analyses and simulations of the upper ocean s response to hurricane felix at the bermuda testbed mooring site 13 23 august 1995 causedalargeincreaseinkineticenergyatnear inertialfrequencies internalgravitywavesin the thermocline and inertial pumping mixed layer deepening and significant vertical redistribution of heat with cooling of the upper 30 m and warming at depths of 30 70 m the temperature evolution was simulated using four one dimensional mixed layer models price weller pinkel pwp k profile parameterization kpp mellor yamada 2 5 my and a modified version of my2 5 my2 the primary differences in the model results were in their simulations of temperature evolution in particular when forced using a drag coefficient thathadalinear dependenceonwindspeed the kppmodelpredicted seasurface cooling mixed layer currents and the maximum depth of cooling closer to the observations than any of the other models this was shown to be partly because of a special parameterization for gradient richardson number rgkpp shear instability mixing in responsetoresolvedshearintheinterior themy2modelpredictedmoreseasurfacecooling and greater depth penetration of kinetic energy than the my model in the my2 model the dissipation rate of turbulent kinetic energy is parameterized as a function of a locally defined richardson number rgmy2 allowing for a reduction in dissipation rate for stable richardsonnumbers rgmy2 wheninternalgravitywavesarelikelytobepresent sensitivity simulations with the pwp model which has specifically defined mixing procedures show that most of the heat lost from the upper layer was due to entrainment parameterized as a function of bulk richardson number rbpwp with the remainder due to local richardson number rgpwp instabilities with the exception of the my model the models predicted reasonable estimates of the north and east current components during and after the hurricane passage at 25 and 45 m although the results emphasize differences between the modeled responsestoagivenwindstress currentcontroversyovertheformulationofwindstressfrom wind speed measurements including possible sea state and wave age and sheltering effects cautions against using our results for assessing model skill in particular sensitivity studies show that my2 simulations of the temperature evolution are excellent when the wind stress is increased albeit with currents that are larger than observed sensitivity experiments also indicate that preexisting inertial motion modulated the amplitude of poststormcurrents butthattherewasprobablynotasignificantresonantresponsebecauseof clockwise wind rotation for our study site index terms 4504 oceanography physical air sea interactions 0312 4572 oceanography physical upper ocean processes 4255 oceanography general numericalmodeling 4544oceanography physical internalandinertialwaves keywords hurricane tropical cyclone mixed layer modeling upper ocean processes inertial currents ocean storms

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

mixed layer simulation of buoy observations taken during hurricane eloise a one dimensional mixed layer model is used to simulate observations made by a noaa buoy in the gulf of mexico during hurricane eloise the model predicted sst mixed layer depth and inertial current agree favorably with the observations in addition model experiments demonstrate the importance of the veering of the wind vector during the passage of the eye to the amplitude of the inertial current generated by the wind and the extent of vertical mixing

applications of autoregressive models and time frequency analysis to the study of volcanic tremor and long period events volcanic tremor and long period lp events are characterized by sharp spectral peaks that generally result from resonance effects at the source and which concentrate most of the radiated energy the understanding of these seismovolcanic phenomena requires good descriptions of the distribution in time and frequency of the different spectral components included in the signals as well as a separation of the resonance effects from less energetic effects such as excitation and propagation we address the issue of extracting from individual records information as detailed as possible on the physical processes involved at the source we introduce and compare several time frequency analysis methods and we describe the application of autoregressive modeling and deconvolution methods to the characterization and separation of the main spectral components we propose a signal analysis approach based on the joint use of a set of complementary methods and we present applications to several examples of volcanic tremor and lp events the time frequency analysis of some of the lp events taken as examples reveals short duration components at the seismogram onsets with energy concentrated at frequencies either higher or lower than the main resonance frequencies these seismic phases are probably related to the excitation processes of the volcanic resonators in several cases the arrival of the main spectral peak has a delay of a few tenths of a second with respect to the first arrival the residual signals obtained by deconvolving and eliminating the main spectral components contain information about the excitation such as duration delay or frequency band the residual signals are short for lp events and continuous for volcanic tremor the autoregressive modeling of the sample records gives precise estimations of the frequency and quality factor of the main spectral peaks the measured parameters cover a wide range of values which is consistent with the great variety of fluids filling resonating cavities in volcanoes

seismic energy releases from volcanoes seismic energy release during the precursory eruptive and declining stages of volcanic activities provides various information about the mechanisms of volcanic eruptions and the temporary developments of their activities hitherto the energy release patterns from precursory earthquake swarms were used to predict the eruption times especially of andesitic or dacitic volcanoes in this paper the discussion is expanded to quantify the total amount of seismic energy released at the threshold of volcanic eruptions with reference to the results observed at several volcanoes the results generally indicate that the cumulative seismic energy release from the precursory earthquake swarms exceed 1017 18ergs before eruptions at any andesitic or dacitic volvanoes this allows the seismic efficiency or the ratio of energy radiated seismically and the energy required for the volumetric expansion to be estimated by incorporating available deformation data with the seismic data the dependency of seismic efficiency on the type of volcanic activity i e non explosive outbreaks phreatic and magmatic eruptions dome formation etc was evaluated from observations at a few volcanoes that provided a variety of examples

a review on phreatic eruptions and their precursors abstract an analysis of the reported information on 132 historical phreatic events indicates that most of these 115 were not followed by a magmatic or phreatomagmatic eruption only in 18 cases precursory phenomena are reportedly lacking whereas they are recognized for the majority 72 of the considered cases these precursors have been analyzed as a function of the kind of phreatic event and of its possible triggering mechanism unfortunately the quality of the available information is poor however data suggest that anomalous seismicity ground deformation changes in the output chemistry and temperature of fumaroles and thermal springs are potential mid term precursors whereas seismic tremor is a common short term precursor

observations of long period earthquakes accompanying hydraulic fracturing waveforms of most seismic events accompanying hydraulic fracturing have been reported to contain clear p and s waves and have fault plane solutions consistent with shear displacement across a fault this observation is surprising since classical hydraulic fracturing theory predicts the creation of a tensile opening of a cavity in response to fluid pressure very small long period events similar to long period earthquakes observed at volcanoes were found to occur during four hydraulic fracturing experiments carried out at fenton hill new mexico since the long period earthquakes occur in the same region as the shear type events it is concluded that the unusual character of the long period earthquake waveforms is due to a source effect and not a path effect the occurrence of long period earthquakes during hydraulic fracturing could indicate tensile fracturing many waveforms of these events are identical which implies that these events represent repeated activation of a given source a proposed source for these long period events is the sudden opening of a channel that connects two cracks filled with fluid at different pressures the sizes of the two cracks differ which causes two or more peaks to appear in the spectra each peak beingmore associated with one physical dimension of each crack from the frequencies at which spectral peaks occur crack lengths are estimated to be between 3 and 20m less

observations and simulation of a bottom ekman layer on a continental shelf a numerical model was used to simulate the bottom ekman layer of a continental shelf region the basis for the model was the mellor and yamada level 2 turbulence closure scheme conservation equations for momentum turbulent kinetic energy and turbulent length scale were utilized in the model the model was used to simulate data taken from a cyclesonde mooring on the peruvian continental shelf in may 1976 as part of the joint ii coastal upwelling ecosystems analysis program the cyclesonde provided mean horizontal velocity temperature salinity and pressure data an intense poleward undercurrent drove the bottom flow regime the most striking feature of the data was the clockwise ekman veering of velocity vectors as the bottom was approached a 48 hour period was chosen for the model simulations the vertical profile of speed 48 hours mean simulated by the model fell within the error bars of the data the corresponding ekman spiral display of the model results also showed good agreement with the observati ons

