atmospheric sulfur dioxide measurements during the 2005 and 2007 eruptions of the piton de la fournaise volcano implications for human health and environmental changes abstract piton de la fournaise is an active volcano located in the south eastern part of reunion island a tiny island found in the south western indian ocean 21 s 55 5 e this volcano erupts regularly at least once a year with notable amount of degassing concerning the volcanic eruptions the regulation of the french ministry of environment on the air quality is mainly focussed on the standards applicable for the sulfur dioxide so 2 in terms of public health and environmental changes air samples have been collected continuously every 10 days on passive diffusion tubes of so 2 an atmospheric tracer of volcanic plumes by ora observatoire reunionnais de l air at 10 sites which have been located around the volcano since september 2005 the mean so 2 concentrations measured over a 10 day period in the absence of any volcanic eruption range between very low values 1 15 g m 3 for all 10 sites however during the december 2005 eruption notable so 2 concentrations factor 5 25 have been measured at the locations situated on the north west flanks of the volcano the so 2 degassing reached concentrations of 65 379 g m 3 which is mainly caused by the volcanic activity when coupled with the local to regional atmospheric circulations land sea breezes easterlies etc a wide range of atmospheric measurements was performed in the vicinity of piton de la fournaise in order to characterize the gaseous and particle emissions during the april may 2007 eruption so 2 concentrations were also measured continuously by sf 2000 analyser at several coastal locations in the vicinity of the volcano during and off eruption activities in the absence of any volcanic eruption the so 2 concentrations showed day to day variations with hourly mean concentrations varying between 1 and 20 g m 3 these values correspond to the background concentrations for this coastal rural location and might as well come in part from non volcanic origin the so 2 concentrations however were increased by a factor 10 30 with a maximum hourly mean concentration of 2486 g m 3 during the april may 2007 eruption hereby several statutory thresholds were exceeded particularly at the tremblet location indeed the information and recommendation threshold 350 g m 3 h as well as the alert threshold 500 g m 3 on 3 h consecutively were exceeded 32 and 5 times respectively at this site these measurements point out that during the times of eruptions with significant amounts of degassing the threshold values for protecting the ecosystems and the air quality for human health were exceeded at several inhabited locations with implications for human health and environmental changes on local to regional scale

observational evidence for westward propagation of temperature inversions in the southeastern arabian sea 1 a warm pool forms in the southeastern arabian sea seas prior to the onset of the summer monsoon over india in early june the core of this warm pool is in the lakshadweep sea ls xbt and surface salinity data collected in the ls during may 2002 april 2003 show that temperature inversions occur off the southwest coast of india in early december with the arrival of low salinity waters from the bay of bengal the low salinity waters and the inversions propagate westward along with the downwelling rossby waves that constitute the lakshadweep sea level high inversions occur in the western ls 73 e about 40 days after they occur near the coast in the eastern ls 75 5 e they disappear in april when the tropical convergence zone moves over the seas and the warm pool engulfs the region ocean dynamics and air sea fluxes are together responsible for the formation and westward propagation of the inversions

role of narrow mountains in large scale organization of asian monsoon convection abstract the asian summer monsoon is organized into distinct convection centers but the mechanism for this organization is not well understood analysis of new satellite observations reveals that narrow mountain ranges are an important organizing agent anchoring monsoon convection centers on the windward side the bay of bengal convection in particular features the heaviest precipitation on its eastern coast because of orographic lifting as the southwest monsoon impinges on the coastal mountains of myanmar also known as burma this is in contrast to the widely held view that this convection is centered over the open ocean as implied by coarse resolution datasets a view that would require an entirely different explanation for its formation narrow in width and modest in height 1 km these mountains are hardly mentioned in conceptual depictions of the large scale monsoon and poorly represented in global climate models the numerical simulations of this study show that orographic rainbands are not a

time dependent spatial amplitude patterns of harmonic tremor at arenal volcano costa rica seismic wave interferences seismograms recorded at the receivers of a small aperture seismic array usually display very similar waveforms and amplitudes as a consequence of their close proximity during the analysis of the volcanic tremor wave field at arenal volcano costa rica we detected significant differences in the amplitudes of harmonic tremor recorded at the stations of a small aperture 210 m seismic array the amplitude distributions are geometrically complex and characterized by strong gradients they occur just for harmonic tremors any other type of seismic event produces nearly uniform amplitudes across the array this suggests some relation with harmonic frequency content moreover the spatial amplitude patterns change with time some of these observations could be explained by an extreme combination of source path and site effects but they also could be produced by interference of different components of the seismic wave field we use numerical calculations to investigate the amplitude pattern generated by two interfering plane waves and are able to reproduce the main features of the observed amplitude patterns we propose mechanisms that might generate seismic wave fields with multiple components and conclude that interference can explain the complexity and variability of the harmonic tremor wave field at arenal volcano online material wave field animation

the relation between site amplification factor and surficial geology in central california abstract site amplification factors at frequencies of 1 5 3 6 and 12 hz were determined for 132 stations of the usgs seismic network in central california from coda waves of 185 local earthquakes in this area using a recursive stochastic inversion method we found that the site amplification at a station is systematically related to the geology underlying that station the site amplification is high for young quaternary sediments and decreases with increasing geologic age at all frequencies between 1 5 and 12 hz the rate of decrease varies with frequency where site amplification at low frequencies shows a faster rate of decrease with age than at higher frequencies to quantify the relation between site amplification factor and site geology the surface geology of station sites was classified into five groups namely 1 quaternary sediments 2 pliocene sediments 3 miocene through cretaceous sediments 4 franciscan formation and mesozoic granitic rocks and 5 pre cretaceous metamorphic rocks the station site amplification factors for each group were logarithmically averaged and the mean value was assigned to the median geologic age of that group a smooth power law relation was found between the mean site amplification and the median geologic age this relation provides a simple way of estimating site effect at a specific site with known surficial geology our site amplification factors were compared with magnitude station residuals determined by eaton 1990 for the same network a remarkable linear correlation was found between the logarithmic coda amplification factor and the magnitude station residual value confirming that the coda method provides an effective means of estimating site amplification factor comparison of our site amplification factor with strong motion results obtained from the loma prieta earthquake boore et al 1989 maley et al 1989 shakal et al 1989 chin and aki 1991 suggests that weak and strong motion site amplification factors correlate well in the region outside the epicentral source region beyond epicentral distances of about 50 km within the epicentral source region however the weak motion amplification factors estimated from coda waves do not agree with the observed for strong ground motion suggesting a nonlinear behavior at sediment sites these results together with studies on the correlation between weak motion site amplification and earthquake intensity borcherdt 1970 borcherdt and gibbs 1976 chavez garcia et al 1990 king et al 1990 demonstrate the importance of in situ determination of weak motion site amplification for seismic zonation

formation and spreading of arabian sea high salinity water mass the formation and seasonal spreading of the arabian sea high salinity water ashsw mass were studied based on the monthly mean climatology of temperature and salinity in the arabian sea north of the equator and west of 80 e on a 2 2 grid the ashsw forms in the northern arabian sea during winter and spreads southward along a 24 sigma t surface against the prevailing weak zonal currents the eastern extent of the core is limited by the strong northward coastal current flowing along the west coast of india during the southwest monsoon the northern part of the core shoals under the influence of the findlater jet while the southern part deepens throughout the year the southward extent of the ashsw is inhibited by the equatorial currents the atmospheric forcing that leads to the formation of ashsw was delineated using the monthly mean climatology of heat and freshwater fluxes monsoon winds dominate all the flux fields during summer june september while latent heat release during the relative calm of the winter november february monsoon driven by cool dry continental air from the north results in an increased density of the surface layer thus excess evaporation over precipitation and turbulent heat loss exceeding the radiative heat gain cool the surface waters of the northern arabian sea during winter and drive convective formation of ashsw

hybrid collapse mechanism at piton de la fournaise volcano reunion island indian ocean 1 recent studies have shown that hydrothermal alteration in the core of volcanoes may weaken the edifice and trigger sector collapse lopez and williams 1993 day 1996 voight and elsworth 1997 van wyk de vries et al 2000 reid et al 2001 alteration of volcanic products must take place over long periods of times before collapse can occur so this process is considered to be less frequent than volcanic failure generated by magmatic intrusion and flank spreading however acceleration of this slow process may occur along one direction as a result of a weak lateral confinement following outward gravitational sliding of a flank of the volcano we present here evidence that the enclos fouque depression of piton de la fournaise volcano results from such a hybrid mechanism seaward sliding of the grand brule trough on top of an ancient hypovolcanic complex led to a lateral unconfined boundary along which collapse of the altered core of the edifice took place the result is a caldera like structure breached on the grand brule slide scaled experiments to simulate this process of pseudocaldera formation reveal tectonic features remarkably similar to those encountered in the field and demonstrate the mechanical consistency of the model similar processes may have played a role in the evolution of other volcanoes

