pit crater waveform inversions with a dual dike model suggest dimensions of 0 7 0 7 km to 2 6 2 6 km for this segment further elaboration of the complex dike system under halemaumau does not appear to be feasible with presently available data

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

problems of nonlinear seismology abstract experimental seismic activations in situ undertaken during recent years reveal the character of three different types of nonlinear effect these are wave velocity temporal changes due to temporal changes of the stress field seismic wave interactions during comparatively small deformations 1 2 10 12 strong influence of the slow changes of the stress field and seismic vibrations on the seismic activity of the real geological media i e parameters of the seismic emission process new opportunities for detailed investigation of nonlinear effects are provided by the use of seismic vibrators that generate sinusoidal signals as well as by highly sensitive narrow frequency band recording channels these two tools open up broad new possibilities for investigation of nonlinear effects in a large variety of geological conditions and wave propagation situations these results change our opinion that nonlinear effects play a remarkable role only for strong wave propagation even very weak but detectable nonlinear effects can be used for purposes of investigating media structure and geodynamical processes for seismic prospecting and for the monitoring of oil and gas exploration

a comparison of observations of ground response to weak and strong ground motion at coalinga california abstract measurements of the response to earthquake motion of an unsaturated soil in coalinga california indicate that this response is linear within the limits of random errors for frequencies below 10 hz and for accelerations up to 0 7 g the response of the soil site relative to a bedrock site was determined by dividing the amplitude spectrum of the soil site ground motion for a given event by the amplitude spectrum of the bedrock site ground motion for the same event the relative response of this pair of sites to 23 regional and small local earthquakes is the same in the 1 to 10 hz band as the response to seven strong motion events within a random error of a factor of 1 3 at 10 to 11 hz the relative response to strong motion is significantly reduced by as much as a factor of 2 from the relative response to the 23 regional and small local earthquakes at the 95 per cent confidence level suggesting the possibility of nonlinear response the response of the soil site is a factor of 2 to 3 times larger than that of the bedrock site the variation in the spectral ratios for strong motion events and for regional and small local events about their respective averages has a standard deviation of about a factor of 2

mechanism of phreatic eruptions at aso volcano inferred from near field broadband seismic observations broadband seismometers deployed at aso volcano in japan have detected a hydrothermal reservoir 1 to 1 5 kilometers beneath the crater that is continually resonating with periods as long as 15 seconds when phreatic eruptions are observed broadband seismograms elucidate a dynamic interplay between the reservoir and discharging flow along the conduit gradual pressurization and long period 20 seconds pulsations of the reservoir during the 100 to 200 seconds before the initiation of the discharge followed by gradual deflation of the reservoir concurrent with the discharging flow the hydrothermal reservoir where water and heat from the deeper magma chamber probably interact appears to help control the surface activity at aso volcano

crustal deformation caused by magma migration in the northern izu islands japan intense crustal activity including earthquake swarms eruptions and a caldera formation in the northern izu islands started on june 26 2000 accompanied with large crustal deformation permanent gps data reveals the spatial pattern and time evolution of ground deformation the observations reveal shrinking and subsidence of miyakejima and extension between kouzushima and niijima we constructed a source model to explain the observed displacements during the period between june 26 and the end of august the model consists of a deflation source 0 12km beneath miyakejima tensile faults 1 04km located between miyakejima and kouzushima and several shear faults mass balance considerations suggest that a large amount of magma migrated 30km from miyakejima toward kouzushima

propagation of acoustic waves in a visco elastic two phase system influences of the liquid viscosity and the internal diffusion abstract the main purpose of the present paper is to present the mathematical expression for the frequency dependent effective acoustic properties of a liquid bubble mixture effects of the bubble resonance the heat and mass transfer between the liquid and bubbles and the viscoelasticity of the liquid are included in the expression several characteristic frequencies associated with these internal processes are represented by simple functions of the material and condition parameters using these expressions the acoustic properties of bubbly magmas are calculated and analyzed it is shown that the dispersion and attenuation of the pressure wave are particularly considerable in the frequency range lower than the characteristic frequency of the mass transfer and in the range near the characteristic frequency of the viscous response of the bubble radius in the frequency range bounded by these two frequencies the bubbly magma can be regarded as an elastic medium with the slow sound speed the significance of such acoustic properties on resonance of a body of bubbly magma is demonstrated in a simple one dimensional system

very long period signals associated with vulcanian explosions at popocatepetl volcano mexico very long period vlp seismic signals associated with large summit eruptions of popocatepetl volcano in the last four years are investigated using data from a broadband seismometer 0 04 120 s deployed on the north flank of the volcano at a radial distance of 5 km from the active crater the vlp signals associated with individual eruptions share similar waveforms discrete vlp signals accompanying long period lp events also share similar signatures and have dominant periods that are nearly identical to those observed in the vlp waveforms of explosions the vlp particle motions for eruption onsets consistently point to a source located a few km beneath the crater the vlp ground displacement response to each explosion is marked by a compression followed by a dilatation and terminating with another compression suggesting a sequence of pressurization depressurization repressurization of the conduit the repetitive nature of the waveforms points to a non destructive source process which has remained active in the magmatic system of popocatepetl at least since april 1997

