surface stresses associated with arrested dykes in rift zones many theoretical models predict that arrested dykes may generate major grabens at rift zone surfaces arrested dyke tips in eroded rift zones however are normally not associated with major grabens or normal faults that could be generated by dyke induced stresses ahead of the tips and normal faults and grabens tend to be less common in those parts of eroded rift zones where dykes are comparatively abundant similarly there are feeder dykes as well as dykes arrested a few metres below the surface that do not generate faults or grabens at the surface here i propose that this discrepancy between theoretical models and field observations may be explained by the mechanical layering of the crust numerical models presented here show that abrupt changes in young s moduli layers with high dyke normal compressive stresses stress barriers and weak horizontal contacts have large effects on the dyke induced stress fields for the models considered the surface tensile stresses induced by arrested dykes are normally too small to lead to significant fault or graben formation at the rift zone surface the only significant dyke induced surface tensile stresses 2 mpa in these models are for a dyke tip arrested at 1 km depth below the surface of a rift zone with a weak contact at 400 m depth and subject to extension that tensile stress however peaks above the ends of the weak horizontal contact which in the model considered occur at distances of 4 km to either side of the dyke and shows no simple relation to the depth to the dyke tip thus for a layered crust with weak contacts straightforward inversion of surface geodetic data to infer dyke geometries may result in unreliable results

annual variations of sea surface elevation and currents over the scotian shelf and slope abstract topex poseidon t p altimeter data over the period 1992 98 have been analyzed to examine annual variability of sea surface elevation and currents over the scotian shelf and slope a modified orthogonal response analysis is used to derive the annual cycle while simultaneously removing the residual tides and other dynamical processes at the appropriate t p alias periods an evaluation of the m2 and k1 alias variations is carried out suggesting notable tidal correction errors off cape cod and over georges bank the along track sea surface slopes which represent surface geostrophic current components normal to the track are estimated on selected t p ascending and descending ground tracks the annual altimetric sea level harmonic is compared with steric height anomalies and wind driven setup the comparison indicates that the altimetric sea surface elevation variability is dominated by the baroclinic and associated barotropic component and supplemented by the wind driven and remotely forced comp

effects of internal structure and local stresses on fracture propagation deflection and arrest in fault zones the way that faults transport crustal fluids is important in many fields of earth sciences such as petroleum geology geothermal research volcanology seismology and hydrogeology for understanding the permeability evolution and maintenance in a fault zone its internal structure and associated local stresses and mechanical properties must be known this follows because the permeability is primarily related to fracture propagation and their linking up into interconnected clusters in the fault zone here we show that a fault zone can be regarded as an elastic inclusion with mechanical properties that differ from those of the host rock as a consequence the fault zone modifies the associated regional stress field and develops its own local stress field which normally differs significantly both as regard magnitude and orientation of the principal stresses from the regional field the local stress field together with fault rock heterogeneities and interfaces discontinuities fractures contacts determine fracture propagation deflection along discontinuities interfaces and arrest in the fault zone and thereby its permeability development we provide new data on the internal structure of fault zones in particular the fracture frequency in the damage zone as a function of distance from the fault core new numerical models show that the local stress field inside a fault zone modelled as an inclusion differ significantly from those of the host rock both as regards the magnitude and the directions of the principal stresses also when the mechanical layering of the damage zone due to variation in its fracture frequency is considered the numerical models show abrupt changes in local stresses not only between the core and the damage zone but also within the damage zone itself abrupt changes in local stresses within the fault zone generate barriers to fracture propagation and contribute to fracture deflection and or arrest also analytical solutions of the effects of material toughness the critical energy release rate of layers and their interfaces show that propagating fractures commonly become deflected into and often arrested at the interfaces generally fractures propagating from a compliant soft layer towards a stiffer one tend to become deflected and arrested at the contact between the layers whereas fractures propagating from a stiff layer towards a softer one tend to penetrate the contact thus it is normally easier for fractures to propagate from the host rock into the damage zone than vice versa similarly it is easier for fractures to propagate from the outer stiffer parts of the damage zone to the inner softer parts and from the stiff host rock to the outer damage zone than in the opposite directions these conclusions contribute to increased understanding as to how fractures propagate and become arrested within fault zones and how the fault zone thickness is confined at any particular time during its evolution

how mechanical layering affects local stresses unrests and eruptions of volcanoes 1 in most active volcanoes unrest periods with dike injections are much more common than eruptions while widely recognized this simple observation has not been satisfactorily explained surface deformation in volcanoes is commonly attributed to dikes injected from shallow magma chambers that fail to reach the surface field observations of dike tips many of which are blunt indicate arrest that is primarily controlled by the local stresses in the layers through which the dikes propagate numerical models on the stress fields around magma chambers located in an anisotropic heterogeneous layered crust indicate that for uniform loading a layered crust normally develops stress fields that are unfavorable for feeder dike formation in particular the models together with the field observations indicate that an essentially homogeneous stress field along the potential pathway of a dike is a necessary condition for its reaching the surface to supply magma to a volcanic eruption

propagation pathways and fluid transport of hydrofractures in jointed and layered rocks in geothermal fields abstract palaeofluid transporting systems observed as networks of mineral filled veins in deeply eroded parts of extinct geothermal fields indicate that hydrofractures commonly supply fluids to geothermal fields here we examine well exposed vein networks that occur at crustal depths of around 1 5 km below the initial surface of the tertiary lava pile in north iceland the veins are located in the damage zone of a major fault zone that dissects basaltic lava flows the most common host rocks of geothermal fields in iceland the lava flows contain numerous weaknesses particularly columnar cooling joints and contacts for hydrofractures to supply fluids to geothermal fields the fractures must be able to propagate and transport fluids to the surface we explore hydrofracture pathway formation using boundary element models of hydrofractures with fluid overpressure varying linearly from 10 mpa at the fracture centre to 0 mpa at the fracture tip or the fluid front the hydrofractures propagate through a vertically jointed and horizontally layered pile of lava flows with a general rock matrix young s modulus of 1 10 10 pa and a poisson s ratio of 0 25 the joints and contacts between layers are modelled as internal springs each with a stiffness strength of 6 mpa m the location and sizes of discontinuities as well as the location of the hydrofracture tip vary between the models the results indicate that tensile stresses generated at the tip of an overpressured hydrofracture can open up horizontal and vertical discontinuities out to a considerable distance from the tip and that these discontinuities eventually link up to form the hydrofracture pathway analytical models indicate that for a hot spring of a given yield associated with a fault the dimensions of the fluid transporting part of the fault are likely to be similar for a typical normal fault and a strike slip fault also a hot spring of yield 180 l s the maximum in the low temperature fields of iceland can be supplied through a hydrofracture of aperture 3 mm and trace length 1 2 m these dimensions are very similar to those of typical veins in the studied networks buoyancy rather than excess pressure in the fluid source appears to be the primary driving force of hydrofractures in the geothermal fields of iceland

fracture zones constrained by neutral surfaces in a fault related fold insights from the kelasu tectonic zone kuqa depression abstract stress variation associated with folding is one of the controlling factors in the development of tectonic fractures however little attention has been paid to the influence of neutral surfaces during folding on fracture distribution in a fault related fold in this study we take the cretaceous bashijiqike formation in the kuqa depression as an example and analyze the distribution of tectonic fractures in fault related folds by core observation and logging data analysis three fracture zones are identified in a fault related fold a tensile zone a transition zone and a compressive zone which may be constrained by two neutral surfaces of fold well correlation reveals that the tensile zone and the transition zone reach the maximum thickness at the fold hinge and get thinner in the fold limbs a 2d viscoelastic stress field model of a fault related fold was constructed to further investigate the mechanism of fracturing statistical and numerical analysis reveal that the tensile zone and the transition zone become thicker with decreasing interlimb angle stress variation associated with folding is the first level of control over the general pattern of fracture distribution while faulting is a secondary control over the development of local fractures in a fault related fold

