water solubility in pyrope to 100 kbar the solubility and incorporation mechanism of water in natural almost pure pyrope from dora maira western alps was investigated the infrared spectrum of the natural untreated sample 58 ppm water shows several exceptionally sharp bands in the oh stretching region including a single band at 3601 9 cm 1 and a band system with main components at 3640 5 3650 8 and 3660 6 cm 1 high temperature and high pressure infrared spectra suggest that the two absorption features arise from almost free oh groups in sites with different compressibility and thermal expansivity with the site causing the 3601 9 cm 1 band being much stiffer pyrope samples were annealed in a piston cylinder or multi anvil apparatus for several days in the presence of excess water excess sio2 and excess al2sio5 to determine the equilibrium solubility of water in pyrope to 100 kbar total solubility increases with pressure however this is exclusively due to the high frequency band system while the intensity of the low frequency band decreases with pressure at 1000 c and the oxygen fugacity of the ni nio buffer the bulk solubility can be described by the equation c oh af h2o 0 5exp p v rt with a 0 679 ppm bar0 5 and v 5 71 cm3 mol this equation implies the incorporation of water in the crystal as isolated oh groups with increasing temperature solubility appears to decrease with h 14 kj mol at fe feo buffer conditions solubility is 30 to 50 lower than with the ni nio buffer suggesting that the incorporation of oh is not coupled to the reduction of fe3 possibly the 3601 9 cm 1 band is associated with the tetrahedral oh b defect and the high frequency system with the dodecahedral oh li defect based on the experimentally established solubility model it is estimated that garnet in a hot subducted slab will transport 170 ppm of water into the mantle beyond the breakdown limit of amphibole in a cold slab 470 ppm of water can be incorporated into garnet at the breakdown limit of phengite these numbers imply that a significant fraction of the total water in the hydrosphere has been recycled into the mantle since the proterozoic

dislocation microstructures in naturally deformed silicate garnets abstract dislocation microstructures of naturally deformed silicate garnets and olivines in garnet peridotites and silicate garnets in eclogites from four localities have been observed with a transmission electron microscope tem to clarify the dislocation characteristics of silicate garnets we have obtained the following results 1 dislocation densities of garnets in all the garnet peridotites 105 107 cm 2 are always nearly an order of magnitude lower than those of co existing olivines 2 dislocation densities of garnets in eclogites 105 108 cm 2 which are embedded in garnet peridotites are almost an order of magnitude higher than those of garnets in the surrounding garnet peridotites 3 the dominant burgers vector b of mainly edge dislocations in garnet is 100 for specimens with dislocation density 105 106 cm 2 while b 1 2 111 for specimens with 107 108 cm 2 result 1 indicates that the observed dislocations in garnets were formed by plastic deformation under the same stresses as for co existing olivines and that there is a similar relationship between applied stress and dislocation density for garnets as for olivines result 2 suggests that the stress concentration occurred around eclogites embedded in garnet peridotites and the resulting differential stress in garnets in eclogites was further elevated by the interlocking of neighboring hard garnet grains finally result 3 indicates that the dominant burgers vector of mainly edge dislocations in garnet changes from 100 to 1 2 111 with increasing applied differential stress

normal faulting earthquakes beneath the outer slope of the japan trench after the 2011 tohoku earthquake implications for the stress regime in the incoming pacific plate 1 after the 2011 mw 9 1 tohoku earthquake numerous intraplate earthquakes occurred beneath the outer slope of the japan trench based on ocean bottom seismograph observations these earthquakes occurred in the oceanic crust and uppermost mantle of the pacific plate at depths shallower than about 40 km and had normal faulting focal mechanisms at all depths before the 2011 earthquake normal faulting earthquakes beneath the outer trench slope occurred only at depths shallower than 20 km whereas those at depths of around 40 km had reverse faulting mechanisms these observations suggest that the stress regime in the pacific plate was changed by the 2011 earthquake the tensional stresses that now extend to depths of about 40 km may play an important role not only in the occurrence of large normal faulting earthquakes but also in hydration of the uppermost mantle of the incoming pacific plate prior to the subduction

the olivine spinel transformation and the rheology of subducting lithosphere during subduction relatively hot lithospheric slabs are expected to deform in a superplastic flow regime below a depth of 300 km if olivine reacts to fine grained spinel this process reduces the flow strength of such slabs below the phase boundary so that they become aseismic at about this depth in colder slabs temperatures are too low for superplastic deformation and a high flow strength and seismic activity are maintained to a depth of 600 700 km

