north atlantic storm driving of extreme wave heights in the north sea the relationship between storms and extreme ocean waves in the north sea is assessed using a long period wave dataset and storms identified in the interim ecmwf re analysis era interim an ensemble sensitivity analysis is used to provide information on the spatial and temporal forcing from mean sea level pressure and surface wind associated with extreme ocean wave height responses extreme ocean waves in the central north sea arise due to intense extratropical cyclone winds from either the cold conveyor belt northerly wind events or the warm conveyor belt southerly wind events the largest wave heights are associated with northerly wind events which tend to have stronger wind speeds and occur as the cold conveyor belt wraps rearwards round the cyclone to the cold side of the warm front the northerly wind events provide a larger fetch to the central north sea to aid wave growth southerly wind events are associated with the warm conveyor belts of intense extratropical cyclones that develop in the left upper tropospheric jet exit region ensemble sensitivity analysis can provide early warning of extreme wave events by demonstrating a relationship between wave height and high pressure to the west of the british isles for northerly wind events 48 hours prior southerly wind extreme events demonstrate sensitivity to low pressure to the west of the british isles 36 hours prior

origin of 3 45 ga coniform stromatolites in warrawoona group western australia a new occurrence of conical and branched pseudocolumnar stromatolites in archean dolostones in the pilbara region australia contributes significant new morphologic information on such structures these remains are interpreted as probably representing in part microbially mediated accretionary growth surfaces in an archean hypersaline depositional basin the structures comprise laterally linked pseudocolumns of centimeter width and decimeter height with first order conical laminae of as much as 15 cm of synoptic relief and apical angles of 30 80 the conical laminae are modified by a second order centimeter scale low amplitude primary corrugate lamination with crests and troughs occasionally stacked to form satellitic obliquely directed pseudocolumns bedding surfaces exhibit a preferred direction of elongation of the cones an orientation that is orthogonal and unrelated to the trend of younger folding the microstructure is secondary the stromatolites are better preserved than those previously known from chert in the warrawoona succession the remains exhibit certain distinct morphologic attributes corresponding to those in younger stromatolites such as displayed by thyssagetes and jacutophyton whose biogenicity is generally accepted although difficult to demonstrate conclusively the conical warrawoona forms may represent the oldest known precursor of these taxa

sting jets in simulations of a real cyclone by two mesoscale models the existence of sting jets as a potential source of damaging surface winds during the passage of extratropical cyclones has recently been recognized however there are still very few published studies on the subject furthermore although it is known that other models are capable of reproducing sting jets in the published literature only one numerical model the met office unified model metum has been used to numerically analyze these phenomena this article aims to improve our understanding of the processes that contribute to the development of sting jets and show that model differences affect the evolution of modeled sting jets a sting jet event during the passage of a cyclone over the united kingdom on 26 february 2002 has been simulated using two mesoscale models namely the metum and the consortium for small scale modeling cosmo model to compare their performance given the known critical importance of vertical resolution in the simulation of sting jets the vertical resolution of both models has been enhanced with respect to their operational versions both simulations have been verified against surface measurements of maximum gusts satellite imagery and met office operational synoptic analyses as well as operational analyses from the ecmwf it is shown that both models are capable of reproducing sting jets with similar though not identical features through the comparison of the results from these two models the relevance of physical mechanisms such as evaporative cooling and the release of conditional symmetric instability in the generation and evolution of sting jets is also discussed

structure of a frontal cyclone a diagnostic study of a mid latitude cyclone has been carried out using routinely available numerical weather prediction model products and imagery the cyclone was intense but not exceptionally so and the results are believed to have some generality the detailed description of the cyclone structure just before it began to deepen rapidly integrates concepts from a number of researchers into a common framework a dominant feature of the cyclone close to its centre was the cloud head a region of cloud with a sharp convex outer edge which formed poleward of the main polar front cloud band the cloud head was caused by two flows that entered it from the east ascending and fanning out within it one flow the cold conveyor belt brought low wet bulb potential temperature w air back into the cloud head from low levels ahead of the warm front the other flow was due to high w air that peeled off from the base of the main warm sector airflow i e part of the warm conveyor belt and travelled in the boundary layer back towards the cyclone centre first undercutting dry air that had earlier descended from the upper troposphere called a dry intrusion and then ascending at the upper boundary of the cloud head above the cold conveyor belt the transverse circulation that gave the ascent within the cloud head also led to the cold front fracturing along its length into two separate sharp surface cold fronts with a more diffuse frontal region in between frontal fracture the two sharp surface cold fronts were associated with narrow cold frontal rainbands line convection one of the line convection segments forming the southern edge of the cloud head the overrunning of the dry intrusion in the region of the frontal fracture led to a structure known as a split front in which an upper level humidity front began to run ahead of the position of the surface cold front a feature of the cyclone at this intermediate stage in its evolution was that a large proportion of the precipitation was being generated by ascent of relatively cold air the cold conveyor belt in the cloud head as part of the thermally indirect circulation at the left exit of a developing secondary upper level jet

fabric transitions from shell accumulations to reefs an introduction with palaeozoic examples one unresolved conceptual problem in some palaeozoic sedimentary strata is the boundary between the concepts of shell concentration and reef in fact numerous bioclastic strata are transitional coquina reef deposits because either distinct frame building skeletons are not commonly preserved in growth position or skeletal remains are episodically encrusted by stabilizer reef like organisms such as calcareous and problematic algae encrusting microbes bryozoans foraminifers and sponges the term parabiostrome coined by kershaw can be used to describe some stratiform bioclastic deposits formed through the growth and destruction by fair weather wave and storm wave action of meadows and carpets bearing frame building archaeocyaths bryozoans corals stromatoporoids etc and or epibenthic non frame building e g pelmatozoan echinoderms spiculate sponges and many brachiopods organisms this paper documents six palaeozoic examples of stabilized coquinas leading to pseudo reef frameworks some of them formed by storm processes generating reef soles aborted reefs or being part of mounds on ramps and shelves and were consolidated by either encrusting organisms or early diagenesic processes whereas others bioclastic dominated shoals in barrier shelves were episodically stabilized by encrusting organisms indicating distinct episodes in which shoals ceased their lateral migration a paramount quantity of information characterizes the formation and distribution of shell concentrations and reefs in modern and cenozoic strata but the knowledge of phanerozoic shell concentrations and reefs is decreasing when increasing in age the palaeozoic is a key time span in the history of life owing to the wide occurrence of skeletonized metazoans the so called cambrian explosion zhuravlev riding 2000 and the successive biodiversifications related to i major extinctions such as the end ordovician cooper 2004 the frasnian famenian boundary buggisch 1991 copper 2002 racki house 2002 and the endpermian extinction wignall hallam 1992 and ii major community replacements such as the lower middle cambrian transition 2 j j alvaro et al remains webb 1996 following wood s 1998 definition reefs develop due to the aggregation of sessile epibenthic marine organisms with the resultant higher rate of in situ carbonate production than in surrounding sites although the relative capacity of some gregarious epibenthic organisms bearing mineralized skeletons to be preserved in living position is a common characteristic of reef organisms this character is also shared with other non reef metazoans adapted to soft substrates and forming bundles like clusters one group of these organisms named secondary soft bottom dwellers by seilacher 1984 differs from mud stickers e g non encrusting pelmatozoans and sponges in the heavy weight of their shells these metazoans mainly brachiopods and molluscs develop common cup boulderand fan shaped convergent morphologies favouring recliner strategies seilacher 1984 savazzi 1999 skeletal concentrations can be subdivided according to their biostratinomic features into biogenic sedimentary diagenetic and mixed concentrations kidwell et al 1986 biogenic concentrations can be intrinsic or extrinsic in character the former generated by the organisms that produce the hard parts resulting from intrinsic gregarious behaviours of autochthonous and parautochthonous skeletal organisms e g preferential colonization by larvae and single colonization events of opportunistic species and the latter produced by other organisms that interact with skeletonized organisms on their discarded hard parts leading to the formation of parautochthonous and allochthonous concentrations e g hard part rich fecal masses and shell filled pits sedimentary concentrations result from physical usually hydraulic processes of concentration in which hard parts behave as sediment particles and non bioclastic matrix is either reworked or fails to accumulate e g shelly storm lags aeolian beach pavements channel lags in fluvial intertidal and subtidal environments or shell paved turbidities diagenetic concentrations form or are significantly enhanced by processes acting after burial such as compaction or selective dissolution of matrix and finally mixed concentrations form by the interplay of two or more kinds of the aforementioned processes and can display both autochthonous parautochthonous and allochthonous shell

model of earthquake recurrence role of elastic wave radiation relaxation of friction and inhomogeneity we have constructed a dynamical model of seismicity wherein a fault is embedded in an infinite continuous elastic medium therefore the influence of the energy dissipated in seismic wave radiation oil the sequential history of model earthquakes is fully taken into account in this model the drop in friction at rupture takes place gradually thus introducing a relaxation dimension as an example we consider a finite homogeneous fault that is terminated by infinitely strong barriers at the ends the features of the seismicity are dominated by the stresses that are reflected from the unbreakable barriers there is a strong dependence of the patterns of seismicity on the ratio of the relaxation dimension to the distance between the barriers at the ends for large values of this parameter we find that periodicity begins after a short transient interval and a dominance of the statistical distributions by large events that break completely through the fault from end to end for small values of this parameter smaller scale seismicity is interspersed with the large events and no periodicity is observed within the time spanned by the computations we conclude that major unquenched heterogeneities such as those found at barriers which we suppose arise in nature due to the nonuniform geometry of faults are vital ingredients for generating complex seismic histories as well as giving rise to the complex features of individual earthquake source time functions in models of seismicity as a dynamical process

