observing earthquakes triggered in the near field by dynamic deformations we examine the hypothesis that dynamic deformations associated with seismic waves trigger earthquakes in many tectonic environments our analysis focuses on seismicity at close range within the aftershock zone complementing published studies of long range triggering our results suggest that dynamic triggering is not confined to remote distances or to geothermal and volcanic regions long unilaterally propagating ruptures may focus radiated dynamic deformations in the propagation direction therefore we expect seismicity triggered dynamically by a directive rupture to occur asymmetrically with a majority of triggered earthquakes in the direction of rupture propagation bilaterally propagating ruptures also may be directive and we propose simple criteria for assessing their directivity we compare the inferred rupture direction and observed seismicity rate change following 15 earthquakes m 5 7 to m 8 1 that occurred in california and idaho in the united states the gulf of aqaba syria guatemala china new guinea turkey japan mexico and antarctica nine of these mainshocks had clearly directive unilateral ruptures of these nine seven apparently induced an asymmetric increase in seismicity rate that correlates with the rupture direction the two exceptions include an earthquake preceded by a comparable magnitude event on a conjugate fault and another for which data limitations prohibited conclusive results similar but weaker correlations were found for the bilaterally rupturing earthquakes we studied although the static stress change also may trigger seismicity it and the seismicity it triggers are expected to be similarly asymmetric only if the final slip is skewed toward the rupture terminus for several of the directive earthquakes we suggest that the seismicity rate change correlates better with the dynamic stress field than the static stress change manuscript received 1 march 2002

fault interactions in the sea of marmara pull apart north anatolian fault earthquake clustering and propagating earthquake sequences summary knowledge on large earthquakes m 7 0 geology and fault kinematics is used to analyse conditions that favour isolated seismicity clustered earthquakes or propagating sequences along the north anatolian fault naf and the sea of marmara pull apart the overall naf marmara fault system is one of the most appropriate on earth to document fault interactions because reliable information covers almost completely two seismic cycles the past 500 yr coulomb stress analysis is used to characterize loading evolution in well identified fault segments including secular loading from below and lateral loading imposed by the occurrence of previous earthquakes earthquakes along the naf tend to occur where previous events have increased the stress but significant isolated events in the sea of marmara region 1894 1912 have occurred suggesting the secular loading has been the determining factor present day loading appears to be particularly high along the 70 km long segment located in the central marmara sea southwest of istanbul for the 18th century m 7 0 earthquake clusters we construct scenarios consistent with the tectonic and historical data we find that scenarios consistent with slip deficit and secular loading distributions from below clearly involve a sequence that propagates westward through the sea of marmara despite the structural complexity however the inference of a propagating sequence implies that each event has occurred in a segment previously stressed by lateral coulomb stress interactions the most likely scenarios for the propagating sequence are also consistent with coulomb stress interactions between faults with significant normal slip across the cinarcik basin propagating earthquake sequences do not occur every seismic cycle along the naf the loading has to be in a particular state of stress close to failure and uniform all along the fault segments to experience propagating earthquake sequences non uniform stress relief during the 18th century sequence explains the occurrence of isolated events in marmara in 1894 and 1912 as a consequence the wellknown 20th century sequence along the naf has not propagated as a sequence across the sea of marmara the most linear part of the naf across northern turkey behaves as a single fault segment accumulating stress during hundreds of years and rupturing entirely during very short periods the marmara pull apart fault system behaves as a major geometric complexity stopping or delaying the progression of earthquake clustering and propagating sequences fault zones interact with each other at a very large scale

mechanical strength and physical properties of oklahoma s igneous basement abstract from 2009 to 2016 a drastic increase in seismic activity occurred in the central and eastern us ceus particularly in the oklahoma kansas region the majority of hypocenters were focused in the crystalline basement rock information regarding the physical properties elastic wave velocity peak strength etc of rocks in the ceus basement to date is sparse forecasting future seismic hazard and predicting the in situ response of the crystalline basement requires their geomechanical parameters be adequately constrained this work assesses the mechanical and petrophysical properties of several sets of basement rocks from oklahoma to provide a better framework for understanding intraplate seismicity and overall basement deformation in the continental united states laboratory experiments were conducted with granite rhyolite and diabase basement rock samples collected from southern oklahoma evolution of compressional and shear wave velocity with increasing confinement was measured through a series of ultrasonic velocity tests a suite of uniaxial and triaxial tests were conducted to measure the elastic and inelastic deformation behavior of the basement rocks deformation data was evaluated using the mohr coulomb criterion and compared with additional preexisting deformation data of igneous basement rocks dynamic and static elastic properties compare favorably with available field measurements and demonstrate the role physical properties can play in varying mechanical behavior granitic samples demonstrate moderate variation of intrinsic physical properties can alter elastic properties and failure behavior significantly water weakening in the basement rocks may indicate fluid assisted processes such as stress corrosion cracking enhance deformation in the crystalline basement

