broadband seismic experiment at merapi volcano java indonesia very long period pulses embedded in multiphase earthquakes abstract multiphase mp and low frequency lf earthquakes with spectral peak amplitudes at 3 4 and 1 hz respectively are two common types of shallow volcanic earthquakes previously recognized at merapi volcano their mechanisms are poorly understood but mps have been temporally associated with lava dome growth we conducted a seismic experiment in january february 1998 using four broadband seismographs to investigate the nature of seismic activity associated with dome growth during our experiment merapi experienced mild dome growth with low level seismic activity we compare our data to that recorded on a local short period sp network with the following preliminary results mp and lf events as recorded and classified on the short period network instruments were recognized on the broadband network frequency spectrograms revealed similar patterns in the near summit region at widely separated broadband stations higher frequency spectra than previously recognized were identified for both mp and lf events and were strongly attenuated as a function of radial distance from the source thus the spectral characteristics of these events as recorded on far field stations are not fully indicative of the source processes in particular many events classified as lf type appear to have much high frequency energy near the source this aspect of these so called lf earthquakes and their association with very long period vlp pulses suggests that many events identified in the far field as lf events are in actuality a variety of the mp event and involve similar source processes broadband records indicated that simple large amplitude vlp pulses were embedded in mp and lf wavetrains from event to event these pulses were similar in their waveforms and had periods of 4 s vlp events embedded in lf and mp earthquakes were located using particle motions the epicenters were clustered in a central region of the dome complex and preliminary source depths were within about 100 m of the dome surface suggesting a source region deep within the dome or the uppermost conduit a similar source location was established by study of mp high frequency onsets our broadband data suggests that we have recorded both elastic seismic waves and a simple embedded pulse that is interpreted to represent a surface tilt at the seismometer site the inferred tilt indicates an inflation and subsequent deflation possibly caused by a gas pressure pulse or episodic shallow magma transport with stick slip movement of the conduit wall

volcanic coseismic and seasonal changes detected at white island whakaari volcano new zealand using seismic ambient noise ambient noise interferometry is becoming increasingly popular for studying seismic velocity changes such changes contain information on the structural and mechanical properties of earth systems application to monitoring however is complicated by the large number of processes capable of inducing crustal velocity changes we demonstrate this at white island volcano over a 10 year period containing multiple well documented eruptions using individual seismic stations we detect velocity perturbations that we ascribe to volcanic activity large earthquakes and seasonality distant seismic stations capture widespread nonvolcanic changes that are also present at the volcano comparison between velocity changes recorded by distant and local stations then allows us to distinguish volcanic phenomena from seasonality through this we resolve distinct features in ambient noise derived velocity changes that relate to volcanic unrest and a phreatic eruption illustrating the strength of the approach plain language summary detecting small changes in physical properties at volcanoes is important toward effectively forecasting volcanic eruptions one approach is to monitor the speed of seismic waves at the earth s surface which are sensitive to changes in the rock they pass through at volcanoes such changes may manifest through subsurface pressure increases preceding eruptions correctly interpreting these changes however is complicated many other nonvolcanic processes are also capable of producing similar wave speed perturbations at white island volcano new zealand we detect changes associated with volcanic activity large earthquakes and weather related processes using seismometers located on the volcano we demonstrate that volcanic and nonvolcanic features can be distinguished by comparing changes recorded at the volcano with those recorded at large distances where volcanic changes are not expected to be observed through this we resolve distinct differences that can be related to volcanic activity illustrating the strength of this approach

monitoring velocity variations in the crust using earthquake doublets an application to the calaveras fault california we present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates we compute differences in arrival times between seismograms recorded at the same station in the freqency domain by cross correlation of short windows of signal a moving window analysis of the entire seismograms including the coda gives t the difference in arrival times versus running time along the seismogram the time resolution of the method is an order of magnitude better than the digitization interval the t technique is illustrated with a pair of microearthquakes m 1 7 and 2 0 that occurred before and after the coyote lake california earthquake m 5 9 of august 6 1979 and on the same segment of the calaveras fault that ruptured during the earthquake the coda wave arrivals for some stations are progressively delayed for the second earthquake in the doublet so that its seismogram appears as a stretched version of the earlier event we interpret this systematic variation in t along the coda as a change in the average s velocity in the upper crust in the time interval between the two doublets s wave velocities appear to have decreased by 0 2 in an oblong region 5 10 km in radius at the south end of the aftershock zone

