tomographic imaging of the p wave velocity structure beneath the kamchatka peninsula summary a total of 5270 shallow and intermediate depth earthquakes recorded by the 32 stations of the regional seismic network of the geophysical service of russia are used to assess the p wave velocity structure beneath the kamchatka peninsula in the western pacific the tomographic inversion is carried out in three steps first a 1 d tomographic problem is solved in order to obtain an initial velocity model based on the 1 d velocity model 3 d tomographic inversions with homogeneous and heterogeneous starting models are obtained the conrad 15 km depth and moho 35 km depth discontinuities determined from the 1 d tomographic inversion and the upper boundary of the subducting slab are taken into account in the heterogeneous starting model for the traveltimes and ray path determinations both velocity structure and hypocentral locations are determined simultaneously in the inversion the spacing of the grid nodes is a half degree in the horizontal direction and 20 50 km in the vertical direction a detailed p wave tomographic image is determined down to a depth of 200 km the resulting tomographic image has a prominent low velocity anomaly that shows a maximum decrease in p wave velocity of approximately 6 per cent at 30 km depth beneath a chain of active volcanoes at depth low velocity anomalies are also observed in the mantle wedge extending down to a depth of approximately 150 km these anomalies are apparently associated with the volcanic activity the sedimentary basin of the central kamchatsky graben to the west of the volcanic front and the accretionary prism at the trench correlate with shallow low velocity anomalies highvelocity anomalies observed at a depth of 10 km may be associated with the location of metamorphic basements in the ganalsky valaginskoe uplift and upper crust of shipunsky cape the results also suggest that the subducted pacific plate has p wave velocities approximately 2 7 per cent higher than those of the surrounding mantle and a thickness of approximately 70 km

dynamics of seismogenic volcanic extrusion at mount st helens in 2004 05 the 2004 05 eruption of mount st helens exhibited sustained near equilibrium behaviour characterized by relatively steady extrusion of a solid dacite plug and nearly periodic shallow earthquakes here we present a diverse data set to support our hypothesis that these earthquakes resulted from stick slip motion along the margins of the plug as it was forced incrementally upwards by ascending solidifying gas poor magma we formalize this hypothesis with a dynamical model that reveals a strong analogy between behaviour of the magma plug system and that of a variably damped oscillator modelled stick slip oscillations have properties that help constrain the balance of forces governing the earthquakes and eruption and they imply that magma pressure never deviated much from the steady equilibrium pressure we infer that the volcano was probably poised in a near eruptive equilibrium state long before the onset of the 2004 05 eruption

location and mechanism of very long period tremor during the 2008 eruption of okmok volcano from interstation arrival times 1 we describe continuous very long period vlp tremor that occurred during the 2008 eruption of okmok volcano alaska due to its low frequency content in band from the 0 2 0 4 hz the wave field of the vlp tremor is relatively free of path effects from continuous recordings of the vlp tremor on 2 three component broadband and 3 single component short period instruments we devise a method to locate the epicenter of the tremor based on interstation arrival times computed with cross correlation we find the epicenter since the vertical and radial components of the vlp tremor wave field are dominated by rayleigh waves and the time shifts are related to lateral propagation over the 4 h period studied this procedure yields a location nnw of cone d close to the new cone built over the course of the eruption similar analysis using the transverse horizontal components from the 2 three component broadband instruments yields strong constraints on the source mechanism of the vlp tremor we observe an anomalous interstation arrival time due to the existence of a nodal plane in the love wave radiation pattern the orientation of a compensated linear vector dipole clvd source estimated from the transverse components closely aligns with the regional maximum horizontal stress direction the depth of the clvd source is constrained by matching the vertical components to the rayleigh wave radiation pattern at all five stations we find the vlp tremor source depth to be 2 km bsl positioned between the magma chamber at okmok 3 km bsl and the surface

evidence for 17th century tsunamis generated on the kuril kamchatka subduction zone lake tokotan hokkaido japan abstract in the seventeenth century two tsunamis that were generated by earthquakes on the kuril kamchatka subduction zone inundated the eastern coast of hokkaido northern japan stratigraphic evidence for these two tsunamis and related land level change in coastal hokkaido consists of two landward thinning sand layers in the sediments of lake tokotan a coastal lagoon on the hokkaido coast the marine origin of these sand layers is indicated by the presence of brackish marine diatoms the rarity and high degree of fragmentation of diatom valves suggests that the sands were transported in a short time over a considerable distance tsunamis at this site were probably generated by great earthquakes along the kuril kamchatka trench volcanic ash deposits lying just above the sands suggest that tsunamis occurred in the late 17th century tsunamis during the historic period are not recorded in lake tokotan which suggests that the sand layers were deposited by tsunamis substantially larger than historic tsunamis

