fractal geometry based quantification of shock induced rock fragmentation in and around an impact crater shock induced fragmentation structures of basement rocks and their limestone cover in and around the ries impact crater germany were recorded on outcrop hand sample and thin section scale and quantified mainly by fractal geometry methods quantification was performed by automated procedures and in areas of square centimetres to square decametres with a maximum resolution of micrometre scale in 2d and on all scales the fragmentation structures form complex statistically self similar patterns fractals with specific characteristics i the pattern fractality is scale dependent ii three different power law relationships exist which reflect the effect of three fragmentation processes iii the fracture patterns are anisotropic and inhomogeneous over larger areas iv complexity and anisotropy of the fracture patterns vary systematically such systematic variation appears typical for impact related fragmentation

displacement and dynamic weakening processes in smectite rich gouge from the central deforming zone of the san andreas fault the strength of clay rich gouge from the central deforming zone cdz of the san andreas fault saf was measured using a high speed rotary shear apparatus to evaluate the potential for unstable slip along the creeping segment of the saf wet and dry gouge was sheared at 0 1 1 3 m s 0 5 1 5 mpa normal stress and 1 20 m displacement cdz gouge is weaker wet than dry and exhibits displacement strengthening to peak friction followed by weakening to steady state strength that decreases with increasing velocity a clay foliation unit 2 develops from the initial microstructure unit 1 during the first 1 5 m of slip coincident with increasing strength subsequent weakening occurs during shear within unit 2 and subsequently with development of a localized foliated slip zone unit 4 and fluidized material unit 3 displacement and dynamic weakening result from slip along clay foliation assisted by shear heating pressurization of pore fluid in wet gouge and additional grain size reduction and possible clay dehydration in dry gouge peak strength is proportional to normal stress but steady state strength is insensitive to normal stress probably because pore pressure approaches the normal stress as such cdz gouge is weak at coseismic rates relative to interseismic creep strength the potential for sustaining rupture propagation into the cdz from an adjacent seismic segment is sensitive to the relationship used to extrapolate the critical weakening displacement from experimental to in situ conditions rupture propagation from a microseismic patch within the cdz is unlikely but sustained propagation from a large earthquake e g parkfield event may be possible

an offshore onland transect across the north eastern black sea basin crimean margin evidence of paleocene to pliocene two stage compression abstract the tectonic evolution of the black sea bs is a subject of debate there are several unsolved questions 1 the timing and the spatial progression of the bs basin opening and 2 the timing of cenozoic shortening along the northern margin of the eastern bs basin the timing of the main compressional deformations related to the inversion of the greater caucasus gc basin is assumed to be oligo miocene however late cretaceous early paleocene shortening linked to the final closure of the northern branch of the neotethys is also suggested the crimean mountains cm to the north of the eastern bs is one of the key areas to investigate in order to fix the tectonic evolution of the bs to precise the timing of the cenozoic shortening of the eastern bs we focus on an integrated onshore offshore transect from the eastern cm to the sorokin trough north of eastern bs we use newly collected stratigraphic and structural data from the eastern cm and a new interpretation of multichannel seismic lines we define 1 the offshore seismic stratigraphy and constrain the relative chronology of deformations 2 the age of seismic units by correlation of the seismic data with the subbotina 403 well log and 3 we construct an on to off shore transect of eastern cm northern eastern bs region our results evidence a polyphased cenozoic compression in the northern part of the eastern bs 1 paleocene earliest eocene and 2 oligocene miocene maikopian normal faults appear to be related to a formation of the foreland basin instead of evidencing the eastern bs cretaceous rifting finally this study allows precising the shortening phases within eastern cm and eastern bs since the early paleocene linking them to the neotethys closure and the gc tectonic evolution

rethinking conditions necessary for pseudotachylyte formation observations from the otago schists south island new zealand abstract pseudotachylytes and two distinct types of cataclasite in the otago schist at tucker hill south island new zealand provide evidence for both seismic slip and aseismic creep on a normal fault zone during regional crustal extension in late cretaceous time regional geologic evidence suggests that the fault had its present low angle dip ca 10 at the time it was active type a cataclasites presumably aseismic can be recognized by bi fractal grain size distributions monomict composition angular clasts of uniform textural maturity and a crude fabric defined by oriented grains and transgranular fractures type b cataclasites possibly cosesimic have characteristics consistent with fluidized grain flow including heterogeneous clast shapes and types a bimodal grain size distribution intrusive relationships with other rocks and the absence of any fabric or transecting fractures pseudotachylyte which occurs as fault veins injection veins and more complex types of intrusive structures consistently cuts across and invades type a cataclasites but is both intrusive into and included as clasts in type b cataclasites these relationships are consistent with a fault evolution model in which the development of a damage zone through aseismic cataclasis type a facilitates the formation of pseudotachylyte in a subsequent seismic event by providing a permeable matrix through which fluids can drain in the early stages of slip thereby maintaining frictional contact between rock surfaces the formation of pseudotachylyte in turn may seal the fault zone and lead to thermal pressurization in a later seismic cycle forming fluidized type b cataclasites seismic slip on the low angle normal fault zone at tucker hill may have occurred by two distinct modes of dynamic weakening melt lubrication and thermal pressurization in successive seismic events although there is a perception among geologists that pseudotachylyte is most likely to form in intact crystalline rocks geophysical models of fault zones clearly demonstrate that pseudotachylyte formation is actually suppressed in low permeability rock because any fluids present would be unable to escape the fault zone and thermal pressurization would rapidly reduce frictional resistance the paradigmatic occurrences of pseudotachylyte in otherwise pristine crystalline rocks probably represent somewhat exceptional circumstances single rupture events at very high effective stress in dry rock coseismic frictional melts may actually be more common in hydrated rocks like the schist at tucker hill but harder to recognize and also vulnerable to overprinting as a fault zone matures in such rocks pseudotachylyte may represent an intermediate stage in the evolution of a fault zone the period between the formation of a high permeability damage zone and the development of a low permeability fault core

high velocity frictional properties of alpine fault rocks mechanical data microstructural analysis and implications for rupture propagation abstract the alpine fault in new zealand is a major plate bounding structure that typically slips in m8 earthquakes every c 330 years to investigate the near surface high velocity frictional behavior of surface and borehole derived alpine fault gouges and cataclasites twenty one rotary shear experiments were conducted at 1 mpa normal stress and 1 m s equivalent slip velocity under both room dry and water saturated wet conditions in the room dry experiments the peak friction coefficient p p n of alpine fault cataclasites and fault gouges was consistently high mean p 0 67 0 07 in the wet experiments the fault gouge peak friction coefficients were lower mean p 0 20 0 12 than the cataclasite peak friction coefficients mean p 0 64 0 04 all fault rocks exhibited very low steady state friction coefficients ss room dry experiments mean ss 0 16 0 05 wet experiments mean ss 0 09 0 04 of all the experiments performed six experiments conducted on wet smectite bearing principal slip zone psz fault gouges yielded the lowest peak friction coefficients p 0 10 0 20 the lowest steady state friction coefficients ss 0 03 0 09 and commonly the lowest specific fracture energy values e g 0 01 0 69 mj m 2 microstructures produced during room dry and wet experiments on a smectite bearing psz fault gouge were compared with microstructures in the same material recovered from the deep fault drilling project dfdp 1 drill cores the near absence of localized shear bands with a strong crystallographic preferred orientation in the natural samples most resembles microstructures formed during wet experiments mechanical data and microstructural observations suggest that alpine fault ruptures propagate preferentially through water saturated smectite bearing fault gouges that exhibit low peak and steady state friction coefficients

geological record of thermal pressurization and earthquake instability of subduction thrusts abstract during an earthquake fault strength decreases with slip over the slip weakening distance dc to a residual strength the estimation of dc is crucial for the evaluation of fault instability during earthquakes however it has been difficult to determine dc from natural faults we found geological evidence of thermal pressurization from the on land analog of a subduction thrust exhumed from seismogenic depths thermal pressurization was indicated by the fluidization of comminuted material and increase in the volume of fluid inclusions by frictional heating numerical analysis of thermal pressurization with the constraints on the thickness of the seismic slip zone the temperature range of frictional heating and ambient conditions of subduction thrusts indicates that the dc of subduction thrusts ranges from 0 03 to 0 22 m which is independent of initial pore fluid pressure on subduction thrusts the short dc associated with the effect of thermal pressurization on subduction thrusts indicates the occurrence of rapid stress relief and high radiated energy during subduction earthquakes

experimental evidence of contact loss during stick slip possible implications for seismic behaviour abstract we present results of an experimental study on the stick slip phenomenon focused on detailed measurements of the relative normal displacement this was done mainly to determine whether or not the sliding surfaces become separated during the slip phase as suggested in previous works experiments were performed on pmma as it has mechanical properties comparable to those of brittle rocks and has proved to be a good analogue for rocks in rupture mechanics experiments results show clearly that normal displacement occurs during and after the slip phase the characterisation of the sliding surface enables us to compare the maximum relative normal displacement during the slip phase with asperity height in most cases the maximum relative normal displacement was found to be higher than the average value of the peak to trough relief of the surface showing that sliding surfaces were at least partially separated the phenomenon generally consists of a monotonous slip opening phase followed by a monotonous slip closure phase in some cases the slip closure phase shows oscillations which have been interpreted as elastic bounces this last phenomenon was observed irrespective of the experimental conditions with a probability ranging from 0 1 to 0 3 but no clear variations of this probability have been found as a function of normal stress and roughness these observations may give insights for the explanations of earthquake related problems such as the heat flow paradox anomalous p wave radiation or the inferred low average friction coefficients in subduction zones

the black sea basins structure and history new model based on new deep penetration regional seismic data part 2 tectonic history and paleogeography abstract a new lithostratigraphy scheme has been compiled for the western black sea basin and a new geological history scheme from middle jurassic till neogene is suggested for the entire black sea region continental rifting manifested itself from the late barremian to the albian while the time of opening of the basins with oceanic crust was from cenomanian till mid santonian origination of the western and eastern black sea basins took place almost simultaneously during cenozoic time numerous compressional and transpressional structures were formed in different part of the black sea basins it is shown that in pleistocene quaternary time turbidities mass transport deposits and leveed channels were being formed in the distal part of the danube delta

cenozoic evolution of the eastern black sea a test of depth dependent stretching models abstract subsidence analysis of the eastern black sea basin suggests that the stratigraphy of this deep extensional basin can be explained by a predominantly pure shear stretching history a strain rate inversion method that assumes pure shear extension obtains good fits between observed and predicted stratigraphy a relatively pure shear strain distribution is also obtained when a strain rate inversion algorithm is applied that allows extension to vary with depth without assuming its existence or form the timing of opening of the eastern black sea which occupied a back arc position during the closure of the tethys ocean has also been a subject of intense debate competing theories called for basin opening during the jurassic cretaceous or paleocene eocene our work suggests that extension likely continued into the early cenozoic in agreement with stratigraphic relationships onshore and with estimates for the timing of arc magmatism further basin deepening also appears to have occurred in the last 20 myr this anomalous subsidence event is focused in the northern part of the basin and reaches its peak at 15 10 ma we suggest that this comparatively localized shortening is associated with the northward movement of the arabian plate we also explore the effects of paleowater depth and elastic thickness on the results these parameters are controversial particularly for deep water basins and margins but their estimation is a necessary step in any analysis of the tectonic subsidence record stored in stratigraphy

