temporal changes of shallow seismic velocity around the karadere duzce branch of the north anatolian fault and strong ground motion we analyze temporal variations of seismic velocity along the karadere duzce branch of the north anatolian fault using seismograms generated by repeating earthquake clusters in the aftershock zones of the 1999 mw7 4 izmit and mw7 1 duzce earthquakes the analysis employs 36 sets of highly repeating earthquakes each containing 4 18 events the events in each cluster are relocated by detailed multi step analysis and are likely to rupture approximately the same fault patch at different times the decay rates of the repeating events in individual clusters are compatible with the omori s law for the decay rate of regional aftershocks a sliding window waveform cross correlation technique is used to measure travel time differences and evolving decorrelation in waveforms generated by each set of the repeating events we find clear step like delays in the direct s and early s coda waves sharp seismic velocity reduction immediately after the duzce main shock followed by gradual logarithmic type recoveries a gradual increase of seismic velocities is also observed before the duzce main shock probably reflecting post seismic recovery from the earlier izmit main shock the temporal behavior is similar at each station for clusters at various source locations indicating that the temporal changes of material properties occur in the top most portion of the crust the effects are most prominent at stations situated in the immediate vicinity of the recently ruptured fault zones and generally decrease with normal distance from the fault a strong correlation between the co seismic delays and intensities of the strong ground motion generated by the duzce main shock implies that the radiated seismic waves produced the velocity reductions in the shallow material

temporal change of seismic structure around iwate volcano inferred from waveform correlation analysis of similar earthquakes 1 we investigate the temporal change of crustal structure around iwate volcano northeastern japan using calculations of the cross correlation coefficients of p and s waves of pairs of similar earthquakes that occurred between 1995 2002 at the subducting pacific plate boundary while large coefficients are observed at most stations throughout the period two stations located on the southwestern slope of iwate volcano exhibit small s wave coefficients the coefficients at these two stations decreased remarkably from 1998 corresponding to a period of significant volcanic activity and an m6 1 earthquake since 2000 the coefficients have recovered gradually suggesting their correlation with the activity of iwate volcano the coefficients of p waves at these stations are large compared to those of s waves suggesting that temporal change in the crustal structure beneath these stations occurred in elastic properties to which s waves are sensitive such as rigidity related to magmatic and or seismic activity in and around the volcano

temporal variation in the shear wave anisotropy detected using the accurately controlled routinely operated signal system across 1 temporal variation in shear wave anisotropy was detected in a monitoring experiment using an accurately controlled routinely operated signal system accurately controlled routinely operated signal system across we conducted an experiment that lasted for 15 months between january 2000 and april 2001 at a site near the nojima fault which ruptured during the 1995 kobe earthquake mw 7 2 yamaoka et al 2001 ikuta et al 2002 two vibration sources that generated 2 105 n with centrifugal force which were firmly fixed on the ground were used to emit elastic waves seismometers deployed at the bottom of 800 m and 1700 m deep boreholes near the across sources were used to receive the signal we extracted small temporal changes in the travel time of the p and s wave by calculating cross spectral density among the records every hour during the experiment sudden delays in travel times for the s wave were observed when the 2000 western tottori earthquake mw 6 6 and the 2001 geiyo earthquake mw 6 4 occurred their epicenters were 165 and 215 km away from the site respectively the travel times of the s waves between the surface and the bottom of 800 m deep borehole abruptly slowed down and gradually speeded up with each earthquake the delay in s was about 0 4 and 0 1 of the absolute travel time for the western tottori earthquake and the geiyo earthquake respectively the delays were polarized in a direction perpendicular to the nojima fault in both cases this indicates that the density of the cracks parallel to the fault increased in association with the earthquakes these cracks can be regarded as opened by the increase in pore pressure the small changes in p wave velocities support this interpretation an additional experiment to determine the static anisotropy revealed that there was a preferred orientation of the cracks that was enhanced with the strong shaking of earthquakes in the middle distance

geomorphology and ecology unifying themes for complex systems in biogeomorphology the interaction of geomorphic and ecologic landscape components has been largely conceptualized as independent in one direction geomorphic processes and landforms shape the distribution of biota conversely in the other direction biota modify geomorphic processes and landforms increasingly the interactions between geomorphic and ecological components are more circular and developmentally intertwined in this paper i integrate these two independent perspectives within the framework of complexity theory i outline four themes that characterize complex systems in biogeomorphology multiple causality and the concept of recursivity the influence of organisms that function as ecosystem engineers the expression of an ecological topology and ecological memory implicit in all of these themes is the recognition that biogeomorphic systems are open and path dependent they may exhibit a range of assembly states from self reinforcing stability domains to more transient configurations of organisms and environment

