structure of large amplitude internal solitary waves the horizontal and vertical structure of large amplitude internal solitary waves propagating in stratified waters on a continental shelf is investigated by analyzing the results of numerical simulations and in situ measurements numerical simulations aimed at obtaining stationary solitary wave solutions of different amplitudes were carried out using a nonstationary model based on the incompressible two dimensional euler equations in the frame of the boussinesq approximation the numerical solutions which refer to different density stratifications typical for midlatitude continental shelves were obtained by letting an initial disturbance evolve according to the numerical model several intriguing characteristics of the structure of the simulated large amplitude internal solitary waves like for example wavelength amplitude and phase speed amplitude relationship as well as form of the locus of zero horizontal velocity emerge consistent with those obtained previously using stationary euler models the authors approach which tends to exclude unstable oceanic internal solitary waves as they are filtered out during the evolution process was also employed to perform a detailed comparison between model results and characteristics of large amplitude internal solitary waves found in high resolution in situ data acquired north and south of the strait of messina in the mediterranean sea from this comparison the importance of using higher order theoretical models for a detailed description of large amplitude internal solitary waves observed in the real ocean emerge implications of the results showing the complexity related to a possible inversion of sea surface manifestations of oceanic internal solitary waves into characteristics of the interior ocean dynamics are finally discussed

quiescent explosive transitions during dome forming volcanic eruptions using seismicity to probe the volcanic processes leading to the 29 july 2008 vulcanian explosion of soufriere hills volcano montserrat

external modulation of volcanic activity summary time and again records of seismovolcanic activity that show a diurnal and semi diurnal modulation have been related to the earth s tidal stress field as an external triggering mechanism several seismic data sets from different volcanoes are examined including stromboli volcano italy mt ruapehu new zealand and merapi and batur indonesia where in some cases weather data are also incorporated a comparison with theoretical body tides in the spectral domain reveals strong evidence against a correlation between seismovolcanic activity and tidal stress however other parameters such as temperature and barometric pressure show the same diurnal and semi diurnal modulation and are therefore candidates for a possible external modulation of volcanic activity several mechanisms are discussed for stromboli a clear correlation between volcanic activity and barometric pressure is shown

waveform classification of volcanic low frequency earthquake swarms and its implication at soufriere hills volcano montserrat low frequency volcanic earthquakes are indicators of magma transport and activity within shallow conduit systems at a number of volcanoes these events exhibit a high degree of waveform similarity providing a criterion for classification using cross correlation techniques to quantify the degree of similarity we develop a method to sort events into families containing comparable waveforms events within a family have been triggered within one small source volume from which the seismic wave has then travelled along an identical path to the receiver this method was applied to a series of 16 low frequency earthquake swarms well correlated with cyclic deformation recorded by tiltmeters at soufriere hills volcano montserrat in june 1997 nine waveform groups were identified containing more than 45 events each the families are repeated across swarms with only small changes in waveform indicating that the seismic source location is stable with time the low frequency seismic swarms begin prior to the point at which inflation starts to decelerate suggesting that the seismicity indicates or even initiates a depressurisation process a major dome collapse occurred within the time window considered removing the top 100 m of the dome this event caused activity within some families to pause for several cycles before reappearing this shows that the collapse did not permanently disrupt the source mechanism or the path of the seismic waves

airborne synthetic aperture radar tracking of internal waves in the strait of gibraltar abstract as part of the international gibraltar experiment we realized on june 22 and 24 1986 two surveys of the strait of gibraltar on board an aircraft equipped with a synthetic aperture radar our objective was to observe at spring tides and during two twelve hour tidal cycles at 24 h interval the generation of internal wave trains linked to the hydraulic jump formed west of the sill during the westward phase of the tidal current and their eastward propagation in the strait the speed of propagation of these waves and the effect of the diurnal component of the tide on their generation and propagation could then be determined our results suggest that two solitary waves of equal amplitude propagated eastwards in the strait on june 22 the tidal coefficient being equal to 92 with a speed relative to the ground of 2 1 to 2 6 m s 1 24 h later during the second survey on june 24 tidal coefficient 90 we observed the propagation of a train of non linear waves the speed of the leading wave of which being about 1 9 ms 1 our data show that other waves pass over the camarinal sill after the release of the bore and secondary internal wave trains are shown to propagate eastwards from there although our sar data show the appearance of waves west of the northern sill at about 4 h after high water hw the mechanism leading to their generation is not clear these waves could propagate eastwards all along the strait and or northwestwards along the western spanish coast they could be responsible for the solitary type events observed at the eastern entrance of the strait at about 7 h after hw by ziegenbein 1969 1970 these events are noticeable in the hydrological parameters time series of armi and farmer 1988 and in the high rate current data 2 min apart from their april 1986 cruise besides these alongstrait waves our sar data show the existence of cross strait waves and give an idea of their wavelength and speed of propagation their presence leads to perturbations in the current revealed by simultaneous current data at the camarinal sill and north of cape cires

repeated fracture and healing of silicic magma generate flow banding and earthquakes textures in an exceptionally preserved effusive rhyolite conduit at torfajokull iceland indicate that rising magma repeatedly fractured and healed at shallow levels in the conduit rfh process anastomosing tuffisite veins filled by fine grained juvenile clasts were generated by shear fracture of highly viscous magma in the glass transition interval welding of the particulate material during subsequent deformation led to thorough healing of veins allowing repeated fracture of the same body of magma we propose that the rfh process is a rechargeable trigger mechanism for hybrid seismicity and show that the time scale of the process and the fractures formed by it are consistent with the repeat time and magnitude of hybrid earthquakes during silicic eruptions the rfh process may also form the flow banding that is nearly ubiquitous in obsidian

coastal lee waves on ers 1 sar images alternative dark bright patterns on ers 1 synthetic aperture radar sar images of the west side of the taiwan strait taken on december 8 1994 were recognized to be the sea surface signature of a coastal lee wave such waves are called coastal lee waves because they occur along the lee side of the coast the coastal lee waves appeared in the form of a wave packet distributed within an offshore band 20 40 km wide the first packet which occurred in the northern portion of the observed area contained six waves with variable wavelengths defined as the spatial separation between two waves from 1 7 to 2 7 km the second packet in the middle contained 10 waves with a relatively uniform wavelength of 4 2 km the third packet in the southern portion contained 17 waves with an average wavelength of 2 0 km the crest lengths were from 20 to 80 km local meteorologic parameters observed simultaneously at fuzhou china close to the imaged area showed an offshore wind of 1 5 3 5 m s and a land surface air temperature of 19 c which was 4 c lower than the sea surface temperature sst thus the lower atmospheric boundary conditions at imaging time were very favorable both for generating the land breeze circulation and small wind waves on the sea surface which are in the bragg scattering wavelength band of the c band ers 1 sar a physical model of a three layer atmosphere was developed in order to explain how the land breeze circulation can generate the coastal lee waves the results showed that the vertical velocity disturbance caused by the wind convergence at the land breeze frontal zone is of vital importance for the generation of coastal lee waves and the model gave very good estimates of the processes observed the sar imaging mechanisms of the waves were analyzed in detail the differences between coastal lee waves and ocean internal waves which appear as similar alternative dark bright patterns on sar images were also discussed

seismic hybrid swarm precursory to a major lava dome collapse 9 12 july 2003 soufriere hills volcano montserrat abstract a swarm of 9500 hybrid earthquakes preceded the 12 13 july 2003 dome collapse at soufriere hills volcano montserrat most events had nearly identical waveforms and cross correlation was applied to measure inter event periods as well as phase arrival times to determine accurate relative location hypocenter depths were shallow

precursory characteristics of the seismicity before the 6 august 2012 eruption of tongariro volcano north island new zealand abstract the 6 august 2012 eruption from the upper te maari crater of tongariro volcano followed approximately three weeks of precursory seismic activity earthquake relocations including data from extra temporary stations indicated that nearly all events were in a small area very close to upper te maari most of these relocated events were very shallow with nearly all events being between 1000 and 1500 m below the ground surface the pre eruption seismicity occurred in three main swarms during the first swarm on 12 13 july 2012 all the earthquakes had consistent inter event times of 71 8 min while in the later swarms 17 20 and 29 30 july many events had a similar pattern of consistent inter event times the stationary quasi periodic clockwork earthquake process suggests that a single fracture point was excited by a nearly constant rate flux process the dominant type of earthquake observed in these swarms had a sharp onset and a broad spectrum with strong energy from 2 to 10 hz most events seen had a local magnitude of 1 5 to 2 5 with virtually no smaller events most of these earthquakes appeared to belong to a main earthquake family whose characteristics included a strong spectral component at about 2 hz and three bursts of energy spaced at intervals of about 1 5 s of the 116 located earthquakes 75 had a correlation coefficient greater than 0 70 with a master event the spectra of these events did not change with size with matching frequency peaks for all the events with a high correlation the last event of this type was the day before the 6 august 2012 eruption none have been seen since and there has been very little seismicity under tongariro this seismicity alerted gns science and other organisations to the unrest of tongariro and the volcanic alert level and aviation colour code were raised to publicise this gns science also increased its monitoring of tongariro and discovered that the magmatic gas concentrations had increased compared to previous measurements in may 2012 however the seismicity did not show any accelerating trend that suggested an immediate eruption threat indicating the difficulty of predicting small eruptions in tongariro and similar volcanoes

swarms of repeating long period earthquakes at shishaldin volcano alaska 2001 2004 abstract during 2001 2004 a series of four periods of elevated long period seismic activity each lasting about 1 2 months occurred at shishaldin volcano aleutian islands alaska the time periods are termed swarms of repeating events reflecting an abundance of earthquakes with highly similar waveforms that indicate stable non destructive sources these swarms are characterized by increased earthquake amplitudes although the seismicity rate of one event every 0 5 5 min has remained more or less constant since shishaldin last erupted in 1999 a method based on waveform cross correlation is used to identify highly repetitive events suggestive of spatially distinct source locations the waveform analysis shows that several different families of similar events co exist during a given swarm day but generally only one large family dominates a network of hydrothermal fractures may explain the events that do not belong to a dominant repeating event group i e multiple sources at different locations exist next to a dominant source the dominant waveforms exhibit systematic changes throughout each swarm but some of these waveforms do reappear over the course of 4 years indicating repeatedly activated source locations the choked flow model provides a plausible trigger mechanism for the repeating events observed at shishaldin explaining the gradual changes in waveforms over time by changes in pressure gradient across a constriction within the uppermost part of the conduit the sustained generation of shishaldin s long period events may be attributed to complex dynamics of a multi fractured hydrothermal system the pressure gradient within the main conduit may be regulated by temporarily sealing and reopening of parallel flow pathways by the amount of debris within the main conduit and or by changing gas influx into the hydrothermal system the observations suggest that shishaldin s swarms of repeating events represent time periods during which a dominant source is activated