sliding behavior and deformation textures of heated illite gouge abstract the run products of a series of triaxial friction experiments on an illite rich gouge have been examined petrographically to study the relationship between textural development and sliding mode the samples show a complete range of textures from ones in which the entire gouge layer is deformed to ones in which the deformation is concentrated along narrow subsidiary shears and the rest of the gouge layer is massive the samples with a pervasively developed deformation fabric slide stably whereas the samples containing shear bands show stick slip motion if the intersection angles between boundary parallel and cross cutting riedel shears are also relatively high these textural differences suggest that localization of shear combined with higher angle riedel shears are somehow involved in stick slip motion the orientation of riedel type shears in natural fault zones may also have potential as a paleoseismological tool

smoothing and re roughening processes the geometric evolution of a single fault zone abstract the geometry of a fault zone exerts a major control on earthquake rupture processes and source parameters observations previously compiled from multiple faults suggest that fault surface shape evolves with displacement but the specific processes driving the evolution of fault geometry within a single fault zone are not well understood here we characterize the deformation history and geometry of an extraordinarily well exposed fault using maps of cross sectional exposures constructed with the structure from motion photogrammetric method the la quinta fault located in southern california experienced at least three phases of deformation multiple layers of ultracataclasite formed during the most recent phase crosscutting relations between the layers define the evolution of the structures and demonstrate that new layers formed successively during the deformation history wear processes such as grain plucking from one layer into a younger layer and truncation of asperities at layer edges indicate that the layers were slip zones and the contacts between them slip surfaces slip surfaces that were not reactivated or modified after they were abandoned exhibit self affine geometry preserving the fault roughness from different stages of faulting roughness varies little between surfaces except the last slip zone to form in the fault which is the smoothest this layer contains a distinct mineral assemblage indicating that the composition of the fault rock exerts a control on roughness in contrast the similar roughness of the older slip zones which have comparable mineralogy but clearly crosscut one another suggests that as the fault matured the roughness of the active slip surface stayed approximately constant wear processes affected these layers so for roughness to stay constant the roughening and smoothing effects of fault slip must have been approximately balanced these observations suggest fault surface evolution occurs by nucleation of new surfaces and wear by competing smoothing and re roughening processes

signature of coseismic decarbonation in dolomitic fault rocks of the naukluft thrust namibia unequivocal geological signatures of seismic slip are rare exceptionally so in carbonate hosted faults where carbonate minerals dissociate at temperatures lower than those required for producing a friction melt this thermal dissociation leads to significant fault weakening by increased fluid pressure and or nanoparticle lubrication preventing further heating of the fault surface pseudotachylyte is therefore unlikely to form in carbonate hosted faults and other evidence for seismic slip must be identified we studied the lower cambrian naukluft thrust which crops out in central namibia it contains a cataclastic dolomite fault rock referred to as gritty dolomite which we interpret as a signature of coseismic carbonate dissociation and subsequent fluid rock interactions the fault was active at ambient temperatures below 2001c gritty dolomite contains rounded low aspect ratio dolomite clasts with a uniform fe rich dolomite coating euhedral to subhedral magnetite quartz and k feldspar in a fine grained massive to laminated carbonate matrix of particulate dolomite and crystalline calcite cement the fault rock texture combined with evidence of injectites of gritty dolomite into the wallrock indicates the cataclasite deformed as a fluidized granular flow at seismic slip velocities frictional heating caused dissociation of dolomite to co 2 and ca fe and mg oxides this release of co2 decreased the ph of the pore fluid in the fault causing dissolution and rounding of dolomite clasts within an inertial grain flow and precipitation of carbonate coatings and euhedral silicates and oxides during subsequent cooling and co2 escape examples of similar rocks having some if not all of these characteristics have been described from other carbonate hosted faults the geological setting of the naukluft thrust is unique in spatial extent and quality of exposure allowing us to eliminate alternative hypotheses for sources of co2 to drive fluidization

dating of the black sea basin new nannoplankton ages from its inverted margin in the central pontides turkey the eocene uplift and inversion of a part of the black sea margin in the central pontides allows to study the stratigraphic sequence of the western black sea basin the revision of this sequence with 164 nannoplankton ages indicates that subsidence and rifting started in the upper barremian and accelerated during the aptian the rifting of the western black sea basin lasted about 40 myr from late barremian to coniacian in the inner inverted black sea margin the syn rift sequence ends up with shallow marine sands the uppermost albian to turonian was a period of erosion or non deposition this regional mid cretaceous stratigraphical gap might result from rift flank uplift as expected in the case of a thick and cold pre rift lithosphere however coeval collision of the kargi block along the north tethyan subduction zone at the southern margin of the pontides might also have contributed to this uplift a rapid thermal post rift subsidence of the margin occurred during the coniacian santonian collision of the kirsehir continental block commenced in early eocene time zone np12 giving rise to compressional deformation and sedimentation in piggyback basins in the central pontides whereas the eastern black sea was still opening

late palaeozoic marginal basin and subduction accretion the palaeotethyan kure complex central pontides northern turkey the kure complex located in the central pontides of northern turkey is a c 20 km thick pile of thrust imbricated deep sea sediments intercalated with a dismembered ophiolite the ophiolitic rocks include serpentinized harzburgite massive gabbro cumulate and isotropic sheeted dykes and basic volcanic rocks the extrusive rocks are mainly pillow lavas sheet flows and lava breccias geochemical evidence of immobile major and trace elements and pyroxene chemistry indicate mid ocean ridge mor and volcanic arc basalt vab compositions and suggest that the kure ophiolite was generated above a subduction zone chrome spine1 analysis also supports this interpretation in some thrust sheets the extrusives are depositionally overlain by hemi pelagic shales passing up into terrigenous turbidites and shales which are up to several hundred metres thick in intact successions cyprus type massive sulphides interpreted as precipitates from black smokers are located along the lava sediment contact individual intact sediment units up to several kilometres thick within the kure complex are separated by narrow up to 10 m wide zones of intense shearing layer parallel extension and melange formation asymmetrical folds reverse faults thrusts and duplex structures throughout the kure complex indicate mainly northwards emplacement the kure complex is thought to have opened in the late palaeozoic as a marginal basin above a northward dipping palaeotethyan subduction zone located along the southern margin of eurasia the kure marginal basin later closed in response to inferred southward subduction leading to development of an accretionary prism prior to late jurassic time the kure complex is unlikely to represent the main palaeotethyan suture as has been suggested in some earlier tectonic reconstructions regional comparisons with dobrogea crimea and caucasus suggest the kure basin opened then closed along a south eurasia active margin

fault rocks and past to recent fluid characteristics from the borehole survey of the nojima fault ruptured in the 1995 kobe earthquake southwest japan the mineralogy fluid inclusions and distribution of fault rocks of the nojima fault were examined in the core recovered from a borehole drilled by the geological survey of japan gsj 12 months after the 1995 kobe hyogo ken nanbu earthquake mjma 7 2 in southwest japan the borehole was drilled across a slipped portion of the fault to a depth of 746 7 m nearly continuous coring between 152 2 and 746 7 m recovered granodiorite protolith porphyry dikes and fault related rocks the fault zone was intersected at 426 2 m and is characterized by a greater intensity of brittle deformation and or hydrothermal alteration than typical host granodiorite the fault core consists of three types of fault gouge and occurs at the depth range of 623 1 to 625 3 m the fault normal thicknesses of the fault core and the fault zone are 0 3 m and 46 5 m respectively three types of hydrothermal alteration are recorded by mineral assemblages and fluid inclusions the first type is characterized by chloritization of mafic minerals at 200 c and occurred prior to the fault activity during the intrusion and cooling of the granodiorite the second type occurred during faulting and is recorded by zeolite mineralization at 200 c the third type is recorded by carbonate mineralization related to recent fluid flow although most of the second type of alteration occurred prior to the third type repeated mineralization is recorded by mutually crosscutting relationships between zeolite and carbonate veins and between zeolite vein and carbonate precipitated fault gouge this may record repeated changes in fluid chemistry within the fault zone in connection with the seismic cycle although the nojima fault slipped in the 1995 earthquake ancient fault related textures and mineral alteration are well preserved in the fault rocks

northern caucasus basin thermal history and synthesis of subsidence models abstract burial histories of the eastern central and western parts of the northern caucasus basin are reconstructed on the basis of well data and seismic sections subsidence began in the early triassic after the late carboniferous permian orogeny triassic sediments were mainly removed during late triassic early jurassic uplift and erosion platform cover began to form in the middle jurassic and albian sediments covered the whole territory of the basin thermal modelling shows that jurassic eocene subsidence was mainly controlled by late triassic early jurassic intrusive warming this heating event induced thermal uplift of the whole territory followed by exponentially decelerating subsidence due to cooling of the lithosphere in the southern areas adjacent to great caucasus subsidence was also affected by caucasian extensional and compressional events in the oligocene early miocene the eastern and the central basins underwent rapid long wavelength subsidence maikopian subsidence the geodynamic cause of this subsidence is probably associated with the mantle flow appearance after cessation of the tethyan subduction due to reequilibration of subducted slab while in the late miocene quaternary times the eastern and the western basins underwent foreland type asymmetrical subsidence due to loading of the great caucasus orogen the central basin was uplifted according to flexural modelling the main component of orogen loading was the lithospheric root load delamination of the latter under the central caucasus caused rapid uplift of the orogen and adjacent basin

tectonic melange as fault rock of subduction plate boundary abstract an assemblage of quantitative data sets is examined to evaluate tectonic melange as a plate boundary fault rocks in subduction zone the research object is the latest cretaceous mugi melange in the shimanto belt southwest japan systematic age younging from pelagic to terrigenous through hemipelagic sediments is well documented even though original stratigraphy is disrupted systematic shear fabric consistent with ancient plate convergence is reconstructed the melange was formed at temperatures of 130 200 c by cataclastic comminution of sandstone layers accompanied by tensile cracking and plastic deformation and the dehydration of clayey shale matrix with subsequent peeling off and underplating of the oceanic basement the temperature setting for the mugi melange indicates around the up dip limit of the seismogenic zone therefore includes various fault rocks suggestive of earthquake fault pseudotachylyte fluidized ultracataclasite with heating evidence amorphous silica and so on these suggest that fluid induced lubrication was dominated localized cataclastic shear which is a candidate of small earthquake or very low frequency earthquake is also recognized especially in sandstone blocks dominated portion in melange these observations are consistent with the melange being a fault rock along the plate boundary that records various types of earthquakes in a subduction zone the quantitative examination of the mugi melange suggests several criteria to define the tectonic melange of the plate boundary fault in subduction zone from other melanges in orogenic belt

western versus eastern black sea tectonic evolution pre rift lithospheric controls on basin formation abstract we demonstrate the key role of pre rift rheology on the kinematics of basin formation in the western and eastern black sea basins constraints on modelling results are provided by a large data set based on more than 50 000 km of multichannel seismics offshore and onshore wells regional gravity and magnetic surveys refraction seismics and field studies the model supports the presence of important differences in the thickness and in the thermal state of the lithosphere which rifted to form the western middle barremian and the eastern middle paleocene black sea subbasins a 200 km and a 80 km thick pre rift lithosphere appear to have driven the deformation in the western and in the eastern black sea respectively differences in the geometry and in the mechanical properties of the pre rift lithosphere have a strong control on the depth of necking and thus on the basin morphology the model sheds light on palaeotectonic and palaeogeographic reconstructions duration of rifting events location of subsiding areas and erosional surfaces the western and the eastern parts of the black sea appear to be two distinct basins characterised by different evolutionary paths determined by different pre rift conditions