post spreading deformation and associated magmatism along the iberia morocco atlantic margins insight from submarine volcanoes of the tore madeira rise abstract a new high resolution bathymetric map combined with a regional digital elevation model dem analysis reveal the modalities of occurrence and emplacement of post spreading magmatism along the nne ssw oriented 1000 km long tore madeira rise tmr as well as its relationship with the activity of major fault systems including the estremadura fault system esf and the azores gibraltar fracture zone agfz morphological and structural analysis of the bathymetric map were performed to map volcanic features such as eruptive cones vents and fissures together with faults along the tmr the new bathymetric map shows that the main nnw sse seamount alignment is formed by three structurally distinct volcanic massifs the tore the josephine and the southern volcanic groups the majority of the volcanoes of each group emplaced within or along specific portion of pre existing faults esf and agfz including splay fault releasing bend fault tips and interaction zones between different segments magmas were channelled into sub vertical pre existing lithospheric faults that acted as preferential pathways for the vertical magma ascent migration and final eruption of magma are controlled by the local stress variation induced by complex fault geometries change in plate kinematics as well as strong shear zone anisotropy as suggested by the emplacement within localised areas of transtension we conclude that post spreading magma emplacement in the southern part of the iberia margin was related to the development of a transtensional plate boundary between the iberian and african plate during the late cretaceous more generally our findings emphasize that the distribution of volcanism as the expression of the interaction between shallow plate tectonic and mantle processes should be included in plate kinematic reconstruction this study also demonstrates that the accurate mapping of oceanic seafloor is pivotal to better understand tectono magmatic evolution of volcanic seamount chains and geological processes in oceanic domains

spacing and distribution of bed perpendicular joints throughout layered shallow marine carbonates granada basin southern spain abstract this contribution focuses on the controls exerted by sedimentological petrographic and mechanical rock properties on the distribution of bed perpendicular joints throughout layered carbonates the study was conducted on tortonian shallow marine skeletal grainstones and rudstones cropping out in the granada basin southern spain the results of combined field and laboratory analyses are consistent with the rock grain size of the studied carbonates exerting a key control on distribution of the bed perpendicular joints a positive correlation between joint spacing and mechanical unit thickness is computed for the grainstones whereas joints are almost absent in rudstones the rock grain size affected the diagenetic processes such as cementation and dissolution and therefore the resulting porosity and uniaxial compressive strength ucs values quantitative data show that higher ucs values are commonly associated with greater calcite amounts lower values of porosity and finer grain sizes and hence denser bed perpendicular joint sets in conclusion this study documents that it is possible to infer the density of bed perpendicular joints in layered carbonates based on the sedimentological petrographic and mechanical parameters considering the impact that this type of joints has on subsurface fluid flow the acquired knowledge can help the management of geofluids as well as the overall prediction of carbonate reservoir quality

insights into the damage zones in fault bend folds from geomechanical models and field data abstract understanding the rock mass deformation and stress states the fracture development and distribution are critical to a range of endeavors including oil and gas exploration and development and geothermal reservoir characterization and management geomechanical modeling can be used to simulate the forming processes of faults and folds and predict the onset of failure and the type and abundance of deformation features along with the orientations and magnitudes of stresses this approach enables the development of forward models that incorporate realistic mechanical stratigraphy e g the bed thickness bedding planes and competence contrasts include faults and bedding slip surfaces as frictional sliding interfaces reproduce the geometry of the fold structures and allow tracking strain and stress through the whole deformation process in this present study we combine field observations and finite element models to calibrate the development and distribution of fractures in the fault bend folds and discuss the mechanical controls e g the slip displacement ramp cutoff angle frictional coefficient of interlayers and faults that are able to influence the development and distribution of fractures during fault bend folding a linear relationship between the slip displacement and the fracture damage zone the ramp cutoff angle and the fracture damage zone and the frictional coefficient of interlayers and faults and the fracture damage zone was established respectively based on the geomechanical modeling results these mechanical controls mentioned above altogether contribute to influence and control the development and distribution of fractures in the fault bend folds

implications of fracturing mechanisms and fluid pressure on earthquakes and fault slip data in the east iceland rift zone comparison of the eroded off rift zone left inactive by plate motion with the inner active seismic rift zone allows us to constrain the fracturing mechanisms in eastern off rift zone we measured 423 fault slips including normal and strike slip faults inversion of fault slip data reveals the parallelism of the minimum stress 3 computed for the normal and for the strike slip faulting and consistency with the direction of plate divergence north of the vatnajokull in the active rift zone we analysed 14 250 earthquakes recorded by the icelandic meteorological office imo between 2004 and 2009 especially northeast of the askja volcano two main average focal depths were determined at 5 km her ubrei table mountain and 15 km upptyppingar hyaloclastite ridge the double couple focal mechanisms determined by imo revealed that more than half of the mechanisms are strike slip faulting type both in active and off rift zone reveals an unusual importance of strike slip regime in such an extensional tectonic context this can be explained by stress permutations 1 2 similarities in terms of stress orientations and type of faulting are observed both in the old and present day rift zones we assume that the seismic events may be generated by rapid deep magma intrusion also associated with shallower hydrothermal activities we thus propose that the presence of fluids shear failure double couple focal mechanism and stress permutations in both active and off rift zones are closely linked assuming a drucker prager failure criterion we evaluated analytically that a state near of lithostatic pore pressure is a necessary condition for shear failure at shallow 5 km and deep 15 km depth in a simple context of crustal extension that allows for stress permutations however processes favouring stress permutations cannot be further constrained from our observations since the dynamics of fluid materiel heterogeneity and post glacial rebound can also play a significant role

length displacement scaling and fault growth abstract following an earthquake in a fault zone commonly the co seismic rupture length and the slip are measured similarly in a structural analysis of major faults the total fault length and displacement are measured when possible it is well known that typical rupture length slip ratios are generally orders of magnitude larger than typical fault length displacement ratios so far however most of the measured co seismic ruptures and faults have been from different areas and commonly hosted by rocks of widely different mechanical properties which have strong effects on these ratios here we present new results on length displacement ratios from 7 fault zones in holocene lava flows on the flanks of the volcano etna italy as well as 10 co seismic rupture length slips and compare them with fault data from iceland the displacement and slip data from etna are mostly from the same fault zones and hosted by rocks with largely the same mechanical properties for the co seismic ruptures the average length is 3657 m the average slip 0 31 m and the average length slip ratio 19 595 for the faults the average length is 6341 m the average displacement 73 m and the average length displacement ratio 130 thus the average rupture slip ratio is about 150 times larger than the average length displacement ratio we propose a model where the differences between the length slip and the length displacement ratios can be partly explained by the dynamic young s modulus of a fault zone being 101 2 times greater than its static modulus in this model the dynamic modulus controls the length slip ratios whereas the static modulus controls the length displacement ratio we suggest that the common aseismic slip in fault zones is partly related to adjustment of the short term seismogenic length slip ratios to the long term length displacement ratios fault displacement is here regarded as analogous to plastic flow in which case the long term displacement can be very large so long as sufficient shear stress concentrates in the fault

scotian slope circulation and eddy variability from topex poseidon and frontal analysis data 1 sea level observations from topex poseidon t p altimetry in conjunction with concurrent frontal analysis data from infrared imagery are used to study temporal and spatial variability of sea surface currents over the scotian slope geostrophic surface current anomalies normal to ground tracks are derived from the sea level anomalies relative to local means for the study period the altimetric results reveal prominent spatial variability of cross track currents with an overall intensification toward the west and south typically 20 30 cm s over the upper and lower slope 20 50 cm over the continental rise and up to 70 75 cm s near the gulf stream northern wall a rapid westward intensification on the western slope contrasts with nearly uniform distribution on the eastern slope the intensification seems to be associated with the high occurrence of gulf stream warm core rings wcr and with the close proximity to the gulf stream crossover analyses of altimetric current anomalies indicate that the total current variability can be estimated by a factor of 1 5 from the cross track current variability and the variance is isotropic to within 14 the rotational speed of the gulf stream rings can reach 1 2 m s over the scotian slope with the root mean square variability of 60 cm s the relative vorticity of the interior core is estimated to be 1 5 10 5 1 s when combined with ctd data t p observations can produce the vertical profile of the total geostrophic current that is in approximate agreement with adcp measurements

