landward dipping reflectors in accretionary wedges active dewatering conduits landward dipping seismic reflectors ldrs within the accretionary wedge at convergent plate margins have generally been interpreted as tilted bedding or thrust fault surfaces e g mexico northern japan this interpretation accords with models in which trench axis sediments are scraped off the descending plate to form a series of imbricate thrust sheets however intensely disturbed melanges with a regionally extensive landward dipping foliation are found beneath slope sediments in many ancient and active subduction complexes this observation combined with the fact that large volumes of fluid are released during dewatering of subducting and previously accreted sediments leads to the proposal that some of the seismic reflectors are porous laterally extensive fractureways filled with dewatering fluids derived from deeper underthrust water rich sediments these fractureways trend subparallel to the regional foliation of the accreted melange wedge the contrast in acoustic impedance between the high porosity fluid filled fractureways and the melange wall rocks is enhanced whenever methane and or carbon dioxide exsolve from rising waters ancient ldrs may be recognized where mineralized veins trend subparallel to the regional foliation of melange belts generated during subduction accretion 42 references 2 figures

chronology of deformation within the turbidite dominated lachlan orogen implications for the tectonic evolution of eastern australia and gondwana ar ar data from fabric forming white mica in slates syntectonic quartz veins and granitic mylonites constrain the timing of metamorphism deformation and exhumation in the lachlan orogen australia these data also help define the tectonic evolution of the tasmanides during paleozoic time the lachlan orogen formed by the progressive accretion of a thick turbidite fan sequence and volcanic terrains to gondwana during the closing of a small marginal ocean or back arc basin this tectonic setting was similar to the present western and southwestern pacific region accretion of the lachlan orogen to gondwana occurred by closing of the basin system by subduction accretion processes and some translation the process is typified in the western lachlan orogen by a major eastward migrating deformation involving chevron folding and faulting over an eastward propagating decollement melange zone and is recorded by ar ar mica ages ranging from 455 ma in the western part to 390 ma in the eastern part in the central lachlan orogen deformation migrated southwestward from 440 430 to 405 ma away from the high temperature wagga omeo metamorphic complex where deformation metamorphism occurred between 440 and 400 ma in the north 400 ma mica ages record deformation and inversion of structures in the cobar basin in the eastern lachlan orogen ar ar mica dates range from 450 to 340 ma ages of 455 445 ma are yielded by the narooma accretionary complex 405 390 ma ages are found along the major thrust faults bounding high grade metamorphic complexes and 360 340 ma cooling ages are found in the inverted extensional basins e g hill end and related structural zones the ar ar results also document periods of reactivation on early formed structures during later deformation elsewhere in the orogen

locating spatial changes of seismic scattering property by sparse modeling of seismic ambient noise cross correlation functions application to the 2008 iwate miyagi nairiku mw 6 9 japan earthquake

methane derived authigenic carbonates formed by subduction induced pore water expulsion along the oregon washington margin authigenic magnesian calcite dolomite and aragonite are precipitated in the uppermost terrigenous sediments of the washington oregon accretionary prism by subduction induced dewatering these distinctive carbonates are methane derived and occur at sites of concentrated pore water expulsion unique biologic communities that subsist at least indirectly on methane suess et al 1985 are also found at some of these sites the methane which is dominantly biogenic is carried to the uppermost sediments of the prism by fluids and is oxidized by sulfate reducers before being incorporated into a carbonate cement carbonate precipitation occurs below the oxic layer probably no deeper than several centimetres to a few metres below the seabed cementation may be induced by three factors 1 increased carbonate alkalinity resulting from microbial sulfate reduction 2 decreased co 2 solubility resulting from a pressure decrease when the pore water escapes the prism and or 3 the addition of ca 2 and mg 2 ions from sea water near the sediment water interface the convergent margin setting engenders precipitation of authigenic carbonates in several ways compressive stresses induce anomalously rapid compaction and dewatering rates and they may cause overpressuring in migrating pore water thereby delaying precipitation of carbonates until pressure is released near the sediment water interface structural deformation of the accretionary prism creates pathways such as fault zones secondary fracture porosity and dipping permeable layers often exposed by mass movement for efficient advection and expulsion of methane enriched pore water these characteristic conditions which lead to the precipitation of methane derived carbonates may be found at other convergent margins

the effects of pressure and porosity on the micromechanics of the brittle ductile transition in quartzite room temperature experiments on a quartzite with 7 porosity show that with increasing pressure there is a transition from brittle faulting to ductile cataclastic flow at about 600 mpa in contrast experiments on nonporous quartzite show only faulting up to 1000 mpa the transition to cataclastic flow in the porous quartzite is due to the changing influence of the pores microstructural observations and elastic theory suggest that the transition occurs at the pressure where the differential stress producing a compressive stress concentration sufficient to initiate pore collapse becomes less than that producing a tensile stress concentration sufficient to nucleate axial microcracks at the tops and bottoms of pores cataclastic flow of the porous quartzite is only transient deformation remains distributed and accompanied by work hardening only as long as pore collapse continues to 16 strain at higher strains microcracking produces a net dilatancy which causes strain weakening that leads to faulting at 26 strain at a confining pressure of 750 mpa the faults are stable whereas at 1000 mpa they are unstable the results indicate that porous rocks may undergo limited ductile deformation at shallow levels in the crust but higher strains will cause deformation to localize

tectonics and hydrogeology of accretionary prisms role of the decollement zone abstract at convergent margins the decollement zone comprises the plate boundary and is marked by profound structural disharmony by changes in stress orientation and by a discontinuity in plate velocity the decollement zone initiates in a weak sediment layer typically a low permeability hemipelagic mud lying below a more rapidly deposited stronger more permeable trench turbidite sequence at the deformation front trench turbidites tend to be offscraped whereas the finer grained hemipelagic and pelagic sediments are more likely to be underthrust offscraped materials may undergo only limited burial whereas underthrust deposits can be deeply buried undergo high pressure metamorphism and are more likely to be preserved in the stratigraphic record burial rates associated with underthrusting are high exceeding 20 km my with high rates of underthrusting sediment descending below the decollement zone is probably buried faster than it can dewater resulting in emplacement of relatively high porosity deposits at depth fluids flowing from modern decollement zones have migrated substantial distances laterally and tapped deep sources the episodicity of flow suggests pumping of fluid by cycles of dilation and flow to the decollement zone followed by failure and fluid expansion along the decollement zone possible pressure gradients below the decollement zone allow flow upward into it while maintaining minimum effective stress along it the thickness of sediment underthrust beneath the decollement zone determines whether these deposits are emplaced by diffusive underplating with stratal disruption and efficient dewatering or by coherent underplating with the formation of macroscopic duplexes and transfer of fluid to the base of the accretionary prism deformation mechanisms affecting accreted sediment depend on depth of entrainment into the decollement zone and duration of residence

earthquake faulting as a structural process abstract structural geology is concerned with the history of movement in the earth s crust and the processes by which displacements occur in the upper one third to one half of deforming continental crust displacement is accommodated largely by seismic slip increments on existing faults it follows that earthquakes and related processes are an integral part of structural geology traditionally structural geologists have been preoccupied with the complexity of the finite deformation within fault zones and with the stress states prevailing at the initiation of faults in intact crust future structural work should be directed more towards understanding the dynamic character of fault reactivation during incremental slip and related effects questions of interest include rheological and geometrical controls on the initiation perturbation and termination of ruptures directivity effects associated with rupture propagation the recognition of structures resulting from repeated stress cycling within seismogenic crust and identification of structural features diagnostic of shear stress levels during faulting structures arising from the inter relationships between slip episodes and induced fluid flow are of special importance because these dynamic fault processes appear influential in the development of much fault hosted mineralization mesothermal gold quartz lodes hosted in high angle reverse shear zones of mixed brittle ductile character form illustrative examples of structures that arguably can only be interpreted by seismo structural analysis embodying the concepts listed above