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

zoogeomorphology in the anthropocene abstract the anthropocene embodies the concept of human impacts on the natural environment but disagreements exist as to when to identify its inception starting date in this paper i illustrate that regardless of the proposed starting date of the anthropocene important zoogeomorphic impacts were initiated at each of these proposed starting dates humans have profoundly altered geomorphic pathways through extinctions and the near extirpation of native populations of animal species that strongly influenced hydrology and removal of surface sediment and through the introduction of populations of animals that bring to bear a suite of different geomorphic effects on environmental systems domestication of animals brought its own suite of zoogeomorphic implications introductions of exotic species and the spread of feral species often led to dramatic new geomorphic landscapes because of the absence of natural controls on population expansion in the mountains of the western usa and elsewhere the geomorphic actions of animals are being impacted by human induced climate change climate change in some cases affects the spatial pattern and range of species whereas in other cases it may lead to the extirpation of species with zoogeomorphic impacts

a shallow fault zone structure illuminated by trapped waves in the karadere duzce branch of the north anatolian fault western turkey summary we discuss the subsurface structure of the karadere duzce branch of the north anatolian fault based on analysis of a large seismic data set recorded by a local passcal network in the 6 months following the mw 7 4 1999 izmit earthquake seismograms observed at stations located in the immediate vicinity of the rupture zone show motion amplification and long period oscillations in both p and s wave trains that do not exist in nearby off fault stations examination of thousands of waveforms reveals that these characteristics are commonly generated by events that are well outside the fault zone the anomalous features in fault zone seismograms produced by events not necessarily in the fault may be referred to generally as fault zone related site effects the oscillatory shear wave trains after the direct s arrival in these seismograms are analysed as trapped waves propagating in a low velocity fault zone layer the time difference between the s arrival and trapped waves group does not grow systematically with increasing source receiver separation along the fault these observations imply that the trapping of seismic energy in the karadere duzce rupture zone is generated by a shallow fault zone layer traveltime analysis and synthetic waveform modelling indicate that the depth of the trapping structure is approximately 3 4 km the synthetic waveform modelling indicates further that the shallow trapping structure has effective waveguide properties consisting of thickness of the order of 100 m a velocity decrease relative to the surrounding rock of approximately 50 per cent and an s wave quality factor of 10 15 the results are supported by large 2 d and 3 d parameter space studies and are compatible with recent analyses of trapped waves in a number of other faults and rupture zones the inferred shallow trapping structure is likely to be a common structural element of fault zones and may correspond to the top part of a flower type structure the motion amplification associated with fault zone related site effects increases the seismic shaking hazard near fault zone structures the effect may be significant since the volume of sources capable of generating motion amplification in shallow trapping structures is large

nonlinear ground motion amplification by sediments during the 1994 northridge earthquake it has been known since at least 1898 ref 1 that sediments can amplify earthquake ground motion relative to bedrock for the weak ground motion accompanying small earthquakes the amplification due to sediments is well understood in terms of linear elasticity hooke s law 2 but there has been a long standing debate regarding the amplification associated with the strong ground motion produced by large earthquakes the view of geotechnical engineers based largely on laboratory studies is that hooke s law breaks down at larger strains causing a reduced nonlinear amplification seismologists on the other hand have tended to remain sceptical of this nonlinear effect mainly because the relatively few strong motion observations seemed to be consistent with linear elasticity although some recent earthquake studies have demonstrated nonlinear behaviour under certain circumstances3 4 the significance of nonlinearity for the type of stiff soil sites found in the greater los angeles region remains unresolved5 here we report that ground motion amplification due to sediments for the main shock of the 1994 northridge earthquake was up to a factor of two less than the amplification observed for its aftershocks these observations imply significant nonlinearity in such amplification and bring into question the use of measurements of weak ground motion to predict the strong ground motion at sedimentary sites

zoogeomorphology and resilience theory abstract zoogeomorphology the study of animals as geomorphic agents has been largely overlooked in the context of resilience theory and biogeomorphic systems in this paper examples are provided of the interactions between external landscape disturbances and zoogeomorphological agents we describe cases in which naturally occurring zoogeomorphological agents occupy a landscape and examine whether those zoogeomorphic agents provide resilience to a landscape or instead serve as a landscape stress capable of inducing a phase state shift several cases are described whereby the presence of exotic introduced zoogeomorphic agents overwhelms a landscape and induce collapse the impact of climate change on species with zoogeomorphological importance is discussed in the context of resilience of a landscape we conclude with a summary diagram illustrating the relationships existing between zoogeomorphic impacts and landscape resilience in the context of our case studies and speculate about the future of the study of zoogeomorphology in the framework of resilience theory

human induced changes in animal populations and distributions and the subsequent effects on fluvial systems abstract humans have profoundly altered hydrological pathways and fluvial systems through their near extirpation of native populations of animal species that strongly influenced hydrology and removal of surface sediment and through the introduction of now feral populations of animals that bring to bear a suite of different geomorphic effects on the fluvial system in the category of effects of extirpation examples are offered through an examination of the geomorphic effects and former spatial extent of beavers bison prairie dogs and grizzly bears beavers entrapped hundreds of billions of cubic meters of sediment in north american stream systems prior to european contact individual bison wallows that numbered in the range of 100 million wallows each displaced up to 23 m 3 of sediment burrowing by prairie dogs displaced more than 5000 kg and possibly up to 67 500 kg of sediment per hectare in the category of feral populations the roles of feral rabbits burros and horses and pigs are highlighted much work remains to adequately quantify the geomorphic effects animals have on fluvial systems but the influence is undeniable