overview of the fracture zone project at finnsjon sweden abstract at the finnsjon site central sweden a 100 m wide low angle fracture zone in granodiorite zone 2 has been studied by means of borehole investigations this has included core and geophysical logging as well as hydraulic tests and groundwater sampling zone 2 was developed at 1 7 1 6 ga as a ductile shear zone at a depth of approximately 10 15 km and repeated reactivation has occurred during precambrian time and later today the upper boundary of the zone is defined in nine boreholes at depths ranging from 100 to 295 m pumping tests have demonstrated that the upper part of the zone is highly water conductive with a transmissivity in excess of 10 3 m 2 s 1 from tracer tests the equivalent single fracture hydraulic conductivity was calculated to be 0 03 0 2 ms 1 this extremely high transmissivity and conductivity over such a large areal extent can be speculated to be the result of recent opening of zone 2 during the last inland ice period in situ measurements of the natural groundwater flow show that the flow is high 67 90 m 3 m 2 year 1 at the upper boundary of zone 2 whereas near stagnant conditions occur at the lower boundary and in the relict saline water beneath the zone isotope data suggest a complex origin for the saline water the hydraulic head measurements as well as the groundwater chemistry strongly suggest that the low angle zone 2 acts as a hydraulic barrier preventing ground water from percolating downward through the zone these studies have helped to focus on repository safety assessment problems which hitherto had been oversimplified for the benefit of performance models furthermore the results have shown that these low angle large scale fracture zones are likely to be even more important controls than steep zones when considering bedrock stability rock stress regimes and lateral groundwater flow patterns quantification of such phenomena should provide an invaluable input into the various safety assessment performance codes for model validation and siting criteria for a repository

structural and statistical characterization of joints and multi scale faults in an alternating sandstone and shale turbidite sequence at the santa susana field laboratory implications for their effects on groundwater flow and contaminant transport abstract this paper describes the properties of faults and fractures in the upper cretaceous chatsworth formation exposed at santa susana field laboratory and its surroundings simi hills california where groundwater flow and contamination have been studied for over three decades the complex depositional architecture of this turbidite consisting of alternating sandstones and shales interacting with formative stress conditions are responsible for multi scale fault hierarchies and permeable fractures in which nearly all groundwater flow occurs intensity and distribution of background fractures and their relation to bedding thickness are established for sandstones the dominant lithology the architecture of faults with increasing displacement is described and relationships among fault dimensional parameters captured data from 400 boreholes and piezometers reveal the effect of faults and fractures on groundwater flow large hydraulic head differences observed across fault zones with shale rich cores indicate these structures as cross flow barriers moreover hydraulic head profiles under ambient conditions and pumping tests suggest strong hydraulic connectivity in all directions to depth of hundreds of meters this outcrop based structural characterization relates the horizontal hydraulic conductivity to the observed well connected fracture network and explains the strong vertical connectivity across low hydraulic conductivity shales as faults and sheared fractures provide flow pathways

fracturing and hydrothermal alteration in normal fault zones large normal fault zones are characterized by intense fracturing and hydrothermal alteration displacement is localized in a slip zone of cataclasite breccia and phyllonite surrounding corrugated and striated fault surfaces slip zone rock grades into fractured but less comminuted and hydrothermally altered rock in the transition zone which in turn grades abruptly into the wall rock fracturing and fluid flow is episodic because permeability generated during earthquakes is destroyed by hydrothermal processes during the time between earthquakes

deflection and propagation of fluid driven fractures at frictional bedding interfaces a numerical investigation propagation of fluid driven or hydraulic fractures deflected at bedding interfaces in layered sedimentary rocks and subsequent fluid invasion is investigated numerically using a two dimensional boundary element model the fracture is driven by an incompressible newtonian fluid injected at a constant rate the frictional stress on the interface is assumed to obey coulomb s frictional law without cohesion the bedding interface can be given a non zero minimum fluid conductivity a numerical scheme that deals with both rock deformation and fluid flow is presented and its accuracy is verified in terms of comparisons with existing results to explore the mechanisms involved in fluid and fracture invasion into the interface parametric studies are carried out for different elastic modulus contrasts in situ stresses interfacial frictional coefficients distances from the injection point to the interface and fluid viscosities the results are provided as time dependent variations of displacements fluid pressures contact stresses and fluid fronts fracture deflection and fluid invasion into the interface are found to rely essentially on local stress and deformation states at the intersection point fluid invasion and fracture growth may be delayed or inhibited when the interface is subjected to large confining stress or when fluid viscosity is relatively low for cases where the fluid driven fracture originates in the softer layer in this case a greater layer parallel tensile stress is produced and can lead to fracture propagation through the bedding contact low to medium frictional strength is found to promote fluid penetration and t shaped fracture formation by interfacial opening if the hydraulic fracture originates in a stiffer layer fluid invasion into bedding contacts can occur smoothly without the occurrence of interface closure and the fracture is thus terminated by forming a t shaped fracture at the bedding interface for fracture deflection into and growth along the interface in the absence of interface closure the long time responses resemble the solution for a fluid driven fracture growing along a frictionless interface with vanishing toughness

cool season sea level anomalies and storm surges along the u s east coast climatology and comparison with the 2009 10 el nino abstractclimatologies of sea level anomalies 0 05 m and daily mean storm surges 0 3 m are presented for the 1960 2010 cool seasons october april along the east coast of the united states at boston massachusetts atlantic city new jersey sewells point norfolk virginia and charleston south carolina the high sea level anomaly and the number of storm surges among the highest in the last half century during the 2009 10 cool season are comparable during strong el nino cool seasons high numbers of daily storm surges occur in response to numerous east coast extratropical cool season storms and have a positive correlation with the el nino phase of the el nino southern oscillation enso patterns of anomalously high sea levels are attributed to el nino related changes to atmospheric pressure over the gulf of mexico and eastern canada and to the wind field over the northeast u s continental shelf

damage patterns stress rotations and pore fluid pressures in strike slip fault zones 1 active faults unfavorably oriented with respect to the regional maximum compressive stress have been labeled as weak the seismic hazards posed by these faults make understanding this apparent weakness a priority stress rotations in these fault zones together with an increase in mean stress could enable high pore fluid pressures to weaken a fault zone such a model requires a foundation in the physics and mechanics of damage this paper presents a new model for stress rotations in fault zones by combining the effective medium theory with anisotropic poroelasticity this approach enables the quantitative characterization of crack damage and the prediction of progressive changes in the elastic properties of rocks across the fault zone the processes of fault growth and wear will lead to distinct patterns of crack damage with different effects on the elastic properties elevated pore fluid pressures have long been known to change the effective normal and shear stresses of anisotropic rocks and this work incorporates these effects into a multilayer fault zone model it is shown that high pore fluid pressures in the anisotropic rocks of the core zone can generate large stress rotations i e more fault parallel and increases in mean stress sufficient to weaken the fault stress rotations in the damage zones of unfavorably oriented faults tend to be away from the fault i e more fault normal for likely combinations of damage patterns and pore fluid pressure

relation between permeability and effective stress along a plate boundary fault barbados accretionary complex in situ bulk permeability was measured in a borehole that intersected the decollement zone a low angle detachment fault between the north american and caribbean plates permeability measurements were made at a variety of fluid pressure conditions defining a quantitative relation between bulk permeability and effective stress for this plate boundary fault zone the bulk permeability in this zone changed by several orders of magnitude as a consistent function of fluid pressure this relation may help to explain the dynamics of fluid fault interactions and the transient nature of hydrologic processes during deformation at convergent margins