si and o diffusion in mg fe 2sio4 wadsleyite and ringwoodite and its implications for the rheology of the mantle transition zone si and o diffusion rates on polycrystalline mg fe 2 sio 4 wadsleyite and ringwoodite have been determined at pressures between 16 and 22 gpa and temperatures between 1400 and 1600 c using a kawai type multi anvil high pressure apparatus pre synthesized polycrystalline wadsleyite or ringwoodite was used as starting materials diffusing sources of 29 si and 18 o enriched mg fe 2 sio 4 thin film were deposited on the surface of wadsleyite and ringwoodite by pulsed laser deposition the diffusion profiles were obtained using secondary ion mass spectrometry in the depth profiling mode all measured diffusion profiles were composed of volume and grain boundary diffusion regimes arrhenius relations for volume and grain boundary diffusion rates of si and o in wadsleyite and ringwoodite have been determined the results show that si is the slowest diffusing element among the major elements in both wadsleyite and ringwoodite under mantle transition zone as well as slab conditions therefore si should be the rate controlling species for high temperature creep in wadsleyite and ringwoodite comparisons with si and o diffusion rates obtained in this study and those in olivine and silicate perovskite suggest that si and o diffusion rates are enhanced at both 410 and 660 km seismic discontinuities the deformation mechanism maps constructed from si diffusion data in wadsleyite and ringwoodite suggest that the dominant deformation mechanism operating in the mantle transition zone is dislocation creep which may be the origin of the observed global seismic anisotropy under cold subduction zone conditions grain size sensitive diffusion creep becomes dominant when the grain size is reduced to less than 10 100 m below the metastable olivine wedge

on the separation of crustal component from subducted oceanic lithosphere near the 660 km discontinuity the recent mineral physics observations suggest that the crustal and mantle components of subducted oceanic lithosphere have distinct densities and viscosities the deformation of such chemically stratified oceanic lithosphere as it collides with the 660 km discontinuity is examined using a simple analytical model it is shown that the separation of the crustal component can occur through a small scale folding 10 20 km if the viscosity of the crustal garnetite layer is significantly higher than the surrounding mantle 1021 pa s but is less than 1023 pa s leading to a garnet enriched transition zone behind subduction zones

the eclogite garnetite transformation at high pressure and some geophysical implications mineral assemblages displayed by morb and alkali poor olivine tholeiites have been investigated over the pressure interval 4 6 18 gpa at 1200 c both compositions crystallize to form normal eclogites between 4 6 and 10 gpa and there is little change in the relative proportions of garnet and pyroxene over this range however the proportion of garnet increases rapidly above 10 gpa as pyroxene dissolves in the garnet structure and pyroxene free garnetites stishovite are produced by 14 15 gpa dependent upon composition the garnetite facies for both compositions possess zero pressure densities of 3 75 g cm3 implying that subducted oceanic crust remains appreciably denser than surrounding mantle to depths exceeding 600 km it is demonstrated that the seismic velocity distributions in the mantle between 400 and 650 km are inconsistent with anderson s hypothesis that this region is of eclogitic composition

bending of the subducting oceanic plate and its implication for rupture propagation of large interplate earthquakes off miyagi japan in the japan trench subduction zone 1 we present the results of an onshore offshore wide angle refraction and reflection experiment off miyagi in the central japan trench forearc region there are two rupture zones of large interplate earthquakes here the landward rupture zone and the trenchward rupture zone to examine the influence of plate boundary geometry on the distributions of the rupture zones we determined reflector geometries from reflections the subducting oceanic plate increases its dip from about 5 to 13 around 143 2 e this bending point in the oceanic plate corresponds to the eastern edge of the trenchward rupture zone moreover another bending point may be present at approximately 142 3 e which corresponds to the eastern edge of the landward rupture zone the coincidence between bending points in the oceanic plate and the edges of rupture zones suggests that changes in the plate boundary geometry may affect rupture propagation of interplate earthquakes in the direction of plate convergence

grain size evolution in subducted oceanic lithosphere associated with the olivine spinel transformation and its effects on rheology we investigate the role of grain size reduction during the olivine spinel transformation on rheological properties of subducting slabs on the basis of a scaling model for microstructural development during nucleation and growth in this model the size of spinel grains nucleating at olivine grain boundaries is controlled by the relative rates of nucleation and growth taking into account the impingement through the collision of grains due to growth when the volume fraction of spinel reaches a certain threshold value critical volume fraction 1 10 depending on the p t conditions in the slab the new phase will form a continuous film and will significantly reduce the strength of the two phase aggregate if spinel grain size is small the size of spinel grains d at this stage is calculated and is shown to be highly sensitive to 0 size and 2 a subducting slab has a complicated rheological structure containing a weak region below the tip of a metastable olivine bearing wedge in a cold slab possible implications of these anomalous rheological structures of slabs on the dynamics of subduction are discussed including the mechanisms of deep earthquakes

