tremor rich shallow dyke formation followed by silent magma flow at barðarbunga in iceland magma movement is thought to trigger volcanic tremor however analysis of seismic data suggests that tremor prior to the bar arbunga eruption in iceland instead marked the crust cracking open whereas subsequent magma flow was seismically silent

variability of sulphur isotope ratios in pyrite and dissolved sulphate in granitoid fractures down to 1km depth evidence for widespread activity of sulphur reducing bacteria euhedral pyrite crystals in 46 open bedrock granitoid fractures at depths down to nearly 1 km were analysed for sulphur isotope ratios 34s by the in situ secondary ion mass spectrometry sims technique and by conventional bulk grain analysis and were compared with groundwater data twenty nine of the fractures sampled for pyrite had corresponding data for groundwater including chemistry and isotopic ratios of sulphate which provided a unique opportunity to compare the sulphur isotopic ratios of pyrite and dissolved sulphate both at site and fracture specific scales assessment of pyrite age and formation conditions were based on the geological evolution of the area laxemar se sweden and on data on co genetic calcite as follows 1 the isotopic ratios of the calcite crystals 18o 13c 87sr 86sr were compared with previously defined isotopic features of fracture mineral assemblages precipitated during various geological periods and 2 the 18o of the calcites were compared with the 18o of groundwater in fractures corresponding to those where the calcite pyrite assemblages were sampled taken together the data show that all the sampled fractures carried pyrite calcite that are low temperature and precipitated from the current groundwater or similar pre existing groundwater except at depths of 300 to 600 m where water with a glacial component dominates and the crystals are from pre modern fluids an age of 10 ma are anticipated for the pre modern fluids the 34spyr showed huge variations across individual crystals such as 32 to 73 and extreme minimum 50 and maximum 91 values for this kind of extreme s isotopic variation at earth surface conditions there is no other explanation than activity of sulphur reducing bacteria coupled with sulphate limited conditions indeed the most common subgrain feature was an increase in 34spyr values from interior to rim of the crystal which we interpret are related to successively higher 34s values of the dissolved source so42 caused by ongoing bacterial sulphate reduction in fractures with low flow or stagnant waters the measured groundwater had 34sso4 values of 9 to 37 with the highest values associated with low sulphate concentrations these values are overall and especially in the sulphate poor waters down to 400 m somewhat higher than the anticipated initial values and can thus like for the 34s enriched pyrites be explained by a rayleigh distillation process driven by microbial sulphate reduction an intriguing feature was that the 34sso4 values of the groundwater were in no case reaching up to the values required to produce biogenic pyrite with 34s values of 40 to 91 to explain this feature we suggest that groundwater in low flow fractures with near stagnant water carrying sulphate and pyrite with high 34s is masked by high flow parts of the fracture system carrying groundwater that often contains sulphate in abundance and considerably less fractionated with respect to 34s and 32s in order to gain detailed knowledge of chemical processes and patterns in groundwater in fractured rock fracture mineral investigations are a powerful tool as we have shown here for the sulphur system

on the correlation of seismic microtremors 1 we present results of the analysis of microtremor measurements using a small array our analysis is based on the computation of cross correlation functions between stations in both frequency and time domains we obtain similar results in both domains and link those results to the application of aki s spatial autocorrelation method of using a single station pair and to recent studies that have shown that the green s function between two stations can be retrieved from the temporal cross correlation of seismic noise we show that the same simple subsoil structure allows interpretation of our correlation results in time and frequency we observe both love and rayleigh waves however love waves dominate the records in our lower frequency range between 3 6 and 6 hz while rayleigh waves are prevalent in the records in our higher frequency band from 6 to 20 hz frequency domain cross correlation yields better results in the lower frequency range while time domain cross correlation shows very clear results in the higher frequency band thus both analyses are complementary our results show that ambient vibration recorded at the free surface includes different types of waves but that the correlation between any two stations is governed by the more stable propagation mode between them surface waves in the case of a layered medium our results shed some light on the nature of microtremors and on the reasons why the spatial autocorrelation method or the horizontal to vertical spectral ratios are useful in geophysical and site response studies