water flow in the barbados accretionary complex we present a simple analytic kinematic model of the barbados accretionary complex assuming a porosity depth law and deformation by pure vertical shear the model is applied to two sections a northern one with a 900 m thick basin sedimentary column near 16 n and a southern one with a 4 5 km thick one to the south this simple model is compatible with growth of the barbados accretionary complex since 50 ma assuming a constant subduction rate and a constant basin sedimentary column equal to the present one this conclusion is not affected by reasonable changes in the porosity depth law it suggests that the totality of the entering sedimentary column is either accreted or subcreted to the wedge the accretion velocity decreases dramatically with age and its variation should be taken into account in any quantitative model the average strain rates show remarkably different distributions between the two sections the thinner wedge having a much higher rate in a narrow area at the toe we then use the model to compute the sediment grains flow the fluid flow and their thermal effects these effects are small and do not exceed 5 of the heat flow in the absence of other internal flows in contrast the thermal effect of the burial of the slab can result in a lowering of the surface heat flow by as much as 40 the temperature at the base of the wedge on its arc side is close to 300 c on the southern section and half that amount on the northern one this high temperature could account for the absence of large earthquakes to the south and their presence to the north the amount of water discharged if collected by faults over the whole toe area is unable to account for some of the manifestations observed over the toe or seaward of the toe in the barbados area we suggest two possible other sources one for the southern section is the orinoco fan area the other for the northern section might be seismic pumping at the limit of the seismogenic zone along the backthrusts between the accretionary wedge and the forearc basin

initiation of the great mw 9 0 tohoku oki earthquake abstract we determined the location size mechanism and the frequency content of the first 4 0 s of the 2011 tohoku oki earthquake since the beginning of this earthquake is very small we develop a comparative approach against a near by reference earthquake the master event we first determined the water depth near the master event using the differential timing between the water phase pwp reflected from the air water interface and the depth phase pp reflected from the water crust interface then we located the master event using the well known ocean bathymetry in the area after calibrating teleseismic arrays 30 to 90 at short periods for timing and amplitude with respect to the master event we were able to determine the initiation of the main event it began as a small m w 4 9 thrust event located at 38 19 n 142 68 e at a depth of 21 km and a few seconds later evolved into a slower extremely large slip event up dip

tectonothermal history of the western lachlan fold belt australia insights from white mica studies detailed b lattice parameter and illite crystallinity ic studies of k white micas in slates from the stawell and ballarat bendigo zones sz bbz in the western lachlan fold belt of victoria australia reveal a metamorphic pattern characterized by regional metamorphism associated with crustal thickening and younger contact metamorphism accompanied by deformation the ic data indicate that rocks regionally metamorphosed prior to the intrusion of the early and late devonian granitoids vary in grade from epizonal greenschist facies to diagenetic zeolite facies and that most are of epizonal to anchizonal prehnite pumpellyite facies grade in the bbz a decrease in grade from west to east occurs across fault zones ic values show little change indicating that limited vertical displacement has occurred this is in accord with the thin skinned deformation model proposed for the western lachlan fold belt the b lattice parameters x 9 022 a n 137 s n 0 009 indicate baric conditions intermediate between those of new hampshire p al 2 sio 5 triple point and otago intermediate p thus a moderately low geother mal gradient existed 450 430 ma ago when these rocks were deformed k d fe mg actinolite fe mg chlorite values 0 52 0 70 obtained from coexisting actinolite and chlorite in metabasites from fault zones support the moderately high p c 4 kbar metamorphism suggested by the b cell parameter values the metamorphic conditions indicated by these data are contrary to the low p high t conditions pro posed by previous authors who inferred an intimate association between deformation granitoid intrusion and gold mineralization the b lattice parameter of white micas in slates adjacent to early devonian c 400 ma granitoids with schist bearing aureoles in the north eastern part of the bbz x 9 002 a n 27 s n 0 007 indicate pressures in the order of c 2 5 kbar which are in accord with those obtained from andalusite cordierite and zoisite garnet bearing assemblages observed in the higher grade metapelitic and calcareous rocks this contrasts with the higher pressure c 4 kbar existing during regional metamor phism and implies that c 6 5 8 km of metasedimentary rocks in the bbz were removed before the emplacement of the early devonian granitoids metamorphic assemblages in hornfelses associated with late devonian granitoids indicate a further 5 6 km of metasediment were removed in the next 40 ma prior to their emplacement this study shows the value of white mica studies in elucidating the tectono thermal history of a low grade metamorphic terrane dominated by metapelitic rocks

divergent double subduction tectonic and petrologic consequences divergent double subduction involving removal of an oceanic basin from both sides and collision has distinct fingerprints of magmatism and significant implications for the tectono magmatic evolution of orogenic belts the complete evolution of a divergent double subduction system involves four stages 1 initial interaction between the two divergent subduction zones on both sides of a single oceanic plate 2 closure of the oceanic basin when the two overriding plates meet followed by 3 detachment of the oceanic lithosphere from the overlying crust and sedimentary sections 4 sinking and disappearance of the oceanic slab into the mantle detachment of the oceanic slab leads to intense decompressional melting of mantle and triggers melting of accretionary wedge strata and lower crust resulting in large scale magmatic and volcanic activity the main consequences of a divergent double subduction system are that it produces opposed thrust systems extensive long lived granitoid magmatism with mantle isotopic signature and volcanism that evolves toward bimodalism this model can be applied to the western half of the paleozoic lachlan fold belt southeastern australia to explain the wide scale silurian to early carboniferous granitoid magmatism its spatial and temporal relationships and late bimodal magmatism closure of the oceanic basin is thought to have occurred during the early to middle devonian detachment of the oceanic slab led to felsic to intermediate composition magmatism bimodal volcanism involving local basaltic flows is a reflection of subsequent sinking of the slab

internal structure of the precordilleran fault system chile insights from structural and geophysical observations abstract geological field work and audiomagnetotelluric data from two profiles crossing the west fissure zone in northern chile were used to describe the geometry and structure of the fracture damaged zone surrounding this strike slip fault system the w e profiles show that the width of the west fissure zone based on the fracture density distribution derived from aerial photographs is 4000 m on profile a and 7000 m on profile b the estimated widths correspond roughly to the region where the fault is kinematically uniform the ratio of the fault width to the fault length ranges from 0 024 to 0 041 this ratio compares favourably with the measured ratio of small metre scale natural faults audio frequency magnetotelluric imaging shows low electrical resistivity zones resistivity of 5 30 m coincident with the mapped surface traces of the fault however these zones are very narrow width about 100 m and only 50 m profile a and 200 m profile b deep respectively on profile b the shallow high conductive zone is underlain by a resistive zone 1000 m the conductivity enhancement in these shallow and narrow zones contrasts with the broad process zone revealed by structural analysis we assume that the conductivity enhancement is due to meteoric water entering a zone of ruptured rocks along the fault trace fault core at present we have no indication for seismic slip along the investigated segments of the west fissure zone fault models have shown that during aseismic periods of fault evolution fault healing i e strength recovery due to compaction and cementation is active fluids and fluid transport which are probably responsible for enhanced conductivity are confined to the remaining fractures of the fault core at shallow depth

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

shallow dynamic overshoot and energetic deep rupture in the 2011 mw 9 0 tohoku oki earthquake strong spatial variation of rupture characteristics in the moment magnitude mw 9 0 tohoku oki megathrust earthquake controlled both the strength of shaking and the size of the tsunami that followed finite source imaging reveals that the rupture consisted of a small initial phase deep rupture for up to 40 seconds extensive shallow rupture at 60 to 70 seconds and continuing deep rupture lasting more than 100 seconds a combination of a shallow dipping fault and a compliant hanging wall may have enabled large shallow slip near the trench normal faulting aftershocks in the area of high slip suggest dynamic overshoot on the fault despite prodigious total slip shallower parts of the rupture weakly radiated at high frequencies whereas deeper parts of the rupture radiated strongly at high frequencies

the role of fluids in faulting deformation a case study from the dead sea transform jordan the geochemistry of carbonate fault rocks has been examined in two areas of the arava fault segment which forms the major branch of the dead sea transform between the dead sea and the gulf of aquaba the role of fluids in faulting deformation in the selected fault segment is remarkably different from observations at other major fault zones our data suggest reduced fluid rock interactions in both areas and limited fluid flow the fault did not act as an important fluid conduit there are no indications that hydrothermal reactions cementation dissolution did change the strength and behavior of the fault zone although the two areas show considerable differences with respect to fluid sources and fluid flow in one area the investigated calcite mineralization reveals an open fluid system with fluids originating from a variety of sources stable isotopes 13c 18o strontium isotopes and trace elements indicate both infiltration of descending meteoric and or sea water and ascending hydrothermal fluids in the other area all geochemical data indicate only local small scale fluid redistribution these fluids were derived from the adjacent limestones under nearly closed system conditions

