a history of cleavage and folding an example from the goldenville formation nova scotia temporal relationships between cleavage formation and folding in sedimentary rock sequences can vary from either phenomena preceding the other to both occurring simultaneously knowledge of this relationship however is required to understand fully the relationship of cleavage orientation to finite strain and the origin of cleavage refraction across competent incompetent layers evidence from the goldenville formation provides an example of cleavage formed before folding by 50 pressure solution removal of material resulting in cleavage planes normal to bedding during active folding this layer parallel shortening was accompanied by excess pore pressure that in some cases exceeded lithostatic pressure causing formation of bedding parallel quartz veins with crack seal textures folds developed by a mechanism of differential flexural flow with no loss of coherence across bedding surfaces en echelon veins formed sequentially across some beds during active folding and subsequently were deformed by various increments of bedding parallel shear after folds reached 80 limb dips continued horizontal shortening was accommodated by additional pressure solution but no recognizable new cleavage was formed because cleavage in the goldenville formation formed perpendicular to bedding before folding and was passively rotated and extended by bedding parallel simple shear during fold amplification the resulting cleavage planes cannot lie in the xy plane of the finite strain ellipsoid differential shear between metagray wacke and slate beds accounts for the observed cleavage refraction and the bedding cleavage angle provides a good estimate of the shearing across these beds during active folding if cleavage can be shown to postdate folding in other examples it is possible that cleavage planes will lie in the xy plane of the finite strain ellipsoid

practical application of the sequential balancing technique an example from the irish variscides the process of sequential restoration presented by cooper trayner 1986 is applied to a n s cross section through the irish variscides to demonstrate that this approach improves the accuracy of thin skinned structural modelling and allows the progressive deformation of a marginal belt to be examined the principles and methods of sequential restoration are illustrated the cross section is restored in four steps and gives a bulk shortening of 52 in this model the fold belt evolved as the basal decollement migrated northwards and considerable ductile shortening by folding and cleavage formation preceded faulting although faulting gradually became more important towards the north the section is divided into four structural domains based upon different deformation histories each is restored independently by removing the ductile strain before restoring the faulting from this example it is clear that many models derived from single step balancing especially those through ductile deformed areas should be re examined

mechanics of low stress forearcs nankai and cascadia the nankai and cascadia subduction zones have low stress forearcs where the margin normal horizontal compressive stress is similar to or less than the vertical stress except in the accretionary prisms in the absence of active back arc spreading the forearc margin normal stress is controlled mainly by the total shear force along the subduction fault or the plate coupling force and the gravitational force the plate coupling force creates compression and the gravitational force in the presence of margin topography creates lateral tension we give a simple expression that relates the forearc stress to topography and average fault strength with the latter represented by an effective coefficient of friction we also use a finite element model of two converging plates in frictional contact to model the forearc stresses the analyses indicate that a low stress forearc requires not only the subduction fault to be very weak but also the mechanically coupled fault area to be narrow in the downdip direction and shallow in depth for nankai and cascadia where the coupled fault areas are narrow and shallow because of the young and hot subducting plates is about 0 05 or less and in any case less than 0 09 the low fault strength is probably not a unique property of low stress forearcs since the same low values combined with wider and deeper coupled areas can be shown to create large margin normal compression in addition there does not seem to be any relation between subduction earthquake magnitudes and plate coupling forces great earthquakes occur at subduction zones having low stress forearcs such as nankai and cascadia

impact of particle shape on saltating mode of bedload transport sheared by turbulent flow abstractthe saltating mode of sediment transport is the dominant mechanism of bedload transport in a fluvial stream especially in mountainous rivers in most simulation studies the actual shapes

experiments on saltation of sand in water a high speed video system was used to study saltation of sand in an open channel flow high rates of image acquisition provided the information needed to resolve details of the lagrangian properties of particle motion saltation of sand is described in terms of statistical properties of particle trajectories such as mean values and standard deviations of saltation length height and streamwise particle velocity results are compared with available empirical data saltation height seems to be independent of particle size when made dimensionless with the particle diameter however the dimensionless saltation length appears to increase as the particle size decreases particle collision with the bed is also analyzed observations of this process indicate that most of the interactions between saltating particles and the bed are of the collision rebound type which contradicts previous discussions on the subject the estimated value of the dynamic friction coefficient is about half that proposed by bagnold i

geological evidence for past large earthquakes and tsunamis along the hikurangi subduction margin new zealand abstract the hikurangi subduction margin new zealand has not produced large subduction earthquakes within the short written historic period 180 years and the potential of the plate interface to host large m 7 to great m 8 earthquakes and tsunamis is poorly constrained the geological record of past subduction earthquakes offers a method for assessing the location frequency and approximate magnitude of subduction earthquakes to underpin seismic and tsunami hazard assessments we review evidence of holocene coseismic coastal deformation and tsunamis at 22 locations along the margin a consistent approach to radiocarbon age modelling is used and earthquake and tsunami evidence is ranked using a systematic assessment of the quality of age control and the certainty that the event in question is an earthquake to identify possible subduction earthquakes we use temporal correlation of earthquakes combined with the type of earthquake evidence likely primary fault source and the earthquake certainty ranking we identify 10 past possible subduction earthquakes over the past 7000 years along the hikurangi margin the last subduction earthquake occurred at 520 470 years bp in the southern hikurangi margin and the strongest evidence for a full margin rupture is at 870 815 years bp there are no apparent persistent rupture patches suggesting segmentation of the margin is not strong in the southern margin the type of geological deformation preserved generally matches that expected due to rupture of the interseismically locked portion of the subduction interface but the southern termination of past subduction ruptures remains unresolved the pattern of geological deformation on the central margin suggests that the region of the interface that currently hosts slow slip events also undergoes rupture in large earthquakes demonstrating different modes of slip behaviour occur on the central hikurangi margin evidence for subduction earthquakes on the northern margin has not been identified because deformation signals from upper plate faults dominate the geological record large uncertainties remain in regard to evidence of past subduction earthquakes on the hikurangi margin with the greatest challenges presented by temporal correlation of earthquake evidence when working within the uncertainties of radiocarbon ages and the presence of upper plate faults capable of producing deformation and tsunamis similar to that expected for subduction earthquakes however areas of priority research such as improving the paleotsunami record and integration of submarine turbidite records should produce significant advances in the future

geometric analysis of fold development in overthrust terranes abstract fault bend folding fault propagation folding and detachment or decollement folding are three distinct scenarios for fold thrust interaction in overthrust terranes simple kink hinge models are used to determine the geometric associations implicit in each scenario bedding maintains constant thickness in the models except in the forelimb of the fold the forelimb is allowed to thicken or thin without limit the models address individual folds and the calculated fold geometries are balanced structures each mode of fold thrust interaction has a distinct set of geometric relationships final fold geometry is adequate in itself to discern many fault bend folds this is not the case for fault propagation and detachment folds these two fold forms have very similar geometric relationships some knowledge of the nature of the underlying thrust or decollement zone is usually needed to distinguish between them the geometry of a fold is altered in a predictable fashion by transport through an upper ramp hinge and by fault parallel shearing of the structure the shearing results in a tighter fold whereas transport through the ramp hinge produces a broader fold the viability of the geometric analysis technique is demonstrated through its application to a pair of detachment folds from the canadian cordillera the geometric analysis is also used to evaluate cross sections through subsurface structures in an example from the turner valley oil field the analysis indicates how the interpretation should be altered so as to balance the cross section the analysis reveals hidden assumptions and specific inconsistencies in structural interpretations

long distance fluid and heat transport in the oceanic crust entering the nankai subduction zone nantroseize transect abstract i examine the potential causes of anomalous seafloor heat flux on the oceanic plate in the nankai trough seismogenic zone experiment nantroseize transect offshore southern japan the most prominent anomaly is a 50 mw m 2 change in heat flux between integrated ocean drilling program sites c0011 and c0012 over a distance of 30 km wide transition at the seafloor the observed surface heat flux pattern is indicative of hydrothermal circulation in the basement aquifer and advection of heat from the subducted crust into the aquifer on the incoming plate for a 600 m thick aquifer the permeability is likely 7 10 11 m 2 and hydrothermal circulation transports at least 300 times more heat than conduction alone the heat flux from the subduction zone seaward to the incoming plate is consistent with hydrothermal circulation in the subducting crust persisting to 100 km landward of the deformation front vigorous fluid circulation in the basaltic basement is consistent with both the seafloor thermal anomalies and geochemical anomalies near the sediment basement interface

large heat and fluid fluxes driven through mid plate outcrops on ocean crust geophysical data for the cocos plate sea floor suggest that basement outcrops along mid ocean ridge flanks can discharge very large quantities of heat and fluid this is indicative of high crustal permeability at the regional scale

investigations of continuous bed load saltating process particle saltating motions during bed load transport are dominated by the forces acting upon particles and the random process of the particles impacting on and rebounding from the channel bed a real time flow visualization technique is developed in this study to measure particle saltating trajectories corresponding velocities and impacting and rebounding angles based on the experimental data regression equations for the dimensionless saltating length height and velocity were obtained a numerical model that is able to simulate the continuous saltating process of a single particle was developed the model was calibrated and verified with the experimental data and the results were satisfactory the model was also used to generate a series of synthetic data based on these data and the flume data collected by previous investigators a bed load equation was derived

