soft sediment deformation structures in alkaline lake deposits of lower permian fengcheng formation junggar basin nw china implications for syn sedimentary tectonic activity abstract soft sediment deformation structures ssds are an important tool for interpreting paleoseismicity and depositional environments in ancient basin successions the northwestern margin of junggar basin is a key region for understanding the paleogeography and basin attribute of the junggar basin during the early permian in the lower permian kungurian fengcheng formation nine lithofacies are grouped into fan delta fluvial delta and shallow deep and alkaline lacustrine facies associations vertical transitions of the sedimentary environments show that the lake basin experienced expansion during deposition of the lower p1f1 and middle p1f2 members and the shrinkage during the upper member p1f3 which is consistent with the paleogeographic distribution of lithofacies in different members conventional cores show a wide variety of ssds including ductile folds convolute lamination and load structures hybrid ductile brittle and brittle deformation structures microfaults breccias boudinage and sedimentary dikes ssds mainly occurred in a still and deep lacustrine environment these deformation structures were not formed in any specific lacustrine environment as there is no difference with the undeformed sedimentary units of the same sedimentary facies thus the triggering mechanism is interpreted as intermittent earthquakes lake expansion under arid condition and ssds intervals with vertical repetition and possible lateral continuity indicate that most seismicity was during the middle member p1f2 corresponding with the main activity on basin bounding normal faults the enhanced faulting at this time generated accommodation creating lacustrine conditions in the basin depocenter it is thus clear that the early permian mahu sag represents an active rift basin with bounding faults and is not a foreland basin

non traditional and emerging methods for characterizing diffusion in minerals and mineral aggregates the data summarized in this rimg volume reflect the growing interest among geoscientists in the characterization of atomic transport in natural materials interest in diffusion dates back to the early 20th century e g bowen 1921 but the need for constraints on mobility of atoms became especially important in the 1950s and 60s with our increasing reliance upon radioactive decay for determination of mineral and rock ages the question of decay product retention in relevant phases became vitally important with a few notable exceptions however experimental geoscientists did not take up the cause of diffusion in solids until the 1970s and 80s by that time the motivation for acquiring diffusion data had spread to many areas of petrology mineralogy and geochemistry and experimental techniques began to blossom the result is very much in evidence in this volume all experiments aimed at measuring a diffusion coefficient have two things in common a technique to introduce the diffusant of interest to the sample and a method to determine the extent of diffusion traditionally diffusion experiments are designed to take advantage of an existing solution to the non steady state diffusion equation and experiments are conducted in such a way as to reproduce as well as possible the boundary conditions specified for the solution for ease of analysis and interpretation most experiments are set up to limit diffusion to just one dimension most researchers have further settled on one of three general experiment designs 1 the interdiffusion couple 2 the thin film geometry or 3 the constant surface concentration design fig 1 noble gas geochemists including those interested in k ar ar ar and u th he dating methods have exploited 3 d variants of this last approach by conducting bulk degassing studies of minerals in which radiogenic noble gases have accumulated over time in the natural environment baxter 2010

initial investigation of the landers california earthquake of 28 june 1992 using terrascope the 1992 landers earthquake m s 7 5 m w 7 3 was recorded at six terrascope stations in southern california peak accelerations ranged from 0 16 g at svd 63 km to 0 0092 g at isa 245 km decreasing with distance away from the fault zone the peak velocity showed a different pattern reflecting the rupture directivity from south to north the largest peak velocity 19 cm sec was observed at gsc 125 km moment tensor inversion of long period surface waves yielded a mechanism with m 0 1 1 10 27 dyne cm m w 7 3 dip 74 rake 176 and strike 340 inversion of teleseismic p and s waves revealed two distinct sub events of 6 and 8 sec duration and about 10 sec apart the source parameters for the first and second events are m 0 1 9 10 26 dyne cm dip 83 rake 179 strike 359 and m 0 6 1 10 26 dyne cm dip 87 rake 178 strike 333 respectively the radiated wave energy e s was estimated as 4 3 10 23 ergs the ratio e s m 0 3 9 10 4 corresponds to a stress drop of 280 bars and suggests that the landers earthquake belongs to the group of high stress drop earthquakes and occurred on a fault with a long recurrence time the rupture directivity can be seen clearly in the records from pfo 68 km located to the south and gsc located to the north of the epicenter the maximum displacement at pfo is only 13 of that at gsc despite the shorter epicentral distance to pfo than to gsc the slip distribution determined with the empirical green s function method indicates that the landers earthquake consists of two distinct sub events about 30 km apart with the second sub event to the north being about twice as large as the first one this slip distribution is consistent with the teleseismic data and the surface offsets mapped in the field

late quaternary environmental and landscape dynamics revealed by a pingo sequence on the northern seward peninsula alaska a terrestrial sediment sequence exposed in an eroding pingo provides insights into the late quaternary environmental history of the northern seward peninsula alaska we have obtained the first radiocarbondated evidence for a mid wisconsin thermokarst lake demonstrating that complex landscape dynamics involving cyclic permafrost aggradation and thermokarst lake formation occurred over stadiale interstadial as well as glacialeinterglacial time periods high values of picea pollen and the presence of larix pollen in sediments dated to 50e40 ka bp strongly suggest the presence of forest or woodland early in mis 3 the trees grew within a vegetation matrix dominated by grass and sedge and there is indirect evidence of grazing animals thus the interstadial ecosystem was different in structure and composition from the holocene or from the preceding last interglacial period an early holocene warm period is indicated by renewed thermokarst lake formation and a range of fossil taxa multiple extralimital plant taxa suggest mean july temperatures above modern values the local presence of spruce during the early holocene warm interval is evident from a radiocarbon dated spruce macrofossil remain and indicates significant range extension far beyond the modern tree line the first direct evidence of spruce in northwest alaska during the early holocene has implications for the presence of forest refugia in central beringia and previously assumed routes and timing of post glacial forest expansion in alaska

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

rheology of the lithosphere selected topics we review recent results concerning the rheology of the lithosphere with special attention to the following topics 1 the flexure of the oceanic lithosphere 2 deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins 3 the rheological stratification of the continents 4 strain localization and shear zone development and 5 strain induced crystallographic preferred orientations and anisotropies in body wave velocities we conclude with a section citing the 1983 1986 rock mechanics literature by category

experimental analysis of slip distribution along a fault segment under stick slip and stable sliding conditions abstract this paper presents the results of an experimental study of slip distribution along fault models with different sliding surface morphologies submitted to various orientations of fault and loading direction uniaxial compression tests were done on pmma plates to measure the relative displacement of markers perpendicular to the sliding surfaces slip distribution profiles were then constructed for different stages of shortening of the samples it was shown that fault morphology determines both the sliding regime and the slip distribution along the sliding surfaces along fault models with grounded surfaces fmgs stable sliding giving a symmetrical smooth distribution was observed for fault models with natural fracture surfaces fmns stick slip was observed in this case the slip distribution exhibited significant irregularities in a generally symmetrical profile analysis of this profile enabled four types of local slip behaviour to be identified which may provide a physical basis for the interpretation of coseismic slip distributions the local slip behaviours were interpreted in terms of interaction of irregular asperities and helped understand the discrepancy observed between theoretical slip distributions and the displacement measured along the active faults analysis of the slip distribution profiles along the fmgs and the fmns also showed that they evolved systematically after the appearance of branching for a large amount of shortening mode i branching was observed at the tips of the sliding surfaces after its development the global amount of slip along the faults increased and the slip gradient between the centre and the tips of the faults decreased this effect is consistent with numerical modelling studies finally the observed profiles were compared with the linear the tapered and the elliptic theoretical models using two different procedures we conclude that in the case of the fmns where the sliding surface topography is complex no model could correctly describe the slip distribution and that in both cases of fmns and fmgs branching caused a change in the shape of the slip distribution profiles

geomorphology and hydrogeological significance of the holocene pingos in the karup valley area traill island northern east greenland many of the geomorphologically diverse hydraulic pingos of holocene age are described from within the catchment of the karup river pingo morphology ranges from single features to complexes with over 10 from mature forms to degraded types evidence for different cycles of reactivation is seen the two instances of active pingo springs are associated with substantial icings landform changes since fritz muller s observations in 1956 are generally minor it is hypothesised that the concentration of hydraulic pingos in east greenland may initially reflect residual higher heat flows following extensive early intrusive tertiary volcanism despite a continuous permafrost climatic environment the undisputed presence of ground water flows and discharges as evidenced by major icings and pingos in the valleys suggests that structural weaknesses are controlling the taliks associated with the intrapermafrost hydrology

ice wedges growth thaw transformation and palaeoenvironmental significance frost cracking and ice wedge growth are fundamental processes within the permafrost environment extensive areas of contemporary permafrost terrain are characterised by frost fissure polygons formed by repeated thermal contraction cracking of the ground the incremental growth of ice veins and wedges along the axes of contraction cracks contributes significantly to the volume of ground ice in near surface permafrost in areas beyond the present limit of permafrost the recognition of ice wedge pseudomorphs provides one of the few unambiguous indications of the former existence of permafrost conditions an understanding of the processes of ice wedge growth and thaw transformation is essential if contemporary ice wedges are to be used as analogues for pleistocene frost fissure structures in palaeoenvironmental reconstructions

complex circular subsidence structures in tephra deposited on large blocks of ice varða tuff cone oraefajokull iceland several broadly circular structures up to 16 m in diameter into which higher strata have sagged and locally collapsed are present in a tephra outcrop on southwest oraefajokull southern iceland the tephra was sourced in a nearby basaltic tuff cone at var a the structures have not previously been described in tuff cones and they probably formed by the melting out of large buried blocks of ice emplaced during a preceding jokulhlaup that may have been triggered by a subglacial eruption within the oraefajokull ice cap they are named ice melt subsidence structures and they are analogous to kettle holes that are commonly found in proglacial sandurs and some lahars sourced in ice clad volcanoes the internal structure is better exposed in the var a examples because of an absence of fluvial infilling and reworking and erosion of the outcrop to reveal the deeper geometry the ice melt subsidence structures at var a are a proxy for buried ice they are the only known evidence for a subglacial eruption and associated jokulhlaup that created the ice blocks the recognition of such structures elsewhere will be useful in reconstructing more complete regional volcanic histories as well as for identifying ice proximal settings during palaeoenvironmental investigations

inverting measurements of surface slip on the superstition hills fault we derive and test a set of inversions of surface slip measurements based on the empirical relation u t uf 1 t t c proposed by sharp and saxton 1989 to estimate the final slip uf the power law exponent c and the power law duration t at short times sharp s relation behaves like the simple power law u t u 1 tc where u 1 is the initial slip that is the slip at 1 day after the earthquake at long times the slip approaches the final slip asymptotically the inversions are designed in part to exploit the accuracy of measurements of differential slip that is measurements of surface slip which are made relative to a set of nails or stakes emplaced after the earthquake we apply the inversions to slip measurements made at 53 sites along the superstition hills fault for the 11 months following the m 6 2 and 6 6 earthquakes of 24 november 1987 in general estimates of the initial slip and the power law exponent are well resolved while estimates of the power law durations and the final slip are less well resolved because the durations of the surface slip measurements are often less than the derived power law durations the slip on the three fault strands is a relatively smooth function of position the initial slip and final slip are well correlated the time dependence of surface slip at the 53 sites is roughly similar along the entire fault where the power law exponents are distributed as c 0 14 0 04 and the power law durations range from 100 t 1000 days

