deep seated gravitational slope deformations related landslides and tectonics abstract deep seated gravitational slope deformations and their relationships with tectonic deformation of rocks is considered to examine the viewpoint of tectonics as a causative factor in slope deformation first a distinction is made between the different types of deep seated gravitational slope deformation then the geomorphological and structural effects of the different macrostructural deformations induced by tectonics on the scale of the whole deforming ridge is briefly discussed finally some case studies that represent either verified or possible cases of gravity deformation in response to tectonic activity are used as illustration

landslides and climate change in the italian dolomites since the late glacial abstract the paper deals with the relationship between the temporal occurrence of landslides and climatic changes in the italian dolomites since the late glacial after an introduction on the state of the art with particular reference to the alpine region the results of recent investigations in the two study sites are illustrated at cortina d ampezzo several landslides were dated mainly by the radiocarbon method the most ancient landslide event there involved large rock slides which affected the dolomitic slopes following the withdrawal of glaciers after the last glacial maximum lgm and also slides and flows mainly occurring in pelitic materials of the valley floors from 13 000 to 10 000 cal bp a later series of flows occurred between 5500 and 2500 cal bp in the upper badia valley alta badia the most ancient events go back to 10 000 and 9000 cal bp and correspond with earth flows that followed vast rotational slides affecting the bedrock up to a depth of about 50 m more recent earth flows involving more modest amounts of material took place between 6500 and 2300 cal bp by analysing the dates from the two study areas it was possible to correlate the recorded increase of landslide activity with the climatic changes occurring at the boundary between the late glacial and the holocene and between the atlantic and the subboreal and to compare the results with those derived from other european regions the types and causes of landslides taking place in these two periods were substantially different reflecting the different morphoclimatic conditions that existed in the two areas when these mass movements were triggered finally notwithstanding the importance of non climatic causes such as geological structural factors and possible human influences it is concluded that many of the dated landslides can be considered as indicators of climatic change

effect of mechanical interaction on the development of strike slip faults with echelon patterns abstract the overlapping geometry of echelon strike slip faults is well known we have quantified this observation by measuring the amount of overlap and separation and plotting them against each other for over 120 examples although there is large scatter the data show a linear trend suggesting that the overlap increases proportionally with separation up to a limiting value we have analyzed this conspicuous relationship in terms of fault interaction by using a numerical model based on displacement discontinuity the results show that fault interaction is in fact an important factor in contributing to the overlapping geometry of echelon strike slip faults

the effects of double fault bends on rupture propagation a geometrical parameter study we use the 2d finite element method to determine how geometrical parameters determine whether rupture will propagate across a linked stepover in a strike slip fault the end segments of the fault system are aligned in the direction of maximum shear and the length and angle of the linking segment are allowed to vary we observe that ruptures propagate through extensional stepovers with steeper angles and longer linking segments than otherwise equivalent compressional step overs these different rupture behaviors form distinct regions in angle stepover length parameter space the boundary between these regions takes the shape of an asymptotic curve in both the extensional and compressional cases models in which the size of the entire fault system was made larger or smaller revealed that the location of the bound aries between regions of different rupture behavior do not scale linearly with the system size it was easier to rupture steeper and relatively longer stepovers in fault systems that were larger overall a separate set of models in which the stress field is rotated so that the parallel end segments were optimally aligned for rupture significantly altered the rupture behavior curves in this stress field it was easier to rupture compressional stepovers with steeper angles and longer linking segments than it was to rupture equivalent extensional stepovers in both the case in which the end segments are aligned with the direction of maximum shear and the case in which the end segments are optimally oriented for rupture the angles at which rupture could no longer propagate through the entire fault corresponded with peaks in the fault s s value

north atlantic potential vorticity and its relation to the general circulation abstract maps and sections of the large scale north atlantic potential vorticity q are presented here q is fd dz where f is the coriolis frequency the potential density and z the vertical coordinate they bear on the general circulation and on geostrophic waves instability and turbulence in many ways both eulerian and lagrangian mean circulations proceed along isostrophes q constant in a zero dissipation region in a resting fluid q varies simply as the sine of the latitude but we show here that the wind driven circulation reshapes the q field creating bowls and plateaus which allow the flow to cross latitude circles the implied nature of the western boundary current is very different than in classical frictional theory the maps show a region of uniform potential vorticity in the wind gyre 26 5 27 0 which fills the ocean between 15 37 n and 20 80 w such regions were prominent features of a circulation theory of rhines and young 1982a b at deeper levels and close to surface out

adjustment of the ocean under buoyancy forces part i the role of kelvin waves abstract the early stages of the adjustment of an ocean toward equilibrium is examined using an ocean general circulation model the initial state is one with uniform meridional potential temperature gradients yielding density gradients representative of those observed in the north atlantic the main adjustment in the time examined here the first few months is by coastal kelvin waves the first baroclinic mode dominates so the behavior proves to be very similar to that in a shallow water model also the dynamics is locally close to that for an f plane but account must be taken of the way f varies with latitude the essential result of the coastal adjustment is to reduce the temperature gradients around the perimeter of the basin especially at the level where the first mode has the maximum effect this study also examines the way this adjustment process is distorted in models due to the constraints imposed by computer limitations namely in a model with too coarse a horizontal resolution and an artif

