simulation of curved open channel flows by 3d hydrodynamic model a mathematical model of three dimensional 3d free surface flows has been applied to simulate the curved channel flows and mass transport in the horizontal plane a channel fitted curvilinear coordinate system is used whereas in the vertical plane the transformation is adopted to track the free surface and variable bed topography to reduce the numerical diffusion the second order upwind scheme of roe is incorporated to discretize the convection terms the standard k e model has been modified to take account of some anisotropic effects appearing in shallow curved channels i e streamline curvature and the damping effects of free surface and solid walls the governing equations are solved in a collocated grid system by a fractional three step implicit algorithm two test cases from curved flumes have been studied 1 a 270 channel bend with a sloped outer bank and 2 a meandering channel with mass transport the results are compared with the available data which shows generally good agreement

structure of the california coast ranges and san andreas fault at safod from seismic waveform inversion and reflection imaging 1 a seismic reflection and refraction survey across the san andreas fault saf near parkfield provides a detailed characterization of crustal structure across the location of the san andreas fault observatory at depth safod steep dip prestack migration and frequency domain acoustic waveform tomography were applied to obtain highly resolved images of the upper 5 km of the crust for 15 km on either side of the saf the resulting velocity model constrains the top of the salinian granite with great detail steep dip reflection seismic images show several strong amplitude vertical reflectors in the uppermost crust near safod that define an 2 km wide zone comprising the main saf and two or more local faults another prominent subvertical reflector at 2 4 km depth 9 km to the northeast of the saf marks the boundary between the franciscan terrane and the great valley sequence a deep seismic section of low resolution shows several reflectors in the salinian crust west of the saf two horizontal reflectors around 10 km depth correlate with strains of seismicity observed along strike of the saf they represent midcrustal shear zones partially decoupling the ductile lower crust from the brittle upper crust the deepest reflections from 25 km depth are interpreted as crust mantle boundary

two dimensional waveform inversion of multi component data in acoustic elastic coupled media in order to account for the effects of elastic wave propagation in marine seismic data we develop a waveform inversion algorithm for acoustic elastic media based on a frequency domain finite element modelling technique in our algorithm we minimize residuals using the conjugate gradient method which back propagates the errors using reverse time migration without directly computing the partial derivative wavefields unlike a purely acoustic or purely elastic inversion algorithm the green s function matrix for our acoustic elastic algorithm is asymmetric we are nonetheless able to achieve computational efficiency using modern numerical methods numerical examples show that our coupled inversion algorithm produces better velocity models than a purely acoustic inversion algorithm in a wide variety of cases including both single and multi component data and low cut filtered data we also show that our algorithm performs at least equally well on real field data gathered in the korean continental shelf

observations and analysis of b type earthquakes explosions and volcanic tremor at pavlof volcano alaska an eight station network of short period seismometers has been operated near pavlof volcano 55 25 n 161 54 w alaska peninsula since 1976 high quality analog to digital and direct digital data were recorded during eruptions in 1980 through 1983 data are analyzed from explosions with distinct air phases b type volcanic earthquakes shallow low frequency events lacking clear s phases and volcanic tremor to determine source and propagation effects between zero and several hundred b type events and explosions per day are recorded with higher numbers during eruptions magnitudes range between 0 5 and 1 3 and b values range between 1 9 0 1 and 2 6 0 1 with no systematic relation to eruptive activity six results are most important 1 data from a recently installed three component station reveal that the highest amplitude waves of the b type events show retrograde elliptical particle motion and normal dispersion and are hence probably rayleigh waves 2 stacking of the events enhances the p wave which has a velocity of 3 1 0 1 km sec 1 3 the explosions and b type events have similar hypocenters as evidenced by signal characteristics and wave arrival times 4 the b type events contain virtually no high frequency energy even when allowing for attenuation effects in particular we estimate the anelastic attenuation coefficient q to have a value of 45 20 for rayleigh waves in the shallow part of the volcano 5 volcanic tremor spectra exhibit evenly spaced narrow peaks which we model as eigenvalues of organ pipe resonance in the magma conduit we estimate the length of the conduit to be a maximum of 1 6 km 6 the volcano shows evidence of extreme lateral variation of velocity and attenuation in its shallow structure

infrasonic waves and volcanic tremor at stromboli the origin of the volcanic tremor is still under debate many theories have been proposed in the last years but none has yet been completely accepted in 1993 highly sensitive pressure sensors 2 175 pa volt used to monitor the explosive activity at stromboli have revealed unexpected correlation between small spike shaped pressure signals 1 2 pa and volcanic tremor these pressure pulses repeat regularly in time with a recurrent period of ca 1 s video camera images allowed us to correlate the pressure pulses with small gas bursts occurring at one of the active vents the striking correlation 0 971 between infrasonic and seismic energy fluctuations is particularly meaningful in the frequency domain infrasonic and seismic signal share the same spectral content 3 hz for every station within a range of 700 m around the craters correlations in time and frequency domain remained unaltered during the 1994 field experiments moreover during 1994 the increased degassing activity has been followed by an increase in pressure release 7 8 pa and by a shift towards higher frequencies 8 hz both in the infrasonic and seismic records infrasonic waves and volcanic tremor show similar energy fluctuations and frequency contents appearing therefore to be produced by the same dynamical process on this basis we claim that volcanic tremor at stromboli originates by continuous outbursting of small gas bubbles in the upper part of the magmatic column

