faulting of rocks in three dimensional strain fields i failure of rocks in polyaxial servo control experiments abstract the dependence of the number of sets of faults and their orientation on the intermediate strain axis is investigated through polyaxial tests reported here and theoretical analysis reported in an accompanying paper in the experiments cubic samples of berea sandstone sierra white and westerly granites and candoro and solnhofen limestones were loaded on their three pairs of faces by three independent mutually perpendicular presses at room temperature two of the presses were servo controlled and applied constant displacement rates throughout the experiment most samples display three or four sets of faults in orthorhombic symmetry these faults form in several yielding events that follow a stage of elastic deformation in many experiments the maximum and the intermediate compressive stresses interchange orientations during the yielding events where the corresponding strains are constant the final stage of most experiments is characterized by slip along the faults

the roles of vortex rossby waves in hurricane secondary eyewall formation abstract a high resolution full physics model initiated with an idealized tropical cyclone like vortex is used to simulate and investigate the secondary eyewall formation the beta skirt axisymmetrization bsa hypothesis previously proposed is examined and the roles of axisymmetrizing vortex rossby waves vrws in the secondary eyewall formation are further investigated during the formation period convection outside the inner core region is organized into an outer spiral rainband the pv dipoles that are persistently generated by convective updrafts through tilting effect move along the rainband and inward toward inner core region and are finally axisymmetrized in the preexisting beta skirt region the formation of the secondary eyewall is preceded by a rapid intensification period during which vortical hot towers discrete vrws and sheared vrws dominate the inner core asymmetric structures sheared vrws are repeatedly emanated from the outer edge of the eyewall and become more concentric when propa

hurricane eyewall replacement cycle thermodynamics and the relict inner eyewall circulation abstractflight level aircraft data are used to examine inner core thermodynamic changes during eyewall replacement cycles ercs and the role of the relict inner eyewall circulation on the evolution of a hurricane during and following an erc near the end of an erc the eye comprises two thermodynamically and kinematically distinct air masses separated by a relict wind maximum inside of which high inertial stability restricts radial motion creating a containment vessel that confines the old eye air mass restricted radial flow aloft also reduces subsidence within this confined region subsidence induced warming is thus focused along the outer periphery of the developing post erc eye which leads to a flattening of the pressure profile within the eye and a steepening of the gradient at the eyewall this then causes a local intensification of the winds in the eyewall the cessation of active convection and subsidence near the storm center which has been occurring over the course of the erc leads to an

the governing dynamics of the secondary eyewall formation of typhoon sinlaku 2008 abstractthrough successful convection permitting simulations of typhoon sinlaku 2008 using a high resolution nonhydrostatic model this study examines the role of peripheral convection in the storm s secondary eyewall formation sef and its eyewall replacement cycle erc the study demonstrates that before sef the simulated storm intensifies via an expansion of the tangential winds and an increase in the boundary layer inflow which are accompanied by peripheral convective cells outside the primary eyewall these convective cells which initially formed in the outer rainbands under favorable environmental conditions and move in an inward spiral play a crucial role in the formation of the secondary eyewall it is hypothesized that sef and erc ultimately arise from the convective heating released from the inward moving rainbands the balanced response in the transverse circulation and the unbalanced dynamics in the atmospheric boundary layer along with the positive feedback between these processes

concentric eyewall formation in typhoon sinlaku 2008 part iii horizontal momentum budget analyses abstract this is a follow up work to two prior studies examining secondary eyewall formation sef in typhoon sinlaku 2008 this study shows that in the sef region the majority of the elevated

evidence for extended hercynian basement and a preserved jurassic basin margin tract in northern calabria southern italy the longobucco basin abstract in the longobucco basin northeastern calabria southern italy a mesozoic succession covers the hercynian basement documenting the evolution of a continental margin during the early jurassic extensional tectonic phase correlated with the western tethys rift the basin evolved from continental red beds around the rhaetian hettangian boundary to shallow marine and eventually deep sea siliciclastic turbidites in the late pliensbachian toarcian to dominantly pelagic deposits middle jurassic onwards around the sinemurian pliensbachian boundary following a prominent phase of normal faulting sedimentation took different paths in either hangingwall block or footwall block settings this study based on geological mapping focuses on the southwestern boundary of the longobucco basin and in particular on the mutual relationships existing between the deeper water basin fill units fiume trionto and fosso petrone formations the basement and the shallow water limestone of the caloveto formation which forms a narrow strip running parallel to the rift shoulder the contacts among the above mentioned units are generally all stratigraphic unconformities of various types onlap downlap nonconformity these characteristics separate the study area from the depocentral parts of the basin in terms of vertical stratigraphy nature of contacts among stratigraphic units unconformable vs conformable and impact of synsedimentary tectonics the signature of early jurassic extension occurs in the form of 1 laterally continuous clastic bodies interpreted as products of catastrophic basin margin collapse and avalanching 2 exhumation of the pre rift units which are otherwise deeply buried and 3 neptunian dykes of at least two generations our new data provide evidence for the presence of a 20 km long nw se trending preserved paleoescarpment where the basinal units onlap either the basement or the caloveto formation which forms a fringing carbonate body with intriguing facies and bio sedimentological features the paleoescarpment was the submarine morphological expression of a sinemurian pliensbachian fault as testified by the age of the clastic body that seals it another pulse of synsedimentary extension took place in the latest pliensbachian toarcian overprinting the existing rift architecture and reviving the production of megaclastic deposits

effect of the altiplano puna plateau south america on the regional intraplate stresses abstract a previous compilation of stress data for the sub andean region of northwest argentina is complemented with eight additional earthquake focal mechanisms seven events 5 3 5 5 mb had their mechanisms determined by inversion of teleseismic body waves short period p waves and long period sh waves all events had predominantly reverse faulting mechanisms five had almost pure dip slip motion and two had a component of oblique motion the other mechanism was a composite fault plane solution of the hualfin catamarca series of july 1986 maximum 4 mb determined with data from a local temporary network and the permanent inpres regional network the local data shows that the hualfin events occurred on a single fault plane oriented nw se with predominantly strike slip motion the stress data in the sub andean region suggests a radial pattern around the altiplano puna plateau with compressional stresses tending to be perpendicular to the eastern front of the plateau this indicates that local spreading stresses due to lateral density variations crustal thickening or lithospheric thinning of the plateau may be comparable or even exceed the plate wide regional stresses at the southeastern border of the puna plateau where a stress rotation of about 30 may be detected preliminary order of magnitude calculations indicate that the local plateau induced compression can be about 1 2 times greater than the regional horizontal deviatoric stress the present predominance of the local stress over the regional stress is consistent with the decrease of the nazca south america convergence rate observed since about 10 20 ma

