eruptive history of earth s largest quaternary caldera toba indonesia clarified single grain laser fusion sup 40 ar sup 39 ar analyses of individual sanidine phenocrysts from the two youngest toba indonesia tuffs yield mean ages of 73 plus minus 4 and 501 plus minus 5 ka in addition glass shards from toba ash deposited in malaysia were dated at 68 plus minus 7 ka by the isothermal plateau fission track technique these new determinations in conjunction with previous ages for the two oldest tuffs at toba establish the chronology of four eruptive events from the toba caldera complex over the past 1 2 m y ash flow tuffs were erupted from the complex every 0 34 to 0 43 m y culminating with the enormous 2500 3000 km sup 3 youngest toba tuff eruption caldera formation and subsequent resurgence of samosir island timing of this last eruption at toba is coincident with the early wisconsin glacial advance the high precision sup 40 ar sup 39 ar age eruption of such magnitude may provide an important marker horizon useful as a baseline for research and modeling of the worldwide climatic impact of exceptionally large explosive eruptions

upper crustal structure of central java indonesia from transdimensional seismic ambient noise tomography summary delineatingthecrustalstructureofcentraljavaiscrucialforunderstandingitscomplextectonic setting however seismic imaging of the strong heterogeneity typical of such a tectonically active region can be challenging particularly in the upper crust where velocity contrasts are strongestandsteepbodywaveraypathsprovidepoorresolution toovercomethesedifficulties we apply the technique of ambient noise tomography ant to data collected during the merapi amphibious experiment meramex which covered central java with a temporary deployment of over 120 seismometers during 2004 may october more than 5000 rayleigh wave green s functions were extracted by cross correlating the noise simultaneously recorded at available station pairs we applied a fully non linear 2 d bayesian probabilistic inversion technique to the retrieved traveltimes features in the derived tomographic images correlate well with previous studies and some shallow structures that were not evident in previous studies are clearly imaged with ant the kendeng basin and several active volcanoes appear with very low group velocities and anomalies with relatively high velocities can be interpreted in terms of crustal sutures and or surface geological features

p s velocity and vp vs ratio beneath the toba caldera complex northern sumatra from local earthquake tomography summary in this paper we investigate the crustal and uppermost mantle structure beneath toba caldera which is known as the location of one of the largest cenozoic eruptions on earth the most recent event occurred 74 000 yr bp and had a significant global impact on climate and the biosphere in this study we revise data on local seismicity in the toba area recorded by a temporary passcal network in 1995 we applied the newest version of the lotos 07 algorithm which includes absolute source location optimization of the starting 1 d velocity model and iterative tomographic inversion for 3 d seismicp s or thevp vs ratio and source parameters special attention is paid to verification of the obtained results beneath the toba caldera and other volcanoes of the arc we observe relatively moderate for volcanic areas negative p and s velocity anomalies that reach 18 per cent in the uppermost layer 10 12 per cent in the lower crust and about 7 per cent in the uppermost mantle much stronger contrasts are observed for the vp vs ratio that is a possible indicator of dominant effect of melting in origin of seismic anomalies at a depth of 5 km beneath active volcanoes we observe small patterns 7 15 km size with a high vp vs ratio that might be an image of actual magmatic chambers filled with partially molten material feeding the volcanoes in the mantle wedge we observe a vertical anomaly with low p and s velocities and a high vp vs ratio that link the cluster of events at 120 140 km depth with toba caldera this may be an image of ascending fluids and melts released from the subducted slab due to phase transitions however taking into account poor vertical resolution these results should be interpreted with prudence although the results show clear signatures that are quite typical for volcanic areas low velocity and high vp vs ratio beneath volcanoes we do not observe any specific features in seismic structure that could characterize toba as a super volcano

seismic vp and vp vs structure of the geothermal area around tarutung north sumatra indonesia derived from local earthquake tomography abstract a passive seismic experiment with 42 short period stations was setup for 10 months from may 2011 within a 20 30 km radius covering the tarutung basin and the northern part of the sarulla graben along the seismically active sumatran fault north sumatra indonesia the objective of the project is to investigate the geothermal setting based on the vp and vp vs structures and the distribution of seismicity we recorded 2856 local earthquakes by at least 8 stations which were reduced to 809 events having gap angle less than 180 the initial earthquake locations were determined using simultaneous inversion for hypocenters and 1d velocity structure followed by 3d tomographic inversion the resulting seismicity distribution vp and vp vs structure reveal systematic differences between the tarutung basin and the sarulla graben the tarutung pull apart basin is characterized by a complex structure reflected by a broader distribution of seismicity compared with the very narrow rather vertical hypocenter distribution in the sarulla graben which was formed by fault perpendicular extension and not by pull apart tectonics high vp vs values near to the surface are imaged within the sarulla graben and northeast of the tarutung basin these features are interpreted as fluid bearing sediments with fracturing indicating potentially favorable conditions for geothermal exploitation the localized fluid flow northeast of tarutung could be explained by the releasing step over structure of the pull apart basin and resulting dilatational stress regime in this part of the basin heat sources are assumed to be located at greater depth in association with magmatic activities accompanying the subduction process and the heat is transported along the sumatran fault to shallow depth