early and late lithification of aragonitic bivalve beds in the purbeck formation upper jurassic lower cretaceous of southern england abstract beds of euryhaline bivalves alternating with shales constitute much of the middle purbeck formation they originated on tidal flats at the western margin of an extensive brackish lagoon when these shell beds are thin and enclosed in shale they are often still preserved as aragonite and are associated with beef fibrous calcite formed during compaction in most cases however the shell debris has been converted by diagenesis into calcitic biosparrudite limestones a compacted type has been lithified at a late stage after deep burial in this pyrite is abundant and most of the shell aragonite has been replaced neomorphically by ferroan pseudopleochroic calcite a contrasting uncompacted type of biosparrudite is characterised by bivalve fragments with micrite envelopes shells and former pores are occupied by non ferroan sparry calcite cement and there is little pyrite these limestones frequently contain dinosaur footprints and originated in supratidal environments where they were cemented early mainly in meteoric water once lithified they were unaffected by compaction this uncompacted type indicates phases of mild uplift or halts in subsidence these shell bed lithologies and also intermediate types described here will probably be recognised in other lagoonal formations

feeding volcanoes of the kluchevskoy group from the results of local earthquake tomography 1 we present a seismic model of the area beneath the kluchevskoy volcano group kamchatka russia based on the tomographic inversion of more than 66000 p and s arrival times from more than 5000 local earthquakes that occurred in 2004 and that were recorded by 17 permanent stations below a depth of 25 km beneath the kluchevskoy volcano we observed a very strong anomaly in the vp vs ratio that reached as high as 2 2 this is a probable indicator of the presence of partially molten material with a composition corresponding to deeper mantle layers the upper part of this anomaly at a depth of 25 30 km coincides with a cluster of strong seismicity that can be explained by strong mechanical stresses in the lowermost crust due to magma ascension water release and or phase transitions in the crust we observed regular seismicity clusters that link the mantle anomaly with the kluchevskoy volcano and most likely indicate the paths of magma migration between depths of 8 and 13 km we see several patterns of high vp vs ratios interpreted as intermediate depth magma storages directly below the kluchevskoy volcano we observed a shallow body of high vp vs which probably represents the activated magma chamber just beneath the volcano cone which erupted in the beginning of 2005 the existence of three levels of magma storage based on results of local earthquake tomography may explain the variety of the lava composition and eruption regimes in different volcanoes of the kluchevskoy group

detailed investigation of long period activity at campi flegrei by convolutive independent component analysis abstract this work is devoted to the analysis of seismic signals continuously recorded at campi flegrei caldera italy during the entire year 2006 the radiation pattern associated with the long period energy release is investigated we adopt an innovative independent component analysis algorithm for convolutive seismic series adapted and improved to give automatic procedures for detecting seismic events often buried in the high level ambient noise the extracted waveforms characterized by an improved signal to noise ratio allows the recognition of long period precursors evidencing that the seismic activity accompanying the mini uplift crisis in 2006 which climaxed in the three days from 26 28 october had already started at the beginning of the month of october and lasted until mid of november hence a more complete seismic catalog is then provided which can be used to properly quantify the seismic energy release to better ground our results we first check the robustness of the method by comparing it with other blind source separation methods based on higher order statistics secondly we reconstruct the radiation patterns of the extracted long period events in order to link the individuated signals directly to the sources we take advantage from convolutive independent component analysis that provides basic signals along the three directions of motion so that a direct polarization analysis can be performed with no other filtering procedures we show that the extracted signals are mainly composed of p waves with radial polarization pointing to the seismic source of the main lp swarm i e a small area in the solfatara also in the case of the small events that both precede and follow the main activity from a dynamical point of view they can be described by two degrees of freedom indicating a low level of complexity associated with the vibrations from a superficial hydrothermal system our results allow us to move towards a full description of the complexity of the source which can be used by means of the small intensity precursors for hazard model development and forecast model testing showing an illustrative example of the applicability of the cica method to regions with low seismicity in high ambient noise

