mechanical interactions between rigid particles in a deforming ductile matrix analogue experiments in simple shear flow abstract the mechanical interaction between two or more particles is investigated in newtonian simple shear flow the experimental models allow observation of both the particle rotation and the deformation pattern around the particles the finite and instantaneous strain patterns around rigid particles are strongly heterogeneous and asymmetric with high finite strain zones aligned to the direction of maximum finite stretch these correspond to local flow with low vorticity number heterogeneous strain patterns around rigid particles spread over a distance of 1 2 times the particle length and this distance increases with increasing bulk strain where rigid particles are more concentrated these patterns coalesce and the overall pattern is then strongly controlled by the particles and cannot be simply related to the external boundary conditions in rocks the characteristic asymmetric strain pattern around rigid isolated particles is a reliable shear criterion which becomes unreliable with high concentrations of rigid particles particle rotation is significantly disturbed when the distance between adjacent particles of equal size is shorter than their length that is only in very concentrated suspensions of rigid particles in a composite shape fabric the development of the sub fabric corresponding to the smaller minerals will be more disturbed

the motion of rigid ellipsoidal particles in slow flows abstract preferred orientations of fabric elements in tectonites are usually interpreted with reference to two continuum models namely those of march 1932 and jeffrey 1922 it is argued that the first of these is usually inappropriate if the fabric elements are rigid inhomogeneities embedded in a deformable matrix jeffrey s model is more applicable but until recently its use has been limited to problems involving axisymmetric particles and simple flow geometries in this paper jeffrey s equations have been solved numerically in order to investigate the behaviour of more general systems the motions of two particle shapes one a prolate spheroid the other a triaxial ellipsoid are considered in parallel for four specified flow geometries which involve pure or simple shear and combinations of both any departures from particle axisymmetry or from simple flow geometries have a significant effect on particle behaviour compared with that predicted by spheroid simple flow solutions

age and significance of earthquake induced liquefaction near vancouver british columbia canada in late 1994 sand dykes large sand blows and deformed strata were exposed in the walls of an excavation at annacis island on the fraser river delta near vancouver british columbia the features record liquefaction during a large earthquake about 1700 years ago this was perhaps the largest earthquake to affect the vancouver area in the last 3500 years similar less well dated features have been reported from several other sites on the fraser delta and may be products of the same earthquake three radiocarbon ages that closely delimit the time of liquefaction on annacis island are similar to the most precise radiocarbon ages on coseismically subsided marsh soils at estuaries in southern washington and oregon both the liquefaction and the subsidence may have been produced by a single great plate boundary earthquake at the cascadia subduction zone alternatively liquefaction at annacis island may have been caused by a large crustal or subcrustal earthquake of about the same age as a plate boundary earthquake farther west the data from annacis island and other sites on the fraser delta suggest that earthquakes capable of producing extensive liquefaction in this area are rare events further liquefaction analysis using historical seismicity suggests that current assessment procedures may overestimate liquefaction risk

2 d rotation behavior of a rigid ellipse in confined viscous simple shear numerical experiments using fem abstract the rotation behavior of rigid elliptical inclusions adherent to the viscous matrix in simple shear flow is investigated using a 2 d finite element numerical model several simulations were performed using different ratios s between shear zone width and inclusion s least principal axis a computational strategy was devised to calculate pressure and viscous forces exerted on the inclusion and deduce its angular velocity for large s values results agree remarkably well with theoretical predictions while for small s values results deviate significantly from theory but are in agreement with previous analogue experiments the numerical model provided detailed and coherent information about the physical parameters involved in the process e g pressure strain rate and vorticity distributions within the model

effect of finite strain on clast based vorticity gauges abstract clast based vorticity gauges utilize orientations of grains assumed to have behaved as isolated rigid particles suspended in a flowing viscous matrix a fundamental assumption behind use of the method is that sufficient strain has accumulated for high aspect ratio grains to rotate into positions approaching their stable sink orientation and that clasts below a critical aspect ratio may be observed in any orientation relative to the flow plane we constructed a numerical model to explore the effect of variable finite strain on development of the orientation distribution of a large population of rigid clasts embedded in a viscous medium for end member pure and simple shear and for several distinct general shear flows our model predicts the technique will tend to produce vorticity overestimates for lower vorticity flows for a wide range of finite strain the model also indicates that clast populations in moderate to high vortical flows tend to develop shape preferred orientations that closely resemble those expected for flows of lower vorticity we conclude that clast based methods are not effective for extracting detailed kinematic information from a mylonite deformed in a flow with arbitrary boundary conditions in fact it appears that most general shear flows continued long enough to develop moderate high finite strains will tend to produce a clast orientation distribution that will yield a visual estimate of the critical aspect ratio that suggests approximately equal contributions of pure and simple shear components

strain memory of 2d and 3d rigid inclusion populations in viscous flows what is clast spo telling us abstract we model the development of shape preferred orientation spo of a large population of two and three dimensional 2d and 3d rigid clasts suspended in a linear viscous matrix deformed by superposed steady and continuously non steady plane strain flows to investigate the sensitivity of clasts to changing boundary conditions during a single or superposed deformation events resultant clast spos are compared to one developed by an identical initial population that experienced a steady flow history of constant kinematic vorticity and reached an identical finite strain state allowing examination of spo sensitivity to deformation path rotation paths of individual triaxial inclusions are complex even for steady plane strain flow histories it has been suggested that the 3d nature of the system renders predictions based on 2d models inadequate for applied clast based kinematic vorticity gauges we demonstrate that for a large population of clasts simplification to a 2d model does provide a good approximation to the spo predicted by full 3d analysis for steady and non steady plane strain deformation paths predictions of shape fabric development from 2d models are not only qualitatively similar to the more complex 3d analysis but they display the same limitations of techniques based on clast spo commonly used as a quantitative kinematic vorticity gauge our model results from steady superposed and non steady flow histories with a significant pure shearing component at a wide range of finite strain resemble predictions for an identical initial population that experienced a single steady simple shearing deformation we conclude that individual 2d and 3d clasts respond instantaneously to changes in boundary conditions however in aggregate the spo of a population of rigid inclusions does not reflect the late stage kinematics of deformation nor is it an indicator of the unique mean kinematic vorticity experienced by a deformed rock volume

a sand sheet deposited by the 1964 alaska tsunami at port alberni british columbia the stratigraphic record of 137cs activity in a tidal marsh at port alberni british columbia suggests that a widespread sand sheet just below the marsh surface was deposited by the tsunami from the great alaska earthquake of 1964 we propose by analogy that similar deeper sand sheets at port alberni also may have been deposited by earthquake induced tsunamis

post lgm grounding line positions of the bindschadler paleo ice stream in the ross sea embayment antarctica the west antarctic ice sheet wais retreated more than 1000 km since last grounding at the ross sea outer continental shelf here we show an interpretation of former grounding line positions from a new large area multibeam survey and a regional grid of chirp cross section data from the whales deep basin in eastern ross sea the basin is a paleo glacial trough that was occupied by the bindschadler ice stream when grounded ice advanced to the shelf edge during the last glacial maximum lgm these new geophysical data provide unambiguous evidence that the wais occupied at least seven grounding line positions within 60 km of the shelf edge four of seven grounding zone wedges gzws are partly exposed over large areas of the trough the overlapping stratal arrangement created a large volume compound gzw cgzw some of the grounding events involved local re advance of the grounding line subsequent to these seven outer continental shelf groundings the ice sheet retreated more than 200 km toward roosevelt island on the middle continental shelf the major retreat across the middle continental shelf is recorded by small scale moraine ridges that mantle the top of gzw7 and these are suggestive of relatively continuous grounding line recession the results indicate that retreat was considerably more complex than was possible to reconstruct with reconnaissance level data the added details are important to climate models which must first be able to reproduce the recent retreat pattern in all of its complexities to improve confidence in model predictions of the system s future response

tsunami deposits beneath tidal marshes on northwestern vancouver island british columbia two sand sheets underlying tidal marshes at fair harbour neroutsos inlet and koprino harbour on the northwestern coast of vancouver island british columbia were probably deposited by tsunamis the sand sheets become thinner and finer grained landward drape former land surfaces contain marine microfossils are locally graded or internally stratified and can be correlated with earthquakes that generated tsunamis in the region 137cs dating and historical accounts indicate that the upper sand sheet was deposited by the tsunami from the great alaska earthquake in 1964 radiocarbon ages on plant fossils within and on top of the lower sand sheet show that it was deposited sometime after about a d 1660 we attribute the lower sand sheet to a tsunami from the most recent plate boundary earthquake on the cascadia subduction zone about 300 yr ago extending the documented effects of this earthquake north of the nootka fault zone the 1964 tsunami deposits differ little in thickness and continuity among the three marshes in contrast the lower sand sheet becomes thinner and less continuous to the north implying a tsunami source south of the study area