acoustic green s function extraction from ambient noise in a coastal ocean environment we report on the results of an underwater acoustic field experiment conducted in december 2012 on the continental shelf off the florida keys in water of approximately 100 m depth ambient noise was recorded concurrently on three moored near bottom instruments with horizontal separations of approximately 5 km 10 km and 15 km we focus in this letter on instrument pairs with 5 km and 10 km separations consistent with theoretical predictions coherent sums of many realizations of cross correlations of ambient noise records at two measurement locations are shown to yield approximations to deterministic acoustic green s functions that describe propagation between those two locations the results presented demonstrate the feasibility of extracting information suitable for use in tomographic inversions from measurements of underwater acoustic ambient noise

a gravity and volcanostratigraphic interpretation of the lake toba region north sumatra indonesia abstract in northern and central sumatra a wide distribution of ignimbrite and volcanic sediments is observed some geologists consider that these volcanic products were erupted from lake toba the subduction of the indian ocean plate along the trench of central sumatra started at least as long ago as the late miocene fitch s model 1972 obtained the plate convergence vector 67 mm yr decomposed into its components perpendicular 58 mm yr and parallel 34 mm yr to the trench axis tears seaward of the mountain range created the sumatran fault about 2 ma ago at that time the edge of the plate reached a depth of almost 100 km and a large amount of dacite magma was generated the tuk tuk dacite a kind of ignimbrite was erupted along the sumatran fault and covered a broad area the age of this ignimbrite was obtained as 1 9 0 4 ma k arage and 2 0 0 3 ma fission track age since this eruption the hinterland of this fault has been changed to a tensional field forming a graben structure at the northern end of this graben west of harranggaoul the ignimbrite haranggaoul formation was erupted 1 3 0 3 ma ago forming a caldera the lacustrine sediments of samosir island have a normal magnetization and overlie the tuk tuk dacite unconformably from this we can conclude that the graben structure has been covered with water lake toba at 0 7 0 6 ma ago this tectonic movement has continued so that it is difficult to distinguish the caldera structure on the gravity anomaly map of the northern part of lake toba from the results of the gravity survey it can be concluded that at 0 1 ma ignimbrite flowed down along the asahan river and filled the old river along the lowland between parapat and porsea forming a caldera 30 000 years ago dacite and and esite eruptions have occurred around lake toba forming the volcanic cones

three dimensional shear velocity anisotropic model of piton de la fournaise volcano la reunion island from ambient seismic noise we cross correlate 4 years of seismic noise from the seismic network of piton de la fournaise volcano la reunion island to measure the group velocity dispersion curves of rayleigh and love waves we average measurements from vertical and radial components to obtain 577 rayleigh wave dispersion curves the transverse components provided 395 love wave dispersion curves we regionalize the group velocities measurements into 2 d velocity maps between 0 4 and 8 s finally we locally inverted these maps for a pseudo 3 d anisotropic shear velocity model down to 3 km below the sea level using a neighborhood algorithm the 3 d isotropic shear wave model shows three distinct high velocity anomalies surrounded by a low velocity ring the anomaly located below the present plaine des sables could be related to an old intrusive body at the location of the former volcanic center before it migrated toward its present location the second high velocity body located below the summit of the volcano likely corresponds to the actual preferential dyke intrusion zone as highlighted by the seismicity the third high velocity anomaly located below the grandes pentes and the grand brule areas and is an imprint of the solidified magma chamber of the dismantled les alizes volcano radial anisotropy shows two main anomalies positive anisotropy above sea level highlighting the recent edifice of piton de la fournaise with an accumulation of horizontal lava flows and the second one below the sea level with a negative anisotropy corresponding to the ancient edifice of piton de la fournaise dominated by intrusions of vertical dykes

s wave velocity images of the dead sea basin provided by ambient seismic noise abstract based on passive seismic interferometry applied to ambient seismic noise recordings between station pairs belonging to a small scale array we have obtained shear wave velocity images of the uppermost materials that make up the dead sea basin we extracted empirical green s functions from cross correlations of long term recordings of continuous data and measured inter station rayleigh wave group velocities from the daily correlation functions for positive and negative correlation time lags in the 0 1 0 5 hz bandwidth a tomographic inversion of the travel times estimated for each frequency is performed allowing the laterally varying 3 d surface wave velocity structure below the array to be retrieved subsequently the velocity frequency curves are inverted to obtain s wave velocity images of the study area as horizontal depth sections and longitude and latitude depth sections the results which are consistent with other previous ones provide clear images of the local seismic velocity structure of the basin low shear velocities are dominant at shallow depths above 3 5 km but even so a spit of land with a depth that does not exceed 4 km is identified as a salt diapir separating the low velocities associated with sedimentary infill on both sides of the lisan peninsula the lack of low speeds at the sampling depth of 11 5 km implies that there are no sediments and therefore that the basement is near 10 11 km depth but gradually decreasing from south to north the results also highlight the bowl shaped basin with poorly consolidated sedimentary materials accumulated in the central part of the basin the structure of the western margin of the basin evidences a certain asymmetry both whether it is compared to the eastern margin and it is observed in north south direction infill materials down to 8 km depth are observed in the hollow of the basin unlike what happens in the north and south where they are spread beyond the western dead sea shore