effects of pressure and temperature on the silicon diffusivity of pyrope rich garnet abstract we have determined the pressure and temperature dependencies of si volume diffusion rates in a single crystal of pyp75alm15gr10 garnet at 6 25 gpa and 1400 1800 c by the 29si tracer diffusion method high pressure experiments were conducted using the kawai type multi anvil high pressure apparatus diffusion profiles were obtained using secondary ion mass spectrometry in the depth profiling mode the si diffusion coefficient in garnet dgt is expressed by the arrhenius equation dgt d0 exp e pv rt with log10d0 7 1 1 7 m2 s e 345 56 kj mol and v 4 7 0 5 cm3 mol si diffusion seems to be the slowest in the major constituent elements in a pyrope rich garnet and control rates of plastic deformation the comparison between si diffusion rates in garnet and wadsleyite ringwoodite suggests that garnet has similar or slightly lower strength at most 2 times compared with wadsleyite and has similar or slightly higher strength at most 3 times compared with ringwoodite at temperatures ranging from 900 to 1300 c thus strength contrast between subducted oceanic crust and underlying peridotite layer may be small at the mantle transition zone conditions this result suggests that the separation of subducted oceanic crust from an underlying peridotite layer may not occur

some mineral physics constraints on the rheology and geothermal structure of earth s lower mantle we explore the implications of recent mineral physics measurements of diffusion coefficients and melting temperatures of lower mantle materials on the rheological and geothermal structure of earth s lower mantle we show that mgsio3 perovskite is significantly stronger than mgo periclase and therefore the rheology of the lower mantle depends strongly on the geometry of a weaker phase periclase we calculate viscosities of the lower mantle for two cases 1 where periclase occurs as isolated grains and 2 where periclase occurs as continuous films using mineral physics data and models of two phase rheology we find that the effective viscosity for the former is about 10 1000 times higher than the latter we therefore suggest that the rheology of the lower mantle is structure and hence strain dependent leading to weakening at large strains due to the formation of continuous films of periclase overall depth variation of viscosity depends not only on the pressure dependence of creep but also on the geothermal gradient both mgsio3 perovskite and periclase have relatively small activation energies e g r t m with g 10 14 where r is the gas constant and t m is melting temperature and therefore the depth variation of viscosity is rather small even for a nearly adiabatic temperature gradient however the geothermal gradients consistent with the geodynamical inference of nearly depth independent viscosity are sensitive to the pressure dependence of viscosity which is only poorly understood a superadiabatic gradient of up to 0 6 k km is also consistent with mineral physics and geodynamical observations

aftershocks near the updip end of the 2011 tohoku oki earthquake abstract the march 2011 m w 9 0 tohoku oki earthquake activated shallow aftershocks with normal faulting focal mechanisms near the trench axis to investigate stress state in the shallow subduction zone near the trench axis we used ocean bottom seismographs obss to record earthquakes from august to october 2011 we estimated hypocenter locations and focal mechanisms of the recorded earthquakes by using a grid search method in a 2 d velocity model based on an active seismic survey the results show that most of the earthquakes occurred within both the overriding and subducting plates with very few on the plate interface and none in the most seaward 45 km of the overriding plate aseismic wedge the low seismicity along the plate interface is consistent with the nearly complete stress drop on the megathrust fault in the m w 9 0 earthquake focal mechanisms indicate that trench normal tension is pre dominant in both plates and extends to a depth of about 30 km at least on the other hand several trench normal compressional earthquakes were located at the landward end of the aseismic wedge these earthquakes suggest horizontal compression of the overriding prism that may be caused by a strengthening of the shallowest part of the megathrust

silicon and oxygen self diffusion in stishovite implications for stability of sio2 rich seismic reflectors in the mid mantle abstract diffusion of si and o in single crystal stishovite was examined at pressures of 14 0 21 5 gpa and temperatures of 1673 2073 k self diffusion coefficients of si dsi and o d o were determined as dsi m 2 s 2 4 10 12 exp 237 kj mol 6 0 cm 3 mol p r t and d o m 2 s 7 2 10 11 exp 263 kj mol 4 8 cm 3 mol p r t respectively where p is pressure in gpa t is absolute temperature in k and r is the ideal gas constant it was revealed that diffusion of si is approximately one order of magnitude slower than that of o and thus si is the rate controlling element for plastic deformation of stishovite si diffusion in stishovite is assessed to be at least three orders of magnitude slower than that in bridgmanite under mid mantle conditions therefore it is anticipated that highly viscous sio2 rich components subducted into the lower mantle persist as the seismic reflectors for long term without mixing up with the bridgmanite dominated surrounding mantle

