complex conductivity imaging for the understanding of landslide architecture abstract geophysical methods are widely used for landslide investigation to delineate depth and geometry of the sliding plane in particular electrical resistivity tomography ert is often used because both porosity and water saturation control the electrical resistivity of the subsurface materials and are critical for slope stability moreover ert can be employed to monitor changes in pore fluid pressure which is an important factor triggering landslides however the interpretation of ert results in clay rich landslides can be challenging considering that high electrical conductivity values may not only be related to an increase in saturation but also to the surface conduction mechanism which becomes dominant in the presence of clays recently environmental investigations have demonstrated an improved subsurface characterization through induced polarization ip imaging an extension of the ert method which permits to gain information about electrical conductive and capacitive i e polarization effect properties of the subsurface as the polarization effect is mainly controlled by surface charge which is large in clays ip images are expected to improve the lithological interpretation and overcome the limitations of the ert method additionally measurements collected over a broad frequency bandwidth the so called spectral ip sip have been successfully used in laboratory experiments to quantify textural and hydrogeological parameters however the application of sip field measurements for the delineation of hydrogeological structures in landslides has not been addressed to date to fill this gap in this study we present sip imaging results for data collected at the la valette landslide south east french alps where an existing geotechnical model of the landslide is available for evaluation moreover our study provides a detailed revision on the collection and processing of sip datasets as well as a description of the diverse sources of error in ip surveys to stress the importance of data error quantification for a quantitative application of the sip method our results demonstrate that adequate data processing allows obtaining consistent results at different frequencies and independently of the measuring protocol furthermore the frequency dependence of the complex conductivity obtained in the field scale sip survey is consistent with earlier laboratory experiments in conclusion our study shows the potential of the sip method to improve our understanding of subsurface properties and an improved delineation of the contact between the mobilized material and the bedrock as well as variations in the clay content within the landslide and the bedrock

geometrical effects and low attenuation resonance of volcanic fluid inclusions for the source mechanism of long period earthquakes 1 we formulate the resonances of three simple geometrical inclusions a plane a cylinder and a sphere and find several clues to distinguishing the shape of volcanic fluid systems and their relevance to the observation of long period earthquakes the series of eigenfrequencies for a cylindrical and a spherical inclusion have shifts of 4 and 2 respectively in their higher modes from the eigenfrequencies of a planar inclusion the ratios between the higher and fundamental characteristic frequencies can be indicators of the geometry of volcanic fluid inclusions furthermore the eigenattenuation factor of a planar inclusion is a constant value that is determined uniquely by the impedance contrast between the fluid and the surrounding elastic medium and is independent of mode in marked contrast cylindrical and spherical inclusions have smaller or greater eigenattenuation factors particularly in lower modes under certain conditions of p wave velocity contrast and poisson s ratio of the surrounding elastic medium lower modes have less than 0 1 times the attenuation factor of higher modes we name these low attenuation modes lams lams are physically related to the conversion of volumetric changes to shear deformation of the surrounding elastic medium and the radiation of shear waves from the curved boundaries some monotonic waveforms of long period earthquakes can be interpreted by the excitation of these lams crack modes are also simply formulated by the resonance of a rectangular inclusion and also become lams whose attenuation factors are related to the aspect ratio of the crack

intermittent inflations recorded by broadband seismometers prior to caldera formation at miyake jima volcano in 2000 abstract very long period vlp pulses with widths of 20 s on velocity seismograms were observed during volcanic activity at miyake jima volcano japan in 2000 the vlp events occurred repeatedly during a few days prior to caldera formation and essentially vanished following the onset of caldera collapse waveform inversions of the pulse like signals point to a source offset 3 5 km beneath and 1 km south of the summit a candidate for the source mechanism is the inflation of an elliptical cylinder with axis tilted 20 30 from vertical and major axis of the elliptical cross section oriented northeast southwest the inferred mechanism appears consistent with a step like pressurization of a magma reservoir impacted by a falling rock mass in response to gravitational instability the repeated occurrences of the rock collapses lead to the caldera formation at miyake jima