long term gravitational deformation of rocks by mass rock creep abstract subsurface rocks beneath slopes are deformed to various degrees in various ways by mass rock creep mrc when they are subjected to a gravitationally unstable state for a long period mrc forms folds faults and numerous kinds of fractures such deformation is one of the main factors for deteriorating rock masses on slopes and also precursors of many landslides mrc deformations which have often been ascribed to tectonic origins can be distinguished from tectonic ones by their deformational features landforms and relationships between slope morphology and subsurface structures mrc folds are flexural slip folds that have the following mesoscopic to microscopic characteristics their axial surfaces are not smooth but are jagged and many visible openings or open fractures develop in association with the folds the jagged axial surfaces become smoother at depth and openings decrease in width with increasing overburden at the deformation site macroscopic types of mrc folds change according to the relationship between foliations and slopes buckling folds form in consequent slopes drag folds form in a deeper part of obsequent slopes and bending folds form in slopes with steep dipping foliations consequent or obsequent by downslope bowing of foliations shear fractures and tension fractures are the main deformational structures formed by mrc in massive rocks among shear fractures those of listric origin are remarkable tension fractures in general occur either in networks dividing rocks into fragments that slip and rotate irregularly in relation to each other or in parallel arrays of steeply dipping fractures an mrc fault has a shear zone consisting of a pulverized zone with gouge and a phyllitic or brecciated zone in a densely foliated rock the phyllitic zone is formed by microscopic slip along foliations in a sparsely foliated rock the brecciated zone is formed by random crushing except for the faults made through the shear fractures in massive rocks landforms due to mrc are gentle slopes bounded by horseshoe knicklines upslope convex slopes ridge top depressions multiple ridges uphill facing scarps and ridge crossing depressions

upper ocean modeling in a coastal bay a numerical model of the upper ocean is developed to study the dynamics and thermodynamics of the baie des chaleurs gulf of st lawrence canada the model has primitive equation dynamics with two active layers embedded with a niiler kraus niller and kraus 1977 type mixed layer model at the top proper open boundary conditions and forcing functions are constructed the model is eddy permitting with a horizontal grid spacing of 2 4 km an arakawa c grid scheme is used forced by observed wind atmospheric heat fluxes river runoff and appropriate remote forcing in particular the gaspe current gc the model demonstrates that the mean cyclonic general circulation pattern in the bay is a consequence of the intrusion of the gc the strength of the circulation depends on the resultant stress of prevailing westerly winds and the opposing gc intrusion in the mixed layer atmospheric heat fluxes and horizontal thermal advection play a key role in the thermal balance at the eastern part of the bay the local mixed layer fluctuations are controlled by wind and gc induced divergence the entrainment and its corresponding heat flux is important at the western part of the bay and changes the mean mixed layer depth on a timescale of more than a week varying gc intensifies the flow variations induced by the wind in the bay and improves simulation results as compared with observations

sequence response to syndepositional regional uplift insights from high resolution sequence stratigraphy of late early pleistocene strata periadriatic basin central italy abstract this paper deals with the depositional sequences that occur within the uppermost part of the plio pleistocene periadriatic basin fill in the southern marche region central italy the succession is an early pleistocene easterly dipping clastic wedge showing an overall shallowing trend from slope clays to shallow marine and non marine deposits comprising two major sequences namely qmb and qmc analysis has provided new insights into i the nature of sedimentary facies and facies associations occurring within the upper part of qmb and qmc ii the gradual contact within qmb between regressive littoral deposits rld and underlying deep marine blue clays iii the composite origin of the emilian surface which is a widespread erosional unconformity separating qmb from qmc iv the cyclothemic pattern of qmc composed of downstepping small scale depositional sequences v the role played by synsedimentary uplift on the stacking pattern of small scale sequences and their internal architecture up to three small scale depositional sequences have been recognised within qmc qmc1 qmc2 and qmc3 they are up to 50 m thick and defined by previously unrecorded lower rank regionally extensive surfaces facies organization indicates that as a rule in ascending stratigraphic order each small scale sequence may includes a distinctive basal unconformity surface that can be traced from incised valleys to associated interfluves an incised valley fill a transgressive surface of marine erosion a transgressive systems tract a highstand systems tract a regressive surface of marine erosion and an attached falling stage systems tract in proximal positions the small scale sequences are dominated by transgressive and highstand systems tracts with incised valley fills and falling stage systems tracts absent or volumetrically much less significant in relatively basinward locations where the regressive surfaces of marine erosion converge with the lower sequence boundary the falling stage systems tract may represent the entire depositional sequence high frequency sequences display a distinctive stacking pattern and form a tectonically induced forced regressive sequence set underlain by a composite tectonically enhanced regressive surface of marine erosion formed by the lateral connection of lower rank sequence boundaries