small intermediate fault segments can either aid or hinder rupture propagation at stepovers 1 large scale geometrical complexities along faults are known to be likely endpoints for coseismic rupture as suggested by analysis of historic ruptures and corroborated by models of rupture on bent or discontinuous faults however natural faults also include smaller scale complexities we use the 3d finite element method to model dynamic ruptures on strike slip fault stepovers with a smaller intermediate fault between the main strands we find that such small faults can have a controlling effect on rupture behavior and ground motion intensity and distribution in particular the intermediate fault can either aid or prevent rupture propagation across the stepover depending on its length and basal depth the results have important implications for hazard assessment of faults with large and small scale geometrical complexities and also suggest that more site specific modeling studies may be necessary to develop realistic rupture scenarios for individual complex fault systems

geomagnetic and mineral magnetic characterization of the anthropocene geomagnetic and mineral magnetic data provide geological indices that are both independent of human impact i e geomagnetic and respond to human induced environmental impact i e mineral magnetic we provide the first discussion of such magnetic events for help in defining the anthropocene within the holocene a potential geomagnetic marker for the anthropocene is the low dipole latitude at c 2700 cal a bp which is associated with distinct palaeosecular variation features in northerly mid to high latitude sites mineral magnetic records from lake and marine sediments identify major deforestation and soil delivery events from catchment systems in many parts of the world during the last 4000 years in europe clusters of these events occur around both 2600 cal a bp and ad 1100 the former coinciding with a low in geomagnetic field dipole latitude and peak intensity mineral magnetic records in peats and lake sediments can reflect particulate pollution from fossil fuel burning the expansion of major coal burning began c ad 1800 in western europe and eastern north america but around ad 1900 this expanded due to more widely distributed coal use and this event is the most clear mineral magnetic marker for the base of the anthropocene

the 2002 denali fault earthquake alaska a large magnitude slip partitioned event the mw moment magnitude 7 9 denali fault earthquake on 3 november 2002 was associated with 340 kilometers of surface rupture and was the largest strike slip earthquake in north america in almost 150 years it illuminates earthquake mechanics and hazards of large strike slip faults it began with thrusting on the previously unrecognized susitna glacier fault continued with right slip on the denali fault then took a right step and continued with right slip on the totschunda fault there is good correlation between geologically observed and geophysically inferred moment release the earthquake produced unusually strong distal effects in the rupture propagation direction including triggered seismicity

ploughing the deep sea floor bottom trawling is a fishing technique whereby heavy nets and gear scrape along the sea bed and is shown here to disturb sediment fluxes and modify the sea floor morphology over large spatial scales the direct impact of bottom trawling on local fish populations has received much attention but trawling also affects other aspects of the ocean environment this paper shows that bottom trawling a commercial practice in which heavy nets and gear are dragged along the ocean floor induces sediment reworking and erosion causing the gradient of the sea floor to become smoother over time this reduces the morphological complexity of deep sea environments the authors draw parallels between the effects of bottom trawling at sea and intensive agriculture on land with the important difference that on land ploughing takes place once or twice a year whereas at sea bottom trawling can be a frequent occurrence bottom trawling is a non selective commercial fishing technique whereby heavy nets and gear are pulled along the sea floor the direct impact of this technique on fish populations1 2 and benthic communities3 4 has received much attention but trawling can also modify the physical properties of seafloor sediments water sediment chemical exchanges and sediment fluxes5 6 most of the studies addressing the physical disturbances of trawl gear on the seabed have been undertaken in coastal and shelf environments7 8 however where the capacity of trawling to modify the seafloor morphology coexists with high energy natural processes driving sediment erosion transport and deposition9 here we show that on upper continental slopes the reworking of the deep sea floor by trawling gradually modifies the shape of the submarine landscape over large spatial scales we found that trawling induced sediment displacement and removal from fishing grounds causes the morphology of the deep sea floor to become smoother over time reducing its original complexity as shown by high resolution seafloor relief maps our results suggest that in recent decades following the industrialization of fishing fleets bottom trawling has become an important driver of deep seascape evolution given the global dimension of this type of fishery we anticipate that the morphology of the upper continental slope in many parts of the world s oceans could be altered by intensive bottom trawling producing comparable effects on the deep sea floor to those generated by agricultural ploughing on land

benthic foraminifera from the necop study area impacted by the mississippi river plume and seasonal hypoxia abstract benthic foraminifera influenced by the mississippi river plume and seasonal hypoxia were assessed from louisiana inner continental shelf sediment samples surface foraminifera assemblages were representative of in situ populations as established by staining techniques community diversity and richness evenness analyses indicate three regimes high stress sediment dominated intermediate stress hypoxia dominated and low stress low sediment accumulation high oxygen epistominella vitrea and buliminella morgani are useful tracers of rapid sediment accumulation rate and hypoxia a bottom water productivity signal west of the mississippi river plume is indicated by benthic and planktic foraminifera abundance peaks surface benthic foraminifera trends are utilized to interpret changes in historical community structure from hypoxic area sediments deposited since the turn of the century the hypoxia tolerant species buliminella morgani increases markedly upcore while hypoxia intolerant species decrease or disappear diversity and dominance trends temporally correspond to a dramatic increase in u s fertilizer application the results of this study have application to paleoenvironmental research spanning longer geologic timescales the documented relationships between population structure and stressors in river dominated marine systems may provide a useful analog for recognition of these conditions in the fossil record

a new observation of dynamically triggered regional seismicity earthquakes in greece following the august 1999 izmit turkey earthquake the m w 7 4 izmit turkey earthquake triggered widespread regional seismicity in greece over a study region extending from 400 km to nearly 1000 km away from the epicenter small events began immediately after the passage of the mainshock surface waves suggesting that the transient stresses of the seismic waves were the trigger the increase in cataloged earthquakes in ordinary continental crust is a new observation and is statistically significant at the 95 level unlike the previous example of distant triggering during the landers earthquake the activated seismicity occurred entirely in non volcanic areas the greek sites were triggered by waves with amplitudes at least a factor of 3 lower than the observed triggering threshold for imperial valley we speculate that dynamic triggering on a regional scale results in countrywide episodes of increased seismicity or superswarms in regions with low triggering thresholds such as greece