palaeogeographical controls on the cambrian trilobite immigration and evolutionary patterns reported in the western gondwana margin abstract southward drifting of the western gondwanan margin during the cambrian has been demonstrated by means of both palaeomagnetic methods and lithological indicators of climate such as carbonates and evaporites recent improvements in biostratigraphical correlations permit an enhanced understanding of the climatic and palaeobiogeographical constraints that controlled the distribution of cambrian benthic communities palaeogeographical and biogeographical reconstructions based on trilobites are reported in this paper in order to test interaction between migration speciation and extinction rates the variability of the documented biogeographical patterns is directly related to species diversity in which wider distribution coincides with transgressive trends and subsequent connection of neighbouring platforms early cambrian trilobite faunas show a high degree of both substrate control and endemicity although transgressions led to parallel shifts in faunal compositions by contrast mid cambrian trilobite faunas are relatively uniform across western gondwana and latest mid and late cambrian associations document influence of an increased similarity with asian trilobite faunas

wind profiler observations of a sting jet some of the most damaging surface winds experienced in midlatitude cyclonic storms have been attributed to a phenomenon known as a sting jet previous studies have deduced how sting jets develop from their midtropospheric origin but there have been no direct observations of these wind features in the midtroposphere during windstorm jeanette on 27 october 2002 the tip of the storm s cloud head passed over a vhf wind profiler at aberystwyth wales allowing the structure of a sting jet to be measured with high spatial and temporal resolution these observations showed a multiple slantwise structure to the sting jet region with two tails of increased winds that persisted after the passing of the cloud head aloft simulations by the met office unified model um showed that the slantwise structure followed w surfaces and that the sting jet descended along surfaces as it passed over the uk accelerating and drying during its descent the horizontal and vertical scales of the observed structures are compatible with slantwise convection releasing conditional symmetric instability within the cloud head further observations of the sting jet were obtained by a uhf wind profiler at cardington in eastern england where the sting jet had merged with the cold conveyor belt circulating around the storm an unstable temperature profile in the lowest kilometre over cardington enabled damaging gusts of strong winds to be brought to the surface in convective plumes however this strong vertical mixing was not represented correctly in the um copyright 2009 royal meteorological society

frictional sliding of dolomite a variation in constitutive behavior fault slip occurs via earthquakes or stable creep depending on the manner in which frictional resistance varies with sliding velocity and displacement if the form of this dependence is a function of rock type observed spatial variations in slip behavior along faults could be explained by lithologic variation we have used a rotary shear apparatus to investigate the frictional response of dolomite marble to changes in sliding velocity we have modeled the results using a state variable constitutive law for rock friction and a numerical method to solve for the interaction between the friction law and the compliance of our machine dolomite marble displays steady state velocity strengthening as contrasted with granite and quartzite which show velocity weakening at the same conditions to model the dolomite results it is necessary to use two state variables and surprisingly the parameters specifying the decay magnitudes associated with these state variables differ in sign from each other the magnitude of the parameter associated with the longer decay is negative leading to a downward decay of frictional strength associated with a decrease in velocity if the shorter decay is of sufficient magnitude as we observe at low velocity it is possible for the machine rock system to exhibit instability and oscillatory behavior even though the steady state response is velocity strengthening another way in which dolomite contrasts with granite and quartzite is that the friction parameters vary strongly with velocity a transition from unstable to stable sliding with increasing velocity has been observed previously and our observed variation of the constitutive parameters with velocity can explain this behavior there is some indication that the evolution of the state variables for dolomite occurs as a function of time rather than displacement in contrast with granite and quartzite the frictional behavior of dolomite shows that the constitutive laws that have been developed based on results from granite and quartzite are inadequate to describe all rock types and that more general laws are required

the sting at the end of the tail damaging winds associated with extratropical cyclones strong surface winds often accompany the low level jets that occur along the cold fronts of extratropical cyclones but there is evidence that the strongest surface winds occur in a distinctly different part of a certain class of cyclone the most damaging extratropical cyclones go through an evolution that involves the formation of a bent back front and cloud head separated from the main polar front cloud band by a dry slot when the cyclone attains its minimum central pressure the trailing tip of the cloud head bounding the bent back front forms a hook which goes on to encircle a seclusion of warm air the most damaging winds occur near the tip of this hook the sting at the end of the tail observations of the great storm of october 1987 in south east england are re examined in some detail to study this phenomenon the cloud head is shown to have a banded structure consistent with the existence of multiple mesoscale slantwise circulations air within these circulations leaves the hooked tip of the cloud head and enters the dry slot much faster than the rate of travel of the cloud head tip implying rapid evaporation and diabatic cooling immediately upwind of the area of damaging surface winds the circumstantial evidence from the observational study leads one to hypothesize that the mesoscale circulations and the associated evaporative heat sinks may play an active role in strengthening the damaging winds regardless of how important this role may be the evolution of the cloud pattern seen in satellite imagery is a useful tool for nowcasting the occurrence and location of the worst winds copyright 2004 royal meteorological society

a microphysical interpretation of rate and state dependent friction for fault gouge the evolution of fault strength during the seismic cycle plays a key role in the mode of fault slip nature of earthquake stress drop and earthquake nucleation laboratory based rate and state dependent friction rsf laws can describe changes in fault strength during slip but the connections between fault strength and the mechanisms that dictate the mode of failure from aseismic creep to earthquake rupture remain poorly understood the empirical nature of rsf laws remains a drawback to their application in nature here we analyze an extensive data set of friction constitutive parameters with the goal of illuminating the microphysical processes controlling rsf we document robust relationships between 1 the initial value of sliding or kinetic friction 2 rsf parameters and 3 the time rates of frictional strengthening aging we derive a microphysical model based on asperity contact mechanics and show that these relationships are dictated by 1 an activation energy that controls the rate of asperity growth by plastic creep and 2 an inverse relationship between material hardness and the activation volume of plastic deformation collectively our results illuminate the physics expressed by the rsf parameters and which describe the absolute value of frictional strength and its dependence on time and slip rate moreover we demonstrate that seismogenic fault behavior may be dictated by the interplay between grain properties and ambient conditions controlling the local shear strength of grain scale asperity contacts

the role of mesoscale instabilities in the sting jet dynamics of windstorm tini sting jets sj occur as an additional region of low level strong winds in some shapiro keyser type extra tropical cyclones while sjs are widely accepted as being distinct from the warm and cold conveyor belts the mechanisms responsible for their occurrence are still not fully understood here we determine the relative importance of the release of mesoscale instabilities and synoptic scale cyclone dynamics so addressing an area of current debate numerical weather prediction simulations of a sj containing windstorm are analysed and lagrangian trajectories used to assess the evolution of and mesoscale atmospheric instabilities e g symmetric and inertial instabilities in the descending airstream the sj undergoes a two stage descent cooling via sublimation followed by a large acceleration accompanied by instability release combined tilting and stretching of vorticity play a major role in the local onset of instability on the airstream vorticity and frontogenesis fields have a narrow slantwise banded structure in the cloud head and around the sj the descending sj modifies the widespread frontolysis expected from the large scale dynamics alone in the frontal fracture region a coarser resolution simulation also generates strong winds in the frontal fracture region although these are significantly weaker than in the higher resolution simulation the sj airstream in the coarser resolution simulation undergoes a weaker descent without instability generation and descends in a widespread frontolytic region hence while the sj undergoes a process of destabilisation that enhances its descent and acceleration in the higher resolution simulation enhancing the strong winds already generated by the synoptic scale cyclone dynamics this destabilisation does not occur in the sj produced by a coarser resolution simulation resulting in weaker winds this analysis reveals the synergy between the paradigms of sj occurrence through the release of mesoscale instabilities and synoptic scale cyclone dynamics and demonstrates that the current debate may in part be a consequence of the model resolutions used by different studies

frictional constraints on crustal faulting we consider how variations in fault frictional properties affect the phenomenology of earthquake faulting in particular we propose that lateral variations in fault friction produce the marked heterogeneity of slip observed in large earthquakes we model these variations using a rate and state dependent friction law where we differentiate velocity weakening behavior into two fields the strong seismic field is very velocity weakening and the weak seismic field is slightly velocity weakening similarly we differentiate velocity strengthening behavior into two fields the compliant field is slightly velocity strengthening and the viscous field is very velocity strengthening the strong seismic field comprises the seismic slip concentrations or asperities the two intermediate fields weak seismic and compliant have frictional velocity dependences that are close to velocity neutral these fields modulate both the tectonic loading and the dynamic rupture process during the interseismic period the weak seismic and compliant regions slip aseismically while the strong seismic regions remain locked evolving into stress concentrations that fail only in main shocks the weak seismic areas exhibit most of the interseismic activity and aftershocks but can also creep seismically this mixed frictional behavior can be obtained from a sufficiently heterogeneous distribution of the critical slip distance the model also provides a mechanism for rupture arrest dynamic rupture fronts decelerate as they penetrate into unloaded complaint or weak seismic areas producing broad areas of accelerated afterslip aftershocks occur on both the weak seismic and compliant areas around a fault but most of the stress is diffused through aseismic slip rapid afterslip on these peripheral areas can also produce aftershocks within the main shock rupture area by reloading weak fault areas that slipped in the main shock and then healed we test this frictional model by comparing the seismicity and the coseismic slip for the 1966 parkfield 1979 coyote lake and 1984 morgan hill earthquakes the interevent seismicity and aftershocks appear to occur on fault areas outside the regions of significant slip these regions are interpreted as either weak seismic or compliant depending on whether or not they manifest interevent seismicity