how deep is deep enough ocean iron fertilization and carbon sequestration in the southern ocean artificial ocean iron fertilization oif enhances phytoplankton productivity and is being explored as a means of sequestering anthropogenic carbon within the deep ocean to be considered successful carbon should be exported from the surface ocean and isolated from the atmosphere for an extended period e g the intergovernmental panel on climate change s standard 100 year time horizon this study assesses the impact of deep circulation on carbon sequestered by oif in the southern ocean a high nutrient low chlorophyll region known to be iron stressed a lagrangian particle tracking approach is employed to analyze water mass trajectories over a 100 year simulation by the end of the experiment for a sequestration depth of 1000 m 66 of the carbon had been reexposed to the atmosphere taking an average of 37 8 years upwelling occurs predominately within the antarctic circumpolar current due to ekman suction and topography these results emphasize that successful oif is dependent on the physical circulation as well as the biogeochemistry

the structure of the sumatran fault revealed by local seismicity the combination of the sunda megathrust and the strike slip sumatran fault sf represents a type example of slip partitioning however superimposed on the sf are geometrical irregularities that disrupt the local strain field the largest such feature is in central sumatra where the sf splits into two fault strands up to 35 km apart a dense local network was installed along a 350 km section around this bifurcation registering 1016 crustal events between april 2008 and february 2009 528 of these events with magnitudes between 1 1 and 6 0 were located using the double difference relative location method these relative hypocentre locations reveal several new features about the crustal structure of the sf northwest and southeast of the bifurcation where the sf has only one fault strand seismicity is strongly focused below the surface trace indicating a vertical fault that is seismogenic to 15 km depth by contrast intense seismicity is observed within the bifurcation displaying streaks in plan and cross section that indicate a complex system of faults bisecting the bifurcation in combination with analysis of topography and focal mechanisms we propose that the bifurcation is a strike slip duplex system with complex faulting between the two main fault branches

noble gas geochemistry in thermal springs abstract the composition of noble gases in both gas and water samples collected from horseshoe spring yellowstone national park was found to be depth dependent the deeper the sample collection within the spring the greater the enrichment in kr xe radiogenic 4he and 40ar and the greater the depletion in ne relative to 36ar the compositional variations are consistent with multi component mixing the dominant component consists of dissolved atmospheric gases acquired by the pool at the surface in contact with air this component is mixed in varying degree with two other components one each for gas and water entering the bottom of the pool the two bottom components are not in equilibrium in horseshoe spring the bubbles entering at the bottom strip the atmospheric derived pool gases from the surrounding water while en route to the surface if the original bottom bubbles are noble gas poor as in the case of horseshoe the acquired pool gases can then quickly obliterate the original bubble composition these results are used to demonstrate that yellowstone spring surface gas samples and perhaps similarly sampled thermal springs from other hydrothermal systems have gas abundances that depend more on spring morphology than processes occurring deeper in the hydrothermal system

melts mush and more evidence for the state of intermediate to silicic arc magmatic systems understanding the physical state of intermediate to silicic arc magmatic systems is necessary for our petrologic models of these systems researchers have generated a plethora of data geophysical geochronological petrological theoretical over the past few decades these data have changed how we view arc magmatic systems leading to a model of crystal mush that is rejuvenated repeatedly over the lifespan of the magmatic system however much data are either circumstantial or incomplete paterson et al 2016 october issue use a combined set of textural geochemical and temporal data to demonstrate the changing physical state of the tuolumne intrusive complex in california over its 10 million year history they offer evidence for magmatic erosion and recycling along with the potential for a surge growth of the batholith that allows for significant volumes of magma to exist ephemerally under arc volcanoes most intermediate to silicic arc magmas henceforth arc magma are stored 3 km depth so direct observation is impossible instead this question has been approached in four main ways 1 geophysical inspections of active arcs 2 mineral geochronology 3 field observations of plutons and 4 thermal and physical modeling of magmatic systems each of these four avenues has their own strengths and shortcomings many times the interpretation of these data appears to be at odds some overarching observations can be made about what we know of the state of active intermediate to silicic arc magmatic systems geophysical observations such as seismic tomography have yielded little evidence for large bodies of fully molten magma persistently underneath arc volcanoes if anything only small lenses of partial melt are observed at

the regional geology and evolution of the toba volcano tectonic depression indonesia the late quaternary toba volcano tectonic depression in the sunda arc is the largest resurgent cauldron in the world and lies in one of the largest ignimbrite fields the toba tuffs although composed of at least 3000 km 3 of acid tuffs spread over 20000 km 2 of mainland sumatra the greater part of the toba tuffs is believed to be a single ignimbrite cooling unit formed about 100 000 years ago the toba tuffs also include a 30000 year old airfall tuff which was erupted from a centre just n of the toba depression the toba depression developed through the same stages as other resurgent cauldrons it formed after lithification of the toba tuffs by collapse along regional faults crossing an eastwards bulge in the sumatran geanticline resurgent uplift raised lake sediments within the depression by about 500 m the uplift which was not confined to the depression was probably caused by continuing influx of magma and it is possible that the toba depression is still in the stage of post resurgence volcanism the eruption of the toba tuffs and of all post ignimbrite volcanism took place on the line of the western marginal fault of the depression this marginal fault once extended northwards offshore into a zone of miocene back arc rifting