stochastic simulation of volcanic tremor from ruapehu abstract the most common volcanic tremor produced by ruapehu is a continuous signal with a dominant frequency of about 2 hz this signal has a sharply peaked spectrum and an autocorrelation function with a high degree of coherence even for lags of over 20 seconds these characteristics strongly suggest that the cause of this tremor is a single resonator probably a fluid filled cavity resonating in an organ pipe mode the stochastic simulation of such a resonator uses the equation of motion of a simple harmonic oscillator which applies to an organ pipe fundamental resonance with either the characteristics of the oscillator or the forcing function containing a random element a white noise forcing function which would be appropriate for excitation of the cavity by a high pressure gas input gave good agreement with the observed spectra and autocorrelation functions another possible model used an oscillator with a damping factor which varied randomly and was sometimes negative so oscillations built up rather than decayed this also gave a reasonable simulation of ruapehu tremor the third excitation model used a poisson process in which during each time interval there was a certain probability of applying a fixed impulse to the resonator it was found that the impulses had to be frequent i e several times a second to match the characteristics of ruapehu tremor it has been suggested that tremor is composed of a succession of low frequency b type earthquakes the results of this simulation show that at ruapehu tremor could be produced by a resonator with positive feedback just sustaining oscillation or by a resonator excited by external impulses the most promising model for low frequency earthquakes describes them as the result of a major external disturbance of the resonator

source mechanism of volcanic tremor low frequency 10 hz volcanic earthquakes originate at a wide range of depths and occur before during and after magmatic eruptions the characteristics of these earthquakes suggest that they are not typical tectonic events physically analogous processes occur in hydraulic fracturing of rock formations low frequency icequakes in temperate glaciers and autoresonance in hydroelectric power stations we propose that unsteady fluid flow in volcanic conduits is the common source mechanism of low frequency volcanic earthquakes tremor the fluid dynamic source mechanism explains low frequency earthquakes of arbitrary duration magnitude and depth of origin as unsteady flow is independent of physical properties of the fluid and conduit fluid transients occur in both low viscosity gases and high viscosity liquids a fluid transient analysis can be formulated as generally as is warranted by knowledge of the composition and physical properties of the fluid material properties geometry and roughness of the conduit and boundary conditions to demonstrate the analytical potential of the fluid dynamic theory we consider a single phase fluid a melt of mount hood andesite at 1250 c in which significant pressure and velocity variations occur only in the longitudinal direction further simplification of the conservation of mass and momentum equations presents an eigenvalue problem that is solved to determine the natural frequencies and associated damping of flow and pressure oscillations for a simple constant pressure reservoir conduit orifice fluid system a change in orifice size can cause the source signal duration due to a single disturbance to change from several seconds to in excess of an hour fluid kinematic viscosity 0 412 m2 s is both included and neglected in the analysis to illustrate its effect upon system damping tremor magnitude is related to the magnitude of the conduit wall motion occurring in response to oscillating fluid pressures the entire volcanic fluid system does not generally experience a transient flow condition at a given time closed end and constant pressure fluid system boundaries reflect pressure waves and isolate components of the fluid system total fluid movement may not be accurately monitored by tremor data alone since steady state and slowly changing flows are aseismic

deep fault plane geometry inferred from multiplet relative relocation beneath the south flank of kilauea dense microearthquake swarms occur in the upper south flank of kilauea providing multiplets composed of hundreds of events the similarity of their waveforms and the quality of the data have been sufficient to provide accurate relative relocations of their hypocenters a simple and efficient method has been developed which allowed the relative relocation of more than 250 events with an average precision of about 50 m horizontally and 75 m vertically relocation of these events greatly improves the definition of the seismic image of the fault that generates them indeed relative relocations define a plane dipping about 6 northward although corresponding absolute locations are widely dispersed in the swarm a composite focal mechanism built from events providing a correct spatial sampling of the multiplet also gives a well constrained northward dip of about 5 to the near horizontal plane this technique thus collapses the clouds of hypocenters of single event locations to a plane coinciding with the slip plane revealed by previous focal mechanism studies we cannot conclude that all south flank earthquakes collapse to a single plane there may locally be several planes perhaps with different dips and depths throughout the south flank volume the 6 northward dipping plane we found is too steep to represent the overall flexure of the oceanic crust under the load of the island of hawaii this plane is probably an important feature that characterizes the basal slip layer below the upper south flank of kilauea volcano differences in seismicity rate and surface deformations between the upper and lower south flank could be related to the geometry of this deep fault plane the present work illustrates how high precision relative relocations of similar events in dense swarms combined with the analysis of geodetic measurements can help to describe deep fault plane geometry systematic selection and extensive relative relocation of similar earthquakes could be attempted in other well instrumented highly seismic areas to provide reliable basic information especially useful for understanding of earthquake generation processes

hurricane induced surge and currents on the texas louisiana shelf this study consists of numerical model simulations of hurricane induced surge and currents on the texas louisiana shelf the numerical experiment includes the simulation of multiple hurricane tracks with landfalling points along the texas louisiana coast a parallel storm that traverses the entire texas louisiana coastline is also modeled to assess the difference in shelf response between landfalling and parallel storms the grid extends from the texas mexico border to the gulf coast of florida with the ocean open boundary seaward of the shelf break along shelf and cross shelf surge and current variability are assessed as a function of shoreline geometry and bottom topography a complementary one dimensional mixed layer model is used to evaluate the vertical structure of the currents and the maximum depth of hurricane influence the choice of landfalling storm tracks is based principally on historical storm tracks for the texas louisiana area storm intensity i e central pressure depression for all storms is set equal to the 10 year recurrence interval central pressure strong cyclonic flow is induced by the hurricane wind field within a distance from the storm s center equal to 3 to 5 times the storm s radius of maximum winds far field hurricane winds generate a northward moving coastal jet along the west coast of florida particularly for the landfalling storms the far field continental shelf currents are topographically steered by the shoreline and bathymetry there is strong evidence of a cyclonic anticyclonic eddy pair being generated in the wake of the parallel storm traveling eastward over the continental shelf an intercomparison of the one and two dimensional models shows that for depths less than 50 m the combined use of the surge and mixed layer models permits a description of the vertical and horizontal hurricane induced current patterns the surge height computations for a given storm strength point to the importance of several factors that determine surge levels as a function of offshore distance these factors are bathymetry topography angle of approach of the storm distance to landfall location and shelf width the most dramatic increase in surge levels occurs in depths less than 10 m where the surge profile mirrors the changes in the bottom slope in contrast the sensitivity of surge dynamics to shelf width is neither strong nor consistent a narrow spread of maximum surge values is observed each transect is examined individually to explain local behavior and the reason for the modest variation in surge values among dissimilar geographical areas no critical dependence on the exact storm angle exists for storm angles within the range of angles associated with maximum surge generation within 20 counterclockwise from the shore normal direction since the landfalling storms used in this study fall into this category no significant dependence of surge height on the landfalling angle is observed