slip system domains 2 kinematic aspects of fabric development in polycrystalline aggregates abstract in the first paper of the present series cobbold and gapais 1986 we develop theoretical models of plane strain domainal deformation by slip along inextensible and indestructible fibres for such extreme mechanical conditions we show that deformation is largely controlled by kinematic factors we use our models to explain domainal patterns of natural slip systems including bedding and foliation planes faults ductile shear zones and lattice planes the present paper focusses on kinematic aspects of fabric development in polycrystalline aggregates a three dimensional kinematic model is developed it reveals that common quartz fabrics may develop domainally by reorientation and selection of inextensible slip directions a axes or slip planes with initially random orientation stable orientations of slip directions are close to both surfaces of no finite extension and orientations of large amount of shear we explain 1 1 common patterns of quartz a and c axis fabrics e g small circles and crossed girdles 2 2 characteristic differences between fabric patterns according to the shape of the finite strain ellipsoid 3 3 development of asymmetric fabrics during non coaxial deformation histories this last process involves selective destruction or replacement of certain orientation domains so that a preferred orientation of slip lines develops close to the bulk shear direction rotation recrystallization is shown to be an efficient natural selection mechanism the models also account for many microstructural features found in oriented polycrystalline rocks especially 1 1 alternating band like or kink like domains of twinned preferred orientations 2 2 individual grains or clusters of grains with retort like shapes and extensive recrystallisation at boundaries 3 3 small scale shear bands formed by strain partitioning and shear localization

theory of slickenline patterns based on the velocity gradient tensor and microrotation abstract brittle fault zones commonly are characterized by a multitude of lineated shear planes having a wide distribution of orientations in our model we assume the faulted rock comprises an aggregate of rigid blocks whose surfaces are the shear planes we define two independent scales of motion to distinguish the local rigid rotation of the blocks with their shear planes the micromotion from the average deformation of the material on a macroscopic scale the macromotion the macromotion is defined by the macrovelocity gradient tensor which is separated into symmetric and antisymmetric parts the deformation rate and the macrospin tensors respectively the micromotion is defined by a microspin tensor on any shear plane slickenlines form parallel to the direction of the maximum rate of shear which we assume is determined by the direction of the maximum component of the macrovelocity gradient tensor tangent to the shear plane and by a component of the microspin in the shear plane for a restricted kinematic model patterns of slickenline orientations are defined on a uniform distribution of shear plane orientations by the values of d and w d is a ratio of differences in the principal values of the deformation rate tensor and w is a ratio of the net spin to the maximum rate of macroshear we distinguish between instantaneous slickenline patterns and finite deformation patterns the two are different if the shear planes rotate relative to the principal deformation rate axes in which case finite deformation slickenlines form curved or crossing lineations if w 0 the instantaneous slickenline patterns have orthorhombic symmetry 0 d d 1 or 0 if w 0 the instantaneous slickenline patterns have monoclinic symmetry for pure shear in an isotropic body instantaneous slickenline patterns have orthorhombic symmetry w 0 d 0 5 whereas for pure shear accommodated by shear on a planar anisotropy w 1 d 0 5 the pattern is monoclinic for simple shear with the rigid rotation of local shear planes defined by the shear induced spin w 0 d 0 5 the instantaneous slickenline pattern is orthorhombic but the finite deformation pattern is monoclinic for simple shear with no shear plane rotation w 1 d 0 5 the instantaneous pattern is monoclinic special cases of our hypothesis are equivalent to the hypothesis that slickenlines are parallel to the direction of maximum resolved shear stress e g angelier 1979 1984 the slickenline patterns predicted for this case are always of orthorhombic or higher symmetry and are equivalent to our instantaneous patterns for which w 0 and to our finite deformation patterns for which in addition there is no microspin

the concentric eyewall cycle of hurricane gilbert abstract hurricane gilbert of 1988 formed an outer eyewall as it intensified rapidly toward a record minimum pressure of 888 hpa in the western caribbean the outer eyewall strengthened and contracted while the inner eyewall showed some signs of weakening before landfall on the yucatan peninsula remarkably both eyewalls survived passage over land but the storm was much weaker when it entered the gulf of mexico although the primary cause of weakening was passage over land the effect of the contracting outer eyewall may have contributed later the outer eyewall completely replaced the inner eyewall subsequently it contracted steadily but slowly as gilbert maintained nearly constant intensity over the cooler waters of the gulf before final landfall on the mainland of mexico

secondary eyewall formation in an idealized tropical cyclone simulation balanced and unbalanced dynamics abstractthe secondary eyewall formation sef in an idealized simulation of a tropical cyclone tc is examined from the perspective of both the balanced and unbalanced dynamics and through the tangential wind vt budget analysis it is found that the expansion of the azimuthal mean vt above the boundary layer occurs prior to the development of radial moisture convergence in the boundary layer the vt expansion results primarily from the inward angular momentum transport by the mid to lower tropospheric inflow induced by both convective and stratiform heating in the spiral rainbands in response to the vt broadening is the development of radial inflow convergence and the supergradient flow near the top of the inflow boundary layer results from the vt budget analysis show that the combined effect of the mean advection and the surface friction is to spin down vt in the boundary layer while the eddy processes eddy radial and vertical advection contribute positively to the spinup of vt in the sef region

impact of stratiform rainband heating on the tropical cyclone wind field in idealized simulations abstractusing idealized simulations we examine the storm scale wind field response of a dry hurricane like vortex to prescribed stratiform heating profiles that mimic tropical cyclone tc spiral

tectonic deformation by rotating parallel faults the bookshelf mechanism abstract in various tectonic environments extension of crustal parts and shear distortion has been accommodated by the rotation of an array of parallel faults because of its kinematic resemblance to the tilting of a row of books on a shelf the tectonic process may be referred to as a bookshelf mechanism its most important manifestions are cross faulting between normal faults or parallel wrench faults the extension of deltaic slope deposits and all forms of tilted block tectonics kinematically there are two basic modes of the mechanism a the dilational mode where rotating faults tend to open up and possibly become paths for fluid migration and b the domino style where reclining faults remain closed in both cases formation and rotation of the faults may take place in one tectonic event fault displacements may therefore often remain small and difficult to detect from the mechanical point of view bookshelf operations that accommodate shearing between parallel and predominantly parallel moving rock boundaries bookshelf mechanisms proper have to be differentiated from those operations responding to an imposed crustal extension or shortening after a review of geological evidence the process is addressed from a geomechanical point of view in order to determine the geological operating conditions and controlling parameters the crucial mechanical factor in the bookshelf mechanism is the component of normal stress that acts in the direction of the imposed displacement component parallel to the driving boundary plates in contrast to the usual assumption the driving shear stress on the boundary plates not only depends on the normal stress on the plates but it also varies with the value of the normal stress that acts inside the sheared material in the direction of the plate parallel displacement component it is the relationship between the two normal stresses that also determines the type of rotating parallel faults large scale rotation of parallel normal faults in domino style tilted block tectonics is primarily associated with the extension of ductile substrata from mechanical arguments and sand box experiments it has been inferred how the process and in particular the dip direction of the parallel faults is controlled by the way substratal extension progresses by means of the direction of a substratal squeeze flow the presence of a surface slope the strength anisotropy associated with fore set beds and by the configuration of competent boundaries of the extending overburden

