source process of very long period events accompanying long period signals at cotopaxi volcano ecuador abstract renewed seismic activity of cotopaxi ecuador began in january 2001 with the increased number of long period lp events followed by a swarm of volcano tectonic vt earthquakes in november 2001 in late june 2002 the activity of very long period vlp 2 s events accompanying lp 0 5 1 s signals began beneath the volcano the vlp waveform was characterized by an impulsive signature which was accompanied by the lp signal showing non harmonic oscillations we observed temporal changes of both the vlp and lp signals from the beginning until september 2003 the vlp signal gradually disappeared and the lp signal characterized by decaying harmonic oscillations became dominant assuming possible source geometries we applied a waveform inversion method to the observed waveforms of the largest vlp event our inversion and particle motion analyses point to volumetric changes of a sub vertical crack as the vlp source which is located at a depth of 2 3 km beneath the northeastern flank the spectral analysis of the decaying harmonic oscillations of lp events shows frequencies between 2 0 and 3 5 hz with quality factors significantly above 100 the increased vt activity and deformation data suggest an intrusion of magma beneath the volcano a release of gases with small magma particles may have repetitively occurred due to the pressurization which was caused by sustained bubble growth at the magma ceiling the released particle laden gases opened a crack above the magma system and triggered the resonance of the crack we interpret the vlp and lp events as the gas release process and the resonance of the crack respectively

interpreting avulsion process from ancient alluvial sequences guadalope matarranya system northern spain and wasatch formation western colorado alluvial deposits of the guadalope matarranya system oligocene ebro basin spain and the wasatch formation eocene western colorado provide time integrated records of the process of river channel avulsion these sequences consist of isolated channel belt sandstones incised into and abruptly overlain by flood plain siltstones indicating deposition by avulsive river systems the geometry and distribution of channel incisions suggest that avulsion was not controlled by tectonics climate or base level changes but formed by autocyclic processes measurements from 221 channel fills in the guadalope matarranya system and 38 from the wasatch formation allow us to statistically characterize channel geometries we infer to be associated with establishment and abandonment of individual river avulsions paleoflow depths in both systems average 1 4 to 1 6 m aggradation height superelevation of channel margin levees are on average 0 6 and 1 1 times paleoflow depth in the guadalope matarranya and wasatch systems respectively these results are consistent with values from recently avulsed modern rivers and suggest that 1 flow depth is the appropriate parameter against which to scale the critical superelevation necessary for channel avulsion and 2 the increase in potential energy due to channel perching drives the lateral instability that is needed for avulsion to be successful numerous stacked channel fills indicate repeated reoccupation of the same site by avulsing channels these reoccupation channels indicate that inherited flood plain topography here abandoned channel forms was an important control on the arrival site of newly avulsed channels comparison of our results to others suggests two end member types of avulsion can take place incisional avulsion seen here is characterized by an early incision phase followed by infilling by migrating bar forms aggradational avulsion begins with aggradation followed in time by stream integration into a single downcutting channel we suggest that the type of avulsion is strongly influenced by whether or not the adjacent flood plain is well or poorly drained in both cases subsequent aggradation and channel perching increase the chances that some triggering event will lead to avulsion

a review on phreatic eruptions and their precursors abstract an analysis of the reported information on 132 historical phreatic events indicates that most of these 115 were not followed by a magmatic or phreatomagmatic eruption only in 18 cases precursory phenomena are reportedly lacking whereas they are recognized for the majority 72 of the considered cases these precursors have been analyzed as a function of the kind of phreatic event and of its possible triggering mechanism unfortunately the quality of the available information is poor however data suggest that anomalous seismicity ground deformation changes in the output chemistry and temperature of fumaroles and thermal springs are potential mid term precursors whereas seismic tremor is a common short term precursor

causes of recent himalayan uplift deduced from deposited patterns in the ganges basin the hypothesis1 that late cenozoic uplift of many of the world s mountain ranges was a response to climate change rather than to tectonic processes is based on the premise that enhanced erosion in an altered climate led to a reduction in both the total mass of a mountain range and its mean elevation this reduction was coeval with increased regional relief and with passive isostatic uplift of the remaining summits the hypothesis is difficult to evaluate because both climate and tectonic forces affect uplift in many active ranges in the absence of sufficient denudational and uplift data from the mountains themselves depositional patterns in adjacent basins may sometimes be used to distinguish between uplift arising from erosional or from tectonic processes in foreland basins uplift of the proximal basin and a reduction or absence of asymmetric subsidence are predicted responses to erosionally driven uplift2 here i show that patterns of sediment accumulation and the position of major rivers in the neogene gangetic foreland basin seem to have changed markedly in plio pleistocene times these changes lend support to the hypothesis that the importance of erosional unloading has increased in the himalayas during the past 4 myr

avulsions and the spatio temporal evolution of debris flow fans debris flows are water laden masses of sediment that move rapidly through channel networks and over alluvial fans where they can devastate people and property episodic shifts in the position of a debris flow channel termed avulsions are critical for debris flow fan evolution and for understanding flow hazards because avulsions distribute debris flow deposits through space and time however both the mechanisms of flow avulsion and their effects on the long term evolution of debris flow fans are poorly understood here we document and analyze the spatial and temporal patterns of debris flow activity obtained by repeat topographic analyses dendrogeomorphic and lichenometric reconstructions and cosmogenic radionuclide dating on 16 fans from japan usa switzerland france and kyrgyzstan where possible we analyze the observed spatio temporal patterns of debris flow activity in conjunction with high resolution topographic data to identify the main controls on avulsion we identify two main processes that control avulsions on debris flow fans operating over distinct time scales first during individual flows or flow surges deposition of sediment plugs locally blocks channels and forces subsequent flows to avulse into alternative flow paths plug deposition is a stochastic process but appears to depend in part on the sequence of flow volumes the geometry of the channel and the composition of the flows second over time scales of tens of events the average locus of debris flow deposition gradually shifts toward the topographically lower parts of a fan highlighting the importance of topographic compensation for fan evolution our documented debris flow avulsions often but not always follow a pattern of channel plugging backstepping of deposition toward the fan apex over one or more flows avulsion and establishment of a new active channel large flows can have contrasting impacts depending on whether or not they follow smaller flows that have deposited channel plugs these results suggest that avulsions and spatio temporal patterns of debris flow fan formation strongly depend on both the magnitude frequency distribution and the sequence of the flows feeding a fan while individual avulsions are generally abrupt and difficult to predict the presence of debris flow plugs and patterns of backstepping may be useful as indicators of impending avulsions over longer time scales the compensational tendency of flows to avulse into topographic depressions on the fan may also be used to identify sectors of the fan that are at risk of future inundation

source mechanisms of explosions at stromboli volcano italy determined from moment tensor inversions of very long period data 1 seismic data recorded in the 2 30 s band at stromboli volcano italy are analyzed to quantify the source mechanisms of strombolian explosions during september 1997 to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous elastic medium that takes topography into account two source centroids are identified each representative of the distinct event types associated with explosive eruptions from two different vents the observed waveforms are well reproduced by our inversion and the two source centroids that best fit the data are offset 220 and 260 m beneath and 160 m northwest of the active vents the source mechanisms include both moment tensor and single force components the principal axes of the moment tensor have amplitude ratios 1 1 2 which can be interpreted as representative of a crack if one assumes the rock matrix at the source to have a poisson ratio n 1 3 a value appropriate for hot rock both imaged cracks dip 60 to the northwest and strike northeast southwest along a direction parallel to the elongation of the volcanic edifice and a prominent zone of structural weakness as expressed by lineaments dikes and brittle structures for our data set the volume changes estimated from the moments are 200 m 3 for the largest explosion from each vent together with the volumetric source is a dominantly vertical force with a magnitude of 10 8 n consistent with the inferred movement of the magma column perched above the source centroid in response to the piston like rise of a slug of gas in the conduit index terms 7215 seismology earthquake parameters 7280 seismology volcano seismology 8419 8414 volcanology eruption mechanisms keywords very long period seismicity moment tensor inversions eruption mehanics