sea fetch observed by synthetic aperture radar two satellite synthetic aperture radar sar observations of the fetch in the bohai sea of china are presented the sea surface winds derived from sar data indicated a high wind of 15 16 m s that occurred in the fetch zone the winds are shown to have immediate direct mechanical forcing impacts on the significant wave heights hs of ocean surface gravity waves buoy measurements and numerical wave modeling results show that the hs increased to a maximum of 3 5 m in the semienclosed sea 3 h after the passage of the fetch winds and the high hs in the sea was sustained for a total of 6 h the weather research and forecasting wrf model implemented in our modeling simulation captured the wind field responsible for the evolution of the fetch event the model simulated surface horizontal winds agree with the sar derived winds in addition the vertical wind distribution reveals that the fetch wind field reached the 800 hpa level and the event lasted less than one day this study demonstrates the synergy of using sar imagery and the wrf model as effective tools to investigate the lateral and vertical structures of coastal wind

chronology and products of the 2000 eruption of miyakejima volcano japan lateral migration of magma away from miyakejima volcanic island japan generated summit subsidence associated with summit explosions in the summer of 2000 an earthquake swarm beneath miyakejima began on the evening of 26 june 2000 followed by a submarine eruption the next morning strong seismic activity continued under the sea from beneath the coast of miyakejima to a few tens of kilometers northwest of the island summit eruptive event began with subsidence of the summit on 8 july and both explosions and subsidence continued intermittently through july and august the most intense eruptive event occurred on 18 august and was vulcanian to subplinian in type ash lofted into the stratosphere fell over the entire island and abundant volcanic bombs were erupted at this time another large explosion took place on 29 august this generated a low temperature pyroclastic surge which covered a residential area on the northern coast of the island the total volume of tephra erupted was 9 3 106 m3 dre much smaller than the volume of the resulting caldera 6 108 m3 migration of magma away from miyakejima was associated with crustal extension northwest of miyakejima and coincident shrinkage of miyakejima island itself during july august 2000 this magma migration probably caused stoping of roof rock into the magma reservoir generating subsurface cavities filled with hydrothermal fluid and or magmatic foam and formation of a caldera oyama caldera at the summit interaction of hydrothermal fluid with ascending magma drove a series of phreatic to phreatomagmatic eruptions it is likely that new magma was supplied to the reservoir from the bottom during waning stage of magma s migration resulting in explosive discharge on 18 august the 18 august event and phreatic explosions on 29 august produced a conduit system that allowed abundant so2 emission as high as 460 kg s 1 after the major eruptive events were over at the time of writing inhabitants of the island about 3 000 have been evacuated from miyakejima for more than 3 years

gulf stream and wind induced current variability on the georgia continental shelf winter 1978 low frequency longshore current fluctuations on the continental shelf off georgia and their relationships with local atmospheric forcing and gulf stream displacement were examined for a 3 month period from january to april 1978 acoustic travel time and bottom pressure measurements at a station on the continental slope were used to determine the depth of the main thermocline as an indicator of gulf stream displacement on the middle shelf current variability was dominated by local wind forcing at periods longer than 2 days with very little gulf stream influence longshore wind stress was the main driving force at periods longer than 4 days while cross shore wind contributed at shorter periods in contrast on the outer shelf current fluctuations in the upper layer were highly coherent with gulf stream displacement at a 12 day period and marginally coherent with longshore wind at a 6 day period linear regression analysis showed that gulf stream and local wind forcing accounted for most of the fluctuations in the upper layer over the shelf break for time scales greater than 5 days and at around 2 days a low multiple coherence window at 2 8 5 days was probably due to gulf stream frontal eddies in the lower layer over the shelf break the current fluctuations had a character intermediate between the upper layer currents gulf stream dominated and mid shelf currents wind dominated

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

an extraordinary breach of the gulf stream north wall by a cold water intrusion 1 a breach of the gulf stream gs north wall by a parcel of cold middle atlantic bight shelf water was observed from october 2 to 5 2001 by a sequence of noaa avhrr sea surface temperature sst images unlike the warm cold core rings generated by gs meanders the path of cold water eventually cuts into the gs subsequently the cold water remained intact and eventually penetrated and transversed the entire width of the gs this is readily apparent in the 3 day sst sequence analysis of wind data from a nearby cman station reveals a high over 12 8 m s and persistent 3 days alongshore wind event occurred prior to the breach an 11 year time series 1991 2001 of local wind measurements show that this type of strong and persistent wind situation is uncommon which may explain why the large scale surface shelf water breach of the gs has not been previously reported