tertiary tectonic evolution of the external east carpathians romania abstract paleostress calculation and analysis of mesoscopic structures are integrated with depth interpreted geological profiles based on seismic studies and well correlation to derive a tertiary tectonic model for the east carpathians following early miocene and older orogenic phases the first tectonic event that affected the studied area is characterised by a wsw ene oriented shortening of middle miocene late burdigalian in age resulting deformations induced ene ward thrusting of tarcau and marginal units as well as the internal part of the subcarpathian nappe a second shortening event with an e w to wsw ene contraction direction took place in the late miocene sarmatian characterised by further foreland thrusting of the subcarpathian nappe and out of sequence deformation in the tarcau and marginal folds nappes along strike differences in deformation mechanisms are controlled by the friction coefficients along the main detachment layers by the lateral variations in the wedge thickness and by the involvement in the northern part of the thrusting system of the thick competent east european platform tear faulting occurred in both tectonic events the main resulting structure being the triangle zone developed south of the trotus valley the latest miocene latest sarmatian early pliocene is characterised by a strike slip stress field with nne ssw compression and wnw ese tension axis left lateral faults being dominant the last deformation which affected the studied area is characterised by nnw sse shortening during the pliocene major deformations taking place mainly in the sw most bending zone

dynamical weakening of faults by acoustic fluidization when a fault slips seismically some of the energy released may excite strong short wavelength vibrations near the fault core such vibrations can temporarily reduce the normal stress on the fault allowing it to slip at lower shear stresses than predicted by laboratory coefficients of friction this phenomenon of acoustic fluidization provides an alternative to theories that invoke pressurized fluids as an explanation for why some faults appear to be so weak

analyses of pseudotachylyte from hole b of taiwan chelungpu fault drilling project tcdp their implications for seismic slip behaviors during the 1999 chi chi earthquake abstract the seismic slip behavior during the 1999 chi chi taiwan earthquake m w 7 6 was contrastive between the northern and southern segments of the activated chelungpu fault large fast and smooth slips with large stress drop in the north while smaller slower and irregular slips with smaller stress drop in the south we analyzed the pseudotachylyte samples recovered from 1194 m 1243 m and 1314 m depths of hole b of taiwan chelungpu fault drilling project tcdp to reveal the spatial difference in friction mechanism all pseudotachylyte layers are thin 0 7 2 8 cm the volume fraction of protoliths is very large more than 63 and the estimated temperature distribution is very heterogeneous from ca 750 1750 c these observations suggest that these pseudotachylyte melts were in the partial melting regime of montgomery montgomery r s 1976 friction and wear at high sliding speeds wear 36 275 298 where friction coefficient is abnormally large similar pseudotachylyte was found already in the core sample from 175 m depth of the nanto borehole penetrating the southern fault since both pseudotachylyte samples from the two boreholes are older than the 1999 chi chi event and have been uplifted from depths farther down dip of their current locations it is likely that recent seismic ruptures also would have encountered these mechanical barriers of viscous melt patches at deeper parts in the north than in the south elastohydrodynamic lubrication of clayey gouge worked effectively at the shallower parts of the northern segment however there is no evidence that it played an important role in the south these differences are the plausible causes of the contrastive local slip behaviors during the chi chi earthquake

fluidization and melting of fault gouge during seismic slip identification in the nojima fault zone and implications for focal earthquake mechanisms 1 the record of physical processes that occur during seismic slip events is well preserved in fault rocks from the active nojima fault in japan the fault rocks formed at about 3 km depth and comprise thin alternating layers of very fine gouge and pseudotachylyte derived from granite each layer is thinner than a few millimeters and corresponds to one seismic slip event the very thin slip zone width suggests that some mechanisms of slip weakening operated and our studies of the fault rocks suggest that fluidization and melting of gouge were particularly important fluidized and nonfluidized gouges were distinguished using the detection probability of fragmented counterparts method it is known from granular material science that the phase transition from a grain friction regime to fluidization of granular materials can occur only by a very small decrease in volume fraction of solid grains once fluidization occurs the frictional resistance decreases abruptly to nearly zero even before thermal pressurization reaches its extreme state when fault gouge is melted frictional resistance is governed by the viscosity of melt which depends mainly on temperature chemical composition h2o concentration and the volume fraction of unmelted grains for each pseudotachylyte layer we estimated the temperature of melt using various temperature indices and measured volume fraction of unmelted grains we synthesized these data to reconstruct the change in viscosity during seismic slip events the melt viscosity is very high 107 9 pas during initial melting due to the combined effect of low temperature 750 800 c and large volume fraction of solid grains thus seismic slip is inevitably restrained instantaneously once this mechanical barrier is overcome the viscosity reduces continuously and dramatically as slip increases at 1000 c the viscosity reduces to 104pas and eventually to 10pas at 1280 c thus stress drops almost completely and rupturing tends to run away

hydrocarbon bearing areas in the eastern part of the ukrainian black sea the eastern part of the ukrainian black sea consists of the kerch shelf with water depth less than 100 m that covers an area of 5500 km2 to the se of the crimean peninsula the much larger deepwater domain about 40 000 km2 has a maximum water depth of about 2200 m figure 1 the main tectonic units of the deepwater domain are as follows the easternmost part of the western black sea depression the northwestern part of the eastern black sea depression the south crimean cenozoic orogen the tetyaev shatsky and andrusov ridges and the sorokin trough all of these tectonic units were formed from the middle mesozoic until the present day

extreme frictional processes in the volcanic conduit of mount st helens usa during the 2004 2008 eruption abstract the 2004 2008 eruption of mount st helens saw the extrusion of seven high viscosity spines and formation of discrete shear zones along the conduit margin at spine 7 this shear zone consists of four structurally distinct layers the outer surface gouge l1 crosscuts a dark banded layer l2 which grades into a moderately sheared layer l3 and undeformed rock l4 inside the spine field observations porosity measurements geochemistry mineralogy microstructure crystal size and shape distribution kinetic properties and magnetic analyses chart the evolution of deformation processes and products throughout the eruption gouge formation was concomitant with characteristic microseismic drumbeats at depths 0 5 1 km in addition the seismic record shows two larger earthquakes with similar seismic signatures in august 2006 which we conclude represent larger slip amounts along the conduit margin of spine 7 extensive slip resulted in frictional heating on the order of several hundreds of degrees melting the highly viscous crystalline ascending magma plug and forming a pseudotachylyte high ambient temperatures in the conduit resulted in near equilibrium melting and slow recrystallisation thus impeding the development of signature pseudotachylyte characteristics and hindering identification thus frictional melting and recrystallisation in ascending magma plugs may be a common but unidentified phenomena at composite volcanoes worldwide

fractal particle size distribution of pulverized fault rocks as a function of distance from the fault core the size distributions of particle in pulverized rocks from the san andreas fault and the arima takatsuki tectonic line were measured the rocks are characterized by the development of opening mode fractures with an apparent lack of shear fragments in the rocks in both fault zones show a fractal size distribution down to the micron scale fractal dimensions dependent on mineral type decrease from 2 92 to 1 97 with increasing distance normal to the fault core the fractal dimensions of the rocks are higher than those of both natural and experimentally created fault gouges measured in previous studies moreover the dimensions are higher than the theoretically estimated upper fractal limit under confined comminution dimensions close to 3 0 have been reported in impact loading experiments the observed characteristics indicate that pulverization is likely to have occurred by a dynamic stress pulse with instantaneous volumetric expansion possibly during seismic rupture propagation similar to impact loading

late cenozoic burial history and dynamics of the northern caucasus molasse basin implications for foreland basin modelling abstract the collisional history of the caucasus segment of the alpine himalayan fold belt started at the end of the eocene the associated development of the northern caucasus foreland basin occurred during two syn collisional stages each displaying different subsidence patterns the 34 16 ma maikopian or pre foreland stage displays a long wavelength subsidence of a broad area whereas the 16 0 ma foreland stage displays asymmetrical foreland subsidence the first is correlated with the termination of subduction in the southern area and can be associated with mantle flow induced by the re equilibration of the subducted slab the along strike configuration of the second molasse basin stage contradicts the hypothesis in which topographical loading is considered to be the main control on foreland subsidence there is a clear anti correlation between basin depths and orogen heights the deepest parts of the basin are at the tips of the orogen where mountain heights are negligible while the area adjacent to the highest mountains central caucasus is uplifted the influence of other types of loading in foreland basin development has therefore been investigated and it has been possible to find a good fit with both gravity and basin architecture by including only two additional model parameters into the model these are crustal and lithospheric thickening thinning the results demonstrate that crustal thickening and removal of lithospheric roots are responsible for supporting the high central caucasus mountains and uplift of adjacent areas the subsidence of the basins at the orogen tips is explained by loading of lithospheric roots both effects are important in the geographically intermediate areas in general it is concluded that topography should not be considered as the main control on foreland subsidence but only as one of several counterbalancing mechanisms the existing flexural model therefore needs improvements such that it can be related directly to subsurface loading by real structures and processes during collision

fluidization of granular material in a subduction thrust at seismogenic depths abstract subduction thrusts exhumed from seismogenic depths may record the dynamic slip processes during subduction zone earthquakes the thrust faults in the shimanto accretionary complex of southwest japan imbricate the melange derived from sedimentary rocks and basalt which represent a duplex underplating associated with the downward step of the subduction thrust at seismogenic depths 4 6 km in depth temperature 130 150 c one well exposed duplex fault zone consists mainly of foliated cataclasites and ultracataclasites derived from basalt the fault zone structure suggests slip localization along the 2 20 cm thick ultracataclasite layer at the boundary between different lithologies the common features observed along the ultracataclasite layer are the injection of granular material into the melange without the sorting of fine grained particles along with a small detection probability of the fragmented counterparts in the injected materials which suggests a rapid injection of fluidized granular material during faulting the ultracataclasite layer is marked by fluid related processes as indicated by the alteration and precipitation of amorphous silica gel along the ultracataclasite and the concentration of veins near the ultracataclasite the fluidization during localized slip under fluid infiltrated conditions could be due to thermal pressurization which causes the fluid pressure to approach lithostatic values the injection of fluidized granular material may result from hydraulic fracturing in response to an increase in the fluid pressure associated with thermal pressurization the plate boundary subduction thrust could be lubricated when the granular material fluidizes due to thermal pressurization during earthquakes

thermo mechanical modelling of black sea basin de formation abstract we present the results of a thermo mechanical modelling study carried out to investigate the effect of pre rift rheology on subsequent basin de formation in the black sea area important differences are inferred for the bulk lithosphere structure and mechanical properties expressed in terms of different estimates for levels of necking in the western and eastern black sea respectively gravity data provide constraints on the mode of flexure in the black sea pointing to significant lateral variations in pre rift lithospheric strength these features strongly affect predictions for mesozoic cenozoic basin stratigraphy and have implications for the presence and development of rift shoulder topography on the margins of the black sea basins differences in lithosphere strength affect the mode of stress propagation from the basin margins into the central parts of the black sea basins during the post rift phase these post rift compressional stresses could be of key importance for long wavelength late neogene differential motions within the basins superimposed on vertical motions induced by rifting and subsequent sediment loading thermo mechanical modelling of integrated lithospheric strength points to a rapid increase of strength during the later stages of post rift evolution and the presence of relatively strong lithosphere in the centre of the basin these features predict preferential shortening induced by compressional activity of surrounding orogens to be primarily accommodated at the basins margins