simplified process modeling of river avulsion and alluvial architecture connecting models and field data abstract modeling is an invaluable tool for studying sedimentary basin filling and for understanding depositional processes with long recurrence intervals including channel avulsion simplified modeling approaches such as cellular models and process analogue experiments are particularly useful for efficiently exploring alternative hypotheses and evaluating first order controls on river avulsion and alluvial architecture here we review the history and current state of the art in simplified avulsion and alluvial architecture models with a particular focus on how results and insights from these models can be incorporated into field and subsurface studies and vice versa simplified avulsion and alluvial architecture models have proliferated in the past decade providing a wide variety of models to serve as a basis for future coupled field modeling studies we compare features of leading models and discuss avenues for effectively pairing model capabilities with hypotheses and field data outstanding questions highlighted by recent modeling efforts include 1 what thresholds control avulsion initiation in different systems 2 how do floodplain processes and topography influence avulsion dynamics and alluvial architecture 3 what factors determine where avulsion channels stabilize answering these questions will require targeted modeling efforts coupled to data from ancient systems hence our model comparison emphasizes features that can be used to choose or design fit for purpose models and we outline how quantitative data useful for model selection and validation can be obtained from modern systems and ancient deposits matching model goals with targeted questions and model parameters and predictions with quantitative field data will help tighten communication between field and model oriented sedimentary geologists facilitating advances in our understanding of river avulsion and alluvial architecture

modeling the dynamics of a phreatic eruption based on a tilt observation barrier breakage leading to the 2014 eruption of mount ontake japan although phreatic eruptions are common volcanic phenomena that sometimes result in significant disasters their dynamics are poorly understood in this study we address the dynamics of the phreatic eruption of mount ontake japan in 2014 based on analyses of a tilt change observed immediately 450 s before the eruption onset we conducted two sets of analysis a waveform inversion and a modified phase space analysis our waveform inversion of the tilt signal points to a vertical tensile crack at a depth of 1100 m our modified phase space analysis suggests that the tilt change was at first a linear function in time that then switched to exponential growth we constructed simple analytical models to explain these temporal functions the linear function was explained by the boiling of underground water controlled by a constant heat supply from a greater depth the exponential function was explained by the decompression induced boiling of water and the upward darcy flow of the water vapor through a permeable region of small cracks that were newly created in response to ongoing boiling we interpret that this region was intact prior to the start of the tilt change and thus it has acted as a permeability barrier for the upward migration of fluids it was a breakage of this barrier that led to the eruption

source mechanism of vulcanian degassing at popocatepetl volcano mexico determined from waveform inversions of very long period signals 1 the source mechanism of very long period vlp signals accompanying volcanic degassing bursts at popocatepetl is analyzed in the 15 70 s band by minimizing the residual error between data and synthetics calculated for a point source embedded in a homogeneous medium the waveforms of two eruptions 23 april and 23 may 2000 representative of mild vulcanian activity are well reproduced by our inversion which takes into account volcano topography the source centroid is positioned 1500 m below the western perimeter of the summit crater and the modeled source is composed of a shallow dipping crack sill with easterly dip of 10 intersecting a steeply dipping crack northeast striking dike dipping 83 northwest whose surface extension bisects the vent both cracks undergo a similar sequence of inflation deflation and reinflation reflecting a cycle of pressurization depressurization and repressurization within a time interval of 3 5 min the largest moment release occurs in the sill showing a maximum volume change of 500 1000 m3 pressure drop of 3 5 mpa and amplitude of recovered pressure equal to 1 2 times the amplitude of the pressure drop in contrast the maximum volume change in the dike is less 200 300 m3 with a corresponding pressure drop of 1 2 mpa and pressure recovery equal to the pressure drop accompanying these volumetric sources are single force components with magnitudes of 108 n consistent with melt advection in response to pressure transients the source time histories of the volumetric components of the source indicate that significant mass movement starts within the sill and triggers a mass movement response in the dike within a few seconds such source behavior is consistent with the opening of a pathway for escape of pent up gases from slow pressurization of the sill driven by magma crystallization the opening of this pathway and associated rapid evacuation of volcanic gases induces the pressure drop pressure recovery in the magma filling the sill is driven by diffusion of gases from the resulting supersaturated melt into bubbles assuming a penny shaped crack at ambient pressure of 40 mpa the observed pressure and volume variations can be modeled with the following attributes crack radius 100 m crack aperture 5 m bubble number density 1010 1012 m 3 initial bubble radius 10 6 m final bubble radius 10 5 m and net decrease of gas concentration in the melt 0 01 wt

a coral oxygen isotope record from the northern red sea documenting nao enso and north pacific teleconnections on middle east climate variability since the year 1750 a 245 year coral oxygen isotope record from the northern red sea ras umm sidd egypt 28 n in bimonthly resolution is presented the mean annual coral 18o signal apparently reflects varying proportions of both sea surface temperature and 18oseawater variability in conjunction with instrumental observations of climate the coral record suggests for interannual and longer timescales that colder periods are accompanied by more arid conditions in the northern red sea but increased rainfall in the southeastern mediterranean whereas warmer periods are accompanied by decreased rainfall in the latter and less arid conditions in the northern red sea a 70 year oscillation of probably north atlantic origin dominates the coral time series interannual to interdecadal variability is correlated with instrumental indices of the north atlantic oscillation nao the el nino southern oscillation enso and north pacific climate variability the results suggest that these modes contributed consistently to middle east climate variability since at least 1750 preferentially at a period of 5 7 years

tectonics and climate of the southern central andes the history of the southern central andes including the world s second largest plateau and adjacent intermontane basins and ranges of the eastern cordillera and the northern sierras pampeanas of argentina and bolivia impressively documents the effects of tectonics and topography on atmospheric circulation patterns the development of orographic barriers and their influence on erosion and landscape evolution at various timescales protracted aridity in the orogen interior has facilitated the creation and maintenance of the puna altiplano plateau contraction and range uplift filling of basins and possibly wholesale uplift of the plateau increased gravitational stresses in the orogen interior which caused the eastward migration of deformation into the foreland and successive aridification the uplift of the andean orogen has also had a far reaching influence on atmospheric and moisture transport patterns in south america this is documented by the onset of humid climate conditions on the eastern side of the andes in late miocene time which was coupled with the establishment of dramatic precipitation gradients perpendicular to the orogen and changes in tectonic processes in the andean orogenic wedge

variability in eruption style and associated very long period events at fuego volcano guatemala 1 repeated short term deployments of seismic infrasound video and gas emission instruments at fuego volcano guatemala have revealed three types of very long period vlp events associated with conduit sealing pressure accumulation and release in 2008 ash rich explosions issued from a vent on the western flank and produced one type of vlp type 1 impulsive bomb rich explosions from the summit vent in 2009 produced a shorter period vlp type 2 but also generated ash release type 3 vlp events occurred during ash free exhalations from the summit in 2008 and had waveform shapes similar to type 2 events weak infrasound records for type 1 explosions compared to type 2 suggest lower pressures and higher magma porosity for type 1 type 3 events correlate with spikes in so2 emission rate and are driven by partial sealing and rapid release of ash free gas at the summit vent variations in the vlp period may provide a new tool for monitoring conditions within the conduit

complexity in a cellular model of river avulsion abstract we propose a new model of river avulsion that emphasizes simplicity self organization and unprogrammed behavior rather than detailed simulation the model runs on a fixed cellular grid and tracks two elevations in each cell a high elevation representing the channel levee top and a low one representing the channel bottom the channel aggrades in place until a superelevation threshold for avulsion is met after an avulsion is triggered a new flow path is selected by steepest descent based on the low values of elevation flow path depends sensitively on floodplain topography particularly the presence of former abandoned channels several behavioral characteristics emerge consistently from this simple model 1 a tendency of the active flow to switch among a small number of channel paths which we term the active channel set over extended periods leading to clustering and formation of multistory sand bodies in the resulting deposits 2 a tendency for avulsed channels to return to their previous paths so that new channel length tends to be generated in relatively short segments and 3 avulsion related sediment storage and release leading to pulsed sediment output even for constant input each of these behaviors is consistent with observations from depositional river systems a single valued threshold produces a wide variety of avulsion sizes and styles larger nodal avulsions are rarer because pre existing floodplain topography acts to steer flow back to the active channel channel stacking pattern is very sensitive to floodplain deposition this work highlights the need to develop models of floodplain evolution at large time and space scales to complement the improving models of river channel evolution