finite strain analysis of the zhangbaling metamorphic belt se china crustal thinning in transpression abstract finite strain analysis of pebbles in the metatillite and phyllite shows that the deformation of the metatillite phyllite zone is flattening to plane strain dominated results of spo analysis of the rigid plagioclase porphyroclasts in three perpendicular planes indicate monoclinic strain symmetry of the zhangbaling schist and oblate geometry of the clast forward strain modeling of rigid clasts is performed based on the shape fabric of the clast population integrated results of finite strain modeling and finite strain analysis indicate that this midcrustal section experienced at least 18 36 thinning in the oblique convergence between north and south china blocks

sudden probably coseismic submergence of holocene trees and grass in coastal washington state growth position plant fossils in coastal washington state imply a suddenness of holocene submergence that is better explained coseismic lowering of the land than be decade or century long rise of the sea these fossils include western red cedar and sitka spruce whose death probably resulted from estuarine submergence close to 300 years ago rings in eroded bark free trunks of the red cedar show that growth remained normal within decades of death rings in buried bark bearing stumps of the spruce further show normal growth continuing until the year of death other growth position fossils implying sudden submergence include the stems and leaves of salt marsh grass entombed in tide flat mud close to 300 years ago and roughly 1 700 and 3 100 years ago the preservation of these stems and leaves shows that submergence and initial burial outpaced decomposition which appears to take just a few years in modern salt marshes in some places the stems and leaves close to 300 year old are surrounded by sand left by an extraordinary landward directed surge probably a tsunami from a great thrust earthquake on the cascadia subduction zone

porphyroclast systems as kinematic indicators porphyroclasts of relatively strong minerals in mylonites commonly have an internal monoclinic shape symmetry defined by tails of dynamically recrystallized material the geometry of a porphyroclast and its tails called a porhyroclast system can serve as a valuable indicator of the sense of vorticity porphyroclast systems have been divided into and types on the basis of the geometry of the tails types have wedge shaped recrystallized tails whose median lines lie on opposite sides of a reference plane parallel to the tails and containing the symmetry axis for the system types are further subdivided into a a types in which the porphyroclast is isolated in a relatively homogeneous matrix and b types in which the porphyroclast system is associated with a shear band foliation in the matrix types typically have narrow recrystallized tails whose median lines cross the reference plane adjacent to the porphyroclast consequently embayments of matrix material occur adjacent to the porphyroclasts and the tails display characteristic bends a porphyroclast system in a mylonite develops when the relatively weak dynamically recrystallized grain aggregate in the porphyroclast mantle changes its shape due to non coaxial flow in the adjacent matrix this behaviour has been modelled in shear box experiments passive marker lines around rigid cylinders embedded in silicone putty were subjected to simple shear the experiments were modified to simulate a change in recrystallization rate r with respect to rate of deformation by decreasing the diameter of the rigid cylinder during deformation at variable rates the ratio r appears to be one of the most important factors in determining which porphyroclast system will develop at high r values flow of recrystallized material away from the porphyroclast is continuously appended by the production of new grains and wedge shaped a type tails develop at low r values relatively few new grains are added to the tails which become thinned and deflected by drag due to the spinning motion of the porphyroclast in addition most porphyroclast systems at low shear strains are of a type or lack monoclinic symmetry whereas types are only developed at high shear strain values complex porphyroclast systems characterized by two generations of tails are observed in many of the natural and model shear zones studied and may form due to fluctuating r conditions that allow isolated a and type porphyroclast systems to be used as sense of vorticity indicators are the systems should have a monoclinic shape symmetry matrix grain size should be small with respect to porphyroclast size matrix fabric should be homogeneous deformation history should be simple and observations should be made on sections normal to the inferred bulk vorticity vector for the mylonite

west coast tides during cascadia subduction zone tsunamis low neap tides occurred along the west coast of the united states and canada around 0500 ut january 27 1700 a time for the last major cascadia earthquake tsunami based on teletsunami arrival times in japan satake et al 1996 however high range perigean spring tides occurred only a week later illustrating how accurately occurrence times must be known to constrain the region s background water levels during such events the ranges of background water levels increase northward from 3 m at monterey to 8 5 m at queen charlotte as estimated from the amplitudes of perigean spring tides and subtidal winter fluctuations

tsunamis and tectonic deformation at the northern cascadia margin a 3000 year record from deserted lake vancouver island british columbia canada three layers of sand occur within a sequence of muddy gyttja in a 3 m core recovered from deserted lake which lies at the head of a fjord on the central west coast of vancouver island british columbia canada the sedimentology and microfossil assemblages of these layers are consistent with deposition by tsunamis radiocarbon ages suggest that the tsunamis were generated by plate boundary earthquakes at the cascadia subduction zone about 2600 1600 and 300 years ago diatom and protozoan contents of the gyttja layers indicate that relative sea level fell in the periods between tsunamis the sea level changes are probably a product of interseismic uplift of the north america plate margin post tsunami diatom and protozoan assemblages are generally more marine than their pre tsunami counterparts suggesting that the study site subsided during earth quakes estimates of interseismic and coseismic deformation during one earthquake cycle indicate that less than half of the interseismic uplift was recovered during the earthquake leading to cumulative or permanent uplift of the area

rolling structures at large shear strain abstract at large shear strain shear criteria are often obliterated or become ambiguous from examination of both natural examples and experimental models we describe a new criterion called rolling structure widely represented in sheared rocks a typical rolling structure is composed of a rigid or competent object e g porphyroclast boudin fossil etc with two tails asymmetrically disposed around it in most cases tails are of the same material as that of the rotating object and result from strain softening and grain size reduction at the object periphery forming a mantle z and s asymmetries of rolling structures represent dextral and sinistral senses of shearing respectively tails must not be confused with pressure shadows which usually present an opposite asymmetry for a given shear sense besides the determination of the sense of shear the occurrence of these structures allows a minimum estimate of the strain intensity in strongly sheared rocks since rolling structure length is proportional to shear strain

a holocene tsunami deposit in eastern scotland a thin regionally extensive laterally persistent sand layer identified within the holocene coastal sequences of eastern scotland dated to 7000 years bp is suggested to be a tsunami deposit the likely source of the tsunami wave is the earthquake induced second storegga slide on the norwegian continental slope at least 750 km northeast of the deposit

the application of intertidal foraminifera to reconstruct coastal subsidence during the giant cascadia earthquake of ad 1700 in oregon usa abstract changes in species assemblages of intertidal foraminifera can be used to estimate the amount of earthquake related subsidence during plate boundary earthquakes at the cascadia subduction zone the accuracy and precision of foraminiferal methods in paleoenvironmental reconstruction is underpinned by the relations between contemporary taxa and their environment which are used to calibrate fossil foraminiferal assemblages in sediment sequences a contemporary training set of surface sediment samples from five intertidal marshes along the oregon coast was used to determine foraminiferal distributions and prevailing environmental control s along elevational transects dominant taxa include balticammina pseudomacrescens trochamminita irregularis haplophragmoides wilberti trochammina inflata jadammina macrescens and miliammina fusca unconstrained cluster analysis and detrended correspondence analysis was used to identify two elevation dependent faunal zones faunal zone i upland high marsh middle marsh dominated by balticammina pseudomacrescens haplophragmoides wilberti and trochammina inflata and faunal zone ii low marsh and tidal flat dominated by miliammina fusca site specific differences in assemblages at three marshes enabled further subdivision of faunal zone i zone ia is based on one or more of balticammina pseudomacrescens trochammina inflata trochamminita irregularis and haplophragmoides sp and zone ib on jadammina macrescens haplophragmoides sp trochammina inflata and miliammina fusca canonical correspondence analysis cca and partial cca of the training set from the nehalem river marsh transect was used to infer that the zonation of foraminifera is elevation dependent 39 of explained variance a transfer function was developed to reconstruct sudden changes in relative sea level during plate boundary earthquakes in oregon the results indicate a robust performance of the transfer function r jack 2 0 82 with the error estimate rmsep jack 0 20 m comparable to local and regional transfer functions from other temperate marshes to illustrate the potential of the technique the transfer function was applied to reconstruct subsidence during the ad 1700 earthquake using at alsea bay oregon the reconstruction 0 18 0 20 m is less than half the subsidence estimate of nelson et al 2008 great earthquake palogeoesy and tsunamis of the past 2000 years at alsea bay central oregon coast usa quaternary science reviews 27 747 768 using their foraminiferal transfer function perhaps because of differences in taxonomy and the species relationship to elevation

effect of shape and orientation on rigid particle rotation and matrix deformation in simple shear flow the rotation behaviour of rigid particles from a wide range of symmetry classes was analysed in a series of three dimensional analogue experiments in which the particles were embedded in a transparent linear viscous matrix deformed to large shear strains comparison of the measured trajectories with theoretical periodic paths for rigid ellipsoids shows that quadratic slightly orthorhombic and monoclinic particles have trajectory paths and rotation rates closest to theory orthorhombic and monoclinic particles with a minimum aspect ratio 1 5 develop non periodic trajectories the results establish that the simplified theoretical model for ellipsoidal forms is a good approximation for a wide range of natural particle shapes the relationship between the rotation of a rigid particle and deformation of the adjacent matrix was also determined in a series of experiments by placing the particle at different depths relative to an imprinted grid the results are well illustrated by the surface passing through the centre of the particle and initially parallel to the shear plane two deformed regions in the matrix are recognised in the first region the matrix rotates with the particle together forming an approximately ellipsoidal object the second region is dominated by folds of limited extent along the rotation axis and greatest extent in a direction that rotates asymptotically toward the shear direction the folds rotate more slowly than the principal direction of maximum finite stretch

