quantitative constraints on the sea level fall that terminated the littorina sea stage southern scandinavia abstract the island of anholt in the kattegat sea southern scandinavia is made up largely of an extensive beach ridge plain as a result of post glacial uplift the earliest beach ridge and swale deposits are now raised 8 9 m above present mean sea level it appears that growth of the plain has been almost uninterrupted over the past 7500 years here we constrain the evolution of this plain between 6300 and 1300 years ago using optically stimulated luminescence dates the topography and internal architecture of the fossil shoreline deposits were measured on high resolution maps and in ground penetrating radar gpr reflection data with a vertical resolution of 0 25 m shoreline topography shows significant changes with time and it appears that one of the most striking changes took place between 4300 and 3600 years ago in the shoreline deposits corresponding to this time interval the surface drops by around 3 5 m suggesting a marked fall in relative sea level assuming a constant uplift rate of 1 2 mm yr the corresponding drop in absolute sea level is estimated to be around 2 6 m this marked sea level fall in 700 years took place at the transition from the middle holocene thermal maximum to the late holocene thermal decline or at the end of the littorina sea stage in the baltic sea region

current stress state and principal stress rotations in the vicinity of the chelungpu fault induced by the 1999 chi chi taiwan earthquake 1 we carried out various stress measurements in boreholes penetrating the northern segment of the chelungpu fault drilled about 5 years after the 1999 chi chi taiwan earthquake in the possible depth range of the chelungpu fault three major fault zones were encountered clearly recognizable principal stress rotations in the vicinity of the shallowest major fault zone at 1133 m depth in hole b suggest that this fault zone ruptured during the 1999 earthquake moreover the fault s rupturing altered the stress state in the area surrounding this fault zone in this paper we constrain the possible magnitudes of the current principal horizontal stresses around the fault zone and show that the current stress state belongs to a normal or strike slip fault regime therefore the stress state was changed from that of a reverse fault regime by the rupturing

the present rate of uplift of fennoscandia implies a low viscosity asthenosphere the rate of displacement in fennoscandia has been intensively discussed for many years it is now widely accepted to be an isostatic response of the glacial history of the area the earth s present response to deglaciation in fennoscandia is simulated using a three dimensional 3d viscoelastic model in which the asthenosphere and mantle viscosity are allowed to vary so that the maximum rate of present uplift matches its observed value the deglaciation history is considered to be known and the c14 datings are converted to sidereal years the pattern of the present uplift gives a firm match with the observed data when a low viscosity asthenosphere is introduced assuming a 15 000 years load cycle i e the glacier was applied to the surface for 15 000 years before the melting started the best fitting earth viscosity model is a 1024 nm lithosphere overlying a 75 km thick 2 0 1019 pas asthenosphere and a 1 2 1021 pas mantle the simulations suggest a remaining maximum uplift of 40 m

brittle failure mode plots for compressional and extensional tectonic regimes abstract equations governing different macroscopic modes of brittle rock failure extensional fracturing extensional shear fracturing compressional shear failure and reshear of existing faults can be represented on plots of differential stress vs effective vertical stress for a set of material properties such plots can be constructed for different tectonic regimes and correlated to depth for particular fluid pressure conditions allowing easy evaluation of the physical controls on brittle rock failure and ready comparison of the fields occupied by the three failure modes in different tectonic settings they emphasize the relative ease in terms of differential stress and fluid pressure levels of deforming a rock mass by brittle fracturing and faulting in extensional regimes compared with compressional aside from their relevance to general structural mechanics these generic failure plots have wide ranging application to understanding the initial development and progressive evolution of fault fracture systems both in sedimentary basins and as hosting structures for hydrothermal mineralization in different tectonic settings

fabric and anisotropy of slates from classical studies to new results abstract slates are low grade metamorphic argillaceous rocks which have developed an intense tectonic fabric referred to as slaty cleavage due to their unique properties they have long been used as building materials especially tiles for roofs and floors the fabric characterized by strong alignment of platy phyllosilicate crystals produces extreme anisotropy that has been of great interest in structural geology what different fabric types are observed how do they form here we review crystal preferred orientation cpo and add new information to establish a comprehensive base for future studies slates are composed of fine grained phyllosilicates dominantly white mica and chlorite sometimes chloritoid quartz and accessories texture analyses of these polyphase rocks with high energy synchrotron x ray diffraction and high resolution ebsd reveal strong alignment of mica and chlorite in some cases exceeding any previously reported texture strength including metals interestingly the cpo of quartz with highly flattened grains shape preferred orientation or spo is practically random recrystallization microstructures observed by scanning electron microscopy suggest that the phyllosilicate preferred orientation is largely caused by crystal growth under stress and that quartz was subject to pressure solution and reprecipitation producing an anisotropic shape while phyllosilicates preferred orientation in slates is much higher than reports for shale schists and gneiss elastic seismic anisotropy for slates is similar to shales where a significant component is due to aligned porosity

vein mineralization at the damang gold mine ghana controls on mineralization abstract two distinct styles of au mineralization occur at the damang gold mine palaeoproterozoic sediments of the tarkwaian group host both one style of mineralization is stratabound within quartz lithic conglomerates of the banket series the second style of mineralization is associated with an extensive low displacement fault fracture mesh that formed in a compressional stress regime late in the deformational history and after the peak metamorphism regional deformation within the tarkwaian involved initial nw se directed shortening d 1 a major nne trending f 1 anticline hosts the damang orebody broadly n s shortening during d 2 resulted in the formation of e w trending thrusts with small displacements the d 3 shortening direction was similar to that of d 1 steep d 1 faults were reactivated and a new set of low angle thrusts and associated flat lying extension veins were formed the bulk of the mineralization observed at damang is associated with the low displacement d 3 fault fracture mesh the presence of flat lying extensional veins and the reactivation of some misoriented d 1 structures is indicative of periodic episodes of supralithostatic fluid pressures low differential stress and fault valve behavior towards the end of the deformation history

interpreting fold and fault geometries from within the lateral to oblique parts of slumps a case study from the anglo brabant deformation belt belgium abstract using a rigorous comparison of as many slump fold based and slump related fault based methods as possible also small complex data sets can be used to deduce a reliable slump transport direction and sense this is exemplified using late early ordovician to middle ordovician slump features of the anglo brabant deformation belt the suggested procedure involves a an analysis of fold data by means of 1 the mean axis method 2 the separation arc method 3 the axial planar intersection method 4 the fold hinge azimuth and interlimb angle method 5 the fold axial surface strike and interlimb angle method and 6 the axial surface dip and dip direction method b an analysis of slump related fault data by means of 1 the mean fault orientation method 2 the fault separation method 3 the fault intersection method and 4 the best fit girdle to fault poles method and finally c a rigorous comparison of the results of the different methods several possible diagnostic criteria are put forward for distinguishing slump deformation features trending at low angles to transport direction oblique to lateral parts of slump sheets or internal lobes or tongues and slump deformation features trending at high angles to transport direction frontal to central parts of slump sheets these criteria include the relationship between fold interlimb angle and axial surface dip the plunge of the fanning axis of the reverse slump related faults and the plunge of the intersection of the reverse and normal slump related faults such criteria greatly facilitate the interpretation of the often confusing results of many classical methods moreover the plunge azimuth of the intersection of the normal and reverse slump related faults and the mismatch between slump transport direction inferred from fold based and fault based methods may both be diagnostic for dextrally deformed or sinistrally deformed slump sheet parts

determination of three dimensional in situ stresses by anelastic strain recovery in wenchuan earthquake fault scientific drilling project hole 1 wfsd 1 abstract the wenchuan earthquake fault scientific drilling project was implemented rapidly after the great 12 may 2008 earthquake mw 7 9 to better understand rupture mechanisms of the seismic faults the first borehole of the project wfsd 1 was located in hongkou township dujiangyan city sichuan province china on the hanging wall of the yingxiu beichuan fault which underwent large dextral and vertical displacement during the earthquake the near vertical borehole was 1201 m long in situ stresses were measured in rock samples from depths between 424 and 1173 m drilling depth by the anelastic strain recovery asr method the average trend of the maximum principal stress 1 was n309 ranging from n291 to n325 rotated with increasing borehole depth from nw se to wnw ese the magnitude of the in situ maximum principal stress was estimated to be 35 3 mpa at the depth of 1173 m the relations between horizontal and vertical stresses are vertical stress v maximum horizontal stress h minimum horizontal stress h at depths above 424 m h h v at depths from 424 m to 800 m and h v h below the depth of 800 m these indicate that the stress states are in a normal faulting stress regime above 424 m a reverse faulting regime from 424 m to 800 m and a dextral strike slip regime below 800 m the stress measurements from wfsd 1 are consistent with the focal mechanism solution in which the mainshock was dominated by thrusting accompanied by dextral strike slip motion the orientations of 1 are roughly consistent with the tectonic displacement direction of the longmenshan area which provides further evidence of nw se movements representing compression of the songpan ganzi block toward the sichuan basin

scale matters the influence of structural inheritance on fracture patterns abstract fracture systems are often geometrically invariant across a range of scales but the impact of structural inheritance on this relationship is poorly understood this paper shows how fracture orientations in sedimentary rocks vary at different scales when influenced by pre rift basement structures we use high resolution unmanned aerial vehicle uav orthophotos to map folds and fractures in the basement and cover rocks of the gippsland basin southeast australia outcrop scale observations are compared with 1 km long faults previously interpreted from potential field data we use length coloured rose diagrams of fracture traces to compare trends in fracture orientations early cretaceous syn rift normal faults exhibit the same ene wsw trend at basin 1 km and outcrop meters scales pervasive outcrop scale subvertical nnw sse striking joints record a subsequent regional shortening event but at the basin scale this is only expressed as reverse reactivated ene wsw striking faults thus fabrics and or faults in the underlying basement exert significant control on the orientation of basin scale fractures in the cover but appear to have limited influence on outcrop scale fracture orientations our observations show that fracture systems influenced by structural inheritance are not scale invariant and that a proper understanding of structural architecture can only be achieved by analysing data that span multiple scales