structural and chemical characterization of shear zones in the freshly activated nojima fault awaji island southwest japan behavior and role of each shear zone in a shallow fault zone of granitic origin during seismic cycles are revealed by comprehensive examinations of petrographic and chemical characterization on a fault zone in the geological survey of japan gsj drill core penetrating the nojima fault which was activated during the 1995 hyogoken nanbu earthquake m 7 2 the gsj core consists of granodiorite and porphyritic intrusive rocks including a nojima fault zone which involves seven thin shear zones main shear zone msz 625 m depth upper cataclasite zone ucz upper shear zone usz lower shear zones lsz 1 and lsz 2 and lower cataclasite zones lcz 1 and lcz 2 these shear zones are generally surrounded by weakly pulverized and altered fault related rocks wpar which generally show volume gain the fault zone architecture is clarified as follows 1 total thickness of the nojima fault zone is 70 m 2 all shear zones except the older cataclasite zones ucz 1 lcz 1 and lcz 2 were evolved from wpar indicating that pulverization and alteration of recent activity were more diffused at the initial stage of faulting and gradually localized to each shear zone 3 the msz 2 m thick can be regarded as a high velocity frictional zone with accompanying volume loss compaction and possibly with heat generation during coseismic periods 4 the lsz 1 3 6 m thick located just beneath the msz and typically showing explosion brecciation texture is also regarded as a coseismic shear zone this zone could function as a trap zone for fluid or gas during postseismic interseismic periods 5 the lsz 2 2 7 m thick located around 710 m depth contains foliated fault gouge enriched with clay minerals and characterized by a large degree of volume gain possibly a result of slow velocity motion or creep during the interseismic and or postseismic periods

seismic cycle recorded in cockade bearing faults col de teghime alpine corsica abstract few fault rocks are known to be associated undoubtedly with seismic faulting here we investigated the formation mechanism of cockade breccias found in transtensional faults cutting marbles and quartzites from the col de teghime area alpine corsica france field surveys coupled with detailed microanalytical investigations indicated that i the core clasts of the cockades are composed of host rock fragments 310 m in size that are suspended in the slipping zones and arranged in inverse grading ii the concentric rims of the cockades show a cyclic zoning made of saddle dolomite mg calcite goethite anatase iii the cockade bearing veins are associated with minor fault veins filled with fine fragments we propose that the cockade bearing faults formed at shallow crustal depths

fault textures in volcanic conduits evidence for seismic trigger mechanisms during silicic eruptions it is proposed that fault textures in two dissected rhyolitic conduits in iceland preserve evidence for shallow seismogenic faulting within rising magma during the emplacement of highly viscous lava flows detailed field and petrographic analysis of such textures may shed light on the origin of long period and hybrid volcanic earthquakes at active volcanoes there is evidence at each conduit investigated for multiple seismogenic cycles each of which involved four distinct evolutionary phases in phase 1 shear fracture of unrelaxed magma was triggered by shear stress accumulation during viscous flow forming the angular fracture networks that initiated faulting cycles transient pressure gradients were generated as the fractures opened which led to fluidisation and clastic deposition of fine grained particles that were derived from the fracture walls by abrasion fracture networks then progressively coalesced and rotated during subsequent slip phase 2 developing into cataclasite zones with evidence for multiple localised slip events fluidisation and grain size reduction phase 2 textures closely resemble those formed on seismogenic tectonic faults characterised by friction controlled stick slip behaviour increasing cohesion of cataclasites then led to aseismic distributed ductile deformation phase 3 and generated deformed cataclasite zones which are enriched in metallic oxide microlites and resemble glassy pseudotachylite continued annealing and deformation eventually erased all structures in the cataclasite and formed microlite rich flow bands in obsidian phase 4 overall the mixed brittle ductile textures formed in the magma appear similar to those formed in lower crustal rocks close to the brittle ductile transition with the rheological response mediated by strain rate variations and frictional heating fault processes in highly viscous magma are compared with those elsewhere in the crust and this comparison is used to appraise existing models of volcano seismic activity based on the textures observed it is suggested that patterns of long period and hybrid earthquakes at silicic lava domes reflect friction controlled stick slip movement and eventual healing of fault zones in magma which are an accelerated and smaller scale analogue of tectonic faults

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

fracture healing in a magma an experimental approach and implications for volcanic seismicity and degassing 1 the healing of magmatic fractures is considered essential to repetitive seismicity and the closure of degassing paths during emplacement of lavas to estimate the healing time of magmatic fractures we performed healing experiments on rhyolitic melts at 850 1000 c and 1 6 3 2 mpa for 0 5 94 h two cylindrical obsidian cores were juxtaposed on surfaces prepared by cutting the cores both with and without polishing these were annealed in an open system cell the contact interface became coherent and finally disappeared the water content across the contact initially decreased toward the interface via diffusive dehydration but later homogenized this change was interpreted to reflect atomic scale closure of the interface probably by chemical bonding we defined this closure interval as microscopic healing time and determined this by fitting the measured profiles with a diffusion model the microscopic healing time was strongly dependent on temperature and roughness of the interface and was for the nonpolished interfaces 67 74 4 0 4 9 and 0 36 0 38 h at 850 900 and 950 c respectively whereas for the polished examples it was 1 3 and 0 5 0 6 h at 850 and 900 c respectively this microscopic healing time is consistent with the period of actual seismicity and is prolonged sufficiently to permit the formation of millimeter thick bubble free obsidian layers along fractures in vesicular lavas through bubble resorption due to diffusive degassing

stratigraphic and structural characteristics of the romanian black sea shelf abstract the western black sea basin opened during cretaceous times by back arc rifting in association with a north dipping subduction at the rear of the cretaceous early tertiary pontide volcanic arc the sedimentary wedge developed on the shelf of the romanian black sea sector reflects a complex interplay between large scale rifting uplift of the orogenic flanks large scale post rift subsidence and sea level changes we examine the detailed structural configuration of this sector for a regional correlation with the adjacent offshore in ukraine and bulgaria the evolution of the western black sea basin started in the albian cenomanian times when two extensional phases with significantly different directions n s and subsequently e w lead to the formation of a complex interplay between isolated blocks organised in horsts and grabens generally deepening eastwards superposition of normal faults footwall blocks from the two extensional episodes generated a deeply subsided area with enhanced accommodation space i e the histria depression and consequently recorded a larger thickness of paleogene sediments in the post rift stage re activation of faults and associated folding reflects repeated inversion during the late cretaceous oligocene times associated with subsequent periods of non deposition and or erosion during moments of basin fill exposure these periods of inversion recorded in the black sea are controlled by coeval orogenic deformations taking place in the balkans pontides and the crimean thrust belt sea level fluctuations during the neogene and late alpine tectonics in the neighbouring orogens caused massive sedimentation followed by sediment starvation and or significant erosion large thicknesses of sediments accumulated during the pontian presumably associated with an extensional episode deepening the distal parts of the basin and with differential compaction structures the interpretation of a high quality seismic dataset combined with published data allowed the correlation of major structural units and lineaments defined onshore towards the carpathians with the ones deeply buried below the western black sea basin sediments unit correlations are furthermore used to derive an integrated tectonic image of the western black sea area

healing microstructures of experimental and natural fault gouge 1 the healing of fault gouge was studied by examining microstructures of naturally and experimentally produced granitoid fault rock we performed deformation experiments on intact granitoid rock samples at t 300 500 c pc 500 mpa and 1 2 10 4 1 3 10 7 s 1 with 0 2 wt h2o added healing experiments were carried out on deformed samples at t 200 500 c pc 500 mpa for 4 h to 14 days under hydrostatic and nonhydrostatic conditions the grain size distributions gsd of the deformed samples were quantified using the d value slope of log frequency log radius of the gsd for quartz and feldspar fault gouge healing causes a decrease in the d value from 2 0 to 1 5 the time dependence of the d decrease is described by a hydrostatic healing law of the form d d t df a e t the results of the laboratory experiments were compared to three natural fault systems 1 nojima fault zone japan 2 fault zones in the black forest germany and 3 orobic thrust italian alps natural and experimental gouges have similar d values healing is only observed in monomineralic aggregates polymineralic i e mixed fault gouges retain their high d value after extended healing times because grain growth is inhibited healing under nonhydrostatic conditions is more rapid than hydrostatic healing the low strain rates which were measured during nonhydrostatic healing are temperature dependent and suggest that diffusive mass transfer processes take place during deformation thus fault rocks at upper to midcrustal depth may deform by combined cataclasis and diffusive mass transfer

inverted isograds at sulitjelma norway the result of shear zone deformation at sulitjelma norway there is a major inversion of metamorphic isograds beneath an inverted but undisrupted ophiolite the flysch like furulund schist in which the inverted isograds occur is also inverted and the early folds in it are downward facing the isograds cut across the axial surfaces of early folds and across the schistosity these relationships are explained as the consequence of metamorphism during the progressive development of a large overfold the inverted limb of the overfold is regarded as a major thick gently dipping shear zone separating the lower grade lower part of the caledonian allochthon below from the higher grade upper part of the allochthon above the association between stratigraphical inversion downward facing of syn schistosity folds and metamorphic inversion is explained by the progressive development of the shear zone it is suggested that the presence of such shear zones is a common feature of orogenic belts formed by continental collision

geodynamics of dobrogea romania new constraints on the evolution of the tornquist teisseyre line the black sea and the carpathians abstract dobrogea is the only place south of poland where the tornquist teisseyre line europe s longest lineament outcrops to characterize and date the tectonic activity of this line and to understand its relations with the neighboring structures e g the carpathians and the black sea basin the fracturing of late jurassic to neogene rocks in north central and south dobrogea is analyzed these paleostress reconstructions indicate that the dobrogea orogen was built under a n s compression with strain partitioning between thrusting at its front and dextral reverse slip along the peceneaga camena and capidava ovidiu faults during the late jurassic barremian from aptian to coniacian the dobrogea platform was characterized by se directed extension compatible with the aptian cenomanian rifting of the western black sea followed by the se directed drifting of a part of the moesian block i e the istanbul block on its southern extremity the tornquist teisseyre line does not show evidence for any large scale alpine strike slip movements postulated by many the peceneaga camena fault being reactivated in latest cretaceous paleogene as a pure reverse fault during the late tertiary the carpathian compression was poorly transmitted to dobrogea extension dominated the neogene deformation which indicates a weak coupling between the carpathians and its foreland

seabed morphology and gas venting in the black sea mudvolcano area observations with the mak 1 deep tow sidescan sonar and bottom profiler abstract the central part of the black sea was investigated with the mak 1 deep tow acoustic system providing sidescan observations and acoustic profiling subsequently underwater tv recordings and bottom sampling was done in an area with extensive mudvolcanism the mud volcanoes can be divided into three types according to their dimensions and morphology the first type has a seabed diameter of more than 2 km reaches a height of 100 150 m has a complex top with a crater like structure and gentle slopes and reflects massive mudflows in the crater and at its flanks the second type has smaller dimensions is more conical in cross section almost without relief on its relatively steep slopes and is characterised by small radial mudflows the third type is made up by the only mud volcano with a partially collapsed rim and with massive and liquid mudflows the first type expectedly is in a mature relatively passive stage the latter two types seem to be younger and more active various types of low relief slides are found in the area and are related to the presence of shallow subbottom gas 40 100 m below the seafloor or mudvolcano activity evidence for the presence of gas in the mudvolcano area is shown by gas venting acoustic turbidity acoustic masking numerous pockmarks acoustic voids and acoustic windows gashydrates do occur associated with some of the mudvolcanoes

