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

experimental synthesis and phase relations of phengitic muscovite from 6 5 to 11 gpa in a calcareous metapelite from the dabie mountains china the stability and phase relations of phengitic muscovite in a metapelitic bulk composition containing a mixed h2o co2 fluid were investigated at 6 5 11 gpa 750 1050 c in synthesis experiments performed in a multianvil apparatus starting material consisted of a natural calcareous metapelite from the coesite zone of the dabie mountains china ultrahigh pressure metamorphic complex that had experienced peak metamorphic pressures greater than 3 gpa the sample contains a total of 2 1 wt h2o and 6 3 wt co2 bound in hydrous and carbonate minerals no additional fluid was added to the starting material phengite is stable in this bulk composition from 6 5 to 9 gpa at 900 c and coexists with an eclogitic phase assemblage consisting of garnet omphacite coesite rutile and fluid phengite dehydrates to produce k hollandite between 8 and 11 gpa 750 900 c phengite melting dissolution occurs between 900 c and 975 c at 6 5 8 gpa and is associated with the appearance of kyanite in the phase assemblage the formation of k hollandite is accompanied by the appearance of magnesite and topaz oh in the phase assemblage as well as by significant increases in the grossular content of garnet average xgrs 0 52 xpy 0 19 and the jadeite content of omphacite xjd 0 92 mass balance indicates that the volatile content of the fluid phase changes markedly at the phengite k hollandite phase boundary at p 8 gpa fluid coexisting with phengite appears to be relatively co2 rich xco2 xh2o 2 2 whereas fluid coexisting with k hollandite and magnesite at 11 gpa is rich in h2o xco2 xh2o 0 2 analysis of quench material and mass balance calculations indicate that fluids at all pressures and temperatures examined contain an abundance of dissolved solutes approximately 40 mol at 8 gpa 60 mol at 11 gpa that act to dilute the volatile content of the fluid phase the average phengite content of muscovite is positively correlated with pressure and ranges from 3 62 si per formula unit pfu at 6 5 gpa to 3 80 si pfu at 9 gpa the extent of the phengite substitution in muscovite in this bulk composition appears to be limited to a maximum of 3 80 3 85 si pfu at p 9 gpa these experiments show that phengite should be stable in metasediments in mature subduction zones to depths of up to 300 km even under conditions in which ah2o 1 other high pressure hydrous phases such as lawsonite mgmgal pumpellyite and topaz oh that may form in subducted sediments do not occur within the phengite stability field in this system and may require more h2o rich fluid compositions in order to form the wide range of conditions under which phengite occurs and its participation in mixed volatile reactions that may buffer the composition of the fluid phase suggest that phengite may significantly influence the nature of metasomatic fluids released from deeply subducted sediments at depths of up to 300 km at convergent plate boundaries

primary surface ruptures of the great himalayan earthquakes in 1934 and 1255 it is unclear where plate boundary thrusts generate giant rather than great earthquakes along the himalayas the source sizes and recurrence times of large seismic events are particularly uncertain since no surface signatures were found for those that shook the range in the twentieth century here we challenge the consensus that these events remained blind and did not rupture the surface we use geomorphological mapping of fluvial deposits palaeo seismological logging of river cut cliffs and trench walls and modelling of calibrated 14c ages to show that the mw 8 2 bihar nepal earthquake on 15 january 1934 did break the surface traces of the rupture are clear along at least 150 km of the main frontal thrust fault in nepal between 85 50 and 87 20 e furthermore we date collapse wedges in the sir valley and find that the 7 june ad 1255 earthquake an event that devastated kathmandu and mortally wounded the nepalese king abhaya malla also ruptured the surface along this stretch of the mega thrust thus in the past 1 000 years two great earthquakes 679 years apart rather than one giant eleventh century ad event contributed to the frontal uplift of young river terraces in eastern nepal the rare surface expression of these earthquakes implies that surface ruptures of other reputedly blind great himalayan events might exist the recurrence times of great himalayan earthquakes are difficult to assess because they rarely rupture the surface field mapping and 14c dating of offset fluvial deposits are used to identify two great himalayan quakes that ruptured the surface along the main plate boundary fault in ad 1255 and 1934

