microbe clay mineral interactions clays and clay minerals are common components in soils sediments and sedimentary rocks and they play an important role in many environmental processes iron is ubiquitous in clays and clay minerals and its oxidation state in part controls the physical and chemical properties of these fine grained minerals the structural ferric iron in clay minerals can be reduced either chemically or biologically biological reductants include mesophilic and thermophilic microorganisms from diverse environments such as soils sediments sedimentary rocks and hydrothermal hot springs multiple clay minerals have been used for microbial reduction studies including dioctahedral smectiteillite series palygorskite chlorite and their various mixtures in natural soils and sediments all of these clay minerals are reducible by microorganisms under various conditions with smectite nontronite being the most reducible and illite the least the rate and extent of bioreduction depends on many experimental factors such as the type of microorganisms and clay minerals solution chemistry and temperature despite significant efforts current understanding of the mechanisms of microbial reduction of ferric iron in clay minerals is still limited whereas some studies have presented evidence for a solid state reduction mechanism others argue that the clay mineral structure partially dissolves when the extent of reduction is high this inconsistency may be related to several experimental conditions and their specific effects are discussed in this paper whereas past experiments have been largely conducted in well controlled laboratory systems recent efforts have attempted to transfer knowledge to the field to improve our understanding of more complex soil systems for better agricultural practices biologically reduced clay minerals are also important agents in remediating inorganic and organic contaminants in soil and groundwater systems this paper reviews the most recent developments and suggests some directions for future research

seismic interaction and delayed triggering along the north anatolian fault 1 the deformation of northwestern turkey is the result of the encounter of the westward extrusion of the anatolian plate with the north south extension of the aegean domain while the north anatolian fault localizes the former type of deformation and has been the site of more large earthquakes 9 events of magnitude 7 than any other continental fault over the past 100 years the extension is diffuse and is characterized by spatial clusters of smaller earthquakes and near continuous activity we study the evolution of seismicity along the fault and in the clusters neighboring the fault before and after the two large earthquakes of 1999 we observe that the un ruptured section of the fault and the extension clusters respond very differently to the earthquakes while significant aftershock activity on the fault segments adjacent to the rupture only occurs at relatively short distance from the rupture 30 km the clusters can be activated at much larger distances 300 km remarkably their triggering is not immediate after the earthquake but is delayed in time their peak seismic activation may occur weeks or months after the earthquake this distant and delayed triggering which is consistent with recent gps observations may help resolve some of the previously unexplained characteristics of the 1939 1999 sequence of large earthquakes along the fault

dynamics of izmit earthquake postseismic deformation and loading of the duzce earthquake hypocenter we have developed dynamic finite element models of izmit earthquake postseismic deformation to evaluate whether this deformation is better explained by afterslip via either velocity strengthening frictional slip or linear viscous creep or by distributed linear viscoelastic relaxation of the lower crust we find that velocity strengthening frictional afterslip driven by coseismic shear stress loading can reproduce time dependent global positioning system data better than either linear viscous creep on a vertical shear zone below the rupture or lower crustal viscoelastic relaxation our best frictional afterslip model fits the main features of postseismic slip inversions in particular high slip patches at and below the hypocenter and on the western karadere segment and limited afterslip west of the hersek delta burgmann et al 2002 the model requires a weakly velocity strengthening fault that is either low effective normal stress in the slipping regions or a smaller value for the parameter describing rate dependence of friction a b than is indicated by laboratory experiments our best afterslip model suggests that the coulomb stress at the duzce hypocenter increased by 0 14 mpa 1 4 bars during the izmit earthquake assuming right lateral slip on a surface dipping 50 to the north and by another 0 1 mpa during the 87 days between the izmit and duzce earthquakes in the marmara sea region within about 160 km of the izmit earthquake rupture this model indicates that the coulomb stresses increased by 15 25 of the coseismic amount during the first 300 days after the earthquake three hundred days after the earthquake postseismic contributions to coulomb stressing rate on the maramara region faults had fallen to values equal to or less than the inferred secular stress accumulation rate our estimates of postseismic coulomb stress are highly model dependent in the marmara region the linear viscous shear zone and viscoelastic lower crust models predict greater postseismic coulomb stresses than the frictional afterslip model near field stress and fault zone rheology estimates are sensitive to the earth9s elastic structure when a layered elastic structure is incorporated in our model it yields a coulomb stress of 0 24 mpa at the duzce hypocenter significantly more than the 0 14 mpa estimated from the uniform elastic model because of the higher near field coseismic stresses the layered elastic model requires a higher value of velocity strengthening parameter a b a b times effective normal stress r to produce comparable postseismic slip a b is estimated at 0 4 and 0 2 mpa respectively for the layered and uniform elastic models these results highlight the importance of understanding the earth9s elastic structure and the mechanism for postseismic deformation if we wish to accurately model coseismic and postseismic crustal stresses

the seismicity in the eastern marmara sea after the 17 august 1999 izmit earthquake we used seismic stations that we deployed after the izmit earthquake along the shores and islands of the izmit bay cinarcik basin to study the seismic activity that took place after the earthquake in the eastern marmara sea the aftershock distribution indicates the existence of three clusters of activity there in the days that followed the earthquake one of the clusters shows the extension of the e w trending izmit rupture into the eastern marmara sea the seismic activity there clearly outlines the fault plane of the main rupture and shows its termination 35 km beyond the hersek peninsula two other clusters of activity are present in the region one is in the armutlu peninsula and the other one is located a few kilometers southwest of the tuzla peninsula beneath the northern slope of the cinarcik basin the focal mechanism solutions indicate strike slip faulting along the main branch of the izmit rupture and normal faulting within the two swarms the presence of the different mechanisms suggests the existence of slip partitioning in the region a remarkable feature of the aftershock data is the absence of seismicity above 4 km in the marmara sea manuscript received 30 august 2000

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

link between coulomb stress changes and seismic activation in the eastern marmara sea after the 1999 izmit turkey earthquake 1 we investigate the effect of dynamic and static stress changes produced by the 1999 izmit earthquake on four preexisting seismic clusters located in the eastern marmara sea beyond the western termination of the earthquake rupture these four clusters show long lasting modifications in their seismicity rate we observe that these seismic activity variations are related to stress changes dynamic stress pulses activate strike slip faulting instantaneously but in the absence of a concomitant static coulomb stress increase this activation is short lived indeed a large dynamic stress combined with a negative static coulomb stress may result in an immediate activation followed by the occurrence of a seismicity shadow in contrast the activation of extensional clusters begins slowly and takes a few days to fully develop it is also remarkably long lasting and does not follow a classical omori decay more than 10 years after the earthquake the extensional clusters located near the termination of the rupture where static stress and pressure changes were high are still activated