spatial extent of a hydrothermal system at kilauea volcano hawaii determined from array analyses of shallow long period seismicity 2 results we present a probabilistic method to locate the source of seismic events using seismic antennas the method is based on a comparison of the event azimuths and slownesses derived from frequency slowness analyses of array data with a slowness vector model several slowness vector models are considered including both homogeneous and horizontally layered half spaces and also a more complex medium representing the actual topography and three dimensional velocity structure of the region under study in this latter model the slowness vector is obtained from frequency slowness analyses of synthetic signals these signals are generated using the finite difference method and include the effects of topography and velocity structure to reproduce as closely as possible the behavior of the observed wave fields a comparison of these results with those obtained with a homogeneous half space demonstrates the importance of structural and topographic effects which if ignored lead to a bias in the source location we use synthetic seismograms to test the accuracy and stability of the method and to investigate the effect of our choice of probability distributions we conclude that this location method can provide the source position of shallow events within a complex volcanic structure such as kilauea volcano with an error of 200 m

synopsis of strontium isotope variations in groundwater at aspo southern sweden strontium isotope ratios are used to identify end member ground water compositions at aspo in southeastern sweden where the hard rock laboratory hrl has been constructed to evaluate the suitability of crystalline rock for the geologic disposal of nuclear waste the hard rock laboratory is a decline tunnel constructed in 1 8 ga old granitic rock that forms islands in an archipelago along the swedish coast ground water samples were obtained for isotopic analyses from boreholes drilled from the surface and from side boreholes drilled within the hrl infiltration at aspo occurs primarily through fractures zones in the granitic bedrock beneath thin soils throughout the area because of extremely low sr concentrations rain and snow are not important contributors to the sr isotope budget of the ground water system at shallow levels water percolating downward along fractures and fracture zones acquires a 87sr between 9 5 and 10 0 and maintains this value downward while sr concentrations increase by two orders of magnitude ground water samples from both boreholes and from in the hrl show the effects of mixing with saline waters containing as much as 59 mg l sr and 87sr values as large as 13 9 baltic sea water is a potential component of the groundwater system with 87sr values only slightly larger than modern marine values 0 3 but with much lower concentrations 1 5 mg l than ocean water 8 mg l however because of large sr concentration differences between the saline groundwater 59 mg l and baltic sea water 1 5 mg l 87sr values are not particularly sensitive indicators of sea water intrusion even though their 87sr values differ substantially

velocity models and site effects at kawah ijen volcano and ijen caldera indonesia determined from ambient noise cross correlations and directional energy density spectral ratios abstract two different ambient seismic noise techniques allow the determination of velocity models at ijen caldera and kawah ijen volcano at ijen caldera two average velocity models are constrained down to a depth of 3 km by inverting the stacked dispersion curve obtained by ambient noise cross correlation in addition four local velocity models were obtained by inverting the horizontal to vertical spectral ratio of the directional energy densities of ambient noise dedhvr i e computed through auto correlation of ambient noise this set of velocity models is then compared to the geology of the caldera and the local discontinuities are evidenced at kawah ijen volcano a map of local dominant frequencies is provided by the dedhvr measurements recorded at 87 sites around kawah ijen volcano the horizontality of the shallow layers and the great outcrop of the crater rim facilitate the interpretation of the dedhvrs furthermore the inversion of several juxtaposed dedhvrs provided a complete 2 d velocity model of the flank of the crater unlike other stratovolcanoes the kawah ijen appears to have a remarkably homogeneous structure the dedhvr technique is used for the first time in a volcanic environment and shows a great potential for an accurate and fast computation of the velocity model on volcanoes