crustal imaging of western michoacan and the jalisco block mexico from ambient seismic noise abstract detailed crustal imaging of western michoacan and the jalisco block is obtained from ambient noise tomography results show a deep and well delineated volcanic system below the colima volcano complex rooting up to 22 km depth with a shallow magmatic chamber constrained to the first 7 km a shallow low velocity system to the south of the chapala rift and west of the michoacan guanajuato volcanic field merges underneath the colima rift with the colima volcano system at about 20 km depth honoring the geometry of the trans mexican volcanic belt for depths greater than 30 km low velocity features become parallel to the slab strike right beneath the mascota ayutla and tapalpa volcanic fields suggesting the presence of the mantle wedge above the rivera plate all mentioned low velocity bodies are spatially correlated with the superficial volcanic activity suggesting their magmatic origin so that the shallower these bodies the younger are the associated volcanic deposits along the coast different depths of the uppermost layer of the rivera and the cocos plates suggest that the latter plate subducts with an angle 9 steeper than the former

studying deep sources of volcanism using multiscale seismic tomography abstract this paper presents an overview of several examples of multiscale studies of different volcanic systems including intracontinental collisional and subduction related volcanic areas regional tomographic models of the upper mantle are presented for three regions with the cenozoic intracontinental volcanism in eurasia namely europe southern siberia and eastern arctic in all cases recent volcanic fields correlate with low velocity anomalies in the mantle the modeling results show that these volcanic manifestations are related to large hot areas in the mantle and not to thin column shaped contrasted plumes as presumed by many collisional type volcanism is discussed with an example of the caucasus and the surrounding areas the regional tomographic model for this region reveals a lack of mantle lithosphere beneath the collision zone volcanism in this area is most likely due to the direct heating of the thick crust by the hot asthenosphere a dominantly felsic composition of the crust facilitates upward transport of the fluids and melts that leads to volcanic eruption subduction related volcanic systems are discussed for three different scale levels an example of a regional model of the mantle beneath the sunda arc reveals the general configuration of the slab middle scale tomographic models in areas of the toba caldera central java and central andes display feeding paths of the arc volcanoes from the slab the feeding paths are apparent in all of the considered cases but have different shapes depending on the unique features of the subduction regimes an example of a detailed local scale study of magmatic sources in the crust is discussed for the kluchevskoy volcano group it is found that the main volcano kluchevskoy is fed through a complex three layered system of magma sources another volcano of the same group bezymianny seems to be connected with the mantle through a direct short lived channel which appears only during the eruption periods a time dependent tomography study performed for this group over a period of ten years clearly reveals the correlation between the changes in the seismic structures and the stages of the volcanic process namely preparation activation and relaxation

new insight into cainozoic sedimentary basins and palaeozoic suture zones in southeast australia from ambient noise surface wave tomography 1 detailed images of rayleigh wave group velocity are derived from ambient seismic noise recorded by wombat a large rolling seismic array project in southeast australia group velocity maps sensitive to crustal structure exhibit low velocity anomalies in the presence of sedimentary basins and recent hot spot volcanism and high velocities in regions of out cropping metamorphic and igneous rocks distinct and well constrained patches of low velocity within the murray basin provide new insight into the spatial extent and possible composition of pre tertiary infra basins in a broader tectonic context our results show little evidence for the palaeozoic building blocks of the southeast australian continent that have been inferred from geological mapping and potential field data this may mean that apparent changes in basement terrane near the surface are not associated with major changes in composition at depth

stratigraphy paleomagnetism and magnetic fabric of the toba tuffs constraints on the sources and eruptive styles the toba depression in north central sumatra is a complex of several overlapping calderas resulting from three major ignimbrite forming eruptions within the depression the upland masses of samosir and northern uluan consist of welded ignimbrite capped by coarse breccia and lacustrine sediment hitherto interpreted to be two parts of a single resurgent dome this study has demonstrated that the welded tuffs of samosir and uluan have different magnetic polarities and therefore at least two different ignimbrites are present the samosir uluan massif may consist of parts of two resurgent domes the first ignimbrite eruption occurred at 0 84 ma and produced a very thick 400 m densely welded unit having a reversed polarity anisotropy of magnetic susceptibility ams flow direction and lithic size data indicate that the source lies in the southern part of the toba depression and the thick deposit of uluan is thought to have ponded in a 40 km wide caldera the second ignimbrite is normally magnetized ams flow direction data indicate two separate source vents one to the north in the haranggaol caldera and another to the south the thick deposit at samosir is thought to have ponded in the southern caldera coarse sediments then accumulated over samosir and northern uluan and were capped by lacustrine deposits a renewed episode of resurgence then uplifted samosir island and possibly the northern part of uluan at approximately 0 075 ma the last and apparently largest ignimbrite eruption occurred from calderas in the north and south parts of the toba depression this ignimbrite is mostly nonwelded and normally magnetized part of the uluan dome was destroyed by collapse of the sibandung caldera and latung graben and concomitant with renewed subsidence of the haranggaol and porsea calderas