prediction of the behaviour of landslide dams using a geomorphological dimensionless index landslide dams are a common phenomenon they form when a landslide reaches the bottom of a river valley causing a blockage the first effect of such a dam is the infilling of a lake that inundates the areas upstream while the possibility of a sudden dam collapse with a rapid release of the impounded waters poses a higher flood risk to the downstream areas the results of the main inventories carried out to date on landslide dams have been examined to determine criteria for forecasting landslide dam evolution with particular emphasis on the assessment of dam stability not all landslides result in the blockage of a river channel this only occurs with ones that can move a large amount of material with moderate or high velocities in most cases these landslides are triggered by rainfall events or high magnitude earthquakes a relationship also exists between the volume of the displaced material and the landslide dam stability several authors have proposed that landslide dam behaviour can be forecast by defining various geomorphological indexes that result from the combination of variables identifying both the dam and the dammed river channel further developments of this geomorphological approach are presented in this paper by the definition of a dimensionless blockage index starting with an analysis of 84 episodes selected worldwide it proved to be a useful tool for making accurate predictions concerning the fate of a landslide dam copyright 2002 john wiley sons ltd

spatial distribution of landslides triggered by the 2008 ms 8 0 wenchuan earthquake china abstract the ms 8 0 wenchuan earthquake of may 12 2008 is one of the most disastrous earthquakes in china the earthquake triggered tens of thousands of landslides over a broad area including shallow disrupted landslides rock falls deep seated landslides and rock avalanches some of which buried large sections of some towns and dammed the rivers the purpose of this study is to investigate correlations between the occurrence of landslides with geologic and geomorphologic conditions and seismic parameters over 56 000 earthquake triggered landslides with a total area of 811 km 2 are interpreted using aerial photographs and remote sensing images taken following the earthquake the spatial distribution of these landslides is analyzed statistically using both landslide point density lpd defined as the number of landslides per square kilometer and landslide area density lad the percentage of the area affected by landslides to determine how the occurrence of landslides correlates with distance from the epicenter distance from the major surface rupture seismic intensity and peak ground acceleration pga slope angle slope aspect elevation and lithology it is found that both lad and lpd have strong positive correlations with slope steepness distance from the major surface rupture and seismic intensity and that pre sinian schist and cambrian sandstone and siltstone intercalated with slate have the most concentrated landslide activities followed by the permian limestone intercalated with shale and devonian limestone statistical analyses also indicate that the major surface rupture has influence on the spatial distribution of landslides because lad and lpd are relatively higher on the hanging wall than on the footwall however the correlation between the occurrence of landslides with distance from the epicenter of the earthquake is complicated rather than a relatively simple negative correlation as found from other reported cases of earthquakes this is possibly due to complicated rupture processes of the 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

hugoniot and impact induced phase transition of magnesite hugoniot equation of state and release adiabat results are presented for magnesite to a pressure of 140 gpa a sharp change in the shock velocity and particle velocity relation suggests that a phase transition to a high pressure phase occurs at 107 10 gpa decomposition of magnesite was observed by abrupt volume expansion during the pressure release from a pressure over the phase transition and by investigating post shock magnesites recovered from hypervelocity impacts of mini flyers performed using a laser driven acceleration post shock magnesites above 95 gpa contained mgo crystallites and the amount of mgo increased with increasing shock pressure

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

convergence rate across the nepal himalaya and interseismic coupling on the main himalayan thrust implications for seismic hazard we document geodetic strain across the nepal himalaya using gps times series from 30 stations in nepal and southern tibet in addition to previously published campaign gps points and leveling data and determine the pattern of interseismic coupling on the main himalayan thrust fault mht the noise on the daily gps positions is modeled as a combination of white and colored noise in order to infer secular velocities at the stations with consistent uncertainties we then locate the pole of rotation of the indian plate in the itrf 2005 reference frame at longitude 1 34 3 31 latitude 51 4 0 3 with an angular velocity of 0 5029 0 0072 myr the pattern of coupling on the mht is computed on a fault dipping 10 to the north and whose strike roughly follows the arcuate shape of the himalaya the model indicates that the mht is locked from the surface to a distance of approximately 100 km down dip corresponding to a depth of 15 to 20 km in map view the transition zone between the locked portion of the mht and the portion which is creeping at the long term slip rate seems to be at the most a few tens of kilometers wide and coincides with the belt of midcrustal microseismicity underneath the himalaya according to a previous study based on thermokinematic modeling of thermochronological and thermobarometric data this transition seems to happen in a zone where the temperature reaches 350 c the convergence between india and south tibet proceeds at a rate of 17 8 0 5 mm yr in central and eastern nepal and 20 5 1 mm yr in western nepal the moment deficit due to locking of the mht in the interseismic period accrues at a rate of 6 6 0 4 10 19 nm yr on the mht underneath nepal for comparison the moment released by the seismicity over the past 500 years including 14 m w 7 earthquakes with moment magnitudes up to 8 5 amounts to only 0 9 10 19 nm yr indicating a large deficit of seismic slip over that period or very infrequent large slow slip events no large slow slip event has been observed however over the 20 years covered by geodetic measurements in the nepal himalaya we discuss the magnitude and return period of m 8 earthquakes required to balance the long term slip budget on the mht