conditions for branching in depositional rivers it is often taken for granted that rivers organize transport into a single active channel in some net depositional environments however flow of water and sediment is distributed in several stable channels such branching rivers may be confined in valleys anabranching or anastomosed or unconfined on deltas distributaries and their existence confronts us with the very basic question of what governs the spatial organization of channel patterns in sedimentary landscapes current models for equilibrium channel morphology cannot predict the occurrence of branching rivers because they do not consider dynamical processes such as avulsion i e the rapid abandonment of a channel in favor of a new path at lower elevation the requisite conditions for avulsion have been the subject of ongoing debate here we resolve the conditions leading to channel avulsion and show that branching rivers occur when avulsion is the dominant mechanism of lateral channel motion a compilation of field and laboratory data demonstrates that avulsion frequency scales with the time required for sedimentation on channel beds to produce a deposit equal to one channel depth from the relative rates of bank erosion and channel sedimentation we derive a dimensionless mobility number that accurately predicts the conditions under which anabranching and distributary channels occur results may be directly applied to modeling landscape evolution over human and geologic time scales and for inverting formative environmental conditions from channel deposits on earth and other planetary surfaces

significance of channel belt clustering in alluvial basins the distribution of channel deposits in alluvial basins is commonly used to interpret past changes in climate tectonics and sea level here we present preliminary evidence that longtime scale 10 3 10 5 yr self organization in fl uvial systems may generate structured stratigraphic patterns spontaneously in the absence of or independent from changing basin boundary conditions a physical experiment and an ancient alluvial succession ferris formation latest cretaceous paleogene south central wyoming both show stratigraphy where clusters of many closely spaced channel deposits are separated from each other by extensive intervals of overbank mudstones analysis using spatial point process methods shows that channel deposits in both basins are statistically clustered over intermediate basin length scales in the experiment external controls base level subsidence rate and sediment water supplies were not varied and therefore not factors in cluster formation likewise the ancient system lacks stratigraphic and sedimentologic evidence of external controls on channel clustering we propose that channel clusters as seen in this study refl ect a scale of flself organization that is not usually recognized in ancient deposits this type of internally generated stratigraphy should be considered when reconstructing tectonic climate and sea level changes from

avulsion flow path selection on rivers in foreland basins river avulsions help distribute sediment across the floodplain and the frequency and flow path selected by each avulsion determines flooding and sedimentation patterns however rivers avulse infrequently making it difficult to quantify flow path behavior and test hypotheses posed by experimental and numerical studies we used google earth engine to create a novel data set of 55 avulsions that occurred from a d 1984 to 2014 in the andean and himalayan foreland basins on each avulsion we measure hop length the displacement of the avulsion across the floodplain orthogonal to the parent channel and avulsion length the length of the parent channel reach without controlling for external factors such as climate or geology we find that both hop length and avulsion length scale with parent channel belt width avulsion channels tend to hop 2 5 channel belt widths away from their parent channel and avulsion length is 13 4 parent channel belt widths we use these data to test between end member scenarios where flow paths are randomly selected or steered by floodplain topography observed avulsions are inconsistent with flow path predictions derived from a directed random walk model and a scaling analysis of alluvial ridge size shows that hop lengths are set by alluvial ridge widths these results suggest that avulsion flow path selection in the andean and himalayan basins is driven by alluvial ridge topography which promotes evenly spaced or compensational channel sand bodies over decadal time scales these data and results are important for understanding controls on avulsion flow path selection and how avulsion processes are represented in the stratigraphic record of foreland basins

configuration of subducting philippine sea plate and crustal structure in the central japan region a seismic experiment with six explosive sources and 391 seismic stations was conducted in august 2001 in the central japan region the crustal velocity structure for the central part of japan and configuration of the subducting philippine sea plate were revealed a large lateral variation of the thickness of the sedimentary layer was observed and the p wave velocity values below the sedimentary layer obtained were 5 3 5 8 km s p wave velocity values for the lower part of upper crust and lower crust were estimated to be 6 0 6 4 and 6 6 6 8 km s respectively the reflected wave from the upper boundary of the subducting philippine sea plate was observed on the record sections of several shots the configuration of the subducting philippine sea slab was revealed for depths of 20 35 km the dip angle of the philippine sea plate was estimated to be 268 for a depth range of about 20 26 km below this depth the upper boundary of the subducting philippine sea plate is distorted over a depth range of 26 33 km a large variation of the reflected wave amplitude with depth along the subducting plate was observed at a depth of about 20 26 km the amplitude of the reflected wave is not large and is explained by the reflected wave at the upper boundary of the subducting oceanic crust however the reflected wave from reflection points deeper than 26 km showed a large amplitude that cannot be explained by several reliable velocity models some unique seismic structures have to be considered to explain the observed data such unique structures will provide important information to know the mechanism of inter plate earthquakes d 2004 elsevier b v all rights reserved

source mechanism of a very long period event at mt ontake central japan response of a hydrothermal system to magma intrusion beneath the summit abstract a very long period vlp volcanic event which occurred on 25 january 2007 beneath mt ontake central japan was recorded by nearby broadband seismometers as well as the japanese nationwide hi net and f net seismic networks the vlp waveforms show a pulse like shape with a duration of approximately 1 min the vlp event was accompanied by a burst sequence of long period lp events we carried out waveform inversion to determine the source mechanism and location of the vlp event our analysis indicates volumetric changes in an inclined crack seismic moment of 10 14 nm at the vlp source which is located at 0 6 km above sea level beneath the summit of mt ontake and above dikes determined from gps data the source time functions of the vlp event showed a pulse like triangular shape indicating inflation followed by deflation of the crack at the source we interpreted the result of the waveform inversion as follows gases released from the intruded magma heated an aquifer system beneath the summit of mt ontake a break of unstable superheated water in a hydrothermal crack in the system caused vaporization of water and associated crack inflation which was followed by discharge of steam from the crack resulting in its collapse these processes caused the vlp event which may have been a precursor of a small phreatic eruption that occurred in late march 2007

mechanism of phreatic eruptions at aso volcano inferred from near field broadband seismic observations broadband seismometers deployed at aso volcano in japan have detected a hydrothermal reservoir 1 to 1 5 kilometers beneath the crater that is continually resonating with periods as long as 15 seconds when phreatic eruptions are observed broadband seismograms elucidate a dynamic interplay between the reservoir and discharging flow along the conduit gradual pressurization and long period 20 seconds pulsations of the reservoir during the 100 to 200 seconds before the initiation of the discharge followed by gradual deflation of the reservoir concurrent with the discharging flow the hydrothermal reservoir where water and heat from the deeper magma chamber probably interact appears to help control the surface activity at aso volcano

helium 3 emission related to volcanic activity the helium 3 helium 4 ratio in bubbling gases from ten hot springs located around mount ontake an active volcano in central japan ranges from 1 71 r sub atm 1 71 times the atmospheric ratio of 1 40 x 10 sup 6 to 6 15 r sub atm the value of the ratio decreases with distance from the central cone of the volcano such a tendency may be a characteristic of helium 3 emission in volcanic areas and suggests more primitive helium 3 is carried with fluid flowing through a conduit during volcanic activity 6 references 1 figure 1 table

tilt effects on moment tensor inversion in the near field of active volcanoes dynamic tilts rotational motion around horizontal axes change the projection of local gravity onto the horizontal components of seismometers this causes sensitivity of these components to tilt especially at low frequencies we analyse the consequences of this effect onto moment tensor inversion for very long period vlp events in the near field of active volcanoes on the basis of synthetic examples using the station distribution of a real deployed seismic network and the topography of mt merapi volcano java indonesia the examples show that for periods in the vlp range of 10 30 s tilt can have a strong effect on the moment tensor inversion although its effect on the horizontal seismograms is significant only for few stations we show that tilts can be accurately computed using the spectral element method and include them in the green s functions the simulated tilts might be largely influenced by strain tilt coupling stc however due to the frequency dependence of the tilt contribution to the horizontal seismograms only the largest tilt signals affect the source inversion in the vlp frequency range as these are less sensitive to stc than the weaker signals the effect of stc can likely be neglected in this application in the converse argument this is not necessarily true for longer periods where the horizontal seismograms are dominated by the tilt signal and rotational sensors would be necessary to account for it as these are not yet commercially available this study underlines the necessity for the development of such instruments