thermal regimes anatexis and orogenesis relations in the western lachlan fold belt southeastern australia abstract crustal evolution of the lachlan fold belt of southeastern australia has involved the mobilisation of significant melt volumes now preserved as granites suggesting that large parts of the lower crust were at t 800 c for part of the thermal evolution this anomalous thermal activity has been variously related to continental extension magmatic underplating and to thinning of the mantle lithosphere overriding considerations reflected in the surface geology must include the tectonic setting the thermal regime and the state of stress in the crust at the time of anatexis one dimensional geothermal modelling suggests that no one mechanism can generate the required thermal regime necessary to produce the volume of granite observed in the crust the observed geological relationships do not match those predicted for lithospheric thinning due to continental extension magmatic underplating can cause melting but must involve extensive source zones and allow continual feeding of the magma to higher crustal levels the crustal thickening lithospheric thinning mechanism involves upwelling of hot asthenospheric mantle to the base of the crust but the melt products are confined to a very thin layer at the crust mantle boundary mechanisms for melt extraction and emplacement to higher crustal levels must be explained in the western lachlan fold belt the presence of a major mid crustal detachment fault ductile shear zones in the lower crust and marked internal shortening of the upper and possibly lower crustal blocks suggests that shear heating may also provide a significant component to the heat budget of the evolving crust melting will not occur however unless thermal equilibration of both the upper and lower plates takes place prior to shear heating such equilibration will involve time scales in the order of 30 50 ma unless extra heat is added into the lower crust e g advective input inferred flexural rigidity of the lithosphere related to basinal subsidence during the period of orogenesis in central victoria suggests that thermal effects related to granitoid intrusion must be largely post tectonic and that felsic intrusive activity is a consequence of the crustal thickening rather than the cause thermal regimes during orogenesis cannot be restricted to a single mechanism upwelling of hot asthenosphere causing significantly higher heat input at the base of the crust coupled with shear heating and internal strain heating of the crust during the crustal thickening stage as well as thermal effects related to magma intrusion into the lower crust result in a complex thermal history during collisional orogenesis

sequential rotation of stretching axes and block rotations a structural and paleomagnetic study along the north anatolian fault abstract fault kinematics of the western part of the north anatolian fault an active transcurrent fault were investigated consistent successive counterclockwise rotation of incremental stretching directions was derived from the seven areas investigated we assumed that the changes in stretching directions correlate to the consistent rotation of one or several blocks caused by interaction of major fault segments in order to test this hypothesis we compared magnetic remanence directions measured within tertiary calc alkaline volcanic rocks with the changes in stretching direction in spite of the successive changes in stretching systematic changes in remanence directions were not observed most of the latter show no or low angular distances to the reference direction of d 335 i 50 both positive and negative signs are inferred for movements about subhorizontal and subvertical axes where magnetic remanence directions suggest rotation we conclude that changes in the overall deformation explain the systematic changes in incremental directions better than consistent external rotation a deformation path is proposed that includes ne sw and n s shortening during the paleogene and possibly lower miocene nw se shortening and penecontemporaneous local n s extension for the miocene and nw se to e w shortening and sw ne to n s extension for the pliocene until the present

hydrogeochemistry of the northern barbados accretionary complex transect ocean drilling project leg 110 detailed studies of the major element geochemistry oxygen and hydrogen isotope ratios of pore fluids and the 87sr 86sr ratio of dissolved strontium have made it possible to unravel physical and chemical processes that affect the pore fluid chemistry in a transect of drill holes across the northern barbados accretionary complex these processes include 1 alteration of volcanic ash buried in the pleistocene pliocene sediment column 2 alteration of underlying basalts of layer 2 of the oceanic crust 3 movement of fluids from deep in the accretionary complex along fault zones particularly the decollement and minor permeable layers these fluids from deeper in the complex are characterized by low chloride concentrations and increased 18o h2o values presumably as a result of dehydration of smectite interlayers and 4 mixing processes involving the migrating fluids cause incongruities in the geochemical anomalies of these fluids

hydrologic properties and structure of the mozumi fault central japan 1 analyses of rocks from the active fault survey tunnel afst provides insight into the structure and hydrogeology of the northeast trending mozumi sukenobu fault an active strike slip fault with 125 to 500 m of right lateral slip in central japan interlayered regions of sub vertical permeability zones formed by cataclasis and slip on clay rich foliated zones core samples range from 10 19 m2 to almost 10 13 m2 cfc analyses of waters from the fault zone show that water entering the tunnel is 27 36 years old yielding a bulk fault permeability of 10 14 to 10 15 m2 the data support a fault zone model of a fluid saturated low velocity zone with a sharp velocity contrasting with the protolith pore fluid pressures could build and dissipate in isolated high permeability pods 10 s 100 s m in dimension

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

anatomy of a buried thrust belt activated during hydraulic fracturing abstract tectonically active fault networks are often inter connected but in the case of injection induced seismicity prior knowledge of fault architecture tends to be severely limited in most cases reactivated faults due to fluid injection are inferred after the fact by the spatial distribution of induced seismicity hypocenters such reliance on post injection seismicity impedes any pre operational risk analysis as well as development of a more holistic understanding of fault system models by combining high resolution depth migrated 3 d seismic data with a new focal depth estimation method that reduces spatial uncertainty of hypocenters this study pinpoints microearthquake fault activation within a buried thrust belt in the montney formation in western canada british columbia during hydraulic fracturing operations rupture nucleation occurred on seismically imaged thrust ramps that cut through the debolt formation a massive carbonate layer that underlies the stimulated zone high resolution seismic images reveal transverse structures interpreted as basement controlled fold hinges or tear faults that transferred displacement between thrust faults during late cretaceous paleogene compressional shortening the spatio temporal pattern of induced seismicity suggests that these transverse structures provide permeable pathways for aseismic pore pressure diffusion thus connecting distinct thrust faults and enabling earthquake triggering on a timescale of days and at distances of up to 2 km from the injection wells inferred relationships highlight how the fault system is connected including apparent stress concentrations at the intersections of transverse structures and orogen parallel thrust ramps

mapping folds and fractures in basement and cover rocks using uav photogrammetry cape liptrap and cape paterson victoria australia abstract brittle and ductile deformation of alternating layers of devonian sandstone and mudstone at cape liptrap victoria australia resulted in upright folds with associated fold accommodation faults and multiple fracture sets structures were mapped at the fold stack locality at cape liptrap using high resolution aerial photographs acquired by a digital camera mounted on an unmanned aerial vehicle uav subsequent photogrammetric modelling resulted in georeferenced spatial datasets point cloud digital elevation model and orthophotograph with sub cm resolution and cm accuracy which were used to extract brittle and ductile structure orientation data an extensive dataset of bedding measurements derived from the dense point cloud was used to compute a 3d implicit structural trend model to visualise along strike changes of devonian tabberabberan folds at the fold stack locality and to estimate bulk shortening strain this model and newly collected data indicate that first generation shallowly south southwest plunging upright folds were gently refolded about a steeply plunging subvertical fold axis during a devonian low strain north south shortening event this also led to the local tightening of first generation folds and possibly strike slip movement along regional scale faults in order to distinguish fractures associated with devonian compression from those that formed during cretaceous extension and later inversion we compared the five fracture sets defined at cape liptrap to previously mapped joints and faults within the overlying sedimentary cover rocks of the cretaceous strzelecki group gippsland basin which crop out nearby an east southeast trending fracture set that is not evident in the strzelecki group can be linked to the formation of devonian folds additionally hinge line traces extracted from the fold stack dataset are aligned parallel to a dominant fracture set within the overlying cover sediments this suggests that basement structures folds and coeval parallel faults have an important influence on fault and joint orientations within cretaceous cover rocks

