ocean drilling program leg 112 peru continental margin part 1 tectonic history studies of ocean drilling program leg 112 cores and geophysical data define early eocene quaternary normally faulted continental sediment sequences across the peru margin to the middle slope and a 15 km wide late miocene quaternary accretionary complex beneath the lower slope the eocene shelf and upper slope sea floor were eroded during the oligocene and in middle miocene the seaward part had subsided to lower slope depths this subsidence and the missing paleogene continental slope indicate tectonic erosion during normal plate convergence subduction of the nazca ridge locally accelerated tectonic erosion leaving a scarp but no associated compressional structure nearby late miocene sediment accreted against the erosional scarp local tectonic mechanisms of forearc basin subsidence are suggested by the rapid subsidence of a late miocene forearc basin and stability of the adjacent one despite similar histories of plate convergence

extracting time domain green s function estimates from ambient seismic noise 1 it has been demonstrated experimentally and theoretically that an estimate of the green s function between two seismic stations can be obtained from the time derivative of the long time average cross correlation of ambient noise between these two stations this tdgf estimate from just the noise field includes all tensor components of the green s function and these green s function estimates can be used to infer earth structure we have computed cross correlations using 1 to 30 continuous days of ambient noise recorded by over 150 broadband seismic stations located in southern california the data processing yielded thousands of cross correlation pairs for receiver separations from 4 500 km which clearly exhibit coherent broadband propagating dispersive wavetrains across frequency band 0 1 2 hz

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

hydrodynamics of a forced riffle pool in a gravel bed river 1 mean velocity and turbulence intensity 1 riffle pools are fundamental units of many gravel bed rivers considerable debate exists as to an appropriate hydrodynamic model for this bed form type sampling designs in previous studies have not always anticipated the degree of spatial variability of flow parameters in riffle pools nor considered the effect of the nonuniform boundary on hydrodynamics the objective of this paper is to detail the distribution of mean velocities and turbulence intensities in a forced riffle pool while limited by the lack of lateral velocity measurements the data set is of high quality and includes measurements during a bankfull flood key observations include the perturbation of velocity profiles from what is observed in uniform flow lateral convergence and divergence of flow and the generation of turbulence away from the channel boundary in the thalweg of the pool head velocities are high near the water surface and low near the bed turbulence intensities are relatively high near the bed and may be significant for sediment entrainment higher mean velocities occur over the side bar and could indicate that sediment is routed around the thalweg the midpool is characterized by the lateral constriction of flow and a shear zone downstream of the forcing element the pool tail has very high velocities and turbulence intensities near the bed a velocity reversal occurs in the pool tail at bankfull flow but does not occur in the pool head a consideration of deceleration and acceleration as a result of vertical expansion and contraction is shown to explain many of the key observations

analysis of the 15 december 2017 mw 6 5 and the 23 january 2018 mw 5 9 java earthquakes

crustal thickness beneath mt merapi and mt merbabu central java indonesia inferred from receiver function analysis abstract in this study we analysed 2708 receiver functions rfs using data recorded by 53 seismographic stations that surround mt merapi and mt merbabu two volcanos in central java to map the boundary between earth s crust and upper mantle we observe that a number of rfs from this new dataset have complex signals and do not exhibit typical rf characteristics in particular where the converted ps signal from the moho discontinuity is the clearest and strongest amplitude arrival following the p onset this effect may be related to complex shallow velocity structure due to the presence of magmatic rocks and sediments further analysis of the rf results using the h method suggests that moho depth varies between 27 and 32 km beneath the array with no apparent correlation between crustal thickness and surface topography as one might expect from airy isostacy for instance the moho is quite shallow beneath mt merapi up to 27 km depth despite its elevation of nearly 3 km this may be a consequence of dynamic support from an active upper mantle coupled with erosion and or weakening of the lower crust due to the active volcanic plumbing system to the north of mt merapi the moho is deeper 30 31 km depth below mt merbabu vp vs ratio estimates from the h method are relatively high 1 9 beneath the mt merapi and kendeng basin area which may indicate the presence of a zone of hydrous and active partial melting in the underlying crust lower vp vs ratios 1 7 are found beneath mt merbabu which may be due to its relative lack of volcanic activity compared to mt merapi

the depth of trenches as a function of the subduction rate and age of the lithosphere abstract the trench is one of the most characteristic features of the subduction zones for a given arc or for all the subduction zones put together relationships between their depth variations the variations of the subduction rate and the age of the sinking lithosphere can be established certain other parameters have been examined with those mentioned above but without success it will be demonstrated that the observed relationships can be interpreted in terms of an elastic model and of a viscous model

detection and reconstruction of large scale coherent flow structures in gravel bed rivers large scale flow structures lsfs in the streamwise direction are important features of gravel bed river flows because they may contribute to sediment transport and gas exchange in the present study these structures are detected using huang s empirical mode decomposition and reconstructed with phase averaging techniques based on a hilbert transform of the velocity signal the analysis is based on the fluctuating component of 15 quasi instantaneous velocity profiles measured with a three dimensional 3d acoustic doppler velocity profiler advp in an armoured gravel bed river with a low relative submergence of 2 9 ratio between flow depth and bed grain diameter lsfs were identified in most of the measured profiles and consistently showed similar features we were able to characterize the geometry of these large scale coherent structures the front has a vertical linear shift in the time domain and a vertical profile corresponding to a first quarter moon with the apex situated at z h approximate to 0 4 in the vertical the front scales with flow depth h and in the streamwise direction lsfs scale with three to seven times the mean flow depth on the bed the effect of lsfs is a periodic non linear variation of the friction velocity on average between 0 90 and 1 10 times the mean value a model for the friction velocity cycle resulting from lsfs oscillation is presented copyright c 2014 john wiley sons ltd

relations among subduction parameters clues to the dynamics of the subduction process are found in the many measurable parameters of modern subduction zones based on a critical appraisal of the geophysical and geological literature 26 parameters are estimated for each of 39 modern subduction zones to isolate causal relationships among these parameters multivariate analysis is applied to this data set this analysis yields empirical quantitative relations that predict strain regime and strike slip faulting in the overriding plate maximum earthquake magnitude benioff zone length slab dip arc trench gap and maximum trench depth excellent correlation is found between length of the benioff zone and the product of convergence rate and age of the downgoing slab this relationship is consistent with the conductive heating model of molnar et al 1979 if the model is modified in one respect the rate of heating of the slab is not constant it is substantially slower during passage of the slab beneath the accretionary prism and overriding plate the structural style in the overriding plate is determined by its stress state though the stress state of overriding plates cannot be quantified one can classify each individual subduction zone into one of seven semiquantitative strain classes that form a continuum from strongly extensional class 1 back arc spreading to strongly compressional class 7 active folding and thrusting this analysis indicates that strain class is probably determined by a linear combination of convergence rate slab age and shallow slab dip interplate coupling controlled by convergence rate and slab age is an important control on strain regime and the primary control on earthquake magnitude arc parallel strike slip faulting is a common feature of convergent margins forming a forearc sliver between the strike slip fault and trench optimum conditions for the development of forearc slivers are oblique convergence a compressional environment and a continental overriding plate the primary factor controlling presence of strike slip faulting is coupling strongly oblique convergence is not required the rate of strike slip faulting is affected by both convergence obliquity and convergence rate maximum trench depth is a response to flexure of the underthrusting plate the amount of flexural deflection at the trench depends on the vertical component of slab pull force which is very sensitive to slab age and shallow slab dip shallow slab dip conforms to the cross sectional shape of the overriding plate which is controlled by width of the accretionary prism and duration of subduction deep slab dip is affected by the mantle trajectory established at shallow depth but may be modified by mantle flow much of the structural complexity of convergent margins is probably attributable to terrane juxtaposition associated with temporal changes in both forearc strike slip faulting and strain regime empirical equations relating subduction parameters can provide both a focus for future theoretical studies and a conceptual and kinematic link between plate tectonics and the geology of subduction zones

mechanics of fold and thrust belts and accretionary wedges cohesive coulomb theory a critically tapered fold and thrust belt or submarine accretionary wedge is one that is on the verge of coulomb failure everywhere including its base where frictional sliding along a decollement is assumed to be occurring cohesion within a wedge can add significantly to the overall strength near the toe the effect of this is to decrease the near toe taper leading to a critical topographic profile that is concave upward if the decollement is planar we obtain an approximate self consistent solution for the state of stress within a thin skinned cohesive critical coulomb wedge and determine the relationship between the wedge taper and its strength and basal friction the theory is then applied to the presently deforming fold and thrust belt of western taiwan fitting of theoretical critical wedge shapes to topographic profiles and measurements of the step up angles of thrust faults from the basal decollement are used to constrain the taiwan wedge strength parameters an attractive assertion fully consistent with all the observations is that the mechanics of fold and thrust belts and accretionary wedges is governed by normal frictional and fracture strengths of rocks measured in the laboratory in particular if byerlee s law b 0 85 is adopted as the coefficient of sliding friction on the base we find a coefficient of internal friction 0 9 1 0 in the wedge and a wedge cohesion so 5 20 mpa other solutions having strengths and ambient stresses up to 4 times lower than this can also however satisfy the data