two paradigms of baroclinic wave life cycle behaviour two idealized baroclinic wave 6 life cycles examined here suggest a framework of opposite extremes a in which to view the behaviour of real synoptic scale disturbances in middle latitudes and b in which to interrelate the synoptic and wave theoretic viewpoints using the saturation propagation saturation sps picture of wave 6 life cycle behaviour the two life cycles dented by lc1 and lc2 are higher resolution versions of the simmons hoskins basic and anomalous cases showing strong and weak late decay of eddy kinetic energy eke they illustrate in varying degrees two extreme types of behaviour here disignated anticyclonic and cyclonic and epitomized by strongly contrasting upper air trough behaviour anticyclonic behaviour dominates the late stages of lc1 and is characterized by backward tilted thinning troughs being advected anticyclonically and equatorward as in the commoner cases of planetary scale mid stratospheric rossby wave breaking cyclonic behaviour dominates lc2 and is characterized by forward tilted broadening troughs wrapping themselves up cyclonically and poleward producing major cut off cyclones in high latitudes these morphologies are visualized by upper air maps of potential temperature on the nominal tropopause defined as a constant potential vorticity surface some atmospheric mid latitude disturbances examined here using the same visualization applied to operational analyses show the same two extreme types of trough behaviour together with intermediate cases the sps picture is re examined using eliassen palm and refractive index cross sections it is shown in particular by reference to a wave activity theorem of haynes that the late stages of lc2 can be looked upon as a remarkably clear and morphologically novel large amplitude counterpart of the nonlinear reflection scenario of rossby wave critical layer theory the late stages of lc1 by constrast look more akin to an nonlinear critical layer absorption scenario lc2 exhibits region of largely undular pv contours adjacent to a nonlinear of irreversiby deformen pv contous in the latter region pv rearrangement and hence absorption of rossby wave activity has largely ceased this accounts for the more persistent ekee in the lc2 case

microbial crusts as indicators of stratigraphic diastems in the cambrian breche a micmacca atlas mountains of morocco the presence of microbial crusts interrupting high energy clastic sediments in carbonate and mixed carbonate siliciclastic platforms can be considered as distinct indicators of stratigraphic diastems characterized by either very low rates of deposition or non deposition this analysis is based on a microfacies study of the cambrian breche a micmacca atlas mountains morocco which contains some stratigraphically condensed limestones characterized by i disarticulation and fragmentation of skeletons ii abundance of volcanigenic debris iii rarity of muddy fraction iv dominance of a sessile epibenthic shelly fauna dominated by echinoderms chancelloriids and sponge spicules and v a complex diagenetic history due to erosion and reworking of lithified substrates the breche a micmacca limestones are composite event concentration low relief shoal complexes composed of parautochthonous and allochthonous bioclastic assemblages these units can be desribed as hiatal accumulations because of the subdivision of the coquinas by minor discontinuities or hiatal surfaces and the composite multiple event nature of the grainstones packstones the growth of microbial mats can be used as a record of time interrupting background sedimentation patterns characterized by the amalgamation of high energy events the breche a micmacca was deposited in an environment in which some intervals of non deposition or under extremely low sedimentation rates alternated with the succession of sedimentary events the biological response of microbial communities to coat stratigraphic discontinuities can be considered as an integral part of event stratigraphy they enhance the preservation and identification potential of interruption in the background sedimentation on substrates devoid of burrowing activity a distinct event of non deposition is also recognized based on the presence of microbial fabrics at the top of the breche a micmacca its microkarst structures reflect a major fall in the relative sea level of a reduced region of the platform resulting in dissolution and colonization of coelobiontic cavities by microbial mats and branching filaments

dynamic faulting under rate dependent friction we discuss the effects of rate dependent friction on the propagation of seismic rupture on active faults several physicists using burridge and knopoff s box and spring model of faulting have proposed that fault complexity may arise from the spontaneous development of a self similar stress distribution on the fault plane if this model proves to be correct it has important consequences for the origin of the complexity of seismic sources in order to test these ideas on a more realistic earthquake model we developed a new boundary integral equation method for studying rupture propagation along an antiplane fault in the presence of nonlinear rate dependent friction we study rupture dynamics of models with single and twin asperities in our models asperities are places on the fault with a higher value of prestress othewise all fault parameters are homogeneous we show that for models with such asperities a slip velocity weakening friction leads to the propagation of supersonic healing phases and to the spontaneous arrest of fracture if the prestress outside the asperities is low enough for models with asperities we can also observe narrow slip velocity pulses qualitatively similar to the so called heaton pulses observed in some earthquake accelerograms we also observe a complex distribution of stress after the rupture that depends on details of the initial distribution of asperities and on the details of the friction law

the sting at the end of the tail model diagnostics of fine scale three dimensional structure of the cloud head this is the second in a series of papers on the sting at the end of the tail a mesoscale region of potentially damaging surface winds that can occur close to the evaporating tip of a cloud head wrapped around the bent back front of an extratropical cyclone in the first paper the sting phenomenon was identified from a purely observational study of the great storm of october 1987 in the present paper an observationally validated forecast run from a high resolution numerical weather prediction model is used to examine the evolving three dimensional structure of the sting phenomenon it is shown that the damaging surface winds in the october 1987 storm were due to a well defined mesoscale sting jet sj identifiable as a coherent ensemble of trajectories originating in cloudy air at about 650 hpa there is evidence of multiple mesoscale slantwise circulations and the sj appears to form within the descending part of these circulations air within the sj descends to the 900 hpa level over a period of about 4 h during which time it accelerates from less than 20 to above 45 m s 1 with extremes greater than 50 m s 1 although the wet bulb potential temperature of air in the sj remains constant during its descent to 900 hpa evaporation leads to a reduction of up to 5 k or more in dry bulb potential temperature in some parts of the jet the sj is situated behind the primary cold front and is distinct from the associated warm conveyor belt low level jet it is also distinct from the cold conveyor belt low level jet which remains below and behind it as the sj skirts the bent back front crown copyright 2005

a potential vorticity based study of the role of diabatic heating and friction in a numerically simulated baroclinic cyclone abstract a particularly intense case of western atlantic baroclinic cyclogenesis was investigated in this study specifically the roles of latent heat of condensation and surface friction were examined from the potential vorticity or pv thinking perspective the methodology used for this study involves three key components 1 a full physics mesoscale model which provides a continuous and dynamically consistent dataset and provides full user control over physical processes 2 a partitioned pv integration which temporally integrates the accumulation of pv due to various physical processes in the model s eulerian framework and 3 the piecewise inversion method of davis and emanuel which calculates the balanced wind and mass field associated with particular pv anomalies potential vorticity features obtained through the partitioned integration technique were inverted to yield their direct contributions to the total circulation in addition sensitivity studies were carried out to determine the overal

sedimentology and sequence stratigraphy of a tithonian valanginian carbonate ramp vaca muerta formation a misunderstood exceptional source rock in the southern mendoza area of the neuquen basin argentina abstract the vaca muerta formation early tithonian early valanginian is a rhythmic succession of marls and limestones cropping out in the neuquen basin west central argentina this lithostratigraphic unit was traditionally interpreted as basinal to slope deposits detailed facies analysis allows to differentiate seven facies associations representing basinal to middle ramp facies of a homoclinal ramp system prograding westward from the eastern margin and slope facies attributed to a distally steepened ramp system that progrades eastward from the andean volcanic arc in the west two sequence hierarchies are recognized five third order depositional sequences and fifteen fourth order high frequency sequences fluctuations in organic matter content within the vaca muerta formation suggest relationship with depositional sequences finding the highest values associated with transgressive system tracts this work represents an important advance in the understanding of the sedimentary and stratigraphic evolution of this exceptional unconventional reservoir our sequence stratigraphic approach contributes to the understanding of the relationship between organic matter facies and sea level changes

middle late cambrian rankenella girvanella reefs of the mila formation northern iran following the collapse of the early cambrian archaeocyathan calcimicrobial reef consortium the middle late cambrian furongian was an interval dominated by purely microbial dendrolite and stromatolite reefs however among these latter a few exceptional occurrences of metazoan reefs are known one such reef complex occurs in the late middle early late cambrian furongian portion of the mila formation of northern iran in the otherwise low energy interval of this formation the anthaspidellid demosponge rankenella hamdii sp nov is associated with encrusting girvanella eocrinoid plates rhynchonelliformean brachiopod valves and subordinate hyoliths and trilobites in tempestite shell beds these beds underwent synsedimentary cementation on the seafloor to form hardgrounds in the succeeding higher energy interval a complex of metre scale bioherms and or taphoherms incorporates toppled or transported rankenella hamdii in association with brachiopods echinoderm plates trilobites and some red arg

