intraplate shortening and underthrusting of a large basement ridge in the eastern nankai subduction zone abstract due to the collision of the izu bonin arc with central japan the subducting philippine sea oceanic plate is affected by lithospheric shortening seaward of the eastern nankai trough in the zenisu ridge area seismic reflection and refraction profiles across the ridge show a series of low angle thrusts cutting through the entire oceanic crust they also indicate that the formation of this ridge is related to a single lithospheric thrust with 10 km throw that inserts a corner of upper mantle within the lower crust we propose that the serpentinized mantle crust transition acts as a decoupling level above which distributed shortening results in the formation of a crustal prism although the amount of deformation is much smaller than in a mountain belt such as the pyrenees a parallelism can be proposed between both systems that correspond to intraplate shortening and have in common a single mantle shear zone and overlying distributed crustal deformation the underthrusting below the eastern nankai accretionary prism of a similar and now inactive tectonic structure the paleo zenisu ridge is evidenced by the deformation pattern of the margin this ridge is probably detached on top of the subduction decollement at least where volcanoes are impinging the continental margin part of the ridge may thus be accreted to the prism backstop we show that both zenisu and paleo zenisu systems accommodate the same n s compression related to convergence partitioning process this subduction kinematics can be understood in terms of a steady state model partially constrained by the trails of volcanoes that have impinged the margin n s shortening is accommodated by the thrusts seaward of the trough and right lateral motion is prevalent along the subduction system based on these kinematics we propose that the formation of the paleo zenisu and zenisu ridges are related to the successive collisions of volcanic massifs of the izu bonin arc with the japanese arc the zenisu system is a result of the collision of the izu block since 2 ma while the paleo zenisu system was the result of the earlier collision of the tanzawa massif between 5 and 3 ma

seismic evidence for overpressured subducted oceanic crust and megathrust fault sealing water and hydrous minerals play a key role in geodynamic processes at subduction zones however there are few seismological constraints on the presence of water within the subducting plate audet et al model converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the cascadia continental margin to its intersection with the forearc mantle their observations suggest that water is pervasively present in fluid form at high pore pressures indicating that the megathrust is a low permeability boundary these results may hold important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip this study models converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the cascadia continental margin to its intersection with the forearc mantle the observations suggest that water is pervasively present in fluid form at high pore pressures indicating that the megathrust is a low permeability boundary these results may hold important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip water and hydrous minerals play a key part in geodynamic processes at subduction zones1 2 3 by weakening the plate boundary aiding slip and permitting subduction and indeed plate tectonics to occur4 the seismological signature of water within the forearc mantle wedge is evident in anomalies with low seismic shear velocity marking serpentinization5 6 7 however seismological observations bearing on the presence of water within the subducting plate itself are less well documented here we use converted teleseismic waves to obtain observations of anomalously high poisson s ratios within the subducted oceanic crust from the cascadia continental margin to its intersection with forearc mantle on the basis of pressure temperature and compositional considerations the elevated poisson s ratios indicate that water is pervasively present in fluid form at pore pressures near lithostatic values combined with observations of a strong negative velocity contrast at the top of the oceanic crust our results imply that the megathrust is a low permeability boundary the transition from a low to high permeability plate interface downdip into the mantle wedge is explained by hydrofracturing of the seal by volume changes across the interface caused by the onset of crustal eclogitization and mantle serpentinization these results may have important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip

a scaling law for slow earthquakes with the availability of the global positioning system and other technical advances a growing number of unusual earthquake phenomena occurring at relatively long periods have been recognized they include deep episodic tremor low frequency earthquakes slow slip events and silent earthquakes based on data chiefly from western japan ide et al report that these slow seismic events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes a diverse array of unusual earthquake phenomena occurring at relatively long periods slow events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes indicating that they comprise a new earthquake category recently a series of unusual earthquake phenomena have been discovered including deep episodic tremor1 low frequency earthquakes2 very low frequency earthquakes3 slow slip events4 and silent earthquakes5 6 7 8 9 each of these has been demonstrated to arise from shear slip just as do regular earthquakes but with longer characteristic durations and radiating much less seismic energy here we show that these slow events follow a simple unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes we find that their seismic moment is proportional to the characteristic duration and their moment rate function is constant with a spectral high frequency decay of f 1 this scaling and spectral behaviour demonstrates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category the observed scale dependence of rupture velocity for these events can be explained by either a constant low stress drop model or a diffusional constant slip model this new scaling law unifies a diverse class of slow seismic events and may lead to a better understanding of the plate subduction process and large earthquake generation

carbon delivery to deep mineral horizons in hawaiian rain forest soils 1 this study aimed to better understand the mechanisms for soil organic matter delivery to and accumulation in mineral horizons of tropical rain forest volcanic soils we used soil morphology lysimetry isotopes and spectroscopy to investigate the role of preferential flow paths in the delivery of carbon c to the subsoil high rainfall high primary productivity and the dominance of highly reactive short range order minerals combine to sequester substantial stocks of soil c with long mean residence times the soils have large peds separated by wide cracks which form a network of channels propagating downward through the top 40 to 60 cm facilitating macropore flow the channel infillings and crack surfaces were enriched in organic material om with lower c n ratios and had higher ammonium oxalate extractable al and lower ammonium oxalate extractable fe than the adjacent mineral bulk soil cp mas 13c nmr spectra of om accumulating at depth showed strong signal intensities in the carboxyl and carbonyl c regions indicative of organic acids while decaying roots showed greater contributions of aromatic and o alkyl c the ratios of alkyl to o alkyl c in the organic infillings were more similar to those of the bulk bh and to dissolved organic matter than to those of decaying roots radiocarbon based ages of om infillings at 50 cm depth were significantly younger than the mineral soil 2000 years versus 7000 years respired co2 from incubated soils showed that om accumulating at depth is a mixture of modern and much older c providing further evidence for the downward movement of fresh c

dynamic modeling of slow slip coupled with tremor 1 we theoretically study the generation mechanism of slow slip in a dynamical framework assuming a fault in a fluid saturated thermoporoelastic medium the fluid flow is taken into consideration dynamic slip is assumed to create pores and cause shear heating on the fault key parameters in the modeling are su and su the nondimensional parameter su represents the relative dominance of the effect of pore creation on the fluid pressure change over that of shear heating while su is associated with the dominance of fluid flow effect over the effect of shear heating our calculation shows that we have to assume su 1 and relatively small values for su to simulate rupture speed that is negligibly small compared to the shear wave velocity although this was also found in our former paper our new finding here is the simulation of slow slip coupled with tremor we find that frozen slip is reactivated sporadically because the fluid inflow triggered by the pore creation elevates the fluid pressure on the fault the slip reactivation actually occurs if su is smaller than a threshold such sporadic reactivation of slips can be a model for slow slip coupled with tremor we also show that the moment evolution curves are categorized into two separate groups when su 0 1 one of them represents slow slips while the other represents ordinary earthquakes

