reverse slip structures at oceanic diverging plate boundaries and their kinematic origin data from tertiary crust of west and south iceland abstract normal faulting predominates within rift zones but reverse fault plane solutions are occasionally found for earthquakes along the mid atlantic ridge furthermore field observations of striae and in situ measurements in places show off rift compression and reverse faulting we analyse eight cases of reverse slip motion observed in the eroded tertiary crust of the borgarfjor ur and hreppar rift jump blocks respectively in west and south iceland these structures were the only ones observed where both striae and marker horizons could be used to deduce the sense of reverse slip motion the vertical displacements are less than 10 m and the motions are of local origin we believe these structures are formed independently from regional compression as they have variable kinematic origins some occur in association with dykes sills or cone sheet without evidence of horizontal shortening across intrusions others are due to local bends of regional steeply dipping normal faults or secondary fractures riedel or secondary fractures reverse slip striations are found at the irregularities of steeply dipping normal faults or at the tips of steeply dipping normal faults uplifted by an underlying propagating dyke striations even conspicuous ones do not necessarily reflect significant amounts of displacement if horizontal compression acts in iceland its magnitude is not sufficient to shorten the rocks and to close the fractures of various tectonic settings the observed examples are explained as local kinematic adjustments to companion structures without regional compressional stress field or shortening and can lead to misinterpretation if not put into the correct context

a newly recognized type of slickenside striation abstract this note summarizes current views on the origin of slickenside striations and points to the existence of a type of striation not readily explained by established genetic ideas such striations have been seen on fault surfaces in naturally deformed shale and in experimentally deformed paraffin wax they are defined by arrays of shallow slip parallel ridges and grooves of millimetric width and below on any given slip surface the ridges are as common as the grooves and display similar dimensions and profile shapes across any pair of slip surfaces in contact at the end of faulting ridges protruding from one surface fit into or nest with grooves on the other surface the origin of these features is not yet understood

new insights into the vertical structure of clouds in polar lows using radar lidar satellite observations for the first time we characterize the vertical distribution of cloud microphysical properties in polar lows pls we base our investigation on colocations found between a train satellites overpasses and 82 pl occurrences evidenced from avhrr observations in the nordic seas we use the radar lidar dardar satellite cloud products to retrieve the thermodynamic phase and ice microphysical properties of clouds ice water content iwc and ice crystal effective radius r eff two thirds of the investigated pls show cloud tops higher than commonly documented 5 km and up to 9 km pls are largely dominated by the ice phase with more supercooled liquid occurrences in the eye we also show that spiraliform clouds have larger average iwc in the few kilometers below cloud top by up to a factor of 2 compared to comma shaped pls plain language summary polar lows are intense maritime cyclones posing serious threats to mariners and coastal populations due to their limited size and sudden development operational forecast struggles to correctly predict them additionally the limited amount of observational constraints renders improvements of simulations difficult we provide the first statistical analyses of cloud microphysical properties of these storms using radar and lidar satellite observations we demonstrate much higher cloud tops than usually assumed we highlight the cloud phase describe the vertical distribution of ice mass and crystal size and stress some differences between spiraliform and comma shaped cyclones these new constraints can be readily used to improve polar lows simulations

the effects of pressure and porosity on the micromechanics of the brittle ductile transition in quartzite room temperature experiments on a quartzite with 7 porosity show that with increasing pressure there is a transition from brittle faulting to ductile cataclastic flow at about 600 mpa in contrast experiments on nonporous quartzite show only faulting up to 1000 mpa the transition to cataclastic flow in the porous quartzite is due to the changing influence of the pores microstructural observations and elastic theory suggest that the transition occurs at the pressure where the differential stress producing a compressive stress concentration sufficient to initiate pore collapse becomes less than that producing a tensile stress concentration sufficient to nucleate axial microcracks at the tops and bottoms of pores cataclastic flow of the porous quartzite is only transient deformation remains distributed and accompanied by work hardening only as long as pore collapse continues to 16 strain at higher strains microcracking produces a net dilatancy which causes strain weakening that leads to faulting at 26 strain at a confining pressure of 750 mpa the faults are stable whereas at 1000 mpa they are unstable the results indicate that porous rocks may undergo limited ductile deformation at shallow levels in the crust but higher strains will cause deformation to localize