3d simulations of multi segment thrust fault rupture thrust faults such as those that underlie the los angeles basin are typically segmented by tear faults that offset the thrust fault segments we perform 3d finite difference simulations of earthquake rupture to evaluate the effectiveness of these offsets in retarding rupture the simulations include orthogonal intersecting faults to model the interaction of the thrust fault segments with the tear fault for reasonable assumptions for fault segment length strength and stress drop rupture can jump offsets of up to 2 km if a tear fault is present consistent with observations of well studied thrust earthquakes absent a tear fault the maximum offset that can be breached is an order of magnitude smaller

earthquake rupture through a step over fault system an exploratory numerical study of the leech river fault southern vancouver island the leech river fault lrf zone located on southern vancouver island is a major regional seismic source we investigate potential interactions between earthquake ruptures on the lrf and the neighb

heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike slip faults 1 we combine a viscoelastic model for the interseismic process and an elastodynamic model for the coseismic process to explore the dynamics over multiple earthquake cycles of two parallel strike slip faults embedded in a two dimensional full space the step over fault geometry results in a buildup of heterogeneous fault stress near the step over this heterogeneous stress accumulates at the early stage of the evolution of the fault system and finally stabilizes after a number of earthquake cycles the heterogeneity in fault stress varies with the geometrical parameters e g width and along strike overlap gap of the step over as well as the rupture history of the fault system this heterogeneous fault stress from previous earthquakes has significant effects on earthquake rupture initiation propagation and termination the locations with a low normal stress level near a step over are favorable points for earthquake initiation rupture can jump a 4 km wide compressional step over and a 8 km or wider dilational step over if the fault system has historically experienced many earthquakes a young step over with less induced heterogeneity allows rupture to jump only smaller step over widths these results may have important implications for seismic hazard analysis in areas where segmented strikeslip faults predominate particularly for estimating maximum earthquake potential citation duan b and d d oglesby 2006 heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike slip faults j geophys res 111 b05309 doi 10 1029 2005jb004138

fault interaction near hollister california a numerical model is used to study fault stress slip near hollister california the geometrically complex system of interacting faults including the san andreas calaveras sargent and busch faults is approximated with a two dimensional distribution of short planar fault segments in an elastic medium the steady stress and slip rate are simulated by specifying frictional strength and stepping the remote stress ahead in time the resulting computed fault stress is roughly proportional to the observed spatial density of small earthquakes suggesting that the distinction between segments characterized by earthquakes and those with aseismic creep results in part from geometry a nonsteady simulation is made by introducing in addition stress drops for individual moderate earthquakes a close fit of observed creep with calculated slip on the calaveras and san andreas faults suggests that many changes in creep rate averaged over several months are caused by local moderate earthquakes in particular a 3 year creep lag preceding the august 6 1979 coyote lake earthquake on the calaveras fault seems to have been a direct result of the november 28 1974 thanksgiving day earthquake on the busch fault computed lags in slip rate preceding some other moderate earthquakes in the area are also duemore to earlier earthquakes although the response of the upper 1 km of the fault zone may cause some individual creep events and introduce delays in others the long term rate appears to reflect deep slip less

rupture termination and jump on parallel offset faults proper evaluation of seismic hazard depends on accurate estimates of potential earthquake size in areas with complex multisegment fault systems such an estimate in turn depends on an ability to predict the circumstances under which rupture may jump between fault segments many observational and numerical studies have analyzed the phenomenon of jumping rupture but none has focused on how the process of rupture termination on the primary nucleating fault segment affects the ability of rupture to jump to a secondary fault segment in the current study i model the dynamics of a simple 2d strike slip fault system with two parallel segments arranged with either a compressional or extensional stepover i vary the suddenness with which the initial shear stress tapers to zero on the primary section if the initial shear stress goes to zero over a very small 100 m distance rupture readily jumps both compressional and extensional stepovers of 1 km if the initial shear stress tapers to zero over 1 km rupture can jump the compressional stepover but not the extensional stepover if the initial shear stress tapers to zero over 2 5 km rupture cannot jump either the compressional or the extensional stepover the results illustrate the importance of the slip gradient and the resultant static stress field and the acceleration of the rupture front and the resultant generation of stopping phases in determining the probability of jumping rupture