geometry of isograds thermodynamic constraints on inversion abstract inverted isograds have been reported from metamorphic terrains ranging in age from precambrian to tertiary most of the workers believe that metamorphic inversion was caused by an inverted temperature gradient associated with large scale thrusting however isograds are not isotherms and the former may develop at large angles to the latter it is shown here that the orientation of isograds depends not only on the orientation of isotherms but also on the value of t p of an isograd reaction and that of the temperature gradients accordingly four different sets of conditions for inversion are recognised two for inverted temperature gradients one for a horizontal temperature gradient and one for a normal temperature gradient these conditions have been worked out for four different isograds staurolite in staurolite out muscovite breakdown and partial melting of granitic compositions it is shown that isograds may be in normal or inverted attitudes depending on the orientation and magnitude of the temperature gradient and also on the slope t p of an isograd reaction published accounts of metamorphic inversion do not provide all of these data but explain them in terms of only an inverted temperature gradient which may not be correct and may need re investigation

comminution and fluidization of granular fault materials implications for fault slip behavior abstract whilst faulting in the shallow crust is inevitably associated with comminution of rocks the mechanical properties of the comminuted granular materials themselves affect the slip behavior of faults therefore the mechanical behavior of any fault progresses along an evolutionary path we analyzed granular fault rocks from four faults and deduced an evolutionary trend of fractal size frequency comminution of fault rocks starts at a fractal dimension close to 1 5 2 d measurement at which a given grain is supported by the maximum number of grains attainable and hence is at its strongest as comminution proceeds the fractal dimension increases and hence comminution itself is a slip weakening mechanism under the appropriate conditions comminuted granular materials may be fluidized during seismic slip events in this paper we develop a new method to identify the granular fault rocks that have experienced fluidization where the detection probability of fragmented counterparts is a key parameter this method was applied to four fault rock samples and a successful result was obtained knowledge from powder technology teaches us that the volume fraction of grains normalized by maximum volume fraction attainable is the most important parameter for dynamic properties of granular materials and once granular fault materials are fluidized the fault plane becomes nearly frictionless a small decrease in the normalized volume fraction of grains from 1 is a necessary condition for the phase transition to fluidization from the deformation mechanism governed by grain friction and crushing by contact stresses this condition can be realized only when shearing proceeds under unconstrained conditions and this demands that the gap between fault walls is widened normal interface vibration proposed by brune et al tectonophysics 218 1993 59 appears to be the most appropriate cause of this and we presented two lines of field evidence that support this mechanism to work in nature

recognizing the seismic cycle along ancient faults co2 induced fluidization of breccias in the footwall of a sealing low angle normal fault abstract the zuccale low angle normal fault exposed on the island of elba italy is a crustal scale structure which contains a strongly foliated fault core in the immediate footwall of the zuccale fault cohesive fault related breccias which were initially deformed by typical frictional deformation mechanisms experienced fluidization over areas of at least 10 2 10 3 km 2 three internal variants of fluidized breccia are recognized with each related to a separate fluidization event characteristics of the fluidized breccias include 1 a highly irregular intrusive boundary with the overlying fault core 2 no grain scale evidence for typical frictional deformation mechanisms 3 an association with carbonate cements indicating that fluids contained co 2 and 4 a clast preferred orientation suggesting that fluids were moving vertically and spreading laterally as they encountered the foliated fault core our observations suggest that the fluidized breccias are representative of the interseismic period along the zuccale low angle fault and developed across small fault patches during build ups in fluid overpressure attainment of a critical fluid overpressure triggered embrittlement and the formation of low angle slip surfaces and sub vertical tensile veins within the overlying fault core which may account for the presence and the dimensions 10 1 10 3 km 2 of rupture surfaces which produce microseismicity along active low angle normal faults in central italy

geometry of isograds in metamorphic terrains abstract a simple mathematical relation among the dip of isograd surface dip of isotherm surface temperature gradient t g pressure gradient p g and t gdp of reaction is given by 1 sin ga t p p g 1 t g cos cot p g is taken to be constant at 0 3 kb km four major theoretical models for shapes and orientations of isograds are formulated on the basis of the parameters t g and t p this offers a rational basis for studying the geometry of isograds normal reverse metamorphism and determination of temperature gradient two examples have been studied in the light of these models in one case the domed shape of the isograd is best explained by a downwardly directed t g in the other case reverse metamorphism is best explained as the result of a horizontal t g of 18 c km

effects of frictional heating on the thermal hydrologic and mechanical response of a fault the mechanical response of a fault zone during an earthquake may be controlled by the diffusion of excess heat and fluid pressures generated by frictional heating in this study we formulate a fault model which incorporates the effects of frictional heating on the thermal hydrologic and mechanical response of a small patch of the failure surface this model is used to examine the parameters that control the fault response and to determine their critical range of values where thermal pressurization is significant the problem has two time scales a characteristic slip duration and a characteristic time for thermal pressurization the slip duration is set by the fault geometry the characteristic time for thermal pressurization is set by the slip rate the friction coefficient and the thermal and hydraulic characteristics of the medium the response of the fault depends on the relative magnitude of these two times results suggest that the fault width and hydraulic characteristics of the fault zone and adjacent medium are the primary parameters controlling the mechanical response for earthquakes occurring across zones of low porous medium compressibility 10 9 pa 1 and permeability 10 18 m2 the characteristic time for thermal pressurization is small in this case frictional heating can cause fluid pressures to approach lithostatic values the shear strength to approach zero and the temperature rise to stabilize at a maximum value dependent on the pore dilatational and transport properties of the porous medium whether the patch acts as a barrier to slip or exhibits substantial strain weakening is dependent on the shear strain across the fault moderate slip events where shear strains exceed two cause substantial strain weakening and consequently large stress drops accelerations and displacements thus it is possible for the patch to act as a barrier for small earthquakes but not for large ones both the dynamic stress drop and total displacement decrease for zones with larger compressibility permeability or width if the compressibility or permeability exceeds 10 8 pa 1 or 10 14 m2 or the shear strain is less than one then the effects of frictional heating may be negligible and the fault will exhibit no strain weakening characteristics consequently the patch acts as barrier that halts or resists further fault motion extrapolation of these results suggests that spatial variations in fault width and hydraulic characteristics will cause a heterogeneous stress drop and fault slip over the failure surface explaining many of the features of active faulting e g barriers nonuniform slip rupture stoppage random ground accelerations strong motions and frequency magnitude relations

geological implication of grain size segregation in dense granular matter to the current common belief grain size segregation in granular matter requires sufficient porosity therefore grain size segregation found in a natural fault gouge could imply elevated fluid pre

jurassic arc volcanism on crimea ukraine implications for the paleo subduction zone configuration of the black sea region article i nfo the early cretaceous and younger opening of the black sea has obliterated much of the older record of tethyan subduction below southeastern europe the earlier mesozoic evolution was dominated by opening and closure of tethyan oceans between gondwana and laurasia with their consumption at least in part accommodated along the southern eurasian margin crimea ukraine a peninsula in the northern black sea represents the northernmost region of southeastern europe that exposes a record of a pre cretaceous tethyan active margin to shed new light on the paleosubduction zone configuration of the southeastern european margin in the jurassic we report 40

reconstruction of seismic faulting by high velocity friction experiments an example of the 1995 kobe earthquake 1 high velocity friction experiments on a fault gouge collected from the nojima fault activated during the 1995 kobe earthquake showed that the friction coefficient decreased from 0 63 to 0 18 over a slip weakening distance dc at high slip rates of 1 m s the dramatic drop in friction coefficient of more than 0 3 is consistent with that for the kobe earthquake estimated from seismological observations experimentally determined dc becomes 5 m at a higher normal stress of 1 85 mpa close to the order of magnitude of seismologically determined dc of 0 5 to 1 m the difference in dc is not significant because the fracture energy consumed during frictional slip is the same order of 106 n m for both cases here we show that frictional behavior of a fault during an earthquake can be predicted by conducting high velocity friction experiments

rise and fall of the paratethys sea during the messinian salinity crisis abstract extremely thick evaporite units were deposited during the so called messinian salinity crisis msc 5 96 5 33 ma in a deep mediterranean basin that was progressively disconnected from the atlantic ocean a crucial but still poorly understood component in messinian evaporite models is the connectivity between mediterranean and paratethys i e the former black sea domain inadequate stratigraphic correlations and insufficient age control for paratethys sediments have so far hampered a thorough understanding of hydrological fluxes and paleoenvironmental changes here we present a new chronology for the eastern paratethys by integrating biostratigraphic and paleomagnetic data from mio pliocene sedimentary successions of romania and russia we show that a major flooding event from the mediterranean surged the paratethys basins at the maeotian pontian boundary 6 04 million years ago this indicates that sea level in both mediterranean and paratethys was high at the beginning of the msc we argue in favor of changes in paratethys mediterranean connectivity to initiate the msc in combination with elusive tectonic processes in the gibraltar arc a subsequent fall of paratethyan water level closely coincides to the mediterranean isolation event corresponding in age to the glacial cycles tg12 14 5 60 5 50 myr in the latest messinian a major climate change towards more humid conditions produced a positive hydrological balance and likely a transgression in the paratethys although our stratigraphic resolution cannot exclude a possible relation to the pliocene flooding of the mediterranean here

a review of deformation pattern templates in foreland basin systems and fold and thrust belts implications for the state of stress in the frontal regions of thrust wedges aesthetically appealing thrust systems and related large scale anticlines in both active and fossil foreland fold and thrust belts and the economic potential associated with the m have captured the interest of structural geologists for many decades as a consequence a large amount of data on sub seismic deformation patterns from thrust related an ticlines is available in the literature we provide a review of deformation pattern templates from fi eld data in foreland fold and thrust belts and show that the most frequent tre nds of sub seismic syn orogenic deformation structures hosted in km scale thrust related folds frequently and pa radoxically indicate a syn th rusting strike slip stress fi eld con fi guration with a near vertical 2 and a sub horizontal 3 rather than a contractional one where the latter is expected to be the vertical principal axis of the stress ellipsoid this a pparent inconsistency between sub seismic syn orogenic deformation structures and stress fi eld orientation is here named the 2 paradox field data support a possible expla nation of the paradox provided by the major role played by i nherited early orogenic extensional deformation struc tures on thrust fault nucleation nucleation of major thru sts and their propagation is facilitated and driven by the positive inversion and linkage of the early orogenic sub s eismic extensional inheritance developed in the foreland basin this process eventually leads to the development of l argereversefaultzonesandcanoccurbothincontractional and strike slip stress fi eld con fi gurations