p t conditions in the south wales coalfield evidence from coexisting hydrocarbon and aqueous fluid inclusions siderite nodules in the carboniferous coal measures of south wales contain cavities which are often infilled with quartz carbonates sulphides and hydrocarbons the quartz contains a mixture of hydrocarbon and aqueous fluid inclusions the aqueous fluid inclusions consist of a dilute brine 3 wt nacl equivalent and have homogenization temperatures in the range 97 212 oc mean 143 oc the hydrocarbon fluid inclusions are dominated by methane with a small component of higher order hydrocarbons their homogenization temperatures are in the range 35 78 c mean 54 c it is assumed that the two fluids were trapped simultaneously during growth of the quartz and thus a p t estimate of entrapment can be obtained by graphical intersection of the hydrocarbon isochores and the aqueous fluid bubble point homogenization temperatures assuming hydrocarbon saturation this method gives temperatures between 130 and 160 oc and pressures between 40 and 55 mpa the timing of mineralization is uncertain but it is suggested that it took place during burial and low grade metamorphism of the subsiding sedimentary basin i e in the upper carboniferous the hydrothermal fluids were probably derived from evolved meteoric or connate waters expelled during subsidence and sediment compaction

character and kinematics of faults within the turbidite dominated lachlan orogen implications for tectonic evolution of eastern australia reply fault zones within turbidite dominated orogenic systems typified by the lachlan orogen of eastern australia are characterised by higher than average strain and intense mica fabrics transposition foliation and isoclinal folds poly deformation with overprinting crenulation cleavages and steeply to moderately plunging meso and micro folds they have a different character compared to the brittle ductile fault zones of classic foreland fold and thrust belts such as the appalachians and the canadian rocky mountains multiple cleavages and transposition layering record a progressive shear related deformation history an intense mica fabric evolves initially during shortening of the overlying sedimentary wedge but is progressively modified during rotation and emplacement to higher structural levels along the steep parts of inferred listric faults the deformed wedge outside the fault zones generally undergoes one phase of deformation shown by a weak to moderately developed slaty cleavage which is parallel to the axial surface of upright subhorizontally plunging chevron folds other faults within the turbidites of the lachlan orogen include the steep zones of ductile strike slip deformation that bound a centrally located high t low p metamorphic complex characterised by s c mylonites these ductile shear zones indicate a southward passage of the metamorphic complex as a crustal wedge with emplacement to higher structural levels along a leading edge ductile thrust fault ar ar dating constrains the timing of regional deformation to be mostly late ordovician through silurian across the lachlan orogen faults in the low grade turbidite sequences record the kinematic evolution of the developing lachlan orogen and indicate progressive deformation associated with simultaneous eastward propagating and migrating deformation fronts in both the western and eastern parts of the fold belt these deformation fronts are related to accretionary style deformation at the leading edges of overriding plates in an inferred southwest pacific type subduction setting from the late ordovician to the mid devonian along the former gondwana margin the fault zones effectively accommodate and preserve movements within the structurally thickening migrating and prograding accretionary wedge

carbonate cements indicate channeled fluid flow along a zone of vertical faults at the deformation front of the cascadia accretionary wedge northwest u s coast to understand the relation between fluid seeps and structures sedimentary rocks were collected with the dsrv alvin from a vertical fault zone that transects the deformation front of the cascadia accretionary wedge the rocks contained diagenetic carbonate cement that was precipitated from fluids expelled during accretion carbon oxygen and strontium isotope data are consistent with a fluid source at 2 km depth most carbon isotopes range from 1 to 25 pdb peedee belemnitel standard consistent with a thermogenic methane source oxygen isotopes show extreme 18 o depletions 4 to 13 pdb that are consistent with precipitation from fluids with temperatures as high as 100 c 87 sr 86 sr values of 0 70975 to 0 71279 may be due to strontium in fluids derived from clay rich parts of the stratigraphic section the ubiquity of carbonate precipitates and the isotope data indicate that the vertical fault zone is an efficient conduit for fluid dewatering from deep levels of the accretionary wedge

tectonically driven fluid flow in the kodiak accretionary complex alaska sandstone and chert boudins that have syntectonic extensional veins are dominant structural elements in melanges of the kodiak accretionary complex alaska detailed analyses of cogenetic methane rich and water rich fluid inclusions in syntectonic quartz veins indicate that fluid pressures dropped by 20 to 45 during crystal growth this drop occurred faster than uplift of the rock and probably represents the local effect of fluid escaping to shallow levels in the subduction complex during melange deformation possibly along an interconnected fracture network an important implication of channelized fracture flow to higher levels in a subduction complex is that fluids may transport heat and solutes thereby generating thermal and chemical anomalies along shallow faults

barbados ridge hydrogeologic tests implications for fluid migration along an active decollement hydrogeologic tests were conducted at a sealed borehole penetrating the decollement of the barbados ridge accretionary complex at low excess pore pressures p p p h p l p h 0 0 to 0 36 where p p pore pressure p h hydrostatic pressure and p l lithostatic pressure estimated permeabilities were comparable to those of similar unfractured sediment these tests complement shipboard packer tests completed at higher fluid pressures 0 5 to 1 0 during ocean drilling program odp leg 156 together the test results suggest a 4 to 5 order of magnitude permeability increase as fluid pressure varied from hydrostatic 0 to lithostatic 1 however unlike the results of the shipboard packer tests the test results presented here exhibit no evidence of a relationship between permeability and pore pressure the combined findings from the two sets of hydrogeologic tests indicate that significant permeability increases can occur within the decollement at pore pressures below lithostatic pressure

warm fluid migration along tectonic melanges in the kodiak accretionary complex alaska analyses of methane water fluid inclusions from syntectonic quartz veins in melange boudins of the kodiak accretionary complex alaska indicate fluid temperatures ranging from 215 to 290 c at depths between 10 and 14 km these fluid temperatures are significantly higher than those predicted by conductive heat flow models of subduction zones given the available geological constraints this discrepancy is interpreted as the result of migration of warm fluids from deeper structural levels along active fault zones during subduction related underthrusting of these units this interpretation requires more careful consideration of how migrating fluids affect the general thermal structure of subduction zones

compressive sensing of the tohoku oki mw 9 0 earthquake frequency dependent rupture modes 1 compressive sensing cs is a technique for finding sparse signal representations to underdetermined linear measurement equations we use cs to locate seismic sources during the rupture of the 2011 tohoku oki mw9 0 earthquake in japan from teleseismic p waves recorded by an array of stations in the united states the seismic sources are located by minimizing the l2 norm of the difference between the observed and modeled waveforms penalized by the l1 norm of the seismic source vector the resulting minimization problem is convex and can be solved efficiently our results show clear frequency dependent rupture modes with high frequency energy radiation dominant in the down dip region and low frequency radiation in the updip region which may be caused by differences in rupture behavior more intermittent or continuous at the slab interface due to heterogeneous frictional properties

earthquakes as a coupled shear stress high pore pressure dynamical system the migration coalescence and localization of slip seismicity and zones of high pore pressure are modeled using a porosity reduction mechanism to drive pore pressure within a fault zone in excess of hydrostatic increased pore pressure in discrete cells creates zones of low effective stress which induces slip that may propagate to surrounding cells depending on the local state of stress at slip stress is transferred using the solution for a rectangular dislocation in an elastic half space and pore pressures are redistributed by conserving fluid mass using simple assumptions about fault rheology and permeability it is shown that the interaction between shear stress and effective stress evolves to a state of earthquake clustering with repeated events locked zones and large variations in fault strength the model evolves from a uniform shear stress state on a strong fault to a heterogeneous shear stress state on a weak fault