sedimentological evidence of pleistocene earthquakes in nw poland induced by glacio isostatic rebound abstract soft sediment deformation structures are abundantly present in two levels within warthanian eemian lacustrine sediments at siekierki near the polish german border the two event horizons show intense folding collapse sag and load structures indicative of liquidization and fluidization the structures must have been caused by sudden shocks most probably resulting from earthquakes that were induced by glacio isostatic rebound probably after the warthanian deglaciation such seismites have not been previously recognized in polish quaternary sediments they provide supporting evidence for glacio isostatic movements that were interpreted up till now based on drilling lithostratigraphic geophysical and geodetic data the recognition of seismites in nw poland may help recognize other deformed event horizons in pleistocene sediments as glacio isostatic or neotectonic seismites

structures caused by repeated freezing and thawing in various loamy sediments a comparison of active fossil and experimental data in this paper the authors present the results of both macroscopic and microscopic investigations on structure development created by repeated ice lensing in various loamy experiments experimental data are compared with observations performed on active forms in high arctic and alpine mountain environments those observations are also compared with phenomena observed in fossil periglacial formations of western europe platy and short prismatic structure formation is bonded to the hydraulic and thermal conditions during ice segregation when a long series of alternating freezing and thawing affects platy structures the fabric evolves also being influenced by slope and drainage conditions cryoturbations frostcreep and gelifluction can appear they are characterized by specific microfabrics which are better developed with an increasing number of cycles this is clear in experiments where hydraulic and thermal parameters are better controlled vesicles are also a prominent characteristic of the surface horizon in experiments and arctic soils the genesis of vesicles is discussed on the basis of new observations and is related to the mechanical collapse of frost created aggregates under the mechanical work of soil air escape during soil saturation by water at thaw

lithium isotope fractionation by diffusion in minerals part 2 olivine abstract recent experiments have shown that lithium isotopes can be significantly fractionated by diffusion in silicate liquids and in augite here we report new laboratory experiments that document similarly large lithium isotopic fractionation by diffusion in olivine two types of experiments were used a powder source method where lithium from finely ground spodumene lialsi2o6 diffused into oriented san carlos olivine and piston cylinder annealing experiments where kunlun clinopyroxene 30 ppm lithium and oriented san carlos olivine 2 ppm lithium were juxtaposed the lithium concentration along traverses across the run products was measured using both laser ablation as a source for a varian 820 ms quadrupole mass spectrometer and a cameca 1270 secondary ion mass spectrometer the cameca 1270 was also used to measure the lithium isotopic fractionation across olivine grains recovered from the experiments the lithium isotopes were found to be fractionationed by many tens of permil in the diffusion boundary layer at the grain edges as a result of 6li diffusing significantly faster than 7li the lithium concentration and isotopic fractionation data across the olivine recovered from the different experiments were modeled using calculations in which lithium was assumed to be of two distinct types one being fast diffusing interstitial lithium the other much less mobile lithium on a metal site the two site diffusion model involves a large number of independent parameters and we found that different choices of the parameters can produce very comparable fits to the lithium concentration profiles and associated isotopic fractionation because of this nonuniqueness we are able to determine only a range for the relative diffusivity of 6li compared to 7li when the mass dependence of lithium diffusion is parameterized as d 6 li d 7 li 7 6 the isotope fractionation for diffusion along the a and c crystallographic direction of olivine can be fit by 0 4 0 1 while the fractionation in the b direction appears to be somewhat lower model calculations were also used to fit the lithium concentration and isotopic fractionation across a natural olivine grain from a peridotite xenolith from the eastern north china craton the isotopic data were fit using values 0 3 0 36 similar to that of the laboratory experiments this along with the fact that the isotopic fractionation is restricted to that part of the mineral with a gradient in lithium concentration is strong evidence that the lithium zoning of this mineral grain is the result of lithium loss by diffusion and thus that it can be used as illustrated to constrain the cooling history

experimental studies of the fluidization of layered sediments and the formation of fluid escape structures experiments demonstrate that fluid escape structures can be produced as a result of unstable fluidization behaviour where a lower base layer of granular material is inhibited from fluidizing by the presence of an overlying non fluidizing top layer before the base layer can fluidize the weight of the overlying material must be balanced and this is accomplished by base layer material pressing against the bottom surface of the confining top layer forming a static layer this static layer allows the top layer to lift away from the base layer which is then free to fluidize a water filled crack forms below the static layer and as this grows instability causes the static layer and top layer to bend and conical voids to form below the antiformal sections rupture occurs at the apex of the water void allowing the underlying water and fluidizing material to burst out through the top layer the fluidized base layer material then flows through the rupture until all of this material except that in the static layer is deposited above the previously overlying layer and a stable fluidization system results the top layer material is bent upwards around the rupture and the resulting pillar type escape structure is preserved if flow then ceases the vigour of the burst out is greatest when the base layer material has a grain size 15 of the top layer material if the base layer grain size is less than 8 of the top layer then base layer material will pass through the top layer pore spaces without forming an escape structure if cohesive material is present escape structures form when a layer of fine grained cohesive material overlies a layer of cohesionless material at low flow rates small pipes with scattered angular bends pierce the top layer and base layer material passes through them the base layer material is ejected on to the top layer and builds up around the mouth of each pipe to form constructional structures sand volcanoes this is in contrast to the cohesionless experiments where the weight of material being deposited on the top layer caused an ejecta filled depression to form around the rupture if flow then ceases both the pipes and the sand volcanoes are preserved at high flow rates where the base layer fluidizes the top cohesive layer becomes fragmented small fragments circulate within the fluidizing base layer and are preserved as floating clasts large fragments sink to the bottom of the fluidizing base layer erosion of the bottom surface of these larger fragments causes this surface to become convex downward the experimentally derived structures are similar to pillar type structures observed in the field and the processes described can be used to investigate the development of these structures fluidization experiments also demonstrate the genesis of dish structures and the cohesive behaviour can be applied to the deformation of these structures after initial formation

physical modelling of sand injectites abstract sand injectites are structures that result from intrusion of fluidized sand into fractures we have studied them in the tampen spur area of the north sea and have reproduced them experimentally by driving compressed air through layers of sand glass microspheres and silica powder the silica powder was cohesive and capable of hydraulic fracturing whereas the sand and glass microspheres were almost non cohesive and therefore able to fluidize the models were dynamically similar to their natural counterparts for as long as equilibrium was static when the processes became dynamic so that inertial forces were significant the scaling was approximate and the corresponding reynolds numbers differed the experimental apparatus was a square box 1 m 1 m wide resting on a grid of fluid diffusers during the experiments the fluid pressure increased until it attained and surpassed the weight of overburden flat lying hydraulic fractures containing air formed within cohesive and least permeable layers heterogeneities in material properties and layer thicknesses were responsible for localizing fracture networks when any one network broke through to the surface rapid flow of air through the fractures fluidized the underlying mobile materials and even depleted some of the layers some of the fluidized material extruded at the surface through vents forming volcanoes and sheets the remainder lodged at depth forming sand injectites or laccoliths conical sand injectites formed preferentially where layers had high resistance to bending laccoliths formed nearer the surface where overlying layers had low resistance to bending the experimental sand injectites were broadly similar to those in the tampen spur area of the north sea as well as other areas

reconciling li and o diffusion in zircon with protracted magmatic crystal residence lithium and o in zircon have strong potential as diffusion chronometers for assessing thermal histories of magmatic and metamorphic systems but their diffusion mechanisms remain controversial zircon populations erupted from el chichon volcano chiapas mexico often contain xenocrysts of detrital origin with juvenile overgrowth forming a natural diffusion boundary within individual crystals high spatial resolution o and li isotope analyses u pb and u th geochronology and li along with al and y scanning ion imaging were acquired to compare diffusion model timescales with those derived from radiometric dating oxygen isotopes in el chichon zircon xenocrysts preserve source heterogeneities with xenocrystic and juvenile domains of zircon being in o isotopic disequilibrium with the melt at the time of eruption preservation of these heterogeneities is consistent with recently determined o isotope diffusion parameters when crystal residence at magmatic temperatures is assumed over the 103 104 year timescales indicated by u th geochronology lithium concentration gradients across the same boundaries are sharp within the 2 5 m lateral resolution of the ion beam whereas li isotopic compositions for xenocrystic cores are homogeneous at 7li 7 8 2 3 1 standard error and different from their putative source diffusive equilibration of li isotopes in zircon is consistent with protracted magmatic crystal residence but preservation of li abundance heterogeneities is difficult to reconcile with evidence for recurrent high temperature exposure of zircon in a highly active magmatic system we speculate that li partitioning in zircon is in part coupled to slow diffusing trivalent cations which can cause severe underestimation of diffusion timescales extracted from li diffusion modeling

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

roughness of natural fault surfaces the roughness of fault surfaces is important in the mechanics of fault slip and could play a role in determining whether sliding occurs via earthquakes or fault creep we have made preliminary measurements of the power spectral density of several fault surfaces over the wavelength range from 10 5 to 1 m using field and laboratory scale profilimeters the fault surfaces are strongly anisotropic profiles parallel to the slip direction have amplitudes about one order of magnitude lower than those perpendicular to the slip direction over most of the wavelength interval measured fault roughness perpendicular to the slip direction is similar to the roughness of natural joints the greater smoothness in the slip direction presumably represents wear resulting from slip combining our data with previous measurements of the roughness spectrum of the san andreas fault shows that fault surfaces are fractal over nearly eleven orders of magnitude in wavelength

coseismic displacements 1992 landers california earthquake the rupture associated with the 1992 landers earthquake ms 7 5 extended along the west edge of a 60 50 km trilateration network that had been surveyed two months before the earthquake and was resurveyed a month after it the coseismic displacement field within the network was calculated from the changes observed in the trilateration network supplemented by the displacements measured at four gps stations and other less timely trilateration measurements stations near the rupture were displaced by as much as 3 m the observed changes are reproduced reasonably well by dislocation modeling in which the landers rupture is represented by 8 vertical fault segments each extending from the surface to 9 km depth two additional segments represent the big bear and eureka peak faults the average modeled right lateral slip on the landers rupture is about 5 m however the residuals for the best fit slip distribution are about four times greater than expected from measurement error given that uncertainty a broad range of slip models furnish acceptable fits to the data the large residuals are attributed to inelastic deformation principally sympathetic slip on numerous unmodeled faults within the fault blocks assumed to be elastic in the model

impact related clastic injections in the marine ordovician lockne impact structure central sweden clastic injections generated in connection with the formation of impact craters show many similarities to injections created by other geological processes however circumstances such as their position relative to the impact structure and the evidence of forceful processes indicate an impact origin the ordovician lockne impact structure was formed in a marine environment with both sedimentary cambrian and ordovician and underlying crystalline proterozoic target rocks sea water played a substantial part in the cratering process especially in the modification of the newly formed crater as the water surged back into the structure in the lockne area clastic dykes and sills have long been known and have earlier been interpreted as neptunian dykes and conglomerates so far seven cases of dykes and sills are known in the area in this work these are interpreted as clastic injections formed in connection with the lockne impact the clastic injections occur in the crystalline basement and the sedimentary sequence the material in the injections comes from all local lithologies both sedimentary and crystalline but the sedimentary sequence dominates as a source the dykes and sills were injected simultaneously with the fracturing and dilation of the host rock in the cratering process and occur at different stratigraphic levels in some dykes clasts from the host rock wall can be fitted back to their original position the clasts are slightly rotated and surrounded by exotic material quartz grains with planar deformation features were observed in the injected material most of the sills within the bedded ordovician limestone are restricted to marly beds except for the feeder dykes which cut through the overlying beds this circumstance demonstrates how the decompression has opened the strata along weaker layers and that the underpressure created subsequently sucked the material down laminar flow is a conspicuous internal structure in the dykes and sills and indicates viscous flow of injected material the lamination in the injected material is parallel to the walls in each case the material was lithified prior to the event and was crushed mobilized in a water sediment slurry and injected as dykes and sills