seismic imaging of complex onshore structures by 2d elastic frequency domain full waveform inversion quantitative imaging of the elastic properties of the subsurface at depth is essential for civil engineering applications and oil and gas reservoir characterization a realistic synthetic example provides for an assessment of the potential and limits of 2d elastic full waveform inversionfwiof wide aperture seismic data for recovering high resolution p and s wave velocity models of complex onshore structures fwi of land data is challengingbecauseoftheincreasednonlinearityintroducedbyfreesurface effects such as the propagation of surface waves in the heterogeneous near surface moreover the short wavelengths of the shear wavefield require an accurate s wave velocity starting modeliflowfrequenciesareunavailableinthedata weevaluated different multiscale strategies with the aim of mitigating the nonlinearities massively parallel full waveform inversion was implemented in the frequency domain the numerical optimization relies on a limited memory quasi newton algorithm that outperforms the more classic preconditioned conjugate gradient algorithm the forward problem is based upon a discontinuous galerkin dg method on triangular mesh which allows accuratemodelingoffree surfaceeffects sequentialinversionsofincreasingfrequenciesdefinethemostnaturallevelofhierarchyin multiscale imaging in the case of land data involving surface waves the regularization introduced by hierarchical frequency inversions is not enough for adequate convergence of the inversion a second level of hierarchy implemented with complexvalued frequencies is necessary and provides convergence of the inversion toward acceptable p and s wave velocity models amongthepossiblestrategiesforsamplingfrequenciesintheinversion successive inversions of slightly overlapping frequency groups is the most reliable when compared to the more standard sequential inversion of single frequencies this suggests that simultaneous inversion of multiple frequencies is critical when consideringcomplexwavephenomena

roughness effects on flow and shear stress near outside bank of curved channel velocity and turbulence distributions are measured in a 270 curved open channel of half trapezoidal section with extra roughness applied to the outside bank slope the purpose of this investigation is to provide some understanding of flow mechanics that may be useful in the design of riprap protection profile averaged velocity and bed shear velocity distributions are calculated a significant variation of bed shear up the slope and a much higher stress near the toe of the slope are found for the roughened outside bank slope it is found that a reasonable correlation of the velocity and bed shear stress on the bank is given by a form of the colebrook equation lateral momentum transfer by secondary flow and turbulent stress are also evaluated and found to be significant in the bank vicinity

monitoring volcanic activity using correlation patterns between infrasound and ground motion 1 this paper presents a simple method to distinguish infrasonic signals from wind noise using a cross correlation function of signals from a microphone and a collocated seismometer the method makes use of a particular feature of the cross correlation function of vertical ground motion generated by infrasound and the infrasound itself contribution of wind noise to the correlation function is effectively suppressed by separating the microphone and the seismometer by several meters because the correlation length of wind noise is much shorter than wavelengths of infrasound the method is applied to data from two recent eruptions of asama and shinmoe dake volcanoes japan and demonstrates that the method effectively detects not only the main eruptions but also minor activity generating weak infrasound hardly visible in the wave traces in addition the correlation function gives more information about volcanic activity than infrasound alone because it reflects both features of incident infrasonic and seismic waves therefore a graphical presentation of temporal variation in the cross correlation function enables one to see qualitative changes of eruptive activity at a glance this method is particularly useful when available sensors are limited and will extend the utility of a single microphone and seismometer in monitoring volcanic activity

flow near sloped bank in curved channel shear and velocity distributions near a sloped bank in a 270 open channel bend are studied data which include detailed velocity and turbulence measurements in both the longitudinal and transverse flow directions are collected with a laser doppler anemometer system the flow adjacent to a 2 1 horizontal vertical and a 3 1 sloped bank is examined the purpose is to examine in unprecedented detail the developing flow near a sloped bank in a curved channel including the effect of varying side slope it is found that the longitudinal flow redistribution is fully developed at the downstream end of this 270 bend although the spiral flow is found to develop much more quickly in the straight reach upstream of the bend it is found that the friction factor on the sloped bank is more dependent on channel shape than a local velocity shear stress relationship within the bend velocities and shear stresses on the sloped bank increase significantly with the shear stress correlating more directly with the loc

crustal seismic imaging from multifold ocean bottom seismometer data by frequency domain full waveform tomography application to the eastern nankai trough 1 in offshore surveys the deep crust is generally investigated by traveltime tomography applied to sparse ocean bottom seismometer data the inferred velocity models are of limited resolution precluding a quantitative analysis of deep tectonic discontinuities if dense arrays of ocean bottom seismometers can be deployed the resulting data sets become amenable to full waveform processing which should lead to a significant improvement in the resolution of structures such acquisition and processing were achieved on the eastern nankai subduction zone full waveform inversion is entirely implemented in the frequency domain enabling efficient finite difference wave modeling and allowing to limit the inversion to a few discrete frequencies of increasing value such a hierarchical procedure defines a multiresolution approach to seismic imaging the data set was recorded by 93 instruments deployed along a 105 km long profile thirteen frequencies ranging from 3 to 15 hz were inverted sequentially wavelengths imaged by the full waveform inversion typically range between 0 5 and 8 km full waveform tomography reveals an intense compression in the upper prism and underlying backstop as evidenced by several thrusts the frontal ones still active corresponding to negative velocity anomalies the subducting paleo zenisu ridge is also reconstructed above which stands the decollement velocities in the upper mantle beneath the ridge are rather low 7 5 km s 1 suggesting partially serpentinized mantle beneath the ridge this paper demonstrates the feasibility of full waveform tomography based on dense ocean bottom seismometer data sets and its ability to quantitatively image the entire crust with a significantly improved resolution compared to what is usually achieved through traveltime tomography