nature of surface electrical conductivity in natural sands sandstones and clays the electrical conductivity of rocks results from conduction through the bulk solution occupying the pores and from surface conduction occurring at the fluid grain interface the nature of the surface electrical conductivity of shaly and clean sands and sandstones is examined surface conduction is characterized by the specific surface conductance which is the sum of three contributions i conduction within the electrical diffuse layer which makes a negligible contribution to the total specific surface conductance ii conduction in the stern layer which is shown to vary significantly with the salinity of the pore fluid at low salinities 10 6 to 10 3 mol 1 1 but becomes independent of salinity at higher salinities iii a mechanism operating directly on the mineral surface independent of salinity and perhaps associated with proton transfer at salinities higher than 10 3 mol 1 1 and at 25 c the specific surface conductance of quartz and clays is equal to 8 9 10 9 s and 2 5 10 9 s respectively equations describing the influence of surface conductivity and microstructure upon the macroscopic electrical conductivity of sands sandstones and shales are also developed

drainage of a deep magma reservoir near mayotte inferred from seismicity and deformation the dynamics of magma deep in the earth s crust are difficult to capture by geophysical monitoring since may 2018 a seismically quiet area offshore of mayotte in the western indian ocean has been affected by complex seismic activity including long duration very long period signals detected globally global navigation satellite system stations on mayotte have also recorded a large surface deflation offshore here we analyse regional and global seismic and deformation data to provide a one year long detailed picture of a deep rare magmatic process we identify about 7 000 volcano tectonic earthquakes and 407 very long period seismic signals early earthquakes migrated upward in response to a magmatic dyke propagating from moho depth to the surface whereas later events marked the progressive failure of the roof of a magma reservoir triggering its resonance an analysis of the very long period seismicity and deformation suggests that at least 1 3 km3 of magma drained from a reservoir of 10 to 15 km diameter at 25 to 35 km depth we demonstrate that such deep offshore magmatic activity can be captured without any on site monitoring recent seismicity near mayotte in the indian ocean is due to dyke propagation from and drainage of a 25 35 km deep magma reservoir according to an analysis of earthquake and deformation data

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

time variable 3d ground displacements from high resolution synthetic aperture radar sar application to la valette landslide south french alps abstract we apply an image correlation technique to multi orbit and multi temporal high resolution hr sar data image correlation technique has the advantage of providing displacement maps in two directions e g the line of sight direction los and the azimuth direction this information derived from the two modes of data acquisition ascending and descending can be combined routinely to infer the three dimensional surface displacement field at different epochs in this study a methodology is developed to characterize the displacement pattern of the large la valette landslide south french alps using terrasar x images acquired in 2010 the results allow mapping the dynamics of different units of the la valette landslide at high spatial resolution the study demonstrates the potential of this new application of high resolution sar image correlation technique for landslide ground surface deformation monitoring

earthquake swarms preceding the 2000 eruption of miyakejima volcano japan the first sign of magma accumulating beneath miyakejima an island volcano in the northern izu islands japan came at around 18 00 on 26 june 2000 when a swarm of earthquakes was detected by a volcano seismic network on the island earthquakes occurred initially beneath the southwest flank near the summit and gradually migrated west of the island where a submarine eruption occurred the next morning earthquakes then migrated further to the northwest between miyakejima and kozushima another volcanic island and developed to the most intense earthquake swarm ever observed in and around japanese archipelago to better image how the initial magma intrusion occurred we relocated hypocenters by using a station correction method and a double difference method the relocated epicenters are generally concentrated near the upper bound of dyke intrusions inferred from geodetic studies throughout the initial stages of the 2000 eruption at miyakejima from 26 to 27 june 2000 as for seismic activity westward off miyakejima in the morning on 27 june hypocenters from both a nationwide seismic network that were relocated by the double difference method and those from the volcano seismic network relocated by the station correction method formed a very shallow cluster that ascended slowly with time as it propagated northwestward from miyakejima this suggests that the dykes have both a radial and upward component of movement

continental shelf circulation induced by a moving localized wind stress abstract a linear two dimensional model of a rotating stratified fluid is constructed to investigate the circulation induced by a moving localized line of surface stress this model is used to analyze the effect of moving cold fronts on continental shelf circulation the nature of the induced circulation depends on the relative magnitude of the translation speed of the storm and the natural internal wave speed if the surface stress moves slower than the internal wave speed the disturbance is quasi geostrophic and moves with the storm if the storm moves faster than the internal wave speed two sets of internal inertial waves are produced one set of waves is forced by the surface forcing and travels at the speed of the storm another set of waves is produced by reflection of the directly forced waves from the coastal wall we conclude that free surface deflection slope is responsible for the low frequency quasi geostrophic currents due to passing cold fronts the internal response is composed of t

