3 d inhomogeneities in the upper mantle abstract the method developed by aki christofferson and husebye for determining a 3 d seismic image of the earth s interior from the travel time data obtained at a 2 d array has been applied to seventeen arrays around the world by various authors the most outstanding results from these works are that small scale lateral velocity anomalies exist in the lower crust and upper mantle everywhere studied the reality of these deep seated anomalies is supported by 1 1 significant reduction of residual variance 2 2 resolution analysis for decoupling from shallower anomalies and 3 3 error analysis for the significance of anomalies in this paper we try to strengthen the credibility of these deep seated anomalies by drawing attention to those found where they were expected namely low velocity bodies under several geothermal areas and high velocity anomalies associated with the subducting plate

correlations in aftershock and seismicity patterns correlations in space and time play a fundamental role in earthquake processes one direct manifestation of the effects of correlations is the occurrence of aftershocks due to the stress transfer in the vicinity of a main shock less obvious and more speculative changes in correlations may occur in the background seismicity before large earthquakes using statistical physics it is possible to introduce a measure of spatial correlations through a correlation length this quantity characterizes how local fluctuations can influence the occurrence of earthquakes over distances comparable with the correlation length in this work the physical basis of spatial correlations of earthquakes is discussed in the context of critical phenomena and the percolation problem the method of two point correlation function is applied to the seismicity of california well defined variations in time of the correlation length are found for aftershock sequences and background seismicity the scaling properties of our obtained distributions are analyzed with respect to changes in several scaling parameters such as lower magnitude cutoff of earthquakes the maximum time interval between earthquakes and the spatial size of the area considered this scaling behavior can be described in a unified manner by utilizing the multifractal fit utilizing the percolation approach the time evolution of clusters of earthquakes is studied with the correlation length defined in terms of the radius of gyration of clusters this method is applied to the seismicity of california

aftershock decay rates in the iranian plateau motivated by the desire to have more information following the occurrence of damaging events the main purpose of this article is to study aftershock sequence parameters in the iranian plateau to this end the catalogue of the iranian earthquakes between 2002 to the end of 2013 has been collected and homogenized among which 15 earthquakes have been selected to study their aftershock decay rates for different tectonic provinces the completeness magnitudes mc of the earthquake catalogue have been calculated in different time intervals also the mc variability in spatial and temporal windows has been determined for each selected event for major iranian earthquakes catalogue of aftershocks has been collected thanks to three declustering methods first the classical windowing method of gardner and knopoff bull seismol soc am 64 1363 1367 1974 second a modified version of this using spatial windowing based on the wells and coppersmith bull seismol soc am 84 974 1002 1994 relations and third the burkhard and grunthal swiss j geosci 102 149 188 2009 scheme effects of the temporal windows also have been investigated using the time periods of 1 month 100 days and 1 year in the declustering method of gardner and knopoff bull seismol soc am 64 1363 1367 1974 in the next step the modified omori law coefficients have been calculated for the 15 selected earthquakes the calibrated regional generic model describing the temporal and magnitude distribution of aftershocks is of interest for time dependent seismic hazard forecasts the regional characteristics of the aftershock decay rates have been studied for the selected iranian earthquakes in the alborz zagros and central iran regions considering their different seismotectonics regimes however due to the lack of sufficient data no results have been reported for the kopeh dagh and makran seismotectonic regions