a new boundary layer mixing scheme part i scheme description and single column model tests a new boundary layer turbulent mixing scheme has been developed for use in the ukmo weather forecasting and climate prediction models this includes a representation of nonlocal mixing driven by both surface fluxes and cloud top processes in unstable layers either coupled to or decoupled from the surface and an explicit entrainment parameterization the scheme is formulated in moist conserved variables so that it can treat both dry and cloudy layers details of the scheme and examples of its performance in single column model tests are presented

linearized inversion for fault rupture behavior application to the 1984 morgan hill california earthquake we present a technique to infer the rupture history of an earthquake from near source records of ground motion unlike most previous studies each point on the fault is assumed to slip only once when the rupture front passes with a spatially variable slip intensity in this parameterization the data are linearly related to slip intensity but nonlinearly related to rupture time we perform a linearized inversion for slip intensity and rupture time by iteratively perturbing an assumed starting model the inverse problem for the model perturbation is solved using a tomographic back projection technique smoothing and inequality constraints are applied to ensure that the resulting solution is stable and feasible asymptotic ray theory is used to calculate theoretical seismograms and partial derivatives with respect to model parameters in test cases with noisy synthetic data sets we found that it is possible to distinguish between rupture models having variable slip amplitude and models having variable rupture velocity provided the station coverage is adequate we apply the technique to recordings of the april 24 1984 morgan hill earthquake the results indicate that slip amplitude on the fault plane was extremely variable and that the rupture front did not propagate uniformly away from the hypocenter in particular rupture was delayed on a 12 km2 section of the fault approximately 14 km to the southeast of the hypocenter the rupture front surrounded the region which subsequently failed with a component of rupture propagation back toward the hypocenter similar behavior has been observed in dynamic rupture models with stress or strength inhomogeneities this segment of the fault ruptured with a large slip amplitude releasing 12 of the total seismic moment from 4 of the total area of the aftershock zone the surface trace of this section of the fault is characterized by a complex left step that could act to increase the normal stress acting across the fault however the distribution of aftershocks suggests that the fault at depth is simpler and that it may bend to the right in either case our rupture model suggests that this segment of the fault represents an asperity which initially resisted rupture but eventually ruptured massively we estimate the shear fracture energy for this earthquake to be 2 106 j m2

constitutive behavior and stability of frictional sliding of granite an understanding of the frictional sliding on faults that can lead to earthquakes requires a knowledge of both constitutive behavior of the sliding surfaces and its mechanical interaction with the loading system we have determined the constitutive parameters for frictional sliding of initially bare surfaces of westerly granite using a recently developed high pressure rotary shear apparatus that allows long distances of sliding and therefore a greater assurance of attaining steady state behavior from experiments conducted at room temperature and normal stresses of 27 84 mpa several important results have been found 1 a gouge layer 100 to 200 m thick was developed from the initially bare rock surfaces after 18 to 70 mm of sliding 2 the steady state frictional resistance attained after about 10 mm of sliding is proportional to the negative of the logarithm of the sliding velocity 3 abrup changes in the velocity of sliding result in initial changes in the frictional resistance which have the same sign as the velocity change and are followed by a gradual decay to a new steady state value over a characteristic distance of sliding this velocity weakening behavior is essentially identical with that found by several previous workers on the same material at lower normal stress 4 our results are well described by a two state variable constitutive law the values of the constitutive parameters are quite similar to those found previously at low normal stress but the characteristic distance is about an order of magnitude smaller than that found at 10 mpa normal stress with thicker layers of coarser gouge 5 we have approximated our results with a one state variable constitutive law and compared the results with the predictions of existing nonlinear stability analysis in addition we have extended the stability analysis to systems possessing two state variables with such formulations good agreement is found between the experimentally observed and theoretically predicted transitions between stable and unstable sliding these results allow a better understanding of the instabilities that lead to earthquakes

origin of strong winds in an explosive mediterranean extratropical cyclone abstractduring 2 3 december 2012 the black sea and east coast of romania were affected by a rapidly deepening mediterranean cyclone the cyclone developed a bent back front along which short lived

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

seismicity simulation with a mass spring model and a displacement hardening softening friction law dieterich simulated aftershocks numerically using a one dimensional mass spring model with a time dependent friction law but an important precursory phenomenon called quiescence cannot be produced by this model unless as mikumo and miyatake showed with a three dimensional continuum model a somewhat arbitrary bimodal distribution of frictional strength is assumed here we used the friction law proposed by stuart which is a displacement hardening softening model and simulated the quiescence by varying the parameters of the friction law in our mass spring model we found a variety of seismicity patterns when we choose extremely large critical displacement we get a recurrent sequence of creep followed by mainshock without small earthquakes but when we choose a critical displacement in the same order of magnitude as the slip weakening critical displacement estimated by papageorgiou and aki from strong motion data we get a normal seismicity pattern including quiescence before large events this simple model points to a promising approach for the interpretation of the rupture process during an earthquake by the same physical model

skeletal carbonate productivity and phosphogenesis at the lower middle cambrian transition of scania southern sweden the lower middle cambrian transitional interval of scania is largely represented by condensed limestone beds lithostratigraphically grouped in the gislov formation 1 5 7 m thick and the forsemolla and exsulans limestone beds lower part of the alum shale formation up to 4 in thick the strata display a combination of skeletal carbonate productivity episodic nucleation of phosphate hardground nodules and polyphase reworking recorded on a platform bordering the nw corner of baltica the shell accumulations can be subdivided into three deepening upward parasequences separated by distinct erosive unconformities the parasequences correspond biostratigraphically to the holmia kjerulfi ornamentaspis linnarssoni and ptlychagnostus gibbus zones the latter two generally being separated by a stratigraphic gap that includes the middle cambrian acadoparadoxides oelandicus superzone except for the exsulans limestone the carbonates reflect development of a prolific epibenthic biota dominated by filter feeding nonreefal chancelloriid echinoderm sponge meadows rich in trilobites and brachiopods and which were subjected to high energy conditions the absence of microbial mats or veneers encrusting the erosive surfaces of these event concentration low relief shoal complexes may be related to long hiatal episodes resulting in microboring proliferation high levels of nutrient supply resulted in high primary productivity eutrophic conditions glauconite precipitation phosphogenesis in some case microbially mediated and rnicroendolithic infestation an early diagenetic mildly reducing environment is suggested by the presence of authigenic subsequently reworked pyrite which contrasts with the syndepositional normal oxygenated conditions reflected by macroburrowing and the abundance of benthic fossils

numerical modelling of space and time variations of seismic activity before major earthquakes summary the spatial and temporal variations of seismic activity before large earthquakes including precursory swarm earthquakes clustering pre seismic quiescence in the epicentral area doughnut patterns and foreshocks are numerically modelled by quasi static and dynamical rupture processes on three dimensional heterogeneous faults with various types of non uniform strength distributions the main physical parameters that could yield these precursory changes of seismicity patterns are the form of distributions of static and sliding frictional strengths and their spatial variations over the fault and also the rate of increase of tectonic stress for weakly heterogeneous faults a large scale main shock rupturing the entire fault surface occurs without any precursory indications if the fault has moderately to heavily non uniform strengths on a small scale gradually increasing activity tends to occur over a long period prior to a main event with no swarms or quiescence for extremely heterogeneous faults including a number of small to moderate size asperities with medium to high strengths a typical sequence appears with swarms quiescence foreshocks and a main shock event the temporal behaviour of these events seems to depend primarily on the form of distribution of the strengths if the fault includes a large size asperity with medium to high strengths in its central part a doughnut pattern of seismicity repeatedly appears with high activity and quiescence in the surrounding and central asperity regions if a belt like barrier region with extremely high strengths lies in the central part of the fault dividing the entire region into two sections large scale shocks take place successively in the adjacent unruptured regions at slightly different times and a main shock event rupturing the entire fault occurs after a long period of quiescence these results from numerical simulations could provide possible explanations of observed seismicity patterns prior to major earthquakes

dynamics of fault interaction parallel strike slip faults we use a two dimensional finite difference computer program to study the effect of fault steps on dynamic ruptures our results indicate that a strike slip earthquake is unlikely to jump a fault step wider than 5 km in correlation with field observations of moderate to great sized earthquakes we also find that dynamically propagating ruptures can jump both compressional and dilational fault steps although wider dilational fault steps can be jumped dilational steps tend to delay the rupture for a longer time than compressional steps do this delay leads to a slower apparent rupture velocity in the vicinity of dilational steps these dry cases assumed hydrostatic or greater pore pressures but did not include the effects of changing pore pressures in an additional study we simulated the dynamic effects of a fault rupture on undrained pore fluids to test sibson s 1985 1986 suggestion that wet dilational steps are a barrier to rupture propagation our numerical results validate sibson s hypothesis by demonstrating that the effect of the rupture on the undrained pore fluids is to inhibit the rupture from jumping dilational stepovers the basis of our result differs from sibson s hypothesis in that our model is purely elastic and does not necessitate the opening of extension fractures between the fault segments