alkaline earth metal and rare earth element incorporation control by ionic radius and growth rate on a stalagmite from the chauvet cave southeastern france abstract a multi element study involving major alkaline earth cations mg ca sr ba and trace elements like na u mn y and rare earth elements ree in calcite of a stalagmite from the chauvet cave se of france was carried out using icp qms analysis this study focused on the chau stm6 stalagmite which displays a record of the last deglaciation until the end of the younger dryas with ages ranging from 33 kyr to 11 5 kyr bp in this study profiles of the alkaline earth elements sr and ba show concentrations increasing sharply at the beginning of the deglaciation while mg and u show a decreasing trend rey ree y concentrations decrease sharply during early deglaciation the clear record of the onset of the younger dryas by stable isotopes is not well marked by these elements the absence of a significant correlation between rey and mn suggests that ree were here not strongly bound to particulate colloidal phases but were mainly controlled by limestone groundwater interaction shale normalized ree patterns in stalagmite characterized by a negative ce anomaly and hree enrichment compared to lree is thought to mainly arise from the dissolution of bedrock since chau stm6 patterns are similar to those of the bedrock chau stm6 rey patterns are even more depleted in lree than those of the bedrock showing that part of the lree were removed from groundwater upstream from the stalagmite some particular rey pattern changes were observed for the different climatic conditions 1 glacial samples often display a more marked negative ce anomaly 0 3 and a high y ho ratio 0 6 2 bolling allerod and younger dryas samples display a variable and less pronounced anomaly 0 5 0 8 and a lower y ho ratio 0 35 0 55 climatic changes modified the rate of the stalagmite growth which likely caused a change in the properties of element incorporation in the calcite lattice consequently the concentration variations of mg ca sr ba u and rey would be directly controlled by ionic radii of each element

a generic formulation for microtremor exploration methods using three component records from a circular array summary we present a generic formulation for analysis methods that estimate phase velocities of rayleigh and love waves by way of intermediary quantities called spectral ratios using three component records of microtremors from a circular array of sensors at each time instant the set of records are expanded in a fourier series with respect to azimuth so that we obtain a set of fourier coefficients that are represented in the form of complex time histories we then estimate power and cross spectral densities of those fourier coefficients the spectral densities thus obtained generally contain information on the phase velocities powers and arrival directions of individual modes of rayleigh and love waves by taking the quotient of two different sorts of such spectral densities we can cancel out information on their powers and arrival directions and extract information on their phase velocities alone the spectral ratios have to be estimated in practice on the basis of records from a finite number of seismic sensors that are either evenly or unevenly spaced around a circumference we describe a general procedure for their estimation and discuss the effects of directional aliasing that the finite number of sensors and their configuration have on the estimates of spectral ratios we also discuss biases in the estimates of spectral ratios caused by the presence of incoherent noise by using our method it is also possible to estimate the central arrival direction of the microtremors the ellipticity of the rayleigh waves and whether the rayleigh waves are prograde or retrograde

long period seismicity in the shallow volcanic edifice formed from slow rupture earthquakes volcanic eruptions are often preceded by long period seismic events that were thought to be generated by the resonance of cracks filled with magmatic fluid analysis and modelling of long period seismicity at volcanoes in italy costa rica and peru shows that it could instead be caused by slow rupture along faults in the upper volcanic edifice

near surface velocity structure of pacaya volcano guatemala derived from small aperture array analysis of seismic tremor knowledge of the typically complicated near surface structure on volcanoes is critical for determining accurate seismic event locations and seismic source mechanisms associated with precursory and eruptive activity to generate a near surface velocity model for the active cone of pacaya volcano guatemala we recorded seismic tremor and ambient noise with a small aperture array of 11 short period seismometers in january 2011 the diffuse wavefield was investigated using the spatial autocorrelation spac method and we computed rayleigh and love dispersion curves at the array location the phase velocities for rayleigh waves range from 1000 m s at 2 hz to 230 m s at 10 hz those for love waves range from 600 to 250 m s over the same frequency band such low velocities are consistent with the presence of unconsolidated tephra on the surface of the volcano interspersed with lava flows assuming they represent the fundamental modes of rayleigh and love waves we inverted the dispersion curves to produce a shear wave velocity model of the upper 500 m beneath the array online material s wave velocity models obtained from inversion and love and rayleigh wave dispersion curves