determination of stress from slip data faults and folds a new technique is derived to invert slickenside data for the stress field that caused the faulting episode this inversion is simplified by the assumption that the magnitude of the tangential traction on the various fault planes at the time of rupture is similar study of three normal faulting regimes shows that the inversion derived with this assumption yields results that closely match older inversions that did not include the assumption hence the assumption may be valid and is shown to be justified by analyzing a simple fracture criterion application of slip data inversions is extended from faulting regimes to the slip on bedding plane faults in folding regimes comparison of the inversion results with the geometry of the folds shows this application to be successful greatly increasing the number of data sets that can be used to find the paleostress field

analysis of fault slip inversions do they constrain stress or strain rate fault slip data commonly are used to infer the orientations and relative magnitudes of either the principal stresses or the principal strain rates which are not necessarily parallel or equal at the local scale of an individual fault the shear plane and slip direction define the orientations of the local principal strain rate axes but not in general the local principal stress axes at a large scale the orientations of p and t axes maxima for sets of fault slip data do not provide accurate inversion solutions for either strain rate or stress the quantitative inversion of such fault slip data however provides direct constraints on the orientations and relative magnitudes of the global principal strain rates to interpret the inversion solution as constraining the global principal stresses requires that 1 the fault slip pattern must have a characteristic symmetry no lower than orthorhombic 2 the material must be mechanically isotropic and 3 there must be a linear constitutive relationship between the global stress and the global strain rate isotropic linear elastic constitutive equations are appropriate to describe the local deformation surrounding an individual slip discontinuity fault slip inversions however constrain the characteristics of a large scale cataclastic flow which is described by constitutive equations that are probably but to an unknown degree anisotropic and nonlinear such material behavior would not strictly satisfy the requirements for the stress interpretation thus at the present state of knowledge fault slip inversion solutions are most reliably interpreted as constraining the principal strain rates

the roles of asymmetric inflow forcing induced by outer rainbands in tropical cyclone secondary eyewall formation abstractthis study analyzes the secondary eyewall formation sef process in an idealized cloud resolving simulation of a tropical cyclone in particular the unbalanced boundary layer response to asymmetric inflow forcing induced by outer rainbands orbs is examined in order to understand the mechanisms driving the sustained convection outside the primary eyewall during the early phase of sef the enhancement of convection in the sef region follows the formation and inward contraction of an orb the azimuthal distribution of the enhanced convection is highly asymmetric but regular generally along a half circle starting from the downwind portion of the orb it turns out that the descending radial inflow in the middle and downwind portions of the orb initiates maintains a strong inflow in the boundary layer the latter is able to penetrate into the inner core region sharpens the gradient of radial velocity and reinforces convergence consequently warm and moist air is continuously lifted up at the lead

the typical large scale superposed folds in the central south china implications for mesozoic intracontinental deformation of the south china block abstract the south china block has experienced polyphase intensive intracontinental deformation in the mesozoic time large scale superposed folds in central south china document the mesozoic tectonic events within the south china block here we present new structural data related to synfolding deformation coupling with chronological data to reconstruct the deformation sequence and tectonic regime during crustal shortening these data indicate that the superposed folds dominated by a two stage tectonic compressive regime experienced two phases of superposed buckle folding leading to the orthogonal superposition of ne sw trending folds onto wnw ese trending folds between the late middle jurassic and the earliest early cretaceous our structural analysis together with geochronological data for this area suggests that the south china block predominately underwent two phases of intracontinental deformation during the mesozoic the early phase of tectonism d1 is characterized by a late middle triassic to earliest early jurassic ne sw compression causing the occurrence of an orogeny perpendicular shortening accompanying with evident magmatism this tectonic event was most likely associated with progressive clockwise collision of the south china block toward the north in the indosinian event subsequent tectonic activity d2 between the late middle jurassic and the earliest early cretaceous contributed to a phase of nw se contraction that overprinted the early ne sw shortening in the interior of the south china block generating a large scale nw convex fold belt and the typical large scale superposed folds within the central south china block the later tectonism was probably driven by the nw directed subduction of the paleo pacific plate beneath the eastern part of the asian continent

inversion of field data in fault tectonics to obtain the regional stress i single phase fault populations a new method of computing the stress tensor summary we attempt a general definition of the inverse problem of computing the components of the regional stress tensor from a set of field data including the measurements of the strike and dip of several faults and the directions and senses of relative motion along these faults as indicated by slickenslides in previous treatments of this problem no experimental errors could be taken into account except those in measuring the pitch of slickenslides thus errors in the orientation of the fault strike and dip which have considerable practical importance were neglected in our work all experimental errors in the field measurements are taken into account so that the agreement between the computed stress tensor and the set of field measurements can be rigorously checked

dynamical and physical processes leading to tropical cyclone intensification under upper level trough forcing abstractthe rapid intensification of tropical cyclone tc dora 2007 southwest indian ocean under upper level trough forcing is investigated tc trough interaction is simulated using a limited area operational numerical weather prediction model the interaction between the storm and the trough involves a coupled evolution of vertical wind shear and binary vortex interaction in the horizontal and vertical dimensions the three dimensional potential vorticity structure associated with the trough undergoes strong deformation as it approaches the storm potential vorticity pv is advected toward the tropical cyclone core over a thick layer from 200 to 500 hpa while the tc upper level flow turns cyclonic from the continuous import of angular momentum it is found that vortex intensification first occurs inside the eyewall and results from pv superposition in the thick aforementioned layer the main pathway to further storm intensification is associated with secondary eyewall formation triggered by external

how does the boundary layer contribute to eyewall replacement cycles in axisymmetric tropical cyclones abstractthree diagnostic models of the axisymmetric tropical cyclone boundary layer with different levels of approximation are applied to the problem of tropical cyclones with concentric eyewalls the outer eyewall is shown to have an inherently stronger frictional updraft than the inner because it is in an environment of lower vorticity similarly a relatively weak local enhancement of the radial vorticity gradient outside the primary radius of maximum winds can produce a significant frictional updraft even if there is no outer wind maximum based on these results it is proposed that the boundary layer contributes to the formation of outer eyewalls through a positive feedback among the local enhancement of the radial vorticity gradient the frictional updraft and convection the friction induced secondary circulation associated with the inner eyewall is shown to weaken as the outer wind maximum strengthens and or contracts so boundary layer processes will contribute along with the heating induced

toward clarity on understanding tropical cyclone intensification abstractthe authors review an emerging paradigm of tropical cyclone intensification in the context of the prototype intensification problem which relates to the spinup of a preexisting vortex near tropical storm strength in a quiescent environment in addition the authors review briefly what is known about tropical cyclone intensification in the presence of vertical wind shear the authors go on to examine two recent lines of research that seem to offer very different views to understanding the intensification problem the first of these proposes a mechanism to explain rapid intensification in terms of surface pressure falls in association with upper level warming accompanying outbreaks of deep convection the second line of research explores the relationship between the contraction of the radius of maximum tangential wind and intensification in the classical axisymmetric convective ring model albeit in an unbalanced framework the authors challenge a finding of the second line of research that appears

