shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

texture development and deformation mechanisms in ringwoodite ringwoodite mg2sio4 with spinel structure is an important phase in the earth s mantle transition zone controlled deformation experiments showed that ringwoodite underwent ductile deformation when compressed axially at 6 10 gpa and at room temperature in a multianvil d dia deformation apparatus texture evolution during cyclic compression has been recorded in situ using x ray transparent anvils with monochromatic synchrotron x ray diffraction and a two dimensional detector quantitative analysis of the images with the rietveld method revealed a 1 1 0 fiber texture by comparing this texture pattern with polycrystal plasticity simulations it is inferred that 111 slip is the dominant deformation mechanism in ringwoodite consistent with high temperature mechanisms observed in other spinel structured materials although strong ringwoodite textures may develop in the transition zone the contribution to bulk anisotropy is minimal due to the weak single crystal anisotropy 2005 elsevier b v all rights reserved

seismic anisotropy in the java banda and philippine subduction zones and its implications for the mantle flow system beneath the sunda plate

laboratory and seismological observations of lower mantle isotropy we have carried out seismological and mineral physics investigations to identify the extent and origin of elastic anisotropy in the lower mantle based on observations of shear wave splitting we conclude that the lower mantle is effectively isotropic this result is surprising since the lower mantle is composed of elastically anisotropic minerals silicate perovskite mgo sio 2 that have been extensively strained by geologic processes to reconcile the seismic observations we have measured texture development during deformation and high temperature recrystallization of mantle silicates we show that these experiments provide a direct explanation for the shear wave splitting measurements the lower mantle appears isotropic because silicate perovskite maintains an isotropic texture during deformation and recrystallization

upper and mid mantle anisotropy beneath the tonga slab measurements of source side splitting in s waves fromevents within the tonga slab reveal anisotropy in the upperand mid mantle beneath the slab we observed splitting forevents originating at both upper mantle and transition zonedepths anisotropic fast directions are trench parallel orsub parallel for both upper mantle and transition zoneevents delaytimes dt decreasewithdepthforuppermantleevents the source of anisotropy for the upper mantle eventsis likely in the sub slab mantle and is likely indicative oftrench parallel flow due to slab rollback the source ofanisotropy for the deeper earthquakes is more difficult toconstrain but the pattern of splitting measurements arguesfor an uppermost lower mantle anisotropic source and slabinduced deformation may be responsible for this anisotropyas well additional constraints from mineral physics studiesare necessary to interpret the mid mantle anisotropy signalin terms of geodynamical processes

the mw 8 0 antofagasta northern chile earthquake of 30 july 1995 a precursor to the end of the large 1877 gap abstract an m w 8 0 earthquake occurred on 30 july 1995 in the antofagasta region northern chile the main rupture corresponding to thrust faulting developed from 10 to 50 km in depth along the subduction interface between the nazca and the south american plates the 1995 earthquake took place just south of the large seismic gap where a great earthquake m 9 had occurred in 1877 most of the 1995 rupture was located within a local network consisting of nine short period stations that had been previously installed at the southern end of the 1877 gap and the aftershock sequence could be accurately monitored little destruction resulted from the 1995 earthquake in spite of its large size ground acceleration in antofagasta reached 29 of gravity a tsunami wave 2 to 2 5 m high was observed along the coast from mejillones to taltal one strong foreshock m w 6 2 occurred in the 1995 hypocentral region 6 months before the main event body wave modeling of broadband seismograms from the global network along with the analysis of the aftershock distribution allows us to propose a well constrained model for the whole rupture process some additional details of the rupture were obtained from an accelerometer record at antofagasta the main rupture started as a double even with thrust mechanism below the southern part of the mejillones peninsula and it propagated southward in a n200 e direction with an average velocity of 2 8 km sec it ended near the trench in normal faulting the total rupture area and seismic moment are 185 90 km 2 and 1 2 10 28 dyne cm respectively the aftershock distribution delineates a well defined rupture surface along the subduction interface the distribution of epicenters during the first 20 h of aftershock activity shows a sharp northern boundary beneath the mejillones peninsula hence the 1995 main rupture did not propagate north of the mejillones peninsula into the 1877 gap aftershocks during the following 2 weeks indicate a growth of the initial rupture zone toward the north the mechanisms of the strongest aftershocks are similar to that of the mainshock the down dip termination of the main rupture corresponds to the maximum depth 50 km of the region that had been identified as the locked part of the subduction interface from the analysis of the microseismicity recorded by the local network prior to the 1995 event a well constrained dislocation model is proposed for the 1995 main rupture which produces surface displacements in good agreement with available observations of coastal uplift and gps measurements the dislocation model as well as global positioning system gps measurements indicate that the 1995 earthquake generated e w extension in the coastal region of antofagasta the atacama fault located 40 to 50 km above the 1995 main rupture showed small fresh surface ruptures near sierra remiendos 70 km to the sse of antofagasta with a maximum vertical offset of 20 cm this offset corresponds to normal faulting which is in agreement with the e w co seismic extension the mejillones peninsula appears to be the surface expression of a barrier that interrupted the propagation of the 1995 rupture to the north into the region of the 1877 gap modeling of static stress changes induced by the antofagasta earthquake indicates an increase in compressive stresses along a direction transverse to the trench immediately to the north of the 1995 rupture surface thus the chances for the reactivation of the 1877 gap after this event are greater now

hydrodynamic implications of textural trends in sand deposits of the 2004 tsunami in sri lanka abstract field observations and sediment samples at a coastal plain setting in southeastern sri lanka were used to document the erosional and depositional impacts of the 2004 indian ocean tsunami and to interpret the hydrodynamic processes that produced an extensive sand sheet deposit tsunami deposit thicknesses ranged from 6 to 22 cm with thickness being controlled partly by antecedent topography the deposit was composed of coarse to medium sand organized into plane parallel laminae and a few laminasets vertical textural trends showed an overall but non systematic upward fining and upward thinning of depositional units with an upward increase in heavy mineral laminations at some locations repeated patterns in the vertical textural trends upward fining upward coarsening uniform were used to subdivide and correlate the deposit into five hydro textural stratigraphic units the depositional units were linked to hydrodynamic processes and upcurrent conditions such as rates of sediment supply and composition of the sediment sources vertical changes in grain size distributions recorded the depositional phases associated with flow acceleration initial unsteady pulsating flow relatively stable and uniform flow flow deceleration slack water and return flow or flow redirection study results suggest that vertical textural trends from multiple cross shore sections can be used to interpret complex tsunami flow histories but at the location examined interpretation of the lateral textural trends did not provide a basis for identifying the correct sediment transport pathways because flow near the landward boundary was multidirectional

sub slab anisotropy beneath the sumatra and circum pacific subduction zones from source side shear wave splitting observations understanding the dynamics of subduction is critical to our overall understanding of plate tectonics and the solid earth system observations of seismic anisotropy can yield constraints on deformation patterns in the mantle surrounding subducting slabs providing a tool for studying subduction dynamics while many observations of seismic anisotropy have been made in subduction systems our understanding of the mantle beneath subducting slabs remains tenuous due to the difficulty of constraining anisotropy in the sub slab region recently the source side shear wave splitting technique has been refined and applied to several subduction systems worldwide making accurate and direct measurements of sub slab anisotropy feasible and offering unprecedented spatial and depth coverage in the sub slab mantle here we present source side shear wave splitting measurements for the central america alaska aleutians sumatra ryukyu and izu bonin japan kurile subduction systems we find that measured fast splitting directions in these regions generally fall into two broad categories aligning either with the strike of the trench or with the motion of the subducting slab relative to the overriding plate trench parallel fast splitting directions dominate beneath the izu bonin japan and southern kurile slabs and part of the sumatra system while fast directions that parallel the motion of the downgoing plate dominate in the ryukyu central america northern kurile western sumatra and alaska aleutian regions we find that plate motion parallel fast splitting directions in the sub slab mantle are more common than previously thought we observe a correlation between fast direction and age of the subducting lithosphere older lithosphere 95 ma is associated with trench parallel splitting while younger lithosphere 95 ma is associated with plate motion parallel fast splitting directions finally we observe source side splitting for deep earthquakes transition zone depths beneath japan and sumatra suggesting the presence of anisotropy at midmantle depths beneath these regions

seismological and experimental constraints on metastable phase transformations and rheology of the mariana slab abstract a wedge with a low seismic wave velocity implying the presence of metastable olivine and the depression of the 660 km seismic discontinuity have been observed inside the mariana slab based on these seismic observations and numerical calculation of thermal structures of the slab we suggest that the phase transformations from olivine to ringwoodite and from ringwoodite to perovskite ferropericlase the post spinel transformation occur at the depth of 630 km and 550 c and at 690 km and 700 c respectively in the central coldest part of the mariana slab combining this information with recent experimental kinetic data we constrain the details of non equilibrium phase transformations and rheology of the mariana slab the observed depth of the metastable olivine inside the mariana slab can be explained by growth controlled olivine ringwoodite transformation under relatively dry condition such as the water content of about 150 wt ppm h2o on the other hand nucleation process controls the depth of the post spinel transformation in the mariana slab and therefore the observed depressions of the 660 km discontinuity should depend on both the overpressure needed for the nucleation and the negative clapeyron slope for the transformation when the overpressure for the nucleation is 0 5 gpa the observed depressions can be explained by the clapeyron slope of 0 7 mpa k grain size evolution and viscosity structures in the mariana slab are estimated based on these metastable phase transformations the slab weakening due to the grain size reduction is limited in about 40 km in width below the metastable olivine wedge at the depths from 630 to 690 km whereas the width of the weakened portion of the slab increases to more than 120 km at deeper than the 690 km depth after the post spinel transformation these viscosity structures are consistent with the behaviors of the mariana slab estimated from seismic tomography the slab vertically descends to the bottom of the transition zone and substantially deforms and thickens at the top of the lower mantle