conditional symmetric instability in sting jet storms sting jets are transient mesoscale jets of air that descend from the tip of the cloud head towards the top of the boundary layer in severe extratropical cyclones and can lead to damaging surface wind gusts this recently identified jet is distinct from the well documented jets associated with the cold and warm conveyor belts one mechanism proposed for their development is the release of conditional symmetric instability csi here the spatial distribution and temporal evolution of several csi diagnostics in four severe storms are analysed a sting jet has been identified in three of these storms for comparison we also analysed one storm that did not have a sting jet even though it had many of the apparent features of sting jet storms the sting jet storms are distinct from the non sting jet storms by having much greater and more extensive conditional instability ci and csi csi is released by ascending air parcels in the cloud head in two of the sting jet storms and by descending air parcels in the other sting jet storm by contrast only weak ci to ascending air parcels is present at the cloud head tip in the non sting jet storm csi released by descending air parcels as diagnosed by decaying downdraught slantwise convective available potential energy dscape is collocated with the sting jets in all three sting jet storms and has a localised maximum in two of them consistent evolutions of saturated moist potential vorticity are found we conclude that csi release has a role in the generation of the sting jet that the sting jet may be driven by the release of instability to both ascending and descending parcels and that dscape could be used as a discriminating diagnostic for the sting jet based on these four case studies copyright 2011 royal meteorological society and british crown copyright the met office

asperities barriers characteristic earthquakes and strong motion prediction recent results from paleoseismology suggest that earthquakes recurrent on a given fault may often have the same characteristic length and amount of slip stable asperities and barriers which survive many earthquakes can explain these results the activity of volcano usu japan since 1977 which produced a dacite dome with a total upheaval of 180 m offered a great opportunity to study the recurrence behavior of a fault seismologists at hokkaido university revealed a family of repeated earthquakes with nearly the same amount of slip generated from the same fault plane on the crater wall along which the dome moved upward this family can be explained by the existence of a stable asperity on the crater wall and is called the asperity type family they found however another type of family of earthquakes which share the same fault plane but show a great range of variation in the amount of slip the behavior of the latter family can be explained by the presence of weak barriers over a fault plane defined by strong stable barriers and this family is referred to as the barrier type family this type of earthquake model has been used successfully in the interpretation of observed strong motion acceleration spectra from california and the results reveal the stability of local stress drop among different earthquakes the agreement found between local stress drops estimated from strong motion data and those inferred from geological observation supports the possibility for predicting earthquake strong motion directly from geological observation of the causative fault

the dynamics of a one dimensional fault in the presence of friction summary the tearing and healing of a one dimensional crack in a solid in the presence of external tectonic forces pre stress static friction cohesion and dynamic friction is investigated it is found that cohesive forces have a strong influence on the velocity of rupture the velocity of rupture is always less than or equal to the velocity of sound the extension of the crack ceases either when the crack enters a region with too high a cohesive force or when the difference between the tectonic stress and the dynamical shear stress becomes negative over a substantial region of space for one simple model a high displacement high energy release event has been found while in another model of the same fault length a low displacement low energy release event with the same stress drop takes place the difference between the two models is in the mode of healing and in particular whether the fault breaks out at the free surface of the earth

attribution of strong winds to a cold conveyor belt and sting jet a high resolution version of the wrf weather research and forecasting model has been used to study the fine structure of a cloud head and its associated cold conveyor belt jet cj and sting jet sj in an intense extratropical cyclone that produced damaging surface winds in northern ireland and central scotland on 3 january 2012 the model was run with many different initialisation times and physical parametrisations and a run was selected that verified well against a variety of observations new methods have been devised to visualise the 3d structure of the cj and sj and to attribute strong surface winds to one or other of them and the validity of regarding the sj as a semi lagrangian feature has been assessed the model suggests that whereas the cj remained mainly below the 850hpa level as it circulated around the bent back front the sj consisted of a stream or streams of air within the bent back frontal zone that first ascended from close to the surface into the middle and upper level parts of the cloud head before descending from evaporating cloud filaments at the tip of the cloud head and reaching the top of the boundary layer slightly ahead of the cj the simulations did not support the idea that either the evaporation or conditional symmetric instability csi played a major role in the development of these jets the strong gusts up to 47ms 1 w hich were recorded on the north coast of ireland appear to have been due mainly to the cj which by then was undercutting the sj the sj was responsible for stronger surface winds than the cj several hours earlier during the initial stage of frontal fracture but only for a limited period

the role of evaporating showers in the transfer of sting jet momentum to the surface the most damaging winds in a severe extratropical cyclone often occur just ahead of the evaporating ends of cloud filaments emanating from the so called cloud head these winds are associated with low level jets lljs sometimes occurring just above the boundary layer the question then arises as to how the high momentum is transferred to the surface an opportunity to address this question arose when the severe st jude s day windstorm travelled across southern england on 28 october 2013 we have carried out a mesoanalysis of a network of 1 min resolution automatic weather stations and high resolution doppler radar scans from the sensitive s band chilbolton advanced meteorological radar camra along with satellite and radar network imagery and numerical weather prediction products we show that although the damaging winds occurred in a relatively dry region of the cyclone there was evidence within the llj of abundant precipitation residues from shallow convective clouds that were evaporating in a localized region of descent we find that pockets of high momentum were transported towards the surface by the few remaining actively precipitating convective clouds within the llj and also by precipitation free convection in the boundary layer that was able to entrain evaporatively cooled air from the llj the boundary layer convection was organized in along wind rolls separated by 500 to about 3000 m the spacing varying according to the vertical extent of the convection the spacing was greatest where the strongest winds penetrated to the surface a run with a medium resolution version of the weather research and forecasting wrf model was able to reproduce the properties of the observed llj it confirmed the llj to be a sting jet which descended over the leading edge of a weaker cold conveyor belt jet

dynamics of sting jet storm egon over continental europe impact of surface properties and model resolution intense shapiro keyser cyclones are often accompanied by a sting jet sj an air stream that descends from the cloud head into the frontal fracture region and can cause extreme surface gusts previous case studies have concentrated on the north atlantic and the british isles here we present the first ever detailed analysis of an sj over continental europe and investigate the influence of topography on its dynamical evolution based on observations and high resolution simulations using the icosahedral nonhydrostatic model icon windstorm egon intensified over the english channel and then tracked from northern france to poland on 12 13 january 2017 causing gusts of almost 150 km h 1 and important damage icon reproduces the storm dynamics although it delays the explosive deepening shifts the track southward over belgium and germany and underestimates gusts over land storm characteristics show weak sensitivity to varying grid spacing between 1 6 and 6 5 km while switching off the convection parametrization at 3 3 km grid spacing improves correlations with surface observations but deteriorates the mean error trajectories reveal typical sj characteristics such as mid level descent strong acceleration and conditional symmetric and other mesoscale instabilities while evaporative cooling is stronger than in previous cases from the literature preventing drying during descent the sj identification and the occurrence of mesoscale instabilities depend considerably on model resolution convective parametrization output frequency and employed thresholds for trajectory selection sensitivity experiments with modified surface characteristics show that the combined effects of warm air blocking by the alps higher roughness over land and reduced surface fluxes cause egon to fill more quickly and to move on a faster more northern track across germany while the sj response is complex showing some compensating effects surface gusts strongly increase when roughness is reduced these results suggest that weather forecasters in continental europe should be more aware of the potential risks associated with sjs

transpressional tectonics and nappe stacking along the southern variscan front of morocco the southern variscan front in the tinerhir area involves palaeozoic allochthonous units ouaklim and tilouine units thrust onto the northern edge of the west african craton during late carboniferous time illite crystallinity data highlight an anchizonal grade for the ouaklim unit and a diagenesis anchizone transition for the tilouine unit during deformation phase d1 the tectonic stack is crosscut by major dextral reverse faults bounding e w trending domains of dominant shortening deformation central domain and strike slip deformation northern and southern domains later segmented by a network of post variscan faults this complex deformation pattern is the result of kinematic partitioning of dextral transpression along the southern variscan front coeval with the neovariscan 300 290 ma oblique convergence observed at the scale of the whole moroccan variscides partitioning of dextral transpression described in the tinerhir area is consistent with dextral wrench faulting along the tizi n test fault and with appalachian style south directed thrusting in the tinerhir and bechar bou arfa areas

physical models of earthquake instability and precursory processes this paper selectively reviews physical models of earthquake instability in these models instability arises as a result of interaction of a fault constitutive relation with deformation of the surrounding material that occurs in response to remote tectonic loading in contrast to kinematic models in which the fault slip is imposed it is calculated in physical models and consequently these models are essential for understanding precursory processes some kind of weakening behavior for the fault constitutive relation is required to produce an instability analogous to an earthquake two commonly employed idealizations discussed here are rate independent slip weakening and rate state dependent friction when these constitutive models are employed on surfaces embedded in elastic half spaces or layers possibly coupled to a viscoelastic substrate the results are capable of simulating realistically some aspects of earthquake occurrence common to all models is the prediction that earthquake instability is preceded by precursory slip which produces a departure of surface strain rate from the background level near the epicenter of a moderate to large earthquake the magnitude of this departure appears to be well within the range of current geodetic measurement accuracy and its duration is of the order of months to years however details depend on a variety of factors including the modelling of the constitutive relation near peak stress coupling of elastic crust to the asthenosphere and coupling of deformation with pore fluid diffusion