rayleigh fractionation of iron isotopes during pedogenesis along a climate sequence of hawaiian basalt abstract we measured iron isotopic composition of surface 10 20 cm and subsurface 50 70 cm basaltic soil horizons from the island of maui along a climate gradient mcg ranging from 2 2 to 4 2 m mean annual precipitation map all soil forming factors except climate were conserved the mcg has a documented decrease in fe with increasing rainfall that is highly correlated with decreasing mean annual eh values we found that increasing map from 2 8 to 4 2 m resulted in a surface plus subsurface average increase of 0 56 0 09 56fe with the subsurface consistently 0 33 0 06 56fe greater than the surface horizons based on loss of fe relative to nb rayleigh fractionation was observed with 103ln lost retained values of 0 37 0 03 and 0 34 0 04 for the surface and subsurface respectively equivalent 103ln lost retained values for the surface and subsurface soils suggests fe loss is driven by similar mechanisms throughout the soil profile our calculated fractionation factor is about 1 3 the magnitude of laboratory determined fractionation factors for fe reduction suggesting other processes organic complexation fe re precipitation modulate the net fe loss along the mcg these results offer field scale confirmation of laboratory experiments on model systems that show anoxic weathering reactions produce materials enriched in heavy fe isotopes

a review of earthquake statistics fault and seismicity based models etas and bass there are two fundamentally different approaches to assessing the probabilistic risk of earthquake occurrence the first is fault based the statistical occurrence of earthquakes is determined for mapped faults the applicable models are renewal models in that a tectonic loading of faults is included the second approach is seismicity based the risk of future earthquakes is based on the past seismicity in the region these are also known as cluster models an example of a cluster model is the epidemic type aftershock sequence etas model in this paper we discuss an alternative branching aftershock sequence bass model in the bass model an initial or seed earthquake is specified the subsequent earthquakes are obtained from statistical distributions of magnitude time and location the magnitude scaling is based on a combination of the gutenberg richter scaling relation and the modified bath s law for the scaling relation of aftershock magnitudes relative to the magnitude of the main earthquake omori s law specifies the distribution of earthquake times and a modified form of omori s law specifies the distribution of earthquake locations unlike the etas model the bass model is fully self similar and is not sensitive to the low magnitude cutoff

bath s law derived from the gutenberg richter law and from aftershock properties 1 the empirical bath s law states that the average difference in magnitude between a mainshock and its largest aftershock is 1 2 regardless of the mainshock magnitude following vere jones 1969 and console et al 2003 we show that the origin of bath s law is to be found in the selection procedure used to define mainshocks and aftershocks rather than in any difference in the mechanisms controlling the magnitude of the mainshock and of the aftershocks we use the etas model of seismicity which provides a more realistic model of aftershocks based on i a universal gutenberg richter gr law for all earthquakes and on ii the increase of the number of aftershocks with the mainshock magnitude using numerical simulations of the etas model we show that this model is in good agreement with bath s law in a certain range of the model parameters

aftershock detection thresholds as a function of time results from the anza seismic network following the 31 october 2001 ml 5 1 anza california earthquake we examine aftershock detectability thresholds for events in the initial part of the 31 october 2001 m l 5 1 sequence in southern california this sequence occurred directly below the broadband anza seismic network which recorded continuous waveform data at 13 azimuthally well distributed stations within the study region seven had epicentral distances 20 km of the 608 aftershocks 0 m l 2 8 in the initial 2 hr of this sequence the first five aftershocks recorded were only identifiable at stations within 30 km after applying a high pass filter using a cluster radius 1 1 km of 200 representative aftershocks we track the maximum seismogram amplitude versus earthquake magnitude this relationship helps us quantify the visibility of aftershocks within the mainshock coda and assess our detection capabilities we estimate that detectable aftershocks within the mainshock coda include 1 those over magnitude 3 that are within 15 km of the network centroid that occur 12 sec or more into the sequence and 2 those over magnitude 2 that are within 30 km of the centroid of the network that occur 60 sec or more into the sequence we find a lack of large aftershocks in this sequence the largest aftershock m l 2 8 is substantially smaller than the mainshock m l 5 1 we suggest this relatively large magnitude differential is dictated by a combination of factors that includes complexity of the san jacinto fault system and the lack of large earthquakes in the region in the past 20 years online material quicktime movies juxtaposing a 3 2 aftershock in the coda of a 5 1 mainshock