structural constraints on deep seated slope deformation kinematics abstract a significant sackung type deep seated slope gravitational deformation dsgsd was recognised for the first time by the authors in the middle part of valfurva east of bormio rhaetian alps italy the reconstruction of its kinematics age and state of activity is presented through a detailed description of its morphological geomechanical and structural features an integrated multi disciplinary approach was performed to achieve a clear comprehension of the phenomenon field surveys and aero photo interpretation were carried out in order to clarify the structural geological and geomorphological setting in which the dsgsd developed a kinematic conceptual model of the slope deformation was developed through the analysis of morpho structures of their significance and relationships with lithological markers and quaternary deposits after a geomechanical characterisation of the rock mass involved in the slope deformation numerical modelling was performed to verify the hypotheses made on kinematics and driving factors of the phenomenon the sackung affects pre permian metapelites metabasites and marbles belonging to the upper austroalpine basement of the campo nappe as well as late pleistocene and holocene glacial and rock glacier deposits the deformation started after the late wurmian age 15 000 11 000 years b p and continued until few centuries ago not excluding a present day low rate activity deformation consists in a large oblique sagging along a deep confined sliding surface associated with gravitational reactivation of pre existing late alpine and recent tectonic brittle structures leading to the formation of n s and wnw ese trending gravitational morpho structures the evolution of the wnw ese trending system resulting in asymmetric trenches led to progressive failure of the lower part of the slope during the last 10 000 years as testified by large paleo landslide accumulations and it is still in progress numerical modelling indicates post glacial unloading as the main triggering factor of the slope deformation the importance of this deep seated slope deformation is enhanced by the occurrence of the 30 mm 3 active ruinon landslide in the lower part of the slope such landslide is subjected to rapid evolution and threatens the valley floor establishing an important risk factor connected to human lives and socio economic activities

numerical experiments with a wind and buoyancy driven two and a half layer upper ocean model we describe numerical experiments with a limited domain 15 67 n 65 west to east coarse resolution two and a half layer upper ocean model the model consists of two active variable density layers a niiler and kraus 1977 type mixed layer and a pycnocline layer which overlays a semipassive deep ocean the mixed layer is forced with a cosine wind stress and haney type heat and precipitation evaporation fluxes which were derived from zonally averaged climatological levitus 1982 surface temperatures and salinities for the north atlantic the second layer is forced from below with 1 newtonian cooling to climatological temperatures and salinities at the lower boundary 2 convective adjustment which occurs whenever the density of the second layer is unstable with respect to climatology and 3 mass entrainment in areas of strong upwelling when the deep ocean ventilates through the bottom surface the sensitivity of this model to changes in its internal mixed layer and external e g a newtonian coupling coefficient parameters is investigated and compared to the results from a control experiment we find that the model is not overly sensitive to changes in most of the parameters that were tested albeit these results may depend to some extent on the choice of the control experiment

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

aftershocks of the coyote lake california earthquake of august 6 1979 a detailed study aftershock hypocenters and focal mechanism solutions for the coyote lake california earthquake reveal a geometrically complex fault structure consisting of multiple slip surfaces the faulting surface principally consists of two right stepping en echelon northwest trending partially overlapping nearly vertical sheets and is similar in geometry to a slip surface inferred for the 1966 parkfield california earthquake the overlap occurs near a prominent bend in the surface trace of the calaveras fault at san felipe lake slip during the main rupture as inferred from the distribution of early aftershocks appears to have been confined to a 14 km portion of the northeastern sheet between 4 and 10 km depth focal mechanisms and the hypocentral distribution of aftershocks suggest that the main rupture surface itself is geometrically complex with left stepping imbricate structure seismic shear displacement on the southwestern slip surface commenced some 5 hours after the mainshock aftershocks in this zone define a single vertical plane 8 km long between 3 and 7 km depth within the overlap zone between the two main slip surfaces the average strike of aftershock nodal planes is significantly rotated clockwise relative to the strike of the fault zone in close agreement with the stress perturbations predicted by crack interaction models aftershock activity in the overlap zone is not associated with a simple dislocation surface space and time clustering within the entire aftershock set suggest an alternation of seismic displacement between the component parts of the fault zone this alternation is consistent with local stress perturbations predicted by crack interaction models we conclude that the fault structure is geometrically complex and that the displacements that occur on its component surfaces during the aftershock process dynamically interact by generating perturbations in the local stress field which in turn control the displacements table 5 is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j82 006 1 00 payment must accompany order

failure and flow development of a complex slide the 1993 sesa landslide abstract large landslides are often characterised by complex activity resulting from their ability to suddenly change behaviour in fact these landslides can pass from a slump to a flow characterised by relatively high mobility this characteristic is a cause of extremely high severity and hazard in areas affected by such phenomena an interesting case of a large slide in glacial deposits which occurred in 1993 in the valcamonica of the italian alps is presented different approaches both to characterise the coarse frictional materials involved in the slide and to model the slide initiation and its evolution are adopted the initial slide mass had a volume of almost 2 mm 3 and after its initial sliding motion along the slope flowed for about 7 km down the main valley stream voight s method has been used to analyse measured slope displacements recorded for a few years before the slope failure this analysis provided evidence that different times of failure could have been predicted beforehand by rigorous examination of the available data laboratory tests and image processing techniques have been performed to characterise the landslide material as resembling a bimrock block in matrix material slope stability analyses have been performed and a dynamic modelling method has been tested on the flow by comparing its results to those obtained by analysis of eyewitness statements and field observations on the mudline left by the flow finally existing empirical approaches for hazard assessment on an alluvial fan have been applied and modified to produce a hazard zonation map for the alluvial fan area by considering maximum expected discharge local geometry of the channel and the possibility of channel occlusion and subsequent avulsion