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

magnetic and electric field observations during the 2000 activity of miyake jima volcano central japan magnetic and electric field variations associated with the 2000 eruption of miyake jima volcano are summarized for about 1 week prior to the july 8 phreatic explosion significant changes in the total intensity were observed at a few stations which indicated uprising of a demagnetized area from a depth of 2 km towards the summit this nonmagnetic source can be regarded as a vacant space itself electric and magnetic field variations were observed simultaneously associated with the tilt step event which was the abrupt v50 s inflation at a few km depth within the volcano followed by gradual recovery vseveral hours the electric field is ascribed to the electrokinetic effect most probably due to forced injection of fluids from the source while the magnetic field to the piezomagnetic effect due to increased pressure large magnetic variations amounting to a few tens of nt were observed at several stations since july 8 and they turned almost flat after the august 18 largest eruption magnetic changes are explained mostly by the vanishing of magnetic mass in the summit and additionally by the thermal demagnetization at a rather shallow depth a large increase in the self potential by 130 mv was also observed near the summit caldera associated with the august 18 eruption which suggests that the hydrothermal circulation system sustained within the volcano for the past more than 10 years was destroyed by this eruption 9 2002 published by elsevier science b v

a note on the charleston gyre the deflection of the gulf stream caused by a topographic feature the charleston bump located offshore of savannah georgia results in a quasi stationary cyclonic eddy the charleston gyre which is situated over the continental slope east of charleston and cape romain occasionally the upwelling associated with this eddy produces an enhancement in the surface layer primary production that is great enough to be detected by the nimbus 7 coastal zone color scanner czcs in this note a czcs image with simultaneous hydrography current and wind observations is presented that documents an unusual manifestation of the gyre in addition to the czcs image a seasat synthetic aperture radar sar image is included that clearly indicates the presence of the eddy adjacent to the gulf stream front

very long period seismic signals observed before the caldera formation with the 2000 miyake jima volcanic activity japan 1 very long period seismic signals whose waveform consists of an initial impulsive signal and a later oscillatory wave with 0 2 or 0 4 hz in dominant frequency were observed before the caldera formation in the 2000 activity of miyake jima volcano japan the results of waveform inversion show that the initial and later parts can be explained by a northward single force of 1 5 108 n working at a depth of 2 km beneath the summit and a moment tensor solution at a depth of 5 km below and 2 km southwest of the summit with 1012 nm respectively a clear positive correlation of the amplitudes between the two sources strongly suggests that the shallow single force triggers the deeper moment source in spite of the several km distance between the two sources to analyze the source time functions of the moment tensor that do not always oscillate in phase we introduce a new method of moment tensor diagonalization which is performed in the frequency domain according to the analysis the two principal components have similar amplitudes and are greater than the third principal component suggesting an axially symmetric oscillation one of the possible systems is a combination of two cracks intersecting perpendicularly our interpretation is that the single force was generated when magma containing rock blocks suddenly began to move in a choked subsurface magma path and the resultant pressure waves propagated and excited a resonance oscillation of the two cracks

small inflation sources producing seismic and infrasonic pulses during the 2000 eruptions of miyake jima japan abstract during the 2000 activity of miyake jima volcano japan we detected long period seismic signals with initial pulse widths of 1 2 s accompanied by infrasonic pulses with almost the same pulse widths the seismic signals were observed from 13 july 2000 a day before the second summit eruption the occurrences of the seismic signals were intermittent with a gradual increase in their magnitudes and numbers building toward a significant explosive eruption on 18 august after the eruption the seismic and infrasonic events ceased the results of a waveform inversion show that the initial motions were excited by an isotropic inflation source beneath the south edge of the caldera at a depth of 1 4 km on the other hand the sources of the infrasonic pulses were located in the summit caldera area the times at which the infrasonic pulses were emitted at the surface were delayed by about 3 s from the origin times of the seismic events it is suggested that small isotropic inflations excited seismic waves in the crust and simultaneously caused acoustic waves that traveled in the conduit and produced infrasonic pulses at the crater bottom considering the observed time differences and gas temperatures emitted from the vent the conduit should have been filled with vapor mixed with so 2 gas and volcanic ash the change of the time differences between the seismic and infrasonic signals suggests that the seismic source became shallower within half a day before the august 18 explosive eruption we interpret the source process as a fragmentation process of magma in which gas bubbles burst and quickly released part of the pressure that had been sustained by the tensional strength of magma