plastic deformation of garnets systematics and implications for the rheology of the mantle transition zone abstract plastic properties of materials with garnet structure have been studied under wide temperature conditions ranging from room temperature to 95 of the melting temperatures using uniaxial compression and hot microhardness tests garnets studied include single crystals of oxide garnets y 3 al 5 o 12 gd 3 ga 5 o 12 and y 3 fe 5 o 12 and silicate garnets various solid solutions including grossular almandine andradite pyrope spessartine and uvarovite both uniaxial compression and hot hardness tests indicate that there is a general trend in the plasticity of garnets when the data are compared at normalized conditions t t m and and that the resistance to plastic deformation in garnets is significantly higher than most of the other minerals in the earth s mantle based on both stress dip tests and microstructural observations it is proposed that the creep strength of garnet is largely controlled by the resistance to dislocation glide rather than by recovery processes this conclusion is consistent with the high peierls stress inferred from the hot hardness tests the high peierls stress in garnets is presumably due to the large unit cell i e long burgers vectors and or the bcc packing which are common to all garnets we postulate therefore that the present results can be applied to the strength of high pressure garnet majorite and suggest that garnet rich layers in the earth such as subducted oceanic crust in the transition zone or a possibly garnet rich bottom part of the transition zone will be considerably stronger than surrounding regions

rheological control of oceanic crust separation in the transition zone mineral physics observations suggest that distinct density and rheological differences exist between the crustal component of oceanic lithosphere and the underlying mantle we have conducted numerical experiments to investigate the influence of both density and viscosity on the effectiveness of recycling of oceanic crust into the lower mantle confirming previous results the density inversion at 670 km depth alone is not sufficient to prevent crustal recycling however a soft layer may exist between the strong garnet crust and cold slab interior models employing a simplified newtonian sandwich model show that this thin weak layer can effectively decouple the crust and slab once entrained into the lower mantle the then lighter crust can rise sufficiently fast as a rayleigh taylor instability to avoid further entrainment these results suggest that the crustal component of slabs may be trapped at 670 km depth leading to a garnet enriched transition zone

effects of water and iron content on the rheological contrast between garnet and olivine abstract the effects of water and iron content on the relative creep strengths of garnet and olivine were investigated by shear deformation experiments garnet and olivine samples were sandwiched together between alumina pistons in a simple shear geometry and were deformed at p 1 2 gpa t 1473 k and strain rates ranging from 10 5 to 10 3 s 1 using a griggs type solid medium apparatus the stress and strain rate relation as well as the deformation microstructures including lattice preferred orientation and dynamic recrystallization indicates that the deformation by dislocation creep the creep tests show that the fe rich garnet alm 67 prp 29 grs 3 was slightly weaker than olivine fo90 whereas the mg rich garnet alm 19 prp 68 grs 12 was significantly stronger than olivine under dry conditions the wet experiments show that the creep rate of the mg rich garnet is more sensitive to water than olivine the water fugacity exponent on strain rate was estimated to be 2 4 for garnet and 1 2 for olivine and the mg rich garnet becomes weaker than olivine in a water rich environment the experimental results show that the rheological contrast between garnet and olivine depends strongly on water content and to a lesser degree on fe content consequently the geodynamic behavior of geochemical reservoirs can be sensitive to their chemical environments in the upper mantle

the 2011 tohoku oki earthquake displacement reaching the trench axis we detected and measured coseismic displacement caused by the 11 march 2011 tohoku oki earthquake moment magnitude mw 9 0 by using multibeam bathymetric surveys the difference between bathymetric data acquired before and after the earthquake revealed that the displacement extended out to the axis of the japan trench suggesting that the fault rupture reached the trench axis the sea floor on the outermost landward area moved about 50 meters horizontally east southeast and 10 meters upward the large horizontal displacement lifted the sea floor by up to 16 meters on the landward slope in addition to the vertical displacement

tem observations of several spinel garnet assemblies toward the rheology of the transition zone in order to better identify the mineral phase which controls the rheology of the transition zone between 410 and 660 km depth transmission electron microscopy observations were made on several coexisting spinel garnet assemblies alkremite xenolith pyrope rich mgo 1 1al2o3 spinel assembly deformed at 1173k 800 mpa in a griggs apparatus mg fe 3 al mg si 2si3o12 majorite mg fe 2sio4 spinel assembly synthesized in a laser heated diamond anvil cell it was found that garnet crystals systematically remain undeformed while spinel crystals are plastically deformed these results are in accord with the assumption that the rheology of majorite is stronger than the rheology of spinel in the conditions of the transition zone