saturated and subcooled hydrothermal boiling in groundwater flow channels as a source of harmonic tremor the potential of hydrothermal boiling in groundwater flow channels for generating harmonic tremor a relatively monochromatic ground vibration associated with volcanic activity is examined we use simple organ pipe theory of normal mode fluid vibration and fundamental energy considerations to develop a first order analytical model of a hydrothermal boiling source of harmonic tremor we use this model to estimate order of magnitude groundwater flow channel lengths and boiling heat transfer rates required to produce harmonic tremor with dominant frequencies in the range 0 5 5 hz and surface wave reduced displacements of up to 100 cm2 depending on groundwater sound speed flow channel lengths of the order of 1 1000 m are required to produce fluid vibration eigenfrequencies in the range 0 5 5 hz the boiling heat transfer rate required to produce tremor with a given surface wave reduced displacement depends on the tremor frequency and on whether saturated boiling or subcooled boiling is the cause of the tremor saturated boiling produces groundwater vibration via steam bubble growth whereas subcooled boiling produces groundwater vibration via steam bubble collapse we find that subcooled hydrothermal boiling is from 102 to 104 times more efficient than saturated boiling in converting boiling thermal power to seismic power for example the boiling heat transfer rates required to produce 1 hz tremor with reduced displacements of up to 100 cm2 via subcooled boiling are generally less than a few thousand megawatts for saturated boiling the required boiling heat transfer rates are several orders of magnitude larger than this the highest values of heat flow reported in the literature for volcanic crater lakes and terrestrial and ocean floor geothermal areas are of the order of 1000 mw taking this value as a first order estimate of an upper limit on possible boiling heat transfer rates in volcanic hydrothermal systems our results suggest that saturated hydrothermal boiling is capable of generating only low amplitude harmonic tremor with surface wave reduced displacements no higher than a few square centimeters however subcooled hydrothermal boiling could potentially generate high amplitude harmonic tremor with reduced displacements as large as several hundred square centimeters as a specific application of our model we evaluate the potential of hydrothermal boiling for generating harmonic tremor at recently active mount st helens and nevado del ruiz volcanoes we conclude that subcooled boiling likely could have produced the tremor episodes considered at both volcanoes saturated boiling also could explain the nevado del ruiz tremor but probably not the more powerful mount st helens tremor

hurricane generated currents on the outer continental shelf 1 model formulation and verification a numerical model is developed to simulate currents generated by hurricanes on the outer continental shelf and slope emphasis is on the mixed layer response within a few hours of storm passage however some attention is given to the lower layer and shelf wave responses the model is based on a layered explicit finite difference formulation using the nonlinear primitive equations including conservation of heat the problem of topography intersecting the model layer is resolved by introducing artificial steps of the order of 100 m where the layer intersects the slope model comparisons are presented for three gulf of mexico hurricanes using a 0 2 grid for two of the storms the model reproduces better than 80 of the observed velocity variance with correlation coefficients of greater than 0 8 for the mixed layer discrepancies in the comparisons are traced to unresolved local topography and nonstorm forcing such as warm core rings further model simulations reveal that 1 substantial shelf waves were generated with phase speeds of 4 to 10 m s 1 2 the response is primarily baroclinic even in water as shallow as 200 m 3 an entrainment law which scales with the velocity difference between the mixed layer and upper thermocline yields markedly better comparisons than one which scales with the wind stress and 4 deviations from a straight line storm path can significantly alter the response

operation of a digital seismic network on mount st helens volcano and observations of long period seismic events that originate under the volcano during 1981 we operated with the cooperation of the u s geological survey a 9 station digital seismic array on mount st helens volcano in washington state one of our stations was placed inside the crater of the volcano six were located on the flanks of the volcano within two km of the crater and two were approximately ten km from the crater four of the instruments recorded three components of motion and the remaining five recorded only the vertical component in addition to the monitoring and recording performed by the digital instruments we carried out a one day experiment during which we complimented our crater monitoring seismometer by the addition of two ink recording instruments during the one day experiment we had six observers including 4 usgs scientists who had significant experience working and making observations in the crater recording times of rockfall felt earthquake occurrences and changes in steam emissions from the dome in the crater using information obtained during the one day experiment we are able to classify seismic events recorded by our digital instruments as earthquakes rockfalls helicopter noise and a type of event that is unique to volcanoes which we call long period waveforms of these long period events have a duration of up to 30 seconds and a spectrum that is peaked at approximately 2 hz the frequency at which the peak in the spectrum occurs is nearly the same at all stations which means that the unique waveform of long period events is due to a source effect not a path effect the peak frequency is fairly insensitive to the amplitude of the signal which means that the size of the source region is constant independent of the signal amplitude long period events were not felt and were accompanied by no visible changes inside the crater which lead us to conclude that they are some sort of seismic disturbance generated inside the volcano

volcanic earthquakes of kamchatka classification nature of source and spatio temporal distribution abstract volcanic earthquakes on kamchatka can be divided into two large groups earthquakes with depths of 0 40 km generated by stresses which arise during magma migration in the earth s crust under volcanos the first group and the earthquakes directly connected with the eruptions volcanic tremor explosive earthquakes etc the second group this paper presents a review of some energetic spectral and spatio temporal characteristics of the kamchatkan volcanic earthquakes of the first group and their relationship with volcanic phenomena seismicity related to volcanic activity has the following specific features a local and predominantly swarm like pattern of earthquake origination iteration of earthquake swarms in the same seismically active zones many shallow and relatively small events a small magnitude limit up to 5 5 6 the existence of longer period variations of volcanic earthquake foci as compared to the tectonic one and a comparatively high value of the slope of the earthquake recurrence plot at the same time similarity in behaviour of some parameters of the seismic regime during the preparation and development of eruptions and prior to large earthquakes as well as the destruction of samples are noted

satellite measurements of sea surface cooling during hurricane gloria hurricanes and other strong storms can cause important decreases in sea surface temperature by means of vertical mixing within the upper ocean and by air sea heat exchange here we use satellite derived infrared images of the western north atlantic to study sea surface cooling caused by hurricane gloria 1985 significant regional variations in sea surface cooling are well correlated with hydrographic conditions the greatest cooling up to 5 c occurred in slope waters north of the gulf stream where the seasonal thermocline is shallowest and most compressed moderate cooling up to 3 c occurred in the open sargasso sea where the thermocline is deeper and more diffused little or no cooling occurred in shallow coastal waters bottom depth less than 20 m which were isothermal before the passage of hurricane gloria there is a pronounced right side asymmetry of sea surface cooling with stronger by a factor of 4 and more extensive by a factor of 3 cooling found on the right side of the hurricane track these qualitative results are consistent with the notion that vertical mixing within the upper ocean is the dominant sea surface cooling mechanism of hurricanes

a model of the vertical mixing in lake erie in summer a vertical one dimensional model is proposed to describe the vertical mixing in the central portion of the central basin of lake erie in summer the model explicitly describes the various mechanisms which operate in the well mixed upper and bottom layers the model predictions are in good agreement with the observed thermal structure over the entire water column during a month long simulation period the central basin of lake erie has been the subject of intensive investigation in recent years due in large part to concern over the depletion of dissolved oxygen in the hypolimnion during the stratified summer period burns and ross 1972 burns 1976 the central basin encompasses an area about 80 km wide and 200 km long but with a mean depth of only 18 m and a maximum depth of 26 m during summer the lake is strongly stratified and is characterized by an upper mixed layer uml a strong temperature gradient region and a near isothermal bottom mixed layer bml see

a monochromatic earthquake suggesting deep seated magmatic activity beneath the izu ooshima volcano japan after a quiescence of 12 years the izu ooshima volcano located about 30 km east of the izu peninsula in central japan erupted on november 15 1986 on august 27 1985 about 1 year before the eruption a peculiar earthquake of magnitude 2 7 took place near the moho boundary just beneath the izu ooshima volcano where seismic activity is otherwise absent analysis of digital data obtained by the telemetered seismic network of the national research center for disaster prevention reveals the following distinctive features of the seismic waves 1 the main part of the wave train is composed of s waves and a small p phase precedes it 2 the spectral density has a sharp peak at 1 0 hz which is independent of the epicentral distance azimuth and time indicating a monochromatic spectrum at the source 3 ground motion for the initial part of the s wave is polarized in the n s direction at almost all the stations the amplitude ratios of s to p waves and the polarization pattern of s waves suggest that a traction force caused by magma flow is a more probable source than a double couple mechanism free oscillation of the magma reservoir or opening of a tensile crack we propose a traction force model for this earthquake in which magma flow through a conduit produces unidirectional viscous force on the conduit walls the observations imply a n s force direction and a maximum force of about 2 8 1010 n the pressure difference between the ends of the conduit is estimated as 6 1 107 pa 610 bar under the assumption of conduit dimensions of 2 km 1 km the monochromatic nature of the source spectrum is difficult to account for by the free oscillation of a magma reservoir we tentatively suggest the intermittent opening of a barrier in the conduit as a plausible mechanism of the periodic oscillation