geomorphological evidence for anti apennine faults in the umbro marchean apennines and in the peri adriatic basin italy abstract the apennines are a relatively recent mountain chain which has been affected by uplift movements since the upper pliocene in fact the remnants of an erosional surface reduced close to base level is preserved at the top of the relief there is no general agreement on the geodynamic stress field and mechanisms which are creating the chain however it is largely accepted that uplift occurred together with the activation on the western side of the chain of extensive faults oriented in the apennine direction nw se which have been linked to the opening of the tyrrhenian sea a great debate is going on about the presence and significance of anti apennine faults ne sw which have been observed by some authors but completely denied by others the main evidence is represented by 1 block faulting of the remnants of the erosional surface along the marchean ridge more elevated relief delimiting relatively depressed areas was created in correspondence with the sibillini mts and mt s vicino similar evidence has been found in the umbro marchean ridge locally more than 1500 metres of displacement have been observed between more and less uplifted remnants 2 block faulting of fan deltas and related beaches of sicilian to crotonian age with more elevated sediments preserved between the tronto and tenna rivers and between the musone and esino rivers maximum displacement along a transect parallel to the coast is 200 metres 3 fault scarps affecting the middle pleistocene river terraces as observed along the esino the tronto the chienti and the tenna river valleys maximum displacements are in the order of 50 metres 4 faulting of horizontal karst galleries and reorientation of the cave network as in the frasassi gorge maximum displacements are about 100 metres 5 captures and alignments in the drainage network of the main river courses 6 large scale gravitational movements as in the ancona landslide and along the chienti and esino rivers their activation occurred in most cases after the lower pleistocene and although their displacements may be of relatively limited extent dispite their recent activity they played a major role in the modelling of the landscape these faults display transtensive extensional and trascurrent movements apart from the controversial geodynamic significance of these faults from a geomorphological point of view they must be considered transverse elements of the stress field from blocks more or less uplifted along the apennine chain the importance and timing of activity of these faults in the quaternary geomorphological evolution of the umbria marchean apennines is demonstrated using evidence usually underestimated by structural geologists which can contribute to a debate based on a multidisciplinary approach

a coupled one dimensional sea ice ocean model a prognostic one dimensional mixed layer pycnocline model describing the vertical structure of the upper ocean is coupled to a thermodynamic sea ice model the coupled prognostic model is compared with the more usual sea ice model overlying a fixed mixed layer with constant oceanic heat flux and is then applied to investigate the effect of temporal and regional variations of the entrained oceanic heat flux on the sea ice cover in both polar regions in the southern ocean a standard simulation is compared with two perturbation experiments which both describe the occurrence of a polynya in the arctic ocean the effect of possible soviet river diversions is investigated finally the response of the coupled model to paleoclimatic forcing and boundary conditions is presented

the dynamics of strike slip step overs with linking dip slip faults fault step overs with linking dip slip faults are common features on long strike slip fault systems worldwide it has been noted by various researchers that under some circumstances earthquakes can jump across fault step overs to cascade into large events while under other circumstances rupture is arrested at step overs there is also evidence that fault step overs may be preferential locations for earthquake nucleation the present work uses the 3d finite element method to model the dynamics of strike slip fault systems with step overs and linking dip slip faults i find that the presence of a linking normal or thrust fault greatly increases the ability of earthquake rupture to propagate across the step over leading to a larger event additionally dilational step overs with linking normal faults are more prone to through going rupture than compressional step overs with linking thrust faults this difference is due to the sign of the normal stress increment on the dip slip fault caused by slip on the strike slip segments slip on the strike slip segments causes a negative unclamping normal stress increment on the linking normal fault in a dilational step over whereas the opposite effect occurs on the linking thrust fault in a compressional step over even in cases for which both dilational and compressional step overs can experience through going rupture dilational step overs typically experience higher slip particularly on the linking normal fault in the compressional case rupture nucleation on the linking thrust fault may increase the likelihood of through going rupture compared to nucleation on one of the strike slip segments near the intersections between the fault segments the stress interaction between the fault segments also causes a significant rotation of rake away from that which would be inferred from the regional stress field the results help to emphasize the importance of two way interactions between nearby fault segments during the earthquake rupture process the results also may have implications for the probability of large earthquakes along geometrically complex strike slip fault systems and may help explain why step overs sometimes act as barriers and other times as nucleation locations for large earthquakes