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

thermodynamic and elastic properties of magnesite at mantle conditions first principles calculations magnesite mgco3 is a likely main host of carbonates in the mantle and plays an important role in the transport and storage of carbon in the earth s mantle its physical properties at high pressure and high temperature pt are crucial for understanding the deep carbon cycle here we investigated thermodynamic and elastic properties of magnesite under the mantle pt conditions using first principles calculations with local density approximation lda magnesite has the seismic velocities close to those of forsterite the effect of the magnesite on seismic velocity of the carbonated peridotite and eclogite is subtle in the upper mantle however magnesite has much smaller seismic velocities and far larger elastic anisotropy than major minerals in the transition zone and lower mantle the enrichment of magnesite in the transition zone and lower mantle will likely produce seismically detectable low velocity zone and velocity anisotropy

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

application and evaluation of a rapid response earthquake triggered landslide model to the 25 april 2015 mw 7 8 gorkha earthquake nepal abstract the 25 april 2015 m w 7 8 gorkha earthquake produced strong ground motions across an approximately 250 km by 100 km swath in central nepal to assist disaster response activities we modified an existing earthquake triggered landslide model based on a newmark sliding block analysis to estimate the extent and intensity of landsliding and landslide dam hazard landslide hazard maps were produced using shuttle radar topography mission srtm digital topography peak ground acceleration pga information from the u s geological survey usgs shakemap program and assumptions about the regional rock strength based on end member values from previous studies the instrumental record of seismicity in nepal is poor so pga estimates were based on empirical ground motion prediction equations gmpes constrained by teleseismic data and felt reports we demonstrate a non linear dependence of modeled landsliding on aggregate rock strength where the number of landslides decreases exponentially with increasing rock strength model estimates are less sensitive to pga at steep slopes 60 compared to moderate slopes 30 60 we compare forward model results to an inventory of landslides triggered by the gorkha earthquake we show that moderate rock strength inputs over estimate landsliding in regions beyond the main slip patch which may in part be related to poorly constrained pga estimates for this event at far distances from the source area directly above the main slip patch however the moderate strength model accurately estimates the total number of landslides within the resolution of the model landslides 0 0162 km 2 observed n 2214 modeled n 2987 but the pattern of landsliding differs from observations this discrepancy is likely due to the unaccounted for effects of variable material strength and local topographic amplification of strong ground motion as well as other simplifying assumptions about source characteristics and their relationship to landsliding

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

development of a globally applicable model for near real time prediction of seismically induced landslides substantial effort has been invested to understand where seismically induced landslides may occur in the future as they are a costly and frequently fatal threat in mountainous regions the goal of this work is to develop a statistical model for estimating the spatial distribution of landslides in near real time around the globe for use in conjunction with the u s geological survey usgs prompt assessment of global earthquakes for response pager system this model uses standardized outputs of ground shaking from the usgs shakemap atlas 2 0 to develop an empirical landslide probability model combining shaking estimates with broadly available landslide susceptibility proxies i e topographic slope surface geology and climate parameters we focus on four earthquakes for which digitally mapped landslide inventories and well constrained shakemaps are available the resulting database is used to build a predictive model of the probability of landslide occurrence the landslide database includes the guatemala 1976 northridge 1994 chi chi 1999 and wenchuan 2008 earthquakes performance of the regression model is assessed using statistical goodness of fit metrics and a qualitative review to determine which combination of the proxies provides both the optimum prediction of landslide affected areas and minimizes the false alarms in non landslide zones combined with near real time shakemaps these models can be used to make generalized predictions of whether or not landslides are likely to occur and if so where for earthquakes around the globe and eventually to inform loss estimates within the framework of the pager system