incorporating seismic observations into 2d conduit flow modeling conduit flow modeling aims to understand the conditions of magma at depth and to provide insight into the physical processes that occur inside the volcano low frequency events characteristic to many volcanoes are thought to contain information on the state of magma at depth therefore by incorporating information from low frequency seismic analysis into conduit flow modeling a greater understanding of magma ascent and its interdependence on magma conditions and physical processes is possible the 2d conduit flow model developed in this study demonstrates the importance of lateral pressure and parameter variations on overall magma flow dynamics and the substantial effect bubbles have on magma shear viscosity and on magma ascent the 2d nature of the conduit flow model developed here allows in depth investigation into processes which occur at or close to the wall such as magma cooling and brittle failure of melt these processes are shown to have a significant effect on magma properties and therefore on flow dynamics by incorporating low frequency seismic information an advanced conduit flow model is developed including the consequences of brittle failure of melt namely friction controlled slip and gas loss this model focuses on the properties and behaviour of magma at depth within the volcano and their interaction with the formation of seismic events by brittle failure of melt

theory of radar imaging of internal waves radar images taken over ocean areas in particular those obtained by the synthetic aperture radar sar onboard the american seasat satellite in 19781 2 sometimes show features that seem to be surface manifestations of oceanic internal waves3 11 here i present a theory explaining the large radar signatures of internal waves in which the imaging is attributed to variations in the short scale surface roughness induced by current variations associated with internal waves

numerical study on signatures of atmospheric convective cells in radar images of the ocean current and wind variations at the ocean surface can give rise to a modulation of the sea surface roughness and thus become visible in radar images the discrimination between radar signatures of oceanic and atmospheric phenomena can be quite difficult since signatures of different origin can have very similar shapes and magnitudes and are often superimposed upon each other in this work we employ a numerical radar imaging model for an investigation of typical properties of radar signatures of atmospheric convective cells and of theoretical differences between such atmospherically induced radar signatures and those of oceanic phenomena we show that main characteristics of observed multifrequency multipolarization radar signatures of atmospheric convective cells over the gulf stream are reproduced quite well by the proposed model this encourages us to vary wind and radar parameters systematically in order to get a general overview of the dependency of atmospherically induced radar signatures on these parameters finally we compare typical characteristics of radar signatures of atmospheric and oceanic phenomena and we present simulated radar images of a scenario of superimposed atmospheric convective cells and oceanic internal waves we show that the proposed model supports the experimental finding that radar signatures of oceanic phenomena are stronger at horizontal hh than at vertical vv polarization while atmospherically induced radar signatures are better visible at vv polarization

application of artificial neural networks for the classification of the seismic transients at soufriere hills volcano montserrat 1 seismic activity at soufriere hills volcano is characterized by a variety of transients such as tectonic earthquakes long period events hybrid events and rockfalls the huge quantity of seismic data daily recorded on the volcano makes the application of automatic processing highly recommendable we propose a method of supervised classification of the transients based on artificial neural networks ann which may be useful for processing the large data sets piled up in the past particularly data sets recorded before the climactic eruptions from 1995 to 2002 may allow us to reconstruct the distribution of the different classes of seismic transients in time we believe that this analysis may give useful insights into impending eruptive scenarios the good performance of the ann with 70 of transients correctly classified in a test set of 156 data along with the opportunity to revise the misfits make ann a powerful tool for data processing

faulting within the mount st helens conduit and implications for volcanic earthquakes the 2004 2008 eruption of mount st helens produced seven dacite spines mantled by cataclastic fault rocks comprising an outer fault core and an inner damage zone these fault rocks provide remarkable insights into the mechanical processes that accompany extrusion of degassed magma insights that are useful in forecasting dome forming eruptions the outermost part of the fault core consists of finely comminuted fault gouge that is host to 1 to 3 mm thick layers of extremely fine grained slickenside bearing ultracataclasite interior to the fault core there is an 2 m thick damage zone composed of cataclastic breccia and sheared dacite and interior to the damage zone there is massive to flow banded dacite lava of the spine interior structures and microtextures indicate entirely brittle deformation including rock breakage tensional dilation shearing grain flow and microfaulting as well as gas and fluid migration through intergranular pores and fractures in the damage zone slickenside lineations and consistent orientations of riedel shears indicate upward shear of the extruding spines against adjacent conduit wall rocks paleomagnetic directions demagnetization paths oxide mineralogy and petrology indicate that cataclasis took place within dacite in a solidified steeply dipping volcanic conduit at temperatures above 500 c low water content of matrix glass is consistent with brittle behavior at these relatively high temperatures and the presence of tridymite indicates solidification depths of more than a million small and low frequency drumbeat earthquakes with coda magnitudes m d 2 slip patches possibly along observed extensive principal shear zones within the fault core but probably not along the smaller riedel shears although our field and structural data are compatible with stick slip models they do not rule out seismic and infrasound models that call on resonance of steam filled fractures to generate the drumbeat earthquakes we suggest that stick slip and gas release processes may be coupled and that regardless of the source mechanism the distinctive drumbeat earthquakes are proving to be an effective precursor for dome forming eruptions our data document a continuous cycle of deformation along the conduit margins beginning with episodes of fracture in the damage zone and followed by transfer of motion to the fault core we illustrate the cycle of deformation using a hypothetical cross section of the mount st helens conduit extending from the surface to the depth of magmatic solidification

multiple ruptures for long valley microearthquakes a link to volcanic tremor despite several episodes of ground deformation and intense seismic activity starting in 1978 the long valley california volcanic area has not produced clearly recognized volcanic tremor instead a variety of atypical microearthquakes have been recorded during these episodes including events dominated by low frequency long period or mixed high and low frequency hybrid signals during a 1997 episode a number of unusual microearthquakes occurred within a temporary 40 station seismic network surrounding the casa diablo area allowing the events to be precisely located and analyzed as a function of azimuth offset and source characteristics eight prime examples lie within two 7 km deep clusters of seismicity separated by about 1 km with four events in each cluster empirical green s function deconvolution shows that these events are composed of two to three sub events the sub events consisting of ordinary single rupture double couple microearthquakes the delay times between the sub events are constant within each cluster equaling 0 092 s in one and 0 06 s in the other events from other clusters show similar delays the signal interference produced by the closely spaced sub events gives rise to modulated delay dependent source spectra the regularity of the delays suggests that the sub events are being triggered by a fixed length and or time scale process an example being the length inflation rate of a magmatic or hydrothermal flow structure with continued action of the triggering process the sub events could proliferate and evolve into observable volcanic tremors at mammoth

observation of tropical cyclones by high resolution scatterometry unprecedented views of surface wind fields in tropical cyclones hereafter tcs are provided by the european remote sensing satellite ers c band scatterometer scatterometer measurements at c band are able to penetrate convective storms clouds observing the surface wind fields with good accuracy however the resolution of the measurements 50x50 km 2 limits the interpretation of the scatterometer signals in such mesoscale events the strong gradients of the surface wind existing at scales of a few kms are smoothed in the measured features such as the intensity and location of the wind maxima and the position of the center beyond the ers systems the scatterometers on board the adeos and metop satellites designed by the jet propulsion laboratory and by the european space agency respectively will be able to produce measurements of the backscattering coefficient at about 25x25 km 2 resolution a few sets of ers 1 orbits sampling tc events were produced with an experimental 25x25 km 2 resolution enhancing the resolution by a factor of 2 allows location of the wind maxima and minima in a tc with a much better accuracy than at 50 km resolution in addition a better resolution reduces the geophysical noise variability of wind speed within the cell and effect of rain that dominates the radiometric noise and hence improves the definition of the backscattering measurements a comprehensive analysis of the backscattering measurements in the case of high winds and high sea states obtained within tcs is proposed in order to refine the interpretation of the wind vector derived from a backscattering model that is currently only calibrated up to moderate winds 20 m s in neutral conditions observations of the topex poseidon dual frequency altimeter are also used for that purpose patterns of the surface winds in tcs are described and characteristic features concerning asymmetries in the maximum winds and in the divergence field are discussed

travelling waves and bores in the lower atmosphere the morning glory and related phenomena abstract observations of solitary wave and travelling bore like disturbances in the lower atmosphere are reviewed together with relevant theoretical laboratory and numerical studies concerning the structure propagation and genesis of such disturbances primary emphasis is given to a discussion of the morning glory phenomenon in northern australia the example par excellence of these types of disturbance and the best documented observationally to date observations of related phenomena elsewhere are reviewed briefly while such occurrences appear to be less frequent in any single location than in the southern gulf of carpentaria region of northern australia reported occurrences are widespread and there is mounting evidence that such disturbances are more common than is generally supposed the evidence suggests that whenever a suitable wave guide exists for the propagation of disturbances the latter can be generated as the natural response of quite general forcing mechanisms examples being the collision of two sea breezes from opposite directions on a peninsula the interaction between a thunderstorm outflow and a sea breeze front or simply the transformation of a thunderstorm or squall line outflow as it moves into a low level stable layer because of the large vertical displacements they produce the larger amplitude disturbances typically with surface pressure jumps of 1 mb or more must be considered as potential triggers for deep convection if the atmosphere is sufficiently conditionally unstable and the large low altitude wind shears associated with them present a serious hazard to low flying aircraft