anisotropy pore fluid pressure and low angle normal faults low angle normal faults lanfs are commonly associated with high angle normal faults high pore fluid pressures and foliated fault cores explanations for lanf slip based on high pore fluid pressure critically depend on stress rotations in the fault core zone which have been based on an assumption of isotropy anisotropy fundamentally changes the coupling between pore fluid pressure and effective stress the response of saturated fault core rocks in lanfs can be explored by combining the effective medium theory with anisotropic poroelasticity the nucleation and evolution of lanfs are investigated in a framework of local changes in rock properties and the interaction of a pressurised pore fluid with intrinsic lithological and extrinsic damage anisotropies this quantitative approach enables comparison with detailed field and laboratory measurements of fault rock properties

structural setting of the 2008 mw 7 9 wenchuan china earthquake the 2008 m w 7 9 wenchuan earthquake ruptured an imbricate thrust system in the longmen shan range which forms the eastern boundary of the tibetan plateau we use seismic reflection data and surface geology to construct geologic cross sections and a three dimensional 3d fault model in the range front the rupture was complex with slip on both the steeply dipping beichuan fault and the more shallowly dipping pengguan fault which appear to merge at depth in contrast only the beichuan fault ruptured in the north with the transition near a lateral fault offset thus the earthquake involved multiple thrust splays and breached a significant segment boundary to investigate the tectonic setting of the earthquake we extend our previous measurements of crustal shortening hubbard and shaw 2009 into the interior of the range and show that shortening correlates with topography this suggests that upper crustal shortening can produce the high topography of the longmen shan without calling on other uplift mechanisms based on this understanding we model the thrust belt as a critical taper wedge to assess what rock and fault strengths are required to explain the topographic slopes within the range front and basin the low taper within the basin is consistent with a weak detachment f 0 1 while a slightly stronger f 0 3 0 4 detachment is necessary to explain the higher taper of the range front this difference may relate to the localization of the detachment within a triassic evaporite sequence within the basin while the faults beneath the range front are rooted in precambrian metasedimentary or igneous rocks critical taper theory implies that shortening in the range front where the 2008 wenchuan earthquake occurred is many times greater than in the basin consistent with our shortening measurements we examine the implications of these findings for seismic hazard assessment in the region and in other active mountain belts around the world

are open fractures necessarily aligned with maximum horizontal stress abstract fluid flow in fractured rock is an increasingly central issue in recovering water and hydrocarbon supplies and geothermal energy in predicting flow of pollutants underground in engineering structures and in understanding large scale crustal behaviour conventional wisdom assumes that fluids prefer to flow along fractures oriented parallel or nearly parallel to modern day maximum horizontal compressive stress or s hmax the reasoning is that these fractures have the lowest normal stresses across them and therefore provide the least resistance to flow for example this view governs how geophysicists design and interpret seismic experiments to probe fracture fluid pathways in the deep subsurface contrary to these widely held views here we use core stress measurement and fluid flow data to show that s hmax does not necessarily coincide with the direction of open natural fractures in the subsurface 3 km depth consequently in situ stress direction cannot be considered to predict or control the direction of maximum permeability in rock where effective stress is compressive and fractures are expected to be closed chemical alteration dictates location of open conduits either preserving or destroying fracture flow pathways no matter their orientation

origin of dinantian zebra dolomites south of the brabant wales massif belgium zebra dolomites characterized by a repetition of dark grey a and light b coloured dolomite sheets building up abbabba sequences occur in dinantian strata from deep boreholes 2000 m south of the brabant wales massif in belgium these zebra dolomite sequences are several tens of metres thick the dark grey dolomite sheets a consist of non planar crystals 80 150 m in diameter these crystals display a mottled red orange luminescence and are interpreted to be replacive in origin the white dolomite sheets b consist of coarse crystalline nonplanar b1 dolomite which evolves outwards into transparent saddle shaped b2 dolomite the b1 dolomites possess a mottled red orange luminescence similar to the a dolomites while the saddle shaped b2 rims display red to dark brown luminescent zones the b1 dolomites are possibly partly replacive and partly cavity filling their b2 rims display criteria typical for a cement origin locally cavities exist between two succeeding white dolomite sheets these cavities make up 5 of the zebra rocks and are locally filled by saddle shaped ankerite and or xenomorphic ferroan calcite geochemical and fluid inclusion data th 120 c indicate a burial diagenetic origin for these zebra dolomites the a and b1 dolomites are characterized by similar geochemical compositions and fluid inclusion data pointing toward a related origin to explain the development of the zebra textures suprahydrostatic pressures in conjunction with late variscan tectonic compression are invoked a model involving dolomitizing fluids expelled during the variscan orogeny is proposed an overpressured system is also invoked to explain the important porosity development the creation of centimetre scale subvertical displacements of the zebra pattern and the microfractures affecting the b1 b2 dolomite crystals

the boudinage question in the high ardenne slate belt belgium a combined structural and fluid inclusion approach abstract the terms boudin and boudinage 1 were first introduced as descriptive terms for particular geometric features associated with quartz veins in competent metaquartzitic layers in the high ardenne slate belt belgium the occurrence of the boudins has subsequently been used to draw kinematic conclusions on a pre variscan extensional event in the rhenohercynian belt in this paper a combined structural and fluid inclusion approach allows proposing a new and more representative kinematic model for the development of the veins and associated structures moreover the kinematic significance of interboudin veins is emphasized in this regard microthermometry of primary co 2 n 2 fluid inclusions in the quartz of the interboudin veins suggests that the origin of vein development is hydraulic fracturing in an already compressional setting this suggestion implies the presence of fluid and near lithostatic fluid pressures to permit fracturing at great depths where the rocks otherwise would be either stable or in the realm of ductile behaviour the vein filling fluid had a local origin and was most likely related to the formation of bedding parallel dissolution seams within the host rock veining is followed by layer parallel shortening resulting in the development of double sided mullions at both interfaces of metaquartzitic layers pinned by pre existing veins subsequently these polyphase structures behave passively in the variscan deformation

vein reactivation and complex vein intersection geometries in the taconic slate belt abstract this paper describes some complex intersection geometries for veins in the taconic slate belt of western new england u s a the complexity is primarily a result of the preferential reactivation during slaty cleavage development of one set of veins within an orthogonal system of pre cleavage veins the relative age of the precleavage veins also influences the intersection geometry in that the non reactivated veins which form the younger set of pre cleavage veins act as barriers to the propagation of the syn cleavage veins these types of intersection geometries are easily misinterpreted without microscale observations of vein textures and may be more common than is currently appreciated

determination of three dimensional in situ stresses from anelastic strain recovery measurement of cores at great depth in order to examine whether the anelastic strain recovery asr method can be applied for determining the in situ stress in hard rocks at great depths the anelastic strain recovery of oriented cores was measured in six independent directions the core specimens were taken from four depths within the range of about 2400 4500 m md at the meti niitsu well in japan the rock materials were mudstone dolerite basalt and andesite for all the rocks the expansional anelastic strains were obtained the magnitude of the strains in various directions continuously measured for 1 or 2 weeks was of the order of 1000 10 6 in mudstone in contrast strains of the other cores did not exceed a few hundred microstrains these strains were used for a three dimensional analysis of the principal in situ stresses at the third depth the principal stress directions were considered to be affected by fractures pre existing near the core and showed the features of a very local stress state with the exception of this data the directions determined by the asr method were in agreement with those determined using other in situ measurement methods based on two assumptions i e i the rock stress in vertical direction is equal to density related gravitational overburden stress ii the ratio of anelastic strain recovery compliance of shear deformation mode and the compliance of volumetric deformation mode is equal to 2 the values of the three principal stresses were estimated the values of the minimum principal stress in the plane perpendicular to the well axis determined in this study were in agreement with those determined based on extended leak off tests elot or xlot conducted at the same well therefore it can be said that the asr method is well suited for use in directly determining the directions of principal in situ stresses in three dimensions and in estimating the magnitude of the stresses in isotropic rocks at great

the effects of plate margin inhomogeneity on the deformation pattern within west central zagros fold and thrust belt abstract zagros folded and thrust belt zftb is a cenozoic mountain belt in ssw of iran and northeast of arabia that resulted from closure of neo tethys and collision between arabia passive margin and central iran active margin at this tectonic grain of alp himalayan chain change of the tectonic regime degree of basement involvement and character of accommodation of the deformation in time and space has been under debate the results show that the deformation along the zagros is not uniformly accommodated although the researchers have already paid attention to basement involvement in addition to the sedimentary cover rocks little has been shown on the role of the basement s rigidity and lower crust s rheology on the deformation pattern along and across the belt this study tries to address these questions in terms of inversion of slip vector of basement earthquakes measurement of fault slip data on the cover rocks geomorphic and field observations and existing geodetic and gravity data with especial focus on dezful embayment and surrounding area the results show the dezful embayment plays an indenter role it with the other reentrants changes the obliquity of arabian plate convergence facilitates the escape of the upper crust toward free mechanical boundaries in salients controls the slip rate of zagros main recent fault at the rear of the belt and contributes in forming zagros fold and thrust belt as an orocline the viscous lower crust helps the strain partitioning by providing a ductile shear base under the rigid upper crust

a first step to reconciling the grip and gisp2 ice core chronologies 0 14 500 yr b p abstract 18o records from the gisp2 and grip ice cores are widely used as benchmark paleoclimate chronologies but there are significant differences between the two time scales the present study shows that offsets between the two chronologies over the past 14 500 yr do not accumulate gradually but appear over two short intervals of 100 200 yr an initial offset of 80 yr occurs close to 3300 3400 yr b p and another 100 yr of slip appears at the start of the younger dryas since these discrepancies are localized resolving them may be far easier than if large sections of both cores required reexamination

high resolution geological mapping towards an understanding of post glacial development and holocene sedimentation processes in the eastern gulf of finland an emodnet geology case study