the impact of climate change on patterns of zoogeomorphological influence examples from the rocky mountains of the western u s a abstract many animals in the mountains of the western u s a and elsewhere are geomorphically active the spatial pattern and intensity of these impacts associated with activities such as digging for food burrowing for shelter and damming of streams may change as a result of climate change food sources utilized will be affected by processes such as meadow infilling with trees upward advancement of trees and changes in intensity of other geomorphic processes such as avalanching and glacial action and associated meltwater examples are presented here that illustrate the importance of accurate habitat mapping to be able to assess the impact of climate change on geomorphically active animals as well as the importance of knowledge of food sources of these animals as climate change impacts food sources and habitats some geomorphically active animals may become much more limited in the geographic range and intensity of their influence and some may disappear altogether if the habitat disappears

migration of seismic scatterers associated with the 1993 parkfield aseismic transient event the time varying deformation field within a fault zone particularly at depths where earthquakes occur is important for understanding fault behaviour and its relation to earthquake occurrence1 2 3 but detection of this temporal variation has been extremely difficult although laboratory studies have long suggested that certain structural changes such as the properties of crustal fractures should be seismically detectable4 here we present evidence that such structural changes are indeed observable in particular we find a systematic temporal variation in the seismograms of repeat microearthquakes that occurred on the parkfield segment of the san andreas fault over the decade 1987 97 our analysis reveals a change of the order of 10 m in the location of scatterers which plausibly lie within the fault zone at a depth of 3 km the motion of the scatterers is coincident in space and time with the onset of a well documented aseismic transient deformation event we speculate that this structural change is the result of a stress induced redistribution of fluids in fluid filled fractures caused by the transient event

quantitative measurements of shear wave polarizations at the anza seismic network southern california implications for shear wave splitting and earthquake prediction we analyze shear wave polarizations from local earthquakes recorded by the anza network in southern california using an automated method which provides unbiased and quantitative measurements of the polarization and the duration of linear motion following the shear wave arrival the linearity interval initial shear wave particle motions are strongly aligned at four stations a feature that is not predicted by focal mechanisms the particle motion alignment is most likely caused by shear wave splitting due to anisotropy beneath these stations a result supported by the clear shear wave splitting seen in a borehole recording near one of the anza stations these results are consistent with an earlier analysis of these data by peacock et al 1988 however our analysis does not support claims by crampin et al 1990 that shear wave splitting delay times at station knw exhibit temporal variations which can be correlated with the occurrence of the north palm springs earthquake ml 5 6 of july 8 1986 automatically determined linearity intervals scatter widely from 0 02 to 0 15 s and exhibit no clear temporal trends we find a correlation between earthquake moment and the linearity interval possibly a result of longer effective source time functions for the larger events the inability to identify a distinct slow quasi shear wave pulse for the vast majority of these events indicates that scattering strongly affects the particle motion even in the very early shear wave coda analysis of earthquake clusters with similar waveforms recorded at knw shows that seismic green functions are stable throughout the observational period and that most linearity interval variation is due to source and ray path differences between events if shear wave splitting is causing the observed delay times between horizontal components the waveform stability for events in these clusters restricts any temporal changes in shear wave splitting delay times to less than 5 10

high resolution image of calaveras fault seismicity 1 by measuring relative earthquake arrival times using waveform cross correlation and locating earthquakes using the double difference technique we are able to reduce hypocentral errors by 1 to 2 orders of magnitude over routine locations for nearly 8000 events along a 35 km section of the calaveras fault this represents 92 of all seismicity since 1984 and includes the rupture zone of the m 6 2 1984 morgan hill california earthquake the relocated seismicity forms highly organized structures that were previously obscured by location errors there are abundant repeating earthquake sequences as well as linear clusters of earthquakes large voids in seismicity appear with dimensions of kilometers that have been aseismic over the 30 year time interval suggesting that these portions of the fault are either locked or creeping the area of greatest slip in the morgan hill main shock coincides with the most prominent of these voids suggesting that this part of the fault may be locked between large earthquakes we find that the calaveras fault at depth is extremely thin with an average upper bound on fault zone width of 75 m given the location error however this width is not resolvably different from zero the relocations reveal active secondary faults which we use to solve for the stress field in the immediate vicinity of the calaveras fault we find that the maximum compressive stress is at a high angle only 13 from the fault normal supporting previous interpretations that this fault is weak

characterization of fault zones there are currently three major competing views on the essential geometrical mechanical and mathematical nature of faults the standard view is that faults are possibly segmented and heterogeneous euclidean zones in a continuum solid the continuum euclidean view is supported by seismic gravity and electromagnetic imaging studies by successful modeling of observed seismic radiation geodetic data and changes in seismicity patterns by detailed field studies of earthquake rupture zones and exhumed faults and by recent high resolution hypocenter distributions along several faults the second view focuses on granular aspects of fault structures and deformation fields the granular view is supported by observations of rock particles in fault zone gouge by studies of block rotations and the mosaic structure of the lithosphere which includes the overall geometry of plate tectonics by concentration of deformation signals along block boundaries by correlation of seismicity patterns on scales several times larger than those compatible with a continuum framework and by strongly heterogeneous wave propagation effects on the earth s surface the third view is that faults are fractal objects with rough surfaces and branching geometry the fractal view is supported by some statistical analysis of regional hypocenter locations by long range correlation of various measurements in geophysical boreholes by the fact that observed power law statistics of earthquakes are compatible with an underlying scale invariant geometrical structure by geometrical analysis of fault traces at the earth s surface and by measurements of joint and fault surfaces topography