pressure waves in a supersaturated bubbly magma summary we study the interaction of acoustic pressure waves with an expanding bubbly magma the expansion of magma is the result of bubble growth during or following magma decompression and leads to two competing processes that affect pressure waves on the one hand growth in vesicularity leads to increased damping and decreased wave amplitudes and on the other hand a decrease in the effective bulk modulus of the bubbly mixture reduces wave velocity which in turn reduces damping and may lead to wave amplification the additional acoustic energy originates from the chemical energy released during bubble growth we examine this phenomenon analytically to identify conditions under which amplification of pressure waves is possible these conditions are further examined numerically to shed light on the frequency and phase dependencies in relation to the interaction of waves and growing bubbles amplification is possible at low frequencies and when the growth rate of bubbles reaches an optimum value for which the wave velocity decreases sufficiently to overcome the increased damping of the vesicular material we examine two amplification phase dependent effects 1 a tensile phase effect in which the inserted wave adds to the process of bubble growth utilizing the energy associated with the gas overpressure in the bubble and therefore converting a large proportion of this energy into additional acoustic energy and 2 a compressive phase effect in which the pressure wave works against the growing bubbles and a large amount of its acoustic energy is dissipated during the first cycle but later enough energy is gained to amplify the second cycle these two effects provide additional new possible mechanisms for the amplification phase seen in long period lp and very long period vlp seismic signals originating in magma filled cracks

broadband seismic observations at satsuma iwojima volcano japan this paper reports the results of preliminary analysis of broadband seismic observations conducted at satsuma iwojima volcano japan the recorded broadband data show a wide variety of seismic features small m 0 short period volcanic earthquakes characterized by a long 5 s emergent phase and by nearly identical waveforms are located at the very shallow part of the summit crater long period seismic pulses synchronized with a regular amplitude modulation of volcanic tremor have an interval of approximately 46 to 50 min each of the long period pulses has almost identical waveform polarization of the long period events suggests a very shallow source which can be interpreted as a result of a volume expansion mechanism the correlation between the long period seismic pulses and volcanic tremor seems to be associated with magma convection and the degassing process inside the conduit of the volcano

source process of very long period seismic events associated with the 1998 activity of iwate volcano northeastern japan we observed very long period seismic events that are associated with the 1998 activity of iwate volcano northeast japan the events show a dominant period of 10 s and duration of 30 60 s often with accompanying short period waves at the beginning and at the end of the long period signals by analyzing the broadband seismograms we find that the source elongates in the east west direction for 4 km at a depth of 2 km beneath the western part of iwate volcano results of moment tensor inversions show a source mechanism of mutual deflation and inflation of two chambers located at the western and eastern edges of the source region the source region coincides with the low seismic velocity zone detected by seismic tomography and is very close to the locations of pressure sources estimated from crustal deformation data on the basis of these results we infer that the very long period seismic events are generated by transportation and movement of magmatic fluid hot water and or magma in a shallow part of the volcano we further present a simple source model of very long period seismic events based on one dimensional flow dynamics and propose a new parameter to characterize the size of very long period event the energy flow rate which is obtained by dividing the seismic moment by the dominant period the energy flow rate was estimated as 3 1 1012 j s for the event on july 29 1998

waveform inversion of volcano seismic signals assuming possible source geometries 1 we propose an approach to quantify the source of volcano seismic signals assuming possible source geometries such an assumption reduces the number of free parameters in a waveform inversion so we can quantify the source of these signals observed by a small number of seismic stations we test this method by using the synthesized waveforms radiated by a fluid filled crack and with seismic data observed at kusatsu shirane volcano we find that waveform data from 2 to 3 three component seismic stations surrounding the source enable us to estimate the source mechanism and location in the present approach

very long period seismic signals and caldera formation at miyake island japan over a period of roughly 40 days starting on 8 july 2000 a caldera structure 1 7 kilometers in diameter developed by means of gradual depression and expansion of the summit crater at miyake island japan at the same time very long period vlp seismic signals were observed once or twice a day source mechanism analyses of the vlp signals show that the moment tensor solutions are smooth step functions over a time scale of 50 seconds with dominant volumetric change components we developed a model to explain the caldera and the vlp signals in which a vertical piston of solid materials in the conduit is intermittently sucked into the magma chamber by lateral magma outflow this model offers potential for making quantitative estimations of the characteristic physical properties of magma systems

experimental investigations of nonlinear seismic effects abstract special experimental investigation using seismic vibrators allowed the propagation of periodic seismic signals accompanied by strong nonlinear effects to be demonstrated these effects are caused by the physical nonlinearity of a real geological medium the effects of higher harmonic generation and self demodulation of signals are studied over a large range of distances from a source a conclusion is that nonlinear properties of the medium should be taken into account in corresponding physical models used in seismology and seismic prospecting