real time and in situ assessment of conduit permeability through diverse long period tremors beneath aso volcano japan abstract long period signal lps 0 2 2 s and very long period signal vlp 2 100 s observed in the shallow volcanic plumbing system are typically repetitive and time invariant in their location and source mechanism offering in situ probes of hot fluid transport over the eruption cycles while the amplitude and activity of volcanic tectonic earthquakes and lp events have been commonly used to infer overpressure within their source region one missing link is an observable that may permit inference on the change in the permeability of the conduit plug wall which can regulate the degree of pressurization affect the mechanical strength of the surrounding rock and consequently the likelihood of an upcoming eruption here we show that during the 2011 2016 eruption cycle at aso volcano in japan long period tremor events a vlp of 15 s period with opposite waveform polarity can be systematically detected and categorized as pressurization and depressurization events in the same crack like conduit we suggest that depending on the strength of the surrounding rock and the permeability of the crack like conduit wall plug pressurization due to magmatic heat and vaporization is more likely to occur when a less permeable conduit plug wall can effectively keep the gas inside the crack like conduit on the other hand depressurization is prone to occur if the conduit wall plug permeability is sufficiently high to allow gas to escape from the conduit considering the amplitude of lpt proportional to the conduit overpressure contrasting energetics of these diverse lpt events allows us to define whether the conduit is prone to pressurization or depressurization providing a framework to infer how the permeability of the conduit wall plug may evolve over an eruption cycle

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

influence of artificial channels on the source and extent of saline water intrusion in the wind tide dominated wetlands of the southern albemarle estuarine system usa saline water intrusion is degrading water quality in the channelized coastal wetlands of the southern albemarle estuarine system aes the source transport and fate of the saline water in the southern aes was determined by monitoring specific conductivity and water levels in small artificial channels the alligator river the alligator pungo canal and the groundwater system for 12 months results indicate that water levels are affected by wind tides which trigger the movement of saline water into the interior of the wetlands via the small canals the wind tides are mostly driven by episodic southerly winds pushing saline water into the canal network and the groundwater regime proximal to the alligator river the saline waters persist in the canals as long as the wind tide events last specific conductivities from canals and groundwater are shown to be unexpectedly higher closer to the source of the alligator river than toward the albemarle sound suggesting that the large alligator pungo canal facilitates the northward migration of saline water from the pamlico sound to the alligator river overwash and reversals in the flow directions between groundwater and surface water bodies suggest that saline water that is present during wind tide events may migrate into the groundwater system from surface water bodies the results of this study reveal that whereas the large alligator pungo canal channels saline water to the aes small artificial channels may also play significant roles in degrading water quality in the interior of channelized coastal wetlands