postseismic deformation induced by brittle rock damage of aftershocks 1 large earthquakes are commonly followed by abundant aftershocks that are densely located around the coseismic rupture zone laboratory experiments indicate that microscopic brittle rock failures acoustic emission are associated collectively with a macroscopic damage related inelastic relaxation utilizing basic relations between local brittle failures and gradual inelastic strain in a viscoelastic damage rheology model we develop connections between aftershock decay rates and the aftershocks induced component of geodetic deformation the discussed mechanism is relevant for postseismic relaxation produced by sources located within the seismogenic zone and especially in regions that overlap locations of high aftershocks activity assuming the omori utsu decay rate for aftershocks we find that the temporal decay of the damage related postseismic relaxation follows a generalized power law relation with the standard omori utsu law as a limit case the results provide a way for estimating the separate contributions to observed postseismic displacements that stem from brittle failures in the seismogenic zone aftershocks and other aseismic processes using the obtained theoretical expectations we analyze postseismic displacements measured by gps stations around the north anatolian fault 3 months following the 1999 m7 4 izmit earthquake we find that the observed postseismic displacements decay slower than the aftershock seismicity based on our theoretical results we conclude that up to 50 of the measured surface displacements at near fault sites can be attributed to aftershock induced inelastic deformation in the seismogenic zone the remainder postseismic deformation can generally be explained by relaxation in the deeper ductile substrate

evolution of the seismicity in the eastern marmara sea a decade before and after the 17 august 1999 izmit earthquake we review the long term evolution of seismicity in the eastern marmara sea over a decade before and after the 1999 mw 7 6 izmit earthquake we analyze large scale space time variations of seismicity in the region and illustrate the impact of the recent large strike slip earthquakes on the background activity composed of distinct pre existing seismic clusters two types of aftershocks activity are observed the first type of enhancement is on strike slip fault segments izmit fault princes island section of the main marmara fault gemlik fault immediately following the main shock and related to coulomb stress transfer the second type of enhancement is attached to extensional clusters yalova tuzla with a few days delay in the onset of strong activation probably related to pore pressure increase we observe a fast decay of the activity on strike slip segments and slower evolution of seismic clusters with extensional features two years after the izmit earthquake seismic activity returned to the pre earthquake pattern with most of the activity occurring within extensional clusters it appears that the influence of the last large strike slip event on the spatial seismicity distribution in the eastern marmara sea is less significant than the effect of the long term regional extension

measuring the heterogeneity of the coseismic stress change following the 1999 mw7 6 chi chi earthquake seismicity quiescences are expected to occur in places where the stress has been decreased in particular following large main shocks however such quiescences can be delayed by hours to years and be preceded by an initial phase of earthquake triggering this can explain previous analyses arguing that seismicity shadows are rarely observed since they can only be seen after this triggering phase is over such is the case of the main rupture zone which experiences the strongest aftershock activity despite having been coseismically unloaded by up to tens of bars the 1999 m w 7 6 chi chi taiwan earthquake is characterized by the existence of several such delayed quiescences especially off the chelungpu fault on which the earthquake took place we here investigate whether these delays can be explained by a model of heterogeneous static stress transfer coupled with a rate and state friction law we model the distribution of coseismic small scale stress change by a gaussian law with mean tau bar and standard deviation the latter measures the level of local heterogeneity of the coseismic change in stress the model is shown to mimic the earthquake time series very well robust inversion of the tau bar and parameters can be achieved at various locations although on fault seismicity has not been observed for a sufficiently long time to provide more than lower bounds on those estimates for the chelungpu fault several quiescences have delays that can be well explained by local stress heterogeneity even at relatively large distances from the chi chi earthquake

a note on seismic activity near the eastern termination of the izmit rupture in the hours preceding the duzce earthquake we use continuous recordings at four stations installed near the eastern termination of the izmit rupture to analyze the seismic activity there during the 5 hr leading to the duzce earthquake the records clearly show the presence of three groups of events one of the groups originates from the middle of the izmit rupture and consists of aftershocks of the m 5 7 spanca lake earthquake that had occurred a day earlier and was itself to date the second largest aftershock in the izmit sequence a second group of events is spread over the 30 km long eastern karadere segment of the izmit rupture and a comparison with the number of aftershocks expected based on decay laws for similar sequences in other regions suggests that seismic activity was high on the eastern segment in the hours leading to the duzce earthquake the third group of events occurs beyond the termination of the izmit rupture and clusters around the hypocenter of the duzce earthquake it shows that in the little over 5 hr leading to the duzce earthquake this destructive event was preceded by six precursory shocks ranging in magnitude from 0 9 to 2 6 manuscript received 30 august 2000

rupture process of the 1999 november 12 duzce turkey earthquake deduced from strong motion and global positioning system measurements summary we use the strong motion data recorded at near fault accelerometers combined with global positioning system gps measurements to infer the space and time evolution of the mw 7 2 1999 november 12 duzce turkey earthquake we confirm that the rupture is subshear towards the west whereas it overpassed the shear speed towards the east the mechanism of the earthquake is predominantly right lateral on a 65 north dipping fault the strike slip we infer represents at least 75 of the total seismic moment we stress that the use of strong motion data allows us to constrain a strong spatial variation of the slip direction during faulting to the west of the hypocentral region the slip is oblique accompanied by a significant normal component in the central and eastern part of the activated fault the slip is almost pure right lateral this result is consistent both with the surface offset observations and with the long term morphology of the fault neither strong motion data nor gps data can resolve the complexity of the eastern termination of the duzce rupture

spatial variation of aftershock activity across the rupture zone of the 17 august 1999 izmit earthquake turkey we examined the spatial variation in the aftershock activity from the 17 august 1999 izmit turkey earthquake we found that this aftershock sequence is non uniform both in space and time aspects that need to be taken into account in any further statistical analysis other aspects of this aftershock sequence are similar to other aftershock sequences namely low b values and a high degree of spatial variation we have detected three zones of relatively high b values two of which coincide with asperities revealed by previous slip inversion studies the third zone with an anomalous b value is located beyond the fault rupture and indicates a weakened fractured zone in the yalova tuzla area this b value analysis provided no evidence for any significant difference that may exist between the two sides of the mainshock fault plane d 2004 elsevier b v all rights reserved

triggering of seismicity at short timescales following californian earthquakes 1 a method for measuring seismicity rate changes caused by the occurrence of major earthquakes in the surrounding crust is proposed it is based on a nonstationary poisson modeling of earthquake activity an estimate of the seismicity rate change and a probability measure of seismicity triggering following a large shock are derived and the removal of the influence of independent aftershock sequences of other nearby previous earthquakes is attempted without using more traditional declustering techniques the seismicity rate change estimator is corrected for its natural bias in favor of positive changes at short timescales that has so far strongly hindered measures of seismicity quiescences three californian earthquakes are examined using this method the 1989 m7 1 loma prieta the 1992 m7 3 landers and the 1994 m6 7 northridge earthquakes positive triggering is very commonly observed as expected but quiescence is however more seldomly obtained for timescales up to 100 days after the main shock this relative absence of quiescence as compared to typical predictions of coulomb modeling for example is also independently observed through direct correlation analyses of californian seismicity the possibility that the stresses caused by the main shock are spatially highly variable may explain these observations