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

the importance of earthquake induced landslides to long term slope erosion and slope failure hazards in seismically active regions abstract this paper describes a general method for determining the amount of earthquake induced landsliding that occurs in a seismically active region over time this determination can be used as a quantitative measure of the long term hazard from seismically triggered landslides as well as a measure of the importance of this process to regional slope erosion rates and landscape evolution the method uses data from historical earthquakes to relate total volume of landslide material dislodged by an earthquake to the magnitude m and seismic moment m0 of the earthquake from worldwide data a linear regression relation between landslide volume v and m0 is determined as v m0 1018 9 0 13 where v is measured in m3 and m0 is in dyn cm to determine the amount of earthquake generated landsliding over time this relation is combined with data on seismic moment release for a particular region which may be derived from either earthquake history or fault slip data the form of the m0 v relation allows the rate of production of earthquake induced landslides over time to be determined from total rate of seismic moment release without regard to the distribution of individual events thus simplifying and generalizing the determination application of the method to twelve seismically active regions with areas ranging from 13 275 to 2 308 000 km2 shows that erosion rates from earthquake induced landslides vary significantly from region to region of the regions studied the highest rates were determined for the island of hawaii new zealand western new guinea and the san francisco bay region of california significantly lower rates were determined for iran tibet the sierra nevada great basin region of california and central japan for the time period from 715 ad to the present intermediate rates were determined for peru southern california onshore california turkey and central japan for the time period from 1586 ad to the present to determine the relative long term importance of seismically triggered landslides these erosion rates are compared to erosion rates calculated for other slope processes and to rates calculated from fluvial sediment discharge comparisons with other slope processes indicate that earthquake induced landslides are the predominant agents of slope erosion on the island of hawaii in the san francisco bay region and in western new guinea for hawaii the san francisco bay region and sierra nevada great basin region of california the erosion rates calculated for earthquake induced landslides also exceed the regional erosion rates calculated from fluvial sediment discharge

topographic effects on the seismic response of steep slopes a frequency domain parametric study using generalized consistent transmitting boundaries has been performed to evaluate the significance of topographic effects on the seismic response of steep slopes the results show that the peak amplification of motion at the crest of a slope occurs at a normalized frequency h 0 2 where h is the slope height and is the wavelength of the motion the importance of the natural site frequency is illustrated by the analysis of a stepped layer over a half space it was found that the natural frequency of the region behind the crest can dominate the response relative to the topographic effect for the conditions studied moreover the effect of topography can be handled separately from the amplification due to the natural frequency of the deposit behind the crest of the slope this concept of separating the amplification caused by topography from that caused by the natural frequency is advantageous to the development of a simplified method to estimate topographic effects

regional coseismic landslide hazard assessment without historical landslide inventories a new approach currently regional coseismic landslide hazard analyses require comprehensive historical landslide inventories as well as detailed geotechnical data consequently such analyses have not been possible where these data are not available a new approach is proposed herein to assess coseismic landslide hazard at regional scale for specific earthquake scenarios in areas without historical landslide inventories the proposed model employs fuzzy logic and geographic information systems to establish relationships between causative factors and coseismic slope failures in regions with well documented and substantially complete coseismic landslide inventories these relationships are then utilized to estimate the relative probability of landslide occurrence in regions with neither historical landslide inventories nor detailed geotechnical data statistical analyses of inventories from the 1994 northridge and 2008 wenchuan earthquakes reveal that shaking intensity topography and distance from active faults and streams are the main controls on the spatial distribution of coseismic landslides average fuzzy memberships for each factor are developed and aggregated to model the relative coseismic landslide hazard for both earthquakes the predictive capabilities of the models are assessed and show good to excellent model performance for both events these memberships are then applied to the 1999 chi chi earthquake using only a digital elevation model active fault map and isoseismal data replicating prediction of a future event in a region lacking historic inventories and or geotechnical data this similarly results in excellent model performance demonstrating the model s predictive potential and confirming it can be meaningfully applied in regions where previous methods could not for such regions this method may enable a greater ability to analyze coseismic landslide hazard from specific earthquake scenarios allowing for mitigation measures and emergency response plans to be better informed of earthquake related hazards

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

relation of landslides triggered by the kiholo bay earthquake to modeled ground motion abstract the 2006 kiholo bay hawaii earthquake triggered high concentrations of rock falls and slides in the steep canyons of the kohala mountains along the north coast of hawaii within these mountains and canyons a complex distribution of landslides was triggered by the earthquake shaking in parts of the area landslides were preferentially located on east facing slopes whereas in other parts of the canyons no systematic pattern prevailed with respect to slope aspect or vertical position on the slopes the geology within the canyons is homogeneous so we hypothesize that the variable landslide distribution is the result of localized variation in ground shaking therefore we used a state of the art high resolution ground motion simulation model to see if it could reproduce the landslide distribution patterns we used a 3d finite element analysis to model earthquake shaking using a 10 m digital elevation model and slip on a finite fault model constructed from teleseismic records of the mainshock ground velocity time histories were calculated up to a frequency of 5 hz dynamic shear strain also was calculated and compared with the landslide distribution results were mixed for the velocity simulations with some areas showing correlation of landslide locations with peak modeled ground motions but many other areas showing no such correlation results were much improved for the comparison with dynamic shear strain this suggests that 1 rock falls and slides are possibly triggered by higher frequency ground motions velocities than those in our simulations 2 the ground motion velocity model needs more refinement or 3 dynamic shear strain may be a more fundamental measurement of the decoupling process of slope materials during seismic shaking