on the development of zones of reverse shearing in mylonitic rocks abstract most shear zones contain a minor proportion of domains recognizable from thin section to outcrop scale which show an opposing shear sense relative to the overall kinematic framework in this paper we discuss how these universal features result from the evolving deformation strain partitioning that generally accompanies progressive general shear principally in low metamorphic grade shear zones because the rheologic properties and consequently the contributions of the different deformation mechanisms change continuously with progressive strain an individual domain with a predominant deformation mechanism much faster or slower than the average may depart from the general kinematics enhancing the viscosity contrast between adjacent layers and causing locally reverse shear in the domain boundaries care is needed therefore in interpreting opposing shear senses in the same shear zone as indicating superimposed deformation events

slickenside and fault surface kinematic indicators on active normal faults of the alpine betic cordilleras granada southern spain abstract twenty four mesoscopic slickenside kinematic indicators are described here for the pliocene quaternary active normal faults of the alpine betic cordilleras granada southern spain the indicators are classified into twelve groups depending on the down or up slope asymmetric orientation of features such as concavities damaged versus sharp grain borders or step edges v shaped markings fractures and trailed material seventeen of the indicators were not previously described in the literature the new kinematic indicators include two types of asymmetric grains a carrot shaped marking six substructures of congruous and incongruous steps trailed fault material a drop shaped figure a v shaped marking three types of synthetic hybrid fractures with congruous steps and two varieties of pluck holes we think that some of these kinematic indicators provide information on the amount of displacement aseismic versus seismic slip rates cataclastic flow frictional wear or surface polishing

an assessment of a greenland lee cyclone during the greenland flow distortion experiment an observational approach on 3 march 2007 between 0920 and 1545 utc the mesoscale structure of a mature lee cyclone southeast of greenland was successfully captured during a flight with a research aircraft during the greenland flow distortion experiment gfdex the cyclone was accompanied by hazardous weather conditions such as extensive icing and low level wind speeds exceeding 34 m s 1 calculations based on atmospheric soundings from egedesminde on the west coast of greenland indicate that conditions were favourable for flow splitting and hence cyclogenesis in the lee of greenland during the formation of the cyclone pv inversion carried out on an upper level southward moving potential vorticity pv anomaly indicates that upper level forcing as well as orographic forcing had an important role in the cyclone development the frontal seclusion of the cyclone s warm core was consistent with both the norwegian cyclone model and shapiro and keyser s model however it was not possible to match this cyclone precisely with any of these models which is probably a consequence of the strong influence from greenland on the cyclone development in situ measurements showing a combination of warm dry air with relatively high ozone concentrations in the centre of the cyclone together with trajectory calculations indicate that this air had experienced considerable descent probably induced by greenland s orography the observations documented the cyclone s mesoscale structure and clearly revealed a deep tropopause fold this tropopause fold is a manifestation of the forcing on the cyclone from the upper level pv anomaly copyright c 2009 royal meteorological society

near n s paleo extension in the western deccan region india does it link strike slip tectonics with india seychelles rifting this is the first detailed report and analyses of deformation from the w part of the deccan large igneous province dlip maharashtra india this deformation related to the india seychelles rifting during late cretaceous early paleocene was studied and the paleostress tensors were deduced near n s trending shear zones lineaments and faults were already reported without significant detail an e w extension was envisaged by the previous workers to explain the india seychelles rift at 64 ma the direction of extension however does not match with their n s brittle shear zones and also those faults sub vertical ne sw nw se and few n s we report and emphasize in this work slickenside bearing fault planes brittle shear zones and extension fractures in meso scale enabled us to estimate the paleostress tensors directions and relative magnitudes the field study was complemented by remote sensing lineament analyses to map dykes and shear zones dykes emplaced along pre existing n s to ne sw nw se shears fractures this information was used to derive regional paleostress trends a nw se ne sw minimum compressive stress in the oldest kalsubai subgroup and a n s direction for the younger lonavala wai and salsette subgroups were deciphered thus a nw ne to n s extension is put forward that refutes the popular view of e w india seychelles extension paleostress analyses indicate that this is an oblique rifted margin field criteria suggest only ne sw and nw se with some n s strike slip faults brittle shear zones we refer this deformation zone as the western deccan strike slip zone wdsz the observed deformation was matched with offshore tectonics deciphered mainly from faults interpreted on seismic profiles and from magnetic seafloor spreading anomalies these geophysical findings too indicate oblique rifting in this part of the w indian passive margin we argue that the seychelles microcontinent separated from india only after much of the dlip erupted further studies of magma rich passive margins with respect to timing and architecture of deformation and emplacement of volcanics are required