geometry and spatial variations of seismic reflection intensity of the upper surface of the philippine sea plate off the boso peninsula japan abstract in the region off the boso peninsula japan the pacific plate is subducting westward beneath both the honshu island arc and philippine sea plate while the philippine sea plate is subducting northwestward beneath the honshu island arc these complex tectonic interactions have caused numerous seismic events occurred in the past to better understand these seismic events it is important to determine the geometry of the plate boundary in particular the upper surface of the philippine sea plate we conducted an active source seismic refraction survey in july and august 2009 from which we obtained a 2 d p wave velocity structure model along a 216 km profile we used the velocity model and previously published data that indicate a p wave velocity of 5 0 km s for the upper surface of the subducting philippine sea plate to delineate its boundary with the overriding honshu island arc our isodepth contours of the upper surface of the philippine sea plate show that its dip is shallow at depths of 10 to 15 km far off the boso peninsula this shallow dip may be a result of interference from the pacific plate slab which is subducting westward under the philippine sea plate within our survey data we recognized numerous seismic reflections of variable intensity some of which came from the upper surface of the philippine sea plate an area of high seismic reflection intensity corresponds with the main slip area of the boso slow slip events our modeling indicates that those reflections can be explained by an inhomogeneous layer close to the upper surface of the philippine sea plate

storage and depth distribution of organic carbon in volcanic soils as affected by environmental and pedological factors abstract it has been recognised that volcanic soils particularly andosols can store large amounts of soil organic carbon soc this study investigates the factors controlling the regional and vertical distributions of soc in soils of volcanic origin to this aim we investigated the vertical distribution of soc in a total of 212 soil profiles representing all combinations of soil forming factors in a volcanic area with a high diversity of ecosystems and soil types we analysed the soc contents in relation to intrinsic soil type and relevant soil properties texture and ph and extrinsic factors climate parent material relief and we studied the patterns of soc distribution with depth by fitting the soc contents to different curve models furthermore we selected ten soil profiles for a more detailed study to assess the effect of vegetation by examining the relationships of the soc storage and depth distribution to the amount and allocation of plant roots and litterfall soc storage was controlled by the interaction of climatic rainfall time substrate age topographic slope and biotic plant mediated factors our results indicate that under humid conditions large organic inputs and the inhibition of microbial degradation due to low ph al toxicity and persistent anaerobiosis within soil microaggregates largely contributed to soc accumulation soil type was a poor predictor of soc storage most likely due to the co occurrence of young and evolved andosols and a certain andic character in many soils that did not qualify as andosols the distributions of root carbon and soc appeared to be closely interrelated suggesting a major role of roots in the supply of organic matter and the lack of significant bioturbation the depth distribution of soc was best fitted by the quadratic cubic and power models the latter being a feasible alternative that should be used to this aim in volcanic soils rather than the widely used exponential model

a large silent earthquake in the guerrero seismic gap mexico 1 geodetic measurements from a network of permanent gps stations along the pacific coast of mexico reveal a large silent earthquake along the segment of the cocos north american plate interface identified as the guerrero seismic gap the event began in october of 2001 and lasted for 6 7 months average slip of 10 cm produced measurable displacements over an area of 550 250 km2 the equivalent moment magnitude of the event was mw 7 5 recognition of this and previous slow event here indicate that the seismogenic portion of the plate interface is not loading steadily as hitherto believed but is rather partitioning the stress buildup with episodic as opposed to steady state or periodic slip downdip of the seismogenic zone this process increases the stress at the base of the seismogenic zone bringing it closer to failure these results call for a reassessment of the seismic potential of guerrero and other seismic gaps in mexico

effect of pore geometry on vp vs from equilibrium geometry to crack seismic wave velocities of melt or aqueous fluid containing systems are studied over a wide range of pore shapes including oblate spheroids tubes cracks and an equilibrium geometry controlled by a dihedral angle the relative role of liquid compressibility and pore geometry on the v p v s velocity ratio is clarified the result clearly indicates that p and s velocity structures determined by seismic tomography can be used to verify whether interfacial energy controlled melt or fluid geometry equilibrium geometry is achieved relationships between the diverse models are clearly established by relating each model to the oblate spheroid model in terms of the equivalent aspect ratio as a function of the aspect ratio a significant effect of pore geometry on d in v s d in v p the ratio of the fractional changes in v s and v p is shown equilibrium geometry of the partially molten rocks characterized by a dihedral angle of 20 40 corresponds to an aspect ratio of 0 1 0 15 the value of d in v s d in v p expected for the texturally equilibrated partially molten rocks is shown to be 1 1 5 which is much smaller than that expected for cracks and dikes with an aspect ratio of 10 2 10 3 in the upper mantle low velocity regions the seismologically obtained value of d in v s d in v p is within this range beneath the bolivian andes 1 1 1 4 but is as high as 2 beneath iceland 1 7 2 3 and beneath northeastern japan 2 0 the former region can be regarded as a region where equilibrium geometry is achieved and the latter regions can be regarded as regions where dikes and veins typical of a system far from the textural equilibrium dominate

subducting slab ultra slow velocity layer coincident with silent earthquakes in southern mexico great earthquakes have repeatedly occurred on the plate interface in a few shallow dipping subduction zones where the subducting and overriding plates are strongly locked silent earthquakes or slow slip events were recently discovered at the down dip extension of the locked zone and interact with the earthquake cycle here we show that locally observed converted sp arrivals and teleseismic underside reflections that sample the top of the subducting plate in southern mexico reveal that the ultra slow velocity layer usl varies spatially 3 to 5 kilometers with an s wave velocity of 2 0 to 2 7 kilometers per second most slow slip patches coincide with the presence of the usl and they are bounded by the absence of the usl the extent of the usl delineates the zone of transitional frictional behavior