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

a stratigraphical basis for the anthropocene recognition of intimate feedback mechanisms linking changes across the atmosphere biosphere geosphere and hydrosphere demonstrates the pervasive nature of humankind s influence perhaps to the point that we have fashioned a new geological epoch the anthropocene to what extent will these changes be evident as long lasting signatures in the geological record to establish the anthropocene as a formal chronostratigraphical unit it is necessary to consider a spectrum of indicators of anthropogenically induced environmental change and to determine how these show as stratigraphic signals that can be used to characterize an anthropocene unit and to recognize its base it is important to consider these signals against a context of holocene and earlier stratigraphic patterns here we review the parameters used by stratigraphers to identify chronostratigraphical units and how these could apply to the definition of the anthropocene the onset of the range of signatures is diachronous although many show maximum signatures which post date1945 leading to the suggestion that this date may be a suitable age for the start of the anthropocene

assessing the anthropocene with geochemical methods anthropogenic chemical contamination is one of the most evident signals of human influence on the environment the large amounts of industrially produced pollutants that have been introduced over decades into air soil and water have caused modifications to natural elemental cycling anthropogenic contamination usually leads to enrichment in many elements particularly in industrial areas thus certain elements and their isotopes can be used as geochemical tracers of anthropogenic impact some human induced changes in the environment may be regarded as a secondary effect of pollution such as acidification which causes increased geochemical mobility of several trace elements in surficial deposits methods used by geochemists to assess the scale of anthropogenic influence on the environment include calculations of anthropogenic influence on the environment via enrichment and contamination factors geoaccumulation index and pollution load index the use of geochemical background levels for delineating between natural and anthropogenic pollution is important a historical perspective of anthropogenic contamination allied with isotopic and geochemical signatures in dated sediment cores may be applied to help define the anthropocene human influence on the environment has been complex encompassing different environmental compartments air water soil and scales of changes local regional global the earth is a dynamic system and geochemical dynamics are best illustrated by consideration of element cycling although anthropogenic pollution sources have contributed to chemical changes in the atmosphere hydrosphere pedosphere and biosphere their impact on the total environment is best preserved in sediments which are often referred to as archives of contamination choi wania 2011 significant evidence of a distinctive anthropocene signal can be found in recent sedimentary deposits that have been impacted by anthropogenic activity and dated sediment cores can be used to reconstruct the chronology of contamination buckley et al 1995 in assessing the anthropocene it is important to quantify the human influence on the environment the results of this influence recorded in sediments can be evaluated using different approaches and criteria depending on the nature of the signal mechanical biological or chemical fig 1 zalasiewicz et al 2011a b price et al 2011 vane et al 2011 schrag 2012 geochemical methodology may help discriminate natural and anthropogenic sources of a given substance in the environment some of the methods and concepts e g anomaly background concentrations geochemical calculations and geochemical tracers traditionally used in geochemical exploration and further adapted to the needs of environmental geochemistry have found application in the study of anthropogenic contamination reimann de caritat 2005 reimann et al 2005 galuszka 2007 galuszka migaszewski 2011 these methods may be extended in assessment of the anthropocene anthropogenic anomalies and geochemical background concept geochemical anomalies can be defined as abnormal concentrations of elements in earth materials compared with background levels allaby allaby 1999 anomalous concentrations of elements are both of natural origin e g via oreforming processes weathering of ore bodies or mineralized rock formations sorption by mineral phases volcanic and hydrothermal activity and of anthropogenic origin mcqueen 2009 of the different types of geochemical anomalies fig 2 the positive anthropogenic anomalies of regional scale may provide a useful marker for the anthropocene selinus esbensen 1995 identification of geochemical anomalies requires knowledge of the normal or average distribution of elements in the environment which is usually referred to as a geochemical background lower and upper limits of the geochemical background from waters c n zalasiewicz j a williams m ellis m a snelling a m eds a stratigraphical basis for the anthropocene geological society london special publications 395 http dx doi org 10 1144 sp395 5 the geological society of london 2013 publishing disclaimer www geolsoc org uk pub ethics range are considered thresholds of negative depletion in an element and positive enrichment in an element anomalies fig 3 historically the search for positive anomalies has been essential to mineral exploration and in the 1960s geochemists established several methodologies for separating anomalies from the geochemical background hawkes webb 1962 miesch 1967 many fig 1 types of human induced changes their possible effects and sedimentary record fig 2 systematics of geochemical anomalies a ga uszka et al

