las canadas caldera tenerife canary islands a review or the end of a long volcanological controversy abstract the las canadas caldera is one of the best exposed volcanic calderas in the world and one of the few known evolved alkaline volcanoes it truncates the pre teide pico viejo central volcanic edifice the las canadas edifice which started to take shape at the end of the formation of a large basaltic shield that forms the main part of island of tenerife historically the origin of the las canadas caldera has been controversial as it has been interpreted as the result of either multiple vertical collapses or due to a giant sector collapse the available stratigraphical structural volcanological geochronological and geophysical data as well as its comparison to other well known collapse calderas should not offer any doubt as to its direct relationship with a long history of phonolitic explosive volcanism however the existence of large landslide events on tenerife which have significantly modified the flanks of the las canadas volcano have also been used as a potential explanation for the origin of the las canadas depression this contribution reviews the available information on the las canadas caldera the causes of this controversy and rationalises the most plausible explanation for the origin of las canadas caldera based on the current evidence gathered from all previous studies

electrical impedance variation with water saturation in rock we measured the electrical impedances of 22 sandstone samples during oil driving water tests using the two electrode method experiments show that the imaginary part x of the impedance r ix of rock may respond well to water saturation in the frequency range 100 hz 15 mhz we found that the maximum x values and their corresponding interfacial polarization frequencies are linear with water saturation the lower critical frequency is found to vary with water saturation in an unclear relationship with the characteristic length of rock the dissipation factor at the interfacial polarization frequency remains quite stable and may be an indicator of the pore structure of rock we used an equivalent circuit to explain the dispersive behavior of rock more than one interfacial polarization frequency in the impedance argand plot is predicted and can be observed if the measurement frequency range is wide enough

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

137cs and 210pb dating of sediments from soft water lakes in new england u s a and scandinavia a failure of 137cs dating abstract deep water sediment cores from 32 scandinavian and 19 northern new england u s a lakes were analyzed for 137cs 210pb was analyzed in cores from 16 and 14 of these lakes respectively additional dating of the new england cores was based on chronostratigraphic pollen markers the profiles in sediment of 137cs deviate greatly from expectations based on fallout history the profiles have their maxima at the surface and 137cs occurs at depths dated by 210pb and pollen as many decades older than the beginning of 137cs fallout non exponential 210pb profiles in certain lakes most in new england and pollen dates suggest that bioturbation physical mixing changes in sedimentation rate or acidification may be occurring but this is insufficient to account for the deviant 137cs profiles in most of the lakes there is no evidence of mixing we argue that the occurrence of 137cs at prefallout sediment depths is due mostly to net downward molecular diffusion and adsorption and that surface concentration is due to net upward diffusion and adsorption and possibly also biological uptake recycling of sedimentary 137cs in the water column and delayed input from the watershed it is probable that much of the 137cs entering these lakes is carried by organic detritus mobility of 137cs in this sediment may be a function of release by organic decomposition and scarcity of clay minerals for adsorption correlation analyses of the sedimentary radionuclide activities vs physical and chemical characteristics of the lake water sediment and watersheds suggest that considerable trapping of 137cs and 210pb by terrestrial vegetation and organic soils is occurring the resultant delayed export to these lakes is contributing to the failure of 137cs as a dating tool but 210pb dating can be valid under these circumstances

seismotectonics of the canary islands abstract a revision of the seismicity both historical and instrumental for the canary islands is presented the occurrence on may 9 1989 of an earthquake of magnitude 5 2 between the islands gran canaria and tenerife followed by a large number of aftershocks have been interpreted on seismotectonic grounds the main conclusion is that a horizontal compressional stress regime in nw se direction is present in the region which is compatible with the tectonics in the northwestern part of the african continent

regional variations in atmospheric deposition and sources of anthropogenic lead in lake sediments across the canadian arctic stable pb isotope profiles in dated lake sediment cores were used to gauge the relative amounts and possible sources of anthropogenic pb deposited from the atmosphere in different regions of the canadian arctic a distinct north south difference was found in four high arctic lakes i e north of 66 n in this study recent pb isotopic shifts or concentration increases attributable to anthropogenic pb were negligible the maximum possible contribution from anthropogenic pb was 0 to 19 of acid leachable pb in the 1980s or 1990s in contrast two lakes in the hudson bay region displayed significantly lower pb isotope ratios and threefold to fivefold increases of pb concentrations in modern sediments corresponding to anthropogenic pb inputs of at least 72 to 91 of leachable pb eurasian urban and industrial pb is known to dominate the high arctic atmosphere a possible explanation for its negligible influence on northern lake sediments is that atmospheric pb deposition at northern latitudes is reduced compared with southern regions and is small compared to local geological inputs 210pb deposition declines with increasing latitude apparently because of declining precipitation rates stable pb deposition may be similarly affected meteorological considerations and variations in the post 1900 pb isotopic trajectories indicated that the predominant anthropogenic pb source region in nw hudson bay was eurasia while in se hudson bay it was canada and the united states with a minor eurasian component

importance of lateral transport processes to 210pb budget in the eastern chukchi sea during summer 2003 chinese ipy research program national natural science foundation of china 41125020 fujian natural science foundation 2009j06026 state oceanic administration of china 201105022 4 ministry of education of china

137cs and 210pb transport and geochronologies in urbanized reservoirs with rapidly increasing sedimentation rates sedimentation rates have been measured in three reservoirs in northeastern ohio u s a by means of 137cs and 210pb geochronologies volumetric surveys and varve counting these various methods while only partially overlapping for each reservoir show dramatic three fold increases in rates of sediment accumulation in each system between about 1940 and 1977 mass sedimentation rates are very nearly proportional to the size of the population in the region and possess a doubling time of roughly 19 yr in these systems with changing sedimentation rates the preferred model for use with 210pb geochronologies is one which assumes a constant activity of material added to surface sediments in systems possessing large watershed reservoir area ratios increasing erosion is evidently accompanied by a proportionate increase in the erosion of excess 210pb high near surface activities of 137cs are due to system integration effects with time constants the order of 10 yr to a few decades total accumulation of fallout 137cs and excess 210pb far exceed direct atmospheric loadings thus indicating the importance of watershed contributions and implying annual retention of the radionuclides in the reservoirs of between 15 and 80 in lake rockwell sedimentary fluxes of zn pb and cu have increased with time the flux of cu in particular has increased very markedly since 1970 and concentrations are high in surface materials due in large part to addition of cuso4 an algicide to the water because of increased rates of sedimentation the remaining useful life of lake rockwell has decreased from 203 to 67 yr while the remaining useful life of mayfair lake is now less than 5 yr

observations of high frequency scattered waves using dense arrays at teide volcano abstract a study of the seismic coda of seven small earthquakes recorded on the teide volcano canary islands spain was carried out using a temporary small aperture 12 station seismic array the purpose was to measure backazimuth apparent velocity and the type of waves that compose the coda in the frequency range 4 to 6 hz we used the zero lag cross correlation zlc method to obtain the components of the wave vector and three component analysis techniques based on the covariance matrix of the signal in the time domain to investigate the polarization properties of the signals the results show that a great part of the coda signals in the analyzed frequency range are almost uncorrelated while a low number of isolated correlated arrivals show an apparent slowness between 2 10 3 and 2 5 10 4 sec m and an almost random distribution of backazimuths the correlated arrivals have been interpreted as generated by strong scatterers probably related to the presence in the study area of surface topography irregularities the volcanic cone and the caldera rim the wave type varies from pure s type waves to mixed surface waves with some rayleigh components