an image of a magma intrusion process inferred from precise hypocentral migrations of the earthquake swarm east of the izu peninsula summary earthquake swarms in the area east of the izu peninsula central japan have been active and have been repeated intermittently since 1978 after 40 years of quiescence the activities were always accompanied by crustal deformations which were well modelled by dyke intrusions to study the process of a dyke intrusion precise hypocentres of the latest activity occurring in 1998 are obtained in this paper using waveform similarity by which new images of volcanic processes have been successfully acquired at several volcanoes the relocated hypocentres are mainly aligned on a thin vertical plane with a circular shape at a depth of 3 7 km and there is an aseismic area at the centre the normal direction to the plane coincides well with the direction of tectonic extensional stress around the hypocentral area and matches theoretical models well at the beginning of the activity a small fraction of the events occurred at greater depth where hypocentres align on a vertical line and migrate upward at a rate of 1 km h 1 the migration rate in this stage agrees well with a theoretical model of buoyancy driven dyke propagation after 1 day from the beginning earthquakes began to occur around the aseismic area and hypocentres spread on the thin circular plane described above during this activity the hypocentres seemed to migrate downwards and upwards from the centre the earthquakes are caused by shear fracture at the tip of the dyke and the migration of hypocentres reflects that the dyke expands downward and upward from the neutrally buoyant layer that is located at the centre of the swarm in this paper we also propose a process of magma intrusion based on the precise migration of hypocentres and show that the 1998 activity is composed of a few simple volcanic processes magma rising by buoyancy it staying at a neutral buoyancy point and spreading outward from the neutral point with elastic fracture by an inside excess magma pressure

the formation of the alleghenian isthmus triggered the bashkirian glaciation constraints from warm water benthic foraminifera abstract the timing of the final collision of laurentia and gondwana as well as the disappearance of the gateway between the rheic and tethyan oceans are quite controversial and poorly established accurate constraints on the gateway closure are vitally important for the understanding of global sea level fluctuations ocean circulation regional and global environments salinity and reorganization of the thermohaline circulation in the western tethys the bashkirian glacial episode and the overall decline of atmospheric co 2 concentrations here we present a new approach by applying warm water benthic foraminifera wwbf data to precisely constrain the rheic tethys gateway rtg closure utilizing taxonomic and statistical methods the link to the rtg closure and the profound biotic transformations in the oceans sea level and expansion of the gondwana ice sheet are discussed herein the wwbf records in the studied regions constrain the timing of the rtg disappearance and support a linkage between the appearance of the alleghenian isthmus and the onset of the bashkirian glaciation

evidence from the ad 2000 izu islands earthquake swarm that stressing rate governs seismicity magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat such swarm seismicity also migrates with time and often exhibits a dog bone shaped distribution the largest earthquakes in swarms produce aftershocks that obey an omori type exponential temporal decay but the duration of the aftershock sequences is drastically reduced relative to normal earthquake activity here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion a 1 000 fold increase in seismicity rate and a 1 000 fold decrease in aftershock duration occurred during the two month long dyke intrusion we find that the seismicity rate is proportional to the calculated stressing rate and that the duration of aftershock sequences is inversely proportional to the stressing rate this behaviour is in accord with a laboratory based rate state constitutive law suggesting an explanation for the occurrence of earthquake swarms any sustained increase in stressing rate whether due to an intrusion extrusion or creep event should produce such seismological behaviour

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

quantifying the origin and geometry of circular sag structures in northern fort worth basin texas paleocave collapse pull apart fault systems or hydrothermal alteration three dimensional seismic data reveal numerous subcircular sag structures in the northern fort worth basin the structures are defined by concentric faults that extend vertically upward 760 1060 m 2500 3500 ft from the lower ordovician ellenburger group the largest structures remained active into the lower desmoinesian strawn group criteria are outlined for defining seismically resolvable sag structures and a detailed quantitative analysis of the geometries of these circular features was undertaken results are compared and contrasted with reviews of subsurface collapse mechanisms and strike slip processes that are known to produce subsurface circular to subcircular sag geometries in plan view in this manner we develop several constraints for differentiating collapse related sag structures from strike slip related sag structures qualitative analyses indicate that the geometries observed are strongly analogous to subsurface collapse features where material is removed at depth to create a void into which the overburden subsequently sags and collapses quantitative analyses support the formation of these features by incremental collapse and suprastratal deformation above a linked system of coalesced collapsed paleocaves within the ellenburger group observations and criteria presented herein provide valuable information in defining seismically resolvable collapse features worldwide and help distinguish sag features of collapse affinity from those of other origins