differential analysis of coda q using similar microearthquakes in seismic gaps part 2 application to seismograms recorded by the parkfield high resolution seismic network abstract nearly two thirds of the microseismicity occurring at parkfield california consists of repeating clusters of closely located events exhibiting waveform cross correlation values exceeding 0 95 this observation coupled with a high probability for an m 6 earthquake within the next decade working group on california earthquake probabilities 1988 make this segment of the san andreas fault system a prime location to search for temporal variations in coda q associated with crustal changes that may occur during the earthquake cycle the coda comparison analysis method described in part 1 of this study aster et al 1996 is applied to data from four borehole stations of the parkfield high resolution seismic network hrsn for the period january 1987 through february 1994 we examine 21 of the nearly 300 repeating clusters observed to date the restriction of the data set to only the most highly similar sources is observed to be critical small differences in the source process even for event pairs with centroid locations within approximately 20 m significantly increase the spurious noise level in the parameter estimates absolute 68 confidence bound estimates obtained on the repeatability of coda q for all microearthquake pairs are 10 for frequencies below 20 hz tighter constraints are obtainable by reconstructing the temporal history of coda q from the first difference measurements between microearthquake pairs these functional reconstructions show that the mean value of coda q has not varied by more than approximately 5 from 3 to 30 hz at the 1 level during the study period however other observables such as an increased level of microseismicity suggest that a preparatory stage for the next parkfield earthquake has begun indicating that coda q is so far showing no sign of sensitivity to preparatory processes at parkfield

replication of apparent nonlinear seismic response with linear wave propagation models it is necessary to understand ground motion amplification by sediment defined as the ratio of ground motions at sediment sites to those at rock sites to predict seismic loadings for earthquake engineering at sediment sites observed weak motion amplifications from magnitude 3 to 4 aftershocks of the 1994 northridge earthquake were twice as large as magnitude 6 7 mainshock amplifications amplitude dependent nonlinear amplification by sediment is one explanation however earthquake simulations with empirical impulse responses and elastic finite difference calculations with weakly heterogeneous random three dimensional 3d crustal velocity variations show that linear wave propagation can explain observed apparently nonlinear sediment responses random 3d velocity variations also reproduce the observed log normal dispersion of peak ground motions deterministic wave propagation models are not adequate to quantify the scaling and dispersion of near source ground motions

coda wave interferometry for estimating nonlinear behavior in seismic velocity in coda wave interferometry one records multiply scattered waves at a limited number of receivers to infer changes in the medium over time with this technique we have determined the nonlinear dependence of the seismic velocity in granite on temperature and the associated acoustic emissions this technique can be used in warning mode to detect the presence of temporal changes in the medium or in diagnostic mode where the temporal change in the medium is quantified

coseismic and postseismic velocity changes measured by repeating earthquakes 1 repeating earthquakes that rupture approximately the same fault patch and have nearly identical waveforms are a useful tool for measuring temporal changes in wave propagation in the earth s crust since source and path effects are common to all earthquakes in a repeating earthquake sequence multiplet differences in their waveforms can be attributed to changes in the characteristics of the medium we have identified over 20 multiplets containing between 5 and 40 repeating events in the aftershock zones of the 1989 loma prieta and 1984 morgan hill california earthquakes postmain shock events reveal delays of phases in the early s wave coda of as much as 0 2 s relative to premain shock events the delay amounts to a path averaged coseismic velocity decrease of about 1 5 for p waves and 3 5 for s waves since most of the multiplets are aftershocks and follow omori s law we have excellent temporal sampling in the immediate postmain shock period we find that the amplitude of the velocity decrease decays logarithmically in time following the main shock in some cases it returns to the premain shock values while in others it does not similar results are obtained for the morgan hill main shock because the fractional change in s wave velocity is greater than the fractional change in p wave velocity it suggests that the opening or connection of fluid filled fractures is the underlying cause the magnitude of the velocity change implies that low effective pressures are present in the source region of the velocity change our results suggest that the changes are predominantly near the stations and shallow but we cannot exclude the possibility that changes occur at greater depth as well if the variations are shallow we may be detecting the lingering effects of nonlinearity during main shock strong ground motion if the variations are deep it suggests that pore pressures at seismogenic depths are high which would likely play a key role in the earthquake process

distributed damage faulting and friction we present a formulation for mechanical modeling of geological processes in the seismogenic crust using damage rheology the seismogenic layer is treated as an elastic medium where distributed damage modifying the elastic stiffness evolves as a function of the deformation history the model damage rheology is based on thermodynamic principles and fundamental observations of rock deformation the theoretical analysis leads to a kinetic equation for damage evolution having two principal coefficients the first is a criterion for the transition between strength degradation and recovering healing and is related to friction the second is a rate coefficient of damage evolution which can have different values or functional forms for positive degradation and negative healing evolution we constrain these coefficients by fitting model predictions to laboratory data including coefficient of friction in sawcut setting intact strength in fracture experiments first yielding in faulting experiments under three dimensional strain onset and evolution of acoustic emission and dynamic instability the model damage rheology accounts for many realistic features of three dimensional deformation fields associated with an earthquake cycle these include aseismic deformation gradual strength degradation development of process zones and branching faults around high damage areas strain localization brittle failure and state dependent friction some properties of the model damage rheology e g cyclic stick slip behavior with possible accompanying creep are illustrated with simplified analytical results the developments of the paper provide an internally consistent framework for simulating long histories of crustal deformation and studying the coupled evolution of regional earthquakes and faults this is done in a follow up work