lateral variation in slab orientation beneath toba caldera northern sumatra the investigator fracture zone ifz subducts beneath toba caldera the earth s largest quaternary caldera in northern sumatra suggesting a possible relationship between them locations of sub crustal earthquakes based on arrival times of p and s waves at a seismograph network surrounding toba reveal the geometry of the subducted slab and the ifz beneath toba a vertical tear of less than 20 km in the slab across the ifz as previously suggested cannot be ruled out but the large scale geometry of the slab is dominated by a broad bend of slab contours parallel to the concaveseaward indentation of the trench the slab shape is probably a response to the trench curvature can explain the change in trend of the volcanic arc near toba and may cause shallowing of the forearc basin near nias island the decrease in radius of curvature of the slab contours is not accompanied by an observable decrease in dip angle possibly resulting in lateral compressive stress in the slab the high rate of seismicity along the subducted investigator fracture zone that intersects the slab obliquely to its plunge direction is uncommon at subducted fracture zones and is likely caused by such lateral stress in the slab

a large magmatic sill complex beneath the toba caldera an understanding of the formation of large magmatic reservoirs is a key issue for the evaluation of possible strong volcanic eruptions in the future we estimated the size and level of maturity of one of the largest volcanic reservoirs based on radial seismic anisotropy we used ambient noise seismic tomography below the toba caldera in northern sumatra to observe the anisotropy that we interpret as the expression of a fine scale layering caused by the presence of many partially molten sills in the crust below 7 kilometers this result demonstrates that the magmatic reservoirs of present non eroded supervolcanoes can be formed as large sill complexes and supports the concept of the long term incremental evolution of magma bodies that lead to the largest volcanic eruptions

three dimensional upper crustal structure of the geothermal system in tarutung north sumatra indonesia revealed by seismic attenuation tomography the geothermal potential in tarutung is controlled by both the sumatra fault system and young arc volcanism in this study we use the spatial distribution of seismic attenuation calculated from local earthquake recordings to image the 3 d seismic attenuation of the area and relate it with the temperature anomalies and the fluid distribution of the subsurface a temporary seismic network of 42 stations was deployed around tarutung and sarulla south of tarutung for a period of 10 months starting in 2011 may within this period the network recorded 2586 local events a high quality subset of 229 events recorded by at least 10 stations was used for the attenuation inversion tomography path average attenuation t p was calculated by using a spectral inversion method the spread function the contour lines of the model resolution matrix and the recovery test results show that our 3 d attenuation model q p has good resolution around the tarutung basin and along the sarulla graben high attenuation low q p related to the geothermal system is found in the northeast of the tarutung basin suggesting fluid pathways from below the sumatra fault the upper part of the studied geothermal system in the tarutung district seems to be mainly controlled by the fault structure rather than by magmatic activities in the southwest of the tarutung basin the high attenuation zone is associated with the martimbang volcano in the sarulla region a low q p anomaly is found along the graben within the vicinity of the hopong caldera

diverse late stage crystallization and storage conditions in melt domains from the youngest toba tuff revealed by age and compositional heterogeneity in the last increment of accessory phase growth the chemical record contained within the final increment of growth on crystals is utilized to reveal the dynamics and timescales of magma assembly and storage before eruption of the cataclysmic 2800 km3 youngest toba tuff ytt indonesia in situ u th disequilibrium dates and trace element concentrations were obtained via secondary ionization mass spectrometry sims on unsectioned and unpolished faces of individual zircon and allanite crystals the six high silica 73 wt sio2 pumices from which crystals were derived are among the more evolved and lower crystallinity 25 wt pumices from the ytt eruption and likely represent the melt dominated portion of the magma system discrete sims measurement cycles were coupled with statistical treatments to detect zircon and allanite surface zoning domains at the 1 m scale coupled r melts and accessory phase saturation modeling indicates that at the granite ternary minimum or eutectoid conditions that define this portion of the ytt zircon and allanite crystallization is dependent on and proportionate to major phase crystallization and is more limited than at pre eutectoid conditions a lower proportion of near eruption zircon surface ages in the comparatively cool and wet ytt relative to other hotter and drier voluminous silicic eruptions could reflect the influence of eutectoid storage conditions on magmatic responses to remobilization related magmatic recharge

three dimensional models of p wave velocity and p to s velocity ratio in the southern central andes by simultaneous inversion of local earthquake data the pisco 94 proyecto de investigation sismologica de la cordillera occidental 1994 seismological network of 31 digital broad band and short period three component seismometers was deployed in northern chile between the coastal cordillera and the western cordillera more than 5300 local seismic events were observed in a 100 day period a subset of high quality p and s arrival time data was used to invert simultaneously for hypocenters and velocity structure additional data from two other networks in the region could be included the velocity models show a number of prominent anomalies outlining an extremely thickened crust about 70 km beneath the forearc region an anomalous crustal structure beneath the recent magmatic arc western cordillera characterized by very low velocities and a high velocity slab a region of an increased vp vs ratio has been found directly above the wadati benioff zone which might be caused by hydration processes a zone of lower than average velocities and a high vp vs ratio might correspond to the asthenospheric wedge the upper edge of the wadati benioff zone is sharply defined by intermediate depth hypocenters while evidence for a double seismic zone can hardly be seen crustal events between the precordillera and the western cordillera have been observed for the first time and are mainly located in the vicinity of the salar de atacama down to depths of about 40 km