interactions between mantle upwelling drainage evolution and active normal faulting an example from the central apennines italy summary in this paper we show that the processes that have shaped the quaternary surface development of the apennines in central italy are all consequences of a single subcrustal process the upwelling of the mantle the relationship between gravity and topography shows that mantle convection is responsible for a long wavelength 150 200 km topographic bulge over the central apennines and stratigraphic evidence suggests this bulge developed in the quaternary active normal faulting is localized at the crest of this bulge and produces internally draining fault bounded basins these basins have been progressively captured by the aggressive headward erosion of major streams that cut down to the sea on the flanks of the regional bulge the only surviving closed basins are those on the apennine watershed most distant from the marine base level where continued normal faulting is still able to provide local subsidence that defeats their capture by the regional drainage network understanding the competition between regional capture and local fault related subsidence of intermontane basins is crucial for recognizing potentially hazardous active faults in the landscape and also for interpreting the sediment supply to adjacent offshore regions central italy provides a good modern analogue for processes that are probably common in the geological record particularly on rifted margins and intracontinental rifts but may not have been fully appreciated

fault steps and the dynamic rupture process 2 d numerical simulations of a spontaneously propagating shear fracture fault steps may have controlled the sizes of the 1966 parkfield 1968 borrego mountain 1979 imperial valley 1979 coyote lake and the 1987 superstition hills earthquakes this project investigates the effect of fault steps of various geometries on the dynamic rupture process we have used a finite difference code to simulate spontaneous rupture propagation in two dimensions we employ a slip weakening fracture criterion as the condition for rupture propagation and examine how rupture on one plane initiates rupture on parallel fault planes the geometry of the two parallel fault planes allows for stepover widths of 0 5 to 10 0 km and overlaps of 5 to 5 km our results demonstrate that the spontaneous rupture on the first fault segment continues to propagate onto the second fault segment for a range of geometries for both compressional and dilational fault steps a major difference between the compressional and dilational cases is that a dilational step requires a longer time delay between the rupture front reaching the end of the first fault segment and initiating rupture on the second segment therefore our dynamic study implies that a compressional step will be jumped quickly whereas a dilational step will cause a time delay leading to a lower apparent rupture velocity we also find that the rupture is capable of jumping a wider dilational step than compressional step

the effects of d0 on rupture propagation on fault stepovers abstract according to the slip weakening friction law andrews 1976a fault friction drops from a static value to a sliding value over some slip weakening distance d 0 laboratory studies of fault friction confirm this weakening but do not settle on a single value for d 0 however this parameter is a critical input in dynamic earthquake models as it affects rupture nucleation and propagation we use the 2d finite element method to test how the specific value of d 0 affects rupture behavior we consider the ability of rupture to jump from segment to segment of a disconnected stepover or to propagate through the double bends of a connected stepover as a way to gauge rupture energy and behavior we find the stepover width or bend angle through which rupture can propagate is affected by the choice of d 0 but it is not a linear relationship this is true regardless of whether the stepover is connected or disconnected compressional or extensional or whether the initial rupture velocity is supershear or subshear we do find however that scaling the intensity of the regional stress field up or down does linearly correspond to scaling d 0 down or up we interpret the nonlinearity of the d 0 scaling results to be related to the area of the secondary fault that intersects the lobe of failure level coulomb stress change induced by rupture of the first fault segment because 1 the d 0 controlled critical patch size for renucleation must be exceeded on the second segment and 2 the area of this overlap also does not change linearly with distance from the first fault

testing a coupled ice mixed layer model under subarctic conditions abstract a one dimensional oceanic mixed layer model has been coupled with a thermodynamic sea ice model in order to study the seasonal cycle of ice ocean interaction in the subarctic ocean the ice thickness is assumed constant and only variations of ice compactness under the effect of the atmospheric and oceanic heat fluxes are considered the mixed layer model allows prediction of the rate of entrainment mainly as the result of the penetrative buoyancy driven convection both heat and salt conservation equations are included so that the respective efficiency with regard to vertical mixing of brine rejection below the ice and intense surface cooling in open water can be compared the model has been run for ten years on a zonal vertical section across the greenland sea the annual entrainment retreat cycle of the mixed layer is well reproduced with maximum depths occurring in late winter even down to the bottom at some locations near the ice edge surface cooling is found to be a more efficient mecha