volcanic activity influenced by tectonic earthquakes static and dynamic stress triggering at mt merapi 1 mt merapi is one of the most dangerous volcanoes in indonesia located within the tectonically active region of south central java this study investigates how mt merapi affected and was affected by nearby tectonic earthquakes in 2001 a mw6 3 earthquake occurred in conjunction with an increase in fumarole temperature at mt merapi in 2006 another mw6 3 earthquake took place concomitant with an increase of magma extrusion and pyroclastic flows here we develop theoretical models to study the amount of stress transfer between the earthquakes and the volcano showing that dynamic rather than static stress changes are likely responsible for the temporal and spatial proximity of these events our examination of the 2001 and 2006 events implies that volcanic activity at mt merapi is influenced by stress changes related to remote tectonic earthquakes a finding that is important for volcano hazard assessment in this densely inhabited area

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

shear wave velocity changes induced by earthquakes and rainfall at the rotokawa and ngatamariki geothermal fields taupō volcanic zone new zealand

earthquake volcano interaction imaged by coda wave interferometry 1 large earthquakes are often assumed to influence the eruptive activity of volcanoes a major challenge to better understand the causal relationship between these phenomena is to detect and image in detail all induced changes including subtle non eruptive responses we show that coda wave interferometry can be used to image such earthquake induced responses as recorded at yasur volcano vanuatu following a magnitude 7 3 earthquake which occurred 80 km from its summit we use repeating long period events to show that the earthquake caused a sudden seismic velocity drop followed by a slow partial recovery process the spatial distribution of the response amplitude indicates an effect centered on the volcano our result demonstrates that even if no major change in eruptive activity is observed volcanoes will be affected by the propagation of large amplitude seismic waves through their structure suggesting that earthquake volcano interaction is likely a more common phenomenon than previously believed

stress strain and mass changes at mt etna during the period between the 1991 93 and 2001 flank eruptions abstract during the 8 year period between the 1991 93 and 2001 flank eruptions the eruptive activity of mt etna was confined to the summit craters deformation and tomography studies indicate that this activity was fed by a magma accumulation zone centered ne of the summit at a depth of 5 to 9 km below sea level the most significant gravity changes measured during the same period were induced by mass redistributions at shallower depth below the southeastern flank of the volcano where minor ground deformation was observed i e vertical displacements within 2 cm the mismatch between the position of pressure and mass sources is difficult to explain under the assumption that both are directly related to magma dynamics past studies have suggested that the gravity changes observed during 1994 2001 may primarily reflect changes in the rate of microfracturing along the nnw sse fracture weakness zone fwz that crosses the se slope of etna we use the finite element method to shed new light on the complex relations between stress strain and mass changes that occurred at etna during the studied period in particular following previous results on the degradation of the mechanical properties of rocks we perform a set of simulations assuming that the part of the medium containing the fwz is characterized by a lower young s modulus than would be expected from interpolation of tomographic data we find that the presence of the fwz creates a distortion of the displacement field induced by the deeper pressure source locally resulting in a weak extensional regime this finding supports the hypothesis of a cause effect relationship between pressurization beneath the nw flank and tensile extension beneath the se slope of the volcano we propose that this extensional regime enhanced the propagation of pressurized gas that in turn amplified the tensile strain across the fwz we also find that decreasing the value of young s modulus in the fwz allows for a larger amount of extension at depth with no change in the magnitude of surface displacements this result provides an indication of how the changes in the rate of microfracturing at depth which are needed to induce the observed gravity changes might have occurred without large ground deformation

monitoring a temporal change of seismic velocity in a volcano application to the 1992 eruption of mt merapi indonesia multiplets i e events with similar waveforms are selected from shallow earthquakes recorded on merapi volcano indonesia before the eruption of february 2nd 1992 two multiplet families are found with their sources close to the summit their seismograms are analyzed using the moving window cross spectrum technique which measures the precise time delay between seismic phases in the entire seismogram for both families of multiplets a gradual decrease in the arrival times of coda waves is observed as a function of the date prior to the eruption coda waves are becoming progressively faster up to 1 2 per cent as the time interval to the eruption shortens this observation is interpreted as the consequence of an increase in the seismic velocity inside the volcano the increase in velocity started in may 1991 and was observed until september 1991 4 months before the eruption this velocity increase may be related to an increase in pressure in the magma chamber or in the conduits and to the resulting closure of the surrounding cracks