volcano topography structure and intrinsic attenuation their relative influences on a simulated 3d visco elastic wavefield the seismic wavefield recorded on volcanoes can be significantly influenced by path effects scattering from the topography and internal volcanic structure can play a dominant role in the recorded seismograms intrinsic attenuation is also thought to play an important role in the characteristics of volcano seismic signals we use 3d numerical modelling of wave propagation in elastic and visco elastic media including complex velocity models and topography to investigate the scattering and attenuation characteristics of synthetic seismograms we generate 5 distinct volcano models and simulate wave propagation through these models using shallow and deep double couple broadband sources we then analyse 129 synthetic seismograms calculated on the free surface the synthetic seismograms resemble vt a and vt b events the scattering effect of the topography alone is capable of producing complex seismograms the introduction of an internal velocity structure increases the duration of these seismograms while the introduction of intrinsic attenuation decreases the duration but not the complexity we fitted our synthetic seismograms to the diffusion in a half space model to quantify the scattering and attenuation coefficients the scattering quality factor measured on all 129 stations for all 5 volcano models was similar therefore we deduce that the topography appears to be the dominant scatterer the intrinsic attenuation quality factor for each of the specific models cannot be accurately recovered using the diffusion in a half space model the measured quality factor is not only sensitive to the attenuation properties but also to the structural properties in all cases the scattering is more dominant than the intrinsic attenuation

seismic cycles recorded in late quaternary calcite veins geochronological geochemical and microstructural evidence southwest turkey is seismically active as a result of the hellenic subduction process in the eastern mediterranean we conducted high resolution micro sampling high precision u series dating and microchemical analysis on an extensional vein system in a tectonically active but non hydrothermal area u th age data and microscopic observations provide evidence of repeated fracturing of a previously sealed crack system followed by a new increment of veining repeated injection of veinlets suggests that the vein system was formed by the crack seal mechanism four major u th age groups for the emplacement of the vein system fall between 23 9 0 2 ka and 23 2 0 4 ka 21 7 0 4 ka and 19 2 0 2 ka 17 3 0 1 ka and 16 2 0 3 ka and at 11 8 0 2 ka stable and sr isotope geochemistry of the calcite vein samples indicates that surface water interacting with the soil cover was the major component of the groundwater system from which the extensional veins precipitated trace element and 0 isotope data of the vein system are interpreted to reflect carbonate precipitation associated with seismic cycles involving fluids with different trace element compositions and co2 contents initial carbonate precipitation during a single seismic cycle occurred from co2 dominated fluids that were degassed from the original co2 water mixture this was followed consecutively by carbonate precipitation from the remaining water which was relatively impure with higher trace element contents millimetre to submillimetre scale u series dating in conjunction with geochemistry of carbonate veins related to active tectonism offers an innovative means of constraining the absolute timing of late quaternary seismic and inter seismic events c 2010 elsevier b v all rights reserved

shallow structure of mt vesuvius volcano italy from seismic array analysis data from a portable dense seismic array deployed on mt vesuvius in may 1994 during a 2d seismic tomography experiment are analyzed in the present paper the array consisted of two groups of short period geophones 4 5 hz natural frequency formed by 16 and 25 vertical components plus two horizontal components distributed along an arc like shape along the summit crater stacks of later arrivals interpreted as reflected phases provide a significant constraint to a boundary layer located in the depth range 1 5 2 2 km beneath the summit crater with average velocity v 1 8 2 2 km s interpreted as the top of the limestone basement the correlation methods applied on microtremor records allowed to infer the shallow velocity structure up to 400 m beneath the crater rim