source mechanism of a large scale gas outburst at sunagawa coal mine in japan on january 29th 1986 the third largest gas outburst in japan took place at sunagawa coal mine which is the only hydraulic mine in japan it occurred at a face of a cross cut just after a coal seam was outcropped by blasting for drivage of the cross cut the site of the gas outburst was located 1 180 m below the surface no workers were injured but the cross cut was plugged with 1 600 m3 of coal fragments extending over 100 m behind the face and 60 000 m3 of methane gas was emitted

the off shore continuation of an active basaltic volcano piton de la fournaise reunion island indian ocean structural and geomorphological interpretation from sea beam mapping abstract in 1984 a sea beam survey of the submarine east flank of piton de la fournaise was performed with r v jean charcot three main types of volcanic or volcano tectonic features have been identified 1 1 the subaerial ne and se volcanic rift zones of piton de la fournaise do not extend more than about five kilometers offshore unlike typical hawaiian rift zones which form narrow 2 4 km ridges extending tens of kilometers from the summit the active rift zones of piton de la fournaise widen downslope attaining more than 10 km at their front 2 2 the submarine extension of the grand brule slide is larger than the subaerial portion the entire slide forms a 7 24 km scar bounded by two ramparts to the north and south the slumped material may have moved as a debris flow forming a large talus downslope of the slide however the submarine counterpart of the south area of the grand brule seems to be composed by a slumped block whose structure is apparently not disturbed 3 3 another prominent feature is a conspicuous topographic high that occupies nearly all the center of the surveyed zone this cast flank submarine plateau cannot be associated with any active structure of piton de la fournaise its surface generally dips gently 2 3 and its northern and southern flanks are extensively cut by landslides cones of variable dimensions are observed on the plateau and farther to the east three hypotheses are examined to account for the origin of this morphology a remnant flank of an ancestral fournaise volcano associated with a large buried intrusion found by drilling beneath the grand brule b distinct volcanic massif or c material of a huge and ancient landslide the geophysical data show that the western part of this submarine plateau is reversely magnetized and associated with a moderate positive gravity anomaly this confirms that as suggested by the bathymetric analysis this part of the plateau is relatively coherent conversely the eastern portion of the plateau appears to be poorly magnetized and composed of low density material probably chaotic materials derived from landslides the reversed magnetization of the western part shows that the whole structure is older than 0 7 ma these results show that the volcanic history of piton de la fournaise is more complex than previously thought

impact of remote equatorial winds and local mesoscale eddies on the existence of river in the sea along the east coast of india inferred from satellite smap

location of tremor sources and estimation of lava output using tremor source amplitude on the piton de la fournaise volcano 2 estimation of lava output abstract we propose several relations for estimating the amounts of lava emitted during eruptions of the piton de la fournaise volcano based on the use of tremor source amplitude sources for eruption tremor are located in several frequency bands with a location method based on the use of seismic amplitudes corrected for recording site effects sources are usually found at shallow depth and close to the eruptive vents suggesting that tremor is directly generated by the eruptive activity simultaneously with the location of the tremor sources our program gives the source amplitude of the phenomenon we assume a linear or a quadratic relation between the lava output and the tremor source amplitude both relations are calibrated using data for the march 1998 eruption and tested using the volumes emitted during the july and september 1999 and february 2000 eruptions we found that the 5 10 hz frequency band gives lava output much higher than for lower frequencies suggesting that for that band the tremor generation depends on the eruption site in addition to the lava output or that tremor at those frequencies is not directly caused by the outflow of lava but maybe rather by gas the best estimations are obtained using the quadratic relation for frequencies below 5 hz with an agreement better than 15 with the field observations for the july and september 1999 eruptions and 30 for the february 2000 eruption our results show that the cumulative amplitude of tremor recorded during eruptions of the piton de la fournaise is directly related to the amounts of lava erupted

inferred attenuation from site effect corrected t phases recorded on the island of hawaii coda site amplification factors are used to eliminate the site effect from records of three circum pacifict phases recorded by the hawaiian volcano observatory hvo network on the island of hawaii observedt phase amplitudes across the island generally decrease with increasing distance from the conversion point where acoustic waves in the sofar channel become seismic waves propagating through the crust however the decay of the observedt phase signal across the island is not regular in regions of dense station coverage in particular the kilauea caldera region we divide the maximum observedt phase amplitudes at a given station by the coda site amplification factor obtained for the same station and frequency band 3 0hz the distribution of these amplitudes reveals a smooth pattern over the entire island the distance over which the site effect correctedt phase amplitude decreases by one half combined with the apparent velocity of propagation oft phases across the island allows for an approximate determination of near surfaceq over much of the island of hawaii we found a region of lowq in the kilauea summit area q 30 and east rift zone q 60 with considerably higherq in the kaoiki and northern portions of the island q 150 to 200 the lowq values obtained in the kilauea summit region and east rift zone are significantly lower than estimates of codaq in the same region suggestingt phases may be sampling the earth s near surface properties

dynamic dyke propagation deduced from tilt variations preceding the march 9 1998 eruption of the piton de la fournaise volcano during the hour preceding the march 9 1998 eruption of the piton de la fournaise volcano the deformation network of the observatory recorded some large deformations in the summit area a broadband seismic station of the geoscope global network rer is located about 8 km away from the summit of the volcano signals from that station may be interpreted as tilt changes the combination of the above two kinds of signals allows by using a tensile fault model to constrain the geometry as well as some characteristics volume propagation velocity of the dyke that intruded the summit area during the hour preceding the beginning of eruptive activity

a temporal change in coda wave attenuation observed during an eruption of mount st helens during the past few years there have been numerous reports of changes in coda wave attenuation occurring before major earthquakes these observations are important because they may provide insight into stress related structural changes taking place in the focal region prior to the occurrence of large earthquakes the results of these studies led us to suspect that temporal changes in coda wave attenuation might also accompany volcanic eruptions by measuring power decay envelopes for earthquakes at mount st helens recorded before during and after an eruption that took place during september 3 6 1981 we found that coda q sup 1 for frequencies between 6 and 30 hz was 20 30 higher before the eruption than after the change is attributed to an increase in the density of open microcracks in the rock associated with inflation of the volcano prior to the eruption q sup 1 was found to be only weakly dependent on frequency and displayed a slight peak near 10 hz the weak frequency dependence is attributed to the dominance of intrinsic attenuation over scattering attenuation since it is generally accepted that intrinsic attenuation is constant with frequency whereas scattering attenuation decreases strongly at higher frequencies the weak frequency dependence of q sup 1 more at mount st helens contrasts with results reported for studies in nonvolcanic regions the peak in q sup 1 near 10 hz at mount st helens is attributed to the scale length of heterogeneity responsible for generating backscattered waves results for nonvolcanic regions have shown this peak to occur near 0 5 hz thus a smaller scale length of heterogeneity is required to explain the 10 hz peak at mount st helens copyright american geophysical union 1988 less

source and propagation effects on near field co eruptive ground motion at santiaguito volcano guatemala abstract data from a december 2008 january 2009 seismometer deployment show substantial variation in seismic signal characteristics among different sites and eruptive events at santiaguito volcano a station on one of the inactive domes typically records higher amplitudes and a more peaked spectrum than does another station closer to the vent on lower ground amplitude ratios between the stations and spectral peakedness of the station on the dome vary substantially and depend on vertical signal polarity which is controlled by seismic source mechanism finite difference models considering two likely source mechanisms and several hypothetical subsurfaces show that the topography of the free surface and subsurface units can increase or decrease amplitudes by focusing or obstructing body waves a homogeneous velocity structure is shown not to be a close approximation to the actual shallow subsurface while a subsurface including a dipping reflective layer produces results that fit observations better these models also indicate that path effects act more strongly on waves originating from an implosion than from a downward force possibly due to differences in body and surface wave proportions and differing susceptibilities of body and surface waves to these path effects thus recorded data and models both indicate that the level of wave field distortion associated with propagation effects is controlled by the source mechanism