seismic and experimental insights into eruption precursors at volcan de colima we combine geophysical and experimental observations to interpret preeruptive unrest at volcan de colima in 1998 17 893 volcanic earthquakes were detected between 1 october and 31 december 1998 including 504 clusters using seismic ambient noise interferometry we observe a drop in velocity prior to the eruption linked to damage accumulation during magma ascent this is supported by experimental observations where static stress causes a velocity decrease prior to failure furthermore we observe acoustic emission clusters during the experiments with lower porosity samples producing higher numbers of repeaters this behavior introduces tensile failure as an additional viable mechanism for clusters during magma ascent the findings suggest that preeruptive magma ascent may be monitored to variable degrees of accuracy via descriptions of damage accumulation and associated seismic velocity changes

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

coda wave interferometry for estimating nonlinear behavior in seismic velocity in coda wave interferometry one records multiply scattered waves at a limited number of receivers to infer changes in the medium over time with this technique we have determined the nonlinear dependence of the seismic velocity in granite on temperature and the associated acoustic emissions this technique can be used in warning mode to detect the presence of temporal changes in the medium or in diagnostic mode where the temporal change in the medium is quantified

coseismic and postseismic velocity changes measured by repeating earthquakes 1 repeating earthquakes that rupture approximately the same fault patch and have nearly identical waveforms are a useful tool for measuring temporal changes in wave propagation in the earth s crust since source and path effects are common to all earthquakes in a repeating earthquake sequence multiplet differences in their waveforms can be attributed to changes in the characteristics of the medium we have identified over 20 multiplets containing between 5 and 40 repeating events in the aftershock zones of the 1989 loma prieta and 1984 morgan hill california earthquakes postmain shock events reveal delays of phases in the early s wave coda of as much as 0 2 s relative to premain shock events the delay amounts to a path averaged coseismic velocity decrease of about 1 5 for p waves and 3 5 for s waves since most of the multiplets are aftershocks and follow omori s law we have excellent temporal sampling in the immediate postmain shock period we find that the amplitude of the velocity decrease decays logarithmically in time following the main shock in some cases it returns to the premain shock values while in others it does not similar results are obtained for the morgan hill main shock because the fractional change in s wave velocity is greater than the fractional change in p wave velocity it suggests that the opening or connection of fluid filled fractures is the underlying cause the magnitude of the velocity change implies that low effective pressures are present in the source region of the velocity change our results suggest that the changes are predominantly near the stations and shallow but we cannot exclude the possibility that changes occur at greater depth as well if the variations are shallow we may be detecting the lingering effects of nonlinearity during main shock strong ground motion if the variations are deep it suggests that pore pressures at seismogenic depths are high which would likely play a key role in the earthquake process

high precision relative locations of earthquakes at mount st helens washington several earthquake sequences have occurred at mount st helens as clusters of shallow events with nearly identical waveforms multiplets we present a technique that allows the relative relocation of events within a multiplet to at least an order of magnitude higher precision than is typically possible with traditional techniques a multiplet is studied in pairs of events called doublets each doublet is made up of a reference event and one other event from the multiplet the cross spectrum of a short window beginning just before the p arrival is used to compute differences in arrival times between seismograms from the same station for each doublet these time differences computed with a precision of 1 2 ms are then used to locate each earthquake relative to the reference event engineering explosions with well known locations are used to test the relocation technique explosions can be relocated with accuracy better than 20 m for events within 250 m of the reference explosion the relocation technique is applied to earthquakes preceding the september 10 1984 and the may june 1985 dome building eruptions of mount st helens forty events that occurred during a 12 hour period in september 1984 are located in a volume approximately 30 m in diameter beneath the lava dome the earthquakes following the extrusion do not occur in multiplets and appear to be distributed over a much larger volume in the may june 1985 eruption we recognize three multiplet sets that took place successively in time the multiplets are interpreted as repeated failure or slip within a relatively small volume due to high strain rates around the magma supply conduit

seismological significance of the 1977 1978 eruptions and the magma intrusion process of usu volcano hokkaido abstract an earthquake swarm and the major pumice eruptions in august 1977 which followed marked the start of the dacitic doming activity of usu volcano in southwestern hokkaido japan the sequence of magma intrusion processes was investigated in detail by means of seismological and other geophysical data the distribution of the abundant hypocenters shows clearly an earthquake free zone beneath the summit crater the hypocenters migrated in a manner consistent with the development of the observed asymmetrical surface deformations considered due to magma intrusion into this earthquake free zone the earthquake mechanism solutions are mostly of dip slip type and are interpreted in terms of the doming deformations the existence of earthquake families earthquakes with similar waveforms is the main cause of the peculiar occurrence of earthquakes in space time and magnitude the concept of scattered barriers of different sizes and strengths can explain well the distinct characteristics of the occurrence of the swarm and the observed episodic deformations