block rotation and deformation by strike slip faults 2 the properties of a type of macroscopic discontinuous deformation study of the general features of deformation by systems of subparallel strike slip faults shows that the governing constraints are kinematic the fault blocks must remain in contact with each other and the deformed area must fit with its surroundings as a result fault blocks that move laterally without significant internal deformation also rotate about vertical axes relative to boundaries of the fault domain by an amount that is quantitatively related to fault slip spacing and orientation areas where left and right lateral faults move simultaneously are usually divided into domains that contain faults of one kind only deformation of such multidomain areas is nonhomogeneous but the differences between domains can compensate for each other so that the regional deformation is quite simple strike slip faulting combined with block rotation is an efficient mechanism of deformation because modest offsets and rotations change the linear dimensions of faulted areas by several tens of percents which may often greatly exceed the results of other types of coeval deformation paleomagnetic data can provide an independent measure of block rotations and should be used to supplement structural data block rotation changes the initial angles between right and left lateral faults and also their orientation relative to the stress field the faults probably tend to rotate away from the axis of maximum compression rotated faults continue to move because they are weak surfaces since the deformation depends on geometric factors such as fault orientation and domain geometry it is not simply related to the stress field these properties including rotation of material units characterize discontinuous deformation in general

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

post collisional tectonics in the northern cottian alps italian western alps field mapping and structural analysis have allowed us to characterise the fault geometry and the post metamorphic tectonics of an area located in the northern cottian alps inner western alps two main faulting stages were distinguished here the first oligocene early miocene is related to the development of an e w striking left normal shear zone this shear zone is interpreted as an antithetical of two regional n s right lateral structures the col del lis trana deformation zone ltz and the colle delle finestre deformation zone cfz the second faulting stage post early miocene is related mainly to the development of n s normal faults coeval with the extensional reactivation of the ltz and the cfz we discuss this kinematic evolution in the framework of the geodynamic evolution of the western alps

tectonic significance of fault slip data abstract the statistical analysis of populations of minor faults is commonly used by structural geologists working in areas of brittle rock it is based on measurements of fault attitude direction and sense of slip at individual sampling localities results are classically interpreted as indicators of stress or strain rate fields assuming a homogeneous stress or strain rate tensor respectively however fault patterns are expected to vary with time because of displacements rigid rotations and internal strains which generally occur along boundaries of fault bounded blocks as deformation proceeds thus in the general situation where early faults accumulate displacements and rigid rotations and where new faults develop during progressive deformation fault slip data can be rather complex and variable in space and reflect neither local stress or strain rate tensors nor finite strains and finite rotations in a simple way we use two examples of faulted regions to illustrate the spatial variability of fault slip data this can be due to local complications at the edges of fault blocks or to complex kinematic conditions at regional boundaries such complications may make it difficult to deduce a consistent and simple pattern of either stresses or strain rates instead our results suggest that information contained in fault slip data can be pertinent to finite deformation in particular the principal axes that we have deduced from the analysis of fault slip data are consistent with the finite displacements at block boundaries that we have calculated by numerical restoration

concentric eyewall asymmetries in hurricane gonzalo 2014 observed by airborne radar abstracttwo eyewall replacement cycles were observed in hurricane gonzalo by the noaa p3 tail ta radar and the recently developed nasa high altitude imaging wind and rain airborne profiler hiwrap radar these observations captured detailed precipitation and kinematic features of gonzalo s concentric eyewalls both before and after the outer eyewall s winds became the vortex maximum winds the data were analyzed relative to the deep layer environmental wind shear vector during the beginning eyewall replacement cycle stages the inner and outer eyewalls exhibited different asymmetries the inner eyewall asymmetry exhibited significant low level inflow updrafts and positive tangential acceleration in the downshear quadrants consistent with observational and theoretical studies the outer eyewall asymmetry exhibited these features in the left of shear quadrants further downwind from those of the inner eyewall it is suggested that the low level inflow occurring at the outer but not at the inner eyewal

interaction of faults and perturbation of slip influence of anisotropic stress states in the presence of fault friction and comparison between wallace bott and 3d distinct element models abstract two decades after their birth the validity of fault slip inversion methods is still strongly debated these methods are based upon a very simplified mechanical background the wallace bott hypothesis following previous studies the 3d distinct element method 3dec software is used to explore the effect of varying stress anisotropy i e the shape ratio on slip perturbation along pairs of faults two end member configurations are modelled in taking into account fault friction and internal deformation of faulted blocks the first model deals with a relatively simple case where two nonintersecting conjugate normal faults are reactivated in an oblique normal stress regime the second one simulates an extreme situation where two perpendicular intersecting faults are submitted to oblique extension the average direction of fault slip predicted by 3dec models is compared to the corresponding slip predicted by the simplified wallace bott model for the two simulated cases it is shown that results from 3dec and wallace bott models are mutually consistent and argue for the validity of fault slip data inversion methods consistency remains even if slip is significantly deviated near the intersection line of faults these deviations depend on the degree of anisotropy of applied stresses in presence of fault friction furthermore modelling results suggest that for intersecting faults with convergent slip directions consideration of fault friction in the models leads to reduction of slip perturbation in other words modelling results lead to the nonintuitive conclusion that the validity of the simplified wallace bott model is strengthened when 3dec model s complexity i e the number of parameters incorporated increases

forty years of paleostress analysis has it attained maturity abstract powerful methods of paleostress analysis from fault slip data have been used since the 1970 s and have demonstrated their capacity for reconstructing stress fields with tectonic significance however in some cases these methods have been applied to samples that do not fulfill basic requirements or developed on the basis of unsound conceptual models most methods of fault slip are based on the wallace bott principle dynamic paradigm while others invoke the necessity of remaining within the alternative kinematic paradigm therefore inferring only finite strain or strain rate axes the scientific community shares neither standard procedures for applying these methods nor standard parameters for assessing the quality of results this indicates that paleostress analysis has not attained maturity it is necessary to see back to the conceptual and methological bases following accurate procedures of data collection using additional field observations and critically assessing the results within the tectonic setting spatial and temporal heterogeneity of stress fields over all scales makes the mean stress tensor obtained from site analysis just an abstract notion though indispensable for understanding lithosphere dynamics

tests of an ensemble kalman filter for mesoscale and regional scale data assimilation part i perfect model experiments abstract through observing system simulation experiments this two part study exploits the potential of using the ensemble kalman filter enkf for mesoscale and regional scale data assimilation part i focuses on the performance of the enkf under the perfect model assumption in which the truth simulation is produced with the same model and same initial uncertainties as those of the ensemble while part ii explores the impacts of model error and ensemble initiation on the filter performance in this first part the enkf is implemented in a nonhydrostatic mesoscale model the fifth generation pennsylvania state university ncar mesoscale model mm5 to assimilate simulated sounding and surface observations derived from simulations of the surprise snowstorm of january 2000 this is an explosive east coast cyclogenesis event with strong error growth at all scales as a result of interactions between convective meso and subsynoptic scale dynamics it is found that the enkf is very effective in keeping th