source process of the 1995 kobe earthquake determination of spatio temporal slip distribution by bayesian modeling the kobe hyogo ken nanbu earthquake ms 6 8 occurred on 16 january 1995 in western japan bringing about a tremendous disaster we constructed its source model by determining a spatio temporal slip distribution using strong motion seismograms recorded at a number of stations near the hypocenter the source area is expressed using both a rough and a detailed subfault discretization system and a source time function expanded with a finite number of basis functions at each subfault is determined to perform stable inversions with many parameters we construct a bayesian model with unknown hyperparameters incorporating prior constraints on the smoothness of spatio temporal slip distribution in the observation equation using akaike s bayesian information criterion abic the optimal set of hyperparameters are objectively determined from observed data which enables us to uniquely determine a spatio temporal slip distribution after rough analysis in which the actual rupture area is estimated as 45 20 km we carried out a detailed analysis with a finer subfault discretization system 5 5 km in our final source model most of the slip exists beneath awaji island and the rupture below the city of kobe where the damage was most serious is relatively smaller the large slips of about 2 m in the shallowest subfaults located southwest of the hypocenter correspond to the surface offsets observed along the nojima fault the overall focal mechanism of the source is right lateral strike slip with a small thrust component while total seismic moment is 2 0 1019 nm the source time functions at shallow subfaults show a longer duration than those at deeper ones being hypothesized to represent a possible combined effect of low rupture propagation velocity and varying friction behavior in shallow regions of crust

growth of a normal fault system observations from the lake malawi basin of the east african rift abstract we have studied the growth history of the usisya normal fault system which bounds the west side of the lake malawi basin one of the largest rift basins in the east african rift system the lake malawi rift basin is a complex of intrabasins and intrabasin highs formed by three major fault segments each about 100 km in length the basin has been actively subsiding since the late miocene and has a maximum depth of about 3 km unlike the majority of previous studies of fault systems we are able to define the temporal evolution of this fault system using the patterns of sediment infill this is due almost exclusively to the availability of a high density seismic reflection network in combination with several clearly identifiable temporal marker beds an analysis of the seismic reflection data reveals that growth of the basin bounding faults occurred in the following sequence 1 in the early stages of rifting starting about 8 6 ma the northern fault was the most active 2 then extension shifted to the southernmost fault segment and lasted until about 2 5 ma 3 during the interval between about 2 3 ma and 1 6 ma the central segment was most active prior to the last interval the central segment accrued the least total displacement of the three segments this contradicts the common notion that the location of maximum displacement remains at a fixed location from fault inception or that the largest fault in any population of faults always maintained the highest displacement rate consistent with observations on smaller faults there is a marked increase in the displacement gradient on individual faults in the regions of overlapping segments although there is an observable asymmetry in individual segment displacement profiles there is a clear evolution toward a flattened bell shaped total displacement profile for the fault system that is consistent with the shape and scaling relationships of displacement vs length that are observed on a wide range of individual normal faults this suggests that the irregularities in the shape and scaling relationships observed in complex fault systems will eventually smooth out moreover the observed growth pattern suggests that the profile of the fault system will progress toward that of isolated faults provided the system is allowed sufficient time to evolve this in turn describes a process for maintaining a self similar scaling observed in large populations of faults which span several orders of magnitude in fault length

soft sediment deformation structures in nw germany caused by late pleistocene seismicity new data on seismically triggered soft sediment deformation structures in pleniglacial to late glacial alluvial fan and aeolian sand sheet deposits of the upper senne area link this soft sediment deformation directly to earthquakes generated along the osning thrust which is one of the major fault systems in central europe soft sediment deformation structures include a complex fault and fold pattern clastic dikes sand volcanoes sills irregular intrusive sedimentary bodies flame structures and ball and pillow structures the style of soft sediment deformation will be discussed with respect to brittle failure liquefaction and fluidization processes and was controlled by 1 the magnitude of the earthquake and 2 the permeability tensile strength and flexural resistance of the alluvial and aeolian sediments it is the first time in northern germany that fluidization and liquefaction features can be directly related to a fault the occurrence of seismicity in the late pleistocene and in the seventeenth century indicates ongoing crustal movements along the osning thrust and sheds new light on the seismic activity of northern germany the late pleistocene earthquake probably occurred between 15 9 1 6 and 13 1 1 5 ka the association of soft sediment deformation structures implies that it had a magnitude of at least 5 5

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

clastic injection dynamics during ice front oscillations a case example from solheimajokull iceland abstract soft sediment deformation structures are being increasingly used as a tool for reconstructing palaeoenvironments and porewater pressure conditions in glacial settings however the potential of hydrofractures and clastic injections in the reconstruction of ice dynamics remains poorly constrained this paper presents the results of a detailed study of a clastic injection network outcropping in the solheimajokull forefield south iceland sedimentological descriptions are combined with microscopic to macroscopic analyses of clastic injection geometries sediment fills and cross cutting relationships the 250 m long and 20 m high exposure observed along the east flank of the proglacial braid plain displays alternating glaciofluvial sediments and subglacial tills illustrating oscillations of the ice margins these sediments are cross cut by a dense network of injection composed of dykes propagating upward or downward sills and stepped sills these clastic injections result from processes of hydrofracturing and the sediment fills in these hydrofractures are generally laminated with an increase of grain size towards the centre of the injections these fracture fill characteristics suggest multiple injection phases within the hydrofractures and an increase of porewater pressure over time five main generations of clastic injections showing different senses of propagation and dip directions are determined and are interpreted as forming in different environments per descensum clastic dykes dipping down ice demonstrate subglacial hydrofracturing underneath flowing ice while sills and per ascensum clastic dykes form in submarginal to marginal environments due to the decrease of ice overburden pressure the integration of these results with the sedimentological characteristics allows the holocene ice front oscillations of the solheimajokull to be reconstructed this study demonstrates the importance of hydrofracture systems and their sediment fills in the reconstruction of palaeo ice dynamics

the principles of cryostratigraphy abstract cryostratigraphy adopts concepts from both russian geocryology and modern sedimentology structures formed by the amount and distribution of ice within sediment and rock are termed cryostructures typically layered cryostructures are indicative of syngenetic permafrost while reticulate and irregular cryostructures are indicative of epigenetic permafrost cryofacies can be defined according to patterns of sediment characterized by distinct ice lenses and layers volumetric ice content and ice crystal size cryofacies can be subdivided according to cryostructure where a number of cryofacies form a distinctive cryostratigraphic unit these are termed a cryofacies assemblage the recognition if present of i thaw unconformities ii other ice bodies such as vein ice ice wedges aggradational ice and thermokarst cave pool ice and iii ice sand and gravelly pseudomorphs is also important in determining the nature of the freezing process the conditions under which frozen sediment accumulates and the history of permafrost

large lithium isotopic variations in minerals from peridotite xenoliths from the eastern north china craton abstractto investigate the effects of melt rock interaction on li isotope fractionation we report in situ li concentrations and 7li of olivine ol orthopyroxene opx and clinopyroxene cpx for six peridotite xenoliths from the eastern north china craton these xenoliths contain two lherzolites two cpx rich lherzolites and two wehrlites and are variably metasomatized lithium isotope zonation is observed in most peridotite minerals the majority of cpx grains display isotopically light cores with lower li concentrations than the heavy rims however the opx grains show a different style of zonation from cpx where higher li concentrations in the cores are associated with much lighter 7li olivines in most peridotites have a restricted range of li concentration and 7li within individual grains whereas the olivines in a lherzolite show isotopically light cores 10 3 with high li concentrations 2 3 ppm and heavy rims 5 5 with low li concentrations 1 7 ppm these li isotopic variations in m

field occurrences of liquefaction induced features a primer for engineering geologic analysis of paleoseismic shaking discussed in this paper are the factors that control the typical manifestations of liquefaction that are found in continental field settings the factors are given mainly in terms of the local geologic field situation and the geotechnical properties there a meaningful interpretation of liquefaction based data for quantitative analysis of paleoseismic shaking requires understanding of both geologic and geotechnical roles in the mode of ground failure at a specific site recommendations are made for the size of the field area that must be searched for liquefaction effects in order to develop adequate data for engineering geologic geotechnical analyses of paleoseismicity the areal extent must be based on an appreciation that the tectonic situation can cause seismically induced liquefaction effects to form in some locales but not in others nearby even for a strong earthquake in the region our guidelines for the conduct of the field search and preliminary analysis of the data relate to three issues for which liquefaction features are especially useful in answering has there been strong holocene latest pleistocene shaking in the region where was the tectonic source and what was the strength of shaking understanding of the various factors that control the manifestations of liquefaction effects which we present in this paper is essential for developing credible answers to these questions

isotope fractionation by chemical diffusion between molten basalt and rhyolite abstract experimental diffusion couples were used to study chemical diffusion between molten rhyolite and basalt with special emphasis on the associated fractionation of calcium and lithium isotopes diffusion couples were made by juxtaposing firmly packed powders of a natural basalt suny morb and a natural rhyolite lake county obsidian and then annealing them in a piston cylinder apparatus for times ranging from 0 1 to 15 7 h temperatures of 1350 1450 c and pressures of 1 2 1 3 gpa profiles of the major elements and many trace elements were measured on the recovered quenched glasses the diffusivities of all elements except lithium were found to be remarkably similar while the diffusivity of lithium was two to three orders of magnitude larger than that of any of the other elements measured chemical diffusion of calcium from molten basalt into rhyolite was driven by a concentration ratio of 18 and produced a fractionation of 44ca from 40ca of about 6 because of the relatively low concentration of lithium in the natural starting materials a small amount of spodumene lialsi2o6 was added to the basalt in order to increase the concentration difference between basalt and rhyolite which was expected to increase the magnitude of diffusive isotopic fractionation of lithium the concentration ratio between li doped basalt and natural rhyolite was 15 and the resulting diffusion of lithium into the rhyolite fractionated 7li from 6li by about 40 we anticipate that several other major rock forming elements such as magnesium iron and potassium will also exhibit similarly larger isotopic fractionation whenever they diffuse between natural melts with sufficiently large differences in the abundance of these elements

kinetic instabilities during the propagation of a branch crack effects of loading conditions and internal pressure abstract in order to understand the physical processes controlling the formation of various branch features stemming from pre existing defects in rocks this paper presents a model based on fracture mechanics concepts we examine the consequences of the elastic stress field around an open oblique elliptical defect subjected to constant uniaxial or biaxial stress on the kinetics of the classical branch crack assuming that propagation does not fundamentally change the elastic stress field the strain energy release rate g is computed for each branch crack length l by integrating the values of the principal stress acting perpendicular to the stress trajectory of the other principal stress starting exactly from the point of maximum tensile stress at the edge of the elliptical defect the propagation regime depends on the slope of the g l curve and on its position with respect to the equilibrium value g o and the critical value g c for which catastrophic rupture occurs without internal pressure the unimodal curves predict three possible successive propagation regimes 1 stable propagation with increasing velocity 2 catastrophic propagation with velocity jump and associated acoustic emission and 3 stable propagation with decreasing velocity the catastrophic regime is limited to high load values experimentally the triggering of the propagation can be very difficult to predict as it depends on slight variations in the length of pre existing microcracks stemming from the elliptical defect at the root of the branch crack path with internal pressure the stress field is modified so that the maximum tensile stress is present at some distance from the edge of the elliptical defect this can result in a change in the shape of g l curves which indicates that two independent velocity jumps may occur the first one is mainly linked to the local influence of the defect the second leading to a large extension is due to the general influence of the internal pressure