enhanced zoogeomorphological processes in north africa in thehuman impacted landscapes of the anthropocene abstract new zoogeomorphological features discovered in dryland landscapes of northern africa reflect human animal agency since prehistory and attest to complex networked activities over great distances we discuss the role of zoogeomorphology in shaping earth s surface since the beginning of the anthropocene the timeframe when natural processes shifted and landscape evolution became more human dominated we focus on contexts in arid and semiarid lands of northern africa which are metastable sensitive ecosystems that are prone to modifications triggered by climatic and anthropogenically forced factors studying the geoarchaeological record in context of landscape impact and animal procurement by people throughout antiquity is important for reconstructing domestication and husbandry of cattle sheep and goats in this region among the features we recognize in association with transhumance pastoralism and herding are trails trackways footholds animal daybeds stables animal dwellings rockshelters game blinds and monuments to name a few related activities with landscape scale impacts include herding transport corralling and browsing of cattle bos sp goats and sheep ovicaprines as well as pasturage activities like cropping fire setting and manuring these activities were disturbances that affected surface processes like erosion and dust mobilization as well as reduced vegetation and ecosystems productivity in dryland africa and especially in the sahara intensive herding led to the alteration of the pristine aspects of bare rock surfaces and of the stone desert pavement i e the hamada many regions preserved evidence of middle late holocene animal daybeds trampled areas and barren tracks and trails we suggest that human and herd animal activities affected geomorphic surfaces that affected slope stability intensified erosion and dust mobilization and enhanced dust export from the african continent offshore we reinterpret the increased dust emission from north africa during the mid holocene at the end of the african humid period as has been interpreted from ocean cores aridification of the green sahara followed the insolation forced monsoonal maximum and was exacerbated by human animal activities across the sahara and the sahel we argue that the spread of human activities and intensive husbandry of cattle and caprines goat and sheep in this region significantly influenced the geomorphic stability ecosystem and landscape sustainability in a comparable manner of overuse observed in present day arid and marginal environments where pastoral overgrazing pressure increases erosion processes and enhances dust mobilization we suggest that human animal activities have amplified dust generation from the north african continental interior since 7 ka bp this evidence of prehistoric human impacts on surface processes in north africa supports arguments for an early beginning of the anthropocene

the beaver meadow complex revisited the role of beavers in post glacial floodplain development we evaluate the validity of the beaver meadow complex hypothesis used to explain the deposition of extensive fine sediment in broad low gradient valleys previous work establishes that beaver damming forms wet meadows with multi thread channels and enhanced sediment storage but the long term geomorphic effects of beaver are unclear we focus on two low gradient broad valleys beaver meadows and moraine park in rocky mountain national park colorado usa both valleys experienced a dramatic decrease in beaver population in the past century and provide an ideal setting for determining whether contemporary geomorphic conditions and sedimentation are within the historical range of variability of valley bottom processes we examine the geomorphic significance of beaver pond sediment by determining the rates and types of sedimentation since the middle holocene and the role of beaver in driving floodplain evolution through increased channel complexity and fine sediment deposition sediment analyses from cores and cutbanks indicate that 33 50 of the alluvial sediment in beaver meadows is ponded and 28 40 was deposited in channel in moraine park 32 41 is ponded sediment and 40 52 was deposited in channel radiocarbon ages spanning 4300 years indicate long term aggradation rates of 0 05 cm yr 1 the observed highly variable short term rates indicate temporal heterogeneity in aggradation which in turn reflects spatial heterogeneity in processes at any point in time channel complexity increases directly downstream of beaver dams the increased complexity forms a positive feedback for beaver induced sedimentation the multi thread channel increases potential channel length for further damming which increases the potential area occupied by beaver ponds and the volume of fine sediment trapped channel complexity decreased significantly as surveyed beaver population decreased beaver meadows and moraine park represent settings where beaver substantially influence post glacial floodplain aggradation these findings underscore the importance of understanding the historical range of variability of valley bottom processes and implications for environmental restoration copyright 2011 john wiley sons ltd

tectonic shortening and crustal thickening in subduction zones evidence from middle late jurassic magmatism in southern qiangtang china abstract we report new zircon u pb geochronologic and hf isotopic data and whole rock major and trace element data for the labuco granitoids of the southern margin of the southern qiangtang terrane sq tibet five intermediate felsic samples yielded zircon u pb ages of 169 156 ma making the labuco granitoids contemporaneous with middle late jurassic magmatism in the sq the granitoids exhibit a range of zircon ehf t values from 7 3 to 0 6 the samples from labuco can be divided into low sr y granitoids lsg and high sr y granitoids hsg the lsg are normal calc alkaline i type granitoids characterized by varying major and trace element contents indicative of partial melting of ancient mafic lower crust the hsg are characterized by high sr y ratios 64 75 la yb n chondrite normalized ratios of 57 76 and gd yb n ratios of 6 6 8 9 these signatures indicate that the hsg were derived by partial melting of garnet bearing thickened lower crust the across arc variation in magma geochemistry in the sq was caused by tectonic shortening and crustal thickening which occurred as a result of the northward subduction of the bangong nujiang ocean lithosphere during the middle late jurassic these results have important implications for our understanding of tectonic shortening crustal thickening and the geometry of modern and ancient subduction zones