extension fracture propagation in rocks with veins insight into the crack seal process using discrete element method modeling 1 we investigate how existing veins interact with extension fractures in rocks using 3 d discrete element method models with a geometry inspired by tension tests with notched samples in a sensitivity study we varied a the angle between the vein and the bulk extension direction and b the strength ratio between host rock and vein material results show a range of vein fracture interactions which fall into different robust structural styles veins which are weaker than the host rock tend to localize fracturing into the vein even at high misorientation angles veins which are stronger than the host rock cause deflection of the fracture tip along the vein host rock interface fractures are arrested at the interface from weak to stronger material when propagating from a stronger to a weaker material macroscopic bifurcation of the fracture is common complex interactions are favored by a low angle between the vein and the fracture and by high strength contrast the structural styles in the models show good agreement with microstructures and mesostructures of crack seal veins found in natural systems we propose that these structural styles form the basis for criteria to recognize strength contrasts and stress of crack seal systems in nature

how local stress fields prevent volcanic eruptions recent studies show that dike injections in composite volcanoes and rift zones are much more common than dike fed eruptions although this observation is of fundamental importance in volcanic hazard studies and for understanding the formation and structure of the ocean crust the mechanisms that prevent dikes from reaching the surface are still poorly understood here we present new numerical models of magma chambers hosted by crustal layers of contrasting mechanical properties such as stiff lava flows and soft pyroclastic rocks the numerical models vary in sophistication from simple 4 layer models to a complex and realistic 30 layer model in the latter the layer thicknesses approach those of individual lava flows and pyroclastic flows as observed in the field in iceland and elsewhere more specifically for a magma chamber with a top at the depth of 1 5 km as is common in iceland each layer in the 30 layer model has a thickness of 50 m this is similar to the thicknesses of many pahoehoe lava flows and pyroclastic hyaloclastite and sedimentary units in iceland tilting of the lava pile is a general feature of volcanic areas to take this into account we also present several numerical models with dipping layers where in accordance with observations the dips of the layers increase with depth in the lava pile all the numerical models for thick and thin layers as well as for tilted layers yield some common results first that during magma chamber inflation local stresses in the stiff layers encourage dike propagation while those in the soft layers tend to arrest dike propagation and prevent volcanic eruptions second that the local stresses in the stiff layers may trigger seismogenic faulting while the soft layers remain seismically quiet the models with the dipping layers indicate that the general tilting of the lava pile may result in shifting of volcanic activity at the surface the shifting is because the local stresses that develop above a magma chamber located in a tilted lava pile control the pathways of injected dikes the direction of shifting is in the dip direction of the tilted lava pile and the amount of shifting increases with increasing dip all the results suggest that for an eruption to occur the stress conditions along the potential pathway of a dike must be basically homogeneous

san andreas fault damage at safod viewed with fault guided waves 1 highly damaged rocks within the san andreas fault zone at parkfield form a low velocity waveguide for seismic waves giving rise to fault guided waves prominent fault guided waves have been observed at the san andreas fault observatory at depth safod site including a surface array across the fault zone and a borehole seismograph placed in the safod well at a depth of 2 7 km below ground the resulting observations are modeled here using 3 d finite difference methods to fit the amplitude frequency and travel time characteristics of the data the models require a downward tapering 30 40 m wide fault core embedded in a 100 200 m wide jacket compared with the intact wall rocks the core velocities are reduced by 40 and jacket velocities by 25 based on the depths of earthquakes generating guided waves we estimate that the low velocity waveguide along the fault at safod extends at least to depths of 7 km more than twice the depth reported in pervious studies

u series dating of co seismic gypsum and submarine paleoseismology of active faults in northern chile 23 s abstract the convergence of the nazca and south american plates along the subduction margin of the central andes results in large subduction earthquakes and tectonic activity along major fault systems despite its relevance the paleoseismic record of this region is scarce hampering our understanding about the relationship between the andes building and earthquake occurrence in this study we used the u series disequilibrium method to obtain absolute ages of paleoearthquake events associated with normal displacements along the active mejillones and salar del carmen faults in the coastal range of the atacama desert of northern chile the 230th 234u disequilibrium ages in co seismic gypsum salts sampled along the fault traces together with marine evidences indicate that earthquakes occurred at ca 29 7 1 7 ka 11 4 ka and 2 4 0 8 ka when coupled with paleoseismic marine and radiocarbon 14c records in the nearby mejillones bay evidencing large dislocations along the mejillones fault the geochronological dataset presented here is consistent with the notion that gypsum salts formed during large earthquakes as a result of co seismic dilatancy pumping of saline waters along the major faults based on maximum observed cumulative vertical offsets in the studied faults this phenomena could have occurred episodically at a rate in the order of 1 40 to 1 50 with respect to the very large subduction earthquakes during the latest pleistocene holocene period the results presented here reveal that the u series disequilibrium method can be successfully applied to date the gypsum salts deposited along faults during seismic events and therefore directly constrain the age of large paleoearthquakes in hyperarid and seismically active zones

interannual variations of volume transport in the western labrador sea based on topex poseidon and woce data abstract the interannual variations of volume transport in the western labrador sea are estimated using six years of topex poseidon altimeter data and hydrographic data from a woce repeat section and a method based on the linear momentum equation in which the sea surface is the level of known motion the interannual variation of the total transport in spring summer has a range of 6 2 sv sv 106 m3 s 1 and is positively correlated with the fall winter north atlantic oscillation nao index and wind patterns in the northwest north atlantic the total transport anomaly is decomposed into a barotropic and a baroclinic component the interannual change of the barotropic transport is similar to that of the total transport and is positively correlated with the fall winter nao index the baroclinic transport anomaly in comparison has a smaller magnitude and the opposite sign the authors conjecture that the deepened icelandic low in high index years generates a strong cyclonic wind stress curl which in tur

the model of fracture development in the faulted folds the role of folding and faulting abstract tectonic fractures are otherwise known as joints or fissures the density of tectonic fractures is governed by the lithology layer thickness and structures the distribution and density of tectonic fractures in the kuqa depression in the northern tarim basin of northwest china are dominantly controlled by the regional faulted fold belt our purpose of this paper is to analyze how folding and faulting control the development of tectonic fractures based on outcrop and logs of drill data in the folded tight sandstone reservoirs in the kuqa depression the extensional area transition area and shortening area have been separated by two neutral lines which control the distribution and density of tectonic fractures in the buckle folds from the twelve sites of field measurements six logs of drill core data and analysis of the micro texture of tectonic fractures it can be deduced that the fracture development in the sub salt faulted fold belt is related to the neutral lines and related faults the high density tensile fractures in the vicinity of fold hinges are more developed than in the limbs of the fold folding is thus the first level of control over the general pattern of fracture distribution the fractures in the hanging wall of the thrust faults are more developed than those in the footwall further more the fractures in the hinge zone and steeply tilted limbs of folds close to thrust faults are more developed than the gently tilted limbs which are far from faulting this suggests that faulting is a secondary control over the development of local fractures within the faulted fold belt the development of fractures related to faulted folds in the kuqa depression can be also divided into three episodes pre folding syn folding and post folding which are identified by field observation