metamorphic evolution of two different eclogites in the franciscan complex california u s a the eclogites in california u s a have been regarded as tectonic blocks which formed 150 160 ma ago and have been tectonically incorporated into younger rocks of the franciscan complex of 90 130 ma however in ward creek northern california two different types of eclogites were identified type i is a typical tectonic block and type ii is a possible in situ eclogite formed during the franciscan metamorphism most eclogites in the franciscan complex are type i eclogites type i eclogites in ward creek consist of garnet omphacite epidote glaucophane phengite rutile barroisite quartz and have coarse grained gneissic texture they have precursors of the epidote amphibolite facies and are overprinted in various degrees by blueschist facies retrograde metamorphism remnants of metamorphic rinds which consist of actinolite talc chlorite and formed during metasomatic interaction with serpentinizing peridotite occur at the margins of type i eclogite blocks type ii eclogites are medium grained and consist of garnet chloromelaniticclinopyroxene epidote glaucophane paragonite phengite rutile quartz petrochemical characters of type ii eclogites are similar to those of in situ eclogitic schists in the ward creek metabasite sequence epidote amphibolite f facies precursors metamorphic rinds and overprint of retrogressive blueschist facies metamorphism are not found in type ii eclogites garnets in type ii eclogites are medium grained unaltered and idioblastic and have higher spessartine contents sp14 25 whereas garnets in type i eclogites are coarse grained and chloritized and have lower spessartine contents sp2 7 the pt conditions of peak metamorphism for type ii eclogites are 380 10 11 5 kb type i eclogites follow a counter clockwise pt path from the epidote amphibolite through eclogite to blueschist facies whereas the presumable in situ type ii eclogites follow a clockwise pt path from the blueschist to eclogite facies

experimental investigation of the kinetics of the spinel to garnet transformation in peridotite a preliminary study to study the kinetics of the spinel to garnet transformation in peridotite we conducted reaction experiments in the garnet peridotite stability field 3 2 gpa 1020 1220 c for 0 6 30 h using a single spinel crystal embedded in monomineralic orthopyroxene powder or in a mixture of powdered orthopyroxene and clinopyroxene the growth textures observed in the reaction rim between the spinel crystal and the polycrystalline pyroxenes show that the reaction rim grew in both the spinel and pyroxenes directions suggesting mobility of both sio 2 and r 2 o 3 components where r is a trivalent cation olivine grains formed only in the presence of monomineralic orthopyroxene and were present in some domains without forming reaction rims based on a diffusion controlled growth model the growth kinetics of the garnet reaction rim can be described by x t 2 k 0 exp h r t t where x t is the rim width at time t r is the gas constant t is the absolute temperature and h is the activation enthalpy of reaction k 0 and h are respectively k 0 10 19 8 4 9 m 2 s and h 171 58 kj mol the development of a garnet reaction rim around a spinel core has been observed in alpine type peridotitic rocks and mantle xenoliths the reaction rims experimentally produced in this study are characteristic of corona textures observed in natural rocks and the experimentally measured growth rate of the rims places important constraints on dynamic transformation processes involving spinel and garnet in peridotite however to reconstruct the p t t history of the corona texture based on these elementary processes additional detailed studies on the textural evolution and quantitative kinetics of the garnet rim growth stage are required

three dimensional seismic refraction tomography a comparison of two methods applied to data from the faeroe basin this paper presents a comparison of two tomographic methods for determining three dimensional 3 d velocity structure from first arrival travel time data the first method is backprojection in which travel time residuals are distributed along their ray paths independently of all other rays the second method is regularized inversion in which a combination of data misfit and model roughness is minimized to provide the smoothest model appropriate for the data errors both methods are nonlinear in that a starting model is required and new ray paths are calculated at each iteration travel times are calculated using an efficient implementation of an existing method for solving the eikonal equation by finite differencing both inverse methods are applied to 3 d ocean bottom seismometer obs data collected in 1993 over the faeroe basin consisting of 53 479 travel times recorded at 29 obss this is one of the most densely spaced large scale 3 d seismic refraction experiments to date different starting models and values for the free parameters of each tomographic method are tested a new form of backprojection that converges more rapidly than similar methods compares favorably with regularized inversion but the latter method provides a simpler model for little additional computational expense when applied to the faeroe basin data bounds on two model features are assessed using regularized inversion with combined smoothness and flatness constraints an inversion of synthetic data corresponding to 100 data recovery from the real experiment shows a marked improvement in lateral resolution at deeper depths and demonstrates the potential of currently feasible 3 d refraction experiments to provide well resolved long wavelength velocity models the similarity of the final models derived from the two tomographic methods suggests that the results from the new form of backprojection can be relied on when limited computational resources rule out regularized inversion

application of the cbω model to the calculation of diffusion parameters of si in silicates silicon diffusion in major mantle minerals plays an important role in understanding a number of physical and chemical processes in the earth s interior inspection of existing experimental data reveals linear compensation law between the preexponential factors and the activation energies for si diffusion in various minerals by focusing on those of geophysical interest on the basis of the observed compensation relationship here we propose a thermodynamic model the so called cb model that interconnects point defect parameters with the bulk properties to reproduce the si self diffusion coefficients in different rock forming minerals when the uncertainties are considered the predicted results show that the temperature and pressure dependences of self diffusion coefficients concur with existing experimental data and theoretical calculations in most cases