seismic precursors of the february 10 1990 eruption of kelut volcano java abstract kelut volcano eastern java indonesia erupted on february 10 12 1990 seismic activity and an increase of temperature and acoustic noise in the crater lake appeared three months before the eruption and were the main precursory signs of this eruption during the pre eruptive stage the number of events was eight per day on average and the cumulative seismic energy released was 5 6 10 15 erg these low values are uncommon for an andesitic volcano seismic activity mainly consisted of swarms of very shallow volcano tectonic earthquakes many of which were part of seismic multiplets in the last three weeks before the eruption seismic activity remained at a very low level this quiescent period was followed 24 hours prior to the eruption initiation by an intense swarm of low energy events which progressively became continuous spasmodic tremor most of the data obtained during the pre eruptive stage are consistent with a process of fracturation of a shallow and low strength plug blocking the eruptive conduit before the eruption several observations suggest that water is an important element in the preeruptive and eruptive phenomena at kelut volcano in particular the monochromatic events observed at kelut are characterized by one narrow peak in their spectra the estimations of q value and impedance contrast for these events suggest that the fluid which fills the source resonator could be water

observations stratigraphy and eruptive processes of the 1990 eruption of kelut volcano indonesia the february 10 1990 eruption of kelut volcano eastern java reportedly began with seven discrete short lived explosions between 11 41 and 12 35 local times deposits of this initial phreatomagmatic stage include a basal ash fall layer unit a1 widespread pumice surge deposits unit s and related pisolitic ash layer unit a2 the main plinian phase of the eruption lasted about 4 hours from 12 35 and produced pumice flow deposits unit pf overlain by a pumice fallout layer distributed mainly to the southwest unit p and intra plinian scoria flow deposits unit sf uppermost scoria rich ash fall layers unit a3 likely relate to late discrete eruptive pulses a few small explosions resumed on february 11 and 12 leaving no recognizable deposit an embryonic lava dome had formed in the crater bottom by april then was submerged by the new crater lake destruction of the summit area resulted from emplacement of the pre plinian pumice surge up to 4 5 km on the south and west flanks and of the early plinian pumice flows up to 1 2 km radially from the crater before these were channelized in the main valleys to further travel 3 km most of the 32 human deaths resulted from roof collapse under the load of fallout tephra beyond the devastated area which had been evacuated before the eruption began the eruption produced 0 13 km3 of tephra of which 0 12 km3 represent the products of the plinian phase the average eruptive rate of the plinian phase is estimated to have been 7 5 106 kg s magma dre the pumice flows are interpreted to have been formed due to unsteadiness and low velocity of the eruptive column at the beginning of the plinian phase the intra plinian scoria flows incorporate either more degassed or colder juvenile magma they were presumably erupted at the edge of the column due to fluctuations in the mass flux and in pressure in the conduit

analogue modeling of instabilities in crater lake hydrothermal systems 1 we carried out analogue experiments on two phase boiling systems using a porous vertical cylinder saturated with water the base of the cylinder was heated and the top was cooled as in a natural hydrothermal system previous work had shown that once the two phase zone reached a certain level thermal instabilities would develop we made measurements of the acoustic energy related to boiling and we found that high levels of acoustic noise were associated with the part of the cycle in which there was upward water movement we repeated our experiments with a cooling water tank at the top of the system representing a crater lake this showed that periodic thermal instabilities still developed in this situation we then compared our analogue measurements to two natural systems known to exhibit periodic behavior there is good agreement between the thermal and acoustic cycling seen in our model and the observations made at inferno crater lake in the waimangu geothermal area new zealand whose level cycles by nearly 10 m with a typical period of 38 days particularly notable is how in both systems high levels of acoustic noise are associated with rising water level the much larger ruapehu crater lake also in new zealand cycled with a period of several months to a year for over a decade prior to the 1995 eruption strong acoustic and seismic energy usually occurred just before the lake temperature started to rise this suggests a slightly different model in which the increasing two phase flow zone triggers more general convection once it reaches the base of the lake

a process based model of pre eruption seismicity patterns and its use for eruption forecasting at dormant stratovolcanoes abstract using long term data sets the eruptive size timing and style can typically be successfully forecast for dormant volcanoes using current monitoring data and knowledge of precursory eruptive patterns the usaid usgs volcano disaster assistance program vdap utilizes seismic data over multiple eruption cycles and across volcano types to successfully forecast eruption size style and onset times as well as changes within ongoing eruptions from millions of seismic event observations we show that seismic data a proxy for rate dependent strain changes in the magmatic system combined with a process based conceptual geologic model enables eruption forecasting especially for stratovolcanoes dormant 20 years we show that this model often works for some open systems ones that sufficiently reseal to plug the conduit and also where a deep intrusion occurs after phreatic or phreatomagmatic explosions have begun this model is divided into four seismicity and geologic stages we describe each of the four stages of seismicity in detail and how they relate to the ongoing geologic process of that stage stage 1 deep intrusion and seismicity occurring at 10 to 40 km depth below the volcanic edifice stage 2 distal vt seismicity induced at distances from 2 to 30 km laterally from the summit by magma intruding into and inflating the upper crustal magma storage region stage 3 vent clearing seismicity associated with the initial vent creation and clearing phase of eruptive activity stage 4 repetitive event seismicity associated with the final ascent of magma from 2 km to the surface we present 36 examples of this seismic progression from 26 volcanoes we believe that this progression generally correlates with the magma flux and the eventual explosivity and is invaluable for forecasting eruptions

comparison of short term seismic precursors and explosion parameters during the 2016 2017 bogoslof eruption in december 2016 the unmonitored bogoslof volcano unexpectedly began erupting producing at least 70 explosions over the next 8 5 months roughly half of the explosions were preceded by observable short term precursory activity defined here as seismic activity ending within 30 min of the explosion onset or an earthquake swarm ending within a few hours before the explosion onset five different types of precursors were noted during the bogoslof eruption non swarm earthquakes earthquake swarms rapid rate events tremor and chromatic tremor most of the precursors that were detectable by the nearby seismic networks 45 km away occurred during the first 3 months of the eruption with nearly all precursory earthquake swarms occurring during this period a hydrophone deployed 7 km northeast of the summit for the last 3 months of the eruption detected weaker activity that was not recorded by the more distant seismic networks we describe the observed precursors and discuss their inter relations overall the precursors seem indicative of processes occurring throughout the volcanic system and suggest possible changes in the system during the eruption we then compare the short term precursors with explosion parameters such as plume height duration and occurrence of lightning to look for relations that may provide more insight into the eruption dynamics and subsurface processes and help to further improve forecasting we find no obvious relations between any of the precursor or explosion parameters suggesting that their use in forecasting eruption characteristics at bogoslof is limited