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

synthetic aperture radar observation of the sea surface imprints of upstream atmospheric solitons generated by flow impeded by an island 1 two cases of upstream propagation of atmospheric solitons generated by atmospheric flow over topography were identified on two radarsat 1 synthetic aperture radar sar images acquired near st lawrence island in the bering sea on 7 september 1997 and 6 june 2001 respectively in both cases a group of solitons was shown as three dark bright linear features on the sar images the soliton width and peak to peak distance measured from the two sar images are about 3 km and 4 5 km respectively simultaneous radiosonde measurements a surface weather map and operational weather model results confirm that these waves did not propagate on the lee side of the island as is commonly observed with island lee waves but indeed propagated against the flow in the upstream direction in the second case the same group of solitons was also identified as a wave like cloud pattern on a modis image taken about 4 5 hours later in this modis image the soliton train propagated further upstream with the leading crest reaching about 30 km north of the island and the number of crest trough features increased from three to seven in this study we describe the generation and evolution of upstream atmospheric solitons using the force kdv fkdv model with radiosonde and island topography data the numerical solution of the fkdv exhibits a sequence of solitons propagating upstream of the island both temporal and spatial scales of the solitons are in good agreement with that estimated from the successive sar and modis satellite images

seismicity associated with dome growth and collapse at the soufriere hills volcano montserrat varied seismicity has accompanied growth and collapse of the lava dome of the soufriere hills volcano montserrat earthquakes have been classified as either volcano tectonic long period or hybrid and daily variations in the numbers of events have mapped changes in the style of eruption repetitive hybrid earthquakes were common during the first months of dome growth in july 1996 the style of seismicity changed and regular short lived hybrid earthquake swarms became common this change was probably caused by an increase in the magma flux earthquake swarms have preceded almost all major dome collapses and have accompanied cyclical deformation thought to be due to a build up of pressure in the upper conduit which is later released by magma moving into the dome

internal waves in the strait of messina studied by a numerical model and synthetic aperture radar images from the ers 1 2 satellites a new numerical two layer model is presented which describes the generation of internal tidal bores and their disintegration into internal solitary waves in the strait of messina this model is used to explain observations made by the synthetic aperture radar sar from the european remote sensing satellites ers 1 and ers 2 the analysis of available ers 1 2 sar data of the strait of messina and adjacent sea areas show that 1 northward as well as southward propagating internal waves are generated in the strait of messina 2 southward propagating internal waves are observed more frequently than northward propagating internal waves 3 sea surface manifestations of southward as well as northward propagating internal waves are stronger during periods where a strong seasonal thermocline is known to be present 4 southward propagating internal bores are released from the sill between 1 and 5 hours after maximum northward tidal flow and northward propagating internal bores are released between 2 and 6 hours after maximum southward tidal flow and 5 the spatial separation between the first two internal solitary waves of southward propagating wave trains is smaller in the period from july to september than in the period from october to june the numerical two layer model is a composite of two models consisting of 1 a hydrostatic generation model which describes the dynamics of the water masses in the region close to the strait s sill where internal bores are generated and 2 a weakly nonhydrostatic propagation model which describes the dynamics of the water masses outside of the sill region where internal bores may disintegrate into internal solitary waves due to a technique for movable lateral boundaries the generation model is capable of simulating the dynamics of a lower layer that may intersect the bottom topography the proposed generation propagation model depends on one space variable only but it retains several features of a fully three dimensional model by including a realistic channel depth and a realistic channel width it is driven by semidiurnal tidal oscillations of the sea level at the two open boundaries of the model domain numerical simulations elucidate several observed characteristics of the internal wave field in the strait of messina such as north south asymmetry times of release of the internal bores from the strait s sill propagation speeds and spatial separations between the first two solitary waves of internal wave trains

multiplets their behavior and utility at dacitic and andesitic volcanic centers 1 multiplets or groups of earthquakes with similar waveforms are commonly observed at volcanoes particularly those exhibiting unrest using triggered seismic data from the 1980 1986 mount st helens msh eruption we have constructed a catalog of multiplet occurrence our analysis reveals that the occurrence of multiplets is related at least in part to the viscosity of the magma we also constructed catalogs of multiplet occurrence using continuous seismic data from the 2004 eruption at msh and 2007 eruption at bezymianny volcano russia prior to explosions at msh in 2004 and bezymianny in 2007 the multiplet proportion of total seismicity mpts declined while the average amplitudes and standard deviations of the average amplitude increased the life spans of multiplets time between the first and last event were also shorter prior to explosions than during passive lava extrusion dome forming eruptions that include a partially solidified plug like msh 1983 1986 and 2004 2008 often possess multiplets with longer life spans and mpts values exceeding 50 conceptually the relatively unstable environment prior to explosions is characterized by large and variable stress gradients brought about by rapidly changing overpressures within the conduit we infer that such complex stress fields affect the number of concurrent families mpts average amplitude and standard deviation of the amplitude of the multiplets we also argue that multiplet detection may be an important new monitoring tool for determining the timing of explosions and in forecasting the type of eruption

repeating coupled earthquakes at shishaldin volcano alaska since it last erupted in 1999 shishaldin volcano aleutian islands alaska has produced hundreds to thousands of longperiod 1 2 hz lp earthquakes every day with no other sign of volcanic unrest in 2002 the earthquakes also exhibited a short period 4 7 hz sp signal occurring between 3 and 15 s before the lp phase although the sp phase contains higher frequencies than the lp phase its spectral content is still well below that expected of brittle failure events the sp phase was never observed without the lp phase although lp events continued to occur in the absence of the precursory signal the twophased events are termed bcoupled eventsq reflecting a triggered relationship between two discrete event types both phases are highly repetitive in time series suggestive of stable non destructive sources waveform cross correlation and spectral coherence are used to extract waveforms from the continuous record and determine precise p wave arrivals for the sp phase although depths are poorly constrained the sp phase is believed to lie at shallow b4 km depths just west of shishaldin s summit the variable timing between the sp and lp arrivals indicates that the trigger mechanism between the phases itself moves at variable speeds a model is proposed in which the sp phase results from fluid moving within the conduit possibly around an obstruction and the lp phase results from the coalescence of a shallow gas bubble the variable timing is attributed to changes in gas content within the conduit the destruction of the conduit obstacle on november 21 2002 resulted in the abrupt disappearance of the sp phase published by elsevier b v

observation of a nonlinear wave disturbance in the marine atmosphere by the synthetic aperture radar aboard the ers 1 satellite a nonlinear wave disturbance in the marine atmosphere associated with an atmospheric cold front has been identified on a spaceborne radar image of the north sea by its imprint on the sea surface this nonlinear wave disturbance is either a solitary wave disturbance or an undular bore propagating in the lower marine atmosphere the radar image showing sea surface manifestations of this atmospheric wave disturbance was acquired over the north sea by the synthetic aperture radar sar aboard the first european remote sensing satellite ers 1 on march 8 1992 atmospheric waves become visible on radar images of the sea surface because they are associated with a varying wind field at the sea surface which modulates the sea surface roughness and thus the backscattered radar power the identification of the wave pattern visible on the ers 1 sar image as a sea surface manifestation of an atmospheric nonlinear wave disturbance has been possible because this disturbance was also captured by meteorological sensors mounted on an 80 m high meteorological mast located on the island of heligoland geophysical parameters characterizing the atmospheric wave disturbance are derived from the ers 1 sar image and from the in situ meteorological data the wave period in the reference frame moving with the average wind is 9 5 min the average wavelength is 2300 m and the propagation velocity is 4 5 4 9 m s 1 estimates of the amplitude of the wind speed fluctuations in the wave propagation direction derived from the meteorological measurements at heligoland and from the gray level variations in the sar image yield values between 1 3 and 3 0 m s 1 the experimental data are interpreted in terms of theories of atmospheric nonlinear gravity waves

on the discrimination of radar signatures of atmospheric gravity waves and oceanic internal waves on synthetic aperture radar images of the sea surface synthetic aperture radar sar images acquired over the ocean frequently show sea wave like patterns that have wavelengths well above those of ocean surface waves and that are sea surface signatures of oceanic internal waves oiws or of atmospheric gravity waves agws however it is often difficult to decide whether they result from the first or the second kind of waves which has led many investigators to misinterpret sar images of the sea surface based on solitary wave and radar imaging theories of agws and oiws we present criteria that help distinguish between them however there are cases where these criteria which are based solely on the shape and structure of the features visible on the sar images yield ambiguous results in these cases one must resort to additional information on the generation of agws and oiws which are listed in this paper

existence de mineralisations plombo zinciferes syngenetiques du substratum cambrien du district des malines gard france l essentiel du minerai actuellement exploite dans le district minier des malines gard france provient d amas plombo zinciferes apparamment constitues par le remplissage de cavites paleo karstiques post stephaniennes developpees dans la dolomie cambrienne a proximite de la surface de discordance qui la separe de sa couverture mesozoique l etude detaillee des mineralisations du substrat carbonate revele l existence de concentrations egalement plombo zinciferes mais stratoides et syngenetiques de la dolomie qui les supporte en effet ces mineralisations ont enregistre tous les phenomenes ayant affecte la dolomie encaissante figures de sedimentation et de deformation synmetamorphe orogenie varisque fracturation post schisteuse anterieure a la discordance permo triasique il est propose de considerer que ce type de mineralisation alimenta en metaux de base voire en soufre les pieges karstiques post hercyniens on en trouve notamment remanie a l etat d elements brechiques dans les remplissages paleo karstiques

seismological studies of the soufriere of st vincent 1953 79 implications for volcanic surveillance in the lesser antilles abstract the soufriere of st vincent has been monitored for more than 25 years as part of a regional programme in the lesser antilles in that time the volcano has erupted twice but our studies have shown no discernible change in regional seismicity before either event however very small seismic events were observed in the crater during the 1971 1972 eruption and were detected before the start of the 1979 explosive eruption we believe that they were generated by thermally induced hydraulic fracturing within the lava mass inside the crater lake we conclude that seismographic monitoring of lesser antillean volcanoes can give ambiguous results but that at least one instrument must be placed within 1 km of the vent if the earliest signs of activity are to be detected

the rise and fall of periodic drumbeat seismicity at tungurahua volcano ecuador abstract highly periodic drumbeat long period lp earthquakes have been described from several andesitic and dacitic volcanoes commonly accompanying incremental ascent and effusion of viscous magma however the processes controlling the occurrence and characteristics of drumbeat and lp earthquakes more generally remain contested here we use new quantitative tools to describe the emergence evolution and degradation of drumbeat lp seismicity at the andesitic tungurahua volcano ecuador in april 2015 the signals were recorded during an episode of minor explosive activity and ash emission without lava effusion and are the first to be reported at tungurahua during the ongoing 17 yrs of eruption following four days of high levels of continuous and pulsed tremor highly periodic lp earthquakes first appear on 10 april over the next four days inter event times and event amplitudes evolve through a series of step wise transitions between stable behaviors each involving a decrease in the degree of periodicity families of similar waveforms persist before during and after drumbeat activity but the activity levels of different families change coincidentally with transitions in event rate amplitude and periodicity a complex micro seismicity initiation sequence shows pulse like and stepwise changes in inter event times and amplitudes in the hours preceding the onset of drumbeat activity that indicate a partial de coupling between event size and rate the observations increase the phenomenology of drumbeat lp earthquakes and suggest that at tungurahua they result from gas flux and rapid depressurization controlled by shear failure of the margins of the ascending magma column