on the choice of boundary conditions in continuum models of continental deformation recent studies of continental deformation have treated the lithosphere as a viscous media and investigated the time evolution of the deformation caused by tectonic and buoyancy forces we examine the differences between continuum models that keep velocity boundary conditions b c constant with time and models that keep stress b c constant with time and demonstrate these differences by using a simple example of a continental lithosphere that is subjected to horizontal compression our results show that in the case of constant stress b c the indentation velocity decreases with time while in the case of constant velocity b c the indentation velocity remains constant with time observations from the tibetan plateau and from the andes indicate that the rate of indentation decreases with time this suggests that when buoyancy forces are comparable in magnitude to tectonic forces constant stress b c are more appropriate for time evolutionary models of continental lithosphere we propose a simple procedure that translates velocity b c which are easy to estimate into stress b c at the initial stage and keep the stress b c constant along the time progression of the calculations

a mixing layer theory for flow resistance in shallow streams 1 a variety of surface roughness characterizations have emerged from nineteenth and twentieth century studies of channel hydraulics when the water depth h is much larger than the characteristic roughness height ks roughness formulations such as manning s n and the friction factor f can be explicitly related to the momentum roughness height zo in the log law formulation for turbulent boundary layers thereby unifying roughness definitions for a given surface however when h is comparable to or even smaller than ks the log law need not be valid using a newly proposed mixing layer analogy for the inflectional velocity profile within and just above the roughness layer a model for the flow resistance in shallow flows is developed the key model parameter is the characteristic length scale describing the depth of the kelvin helmholtz wave instability it is shown that the new theory originally developed for canopy turbulence recovers much of the earlier roughness results for flume experiments and shallow gravel streams this study is the first to provide such a unifying framework between canopy atmospheric turbulence and shallow gravel stream roughness characterization the broader implication of this study is to support the merger of a wealth of surface roughness characterizations independently developed in nineteenth and twentieth century hydraulics and atmospheric sciences and to establish a connection between roughness formulations across traditionally distinct boundary layer types

shear velocity estimates in rough bed open channel flow shear velocity u is an important parameter in geophysical flows in particular with respect to sediment transport dynamics in this study we investigate the feasibility of applying five standard methods the logarithmic mean velocity profile the reynolds stress profile the turbulent kinetic energy tke profile the wall similarity and spectral methods that were initially developed to estimate shear velocity in smooth bed flow to turbulent flow over a loose bed of coarse gravel d 50 15cm under sub threshold conditions the analysis is based on quasi instantaneous three dimensional 3d full depth velocity profiles with high spatial and temporal resolution that were measured with an acoustic doppler velocity profiler advp in an open channel the results of the analysis confirm the importance of detailed velocity profile measurements for the determination of shear velocity in rough bed flows results from all methods fall into a range of 20 variability and no systematic trend between methods was observed local and temporal variation in the loose bed roughness may contribute to the variability of the logarithmic profile method results estimates obtained from the tke and reynolds stress methods reasonably agree most results from the wall similarity method are within 10 of those obtained by the tke and reynolds stress methods the spectral method was difficult to use since the spectral energy of the vertical velocity component strongly increased with distance from the bed in the inner layer this made the choice of the reference level problematic mean shear stress for all experiments follows a quadratic relationship with the mean velocity in the flow the wall similarity method appears to be a promising tool for estimating shear velocity under rough bed flow conditions and in field studies where other methods may be difficult to apply this method allows for the determination of u from a single point measurement at one level in the intermediate range 036 copyright c 2013 john wiley sons ltd

italian and alpine three dimensional crustal structure imaged by ambient noise surface wave dispersion we derive the 3 d crustal structure s wave velocity underneath italy and the alpine region expanding and exploiting the database of ambient noise rayleigh wave phase and group velocity of verbeke et al 2012 we first complement the database of verbeke et al 2012 with a dense set of new ambient noise based phase velocity observations we next conduct a suite of linear least squares inversion of both phase and group velocity data resulting in 2 d maps of rayleigh wave phase and group velocity at periods between 5 and 37 s at relatively short periods these maps clearly reflect the surface geology of the region e g low velocity zones at the po plain at longer periods deeper structures such as moho topography under alps and apennines and lower crust anomalies are revealed our phase and group velocity models are next inverted via the neighbourhood algorithm to determine a set of one dimensional shear velocity models one per phase group velocity pixel resulting in a new three dimensional model of shear velocity vs parameterized in the same way as the european reference crustal model epcrust we also show how well vs is constrained by phase and group dispersion curves the model shows the low velocity area beneath the po plain and the molasse basin the contrast between the low velocity crust of the adriatic domain and the high velocity crust of the tyrrhenian domain is clearly seen as well as an almost uniform crystalline crust beneath the alpine belt our results are discussed from the geological geodynamical standpoint and compared to those of other interdisciplinary studies

the evolution of deformation and topography of high elevated plateaus 1 model numerical analysis and general results a temperature dependent viscoplastic flow model of continental lithosphere is used to investigate the evolution of deformation and topography of high elevated plateaus such plateaus are products of both continent continent collision tibetan plateau and ocean continent collision the altiplano and develop in the overriding continental plate in this study we emphasize the mechanically simpler case of oceanic collision because it does not involve mass transfer between the two plates the lithosphere is deformed in response to tectonic and buoyancy forces the tectonic forces arise from subduction of an oceanic plate or underthrusting of continental lithosphere that horizontally indents and vertically shears the overriding lithosphere the buoyancy forces arise in response to horizontal density variations and tend to relax existing topography or thick crust the time evolution of the deformation and topography is investigated using a finite element technique that solves for the flow field in the overriding lithosphere the model produces dynamically supported near trench topography and inland mountain topography that is isostatically supported by a thick crust a finite region of localized deformation thick crust and high topography develops only if the model includes a horizontal thermal perturbation or an initially thick crust however only thermally perturbed lithosphere generates a plateau topography the shape and size of the calculated plateau depend on the wavelength of the thermal perturbation grashof number and density contrast between the crust and mantle the time evolution of the deformation shows a significant change in the deformation pattern as the high elevated plateau evolves during early stages compressional deformation of the crust and mantle are localized in the thermally perturbed weak zone at later stages as the crust thickens buoyancy forces of larger magnitude resist further thickening of the crust and the locus of compressional crustal deformation migrates inland this migration does not affect the location of the mantle deformation which remains in the thermally weak region but it is accompanied by a significant shear deformation in the weak lower crust the separation of the crustal locus from the mantle locus of deformation emphasizes the importance of vertically dependent deformation in the formation of high elevated plateaus this demonstrates the limitations of models that ignore changes of deformation with depth such as plane stress or thin sheet models

crustal structure beneath hudson bay from ambient noise tomography implications for basin formation summary the hudson bay basin is the least studied of four major phanerozoic intracratonic basins in north america and the mechanism by which it formed remains ambiguous we investigate the crustal structure of hudson bay based on ambient noise tomography using 21 months of continuous recordings from 37 broad band seismograph stations that encircle the bay green s functions that emerge from the cross correlation of these ambient noise recordings are dominated by fundamental mode rayleigh waves in the microseismic period band 5 20 s these signals are most prominently expressed in certain preferred azimuths indicative of stationary coastal source regions in southern alaska and labrador seasonal variations are subtle but consistent with more energetic noise sources during winter months when wave heights in the pacific and north atlantic are larger than in the summer noise emanating from hudson bay does not appear to contribute significantly to the cross correlograms group velocity dispersion curves are obtained by time frequency analysis of cross correlation functions we test and implement a signal to noise ratio snr selection method for producing one sided cross correlograms which yields better defined dispersion ridges than the standard two sided averaging approach tomographic maps and cross sections obtained in the 5 40 s period range reveal significantly lower crustal velocities beneath hudson bay than in the bounding archean superior craton the lowest mid crustal velocities correspond to a previously determined region of maximum lithospheric stretching near the centre of the basin pseudosections extracted from the tomographic inversions along profiles across hudson bay provide the first compelling direct evidence for crustal thinning beneath the basin our results are consistent with a recent estimate of 3 km of crustal thinning but not consistent with a proposed model for basin subsidence triggered by eclogitization of a remnant crustal root