using lagrangian particle saltation observations for bedload sediment transport modelling a lagrangian model for the saltation of sand in water is proposed simulated saltation trajectories neglecting particle rotation and turbulence effects compare fairly well with experimental observations the model for particle motion is coupled with a stochastic model for particle collision with the bed such that a number of realizations of the saltation process can be simulated numerically model predictions of mean values and standard deviations of saltation height length and streamwise particle velocity agree fairly well with experimental observations model predictions of the dynamic friction coefficient are also in good agreement with experimental observations but they underestimate the value of 0 63 proposed by bagnold for this coefficient the saltation model is applied to the estimation of bedload transport rates of sand using a bagnoldean formulation modelled values of the bedload transport rates overestimate those predicted by commonly used bedload formulae which appears to be a consequence of problems in the definition of the dynamic friction coefficient these results seem to indicate a few problems with the bagnoldean formulation particularly regarding the continuum assumption for the bedload layer which would be valid only for very high particle concentrations and small particle diameters and also regarding the evaluation of the shear stress exerted on the bed by the saltating particles 1998 john wiley sons ltd

high frequency turbulence and suspended sediment concentration measurements in the garonne river tidal bore the study details new sediment concentration measurements associated with some turbulence characterisation conducted at high frequency in the undular tidal bore of the garonne river france acoustic doppler velocimetry was used and the suspended sediment concentration was deduced from the acoustic backscatter intensity the field data set demonstrated some unique flow features of the tidal bore including some large and rapid turbulent velocity fluctuations during and after the bore passage some unusually high suspended sediment concentration was observed about 100 s after the tidal bore front lasting for more than 10 min it is thought that the tidal bore passage scoured the bed and convected upwards the bed material reaching the free surface after the bore passage behind the tidal bore the net sediment flux magnitude was 30 times larger than the ebb tide net flux and directed upstream a striking feature of the data set was the intense mixing and suspended sediment motion during the tidal bore and following flood tide this feature has been rarely documented

detection and monitoring of ongoing aseismic slip in the tokai region central japan analysis of global positioning system data shows that the rate of crustal deformations in the tokai region of japan a seismic gap area changed over the past 18 months kalman filtering analysis shows aseismic slip on the plate boundary in the western tokai region centered on lake hamana adjacent to the anticipated tokai earthquake source area the cumulative moment magnitude reaches 6 7 in june 2002 with a relative slip increase northeast of lake haman from january 2002 an existence of aseismic slip in the western tokai supports the hypothesis of a silent event as the cause of uplifting several days before the 1944 tonankai earthquake

short term slow slip and correlated tremor episodes in the tokai region central japan 1 we observe the related phenomenon of short term slow slip event sse and low frequency nonvolcanic tremor on the deeper extension of the 1944 tonankai and the anticipated tokai earthquake rupture areas central japan japan nation wide seismometer and tiltmeter array nied hi net has recorded these correlated episodes of sse and tremor known as episodic tremor and slip ets in 2004 and 2005 the events are located on two areas in the tokai region one is near the shima peninsula and the other is around the aichi area both episodes have a typical duration of 2 3 days and released seismic moment corresponding to mw 6 0 moreover these episodes repeatedly occur with a recurrence interval of about six months in both areas this evidence suggests that the coincidence between the sse and the tremor is a characteristic behavior in the whole tremor belt like zone in the nankai trough subduction zone

aluminium stabilization controls organic carbon levels in chilean volcanic soils chilean volcanic soils are known to contain large amounts of organic matter om and amorphous e g allophanic clay here we test the hypothesis that al rather than clay content and climatic conditions is the most important factor for om levels in volcanic soils this was achieved by compiling a total of 225 pedons from two national wide datasets of south central chilean soils sampled in the first 20 cm depth all selected soils are of volcanic origin previously under native nothofagus forest and now used as pasture or arable land the relationships between soil organic c from now soil c and environmental and soil characteristics clay allophane al content were analysed by simple and multiple linear regression analyses soils classify as alfisols andisols inceptisols and ultisols al was extracted by kcl alk acid ammonium acetate ala and acid ammonium oxalate alo the simple regression models showed that ala correlated best r 2 0 52 with soil c variations for the four soil orders studied while alk r 2 0 08 and alo r 2 0 17 were poorly correlated in all soils types especially in inceptisols ala was highly correlated with soil c r 2 0 88 clay content and hence allophanic content was poorly correlated with soil c r 2 0 14 as was the mean annual precipitation r 2 0 21 and temperature r 2 0 15 these patterns were supported by the multiple regression analyses results therefore support the idea that al is the principal factor for immobi lization of om in acid volcanic soils as ammonium acetate extractable al at ph 4 8 correlated well with om and as this is a rarely used method to interpret pedogenic processes this extraction method warrants further attention d 2005 elsevier b v all rights reserved

double difference tomography the method and its application to the hayward fault california we have developed a double difference dd seismic tomography method that makes use of both absolute and relative arrival times by reducing systematic errors using the more accurate relative arrival times the method produces an improved velocity model simultaneously it yields event locations of a quality equivalent to those of the dd location method while avoiding simplifying assumptions of that method we test this method on a synthetic dataset and find that it produces a more accurate velocity model and event locations than standard tomography we also test this method on a hayward fault california earthquake dataset spanning 1984 1998 the earthquakes relocated by this method collapse to a thin line along the fault trace consistent with previous results the dd velocity model has sharper velocity contrasts near the source region than the standard tomography model

nature of the low velocity zone in cascadia from receiver function waveform inversion abstract a dipping low velocity zone lvz is a ubiquitous structural element of subduction zones worldwide in this study we map seismic attributes characterizing the lvz beneath the cascadia subduction zone from northern vancouver island to northern california using receiver function waveform inversion throughout this region the lvz is characterized by high v p v s ratios mean 2 77 strong s velocity contrasts 50 and thicknesses averaging 3 37 km the lvz is immediately underlain by a second weaker layer exhibiting moderate v p v s ratios mean 1 85 with mean thickness of 4 62 km we interpret the combined structure in terms of subducting oceanic crust based on classical structural petrological descriptions and constraints from previous studies of ophiolites and ocean drill cores the lvz is identified with pervasively hydrated high porosity pillow basalts and sheeted dikes of layer 2 with possible contributions from sediments layer 1 fluids released from metamorphic dehydration reactions are maintained near lithosphere fluid pressures through an impermeable plate boundary above and a low porosity gabbroic mafic cumulate dominated layer 3 below