nonuniform prestress from prior earthquakes and the effect on dynamics of branched fault systems 1 to examine the effects of branched fault geometry on the dynamics of fault systems in the long term we perform multicycle simulations on generic faulting models an explicit finite element algorithm is used to simulate spontaneous dynamic rupture of earthquakes the fault stress during the interseismic period is evaluated by an analytical viscoelastic model we find that the fault prestress field becomes highly nonuniform near the branch point and on the two branch segments over multiple earthquake cycles owing to the branched fault geometry and stress interaction between the two segments the principal prestress on faults rotates over multiple earthquake cycles and departs from the regional stress field significantly near the branch point after a number of earthquake cycles the branched fault systems evolve to a steady state in which several patterns of the fault prestress and earthquake rupture repeat the nonuniform prestress developed from previous earthquakes has large effects on the rupture and slip patterns several different rupture scenarios can occur on a given branched fault system in addition backward branching can occur in the nonuniform prestress field either driven by slip on the stem of the fault system or through a triggering mechanism these modeling results may have important implications for understanding fault branching behavior observed in the 1992 landers the 1999 hector mine and the 2002 denali fault earthquakes and for seismic hazard analysis in the areas where branched fault systems exist

geomorphological features and 3d modelling of montelparo mass movement central italy abstract the ancient village of montelparo marche region central italy is affected by a large translational mass movement the relief is modeled on arenaceous and arenaceous pelitic units overlying pelitic arenaceous terrains the bedding strata form a gently dipping monocline the translational slide is about 1100 m long and 500 700 m wide the upper boundary between the stable area and the sliding mass is marked by a large active trench near the hilltop the main sliding surface is located at a depth ranging between 65 and 100 m in the politic arenaceous unit we studied the mechanism of the slope instability along the stratigraphic contact between a rigid arenaceous unit and an underlying ductile pelitic unit the uncovering of the contact caused by the intense downcutting processes of the river at the hill foot during the holocene favoured the onset of the movement this was enhanced by the fractured bedrock and especially by the jointing we created a numerical model based on the finite differences code flac 3d by using a specific approach for mesh generation the model suggests a further enlargement and deepening of the trench and a sliding direction not aligned with the slope dip direction failure in the model concentrates at and around the main trench all the other elements staying in an elastic state and inducing a rigid sliding the model shows that both the failure onset and the current evolutionary state can be explained by the geological and static conditions of the slope

effect of seismogenic depth and background stress on physical limits of earthquake rupture across fault step overs earthquakes can rupture geometrically complex fault systems by breaching fault step overs quantifying the likelihood of rupture jump across step overs is important to evaluate earthquake hazard and to understand the interactions between dynamic rupture and fault growth processes here we investigate the role of seismogenic depth and background stress on physical limits of earthquake rupture across fault step overs our computational and theoretical study is focused on the canonical case of two parallel strike slip faults with large aspect ratio uniform prestress and friction properties we conduct a systematic set of 3 d dynamic rupture simulations with different seismogenic depth step over distance and initial stresses we find that the maximum step over distance h c that a rupture can jump depends on seismogenic depth w and strength excess to stress drop ratio s commonly used to evaluate probable rupture velocity as h c w s n where n 2 when h c w 1 5 and n 1 otherwise the critical nucleation size largely controlled by frictional properties has a second order effect on h c rupture on the secondary fault is mainly triggered by the stopping phase emanated from the rupture end on the primary fault asymptotic analysis of the peak amplitude of stopping phases sheds light on the mechanical origin of the relations between h c w and s and leads to the scaling regime with n 1 in far field and n 2 in near field the results suggest that strike slip earthquakes on faults with large seismogenic depth or operating at high shear stresses can jump wider step overs than observed so far in continental interplate earthquakes

rupture and ground motion models on the northern san jacinto fault incorporating realistic complexity we use the 3d finite element method to conduct dynamic models of rupture and resulting ground motion on the claremont casa loma stepover of the northern san jacinto fault we incorporate complex fault geometry from the u s geological survey usgs quaternary faults database see data and resources 1 a realistic velocity structure the southern california earthquake center community velocity model s a realistic regional stress field with an orientation taken from seismicity relocation literature and several stochastic self similar shear stress distributions as we incorporate more types of complexity the specific effects of any individual factor become less apparent within the overall rupture behavior we also find that the distribution of high and low shear stress that arises from combining regional and stochastic stress fields has the strongest control over where the rupture terminates using a regional stress field alone as well as with the combined regional and stochastic stress realization we find that the stepover presents a significant barrier to rupture regardless of our choice of initial nucleation point and that it is difficult for rupture to propagate the full length of either fault segment greater heterogeneity of stresses tends to produce shorter ruptures within this result we find that the claremont strand is more favorable for long ruptures than the casa loma clark strand low frequency ground motion intensity and distribution are controlled largely by the velocity structure rather than by stress heterogeneity the strongest motions produced in these models are in the san bernardino basin although directivity effects do contribute to the low frequency ground motion distribution particularly in the near field they are secondary to the effects of the velocity structure online material figures of ground motions from models used to calibrate the stress conditions for dynamic rupture propagation 1 sec 18