structural characteristics off miyagi forearc region the japan trench seismogenic zone deduced from a wide angle reflection and refraction study abstract the japan trench subduction zone located east of ne japan has regional variation in seismicity many large earthquakes occurred in the northern part of japan trench but few in the southern part off miyagi region is in the middle of the japan trench where the large earthquakes m 7 with thrust mechanisms have occurred at an interval of about 40 years in two parts inner trench slope and near land a seismic experiment using 36 ocean bottom seismographs obs and a 12 000 cu in airgun array was conducted to determine a detailed 2d velocity structure in the forearc region off miyagi the depth to the moho is 21 km at 115 km from the trench axis and becomes progressively deeper landward the p wave velocity of the mantle wedge is 7 9 8 1 km s which is typical velocity for uppermost mantle without large serpentinization the dip angle of oceanic crust is increased from 5 6 near the trench axis to 23 150 km landward from the trench axis the p wave velocity of the oceanic uppermost mantle is as small as 7 7 km s this low velocity oceanic mantle seems to be caused by not a lateral anisotropy but some subduction process by comparison with the seismicity off miyagi the subduction zone can be divided into four parts 1 seaward of the trench axis the seismicity is low and normal fault type earthquakes occur associated with the destruction of oceanic lithosphere 2 beneath the deformed zone landward of the trench axis the plate boundary is characterized as a stable sliding fault plain in case of earthquakes this zone may be tsunamigenic 3 below forearc crust where p wave velocity is almost 6 km s and larger this zone is the seismogenic zone below inner trench slope which is a plate boundary between the forearc and oceanic crusts 4 below mantle wedge the rupture zones of thrust large earthquakes near land e g 1978 off miyagi earthquake are located beneath the mantle wedge the depth of the rupture zones is 30 50 km below sea level from the comparison the rupture zones of large earthquakes off miyagi are limited in two parts plate boundary between the forearc and oceanic crusts and below mantle wedge this limitation is a rare case for subduction zone although the seismogenic process beneath the mantle wedge is not fully clarified our observation suggests the two possibilities earthquake generation at the plate boundary overridden by the mantle wedge without serpentinization or that in the subducting slab

rupture process of the 2011 tohoku oki earthquake and absolute elastic strain release 1 on 11 march 2011 the tohoku oki earthquake in eastern japan and the devastating tsunami that followed it caused severe damage and numerous deaths to clarify the rupture process of the earthquake we inverted teleseismic p wave data applying a novel formulation that takes into account the uncertainty of green s function which has been a major error source in waveform inversion the estimated seismic moment is 5 7 1022 nm mw 9 1 associated with a fault rupture 440 km long and 180 km wide along the plate interface the source process is characterized by asymmetric bilateral rupture propagation but we also found continuous slips up dip from the hypocenter which led to a large maximum slip 50 m long slip duration 90 s and a large stress drop 20 mpa the long slip duration large stress drop extensional normal faulting aftershocks in a previously compressional stress regime and low angle normal slips at approximately the depth of the plate interface suggest that the earthquake released roughly all of the accumulated elastic strain on the plate interface owing to exceptional weakening of the fault the stress accumulated on the plate interface was about 20 mpa near the trench and 0 10 mpa in the down dip source region

plastic flow of pyrope at mantle pressure and temperature despite the abundance of garnet in deforming regions of the earth such as subduction zones its rheological properties are not well defined by laboratory measurements here we report measurements of steady state plastic properties of pyrope in its stability field temperature up to 1573 k pressure up to 6 8 gpa strain rate approx 10 5 s 1 using a deformation dia apparatus d dia coupled with synchrotron radiation synthetic pyrope py100 and natural pyrope py70alm16gr14 are both studied in a dry environment transmission electron microscopy tem investigation of the run products indicates that dislocation glide assisted by climb within grains and dynamic recrystallization for grain boundary strain accommodation is the dominant deformation process in pyrope both synthetic and natural pyropes stress and strain rate data as measured in situ by x ray diffraction and imaging are best fitted with the single flow law