reciprocity based passive monitoring with individual sources time lapse changes in the subsurface can be analyzed by comparing seismic reflection data from two different states one serving as the base survey and the second as the monitor survey conventionally reflection data are acquired by placing active seismic sources at the acquisition surface alternatively these data can be acquired from passive sources in the subsurface using seismic interferometry si unfortunately the reflection responses as retrieved by si inherit an imprint of the passive source distribution therefore monitoring with si requires high passive source repeatability which is very often not achievable in practice we have developed an alternative by using active seismic data for the base survey and a single passive source e g a seismic tremor produced by induced seismicity for the monitor survey by constraining the source radiation pattern of the active base survey according to the characteristics of the passive monitor survey we succeed in extracting the time lapse response in the image domain we tested our method with numerically modeled data

volcanism and the dynamics of open magma chambers the repeated eruption of many volcanoes is now accounted for by events taking place in a subterranean magma chamber which is open in the sense that the inflow of material to the chamber from below leads to a magma pressure p which exceeds the lithostatic pressure pl by an amount greater than the tensile strength of the chamber walls before the contents of the magma chamber have reached thermodynamic and geochemical equilibrium this is the condition which must be satisfied when an eruption occurs we have now derived a relationship giving the critical volume of added material v required to cause an eruption as a function of magma compressibility and the volume by which the chamber expands

internal structure of mount merapi indonesia derived from long offset transient electromagnetic data 1 a long offset transient electromagnetic lotem survey was carried out on merapi volcano indonesia in 1998 lotem data have been recorded at 41 receiver locations which cover a 10 km w e and a 15 km s n profile the signals were transmitted at four locations on the south west and north sides of merapi the data were interpreted with one dimensional 1 d inversions in addition two particular features were investigated with 3 d modeling on the south flank the magnetic field data show strong 3 d distortions consistently over the profile which can only be explained by a conductive near surface structure like a fracture filled with conductive fluids the simulation of topographic effects shows that the interpretation is not significantly affected on both profiles the most striking feature is a conductive layer of 20 m at depths of 500 1000 m below the surface and a thickness of 1 2 km the cause of the increased conductivity may be different for the summit area the intermediate zone and at the flanks below the summit in vicinity of the conduit the decrease in resistivity is produced either by hydrothermal fluids by partial melts or rocks altered by the hydrothermal system or by a combination in the intermediate zone between the conduit and the flanks either alteration or hydrothermal fluids may be the source of the conductivity increase fluids seem to be the most likely cause for the conductive layer at the flanks and the west east striking anomaly from the resistivity of the conductive layer and the typical porosity of volcanic rock we estimate fluid resistivities of 0 2 1 m

estimation of arrival times in intense seismic sequences using a master events methodology based on waveform similarity summary intense seismic sequences involve a large number of earthquakes densely clustered in space and time their detailed analysis is important for the geometry of the activated faults which contributes to studies of the seismotectonic characteristics of an area the sheer number of small events as well as their low energy content renders their processing problematic in this work we have developed and applied a methodology to automatically pick the arrival times of p and s waves using a correlation detector event detection is performed using the waveform recordings of a reference station located close to the epicentral area of an intense seismic sequence such as aftershocks or swarms cross correlation matrices are constructed followed by nearest neighbour clustering and the formation of multiplets a master event is chosen from each cluster and its arrival times are picked manually the automatic algorithm uses the p o rs wave of each master event as a correlation detector searches the waveforms of the other events of the same multiplet and imposes the corresponding arrival time when the bestfit is achieved the picks are characterized by observation weights which derive from the quality of thefit the type of the available waveform components and the consistency between multiple measurements the proposed methodology was applied to an important seismic sequence that occurred between 2010 january 18 and 26 near the city of efpalio greece this procedure has the potential to increase 10 fold the amount of information and provide sufficient detail for a subsequent analysis of the spatiotemporal distribution of a seismic series