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

location of long period events below kilauea volcano using seismic amplitudes and accurate relative relocation 1 we present methods for improving the location of long period lp events deep and shallow recorded below kilauea volcano by the permanent seismic network lp events might be of particular interest to understanding eruptive processes as their source mechanism is assumed to directly involve fluid transport however it is usually difficult or impossible to locate their source using traditional arrival time methods because of emergent wave arrivals at kilauea similar lp waveform signatures suggest the existence of lp multiplets the waveform similarity suggests spatially close sources while catalog solutions using arrival time estimates are widely scattered beneath kilauea s summit caldera in order to improve estimates of absolute lp location we use the distribution of seismic amplitudes corrected for station site effects the decay of the amplitude as a function of hypocentral distance is used for inferring lp location in a second stage we use the similarity of the events to calculate their relative positions the analysis of the entire lp seismicity recorded between january 1997 and december 1999 suggests that a very large part of the lp event population both deep and shallow is generated by a small number of compact sources deep events are systematically composed of a weak high frequency onset followed by a low frequency wave train aligning the low frequency wave trains does not lead to aligning the onsets indicating the two parts of the signal are dissociated this observation favors an interpretation in terms of triggering and resonance of a magmatic conduit instead of defining fault planes the precise relocation of similar lp events based on the alignment of the high energy low frequency wave trains defines limited size volumes

magma reservoir systems inferred from tilt patterns inflation patterns based on water tube tiltmeter and levelling observation show different features for krafla volcano in iceland and kilauea volcano in hawaii monotonous sawtooth shape inflation is observed at krafla while inflation curves at kileauea are more or less complicated the difference was attributed to differences in the system of magma reservoir for the two volcanoes by using the electrical equivalent of a magma reservoir and volcanic conduit as a capacitor and a resistor an electrical oseillator was considered to be a possible model for a magma reservoir system in the case of krafla the magma reservoir system is replaced with one electric oscillator called single system or icelandic type system

site amplification of coda waves from local earthquakes in central california the goals of this study are two fold 1 to examine the site effect of coda waves believed to be the average site effect of shear waves in order to understand its spatial and frequency dependent behavior and 2 to learn what we can about the processes that generate the coda itself we use digital data from over 90 earthquakes each recorded by a subset of some 150 stations in the coast ranges of central california between san francisco and san luis obispo results from the band 1 5 to 24 hz indicate that site amplification depends strongly on surface geology and frequency at low frequencies 1 5 to 3 0 hz changes in amplification up to a factor of 20 are observed amplification generally varies inversely with deposit age at sediment sites and is lowest at granite and franciscan basement sites at high frequencies 6 to 24 hz the pattern changes many granite sites the majority in the gabilan range exhibit increasing amplification with frequency relative to the average station this behavior differs strikingly from that observed at sediment and franciscan sites which roll off at an intermediate rate and many sediment sites adjacent to the san andreas fault zone which decay away even more rapidly with frequency these results can be explained qualitatively by appealing to variable near site impedance and attenuation however complicating phenomena such as mode excitation in valley sediments must exist at low frequencies peaked behavior at a few hard rock sites at high frequency 12 hz currently lacks explanation at a few sediment sites the low frequency excitation is so strong that the coda envelopes begin to take on different shapes this contradicts the assumption based on previous observations that the coda shape is independent of source receiver location thus some site measurements may be artificially high the working model of coda waves as body wave energy backscattered from randomly distributed inhomogeneities must be modified to include the possibility of efficient near site resonance excited by incident direct and coda wave energy

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

the upper ocean response to monsoonal forcing in the arabian sea seasonal and spatial variability abstract observations from four towed profiler surveys undertaken between december 1994 and october 1995 examine the seasonal and spatial variability of the upper ocean response to the monsoon cycle in the arabian sea although observed atmospheric forcing agrees well with modern climatologies cross basin patterns of mixed layer depth and water properties observed in 1994 1995 are not entirely consistent with an upper ocean response dominated by ekman pumping during the winter monsoon the mixed layer deepens dramatically with distance offshore surface cooling intensifies with offshore distance and a one dimensional response dominated by convective overturning could explain observed wintertime mixed layer depths except for waters associated with a filament extending offshore from the omani coast mixed layer depths and water properties show only modest cross basin contrasts during the southwest monsoon filament waters differ from surrounding mid basin waters having shallow mixed layers and water properties similar to those of waters upwelled near the omani coast in september following the southwest monsoon waters within 1000 km of the omani coast have cooled and freshened with marked changes in stratification extending well into the pycnocline estimates of ekman pumping and wind driven entrainment made using the southampton oceanographic center 1980 1995 surface flux and the levitus mixed layer climatologies indicate that during the southwest monsoon wind driven entrainment is considerably stronger than ekman pumping inshore of the windstress maximum ekman pumping partially counters wind driven entrainment while offshore the two processes act together to deepen the mixed layer as ekman pumping is too weak to counter wind driven mixed layer deepening inshore of the windstress maximum another mechanism must act to maintain the shallow mixed layers seen in our observations and in climatologies offshore advection of coastally upwelled water offers a mechanism for maintaining upper ocean stratification that is consistent with observed changes in upper ocean water properties ekman upwelling will modulate wind driven entrainment but these results indicate that the primary mechanisms acting inshore of the windstress maximum are wind driven mixing and horizontal advection

evidence for extensile crack initiation in point source time dependent moment tensor solutions abstract a time dependent moment tensor inversion technique is applied to 20 seismic events recorded ahead of an advancing tunnel excavation at the underground research laboratory url in canada the data are recorded on a 16 sensor triaxial accelerometer array and the events are chosen from a section of the tunnel such that the event sensor paths are unaffected by the presence of the tunnel factorization of the moment tensor rate functions for each event and subsequent decomposition of the subevents into isotropic and deviatoric components indicate that the events are of three types the first group shows implosional shear failure source mechanisms these are associated with the observed collapse of excavation holes drilled at the side of the tunnel and provide confidence that the method is producing realistic results the second group of events occurs in the region ahead of the face and show tensile shear failure mechanisms these are interpreted in terms of crack initiation ahead of the face and may explain why the tunnel undergoes notching and failure in the floor and roof when the modeled stresses are below the measured rock strength the third group of events shows predominant shear failure throughout their rupture history these are interpreted in terms of failure on pre existing crack surfaces this study highlights the value of using source mechanism studies of associated seismicity to understand the processes that may be taking place in environments where the stress field is complex both spatially and temporally

magma supply and storage at kilauea volcano hawaii 1956 1983 abstract shallow crustal magma reservoirs beneath the summit of kilauea volcano and within its rift zones are linked in such a way that the magma supply to each can be estimated from the rate of ground deformation at the volcano s summit our model builds on the well documented pattern of summit inflation as magma accumulates in a shallow summit reservoir followed by deflation as magma is discharged to the surface or into the rift zones magma supply to the summit reservoir is thus proportional to summit uplift and supply to the rift zones is proportional to summit subsidence the average proportionality constant is 0 33 10 6 m 3 rad this model yields minimum supply estimates because it does not account for magma which escapes detection by moving passively through the summit reservoir or directly into the rift zones calculations suggest that magma was supplied to kilauea during july 1956 april 1983 at a minimum average rate of 7 2 10 6 m3 month roughly 35 of the net supply was extruded the rest remains stored within the volcano s east rift zone 55 and southwest rift zone 10 periods of relatively rapid supply were associated with the large kapoho eruption in 1960 and the sustained mauna ulu eruptions in 1969 1971 and 1972 1974 bursts of harmonic tremor from the mantle beneath kilauea were also unusually energetic during 1968 1975 suggesting a close link between kilauea s deep magma supply region and shallow storage reservoirs it remains unclear whether pulses in magma supply from depth give rise to corresponding increases in shallow supply or if instead unloading of a delicately balanced magma transport system during large eruptions or intrusions triggers more rapid ascent from a relatively constant mantle source

seismic monitoring and modeling of an active volcano for prediction we describe seismic monitoring and modeling of an active volcano for the purpose of predicting the magma transport process in real time we selected the piton de la fournaise which has been monitored by an observatory since the early 1980s and is active with 28 eruptions from 1980 until august 1992 it erupted on march 9 1998 after an unusually long quiet period the eruption lasted until september 21 1998 before the march eruption we completed the initial construction of a model of a magma system based primarily on long period lp events and coda localization we found that lp events are associated with the lateral movement of magma to the rift zone and not with the vertical movement to the summit we also found that the source of 2 hz lp events is located below that of 1 hz lp events the coda localization is a newly discovered phenomenon that helped to locate a magma body this model was used for interpreting the incoming information from the precursory seismic crisis and the eruption tremor during the 6 months of the eruption the simultaneous monitoring and modeling of an active volcano led us to a quantitative simulation of the eruption process computing excess pressure and flow rate in a system of reservoirs connected by channels