monitoring aseismic forcing in fault zones using earthquake time series the dynamics of earthquake occurrences is controlled both by fault in teraction processes and by long term tectonic loading of the faults in addition tran sient loading can be caused by aseismic deformation episodes for example during crustal fluid migration or slow slip events these forcing transients are best revealed by geodetic measurements however this type of instrumentation is not always avail able or is not always sensitive enough to detect significant anomalies in such cases one is better off exploiting the seismicity signature of these transients in order to char acterize them we here explore different ways to do so interearthquake time statistics are found to be prone to damping out fluctuations in forcing rate a more accurate method is developed by comparing the data with a triggering model that accounts for earthquake interactions the changes in fault loading rates are then well recovered both in duration and in intensity

geochemical balance of lateritization processes and climatic signatures in weathering profiles overlain by ferricretes in central africa a simple geochemical balance of lateritization processes governing the development of several tens of meters of weathering profiles overlain by ferricretes is estimated on the basis of detailed mineralogical and geochemical data the lateritic weathering mantle of the haut mbomou area in central africa is composed of different weathering layers described from the base to the top of vertical profiles as a saprolite a mottled clay layer a soft nodular layer a soft ferricrete and a ferricrete in which kaolinite gibbsite goethite and hematite occur in various quantities incongruent dissolution of kaolinite leads to the formation of gibbsite in the upper saprolite whereas the hematite does not clearly replace the kaolinite according to an epigene process in the upper ferruginous layers of the profiles instead that kaolinite is also transformed into gibbsite according to an incongruent dissolution under hydrated and reducing conditions induced by a relatively humid climatic pattern the respective relations of the silica iron and aluminum balances and the al substitution rate of the hematite on the one hand and of rhg rhg 100 hematite hematite goethite and the kaolinite on the other hand to the consumption or the release of protons h permit differentiation of aggrading ferruginization and degradation processes operating in the different lateritic weathering profiles the al substitution rate of the fe oxyhydroxides varies according to the nature of lateritization processes e g saprolitic weathering and aggrading ferruginization vs degradation the observations and results indicate that the ferruginization process of the weathering materials of parent rocks is not a simple ongoing process as often thought this suggests that the actual lateritic weathering mantle of the haut mbomou area may result from different stages of weathering and erosion during climatic changes

perturbation of the izmit earthquake aftershock decaying activity following the 1999 mw 7 2 duzce turkey earthquake triggering and quiescence patterns of seismicity in western turkey following the occurrence of the 12 november 1999 m w 7 2 duzce earthquake are investigated the changes in seismicity rate are analyzed along the north anatolian fault segments that had ruptured 3 months earlier during the 17 august 1999 m w 7 4 izmit earthquake detection of triggering and quiescence is done by comparing the seismicity rate that would be expected if the duzce earthquake had not happened to the actual observed rate the expected rates are estimated by extrapolating the preexisting seismicity pattern using two complementary models a simple omori utsu s law and the etas model fault segments located to the east of the izmit epicenter show a mild case of quiescence following the duzce earthquake these segments had previously experienced an anomalous triggering episode in the 5 days preceding the duzce earthquake correlated with the occurrence of two strong m w 5 izmit aftershocks however it is not clear whether this observed quiescence is real or spurious as it coincides with a local reconfiguration of the seismological network a temporary increase of 0 1 to 0 15 in completeness magnitude would be enough to explain this apparent deactivation fault segments located to the west of the izmit epicenter exhibit triggering of seismicity following the duzce earthquake this observed triggering is mostly restricted to a cluster of events located in the geothermal area of yalova the increase of seismicity rate is delayed by 18 hours after the waves travelling from the duzce rupture had hit this zone our analysis suggests that this 15 day long reactivation can be explained by a short lived perturbation the local seismic activity then sustaining itself for the remaining 15 days we argue that this particular behavior is likely to correspond to a case of dynamic triggering by the end of year 1999 the yalova cluster shows a significant quiescence that lasted for several months this shutting down does not coincide with the occurrence of any local earthquake that would be large enough to stress shadow this area suggesting an aseismic cause to this pattern these results highlight the fact that 1 seismicity triggered by a major earthquake is not restricted to areas loaded by static stress and 2 that seismic activity associated with geothermal geological settings is highly sensitive to stress perturbations but also to aseismic processes that can both delay reactivation and cause this activity to suddenly decrease

stress interactions of three moderate size earthquakes in afyon southwestern turkey abstract we analyze three moderate size earthquakes occurred in the afyon region of southwestern turkey on december 15 2000 m w 6 0 and february 3 2002 m w 6 5 and m w 5 8 this earthquake sequence took place on the sultandag fault having dominantly normal faulting mechanisms with different orientations in an extensional tectonic regime we relocate these mainshocks and their large aftershocks and use the waveform data to determine the rupture dimensions and directivities we carry out both static and dynamic stress analysis to investigate stress interactions and possible earthquake triggering mechanisms in this sequence we show that the 2002 m w 6 5 rupture started at the termination of the 2000 m w 6 0 earthquake where the calculated coulomb stress changes increased more than 0 5 bar thus we conclude that the coseismic stress increase by the 2000 event favored the nucleation and promoted the timing of the 2002 event an intense seismic activity identified as the kizildag aftershock zone developed following both of the large mainshocks where the third largest earthquake m w 5 8 of the sequence occurred 2 h after the 2002 m w 6 5 mainshock the coulomb stress calculations of the 2000 earthquake shows no influence in this zone while the static coulomb stress changes due to the 2002 m w 6 5 mainshock raised the coulomb stresses an additional 0 3 0 7 bar in the kizildag aftershock zone thus we infer that such changes in the coulomb stresses positively influence the occurrence of the aftershocks in this zone since the kizildag aftershock zone takes place in a geothermal area we compute dynamic stress changes imposed by the 2000 and 2002 mainshocks the computed peak dynamic stress levels for both mainshocks are found much higher than the static stress changes calculated within the kizildag aftershock zone thus we propose that transient stress triggering most likely involving elevated fluid pressures in the hydrothermal systems present in this region may have played a major role in the initiation of increased seismicity followed by local multiple elastic stress triggering leading to the further development of aftershocks and the occurrence of the m w 5 8 mainshock

a hypothesis for delayed dynamic earthquake triggering 1 it s uncertain whether more near field earthquakes are triggered by static or dynamic stress changes this ratio matters because static earthquake interactions are increasingly incorporated into probabilistic forecasts recent studies were unable to demonstrate all predictions from the static stress change hypothesis particularly seismicity rate reductions however current dynamic stress change hypotheses do not explain delayed earthquake triggering and omori s law here i show numerically that if seismic waves can alter some frictional contacts in neighboring fault zones then dynamic triggering might cause delayed triggering and an omori law response the hypothesis depends on faults following a rate state friction law and on seismic waves changing the mean critical slip distance dc at nucleation zones