the effect of early diagenesis on the fe isotope compositions of porewaters and authigenic minerals in continental margin sediments abstract iron isotope compositions in marine pore fluids and sedimentary solid phases were measured at two sites along the california continental margin where isotope compositions range from 56fe 3 0 to 0 4 at one site near monterey canyon off central california organic matter oxidation likely proceeds through a number of diagenetic pathways that include significant dissimilatory iron reduction dir and bacterial sulfate reduction whereas at our other site in the santa barbara basin dir appears to be comparatively small and production of sulfides fes and pyrite was extensive the largest range in fe isotope compositions is observed for fe ii aq in porewaters which generally have the lowest 56fe values minimum 3 0 near the sediment surface and increase with burial depth 56fe values for fes inferred from hcl extractions vary between 0 4 and 0 4 but pyrite is similar at both stations where an average 56fe value of 0 8 0 2 was measured we interpret variations in dissolved fe isotope compositions to be best explained by open system behavior that involves extensive recycling of feflux this study is the first to examine fe isotope variations in modern marine sediments and the results show that fe isotopes in the various reactive fe pools undergo isotopic fractionation during early diagenesis importantly processes dominated by sulfide formation produce high 56fe values for porewaters whereas the opposite occurs when fe iii oxides are present and dir is a major pathway of organic carbon respiration because shelf pore fluids may carry a negative 56fe signature it is possible that the fe isotope composition of ocean water reflects a significant contribution of shelf derived iron to the open ocean such a signature would be an important means for tracing iron sources to the ocean and water mass circulation

statistical analysis of the 2002 mw 7 9 denali earthquake aftershock sequence we study the scaling properties of the aftershock sequence of the 2002 m w 7 9 denali earthquake the sequence exhibits nontrivial scaling behavior in magnitude aftershock decay rates and aftershock inter occurrence times in particular we observe a marked variability in the gutenberg richter gr exponent the b value in space between early and late times after the mainshock and over different magnitude ranges we find strong indications that certain aspects of this variability might be ascribed to the occurrence of some of the aftershocks on and around a supershear rupture associated with this event particularly we observe a statistically higher b value for the aftershocks that occurred in the zone surrounding the supershear rupture we further outline a method to obtain an average b value consistent with the theory and statistical properties of the data we find a significant difference between the magnitude of the largest aftershock and the mainshock this is analyzed and discussed using the modified bath s law it is observed that the aftershock decay rate can be approximated by the modified omori law the distribution of inter occurrence times is studied and we show that it can be explained in terms of a nonhomogeneous poisson process through time we further observe that the rescaled inter occurrence time distributions for various magnitude thresholds collapse into a universal functional form which indicates that the aftershock sequence exhibits self similarity in both magnitude and time in particular the statistical features of the aftershock sequence show that the rupture process or the preconditions that lead to it may influence aftershock statistics

seismicity rate immediately before and after main shock rupture from high frequency waveforms in japan 1 we analyze seismicity rate immediately before and after 82 main shocks with the magnitudes ranging from 3 to 5 using waveforms recorded by the hi net borehole array in japan by scrutinizing high frequency signals we detect 5 times as many aftershocks in the first 200 s as in the japan meteorological agency catalogue after correcting for the changing completeness level immediately after the main shock the aftershock rate shows a crossover from a slower decay with an omori s law exponent p 0 58 0 08 between 20 and 900 s after the main shock to a faster decay with p 0 92 0 04 after 900 s the foreshock seismicity rate follows an inverse omori s law with p 0 73 0 08 from several tens of days up to several hundred seconds before the main shock the seismicity rate in the 200 s immediately before the main shock appears steady with p 0 35 0 50 these observations can be explained by the epidemic type aftershock sequence etas model and the rate and state model for a heterogeneous stress field on the main shock rupture plane alternatively nonseismic stress changes near the source region such as episodic aseismic slip or pore fluid pressure fluctuations may be invoked to explain the observation of small p values immediately before and after the main shock