late holocene paleopedological records contained in tephra from el chichon volcano chiapas mexico abstract high rates of pedogenesis on unconsolidated volcanic materials imply the accelerated generation of the soil memory the purpose of this research was to extract the high resolution centennial scale paleopedological records from the late holocene paleosols of the el chichon volcano formed during the last 2000 years we studied buried monogenetic andosols on the dated tephras and a pedocomplex formed from a set of thin ash layers deposited on older acrisol derived from shales particle size distribution dcb extractable fe oxalate extractable fe al and si sand and clay mineralogy organic carbon content and stable c isotope composition in humus were evaluated and interpreted as the elements of the soil memory however some differences were found in properties of two buried soils especially in the kind of a horizons we attribute such differences of individual andosols to be caused by ancient human impact because it has been demonstrated that humid conditions persisted during the last 1300 years thus the drought that was supposed to provoke the collapse of the maya civilization at the end of i millennium a d should have been a short term event below the resolution of this paleopedological record the andic acrisol pedocomplex demonstrated the domination of the humid tropical climate over longer time intervals probably major part of the holocene with possible minor dry episodes

high pore fluid pressure may cause silent slip in the nankai trough silent slip events have been detected at several subduction zones but the cause of these events is unknown using seismic imaging we detected a cause of the tokai silent slip which occurred at a presumed fault zone of a great earthquake the seismic image that we obtained shows a zone of high pore fluid pressure in the subducted oceanic crust located down dip of a subducted ridge we propose that these structures effectively extend a region of conditionally stable slips and consequently generate the silent slip

seismic evidence for deep water transportation in the mantle we report seismic evidence for the transportation of water into the deep mantle in the subduction zone beneath northeastern japan our data indicate that water is released from the hydrated oceanic crust at shallow depths approximately 100 kilometers and then forms a channel of hydrated mantle material on top of the subducting plate that is the pathway for water into the deep mantle our result provides direct evidence that shows how water is transported from the ocean to the deep mantle in a cold subduction zone environment

inception of bed load motion beneath a bore abstract a tidal bore is a series of waves propagating upstream in the river mouth as the tidal flow turns to rising in macro tidal conditions some related geophysical processes include the tsunami induced bores and uprushing bores on beaches in the present study the inception of sediment motion beneath tidal bores was investigated physically no sediment motion was observed in the initially steady flow and beneath undular bores a transient sheet flow motion was observed beneath breaking bores and the onset of sediment motion was closely linked with the passage of the roller toe the forces acting on the movable gravel bed particles were estimated from the physical measurements the results showed that the longitudinal pressure gradient force was the dominant contribution de stabilising the particles and inducing the onset of sediment motion the drag force added a sizeable contribution to maintain the upstream particle motion although the entire sheet flow motion was brief

flow and turbulence structure in a hypertidal estuary with the world s biggest tidal bore turbulent and flow structure associated with breaking tidal bores are deliberately investigated on the basis of field measurements high resolution velocity and hydrographic data are collected in the middle qiantang estuary by a vertical array of acoustic doppler velocimeters and optical backscatter sensors collaborated with a bottom mounted acoustic doppler current profiler besides obvious variations in diurnal and spring neap tidal cycles the estuarine dynamics is featured by extreme asymmetry in flood and ebb tides the flood tide is abnormally accelerated to generate tidal bores at the first 10 min or more with breaking or undular configurations at the front the occurrence of peak flow velocity turbulent kinetic energy tke and tke dissipation rate e is definitely associated with breaking bores with their values several times to 2 orders of magnitude larger than the corresponding secondary peak values during the maximum ebb flows flow and turbulence dynamics are significantly affected by the tidal bore froude number a sandwich e structure is clear exhibited with the maximum value at the surface secondary maximum near the bed and the minimum at the intermediate dual tke sources are indicated by an approximate local balance between shear production and dissipation near the bottom and a top down tke dissipation using the modified froude scaling in the vertical water column the highly elevated dissipation by breaking bores is comparable to that by intense breaking waves in the surf zone and the former potentially penetrates the entire water column to produce extreme sediment resuspension events in combination with intense bottom shear stress

long term controls on soil organic carbon with depth and time a case study from the cowlitz river chronosequence wa usa abstract over timescales of soil development millennia the capacity of soils to stabilize soil organic carbon soc is linked to soil development through changes in soil mineralogy and other soil properties in this study an extensive dataset of soil profile chemistry and mineralogy is compiled from the cowlitz river chronosequence crc wa usa the crc soils range in age from 0 25 to 1200 kyr spanning a developmental gradient encompassing clear changes in soil mineralogy chemistry and surface area comparison of these and other metrics of soil development with soc properties reveal several relationships that may be diagnostic of the long term coupling of soil development and c cycling specifically soc content was significantly correlated with sodium pyrophosphate extractable metals emphasizing the relevance of organo metal complexes in volcanic soils the depth distributions of organo metals and other secondary weathering products including the kaolin and short range order sro minerals support the so called binary composition of volcanic soils the formation of organo metal complexes limits the accumulation of secondary minerals in shallow soils whereas in deep soils with lower soc content secondary minerals accumulate in the crc soils secondary minerals formed in deep soils below 50 cm including smectite allophane fe oxides and dominated by the kaolin mineral halloysite the abundance of halloysite was significantly correlated with bulk soil surface area and 14 c content a proxy for the mean age of soc implying enhanced stability of c in deep soils allophane an sro mineral commonly associated with soc storage was not correlated with soc content or 14 c values in crc soils we propose conceptual framework to describe these observations based on a general understanding of pedogenesis in volcanic soils where soc cycling is coupled with soil development through the formation of and fate of organo metal or other mobile weathering products this framework highlights interactions between soc and soil development which may be applicable to other soils where organic inputs interact with the products of chemical weathering

small earthquakes provide insight into plate coupling and fluid distribution in the hikurangi subduction zone new zealand abstract to better understand the nature of interplate coupling in the southern north island of new zealand we compare the distribution of relocated small earthquakes with interseismic geodetic locking of the plate interface from gps and structure within the overlying plate from tomographic inversions relocated seismicity shows a good correlation with both the distribution of strong geodetic locking and geological terranes in the overlying plate it appears that the strong permian triassic rakaia geological terrane controls coupling at the plate interface this relatively impermeable terrane also modulates the small earthquake distribution within the underlying slab promoting clustered seismicity in the slab crust and suppressing lower plane seismicity in the mantle the seismicity and structural data suggest a model where plate coupling is controlled by the ability of fluid to cross the plate interface when an impermeable terrane in the overlying plate prevents such fluid flow plate coupling appears to be strong