soft sediment deformation of late pleistocene sediments along the southwestern coast of the baltic sea ne germany a 1 460 m long profile of a late glacial subglacial glacio fluvial glacio limnic and glacio deltaic sequence exposed at a cliff section on usedom island sw baltic sea coast is described the sequence is up to 31 m thick and shows sedimentary structures typical of a glacial setting soft sediment deformation is encountered and is associated with changes in lithology these deformations include liquefaction slumping and faulting as the most plausible cause earthquake induced shaking is discussed the associated neotectonic activity is seen as a consequence of the postglacial isostatic crustal rebound as the deglaciation earthquake ratio diminishes with time and as the rebound is phasing out no large earthquakes are anticipated for northern germany although in conclusion the lithosphere of the north german basin has to be regarded as weakened by repeated ice loading and deloading

reassessing the cooling rate and geologic setting of martian meteorites mil 03346 and nwa 817 abstract lithium concentration and isotopic fractionation profiles across augite grains from two martian meteorites mil 03346 and nwa 817 were used to determine their thermal history and implications for their geologic setting the iron magnesium zoning and associated magnesium isotopic fractionation of olivine grains from nwa 817 were also measured and provide a separate estimate of the cooling rate the observed correlation of concentration with isotopic fractionation provides the essential evidence that the zoning of these grains was in fact due to diffusion and thus can be used as a measure of their cooling rate the diffusion rate of lithium in augite depends on the oxygen fugacity which has to be taken into account when determining a cooling rate based on the lithium zoning the fe mg exchange in olivine is much less sensitive to oxygen fugacity but it is significantly anisotropic and for this reason we determined the direction relative to crystallographic axes of the line along which the fe mg zoning was measured we found that the cooling rate of nwa 817 determined from the lithium zoning in augite grains and that based on the fe mg zoning of olivines are in good agreement at an oxygen fugacity close to that of quartz fayalite magnetite oxygen buffer the cooling rate of mil 03346 was found to be resolvably faster than that of nwa 817 of the order of 1 c h for the former and of the order of 0 2 c h for the latter an important observation regarding the history of mil 03346 and nwa 817 is that the lithium and fe mg zoning are only observed where the augite or olivine is in contact with the mesostasis which implies that they were already about 80 crystallized at the time diffusion began the augite and olivine core compositions while very homogeneous are not in equilibrium with each other which we interpret to imply that prior to the rapid cooling there must have been a protracted period of the order of years above the solidus during which the much faster fe mg exchange in olivine compared to that in augite allowed the olivine to maintain equilibrium with a changing melt composition while the augite was not significantly affected we suggest two possible geological settings for the origin and evolution of mil 03346 and nwa 817 1 a slow cooling stage in a crystallization front in a crustal magma chamber followed by eruption of melt plus portions of the crystallization front onto the surface where the final fast cooling took place at the bottom of a lava flow or melt pond and 2 eruption of a crystal laden melt as a thick long lived lava flow where the crystals continued to grow as a cumulate and were rapidly cooled when the overlying lava layer was suddenly drained

response to the discussion by van vliet lanoe et al of the paper features caused by ground ice growth and decay in late pleistocene fluvial deposits paris basin france bertran et al 2018 geomorphology 310 84 101 abstract the response by van vliet lanoe et al to our paper on potential thermokarst features in pleistocene alluvial deposits from the paris basin france presents inconsistencies that we consider here successively these are 1 the map of the maximum extent of pleistocene permafrost in france 2 the genesis of liquefaction and fluidization structures in periglacial environments 3 the origin of thermokarst lakes and recumbent folds 4 the depositional context of sandy units and 5 the age of the studied deposits all structures result from the interplay between 1 the growth and degradation of ice wedges which are responsible for the development of a mound like topography badland thermokarst reliefs on the edge of the alluvial terrace and from the initiation of ponding elsewhere on the terrace 2 the degradation of lithalsa that developed later in the lacustrine deposits the sequence was dated confidently to the late weichselian

genesis and diagnostic value of soft sediment deformation structures a review abstract soft sediment deformation structures are recognized as important diagnostic features in the rock record for determination of depositional environments and slope processes the diagnostic value of these structures is reevaluated by analysis of the parameters controlling sediment deformation soft sediment deformation is contemporaneous with deposition and occurs dominantly in course silt to fine sand the high depositional rate low permeability and low shear strength of grains within this sediment range maximize the occurrence of deformation the dominant mechanisms responsible for sediment deformation include 1 liquefaction or fluidization 2 reverse density gradation 3 slumping or slope failure and 4 shear stress in most cases a combination of these mechanisms occurs the processes function in a continuum producing features that are microscopic to megascopic in scale it is shown that the processes and thus the structures are not environment specific the true diagnostic value of the structures may be in defining hydrodynamic conditions and in interpreting paleocurrents and paleoclimatic and paleoseismic events ultimately for the best diagnostic results soft sediment deformation structures should be studied in association with all other available lithologic structural and paleontological information

southern surface rupture associated with the 1992 m7 4 landers earthquake did it all happen during the mainshock approximately three minutes after the magnitude 7 4 landers mainshock on 28 june 1992 a m5 7 aftershock occurred south of the mainshock epicenter with a location of 34 7 65 n 116 23 82 w this aftershock was recorded on an array of portable digital seismic instruments deployed in morongo valley 21 km southwest of the event although peak accelerations are found to differ by approximately 50 at stations with similar general site conditions within 500 m of each other there is good coherence of arrivals across the array for frequencies 1 hz we use the recordings to determine the apparent phase velocity and azimuth of propagation across the array and show that the event clearly ruptured to the south with a rupture length of 11 km and a rupture velocity of approximately 3 0 km s our results suggest that at least some of the mapped surface rupture south of the town of yucca valley 11 km in extent maximum displacement of 20 cm may have been associated with this aftershock if this is the case then the fault that produced the southern end of the landers mainshock the johnson valley fault need not continue at depth across the active left lateral east west trending pinto mountain fault

multicycle slip distribution along a laboratory fault slip distribution along a laboratory fault which consists of eight spring connected blocks that are elastically driven to slide on a frictional surface has been examined for a long sequence of slip events to test the applicability of some conceptual models proposed recently in the literature the distributions of large slip events are found to be quite variable and do not fit the uniform slip or characteristic earthquake models the rupture initiation points are usually not near the corresponding maximum slip points in contrast to observations by thatcher 1990 and by fukao and kikuchi 1987 that earthquake hypocenters are commonly near corresponding regions of maximum slip in the fault planes this contrast may suggest that either the present observations or theirs are not representative or the teleseismically determined hypocenters may not always be true rupture initiation points as usually assumed large slip events are also found to be a stress roughening process they are triggered by some small events after the stresses have been adjusted by some earlier small to moderate events to be near the critical levels at most locations along the fault this suggests that earthquake prediction monitoring efforts should not be limited to a small region near an asperity but should be spread out to cover the entire fault segment in a seismic gap in order to detect the condition of simultaneous strain buildup

predictability of slip events along a laboratory fault a long sequence of stick slip events generated along a laboratory fault which consists of eight spring connected masses that are elastically driven to slide on a frictional surface has been examined to check whether the large events are predictable the large events are found to recur at intervals of very different durations although the elastic and frictional properties along the fault are quite uniform the recurrence intervals are however approximately proportional to the displacements of the preceding events but not of the following events thus the occurrence time of a large event is approximately predictable whereas its displacement is not the size logarithmic energy release distribution of all the events of different sizes can be fitted by a maximum entropy model which has an upper bound in size corresponding to the complete release of the maximum strain energy stored along the fault

photoelastic and numerical investigation of stress distributions around fault models under biaxial compressive loading conditions abstract this paper presents the results of a photoelastic and numerical study of stress distributions contours and trajectories around fault models of various geometries submitted to a biaxial compressive load it aims to describe typical biaxial stress behaviours and emphasize the existing differences with the well known uniaxial compressive load case stress trajectories are sometimes shown by joint sets acting as markers of a paleostress field and they can be interpreted by particular shallow tension compression situations at depth fractures can be reactivated or can dilate under conditions of triaxial compression and behaviour is essentially controlled by a high stress ratio high 3 1 ratio in spite of the potential importance of such stress states on fracture permeability and fluid flow and although they are frequently found at depth in a reservoir context such stress conditions are poorly investigated particularly in terms of stress perturbations the presented analogue experiments consisted of compression tests done on polymethylmethacrylate pmma plates this material has mechanical properties comparable to those of brittle rocks in the upper crust and presents birefringence the samples contained open defects acting as faults and the stress trajectories around these faults were investigated using a photoelastic device comparable numerical experiments were realised with a finite element code franc 2d using frictionless fault models first the effect of an increasing biaxial compressive load ratio 3 1 on stress trajectories around an isolated open defect was explored it was shown that the stress trajectories were drastically modified when 3 1 increased from 0 2 to 0 4 this result being consistent with previous studies in particular when 3 1 was superior or equal to 0 4 external isotropic points around where trajectories diverged called repulsive isotropic points appeared near the tips but away from the defects they tended to move away from the defects towards the main load direction when 3 1 increased the described isotropic points were points of stress trajectory divergence i e points where stress decreased implying that zones around them were strongly unfavourable to shear reactivation second stress trajectories around fault models of various geometries oblique isolated defect dilational jog compressive jog and complex patterns were studied the applied biaxial compressive load ratio being 0 7 these biaxial stress trajectories were compared with similar uniaxial stress trajectories in order to explore the existing differences between the two regimes it enabled new stress trajectory geometries to be described and interpreted in particular numerous external repulsive isotropic points were observed and defect tips were shown to be zones of high convergence of stress trajectories furthermore in contrast to the uniaxial compressive load case stress trajectories and stress contours were geometrically similar within dilational and compressive jogs under biaxial compressive load for both jog types the centre of the overlapping zone and the areas along the wall of a jog defining fault and facing the overlapping tip of the other fault proved to be zones of low mean stress implying that fluids may migrate towards them from the tips of the faults in response to mean stress gradients furthermore the centre of the jogs exhibiting a high differential stress was a favourable area in terms of fracture reactivation which may facilitate fluids transfer and storage it was also observed that for both the uniaxial and biaxial compressive loads isotropic zones were localised at the acute angle between branching defects