evidence for gas influence on volcanic seismic signals recorded at stromboli abstract the meaning of the large variety of seismic waveforms showing different frequencies associated with volcanic activity is still uncertain no definitive model for source dynamics has been proposed yet at present seismic models explaining the origin of the spectral content of the seismic signal are mainly linked to geometrical features of the volcanic conduit and to resonant effects induced by pressure fluctuations in a fluid filled conduit such models assume the physical system to be in a steady state over a long interval of time at stromboli the seismicity produced by each of the three active vents is not stable and can suddenly change in time therefore the application of stable resonator models appears to be unwarranted on the basis of infrared image analyses atmospheric pressure and seismic wavefield signals we show that different frequency contents and different explosive styles occur at stromboli at the same time at different vents moreover we give evidence to support the idea that seismicity and explosivity are both controlled by a variable gas flow regime released during explosions at the top of the magma column we have recognized two main pressure regimes controlling the explositivity at stromboli one is impulsive short and possibly produced by a gas accumulation beneath a cap rock the other has an intermittent regime feature and lasts longer we demonstrate how the first one generates a monochromatic low frequency wavefield while the second shows a high frequency spectrum where the frequency content depends on pressure fluctuations and on pressure gradient we suggest different pressure growth and gas flow in the magma as the common source for both explosive style and seismic wavefield

large woody debris structures for sand bed channels described is a method for channel erosion control and habitat rehabilitation featuring intermittent placement of structures made of large woody debris this method is expressly tailored to address severe problems typical of incised channels with little sediment coarser than sand in these types of environments buoyancy forces are typically more important factors in woody debris stability than fluid drag buoyant forces are counteracted by the weight of the structure earth anchors and sediment deposits design concepts were tested in a demonstration project constructed along 2 km of channel draining a 37 km watershed large woody debris structures reduced velocities in the region adjacent to the bank toe and induced sediment deposition and retention construction costs per unit channel length were 23 58 of costs for recent stone bank stabilization projects within the same region during the second year following construction 31 of the structures failed during high flows probably due to inadequate anchoring

main flow velocity in short river bends results of a mathematical model for the depth averaged main flow velocity in shallow river bends are compared with measurements in two consecutive sharply curved short bends in the river dommel the netherlands the computed main velocity distribution agrees rather well with the measured one in the larger part of each bend near the bend exits however deviations occur which indicate that secondary flow convection should be included in the mathematical model also the present model is used to verify some qualitative explanations for the skewing of the main velocity distribution towards the inner bank in the first part of a bend outwards further downstream and to show the effect of flow stage variations on the streamline pattern

application of wave theoretical seismoacoustic models to the interpretation of explosion and eruption tremor signals radiated by pavlof volcano alaska tremor and explosion signals recorded on september 29 during the fall 1996 pavlof eruption are interpreted using video images field observations and seismic data waveform analysis of tremor and explosions provided estimates of the melt s volcano acoustic parameters and the magma conduit dimensions initial mass fractions of 0 25 water and 0 025 carbon dioxide in the melt can explain the resonance characteristics of the tremor and explosion pulses inferred from seismic data the magma conduit is modeled as a three section rectangular crack we infer that the tremor radiating region consists of the lowermost two sections both with cross sectional areas of 10 m2 the deeper section is 43 m long with magma sound speed of 230 m s density of 2600 kg m3 and viscosity of 1 0 106 pa s the section above it defined by the water nucleation depth is 64 m long with magma sound speed of 91 m s density of 2000 kg m3 and viscosity of 1 4 l06 pa s an average magma flow velocity of 1 2 m s with superposed random oscillations acts as the tremor source explosions are postulated to occur in the uppermost part of the magma conduit after water comes out of solution the explosion source region consists of a 15 m long section with cross sectional area of 20 m2 sound speed of 51 m s density of 1000 kg m3 and viscosity of 1 5 103 pa s a burst pressure of 220 mpa at 14 m depth would generate an acoustic pulse whose amplitude and character match the observed signal waveform analysis of the explosion pulses shows that the explosive event may be preceded by a long period fluid transient which may trigger the metastable magma gas mixture the modeling procedure illustrates the synergy of fluid dynamic seismic and acoustic models and data with geological and visual observations

quantification of the gas mass emitted during single explosions on stromboli with the so2 imaging camera we performed measurements using an so2 imaging camera of the so2 gas mass emitted during five discrete explosive events on stromboli volcano on 3 october 2006 the so2 gas mass released during discrete explosions was 15 40 kg per explosion producing 3 8 of the total daily so2 gas emission demonstrating that in terms of gas flux strombolian explosions are a second order phenomenon compared with quiescent degassing using the typical gas composition measured with op ftir allows us to determine the total gas mass released during an explosion as 360 960 kg with a volume of 1500 4100 m 3 at 1 bar at the probable source pressure of gas slug formation of 75 mpa this gas amount would occupy a volume equivalent to a sphere with a radius of 0 8 1 m comparable with estimates of stromboli s conduit geometry c 2009 elsevier b v all rights reserved