precise determination of the relative wave propagation parameters of similar events using a small aperture seismic array 1 we propose a method to determine accurately the relative wave propagation parameters apparent slowness and propagation azimuth of a cluster of seismic events with similar waveforms recorded on a seismic array this relative slowness estimate relse method is based on precise measurements of the delays among arrivals of different earthquakes to each of the array receivers delays are determined using interpolations of the cross correlation functions of the earthquake waveforms accurate relative slowness vectors are estimated using a least squares fit of the observed delays to the delays corresponding to the arrivals of plane wave fronts we tested the method using both synthetics and real data in order to understand its resolution capabilities in presence of seismic noise and to assess the uncertainty regions associated with the slowness vector estimates from these analyses we establish a procedure to determine the 90 uncertainty regions associated with the estimates of relative slowness vectors as an example of application of the relse method we analyzed a multiplet composed of 16 similar earthquakes recorded during the 1999 seismic crisis at deception island volcano antarctica using a conventional slowness estimate method produces virtually the same result for every earthquake because of the large uncertainties alternatively using the relse method reduces the uncertainties of the estimates and allows to resolve the detailed distribution of relative apparent slowness vectors our results show that the slowness vectors are aligned within a narrow north south trending band which represents a clue toward the features of the source region and or source distribution we repeated the procedure using different earthquakes as master events the estimated distribution of slowness vectors is similar in every case which demonstrates that our results are independent of the choice of reference event index terms 7299 seismology general or miscellaneous 7203 seismology body wave propagation 7215 seismology earthquake parameters 7230 seismology seismicity and seismotectonics 7280 seismology volcano seismology 8419 keywords seismic arrays slowness vectors multiplet analysis deception island volcano

array analysis using circular wave front geometry an application to locate the nearby seismo volcanic source summary the zero lag cross correlation technique used for array analysis in the hypothesis of plane waves has been modified to allow the wave front to be circular synthetic tests have been performed to check the capability of the method which returns the input test data when the source array distances are not greater than two or three times the array aperture for this distance range the method furnishes an estimate of the apparent velocity and the epicentral coordinates of the source for more distant sources the method becomes equivalent to that based on the planar wave approximation which gives an estimate of the backazimuth to the source and the apparent velocity the method has been applied to seismic data recorded at the active volcano located at deception island antarctica 35 volcanic long period events occurring in a small swarm were selected results show that the epicentres are close to the array between 0 4 and 2 km and aligned in a sw direction in agreement with one of the main directions of the fracture system of deception volcano

characteristics of seismic waves composing hawaiian volcanic tremor and gas piston events observed by a near source array a correlation method specifically designed for describing the characteristics of a complex wave field is applied to volcanic tremor and gas piston events recorded by a semicircular array of geos instruments set at the foot of the puu oo crater on the east rift of kilauea volcano hawaii the spatial patterns of correlation coefficients obtained as functions of frequency for the three components of motion over the entire array are similar for gas piston events and tremor and clearly depict dispersive waves propagating across the array from the direction of puu oo the wave fields are composed of comparable amounts of rayleigh and love waves propagating with similar and extremely slow phase velocities ranging from 700 m s at 2 hz to 300 m s at 8 hz the highly cracked solidified lava flow on which the array was deployed and subjacent structure of alternating lava and ash layers formed during repeated eruptions of puu oo since 1983 appear to be responsible for the low velocities observed the results from puu oo stand in sharp contrast to those obtained in an experiment conducted in 1976 on the partially solidified lava lake of kilauea iki rayleigh waves were not observed in kilauea iki but well developed trains of love waves were seen to propagate there with velocities twice as high as those observed near puu oo these differences in the propagation characteristics of surface waves at the two sites may be attributed to the presence of a soft horizontal layer of molten rock in kilauea iki which may have lowered the phase velocity of rayleigh waves more drastically than that of love waves resulting in severe scattering of the rayleigh wave mode on the other hand the thin superficial pahoehoe flow under our array at puu oo may have favored the development of vertical columnar joints more extensively at this location than at kilauea iki which may have reduced the shear moduli controlling the love wave mode the average phase velocities in the frequency band from 2 to 5 hz found at puu oo are roughly similar to those determined for tremor at klyuchevskoy volcano kamchatka but the frequency dependence appears much stronger at puu oo