a regionalized upper mantle rum seismic model seismic velocity heterogeneity in the earth s mantle is strongly concentrated near its top the shallow heterogeneity of the mantle correlates strongly with surface tectonics we use these observations as constraints of a tomographic experiment aimed at building a regionalized upper mantle rum reference model we use a select set of teleseismic travel times to minimize the mapping of mislocation into structure the data selection emphasizes the robustness of individual picks the form of the rum model is a set of velocity profiles as functions of depth through the upper mantle for each of the different tectonic provinces of earth together the profiles constitute a three dimensional model which incorporates considerable structural detail but is described by only 90 parameters and has only about 22 degrees of freedom this is achieved by irregularly sampling a detailed regionalization of the globe by detailed mapping of subducted lithosphere in the mantle as defined by seismicity and by combining these structures in an irregular grid in which bookkeeping is efficiently handled the resulting rum model includes subducting slabs as sharp fast features in the upper mantle old continents are fast young oceans are slow models have been derived for both compressional and shear velocity the rum model is designed to represent as much of upper mantle heterogeneity as seen by body wave travel times as possible with a simple model it can be useful as a reference model for individual tectonic regions travel times are efficiently generated for the rum model mislocations of explosions of known location are significantly reduced when corrections for the rum model are applied to travel time residuals for a spherically symmetrical earth model

gradual unlocking of plate boundary controlled initiation of the 2014 iquique earthquake a long foreshock series unlocked the south american plate boundary until eventually initiating the m 8 1 iquique chile earthquake two groups publishing in this issue of nature analyse the seismic context of the iquique earthquake that occurred off the coast of northern chile on 1 april 2014 in a seismic zone that had been quiescent since a significant event in 1877 gavin hayes et al identify areas of remaining or elevated earthquake hazard along the megathrust fault in the region and conclude that the 2014 iquique event was not the earthquake that had been anticipated given that significant sections of the northern chile subduction zone have not ruptured in almost 150 years they suggest that it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 iquique sequence bernd schurr et al show that the april 2014 earthquake broke a central fraction of the northern chile seismic gap the last major segment of the south american plate boundary that had yet to rupture in the past century from july 2013 up to the april earthquake they identify three seismic clusters along this part of the plate boundary each lasting a few weeks with earthquakes of increasing peak magnitudes they conclude that these seismic clusters and their slip transients reflect a gradual weakening of the central part of the seismic gap that was instrumental in initiating the final failure on 1 april 2014 northern chile was struck by a magnitude 8 1 earthquake following a protracted series of foreshocks the integrated plate boundary observatory chile monitored the entire sequence of events providing unprecedented resolution of the build up to the main event and its rupture evolution here we show that the iquique earthquake broke a central fraction of the so called northern chile seismic gap the last major segment of the south american plate boundary that had not ruptured in the past century1 2 since july 2013 three seismic clusters each lasting a few weeks hit this part of the plate boundary with earthquakes of increasing peak magnitudes starting with the second cluster geodetic observations show surface displacements that can be associated with slip on the plate interface these seismic clusters and their slip transients occupied a part of the plate interface that was transitional between a fully locked and a creeping portion leading up to this earthquake the b value of the foreshocks gradually decreased during the years before the earthquake reversing its trend a few days before the iquique earthquake the mainshock finally nucleated at the northern end of the foreshock area which skirted a locked patch and ruptured mainly downdip towards higher locking peak slip was attained immediately downdip of the foreshock region and at the margin of the locked patch we conclude that gradual weakening of the central part of the seismic gap accentuated by the foreshock activity in a zone of intermediate seismic coupling was instrumental in causing final failure distinguishing the iquique earthquake from most great earthquakes finally only one third of the gap was broken and the remaining locked segments now pose a significant increased seismic hazard with the potential to host an earthquake with a magnitude of 8 5

spatially dependent seismic anisotropy in the tonga subduction zone a possible contributor to the complexity of deep earthquakes abstract the deep part of the tonga subduction zone consists of two differently oriented slab segments the northern segment within latitudes 17 19 s and the southern segment within latitudes 19 5 27 s the orientation of the slab is strike dip 110 57 in its northern part and 210 46 in its southern part both segments are seismically active at depths from 500 to 700 km the mechanisms of deep focus earthquakes reported in the harvard moment tensor catalogue contain compensated linear vector dipole clvd components that behave differently in both segments the mean value of the clvd is 3 for the northern segment but 10 for the southern segment the mean absolute value of the clvd is 12 for the northern segment and 16 for the southern segment the complex behaviour of the clvd is explained by spatially dependent seismic anisotropy in the slab the inversion for anisotropy from the non double couple components of moment tensors points to orthorhombic anisotropy in the both slab segments the anisotropy seems to have a uniform strength of 5 7 for p waves and 9 12 for s waves and is oriented according to the orientation of each segment and the stress acting in it the spatial variation of velocities is roughly similar in both segments the retrieved anisotropy might have several possible origins it can be 1 intrinsic caused by preferentially aligned anisotropic minerals such as wadsleyite ringwoodite ilmenite or others 2 effective caused for example by intra slab layering or 3 partly apparent produced by systematic errors in the moment tensors due to neglecting 3d slab geometry and the slab mantle velocity contrast when calculating the green functions in the moment tensor inversion

origin of crustal anisotropy shear wave splitting studies in japan shear wave splitting manifested as leading shear wave polarization that is parallel alignment of leading shear wave particle motions from a variety of sources has been observed at a number of seismograph stations in japan detected on shear wave seismograms from crustal earthquakes over a wide range of source zones and source receiver azimuths the shear wave splitting can be attributed to crustal anisotropy this paper discusses the relation between leading shear wave polarization directions and tectonic features of japan to explain the observed shear wave splitting the author proposes that at least three phenomena should be taken into account stress induced microcracks primarily aligned in vertical or subvertical planes cracks or fractures in the vicinity of active faults having their orientation parallel to the fault planes and intrinsic rock anisotropy resulting from preferred orientation of minerals travel time differences between leading and slower split shear waves from crustal and upper mantle earthquakes analyzed for about one third of the stations suggest that the crustal anisotropy which causes the observed shear wave splitting may be limited to the upper 15 25 km this implies that the density of nonhorizontally aligned cracks or fractures below 15 25 km and into the upper mantle is muchmore smaller than that in the crust above 15 25 km less

upper mantle anisotropy beneath japan from shear wave splitting in this study we utilize data from 64 broadband seismic stations of the japanese f net network to investigate the threedimensional pattern of anisotropy in the subduction system beneath japan we have compiled a database of approximately 1900 high quality splitting measurements selected by visual inspection of over 25 000 records of s sks and skks phases at f net stations covering a wide range of incidence angles incoming polarization angles and backazimuths analysis of the variations of measured splitting parameters with these parameters allows us to consider complexities in structure such as multiple anisotropic layers dipping symmetry axes and small scale lateral variations in anisotropic properties here we focus on the presentation of the splitting measurements themselves a detailed interpretation in terms of tectonics and mantle flow is beyond the scope of this paper in the southern part of the f net array along the ryukyu arc we find that fast directions are consistently trench parallel with splitting times of 1 s or more moving northward along the array the measured splitting patterns become more complicated with significant variations in apparent splitting parameters that indicate complex anisotropic structure additionally measured fast directions vary significantly over short length scales and stations separated by less than 100 km often exhibit very different splitting behavior this increase in complexity of anisotropic structure coincides geographically with the complicated slab morphology of the subducting pacific plate at stations on hokkaido to the north and kyushu to the south we see some evidence that the fast direction of anisotropy may rotate from trench parallel close to the trench to subduction parallel further away from the trench which may correspond either to a change in stress conditions and or volatile content or to a change in flow regime 2005 elsevier b v all rights reserved

space geodetic estimation of the nazca south america euler vector abstract gps data from four sites in the nazca plate easter island galapagos robinson crusoe and san felix islands and from five sites in the stable core of the south american plate enabled us to estimate the euler vector of the nazca plate with respect to south america the observed velocities of easter island 6 6 cm yr at 102 3 galapagos 5 1 cm yr at 90 0 robinson crusoe 6 6 cm yr at 80 1 and san felix 6 0 cm yr at 82 1 are significantly slower than the global plate model nuvel 1a velocites for those four sites our estimated euler pole is located at 48 8 n 91 7 w with a rate of 0 59 m y the nuvel 1a and earlier space geodetic studies give rotation rates that are 20 faster