role of viscous plate coupling in the late tertiary andean tectonics 1 plate coupling between oceanic and continental plates in convergent margins of andean type is analyzed from the continuum mechanics approach we postulate a simple mechanism that accounts for the compressive regime in andean type environments in this mechanism deformation in the continental lithosphere is split into two distinctive domains the forearc domain and the arc foreland domain the forearc deformation is controlled by the balance between buoyancy forces associated with the trench and continental slope relief and the stress transferred from the convergence velocity through the age and velocity dependent slip zone the arc foreland deformation is controlled by the absolute plate velocity of the continental plate and the resistance at the slip zone strength of the coupling zone is determined by analyzing the dynamic trench topography along the active margin of south america between 0 and 55 s using this approach we found strength values in the range of 20 95 mpa in strong direct correlation with the age of the subducting plate the slip layer strength observation has been successfully tested against a thermal and strain rate dependent rheological model from this theoretical result we define an empirical relationship between strength of the slip zone and the age and convergence velocity applying this plate coupling model we reproduce shortening rates in the order of 1 10 km myr in agreement with those reported for the late tertiary evolution of the andes model results reproduce some first order features of the geological evolution of the margin such as the shape of the trench the overall andes relief the altiplano buildup and block rotation patterns in addition the model provides a mechanism to explain the evolution of the central depression the inversion of tertiary basins under slow convergence rates during the miocene and the segmentation of the margins tectonic erosion

comparing different methods of bed shear stress estimates in simple and complex flow fields bed shear stress is a fundamental variable in river studies to link ow conditions to sediment transport it is however dif cult to estimate this variable accurately particularly in complex ow elds this study compares shear stress estimated from the log pro le drag reynolds and turbulent kinetic energy tke approaches in a laboratory ume in a simple boundary layer over plexiglas and over sand and in a complex ow eld around de ectors results show that in a simple boundary layer the log pro le estimate is always the highest over plexiglas the tke estimate was the second largest with a value 30 per cent less than the log estimate however over sand the tke estimate did not show the expected increase in shear stress in a simple boundary layer the reynolds shear stress seems the most appropriate method particularly the extrapolated value at the bed obtained from a turbulent pro le in a complex ow eld around de ectors the tke method provided the best estimate of shear stress as it is not affected by local streamline variations and it takes into account the increased streamwise turbulent uctuations close to the de ectors it is suggested that when single point measurements are used to estimate shear stress the instrument should be positioned close to 0 1 of the ow depth which corresponds to the peak value height in pro les of reynolds and tke shear stress copyright 2004 john wiley sons ltd

computational fluid dynamics modelling of boundary roughness in gravel bed rivers an investigation of the effects of random variability in bed elevation results from a series of numerical simulations of two dimensional open channel flow conducted using the computational fluid dynamics cfd code fluent are compared with data quantifying the mean and turbulent characteristics of open channel flow over two contrasting gravel beds boundary roughness effects are represented using both the conventional wall function approach and a random elevation model that simulates the effects of supra grid scale roughness elements e g particle clusters and small bedforms results obtained using the random elevation model are characterized by a peak in turbulent kinetic energy located well above the bed typically at y h 0 1 0 3 this is consistent with the field data and in contrast to the results obtained using the wall function approach for which maximum turbulent kinetic energy levels occur at the bed use of the random elevation model to represent supra grid scale roughness also allows a reduction in the height of the near bed mesh cell and therefore offers some potential to overcome problems experienced by the wall function approach in flows characterized by high relative roughness despite these benefits the results of simulations conducted using the random elevation model are sensitive to the horizontal and vertical mesh resolution increasing the horizontal mesh resolution results in an increase in the near bed velocity gradient and turbulent kinetic energy effectively roughening the bed varying the vertical resolution of the mesh has little effect on simulated mean velocity profiles but results in substantial changes to the shape of the turbulent kinetic energy profile these findings have significant implications for the application of cfd within natural gravel bed channels particularly with regard to issues of topographic data collection roughness parameterization and the derivation of mesh independent solutions copyright 2001 john wiley sons ltd

crustal thickness beneath central and east java indonesia inferred from p receiver functions abstract we compute receiver functions from teleseismic earthquake data recorded at the dense meramex network in central and east java indonesia in order to map the moho depths h and the bulk crustal vp vs ratio we apply the h stacking technique of zhu and kanamori 2000 though the interpretation of the results is hampered by the high complexity of the recorded waveforms in the context of a high noise level and of the heterogeneous assemblage of continental fragments and ophiolitic suture zones forming southeast asia we were able to derive an average crustal thickness of about 34 km support for the assumption of ophiolitic basement in the center of the island related to the meratus suture zone comes from shallowing of the moho to about 30 km beneath the kendeng zone north and west of the kendeng zone the moho is imaged at anomalous depths down to 39 km the observed anomalies line up along the hypothetical boundary between the continental sw borneo fragment and the meratus suture and are indicative of crustal thickening caused by overthrusting and compressional deformation in the context of a former collision zone resulting vp vs ratios cannot be inferred reliably due to the complexity of the waveforms our results do not corroborate the hypothesis of a major structural change along the southern coast at the division between central and east java likewise we do not find clear evidence for the existence of the postulated muria progo lineament

anisotropic structure beneath central java from local earthquake tomography 1 in this study we present the new tomographic code anita which provides 3 d anisotropic p and isotropic s velocity distribution based on p and s traveltimes from local seismicity for the p anisotropic model we determine four parameters for each parameterization cell this represents an orthorhombic anisotropy with one predefined direction oriented vertically three of the parameters describe slowness variations along three horizontal orientations with azimuths of 0 60 and 120 and one is a perturbation along the vertical axis the nonlinear iterative inversion procedure is similar to that used in the lotos code we have implemented this algorithm for the updated data set of central java part of which was previously used for the isotropic inversion it was obtained that the crustal and uppermost mantle velocity structure beneath central java is strongly anisotropic with 7 10 of maximal difference between slow and fast velocity in different directions in the forearc area between southern coast and volcanoes the structure of both isotropic and anisotropic structure is strongly heterogeneous variety of anisotropy orientations and highly contrasted velocity patterns can be explained by a complex block structure of the crust beneath volcanoes we observe faster velocities in vertical direction which is probably an indicator for vertically oriented structures channels dykes in the crust beneath the middle part of central java north to merapi and lawu volcanoes we observe a large and very intense anomaly with a velocity decrease of up to 30 and 35 for p and s models respectively inside this anomaly e w orientation of fast velocity takes place probably caused by regional extension stress regime in a vertical section we observe faster horizontal velocities inside this anomaly that might be explained by layering of sediments and or penetration of quasi horizontal lenses with molten magma in the mantle trench parallel anisotropy is observed throughout the study area such anisotropy in the slab entrained corner flow may be due to presence of b type olivine having predominant axis parallel to the shear direction which appears in conditions of high water or and melting content

joint inversion of active and passive seismic data in central java seismic and volcanic activities in central java indonesia the area of interest of this study are directly or indirectly related to the subduction of the indo australian plate in the framework of the merapi amphibious experiments meramex a network consisting of about 130 seismographic stations was installed onshore and offshore in central java and operated for more than 150 days in addition 3 d active seismic experiments were carried out offshore in this paper we present the results of processing combined active and passive seismic data which contain traveltimes from 292 local earthquakes and additional airgun shots along three offshore profiles the inversion was performed using the updated lotos 06 code that allows processing for active and passive source data the joint inversion of the active and passive data set considerably improves the resolution of the upper crust especially in the offshore area in comparison to only passive data the inversion results are verified using a series of synthetic tests the resulting images showan exceptionally strong low velocity anomaly 30 per cent in the backarc crust northward of the active volcanoes in the upper mantle beneath the volcanoes we observe a low velocity anomaly inclined towards the slab which probably reflects the paths of fluids and partially melted materials in the mantle wedge the crust in the forearc appears to be strongly heterogeneous the onshore part consists of two high velocity blocks separated by a narrow low velocity anomaly which can be interpreted as a weakened contact zone between two rigid crustal bodies the recent java mw 6 3 earthquake 2006 05 26 utc occurred at the lower edge of this zone its focal strike slip mechanism is consistent with the orientation of this contact

flow turbulence over fixed and weakly mobile gravel beds characteristics of turbulence structure in quasi 2d flows with static and weakly mobile gravel beds are presented three sets of measurements with acoustic doppler velocimeters in an irrigation canal were used two with subcritical bed shear stress static beds and one with the bed shear stress o close to critical oc weakly mobile bed the analyses included vertical distributions of local mean velocities turbulence intensities turbulent shear stresses velocity auto and cross spectra the quadrant method and high order velocity moments a number of properties of turbulence intensities high order moments streamwise bursting parameters and velocity spectra appeared to be similar for all three flows but some properties were different the most important one was an observed reduction in the von karman constant for the flow with weakly mobile bed comparison of these results with other studies and analogies with drag reducing flows suggest that at o oc 1 the drag on the bed for a given granula