geology and archaeology submerged landscapes of the continental shelf an introduction sea level change has influenced human populations globally since prehistoric times even in early phases of cultural development human populations were faced with marine regression and transgression associated with the glacial interglacial climatic cycle amplified by glacio isostatic adjustments in some regions global marine regression during the last glaciation changed the palaeogeography of the continental shelf converting former marine environments to attractive terrestrial habitats for prehistoric human occupation and adding an extensive new increment of land in the case of europe amounting to an additional 40 of the existing land area and on a global scale to some 20 million km of additional territory that is now submerged these areas of the shelf were used as hunting and gathering areas and as pathways of dispersal between regions and between continents until they were resubmerged by the post glacial marine transgression they also most probably witnessed the earliest developments in seafaring marine exploitation and permanent settlements based on modern marine research technologies and the integration of large databases proxy data are now becoming available for the reconstruction of these submerged quaternary landscapes concerted efforts are also now being devoted to the search for prehistoric archaeological sites and artefacts on the seabed often in collaboration with marine scientists this search has been stimulated by the increasing amount of material that has demonstrably survived inundation often with excellent preservation of organic remains by closer collaboration with offshore industry and by the growing realization of the importance of these submerged data for understanding human prehistoric developments during periods of rapidly changing climate and environment moreover these new research trends are not simply being driven by an archaeological need for scientific and technological input from other disciplines but by collaborations involving genuine mutual benefit in which all partners have something to gain archaeological problems often pose new questions about geological change stimulating new techniques of observation new technologies and new investigations which in their turn can offer new data often at higher resolution and with better dates in relation to geological and environmental issues such as sea level change and palaeoclimatic variability on the continental shelf the expansion of early human populations to occupy new territory and new continents is one of the great narratives of human evolution it is currently a theme of wide interest and topicality and has received significant impetus and publicity from the new science of palaeogenetics together with ongoing discoveries of new fossil and archaeological material and new studies of palaeoclimate and palaeoenvironment the field itself is rapidly expanding leading to new discoveries and new controversies grine et al 2009 gamble 2013 smith ahern 2013 all the current indications are that the human species originated in africa with at least two major episodes of dispersal the earliest some time after about 2 myr ago led to the expansion of homo ergaster erectus populations across southern europe and asia extending from britain in the west to china and indonesia in the east and south the second involved our own species homo sapiens anatomically modern humans or amh and took place some time after about 200 ka this resulted in the replacement of earlier hominin populations in europe and asia and expansion further afield into new guinea and australia certainly involving sea crossings over distances of at least 50 km by about 50 ka to the higher latitudes of northern eurasia with entry into the americas by at least 15 ka and into new territory exposed by the melting of the northern hemisphere ice sheets less than 10 kyr ago anthropological and archaeological investigations of these processes are directly connected

pre and synorogenic burial metamorphism in the ardenne and neighbouring areas rhenohercynian zone central european variscides abstract the rhenohercynian zone of the central european variscides contains in the central ardenne eifel brabant campine region of belgium france germany and luxemburg an omnipresent thermal overprint which reaches in places uppermost epizonal conditions because of its distribution and structural relationships this metamorphism cannot be explained by a singular tectonometamorphic event field and microstructural observations new illite crystallinity and other data relating to this metamorphism are presented together with a review of existing petrological illite crystallinity vitrinite reflectance conodont alteration index and fluid inclusion data and their relationship to small and regional scale geological structures three distinct geotectonic situations can be described which overlap and alternate in space and time 1 the oldest metamorphism which reached epizonal conditions can be localized in the pre devonian basement rocks of the brabant massif and with minor evidence of the stavelot massif further south it is clearly related to a pre variscan caledonian deformation event and could be of burial origin 2 the main regional metamorphism affected all devonian and carboniferous rocks and the lower palaeozoic basement highs of the ardenne eifel area it does not exceed diagenetic conditions in some areas but reaches maximal values of 500 c and 400 mpa in the serpont and rocroi massif areas theye and fransolet 1993 robion et al 1995 it is pre to synkinematic to the main variscan contractional penetrative deformation and correlates well with the age and thickness of the sedimentary cover rocks the metamorphism is associated with the pre carboniferous preorogenic rifting stage of the rhenohercynian basin and documents the peak of subsidence and sediment accumulation we interpret it as diastathermal metamorphism it reaches its maximum in the low grade metamorphic zones of the ardenne area which are inverted synsedimentary structures 3 the diastathermal metamorphism is overprinted in the central part of the ardenne eifel area middle devonian to carboniferous rocks of the dinant synclinorium by an anchizonal beginning epizonal metamorphism in the foreland basins north of the midi fault zone it reaches diagenetic to lowermost anchizonal conditions it is the expression of the burial by thick synorogenic mid to upper carboniferous cover rocks which were deposited in piggyback and foreland basins this clastic wedge relates to the carboniferous contraction of the rhenohercynian basin whose metamorphosed rocks were themselves affected by the deformation of the advancing orogenic front

global positioning system measurements from eastern tibet and their implications for india eurasia intercontinental deformation we present and interpret global positioning system gps measurements of crustal motions for the period 1991 1998 for a network encompassing the eastern part of the tibetan plateau and its foreland relative to a eurasian frame defined by minimizing the velocities of 16 gps stations in europe central asia and siberia stations within all parts of the plateau foreland in south china move 6 10 mm yr east southeast indicating that the eastward movement within the plateau is part of a broader eastward movement that involves the plateau and its eastern and northern foreland north of the plateau foreland stations move northeastward at 10 mm yr indicating that the northern boundary of the deformation zone lies north of the plateau with this realization of a eurasian frame the velocity of the gps station at bangalore in southern india implies that the northward motion of india is 5 12 mm yr slower than that predicted from the nuvel 1a plate reconstruction viewed relative to the south china block stations of the northeast plateau bounded on the north by the qilian shan and the altyn tagh fault move nne to ne with velocities ranging from 19 mm yr within the plateau to 5 11 mm yr in its foreland the altyn tagh fault shows left lateral slip of 10 mm yr at 95 e and shortening across the fault of 5 mm yr stations south and west of the xianshuihe xiaojiang fault system define a crustal fragment rotating clockwise at 10 mm yr relative to the south china block around the eastern himalayan syntaxis the gps measurements indicate no significant shortening 3 mm yr within the longmen shan of the central eastern plateau and its adjacent foreland although the longmen shan rise over 6 km in 100 km horizontal distance geological studies indicate that the deformational field was established diachronously in late miocene to pliocene time was characterized by no east west shortening of tibetan crust and has an inhomogeneous style of deformation resulting from a balance of different tectonic processes

lithology dependent minimum horizontal stress and in situ stress estimate abstract based on the generalized hooke s law with coupling stresses and pore pressure the minimum horizontal stress is solved with assumption that the vertical minimum and maximum horizontal stresses are in equilibrium in the subsurface formations from this derivation we find that the uniaxial strain method is the minimum value or lower bound of the minimum stress using anderson s faulting theory and this lower bound of the minimum horizontal stress the coefficient of friction of the fault is derived it shows that the coefficient of friction may have a much smaller value than what it is commonly assumed e g f 0 6 0 7 for in situ stress estimate using the derived coefficient of friction an improved stress polygon is drawn which can reduce the uncertainty of in situ stress calculation by narrowing the area of the conventional stress polygon it also shows that the coefficient of friction of the fault is dependent on lithology for example if the formation in the fault is composed of weak shales then the coefficient of friction of the fault may be small as low as f 0 2 this implies that this fault is weaker and more likely to have shear failures than the fault composed of sandstones to avoid the weak fault from shear sliding it needs to have a higher minimum stress and a lower shear stress that is the critically stressed weak fault maintains a higher minimum stress which explains why a low shear stress appears in the frictionally weak fault

fluid evolution during burial and variscan deformation in the lower devonian rocks of the high ardenne slate belt belgium sources and causes of high salinity and c o h n fluids fluid inclusions in quartz veins of the high ardenne slate belt have preserved remnants of prograde and retrograde metamorphic fluids these fluids were examined by petrography microthermometry and raman analysis to define the chemical and spatial evolution of the fluids that circulated through the metamorphic area of the high ardenne slate belt the earliest fluid type was a mixed aqueous gaseous fluid h2o nacl co2 ch4 n2 occurring in growth zones and as isolated fluid inclusions in both the epizonal and anchizonal part of the metamorphic area in the central part of the metamorphic area epizone in addition to this mixed aqueous gaseous fluid primary and isolated fluid inclusions are also filled with a purely gaseous fluid co2 n2 ch4 during the variscan orogeny the chemical composition of gaseous fluids circulating through the lower devonian rocks in the epizonal part of the slate belt evolved from an earlier co2 ch4 n2 composition to a later composition enriched in n2 finally a late variscan aqueous fluid system with a h2o nacl composition migrated through the lower devonian rocks this latest type of fluid can be observed in and outside the epizonal metamorphic part of the high ardenne slate belt the chemical composition of the fluids throughout the metamorphic area shows a direct correlation with the metamorphic grade of the host rock in general the proportion of non polar species i e co2 ch4 n2 with respect to water and the proportion of non polar species other than co2 increase with increasing metamorphic grade within the slate belt in addition to this spatial evolution of the fluids the temporal evolution of the gaseous fluids is indicative for a gradual maturation due to metamorphism in the central part of the basin in addition to the maturity of the metamorphic fluids the salinity of the aqueous fluids also shows a link with the metamorphic grade of the host rock for the earliest and latest fluid inclusions in the anchizonal part of the high ardenne slate belt the salinity varies respectively between 0 and 3 5 eq wt nacl and between 0 and 2 7 eq wt nacl while in the epizonal part the salinity varies between 0 6 and 17 eq wt nacl and between 3 and 10 6 eq wt for the earliest and latest aqueous fluid inclusions respectively although high salinity fluids are often attributed to the original sedimentary setting the increasing salinity of the fluids that circulated through the lower devonian rocks in the high ardenne slate belt can be directly attributed to regional metamorphism more specifically the salinity of the primary fluid inclusions is related to hydrolysis reactions of cl bearing minerals during prograde metamorphism while the salinity of the secondary fluid inclusions is rather related to hydration reactions during retrograde metamorphism the temporal and spatial distribution of the fluids in the high ardenne slate belt are indicative for a closed fluid flow system present in the lower devonian rocks during burial and variscan deformation where fluids were in thermal and chemical equilibrium with the host rock such a closed fluid flow system is confirmed by stable isotope study of the veins and their adjacent host rock for which uniform 180 values of both the veins and their host rock demonstrate a rock buffered fluid flow system