paleoseismology along the range front fault of helan mountains north central china the nne trending range front fault of the helan mountains along the western margin of yinchuan graben northcentral china is a 13 km long high angle normal and right lateral strike slip fault it cuts late pleistocene to holocene alluvial fans forming a se facing scarp and offsets the great wall of the ming dynasty about 400 years b p right laterally for 1 45 m and vertically for 0 95 m the offset of the great wall is probably a result of the m 8 yinchuan pingluo earthquake of 1739 the 1739 earthquake formed an 88 km long discontinuous surface rupture zone along the fault scarps both the length and height of the fault scarps are largest at hongguozi in the north and suyukou in the south we have prepared large scale topographic and geologic maps along the hongguozi and suyukou scarps surveyed 88 profiles across the scarps and excavated 14 trenches across the fault in order to study holocene paleoseismicity and recurrence intervals of large earthquakes along the fault four levels of terraces were developed on the upthrown block of the fault along some gullies that dissected the alluvial fans the older terraces such as t4 and t3 are tilted to the west whereas the younger terraces are less tilted this indicates that the terraces may have been tilted and rotated by multiple faulting events the height difference between the two adjacent terraces is about 1 2 7 m the elevation differences between the lower original surface and the t3 t2 and t1 terraces were measured in 64 topographic profiles across the scarps the results show that the elevation of t3 is highest averaging 8 4 1 9 m and 5 5 1 1 m along the suyukou and hongguozi fault scarps respectively the elevations of t2 at the two sites are 5 8 1 4 m and 3 4 0 4 m respectively whereas elevations of t1 are 3 1 1 2 m and 1 2 0 3 m respectively ages of terrace risers between t3 and t2 as well as between t2 and t1 are 3600 4600 years and 2000 2800 years respectively as calculated using a diffusion model of scarp development the morphology of the fault scarps is complicated two or three bevels were developed on some fault scarps that were active in an earlier period and the upper and the lower slope sections correspond to t3 and t2 alluvial terraces respectively a free face exists only on t1 terrace the slope angles of the upper and lower slope sections of the scarp at suyukou are 6 22 and 17 38 respectively the difference between the two in the same profiles is consistently in the range of 9 21 in the place where the fault scarp is high the free face with a slope angle up to 60 may be a result of the m 8 earthquake of 1739 we infer that the other two bevels represent two paleoearthquake events eight and six trenches have been excavated across the fault scarps at suyukou and hongguozi respectively all the trenches reveal normal faults multiple offsets and colluvial and filled wedges along the scarps in these trenches we found colluvial wedges formed in four different periods indicating multiple faulting events on the basis of this evidence four holocene seismic events have been identified the timing of the events was determined through 14c dating samples collected from the trenches on the basis of terrace offset scarp morphology and paleoseismic trenching we conclude that the four large earthquakes along the fault occurred 8400 4600 6300 or 5700 2600 and 256 years b p the latest event was the m 8 yinchuan pingluo earthquake of 1739 the recurrence interval of these earthquakes is 2300 3000 years we infer that the magnitudes of these events were probably 8 because the thickness of each colluvial wedge and the height of terrace risers produced by these events are similar to those produced by the 1739 earthquake

extreme lithium isotopic fractionation during continental weathering revealed in saprolites from south carolina the lithium concentration and isotopic composition of two saprolites developed on a granite and diabase dike from south carolina have been measured in order to document the behavior of lithium isotopes during continental weathering both saprolites show a general trend of decreasing d 7 li with increasing weathering intensity as measured by both bulk density and the chemical index of alteration cia the saprolite developed on the granite is isotopically lighter than the fresh igneous rock d 7 li 6 8x to 1 4x vs 2 3x respectively and is generally depleted in lithium these observations are consistent with leaching of lithium via rayleigh distillation during progressive weathering most saprolites fall on a rayleigh distillation curve corresponding to an apparent fractionation factor a of 0 997 however two samples have higher lithium contents than the fresh granite and thus point to additional processes affecting lithium in the saprolite e g sorption of lithium on to clay minerals the saprolite profile developed on the diabase dike shows highly variable d 7 li values ranging down to extremely light compositions 20x previous work has identified a chemical and mineralogical discontinuity at a depth of 2 m but our lithium data show a marked discontinuity at 6 m depth saprolite samples at or above 6 m depth are highly weathered cia 88 95 depleted in lithium having b50 of the original diabase lithium and isotopically light 10x to 20x vs 4 3x for the unweathered diabase most of the data are consistent with leaching of lithium via rayleigh distillation during intense weathering with apparent a values of 0 995 to 0 980 samples experiencing lower apparent a values tend to have higher kaolinite smectite ratios suggesting a mineralogical control on isotopic fractionation however the lightest sample at 20x is only slightly depleted in lithium and would require extremely low a values to explain via rayleigh distilliation this extreme composition remains enigmatic saprolite samples below 6 m have highly variable d 7 li 5x to 14x and importantly lithium concentrations that are higher than that of the unweathered diabase up to 2 4 times the concentration of the fresh diabase these deeper saprolites thus cannot be explained by rayleigh distillation a positive correlation between d 7 li and li

surface slip subsequent to the 24 november 1987 superstition hills california earthquake monitored by digital creepmeters three creepmeters of new design were operated on the superstition hills fault following the 24 november 1987 earthquake each creepmeter consists of a digital displacement sensor interrogated periodically by a computer at the end of each hour the computer determines a recording rate appropriate to the velocity of the slip on the fault in that hour no data are recorded if the fault is inactive data are recorded at a maximum rate of one sample per minute if slip on the fault is detected the resolution and range of the creepmeters are 10 m and 15 cm respectively fault activity is observed to be confined to periods of episodic slip creep events with mean amplitudes 3 to 6 mm and durations less than 4 hr a total of 80 creep events were recorded during the first week following the earthquake creep events occurred several times each day after 6 months events occurred every 3 weeks this increase in the mean time interval between creep events results in the observed decay in afterslip rate between creep events the fault is inactive although more than 200 microstrain of fault zone deformation may accumulate before each event although creep events were observed to propagate unilaterally in both directions along the fault the most impulsive events appeared to propagate bilaterally from a dilatant offset separating the northern and southern halves of the 24 km long fault zone maximum propagation velocities of 30 m sec were observed aftershocks 2 m 4 7 were observed to occur near the creepmeters following 6 to 9 cm of surface slip on the fault a future aftershock in this region is anticipated in mid 1989 based on afterslip rates in the year following the main shock

alkali diffusion in plagioclase feldspar tracer diffusion kinetics at 1 atm pressure under dry conditions using 6li 41k and 87rb in four plagioclase feldspars have been determined diffusion profiles were measured using an ion microprobe sims the arrhenius parameters and 2 uncertainties for li k and rb respectively in albite are pre exponential factor log do 3 8 1 0 3 4 1 4 and 5 8 3 8 in m2 s and activation energies 146 14 296 30 and 283 85 kj mol the diffusion rate of k in albite at 700 c and 100 mpa water pressure equals that at 1 atm dry suggesting that diffusion of k is not dependent on water fugacity between 0 004 and 100 mpa the k diffusion rate depends on plagioclase anorthite content and is approximately 20 times slower in labradorite than albite li diffusion rates in albite and anorthite are identical a linear relation between log d for the alkalis measured and their ionic radius squared permits an estimate of cs diffusion kinetics diffusion rates are isotropic or nearly so in albite

displacement gradients on fault surfaces abstract the maximum displacements and the dimensions of single faults are systematically related and the variation in displacement from a maximum at the centre of a fault to zero at an elliptical tip line loop is described by a simple theoretically derived expression these relationships are used to examine the theoretical ranges and distributions of rates of change of displacement on fault surfaces the dimensions and maximum displacement of a fault can be estimated from a limited number of displacement gradient measurements estimates are further constrained by a knowledge of the effective shear modulus of the rocks containing a fault an understanding of displacement gradients can be applied to problems commonly encountered in mining operations and in the interpretation and use of seismic reflection data in addition to field problems a comparison of theoretical displacement gradients with measured displacement gradients from british coalfield faults shows that i fault surface ellipticities are between 1 5 and 2 5 and ii gross displacement gradients expressed as the ratio of maximum displacement long axis radius of the fault ellipse range from 0 02 to 0 002 the measured displacement gradients indicate that the shear moduli of the faulted rocks range from 3 to 11 gpa which is within the known range for coal measure rocks displacement gradients along an array of fault segments are similar to those of single faults for analysis of displacement gradients it is necessary to sum the discontinuous and continuous components of displacement in extreme cases all the displacement may be accommodated by continuous deformation

seismites an attempt at critical analysis and classification abstract the main types of seismites are reviewed following the proposed classification and are illustrated by our own case studies the large variety of seismites depends on the sedimentologic hydrodynamic and diagenetic characters of the deposits subject to seismic shocks on a given site generally different types of seismites cane be related to the same seismic event these peculiar but widespread sedimentary structures are not always univocal and may often be related to different causes therefore the structures discussed must necessarily be placed in a detailed geological context

deep circulation of groundwater in overpressured subglacial aquifers and its geological consequences abstract it is generally assumed that meltwater from the base of ice sheets is discharged in a relatively thin subglacial zone whereas this may be true for ice sheets resting on impermeable beds many ice sheets such as the glacial period ice sheets of north america and europe flowed over extensive aquifers a theory is developed which suggests that high rates of meltwater discharge into these aquifers would have completely reorganised their flow fields producing intergrated patterns of glacially pressurised flow controlled by the continental scale form of the ice sheet surface rather than the small scale topographic basins which determine modern aquifer extent the theory is applied to the aquifers which underlay the saalian ice sheet in the netherlands where it is shown that potential gradients and groundwater flow velocities would have developed which were two orders of magnitude greater than modern values and that the dominant flow vectors would have been normal to those of the modern flow thus glacial interglacial cycling in areas which have suffered periodic glaciation during the late cenozoic may have experienced alternating phases of greater and lesser flow energy it represents another example of climatically driven cyclical change in the earth under highly energised glacial conditions potential gradients much larger than modern values may have produced many common features of sediment disruption such as diapirs liquifaction structures and pipes and forms such as glacial doughnuts and pock marks which have hitherto been explained by other processes deep and penetrative flushing of aquifers by glacial meltwater may have left a distinctive geochemical signal in them which may be used to test the theory gases such as methane generated at shallow depth may have been trapped beneath the glacial cap rock and may also have played an important role in these processes

co seismic displacements of the 1992 landers earthquake sequence we present co seismic displacement vectors derived from global positioning system gps measurements of 92 stations in southern california these gps results are combined with five well determined gps displacement vectors from continuously tracking stations of the permanent gps geodetic array as well as line length changes from usgs geodolite and two color laser trilateration observations to determine a self consistent set of geodetic data for the earthquake these combined displacements are modeled by an elastic dislocation representation of the primary fault rupture planes on average the model residuals are about twice the estimated measurement errors

the groundwater hydraulics of seasonal frost mounds north fork pass yukon territory seasonal frost mounds occur in the north fork pass area in response to increased hydraulic potentials in perennial spring fed groundwater systems geochemical and isotope analyses indicate that local precipitation is the source of water for flow systems discharging from the springs the direct measurement of pressure potentials in a number of frost blisters and icing blisters undertaken in march 1982 gave values ranging from 30 and 81 kpa for mounds approximately 2 0 m high these pressures exceed theoretical calculated values and are attributed to the tensile strength of the soil and or ice overburden in genetic terms seasonal frost mounds should be clearly differentiated from other morphologically similar features such as palsas