scylla and charybdis observed from space scylla and charybdis are in greek mythology two immortal and irresistible monsters who beset the narrow waters separating the italian peninsula from sicily they give poetic expressions to exceptional oceanographic features encountered in the strait of messina recently the seasat satellite has added new information on the oceanography of this strait for the first time experimental evidence is presented that internal waves are generated in the strait of messina the generation mechanism is linked to tidal currents washing over the shallow sill within the strait the experimental data originate from a synthetic aperture radar sar image obtained from the seasat satellite on sept 15 1978 and from subsequent in situ measurements carried out from the italian research vessel bannock in nov 1980 the circular wave pattern visible on the seasat sar image is interpreted in terms of internal solitons furthermore the seasat sar image also reveals tagli special types of tidal bores encountered in the strait of messina

atmospheric boundary layer rolls observed by the synthetic aperture radar aboard the ers 1 satellite two synthetic aperture radar sar images acquired by the european remote sensing satellite ers 1 over the jade weser estuary in the german bight of the north sea on january 2 and 20 1992 are analyzed the images show sea surface manifestations of atmospheric boundary layer rolls this is inferred from the orientation of the quasi periodic sea surface patterns which are aligned approximately with the wind direction from the ratio of the wavelength of the patterns to the height of the boundary layer and from the conditions encountered in the atmospheric boundary layer as measured quasi simultaneously by radiosondes the atmospheric boundary layer rolls were generated by a dynamic instability on january 2 and by a thermal instability on january 20 for the first time quantitative estimates of variations of the wind velocity at the sea surface associated with the atmospheric rolls are extracted from a spaceborne radar sar image it is shown that wind velocities derived from sar image intensity variations are in agreement with theoretical estimates

observations of hybrid seismic events at soufriere hills volcano montserrat july 1995 to september 1996 swarms of small repetitive events with similar waveforms and magnitudes are often observed during the emplacement of lava domes over 300 000 such events were recorded in association with the emplacement of the lava dome at soufriere hills volcano montserrat from august 1995 through august 1996 these events originated 2 3 km deep they exhibited energy ranging over 1 5 4 5 hz and were broader band than typical long period events we term the events hybrid between long period and volcano tectonic the events were more impulsive and broader band prior to compared with during and after periods of inferred increased magma flux rate individual swarms contained up to 10 000 events often exhibiting very similar magnitudes and waveforms throughout the swarm swarms lasted hours to weeks during which inter event intervals generally increased then decreased often several times long duration swarms began about every two months starting in late september 1995 we speculate that the events were produced as the magma column degassed into adjacent cracks

dome growth behavior at soufriere hills volcano montserrat revealed by relocation of volcanic event swarms 1995 1996 abstract we have relocated a subset of events from the digital waveform catalogue of 17 000 volcanic microearthquakes recorded between july 1995 and february 1996 at soufriere hills volcano shv montserrat using a cross correlation based phase repicking technique with a joint location method hypocenters were estimated for 3914 earthquakes having five or more corrected p wave picks the seismic source region collapsed to a volume of 1 km 3 from an initial 100 km 3 relocated events represent 36 swarms each containing nearly identical waveforms having source dimensions of 10 to 100 m in diameter and spatial separations on the order of 500 m or less each swarm occurred over a span of several hours to a few days triggered data appear to miss between 65 and 98 of the events that occur within these swarms based on review of helicorder records visual estimates of summit dome growth show a rough correspondence between episodes of intense swarming and increases in extruded magma although dome observations are too sparse to make a direct comparison for this time period the limited depth range over which dome growth related events occur is consistent with a dynamic model of cyclic plug extrusion behavior in the shallow conduit governed by magma supply rate overpressure buildup and physical properties of the magma and conduit geometry seismic sources may occur in locally overpressured regions that result from microlite formation in a zone of rapid decompression we propose that this zone exists in the vicinity of a detachment plane associated with the cyclic plug extrusion

an ers 1 synthetic aperture radar image of atmospheric lee waves an ers 1 synthetic aperture radar sar image of the island hopen shows a distinct 7 6 km wavelength wave phenomenon near the island this wave phenomenon is interpreted as the surface imprint on open water of atmospheric lee waves the pattern is visible in the sar image since the lee waves modulate the horizontal wind speed near the ocean surface which in turn modulates the surface roughness and the radar cross section the physical setting for the observation is presented and discussed the lower bound on horizontal wind speed modulation is estimated to range from 3 2 ms 1 for the wind speed minima to 12 2 ms 1 for the wind speed maxima based upon the observed radar cross section modulation and the ers 1 scatterometer wind retrieval model cmod4 the wavelength and wind speed modulation are consistent with linear lee wave model predications the model uses an atmosphere with an exponential profile of the scorer parameter ratio of buoyancy frequency to wind speed to represent a shallow ground based inversion layer observed at bear island and a bell shaped barrier to represent the forcing effects of hopen

analysis of nonlinear internal waves observed by landsat thematic mapper in this work we test the compatibility between the theoretical parameters of a nonlinear wave model and the quantitative information that one can deduce from satellite derive0 data the theoretical parameters are obtained by applying an inverse problem to the solution of the cauchy problem for the korteweg de vries equation our results are applied to the case of internal wave patterns elaborated from two different satellite sensors at the south of messina the thematic mapper and at the north of messina the synthetic aperture radar

automatic classification of volcano seismic signatures the prediction of volcanic eruptions and the evaluation of associated risks remain a timely and unresolved issue this paper presents a method to automatically classify seismic events linked to volcanic activity as increased seismic activity is an indicator of volcanic unrest automatic classification of volcano seismic events is of major interest for volcano monitoring the proposed architecture is based on supervised classification whereby a prediction model is built from an extensive data set of labeled observations relevant events should then be detected three steps are involved in the building of the prediction model i signals preprocessing ii representation of the signals in the feature space and iii use of an automatic classifier to train the model our main contribution lies in the feature space where the seismic observations are represented by 102 features gathered from both acoustic and seismic fields ideally observations are separable in the feature space depending on their class the architecture is tested on 109 609 seismic events that were recorded between june 2006 and september 2011 at ubinas volcano peru six main classes of signals are considered long period events volcanic tremors volcano tectonic events explosions hybrid events and tornillos our model reaches 93 5 0 50 accuracy thereby validating the presented architecture and the features used furthermore we illustrate the limited influence of the learning algorithm used i e random forest and support vector machines by showing that the results remain accurate regardless of the algorithm selected for the training stage the model is then used to analyze 6 years of data

detection and classification of mesoscale atmospheric phenomena above sea in sar imagery abstract satellite radar observations above sea are dedicated to small scale and mesoscale phenomena in the ocean and the marine boundary layer what the synthetic aperture radar sar sensors see on the ocean surface is primarily the variation of the bragg resonant waves providing signatures of local wind changes and imprints of atmospheric phenomena and the areas of enhanced wave breaking associated with wave current interaction for oceanographic processes like currents fronts and eddies sar images contain information about the processes in the marine atmosphere boundary layer mabl in particular when variation of wind speed and direction is significant several publications are available in the literature modeling and explaining each phenomenon separately however only a few focus on the identification of each phenomenon in an automatic or semi automatic way the objective of the present paper is to detect and to classify five atmospheric phenomena in sar images low wind areas katabatic wind island wakes atmospheric gravity waves and atmospheric convective cells an object based environment was used to identify the phenomena and fuzzy logic used to classify them several features extracted for each phenomenon were used for feeding the classifier the proposed method used 16 sar images and accuracy was examined in another 16 sar images using 457 object samples the method proved to be successful with an overall accuracy of 80 and kappa index of 0 75 the class of low wind areas negatively affected the overall accuracy due to overlapping feature values with the rest of the categories

simultaneous observations of rain cells over the ocean by the synthetic aperture radar aboard the ers satellites and by surface based weather radars radar images acquired over the ocean by the c band synthetic aperture radar sar aboard the european remote sensing satellites ers 1 and ers 2 often show sea surface manifestations of rain cells we have searched the archives of several weather stations for weather radar data acquired concurrently with ers sar data and have found four concurrent data pairs one in the south china sea two in the baltic sea and one in the north sea the comparison of ers 1 2 sar images showing radar signatures of rain cells with weather radar images reveals that the radar signatures of rain cells on ers sar images vary considerably which makes it often difficult to distinguish them from radar signatures of other mesoscale or submesoscale atmospheric and oceanic phenomena the present analysis together with results obtained from previous analyses of spaceborne multifrequency sar data and laboratory data as well as results obtained from theoretical models on radar backscattering at the sea surface suggest the following c band radar signatures of rain cells with rain rates below 50 mm h are mainly caused by a modification of the sea surface roughness induced by 1 the raindrops impinging on the sea surface and thus modifying the sea surface roughness and by 2 local wind field variations associated with rain cells spreading downdrafts raindrops impinging on the sea surface generate ring waves as well as turbulence in the upper water layer depending on rain rate drop size distribution wind speed and temporal evolution of the rain event the net effect can be an increase or a reduction of the amplitude of the c band bragg waves and thus of the backscattered radar power thus ocean areas struck by rain can show up on ers sar images as areas with higher or lower image brightness than the surroundings