waveform inversion in the frequency domain for the simultaneous determination of earthquake source mechanism and moment function summary we propose a method of waveform inversion to rapidly and routinely estimate both the moment function and the centroid moment tensor cmt of an earthquake in this method waveform inversion is carried out in the frequency domain to obtain the moment function more rapidly than when solved in the time domain we assume a pure double couple source mechanism in order to stabilize the solution when using data from a small number of seismic stations the fault and slip orientations are estimated by a grid search with respect to the strike dip and rake angles the moment function in the time domain is obtained from the inverse fourier transform of the frequency components determined by the inversion since observed waveforms used for the inversion are limited in a particular frequency band the estimated moment function is a bandpassed form we develop a practical approach to estimate the deconvolved form of the moment function from which we can reconstruct detailed rupture history and the seismic moment the source location is determined by a spatial grid search using adaptive grid spacings which are gradually decreased in each step of the search we apply this method to two events that occurred in indonesia by using data from a broad band seismic network in indonesia jisnet one northeast of sulawesi m w 7 5 on 2007 january 21 and the other south of java m w 7 5 on 2006 july 17 the source centroid locations and mechanisms we estimated for both events are consistent with those determined by the global cmt project and the national earthquake information center of the u s geological survey the estimated rupture duration of the sulawesi event is 16 s which is comparable to a typical duration for earthquakes of this magnitude while that of the java event is anomalously long 176 s suggesting that this event was a tsunami earthquake our application demonstrates that this inversion method has great potential for rapid and routine estimations of both the cmt and the moment function and may be useful for identification of tsunami earthquakes

upstream and downstream controls of recent avulsions on the taquari megafan pantanal south western brazil avulsion the natural relocation of a river is a key process in the evolution of subaerial fans river floodplains and deltas the causes of avulsion are poorly understood which is partly due to the scarcity of field studies of present avulsions at present two avulsions are occurring on the middle and lower taquari megafan pantanal basin south western brazil here we present an analysis of the causes of these avulsions based on field and remote sensing data and show that avulsions on megafans can be controlled by both upstream and downstream processes the middle fan avulsion started in 1997 1998 is a result of upstream control overbank aggradation was caused by the variable input of sandy sediment into the system which caused channel belt superelevation and also created an easily erodible subsurface favouring bank retreat crevassing and scour of deep floodplain channels the sandy subsurface in this area is inferred to have been a major factor in the causation of this avulsion under conditions of little gradient advantage the lower fan avulsion started c 1990 results from interplay of upstream and downstream controls the latter being related to the local base level the paraguay river floodplain at the toe of the fan channel and overbank aggradation on the lower fan was influenced by fan sub lobe progradation and channel backfilling fan sub lobe progradation caused a significant gradient advantage of the avulsion channel over the parent channel avulsions are commonly supposed to be preferentially triggered by high magnitude floods when there is considerable channel belt superelevation however both avulsions studied by us were triggered by small to average floods with modest channel belt superelevation we conclude that flood magnitude and channel belt superelevation have been overrated as causes of avulsion and demonstrate additional causes that influence the growth of crevasses into avulsions

the use of earthquake rate changes as a stress meter at kilauea volcano stress changes in the earth s crust are generally estimated from model calculations that use near surface deformation as an observational constraint but the widespread correlation of changes of earthquake activity with stress has led to suggestions that stress changes might be calculated from earthquake occurrence rates obtained from seismicity catalogues although this possibility has considerable appeal because seismicity data are routinely collected and have good spatial and temporal resolution the method has not yet proven successful owing to the non linearity of earthquake rate changes with respect to both stress and time here however we present two methods for inverting earthquake rate data to infer stress changes using a formulation for the stress and time dependence of earthquake rates application of these methods at kilauea volcano in hawaii yields good agreement with independent estimates indicating that earthquake rates can provide a practical remote sensing stress meter

river avulsions on the taquari megafan pantanal wetland brazil abstract the pantanal wetland is located in a tectonically active interior sedimentary basin in west central brazil the south flowing paraguay river is the trunk river of an alluvial constructional landform comprising several large alluvial fans the largest one of which is the taquari megafan the taquari river flows in two distinct geomorphologic zones within the megafan entrenched on sediments of pleistocene fan lobes the taquari river flows in a 3 to 5 km wide meander belt in the upper fan where avulsion is hindered by entrenchment downstream of the intersection point stream discharge progressively decreases and the taquari river becomes narrow and shallow toward the paraguay river plain within the distributary fan lobe the channel levee sandy complex is topographically higher than the adjacent floodplains and avulsion is a natural consequence of crevasses in the natural levees many channel avulsions have occurred during the last decades and documented cases show that significant channel changes may take place in a few years beginning with crevassing in 1988 and ending with the abandonment of the former channel in 1998 the river completely changed course in the lower fan presently a major avulsion is occurring in the upper portion of the growing fan lobe where many crevasses have appeared in the natural levees with associated splays onto the floodbasin new anastomosed channels have formed north of the taquari river but downstream of them the flow is unconfined and the water spreads into natural floodbasins this avulsion is still in process and allows observation of channel evolution the geomorphic features produced the sedimentary processes involved and resulting effects if the new channels do not rejoin the main channel the river mouth may abandon its present master channel and shift to a position a hundred kilometers north from its present position a large volume of sediment has been transferred to the floodbasin with progradation of crevasse splay deposits over fine overbank sediments many geomorphic features recognizable in satellite and radar images clearly show that avulsion has occurred many times before in the taquari river avulsion belt deposits and former diverted channels testify to ancient avulsion events within the fan lobe and show that progradation of splays onto the floodbasin is the most important infilling process within the taquari distributary fan lobe the avulsion process in the lower taquari river has accelerated in the last 30 years along with the magnitude of flooding pasture and intensive agriculture in the catchment area has increased the sediment supply to the wetland but larger floods are also a consequence of higher rainfall since 1973 avulsion and floods have been a cause of great concern among the local population and landowners before human intervention in attempting to control floods however a better understanding of the avulsive river system is needed especially because a major navigation project including the channelization of the paraguay river was recently proposed

scale dependent compensational stacking an estimate of autogenic time scales in channelized sedimentary deposits recent studies show that paleoenvironmental allogenic signals preserved in the stratigraphic record may be contaminated or overprinted by internally generated autogenic sedimentation this is problematic but it is unclear over what temporal and spatial scales autogenic patterns are most prevalent we propose that scale breaks in basin fi lling trends can be used to identify the transition between allogenic and autogenic stratigraphy using data from numerical and physical experiments and an ancient outcrop we explore how compensation the tendency for sediment transport systems to preferentially fi ll topographic lows varies with stratigraphic scale object based models demonstrate the temporal scales at which stratigraphy changes from being partially infl uenced by autogenic processes to being completely determined by allo genic forcings and suggest that this transition occurs at a time scale set by the maximum scale of surface roughness in a transport system divided by the long term aggradation rate this hypothesis is validated in a physical experiment where delta topography was monitored along fl ow perpendicular transects at a high temporal resolution relative to channel kine matics the strength of compensation in the experiment changes at the predicted time scale where the maxi mum surface roughness is equal to the depth of the experimental channels above this compensation time scale deposits stack purely compensationally but below this time scale deposits stack somewhere between randomly and deterministically similar scale dependent stacking is also observed in the ferris formation cretaceous paleogene hanna basin wyoming united states this study demonstrates that scale dependent compensational stack ing may be useful for isolating allogenic and autogenic stratigraphy in sedimentary basins

eruption dynamics at mount st helens imaged from broadband seismic waveforms interaction of the shallow magmatic and hydrothermal systems 1 the current eruption at mount st helens is characterized by dome building and shallow repetitive long period lp earthquakes waveform cross correlation reveals remarkable similarity for a majority of the earthquakes over periods of several weeks stacked spectra of these events display multiple peaks between 0 5 and 2 hz that are common to most stations lower amplitude very long period vlp events commonly accompany the lp events we model the source mechanisms of lp and vlp events in the 0 5 4 s and 8 40 s bands respectively using data recorded in july 2005 with a 19 station temporary broadband network the source mechanism of the lp events includes 1 a volumetric component modeled as resonance of a gently nnw dipping steam filled crack located directly beneath the actively extruding part of the new dome and within 100 m of the crater floor and 2 a vertical single force attributed to movement of the overlying dome the vlp source which also includes volumetric and single force components is 250 m deeper and nnw of the lp source at the sw edge of the 1980s lava dome the volumetric component points to the compression and expansion of a shallow magma filled sill which is subparallel to the hydrothermal crack imaged at the lp source coupled with a smaller component of expansion and compression of a dike the single force components are due to mass advection in the magma conduit the location geometry and timing of the sources suggest the vlp and lp events are caused by perturbations of a common crack system