lagoon subsidence and tsunami on the west coast of new zealand abstract sediment core and trench data from a coastal lagoon on the west coast of the south island new zealand are used to investigate evidence for co seismic subsidence and associated tsunami inundation physical data are used to document a salt marsh soil buried 80 cm below the modern sediment surface that is locally covered by a gravelly sand bed the sediment record also contains geochemical and biological diatom and foram evidence for abrupt changes in salinity of lagoon waters that link to subsidence tsunami flooding and to the open versus closed state of the lagoon tidal entrance at the local scale these relationships allow for separation of tsunami evidence from other agents of environmental change in the lagoon we also propose a conceptual connection between these local changes and regional drivers of landscape development most notably major earthquakes and resultant pulses in sediment supply to the coast

enso tropical extratropical climate teleconnections and mechanisms for holocene debris flows along the hyperarid coast of western south america 17 24 s abstract el nino the warm phase of the enso cycle involves ocean climate anomalies in the tropical pacific ocean and in the extratropics which frequently result in heavy rainfall episodes along the equatorial and subtropical regions of western south america here we investigate meteorological mechanisms producing heavy rains floods and debris flows along the less known hyperarid coasts of southern peru and northern chile to evaluate the paleoclimate significance of holocene debris flow deposits our results reveal that heavy rainfall over the coast of southernmost peru occurs either during austral summer at the mature stage of el nino in connection with warmer sea surface temperatures and anomalous jet streams off northern chile or during the previous austral winter spring associated with equatorward shifted pacific south america psa atmospheric teleconnection patterns at antofagasta in northern chile such events occur almost exclusively in the latter season when deeper psa related anomaly poles extend their influence equatorwards beyond central chile during non el nino conditions short lived heavy rainfall episodes in southernmost peru can be associated with similar albeit weaker or less persistent circulation anomalies in addition to that a seasonally enhanced low level southerly flow provides orographic uplift rainfall favourable conditions by the andes at the 18 s coastal bend ultimately the trigger for rainfall events in all seasons and phases of the enso cycle was invariably connected with mid troposphere wave disturbances from mid latitudes the chronostratigraphy of debris flow deposits from both areas and its comparison with other paleoclimate records at the western side of the andes suggests that the enso related teleconnection patterns operated only during the second half of the holocene supporting an onset of modern el nino manifestations at 5300 5500 cal bp and increased frequency of major events during recent times we suggest that several debris flows dated between 12 900 and 8400 cal bp in southernmost peru previously interpreted as an indication of strong el nino events were associated with short and intense heavy rainfall episodes similar to those described here during the late winter spring season in non el nino conditions concomitant with stronger low level southerlies strengthened south eastern pacific subtropical anticyclone and intensified coastal upwelling

predecessor to new zealand s largest historic trans south pacific tsunami of 1868 ad multiproxy analyses of coastal sediments at cape pattisson chatham island identified evidence of two past tsunamis the most recent event was the 1868 ad tsunami for which there is a wealth of historical evidence we argue that the earlier event is most probably the 1604 ad south american tsunami the chronology for these two events was established using palynological data from the chatham island sediments and historical data from south america it is unlikely that the exposed coastline of cape pattisson preserves evidence of earlier events but given the historical and palaeotsunami records in south america it seems likely that many earlier trans south pacific tsunamis would have struck the chatham islands and possibly mainland new zealand this is the first time that sedimentological evidence for a prehistoric trans south pacific tsunami has been documented in new zealand albeit on an outlying island in the light of the findings on chatham island a reassessment of the new zealand palaeotsunami database indicates that there are several possible 1604 ad deposits on the east coast of both mainland islands further work needs to be done to determine whether these are indeed associated with the 1604 ad event this use of data from a country with a relatively long historical record adds immense value to understanding the timing of palaeotsunamis in countries with shorter records this technique offers an excellent opportunity to evaluate the magnitude and frequency of past trans south pacific tsunamis and to assess the risks posed to individual pacific islands

a search for source side mantle anisotropy shear wave splitting due to source side mantle anisotropy is estimated from broadband teleseismic s waves using a suite of 19 subduction zone events more than 50km depth and recorded at several rstn stations we assume that there are at most two anisotropic regions along the ray path one on the source side and one on the receiver side and that receiver side splitting is known from analysis of sks it is found that splitting is not detectable below the slab in most cases there are however two specific regions one beneath peru and one beneath kamchatka that indicate significant source side anisotropy based on two nearby intermediate focus events in each region splitting delay times are found to be 1 0 1 5s with the fast polarization direction perpendicular to the trench assuming 4 intrinsic anisotropy this would correspond to path lengths of 100 170 km below the slab both regions are characterized by abrupt changes in along strike slab properties a change in slab dip in the case of peru and a cessation of deep focus seismicity in the case of kamchatka we speculate that the anisotropy is caused by an associated local disturbance in asthenospheric flow that the shear wave splitting parameters of s and sks are consistent with each other in most cases suggests that large scale anisotropy in the lower mantle is very small probably no more than a fraction of a percent

five centuries of tsunamis and land level changes in the overlapping rupture area of the 1960 and 2010 chilean earthquakes a combination of geological and historical records from south central chile provides a means to address general questions about the stability of megathrust rupture patches and the range of variation expected among earthquakes and tsunamis along a particular stretch of a subduction zone the tirua river estuary 38 3 s records four large tsunamis and coseismic land level changes over the past 450 years within the overlapping rupture zones of the great subduction zone earthquakes of a d 1960 mw 9 5 and 2010 mw 8 8 sand layers 2 km up the tirua river represent the 2010 and 1960 tsunamis and two historical tsunamis most likely in a d 1751 and 1575 differing land level changes during these earthquakes likely denote differences in the spatial distribution of slip on the megathrust in both the strike and dip directions within the overlapping rupture zone with the uplift at tirua in 1751 and 2010 probably caused by slip extending farther landward and to greater depth than in 1575 and 1960 which showed subsidence or little change

episodic emergence in the past 3000 years at the akkeshi estuary hokkaido northern japan at the akkeshi estuary rapid emergence interrupted holocene submergence at least four times in the past 3000 years each emergence event produced an upward change from estuarine mud to freshwater peat while the estuarine mud abounds in brackish and marine diatoms freshwater taxa dominate the peat emergence events occurred from 1700 to 2300 1000 to 1300 and 500 to 700 cal yr b p an additional emergence event predated by several decades a volcanic ash that erupted in a d 1694 at least three of the events produced contacts abrupt enough to represent uplift during earthquakes such uplift may reconcile seemingly conflicting records of vertical crustal movement in eastern hokkaido this tectonically active area which is being subducted by the pacific plate at 8 cm yr contains marine terraces that imply 0 1 0 5 mm yr of net uplift in the late quaternary however these terraces adjoin tide gages that recorded 8 9 mm yr of steady submergence in the 20th century the terrace uplift need not conflict with the gaged submergence if the region is subject to occasional coseismic uplift as during the emergence events implied by holocene geology near akkeshi

anisotropic loci in the mantle beneath central peru abstract seismic anisotropy of the upper mantle beneath the central part of peru is examined by analyzing shear waves observed at broad band stations and a temporary array of short period stations shear wave splitting is seen on various shear phases such as direct s waves from local intermediate to deep earthquakes scs waves from regional deep earthquakes and sks waves from teleseismic earthquakes it is inferred that the shear wave anisotropy in the uppermost 100 km of the subcontinental mantle overlying the subducted nazca plate is 0 5 at most while the anisotropy in the subslab asthenosphere depth range of about 150 350 km is 2 or greater the fast shear wave polarization direction in this depth range as observed at two broad band stations is 30 40 different from the absolute motion of the nazca plate this does not fit simple two dimensional 2 d models of olivine alignment caused by slab induced mantle flow and implies either the existence of a complex flow pattern in the asthenosphere underneath the nazca plate or the presence of an unknown mechanism for the anisotropy formation the lower mantle beneath central peru is found to be effectively isotropic for nearly vertically propagated shear waves

midmantle deformation between the australian continent and the fiji tonga subduction zone 1 shear wave splitting measurements are performed at temporary stations deployed across the australian continent for direct s waves from events occurring in the neighboring subduction zones especially fiji tonga unlike core refracted shear waves direct s waves are not polarized at the core mantle boundary and are therefore subject to influences on the source side on the receiver side and along the ray path in between source side contamination due to the development of lattice preferred orientation of olivine can be minimized by considering deep events with an epicentral location below 410 km depth the olivine spinel phase transition depth anisotropic contributions from the transition zone or lower mantle can only be reliably inferred in the case of high delays that cannot be generated solely by the upper mantle structure underneath a station the analysis of a comprehensive data set for direct s waves from deep events leads to an average delay time of 0 9 s at stations deployed across the continent despite the limitations of such an arithmetic average the result highlights the lack of evidence for midmantle deformation between the fiji tonga subduction zone and the australian continent unlike previously suggested in studies dealing with the permanent seismological stations only a striking consistency between measurements performed across several stations belonging to an array in western australia suggests a very coherent lithospheric structure underneath the yilgarn craton