rheological structure and deformation of subducted slabs in the mantle transition zone implications for mantle circulation and deep earthquakes abstract rheological structure of subducted slabs of oceanic lithosphere in the mantle transition zone is investigated based on mineral physics observations incorporating grain size stress temperature and pressure dependence of rheology it is shown that the rheological structure of slabs depends strongly on subduction parameters through temperature that controls the grain size of spinel ringwoodite and the magnitude of forces acting on a slab we use a theoretical model of grain size evolution associated with the olivine spinel transformation plastic flow laws of olivine and spinel combined with a thermal model of subducting slab in which the effect of latent heat release is incorporated three deformation mechanisms for olivine and spinel diffusional creep power law dislocation creep and the peierls mechanism are considered due to the large variation in temperature stress and grain size a subducting slab is shown to have a complicated rheological structure which varies both laterally and with depth a cold slab in the deep transition zone is characterized by a weak fine grained spinel region surrounded by narrow but strong regions the flexural rigidity and the curvature of a slab are calculated using a new formulation in which the effects of stress dependent rheology is incorporated in a self consistent fashion although uncertainties in both the transformation kinetics and the rheology of high pressure phases are still large the general trend of dependence of slab flexural rigidity and the curvature on the subduction parameters is well constrained slabs with very low thermal parameters warm slabs are weak but slabs with large thermal parameters cold slabs are also weak due to small spinel grain size and large external force bending moment slabs with intermediate thermal parameters will have a relatively large flexural rigidity and could penetrate into the lower mantle without much deformation thus the 660 km discontinuity may work as a rheological filter for mantle convection this prediction provides a natural explanation for a paradoxical observation that significant deformation of slabs is observed exclusively in the western pacific where temperatures of the slabs are considered to be low our slab rheology models also have important implications for deep earthquakes overall rheological weakening of slabs in the deep transition zone results in high rates of deformation under relatively low temperatures providing a favorable environment for thermal runaway instability adiabatic shear instability our model predicts heterogeneous energy dissipation as a result of heterogeneous rheology energy dissipation in deep cold slabs is concentrated in high strength regions surrounding a weak fine grained spinel core the regions of high energy dissipation are prone to thermal runaway instability and are likely to be seismogenic the width of this seismogenic region is well constrained by our model and is predicted to be 40 60 km which is in excellent agreement with seismological observations other features of deep earthquakes including low seismic efficiency and low aftershock activities can also be explained by the thermal instability model

frontal wedge deformation near the source region of the 2011 tohoku oki earthquake 1 we report an uplift of 5 m with a horizontal displacement of more than 60 m due to the 2011 tohoku oki earthquake the uplift was measured by an ocean bottom pressure gauge installed before the earthquake on a frontal wedge which formed an uplift system near the japan trench horizontal displacements of the frontal wedge were measured using local benchmark displacements obtained by acoustic ranging before and after the earthquake the average displacements at the frontal wedge were 58 m east and 74 m east southeast these results strongly suggest a huge coseismic slip beneath the frontal wedge on the plate boundary the estimated magnitude of the slip along the main fault was 80 m near the trench our results suggest that the horizontal and vertical deformations of the frontal wedge due to the slip generated the tremendous tsunami that struck the coastal area of northeastern japan

stagnation of subducting slabs in the transition zone due to slow diffusion in majoritic garnet subducting slabs of oceanic lithosphere often stagnate before reaching the lower mantle laboratory experiments under high pressures and temperatures show that pyroxene a common mineral in such slabs is transformed to its dense high pressure counterpart majorite garnet at a very slow rate temporarily keeping the slabs buoyant compared to the surrounding mantle

stress state in the largest displacement area of the 2011 tohoku oki earthquake the 2011 moment magnitude 9 0 tohoku oki earthquake produced a maximum coseismic slip of more than 50 meters near the japan trench which could result in a completely reduced stress state in the region we tested this hypothesis by determining the in situ stress state of the frontal prism from boreholes drilled by the integrated ocean drilling program approximately 1 year after the earthquake and by inferring the pre earthquake stress state on the basis of the horizontal stress orientations and magnitudes estimated from borehole breakouts and the increase in coseismic displacement during propagation of the rupture to the trench axis in situ horizontal stress decreased during the earthquake the stress change suggests an active slip of the frontal plate interface which is consistent with coseismic fault weakening and a nearly total stress drop

slow si al interdiffusion in garnet and stagnation of subducting slabs abstract si 4 m 2 2al 3 m mg fe ca interdiffusion rates in majoritic garnet have been determined at pressure of 17 gpa and temperatures of 1550 1700 c using a kawai type high pressure apparatus the diffusion profiles were measured across the interface between pyropic garnet and majoritic garnet samples by an analytical transmission electron microscope and the rate of the si 4 m 2 2al 3 interdiffusion was determined to be a d si al m 2 s 1 2 10 10 exp 364 kj mol 1 rt we found that the diffusion rate is low compared to the si diffusion rate in other silicate minerals relevant to the deep mantle slow kinetics of the pyroxene garnet transformation due to the low diffusion rate indicates that large low density metastable regions may exist in the slab greatly contributing to the slab stagnation around the transition region stagnant slabs possibly stay in this region over 10 8 yr because of the sluggish pyroxene garnet transformation but may eventually fall into the lower mantle after the completion of the transformation

relationships between compressional wave and shear wave velocities in clastic silicate rocks new velocity data in addition to literature data derived from sonic log seismic and laboratory measurements are analyzed for clastic silicate rocks these data demonstrate simple systematic relationships between compressional and shear wave velocities for water saturated clastic silicate rocks shear wave veloci ty is approximately linearly related to compressional wave velocity and the compressional to shear velocity ratio decreases with increasing compressional velocity laboratory data for dry sandstones indicate a nearly constant compressional to shear velocity ratio with rigidity approximately equal to bulk modulus ideal models for regular packings of spheres and cracked solids exhibit behavior similar to the observed water saturated and dry trends for dry rigidity equal to dry bulk modulus gassmann s equations predict velocities in close agreement with data from the water saturated

