spatial distribution of intrinsic and scattering seismic attenuation in active volcanic islands ii deception island images this work has been partially supported by the spanish project ephestos cgl2011 29499 c02 01 by the eu project ec fp7 mediterranean supersite volcanoes med suv by the basque government researcher training program bfi09 277 and by the regional project grupo de investigaci on en geof isica y sismolog ia de la junta de andaluc ia rnm104 edoardo del pezzo was partly supported by dpc ingv projects unrest speed and v2 precursori

array analysis of seismograms from explosive sources evidence for surface waves scattered at the main topographical features in this article we analyze the seismic wavefield produced by blasts fired at mt vesuvius for a deep seismic sounding experiment and recorded by a dense short period three component seismic array seismograms from five explosions occurring at the bottom of wells located at different distances and azimuth with respect to the array site have been analyzed with the zero lag cross correlation technique applied to both vertical and horizontal components in the frequency range 3 7 hz the aim is to analyze the portion of the seismograms long after the first p onset in order to obtain the slowness and backazimuth distribution of correlated secondary phases polarization analysis in time domain carried out using the array covariance matrix technique has also been applied to the well correlated phases to determine their wave composition results show that the correlated phases detected in the coda of the seismogram shots are composed almost entirely of surface waves location of the scatterers shows a high concentration of the scatterers in and around the volcanic edifice of mt vesuvius confirming that topographical irregularities play an important role in the generation of the high frequency scattering phenomena

time resolved seismic tomography detects magma intrusions at mount etna the continuous volcanic and seismic activity at mount etna makes this volcano an important laboratory for seismological and geophysical studies we used repeated three dimensional tomography to detect variations in elastic parameters during different volcanic cycles before and during the october 2002 january 2003 flank eruption well defined anomalous low p to s wave velocity ratio volumes were revealed absent during the pre eruptive period the anomalies trace the intrusion of volatile rich 4 weight percent basaltic magma most of which rose up only a few months before the onset of eruption the observed time changes of velocity anomalies suggest that four dimensional tomography provides a basis for more efficient volcano monitoring and short and midterm eruption forecasting of explosive activity

spatial distribution of intrinsic and scattering seismic attenuation in active volcanic islands i model and the case of tenerife island this work has been partially supported by the spanish project ephestos cgl2011 29499 c02 01 by the eu project ec fp7 mediterranean supersite volcanoes med suv by the basque government researcher training program bfi09 277 and by the regional project grupo de investigaci on en geof isica y sismolog ia de la junta de andaluc ia rnm104 edp has been partly supported by dpc ingv projects unrest speed and v2 precursori

tomographic inversion of p wave velocity and q structures beneath the kirishima volcanic complex southern japan based on finite difference calculations of complex traveltimes summary we estimate the p wave velocity and attenuation structures beneath the kirishima volcanic complex southern japan by inverting the complex traveltimes arrival times and pulse widths of waveform data obtained during an active seismic experiment conducted in 1994 in this experiment six 200 250 kg shots were recorded at 163 temporary seismic stations deployed on the volcanic complex we use first arrival times for the shots which were hand measured interactively the waveform data are fourier transformed into the frequency domain and analysed using a new method based on autoregressive modelling of complex decaying oscillations in the frequency domain to determine pulse widths for the first arrival phases a non linear inversion method is used to invert 893 first arrival times and 325 pulse widths to estimate the velocity and attenuation structures of the volcanic complex wavefronts for the inversion are calculated with a finite difference method based on the eikonal equation which is well suited to estimating the complex traveltimes for the structures of the kirishima volcano complex where large structural heterogeneities are expected the attenuation structure is derived using ray paths derived from the velocity structure we obtain 3 d velocity and attenuation structures down to 1 5 and 0 5 km below sea level respectively high velocity pipe like structures with correspondingly low attenuation are found under the summit craters these pipe like structures are interpreted as remnant conduits of solidified magma no evidence of a shallow magma chamber is visible in the tomographic images