near field etas constraints and applications to seismic hazard assessment the epidemic type aftershock sequence etas statistical model of aftershock seismicity combines various earthquake scaling relations to produce synthetic earthquake catalogs or estimates of aftershock seismicity rates based on recent earthquake activity one challenge to etas based hazard assessment is the large number of free parameters involved in this paper we introduce an approach to constrain this parameter space from canonical scaling relations empirical observations and fundamental physics we show that etas parameters can be estimated as a function of an earthquake s magnitude m based on the finite temporal and spatial extents of the rupture area this approach facilitates fast etas based estimates of seismicity from large seed catalogs and it is particularly well suited to web based deployment and otherwise automated implementations it constitutes a significant improvement over contemporary etas by mitigating variability related to instrumentation and subjective catalog selection

iron isotopic fractionation during continental weathering abstract the effect of continental weathering on the iron isotope compositions of natural materials is investigated unweathered igneous rocks pelagic clay and dust fall within the range 56 fe 0 0 3 rivers with large suspended loads also have 56 fe values near zero dilute streams have 56 fe values that trend towards lower 56 fe 1 suggesting that dissolved riverine iron is isotopically light relative to igneous rocks bulk soil and soil leaches display systematically different 56 fe profiles indicating that isotopically distinct fe pools are generated during pedogenesis nannofossil ooze which contains fe scavenged from the ocean water column has 56 fe 0 but is consistent with seawater dissolved fe having negative 56 fe it is inferred that continental weathering under modern oxidizing earth surface conditions preferentially releases dissolved fe with negative 56 fe which is transported in rivers to the ocean a preliminary analysis of the marine fe budget suggests that riverine fe has a substantial role in determining the 56 fe of both the modern and ancient oceans but other inputs particularly that from diagenesis of marine sediments may also be important since the chemical pathways of fe processing during weathering are dependent on oxidation state and biological activity fe isotopes may prove useful for detecting changes in these parameters in the geologic past

including foreshocks and aftershocks in time independent probabilistic seismic hazard analyses time independent probabilistic seismic hazard analysis treats each source as being temporally and spatially independent hence foreshocks and aftershocks which are both spatially and temporally dependent on the mainshock are removed from earthquake catalogs yet intuitively these earthquakes should be considered part of the seismic hazard capable of producing damaging ground motions in this study i consider the mainshock and its dependents as a time independent cluster each cluster being temporally and spatially independent from any other the cluster has a recurrence time of the mainshock and by considering the earthquakes in the cluster as a union of events dependent events have an opportunity to contribute to seismic ground motions and hazard based on the methods of the u s geological survey for a high hazard site the inclusion of dependent events causes ground motions that are exceeded at probability levels of engineering interest to increase by about 10 but could be as high as 20 if variations in aftershock productivity can be accounted for reliably

plant induced weathering of a basaltic rock experimental evidence abstract the active role of higher plants in the weathering of silicate minerals and rocks is still a question for debate the present work aimed at providing experimental evidence of the important role of a range of crop plants in such processes in order to quantitatively assess the possible effect of these diverse plant species on the weathering of a basaltic rock two laboratory experiments were carried out at room temperature these compared the amounts of elements released from basalt when leached with a dilute salt solution in the presence or absence of crop plants grown for up to 36 days for si ca mg and na plants resulted in an increase in the release rate by a factor ranging from 1 to 5 in most cases ca and na seemed to be preferentially released relative to other elements suggesting that plagioclase dissolved faster than the other constituents of the studied basalt negligible amounts of fe were released in the absence of plants as a consequence of the neutral ph and atmospheric po2 that were maintained in the leaching solution however the amounts of fe released from basalt in the presence of plants were up to 100 to 500 fold larger than in the absence of plants for banana and maize the kinetics of dissolution of basalt in the absence of plants showed a constantly decreasing release rate over the whole duration of the experiment 36 days no steady state value was reached both in the absence and presence of banana plants however in the latter case the rates remained at a high initial level over a longer period of time up to 15 days before starting to decrease for fe the maximum rate of release was reached beyond 4 days and this rate remained high up to 22 days of growth of banana the possible mechanisms responsible for this enhanced release of elements from basalt in the presence of plants are discussed although these mechanisms need to be elucidated the present results clearly show that higher plants can considerably affect the kinetics of dissolution of basalt rock therefore they need to be taken into account when assessing the biogeochemical cycles of elements that are major nutrients for plants such as ca mg and k but also micronutrients such as fe and nonessential elements such as si and na