can dispersive pressure cause inverse grading in grain flows discussion the concept of dispersive pressure was originally proposed by bagnold 1954 who showed experimentally that sheared granular material develops a dispersive pressure that is proportional to the shear stress and the particle concentration legros 2002 presented a theoretical analysis suggesting that dispersive pressure cannot account for the inverse grading commonly observed in grain flows modified grain flows or traction carpets contrary to what has been accepted for decades by many sedimentologists he pointed out that if the dispersive pressure in a sheared granular mass increases and exceeds the applied normal stress or static pressure the net upward force acting upon the bed causes it to expand as has in fact been observed in experiments bed expansion immediately causes a decrease in particle concentration and consequently in dispersive pressure until the latter balances the static pressure and expansion stops if the dispersive pressure becomes less than the static pressure the net downward force acting upon the granular bed causes compaction thus increasing the particle concentration and dispersive pressure this is an important concept enhancing our understanding of an as yet poorly understood process however legros 2002 went further to state that the dispersive pressure must always equal the applied normal shear stress at every level emphasis mine through the shearing granular bed this implies that the whole sheared bed is in constant equilibrium which is probably not the case in this discussion a modified process is proposed that accounts for the bipartite traction carpet structure proposed by sohn 1997 traction carpets are moving layers of highly concentrated bedload material developed beneath and driven by an overlying turbulent flow dzulynski and sanders 1962 sohn 1997 on the basis of numerical analyses computer simulations field measurements and experimental studies bagnold 1955 1963 hanes and bowen 1985 wan

evidence of midmantle anisotropy from shear wave splitting and the influence of shear coupled p waves 1 until recently the midmantle region of the earth the transition zone and the uppermost lower mantle has been considered isotropic recent work by wookey et al 2002 presented evidence of anisotropy in the midmantle region near the tonga kermadec subduction zone inferred from shear wave splitting in teleseismic s phases at australian seismic stations this data set is revisited to examine the possibility of contamination by shear coupled p waves using reflectivity modeling we explore the effects of these phases on the measurement of shear wave splitting contamination of such measurements is demonstrated for short epicentral distances 30 wave field decomposition is a simple technique which can be used to separate these phases from the main s wave arrival the tonga australia data set is reprocessed after wave field decomposition shear wave splitting ranging between 0 7 and 6 2 s is observed a range comparable to that observed by wookey et al 2002 as before the polarization of the fast shear wave is observed to be predominantly horizontal however the magnitudes of splitting for several events at short epicentral distances are significantly reduced suggesting some influence of shear coupled p waves in the original analysis the results are compared with possible models of mantle anisotropy and the results can be best explained by significant anisotropy in the midmantle region the best candidate location for this anisotropy is in the uppermost lower mantle and scenarios involving the alignment of lower mantle or subducted materials by regional dynamic processes are suggested to account for this

shear wave polarization anisotropy in the upper mantle beneath honshu japan shear wave polarization anisotropy in the wedge portion of the upper mantle between a subducting plate and the earth s surface is investigated using three component seismograms of intermediate depth and deep earthquakes recorded at 14 local stations in honshu japan eighty nine high quality seismograms were selected from a period of 3 years the data used in this study are restricted such that incidence angles are smaller than the critical angle of 30 to the earth s surface in order to avoid phase shifts in the shear wave train to find directions of the maximum and minimum velocities in split shear waves where shear waves are resolved into two phases with the maximum time separation each set of the two horizontal component seismograms is rotated in the horizontal plane the split shear waves thus obtained are again recombined after the correction of anisotropy and the anisotropy corrected particle motion is compared with the focal mechanism for a cross check of the observed anisotropy directions of the maximum axes are plotted on azimuthincidence angle stereograms at each station the stereograms and the cross sections of seismic ray paths show that 1 the anisotropic material is distributed at intermediate location between earthquake sources and receiving stations and 2 the anisotropic region is separated into two parts one in the north of the present study area with the polarization of the maximum velocity shear wave trending 0 to 30 from the north north anisotropy and the other in the south with it trending 90 to 120 south anisotropy the maximum time delays between the two shear waves along a vertical seismic ray is about l s for both the anisotropic regions the horizontal extent of the anisotropic area in the north is 50 km at depths of 50 to 150 km perhaps prevalent in west honshu however the depth of anisotropic material is not well constrained because of insufficient coverage of seismic ray paths and angles if we assume the vertical extent of the anisotropic material to be 100 km the maximum velocity contrast would be 4 if we adopt a crack alignment model for the observed anisotropy cracks are inferred to be distributed vertically trending 0 to 30 in the north and 90 to 120 in the south if we assume an olivine alignment model olivine crystals are inferred to be aligned in the north with the a axis of the slip direction trending 0 to 30 and the slip plane normal to the b axis being vertical and in the south anisotropy with the axis trending 90 to 120 and the slip plane being horizontal

geophysical and mineralogical constraints on the post spinel transformation for the tonga slab abstract the depth of the post spinel transformation is investigated for the tonga slab by using data from short period seismic networks at western united states and japan for about 100 deep and intermediate depth earthquakes within a small 200 km by 200 km area near 20 s later phases in a time window 3 to 20 s after direct p waves are analyzed to search for s to p converted waves at the 660 km discontinuity which represents the post spinel transformation we find that immediately beneath the foci of the deepest earthquakes the discontinuity is depressed down to the depths of 685 5 km on average and that it dips towards wnw by 10 3 km within 70 km laterally we constrain the thermal structure near the s to p conversion points based on a plausible assumption that the deepest earthquakes occur around the coldest core of the tonga slab the distribution of the hypocenters relocated in this study as well as previously published tomographic images of the same region suggest that the tonga slab bends upward when approaching the 660 km discontinuity and transiently stagnates around the discontinuity with these observations as the constraints we numerically model the thermal structure of the tonga slab and estimate the temperature around the conversion points as 1200 100 c which is 300 100 k colder than the surrounding mantle as the average depression of the discontinuity down to 685 5 km corresponds to an pressure excess over the global average 660 km by 1 0 0 2 gpa the assumption of equilibrium post spinel transformation results in an estimate of the clapeyron slope c1 of 3 3 2 7 1 3 mpa k we also obtain an independent estimate of the clapeyron slope c2 of 2 0 1 0 mpa k based on the observation of the dip of the discontinuity and the computed temperature variation by about 200 k the discrepancy between c1 and c2 is marginally significant and can be diminished by considering that the slab materials at the conversion points are currently descending across the phase boundary fast enough and thus the depth of the post spinel transformation is controlled by nucleation kinetics as well as by the temperature

coseismic coastal uplift and coralline algae record in northern chile the 1995 antofagasta earthquake case coralline algae that may be predominant in the upper part of the infralittoral zone along rocky shorelines proved to be a useful indicator of rapid coastal uplift as these encrusting algae cannot survive desiccation even for short periods at low tide they can provide estimates of positive vertical motions like those which may accompany seismic events the desiccation of a fringe of the algal encrustment at the base of the intertidal area infralittoral fringe combined with effects of solar radiation rapidly kills the organisms this mortality results in a conspicuous alteration of the pigmentation from pink beige reddish to white after the july 30 1995 antofagasta earthquake mw 8 1 in northern chile such a white fringe appeared in some parts of the bay of antofagasta and surroundings the width of the dead algae fringe varied from 0 to more than 1 8 m the widest observed widths are related to local parameters exposition to wave splash geometric disposition that account for an amplification of the width of the dead algae fringe and must be identified thus a careful study of each locality led us to determine the extent of the coastal areas that had been uplifted and to reconstruct with a precision of the order of 2 cm the amount of the vertical deformation along the antofagasta bay and southern mejillones peninsula it was thus shown that the coastline bordering the town of antofagasta suffered practically no coseismic uplift while areas to the south and to the west of antofagasta bay proved to have been uplifted by as much as 25 and 40 cm respectively the maximum uplift 80 cm was seen at the southwestern tip of the peninsula of mejillones these precise reconstructions are of great help for the calibration of geodetic studies performed independently and for the modelling of the coseismic deformation at a regional scale

aeolian erosion and sand transport over the mejillones pampa in the coastal atacama desert of northern chile article i nfo the mejillones peninsula in the coastal atacama desert of northern chile is a region in which ocean atmosphere land interactions are particularly strong resulting in enhanced alongshore winds that erode the surface and transport sand particles to the sea because the aeolian particles in the laminated sediments at the bottom of mejillones bay record long term changes in the intensity of prevailing southerly winds it is fundamental to understand aeolian processes such as wind erosion and sand transport to improve paleoceanographic reconstructions the aim of the present study is to characterize the wind erosion process over the flat geomorphology of the northern portion of the mejillones peninsula the mejillones pampa including the influence of wind erosion on the initial particle size distribution and the associated fractionation processes of the mineralogical composition of moving particles through field measurements in addition we test the ability of an existing saltation model mb95 to reproduce the variability of the erosion process during the field experiment soil samples from 17 locations on this flat surface contain significant amounts of highly erodible particles with diameters in the 200 300 m and 100 150 m size ranges aeolian particles collected in bsne sand traps located at different heights near the surface exhibit a bimodal size distribution similar to that of the erodible fraction of the soils the abundance of the fine class increasing with height small stones that have a spatially variable distribution can locally reduce the intensity of wind erosion the mineralogical composition of moving particles is similar to that of the soils with quartz feldspar and calcite as the most important minerals followed by clay minerals gypsum and amphibole a value of u t is calculated for each soil particle size class subsequently the elementary contribution of each size class to the horizontal flux is calculated using white 1979 s equation and the total flux is finally obtained by integration the saltation model successfully reproduces the variability of the wind erosion process during the field experiment but over estimates the vertically integrated mass fluxes measured in situ by two orders of magnitude