thermal regime of the costa rican convergent margin 2 thermal models of the shallow middle america subduction zone offshore costa rica at the costa rica margin along the middle america trench along strike variations in heat flow are well mapped these variations can be understood in terms of either ventilated fluid flow where exposed basement allows fluids to freely advect heat between the crustal aquifer and ocean or insulated fluid flow where continuous sediment cover restricts heat advection to within the crustal aquifer we model fluid flow within the subducting aquifer using nusselt number approximations coupled with finite element models of subduction and explore its effect on temperatures along the subduction thrust the sensitivity of these models to the initial thermal state of the plate and styles of fluid flow either ventilated or insulated is explored heat flow measurements on cool crust accreted at the east pacific rise are consistent with ventilated hydrothermal cooling that continues with subduction these models yield much cooler temperatures than predicted from simulations initialized with conductive predictions and without hydrothermal circulation heat flow transects on warm crust accreted at the cocos nazca spreading center are consistent with models of insulated hydrothermal circulation that advects heat updip within the subducting crustal aquifer near the trench these models are warmer than conductive predictions and cooler than conductive predictions downdip of the trench comparisons between microseismicity and modeled isotherms suggest that the updip limit of microseismicity occurs at temperatures warmer than 100 c and that the downdip extent of microseismicity is bounded by the intersection of the subduction thrust with the base of the overriding crust

deep lithospheric structures along the southern central chile margin from wide angle p wave modelling p crustal and upper mantle structures of the subduction zone in south central chile between 42 degrees s and 46 degrees s are determined from seismic wide angle reflection and refraction data using the seismic ray tracing method to calculate minimum parameter models three profiles along differently aged segments of the subducting nazca plate were analysed in order to study subduction zone structure dependencies related to the age that is thermal state of the incoming plate the age of the oceanic crust at the trench ranges from 3 ma on the southernmost profile immediately north of the chile triple junction to 6 5 ma old about 100 km to the north and to 14 5 ma old another 200 km further north off the island of chiloe remarkable similarities appear in the structures of both the incoming as well as the overriding plate the oceanic nazca plate is around 5 km thick with a slightly increasing thickness northward reflecting temperature changes at the time of crustal generation the trench basin is about 2 km thick except in the south where the chile ridge is close to the deformation front and only a small 800 m thick trench infill could develop in south central chile typically three quarters 1 5 km of the trench sediments subduct below the decollement in the subduction channel to the north and south of the study area only about one quarter to one third of the sediments subducts the rest is accreted above similarities in the overriding plate are the width of the active accretionary prism 35 50 km and a strong lateral crustal velocity gradient zone about 75 80 km landward from the deformation front where landward upper crustal velocities of over 5 0 5 4 km s su 1 su decrease seaward to around 4 5 km s su 1 su within about 10 km which possibly represents a palaeo backstop this zone is also accompanied by strong intraplate seismicity differences in the subduction zone structures exist in the outer rise region where the northern profile exhibits a clear bulge of uplifted oceanic lithosphere prior to subduction whereas the younger structures have a less developed outer rise this plate bending is accompanied by strongly reduced rock velocities on the northern profile due to fracturing and possible hydration of the crust and upper mantle the southern profiles do not exhibit such a strong alteration of the lithosphere although this effect may be counteracted by plate cooling effects which are reflected in increasing rock velocities away from the spreading centre overall there appears little influence of incoming plate age on the subduction zone structure which may explain why the m w 9 5 great chile earthquake from 1960 ruptured through all these differing age segments the rupture area however appears to coincide with a relatively thick subduction channel

cleavage strain in the variscan fold belt county cork ireland estimated from stretched arsenopyrite rosettes abstract in south west ireland hydrothermally formed arsenopyrite crystals in a devonian mudstone have responded to variscan deformation by brittle extension fracture and fragment separation the interfragment gaps and terminal extension zones of each crystal are infilled with fibrous quartz stretches within the cleavage plane have been calculated by the various methods available most of which can be modified to incorporate terminal extension zones the strain reversal method is the most accurate currently available but still gives a minimum estimate of the overall strain the more direct hossain method which gives only slightly lower estimates with this data is more practical for field use a strain ellipse can be estimated from each crystal rosette composed of three laths assuming the original interlimb angles were all 60 and because actual rather than relative stretches are estimated this provides a lower bound to the area increase in the plane of cleavage based on the average of our calculated strain ellipses this area increase is at least 114 and implies an average shortening across the cleavage of at least 53 however several lines of evidence suggest that the cleavage deformation was more intense and more oblate than that calculated and we argue that a 300 area increase in the cleavage plane and 75 shortening across the cleavage are more realistic estimates of the true strain furthermore the along strike elongation indicated is at least 80 which may be regionally significant estimates of orogenic contraction derived from balanced section construction should therefore take into account the possibility of a substantial strike elongation and tectonic models that can accommodate such elongations need to be developed

segmentation and supercycles a catalog of earthquake rupture patterns from the sumatran sunda megathrust and other well studied faults worldwide abstract after more than 100 years of earthquake research earthquake forecasting which relies on knowledge of past fault rupture patterns has become the foundation for societal defense against seismic natural disasters a concept that has come into focus more recently is that rupture segmentation and cyclicity can be complex and that a characteristic earthquake model is too simple to adequately describe much of fault behavior nevertheless recognizable patterns in earthquake recurrence emerge from long high resolution spatially distributed chronologies researchers now seek to discover the maximum minimum and typical rupture areas the distribution variability and spatial applicability of recurrence intervals and patterns of earthquake clustering in space and time the term supercycle has been used to describe repeating longer periods of elastic strain accumulation and release that involve multiple fault ruptures however this term has become very broadly applied lumping together several distinct phenomena that likely have disparate underlying causes we divide earthquake cycle behavior into four major classes that have different implications for seismic hazard and fault mechanics 1 quasi periodic similar ruptures 2 clustered similar ruptures 3 clustered complementary ruptures rupture cascades and 4 superimposed cycles segmentation is likewise an ambiguous term we identify master segments and asperities as defined by barriers to fault rupture these barriers may be persistent rarely or never traversed frequent occasionally traversed or ephemeral changing location from cycle to cycle we compile a catalog of the historical and paleoseismic evidence that currently exists for each of these types of behavior on major well studied faults worldwide due to the unique level of paleoseismic and paleogeodetic detail provided by the coral microatoll technique the sumatran sunda megathrust provides one of the most complete records over multiple earthquake rupture cycles long historical records of earthquakes along the south american and japanese subduction zones are also vital contributors to our catalog along with additional data compiled from subduction zones in cascadia alaska and middle america as well as the north anatolian and dead sea strike slip faults in the middle east we find that persistent and frequent barriers rupture cascades superimposed cycles and quasi periodic similar ruptures are common features of most major faults clustered similar ruptures do not appear to be common but broad overlap zones between neighboring segments do occur barrier regions accommodate slip through reduced interseismic coupling slow slip events and or smaller more localized ruptures and are frequently associated with structural features such as subducting seafloor relief or fault trace discontinuities this catalog of observations provides a basis for exploring and modeling root causes of rupture segmentation and cycle behavior we expect that researchers will recognize similar behavior styles on other major faults around the world

the 1960 chile earthquake inversion for slip distribution from surface deformation summary a total of 166 observations of sea level change 130 measurements of elevation difference and 16 determinations of horizontal strain provide an excellent view of the quasi static source process of the great 1960 chilean earthquake these surface deformation data were employed in classical uniform slip fault models as well as more recently developed models that allow spatial variability of slip the best uniform slip planar usp model is 850km long 130km wide and dips 20 seventeen metres of fault displacement contributed to a usp moment of 9 4 times 1022 n m the variable slip planar vsp model concentrates slip on a 900 km long 150 km wide band parallel to the coast several peaks of slip with dimensions of 50 100 km appear in this band and are thought to represent major subduction zone asperities important fractures of the oceanic lithosphere bound the 1960 rupture and are offered as a potential source of fault segmentation within the chilean subduction zone the vsp moment for 1960 earthquake totals 9 5 times 1022 n m about one fifth of the value estimated for the foreshock mainshock sequence from seismic methods except for areas out to sea geodetic resolution on the fault is fairly uniform thus it is unlikely that slip missed by the network could increase the vsp moment much beyond 1 8 times 1023 n m several patches of moment isolated from the main body at 80 110 km depth are found down dip in the vsp model and are presumably indicative of aseismic slip one patch at the northern end of the rupture is probably associated with the initiation phase of the mainshock although the time sequence of the relationship is unknown tide gauge records suggest that another patch between 40 and 43 s responsible for the observed strain and uplifts inland at those latitudes is not of coseismic origin but derives from in place post seismic creep over several years apparently great 1960 type events are not typical members of the 128 yr earthquake cycle in south central chile the nazca south america boundary here is characterized by a variable rupture mode in which major asperities are completely broken by great earthquakes only once in four or five earthquake cycles the more frequent large earthquakes that geographically overlap the great events fill in between the locked zones

episodic development of a convergent margin inferred from structures and processes along the southern chile margin seismic reflection data acquired in the vicinity of isla mocha across the southern coast of chile image structures formed along the continental margin and reveal an episodic history of accretion nonaccretion and possibly erosion structures formed at the toe of the continental slope suggest frontal accretion of to 1 km of trench fill seismic images also reveal that a small accretionary wedge 20 30 km wide abuts the truncated continental metamorphic basement that extends seaward from beneath the shelf the small size of the accretionary wedge on three profiles examined here is not consistent with a long history of accretion with the current deformational style as current rates of frontal accretion could have accumulated all of the existing accretionary wedge in less than 1 2 m y this is a small fraction of convergence history along this margin and the current accretionary mode has not been consistently maintained in the past the isla mocha region is located between the temperate climate of central chile and the glacial climate of southern chile and climatic conditions in this region have likely fluctuated sufficiently to cause significant variation in trench sediment supply accretionary and nonaccretionary or erosional episodes are probably linked to temporal variations in trench sediment thickness as suggested by observations along the chile margin currently thick trench sediment correlates with accretion along the southern chile margin and thin trench sediment correlates with nonaccretion tectonic erosion as near the chile ridge and from the juan fernandez ridge to northern chile the isla mocha region also lies 900 1000 km north of the chile triple junction and the chile ridge lies approximately 2000 km to the west and has not yet collided and affected the margin near isla mocha this part of the precollision zone provides an excellent reference to examine the effects of chile ridge collision in the development of the chile margin the most apparent effect of subduction of the buoyant young crust of the chile ridge is a shallow trench that is nearly devoid of sediment consequently the triple junction is undergoing nonaccretion or erosion and the accretionary complex near the triple junction remains smaller than to the north or south because the current phase of rapid accretion elsewhere in the trench has bypassed the triple junction region the interplay of subduction zone processes such as trench sedimentation and ridge collision has resulted in an episodic development of the margin and produced a discontinuous record of convergence history within the accretionary wedge