geochemical evidence for the melting of subducting oceanic lithosphere at plate edges most island arc magmatism appears to result from the lowering of the melting point of peridotite within the wedge of mantle above subducting slabs owing to the introduction of fluids from the dehydration of subducting oceanic crust1 volcanic rocks interpreted to contain a component of melt not just a fluid from the subducting slab itself are uncommon but possible examples have been recognized in the aleutian islands baja california patagonia and elsewhere2 3 4 the geochemically distinctive rocks from these areas termed adakites are often associated with subducting plates that are young and warm and therefore thought to be more prone to melting5 but the subducting lithosphere in some adakite locations such as the aleutian islands appears to be too old and hence too cold to melt6 7 this implies either that our interpretation of adakite geochemistry is incorrect or that our understanding of the tectonic context of adakites is incomplete here we present geochemical data from the kamchatka peninsula and the aleutian islands that reaffirms the slab melt interpretation of adakites2 but in the tectonic context of the exposure to mantle flow around the edge of a torn subducting plate we conclude that adakites are likely to form whenever the edge of a subducting plate is warmed or ablated by mantle flow the use of adakites as tracers for such plate geometry may improve our understanding of magma genesis and thermal structure in a variety of subduction zone environments

automatic detection of long period events at campi flegrei caldera italy 1 we propose a novel approach to analyze continuous seismic signal and separate the sources from background noise a specific application to the seismicity recorded at campi flegrei caldera during the 2006 ground uplift is presented the fundamental objective is to improve the standard procedures of picking the emergent onset arrivals of the seismic signals often buried in the high level ambient noise in order to obtain an appropriate catalogue for monitoring the activity of this densely populated volcanic area this is particularly useful in order to estimate the release of the seismic energy and to put constraints on the source dynamics an independent component analysis based approach for the blind source separation of convolutive mixtures is adopted to obtain a clear separation of long period events from the ambient noise the approach presents good performance and it is suitable for real time implementation in seismic monitoring its application to the continuous seismic signal recorded at campi flegrei has allowed the extraction of high quality waveforms considerably improving the detection of low energy events

rapid changes in magma storage beneath the klyuchevskoy group of volcanoes inferred from time dependent seismic tomography abstract we present the results of time dependent local earthquake tomography for the kluchevskoy group of volcanoes in kamchatka russia we consider the time period from 1999 to 2009 which covers several stages of activity of kluchevskoy and bezymianny volcanoes the results are supported by synthetic tests that recover a common 3d model based on data corresponding to different time windows throughout the period we observe a robust feature below 25 km depth with anomalously high v p v s values up to 2 2 we interpret this feature as a channel bringing deep mantle materials with high fluid and melt content to the bottom of the crust this mantle channel directly or indirectly determines the activity of all volcanoes of the kluchevskoy group in the crust we model complex structure that varies over time during the pre eruptive period we detected two levels of potential magma storage one in the middle crust at 10 12 km depth and one close to the surface just below kluchevskoy volcano in 2005 a year of powerful eruptions of kluchevskoy and besymiyanny volcanoes we observe a general increase in v p v s throughout the crust in the relaxation period following the eruption the v p v s values are generally low and no strong anomalous zones in the crust are observed we propose that very rapid variations in v p v s are most likely due to abrupt changes in the stress and deformation states which cause fracturing and the active transport of fluids these fluids drive more fracturing in a positive feedback system that ultimately leads to eruption we envision the magma reservoirs beneath the kluchevskoy group as sponge structured volumes that may quickly change the content of the molten phases as fluids pulse rapidly through the system

locating sources of volcanic tremor and emergent events by seismic triangulation application to arenal volcano costa rica 1 we address the issue of locating the sources of volcanic tremor and emergent events with a method requiring a limited amount of equipment a network of several triangular seismic antennas made of vertical sensors is used the slowness vectors are estimated at each array on a sliding window by inverting the time delays between the sensors calculated with the cross spectral method a probabilistic approach is adopted whereby each measure and its error are represented by a probability density function pdf a weighted summation of the pdfs is carried out in which the stable directions of propagation are enhanced the effects of the structural heterogeneities are taken into account by introducing an additional error associated to a robust hyperbolic secant sech type pdf the resulting pdfs of the back azimuth are combined to calculate a pdf of the source location the maximum likelihood of this pdf is taken as an estimate of the source position and its spread is characterized by a covariance analysis data from an experiment carried out at arenal volcano costa rica with four arrays are analyzed the precision and robustness of the method are tested by exploring the influence of the array configuration and other parameters the mean standard deviation on the position of the sources is 600 m for the tremor and 400 m for the explosions and long period lp events several tremors explosions and lp events are analyzed and their sources located the seismogenic zone is located in a 600 m radius area centered on the active crater