the grand brule exploration drilling new data on the deep framework of the piton de la fournaise volcano part 1 lithostratigraphic units and volcanostructural implications abstract the sinking of a deep drill hole 3003 5 m for geothermal exploration in the eastern part of the piton de la fournaise volcano on reunion island has revealed the underlying lithostratigraphy six principal sequences have been distinguished a 0 440 m subaerial basaltic flows b 440 556 m a transitional series characterized by an alternation of subaerial basalts and submarine deposits vitric basalt and hyaloclastic breccia c 556 616 m submarine basalts lavas and hyaloclastites d 616 890 m subaerial basalts e 890 1010 m submarine basaltic deposits with abundant argillized hyaloclastites f 1010 3003 5 m a layered intrusive complex comprising 1010 1129 m sheets of gabbro injected into the lavas and hyaloclastites 1129 1920 m a zoned intrusion of olivine gabbro and dolerite 1920 3003 5 m stratified cumulate gabbro wehrlite dunite the occurrence of the first submarine deposits at 440 m 268 m below present sea level and the intercalation with them of subaerial basalts down to 890 m 728 m below present sea level tend to support a hypothesis of sliding into the sea during subsidence of the eastern flank of the fournaise massif the intrusive complex intersected from 1010 m down is regarded as a former shallow magma chamber a large positive gravimetric anomaly 40 50 mgal centered over grand brule and attributed to the intrusive complex indicates that its roof forms an ellipse 3 20 km elongated n s stratigraphic and morphological structural evidence on land and on the sea floor and the results of the mineralogical study of this very large magma chamber suggest that it belongs to an ancient edifice proto fournaise whose activity preceded the construction of the present fournaise and ended at about 0 6 ma on land the evidence for this earlier edifice is to be found in the zeolitised basalts and differentiated lavas hawaiites forming the basement to the phase 1 lava flows certain subsidence structures on the present fournaise are interpreted as resulting from settling of the proto fournaise volcano the destabilization of the east flank grand brule area of the currently active volcano and the location of the ne and se rift zones could be attributed to the same phenomenon

time lapse monitoring of rock properties with coda wave interferometry 1 the coda of seismic waves consists of that part of the signal after the directly arriving phases in a finite medium or in one that is strongly heterogeneous the coda is dominated by waves which have repeatedly sampled the medium small changes in a medium which may have no detectable influence on the first arrivals are amplified by this repeated sampling and may thus be detectable in the coda we refer to this use of multiple sampling coda waveforms as coda wave interferometry we have exploited ultrasonic coda waves to monitor time varying rock properties in a laboratory environment we have studied the dependence of velocity on uniaxial stress in berea sandstone the temperature dependence of velocity in granite and in aluminum and the change in velocity due to an increase of water saturation in sandstone there are many other possible applications of coda wave interferometry in geophysics including dam and volcano monitoring time lapse reservoir characterization earthquake relocation and stress monitoring in mining and rock physics

internal structure of piton de la fournaise volcano from seismic wave propagation and earthquake distribution abstract arrival times of seismic waves from local earthquakes are inverted for both locating the source and defining the 3 d velocity heterogeneity of piton de la fournaise the lateral heterogeneity of the 2632 m high edifice is resolved as a high velocity plug 1 5 km in diameter surrounded by a low velocity ring which may be interpreted as due to the construction of fournaise on the flank of the older volcano piton des neiges wave mode conversion detected on three component seismograms provides evidence for boundaries of contrasted velocities pre eruptive swarm earthquakes cluster in the high velocity zone under the dolomieu summit crater low strength and cohesion of the surrounding material account for the lack of seismicity for the final 1 3 km radial flow of magma to the vents in enclos fouque beneath the high velocity plug the existence of a body with low velocity for p and even for s waves is well constrained however the walls and base are poorly defined because of the lack of deep earthquakes for sampling the few earthquakes that are located in this depth region usually occur at a depth of around 1 5 km below sea level in the region of the cone this can be considered providing the upper constraint on the lower limit of the aseismic part of the low velocity body the coincidence in time of their occurrence with the swarms above sea level and the eruptions suggests magmatic activation of the low velocity aseismic volume 1 5 km below sea level under the high velocity plug of the cone further down the concentration of seismicity in two swarms between 2 and 4 km under the eastern flank does not allow the structure to be sampled effectively

stress failure and fluid flow deduced from earthquakes accompanying eruptions at piton de la fournaise volcano abstract in the present episode of eruptive activity evidence from seismicity for sustained magma inflow from depth into the edifice of piton de la fournaise is lacking pre eruptive main deformation and shallow seismicity help to identify very small volumes of magma that are in motion beneath the rim of the dolomieu summit crater and oriented along the azimuth of the future vents small magma pockets may reside in the cone above sea level or may be expelled repeatedly due to crystallisation in a small low velocity aseismic region below sea level under the high velocity central plug of the cone in which pre eruptive earthquake swarms are located in cross section the hypocentres define two steep sheets diverging from the aseismic zone at sea level towards 1 5 km above sea level or 1 km beneath the 2632 m high cone however failure induced by increased pressure in the suggested chamber does not account for the observed focal mechanisms the occurrence and timing of magma transport are attested by eruption and seismic activity may be related to magma transport focal mechanisms document strike slip not normal faulting or tensile failure vertical propagation of the edge of a feeder dike may enhance strike slip motion above the edge in a region where effective normal stress is decreased by thermally induced groundwater flow the strike slip mechanisms could also be caused by a tensile shear widening of the horizontal section of vertical conduits fournaise strike slip earthquakes occur in two orientations with p axes orthogonal between them within a single pre eruptive event earthquakes are distributed in the same volume but mechanisms switch from one to another type systematically with time indicating a reversal of stress conditions the orientations of p axes with respect to the epicentral trend suggest that in the later parts of events leading to eruptions a compression of the medium occurs after a dilation in the first part the activated zone might respond successively to the arrival and the departure of the magma on its way from the reservoir at depth to the vent radial to the cone

the november 2002 eruption at piton de la fournaise volcano la reunion island ground deformation seismicity and pit crater collapse an eruption on the eastern flank of piton de la fournaise volcano started on 16 november 2002 after 10 months of quiescence after a relatively constant level of activity during the first 13 days of the eruption lava discharge volcanic tremor and seismicity increased from 29 november to 3 december lava effusion suddenly ceased on 3 december while shallow earthquakes beneath the dolomieu summit crater were still recorded at a rate of about one per minute this unusual activity continued and increased in intensity over the next three weeks ending with the formation of a pit crater within dolomieu based on ground deformation measured by rapid static and continuous gps and an extensometer seismic data and lava effusion patterns the eruptive period is divided into five stages 1 slow summit inflation and sporadic seismicity 2 rapid summit inflation and a short seismic crisis 3 rapid flank inflation onset of summit deflation sporadic seismicity accompanied by stable effusion 4 flank inflation coupled with summit deflation intense seismicity and increased lava effusion and finally 5 little deflation intense shallow seismicity and the end of lava effusion we propose a model in which the pre intrusive inflation of stage 1 in the months preceding the eruption was caused by a magma body located near sea level the magma reservoir was the source of an intrusion rising under the summit during stage 2 in stage 3 the magma ponded at a shallow level in the edifice while the lateral injection of a radial dike reached the surface on the eastern flank of the basaltic volcano causing lava effusion pressure decrease in the magmatic plumbing system followed resulting in upward migration of a collapse front forming a subterranean column of debris by faulting and stoping this caused intense shallow seismicity increase in discharge of lava and volcanic tremor at the lateral vent in stage 4 and eventually the formation of a pit crater in stage 5

coda q before and after the eruptions of 13 november 1985 and 1 september 1989 at nevado del ruiz volcano colombia coda q 1 was calculated at nevado del ruiz volcano nrv before and after two phreatomagmatic eruptions november 1985 september 1989 and for a period of stability may 1987 using a functional form for coda derived from a single scattering model sato 1977 substantial changes were found before and after the eruptions the highest value of q 1 was found during the november 1985 eruption an intermediate value for the september 1989 eruption and the lowest value for may 1987 it seems that the changes in coda q 1 at nrv have a still unknown relationship with the volume or magnitude of the eruption a relatively strong frequency dependence was found for all periods also q 1 clearly changed with time suggesting that the scattering was strong for the eruption of november 1985 and decreased for the eruption of september 1989 and that the intrinsic absorption probably increased this suggests the possibility that crystallization is taking place in the nrv magma the clear change of coda q 1 before and after the eruptions at nrv also suggests the possibility that coda q 1 is a premonitory tool of activity at this volcano