the role of carbonate complexes and crystal habit on rare earth element uptake in low temperature calcite in fractured crystalline rock abstract this study focuses on rare earth element ree geochemistry of low temperature calcite coatings occurring on the walls of fractures throughout the upper kilometer of crystalline rocks of the baltic shield fifty one calcite coatings were sampled from cores drilled with the triple tube technique which successfully preserved the fragile calcite coatings on the fracture walls the calcites which based on geological and isotopic evidence were precipitated over the last 10 million years had highly variable ree concentrations 0 61 2276 ppm that decreased weakly with the depth the calcite was sampled from when normalized to shale and host rock the ree concentrations of habits with c axis a axes and the closely associated c axis a axes the most abundant crystal morphologies in the system decreased strongly and smoothly across the series in contrast the rees of habits with c axis a axes identified only in fractures in the uppermost 260 m of the bedrock were flatter and occasionally expressed a weak middle ree enrichment by using calcite water partition coefficients derived for rees in previous laboratory experiments the la yb of the paleogroundwater from which the calcites precipitated was back calculated and found to be overall similar range 0 15 452 overlap to the corresponding ratio of the present groundwater range 2 1 36 4 in terms of ree ca the values for the back calculated paleogroundwater la ca 9 9 10 11 3 9 10 7 yb ca 1 5 10 10 2 2 10 7 were similar to those of laco3 ca 4 5 10 10 8 5 10 7 and ybco3 yb co3 2 ca 5 4 10 11 1 8 10 8 respectively in the present groundwater these patterns indicate that the lree to hree and ree to ca ratios in the groundwater at the site are broadly similar to those existing when the calcites precipitated and that carbonate complexes present in the paleogroundwater played a crucial role in sequestration and fractionation of rees in calcite the findings have implications for bedrock storage of high level radioactive waste which contains actinides for which the rees can be used as natural analogues

attenuation of short period seismic waves at mt vesuvius italy we analysed short period seismograms from about 250 very local events recorded by a network of high dynamic range short period seismic stations deployed on mt vesuvius to estimate the site corrected short period seismic attenuation we calculated qc 1 the inverse of the quality factor for coda waves for short lapse times 12 s and qp 1 and qs 1 the inverse of the direct body wave quality factors for p and s waves follow ing shallow ray paths we used the single scattering assumption to fit the amplitude envelopes of the coda at different frequency bands obtaining a qc 1 slowly varying with frequency similar to values measured for other volcanoes at the same lapse time site corrected qp 1 and qs 1 were estimated using the frequency decay method for both p and s waves in two frequency bands 1 6 hz and 15 24 hz results show that qp 1 is 0 028 in both frequency bands and qs 1 is 0 015 and 0 017 at low and high frequencies respectively almost independent of the frequency and that the value of qp 1 is about twice that of qs 1 as measured worldwide a check was made by measuring the broadening of the first p wave pulse with station source distance finding qp 1 0 024 using the independent estimates of qc 1 and qs 1 we separated the intrinsic from the scattering quality factor at mt vesuvius obtaining a high scattering and a low intrinsi c q 1 as already observed for other volcanoes this result confirms the hypothesis of the predominant role of the scattering phenomena with respect to the intrinsic dissipation in the seismogram formation for volcanic earthquakes

subsoil structure using spac measurements along a line the spac spatial autocorrelation method was proposed almost 50 years ago by aki 1957 this method allows a phase velocity dispersion curve to be obtained from microtremor measurements using an array of stations arranged in a circle the subsoil structure is subsequently derived from the inversion of that dispersion curve in this article we show that it is possible to get similar results using microtremors recorded along a line we use microtremor records obtained by using four broadband seismographs disposed along a line with different interstation spacings 5 10 20 and 40 m our data are precessed by using the standard spac procedure with the exception of the azimuthal average the final subsoil structure as determined from the inversion of the phase velocity dispersion curve shows excellent agreement with previous results at the site of our measurements our results suggest that the use of the spac method is not restricted to a particular geometry of the array provided that the basic requirement of stationarity is fulfilled