preservation potential of tsunami deposits on arid siliciclastic coasts abstract numerous post tsunami surveys have been conducted in the last two decades especially since the 2004 indian ocean tsunami these studies have documented a variety of characteristic sedimentary and erosional features that can be ascribed to known events nevertheless the question arises whether these structures are just ephemeral or have a potential to be preserved in the geological record this review describes the changes that have affected muddy to sandy siliciclastic tsunami deposits in peru each of these was surveyed in the first months after the tsunami chimbote 1996 camana 2001 and pisco paracas 2007 here we describe the changes we observed during re surveys in 2007 and 2008 it has long been recognized that onshore tsunami deposits may suffer from surficial processes tectonic movements and anthropogenic alteration earthquake induced uplift or subsidence may subject a tsunami deposit to erosion or burial respectively quick burial in rapidly subsiding coastal areas may enhance preservation deposits of the last or most landward reaching wave may be preferentially preserved if they escape erosion by subsequent tsunami waves however inland areas are also vulnerable to subaerial reworking including by wind and by humans the peruvian examples reviewed here show that the preservation of arid coast tsunami deposits depends on interactions that are more complex that hitherto perceived these involve sediment type grain size depositional setting co seismic movement bioturbation winds and anthropogenic modification in one example all traces of the tsunami have been removed or reworked by flash floods and ocean waves in another example clasts on a coastal plain from tsunami backwash began to be rounded and abraded by eolian sands immediately after the event eolian processes also smoothed and filled tsunami scours by contrast muddy tsunami deposits in certain areas escaped erosion by wind probably because of their greater cohesion in still another example 0 5 m of co seismic uplift was not enough to prevent ocean waves from removing a tsunami sand sheet that had mantled a coastal marsh the buried record of tsunami deposits on modern coasts may therefore not fully represent the vulnerability of these regions to tsunamigenic hazards

identifying coseismic subsidence in tidal wetland stratigraphic sequences at the cascadia subduction zone of western north america tidal wetland stratigraphy reveals that great plate boundary earthquakes have caused hundreds of kilometers of coast to subside at the cascadia subduction zone however determining earthquake recurrence intervals and mapping the coastal extent of past great earthquake ruptures in this region are complicated by the effects of many sedimentologic hydrographic and oceanographic processes that occur on the coasts of tectonically passive as well as active continental margins tidal wetland stratigraphy at many cascadia estuaries differs little from that at similar sites on passive margin coasts where stratigraphic sequences form through nonseismic processes unrelated to coseismic land level changes methods developed through study of similar stratigraphic sequences in europe provide a framework for investigating the cascadia estuarine record five kinds of criteria must be evaluated when inferring regional coastal subsidence due to great plate boundary earthquakes the suddenness and amount of submergence the lateral extent of submerged tidal wetland soils the coincidence of submergence with tsunami deposits and the degree of synchroneity of submergence events at widely spaced sites evaluation of such criteria at the cascadia subduction zone indicates regional coastal subsidence during at least two great earthquakes evidence for a coseismic origin remains equivocal however for the many peat mud contacts in cascadia stratigraphic sequences that lack 1 contrasts in lithology or fossils indicative of more than half a meter of submergence 2 well studied tsunami deposits or 3 precise ages needed for regional correlation paleoecologic studies of fossil assemblages are particularly important in estimating the size of sudden sea level changes recorded by abrupt peat mud contacts and in helping to distinguish erosional and gradually formed contacts from coseismic contacts reconstruction of a history of great earthquakes for the cascadia subduction zone will require rigorous application of the above criteria and many detailed investigations

mid mantle seismic anisotropy beneath southwestern pacific subduction systems and implications for mid mantle deformation abstract observations of seismic anisotropy can offer relatively direct constraints on patterns of mantle deformation but most studies have focused on the upper mantle while much of the lower mantle is thought to be isotropic several recent studies have found evidence for anisotropy in the transition zone and uppermost lower mantle the mid mantle particularly in the vicinity of subducting slabs here we investigate anisotropy at mid mantle depths in the tonga kermadec sumatra new britain new hebrides and philippines subduction zones using the source side shear wave splitting technique we measure splitting of direct teleseismic s phases originating from deep events 300 km that have been corrected for the effect of upper mantle anisotropy beneath the seismic stations we find evidence for considerable anisotropy at mid mantle depths in all subduction systems studied with delay times averaging 1 0 1 5 s several measurements originating from depths greater than 600 km exhibit delay times greater than 1 s suggesting a significant contribution from anisotropy in the uppermost lower mantle we combine our results with those documented in previous studies into a quasi global set of source side shear wave splitting measurements that reflect mid mantle anisotropy we document significant variability in the dominant fast directions both within and among individual subduction systems suggesting different deformation geometries among different subduction systems as further constraints on the elasticity and deformation of mid mantle minerals become available our dataset can be used to constrain patterns of mid mantle flow associated with subduction

predicted glide systems and crystal preferred orientations of polycrystalline silicate mg perovskite at high pressure implications for the seismic anisotropy in the lower mantle abstract we use first first principle methods and the peierls nabarro model to evaluate the resistance to glide characterized by the peierls stress of glide systems for end member mgsio 3 perovskite at mantle pressures 010 100 is the easiest glide system in mg perovskite at all pressures peierls stresses increase systematically with pressure for all systems except 001 010 indicating the importance of lattice friction at lower mantle pressures the ratio of the maximum peierls stress for each system relative to the 010 100 value defines their critical resolved shear stress crss these crss are used in a visco plastic self consistent homogenization model to predict the evolution of crystal preferred orientations cpo during deformation of polycrystalline mg perovskite in axial compression 100 tends to align with the compression direction in agreement with in situ observations in axial compression experiments in simple shear 010 concentrates near the shear direction and 100 although more dispersed tends to align near the shear plane consistent with the dominant activity of the easier 010 100 system the calculated seismic anisotropy for a 100 mg perovskite aggregate using the cpo in simple shear and the elastic constants of mgsio 3 perovskite at lower mantle pressures and temperatures is weak 3 for p waves with and 2 for s waves and decreases with increasing temperature and pressure p waves show the fastest propagation parallel to the lineation and s waves fast polarization is in the foliation at 38 gpa and normal to the lineation at 88 gpa this weak anisotropy is consistent with global seismological observations of a nearly isotropic lower mantle there are however two regions where strain induced mg perovskite cpo could contribute to anisotropy a low temperature regions in the uppermost lower mantle where the predicted s wave polarization anisotropy may attain 1 6 with a fast polarization parallel to the foliation b in high high temperature domains in the d layer where mg perovskite may be the major stable phase leading to polarization of fast s waves normal to the lineation for propagation directions at high angle to the lineation and an apparent isotropy for all other propagation directions

paleoseismic inferences from a high resolution marine sedimentary record in northern chile 23 s abstract the active margin of northern chile is characterized by strong seismic events which induce gravity instability for sedimentary sequences located along the outer forearc of the andean range even though the narrow continental platform of this area limits the accumulation of marine sediments a detailed paleoceanographic reconstruction using high resolution sedimentological and geochronological techniques of a holocene sedimentary sequence in mejillones bay 23 s provides important tools to infer the occurrence of past great subduction earthquakes and or associated tsunamis from the analyses of short cores retrieved in this shallow marine basin we infer the occurrence of two strong seismic events during historical times the first one dated between the years 1409 and 1449 ad produced an angular unconformity and associated lenticular coarse grained deposits generated after local reworking of shallower material the second one dated between the years 1754 and 1789 ad caused slumping erosive processes and local reworking of material the analysis of seismic profile data acquired in this bay allowed the recognition of a major slump deposit within the upper sedimentary sequence tentatively dated as of middle holocene age this event might record the greatest earthquake and tsunami affecting the basin within the last few thousand years we interpret that destabilization of sediments occurs most probably in response to local reactivation of faults within the mejillones peninsula during strong earthquakes especially the mejillones fault

evidence from core reflected shear waves for anisotropy in the earth s mantle seismologists have begun to recognize that the upper mantle at depth is anisotropic and that seismological data are not fully explicable if anisotropy is ignored1 5 on entering an anisotropic zone a plane shear wave splits into two orthogonally polarized phases6 an effect observed by several researchers7 notably by ando et al 5 8 9 the near vertical scs wave an s wave reflected once at the core mantle boundary is one of the most suitable phases to study the phenomenon of shear wave birefringence because it is isolated from other phases and because its particle motion is nearly horizontal and thus free from s to p conversion the split scs shear waves travel with different velocities in the anisotropic zone and consequently there is a time delay between their arrival at stations my aim was to determine this time delay and the azimuth of polarization using the scs records of two horizontal components from the japanese islands for a deep shock beneath the sea of okhotsk from the total of 41 stations 34 show a polarization of the maximum velocity phase in the nnw sse direction with an average time advance of 0 8s from the minimum velocity phase the relevant anisotropic zone seems to be deep seated