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

magnetotelluric study of the teide tenerife and timanfaya tanzarote volcanic areas the application of a magnetotelluric surveying method developed specifically for detection of strong conductivity contrasts has permitted interpretations of the deep structure of two important volcanic formations in the canary archipelago the timanfaya lanzarote and teide tenerife volcanoes beneath the timanfaya volcano a highly conductive body p 1 m has been detected which is interpreted as a shallow magma chamber associated with the eruption which took place between the years 1730 and 1736 the core of this intrusion still largely molten would be located at approximately 4 km depth and would still maintain temperatures in excess of 900 c in the telde caldera the asymmetry of the apparent resistivity components indicates a double depression furthermore a highly conductive level encountered in the centre of the eastern part of the volcanic complex has been attributed to the persistance of relatively high temperatures in the root of the last salic dome extruded inside the caldera in both zones the deep limiting horizon is a highly conductive layer corresponding to the mantle 15 km in lanzarote and 13 km in tenerife whereas other more superficial discontinuities have been related to local structures

seasonal and spatial patterns of sedimentary denitrification rates in the chukchi sea abstract recent constructions of the global nitrogen budget estimate that at least half of the ocean s fixed nitrogen is lost by sedimentary denitrification the majority of which occurs in continental shelves the arctic contains approximately 20 of the world s continental shelf suggesting it is a substantial contributor to the global sedimentary denitrification rate during two cruises in the summer and spring of 2002 and 2004 respectively denitrification rates were calculated from the downward diffusive flux of nitrate in the shelf and slope sediments of the chukchi sea in the western arctic additionally in the spring of 2004 denitrification rates were determined by whole core incubations in which the flux of nitrogen gas out of the sediments was measured measurements were made along three transects crossing the shelf and slope 50 3000 m each transect having different overlying water characteristics denitrification rates generally decreased with increasing water depth rates varied from about 1 6 mmol n m 2 d 1 for the shallow water sediments to undetectable in deep water sediments rates showed little variation between the two seasons however rates were found to correspond with differences in annual overlying primary productivities and particulate organic carbon export fluxes an extrapolation to the whole arctic yielded an average arctic sedimentary denitrification rate of 13 tg n yr 1 taken in the context of the global nitrogen budget it is about 4 13 of the total sink of fixed nitrogen in the ocean

volcanic evolution of the island of tenerife canary islands in the light of new k ar data new age determinations from tenerife together with those previously published 93 in all provide a fairly comprehensive picture of the volcanic evolution of the island the oldest volcanic series with ages starting in the late miocene are formed mainly by basalts with some trachytes and phonolites which appear in anaga teno and roque del conde massifs in anaga ne three volcanic cycles occurred one older than 6 5 ma a second one between 6 5 and 4 5 ma with a possible gap between 5 4 and 4 8 ma and a late cycle around 3 6 ma in teno nw after some undated units the activity took place between 6 7 and 4 5 ma with two main series separated by a possible pause between 6 2 and 5 6 ma in the zone of roque del conde s the ages are scattered between 11 6 and 3 5 ma between 3 3 and 1 9 ma the whole island underwent a period of volcanic quiescence and erosion the large canadas volcano made up of basalts trachytes and phonolites was built essentially between 1 9 and 0 2 ma to the ne of this central volcano linking it with anaga is a chain of basaltic emission centers with a peak of activity around 0 8 ma the canadas caldera had several collapse phases associated with large ignimbrite emissions there were at least an older phase more than 1 ma old on the western part of the volcano and a younger one less than 0 6 ma old in the eastern side the two large valleys of guimar and la orotava were formed by large landslides less than 0 8 ma ago and probably before 0 6 ma ago the present canadas caldera was formed by another landslide less than 0 2 ma ago this caldera was later filled by the huge teide volcano which has been active even in historic times during the same period a series of small volcanoes erupted at scattered locations throughout the island the average eruptive rate in tenerife was 0 3 km3 ka with relatively small variations for the different eruptive periods this island and la gomera represent a model of growth by discontinuous pulses of volcanic activity separated by gaps often coinciding with episodes of destruction of the edifices and sometimes extended for several million years the neighbouring gran canaria on the other hand had an initial rapid shield building phase during which more than 90 of the island was built and a series of smaller pulses at a much later period a comparison between these three central islands indicates that the previously postulated westward displacement in time of a gap in the volcanic activity is valid only as a first approximation several gaps are present on each island overlapping in time and not clearly supporting either of the models proposed to explain the evolution of the canaries

a new non archie model for pore structure numerical experiments using digital rock models summary tortuosity is a key parameter for investigating the pore structure of sedimentary rock the conventional model for calculating the tortuosity is derived from archie s law which is only valid for one conductive phase contained in a porous rock however there have been increasingly cases to show the non archie phenomenon in instances where the rock matrix has extra conductive phases such as surface conductivity caused by the electrical double layer therefore such model may be inapplicable in these cases and in calculations involving partial melting we investigated the relation between formation factor and porosity f o ver aw ide range of porosities by the lattice gas automata method lga with the electrical double layer the digital rock samples were constructed by packing up solid grains with different shapes and size distribution as previously measured in the laboratory on real rock specimens our purpose was to identify the origin of non archie behaviour of the f relation sometimes observed the simulations show that archie s law may only be an approximation of the f relation in a high porosity range based on our lga simulations and additional laboratory experimental data we developed new equations for non archie f relation and tortuosity potentially useful for improving the evaluation of pore structure

210pb and 137cs chronology of sediments from small shallow arctic lakes abstract arctic environmental conditions present special difficulties with the use of nuclides 210pb and 137cs for measuring lake sediment chronology fluxes of these nuclides are lower in the arctic than in mid latitudes shortening the history that can be resolved ice prevents atmospheric input of nuclides to sediment during much of the year and can cause redistribution of sediment in shallow lakes results from analyses of seven sediment cores from two lakes on the belcher islands in southeastern hudson bay show that sediment redistribution by ice is a major process in one of the lakes in order to measure an undisturbed sedimentation rate it is necessary that a total input or flux of 137cs and 210pb be measured or estimated total unsupported 210pb in the area 14 8 dpm cm2 is the average of measurements in three cores from two lakes that have consistent total 137cs inventories closest to the estimated 137cs flux cores from undisturbed sites have slower sedimentation rates and 137cs appears in layers dated before the early 1950s when it would have first appeared in sediment 137cs cannot be used for chronological evaluation of these cores mixing of surface sediment layers and lower dating resolution than in other cores are responsible for the apparent downward movement of this nuclide 210pb measurements of undisturbed sedimentation rates in the lakes range from 0 0044 to 0 0180 g cm2 a the sedimentation rate in a lake used for raw sewage oxidation doubled after the beginning of sewage input rates at sites where sediment is redistributed range from 0 0259 to 0 0309 g cm2 a with similarly higher total 137cs and unsupported 210pb values dates of sediment layers measured using the constant rate of supply model are verified by 210pb profile discontinuities corresponding to major storms in 1958 and in 1940

natural 210pb 7be and fallout 137cs 239 240pu 90sr radionuclides as geochemical tracers of sedimentation in greifensee switzerland the average sedimentation rate of greifensee has been evaluated by using varve counting and 210pb and fallout radionuclide dating from 4 different sites in the lake to amount to 0 14 0 02 g cm 2 yr 1 the geochronology of greifensee agrees with previous dating attempts based on varve counting of sediments from the deepest part of the lake emerson and widmer 1978 a simple erosion model for substances derived predominantly from the drainage basin can explain the inventories of the natural and fallout radionuclides in the lake sediments

tsunami deposits related to flank collapse in oceanic volcanoes the agaete valley evidence gran canaria canary islands abstract enigmatic marine conglomerates are attached at 41 188 m asl to the walls of the valley of agaete on the northwest coast of gran canaria canary islands they are formed by heterogeneous angular to rounded heterometric volcanic clasts roundness and maximal size decreasing with altitude and fossils rhodolites and marine shells never found in growth position and often broken the deposits are internally stratified into several layers most of them showing very poor sorting matrix supported and reverse grading they present lenticular morphologies with poor lateral continuity in transversal and longitudinal sections slopes show values and orientations similar to those of the relief of the substratum to which they seem to adapt although they show clear evidence of erosive contact with the substratum rip up clasts they do not tend to form horizontal terraces soft materials soils and colluviums are preserved in the contact with the substratum in outcrops with deposit slopes of up to 15 the age of the deposits is constrained between 1 75 ma and 32 ka their altitude and slope distributions are not related to pleistocene interglacial sea level changes storm deposits or isostatic movements all the above suggests that the agaete marine deposits were generated by tsunami waves the most probable source being a flank failure at least nine major such events having occurred in the canary islands during the pleistocene the guimar sector collapse east coast of tenerife 30 km 3 is the closest possible source for the tsunami and the sole flank failure that is directed towards another island in the canaries