chronology and tectonic framework of turbidite hosted gold deposits in the western lachlan fold belt victoria results abstract 40 ar 39 ar data constrain the history of metamorphism deformation and mineralization in the western subprovince of the lachlan fold belt rocks in the mount stavely volcanic complex and the bushy creek pluton give 40 ar 39 ar ages of about 500 ma for hornblende and biotite the dates from the mount stavely volcanic complex limit the age of mineralization in the metavolcanic rocks of the stavely belt whereas the date for the bushy creek pluton extends the area of cambrian ordovician plutons of the delamerian orogeny to east of the grampians mountains and helps define the surface expression of the western border of the paleozoic lachlan fold belt 40 ar 39 ar dating of metamorphic mica growth phengite in cleaved slates and phyllites within the landsborough fault avoca fault zone heathcote fault zone and mount wellington fault zone gives ages of 453 2 440 2 426 4 and 410 390 ma respectively these data indicate a progression of deformation from west to east starting in late ordovician early silurian time in the stawell and bendigo ballarat structural zones the major phase of deformation in the western subprovince of the lachlan fold belt is therefore silurian and not devonian sericites from major gold deposits in the stawell zone and bendigo ballarat zone give 40 ar 39 ar dates of about 440 ma that are coincident with folding and thrusting a second episode of mineralization and fault reactivation at about 420 to 410 ma is found in some deposits in these zones based on data from a previous study in the melbourne zone including the woods point dike swarm and locally in the bendigo ballarat zone some gold deposits give sericite dates of about 380 360 ma these ages are consistent with the close association of many melbourne zone gold deposits with devonian dikes and plutons the results indicate that gold mineralization in the stawell zone bendigo ballarat zone and melbourne zone was episodic and both temporally and spatially associated with crustal heating linked to regional metamorphism and plutonism initial stages of mineralization in the province comprising many of the large deposits in western and central victoria e g bendigo ballarat stawell wattle gully tarnagulla accompanied metamorphism folding and thrusting subsequent mineralization is widespread but produced mainly smaller deposits

insights into the mechanics of en echelon sigmoidal vein formation using ultra high resolution photogrammetry and computed tomography abstract two novel techniques photo based reconstruction photogrammetry and computed tomography ct are used to investigate the formation of an exceptional array of sigmoidal veins in a hand sample from cape liptrap southern victoria and to provide constraint on models for their development the accuracies of the photogrammetric models were tested by comparison with a laser scan generated three dimensional 3d model the photogrammetric model was found to be accurate to at least 0 25 mm and substantially more detailed than the laser scan a methodology was developed by which 3d structural measurements could be extracted from the photogrammetric model this was augmented with the ct model which through its capacity to elucidate internal structure was used to constrain the geometry and linkage of structures within the rock volume the photogrammetric and ct data were then combined with detailed photomicrographs to evaluate the evolution of the sigmoidal veins in the sample the angle between the sigmoidal vein margins and an inferred shear zone as well as the orientations of the crystal fibres were found to imply a rotation of 27 however coeval pressure solution seams and older veinlets in the rock bridges between the veins were only found to have rotated by 10 an observation not easily explained using existing models for sigmoidal vein formation a new model is proposed in which a significant component of sigmoidal vein geometry is due to localised dilation caused by slip on the pressure solution seams the process involves strain partitioning onto pressure solution seams which leads to exaggeration of sigmoidal vein geometries if not accounted for the apparent vein rotation due to slip partitioning introduces errors into calculations of simple shear and volume strain based on sigmoidal arrays of this type furthermore the ct data demonstrated that in 3d the veins are continuous and channel like implying a far higher degree of connectivity and fluid transport than is suggested by their 2d form

deterministic frequency wavenumber methods and direct measurements of rupture propagation during earthquakes using a dense array data analysis data recorded by the smart 1 array in taiwan are used to make the first direct measurements of two dimensional earthquake rupture propagation using frequency wavenumber techniques and ray theory we obtain estimates of the spatial extent duration and directions of rupture propagation during two earthquakes located offshore taiwan our estimates include uncertainties due to errors in fault plane location and orientation velocity structure and slowness ray parameter measured at the array we find that the january 29 1981 ml 6 3 taiwan earthquake ruptured unilaterally updip and toward the west on a 60 dipping 109 striking reverse fault using p waves we find its fault length and duration to be 25 18 km and 7 4 3 4 s respectively s waves indicate a fault length and duration of 27 15 km and 9 4 3 6 s respectively we suggest that the november 14 1986 ml 7 0 hualien taiwan earthquake was triggered by a shallow h 14 km foreshock ml 5 4 which occurred on a subparallel or splay fault approximately 5 s before the mainshock based on p waves rupture propagation during the foreshock is unilateral towards the northeast and slightly downdip on a 58 dipping 38 striking reverse fault its spatial extent and duration are approximately 23 km and 5 4 s the mainshock initiated at greater depth h 34 km than the foreshock with its primary direction of rupture unilateral toward the northeast and slightly updip on a 57 dipping 43 striking reverse fault using p waves we found a spatial extent and duration of 68 15 km and 12 4 2 2 s s waves indicate a similar extent duration and direction of propagation for the mainshock however we found it difficult to distinguish the foreshock and mainshock 5 waves we show by example that these results represent an improvement over what can be obtained using long period t 5 s teleseismic methods comparison of our results with those obtained using teleseismic data suggests either a short duration slip time function or that most slip occurs near the rupture front our results indicate that much of the complexity in the seismograms recorded during these events by the smart 1 array is due to spatial and temporal variations of the source this suggests that at least in some cases predictions of both the phase and amplitude of strong ground motion as a function of time would require a priori knowledge of source properties finally we recommend siting small 10 station dense arrays on land above offshore subduction zones which are considered seismic gaps because they can provide more detailed measurements of rupture propagation than is presently possible

the 2011 magnitude 9 0 tohoku oki earthquake mosaicking the megathrust from seconds to centuries geophysical observations from the 2011 moment magnitude m w 9 0 tohoku oki japan earthquake allow exploration of a rare large event along a subduction megathrust models for this event indicate that the distribution of coseismic fault slip exceeded 50 meters in places sources of high frequency seismic waves delineate the edges of the deepest portions of coseismic slip and do not simply correlate with the locations of peak slip relative to the m w 8 8 2010 maule chile earthquake the tohoku oki earthquake was deficient in high frequency seismic radiation a difference that we attribute to its relatively shallow depth estimates of total fault slip and surface secular strain accumulation on millennial time scales suggest the need to consider the potential for a future large earthquake just south of this event

the north anatolian fault zone and the role of fluids in seismogenic deformation a study of the north anatolian fault zone turkey in dicates significant spatial variations of deformation mechanisms and fluid flow along and across a major active strike slip fault brittle deformation and later dissolution are mostly localized within the fault core whereas crystal plastic deformation and diffusive mass transfer are more widely distributed the fault underwent a three stage development i repeated episodes of frictional failure pressure solution fluid migration and subsequent healing cataclasites and veins were formed during this stage we propose that the episodic events are associated with open and closed fluid systems during seismogenic cycles the progressive brittle failure led to stage ii a more open system with increasing dilation connected with dissolution the dramatic increase of dissolution processes terminated the episodic character of deformation and marked the beginning of a stage iii mostly characterized by diagenetic processes the fluid regime is now an op

thrust related strain gradients and thrusting mechanisms in a chevron folded sequence southeastern australia an e directed imbricate fan thrust system within a chevron folded monotonous quartz rich turbidite succession shows marked gradients in strain from the upper to lower parts of individual thrust sheets upper parts of thrust sheets show low to moderate strains xz strains 30 1 tight inclined chevron folds ila 30 with predominantly w dipping axial surfaces intense phyllitic cleavage with a strong down dip mineral stretching lineation and long curved tapering quartz pressure shadows on pyrite such differences in fold geometry the intensity of the cleavage and the geometry of quartz fibres in pressure shadows require thrust sheet emplacement to be synchronous with the internal deformation of sheets thrust sheets show a change from an approximately constant volume plane strain coaxial deformation in their upper parts to non coaxial high strain deformation with incremental i between those expected for pure shear and simple shear i e 0 i 5 45 in their basal parts observed geometries and intensities reflect partitioning of strain and deformation mechanisms within individual thrust sheet volumes both during the initiation and propagation of subsurface detachment faults and with their emplacement to shallower crustal levels strain softening related to chevron folding and more intense cleavage development within a 500 m basal zone has controlled the emplacement of these turbidite dominated thrust sheets transport and internal deformation of the thrust sheets did not involve gravitationally induced spreading but required either a push from the rear or some form of underthrusting