fault textures in volcanic conduits evidence for seismic trigger mechanisms during silicic eruptions it is proposed that fault textures in two dissected rhyolitic conduits in iceland preserve evidence for shallow seismogenic faulting within rising magma during the emplacement of highly viscous lava flows detailed field and petrographic analysis of such textures may shed light on the origin of long period and hybrid volcanic earthquakes at active volcanoes there is evidence at each conduit investigated for multiple seismogenic cycles each of which involved four distinct evolutionary phases in phase 1 shear fracture of unrelaxed magma was triggered by shear stress accumulation during viscous flow forming the angular fracture networks that initiated faulting cycles transient pressure gradients were generated as the fractures opened which led to fluidisation and clastic deposition of fine grained particles that were derived from the fracture walls by abrasion fracture networks then progressively coalesced and rotated during subsequent slip phase 2 developing into cataclasite zones with evidence for multiple localised slip events fluidisation and grain size reduction phase 2 textures closely resemble those formed on seismogenic tectonic faults characterised by friction controlled stick slip behaviour increasing cohesion of cataclasites then led to aseismic distributed ductile deformation phase 3 and generated deformed cataclasite zones which are enriched in metallic oxide microlites and resemble glassy pseudotachylite continued annealing and deformation eventually erased all structures in the cataclasite and formed microlite rich flow bands in obsidian phase 4 overall the mixed brittle ductile textures formed in the magma appear similar to those formed in lower crustal rocks close to the brittle ductile transition with the rheological response mediated by strain rate variations and frictional heating fault processes in highly viscous magma are compared with those elsewhere in the crust and this comparison is used to appraise existing models of volcano seismic activity based on the textures observed it is suggested that patterns of long period and hybrid earthquakes at silicic lava domes reflect friction controlled stick slip movement and eventual healing of fault zones in magma which are an accelerated and smaller scale analogue of tectonic faults

spatio temporal evolution of volcano seismicity a laboratory study we report a laboratory and microstructural study of a suite of deformation experiments in which basalt from mount etna volcano is deformed and fractured at an effective confining pressure representative of conditions under a volcanic edifice 40 mpa particular attention was paid to the formation of a fracture and damage zone with which to stimulate coupled hydro mechanical interactions that create the various types of seismicity recorded on volcanic edifices and which usually precede eruption location of ae events through time shows the formation of a fault plane during which waveforms exhibit the typical high frequency characteristics of volcano tectonic vt earthquakes we found that these vt earthquakes were particularly pronounced when generated using dry samples compared to samples saturated with a pore fluid water vt events generated during deformation of water saturated sample are characterised by a distinctive high frequency onset and a longer low frequency coda exhibiting properties often seen in the field as hybrid events we present evidence that hybrid events are in fact the common type of volcanic seismic event with either vt or low frequency lf events representing end members and whose proportion depend on pore fluid being present in the rock type being deformed as well as how close the rock is to failure we find a notable trend of reducing instances of hybrid events leading up to the failure stage in our experiments suggesting that during this stage the pore fluid present in the rock moves sufficiently quickly to provide a resonance seen as a lf coda our data supports recent modeling and field studies that postulate that hybrid events generated in volcanic areas are likely to be generated through the interaction of hydrothermal fluids moving through a combination of pre existing microcrack networks and larger faults such as those we observe in forensic post test examination

volcanic hybrid earthquakes that are brittle failure events 1 volcanoes generate a variety of pre eruptive low frequency seismic signals hybrid earthquakes comprise a class of these signals having high frequency onsets followed by low frequency ringing they are used empirically to predict eruptions but their ambiguous physical origin limits their diagnostic use the short duration near field hybrid seismograms associated with the 2004 mount st helens eruption indicate that much of the prolonged signal is due to path rather than resonating fluids we show using seismic source spectra that the hybrids have a corner frequency seismic moment relationship that scales consistently with brittle failure the unusually low frequency of these earthquakes can result from low rupture velocities combined with strong path effects due to their shallow sources this new application of near field instrumentation provides the first seismological evidence for brittle failure as a major process in dome building and suggests that hybrids should not be used as direct indicators of fluids

direct influence of gravity waves on surface layer stress during a cold air outbreak as shown by synthetic aperture radar abstract synthetic aperture radar sar images of oceans and the great lakes have provided a highly detailed means of observing atmospheric boundary layer phenomena such as convection land breezes and internal gravity waves this is possible because the backscattered radiation detected by sar can be dominated by scattering from wind driven capillary waves whose spatial variation is visible as patterns in the sar images in this paper we present two case studies in which sar images taken over lake superior demonstrate spatial variability in the surface wind stress created over the lake by coincident gravity waves and boundary layer convection during cold air outbreaks of particular interest is the direct influence of the gravity waves on the lake surface stress despite the intervening highly convective atmosphere as well as the detailed view of the fetch dependence of that stress

investigation of multifrequency multipolarization radar signatures of rain cells over the ocean using sir c x sar data radar signatures of rain cells are investigated using multifrequency multipolarization synthetic aperture radar sar images acquired from the space shuttle endeavour during the spaceborne imaging radar c x band sar sir c x sar missions in april and october 1994 in sir c x sar images radar signatures of rain cells over the ocean usually consist of irregularly shaped bright and dark patches that strongly depend on radar frequency and polarization the radar signatures of rain cells observed in sir c x sar imagery of the ocean originate from 1 the scattering and attenuation of the microwaves by raindrops and ice particles in the atmosphere and 2 the modification of the sea surface roughness induced by the impact of raindrops and by wind gusts associated with rain cells raindrops impinging on the sea surface generate ring waves which enhance the sea surface roughness but they also generate turbulence in the upper water layer which reduces the sea surface roughness depending on the radar wavelength ocean areas struck by rain can have higher or lower normalized radar cross section nrcs than the surrounding rain free area in ocean areas where heavy rain is impinging on the sea surface the x and c band nrcs is usually enhanced and the l band nrcs is reduced from the phase difference between the horizontally and vertically copolarized signals estimates of the rain rate are obtained the present analysis shows further that the presently used wind speed retrieval algorithms for the scatterometers aboard the ers and adeos satellites may yield biased wind fields if several rain cells lie within a scatterometer resolution cell

the relationship between degassing and ground deformation at soufriere hills volcano montserrat we examine the correlations between so2 emission rate seismicity and ground deformation in the month prior to the 25 june 1997 dome collapse of the soufriere hills volcano montserrat during this period the volcano exhibited a pattern of cyclic inflation and deflation with an 8 14 h period we find that so 2 emission rates measured by cospec correlate with the amplitude of these tilt cycles and that higher rates of so 2 emission were associated with stronger ground deformation and enhanced hybrid seismicity within tilt cycles degassing peaks coincide with maximum deformation gradients increases in the amount of gas in the magma conduit feeding the dome probably due to increases in volatile content of ascending magma volume can account for the observed increases in tilt amplitude hybrid seismicity and so2 emission rate q 2000 elsevier science b v all rights reserved

classification of the global sentinel 1 sar vignettes for ocean surface process studies abstract spaceborne synthetic aperture radar sar can provide finely resolved meters scale images of ocean surface roughness day or night in nearly all weather conditions this makes it a unique asset for many geophysical applications initially designed for the measurement of directional ocean wave spectra sentinel 1 sar wave mode wv vignettes are small 20 km scenes that have been collected globally since 2014 recent wv data exploration reveals that many important oceanic and atmospheric phenomena are also well captured but not yet employed by the scientific community however expanding applications of this whole massive dataset beyond ocean waves requires a strategy to automatically identify these geophysical phenomena in this study we propose to apply the emerging deep learning approach in ocean sar scenes classification the training is performed using a hand curated dataset that describes ten commonly occurring atmospheric or oceanic processes our model evaluation relies on an independent assessment dataset and shows satisfactory and robust classification results to further illustrate the model performance regional patterns of rain and sea ice are qualitatively analyzed and found to be very consistent with independent remote sensing datasets in addition these high resolution wv sar data can resolve fine sub km scale spatial structure of rain events and sea ice that complement other satellite measurements overall such automated sar vignettes classification may open paths for broader geophysical application of maritime sentinel 1 acquisitions

seismic and hydroacoustic observations of the 2016 17 bogoslof eruption in mid december 2016 bogoslof volcano alaska began an 8 5 month long eruption that produced at least 70 explosions and three lava domes bogoslof is an emergent submarine volcano with only the very top forming a small island so the eruptive activity mostly occurred from a vent submerged beneath a bay or lagoon the bogoslof eruption was recorded on regional seismic and infrasound arrays as well as by a hydrophone that was deployed locally during the second half of the eruption since few emergent volcanic eruptions have seismo acoustic recordings these observations taken in context with satellite and other observations provide an opportunity to greatly improve our understanding of the seismo acoustic signals produced by these eruptions the instruments detected a range of activity including earthquakes tremor and mass flow events earthquakes occurred before during after and unassociated with explosions and also often occurred in swarms the 47 seismically detected swarms and 27 additional hydroacoustically detected swarms can be further broken into four types precursory post eruptive general and tremor dominated most seismic swarms were less than 10 h long had fewer than 50 earthquakes and had average earthquake rates below 20 h for the explosions we calculate a tremor magnitude frequency index and average frequency the tremor magnitudes determined from the hydrophone data show a roughly linear relation to explosion plume height though this relation was not clear in the more limited seismic data lastly we categorize the activity into five eruption phases based on seismo acoustic character precursory opening explosive i pause and explosive ii

high precision relative locations of earthquakes at mount st helens washington several earthquake sequences have occurred at mount st helens as clusters of shallow events with nearly identical waveforms multiplets we present a technique that allows the relative relocation of events within a multiplet to at least an order of magnitude higher precision than is typically possible with traditional techniques a multiplet is studied in pairs of events called doublets each doublet is made up of a reference event and one other event from the multiplet the cross spectrum of a short window beginning just before the p arrival is used to compute differences in arrival times between seismograms from the same station for each doublet these time differences computed with a precision of 1 2 ms are then used to locate each earthquake relative to the reference event engineering explosions with well known locations are used to test the relocation technique explosions can be relocated with accuracy better than 20 m for events within 250 m of the reference explosion the relocation technique is applied to earthquakes preceding the september 10 1984 and the may june 1985 dome building eruptions of mount st helens forty events that occurred during a 12 hour period in september 1984 are located in a volume approximately 30 m in diameter beneath the lava dome the earthquakes following the extrusion do not occur in multiplets and appear to be distributed over a much larger volume in the may june 1985 eruption we recognize three multiplet sets that took place successively in time the multiplets are interpreted as repeated failure or slip within a relatively small volume due to high strain rates around the magma supply conduit