warm water benthic foraminifera document the pennsylvanian permian warming and cooling events the record from the western pangea tropical shelves abstract shallow warm water benthic foraminifera swwbf including all larger fusulinids symbiont bearing benthic foraminifera are among the best indicators of paleoclimate and paleogeography in the carboniferous and permian the distribution of benthic foraminifera in space and time constrain important tectonic paleogeographic and climatic events at a global scale the north american shelves during pennsylvanian and permian time though geographically within the tropical belt are characterized by temperate environments with significantly lower foraminifera diversification and rare occurrences of warm water tethyan forms that are in general appear in the region as a migration entities such environments allow documentation of warming episodes associated with sudden immigration of warm water and exotic forms of swwbf that evolved elsewhere into the area first occurrence datum fod of the forms exotic to north america during warming episodes are always delayed in respect of their first appearance datum fad elsewhere the time of delay and taxonomic diversity of fusulinids in north america shelves depended on the scale and intensity of the warming episodes cooling events on the other hand are associated with decreased taxonomic diversity and appearances of endemic forms characteristic only of temperate water provinces the occurrence of these forms in boreal and north american provinces appears to be isochronous as their environments are uniform and induce their uniform and isochronous distribution several warming and cooling episodes during pennsylvanian permian time are recognized the differences between taxonomic variations in each event could potentially be used for provisional estimation of the degree of climatic change a strong link between biotic and climatic events in north american province and the similarity of biotic changes in the north american and other provinces suggests that paleoclimatic events in north american province were controlled by global factors

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

magmatic dike resonances inferred from very long period seismic signals very long period vlp signals showing simple decaying harmonic oscillations with periods near 10 seconds and lasting for about 300 seconds were observed in association with an earthquake swarm that occurred beneath hachijo island japan results from the source mechanism analysis and waveform simulation based on a fluid filled crack model consistently point to the resonance of a dike filled with a basaltic magma as the source of the vlp signals thus vlp signals can be used to probe the state of the fluid and dynamic processes within a volcanic system

temporal evolution of long period seismicity at etna volcano italy and its relationships with the 2004 2005 eruption abstract between december 2004 and august 2005 more than 50 000 long period events lp accompanied by very long period pulses vlp were recorded at mt etna encompassing the effusive eruption which started in september 2004 the observed activity can be explained by the injection of a gas slug formed within the magmatic column into an overlying cavity filled by either magmatic or hydrothermal fluids thus triggering cavity resonance although a large number of lp events exhibit similar waveforms before the eruption they change significantly during and after the eruption we study the temporal evolution of the lp vlp activity in terms of the source movement change of the waveforms temporal evolution of the dominant resonance frequencies and the source q factor and changes in the polarization of the signal the lp source locations before and after the eruption respectively do not move significantly while a slight movement of the vlp source is found the intensity of the lp events increases after the eruption as well as their dominant frequency and q factor while the polarization of the signals changes from predominantly transversal to pure radial motion although in previous studies a link between the observed lp activity and the eruption was not found these observations suggest that such a link was established at the latter end of the eruptive sequence most likely as a consequence of a reestablishment of the pressure balance in the plumbing system after it was undermined due to the discharge of large amounts of resident magma during the eruption based on the polarization properties of the signal and geological setting of the area a fluid filled crack is proposed as the most likely source geometry the spectral analysis based on the autoregressive models sompi is applied to the signals in order to analyse the resonance frequencies and the source q factors the results suggest water and basalt at low gas volume fraction as the most likely fluids involved in the source process using theoretical relations for the slow waves radiated from the fluid filled crack we also estimate the crack size for both fluids respectively

foraminiferal characterization of the morrowan atokan lower middle pennsylvanian boundary designation of a lower atokan lower middle pennsylvanian boundary stratotype is necessary because the traditional type atokan series is inadequate as a chronostratigraphic standard of reference foraminiferally the boundary between the atokan and the underlying morrowan series lower pennsylvanian is best defined by the appearances of the primitive fusulinaceans eoschubertella and pseudostaffella recrystallized staffellids staffella and nankinella appear at or near this level at some localities the appearance of the fusiform fusulinid profusulinella is considerably higher and its range defines an informal middle atokan interval upper atokan rocks are characterized by the range of fusulinella below the appearance of beedeina and or wedekindellina foraminiferal successions across the morrowan atokan boundary have been documented at many localities in the south central and western united states and in the arctic the merits of these sites as potential boundary stratotypes are evaluated herein the arctic is unsuitable as a reference area for the atokan series because taxon ranges there are seemingly atypical of ranges elsewhere in north america of the remaining sites where successions have been reported those in southern new mexico type derryan area southeastern arizona pedregosa basin southern nevada las vegas area and east central idaho lost river and lemhi ranges exhibit the best foraminiferal faunas in apparently continuously deposited strata