effects of fluid displacement pattern on complex electrical impedance in berea sandstone over frequency range 104 106 hz to better understand the effect of fluid distribution on the electric response of rocks saturated with oil and brine we conducted experimental studies on the complex electrical impedance in a berea sandstone together with in situ acquisitions of oil distribution images employing a high resolution medical x ray computed tomography we performed two tests of brine displacement by oil under high 10 mpa and low 5 mpa pressures which were accompanied by fingering and stable displacement patterns respectively the measured complex impedance data were fitted to the cole model to obtain the resistance capacitance peak frequency of the imaginary impedance and the exponent of the rock fluid system with increasing oil saturation the resistance showed an increasing trend whereas the other three parameters decreased the fingering displacement exhibited lower resistance and capacitance than the stable displacement the analysis of the resistance changes using a simple parallel connection model indicates that there are more components of residual brine in parallel connections in the fingering pattern than in the stable displacement pattern at the same saturation we also interpreted the normalised changes in the capacitance or apparent dielectric constant with respect to the oil saturation via an analysis of the shape factor of fluid distribution based on the maxwell wagner brugermann hanai model the changes in the shape factor suggest that the pinch off of the brine in parallel connection by the oil is a dominant mechanism reducing the capacitance in the stable displacement most of the connections in the brine phase are immediately pinched off by oil displacement front at a local oil saturation of 65 conversely in the fingering displacement there is a transition from the bulk or layered brine to the pinched off at a local oil saturation below 60 the analyses indicate that the difference in the fluid distribution under different fluid conditions is responsible for the non archie behaviour

contribution of dense array analysis to the identification and quantification of basin edge induced waves part i methodology recent earthquakes have shown that edge generated surface waves can significantly contribute to increased damages most observations of edge generated surface waves are concerning long period surface waves propagating in large size valleys since travel times of such waves between valley edges can reach several tens of seconds they are quite easy to isolate in small size structures reverberating wave trains are mixed and very dense array analysis is required for the identification of basin induced surface wave trains the city of grenoble french alps is located in a small size deep alluvial valley and faces important site effects lebrun et al 2001 in order to identify and quantify multidimensional site effects in this basin a very dense array of 29 three component seismometers over a 1 km aperture was installed within the city the wave field complexity as well as the in situ noise characteristics colored correlated noise and low signal to noise ratio led us to develop a procedure based on time frequency coherence of signal waveforms and the multiple signal classification music schmidt 1981 algorithm to identify the main energetic contributions crossing the array next the nature and energy of waves were estimated using some properties of the analytical three component covariance matrix careful methodological investigations were performed in order to better understand and quantify the effects of site constraints on the estimation of wave parameters with the music technique simulations outline the ability of array antennas first to handle difficult scenarios involving multiple nonstationnary and correlated propagating phases and second to estimate the polarization and energy of waves the velocity estimation is shown to be much more unstable than backazimuth estimation and a low signal to noise ratio introduces some variation in estimates finally considering the very large number of identified waves a statistical view of final estimates is suggested for improving the reliability of analysis in an accompanying article cornou et al 2003 we use this method to investigate the entire wave field of seismic events recorded by the array in order to isolate basin induced waves manuscript received 21 june 2002

a record of climate over the last millennium based on varved lake sediments from the canadian high arctic a varved sediment record that extends back over the last millennium was recovered from lower murray lake northern ellesmere island nunavut canada 81 20 n 69 30 w flatbed scan images and back scattered electron images were analysed to provide varve thickness and other quantitative sedimentary indices on an annual basis in many studies of lakes from the high arctic varve thickness is a good proxy for summer temperature and we interpret the lower murray lake varves in this way on that basis the lower murray lake varve thickness record suggests that summer temperatures in recent decades were among the warmest of the last millennium comparable with conditions that last occurred in the early twelfth and late thirteenth centuries but estimates based on the sediment accumulation rate do not show such a recent increase the coldest conditions of the little ice age were experienced from ad 1700 to the mid nineteenth century when extensive ice cover on the lake led to widespread anoxic conditions in the deepest parts of the lake basin an overall decline in median grain size over the last 1000 years indicates a reduction in the energy available to transport sediment to the lake many of these features of the record are also observed in other palaeoclimatic records from the north american arctic the very recent appearance of the diatom campylodiscus which was not observed through out the record of the last millennium suggests that a new threshold in the ontogenetic development of the lake has now been passed

radionuclide tracer profiles at the cesar ice station and canadian ice island in the western arctic ocean abstract water column profiles of naturally occurring 210pb 210po 226ra and fallout 137cs 239 240pu radionuclides measured at the canadian ice island in 1985 1986 and 1989 over the arctic ocean continental shelf were compared to profiles measured at the cesar ice station in the central arctic ocean in 1983 cesium 137 concentrations at cesar decreased from a mean value of 4 2 bq m3 in the surface mixed layer to less than 1 0 bq m3 in the atlantic layer and deep waters cesium 137 concentrations were similar to cesar values in the surface mixed layer at the ice island but in halocline water they were lower than values measured at comparable water depths at cesar indicating that the arrival of fallout 137cs in the ice island halocline had been delayed compared to its arrival in the cesar halocline these data are consistent with a combination of mixing box and lateral advection models with mixing occurring over the russian continental shelves followed by lateral advection through the interior halocline waters of the canada basin dissolved 210pb and 210po concentrations were higher in nutrient maximum water at the ice island compared to cesar low values at cesar are caused by scavenging of particle reactive radionuclides during modification of bering sea water in continental shelf environments the elevated 210pb and 210po concentrations measured in nutrient maximum water at the ice island are assumed to result from ingrowth of 210pb from 226ra during lateral advection of upper halocline water between the cesar and ice island locations a process that is estimated to take approximately 11 years plutonium 239 240 is also depleted relative to 137cs in the surface mixed layer and upper halocline at the ice island owing to its scavenging during modification of pacific water in shelf environments the 239 240 pu 137 cs ratio increases to values approaching fallout levels in lower halocline and atlantic water owing to both reduced 239 240pu removal in source waters and vertical transport of 239 240pu with sinking particles

a double seismic antenna experiment at teide volcano existence of local seismicity and lack of evidences of volcanic tremor data analyzed in the present work correspond to a 40 days field experiment carried out in teide volcano canary islands spain with two short period small aperture dense seismic antennas in 1994 the objective of this experiment was to detect analyze and locate the local seismicity we analyzed also the background seismic noise to investigate the possible presence of volcanic tremor from a set of 76 events we selected 21 of them in base of their good signal to noise ratio and their possibility to locate their seismic source by using the seismic antennas a visual classification based on the s p time and seismogram shape has permitted to establish three groups of events local seismicity s p time between 3 and 5 s very local earthquakes s p time smaller than 3 s and artificial explosions these earthquakes have been located by applying the zero lag crosscorrelation technique and the inverse ray tracing procedure those earthquakes that were recorded simultaneously by both seismic antennas were also located by intersecting both back azimuths the analysis of the seismicity has revealed that the amount of seismicity in teide volcano is moderate this seismicity could be distributed in three main areas inside the caldera edifice below the teide pico viejo complex in the eastern border of the caldera edifice and offshore of the island at present this activity is the only indicator of the volcano dynamics the analysis of the back ground seismic noise has revealed that at frequencies lower than 2 hz the oceanic load signal is predominant over other signals even over local earthquakes with a magnitude of 2 0 due to this although if in the teide area were present a weak volcanic tremor or other volcanic signals with predominant peaks below 2 hz to observe them would be a very difficult task q 2000 elsevier science b v all rights reserved