fracture networks and strike slip deformation along reactivated normal faults in quaternary travertine deposits denizli basin western turkey abstract the denizli basin in the west anatolian extensional province in western turkey is known for its numerous quaternary travertine occurrences travertine morphology is often dependant on the relative position of the deposition with respect to basin bounding faults the travertine occurrences examined in this study are situated at the intersection of the locally e w oriented denizli basin and the adjacent ne sw oriented baklan graben in the ne based on an extensive field campaign including lidar scanning several high resolution fault fracture maps of five large quarries 300 m in length and 60 m in height are constructed in which this world class travertine deposit is currently excavated a structural analysis is performed in order to determine the tectonic overprinting of the travertine body and to derive the stress states of the basin after travertine deposition the mostly open non stratabound joints are several tens of metres long and often bifurcate creating a dense fracture network minor infill of the joints resulted in the presence of a few colour banded calcite veins based on the e w ne sw and nw se orientation of three dominant joint sets it is concluded that the joint network is caused by local n s extension alternated by nw se and ne sw extension exemplifying the presence of stress permutations in the quaternary high angle e w to wnw ese faults cross cut the quarries faults are filled with travertine debris and clastic infill of above lying sedimentary units indicative of the open nature of the faults the specific e w fault orientation in the locally e w trending denizli basin indicates that they initiated as normal faults a paleostress inversion analysis performed on kinematic indicators such as striations on the clayey fault infill and the sinistral displacement of paleosols shows that some of the normal faults were reactivated causing left lateral deformation in a transient strike slip stress field with a ne sw oriented 1

characteristics of the fault related rocks fault zones and the principal slip zone in the wenchuan earthquake fault scientific drilling project hole 1 wfsd 1 abstract scientific drilling in active faults after a large earthquake is ideal to study earthquake mechanisms the wenchuan earthquake fault scientific drilling project wfsd is an extremely rapid response to the 2008 ms 8 0 wenchuan earthquake which happened along the longmenshan fault eastern margin of the tibetan plateau in order to better understand the fault mechanism and the physical and chemical characteristics of the rocks the wfsd project will eventually drill 5 boreholes along the two main faults this paper focuses on the first hole wfsd 1 which started just 178 days after the earthquake down to a final depth of 1201 15 m petrological and structural analyses of the cores allowed the identification of fault related rocks in the yingxiu beichuan fault fault gouge cataclasite and fault breccia and the principle slip zone psz location of the wenchuan earthquake was determined we found 12 fault zones in the entire core profile with at least 10 including the yingxiu beichuan fault zone with a multiple cores structure and minimum width of 100 m the co seismic slip plane of the wenchuan earthquake at depth corresponding to the yingxiu beichuan fault zone at the outcrop as well as its psz was expected to be located at the bottom of the fault zone at 759 m depth instead it was found at 590 m depth with 1 cm wide fresh fault gouge as determined by logging data such as temperature natural gamma ray p wave velocity and resistivity combined with the fresh appearance magnetic susceptibility and microstructure of the gouge the wenchuan earthquake slip plane has a dip angle of 65 showing the high angle thrust feature the distribution of fault gouge with several meters thick the location of the wenchuan earthquake s psz and the thickness of fresh gouge all imply a correlation between the width of the fault zone and the number of seismic events

stress state evolution of the brittle upper crust during compressional tectonic inversion as defined by successive quartz vein types high ardenne slate belt germany abstract in the frontal part of the rhenohercynian fold and thrust belt high ardenne slate belt germany two successive types of quartz veins oriented normal and parallel to bedding respectively are interpreted to reflect the early variscan compressional tectonic inversion of the ardenne eifel sedimentary basin fracturing and sealing occurred in lower devonian siliciclastic multilayers under very low grade metamorphic conditions in a brittle upper crust a geometrical and microthermometric analysis of these veins has helped to constrain the kinematic and pressure temperature conditions of both vein types allowing the reconstruction of the stress state evolution in a basin during tectonic inversion it is demonstrated that bedding normal extension veins which developed under low differential stresses and repeatedly opened and sealed crack seal under near lithostatic fluid pressures reflect the latest stage of an extensional stress regime bedding parallel veins which developed at differential stresses that were still low enough to allow the formation of extension veins cross cut the bedding normal veins and preceded the regional fold and cleavage development these veins show a pronounced bedding parallel fabric reflecting bedding normal uplift and bedding parallel shearing under lithostatic to supra lithostatic fluid pressures during the early stages of a compressional stress regime this kinematic history corroborates that fluid overpressures are easy to maintain during compressional tectonic inversion at the onset of orogeny

pleistocene holocene tectonic reconstruction of the ballik travertine denizli graben sw turkey de formation of large travertine geobodies at intersecting grabens abstract travertine geobodies have been identified as potential reservoir analogues to carbonate build ups in pre salt hydrocarbon systems to investigate travertine geobody deformation faults were mapped in 35 travertine quarries that excavate the ballik travertine i e a c 12 5 km2 large travertine geobody that precipitated at the intersection of the ne margin of the denizli basin and neighbouring baklan graben sw turkey this travertine precipitated from cooling carbonate saturated thermal spring waters that resurfaced along the margin fracture fault network and through neogene unconsolidated underlying sediments from the denizli basin floor to the uplifted graben shoulders fault orientation is dominantly wnw ese oriented with major basin faults showing a left stepping trend along the upper denizli margin travertine is only deformed by extensional normal faults along the lower margin travertine starts with a subhorizontal facies but evolves to a travertine facies formed by a sloping topography with a domal architecture paleostress inversion of fault slip data reveals that an early pleistocene nne ssw extensional transtensional phase initiated the wnw ese oriented graben facing normal fault network in the middle pleistocene the ballik fault network was left lateral strike slip reactivated because it acted as a transfer zone between the nw se extending neighbouring baklan basin and nw se extension along ne sw oriented margin faults of the dghs in this stress configuration travertine precipitated along the sw margin fault of the baklan graben after strike slip reactivation a late pleistocene to current nne ssw extensional stress regime reinstalled during which margin faults widened and active travertine precipitation moved to more central parts of the dghs as different tectonic regimes affect graben intersections reservoir analogues can have a complex deformation history driven by fault reactivation and recurrent stress permutations this study concludes that large travertine geobodies can form at graben intersections because of their susceptibility to enhanced fluid flow through the complex fault fracture network

wellbore breakouts of the main borehole of chinese continental scientific drilling ccsd and determination of the present tectonic stress state abstract the sulu dabie high pressure hp ultrahigh pressure uhp metamorphic belt as the product of subduction collision between the northern china plate and yangtze plate underwent a process of formation and evolution from deep subduction exhumation extension slow uplift the study of its modern tectonic stress field has great significance for a complete understanding of the process of formation and evolution of the hp uhp metamorphic belt especially the exhumation and uplift of the belt wellbore breakouts are the most visual tectonic phenomenon which can characterize the modern stress action in the main borehole of chinese continental scientific drilling ccsd ultrasonic borehole televiewer reflection wave data show that wellbore breakouts began to occur at 1216 m depth of the main borehole a total of 143 borehole televiewer images were collected from 1216 to 5118 m depth hole completion depth after data processing and statistics the average azimuth of the long dimension of the wellbore breakout obtained was 319 5 3 5 indicating that the average azimuth of the maximum horizontal principal stress causing wellbore breakout initiation was 49 5 3 5 the maximum and minimum horizontal principal stress values at 52 depths in the interval of 1269 to 5047 m were estimated using the elements of wellbore shapes wellbore depth and width combined with the cohesive strength and internal frictional angle of the rock obtained by rock mechanical tests on samples and the static load stresses at corresponding depths were calculated according to the rock density logging data the results indicate that the maximum and minimum horizontal principal stresses are 41 4 and 25 3 mpa at 1269 m depth respectively and 164 7 and 122 mpa at 5047 m depth respectively the maximum vertical stress is 141 3 mpa at 5047 m depth with a density of 2 8 g cm 3 the in situ stresses increase nearly linearly with depth the magnitudes and directions of the three principal stresses reflect that the regional stress field around the ccsd main borehole is mainly in a strike slip state which is consistent with the basic features of the regional stress field determined using other methods

syn to late orogenic quartz veins marking a retrograde deformation path in a slate belt examples from the high ardenne slate belt belgium abstract an integrated structural petrographic and microthermometric methodology has been applied on syn to late orogenic quartz veins from the high ardenne slate belt belgium to define their relative timing the quartz precipitates which do not show any mutual cross cutting relationships represent the meso scale brittle accommodation during fold initiation amplification and locking crystal plastic deformation structures and p t trapping conditions indicate that the different processes accommodating folding occurred in a progressive manner along a retrograde deformation path associated with the gradual exhumation of the slate belt from ca 7 5 to 6 km depth successive veining occurred from peak metamorphic conditions ca 300 c and 190 mpa measured in extrados veins to subsequent lower p t conditions in the periphery of a lenticular vein ca 275 c and 180 mpa late orogenic saddle reef filling ca 245 c and 160 mpa and the core of a lenticular vein ca 220 c and 150 mpa open cavity growth and fluid assisted brecciation indicate that veining occurred under overpressured fluid conditions it is therefore fair to assume that the high ardenne slate belt acted at least episodically as a mid crustal overpressured fluid reservoir not only in the earliest and latest stages but also during the main stage of orogeny