a note on photography in structural geology abstract when photographs of outcrops are required for detailed and or accurate structural work the photographic image should be parallel to the outerop surface a method has been developed which allows oblique photographs to be corrected when processed the method imposes certain restrictions on the combinations of camera and enlarger lenses which will yield a correctly proportioned print and graphs are presented which predict suitable combinations for a wide range of conditions the technique has been successfully applied to several problems one of which is presented as an illustrative example

coastal lake sediments reveal 5500 years of tsunami history in south central chile abstract we present an exceptionally long and continuous coastal lacustrine record of 5500 years from lake huelde on the west coast of chiloe island in south central chile the study area is located within the rupture zone of the giant 1960 ce great chilean earthquake mw 9 5 the subsequent earthquake induced tsunami inundated lake huelde and deposited mud rip up clasts massive sand and a mud cap in the lake long sediment cores from 8 core sites within lake huelde reveal 16 additional sandy layers in the 5500 year long record the sandy layers share sedimentological similarities with the deposit of the 1960 ce tsunami and other coastal lake tsunami deposits elsewhere on the basis of general and site specific criteria we interpret the sandy layers as tsunami deposits age control is provided by four different methods 1 210pb dating 2 the identification of the 137cs peak 3 an infrared stimulated luminescence irsl date and 4 22 radiocarbon dates the ages of each tsunami deposit are modelled using the bayesian statistic tools of oxcal and bacon the record from lake huelde matches the 8 regionally known tsunami deposits from documented history and geological evidence from the last 2000 years without over or underrepresentation we extend the existing tsunami history by 9 tsunami deposits we discuss the advantages and disadvantages of various sedimentary environments for tsunami deposition and preservation e g we find that lake huelde is 2 3 times less sensitive to relative sea level change in comparison to coastal marshes in the same region

low frequency source characteristics of the great 1960 chilean earthquake the low frequency nature of the great 1960 chilean earthquake the earth s largest recorded event is characterized and a source model composed of three events with a combined seismic moment of 5 5 1023 n m and a duration of 1500 s is presented the results show conclusively that large scale slip which is only observed at low frequencies preceded the main shock complex amplitude measurements of normal mode data in the band 1 0 5 0 mhz recorded at eight vertical component stations comprise the data set in this band the earthquake source is assumed to be described by a line source propagating at a constant rupture velocity the data set is the basis for a sequence of least squares inversions to determine the seismic moment rupture velocity spatial slip distribution and the temporal slip function the data are best explained by a source model that begins 1150 s before the main shock with an event of moment 1 9 1023 n m and rise time of 300 s a main shock with moment of 3 2 1023 n m and for which most of the low frequency energy was released beginning about 50 s after the short period origin time and an event 350 s later with moment of 0 4 1023 n m the uncertainty in the moment estimate of the great 1960 chilean earthquake is about 50 and is due primarily to the probable range of fault plane dip which is not well constrained at this time

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

stratigraphic controls on eformation patterns in fault related folds a detachment fold example from the sierra madre oriental northeast mexico abstract deformation patterns are described by the style intensity and distribution of structures throughout a volume of rock in fault related folds presently observed deformation patterns are controlled by structural factors like kinematic history environmental factors like burial history and stratigraphic factors like layer thickness and competence to demonstrate the role of stratigraphy in controlling fold related deformation patterns we document the stratigraphic variability of mesostructures at one structural position on a map scale detachment fold unique assemblages of faults fractures and cleavages in certain stratigraphic intervals define a mechanical stratigraphy comprised of several units each exhibiting a characteristic deformation response to the folding process the varying response of each mechanical unit suggests that folding mechanisms such as orthogonal flexure flexural slip or flexural flow were sequentially or coevally operative in each of the units using the simple theoretical strain distributions associated with each folding mechanism and the fact that each mechanical unit accommodates fold related strain by developing a characteristic set of mesostructures we are able to predict general deformation patterns elsewhere in the fold the significance of this approach is that it recognizes that even in a single structure fold kinematics and deformation response may be dramatically different in various parts of a stratigraphic section because of this the quality and character of reservoir rocks in anticlinal traps may change markedly over short stratigraphic distances predictions of fold related deformation based solely on fold kinematics are unlikely to resolve these variations

the evolution of a thick shallow marine succession the south munster basin ireland the relatively fine grained late devonian to early carboniferous cork beds succession of the south munster basin includes continuous sections of paralic facies that are over 1000 m thick and individual sandstone units over 300 m thick however the succession does not reflect prolonged phases when facies belts were stationary but rather multiple stacking of small scale high frequency sequences each associated with pronounced migration of shorelines what seems to have been unusual about the south munster basin succession was that the geographical positioning of these high frequency sequences was fixed this resulted from an unusual combination of tectonics shelf hydrodynamics sedimentation rates and the textural maturity of the sediment within the basin of these tectonics was probably most critical particularly the juxtaposition of rapid subsidence in basinal areas and a basin margin zone to the north that was sufficiently up standing to pin the maximum extent of transgression during repeated highstands of sea level yet not so upstanding as to have diverted the major regional drainage system the embayed palaeogeography of the area may also have been influential

the southern andes between 36 and 40 s latitude seismicity and average seismic velocities abstract the project issa 2000 integrated seismological experiment in the southern andes consists of a temporary seismological network and a seismic refraction profile a network of 62 seismological stations was deployed across the southern andes at 38 s three hundred thirty three local seismic events were observed in a 3 month period p and s arrival times of a subset of high quality data were inverted simultaneously for 1 d velocity structure hypocentral coordinates and station delays seismic refraction data along a transect at 39 s provide further constraints on the crustal structure low crustal velocities beneath the forearc may be either due to subducted trench sediments or serpentinized mantle material of the continental lithosphere the continental moho is not clearly observed in this region average velocities of the crust beneath the arc are higher than those beneath the forearc crustal thickness is about 40 km crustal seismicity concentrates in the forearc region along the bio bio and gastre fault zones the area between these two prominent fault zones seems to be nearly devoid of crustal seismicity but shows highest uplift and topography in the forearc region benioff seismicity is observed down to 150 km depth resulting in the first accurate image of the benioff zone in the southern andes a maximum of seismicity at 60 km depth may be caused by dehydration embrittlement

numerical simulation of turbulence and sediment transport of medium sand a model of sand transport in water is produced by combining a turbulence resolving large eddy simulation les with a discrete element model dem prescribing the motion of individual grains of medium sand the momentum effect of each particle on the fluid is calculated at the les cell containing the particle and the fluid velocity and pressure interpolated to each particle center is used to derive fluid force on each particle in the dem eleven numerical experiments are conducted of an initially flat bed of particles the experiments span a range of motion from essentially no motion to vigorous suspension hydraulic roughness is found to increase abruptly at the transition from bed load to suspended load transport suspended sediment extracts momentum from the flow and decreases the rate of shear whereas slightly higher in the flow vertical drag by suspended grains damps turbulence and increases the rate of shear vertical sediment diffusivity and effective particle settling velocity are much smaller than is commonly assumed in suspended sediment models the bed load experiments suggest that saltation by itself is a poor model of bed load sand transport in contrast to expectations from saltation models the peak bed load flux occurs at essentially the same level as the bed and grains move slowly in frequent contact with other grains higher and faster moving bed load grains that can be considered to be in saltation represent a smaller portion of the total flux entrainment of bed load grains occurs in response to fluid penetration of the bed by high vorticity turbulence structures embedded within broader high speed fluid regions referred to as a sweeps or high speed wedges

conical fold terminations in the bannisdale slates of the english lake district abstract the structure of an area of silurian rocks in the non metamorphic caledonides near kendal cumbria u k is briefly described the main folds are periclinal and die away in the southeast of the area the uniform thickness of sandstone beds around folds shows that they deformed dominantly by buckling and only locally is flattening important a model is developed to explain the conical attitude of bedding within the periclinal terminations the model is erected on the basis of buckling alone and is developed to examine the effects of flattening inhomogeneity in buckling and flattening over the area is demonstrated using the model and discussed the pattern of folding is compared to that predicted by earlier published experimental work

a chronology of foreland deformation ultra violet laser 40ar 39ar dating of syn late orogenic intrusions from the variscides of southwest ireland abstract the upper palaeozoic sedimentary rocks of the munster and south munster basins southern ireland lie within the rhenohercynian zone of the european variscan orogeny this foreland region accommodated shortening during the asturian phase of variscan deformation at the end of the carboniferous by the development of kilometre scale and lower order folding high angle reverse faulting and regional fabric development at the southwestern extremity of the belt lies the black ball white ball heads area of the beara peninsula where high level igneous intrusions locally exhibit a close relationship with both the ductile and late brittle phases of variscan deformation 40 ar 39 ar ultra violet laser analysis of phlogopite crystals from these intrusions principally trachytic dykes has yielded ages that when combined with structural field relationships help to constrain the timing of variscan deformation in southern ireland these ages include 314 44 1 00 ma for a penetratively deformed lamprophric pipe on black ball head 301 98 1 47 298 08 0 61 ma for dyke material associated with later stage brittle deformation and a date of 296 88 0 60 ma for an undeformed post orogenic dyke on white ball head

reawakening of large earthquakes in south central chile the 2016 mw 7 6 chiloe event on 25 december 2016 the mw 7 6 chiloe earthquake broke a plate boundary asperity in south central chile near the center of the rupture zone of the mw 9 5 valdivia earthquake of 1960 to gain insight on decadal scale deformation trends and their relation with the chiloe earthquake we combine geodetic teleseismic and regional seismological data gps velocities increased at continental scale after the 2010 maule earthquake probably due to a readjustment in the mantle flow and an apparently abrupt end of the viscoelastic mantle relaxation following the 1960 valdivia earthquake it also produced an increase in the degree of plate locking the chiloe earthquake occurred within the region of increased locking breaking a circular patch of 15 km radius at 30 km depth located near the bottom of the seismogenic zone we propose that the chiloe earthquake is a first sign of the seismic reawakening of the valdivia segment in response to the interaction between postseismic viscoelastic relaxation and changes of interseismic locking between nazca and south america