slowness anomalies from two dense seismic arrays at deception island volcano antarctica in this article we analyze the data collected by two short period seismic arrays deployed at deception volcano southern shetland islands antarctica the field survey was conducted during the 1998 1999 austral summer and was aimed at a quantitative assessment of the complex wave fields associated with the magmatic and hydrothermal activity of the volcano the two arrays had apertures of 320 m and 240 m and were separated by a distance of about 3 km during the experiment the arrays recorded several regional earthquakes related to the dynamics of the brans field strait and adjoining areas and local volcano tectonic earthquakes seismograms of earthquakes recorded at regional distances reveal a marked difference in the ap parent velocities measured at the two array sites we investigate the causes and implications of these anomalies by first comparing the effectiveness of estimating the horizontal slowness vector using three different techniques the multiple signal classification music approach the zero lag cross correlation zlc method and plane wave fitting to p wave arrival times while each technique provides the same horizontal slowness vector as the most likely estimates the plane wave fitting is associated with the most robust definition of measurement uncertainties we then investigate the dispersive properties of rayleigh waves in the 1 8 hz frequency band at both arrays and invert the two dispersion curves for a shallow velocity structure the results indicate a marked difference in the seismic velocities for the shallower 200 m beneath the two sites this may be reconciled with the observed wave vector anomalies by assuming the existence of a sharp lateral velocity heterogeneity the effect of which would be to bend downward rays impinging at the northernmost array the reliability of this hypothesis is verified by computing finite difference wave fronts in a 2d heterogeneous medium based on the morpho structural char acteristics of the volcano the inferred velocity discontinuity maybe associated with the ring fracture system bordering the collapsed caldera structure that extends over the inner part of the island

shallow structure of deception island antarctica from correlations of ambient seismic noise on a set of dense seismic arrays summary we investigated the shallow velocity structure of deception island volcano antarctica using correlations of ambient seismic noise we selected long records of noise obtained by eight seismic arrays deployed along the inner coast of deception during the period 2003 2005 using these data we calculated average dispersion curves and estimated local 1 d velocity models for the array sites the combination of these profiles allowed us to obtain a comprehensive model of the shallow velocity structure of the island the volcano is composed of relatively soft layers of pyroclastic deposits and sediments extending to a depth of about 400 m with different degrees of compaction two layers with thicknesses of about 100 and 300 m and s wave velocities of around 0 2 0 8 and 0 7 1 1 km s 1 respectively can be differentiated the deeper structure is highly variable in terms of wave velocities and layer depths although the resolving capabilities are reduced for these layers the larger s wave velocities in the range 1 3 2 8 km s 1 indicate that they can be associated with pre caldera structures and products there are substantial differences between the different models which can be spatially related to heterogeneities in the volcano structure the lowest s wave velocities may be related to the alterations produced by hydrothermal activity near the surface on the contrary the largest velocities occur near the caldera border revealing the presence of compact materials at shallow depths sharp lateral variations can also be observed in the northwest of the bay which points to the presence of nw se faults and or strong velocity gradients

analysis of multiple scattering at vesuvius volcano italy using data of the tomoves active seismic experiment data from the tomoves active seismic experiment are used to study scattering effects in the shallow heterogeneous structure of vesuvius volcano seismograms from shots located on the volcano itself are characterised by spindle like envelopes small or missing p onsets missing s onsets and long codas seismograms from shots in the surroundings of the volcano on the contrary show clear and impulsive p and s onsets and short codas the different shapes of the envelopes can be explained by strong multiple scattering in the shallow heterogeneous eruptive material of the volcano and single scattering in the surrounding crust the seismograms of shots located on the volcano are modeled using the diffusion model with a diffusivity of d 0 1 km2 s for the frequency range of 2 16 hz assuming the dominance of s waves in the coda and a typical s wave velocity of around 1 5 km s this corresponds to a transport mean free path ltr of only 200 m which is 3 orders of magnitude smaller than for normal earth crust these results show that multiple scattering is an important effect which cannot be neglected in the modeling of seismic wave propagation in volcanic environments