self diffusion of oxygen and silicon in mgsio3 perovskite abstract we present results of simultaneous measurements of self diffusion of oxygen and silicon in magnesium silicate perovskite oxygen diffusion is 2 orders of magnitude faster than si self diffusion and fe mg interdiffusion in perovskite with d0 9 16 10 4 0 16 9 2 10 6 m2 s and q 501 80 kj mol at 25 gpa despite this high o diffusivity however the electrical conductivity of the lower mantle will be dominated by electronic conduction and the present day core is likely to be out of redox equilibrium with the mantle

rare earth diffusion kinetics in garnet experimental studies and applications abstract we determined the diffusion coefficient of sm in almandine garnet as function of temperature at 1 bar and fo 2 corresponding to that of wustite iron buffer and to a limited extent that of a few other selected rare earth elements in almandine and pyrope garnets both garnets were demonstrated to have metastably survived the diffusion annealing at conditions beyond their stability fields the experimental diffusion profiles were analyzed by secondary ion mass spectrometry and in addition by rutherford back scattering spectroscopy for two samples transmission electron microscopic study of an almandine crystal that was diffusion annealed did not reveal any near surface fast diffusion path using reasonable approximations and theoretical analysis of vacancy diffusion the experimental data were used to develop an expression of rare earth element ree diffusion coefficient in garnet as a function of temperature pressure fo 2 ionic radius and matrix composition calculation of the closure temperature for the sm nd decay system in almandine garnet in a metamorphic terrain shows very good agreement with that constrained independently modeling of the ree evolution in melt and residual garnet suggests that for dry melting condition the ree pattern in the melt should commonly conform closely to that expected for equilibrium melting however for much lower solidus temperatures that would prevail in the presence of a h 2 o co 2 fluid the concentration of light ree in the melt could be significantly lower than that under equilibrium melting condition a reported core and rim differences in the ree content of a garnet crystal in a mantle xenolith in kimberlite have been reproduced by assuming that the ree zoning was a consequence of entrapment in a magma derived from an external source for 32 000 yr before the eruption

silicon self diffusion in single crystal natural quartz and feldspar abstract silicon diffusion was measured in natural quartz and anorthitic feldspar under dry low pressure 0 1 mpa conditions using a 30 si tracer sources of diffusant consisted of 30 si enriched silica powder for experiments on quartz and microcrystalline 30 si doped synthetic feldspar of composition comparable to the feldspar specimens distributions of 30 si were measured with rutherford backscattering spectrometry and nuclear reaction analysis using the reaction 30 si p 31 p the following arrhenius relations were obtained for anneals at 1 atm in air for quartz transport normal to c d qtz c 7 97 10 6 exp 447 31 kj mol 1 rt m 2 s 1 transport parallel to c d qtz c 6 40 10 6 exp 443 22 kj mol 1 rt m 2 s 1 for anorthitic feldspar an 93 d an 3 79 10 7 exp 465 50 kj mol 1 rt m 2 s 1 the few successful experiments on diffusion in plagioclase of more albitic compositions an 67 and an 23 reveal si diffusivities a few orders of magnitude faster than that in the anorthite the results for these feldspars bracket the determination of caal nasi interdiffusion under dry conditions by grove et al geochim cosmochim acta 48 1984 2113 2121 suggesting that the rate limiting process is indeed si diffusion si diffusion in quartz under more reducing conditions nno is slightly slower by about half an order of magnitude than diffusion in samples annealed in air this is consistent with observations made in studies of synthetic quartz bejina and jaoul phys earth planet inter 50 1988 240 250

aftershock patterns and main shock faulting we have compared aftershock patterns following several moderate to large earthquakes with the corresponding distributions of coseismic slip obtained from previous analyses of the recorded strong ground motion and teleseismic waveforms well located aftershock hypocenters are projected onto the main shock fault plane and their positions are examined relative to the zones of coseismic displacement indicated by the estimated distributions of main shock slip we also examine the aftershock focal mechanisms when these data are available in an attempt to identify possible patterns of secondary faulting within the aftershock zone our results are consistent with a hypothesis of aftershock occurrence that requires a secondary redistribution of stress following primary failure on the earthquake fault aftershocks following the earthquakes examined in this study occur mostly outside of or near the edges of the source areas indicated by the patterns of main shock slip the spatial distribution of aftershocks reflects either a continuation of slip in the outer regions of the areas of maximum coseismic displacement or the activation of subsidiary faults within the volume surrounding the boundaries of main shock rupture