properties of aftershock sequences in southern california the temporal behavior of 39 aftershock sequences in southern california 1933 1988 was modeled by the modified omori relation minimum magnitudes for completeness of each sequence catalog were determined and the maximum likelihood estimates of the parameters k p and c with the standard errors on each were determined by the ogata algorithm the b value of each sequence was also calculated many of the active faults in the region both strike slip and thrust were sampled the p values were graded in terms of the size of the standard error relative to the p value itself most of the sequences were modeled well by the omori relation many of the sequences had p values close to the mean of the whole data set 1 11 0 25 but values significantly different from the mean as low as 0 7 and as high as 1 8 exist no correlation of p with either the b value of the sequence or the mainshock magnitude was found the results suggest a direct correlation of p values is with surface heat flow with high values in the salton trough high heat flow and one low value in the san bernardino mountains and on the edge of the ventura basin both low heat flow the large fraction of the sequences with p values near the mean are at locations where the heat flow is near the regional mean 74 mw m2 if the hypothesis that aftershock decay rate is controlled by temperature at depth is valid the effects of other factors such as heterogeneity of the fault zone properties are superimposed on the background rate determined by temperature surface heat flow is taken as an indicator of crustal temperature at hypocentral depths but the effects on heat flow of convective heat transport and variations in near surface thermal conductivity invalidate any simple association of local variations in heat flow with details of the subsurface temperature distribution the interpretation is that higher temperatures in the aftershock source volume caused shortened stress relaxation times in the fault zone materials leading to a faster decay rate higher p value in 1967 mogi proposed such a relation on the basis of japanese data seismic velocity distributions published for southern california generally support the hypothesis with low velocities higher temperatures corresponding to high p values and vice versa

can damage mechanics explain temporal scaling laws in brittle fracture and seismicity time delays associated with processes leading to a failure or stress relaxation in materials and earthquakes are studied in terms of continuum damage mechanics damage mechanics is a quasi empirical approach that describes inelastic irreversible phenomena in the deformation of solids when a rock sample is loaded there is generally a time delay before the rock fails this period is characterized by the occurrence and coalescence of microcracks which radiate acoustic signals of broad amplitudes these acoustic emission events have been shown to exhibit power law scaling as they increase in intensity prior to a rupture in case of seismogenic processes in the earth s brittle crust all earthquakes are followed by an aftershock sequence a universal feature of aftershocks is that their rate decays in time according to the modified omori s law a power law decay in this paper a model of continuum damage mechanics in which damage microcracking starts to develop when the applied stress exceeds a prescribed yield stress a material parameter is introduced to explain both laboratory experiments and systematic temporal variations in seismicity