large scale deformation associated with ridge subduction summary continuum models are used to investigate the large scale deformation associated with the subduction of aseismic ridges formulated in the horizontal plane using thin viscous sheet theory these models measure the horizontal transmission of stress through the arc lithosphere accompanying ridge subduction modelling was used to compare the tonga arc and louisville ridge collision with the new hebrides arc and d entrecasteaux ridge collision which have disparate arc ridge intersection speeds but otherwise similar characteristics models of both systems indicate that diffuse deformation low values of the effective stress strain exponent n are required to explain the observed deformation deformation is somewhat insensitive to the vertically integrated strength of the arc inversely proportional to the argand number ar but indicates that the arc lithosphere is not extremely weak ar 100 low values of both ar and n suggest that the thermal structure is typical of cold or normal arcs and that deformation is dominated by flow in the lower crust and mantle in addition low values of n approaching newtonian flow may indicate that specific deformation mechanisms dictate deformation of the arc lithosphere possible mechanisms include low stress grain size dependent creep pyroxenite controlled rheology and mechanisms associated with water weakening changes in the boundary conditions greatly affect deformation within island arcs high rates of arc ridge intersection speed tonga louisville system yield arc parallel tension and crustal thickening in the wake of ridge subduction in contrast low rates of arc ridge intersection speed new hebrides d entrecasteaux system yield compressional deformation directly arcward of the collision zone and transverse strike slip faulting adjacent to the region of compressional deformation localized regions of extensional deformation along the frontal part of the arc adjacent to the collision zone may contribute to the formation of re entrants

bed form initiation from a flat sand bed 1 bed form initiation in unidirectional flow is examined on a flat bed composed of a homogeneous 0 5 mm sand velocity profiles taken prior to bed form development indicate that the examined flows are typical of fully turbulent uniform open channel flows under these conditions two separate modes of bed form initiation are observed defect and instantaneous initiation defect initiation occurs at lower flow stages where sediment transport is sporadic and patchy and is characterized by defect propagation associated with flow separation instantaneous initiation occurs at larger flow strengths where sediment transport is general and widespread this form of bed form initiation begins with the imprinting of a cross hatch pattern on the flat sediment bed which leads to chevron shaped forms that migrate independently of the initial pattern the chevrons eventually align to form incipient crest lines this mode of bed form initiation does not appear to be linked to turbulent structures but integral scales derived from velocity measurements prior to bed form development are similar to the initial bed form length scales

measurements of the reynolds stress components close to a marine sand bank abstract soulsby r l 1981 measurements of the reynolds stress components close to a marine sand bank mar geol 42 35 47 observations of turbulence have been made at a height of 65 cm above the sea bed in water 42 m deep on the edge of the skerries sand bank off southwest england the observations extended over a 4 h period from the time of maximum flood velocity to slack water electromagnetic current meters were used to measure the streamwise u cross stream v and vertical w velocity components while simultaneously a conventional current meter measured the speed and direction 5 m below the water surface ratios of u2 1 2 v2 1 2 and w2 1 2 to shear velocity agreed with accepted values for laboratory and atmospheric flows near to the surface the current was found to flow across the bank while near the bed it ran nearly parallel to the isobaths consequently the bottom current was directed 480 clockwise of the surface current the azimuth of the reynolds stress uw vw near the bed lay between these directions and was directed about 60 anticlockwise of the near bed current this balanced the cross stream as well as the streamwise shear a lateral shear stress uv associated with the bank was observed taken together with previous measurements of the velocity distribution over the bank this yielded a value for lateral eddy viscosity of 1 2 105 cm2 s 1 the scale over which this acts is of the order 1 km and the value is appreciably smaller than reported values deduced for larger scales the veering of the current acts to lessen the bottom current convergence associated with coriolis and curvature effects and may contribute to lateral sorting by preferentially carrying finer sediment toward the crest of the bank the lateral eddy viscosity coefficient may be useful in assessing the diffusion of sediment on or off the bank

a fluid model for the shape of accretionary wedges in this paper the accretionary wedges landward of most oceanic trenches are modelled assuming a newtonian fluid rheology it is shown that lubrication theory is applicable and that the addition of material to the wedges can be neglected in determining the shape of the wedges the predicted shape of the wedges is in good agreement with bathymetric profiles across the kurile ryukyu and aleutian wedges from the shape of the above wedges it is deduced that accretionary sediments have viscosities between 1018 and 1019 poise

1 d 2 d and 3 d monte carlo ambient noise tomography using a dense passive seismic array installed on the north sea seabed

a bayesian partition modelling approach to resolve spatial variability in climate records from borehole temperature inversion summary collections of suitably chosen borehole profiles can be used to infer large scale trends in ground surface temperature gst histories for the past few hundred years these reconstructions are based on a large database of carefully selected borehole temperature measurements from around the globe since non climatic thermal influences are difficult to identify representative temperature histories are derived by averaging individual reconstructions to minimize the influence of these perturbing factors this may lead to three potentially important drawbacks the net signal of non climatic factors may not be zero meaning that the average does not reflect the best estimate of past climate the averaging over large areas restricts the useful amount of more local climate change information available and the inversion methods used to reconstruct the past temperatures at each site must be mathematically identical and are therefore not necessarily best suited to all data sets in this work we avoid these issues by using a bayesian partition model bpm which is computed using a trans dimensional form of a markov chain monte carlo algorithm this then allows the number and spatial distribution of different gst histories to be inferred from a given set of borehole data by partitioning the geographical area into discrete partitions profiles that are heavily influenced by non climatic factors will be partitioned separately conversely profiles with climatic information which is consistent with neighbouring profiles will then be inferred to lie in the same partition the geographical extent of these partitions then leads to information on the regional extent of the climatic signal in this study three case studies are described using synthetic and real data the first demonstrates that the bayesian partition model method is able to correctly partition a suite of synthetic profiles according to the inferred gst history in the second more realistic case a series of temperature profiles are calculated using surface air temperatures of a global climate model simulation in the final case 23 real boreholes from the united kingdom previously used for climatic reconstructions are examined and the results compared with a local instrumental temperature series and the previous estimate derived from the same borehole data the results indicate that the majority 17 of the 23 boreholes are unsuitable for climatic reconstruction purposes at least without including other thermal processes in the forward model

diversion of flow and sediment towards a side channel separated from a river by a longitudinal training dam a human made entrance to a side channel separated from the river by a longitudinal training dam can be considered a new emergent type of river bifurcation to understand the processes controlling the diversion of flow and sediment towards the side channel at such bifurcations a comprehensive field monitoring programme was performed in the waal river which is the main branch of the rhine river in the netherlands local processes govern the flow field in the bifurcation region the angle between the main river flow and the flow into the side channel increases with decreasing lateral and longitudinal distance to the bifurcation point which corresponds to the head of the training dam the general flow pattern can be well reproduced with a uniform depth potential flow model consisting of a superposition of main channel flow and lateral outflow for submerged flow conditions over the sill the side channel hydraulic conditions influence the exchange processes yet free flow side weir theory describes the flow field at this bifurcation type qualitatively well the vertical flow structure in the side channel which governs the sediment exchange between the main channel and the side channel is steered by the geometrical details of the sill the presence of the sill structure is key to controlling the morphological stability of this type of bifurcation given its primary influence on bed load sediment import and exerts an indirect impact on suspended sediment exchange

control of forearc density structure on megathrust shear strength along the chilean subduction zone abstract unveiling how the interaction of friction pore pressure p and normal stress n controls the shear strength distribution along megathrust faults at convergent plate boundaries is crucial to our understanding of processes leading to the occurrence of devastating earthquake and the construction of mountains an existing density model of the chilean margin 18 45 s allows the computation of the so called vertical stress anomaly vsa that accounts for the component of normal stress due to the weight of the overlying crustal column a spatial correlation between vsa surface geology and several earthquake parameters suggests a significant control exerted by the geologically dominated density structure of the crust on megathrust shear strength the very seismogenic forearc in front of the high central andes 18 34 s has positive vsa values up to 60 mpa and a mafic dominated crust which suggest high values of shear strength at the megathrust that are partially controlled by the weight of a dense forearc crustal column in addition to a likely dry subduction channel characterized by high and low p in contrast the southern andean forearc 34 45 s shows neutral to negative vsa down to 30 mpa correlated with a felsic dominated crust which added to a presumably wet subduction channel low and high p configures a rather weak megathrust below a light forearc earthquakes here are concentrated around the arauco peninsula a first order morpho structural anomaly characterized by comparatively higher values of vsa than the rest of this segment which is the nest of the giant mw 9 5 valdivia 1960 earthquake and the southern rupture termination of the recent mw 8 8 maule earthquake the ultimately giant size of the 1960 earthquake resulted from rupture propagation along a 1000 km long region characterized by negative vsa values the correlation between vsa and the along strike segmentation of the andean orogen indicates that the geologically inherited density structure of the forearc also rules long term mechanical coupling between converging plates and prescribes the possible structure of the orogen because central and southern andes represent two extremes in terms of orogenic structure and seismogenic behavior results presented here have significant implications for the general comprehension of processes occurring at short and long time scale at convergent margins