dynamic triggering of earthquakes is promoted by crustal heterogeneities and bimaterial faults remotely triggered earthquakes and aftershocks constitute a great challenge in assessing seismic risk a growing body of observations indicates that significant earthquakes can be triggered by moderate to great earthquakes occurring at distances of up to thousands of kilometres currently we lack the knowledge to predict the location of triggered events we present numerical simulations showing that dynamic interactions between material heterogeneities e g compliant fault zones sedimentary basins and seismic waves focus and enhance stresses sufficiently to remotely trigger earthquakes numerical simulations indicate that even at great distances 100 km the amplified transient dynamic stress near heterogeneities is equivalent to stress levels near the source rupture tip 5 km such stress levels are widely considered capable of nucleating an earthquake rupture on a pre stressed fault analysis of stress patterns in dynamic rupture simulations which include a heterogeneous zone with a range of material and geometrical properties reveals various mechanisms of stress enhancement we conclude that both stiff and weak heterogeneities may focus stress waves to form zones of enhanced stress and that bimaterial interfaces distort under static and dynamic loading in a way that induces local stress concentrations our work provides insights for understanding non uniform distribution of remotely triggered seismicity and recurrence of such events along complex fault systems and near magmatic intrusions and geothermal zones

simulation of seismic wave propagation through geometrically complex basins the dead sea basin abstract the dead sea transform dst is the source for some of the largest earthquakes in the eastern mediterranean the seismic hazard presented by the dst threatens the israeli palestinian and jordanian populations alike several deep and structurally complex sedimentary basins are associated with the dst these basins are up to 10 km deep and typically bounded by active fault zones the low seismicity of the dst the sparse seismic network and limited coverage of sedimentary basins result in a critical knowledge gap therefore it is necessary to complement the limited instrumental data with synthetic data based on computational modeling in order to study the effects of earthquake ground motion in these sedimentary basins in this research we performed a 2d ground motion analysis in the dead sea basin dsb using a finite difference code cross sections transecting the dsb were compiled for wave propagation simulations results indicate a complex pattern of ground motion amplification affected by the geometric features in the basin to distinguish between the individual contributions of each geometrical feature in the basin we developed a semiquantitative decomposition approach this approach enabled us to interpret the dsb results as follows 1 ground motion amplification as a result of resonance occurs basin wide due to a high impedance contrast at the base of the uppermost layer 2 steep faults generate a strong edge effect that further amplifies ground motions 3 sub basins cause geometrical focusing that may significantly amplify ground motions and 4 salt diapirs diverge seismic energy and cause a decrease in ground motion amplitude

triggering of earthquake aftershocks by dynamic stresses it is thought that small static stress changes due to permanent fault displacement can alter the likelihood of or trigger earthquakes on nearby faults many studies of triggering in the near field particularly of aftershocks rely on these static changes as the triggering agent and consider them only in terms of equivalent changes in the applied load on the fault here we report a comparison of the aftershock pattern of the moment magnitude mw 7 3 landers earthquake not only with static stress changes but also with transient oscillatory stress changes transmitted as seismic waves that is dynamic stresses dynamic stresses do not permanently change the applied load and thus can trigger earthquakes only by altering the mechanical state or properties of the fault zone these dynamically weakened faults may fail after the seismic waves have passed by and might even cause earthquakes that would not otherwise have occurred we find similar asymmetries in the aftershock and dynamic stress patterns the latter being due to rupture propagation whereas the static stress changes lack this asymmetry previous studies have shown that dynamic stresses can promote failure at remote distances but here we show that they can also do so nearby

stratigraphic expressions of the holocene anthropocene transition revealed in sediments from remote lakes stratigraphic boundaries are ideally defined by distinct lithological geochemical and palaeobiological signatures to which a chronological framework can be applied we present a range of observations that illustrate how the holocene anthropocene transition meets these criteria in its expression in sediments from remote arctic and alpine lakes removed from direct catchment scale anthropogenic influences in glaciated lake basins the retreat of glaciers commonly leads to lithological successions from proglacial clastic sedimentation to non glacial organic deposition sediments from the majority of lakes record marked depletions in the nitrogen stable isotopic composition of sediment organic matter reflecting anthropogenic influences on the global nitrogen cycle in all cases siliceous microfossil assemblages diatoms and chrysophytes change markedly and directionally with regional nuances these stratigraphic fingerprints begin to appear in the sediment record after ad 1850 but accelerate in pulses between ad 1950 and 1970 and again after ad 1980 our review indicates that recent environmental changes associated with humankind s dominance of key global biogeochemical cycles are sufficiently pervasive to be imprinted on the sediment record of remote lakes moreover these changes are of sufficient magnitude to conclude that the holocene has effectively ended and that the concept of anthropocene more aptly describes current planetary dynamics the synthesis of these observations pertains directly to ongoing discussions concerning the eventual formalization of a new stratigraphic boundary

predicting rupture arrests rupture jumps and cascading earthquakes the devastation inflicted by recent earthquakes demonstrates the danger of under predicting the size of earthquakes unfortunately earthquakes may rupture fault sections larger than previously observed making it essential to develop predictive rupture models we present numerical models based on earthquake physics and fault zone data that determine whether a rupture on a segmented fault could cascade and grow into a devastating multisegment earthquake we demonstrate that weakened damaged fault zones and bi material interfaces promote rupture propagation and greatly increase the risk of cascading ruptures and triggered seismicity this result provides a feasible explanation for the outstanding observation of a very large 10 km rupture jump documented in the mw7 8 2001 kunlun china earthquake however enhanced inter seismic deformation and energy dissipation at fault tips suppress rupture propagation and may turn even small discontinuities into effective earthquake barriers by assessing fault stability identifying rupture barriers and foreseeing multisegment earthquakes we provide a tool to improve earthquake prediction and hazard analysis