systematic variations in recurrence interval and moment of repeating aftershocks 1 the recurrence intervals for 194 repeating clusters on the calaveras fault follow a power law decay relation with elapsed time after the 1984 m6 2 morgan hill california mainshock the decay rates of repeating aftershocks in the immediate vicinity of a high slip patch that failed during the mainshock systematically exceed those that are farther away the trend between relative moment and recurrence interval which is a measure of the fault healing rate varies systematically with depth and changes from negative to positive value as the distance between the repeating aftershock and the mainshock slip patch increases we speculate that high strain rate in the early postseismic period may cause transient embrittlement and strengthening of the deep repeating clusters in the areas adjacent to the mainshock slip patch resulting in large moments that decrease with time as the strain rate diminishes our observations suggest that systematic behavior of repeating aftershocks reflect variations in the fault zone rheology

anisotropic scattering and travel time delay analysis in kilauea volcano hawaii earthquake coda waves we study the s wave coda of microearthquake multiplets earthquakes showing similar seismograms recorded on the kilauea volcano and we analyze the direction of emission for wavelets composing the coda our data set consists of 71 small magnitude well relocated clustered events that occurred in an area of about 1 km2 in the southern flank of kilauea recorded at hypocentral distances of 10 to 20 km for each station we apply a cross spectral moving window technique to each pair of multiplet records to estimate the travel time delays due to source location offsets these delays are computed for consecutive windows starting at the p wave arrival time and ending at 4 times the s wave travel time they are next used to estimate the slowness vector for each window along the seismograms our analysis shows 1 that scattered waves are emitted anisotropically along some preferred directions as late as 4 times the s wave travel time and 2 that for some stations the azimuthal plane rotates during the seismogram with a clear travel time delay signature our analysis shows that travel time delay variation in the coda can be purely due to geometrical propagation effects this conclusion is of special interest when trying to use travel time delays to infer temporal changes in the crust our results do not support a coda diffracted isotropically in the crust in the magnitude range and at the hypocentral distances we investigated

stability of coda q in the region of parkfield california view from the u s geological survey parkfield dense seismograph array many investigators have proposed that changes in the rate at which the coda decays may be an intermediate term precursor to moderate to large earthquakes parkfield california on the san andreas fault is a promising location for studying premonitory changes in coda q qc because a large earthquake is likely to occur there we have investigated qc using recordings from the u s geological survey parkfield dense seismograph array which is a digital array with 14 triaxial sensors and an aperture of about 1 km for each earthquake we can measure qc from up to 42 recordings their average is more stable than the measurement from a single station using clustered seismicity we have developed criteria for selecting events and reducing scatter in the measurement the qc value determined from a seismogram depends on the position and length of the analysis window thus qc should always be measured from the same length window starting at the same lapse time regardless of the source location in addition the band limited signal to noise ratio at the end of the analysis window is important qc determined in two frequency bands 4 8 hz and 8 16 hz from a tight cluster of 26 events which occurred between december 1989 and january 1994 has not changed despite m 4 7 and m 4 6 events in october 1992 and november 1993 qc measured from local events 60 km in three frequency bands shows larger scatter but has also not changed during this period for monitoring qc observations should include array averaged measurements from a single lapse time because qc measurements made using an analysis window that starts at a constant multiple of the s wave lapse time depend on epicentral distance a procedure combining the evaluation of the time and distance dependences of qc also gives stable observations

characteristics of beaver ponds on deltas in a mountain environment many beaver ponds in the rocky mountains that have been described in the literature are in channel ponds that are relatively small and short lived this paper describes floodplain beaver ponds on low gradient deltas in glacial finger lakes in glacier national park montana these ponds are distinctly larger probably fed by hyporheic flow and stable and long lived ponds examined were with one exception 44 years old glacial discharge is present in each valley where beaver ponds occupy low gradient deltas and this discharge likely sustains pond water level over the course of the summer as glaciers recede and disappear deltaic beaver ponds dependent on hyporheic flow may be negatively affected copyright 2012 john wiley sons ltd

joint inversion of fault zone head waves and direct p arrivals for crustal structure near major faults a newly recognized class of seismic phases namely fault zone head waves arising from refraction at a transfault velocity contrast provides additional constraints to direct p waves in inversions of near fault arrival time data for earthquake location and velocity structure incorporation of fault zone head waves in the inversion process increases the available data and broadens the spatial coverage of ray paths between sources and receivers equally important the explicit recognition of fault zone head waves eliminates a source of error resulting from misidentifying head wave first arrivals as direct p waves a simple algorithm for the joint inversion of fault zone head waves and direct p phases is illustrated with observed and synthetic data application to a small data set recorded by the borehole seismic network at parkfield california provides separate seismic velocity depth profiles for the crustal blocks on the two sides of the san andreas fault for depths less than 3 km the obtained velocity contrast is 10 20 for greater depths it decreases to 3 7 numerical tests with synthetic data show that for sources with known locations and for well located local earthquakes randomized mislocation errors of up to 600 m proper use of fault zone head waves can significantly improve the accuracy of the fitted velocity structure the results of this work motivate the inclusion of fault zone head waves in state of the art joint structure hypocenter inversions using high quality near fault data