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

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

the source of explosive eruptions of sakurajima volcano japan to understand the nature of explosive eruptions in particular the role played by exsolution of magmatic gases we studied the seismic waveforms produced by two such eruptions of sakurajima volcano on october 30 and november 14 1986 an explosion begins when a mixture of magmatic gases and fragmented magma flows upward through a narrow vertical channel to the surface the source region is a reservoir of gas rich magma where the pressure drops as gases flow out the form of low frequency seismic waves can be explained by a source that consists of two components one component is a single force directed downward that represents the reaction to ejection of gas and magma the other more important component is a moment tensor that represents expansion or contraction of rock around a source the first motion of seismic waves produced by an explosion is directed away from the volcano tilt and strain measurements show that the initial motion directed outward is soon followed by subsidence around the volcano the eigenvectors of the seismic moment tensor are either nearly horizontal or vertical the ratio of horizontal to vertical eigenvalues was 1 8 1 for the october 30 explosion this suggests the geometry of the explosive source can be approximated as a buried vertical cylinder the volume of contraction 2 l03 m3 can be produced by a pressure change of 0 3 mpa over a cylinder with a radius of 160 m and a height of 300 m we propose that an explosive eruption occurs after a small shallow source of high pressure forms within a vertical conduit possibly exsolution of magmatic gases eventually the small source bursts and pushes open a pathway to the surface providing an upward escape for trapped gases it is this burst that causes the initial outwardly directed motion at the surface a deeper reservoir of gas rich magma is then subjected to a lower confining pressure and also bursts causing the explosion

response of a hydrothermal system to magmatic heat inferred from temporal variations in the complex frequencies of long period events at kusatsu shirane volcano japan we investigate temporal variations in the complex frequencies frequency and quality factor q of long period lp events that occurred at kusatsu shirane volcano central japan we analyze lp waveforms observed at this volcano in the period between 1988 and 1995 which covers a seismically active period between 1989 and 1993 systematic temporal variations in the complex frequencies are observed in october november 1989 july october 1991 and september 1992 january 1993 we use acoustic properties of a crack filled with hydrothermal fluids to interpret the observed temporal variations in the complex frequencies the temporal variations in october november 1989 can be divided into two periods which are explained by a gradual decrease and increase of a gas volume fraction in a water steam mixture in a crack respectively the temporal variations in july october 1991 can be also divided into two periods these variations in the first and second periods are similar to those observed in november 1989 and in september november 1992 respectively and are interpreted as drying of a water steam mixture and misty gas in a crack respectively the repeated nature of the temporal variations observed in similar seasons between july and november suggests the existence of seasonality in the occurrence of lp events this may be caused by a seasonally variable meteoritic water supply to a hydrothermal system which may have been heated by the flux of volcanic gases from magma beneath this volcano

pressure recovery in magma due to bubble growth 1 pressure recovery in magma subject to sudden depressurization is investigated in terms of the growth of bubbles containing magmatic volatiles assuming conservation of volatile mass and pressure equilibration between the bubbles melt and a surrounding elastic medium the final magma pressure is completely determined by its initial pressure and the magnitude of the pressure drop simulations show that the initial magma pressure is easily recovered or even exceeded when magma containing tiny bubbles is surrounded by a relatively stiff elastic medium under low confining pressure this result suggests that when processes such as magma withdrawal dike intrusion and nearby seismicity decrease the pressure in a magma chamber magma re pressurization can occur without new injection of magma

on the volcanic waveguide an analytical solution for the sound field in a resonant magma conduit with depth dependent magma properties provides a versatile interpretative tool for the analysis of seismoacoustic signals generated by fluid processes in active volcanoes expressions are given for the acoustic field in the atmosphere and the seismic field in the ground radiated through the magma conduit vent and walls respectively a new source model allows the resonance in the conduit to be excited by the vertical fluid velocity at the bottom of the conduit this source model represents acoustic excitation induced by low frequency fluid oscillations or large volume fluctuations originating at depth the magma conduit is modeled as a three section duct with each section having a different density sound speed viscosity and dimension the modal structure of the coupled resonant system is retained as the sound field in the conduit propagates into the surrounding bedrock and the overlying atmosphere the source time function permits estimates of the total mass injected or removed from the magmatic system and the source spectrum acts as a band pass filter on the resonant modes of the conduit theoretical or empirical source functions can be used to drive the seismoacoustic wave field and the amplitude of the source velocity may be constrained by the ballistics of pyroclasts and the height of ash plumes the acoustic properties of the melt may be predicted from the temperature composition and flow conditions of the magma as a function of depth comparisons of synthetic waveforms and spectra with those of seismic and acoustic signals recorded on active volcanoes permit estimates of the conduit geometry density sound speed and attenuation properties of the melt and characterize the temporal and spectral features of the source function the ability to extract this information accurately and efficiently from seismic and acoustic data streams may permit near real time modeling of fluid driven processes in active volcanoes