influence of a permanent low friction boundary on rotation and flow in rigid inclusion viscous matrix systems from an analogue perspective abstract natural occurrences and recent experimental work show that a low friction inclusion matrix boundary can be responsible for antithetical rotation and development of stable shape preferred orientations in simple shear the flow of a viscous matrix around a rigid inclusion to which it may or may not be adherent is still not well studied but it is relevant to the understanding of the behaviour of structural elements in mylonite zones we used two dimensional 2 d analogue experiments to address these issues the experimental results with a permanent low friction inclusion matrix boundary nonadherent mode show the following 1 the rotation behaviour of inclusions in this mode is markedly different from the theoretical predictions and experimental results for the adherent mode 2 inclusions with aspect ratio equal to 1 rotate synthetically at a rate that depends upon inclusion shape and orientation 3 ellipse rectangle and lozenge shaped inclusions rotate antithetically when starting with their greatest axis parallel to the shear direction 4 back rotation is limited in all cases studied and the angle between the inclusion greatest axis and the shear direction represents a stable orientation which depends on inclusion aspect ratio and shape 5 a metastable orientation exists which is strongly dependent upon inclusion shape and aspect ratio and separates fields of antithetic and synthetic rotation our experimental results show that the overall flow pattern is bow tie shaped in adherent and nonadherent modes however there are major differences in the way the matrix flows near the inclusion i in the nonadherent mode the nearby matrix flows past the inclusion whereas in the adherent mode the nearby matrix flows with and follows the inclusion therefore in the adherent mode passive marker lines parallel to the shear direction and streamlines show considerable deflections at the inclusion crests in marked contrast with their straight character in the nonadherent mode ii stagnation points or closed flow lines near the inclusion were not observed in the nonadherent mode which means that there is no closed separatrix around the inclusion in this mode despite the fact that the overall flow shape is bow tie iii in the adherent mode the line of flow reversal is stable throughout deformation but in the nonadherent mode it changes position and orientation with progressive shearing this shifting of the line of flow reversal can be an important factor controlling rotation behaviour in the nonadherent mode iv in the nonadherent mode the inclusion behaviour is similar to that observed in confined flow v the flow pattern in the nonadherent mode provides an explanation for the observed lack of drag folds associated with small scale rigid inclusions in mylonites

lake sediment record of late holocene hurricane activities from coastal alabama coastal lake sediments contain a stratigraphically and chronologically distinct record of major hurricane strikes during late holocene time frederic a category 3 hurricane that struck the alabama coast on the gulf of mexico in 1979 left a distinct sand layer in the nearshore sediments of lake shelby as a result of storm tide overwash of beaches and dunes sediment cores taken from the center of lake shelby contain multiple sand layers suggesting that major hurricanes of category 4 or 5 intensity directly struck the alabama coast at ca 3 2 3 0 2 6 2 2 1 4 and 0 8 ka 14 c yr with an average recurrence interval of 600 yr the alabama coast is likely to be struck by a category 4 or 5 hurricane within the next century

application of rheology gauge to determine rock competency in taili western liaoning ne china abstract the intensive deformation along with the rheological behavior of the tectonic units in taili eastern north china craton ncc are recognized as the manifestation of the presence of the ne sw striking ductile shear zone in the region the presence of two types of granitic veins aplitic and pegmatitic in taili exhibit obvious strain refraction and boudinage structures ten samples from different rock types are collected to analyze their deformation characteristics and the rheological properties the analysis is performed by measuring the rock competency following the methods of mainly two types of rheology gauges 1 pinch and swell structures and 2 refraction of the veins we conclude that two main factors control the deformation patterns in taili i e grain size and proportion of the mineral component grain size is found to be one of the dominant factors controlling the deformation pattern i e the larger the grain size the higher the rock viscosity is the proportion of the mineral content is another important parameter which is critical to infer the rheological contrast along with the deformational style of the studied region the rock viscosity of the samples is inversely proportional to the mica and feldspar content of the same micro structural observation suggests that these rocks experienced strong extensional deformation at a low to middle temperature condition around 450 550 c during the mesozoic this event transformed the granitic veins into boudins associated with intensive strain refraction which are also responsible for the formation of voluminous felsic rocks with high viscosity contrast in this region

applications of inclusion behaviour models to a major shear zone system the nordfjord sogn detachment zone in western norway rigid inclusion models have reached a stage where one should be able to use them to obtain quantitative values from ductile shear zones we used natural data collected in three sites and combined analogue and theoretical modelling to assess vorticity strain nature of rigid inclusion matrix interface and confinement in the large scale ductile nordfjord sogn detachment zone nsdz of the caledonides of western norway our study shows that 1 the observed shape preferred orientation spo at higher structural levels of the nsdz at site 1 gjervika can be explained by simple shear pure shear simple shear ratio sr 0 associated with a slipping inclusion matrix interface 2 the observed spo at deeper structural levels of the nsdz at site 2 near sandane can be produced by simple shear associated with a significant amount of shortening across the shear zone sr z 1 acting upon rigid inclusions in slipping contact with the enclosing matrix 3 observed back rotated boudins deeper in the nsdz at site 3 biskjelneset can form in confined flow associated with a considerable amount of shortening across the shear zone sr 0 4 4 the observed tails of porphyroclasts indicate a minimum at least local strain of ca g z 20 5 the clasts in the studied shear zones strongly depart from jeffery s model jeffery g b 1922 the motion of ellipsoidal particles immersed in a viscous fluid proceedings of the royal society of london a102 161e179 the large scale extensional nsdz under investigation shows evidence of strain partitioning rocks vary from protomylonites to ultramylonites and the simple shear and pure shear components are heterogeneously distributed therefore we conclude that flow in the nsdz was very heterogeneous both at the kilometre and the metre scale however the present study suggests that the amount of shortening across the shear plane throughout the nsdz increases with depth and the flattening component contributes to exhumation of the eclogite facies rocks in its footwall 2007 elsevier ltd all rights reserved

strain insensitive preferred orientation of porphyroclasts in mont mary mylonites abstract the shape preferred orientation spo of porphyroclasts was determined in high temperature mylonites the porphyroclasts approach rhomboidal sillimanite or elliptical garnet plagioclase sillimanite shapes and exhibit aspect ratios r as high as 11 particles with r 3 are dominantly rhomboidal the long axis of the best fit ellipse defines a very strong spo inclined at 5 10 to the mylonitic foliation in an antithetic sense with respect to the shear direction this angle is independent of r the inclination of the long sides of rhomboidal sillimanite increases from 10 to 20 with decreasing r in contrast the short sides have a constant orientation of 15 to 17 irrespective of r and are parallel to extensional crenulation cleavage low aspect ratio mainly elliptical objects show low intensity spo close to the shear plane the two spos appear strain insensitive in the case of r r 3 a stable position is acquired this is not explained by any of the current theoretical and experimental models of spo

expanding the proxy toolkit to help identify past events lessons from the 2004 indian ocean tsunami and the 2009 south pacific tsunami article i nfo some of the proxies used to identify palaeotsunamis are reviewed in light of new findings following the 2004 indian ocean tsunami and the 2009 south pacific tsunami and a revised toolkit provided the new application of anisotropy of magnetic susceptibility ams to the study of tsunami deposits and its usefulness to determine the hydrodynamic conditions during the emplacement of tsunami sequences together with data from grain size analysis are presented the value of chemical proxies as indicators of saltwater inundation associated marine shell and or coral high energy depositional environment and possible contamination is demonstrated and issues of preservation addressed we also provide new findings from detailed studies of heavy minerals new information gathered during the unesco international oceanographic commission ioc international tsunami survey of fine onshore sediments following the 2009 south pacific tsunami is presented and includes grain size chemical diatom and foraminifera data the tsunami deposit varied ranging from fining upward sand layers to thin sand layers overlain by a thick layer of organic debris and or a mud cap grain size characteristics chemical data and microfossil assemblages provide evidence for marine inundation from near shore and changes in flow dynamics during the tsunami

numerical modelling of magma transport in dykes the rheology and dynamics of an ascending pure melt in a dyke have been extensively studied in the past from field observations it is apparent that most dykes actually contain a crystalline load the presence of a crystalline load modifies the effective rheology of such a system and thus the flow behaviour indeed the higher density and viscosity of each crystal compared to the melt cause a decrease of the ascent velocity and modify the shape of the velocity profile from a typical poiseuille flow to a bingham type flow a common feature observed in the field is the arrangement of crystals parallel or at a very low angle to the edge of the dyke such a structural arrangement is often interpreted as the result of magma flow which caused the crystals to rotate and align within the flow direction but this process remains unclear another issue related to the introduction of a crystalline load concerns the possibility for crystals to be segregated from a viscous granitic melt phase during magma ascent the implications of such a process on magmatic differentiation have not previously been considered nor has such a process been previously investigated via numerical models in this study we examine the flow dynamics of a crystal bearing granitic melt ascending in a dyke via numerical models in our models both the crystal and melt phases are represented as highly viscous fluids in a stokes regime our results reveal that the presence of crystals in the melt modifies the magma velocity profile across the dyke furthermore we observe that whilst crystals continually rotate in the shear flow over one period of revolution their major axis has a high probability to be aligned parallel to the flow direction moreover some experiments showed that the melt phase can effectively be squeezed out from a crystal rich magma when subjected to a given pressure gradient range this demonstrates that crystal melt segregation in dykes during granitic magma ascent constitutes a viable mechanism for magmatic differentiation