exploring some issues in acoustic full waveform inversion the least squares error measures the difference between observed and modelled seismic data because it suffers from local minima a good initial velocity model is required to avoid convergence to the wrong model when using a gradient based minimization method if a data set mainly contains reflection events it is difficult to update the velocity model with the least squares error because the minimization method easily ends up in the nearest local minimum without ever reaching the global minimum several authors observed that the model could be updated by diving waves requiring a wide angle or large offset data set this full waveform tomography is limited to a maximum depth here we use a linear velocity model to obtain estimates for the maximum depth in addition we investigate how frequencies should be selected if the seismic data are modelled in the frequency domain in the presence of noise the condition to avoid local minima requires more frequencies than needed for sufficient spectral coverage we also considered acoustic inversion of a synthetic marine data set created by an elastic time domain finite difference code this allowed us to validate the estimates made for the linear velocity model the acoustic approximation leads to a number of problems when using long offset data nevertheless we obtained reasonable results the use of a variable density in the acoustic inversion helped to match the data at the expense of accuracy in the inversion result for the density

shear wave velocity and density estimation from ps wave avo analysis application to an obs dataset from the north sea s wave velocity and density information is crucial for hydrocarbon detection because they help in the discrimination of pore filling fluids unfortunately these two parameters cannot be accurately resolved from conventional p wave marine data recent developments in ocean bottom seismic obs technology make it possible to acquire high quality s wave data in marine environments the use of s waves for amplitude variation with offset avo analysis can give better estimates of s wave velocity and density contrasts like p wave avo s wave avo is sensitive to various types of noise we investigate numerically and analytically the sensitivity of avo inversion to random noise and errors in angles of incidence synthetic examples show that random noise and angle errors can strongly bias the parameter estimation the use of singular value decomposition offers a simple stabilization scheme to solve for the elastic parameters the avo inversion is applied to an obs data set from the north sea special prestac

degassing explosions at karymsky volcano kamchatka during the summer of 1997 karymsky vol cano produced summit explosions about six times each hour typical explosive episodes lasted between 30 seconds and three minutes produced gas and ash columns several hun dred meters high and ejected some incandescent material to better understand the physical source mechanisms re sponsible we recorded hundreds of explosions with a three component broad band seismometer and microphone lo cated 1650 meters from the active vent nearly every explo sion is recorded as an emergent yet identical seismic wavelet which is followed 4 15 s later by an impulsive acoustic ar rival we interpret the signals as a near surface gas volume burst which fractures the vent plug lowers the lithostatic pressure within the magma column and often induces fur ther degassing when degassing continues it is generally manifested as either a series of regular one second chug ging 1 explosions steady higher frequency jetting or a hy brid combination we believe that the seismic signature for chugs short duration harmonic tremor with integer over tones is the result of repeated gas volume bursts at the vent in contrast seismograms for jetting are non harmonic and contain higher frequencies we believe that the competing degassing behaviors are influenced by the gas flux as well as the plug conduit characteristics we propose that a plug exists due to a viscosity gradient caused by volatile depletion in the upper conduit

detecting hidden volcanic explosions from mt cleveland volcano alaska with infrasound and ground coupled airwaves 1 in alaska where many active volcanoes exist without ground based instrumentation the use of techniques suitable for distant monitoring is pivotal in this study we report regional scale seismic and infrasound observations of volcanic activity at mt cleveland between december 2011 and august 2012 during this period twenty explosions were detected by infrasound sensors as far away as 1827 km from the active vent and ground coupled acoustic waves were recorded at seismic stations across the aleutian arc several events resulting from the explosive disruption of small lava domes within the summit crater were confirmed by analysis of satellite remote sensing data however many explosions eluded initial automated analyses of satellite data due to poor weather conditions infrasound and seismic monitoring provided effective means for detecting these hidden events we present results from the implementation of automatic infrasound and seismo acoustic eruption detection algorithms and review the challenges of real time volcano monitoring operations in remote regions we also model acoustic propagation in the northern pacific showing how tropospheric ducting effects allow infrasound to travel long distances across the aleutian arc the successful results of our investigation provide motivation for expanded efforts in infrasound monitoring across the aleutians and contributes to our knowledge of the number and style of vulcanian eruptions at mt cleveland

nonlinear elastic waveform inversion of land seismic reflection data data from 53 shot records collected in a conventional land seismic reflection survey are inverted to obtain subsurface maps of short wavelength variations in elastic parameters impedance the inversion method employs a robust nonlinear iterative gradient algorithm which inverts waveform data thus there is no picking of travel times or amplitudes the algorithm is also computationnally expensive as it relies heavily upon elastic finite difference modeling in addition because a gradient search is employed to minimize the misfit between observed and modeled data we attempt to solve only the weakly nonlinear problem associated with the short wavelenghts of imedance information on the short wavelengths of impedance is mainly derived from amplitude variations of the data resolving the long wavelengths of velocity background is thought to be a highly nonlinear problem at least for waveform inversion and is not attempted herein for the inversion of this data set long wavelenghts have been derived from well logs located along the seismic reflection profile although the data set is dominated by unconverted p wave arrivals we obtain maps of the short wavelenghts of both p impedance and s impedance three well logs in the survey area confirm the validity of the p impedance map however no s velocity well log are available from this area there are channel sands of economic interest which have a thickness of approximately 10 m in one well and are very thin or absent in the other two wells the 10 m occurrence of channel sands is quite visible in both impedance maps we note that because inversion in three dimensions of a realistically sized data set is simply not possible on present day computers all modeling was performed in two dimensions and a rather crude conversion from spherical to cylindrical energy spreading was applied to the original field data before inversion other seismic reflection data in the survey area suggest that there is little lateral variation in the subsurface except for the channel sands thus we feel that a two dimensional inversion with energy compensation is justified