tomographic inversion for three dimensional velocity structure at mount st helens using earthquake data tomographic inversion is applied to 17 659 p phase observations at 21 stations from 2023 earthquakes in the vicinity of mount st helens to study the three dimensional velocity structure block size for the inversion is 2 km horizontally and 2 km or more vertically locations of hypocenters are assumed known and are based on a reference one dimensional layered velocity structure a conjugate gradient technique lsqr is used to invert the large sparse system of equations augmented by regularization with a laplacian roughening matrix resolution is estimated by computing the impulse response of the inversion for various critical locations and uncertainties of the estimates are determined by a jackknife approach the results of the inversion show a remarkable correlation with known geological and geophysical features the spirit lake and spud mt plutons are characterized by high velocity regions extending to approximately 9 km depth the st helens seismic zone a band of diffuse seismicity extending nnw from the volcano is evident as a prominent low velocity lineation the change in character of the velocity anomalies south of st helens corresponds well with the near cessation of seismic activity there a low velocity anomaly beneath the crater from 6 to 16 km depths may represent modern magma accumulations

evidence for hydrothermal venting and sediment volcanism discharged after recent short lived volcanic eruptions at deception island bransfield strait antarctica abstract the results of a combined geophysical and geochemical research programme on deception island an active volcano at 62 43 s 60 57 w in bransfield strait antarctica are presented ultrahigh resolution acoustic data obtained with a topas topographic parameter sonar system and multibeam bathymetry simrad em1000 allow a detailed analysis of submarine vents in port foster the submerged caldera of deception island the data show three different types of seafloor structures low relief mounds high relief mounds wasp nest like and spire like structures we interpret these structures as products of sediment volcanism and seeps caused by heating and boiling of pore fluids in gas charged sediments and related to recent short lived volcanic events possibly those that occurred in 1967 1969 and 1970 in addition subsurface vertical disturbed zones formed by increased amplitude and phase inverse reflectors beneath the mounds suggest the presence of fluidised and brecciated sediments within hydrofracture systems a key finding of this study is that there appears to be a close relationship between the submarine mounds detected by our ultrahigh resolution seismic study geochemical haloes fault pathways and present day thermal anomalies in surface waters we suggest that seafloor hydrofracture systems and subsurface pipes can be re used as fluid migration pathways resulting in hydrothermal seeps and vents on the seafloor possibly up to decades after coeval volcanic eruptions

crustal structure of deception island volcano from p wave seismic tomography tectonic and volcanic implications 1 deception island 62 59 s 60 41 w is an active volcano located in the bransfield strait between the antarctic peninsula and the south shetland islands the island is composed of rocks that date from 0 75 ma to historical eruptions 1842 1967 1969 and 1970 and nowadays most of its activity is represented by vigorous hydrothermal circulation slight resurgence of the inner bay floor and intense seismicity with frequent volcano tectonic and long period events in january 2005 an extensive seismic survey took place in and around the island to collect high quality data for a high resolution p wave velocity tomography study a total of 95 land and 14 ocean bottom seismometers were deployed and more than 6600 air gun shots were fired as a result of this experiment more than 70 000 travel time data were used to obtain the velocity model which resolves strong p wave velocity contrasts down to 5 km depth the joint interpretation of the vp distribution together with the results of geological geochemical and other geophysical magnetic and gravimetric measurements allows us to map and interpret several volcanic features of the island and surroundings the most striking feature is the low p wave velocity beneath the caldera floor which represents the seismic image of an extensive region of magma beneath a sediment filled basin another low velocity zone to the east of deception island corresponds to seafloor sedimentary deposits while high velocities to the northwest are interpreted as the crystalline basement of the south shetland islands platform in general in the tomographic image we observe ne sw and nw se distributions of velocity contrasts that are compatible with the regional tectonic directions and suggest that the volcanic evolution of deception island is strongly conditioned by the bransfield basin geodynamics

attenuation and source parameters at deception island south shetland islands antarctica deception island is the most active volcano of the south shetland islands antarctic peninsula group experiencing eruptions in 1967 1969 and 1970 local attenuation derived from coda analysis and source parameters derived from brune s model for well located seismic events have been studied in order to complement the available geophysical information results show abnormally lowq0 values and an abnormally high frequency dependence as well as large dispersion these factors are strongly dependent on the path travelled by the seismic wave retrieved values of the source parameters stress drop seismic moment and source radius are again abnormally low compared to world wide average values for example those obtained for the oroville california aftershock series between june and september 1976 these results are consistent with some aspects of the geology of deception island such as the very high degree of fracturing and faulting and the existence of a strong hydrothermal alteration affecting most of the subaerial volcanic rocks moreover the pattern defined for the lateral variations ofq0 shows minimum values in the inner bay of the island close to the most recent eruption vents a large reduction in spectral amplitudes over a particular frequency range occurs in several observations corresponding to the path crossing the zone of highest attenuation this observation suggests the existence of a hot magmatic intrusion produced during the most recent eruption and coincides with the superficial low density mass distribution obtained from the gravimetric model and the long wave magnetic field component obtained from magnetic surveys the width of this intrusion is estimated to be about 200 m in agreement with the previous results obtained analyzing residuals of the location of seismic events