trends in long period seismicity related to magmatic fluid compositions abstract sound speeds and densities are calculated for three different types of fluids gas gas mixture ash gas mixture and bubbly liquid these fluid properties are used to calculate the impedance contrast z and crack stiffness c in the fluid driven crack model chouet j geophys res 91 1986 13 967 101 1988 4375 a seismic model for the source of long period events and harmonic tremor in gasparini p scarpa r aki k eds volcanic seismology iavcei proceedings in volcanology springer berlin 3133 the fluid driven crack model describes the far field spectra of long period lp events as modes of resonance of the crack results from our calculations demonstrate that ash laden gas mixtures have fluid to solid density ratios comparable to and fluid to solid velocity ratios lower than bubbly liquids gas volume fractions spectral characteristics are described in terms of the quality factor q 1 q 1 is measured by the ratio of the frequency of the dominant spectral peak to the bandwidth of the peak measured at one half of its amplitude this factor expresses the losses of energy due to elastic radiation q r 1 and other dissipative mechanisms q i 1 at the source q 1 q r 1 q i 1 spectra for lp events recorded at active volcanoes such as galeras in colombia and kilauea in hawaii have q 1 factors in the range of 0 1 0 002 the q r 1 factors due to radiation loss calculated for a sphere filled with a h 2 o co 2 or h 2 o so 2 gas mixture vary between 0 0015 and 0 0040 with a change in wt h 2 o at 800 1600 k and 10 50 mpa for gas rich mixtures q r 1 has a strong dependence on resonator geometry spherical versus rectangular the spectra from a resonating sphere filled with gas rich mixture yields values of q r 1 an order of magnitude smaller than those from a rectangular crack for a resonating crack filled with an ash gas mixture or pseudogas q r 1 varies parabolically from 0 006 for an ash rich mixture to 0 0015 or 0 0023 for a h 2 o rich or co 2 rich mixture at 800 k and 25 mpa for low q r 1 are independent of crack geometry spectra associated with a foam gas volume fractions 10 90 or bubbly basalt gas volume fractions q r 1 on the order of 0 01 and 0 1 respectively the spectra from a resonating sphere filled with a foam containing 20 gas volume fraction yields values of q r 1 similar to those for a rectangular crack as with gas gas and ash gas mixtures an increase in mass fraction narrows the bandwidth of the dominant mode and shifts the spectra to lower frequencies including energy losses due to dissipative processes in a bubbly liquid increases attenuation attenuation may also be higher in ash gas mixtures and foams if the effects of momentum and mass transfer between the phases were considered in the calculations

characterizing landslides through geophysical data fusion example of the la valette landslide france many studies show that certain geophysical methods such as seismic and electrical resistivity imaging appear to be well adapted for investigating the internal structures of landslides and understanding the related hydro mechanical mechanisms these are methods that allow the direct and non intrusive measurement of acoustic p and shear s wave velocities and electrical resistivity which are three physical parameters considered as essential for estimating the mechanical properties of moving reworked material we applied these techniques to the la valette landslide southern french alps a typical example of an intra material landslide carrying out measurements simultaneously along two profiles 400 m and 300 m long and respectively perpendicular to and along the slide direction we then used suitable inversion algorithms to estimate both the p and s wave velocity fields and the electrical resistivity field from the recorded data the results aided by field surface observations show that a correlation exists between the state of the material and the seismic velocity and or electrical resistivity data thus confirming that the simultaneous use of the two methods provides complementary information on the geomechanical behavior of the landslide more particularly the seismic data provide information on fissure density variations and the presence of shear bent material whereas the electrical resistivity data provide information on the groundwater content to enable a more integrated petrophysical interpretation we applied a data fusion strategy based on fuzzy subsets to the geophysical datasets through combining the tomograms we identified a surface layer of soft material along the two profiles the bottom of this layer was also recognized in a borehole from a methodological point of view the results show the applicability of adopting geomechanical hypotheses as inputs of geophysical data fusion for identifying areas where sediment mobilization could occur

broadband seismic monitoring of active volcanoes using deterministic and stochastic approaches 1 we systematically used two approaches to analyze broadband seismic signals for monitoring active volcanoes one is waveform inversion of very long period vlp signals assuming possible source mechanisms the other is a source location method of long period lp events and tremor using their amplitudes the deterministic approach of the waveform inversion is useful to constrain the source mechanism and location but is basically only applicable to vlp signals with periods longer than a few seconds the source location method assumes isotropic radiation of s waves and uses seismic amplitudes corrected for site amplifications this simple approach provides reasonable source locations for various seismic signals such as a vlp event accompanying lp signals an explosion event and tremor associated with lahars and pyroclastic flows observed at five or fewer stations our results indicate that a frequency band of about 5 12 hz and a q factor of about 60 are appropriate for the determination of the source locations in this frequency band the assumption of isotropic radiation may become valid because of the path effect caused by the scattering of seismic waves the source location method may be categorized as a stochastic approach based on the nature of scattering waves systematic use of these two approaches provides a way to better utilize broadband seismic signals observed at a limited number of stations for improved monitoring of active volcanoes