seismic structure changes beneath redoubt volcano during the 2009 eruption inferred from local earthquake tomography we present seismic velocity models of the area beneath redoubt volcano alaska corresponding to two time periods before and after the strong eruption that occurred in march 2009 the calculations were based on tomographic inversion of p and s arrival time data recorded by 19 stations using the local earthquake tomography code lotos we performed thorough analysis of the results based on synthetic tests in each of the time periods that allow real time variations in structure to be distinguished from artifacts caused by changes in the observation system configurations in the resulting images corresponding to the period before the eruption the summit area is characterized by higher values of both p and s velocities and moderate values of the vp vs ratio this may correspond to the rigid igneous rocks composing the body of the volcano that lack significant liquid content in the second episode corresponding to the time of the eruption the p velocity remained high whereas the s velocity became very low the anticorrelation of p and s anomalies in the summit area produced a vp vs ratio as high as 2 2 which is seen down to 2 3 km depth this indicates presence of mobile phase at shallow depth beneath the volcano which can be either in the form of partial melt or fluid saturated rocks

shallow s wave velocity structure from ambient seismic noise at planchon peteroa volcanic complex argentina chileshallow s wave velocity structure from ambient seismic noise at planchon peteroa

attenuation tomography in the western central andes a detailed insight into the structure of a magmatic arc high quality data from 1498 local earthquakes recorded by the pisco 94 proyecto de investigation sismologica de la cordillera occidental 1994 and ancorp 96 andean continental research project 1996 temporary seismological networks allowed the detailed determination of the three dimensional 3 d attenuation structure qp 1 beneath the recent magmatic arc in the western central andes 20 to 24 s assuming a frequency independent qp 1 in a frequency band between 1 and 30 hz whole path attenuation t was estimated from the amplitude spectra of the p waves using spectral ratios and a spectral inversion technique the damped least squares inversion tomography of the data reveals a complex attenuation structure crust and mantle of the forearc and subducting slab are generally characterized by low attenuation qp 1000 crust and mantle beneath the magmatic arc show elevated attenuation the strongest anomaly of extremely low qp is found in the crust between 22 and 23 s beneath the recent volcanic arc qp 100 n s variations can be observed the western flank of the crustal attenuation anomaly follows the curved course of the volcanic front north of 21 s the attenuation is less developed in the northern part of the study area the low qp zone penetrates in the forearc mantle down to the subducting slab in the south a deeper zone of high attenuation is resolved between 23 and 24 s directly above the subducting slab low qp in the mantle correlates with earthquake clusters the strong crustal attenuation is confined to the distribution of young ignimbrites and silicic volcanism and is interpreted as a thermally weakened zone with partial melts the attenuation pattern in the upper mantle might reflect the variable extent of the asthenosphere and maps variations of subduction related hydration processes in the mantle wedge from slab derived fluids

time distance helioseismology the application of seismology to the study of the solar interior1 2 helioseismology has advanced almost solely by the prediction and measurement of the sun s frequencies of free oscillation or normal modes direct measurement of the travel times and distances of individual acoustic waves the predominant approach in terrestrial seismology3 would appear to be more difficult in view of the number and stochastic nature of solar seismic sources here however we show that it is possible to extract time distance information from temporal cross correlations of the intensity fluctuations on the solar surface this approach opens the way for seismic studies of local solar phenomena such as subsurface in homogeneities near sunspots and should help to refine global models of the internal velocity stratification in the sun

lake toba volcano magma chamber imaged by ambient seismic noise tomography 1 for the first time ambient noise tomography is used to clearly image the magma chamber beneath lake toba caldera one of the largest quaternary calderas on earth using data from 40 seismic stations deployed between may and october 2008 around lake toba empirical green s functions are extracted from long term cross correlations of continuous records these functions are dominated by rayleigh waves whose group velocities can be measured in the period range from 2 5 to 12 seconds arrival times of these waves are picked for a given period and inverted using 2 d tomography to calculate lateral variations in velocity for the given period this was done for six different periods which all correspond to different sampling depths thus the six 2 d models presented together provide information on velocity variations with depth the results show a low velocity body coincident with the lake toba caldera representing the magma chamber under the volcano the chamber is observed to have a complex 3 d geometry with at least two separate sub chambers underlying the caldera other results include a deep low velocity body possibly another magma chamber south west of the lake with an upper limit of 7 km depth the maximum depth to which this body reaches could not be resolved the sumatra fault marks a velocity contrast but only down to depths not greater than 5 km the reliability of the results was further confirmed by checkerboard recovery tests