organo metallic complexes in an andosol a comparative study with a cambisol and podzol current soil forming processes were studied in a nonallophanic andosol from the vosges mountains north eastern france for this purpose we conducted comparative studies on the organo metallic fraction dynamics of selected profiles of an andosol and other typical soils from this region cambisol and podzol these soils are derived from old volcanic rocks under mesic soil temperature and udic soil moisture regimes the andosol profile displayed the characteristics of nonallophanic andosols large accumulation of humus active al mostly complexed with humus and low ph special attention was given to physical and microbial stability of these organo metallic associations respectively by disaggregation tests and incubation experiments the results indicated that these associations showed a strong resistance against disaggregation by water and against biodegradation moreover the very low concentration of doc al and fe in soil solutions collected by zero tension lysimeters coupled with very low amounts of water dispersed clays obtained after dispersion tests suggested that no significant translocations of these components occurred in this andosol profile low mobility together with a strong resistance against mineralization may account for the large accumulation of carbon in this andosol

on the role of fluid infiltration into gravel dunes using a 3d numerical model abstract both the hydrodynamic conditions as well as the related sediment transport processes of sandy bedforms are understood fairly well however little is known about the genetic processes of bedforms involved in environments dominated by gravel in the coastal environment storm waves spring tides bore waves and to a lower frequency tsunamis are common phenomena that can provide the required energy to form gravel bedforms given the high energy of such wave events and the formidable practical difficulties of fixed instrumentation and in situ measurements knowledge on the hydrodynamic processes in the direct vicinity and in the interior of gravel bedforms is still limited a 3d numerical flume tank model using smoothed particle hydrodynamics sph was generated to study the nature of flows for an extreme wave above and in the interior of gravel bedforms as a complementary method to in situ measurements with typical flume tank dimensions x 2 68 m y 0 25 m z 0 8 m three experiments were undertaken to test a range of simplified bedform geometries stoss side slopes 42 23 13 using a unimodal grain fraction the water column was represented by 11 million fluid particles and the bedforms by 480 immobile solid particles a single numerical wave was introduced using a vertical paddle that moved to x 0 3 m perpendicular to the bottom of the tank fluid velocities extracted at each timestep at each point of the tank were used to determine free stream pore water flow velocities and residence times from all experiments results showed that when the wave crest was positioned before the bedform crests pore water flows appeared predominantly in the downstream direction however when the position of wave crest was located after the bedform crests a vortex developed at the leeside of all bedforms causing a change of the pore water flow towards the upstream direction regions of inflow outflow and pore water flow through the pore spaces were evident in all experiments but changed as the stoss side slope angles were decreased it is concluded that variations in the stoss side steepness appear to control the locations and the position of the wave crest the directions of pore water flow which was illustrated in a conceptual model

measurement and modelling of the influence of grain size and pressure gradient on swash uprush sediment transport the paper examines the dependency between sediment transport rate q and grain size d i e q dp in the swash zone experiments were performed using a dam break flow as a proxy for swash overtopping on a mobile sediment beach the magnitude and nature of the dependency i e p value is inferred for different flow parameters the initial dam depth or initial bore height do the integrated depth averaged velocity u3 dt and against the predicted transport qp using the meyer peter muller mpm transport model experiments were performed over both upward sloping beds and a horizontal bed the data show that negative dependencies p 0 are obtained for u3 dt this indicates that a given do and qp transport less sediment as grain size increases whereas transport increases with grain size for a given u3 dt the p value is expected to be narrow ranged 0 5 p 0 5 a discernible difference observed between the measured and predicted transport on horizontal and sloping beds suggests different modes of transport the incorporation of a pressure gradient correction dp dx using the surface water slope i e piezometric head in the transport calculation greatly improved the transport predictions on the horizontal bed where dp dx is positive on average the incorporation of a pressure gradient term into the mpm formulation reduces qp in the uprush by 4 fine sand to 18 coarse sand and increases qp over a horizontal bed by 1 fine sand to two orders of magnitude coarse sand the measured transport for fine and coarse sand are better predicted using mpm and mpm dp dx respectively poor predictions are obtained using nielsen 2002 because the pressure gradient in the uprush is of opposite sign to that inferred from velocity data in that paper it is suggested that future swash sediment transport models should incorporate the grain size effect partly through the pressure gradient although the dp dx influence is small for fine sands because of the grain size scaling contained in the stress term

variations of fluid pressure within the subducting oceanic crust and slow earthquakes 1 we show fine scale variations of seismic velocities and converted teleseismic waves that reveal the presence of zones of high pressure fluids released by progressive metamorphic dehydration reactions in the subducting philippine sea plate in tokai district japan these zones have a strong correlation with the distribution of slow earthquakes including long term slow slip ltss and low frequency earthquakes lfes overpressured fluids in the ltss region appear to be trapped within the oceanic crust by an impermeable cap rock in the fore arc and impede intraslab earthquakes therein in contrast fluid pressures are reduced in the lfe zone which is deeper than the centroid of the ltss because there fluids are able to infiltrate into the narrow corner of the mantle wedge leading to mantle serpentinization the combination of fluids released from the subducting oceanic crust with heterogeneous fluid transport properties in the hanging wall generates variations of fluid pressures along the downgoing plate boundary which in turn control the occurrence of slow earthquakes

are organo mineral complexes and allophane content determinant factors for the carbon level in chilean volcanic soils abstract the existing information on soil carbon c stabilisation in allophanic soils is conflicting because active al3 and sesquioxides i e the oxides hydroxides of al and fe as a stabilising agent of soil c are emphasised in opposition to allophane and imogolite type materials two hypotheses were tested in this study 1 al and fe complexed with soil c and allophane content are the key variables to explain the soil c level in chilean allophanic soils and 2 the existing metal som complex and short range ordered aluminosilicate minerals in allophanic soils mainly result from soil ph variation and competition between al and fe for som and allophane formation this study established the relationship among different soil properties such al fe complexes and allophane content on soil c levels in chilean volcanic soils as well as the effect of soil ph on metal om complexes a total of 45 soil samples from 15 soil pedons were sampled at 0 0 1 0 1 0 2 and 0 2 0 4 m the soil samples were analysed for the content of soil organic c allophane clay silt and na pyrophosphate extraction alp fep cp and soil ph water we examined the relationship between the soil c content and soil properties using simple and multiple linear regressions the silt and clay contents explained little while the allophane soil ph and alp explained most of the soil c variation we found an inverse relationship between soil ph and alp and fep indicating that the soil ph was significantly correlated with alp and fep while the allophane content was positively related with soil ph the results also showed a higher atomic ratio al fe p cp in deep 0 2 0 4 m horizons the opposite was true in the top soil horizon 0 0 1 m supporting the idea that som in deep soils is saturated with al and fe leaving extra metal to react with silica for allophane formation