deformation character and palaeo fluid flow across a wrench fault within a palaeozoic subduction accretion system waratah fault zone southeastern australia abstract melange formation cataclasis meso to micro scale faulting and veining reflect faulting processes within turbidite and limestone sequences juxtaposed along a steeply dipping sinistral wrench fault zone in the lachlan orogen southeastern australia fault damage occurs across a zone up to 600 m wide effects of faulting in the turbidites are shown by a 100 150 m wide zone of scaly mudstone matrix melange mud injection dykes and veinlets and refolding of melange fabrics with minor subsidiary brittle faulting and cataclasis extending up to 500 m from the major fault plane veining and cataclastic zones occur in the limestone and are most pronounced up to 100 m from the main brittle fault fluid inclusion data from quartz and calcite veins suggest faulting took place at temperatures between 160 and 200 c whereas folding is inferred to have taken place at temperatures above 300 c fluid assisted fault zone weakening mechanisms pressure solution solution transfer were active over the whole fault zone veining characteristic of fluid assisted fault zone strengthening processes i e rock mass cementation is confined to the limestone sequence here calcite precipation led to fault rocks with lower porosity and permeability than in the turbidite sequence overprinting between different veins and fractures and zonation in vein cement suggest cyclic deformation and fluid flow the repeated change between brittle fracturing and veining cementation led to a combined conduit barrier system in the limestone sequence whereas the melange zone in the turbidites acted as a fluid conduit only

interaction of cataclasis and pressure solution in a low temperature carbonate shear zone the mineralogical and elemental variations across the main shear zone of the saltville thrust at sharp gap in knoxville tennessee u s a were studied in a suite of deformed and undefromed carbonate rock samples using x ray diffraction and electron microprobe methods an examination of the samples for deformation effects at mesoscopic scale and under the optical microscope reveals familiar cataclastic deformation features including foliated cataclasites and microbreccias occurring in a well defined 1 2 m wide zone of intense deformation plus evidence of hydrofracturing and extensive syndeformational pressure solution there exists a clear correlation between the observed cataclastic deformation and mineral and elemental distribution which we interpret to result from a deformation induced dolomite to calcite transformation in the shear zone the transformation has resulted in removal of mg from the shear zone selective deposition of calcite as an intergranular cement in cataclasite microbreccia units and a relative increase in the concentration of detrital quartz and feldspars the compositional difference between the shear zone and wall rocks is explained in connection with cataclastic deformation features in terms of a model in which a dual pressure solution cataclastic flow mechanism leads to a gradual cementation hardening of segments of the shear zone instabilities could occur via permeability reduction and increased pore pressure within these segments hydrofracturing of the hardened segments along with high strain rate reordering of the shear zone materials reset the ruptured zone back to the dual deformation mechanism regime as a long term effect the compositional transformation of the shear zone is expected to prolong periods of creep and cause smaller coseismic stress drops since under the imposed conditions calcite is more ductile and soluble than dolomite

fluid regime in faulting deformation of the waratah fault zone australia as inferred from major and minor element analyses and stable isotopic signatures abstract geochemical studies have been conducted on the waratah fault zone a steep ne sw trending brittle fault zone in the southeastern lachlan fold belt australia strike slip movement along the fault juxtaposed an early devonian turbidite sequence liptrap formation against heavily veined early devonian limestones the fault zone consists of the faulted liptrap formation and faulted limestones and a fault core composed of a fault melange zone and strongly brecciated limestones the fault zone records extensive mineralogical and stable isotope alteration within the deformed turbidites of the liptrap formation and within the limestone sequence for the liptrap formation a volume loss of 28 was calculated for the transition from unaltered sediments to the fault melange zone the volume loss in the limestone gouge is much higher 60 the calculated fluid rock ratios in the limestone sequence are at least an order of magnitude lower than in the fault melange zone stable isotopic and rare earth elemental data document the infiltration of near surface meteoric water during brittle deformation and alteration of the fault zone the interaction of fluids with contrasting lithologies led to different alteration processes affecting fault weakening and or strengthening the cyclic change between large scale fluid infiltration due to brittle failure open system and fault rock cementation closed system may represent a combined conduit barrier system in the limestone sequence within the liptrap formation no cementation took place as the conditions for quartz precipitation were unsuitable hence the fault system remains open in respect to fluids conduit system only additionally the permanent fluid infiltration dissolved silica and altered detrital feldspar resulting in subsequent porosity increase within the fault melange zone our results are consistent with investigations in modern accretionary complexes where major decollements and subsidiary faults have been shown to be important fluid conduits

tectonic affinity of the mathinna group in the lachlan fold belt abstract pre carboniferous rocks of tasmania comprise two disparate terranes which were brought together during the middle palaeozoic the eastern tasmania terrane consists of middle palaeozoic granitoids and the mathinna group a turbidite succession of ordovician to early devonian age the older part of the adjacent western tasmania terrane the only part of the southern tasmanides with exposed precambrian basement is related to the kanmantoo fold belt and older tectonic provinces located northwest of tasmania the younger part of the western tasmania terrane comprises upper cambrian to lower devonian terrestrial to shallow marine siliciclastics and carbonates a marked contrast to the coeval deep water deposits of the mathinna group the contact between the two terranes is concealed by the tamar valley in northern tasmania the main folds in the eastern tasmania terrane verge to the northeast whereas structures in the adjacent western tasmania terrane indicate tectonic transport to the southwest with the break in structural facing coinciding with the tamar valley reinvestigation of the structure of the westernmost eastern tasmania terrane where there is a large recumbent f1 fold 10 km extent in profile view raises the possibility that a second generation of structures previously regarded as of only local importance could have caused rotation of the upright to steeply west dipping axial surfaces of f1 folds to recumbent attitudes during southwesterly directed thrusting in this interpretation recumbent or near recumbent zones could reflect ramps in a sole thrust and the mid devonian imbricate thrust zone near beaconsfield on the west bank of the tamar river would be either the frontal thrust system or a splay off the sole thrust which continues westward beneath the exposed precambrian badger head block the implications of this new interpretation are that docking of the eastern and western tasmania terranes must have occurred after the ordovician but before the middle devonian during the consolidation phase there were two deformations of the mathinna group the first which occurred in the early devonian prior to emplacement of the st marys porphyrite 388 1 ma produced upright to locally overturned folds verging to the northeast the second which took place during the early middle devonian before deposition of givetian cave deposits resulted in the mathinna group being thrust southwestward this sense of thrusting is opposite to the direction of thrusting at the same time in the melbourne zone of victoria where the fold and thrust belt verges eastward away from the craton a concealed devonian transfer fault zone in bass strait could account for this change of polarity

illuminating the near sonic rupture velocities of the intracontinental kokoxili mw 7 8 and denali fault mw 7 9 strike slip earthquakes with global p wave back projection imaging 1 the denali and kokoxili strike slip earthquakes are two of the longest recent intracontinental ruptures previous studies report a range of rupture velocities here we image these earthquakes by reverse time migration of the intermediate frequency p wave train recorded by global broadband seismometers this technique permits a relatively direct measure of rupture velocity speed and direction as constrained by the radiated seismic energy free from restrictive assumptions or rupture speed bounds placed on the solution we compare our results with published seismic gps displacement and surface slip inversion results both ruptures were initially subshear and transitioned over a distance no longer than 40 km to supershear speeds close to the p wave speed of 5 6 km s we investigate the accuracy of our results with synthetic data and experiment with using different imaging parameters and seismic subnetworks these tests allow us to rule out the possibility of subshear speeds along the supershear segments although we cannot exclude supershear speeds of 4 5 6 5 km s our most reliable rupture velocities of 5 6 km s are close to the local p wave speeds we hypothesize that these intracontinental faults have weak shear strengths or high breakdown slips or crustal rigidities and experience at least moderate slip or slip rate weakening our observations and previous published results lead us to speculate that very long surface extending faults with general homogeneity in prestress and fault strength together with smaller adjacent fault segments to provide triggering may be necessary ingredients for the sub rayleigh to supershear rupture speed transition in strike slip earthquakes