tectonic control on sediment accretion and subduction off south central chile implications for coseismic rupture processes of the 1960 and 2010 megathrust earthquakes based on a compilation of published and new seismic refraction and multichannel seismic reflection data along the south central chile margin 33 46 s we study the processes of sediment accretion and subduction and their implications on megathrust seismicity in terms of the frontal accretionary prism fap size the marine south central chile fore arc can be divided in two main segments 1 the maule segment south of the juan fernandez ridge and north of the mocha block characterized by a relative large fap 20 40 km wide and 2 the chiloe segment south of the mocha block and north of the nazca antarctic south america plates junction characterized by a small fap 10 km wide in addition the maule and chiloe segments correlate with a thin 1 km thick and thick 1 5 km thick subduction channel respectively the mocha block lies between 37 5 and 40 s and is configured by the chile trench mocha and valdivia fracture zones this region separates young 0 25 ma oceanic lithosphere in the south from old 30 35 ma oceanic lithosphere in the north and it represents a fundamental tectonic boundary separating two different styles of sediment accretion and subduction respectively a process responsible for this segmentation could be related to differences in initial angles of subduction which in turn depend on the amplitude of the down deflected oceanic lithosphere under trench sediment loading on the other hand a small fap along the chiloe segment is coincident with the rupture area of the trans pacific tsunamigenic 1960 earthquake mw 9 5 while a relatively large fap along the maule segment is coincident with the rupture area of the 2010 earthquake mw 8 8 differences in earthquake and tsunami magnitudes between these events can be explained in terms of the fap size along the chiloe and maule segments that control the location of the updip limit of the seismogenic zone the rupture area of the 1960 event also correlates with a thick subduction channel chiloe segment that may provide enough smoothness at the subduction interface allowing long lateral earthquake rupture propagation

the effects on tsunami hazard assessment in chile of assuming earthquake scenarios with spatially uniform slip we investigated the effect that along dip slip distribution has on the near shore tsunami amplitudes and on coastal land level changes in the region of central chile 29 37 s here and all along the chilean megathrust the seismogenic zone extends beneath dry land and thus tsunami generation and propagation is limited to its seaward portion where the sensitivity of the initial tsunami waveform to dislocation model inputs such as slip distribution is greater we considered four distributions of earthquake slip in the dip direction including a spatially uniform slip source and three others with typical bell shaped slip patterns that differ in the depth range of slip concentration we found that a uniform slip scenario predicts much lower tsunami amplitudes and generally less coastal subsidence than scenarios that assume bell shaped distributions of slip although the finding that uniform slip scenarios underestimate tsunami amplitudes is not new it has been largely ignored for tsunami hazard assessment in chile our simulations results also suggest that uniform slip scenarios tend to predict later arrival times of the leading wave than bell shaped sources the time occurrence of the largest wave at a specific site is also dependent on how the slip is distributed in the dip direction however other factors such as local bathymetric configurations and standing edge waves are also expected to play a role arrival time differences are especially critical in chile where tsunamis arrive earlier than elsewhere we believe that the results of this study will be useful to both public and private organizations for mapping tsunami hazard in coastal areas along the chilean coast and therefore help reduce the risk of loss and damage caused by future tsunamis

subduction zone slip variability during the last millennium south central chile abstract the arauco peninsula 37 38 s in south central chile has been proposed as a possible barrier to the along strike propagation of megathrust ruptures separating historical earthquakes to the south 1960 ad 1837 1737 and 1575 and north 2010 ad 1835 1751 1657 and 1570 of the peninsula however the 2010 mw 8 8 earthquake propagated into the arauco peninsula re rupturing part of the megathrust that had ruptured only 50 years earlier during the largest subduction zone earthquake in the instrumental record mw 9 5 to better understand long term slip variability in the arauco peninsula region we analyzed four coastal sedimentary sections from two sites tirua 38 3 s and quidico 38 1 s located within the overlap of the 2010 and 1960 ruptures to reconstruct a 600 year record of coseismic land level change and tsunami inundation stratigraphic lithologic and diatom results show variable coseismic land level change coincident with tsunami inundation of the tirua and quidico marshes that is consistent with regional historical accounts of coseismic subsidence during earthquakes along the valdivia portion of the subduction zone 1960 ad and 1575 and coseismic uplift during earthquakes along the maule portion of the subduction zone 2010 ad 1835 1751 in addition we document variable coseismic land level change associated with three new prehistoric earthquakes and accompanying tsunamis in 1470 1570 ad 1425 1455 and 270 410 the mixed record of coseismic subsidence and uplift that we document illustrates the variability of down dip and lateral slip distribution at the overlap of the 2010 and 1960 ruptures showing that ruptures have repeatedly propagated into but not through the arauco peninsula and suggesting the area has persisted as a long term impediment to slip through at least seven of the last megathrust earthquakes 600 years

heterogeneous plate locking in the south central chile subduction zone building up the next great earthquake abstract we use global positioning system gps velocities and kinematic finite element models fe models to infer the state of locking between the converging nazca and south america plates in south central chile 36 s 46 s and to evaluate its spatial and temporal variability gps velocities provide information on earthquake cycle deformation over the last decade in areas affected by the megathrust events of 1960 m w 9 5 and 2010 m w 8 8 our data confirm that a change in surface velocity patterns of these two seismotectonic segments can be related to their different stages in the seismic cycle accordingly the northern 2010 segment was in a final stage of interseismic loading whereas the southern 1960 segment is still in a postseismic stage and undergoes a prolonged viscoelastic mantle relaxation after correcting the signals for mantle relaxation the residual gps velocity pattern suggests that the plate interface accumulates slip deficit in a spatially and presumably temporally variable way towards the next great event though some similarity exist between locking and 1960 coseismic slip extrapolating the current decadal scale slip deficit accumulation towards the 300 yr recurrence times of giant events here does neither yield the slip distribution nor the moment magnitude of the 1960 earthquake this suggests that either the locking pattern is evolving in time to reconcile a slip deficit distribution similar to the 1960 earthquake or that some asperities are not persistent over multiple events the accumulated moment deficit since 1960 suggests that highly locked patches in the 1960 segment are already capable of producing a m 8 event if triggered to fail by stress transfer from the 2010 event

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

tectono sedimentary ripples in devonian shallow marine siliciclastic sediments southern ireland abstract tectonically altered sedimentary ripples occur commonly in the marine devonian old head sandstone formation of southern ireland these tectono sedimentary ripples are dominantly wave produced and have sharp v shaped troughs where spaced pressure solution cleavage surfaces are located at a high angle to bedding the ripples control the spacing of cleavage and influence cleavage orientation the profile shape of the ripple is a function of stress refraction and concentration within the stiff sandstone layers of a multilayer sequence ripple symmetry is affected by tectonic deformation which plays an important role in the development of tectono sedimentary ripples tectonically flattened wave produced ripples occur where cleavage is oriented parallel to bedding due to an anomalous deformation in the old head sandstone formation at galley head selected ripple profiles have been undeformed by computer simulation to reconstruct ancient wave conditions this use of tectono sedimentary ripples for this purpose has its limitations and a number of guidelines are given for application of this technique elsewhere

source study and tectonic implications of the historic 1958 las melosas crustal earthquake chile compared to earthquake damage abstract the 4 september 1958 earthquake has been the largest event recorded at shallow depths in the western flank of the andes on chilean territory new estimates of fault orientation depth and size have been carried out using modern techniques of body wave modeling two possible fault planes solutions with right lateral displacement on an east west fault or left lateral displacement on a north south fault nucleated at 5 9 km depth produce the best fit to teleseismic recordings a seismic moment m0 of 0 227 1019 n m associated with a moment magnitude mw of 6 3 has been estimated with these techniques which is a more reliable estimation of earthquake size than the 0 4 0 7 units larger surface wave magnitude ms earlier reported although no surface rupture for the 1958 las melosas crustal earthquake was reported the displacement along east west structures like that one suggested for one of the fault plane in our focal mechanism solution seems to be an efficient mechanism to accommodate differences in shortening from north to south in the high andean cordillera reports on damage landslide effects as well as re analysis of intensities associated with the new seismic source estimations for the 1958 las melosas earthquake are presented to further estimate the hazard to which this zone and others along the western foothills of the andes is exposed

alteration of the subducting oceanic lithosphere at the southern central chile trench outer rise hydrothermal circulation and brittle faulting processes affecting the oceanic lithosphere are usually confined to the upper crust for oceanic lithosphere created at intermediate to fast spreading rates lower crust and mantle rocks are therefore relatively dry and undeformed however recent studies at subduction zones suggest that hydration of the oceanic plate is most vigorous at the trench outer rise where extensional bending related faulting affects the hydrogeology of the oceanic crust and mantle to understand the degree of hydration we studied the seismic velocity structure of the incoming nazca plate offshore of southern central chile 43 s here the deep sea trench is heavily filled with up to 2 km of sediments seismic refraction and wide angle data complemented by seismic reflection imaging of sediments are used to derive a two dimensional velocity model using joint refraction and reflection traveltime tomography the seismic profile runs perpendicular to the spreading ridge and trench axes the velocity model derived from the tomography inversion consists of a 5 3 km thick oceanic crust and shows p wave velocities typical for mature fast spreading crust in the seaward section of the profile with uppermost mantle velocities as fast as 8 3 km s approaching the chile trench seismic velocities are significantly reduced however suggesting that the structures of both the oceanic crust and uppermost mantle have been altered possibly due to a certain degree of fracturing and hydration the decrease of the velocities roughly starts at the outer rise 120 km from the deformation front and continues into the trench even though the trench is filled with sediment basement outcrops in the outer rise frequently pierce the sedimentary blanket anomalously low heat flow values near outcropping basement highs indicate an efficient inflow of cold seawater into the oceanic crust hydration and crustal cracks activated by extensional bending related faulting are suggested to govern the reduced velocities in the vicinity of the trench considering typical flow distances of 50 km water might be redistributed over most of the trench outer rise area where trapped in faults seawater may migrate down to mantle depth causing up to 9 of serpentinization in at least the uppermost 2 km of the mantle between the outer rise and the trench axis