the structure of shelf and gulf stream motions in the georgia bight abstract the structure of the current and temperature fields along 30 n over the mid shelf and western blake plateau in the south atlantic bight has been investigated by combining two moored instrument experiments in the summer of 1981 the shelf moorings were part of the second georgia bight experiment gabex ii and the gulf stream mooring data on the blake plateau have been described by lee and waddell 1983 empirical orthogonal functions eof in the frequency domain are used to extract shelf and gulf stream coherent current and temperature fluctuations in the two to 14 day period band three modes are found of which the first two are interpreted as gulf stream meander and frontal eddy circulations the difference between them is chiefly in the shelf motions the first mode is primarily restricted to the shelf edge whereas the second mode penetrates to the 40m isobath the third mode dominates at mid shelf and is the only mode that shows strong coherence with the windstress and local sea level fluctuations the relationship of the modes to the occurrence of mid and inner shelf cold sub surface intrusions generated by shelf edge gulf stream frontal eddies is examined all three modes are found to play a role in the initiation growth and decay of these structures

spatiotemporal gravity changes at miyakejima volcano japan caldera collapse explosive eruptions and magma movement 1 calderas are ubiquitous topographic features of volcanos yet caldera formation itself has not been recorded intensively by modern measurement techniques here we report the spatiotemporal gravity changes before and after caldera collapse at the miyakejima volcano japan in 2000 a gravity decrease of as much as 145 gal 1 gal 10 8 m s2 at the summit area since june 1998 was detected 2 days prior to the collapse interpreted as reflecting the formation of a large void beneath the volcano gravity changes detected after the initiation of collapse can mostly be corrected by the effect of collapsed topography from which a rapid rate of collapse of more than 1 6 107 m3 d can be inferred correcting for the effect of topography change we identified a temporal decrease in gravity from the middle of july to late august despite ground subsidence the gravity decrease is interpreted as a reduction of the density in a cylindrical conduit attributed to water inflow from an ambient aquifer that also promoted intensive magma water interaction and subsequent explosive eruptions from september to at least november 2000 gravity values at all sites increased significantly by a degree that cannot be explained by ground displacement alone we interpret this temporal evolution as primarily due to magma ascent and refilling of the conduit

kinematics and correlation of the surface wind field in the south atlantic bight surface winds observed at charleston south carolina and at an offshore buoy located some 300 km to the east of charleston are analyzed to determine operational transformations for estimating the offshore winds from the coastal winds both the statistics describing the wind field at each station along with those describing the correlation between stations are found to be seasonally modulated ensemble averaged by season transfer functions computed by using the first 3 years of available data are applied to a fourth independent data year for assessing their predictive utility the transfer functions and predictability are both seasonally modulated and the transformation matrix is nondiagonal each offshore wind velocity component depends upon both coastal components

earthquakes series preceding very long period seismic signals observed during the 2000 miyakejima volcanic activity 1 unusual earthquakes series were observed one to two hours before a very long period vlp seismic pulse that happened once or twice a day during the 2000 activity of miyakejima volcano japan the series on july 11 and 12 have particularly a clear feature the time intervals of the earthquakes in the series decrease at a constant rate in the manner of geometric progression the maximum amplitude of each earthquake is initially almost constant but linearly decreases with time from few minutes before the occurrence of a vlp pulse hypocenters of these earthquakes are below the south western region of the crater and near the sea level in depth we interpret these earthquakes series as repetition of a gradual stress accumulation and release under the variable critical stress level the critical stress level is first constant but linearly decreases later

caldera collapse during the 2000 eruption of miyakejima volcano japan a collapsed caldera 1 6 km in diameter and 450 m in depth was formed at the summit of miyakejima volcano during the 2000 eruption the collapsed caldera appeared on 8 july with a minor phreatic eruption 12 days after seismic activity and magma intrusion occurred northwest of the volcano growth of the caldera took from 8 july to the middle of august with seismic swarms associated with the continuous intrusion of magma northwest of the volcano the growth rate of the caldera was about 1 4 107 m3 day and the final volume of the collapsed caldera was about 6 108 m3 major phreatomagmatic eruptions produced a total of about 1 6 1010 kg 1 1 107 m3 of volcanic ash after caldera growth the caldera structure and the nature of the eruptive materials of the first collapse on 8 july suggest that the surface subsidence was caused by the upward migration of a steam filled cavity with stoping of the roof rock above the magma reservoir the diameter of the stoping column was estimated to be 600 700 m from circumferential faults that developed in the caldera floor and the collapse of the caldera wall enlarged the diameter of the caldera to 1 6 km the total volume of the caldera and the horizontal diameter of the stoping column gave a subsidence of the caldera floor of 1 6 2 1 km

