ice sheet evolution in james ross basin weddell sea margin of the antarctic peninsula the seismic stratigraphic record the stratigraphic architecture of the james ross basin nw weddell sea continental shelf shows three major phases of deposition preglacial ice sheet growth and ice sheet dominated the preglacial phase shows stratigraphic sequences that are similar to low latitude margins during the ice sheet growth phase there is evidence for initial ice sheet grounding in the southern part of the basin which migrated in steps northward sediment supply was also high during the ice sheet growth phase during the ice sheet dominated phase both north and south parts of the basin inherited all the classic features indicative of glacial strata large glacial troughs hundreds of meters deep and tens of kilometers wide truncation of sequences overlain by chaotic seismic facies and topped with coherent laminated reflections and an oversteepened continental slope the james ross basin strata are divided into five units s5 s1 each unit is characterized based upon seismic facies and stratigraphic architecture and the age of each unit is inferred from a seismic stratigraphic age model end member strata s5 and s1 were drilled and dated during shaldril and help to constrain this age model in total 34 grounding events of the antarctic peninsula ice sheet apis are recorded on the continental shelf this is similar to the 31 grounding events imaged on the pacific side of the peninsula ice grounding on the continental shelf is shown to have occurred as early as late middle miocene to early late miocene in the southern part of the basin the ice sheet advanced northward to encompass the northern peninsula by late miocene time the seven oldest glacial unconformities are believed to predate all previously identified unconformities on the peninsula continental shelf an expanded section of late pliocene pleistocene deposits shows a minimum of 10 grounding events this record more closely matches the deep sea oxygen isotope record than previous seismic studies of antarctic margins have shown

a physical basis for the frictional melting of some rock forming minerals abstract under conditions of coseismic slip 0 1 2 0 m s 1 within the upper crust differences in the shear yield strengths fracture toughnesses melting points and to a lesser extent thermal conductivities of rock forming minerals result in a hierarchy of friction melting susceptibilities in many so called pseudotachylytes it is observed that phyllosilicates and amphiboles are preferentially consumed to form the melt phase whilst quartz and feldspar tend to survive as clasts this can be explained in terms of the disequilibrium flash melting of those mineral phases possessing the lower shear yield strengths fracture toughnesses and thermal conductivities rather than by eutectic melting that would otherwise generate equilibrium minimum melts indicative of igneous processes at high strain rates typical of coseismic faulting the mechanical behaviour of minerals is primarily controlled by their fracture toughnesses with progressive comminution during slip leading to fusion the friction melting dependence on the mechanical properties of minerals indicates that there may be an important relationship between wall rock lithology and earthquake magnitude if frictional melting results in fault lubrication

keys and pitfalls in mesoscale fault analysis and paleostress reconstructions the use of angelier s methods whereas most of the stress inversion methods using fault slip data only minimize the angle between the measured striation and a computed shear stress to find the best fitting reduced stress tensor angelier 1990 proposed an alternative method named invd that also takes into account the relative shear stress magnitude which allows the fault to move using artificial datasets and particular fault geometries we compare this method with one of the classical methods based on the minimization of the shear slip angles r4dt angelier 1984 and we show that in most cases the new method has improved the quality of the results furthermore as proposed by angelier we point out that the quality of the stress inversion primarily depends on the quality of the field data we give advice and warn about some pitfalls concerning determination of sense of slip on fault planes recognition of successive faulting events and their chronology drawer or wedge faults stress permutations faults in vertical bedding we also argue that in case of tilted sequences fault diagrams should not be presented without bedding planes but we show that stress inversions when realized with caution and with the correct method can havemuch more applications than reconstructing stress fields like for determining the paleo horizontal the nature and the sense of motion of large faults the chronology and age of large structures

active faulting in the gulf of aqaba new knowledge from the mw 7 3 earthquake of 22 november 1995 abstract on 22 november 1995 the largest earthquake instrumentally recorded in the area with magnitude m w 7 3 occurred in the gulf of aqaba the main rupture corresponding to the strike slip mechanism is located within the gulf of aqaba which forms the marine extension of the levantine fault also known as the dead sea fault the levantine fault accommodates the strike slip movement between the african plate and the arabian plate the gulf of aqaba itself is usually described as the succession of three deep pull apart basins elongated in the n s direction concerning historical seismicity only two large events have been reported for the last 2000 years but they are still poorly constrained the seismicity recorded since installation of regional networks in the early 1980s had been characterized by a low background level punctuated by brief swarmlike activity a few months in duration three swarms have already been documented in the gulf of aqaba in 1983 1990 and 1993 with magnitudes reaching at most 6 1 m w we suggest that the geometry of the rupture for the 1995 event is related to the spatial distribution of these previous swarms body wave modeling of broadband seismograms from the global network along with the analysis of the aftershock distribution allow us to propose a well constrained model for the rupture process northward propagation of the rupture has been found we have demonstrated that three successive subevents are necessary to obtain a good fit between observed and synthetic wave forms the total seismic moment released was 7 42 10 19 n m the location of the subsevents shows that the three stages of the rupture involve three different segments within the gulf substantial surface breakage showing only normal motion up to 20 cm affecting beachrock was observed along the egyptian coast we show that these ruptures are only a secondary feature and are in no case primary ruptures the stress tensor derived from striations collected in quaternary sediments shows radial extension this result supports landsliding of the beach terraces under the action of the earthquake shaking

ultracataclasis sintering and frictional melting in pseudotachylytes from east greenland abstract large volumes of pseudotachylyte an intrusive fault related rock interpreted to form by a combination of cataclasis and melting occur in tertiary normal faults and accommodation zones along 400 km of the east greenland volcanic rifted margin analysis of representative pseudotachylyte samples reveals a wide range of mesoscopic and microscopic textures mineralogies and chemistries in the aphanitic pseudotachylyte matrix three distinct types of pseudotachylyte referred to as angular rounded and glassy are identified based on these characteristics angular pseudotachylyte found primarily in dike like reservoir zones is characterized by angular grains visible on all scales with micron scale fragments of mica and amphibole its matrix is enriched in fe2o3 mgo and tio2 relative to the host rock with minor increases in cao k2o and small decreases in na2o rounded pseudotachylyte is found in reservoir zones injection veins pseudotachylyte filled extension fractures and fault veins small faults with pseudotachylyte along their surfaces it is characterized by smooth surfaced compacted grains on microscopic scales and encloses rounded interpenetrative lithic clasts on outcrop scale its matrix is enriched in fe2o3 mgo tio2 and al2o3 relative to the host rock with minor depletion in na2o and k2o glassy pseudotachylyte is found primarily along fault surfaces its matrix is characterized by isotropic conchoidally fractured material containing microscopic strain free amphibole phenocrysts and is enriched in tio2 al2o3 k2o fe2o3 mgo cao and na2o relative to the host rock these observations suggest that angular pseudotachylyte was produced by cataclasis with enrichment in metallic oxides resulting from preferential crushing of mechanically weak amphibole and mica minerals found in the gneissic host rock cataclasis and concomitant frictional heating resulted in the textural and chemical modification of angular pseudotachylyte by sintering or melting producing rounded and glassy pseudotachylyte respectively compositional and textural observations constrain the temperatures reached during frictional heating 700 900 c which in turn delimit the amount of frictional heat imparted to the pseudotachylytes during slip our results suggest that the east greenland pseudotachylytes formed during small seismic events along faults at shallow crustal levels consistent relative ages and widespread occurrence of pseudotachylyte bearing faults in east greenland suggest that widespread microseismicity accompanied the early development of this volcanic rifted margin

direction of resolved shear stress a construction and discussion abstract a simple construction facilitates identification of the direction of resolved shear stress for andersonian conditions in which one principal axis is vertical a constructed horizontal rake guide for specific stress and strike will project perpendicularly onto any dipping plane as the direction of resolved shear stress consideration of rake guides for different strikes for each fixed stress state illustrates that tectonic regimes are identifiable by ranges but not by individual values of rake the tectonic regime parameter and the rake guide angle are useful parameters for andersonian stress

pseudotachylite generated as a result of a drilling burn in abstract material similar to naturally occurring pseudotachylite was generated in proterozoic lava as a result of frictional overheating of a diamond drill dh 5000 impregnated crown at a depth of 2 4 km below surface bit rotation equation to slip rates of about 1 m s is thought to have caused severe overheating to last for 3 10 s estimates show that melting occurred in the temperature range 800 1100 c under wet conditions and at comparatively low effective normal and shear stresses of about 1 9 107 and 9 7 106 pa respectively associated breccia formed as a result of thermal decrepitation rather than dynamic comminution and as a corollary it is suggested that some cataclasites associated with pseudotachylite bearing faults may also form by the mechanism this implies that the presence of both cataclasite and pseudotachylite on a fault plane does not necessarily indicate reactivation

frictional melting processes in planetary materials from hypervelocity impact to earthquakes frictional melting is the result of the conversion of mechanical deformation to heat under adiabatic conditions of slip within planetary materials which are mainly natural ceramics frictional melting occurs at high strain rates typically 10 2 s 1 and at slip velocities greater than 0 1 m s 1 t he pathway to friction melting is controlled by the mechanical properties of a rock s constituent minerals especially fracture toughness minerals with the lowest fracture toughnesses and breakdown temperatures are preferentially comminuted and fused to form the melt the product is a polyphase suspension comprising mineral and rock fragments enclosed in a liquid matrix this cools to form the rock type known as pseudotachylyte and at even higher strain rates it forms shock veins in meteorites and in impact craters which may contain high pressure mineral polymorphs the generation of melt on sliding surfaces can lubricate earthquake faults facilitate the post shock modification of impact craters and make landslides more hazardous