sar observation and numerical simulation of mountain lee waves near kuril islands forced by an extratropical cyclone several groups of atmospheric gravity waves agws were observed on a sentinel 1a synthetic aperture radar sar image acquired near the kuril islands in the northwest pacific ocean on june 1 2015 during the passage of an extratropical cyclone etc these waves occurred on the lee side of the mountains located on the islands both diverging and transverse waves with wavelengths ranging between 20 and 30 km are shown as alternating bright dark patterns in the sar image for the diverging waves there exists a prominent asymmetry in the wave motions of the two arms the moderate resolution imaging spectroradiometer and landsat 7 enhanced thematic mapper plus images acquired 5 7 h prior to the sentinel 1a pass also contain the same groups of agws the mesoscale weather research and forecasting model simulation confirms that the agws are lee waves triggered by the airflow over the islands agws are aligned perpendicular to the wind direction and locked on the lee side of the islands the life span of the waves is about two days consistent with that of the etc over the region the numerical model also successfully reproduces the main characteristics of the lee waves simulation results demonstrate that the variation in the wave parameters i e wavelength amplitude orientation wedge angle of the diverging wave and vertical propagation characteristic and the wave asymmetry of the diverging wave are mainly caused by the wind and stratification changes the smaller amplitude of the diverging wave seems to be associated with a smaller froude number

magma fracture and hybrid earthquakes in the conduit of augustine volcano 1 we exploit subtle but systematic shifts in seismic waveforms to examine a 2 h cluster of repeating hybrid volcanic earthquakes preceding the first magmatic explosions at augustine volcano in january 2006 we extract differential p wave traveltimes of 0 01 s to determine that the source locations migrated downward by approximately 35 m waveform characteristics gps observations and visual reports of lava effusion at the summit suggest that the earthquakes were sourced by fracturing magma in the upper conduit as the lava cooled and degassed at the surface the conditions in the upper conduit changed causing the zone in which magma fracture could occur to move downward through the magma column these changes may also have been the first indicators that the conduit was becoming choked causing a buildup in pressure that resulted in the large magmatic explosions that followed 36 h later

seismological significance of the 1977 1978 eruptions and the magma intrusion process of usu volcano hokkaido abstract an earthquake swarm and the major pumice eruptions in august 1977 which followed marked the start of the dacitic doming activity of usu volcano in southwestern hokkaido japan the sequence of magma intrusion processes was investigated in detail by means of seismological and other geophysical data the distribution of the abundant hypocenters shows clearly an earthquake free zone beneath the summit crater the hypocenters migrated in a manner consistent with the development of the observed asymmetrical surface deformations considered due to magma intrusion into this earthquake free zone the earthquake mechanism solutions are mostly of dip slip type and are interpreted in terms of the doming deformations the existence of earthquake families earthquakes with similar waveforms is the main cause of the peculiar occurrence of earthquakes in space time and magnitude the concept of scattered barriers of different sizes and strengths can explain well the distinct characteristics of the occurrence of the swarm and the observed episodic deformations

seismicity associated with the 1991 1995 dome growth at unzen volcano japan abstract from may 1991 until february 1995 seismicity in the crater area of unzen volcano southwest japan intensified in conjunction with the growth of a dacite lava dome we used data from seismic stations located near the crater to identify approximately 580 000 summit earthquakes with maximum amplitudes equal to or greater than 1 10 3 cm s the temporal characteristics of the seismicity level were different for exogenous and endogenous periods of dome growth periods of solely exogenous growth were accompanied by several days or weeks of increased seismicity and levels of seismicity were notably reduced between successive seismically active periods in contrast levels of seismicity were generally high during periods when the dome grew endogenously with repeated cycles of increasing and decreasing seismicity of one to two months duration we classified the waveforms of summit earthquakes into high frequency hf medium frequency mf and low frequency lf types on the basis of spectral analysis dominant waveform types varied significantly over time hf was dominant in may 1991 lf from june 1991 until august 1993 mf during september and october 1993 and hf and mf from november 1993 hf and mf events are mainly distributed at depths of 500 1100 m above sea level asl just below the lava dome while lf events are widely distributed at depths from 500 m asl to the interior of the dome itself to efficiently detect earthquake families we conducted a cross correlation analysis of waveforms using the events one by one as reference events we calculated peak correlation coefficients between each reference event and events that occurred within 24 h either side of the reference event the results show that many earthquake families of all waveform types occurred throughout the growth period of the dome the durations of most families were less than two weeks and were not related to the intensity of seismic activity the incidence rate of events within each family reached a peak in the middle of the respective activity period the results also suggest that the waveforms in several analyzed families gradually evolved over time during periods when hf events intensified several families appeared contemporaneously in contrast during periods when lf events intensified the occurrence pattern of earthquake families was relatively simple a new family became active only once the activity of the previous family had declined or ceased completely a possible source mechanism for families of hf events is stick slip within the stiff rocks surrounding the conduit however several different types of source mechanisms should be considered for families of lf events

a new interpretation of multifrequency multipolarization radar signatures of the gulf stream front radar signatures which are observed on sir c x sar multifrequency multipolarization synthetic aperture radar images of the gulf stream off the u s east coast are compared with results of simulations with a numerical radar imaging model based on in situ data current and wind variations are included into the model as well as a variation of the thermal stability of the marine atmospheric boundary layer across the gulf stream front according to our model predictions all of these parameter variations can cause radar signatures of similar shape and modulation depth but due to specific dependencies of radar signatures on variations of surface currents and winds we show that it is possible to distinguish between radar signatures of oceanic and atmospheric origin in multifrequency multipolarization images and to estimate the corresponding current and wind variations independently for one set of radar images we derive a most likely scenario of oceanic and atmospheric parameters during the time of the image acquisition for which good overall agreement between observed and simulated radar signatures is obtained at most radar channels

analysis of laboratory simulations of volcanic hybrid earthquakes using empirical green s functions 1 here we present a new analysis of experimental simulations of the seismic signals characteristically observed in volcanic environments we examine the waveforms of laboratory microseismic events generated during two rock deformation experiments performed on samples of mt etna basalt to determine their source characteristics and establish evidence for a mode of failure events were recorded during deformation under a unsaturated dry conditions and b samples saturated with water we employ an empirical green s function approach to isolate the acoustic emission event source spectra from attenuation and travel path effects and estimate the spectral corner frequency using a least squares fit to a brune spectral model spectral fits indicate that the acoustic emission events occurring under dry conditions follow the expected scaling of moment and corner frequency for standard brittle failure in an elastic medium with constant stress drop namely m0 fc 3 however the events occurring during the fluid decompression phase of the saturated experiment have estimated corner frequencies which are not easily described by any simple scaling relationship the implication of the observed scaling is that the events occurring under dry conditions must result from a standard stick slip i e brittle failure source the observed moment corner frequency scaling also suggests that event durations change in a predictable way with increasing moment for the events occurring under dry conditions conversely events occurring under wet conditions do not show any distinctive relationship between duration and event size the specific dependence of duration on event size exhibited by the events in the dry experiment must consequently rule out fluid flow as a source as there is no plausible reason for the driving pressure for fluid flow to be dependent on duration in such a specific way we compare laboratory observations of brittle failure scaling m0 fc 3 to previous observations of volcanic hybrid events in a field environment scaling dissimilarities between field observations and the wet laboratory events suggest that hybrid seismic signals observed in a volcanic environment do not always require fluid flow to explain their signal

theoretical expression for an ocean internal soliton synthetic aperture radar image and determination of the soliton characteristic half width this paper deals with the development of techniques for satellite synthetic aperture radar sar ocean image interpretation we derived a theoretical model of a radar image for a korteweg de vries type ocean internal soliton and validated the model using ocean internal wave signals taken from ers 1 sar and radarsat sar images the results indicate that the model perfectly simulates ocean internal soliton signatures with double sign variations of radar backscatter on the basis of the model we developed the curve fitting method and the peak to peak method for determining the internal soliton characteristic half widths which then were used to calculate the internal soliton amplitudes the test results indicate that ocean internal soliton amplitudes derived by the two methods agree with in situ data acquired on the portuguese continental shelf and in the south china sea with reasonable accuracy the role that wind fields play in ocean radar remote sensing was also analyzed finally the modulation ratio of ocean internal waves on radar images was quantitatively estimated

precursory swarms of long period events at redoubt volcano 1989 1990 alaska their origin and use as a forecasting tool abstract during the eruption of redoubt volcano from december 1989 through april 1990 the alaska volcano observatory issued advance warnings of several tephra eruptions based on changes in seismic activity related to the occurrence of precursory swarms of long period lp seismic events dominant period of about 0 5 s the initial eruption on december 14 occurred after 23 years of quiescence and was heralded by a 23 hour swarm of lp events that ended abruptly with the eruption after a series of vent clearing explosions over the next few days dome growth began on december 21 another swarm with lp events similar to those of the first began on the 26th and ended in a major tephra eruption on january 2 eruptions continued over the next two weeks and then ceased until february 15 when a large eruption initiated a long phase of repetitive dome building and dome destroying episodes that continued into april warnings were issued before the major events on december 14 and january 2 but as the eruptive sequence continued after january 2 the energy of the swarms decreased and forecasting became more difficult a significant but less intense swarm preceded the february 15 eruption which was not forecast this eruption destroyed the only seismograph on the volcanic edifice and stymied forecasting until march 4 when the first of three new stations was installed within 3 km of the active vent from march 4 to the end of the sequence on april 21 there were eight eruptions six of which were preceded by detectable swarms of lp events although weak these swarms provided the basis for warnings issued before the eruptions on march 23 and april 6 the initial swarm on december 13 had the following features 1 short duration 23 hours 2 a rapidly accelerating rate of seismic energy release over the first 18 hours of the swarm followed by a decline of activity during the 5 hours preceding the eruption 3 a magnitude range from 0 4 to 1 6 4 nearly identical lp signatures with a dominant period near 0 5 s 5 dilatational first motions everywhere and 6 a stationary source location at a depth of 1 4 km beneath the crater this occurrence of long period events suggests a model involving the interaction of magma with groundwater in which magmatic gases steam and water drive a fixed conduit at a stationary point throughout the swarm the initiation of that sequence of events is analogous to the failure of a pressure relief valve connecting a lower supercharged magma dominated reservoir to a shallow hydrothermal system a three dimensional model of a vibrating fluid filled crack recently developed by chouet is found to be compatible with the seismic data and yields the following parameters for the lp source crack length 280 380 m crack width 140 190 m crack thickness 0 05 0 20 m crack stiffness 100 200 sound speed of fluid 0 8 1 3 km s compressional wave speed of rock 5 1 km s density ratio of fluid to rock 0 4 and ratio of bulk modulus of fluid to rigidity of rock 0 03 0 07 the fluid filled crack is excited intermittently by an impulsive pressure drop that varies in magnitude within the range of 0 4 to 40 bar such disturbance appears to be consistent with a triggering mechanism associated with choked flow conditions in the crack