role of hurricanes in the holocene stratigraphy of estuaries examples from the gulf coast of florida abstract sarasota and little sarasota bays are shallow coastal bays located landward of a holocene barrier inlet complex on the west central microtidal gulf coast of florida sediments presently accumulating in the bay consist of 1 fine to very fine quartz sand contributed from the gulf shoreline during storm generated washover through tidal inlets and from reworking of older deposits 2 fine sand to pebble sized quartz and phosphatic sediment contributed by tertiary and pleistocene deposits 3 biogenic carbonate debris which is produced within the bays and or derived from the gulf of mexico 4 clay minerals derived from weathering of tertiary and pleistocene carbonates and clays and 5 particulate organic debris interpretations from 51 vibracores from throughout the bays have enable delineation of four major depositional sedimentary facies resulting from specific environmental conditions protected bay open bay tidal delta washover and storms bedrock in the area ranges from 0 to about 8 m msl and is largely responsible for the areal configuration of the bay and the location of the barrier islands the holocene stratigraphy of both bays has been greatly influenced by the passage of major hurricanes which carried large volumes of sand and shell gravel into the bays at least four of these storms are documented in these cores three storm units from sarasota bay have been radiocarbon dated at 2 270 1 320 and 240 years before present ybp historically documented severe hurricanes influenced this coast in 1848 and 1921 hurricanes interrupted the normal low energy slow deposition in the bays and caused inlets to open and close three storm generated sedimentary facies are identified 1 a graded storm facies which is composed of conspicuously fining upward units ranging from sandy shell gravel to slightly shelly quartz sand 2 a homogenous storm facies consisting of homogenous and relatively thin shelly sand and gravel units and 3 a fluvial storm facies which is muddy and generally free of shells representing terrigenous influx from runoff

fabric evolution of rigid inclusions during mixed coaxial and simple shear flows abstract in a slowly moving viscous fluid a population of non interacting rigid inclusions evolves in an oscillatory fashion or creates a stable fabric depending on the flow geometry and the shape of the inclusions using jeffery s equations for the motion of a rigid ellipsoidal inclusion a mixed coaxial and simple shear flow was investigated both analytically and by numerical modeling exact results were obtained for spheroidal inclusions depending on the axial ratio of the inclusion and the amount of the coaxial component of flow individual inclusions can move cyclically or rotate to a stable orientation in one of two mutually orthogonal directions equations were found which allow us to distinguish between these types of motion and to determine the stable inclusion orientation the relative motions of individual inclusions determine the preferred orientation in a population of inclusions in a heterogeneous population with diverse axial ratios the fabric evolves as the superposition of subfabrics corresponding to subsets with different axial ratios the orientations of stable subfabrics depend on axial ratios and could thus be used as kinematic indicators in cases of a sufficiently large coaxial component of flow the fabric created by a heterogeneous population may comprise two stable mutually orthogonal subfabrics no exact results are available for general i e non spheroidal ellipsoidal inclusions and numerical modeling must be used if the coaxial component of flow is sufficiently strong the non spheroidal inclusions move much like the spheroidal ones orthogonal subfabrics may appear as transient features in the evolution of a homogeneous population of non spheroidal ellipsoidal inclusions

rotation of rigid elliptical cylinders in viscous simple shear flow analogue experiments we used experiments to investigate the behaviour of rigid elliptical cylinders embedded in a viscous fluid of finite thickness and for very small ratios s between shear zone width z and the shortest principal axis e2 of the ellipse that constitutes the base of the elliptical cylinder 3 5 s z e2 1 2 former theoretical and experimental work on the rotation of rigid inclusions immersed in a viscous matrix considered infinite shear zone thickness and or a very large ratio between shear zone thickness and inclusion size s 1 and concluded that inclusions rotate continuously and synthetically with the applied bulk simple shear flow except for inclusions with infinite axial ratio our results depart greatly from the analytical predictions experiments were carried out at constant shear zone thickness but variable s and degree of coupling at the inclusion matrix interface the results show that 1 confined inclusion rotation always deviates from theoretical predictions for infinite shear zone thickness even for synthetic rotation 2 the deviation in the angular velocity and or in the sense of rotation increases as s approaches 1 and antithetic rotation is possible from a position with ellipse longest axis parallel to the shear plane and 3 a slipping inclusion matrix interface greatly enhances deviation from theoretical predictions with antithetic rotations to as much as 20

a tsunami about 1000 years ago in puget sound washington water surged from puget sound sometime between 1000 and 1100 years ago overrunning tidal marshes and mantling them with centimeters of sand one overrun site is 10 kilometers northwest of downtown seattle another is on whidbey island some 30 kilometers farther north neither site has been widely mantled with sand at any other time in the past 2000 years deposition of the sand coincided to the year or less with abrupt probably tectonic subsidence at the seattle site and with landsliding into nearby lake washington these findings show that a tsunami was generated in puget sound and they tend to confirm that a large shallow earthquake occurred in the seattle area about 1000 years ago

analysis of environmental controls on tsunami deposit texture abstract tsunamis transport large amounts of sediment and can leave recognisable signatures in the landscape the form and composition of onshore tsunami deposits are a function of wave dynamics sediment availability and characteristics of the local environment the latter of which also partially controls preservation of the deposit this research reviews these relationships in a global context and assesses the connection between tsunami deposit particle size and four controlling parameters climate temperature and rainfall density of tsunami sediments degree of coastal protection and distance between tsunami source and sediment deposition an international dataset of tsunami deposit locations and texture was compiled from published literature and existing databases values for environmental variables were calculated for each location from global datasets of temperature rainfall coastline shape and tsunami source locations spearman s rank order correlation principal component analysis pca and hierarchical cluster analysis ca were used to analyse relationships between these variables pca results show an inverse relationship between particle size and sediment density climate variables and distance from source ca results support this suggesting a cluster structure controlled primarily by particle size and secondly by climate and sediment density these relationships can be explained by the influence of the environment on antecedent morphology and the composition of sediments available for tsunami transport

rigid inclusions rotate in geologic materials as shown by torsion experiments jeffery showed 86 years ago that a sphere rotates synthetically with applied simple shear at a rate equal to half the shear strain rate however it can be argued that rocks do not behave like viscous fluids hence jeffery s model does not apply in order to test this argument we took a two phase synthetic aggregate rock made of 70 halite and 30 muscovite as anisotropic ductile matrix with embedded rigid bodies with contrasting shapes circular cylinder sphere and cube the sphere approximates the shape of a garnet and the cube the shape of pyrite crystals both so common in nature when subject to torsion at 250 mpa and 100 c the matrix deformed homogeneously and all rigid bodies rotated as theoretically predicted for a viscous fluid matrix therefore we conclude that rocks deforming in a ductile fashion behave macroscopically like a continuum hence fluid mechanics can be used to study rigid inclusion rotation behaviour

asymmetrical to symmetrical magnetic fabric of dikes paleo flow orientations and paleo stresses recorded on feeder bodies from the motru dike swarm romania the fabric in a dike is representative of the magmatic flow considered as newtonian the anisotropy of magnetic susceptibility of the rocks gives a good representation of the shape preferred orientation which in turn is a marker of the magmatic flow generally a symmetrical pattern of the fabric across the dike is in agreement with a flow of magma within a channel the flow direction is then reliable with this imbrication an asymmetrical fabric is dependent on the flow and displacement of the wall we present the case of both symmetrical and asymmetrical dike fabrics recording different emplacements from a pan african calc alkaline dike swarm of basaltic andesitic dacitic rhyolitic composition of the alpine danubian window from south carpathians romania two populations of dikes have been described thick 1 30 m n s trending dikes and thin 1 m e w dikes the first display asymmetrical fabric and record the regional sinistral movement of the walls in contrast the thin dikes are symmetrical and frequently display an arteritic morphology that limits the dike length with no cartographic extension we propose to relate the two types of dikes to the same regional stress field in a continuum of emplacement during a regional brittle event

evidence for eight great earthquake subsidence events detected with ground penetrating radar willapa barrier washington a new approach to detect holocene subduction zone earthquakes combines the results from ground penetrating radar gpr vibracores and accelerator mass spectrometry ams dates from a barrier spit located west of willapa bay southwest washington gpr data show a 10 m thick facies of beach sand within which we identify and vibracores confirm beach parallel wave eroded buried scarps mantled with multiple beds of magnetite the eight gpr detected buried scarps are interpreted to be eroded by minor transgressions caused by instantaneous barrier subsidence during earthquakes associated with the juan de fuca plate subducting under the north american plate of these scarps four have been ams dated at 300 1110 2540 and 4250 radiocarbon yr b p no datable material has yet been found for the other four radar detected scarps but we interpolate and extrapolate dates of 1800 3400 5000 and 5800 yr b p