seismo acoustic signals associated with degassing explosions recorded at shishaldin volcano alaska 2003 2004 in summer 2003 a chaparral model 2 microphone was deployed at shishaldin volcano aleutian islands alaska the pressure sensor was co located with a short period seismometer on the volcano s north flank at a distance of 6 62 km from the active summit vent the seismo acoustic data exhibit a correlation between impulsive acoustic signals 1 2 pa and long period lp 1 2 hz earthquakes since it last erupted in 1999 shishaldin has been characterized by sustained seismicity consisting of many hundreds to two thousand lp events per day the activity is accompanied by up to 200 m high discrete gas puffs exiting the small summit vent but no significant eruptive activity has been confirmed the acoustic waveforms possess similarity throughout the data set july 2003 november 2004 indicating a repetitive source mechanism the simplicity of the acoustic waveforms the impulsive onsets with relatively short 10 20 s gradually decaying codas and the waveform similarities suggest that the acoustic pulses are generated at the fluid air interface within an open vent system so2 measurements have revealed a low so2 flux suggesting a hydrothermal system with magmatic gases leaking through this hypothesis is supported by the steady state nature of shishaldin s volcanic system since 1999 time delays between the seismic lp and infrasound onsets were acquired from a representative day of seismo acoustic data a simple model was used to estimate source depths the short seismo acoustic delay times have revealed that the seismic and acoustic sources are co located at a depth of 240 200 m below the crater rim this shallow depth is confirmed by resonance of the upper portion of the open conduit which produces standing waves with f 0 3 hz in the acoustic waveform codas the infrasound data has allowed us to relate shishaldin s lp earthquakes to degassing explosions created by gas volume ruptures from a fluid air interface

eruptions of pavlof volcano alaska and their possible modulation by ocean load and tectonic stresses re evaluation of the hypothesis based on new data from 1984 1998 thirteen of sixteen magmatic eruptions of pavlof volcano in nine of the years from 1973 to 1998 have occurred between september 9 and december 29 volumes of erupted material range from 0 3 to 16 10 6 m 3 dense rock equivalent a significant correlation exists between the eruptions and yearly nontidal variations in sea level and may result from ocean loading calculated volume changes beneath the volcano due to ocean loading are from 0 02 to 0 6 times eruption volumes and it is postulated that the volcano acts as a long period several months volume strainmeter with lava being preferentially erupted when strain beneath the volcano is compressive previous observations of a tilt reversal and new observations of tectonic activity and eruptions in the spring and summer of 1986 also suggest tectonic modulation of eruptions the volcano appears to be responsive to small slow changes in ambient stresses or strains and these changes may modify or trigger eruptions

interaction of seismic and air waves recorded at stromboli volcano explosion quake seismograms recorded at stromboli show that seismic phases with a high amplitude and high frequency content propagate with a velocity of approximately 330 m s the sound speed the analysis of seismograms recorded at a distance of 500 m from one of the three active vents shows for the first onset a low frequency and particle motion characteristic of a p wave which loses its longitudinal polarization with the onset of the air wave recording the explosion quakes simultaneously with a microphone we could ascertain that the high frequency onset coincided with the air wave s in order to better understand the seismic wavefield generated by the atmospheric pressure we performed a controlled source experiment at stromboli using a seismic gun seismograms with the same two phases and particle motions comparable with the volcano seismic data were obtained a second experiment demonstrated that the air wave propagates at least in the uppermost 1 m of the ground we suggest that the seismic source of the corresponding seismograms is an explosion at the top of the magma column and conclude that the p and air waves are both generated in the same point and at the same time

waveform tomography at a groundwater contamination site vsp surface data set application of 2d frequency domain waveform tomography to a data set from a high resolution vertical seismic profiling vsp experiment at a groundwater contamination site in hill air force base hafb utah reveals a surprisingly complicated shallow substructure with a resolution of approximately 1 5 m variance in the waveform misfit function is reduced 69 4 by using an initial velocity model from first arrival traveltime tomography the waveform tomography model suggests 1 a low velocity layer at 1 to 4 m depth 2 a high vertical velocity gradient of 80 m s m on average and 3 severe lateral variations velocity contrasts as large as about 200 m s occur in a distance as short as 1 5 m the model is well correlated with lithologic logs and is interpreted geologically a q value of 20 is estimated for the target area the extreme lateral and vertical variations of the subsurface compromise many standard seismic processing methods