spatio temporal stress states estimated from seismicity rate changes in the tokai region central japan abstract since unprecedented large scale silent slip was detected by gps in 2001 in the tokai region evaluating whether such movement is uniquely connected to the expected tokai earthquake or repeatedly occurs in this area becomes vitally important because of short history of gps observations and the limited areal coverage surrounding the suruga trough we take advantage of continuously recorded seismicity that is presumed to be sensitive to the deformation at seismogenic depth together with the well maintained nied earthquake data we employ the seismicity to stress inversion approach of rate state friction to infer the spatio temporal stress changes in and around the presumed hypocentral zone of the future tokai earthquake mapping stress changes inverted from microseismicity year by year we find that the stress under lake hamana the western expected future tokai source has been decreasing since 1999 during which the gps data showed a normal trend of plate coupling in contrast stresses in the surrounding regions are calculated to have increased by transfer from lake hamana region we interpret that this continuous process is associated with the 2000 2004 tokai slow slip event the characteristic patterns related to aseismic stress release are also identified in the early 1980s and during 1987 1989 when slow events are inferred to have occurred on the basis of conventional geodetic measurements revisiting the seismotectonics and taking into account the mechanical implications of the inversion results we argue that the transition zone situated between a deep stable creeping zone and a locked zone undergoes episodic creep and plays an important role in the transfer of stress to the locked zone consequently even though we speculate that the current 2000 to present day silent slip event might be one of the repeating events the inferred enlargement of the stress releasing area is significant and possibly raises the likelihood of the next tokai earthquake

an intraslab seismic sequence activated by the 2011 tohoku oki earthquake evidence for fluid related embrittlement 1 using quantitative analysis of waveforms we investigate a seismic cluster that occurred at a depth of 67 km in the philippine sea slab 8 months after the 11 march 2011 megathrust tohoku oki earthquake mw 9 0 the sequence started with an m 4 1 normal fault event on 14 november in the deepest part of the cluster and subsequent earthquakes migrated upward by 6 km along a narrow conduit like zone the earthquakes have stress drops of 0 5 40 mpa and groups of earthquakes with coherent waveforms are observed we explain these observations in terms of fluid related embrittlement and the migration of overpressured fluids the low permeability plate interface of the pacific plate may have been broken by the coseismic or postseismic slips of the tohoku oki earthquake with the fluids subsequently being liberated from the underlying crust of the pacific slab and migrating into the philippine sea slab due to the pore pressure gradient the tensional stresses generated by the coseismic slip promoted the efficient upward migration of fluids and also acted to enhance the deviatoric stress around the source area the heightened pore pressures and the resulting reduced effective normal stress lowered the strength of the faults sufficiently to bring the system into the brittle regime under the enhanced deviatoric stress the lag of 8 months may represent the time needed for the unsealing of the plate interface the upward migration of fluids and the increase in pore pressure to become sufficient to overcome the lithostatic pressure

successive impact of tidal bores on sedimentary processes arcins channel garonne river a tidal bore is a hydrodynamic shock propagating upstream as the tidal flow turns to rising with macro tidal conditions in a funnel shaped system with shallow waters the tidal bore of the garonne river was extensively investigated in the arcins channel between 2010 and 2013 typically over one to two days in 2015 new field measurements were repeated systematically at the same site on 29 august 1 september 2015 and on 27 october 2015 the nature of the observations was comprehensive encompassing hydrodynamics and turbulence as well as sediment properties and transport the tidal bore occurrence had a marked effect on the velocity and suspended sediment field including a rapid flow deceleration and flow reversal during the bore passage with very large suspended sediment concentrations sscs during the passage of the tidal bore front and early flood tide as well as very large suspended sediment flux during the very early flood tide the suspended sediment concentration ssc data indicated a gradual increase in initial mean ssc estimate prior to the bore from 29 august to 1 september 2015 a comparison between suspended sediment flux data showed very significant suspended sediment flux on the first day of tidal bore occurrence with a decreasing magnitude over the next three days the data suggested a two stage bed scour process at each tidal bore event surface erosion occurred initially in the form of stripping the first stage was followed by delayed mass erosion occurring about 5 15 min after the tidal bore

fluid flow and sediment entrainment in the garonne river bore and tidal bore collision a detailed field study was carried out on a tidal bore to document the turbulent processes and sediment entrainment which occurred the measured bore within the arcins channel of the garonne river france was undular in nature and was followed by well defined secondary wave motion due to the local river geometry a collision between the arcins channel tidal bore and the bore which formed within the main garonne river channel was observed about 800m upstream of the sampling site this bore collision generated a transient standing wave with a black water mixing zone following this collision the bore from the main garonne river channel propagated backward to the downstream end of the arcins channel velocity measurements with a fine temporal resolution were complemented by measurements of the sediment concentration and river level the instantaneous velocity data indicated large and rapid fluctuations of all velocity components during the tidal bore large reynolds shear stresses were observed during and after the tidal bore passage including during the backward bore propagation large suspended sediment concentration estimates were recorded and the suspended sediment flux data showed some substantial sediment motion consistent with the murky appearance of the flood tide waters copyright c 2015 john wiley sons ltd

interplate coupling in the tokai district central japan deduced from continuous gps data i invert gps displacement rates in the tokai district to investigate strain accumulation associated with the anticipated tokai earthquake i apply a representation of interseismic strain accumulation at subduction zones by savage 1983 and estimate a distribution of virtual normal fault slip back slip on the plate boundary surface estimated back slip takes its maximum value of 30 40mm year under the sea of enshu this value is nearly equal to the relative plate motion there implying almost complete coupling back slip is smaller under suruga bay and its direction is different from the relative motion between the eurasian and the philippine sea plates localized deformation at the northern tip of the philippine sea plate may be responsible for this discrepancy partitioning tectonic strain due to the plate convergence into faults on both sides of the izu peninsula and also distributed strain inside the peninsula