fractures of lacustrine shale reservoirs the zhanhua depression in the bohai bay basin eastern china abstract fractures play a vital role in the exploration and development of shale oil and gas by providing effective space for shale reservoirs and significantly improving the fluid flow capability core observations microscopic analyses of thin sections scanning electron microscopy and formation microscanner imaging fmi were used to determine the types causes of formation and development characteristics of the fractures in lacustrine shale reservoirs in the lower part of the paleogene shahejie formation es 3 in the zhanhua depression bohai bay basin eastern china x ray diffraction xrd analysis total organic carbon toc measurements and porosity and permeability measurements were used to study the controlling factors of the fractures in the shale reservoirs and to analyze the impact of the fractures on the shale reservoirs properties and subsequent exploration and development the studied shale reservoir mainly displays tectonic fractures as well as various types of non tectonic fractures the non tectonic fractures mainly include over pressure fractures diagenetic fractures inter layer bedding fractures and fractures of mixed origins in the study area the tectonic fractures which were formed under the combined action of tensile and shear stress display the following characteristics the dip angle of the tectonic fractures varies significantly unfilled or half filled effective fractures have a high proportion these fractures are mainly oriented in the ne sw nne ssw and wnw ese directions with fractures in the ne sw direction accounting for the highest proportion the tectonic and non tectonic fracture development is affected by multiple types of factors such as the presence of faults mineral composition lithology abnormal pressure and organic matter content abnormally high pore pressure is a very important factor in the development of non tectonic fracture it is inferred that the over pressure is mainly related to hydrocarbon generation during thermal evolution fractures effectively improve the porosity and permeability of the shale reservoirs and the enhancement of permeability is particularly significant the current stress field affects the fluid flow capability of the fracture reservoirs and the present maximum principal stress in zhanhua depression is oriented in the nee sww direction which has a small angle with fractures in ne sw direction we propose that the fractures in this direction have the greatest connectivity and thus are a high priority target for petroleum exploration and development

hydrofracturing stress measurements in the iceland research drilling project drill hole at reydarfjordur iceland two independent suites of hydrofracturing stress measurements were conducted in the top 600 m of the iceland research drilling project deep hole at reydarfjordur east iceland as indicated by the continuously extracted drill core the tested section consists of tertiary subaerial tholeiitic lava flows cut by many basaltic dikes the density of the basalt was used to estimate the vertical stress v in megapascals at depth d in meters v 0 027d in the 33 to 270 m depth range the horizontal principal stresses hmax and hmin as calculated from hydrofracturing results increase gradually with depth but at a lower rate than the vertical stress hmin 2 1 0 016d hmax 3 3 0 016d in the 300 to 550 m depth range a major perturbation occurs with both horizontal stress magnitudes rapidly rising between 300 and 400 m and then uniformly decreasing between 400 and 550 m to a level apparently predictable by the relationships obtained in the top 270 m conditions favoring normal faulting v hmax hmin were established in the 540 to 580 m range and are conjectured to persist at greater depths since the vertical stress gradient is higher than that of hmax and hmin this would be in accord with the predominant fault type in east iceland the relative low horizontal stress values and the small difference between them are supportive of ocean floor spreading theories and contradict near surface high compressive stresses previously determined by hast 1973 in east iceland the large increase in horizontal stress in the range of 300 to 500 m depth is not understood a correlation appears to exist between the zone of almost unintruded thick lava flows 200 500 m and that of high stresses an intuitive model suggesting locked in stresses in this zone is proposed the hydrofracturing determined overall mean direction of hmax is n50 e while a more selective sampling of results yields n40 e the measured stress directions appear to be reasonably compatible with the local structure such as dike direction nne and lava dip wsw significantly hmax direction is subparallel to the n20 e trend of the nearest fissure swarms in the axial rift zone this almost coincidence of directions like the measured stress magnitudes is also in agreement with the model of spreading lithospheric plates being pulled apart

distant off fault damage and gold mineralization the impact of rock heterogeneity field observations have established that fault related damage can occur at locations far from the principal slip surface which are well outside the fractured region currently predicted by models of fault damage we use a finite element model to simulate fracture initiation due to fault linkage and show how variations in rock properties allow off fault damage to develop at surprisingly large distances away from the main fault off fault damage continues to grow even after two adjacent closely spaced fault segments have interacted and linked we demonstrate that this process was important for the formation of fracture hosted gold deposits in the mount pleasant goldfield western australia the strength of lithological contacts also has a significant impact on off fault damage location and intensity our approach may go some way to explaining the non intuitive distribution of mineralization in certain mineral systems as well as being applicable to predict subsurface fracturing and fluid flow in hydrothermal geothermal reservoirs

geological and geomorphic evidences of neotectonic activity along the himalayan frontal thrust nahan salient nw himalaya india abstract in this paper we report geomorphic signatures of neotectonic activity identified from the area around nahan salient along himalayan frontal thrust hft using remote sensing and field investigations we document two newly discovered exposures of hft fault zone and active fault traces along the mountain front at khetpurali nahan salient nw himalaya india we demonstrate that hft fault zone at khetpurali is not blind instead it is exposed at the surface along with highly deformed folded strata in the hanging wall and its geometry is quite variable with the possibility of along strike segmentation the geometry of fold and various deformational features preserved in the hanging wall indicate a process of fault propagation fold this is in contrast to the previous observation of fault bent folding within the nahan salient two three levels of river terraces are preserved and truncated in the hanging wall along with the active fault scarps which are linked to uplift along hft fault zone the khetpurali anticline ka is a fault propagating fold formed due to displacement and shortening along hft which dips 30 towards north and strike wnw ese the uplift u along the ka is calculated to be 73 m and accommodated 7 3 shortening of the original length before the fault tip truncated the fold various deformational structures have been identified within the hanging wall around tip damage zone of 80 m perpendicular to hft fault zone and in the core of ka northwest of khetpurali a south facing hogback structure 100 m high is formed due to erosion of forelimb of the anticline at khetpurali tectonic control due to folding of strata and uplift of river terraces is evident as the dudhgarh river forms v shaped profile near the thrust compared to the wide floodplain before and after crossing the hft fault zone along strike segmentation of hft and associated anticlines is observed as the surface trace of hft is offset at khetpurali trilokpur and sabilpur due to the strike slip faults the study reveals that hft has been truncated by tear faults and has different subsurface geometries in study area which may have implication on seismic hazard in the nahan salient where three thrusts himalayan frrontal thrust hft nahan thrust nt and main boundary fault mbf are located at relatively shorter distance of 6 km as compared to the surrounding recesses

volcano tectonics of the al haruj volcanic province central libya abstract the al haruj intra continental volcanic province ahvp located at the south western margin of the sirt basin hosts the most extensive and recent volcanic activity in libya which is considered typical for plate interiors from north to south the ahvp is divided into two subprovinces namely al haruj al aswad and al haruj al abiyad the total area of the ahvp is around 42 000 km 2 despite the great size of the ahvp its volcano tectonic evolution and activity have received very little attention and are poorly documented and understood here we present new field data and analytical and numerical results on the volcano tectonics of the ahvp the length thickness ratio of 47 dykes and volcanic fissures were measured to estimate magmatic overpressure at the time of eruption the average dyke length thickness ratio of 421 indicates magmatic overpressures during the associate fissure eruptions of 8 19 mpa depending on host rock elastic properties spatial distributions of 432 monogenetic eruptions sites points lava shields pyroclastic cones in the ahvp reveal two main clusters one in the south and another in the north aligned eruptive vents show the dominating strike of volcanic fissures feeder dykes as wnw ese to nw se coinciding with the orientation of one of main fracture fault zones numerical modelling and field observations suggest that some feeder dykes may have used steeply dipping normal fault zones as part of their paths to the surface

north atlantic surface circulation during the 1990 s observed with satellite tracked drifters a new compilation of lagrangian velocity observations describes the state of the north atlantic surface circulation during the 1990s gridded fields of velocity and eddy kinetic energy eke are constructed from trajectories of more than 1500 15 m drogued satellite tracked surface drifters in service between january 1990 and december 1999 this time period overlaps a coordinated field study of circulation and variability in the north atlantic completed between 1996 2000 as part of the world ocean circulation experiment we describe the construction of a self consistent drifter climatology present decadal mean quasi eulerian velocity and eke fields computed on a 1 grid and compare these results with contemporary satellite measurements detailed discussion of the inferred surface circulation is focused on three regions 1 the gulf stream and north atlantic current 2 the labrador sea and subpolar gyre and 3 the caribbean sea the swiftest drifter motions were found in the equatorial region and along the tropical subtropical and subpolar western boundaries the maximum instantaneous speed determined from a single quality controlled and filtered drifter observation was 273 cm s 1 in the gulf stream southeast of cape cod the highest eke value in the north atlantic 2790 cm2 s 2 was found in the gulf stream just downstream of the new england seamounts over most of the atlantic basin drifter derived eke values were found to be o 100 cm2 s 2 higher than corresponding values derived from satellite altimetry in the labrador sea a region of sharply elevated eke appears to be geographically related to the localized ejection of drifters and by extension mass and kinetic energy from the energetic west greenland current between 60 and 62 n when compared to drifter measurements made in the late 1970s our results suggest but do not statistically confirm an enhancement and slight northward shift of the zonal gulf stream extension such a shift is consistent in sign with expectations based on observed interdecadal variations in wind stress and subtropical gyre potential energy associated with the north atlantic oscillation