convectively generated potential vorticity in rainbands and formation of the secondary eyewall in hurricane rita of 2005 abstracteyewall replacements in mature tropical cyclones usually cause intensity fluctuations one reason for eyewall replacements remaining a forecasting challenge is the lack of understanding of how secondary eyewalls form this study uses high resolution full physics model forecast fields of hurricanes katrina and rita 2005 to better understand potential vorticity pv generation in the rainbands and the role that convectively generated pv played in the formation of a secondary eyewall in hurricane rita previous studies have focused on dynamic processes in the inner core and or the effects of certain specified pv distributions however the initial development of a concentric pv ring in the rainband region has not been fully addressed katrina and rita were extensively observed by three research aircraft during the hurricane rainband and intensity change experiment rainex which was designed to study the interaction of the rainbands and the inner core rita developed a secondary eyewall and went

secondary eyewall formation in wrf simulations of hurricanes rita and katrina 2005 1 an analysis is presented of two high resolution hurricane simulations of katrina and rita 2005 that exhibited secondary eyewall formation sef the results support the notion of vortex rossby waves vrws having an important role in sef and suggest that vrw activity is a defining aspect of the moat sef occurs at a radius of 65 80 km in katrina rita close to the hypothesized stagnation radius of vrws vrw activity appears to be the result of eye eyewall mixing events themselves a product of the release of barotropic instability the convection in the radial region that becomes the moat is mainly in the form of vrws propagating radially outward from the primary eyewall until the negative radial gradient of potential vorticity is no longer conducive for their propagation these convectively coupled waves originating and being expelled from the eyewall are rotation dominated and have the coherency necessary to survive their passage through the strain dominated region outside the eyewall

cenozoic dextral transpression and basin development at the southern edge of the puna plateau northwestern argentina abstract in northwestern argentina the southern edge of the altiplano puna is the most remarkable positive topographic anomaly average altitude 3700 m of the andean chain to the south are the sierras pampeanas a less elevated domain made of alternating compressive basins and ranges developed during the cenozoic at about 27 s the transition between the puna and the sierras pampeanas coincides with a substantial narrowing of the high chain and with a change in the dip of the pacific subduction zone nazca plate from 30 e below the plateau to subhorizontal below the sierras pampeanas we argue that this structural transition which can be identified at the scale of the andean topography is a major dextral transpressional transfer zone the tucuman transfer zone in this region ene wsw to e w directed subhorizontal shortening related to bulk convergence between the nazca and south american plates interferes with nw se directed subhorizontal shortening strains due to lateral influence of changes in the amount of crustal thickening on intraplate kinematics structural observations digital mapping spot satellite images and a microtectonic analysis of fault populations provide general insights into the neogene kinematic evolution of transpressional basins and ranges at the edge of the puna

paleomagnetic evidence for cenozoic block rotations in the tadjik depression central asia this paper presents results of a paleomagnetic study of oligo miocene red beds of the tadjik depression in central asia we sampled about 530 cores at 69 sites and six localities across the depression and along the western border of the pamirs samples were thermally demagnetized and high temperature components appear to predate folding of upper tertiary age throughout the depression paleomagnetic inclinations are consistent with those observed on the stable turan platform at the western margin of the depression however they are shallower by about 30 than the inclination predicted from the reference apparent polar wander path this appears to indicate a 23 difference in latitude which is incompatible with paleogeographic reconstructions for the tertiary a sound interpretation of this anomaly would require a better constrained tertiary paleomagnetic reference for asia inside the tadjik depression paleomagnetic declinations are all significantly rotated counterclockwise with respect to those measured on the turan platform the eastern part of the depression is a domain of large rotation 52 13 to 46 15 whereas smaller amounts of rotation have occurred in the western part 27 14 to 14 15 the similarity between tertiary and cretaceous data available for the area shows that rotations have occurred since the miocene little or no paleomagnetic rotations are observed in the ranges bordering the northern and western parts of the depression paleomagnetic and structural data suggest that block rotations in the tadjik depression are associated with indentation of the pamirs into stable asia at a larger scale observed rotations are compatible with a model of regional sinistral wrenching along a strip running from the gulf of oman to lake baikal

clouds in tropical cyclones abstract clouds within the inner regions of tropical cyclones are unlike those anywhere else in the atmosphere convective clouds contributing to cyclogenesis have rotational and deep intense updrafts but tend to have relatively weak downdrafts within the eyes of mature tropical cyclones stratus clouds top a boundary layer capped by subsidence an outward sloping eyewall cloud is controlled by adjustment of the vortex toward gradient wind balance which is maintained by a slantwise current transporting boundary layer air upward in a nearly conditionally symmetric neutral state this balance is intermittently upset by buoyancy arising from high moist static energy air entering the base of the eyewall because of the radial influx of low level air from the far environment supergradient wind in the eyewall zone and or small scale intense subvortices the latter contain strong erect updrafts graupel particles and large raindrops produced in the eyewall fall out relatively quickly while ice splinters left

intensity and structure changes during hurricane eyewall replacement cycles abstracta flight level aircraft dataset consisting of 79 atlantic basin hurricanes from 1977 to 2007 was used to develop an unprecedented climatology of inner core intensity and structure changes associated with eyewall replacement cycles ercs during an erc the inner core structure was found to undergo dramatic changes that result in an intensity oscillation and rapid broadening of the wind field concentrated temporal sampling by reconnaissance aircraft in 14 of the 79 hurricanes captured virtually the entire evolution of 24 erc events the analysis of this large dataset extends the phenomenological paradigm of ercs described in previous observational case studies by identifying and exploring three distinct phases of ercs intensification weakening and reintensification in general hurricanes intensify sometimes rapidly when outer wind maxima are first encountered by aircraft the mean locations of the inner and outer wind maximum at the start of an erc are 35 and 106 km from storm center respe

the relationship between strain rates crustal thickening palaeomagnetism finite strain and fault movements within a deforming zone the deformation of continental lithosphere generally does not occur on a single fault but is distributed over a zone up to a few hundred kilometers wide if the deformation rate is constant throughout the zone and if the velocity is continuous everywhere and does not change with time the deformation gradient tensor can be obtained analytically this tensor directly determines the amount of crustal thickening and is related in a complicated manner to the finite strain tensor the declination of remnant magnetization measured within the zone can also be rotated by the deformation because palaeomagnetic measurements are generally made on rigid blocks which have not been deformed there is no simple relationship between such rotations and the finite strain expressions for all these quantities are obtained in terms of the velocity gradients which are taken to be constant the history of western north america is used to illustrate the relationship between the present deformation by strike slip and thrust motions the rotations of the remnant magnetization vectors and the shape of accreted terranes at the surface distributed deformation is taken up by motion on faults which separate the zone into blocks the displacement rate on the faults their strike and the finite rotations of the blocks are all controlled by the velocity gradients analytic expressions relating these quantities are obtained a deforming zone containing normal faults which crosses central greece takes up both strike slip and extension and illustrates the relationship between the structures within and the motion across the zone a similar but more complicated zone in northeastern iran involves both strike slip and shortening