shallow velocity models at the kilauea volcano hawaii determined from array analyses of tremor wavefields the properties of the surface wavefield at kilauea volcano are analysed using data from small aperture arrays of short period seismometers deployed in and around the kilauea caldera tremor recordings were obtained during two japan us cooperative experiments conducted in 1996 and 1997 the seismometers were deployed in three semi circular arrays with apertures of 300 300 and 400 m and a linear array with length of 1680 m data are analysed using a spatio temporal correlation technique well suited for the study of the stationary stochastic wavefields of rayleigh and love waves associated with volcanic activity and scattering sources distributed in and around the summit caldera spatial autocorrelation coefficients are obtained as a function of frequency and are inverted for the dispersion characteristics of rayleigh and love waves using a grid search that seeks phase velocities for which the l 2 norm between data and forward modelling operators is minimized within the caldera the phase velocities of rayleigh waves range from 1400 to 1800 m s 1 at 1 hz down to 300 400 m s 1 at 10 hz and the phase velocities of love waves range from 2600 to 400 m s 1 within the same frequency band outside the caldera rayleigh wave velocities range from 1800 to 1600 m s 1 at 1 hz down to 260 360 m s 1 at 10 hz and love wave velocities range from 600 to 150 m s 1 within the same frequency band the dispersion curves are inverted for velocity structure beneath each array assuming these dispersions represent the fundamental modes of rayleigh and love waves the velocity structures observed at different array sites are consistent with results from a recent 3 d traveltime tomography of the caldera region and point to a marked velocity discontinuity associated with the southern caldera boundary

shear wave velocity structure around teide volcano results using microtremors with the spac method and implications for interpretation of geodetic results deformation analysis and simulation of volcanic edifices require the construction of models of elastic properties of those structures in this paper we present an analysis of microtremor measurements recorded during the performance tests of two temporary seismic arrays installed in the eastern portion of the teide caldera in 1994 we take advantage of recent developments of the spac method and use spatial cross correlation computations to estimate phase velocity dispersion of rayleigh waves at the location of the arrays we show that the extension of the standard spac method is valid in the case of our data justifying its use and supporting the generalization of the spac method to single station pairs the phase velocity dispersion curve obtained was inverted to recover the shear wave profile at the site of the arrays our results indicate that the subsoil structure of the caldera is laterally homogeneous at the scale of a few km about the location of the arrays we obtained about 315 m of volcanic sediments overlying rocks with a shear wave velocity of 2 km s these results are robust and are a starting point to further modelling of deformation permanent or transient at this volcanic edifice which can be useful in the interpretation of different observed fields in fact the computation of deformations and gravity changes due to possible volcanic intrusions in two models one considering the volcanic sediments and the other without considering them provided different results in the near field

influence of near surface volcanic structure on long period seismic signals and on moment tensor inversions simulated examples from mount etna 1 long period lp seismicity on volcanoes is thought to be associated with moving fluids or resonating fluid filled conduits hence lp moment tensor mt source inversions might have a direct bearing on our understanding of the plumbing system using 3 d full wavefield simulations and 2 d sensitivity kernels in a digital elevation model of mount etna we investigate the influence of near surface volcanic structure on lp signals and on moment tensor inversions contrary to common wisdom in crustal seismology we find that despite their relatively long wavelengths lps are severely distorted by near surface structures including layering and topographic features in particular near surface low velocity structures which are commonly observed on volcanoes play a critical role in controlling the nature of lp signals if not accounted for these path effects leak into the source solution leading to the emergence of erroneous source geometries spurious forces and incorrect source time functions this is particularly problematic if one adopts an unconstrained solution space for the source with many free parameters hence there is a fine balance in the trade off between the velocity model and the source in the absence of high resolution near surface velocity control we demonstrate the importance of employing a priori source information from other fields e g structural geology for shallow lps constraining the number of free parameters in the inversion a probabilistic approach should then be taken as the model with the best fit is not necessarily the true solution