stability analysis of three dimensional seismic landslides using the rigorous limit equilibrium method abstract in this paper a new method combining the rigorous limit equilibrium method and the pseudo dynamic method is proposed to investigate stability of 3d seismic landslides in which the force equilibrium conditions along three coordinate axes and the overall moment equilibrium conditions around three coordinate axes are all strictly satisfied moreover sinusoidal cosinusoidal wave is applied to simulate earthquake displacement and an amplification factor of peak seismic acceleration is referred to as the amplification of seismic wave when it propagates from the bottom to the top of landslides the pseudo dynamic factor of safety of 3d seismic landslides is determined using trust region reflective iterative algorithm the effects of the parameters of the seismic landslides on the stability are analyzed by the bp neural network algorithm in which a database to investigate the stability of 3d seismic landslides is established in addition the stability of donghekou landslide is studied to verify the accuracy and precision of the present method

on western boundary current separation in an upper ocean general circulation model of the north pacific an upper ocean numerical model of the north pacific is used to investigate the influence on western boundary current separation of different wind stress climatologies variation of net surface buoyancy forcing and flow exchange with the sea of japan it was found previously cherniawsky and holloway 1991 that the modeled kuroshio splits into two branches near 35 n the stronger kuroshio like flow separates east while a weaker east japan coastal current continues to about 42 n the latter is opposite to observed flow the present study explores possible reasons for this discrepancy when we use the harrison 1989 instead of the hellerman and rosenstein 1983 monthly wind stress data the model oyashio front moves south by about 200 km this frontal shift is not sufficient to reverse the direction of the east japan current increasing buoyancy loss at high latitudes also enhances a southward intrusion of the oyashio front which is consistent with thermocline theories however this effect is inhibited by a small subpolar gyre and stability of upper layers in the north pacific separation latitude of the model western boundary current was found to be sensitive to the opening of the sea of japan the latter results in a tsugaru strait outflow driving a southward buoyant jet along the east coast of japan and kuroshio separation near 36 n in better agreement with observations

2d modelling of large scale platform margin collapses along an ancient carbonate platform edge maiella mt central apennines italy geological model and conceptual framework abstract results of numerical simulations of large scale platform margin collapses along the edge of the cretaceous platform of the maiella central apennines are presented adding a new contribution to the understanding of the role and quantification of the various factors that control triggering of these phenomena and the production of breccias and megabreccias for this purpose a sophisticated numerical code widely used in recent contexts to simulate overall mass movements and deep gravity driven deformation is applied for the first time to an ancient system on a scale of several kilometres the modelling carried out is a simplified attempt to understand a very complex phenomenon produced over a very long time span it tests whether the perturbing causes in the model acting together or separately are able to activate such large scale collapse and helps to understand the effects of perturbing causes and their variations in particular modelling was carried out considering both static variations in sea level and dynamic seismic events without and with fault formation conditions and combinations of them variations in sea level alone do not produce all the effects observed but may certainly be a predisposing element seismic shock simulations show that fracturing and shear stresses are concentrated on the platform margin representing the most sensitive and vulnerable area earthquake swarms associated with an active fault are the most likely means of triggering large scale platform margin collapses such as those occurring during the early cretaceous in the maiella

a two level wind and buoyancy driven thermocline model abstract a simple two level model is designed to simulate the thermocline equations applicable for large scale steady oceanic flow the model serves two functions first it replaces problems with the interpretation of slablike dynamics e g luyten et al 1983 by using continuously horizontally varying buoyancy but at the cost of reducing the vertical resolution drastically the equations used are geostrophy plus a small linear drag to close a stommel like western boundary layer mass conservation and buoyancy conservation with a small but necessary horizontal diffusion inclusion of vertical diffusion has little effect the ocean is driven by an ekman layer whose functions are to provide a given surface input of mass through ekman pumping and buoyancy through a specified buoyancy in the ekman layer i e to maintain the same boundary conditions as in classical thermocline studies sidewall conditions are not well understood and are almost certainly over specified in this formulation s

displacement and geometrical characteristics of earthquake surface ruptures issues and implications for seismic hazard analysis and the process of earthquake rupture there now exist about three dozen historical earthquakes for which in vestigators have constructed maps of earthquake rupture traces accompanied by de scriptions of the coseismic slip observed along the fault strike the maps and slip distributions are compiled here to place observational bounds on aspects of seismic hazard analysis and fault mechanics analysis leads to an initial statistical basis to predict the end points of rupture and the amount of surface slip expected at sites along the strike during earthquakes on mapped faults the observations also give support to the ideas that there exists a process zone or volume of about 3 4 km in dimension at the fronts of large laterally propagating earthquake ruptures within which stress changes may be sufficient to trigger slip on adjacent faults and that the ultimate length of earthquake ruptures is controlled primarily by the geometrical complexity of fault traces and variations in accumulated stress levels along faults that arise due to the location of past earthquakes to this may be added the observation that the form of earthquake surface slip distributions is better described by asymmetric rather than symmetric curve forms and that earthquake epicenters do not appear to correlate in any systematic manner to regions of maximum surface slip observed along strike online material maps of surface ruptures digitized values and curve fits to surface slip distributions and notes and references for tables 1 and 2