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

short baseline variations in site response and wave propagation effects and their structural causes four examples in and around the santa clara valley california abstract ground motion records of local and regional events from a portable array are used to investigate the structural causes of variations in ground motion over distances of a few hundred meters to a few kilometers in the sedimentary basin environment of the santa clara valley california and its margins arrays of portable seismic stations are used to target four study areas with different ground motion patterns 1 an edge of the alluvial basin extending up onto a marginal ridge blossom hill 2 a cenozoic basin with a nearly flat bottom cupertino basin 3 a long narrow cenozoic basin with a steep v profile evergreen basin and 4 a line perpendicular to the trace of the hayward fault average peak velocities on blossom hill from local earthquakes are a factor of 2 5 times higher than nearby valley sites three dimensional 3d modeling is used to conclude that the majority of the amplification is due to lower shear wave velocities along a local fault zone shannon berrocal site amplification over the cupertino basin in the frequency band 0 5 4 hz is generally low less than 2 0 relative to a mesozoic rock site and spatially uniform this response is attributed to the shallow flat bottomed shape of the basin and the uniform flat laying sedimentary fill in contrast site amplification in the evergreen basin generally exceeds 3 0 and is attributed to the deep v shaped geometry of the basin and younger sedimentary fill 3d waveform modeling shows the elongated shape of the evergreen basin causes more efficient trapping of long period waves for sources along the long axis of the basin a low velocity zone is postulated along the hayward fault with a width between 100 and 200 m based on elevated site response along the fault trace and 4 5 hz fault zone guided waves on the horizontal components of stations near the fault

siltation of river influenced coastal environments respective impact of late holocene land use and high frequency climate changes abstract the aim of this study is to unravel the respective influence of land use and high frequency climate changes on the siltation of a river influenced coastal environment an 8 4 m long sediment core was recovered in the pertuis charentais western france an accurate 14 c bayesian age model was developed to perform a depth to time conversion of high resolution sedimentological data obtained on the core forest loss and precipitation changes that occurred on the related catchments were reconstructed from data gathered in the literature a sharp increase in winter rainfall 1700 1750 ad intensified erosion of catchments previously sensitised by increased forest loss 1640 1710 ad which resulted in a massive supply of silt to the coast from ca 1775 ad onwards a review of articles reporting similar mud layers is also proposed depending on their age some major phases of mankind migration history could be traced back which confirms the predominant influence of human activities on the siltation of river influenced coastal environments we therefore propose to group these mud layers into the anthropogenic system tracts in reference to widely used sequence stratigraphy nomenclature and we suggest that it might help to identify a holocene to anthropocene stratigraphic boundary in coastal areas

examining tendencies of in plane rupture to migrate to material interfaces summary we perform a numerical parameter space study of 2 d in plane ruptures in a model consisting of two different half spaces separated by a low velocity layer and possible simultaneous slip along multiple faults ruptures are nucleated by a bilateral expanding stress drop in a limited source region and may continue to propagate spontaneously or not along one or several faults most calculations are done for purely elastic media and faults governed by coulomb friction but some simulations employ prakash clifton friction and kelvin voigt viscosity the faults two of which are material interfaces are situated equidistant and parallel to each other using different nucleation locations different initial stress different velocity contrasts different frictional fault separations different widths of a low velocity zone and different number of faults we examine the range of conditions for which ruptures migrate to other faults and continue to propagate in a self sustaining manner the model produces diverse migration and propagation phenomena represented by several phase diagrams however a general result of the study is that ruptures tend to migrate to the material interfaces and become self sustained wrinkle like pulses for wide ranges of conditions the wrinkle like pulses propagate along each material interface unilaterally in the direction of motion on the more compliant side of the interface referred to as the positive direction the existence of a large number of faults produces like viscosity distributed deformation that reduces the divergent behaviour of the wrinkle like pulses in many cases ruptures migrate to the interface with the stronger contrast and propagate unilaterally in the positive direction associated with that interface and the overall contrast across the fault zone in smaller number of cases ruptures migrate to the interface with the weaker contrast and propagate unilaterally in the opposite positive direction associated with that interface for various parameter combinations self sustained unilateral pulses travel simultaneously in the two opposite positive directions along the interfaces on the opposite sides of the low velocity layer a low resolution imaging of these ruptures would lead to an inference on bilateral propagation the m6 2004 september parkfield california earthquake may provide a natural example of such a case