probability distributions of particle hop distance and travel time over equilibrium mobile bedforms the joint probability distribution of streamwise particle hop distance lateral particle hop distance and travel time constrains the relationships between topographic change and sediment transport

moho depth and three dimensional p and s structure of the crust and uppermost mantle in the eastern mediterranean and middle east derived from tomographic inversion of local isc data summary 82 000 p and s arrival times from 3000 sources recorded by 250 seismic stations from the revised isc catalogue are employed to study a circular area of 6 radius centred on the dead sea we use the linearized tomographic approach based on the rays constructed in a 1 d spherical velocity model and corrected for the moho depth variation and relief all the sources were relocated as the result of simultaneous iterative inversion we get 3 d p and s velocity anomalies in the crust and uppermost mantle moho depth and corrected source parameters the resulting images fit well with the existing tectonic elements in the study area in the crust a narrow p and s low velocity anomaly marks the position of the dead sea transform dst that is interpreted as sediments in the shallower layer and a zone of fractured and deformed rocks in the middle and lower crust there is a narrow 50 km wide band of thickening of the crust along the dst in the arava valley between the red sea and dead sea and some 100 km north of the dead sea this zone may be associated with the minimum of the lithospheric strength and therefore explain the location of the dst in the arava valley the velocity anomalies under the crust and the map of the moho depth clearly distinguish the oceanic levant basin and continental types of crust asia minor zagros cyprus and eratosthenes mount verification of the results takes an important part in this study inversions of different starting models and independent processing of data subsets show high robustness of the results synthetic tests clearly show the limits of the resolving power of the inversion with the existing data set

turbulent velocity profiles and boundary shear in gravel bed rivers vertical profiles of turbulent streamwise velocities in several new zealand gravel bed rivers are investigated field measurements made at high and low flows with electronic pitot tubes show logarithmic velocity profiles to extend over much of the flow depth for the gravel bed rivers studied the velocity at 0 6 of the total depth was generally a good indicator of depth averaged flow velocity an unambiguous definition of flow depth is adopted to deal with situations where the bed is uneven or moving when hydraulic roughness z sub 0 is defined as a fitted parameter of a logarithmic velocity profile the river data indicate that the profile origin displacement below the tops of roughness elements scales with z sub 0 no direct relation between z sub 0 and bed material size is evident under mobile bed conditions for these conditions a relation between hydraulic roughness and u squared is identified with u also derived as a log profile parameter a flow resistance equation using this relation is verified by comparison with mobile bed laboratory measurements in which u is not fitted from velocity profiles

turbulence characteristics of new zealand gravel bed rivers gravel bed river turbulence is investigated on the basis of field measurements in new zealand rivers the data include instant longitudinal velocities obtained by two methods point measurements an

estimating local bed shear stress from velocity observations replicate velocity observations using conventional equipment under typical field conditions are used to evaluate the precision of different methods for estimating local boundary shear stress from velocity measurements the bed shear velocity u can be estimated within 3 using the depth averaged velocity in the vertically averaged logarithmic velocity profile to be accurate this method is limited to relatively simple flow geometries which may be expected to have the appropriate velocity structure estimates of u made using a single near bed velocity observation are less precise by a factor of 3 because of the larger uncertainty associated with a single observation accuracy of this method requires appropriate flow conditions only near the bed so it may be applied in a wider range of flow conditions including spatially variable flow estimates of u from the slope of the near bed velocity profile are the least precise and require the most restrictive flow conditions for accuracy but offer the advantage that they may be made without independent knowledge of the bed roughness different methods for estimating roe should be useful in judging the precision of estimates made under similar conditions these estimates of precision together with considerations of convenience and model accuracy provide the basis for select ing the most appropriate or advantageous method for different conditions and purposes

imaging fluid related subduction processes beneath central java indonesia using seismic attenuation tomography abstract we use local earthquake data observed by the amphibious temporary seismic meramex array to derive spatial variations of seismic attenuation qp in the crust and upper mantle beneath central java the path averaged attenuation values t of a high quality subset of 84 local earthquakes were calculated by a spectral inversion technique these 1929 t values inverted by a least squares tomographic inversion yield the 3d distribution of the specific attenuation qp analysis of the model resolution matrix and synthetic recovery tests were used to investigate the confidence of the qp model we notice a prominent zone of increased attenuation beneath and north of the modern volcanic arc at depths down to 15 km most of this anomaly seems to be related to the eocene miocene kendeng basin mainly in the eastern part of the study area enhanced attenuation is also found in the upper crust in the direct vicinity of recent volcanoes pointing towards zones of partial melts presence of fluids and increased temperatures in the middle to upper crust the middle and lower crust seems not to be associated with strong heating and the presence of melts throughout the arc enhanced attenuation above the subducting slab beneath the marine forearc seems to be due to the presence of fluids

transdimensional inversion of ambient seismic noise for 3d shear velocity structure of the tasmanian crust abstractambient seismic noise tomography has proven to be a valuable tool for imaging 3d crustal shear velocity using surface waves however conventional two stage inversion schemes are severely limited in their ability to properly quantify solution uncertainty and account for inhomogeneous data coverage in response to these challenges we developed a two stage hierarchical transdimensional bayesian scheme for inverting surface wave dispersion information for a 3d shear velocity structure and apply it to ambient seismic noise data recorded in tasmania southeast australia the key advantages of our bayesian approach are that the number and distribution of model parameters are implicitly controlled by the data and that the standard deviation of the data noise is treated as an unknown in the inversion furthermore the use of bayesian inference which combines prior model information and observed data to quantify the a posteriori probability distribution means that model uncertainty information can b

uppermost mantle and crustal structure at tristan da cunha derived from ambient seismic noise abstract according to classical plume theory the tristan da cunha hotspot located 400 km east off the mid atlantic ridge is thought to have played a major role in the rifting while creating an aseismic walvis ridge during and after the breakup of the south atlantic margins volcanic activity on the tristan da cunha island shows that the hotspot might still be there influencing the upper mantle and crustal structure in this study we present ambient noise data from 24 broadband obs around tristan da cunha and a seismic station on nightingale island which provide first constraints on the crustal and uppermost mantle structure around the island by combining ambient noise techniques dispersion curve analysis of rayleigh waves 2d tomographic inversion of travel times and 3d depth inversion of dispersion data we derived a 3d v s velocity model around the archipelago of tristan da cunha the model shows an isolated vertically sharp bounded thickened and modified crust beneath the islands surrounded by thin oceanic crust

large trench parallel gravity variations predict seismogenic behavior in subduction zones we demonstrate that great earthquakes occur predominantly in regions with a strongly negative trench parallel gravity anomaly tpga whereas regions with strongly positive tpga are relatively aseismic these observations suggest that over time scales up to at least 1 million years spatial variations of seismogenic behavior within a given subduction zone are stationary and linked to the geological structure of the fore arc the correlations we observe are consistent with a model in which spatial variations in frictional properties on the plate interface control trench parellel variations in fore arc topography gravity and seismogenic behavior

regional compensation of subducted lithosphere effects on geoid gravity and topography from a preliminary model abstract it is proposed that the anomalous mass of subducted lithospheric slabs is partially compensated by two mechanisms a by stresses transmitted up the slab to the surface lithosphere causing the trench and b by stresses transmitted through the mantle wedge overlying the slab which cause a broad shallow depression results calculated from a preliminary two dimensional model show that it can give a first order account of observed topography gravity and geoid anomalies in particular the model can reconcile the large mass anomaly predicted for the slab by thermal conduction theory with the smaller than expected gravity and geoid anomalies preliminary results indicate substantial compensation by mechanism a implying rather large stresses at the top of the slab these could be important for theories of earthquake mechanisms and plate driving mechanisms roughly 50 of the possible compensation by mechanism b is indicated the resulting depression the order of 500 m deep and over 500 km wide could explain anomalously deep marginal basins and some marine transgressions of continents