source process of long period seismic events at taal volcano philippines vapor transportation and condensation in a shallow hydrothermal fissure 1 we analyzed observations of a swarm of more than 40 000 long period lp seismic events at taal volcano philippines in 2010 2011 the event waveforms are strongly correlated to each other consistent with a fixed source location and begin with a dilatational first motion they have a peak frequency around 0 8 hz and a quality factor q of 6 waveform inversion of the events pointed to a tensile crack source dipping 30 60 at a shallow 100 200 m depth a simulation using a fluid filled crack model indicated that the complex frequencies of the waveforms are explained by the fundamental longitudinal mode resonance of a vapor filled crack 188 m long a satellite thermal infrared image acquired during the swarm period suggests that the lp events were not accompanied by surface gas releases we considered a vapor transportation model in which vapor exsolved from magma and rose in a fissure extending to the lp source this model yielded estimates that 105 107 m3 of magma was involved in the lp swarm and that the temperature of vapor in the lp source crack was around 600 k we modeled a triggering mechanism of the crack resonance based on sudden condensation of vapor at the crack tip in a cold aquifer this model explained observed characteristics of the events including the dilatational first motion the total volumetric change and the fixed source location

global time scale and regional stratigraphic reference scales of central and west europe east europe tethys south china and north america as used in the devonian carboniferous permian correlation chart 2003 dcp 2003 the boundaries of the devonian carboniferous and permian stages of the global stratigraphic reference scale abbreviated to global stratigraphic scale gss are described in relation to the biostratigraphic and or lithostratigraphic units of the regional stratigraphic reference scales abbreviated to regional stratigraphic scales rss of central and west europe east europe tethys south china eastern tethys and north america in their type regions the boundaries of gss units rarely coincide with those of homonymous rss units moreover the definitions of some rss units have changed several times over the last decades and subsequent misunderstanding of the stratigraphical significance of these changes has often introduced errors into proposed global correlation charts the stratigraphic framework proposed in our global devonian carboniferous permian correlation chart 2003 dcp 2003 devonian carboniferous permian correlation chart 2003 menning m schneider j w alekseev a s amon e o becker g von bitter p h boardman d r bogoslovskaya m braun a brocke r chernykh v chuvashov b i clayton g dusar m davydov v i dybova jachowicz s forke h c gibling m gilmour e h goretzki j grunt t a hance l heckel p h izokh n g jansen u jin y g jones p kading k ch kerp h kiersnowski h klets a klug ch korn d kossovaya o kotlyar g v kozur h w laveine j p martens th nemyrovska t l nigmadganov a l paech h j peryt t m rohn r roscher m rubidge b schiappa t a schindler e skompski s ueno k utting j vdovenko m v villa e voigt s wahlman g p wardlaw b r warrington g weddige k werneburg r weyer d wilde v winkler prins c f work d m 2004 abschlusskolloquium dfg schwerpunktprogramm 1054 evolution des systems erde wahrend des jungeren palaozoikums im spiegel der sedimentgeochemie abstracts univ erlangen germany 2004 p 43 herein abbreviated to dcp 2003 and cited as dcp 2003 in references is an attempt to reduce these errors the dcp 2003 is the stratigraphic base for project 1054 of the deutsche forschungsgemeinschaft dfg the evolution of the late palaeozoic in the light of sedimentary geochemistry this composite time scale has been carefully balanced as far as data allows to remove unnecessary artificial compression and expansion of time intervals biozonations and depositional events the ages selected in dcp 2003 are markedly different to those in the geologic time scale 1989 gts 1989 harland w b armstrong r l cox a v craig l e smith a g smith d g 1990 a geologic time scale 1989 cambridge univ press cambridge harland w b armstrong r l cox a v craig l e smith a g smith d g 1990 a geologic time scale 1989 cambridge univ press cambridge pp 1 263 and in gradstein and ogg gradstein f m ogg j 1996 a phanerozoic time scale episodes 19 1 2 3 4 insert whereas they are closer to those of the geologic time scale 2004 gts 2004 gradstein f m ogg j g smith a g 2004 a geologic time scale 2004 cambridge univ press cambridge pp 1 589 mostly the ages are rounded to the nearest 0 5 ma in order to avoid estimates of questionable accuracy whereas ages of 0 1 ma in the gts 2004 and their error bars of 0 4 ma to 2 8 ma for the devonian to permian stage boundaries suggest an improved accuracy in contrast in the dcp 2003 questionable ages and positions of stratigraphic boundaries are marked by arrows c 2006 elsevier b v all rights reserved

temporal evolution of a hydrothermal system in kusatsu shirane volcano japan inferred from the complex frequencies of long period events 1 we present a detailed description of temporal variations in the complex frequencies of long period lp events observed at kusatsu shirane volcano using the sompi method we analyze 35 lp events that occurred during the period from august 1992 through january 1993 the observed temporal variations in the complex frequencies can be divided into three periods during the first period the dominant frequency rapidly decreases from 5 to 1 hz and q of the dominant spectral peak remains roughly constant with an average value near 100 during the second period the dominant frequency gradually increases up to 3 hz and q gradually decreases from 160 to 30 during the third period the dominant frequency increases more rapidly from 3 to 5 hz and q shows an abrupt increase at the beginning of this period and then remains roughly constant with an average value near 100 such temporal variations can be consistently explained by the dynamic response of a hydrothermal crack to a magmatic heat pulse during the first period crack growth occurs in response to the overall pressure increase in the hydrothermal system caused by the heat pulse once crack formation is complete heat gradually changes the fluid in the crack from a wet misty gas to a dry gas during the second period as heating of the hydrothermal system gradually subsides the overall pressure in this system starts to decrease causing the collapse of the crack during the third period