formal subdivision of the holocene series epoch a discussion paper by a working group of intimate integration of ice core marine and terrestrial records and the subcommission on quaternary stratigraphy international commission on stratigraphy this discussion paper by a working group of intimate integration of ice core marine and terrestrial records and the subcommision on quaternary stratigraphy sqs of the international commission on stratigraphy ics considers the prospects for a formal subdivision of the holocene series epoch although previous attempts to subdivide the holocene have proved inconclusive recent developments in quaternary stratigraphy notably the definition of the pleistocene holocene boundary and the emergence of formal subdivisions of the pleistocene series epoch mean that it may be timely to revisit this matter the quaternary literature reveals a widespread but variable informal usage of a tripartite division of the holocene early middle or mid and late and we argue that this de facto subdivision should now be formalized to ensure consistency in stratigraphic terminology we propose an early middle holocene boundary at 8200 a bp and a middle late holocene boundary at 4200 a bp each of which is linked to a global stratotype section and point gssp should the proposal find a broad measure of support from the quaternary community a submission will be made to the international union of geological sciences iugs via the sqs and the ics for formal ratification of this subdivision of the holocene series epoch copyright 2012 john wiley sons ltd

a large mw 6 0 aftershock of the 2008 mw 7 9 wenchuan earthquake triggered by shear waves reflected from the earth s core because the earth s outer core is liquid shear waves generated by a large earthquake that travel to the core scs are totally reflected with strong seismic energy it is interesting to note that one large aftershock m w 6 0 of the 2008 wenchuan earthquake m w 7 9 in china occurred when the scs phase returned around 15 5 m after the mainshock estimated peak dynamic stress 3 3 kpa of the scs amplitude reaches the critical level of the lower boundary capable of triggering earthquakes both the temporal correlation between aftershock occurrence and scs arrival as well as the dynamic stress capable of triggering an earthquake suggest that the large aftershock might well have been triggered dynamically by scs waves a similar feature of another large aftershock m b 5 3 occurring around the time of scs arrival has been also found from the 2003 hokkaido earthquake m w 8 3 further statistical examinations of 25 major earthquakes m w 8 0 between 1994 and 2008 shows some large aftershocks m w 5 0 also occurring around the time of scs phase arrival it is reasonable to conclude that these observations suggest aftershocks being triggered dynamically by scs phase arrivals and thus a temporal warning for potentially destructive aftershocks might be considered for future great earthquakes

suppression of large earthquakes by stress shadows a comparison of coulomb and rate and state failure stress shadows generated by california s two most recent great earthquakes 1857 fort tejon and 1906 san francisco substantially modified 19th and 20th century earthquake history in the los angeles basin and in the san francisco bay area simple coulomb failure calculations which assume that earthquakes can be modeled as static dislocations in an elastic half space have done quite well at approximating how long the stress shadows or relaxing effects should last and at predicting where subsequent large earthquakes will not occur there has however been at least one apparent exception to the predictions of such simple models the 1911 m 6 0 earthquake near morgan hill california occurred at a relaxed site on the calaveras fault we examine how the more complex rate and state friction formalism based on laboratory experiments might have allowed the 1911 earthquake rate and state time to failure calculations are consistent with the occurrence of the 1911 event just 5 years after 1906 if the calaveras fault was already close to failure before the effects of 1906 we also examine the likelihood that the entire 78 years of relative quiet only four m 6 earthquakes in the bay area after 1906 is consistent with rate and state assumptions given that the previous 7 decades produced 18 m 6 earthquakes combinations of rate and state variables can be found that are consistent with this pattern of large bay area earthquakes assuming that the rate of earthquakes in the 7 decades before 1906 would have continued had 1906 not occurred these results demonstrate that rate and state offers a consistent explanation for the 78 year quiescence and the 1911 anomaly although they do not rule out several alternate explanations

remotely triggered seismicity in yunnan southwestern china following the 2004 mw9 3 sumatra earthquake 1 following the 2004 mw9 3 sumatra earthquake seismicity rate increased sharply over a wide area of up to 2700 km away in yunnan province southwestern china raised seismicity lasts for 14 days during this period more than 800 earthquakes with magnitude between 1 5 and 5 1 occurred this is perhaps the most impressive example of remotely triggered seismicity yet observed major events were clustered at several sites that exhibit complex fault geometries such as step overs and junctures we use statistic approaches including the statistics to examine the statistical significance of the seismic rate increases associated with the sumatra main shock and conclude that there is a reasonable probability that the raised seismicity was remotely triggered by the sumatra earthquake both rapid onset of dynamic triggering the very first event is a m4 6 earthquake occurred during the passage of the rayleigh wave from the sumatra earthquake and delayed response activated a few hours to a few days after the sumatra earthquake are well established the triggered activities show more earthquake swarm like characteristics as indicated by the epidemic type aftershock sequence modeling results large percentage of random components and less magnitude dependence in omori law type self triggering multiple sources of evidence including intensive hydrothermal activities and low velocity and high vp vs zones in the lower to middle crust suggests that magma mantle generated fluids have a role in the region high fluid pressure in branched fault zones weakened the faults making them sensitive to external disturbances and leading to fluid driven seismicity