delayed seismicity rate changes controlled by static stress transfer on 15 june 2010 a m w5 7 earthquake occurred near ocotillo california in the yuha desert this event was the largest aftershock of the 4 april 2010 m w7 2 el mayor cucapah emc earthquake in this region the emc mainshock and subsequent ocotillo aftershock provide an opportunity to test the coulomb failure hypothesis cfs we explore the spatiotemporal correlation between seismicity rate changes and regions of positive and negative cfs change imparted by the ocotillo event based on simple cfs calculations we divide the yuha desert into three subregions one triggering zone and two stress shadow zones we find the nominal triggering zone displays immediate triggering one stress shadowed region experiences immediate quiescence and the other nominal stress shadow undergoes an immediate rate increase followed by a delayed shutdown we quantitatively model the spatiotemporal variation of earthquake rates by combining calculations of cfs change with the rate state earthquake rate formulation of dieterich 1994 assuming that each subregion contains a mixture of nucleation sources that experienced a cfs change of differing signs our modeling reproduces the observations including the observed delay in the stress shadow effect in the third region following the ocotillo aftershock the delayed shadow effect occurs because of intrinsic differences in the amplitude of the rate response to positive and negative stress changes and the time constants for return to background rates for the two populations we find that rate state models of time dependent earthquake rates are in good agreement with the observed rates and thus explain the complex spatiotemporal patterns of seismicity

slip distribution and stress changes associated with the 1999 november 12 duzce turkey earthquake mw 7 1 the 1999 november 12 duzce earthquake m w 7 1 was apparently the eastward extension of the august 17 izmit earthquake m w 7 4 the duzce event caused heavy damage and fatalities in the cities of duzce and bolu here a finite fault inversion method with five discrete time windows is applied to derive the co seismic slip distribution of the duzce earthquake the fault plane is best modelled as a 40 x 20 km 2 plane with a strike of 262degrees and a dip of 65degrees to the north and that the majority of slip occurred in two distinct patches on either side of the hypocentre implying bilateral rupture the possible triggering of this event by the izmit earthquake is investigated using coulomb stress modelling of all large events since 1943 with the inclusion of secular loading the results show that although the duzce rupture plane was in a stress shadow prior to the izmit earthquake that event caused a significant coulomb stress load taking the duzce fault out of the stress shadow which probably precipitated failure a comparison of the mapped coulomb stress change with the inferred slip shows no correlation between the two finally the stress modelling indicates that the northern branch of the north anatolian fault zone beneath the sea of marmara towards the city of istanbul is presently the most highly loaded segment of the north anatolian fault zone

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

response of seismicity to coulomb stress triggers and shadows of the 1999 mw 7 6 chi chi taiwan earthquake 1 the correlation between static coulomb stress increases and aftershocks has thus far provided the strongest evidence that stress changes promote seismicity a correlation that the chi chi earthquake well exhibits several studies have deepened the argument by resolving stress changes on aftershock focal mechanisms which removes the assumption that the aftershocks are optimally oriented for failure here one compares the percentage of planes on which failure is promoted after the main shock relative to the percentage beforehand for chi chi we find a 28 increase for thrust and an 18 increase for strike slip mechanisms commensurate with increases reported for other large main shocks however perhaps the chief criticism of static stress triggering is the difficulty in observing predicted seismicity rate decreases in the stress shadows or sites of coulomb stress decrease detection of sustained drops in seismicity rate demands a long catalog with a low magnitude of completeness and a high seismicity rate conditions that are met at chi chi we find four lobes with statistically significant seismicity rate declines of 40 90 for 50 months and they coincide with the stress shadows calculated for strike slip faults the dominant faulting mechanism the rate drops are evident in uniform cell calculations 100 month time series and by visual inspection of the m 3 seismicity an additional reason why detection of such declines has proven so rare emerges from this study there is a widespread increase in seismicity rate during the first 3 months after chi chi and perhaps many other main shocks that might be associated with a different mechanism

pre weichselian quaternary glaciations of the british isles the netherlands norway and adjacent marine areas south of 68 n implications for long term ice sheet development in northern europe within this paper we review the pre weichselian glacial history of northern europe focussing on evidence from the british isles netherlands norway and adjacent marine areas that record the activity of the british bis and scandinavian sis ice sheets the objective of the paper is to examine the long term evolution of the two ice sheets in order to determine their level of synchronicity and their relationship to the plio pleistocene record of northern hemisphere glaciation geological evidence demonstrates striking long term similarities between the behaviour of the bis and sis with a step wise intensification in the glacial signal 1 first ice rafted debris ird input onto the continental margin at ca 2 7 2 6 ma and restricted glaciation prior to ca 1 1 ma 2 initiation of more lowland style glaciation from 1 1 ma 3 repeated shelf edge glaciations from 0 45 ma these steps coincide with a major intensification of the northern hemisphere climate signal at the beginning of the quaternary and the mid pleistocene transition temporal and spatial variabilities in the behaviour of different sectors of the bis and sis appear to reflect regional scale geographic latitude elevation climatic moisture temperature and glaciological deformable beds controls that modulate the build up of ice volume in the main ice accumulation areas relative to global climate forcing and its subsequent lateral expansion 2010 nerc

the 1997 kagoshima japan earthquake doublet a quantitative analysis of aftershock rate changes we quantitatively map relative rate changes for the aftershock sequence following the second mainshock of the 1997 earthquake doublet m w 6 1 m w 6 0 in the kagoshima province japan using the spatial distribution of the modified omori law parameters for aftershocks that occurred during the 47 8 days between the two mainshocks we forecast the aftershock activity in the next 50 days and compare it to the actually observed rates the relative rate change map reveals four regions with statistically significant relative rate changes three negative and one positive our analysis suggests that the coseismic rate changes for off fault aftershocks could be explained by changes in static stress however to explain the activation and deactivation of on fault seismicity other mechanism such as unusual crustal properties and the presence of abundant crustal fluids are required

toggling of seismicity by the 1997 kagoshima earthquake couplet a demonstration of time dependent stress transfer 1 two m 6 well recorded strike slip earthquakes struck just 4 km and 48 days apart in kagoshima prefecture japan in 1997 providing an opportunity to study earthquake interaction aftershocks are abundant where the coulomb stress is calculated to have been increased by the first event and they abruptly stop where the stress is dropped by the second event this ability of the main shocks to toggle seismicity on and off argues that static stress changes play a major role in exciting aftershocks whereas the dynamic coulomb stresses which should only promote seismicity appear to play a secondary role if true the net stress changes from a sequence of earthquakes might be expected to govern the subsequent seismicity distribution however adding the stress changes from the two kagoshima events does not fully capture the ensuing seismicity such as its rate change temporal decay or migration away from the ends of the ruptures we therefore implement a stress transfer model that incorporates rate state friction in which seismicity is treated as a sequence of independent nucleation events that are dependent on the fault slip slip rate and elapsed time since the last event the model reproduces the temporal response of seismicity to successive stress changes including toggling decay and aftershock migration nevertheless the match of observed to predicted seismicity is quite imperfect due perhaps to inadequate knowledge of several model parameters however to demonstrate the potential of this approach we build a probabilistic forecast of larger earthquakes on the expected rate of small aftershocks taking advantage of the large statistical sample the small shocks afford not surprisingly such probabilities are highly time and location dependent during the first decade after the main shocks the seismicity rate and the chance of successive large shocks are about an order of magnitude higher than the background rate and are concentrated exclusively in the stress triggering zones