growth and persistence of hawaiian volcanic rift zones hawaiian volcanic rift zones are modeled by representing the rifts and adjacent volcano flanks as long ridges with the geometry of flattened triangular prisms the intrusion of dikes along the axis of a rift requires a mechanism to generate the appropriate dike trapping stress field within the prism possible factors that affect the state of stress in the prism include multiple dike intrusion along the ridge axis faulting and gravitational sagging of the topography in extreme models with very steep slopes and high poisson s ratio corresponding to the gelatin models of rift zones by fiske and jackson 1972 results of finite element calculations indicate that gravity induced stresses are sufficient to trap a dike into propagating within the prism and parallel to the rift zone as proposed by fiske and jackson however the mechanism does not work for gently sloping flanks or a more acceptable poisson s ratio of about 0 25 additionally trapping stresses in the gravity loading and density stratification models will not persist after a few dike injection episodes therefore in mature hawaiian rift zones with possibly thousands of dikes additional processes must act to control the stresses that permit continued dike intrusion and rift persistence it is proposed that accommodation to dike emplacement occurs by slip on deep faults possibly of the type proposed for the 1975 kalapana hawaii earthquake as suggested by others for this earthquake the faults could coincide with the contact of the volcano with the seafloor within the weak seafloor sediments such faulting not only provides a means for the flanks to adjust continuously to intrusions but also generates the stress patterns needed to constrain future dikes to propagate along the rift axis other possible faulting mechanisms such as shallow gravity slides and normal faulting of the flanks do not appear to favor rift zone persistence in this model the horizontal stress generated by a standing column of magma at the time of dike emplacement the stresses in the ridges and the fault strength are coupled this results in a feedback between the maximum height that magma can rise along the rift fault friction and fault width through this feedback the slope of the volcano flank is controlled by the fault friction when applied to kilauea volcano the model yields an estimate for the coefficient of fault friction as high as 0 39 assuming normal hydrostatic pore fluid pressure an implication of this model supported by other studies is that rift intrusion and lateral spreading could be major contributors to volcano growth

dendritic crystallization a single process for all the textures of olivine in basalts the olivine macrocrysts found in oceanites picrites and magnesian basalts erupted at hotspot volcanoes are generally interpreted either as phenocrysts crystallized from the magma or as xenocrysts extracted from a deforming cumulate to constrain the origin of these crystals we studied their texture and composition at piton de la fournaise volcano la reunion we show that macrocrysts are organized and subdivided into parallel units this suggests a crystallization by dendritic growth and ripening rather than by a complex combination of paired nucleation crystal aggregation or synneusis dendritic growth is also evidenced by the occurrence of hollow faces p rich zones melt and cr spinel inclusions formed from the accumulation of slow diffusing impurities p cr al in the liquid at the contact with rapid growing olivine we suggest that early dendritic crystallization may even cause branch misorientations and lattice mismatches yielding subgrain boundaries dislocation lamellae and to a certain extent undulose extinction which have all been formerly interpreted in terms of plastic intracrystalline deformation we interpret olivine macrocrysts as phenocrysts crystallized under a strong degree of undercooling t 60 c and derived from a harrisitic mush formed on the cold walls of the magma reservoir given the growth shapes indicated by p zoning patterns and external faces the olivine macrocrysts which consist of groups of several subcrystals have grown in suspension within the liquid and were neither aggregated into a dense cumulate nor corroded shocked or deformed before or during their transport to the surface the major consequence of our study is that most olivine macrocrysts are not xenocrysts and very few of them if any have experienced intracrystalline deformation the importance of deforming creeping cumulate bodies thought to accommodate the spreading of basaltic volcanoes in la reunion and hawaii may hence have been overestimated

percolation conditions in binary fractal fracture networks applications to rock fractures and active and seismogenic faults 1 the fracture network patterns in crystalline rock are treated using a binary fractal model described by three fractal geometric parameters the fractal dimension d of the spatial distribution of fractures the fractal dimension a of the fracture length distribution and the maximum fracture length lmax normalized by the domain length l lmax l we present a percolation threshold relationship describing the boundary between percolating and nonpercolating conditions in random binary fractal fracture networks rbffns and apply this to observations of natural fractures our results indicate that the three fractal parameters identified indeed control the connectivity of fracture networks and hence the migration of fluids through rock fractures and active and seismogenic faults moreover our numerical approach may be applied in the future to investigating fluid migration associated with seismicity based on fractal parameters determined from earthquake catalog data

30 years in the life of an active submarine volcano a time lapse bathymetry study of the kick em jenny volcano lesser antilles effective monitoring is an essential part of identifying and mitigating volcanic hazards in the submarine environment this is more difficult than onshore because observations are typically limited to land based seismic networks and infrequent shipboard surveys since the first recorded eruption in 1939 the kick em jenny kej volcano located 8km off northern grenada has been the source of 13 episodes of t phase signals these distinctive seismic signals often coincident with heightened body wave seismicity are interpreted as extrusive eruptions they have occurred with a recurrence interval of around a decade yet direct confirmation of volcanism has been rare by conducting new bathymetric surveys in 2016 and 2017 and reprocessing 4 legacy datasets spanning 30 years we present a clearer picture of the development of kej through time processed grids with a cell size of 5m and vertical precision on the order of 1 4m allow us to correlate t phase episodes with morphological changes at the volcano s edifice in the time period of observation 7 09x106 m3 of material has been added through constructive volcanism yet 5 times this amount has been lost through landslides limited recent magma production suggests that kej may be susceptible to larger eruptions with longer repeat times than have occurred during the study interval behavior more similar to sub aerial volcanism in the arc than previously thought t phase signals at kej have a varied origin and are unlikely to be solely the result of extrusive submarine eruptions our results confirm the value of repeat swath bathymetry surveys in assessing submarine volcanic hazards

a comparison of methods to estimate seismic phase delays numerical examples for coda wave interferometry time shift estimation between arrivals in two seismic traces before and after a velocity perturbation is a crucial step in many seismic methods the accuracy of the estimated velocity perturbation location and amplitude depend on this time shift windowed cross correlation and trace stretching are two techniques commonly used to estimate local time shifts in seismic signals in the work presented here we implement dynamic time warping dtw to estimate the warping function a vector of local time shifts that globally minimizes the misfit between two seismic traces we compare all three methods using acoustic numerical experiments we show that dtw is comparable to or better than the other two methods when the velocity perturbation is homogeneous and the signal to noise ratio is high when the signal to noise ratio is low we find that dtw and windowed cross correlation are more accurate than the stretching method finally we show that the dtw algorithm has good time resolution when identifying small differences in the seismic traces for a model with an isolated velocity perturbation these results impact current methods that utilize not only time shifts between multiply scattered waves but also amplitude and decoherence measurements

a constant influx model for dike propagation implications for magma reservoir dynamics 1 most observations of seismicity rate during dike propagation on basaltic volcanoes show 1 rate stationarity despite possible variations of the dike tip velocity 2 frequent lack of clear and monotonic hypocenter migration following dike propagation and 3 event occurrences located backward with respect to the dike tip position on these bases the origin of the seismicity contemporary to dike intrusion within basaltic volcanoes cannot be solely related to the crack tip propagation seismicity rather appears to be the response of the edifice itself to the volumetric deformation induced by the magma intruding the solid matrix the volume change induced into the volcano edifice over time by the intruding magma is equal to the magma flux injected into the dike from the reservoir the consequence of this is that the stationary seismicity rate observed during the intrusion is a proxy for the magma flux withdrawn from the reservoir we consider a two phase dike propagation model including a first vertical propagation followed by a lateral migration along a lithological discontinuity we explore 1 under which geophysical conditions the vertical dike is fed at constant flow rate of magma and 2 dike propagation patterns implications entailed by constant volumetric flux on the piton de la fournaise volcano case study suggest a minimum size for the magma reservoir of about 1 km3 and a maximum value for the initial magma reservoir overpressure of about 2 2 mpa considering similar magma inflow rates during vertical and lateral dike propagation phases we reproduce independent estimates of propagation velocities rise times and injected volumes when applying the model to the august 2003 piton de la fournaise eruption