seismo turbidites in aysen fjord southern chile reveal a complex pattern of rupture modes along the 1960 megathrust earthquake segment grainsize analysis and end member modeling of a long sediment core from aysen fjord southern chile allows to identify over 25 seismo turbidites in the last 9 000 years considering the shaking intensities required to trigger these turbidites v1 2 vi1 2 the majority can be related to megathrust earthquakes multiple studies in south central chile have aimed at finding traces of giant tsunamigenic megathrust earthquakes leading to the current 5 500 year long paleoseismological record of the valdivia segment however none of these cover the southern third of the segment aysen fjord allows to fill this data gap and presents the first crucial paleoseismic data to demonstrate that the 1960 event was not unique for the valdivia segment yielding a recurrence rate of 321 116 years in the last two millennia moreover the oldest identified events in aysen fjord date back to 9 000 cal years bp and thus also extend the regional paleoseismological record in time we infer a large temporal variability in rupture modes with successions of full segment ruptures alternating with partial and cascading ruptures the latter seems to significantly postpone the occurrence of another full rupture when consecutively occurring in different parts of the segment additionally one outstanding period of seismic quiescence during which no megathrust earthquake evidence has been found at any paleoseismic site occurred after a full rupture in ad similar to 745 that presents an unusual uplift subsidence pattern such variability makes it highly speculative to anticipate the rupture mode of the next megathrust earthquake along the valdivia segment

impact of megathrust geometry on inversion of coseismic slip from geodetic data application to the 1960 chile earthquake 1 we analyze the role of megathrust geometry on slip estimation using the 1960 chile earthquake mw 9 5 as an example a variable slip distribution for this earthquake has been derived by barrientos and ward 1990 applying an elastic dislocation model with a planar fault geometry their model shows slip patches at 80 110 km depth isolated from the seismogenic zone interpreted as aseismic slip we invert the same geodetic data set using a finite element model fem with precise geometry derived from geophysical data isoparametric fem is implemented to constrain the slip distribution of curve shaped elements slip resolved by our precise geometry model is limited to the shallow region of the plate interface suggesting that the deep patches of moment were most likely an artifact of the planar geometry our study emphasizes the importance of fault geometry on slip estimation of large earthquakes

reexamination of the magnitudes for the 1906 and 1922 chilean earthquakes using japanese tsunami amplitudes implications for source depth constraints far field tsunami records from the japanese tide gauge network allow the reexamination of the moment magnitudes mw for the 1906 and 1922 chilean earthquakes which to date rely on limited information mainly from seismological observations alone tide gauges along the japanese coast provide extensive records of tsunamis triggered by six great mw 8 chilean earthquakes with instrumentally determined moment magnitudes these tsunami records are used to explore the dependence of tsunami amplitudes in japan on the parent earthquake magnitude of chilean origin using the resulting regression parameters together with tide gauge amplitudes measured in japan we estimate apparent moment magnitudes of mw 8 0 8 2 and mw 8 5 8 6 for the 1906 central and 1922 north central chile earthquakes the large discrepancy of the 1906 magnitude estimated from the tsunami observed in japan as compared with those previously determined from seismic waves ms 8 4 suggests a deeper than average source with reduced tsunami excitation a deep dislocation along the chilean megathrust would favor uplift of the coast rather than beneath the sea giving rise to a smaller tsunami and producing effects consistent with those observed in 1906 the 1922 magnitude inferred from far field tsunami amplitudes appear to better explain the large extent of damage and the destructive tsunami that were locally observed following the earthquake than the lower seismic magnitudes ms 8 3 that were likely affected by the well known saturation effects thus a repeat of the large 1922 earthquake poses seismic and tsunami hazards in a region identified as a mature seismic gap

structural evolution of the irish variscides the effects of the variscan orogeny on the upper palaeozoic succession are recognizable throughout central and southern ireland the deformation can be zoned using structural styles and trends which illustrate a northward decrease in deformation intensity coupled with increasing control by pre variscan structures in the basement the most intense deformation occurs to the south of the dingle dungarvan line where shortening approaches 50 as a result of layer parallel shortening followed by buckling and finally thrusting the deformation is considered to have developed above a shallow dipping sole thrust which has been located offshore by the swat seismic reflection profiles cross faults which are common throughout the orogen resulted from n s shear couples this is consistent with their origin as accommodation structures due to differential shortening along strike the original shape of the munster basin has exerted a control on the distribution and overall facing of the major structures the sole thrust extends to the north of the dingle dungarvan line and the structural zonation of the orogen is due to variations in the stratigraphic level of this thrust the leinster massif is considered to be essentially autochthonous slip on the sole thrust decays towards the massif which acted as a rigid passive block and was partially responsible for the arcuate trend of the orogen

the discovery of a new devonian tetrapod trackway in sw ireland a tetrapod trackway has been discovered in devonian sedimentary rocks of sw ireland it is the first discovery of its kind in europe details of the footprints are not preserved probably because of strong variscan pressure solution cleavage however after removing the effect of variscan deformation the large number of footprints more than 150 makes it possible to calculate the original dimensions of the footprint pattern stride approximately 34 cm and pace approximately 35 cm these values are higher than those for other traces of comparable age the total length of the tetrapod is estimated to be 1 m lithostratigraphical and biostratigraphical arguments indicate an age of mid to late devonian

hydrothermal circulation in subducting crust reduces subduction zone temperatures most thermal models of subduction zones assume no advection of heat by fluid flow because slow flow through underthrusting sediment the decollement and wedge likely transports only a minor amount of heat we model coupled fluid and heat transport in a subduction zone and show that hydrothermal circulation in subducting basaltic basement rocks can have a great influence on subduction zone temperatures fractured basaltic basement has permeability several orders of magnitude higher than a typical decollement allowing fluid circulation to redistribute and extract heat from a subduction zone we simulate systems with upper basaltic basement permeability ranging from 10 13 to 10 10 m2 in addition we incorporate the effect of permeability reduction within the basaltic basement as it is subducted the models with fluid transport show suppressed temperatures along the subducting slab relative to models with no fluid transport with continuous sediment cover heat is extracted from under the margin wedge to the trench in models where faulted ocean crust exposes high permeability basement to the ocean floor cooling from ocean bottom water results in highly suppressed heat flow relative to conductive models hydrothermally cooled ocean crust also acts to slow thermally controlled diagenetic reaction progress within subducting sediment

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

first seismic record for intra arc strike slip tectonics along the liquine ofqui fault zone at the obliquely convergent plate margin of the southern andes a temporal seismic network recorded local seismicity along a 130 km long segment of the transpressional dextral strike slip liquine ofqui fault zone lofz in southern chile seventy five shallow crustal events with magnitudes up to m tief w 3 8 and depths shallower than 25 km were observed in an 11 month period mainly occurring in different clusters those clusters are spatially related to the lofz to the volcanoes chaiten michinmahuida and corcovado and to active faulting on secondary faults further activity along the lofz is indicated by individual events located in direct vicinity of the surface expression of the lofz focal mechanisms were calculated using deviatoric moment tensor inversion of body wave amplitude spectra which mostly yield strike slip mechanisms indicating a ne sw direction of the p axis for the lofz at this latitude the seismic activity reveals the present day activity of the fault zone the recent m tief w 6 2 event near puerto aysen southern chile at 45 4 s on april 21 2007 shows that the lofz is also capable of producing large magnitude earthquakes and therefore imposing significant seismic hazard to this region

orogen parallel extension and oblique tectonics the relation between stretching lineations and relative plate motions many collisional orogens exhibit two distinct deformation phases the first and relatively early phase forms within an obliquely subducting continent and is characterized by regionally consistent stretching lineations subparallel to the orogen and to associated isoclinal and sheath folds second phase folds and stretching lineations develop during and after imbrication of the subducting plate into the overriding plate and they become progressively disharmonic with stretching lineations oriented perpendicular to the orogen structural morphology and stretching lineations indicate that a fundamental kinematic transition occurs as material is imbricated from footwall to hanging wall kinematic modeling based on modern oblique convergent boundaries and considerations of buoyancy forces suggest that only the relatively early structures reflect the relative plate motion but that the correspondence is not simple in particular the orientation of stretching lineations is a function of finite strain kinematics of deformation and angle of subduction and convergence and it will consistently underestimate the angle of oblique convergence second phase structures reflect isostatic emergence of the hanging wall and are independent of relative plate convergence examples are drawn from the south central canadian rockies the western alps the variscides of ireland and france and the himalaya

the palaeoenvironment and deformation of beaconites like burrows in the old red sandstone at gortnabinna sw ireland the gortnabinna area contains a number of well preserved deformed burrows within the fluviatile old red sandstone of s ireland detailed logging of the local succession enables subdivision into four facies facies 1 represents sheet flood deposits facies 2 ephemeral stream channels facies 3 marginal sheet flood deposits and facies 4 low energy settling of fines the burrows occur in facies 1 and 4 the sediments are now folded into a large upright westward plunging anticline the fold has a well developed axial planar cleavage and is extended along strike by listric normal faults the burrows in facies 1 were originally circular and orthogonal to bedding and reveal a n s layer parallel shortening strain of 2 1 followed by a shear strain of 1 48 during folding these burrows have a bimodal distribution of diameters with peaks in the ranges 50 80 and 110 170 mm the burrows of facies 4 are sub parallel to the bedding plane and are generally curved with a maximum width of 180 mm and lengths of up to 2 3 m these burrows display passive infill following abandonment the burrows are morphologically similar though distinct from beaconites barratti which has been described from elsewhere in the old red sandstone and are tentatively interpreted as lungfish burrows