evolution of stress fields and faulting in seismic zones measurements indicate that stress magnitudes in the crust are normally limited by the frictional equilibrium on pre existing optimally oriented faults fault zones where these limitations are frequently reached are referred to as seismic zones fault zones in the crust concentrate stresses because their material properties are different from those of the host rock most fault zones are spatially relatively stable structures however the associated seismicity in these zones is quite variable in space and time here we propose that this variability is attributable to stress concentration zones that migrate and expand through the fault zone we suggest that following a large earthquake and the associated stress relaxation shear stresses of a magnitude sufficient to produce earthquakes occur only in those small parts of the seismic zone that because of material properties and boundary conditions encourage concentration of shear stress during the earthquake cycle the conditions for seismogenic fault slip migrate from these stress concentration regions throughout the entire seismic zone thus while the stress concentration regions continue to produce small slips and small earthquakes throughout the seismic cycle the conditions for slip and earthquakes are gradually reached in larger parts of and eventually the whole seismogenic layer of the seismic zone prior to the propagation of an earthquake fracture that gives rise to a large earthquake the stress conditions in the zone along the whole potential rupture plane must be essentially similar this follows because if they were not then on entering crustal parts where the state of stress was unfavourable to this type of faulting the fault propagation would be arrested the proposed necessary homogenisation of the stress field in a seismic zone as a precursor to large earthquakes implies that by monitoring the state of stress in a seismic zone its large earthquakes may possibly be forecasted we test the model on data from iceland and demonstrate that it broadly explains the historical as well as the current patterns of seismogenic faulting in the south iceland seismic zone

more major earthquakes at the nepal himalaya study on coulomb stress perspective abstract on april 2015 a major earthquake of 7 9 mw occurred in the nepal himalaya followed by 553 earthquakes of local magnitude greater than 4 0 within the first 43 days including another major event of 7 3 mw we resolve the static coulomb failure stress cfs change onto the finite fault models of 7 9 mw after elliott et al 2016 and galezka et al 2015 and its effect on associated receiver faults correlation of aftershocks with the enhanced cfs condition shows that the elliott et al 2016 model explains 60 4 and the galezka et al 2015 model explains about 47 7 of the aftershocks in high stress regions aftershocks were poorly spatially correlated with the enhanced cfs condition after the 7 9 mw main shock and can be explained by correlation with release of seismic energy from the associated secondarily stressed prominent thrust planes and transverse faults stress resolved on the associated receiver faults show increased stress on both transverse and thrust fault systems with the potential of triggering significant aftershocks or subsequent main shocks

is there a north south phase shift in the surface labrador current transport on the interannual to decadal scale 1 the transport of the labrador current has substantial interannual to decadal variability that may significantly impact the ocean climate and marine ecosystem off atlantic canada and northeast united states nevertheless the alongshore coherence of the labrador current on the interannual to decadal scales has been a long standing question here we have used satellite altimetry data to study interannual to decadal variability of the unit depth surface labrador current in the past two decades in the context of the subpolar gyre of the north atlantic the study for the first time reveals that the transport over the labrador and northeastern newfoundland slope is out of phase with that over the scotian slope the surface labrador current transport is positively and negatively correlated with the winter north atlantic oscillation nao index with the transport lagging by about 1 year in the north the labrador and northeastern newfoundland slope and in the south the scotian slope respectively in addition the surface labrador current transport declines over the labrador slope and northeastern newfoundland slope and increases over the scotian slope the north south phase shift suggests two distinct regimes which warrants further studies of underlying dynamic mechanisms and may have important implications for regional ecosystems and climate

structural analysis of the coseismic shear zone of the 2008 mw 7 9 wenchuan earthquake china abstract field investigations reveal that the surface rupture of the 2008 m w 7 9 wenchuan earthquake china occurred along a pre existing shear zone in the longmen shan thrust belt structural analyses of the coseismic fault zone and fault rocks show that i the main coseismic shear zone consists of a fault core that includes a narrow fault gouge zone of 5 m in width that is composed of cataclastic rocks including fractures and subsidiary faults ii the foliations developed in the fault core and damage zones indicate a dominantly thrust slip sense consistent with that indicated by the coseismic surface rupture and iii coseismic slip was largely localized to within a narrow fault gouge zone of

satellite observations of seasonal and interannual changes of sea level and currents over the scotian slope seasonal and interannual sea level and current variations over the scotian slope are examined using 10 years of ocean topography experiment topex poseidon t p satellite altimeter data geostrophic surface current anomalies normal to ground tracks are derived from the along track gradients of sea level anomalies the altimetric current anomalies are combined with a climatological mean circulation field of a finite element model to construct nominal absolute currents the seasonal mean results indicate that the sea level is highest in late summer and lowest in late winter and that the surface slope circulation is strong in winter autumn and weaker in summer spring the total transport associated with the westward shelf edge current and with the eastward slope current calculated by combining the t p data with a climatological seasonal mean density field reveals a substantial seasonal change dominated by the barotropic component the present analysis reveals prominent interannual changes of the sea level and current anomalies for the study period the sea level was lowest in 1996 97 when the gulf stream was in its most southern position the mean winter circulation over the scotian slope was strongest up to 30 c ms 1 in both the southwestward shelf edge current and northeastward slope current in 1998 and weakest weaker and broader shelf edge current in 1996 which may be related to the fluctuation of the equatorward labrador current strength and of the gulf stream north south position the study also suggests that the root mean square current magnitude is positively correlated with the occurrence of the gulf stream warm core rings wcrs on the interannual scale while wcr yearly mean kinematic properties seem to have small variations

calcite veins as an indicator of fracture dilatancy and connectivity during strike slip faulting in toarcian shale tournemire tunnel southern france abstract the reactivation of faults induced by natural human induced fluid pressure increases is a major concern to explain subsurface fluid migration and to estimate the risk of losing the integrity of reservoir seal systems this study focusses on paleo fluid migration in a strike slip fault with 100 m long affecting a toarcian shale causses basin france a high calcite concentration is observed in a 5 cm thick zone at the boundary between the fault core and damage zone cumulated displacements in this zone are of millimeter to centimeter scale offsets and different dilatant deformation textures are observed the zone is affected by thin slip planes containing gouge cathodo luminescence observations indicate that two phases of vein formation occurred the first phase coincides with the fluid migration along this centimeter thick dilatant zone the second one is associated to re shear along the millimeter thick slip planes that results in more localized mineralization but also in a better hydrologic connection through the shale formation these results show that in shales fluids may migrate off a slipping surface in centimeter scale dilatant volumes at first controlled by the intact shale anisotropy related to bedding and then favored by brecciating structures re orientation and strengthening processes induced by calcite sealing effects