stress field evolution in the northwest himalayan syntaxis northern pakistan 1 we have conducted a systematic inversion of striated fault planes throughout northern pakistan in order to better depict the temporal and spatial variations in stress patterns two domains are evidenced at a regional scale separated by the active raikhot fault the western boundary of the nanga parbat spur west of this fault a wrench type stress field with 1 axis oriented around n s predominates in the karakorum and in kohistan it predates pliocene quaternary exhumation of nanga parbat and corresponds to the miocene or earlier regional stress field related to indian asian convergence east of the raikhot fault compression parallel to the belt accounts for initiation of the nanga parbat anticlinorium after 5 ma it is followed by predominant post 2 ma extension both parallel to the belt and nne ssw oriented thus in the n w himalayan syntaxis multidirectional extension is juxtaposed on short timescales to shortening either parallel or perpendicular to the belt such juxtaposition could be characteristic of strain and stress partitioning during oblique convergence

frictional melt pulses during a 1 1 ma earthquake along the alpine fault new zealand our understanding of frictional melting that occurs during large earthquake slip events has been hampered by the extremely fine grain size of frictionally fused rock and the lack of detailed high resolution microscopy studies that describe features at the crystal lattice scale in such a study we here report the complex nature of melting and crystallization in a symmetrically layered pseudotachylyte vein from the alpine fault new zealand two melt pulses are recognized attributed to successive but rapid injections of frictionally generated material the initial injection preserved at the vein margins was proximally derived and contains a high concentration of clasts and a si rich glass this was quickly followed by a second generation of a more distally derived melt dominated fraction which was injected into the weak vein center whereas fragments of wall rock biotite are preserved in the marginal zones neocrystallized microlitic biotite characterizes both margins and center the vein biotite is different in composition microstructure and polytypism from the metamorphic biotite of the wall rock in all melt layers newly formed biotite shows notable signs of syn flow crystallization strain features and erosion at crystal glass contacts with breakdown of neocrystallized microlites along both crystal edges and faces these characteristics imply cyclic pulses of heating melting and crystallization occurred during a single large earthquake episode and probably reflects the stick slip propagation properties of coseismic faulting 40 ar 39 ar total gas ages from the vein center give a 1 11 0 04 ma date for cyclic melting which based on current exhumation rates occurred at a crustal of depth v11 km 2003 elsevier science b v all rights reserved

paleostress analysis of cenozoic faulting in the kraishte area sw bulgaria abstract paleostress calculations from fault planes in paleogene sediments and in the underlying basement were used to determine the orientation and the chronology of the principal stresses during the cenozoic tectonic evolution of the kraishte area southwest bulgaria the results show that middle eocene early oligocene wsw ene extension led to the formation of grabens and half grabens filled with thick continental to marine deposits in the hanging wall of extensional detachments the paleogene sediments and their basement were then intruded by subvolcanic bodies and dykes during sw ne extension between 32 and 29 ma these wsw ene and sw ne extensional stages are related to the general rollback of the hellenic slab from the late oligocene to the earliest miocene sse nnw transtension generated coal bearing sedimentary basins the anticlockwise rotation of the main tensile axis by almost 50 with respect to the previous tectonic stage was probably related to a switch from the aegean back arc extension to crustal stretching and extrusion of continental fragments around the moesian platform since the middle miocene extension in the kraishte area accommodated by faults with relatively small displacement led to the formation of restricted basins filled with alluvial to lacustrine deposits

the thermal response of rock to friction in the drag cutting process abstract significant friction between the cutter and the rock occurs during the drag cutting process this friction is responsible for elevating the temperature of the drag cutter and under certain conditions reducing cutter life because of this effect friction often plays a major role in determining the economics of drilling with drill bits employing polycrystalline diamond compact pdc cutters analytical models have been developed in previous studies for predicting pdc cutter temperatures and their effects on bit wear and performance the current paper investigates the effects of drag cutter friction on the rock mass and on rock chips generated during cutting the thermal and mechanical loading imposed during the cutting process is described and the thermal response of the rock to frictional heating at the cutter rock interface is investigated the results indicate that significant localized rock temperatures can develop as a result of frictional heating caused by drag cutters sliding on the rock surface although conduction of heat is severely limited during the short chip formation process it is possible to attain elevated temperatures throughout a rock chip because of the possibility of internal frictional heating caused by shear deformation it is concluded that temperatures and pressure during drag cutting are sufficient to cause metamorphic changes in some rock constituents

microstructural and chemical changes associated with cataclasis and frictional melting at shallow crustal levels the cataclasite pseudotachylyte connection in pelitic schists of the nason terrane of washington state pseudotachylyte can be demonstrated to have developed subsequent to the formation of foliation parallel cataclasite zones numerous microstructural lines of evidence point to a genetic link between pseudotachylyte and cataclasite and chemical evidence indicates that cataclasis played an important role in controlling pseudotachylyte chemistry besides optical and textural differences between the cataclasite and pseudotachylyte which may occur together there is unambiguous evidence of a melt origin for the pseudotachylyte while such evidence within the cataclasite is absent tem evidence indicates that glass is present in at least some of the veins as demonstrated by a lack of electron diffraction microlites present in the glass lack dislocations high temperature microlites of a mineralogy and composition not present in the host schist occur in various habits which depend on the distance from the vein margin also present are assimilation textures apparently quenched sulfide droplets and vesicles and amygdules in a pseudotachylyte vein studied in detail five microstructural domains occur these include vein margin cataclasite a transitional dark pseudotachylyte vein interior glass opaque and sulfide rich blebs and translucent haloes surrounding some of the blebs the cryptocrystalline cataclasite matrix grades into the dark pseudotachylyte which optically grades into the glass after adjustment for silica the host schist and cataclasite matrix are chemically very similar the dark pseudotachylyte and glass with the exception of na2o and cao are chemically quite similar to the cataclasite matrix the main difference may be the result of the segregation of the opaque plagioclase blebs thus the pseudotachylyte chemistry is strongly dependent upon the chemistry of the material comprising the cataclasite matrix which in turn is dependent on mineral susceptibility to incorporation into the cataclasite matrix fluids infiltrated along the cataclasite zones prior to pseudotachylyte generation as recorded by hydration reactions sulfide veining na2o loss and fluid inclusions this demonstrates that pseudotachylytes can form under fluid rich conditions as opposed to the commonly assumed dry conditions

investigation of temporal variations in stress orientations before and after four major earthquakes in california abstract orientations of the principal stresses before and after four major earthquakes in the greater san francisco bay area were determined by inversions of 34 suites of focal mechanisms of about 1500 small earthquakes recorded by the northern california seismic network over three decades stress orientations are expected to rotate due to the release of shear stress in a major earthquake the degree of rotation can place some constraints on the ambient level of stress in the crust surrounding the mainshock for the four earthquakes studied here the 1986 mt lewis 1984 morgan hill 1979 coyote lake and 1989 loma prieta events modest rotations of the maximum compressive stress sh to a higher angle i e an orientation closer to fault normal appear to occur at the time of the mainshock in some cases sh eventually rotates back towards its original orientation however due to relatively large uncertainties obtained on the stress orientations the constraints that can be inferred on the absolute levels of stress surrounding the mainshock regions are rather weak by considering the largest stress change permitted by the confidence limits we obtain lower bounds on the background deviatoric stress of 3 12 mpa levels only slightly greater than the mainshock static stress drops

breddin s graph for tectonic regimes abstract a simple graphical method is proposed to infer the tectonic regime from a fault and slip data set an abacus is overlaid on a plot of the rake versus strike of the data this yields the horizontal principal stress directions and a constraint on the stress tensor aspect ratio in a manner similar to breddin s graph for two dimensional strain analysis the main requirement is that one of the principal stress directions is close to the vertical this method is illustrated on monophase synthetic and natural data but is also expected to help sort out multiphase data sets

remarks on the relationship between the tectonic regime the rake of the slip vectors the dip of the nodal planes and the plunges of the p b and t axes of earthquake focal mechanisms abstract we use a triangular representation of the plunges of p b and t axes to compare the different ways tectonic regime is inferred from earthquake focal mechanisms in recent works we argue that p b and t axes provide a reasonable estimate of principal stress directions when faulting is close to andersonian conditions and that this can be estimated from the location on a triangular diagram we analyze the geometrical relationship between the plunges of p b and t axes on one hand and the rake of slip and dip of nodal planes on the other hand we show that the rake and dip level curves correspond to trajectories of the vertical direction along great and small circles with respect to the frame of the p b and t axes this shows that dip slip faulting is compatible with vertical p or t axes but does not require it and instead requires horizontal b axes it also shows that strike slip faulting does not require vertical b axes but p and t axes with equal plunges this also reveals that focal mechanisms where p b and t axes all have moderate plunge correspond to two very different types of nodal planes a steeply dipping one with oblique slip and a moderately dipping one with strike slip seismically active and moderately dipping strike slip faults are to be found among these events