active normal faulting and crustal extension a world wide review of fault plane solutions and focal depths for large normal faulting earthquakes on the continents shows that the overwhelming majority of such earthquakes nucleate in the depth range 6 15 km on faults dipping between 30 and 60 in the few cases where levelling or seismic data are good enough these normal faults are shown to be approximately planar from the surface to their nucleation depth at the base of the brittle crust there is evidence that in some cases as a result of the enormous transitory increase in strain rate during large earthquakes rupture continues into the normally ductile lower crust on surfaces with substantially gentler dips these low angle surfaces may be analogous to some of the detachments seen in metamorphic core complexes of the western usa but the nature of the motion on them depends on strain rate as well as on rheological contrasts between the detachments and the blocks on either side such contrasts however are unlikely to introduce substantial curvature to an originally planar shear zone if the observed spread in active normal fault dips is caused by rotation of the faults and the blocks they bound during extension then a maximum value of 1 7 can be accommodated by seismic activity on a single generation of normal faults with continued extension either a new generation of steeper faults cutting the rotated first faults is likely to form or the deformation will continue aseismically on faults dipping at less than 30 large earthquakes have not been observed to nucleate on very low angle 20 normal faults within the continental crust anywhere in the world such faults can of course move aseismically but are unlikely to do so on a large scale within the upper crust in areas where steep normal faults are seismically active thus extensional models that require concentrated simple shear on large sub horizontal faults within the brittle upper crust will also require a spatial separation between aseismic very low angle faulting and seismic highangle faulting since seismogenic high angle faults dominate the topography of extending regions upper crustal very low angle faulting if it occurs on a large scale presumably does so in areas that are relatively fiat

orographic influence of east greenland on a polar low over the denmark strait we present a numerical study of a polar low which hit western iceland in january 2007 with heavy snowfall and mean wind speeds exceeding 20 m s 1 in several locations the operational models at the time captured the polar low formation rather well but there was a large spread in their predictions of the subsequent evolution and track of the polar low the objective of this study is to investigate possible orographic forcing from greenland as a trigger for the polar low development in addition to an analysis of surface observations and satellite imagery sensitivity studies using hirlam were carried out with various degradations of greenland s orography as well as with modifications to the sea surface temperature sst surface roughness and the data assimilation scheme despite the presence of an upper level trough and weak static stability in all the simulations the polar low development was found to be very sensitive to the presence of the high mountains of eastern greenland whereas the control run captured well the main features of the polar low simulations with parts of east greenland s orography removed gave a southward displaced polar low which moved rapidly eastward resulting in substantially underestimated near surface winds and snowfall amounts setting the orographic heights over all of greenland to zero led to the complete disappearance of the polar low on the other hand artificially increasing the sst by 4 k in the denmark strait reducing the orographic roughness or replacing the four dimensional variational assimilation scheme 4d var by 3d var had only a small effect on the polar low we suggest that hitherto unreported interactions between the high mountains of east greenland and polar low development over the denmark strait may be more important for polar low formation than katabatic flow from valleys in east greenland that was highlighted in earlier studies copyright 2011 royal meteorological society

neogene extensional collapse in the western mediterranean betic rif alpine orogenic belt implications for the genesis of the gilbraltar arc and magmatic activity the betic rif orogenic belt crops out in the western mediterranean and constitutes the westernmost part of the alpine edifice the building up of this belt by compressional nappe tectonics occured during a series of alpine deformational episodes subsequent neogene extension resulted from the collapse of the previous compressional edifice through major extensional detachment systems this episode was accompanied by cafe alkaline to shoshonitic and lamproitic volcanism tectonic denudation of metamorphic core complexes and emplacement of peridotite bodies as a final consequence of the evolution of detachment systems furthermore we relate the generation of the gibraltar arc and the opening of the alboran sea to this major extensional event finally two main stages of tectonic denudation of these detachment systems are defined 1 nevado filabride stage with ex humation of metamorphic core complexes and 2 ronda beni boussera stage with a more advanced degree of denudation leading to the exhumation of upper mantle peridotites which may be tentatively termed mantle core complexes