relation between mainshock rupture process and omori s law for aftershock moment release rate summary we compare the source time functions i e moment release rates of three large california mainshocks with the seismic moment release rates during their aftershock sequences aftershock moment release rates computed by summing aftershock moments in time intervals follow a power law time dependence similar to omori s law from minutes to months after the mainshock furthermore in contrast to the previously observed saturation in numbers of aftershocks shortly after the mainshock rupture no such saturation is seen in the aftershock moment release rates which are dominated by the largest aftershocks we argue that the observed saturation in aftershock numbers described by the time offset parameter c in omori s law is likely an artefact due to the underreporting of small aftershocks which is related to the difficulty of detecting large numbers of small aftershocks in the mainshock coda we further propose that it is more natural for c to be negative i e singularity follows the onset of mainshock rupture than positive singularity precedes onset of rupture to make a more general comparison of mainshock rupture process and aftershock moment rates we then scale mainshock time functions to equalize the effects of the varied seismic moments for the three california mainshocks we compare the scaled time functions with similarly scaled aftershock moment rates finally we compare global averages of scaled time functions of many shallow events to the average scaled aftershock moment release rate for six california mainshocks in each of these comparisons the extrapolation using omori s law of the aftershock moment rates back in time to the onset of the mainshock rupture indicates that the temporal intensity of the aftershock moment release is about 1 5 orders of magnitude less than the maximum reached by the mainshock rupture this may be due to the differing amplitudes and relative importance of static and dynamic stresses in aftershock initiation compared to mainshock rupture propagation

intraplate seismicity of a recently deglaciated shield terrane a case study from northern ontario canada the economy of northern ontario canada is heavily dependent on mining so accurate knowledge of seismicity is important for the safe design and op eration of mines and other critical facilities including a proposed underground repos itory for nuclear waste in this study we analyzed 537 cataloged earthquakes that occurred from 1980 to 2006 seismicity is mainly concentrated in topographically elevated archean terranes northwest of lake superior and in the james bay and ka puskasing regions we analyzed waveforms to determine the focal depth for 331 re corded events using the regional depth phase modeling rdpm method coupled with surface wave relative amplitude analysis the majority of events are shallow 350 m although in the east ern part this pattern breaks down and some deeper earthquakes 12 km are ob served based on a moving window event counting technique we show that distinct spatial clusters of seismicity can be delineated that are statistically significant relative to background seismicity levels a particularly active cluster is located within james bay where focal depths range from a few kilometers to more than 20 km another cluster near kapuskasing contains deep focus events and may occur along a hot spot track that runs through western quebec near dryden a shallow 1 km earthquake swarm concentrated in a 1 1 km region commenced in may 2002 faded and then started up again in february 2003 shallow mining induced events are also common around sudbury a major world center for nickel mining the overall pattern of seis micity appears to correlate with upper mantle p wave velocity anomalies suggesting that lateral variations in mantle rheology may play a significant role in controlling intraplate seismicity of shield areas it is also likely that crustal stresses caused by glacial isostatic adjustment are an important factor although the correlation of seis micity with uplift rate is not as clear online material focal depth solutions for earthquakes in northern ontario canada

characteristics of the october 2005 microearthquake swarm and reactivation of similar event seismic swarms over decadal time periods near socorro new mexico seismicity in the rio grande rift in central new mexico southwestern united states has been dominated by microearthquakes occurring above the midcrustal socorro magma body smb for at least the past century the smb is a sill like feature 3400 km2 in area with a top surface at 19 km depth and centered below the inner rift half graben system a recent swarm of microearthquakes above the magma body began on 20 october 2005 the activity intensified toward 30 october 2005 with the largest event being a shallow felt local magnitude m l 2 4 earthquake at 02 57 35 utc seismicity increased in the region following this event with over 1600 earthquakes detectable at a minimum of one local seismic station during the subsequent month seismic waveforms for the earthquakes in this sequence are remarkably similar implying consistently similar location and faulting geometry the time space distribution of earthquakes indicates that this sequence is highly swarmlike in contrast to tectonic mainshock aftershock sequences given the local tectonic setting and shallow 8 km depth of individual events above the smb a likely explanation for the socorro earthquake sequence is fluid flow or pressure induced triggering associated with the evolution of the smb swarms such as the 2005 sequence are not uncommon in this area e g prominent previous sequences occurred in may and july of 1983 here we characterize the 2005 earthquake sequence by presenting composite focal mechanisms magnitude estimates and high precision relative locations based on waveform cross correlation techniques that capitalize on the similar waveforms a new waveform scanning technique identifies over 1600 small similar earthquakes during this period from continuous seismic records waveforms and locations are also observed to be similar between the 2005 and 1983 sequences suggesting consistency in source location geometry and thus mechanism over decadal time scales