crustal structure gravity anomalies and flexure of the lithosphere in the vicinity of the canary islands summary simple elastic plate models have been used to calculate the flexure of the lithosphere caused by volcanic loading at the canary islands and sediment loading at the moroccan continental margin by comparing the calculated flexure to observations based on seismic refraction and free air gravity anomaly data constraints have been placed on the long term 106 years elastic thickness of the lithosphere te the best fit between the calculated and observed flexure in the vicinity of the canary islands is for te 20 km this value of te also explains seismic reflection data in regions that flank the island provided that the lithosphere underlying the moroccan margin is sufficiently weak te 5 km for sediment loading to contribute little to the island flexure a backstripping study in which gravity data are used to constrain the value of te supports the suggestion that the lithosphere underlying the moroccan margin like its conjugate at the baltimore canyon trough is weak although sediment loading at the moroccan margin appears therefore to have exerted little influence on the structure of the canary islands there is evidence that island flexure may have influenced the stratigraphic development of the moroccan margin especially in the region of the slope anticline a te of 20 km is about 15 km lower than would be expected on the basis of the thermal age of the oceanic lithosphere that underlies the canary islands similar low values have been reported from oceanic islands in the pacific superswell region of french polynesia where they have been attributed to re heating of the lithosphere by one or more hotspots a general e w age progression of the volcanic rocks suggests that the canary islands were also generated by a hotspot they lack however the topographic swell and gravity geoid high which usually accompanies these features one possibility is that the low te values are the result of a pre existing weakness in the oceanic crust a te of 20 km is large enough however for a significant part of the mantle to still be involved in the support of the island loads a more likely explanation is thermal weakening by a hotspot which has been localized enough to reduce te but not to produce a swell or gravity geoid high irrespective of its cause the low te suggests that oceanic lithosphere does not necessarily progressively increase its strength with age so that even 140 ma old lithosphere is vulnerable and can in some regions be significantly weakened by later thermal and mechanical processes

observations of loma prieta aftershocks from a dense array in sunnyvale california a small aperture 300 m four station array was deployed in sunnyvale california for 5 days to record aftershocks of the loma prieta earthquake of october 1989 the purpose of the array was to study the seismic response of the alluvium filled santa clara valley and the role of surface waves in the seismic shaking of sedimentary basins strong motion records of the loma prieta mainshock indicate that surface waves produced the peak velocities and displacements at some sites in the santa clara valley we use the recordings from the dense array to determine the apparent velocity and azimuth of propagation for various arrivals in the seismograms of four aftershocks with magnitudes between 3 6 and 4 4 apparent velocities are generally observed to decrease with increasing time after the s wave in the seismograms phases arriving less than about 8 sec after the s wave have apparent velocities comparable to the s wave and appear to be body waves multiply reflected under the receiver site or reflected by crustal interfaces for times 10 to 30 sec after the direct s wave we observe long period 1 to 6 sec arrivals with apparent velocities decreasing from 2 5 to 0 8 km sec we interpret these arrivals to be surface waves and conclude that these surface waves produce the long duration of shaking observed on the aftershock records much of the energy in the 40 sec after the s wave is coming approximately from the direction of the source although some arrivals have backazimuths as much as 60 different from the backazimuths to the epicenters two of the aftershocks show arrivals coming from 30 to 40 more easterly than the epicenters this energy may have been scattered from outcrops along the southeastern edge of the basin in contrast the deepest aftershock studied d 17 km displays later arrivals with backazimuths 30 to 40 more westerly than the epicenter a distinct arrival for one of the aftershocks propagates from the southwest possibly scattered from the western edge of the basin synthetic seismograms derived from a plane layered crustal model do not produce the long period love waves observed in the waveforms of the ml 4 4 aftershock these love waves may be generated by the conversion of incident s waves or rayleigh waves near the edge of the basin

possible interaction between tectonic events and seismic noise at las canadas volcanic caldera tenerife spain continuous seismic noise is recorded in the volcanic island of tenerife canary islands spain the origin of this noise strongly augmented by anthropogenic contamination is still under debate in this paper we discuss the relationship between this noise and the occurrence of local tectonic events in the same area in particular transitions are sought in the time evolution of dynamic parameters computed on the seismic noise and examples are shown where abrupt transitions may be associated with the occurrence of tectonic events these transitions provide further evidence of the existence of a natural origin for at least part of the seismic noise which is strongly contaminated if not dominated by anthropogenic sources

detection of displacements on tenerife island canaries using radar interferometry tenerife is one of the most well monitored islands of the canaries but the surveillance generally is centred on las canadas caldera where the teide volcano is located in the last 180 000 yr the eruptions on tenerife island have never occurred in the same volcanic structure except for the teide and pico viejo central volcanic system so that a complete monitoring network would have to cover the whole island as a result synthetic aperture radar interferometry insar is being used on tenerife because this space technique can provide a displacement map of the surface of the earth with centimetre precision this paper presents the results obtained on tenerife island using 18 sar images acquired by the ers 1 and ers 2 satellites during the period 1992 2000 two important results have been obtained no deformation on las canadas caldera coinciding with results obtained using terrestrial techniques and two subsidence episodes outside monitoring areas in the nw of the island in the region of the last historic eruptions these results show that insar is a useful technique for monitoring the entire island thus allowing us to discover deformations in areas that are not routinely or easily monitored this technique has been used in combination with global positioning system gps observation of a global network on the island to define a new geodetic monitoring system the possible causes of the deformations observed have been studied in an endeavour to discern if they might be of natural origin in particular linked to a reactivation of prior volcanic activity examination of the geophysical observations on the island human activities underway and the results of the modelling seem to indicate that at least part of the deformations may be caused by changes in the groundwater level and therefore are not linked to a volcanic reactivation this result is important because it implies that if geodetic volcano monitoring is to be performed on the island the system used must be capable of discerning between various possible origins of the deformation by analysing their patterns and ancillary information from other sources in this regard insar is a basic tool on account of its unpaired wide area coverage and spatial density

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

induced polarization of shaly sands equations have been developed that relate induced polarization ip in shaly sands to measurable petrophysical parameters the induced polarization process has been modeled in terms of two mechanisms clay counterion displacement and membrane blockage the resulting equations can be used to determine shaliness brine conductivity and oil saturation from in phase and out of phase conductivities laboratory measurements have confirmed the ip dependence on these variables as well as on temperature

determination of recent deposition rates in lake constance with radioisotopic methods sedimentation rates were determined with the 210pb method in eight sediment cores from lake constance the rate of deposition in the main basin obersee varies from about 0 06 g cm 2 y 1 in the central part to 0 13 g cm 2 y 1 in the eastern part of the lake and then increases rapidly towards the rhine delta in the central lake area the rate of deposition has been approximately constant since 1900 and dating with the 210pb method is in good agreement with sedimentological observations in the konstanzer trichter area the deposition rate has been increasing since about 1955 as a result of eutrophication and subsequent high carbonate production dating with 137cs is fairly accurate for sediments deposited at a high rate but is questionable for slowly accumulating ones a positive correlation of 210pb fluxes and sedimentation rates indicates that 210pb flux into sediments follows the distribution pattern of solids 210pb profiles in four sediment cores interpreted in terms of a constant flux model display synchronous fluctuations of the sedimentation rate however their relation to long range particulate input variations remains to be proved sedimentation rates determined with the 210pb method were used to calculate recent nutrient and heavy metal fluxes anthropogenic fluxes of zn and pb are in the same range of magnitude as in other polluted areas in europe and america