the aljibes half graben active extension at the boundary between the trans mexican volcanic belt and the basin and range province mexico the aljibes half graben is located 140 km west northwest of mexico city and is characterized by several parallel 10 km long south dipping and east striking normal faults late miocene basalt flows with 40 ar 39 ar ages of 7 7 0 1 ma and 7 1 0 5 ma are displaced along these faults with reference to this basalt the composite throw and heave of the half graben are 480 m and 270 m respectively and the relative extension is 5 whereas the vertical slip rate along the faults of the aljibes half graben after the deposition of the basalt is 0 07 mm yr the aljibes half graben is located at the northern margin of the trans mexican volcanic belt and perpendicularly intersects northstriking normal faults of the basin and range province the relative sequence of activity of the two stress fields and fault systems cannot be resolved in the study area and the two systems may have been active simultaneously we explain this structural configuration by horizontal migration of the boundary between the two stress provinces with time which requires intermittent permutations between the intermediate and least principal stresses 2 and 3 this is supported by the low stress ratio 2 3 1 3 obtained from modeling the stress tensor associated with the slip along the faults of the aljibes half graben the orientations of the fault planes and slip vectors of the aljibes half graben are practically identical to those of the nearby acambay graben and the venta de bravo fault which caused the acambay earthquake of november 19 1912 m s 6 9 and the maravatio earthquake of february 22 1979 m b 5 3 furthermore the aljibes half graben forms the extrapolated western continuation of the northern master fault of the mezquital graben which ruptured partly in the cardonal earthquake of march 26 1976 m b 5 3 this suggests the aljibes half graben may also be seismically active although no historical earthquake is known to have occurred along this structure further evidence for the likely seismic activity of the aljibes half graben are two east to eastnortheast trending epicenter alignments between the aljibes halfgraben and the mezquital graben and structural indication for stickslip behavior based on the structure of the aljibes half graben we believe the maximum credible earthquake that may occur along the faults of the aljibes half graben is on the order of 2 10 27 dyne cm m 0 6 10 25 dyne cm and 7 5 m w 6 5

the role of horizontal resolution for polar low simulations polar lows are intense mesoscale cyclones that mainly occur during the winter over the sea in polar regions owing to their small spatial scale with a diameter between 200 and 1000 km simulating polar lows is a challenging task in this study we investigated how increased resolution of a numerical weather prediction model impacts its ability to simulate polar lows we focused on a polar low that was successfully captured by three different flights during the ipy thorpex field campaign in 2008 verifying model results against campaign data showed that decreasing the horizontal grid spacing from 12 to 4 km significantly improved the simulation of the developing polar low and a further decrease to 1 km gave further improvement a model run with latent heating reduced to 10 indicated an extensive influence of diabatic heating in this polar low case and we suggest that the improved model performance at higher resolution could be connected to the model s handling of convection additional simulations starting 24 h later showed that the initial conditions were important for the model performance and when simulating another polar low case we found that the model failed to produce the polar low independent of the resolution this shows that while higher resolution indeed may give improved predictions of polar lows other factors like synoptic situation lateral boundaries and the initial condition may also be important copyright 2011 royal meteorological society

applicability of large scale convection and condensation parameterization to meso γ scale hirlam a case study of a convective event abstract this paper presents a case study of a single cold air outbreak event with widespread convective precipitation over southern finland on 25 may 2001 the purpose of the study is to investigate the applicability of the convection and condensation scheme of the high resolution limited area model hirlam on meso scales the study concentrates on the issue of grid size dependent convection parameterization an explicit approach without the convection scheme is also examined at the same time the performance of an experimental nonhydrostatic version of hirlam is evaluated model simulations are conducted with three different horizontal grid spacings 11 5 6 and 2 8 km model results are compared to observed radar reflectivity data utilizing a radar simulation model which calculates radar reflectivities from three dimensional model output the best results are obtained using nonhydrostatic dynamics and a grid size dependent convection scheme with a 5 6 km grid interval however even the best conf