architectural evolution of the nojima fault and identification of the activated slip layer by kobe earthquake 1 evolutionary history of nojima fault zone is clarified by comprehensive examinations of petrological geophysical and geochemical characterizations on a fault zone in deep drilled core penetrating the nojima fault on the basis of the results we reconstruct a whole depth profile of the architecture of the nojima fault and identify the primal slip layer activated by 1995 kobe earthquake the deepest part 8 to 12 km depth of the fault zone is composed of thin slip layers of pseudotachylite 5 to 10 mm thick each 10 cm in total middle depth 4 to 8 km depth of the fault zone is composed of fault core 6 to 10 m thick surrounded by thick 100 m thick damage zone characterized by zeolite precipitation the shallow part of the fault zone 1 to 4 km depth is composed of distributed narrow shear zones which are characterized by combination of thin 0 5 cm thick each 10 cm in total ultracataclasite layers at the core of shear zones surrounded by thicker 1 to 3 m thick damage zones associated with carbonate precipitation an extremely thin ultracataclasite layer 7 mm thick activated by the 1995 kobe earthquake is clearly identified from numerous past slip layers overprinting one of the shear zones as evidenced by conspicuous geological and geophysical anomalies the nojima fault zone was 10 to 100 times thicker at middle depth than that of shallower and deeper depths the thickening would be explained as a combination of physical and chemical effects as follows 1 thickening of fault core at middle depth would be attributed to normal stress dependence on thickness of the shear zone and 2 an extreme thickening of damage zone in middle depth of the crust would result from the weakening of the fault zone due to super hydrostatic fluid pressure at middle depths the high fluid pressure would result from faster sealing with low temperature carbonate at the shallower fault zone

salinity changes in the central baltic sea nw europe over the last 10 000 years a comment on emeis struk blanz kohly voβ we question the effort to date the lower part of a core from the baltic sea with a combination of tephra layers and stratigraphical markers no geochemical data is presented for the two tephra layers believed to be the saksunarvatn ash and vedde ash furthermore the age used for one of the stratigraphical markers is erroneous we present two alternative age models of which the second gives a plausible sediment accumulation rate but excludes the identification of the vedde ash

isotopic constraints of vein carbonates on fluid sources and processes associated with the ongoing brittle deformation within the accretionary wedge of taiwan terra nova 22 251 256 2010 abstract the continuously distributed well preserved fracture filling carbonates were collected from the cores retrieved from the taiwan chelungpu fault drilling program between 400 and 2000 m depth for carbon and oxygen isotope analyses to constrain the fluid compositions and processes associated with brittle deformation within the accretionary wedge the isotope analyses of fracture filling carbonates yielded 18o values steadily increasing with depth the 13c values exhibited a pattern similar to that of 18o values at shallower depths but an opposite trend at greater depths such variations in the isotopic compositions could be best explained by a mixing of shallow meteoric water and deeply rooted fluid carrying isotopic signatures of various microbial processes the notable excursion of 18o values might infer a conduit for the lateral fluid transport along the high vein density zone overall the isotopic patterns preclude the substantial influence of early diagenesis and suggest pervasive fluid percolation through the fracture network

loading of a seismic zone to failure deforms nearby volcanoes a new earthquake precursor the south iceland seismic zone sisz was loaded to failure in june 2000 resulting in two m6 6 earthquakes the sisz is an e w trending zone with an overall sinistral movement numerical models indicate that when the sisz is loaded to failure there are stress concentrations at its ends tensile in the north east and south west quadrants and compressive in the north west and south east quadrants these model predictions fit well with observations geodetic measurements indicate considerable compression uplift and associated intense seismicity in recent years in the volcanoes of hengill and eyjafjallajokull located in the quadrants of compression whereas there have been unusually frequent eruptions in the past decades in the hekla volcano located in one of the quadrants of extension the models predict that following the large june 2000 earthquakes stress relaxation within the sisz should lead to stopping of the intense seismicity and deformation in the volcanoes of hengill and eyjafjallajokull again in agreement with observations however when similar episodes of deformation and seismicity start again particularly in the hengill volcano a large earthquake would be expected within several years in the sisz the numerical models and the deformation and seismic data indicate that monitoring of soft inclusions such as volcanoes many with magma chambers in the vicinity of a seismic zone may serve as precursors to large earthquakes

brittle ice shell thickness of enceladus from fracture distribution analysis abstract we determine the depth of fracture penetration in multiple regions of enceladus by performing self similar clustering and length distribution analysis of fractures the statistical characterization of fault population attribute such as length and clustering provide a productive avenue for exploring deformation rate stress transmission mode rheology of the medium and mechanical stratification of the ice satellite through this analysis we estimate the depth of the mechanical discontinuity of enceladus ice shell that is the depth to which fractures penetrate the brittle ice layer above the ductile one in this work we find that for the south polar terrain spt the brittle ice shell interested by fracture penetration is about 30 km and corresponds to the total depth of the ice shell because the spt has a very high thermal gradient and hence fractures likely reach the ocean ice interface in the other regions analyzed the depth of fracture penetration increases from 31 to 70 km from the south pole to northern regions up to 75

thickness of the seismic slip zone this article reviews geologic and other evidence constraining the thickness of the principal slip zone psz that accommodates the bulk of coseismic shear displacement during an individual rupture event surface deformation from rupturing may occupy swaths tens of meters or more in width but trenches across active faults generally reveal that incremental slip is accommodated by a psz that is tens of centimeters or less in thickness geomorphic evidence coupled with the observations from trenching suggest a psz may stay well localized for distances of several kilometers through many rupture episodes mine exposures and exhumed fault zones demonstrate that pszs separating different lithologies within the fault core although contained within damage zones of variably fractured rock ranging up to hundreds of meters in thickness often comprise just a few centimeters of gouge ultracataclasite that have accommodated large finite displacements 1 km microstructural studies demonstrate incremental slip localized still further down to 1 10 mm as do other fault rock assemblages slickensides and slickenfibers fault veins of pseudotachylyte friction melt intravein septa in hydrothermal fault infills the accumulated evidence indicates that localization of coseismic shearing to less than 10 cm on planar faults is widespread throughout the crustal seismogenic zone with extreme localization to less than 1 cm not uncommon however some distributed coseismic shear may also develop especially at rupture irregularities coseismic reduction of shear resistance from friction melting t 1000 c or from transient thermal pressurization of aqueous fluids t 100 c requires slip during moderate to large earthquakes u 1 m to be restricted to narrow zones respectively a few centimeters or tens of centimeters in thickness given the evidence for slip localization the apparent scarcity of pseudotachylyte suggests either that seismic friction melting is a rare phenomenon or that pseudotachylyte is only rarely preserved in recognizable form within mature hydrated fault zones

regional differences of relative sea level changes in the northwest atlantic historical trends and future projections 1 mean sea level is one of the most important indicators for climate variability and change here we use tide gauge data and satellite measurements to examine recent trends in the mean relative sea level rsl in the northwest atlantic we then combine model output and satellite observations to provide sea level projections in the 21st century the mean rsl trend based on historical tide gauge data shows large regional variations from 2 to 4 mm yr above the global mean rsl rise rate in the southeast to 2 mm yr in the northwest along east canada this spatial difference can to a large degree be attributed to that in the vertical land motion measured by the global positioning system gps the combination of altimeter measured sea level change with the gps data can approximately account for tide gauge measurements at most stations over 1993 2011 when the gps data are used the projected mean rsl rise between 1980 1999 and 2090 2099 ranges from 38 to 63 cm along the scotia fundy and newfoundland coasts and smaller along labrador the northern gulf of st lawrence and the st lawrence estuary in spite of considerable uncertainties the ocean steric and dynamical effect is the dominant contributor 35 70 cm to the rsl rise along the canadian east coast the land ice glaciers and ice sheets melt contributes to the rsl rise by 10 15 cm except at nain where it is negligible the effect of the vertical land uplift is large 40 50 cm at nain sept iles and rimouski significantly reducing the magnitude of the rsl rise

geomechanical models for the quantitatively prediction of multi scale fracture distribution in carbonate reservoirs abstract in order to predict the multi scale fractures in carbonate the geo mechanical model need to be established the key thresholds 0 82 c and c for the micro fractures and macro fractures according to the mass release of the elastic strain energy and bursting was confirmed through ct scanning and some mechanics experiments then two physical models between strain energy density and fracture volume density were built based on the geomechanics theory combined with the mohr coulomb and griffith s criterion the fracture parameters under the complex stress condition were modified and deduced all geo mechanical algorithms were written into the finite element platform combined with the paleo structural restoration of the hetianhe anticline the three dimensional distribution of the multi scale fracture density and aperture were quantitatively simulated the prediction results are consistent with current in situ core and fmi observations