the dichotomous structure of the warm conveyor belt the warm conveyor belt wcb of an extratropical cyclone generally splits into two branches one branch wcb1 turns anticyclonically into the downstream upper level tropospheric ridge while the second branch wcb2 wraps cyclonically around the cyclone centre here the wcb split in a typical north atlantic cold season cyclone is analysed using two numerical models the met office unified model and the cosmo model the wcb flow is defined using off line trajectory analysis the two models represent the wcb split consistently the split occurs early in the evolution of the wcb with wcb1 experiencing maximum ascent at lower latitudes and with higher moisture content than wcb2 wcb1 ascends abruptly along the cold front where the resolved ascent rates are greatest and there is also line convection in contrast wcb2 remains at lower levels for longer before undergoing saturated large scale ascent over the system s warm front the greater moisture in wcb1 inflow results in greater net potential temperature change from latent heat release which determines the final isentropic level of each branch wcb1 also exhibits lower outflow potential vorticity values than wcb2 complementary diagnostics in the two models are utilised to study the influence of individual diabatic processes on the wcb total diabatic heating rates along the wcb branches are comparable in the two models with microphysical processes in the large scale cloud schemes being the major contributor to this heating however the different convective parametrization schemes used by the models cause significantly different contributions to the total heating these results have implications for studies on the influence of the wcb outflow in rossby wave evolution and breaking key aspects are the net potential temperature change and the isentropic level of the outflow which together will influence the relative mass going into each wcb branch and the associated negative pv anomalies at the tropopause level flow

mesoscale dynamics of cold fronts structures described by dropsoundings in fronts 87 the fronts 87 project was a european experiment to make mesoscale observations to deduce the dynamics of active cold fronts approaching north west europe with a minimum of orographic influences in this paper data from dropsoundings made by the meteorological office s c 130 research aircraft are analysed the aircraft flew a pattern with 4 or 5 runs oriented approximately at right angles to the front but with each run displaced in the along front direction by about 100 km the dropsondes gave soundings to a height of approximately 7 km with a cross frontal spacing of 20 km at best and 60 km on average between 30 and 50 soundings were made in each event over an area of 500 500 km2 these data are unique in their mesoscale resolution over a synoptic scale region this was made possible by the ability to track up to 5 sondes in the air at any time several new aspects of cold front dynamics have been identified from these data the approach here is to treat each run as an instantaneous cross frontal section the discussion is centred on the hypotheses postulated before the experiment these were intended to allow verification or refutation of aspects of models of frontal dynamics such as those embodied in semi geostrophic theory a minimal and purely objective analysis has been performed on the data presented here but the high resolution of the dropsonde observations permits evaluation of differentiated quantities such as potential vorticity pv with some confidence issues raised here include the degree of thermal wind balance the structure of conserved variables such as equivalent potential temperature and absolute momentum the cross frontal circulation and the role of diabatic processes such as the evaporation of snow and the potential vorticity structure on the mesoscale and its interpretation the intention is to present an integrated view of the dynamical structure of fronts in the light of theoretical rather than conceptual or airflow models

distinguishing the cold conveyor belt and sting jet airstreams in an intense extratropical cyclone abstractstrong winds equatorward and rearward of a cyclone core have often been associated with two phenomena the cold conveyor belt ccb jet and sting jets here detailed observations of the mesoscale structure in this region of an intense cyclone are analyzed the in situ and dropsonde observations were obtained during two research flights through the cyclone during the diabatic influences on mesoscale structures in extratropical storms diamet field campaign a numerical weather prediction model is used to link the strong wind regions with three types of airstreams or coherent ensembles of trajectories two types are identified with the ccb hooking around the cyclone center while the third is identified with a sting jet descending from the cloud head to the west of the cyclone chemical tracer observations show for the first time that the ccb and sting jet airstreams are distinct air masses even when the associated low level wind maxima are not spatially distinct in the model the ccb experie

recovering paleoearthquake slip record in a highly dynamic alluvial and tectonic region hope fault new zealand from airborne lidar knowing the slip amplitudes that large earthquakes produced in prehistorical times is one key to anticipate the magnitude of large forthcoming events it is long known that the morphology is preserving remnants of paleoearthquake slips in the form of fault offset landforms however the measured offsets that can be attributed to the most recent paleoearthquakes are generally few along a fault so that they rarely allow recovering the slip distributions and largest slips of these earthquakes we acquired 1 m resolution airborne lidar data on a 30 km stretch of a fast slipping strike slip fault eastern hope fault new zealand located in a region of high alluvial dynamics where landforms are rapidly evolving data analysis reveals 200 offset landforms only 30 allow a good to moderate quality offset measurement from these good to moderate quality measures we recover the slip length distributions and largest slips of the four most recent large paleoearthquakes and find evidence of 4 6 prior events the record suggests that large earthquake slip recurred in multiples of about 4 m along the 30 km stretch although they have larger uncertainties the more numerous lower quality offsets that we also measured reveal a similar earthquake slip record this shows that although offset landforms are partly degraded in dynamically active landscapes they store valuable information on paleoearthquake slips this information might be recovered provided that the morphology is analyzed at high resolution and continuously over a significant fault length remote lidar data are powerful to perform such analyses

seismicity simulation with a rate and state dependent friction law the dynamic motions and stabilities of a single degree of freedom elastic system controlled by different friction laws are compared the system consists of a sliding block connected to an elastic spring driven at a constant velocity the friction laws are a laboratory inferred friction law called the rate and state dependent friction law proposed by dieterich and ruina and a simple friction law described by dynamic and static frictions we further extend the solution to a one dimensional mass spring model which is an analog of a fault controlled by the rate and state dependent friction law this model predicts non uniform slip and stress drop along the rupture length of a heterogeneous fault this result is very different from some earlier modelings based on the simple friction law and a slip weakening friction law in those earlier modelings the stress and slip functions become smoother with time along the length of the fault rupture owing to the interactions between fault segments during slip because of this smoothing process the number of small events will decrease with time and the universilly observed stationary magnitude frequency relation cannot be explained the interaction between a fault segment and its neighboring segments can be measured when the post slip stress on this segment is compared with the stress on an identical segment represented by a block in this modeling without neighboring segments if the post slip stress of the former is much higher than that of the latter strong interaction exists if the two are close only weak interaction exists the interaction is determined by the relative motion between fault segments and the time duration of interaction our new modeling with the rate and state dependent friction law appears to show no such smoothing effect and provides a physical mechanism for the roughening process in the difference between the fault strength and stress that is necessary to explain the observed stationary magnitude frequency relation the noninstantaneous healing predicted by the rate and state dependent friction law may be repsonsible for the recurring nonuniform slip and stress drop and may be explained by the reduction of interaction among fault segments due to the low frictional strength during the fault stopping the very low friction during slip stopping allows much longer times than does the higher friction due to instantaneous healing for the fault segments to adjust their motions from an upper limit slip velocity to almost rest according to newton s second law a process with fixed masses and constant velocity changes involves low forces and weak interactions if it is accomplished in a long time period and vice versa our modeling also indicates that the existence of strong patches with higher effective stress on a fault is needed for the occurrence of major events the creeping section of a fault such as the one along the san andreas fault in central california on the other hand can be simulated with the rate and state dependent friction law by certain model parameters which however must not include strong patches in this case small earthquakes and aseismic creep relieve the accumulating strain without any large events

nature of the high speed rupture of the two dimensional burridge knopoff model of earthquakes the nature of the high speed rupture or the main shock of the burridge knopoff spring block model in two dimensions obeying the rate and state dependent friction law is studied by means of extensive computer simulations it is found that the rupture propagation in larger events is highly anisotropic and irregular in shape on longer length scales although the model is completely uniform and the emergent rupture propagation velocity is nearly constant everywhere at the rupture front the manner of the rupture propagation sometimes mimics the successive ruptures of neighbouring asperities observed in real large earthquakes large events tend to be unilateral with its epicentre lying at the rim of its rupture zone the epicentre site of a large event is also located next to the rim of the rupture zone of some past event event size distributions are computed and discussed in comparison with those of the corresponding one dimensional model the magnitude distribution exhibits a power law behaviour resembling the gutenberg richter law for smaller magnitudes which changes over to a more characteristic behaviour for larger magnitudes for very large events the rupture length distribution exhibits mutually different behaviours in one dimension and in two dimensions reflecting the difference in the underlying geometry this article is part of the theme issue statistical physics of fracture and earthquakes