transformation of cataclastically deformed rocks to pseudotachylyte by pervasion of frictional melt inferences from clast size analysis abstract optical contrast between clasts and surrounding dark coloured matrix in thin sections has been used in a computer aided method which has been applied for clast size analysis of pseudotachylyte exposed in a 25 km long brittle deformation zone in the precambrian terrain of western india while the number of clasts n2 equal to or coarser than size u shows a power law distribution n2 u d the area a1 occupied by the clasts of different size fractions shows a log normal distribution the clast size distribution pattern indicates transformation of cataclastically deformed rocks to pseudotachylytes by pervasion of a rock melt generated at the frictional slip planes it is inferred that the melt pervaded the permeable cataclastically damaged zones and so occupied the intergranular space this melt mixed with the comminuted material flowed further as a slurry to form the pseudotachylyte veins the clast laden final product retained the grain size distribution pattern of the parent comminuted material with minor modifications fusion of clast rinds due to heat transfer from the melt slightly modified the initial grain size distribution pattern because of the short duration of the heat transfer process combined with the low conductivity and high specific heat of rocks the temperature at the centre of the coarse grains remained at the initial temperature ti and reduction w of radius r by fusion was a negligible fraction of r as a consequence the population of coarse clasts retained the pre fusion size distribution pattern in contrast w r of the smaller grains was considerable the initial grain size distribution pattern did not survive in the finer fraction of the clasts this difference in thermal response of the smaller versus larger grains to the heat transfer process is revealed in clast size distribution graphs for the pseudotachylytes moreover the observed proportion of matrix can not be explained by cataclasis alone the extent of comminution in the parent material and size of the openings through which the clast laden melt flowed to form veins controlled the clast matrix ratio in the pseudotachylytes

analysis of a gradual change in stress regime example from the eastern iberian chain spain abstract the compression extension passage in the eastern iberian chain during the miocene is analyzed structural data suggest that it is a gradual change in stress regime which does not involve rotation but interchange of 1 and 2 axes one of them remaining always vertical the gradual stress evolution is interpreted by a numerical graphic method y r diagram which optimizes combinations of y azimuth of the maximum horizontal axis and r stress ratio explaining groups of fault movements the y r diagrams of some fault populations measured in the castellon region provide optimum tensors appearing within a continuous cloud of solutions from the compressional field to the extensional one movement sequences obtained from superimposed striations indicate a systematic stress change between these two regimes

frictional melting of sedimentary rock during high speed diamond drilling an analytical sem and tem investigation abstract high speed drilling at 900 rpm with a downhole motor driven natural diamond drag bit has resulted in the extreme alteration of sedimentary rock in an offshore canadian wildcat well these effects as revealed in the rock cuttings retrieved from the drilling fluid at surface include discolouration darkening cataclasis slickensiding and partial fusion calcareous siltstones are the most susceptible to alteration especially melting whereas sandstone and limestone cuttings mainly exhibit fracturing and surface glazing analytical scanning electron microscopy reveals that the calcareous siltstones have undergone decalcification via decarbonation and the loss of cao to the drilling fluid decarbonation combined with dehydration resulted in the vesiculation and explosive fragmentation of certain cuttings analytical transmission electron microscopy shows that glass is present in the calcareous siltstone cuttings most of the modifications exhibited by the sedimentary rocks can be attributed to the effects of high strain rate deformation and frictional heating at the bit rock interface that melting took place is supported by thermal calculations which indicate that for a coefficient of friction of 0 5 temperatures of approximately 1200 c were realized at diamond rock contacts such high temperatures can accelerate the wear of diamond and its substrate and hence shorten bit life as well as obliterate potentially important geological information in the rock cuttings

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

characterization of various types of deformation and their corresponding deviatoric stress tensors using microfault analysis abstract considering an ideally prefractured material based on mohr s representation and bott s model we define the geometry and the peculiarities of the different theoretical fault domains which are likely to be reactivated under different tectonic regimes the theoretical striations associated with the different types of deformation are also calculated the compressive strike slip extensive strike slip radial extensive and constrictive types of deformation are specified in the second part of this paper using etchecopar s computer aided method a quantitative structural analysis of various types of superficial deformation has been carried out in different study areas southern france greece spain tunisia and nigeria the geometry of the microfault domains as well as the nature of the associated tensors are determined for each type of regional deformation the problem of the spatial homogeneity of the tensors deduced by the microtectonic analysis within the framework of a particular tectonic phase is also discussed

role of faults and layer interfaces on the spatial variation of stress regimes in basins inferences from numerical modelling abstract the spatial variation of the computed state of stress is studied in a series of numerically solved boundary value problems of basin scale deformation these numerical experiments illustrate simple situations of decollement tectonism under compression the study focuses on the local variation of the state of stress in a sedimentary overburden where major discontinuities such as large scale faults and layer interfaces are present the states of stress are computed using either the distinct element method or the finite element method classic elasto plasticity laws are used for the behaviour of the continuum and the discontinuities are modelled as coulomb contact surfaces a geologic interpretation of the numerical experiments is proposed to highlight the role played by major structural discontinuities in the local variations of the stress regime the models are two dimensional in space and assume plane strain but the full three dimensional stress strain constitutive relation is used therefore the stress regime variations can be represented by constructing the contour map of the wallace bott stress ratio this simple technique together with the construction of diagrams of principal stress magnitude across the model enables us to rapidly examine the stress field pattern and further discuss the deformation modes of faulting and fracturing which may take place at a small scale we have found that the local variations of the stress tensor are in good agreement with common geologic interpretation of brittle deformations in foreland and thrust systems we demonstrate how the presence of layer interface and the difference in mechanical properties of formation lithology may strongly affect the variation of stress in space this modelling approach has important issues when interpreting well tests to gain access to in situ stresses

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

strong velocity weakening and powder lubrication of simulated carbonate faults at seismic slip rates 1 high velocity friction tests were conducted on solid and hollow cylinders of carrara calcite marble dolomite marble silicate bearing calcite marble and calcite gouge to investigate the strength of carbonate faults during seismic slip the experiments performed at normal stresses of 0 6 14 7 mpa slip rates of 0 03 1 60 m s and room temperature in a rotary shear friction testing machine yielded an extraordinarily low steady state friction coefficient 0 1 at slip rates of 1 1 1 2 m s the slip weakening distance of 4 28 m became shorter at higher normal stress or frictional work rate strong velocity weakening was observed not only in steady state but also in nonsteady state friction while the slip rate was changing thus slip deceleration was accompanied by fault strength recovery large rapid temperature rises in narrow shear localization zones less than a few micrometers induced carbonate decomposition such as the breakdown of calcite into aggregates of cao nanograins and co2 in carrara marble scanning electron microscope observation revealed that the shear localization zone in the highly porous decomposition product was a layer of scattered small grains mostly 1 m in diameter these microstructures and the measured high permeability 10 14 m2 of the decomposed marble indicate that the dominant weakening mechanism in our experiments was possibly powder lubrication powder rheology at high slip rates is not yet well understood but the frictional behavior of nanograins appears to be strongly velocity dependent if decarbonation occurs during seismic slip in natural carbonate faults powder lubrication may make the faults slippery even under fluid drained conditions

a preliminary assessment of the hydrocarbon potential of the larsen basin antarctica abstract the larsen basin on the northwest margin of the weddell sea formed as a mesozoic ensialic basin during gondwana breakup deposition was either in half grabens on the extending weddell sea margin or in a restricted back arc basin at the northern end of this basin 5 6 km of sedimentary rock crop out on james ross island exposing elements of a large potential hydrocarbon system aeromagnetic and outcrop data suggest that the basin structure inferred from james ross island can be recognised at least as far south as 70 s upper jurassic anoxic marine strata deposited prior to the main phase of arc development form a rich potential source t o c up to 3 5 with both marine and terrestrial kerogens arc derived volcaniclastic sediments of barremian oligocene age form a regressive megasequence basal strata represent slope apron and rudaceous submarine fan deposits proximal to the margin fan conglomerates form lenticular bodies hundreds of metres thick and tens of kilometres across enveloped in slope apron mudstones late cretaceous fault reactivation and uplift led to dramatic shallowing of the basin with deposition of shelf facies although there are many potentially attractive reservoir targets there may be problems of pore occlusion due to the abundant labile volcanic grains however there is evidence of more quartzose sandstone towards the top of the section and inferentially toward the basin centre in the larsen basin there is moderate potential for oil generated from upper jurassic source rocks and reservoired in cretaceous and tertiary sandstones and conglomerates in large stratigraphic or structural traps caused by partial basin inversion during deposition

estimation of the potential type of faulting in relation to the stress field the north aegean case study the relation between the angle of slip during fault reactivation and the applied stress field is investigated through a plot of the deviatoric stress ratio r v h h h vs the fault strike direction measured from h assuming that one of the principal stresses is vertical this approach is applied to the north aegean trough fault zone on the basis of neotectonic data presented previously by other authors and conclusions are drawn as to the potential type of faulting along the trough since late miocene the same reasoning is also applied to earthquake focal mechanisms of the northern aegean region

slip preference on pre existing faults a guide tool for the separation of heterogeneous fault slip data in extensional stress regimes abstract synthetic fault slip data have been considered in the present paper in order to examine through a simple graphical manner the validity and use of the widely mentioned and applied criteria such as the slip preference slip tendency kinematic p and t axes transport orientation and strain compatibility the examination and description concern extensional stress regimes whose greatest principal stress axis 1 always remains in vertical position as in andersonian stress states in particular radial extension re radial pure extension re pe pure extension pe pure extension transtension pe trn and transtension trn are examined with the aid of the win tensor stress inversion software in all of these extensional stress regimes only extensional faults can be activated the lower dip angle of the reactivated faults is about 40 assuming that the coefficient of friction is no smaller than 0 6 the increase of the stress ratio and or the fault dip angle up to 70 results in the increase of the slip deviation from the normal activation based on the present examination of the slip preference and slip tendency in different extensional stress regimes a new simple and practical method is proposed herein in order to separate originally heterogeneous fault slip data into homogeneous fault groups by which different extensional stress regimes could be determined the application of the method on the already published fault slip data of lemnos island supports its validity since over 90 the resulted fault groups and stress regimes coincide to the already published ones