flexural shear in a periclinal fold from the irish variscides abstract periclinal folds occur in a structural culmination in the centre of the irish variscan fold belt the culmination marks a zone of enhanced shortening which is associated with a locally attenuated stratigraphy and an anomalous deformation sequence with respect to the remainder of the orogen originally vertical burrows have been used along with cleavage fold relations to study both the three dimensional evolution of the periclinal folding and the temporal relationship between folding and cleavage as well as cleavage forming flattening strains the burrows record along strike shear related to the propagation of the periclinal folds a comparison with strain measurements made outside the culmination zone shows that the galley head area suffered higher strains integration of field data with published analyses of plasticine modelling of periclinal folds yields models for the propagation of a pericline and for the geometry of its lateral terminations

regional heat flow variations across the sedimented juan de fuca ridge eastern flank constraints on lithospheric cooling and lateral hydrothermal heat transport seafloor heat flow has been estimated continuously along a transect on the sedimented eastern flank of the juan de fuca ridge to provide constraints on the scale and rate of lateral heat and fluid transport in the upper igneous crust and on the total flux from the young lithosphere beneath the profile extends from 20 km east of the ridge axis where turbidite sediments lap onto the oceanic crust at an age of less than 1 ma and ends 110 km east of the axis over 3 6 ma crust estimated heat flow is derived from the combination of the depth to igneous basement determined from seismic reflection profiles and basement temperatures measured in nine ocean drilling program boreholes along the transect the strategy is based on the knowledge that in this young area upper basement temperatures are locally homogenized by vigorous hydrothermal circulation and hence vary smoothly between drilling sites at the young end of the transect near the region of extensive outcrop heat flow is only 15 of that predicted for lithosphere of this age heat flow increases systematically to the east reaching the full predicted level about 20 km from the point of sediment basement onlap the anomaly can be accounted for by mixing and or eastward flow of cool water in the upper igneous crust beneath the sediment at a darcian rate of the order of 1 m yr a geochemical signature of fresh seawater in basement is observed many tens of kilometers farther to the east although the thermal signature is no longer present along the remainder of the transect the heat flow conforms very well to that predicted by simple boundary layer cooling theory once the thermal effects of rapid sedimentation on this ridge flank are accounted for

a comparison of sanderson s and panozzo s strain measurement methods using calcite grain boundaries from the variscan fold and thrust belt in ireland abstract two methods of determining strain from the two dimensional preferred orientation of lines by sanderson and panozzo are compared using grain boundaries in limestones from s ireland the panozzo method utilizes the orientations and lengths of lines whereas the sanderson method uses only the orientations the panozzo method is shown to be more sensitive to inhomogeneous deformation or dubious data than the simpler method of sanderson

the reflection seismic survey of project tipteq the inventory of the chilean subduction zone at 38 2 s summary we describe results of an active source seismology experiment across the chilean subduction zone at 38 2 s the seismic sections clearly show the subducted nazca plate with varying reflectivity below the coast the plate interface occurs at 25 km depth as the sharp lower boundary of a 2 5 km thick highly reflective region which we interpret as the subduction channel that is a zone of subducted material with a velocity gradient with respect to the upper and lower plate further downdip along the seismogenic coupling zone the reflectivity decreases in the area of the presumed 1960 valdivia hypocentre the plate interface itself can be traced further down to depths of 50 60 km below the central valley we observe strong reflectivity at the plate interface as well as in the continental mantle wedge the sections also show a segmented forearc crust in the overriding south american plate major features in the accretionary wedge such as the lanalhue fault zone can be identified at the eastern end of the profile a bright west dipping reflector lies perpendicular to the plate interface and may be linked to the volcanic arc

three dimensional viscoelastic finite element model for postseismic deformation of the great 1960 chile earthquake 2 5 10 19 pa s for the continental upper mantle the model well explains the gps observations numerical tests suggest that the continental mantle viscosity value is reasonably well constrained the model shows the prolonged postseismic seaward motion of the inland area to be a unique feature of earthquakes with very long rupture along strike and large coseismic fault slip for short rupture and small coseismic slip the motion will stop very quickly after the earthquake explaining why this phenomenon is not more commonly observed with an oceanic mantle viscosity of 10 20 pa s the model also provides an explanation for tide gauge constrained postseismic uplift 200 km from the trench that had previously been explained using a model of prolonged afterslip of a deep segment of the chile subduction fault index terms 1236 geodesy and gravity rheology of the lithosphere and mantle 8160 1242 geodesy and gravity seismic deformations 7205 3230 mathematical geophysics numerical solutions 7209 seismology earthquake dynamics and mechanics 7260 seismology theory and modeling keywords postseismic deformation viscoelastic stress relaxation gps finite element modeling chile subduction zone upper mantle viscosity

seismogenic zone temperatures and heat flow anomalies in the to nankai margin segment based on temperature data from iodp expedition 333 and thermal model the location of the seismogenic zone across the to nankai margin segment has been widely investigated using geodetic tsunami seismologic and heat flow data as well as thermal models seafloor heat flow measurements show large scatter raising questions about the thermal state of the incoming and overriding plates in this study new temperature and conductivity measurements recorded in the philippine sea plate psp and in the accretionary prism during iodp expedition 333 are integrated with recent data on the margin structure and seismicity to improve constraints on the thermal structure of the incoming plate and the subduction zone as well as the thermal conditions within the seismogenic zone iodp expedition 333 measurements provide heat flow values that are lower than the average of nearby seafloor measurements thermal modeling for the psp suggests that hydrothermal warming is insignificant in the trench thus an observed widespread positive thermal anomaly in the shikoku basin that peaks at the kashinozaki knoll more likely results from vigorous thermal convection in the upper mantle in back arc context the modeled thermal structure of the margin from the trench to the mantle shows a significantly colder interplate contact than in previous studies the seismogenic zone is likely to be 30 170 km from the deformation front corresponding to the 100 340 c temperature range the 1944 co seismic slip zone extends farther southward where temperatures are about 60 c slow slip earthquakes are located in the downdip transition zone between 340 and 440 c across the intersection of the moho and the megathrust fault this improved thermal structure from the trench to the mantle results mainly from a better estimate of oceanic plate age slab dip and sedimentation rate variations in the trench this last parameter cools the interplate contact until a depth of 35 km shifting the thermally defined seismogenic zone landward by 20 km and significantly diminishing its influence near the corner flow area

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

unusual geologic evidence of coeval seismic shaking and tsunamis shows variability in earthquake size and recurrence in the area of the giant 1960 chile earthquake an uncommon coastal sedimentary record combines evidence for seismic shaking and coincident tsunami inundation since ad 1000 in the region of the largest earthquake recorded instrumentally the giant 1960 southern chile earthquake mw 9 5 the record reveals significant variability in the size and recurrence of megathrust earthquakes and ensuing tsunamis along this part of the nazca south american plate boundary a 500 m long coastal outcrop on isla chiloe midway along the 1960 rupture provides continuous exposure of soil horizons buried locally by debris flow diamicts and extensively by tsunami sand sheets the diamicts flattened plants that yield geologically precise ages to correlate with well dated evidence elsewhere the 1960 event was preceded by three earthquakes that probably resembled it in their effects in ad 898 1128 1300 1398 and 1575 and by five relatively smaller intervening earthquakes earthquakes and tsunamis recurred exceptionally often between ad 1300 and 1575 their average recurrence interval of 85 years only slightly exceeds the time already elapsed since 1960 this inference is of serious concern because no earthquake has been anticipated in the region so soon after the 1960 event and current plate locking suggests that some segments of the boundary are already capable of producing large earthquakes this long term earthquake and tsunami history of one of the world s most seismically active subduction zones provides an example of variable rupture mode in which earthquake size and recurrence interval vary from one earthquake to the next

strain refraction in layered systems abstract strain refraction across competence contrasts is presented as a simple model consisting of two components a homogeneous strain and a heterogeneous simple shear for newtonian materials the ratio of the layer parallel simple shear component in adjacent layers is the inverse of their viscosity ratio strong changes in ellipsoid size shape and orientation are predicted across viscosity contrasts the geological implications of strain refraction theory are considered within the context of the cleavage strain debate the particular relationships of relative competence and strain revealed by the refraction model may contribute to the problem of why cleavages of different morphologies in rocks of different lithologies and kinematic histories should appear to be subparallel to the xy planes of measured strain ellipsoids competent rocks should develop dominantly layer orthogonal strain and incompetent layers shear dominated deformation a variety of structural features ranging from cleavage refraction changing lineation orientations folds transected by cleavage changes from coaxial to non coaxial deformation and ramp flat fault geometry may be the result of stress and strain refraction in rocks

lacustrine turbidites as a tool for quantitative earthquake reconstruction new evidence for a variable rupture mode in south central chile understanding the long term earthquake recurrence pattern at subduction zones requires continuous paleoseismic records with excellent temporal and spatial resolution and stable threshold conditions south central chilean lakes are typically characterized by laminated sediments providing a quasi annual resolution our sedimentary data show that lacustrine turbidite sequences accurately reflect the historical record of large interplate earthquakes among others the 2010 and 1960 events furthermore we found that a turbidite s spatial extent and thickness are a function of the local seismic intensity and can be used for reconstructing paleo intensities consequently our multilake turbidite record aids in pinpointing magnitudes rupture locations and extent of past subduction earthquakes in south central chile comparison of the lacustrine turbidite records with historical reports a paleotsunami subsidence record and a marine megaturbidite record demonstrates that the valdivia segment is characterized by a variable rupture mode over the last 900 years including i full ruptures mw 9 5 1960 1575 1319 9 1127 44 ii ruptures covering half of the valdivia segment mw 9 1837 and iii partial ruptures of much smaller coseismic slip and extent mw 7 5 8 1737 1466 4 also distant or smaller local earthquakes can leave a specific sedimentary imprint which may resolve subtle differences in seismic intensity values for instance the 2010 event at the maule segment produced higher seismic intensities toward southeastern localities compared to previous megathrust ruptures of similar size and extent near concepci n