on the secondary eyewall formation of hurricane edouard 2014 abstracta first observationally based estimation of departures from gradient wind balance during secondary eyewall formation is presented the study is based on the atlantic hurricane edouard 2014 this storm was observed during the national aeronautics and space administration s nasa hurricane and severe storm sentinel hs3 experiment a field campaign conducted in collaboration with the national oceanic and atmospheric administration noaa a total of 135 dropsondes are analyzed in two separate time periods one named the secondary eyewall formation period and the other one referred to as the decaying double eyewalled storm period during the secondary eyewall formation period a time when the storm was observed to have only one eyewall the diagnosed agradient force has a secondary maximum that coincides with the radial location of the secondary eyewall observed in the second period of study the maximum spinup tendency of the radial influx of absolute vertical vorticity is within the boundary la

least squares palinspastic restoration of regions of normal faulting application to the campos basin brazil we have developed an iterative least squares method for palinspastic restoration of regions of normal faulting the method closes the gaps cut off lenses across normal faults on a structure contour map of a given stratigraphie horizon such data are often available for sedimentary basins covered by seismic surveys before restoration we first produce a fault block map where each block is completely surrounded by faults whether real or artificial we then apply an algorithm to minimize d the sum of the squares of the distances across cut off lenses with respect to unknown rigid block translations and rotations minimization results in non linear equations which we solve by an iterative method we deem the solution to have converged when d falls below a given critical level in general restoration not only closes the original gaps but also results in strike slip displacements between blocks thus the deformation need not be a plane strain and displacement vectors need not be parallel we have applied the method to an area of the campos basin on the atlantic margin of brazil where the stratigraphy and structure are well known from seismic surveys and from wells cretaceous and tertiary sediments have glided downslope on a lubricating layer of aptian evaporites producing an uppermost domain of normal faulting the normal faults occupy a strip lying between undisturbed continental crust to the west and relatively unstructured sediments to the east assuming the western boundary to be stationary we have restored an upper oligocene stratigraphie level the marco azul convergence was achieved rapidly and the degree of fit is good according to our restoration the eastern boundary of the area has bowed out seawards since the oligocene block displacement vectors form a fan like pattern with an element of mirror symmetry about a line trending nw se maximum displacements occur in an apical domain bounded by a horseshoe pattern of faults there is a general pattern of block rotations counterclockwise in the northeast clockwise in the southwest some notable exceptions to this general pattern are due to local domino motions we attribute the overall displacement field to divergent gravitational gliding off a local salient in the sea bottom topography because of the three dimensional nature of the displacement field restoration of vertical cross sections alone would yield gross errors this demonstrates the value of palinspastic methods such as ours

estimates of strain due to brittle faulting sampling of fault populations abstract the geometry of sampling domains is a first order consideration in the characterization of brittle fault populations in most cases descriptions of fault size distributions based on map cross section traverse or borehole data systematically underestimate the number of small faults present in a volume the geometry of sampling domains may be accounted for using an empirical proportionality between fault displacement and trace length estimates of strain in which the sampling geometry is considered suggest that small faults accommodate a significant portion of the total strain due to the brittle faulting process

least squares restoration of tertiary thrust sheets in map view tajik depression central asia the tajik depression located west of the pamirs and south of the tien shan is a compressional intermontane basin bounded by basement overthrusts and filled with mesozoic and cenozoic sediments the internal structure is typical of a thin skinned tbld and thrust belt kinematic data available in the literature suggest that indentation of the pamirs into asia durino the cenozoic collision of india and asia has been accommodated in various ways within the depression including westward extrusion thickening combined with wrenching along n s tblds and thrusts and counterclockwise rotations these various detbrmation processes can be analyzed and quantified by reconstruction of the predeformed state of the depression however the combina tion of thrusting wrenching and block rotations implies a nonplane deformation which cannot be restored properly using balanced cross sections alone we have therefore developed a numerical method for restoration of stratigraphic surfaces designed for regions of nonplane compressional tectonics the deformed region is represented in map view as a mosaic of fault bounded blocks overlapping each other along the faults blocks are separately unfolded and then numerically packed together by least squares minimization of overlaps yielding fields of finite horizontal translations and rotations about vertical axes to analyze the deformation postdating the collision of india and asia we have restored a stratigraphic surface at the base of the cenozoic first in order to test the numerical method we restored a map that had previously been restored by a purely manual method restoration of a second map drawn from newly available subsurface data leads to geometrical inconsistencies overlaps and gaps which cannot be reduced remain in the restored state after correction of these inconsistencies restoration yields a complex mode of deformation for the depression individual thrust slices have undergone counterclockwise rotations about verti cal axes the magnitudes increasing from west to east up to a maximum of 40 o near the pamirs horizontal shortening is 150 km 35 in the center of the depression and 240 km 85 in the northeastern part between the pamirs and the tien shan strike slip motions commonly not revealed by balancing cross sections are associated with thrusting on faults striking n s inde pendent paleomagnetic data and slip directions on small scale faults provide positive checks on the results of our restoration

vertical structure of tropical cyclones with concentric eyewalls as seen by the trmm precipitation radar ten years of data from the tropical rainfall measurement mission satellite s precipitation radar are analyzed to determinethe typical vertical structure of the concentric eyewalls of tropical cyclones undergoing eyewall replacement the vertical structure of the secondary outer eyewall is different from the primary inner eyewall and also different from the eyewall of single eyewall storms the upper troposphere portions of the outer eyewalls are like the rainbands from which they evolve their lower tropospheric portions are more intense and more uniform than rainbands of single eyewall storms suggesting that these secondary eyewalls are forming from rainbands undergoing axisymmetrization and building from below the inner concentric eyewalls are more strongly affected by shear than are the eyewalls of single eyewall storms while the outer eyewalls are relativelyunaffectedby shear which suggeststhe outereyewall is amplifyingthe shearinduced asymmetry of the inner eyewall

the dynamics of intensification in a hurricane weather research and forecasting simulation of hurricane earl 2010 we use a high resolution numerical simulation of atlantic hurricane earl 2010 to increase our understanding of earl s intensification in relatively strong vertical shear in the context of a recent paradigm for tropical cyclone intensification the integrity of the simulation is judged by comparing analyses thereof with those of the unprecedented observational data gathered in earl consistent with the classical view of spin up the amplification of the tangential wind field above the boundary layer is found to occur as the absolute angular momentumsurfaces are drawn inwards by the aggregate heating of the rotating convective clouds in the interior of the vortex in addition to this classical pathway spin up occurs within the inner core boundary layer where the maximum tangential winds occur the latter is another element of the new paradigm despite the detrimental influence of the shear on the vortex alignment and on depressing the pseudo equivalent potential temperature outside the developing eyewall the combined eddy processes associated with the vortical plume structures in and around the developing eyewall region are shown to contribute to an enhanced overturning circulation and an intensifying storm these eddy processes are distinctly agradient effects that are not features of the classical spin up mechanism it remains to be understood how the rotating convective updraughts combine to produce the diagnosed structures of the eddy terms themselves and how vortex rossby waves and other eddies contribute to the alignment of the vortex during intensification