underthrusting at the hjort trench australian pacific plate boundary incipient subduction 1 the southernmost portion of the macquarie ridge complex mrc comprises the hjort ridge trench and plateau the topographic expression of the australian pacific plate boundary south of new zealand on the basis of marine geophysical swath bathymetry reflectivity seismic reflection gravity magnetic data teleseismic data and gravity modeling we argue that the australian plate is actively underthrusting the pacific plate along the hjort trench but self sustaining subduction does not yet appear to have commenced we interpret a crustal discontinuity in the trench as a shallowly dipping thrust splay off a sub vertical transform fault in the crest of the hjort ridge hjort fault the hjort fault separates oceanic crust generated at the southeast indian ridge seir crust located to the south from oceanic crust generated at the extinct australian pacific spreading center located to the north mrc crust oblique convergence on the transform has initiated a significant plate boundary decollement in the trench but our estimate of 50 km of underthrusting does not support the existence of an eastwardly dipping australian slab below 20 km depth for the length of the hjort ridge and trench system oblique convergence is partitioned between the decollement in the trench and the hjort fault south of 57 5 s the trench decollement accommodates thrusting north of 57 5 s the boundary parallel component of convergence becomes dominant the trench gradually shallows and the trench decollement evolves into a low angle oblique slip fault the trench decollement and strike slip system in the hjort ridge are structural boundaries that contain tectonic slivers of inferred seir crust of the western flank of the hjort ridge that currently belong to neither the australian nor the pacific plates

estimating bottom stress in tidal boundary layer from acoustic doppler velocimeter data bed stresses in the bottom boundary layer of the york river estuary virginia were estimated from three dimensional near bottom velocities measured by acoustic doppler velocimeters advs and also by a profiling array of electromagnetic current meters by assuming the measurements were made in a constant stress layer four methods of stress estimation were evaluated using advs direct covariance cov measurement turbulent kinetic energy inertial dissipation utilizing the kolmogorov spectrum and log profile the four methods yielded similar estimates of frictional velocity u based on adv output from both 14 cm and 44 cm above bed all eight estimates of average u were consistent with the overall mean of 1 10 cm s to within the 95 confidence interval for individual burst estimates the cov method worked slightly better nearer the bed possibly because of the sensitivity of cov to the upper limit of the constant stress layer the inertial dissipation method performed marginally well at 14 cm above bed likely because of sediment induced stratification and insufficient separation of turbulent production and dissipation scales the log profile method was the most variable and appeared most sensitive to stratification and to the thickness of the constant stress layer the turbulent kinetic energy method was the most consistent at both heights and appears most promising for further development results encourage future use of the adv in estuarine environments but also favor the simultaneous use of several methods to estimate bottom stress

flow over rough mobile beds friction factor and vertical distribution of the longitudinal mean velocity 1 the main objective of the present study is to identify the impacts of bed mobility on the vertical profile of the mean longitudinal velocity and on resistance in flows over water worked beds of poorly sorted mixtures of sand and gravel water worked beds with sediment transport are explicitly distinguished from immobile beds with imposed sediment feed flows with different equilibrium sediment transport rates are generated in a laboratory flume the initial bed mixtures featured combinations of sand and gravel modes data collection included instantaneous velocities measured with laser doppler annemometry wall similarity in the sense of townsend 1976 is assumed the parameters of the formulae are discussed within three scenarios comprising different definitions ofu and ks combined with different conceptions of the von karman constant flow independent or flow dependent it is shown that the parameters of the formulae that express the velocity profile vary with the shields number and with the initial bed composition the variation is independent of the adopted scenario except in what concerns the formulation of hydraulic smoothening in the presence of sand sizes which depends on the definition of ks

estimating bed shear stress from remotely measured surface turbulent dissipation fields in open channel flows synoptic information on bed shear stress is necessary in predicting the transport of sediments and environmental contaminants in rivers and open channels existing methods of estimating bed shear stress typically involve measuring vertical profiles of streamwise velocity or reynolds stress and taking advantage of the logarithmic or the constant stress region respectively to determine friction velocity and subsequently bed shear stress while effective these methods yield local measurements of bed shear stress only direct measurements of bed shear stress can also be obtained through measurements with a drag plate however this method yields average shear stress information over the area of the plate and is impractical for large scale implementation in the field here we present a method capable of providing continuous synoptic measurements of bed shear stress over a large field of view a series of large scale particle image velocimetry lspiv and acoustic doppler velocimetry adv measurements were made in a variety of flows generated in a wide open channel facility turbulent dissipation is calculated on the free surface from the 2 d lspiv results and is correlated with near surface adv measurements of turbulent dissipation in the water column the adv results are consistent with the nezu 1977 established relationship for the vertical variation of turbulent dissipation in the water column knowledge of the correlation between free surface and near surface dissipation values coupled with nezu s 1977 relationship allow a robust and accurate estimate of friction velocity to be made and subsequently shear stress at the bed can be estimated this article is protected by copyright all rights reserved

velocity variations associated with the large 2010 eruption of merapi volcano java retrieved from seismic multiplets and ambient noise cross correlation we present a study of the seismic velocity variations that occurred in the structure before the large 2010 eruption of merapi volcano for the first time to our knowledge the technique of coda wave interferometry is applied to both families of similar events multiplets and to correlation functions of seismic noise about half of the seismic events recorded at the summit stations belong to one of the ten multiplets identified including 120 similar events that occurred in the last 20 hr preceding the eruption onset daily noise cross correlation functions ncf were calculated for the six pairs of short period stations available using the stretching method we estimate time series of apparent velocity variation avv for each multiplet and each pair of stations no significant velocity change is detected until september 2010 from 10 october to the beginning of the eruption on 26 october a complex pattern of avv is observed with amplitude of up to 1 5 per cent velocity decrease is first observed from families of deep events and then from shallow earthquakes in the same period avv with different signs and chronologies are estimated from ncf calculated for various station pairs the location in the horizontal plane of the velocity perturbations related with the avv obtained from ncf is estimated by using an approach based on the radiative transfer approximation although their spatial resolution is limited the resulting maps display velocity decrease in the upper part of the edifice in the period 12 25 october after the eruption onset the pattern of velocity perturbations is significantly modified with respect to the previous one we interpret these velocity variations in the framework of a scenario of magmatic intrusion that integrates most observations the perturbation of the stress field associated with the magma migration can induce both decrease and increase of the seismic velocity of rocks thus the detected avvs can be considered as precursors of volcanic eruptions in andesitic volcanoes without taking their sign into account

a critical assessment of viscous models of trench topography and corner flow stresses for newtonian viscous flow in a simple geometry e g corner flow bending flow are obtained in order to study the effect of imposed velocity boundary conditions stress for a delta function velocity boundary condition decays as 1 r 2 for a step function velocity stress goes as 1 r for a discontinuity in curvature the stress singularity is logarithmic for corner flow which has a discontinuity of velocity at a certain point the corresponding stress has a 1 r singularity however for a more realistic circular slab model the stress singularity becomes logarithmic thus the stress distribution is very sensitive to the boundary conditions and in evaluating the applicability of viscous models of trench topography it is essential to use realistic geometries topography and seismicity data from northern hoshu japan were used to construct a finite element model with flow assumed tangent to the top of the grid for both newtonian and non newtonian flow power law 3 rheology normal stresses at the top of the grid are compared to the observed trench topography and gravity anomalies there is poor agreement purely viscous models of subducting slables with specified velocity boundary conditions do not predict normal stress patterns compatible with observed topography and gravity elasticity and plasticity appear to be important for the subduction process