seismovolcanic signals at deception island volcano antarctica wave field analysis and source modeling the seismovolcanic signals associated with the volcanic activity of deception island antarctica recorded during three antarctic summers 1994 1995 1995 1996 and 1996 1997 are analyzed using a dense small aperture 500 m seismic array the visual and spectral classification of the seismic events shows the existence of long period and hybrid isolated seismic events and of low frequency quasi monochromatic and spasmodic continuous tremors all spectra have the highest amplitudes in the frequency band between 1 and 4 hz while hybrids and spasmodic tremors have also significant amplitudes in the high frequency band 4 10 hz the array analysis indicates that almost all the well correlated low frequency signals share similar array parameters slowness and back azimuth and have the same source area close to the array site the polarization analysis shows that phases at high frequency are mostly composed of p waves and those phases dominated by low frequencies can be interpreted as surface waves no clear shear waves are evidenced from the energy evaluation we have found that the reduced displacement values for surface and body waves are confined in a narrow interval volcano tectonic seismicity is located close to the array at a depth shallower than 1 km the wave field properties of the seismovolcanic signals allow us to assume a unique source model a shallow resonating fluid filled crack system at a depth of some hundreds of meters all of the seismic activity is interpreted as the response of a reasonably stable stationary geothermal process the differences observed in the back azimuth between low and high frequencies are a near field effect a few episodes of the degassification process in an open conduit were observed and modeled with a simple organ pipe

quantitative analysis of seismic wave propagation anomalies in azimuth and apparent slowness at deception island volcano antarctica using seismic arrays summary we analyse shot data recorded by eight seismic arrays during an active source seismic experiment carried out at deception island antarctica in 2005 january for each source we estimate the apparent slowness and propagation azimuth of the first wave arrival since both source and receiver positions are accurately known we are able to interpret the results in terms of the effect of the heterogeneities of the medium on wave propagation the results show the presence of significant propagation anomalies nearby shots produce large apparent slowness values above 0 6 s km 1 while distant shots produce small values down to about 0 15 0 20 s km 1 these values are different for each array which shows the importance of the local structure under the receiver the spatial distributions of apparent slowness are not radial as we would expect in a flat layered medium and again these distributions are different for each array the azimuth anomalies defined as the difference between the empirical estimates and the values expected in a 1 d model i e the source array directions suggest ubiquitous wave front distortions we have detected both positive and negative anomalies for some shot array geometries azimuth anomalies are quite large with values up to 60 the distribution of the anomalies depends on the position of the array some of these features can be interpreted in terms of a shallow magma chamber and shallow rigid bodies imaged by high resolution seismic tomography however several details remain unexplained further work is required including modelling of synthetic wavefields on realistic models of deception island and or apparent slowness vector tomography

sandstone petrology and provenance of the siwalik group northwestern pakistan and western southeastern nepal abstract the siwalik group consists of a neogene sedimentary succession 5 8 km thick deposited as the himalayan foreland basin developed following collision between the indian and eurasian continents it consists of fluvial deposits composed of shale siltstone and sandstone in the lower part and thick sandstone and conglomerate in the upper part this paper presents new petrologic data on the sandstone composition of two coeval petrofacies of siwalik group in two areas the potwar plateau of northwestern pakistan and the surai khola and bakiya khola localities of western and southeastern nepal in both regions detrital modes reflect a collisional orogen provenance petrologic parameters indicate derivation from mid crustal rocks and overlying sedimentary strata ascribed to different tectonostratigraphic units of the high himalaya and tibetan zone the siwalik sandstones of the potwar plateau nw pakistan are composed of low to medium grade metamorphic and sedimentary detritus and subordinately of ophiolitic and volcanic detritus abundant metamorphic detritus consists of phyllite fine grained schist lithics and coarse grained gneiss derived from the high and or lesser himalaya sedimentary detritus is represented by abundant limestone radiolarian chert siltstone shale very fine grained quartzarenite and other sandstone grains the siliciclastic grains probably were eroded from older terrigenous sequences belonging to the tethys himalayan and lesser himalayan zones uplifted during the india eurasia collision ophiolitic volcanic lithic grains and radiolarian chert reflect a provenance from the indus suture and tran himalayan belt the sandstones of western and southeastern nepal surai khola and bakiya khola sections have higher quartz and lower feldspar contents than those of northwestern pakistan and contain sedimentaclastic western nepal and metamorphiclastic sandstones southeastern nepal comparison of the data presented here with previous work on pre and post siwalik sandstones of the himalaya range and of the remnant ocean basins along both sides of the indian peninsula also derived from the himalayan suture belt suggests abundant quartzolithic detritus from the eocene to the present varying proportions of lithic populations in time are related to rapid uplift of the himalayas and intense unroofing of sedimentary metasedimentary and deeper terranes