resonance and elastic nonlinear phenomena in rock in a great variety of laboratory experiments over large intervals in stress strain and frequency rocks display pronounced nonlinear elastic behavior here we describe nonlinear response in rock from resonance experiments two important features of nonlinear resonant behavior are a shift in resonant frequency away from the linear resonant frequency as the amplitude of the disturbance is increased and the harmonics in the time signal that accompany this shift we have conducted young s mode resonance experiments using bars of a variety of rock types limestone sandstone marble chalk and of varying diameters and lengths typically samples with resonant frequencies of approximately 0 5 1 5 khz display resonant frequency shifts of 10 or more over strain intervals of 10 7 to 10 6 and under a variety of saturation conditions and ambient pressure conditions correspondingly rich harmonic spectra measured from the time signal progressively develop with increasing drive level in our experiments to date the resonant peak is observed to always shift downward if indeed the peak shifts indicating a net softening of the modulus with drive level this observation is in agreement with our pulse mode and static test observations and those of other researchers resonant peak shift is not always observed even at large drive levels however harmonics are always observed even in the absence of peak shift when detected strain levels exceed 10 7 or so this is an unexpected result important implications for the classical perturbation model approach to resonance results from this work observations imply that stress strain hysteresis and discrete memory may play an important role in dynamic measurements and should be included in modeling this work also illustrates that measurement of linear modulus and q must be undertaken with great caution when using resonance

diagenetic evaluation of a pennsylvanian carbonate succession bird spring formation arrow canyon nevada u s a 1 brachiopod and whole rock comparison abstract diagenetic evaluation of the pennsylvanian bird spring formation arrow canyon nevada u s a involved the detailed petrographic and geochemical examination of its brachiopod and whole rock components 13 c 18 o and 87 sr 86 sr of whole rock wr statistically p 0 0001 do not agree with isotope values of coeval brachiopod low mg calcite lmc more importantly a detailed investigation of the best preserved fine grained whole rock material demonstrates that it does not universally preserve its carbon isotope values in contrast with hypothetical predictions furthermore lumped trace chemistry or stable isotope tests do not unequivocally identify brachiopod or whole rock fine to coarse grained samples that carry an original seawater signal instead diagenetic evaluation involving as many screening tests as possible on a horizon by horizon level to compensate for spatial and temporal variations is necessary to identify the sample s that carries an original seawater signature many brachiopods from the bird spring formation are blue to non luminescent and carry microstructures and trace element contents similar to those of their modern tropical counterparts concurrence of chemical results between well preserved brachiopods and whole rock if originally low mg calcite is achieved in 22 of coeval samples for 13 c blmc wr with natural limits of 0 25 in 20 of samples for 18 o blmc wr with natural limits of 0 25 and in 9 of samples for 87 sr blmc wr with global limits of 0 000025 after an adjustment for mineralogical fractionation if whole rock is considered originally aragonite the concurrence of 13 c blmc wr drops to 0 and for 18 o blmc wr it drops to 6 furthermore comparison of stable isotopes of our well preserved brachiopods with those of preserved whole rock from the literature suggests that they are significantly different p 0 0001 with results of the latter dataset being more negative by about 0 77 2 57 with mineralogical adjustment for 13 c pdb and 1 31 2 11 for 18 o pdb thus our integrated screening and comparative tests indicate that 1 an overwhelming number of the whole rock samples from the bird spring formation carry a diagenetic instead of a primary signal for both carbon and oxygen isotopes and 2 many of the biogenic low mg calcite brachiopods in this succession carry an original chemical signal suitable for the reconstruction of high resolution seawater isotope curves representative of the pennsylvanian north american epeiric sea and potentially of the global oceans

resonances of a volcanic conduit triggered by repetitive injections of an ash laden gas 1 a swarm of long period lp seismic events was recorded in december 2001 before heightened eruptive activity of tungurahua volcano an andesitic stratovolcano in ecuador the lp events showed simple decaying harmonic oscillations with frequencies ranging from 2 to 3 5 hz and quality factors q significantly larger than 100 our spectral analysis of the lp events identified systematic temporal variations in both frequency and q of the lp events assuming a crack resonator at the source of lp events the temporal variations can be consistently explained by increasing the ash content within the resonator which may be caused by repetitive injections of an ash laden gas into a pre existing crack in the conduit as a preparatory process for eruptions