coseismic radiation of the 2008 m w 7 9 wenchuan earthquake and its relationship to fault complexities the long rupture length and complex fault geometries of the 2008 mw 7 9 wenchuan earthquake offer a great opportunity to investigate the relationship between coseismic radiation and fault complexities in this study we first improved the compressive sensing back projection method cs bp with window time adjustment and parallel computation to enhance its spatial temporal resolution and computational efficiency then we applied the cs bp to invert for the coseismic radiation of the wenchuan earthquake in multiple frequency bands our results show that the coseismic radiation of the wenchuan earthquake is frequency dependent and strongly associated with the fault geometries low frequency radiation sources are concentrated on smooth fault segments with large coseismic slip while higher frequency sources are mainly related to fault complexities e g xiaoyudong fault gaochuan fault bend leigu fault bend and nanba fault step over an acceleration of rupture speed from 1 5 to 3 0 km s is also observed the near xiaoyudong fault where strong high frequency energies were radiated finally we discuss the role of rupture speed in mediating the relationship between coseismic radiation and fault complexities on one hand sudden changes of rupture speeds contribute to strong high frequency radiation on the other hand fault complexities can also strongly affect the rupture speed a sudden break of a large asperity is able to propel the acceleration while rupture front may decelerate when it jumps across geometric barriers

intracrustal detachments and implications for crustal evolution within the lachlan fold belt southeastern australia seismic reflection profiling in the southern lachlan fold belt australia indicates geometrically complex mid to lower crustal detachments possibly associated with crustal thickening by tectonic underplating of collided microplates and or oceanic plateaus low angle detachments either intersect or sole into the crust mantle boundary forming a crustal stacking wedge typical of lithospheric or a type subduction upper crustal reflections show that major moderately to steeply dipping reverse faults exposed at the surface flatten with depth and have listric form the chevron folded quartz rich turbidite sequence of the lachlan fold belt is therefore allochthonous with respect to the lower crust like the northern appalachian maritimes the lachlan fold belt has a composite crust with diverse lower crustal blocks overlain by allochthonous imbricated terranes of the surface rocks

recycled gabbro signature in hotspot magmas unveiled by plume ridge interactions the geochemistry of lavas erupted at locations where mantle plumes interact with mid ocean ridges reflects the mixing between the two sources analysis of lavas erupted above the foundation hotspot near the pacific antarctic ridge reveal a geochemical signature indicative of both a primitive mantle plume source and a recycled oceanic lithosphere source

rupture imaging of the mw 7 9 12 may 2008 wenchuan earthquake from back projection of teleseismic p waves 1 the mw 7 9 wenchuan earthquake of 12 may 2008 was the most destructive chinese earthquake since the 1976 tangshan event tens of thousands of people were killed hundreds of thousands were injured and millions were left homeless here we infer the detailed rupture process of the wenchuan earthquake by back projecting teleseismic p energy from several arrays of seismometers this technique has only recently become feasible and is potentially faster than traditional finite fault inversion of teleseismic body waves therefore it may reduce the notification time to emergency response agencies using the iris dmc we collected 255 vertical component broadband p waves at 30 95 from the epicenter we found that at periods of 5 s and greater nearly all of these p waves were coherent enough to be used in a global array we applied a simple down sampling heuristic to define a global subarray of 70 stations that reduced the asymmetry and sidelobes of the array response function arf we also considered three regional subarrays of seismometers in alaska australia and europe that had apertures less than 30 and p waves that were coherent to periods as short as 1 s individual arfs for these subarrays were skewed toward the subarrays however the linear sum of the regional subarray beams at 1 s produced a symmetric arf similar to that of the groomed global subarray at 5 s for both configurations we obtained the same rupture direction rupture length and rupture time we found that the wenchuan earthquake had three distinct pulses of high beam power at 0 23 and 57 s after the origin time with the pulse at 23 s being highest and that it ruptured unilaterally to the northeast for about 300 km and 110 s with an average speed of 2 8 km s it is possible that similar results can be determined for future large dip slip earthquakes within 20 30 min of the origin time using relatively sparse global networks of seismometers such as those the usgs uses to locate earthquakes in near real time

a window into the complexity of the dynamic rupture of the 2011 mw 9 tohoku oki earthquake the 2011 mw 9 tohoku oki earthquake recorded by over 1000 near field stations and multiple large aperture arrays is by far the best recorded earthquake in the history of seismology and provides unique opportunities to address fundamental issues in earthquake source dynamics here we conduct a high resolution array analysis based on recordings from the usarray and the european network the mutually consistent results from both arrays reveal rupture complexity with unprecedented resolution involving phases of diverse rupture speed and intermittent high frequency bursts within slow speed phases which suggests spatially heterogeneous material properties the earthquake initially propagates down dip with a slow initiation phase followed by sustained propagation at speeds of 3 km s the rupture then slows down to 1 5 km s for 60 seconds a rich sequence of bursts is generated along the down dip rim of this slow and roughly circular rupture front before the end of the slow phase an extremely fast rupture front detaches at about 5 km s towards the north finally a rupture front propagates towards the south running at about 2 5 km s for over 100 km key features of the rupture process are confirmed by the strong motion data recorded by k net and kik net the energetic high frequency radiation episodes within a slow rupture phase suggests a patchy image of the brittle ductile transition zone composed of discrete brittle asperities within a ductile matrix the high frequency is generated mainly at the down dip edge of the principal slip regions constrained by geodesy suggesting a variation along dip of the mechanical properties of the mega thrust fault or their spatial heterogeneity that affects rise time

implications for mechanical properties of brittle faults from observations of the punchbowl fault zone california field observations of the punchbowl fault zone an inactive trace of the san andreas are integrated with results from experimental deformation of naturally deformed punchbowl fault rocks for a qualitative description of the mechanical properties of the fault and additional information for conceptual models of crustal faulting the punchbowl fault zone consists of a single continuous gouge layer bounded by zones of extensively damaged host rock fault displacements were not only localized to the gouge layer but also to discrete shear surfaces within the gouge deformation in the exposure studied probably occurred at depths of 2 to 4 km and was dominated by cataclastic mechanisms textural data also suggest that significant amounts of pore fluids were present during faulting and that fluid assisted mechanisms such as dissolution diffusion and precipitation were operative the experimental data on specimens collected from the fault zone suggest that there is a gradual decrease in strength and elastic modulus and an increase in relative ductility and permeability toward the main gouge zone the gouge layer has fairly uniform mechanical properites and it has significantly lower strength elastic modulus and permeability than both the damaged and the undeformed host rock for the punchbowl fault and possibly other brittle faults the variations in loading of the gouge zone with time are primarily governed by the morphology of the fault and the mechanical properties of the damaged host rock in addition the damaged zone acts as the permeable unit of the fault zone and surrounding rock it appears that the gouge primarily governs whether displacements are localized and it therefore may have a significant influence on the mode of slip

lateral variations in mylonite zone thickness as influenced by fluid rock interactions linville falls fault north carolina abstract over a distance of approximately 20 km along strike the linville falls mylonite varies in thickness from 1 m at linville falls to 60 m at banner elk along strike pressure temperature and displacement variations are minimized allowing this study to focus on the influences of fluid behavior and protolith mineralogy on fault zone development the protolith at linville falls contains mainly k feldspar perthite and quartz while at banner elk the protolith contains plagioclase and quartz at linville falls quartz deformed by dynamic recrystallization feldspar by intragranular fracturing and alteration to quartz and mica and mica by sliding along cleavage planes modal mineralogies change from the protolith to the mylonite with quartz decreasing from 39 to 19 and feldspar from 59 to 1 5 muscovite increases from mass balance calculations based on major and trace element geochemistry indicate approximately 75 volume loss at linville falls and 20 at banner elk fluid rock ratios estimated from the calculated depletions of si are an order of magnitude higher at linville falls than at banner elk fluids infiltrated the fault zone over a thicker zone at banner elk than at linville falls because the plagioclase altered more readily than k feldspar creating new pathways for fluids fluids migrated preferentially through channels along the fault zone creating a three dimensional network of higher fluid flow