late cenozoic evolution of the eastern margin of the tibetan plateau inferences from 40ar 39ar and u th he thermochronology high topography in central asia is perhaps the most fundamental expression of the cenozoic indo asian collision yet an understanding of the timing and rates of development of the tibetan plateau remains elusive here we investigate the cenozoic thermal histories of rocks along the eastern margin of the plateau adjacent to the sichuan basin in an effort to determine when the steep topographic escarpment that characterizes this margin developed temperature time paths inferred from 40 ar 39 ar thermochronology of biotite multiple diffusion domain modeling of alkali feldspar 40 ar release spectra and u th he thermochronology of zircon and apatite imply that rocks at the present day topographic front of the plateau underwent slow cooling 30 50 c m y coincident with exhumation from inferred depths of 8 10 km at denudation rates of 1 2 mm yr samples from the interior of the plateau continued to cool relatively slowly during the same time period 3 c m y suggesting limited exhumation 1 2 km however these samples record a slight increase in cooling rate from 1 to 3 c m y at some time during the middle tertiary the tectonic significance of this change remains uncertain regardless late cenozoic denudation in this region appears to have been markedly heterogeneous with the highest rates of exhumation focused at the topographic front of the plateau margin we infer that the onset of rapid cooling at the plateau margin reflects the erosional response to the development of regionally significant topographic gradients between the plateau and the stable sichuan basin and thus marks the onset of deformation related to the development of the tibetan plateau in this region the present margin of the plateau adjacent to and north of the sichuan basin is apparently no older than the late miocene or early pliocene 5 12 ma

antitaxial crack seal vein microstructures and their relationship to displacement paths abstract the microstructures developed in an example of a syntectonic crack seal vein indicate that antitaxial fibres do not necessarily track the incremental opening history during crack seal vein growth this observation serves as a caution against the uncritical use of fibrous microstructures to make inferences about displacement histories during fibre formation it is demonstrated that crack seal processes can lead to the development of both irregular and laminated vein microstructures as well as fibrous microstructures the types of microstructures which develop in crack seal veins and the extent to which they reflect the opening paths of veins depend on a range of factors the most important of these include the nucleation and growth kinetics of phases precipitated from fluids in opening fractures and the location of sites of material accretion during successive crack seal increments

coseismic reverse and oblique slip surface faulting generated by the 2008 mw 7 9 wenchuan earthquake china the mw 7 9 wenchuan china earthquake ruptured two large thrust faults along the long menshan thrust belt at the eastern margin of the tibetan plateau this earthquake generated a 240 km long surface rupture zone along the beichuan fault and an additional 72 km long surface rupture zone along the pengguan fault maximum vertical and horizontal offsets of 6 5 m and 4 9 m respectively were measured along the beichuan fault a maximum vertical offset of 3 5 m was measured along the pengguan fault coseismic surface ruptures integrated with aftershocks and industry seismic profiles show that two imbricate structures have ruptured simultaneously resulting in the largest continental thrust event ever documented large oblique thrusting observed during this earthquake indicates that crustal shortening is an important process responsible for the high topography in the region as everywhere along the edge of tibetan plateau

longmen shan fold thrust belt and its relation to the western sichuan basin in central china new insights from hydrocarbon exploration the longmen shan fold thrust belt is one of the key regions of demonstrable mesozoic cenozoic tectonic evolution in china and the sichuan basin was the first natural gas producing area in china in this article the structural features of the longmen shan belt are presented using both seismic profiles and field data the complex structures of the northeast trending longmen shan fold thrust belt and its foreland in the western sichuan basin are formed by southeast directed thrusting several eastward verging rootless thrust sheets and imbricates of cambrian triassic rocks have been recognized in the northern longmen shan belt evidence suggests that the northern longmen shan belt experienced at least two major periods of deformation in the late triassic and cenozoic however the southern longmen shan belt is represented by the basement involved thrust structures and klippen and its major periods of deformation were in the latest cretaceous early cenozoic sedimentary features in the western sichuan basin reflect a two phase flexural loading history and illustrate that the late triassic foreland basin extends along the foredeep of the entire length of the longmen shan belt but the uppermost cretaceous paleogene rejuvenated foreland basin is restricted in the southern part of the western sichuan basin structural geometries suggest that prospective traps are mainly developed in the frontal zone of the longmen shan fold thrust belt and in the southern part of the western sichuan basin one of the major contributions of this article is finding preexisting paleozoic rift basins under the cenozoic thin skinned thrust belts which represent a new potential hydrocarbon play

stress state differences between sedimentary cover and basement of the songliao basin ne china in situ stress measurements at 6 7 km depth of an icdp scientific drilling borehole sk ii abstract the stress state down to the basement within sedimentary basins yet remains poorly understood the anelastic strain recovery asr method was employed to measure the stress state in the sk ii borehole in the songliao basin northeast china the results show that the stress state differs significantly between the sedimentary cover and basement in the sedimentary cover 6296 6335 m the maximum principal stress 1 is nearly vertical which is in the normal faulting stress regime dominated by gravitation in accordance with the normal faults observed on seismic reflection profiles within the sedimentary cover in contrast the basement 6646 6846 m shows that 1 is nearly horizontal suggesting a strike slip or reverse faulting regime the stress state of the basement is close to the reasonable stress condition for the eurasian plate far from a western pacific plate subduction zone and consistent with the focal mechanisms of earthquakes 7 15 km in the vicinity of icdp sk ii borehole the difference of stress state may imply that the far field stress generated by the western pacific plate has limited effects on the sedimentary cover an increase in thickness correlates with an increasing influence of tectonic stress with depth

variscan transpressive inversion in the northwestern central rhenohercynian belt of western germany abstract important orogen parallel strike slip components during the convergence of the variscan orogen of central europe have been increasingly recognized these oblique slip faults often develop from pre existing tectonic boundaries and are influenced by pre existing structural trends in the basement in this paper evidence is presented for a 3 6 km wide distributed shear zone here named the monschau shear zone in epizone metamorphic cambro ordovician and lower devonian clastic rocks of the northwestern rhenohercynian belt kinematic indicators including field observations of anomalous mullion and fold axes patterns a set of two cleavages stretching lineations and shear and kink bands microscopical observations of stretching parallel asymmetric pressure shadows of quartz on prekinematic epizone metamorphic pyrite porphyroblasts and microfabrics of phyllosilicates by x ray texture goniometry point to a sinistral tranpressive shear zone with emplacement of the southeast hangingwall under retrograde conditions coincidence of the anchizone epizone metamorphic boundary with the change along strike from penetrative shearing to distributed thrusting suggests a ductile brittle transition the monschau shear zone is situated on the backlimb of an allochthonous anticlinorium located above a basement ramp that corresponds roughly to a pre orogenic synsedimentary normal fault its continuation shows up clearly in a dekorp seismic reflection profile to a depth of 12 15 km

fluid circulation in the upper brittle crust thickness distribution hydraulic transmissivity fluid inclusion and isotopic data of veins hosted in the oligocene sandstones of the macigno formation in southern tuscany italy abstract we present structural analysis fluid inclusion data on calcite and quartz and isotopic composition of calcite forming veins occurring in the upper crustal level and hosted in oligocene sandstone in southern tuscany italy the veins have been analysed in two sites few kilometres apart along well exposed coastal cliffs and in an abandoned quarry these two sites were at a different depths at the time of the vein formation with a h 100 m structural analysis of veins provided estimations of stress ratio 2 3 1 3 driving stress ratio r pf 3 1 3 and fluid overpressure po pf 3 at the time of vein formation the estimated po is in the range of 42 103 mpa 0 24 and r 0 45 indicating that fluid pressure was higher than the intermediate principal stress at the time of veins formation the veins thickness t shows a clear power law distribution d 1 8835 and r2 0 9762 in the lowermost site coast and a negative exponential distribution a 0 6943 and r2 0 9921 in the uppermost site abandoned quarry the vein thickness distributions have been used to compute the average transmissivity of the veins in the two sites the computed transmissivity for the vein formation is 10 4 m2 s 1 with higher values attained by the veins having negative exponential thickness distribution fluid inclusions studies highlighted that in both calcite and quartz water rich inclusions with salinities of 2 2 4 3 wt nacl equiv and methane rich inclusions were coevally trapped during fluid un mixing processes thermogenic origin from thermal maturation of organic matter present in the macigno formation is proposed for methane whereas the similarity between the 18o from 14 9 to 17 4 and 13c from 0 4 to 2 4 data of representative calcite veins and the isotopic composition 18o 16 1 13c 1 0 of host rock carbonate component indicates that the fluid which formed calcite was in isotopic equilibrium with the carbonates present in the oligocene sandstones the calculated pressure temperature conditions during the formation of these inclusions are prevalently within the 40 145 mpa and 160 260 c ranges the highest pressure values approximate the lithostatic pressure 120 mpa computed from geological data and are coherent with a geothermal gradient ranges of 35 45 c km whereas the lower pressure values are comparable with hydrostatic pressure conditions the pressure range indicated by fluid inclusion data is also comparable with the fluid pressure estimated from structural analysis the considerable pressure range can be related to pressure cycling between lithostatic and hydrostatic conditions as a consequence of fault valve actions and rock fracturing with subsequent pressure recover due to self sealing process