weathering and soil formation in rhyolitic tephra along a moisture gradient on alcedo volcano galapagos abstract the galapagos archipelago has extensively been studied because of its geological and climatic setting and especially for its peculiar flora and fauna however there is still little information about its soils the objective of this study was to investigate weathering and soil formation on alcedo volcano which is the only volcano of galapagos that has erupted abundant rhyolitic materials soils were sampled from three sites along an elevation moisture gradient site 1 at 872 m above sea level a s l humid zone site 2 at 621 m a s l dry zone and site 3 at 377 m a s l very dry zone soil ph in h2o ranged from 6 0 to 6 6 but did not vary significantly among the three sites water retention at 1500 kpa and phosphate retention increased with elevation moisture similarly soil organic carbon soc stocks increased from approx 1 1 kg m 2 in the very dry zone to approx 7 5 kg m 2 in the humid zone allophane and ferrihydrite were the dominant colloidal constituents in the humid zone site 1 whereas halloysite was found in the dry zone site 2 and only traces of halloysite in the very dry zone site 3 at site 1 the soil was borderline between andic and vitric properties and was classified as silandic tephric andosol or vitric tephric andosol for andic and vitric character respectively at site 2 the soil had vitric properties and was classified as vitric tephric skeletic andosol and at site 3 the soil was borderline with respect to the expression of vitric properties and was classified as vitric tephric skeletic andosol in the presence and as tephric skeletic regosol in the absence of vitric properties our results show that different moisture availability strongly affected soc accumulation and favored the formation of different types of colloidal constituents amorphous vs crystalline in the rhyolitic tephra of alcedo volcano this has important bearings on the expression of andic and vitric soil properties and hence on the distribution of andosols in the studied environment

pore pressure and oceanic crustal seismic structure summary marine refraction studies during the past decade have found considerable lateral variability in the seismic properties of the upper basaltic regions of the oceanic crust in many localities compressional and shear wave velocities are quite low at the top of the basalt section and velocities increase rapidly with depth it is concluded that pore pressure may be at least in part responsible for the low upper crustal velocities and contribute significantly to the lateral variability this is supported by compressional and shear wave velocity measurements as functions of confining pressure and pore pressure for basalt from the juan de fuca ridge and dolerite from the samail ophiolite oman within the oceanic crust regions of overpressure and underpressure will possess anomalous velocities the magnitude of which will depend upon the porosity and the deviation of the pore pressure from hydrostatic the influence of pore pressure on velocities is expected to diminish with depth and is unlikely to be significant at lower crustal depths where porosity is extremely low of significance poisson s ratio is shown to be dependent on pore pressure as well as confining pressure at constant confining pressure poisson s ratio increases with increasing pore pressure thus overpressured regions within the upper oceanic crust are likely to have relatively high poisson s ratios as well as low compressional and shear wave velocities

lack of additional triggered tectonic tremor around the simi valley and the san gabriel mountain in southern california abstract we conduct a systematic search of tectonic tremor triggered by distant large earthquakes around the simi valley sv and the san gabriel mountain sgm in southern california out of 59 large earthquakes between 2000 and 2013 only the 2002 m w 7 9 denali fault earthquake triggered clear tremor in the region the observed travel times of the triggered tremors are consistent with theoretical predictions from tremor sources that are spatially clustered in the sv close to the rupture zone of the 1994 m w 6 7 northridge earthquake we also estimate the triggering stress threshold as 12 kpa from measuring the peak ground velocities near the tremor source the lack of clear tremor beneath the sgm provides a negative example for a region where tremor is expected to occur because of clear evidence of fluid rich zones at the middle crust the results imply that the necessary conditions for tremor to occur are more than fluid induced low effective normal stress online material figures of additional tremor inspection tables of earthquake catalogs and tremor locations

subduction of the philippine sea plate beneath southwestern japan slab geometry and its relationship to arc magmatism 1 we carry out high resolution three dimensional seismic tomography of the crust and upper mantle beneath southwestern sw japan using arrival time data obtained from the nationwide seismograph network the tomographic images provide new insights into the configuration of the philippine sea slab and arc magmatism the results confirm the existence of an aseismic portion of the philippine sea slab at greater depths beyond the seismic portion the philippine sea slab is subducting aseismically down to at least a depth of 200 km in chubu 60 80 km in kinki and 60 km in chugoku and is subducting seismically to depths of 150 200 km in kyushu in the chubu district it is subducting seismically at a shallow dip and then bends downward beneath the volcanic area whereas in the kinki district it is subducting subhorizontally as far as the japan sea the differences in the slab geometry between adjacent regions correlate with the differences in volcanic activity suggesting the importance of the geometry of the philippine sea slab on arc magmatism our tomographic images further imply subduction of the philippine sea slab down to a depth of around 70 km northwest of the izu peninsula the philippine sea slab in that region might have split into western and eastern parts separated by a slab tear and collided with the pacific slab at depths of 150 200 km

spontaneous and triggered aseismic deformation transients in a subduction fault model 1 aseismic deformation transients can emerge as a natural outcome of the rate and state friction processes revealed in laboratory fault sliding experiments when that constitutive formulation is applied to model subduction earthquake sequences transients can arise spontaneously for certain effective stress variations with depth we show that if interstitial fluids are present and pore pressure is near lithostatic around and downdip from the frictional stability transition transients with recurrence intervals of 1 year are predicted on the basis of laboratory friction parameters and their temperature hence depth variations the recurrence interval decreases with and reaches 14 months when is 2 3 mpa dimensional analysis and numerical studies show that the fault response primarily depends on a parameter w h here the high pore pressure zone extends distance w updip from the stability transition and h is the stable patch size for steady sliding evidence that such fluid conditions may actually be present is independently provided by the occurrence of nonvolcanic tremors as apparent responses to extremely small stress changes and by petrological constraints on expected regions of dehydration for the shallow dipping subduction zones where transients are observed transient sequences can also be triggered by a modest one time step like interseismic stress perturbation on the subduction fault due to nearby earthquakes or to pore pressure changes e g during episodes of metamorphic fluid release properties of triggered transients and future thrust earthquakes depend on the interseismic time when the perturbation is introduced its relative location along the subduction fault and its magnitude