artificial generation of pseudotachylyte using friction welding apparatus simulation of melting on a fault plane a 150 m thick fused layer of rock has been produced by rotating two metadolerite core faces against each other at 3000 r p m under an axial load of 330 kg for 11 s using friction welding apparatus scanning electron microscopy and electron microprobe analysis reveal that the melt layer comprises sub angular to rounded porphyroclasts of clinopyroxene feldspar and ilmenite 20 m diameter derived from the host metadolerite set within a silicate glass matrix thermal calculations confirm that melting occurred at the rock interface and that mean surface temperatures in excess of 1400 c were attained the fused layer shows many textural similarities with pseudotachylyte described from fault zones morphologically the fused layer consists of a series of stacks of porphyroclasts welded together by melt to form build ups oriented at right angles to the friction surface there is also evidence of gouging ploughing and plucking as well as transfer and adhesion of material having occurred between the rock faces the mean surface velocity attained by the metadolerite 0 24 m s 1 and duration of the experiment are comparable with velocities and rise times of typical single jerk earthquakes occurring during stick slip seismic faulting within brittle crust i e slip rates of 0 1 0 5 m s 1 for say 1 10s in these respects the experiment successfully simulated frictional fusion on a fault plane in the absence of an intergranular fluid power dissipation during the experiment was about mw m 2 comparable only to very low values for earthquakes e g 1 100 mw m 2 for displacement rates of 0 1 0 5 m s 1 at shear stresses of 100 1000 bars this indicates that melting on fault planes during earthquakes should be commonplace field evidence however does not support this contention either pseudotachylyte is not being recognized in exhumed ancient seismic fault zones or melting only occurs under very special circumstances

continental rift to back arc basin jurassic cretaceous stratigraphical and structural evolution of the larsen basin antarctic peninsula the larsen basin developed in jurassic times as a result of continental rifting during the early stages of gondwana break up lower upper jurassic non marine sedimentary and volcanic rocks constitute a syn rift megasequence recording initial largely amagmatic extension and subsequent widespread extension related silicic volcanism a succeeding kimmeridgian early berriasian transgressive megasequence consisting largely of anoxic dysoxic hemipelagic mudstones is thought to have been deposited during a thermal subsidence phase when relative magmatic quiescence and peak jurassic eustatic sea levels served to maximize sediment starvation the fragmentary record for late berriasian barremian times suggests that a regressive megasequence may have developed in the earlier part of this period recording increased sediment yield to the larsen basin from the increasingly emergent antarctic peninsula arc subsequently strata in the southern but not the northern part of the basin underwent relatively intense eastward verging deformation possibly during the formation of a retro arc fold thrust belt where exposed the lower part of the succeeding aptian eocene megasequence consists of a deep marine clastic wedge deposited along the fault bounded western basin margin during a phase of arc uplift and related differential subsidence following partial basin inversion in late cretaceous times regression took place as reduced basinal subsidence rates allowed shallow marine facies to prograde basinward

pseudotachylyte generated in the semi brittle and brittle regimes bench canyon shear zone central sierra nevada pseudotachylyte cuts cretaceous plutonic and volcanic rocks in the bench canyon shear zone central sierra nevada california as documented by optical and scanning electron microscopy the pseudotachylyte displays evidence for a friction melt origin including vesicles amygdules crystallites flow fabrics and embayed crystal fragments based on fault related rock association vein morphology and inferred crustal level of generation two distinct types of pseudotachylyte are documented in the shear zone pseudotachylyte associated with cataclasite was generated at shallow crustal levels 1 10 km via unstable velocity weakening abrasive wear friction pseudotachylyte associated and interlayered with mylonite was generated at deeper crustal levels 10 15 km most likely via stable velocity strengthening adhesive wear friction this pseudotachylyte underwent ductile deformation in the solid state interlayered pseudotachylyte and mylonite records cyclic aseismic seismic slip at a transitional crustal level between the semi brittle field of quartzofeldspathic rocks and the base of the seismogenic zone the cyclicity is attributed to strain rate fluctuation effected by strain resistant phacoids pore fluid pressure variation ductile instabilities or downward fault propagation the mode of deformation within the shear zone progressed from i production of mylonite during amphibolite to greenschist facies conditions to ii generation of pseudotachylyte by intermittent seismic faulting within a background of aseismic shear in the upper realm of the semi brittle field 300 400 c to iii generation of pseudotachylyte through seismic events in the brittle 300 c during uplift exhumation and cooling some of the latter may have been generated at shallow enough crustal levels 4 km to allow vesicle formation the exhumation of a crustal level exposing such an assemblage provides a rare opportunity to study the enigmatic nature of the transitional change from semi brittle flow to seismogenic rupturing

experimental generation of volcanic pseudotachylytes constraining rheology volcanic systems are highly dynamic environments that comprise rocks and magmas which in the process of strain localisation e g in catastrophic flank collapse or dome building events are candidate materials for the occurrence of frictional melting and the formation of pseudotachylytes we evaluate the frictional behaviour of a plagioclase two pyroxene and glass bearing andesite and introduce an approach to constrain the rheology of frictional melts frictional slip at a rate of 1 3 m s under an axial stress of 1 5 mpa induces heating at a rate approximating 130 c per meter of slip and frictional melting of the andesite occurs at 1000 c which corresponds to a peak in shear stress with continuing displacement the shear stress decreases by 25 from the peak strength and stabilises while the temperature equilibrates to 1230 1290 c the shear stress for the system is congruent with a non arrhenian temperature dependent frictional melt rheology exhibiting a non newtonian viscosity evolving from approximately 104 2 to 103 4 pa s post experiment analysis show a gradation from 1 the host rock to 2 an extraordinary zone of unmelted yet viscously deformed material to 3 a thin outer region of chemically heterogeneous protomelts and to 4 an inner region of chemically homogeneous frictionally generated modified melt in the core of the slip zone we discuss the role and identification of frictional melting in volcanic systems and the implication of viscous remobilisation of magmatic plugs during frictional slip of glass bearing volcanic materials

shock induced melting and vaporization of shatter cone surfaces evidence from the sudbury impact structure analytical scanning electron microscopy has been used to investigate the surface textures and compositions of newly exposed shatter cones from the 1 85 ga sudbury impact structure canada unusual surface microstructures are observed at the micron scale including silicate melt smears melt fibres and melt splats silicate and ni rich spherules up to 5 m in diameter adorn earlier formed surface features and we interpret these to be condensates formed due to shock induced vaporization of the shatter cone surfaces the development of striations on the shatter cones is attributed to shock related fracture and slip formation of melts and spherules indicates that the highest ranks of shock metamorphism stages iv and v were realized but only on a very localized scale shatter cone surfaces are therefore likely sites for the development of high pressure polymorphs and if the chemistry is appropriate fullerenes as such they may be equivalent to type a pseudotachylytes and shock veins in meteorites

fault kinematic and geomorphic observations along the north tehran thrust and mosha fasham fault alborz mountains iran implications for fault system evolution and interaction in a changing tectonic regime summary neighbouring faults can interact potentially link up and grow and consequently increase the seismic and related natural hazards in their vicinity despite evidence of quaternary faulting the kinematic relationships between the neighbouring mosha fasham fault mff and the north tehran thrust ntt and their temporal evolution in the alborz mountains are not well understood the ene striking ntt is a frontal thrust that delimits the alborz mountains to the south with a 2000 m topographic front with respect to the proximal tehran plain however no large instrumentally recorded earthquakes have been attributed to that fault in contrast the sigmoidally shaped mff is a major strike slip fault located within the alborz mountains sinistral motion along the eastern part of the mff is corroborated by microseismicity and fault kinematic analysis which documents recent transtensional deformation associated with nne ssw oriented shortening to better understand the activity of these faults on different timescales we combined fault kinematic analysis and geomorphic observations to infer the kinematic history of these structures our fault kinematic study reveals an early dextral shear for the ntt and the central mff responsible for dextral strike slip and oblique reverse faulting during nw oriented shortening this deformation regime was superseded by ne oriented shortening associated with sinistral oblique thrusting along the ntt and the central western mff sinistral strike slip motion along subsidiary faults in the central mff segment and folding and tilting of eocene to miocene units in the mff footwall continued thrusting along the ntt took place during the quaternary however folding in the hanging wall and sinistral stream offsets indicate a left oblique component and quaternary strike slip reactivation of the eastern ntt segment close to its termination this complex history of faulting under different stress directions has resulted in a composite landscape with inherited topographic signatures our study shows that the topography of the hanging wall of the ntt reflects a segmentation into sectors with semi independent uplift histories areas of high topographic residuals and apparent high uplift underscore the fault kinematics combined our data suggest an early mechanical linkage of the ntt and mff fault systems during a former dextral transpressional stage caused by nw compression during ne oriented shortening the ntt and mff were reactivated and incorporated into a nascent transpressional duplex the youngest manifestation of motion in this system is sinistral transtension however this deformation is not observed everywhere and has not yet resulted in topographic inversion

possible focal mechanism change during reactivation of a previously ruptured subduction zone and stress tensor implications summary body waveform inversion methods usually assume a constant double couple source or a combination of such subevents previous studies suggest that the source rupture of mature sources in terms of coupling along smooth subduction zones are usually resolved on this assumption however for events where the source area overlaps previously ruptured zones the conventional inversion methods fail to resolve the source process for such events the subduction coupling may vary between the mature source area and the previously ruptured zone causing a variation in the focal mechanism too we study the implications on the stress tensor of the coexistence of two such focal mechanisms using a major aftershock of the 1985 chilean earthquake m 6 0 the 1978 kurile m 7 6 and 1980 santa cruz islands m 7 7 earthquakes for the first event we use the two different sets of focal parameters obtained by a study which describes a focal mechanism change during the process the epicentres of the latter two large events are located in the spots which had remained unbroken in the preceding large events e g the 1963 and 1969 kurile earthquakes and the 1966 santa cruz is earthquake respectively for each event one of the focal mechanism solutions shows a substantial strike slip component the stress tensors are examined under the constraints that the shear stress is parallel to the slip vector and a friction law is satisfied two particular families of stress tensors examined are 1 the tensors that are optimally orientated with respect to the mature source area and 2 the tensors that have a vertical principal stress direction the first type of tensors can fully account for the observed slip orientation only for the chile aftershock but it comes close to the observed one in the case of the kurile island event and would indeed reactivate the decoupled area at a reasonably low stress level the second type of tensors can be compatible with the two observed slip orientations in all cases however for the santa cruz is and kurile is earthquakes the friction law which should be satisfied on each plane requires too high a stress deviation