real time seismic amplitude measurement rsam a volcano monitoring and prediction tool seismicity is one of the most commonly monitored phenomena used to determine the state of a volcano and for the prediction of volcanic eruptions although several real time earthquake detection and data acquisition systems exist few continuously measure seismic amplitude in circumstances where individual events are difficult to recognize or where volcanic tremor is prevalent analog seismic records provide a quick visual overview of activity however continuous rapid quantitative analysis to define the intensity of seismic activity for the purpose of predicing volcanic eruptions is not always possible because of clipping that results from the limited dynamic range of analog recorders at the cascades volcano observatory an inexpensive 8 bit analog to digital system controlled by a laptop computer is used to provide 1 min average amplitude information from eight telemetered seismic stations the absolute voltage level for each station is digitized averaged and appended in near real time to a data file on a multiuser computer system raw realtime seismic amplitude measurement rsam data or transformed rsam data are then plotted on a common time base with other available volcano monitoring information such as tilt changes in earthquake activity associated with dome building episodes weather and instrumental difficulties are recognized as distinct patterns in the rsam data set rsam data for domebuilding episodes gradually develop into exponential increases that terminate just before the time of magma extrusion mount st helens crater earthquakes show up as isolated spikes on amplitude plots for crater seismic stations but seldom for more distant stations weather related noise shows up as low level long term disturbances on all seismic stations regardless of distance from the volcano implemented in mid 1985 the rsam system has proved valuable in providing up to date information on seismic activity for three mount st helens eruptive episodes from 1985 to 1986 may 1985 may 1986 and october 1986 tiltmeter data the only other telemetered geophysical information that was available for the three dome building episodes is compared to rsam data to show that the increase in rsam data was related to the transport of magma to the surface thus if tiltmeter data is not available rsam data can be used to predict future magmatic eruptions at mount st helens we also recognize the limitations of rsam data two examples of rsam data associated with phreatic or shallow phreatomagmatic explosions were not preceded by the same increases in rsam data or changes in tilt associated with the three dome building eruptions

slab portal beneath the western aleutians tomographic images of the distribution of shear wave speed beneath the northwestern pacific delineate the configuration of the subducted oceanic lithosphere beneath the western aleutian arc at 100 km depth a fast shear wave speed anomaly is beneath the aleutian arc everywhere east of 1738e between 1648e and 1738e however seismic velocities at this depth are slow relative to the surrounding mantle the lateral termination of the fast shear wave speed anomaly at depth coincides with a gap in deep seismicity beneath the aleutians the absence of these two distinctive traits of subducting slabs leads us to conclude that this segment of the aleutian arc overlies a very large window in the otherwise continuous lithospheric slab that we term a slab portal this portal is likely to facilitate the production of distinctive volcanic rocks adakites or high mg andesites by partially melting the adjacent edges of the slab the miocene age of most adakites in the westernmost aleutians where no slab is present may indicate that the portal formed relatively recently the chemistry of western aleutian adakites approximates that of typical continental crust so their genesis and subsequent lateral transport toward kamchatka is a plausible mechanism for new continent formation

complex polarization analysis of particle motion knowledge of particle motion polarization aids in identifying phases on three component seismograms the scheme of montalbetti and kanasewich 1970 is extended to analytic three component seismograms where the imaginary part of the signal is the hilbert transform of the real part this scheme has only one free parameter the length of the time window over which the polarization parameters are estimated so it can be applied in a routine way to three component data the azimuth and dip of the direction of maximum polarization and the degree of elliptical polarization as a function of time for the seismograms are obtained polarization analysis of strong motion data from the 1971 san fernando earthquake aids in the discrimination between wave types which is important for the understanding of the complicated earthquake induced shaking observed in basins most arrivals are incident on the receivers in the direction of the back azimuth to the epicenter which suggests that despite the complicated motions two dimensional finite difference methods are sufficient to understand the effect on seismic waves of the los angeles and san fernando basins vidale and helmberger 1986b