morpho tectonic evolution of the crimean mountains ukraine as constrained by apatite fission track data introductionthe crimean mountains cm formthe westernmost prolongation of thecaucasus crimean thrust and foldbelt fig 1 muratov et al 1984 nikishin et al 1998 2001 saintotet al 1999 saintot and angelier 2002 despite the fact that the regionis one of the best explored territoriesin the former soviet union e g muratov 1960 kazantsev 1982 muratov et al 1984 slavin 1989 saintot et al 1999 nikishin et al 2001 mileev et al 2006 the scarcityof geochronological data limits geo dynamic reconstructions and does notallow veri cation of often contradic tory evolutionary scenarios see e g gintov and borisenko 1999 mileevet al 2006 this paper presents the rst ther mochronological data from the cm aimed at improving the existing mod els of exhumation uplift and land scape evolution e g muratov 1960 lysenko 1972 1976 saintot et al 1999 nikishin et al 2001 mileevet al 2006 this work also constrainsthe genesis and chronology of elevatedkarsti ed palaeosurfaces which occurmore extensively in the cm than inother european alpides understand ing the chronology and preservationof the palaeosurfaces in the cm andtheir relationship to post orogenicdeposits has important implicationsfor the survival of old inherited land forms in the mobile mountain belts ingeneral geological and geomorphologicalsettingthe cm are considered to be theremnantsofananticlinoriumstructure destroyed during the formation of theblack sea basin in short the tectonicevolution of the cm comprises i triassic earlycretaceous i e cimme rian compressional phases whenanticlinorium and s to se vergentthrust and fold structures formed mileev et al 1996 yudin 1999 golonka 2004 ii severalextensionalphasesduringthelateberriasian lateeocene associated with platform sed imentation kazantsev 1982 slavin 1989 and iii apost eocenecompres sive stage related to the collision of thearabian plate with eurasia leading tothe subduction of the east black seabasin under the russian platform andexhumation and uplift of individualblocks of the anticlinorium frombeneath the platform deposits saintotet al 1999 nikishin et al 2001 mileev et al 2006 according to mileev et al 1992 the accretional wedge of the cmformed in two main stages during theearly middle jurassic and late juras sic early cretaceous berriasian thelate cimmerian late jurassic berriasian compressional phase isbelieved to be the most importantphase for the genesis of the anticlino rium and the s to se vergent nappes mileev et al 1996 2006 saintotet al 1999 as pointed out by priva lov 2001 during the late cimmerianphase the regional stress eld was notpurely compressional but transpres sional inducing clockwise rotation ofthe cm in the late berriasian subsi dence commenced and late cimmerianstructures were unconformably over lain by platform sediments mainlysandstones conglomerates and lime stones continuous platform depositsare preserved along the northernmargin of the cm kazantsev 1982 with thickness varying from 0 3 to8 km field observations in the north ern slope of the cm revealed localizedthrusting of upper jurassic limestoneonto lower cretaceous platformdeposits kazantsev 1982 yudin 1999 sedimentation in platformregimes terminates in the late eocenein response to the uplift induced bythe east black sea basin indentation which was in turn caused by thearabia eurasia collision nikishinet al 2001 oligocene neogene sed imentation represented e g by theabstract

evidence for an inverted metamorphic gradient associated with a precambrian suture southern wyoming an inverted metamorphic gradient associated with the northern mylonite zone of the cheyenne belt a deeply eroded precambrian suture in southern wyoming has been documented within metasedimentary rocks of the early proterozoic snowy pass supergroup metamorphic grade in the steeply dipping supracrustal sequence increases from the chlorite through the biotite garnet and staurolite zones both stratigraphically and structurally upward toward the northern mylonite zone a minimum temperature increase of approximately 100 c over a km wide zone is required for this transition parallelism of inverted isograds with the trace of the northern mylonite zone implies a genetic relationship between deformation associated with that zone and the inverted metamorphic gradient within the snowy pass supergroup field evidence together with microstructural and petrofabric analysis indicate northward thrusting of amphibolite grade rocks over rocks of the snowy pass supergroup along the northern mylonite zone mineral equilibria and garnet biotite geothermometry on synkinematic mineral assemblages within the snowy pass metasedimentary rocks indicate deformation at minimum temperatures of 480 c and pressures of 350 400 mpa 3 5 4 0 kbar this implies tectonic burial or upper plate thickness of 13 15 km the narrow character of metamorphic zonation and microtextures within the snowy pass supergroup which indicate late synkine matic growth of garnet and staurolite preclude rotation of pre existing isograds by folding as a mechanism for development of the inverted gradient conductive transport of heat from the upper into the lower plate across the originally low angle thrust is insufficient to produce the necessary temperatures in the lower plate shear heating is considered insufficient to produce the observed metamorphic transition unless high shear stresses are postulated up dip advection of metamorphic fluids is a feasible but unproven mechanism for heat transport the possibility that rapid uplift due to stacking of several thrust sheets may have played a role in preserving the inverted metamorphic gradient cannot be evaluated at present

inversion of metamorphic zones in the lower himalayas at gangtok sikkim india inversion of metamorphic zones has been reported from the lower himalayas by many workers an example of such an inverted metamorphic zone has been studied in detail around gangtok theoretical analysis of relationship among isograd isotherm and isobar leads to the conclusion that inversion of metamorphic zones may be caused under three conditions 1 the temperature gradient is horizontal 2 the temperature gradient is upwardly directed and 3 slope of the isotherm is greater than the slope of the isograd both being in the same direction the present example is best explained as the result of an upwardly directed temperature gradient caused by distortion of the isotherms by tectonic deformation

use of fault striations and dislocation models to infer tectonic shear stress during the 1995 hyogo ken nanbu kobe earthquake dislocation models of the 1995 hyogo ken nanbu kobe earthquake derived by yoshida et al 1996 show substantial changes in direction of slip with time at specific points on the nojima and rokko fault systems as do striations we observed on exposures of the nojima fault surface on awaji island spudich 1992 showed that the initial stress that is the shear traction on the fault before the earthquake origin time can be derived at points on the fault where the slip rake rotates with time if slip velocity and stress change are known at these points from yoshida s slip model we calculated dynamic stress changes on the ruptured fault surfaces to estimate errors we compared the slip velocities and dynamic stress changes of several published models of the earthquake the differences between these models had an exponential distribution not gaussian we developed a bayesian method to estimate the probability density function pdf of initial stress from the striations and from yoshida s slip model striations near toshima and hirabayashi give initial stresses of about 13 and 7 mpa respectively we obtained initial stresses of about 7 to 17 mpa at depths of 2 to 10 km on a subset of points on the nojima and rokko fault systems our initial stresses and coseismic stress changes agree well with postearthquake stresses measured by hydrofracturing in deep boreholes near hirabayashi and ogura on awaji island our results indicate that the nojima fault slipped at very low shear stress and fractional stress drop was complete near the surface and about 32 below depths of 2 km our results at depth depend on the accuracy of the rake rotations in yoshida s model which are probably correct on the nojima fault but debatable on the rokko fault our results imply that curved or cross cutting fault striations can be formed in a single earthquake contradicting a common assumption of structural geology

rupture mechanism and interface separation in foam rubber models of earthquakes a possible solution to the heat flow paradox and the paradox of large overthrusts abstract spontaneous stick slip along the interface between stressed foam rubber blocks is a simple analog of earthquake rupture and stick slip results from this model are used to elucidate the role of normal stress variations along the interface in the stick slip process observations indicate significant normal interface vibrations and separation during slip suggesting that dynamic changes in normal stress rather than a drop in the coefficient of friction may control stick slip as suggested for example by tolstoi oden and martins and brune and co workers observations of particle trajectories indicate that stick slip shear motion is associated with various degrees of fault separation for an asymmetric model the motion is consistent with slipping motion of the type suggested by schallamach and price for a symmetric model the motion is similar to that suggested by comninou and dundurs if interface waves of this type involving separation during slip occur in earthquakes they may be a solution to the heat flow paradox since a major part of the slip occurs during separation and during low normal stress thus frictional heat generation is reduced normal interface vibrations during stick slip may explain the high corner frequency of p wave spectra and the generally high levels of p wave spectra beyond the corner frequency schallamach comninou type waves are consistent with the partial stress drop abrupt locking self healing models of brune and heaton

tectonic paleostress fields and structural evolution of the nw caucasus fold and thrust belt from late cretaceous to quaternary abstract the nw caucasus fold and thrust belt essentially corresponds to the inverted western flysch zone of the great caucasus mountains a deep basin that developed from late jurassic to eocene times between the scythian plate to the north and the transcaucasian terranes to the south the shatsky ridge sw of the nw caucasus zone the flysch basin was strongly affected by compression in late eocene times when the characteristic wnw trending folds and thrusts of the nw caucasus belt developed some authors regard the main compressive deformation as miocene in age by means of remote sensing analysis we elucidate the geometry of major structures in the belt wnw trending south vergent thrusts and folds and major vertical and transverse nne ssw to ne sw deep fault zones the later structures are interpreted as ancient faults that were active during the development of the flysch basin paleostress investigations reveal seven main tectonic episodes in the evolution of the nw caucasus since late cretaceous combining structural interpretation remote sensing analysis and paleostress field reconstruction we propose a model for the structural evolution of the belt during the late cretaceous paleocene the western caucasus zone was under transtensional regime with an e w to ne sw trending 3 that generated oblique normal movements along nne ssw transverse faults and wnw ese margins of the flysch basin this tectonism could correspond to rifting related to the formation of the eastern black sea basin at the paleocene eocene boundary a transpressional event with an e w to nw se trending 1 developed and the nne ssw to ne sw trending faults could have been inverted this event could correspond to an attenuation in the eastern black sea basin formation or to the incipient accretion of the transcaucasian terranes during the eocene another e w to nw se oblique extension transtensional event affected the flysch basin that could be related to a known rifting phase in the eastern black sea basin strong nne ssw to ne sw compression characterises late eocene tectonism the fold and thrust belt developed at this time as a result of the direct collision of the shatsky ridge with the scythian plate a ne sw extension followed the late eocene event related to basin development around the newly formed fold belt a wnw ese oblique contraction affected the belt during the early miocene as the result of arabian plate convergence with the caucasian system the latest inferred event is a compressional regime with nnw sse trending 1 that is affecting the nw caucasus belt from sarmatian times until the present under this oblique compression the belt has deformed as in a dextral shear zone and the thrust surfaces have acquired lenticular shapes this study highlights the occurrence of oblique movements in the nw caucasus area prior to and after the dominant late eocene compression from the late cretaceous until the eocene the structural development of the nw caucasus was closely related to the evolution of the eastern black sea basin from the late eocene until quaternary times it was rather related to the arabia eurasia plate convergence

petrological architecture of a magmatic shear zone a multidisciplinary investigation of strain localisation during magma ascent at unzen volcano japan shearing of magma during ascent can promote strain localisation near the conduit margins anymechanical and thermal discontinuities associated with such events may alter the chemical physicaland rheological stability of the magma and thus its propensity to erupt lava spines can record suchprocesses preserving a range of macroscopic and microscopic deformation textures attributed toshearing and friction as magma ascends through the viscous brittle transition here we use a multi disciplinary approach combining petrology microstructures crystallography magnetics and experi mentation to assess the evidence role and extent of shearing across a marginal shear zone of the1994 1995 lava spine at unzen volcano japan our results show that crystals can effectively moni tor stress conditions during magma ascent with viscous remobilisation crystal plasticity and com minution all systematically increasing towards the spine margin accompanying this we find anincrease in mineral destabilisation in the form of pargasitic amphibole breakdown displaying tex tural variations across the shear zone from symplectitic to granular rims towards the spine margin in addition the compaction of pores chemical and textural alteration of interstitial glass and mag netic variations all change systematically with shear intensity the strong correlation between thedegree of shearing crystal deformation and disequilibrium features together with distinct magneticproperties implies a localised thermal input due to shear and frictional processes near the conduitmargin during magma ascent this was accompanied by late stage or post emplacement fluid andgas induced alteration of the gouge as well as oxidation and glass devitrification understandingand recognising evidence for strain localisation during magma ascent may therefore be vital whenassessing factors that regulate the style of volcanic eruptions which may provide insights into thecryptic shifts from effusive to explosive activity as observed at many active lava domes