amorphous material formed by the mechanochemical effect in natural pseudotachylyte of crushing origin a case study of the iida matsukawa fault nagano prefecture central japan abstract pseudotachylytes from the iida matsukawa fault central japan iida pseudotachylytes are described down to the nanometer scale using high resolution electron microscopy scanning electron microscopy analyses of chemical compositions and mercury intrusion porosimetry the pseudotachylyte matrix chiefly consists of nanoscale particles and elongated submicron fragments with biotite composition amorphous material of several tens of nanometers in size is also observed despite the absence of melt textures lattice fringe images reveal that the amorphous phase coexists with lattice distortion in deformed biotite fragments that are several hundreds of nanometers in size the presence of these submicrostructures indicates that the amorphous material formed by mechanical stress during the comminution process that is via the mechanochemical effect we conclude that amorphous material does not always provide evidence of the rapid cooling of melt in pseudotachylyte the amorphous materials present in the iida pseudotachylyte resulted from the mechanochemical effect due to both shear stress and normal stress during the comminution process that accompanied fault motion

tr method a practical tool to analyze focal mechanisms and identify the real seismogenic fault of an extensional or compressional shallow earthquake sequence abstract the recently proposed tr method that separates heterogeneous fault slip data in extensional and compressional stress regimes is applied on focal mechanisms of a number of earthquake sequences aiming to identify the main seismogenic fault plane the method only requires the earthquake sequence to be classified as related to an extensional or compressional stress regime in particular the nodal planes of the compressional or extensional focal mechanisms have been subdivided into two opposite dipping groups taking into account the average trend of their horizontal p or t axis in the tr diagrams where we plot the slip deviation from the dip slip activation of the nodal plane versus the angle between the dip direction of the nodal plane and the average trend of the p or t axis the comparison of the geometric kinematic dynamic and mechanical compatibility of the two opposite nodal plane groups is possible moreover a quality number trn is devised in order to assess the two opposite facing groups quantitatively five earthquake sequences related with an extensional stress regime and two related with a compressional stress regime are processed in order to demonstrate and validate the potential and efficiency of the method these cases indicate that the tr method can be fairly used as a practical tool to assess which nodal planes are more likely to identify the main seismogenic fault plane the main advantages of the method are a the assessment of the nodal plane groups without the necessity to determine all the parameters of the driving stress tensor i e stress axes and stress ratio b the consideration of the slip tendency

review of the upper cretaceous lower tertiary sequence on seymour island antarctica the thick sequence of fossiliferous marine and non marine sandstones and siltstones on seymour i represents the most complete well exposed section of upper cretaceous to lower tertiary rocks known in the southern hemisphere the succession has been divided into the upper campanian to possibly lowermost tertiary marambio group comprised of the lopez de bertodano and sobral formations and the lower tertiary cross valley and la meseta formations of the seymour island group the lopez de bertodano formation consists of c 1067 m of medium grained to silty concretionary sandstones of middle campanian to possibly maestrichtian age and the sobral formation of c 210 m of medium to coarse grained glauconitic concretionary sandstones the precise age of the sobral formation is uncertain but may be maestrichtian to possibly danian the lower 110 m of the seymour island group consists of non marine gravelly to pebbly sandstones and tuffaceous plant bearing siltstones of the cross valley formation overlying which are 450 m of fine grained marine sandstones and siltstones with interbedded fossiliferous pebbly conglomerates recent studies of the diverse and abundant faunas and floras of the seymour island group have shown that they are older than previously thought the cross valley formation being palaeocene and the la meseta formation late eocene to possibly earliest oligocene

stress and fault parameters affecting fault slip magnitude and activation time during a glacial cycle stress and fault parameters affecting fault slip magnitude and activation time during a glacial cycle

additions to the diversity of elasmosaurid plesiosaurs from the upper cretaceous of antarctica abstract three specimens of elasmosaurid plesiosaurs sauropterygia plesiosauria from upper cretaceous beds of antarctica are described here these include postcranial remains of a single adult individual recovered from late maastrichtian beds of marambio seymour island possessing a distinctive combination of features cervical vertebrae having centra with a triangular outline in transverse section a vertical groove on the rostral and caudal edge of the neural spines and a deep articulation over the neural arch for the following postzygapophysis while the scapula shows an unusually large and anteriorly recurved dorsal process this combination of features is unknown in any adult postcranial elasmosaurid genus recovered to date in the upper cretaceous of the weddellian biogeographic province and could represent a new form additional specimens from james ross island comprise the first record of an aristonectinae plesiosauria elasmosauridae in late campanian beds being the oldest known record of this sub family finally a third specimen from the same age and locality reveals the presence of very long necked elasmosaurids with affinities to typical representatives from the upper cretaceous of the northern hemisphere these findings add to the known diversity of upper cretaceous elasmosaurids in high latitudes of the southern hemisphere

reconstructing the geochemical signature of sudbury breccia ontario canada implications for its formation and trace metal content the sudbury breccia is an impact generated pseudotachylitic breccia formed in the footwall of the 1 85 ga sudbury igneous complex in ontario canada the breccia is commonly developed in areas of contrasting country rock types and it represents a common host to footwall style cu ni platinum group element sulfide mineralization developed in the immediate footwall of large contact type ni cu rich ore deposits at the base of the sudbury igneous complex three models have been proposed for the genesis of the sudbury breccia 1 in situ frictional or shock melting of target rocks 2 cataclasis of the target rocks and or 3 injection of allochthonous impact melt from the sudbury igneous complex into the brecciated crater floor this study reports new mineralogical and geochemical data for samples of sudbury breccia and associated host rocks both proximal and distal to mineralization from six different locations around the sudbury structure a mixing model was used to construct the composition of the sudbury breccia matrix using a combination of country rock and quartz diorite from the offset dikes which are believed to provide an estimate of the composition of the early melt sheet we demonstrate that the breccia matrix can be successfully modeled from footwall lithologies with no requirement for a contribution from the impact melt sheet instead we propose a dynamic parautochthonous in situ melt model where the matrix of the breccia was derived in part by high temperature melting of footwall lithologies these inclusion and crystal laden melts were mixed and transported into tensile fracture zones that developed adjacent to weaknesses in the country rocks principal component analysis of sudbury breccia indicates that the trace metal content within the breccia that developed distal from mineralization is associated with assimilation of mafic units in the footwall in contrast the matrix of sudbury breccia developed closer to mineral zones has a contribution of metal derived from the fractionated sulfide melt and or a contribution of hydrothermally remobilized metal thus by comparing the trace metal content in sudbury breccia with local footwall lithologies baselines can be established that can help to identify anomalous metal contributions that may be derived from the periphery of a footwall mineral system

long lasting transcurrent tectonics in sw alps evidenced by neogene to present day stress fields abstract the sw alps are an active orogen undergoing intra mountainous extension and peripheral compression we discuss the significance of syn orogenic extension based on a comparison of paleo stress derived from fault slip data inversion reflecting the long term

sinistral transpression along the main boundary thrust in amritpur area southeastern kumaun himalaya india abstract outcrop mapping and structural analyses in a 100 m thick fault damage zone elucidate geometry and kinematics of the main boundary thrust in the study area the north dipping fault damage zone is sandwiched between the proterozoic amritpur granite in the hangingwall and the neogene siwalik sediments in the footwall the amritpur granite is overlain by the volcanic sedimentary sequence along a top to the south thrust the footwall sediments are deformed into gentle upright and steeply plunging folds by contrast the hangingwall granite is generally massive the km scale folds in the sub himalayan sediments are geometrically discordant to the folds in the lesser himalayan volcanic sedimentary sequence the damage zone contains both the sub himalayan sediments and the lesser himalayan amphibolite it consists of an imbricate structure tectonic wedges and pressure solution bands the imbricate structure is made up of seven fault bounded lithotectonic domains that record the imprints of coaxial refolding and subsequent modification of the folds into sheath like structures the geometry and kinematics of mesoscopic structures and the results of paleostress analysis reveal a sinistral wrench accompanied n s to nne ssw directed subhorizontal shortening in the damage zone the aforesaid evidences also help distinguish between pure contractional pure wrench contraction dominated and wrench dominated deformation in the different domains and the tectonic wedges the sinistral transpression in the damage zone is ascribed to the occurrence of an oblique lateral ramp along the main boundary thrust in the study area

a simple stress inversion of fault slip data assuming andersonian stress state 1 stress inversion from fault slip data is an important modern technique for structural geologists the parameter or sigma space may be reduced from five to three dimensions if an andersonian stress state having a vertical principal direction is assumed in such a case associated fault slip data can be displayed after some transformation on a stereonet homogeneous fault slip data tend to lie in a great circle while heterogeneous data lie in no less than two great circles visual appreciation thus becomes fairly easy in particular separation of the heterogeneous fault slip data set into many homogeneous subsets the unit vectors normal to the great circles are the solutions giving the controlling reduced stress vectors v permitted solutions to a homogeneous set or subset are v and v the acceptability of each solution depends upon the fit between calculated and measured fault slip senses several examples of applications of this method are used for its validation these examples also illustrate the potential value of the method in making a rough simple and visual appreciation of fault slip data under approximately andersonian stress we believe the method will have a broad applicability as andersonian stress represents the ideal states for the various tectonic regimes