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

local stress perturbations associated with the 2008 wenchuan m 8 0 earthquake near the longmenshan fault zone in the eastern margin of the tibetan plateau abstract the 2008 wenchuan m 8 0 earthquake induced local stress perturbations near the longmenshan lms fault zone using in situ measurements and stress tensor inversions from focal mechanisms we investigated the post earthquake perturbed stress field at shallow depths 1 2 km in the upper crust above a basal attachment 5 18 km as well as in the middle crust beneath a basal attachment 19 32 km at shallow depths in the beichuan jiangyou section the maximum principal stress 1 orientations changed from a pre earthquake orientation of nww to a post earthquake orientation of nee however near the baoxing an xian and qingchuan mianxian sections the pre earthquake 1 orientation of nw nww was largely unaltered before the mainshock in the upper crust above the basal detachment the entire lms fault zone exhibited a consistent 1 orientation of nw nww however after the earthquake some sections such as the beichuan nanba section achieved 1 orientations of nee that were distinctly different from the pre seismic stress field in the middle crust beneath the basal detachment the stress field was mostly unchanged the crust beneath the basal detachment along the eastern margin of the tibetan plateau is dominated by nww oriented maximum principle stress and strain directions and a thrust faulting stress regime along the entire lms fault zone these observations are representative of the southeastward motion of the bayan har block and its ongoing collision with the south china block along the lms thrust belt the spatially heterogeneous stress field that occurred in the upper crust 18 km after the mainshock was most likely caused by the co seismic static stress changes associated with the wenchuan earthquake prior to the onset of seismic activity the deviatoric stress magnitudes were estimated at less than 22 mpa and 4 mpa at depths of 10 km and 20 km respectively suggesting that the mainshock fault zone has a relatively low fault strength to overcome in order to initiate significant co seismic rupture and aftershocks especially in the crust beneath the basal detachment these smaller deviatoric magnitudes are indicative of the weaker fault materials that resides in the lms region

fracture analysis and determination of in situ stress direction from resistivity and acoustic image logs and core data in the wenchuan earthquake fault scientific drilling borehole 2 50 1370 m abstract after the wenchuan earthquake on may 12th 2008 the wenchuan earthquake fault scientific drilling project wfsd was initiated in order to investigate the structure of the fault zones and the mechanism of the earthquake the wfsd contains four boreholes wfsd 1 wfsd 2 wfsd 3 and wfsd 4 lying at the maximum displacement locations along the yingxiu beichuan fault zone and the guanxian anxian fault zone and wfsd 2 is the second borehole and is still being drilled core samples resistivity and acoustic image logging data were acquired from 50 to 1370 m the natural fractures borehole breakouts drilling induced fractures and drilling enhanced natural fractures were identified from the cores and the image logs and were statistically analyzed the strikes of the natural fractures systematically vary and can be sorted into four groups according to depth 1 above 637 m mainly striking ene wsw 2 in the interval of 637 932 6 m striking nne ssw 3 in the interval of 932 6 1200 m directed ene wsw then to wnw ese while striking ne sw from 1030 m to 1150 m 4 from 1200 m to 1370 m maintaining a strike of wnw ese the natural fractures from 50 m to 637 m seem to be reverse faults which strike approximately parallelly to the main fault two sets of conjugate fractures around 1002 4 m indicating subvertical maximum principal paleo stress direction may be a subordinate structure of the main fault caused by a local stress field and it reveals the complex stress field of yingxiu beichuan fault zone when the fractures formed a total of 12 bos 2 sets of difs and one set of defs with an overall length of 30 4 m were interpreted from 960 m to 1370 m in wfsd 2 the average shmax orientation interpreted for wfsd 2 960 1370 m is 120 7 300 7 n i e wnw ese with the standard deviation of 9 2 and it is consistent with the stress status of yingxiu beichuan fault zone which is one of the main fault zones in the 2008 wenchuan earthquake

stress states at the subduction input site nankai subduction zone using anelastic strain recovery asr data in the basement basalt and overlying sediments abstract the three dimensional orientations of stress and stress magnitudes in the basement basalt and overlying sediments at the subduction input site iodp site c0012 have been determined using anelastic strain recovery asr analyses the asr results in the sedimentary sequence indicate that 1 is nearly vertical the magnitudes of 2 and 3 are very similar indicating that the stress state in the sedimentary sequence is at rest on the other hand asr analyses in the basement basalt show that 1 is nearly horizontal and oriented ne sw almost parallel or slightly oblique to the trench axis 3 plunges moderately to the nw the stress state of the basement basalts suggests a strike slip or thrust reverse fault regime which is very different from a state at rest condition which is the theoretical stress condition for the ocean floor far from a subduction zone the basement basalt at the subduction input site c0012 has experienced trench parallel compression and trench normal extension consistent with the focal mechanisms of earthquakes in the vicinity the estimated stress magnitudes show only small variations between the principal stresses implying that the directions of principal stress could be easily rotated in association with any tectonically induced local stress variation the stress orientation in the basement basalt seems to be the result of hinge extension during bending of the philippine sea plate either in association with subduction or with the formation of an anticline during intraoceanic thrusting

structural analysis of the adjacent acadian and variscan fold belts in belgium and northern france from geophysical and geological evidence abstract two palaeozoic fold belts are juxtaposed in belgium and northern france the northern belt of the brabant massif traditionally considered a part of the european caledonides was folded during the acadian orogeny in the early devonian although it is largely concealed gravity and magnetic maps give a general picture of the existing structures a curved gravity trend is interpreted as an arc shaped succession of granitic batholiths structures north and south of this arc are completely different the northern subdomain containing magnetic lower cambrian metasediments shows multiple thrust faults towards the south over the granites whereas the southern subdomain without magnetic rocks is moulded around the granitic core the southern variscan belt is characterized in general by thrusting with a north nw and ne vergence during the variscan orogeny the brabant massif acted as an obstacle to the general transport of the ardennes massif to the n nw the oblique convergence with the brabant massif caused differential displacement towards the northwest the western areas having travelled farther as seen from a pattern of wnw oriented strike slip faults

laurentian palaeostress trajectories and ephemeral fracture permeability cambrian eriboll formation sandstones west of the moine thrust zone nw scotland abstract cambrian eriboll formation sandstones of the ardvreck group that crop out west of the moine thrust zone contain joints and quartz filled or quartz lined fractures that resemble cemented joints of the fractures containing quartz five sets strike north nw to wnw ne west and north according to crosscutting relations this is a progression from the oldest to the youngest set sets include opening mode microfractures partly visible in transmitted light as fluid inclusion planes and sharply defined as microveins using sem based cathodoluminescence cl dating the oldest north striking set using inferred quartz accumulation rates fluid inclusions and burial history suggests that these fractures mark a palaeozoic east west least horizontal stress trajectory in laurentia the youngest two sets of porous fractures are associated with faults that cut and postdate the moine thrust zone data indicate that at depth in basins pervasive fracture systems arising from discrete loading events are ephemeral owing to fracture porosity destruction by cementation

conditions during syntectonic vein formation in the footwall of the absaroka thrust fault idaho wyoming utah fold and thrust belt abstract the twin creek limestone in the footwall of the absaroka thrust sheet contains three sets of bed normal syntectonic calcite veins vein formation occurred during cretaceous motion along the absaroka thrust fault as indicated by 1 crosscutting relationships among these vein sets 2 a previously dated solution cleavage and 3 calcite twin analysis fluid inclusions in the veins and overburden estimates constrain inclusion entrapment temperatures to be between 175 c and 328 c results from stable oxygen isotopes indicate that the host and vein fluid compositions were in near isotopic equilibrium applying both reasonable geothermal gradients and constraints on overburden temperature yields fluid pressures during vein precipitation that are near hydrostatic all data taken together suggest both that vein formation within the twin creek formation occurred in a relatively closed system and that the veins filled near hydrostatic fluid pressure because the veins fill precursory cracks vein filling might not reflect the maximum fluid pressure that existed during the complete vein forming process

the jabal akhdar dome in the oman mountains evolution of a dynamic fracture system the mesozoic succession of the jabal akhdar dome in the oman mountains hosts complex networks of fractures and veins in carbonates which are a clear example of dynamic fracture opening and sealing in a highly overpressured system the area underwent several tectonic events during the late cretaceous and cenozoic including the obduction of the samail ophiolite and hawasina nappes followed by uplift and compression due to the arabia eurasia convergence this study presents the results of an extensive tectonic survey and correlates subseismic scale structures in jabal akhdar faults fractures veins and stylolites with the main tectonic events in the northeastern arabian plate as some of the studied formations host large oil reserves in neighboring areas determining the relative timing of these events in the exhumed rocks is important to understand hydrocarbon distribution and fracture patterns in these reservoirs the formation of early veins and stylolites in the oman mountains is followed by top to the south layer parallel shearing that may be associated with the obduction of the samail and hawasina nappes this compressional tectonic event is followed by normal dip slip to oblique slip faults and veins top to the northeast layer parallel shearing which corresponds to the first stage of exhumation of the autochthonous rocks offsets these structures our new data indicate that this first phase of events is overprinted by complex strike slip networks of veins and fractures as well as by the reactivation and onset of seismic scale faults strike slip structures belong to three distinct events the first one nw se oriented compression is probably associated with the oblique collision of the indian plate against the arabian platform during the late campanian to the mid eocene the second event e w oriented compression is likely to have been formed during the late oligocene middle miocene during uplift the last event ne sw oriented compression probably took place during the miocene pliocene structures of the first two strike slip events have the same orientation as seismic scale faults observed in the subsurface of oman and abu dhabi in addition increasing vein intensity towards the top of the autochthonous formations in the oman mountains as well as the small angle between conjugate vein sets indicate that high fluid pressures that are thought to be present during strike slip deformation

mechanisms of fine extinction band development in vein quartz new insights from correlative light and electron microscopy fine extinction bands febs also known as deformation lamellae visible with polarized light microscopy in quartz consist of a range of nanostructures inferring different formation processes previous transmission electron microscopy studies have shown that most feb nanostructures in naturally deformed quartz are elongated subgrains formed by recovery of dislocation slip bands here we show that three types of feb nanostructure occur in naturally deformed vein quartz from the low grade metamorphic high ardenne slate belt belgium prismatic oriented febs are defined by bands of dislocation walls dauphine twin boundaries present along the feb boundaries probably formed after feb formation in an example of two sub rhombohedral oriented febs developed as two sets in one grain the finer feb set consists of elongated subgrains similar to febs described in previous transmission electron microscopy studies the second wider feb set consists of bands with different dislocation density and fluid inclusion content the wider feb set is interpreted as bands with different plastic strain associated with the primary growth banding of the vein quartz grain the nanometre scale fluid inclusions are interpreted to have formed from structurally bounded hydroxyl groups that moreover facilitated formation of the elongate subgrains larger fluid inclusions aligned along febs are explained by fluid inclusion redistribution along dislocation cores the prismatic feb nanostructure and the relation between febs and growth bands have not been recognized before although related structures have been reported in experimentally deformed quartz