slow slip and frictional transition at low temperature at the hikurangi subduction zone temperature changes with depth do not appear to be a primary control for either slow slip or fault locking processes at the hikurangi margin north island new zealand both slow slip events and the geodetically observed transition from fault locking to free slip at depth occur at temperatures as low as 100 c shallow portions of faults exhibit brittle stick slip behaviour that gives way to more stable sliding with increasing depth limiting the depths to which earthquake inducing slip can occur the increase of temperature with depth is often assumed to transform friction in the fault from velocity weakening unstable to velocity strengthening stable and to change conditions from brittle to ductile1 2 3 4 5 a temperature of 350 c has been suggested to mark the base of the frictionally unstable portion of the fault which becomes free slipping at depth where temperatures rise above 450 c refs 2 4 6 here we show that both slow slip events and the geodetically observed transition from fault locking to free slip at the hikurangi subduction zone east of the north island new zealand occur at temperatures as low as 100 c suggesting that temperature is not a primary control on either slow slip or fault locking processes at the hikurangi margin although globally shallow slow slip events are rare five out of seven events observed so far at the hikurangi margin are less than 15 km deep

fluid and deformation regime of an advancing subduction system at marlborough new zealand newly forming subduction zones on earth can provide insights into the evolution of major fault zone geometries from shallow levels to deep in the lithosphere and into the role of fluids in element transport and in promoting rock failure by several modes the transpressional subduction regime of new zealand which is advancing laterally to the southwest below the marlborough strike slip fault system of the northern south island is an ideal setting in which to investigate these processes here we acquired a dense high quality transect of magnetotelluric soundings across the system yielding an electrical resistivity cross section to depths beyond 100 km our data imply three distinct processes connecting fluid generation along the upper mantle plate interface to rock deformation in the crust as the subduction zone develops massive fluid release just inland of the trench induces fault fracture meshes through the crust above that undoubtedly weaken it as regional shear initiates narrow strike slip faults in the shallow brittle regime of interior marlborough diffuse in width upon entering the deeper ductile domain aided by fluids and do not project as narrow deformation zones deep subduction generated fluids rise from 100 km or more and invade upper crustal seismogenic zones that have exhibited historic great earthquakes on high angle thrusts that are poorly oriented for failure under dry conditions the fluid deformation connections described in our work emphasize the need to include metamorphic and fluid transport processes in geodynamic models

kinetics of antigorite dehydration a real time x ray diffraction study antigorite dehydration has been studied in situ using time resolved x ray diffraction xrd in the 1 1 5 5 gpa pressure range the sequence of xrd spectra reveals that the high temperature stability limit of antigorite is decreased by 50 100 c under h2o unsaturated conditions the decomposition of antigorite into the high temperature products forsterite enstatite proceeds via an intermediate assemblage of forsterite and a talc like phase observed within a temperature interval of 130 20 c the analysis of the transformation time data using the avrami model suggests that the breakdown of antigorite and the talc like phase is kinetically controlled by surface growth processes at the edges of grains the overall transformation rates are 10 to 100 times faster than those observed in water saturated experiments and show that the h2o activity is a strong driving force for dehydration the breakdown of antigorite in subducting oceanic mantle with such kinetics would result in a fluid discharge rate of the order of 10 6 to 10 8 s 1 this is faster than the viscous relaxation of serpentinites and could lead to brittle failure or weakening of pre existing faults this provides an explanation for the seismicity in the lower plane of double seismic zones

an inverted continental moho and serpentinization of the forearc mantle volatiles that are transported by subducting lithospheric plates to depths greater than 100 km are thought to induce partial melting in the overlying mantle wedge resulting in arc magmatism and the addition of significant quantities of material to the overlying lithosphere asthenospheric flow and upwelling within the wedge produce increased lithospheric temperatures in this back arc region but the forearc mantle in the corner of the wedge is thought to be significantly cooler here we explore the structure of the mantle wedge in the southern cascadia subduction zone using scattered teleseismic waves recorded on a dense portable array of broadband seismometers we find very low shear wave velocities in the cold forearc mantle indicated by the exceptional occurrence of an inverted continental moho which reverts to normal polarity seaward of the cascade arc this observation provides compelling evidence for a highly hydrated and serpentinized forearc region consistent with thermal and petrological models of the forearc mantle wedge this serpentinized material is thought to have low strength and may therefore control the down dip rupture limit of great thrust earthquakes as well as the nature of large scale flow in the mantle wedge

an automatic monitoring system for nonvolcanic tremors in southwest japan 1 the recent development of a system for exchanging and distributing seismic waveform data over high speed networks enables seismic events to be monitored in real time throughout japan in the present study we have developed an automatic real time monitoring system for deep nonvolcanic tremors in southwest japan the system automatically detects the occurrence of nonvolcanic tremors and determines their hypocenters in real time in addition the system creates image files for the detected tremor activities and makes them accessible via the world wide web to detect tremors we carry out a two step numerical hypothesis test in which the first step is to test whether two given envelope seismograms are correlated and the second step is to test whether an event occurs using the results of the first test this two step test is applied to real time data every 2 min once an event is detected we can regard time lags that generate maximum cross correlations as the travel time differences which we use for hypocenter determination although this procedure detects nontremor signals most of them can be rejected using several criteria since the start of monitoring in 2006 the system has worked well for detecting a wide variety of tremor activities results from the present system will contribute to understanding the stress relaxation process in the transition zone between the locked and stable slip zones of the subducting philippine sea plate interface

contrasting subduction structures within the philippine sea plate hydrous oceanic crust and anhydrous volcanic arc crust we show contrasting subduction structures within the philippine sea plate inferred from active source wide angle reflection data previous studies showed that large amplitude reflections from the slab are observed in southwest japan and indicated that a thin low velocity layer with a high fluid content is formed along the top of the subducting oceanic crust on the contrary we found that the slab reflections have smaller amplitudes in the izu collision zone central japan where the izu bonin volcanic arc has been colliding subducting suggesting that such a low velocity layer does not exist beneath the collision zone this structural difference is also supported by p wave and s wave velocity anomalies by passive source tomography and electrical conductivity and correlates with the regional distribution of deep tremors and intraslab earthquakes both of which are induced by dehydration processes within the downgoing slab based on these comparisons we suggest that the original structure of the incoming plate controls the contrasting subducting systems typical oceanic plate absorbs water by hydrothermal circulation at spreading centers and or seawater infiltration at outer rises whereas volcanic arc crust consumes a large amount of hydrous minerals for melt production and metamorphoses to more stable anhydrous forms before subduction

low frequency earthquakes observed in close vicinity of repeating earthquakes in the brittle upper crust of hakodate hokkaido northern japan we conducted a detailed investigation of an earthquake cluster distributed from the lower crust to the upper crust beneath hakodate hokkaido which included both low frequency earthquakes lfes a