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

the effects of vertical wind shear on the distribution of convection in tropical cyclones abstract the influence of vertical wind shear on the azimuthal distribution of cloud to ground lightning in tropical cyclones was examined using flash locations from the national lightning detection network the study covers 35 atlantic basin tropical cyclones from 1985 99 while they were over land and within 400 km of the coast over water a strong correlation was found between the azimuthal distribution of flashes and the direction of the vertical wind shear in the environment when the magnitude of the vertical shear exceeded 5 m s 1 more than 90 of flashes occurred downshear in both the storm core defined as the inner 100 km and the outer band region r 100 300 km a slight preference for downshear left occurred in the storm core and a strong preference for downshear right in the outer rainbands the results were valid both over land and water and for depression storm and hurricane stages it is argued that in convectively active tropical cyclones deep divergent circulations oppose the ver

the inverse problem in microtectonics and the separation of tectonic phases abstract the algorithm of inverse problems is applied to three cases in microtectonics a collection of striations measured on pre existing faults may be processed automatically and interpreted in terms of tectonic stress a comparison is made between two different methods formerly proposed by the authors both methods are tested with field data the theoretical results agree with independent field criteria for a separation of tectonic phases

transverse fold evolution in the external sierra southern pyrenees spain fault slip data are used to reconstruct varying tectonic regimes associated with transverse fold development along the eastern and southern margins of the jaca basin southern pyrenees spain the spanish pyrenean foreland consists of thrust sheets and leading edge decollement folds which developed within piggyback basins guara formation limestones on the margins of the jaca basin were deposited synchronously with deformation and are exposed in the external sierra within the transverse folds principal shortening axes determined from p and t dihedra plots of fault slip data show a shift from steep shortening in stratigraphically older beds to nne ssw horizontal shortening in younger beds older strata are characterized by extensional faults interpreted to result from halotectonic salt tectonics deformation whereas younger strata are characterized by contraction and strike slip faults interpreted to result from thrust sheet emplacement the interpretation of the timing for the shortening axes in the younger strata is supported by the observation that these axes are parallel to shortening axes determined from finite strain analysis calcite twins and regional thrusting directions determined from fault related folds and slickenlines this study shows that fault population analysis in syntectonic strata provides an opportunity to constrain kinematic evolution during orogeny

kinematics of the secondary eyewall observed in hurricane rita 2005 abstractairborne doppler radar data collected from the concentric eyewalls of hurricane rita 2005 provide detailed three dimensional kinematic observations of the secondary eyewall feature the secondary eyewall radar echo shows a ring of heavy precipitation containing embedded convective cells which have no consistent orientation or radial location the axisymmetric mean structure has a tangential wind maximum within the reflectivity maximum at 2 km altitude and an elevated distribution of its strongest winds on the radially outer edge the corresponding vertical vorticity field contains a low level maximum on the inside edge which is part of a tube of increased vorticity that rises through the center of the reflectivity tower and into the midlevels the secondary circulation consists of boundary layer inflow that radially overshoots the secondary eyewall a portion of this inflowing air experiences convergence and supergradient forces that cause the air to rise and flow radially outward back into th

slip system domains i plane strain kinematics of arrays of coherent bands with twinned fibre orientations abstract slip system in rocks often occupy domains each of uniform slip system orientation examples are conjugate faults shear zones folded bedding and crystal lattices domainal behaviour in plane strain is modelled as simple shearing along inextensible fibres an array of alternating band domains with coherent boundaries can undergo a uniform bulk strain with local perturbations in the domains if 1 domain boundaries are planes of mirror symmetry with respect to fibre attitude and 2 domains have alternating fractional widths a and 1 a motion in the models is shown to be a combination of three independent modes plus a bulk rigid motion during mode 1 motion domain boundaries stretch but do not migrate during mode 2 they do not stretch but migrate by lateral translation during mode 3 they migrate by translation and rotation orientation distribution functions odfs are defined by assigning frequencies a and 1 a to orientations and changes in are shown to be due to mode 1 alone changes in a to mode 2 alone mode 3 has no effect on an odf combinations of modes 1 2 and 3 can be used to accommodate an imposed bulk motion two examples are discussed a bulk simple shear and a rigid motion large amounts of simple shear are possible if fibres are on average parallel to the imposed shear direction if modes 1 and 2 are operative the resulting odf has a maximum peak close to the shear direction this may explain the asymmetry of preferred lattice orientations and the occurrence of unique fault sets in rocks that have undergone a progressive simple shear

determination of the tectonic stress tensor from slip along faults that obey the coulomb yield condition a new method to calculate the stress tensor associated with slip along a population of faults is derived here the method incorporates two constraints first the stresses in the slip direction satisfy the coulomb yield criterion and second the slip occurs in the direction of maximum shear stress along the fault the computations provide the complete stress tensor normalized by the vertical stress and evaluation of the mean coefficient of friction and the mean cohesion of the faults during the time of faulting the present method is applied to three field cases dixie valley nevada wadi neqarot israel and yuli microearthquakes taiwan it is shown that the coefficieet of friction of the three cases varies between 0 1 to 0 8 further it is demonstrated that previous stress inversion methods implicitly assume zero friction along the faults

western north pacific typhoons with concentric eyewalls abstract this study examines the intensity change and moat dynamics of typhoons with concentric eyewalls using passive microwave data and best track data in the western north pacific between 1997 and 2006 of the 225 typhoons examined 55 typhoons and 62 cases with concentric eyewalls have been identified the data indicate that approximately 57 of category 4 and 72 of category 5 typhoons possessed concentric eyewalls at some point during their lifetime while major typhoons are most likely to form concentric eyewalls the formation of the concentric structure may not be necessarily at the lifetime maximum intensity approximately one third of concentric eyewall cases are formed at the time of maximum intensity the moat is known to be heavily influenced by the subsidence forced by the two eyewalls rozoff et al proposed that the rapid filamentation dynamics may also contribute to the organization of the moat this paper examines the possibility of rapid filamentation dynamics by devising a filamentati

outer rainbands driven secondary eyewall formation of tropical cyclones abstractsecondary eyewall formation sef could be considered as the aggregation of a convective ring coupling with a tangential wind maximum outside the primary eyewall of a tropical cyclone tc