ocean noise triggering of rhythmic long period events at deception island volcano 1 we report on swarms of repeating long period lp events with remarkably periodic occurrence at deception island volcano antarctica the lp events show dominant frequencies near 2 hz and characteristic inter event times that range from 10 s to 20 s for individual swarms we observe that lp inter event times are approximate integer multiples of the dominant periods of the oceanic microseism indicating a synchronization of lp activity with the phase of ocean noise we attribute lp periodicity to the coincidence of sustained lp activity in an unstable hydrothermal system and external forcing by ocean noise that introduces periodic pressure variations in volcano fluids we estimate the volumetric strain change generated by the oceanic microseism at the source location and conclude that strain of order 10 7 is sufficient to introduce clear periodicity in the lp sequences and that periodicity increases with increasing strain

sar observing large scale nonlinear internal waves in the white sea abstract the compiled archive of synthetic aperture radar sar images acquired by the advanced sar asar onboard the envisat satellite over the white sea during the extended summer periods may september between 2007 and 2011 provides the first detailed analysis of 2 d patterns of internal waves iws in the white sea unambiguously the primary region of iw activity is the southwestern sw gorlo strait gs iw packets emerging from this area are regularly observed to reach crest lengths up to 200 km and also to propagate a few hundred kilometers from their origin model results confirm that large scale iws can be generated every tidal cycle and are able to cross the entire sea as suggested the source of these packets is governed by the intense dynamics of the frontal zone in the tidal cycle over local complex bottom as further revealed these large scale iws cascade into intense large amplitude short iw packets on the shoaling white sea shelf significantly impacting vertical turbulent exchange and the overall hydrology

temporal variations of repeating low frequency volcanic earthquakes at ngauruhoe volcano new zealand abstract a persistent swarm of micro earthquakes was observed at ngauruhoe volcano new zealand from 2005 to 2010 marking the first unrest episode at the volcano since 1975 detailed waveform and spectral analysis of the continuous seismic record revealed eight earthquake families f1 f8 within a sequence of 8561 low frequency earthquakes an analysis of stacked waveforms of each family allowed the families to be linked systematically into four super families that may indicate four different mechanisms and or source locations or geometries the first super family mostly occurred in 2005 and showed stable waveforms and no significant evolution the second super family was dominant over a two year period starting in mid 2006 and displayed a slow evolution with progressively higher frequency the third super family emerged from early 2008 with intermittent occurrence and high seismicity and progressed to higher peak frequency in 2010 the fourth super family was mainly observed from late 2008 to mid 2009 and had the highest peak frequency in 2009 the observed evolutionary pattern may be driven by a modest multi year input of gas and heat from a deeper relict magmatic zone into the shallow volcano hydrothermal system the interplay of gas from below and seasonal meltwater from above may have modulated the seismic activity and may relate to repeated over pressurization and failure of constricted evolving pathways within a pervasive crack system

study of the generation and propagation of internal waves in the strait of gibraltar using a numerical model and synthetic aperture radar images of the european ers 1 satellite a weakly nonhydrostatic two layer numerical model based on the boussinesq equations is presented which is capable of describing among others the generation and propagation of nonlinear weakly dispersive internal waves in the strait of gibraltar the model depends on one space coordinate only but it retains several features of a fully three dimensional model by including a realistic bottom profile a variable channel width and a trapezoidal channel cross section the nonlinear primitive boussinesq equations include horizontal diffusion bottom friction and friction between the two water layers the model is driven by a height difference of the mean interface depth between the atlantic and the mediterranean boundaries and by semidiurnal tidal oscillations of the barotropic transport the model presented in this paper describes 1 the mean and tidal flow in the strait of gibraltar 2 the variation of the depth of the interface during a tidal cycle 3 the generation of strong depressions of the interface at the western sides of the spartel sill and the camarinal sill 4 the generation of strong eastward propagating internal bores and 5 their disintegration into trains of internal solitary waves the surface convergence patterns associated with depressions of the interface at the camarinal sill internal bores and internal solitary waves are calculated and compared with roughness patterns visible on synthetic aperture radar sar images of the first european remote sensing satellite ers 1 in total 155 ers 1 sar scenes from 94 satellite overflights over the strait of gibraltar which were acquired in the period from january 1992 to march 1995 have been analyzed it is shown that the proposed model is capable of explaining the observed temporal and spatial evolution of surface roughness patterns associated with eastward propagating internal waves inside the strait of gibraltar as well as the observed east west asymmetry of the internal wave field

seismological aspects of the 1989 1990 eruptions at redoubt volcano alaska the ssam perspective abstract ssam is a simple and inexpensive tool for continuous monitoring of average seismic amplitudes within selected frequency bands in near real time on a pc based data acquisition system during the 1989 1990 eruption sequence at redoubt volcano the potential of ssam to aid in rapid identification of precursory long period lp event swarms was realized and since this time ssam has been incorporated in routine monitoring efforts of the alaska volcano observatory in particular an eruption that occurred on april 6 was successfully forecast primarily on the basis of recognizing the precursory lp activity on ssam of twenty two significant eruptions that occurred between december 14 and april 21 eleven had precursory swarms longer than one hour in duration that could be detected on ssam for individual swarms the patterns of relative spectral amplitudes are distinct at each station and remain largely stationary through time thus indicating that one source may have been preferentially and repeatedly activated throughout the swarm typically a single spectral band dominates the signal at each seismic station for the vigorous one day swarm that preceded the first eruption on december 14 signals were sharply peaked in the 1 9 2 7 hz band at the closest station located 4 km from the vent but were dominated by 1 3 1 9 hz energy at three more distant stations located 7 5 22 km from the vent the tendency for the signals from different swarms recorded at the same station to be peaked in the same frequency band suggests that all of the sources are characterized by a predominant length scale signals from the precursory lp swarms became weaker as the eruption sequence progressed and swarms that occurred in march and april could only be detected at seismographs on the volcanic edifice onset times of precursory lp swarms prior to eruptions ranged from a few hours to about one week but after the initial vent clearing phase that ended december 19 these intervals tended to become progressively shorter for successive swarms these trends in the relative onset times and intensities of successive precursory lp swarms are consistent with an overall depressurization of the magmatic system through time in general each of the swarms had an emergent onset but the intensities did not always increase steadily until the eruptions instead as the time of an eruption approached the intensity usually increased more rapidly before peaking and then declining prior to the eruption for three of the swarms two distinct peaks in intensity were apparent the time intervals between final peaks in swarm intensity and ensuing eruptions ranged from about 2 hours to almost 2 days but the peaks always occurred closer to the eruptions than to the swarm onsets both the onset of lp swarm activity and a decline in intensity prior to an eruption may represent critical points in the process of pressurization that drives the flow of fluids and gas in a sealed magmatic system a notable exception to this pattern is the eruption of march 9 which lacked a detectable precursory lp swarm but was followed by an unusually long period of strong lp seismicity that may have been stimulated by a depressurization of the magmatic system resulting from dome failure on both december 14 and january 2 the spectra of early syn eruptive signals have peaked signatures much like those of the spectra of precursory lp activity from shortly before the eruptions these similarities may indicate that the source of precursory seismicity continued to be active during at least the early part of each eruption in syn eruptive signals from march and april recorded at stations on the volcanic edifice the dominant spectral energy progressively shifts with time during the eruption to lower frequencies at least part of the energy in these signals may have been generated by the debris flows associated with dome failures

results from the broadband seismic network on montserrat a digital broadband seismic network has been installed around soufriere hills volcano on montserrat while several distinctive types of seismic events with frequencies ranging from 0 5hz to 30hz could be identified the emphasis is on two types of low frequency events which indicate the involvement of a fluid phase in the source mechanism the so called long period events and the hybrid events the latter occur in swarms with distinct periodicities of 4 to 12 hours and preceed major dome collapses and explosions the swarms correlate very well with the tilt observed at the flanks of the volcanic edifice and hence can be linked to the pressurization of the magmatic system occasionally separate hybrid events merge and form harmonic tremor which sometimes has a shifting spectral content this reveals temporary changes in the source parameters low frequency seismic signals on montserrat are considered to be key parameters for the monitoring of the internal dynamics of the volcano

seismic evolution of the 1989 1990 eruption sequence of redoubt volcano alaska abstract redoubt volcano in south central alaska erupted between december 1989 and june 1990 in a sequence of events characterized by large tephra eruptions pyroclastic flows lahars and debris flows and episodes of dome growth the eruption was monitored by a network of five to nine seismic stations located 1 to 22 km from the summit crater notable features of the eruption seismicity include 1 small long period events beginning in september 1989 which increased slowly in number during november and early december 2 an intense swarm of long period events which preceded the initial eruptions on december 14 by 23 hours 3 shallow swarms 0 to 3 km of volcano tectonic events following each eruption on december 15 4 a persistent cluster of deep 6 to 10 km volcano tectonic earthquakes initiated by the eruptions on december 15 which continued throughout and beyond the eruption 5 an intense swarm of long period events which preceded the eruptions on january 2 and 6 nine additional intervals of increased long period seismicity each of which preceded a tephra eruption hypocenters of volcano tectonic earthquakes suggest the presence of a magma source region at 6 10 km depth earthquakes at these depths were initiated by the tephra eruptions on december 15 and likely represent the readjustment of stresses in the country rock associated with the removal of magma from these depths the locations and time history of these earthquakes coupled with the eruptive behavior of the volcano suggest this region was the source of most of the erupted material during the 1989 1990 eruption this source region appears to be connected to the surface by a narrow pipe like conduit as inferred from the hypocenters of volcano tectonic earthquakes concentrations of shallow volcano tectonic earthquakes followed each of the tephra eruptions on december 15 these shocks may represent stress readjustment in the wall rock related to the removal of magma and volatiles at these depths this shallow zone was the source area of the majority of long period seismicity through the remainder of the eruption the long period seismicity likely reflects the pressurization of the shallow portions of the magmatic system