earthquake triggering by static and dynamic stress changes 1 in this study we aim to understand the effect of static and dynamic stress changes in promoting earthquake failures on secondary faults toward this goal we solve the equation of motion of a spring slider dynamic system including inertia and using rate and state dependent constitutive laws we separately investigate the dynamic response of this fault analog system to a sudden stress change represented either as a stress step or as a stress pulse which are used to model permanent static and transient dynamic stress perturbations the induced earthquake failure does not occur immediately at the application of the coseismic stress change but it is delayed in time we define this time interval as the triggering delay for a given stress perturbation we analyze the dependence of triggering delays on different system conditions and constitutive parameters our results clearly show that the effects of static and dynamic stress changes are quite different while a static stress change is able to advance as well as to delay an induced instability depending on its sign a dynamic stress pulse is only able to promote a nearly instantaneous failure provided its amplitude is positive and large enough with respect to the direct effect of friction in other words dynamic stress changes can only cause nearly instantaneous failures without any relevant triggering delay these results should be considered in interpreting the seismicity rate changes caused by large earthquakes at least as long as seismic events are interpreted as sliding instabilities obeying rate and state dependent friction laws

detection of anomalous seismicity as a stress change sensor 1 anomalous seismicity such as quiescence and activation is defined by a systematic deviation of seismic activity from the predicted rate by the epidemic type aftershock sequence etas model that represents the normal occurrence rate of earthquakes in a region indicating the empirical triggering effect by the previous events the model is fitted to a data set of origin times and magnitudes of earthquakes or aftershocks during may august 2003 in and around northern japan the detected quiescence and activation relative to the predicted seismicity rate are consistent with the coseismic changes of coulomb failure stress cfs in the corresponding regions transferred from certain strong earthquakes few results in this paper agree with the claim that there should be a threshold value of cfs capable of affecting seismic changes thus we expect that significant deviation of actual activity from the predicted rates is sensitive enough to detect a slight stress change furthermore i offer a similar interpretation of the detected seismicity lowering relative to the modeled rates preceding the strong earthquakes assuming some aseismic slips

neodymium and strontium isotopic constraints on soil sources in barbados west indies abstract neodymium and strontium isotopic compositions and sm nd ratios are used to constrain the sources of silicate rich soils developed on uplifted pleistocene coral reef limestones on barbados west indies the geographic and geologic setting of barbados facilitates the application of these tracers to the evaluation of the following soil sources 1 pleistocene reef limestone regolith 2 tertiary carbonate rocks sandstones and mudstones that are exposed in northeastern barbados 3 volcanic ash erupted from the lesser antilles arc 4 saharan dust transported by trade winds and 5 fertilizer the soils have nd values that range from 6 6 to 1 9 87 sr 86 sr values of 0 70890 to 0 71067 and sm nd ratios of 0 223 0 260 the pleistocene limestone component is the most significant source of sr in the soils and a negligible source of nd comparison of sm and nd concentrations and neodymium isotopic compositions of soil samples that are weathered to varying extents indicates that sm and nd are relatively unfractionated and retained in the soils during weathering nd and sm nd variations in the soils therefore primarily reflect the compositions and proportions of the silicate sources mass balance calculations based on sm nd systematics require that the silicate soil components contain between 30 85 volcanic ash with the remaining silicate fraction comprised of old continentally derived sediment in contrast to sm and nd sr is mobilized and removed from the soils during weathering strontium from volcanic and carbonate sources is preferentially removed relative to continental silicate sources the strontium isotopic compositions of the soils therefore reflect the combined effects of the degree of weathering and the compositions and proportions of the soil sources mass balance calculations indicate that at least 35 60 of the initial sr in the soils has been removed by weathering these results illustrate 1 the utility of radiogenic isotopes in identifying and quantifying soil sources and weathering processes 2 the compositional influence of numerous sources on soils even those developed in a relatively isolated area such as barbados and 3 the domination of barbados soil sm nd systematics by nonregolith eolian components

earthquake hazard after a mainshock in california after a strong earthquake the possibility of the occurrence of either significant aftershocks or an even stronger mainshock is a continuing hazard that threatens the resumption of critical services and reoccupation of essential but partially damaged structures a stochastic parametric model allows determination of probabilities for aftershocks and larger mainshocks during intervals following the mainshock the probabilities depend strongly on the model parameters which are estimated with bayesian statistics from both the ongoing aftershock sequence and from a suite of historic california aftershock sequences probabilities for damaging aftershocks and greater mainshocks are typically well constrained after the first day of the sequence with accuracy increasing with time

aftershocks halted by static stress shadows the role of permanent versus transient crustal stress changes in triggering earthquakes is debated analysis of the stress imparted by the joshua tree and nearby landers earthquakes in california in 1992 implies that a permanent drop in stress can halt aftershocks so such static stress changes should be incorporated into seismic hazard assessments

a statistical space time magnitude analysis on the aftershocks occurrence of the july 21th 2017 mw 6 5 bodrum kos turkey earthquake abstract in this study a detailed space time magnitude assessment on the aftershock sequence of july 21th 2017 mw 6 5 bodrum kos earthquake turkey is carried out by focusing on the analyses of aftershock parameters b value p value dc value and mamax b value is estimated as 0 90 0 05 with a completeness magnitude mc 1 6 and this relatively small b value may be resulted from the abundance of aftershocks with magnitude ml 4 0 however it is well represented by the gutenberg richter law with a typically b 1 0 p value is estimated as 1 04 0 02 with a c value 0 224 0 039 and is well characterized nearly close to the global p 1 0 this relatively high p value may be a result of the relative fast decay rate of the aftershock activity dc value is calculated as 1 74 0 09 and it means that aftershocks are homogeneously distributed temporal distribution of b value shows that small b values may be due to a stepwise increase in effective stress before the occurrence of larger aftershocks regional changes range from 0 5 to 1 2 in b value from 0 4 to 1 3 in p value and from 3 0 to 5 2 in mamax the smallest b values are found in and around mainshock including karaada bodrum akyarlar and turgutreis and these regions have high stress as well as coseismic deformation the largest p values are found in and around the mainshock epicenter including karaada and it is interpreted that this situation may be caused by coseismic deformation mamax values larger than 4 4 are observed in and around mainshock epicenter including bodrum and akyarlar and there is a clear correlation between spatial variations of b values and mamax these results show that stress changes and coseismic deformation seem highly effective on b and p value variations therefore a special interest needs to be given to these anomaly regions since aftershock hazard is highly associated with these parameters and may be developed considering their space time magnitude distribution