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

bottom stress estimates and their prediction on the northern california continental shelf during code 1 the importance of wave current interaction abstract high quality near bottom boundary layer measurements obtained at a midshelf location 90 m water depth in the code region off northern california are described bottom tripod velocity measurements and supporting data obtained during typical spring and early summer conditions june 1981 during code 1 are analyzed to obtain bath velocity profiles and mean bottom stress and bottom roughness estimates during the time period described the mean near bottom 0 997 approximately 30 percent of the time effects induced by unsteadiness from internal waves result in some degradation of the profiles 0 96 r 0 997 the rest of the time mean stress profiles indicate the logarithmic layer is approximately a constant stress layer the near bottom flow field is composed of mean currents and oscillatory currents due to well typing mean u values estimated from measurements greater than 30 cm above the bottom have magnitudes of 0 5 1 0 cm s 1 mean stress valu

remote determination of the velocity index and mean streamwise velocity profiles when determining volumetric discharge from surface measurements of currents in a river or open channel the velocity index is typically used to convert surface velocities to depth averaged velocities the velocity index is given by k ub usurf where ub is the depth averaged velocity and usurf is the local surface velocity the usgs united states geological survey standard value for this coefficient k 0 85 was determined from a series of laboratory experiments and has been widely used in the field and in laboratory measurements of volumetric discharge despite evidence that the velocity index is site specific numerous studies have documented that the velocity index varies with reynolds number flow depth relative bed roughness and with the presence of secondary flows a remote method of determining depth averaged velocity and hence the velocity index is developed here the technique leverages the findings of johnson and cowen 2017 and permits remote determination of the velocity power law exponent thereby enabling remote prediction of the vertical structure of the mean streamwise velocity the depth averaged velocity and the velocity index

ambient noise rayleigh wave tomography in western sichuan and eastern tibet abstract we perform rayleigh wave tomography in western sichuan and eastern tibet by applying the ambient noise method to broadband data recorded at 49 stations from the sichuan digital seismic network cross correlations of vertical component ambient noise data are computed in one hour segments and stacked over 7 months from june to december 2007 then rayleigh wave group dispersion curves from 6 to 48 s were measured using the multiple filter analysis method group velocity maps at periods from 8 to 44 s were inverted the resulting group velocity maps generally show good correlations with tectonic features the sichuan basin is clearly resolved with lower group velocities at the short periods 8 to 20 s due to thick sedimentary layers and a prominent low velocity zone exhibits in the middle crust beneath the eastern margin of the tibetan plateau the longmen shan thrust belt marks not only the rapid lateral velocity variation between the topographically high tibetan plateau and low elevation sichuan basin but also the transition from the thick crust beneath the tibetan plateau to the normal continental crust beneath the sichuan basin

seabed stress determinations using the inertial dissipation method and the turbulent kinetic energy method direct measurements of seabed stress are difficult especially in field conditions several methods for estimating these stresses using current meter data are available two of these methods the inertial dissipation method and the turbulent kinetic energy method are described below and a matlab program is used to analyse data from a wave current environment

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

imaging the subsurface using induced seismicity and ambient noise 3 d tomographic monte carlo joint inversion of earthquake body wave traveltimes and surface wave dispersion

structure of magma reservoirs beneath merapi and surrounding volcanic centers of central java modeled from ambient noise tomography we present a three dimensional model of the distribution of s wave velocity in the upper crust to a depth of 20 km beneath central java based on the analysis of seismic ambient noise data recorded by more than 100 seismic stations in 2004 associated with the meramex project to invert the rayleigh wave dispersion curves to construct 2d group velocity maps and 3d distributions of s wave velocity we have used a new tomographic algorithm based on iterative linearized inversion we have performed a series of synthetic tests that demonstrate significantly higher resolution in the upper crust with this model compared to the local earthquake travel time tomography let model previously applied for the same station network beneath the southern flank of merapi we identify a large low velocity anomaly that can be split into two layers the upper layer reflects the 1 km thick sedimentary cover of volcanoclastic deposits the deeper anomaly at depths of 4 8 km may represent a magma reservoir with partially molten rock that feeds several volcanoes in central java beneath the merapi summit we observe another low velocity anomaly as deep as 8 km that may be associated with the active magma reservoir that feeds the eruptive activity of merapi in the southern portion of the study area in the lower crust we identify a low velocity anomaly that may represent the top of the pathways of volatiles and melts ascending from the slab that was previously inferred from the let model results we observe that this anomaly is clearly separate from the felsic magma reservoirs in the upper crust this article is protected by copyright all rights reserved

dynamically supported trench topography a viscous flow model of a subduction zone is used to calculate the near trench deformation and topography of the overriding plate in response to tectonic and buoyancy forces the tectonic force which is associated with global plate motion arises from subduction of a cold oceanic lithosphere that shears the overriding lithosphere along the contact between the two plates the buoyancy force arises in response to horizontal density variations and tends to relax the existing topography the time evolution of the near trench topography is investigated via a finite element technique that solves for the flow field in the overriding plate the results indicate that the near trench topography approaches a steady state configuration in which the upper surface topography produces a buoyancy force that balances the tectonic force induced by the subducting slab the model predicts that the steady state trench depth increases with the subduction rate and hence explains the correlation between trench depth and subduction rate observed by grellet and dubois 1982 transition from one steady state trench topography to another adds or removes material from the overriding plate this may result from a change in subduction rate angle of subduction or subduction of a seamount during a transition to a deeper steady state configuration the near trench stress field has an extensional component which agrees with the observed extension in regions of tectonic erosion similarly during a transition to a shallower steady state configuration the near trench stress field has a compressional component which agrees with the observed compression of accretionary wedges hence the model explains tectonic erosion and accretion at trenches as transitional features that indicate a change from one steady state configuration to another

three dimensional inversion of regional p and s arrival times in the east aleutians and sources of subduction zone gravity highs free air gravity highs over forearcs represent a large fraction of the power in the earth s anomalous field yet their origin remains uncertain seismic velocities as indicators of density are estimated here as a means to compare the relative importance of upper plate sources for the gravity high with sources in the downgoing plate p and s arrival times for local earthquakes recorded by a seismic network in the eastern aleutians are inverted for three dimensional velocity structure between the volcanic arc and the downgoing plate a three dimensional ray tracing scheme is used to invert the 7974 p and 6764 s arrivals for seismic velocities and hypocenters of 635 events one dimensional inversions show that station p residuals are systematically 0 25 0 5 s positive at stations 0 30 km north of the aleutian volcanic arc indicating slow material while residuals at stations 10 30 km south of the arc are 0 1 0 25 s negative both features are explained in three dimensional inversions by velocity variations at depths less than 25 35 km tests using a one dimensional or a two dimensional slab starting model show that below 100 km depth velocities are poorly determined and trade off almost completely with hypocenters for earthquakes at these depths the locations of forearc velocity highs in the crust of the upper plate correspond to the location of the gravity high between the trench and volcanic arc free air anomalies calculated from the three dimensional velocity inversion result match observed gravity for a linear density velocity relationship between 0 1 and 0 3 mg m 3 km s 1 when a 50 km thick slab is included with a density of 0 055 0 005 mg m 3 values outside these ranges do not match the observed gravity the slab alone contributes one third to one half of the total 75 150 mgal amplitude of the gravity high but predicts a high that is much broader than is observed the inclusion of upper plate velocity anomalies predicts the correct width of the anomaly 100 150 km where the anomaly is most positive because the forearc gravity high is continuous along the entire aleutian arc and is found in most arcs globally high upper plate forearc velocities are suspected to be a common feature of the upper plate of most subduction zones the forearc mass excesses appear to be sustained by upward regional flexure of the upper plate that partly balances the depression of the lower plate at the trench thus elevating high density and high velocity material thus a part of the downward flexure of the subducting plate is regionally compensated by shallow positive mass anomalies in the upper plate and the strength of the upper plate helps generate the forearc gravity highs

the plumbing system feeding the lusi eruption revealed by ambient noise tomography lusi is a sediment hosted hydrothermal system featuring clastic dominated geyser like eruption behavior in east java indonesia we use 10 months of ambient seismic noise cross correlations from 30 temporary seismic stations to obtain a 3 d model of shear wave velocity anomalies beneath lusi the neighboring arjuno welirang volcanic complex and the watukosek fault system connecting the two our work reveals a hydrothermal plume rooted at a minimum 6 km depth that reaches the surface at the lusi site furthermore the inversion shows that this vertical anomaly is connected to the adjacent volcanic complex through a narrow 3 km wide low velocity corridor slicing the survey area at a depth of 4 6 km the ne sw direction of this elongated zone matches the strike of the watukosek fault system distinct magmatic chambers are also inferred below the active volcanoes the large scale tomography features an exceptional example of a subsurface connection between a volcanic complex and a solitary erupting hydrothermal system hosted in a hydrocarbon rich back arc sedimentary basin these results are consistent with a scenario where deep seated fluids e g magmas and released hydrothermal fluids flow along a region of enhanced transmissivity i e the watukosek fault system damage zone from the volcanic arc toward the back arc basin where lusi resides the triggered metamorphic reactions occurring at depth in the organic rich sediments generated significant overpressure and fluid upwelling that is today released at the spectacular lusi eruption site