an observational study of an arctic front during he ipy thorpex 2008 campaign the fact that severe weather associated with polar lows and arctic fronts still comes unforeseen and puts human life at risk shows that an effort towards increased understanding of them is required the observations of an arctic front by dropsondes and doppler lidar carried onboard a research aircraft during the ipy thorpex field campaign offered a rare opportunity to investigate the mesoscale structure of the front and to validate the output from operational numerical weather prediction models the observations revealed features similar to those of polar fronts such as a relatively steep frontal zone the presence of a strong low level jet and an elevated dry slot making the arctic front appear as a shallow cold front confined to levels below 700 hpa the dry slot indicated the presence of a downfolding of the tropopause and together with the observations of an upper level jet this strongly supports the inclusion of an arctic tropopause fold connected to the arctic jet stream in a conceptual model of the tropopause a comparison between data from operational numerical weather prediction models and observations obtained during the flight shows that the models simulated the broad features of the frontal zone such as jets dry slot and the depth of the front fairly well although parts of the front were slightly misplaced however the models failed completely in their simulations of one of the three mesoscale cyclones associated with the front as they located it over the coast of northern norway while the correct location was over the greenland sea according to the observations and analysis

structure of a shear line polar low during march 2013 a series of polar lows originated in a high vorticity 10 3 s 1 shear zone that was associated with a prolonged marine cold air outbreak over the norwegian sea a detailed analysis of one shear line polar low at the leading edge of the outbreak is presented using comprehensive observations from a well instrumented aircraft dropsondes scatterometer and cloudsat data and numerical modelling output from a convection resolving configuration of the met office unified model the maximum low level wind gradient across the shear line was 25 m s 1 over 50 km high windsto the north and west were within the cold air mass and were associated with large surface turbulent heat fluxes and convective clouds low wind speed to the south and east of the shear line were associated with low heat fluxes and a clear eye in the polarlow shear line meso scale instabilities merging into the polar low appeared important to its structure and development the model captured the shear line and the polar low structure very well in particular the strength of the horizontal shear and the mesoscale thermodynamic fields the spatialstructure of convective cloud bands around the polar low wassimulated reasonably well but the modelsignificantly underestimated the liquid water content and height of the cloud layers compared to the observations shear line polar lows are relatively common however this case is arguably the first to be examined with a wide range of in situ and remote observations allied with numerical model output

morphologically ductile criteria for the sense of movement on slickensides from an extensional detachment fault in southern spain abstract new criteria for the sense of movement on slickenside surfaces displaying evidence for mesoscopic ductility are described in the neogene jaloche extensional detachment fault in southern spain this detachment develops spectacular slickensides and fault gouges and four of the criteria for the sense of movement observed along the highly polished slip surfaces are new to the literature they are 1 synthetic secondary fractures with hangingwall drag effects in the form of roll over microsynclines 2 metre scale oval shaped asymmetric culmination and depression features 3 microthrusts verging towards the direction of motion of the opposite block and dragging overthrusting previous planar elements on the fault surface and 4 flakes of fault surface material trailed and plastered in the direction of the missing block the geometry and microstructure of these features reveal that they deformed in a morphologically ductile manner by the coupled processes of cataclastic flow and shear localization probably during aseismic sliding during transient seismic pulses deformation occurred along shiny polished slickenside fault planes occasionally bearing jigsaw implosion breccias fluids under high pressure present initially may have promoted distributed cracking whereas the process of dilatancy hardening may have served to facilitate cataclastic flow in the deformation history

ductility in fault gouge from a normal fault system death valley california a mechanism for fault zone strengthening and relevance to paleoseismicity fault gouge along the badwater turtleback fault system displays abundant evidence for mesoscopic ductility as foliation isolated and or rotated inclusions and isoclinal folds fault gouge thicknesses also vary dramatically at the outcrop scale gouge thicknesses can range from 0 to 1 m and at the 100 m scale they can range from 0 to 5 m because these variations are closely associated with other ductility related features they probably also formed because of ductile flow ductile flow appears to locally strengthen the fault zone by severe attenuation of the gouge and by transport of inclusions where gouge pinches out to zero thickness hanging wall rock rests directly on footwall rock a condition that produces an overall stronger fault zone as well as stick slip behavior in laboratory tests transport of inclusions within the gouge zone may create local inclusion jams which may also have a strengthening effect the presence of these stronger portions of the fault zone may give indirect evidence for ancient seismicity on the fault