the p wave velocity structure of deception island antarctica from two dimensional seismic tomography abstract deception island is a volcanic island with a flooded caldera that has a complex geological setting in bransfield strait antarctica we use p wave arrivals recorded on land and seafloor seismometers from airgun shots within the caldera and around the island to invert for the p wave velocity structure along two orthogonal profiles the results show that there is a sharp increase in velocity to the north of the caldera which coincides with a regional normal fault that defines the northwestern boundary of the bransfield strait backarc basin there is a low velocity region beneath the caldera extending from the seafloor to 4 km depth with a maximum negative anomaly of 1 km s refracted arrivals are consistent with a 1 2 km thick layer of low velocity sediments and pyroclastites infilling the caldera synthetic inversions show that this layer accounts for only a small portion of the velocity anomaly implying that there is a significant region of low velocities at greater depths further synthetic inversions and melt fraction calculations are consistent with but do not require the presence of an extensive magma chamber beneath the caldera that extends downwards from 2 km depth

scattering behaviour at merapi volcano java revealed from an active seismic experiment summary the seismic structure of the stratovolcano merapi java indonesia was studied using an active seismic experiment three 3 km long seismic profiles each consisting of up to 30 three component seismometers with an interstation distance of 100 m were built up in an altitude range between 1000 and 2000 m above sea level the detailed study of the seismic properties of the propagation media in active volcanic regions is important to understand the natural seismic signals used for eruption forecasting the seismic experiment at merapi therefore concentrates on the heterogeneous structure within a radius of 5 km from the active dome where the sources of most of the natural volcanic seismic events are located the cone of merapi volcano consists of different materials changing on a small scale due to the layering of eruptive material additionally the topography of the erosion valleys leads to an irregular deposition which cannot be described by a simple 1 d layering these inhomogeneities have a strong influence on seismic signals the direct p and s waves are attenuated quickly and show only small amplitudes on seismograms the energy lost from the direct waves however is not changed into heat but scattered and can be observed as seismic coda following the direct waves the observed seismograms show a spindle like amplitude increase after the direct p phase this shape of the envelope can be explained by the diffusion model according to this model there are so many strong inhomogeneities that the direct wave can be neglected and all energy is concentrated in multiple scattered waves besides the envelope the coherence and polarization properties of the wavefield also indicate strong scattering only the first onset shows coherence over a station spacing of 100 m whereas the late phases carrying the major part of the energy are mainly incoherent the horizontal components of the seismograms have larger amplitudes than the vertical component but within the horizontal plane the polarization is almost arbitrary corresponding to waves arriving from scatterers located arbitrarily in space as a result of the inversion using the diffusion model we obtain values of the s wave scattering attenuation coefficient gs and the s wave intrinsic absorption coefficient gi in the frequency range of 4 20 hz used in this study the scattering attenuation is at least one order of magnitude larger than the intrinsic absorption gs gi the mean free path of s waves is as low as 100 m gs1 100 m the scattering coefficient is independent of frequency gsyf 0 0 whereas the coefficient of intrinsic attenuation increases with increasing frequency giyf 1 6 the natural seismic signals at merapi volcano show similar characteristics to the artificial shots the first onsets have only small amplitudes and the energy maximum arrives delayed compared to the direct waves therefore these signals appear to be strongly affected by multiple scattering also