observation and modeling of source effects in coda wave interferometry at pavlof volcano sorting out source and path effects for seismic waves at volcanoes is critical for the proper interpretation of underlying volcanic processes source or path effects imply that seismic waves interact strongly with the volcanic subsurface either through partial resonance in a conduit garces et al 2000 sturton and neuberg 2006 or by random scattering in the heterogeneous volcanic edifice wegler and luhr 2001 as a result both source and path effects can cause seismic waves to repeatedly sample parts of the volcano leading to enhanced sensitivity to small changes in material properties at those locations the challenge for volcano seismologists is to detect and reliably interpret these subtle changes for the purpose of monitoring eruptions

the 2013 eruption of pavlof volcano alaska a spatter eruption at an ice and snow clad volcano the 2013 eruption of pavlof volcano alaska began on 13 may and ended 49 days later on 1 july the eruption was characterized by persistent lava fountaining from a vent just north of the summit intermittent strombolian explosions and ash gas and aerosol plumes that reached as high as 8 km above sea level and on several occasions extended as much as 500 km downwind of the volcano during the first several days of the eruption accumulations of spatter near the vent periodically collapsed to form small pyroclastic avalanches that eroded and melted snow and ice to form lahars on the lower north flank of the volcano continued lava fountaining led to the production of clastogenic lava flows that extended to the base of the volcano about 3 4 km beyond the vent the generation of fountain fed lava flows was a dominant process during the 2013 eruption however episodic collapse of spatter accumulations and formation of hot spatter rich granular avalanches was a more efficient process for melting snow and ice and initiating lahars the lahars and ash plumes generated during the eruption did not pose any serious hazards for the area however numerous local airline flights were cancelled or rerouted and trace amounts of ash fall occurred at all of the local communities surrounding the volcano including cold bay nelson lagoon sand point and king cove

ground coupled airwaves at pavlof volcano alaska and their potential for eruption monitoring an abnormally high number of explosion quakes were noted during the monitoring effort for the 2007 eruption of pavlof volcano on the alaska peninsula in this study we manually cataloged the explosion quakes from their characteristic ground coupled airwaves this study investigates how the ground coupled airwaves might be used in a monitoring or analysis effort by estimating energy release and gas mass release over 3 104 quakes were recorded the energy release from the explosions is approximated to be 3 1011 j and the total gas mass assuming 100 water released was 450 t the tracking of explosion quakes has the potential to estimate relative eruption intensity as a function of time and is thus a useful component of a seismic monitoring program

interpretation and utility of infrasonic records from erupting volcanoes abstract in the most basic seismo acoustic studies at volcanoes infrasound monitoring enables differentiation between sub surface seismicity and the seismicity associated with gas release under optimal conditions complicated degassing signals can be understood relative explosion size can be assessed and variable seismo acoustic energy partitioning can be interpreted the extent to which these points may be investigated depends upon the quality of the infrasonic records a function of background wind noise microphone sensitivity and microphone array geometry and the type of activity generated by the volcano frequency of explosions bandwidth of the signals and coupling efficiency of the explosion to elastic energy to illustrate the features benefits and limitations of infrasonic recordings at volcanoes we showcase acoustic and seismic records from five volcanoes characterized by explosive degassing these five volcanoes erebus in antarctica karymsky in russia and sangay tungurahua and pichincha in ecuador were the focus of seismo acoustic experiments between 1997 and 2000 each case study provides background information about the volcanic activity an overview of visual observations during the period of monitoring and examples of seismo acoustic data we discuss the benefits and utility of the infrasound study at each respective volcano finally we compare the infrasound records and eruptive activity from these volcanoes with other volcanoes that have been the focus of previous seismo acoustic experiments

determination of large scale velocity structure of the crust and upper mantle in the vicinity of pavlof volcano alaska pavlof volcano is a 2715 m high stratovolcano located at latitude 55 4 n and longitude 161 9 w near the western end of the alaska peninsula in this study the large scale lateral perturbations to a vertical reference velocity structure in the vicinity of pavlof volcano are determined using modified versions of standard three dimensional inversion techniques we use as the primary data set p wave arrival times and residuals from shallow 40 km deep regional earthquakes located by the shumagin islands seismic network relative residuals mainly from refracted e g pn arrivals allow us to constrain models for a laterally varying crustal velocity structure several strong ray path dependent patterns are seen in the residuals the most pronounced is that rays passing through the crust beneath the volcano are delayed positive residuals by up to 1 0 s while those rays traveling subparallel to and behind the volcanic axis on the retroarc bering sea side arrive as much as 0 5 s early negative residuals the corresponding results of a formal velocity inversion show the presence of a lowvelocity body beneath the volcanic arc that coincides geographically with emmons caldera 10 km sw of pavlof computed velocity values are about 12 14 lower than in the surrounding crust and are comparable to values found at other volcanic areas the exact shape and position of the low velocity body and its suitability for geothermal power development have not yet been sufficiently determined for such an assessment a much denser station distribution is required