coastal ocean current response to storm winds design of offshore structures requires knowledge of the appropriate current profile to be used in conjunction with the design wave accurate determination of the current profile will depend on reliable current models vertical transfer of momentum in storm driven current models is commonly treated either by using eddy viscosity or by assuming slab like mixed layer flow these two fundamentally different approaches predict different current speeds and profiles during severe storms the existing data base is inadequate to determine which approach is better but most existing data sets are subject to one or more of four limitations that can lead one improperly to interpret the data as supporting the existence of current velocity shear in otherwise uniform mixed layers one dimensional slab models are found to compare favorably with observed wind driven currents at the ocean test structure in the gulf of mexico deployed in 20 m deep water by using some reasonably simple assumptions these slab models are able to replicate many of the significant features of a wide range of different responses the character of the response appears to depend on an interaction of stratification and topography barotropic responses are characteristic of typical coastal responses currents are oriented longshore and are in phase with the wind baroclinic responses are dominantly inertial as might be expected in the deep sea but with an additional near bottom cross shore counter flow the structure of one observed barotropic response is compared in detail to predictions of both slab and eddy viscosity models and found consistent with a slab model and inconsistent with eddy viscosity models shear observed during this event was not significantly different from zero but was significantly below estimated shear predictions of four eddy viscosity models given the peak 0 4 n m2 wind stress

investigating crater lake warming using aster thermal imagery case studies at ruapehu poas kawah ijen and copahue volcanoes abstract a two channel or split window algorithm designed to correct for atmospheric conditions was applied to thermal images taken by the advanced spaceborne thermal emission and reflection radiometer aster of lake yugama on kusatsu shirane volcano in japan in order to measure the temperature of its crater lake these temperature calculations were validated using lake water temperatures that were collected on the ground overall the agreement between the temperatures calculated using the split window method and ground truth is quite good typically 1 5 c for cloud free images data from fieldwork undertaken in the summer of 2004 at kusatsu shirane allow a comparison of ground truth data with the radiant temperatures measured using aster imagery further images were analyzed of ruapehu poas kawah ijen and copahue volcanoes to acquire time series of lake temperatures a total of 64 images of these 4 volcanoes covering a wide range of geographical locations and climates were analyzed results of the split window algorithm applied to aster images are reliable for monitoring thermal changes in active volcanic lakes these temperature data when considered in conjunction with traditional volcano monitoring techniques lead to a better understanding of whether and how thermal changes in crater lakes aid in eruption forecasting

multiparametric approach in investigating volcano hydrothermal systems the case study of vulcano aeolian islands italy seismic activity ground deformation and soil and fumarole temperatures acquired during 2004 2007 at vulcano aeolian islands are analysed and the time relations among the different time series are discussed changes in temperature of fumarolic gases took place during four anomalous periods november 2004 march 2005 october 2005 february 2006 august october 2006 july december 2007 at the same time as an increasing number of volcano seismic events in particular the temperatures at high temperature vents and at steam heated soil ranged in time from 180 to 440 c and from 20 to 90 c respectively the maximum daily number of volcano seismic events was 57 reached during the second anomalous period this seismicity characterised by focal depth generally lower than 1 km below sea level b s l and composed of different kinds of events associated to both resonance and shear failure processes is related to the shallow dynamics of the hydrothermal system during the analysed period very few volcano tectonic earthquakes took place and tilt recordings showed no sharp or important changes in light of such observations the increases in both temperature and volcano seismic events number were associated to increases in the release of gas from a deep and stable magma body without magma intrusions within the shallow hydrothermal system indeed a greater release of gas from depth leads to increased fluid circulation that can promote increases in volcano seismic events number by both fracturing processes and resonance and vibration in cracks and conduits the different trends observed in the measured geochemical and geophysical series during the anomalous periods can be due to either time changes in the medium permeability or a changing speed of gas release from a deep magma body finally all the observed variations together with the changing temporal distribution of the different seismic event kinds suggest that the hydrothermal system at vulcano can be considered unsteady and dynamic

analysis of the seismic activity associated with the 2010 eruption of merapi volcano java abstract the 2010 eruption of merapi is the first large explosive eruption of the volcano that has been instrumentally observed the main characteristics of the seismic activity during the pre eruptive period and the crisis are presented and interpreted in this paper the first seismic precursors were a series of four shallow swarms during the period between 12 and 4 months before the eruption these swarms are interpreted as the result of perturbations of the hydrothermal system by increasing heat flow shorter term and more continuous precursory seismic activity started about 6 weeks before the initial explosion on 26 october 2010 during this period the rate of seismicity increased almost constantly yielding a cumulative seismic energy release for volcano tectonic vt and multiphase events mp of 7 5 10 10 j this value is 3 times the maximum energy release preceding previous effusive eruptions of merapi the high level reached and the accelerated behavior of both the deformation of the summit and the seismic activity are distinct features of the 2010 eruption the hypocenters of vt events in 2010 occur in two clusters at of 2 5 to 5 km and less than 1 5 km depths below the summit an aseismic zone was detected at 1 5 2 5 km depth consistent with studies of previous eruptions and indicating that this is a robust feature of merapi s subsurface structure our analysis suggests that the aseismic zone is a poorly consolidated layer of altered material within the volcano deep vt events occurred mainly before 17 october 2010 subsequent to that time shallow activity strongly increased the deep seismic activity is interpreted as associated with the enlargement of a narrow conduit by an unusually large volume of rapidly ascending magma the shallow seismicity is interpreted as recording the final magma ascent and the rupture of a summit dome plug which triggered the eruption on 26 october 2010 hindsight forecasting of the occurrence time of the eruption is performed by applying the material failure forecast method ffm using cumulative real time seismic amplitude rsam calculated both from raw records and on signals classified according to their dominant frequency stable estimates of eruption time with errors as small as 4 h are obtained within a 6 day lapse time before the eruption this approach could therefore be useful to support decision making in the case of future large explosive episodes at merapi

hurricane generated currents on the outer continental shelf 2 model sensitivity studies a numerical model described and verified in part 1 of this two part series cooper and thompson this issue is applied to study the sensitivity of hurricane generated currents on the outer shelf and slope numerical experiments are performed in a simple basin with a straight shelf the sensitivity of the response to changes in storm parameters direction of storm approach and topography is quantified response is measured in terms of the mixed layer velocity and depth at sites along the storm track results reveal the most important factors are in decreasing order wind speed storm translation speed direction of storm approach asymmetry in the wind field entrainment parameterization and advection at slower storm translation speeds response is largely insensitive less than 10 to radius of maximum wind shelf and slope configuration bottom friction atmospheric pressure gradients and further reductions in the model grid size for a storm approaching cross shelf the response is primarily baroclinic greater than 90 and only weakly dependent less than 10 on the water depth at the site

shallow repeating seismic events under an alpine glacier at mount rainier washington usa we observed several swarms of repeating low frequency 1 5 hz seismic events during a 3 week period in may june 2010 near the summit of mount rainier washington usa that likely were a result of stick slip motion at the base of alpine glaciers the dominant set of repeating events multiplets featured 4000 individual events and did not exhibit daytime variations in recurrence interval or amplitude volcanoes and glaciers around the world are known to produce seismic signals with great variability in both frequency content and size the low frequency character and periodic recurrence of the mount rainier multiplets mimic long period seismicity often seen at volcanoes particularly during periods of unrest however their near surface location lack of common spectral peaks across the recording network rapid attenuation of amplitudes with distance and temporal correlation with weather systems all indicate that ice related source mechanisms are the most likely explanation we interpret the low frequency character of these multiplets to be the result of trapping of seismic energy under glacial ice as it propagates through the highly heterogeneous and attenuating volcanic material the mount rainier multiplet sequences underscore the difficulties in differentiating low frequency signals due to glacial processes from those caused by volcanic processes on glacier clad volcanoes