stratigraphy and paleohydrology of delta channel deposits jezero crater mars abstract the jezero crater open basin lake contains two well exposed fluvial sedimentary deposits formed early in martian history here we examine the geometry and architecture of the jezero western delta fluvial stratigraphy using high resolution orbital images and digital elevation models dems the goal of this analysis is to reconstruct the evolution of the delta and associated shoreline position the delta outcrop contains three distinct classes of fluvial stratigraphy that we interpret from oldest to youngest as 1 point bar strata deposited by repeated flood events in meandering channels 2 inverted channel filling deposits formed by avulsive distributary channels and 3 a valley that incises the deposit we use dems to quantify the geometry of the channel deposits and estimate flow depths of 7 m for the meandering channels and 2 m for the avulsive distributary channels using these estimates we employ a novel approach for assessing paleohydrology of the formative channels in relative terms this analysis indicates that the shift from meandering to avulsive distributary channels was associated with an approximately four fold decrease in the water to sediment discharge ratio we use observations of the fluvial stratigraphy and channel paleohydrology to propose a model for the evolution of the jezero western delta the delta stratigraphy records lake level rise and shoreline transgression associated with approximately continuous filling of the basin followed by outlet breaching and eventual erosion of the delta our results imply a martian surface environment during the period of delta formation that supplied sufficient surface runoff to fill the jezero basin without major drops in lake level but also with discrete flooding events at non orbital e g annual to decadal timescales

lithium and strontium isotopic systematics of waters around ontake volcano japan implications for deep seated fluids and earthquake swarms abstract since 1976 earthquake swarms have occurred beneath the southeast flank of ontake volcano in central japan electrical conductivity surveys have shown that these earthquake swarms are associated with the upwelling of deep seated fluid to investigate the nature of the deep seated fluid we analyzed 7 li 6 li and 87 sr 86 sr ratios of water samples collected from springs and wells around ontake volcano in 2000 2003 2005 2007 and 2009 the li and sr isotopic compositions of these water samples are largely explained by binary component mixing between near surface meteoric water and non surface fluid at each sampling site on the basis of their cl li and cl sr ratios we singled out water samples whose li and sr isotopic ratios were minimally affected by meteoric water contamination to represent non surface fluids the li and sr isotopic compositions of most ontake non surface fluids except for samples from the earthquake swarm region can be explained as the result of volcanic fluids reacting with basement rocks where they acquired upper crustal signatures we attribute the fluid associated with the region of earthquake swarms to the lower crust beneath the study area

autogenic sedimentation in clastic stratigraphy internally generated or autogenic terrestrial and marine sediment transport dynamics can produce depositional patterns similar to those associated with climatic tectonic or sea level changes a central challenge in accurately interpreting the sedimentary archive is determining what scales and types of deposits reflect autogenic controls on sedimentation in different environments autogenic sediment transport dynamics commonly result from intermittent sediment storage in transient landforms which produces episodic spatially discontinuous sedimentation across a basin the transition from localized variable sedimentation to even basin wide sedimentation marks the shift from stochastic landscape dynamics to deterministic deposition responding to the long term balance between sediment supply and the creation of space to accommodate sediment this threshold can be measured in a wide variety of stratigraphic successions and has important bearing on whether climatic tectonic or sea level signals can be

waveform inversion of volcano seismic signals assuming possible source geometries 1 we propose an approach to quantify the source of volcano seismic signals assuming possible source geometries such an assumption reduces the number of free parameters in a waveform inversion so we can quantify the source of these signals observed by a small number of seismic stations we test this method by using the synthesized waveforms radiated by a fluid filled crack and with seismic data observed at kusatsu shirane volcano we find that waveform data from 2 to 3 three component seismic stations surrounding the source enable us to estimate the source mechanism and location in the present approach

very long period seismic signals and caldera formation at miyake island japan over a period of roughly 40 days starting on 8 july 2000 a caldera structure 1 7 kilometers in diameter developed by means of gradual depression and expansion of the summit crater at miyake island japan at the same time very long period vlp seismic signals were observed once or twice a day source mechanism analyses of the vlp signals show that the moment tensor solutions are smooth step functions over a time scale of 50 seconds with dominant volumetric change components we developed a model to explain the caldera and the vlp signals in which a vertical piston of solid materials in the conduit is intermittently sucked into the magma chamber by lateral magma outflow this model offers potential for making quantitative estimations of the characteristic physical properties of magma systems

evidence from the ad 2000 izu islands earthquake swarm that stressing rate governs seismicity magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat such swarm seismicity also migrates with time and often exhibits a dog bone shaped distribution the largest earthquakes in swarms produce aftershocks that obey an omori type exponential temporal decay but the duration of the aftershock sequences is drastically reduced relative to normal earthquake activity here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion a 1 000 fold increase in seismicity rate and a 1 000 fold decrease in aftershock duration occurred during the two month long dyke intrusion we find that the seismicity rate is proportional to the calculated stressing rate and that the duration of aftershock sequences is inversely proportional to the stressing rate this behaviour is in accord with a laboratory based rate state constitutive law suggesting an explanation for the occurrence of earthquake swarms any sustained increase in stressing rate whether due to an intrusion extrusion or creep event should produce such seismological behaviour

resuspension of ash after the 2014 phreatic eruption at ontake volcano japan abstract we determined the resuspension process of an ash deposit after the phreatic eruption of september 27th 2014 at ontake volcano japan by analyzing the time series data of particle concentrations obtained using an optical particle counter and the characteristics of an ash sample the time series of particle concentration was obtained by an optical particle counter installed 11 km from the volcano from september 21st to october 19th 2014 the time series contains counts of dust particles ash and soil pollen and water drops and was corrected to calculate the concentration of dust particles based on a polarization factor reflecting the optical anisotropy of particles the dust concentration was compared with the time series of wind velocity the dust concentration was high and the correlation coefficient with wind velocity was positive from september 28th to october 2nd grain size analysis of an ash sample confirmed that the ash deposit contains abundant very fine particles

three dimensional model of alluvial stratigraphy theory and applications abstract a three dimensional model of alluvial stratigraphy has been developed to simulate the spatial distribution proportion and connectedness of coarse grained channel belt deposits in alluvial strata as a function of channel belt width floodplain width bankfull channel depth channel belt and overbank sedimentation rates avulsion location and period compaction and tectonism tilting and faulting in this model a floodplain surface of variable width and length is occupied by a single channel belt changes in floodplain topography are produced by spatial and temporal variation of channel belt and floodplain deposition rates and by compaction and local or regional tectonism the location and timing of avulsions are determined by local changes in floodplain slope relative to channel b lt slope and by flood magnitude and frequency the diverted channel belt follows the locus of maximum floodplain slope at the end of each simulation architectural parameters are calculated including channel deposit proportion and connectedness and the dimensions of channel belt sandstone bodies three dimensional perspective diagrams mesh surfaces and two dimensional stratigraphic sections can be plotted to illustrate depositional surfaces time planes and the location and geometry of coarse grained channel belt deposits within finer grained overbank deposits the model predicts that channel belt proportion and connectedness and dimensions of sandstone bodies vary as a function of distance from avulsion points and cross section orientation upstream from avulsion points sandstone bodies have low width thickness ratios because of aggradation in a fixed channel belt immediately downstream from avulsion points channel belts tend to be connected resulting in sandstone bodies with high width thickness ratios avulsion sequences develop where points of avulsion shift up valley with a progressive decrease in avulsion period such sequences may produce successions in which channel belt proportion and connectedness vary vertically with a cyclic period of 103 to 105 years down valley increases in aggradation rate or down valley decreases in floodplain slope for example associated with a rise in base level may result in an increase in channel belt proportion and connectedness because of high avulsion frequencies in down valley regions of the floodplain down valley decreases in aggradation rate as in alluvial fans foreland basins and during base level fall may result in high avulsion frequencies in up valley parts of the floodplain tectonic tilting and faulting locally increase avulsion probabilities and channel belts generally shift toward areas of maximum subsidence under certain conditions however depositional topography may cause channels to shift away from areas of maximum subsidence channel deposit proportion and connectedness are gen rally high near downthrown areas of the floodplain but distribution clustering of channel belts may not be a reliable indicator of fault geometry or displacement models of alluvial architecture that consider only sediment accumulation rate as the main controlling factor are oversimplified the three dimensional model presented here predicts many of the features of channel behavior observed in modern rivers but there is a pressing need for better models and adequate natural data to test them