stress coupling between earthquakes in northwest turkey and the north aegean sea we have investigated the coulomb stress interactions of 29 earthquakes m s greater than or equal to 6 0 that have occurred in the region of northwest turkey and north aegean sea since 1912 of these events 23 may be related to earlier events and 16 are clearly related to earlier events all events after 1967 are related to previous events events in the early part of our time interval that show no correlation could be related to historical events as yet unidentified in some cases faults that have received a stress reduction from earlier events are prepared for an event by an earthquake occurring a few years before that creates a local coulomb stress rise thus regions of coulomb stress shadow can become regions where a damaging earthquake may occur the relation between smaller events and the coulomb stress distribution is less clear but may be related to poor data quality and practical limitations of our modeling technique nonetheless there are 4 times as many events per unit area in regions of enhanced stress than where stress is reduced we discuss the contemporary distribution of coulomb stress and argue that it is possible to identify the likely locations of future damaging earthquakes including identifying the most likely candidate faults

microorganism induced weathering of clay minerals in a hydromorphic soil abstract in order to improve the understanding of factors influencing weathering in hydromorphic soils the clay mineral and chemical compositions iron hydr oxides organic compounds and sr and nd isotopic compositions of hydromorphic soils on the banks of the liangzi lake hubei province south china were investigated the b horizon in the lower profile exhibits a distinct net like pattern with abundant short white veins within the red brown matrix their various 87sr 86sr and 143nd 144nd isotopic compositions showed only small variations of 0 7270 0 7235 and 0 51200 0 51204 respectively consistent with the composition of yangtze river sediments indicating that the soils were all derived from alluvium from the catchment the white veins contained notably more sio2 al2o3 tio2 and mobile elements relative to the red brown matrix while they both showed similar values for the chemical index of alteration of 86 7 and 87 1 respectively and displayed similar degrees of weathering the clay minerals in a ae and e horizons of the soil profile were illite kaolinite and mixed layer illite smectite these same three clay minerals comprised the white net like veins in the soil b horizon whereas only illite and kaolinite were observed in the red brown matrix iron hydr oxides in a ae and e horizons of the soil profile were hematite and goethite whereas in the red brown matrix of the b horizon they were hematite goethite and ferrihydrite different organic compounds were observed for the white vein and the red brown matrix in the soil b horizon an 18 2 fatty acid biomarker for fungi in the net like vein but not in the red brown matrix compared with the red brown matrix the white net like vein also clearly contained more mono unsaturated fatty acids which are sometimes associated with bacteria that have the capacity to reduce fe iii thus migration of iron and the formation of the net like veins involved the participation of biota during the hydromorphic pedogenesis process as ferrihydrite is usually formed with the assistance of biota redoximorphic processes will chemically affect phyllosilicates by changing their charge and fe iii in illite may serve as electron acceptor for fe iii reducing microorganisms this leads to an increase in negative charge in the illite structure which could be neutralized by electrostatic displacement of interlayer cations and adsorption of protons thereby promoting transformation of illite to mixed layer illite smectite and dissolution of the pre existing illite mineral our results suggest that microorganisms brought about iron leaching and dominated the alteration of clay minerals by redox processes and different mineral volumes formed in the net like b horizon of the hydromorphic soil were attributed to the microorganism induced weathering process

methods for measuring seismicity rate changes a review and a study of how the m w 7 3 landers earthquake affected the aftershock sequence of the m w 6 1 joshua tree earthquake the development of fault interaction models has triggered the need for an accurate estimation of seismicity rate changes following the occurrence of an earthquake several statistical methods have been developed in the past to serve this purpose each relying on different assumptions e g stationarity gaussianity pertaining to the seismicity process

time dependent distributed afterslip on and deep below the izmit earthquake rupture surface deformation transients measured with the global positioning system during the 87 days between the 17 august 1999 izmit earthquake and the 12 november 1999 duzce earthquake indicate rapidly decaying aseismic fault slip on and well below the coseismic rupture elastic model inversions for time dependent distributed fault slip using a network inversion filter approach show that afterslip was highest between and below the regions of maximum coseismic slip and propa gated downward to or even below the base of the crust maximum afterslip rates decayed from greater than 2 m yr immediately after the i zmit earthquake to about 1 2 m yr just prior to the duzce earthquake maximum afterslip occurred below the eastern karadere rupture segment and near the i zmit hypocenter afterslip in the upper 16 km decayed more rapidly than that below the seismogenic zone these observations are consistent with a phase of rapid aseismic fault slip concentrated near the base of the seismogenic zone continued loading from the rapid deep afterslip along the eastern rupture zone is a plausible mechanism that helped trigger the nearby mw 7 2 12 november duzce earthquake

low temperature illitization of smectite in the late eocene and early oligocene of the isle of wight hampshire basin u k variegated palaeosols which formed from weathering of clays silts and brackish to freshwater limestones are present in the late eocene early oligocene solent group of the hampshire basin southern u k the detrital clay mineral suite is dominated by illite and illite smectite with minor kaolinite and chlorite in pedogenically modified palaeosol and evaporitic lacustrine clay rich sediments the proportion of illite in the illite smectite is greater than in the non pedogenically modified sediments and where alteration is most intense kaolinite and chlorite are absent the smectite to illite transition has been investigated in the 0 5 m fraction by xrd analysis powder and oriented mounts thermogravimetry tg analytical sem and chemical analysis of fe2 modeling of xrd data reveals that the illite smectite is a mixture of compositions overall 60 95 illite r 0 with high rotational stacking disorder dehydroxylation occurs mainly at 500 c but also at higher temperatures indicating heterogeneous octahedral cation composition analytical sem and chemical analysis of fe2 indicate that the illite to smectite transition occurs through fe reduction in octahedral sites leading to increased layer charge coupled with k fixation the driving mechanism for what appears to be irreversible fe3 reduction is wetting reducing and drying oxidizing cycles in gley soil in which reoxidation of reduced fe is never complete

seismicity in idaho and montana triggered by the denali fault earthquake a window into the geologic context for seismic triggering we present a case study of dynamically triggered seismicity in idaho and western montana from the 2002 mw 7 9 denali fault earthquake to investigate the relationship between measured geological discriminants and propensity for trig gering we first establish triggering we find events that are not reported in the advanced national seismic system catalog in idaho and yellowstone following the denali fault earthquake by filtering broadband waveforms an ml 4 6 earthquake is discovered near new meadows idaho during the passage of the rayleigh waves and another earthquake probably located near yellowstone we find that central western idaho and yellowstone have statistically significant seismicity increases by applying a b test to the cataloged events in the 48 hr after the denali fault earthquake in idaho and surrounding regions we also find that pine idaho may have triggered events but the measurement is not robust because of uncertainty in the background seismicity rate both central western idaho and yellowstone triggered previously during the 1992 landers earthquake we then try to determine the local geological conditions necessary for triggered seismicity to occur geothermal regions with high total dissolved solids and background seismicity appear to be favorable conditions to trigger earthquakes in the study