relationship between spectral induced polarization and hydraulic properties of saturated and unsaturated sandstone there is growing interest in the use of geophysical methods for hydrological model parameterization empirical induced polarization ip hydraulic conductivity k relationships have been developed but these are only applicable to sediments in which the ip response shows limited variation with electrical current frequency here we examine the spectral ip response of samples taken from a uk sandstone aquifer and compare measured parameters with physical and hydraulic properties we demonstrate the limited value of existing ip k models due to the inherent ip frequency dependence of these samples our results show how the mean relaxation time is a more appropriate measure of ip response for these sediments a significant inverse correlation between the surface area to pore volume ratio and is observed suggesting that is a measure of a characteristic hydraulic length scale this is supported by a measured strong positive correlation between log and log k our measurements also reveal evidence of a relationship between and a dominant pore throat size which leads to postulations about the parallelism between the spectral ip behavior and unsaturated hydraulic characteristics additional experiments show how the relaxation time is affected by degree of fluid saturation indicating that saturation levels must be accounted for if our empirical relationships are applied to vadose zone studies our results show clear evidence of the potential value of frequency based ip measurements for parameterization of groundwater flow models

decomposing observations of high frequency radar derived surface currents by their forcing mechanisms locally wind driven surface currents 1 the wind impulse response function and transfer function for high frequency radar derived surface currents off southern san diego are calculated using several local wind observations the spatial map of the transfer function reflects the influence of the coast on wind current dynamics near the coast within 20 km from the shoreline the amplitudes of the transfer function at inertial and diurnal frequencies are reduced due to effects of coastline and bottom bathymetry meanwhile the amplitude of low frequency currents increases near the coast which is attributed to the local geostrophic balance between cross shore pressure gradients against the coast and currents locally wind driven surface currents are estimated from the data derived response function and their power spectrum shows a strong diurnal peak superposed on a red spectrum similar to the spectra of observed winds current magnitudes and veering angles to a quasi steady wind are typically 2 5 of the wind speed and vary 50 90 to the right of the wind respectively a wind skill map is introduced to present the fractional variance of surface currents explained by local winds as a verification tool for wind data quality and relevance moreover the transfer functions in summer and winter are presented to examine the seasonal variation in ocean surface current response to the wind associated with stratification change

submarine flank eruption preceding caldera subsidence during the 2000 eruption of miyakejima volcano japan during the early part of a seismic swarm preceding eruption and caldera formation at miyakejima volcano discoloured sea surfaces were observed 1 5 km off the western coast of miyakejima on 27 june 2000 a later survey of the area using a multi beam side scan sonar and a remotely operated small submarine revealed four craters of 20 30 m diameter aligned east west in a 100 10 30 m area on the seafloor with hot water at 140 c being released from one of the centres each crater consists of submarine spatter overlain in part by scoria lapilli dredged spatter from the craters was fresh and there was no evidence of activity of marine organisms on the spatter surface indicating that the discoloured sea surface resulted from magmatic eruption on the seafloor this eruption occurred when a westward propagating seismic swarm initiated beneath miyakejima s summit passed through the area finding new magma on the seafloor demonstrates that this seismic swarm was associated with intruding magma moving outward from beneath miyakejima submarine spatter shows flattened shapes with a brittle crust formed by cooling in water and its composition is aphyric andesite of 54 wt sio2 the spatter is similar in whole rock and mineral composition to spatter erupted in 1983 however the wide range of cl in melt inclusions in plagioclase of the 27 june submarine spatter shows that it is not simply a remnant of the 1983 magma which has only high cl melt inclusions in plagioclase the mixed character of melt inclusions suggests involvement of a magma with low cl melt inclusions the magma erupted explosively on 18 august from miyakejima s summit considered as the second juvenile magma in this eruption contains low cl melt inclusions in plagioclase based on these observations and the eruption sequence we present the following model 1 a shallow magma chamber was filled with a remnant of 1983 magma that had evolved to a composition of 54 55 wt sio2 2 injection of the 18 august magma into this chamber generated a mixed magma having a wide range of cl in melt inclusions contained plagioclase the magma mixing might have occurred shortly before the submarine eruption and could have been a trigger for the initiation of the removal of magma from the chamber as an extensive dyke which eventually led to caldera subsidence