characterization of scattered seismic wavefields simulated in heterogeneous media with topography 1 we performed numerical simulations of seismic waveforms with frequencies up to 10 hz in heterogeneous media with topography to investigate the effects of topography and structural heterogeneity on seismic scattering we used the simulated waveforms to test the source location method assuming isotropic radiation of s waves for long period events and tremor at volcanoes the assumption of isotropic radiation has been shown previously to be valid in a high frequency band because of the path effect caused by the scattering of seismic waves our simulation results showed that distortion of the wavefields increased as the correlation distance of structural heterogeneity a decreased as the frequency increased and as the travel distance increased topography alone considerably distorted the wavefields however we found that strong scattering due to topography was suppressed if the correlation distance of structural heterogeneity was longer than the s wave wavelength isotropic radiation of s waves by scattering due to topography was not achieved in our simulations our results indicated that scattering due to structural heterogeneity becomes stronger than that due to topography at ka 1 and a 50 m where k is the wave number of the s waves this suggests that strong short scale structural heterogeneity is required to achieve isotropic radiation of s waves although we could not reproduce isotropic radiation our results support the validity of the assumption of isotropic radiation in the source location method

interpreting paleo avulsion dynamics from multistory sand bodies abstract channel avulsion plays a significant role in building alluvial stratigraphy including fluvial sand bodies with through going erosion surfaces called multistory sand bodies msbs consequently msb characteristics may be useful for interpreting paleo avulsion dynamics from fluvial deposits here using a combination of literature review geometric modeling and field observations we explore the degree to which msb characteristics may be useful for interpreting paleo avulsion dynamics from ancient deposits we use published interpretations of msb origins to identify characteristics that are exclusively associated with avulsion related msbs and find that vertical story stacking irregular msb bounding surfaces and floodplain deposits that correlate with individual stories are attributes uniquely associated with avulsion origin msbs to evaluate how avulsion patterns may affect msb properties we use a 2d geometric model to build synthetic stratigraphy and compare characteristics for msbs formed under different avulsion patterns at a range of model aggradation rates avulsion patterns include random equal probability of a channel relocating anywhere across the model domain compensational channels avulse to the lowest elevation in the model domain at each time step and clustered where channel relocation is restricted to a zone near a previously occupied location model results show that at moderate to high aggradation rates msbs formed under clustered avulsion patterns can be differentiated from those formed via random and compensational avulsion patterns specifically msbs formed by clustered avulsion patterns have many stories and commonly contain remnant floodplain deposits we apply these insights to the well exposed lower williams fork formation upper cretaceous piceance basin colorado usa to demonstrate how they can be used in practice fifty four percent of lower williams fork msbs contain clear evidence for avulsion reoccupation 32 have characteristics suggesting intra channel belt origins and the remaining 20 have ambiguous evidence or insufficient exposure to permit confident process interpretations overall this study demonstrates that despite inherent challenges in eliciting information about avulsion dynamics from the stratigraphic record some msb characteristics can be interpreted as clear signals of paleo avulsion processes

heat source of the 2014 phreatic eruption of mount ontake japan we present petrological evidence of the shallow magmatic processes that may have supplied heat and gas to the eruption of mount ontake japan on 27 september 2014 which resulted in 63 fatalities ash from the eruption comprises primarily hydrothermally altered white toned rock fragments however the ash contains trace amounts 0 7 wt of vitreous less altered particles laps which are only altered on their surfaces suggesting rapid ascent through the hydrothermal system the laps are classified into two categories glassy and crystalline glassy laps comprise high silica rhyolitic glass 74 83 wt sio2 with rounded quartz chalcedony free vesicles and reversely zoned plagioclase cores 47 mol an rims 70 mol an indicating magma re heating crystalline laps have a groundmass like texture that suggests eutectic crystallization at shallow depths thermodynamic calculations indicate that the pre eruptive temperatures of the glassy and crystalline laps were 700 1300 c and 700 c respectively and that the storage depth was 4 km pressure 100 mpa the observed petrological features suggest that the laps were sourced from a magma recently intruded at shallow depths although crustal deformation i e the volume change associated with magmatic intrusion was insignificant prior to the 2014 eruption a clear signature of crustal deformation was observed in 2007 the source of which was located 3 km below the summit we suggest that the magma that was intruded 3 km below the summit in 2007 supplied the heat and gas for the 2014 phreatic eruption

shifting of the kosi river northern india the kosi river shifts laterally over the himalaya foreland plain by continual minor cutoffs and bank cutting and by episodic major shifts across watersheds by moving into and then out of preexisting adjacent less actively aggrading streams migration is unidirectional because after a channel is filled to instability floodwater will drain preferentially into a new adjacent low rather than across it to the next watershed or back to the last abandoned channel major shifts seem stochastic and autocyclic they do not correlate with the many severe quakes and floods that undoubtedly helped prime the system for shifts

real time monitoring and massive inversion of source parameters of very long period seismic signals an application to stromboli volcano italy 1 we present a comprehensive processing tool for the real time analysis of the source mechanism of very long period vlp seismic data based on waveform inversions performed in the frequency domain for a point source a search for the source providing the best fitting solution is conducted over a three dimensional grid of assumed source locations in which the green s functions associated with each point source are calculated by finite differences using the reciprocal relation between source and receiver tests performed on 62 nodes of a linux cluster indicate that the waveform inversion and search for the best fitting signal over 100 000 point sources require roughly 30 s of processing time for a 2 min long record the procedure is applied to post processing of a data archive and to continuous automatic inversion of real time data at stromboli providing insights into different modes of degassing at this volcano

experimental alluvial fan evolution channel dynamics slope controls and shoreline growth 1 river deltas and alluvial fans have channelization and deposition dynamics that are not entirely understood but which dictate the evolution of landscapes of great social economic and ecologic value our lack of a process based understanding of fan dynamics hampers our ability to construct accurate prediction and hazard models leaving these regions vulnerable here we describe the growth of a series of experimental alluvial fans composed of a noncohesive grain mixture bimodal in size and density we impose conditions that simulate a gravel sand fan prograding into a static basin with constant water and sediment influx and the resulting fans display realistic channelization and avulsion dynamics we find that we can describe the dynamics of our fans in terms of a few processes 1 an avulsion sequence with a timescale dictated by mass conservation between incoming flux and deposit volume 2 a tendency for flow to reoccupy former channel paths and 3 bistable slopes corresponding to separate entrainment and deposition conditions for grains several important observations related to these processes are an avulsion timescale that increases with time and decreases with sediment feed rate fan lobes that grow in a self similar quasi radial pattern and channel geometry that is adjusted to the threshold entrainment stress we propose that the formation of well defined channels in noncohesive fans is a transient phenomenon resulting from incision following avulsion and can be directly described with dual transport thresholds we present a fairly complete process based description of the mechanics of avulsion and its resulting timescale on our fans because the relevant dynamics depend only on threshold transport conditions and conservation of mass we show how results may be directly applied to field scale systems