the contact between opposing fault surfaces at dixie valley nevada and implications for fault mechanics well exposed normal fault surfaces from dixie valley nevada provide a unique opportunity to study the contact properties of fault surfaces because it is possible to examine both the hanging wall and footwall surfaces of a fault zone which was once seismically active the topography of the individual surfaces as well as the aperture or gap between the two surfaces was measured using surface profiling instruments and a resin replication technique these measurements enable frictional parameters of the surfaces most notably the characteristic decay distance dc to be calculated using contact theory although the individual surfaces are approximately self similar and fractal the aperture between the opposing surfaces is a stationary quantity because the surfaces are well correlated at dimensions larger than approximately 2 mm consequently contact theory can be used to calculate an average size for contact spots between the surfaces and by inference a characteristic decay distance dc for frictional slip between the surfaces direct inspection of resin replicas of the aperture allows an independent estimate of average contact spot size both approaches give contact spot diameters of 0 16 mm and dc of 0 01 0 1 mm because the individual surfaces of the fault are fractal and approximately self similar correlation between the surfaces should decrease significantly during slip events particularly if slip rates are high seismic events decreased correlation between the surfaces should lead to larger contact spot sizes and hence larger dc thus critical slip distances for natural faults should evolve concurrently with seismic fault slip

proterozoic microbial reef complexes and associated hydrothermal mineralizations in the banfora cliffs burkina faso abstract the proterozoic guena souroukoundinga formation of the mopti arm gourma aulacogen southerm taoudeni basin consists of a shale dominated succession up to 200 m thick with scattered microbial reef complexes quarry exposures of the tiara reef complex allow reconstruction of a transect across back reef peritidal laminites reef margin and peri reef ooidal shoals and fore reef slope strata microbial carbonate productivity nucleated on isolated palaeohighs during transgression whereas its end was controlled by two tectonically induced drowning pulses that led to the successive record of onlapping kerogenous limestones and pelagic shales reef carbonates are crosscut by fractures and fissures occluded by hydrothermal mineralizations which are related to the rifting activity of the gourma aulacogen the tiara reef complex is similar to other proterozoic reefs in being composed nearly entirely of stromatolites although calcimicrobial filamentous and thromboid textures are locally abundant which contrast with their scarcity or absence in coeval stable platform microbial reefs of the northern taoudeni basin

reexamining the cold conveyor belt abstract despite the popularity of the conveyor belt model for portraying the airflow through midlatitude cyclones questions arise as to the path of the cold conveyor belt the lower tropospheric airflow poleward of and underneath the warm front some studies beginning with carlson s analysis of the eastern u s cyclone of 5 december 1977 depict the cold conveyor belt moving westward reaching the northwest quadrant of the storm turning abruptly anticyclonically rising to jet level and departing the cyclone downstream hereafter the anticyclonic path other studies depict the cold conveyor belt reaching the northwest quadrant turning cyclonically around the low center and remaining in the lower troposphere the cyclonic path to clarify the path of the cold conveyor belt the present study reexamines carlson s analysis of the cold conveyor belt using an observational and mesoscale numerical modeling study of the 5 december 1977 cyclone this reexamination raises several previously unappreciated

transient triggering of near and distant earthquakes we demonstrate qualitatively that frictional instability theory provides a context for understanding how earthquakes may be triggered by transient loads associated with seismic waves from near and distance earthquakes we assume that earthquake triggering is a stick slip process and test two hypotheses about the effect of transients on the timing of instabilities using a simple spring slider model and a rate and state dependent friction constitutive law a critical triggering threshold is implicit in such a model formulation our first hypothesis is that transient loads lead to clock advances i e transients hasten the time of earthquakes that would have happened eventually due to constant background loading alone modeling results demonstrate that transient loads do lead to clock advances and that the triggered instabilities may occur after the transient has ceased i e triggering may be delayed these simple clock advance models predict complex relationships between the triggering delay the clock advance and the transient characteristics the triggering delay and the degree of clock advance both depend nonlinearly on when in the earthquake cycle the transient load is applied this implies that the stress required to bring about failure does not depend linearly on loading time even when the fault is loaded at a constant rate the timing of instability also depends nonlinearly on the transient loading rate faster rates more rapidly hastening instability this implies that higher frequency and or longer duration seismic waves should increase the amount of clock advance these modeling results and simple calculations suggest that near tens of kilometers small moderate earthquakes and remote thousands of kilometers earthquakes with magnitudes 2 to 3 units larger may be equally effective at triggering seismicity our second hypothesis is that some triggered seismicity represents earthquakes that would not have happened without the transient load i e accumulated strain energy would have been relieved via other mechanisms we test this using two new seismicity models that 1 are inherently unstable but slide at steady state conditions under the background load and 2 are conditionally stable such that instability occurs only for sufficiently large perturbations for the new seismicity models very small amplitude transients trigger instability relative to the clock advance models the unstable steady state models predict that the triggering delay depends inversely and nonlinearly on the transient amplitude as in the clock advance models we were unable to generate delayed triggering with conditionally stable models for both new seismicity models the potential for triggering is independent of when the transient load is applied or equivalently of the prestress unlike in the clock advance models in these models a critical triggering threshold appears to be inversely proportional to frequency further advancement of our understanding will require more sophisticated quantitative models and observations that distinguish between our qualitative yet distinctly different model predictions

the great atlasian reef complex an early cambrian subtropical fringing belt that bordered west gondwana abstract the so called great atlasian reef complex developed during early cambrian time throughout the moroccan margin souss basin of west gondwana according to the syndepositional tectonic activity associated with its intracratonic ediacaran cambrian rift the great reef complex can be subdivided into four major archaeocyathan microbial reef episodes i the atdabanian episode is recorded by a sw ne trending 400 km long barrier reef that extended across the western anti atlas it was controlled by large scale reactivation of an inherited rifting branch which resulted in the nucleation and growth of linear reef complexes located along its margin the interplay of block tilting sharp modifications in accommodation space and relative sea level rise led to a composite retrogradational aggradational reef systems tract characterized by archaeocyathan microbial kalyptrate complexes tiout member and amouslek formation that protected stromatolite dominated back barrier environments lower member of the igoudine formation ii the western anti atlas recorded an early botoman reactivation of the same rifting branch that triggered a lateral migration of frame building centres of carbonate productivity as a result the involved grabens and half grabens recorded the development of fringing mound complexes lower issafen formation these occupied some linear intra platform deeper depressions capped by marls and shales whereas laterally equivalent shallower environments recorded the development of patch reefs and bioherms iii the western anti atlas subsequently recorded a late botoman interval of tectonic quiescence superimposed to a local interval of progradational pulses this favoured the nucleation of dispersed archaeocyathan microbial patch reefs and bioherms iv a distinct palaeogeographic area is recognized in the southern high atlas where the entire atdabanian botoman interval recorded small scale synsedimentary block tilting and high rates of volcaniclastic input as a result this sector was characterized by the record of microbial and archaeocyathan microbial patch reefs and bioherms preferentially developed on the uplifted parts of tilted blocks the end of reef development and carbonate productivity in the souss basin is related to the progradation of siliciclastic depositional systems toyonian regression considered to have caused the collapse of reef communities throughout west gondwana

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

the life cycle of an extratropical marine cyclone part ii mesoscale structure and diagnostics abstract this is the second of two articles describing the evolving structure and selected physical processes within an intense extratropical marine cyclone observed during the experiment on rapidly intensifying cyclones over the atlantic erica field program part i describes the 24 h frontal cyclone evolution through 6 h horizontal analyses of observations taken by specially deployed observing systems from air land and sea part ii presents frontal scale and precipitation structures and physical processes from analyses based primarily on research aircraft observations taken during three phases of the cyclone s life cycle horizontal analyses at 350 m above ground level describe the cyclone s mesoscale frontal baroclinic structure and associated flow patterns the vertical structure and evolution of the cyclone s cold front warm front and bent back front are illustrated in cross sectional analyses of potential temperature wind velocity potential vorticity pv front relative transverse flow vecto

the role of abiotic factors in the cambrian substrate revolution a review from the benthic community replacements of west gondwana abstract the cambrian substrate revolution refers to a substantial and rapid change to the nature of marine sedimentary substrates in the early cambrian and is widely interpreted as a biologically driven event a direct response to evolutionary innovations in metazoan burrowing and the development of new shelly faunas however abiotic factors such as tectonic and climatic evolution also had the potential to restructure cambrian substrates and are here shown to be more plausible drivers of change in the benthic faunas of western gondwana the western mediterranean region underwent a southward drift during cambrian times which drove a switch from subtropical carbonates to temperate siliciclastic substrates with short term episodes of temperate carbonate productivity as a result microbial and shelly carbonates disappeared diachronously in a stepwise manner across the lower middle cambrian boundary interval archaeocyathan microbial reefs were replaced by chancelloriid eocrinoid spiculate sponge meadows in which the stepwise immigration of new echinoderm taxa was primarily controlled by extensional tectonic events first recorded in rifting settings and later in passive margin platforms availability of new kinds of substrate was thus the primary factor that controlled where and when evolutionary innovations in benthic strategies arose examples of this include the early cambrian colonization of phosphatic hardgrounds and thrombolite crusts by chancelloriids archaeocyathan and spiculate sponges and the exploitation by benthos to the increasingly widespread availability of shelly grounds and carbonate firmgrounds by early diagenetic cementation a microbial mat epifaunal antagonistic relationship is demonstrated for echinoderm pelmatozoans based on the non overlapping palaeogeographic distributions of microbial reefs and mats versus mud sticker pelmatozoans cambrian benthic communities thus evolved in parallel with substrates in response to abiotic factors rather than being the primary drivers of substrate change