acoustic measurements of the 1999 basaltic eruption of shishaldin volcano alaska 1 origin of strombolian activity the 1999 basaltic eruption of shishaldin volcano alaska usa displayed both classical strombolian activity and an explosive subplinian plume strombolian activity at shishaldin occurred in two major phases following the subplinian activity in this paper we use acoustic measurements to interpret the strombolian activity acoustic measurements of the two strombolian phases show a series of explosions that are modeled by the vibration of a large overpressurised cylindrical bubble at the top of the magma column results show that the bubble does not burst at its maximum radius as expected if the liquid film is stretched beyond its elasticity but bursting occurs after one cycle of vibration as a consequence of an instability of the air magma interface close to the bubble minimum radius during each strombolian period estimates of bubble length and overpressure are calculated using an alternate method based on acoustic power we estimate gas velocity to be 30 60 m s in very good agreement with synthetic waveforms although there is some variation within these parameters bubble length and overpressure for the first strombolian phase are found to be c82f11 m and 0 083 mpa for the second strombolian phase bubble length and overpressure are estimated at 24f12 m and 0 15 mpa for the first 17 h after which bubble overpressure shows a constant increase reaching a peak of 1 4 mpa just prior to the end of the second strombolian phase this peak suggests that at the time the magma in the conduit may contain a relatively large concentration of small bubbles maximum total gas volume and gas fluxes at the surface are estimated to be 3 3 10 7 and 2 9 10 3 m 3 s for the first phase and 1 0 10 8 and 2 2 10 3 m 3 s for the second phase this gives a mass flux of 1 2 10 3 and 8 7 10 2 kg s respectively for the first and the second strombolian phases

physical parameterization of strombolian eruptions via experimentally validated modeling of high speed observations pressurized gas drives explosive volcanic eruptions existing models can predict the amount and pressure of gas in erupting magma but application and testing of such models is currently limited by the accuracy of input parameters from natural systems here we present a new methodology based on a novel integration of 1 high speed imaging and 2 shock tube modeling of volcanic activity in order to derive estimates of sub second variations in the pressure mass and volume of gas that drive the dynamics of unsteady eruptions first we validate the method against laboratoryscale shock tube experiments having validated the method we then apply it to observations of eruptions at stromboli volcano italy finally we use those results for a parametric study of the weight of input parameters on final outputs we conclude that strombolian explosions with durations of seconds result from discrete releases of gas with mass and pressure in the 4 714 kg and 0 10 0 56 mpa range respectively and which occupy the volcano conduit to a depth of 4 190 m these variations are present both among and within individual explosions

waveform analysis of seismoacoustic signals radiated during the fall 1996 eruption of pavlof volcano alaska theoretical modeling of acoustic and seismic signals associated with the 1996 strombolian eruption of pavlof volcano suggests that volcanic tremor at pavlof originates in the deeper part of the magma conduit and is generated by random fluid oscillations in the magma flow explosions are believed to occur in the shallower part of the magma conduit and to be caused by the rapid and violent expansion of metastable magma gas mixtures the effect of increasing the exsolved quantities of h2o and co2 gas with reduced pressure in the melt is to decrease the sound speed and density of the magma gas mixture this causes an acoustic decoupling of the upper and lower parts of the magma conduit the reduced sound speed and density of the melt at shallow depths present a sharp impedance contrast which strongly reflects acoustic energy originating at depth and traps it in the lower part of the magma conduit alternatively acoustic energy originating from the upper part of the conduit remains trapped in the low velocity region formed by the exsolved gas in the melt and hence shallow explosions may preferentially couple into the atmosphere explosion signals may be triggered by an increased flow of melt at depth and may be preceded and accompanied by vigorous mass flux transients

acoustically induced seismic waves when an airborne acoustic wave is incident at the ground surface energy is coupled into the ground as seismic motion in a previous publication sabatier et al j acoust soc am 78 1345 1352 1986 the ground surface was modeled as an air filled poroelastic layer overlying a semi infinite nonporous elastic substrate in this work the model is extended to include calculations of the normal seismic transfer function ratio of the normal soil particle velocity at a depth d to the acoustic pressure at the surface measurements of the seismic transfer function for three sites are considered and compared to the predicted values generally good agreement between theory and experiment is achieved by best fits assuming the soil or seismic attenuation this is accomplished by specifying the ratio of the imaginary to real part of the measured seismic p and s wave speeds the seismic transfer functions quite typically exhibit minima and maxima which are associated with the seismic layering of the ground su

geological and seismological evidence of increased explosivity during the 1986 eruptions of pavlof volcano alaska we present results of study of the best documented eruptions of pavlof volcano in historic time the 1986 eruptions were mostly strombolian in character a strong initial phase may have been vulcanian the 1986 activity erupted at least 8 106 m3 of feldspar phyric basaltic andesite lava sio2 53 54 and a comparable volume of wind borne tephra during the course of the eruption 5300 explosion earthquakes occurred the largest of which was equivalent to an m l 2 5 earthquake volcanic tremor was recorded for 2600 hours and the strongest tremor was recorded out to a distance of 160 km and had an amplitude of at least 54 cm2 reduced displacement the 1986 eruptions modified the structure of the vent area for the first time in over two decades a possible pyroclastic flow was observed on 19 june 1986 the first time such a phenomenon has been observed at the volcano overall the 1986 eruptions were the strongest and longest duration eruptions in historic time and changed a temporal pattern of activity that had persisted from 1973 1984