signs of magma ascent in lp and vlp seismic events and link to degassing an example from the 2010 explosive eruption at merapi volcano indonesia the link between seismicity and degassing is investigated during the vei 4 eruptions of merapi volcano indonesia in october and in early november 2010 seismicity comprised a large number and variety of earthquakes including volcano tectonic events a sustained period of long period seismicity lps i e long period events lp very long period events vlp and tremor lps seismicity is ascribed to the excitation of fluid filled cavity resonance and inertial displacement of fluids and magma we investigate here lps that occurred between 17 october and 4 november 2010 to obtain insights into the volcano eruption processes which preceded the paroxysmal phase of the eruption on 4 5 november we proceed to the moment tensor inversion of a well recorded large vlp event during the intrusion phase on 17 october 2010 i e before the first explosion on 26 october by using two simplified models crack and pipe we find a shallow source for this vlp event at about 1 km to the south of the summit and less than 1 km below the surface we analyze more than 90 lp events that occurred during the multi phase eruption 29 october 4 november we show that most of them have a dominant frequency in the range 0 2 4 hz we could locate 48 of those lp events at least 3 clusters of lp events occurred successively we interpret these observations as generated by different fluid filled containers in the summit area that were excited while magma rose we also observe significant variations of the complex frequency during the course of the eruption we discuss these changes in terms of a variable ratio of fluid to solid densities and or by possible conduit geometry change and or permeability of the conduit or the edifice and or by resonance of different fluid containers during the release of more than 0 4 tg of so2 and large but unknown masses of other volcanic gases finally we also discuss how the major explosions of the eruption were possibly triggered by passing waves resulting from regional tectonic earthquakes on 3 and 4 november

a model of vulcanian eruptions at galeras volcano colombia abstract a series of six vulcanian eruptions at galeras volcano colombia occurred during 1992 1993 these eruptions followed the emplacement of a lava dome in late 1991 which was accompanied by cooling crystallizing and partial solidification of the column of magma plugging the conduit five of the eruptions were preceded by episodes of monochromatic long period seismicity suggesting cyclic pressurization of the magma the quiescent intervals between eruptions generally decreased with each successive eruption we propose a model of gas release from magma into confined stationary pore spaces by 5 10 crystallization of anhydrous minerals causing repeated overpressurization of the magmatic system using initial lithostatic pressures of 20 100 mpa 800 3900 m depth gas buildup by crystallization indicates overpressures of 3 17 mpa which is the approximate fracture criterion for a magma chamber our galeras data suggest two models of pressurization 1 gas exsolution may have occurred at similar depths but with progressively smaller overpressures being developed before each successive eruption according to this model the comparatively long quiescent periods between the first eruptions resulted in relatively large amounts of gas exsolution from the magma and accumulation in pore spaces whereas the shorter quiescent periods for the later eruptions exsolved less gas the decrease in overpressure with time may have resulted from progressive fracturing of partly solidified magma during the eruptions which progressively decreased the tensile strength and increased the permeability of the magma 2 since overpressures are smaller at shallower depths for a given amount of crystallization the first eruptions of 1992 1993 were caused by gas exsolution at shallow depths while the last eruptions having shorter quiescent intervals resulted from a greater amount of gas exsolution at greater depths in this case the rate of gas exsolution varied as a function of depth the two scenarios for pressurization may be combined into a more general model involving edifice weakening and the development of a shallow hydrothermal system from continued degassing of the magma plug as weakening of the edifice formed an extensive system of fractures the shallow hydrothermal system deepened due to meteoric water input and magmatic degassing with time a greater number of fractures were filled and partly sealed by hydrothermal minerals at progressively deeper levels as a result the source of the overpressure also deepened with time

unusual low frequency volcanic seismic events with slowly decaying coda waves observed at galeras and other volcanoes abstract events with slowly decaying coda waves are observed in active andesitic volcanoes associated mainly with vulcanian type eruptions or large gas emissions however these signals are also recorded in some quiescent volcanoes these unusual signals are considered to be related to magmatic activity and generally occur beneath the active crater the signals have been observed to be a short term precursor galeras volcano colombia 1992 1993 asama yama volcano japan 1983 after eruption tokachi dake volcano japan 1989 during seismic swarms meakan dake volcano japan 1982 and during quiescence puracevolcano colombia 1994 1995 tarumai volcano japan 1970 1971 1975 spectral analysis reveals common characteristics for this type of signal the spectrum is characterized by one or several sharp frequency peaks fundamental frequencies are not affected by epicentral distance azimuth or travel time indicating a source effect the damping coefficient for coda waves ranges from 0 002 to 0 02 and is related to large values of the quality factor q c ranging from 250 to 25 respectively these parameters may be the result of large amounts of gas bubbles in the magma body

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

a numerical study of sediment transport and event bed genesis during tropical storm delia some event beds tempestites are thought to be emplaced on shallow marine shelves by the combined action of strong coastal currents and high waves during fairly short lived storms to test this hypothesis a storm sedimentation system has been constructed from six numerical models describing a cyclonic wind field three dimensional coastal circulation wind waves generated over the continental shelf the combined effect of steady and oscillatory currents within the benthic boundary layer suspended and bed load transport of sediment and conservation of the seafloor this model system is used to hindcast winds currents waves and resulting sedimentation during tropical storm delia which passed over the texas louisiana shelf on september 3 4 1973 sensitivity to the initial substrate is investigated in four experiments using uniform silt uniform sand a mud line at the 20 m isobath and a simplified modern sediment distribution modeled coastal currents are vertically uniform and do not reveal the structure predicted by the mid latitude geostrophic storm circulation model because the predicted depth of the wind mixed layer is greater than the water depth over the shelf shelf currents in excess of 2 m s flow predominantly along the coast to the southwest during most of the storm driven by the wind stress and the trapped coastal wave which peaks at 180 cm near galveston significant wave heights reach 8 m on the outer shelf but are less than 4 m over the inner shelf these waves combine with steady currents to produce bed shear velocities which locally exceed 20 cm s the region of highest stresses always lies to the right of the storm track viewed down the path and moves across the shelf with the eye of the storm three general sediment transport paths are evident 1 onshore transport of finer sediment over the outer shelf to the right of the storm track 2 westward directed along shelf transport of predominantly fine sediment between approximately 40 m and 20 m water depths and 3 minor offshore transport of sand from the shoreface to depths less than 30m the resulting event bed has a ragged appearance with a maximum thickness of about 20 cm in region 1 and covers an area of approximately 3 104 km2 to the right of the storm track aside from local transport associated with finer sediments these results are relatively insensitive to initial sediment type comparison of model results to observed data from buccaneer platform shows that the different models performed adequately during the peak of the storm except for a significant underprediction of the significant wave height by the wind sea model the estimated uncertainty in the calculated combined shear stresses u based on errors produced by the individual model components is most dependent on the wave bottom orbital amplitude the total uncertainty in u is estimated to be approximately 7

tornillos modeled as self oscillations of fluid filling a cavity application to the 1992 1993 activity at galeras volcano colombia abstract tornillos are quasi monochromatic seismic signals with a slowly decaying coda that are observed near active volcanoes and geothermal areas worldwide in this work a lumped parameter model describing the tornillo source process as the self oscillations of fluid filling a cavity is investigated a nonlinear ordinary differential equation is derived that governs the behavior of the model taking into account viscous and nonlinear damping as well as the reaction force of the fluid inside the cavity this equation is numerically integrated both for different cavity sizes and different fluids of volcanological interest such as gas h2o co2 h2o so2 and gas particle mixtures ash so2 water droplets h2o this cavity model predicts that when the filling fluid is a mixture of ash and so2 the signal duration will increase until the mixture becomes enriched in ash and then the duration exhibits a decrease additionally the damping coefficients 1 2q of the synthetic signals are estimated in the range between 0 002 and 0 014 both results agree well with the temporal variation of tornillos duration and the estimated q quality factors damping coefficients observed at galeras volcano in the context of the cavity model tornillo frequency variations from 4 hz to 1 hz observed prior to eruptions can be interpreted as the result of fluid composition changes as more ash particles are added this is in agreement with the observation that gas accumulation at galeras was a steady rather than an episodic process and that tornillos were most likely triggered after a fluid pressure threshold had been exceeded