deformation around rigid particles the influence of slip at the particle matrix interface abstract theoretical and previous experimental studies of rigid particle structures have only considered the behaviour of rigid particles for which the interface between particle and matrix is coherent in natural rocks the boundary behaviour may cover the whole range from free slip to complete coherence examples where slip may be promoted include crack seal deformation during the development of pressure shadows core mantle structures where the mantle is composed of much weaker fine recrystallized material and crystallizing magmas or partially molten rocks where grain boundaries are lubricated by the melt phase analogue scale model experiments have been performed under pure shear and simple shear conditions to compare the particle rotation and the flow in the matrix for both slipping and non slipping particle matrix interfaces when slip does occur particles rotate faster in pure shear and slower in simple shear than for non slip leading to the more rapid development of a shape preferred orientation the preferred orientation tends to be bimodal in simple shear flow the flow and finite strain patterns in the matrix are also strongly influenced by slip at the interface and porphyroclast systems can develop geometries with ambiguous or contradictory shear senses dependent on the original particle orientation in multi particle experiments slip on the interfaces enhances strong strain localization in non linear viscous material to produce patterns very similar to natural s c fabrics

are isolated stable rigid clasts in shear zones equivalent to voids abstract particles in shear enclose important information about a rock s past and can potentially be used to decipher the kinematic history and mechanical behavior of a certain outcrop or region isolated rigid clasts in shear zones often exhibit systematic inclinations with respect to the shear plane at small angles tending towards the instantaneous stretching direction of the shear zone this shape preferred orientation cannot be easily explained by any of the analytical theories used in geology it was recently recognized that a weak mantle surrounding the clast or a slipping clast matrix interface might be responsible for the development of the observed inclinations physical considerations lead us to conjecture that such mantled rigid clasts can be effectively treated as voids that are not allowed to change their shape the resulting equivalent void conjecture agrees well with numerical and field data and has the following important geological implications i clasts in shear zones can have stable positions in simple shear without the requirement of an additional pure shear component ii the stable orientation can be approached either syn or antithetically hence the clast can rotate against the applied shear sense iii the strain needed to develop a strong shape preferred orientation is small 1 and therefore evaluations based on other theories may overestimate strain by orders of magnitude iv the reconstruction of far field shear flow conditions and kinematic vorticity analysis must be modified to incorporate these new findings

2 d shape preferred orientations of rigid particles in transtensional viscous flow ghosh and ramberg tectonophysics 34 1976 1 70 studied the two dimensional 2 d rotational behaviour of individual rigid particles embedded in a viscous medium subject to simple shear and transpression sr 0 at low medium shear strains we now extend this theoretical study to transtension sr 0 by deriving a new analytical solution to non interacting populations of rigid particles and to high shear strains we used different initial orientations of particles in the same graph to simulate populations of particles in an originally isotropic rock our results show that 1 shape preferred orientations spos developed in viscous simple shear flow are transient and cyclical except for particles with aspect ratio or material lines which tend to the shear direction 2 stable spos can develop in transpression they dip towards the shear sense but when defining an s c structure with the shear foliation this composite fabric is always antithetic and thus indicates the wrong sense of shear 3 stable spos can also develop in transtension they dip opposite to the shear sense but when defining an s c structure with the shear foliation this composite fabric is always synthetic and thus indicates the correct sense of shear 4 spos produced in transpression or transtension can be used as vorticity gauges only when they represent stable orientations which must be demonstrated a priori

stratigraphic and microfossil evidence for late holocene tsunamis at swantown marsh whidbey island washington abstract four muddy sand sheets occur within a tidal marsh peat at swantown on the west coast of whidbey island washington the two largest sand sheets pinch out about 100 m inland and became thinner and finer grained landward all four sand sheets contain marine microfossils and have internal stratification they record repeated inundation of the marsh over a short time period by distinct pulses of sediment laden ocean water consistent with deposition by a tsunami wave train the layers have been radiocarbon dated to 1160 1350 1400 1700 1810 2060 and 1830 2120 cal yr b p the overlap in age between the two youngest layers and inferred great earthquake events at the cascadia plate boundary some 250 km to the west suggests they were emplaced by tsunamis from this source area the two older layers do not correlate with plate boundary events they may be products of tsunamis caused by earthquakes on local faults in the strait of juan de fuca or by submarine landslides in this area

microstructure and mechanical properties of halite coarse muscovite synthetic aggregates deformed in torsion abstract we investigated the behavior of a synthetic two phase aggregate composed of 80 halite 20 coarse muscovite under torsion deformation at 100 200 and 300 c a confining pressure of 250 mpa and a constant strain rate of 3e 4 s 1 at all temperatures the two phase aggregate deformed homogeneously at the sample scale the strength of the aggregate and muscovite deformation depended on temperature strain rate and initial orientation of muscovite greatest dimension relative to the shear plane with muscovite initially parallel to the shear plane halite flowed plastically and long muscovite grains were not strong enough to behave as a rigid inclusion rotating in a ductile matrix instead high aspect ratio grains deformed by folding which was visibly accomplished by slip along mica 001 cleavage and by great flattening of halite in the core of the folds when initially normal to the shear plane high aspect ratio muscovite grains passively rotated towards the shear plane in both cases small and low aspect ratio muscovite grains behaved mostly as mica fish with mica grains tilted opposite to shear sense similarly to natural mylonites porphyroclast systems and rolling structures were also common in the microstructure a strong foliation made of halite ribbons and aligned muscovite flakes rapidly developed but did not make the composite aggregate weaker when compared with single phase halite comparison with synthetic aggregates of single phase halite shows that the two phase aggregate was much stronger than single phase halite in all cases comparison with a synthetic aggregate with calcite porphyroclasts shows that the strength of the aggregate with muscovite at 100 c was lower below a strain of ca 2 6 and higher beyond this value and that the aggregate with calcite was stronger at 200 c strain rate stepping tests 1e 5 s 1 2e 3 s 1 indicate that the two phase aggregate behaved as power law viscous with stress exponents of ca 12 and 10 at 100 and 200 c respectively the mechanical data obtained in this study represent the actual rheological behavior of the aggregates because we used soft polymer jackets

coastal sedimentation associated with the june 2nd and 3rd 1994 tsunami in rajegwesi java abstract this paper presents the second detailed study of sediments deposited by modern tusnamis the first being that of the flores indonesia tsunami of december 1992 shi et al 1995 sediment cores were collected from areas in which eyewitnesses reported sediment deposition grain size analysis shows pronounced vertical variations in grain size as well as changes in standard deviation skewness and kurtosis that appear to be indicative of complex tsunami flooding vertical variations in grain size in individual cores are greater than spatial variations between cores taken along a transect completed perpendicular to the coastline the java tsunami deposited sediments do not show unequivocal evidence of local erosion but instead evidence for sediment transport and deposition is clear and is characterised by dominantly unimodal sediments with fine tailed distributions

stable positions of rigid objects in non coaxial flow a study in vorticity analysis abstract distortions of a homogeneous fabric which occur around rigid objects in rocks deformed by non coaxial ductile flow are useful to determine the sense of shear but also contain information on other aspects of the flow rigid objects in a non coaxial flow fall into two categories those which are permanently rotating and those which can reach stable positions at high finite strain the orientation of such immobilized objects with respect to eigenvectors of instantaneous flow is a function of the vorticity number of the flow the ratio of instantaneous stretches and the axial ratio of the object in naturally deformed rocks immobilized rigid objects may be recognized from the geometry of the surrounding fabric tails of recrystallized material around porphyroclasts in a mylonite rotate towards parallellism with the extensional eigenvector of the flow and the shape of tails reflects the rotational behaviour of the porphyroclast the axial ratio of immobilized porphyroclasts and their orientation with respect to the tails can theoretically be used to determine the vorticity number of the flow and deviations from isochoric plane strain in practice such an analysis is as yet difficult but a tentative example is given of the way in which the vorticity number can be calculated from a population of feldspar porphyroclasts in a quartzite mylonite from the french pyrenees

rotated garnets a mechanism to explain the high frequency of inclusion trail curvature angles around 90 and 180 abstract this paper presents numerical data from garnets with inclusion trail curvature angles of up to 260 three hundred and twenty five garnets were studied from an outcrop of greenschist facies phyllite in southern minas gerais state brazil apart from the inclusion trail curvature angle also the aspect ratio r and the angle between the long axis of the garnets and the foliation were measured the results show a remarkable concentration of at 180 and a minor one at 90 r varies between 1 and 2 showing that the garnets deviate from sphericity and shows that all garnets have their long axis in the forward rotated quadrant supporting the rotational interpretation a model is proposed to explain the concentrations of based on preferential growth of the garnets into the mica rich strain caps orthogonal to the foliation causing elongated crystals that because of their shape and position would experience accelerated rotation until relatively stable positions with their long axes parallel to the foliation would be attained renewed growth again into the mica rich strain caps orthogonal to the foliation would first restore the spherical shape and then produce an elongated shape again perpendicular to the foliation forcing a repetition of the process it is concluded that this model is capable of explaining the concentration of in multiples of 90 in a rotational model where this concentration was considered earlier as an argument in favor of the non rotational model