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

stability of infinite slopes under transient partially saturated seepage conditions 1 prediction of the location and timing of rainfall induced shallow landslides is desired by organizations responsible for hazard management and warnings however hydrologic and mechanical processes in the vadose zone complicate such predictions infiltrating rainfall must typically pass through an unsaturated layer before reaching the irregular and usually discontinuous shallow water table this process is dynamic and a function of precipitation intensity and duration the initial moisture conditions and hydrologic properties of the hillside materials and the geometry stratigraphy and vegetation of the hillslope as a result pore water pressures volumetric water content effective stress and thus the propensity for landsliding vary over seasonal and shorter time scales we apply a general framework for assessing the stability of infinite slopes under transient variably saturated conditions the framework includes profiles of pressure head and volumetric water content combined with a general effective stress for slope stability analysis the general effective stress or suction stress provides a means for rigorous quantification of stress changes due to rainfall and infiltration and thus the analysis of slope stability over the range of volumetric water contents and pressure heads relevant to shallow landslide initiation we present results using an analytical solution for transient infiltration for a range of soil texture and hydrological properties typical of landslide prone hillslopes and show the effect of these properties on the timing and depth of slope failure we follow by analyzing field monitoring data acquired prior to shallow landslide failure of a hillside near seattle washington and show that the timing of the slide was predictable using measured pressure head and volumetric water content and show how the approach can be used in a forward manner using a numerical model for transient infiltration

landslides triggered by the 8 october 2005 kashmir earthquake abstract the 8 october 2005 kashmir earthquake triggered several thousand landslides these were mainly rock falls and debris falls although translational rock and debris slides also occurred in addition a sturzstrom debris avalanche comprising 80 million m3 buried four villages and blocked streams to create two lakes although landsliding occurred throughout the region covering an area of 7500 km2 the failures were highly concentrated associated with six geomorphic geologic anthropogenic settings including natural failures in 1 highly fractured carbonate rocks comprising the lowest beds in the hanging wall of the likely earthquake fault 2 tertiary siliciclastic rocks along antecedent drainages that traverse the hazara kashmir syntaxis 3 steep 50 slopes comprising precambrian and lower paleozoic rocks 4 very steep 50 lower slopes of fluvially undercut quaternary valley fills and 5 ridges and spur crests the sixth setting was associated with road construction extensive fissuring in many of the valley slopes together with the freshly mobilized landslide debris constitutes a potential hazard in the coming snowmelt and monsoon seasons this study supports the view that earthquake triggered landslides are highly concentrated in specific zones associated with the lithology structure geomorphology topography and human presence

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

on the effect of aqueous ca on magnesite growth insight into trace element inhibition of carbonate mineral precipitation abstract motivated by the strong effect of aqueous mg on calcite growth rates this study used hydrothermal atomic force microscopy hafm and hydrothermal mixed flow reactor hmfr experiments to explore the effect of aqueous ca on magnesite growth kinetics at 100 c and ph 7 7 obtuse step velocities on 1 0 4 surfaces during magnesite growth were measured to be 4 3 nm s at fluid saturation states equal to the ion activity quotient divided by the equilibrium constant for the magnesite hydrolysis reaction of 86 117 these rates do not vary systematically with aqueous ca concentration up to 3 10 3 mol kg magnesite growth rates determined by hafm are found to be negligibly affected by the presence of aqueous ca at these saturation states and are largely consistent with those previously reported in aqueous ca free systems by saldi et al 2009 and gautier et al 2015 similarly magnesite growth rates measured by hmfr exhibit no systematic variation on aqueous ca concentrations rates in this study however were extended to higher degrees of fluid supersaturation with respect to magnesite than previous studies all measured hmfr rates can be accurately described taking account the combined effects of both the spiral growth and two dimensional nucleation growth mechanisms despite the lack of a clear effect of aqueous ca on magnesite growth rates raman spectroscopy confirmed the incorporation of up to 8 mol percent of ca 2 into the growing magnesite structure