hurricane intensity and eyewall replacement observations made during the historic 2005 hurricane season document a case of eyewall replacement clouds outside the hurricane eyewall coalesce to form a new eyewall at a greater radius from the storm center and the old eyewall dies the winds in the new eyewall are initially weaker than those in the original eyewall but as the new eyewall contracts the storm reintensifies understanding this replacement mechanism is vital to forecasting variations in hurricane intensity processes in the moat region between the new and old eyewall have been particularly unclear aircraft data now show that the moat becomes dynamically similar to the eye and thus is converted into a region inimical to survival of the inner eyewall we suggest that targeting aircraft to key parts of the storm to gain crucial input to high resolution numerical models can lead to improvements in forecasting hurricane intensity

are eyewall replacement cycles governed largely by axisymmetric balance dynamics the authors question the widely held view that radial contraction of a secondary eyewall during an eyewall replacement cycle is well understood and governed largely by the classical theory of axisymmetric balance dynamics the investigation is based on a comparison of the secondary circulation and derived tangential wind tendency between a full physics simulation and the sawyer eliassen balance model the comparison is made at a time when the full physics model exhibits radial contraction of the secondary eyewall during acanonical eyewall replacement cycle it is shownthat thesawyer eliassen model is unable to capture the phenomenology of secondary eyewall radial contraction because it predicts a net spindown of the boundary layer tangential winds and does not represent the boundary layer spinup mechanism that has been articulated in recent work

paleomagnetic study along the southeastern edge of the altiplano puna plateau neogene tectonic rotations in northwestern argentina the transition zone between the puna and the sierras pampeanas was deformed in late miocene and pliocene time structural observations suggest that local clockwise block rotations might be observed associated with dextral transpression this study contributes new paleomagnetic results from four sites in cretaceous rocks and 19 sites in neogene sedimentary sequences when compared with reference paleomagnetic data for stable continental south america the results show an average inclination shallowing error of 10 5 and a pattern of clockwise rotations up to 29 study of the anisotropy of magnetic susceptibility ams on 278 specimens provided for most sites ams tensors with an oblate shape controlled by sedimentation and compaction explaining the observed inclination shallowing a slight ams lineation was measured and we argue that this magnetic lineation reflects late miocene pliocene compression a correlation observed between magnetic lineations deduced from the ams analysis and rotation estimates from remanent magnetizations demonstrates that the inferred shortening directions have also been rotated clockwise

finite strain and rotation from fault slip data abstract the moment tensor summation mts characterizes the infinitesimal strain of a region due to fault rupture during an earthquake tectonic strain on a much longer time scale can be found by applying the mts to fault slip data which represent cumulative fault displacement however the traditional mts assumes infinitesimal strain which may not be appropriate for cumulative displacement on faults therefore it is necessary to examine whether a finite strain treatment is more appropriate we develop a method to find finite strain from fault slip data fsfs and use it to illuminate two general faulting problems finite strain and block rotation first the fsfs method is compared to the mts using both synthetic and real fault data strain due to faults must be high 60 elongation before the infinitesimal strain approximation produces errors greater than the variation of typical field data however some regions do exhibit very high fault strains and require finite strain analysis second the fsfs method is used to solve for rotation in regions cut by domino style faults a common model for high fault strains and rotation given an arbitrary rigid boundary the method can be used to relate fault strain and block rotation for example a paleomagnetic rotation of 40 requires fault strain with a minimum finite elongation of 41

fault mechanics and the kinematics of block rotations in many strike slip tectonic settings large rotations up to 100 of crustal blocks have been inferred from paleomagnetic data these blocks are bounded by sets of parallel faults which accommodate the relative motion between the blocks as regional deformation progresses simple geometrical considerations require that the faults must also rotate in this paper we show that on the basis of mechanical considerations the amount of fault rotation permissible under a stationary stress field is limited to 20 to 45 consequently block rotations that are larger than 40 or 45 require more than one set of accompanying faults to accommodate the block rotation examples of such multiple sets with 40 to 45 between them as predicted by the model were recognized in sistan iran in yerington the lake mead area nevada and in southern california

secondary eyewall formation and eyewall replacement cycles in a simulated hurricane effect of the net radial force in the hurricane boundary layer abstractmultiple secondary eyewall formations sefs and eyewall replacement cycles ercs are simulated with the fifth generation pennsylvania state university psu national center for atmospheric research ncar mesoscale model mm5 at horizontal grid spacing of 0 67 km the simulated hurricane is initialized from a weak synthetic vortex in a quiescent environment on an f plane after spinup and rapid intensification the hurricane enters a mature phase during which the intensity change is relatively slow convective clouds then organize into a ring with a secondary tangential wind maximum at radii beyond the hurricane s primary eyewall this secondary eyewall se then contracts and strengthens the primary eyewall weakens and is eventually replaced by the se the hurricane grows in size and the radius of maximum wind rmw increases as similar ercs repeat 5 times during the simulation two existing hypotheses on sef are evaluated using the simulation output then model diagnostics are used to revea

essential dynamics of secondary eyewall formation abstractthe authors conduct an analysis of the dynamics of secondary eyewall formation in two modeling frameworks to obtain a more complete understanding of the phenomenon the first is a full physics three dimensional mesoscale model in which the authors examine an idealized hurricane simulation that undergoes a canonical eyewall replacement cycle analysis of the mesoscale simulation shows that secondary eyewall formation occurs in a conditionally unstable environment questioning the applicability of moist neutral viewpoints and related mathematical formulations thereto for studying this process of tropical cyclone intensity change the analysis offers also new evidence in support of a recent hypothesis that secondary eyewalls form via a progressive boundary layer control of the vortex dynamics in response to a radial broadening of the tangential wind field the second analysis framework is an axisymmetric nonlinear time dependent slab boundary layer model with radial diffusion when this boundary l

tectonic development southeastern border of the puna plateau northwestern argentine andes the puna altiplano a 500 000 km2 area at an average elevation of 3 7 km in the central andes occurs in a non collisional plate setting over a 30 east dipping segment of the benioff zone and is bounded to the north and south by nearly flat segments of the subducted nazca plate a 120 km long portion of the southeastern boundary of the puna in northwestern argentina was studied to gain insight into the structures associated with uplift of the plateau and into the nature of structures over the transition from flat to steeper subduction the structural geometry and kinematic evolution of the region was determined from geologic mapping and kinematic analysis of minor fault arrays the present southeastern margin of the puna was uplifted between 5 10 and 2 ma northwest southeast horizontal shortening and vertical extension during uplift were produced by northeast striking en echelon thrust faults dipping 17 55 northwest four to seven en echelon structural blocks each 20 30 km long constitute the border of the puna their structural geometry precludes large scale overthrusting as an important mechanism of plateau uplift along the studied segment in the past 2 m y there has been a 45 change in the direction of shortening and locally a 90 change in the extension direction indicating that the structures accompanying uplift are no longer active this change could be due to a change either in the geometry of the subducted plate or in convergence directions although neither of these hypotheses is testable given presently available data