glacial eustasy during the cenozoic sequence stratigraphic implications a newly constructed composite oxygen isotope record is a proxy for eustasy that extends back to the cretaceous tertiary boundary and provides an independent test of sequence stratigraphic based eustatic curves the isotope record shows several eustatic episodes that are consistent with the geological record of ice sheet evolution the first evidence for the existence of an ice sheet in east antarctica occurs near the lower middle eocene boundary base of the lutetian stage there is no evidence for a large ice sheet on antarctica prior to this time however strata of this age are lacking over most of the continent the isotope curve also indicates that the ice sheet experienced phases of growth during the late eocene and middle oligocene followed by a decrease in volume in the early miocene the ross sea stratigraphic record indicates initial evolution of the west antarctica ice sheet during the early miocene by the middle miocene the ice sheet spread across the ross sea weddell sea and antarctic peninsula continental shelves the pliocene pleistocene record of glaciation in antarctica includes numerous glacial erosion surfaces on the continental shelf indicating repeated advance and retreat of both east and west antarctica ice sheets these volume changes in the antarctica ice sheet were in response to the rise and fall of sea level caused by expanding and contracting northern hemisphere ice sheets there is a reasonable correlation between eustatic curves derived from sequence stratigraphic studies and the composite oxygen isotope record since the middle eocene this correlation indicates that glacial eustasy has been the principal factor regulating stratal stacking patterns on a global scale since the middle eocene

a geometric test for possible andersonian stress using striated faults a graphical compilation of the rake guides of fault striations of known sense facilitates a simple test for their compatibility with andersonian stress conditions a compilation of negative double strike angles on tracing paper is superimposed on the rake guide plot if the two register the candidate generating stress is given by the relative position and orientation of the two plots

mebo70 seabed drilling on a polar continental shelf operational report and lessons from drilling in the amundsen sea embayment of west antarctica a multibarrel seabed drill rig was used for the first time to drill unconsolidated sediments and consolidated sedimentary rocks from an antarctic shelf with core recoveries between 7 and 76 we deployed the marum mebo70 drill device at nine drill sites in the amundsen sea embayment three sites were located on the inner shelf of pine island bay from which soft sediments presumably deposited at high sedimentation rates in isolated small basins were recovered from drill depths of up to 36 m below seafloor six sites were located on the middle shelf of the eastern and western embayment drilling at five of these sites recovered consolidated sediments and sedimentary rocks from dipping strata spanning ages from cretaceous to miocene this report describes the initial coring results the challenges posed by drifting icebergs and sea ice and technical issues related to deployment of the mebo70 we also present recommendations for similar future drilling campaigns on polar continental shelves

tectonics of mascon loading resolution of the strike slip faulting paradox subsidence of lunar mascon maria impact basins partly filled with mare basalt and sites of prominent positive gravity anomalies typically led to the formation of concentric graben arcuate rilles around the flanks of the basin while compressive features mare ridges formed in interior regions although previous numerical models of the response of the lunar lithosphere to mascon loading predict that an annulus of strike slip faulting should also have formed around mascon maria no such faults have been observed this strike slip faulting paradox however arises from an oversimplification of the earlier models viscoelastic finite element models of lunar mascon basins that include the effects of lunar curvature heterogeneous crustal strength initial stress conditions and multistage load histories show that the width of a predicted annulus of strike slip faulting may be small the use of anderson s criterion for predicting fault styles may also overpredict the width of strike slip faulting a faulting style criterion that takes into account transitional faulting in which both strike slip and dip slip components are present predicts zones of pure strike slip faulting that are about half of the width predicted by the anderson criterion furthermore strike slip faulting should be observed only in regions in which flexural stresses are sufficient to induce rock failure however since stress patterns consistent with strike slip faulting around mascon loads represent a transition between compressional and extensional provinces differential stresses tend to be low in these regions and for at least part of this region are not sufficient to induce rock failure a mix of concentric and radial thrust faulting is observed in some mascon maria at odds with previous models that predict only radial orientations away from the basin center this apparent discrepancy may be partly explained by the multistage emplacement of mare basalt units a scenario that leads to a stress pattern where concentric and radial orientations of thrust faults are equally preferred detailed models of the serenitatis basin indicate a 25 km thick lunar lithosphere at the time of rille formation and a 75 km thick lithosphere at the time of late stage mare ridge formation the extent of observed mare ridges and the inferred cessation of rille formation around serenitatis prior to the time of emplacement of the youngest mare basalt units is consistent with the superposition of a global horizontal compressive stress field generated by the cooling and contraction of the lunar interior with the local stresses associated with lithospheric loading

depth dependency of stress ratios during the sedimentation of nw gyeongsang basin cretaceous southeast korea estimate of stress parameters and timing of tectonic episodes abstract the natural stress state in the lithosphere consists of the vertical load and poisson ratio and then additional horizontal compression and extension denoted by h and t respectively are assumed to be superimposed upon this gravitational stress field the resulting stress state is composed of the maximum medium and minimum stresses denoted by 1 2 and 3 respectively the stress ratio is given as 2 3 1 3 a linear relation is found between or 1 and the vertical load in wrench faulting and extensional stress regimes respectively the slope and intercept of the linear relation result in the additional horizontal stresses and level of average paleo surface respectively stress ratio is also determinable by the stress tensor inversion of fault slip data the earliest tectonic event t 1 event in the cretaceous gyeongsang basin consists of coexisting e w compression and n s extensional faulting episodes plots of or 1 against the burial depth or vertical load display several linear trends two clusters in extensional episodes and two or three clusters in wrench faulting episodes because h is assumed to be null or negligible in the extensional regime t is determinable from the slopes of two linear clusters as being 2 5 to 4 0 mpa in wrench faulting episodes the values of h are given to be 61 6 101 4 mpa by applying determined additional horizontal extensions determined levels of average paleo surfaces and those of syndepostional structures illustrate that more than five wrench faulting or extensional episodes have occurred during the t 1 event whose active age consequently ranges from the barremian to the coniacian this supports that the coexisting coaxial faulting episodes with the same extension may correspond to the alternation of wrench faulting and extensional episodes

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

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

end cretaceous mass extinction event argument for terrestrial causation the end cretaceous mass extinctions were not a geologically instantaneous event and were selective in character these features are incompatible with the original alvarez hypothesis of their being caused by a single asteroid impact that produced a world embracing dust cloud with devastating environmental consequences by analysis of physical and chemical evidence from the stratigraphic record it is shown that a modified extraterrestrial model in which stepwise extinctions resulted from encounter with a comet shower is less plausible than one intrinsic to the earth involving significant disturbance in the mantle

bit generated rock textures and their effect on evaluation of lithology porosity and shows in drill cutting samples during the drilling phase drill cuttings provide critical data on which costly operational decisions are made the success or failure of a well may depend on the accuracy of the interpretation of drill cutting samples comprised of rock fragments 2 mm or less in diameter these fragments commonly have bit generated textures that differ substantially from those of the in situ rocks under certain conditions the bit may pulverize all or part of the rock fabric to produce bit flour clay or sand the processes by which these and other less common bit generated textures are formed and reach the drill cutting samples are described the generation of bit textures affects the quantitative and qualitative evaluation of the samples these textures must be recognized to interpret samples correctly for lithology porosity and hydrocarbon shows

tectonic regime and slip orientation of reactivated faults the slip orientation of reactivated faults is predicted by assuming that one principal stress direction is vertical that faulting occurs on pre existing planes of weakness with a slip direction along the applied shear stress and by extending the original concept of tectonic regime so as to include the stress tensor aspect ratio the predicted rake of slip is then analysed so as to reveal the respective influence of the fault plane orientation strike and dip and of the tectonic regime the analysis of this direct problem allows one to describe the geometry of the slip directions within any given tectonic regime its evolution as the tectonic regime varies and the constraints provided by slip direction data on the tectonic regime however the question of what fault orientations would satisfy a failure criterion and thus be preferentially reactivated is not addressed in any tectonic regime pure strike slip occurs on vertical planes and only on them except in wrench regimes where it also occurs on all fault planes along four strikes that are determined by the tectonic regime pure dip slip occurs on planes striking along one of the horizontal principal stress directions and only on them except in radial compression and radial extension regimes where it occurs on all planes except vertical ones at fixed strike but varying dip the slip direction is closest to dip slip for zero dip and pure strike slip for vertical dip at fixed dip and varying strike the slip direction is pure dip slip for strikes along one of the horizontal principal stress directions and closest to strike slip for four strikes that are determined by the tectonic regime the horizontal principal stress directions separate four quadrants two where the slip direction is dextral and two where it is sinistral the slip directions of all fault planes of the same dip can be easily deduced from those of subhorizontal planes and can be constructed geometrically as the tectonic regime varies continuously from radial compression to radial extension the domain of fault plane orientations where steep reverse slip directions are possible shrinks and disappears when the extensional regime is entered conversely the domain where steep normal slip directions are possible appears when the wrench regime is entered and grows thereafter the strike slip domain first grows towards shallow dip until the wrench regime is entered and then shrinks after the extensional regime is entered whereas in the model of failure in isotropic rocks dip slip or strike slip data fully determine the original tectonic regime in the model of failure on pre existing planes of weakness constraints on the extended tectonic regime require additional information the sense of shallow slip direction data which are to be found on steeply dipping planes constrains the horizontal principal stress directions and the steepness of slip direction data on shallow dipping planes striking away from the principal stress directions constraints the extended tectonic regime in the case of wrench regimes an extra constraint arises from the fact that the extended tectonic regime also controls the strike at which the dip component of slip changes from normal to reverse these constraints can be quantified by superposing a simple plot of the data rake versus strike with an abacus that is called breddin s graph for tectonic regimes while this graph does not replace inverse techniques it may help in detecting tectonic phases in complex data sets without using this graph or resorting to inverse techniques the transition from wrench to either compressional or extensional regime is difficult to infer from data that display a limited range of fault plane strikes and the same sense of dip component of the slip direction