transient triggering of near and distant earthquakes we demonstrate qualitatively that frictional instability theory provides a context for understanding how earthquakes may be triggered by transient loads associated with seismic waves from near and distance earthquakes we assume that earthquake triggering is a stick slip process and test two hypotheses about the effect of transients on the timing of instabilities using a simple spring slider model and a rate and state dependent friction constitutive law a critical triggering threshold is implicit in such a model formulation our first hypothesis is that transient loads lead to clock advances i e transients hasten the time of earthquakes that would have happened eventually due to constant background loading alone modeling results demonstrate that transient loads do lead to clock advances and that the triggered instabilities may occur after the transient has ceased i e triggering may be delayed these simple clock advance models predict complex relationships between the triggering delay the clock advance and the transient characteristics the triggering delay and the degree of clock advance both depend nonlinearly on when in the earthquake cycle the transient load is applied this implies that the stress required to bring about failure does not depend linearly on loading time even when the fault is loaded at a constant rate the timing of instability also depends nonlinearly on the transient loading rate faster rates more rapidly hastening instability this implies that higher frequency and or longer duration seismic waves should increase the amount of clock advance these modeling results and simple calculations suggest that near tens of kilometers small moderate earthquakes and remote thousands of kilometers earthquakes with magnitudes 2 to 3 units larger may be equally effective at triggering seismicity our second hypothesis is that some triggered seismicity represents earthquakes that would not have happened without the transient load i e accumulated strain energy would have been relieved via other mechanisms we test this using two new seismicity models that 1 are inherently unstable but slide at steady state conditions under the background load and 2 are conditionally stable such that instability occurs only for sufficiently large perturbations for the new seismicity models very small amplitude transients trigger instability relative to the clock advance models the unstable steady state models predict that the triggering delay depends inversely and nonlinearly on the transient amplitude as in the clock advance models we were unable to generate delayed triggering with conditionally stable models for both new seismicity models the potential for triggering is independent of when the transient load is applied or equivalently of the prestress unlike in the clock advance models in these models a critical triggering threshold appears to be inversely proportional to frequency further advancement of our understanding will require more sophisticated quantitative models and observations that distinguish between our qualitative yet distinctly different model predictions

damage in step overs may enable large cascading earthquakes seismic hazard analysis relies on the ability to predict whether an earthquake will terminate at a fault tip or propagate onto adjacent faults cascading into a larger more devastating event while ruptures are expected to arrest at fault discontinuities larger than 4 5 km scientists are often puzzled by much larger rupture jumps here we show that material properties between faults significantly affect the ability to arrest propagating ruptures earthquake simulations accounting for fault step over zones weakened by accumulated damage provide new insights into rupture propagation revealing that lowered rigidity and material interfaces promote rupture propagation our models show for the first time that step overs as wide as 10 km may not constitute effective earthquake barriers our results call for re evaluation of seismic hazard analyses that predict rupture length and earthquake magnitude based on historic records and fault segmentation models

geology of mankind for the past three centuries the effects of humans on the global environment have escalated because of these anthro pogenic emissions of carbon dioxide global climate may depart significantly from natural behaviour for many millennia to come it seems appropriate to assign the term anthropocene to the present in many ways human dominated geological epoch supplementing the holocene the warm period of the past 10 12 millennia

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

observations of static coulomb stress triggering of the november 2011 m5 7 oklahoma earthquake sequence in november 2011 a m5 0 earthquake occurred less than a day before a m5 7 earthquake near prague oklahoma which may have promoted failure of the mainshock and thousands of aftershocks along the wilzetta fault including a m5 0 aftershock the m5 0 foreshock occurred in close proximity to active fluid injection wells fluid injection can cause a buildup of pore fluid pressure decrease the fault strength and may induce earthquakes keranen et al 2013 links the m5 0 foreshock with fluid injection but the relationship between the foreshock and successive events has not been investigated here we examine the role of coseismic coulomb stress transfer on earthquakes that follow the m5 0 foreshock including the m5 7 mainshock we resolve the static coulomb stress change onto the focal mechanism nodal plane that is most consistent with the rupture geometry of the three m 5 0 earthquakes as well as specified receiver fault planes that reflect the regional stress orientation we find that coulomb stress is increased e g fault failure is promoted on the nodal planes of 60 of the events that have focal mechanism solutions and more specifically that the m5 0 foreshock promoted failure on the rupture plane of the m5 7 mainshock we test our results over a range of effective coefficient of friction values hence we argue that the m5 0 foreshock induced by fluid injection potentially triggered a cascading failure of earthquakes along the complex wilzetta fault system

stress strain changes and triggered seismicity at the geysers california the principal results of this study of remotely triggered seismicity in the geysers geothermal field are the demonstration that triggering initiation of earthquake failure depends on a critical strain threshold and that the threshold level increases with decreasing frequency or equivalently depends on strain rate this threshold function derives from 1 analyses of dynamic strains associated with surface waves of the triggering earthquakes 2 statistically measured aftershock zone dimensions and 3 analytic functional representations of strains associated with power production and tides the threshold is also consistent with triggering by static strain changes and implies that both static and dynamic strains may cause aftershocks the observation that triggered seismicity probably occurs in addition to background activity also provides an important constraint on the triggering process assuming the physical processes underlying earthquake nucleation to be the same gomberg this issue discusses seismicity triggered by the mw 7 3 landers earthquake its constraints on the variability of triggering thresholds with site and the implications of time delays between triggering and triggered earthquakes our results enable us to reject the hypothesis that dynamic strains simply nudge prestressed faults over a coulomb failure threshold sooner than they would have otherwise we interpret the rate dependent triggering threshold as evidence of several competing processes with different time constants the faster one s facilitating failure and the other s inhibiting it such competition is a common feature of theories of slip instability all these results not surprisingly imply that to understand earthquake triggering one must consider not only simple failure criteria requiring exceedence of some constant threshold but also the requirements for generating instabilities