mapping the sources of the seismic wave field at kilauea volcano hawaii using data recorded on multiple seismic antennas seismic antennas constitute a powerful tool for the analysis of complex wave fields well designed antennas can identify and separate components of a complex wave field based on their distinct propagation properties the combination of several antennas provides the basis for a more complete understanding of volcanic wave fields including an estimate of the location of each individual wave field component identified simultaneously by at least two antennas we used frequency slowness analyses of data from three antennas to identify and locate the different components contributing to the wave fields recorded at kilauea volcano hawaii in february 1997 the wave field components identified are 1 a sustained background volcanic tremor in the form of body waves generated in a shallow hydrothermal system located below the northeastern edge of the halemaumau pit crater 2 surface waves generated along the path between this hydrothermal source and the antennas 3 back scattered surface wave energy from a shallow reflector located near the southeastern rim of kilauea caldera 4 evidence for diffracted wave components originating at the southeastern edge of halemaumau and 5 body waves reflecting the activation of a deeper tremor source between 02 hr 00 min and 16 hr 00 min hawaii standard time on 11 february

shallow velocity structure and site effects at mt vesuvius italy from hvsr and array measurements of ambient vibrations abstract ambient vibrations were recorded by two dense short period seismic arrays located on mount vesuvius the aim of this study is to derive the surface velocity structure through the application of array techniques and to interpret it in terms of resonance effects mount vesuvius which is located in proximity to the apennines earthquake source zone is one of the most dangerous volcanoes of the world we compared different array techniques to derive the dispersive properties of the surface waves composing the noise wave field the frequency wavenumber f k spectral method applied to the data recorded by array a furnished the rayleigh waves and love waves dispersive functions and proved the time space stationarity of the noise wave field the existence of a stochastic wave field justifies the use of the spatial autocorrelation spac method and the time stationarity autocorrelation tsac method which appear to be most effective at the lowest frequencies the tsac method which time averages is confirmed as the most user friendly because it does not require circular geometries the knowledge of the surface structure is an important goal in site effects studies and is used to determine the frequency response of the near surface geology velocity models have been derived from the dispersion curves using both trial and standard inversion procedure the results are compared with those obtained from array measurements in adjacent areas scarpa et al 2003 revealing similar mechanical properties in the cover deposits and heterogeneities down to 40 m of depth the shear wave velocity profiles derived at the array sites are used to model the 1d transfer functions for vertically incident shear waves the fundamental resonance frequencies agree with the peak frequencies observed in the microtremor horizontal to vertical spectral ratios the frequency band of amplification is also compatible with the results obtained from local earthquakes at sites located at the same elevation on mount vesuvius galluzzo et al 2009

pre collisional anastomosing shear zones in the kohistan arc nw pakistan ductile strain localisation commonly forms a pattern of shear zones anastomosing around lenses of less deformed rock initiation and development history of anastomosing shear zones which are little documented are studied through the description of the structures and the deformation history of plutonic rocks that form the lower crust of the kohistan complex structures and textures developed in these rocks result from primary magmatic to solid state regional strain overprinted by anastomosing shear zones the primary strain was mainly acquired during magmatic emplacement at 100 90 ma strain localisation took place continuously from magmatic emplacement to solid state deformation during cooling of the plutons and formed 3 successive sets of shear zones set 1 is composed of associated discrete riedel and thrust shear zones developed above solidus conditions during sw ward thrusting continuous deformation from solidus to amphibolite facies conditions between 100 and 83 ma formed the second set of shear zones the lower amphibolite facies set 3 shear zones are differentiated by larger strain recorded in the thicker mylonitic zones and enlargement of the spacing between shear zones during cooling the anastomosing pattern of shear zones described here probably represents arc related deformation during subduction of the tethys oceanic lithosphere below the kohistan arc complex

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