how much does slip on a reactivated fault plane constrain the stress tensor given a fault plane and its slip vector the stress tensor which caused the displacement is sought two constraints are considered first a geometrical constraint that the shear stress applied to the fault plane is parallel to the slip wallace 1951 bott 1959 second a frictional constraint that the shear to normal stress ratio equals tan 0 coulomb 1776 in a first step the stress tensors that satisfy the geometrical constraint are sought for tensors belonging to the vectorial space of solutions shear and normal stress magnitudes become a function of the orientation of the principal stresses and are mapped extending a study by mckenzie 1969 in a second step it is investigated which of these tensors also satisfy the frictional constraint within this more restricted vectorial space there is a relationship between the magnitudes 1 2 1 3 and s 1 3 1 and the orientations of the principal stresses both the range of s and the spatial distribution of are more restricted than when the geometrical constraint alone is considered as when the geometrical constraint is solely considered mckenzie 1969 the orientations of the principal stresses may lie significantly away from and up to right angle to the p b t axes however this can happen only in two cases 1 either the effective stress difference s has reached a high value which is unlikely to happen if enough preexisting fractures are available to release the stress or 2 2 becomes close to either 1 or 3 and therefore barely distinguishable from it in that case the delocalization of the orientations of the principal stresses is best described by a tendency for to exchange role with either or when the stress difference remains small and 2 reasonably away from 1 and 3 approach positions that we define as the pf b tf axes and that are obtained from the p b t axes by a rotation of angle 0 2 around b and toward the slip vector this explains why the p b t axes gives reasonable estimates of the orientations of the principal stresses scheidegger 1964 despite objections mckenzie 1969 however whenever the fault plane can be distinguished from the auxiliary plane pf b tf should give a better estimate raleigh et al 1972 in an area where many fault planes are available and a uniform tensor is assumed the scatter in the plane orientations contains information about both the relative position of 2 represented by and the relative stress difference s the higher s or the closer to either 0 or 1 the more scatter this information could then be extracted by inverse methods because a friction law would constrain these inverse method more tightly it may show the necessity of nonuniform tensor to explain scattered fault plane

deep biogenic methane and drilling associated gas artifacts influence on gas based characterization of petroleum fluids classical interpretation of drilling mud gas molecular and isotopic data in petroleum systems can be impacted by both natural and engineering processes which can introduce allochthonous and or isotopically unrepresentative gas species this study investigates 1 widespread primary biogenic methane c1 and its impact on mud gas based petroleum system interpretation and on the properties of the petroleum fluids in the subsurface 2 differentiation of migration mixing versus diffusion leakage in petroleum systems and 3 bias introduced by gases generated at the drill bit including alkenes and isotopically changed gaseous alkanes our goal was to provide solutions to flag impacted intervals by the above processes minimize resulting interpretative bias and extract additional information about the fluid using advanced mud gas logging amgl tools and workflows an amgl interpretative methodology was developed using a combination of logs of c1 to pentane c5 concentrations and 13c c1 this approach allows identification of subsurface intervals containing nearly pure background primary biogenic c1 and can quantify its concentration per rock volume consequently thermogenic end member fluid types can be differentiated from mixtures with the biogenic c1 and assess its impact on the gas oil ratio of the mixture additionally two different processes can be responsible for mixing trends apparent on classical interpretation charts e g modified schoell diagram the presented analysis of amgl allows the deciphering of migration mixing versus diffusion leakage mixing trends using studied wells as examples another bias of mud gas based interpretation originates from artificial gases generated by drill bit metamorphism dbm evidence that dbm produced artificial alkanes in addition to alkenes via cracking of oil based drilling mud included strong correlation of concentrations among alkenes furthermore the concentration of alkenes strongly correlated with the magnitude of shift in 13c of c1 and ethane c2 between mud gas and solution gas from bottomhole fluids sampled at equivalent depths the artificial alkanes contributed by the drilling process can strongly bias and interfere with petroleum systems early interpretation based on mud gas molecular and isotopic ratios the bias depends on relative contributions of petroleum reservoir liberated mud gases and dbm gases which in this study reached half of the total c1 and c2 in the analyzed mud gas conversely alkene concentrations can be used as mud gas quality check parameters and early indicators of excess heat generated at the drill bit

campanian maastrichtian cretaceous stratigraphy of the james ross island area antarctica one of the most important outcrops of uppermost cretaceous campanian maastrichtian sedimentary rocks in the southern high latitudes occurs within the james ross island group northeastern antarctic peninsula these rocks comprise a 1500 2000 m thick sequence of predominantly shallow marine clastic sediments that were deposited within a retro arc basin they are virtually undeformed and have yielded prolific invertebrate and vertebrate faunas and a wide range of plant taxa campanian maastrichtian strata are contained within two component formations of the upper cretaceous lower tertiary marambio group the lower santa marta formation is approximately 1100m thick and has three constituent members ammonites within the santa marta formation indicate an early to late campanian age assignment dinoflagellates suggest that the lower levels of the formation may range into the santonian stage in the northern james ross island to vega island region there is a conformable transition into the overlying lopez de bertodano formation here the basal cape lamb member is unconformably overlain by the sandwich bluff member although there are some lithological and fauna1 discrepancies which are attributed to marked lateral facies changes across the basin it is believed that the cape lamb member can be correlated with the lower to middle regions of the 1200 m thick sequence of undifferentiated lopez de bertodano formation lithologies exposed on seymour island molluscan data indicate a late campanian palaeocene age range for this upper formation dinoflagellates again suggest that the lowest beds may be slightly older the correlation presented provides the basis for a formal subdivision of the campanian and maastrichtian stages in the southern high latitudes it has also revealed two major basin shallowing events in the late campanian early maastrichtian and latest maastrichtian respectively and the existence of a major fault fault zone across southeastern james ross island the improved temporal framework will aid late cretaceous palaeoclimatic and palaeobiological studies in antarctica

fault analysis and paleostress evolution in large strain regions methodological and geological discussion of the southeastern himalayan fold and thrust belt in pakistan abstract we document the structure and kinematics of the southeastern part of the fold and thrust belt of the pakistani himalaya field analysis documents the importance of strike slip faulting associated with folding accordingly a transpression regime is inferred to be responsible for variable amounts of shortening from fault block to fault block the analysis of fault populations that affect the mesozoic to early miocene sediments allows distinguishing two paleostress tensor directions a dominant nw se compression and a minor e w compression are compatible with buckling around the n s axis of the near by hazara kashmir syntaxis from the lack of both systematic overprinting relationships and spatial trend the two tensors were obtained at different locations we conclude that in each location any of these two shortening directions can dominate the distribution of the paleostress tensors substantiates a transpressional regime due to far field himalayan compression and a lateral escape component of the allochthonous fold and thrust belt away from the growing hazara kashmir anticline

tectonic analysis and paleo stress determination of the upper lava section at odp iodp site 1256 east pacific ocean abstract research on the deep sea is of great importance for a better understanding of the mechanism of magma emplacement and the tectonic evolution of oceanic crust however details of the internal structure in the upper levels of the oceanic crust are much less complete than that of the more fully studied sub aerial areas for the first time this study proposes a dynamic analysis using the inversion method on core data derived from the drilled basement of the present day intact oceanic crust at odp iodp site 1256 in the cocos plate the research is based on an innovative core reorientation process and combines different stress hypothesis approaches for the analysis of heterogeneous failure slip data via exploitation of two distinct techniques from the analysis of the failure slip data both techniques produce 5 distinct subsystem datasets all calculated subsystems are mechanically and geometrically admissible interpretation of the results allows the researchers to note a complex local and regional tectonic evolution deriving from the interplay of 1 the ridge push and rotation of both the east pacific rise and the cocos nazca spreading center 2 the effect of the slab pull of the middle america trench 3 the influence of lava emplacement mechanisms and 4 intra plate deformation

ten year recurrence time between two major earthquakes affecting the same fault segment earthquake ruptures stop when they encounter barriers impeding further propagation these barriers can theoretically originate from changes of geometry or nature of the seismic faults or from a strong lowering of the tectonic stresses typically due to the occurrence of a recent major earthquake we show here that this latter mechanism can be ineffective at stopping rupture expansion the 17 november 2013 magnitude 7 8 scotia sea earthquake has propagated into a 100 km long zone already ruptured 10 years ago by a magnitude 7 6 earthquake given the plate velocities between scotia and antarctic plates 8 9 mm yr simple recurrence models would have predicted that the segment affected by the 2003 earthquake could not be reruptured by a major earthquake during several hundreds of years this earthquake pair indicates that the variations of the tectonic stress during the seismic history of the fault are small compared to the stresses dynamically generated by a large earthquake