natural radionuclides and plutonium in sediments from the western arctic ocean sedimentation rates and pathways of radionuclides abstract sediment cores collected during r v polar sea aos94 expedition from the chukchi shelf to the north pole were analyzed for several decay series natural radionuclides and pu isotopes to study sedimentation rates and pathways of radionuclides in the western arctic ocean the measured sedimentation rates vary by more than three orders of magnitude along the transect from 210pb based rates of 200 700 cm kyr 1 over the chukchi shelf and 89 cm kyr 1 at the chukchi slope to 230th based rates of 0 02 0 3 cm kyr 1 at various settings in the deep basin 230thex profiles in the central western arctic basin are characterized by a cyclic pattern and a pronounced sub surface maximum superimposed on an overall decrease with depth sediment inventories of excess 210pb and 230th in the deep basin as a whole cannot account for their in situ production and 210pb fall out the opposite is true at the slope and shallower waters we contend that as with other ocean basins boundary scavenging also exists in the arctic ocean the broad continental shelves and the slope region may have the potential of removing all or most of the particle reactive radionuclides unaccounted for in the deep basin the pu isotope data are consistent with the notion of boundary scavenging sediment inventories and concentrations of pu decrease rapidly offshore isotopic composition of pu suggests mixing of fall out pu which decreases with increasing latitudes and fuels reprocessing pu derived from the russian and atlantic sides of the arctic ocean although fuel reprocessing pu has impinged on the chukchi slope its existence over the chukchi shelf is not evident and probably overshadowed by fall out pu

determination of effective grain geometry for electrical modeling of sedimentary rocks accurate electrical modeling of sedimentary rocks is crucial for the interpretation of electrical survey data and must take into account the geometric information of the rock grains we have developed an incremental model for the multiphase electrical conductivity of sedimentary rocks on the theoretical basis of differential effective medium models the developed incremental model was first validated on clean and clay rich sandstones and then applied to simulate the conductivity offive digitally created rock samples with different spectra of grain aspect ratios the conductivity is calculated as a function of water conductivity at full water saturation and an effective grain aspect ratio for a two phase medium is determined to reproduce the electrical behavior of the digital rocks it was found that the effectivegrain aspect ratio can either be determined analytically or estimated from the aspect ratio spectrum a link between the obtained effective grain aspect ratio and the cementation coefficient widely used in petrophysics has been established the cementation coefficient increases with the decrease of the grain aspect ratio increasing the z axis depolarization factor and grain conductivity and the increase of sample porosity it showed that the cementation coefficient can be interpreted as a measure of the connectivity of pores as well as the conductivity of the grains our results gave us new insights into the physical meanings of the grain aspect ratio and cementation coefficient which could be used to facilitate the electrical modeling or interpretation of reservoir rocks

210pb 226ra 230th systematics in very low sedimentation rate sediments from the mendeleev ridge arctic ocean this article is one of a series of papers published in this special issue on the theme polar climate stability network geotop publication 2008 0031 u series isotope behaviour in subsurface sediment of the arctic ocean is investigated based on high resolution measurements of natural radionuclides 210pb 226ra 230th and a few analyses of anth

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

studies of the seismic coda using an earthquake cluster as a deeply buried seismograph array loosely speaking the principle of green s function reciprocity means that the source and receiver positions in a seismic experiment can be exchanged without affecting the observed seismograms consequently the seismograms observed at a single observation location o and caused by a cluster of microearthquakes at locations ei are identical to the time series that would be measured by an array of stress meters emplaced at positions ei recording waves generated by a source acting at o by applying array analysis techniques like slant stacking and frequency wave number analysis to these seismograms we can determine the directions and velocities of the component waves as they travel in the earthquake focal region rather than at the surface we have developed a computationally rapid plane wave decomposition which we have applied to single station recordings of aftershocks of the 1984 morgan hill california earthquake the analysis is applied to data from three seismic stations having considerably different site geologies one is a relatively hard rock station situated on franciscan metamorphics one is within the calaveras fault zone and one is on semiconsolidated sand and gravels we define the early coda to be the part of the coda initiating immediately after the direct s wave and ending at twice the s wave lapse time the character of the s wave and early coda varies from being impulsive at the first station to highly reverberative at the last we examine waves in sequential time windows starting at the s wave and continuing through the early part of the coda at all seismic stations the early coda is dominated by a persistent signal that must be caused by multiple scattering probably within 2 km of each seismic station despite clear station to station differences in the character of the early coda coda q values measured in the late coda greater than twice the s lapse time agree well among stations implying that the mechanisms causing the varying behavior of the early coda do not control the coda decay rate at the stations we have considered coda q values measured on horizontal components of motion agree within a factor of 2 with those measured on vertical components we have not been able to determine the composition of the late coda because of a low signal to noise ratio our analysis technique however is quite appropriate for such a task

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

a theoretical treatment of the effect of microscopic fluid distribution on the dielectric properties of partially saturated rocks1 microscopic fluid distribution can have a significant effect on the dielectric properties of partially saturated rocks evidence of this effect is found in the laboratory data presented by knight and nur in which different methods for controlling saturation produced very different results for the dependence of the dielectric response on water saturation in this study previously derived models for the dielectric response of a heterogeneous medium are generalized and the case of a pore space occupied by multiple pore fluids is considered by using various geometrical distributions of water and gas it is observed that both the pore geometry in which saturation conditions are changing and the gas water geometry within a given pore space are critical factors in determining the effective dielectric response of a partially saturated rock as an example data for a tight gas sandstone undergoing a cycle of imbibition and drying are analysed previous research has demonstrated that significantly different microscopic fluid distributions result from the application of these two techniques to control the level of water saturation by approximating these microscopic fluid distributions using simple geometrical models good agreement is found between experimental data and calculated dielectric properties

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

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

volcanic tremor and local earthquakes at copahue volcanic complex southern andes argentina abstract in the present paper we describe the results of a seismic field survey carried out at copahue volcano southern andes argentina using a small aperture dense seismic antenna copahue volcano is an active volcano that exhibited a few phreatic eruptions in the last 20 years the aim of this experiment was to record and classify the background seismic activity of this volcanic area and locate the sources of local earthquakes and volcanic tremor data consist of several volcano tectonic vt earthquakes and many samples of back ground seismic noise we use both ordinary spectral and multi spectral techniques to measure the spectral content and an array technique zero lag cross correlation technique to measure the back azimuth and apparent slowness of the signals propagating across the array we locate vt earthquakes using a procedure based on the estimate of slowness vector components and s p time vt events are located mainly along the border of the caviahue caldera lake positioned at the south east of copahue volcano in a depth interval of 1 3 km below the surface the background noise shows the presence of many transients with high correlation among the array stations in the frequency band centered at 2 5 hz these transients are superimposed to an uncorrelated background seismic signal array solutions for these transients show a predominant slowness vector pointing to the exploited geothermal field of las maquinitas and copahue village located about 6 km north of the array site we interpret this coherent signal as a tremor generated by the activity of the geothermal field

pore connectivity electrical conductivity and partial water saturation network simulations the electrical conductivity of brine saturated rock is predominantly dependent on the geometry and topology of the pore space when a resistive second phase e g air in the vadose zone and oil gas in hydrocarbon reservoirs displaces the brine the geometry and topology of the pore space occupied by the electrically conductive phase are changed we investigated the effect of these changes on the electrical conductivity of rock partially saturated with brine we simulated drainage and imbibition as invasion and bond percolation processes respectively in pipe networks assumed to be perfectly water wet the simulations included the formation of a water film in the pipes invaded by the nonwetting fluid during simulated drainage imbibition we measured the changes in resistivity index as well as a number of relevant microstructural parameters describing the portion of the pore space saturated with water except euler topological number all quantities considered here showed a significant level of universality i e insensitivity to the type of lattice used simple cubic body centered cubic or face centered cubic hence the coordination number of the pore network appears to be a more effective measure of connectivity than euler number in general the simulated resistivity index did not obey archie s simple power law in log log scale the resistivity index curves displayed a substantial downward or upward curvature depending on the presence or absence of a water film our network simulations compared relatively well with experimental data sets which were obtained using experimental conditions and procedures consistent with the simulations finally we verified that the connectivity heterogeneity model proposed by bernabe et al 2011 could be extended to the partial brine saturation case when water films were not present