temperature and salinity variability on the scotian shelf and in the gulf of maine 1945 1990 examination of temperature and salinity data from the scotian shelf gulf of maine gulf of st lawrence and the adjacent continental slope has shown that the dominant low frequency event over the last 45 years was a cooling and subsurface freshening of the water masses from 1952 to 1967 followed by a rapid reversal of these trends the largest temperature and salinity changes 1952 1967 were 4 6 c and 0 7 respectively and occurred at about 100 m over the slope exchanges with shelf waters and vertical mixing gave rise to the surface manifestation of this variability the westward transport of the labrador current was found to have similar variability increasing from about 1 106 m3 s 1 in the early 1950s to about 4 106 m3 s 1 in the mid 1960s a simple model that accounts for this variation of transport and has a constant entrainment of north atlantic water indicates that changes of the westward flow of the labrador current could contribute significantly to the t s fluctuations

an experimental investigation of sill formation and propagation in layered elastic media a series of experiments are described where dyed water a magma analogue was intruded into solid gelatine a crustal analogue to investigate the formation of sills we considered a layered gelatine system with contrasting adjacent layers by varying the density and rigidity of the gelatine we found that experimental sills form when the upper layer is more rigid than the lower layer with intrusion occurring in a plane directly below the interface experimental dykes were observed to propagate to the surface when the young s modulus ratio of upper to lower gelatine layers was less than one experimental dyke arrest occurred when the upper layer was more rigid and the interface was strong two varieties of experimental sill formed when the upper layer was more rigid than the lower layer and the interface was sufficiently weak the form of the intrusion depends on the balance of driving pressures and the young s modulus ratio of contrasting adjacent layers when the rigidity ratio is high and there is a large driving pressure the experimental feeder dyke completely converts to propagate as a sill however when the rigidity ratio and driving pressure are both close to one a dyke sill hybrid forms under these conditions the experimental sill formation is accompanied by contemporaneous dyke intrusion into the overlying more rigid layer during sill propagation deformation structures such as faults and en echelon fractures are formed into the lower layer experimental sill propagation dynamics are controlled by viscous dissipation along the length of the sill causing acceleration with increasing length our study suggests that rigidity contrasts may play a major role in the location of sills and development of igneous complexes in ancient cratonic areas the moho is a suitable site for the preferential formation of sills with higher rigidity continental crust overlying weaker mantle mantle plumes impacting ancient continents provide a situation in which large sills can form to fractionate prior to eruption of flood basalts the boundary between the upper and lower crust conrad discontinuity may provide a preferential focus for the emplacement of sheets of silicic magma at continental arcs where the lower crust is weakened by prolonged heating and possible hydration

seasonal variation of the three dimensional mean circulation over the scotian shelf the seasonal mean circulation over the scotian shelf is studied numerically by computing mean and tidal current fields for winter spring and summer using a three dimensional nonlinear diagnostic model the mean current fields are forced by seasonal mean baroclinic pressure gradients tidal rectification uniform wind stresses and associated barotropic pressure gradients a historical hydrographic database is used to determine the climatological mean baroclinic forcing upstream open boundary conditions are estimated from the density fields to give no normal geostrophic bottom flow and are specified as either along boundary elevation gradients or depth integrated normal velocities the numerical solutions for nominal bimonthly periods january february april may and july august reveal the dominant southwestward nearshore and shelf break flows of relatively cool and fresh shelf water from the gulf of st lawrence and newfoundland shelf with speeds up to about 20 cm s the seasonal intensification of the southwestward flows is reproduced by the model with the transport increasing from 0 3 sv in summer to 0 9 sv in winter on the inner halifax section there are also pronounced topographic scale influences of submarine banks basins and cross shelf channels on the circulation such as anticyclonic gyres over banks and cyclonic gyres over basins baroclinicity is the dominant forcing throughout the domain but tidal rectification is comparable on the southwestern scotian shelf e g about 0 2 sv recirculating transport around browns bank for all the periods the mean wind stress generates offshore surface drift in winter the solutions are in approximate agreement with observed currents and transports over the scotian shelf although there are local discrepancies

fault permeability near yucca mountain a deep paleozoic carbonate aquifer is of special concern for the proposed high level nuclear repository at yucca mountain nevada it provides a potential pathway for groundwater transport of contaminants from the repository back to the biosphere the map of groundwater temperature at the water table has been interpreted by several investigators to indicate upwelling groundwater along major fault zones both east and west of yucca mountain of particular concern is the permeability of these fault zones the deep carbonate aquifer has been penetrated by only one test hole in the vicinity of yucca mountain ue 25pl in this borehole the hydraulic head in the deep carbonate aquifer was 20 m higher than head in the overlying tuff aquifer observations in ue 25pl show good earth tide water level fluctuations in the deep carbonate aquifer both the large 2 cm amplitude of the tidal signal and the fact that it is in phase with the tidal potential indicate that the deep aquifer is well confined by a layer of low hydraulic conductivity an estimate of the maximum hydraulic permeability of a fault zone that penetrates the confining is made by simulating the tidal response given a maximum permeability and the head difference one can calculate the upward flow from the deep carbonate aquifer into the overlying tuffs this analysis supports the interpretation of upward flow from the deep carbonate to the overlying tuffs this is a favorable condition for the proposed repository the upward potential for flow from the deep carbonate aquifer protects it from the downward movement of contaminants further deep drilling is necessary to confirm that the high head persists beneath the entire proposed repository nothing should be done either through construction of the repository or through groundwater development to reduce heads in the carbonate aquifer the higher heads protect the carbonate aquifer

inferring stress from faulting from early concepts to inverse methods abstract we review the evolution of concepts on and methods of estimating the state of stress from fault movements theories of failure in isotropic materials suggested a simple geometrical construction of optimal principal stress directions from a fault plane and its associated slip these optimal directions align shear stress and slip directions and maximize the difference between shear stress and frictional resistance on the fault plane optimal stress directions for calcite twinning are obtained by a similar construction with the difference that they maximize shear stress force representation of seismic sources independently introduced pressure p and tension t axes at positions that also maximize shear stress on both nodal planes frictional slip theory and the constraint that slip and shear stress directions be parallel allowed to address reactivation of pre existing faults this suggested that stress could also be inverted from reactivated fault and slip data or earthquake focal mechanisms early methods relied on geometrical constructions as a substitute for calculations whereas later methods relied on software as these calculations became tractable with the help of computers similar methods were developed for the inversion of stress from crystal twin gliding with non optimal geometry with a different criterion that relies on a threshold of the component of shear stress along the gliding line even though these methods seek a common stress tensor compatible with fault and slip data their main use is to separate polyphase data into homogeneous subsets and help deciphering complex tectonic histories fault and slip data can also be analyzed to constrain the strain rather than the stress tensor in most cases this involves a summation and yields an average strain for the considered rock volume stress inversion thus appears better suited for differentiating heterogeneous data whereas strain analysis appears better suited for homogenizing them

spatial variations in damage zone width along strike slip faults an example from active faults in southwest japan abstract field investigations reveal spatial variations in fault zone width along strike slip active faults of the arima takatsuki tectonic line attl and the rokko awaji fault zone rafz of southwest japan which together form a left stepping geometric pattern the fault zones are composed of damage zones dominated by fractured host rocks non foliated and foliated cataclasites and a fault core zone that consists of cataclastic rocks including fault gouge and fault breccia the fault damage zones of the attl are characterized by subsidiary faults and fractures that are asymmetrically developed on each side of the main fault the width of the damage zone varies along faults developed within granitic rocks of the attl and rafz from 50 to 1000 m in contrast the width of the damage zone within rhyolitic tuff on the northwestern side of the attl varies from 30 to 100 m the fault core zone is generally concentrated in a narrow zone of 0 5 5 m in width consisting mainly of pulverized cataclastic rocks that lack the primary cohesion of the host rocks including a narrow zone of fault gouge