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

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

dilution of 10be in detrital quartz by earthquake induced landslides implications for determining denudation rates and potential to provide insights into landslide sediment dynamics the concentration of 10be in detrital quartz 10beqtz from river sediments is now widely used to quantify catchment wide denudation rates but may also be sensitive to inputs from bedrock landslides that deliver sediment with low 10beqtz major landslide triggering events can provide large amounts of low concentration material to rivers in mountain catchments but changes in river sediment 10beqtz due to such events have not yet been measured directly here we examine the impact of widespread landslides triggered by the 2008 wenchuan earthquake on 10beqtz in sediment samples from the min jiang river basin in sichuan china landslide deposit material associated with the wenchuan earthquake has consistently lower 10beqtz than in river sediment prior to the earthquake river sediment 10beqtz decreased significantly following the earthquake downstream of areas of high coseismic landslide occurrence i e with greater than 0 3 of the upstream catchment area affected by landslides because of input of the 10be depleted landslide material but showed no systematic changes where landslide occurrence was low changes in river sediment 10beqtz concentration were largest in small first order catchments but were still significant in large river basins with areas of 104 105 km2104 105 km2 spatial and temporal variability in river sediment 10beqtz has important implications for inferring representative denudation rates in tectonically active landslide dominated environments even in large basins although the dilution of 10beqtz in river sediment by landslide inputs may complicate interpretation of denudation rates it also may provide a possible opportunity to track the transport of landslide sediment the associated uncertainties are large but in the wenchuan case calculations based on 10be mixing proportions suggest that river sediment fluxes in the 2 3 years following the earthquake increased by a similar order of magnitude in the 0 25 1 mm and the 0 25 mm size fractions as determined from 10beqtz mixing calculations and hydrological gauging respectively such information could provide new insight into sediment transfer with implications for secondary sediment related hazards and for understanding the removal of mass from mountains

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

transient deterministic shallow landslide modeling requirements for susceptibility and hazard assessments in a gis framework abstract application of transient deterministic shallow landslide models over broad regions for hazard and susceptibility assessments requires information on rainfall topography and the distribution and properties of hillside materials we survey techniques for generating the spatial and temporal input data for such models and present an example using a transient deterministic model that combines an analytic solution to assess the pore pressure response to rainfall infiltration with an infinite slope stability calculation pore pressures and factors of safety are computed on a cell by cell basis and can be displayed or manipulated in a grid based gis input data are high resolution 1 8 m topographic information derived from lidar data and simple descriptions of initial pore pressure distribution and boundary conditions for a study area north of seattle washington rainfall information is taken from a previously defined empirical rainfall intensity duration threshold and material strength and hydraulic properties were measured both in the field and laboratory results are tested by comparison with a shallow landslide inventory comparison of results with those from static infinite slope stability analyses assuming fixed water table heights shows that the spatial prediction of shallow landslide susceptibility is improved using the transient analyses moreover results can be depicted in terms of the rainfall intensity and duration known to trigger shallow landslides in the study area

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

regression models for estimating coseismic landslide displacement newmark s sliding block model is widely used to estimate coseismic slope performance early efforts to develop simple regression models to estimate newmark displacement were based on analysis of the small number of strong motion records then available the current availability of a much larger set of strong motion records dictates that these regression equations be updated regression equations were generated using data derived from a collection of 2270 strong motion records from 30 worldwide earthquakes the regression equations predict newmark displacement in terms of 1 critical acceleration ratio 2 critical acceleration ratio and earthquake magnitude 3 arias intensity and critical acceleration and 4 arias intensity and critical acceleration ratio these equations are well constrained and fit the data well 71 br 2 b88 but they have standard deviations of about 0 5 log units such that the range defined by the mean one standard deviation spans about an order of magnitude these regression models therefore are not recommended for use in site specific design but rather for regional scale seismic landslide hazard mapping or for rapid preliminary screening of sites 2007 elsevier b v all rights reserved