guided waves from sources outside faults an indication for shallow fault zone structure using 3 d numerical modeling of seismic wave propagation we investigate the possibility of generating fault zone fz trapped wave energy from sources well outside a fault the fz is represented by a o 200 m wide vertical low velocity layer in a half space we find that fz trapped waves can be excited from sources well outside the fault if 1 the low velocity structure extemds only to shallow depth and the source is located at greater depth or 2 the structure of the low velocity zone is such that only the shallow part of the fz traps energy fz trapped waves are not excited from sources well outside a fz continuous with depth the results support in conjunction with recent observational evidence a model for natural faults with shallow trapping structures rather than ones that span the entire seismogenic zone this may have implications for fault mechanics as well as for aspects of shaking hazard near faults

nonlinear strong ground motion in the ml 5 4 chittenden earthquake evidence that preexisting damage increases susceptibility to further damage 1 we use 55 repeating earthquake sequences located near the 1989 mw 6 9 loma prieta earthquake to identify time dependent velocity changes in the shallow crust in addition to large delays caused by the loma prieta mainshock the ml 5 4 chittenden earthquake an aftershock of loma prieta caused direct s wave delays of up to 6ms and s coda delays exceeding 15ms we attribute the delays to cracks formed or opened during the strong shaking of the chittenden earthquake the same mechanism believed responsible for the delays observed following loma prieta the magnitude of the delays caused by chittenden strongly correlate with those caused by loma prieta this suggests that rocks recently damaged by nonlinear strong ground motion are particularly susceptible to further damage until they are completely healed therefore we expect that the onset of nonlinearity will occur at substantially lower ground motion for large aftershocks than would otherwise be anticipated

geomorphic changes upstream of beaver dams in bridge creek an incised stream channel in the interior columbia river basin eastern oregon channel incision is a widespread phenomenon throughout the dry interior columbia river basin and other semi arid regions of the world which degrades stream habitat by fundamentally altering natural ecological geomorphological and hydrological processes we examined the extent of localized aggradation behind beaver dams on an incised stream in the interior columbia river basin to assess the potential for using beaver castor canadensis dams to restore such channels and the effect of the aggradation on riparian habitat we estimated aggradation rates behind 13 beaver dams between 1 and 6 years old on bridge creek a tributary to the john day river in eastern oregon vertical aggradation rates are initially rapid as high as 0 47 m yr 1 as the entrenched channel fills then level off to 0 075 m yr 1 by year six as the sediment begins accumulating on adjacent terraces we found that a 0 5 m elevation contour above the stream channel approximately coincided with the extent of new riparian vegetation establishment therefore we compared the area surrounding reaches upstream of beaver dams that were within 0 5 m elevation of the stream channel with adjacent reaches where no dams existed we found that there was five times more area within 0 5 m elevation of the channel upstream of beaver dams presumably because sediment accumulation had aggraded the channel our results suggest that restoration strategies that encourage the recolonization of streams by beaver can rapidly expand riparian habitat along incised streams copyright 2007 john wiley sons ltd

spatiotemporal variations of crustal anisotropy from similar events in aftershocks of the 1999 m7 4 izmit and m7 1 duzce turkey earthquake sequences summary we analyse spatiotemporal variations of crustal anisotropy along the karadere duzce branch of the north anatolian fault from similar earthquakes in the aftershock regions of the 1999 mw7 4izmit and mw7 1 duzce earthquakes the similar earthquake clusters are identified by performing cross correlation on waveforms generated by 18 000 earthquakes depending on the applied similarity criterion about 4 60 per cent of the events belong to similar event clusters splitting parameters averaged within each cluster show significant variations for slightly different ray paths indicating strong spatial variations of crustal anisotropy in this area we also find clear changes in the spatiotemporal seismicity patterns following the duzce main shock large apparent co seismic changes up to 30 per cent of shear wave splitting delay times are observed across the time of the duzce main shock at stations near the epicentral region however the changes can be mostly explained by the spatial variations of ray paths due to the changing seismicity rather than changes in the properties of the anisotropic medium splitting parameters measured within similar earthquake clusters indicate at most 2 per cent changes in delay times associated with the occurrence of the duzce main shock the results do not show systematic precursory changes before the duzce main shock

biogeomorphology past present and future abstract since the 1970s there has been a considerable expansion in biogeomorphological research which considers the complex two way relationships between biological ecological and geomorphological systems over a wide range of spatial and temporal scales advances have been made in theoretical methodological thematic and applied aspects of biogeomorphology a review of key publications and symposia over the period illustrates growth in biogeomorphology with particular advances in quantitative understandings of biogeomorphic interactions in interdisciplinary participation and in theoretical framings theoretical advances have been influenced by the desire to answer four fundamental questions how do ecological and geomorphological systems interact is there a geomorphological signature of life how important is biodiversity to landscape evolution and vice versa how have life and landscape co evolved a review of methodological advances in biogeomorphology confirms the continuing importance of field monitoring and the increasingly tight collaboration between experimental and modelling based research thematically particularly strong progress has been made in disentangling the complex bidirectional biogeomorphic interactions in coastal sedimentary environments and fluvial and riparian systems it is increasingly obvious that variation in ecological traits leads to large differences in biogeomorphic impacts of different species in different circumstances this poses challenges for applications of biogeomorphology to environmental management and conservation seven key topics emerge from this review and provide the basis for a biogeomorphological research agenda to usher in the next 50 yr of progress