ground coupled acoustic airwaves from mount st helens provide constraints on the may 18 1980 eruption abstract the may 18 1980 mount st helens eruption perturbed the atmosphere and generated atmosphere to ground coupled airwaves which were recorded on at least 35 seismometers operated by the pacific northwest seismograph network pnsn from 102 distinct travel time picks we identify coherent airwaves crossing washington state primarily to the north and east of the volcano the travel time curves provide evidence for both stratospheric refractions at 200 to 300 km from the volcano as well as probable thermospheric refractions at 100 to 350 km the very few first hand reports of audible volcano sounds within about 80 km of the volcano coincide with a general absence of ground coupled acoustic arrivals registered within about 100 km and are attributed to upward refraction of sound waves from the coherent refracted airwave arrivals we identify at least four distinct sources which we infer to originate 10 s 114 s 180 s and 319 s after the onset of an 8 32 11 pdt landslide the first of these sources is attributed to resultant depressurization and explosion of the cryptodome most of the subsequent arrivals also appear to be coincident with a source located at or near the presumed volcanic conduit but at least one of the later arrivals suggests an epicenter displaced about 9 km to the northwest of the vent this dislocation is compatible with the direction of the sector collapse and lateral blast we speculate that this concussion corresponds to a northern explosion event associated with hot cryptodome entering the toutle river valley

diffraction tomography and multisource holography applied to seismic imaging seismic tomography is emerging as an imaging method for determining subsurface structure when the view angle coverage is limited and the scale of the medium inhomogeneities is comparable with the wavelength as is often true in geophysical applications the performance of ordinary ray tomography becomes poor other tomographic methods are needed to improve the imaging process here we study diffraction tomography and multisource holography and evaluate their performances for surface reflection profiling srp vertical seismic profiling vsp and cross hole measurements theoretical formulations are derived for two dimensional geometry in terms of line sources along a source line and line receivers along a receiver line the theory for diffraction tomography is based on the born or rytov approximation the performances of diffraction tomography and multisource holography are evaluated by examining the information coverage in the spatial frequency domain and by numerical examples multisource holography

3d prestack plane wave full waveform inversion prestack depth migration has been used for decades to derive velocity distributions in depth numerous tools and methodologies have been developed to reach this goal exploration in geologically more complex areas exceeds the abilities of existing methods new data acquisition and data processing methods are required to answer these new challenges effectively the recently introduced wide azimuth data acquisition method offers better illumination and noise attenuation as well as an opportunity to more accurately determine velocities for imaging one of the most advanced tools for depth imaging is full waveform inversion prestack seismic full waveform inversion is very challenging because of the nonlinearity and nonuniqueness of the solution combined with multiple iterations of forward modeling and residual wavefield back propagation the method is computer intensive especially for 3d projects we studied a time domain plane wave implementation of 3d waveform inversion we found that plane wave gathers

three distinct regimes of volcanic tremor associated with the eruption of shishaldin volcano alaska 1999 tremor signals associated with the eruption of shishaldin volcano on 19 and 23 april 1999 were the strongest recorded anywhere in the aleutian arc by the alaska volcano observatory avo in its 10 year history reduced displacements dr reached 23 cm2 on 19 april and 43 cm2 on 23 april during the activity dr and spectral data with a frequency resolution of 0 1 hz were computed and put on the world wide web every 10 min these data are analyzed here the general temporal patterns of seismicity of these eruption events were similar but the eruptions and their effects quite different the 19 april event is known to have culminated in a sub plinian phase which ejected ash to an altitude of 16 km despite higher amplitudes and the largest hotspot from satellite data the 23 april event produced little ash reaching only 6 km altitude for several hours prior to the sub plinian phase on 19 april tremor with a peak frequency of 1 3 hz intensified during the sub plinian phase the peak frequency increased to 4 8 hz however in 15 h after the eruption three episodes of stronger tremor occurred with a lower 1 0 hz peak alternating with weaker tremor with a 1 3 hz peak these transitions correspond to dr 8 cm2 although these strong tremor episodes produced higher dr levels than the sub plinian phase data from a pressure sensor show that only strong strombolian explosions occurred the suite of observations suggests three distinct tremor regimes that may correspond to slug flow bubbly flow and sustained strong eruptions or a cyclic change in source parameters e g geometry sound speed or ascent rate this behavior occurred at shishaldin only during the april 1999 sequence and we are not aware of similar behavior at other volcanoes

eruptions of pavlof volcano and their possible modulation by ocean load and tectonic stresses all nine magmatic eruptions at pavlof volcano in six of the years from 1973 to 1984 have occurred between september 9 and november 20 volumes of erupted material range from 0 1 to 15 9 106 m3 dense rock equivalent at an average rate of 3 106 m3 yr 1 the volumes are estimated from eyewitness reports for two eruptions the others are estimated from a relationship that we derive between eruption volume and harmonic tremor duration and amplitude the volume of lava erupted is approximately time predictable a significant correlation exists between the eruptions and yearly nontidal variations in sea level and may result from ocean loading calculated volume changes beneath the volcano due to ocean loading are from 0 02 to 2 times eruption volumes and we postulate that the volcano acts as a long period several month volume strain meter with lava being preferentially erupted when strain beneath the volcano is compressive the volcano did not erupt during the period 1978 1980 when tilt seismic data and sea level data indicate that deep aseismic slip may have occurred models of this event predict a volume increase beneath the volcano that might have compensated strain from magma injection these observations indicate that pavlof volcano may be responsive to small slow changes in ambient stresses or strains and that these changes may modify or trigger eruptions