a three dimensional qp imaging of the shallowest subsurface of campi flegrei offshore caldera southern italy to improve the knowledge of the shallowest subsurface of campi flegrei caldera a 3 d p wave attenuation tomography of the area was performed we analyzed about 18 000 active seismic traces which provided a dataset of 11 873 t measurements e g the differential traveltimes to quality factor ratios these were inverted through an adapted tomographic inversion procedure the 3 d tomographic images reveal an average qp about 70 interpreted as water saturated volcanic and marine sediments an arc like low qp structure at 0 5 1 km depths was interpreted as a densely fractured fluid saturated rock volume well matching the buried rim of campi flegrei caldera the spatial distribution of high and low qp bodies in the inner caldera is correlated with low vp values and may reflect either the differences in the percentage of fluid saturation of sediments or the presence of vapor state fluids beneath fumaroles manifestations

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

the recent seismo volcanic activity at deception island volcano abstract this paper reviews the recent seismic studies carried out at deception island south shetland islands antarctica which was monitored by the argentinean and spanish antarctic programs since 1986 several types of seismic network have been deployed temporarily during each antarctic summer these networks have consisted of a variety of instruments including radio telemetered stations autonomous digital seismic stations broadband seismometers and seismic arrays we have identified two main types of seismic signals generated by the volcano namely pure seismo volcanic signals such as volcanic tremor and long period lp events and volcano tectonic vt earthquakes their temporal distributions are far from homogeneous volcanic tremors and lp events usually occur in seismic swarms lasting from a few hours to some days the number of lp events in these swarms is highly variable from a background level of less than 30 day to a peak activity of about 100 events h the occurrence of vt earthquakes is even more irregular most vt earthquakes at deception island have been recorded during two intense seismic crises in 1992 and 1999 respectively some of these vt earthquakes were large enough to be felt by researchers working on the island analyses of both types of seismic events have allowed us to derive source locations establish seismic source models analyze seismic attenuation calculate the energy and stress drop of the seismic sources and relate the occurrence of seismicity to the volcanic activity pure seismo volcanic signals are modelled as the consequence of hydrothermal interactions between a shallow aquifer and deeper hot materials resulting in the resonance of fluid filled fractures vt earthquakes constitute the brittle response to changes in the distribution of stress in the volcanic edifice the two vt seismic series are probably related to uplift episodes due to deep injections of magma that did not reach the surface this evidence however indicates the high potential for future volcanic eruptions at deception island

shallow seismic attenuation and shear wave splitting in the short period range of deception island volcano antarctica abstract the occurrence of a seismic series in deception island volcano antarctica composed of hundreds of local volcano tectonic earthquakes has permitted us to study the seismic attenuation of such a volcanic environment in the short distance and high frequency range this study has been performed using p waves s waves and coda waves and applying different frequency dependent and independent techniques the methods used for this analysis have been spectral and broadening of the pulse for direct p and s waves coda normalization for s waves and single back scattering model for coda waves the results show that in general q values are significantly smaller for the entire frequency range used 6 30 hz than those found in other volcanic and tectonic areas the attenuation for p waves is greater than for s waves in the frequency independent methods with a q q p ratio that ranges between 1 9 and 3 2 comparing the q factor obtained for s waves we have observed clear differences as a function of the method used the coda normalization method has supplied significantly higher q values q d than the other two methods q we have interpreted this discrepancy as an effect of the methods coda normalization and single back scattering methods eliminate the contribution of the near surface attenuation in their q values comparing both q and q d we have estimated the near surface attenuation under the recording site named q on the other hand we have observed that q d has anomalous frequency dependence with a minimum value at 21 hz this pattern is interpreted as an effect of strong scattering of the seismic waves in the source area of the earthquakes q c values depend clearly with frequency and lapse time and the lapse time dependence could be interpreted as a depth dependence of the seismic attenuation in deception island volcano antarctica the obtained q values have allowed us to separate the contribution of intrinsic and scattering attenuation deriving that the scattering attenuation is predominant over the intrinsic effects finally in order to investigate how the heterogeneous medium of the volcanic island could produce other effects we have checked whether it produces polarization of the shear waves the preliminary results of the polarization direction indicate a main e w strain direction all these evidences reveal the strongly heterogeneous structure of deception island volcano