seismic fracture anisotropy in the earth s crust an overview fluid filled fractures and microcracks are the most stress sensitive component of crustal rock and often determine the pathways and volume of crustal fluid movement if we are to comprehend the role of fractures and fluids in tectonic processes to formulate an accurate hypothesis for phenomena precursory to catastrophic seismic failure or to monitor hydrocarbon and geothermal reservoirs for the presence or absence of major fluid pathways we must understand how seismic waves interact with the fracture crack and microcrack structures within the rock mass a salient feature of fracture related rock structure is the effective seismic anisotropy of aligned fractures and microcracks with the advent of large volume digital seismic data sets it is feasible to use polarized shear waves to explore the anisotropic fracture properties of the crust crustal fracture structures which may be monitored by polarized shear waves range in dimensions from the 10 100 km scale of crustal stress orientation and preseismic stress buildup through the 100 1000 m scale of fluid reservoir structure and characterization and the 1 10 scale of mining and geoengineering rock strain monitoring to millimeter and micrometer or possibly smaller fluid filled inclusions determining the elastic response of the intact rock mass to focus developments in seismic anisotropic studies of crustal fracture phenomena the american geophysical union and the society of exploration geophysicists sponsored a chapman conference on seismic anisotropy in the earth s crust held may 31 to june 4 1988 at the lawrence berkeley laboratory of the university of california this was the third international workshop on seismic anisotropy 3iwsa nineteen conference papers are presented in this special section of the journal of geophysical research

evidence for temporal variation of seismic velocity within the upper continental crust observations of systematic temporal variations of seismic anisotropy are presented for an induced seismicity experiment at 9 km depth these observations were made under particularly well controlled conditions in the german continental deep drilling program ktb borehole using shear wave splitting from similar events recorded at a three component instrument located at 4 km depth from a hydraulic fracturing experiment at 9 km depth in a large set of seismic events recorded during the experiment many can be associated with multiplets exhibiting essentially identical waveforms since they must have approximately the same source location and source radiation pattern these events are particularly useful for testing the hypothesis of time dependent anisotropy anisotropy itself is clearly a very prominent feature in the data a simple approach for waveform matching of split shear waves allows unprecedented resolution of variations in shear wave splitting importantly the variation of shear wave splitting with time is a relative measurement which can be performed with higher accuracy than the associated absolute measurement in particular the relative measurement is not affected by timing errors nor by event distance variations during the experiment the difference between shear wave velocities decreases by 2 within 12 hours after that the medium apparently approaches a state which is stable for at least 5 hours we suggest that the temporal variation is due to the tectonic stress release from seismic events caused by the fluid injection this model requires the presence of fluid filled cracks at depths larger than 4 kin

the contributions of biogeomorphology to the emerging field of geobiology biogeomorphology has developed into a well established research field over the past 15 years with studies examining a range of two way interrelations between organisms and geomorphology in a variety of terrestrial and marine environments this paper starts by defining the core biogeomorphological processes bioerosion bioprotection and bioconstruction particular emphasis is placed on the study of bioconstructional forms providing a clear definition examples of bioconstructions and crucially examining important interactions between bioconstruction and bioerosion three key areas where biogeomorphological research can directly contribute to the emerging field of geobiology are identified 1 the use of biogeomorphological approaches combined with palaeoecological investigations and predictive modelling in the growing field of carbon sequestration and climate change mitigation 2 providing geomorphological expertise to support the emerging field of astrobiology and 3 the potential contributions of biogeomorphology to the blossoming field of bio geoengineering some key research directions and challenges for future biogeomorphological research include exploring how biogeomorphological studies can contribute to and benefit from collaborations with other fields of geobiology and assisting in the development of a useful effective interdisciplinary toolbox of methods to improve quantification of geobiological processes importantly suggestions are made for potentially fruitful collaborations with geomicrobiologists geochemists and palaeoecologists

theory of time dependent rupture in the earth at a velocity x which is a well defined function of k this propagation is stable and quasi static and is referred to as subcritical crack growth we shall use the terms stable quasistatic and subcritical to mean propagation at velocities much less than the sonic velocities of the medium this behavior results from stress induced corrosion at the crack tip the principal corrodent for the present application being h20 this behavior has been firmly established in the laboratory for mode i tensile cracks in a wide variety of materials ineluding silicates and silicate glasses see cholz 1968a 1972a martin 1972 wiederhorn and bolz 1970 atkinson 1979 lawn and wilshaw 1975 knott 1973 the form of the relationship between k and x does not vary significantly with the material only the parameters in the law vary as an example we show in figure 1 data on subcritical crack growth in quartz after atkinson 1979 the empirical relationship is found to take the form