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

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

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

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

a unified model for predicting earthquake induced sliding displacements of rigid and flexible slopes abstract permanent sliding displacement represents a common damage parameter for evaluating the seismic stability of slopes recently developed empirical models for the sliding displacement of shallow rigid sliding masses have demonstrated that including multiple ground motion parameters in the predictive model e g peak ground acceleration and peak ground velocity improves the displacement prediction and reduces it uncertainty a unified framework is developed that extends these empirical displacement models for application to flexible sliding masses where the dynamic response of the sliding mass is important this framework includes predicting the seismic loading for the sliding mass in terms of the maximum seismic coefficient kmax and the maximum velocity of the seismic coefficient time history k velmax the predictive models are a function of the peak ground acceleration pga peak ground velocity pgv the natural period of the sliding mass ts and the mean period of the earthquake motion tm the empirical predictive models for sliding displacement utilize kmax and k velmax in lieu pga and pgv and include a term related to the natural period of the sliding mass this unified framework provides a consistent approach for predicting the sliding displacement of rigid ts 0 and flexible ts 0 slopes

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

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

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

coseismic landslides reveal near surface rock strength in a high relief tectonically active setting we present quantitative estimates of near surface rock strength relevant to landscape evolution and landslide hazard assessment for 15 geologic map units of the longmen shan china strength estimates are derived from a novel method that inverts earthquake peak ground acceleration models and coseismic landslide inventories to obtain material properties and landslide thickness aggregate rock strength is determined by prescribing a friction angle of 30 and solving for effective cohesion effective cohesion ranges are from 70 kpa to 107 kpa for 15 geologic map units and are approximately an order of magnitude less than typical laboratory measurements probably because laboratory tests on hand sized specimens do not incorporate the effects of heterogeneity and fracturing that likely control near surface strength at the hillslope scale we find that strength among the geologic map units studied varies by less than a factor of two however increased weakening of units with proximity to the range front where precipitation and active fault density are the greatest suggests that climatic and tectonic factors overwhelm lithologic differences in rock strength in this high relief tectonically active setting

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

regional patterns of earthquake triggered landslides and their relation to ground motion 1 we have documented patterns of landsliding associated with large earthquakes on three thrust faults the northridge earthquake in california chi chi earthquake in taiwan and two earthquakes on the ramu markham fault bounding the finisterre mountains of papua new guinea in each case landslide densities are shown to be greatest in the area of strongest ground acceleration and to decay with distance from the epicenter in california and taiwan the density of co seismic landslides is linearly and highly correlated with both the vertical and horizontal components of measured peak ground acceleration based on this observation we derive an expression for the spatial variation of landslide density analogous with regional seismic attenuation laws in its general form this expression applies to our three examples and we determine best fit values for individual cases our findings open a window on the construction of shake maps from geomorphic observations for earthquakes in non instrumented regions

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

estimating the return times of great himalayan earthquakes in eastern nepal evidence from the patu and bardibas strands of the main frontal thrust the return times of large himalayan earthquakes are poorly constrained despite historical devastation of cities along the mountain range definitive links between events and specific segments of the main frontal thrust mft are not established and paleoseismological records have not documented the occurrence of several similar events at the same location in east central nepal however recently discovered primary surface ruptures of that megathrust in the a d 1255 and 1934 earthquakes are associated with flights of tectonically uplifted terraces we present here a refined longer slip history of the mft s two overlapping strands patu and bardibas thrusts in that region based on updated geomorphic neotectonic mapping of active faulting two 1 3 km long shallow seismic profiles and logging of two river cut cliffs three paleoseismological trenches and several pits with constraints from 74 detrital charcoals and 14 cosmogenic nuclide ages the amount of hanging wall uplift on the patu thrust since 3650 450 years requires three more events than the two aforementioned the uplift rate 8 5 1 5mm yr thrust dip 25 5 n and apparent characteristic behavior imply 12 17 5m of slip per event on the bardibas thrust discrete pulses of colluvial deposition resulting from the coseismic growth of a flexural fold scarp suggest the occurrence of six or seven paleo earthquakes in the last 4500 50 years the coeval rupture of both strands during great himalayan earthquakes implies that in eastern nepal the late holocene return times of such earthquakes probably ranged between 750 140 and 870 350 years