along dip seismic radiation segmentation during the 2007 mw 8 0 pisco peru earthquake 1 the short period 0 5 2 s seismic radiation properties of the august 15 23 40 57 utc 2007 mw 8 0 pisco peru earthquake are imaged by back projecting p waves recorded at 374 elements of usarray deployed in western north america at distances of 54 74 from the source region the coherent short period seismic energy release has two main intervals similar to moment rate functions determined by inversion of longer period teleseismic body waves however the spatial locations of the coherent bursts of short period energyrelease are located northanddown dip of the region of major slip the contrast between short and long period seismic radiation properties of the pisco earthquake is more subtle than for the 2011 mw 9 0 tohoku earthquake but provides further support for the idea of depth dependent changes in sliding behavior during megathrust ruptures citation sufri o k d koper and t lay 2012 along dip seismic radiation segmentation during the 2007 mw 8 0 pisco peru earthquake geophys res lett 39 l08311 doi 10 1029 2012gl051316

metallogeny and tectonic development of the tasman fold belt system in victoria current evidence suggests that most of victoria is underlain by a relatively thick 20 km basement of sialic composition of assumed proterozoic age this basement is nowhere exposed and its structural relationship with exposed palaeozoic rocks is conjectural this uncertainty has resulted in both ensimatic and ensialic tectonic models being proposed for victoria during the cambrian mineralization associated with cambrian igneous activity shows a variety of styles from minor orthomagmatic chromite deposits through au and cu deposits of syngenetic or epigenetic origin to fe mn ba occurrences of exhalative volcanogenic affiliation cambrian volcanism and associated sedimentation was followed by the deposition of dominantly quartz rich turbidites with interbedded shale and siliceous units subsequent to the epi ordovician benambran orogeny late silurian crustal extension caused several rifts to open along roughly orthogonal nw and ne aligned fractures within these fault bounded depressions thick acid volcanic sequences were deposited in close association with shallow marine sediments mineralization in these upper silurian rocks comprises polymetallic base metal sulphide lenses and minor disseminations at least some of which are of exhalative volcanogenic affiliation the silurian rifts were obliterated and their rocks strongly deformed during the bindian bowning deformation during late silurian to early devonian time this in turn was followed by another episode of crustal extension and rifting during which the formation of a broad meridional trough marks the buchan rift a very thick sequence of largely subaerial bimodal volcanics is overlain by shelf limestone and mudstone a variety of minor base metal barite manganese and iron mineralization is hosted by these volcanics and shelf sediments the mid devonian tabberabberan orogeny was followed in the late devonian by bimodal volcanism and granite intrusion and red bed type non marine sedimentation in central victoria thick bimodal volcanics were erupted into a series of cauldron subsidences and intruded by comagmatic granites bimodal volcanism also occurred in the mount howitt province farther east but was followed by deposition of extensive fluviatile and lacustrine sediments mainly mudstone sandstone and minor conglomerate in the mansfield basin these contain minor sedimentary copper occurrences there are four distinct episodes of granite emplacement in victoria namely late cambrian early ordovician delamerian in the glenelg zone early silurian benambran in the highlands zone early devonian bindian in the grampians ararat bendigo highlands and mallacoota zones and middle devonian carboniferous post tabberabberan in the ararat bendigo melbourne howqua and highlands zones data for the delamerian granitoids are sketchy but in the remaining groups s type granitoids predominate with the exception of eastern victoria east of the yalmy fault i s line where only i and a type granitoids occur a variety of sn mo w deposits and prospects are associated with the benambran and younger intrusive phases victoria is a major gold province which has produced nearly 2 5 106 kg gold primary gold occurs in a number of geological settings including veins and disseminations spatially associated with mafic cambrian volcanism vein deposits in turbiditic sequences of central and eastern victoria veins associated with mafic and intermediate intrusives of mid to late devonian age and minor amounts associated with a variety of granitoids and porphyry dykes

calcite twins their geometry appearance and significance as stress strain markers and indicators of tectonic regime a review twin lamellae are a widespread feature in calcites of any type and origin twinning in calcite is an important intracrystalline deformation mechanism with low critical resolved shear stress and virtually no temperature dependence in contrast to most slip systems in rock forming minerals twinning therefore permits intracrystalline deformation at very low temperature and very little confining pressure twinning alone however cannot lead to large strains because only one independent slip system is effectively available twins lead to discontinuous shearing on the grain scale which gives rise to considerable strain incompatibilities at grain boundaries twinning consequently leads to strain hardening detailed observations of the geometry of twin lamellae show that incompatibilities at grain boundaries are eliminated by pressure solution on the grain scale at low temperature and dynamic recovery processes at higher temperatures twins are found in various tectonic environments and record very small strains in rocks deformed under very little cover different twinning strain and twinning stress methods and palaeopiezometers are critically reviewed all methods are limited to strains of less than 15 shortening or extension by twinning twinning nevertheless is an important although not directly measurable contribution to the total strain in highly strained calcite rocks at least up to middle greenschist facies under which conditions it is the most effective contributor to the formation of strong lattice preferred orientations in calcite tectonites the appearance of calcite twin lamellae changes systematically as a function of deformation temperature micro twins and straight narrow 1 5 m but fewer twins are developed above approximately 200 c curved twins twinned twins and completely twinned grains indicate the progressive importance of other slip systems and larger intracrystalline strains are possible at ca 250 c and above ancient straight twin lamellae are modified into irregular geometries by recrystallization and grain boundary migration the appearance of calcite twins is proposed as an approximate but rapid and easy to use geothermometer in low temperature environments

thrust kinematics and transposition fabrics from a basal detachment zone eastern australia abstract emplacement of an upper crustal leading imbricate fan thrust belt in the lachlan fold belt of eastern australia was accomplished along a 0 5 1 km thick zone of heterogeneously deformed low grade phyllonite in pelitic rock continuous recrystallization and neocrystallization of mica in a zone of transposition layering has provided a weak zone at the base of a 100 km wide 150 km exposed length 10 km thick thrust system the basal deformation zone is characterized by a low moderately dipping strong intense transposition foliation enclosing elongate fault bounded slices up to 20 km long 5 km wide in map view of disrupted cambrian metavolcanics and upper ordovician black shales and slates these are derived from a structurally lower zone of duplexing or from the overturned limbs of anticlinorial structures the detachment zone is a 10 15 km wide zone of intense deformation showing a transition from open upright folds with weak cleavage to inclined tightisoclinal folds with strong axial surface cleavage the intensity of minor faults also increases into the zone leading imbricate fan thrust belts show maximum deformation effects along the basal detachment which forms the frontal or leading fault the leading imbricate geometry is due to emplacement of the basal detachment zone up the lowest and last formed imbricate thrust movement is along a relatively ductile low viscosity layer at the base where strain softening occurs with development of transposition layering this enables confined flow along the basal zone with transport and emplacement of the fold system and duplex zone to higher structural levels reaction enhanced ductility and grain boundary sliding may be important deformation mechanisms responsible for this flow localized polydeformation marked by mesofolds and crenulation cleavage reflects the interaction between thrust sheets and the movement on faults

structural framework and fault analysis in the east central gulf of mexico shelf implications for offshore co2 storage abstract a vast co2 storage resource exists offshore in cretaceous through neogene sandstone in the desoto canyon salt basin in the east central gulf of mexico continental shelf understanding the structural styles the likelihood of reactivation and seal properties of the faults in this area is essential for selecting safe carbon storage sites and minimizing the risk of injected co2 migrating beyond the confines of the storage complex the desoto canyon salt basin has variable structural styles in the basin with different insights for co2 storage the mobile viosca knoll shelf contains stable shelf and a large four way structural closure where provide favorable storage opportunities the destin dome region contains three groups of peripheral faults of the destin fault system faults that strike along shmax dip at 60 and steeply dipping faults are predicted to have elevated risk of slip and dilation the w e striking fault group has an overall higher slip and dilation tendency than the other two groups under the same injection conditions fault seal analysis shows that elevated risk along faults occurs at sandstone sandstone juxtaposition zones and zones with high fault throw and low sgr values storage plans should avoid the faults with elevated risk to ensure that the injectate will not flow into or pressurize the fault zones ideal injection sites within the destin fault system in the destin dome region are in hanging wall rollovers that contain low fault throw and shale sandstone juxtapositions future research should focus on geomechanical pressure and flow simulation of the potential reservoirs and associated seals in the area of the peripheral faults