modelling the time dependent frequency content of low frequency volcanic earthquakes abstract low frequency volcanic earthquakes and tremor have been observed on seismic networks at a number of volcanoes including soufriere hills volcano on montserrat single events have well known characteristics including a long duration several seconds and harmonic spectral peaks 0 2 5 hz they are commonly observed in swarms and can be highly repetitive both in waveforms and amplitude spectra as the time delay between them decreases they merge into tremor often preceding critical volcanic events like dome collapses or explosions observed amplitude spectrograms of long period volcanic earthquake swarms may display gliding lines which reflect a time dependence in the frequency content using a magma filled dyke embedded in a solid homogeneous half space as a simplified volcanic structure we employ a 2d finite difference method to compute the propagation of seismic waves in the conduit and its vicinity we successfully replicate the seismic wave field of a single low frequency event as well as the occurrence of events in swarms their highly repetitive characteristics and the time dependence of their spectral content we use our model to demonstrate that there are two modes of conduit resonance leading to two types of interface waves which are recorded at the free surface as surface waves we also demonstrate that reflections from the top and the bottom of a conduit act as secondary sources that are recorded at the surface as repetitive low frequency events with similar waveforms we further expand our modelling to account for gradients in physical properties across the magma solid interface we also expand it to account for time dependence of magma properties which we implement by changing physical properties within the conduit during numerical computation of wave propagation we use our expanded model to investigate the amplitude and time scales required for modelling gliding lines and show that changes in magma properties particularly changes in the bubble nucleation level provide a plausible mechanism for the frequency variation in amplitude spectrograms

the morning glory of the gulf of carpentaria an atmospheric undular bore abstract this paper presents the results of a field expedition mounted in late september early october 1979 to investigate the structure and origin of the morning glory of the gulf of carpentaria in northern australia the morning glory is a line wind squall accompanied by a pressure jump and often by a long roll cloud or series of such clouds it frequently occurs in the early morning especially in october in the gulf area a light aircraft fitted with a temperature and humidity probe was flown in two glories to determine their thermodynamic structure and wind fields wore obtained principally by tracking pilot balloons using the double theodolite method data also were obtained from a network of surface stations recording wind velocity and pressure installed at locations across cape york peninsula which is believed to be the area of genesis the morning glory is identified as an internal undular bore propagating on the nocturnal and or maritime inversion its origin appears to lie frequently

earthquake classification location and error analysis in a volcanic environment implications for the magmatic system of the 1989 1990 eruptions at redoubt volcano alaska abstract determination of the precise locations of seismic events associated with the 1989 1990 eruptions of redoubt volcano posed a number of problems including poorly known crustal velocities a sparse station distribution and an abundance of events with emergent phase onsets in addition the high relief of the volcano could not be incorporated into the hypoellipse earthquake location algorithm this algorithm was modified to allow hypocenters to be located above the elevation of the seismic stations the velocity model was calibrated on the basis of a posteruptive seismic survey in which four chemical explosions were recorded by eight stations of the permanent network supplemented with 20 temporary seismographs deployed on and around the volcanic edifice the model consists of a stack of homogeneous horizontal layers setting the top of the model at the summit allows events to be located anywhere within the volcanic edifice detailed analysis of hypocentral errors shows that the long period lp events constituting the vigorous 23 hour swarm that preceded the initial eruption on december 14 could have originated from a point 1 4 km below the crater floor a similar analysis of lp events in the swarm preceding the major eruption on january 2 shows they also could have originated from a point the location of which is shifted 0 8 km northwest and 0 7 km deeper than the source of the initial swarm we suggest this shift in lp activity reflects a northward jump in the pathway for magmatic gases caused by the sealing of the initial pathway by magma extrusion during the last half of december volcano tectonic vt earthquakes did not occur until after the initial 23 hour long swarm they began slowly just below the lp source and their rate of occurrence increased after the eruption of 01 52 ast on december 15 when they shifted to depths of 6 to 10 km after january 2 the vt activity migrated gradually northward this migration suggests northward propagating withdrawal of magma from a plexus of dikes and or sills located in the 6 to 10 km depth range precise relocations of selected events prior to january 2 clearly resolve a narrow steeply dipping pencil shaped concentration of activity in the depth range of 1 7 km which illuminates the conduit along which magma was transported to the surface a third event type named hybrid which blends the characteristics of both vt and lp events originates just below the lp source and may reflect brittle failure along a zone intersecting a fluid filled crack the distribution of hybrid events is elongated 0 2 0 4 km in an east west direction this distribution may offer constraints on the orientation and size of the fluid filled crack inferred to be the source of the lp events

the generation of the morning glory abstract a high resolution cloud model is used to explore in detail the generation of the morning glory a low level nonlinear atmospheric internal wave observed on the southwestern side of cape york peninsula australia the model is two dimensional and nonhydrostatic and simulates an east west cross section of the southern part of cape york peninsula at a horizontal resolution of 200 m most of the numerical experiments are initialized at sunrise with a 5 m s 1 easterly flow and a sounding taken upstream from the peninsula the sea breezes that develop over cape york peninsula are highly asymmetric with the east coast sea breeze being both deeper and warmer than its western counterpart when the sea breezes meet the east coast sea breeze rides over that from the west coast and in the process produces a series of waves that propagate on the west coast sea breeze the model calculations show that when the phase speed of these waves matches the westward propagation speed of the east coast sea breeze the

evolution of nonlinear internal waves in the east and south china seas synthetic aperture radar sar images from ers i have been used to study the characteristics of internal waves northeast and south of taiwan in the east china sea and east of hainan island in the south china sea rank ordered packets of internal solitons propagating shoreward from the edge of the continental shelf were observed in the sar images on the basis of the assumption of a semidiurnal tidal origin the wave speed can be estimated and is consistent with the internal wave theory by using the sar images and hydrographic data internal waves of elevation have been identified in shallow water by a thicker mixed layer as compared with the bottom layer on the continental shelf the generation mechanism includes the influences of the tide and the kuroshio intrusion across the continental shelf for the formations of elevation internal waves the effects of water depth on the evolution of solitons and wave packets are modeled by the nonlinear kortweg devries kdv type equation and linked to satellite image observations the numerical calculations of internal wave evolution on the continental shelf have been performed and compared with the sar observations for a case of depression waves in deep water the solitons first disintegrate into dispersive wave trains and then evolve to a packet of elevation waves in the shallow water area after they pass through a turning point of approximately equal layer depths that has been observed in the sar image and simulated by the numerical model the importance of the dissipation effect in the coastal area is also discussed and demonstrated

on the determination of characteristics of the interior ocean dynamics from radar signatures of internal solitary waves in this paper we discuss two different methods of inferring characteristics of the interior ocean dynamics from radar signatures of internal solitary waves visible on synthetic aperture radar sar images the first one consists in the recognition and the interpretation of sea surface patterns of internal solitary waves the second one consists in the analysis of the modulation depth of the normalized radar backscattering cross section nrcs associated with internal solitary waves for this purpose we consider a data set composed of sar and in situ measurements carried out from 1991 to 1997 in the region of the strait of messina the recognition and the interpretation of sea surface patterns of internal solitary waves in the strait of messina can be used to study characteristics of the density distribution in the area the internal wave field varies with seasonal variations in the vertical density stratification and with remotely induced variations i e variations induced by the larger scale circulation in the horizontal density distribution in order to inquire into the possibility of inferring parameters of the interior ocean dynamics by analyzing the modulation of the nrcs associated with internal solitary waves several numerical simulations are carried out using a radar imaging model these simulations are performed by assuming different wind conditions and internal wave parameters it is shown that an accurate knowledge of wind conditions is crucial for deriving internal wave parameters and hence parameters of the interior ocean dynamics from the modulation of measured nrcs associated with internal solitary waves

the sulu sea internal soliton experiment abstract we present the results of a comprehensive study of large amplitude internal solitons generated in the sulu sea in the philippines by intense tidal flow over a sharp bathymetric feature surface signatures of these waves have been observed in images from the dmsp landsat and nimbus 7 satellites and the space shuttle sir a synthetic aperture radar a two week experiment was conducted in the sulu sea in may 1980 from r v oceanograher during which a three mooring phased array of current meters and thermistors was implanted near the wave source and at 82 km and 200 km from the source seventeen soliton packets were observed whose properties underwent significant change as they propagated across the sea vertical profiles of density temperature and acoustic backscatter as well as radar and photographic surface signatures were obtained from the ship data from satellites moorings and the ship give unprecedented information on the spatial and temporal characteristics of solitary waves which ha

an improved composite surface model for the radar backscattering cross section of the ocean surface 2 model response to surface roughness variations and the radar imaging of underwater bottom topography in the companion paper we have presented an improved composite surface model for the calculation of normalized radar backscattering cross sections nrcs of the ocean surface the proposed model accounts for the impact of the full two dimensional ocean wave spectrum on the radar backscatter and was shown to reproduce measured absolute nrcs values for a variety of radar configurations and wind speeds satisfactorily after some reasonable tuning of the input ocean wave spectrum this paper focuses on the modulation of the nrcs in the presence of spatially varying surface currents first the sensitivity of the nrcs to intensity variations of different ocean wave spectral components is investigated then the hydrodynamic modulation of the wave spectrum over underwater bottom topography in tidal waters is computed in different ways and the resulting radar signatures are discussed the composite surface model yields comparable radar signatures at high 10 ghz x band and low 1 ghz l band radar frequencies which is in much better agreement with experimental results than the predictions of a first order bragg scattering model on the other hand measured variations of the nrcs at high radar frequencies appear to be still underestimated in some cases which may be due to shortcomings of our description of the wave current interaction by conventional weak hydrodynamic interaction theory possible improvements of the theory are discussed and requirements for future experiments are formulated

fracture healing in a magma an experimental approach and implications for volcanic seismicity and degassing 1 the healing of magmatic fractures is considered essential to repetitive seismicity and the closure of degassing paths during emplacement of lavas to estimate the healing time of magmatic fractures we performed healing experiments on rhyolitic melts at 850 1000 c and 1 6 3 2 mpa for 0 5 94 h two cylindrical obsidian cores were juxtaposed on surfaces prepared by cutting the cores both with and without polishing these were annealed in an open system cell the contact interface became coherent and finally disappeared the water content across the contact initially decreased toward the interface via diffusive dehydration but later homogenized this change was interpreted to reflect atomic scale closure of the interface probably by chemical bonding we defined this closure interval as microscopic healing time and determined this by fitting the measured profiles with a diffusion model the microscopic healing time was strongly dependent on temperature and roughness of the interface and was for the nonpolished interfaces 67 74 4 0 4 9 and 0 36 0 38 h at 850 900 and 950 c respectively whereas for the polished examples it was 1 3 and 0 5 0 6 h at 850 and 900 c respectively this microscopic healing time is consistent with the period of actual seismicity and is prolonged sufficiently to permit the formation of millimeter thick bubble free obsidian layers along fractures in vesicular lavas through bubble resorption due to diffusive degassing