the deep crust beneath island arcs inherited zircons reveal a gondwana continental fragment beneath east java indonesia abstract inherited zircons in cenozoic sedimentary and igneous rocks of east java range in age from archean to cenozoic the distribution of zircons reveals two different basement types at depth the igneous rocks of the early cenozoic arc found along the southeast coast contain only archean to cambrian zircons in contrast clastic rocks of north and west of east java contain cretaceous zircons which are not found in the arc rocks to the south the presence of cretaceous zircons supports previous interpretations that much of east java is underlain by arc and ophiolitic rocks accreted to the southeast asian margin during cretaceous subduction however such accreted material cannot account for the older zircons the age populations of archean to cambrian zircons in the arc rocks are similar to gondwana crust we interpret the east java early cenozoic arc to be underlain by a continental fragment of gondwana origin and not cretaceous material as previously suggested melts rising through the crust feeding the early cenozoic arc picked up the ancient zircons through assimilation or partial melting we suggest a western australian origin for the fragment which rifted from australia during the mesozoic and collided with southeast asia resulting in the termination of cretaceous subduction continental crust was therefore present at depth beneath the arc in south java when cenozoic subduction began in the eocene

deformation of the central andes 15 27 s derived from a flow model of subduction zones a simple viscous flow model of a subduction zone is used to calculate the deformation within continental lithosphere above a subducting slab our formulation accounts for two forces that dominate the deformation in the overriding lithosphere tectonic forces and buoyancy forces the tectonic forces arise from the subduction of oceanic lithosphere and produce minor extension in the lithosphere near the trench and compression farther inland buoyancy forces can induce horizontal pressure gradients due to variations in crustal thickness which cause lithospheric extension where the crust is thick numerical solutions obtained by using a finite element technique are compared with observations from the central andes 15 27 s the model predicts the observed deformation pattern of extension in the forearc compression in the western monocline corresponding to magmatic activity extension in the altiplano compression in the eastern monocline and subandes and no deformation in the brazilian shield by comparing the calculated solutions with the large scale tectonic observations we are able to evaluate the forces that govern the deformation in the central andes the approximately constant subduction velocity in the past 26 m y suggests that the rate of crustal shortening in the andes has decreased with time due to the thickening of the crust

quantification of the bed load effects on turbulent open channel flows with a computational model combining large eddy simulation and a discrete element model detailed quantification of the bed load effects on turbulent open channel flows is presented the objective is the revelation of bed load particle impact on the mean flow properties and coherent structures two comparative numerical experiments with mobile and immobile beds are conducted mean properties e g velocity and reynolds stress profiles show good agreement with experimental data comparing the mobile and immobile cases the effective bed position is nearly the same whereas the equivalent sand roughness is changed the flow experiences higher bottom shear stress over immobile bed to quantify impact on turbulent structures a revised quadrant analysis is performed to calculate four key parameters of ejection and sweep events duration maximum shear stress transported momentum and period results show that the ejection and sweep events have comparable importance in the outer region however sweep becomes dominant in the near wall region the motion of particles enhances the sweep dominance by breaking up the ejection structures and decreasing their occurrence ratio the results also suggest that the ejection events are easier to be influenced by the particle motions because they originate from the near wall region the duration maximum shear stress and transported momentum decrease close to the bed the period remains relatively constant in the outer region but decreases near the bed visualization of the coherent structure reveals that the instantaneous particle motion has strong correlation with the bursting cycle events

p and s velocity structure of the crust and the upper mantle beneath central java from local tomography inversion here we present the results of local source tomographic inversion beneath central java the data set was collected by a temporary seismic network more than 100 stations were operated for almost half a year about 13 000 p and s arrival times from 292 events were used to obtain three dimensional 3 d vp vs and vp vs models of the crust and the mantle wedge beneath central java source location and determination of the 3 d velocity models were performed simultaneously based on a new iterative tomographic algorithm lotos 06 final event locations clearly image the shape of the subduction zone beneath central java the dipping angle of the slab increases gradually from almost horizontal to about 70 a double seismic zone is observed in the slab between 80 and 150 km depth the most striking feature of the resulting p and s models is a pronounced low velocity anomaly in the crust just north of the volcanic arc merapi lawu anomaly mla an algorithm for estimation of the amplitude value which is presented in the paper shows that the difference between the fore arc and mla velocities at a depth of 10 km reaches 30 and 36 in p and s models respectively the value of the vp vs ratio inside the mla is more than 1 9 this shows a probable high content of fluids and partial melts within the crust in the upper mantle we observe an inclined low velocity anomaly which links the cluster of seismicity at 100 km depth with mla this anomaly might reflect ascending paths of fluids released from the slab the reliability of all these patterns was tested thoroughly

the estimation of shear stresses from near bed turbulent velocities for combined wave current flows abstract high frequency near bottom velocities measured by a combined pressure gauge and flow meter are analysed with a view to understanding and modelling waves and sediment transport in shallow waters data from five stations in different water depth wave and current conditions are compared wave tide surge and turbulence components have been separated from the bottom velocity data and are used to derive a friction velocity and examine the bottom stress parameterisation the horizontal component of turbulent velocity fluctuations near the bed is found to be well correlated with the bed shear stress from a combined wave and current model the model of christoffersen and jonsson christoffersen j b jonsson i g 1985 bed friction and dissipation in a combined current and wave motion ocean engineering 12 5 387 423 is in reasonable agreement with the observed data the observed turbulence can shed light on the wave bed shear stress as well as the shear stress due to the current a fitting procedure gives a derived nikuradse length scale for each station which is similar to that obtained independently from bed grain size estimates

ambient noise rayleigh wave tomography of new zealand summary we present the first new zealand wide study of surface wave dispersion using ambient noise observed at 42 broad band stations in the national seismic network geonet and the global seismic network gsn year long vertical component time series recorded between 2005 april 1 and 2006 march 31 have been correlated with one another to yield estimated fundamental mode rayleigh wave green s functions we filter these green s functions to compute rayleigh wave group dispersion curves at periods of 5 50 s using a phase matched filter frequency time analysis technique the uncertainties of the measurements are estimated based on the temporal variation of the dispersion curves revealed by 12 overlapping 3 month stacks after selecting the highest quality dispersion curve measurements we compute group velocity maps from 7 to 25 s period these maps and 1 d shear wave velocity models at four selected locations exhibit clear correlations with major geological structures including the taranaki and canterbury basins the hikurangi accretionary prism and previously reported basement terrane boundaries

accretionary nature of the crust of central and east java indonesia revealed by local earthquake travel time tomography abstract reassessment of travel time data from an exceptionally dense amphibious temporary seismic network on and offshore central and eastern java meramex confirms the accretionary nature of the crust in this segment of the sunda subduction zone 109 5 111 5e traveltime data of p and s waves of 244 local earthquakes were tomographically inverted following a staggered inversion approach the resolution of the inversion was inspected by utilizing synthetic recovery tests and analyzing the model resolution matrix the resulting images show a highly asymmetrical crustal structure the images can be interpreted to show a continental fragment of presumably gondwana origin in the coastal area east of 110e which has been accreted to the sundaland margin an interlaced anomaly of high seismic velocities indicating mafic material can be interpreted to be the mantle part of the continental fragment or part of obducted oceanic lithosphere lower than average crustal velocities of the java crust are likely to reflect ophiolitic and metamorphic rocks of a subduction melange

transdimensional bayesian seismic ambient noise tomography across se tibet abstract we analyze seismic ambient noise data recorded at a set of permanent and temporary stations across southeastern tibet to image crustal structure high resolution phase velocity maps are presented based on transdimensional bayesian seismic ambient noise tomography seismic images exhibit more apparent horizontal heterogeneities and show more detailed information compared to previous studies based on traditional ambient noise tomography as noted from the phase velocity image at 25 s the rigid high velocity anomalies beneath the sichuan basin and the south china fold system act as a blockage to crustal material expansion and the distribution of velocity anomalies contributes to the interpretation of a surface clockwise rotation pattern our results imply a more complex distributed low velocity zone rather than two isolated channels beneath se tibet

variable and conflicting shear stress estimates inside a boundary layer with sediment transport this paper presents a comparison between two methods for estimating shear stress in an atmospheric internal boundary layer over a beach surface under optimum conditions using wind velocities measured synchronously at 13 heights over a 1 7 m vertical array using ultrasonic anemometry the reynolds decomposition technique determines at a point shear stresses at each measurement height while the law of the wall yields a single boundary layer estimate based on fitting a logarithmic velocity profile through the array data analysis reveals significant inconsistencies between estimates derived from the two methods on both a whole event basis and as time series despite a near perfect fit of the law of the wall the point estimates of reynolds shear stress vary greatly between heights calling into question the assumed presence of a constant stress layer a comparison with simultaneously measured sediment transport finds no relationship between transport activity and the discrepancies in shear stress estimates results do show however that reynolds shear stress measured nearer the bed exhibits slightly better correlation with sand transport rate the findings serve as a major cautionary message to the interpretation and application of single height measurements of reynolds shear stress and their equivalence to law of the wall derived estimates and these concerns apply widely to boundary layer flows in general 2015 the authors earth surface processes and landforms published by john wiley sons ltd

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