detection of large prehistoric earthquakes in the pacific northwest by microfossil analysis geologic and palynological evidence for rapid sea level change 3400 and 2000 carbon 14 years ago 3600 and 1900 calendar years ago has been found at sites up to 110 kilometers apart in southwestern british columbia submergence on southern vancouver island and slight emergence on the mainland during the older event are consistent with a great magnitude m 8 earthquake on the cascadia subduction zone the younger event is characterized by submergence throughout the region and may also record a plate boundary earthquake or a very large crustal or intraplate earthquake microfossil analysis can detect small amounts of coseismic uplift and subsidence that leave little or no lithostratigraphic signature

abrupt uplift within the past 1700 years at southern puget sound washington shorelines rose as much as 7 meters along southern puget sound and hood canal between 500 and 1700 years ago evidence for this uplift consists of elevated wave cut shore platforms near seattle and emerged peat covered tidal flats as much as 60 kilometers to the southwest the uplift was too rapid for waves to leave intermediate shorelines on even the best preserved platform the tidal flats also emerged abruptly they changed into freshwater swamps and meadows without first becoming tidal marshes where uplift was greatest it adjoined an inferred fault that crosses puget sound at seattle and it probably accompanied reverse slip on that fault 1000 to 1100 years ago the uplift and probable fault slip show that the crust of the north america plate contains potential sources of damaging earthquakes in the puget sound region

the southern whidbey island fault an active structure in the puget lowland washington information from seismic reflection profiles outcrops boreholes and potential field surveys is used to interpret the structure and history of the southern whidbey island fault in the puget lowland of western washington this northwest trending fault comprises a broad as wide as 6 11 km steep northeast dipping zone that includes several splays with inferred strike slip reverse and thrust displacement transpressional deformation along the southern whidbey island fault is indicated by along strike variations in structural style and geometry positive flower structure local unconformities out of plane displacements and juxtaposition of correlative sedimentary units with different histories the southern whidbey island fault represents a segment of a boundary between two major crustal blocks the cascade block to the northeast is floored by diverse assemblages of pre tertiary rocks the coast range block to the southwest is floored by lower eocene marine basaltic rocks of the crescent formation the fault probably originated during the early eocene as a dextral strike slip fault along the eastern side of a continental margin rift bending of the fault and transpressional deformation began during the late middle eocene and continues to the present oblique convergence and clockwise rotation along the continental margin are the inferred driving forces for ongoing deformation evidence for quaternary movement on the southern whidbey island fault includes 1 offset and disrupted upper quaternary strata imaged on seismic reflection profiles 2 borehole data that suggests as much as 420 m of structural relief on the tertiary quaternary boundary in the fault zone 3 several meters of displacement along exposed faults in upper quaternary sediments 4 late quaternary folds with limb dips of as much as 9 5 large scale liquefaction features in upper quaternary sediments within the fault zone and 6 minor historical seismicity the southern whidbey island fault should be considered capable of generating large earthquakes m s 7 and represents a potential seismic hazard to residents of the puget lowland

tectonic implication of quantitative micro fabric analyses of quartz c axis development within the tutak gneiss dome zagros hinterland fold and thrust belt quartz c axis fabrics finite strain and kinematic vorticity number analyses were used to investigate deformation characteristics of the tutak gneiss dome located in the eastern edge of the basement involved zagros hinterland fold and thrust belt the opening angle of the quartz c axis fabric patterns was used to estimate deformation temperatures which suggest greenschist to amphibolite facies conditions 430 50 c to 660 50 c the kinematic vorticity number varies from 0 6 to 0 95 mean kinematic vorticity number of 0 81 which indicates that the metamorphic rocks of the tutak gneiss dome experienced a sub simple shear regime by contribution of both pure shear 39 and simple shear 61 deformation components nw se striking foliations have commonly sw and ne dips accompanied by mostly nw se plunging and subordinate ne sw plunging stretching lineations these indicate more extension along the nw se trend to produce a prolate elliptical wedge shape in map view structural and vorticity analysis suggests that the tutak gneiss dome has experienced earlier dome formation followed by thrust stacking rather than the two deformations occurring synchronously and a protracted progressive deformation through a decreasing temperature regime

sheath folds formed by drag induced by rotation of rigid inclusions in viscous simple shear flow nature and experiment abstract natural examples of fold patterns associated with rotated boudins occur in the ossa morena zone s portugal and triggered the present study in ductile marbles with embedded competent mafic boudins the folds seem to have originated by rotation of these bodies and show differential development from gentle deflections to sheath folds this suggests a dependence of the structure type on the distance of the metamorphic layering to the rigid body the experimental work presented here was performed with rotating inclusions in bulk simple shear and introduces a new variable the distance of the marker layer from the rigid inclusion d expressed in terms of e the ratio between the spacing between marker layers d and the greater principal dimension of the inclusion a contrary to previous experimental work in the literature we used planar marker layers without concomitant boudinage our results show new processes of development of sheath folds from planar layers and also that some non cylindrical layer deflections are transient and thus that sheath folds do not originate from them when d is small and the inclusion starts with its longest axis normal to the shear plane sheath folds develop by drag pull processes on originally planar marker layers transient non cylindrical deflections develop on originally planar marker layers when the distance between the marker layers is smaller than the longest principal dimension of the rigid particle the monoclinic symmetry of the drag sheath fold patterns associated with rotating rigid inclusions indicate non coaxial flow and can be used as a shear sense criterion quarter structure

rotation of irregular staurolite porphyroblasts in a simple shear dominated shear zone controlled by initial growth orientation and aspect ratio abstract in a mica schist unit of the bossost dome central pyrenees spain idioblastic interkinematic staurolite porphyroblasts with straight inclusion trails s i have rotated with respect to the main schistosity in the same sense by different amounts orientation data of 600 porphyroblasts were obtained from planes parallel to stretching lineation xz perpendicular to lineation yz and parallel to schistosity xy interpenetrating growth twinning resulted in highly irregular shapes with aspect ratios r a ranging from 1 to 5 initial random porphyroblast growth is inferred from variable length axis la s i angles maximum rotation of 120 is observed in blasts with s i oriented orthogonal to the mineral long axis implying a shear strain of 4 3 in simple shear flow absence of back rotation is indicative of dominant simple shear flow w k 0 8 0 9 elongated porphyroblasts r a 3 with s i parallel to la have rotated very little because they were already in a stable position when shearing commenced rotation of staurolite porphyroblasts was possible because decoupling between blasts and matrix was weak and no significant strain partitioning had developed the wide variety of shapes with different aspect ratios formed by simple blasts and interpenetrating growth twins of staurolite are potential shear strain and vorticity gauges

shape fabric development in rigid clast populations under pure shear the influence of no slip versus slip boundary conditions abstract shape fabrics of elliptical objects in rocks are usually assumed to develop by passive behavior of inclusions with respect to the surrounding material leading to shape based strain analysis methods belonging to the rf family a probability density function is derived for the orientational characteristics of populations of rigid ellipses deforming in a pure shear 2d deformation with both no slip and slip boundary conditions using maximum likelihood a numerical method is developed for estimating finite strain in natural populations deforming for both mechanisms application to a natural example indicates the importance of the slip mechanism in explaining clast shape fabrics in deformed sediments

simple shear of deformable square objects abstract finite element models of square objects in a contrasting matrix in simple shear show that the objects deform to a variety of shapes for a range of viscosity contrasts we catalogue the changing shapes and orientations of objects in progressive simple shear at moderate simple shear 1 5 the shapes are virtually indistinguishable from those in equivalent pure shear models with the same bulk strain r s 4 examined in a previous study in theory differences would be expected especially for very stiff objects or at very large strain in all our simple shear models relatively competent square objects become asymmetric barrel shapes with concave shortened edges similar to some types of boudin incompetent objects develop shapes surprisingly similar to mica fish described in mylonites

rheology and microstructure of synthetic halite calcite porphyritic aggregates in torsion abstract polymer jacketed porphyritic samples of 70 halite 30 coarse calcite were subjected to torsion deformation to investigate the effects of a mixture of coarse calcite on the microstructure and mechanical properties of a two phase aggregate the experiments were run at 100 and 200 c a confining pressure of 250 mpa and a constant shear strain rate of 3e 4 s 1 ultimate strengths of single phase halite synthetic aggregates at 100 and 200 c were ca 32 and 8 nm respectively and of the two phase aggregate 39 and 18 nm respectively this shows that the two phase aggregate was much stronger especially at 200 c stepping strain rate tests show that the two phase aggregate behaved as power law viscous with stress exponents of ca 19 and 13 at 100 c at 200 c respectively from these high exponents we infer that the active deformation mechanisms were not efficient enough to rapidly relax the applied stress halite stress exponents at 100 and 200 c are typically much lower in the order of 4 6 which means that the calcite porphyroclasts were obstacles to halite plastic flow and hampered stress relaxation the drop of the stress exponent with temperature indicates that the main deformation mechanism s was temperature sensitive matrix halite deformed plastically while calcite rotated rigidly or deformed in a brittle fashion with grain size reduction by fracturing e g bookshelf and boudinage we conclude that halite was softer than calcite in the investigated temperature range strain was homogeneous at the sample scale but not at the grain scale where the foliation delineated by plastically flattened halite contoured the rigid calcite clasts the microstructures experimentally produced at 100 and 200 c are very similar and find their counterparts in natural mylonites rolling structures and porphyroclast systems bookshelf and boudinage in brittle calcite porphyroclasts and ductile y and c micro shear bands in the halite matrix