reconstructing green s function by correlation of the coda of the correlation c3 of ambient seismic noise analysis of long range correlation of the microseisms has been shown to provide reliable measurements of surface wave speeds that can be used for seismic imaging and monitoring in the case of an even distribution of noise sources it has been theoretically demonstrated that the correlation is the exact green s function including all types of waves this method is limited in its application by the actual source distribution in practice the azimuthal distribution of energy flux of the noise is dominated by some particular directions resulting in a clear azimuthal dependence of the quality of the reconstruction of rayleigh waves with a poor reconstruction in some azimuths to solve this problem we use noise correlations measured on the entire network we consider two stations a and b for which the rayleigh waves could not be discerned in the in the correlation of continuous records of ambient noise we computed all correlations between the station a respectively b and all the 150 other stations located at regional distances theoretically these virtual seismograms contain direct waves and coda although they are clearly contaminated by the influence of the imperfect ambient noise field and most are inadequate for direct analysis we used these correlation functions as equivalents to seismograms produced by sources acting at the 150 stations locations and recorded in a respectively b we select time windows in those virtual seismograms that correspond to coda and compute correlations between them this metacorrelation is found to exhibit the surface wave part of the green s function that was not visible in the raw correlation of ambient noise we illustrate the legitimacy of the reconstruction by comparison with raw noise correlations this procedure can be used to assess seismic velocity between stations even in presence of a directive and poorly oriented ambient noise the result shows that in spite of the small signal to noise ratios often seen in correlations of ambient noise especially at large lag time corresponding to coda their codas are better equipartitioned than was the ambient noise upon which they were based they are therefore presumably multiply scattered and contain information on both direct surface waves and also on more complex travel paths

rayleigh wave group velocity of the icelandic crust from correlation of ambient seismic noise 1 by cross correlating 2 years of ambient seismic noise from 31 broadband stations distributed across iceland we have been able to measure rayleigh wave group velocity in three discrete frequency bands centered on 4 7 and 17 s sensitive to approximately the top 6 10 and 25 km of the crust for 289 420 and 139 station to station paths respectively these are inverted to yield tomographic group velocity maps of the icelandic crust the results correlate with the major tectonic features on iceland and agree well with earlier seismic studies based on traditional methods active source and earthquake specifically we obtain low velocities in the central parts of iceland coinciding with the rift zones and young crust in contrast the parts of iceland covered with older tertiary volcanics reveal relatively higher velocities at the shorter periods 4 and 7 s this correlation reflects porosity degree of fracturing and alteration at the longest period 17 s i e at greater depth this correlation may reflect the thermal state of the crust with warm and seismically slow material near the rifts and cooler and seismically faster material beneath the tertiary formations to the east and west

distribution of magma beneath the toba caldera complex north sumatra indonesia constrained by three dimensional p wave velocities seismicity and gravity data 1 we estimate the one and three dimensional p wave velocity structure beneath the toba caldera complex a 30 100 km topographic depression in north sumatra using arrival time data of local earthquakes recorded by a 40 station seismic network that operated for 4 months inversions reveal the presence of p velocities up to 37 below normal that likely map the distribution of magma within this subduction related volcanic system considered the world s largest in the upper 10 km of crust the largest low velocity region underlies the southern two thirds of the depression and coincides with a gravity low centered over the resurgent dome a smaller volume of low velocities is observed in the upper crust under the north end of the depression separating the two regions is a zone of locally high velocities indicating that the shallow subcaldera magma system is composed of two separate reservoirs not a single one that extends the entire length of the caldera complex above each low velocity region is a postcollapse volcano that erupted mostly mafic lavas after the last major caldera collapse 74 kyr ago a low velocity column below one of these volcanoes can be traced into the uppermost mantle and corresponds with a planar distribution of low frequency earthquakes in the 20 to 40 km depth range the low frequency earthquakes apparently record the migration of melt in the mafic roots of this large volume crustal magma system

acehseis project provides insights into the detailed seismicity distribution and relation to fault structures in central aceh northern sumatra abstract for the first time a dense seismic network acehseis consisting of 30 short period seismic stations was installed for 10 months from july 2014 in order to record crustal earthquakes in central aceh northern sumatra following the hazardous earthquake with magnitude mw 6 1 july 2nd 2013 the objective of this research is to investigate the active fault characteristics derived from local earthquake data combined with a digital elevation model the network recorded more than 1790 local events occurring along the main great sumatran fault gsf and its secondary faults local earthquakes with azimuthal gap angles greater than 180 were excluded to avoid non unique earthquake locations therefore from all recorded earthquakes 1127 local earthquakes were used for further seismological analysis a method of simultaneous earthquake relocation and 1d velocity determination was applied to obtain better location of earthquakes the output of the first relocated seismicity was then relocated again by using a double difference relocation method after relocation earthquakes are concentrated in a narrow zone along the active fault indicating the reliability of the earthquake location we then determined the focal mechanism of earthquakes based on the first polarity picks the seismicity distribution correlates with the well known gsf and its main secondary faults earthquake locations also clearly revealed several active segments which include the batee beutong tangse geumpang lampahan aceh and seulimeum and nisam faults also less known faults as the pamue and atu lintang peusangan faults are imaged in northern aceh an unknown earthquake cluster associated with an active fault the nisam fault was detected which is also visible in the topography the seismicity along gsf is offset at around 96 7 e constrained by the nearly n s striking atu lintang peusangan fault confirming the segmentation of gsf at this longitude the aceh segment and the seulimum fault in the northernmost region of the network are both active and clearly imaged by the seismicity the pamue and the lampahan faults seem to be the splay of gsf as indicated by identical strike direction as the gsf the lampahan fault is characterized by nw se seismicity lineation which is in agreement with the focal mechanisms the laut tawar lake could be a part of the lampahan fault that is also offset at 96 7 e at the line of the atu lintang peusangan fault the burni geureudong fault on the other hand strikes ene wsw which suggests a conjugate fault of the lampahan fault