intermediate focus earthquakes under south shetland islands antarctica this study is based on data from five field surveys 1992 1996 of seismic monitoring on deception island south shetland islands antarctica in the 1994 95 and 1995 96 surveys earthquakes were recorded by a seismic array in previous surveys data were collected by a high dynamic range short period station the analysis of the events shows evidence of intermediate focus seismicity 50 h 100 km related to the underplating zone of the south shetland plate because of poor station coverage we had to use unconventional techniques to locate the events such as zero lag cross correlation method that provide information about apparent velocity and back azimuth ray tracing procedure and particle motion patterns these criteria allowed us to identify 15 earthquakes that could be considered as intermediate focus events for which some focal parameters were estimated we conclude that the subduction zone between the drake plate and south shetland microplate has a moderate level of intermediate depth microseismicity

intrinsic and scattering seismic wave attenuation in the canary islands the canary islands volcanic complex is studied in terms of coda wave attenuation a multiple lapse time window method based on the hypothesis of multiple isotropic scattering with uniform distribution of scatterers is applied to the available seismic data in order to obtain the intrinsic absorption qi 1 and the scattering attenuation qs 1 in the canarian lithosphere the analysis is performed for two hypocentral distance ranges from 0 to 80 km and from 0 to 140 km results show that in both cases and for all the studied frequency bands 1 2 2 4 6 8 and 8 10 hz intrinsic absorption dominates the low albedos found in the region indicate the low degree of heterogeneity in the canarian lithosphere at the scale length of the studied frequencies on the other hand the coda attenuation qc 1 calculated on the basis of the single scattering theory gives values near qi 1 for low frequencies and near the total attenuation qt 1 for high frequencies the degree of frequency dependence of the attenuation parameters is strong in all cases a correlation of the observed attenuation parameters with the geological evidence for a hotspot type archipelago and with other geophysical studies is suggested

microtremor analyses at teide volcano canary islands spain assessment of natural frequencies of vibration using time dependent horizontal to vertical spectral ratios we use time dependent horizontal to vertical spectral ratios hvsr of microtremors to determine the dominant frequencies of vibration of the geological structures beneath several recording sites in the vicinity of teide volcano canary islands spain in the microtremors the time dependent hvsrs ratiograms are a useful tool to discriminate between the presence of real dominant frequencies linked to resonances of the subsurface structure and the spurious appearance of peaks due to local transients we verified that the results are repeatable in the sense that microtremors recorded at the same site but at different times yield a very similar hvsr function two types of results are found 1 sites where there is no resonance of the propagating microtremors and therefore no value of a dominant frequency can be assessed and 2 sites where a stationary peak in the hvsr is found and a dominant frequency related to resonance of the shallow structure can be estimated these resonant frequencies show substantial spatial variations even for nearby sites which reflects the complexity of the shallow velocity structure in the las canadas area large dominant frequencies occur near the caldera walls and also at a few locations that coincide with the intersections of the inferred rims of the three calderas forming las canadas small dominant frequencies also occur near the caldera rim and may be due to discontinuities in the caldera wall and or to local velocity anomalies intermediate frequencies are mostly found in the eastern part of the caldera where a tentative profile of the basement depth has been obtained intermediate frequencies have also been measured south of ucanca and south of montana blanca in view of the present results we conclude that the use of ratiograms constitutes an improvement of the hvsr method and provides an appropriate tool to investigate the shallow velocity structure of a volcanic region

array analysis of the seismic wavefield of long period events and volcanic tremor at arenal volcano costa rica we use wavefield decomposition methods time domain crosscorrelation and frequency domain music to analyze seismic data recorded by a dense small aperture array located 2 km west of arenal volcano costa rica and operated during 2 5 days the recorded wavefield is dominated by harmonic tremor and includes also spasmodic tremor and long period lp events we find that the initial stages of lp events are characterized by three different wave arrivals these arrivals propagate with similar back azimuths pointing to the volcano summit 80 n and increasing apparent slownesses of 0 4 1 1 and 1 7 s km spasmodic tremors can not be regarded as coherent signals on the contrary harmonic tremors are highly coherent characterized by the stability of the apparent slowness vector estimates apparent slownesses lay in the range 1 2 s km back azimuths point in the general direction of the volcano but with a large variability 40 120 n nevertheless there are long term variations and evidences of multiple simultaneous components in the harmonic tremor wavefield these observations suggest that lp events and tremor are generated in a shallow source area near the volcano summit although they do not share exactly the same source region or source processes the tremor source is located in the shallowest part of the plumbing system beneath the lava crust this dynamic region is subject to complex fluctuations of the physical conditions degassing events at different locations of this region might generate variable seismic radiation patterns the effects of topography and heterogeneous shallow structure of the volcano may amplify these variations and produce the wide directional span observed for volcanic tremor on the other hand the lp source seems to be more repeatable lp events are likely triggered by fragmentation of the fluid flow in a slightly deeper portion of the volcanic conduits

new geodetic monitoring system in the volcanic island of tenerife canaries spain combination of insar and gps techniques even though volcanic activity in tenerife is characterized by the fact that eruptions do not normally occur more than once in the same volcanic edifice geodetic monitoring has mainly focused on the las canadas caldera where a geodetic micronetwork and a levelling profile are located a sensitivity test of this geodetic network showed a clear need to extend it to cover the full island for volcano monitoring purposes this conclusion together with the detection of two unexpected movements on the island using insar that were beyond the scope of the traditional geodetic network prompted the authors to design and observe a gps network covering the whole of tenerife the network was monitored in august 2000 the results obtained were accurate to 1 cm and confirm the deformation in the pinar de chio zone but are not definitive enough to confirm the displacements detected to the south of the village of garachico furthermore new cases of possible subsidence have been detected in areas where insar could not be used to measure deformation due to low coherence future observations will be necessary for further validation and to study the time evolution of the displacements and supplementary research must be conducted to determine the possible causes in particular if they are connected with the water pumping operations performed on the island one important result is that a new geodetic monitoring system based on two complementary techniques insar and gps has been set up on tenerife island this is the first time that the whole surface of any of the volcanic canary islands has been covered with a single network this research has displayed the need for further similar studies in the canary islands at least on the islands which pose a greater risk of volcanic reactivation

geochemical and geothermal constraints on magma bodies associated with historic activity tenerife canary islands abstract the present morphostructure of the island of tenerife is to a great extent conditioned by the large central structure of the teide 3717 m constructed on a large caldera with a collapse 17 km in diameter and whose base is located some 2000 m above sea level nevertheless in addition to this central system with current fumarolic activity there have been a series of isolated historic eruptions on the island whose structures are aligned with two main tectonic direction lines which delimit the caldera ne sw and nw se groundwater is collected on the island for human and agricultural supply by way of horizontal galleries of lengths generally between 1000 and 5000 m which radially penetrate the large central structure the frequent anomalies of temperature up to 45 c chemical composition sio2 b nh4 so42 co3h and high gas contents co2 h2 detected in these galleries which are located between the base of the caldera 2000 m and sea level enable us to evaluate from a geochemical point of view the current residual volcanic emanations of the island it is concluded that these are generated at around 300 c and that they interfere with the basal aquifers of the island at 130 150 c leading to the said anomalies processes are graded by height and so the highest galleries 1500 1800 m which are rich in co2 give rise to considerable carbonate deposits by the interaction at 25 40 c of the gas with the water of the upper perched aquifers the flow of gases necessary to maintain this activity is around 175 1725 kg m2 per day in each anomalous zone which coincide with the sites of the historic volcanoes