mantle core complexes and neogene extensional detachment tectonics in the western betic cordilleras spain an alternative model for the emplacement of the ronda peridotite abstract an alternative model for the emplacement of the ronda peridotite betic alpine orogenic belt southern spain is proposed involving mantle uprising during a major neogene extensional event the development of a detachment system and its further evolution by isostatic rebound and upward arching would have triggered the tectonic denudation of these ultramafic bodies forming what may be termed mantle core complexes mantle core complexes would represent a final step in the core complex forming processes once a complete separation of the upper and lower blocks has been achieved in a detachment system marking probably the transition from an intracontinental to a proto oceanic rift environment

low angle normal faults and seismicity a review although large low angle normal faults in the continental crust are widely recognized doubts persist that they either initiate or slip at shallow dips 30 because 1 global compilations of normal fault focal mechanisms show only a small fraction of events with either nodal plane dipping less than 30 and 2 andersonian fault mechanics predict that normal faults dipping less than 30 cannot slip geological reconstructions thermochronology paleomagnetic studies and seismic reflection profiles mainly published in the last 5 years reinforce the view that active low angle normal faulting in the brittle crust is widespread underscoring the paradox of the seismicity data for dip slip faults large enough to break the entire brittle layer during earthquakes m w 6 5 consideration of their surface area and efficiency in accommodating extension as a function of dip suggests average recurrence intervals of earthquakes r tan assuming stress drop rigidity modulus and thickness of the seismogenic layer do not vary systematically with dip if the global distribution of fault dip normalized to total fault length is uniform the global recurrence of earthquakes as a function of dip is shown to be r tan sin this relationship predicts that the frequency of earthquakes with nodal planes dipping between 30 and 60 will exceed those with planes shallower than 30 by a factor of 10 in good agreement with continental seismicity assuming major normal faults dipping more than 60 are relatively uncommon revision of andersonian fault mechanics to include rotation of the stress axes with depth perhaps as a result of deep crustal shear against the brittle layer would explain both the common occurrence of low angle faults and the lack of large faults dipping more than 60 if correct this resolution of the paradox may indicate significant seismic hazard from large low angle normal faults

forward and reverse shear environments during polar low genesis over the northeast atlantic abstractthe synoptic and subsynoptic environments associated with polar low genesis are examined ambient pre polar low environments are classified as forward or reverse shear conditions based on the angle between the thermal and mean wind forward shear environments are associated with a synoptic scale ridge over scandinavia featuring a zonally oriented baroclinic zone extending throughout the troposphere with a wind speed maximum at the tropopause similar to typical midlatitude cyclogenesis concurrent wavelike development occurs both in the lower and upper troposphere along the baroclinic zone and the mean propagation direction is eastward parallel to isolines of sea surface temperature reverse shear environments exhibit a distinctly different structure and are characterized by a trough over scandinavia associated with a synoptic scale occluded cyclone the genesis area exhibits strong cold air advection on its right hand side and polar low development occurs on the warm side of an intense low le

the low temperature brittle ductile transition in a quartzite and the occurrence of cataclastic flow in nature the paper describes the mechanical and microstructural characteristics associated with the brittle to cataclastic flow transition in an orthoquarzite oughtibridge ganister and compares its microstructural development with features of cataclastic deformation of rocks in nature

kinematic indicators on active normal faults in western turkey quaternary normal fault zones in western turkey comprise multiple slip planes and zone parallel layers of fault breccia they also contain several little known kinematic indicators that are probably typical of many formed at shallow levels in extending terrains the recent exhumation by contractors of about 2000 m2 of slip planes in a sse dipping fault zone separating quaternary colluvium from bedrock carbonates at yavansu 7 km se of kusadasi permits an unusually complete inventory of the indicators to be compiled the most spectacular indicators are metre scale 69 w pitching corrugations in slip planes and recemented breccia sheets underlying them corrugations characterized by sinusoidal profiles normal to their long axes and less commonly culminations and depression along their axes possibly developed as a result of upwards propagating slip planes seeking undemanding pathways through heterogeneous fault precursor breccias that formed in advance of tip lines parallel to corrugation long axes are those of gutters flat floored sleep sided channels a few centimetres wide probably related to the abrasion of subslip plane breccia sheets centimetre scale tool tracks scored in the uppermost subslip plane breccia sheet by resistant colluvial clasts are irregular at their proximal ends but distally they swing into alignment with corrugation axes frictional wear striae centimetres long but only a few millimetres wide and pitching 78 w are superimposed on the other slip parallel lineations comb fractures nearly perpendicular to slip planes define an intersection lineation which is normal to corrugation axes fault plane solutions of earthquakes on sse dipping active faults in the west anatolian extensional province indicate that mainly normal combined with minor dextral slip is the dominant mode a conclusion in accord with the sense of slip inferred from the indicators exposed on the yavansu slip planes