data assimilation strategies for volcano geodesy abstract ground deformation observed using near real time geodetic methods such as insar and gps can provide critical information about the evolution of a magma chamber prior to volcanic eruption rapid advancement in numerical modeling capabilities has resulted in a number of finite element models targeted at better understanding the connection between surface uplift associated with magma chamber pressurization and the potential for volcanic eruption robust model data fusion techniques are necessary to take full advantage of the numerical models and the volcano monitoring observations currently available in this study we develop a 3d data assimilation framework using the ensemble kalman filter enkf approach in order to combine geodetic observations of surface deformation with geodynamic models to investigate volcanic unrest the enkf sequential assimilation method utilizes disparate data sets as they become available to update geodynamic models of magma reservoir evolution while the enkf has been widely applied in hydrologic and climate modeling the adaptation for volcano monitoring is in its initial stages as such our investigation focuses on conducting a series of sensitivity tests to optimize the enkf for volcano applications and on developing specific strategies for assimilation of geodetic data our numerical experiments illustrate that the enkf is able to adapt well to the spatial limitations posed by gps data and the temporal limitations of insar and that specific strategies can be adopted to enhance enkf performance to improve model forecasts specifically our numerical experiments indicate that 1 incorporating additional iterations of the enkf analysis step is more efficient than increasing the number of ensemble members 2 the accuracy of the enkf results are not affected by initial parameter assumptions 3 gps observations near the center of uplift improve the quality of model forecasts 4 occasionally shifting continuous gps stations to provide variability in the locations of observations results in better model predictions than utilizing fixed locations when the number of available instruments is limited 5 spotty insar data coverage on the flanks of a volcano due to topographic shadows and or atmospheric interference does not adversely impact the effectiveness of enkf if the available coverage is 50 and 6 snow or glacial obstruction in the center of uplift can adversely impact enkf forecasts by utilizing these strategies we conclude that the enkf is an effective sequential model data fusion technique for assimilating multiple geodetic observations to forecast volcanic activity at restless volcanoes

converted wave imaging of the toba caldera indonesia 1 receiver functions calculated from data recorded by the 1995 passcal toba seismic experiment in northern sumatra indonesia and the permanent station psi reveal the presence of a low seismic velocity zone at between 8 and 14 km depth which is interpreted to be the top of a magma reservoir the moho under the toba caldera lies near 30 km with a localized thickened region that reaches 39 km beneath the eastern edge of the caldera with an abrupt shallowing to the northeast this thickened crust may be where hot gabbroic material underplates the base of the crust to serve as the heat source for shallower volcanism alternatively the thickened crust and moho offset may be due to localized crustal thickening when this region was situated in a sharp restraining bend of a now extinct segment of the sumatran fault

stratigraphy of the toba tuffs and the evolution of the toba caldera complex sumatra indonesia during the past 1 2 m y a magma chamber of batholithic proportions has developed under the 100 by 30 km toba caldera complex four separate eruptions have occurred from vents within the present collapse structure which formed from eruption of the 2800 km3 youngest toba tuff ytt at 74 ka eruption of the three older toba tuffs alternated from calderas situated in northern and southern portions of the present caldera the northern caldera apparently developed upon a large andesitic stratovolcano the calderas associated with the three older tuffs are obscured by caldera collapse and resurgence resulting from eruption of the ytt samosir island and the uluan block are two sides of a single resurgent dome that has resurged since eruption of the ytt samosir island is composed of thick ytt caldera fill whereas the uluan block consists mainly of the oldest toba tuff ott in the past 74000 years lava domes have been extruded on samosir island and along the caldera s western ring fracture this part of the ring fracture is the site of the only current activity at toba updoming and fumarolic activity the toba eruptions document the growth of the laterally continuous magma body which eventually erupted the ytt repose periods between the four toba tuffs range between 0 34 and 0 43 m y and give insights into pluton emplacement and magmatic evolution at toba

ambient seismic noise tomography reveals a hidden caldera and its relation to the tarutung pull apart basin at the sumatran fault zone indonesia abstract we analyzed the noise recordings of a short period seismic network to derive a shallow crustal s wave velocity model at the sumatra fault in northern sumatra indonesia by correlating the noise of 40 seismic stations recording for 9 months we could recover rayleigh waves from vertical component recordings with sufficient signal to noise ratio group velocities of the rayleigh waves could be determined in the period range from 0 71 to 4 4 s these group velocities were used to invert for 2d group velocity maps at specific periods finally the derived group velocity maps were inverted for a 3d s wave velocity model this model shows a region of a strong velocity decrease off the great sumatran fault zone at the northeastern margin of the young tarutung pull apart basin this observed low velocity block coincides with a caldera like morphological feature which is interpreted as the surface expression of a hidden volcanic caldera considering the surface manifestations of geothermal activity around this anomaly we conclude that the caldera is still acting as a heat source on the other hand the weak morphological expression at the surface indicates a certain age of the caldera which might be older than the tarutung pull apart basin the findings provide important constraints on general concepts for the formation of pull apart basins along the sumatran fault and their relation to volcanism