geomagnetic secular variation of bransfield strait western antarctica from analysis of marine crossover data summary tracking the secular variation of the geomagnetic field in the past is severely limited in some cases by factors relating to the remoteness of the sites this is maximal in the antarctic where the remote location and severe climate lead to logistic limitations that make it difficult to keep a continuous record of magnetic field variations from the magnetic information available from historical marine expeditions it is possible to infer this time varying component from the comparison of readings at crossovers this study focuses on this technique discusses the impact of the different error sources and proposes a simple mathematical procedure to infer average secular variation rates the result is validated by comparing it with local data from the arctowski and livingston magnetic observatories sited in the area additionally using a high quality data set from a local area in the neighbourhood of deception island we have detected a systematic distribution in its secular variation this dichotomy has been interpreted in terms of a volcano magnetic signal this fact and the nature of its principal mechanisms are analysed and discussed

imaging ruptured lithosphere beneath the red sea and arabian peninsula abstract the red sea rift an archetype of a newly formed ocean basin is an ideal environment in which to study the controversial processes associated with continental rifting different models have been proposed to explain how rifting in the red sea evolved however accurate constraints on lithospheric structure have not been available to discriminate rifting models we use the s wave receiver function technique to produce the first images of the lithosphere asthenosphere boundary lab structure along the red sea and throughout the arabian peninsula lithospheric thickness varies considerably with thin lithosphere centered on the rift axis thickening toward the arabian interior gravity data are well fit by our structural model and indicate that high surface topography along the rift flank is not in isostatic equilibrium requiring dynamic compensation for its support while our derived structure is consistent with active rifting processes previous studies demonstrated that the red sea initiated as a passive rift therefore our results suggest a two stage rifting history where extension and erosion by flow in the underlying asthenosphere are responsible for variations in lab depth lab topography guides asthenospheric flow beneath western arabia and the red sea demonstrating the important role lithospheric variations play in the thermal modification of tectonic environments

the three dimensional structure of kilauea volcano hawaii from travel time tomography a linear travel time tomography study of the most active shield volcano of the world kilauea volcano hawaii was undertaken to determine the lateral heterogeneities produced by its intricate magmatic and tectonic environment kilauea provides an ideal setting to do tomography because of its dense seismograph array and many local earthquakes that allow excellent ray coverage of complex subsurface features local p wave data from 12 295 events were inverted using a one dimensional layered velocity model inversions were done for two cell sizes 5 5 5 km and 1 1 1 km to resolve structural regions on different length scales this study provided a view of the average velocity variations relative to a one dimensional velocity model analysis and interpretation of the tomographic images allowed us to infer the following model the main shallow magma reservoir is delineated by a slow velocity region southeast of the summit from 0 to 2 km depth there is a distinct high velocity region centered northwest of the summit from 0 to 2 km depth that represents a cap of dense intrusive dikes surrounding the magma chamber we suggest that the shallow reservoir is a narrow compartmentalized region of sills and dikes centered just south southeast of halemaumau caldera below the main reservoir the summit is imaged as a slightly fast region from 5 to 10 km in the coarse model indicating that the main conduit is structurally defined by an intrusive dike complex until about 10 km the rift zones of kilauea are imaged as major high velocity entities widening to the south with depth until 6 km these fast anomalies are related to the sheeted dike complexes along the rifts on a finer scale slow anomalies suggest the presence of magma pockets centered at 0 2 km depth beneath mauna ulu makaopuhi and puu oo along the east rift zone erz two significant high velocity regions along the lower erz near kalalua and kaliu are inferred to represent intrusive barriers to magma injection along the shallow 0 4 km erz conduit the southwest rift zone may have an intrusive barrier related to a high velocity region just southwest of mauna iki the hilina and kaoiki fault zones are imaged as slow features at shallow depths 5 km related to the open fractures and scarps along the normal faults the koae fault system is imaged as a slightly fast shallow structure 6 km possibly related to intrusive diking from the adjacent rift zones that fill and may even induce the extensional structures associated with this complex fault zone continued inversions with the immense amount of seismic data collected for hawaiian events will allow the detailed development of a three dimensional structural model for kilauea such a model will be extremely useful to seismologists and petrologists alike for understanding the tectonic growth and magmatic evolution of this dynamic shield volcano