site amplification from coda waves validation and application to s wave site response abstract the subject of this article is to see if the response to s waves at a specific site can be determined from coda waves we used aftershock records of the 1992 landers and big bear earthquakes observed at four terrascope stations pas pfo svd and gsc in southern california the wide dynamic range of the terrascope instrument provided a broadband seismogram for s waves and at the same time coda waves over a long lapse time window we analyzed a total of 708 three component waveforms from 65 events whose magnitudes ranged from 3 3 to 5 4 the station svd is located on quaternary alluvium and the remaining stations are on rocks of cretaceous age we first evaluated the coda site amplification factor using a spectral ratio method may eda et al 1991 koyanagi et al 1992 for frequency bands centered at 0 75 1 0 1 5 2 0 3 0 4 0 and 6 0 hz for lapse time windows after 70 sec from the origin time we found that the site amplification factor for the radial component is similar to that for the transverse component this similarity was expected because codas consist of backscattered waves coming from all directions into the station resulting in a directionally averaged site response we then evaluated the s wave site amplification factor using an inversion method andrews 1986 on the direct s wave portion of the same data set we found that the coda site response agrees with the s wave site response within a factor of about 1 5 supporting the earlier findings by tsujiura 1978 and justifying the use of coda waves in determining site specific amplification for s waves this agreement between s wave site response and coda site response is understandable if we assume that coda waves are dominated by s waves as theoretically predicted by aki 1992 and zeng 1993

flexure and seismicity beneath the south flank of kilauea volcano and tectonic implications we present a refined model for the tectonic behavior of kilauea volcano s south flank including flexure calculations and microearthquake data supportive of the model in our model the south flank moves seaward over the downwardly flexed ocean crust in a manner analogous to an accretionary prism in a subduction zone the flank is driven seaward by the gravitational stresses inherent in its shape this driving force is augmented by high density material in kilauea s rift zones elastic flexure calculations predict a configuration for the downwardly flexed crust which agrees with previous seismic refraction and gravity modeling this configuration in turn is consistent with the hypothesis that many earthquakes occur along the volcanic pile ocean crust interface focal mechanisms for these events predominantly indicate southeastward directed overthrusting we also propose a relationship between rift zone intrusion and south flank displacement including a suggestion that the decollement configuration controls the relative activity of kilauea s east and southwest rift zones

formation mechanisms of temperature inversions in the southeastern arabian sea numerical simulations using a high resolution 0 25 0 0 25 0 40 levels ogcm of the indian ocean are used to study the formation mechanisms of temperature inversions ti in the southeastern arabian sea seas during winter to the west and south of india haline stratification is a necessary pre requisite for ti formation off the southern tip of india low salinity water advected from the bay of bengal is cooled by strong winds and leads to ti formation in the southern part of the seas advection of this cooler low salinity water over warm salty seas water leads to the formation of ti and occur at a deeper depth sim 80 m due to the downwelling within the lakshadweep high in the northern part ti occur at a much shallower depth sim 20 m and are caused by shortwave radiation penetrating below the mixed layer of about 12 m

arabian sea and bay of bengal exchange of salt and tracers in an ocean model exchanges of mass and salt between the mixed layers in the arabian sea and the bay of bengal are examined in a model of the indian ocean using passive tracers as a tool to map the pathways inflow of high salinity water from the arabian sea into the bay of bengal is significant and occurs after the mature phase of the southwest monsoon freshwater transport out of the bay of bengal is southward throughout the year along the eastern boundary of the indian ocean low salinity water transport into the arabian sea occurs in the somali current during the southwest monsoon closing a clockwise path of water mass transport only a small fraction of low salinity water is advected into the eastern arabian sea from the bay of bengal

multiscale matched field processing for noise source localization in exploration geophysics abstractin the study we investigate the use of ambient noise data to locate microseismic sources at the exploration scale we develop a multiscale matched field processing mfp approach to localize seismic sources at frequencies below 10 hz an application to an actual data set acquired over a hydrocarbon field is presented to determine the reliability of the mfp procedure the data used were continuously recorded over five days at a total of 397 stations on a 1 km per side square seismic network the mfp results show 1 a dominant and stable surface source associated with human activities road and exploration platforms around the reservoir and 2 weaker sources at depth below the seismic network that are related to the injection extraction process

long period seismicity at shishaldin volcano alaska in 2003 2004 indications of an upward migration of the source before a minor eruption abstract we have analyzed the long period lp seismic activity at shishaldin volcano aleutians islands alaska in the period october 2003 july 2004 during which a minor eruption took place in may 2004 with ash and steam emissions thermal anomalies volcanic tremor and small explosions we have focused the attention on the time evolution of lp rate size spectra and polarization dip angle along the dataset we find an evolution toward more shallow dip angles in the polarization of the waveforms during the sequence the dip angle is a manifestation of the source location because the lp seismic sources are presumed to reflect the aggregation of gas slug or pockets within the melt we use the polarization dip at the lp onset as a proxy for the nucleation depth of the seismic events within the conduit we refer to this parameter as the nucleation dip and the position along the conduit of the gas aggregation as nucleation depth the nucleation dip changes throughout the dataset it shows a sharp decrease between the end of december 2003 and the end of january 2004 followed by a gradual increase until the onset of the eruption at the same time a general increase of the lp rate occurs we have associated the dip evolution with a sinking and a subsequent decrease of the nucleation depth which would quickly migrate up to about 8 km below the crater rim followed by a slow depth decrease which culminates in the eruption the change in the nucleation depth reflects either a pressure variation within the plumbing system which would affect the confining pressure experienced by the gas aggregations we have imputed such a pressure change to the intrusion of batches of magma from a deeper magma chamber 5 km for a cylindric conduit with rigid walls this leads to a volume of the injected new magma of 10 5 10 7 m 3 compatible with estimates in other areas suggesting that the lp process can be considered a good proxy of the thermodynamical conditions of the shallow plumbing system

episodes of pit crater collapse documented by seismology at piton de la fournaise calderas are oval fault bounded depressions in volcanic regions the formation of a small analog a summit pit crater has followed a ten month cycle of eruptive activity at piton de la fournaise volcano reunion island indian ocean in 1985 six short episodes of summit seismic activity with shocks indicating shear failures have been followed by eruptions in five cases the eruptions occurred near the base of the summit cone which is at 2 5 km elevation inside the enclos fouque an ancient caldera 7 km in diameter in another instance the summit seismic crisis did not evolve to an eruption but was followed by a seismic crisis 4 km deeper in march 1986 low level activity both at shallow depth beneath the summit and around 4 km depth to the southeast a simultaneous occurrence not previously observed culminated by a summital swarm on march 18 activity resumed its low level and five hours later a small and short lived eruption occurred at mid distance between the summit and the rim of enclos fouque one day later a flank eruption began at 1000 m elevation outside of the enclos 9 km southeast of the summit four days later effusion began near sea level 14 km southeast of the summit the shift of activity from the vent inside to that outside the enclos occurred whilst both shallow summital and deeper flank seismicity were sustained but without notable shallow activity between one vent and the next then the seismic activity which in all five previous instances stopped when the vents opened persisted for ten days increasing in energy release rate activity only consisted of shallow shocks in the summit area whilst eruption was low on the flank 9 km then 14 km away the focal mechanisms are different from all those previously determined they correspond neither to shear failure nor tensile fracturing by fluid overpressure they suggest cracking due to volume increase in a low fluid flow environment which may be consistent with the simultaneous tapping of magma deeper in the edifice a final paroxysmal seismic crisis lasting one and a half days led to the collapse of a 200 m diameter 80 m deep pit crater inside the dolomieu summital caldera on march 29 this crisis released an order of magnitude more energy than previous activity the long period signature of these seismic events indicates low stress drop with respect to source dimensions sources are shallow however rather than directly marking the progressive development of a depression at the surface they appear to correspond to fractures opening above the retreating magma and progressive stoping of a cavity similarities with seismic observations during the last phase of the fernandina galapagos 8 km2 caldera collapse of june 1968 suggest that the same kind of mechanical behaviour occurred with a scaling of three orders of magnitude in seismic moments and in volumes of collapsed blocks between the two cases