seismological evidence for the existence of anisotropic zone in the metastable wedge inside the subducting izu bonin slab the mechanism of deep earthquakes has been a puzzle since their discovery almost 70 years ago experimental observations at high pressure have reported faulting caused by spinel filled anti cracks in metastable olivine and suggesting that the anticrack mechanism is responsible for deep earthquakes we compared the shear wave splitting of earthquakes from the upper and lower planes of the double seismic zone to detect anisotropy caused by the faultings inside the metastable wedge we detected the anisotropic zone inside the metastable wedge at the depth of about 340 390 km which corresponds to the depth range of a second peak on the histogram of earthquakes the observed polarization direction east west is almost parallel to the direction of subduction which can be explained by a view that the shear wave splitting is caused by the en echelon arrays of spinel filled anti cracks and anticrack associated faultings

high pressure elastic properties of major materials of earth s mantle from first principles the elasticity of materials is important for our understanding of processes ranging from brittle failure to flexure to the propagation of elastic waves seismologically revealed structure of the earth s mantle including the radial one dimensional profile lateral heterogeneity and anisotropy are determined largely by the elasticity of the materials that make up this region despite its importance to geophysics our knowledge of the elasticity of potentially relevant mineral phases at conditions typical of the earth s mantle is still limited measuring the elastic constants at elevated pressure temperature conditions in the laboratory remains a major challenge over the past several years another approach has been developed based on first principles quantum mechanical theory first principles calculations provide the ideal complement to the laboratory approach because they require no input from experiment that is there are no free parameters in the theory such calculations have true predictive power and can supply critical information including that which is difficult to measure experimentally a review of high pressure theoretical studies of major mantle phases shows a wide diversity of elastic behavior among important tetrahedrally and octahedrally coordinated mg and ca silicates and mg ca al and si oxides this is particularly apparent in the acoustic anisotropy which is essential for understanding the relationship between seismically observed anisotropy and mantle flow the acoustic anisotropy of the phases studied varies from zero to more than 50 and is found to depend on pressure strongly and in some cases nonmonotonically for example the anisotropy in mgo decreases with pressure up to 15 gpa before increasing upon further compression reaching 50 at a pressure of 130 gpa compression also has a strong effect on the elasticity through pressure induced phase transitions in several systems for example the transition from stishovite to cacl2 structure in silica is accompanied by a discontinuous change in the shear s wave velocity that is so large 60 that it may be observable seismologically unifying patterns emerge as well eulerian finite strain theory is found to provide a good description of the pressure dependence of the elastic constants for most phases this is in contrast to an evaluation of birch s law which shows that this systematic accounts only roughly for the effect of pressure composition and structure on the longitudinal p wave velocity the growing body of theoretical work now allows a detailed comparison with seismological observations the athermal elastic wave velocities of most important mantle phases are found to be higher than the seismic wave velocities of the mantle by amounts that are consistent with the anticipated effects of temperature and iron content on the p and s wave velocities of the phases studied an examination of future directions focuses on strategies for extending first principles studies to more challenging but geophysically relevant situations such as solid solutions high temperature conditions and mineral composites

modeling lower mantle anisotropy development in a subducting slab a model is presented that simulates anisotropy development in a subducting slab from the upper lower mantle boundary 661 km to the core mantle boundary 2891 km two phases are considered orthorhombic mgsio3 perovskite and cubic magnesiowuestite mg fe o single crystal elastic properties at mantle conditions are obtained from existing density functional theory calculations and quasiharmonic approximation it is assumed that deformation is accommodated by slip a polycrystal plasticity model predicts strong texture development for perovskite and weaker texture for magnesiowuestite when averaging single crystal elastic properties with the orientation distribution this results for both phases in weak p wave anisotropy and shear wave splitting in the upper part of the lower mantle but pronounced anisotropy near the core mantle boundary up to 4 for vp and 7 for vs the anisotropy pattern is complex and asymmetric and local heterogeneity is expected these predictions are consistent with seismic observations

metamorphism and phase relations in carbonate rocks from the nevado filabride complex cordilleras beticas spain application of the ttn rt cal qtz gr buffer phase relations and metamorphic conditions have been studied in metacarbonate rocks from the nevado filabride complex cordilleras beticas through forward modeling in many rock samples the assemblage titanite rutile calcite quartz graphite buffered the composition of the c o h fluid present during metamorphism over a wide range of p t conditions fluid compositions computed for this buffer are essentially binary h2o co2 mixtures this buffer also constrains the chemical potentials of tio2 cao and sio2 consequently it is possible to make a thermodynamic projection through these components to predict the stable phase relations consistent with the buffer using this method phase relations have been analyzed in a rock containing the buffer assemblage and paragonite albite phengite epidote and chlorite the equilibrium p t conditions for this assemblage are constrained by minimization of the differences between predicted and observed mineral compositions to be 560 15 c and 9 5 1 kbar conditions obtained compare well with those estimated from other studies in different lithologic units the inferred metamorphic fluid composition is h2o rich

deformation and mantle flow beneath the sangihe subduction zone from seismic anisotropy abstract subduction of oceanic lithosphere is the most direct feedback between the earth s surface and deep interior however the detail of its interaction with the broader convecting mantle is still unclear mantle flow around subduction zones can be constrained using seismic anisotropy but despite many such studies a simple global picture is lacking the sangihe subduction zone where the molucca sea microplate is subducting westward beneath the eurasian plate is part of the tectonically complex sulawesi philippine region and an ideal natural laboratory to study complex subduction processes we investigate the anisotropic structure of the sangihe subduction zone with shear wave splitting measurements of local s and sks phases at two stations mni in sulawesi dav in the philippines as well as downgoing s phases at five stations at teleseismic distances combining different phases allows a better vertical resolution of anisotropic fabrics than is possible with a single phase the broad depth distribution of local events 60 630 km allows us to observe a change in splitting behaviour at 380 km depth above fast directions are trench parallel and delay times t are 0 34 0 53 s with no increase with depth we suggest this anisotropy is caused by aligned cracks possibly melt filled beneath the volcanic arc and fossil anisotropy in the overriding plate below 380 km is predominantly trench normal and t are slightly higher 0 53 0 65 s as no correlation is observed with inferred distance travelled inside the slab we attribute this anisotropy to shear layers atop the slab which are coherent from 200 to 400 km depth and perhaps extend into the transition zone sks and source side measurements show larger t 1 53 and 1 33 s respectively and trench parallel since these phases predominantly sample sub slab mantle we consider along strike lateral flow associated with the double sided subduction of the molucca sea microplate to be the most likely explanation we thus infer three dominant regions of anisotropy at the sangihe subduction zone one within the overriding lithosphere one along the slab wedge interface and one below the subducting molucca sea slab the mantle wedge above 200 km depth and the slab itself do not seem to contribute notably to the measured anisotropy this study demonstrates the insight seismic anisotropy can provide into mantle dynamics even in tectonically complex subduction systems

seismic anisotropy in the mantle transition zone beneath fiji tonga 1 we demonstrate a rare unequivocal case of anisotropy in the transition zone tz evident from many horizontal polarized shear waves sh that arrive up to 3 s earlier than vertical polarized shear waves sv the anisotropic region correlates with deep earthquakes away from the active subduction zone and known boundaries of lateral heterogeneities in compression and shear wave speeds we interpret the anisotropy as strong fabric associated with a large petrologic anomaly in the core of remnant lithosphere which is buoyant and stagnates in the tz fast subduction of cold slab actually favors such a configuration so slab penetration into the lower mantle does not uniformly occur

heterogeneous seismic anisotropy in the transition zone and uppermost lower mantle evidence from south america izu bonin and japan summary measurements of seismic anisotropy are commonly used to constrain deformation in the upper mantle observations of anisotropy at mid mantle depths are however relatively sparse in this study we probe the anisotropic structure of the mid mantle transition zone and uppermost lower mantle beneath the japan izu bonin and south america subduction systems we present source side shear wave splitting measurements for direct teleseismic s phases from earthquakes deeper than 300km that have been corrected for the effects of upper mantle anisotropy beneath the receiver in each region we observe consistent splitting with delay times as large as 1 s indicating the presence of anisotropy at mid mantle depths clear splitting of phases originating from depths as great as 600km argues for a contribution from anisotropy in the uppermost lower mantle as well as the transition zone beneath japan fast splitting directions are perpendicular or oblique to the slab strike and do not appear to depend on the propagation direction of the waves beneath south america and izu bonin splitting directions vary from trench parallel to trench perpendicular and have an azimuthal dependence indicating lateral heterogeneity our results provide evidence for the presence of laterally variable anisotropy and are indicative of variable deformation and dynamics at mid mantle depths in the vicinity of subducting slabs