characterization of slip zone associated with the 1999 taiwan chi chi earthquake x ray ct image analyses and microstructural observations of the taiwan chelungpu fault abstract to characterize the fault related rocks within the chelungpu fault we performed x ray computed tomography ct image analyses and microstructural observations of hole b core samples from the taiwan chelungpu fault drilling project we identified the slip zone associated with the 1999 chi chi earthquake within the black gouge zone in the shallowest major fault zone by comparison with previous reports the slip zone was characterized by low ct number cataclastic or ultracataclastic texture and high possibility to have experienced a mechanically fluidized state taking these characteristics and previous reports of frictional heating in the slip zone into consideration we suggested that thermal pressurization was the most likely dynamic weakening mechanism during the earthquake

ferrimagnetic resonance signal produced by frictional heating a new indicator of paleoseismicity 1 high speed fault slips during earthquakes may generate sufficient frictional heat to produce fused fault rocks such as pseudotachylyte we have carried out high speed slip tests using natural fault gouge to judge whether or not frictional heating universally occurs during seismic fault slips in our shearing tests natural fault gouge is put between two cylindrical silica glasses and sheared under a fixed axial stress of 0 61 mpa despite such a low stress near the earth s surface a darkened cohesive material resembling pseudotachylyte is made from the fault gouge along the edge of a circular shear plane when shearing at a high speed of 1500 rpm the maximum slip rate reaches 1 96 m s at the edge electron spin resonance measurements reveal that the darkened cohesive material has a strong ferrimagnetic resonance fmr signal which is derived from bulky trivalent iron ions in ferrimagnetic iron oxides fe2o3 the fmr signal is produced by the thermal dehydration of antiferromagnetic iron oxides feooh in the fault gouge this may be applicable to the detection of past heating during seismic fault slip we thus attempt to reconstruct the temperature of frictional heat generated on the nojima fault plane in the 1995 kobe earthquake m 7 3 by inversion using the fmr signal the computer simulation indicates that the frictional heat generated on the nojima fault plane at 390 m depth may have attained 390 c during the 1995 kobe earthquake the temperature in the fault plane may have returned to its initial state after 1 year this result suggests that a heat flow anomaly generated by faulting may be difficult to detect

the black sea basins structure and history new model based on new deep penetration regional seismic data part 1 basins structure and fill abstract this work is based upon results of interpretation of about 8872 km long regional seismic lines acquired in 2011 within the international project geology without limits in the black sea the seismic lines cover nearly the entire black sea basins including russia turkey ukraine romania and bulgaria sectors a new map of acoustic basement relief and a new tectonic structure scheme are constructed for the black sea basins the basement of the black sea includes areas with oceanic crust and areas with highly rifted continental crust a chain of buried seamounts which were interpreted as submarine volcanoes of late cretaceous santonian to campanian age has been identified to the north of the turkish coast on the shatsky ridge probable volcanoes of albian age have also been recognized synorogenic turbidite sequences of paleocene eocene and oligocene ages have been mapped in the cenozoic numerous compressional and transpressional structures were formed in different parts of the black sea basin during the pleistocene quaternary turbidites mass transport deposits and leveed channels were formed in the distal part of the danube delta

fluid inclusions in pseudotachylytes from the nojima fault japan pseudotachylytes i e rocks formed by frictional melting have been observed in the nojima fault that was penetrated by the hirabayashi borehole drilled 1 year after the 1995 hyogo ken nanbu kobe earthquake these rocks display millimeter scale banding defined by different pseudotachylyte layers the nature of unmolten crystal fragments k feldspar albite calcite and or quartz allows us to infer a minimum melting temperature of 1200 c the glass has a 8 3 volatile content and a higher cao content than that of the parent granodiorite thus suggesting that pseudotachylyte formation occurred in an already altered calcite bearing and hydrated fault zone fluid inclusions have been observed in the glass and are filled with a dense low salinity 4 3 1 2 wt eq nacl co2 h2o fluid characterized by steep isochoric curves the intersection between the isochores and the measured 24 c km geothermal gradient indicates a minimum 15 km depth for the pseudotachylyte formation such a depth suggests that an important uplift has brought the studied pseudotachylytes to their present position and that these pseudotachylytes are probably pre miocene in age the calculated thermal evolution of a typical millimeter scale pseudotachylyte layer indicates that cooling does not last more than a few seconds this indicates that related seismic processes such as deceleration of fault movement and healing of the fault were both very rapid the geometry and thermal budget of the millimeter thick pseudotachylytes suggest that seismic events of magnitude 6 to 7 are responsible for their formation

inferring earthquake physics and chemistry using an integrated field and laboratory approach abstract earthquakes are the result of a combination of 1 physico chemical processes operating in fault zones which allow ruptures to nucleate and rock friction to decrease with increasing slip or slip rate and 2 of the geometrical complexity of fault zones in this review paper we summarize recent experimental findings from high velocity conducted at about 1 m s slip rate or typical seismic slip rates rock friction experiments with an emphasis on potential dynamic weakening mechanisms melt lubrication nanopowder lubrication etc and how these mechanisms might be recognized by means of microstructural and mineralogical studies in exhumed fault zones we discuss how earthquake source parameters coseismic fault strength weakening distances energy budgets etc might be derived from the field and laboratory experiments additionally we discuss what needs to be considered in terms of fault zone geometry and morphology focusing on fault surface roughness in order to develop models of realistic fault surfaces and present theoretical considerations for microphysical modeling of laboratory data at seismic slip rates with an emphasis on the case of melt lubrication all experimental data and in the case of melt lubrication microphysical models indicate that faults must be very weak

triassic limestone turbidites and serpentinite the cimmeride orogeny in the central pontides the basement of the central pontides and by implication that of crimea consists of pre permian low grade metaclastic rocks intruded by latest permian early carboniferous 305 290 ma granitoids further up in the stratigraphic sequence are triassic limestones which are now preserved as olistoliths in the deformed upper triassic turbidites new conodont and foraminifera data indicate an anisian to carnian middle to late triassic age for these hemi pelagic hallstatt type limestones the siliciclastic turbidites surrounding the triassic limestone contain the norian late triassic bivalve monotis salinaria the same species is also found in the tauric series in crimea the upper triassic flysch in the central pontides is locally underlain by basaltic pillow lavas and includes kilometre size tectonic slices of serpentinite both the flysch and the serpentinite are cut by an undeformed acidic intrusion with an ar ar biotite age of 162 4 ma callovian oxfordian this indicates that the serpentinite was emplaced into the turbidites before middle jurassic time most probably during latest triassic or early jurassic time and that the deformation of the triassic sequence pre dates the middle jurassic regional geological data from the circum black sea region including widespread upper triassic flysch upper triassic eclogites and blueschists of oceanic crustal affinity and apparent absence of a cimmerian continent between the cretaceous and triassic accretionary complexes indicate that the latest triassic cimmeride orogeny was accretionary rather than collisional and is probably related to the collision and accretion of an oceanic plateau to the southern active margin of laurasia

textural record of the seismic cycle strain rate variation in an ancient subduction thrust active faults slip at different rates over the course of the seismic cycle earthquake slip c 1 m s 1 interseismic creep c 10 100 mm year 1 and intermediate rate transients e g afterslip and slow slip events studies of exhumed faults are sometimes able to identify seismic slip surfaces by the presence of frictional melts and slow creep by textures diagnostic of rate limited plastic processes the pasagshak point thrust preserves three distinct fault rock textures which are mutually cross cutting and can be correlated to different strain rates ultrafine grained black fault rocks including pseudotachylyte were formed during seismic slip on layers up to 30 cm thick well organized s c cataclasites 7 31 m thick were formed by slow creep with pressure solution as a dominant rate limiting mechanism these must have formed at strain rates consistent with long term plate boundary motion but solution creep healing acted to reduce porosity of the cataclasites and eventually restricted fluid connectivity such that creep by this mechanism could not continue disorganized non foliated rounded clast cataclasites were formed at shear rates faster than solution creep and are interpreted as representing shear at intermediate strain rates these could have formed during afterslip or delocalization of slip associated with an earthquake rupture

fragmentation in the val pola rock avalanche italian alps 1 grain size data from the deposit of the 1987 val pola rock avalanche central italian alps are compared with data concerning rock avalanching rock fragmentation and comminution the weibull distribution fits a small part of the entire particle size distribution of debris samples with a mean value of the curve shape factor of 0 54 0 28 this is typical of multiple comminution or fragmentation with much shearing a fractal distribution fits over a greater size range computed fractal dimensions range between 1 3 and 3 2 within the deposit with average values of about 2 6 2 7 these values cover the range between the theoretical values of the plane of weakness model 1 97 and the pillar of strength model 2 84 and are close to the theoretical value for the constrained comminution model 2 58 these suggest that both texturally mature and immature deposits are present and that more than a single comminution process acted during the rock avalanche motion variation of the grain size distribution within the deposit and grain size segregation show as trends in the fractal dimension and arise from variation in the fragmentation process a variety of different physical and empirical laws suggest that 1 30 of the energy expended in the rock avalanche was consumed in fragmentation

geologic evidence for multiple slip weakening mechanisms during seismic slip in crystalline rock we examine exhumed seismogenic faults to investigate the mechanisms that may have achieved dynamic fault weakening during ancient ruptures field and microscope observations imply more than one weakening mechanism must have been active during slip events on the faults pseudotachylytes that are continuous over the scale of field exposures are indicative of melt lubrication a fault breccia crosscutting earlier formed cataclasites was mobilized during faulting and possibly represents a pressurized fault rock that resulted from thermal pressurization or elastohydrodynamic lubrication in some faults pseudotachylytes are developed in patches several meters long cataclasites in which there is no evidence for melting are present immediately along strike from the pseudotachylyte patches by considering the energy required for melting we show that the pseudotachylytes must have formed during ruptures larger than the patches implying that the cataclasites also accommodated seismic slip the distribution of fault rock types shows that the frictional response to slip during a single event was spatially variable reworked pseudotachylytes also indicate that coseismic processes change over time at a point on a fault these observations emphasize that macroscopic dynamic fault weakening is a function of multiple coeval processes at microscales to mesoscales detailed observations of the discontinuous pseudotachylytes show that slip zone thickness is the critical parameter that controls active coseismic processes the frictional response of a fault to slip is therefore dependent on the internal structure of faults given the along strike heterogeneity of most mapped fault zones the coexistence of multiple slip weakening mechanisms in a single earthquake will be common

magnetostratigraphy and radio isotope dating of upper miocene lower pliocene sedimentary successions of the black sea basin taman peninsula russia abstract we present a new chronology for the upper miocene to pliocene deposits of the black sea basin based on high resolution magnetostratigraphic data coupled with 40 ar 39 ar dating from the 475 m long zheleznyi rog section on the taman peninsula russia this section comprises the stratigraphic interval of the khersonian to kimmerian regional stages of the eastern paratethys our magnetostratigraphic record is based on biogenic and early diagenetic greigite components and yields a magnetostratigraphic sequence of 8 polarity zones a volcaniclastic ash layer at the upper part of the khersonian is radio isotopically dated at 8 69 0 18 ma the age of the khersonian meotian transition arrives at 8 6 or 8 2 ma which is significantly younger than earlier estimates the new age has important consequences for the hipparion datum in the eastern paratethys and implies that all vallesian fossil sites are younger than 11 2 ma the meotian stage has a total duration of 2 2 to maximum 2 6 myr and is marked by multiple erosional events the end of the paratethys sea is dated at 5 5 ma when the black sea becomes isolated from the caspian sea the dacian basin and the mediterranean