investigating the source characteristics of long period lp seismic events recorded on piton de la fournaise volcano la reunion abstract magmatic and hydrothermal processes play a significant role in generating seismicity at active volcanoes these signals can be recorded at the surface and can be used to obtain an insight into the volcano s internal dynamics long period lp events are of particular interest as they often accompany or precede volcanic eruptions but they are still not well understood piton de la fournaise volcano la reunion island is one of the most active volcanoes in the world however lp events are rarely recorded there a seismic network of 20 broadband seismometers has been operational on piton de la fournaise volcano since november 2009 between november 2009 and january 2011 the volcano erupted five times but only 15 lp events were recorded three of these eruptions were preceded by lp events and several lp events were recorded during an intrusive phase a family of three repeating lp events exists within the dataset in order to characterize these events we locate and perform moment tensor inversion on the lp family the lp events are located within the summit crater at shallow depths

evidence from geoid data of a hotspot origin for the southern mascarene plateau and mascarene islands indian ocean a high resolution geoid map of the madagascar and mascarene basins is constructed from geos 3 and seasat satellite altimetric data with an accuracy of 0 7 m large positive anomalies are due to topographic highs and their regional compensation the deflection of the lithosphere under volcanic loads and its effect on the geoid are modeled for the southern mascarene plateau mauritius reunion and rodriguez islands assuming a purely elastic lithospheric model the effective flexural rigidity is estimated for the four zones rigidity varies from 1 10 21 to 2 10 23 n m increasing from north to south the highest rigidity occurs under reunion island and suggests a recent origin for the volcanism 3 5 ma the southern mascarene plateau shows the lowest rigidity suggesting a near ridge origin rodriguez island shows the same trend but in another tectonic framework the topographic and geoid swell is studied as an effect of a thermal mantle plume using a conductive model of lithospheric heating we confirm the assumption of hotspot migration for the origin of the southern mascarene plateau and the mascarene islands

evidence for the existence of persian gulf water and red sea water in the bay of bengal the high salinity water masses that originate in the north indian ocean are arabian sea high salinity water ashsw persian gulf water pgw and red sea water rsw among them only ashsw has been shown to exist in the bay of bengal we use ctd data from recent cruises to show that pgw and rsw also exist in the bay the presence of rsw is marked by a deviation of the salinity vertical profile from a fitted curve at depths ranging from 500 to 1000 m this deviation though small of the order of similar to 0 005 psu and therefore comparable to the ctd accuracy of 0 003 psu is an order of magnitude larger than the similar to 0 0003 psu fluctuations associated with the background turbulence or instrument noise in this depth regime allowing us to infer the existence of rsw throughout the bay pgw is marked by the presence of a salinity maximum at 200 450 m in the southwestern bay pgw can be distinguished from the salinity maximum due to ashsw because of the intervening arabian sea salinity minimum this salinity minimum and the maximum associated with ashsw disappear east and north of the south central bay 85a degrees e 8a degrees n owing to mixing between the fresher surface waters that are native to the bay bay of bengal water or bbw with the high salinity ashsw hence ashsw is not seen as a distinct water mass in the northern and eastern bay and the maximum salinity over most of the bay is associated with pgw the surface water over most of the bay is therefore a mixture of ashsw and the low salinity bbw as a corollary we can also infer that the weak oxygen peak seen within the oxygen minimum zone in the bay at a depth of 250 400 m is associated with pgw the hydrographic data also show that these three high salinity water masses are advected into the bay by the summer monsoon current which is seen to be a deep current extending to 1000 m these deep currents extend into the northern bay as well providing a mechanism for spreading ashsw pgw and rsw throughout the bay

a summer monsoon pump to keep the bay of bengal salty the bay of bengal receives a large influx of freshwater from precipitation and river discharge outflow of excess freshwater and inflow of saltier water is required to prevent the bay from freshening relatively fresh water flows out of the bay along its boundaries and inflow of saltier water occurs via the summer monsoon current smc which flows eastward from the arabian sea into the bay this saltier water however slides under the lighter surface water of the bay maintaining the salt balance of the bay therefore demands upward mixing of this saltier subsurface water here we show that an efficient mechanism for this mixing is provided by upward pumping of saltier water in several bursts during the summer monsoon along the meandering path of the smc advection by currents can then take this saltier water into the rest of the basin allowing the bay to stay salty despite a large net freshwater input

eruption at le piton de la fournaise volcano on 3 february 1981 piton de la fournaise in the island of la reunion indian ocean is a young 0 35 myr old basaltic shield volcano built on the flank of the extinct piton des neiges volcano it is one of the most active volcanoes in the world magma output rate of 0 32 m3 s 1 1 2 and has been under continuous surveillance by the volcanological observatory of the institut de physique du globe de paris since august 1980 the first detailed observations on the volcano reveal a remarkably low level of background seismicity the 3 february 1981 eruption was preceded by a deep event of volcanic origin at depths of 10 15 km on 2 january 20 days of quiescence followed this event until the onset of shallow seismicity close to the eruptive centres on 22 january the eruption began after 13 days of sustained shallow seismicity and occurred in three phases over 92 days and produced about 10 106 m3 of lava

depth sensitivity of seismic coda waves to velocity perturbations in an elastic heterogeneous medium summary numerous monitoring applications make use of seismic coda waves to evaluate velocity changes in the earth this raises the question of the spatial sensitivity of coda wave based measurements here we investigate the depth sensitivity of coda waves to local velocity perturbations using 2 d numerical wavefield simulations we calculate the impulse response at the surface before and after a slight perturbation of the velocity within a thin layer at depth is introduced we perform a parametric analysis of the observed apparent relative velocity changes e obs versus the depth of the thin perturbed layer through the analysis of the decay of e obs we can discriminate two different regimes one for a shallow perturbation and the other for a deep perturbation we interpret the first regime as the footprint of the 1 d depth sensitivity of the fundamental surface wave mode to interpret the second regime we need to model the sensitivity of the multiply scattered body waves in the bulk we show that the depth sensitivity of coda waves can be modelled as a combination of bulk wave sensitivity and surface wave sensitivity the transition between these two regimes is governed by mode conversions due to scattering we indicate the importance of surface waves for the sensitivity of coda waves at shallow depths and at early times in the coda at later times bulk waves clearly dominate the depth sensitivity and offer the possibility of monitoring changes at depths below the sensitivity of the surface waves based on the transition between the two regimes we can discriminate a change that occurs at the surface from a change that occurs at depth this is illustrated for shallow depth perturbations through an example from lunar data

elastodynamic analysis for slow tectonic loading with spontaneous rupture episodes on faults with rate and state dependent friction we present an efficient and rigorous numerical procedure for calculating the elastodynamic response of a fault subjected to slow tectonic loading processes of long duration within which there are episodes of rapid earthquake failure this is done for a general class of rate and state dependent friction laws with positive direct velocity effect the algorithm allows us to treat accurately within a single computational procedure loading intervals of thousands of years and to calculate for each earthquake episode initially aseismic accelerating slip prior to dynamic rupture the rupture propagation itself rapid post seismic deformation which follows and also ongoing creep slippage throughout the loading period in velocity strengthening fault regions the methodology is presented using the two dimensional 2 d antiplane spectral formulation and can be readily extended to the 2 d in plane and 3 d spectral formulations and with certain modifications to the space time boundary integral formulations as well as to their discretized development using finite difference or finite element methods the methodology can be used to address a number of important issues such as fault operation under low overall stress interaction of dynamic rupture propagation with pore pressure development patterns of rupture propagation in events nucleated naturally as a part of a sequence the earthquake nucleation process earthquake sequences on faults with heterogeneous frictional properties and or normal stress and others the procedure is illustrated for a 2 d crustal strike slip fault model with depth variable properties for lower values of the state evolution distance of the friction law small events appear the nucleation phases of the small and large events are very similar suggesting that the size of an event is determined by the conditions on the fault segments the event is propagating into rather than by the nucleation process itself we demonstrate the importance of incorporating slow tectonic loading with elastodynamics by evaluating two simplified approaches one with the slow tectonic loading but no wave effects and the other with all dynamic effects included but much higher loading rate

seismicity and deformation induced by magma accumulation at three basaltic volcanoes we analyzed the evolution of volcano tectonic vt seismicity and deformation at three basaltic volcanoes kilauea mauna loa piton de la fournaise during phases of magma accumulation we observed that the vt earthquake activity displays an accelerating evolution at the three studied volcanoes during the time of magma accumulation at the same times deformation rates recorded at the summit of kilauea and mauna loa volcanoes were not accelerating but rather tend to decay to interpret these observations we propose a physical model describing the evolution of pressure produced by the accumulation of magma into a reservoir this variation of pressure is then used to force a simple model of damage where damage episodes are equivalent to earthquakes this model leads to an exponential increase of the vt activity and to an exponential decay of the deformation rate during accumulation phases seismicity and deformation data are well fitted by such an exponential model the time constant deduced from the exponential increase of the seismicity is in agreement with the time constant predicted by the model of magma accumulation this vt activity can thus be a direct indication of the accumulation of magma at depth and therefore can be seen as a long term precursory phenomenon at least for the three studied basaltic volcanoes unfortunately it does not allow the prediction of the onset of future eruptions as no diverging point i e critical time is present in the model