reconstructing paleoseismic deformation 2 1000 years of great earthquakes at chucalen south central chile in this paper we adopt a quantitative biostratigraphic approach to establish a 1000 year long coastal record of megathrust earthquake and tsunami occurrence in south central chile our investigations focus on a site in the centre of the rupture segment of the largest instrumentally recorded earthquake the ad 1960 magnitude 9 5 chile earthquake at chucalen coseismic subsidence in 1960 is recorded in the lithostratigraphy and biostratigraphy of coastal marshes with peat overlain by minerogenic sediment and changes in the assemblages of diatoms unicellular algae indicating an abrupt increase in relative sea level in addition to the 1960 earthquake the stratigraphy at chucalen records three earlier earthquakes the historically documented earthquake of 1575 and two prehistoric earthquakes radiocarbon dated to ad 1270 1450 and 1070 1220 laterally extensive sand sheets containing marine or brackish diatom assemblages suggest tsunami deposition associated with at least two of the three pre 1960 earthquakes the record presented here suggests a longer earthquake recurrence interval averaging 270 years than the historical recurrence interval which averages 128 years the lack of geologic evidence at chucalen of two historically documented earthquakes in 1737 and 1837 supports the previously suggested hypothesis of variability in historical earthquake characteristics our estimates of coseismic land level change for the four earthquakes range from meter scale subsidence to no subsidence or slight uplift suggesting earthquakes completing each 270 year cycle may not share a common characteristic slip distribution the presence of buried soils at elevations below their modern equivalents implies net relative sea level rise over the course of the chucalen paleoseismic record in contrast to relative sea level fall over preceding millennia inferred from sites on the mainland sea level rise may contribute to the preservation of evidence for multiple earthquakes during the last millennium while net relative sea level fall over the last 2000 5000 years may explain the lack of evidence for older earthquakes

crustal motion in the zone of the 1960 chile earthquake detangling earthquake cycle deformation and forearc sliver translation temporary deformation in great earthquake cycles and permanent shear deformation associated with oblique plate convergence both provide critical clues for understanding geodynamics and earthquake hazard at subduction zones in the region affected by the mw 9 5 great chile earthquake of 1960 we have obtained gps observations that provide information on both types of deformation our velocity solutions for the first time span the entire latitudinal range of the 1960 earthquake the new observations revealed a pattern of opposing roughly arc normal motion of coastal and inland sites consistent with what was reported earlier for the northern part of this region this finding supports the model of prolonged postseismic deformation as a result of viscoelastic stress relaxation in the mantle the new observations also provide the first geodetic evidence for the dextral motion of an intravolcanic arc fault system and the consequent northward translation of a forearc sliver the sliver motion can be modeled using a rate of 6 5 mm a accommodating about 75 of the margin parallel component of nazca south america relative plate motion with the rate diminishing to the north furthermore the new gps observations show a southward decrease in margin normal velocities of the coastal area we prefer explaining the southward decrease in terms of changes in the width or frictional properties of the megathrust seismogenic zone because of the much younger age of the subducting plate and warmer thermal regime in the south the currently locked portion of the plate interface may be narrower using a three dimensional viscoelastic finite element model of postseismic and interseismic deformation following the 1960 earthquake we demonstrate that this explanation although not unique is consistent with the gps observations to the first order

finite fault slip model of the 2016 mw 7 5 chiloe earthquake southern chile estimated from sentinel 1 data subduction earthquakes have been widely studied in the chilean subduction zone but earthquakes occurring in its southern part have attracted less research interest primarily due to its lower rate of seismic activity here i use sentinel 1 interferometric synthetic aperture radar insar data and range offset measurements to generate coseismic crustal deformation maps of the 2016 mw 7 5 chiloe earthquake in southern chile i find a concentrated crustal deformation with ground displacement of approximately 50 cm in the southern part of the chiloe island the best fitting fault model shows a pure thrust fault motion on a shallow dipping plane orienting 4 nne the insar determined moment is 2 4 1020 nm with a shear modulus of 30 gpa equivalent to mw 7 56 which is slightly lower than the seismic moment the model shows that the slip did not reach the trench and it reruptured part of the fault that ruptured in the 1960 mw 9 5 earthquake the 2016 event has only released a small portion of the accumulated strain energy on the 1960 rupture zone suggesting that the seismic hazard of future great earthquakes in southern chile is high

three dimensional density model of the nazca plate and the andean continental margin 1 we forward modeled the bouguer anomaly in a region encompassing the pacific ocean 85 w and the andean margin 60 w between northern peru 5 s and patagonia 45 s the three dimensional density model that reproduces the gravity field is a continental scale representation of density structure to 410 km depth that characterizes the mantle and crust of the oceanic nazca plate subducted slab and continental margin with a minimum number of bodies we predefined the density of each body after studying the dependency of density on composition of crustal and mantle materials and pressure temperature conditions appropriate for the andean setting a database of independent geophysical information constrains the geometry of the top of the subducted slab locally the moho of the oceanic and continental crusts and indirectly the lithosphere asthenosphere boundary underneath the continental plate other boundaries notably the intracrustal density discontinuity separating upper from lower crust below the continent were not constrained and their geometry is the result of fitting the observed and calculated bouguer anomaly during forward modeling this contribution presents the model to the andean geoscientific community and contains some tools like a sensitivity analysis that helps potential users of the model to interpret its results we describe and discuss some of these results in order to illustrate the application of the model to the study of a wide range of phenomena e g modification of oceanic plate structure by hot spots shape of the subducted slab thermal structure of the continental lithosphere compensation mechanism and formation of orogenic relieve causes of andean segmentation

seismicity and geometry of the south chilean subduction zone 41 5 s 43 5 s implications for controlling parameters in 2005 an amphibious seismic network was deployed on the chilean forearc between 41 75 s and 43 25 s 364 local events were observed in a 11 month period a subset of the p and s arrival times were inverted for hypocentral coordinates 1 d velocity structure and station delays main seismic activity occurred predominantly in a belt parallel to the coast of chiloe island in a depth range of 12 30 km presumably related to the plate interface the 30 inclination of the shallow part of the wadati benioff zone is similar to observations further north indicating that oceanic plate age is not controlling the subduction angle of the shallower part for the chilean subduction zone the down dip termination of abundant intermediate depth seismicity at approximately 70 km depth seems to be related to the young age and high temperature of the oceanic plate crustal seismicity is associated with the liquine ofqui fault zone and active volcanoes

historical and recent large megathrust earthquakes in chile abstract recent earthquakes in chile 2014 mw 8 2 iquique 2015 mw 8 3 illapel and 2016 mw 7 6 chiloe have put in evidence some problems with the straightforward application of ideas about seismic gaps earthquake periodicity and the general forecast of large megathrust earthquakes in northern chile before the 2014 iquique earthquake 4 large earthquakes were reported in written chronicles 1877 1786 1615 and 1543 in north central chile before the 2015 illapel event 3 large earthquakes 1943 1880 1730 were reported and the 2016 chiloe earthquake occurred in the southern zone of the 1960 valdivia megathrust rupture where other large earthquakes occurred in 1575 1737 and 1837 the periodicity of these events has been proposed as a good long term forecasting however the seismological aspects of historical chilean earthquakes were inferred mainly from old chronicles written before subduction in chile was discovered here we use the original description of earthquakes to re analyze the historical archives our interpretation shows that a priori ideas like seismic gaps and characteristic earthquakes influenced the estimation of magnitude location and rupture area of the older chilean events on the other hand the advance in the characterization of the rheological aspects that controlled the contact between nazca and south american plate and the study of tsunami effects provide better estimations of the location of historical earthquakes along the seismogenic plate interface our re interpretation of historical earthquakes shows a large diversity of earthquakes types there is a major difference between giant earthquakes that break the entire plate interface and those of mw 8 0 that only break a portion of it

remarkably consistent thermal state of the south central chile subduction zone from 36 s to 45 s delineating rupture areas of subduction zone earthquakes is necessary for understanding the controls on seismic and aseismic slip for the largest recorded earthquake the 1960 chile event with moment magnitude 9 5 the rupture area is only loosely defined due to limitations in the global seismic network at the time the rupture extends 900 km along strike coastal deformation is consistent with either a constant rupture width of 180 200 km along the entire length or a narrower 115 km rupture in the southern half a southward narrowing of the seismogenic zone has been hypothesized to result from warming of the subduction zone to the south where the subducting plate is younger we present results of thermal models at 36 s 38 s 43 s and 45 s to examine potential along strike changes in thermal state models most consistent with observed surface heat flux include fluid circulation in the oceanic crust that advects heat to the ocean this ventilated hydrothermal circulation preferentially cools transects with young subducting lithosphere frictional heating preferentially warms transects with older subducting lithosphere the combined effects of frictional heating and hydrothermal circulation increase decollement temperatures in the 36 s and 38 s transects by up to 155 c and decrease temperatures in the 45 s transect by up to 150 c in our preferred models decollement temperatures 200 km landward of the trench in all four transects are 350 400 c this is consistent with a constant 200 km wide seismogenic zone for the 1960 mw 9 5 rupture with decreasing slip magnitude in the southern half of the rupture

the 1960 chilean earthquakes an unusual foreshock sequence that began with an earthquake of moment 2 0 1021 n m and rupture length of about 150 km preceded the great 1960 chilean earthquake earthquake relocations of the sequence show a progression of seismic activity toward the initiation of the main shock the rupture length of the great 1960 chilean earthquake is estimated from the distribution of aftershocks and crustal deformation to be 920 100 km the source mechanisms of a foreshock and two aftershocks are determined and used to constrain the source mechanism of the main shock the first event in the sequence ruptured the segment of the peru chile trench between 37 03 s and 38 74 s whereas the great 1960 chilean main shock ruptured the adjoining segment to the south the great 1960 chilean main shock initiated within the rupture area of the first event and terminated near the intersection of the chile ridge with the peru chile trench 46 5 s