shear veins observed within anisotropic fabric at high angles to the maximum compressive stress some faults seem to slip at unusually high angles 45 relative to the orientation of the greatest principal compressive stress1 2 3 4 5 this implies that these faults are extremely weak compared with the surrounding rock6 laboratory friction experiments and theoretical models suggest that the weakness may result from slip on a pre existing frictionally weak surface7 8 9 weakening from chemical reactions10 elevated fluid pressure11 12 13 or dissolution precipitation creep14 15 here we describe shear veins within the chrystalls beach accretionary melange new zealand the melange is a highly sheared assemblage of relatively competent rock within a cleaved anisotropic mudstone matrix the orientation of the shear veins compared with the direction of hydrothermal extension veins that formed contemporaneously indicates that they were active at an angle of 80 5 to the greatest principal compressive stress we show that the shear veins developed incrementally along the cleavage planes of the matrix thus we suggest that episodic slip was facilitated by the anisotropic internal fabric in a fluid overpressured heterogeneous shear zone a similar mechanism may accommodate shear at high angles to the greatest principal compressive stress in a range of tectonic settings we therefore conclude that incremental slip along a pre existing planar fabric coupled to high fluid pressure and dissolution precipitation creep may explain active slip on severely misoriented faults

well bore breakouts and in situ stress the detailed cross sectional shape of stress induced well bore breakouts has been studied using specially processed ultrasonic borehole televiewer data we show breakout shapes for a variety of rock types and introduce a simple elastic failure model which explains many features of the observations both the observations and calculations indicate that the breakouts define relatively broad and flat curvilinear surfaces which enlarge the borehole in the direction of minimum horizontal compression this work supports the hypothesis that breakouts result from shear failure of the rock where the compressive stress concentration around the well bore is greatest and that breakouts can be used to determine the orientation of the horizontal principal stresses in situ

stress state in the largest displacement area of the 2011 tohoku oki earthquake the 2011 moment magnitude 9 0 tohoku oki earthquake produced a maximum coseismic slip of more than 50 meters near the japan trench which could result in a completely reduced stress state in the region we tested this hypothesis by determining the in situ stress state of the frontal prism from boreholes drilled by the integrated ocean drilling program approximately 1 year after the earthquake and by inferring the pre earthquake stress state on the basis of the horizontal stress orientations and magnitudes estimated from borehole breakouts and the increase in coseismic displacement during propagation of the rupture to the trench axis in situ horizontal stress decreased during the earthquake the stress change suggests an active slip of the frontal plate interface which is consistent with coseismic fault weakening and a nearly total stress drop

stress orientations of taiwan chelungpu fault drilling project tcdp hole a as observed from geophysical logs 1 the taiwan chelungpu fault drilling project tcdp drilled a 2 km deep research borehole to investigate the structure and mechanics of the chelungpu fault that ruptured in the 1999 mw 7 6 chi chi earthquake geophysical logs of the tcdp were carried out over depths of 500 1900 m including dipole sonic imager dsi logs and formation micro imager fmi logs in order to identify bedding planes fractures and shear zones from the continuous core obtained from the borehole a shear zone at a depth of 1110 meters is interpreted to be the chelungpu fault located within the chinshui shale which extends from 1013 to 1300 meters depth stress induced borehole breakouts were observed over nearly the entire length of the wellbore these data show an overall stress direction n115e that is essentially parallel to the regional stress field and parallel to the convergence direction of the philippine sea plate with respect to the eurasian plate variability in the average stress direction is seen at various depths in particular there is a major stress orientation anomaly in the vicinity of the chelungpu fault abrupt stress rotations at depths of 1000 m and 1310 m are close to the chinshui shale s upper and lower boundaries suggesting the possibility that bedding plane slip occurred during the chi chi earthquake citation wu h y k f ma m zoback n boness h ito j h hung and s hickman 2007 stress orientations of taiwan chelungpu fault drilling project tcdp hole a as observed from geophysical logs geophys res lett 34 l01303 doi 10 1029 2006gl028050

slate a new record for crystal preferred orientation abstract this report describes microstructures and preferred orientation of a devonian slate from the belgian ardennes la fortelle quarry the sample composed largely of muscovite chlorite and quartz displays extraordinary texture strength of muscovite exceeding 100 multiples of random distribution m r d for 001 pole figures and thus setting a new record for preferred orientation in rocks quantitative texture analysis was performed with the rietveld method on synchrotron x ray diffraction images interestingly quartz also displays strong shape preferred orientation spo as revealed by x ray microtomography and sem imaging but largely random crystallographic preferred orientation cpo microstructural evidence suggests that this fine grained rock formed by recrystallization of shale under stress with growth of phyllosilicates and dissolution and growth of quartz

palaeoseismic events recorded in archaean gold quartz vein networks val d or abitibi quebec canada archaean gold quartz vein deposits are commonly hosted in high angle reverse shear zones and are interpreted to have formed in a regime of horizontal compression and high fluid pressure environment this paper presents the results of a combined structural and fluid inclusion study on three gold quartz vein deposits of the val d or area abitibi quebec consisting of subhorizontal extensional veins and e w steeply dipping shear veins crack seal structures tourmaline fibres stretched quartz crystals and open space filling textures indicate that the subhorizontal veins formed by hydraulic fracturing under supralithostatic fluid pressure co2 rich and h2o nacl fluid inclusions interpreted as two coexisting immiscible fluids occur typically in microcracks of different orientations interpreted to have formed in the 1 2 plane horizontal co2 rich fluid inclusion planes are contemporaneous with the opening of these veins 3 vertical vertical h2o nacl fluid inclusion planes as well as some microstructures such as deformed minerals indicate that the same extensional veins have experienced episodic vertical shortening 3 horizontal alternating with the opening events deformation and slip opening also occurred in shear veins in which preferred orientation of fluid inclusion planes is not clear except that the h2o nacl fluid inclusion planes tend to be oriented at high angles to the slip direction the successive opening and collapse events in subhorizontal extensional veins are correlated with deformation and slip opening events in shear veins respectively and are attributed to cyclic fluid pressure fluctuations in the system they are thus consistent with the fault valve model sudden drop in fluid pressure from supralithostatic to lower values induces fluid unmixing and occurs immediately post failure following seismic rupturing along the shear zone sealing of the shear veins allows the fluid pressure to build up again and the subhorizontal extensional veins to form the intermittent change in orientation of 3 in horizontal extensional veins is ascribed to a total shear stress release along the neighbouring shear veins after rupture the complex internal structures of the gold quartz veins provide an excellent record of archaean seismic activity along high angle reverse faults

localized rotation of principal stress around faults and fractures determined from borehole breakouts in hole b of the taiwan chelungpu fault drilling project tcdp abstract to reveal details of stress perturbations associated with faults and fractures we investigated the faults and large fractures accompanied by stress induced borehole breakouts or drilling induced tensile fractures in hole b of the taiwan chelungpu fault drilling project tcdp then we determined the relationship between the faults and fractures and stress orientation changes we identified faults and fractures from electrical images of the borehole wall obtained by downhole logging but also from photographs and descriptions of retrieved core samples and measured the variations in the principal horizontal stress orientation ascertained from borehole breakouts observed on the electrical images in the vicinity of the faults and fractures identification of geological structures faults fractures and lithologic boundaries by electrical images only is difficult and may sometimes yield incorrect results in a novel approach therefore we used both the electrical images and core photographs to identify geological structures we found four patterns of stress orientation change or no change in the vicinity of faults and fractures in tcdp hole b i abrupt discontinuous rotation in the vicinity of faults or fractures ii gradual rotation iii suppression of breakouts at faults fractures or lithologic boundaries and iv no change in the stress orientation we recognized stress fluctuations that is heterogeneous mesoscale 10 cm stress distributions with respect to both stress orientation and magnitude in addition we found that stress state changes occurred frequently in the vicinity of faults fractures and lithologic boundaries

anelastic strain recovery reveals extension across sw japan subduction zone 1 sediment dominated convergent margins typically record substantial horizontal shortening often associated with great earthquakes the convergent margin south of japan is arguably one of the most extensively investigated margins and previous studies have documented extensive evidence for accretion and horizontal shortening here we show results from anelastic strains recovered from three partially lithified sediment samples 40 porosities across the southwest japan accretionary prism and propose that the margin is dominated by horizontal extension rather than compression the anelastic strain results are also consistent with stress directions interpreted from two independent techniques bore hole breakout orientations and core scale fault data we interpret this unexpected result to reflect geologically recent underthrusting of a thick sediment package and concomitant weakening of the decollement

scaling relationships of joint and vein arrays from the burren co clare ireland abstract we present a study of the systematics of veins and joints in carboniferous limestones of the burren ireland scaling relationships were established for fracture arrays mapped from low elevation aerial photographs that image fractures on numerous limestone pavements for areas up to ca 1 km2 the veins and joints occur in the same sequence but have contrasting scaling properties the veins strike north south and cut many beds to form vertically persistent non stratabound arrays they are strongly clustered and have scale invariant geometric properties vein geometries suggest they grew sub critically under relatively high differential stresses during north south directed variscan compression the joints form stratabound arrays with regular spacings that scale with bed thickness they show greater strike variation than the veins and have lognormal length distributions the joints formed during uplift under low differential stress conditions the contrasting scaling properties of the joints and veins are attributed to different overburden stresses at the time of formation the veins formed at greater depths than the joints in conditions that favoured fracture propagation across mechanical discontinuities resulting in the development of non stratabound scaling properties

linear to non linear relationship between vein spacing and layer thickness in centimetre to decimetre scale siliciclastic multilayers from the high ardenne slate belt belgium germany abstract typical spacing distributions have frequently been described for fractures in thin sedimentary layers 40 cm vein spacing tends to increase to a maximum value becoming more or less independent of layer thickness the resemblance with fracture spacing suggests that in an unfractured rock vein saturation can occur high fluid pressures are responsible for vein nucleation but the stress state around the initial veins controls the spacing pattern subsequently in a vein saturated rock or the existing veins will thicken by the process of crack sealing or a new cross cutting vein generation will develop in case the regional stress field changes relatively with respect to the existing veins