afterslip and viscoelastic relaxation following the 1999 m 7 4 izmit earthquake from gps measurements summary intensive global positioning system gps monitoring after the 1999 izmit earthquake provides an opportunity to understand the postseismic behaviour of a strike slip fault and the rheology below the brittle upper crust two data sets are available displacements measured during the first 300 days after the izmit earthquake and velocity measurements between 2003 and 2005 using an inversion method and a forward modelling respectively we investigate two mechanisms 1 afterslip on and below the coseismic rupture plane and 2 viscoelastic stress relaxation in the lower crust and upper mantle described by a maxwell or a standard linear solid sls rheology the inversion results show that the first several months following the izmit earthquake were dominated by afterslip at depths shallower than 30 km and the slip amount decayed with time after that apparent afterslip has a very different spatial distribution and is located much deeper for viscoelastic relaxation a model with an elastic upper crust and a maxwell viscoelastic lower crust overlying a maxwell mantle e m m fits the data measured in the first 300 days better in the far field than in the near field however the observed far field 300 day displacement and the long term 2003 2005 displacement which might be dominated by viscoelastic relaxation cannot be described by a maxwell rheological model with constant viscosity the effective viscosity increases over time therefore we have built a refined rheological model an elastic upper crust and an sls lower crust overlying a maxwell viscoelastic mantle e sls m our best solution yields a viscosity for the lower crust of 2 1018 pa s a relaxation strength of 2 3 and a viscosity for the maxwell mantle of 7 1019 pa s finally we explain the data using a composite model consisting of the preferred e sls m model and the afterslip model obtained from the residual displacement after correcting for viscoelastic relaxation for the early time period the residual displacements can be mainly explained by a shallow afterslip whose magnitude decays with time and whose spatial distribution is stable whereas the residual displacements for the later time period require negligible afterslip it indicates that the postseismic deformation in the later time period induced by a deep source can be almost entirely explained by the e sls m model the composite model can generally explain the data in the entire spatial and temporal space

dynamic stress variations due to shear faults in a plane layered medium summary a complete set of expressions is presented for the computation of elastic dynamic stress in plane layered media we use a discrete wavenumber reflectivity method to compute the stress field radiated by arbitrary moment tensor sources the expressions derived here represent an interesting tool for both the observational and theoretical analysis of dynamic stress changes associated with earthquake phenomena dynamic stress changes associated with a strike slip fault having unilateral rupture are shown this modelling which is similar to the 1992 landers california earthquake illustrates the effects of distance directivity and depth on transient stress changes

the 1999 izmit earthquake sequence in turkey seismological and tectonic aspects the izmit duzce earthquake sequence is the largest sequence recorded by modern digital networks in the history of turkish earthquakes the m w 7 4 izmit mainshock occurred at 29 967 e and 40 729 n and 13 km depth at 00 hr 01 min 38 7 sec utc on 17 august 1999 and was preceded by at least eight immediate foreshocks of magnitude m l 3 0 aftershock locations show that a large region has become seismically very energetic following the mainshock and that most of the aftershock zone developed quickly in the first 3 days the distribution of the aftershocks illuminates numerous seismotectonic structures associated with the various branches of the north anatolian fault naf in the aftershock zone the seismicity pattern defines a rupture plane that extends about 80 km east and 75 km west of the mainshock epicenter confirming bilateral rupture during the mainshock the western aftershock activity is almost entirely located offshore extending along the axis of the izmit bay we show that the westernmost extent of the mainshock rupture reached the offshore region just 10 km south of the princes islands the dominance of strike slip motion is one of the main characteristics of the izmit sequence a number of significant aftershock clusters occur off the inferred mainshock rupture plane the spatial and temporal occurrence of these clusters show that they are triggered by the complex redistribution of stresses and dynamic strains imposed by the dislocation of the mainshock the focal mechanisms of the events located in the western end of the rupture zone show both strike slip and normal faulting mechanisms we infer that the yalova cluster was triggered by the mainshock the dominance of the normal faulting mechanisms supports the notion that dynamic extensional strains played a major role in triggering this cluster four events located off the princes islands indicate similar source mechanisms characterized by right lateral strike slip motion parallel to the strike of the northern boundary fault nbf and local trend of aftershock distribution this observation leads to a first order seismotectonic evidence that the nature of the nbf which is known to be a transtensional feature at the surface is dominated by strike slip motion at depth the coexistence of strike slip and extensional seismotectonic features in the sea of marmara highlights the importance of strain partitioning amongst shallow transtentional structures accommodating north south extension and deeper structures associated with the naf accommodating east west right lateral shear manuscript received 22 september 2000

seismicity analysis through point process modeling a review the occurrence times of earthquakes can be considered to be a point process and suitable modeling of the conditional intensity function of a point process is useful for the investigation of various statistical features of seismic activity this manuscript summarizes likelihood based methods of analysis of point processes and reviews useful models for particular analyses of seismicity most of the analyses can be implemented by the computer programs published by the author and collaborators

can coseismic stress variability suppress seismicity shadows insights from a rate and state friction model 1 the paucity of detectable seismicity shadows in the days months following a main shock has raised the question as to whether dynamic rather than static triggering could be the main mechanism driving the seismicity at these timescales the lack of correlation between the stress unloading of the main fault and the typically vigourous aftershock production taking place on it however suggests that the spatial heterogeneity of the coseismic stress change could also be a factor in the apparent suppression of seismicity shadows at least on the main fault here we study whether this stress variability can indeed be an important aspect in the stress modeling of earthquake sequences a rate and state friction model of seismicity is used in conjunction with realistic levels of stress heterogeneity at the earthquake nucleation scale 1 10 m as predicted from these friction laws based on scale invariant models of coseismic slip distribution in this model a relatively weak on fault quiescence is delayed by months to years because of the high stress heterogeneity delayed quiescences due to slip heterogeneity are similarly predicted at distances of up to about half the rupture length away from the fault we also postulate that off fault seismicity can be significantly controlled by stress variability that originates from small scale crustal heterogeneity and the complexity in fault geometries rather than mapping stress changes by providing a single stress value at every grid point these results suggest that an estimate of the likely stress variability acting at the nucleation scale is also needed especially when trying to account for the seismicity occurring at relatively short timescales

remotely triggered seismicity in the yellowstone national park region by the 2002 mw 7 9 denali fault earthquake alaska coincident with the arrival of low frequency large amplitude surface waves of the mw 7 9 denali fault earthquake dfe an abrupt increase in seismicity was observed in the yellowstone national park region despite the large epicentral distance of 3100 km within the first 24 hr following the dfe mainshock we located more than 250 earthquakes which occurred throughout the entire yellowstone na tional park region the elevated seismicity rate continued for about 30 days and followed a modified omori law decay with a p value of 1 02 0 07 for a declus tered earthquake catalog the seismicity following the 2002 dfe uniquely stands out with a significance of 30r the increase in seismicity occurred over all magnitude bands in general we observed that seismicity following the dfe outlined the spatial pattern of past seismicity routinely observed in the yellowstone national parkregion however we found significant differences in triggered seismicity inside and outside the caldera earthquakes inside the yellowstone caldera occurred preferentially as clusters close to major hydrothermal systems were of larger magnitude and seis micity decayed more rapidly this suggests that either different trigger mechanisms were operating inside and outside the caldera or that the crust responded differently to the same trigger mechanism depending on its different mechanicalstate compared with other sites that experienced remote earthquake triggering following the 2002 dfe yellowstone showed the most vigorous earthquake activity we attribute this to strong directivity effects of the dfe which caused relatively large peak dynamic stresses 0 16 0 22 mpa in yellowstone and to the volcanic nature of yellowstone