use of liquefaction induced features for paleoseismic analysis an overview of how seismic liquefaction features can be distinguished from other features and how their regional distribution and properties of source sediment can be used to infer the location and strength of holocene paleo earthquakes abstract liquefaction features can be used in many field settings to estimate the recurrence interval and magnitude of strong earthquakes through much of the holocene these features include dikes craters vented sand sills and laterally spreading landslides the relatively high seismic shaking level required for their formation makes them particularly valuable as records of strong paleo earthquakes this state of the art summary for using liquefaction induced features for paleoseismic interpretation and analysis takes into account both geological and geotechnical engineering perspectives the driving mechanism for formation of the features is primarily the increased pore water pressure associated with liquefaction of sand rich sediment the role of this mechanism is often supplemented greatly by the direct action of seismic shaking at the ground surface which strains and breaks the clay rich cap that lies immediately above the sediment that liquefied discussed in the text are the processes involved in formation of the features as well as their morphology and characteristics in field settings whether liquefaction occurs is controlled mainly by sediment grain size sediment packing depth to the water table and strength and duration of seismic shaking formation of recognizable features in the field generally requires a low permeability cap above the sediment that liquefied field manifestations are controlled largely by the severity of liquefaction and the thickness and properties of the low permeability cap criteria are presented for determining whether observed sediment deformation in the field originated by seismically induced liquefaction these criteria have been developed mainly by observing historic effects of liquefaction in varied field settings the most important criterion is that a seismic liquefaction origin requires widespread regional development of features around a core area where the effects are most severe in addition the features must have a morphology that is consistent with a very sudden application of a large hydraulic force this article discusses case studies in widely separated and different geological settings coastal south carolina the new madrid seismic zone the wabash valley seismic zone and coastal washington state these studies encompass most of the range of settings and the types of liquefaction induced features likely to be encountered anywhere the case studies describe the observed features and the logic for assigning a seismic liquefaction origin to them also discussed are some types of sediment deformations that can be misinterpreted as having a seismic origin two independent methods for estimating prehistoric magnitude are discussed briefly one method is based on determination of the maximum distance from the epicenter over which liquefaction induced effects have formed the other method is based on use of geotechnical engineering techniques at sites of marginal liquefaction in order to bracket the peak accelerations as a function of epicentral distance these accelerations can then be compared with predictions from seismological models

diffusion induced li isotopic fractionation during the cooling of magmatic rocks the case of pyroxene phenocrysts from nakhlite meteorites ion microprobe was used to measure li abundances and isotopic compositions in pyroxenes from three martian meteorites belonging to the nakhlite family the profiles performed across augite crystals from northwest africa 817 show a large isotopic zoning from crystal cores 7li not vert similar 0 to rims 7li not vert similar 20 while li abundances are almost constant not vert similar9 2 g g unlike nwa 817 the pyroxene studied in the miller range 03346 nakhlite shows a zoning in li abundance with concentrations increasing from not vert similar2 5 g g in the core to not vert similar9 g g in the rim the augite rim 7li 7 is slightly enriched in 7li with regard to the core 7li 4 but most of the isotopic variations observed occur at an intermediate position along the profile where 7li falls down to not vert similar 11 in the case of nakhla li concentrations in augite increase from cores not vert similar3 5 g g to rims not vert similar6 5 g g while the 7li variation is restricted i e between 7li 6 0 and 12 6 for the three meteorites the li abundances were also measured in the groundmass which was found to be enriched in lithium not vert similar10 g g conventional magmatic and post magmatic processes such as alteration and fractional crystallization fail to explain the dataset obtained on nakhlites degassing processes which were previously proposed to explain the li distribution in shergottite crystals cannot result in the strong decoupling between li abundances and isotopic composition observed in nakhlites we suggest that the original magmatic li distributions concentrations and isotopic compositions in nakhlites have been modified by diffusion of li from the li rich groundmass towards the pyroxene crystals during sub solidus cooling diffusion appears to have been efficient for nwa 817 and mil 03346 but apparently did not produce a significant migration of li in nakhla possibly because of the lower abundance of groundmass in the latter diffusion induced li redistributions may also affect terrestrial porphyric rocks but very specific cooling rates are required to quench the diffusion profiles as observed in two of the present nakhlites

an integrated model of extrusive sand injectites in cohesionless sediments clastic injection and surface expression of subsurface sediment remobilization is a phenomenon which is becoming increasingly recognized however understanding of the physical mechanisms that control these features remains limited dominated by inference from outcrop and seismic studies here this limitation is addressed through a set of experiments focused on the development and evolution of fluidization features in non cohesive bedded sequences fluidization and the onset of piping are shown to occur progressively through a sequence of discrete phases with initial void formation development of infiltration horizons rupture and finally pipe formation critically the style of piping the stability of piping and the temporal evolution of venting are shown to exhibit considerable variability in particular pipes may either be stable or very mobile migrating laterally over large distances these produce deposits that are typically interpreted in outcrop as being the product of en masse liquefaction rather than localized dynamic fluidization these differing elements are synthesized to produce a model of sand extrudites in addition the implications of this model are explored

investigation of nearfield postseismic slip following the mw 7 3 landers earthquake sequence of 28 june 1992 california repeated precise surveys of six nearfield trilateration arrays reveal that minor horizontal displacements occurred across the several fault ruptures in the five months following the landers earthquake sequence the displacements range from 0 2 mm on the camp rock and emerson faults to 3 2 mm on the landers fault to 9plusmn 2 mm on the johnson valley fault to 40 5 mm on the eureka peak fault consistent in magnitude and duration with gps and creepmeter measurements by other investigators the relative lack of afterslip at all sites except across the eureka peak fault is probably due to the lack of a thick alluvial cover concomitant precise resurveys of level lines across the san andreas fault in coachella valley and of a trilateration array at durmid hill south easternmost san andreas fault failed to reveal vertical or horizontal displacements greater than the allowable uncertainty 1 mm for leveling 2 mm 2 ppm for trilateration therefore the landers earthquake sequence did not perturb the san andreas in any way that was evident from our measurements of near surface strain

modelling seismites with a digital shaking table abstract soft sediment deformation structures induced by seismically triggered liquefaction and or fluidization seismites have been reproduced with a digital shaking table we have used natural sediments with variable granulometric ranges clay silt and sand and an earthquake simulator that is able to reproduce real tridimensional seismograms acceleration and pore pressure recording allowed us to follow liquefaction and or fluidization processes in unconsolidated sediments during earthquakes different types of seismites were produced by variations in the tested sedimentary column

earthquake magnitude frequency epicentral distance and soft sediment deformation in sedimentary basins abstract empirical equations available for earthquake magnitude frequency and the maximum epicentral distance of liquefied sites versus magnitude are combined with the characteristic instantaneous sediment deposition rate at a station in a sedimentary basin to form a model for the local stratigraphic frequency of earthquake induced soft sediment deformation structures both the style of sedimentation and the characteristics of the earthquake source combine to determine the pattern of incidence of the structures in a basin the model is probably most directly applicable to the geodynamic interpretation of fluvial basins in which substantial volumes of readily liquefied sands accumulate at high local short term rates

imaging surface contacts power law contact distributions and contact stresses in quartz calcite glass and acrylic plastic a procedure has been developed to obtain microscope images of regions of contact between roughened surfaces of transparent materials while the surfaces are subjected to static loads or undergoing frictional slip static loading experiments with quartz calcite soda lime glass and acrylic plastic at normal stresses to 30 mpa yield power law distributions of contact areas from the smallest contacts that can be resolved 3 5 m2 up to a limiting size that correlates with the grain size of the abrasive grit used to roughen the surfaces in each material increasing normal stress results in a roughly linear increase of the real area of contact mechanisms of contact area increase are by growth of existing contacts coalescence of contacts and appearance of new contacts mean contacts stresses are consistent with the indentation strength of each material contact size distributions are insensitive to normal stress indicating that the increase of contact area is approximately self similar the contact images and contact distributions are modeled using simulations of surfaces with random fractal topographies the contact process for model fractal surfaces is represented by the simple expedient of removing material at regions where surface irregularities overlap synthetic contact images created by this approach reproduce observed characteristics of the contacts and demonstrate that the exponent in the power law distributions depends on the scaling exponent used to generate the surface topography

soft sediment deformation structures induced by cyclic stress of storm waves in tempestites miocene guadalquivir basin spain the identification of triggering agents for soft sedimentation structures is an enigmatic geological problem mainly seismic induced soft sediment structures have been recognized in ancient sediments rather than those resulting from storm waves we analyse soft sediment deformation structures in upper miocene calcarenitic tempestites of the guadalquivir basin southern spain the most common structures are load casts which vary in height and width from 10 centimetres to several metres the structures are always restricted to a small part of the stratigraphic sections in exclusive association with tempestites the analysed soft deformation structures are interpreted to be the result of liquidization processes chiefly from their inferred depositional environment and subordinately from the deformation style we have devised basic criteria to identify the trigger mechanism in these soft sediment deformation structures the liquefaction was triggered by pore pressure changes induced by cyclic and residual stress of storm waves

incremental growth of normal faults insights from a laser equipped analog experiment we conducted a laser equipped analog experiment aimed at quasi continuously monitoring the growth of a dense population of normal faults in homogeneous conditions to further understand the way geological faults progressively gain in slip and length as they accumulate more strain we measured with great precision the incremental slip and length changes that the analog faults sustain as they grow these measurements show that the analog faults share common features with the natural ones in particular during their growth the faults develop and maintain cumulative slip profiles that are generally triangular and asymmetric the growth takes place through two distinct phases an initial short period of rapid lateral lengthening followed by a longer phase of slip accumulation with little or no lengthening the incremental slip is found to be highly variable in both space along the faults and time resulting in variable slip rates in particular short and long term slip rates are markedly different we also find that slip measurements at local points on fault traces do not contain clear information on the slip increment repeat mode finally while the fault growth process is highly heterogeneous when considered at the scale of a few slip events it appears homogeneous and self similar at longer time scales which integrate many slip increments this is likely to be the result of a feedback between stress heterogeneities and slip development the long term scale homogeneity also implies that the long term faulting process is primarily insensitive to the short term heterogeneities that are rapidly smoothed or redistributed we propose a new conceptual scenario of fault growth that integrates the above observations and we suggest that faults grow in a bimodal way as a result of a self driven and self sustaining process

importance of model parameterization in finite fault inversions application to the 1974 mw 8 0 peru earthquake the spatial and temporal slip distributions for the october 3 1974 mw 8 0 peru subduction zone earthquake and its largest aftershock on november 9 ms 7 1 are calculated and analyzed in terms of the inversion parameterization and tectonic significance teleseismic long period world wide standard seismograph network p and sh waveforms are inverted to obtain the rupture histories we demonstrate that erroneous results are obtained if a parameterization is used that does not allow for a sufficiently complex source involving spatial variation in slip amplitude risetime and rupture time the inversion method utilizes a parameterization of the fault that allows for a discretized source risetime and rupture time well located aftershocks recorded on a local network have the same general pattern as teleseismically determined hypocenters and help to constrain the geometry of the subduction zone for the main shock a hinged fault is preferred having a shallow plane with a dip of 11 and a deeper landward plane with a dip of 30 the preferred nucleation depth lies between 11 and 15 km a bilateral rupture is obtained with two major concentrations of slip one 60 to 70 km to the northwest of the epicenter and a second 80 to 100 km to the south and southeast of the epicenter for these source regions risetimes vary from 6 to 18 s our estimates of risetimes are consistent with the time for the rupture to traverse the dominant local asperity the slip distribution for the november 9 aftershock falls within a conspicuous hole in the main shock rupture pattern near the hypocenter of the main shock the november 9 event has a simple risetime function with a duration of 2 s aftershocks recorded by the local network are shown to cluster near the hypocenter of the impending november 9 event and downdip from the largest main shock source region slip during the main shock is concentrated at shallow depths above 15 km and extends updip from the hypocenter to near the plate boundary at the trench axis the large amount of slip at shallow depths is attributed to the absence of any significant accretionary wedge of sediments and the relatively young age and high convergence rate of the subducted plate which results in good seismic coupling near the trench axis