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

excitation of a buried magmatic pipe a seismic source model for volcanic tremor recent observations of seismic events at various volcanoes suggest that harmonic tremor results from the sustained occurrence of so called long period or low frequency events accordingly we can view the long period volcanic event as the elementary process of tremor and interpret it as the impulse response of the tremor generating system we present a seismic model in which the source of tremor is the acoustic resonance of a fluid filled volcanic pipe triggered by excess gas pressure the model consists of three elements namely a triggering mechanism a resonator and a radiator for simplicity we assume a hemispherical trigger cylindrial resonator and circular radiator set in a vertical configuration with the trigger capping the top of the pipe and the disk shaped radiator shutting off its bottom considering the simple case of a source buried in a homogeneous half space we then apply the discrete wave number method to obtain a complete representation of the ground motion response at near and intermediate distances the results demonstrate that the displacement attributed to the pipe dominates the near field motion while that due to the disk is representative of the intermediate and far fields the trigger itself has a smaller contribution mainly limited to the field in the proximity of the source the characteristics displayed by the free surface response evolve from a strong impulsive signature in the immediate vicinity of the epicenter to a well developed harmonic wave train dominated by rayleigh waves at larger distances no clear shear arrival can be detected in the synthetic seismograms the displacement spectrum reflects the organ pipe modes of the conduit and the bandwidth associated with the dominant spectral peak of motion is controlled by the combined losses due to viscous attenuation in the fluid and elastic radiation into the solid in the case of the cylindrical magma column considered the radiation loss is proportional to the square of the pipe radius while the loss related to viscous damping is inversely proportional to the same factor indicating that the relative importance of the two loss mechanisms is critically dependent on the geometry of the magma reservoir the relative importance of the pipe and disk elements likewise is a function of the conduit cross section this suggests the possibility of determining the geometry of the source as well as the radiation loss and in situ magma viscosity from a comparison of near and far field observations

fluid dynamics inside a wet volcano inferred from the complex frequencies of long period lp events an example from papandayan volcano west java indonesia during the 2011 seismic unrest abstract we present results of our study aimed at understanding the dynamics of fluids inside a wet volcano through the analysis of swarms of long period lp events accompanying the 2011 seismic unrest at papandayan volcano west java indonesia prior to this unrest we measured an extremely high percentage 100 of co2 in the ground at the summit crater however with a very low value of so2 flux 6 tons day increase in volcanic activity was also observed from the records of a tiltmeter a long term inflation was followed by an abrupt deflation that took place concurrently with the swarms of lp events thereafter swarms of local tectonic lt and volcano tectonic vt earthquakes started we focus here on analyzing the lp events in the following manner first we estimate the source location of lp events by applying a 3 d non linear hypocenter localization algorithm which includes topography we then study the waveforms and spectral characteristics of lp events recorded at different stations and investigate whether or not these characteristics are due to source effects subsequently we compute the oscillation frequencies f and the decay characteristics q factor in the complex frequency domain of the coda part of the lp events by using the sompi method which is based on a homogeneous auto regressive ar equation the rectangular fluid filled crack model is used to estimate the physical processes related to the observed temporal variations in the complex frequencies we divide the swarms of lp events into two intervals the first interval occurred between june and july 2011 48 lp events while the second interval extended from september to october 2011 36 lp events the frequencies of lp events observed during these intervals range between 1 1 and 6 2 hz while the q factors are widely scattered between 20 and 400 we estimate the compositions of fluids inside the crack during both intervals as either water foam mixtures of water and h2o gas steam or misty gas mixtures of water droplets and h2o gas steam we finally suggest that if an eruption were to have taken place following the 2011 unrest it would have been in phreatic style rather than magmatic style the results of our study therefore contribute to the effort in the prediction of the behavior of future eruptions and to volcanic hazards assessment and therefore to volcanic risk mitigation

hydroacoustic noise precursors of the 1990 eruption of kelut volcano indonesia abstract the results of a hydroacoustic monitoring experiment in the kelut crater lake indonesia prior to its 1990 eruption are presented with the benefit of hindsight indeed the underwater noise levels in three widely separated frequency bands together with the lake water temperature was radio transmitted and almost continuously recorded from a period of quiescence of the volcano till the onset of its 10 february 1990 eruption which destroyed the monitoring buoy the comparative analysis of the noise variations in the three bands together with seismic and temperature data have shed light on the mechanisms underlying the pre eruptive activity the three acoustic levels had shown conspicuous yet distinctive changes prior to the eruption acoustic level in the low frequency 1 50 hz band which increased one year before the resumption of seismic activity and the lake warming up is interpreted as the result of boiling at depth the source of high acoustic level in the audiometric 500 5000 hz range is clearly the bubbling of volcanic gases occurring as a strong convective column in the middle of the lake from the variations of this audiometric level we have estimated that the degassing rate in the lake increased by a hundred fold during the pre eruptive period variations of ultrasonic 20 100 khz frequency acoustic level seem to be related with pressure and thermal changes within the hydrothermal system and its rock matrix beneath the lake in conclusion this experiment demonstrates the potential of hydroacoustic monitoring as an early warning system at crater lake volcanoes

spectral characteristics of volcano tectonic earthquake swarms in nevado del ruiz volcano colombia abstract spectral analyses for volcano tectonic earthquakes were carried out at nevado del ruiz volcano nrv for the period 1985 1996 for several earthquake swarms around the volcano named north east west south and crater swarm zones important spectral peaks for each earthquake swarm zone were found by counting the number of spectra that had the same spectral peaks each swarm zone showed some characteristic peaks which could help to differentiate between them however the most important peaks were similar for all the zones these results suggest that the earthquake swarms at nrv were influenced directly by the source activity of the volcano and could also be influenced by the site effect some temporal changes were observed in spectral parameters such as a change in the frequency contents in almost all the swarm zones and the frequency of the p waves in the west earthquake swarm zone before the eruptions on november 13 1985 and september 1 1989 p waves showed low frequencies 1 2 hz at the west earthquake swarm after the eruptions the frequencies of p increased 2 4 hz this fact showed that changes decreasing of frequencies in the spectra of p waves at the west earthquake swarm could help in the monitoring of volcanic activity at nrv this swarm zone seems to be related directly with the most important volcanic crises that have occurred this suggests that the west swarm zone should be monitored in more detail in the future

review of seismological studies at mount etna this paper reports the present state of seismological research at mt etna a schematic classification of the earthquakes that occur on the volcano is proposed based on both seismogram and spectrum features we have made both focal solutions and estimates of earthquake source parameters stress drop values between 2 and 20 bars and small source dimensions the crust of etna thus appears as an extremely heterogeneous medium that does not permit great stress accumulation the coexistence of an extensional regime with an older and deeper compressive one seems confirmed at depths greater than about 7 km eruptive and seismic phenomena occur mainly along the principal structural trends of the volcano but often the directions of the eruptive fractures and the earthquake concentration during the same eruption do not coincide tectonics seem to play an important role in controlling seismo volcanic behaviour