testing the stress shadow hypothesis 1 a fundamental question in earthquake physics is whether aftershocks are predominantly triggered by static stress changes permanent stress changes associated with fault displacement or dynamic stresses temporary stress changes associated with earthquake shaking both classes of models provide plausible explanations for earthquake triggering of aftershocks but only the static stress model predicts stress shadows or regions in which activity is decreased by a nearby earthquake to test for whether a main shock has produced a stress shadow we calculate time ratios defined as the ratio of the time between the main shock and the first earthquake to follow it and the time between the last earthquake to precede the main shock and the first earthquake to follow it a single value of the time ratio is calculated for each 10 10 km bin within 1 5 fault lengths of the main shock epicenter large values of the time ratio indicate a long wait for the first earthquake to follow the main shock and thus a potential stress shadow whereas small values indicate the presence of aftershocks simulations indicate that the time ratio test should have sufficient sensitivity to detect stress shadows if they are produced in accordance with the rate and state friction model we evaluate the 1989 mw 7 0 loma prieta 1992 mw 7 3 landers 1994 mw 6 7 northridge and 1999 mw 7 1 hector mine main shocks for each main shock there is a pronounced concentration of small time ratios indicating the presence of aftershocks but the number of large time ratios is less than at other times in the catalog this suggests that stress shadows are not present by comparing our results to simulations we estimate that we can be at least 98 confident that the loma prieta and landers main shocks did not produce stress shadows and 91 and 84 confident that stress shadows were not generated by the hector mine and northridge main shocks respectively we also investigate the long hypothesized existence of a stress shadow following the 1906 san francisco bay area earthquake we find that while bay area catalog seismicity rates are lower in the first half of the twentieth century than in the last half of the nineteenth this seismicity contrast is also true outside of the bay area in regions not expected to contain a stress shadow this suggests that the rate change is due to a more system wide effect such as errors in the historical catalog or the decay of aftershocks of the larger 1857 fort tejon earthquake

petrological and geochemical differentiation of lateritic iron crust profiles abstract lateritic iron crust profiles developed from metabasic rocks in west africa burkina faso were studied from a petrographical and geochemical point of view at the base of profiles a thick gray purple kaolinitic horizon occurs with frequent macroscopic preservation of original pre existing structures in such an horizon chemical balances clearly show that part of kaolinite crystals could be explained by an absolute accumulation from circulating solutions higher up in the profiles fe accumulation leads to two main facies purplered hematitic spots and nodules and yellow kaolinitic and goethitic spots mottled clay horizon hematite and goethite distribution in that horizon is regulated by water activity in microenvironments hematitic nodules form as kaolinite crystals are completely dissolved in goethitic spots fe accumulation is much less abundant and the first generation of well crystallized kaolinite is replaced by a poorly crystallized and smaller kaolinite crystals showing a greater substitution of al 3 for fe 3 in the upper part of profiles all the kaolinite is gradually dissolved and the maximum of ferruginous concretion formation leads to a hard and nodular iron crust

geochemical constraints on provenance of the mid pleistocene red earth sediments in subtropical china abstract the source of mid pleistocene red earth sediments in the middle to lower reaches of the yangtze changjiang river was investigated based on their geochemical characteristics the xuancheng and jiujiang red earth sediments have similar major and trace element distribution patterns compared to the loess and paleosol deposits of the chinese loess plateau the upper continental crust ucc and the post archean australian average shale paas the sediments display notable depletion of cao mgo na2o and accumulation of tio2 al2o3 and fe2o3 t the trace element distribution patterns of the red earth sediments are also different from those of loess and the paas but are similar to those of the loess deposits except for lower values of mobile trace elements sr ba and ni and higher values of zr and y the red earth samples have uniform la th ratios of 2 8 compatible with those of the ucc loess and paleosol they also have similar chondrite normalized ree patterns characterized by enriched lree and relatively flat hree profiles and consistent negative eu anomalies similar to those of the ucc the loess and paleosol and the yangtze deposits these results suggest that the red earth sediments have been subject to considerable mixing prior to deposition and strong subsequent chemical weathering the sediments have very uniform 143nd 144nd and 147sm 144nd ratios this points to well mixed and multi recycled sediments the 143nd 144nd and 87sr 86sr values of the red earth sediments match well with those of the deposits in the middle to lower reaches of the yangtze river but are different from those of the loess and paleosols this suggests that the red earth sediments are derived from the drainage basins of the middle to lower yangtze river and might have experienced more intense chemical weathering relative to the yangtze deposits as reflected by their higher rb sr ratios intense depletion of mobile elements and accumulation of immobile elements as well as their well developed net like structure

earthquake triggering in southern iceland following the june 2000 ms 6 6 doublet 1 in june 2000 two remarkably similar ms 6 6 earthquakes stroke southern iceland in the space of 3 d here this doublet is analyzed to test whether aftershock triggering is linear that is if the triggering patterns of these two similar main shocks are also similar methodologically the key issue is to separate the two contributions to the overall seismicity patterns for this purpose we model the first 3 d 17 21 june of this aftershock sequence with an omori utsu law we then extrapolate it beyond 21 june in order to estimate the variations linked with the second shock we correct for the large transient changes in catalogue completeness our results indicate that instantaneous short lived hours to days dynamic triggering took place at the hengill triple junction on the reykjanes peninsula and around the arnes fault plane that ruptured on 17 june we observe delayed long lasting longer than weeks episodes of quiescence at hengill and on the arnes fault plane at hengill this quiescence remains significant up to at least the end of 2000 these quiescences are more consistent with coulomb stress calculations than the preceding episodes of triggering comparison between the number of triggered events by the two main shocks reveals that the second one triggered only 2 1 at hengill and 0 3 at reykjanes of the number 3 6 and 0 1 respectively of the seismic moment that could be expected with a simple stress threshold model of dynamic triggering this clear nonlinearity in patterns of dynamic triggering is consistent with a model in which the population of nucleating earthquakes is depleted by the first trigger

heightened odds of large earthquakes near istanbul an interaction based probability calculation we calculate the probability of strong shaking in istanbul an urban center of 10 million people from the description of earthquakes on the north anatolian fault system in the marmara sea during the past 500 years and test the resulting catalog against the frequency of damage in istanbul during the preceding millennium departing from current practice we include the time dependent effect of stress transferred by the 1999 moment magnitude m 7 4 izmit earthquake to faults nearer to istanbul we find a 62 15 probability one standard deviation of strong shaking during the next 30 years and 32 12 during the next decade