initiation and propagation of shear zones in a heterogeneous continental lithosphere continental plates represent rheologically heterogeneous media in which complex finite strain fields may develop due to interaction of plate tectonic processes with intraplate heterogeneities such a deformation pattern is displayed by the borborema shear zone system in northeastern brazil it involves continental scale curvilinear e w trending right lateral transcurrent shear zones that branch off from a major ne trending right lateral strike slip deformation zone formed at the northern termination of the sao francisco craton and that finally terminate in transpressive metasedimentary belts we suggest that this strain field results from the compressional deformation of a highly heterogeneous continental lithosphere composed of a stiff domain craton and rheologically weaker domains basins the effect of a low viscosity domain on the deformation of a continental plate and in particular the perturbation induced by this domain on the development of a shear zone formed at the termination of a stiff block were investigated using numerical modeling the low strength domain induces an enhanced strain localization and the geometry of the shear zone is significantly modified it is either split forming a branched shear zone system in which one branch maintains its original orientation while the other rotates toward the low viscosity domain or completely rotated toward the weak block the perturbation of the finite strain field depends on the ability of the weak domain to accommodate deformation which is controlled by its initial viscosity contrast relative to the surrounding lithosphere its orientation relative to the convergence direction and its distance from the shear zone initiated at the termination of the stiff block the interaction between imposed boundary conditions tectonic forces and plate geometry and the internal structure of the plate may give rise to highly heterogeneous strain fields as exhibited by the borborema shear zone system in which intraplate rheological heterogeneities induce the development of branched or sinuous shear zones a heterogeneous continental plate subjected to a normal convergence may therefore display significant lateral variations in strain intensity with shear zones bordering nearly undeformed blocks and in deformation regimes and vertical strains that would result in contrasting metamorphic and uplift histories

transient polar motions and the nature of the asthenosphere for short time scales the role of viscoelastic flows excited by earthquakes in driving short term polar motions is investigated analytically by means of a four layer model consisting of an elastic lithosphere a thin asthenosphere a mean mantle and an inviscid core we have employed a linear maxwell rheology throughout the entire mantle to describe large scale geodynamic processes for time spans less than 100 years the global displacement fields which contribute to the perturbations of the moment of inertia are calculated by solving a two point boundary value problem in which the forcing function is a dislocation source the elements of the perturbated inertia tensor are then employed directly in the liouville equations for determining the changes of the chandler wobble and the rate of the earth s rotation as a consequence of large earthquakes a complete set of solutions to the liouville equation is used for this problem this formulation requires the usage of two classes of eigenspectra one arising from isostatic reequilibration of the mantle due to faulting and the second set involving the gradual readjustment of the spin axis as a result of transient flows in the mantle we find that the polar motions depend sensitively on the viscosity structure of the asthenosphere and not at all on the underlying mantle on the basis of the observed polar motion data and the secular changes of the gravitational harmonic coefficient j2 we can rule out a global low viscosity zone with short term asthenospheric viscosities less than about 5 1018 pa s and widths greater than 50 km

an assessment of lithostratigraphy for anthropogenic deposits the deliberate anthropogenic movement of reworked natural and novel manufactured materials represents a novel sedimentary environment associated with mining waste disposal construction and urbanization anthropogenic deposits display distinctive engineering and environmental properties and can be of archaeological importance this paper shows that temporal changes in the scale and lithological character of anthropogenic deposits may be indicative of the anthropocene however the stratigraphy of such deposits is not readily described by existing classification schemes which do not differentiate separate phases or lithologically distinct deposits beyond a local scale lithostratigraphy is a scalable hierarchical classification used to distinguish successive and lithologically distinct natural deposits many natural and anthropogenic deposits exhibit common characteristics they typically conform to the law or principle of superposition and exhibit lithological distinction the lithostratigraphical classification of surficial anthropogenic deposits may be effective although defined units may be significantly thinner and far less continuous than those defined for natural deposits further challenges include the designation of stratotypes accommodating the highly diachronous nature of anthropogenic deposits and the common presence of disconformities international lithostratigraphical guidelines would require significant modification before being effective for the classification of anthropogenic deposits a practical alternative may be to establish an anthrostratigraphical approach or anthrostratigraphy

magnetite in sediments as an indicator of coal combustion abstract magnetic susceptibility gives an accurate measurement of the magnetite concentration in sediments in all geographical areas studied the magnetite concentration in recent lake estuarine and ocean sediments has been affected by coal burning which releases magnetite spheres to the atmosphere graphs of percent magnetite and percent spheres vs depth age in the various sediments can be used to give information on the history of coal burning in an area as well as the efficiency of air pollution controlling devices chromium zn ti and fe concentrations in the sediments were affected by the input of magnetic spheres cadmium cu mn ni and pb concentrations were not affected