sediment load and floodplain deposition rates comparison of the fly and strickland rivers papua new guinea 1 rates of aggradation and infilling of accommodation space along lowland channels in response to postglacial sea level rise should depend on sediment supply the strickland and fly rivers join at just 6 m above sea level and have experienced the same holocene sea level rise historically the strickland has carried about 7 times the sediment load and 1 4 times the water discharge as the fly therefore we hypothesize that the lowland strickland floodplain should be more developed and consequently should presently be capturing proportionately less sediment than the floodplain of the lowland fly river we use mine derived elevated pb and ag concentrations in 111 shallow 1 m floodplain cores collected in 2003 to determine deposition rates across the lower strickland floodplain sediment deposition rates decrease across the floodplain with distance from the channel bank and the average rate of deposition is 1 4 cm a over the first 1 km overbank deposition along the lowland sandbedded strickland results in 13 loss of the total load 0 05 km of channel length of the main stem deposition rates over the first 1 km from the channel bank on the strickland are about 10 times those on the fly for estimated natural sediment loads however the proportional loss per channel length on the strickland is less than that on the fly 0 09 km of main stem channel length because of an extensive network of tributary and tie channels that convey sediment to the floodplain on the fly furthermore the lateral migration of the strickland channel is 5 times that on the fly such that most overbank deposits on the strickland are returned to the channel causing the net loss of sediment to the floodplain to be small we conclude that the strickland river which has a much higher overbank deposition rate than the fly river as a function of distance from channel bank nonetheless has significantly less net accumulation than the fly because 1 a large proportion of the sediment load is conveyed up tributaries and tie channels on the fly and 2 lateral migration which presumably results from the higher load on the strickland sweeps sediment back into the channel hence our field observations support our initial hypothesis though the primary reason for this is because of active lateral migration rather than low overbank deposition rates

earthquake characteristics before eruptions of japan s ontake volcano in 2007 and 2014 we detect earthquakes associated with japan s ontake eruptions in 2007 and 2014 using the match and locate method thirty seven times more events 4949 than the japan meteorological agency jma catalog 133 and 30 times more events 1880 than the jma catalog 62 are detected during the eruptions of 2007 and 2014 respectively the detected earthquakes are further classified into three different types long period lp events lp associated events and volcano tectonic vt earthquakes both lp and lp associated events are observed in the two eruptions we suggest that the observed intense seismicity before both eruptions indicates the rewaking of ontake volcano and might be used to predict its impending eruption in the long term the temporal persistence and spatial concentration of lp and lp associated events may be used to predict the eventual eruption and eruption location and the maximum magnitude of the lp events may be used as an indicator of eruption magnitude

the source of explosive eruptions of sakurajima volcano japan to understand the nature of explosive eruptions in particular the role played by exsolution of magmatic gases we studied the seismic waveforms produced by two such eruptions of sakurajima volcano on october 30 and november 14 1986 an explosion begins when a mixture of magmatic gases and fragmented magma flows upward through a narrow vertical channel to the surface the source region is a reservoir of gas rich magma where the pressure drops as gases flow out the form of low frequency seismic waves can be explained by a source that consists of two components one component is a single force directed downward that represents the reaction to ejection of gas and magma the other more important component is a moment tensor that represents expansion or contraction of rock around a source the first motion of seismic waves produced by an explosion is directed away from the volcano tilt and strain measurements show that the initial motion directed outward is soon followed by subsidence around the volcano the eigenvectors of the seismic moment tensor are either nearly horizontal or vertical the ratio of horizontal to vertical eigenvalues was 1 8 1 for the october 30 explosion this suggests the geometry of the explosive source can be approximated as a buried vertical cylinder the volume of contraction 2 l03 m3 can be produced by a pressure change of 0 3 mpa over a cylinder with a radius of 160 m and a height of 300 m we propose that an explosive eruption occurs after a small shallow source of high pressure forms within a vertical conduit possibly exsolution of magmatic gases eventually the small source bursts and pushes open a pathway to the surface providing an upward escape for trapped gases it is this burst that causes the initial outwardly directed motion at the surface a deeper reservoir of gas rich magma is then subjected to a lower confining pressure and also bursts causing the explosion

pressure recovery in magma due to bubble growth 1 pressure recovery in magma subject to sudden depressurization is investigated in terms of the growth of bubbles containing magmatic volatiles assuming conservation of volatile mass and pressure equilibration between the bubbles melt and a surrounding elastic medium the final magma pressure is completely determined by its initial pressure and the magnitude of the pressure drop simulations show that the initial magma pressure is easily recovered or even exceeded when magma containing tiny bubbles is surrounded by a relatively stiff elastic medium under low confining pressure this result suggests that when processes such as magma withdrawal dike intrusion and nearby seismicity decrease the pressure in a magma chamber magma re pressurization can occur without new injection of magma

pacific coral oxygen isotope and the tropospheric temperature gradient over the asian monsoon region a tool to reconstruct past indian summer monsoon rainfall having recognized that it is the tropospheric temperature tt gradient rather than the land ocean surface temperature gradient that drives the indian monsoon a new mechanism of el nino southern oscillation enso monsoon teleconnection has been unveiled in which the enso influences the indian monsoon by modifying the tt gradient over the region here we show that equatorial pacific coralline oxygen isotopes reflect tt gradient variability over the indian monsoon region and are strongly correlated to monsoon precipitation as well as to the length of the rainy season using these relationships we have been able to reconstruct past indian monsoon rainfall variability of the first half of the 20th century in agreement with the instrumental record additionally an older coral oxygen isotope record has been used to reconstruct seasonally resolved summer monsoon rainfall variability of the latter half of the 17th century indicating that the average annual rainfall during this period was similar to that during the 20th century copyright 2011 john wiley sons ltd

a 900 year 600 to 1500 a d record of the indian summer monsoon precipitation from the core monsoon zone of india 1 we present a near annually resolved record of the indian summer monsoon ism rainfall variations for the core monsoon region of india that spans from 600 to 1500 a d from a 230th dated stalagmite oxygen isotope record from dandak cave our rainfall reconstruction which spans the medieval warm period mwp and the earliest portion of the little ice age lia indicates that the short instrumental record of ism underestimates the magnitude of monsoon rainfall variability periods of severe drought lasting decades occurred during the 14th and mid 15th centuries and coincided with several of india s most devastating famines

holocene avulsion styles and sedimentation patterns of the saskatchewan river cumberland marshes canada abstract this paper describes the styles and sedimentation patterns of holocene avulsions of the saskatchewan river at the cumberland marshes predating the most recent 1870 s avulsion holocene avulsions involved two major styles 1 progradation of lacustrine deltas and splay complexes and 2 local reoccupation or appropriation of preavulsive channels most avulsions were progradational and occurred in floodplain lakes occupying floodbasin areas between elevated alluvial ridges the two most recent avulsions old channel and 1870 s diverted mainly into inundated peatland progradational avulsions were accompanied by deposition of avulsion belt sediments associated with multiple channel networks the characteristics of avulsion belt deposits include 1 sediments dominated by poorly sorted silt and very fine sand 2 lateral continuity in transverse and longitudinal directions with subhorizontal upper and lower boundaries 3 predominantly nonerosional contacts with underlying sediments 4 coarsening upward successions 5 consistent radiocarbon dates for the tops of preavulsive substrates and 6 occurrence beneath levee and overbank deposits of the associated major channel belt indicating that avulsion belt deposition occurs prior to the development of a new master channel the width of ancient avulsion belts reaches 18 km with typical thicknesses of 2 3 m avulsion belt deposition accompanied by many small channels was followed by flow reversion to a few larger channels and eventually to one single channel accompanied by deposition of levee and channel deposits reoccupational avulsions were not accompanied by deposition of widespread avulsion belt sediments and led mainly to the modification of pre existing channel belts the sedimentation patterns of holocene avulsions of the saskatchewan river reveal that avulsion belt sediments represent major components of the floodplain deposits supporting the model developed from observations of the 1870 s avulsion

configuration of subducting philippine sea plate and crustal structure in the central japan region abstract a seismic experiment with six explosive sources and 391 seismic stations was conducted in august 2001 in the central japan region the crustal velocity structure for the central part of japan and configuration of the subducting philippine sea plate were revealed a large lateral variation of the thickness of the sedimentary layer was observed and the p wave velocity values below the sedimentary layer obtained were 5 3 5 8 km s p wave velocity values for the lower part of upper crust and lower crust were estimated to be 6 0 6 4 and 6 6 6 8 km s respectively the reflected wave from the upper boundary of the subducting philippine sea plate was observed on the record sections of several shots the configuration of the subducting philippine sea slab was revealed for depths of 20 35 km the dip angle of the philippine sea plate was estimated to be 26 for a depth range of about 20 26 km below this depth the upper boundary of the subducting philippine sea plate is distorted over a depth range of 26 33 km a large variation of the reflected wave amplitude with depth along the subducting plate was observed at a depth of about 20 26 km the amplitude of the reflected wave is not large and is explained by the reflected wave at the upper boundary of the subducting oceanic crust however the reflected wave from reflection points deeper than 26 km showed a large amplitude that cannot be explained by several reliable velocity models some unique seismic structures have to be considered to explain the observed data such unique structures will provide important information to know the mechanism of inter plate earthquakes