high resolution 3d p wave velocity structure beneath tenerife island canary islands spain based on tomographic inversion of active source data 1 we present a high resolution 3 dimensional 3d p wave velocity model for tenerife island canaries covering the top of teide volcano 3 718 m a s l down to around 8 km below sea level b s l the tomographic inversion is based on a large data set of travel times obtained from a 3d active seismic experiment using offshore shots air guns recorded at more than 100 onshore seismic stations the obtained seismic velocity structure is strongly heterogeneous with significant up to 40 lateral variations the main volcanic structure of the las canadas teide pico viejo complex ctpvc is characterized by a high p wave velocity body similar to many other stratovolcanoes the presence of different high p wave velocity regions inside the ctpvc may be related to the geological and volcanological evolution of the system the presence of high p wave velocities at the center of the island is interpreted as evidence for a single central volcanic source for the formation of tenerife furthermore reduced p wave velocities are found in a small confined region in ctpvc and are more likely related to hydrothermal alteration as indicated by the existence of fumaroles than to the presence of a magma chamber beneath the system in the external regions surrounding ctpvc a few lower p wave velocity regions can be interpreted as fractured zones hydrothermal alterations porous materials and thick volcaniclastic deposits

modeling radiotracers in sediments comparison with observations in lakes huron and michigan a comprehensive model for the activity of radionuclides in sediments is presented the model is based on the advection diffusion equations for sediment solids and a radioactive tracer mixing caused by deposit feeders is taken into account by a half gaussian hg integrated gaussian ig or exponential ex diffusion coefficient with a maximum value d0 at the sediment water interface and an effective mixing depth m where m hg zm ig or a ex compaction is described by an exponential bulk sediment density the differential equations are solved by finite differences in particular the crank nicolson method for the time dependent case cs 137 estimation of the mixing parameters d0 and m is carried out efficiently by minimizing chi square for measured and calculated steady state pb 210 activities the derived mixing depths of zm 4 6 0 1 cm station 14 and a 0 8 0 1 cm station 18 for the cores from lake huron are in good agreement with the organism distributions the corresponding d0 values are 12 2 and 1 5 0 5 cm2 yr respectively where the latter number is lower than a previous lower limit estimate 3 3 cm2 yr based on 1974 data these diffusion coefficients are in excellent agreement with those inferred from the densities of pontoporeia and tubificid oligochaetes 9 3 and 1 6 cm2 yr respectively compared with southern lake michigan there appears to be less sediment focusing in northern lake michigan where the ratios of measured to atmospheric cs 137 inventories have an average value of 0 89 and range from 0 32 to 1 41 for six cores from the deep basin when these ratios are used to correct the pb 210 fluxes we obtain an atmospheric pb 210 flux of 0 99 0 06 dpm cm2 yr because of its more realistic activity profiles we consider the present model to be generally better than previous models

biolaminated sedimentation in a high arctic freshwater lake a laminated sequence of lacustrine sediment from an arctic coastal lake was examined for potential chronological and successional information the laminae are microbially induced sedimentary structures the unlithified precursor of stromatolites and are previously unreported in the arctic the inferred annual sequence was interpreted to contain a basal clastic unit overlain with successive cyanobacterial and extracellular polymeric substance units the complex succession of laminae and inconclusive dating provide a challenge for identifying the chronological nature of the sedimentary structures markov chain and time series analyses suggest that a plausible quasi annual sequence can be identified to provide a context for palaeo environmental reconstruction recognition of sedimentary structure in recent biolaminated sediments offers a first step towards the palaeo environmental evaluation of the geomicrobiological sequence

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

reply to comment from blanco et al 2015 on evidence from acoustic imaging for submarine volcanic activity in 2012 off the west coast of el hierro canary islands spain by perez et al bull volcanol 2014 76 882 896

a combined radiometric and mineral magnetic approach to recent geochronology in lakes affected by catchment disturbance and sediment redistribution abstract as a result of empirical testing of 210 pb dating models in a wide variety of lakes we conclude that there are many situations where despite major changes in sedimentation rates as a result of lake or catchment disturbance the crs constant flux model provides a sound basis for establishing recent chronology factors which may complicate or vitiate the assumptions of the model include short water residence time bioturbation for which we propose a modified dating model discontinuous or disturbed sedimentation sediment resuspension and shifts in sediment source in the case of the last three processes we illustrate ways in which the problems can be identified and evaluated using mineral magnetic measurements we propose an evaluative approach to 210 pb dating projects with emphasis on independent dating evidence on tests of internal consistency and on the use of data from several correlatable cores

three dimensional indirect boundary element method for deformation and gravity changes in volcanic areas application to teide volcano tenerife canary islands 1 most deformation models of volcanoes assume that the earth is a linear elastic isotropic and homogeneous half space although some volcanic areas are associated with significant relief we investigate the effects of topography on surface deformation and gravity changes caused by a magma intrusion in the earth s crust a three dimensional 3 d indirect boundary element method ibem that incorporates realistic topographic features is developed in order to perform this analysis our results show that the topography alters both the magnitude and pattern of the deformation and gravity signal as an example of realistic topography we consider a spherical source of dilatation located at 4 km depth below teide volcano summit tenerife canary islands in order to simulate the deformation and gravity changes that could be observed at tenerife if a hypothetical intrusion occurred in the volcanic system this approach gives a picture of the 3 d topographic effect at teide that can provide insight in order to improve the geodetic monitoring of the volcano

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

210pb and 137cs in margin sediments of the arctic ocean controls on boundary scavenging 1 210pb and 137cs were measured in 25 sediment cores collected during the international polar year from a transect spanning the north american arctic margin from the north bering sea to baffin bay davis strait profiles and inventories of the radioisotopes were used to determine sediment mixing and accumulation at each site and to assess the intensity of scavenging and burial sediment accumulation rates derived from 210pb and validated using 137cs are between 0 04 and 0 23 g cm 2 yr 1 210pb cannot be used to derive sedimentation rates for vigorously biomixed sediments from the north bering chukchi shelf elevated 137cs activities and inventories in recently deposited sediments imply delayed inputs of particle associated 137cs to the sediments likely transported from the watershed to the coast and subsequently redistributed to shelf slope sediments inventories of 210pbex in all cores meet or exceed the estimated supply of 210pbex from atmospheric deposition and decay of 226ra in the water column this implies that in contrast to the deep arctic ocean basin there is a sufficient supply of suspended particulates along the north american arctic margin to scavenge the supply of 210pbex 210pbex inventories in sediments are up to 21 fold greater than the in situ supply at some sites large inventories of 210pbex in sediments along the north bering chukchi shelf result primarily from focusing while those along the north chukchi slope barrow canyon and in baffin bay davis strait reflect strong boundary scavenging likely supported by lateral exchanges with deep interior atlantic origin waters

permanent tremor of masaya volcano nicaragua wave field analysis and source location the masaya volcano nicaragua is a basaltic caldera in a subduction zone the permanent source of the volcanic tremor was located inside santiago crater at the lava lake s position and 400 m below the ne rim and therefore corresponds to superficial magma activity we used two tripartite arrays 90 m side one semicircular array r 120 m in 1992 and two semicircular arrays r 60 m and a 2500 m long linear array radiating out from the source and on the flank of the crater in 1993 we used both a cross spectrum method and a correlation method to determine the wave delay time between the reference station and the other stations of an array and to quantify the wave field using the delays therefore by intersecting the back azimuth wave directions from the arrays we could pinpoint the source additionally the correlation coefficients obtained as functions of frequency for the three components of motion confirm the inferred position of the source of tremor the tremor s wave field is composed of comparable quantities of dispersed rayleigh and love surface waves whose phase velocities lie in the ranges 730 1240 m s at 2 hz and 330 550 m s at 6 hz the dispersive phase velocities were inverted to obtain crustal structures with a minimal number of layers the resulting velocity models are similar for the northern and southern parts of the volcano after geometrical spreading corrections q2hz 14 and q3hz 31 were determined along the northern linear array the typical low velocities and low q corresponding to the cone structure and are similar to those of other basaltic volcanoes like puu oo hawaii and klyuchevskoy kamchatka