three sets of crystallographic sub planar structures in quartz formed by tectonic deformation abstract in quartz multiple sets of fine planar deformation microstructures that have specific crystallographic orientations parallel to planes with low miller bravais indices are commonly considered as shock induced planar deformation features pdfs 1 diagnostic of shock metamorphism using polarized light microscopy we demonstrate that up to three sets of tectonically induced sub planar fine extinction bands febs sub parallel to the basal and crystallographic planes are common in vein quartz in low grade tectonometamorphic settings we conclude that the observation of multiple 2 3 sets of fine scale closely spaced crystallographically controlled sub planar microstructures is not sufficient to unambiguously distinguish pdfs from tectonic febs

the complexity of 3d stress state changes during compressional tectonic inversion at the onset of orogeny compressional tectonic inversions are classically represented in 2d brittle failure mode bfm plots that illustrate the change in differential stress s1 2 s3 versus the pore fluid pressure during orogenic shortening in these bfm plots the tectonic switch between extension and compression occurs at a differential stress state of zero however mostly anisotropic conditions are present in the earth s crust making isotropic stress conditions highly questionable in this study theoretical 3d stress state reconstructions are proposed to illustrate the complexity of triaxial stress transitions during compressional inversion of andersonian stress regimes these reconstructions are based on successive late burial and early tectonic quartz veins which reflect early variscan tectonic inversion in the rhenohercynian foreland fold and thrust belt high ardenne slate belt belgium germany this theoretical exercise predicts that no matter the geometry of the basin or the orientation of shortening a transitional wrench tectonic regime should always occur between extension and compression to date this intermediate regime has never been observed in structures in a shortened basin affected by tectonic inversion our study implies that stress transitions are therefore more complex than classically represented in 2d ideally a transitional wrench regime should be implemented in bfm plots at the switch between the extensional and compressional regimes extension mode i fractures are classically interpreted to form at low differential stresses less than four times the tensile strength t of rock e g secor 1965 they open perpendicular to the minimum principal stress s3 and propagate in the plane of the maximum s1 and intermediate s2 principal stresses the alignment of fractures has therefore often been used in orogenic belts to determine the orientation of the palaeostress field at the time of fracturing cox et al 2001 gillespie et al 2001 laubach et al 2004 if veins which initiated as extension fractures are uniform in trend over a large area then they can also be used as such a palaeostress indicator e g boullier robert 1992 cosgrove 2001 gillespie et al 2001 mazzarini et al 2010 van noten sintubin 2010 different cross cutting or successive vein generations are even more interesting because they have the potential 1 to serve as a tool to decipher changes in the overall stress regime during multiple phases of fracturing and 2 to define the p2t conditions at which these stress changes occurred on the one hand different crosscutting fracture and or vein generations have been used in many studies to deduce local stress field rotation in a consistent remote stress regime jackson 1991 crespi chan 1996 stowell et al 1999 laubach diaz tushman 2009 wiltschko et al 2009 on the other hand successive cross cutting veins i e vein sets that are oriented differently with respect to bedding have often been used to determine a transition in regional stress regime from extension to compression or reversely manning bird 1991 boullier robert 1992 teixell et al 2000 hilgers et al 2006b van noten et al 2008 2011 laubach diaz tushman 2009 alternatively cross cutting vein sets are observed in close relationship to faults in which they represent fluctuating fluid pressures during fault valve activity and are related to short lived local stress transitions in a consistent remote stress regime boullier robert 1992 sibson 1995 nielsen et al 1998 muchez et al 2000 collettini et al 2006 local mutually cross cutting vein sets may also develop in the presence of mechanical anisotropy around fault planes in a consistent remote stress field healy 2009 fagereng et al 2010 in all these studies transitions between regional stress regimes are defined as tectonic inversions a positive compressional tectonic inversion corresponds to a transition from an extensional to a compressional stress regime while a negative extensional tectonic inversion reflects the transition from compression to extension from healy d butler r w h shipton z k sibson r h eds 2012 faulting fracturing and igneous intrusion in the earth s crust geological society london special publications 367 51 69 http dx doi org 10 1144 sp367 5 the geological society of london 2012 publishing disclaimer www geolsoc org uk pub ethics by guest on august 9 2012 http sp lyellcollection org downloaded from

seismotectonic significance of the 2008 2010 walloon brabant seismic swarm in the brabant massif belgium abstract between 12 july 2008 and 18 january 2010 a seismic swarm occurred close to the town of court saint etienne 20 km se of brussels belgium the belgian network and a temporary seismic network covering the epicentral area established a seismic catalogue in which magnitude varies between ml 0 7 and ml 3 2 based on waveform cross correlation of co located earthquakes the spatial distribution of the hypocentre locations was improved considerably and shows a dense cluster displaying a 200 m wide 1 5 km long nw se oriented fault structure at a depth range between 5 and 7 km located in the cambrian basement rocks of the lower palaeozoic anglo brabant massif waveform comparison of the largest events of the 2008 2010 swarm with an ml 4 0 event that occurred during swarm activity between 1953 and 1957 in the same region shows similar p and s wave arrivals at the belgian uccle seismic station the geometry depicted by the hypocentral distribution is consistent with a nearly vertical left lateral strike slip fault taking place in a current local wnw ese oriented local maximum horizontal stress field to determine a relevant tectonic structure a systematic matched filtering approach of aeromagnetic data which can approximately locate isolated anomalies associated with hypocentral depths has been applied matched filtering shows that the 2008 2010 seismic swarm occurred along a limited sized fault which is situated in slaty low magnetic rocks of the mousty formation the fault is bordered at both ends with obliquely oriented magnetic gradients whereas the nw end of the fault is structurally controlled its se end is controlled by a magnetic gradient representing an early orogenic detachment fault separating the low magnetic slaty mousty formation from the high magnetic tubize formation the seismic swarm is therefore interpreted as a sinistral reactivation of an inherited nw se oriented isolated fault in a weakened crust within the cambrian core of the brabant massif

stress and fluid control on decollement within competent limestone abstract the larra thrust of the pyrenees is a bedding parallel decollement located within a competent limestone unit it forms the floor of a thrust system of hectometric scale imbrications developed beneath a synorogenic basin the fault rock at the decollement is a dense stack of mainly bedding parallel calcite veins with variable internal deformation by twinning and recrystallization veins developed as extension fractures parallel to a horizontal maximum compressive stress cemented by cavity type crystals conditions during vein formation are interpreted in terms of a compressional model where crack arrays develop at applied stresses approaching the shear strength of the rock and at fluid pressures equal to or less than the overburden pressure the cracks developed in response to high differential stress which was channelled in the strong limestone and high fluid pressure in or below the thrust plane ductile deformation although conspicuous cannot account for the kilometric displacement of the thrust which was mostly accommodated by slip on water sills constituted by open cracks a model of cyclic differential brittle contraction stress reorientation slip and ductile relaxation at a rheological step in the limestone is proposed as a mechanism for episodic decollement movement the model accounts for the peculiar microstructural character of the fault zone for alternating sequences of bedding parallel shortening leading to crack dilation and bedding parallel shear leading to decollement slip and for hanging wall imbrication consequent upon decollement slip

3 d digital outcrop model for analysis of brittle deformation and lithological mapping lorette cave belgium abstract acquiring and building digital outcrop models dom becomes an essential approach in geosciences this study highlights the strong potential of structure from motion sfm photogrammetry for full 3d mapping of inaccessible outcrops combining pictures captured from field and from unmanned aerial vehicle embedded digital cameras we present a workflow for i acquiring and reconstructing a dom of a geometrically complex natural cave site using digital photogrammetry in a lowlight environment ii georeferencing the 3d model in underground environments iii identifying and characterizing the geometry of inaccessible geological structures and their tectonic kinematics e g faults joints sedimentary bedding planes slickenlines for structural geology purposes we illustrate our method by modelling a challenging case study the main chamber of the lorette cave rochefort cave laboratory belgium first we produced a high resolution highly realistic model made of 395 million points cloud this allowed to draw a detailed lithostratigraphic log of the exposed sedimentary pile alternating decimetric carbonate mudstones with minor centimetric clay rich layers secondly we extract the orientation of brittle structures from the cave dom which consist of joints calcite filled veins fault planes with observable slickenlines and their kinematic indicators calcitic veins consist of tension gashes structures two subsets of tension gashes are distinguished based on their orientation wnw striking with low vs subhorizontal dips and morphology planar vs en echelon sigmoidal veins two faults subsets are identified i a first one comprises south dipping fault planes with mean strike dip of n069 s42 and consist of bedding surface slip ii a second one which corresponds to neoformed north dipping faults mean strike dip n279 n60 we recognize and characterize tectonic markers on fault planes directly from the high resolution dom slickenlines and asymmetrical microscarps pointing to a reverse shearing movement for all investigated faults based on their geometrical relations and fault slip data paleostress reconstruction points to a nw se to nnw sse subhorizontal compressive regime this one is interpreted as the record of early phases of variscan tectonics during the fold to fault progression this research paper also highlights future possibilities for rapid semi automatic interpretation of such 3d dataset for structural geology purposes as well as advances in technology and perspectives in terms of risk assessments and mitigation

compressional residual stress in bastogne boudins revealed by synchrotron x ray microdiffraction lattice distortions in crystals can be mapped at the micron scale using synchrotron x ray laue microdiffraction xrd from lattice distortions the shape and orientation of the elastic strain tensor can be derived and interpreted in terms of residual stress here we apply the new method to vein quartz from the original boudinage locality at bastogne belgium a long standing debate surrounds the kinematics of the bastogne boudins the xrd measurements reveal a shortening residual elastic strain perpendicular to the vein wall corroborating the model that the bastogne boudins formed by layer parallel shortening and not by layer parallel extension as is in the geological community generally inferred by the process of boudinage