the updip and downdip limits to great subduction earthquakes thermal and structural models of cascadia south alaska sw japan and chile this study examines thermal and structural controls of the updip and downdip rupture limits of great subduction thrust earthquakes data on past great earthquake seismic limits have been compiled for four continental subduction zones cascadia sw japan south alaska and chile these limits have then been compared to the predictions of several models for what constrains great earthquake rupture temperatures on the subduction thrusts have been estimated by finite element numerical models the landward limits of the observed updip aseismic zones correspond to the position where the thrust temperature reaches about 100 c that is depths of about 2 to 10 km for the subduction zones studied this temperature agrees with the dehydration of stable sliding smectite clays to illite chlorite the temperatures in this region are controlled mainly by the thickness of sediment on the incoming crust and by the crustal age and thus heat flow the downdip limits correspond to the depth on the thrust where either 1 the temperature reaches about 350 c which corresponds to thermally activated stable sliding behavior for crustal rocks with a transition to 450 c or 2 about 40 km depth if 350 c is reached at greater depth depths of about 40 km approximately correspond to the intersection of the thrust with the continental forearc moho and this downdip limit may be a consequence of stable sliding serpentinite or talc and other hydrated forearc mantle rocks the primary temperature controls on the downdip region are the age of the subducting oceanic plate and the thrust dip profile secondary control comes from the thickness of incoming sediment the convergence rate and the radioactive heat generation in the overlying forearc the 100 c updip limit occurs near the trench for young subducting plates with a thick sediment section such as cascadia 6 8 ma and up to 80 km landward for older oceanic crust such as south alaska 50 ma the 350 c downdip thermal limit is applicable for young oceanic plates e g cascadia and nankai whereas the forearc mantle limit applies for older plates e g south alaska and chile except near the chile rise for the margins studied that have experienced great earthquakes there is generally good agreement between the postulated thermal and moho limits and the rupture or seismogenic zone as defined by the distribution of aftershocks and by waveform tsunami and dislocation modeling the downdip limit of the interseismic locked zone from dislocation modeling is also in agreement with these limits

a theory of finite strain variation through contrasting layers and its bearing on cleavage refraction abstract a theory of finite strain variation in contrasting viscous layers is presented the theory is applicable to layers which are oblique to two principal strains but parallel to the third and is not restricted to plane strain results may be obtained algebraically or by use of the mohr diagram for strain solutions are given for various examples of layering attitude and viscosity ratio measured with respect to a reference layer it is shown that the finite strain ellipsoid changes in shape and orientation across contrasting layers and in some cases the principal axes may be exchanged low strain is indicated in relatively more viscous layers and high strain with extension at a smaller angle to the layering in less viscous layers the latter may approximate simple shear parallel to layering if the strain is sufficiently high the geological implications of the theory are strong strain variations in layered rock sequences it is suggested that in general strain will be inhomogeneous from layer to layer both in orientation and amount the relationship of strain and cleavage are reviewed in the introduction to establish the validity of predicting cleavage patterns from strain data qualitative comparisons between the theoretical results of strain variation and natural cleavage refraction in layered rocks would appear to justify the assumption that cleavages of varied morphologies are sub parallel to the xy planes of strain with this assumption some three dimensional features of planar and linear fabric refraction in contrasting rocks are predicted

analytical method for estimating palaeowave climate and water depth from wave ripple marks analytical expressions are developed for evaluating palaeodepth and palaeowave conditions from wave ripple marks palaeodepth and palaeowave climate estimates can be extremely powerful predictors in reconstructions of vertical movements related to basin subsidence local and regional ancient wave climate trends and the basin shape the analytical expressions developed herein are applied to wave ripple marks preserved in the lower marine molasse of switzerland western austria and southern germany the results suggest that in contrast to traditional concepts of an eustatic sea level change the lower marine molasse regression was a result of mainly depositional processes the subsidence rate greatly exceeded the rate of sea level fall over a wide geographical area furthermore the widening of the lower marine molasse basin to the ene is well documented by the increase of the ancient wave period and wave power calculated from wave ripple marks found in storm deposits

the first since 1960 a large event in the valdivia segment of the chilean subduction zone the 2016 m7 6 melinka earthquake abstract we present results for joint kinematic inversion of high rate gps strong motion and insar data for the 2016 m7 6 melinka earthquake we show that the source is a compact 35 s long rupture with 5 0 0 15 m of peak slip we find the melinka earthquake occurs inside the slip region for the 1960 m9 5 valdivia earthquake and within the highly locked portion of the megathrust inferred from inter seismic velocity analysis we show that there is very modest post seismic deformation at a nearby gps site qlln and argue that this indicates the melinka earthquake ruptures within the intermediate portion of the megathrust and is an isolated asperity surrounded by locked velocity weakening material further we find that the peak slip observed during this earthquake is larger than what has been accumulated in the intervening 57 years since the 1960 rupture and conclude that at least in the area of the melinka earthquake this is indicates that the 1960 valdivia event might not have used all the slip deficit available on the megathrust

coseismic strengthening of the shallow portion of the subduction fault and its effects on wedge taper 1 according to the dynamic coulomb wedge model coseismic strengthening of the shallowest part of the subduction interface can cause permanent deformation of the overlying outer wedge so that the cumulative effects of great interplate earthquakes control the geometry of the wedge in this work we use a numerical model which is a hybrid of the frictional contact model and the classical crack model to study how stress is coseismically transferred from the seismogenic zone to the strengthening updip zone to cause wedge deformation in this static model the critical strengthening required to prevent the rupture from breaking the trench depends on the force drop of the seismogenic zone defined as the product of the average shear stress drop and the area of the seismogenic zone in a simple model of uniform material properties with a few megapascals average stress drop over a seismogenic zone of 120 km downdip width the critical strengthening for a 30 km wide updip zone is an increase in the effective friction coefficient by about 0 05 using the coulomb wedge theory we demonstrate that this level of strengthening can readily push the overlying wedge into a critical state of failure with much greater strengthening the rupture is able to extend into the updip zone only slightly causing localized wedge compression in the area of slip termination we examined wedge geometry of 22 subduction zones in the light of the model results we found that the surface slope of these wedges is generally too high to be explained using the classical wedge theory but can be explained using the dynamic coulomb wedge model including coseismic strengthening of the shallow portion of the megathrust

interaction between the chile ridge and chile trench geophysical and geothermal evidence geophysical and geothermal data are examined from the three southernmost sections of the chile ridge starting at 44 s and continuing south to the triple junction of the nazca antarctic and south america plates at 47 s these sections represent three progressively younger stages in a ridge trench collision event corresponding to 3 m y before the collision 1 m y before the collision and culminating in an ongoing collision at the triple junction magnetic and bathymetric data across the chile rise indicate that there is little change in the configuration of the spreading center as the ridge approaches and then collides with the trench in the collision zone a normal looking rift valley can be traced for 40 km before it disappears beneath the toe of the landward trench slope there is no evidence for the complex pattern of ridge jumps and spreading center rotations that occurred when the pacific farallon spreading center collided with north america in contrast the overriding plate is greatly affected by the ridge collision the landward trench slope steepens and narrows as the collision zone is approached at the southern end of the collision zone a ridge associated with the taitao fracture zone is colliding with the trench and may be in the process of being obducted onto the landward trench slope geothermal measurements were made along three transects of the margin corresponding to the time 3 m y before the collision during the collision and 6 m y after the collision the heat flow measurements in the collision zone document a large pulse of heat associated with the subduction of the ridge values as high as 345 mw m2 were recorded on the lower trench slope a prominent bottom simulating reflector bsr observed over a wide area of the landward trench slope north of the triple junction and more locally south of the triple junction is used to expand the grid of heat flow observations excellent agreement is found between measured heat flow and estimates of heat flow based on the depth to the bsr the heat flow measurements compare favorably with a theoretical model assuming conductive heat flow we estimate that the accretionary prism has been substantially removed in the collision zone and conclude that the landward trench slope is undergoing an episode of rapid tectonic erosion periodic ridge collisions in the past may account for the apparent truncation of the andean forearc region

crustal thickness and mantle wedge structure from receiver functions in the chilean maule region at 35 s a temporary passive seismic network of 21 broad band stations was deployed in central chile between 35 s to 36 s the network recorded data prior to the magnitude mw 8 8 2010 maule earthquake at a latitude of the major slip and surface deformation the experiment was conducted to survey crustal and mantle structures and to assess the state of hydration of the mantle wedge we present results of a teleseismic p receiver function study supporting a continental moho at approx 38 km depth phase conversion at this boundary could be observed continuously from the intersection of the subducting slab with the continental moho towards the andes the character of receiver functions indicated little evidence for infiltration of water from the subducting plate into the overlying mantle wedge suggesting that only a small amount of water is released from the subducting plate aftershocks of the maule earthquake and post seismic slip reached depths of 50 km and hence slip spread down dip of the continental moho in the post seismic phase co seismic rupture however occurred updip of the continental moho spare aftershock seismicity is observed at the intersection of the continental moho with the subducting slab

cleavage geometry and the development of the church bay anticline co cork ireland abstract the church bay anticline is one of a series of e w trending hercyman folds in southern ireland the fold has a crudely axial planar cleavage which was initiated early in the buckling history the cleavage was deformed subsequently by a number of discrete bedding parallel shear zones as the fold continued to amplify this has resulted in a characteristically sigmoidal cleavage geometry in the fold profile plane the cleavage also displays kink bands and sharp angular changes across bedding planes in the fold hinge as a result of shearing within these sheared zones the cleavage is intensified indicating that conditions for cleavage formation were maintained throughout the development of the fold no new cleavage has formed despite the rotation of the cleavage during the deformation history