les pseudotachylites en conditions granulitiques de la zone de cisaillement paleoproterozoique de tikachitine terrane d in ouzzal bouclier touareg algerie le terrane paleoproterozoique d in ouzzal appartenant au hoggar occidental affleure au sein de la chaine panafricaine trans saharienne du nw de l afrique il montre les parties les plus profondes d une croute continentale formee durant l archeen et recyclee a l eburneen sous les conditions de facies granulite de tres haute temperature les orthogneiss charnockitiques archeens impliques dans la zone de cisaillement eburneenne de tikachitine montrent des veines d injection de pseudotachylites fentes de tension et echelon de structures en pull apart ces pseudotachylites presentent des contacts francs avec l encaissant charnockitique et des matrices sombres parfois litees incluant de nombreux clastes de pyroxene feldspath quartz et rarement de biotite les associations minerales presentes dans les matrices et en aureoles autour des clastes sont de type facies granulite et similaires a celles des orthogneiss charnockitiques excepte l absence de mesoperthite elles sont composees de tres fins crist

drilling conditions making wells unsuitable for fluid inclusion studies on drill cuttings a fluid inclusion study conducted on a well in the northern north sea showed a remarkable correlation between fluid inclusion stratigraphy responses and depths of drilling bit changes further investigation of the well data suggested that extreme temperatures occasionally had been generated at the bit sediment interface during drilling cracking of larger organic molecules to an abundance of smaller ones and trapping of these in inclusions formed by supercooling of partly melted sediment explain the correlation not all wells are consequently suitable for fluid inclusion screening analyses thus before initiating fluid inclusion studies wells that have experienced intense heat during drilling should be identified and avoided

fault systems and paleo stress tensors in the indus suture zone nw pakistan abstract analysis of fault striations measured in the kohistan part of the indus suture zone nw himalaya pakistan has been carried out to document dynamic evolution during the brittle stage of the collision of india and asia processing of the data with a direct inversion method identified four stress fields which were chronologically ordered from field evidence as sse nnw compression e w compression radial extension and ssw nne compression the last corresponds to the present day stress field defined from seismic activity the earlier stress fields are related to times during the miocene when convergence related stresses were disturbed by the formation of the nearby nanga parbat and indus syntaxes

orientation of the stress field surrounding the creeping section of the san andreas fault evidence for a narrow mechanically weak fault zone we determine how the orientations of the principal stresses change with distance from the creeping section of the san andreas fault saf our data are 2392 earthquake focal mechanisms which are grouped according to distance from the saf into 33 bins parallel to fault strike the width of the bins are dictated by the spatial organization and density of the seismicity only events with m 1 5 depth 2 km and well constrained focal mechanisms are used the focal mechanisms are inverted simultaneously for the orientations and relative amplitudes of the principal stresses using two different inversion programs a bootstrap resampling method provides confidence limits on the stress orientations our general result is that the maximum horizontal compression lies mostly at high angles to the saf except in a narrow zone on the fault no wider than 1 3 km in which it appears to lie at a smaller angle 45 from the fault strike in particular the maximum horizontal compression lies at a high angle to the saf trend immediately adjacent to the fault this stress state is most readily interpreted as due to a narrow mechanically weak saf in this region the narrowness of this zone contrasts with the region wider than 20 30 km of rotated stresses found surrounding the saf in southern california hardebeck and hauksson 1999 suggestive of different mechanical behaviors of the saf in these two regions this approach may provide a way to define the width of the mechanically weak part of faults

modelling of structural complexity in sedimentary basins the role of pre existing faults in thrust tectonics abstract analogue and numerical models have been used to study the role of pre existing faults in compressive regimes from a theoretical point of view reactivation is mainly controlled by fault attitude stress regime and frictional properties of fault planes in scaled down sandbox experiments precut faults are introduced in the homogeneous granular media with a nylon wire which is forced through the sand cake producing a thin planar disturbed zone systematic experiments of thrust inversion with various dips and strikes of such planar discontinuities have been modelled comparison of experimental results with theoretical diagrams indicate that disturbed zones have a friction angle which is 10 20 lower than the homogeneous sand and that the compressive regime in the sandbox has a shape factor close to 0 4 the static analysis of fault reactivation is in accordance with the experimental observations except for pre existing faults dipping at very low angle however numerical modelling using the udec code shows that low angle faults can be reactivated as a result of stress concentration in the lower part of the fault in addition sandbox experiments indicate that in thrust systems reactivation of pre existing faults is not only dependent on their attitude but also on their spacing and location relative to the thrust system

the influence of inherited continental margin structures on the stress and strain fields of the south central taiwan fold and thrust belt in this paper we test whether or not structural and morphological features inherited from the eurasian continental margin are affecting the contemporary stress and strain fields in south central ta

the biotic record of events in the marine realm at the end of the cretaceous calcareous siliceous and organic walled microfossils and macroinvertebrates abstract the calcareous micro and nannoplankton were severely affected at the end of the cretaceous as known from numerous sections but the change was not quite as sudden or drastic as sometimes claimed the organic walled phytoplankton seem to have survived the k t boundary event s better than other plankton little is known about the fate of siliceous plankton from the relatively few more or less complete sections across the k t boundary that are rich in benthic macroinvertebrates it is clear that there was a striking change at species level in some groups which is apparently directly attributable to the disaster that overtook the plankton and hence requires no additional explanation other groups however were already in decline if not completely extinct before the end cretaceous catastrophe took place

paleostress regimes from brittle structures of the karakoram kohistan suture zone and surrounding areas of nw pakistan paleostress orientations were calculated from fault populations at 24 sites along the sw ne segment and five sites along the e w yasin segment of the karakoram kohistan suture zone in nw pakistan they demonstrate the importance of combined thrusting and strike slip faulting however several paleostress tensor directions are distinguished a dominant nw se compression and a minor e w compression are compatible with the recent evolution of this part of the hindu kush from the lack of both systematic overprinting relationships and spatial trend the two tensors were obtained at different locations we conclude that in each location any of these two shortening directions can dominate heterogeneously distributed extension is found in some places and is likely due to local conditions these paleostress tensors substantiate a transpressional regime due to far field himalayan compression and document the long term background of the seismogenic deformation in this region

stress ratio determinations from striated faults a spherical plot for cases of near vertical principal stress for stress regimes with one principal axis z vertical the stress ratio is best represented by an angular function f arctan 3 z x1 x2 z 3 x1 x2 or if the larger of the horizontal principal stresses x1 and x2 is designated y by f arctan 3 z x y z 3 y x traditional palaeostress regimes normal wrench reverse represent equal angular sectors of f or f and may be subdivided on a spherical projection of f against 2y where y is the bearing of maximum horizontal stress the locus of all combinations of stress orientation and stress ratio capable of generating one datum known slip direction on a known fault plane is a great circle since tanf cos 2y 2s b 3 cosb where tanb tan cosd and s d and are the fault strike dip and striation pitch respectively stereographic construction is simple using pencil and paper and gives a visual appreciation of the definition of palaeostress states which could have generated the fault motions it facilitates better than previous methods 1 the identification of radially symmetrical stress states 2 recognition of suspect or incompatible data and 3 delimiting the palaeostress state according to sense of shear where this is known great circle and pole representations are suited to different purposes and data types for which examples are given

pseudotachylyte petrogenesis constraints from the sudbury impact structure pseudotachylytes and their host rocks from the north range of the 1 85 ga sudbury impact structure have been investigated using analytical scanning electron microscopy electron microprobe analysis and xrf spectrometry the results show that the pseudotachylytes were produced in high speed slip zones by the frictional comminution and selective melting of wall rock lithologies the preferential assimilation of hydrous ferromagnesian phases during frictional melting produced relatively basic melts leaving the more mechanically resistant quartz and to a lesser extent plagioclase as included mineral clasts three distinct assemblages are identified within the pseudotachylytes a pre impact 1 85 ga rock and mineral clasts derived from host lithologies b a syn to immediately post impact 1 85 ga rapidly cooled quartz sanidine labradorite phlogopitic biotite matrix assemblage formed due to crystallization from a melt at 800 900 c and c a post impact 1 85 ga retrograde assemblage which overprints both clasts and matrices field evidence indicates that most pseudotachylyte formed in large displacement fault systems during gravitational collapse of the impact generated transient cavity the sudbury pseudotachylytes like endogenic pseudotachylytes were generated by frictional melting on fault surfaces the difference is primarily one of scale large km displacements occurring on impact induced ring faults can generate immense volumes of friction melt resulting in spectacular pseudotachylyte bodies up to 0 5 km thick and more than 10 km long

geomechanical model of the marmara sea region ii 3 d contemporary background stress field summary we present the contemporary 3 d background stress field of the marmara sea region derived from a geomechanical model the background stress field i e the component of the absolute stress state that is time independent over the seismic cycle primarily depends on the distribution of density and elastic parameters on the acting far field stresses from plate boundary forces and on fault geometries we take these into account to predict the 3 d background stress field including its spatial variations technically our model concept involves the definition of an appropriate initial stress state accounting for the gravitational reference stress state of the crust which is then changed by plate tectonics until the 3 d background stress field has evolved the modelled stress field agrees well with observations from earthquake focal mechanism solutions and their formal stress inversion with orientation of maximum horizontal stress and with the distribution of seismicity in the marmara sea in particular in the vicinity of fault bends the stress field deviates considerably from the regional nw se oriented maximum horizontal stress and exhibits variability of the stress regime our model results are consistent not only with dynamic observations but also with kinematic ones various kinematic observations are understandable from the stress field we show that a stress regime that indicates normal faulting in the basins is nonetheless reconcilable with almost pure strike slip motion on the main marmara fault the distribution of seismicity in the marmara sea can be explained in first order by the distribution of critical differential stress which is closely related to local fault geometries we refer the wide absence of seismicity between the bend of the main marmara fault near istanbul and the central basin to the relatively plane fault geometry of that segment normal stress on the main marmara fault is highly variable along strike which makes segment wise rupture more likely than a rupture of the seismic gap at once comparably low normal stress on the prince s islands segment indicates a shorter interevent time for this fault segment than for the central segment of the main marmara fault