microstructures imply cataclasis and authigenic mineral formation control geomechanical properties of new zealand s alpine fault abstract the alpine fault is capable of generating large mw 8 earthquakes and is the main geohazard on south island nz and late in its 250 291 year seismic cycle to minimize its hazard potential it is indispensable to identify and understand the processes influencing the geomechanical behavior and strength evolution of the fault high resolution microstructural mineralogical and geochemical analyses of the alpine fault s core demonstrate wall rock fragmentation assisted by mineral dissolution and cementation resulting in the formation of a fine grained principal slip zone psz a complex network of anastomosing and mutually cross cutting calcite veins implies that faulting occurred during episodes of dilation slip and sealing fluid assisted dilatancy leads to a significant volume increase accommodated by vein formation in the fault core undeformed euhedral chlorite crystals and calcite veins that have cut footwall gravels demonstrate that these processes occurred very close to the earth s surface microstructural evidence indicates that cataclastic processes dominate the deformation and we suggest that powder lubrication and grain rolling particularly influenced by abundant nanoparticles play a key role in the fault core s velocity weakening behavior rather than frictional sliding this is further supported by the absence of smectite which is reasonable given recently measured geothermal gradients of more than 120 c km 1 and the impermeable nature of the psz which both limit the growth of this phase and restrict its stability to shallow depths our observations demonstrate that high temperature fluids can influence authigenic mineral formation and thus control the fault s geomechanical behavior and the cyclic evolution of its strength

pedogenic slickensides indicators of strain and deformation processes in redbed sequences of the appalachian foreland pedogenic slickensides are convex concave slip surfaces that form during expansion contraction in expansive clay soils such as vertisols in the central appalachians they occur near the tops of fining upward cycles in paleozoic redbeds such as the bloomsburg catskill and mauch chunk formations pedogenic slickensides are found in association with other pedogenic or paleosol features such as clay skinned peds in situ calcareous nodules and root impressions repeated movements along these shear planes during pedogenesis produce strongly aligned clay particles adjacent to pedogenic slickensides as a result they are preserved as discrete fractures throughout diagenesis compaction and superimposed tectonic deformation during whole rock deformation pedogenic slickensides segregate penetratively deformed rocks into independent foliated packets and serve as discontinuities that are followed by later structural features because the original morphology of pedogenic slickensides is known they can be used as crude strain markers

pressure solution structures in a granite abstract syntectonic two mica granites in northwest spain have suffered regional late variscan shear deformation the deformed corcoesto granite shows a marked planar and linear fabric resulting from ductile behaviour and contains quartz veins at about 60 to the foliation offsets of these quartz veins along shear planes are commonly contrary to the general sense of shear and thus provide evidence for pressure solution processes

seasat synthetic aperture radar observations of wave current and wave topographic interactions this study investigated the capability of a spaceborne imaging radar system to detect subtle changes in the propagation characteristics of ocean wave systems specifically an evolving surface gravity wave system emanating from hurricane ella and propagating toward cape hatteras north carolina formed the basis of this investigation this wave system was successfully imaged by the seasat synthetic aperture radar sar during revolution 974 on september 3 1978 estimates of the dominant wavelength and direction of the ocean waves were derived from the sar data by using optical fourier transforms environmental data of the test area which included the surface velocity vector within the gulf stream the location of hurricane ella and local bathymetric information were used in conjunction with the sar data to form the basis of this comparative study favorable agreement was found between wave rays calculated by utilizing theoretical wave current and wave topographic interactions and sar observed dominant wavelength and direction changes across the gulf stream and continental shelf