numerical investigation of slip and fracture instability mechanism of coal rock parting coal structure crcs abstract based on theoretical analysis and numerical simulations the factors that influence the slip and fracture instability of coal rock parting coal structure crcs were investigated stress coefficient of friction and energy dissipation during slip and fracture instability were analysed individually the macro and microscopic mechanical behaviours especially acoustic emission ae characteristics were determined according to the variations in stress energy and b value of ae events the precursors of crcs slip and fracture instability were summarized finally the instability mechanism was proposed this work is relevant for early warning coal rock dynamic disasters that are triggered by slip and fracture instability of crcs in coal mines

soft sediment deformation during thawing of ice rich frozen soils results of scaled centrifuge modelling experiments the origin of periglacial involutions remains uncertain largely because of the difficulties of field monitoring in modern permafrost regions this paper describes an alternative approach in which process studies are based on scaled centrifuge modelling of thawing ice rich soils centrifuge scaling laws allow similitude in self weight stresses between the model scale and the prototype field scale to be achieved in these experiments 120 to 130 mm thick frozen models comprising a sand unit overlying ice rich kaolinite clay three models or ice rich silt one model were thawed under an acceleration of 20 gravities the models were therefore equivalent to 4 6 m of frozen sediments permafrost at the prototype scale temperature profiles and porewater pressures during the thawing of each model are described porewater pressures significantly in excess of hydrostatic were not observed in the sand silt model in the sand clay models however excess pressures developed rapidly after thawing and observed fluctuations in pressure were interpreted as water escape events after thawing careful sectioning of the models revealed small scale deformation structures at the clay sand interface resulting from loading of the upper sand layer into very soft fluid like clay and injection of clay upwards into the base of the sand it is concluded that these experiments provide analogues for some pleistocene involutions such involutions therefore mark phases of permafrost degradation when high porewater pressures caused loading and injection along sedimentary boundaries

the 1992 landers earthquake sequence earthquake occurrence and structural heterogeneities the june 28 1992 mw 7 3 landers earthquake occurred in the southeastern mojave desert california over 10 000 aftershocks of the earthquake were recorded by the caltech usgs southern california seismic network scsn in 1992 to investigate the relationship between complexities in the crustal structure and variations in seismicity we have used a tomographic method to invert 145 098 p wave arrival times from 3740 landers earthquake aftershocks and 1148 other events recorded by 60 permanent and temporary scsn stations we determined a detailed p wave tomographic image with a spatial resolution of about 5 km and relocated the hypocenters with the obtained 3 d velocity model the results show a correlation between seismicity patterns and velocity patterns and a tendency for regions rich in seismicity to be associated with higher velocities the higher velocity areas are considered to be strong and brittle parts of the fault zone which are apt to generate earthquakes in contrast low velocity areas are probably more ductile and weaker allowing aseismic slippage

laboratory observations of fault normal vibrations during stick slip we report laboratory observations of interface separation waves during stick slip on a fault in a uniform polymer material our observations made at stress levels expected at midcrustal depths share many macroscopic properties with ruptures of faults in rocks we observed a drop in fault normal stress shortly before the onset of and during stick slip at points along the fault during a rupture we suggest that ital p wave energy in front of the propagating rupture tip is responsible for the drop in normal stress we also interpret that stick slip took place within a traveling slip pulse and we suggest that the dynamic stress drop within the slipping patch exceeded the overall static stress drop by a factor of at least 5 within a few millimeters of the fault our experiments did not resolve whether the fault surfaces actually separate or if fault normal stress is just greatly reduced in either case the net result is that fault slip is permitted to take place with much less frictional resistance than that expected from the applied load our observations provide laboratory evidence that fault normal vibrations may play an important role in sustaining a rupture by facilitating the propagation of a transientmore instability faults may appear weak in part because they are dynamically weakened as they slip during rupture while retaining their strength during the interseismic period copyright 1998 american geophysical union less

dynamics of fault interaction parallel strike slip faults we use a two dimensional finite difference computer program to study the effect of fault steps on dynamic ruptures our results indicate that a strike slip earthquake is unlikely to jump a fault step wider than 5 km in correlation with field observations of moderate to great sized earthquakes we also find that dynamically propagating ruptures can jump both compressional and dilational fault steps although wider dilational fault steps can be jumped dilational steps tend to delay the rupture for a longer time than compressional steps do this delay leads to a slower apparent rupture velocity in the vicinity of dilational steps these dry cases assumed hydrostatic or greater pore pressures but did not include the effects of changing pore pressures in an additional study we simulated the dynamic effects of a fault rupture on undrained pore fluids to test sibson s 1985 1986 suggestion that wet dilational steps are a barrier to rupture propagation our numerical results validate sibson s hypothesis by demonstrating that the effect of the rupture on the undrained pore fluids is to inhibit the rupture from jumping dilational stepovers the basis of our result differs from sibson s hypothesis in that our model is purely elastic and does not necessitate the opening of extension fractures between the fault segments

sand boils without earthquakes sedimentary deformation caused by liquefaction has become a popular means for inferring prehistoric strong earthquakes in this report we describe a new mechanism for generating such features in the absence of earthquakes sand boils and a 180 m long sand dike formed in fremont valley california when sediment laden surface runoff was intercepted along the upslope part of a 500 m long preexisting ground crack flowed subhorizonally in the crack and then flowed upward in the downslope part of the crack where it discharged as sand boils on the land surface if the sand boils and their feeder dike were stratigraphically preserved they could be misinterpreted as evidence for earthquake induced liquefaction

physical and temporal factors controlling the development of near surface ground ice at illisarvik western arctic coast canada near surface permafrost was sampled in summer 2010 at 26 sites in the illisarvik drained lake basin and nine sites in the surrounding tundra on richards island nwt to investigate the growth of segregated near surface ground ice permafrost and ground ice have developed in the lake basin since drainage in 1978 the lake bed soils are predominantly silts of varying moisture and organic matter contents with sandier soils near the lake margins excess ice contents in the basin were also variable and ice enrichment was observed to a maximum depth of 60 cm below the 2010 permafrost table shrub covered wet areas had the highest mean excess ice content in the top 50 cm of permafrost 10 while grassy dryer areas 4 and poorly vegetated marginal areas 1 were less enriched with ice site wetness was the most important variable associated with near surface excess ice content in the lake basin silt content was a secondary variable mean excess ice content in the top 50 cm of permafrost at tundra sites

experimental soft sediment deformation structures formed by the liquefaction of unconsolidated sands and some ancient examples the effects of liquefaction in saturated sand bodies under a variety of driving forces are described from shaking table experiments and structures from the geological record are presented which are analogous to the experimental structures the collapse of sloping heaps of cross bedded sand under a gravitational body force generates low angle essentially uncontorted stratification a basal zone of shearing may be present with steepened and folded foresets stretching of foresets may be accommodated on normal faults and bottomsets may be contorted into inclined folds in natural systems the substrate may also liquefy causing deformation driven by an unevenly distributed confining load stratification in the surface bedform is flattened and stratification in the substratum contorted experiments failed to produce relative displacement at the interface between stacked sand bodies liquefaction of gravitationally unstable systems in sands generates load structures comparable to those from sand mud systems recumbent folded deformed cross bedding is formed by current shear over a liquefied bed as has been inferred from field and theoretical analyses shear of nonliquefied sand forms angular folds other deformation mechanisms such as fluidization or seepage may generate structures similar to all of these local water escape structures driven by fluidization occur in the upper parts of some liquefied sand bodies they include cusps sand volcanoes and clastic dykes transient cavities formed in some experiments and seemed to be preserved as breached cusps although the experiments tried to isolate individual driving forces driving forces may operate together and there may be a continuum between deformation driven by water escape and deformation driven by loading different structures from those described here may form where liquefaction develops in a buried layer as opposed to at the sediment surface

nitrogen diffusion in silicate minerals with implications for nitrogen transport and cycling in the lithosphere abstract diffusion laws for nitrogen in orthoclase quartz olivine and clinopyroxene were determined using a combination of experimental strategies that included in diffusion from c h o n vapor in diffusion from molten nh4cl and ion implantation followed by heating to mobilize n most experiments were conducted at pressures near 1 bar but seven experiments were also run in a piston cylinder device at ptotal 1 gpa the c h o n source experiments were wet h2o present those on ion implanted samples were dry all n sources were highly enriched in 15n to avoid spurious 14n signals resulting from surface contamination use of 15n also enabled depth profiling by nuclear reaction analysis nra using the 15n p 12c reaction which has a detection limit of 10 ppm nitrogen profiles in three samples were characterized by both nra and sims with similar results a total of 17 to 28 diffusion coefficient measurements were made on each of the four minerals 83 in all yielding results that conform for each mineral to an arrhenius relation of the form d d0exp ea rt the following values for the pre exponential constant d0 and activation energy ea were obtained mineral log d0 m2 s ea kj mol t range c orthoclase 13 9 0 4 95 4 6 6 500 900 quartz 12 4 0 3 147 3 5 7 550 1150 olivine 14 2 0 3 135 2 6 6 650 1400 clinopyroxene 14 1 0 3 135 6 7 4 750 1300 the various experimental strategies yield generally indistinguishable results at a given temperature and no significant effects of total pressure or h2o are discernible in the overall diffusion data set experiments that involved in diffusion from external n sources provide qualitative insight into the compatibility of n in the structures of the four minerals nitrogen concentrations attain the highest levels in orthoclase 100 8000 ppm atomic with quartz olivine and clinopyroxene falling in the tens to hundreds of ppm range the new diffusion laws enable us to model the diffusive release of n acquired at depth in the crust during fluid absent exhumation and cooling in general orthoclase is the least retentive of the minerals investigated and will lose most of its n during cooling from 600 c at tectonically typical rates olivine and clinopyroxene are the most retentive of n quartz is intermediate in retentivity between the mafic minerals and feldspar but in all cases the extent of n exchange with the surroundings depends critically on the specific t t path of the mineral of interest in subduction settings where n bearing fluid is released to the mantle wedge diffusion is sufficiently fast to homogenize individual mafic mineral grains with respect to n over geologically plausible time scales but equilibration on the outcrop or regional scale via volume diffusion is precluded by our data

lithium isotopic compositions of post collisional mafic ultramafic rocks from dabieshan china implications for recycling of deeply subducted continental crust abstract lithium li isotopes are potential tracers of processes related to crust mantle interaction and recycled crustal materials previous studies have reported that li isotopic compositions of island arc lavas are similar to those of fresh mid ocean ridge basalts morbs although the former are expected to record high slab derived 7li values caused by fluid metasomatism however it is unclear whether li isotopic signatures of subducted continental crust were transported to mantle depths and preserved there for clarification we determined whole rock major and trace element and li isotopic compositions of post collisional mafic ultramafic rocks from northern dabieshan china the analyzed samples have high mgo up to 20 67 wt and low sio2 41 06 56 20 wt contents and arc like trace element distribution patterns suggesting derivation by partial melting of fertile mantle sources the samples have 7li values of 2 9 to 7 2 average 2 7 n 42 and li concentrations of 2 50 to 28 1 g g average 9 20 g g both of which are beyond the relatively limited ranges of mantle values 7li 2 9 to 4 3 average 3 5 1 0 and li 1 20 0 10 g g excluding possible effects of wall rock assimilation and contamination magmatic crystallization and li isotopic fractionation during subduction exhumation processes the observed li isotopic heterogeneity is most likely related to the recycling of crustal materials based on a comparison with li isotopic compositions of ultrahigh pressure uhp metamorphic rocks from the dabie sulu orogenic belt and terrestrial sediments we suggest that the recycled continental crustal materials likely comprised gneisses sediments eclogites and or minor carbonate rocks i e marbles our study demonstrates that li isotopes may provide a novel means of tracing deeply subducted continental materials