geo archaeological records of large holocene tsunamis along the hyperarid coastal atacama desert in the major northern chile seismic gap abstract the coastal atacama desert is exposed to strong earthquakes and giant tsunamis associated with the subduction of the nazca plate beneath the south american plate nevertheless historical and geological records of tsunamis and paleotsunamis in this region are scarce taltal 25 4 s is located at the southern edge of the hyperarid atacama desert within a major historical 1000 km long megathrust seismic gap in northern chile where the most recent large tsunamigenic earthquakes occurred in 1877 ce and 1922 ce rupturing its northern and southern segments respectively by multiproxy geological and archaeological analyses from pits and trenches we report distinctive strata of reworked archaeological material as well as sedimentary layers that we interpret as being produced by tsunami run up and or backwash deposition we identified two large holocene paleotsunamis dated close to 4000 cal yrs bp and younger than 863 199 ce 1087 cal years bp by comparing the run ups of the last historical tsunamis with our minimum run up estimates from the geo archaeological record we conclude that the impact of these holocene paleotsunamis was larger than any known historical event suggesting the need to re evaluate local regional and pacific basin scale tsunami hazard assessments

mantle anisotropy beneath northwest pacific subduction zones to assess the location strength and orientation of seismic anisotropy in the southern kuril japan and izu bonin subduction zones we analyzed shear wave splitting in local s phases and teleseismic sks phases fast directions from these phases are roughly parallel to the direction of absolute pacific plate motion wnw in izu bonin roughly parallel to the strike of the trench nne in central honshu and roughly n in the southern kuril back arc in the vicinity of sakhalin island assuming that the orientation and strength of anisotropy does not vary with depth modeling of splitting times from local s and teleseismic phases recorded at sakhalin island requires that the maximum depth of anisotropy lies between 480 km and 950 km in contrast splitting times for local s phases from events in izu bonin rule out anisotropy in the transition zone all the data are consistent with a model in which the lower transition zone 520 660 km and lower mantle are largely isotropic and in which anisotropy occurs intermittently in the upper transition zone 410 520 km possibly due to preferred orientation of spinel assuming that splitting in the upper mantle is produced by preferred orientation of olivine the observed fast directions indicate that the geometry of back arc strain varies systematically between subduction zones the relationship of fast directions and plate motions suggests that the subducting slab exerts significant control on back arc flow but that flow correlated with upper plate deformation must also exist

subducted slabs beneath the eastern indonesia tonga region insights from tomography tomographic images of mantle structure beneath the region north and northeast of australia show a number of anomalously fast regions these are interpreted using a recent plate tectonic reconstruction in terms of current and former subduction systems several strong anomalies are related to current subduction the inferred slab lengths and positions are consistent with neogene subduction beneath the new britain and halmahera arcs and at the tonga and the new hebrides trenches where there has been rapid rollback of subduction hinges since about 10 ma there are several deeper flat lying anomalies which are not related to present subduction and we interpret them as former subduction zones overridden by australia since 25ma beneath the bird s head and arafura sea is an anomaly interpreted to be due to north dipping subduction beneath the philippines halmahera arc between 45and 25ma a very large anomaly extending from the papuan peninsula to the new hebrides and from the solomon islands to the east australian margin is interpreted to be the remnant of south dipping subduction beneath the melanesian arc between 45and 25ma this interpretation implies that a flat lying slab can survive for many tens of millions of years at the bottom of the upper mantle in the lower mantle there is a huge anomaly beneath the gulf of carpentaria and east papua new guinea this is located above the position where the tectonic model interprets a change in polarity of subduction from north dipping to south dipping between 45and 25ma we suggest this deep anomaly may be a slab subducted beneath eastern australian during the cretaceous or subducted north of australia during the cenozoic before 45ma the tomography also supports the tectonic interpretation which suggests little neogene subduction beneath western new guinea since no slab is imaged south of the new guinea trench however one subduction zone in the tectonic model and many others that associated with the trobriand trough east of papua new guinea and the miocene maramuni arc is not seen in the tomographic images and may require reconsideration of currently accepted tectonic interpretations 4 2002 elsevier science b v all rights reserved

inferences on flow at the base of earth s mantle based on seismic anisotropy we applied global waveform tomography to model radial anisotropy in the whole mantle we found that in the last few hundred kilometers near the core mantle boundary horizontally polarized s wave velocities vsh are on average faster by 1 than vertically polarized s wave velocities vsv suggesting a large scale predominance of horizontal shear this confirms that the d region at the base of the mantle is also a mechanical boundary layer for mantle convection a notable exception to this average signature can be found at the base of the two broad low velocity regions under the pacific ocean and under africa often referred to as superplumes where the anisotropic pattern indicates the onset of vertical flow

flow speed estimated by inverse modeling of sandy tsunami deposits results from the 11 march 2011 tsunami on the coastal plain near the sendai airport honshu japan abstract tsunami deposits contain information about the flow that created them which can be interpreted to estimate tsunami magnitude sandy deposits near sendai airport are modeled using an inverse sediment transport model to explore the spatial and temporal variation of tsunami flow speed in the 11 march 2011 tohoku oki tsunami the 2011 deposits contain grain size signatures of both sediment transport convergences and sediment settling out of suspension sediment transport convergences form massive or inversely graded intervals sediment falling out of suspension forms a specific type of normal grading termed suspension grading the jaffe and gelfenbaum 2007 inverse sediment transport model which relates the thickness and bulk grain size of suspension graded intervals to tsunami flow speed was applied to 24 suspension graded intervals ranging in thickness from 2 to 4 cm at 7 trenches located from about 250 to 1350 m inland from the shoreline modeled tsunami flow speeds range from 2 2 to 9 0 m s and were strongly dependent on the choice of manning s n roughness parameterization flow speeds were highest from about 75 300 m landward of the forested sand dunes where the tsunami encountered lower roughness in a low lying area as it traveled downslope and decreased by 16 as the tsunami moved inland over the subsequent 596 m as many as 5 suspension graded intervals interpreted as forming during the onshore flow of up to 5 waves were identified at each location with a tendency for an inland decrease in the number of suspension graded intervals suggesting fewer waves inland tsunami flows tended to be fastest in the lower two intervals earlier waves and slowest in the uppermost interval last wave of the deposits modeled reconstructions of the suspension graded intervals at a vertical resolution of 1 cm reproduced observed upward fining of the distributions reasonably well supporting the use of the inverse model estimates of the time required to form 99 of the thickness of the suspension graded intervals ranged 2 to 5 min allowing that sediment falling from suspension could have formed these portions of the deposits in the time between waves application of the inverse model to determine paleotsunami flow speeds from deposits although now possible is complicated by uncertainty in roughness as inverse approaches to estimating roughness and tsunami flow speed improve the magnitude of paleotsunamis will be better understood and the ability to assess tsunami hazard from paleotsunami deposits will improve

seismic anisotropy and mantle flow below subducting slabs abstract subduction is integral to mantle convection and plate tectonics yet the role of the subslab mantle in this process is poorly understood some propose that decoupling from the slab permits widespread trench parallel flow in the subslab mantle although the geodynamical feasibility of this has been questioned here we use the source side shear wave splitting technique to probe anisotropy beneath subducting slabs enabling us to test petrofabric models and constrain the geometry of mantle fow our global dataset contains 6369 high quality measurements spanning 40 000 km of subduction zone trenches over the complete range of available source depths 4 to 687 km and a large range of angles in the slab reference frame we find that anisotropy in the subslab mantle is well characterised by tilted transverse isotropy with a slow symmetry axis pointing normal to the plane of the slab this appears incompatible with purely trench parallel flow models on the other hand it is compatible with the idea that the asthenosphere is tilted and entrained during subduction trench parallel measurements are most commonly associated with shallow events source depth 50 km suggesting a separate region of anisotropy in the lithospheric slab this may correspond to the shape preferred orientation of cracks fractures and faults opened by slab bending meanwhile the deepest events probe the upper lower mantle where splitting is found to be consistent with deformed bridgmanite

development of finite strain in the convecting lower mantle and its implications for seismic anisotropy 1 seismological observations have revealed patches of seismic anisotropy in regions related to mantle upwelling and paleosubduction within an otherwise isotropic lower mantle a combination of numerical modeling and mineral physics is used to constrain the source of anisotropy in these regions in an effort to better understand lower mantle dynamics and mineral physics specifically it is investigated whether lattice preferred orientation lpo can explain the anisotropy observed in regions of paleosubduction since lpo is caused by dislocation creep and is destroyed by diffusion creep we can develop deformation mechanism maps to determine which regions allow for the development of a mineral fabric strain is then calculated in these regions and is related to mineral physics experiments combined with high pressure elastic constants of lower mantle minerals in order to assess the predicted seismic anisotropy uncertainties in rheological parameters such as the transition stress between dislocation creep and diffusion creep necessitate a full evaluation of the parameter range the effect of variations in transition stress activations parameters and strength of slabs on fabric development is investigated it is shown that lpo is a likely candidate for the cause of lowermost mantle anisotropy in regions of paleosubduction