thick dyke emplacement and internal flow a structural and magnetic fabric study of the deep seated dolerite dyke of foum zguid southern morocco 1 knowledge on forced magma injection and magma flow in dykes is crucial for the understanding of how magmas migrate through the crust to the earth s surface because many questions still persist we used the long thick and deep seated foum zguid dyke morocco to investigate dyke emplacement and internal flow by means of magnetic methods structural analysis petrography and scanning electron microscopy we also investigated how the host rocks accommodated the intrusion regarding internal flow 1 important variations of the rock magnetic properties and magnetic fabric occur with distance from dyke wall 2 anisotropy of anhysteretic remanent magnetization reveals that anisotropy of magnetic susceptibility ams results mainly from the superposition of subfabrics with distinct coercivities and that the imbrication between magnetic foliation and dyke plane is more reliable to deduce flow than the orientation of the ams maximum principal axis and 3 a dominant upward flow near the margins can be inferred the magnetic fabric closest to the dyke wall likely records magma flow best due to fast cooling whereas in the core the magnetic properties have been affected by high temperature exsolution and metasomatic effects due to slow cooling regarding dyke emplacement this study shows that the thick forceful intrusion induced deformation by homogeneous flattening and or folding of the host sedimentary strata dewatering related to heat as recorded by thick quartz veins bordering the dyke in some localities may have also helped accommodating dyke intrusion the spatial arrangement of quartz veins and their geometrical relationship with the dyke indicate a preintrusive to synintrusive sinistral component of strike slip

episodic tectonic subsidence of late holocene salt marshes northern oregon central cascadia margin salt marsh subsurface deposits 0 4 m depth in netarts bay a small coastal lagoon of northern oregon record six events of marsh burial in the last several thousand years five of the buried marsh surfaces show sharp nonerosional upper contacts with either anomalous sand layers tsunami deposits or tidal flat mud deposits these sequences indicate episodic abrupt subsidence of the marsh surfaces to low intertidal levels in contrast lower marsh contacts with underlying intertidal muds are gradational indicating gradual uplift and development of the marsh three independent measures of deposit elevation relative to mean tidal level percent organics diatom assemblages and percent eolian sand have been used to estimate vertical displacements of marsh surfaces abrupt subsidence displacements of 1 1 5 m alternate with gradual uplift displacements of the order of 0 5 1 0 m the vertical tectonic movements are interpreted to reflect coseismic strain release abrupt subsidence following interseismic strain accumulation gradual uplift associated with interplate coupling between the juan de fuca plate and the north american plate in the cascadia subduction zone recurrence intervals between subsidence events range from possibly less than 300 years to at least 1000 years with the last dated event likely occurring 300 400 radiocarbon years before present rcybp significant 14c age overlaps of at least four subsidence events recorded at netarts and reported for southern washington and other northern oregon bays at 300 500 1000 1300 1400 1800 and 3000 3300 rcybp suggest the potential for event synchroneity over at least 200 km of the central part of the cascadia subduction zone additional work is needed to test the synchroneity of these episodic events of coseismic subsidence

structural micro structural and kinematic analyses of channel flow in the karmostaj salt diapir in the zagros foreland folded belt fars province iran abstract one of the main characteristic of the zagros foreland fold and thrust belt and the zagros foreland folded belt are wide distributions of surface extrusion from the hormuz salt diapirs this study examines the structure and kinematic of channel flow in the karmostaj salt diapir in the southwestern part of the zagros foreland folded belt this diapir has reached the surface as a result of the channel flow mechanism and has extruded in the southern limb of the kuh gach anticline which is an asymmetric decollement fold with convergence to the south structural and microstructural studies and quantitative finite strain rs and kinematic vorticity number wk analyses were carried out within this salt diapir and its namakier this was in order to investigate the structural evolution in the salt diapiric system the characteristics and mechanism of the salt flow and the distribution of flow regimes within the salt diapir and interaction of regional tectonics and salt diaprism the extruded salt has developed a flow foliation sub parallel to the remnant bedding recorded by different colors a variety of internal folds including symmetrical and asymmetrical folds and interference fold patterns shear zones and boudins these structures were used to analyze mechanisms and history of diapiric flow and extrusion the microstructures reveal various deformation mechanisms in various parts of salt diapir the measurements of finite strain show that rs values in the margin of salt diapir are higher than within its namakier which is consistent with the results of structural studies mean kinematic vorticity number wm measured in steady state deformation of diapir and namakier is wm 0 45 0 48 0 13 the estimated mean finite deformation wm values indicate that 67 8 pure shear and 32 2 simple shear deformation were involved the implications of which are discussed the vorticity of flow indicates that in the early stage of growth poiseuille flow was the dominate mechanism especially in the core of diapir with higher pure shear component relative to simple shear component whilst a couette flow at the margins of diapir is the dominate mechanism with higher simple shear component relative to pure shear component the obtained kinematic vorticity number reflects spatial partitioning of dominantly poiseuille flow in core and couette flow along edges of diapir these two mechanisms reflect a persistent flow governed by a simultaneous combination of pure shear and simple shear in a hybrid poiseuille coutte flow

an analytical solution in 2d for the motion of rigid elliptical particles with a slipping interface under a general deformation a mathematical model for rigid inclusions with a slipping interface immersed in a general 2d homogeneous deformation is developed under bulk pure shear inclusions are expected to rapidly approach the stretching axis when compared to the behaviour of inclusions with no slip at the interface the derived model predicts synthetic and antithetic motion into a stable orientation under simple shear and thereafter the inclusion makes an antithetic angle with the shear direction under simple shear rotation rates can be higher or lower than those of no slip inclusions depending on orientation a direct relationship between object inclination to the shear direction and the vorticity of the bulk flow is predicted the model compares well with published analogue and numerical experiments

tsunami deposits beneath tidal marshes on vancouver island british columbia thin sheets of sand occur within holocene mud and peat deposits beneath tidal marshes at tofino ucluelet and port alberni on vancouver island british columbia the sand sheets are extensive and have sharp upper and lower contacts in most cases they consist of moderately sorted massive sand and silty sand with abundant wood and other plant detritus at port alberni the thickest sheet has gravel and is graded the upper two sand sheets in the tofino ucluelet area and possibly the third are also present at port alberni eyewitness accounts and 137 cs analysis suggest that the uppermost thinnest sand was deposited by the tsunami triggered by the great alaska earthquake in 1964 the next oldest sand sheet has been radiocarbon dated at our data suggest that large tsunamis have struck the southern british columbia coast several times during the late holocene and that some were much larger than the 1964 tsunami which caused about 10 million damage 1964 canadian dollars to communities on vancouver island because such tsunamis can be expected in the future they pose a hazard to people and property in some coastal areas

influence of a low viscosity layer between rigid inclusion and viscous matrix on inclusion rotation and matrix flow a numerical study abstract we have used 2 d finite element modelling to investigate the influence of a permanent low viscosity layer between matrix and inclusion on matrix flow and inclusion rotation under viscous simple shear flow rigid inclusions of different shape circle square ellipse lozenge rectangle and skewed rectangles and aspect ratio r were used the calculated matrix flow pattern is neither bow tie nor eye shaped it is a new flow pattern that we call cat eyes shaped which is characterized by i straight streamlines that slightly bend inwards at the inclusion s crests ii elongate eye shaped streamlines on each side of the inclusion iii stagnation points in the centre of the eyes iv absence of closed streamlines surrounding the inclusion v changes in flow configuration with inclusion orientation the lines of flow reversal bend and tilt closed streamline circuits may disappear and streamlines may bend outwards at the inclusion s crests concerning inclusion rotation the numerical results show that i a low viscosity layer lvl makes inclusions with r 1 rotate synthetically but the rotation rate depends upon shape circle or square and orientation therefore shape matters in the slipping mode ii all studied shapes with r 1 rotate antithetically when starting with the greatest principal axis e 1 parallel to the shear direction 0 iii rotation is limited because there is a stable equilibrium orientation se for all studied shapes with r 1 iii there is also an unstable equilibrium orientation ue and both se and ue depend upon inclusion s r and shape the present numerical results closely agree with previous results of analogue experiments with a permanent low viscosity interface only minor deviations related with small shape differences were detected