textural and mineral chemistry constraints on evolution of merapi volcano indonesia abstract we analyze and compare the textures of merapi lavas basalts and basaltic andesites ranging in age from proto merapi through modern activity with the goal of gaining insights on the temporal evolution of merapi s magmatic system analysis of textural parameters such as phenocryst and microphenocryst crystallinity coupled with crystal size distribution theory provides information about the storage and transport of magmas we combine textural analyses with geochemical investigations for a comprehensive comparison of erupted lavas over time the chemical analyses identify crystal growth processes in magma chambers and underline differences between sample groups our work suggests the occurrence of two distinct histories presumably associated with at least two generally distinct types of rheological behaviors and storage transport systems these behaviors are associated with different plagioclase growth patterns with both groups influenced by late stage shallow decompression degassing induced microlite crystallization both groups contain amphibole crystals that indicate an early period of mid crustal to deep crustal storage of water rich magmas dome lavas from the 20th century eruptive activity indicate quasi steady state nucleation and growth evolution interspersed with episodes of reheating and textural coarsening suggesting residence in magma storage at multiple depths both 10 km and

seasonal variations of seismic velocities in the san jacinto fault area observed with ambient seismic noise s u m m a r y we observe seasonal seismic wave speed changes dv v in the san jacinto fault area and investigate several likely source mechanisms velocity variations are obtained from analysis of 6 yr data of vertical component seismic noise recorded by 10 surface and six borehole stations we study the interrelation between dv v records frequency dependent seismic noise properties and nearby environmental data of wind speed rain ground water level barometric pressure and atmospheric temperature the results indicate peak to peak seasonal velocity variations of 0 2 per cent in the 0 5 2 hz frequency range likely associated with genuine changes of rock properties rather than changes in the noise field phase measurements between dv v and the various environmental data imply that the dominant source mechanism in the arid study area is thermoelastic strain induced by atmospheric temperature variations the other considered environmental effects produce secondary variations that are superimposed on the thermal based changes more detailed work with longer data on the response of rocks to various known external loadings can help tracking the evolving stress and effective rheology at depth

microearthquake location a nonlinear approach that makes use of a simplex stepping procedure we present an earthquake location scheme that uses the simplex algorithm in the solution this method of direct iteration is conceptually simple does not require derivative calculations and avoids matrix inversions the algorithm can be programmed on a small computer and its performance compares favorably with other methods of earthquake location the method can be used for any velocity structure for which source to geophone times can be calculated we use a horizontally layered velocity model and consider both critically and noncritically refracted rays it is easy to incorporate any time residual misfit norm into the location calculation we generally use the l 1 or l 2 least squares norm the routine we present is used in two different microseismic monitoring systems at two potash mines in saskatchewan canada

the magmatic plumbing system beneath santiaguito volcano guatemala abstract the silicic dome complex of santiaguito guatemala has exhibited continuous extrusive activity for 90 years despite its longevity remarkably little is known about the magmatic plumbing system beneath santiaguito here we use petrological analyses of lava samples to define this plumbing system from storage in the lower to mid crust through to extrusion onto the surface magmatic storage conditions are constrained using amphibole and plagioclase phenocrysts ascent processes are examined using the breakdown rims of amphibole phenocrysts and the texture and composition of groundmass while shallow processes are revealed by the alteration of titanomagnetites and matrix glass santiaguito magmas contain amphiboles that formed from 24 km to 12 km beneath the surface with temperatures of 940 to 980 c and f o2 of nno 0 4 to nno 1 2 amphibole breakdown rims suggest that during the final phases of ascent magma may rise from 12 km the limit of amphibole stability relatively rapidly 27 to 84 m h 1 we infer from the texture of the groundmass that melt rigidifies prior to extrusion a finding that may have important consequences for conduit dynamics