breccia formation by particle fluidization in fault zones implications for transitory rupture controlled fluid flow regimes in hydrothermal systems breccias in the rusey fault cornwall uk and the roamane fault porgera gold deposit papua new guinea provide insights about the dynamics of fluid flow and flow velocities when fault ruptures breach overpressured reservoirs of hydrothermal fluid these faults contain cockade like breccias in which rock fragments are mantled by spheroidal overgrowths of hydrothermal minerals at rusey the overgrowths are quartz dominant whereas in the roamane fault overgrowths are composed of calcite quartz or gold rich pyrite although none of the rock fragment cores of accretionary spheroids are in contact with their neighbours the spheroidal overgrowths do contact each other and are at least partially cemented together the hydrothermal overgrowths mostly comprise either outwards coarsening crystals that radiate from the surface of the core rock fragment or finer grained inequigranular to mesh like intergrowths concentric textural banding and oscillatory growth zones are present in some hydrothermal mantles the breccias occur as fault parallel layers and lenses each up to several tens of centimeters thick adjacent layers are characterized by texturally distinct ranges of clast sizes and different proportions of clasts to hydrothermal overgrowths in the rusey fault many texturally distinct breccia layers are present within a 3m wide fault core some layers truncate others and many breccia layers exhibit grainsize grading or banding clasts in the breccias include fragments of wall rock veins and various fault damage products including fragments of earlier generations of cemented breccia brecciation was episodic and separated by periods of cementation the distinctive textures of the breccias are interpreted to have formed by fluidization of fault damage products in a high fluid flux regime hydrothermal coatings developed while clasts were in a suspended state during fluid ascent through dilatant fault segments layered breccias record multiple episodes of particle fluidization and indicate that the faults provided conduits for repeated transitory fluid upflow particle size distributions indicate that fluid velocities during fluidization were in the range 0 1 ms 1 to 1 ms 1 the maximum flow rates correspond to fluid fluxes of 10 to 100 l s 1 per meter strike length of fault through dilatant fault apertures up to several tens of centimeters wide such high flow rates characteristically induce intense swarm seismicity rather than mainshock aftershock seismicity and have implications for the dynamics and rates of formation of fault related hydrothermal ore deposits

the region of the strandja sill north turkey and the messinian events the two sides of the strandja sill show a highly discontinuous stratigraphic succession since the late oligocene this area together with the sea of marmara basin is usually proposed as the gateway for the paratethyan freshwaters and organisms that constituted the lago mare facies in the mediterranean sea during the messinian salinity crisis msc our investigations involving new field observations and datings together with previous studies suggest that the sill has possibly experienced such a connection at around 8 ma i e significantly before the crisis the proposal of a sea level drop of the black sea before 7 ma is not supported by our data on dinoflagellate cysts consistency of calcareous nannofossil succession at dsdp site 380 is reinforced allowing to reassert that subaerial erosion impacted both the southwestern black sea and the central marmara dardanelles area during the peak of the msc at that time this region was crossed by two oppositely directed fluvial networks further supporting the absence of a marine gateway through the strandja sill it is concluded that none of the lago mare events recorded in the mediterranean during the msc were the consequence of the passage of paratethyan waters and organisms through this area in the black sea the well dated messinian fluvial erosion can be followed offshore the overlying prograding deltaic deposits attest to a fast marine reflooding after the crisis this constitutes a comprehensive erosion sedimentation model in an area intensively explored for hydrocarbons

kinematics of back arc inversion of the western black sea basin 1 back arc basin evolution is driven by processes active at the main subduction zone typically assuming the transition from an extensional back arc during the retreat of a mature slab to a contractional basin during high strain collisional processes such a transition is observed in the black sea where the accurate quantification of shortening effects is hampered by the kinematically unclear geometries of cenozoic inversion by means of seismic profiles interpretation quantified deformation features and associated syn tectonic geometries on the romanian offshore this study demonstrates that uplifted areas observed by exploration studies form a coherent thick skinned thrust system with n ward vergence thrusting inverted an existing geometry made up by successive grabens that were inherited from the cretaceous extensional evolution the shortening started during late eocene times and gradually affected all areas of the western black sea basin during oligocene and miocene times deformation being coherently correlated across its western margin the mechanism of this generalized inversion is the transmission of stresses during the collision recorded in the pontides balkanides system syn tectonic sedimentation in the western black sea demonstrates that this process was continuous and took place through the onset of gradual shortening migrating northward although the total amount of shortening is roughly constant in an e w direction individual thrusts have variable offsets deformation being transferred between structures located at distance across the strike of the system the black sea example demonstrates that the vergence and offset of thrusts can change rapidly along the strike of such a compressional back arc system this generates apparently contrasting geometries that accommodate the same orogenic shortening

petroleum geology of the black sea abstract the black sea comprises two extensional basins formed in a back arc setting above the northward subducting tethys ocean close to the southern margin of eurasia the two basins coalesced late in their post rift phases in the pliocene forming the present single depocentre the western black sea was initiated in the aptian when a part of the moesian platform now the western pontides of turkey began to rift and move away to the south east the eastern black sea probably formed by separation of the mid black sea high from the shatsky ridge during the palaeocene to eocene subsequent to rifting the basins were the sites of mainly deep water deposition only during the late miocene was there a major sea level fall leading to the development of a relatively shallow lake most of the margins of the black sea have been extensively modified by late eocene to recent compression associated with closure of the tethys ocean gas chromatography mass spectrometry and carbon isotope analysis of petroleum and rock extracts suggest that most petroleum occurrences around the black sea can be explained by generation from an oil prone source rock of most probably late eocene age although a wider age range is possible in the basin centres burial history modelling and source kitchen mapping indicate that this unit is currently generating both oil and gas in the post rift basin a palaeozoic source rock may have generated gas condensate in the gulf of odessa in bulgarian waters the main plays are associated with the development of an eocene foreland basin kamchia trough and in extensional structures related to western black sea rifting the latter continue into the romanian shelf where there is also potential in rollover anticlines due to gravity sliding of neogene sediments in the gulf of odessa gas condensate has been discovered in several compressional anticlines and there is potential in older extensional structures small gas and oil discoveries around the sea of azov point to further potential offshore around the central azov high in offshore russia and georgia there are large culminations on the shatsky ridge but these are mainly in deep water and may have poor reservoirs there are small compressional structures off the northern turkish coast related to the pontide deformation these may include eocene turbidite reservoirs the extensional fault blocks of the andrusov ridge mid black sea high are seen as having the best potential for large hydrocarbon volumes but in 2200 m of water

geothermometry and geobarometry of inverted metamorphic zones in the w central scottish dalradian the attitude of the garnet isograd surface in the balquhidder region of the scottish dalradian is such that the metamophic zones must be inverted higher grade rocks overlying lower grade rocks textural and structural information indicates that peak barrovian metamorphism post dates emplacement of the tay nappe as post metamorphic folds are open and upright no tectonic means of overturning the isograd surface can be invoked metamorphism must have occurred in a negative thermal gradient the metamorphic temperature at the garnet isograd is about 500 c and increases along a negative metamorphic gradient perpendicular to the isograd surface of about 27 c km metamorphic pressure is about 9 kbar the initial temperature inversion was probably caused by emplacement of the tay nappe it is unlikely that subsequent conductive thermal relaxation alone would have caused inverted metamorphic zonation however the relaxative process may have been sufficiently modified by convective transfer of heat by fluid evolved from metamorphic reactions for this to occur

record of mega earthquakes in subduction thrusts the black fault rocks of pasagshak point kodiak island alaska on kodiak island alaska decimeterthick black fault rocks are at the core of foliated cataclasites that are tens of meters thick the cataclasites belong to melange zones that are regarded as paleodecollements active at 12 14 km depth and 230 260 c each black layer is mappable for tens of meters along strike the black fault rocks feature a complex layering made at microscale by alternation of granular and crystalline micro textures both composed of micronscale subrounded quartz and plagioclase in an ultrafi ne phyllosilicate rich matrix in the crystalline microlayers tabular zoned micro lites of plagioclase make up much of the matrix no such feldspars have been found in the cataclasite we interpret these crystalline microlayers as pseudotachylytes the granular microlayers show higher grainsize variability crushed microlites and textures typical of fl uidization and granular fl ow deformation crosscutting relationships between granular and crystalline microlayers include fl ow and intrusion structures and mutual brittle truncation this suggests that each decimeters thick composite black fault rock layer records multiple pulses of seismic slip in each pulse ultracomminuted fl uidized material and friction melt formed and deformed together in a ductile fashion brittle truncation by another pulse occurred after solidifi cation of the friction melt and the fl uidized rock x ray powder diffraction xrpd and x ray fl uorescence xrf analyses show that black fault rocks have similar mineral composition and chemical content as the cataclasites the observed systematic chemical differences cannot be explained by bulk or preferential melting of any of the cataclasite components the presence of an open fl uidinfi ltrated system with later alteration of black fault rocks is suggested the geochemical results indicate that these subductionrelated pseudotachylytes differ from those typically described in crystalline rocks and other tectonic settings

deformation at the frictional viscous transition evidence for cycles of fluid assisted embrittlement and ductile deformation in the granitoid crust abstract mid crustal deformation is classically characterized by the transition from ductile to brittle deformation defining the frictional to viscous transition fvt here we investigate an exhumed continental mid crustal basement section in order to envisage the relationship between ductile and brittle deformation at the fvt our detailed study from km to micro scale shows that under greenschist metamorphic conditions deformation is accommodated by a dense network of highly localized ductile shear zones in the investigated case it is not quartz which defines the overall ductile deformation behavior but the viscous granular deformation in shear zones with an ultrafine grained polymineralic matrix consisting of quartz feldspar sheet silicates and epidote during viscous granular flow mass transfer processes under the presence of fluids promote a chemo mechanical mixing resulting in grain size reduction and reaction softening coeval with this ductile deformation fluid assisted embrittlement occurs as indicated by biotite coated fractures cataclasites and injection of non cohesive polymineralic gouge material into secondary fractures inside the host rock the embrittlement during predominant ductile deformation occurs in cycles i e prolonged periods of slow viscous granular flow are interrupted by rapid brittle deformation we interpret this fluid assisted cyclic embrittlement evidenced by injection of the fluidized material into off fault fractures as an alternative equivalent to pseudotachylites and as a microstructural indicator for paleo seismic activity with exhumation and associated cooling localized deformation persists in the ultrafine grained polymineralic shear zones but progressively transitions to cataclastic flow and finally to pressure dependent frictional flow always showing cycles of slow interseismic flow and fast seismic injection events overall in the granitic crust of the aar massif brittle and ductile deformation coexist up to deformation temperatures of minimum 450 c indicating that the fvt has to be placed in a rather wide range from 8 km up to 18 20 km in the granitoid crust

the modern foreland basin system adjacent to the central andes regional variations in sediment thickness internal structures average elevation and bouguer gravity define a four component foreland basin system adjacent to the central andes in the most proximal part of the foreland basin system the eastern subandean zone and westernmost chaco plain 1 3 km of cenozoic deposits overlies active folds and thrusts of the frontal andean orogenic wedge these wedge top deposits pass cratonward into a foredeep depozone containing a 3 4 km thick sedimentary prism that tapers toward and locally pinches out against a broad wavelength forebulge in the central eastern chaco plain the forebulge is underlain by precambrian mesozoic rocks and is largely covered by a thin veneer of quaternary alluvium east of the forebulge a thin 0 5 km saucer shaped accumulation of sediment beneath the pantanal wetland represents a back bulge depozone ancient counterparts of these four depozones can be identified in the central andes suggesting that modern basin architecture is the result of continuous eastward migration of the coupled orogenic wedge and foreland basin system since the late cretaceous paleocene