microstructural and mechanical effects of strong fine grained muscovite in soft halite matrix shear strain localization in torsion 1 torsion experiments were performed on polymer jacketed samples of 80 halite 20 fine mica at 373 473 and 573 k a confining pressure of 250 mpa and a shear strain rate of 3 10 4 s 1 the strength of the aggregate depended on temperature strain rate mica distribution produced by cold pressing and mica orientation emerging during experiments comparison with synthetic aggregates of pure halite shows that halite mica mixtures were stronger in all cases from strain rate stepping tests we deduced stress exponents of 12 and 10 at 373 and 473 k respectively in contrast to values of approximately 4 and 3 for halite at the same temperatures strain localized only at 573 k except for one run at 373 k and high strain shear bands formed parallel to the applied shear plane at 573 k we infer that the strength contrast between halite and mica increased with temperature and promoted strain localization which occurred where the local mica content was low while unstrained domains persisted where the locally high mica content formed a strong framework mica reorientation and strain softening at 573 k increased with strain from which we deduce that mica alignment promoted softening we conclude that small amounts of a strong mineral phase can significantly increase the strength and stress dependence of a rock and that the heterogeneous connectivity between strong grains can trigger shear strain localization

development of highly non cylindrical folds around rigid ellipsoidal inclusions in bulk simple shear regimes natural examples and experimental modelling abstract the three dimensional development of strongly non cylindrical folds around competent ellipsoidal inclusions in bulk simple shear regimes is studied in experiments and natural examples examples from the continental allochthonous terrane of the braganca nappe complex ne portugal show rim folds and sheath folds associated with different parts of rigid ellipsoidal boudins experimental work has been carried out with models made from analogue materials silicone putty and plasticine and deformed in a simple shear machine we have considered three different models to simulate natural examples and the results show that fold morphology depends on the shape of the inclusion and position around the inclusion although the bulk deformation regime is layer parallel homogeneous simple shear we can distinguish local deformation regimes responsible for the folding associated with different parts of the rigid body flow and strain patterns must therefore be complex around inclusions or populations of inclusions prolate to oblate strain ellipsoids can be expected in different positions close to the rigid inclusion in our experiments the competent inclusions do not rotate synthetically with the applied bulk simple shear e g clockwise rotation of inclusion in dextral shear instead they back rotate early in the shearing history and keep this position throughout the experiment this is the result of the size relationship between the inclusion and the finite width of the shear zone the fold pattern around rigid inclusions may be used as a shear sense criterion

mineral lineation produced by 3 d rotation of rigid inclusions in confined viscous simple shear abstract the solid state flow of rocks commonly produces a parallel arrangement of elongate minerals with their longest axes coincident with the direction of flow a mineral lineation however this does not conform to jeffery s theory of the rotation of rigid ellipsoidal inclusions reis in viscous simple shear because rigid inclusions rotate continuously with applied shear in 2 dimensional 2 d flow the rei s greatest axis e1 is already in the shear direction therefore the problem is to find mechanisms that can prevent the rotation of the rei about one axis the vorticity axis in 3 d flow the problem is to find a mechanism that can make e1 rotate towards the shear direction and so generate a mineral lineation by rigid rotation about two axes 3 d analogue and numerical modelling was used to test the effects of confinement on rei rotation and for narrow channels shear zone thickness over inclusion s least axis wr 1 can rotate backwards from an initial orientation w e1 parallel to the shear plane in great contrast to jeffery s model 3 back rotation is limited because inclusions reach a stable equilibrium orientation 4 most importantly and in contrast to jeffery s model and to the 2 d simulations in 3 d the confined rei gradually rotated about an axis orthogonal to the shear plane towards an orientation with e1 parallel to the shear direction thus producing a lineation parallel to the shear direction the modelling results lead to the conclusion that confined simple shear can be responsible for the mineral alignment lineation observed in ductile shear zones

simulation of tsunamis from great earthquakes on the cascadia subduction zone large earthquakes occur episodically in the cascadia subduction zone a numerical model has been used to simulate and assess the hazards of a tsunami generated by a hypothetical earthquake of magnitude 8 5 associated with rupture of the northern sections of the subduction zone wave amplitudes on the outer coast are closely related to the magnitude of sea bottom displacement 5 0 meters some amplification up to a factor of 3 may occur in some coastal embayments wave amplitudes in the protected waters of puget sound and the strait of georgia are predicted to be only about one fifth of those estmated on the outer coast

time and size of a giant earthquake in cascadia inferred from japanese tsunami records of january 1700 geological evidence shows that great earthquakes have occurred in the recent prehistoric past in the cascadia subduction zone off the pacific coast of north america the most recent event or series of events is dated at about 300 years ago1 4 but the precise date and magnitude have not been determined geological investigations have not been able to distinguish a single giant earthquake from a series of great earthquakes occurring over a timespan of a decade or two4 although this information is important for the assessment of future hazard5 we have found several tsunami records in japan from ad 1700 with no indication of a local cause historical earthquake records and palaeoseismic evidence indicate the absence of a large earthquake in 1700 in south america alaska or kamchatka leaving cascadia as the most likely source of this tsunami the estimated time of the earthquake is the evening about 21 00 local time of 26 january 1700 the magnitude is estimated as 9 from the tsunami heights in which case the earthquake ruptured the entire length of the cascadia subduction zone2 these estimates are consistent with native american legends that an earthquake occurred on a winter night6

holocene sea level variations and geomorphological response an example from northern brittany france in northern brittany an important geomorphological response to holocene sea level rise has been the development of coastal dunes with associated lagoons and marshes at anse du verger a marsh has formed behind a dune system which has been developing in situ for the last 4000 years the lithostratigraphy of the marsh comprises extensive peat formation with sands silts and occasional sand lenses the latter probably associated with storm surges the sequence dates from 10 320 120 bp after 3000 bp flood episodes on the marsh are more common while the upper marsh deposits can be correlated with the recent period of dune building prehistoric artifacts remains of cooking implements have been found on a cliff to the east of the marsh and are buried by washover deposits which indicates a sudden abandonment of a settlement possibly due to a storm surge soon after 2460 80 bp surge levels are proposed as a controlling factor on dune crest elevation

coastal storm deposition salt marsh response to a severe extratropical storm march 1993 west central florida on march 12 13 1993 the passage of a severe extratropical storm popularly referred to as the storm of the century resulted in the deposition of storm suspended sediments along florida west central coastline in waccasassa bay surge waters near 3 m in height inundated the coast and transported resuspended nearshore sediments onto the open marine marshes rimming the embayment the thickness of the resulting storm deposit reached 12 cm on the levees and up to 2 cm on the marsh surface and visible sedimentation occurred several hundred metres from the creek banks into the marsh interior the tan to gray storm layer was composed of mixed clays silt to very fine sand sized quartz and marine biogenic sediments all similar to those of the underlying marsh sediments despite the evidence for severe storm conditions this event was characterized further by the absence of shoreline erosion along the marsh coast this condition contrasts with sandy coasts where strong storms often result in shoreline erosion as compared to sandy shorelines the stability of this marsh fronted coast is enhanced by the cohesive nature of the fine grained marsh muds baffling by the marsh grass canopy and sediment binding by plant root matrices locally the waccasassa bay coastal system has developed under sediment poor sand starved and low energy conditions and large scale storm events may be an important component in sediment transport processes and marsh surface accumulation the response of the waccasassa bay system to this event offers a different view of storm related shoreline effects and in particular the role that storms may play in long term shoreline stability

boudinage and shearband boudins a meso to micro scale tool in structural analysis abstract a classification of boudinage and boudins is made presenting a simplified parametric description of boudin block geometry end members the most important shearband boudins parameters ratios microstructural domains and internal evolutions are described and interpreted shearband boudins are related to a large number of geological meso and microstructures e g pinch and swell drawn or torn boudins mica fish porphyroclasts foliation boudinage tectonic lozenges and c s c several factors can control the asymmetric boudinage process such as the obliquity of a competent layer the orientation of an initial fracture boudin axial ratio the viscosity ratio between matrix and layer flow type and shear strain this review highlights the correlation of shearband boudins with other asymmetrically deformed structures and shows their geological relevance finally this study presents a phenomenological framework for shearband boudins

effect of mechanical interactions on the development of shape preferred orientations a two dimensional experimental approach abstract modifications in the development of preferred orientations of rigid particles due to mechanical interactions between particles are studied experimentally in two dimensions experiments in both pure shear and simple shear were performed and the results analysed using an easy and fast new automatic method for increased concentration of rigid particles the rotation of individual particles may be slowed down or even stopped due to collisions or disturbance of the flow in the matrix caused by neighbours in coaxial flow the fabric intensity is consequently reduced in simple shear flow the fabric evolution is no longer cyclic the intensity is on average weaker and the fabric axis rotates asymptotically toward the shear plane in the case of preferred orientations of particles having a low aspect ratio 2 5 the fabric rotates through the shear plane then undergoes a reverse rotation and rotates toward the shear plane again in the light of these experimental results we emphasize that quantification of finite strain based on such fabrics may lead to significant underestimates and calculated values should be taken as minimum estimates the kinematic significance of concentrated rigid particle preferred orientations in rocks is modified by interactions between particles techniques for qualitative or quantitative kinematic analysis may become unreliable for simple shear flows the concentrated population fabrics show an angular behaviour close to that of passive markers they tend to align parallel to the shear plane in simple shear flow