frequency domain inversion of strong motions application to the 1992 landers earthquake we present a frequency domain inversion in which the observed earthquake strong ground motions are used to constrain the space time dependence of slip on a fault green s functions are numerically evaluated and the parameters describing the rupture are the local slip rupture time and rise time these parameters are simultaneously evaluated without additional constraints this procedure allows for large variations in the local rupture velocity the june 28 1992 landers earthquake mw 7 3 offers an exceptional opportunity to apply this technique to a major strike slip event we model the rupture evolution including local differences in slip durations and variations in rupture velocity our final results are in good agreement with other inversion studies geodetic and surface observations the main discrepancies occurred at depth and at the end of the johnson valley fault we show that a relatively low resolution could be an explanation for these differences rupture velocity and slip are extremely heterogeneous both along strike and with depth a moment of 0 90 1020 n m was found the slip distribution shows that this event consists of a series of regions of high slip subevents separated by regions of relative low slip approximately 50 of the moment was released on the homestead valley fault in this region of large slip the rupture velocity inferred by our inversion is well constrained and is equal to 3 0 km s at depth and 2 5 km s near the surface our inversion favors the hypothesis that the duration of the slip at each point of the fault is of the order of the duration of rupture of each subevent

syn rift unconformities punctuating the lower middle cambrian transition in the atlas rift morocco the cambrian tamdroust and bab n ali volcanic complexes represent two magmatic episodes developed in the latest ediacaran cambrian atlas rift of morocco their rifting pulses were accompanied by accumulation of volcanosedimentary edifices dominated by effusive lava flows in the former and explosive acidic aprons in the latter associated with active tilting and uplift sealing of their peneplaned horst and graben palaeotopographies led to the onset of distinct onlapping geometries and angular discordances capping eroded basements ranging from the ediacaran ouarzazate supergroup to the cambrian asrir formation previous interpretations of these discordances as pull apart or compressive events are revised here and reinterpreted in an extensional rifting context associated with active volcanism the record of erosive unconformities stratigraphic gaps condensed beds and onlapping patterns across the traditional lower middle cambrian or cambrian series 2 3 transition of the atlas rift must be taken into consideration for global chronostratigraphic correlation based on their trilobite content

a faulting model for the 1979 imperial valley earthquake by comparing synthetic particle velocities with the near source strong motion data we have constructed by trial and error a faulting model for the 1979 imperial valley earthquake the calculation of the synthetic seismograms takes into account the vertical inhomogeneity of the elastic parameters in the imperial valley and the spatial variation of the slip rate parameters on the fault plane the independent slip rate parameters are 1 the strike slip rate amplitude 2 the dip slip rate amplitude 3 the duration that slip rate is nonzero the rise time of the slip function and 4 the rupture time which determines when the slip rate is initiated our faulting model has the following principal features 1 faulting occurred on the imperial fault and on the brawley fault rupture on the brawley fault being triggered by rupture on the imperial fault 2 the imperial fault is a plane 35 km long and 13 km wide with a strike of 323 measured clockwise from north and a dip of 80 ne the brawley fault is a 10 km long and 8 km wide plane with a strike of 360 and a dip of 90 3 faulting on the imperial fault is primarily right lateral strike slip with a small component of normal dip slip in the sediments at its northern end the larger strike slip rates are generally confined between depths of 5 and 13 km with maximum values of about 1 0 m s the duration varies on the fault with a maximum of 1 9 s which is considerably shorter than the total time for the rupture to take place 4 the rupture velocity on the imperial fault is highly variable locally it exceeds the shear wave velocity and in one instance the compressional wave velocity the average rupture velocity though is less than the shear wave velocity 5 although the slip on the brawley fault contributes only about 4 of the total moment it greatly affects the ground motion at nearby stations 6 the total seismic moment is 6 7 1018 n m where the imperial fault contributes 6 4 1018 n m and the brawley fault contributes 2 7 1017 n m in the process of trying almost 300 faulting models we found that given the elastic parameters of the medium the synthetic seismograms were most sensitive to the specification of the rupture time although the slip rate amplitudes are linearly related to the data the rupture time and the duration are not the parameterization of the nonlinear variables has a strong effect on the generation of synthetic seismograms from a finite fault

inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 imperial valley california earthquake a least squares point by point inversion of strong ground motion and teleseismic body waves is used to infer the fault rupture history of the 1979 imperial valley california earthquake the imperial fault is represented by a plane embedded in a half space where the elastic properties vary with depth the inversion yields both the spatial and temporal variations in dislocation on the fault plane for both right lateral strike slip and normal dip slip components of motion inversions are run for different fault dips and for both constant and variable rupture velocity models effects of different data sets are also investigated inversions are compared which use the strong ground motions alone the teleseismic body waves alone and simultaneously the strong ground motion and teleseismic records the inversions are stabilized by adding both smoothing and positivity constraints the moment is estimated to be 5 0 10 25 dyne cm and the fault dip 90 5 dislocation in the hypocentral region south of the united states mexican border is relatively small and almost dies out near the border dislocation then increases sharply north of the border to a maximum of about 2 m under interstate 8 dipslip motion is minor compared to strike slip motion and is concentrated in the sediments the best fitting constant rupture velocity is 80 per cent of the local shear wave velocity however there is a suggestion that the rupture front accelerated from the hypocenter northward the 1979 imperial valley earthquake can be characterized as a magnitude 5 earthquake at the hypocenter which then grew into or triggered a magnitude 6 earthquake north of the border

earthquake aftereffects and triggered seismic phenomena the physical basis for delayed aftereffects of large crustal earthquakes is analyzed these effects apparently range in scale from typical aftershocks near the source region of a prior earthquake to the triggering of groundwater and deformation related anomalies possibly including other large earthquakes at locations as much as a few hundred kilometers from the source of a great earthquake observational reports of such aftereffects are reviewed and possible mechanisms for their occurrence are discussed

morphological assessment of the earliest paradoxidid trilobites cambrian series 3 from morocco and spain a cambrian immigration event of paradoxidid trilobites has traditionally marked some regional lower middle cambrian boundaries in the acado baltic subprovince including baltica and the mediterranean and avalonian margins of west gondwana the earliest paradoxidine species in morocco and the iberian peninsula have been used as a chronostratigraphic link to support the definition of a common base for the cambrian series 3 but recent studies have proposed new species without revising previously established ones this paper offers a morphological statistical analysis based on both linear measurement and landmark based geometric morphometric approaches performed on the earliest paradoxinine trilobites sampled in the anti atlas morocco and the iberian chains spain as a result the diagnosis of acadoparadoxides mureroensis is emended and several species recently erected in morocco a cf mureroensis a levisettii a ovatopyge and a pampalius are suggested as synonyms of a mureroensis until 3d statistical analyses are available based on material preserved on carbonate or silica nodules the first appearance of a mureroensis in both areas can be provisionally used for regional correlation until homotaxic tests are checked

on the dynamic sliding with friction of a rigid block and of an infinite elastic slab we consider dynamic motions of two elastic systems undergoing frictional slip the first one is the classical model of the frictional slider loaded through an elastic spring the second one is an infinite elastic slab bounded by two planes which is in contract with a rigid body and submitted to shearing slip weakening and slip rate weakening friction laws are both considered the two simple systems show very different qualitative behaviors in the case of the slip dependent friction a slider moves with a single slip event when a critical stress level is reached under the same conditions a series of slip events occur for the infinite slab this difference between the behavior of the two systems is due to the important part played by inertia in the mass concentrated block slider model in the case of slip rate weakening the analysis of the problem for the infinite slab indicates a major difficulty this problem has no unique solution if the rate of weakening exceeds a limit that is explicitly given whatever is the selection rule chosen to discriminate the solution shocks will occur the slip history obtained for the slab is very different from the one obtained with a block slider for the infinite elastic slab the slip velocity exhibits sharp variations shocks on the contrary a block slider does not exhibit this behavior it is a clear example of the limitation of the use of such a simple analogy to describe the actual properties of the relative motions of two media in contact with friction

sting jets in extratropical cyclones a review this paper reviews the current state of knowledge of sting jets in extratropical cyclones sting jets were formally identified in 2004 by the pioneering work of keith browning reviewing this and subsequent studies we define the sting jet as a coherent air flow that descends from mid levels inside the cloud head into the frontal fracture region of a shapiro keyser cyclone over a period of a few hours leading to a distinct region of near surface stronger winds it therefore lies above the cold conveyor belt during some stage its life but at least in some cases descends to reach the top of boundary layer ahead of the cold conveyor belt it is not attributed to a specific mechanism in this definition we conclude that it is likely that a continuum of sting jet descent and speed up mechanisms exists at one extreme is balanced descent partly associated with frontolysis in the frontal fracture region more horizontally small scale and stronger frontolytic descent may occur associated with weak stability to slantwise convective downdraughts instability to slantwise convective downdraughts may occur in some systems leading to multiple slantwise convective downdraughts associated with the release of conditional symmetric instability and even possibly symmetric instability the global climatology of sting jets and the interaction between the atmospheric boundary layer and sting jets are revealed as specific areas where more research is needed finally we describe eight myths and misunderstandings that exist in the current literature with the aim of guiding future research into the sting jet phenomenon