systematic variation in anisotropy beneath the mantle wedge in the java sumatra subduction system from shear wave splitting the tectonic context of south east asia is dominated by subduction one such major convergent boundary is the java sunda trench where the australian indian plates are being subducted beneath the eurasian plate we measure shear wave splitting in local and teleseismic data from 12 broadband stations across sumatra and java to study the anisotropic characteristics of this subduction system which can provide important constraints on dynamical processes involved splitting in s waves from local earthquakes between 75 and 300 km deep show roughly trench parallel fast directions and with time lags 0 1 1 3 s 92 0 6 s splitting from deeper local events and sks however shows larger time lags 0 8 2 0 s and significant variation in fast direction in order to infer patterns of deformation in the slab we apply a hybrid modelling scheme we raytrace through an isotropic subduction zone velocity model obtaining event to station raypaths in the upper mantle we then apply appropriately rotated olivine elastic constants to various parts of the subduction zone and predict the shear wave splitting accrued along the raypath finally we perform grid searches for orientation of deformation and attempt to minimise the misfit between predicted and observed shear wave splitting splitting from the shallow local events is best explained by anisotropy confined to a 40 km over riding plate with horizontal trench parallel deformation however in order to explain the larger lag times from sks and deeper events we must consider an additional region of seismic anisotropy in or around the slab the slab geometry in the model is constrained by seismicity and regional tomography models and many sks raypaths travel large distances within the slab models placing anisotropy in the slab produce smaller misfits than those with anisotropy outside for most stations there is a strong indication that inferred flow directions are different for sub sumatran stations than for sub javanese with 60 change over 375 km the former appear aligned with the subduction plate motion whereas the latter are closer to perpendicular parallel to the trench direction there are significant differences between the slab being subducted beneath sumatra and that beneath java age of seafloor maximum depth of seismicity relative strength of the bulk sound and shear wave velocity anomaly and location of volcanic front all vary along the trench we speculate therefore that the anisotropy may be a fossilised signature rather than due to contemporary dynamics

seismic anisotropy of the pacific slab and mantle wedge beneath the japanese islands 1 the mantle beneath the japanese islands is complex because of subduction of the pacific and philippine sea plates and the deformation associated with it detection of seismic anisotropy should be useful for understanding the processes occurring in such mantle here we resolve seismic anisotropy of the mantle wedge from that of the underlying subducted pacific slab using a large number of measurements of shear wave splitting for a family of core reflected shear phases scs sscs scs2 and sscs2 the anisotropy of the mantle wedge changes sharply across the volcanic front on the pacific side of the volcanic front a vertically propagating shear wave is polarized with the fast direction approximately parallel to the trench whereas on the back arc side it is polarized with the fast direction approximately parallel to the plate convergence direction the pacific slab is uniformly anisotropic with the nnw fast direction consistent with the paleospreading direction of the northwestern pacific seafloor the preferential alignment of anisotropic crystals frozen in the plate at the time of its formation appears to be preserved down to depths beyond 400 km within the slab

in situ observation of texture development in olivine ringwoodite magnesiowustite and silicate perovskite at high pressure magnesium silicates are the dominant minerals in the earth s mantle their preferred orientation is important for understanding the rheology and seismic anisotropy in the deep earth here we report results of radial synchrotron diffraction diamond anvil cell dac experiments on san carlos olivine axially compressed to 50 gpa experiments were performed at room temperature except for brief laser heating to induce phase transformations high stresses and development of preferred orientation were observed in diffraction images quantitative texture information was obtained by analyzing the images with the rietveld method with increasing pressure between 9 and 43 gpa olivine develops a texture with 001 axes perpendicular to the compression direction that is compatible with hk0 001 pencil glide ringwoodite between 20 and 50 gpa develops weak preferred orientation with 011 lattice planes perpendicular to the compression direction after the phase transformation perovskite and magnesiowqstite display transformation textures that are then modified by continuing deformation magnesiowqstite has a weak h111i maximum parallel to the compression direction that changes towards h001i with increasing deformation perovskite transforming from olivine has a pronounced 100 transformation texture and with increasing deformation a 012 maximum develops the transformation texture is probably produced by mechanical 110 twinning and nucleation in orientations that minimize elastic strain energy the deformation texture of perovskite is due to slip d 2004 elsevier b v all rights reserved

seismic anisotropy beneath the continents probing the depths of geology seismic anisotropy beneath continents is analyzed from shear wave splitting recorded at more than 300 continental seismic stations anisotropy is found to be a ubiquitous property that is due to mantle deformation from past and present orogenic activity the observed coherence with crustal deformation implies that the mantle plays a major if not dominant role in orogenies no evidence is found for a continental asthenospheric decoupling zone suggesting that continents are coupled to general mantle circulation

land level changes produced by the mw 8 8 2010 chilean earthquake we observed vertically displaced coastal and river markers after the 27 february 2010 chilean earthquake moment magnitude mw 8 8 land level changes range between 2 5 and 1 meters evident along an approximately 500 kilometers long segment identified here as the maximum length of coseismic rupture a hinge line located 120 kilometers from the trench separates uplifted areas to the west from subsided regions a simple elastic dislocation model fits these observations well model parameters give a similar seismic moment to seismological estimates and suggest that most of the plate convergence since the 1835 great earthquake was elastically stored and then released during this event

sedimentary deposits from the 17 july 2006 western java tsunami indonesia use of grain size analyses to assess tsunami flow depth speed and traction carpet characteristics the 2006 western java tsunami deposited a discontinuous sheet of sand up to 20 cm thick flooded coastal southern java to a depth of at least 8 m and inundated up to 1 km inland in most places the primarily heavy mineral sand sheet is normally graded and in some it contains complex internal stratigraphy structures within the sand sheet probably record the passage of up to two individual waves a point noted in eyewitness accounts we studied the 2006 tsunami deposits in detail along a flow parallel transect about 750 m long 15 km east of cilacap the tsunami deposit first becomes discernable from the underlying sediment 70 m from the shoreline from 75 to 300 m inland the deposit has been laid down in rice paddies and maintains a thickness of 10 20 cm landward of 300 m the deposit thins dramatically reaching 1 mm by 450 m inland from 450 m to the edge of deposition around 700 m inland the deposit remains 1 mm thick deposition generally attended inundation along the transect the tsunami deposited sand to within about 40 m of the inundation limit the thicker part of the deposit contains primarily sand indistinguishable from that found on the beach 3 weeks after the event but after about 450 m and roughly coinciding with the decrease in thickness the tsunami sediment shifts to become more like the underlying paddy soil than the beach sand grain sizes within the deposit tend to fine upward and landward although overall upward fining takes place in two discrete pulses with an initial section of inverse grading followed by a section of normal grading the two inversely graded sections are also density graded with denser grains at the base and less dense grains at the top the two normally graded sections show no trends in density the inversely graded sections show high density sediment to the base and become less dense upward and represents traction carpet flows at the base of the tsunami these are suggestive of high shear rates in the flow because of the grain sorting in the traction carpet the landward fining trends usually seen in tsunami deposits are masked although lateral changes of mean sediment grain size along the transect do show overall landward fining with more variation as the deposit tapers off the deposit is also thicker in the more seaward portions than would be produced by tsunamis lacking traction carpets

holocene coastal evolution and evidence for paleotsunami from a tectonically stable region tasmania australia stratigraphic investigations of three coastal waterbodies in southeastern tasmania reveal major paleoenvironmental phases related to sea level change and anomalous deposits consistent with tsunami

marine radiocarbon reservoir effect along the northern chile southern peru coast 14 24 s throughout the holocene abstract through an extensive sampling and dating of pairs of associated shells and charcoal fragments combined with reanalysis of all the available previous data we reconstruct the evolution throughout the holocene of the regional marine radiocarbon reservoir effect r values along the northern chile southern peru area 14 24 s after elimination of the cases in which the terrestrial component yielded older ages than the marine shells to which they were associated the study is based upon data from 47 pairs of associated marine and terrestrial material our results suggest major changes in both the magnitude and variability range of r during the whole holocene period 1 between 10 400 and 6840 cal yr bp high values 511 278 yr probably result from a strengthened se pacific subtropical anticyclone and shoaling of equatorial subsurface waters during intensified upwelling events 2 between 5180 and 1160 cal yr bp lower values 226 98 yr may reflect a major influence of subtropical water and diminished coastal upwelling processes 3 during the last thousand years high values between 355 105 and 253 207 yr indicate an increased influence of 14 c depleted water masses and of enso for the early twentieth century a r value of 253 207 yr was calculated

high temperature anomalies oceanward of subducting slabs at the 410 km discontinuity abstract our p wave whole mantle tomography revealed a low velocity region oceanward of the northern honshu slab of the pacific plate at depths around the 410 km seismic discontinuity resolution tests and scrutiny of the traveltime residuals for the ray paths passing through the low velocity region indicate that this anomaly is a resolvable feature and not an artifact due to the strong slab anomalies the existence of the slow anomalies is also supported by the analysis of the p wave records from the j array a large aperture seismic array in japan for a bonin earthquake the p arrivals to northern honshu at epicentral distances of 13 20 are strongly triplicated because of the 410 km discontinuity the later arrivals along the retrograde branch where ray paths pass through the low velocity region are anomalously slow comparison of the observed and synthetic waveforms indicates not only slow anomalies but also depression of the 410 km discontinuity this depression represents the direct evidence for the low velocity zone of primarily thermal origin an excess temperature of 200 k and the associated fractional melt of less than 1 can explain both the results of the tomographic and waveform analyses