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

the influence of different simplified sliding block models and input parameters on regional predictions of seismic landslides triggered by the northridge earthquake abstract regional seismic landslide hazard maps are based on predictions of rigid sliding block displacement derived from estimates of earthquake ground shaking topography geology and shear strength the confidence in these predictions requires comparisons with field observations of landslide occurrence during previous well documented earthquakes this paper presents a comparison between observed landslides from the 1994 northridge california earthquake and predicted landslides based on sliding block displacement estimates seven empirical displacement models each of which uses a different combination of ground motion parameters are investigated to evaluate which models and associated ground motion parameters best predict seismic landslides using best estimates of ground shaking and shear strength properties from the northridge earthquake sliding displacements are calculated and compared with the locations of observed landslides only 20 40 of the observed landslides are captured and the total area of predicted landslides is much larger than observed the ability to predict landslide occurrence accurately depends less on the displacement model and associated ground motion parameters and more on the uncertainty in the model parameters particularly the assigned shear strengths because current approaches do not take into account the spatial variability of shear strength within individual geologic units the accuracy of the predictive models is controlled predominantly by the distribution of slope angles within a geologic unit assigning overly conservative low shear strength values results in a higher percentage of landslides accurately identified but also results in a large over estimation of the total landslide area making more accurate maps of seismic landslide hazards will require methods to define intra formational variations in shear strength

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

lower edge of locked main himalayan thrust unzipped by the 2015 gorkha earthquake faults are unlocked by earthquakes analysis of seismic data from the 2015 nepal earthquake shows that only part of the main himalayan thrust fault was unzipped by the quake leaving much of the fault locked and ready to slip in a future event

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

how rivers react to large earthquakes evidence from central taiwan earthquakes and bedrock river incision are fundamental processes in the evolution of tectonically active landscapes yet little work has focused on understanding how a bedrock river responds to a single large earthquake data from the 1999 m w 7 6 chi chi earthquake in central taiwan show dramatic differences in river response that depend on the proximity to the rupture zone near the fault scarp vertical ground deformation intensifi es river incision on a time scale of years to decades while distal to the fault landslides induced by the earthquake mantle bedrock on the river bed with sediment impeding incision for decades to centuries as the material is evacuated this surprising spatial and temporal variability in bedrock incision caused by earthquakes has implications for the paleoseismic interpretation of bedrock terraces and for the evolution of tectonically active landscapes

stability of the mgco3 structures under lower mantle conditions the presence of carbon in the earth makes the search for high pressure carbon containing phases essential for our understanding of mineral compositions of the earth s mantle in a recent study issh

age of initiation of collision between india and asia a review of stratigraphic data abstract the collision of india with asia is perhaps the most profound tectonic event to have occurred in past 100 ma it is responsible for the uplift of the himalayas and tibetan plateau and has been argued to have been responsible for geological geochemical and climatological consequences of global extent yet the age of initiation of this collision remains poorly constrained the literature is replete with estimates that range from the late cretaceous 65 ma to latest eocene

india asia collision and the cenozoic slowdown of the indian plate implications for the forces driving plate motions the plate motion of india changed dramatically between 50 and 35 ma with the rate of convergence between india and asia dropping from 15 to 4 cm yr this change is coincident with the onset of the india asia collision and with a rearrangement of plate boundaries in the indian ocean on the basis of a simple model for the forces exerted upon the edges of the plate and the tractions on the base of the plate we perform force balance calculations for the precollision and postcollision configurations we show that the observed euler poles for the indian plate are well explained in terms of their locations and magnitudes if 1 the resistive force induced by mountain building in the himalaya tibet area is 5 6 10 12 n m 2 the net force exerted upon the indian plate by subduction zones is similar in magnitude to the ridge push force 2 5 10 12 n m and 3 basal tractions exert a resisting force that is linearly proportional to the plate velocity in the hot spot reference frame the third point implies an asthenospheric viscosity of 2 5 10 19 pa s assuming a thickness of 100 150 km synthetic euler poles show that crustal thickening in the tibetan plateau was the dominant cause of the cenozoic slowdown of the indian plate

landslide mobility and hazards implications of the 2014 oso disaster abstract landslides reflect landscape instability that evolves over meteorological and geological timescales and they also pose threats to people property and the environment the severity of these threats depends largely on landslide speed and travel distance which are collectively described as landslide mobility to investigate causes and effects of mobility we focus on a disastrous landslide that occurred on 22 march 2014 near oso washington usa following a long period of abnormally wet weather the landslide s impacts were severe because its mobility exceeded that of prior historical landslides at the site and also exceeded that of comparable landslides elsewhere the 8 10 6 m 3 landslide originated on a gently sloping

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

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

himalayan seismic hazard the devastating earthquake in bhuj on 26 january 2001 highlighted the high earthquake risk in the indian region of gujarat in their perspective bilham et al warn that major earthquakes may be expected in another part of india the himalayan arc an analysis of historic earthquakes suggests that several major earthquakes are overdue in this region but that recent low activity has focused attention away from the himalayan arc projections from earlier earthquakes suggest that just one of the possibly overdue himalayan earthquakes may lead to 200 000 predictable fatalities

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