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

analysis of the seismic wavefield properties of volcanic explosions at volcan de colima mexico insights into the source mechanism summary we have investigated the wavefield properties of the seismic signals generated by the explosions of volc an de colima mwe have analysed these properties to understand the initial mechanism that triggered the explosive events our study is focused on the direct waves coming from the crater area thus we have analysed a set of moderate volcanic explosions at volc an de colima that was recorded by a small aperture seismic array over two periods october 2005 and april 2006 we can distinguish two types of explosions vulcanian and ash free events both types of explosions share the same characteristics that is a long period signal not related to any type of emission before the arrival of high frequency phases and a later high frequency signal directly related to ash or gas emission we have applied the zero lag cross correlation technique to obtain backazimuth and apparent slowness of the incoming waves we have also applied polarization analysis to the record of every detected volcanic explosion by comparing the results of both of these analyses we have been able to identify the dominant wave types that comprise the seismic wavefield and infer in time and space a possible primary source mechanism that would trigger the volcanic explosions we have observed an apparent slowness variation of the first onset of the long period lp signal with a possible upward migration of the source the depth of the source has been identified at a range between 2 6 and 3 3 km below the crater associated with the range of measured apparent velocities relative to the first onset of the lp signal

ground deformation control by statistical analysis of a geodetic network in the caldera of teide in order to determine with reliability criteria ground deformations an experimental geodetic network has been established in a volcanic area a methodology of hypothesis testing to compare successive observations has been set up and computer programs for the adjustment of the geodetic network and for the statistical analysis of both observations and adjustment results have been written this methodology has been applied to the data obtained from five surveys made from 1984 up to 1988 in the caldera of teide area tenerife canary islands during this period no significant deformations have been detected

relationship between spectral induced polarization and hydraulic properties of saturated and unsaturated sandstone there is growing interest in the use of geophysical methods for hydrological model parameterization empirical induced polarization ip hydraulic conductivity k relationships have been developed but these are only applicable to sediments in which the ip response shows limited variation with electrical current frequency here we examine the spectral ip response of samples taken from a uk sandstone aquifer and compare measured parameters with physical and hydraulic properties we demonstrate the limited value of existing ip k models due to the inherent ip frequency dependence of these samples our results show how the mean relaxation time is a more appropriate measure of ip response for these sediments a significant inverse correlation between the surface area to pore volume ratio and is observed suggesting that is a measure of a characteristic hydraulic length scale this is supported by a measured strong positive correlation between log and log k our measurements also reveal evidence of a relationship between and a dominant pore throat size which leads to postulations about the parallelism between the spectral ip behavior and unsaturated hydraulic characteristics additional experiments show how the relaxation time is affected by degree of fluid saturation indicating that saturation levels must be accounted for if our empirical relationships are applied to vadose zone studies our results show clear evidence of the potential value of frequency based ip measurements for parameterization of groundwater flow models

210pb derived chronology and the fluxes of 210pb and 137cs isotopes into continental shelf sediments east chukchi sea alaskan arctic abstract eleven sediment cores and eight sediment trap samples from the continental shelf of the eastern chukchi sea were analyzed for 210pb cs and 2226ra in selected samples the organic carbon content and stable carbon isotope ratios were also determined the excess 210pb 210pbxs concentrations in the 1 cm core tops are generally lower than those of surficial sediments of subarctic shelves and arctic lakes the sediment inventory derived depositional fluxes of 210ph vary between 0 09 and 0 38 dpm cm 2y 1 with a mean of 0 18 dpm cm 2 y 1 the apparent mass sediment accumulation rates which vary between 31 and 324 mg cm 2 y 1 with a mean value of 133 mg cm 2 y 1 are about an order of magnitude lower than the yearly particle flux obtained from the sediment trap experiments this difference between the relatively long term and short term yearly accumulation rates is likely due to the occasional resuspension of fine particles in the continental shelf areas and their advective transport to sites other than their initial deposition the sediment inventory of 137cs varied between 0 64 and 4 09 dpm cm 2 with a mean of 2 18 dpm cm 2 a comparison of this inventory with the expected fallout inventory of 137cs suggests that there had been no detectable input of 137cs to the study area from the former ussr nuclear dump sites

stratigraphy structure and geochronology of the las canadas caldera tenerife canary islands after a long period of subaerial fissure fed extrusions of basaltic magmas 12 to 3 ma volcanic activity was then concentrated in the central part of tenerife phonolitic magma chambers formed and a central volcanic complex was constructed the las canadas edifice the formation of a large depression the las canadas caldera truncated the top of the edifice the active twin strato cones teide pico viejo are sited in this depression the history of the las canadas caldera and edifice are established from stratigraphy geochronology k ar dates and volcanological studies two different groups are recognized separated by a major unconformity the lower group is dated at 2 to 3 ma and includes the products of several volcanic centres which together represent several cycles the upper group ranges from 1 56 to 0 17 ma and includes three different formations representing three long term 100 to 300 ka volcanic cycles the periods of dormancy between each formation were of 120 to 250 ka duration the las canadas caldera is a multicyclic caldera which formed over the period 1 18 0 17 ma each cycle of activity represented by a formation culminated in caldera collapse which affected different sectors of the las canadas edifice geological observation and geochronology support an origin by collapse into a magma chamber the minimum volume of pyroclastic ejecta is substantially greater than the present caldera depression volume 45 km3 but approaches the inferred volume of the original caldera depression 140 km3 after the formation of the caldera sector collapses could also occur at the northern flank of the volcano causing the disappearance of the northern side of the caldera wall

characterization of fracture systems using precise array locations of earthquake multiplets an example at deception island volcano antarctica 1 volcano tectonic earthquakes are common seismic events in active volcanic areas the stress produced by volcanic processes is released through fracturing of the shallow crust very often these earthquakes occur in multiplets with similar waveforms a fact which indicates common source characteristics in this work we introduce a method that uses array techniques to calculate precise relative locations of earthquake multiplets we use the relative slowness estimate method to determine accurately the apparent slownesses and propagation azimuths of the earthquakes relative to a selected master event we also obtain precise estimates of the s p delays this information is used to calculate precise relative locations by ray tracing in an earth model we applied this method to determine the characteristics of the fractures activated during the 1999 seismic series at the deception island volcano antarctica we selected a set of 17 earthquake multiplets initially located in a small 4 4 km region a few km ne of the array site we estimated precise locations for 14 of the clusters in most cases hypocenters were distributed in well defined planar geometries we found the best fitting planes which we interpreted as fractures in the medium for two clusters the method spatially separated the earthquakes into two subgroups thus we obtained two planes for each of these clusters resulting in a total of 16 fracture planes this is the first time that the orientations of fracture planes related to a seismic series have been obtained using a seismic array we performed several tests to check various aspects in relation to the stability of the method and concluded that the results were robust the dip angles indicate that the planes are mostly subvertical while the strike angles clearly show a nw se trend for most of the planes and a few planes with ne sw trends the geometry and position of these planes suggest that the 1999 seismic series was influenced by regional tectonics although the origin of the destabilization of the system may be related to the reactivation of a shallow magma chamber

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

modelling the low frequency electrical properties of pyrite bearing reservoir sandstones abstract marine controlled source electromagnetic sounding has developed rapidly in recent years to complement conventional seismic method for better discrimination of pore fluid to obtain quantitative and reliable interpretation of the csem data a robust rock physics model is vital to link the bulk rock electrical conductivity to the electrical properties and microstructure of the rock constituents especially when some of the constituents exhibit extreme electrical behaviours e g pyrite a common mineral associated with reservoir rocks based on the multi phase incremental model validated on published experimentally measured electrical conductivity of pyrite bearing sandstones the effects of key parameters i e pyrite content porosity pyrite conductivity grain aspect ratio and water saturation on the electrical conductivity of pyrite bearing sandstones and their corresponding csem responses were comprehensively studied the results are expected to assist in the csem data interpretation when a pyrite bearing sandstone reservoir is encountered in the future