shallow magma pathway geometry at mt etna volcano 1 a fundamental goal of volcano seismology is to understand the dynamics of active magmatic systems in order to assess eruptive behavior and the associated hazard imaging of magma conduits quantification of magma transport and investigation of long period seismic sources together with their temporal variations are crucial for the comprehension of eruption triggering mechanisms at mt etna volcano several intense episodes of tremor activity were recorded during 2007 in association with strombolian activity and or intense fire fountaining episodes occurring from the south east crater sec the locations of the tremor sources and of the long period seismic events are used here to constrain both the area and the depth range of magma degassing highlighting the geometry of the shallow conduits feeding sec the imaged conduits consist of two connected resonating dike like bodies nnw sse and nw se oriented extending from sea level to the surface in addition we show how tremor long period lp and very long period vlp event locations and signatures reflect pressure fluctuations in the plumbing system associated with the ascent discharge of gas rich magma linked to the lava fountains the evidence here reported also corroborated by ground deformation variations can help develop a better prediction and early warning system for those eruptions effusive or explosive that apparently manifest no clear precursors

temporal evolution of a magmatic dike system inferred from the complex frequencies of very long period seismic signals 1 i present a detailed description of temporal variations in the complex frequencies of very long period vlp events observed in association with an earthquake swarm that occurred beneath hachijo island japan the individual vlp signals show simple decaying harmonic oscillations with periods near 10 s and they last for about 300 s the vlp activity began on 20 august 2002 and continued until 2 april 2003 spectral analysis of the vlp waveforms identifies two spectral peaks of which the complex frequencies show systematic temporal variations at the beginning of the vlp activity the q values of both the peaks show increasing trends from roughly 15 to 35 in the time period between 22 and 26 august the frequency of one peak shows a decreasing trend from 0 1 to 0 09 hz while the frequency of the other peak shows an increasing trend from 0 128 to 0 136 hz during this time after these systematic variations the frequencies and q values of the two peaks remain roughly constant waveform simulations based on a fluid filled crack model indicate that the observed systematic temporal variations can be reasonably explained by gradual expansion of a crack containing a basalt gas mixture the roughly constant frequencies and q values of the two peaks after these systematic variations suggest that the magmatic dike persistently existed beneath hachijo island for more than 6 months mass and heat advection is required to sustain the dike system implying magmatic flow and convection in the dike and magma chamber beneath this island

towards an automatic monitoring system of infrasonic events at mt etna strategies for source location and modeling active volcanoes characterized by open conduit conditions generate sonic and infrasonic signals whose investigation provides useful information for both monitoring purposes and studying the dynamics of explosive processes in this work we discuss the automatic procedures implemented for a real time application to the data acquired by a permanent network of five infrasound stations running at mt etna volcano the infrasound signals at mt etna consist in amplitude transients called infrasound events the adopted procedure uses a multi algorithm approach for event detection counting characterization and location it is designed for an efficient and accurate processing of infrasound records provided by single site and array stations moreover the source mechanism of these events can be investigated off line or in near real time by using three different models 1 strombolian bubble 2 resonating conduit and 3 helmholtz resonator the infrasound waveforms allow us to choose the most suitable model to get quantitative information about the source and to follow the time evolution of the source parameters

10s period volcanic tremors observed over a wide area in southwestern japan unusual seismic oscillations with a period of 10 seconds were observed over a wide area of southwestern japan several lines of evidence indicate that the origin of these 10s waves must be around the aso volcano located in the central part of kyushu island japan although a 10s period is unusually long for a volcanic tremor and no corresponding surface activity at the crater was reported by the local observatory the volcanic origin of the tremor is indisputable a further astonishing aspects of the observation is that there exists a strong correlation between the onset of 10s waves observed remotely and cessation of high frequency 1hz volcanic tremors at the aso volcano the aso volcano appears to be trembling with a 10s period without this having been noticed since seismic monitoring of volcanic activity is limited to high frequencies above 1 hz at the most of the volcanoes in the world long period tremors of the type observed here might be a widespread phenomenon that has been overlooked

moment tensor analysis of near field broadband waveforms observed at aso volcano japan abstract locations and focal mechanisms of long period volcanic events observed at aso volcano japan are determined by waveform inversion near field broadband three component seismograms of four to seven stations are simultaneously inverted in the time domain in order to find the six component seismic moment tensor a linear inversion is performed at each point of a 3d grid located under the volcano in order to constrain the centroid position and the focal mechanism of the source the complete displacements including near field waves in a homogeneous half space for a general point source are taken into account inversions of 43 long period tremors and six phreatic eruptions exhibit mainly an isotropic mechanism with a minor deviatoric component that may originate from a north south trending crack these events are all located in a small region at about 1 3 km depth beneath the active crater the high accuracy both of locations a few hundred meters and of focal mechanisms given by the inversion is partly attributed to the rapid variation of the amplitude of the static displacement seen in the long period part of the near field seismograms