anomalous seismic structure beneath the klyuchevskoy group kamchatka 1 the klyuchevskoy group is among the most active volcanic features on earth yet its position within the kamchatka subduction zone is hard to explain with a simple tectonic mechanism the geochemistry of klyuchevskoy group lavas is typical for volcanic products resulting from flux melting in the mantle wedge yet the depth to the subducting pacific plate beneath it is much larger than the average depth of volatile release in subduction zones we present new seismological constraints on the upper mantle structure beneath the klyuchevskoy group and identify a planar dipping seismic feature in the mantle wedge which is 100 km deep and appears to be sharply bounded we hypothesize that this upper mantle structure may be the true source of melts erupting at the klyuchevskoy group and that the presence of this feature may explain both the extraordinary productivity of the klyuchevskoy group and its unusual location

array tracking of the volcanic tremor source at deception island antarctica we have found experimental evidence which shows that the volcanic tremor recorded at deception island south shetland islands antarctica is a superposition in time of overlapping hybrid events we studied data from a small aperture seismic array data analysis for tremor and hybrids included 1 spectral analysis 2 apparent slowness and back azimuth determination by using the zero lag cross correlation method and 3 polarization analysis both types of events share these common features a two dominant spectral bands at frequencies 1 3 hz the most energetic and 4 8 hz b several coherent phases with the same back azimuth to the source and apparent slowness along the whole signal c in the high frequency band the apparent slowness is very low around 0 17 s km indicating the propagation of body waves d in the low frequency band the apparent slowness is high around 1 6 s km consistent with the presence of surface waves and e clear p wave onset followed by a complex pattern of rayleigh waves therefore both types of events are strongly related because they share the same source region the same wave propagation properties and the same wave composition moreover several arrivals that resemble a single hybrid event have been found along the tremor signals due to these reasons we hypothesize that volcanic tremor of deception island is a superposition of hybrid type events the source of both types could be the interaction between thaw water and hot materials in a shallow aquifer

array measurements and modeling of sources of shallow volcanic tremor at kilauea volcano hawaii we show that resonances in near surface layers path effects or a combination of near surface resonances and source resonances source effects could be responsible for the sharp spectral peaks found in the records of gas piston activity and volcanic tremor recorded near puu oo crater on kilauea volcano hawaii two types of sources are found to be compatible with observations and can not be distinguished using our data in one model impulsive explosion point sources are embedded in the puu oo structure in the other model impulsive point sources of pressure excite the resonances of a fluid filled crack embedded in that structure both models require shallow sources z 100 m and display a strong dependence of the radiated spectrum on source depth over a depth range comparable to the overall thickness of the surficial layers based on these results it may be possible to track changes in source depth through temporal changes in observed spectra a potentially useful tool for monitoring volcanic activity at this site we estimate the depth and spatial extent of volcanic tremor and gas piston activity using two dense arrays with respective apertures of 800 and 120 m located near puu oo measurements of slowness ray parameter and azimuth as a function of time clearly indicate that the sources of volcanic tremor and gas piston activity are located beneath or in close proximity to the puu oo crater at depths shallower than approximately 1 km based on slowness and particle motion analyses we find that the records of volcanic tremor and gas piston events at puu oo consist of a complex combination of body and surface waves

the origin of volcano tectonic earthquake swarms volcano tectonic vt seismicity is commonly recorded prior to and during eruptions vt seismicity may reflect stresses induced by dike propagation as indicated by propagating hypocenters and fault plane solutions fps reflecting regional stresses or stresses induced by dike inflation indicated by randomly distributed hypocenters and fps with pressure axes rotated 90 to regional maximum compression although numerical models of dike induced stresses indicate that both regimes should occur during dike emplacement this has not yet been observed according to published seismic data instead 90 rotated fps are observed in some cases while propagating hypocenters mark dike formation in other cases we suggest that differences in the seismic expression of upper crustal magma migration may result from differences in the regional tectonic setting and in the nature of magma wall rock interactions ultimately it may be possible to use information contained in vt seismicity to forecast changes in a volcano s behavior by establishing the characteristic stress field response for a given volcano or through a deeper understanding of the complex relationships between vt seismicity local crustal stresses and the physical mechanisms of magma migration