kar age determination of late quaternary volcanic rocks using the mass fractionation correction procedure application to the younger ontake volcano central japan abstract we propose an age derivation procedure for the k ar dating method to be applied to late quaternary volcanic rocks of low to medium k 2 o content whose k ar ages calculated by the conventional derivation procedure provide insufficient age information in this procedure which we call the mass fractionation correction procedure mfcp the initial 40 ar 36 ar ratios of the samples are estimated from the stable 38 ar 36 ar ratios determined by the unspiked technique assuming that the initial argon isotope ratios of all the samples should lie on a theoretical mass fractionation line of argon in the atmosphere to examine the usefulness of the mfcp systematic k ar age determinations using this procedure were made on volcanic rocks from the stratigraphically well known younger ontake volcano in central japan which has erupted repeatedly over the past 100 ka the k ar ages determined for these volcanics by this procedure generally have analytical uncertainties within 25 1 level and are consistent with the volcanostratigraphy exceptions were the large phenocrysts in pumice fall deposits these may contain significant amounts of excess 40 ar and we considered them to be unsuitable for accurate k ar age determinations of young volcanic rocks in the cases of lava flows which underlie a widespread fallout tephra the k ar ages determined by the mfcp were consistent with the 14 c age of the tephra 21 22 ka

is river avulsion style controlled by floodplain morphodynamics river relocation or avulsion is a fundamental process that fills alluvial basins however it is difficult to predict avulsion patterns because the landscape conditions associated with different avulsion styles are currently unknown two end member avulsion styles have been documented in modern rivers progradational avulsions during which significant floodplain deposition occurs as a new channel is built and incisional avulsions during which floodplain erosion captures flow from a parent channel here we propose that avulsion style is related to the tendency for overbank flows to erode or deposit sediment i e floodplain morphodynamics we present a scaling comparison of floodplain erosion and deposition rates test it with morphodynamic modeling and show field data from ancient deposits that are consistent with modeling results these results demonstrate that floodplain morphodynamics may determine how rivers relocate and that assessing the relative influence of floodplain erosion and deposition may be useful for predicting sedimentation patterns in avulsive systems

spatial variation of overbank aggradation rate and its influence on avulsion frequency river avulsions are commonly considered to be driven by the aggradation and growth of alluvial ridges and the associated increase in cross valley slope relative to either the down channel slope or the down valley slope the latter is termed the slope ratio in the present paper therefore spatial patterns of overbank aggradation rate over stratigraphically relevant time scales are critical in avulsion dominated models of alluvial architecture detailed evidence on centennial to millennial scale floodplain deposition has to date been largely unavailable new data on such long term overbank aggradation rates from the rhine meuse and mississippi deltas demonstrate that the rate of decrease of overbank deposition away from the channel belt is much larger than has been supposed hitherto and can be similar to observations for single overbank floods this leads to more rapid growth of alluvial ridges and more rapid increase in slope ratios potentially resulting in increased avulsion frequencies a revised input parameter for overbank aggradation rate was used in a three dimensional model of alluvial architecture to study its effect on avulsion frequency realistic patterns of avulsion and interavulsion periods 1000 years were simulated with input data from the holocene rhine river with avulsions occurring when the slope ratio is in the range 3 5 however caution should be practised with respect to uncritical use of these numbers in different settings evidence from the two study areas suggests that the avulsion threshold cannot be represented by one single value irrespective of whether critical slope ratios are used as in the present study or superelevation as has been proposed by other investigators

avulsion frequency avulsion duration and interavulsion period of holocene channel belts in the rhine meuse delta the netherlands abstract avulsion parameters greatly influence alluvial architecture because they determine channel density and interconnectedness reliable data on avulsion parameters is still scarce from a detailed reconstruction of the holocene avulsion history of the whole rhine meuse delta we determined quantitative values for the avulsion parameters avulsion frequency avulsion duration and interavulsion period in the rhine meuse delta the number of coeval channels is related to the avulsion frequency calibrated 14c intensity histograms are used to analyze 14c dates of beginning and ending river activity the histograms show that instantaneous and gradual avulsions were almost equally important in the rhine meuse delta a high avulsion frequency occurred from 8000 to 7300 cal yr bp a total of 17 avulsions i e 2 43 avulsions 100 years during this period the avulsion frequency was related to the high rate of sea level rise which induced fluvial sedimentation in the present near coastal area after 7300 cal yr bp avulsion frequency decreased as a result of a continuously decreasing rate of sea level rise from 7300 to 3200 cal yr bp avulsion frequency was low 35 avulsions took place within 4100 years 0 85 avulsions 100 years approximately 5000 cal yr bp the coastal barriers became closed and large scale peat formation occurred this resulted in fixation of the river channels and low cross valley gradients reducing the chances for avulsion between 3200 and 1400 cal yr bp avulsion frequency was high again a total of 34 avulsions i e 1 89 avulsions 100 years as a result of increased discharge and or within channel sedimentation which enhanced chances for avulsion the period of activity of channel belts shows no significant trend on the time scale of the holocene it is highly variable and averages 1280 820 cal yr the avulsion duration fluctuates between less than 200 and 1250 cal years and averages 335 cal years the avulsion duration shows no significant trend through time and remained constant until at least 1900 cal yr bp avulsion duration seems not to be influenced by aggradation rate average interavulsion period is shorter than the period of activity of channel belts and is approximately 945 cal years in the rhine meuse delta on the time scale of the holocene interavulsion period and avulsion duration are on average constant therefore the number of coeval channels is directly related to avulsion frequency available evidence from other rivers and deltas around the world however suggests that the relationship between these avulsion parameters is not everywhere the same

rheological behavior of water ash mixtures from sakurajima and ontake volcanoes implications for lahar flow dynamics lahars represent one of the most serious volcanic hazards potentially causing severe damage to the surrounding environment not only immediately after eruption but also later due to rainfall or snowfall the flow of a lahar is governed by volcanic topography and its rheological behavior which is controlled by its volume microscale properties and the concentration of particles however the effects of particle properties on the rheology of lahars are poorly understood in this study viscosity measurements were performed on water ash mixtures from sakurajima and ontake volcanoes samples from sakurajima show strong and simple shear thinning whereas those from ontake show viscosity fluctuations and a transition between shear thinning and shear thickening particle analysis of the volcanic ash together with a theoretical analysis suggests that the rheological difference between the two types of suspension can be explained by variations in particle size distribution and shape in particular to induce the complex rheology of the ontake samples coexistence of two particle size groups may be required since two independent behaviors one of which follows the streamline stokes number st 1 inertial number i 0 001 and the other shows a complicated motion st 1 i 0 001 compete against each other the variations in the spatial distribution of polydisperse particles and the time dependence of this feature which generates apparent rheological changes indicate that processes related to microscale particle heterogeneities are important in understanding the flow dynamics of lahars and natural polydisperse granular fluid mixtures in general

probable dynamic triggering of phreatic eruption in the tatun volcano group of taiwan abstract on 16 march 2014 utc a small phreatic eruption occurred in the tatun volcano group tvg of taiwan although it was not reported until analysis of both seismic and acoustic data revealed that the source was in the vicinity of the hsiaoyukeng fumarole a replay of the acoustic data accelerated 60 fold reveals that the gradual decrease in frequency that was recorded produces a volcanic whistle similar to the jet of steam released from a heating kettle the phreatic eruption may have been dynamically triggered by a m6 7 earthquake in chile a similar phenomenon occurred on 5 january 2015 when a phreatic eruption was recorded in the tvg immediately after the generation of dynamic seismic waves by an m5 0 earthquake in japan this is the first scientific report of a phreatic eruption detected in the tvg indicating that these volcanoes are still active as a result it is important to monitor their volcanic activity and identify volcanic reservoirs beneath the tvg to mitigate future possible volcanic impact