towards monitoring the englacial fracture state using virtual reflector seismology in seismology coda wave interferometry cwi is an effective tool to monitor time lapse changes using later arriving multiply scattered coda waves typically cwi relies on an estimate of the medium s impulse response the latter is retrieved through simple time averaging of receiver receiver cross correlations of the ambient field that is seismic interferometry si in general the coda is induced by heterogeneities in the earth being comparatively homogeneous however ice bodies such as glaciers and ice sheets exhibit little scattering in addition the temporal stability of the time averaged cross correlations suffers from temporal variations in the distribution and amplitude of the passive seismic sources consequently application of cwi to ice bodies is currently limited nevertheless fracturing and changes in the englacial macroscopic water content alter the bulk elastic properties of ice bodies which can be monitored with cryoseismological measurements to overcome the current limited applicability of cwi to ice bodies we therefore introduce virtual reflector seismology vrs vrs relies on a so called multidimensional deconvolution mdd process of the time averaged crosscorrelations the technique results in the retrieval of a medium response that includes virtual reflections from a contour of receivers enclosing the region of interest i e the region to be monitored the virtual reflections can be interpreted as artificial coda replacing the lacking natural scattered coda hence this artificial coda might be exploited for the purpose of cwi from an implementation point of view vrs is similar to si by mdd which as its name suggests also relies on a multidimensional deconvolution process si by mdd however does not generate additional virtual reflections advantageously both techniques mitigate spurious coda changes associated with temporal variations in the distribution and amplitude of the passive seismic sources in this work we apply si by mdd and vrs to synthetic and active seismic surface wave data the active seismic data were acquired on glacier de la plaine morte switzerland we successfully retrieve virtual reflections through the application of vrs to this active seismic data in application to both synthetic and active seismic data we show the potential of vrs to monitor time lapse changes in addition we find that si by mdd allows for a more accurate determination of phase velocity

timing of a large volcanic flank movement at piton de la fournaise volcano using noise based seismic monitoring and ground deformation measurements in volcanic domains magma transport and pressure build up induce high stress strain perturbations in the surrounding volcanic edifice that may lead to volcanic flank movements and possible instability in this study we focus on the 2007 march april episode of volcanic activity at piton de la fournaise pdf volcano la r eunion island this episode was associated with a large volume of emitted lava 240 106 m3 and a 340 m caldera collapse we present observations of continuous seismic velocity changes measured using cross correlations of ambient seismic noise over 10 yr at pdf overall we observe a large velocity reduction starting a few days prior to the major 2007 april 2 eruption comparison of seismic velocity change measurements with observations of deformation from insar and gps shows that the seismic velocity reduction coincided with a widespread flank movement starting at the time of injection of magma to feed an initial eruption a few days before the 2007 april 2 eruption we emphasize the potential of noise based seismic velocity change measurements together with geodetic observations to detect and monitor possibly hazardous slope instabilities

a late vendian age for the kinlochlaggan boulder bed dalradian the kinlochlaggan boulder bed occurs in neoproterozoic dalradian rocks of the grampian mountains of scotland it is currently thought to represent a glacial event c 800 ma unique in the north atlantic region and be part of a sequence correlated by different workers with either the grampian or appin groups we correlate the boulder bed with the port askaig tillite of vendian c 650 ma age and deduce that the sequence in which it occurs belongs to the younger argyll group the latter is preserved within the d2 kinlochlaggan synform and a previously unrecognized discontinuity of regional importance may separate inverted argyll group rocks from the underlying grampian group

glaciological and oceanographic evidence of high melt rates beneath pine island glacier west antarctica satellite imagery indicates that the floating terminus of pine island glacier has changed little in extent over the past two decades data on the velocity and thickness of the glacier reveal that calving of 28 4 gt a 1 accounts for only half of the ice input near the grounding line the apparently steady configuration implies that the remainder of the input is lost by basal melting at a mean rate of 12 3 m a 1 ocean circulation in pine island bay transports 1 c waters beneath the glacier and temperatures recorded in melt laden outflows show that heat loss from the ocean is consistent with the requirements of the calculated melt rate the combination of iceberg calving and basal melting lies at the lower end of estimates for the total accumulation over the catchment basin drawing into question previous estimates of a significantly positive mass budget for this part of the ice sheet

time dependent seismic tomography summary of methods for measuring temporal changes in seismic wave speeds in the earth seismic tomography is among those that offer the highest spatial resolution 3 d tomographic methods are commonly applied in this context by inverting seismic wave arrival time data sets from different epochs independently and assuming that differences in the derived structures represent real temporal variations this assumption is dangerous because the results of independent inversions would differ even if the structure in the earth did not change due to observational errors and differences in the seismic ray distributions the latter effect may be especially severe when data sets include earthquake swarms or aftershock sequences and may produce the appearance of correlation between structural changes and seismicity when the wave speeds are actually temporally invariant a better approach which makes it possible to assess what changes are truly required by the data is to invert multiple data sets simultaneously minimizing the difference between models for different epochs as well as the rms arrival time residuals this problem leads in the case of two epochs to a system of normal equations whose order is twice as great as for a single epoch the direct solution of this system would require twice as much memory and four times as much computational effort as would independent inversions we present an algorithm tomo4d that takes advantage of the structure and sparseness of the system to obtain the solution with essentially no more effort than independent inversions require

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