the role of salinity on the dynamics of the arabian sea mini warm pool warmer 28 c sea surface temperature sst occurs in the south eastern arabian sea seas 5 13 n 65 76 e during march april and is known as the arabian sea mini warm pool asmwp in this study we address the role of salinity and the upper layer heat and salt budgets in the formation and collapse of this asmwp an assessment of level 3 sea surface salinity sss data from the soil moisture and ocean salinity smos satellite mission for the year 2010 shows that smos is able to capture the sss variability in the seas analysis of temperature salinity and currents from the hybrid coordinate ocean model hycom during 2003 06 and in situ temperature and salinity data from argo floats during 2003 06 for the seas revealed that low salinity waters cap the top 60 m of the seas in january february this minimum salinity was concurrent with the formation of a barrier layer and with the time when the seas gained little net heat flux and the equatorward flowing east india coastal current eicc fed low saline waters into the seas subsequently the net heat flux increased to a peak value under the increased salinity stratification leading to the formation of the asmwp in march april the asmwp collapsed by may due to increase in sss and the associated weakening of the salinity stratification the monsoon onset vortex in may 2004 could be related to the minimum sss that occurred in february 2004 followed by higher sst and heat content of the asmwp in april 2004

imaging of three dimensional small scale heterogeneities in the hidaka japan region coda spectral analysis summary while large scale heterogeneities have been studied intensively by seismic tomography with traveltime data small scale heterogeneities are not fully investigated yet we obtained the 3d spatial distribution of small scale heterogeneities as relative scattering coefficients in the hidaka japan region using the spatial variation of high frequency coda power spectra we analysed 530 seismograms recorded at 62 stations for nine local earthquakes in the frequency range of 1 32 hz after correcting source station and propagation effects we assigned the spatial and temporal variations of observed power spectra of coda waves into the 3 d distribution of scattering coefficient based on single and isotropic scattering models small scale heterogeneities are distributed not only in a non uniform manner but also differently among scale lengths estimated from their frequency dependence an area of large relative scattering coefficient in 2 and 16 hz is located at a depth shallower than 45 km in the southwest of the hidaka mountains correlating well with a highly active area of microearthquakes at a depth of 60 120 km two dipping zones of large scattering coefficient are imaged beneath the summit of the hidaka mountains these zones may imply two layers of strong seismic wave reflection consistent with the upper and lower planes of the double seismic zone in the subducting pacific plate as determined by the hypocentral distribution in this region

modelling of seismic energy transport at volcanoes with real topography and complex propagation medium abstract in stratovolcanoes multiple scattering of seismic waves is caused by a strongly heterogeneous propagation medium additionally these waves are scattered by the rough topography of the volcano we devised an algorithm to model seismic energy transport in volcanoes based on a monte carlo simulation of the equation of radiative transfer this algorithm takes into account both the real topography of volcanoes which is described by a digital elevation model and the complex subsurface structure of the volcanic edifice which is treated as a random medium theoretical energy densities of two different models were compared to observed energy densities derived from seismograms of shallow volcano tectonic earthquakes that occurred at merapi volcano indonesia a model consisting of a heterogeneous volcano shaped medium over a homogeneous half space was found to be suitable to explain the observed data for merapi volcano our modelling results in a mean free path of 250 m and a thickness of 1 7 km of the scattering volcanic edifice the systematic decrease of the coda energy with source distance of the observed data referred to as coda localization can be successfully explained by our model

new geophysical insight into the dynamics of stromboli volcano italy abstract a 56 hour gravity sequence recorded in the crater area of stromboli volcano is presented data were acquired during a period of normal strombolian activity high frequency gravity anomalies up to 20 gal t tens of seconds are observed comparison with independent data reveals that these changes reflect the response of the gravimeter excited by seismic waves during strombolian explosions correlated changes in the energy distribution over time appear in the continuous wavelet transforms of gravity and rms tremor but over different scales corresponding to periods centered at about 50 and 25 min for gravity and tremor respectively we infer that the rate of fresh magma supply to the shallow feeding system controls the energy distribution over time of the coupled components in gravity and rms tremor signals in particular the gravity signal with an average amplitude of 1 2 gal could be induced by temporary accumulations at shallow depth of the volatiles discharged by quiescent degassing changes in the rate of explosions from the summit craters correlate with changes in the amplitude of the coupled gravity and volcanic tremor oscillations implying that even though the slug genesis process behind the explosions occurs at deeper levels it is also controlled by the rate of gas rich magma supply from below negative gravity anomalies of about 20 gal over intervals of some hours are also observed separated by intervals of about 24 h they could be induced by increases in magma vesicularity in the uppermost part of the conduit plexus a view supported by i changes in the time space distribution of tremor amplitudes and ii increases in spattering activity from a summit vent both occurring during the development of the negative gravity anomalies the processes behind mild strombolian explosions do not trigger measurable gravity changes nevertheless the slug ascent before a major explosion could induce a precursory gravity signal

complete gravity study of piton de la fournaise volcano reunion island abstract we present an interpretation of all available gravity data on piton de la fournaise volcano including a new set collected in the summit area using a linear programming inversion method we determine the extension of the grand brule ultramafic body drilled in 1985 and we propose to interpret it as a frozen magma chamber related to a disappeared volcano we also present evidence for superficial mass excess under the enclos fouque and plaine des sables calderas that we link to the present piton de la fournaise volcanism the detailed gravity survey of the summit area allows us to emphasize the great importance of dyke complexes associated with the ne and se rift zones and with the shallow magma chamber a negative anomaly in the summit area is interpreted as a relative minimum between the positive anomaly of grand brule and those of the western part of the enclos fouque and plaine des sables calderas

monitoring an effusive eruption at piton de la fournaise using radar and thermal infrared remote sensing data insights into the october 2010 eruption and its lava flows

partial stress drop and frictional overshoot mechanism of seismic events induced by mining the values of uniformly estimated apparent stress a and brune s stress drop taken as a measure of static stress drop from 850 seismic events with moment magnitude ranging from 3 6 to 3 6 induced at the underground research laboratory url in canada western deep levels wdl gold mine in south africa and two coal and two copper mines in poland were collected to study the stress release mode in various mining environments for this the quantity epsilon a 2 where is the static stress drop proposed by zuniga 1993 as an indicator of stress drop mechanism was used the events induced at the url are characterized by low values of epsilon corresponding to a partial stress drop mechanism whereas all the events at wdl display a frictional overshoot mechanism in which final stress reaches a lower value than that of frictional stress the events at polish coal and copper mines on the other hand are in good agreement with the well known orowan s condition such that the final stress is equal to the dynamic frictional stress the brune stress drop however is heavily model dependent through the source radius corner frequency relation the orowan s condition for the events from the url would be met if a constant in the source radius corner frequency relation is equal to 1 82 0 12 and for the events from wdl if it is equal to 3 92 0 40 in contrast to brune s constant of 2 34 the smoothed values of epsilon displayed as a function of time represented by the consecutive event numbers for selected sets of events imply that the largest seismic events in a given set occur when the epsilon is low and a partial stress drop mechanism is dominant the large events are then followed by high epsilon values when a frictional overshoot mechanism begins to dominate

anomalous character of the coda envelopes on mt vesuvius explained in terms of depth dependent q summary many observations made on volcanic areas showed that a non uniform distribution of coda wave energy is present between regions with differing geological structures this observation was carried out in la reunion and interpreted by aki and ferrazzini as due to a trapping process of the scattered waves in the volcanic cone named by these authors as coda localization the same properties were found in mt vesuvius examining codas from shots fired for active tomography in this paper we experimentally check whether the scattered wave field produced by local vt earthquakes is inhomogeneous as found for codas from shots in the same volcano we examine the log plot of s wave direct amplitude normalized for the coda amplitude at a given lapse time coda normalization for all the recording stations and the site transfer functions calculated for the same stations using both the direct s wave spectra and the coda wave spectra results show that the log normalized amplitude increases with distance the opposite of what commonly observed in non volcanic zones this effect may be caused by an effective inhomogeneity of the scattering wave field or in different words by a total q increasing with depth