an experimental setup for fluid venting in unconsolidated sediments new insights to fluid mechanics and structures abstract focused outflow of water at the seafloor termed seepage or fluid venting is a widely recognized global phenomenon in an effort to better understand the mechanisms by which fluid flow related structures form we performed laboratory seepage experiments using samples representing a broad range of grain sizes and hydraulic conductivities 10e 3 to 10e 7 m s detailed observations led to the recognition of a typical often repeated progression of fluid flow structures that form during processes of increasing and decreasing hydraulic gradients the development of fluid flow structures like macro pores conduits and pipes is strongly dependant upon cohesion but is unrelated to grain size variations from sample to sample partial liquefaction leads to permanent changes in the grain fabric and to an increase in hydraulic conductivity our observations explain the longevity of seep sites and systematic relationships between hydraulic gradients grain fabric appearance and hydraulic conductivity that could be used to estimate flow rates based on structural findings

perennial frost blisters of the outer mackenzie delta western arctic coast canada saturated floodplains in arctic deltas provide conditions favourable for frost mound growth little work has been reported from these settings to determine the origin of frost mounds and the controls on their distribution to assess the longevity of individual mounds or to quantify variation of mound distribution over time a case study is presented on low mounds in low centred syngenetic ice wedge polygons of big lake delta plain outer mackenzie delta in 2008 and 2009 12 mounds were examined by drilling to describe their morphologic variations and to investigate their growth processes the mounds containing a core of ice 15 to 58 cm thick were less than 1 m high and 3 7 to 8 5 m in diameter other mounds were over 10 m long organic inclusions in the ice bubble densities electrical conductivity profiles and ice crystal structure indicated that the mounds were hydrostatic frost blisters up to six frost blisters were found within individual polygons due to the relatively small volume of water needed to create each mound frost blister densities of greater than 1700 km 2 increased toward the wet centres of alluvial islands down gentle topographic gradients the frost blisters were perennial with individuals remaining identifiable on aerial photographs and satellite images for up to 10 years frost blisters collapsed along dilation cracks opened by hydrostatic uplift and by thawing from their sides caused by snow drifting and water ponding cyclical growth and decay of the mounds may degrade the visible polygonal network over time copyright 2013 john wiley sons ltd

thaw modification of frost fissure wedges richards island pleistocene mackenzie delta western arctic canada thaw modification is the general process whereby frost fissure wedges are modified during thaw and by which frost fissure pseudomorphs may develop specific processes of thaw modification are inferred from ice wedge pseudomorphs composite wedge pseudomorphs and deformed sand wedges in the pleistocene mackenzie delta i e thermal erosion collapse subsidence refreezing loading buoyancy spreading folding and shearing thaw modification is believed to result in selective preservation of pseudomorphs and wedges sand wedges are more likely to be preserved than are ice wedge pseudomorphs or compositewedge pseudomorphs because only those sand wedges that penetrate massive ice or icy sediments are prone to thaw modification furthermore whereas ice wedges preferentially develop in ice rich fine grained sediments thaw sensitive their pseudomorphs appear to be selectively preserved in ice poor coarse grained sediments thaw stable

diffusion driven extreme lithium isotopic fractionation in country rocks of the tin mountain pegmatite abstract lithium concentrations and isotopic compositions in the country rocks amphibolites and schists of the tin mountain pegmatite show systematic changes with distance to the contact both li and 7 li decrease dramatically along a 10 m traverse from the pegmatite into amphibolite with li concentration decreasing from 471 to 68 ppm and 7 li decreasing from 7 6 to 19 9 rubidium and cs also decrease from the pegmatite contact into the country rock but only within the first 2 m of the contact after which their concentrations remain constant neither mixing between pegmatite fluids and amphibolite nor li isotope fractionation by rayleigh distillation during fluid infiltration is a likely explanation of these observations due to the extremely light isotopic composition required for the amphibolite end member in the mixing model 7 li 20 and the similarly extreme isotopic fractionation required in a rayleigh distillation model rather these variations are likely due to isotopic fractionation accompanying li diffusion from the li rich pegmatite li 450 to 730 ppm into amphibolites li 20 ppm the fact that other alkali element concentrations vary only within 2 m of the contact reflects the orders of magnitude faster diffusion of li relative to heavier elements quartz mica schists in contact with the pegmatite also show large variations in both li and 7 li as a function of distance from contact 1 wt to 70 ppm and 10 8 to 18 6 respectively but over a longer distance of 30 m lithium concentrations of the schist decrease from 1 wt adjacent to the contact to 70 ppm 300 m from the contact the latter is a typical concentration in metapelites the nature of the 7 li variations in the schists is different than in the amphibolites schists within the first 2 m of the contact have nearly identical 7 li of 10 which mimics that of the estimated bulk pegmatite 8 to 11 at a distance of 30 m the 7 li reaches the lowest value in the schists of 18 6 similar to the lowest amphibolite measured at a distance of 300 m the 7 li climbs back to 2 5 which is within the range of 7 li of other schists in the region and metapelites worldwide the behavior of li in the schists can also be modeled by li diffusion with the effective diffusion coefficient in the schist being 10 times greater than that in the amphibolite the effective diffusion coefficients of li in the amphibolite and schist are 2 orders of magnitude greater that those in minerals which implicates the importance of fluid assisted grain boundary diffusion over solid state diffusion in transporting li through these rocks

application of an iterative least squares waveform inversion of strong motion and teleseismic records to the 1978 tabas iran earthquake an iterative least squares technique is used to simultaneously invert the strong motion records and teleseismic p waveforms for the 1978 tabas iran earthquake to deduce the rupture history the method solves for both slip amplitudes and rupture times on a finite fault several inversions of the data are done to determine the best fitting hypocenter average rupture velocity and source time function within the range of our parameter search the effects of using different data sets and different parametrizations of the problem linear versus nonlinear are also considered teleseismic body waves are shown to be essential to obtain a reliable solution due to the sparse coverage of the fault plane by strong motion stations a simple triangular source time function is compared with a modified kostrov source time function for a circular rupture and a constant propagating stress drop although the waveforms used in the inversions can not resolve between these two time functions the kostrov source time function gives a moment estimate and maximum fault displacement more consistent with long period surface waves and field observations the results of the iterative inversion for slip amplitudes and rupture times are compared with the results of a linear inversion for slip amplitudes in which the rupture velocity is fixed flexibility in the sequence of faulting for the linear inversion is obtained by allowing multiple rupture intervals a consensus of all the inversion runs indicates a complex multiple source for the tabas earthquake with four main source regions over a fault length of 90 km and an average rupture velocity of 2 5 km sec

isotope geochemistry of frost blister ice north fork pass yukon canada oxygen 18 and deuterium abundances vary with depth in ice from a frost blister at a spring site near north fork pass yukon they indicate that the ice was formed by continuous downward freezing under nearly ideal closed system conditions in a water filled cavity weighted mean values of 18o and 2h for the ice samples indicate that the frost blister ice was formed from groundwater similar to that of nearby springs the slope of the regression line 5 1 for the 18o and 2h data of the frost blister ice suggests that nonequilibrium fractionation conditions existed during freezing tritium concentrations in the ice show irregular variations with depth the weighted mean 3h concentration for the ice is however similar to that of the spring water

lithium isotope analysis of olivine by sims calibration of a matrix effect and application to magmatic phenocrysts high spatial resolution analysis of light element isotope variations by secondary ion mass spectrometry sims has numerous applications in geochemistry and cosmochemistry recent attention has focused on 7li 6li variations in magmatic phenocrysts to infer the volatile degassing history of their parent magmas and on minerals from mantle samples to determine source region processes and the recycling history of mantle reservoirs in these studies the effect of mineral composition on the 7li 6li ratio measured by sims has been considered secondary and generally disregarded we show using a suite of nine olivines analyzed by mc icp ms or tims that there is a substantial effect of composition on the 7li 6li ratio of olivine measured by sims for magnesian olivine 74 fo 94 the effect is a linear function of composition with 7li increasing by 1 3 for each mole percent decrease in forsterite component at higher fe contents the relationship ceases to be linear the composition range over which linear behavior is exhibited appears to depend on instrumental conditions a calibration of this matrix effect over the linear range is presented assuming the measurement of 7li 6li relative to an olivine standard of known composition application of this calibration to a suite of olivines separated from basaltic lavas from ko olau hawai i demonstrates that the matrix effect is responsible for a geologically spurious correlation between 7li and mg however after correction the olivines retain evidence of li isotope heterogeneity the degree and nature of which differs in each of the four separates studied these results emphasize the importance of compositional correction for sims measurement of 7li in olivine particularly in zoned crystals and support previous conclusions that li isotope variability in igneous materials is subject to late stage disturbance the significant matrix effect demonstrated for olivine suggests that matrix effects in other minerals require further evaluation

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

relationship between caldera collapse and magma chamber withdrawal an experimental approach collapse calderas have received considerable attention due to their link to earth s ore deposits and geothermal energy resources but also because of their tremendous destructive potential although calderas have been investigated through fieldwork numerical models and experimental studies some important aspects on their formation still remain poorly understood one key issue concerns the volume of magmas involved in caldera forming eruptions we perform analogue experiments to correlate the structural evolution of a collapse with the erupted magma chamber volume fraction the experimental device consists of a transparent box 60 60 40 cm filled with dry quartz sand and a water filled latex balloon as a magma chamber analogue evacuation of water through a pipe causes a progressive deflation of the balloon that leads to a collapse of the overlying structure the experimental design allows to record the temporal evolution of the collapse and to track the evolution of fractures and faults we study the appearance and development of specific brittle structures such as surface fractures or internal reverse faults and correlate each different structure with the corresponding removed magma chamber volume fraction we also determine the critical conditions for caldera onset experimental results show that at any stage of caldera developments the experimental relationship between volume fraction and chamber roof aspect ratio fits a logarithmic curve it implies that volume fractions required to trigger caldera collapse are lower for chambers with low aspect ratios shallow and wide than for chambers with high aspect ratios deep and small these results are in agreement with natural examples and previous theoretical studies

seasonal growth bands in pingo ice field studies of pingo ice show that alternating clear and bubble bands may grow when water freezes at the top of a subpingo water lens a study of the banding at one excellent exposure of pingo ic

the repetition of large earthquake ruptures abstract this survey of well documented repeated fault rupture confirms that some faults have exhibited a characteristic behavior during repeated large earthquakes that is the magnitude distribution and style of slip on the fault has repeated during two or more consecutive events in two cases faults exhibit slip functions that vary little from earthquake to earthquake in one other well documented case however fault lengths contrast markedly for two consecutive ruptures but the amount of offset at individual sites was similar adjacent individual patches 10 km or more in length failed singly during one event and in tandem during the other more complex cases of repetition may also represent the failure of several distinct patches the faults of the 1992 landers earthquake provide an instructive example of such complexity together these examples suggest that large earthquakes commonly result from the failure of one or more patches each characterized by a slip function that is roughly invariant through consecutive earthquake cycles the persistence of these slip patches through two or more large earthquakes indicates that some quasi invariant physical property controls the pattern and magnitude of slip these data seem incompatible with theoretical models that produce slip distributions that are highly variable in consecutive large events