numerical simulation of a response of an oceanic front to an atmospheric frontal passage the influence of middle latitude cyclones and their associated cold fronts on open ocean fronts is studied with an embedded mixed layer ocean circulation model similar to that of adamec et al 1981 finite differences with horizontal resolution of 5 km in a staggered grid are used to solve the model equations within a domain of total meridional extension of 300 km and 500 m depth three numerical experiments were performed to investigate the response of an oceanic front similar to the south atlantic subtropical convergence zone to an atmospheric frontal passage under the effect of the cold air outbreak the thermal and dynamic structures of the upper layers are substantially modified with a higher sinking cooling rate of the mixed layer the sinking cooling rate depends strongly on the magnitude of the thermal gradient at the top of the thermocline and on the mixed layer depth due to the differences in sinking cooling rates a single storm can move the oceanic front up to 20 km from its initial position for low intensity winds a change in the wind direction does not affect the thermal structure of the upper layer ocean even in the frontal region the mixed layer oscillations are entirely a function of the daily scale of the solar heating for a sudden change in the wind direction the response of the current velocity field in the mixed layer is almost instantaneous

noble gases in ocean waters and sediments noble gases are widely used in studies of the basic properties and dynamics of natural systems including the ocean this chapter describes some of the more extensive applications of noble gases mainly helium isotopes to studies of oceanographic problems they include the modern oceanic circulation paleo oceanography hydrothermal and cold brine systems in the deep ocean and ocean atmosphere gas exchange originally oceanic noble gas studies were focused on geochemical problems such as the question of the existence of excess helium in seawater derived from radioactive decay of the elements of the uranium and thorium series in ocean sediments suess and wanke 1965 bieri et al 1966 after the discovery of mantle primordial helium during the 1960s clarke et al 1969 craig and weiss 1971 craig et al 1975 and 3he derived from decay of tritium in the near surface waters of the ocean jenkins and clarke 1976 large programs were developed to exploit helium isotopes frequently in combination with tritium for studies of water mass formation circulation and variability e g jenkins 1987 schlosser et al 1991 more recent studies started to explore the use of helium isotopes to paleoceanographic objectives these studies build upon the discovery of extraterrestrial helium in deep sea sediments in the early 1960s merrihue 1964 this signal is now being systematically examined for its potential as a tool for investigations of sediment accumulation rates on very long time scales millions of years and their correlation with changes in paleoceanography e g farley 1995 farley and patterson 1995 marcantonio et al 1995 1996 2001 soon after the discovery of mantle helium in seawater noble gases were applied to studies of hydrothermal systems originally these studies were focused on the source of the fluids emanating from hydrothermal vents as well as

ground motion in the near field of a fluid driven crack and its interpretation in the study of shallow volcanic tremor we present a study of the motion of the ground in the near field of a fluid driven tensile crack embedded in a layered half space the source that we consider is the jerky opening of a channel connecting two fluid filled cracks and the cause of this opening is the excess pressure of fluid in one of the cracks we make a complete representation of the three components of ground motion in the space time and frequency domains and analyze the effects of fluid compressibility source depth and medium structure on the ground response the calculations show the presence of a dominant frequency of motion which depends not only on the source geometry and bulk modulus of the fluid but also on medium characteristics receiver position and the component of motion being considered using this source model we view an episode of volcanic tremor as a continuous sequence produced by numerous jerky openings of channels occurring randomly in time along a chain of cracks our results are applied to the october 5 6 1963 east rift eruption of kilauea volcano hawaii and found to be compatible with available seismic data suggesting that magma is transported through an ensemble of cracks with the area of 1 1 km each pair of cracks constituting an individual dike segment which opens in discrete increments at a rate of 1 s we obtain the following parameters for each dike segment opening increase in cavity volume 40 m3 stress drop 0 004 bar seismic moment 1019 dyn cm and force applied by the fluid to open the dike 1014 dyn the total moment integrated over the entire duration of tremor for the eruption is 0 5 1024 dyn cm roughly equivalent to a single magnitude m 5 earthquake the seismic source parameters and other field observations offer constraints on the process of mass transport and are compatible with the excess pressure and viscosity of magma of about 40 bars and 102 p respectively

sea surface cooling caused by typhoons in the tohoku area in august 1989 a remarkable sea surface cooling event was observed in the north western pacific off japan coast which is known as the tohoku area by using well calibrated satellite sea surface temperature images when typhoons t8914 and t8915 passed over the tohoku area in august 1989 the sea surface cooling maximum reached up to 9 c which is much larger than that reported in the previous studies the corresponding hydrographic data show that the sea surface cooling state is closely related with the ocean structure in the tohoku area the larger sea surface cooling occurs in the oyashio area the numerical experiments taking account of the ocean structure show that the surface cooling maximum is 3 4 times larger in case of the oyashio profile than that of the kuroshio profile and clarify the mechanism of the sea surface cooling

sediment focusing in the central equatorial pacific ocean at four sites in the central equatorial pacific ocean the flux of extraterrestrial he determined using the excess 230th profiling method is 8 10 13 cm stp cm 2 ka 1 this supply rate is constant to within 30 at these same sites however the burial rate of he determined using chronostratigraphic accumulation rates varies by more than a factor of 3 the lowest burial rates which occur north of the equator at 1 n 139 w are lower than the global average rate of supply of extraterrestrial he by 20 and indicate that sediment winnowing may have occurred the highest burial rates which are recorded at the equator and at 2 s are higher than the rate of supply of extraterrestrial he by 100 and these provide evidence for sediment focusing by analyzing several proxies measured in core pc72 sediments spanning the past 450 kyr we demonstrate that periods of maximum burial rates of 230th he 10be ti and barite with a maximum peak to trough amplitude of a factor of 6 take place systematically during glacial time however the ratio of any one proxy to another is constant to within 30 over the entire length of the records given that each proxy represents a different source 234u decay in seawater interplanetary dust upper atmosphere continental dust or upper ocean our preferred interpretation for the covariation is that the climate related changes in burial rates are driven by changes in sediment focusing

locating microearthquakes induced by hydraulic fracturing in crystalline rock microearthquakes induced by hydraulic fracturing in crystalline rock at a depth of 3 5 km were located with a precision of better than 30 m to obtain information about the geometry and dimensions of the fracture system produced the induced microseismicity was monitored by a network of five vorehole seismic stations a total of about 800 induced events were reliably located from arrival times event locations show a tabular distribution that strikes 350 sup 0 and dips 65 sup 0 east subparallel to the injection well the injection was intended to produce a fracture system that would hydraulically connect two subparallel wells a lack of fluid communication between them is consistent with a lack of induced microearthquakes near the target wellbore the 150 m thickness of the zone of seismicity far exceeds the relative locational uncertainties the injected fluid appears to have stimulated a zone of rock rather than simply a single fracture the distribution of microseismic events presumably envelopes the zone of fluid paths created by the fracture experiment

the 2007 eruption of kelut volcano east java indonesia phenomenology crisis management and social response we focus in this paper on the processes and consequences of an unusual volcanic eruption at kelut volcano east java in november 2007 after two months of worrying precursor signs kelut volcano erupted but neither explosions nor the usual hazards observed during the historic eruptions happened e g ash falls volcanic bombs and pyroclastic flows instead of an explosive eruption the 2007 eruption was extrusive given than such an eruption could not be predicted the authorities had to manage a new situation we conducted interviews with nine stakeholders of the crisis management team and undertook a questionnaire based survey in the settlement nearest to the crater in order to understand how the authorities managed the crisis and how people reacted inquiries and questionnaires were carried out shortly after the end of the evacuation process when the volcano was still under surveillance for fear of an explosive phase the results display a real gap in what it takes to manage a crisis or live through a crisis this suggests that the unusual eruption pattern of kelut volcano was not the only factor of the misunderstanding between the authorities and the population these problems stem from more structural causes such as the lack of communication and information when there is a need to adapt to a new scenario in such a situation the inability of the crisis management system to take decisions underscored the intrinsic vulnerability of the population despite a hierarchical and strategic top down crisis management approach

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