post seismic motion following the 1997 manyi tibet earthquake insar observations and modelling summary on november 8 1997 a mw 7 6 earthquake occurred in the manyi region of northern tibet near the western end of the kunlun fault over 7 m of left lateral slip occurred on a 200 kmlong fault here we use insar observations of post seismic surface deformation following the manyi earthquake to investigate possible causal mechanisms time series of deformation are constructed from 26 interferograms covering the entire length of the fault for nearly 4 yr after the earthquake three different modelling approaches are used to try and understand the observed variations in surface displacement first order poroelastic models predict displacement fields which do not match those observed modelling of viscoelastic stress relaxation in a half space with standard linear solid rheology beneath an elastic lid provides a reasonable fit to the observations and demonstrates that two relaxation times are needed to characterize the post seismic transient the best fitting viscosity is 4 10 18 pa s and the fully relaxed shear modulus is 32 per cent of the purely elastic value a model with a maxwell viscoelastic halfspace underlying the lid cannot explain the observations at later times larger viscosities are required than at earlier times this increase in effective viscosity with time may be consistent with stress relaxation occurring in a power law rheology the time series are also inverted for distributed afterslip on an extension of the coseismic rupture along strike correlation of coseismic and post seismic slip maxima suggests that afterslip is a plausible mechanism the maximum slip in the afterslip model is 0 72 m after 3 yr and the equivalent moment release is approximately 20 per cent of the coseismic moment this study shows that it is possible to rule out certain mechanisms as the dominant post seismic process but with the current insar data set it is difficult to distinguish between other plausible options

quantifying early aftershock activity of the 2004 mid niigata prefecture earthquake mw6 6 1 we analyze the early aftershock activity of the 2004 mid niigata earthquake using both earthquake catalog data and continuous waveform recordings the frequency magnitude distribution analysis of the japan meteorological agency jma catalog shows that the magnitude of completeness of the aftershocks changes from values around 5 0 immediately after the main shock to about 1 8 12 hours later such a large incompleteness of early events can bias significantly the estimation of aftershock rates to better determine the temporal pattern of aftershocks in the first minutes after the niigata earthquake we analyze the continuous seismograms recorded at six high sensitivity seismograph network hi net stations located close to the aftershock distribution clear aftershocks can be seen from about 35 s after the main shock we estimate that the events we picked on the waveforms recorded at two seismic stations ngoh and ynth situated on opposite sides of the aftershock distribution are complete above a threshold magnitude of 3 4 the c value determined by taking these events into account is about 0 003 days 4 3 min statistical tests demonstrate that a small but nonzero c value is a reliable result we also analyze the decay with time of the moment release rates of the aftershocks in the jma catalog since these rates should be much less influenced by the missing small events the moment rates follow a power law time dependence from few minutes to months after the main shock we finally show that the rate and state dependent friction law or stress corrosion could explain well our findings

spatial distribution of the difference between the magnitudes of the main shock and the largest aftershock in the circum pacific belt the distribution of the magnitude difference d 1 between the main shock and the largest aftershock for large circum pacific earthquakes is observed to be peaked at 1 2 magnitude units in accord with bath s law but also at 1 8 magnitude units the peak at 1 8 has been not noted before and is shown here with the t test to be statistically valid the observed spatial distribution of the sequences is the basis to suggest that along circum pacific convergent plate boundaries values of d 1 tend to be larger for earthquake sequences within back arc areas as compared to sequences closer to the plate interface although admittedly a good number of exceptions to this generalization are also observed to exist

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

aftershock zone scaling we investigate the distribution of aftershock zones for large earthquakes scalar seismic moment m 10 19 5 n m moment magnitude m 7 mainshocks are selected from the harvard centroid moment tensor catalog and aftershocks are selected from the preliminary determination of epicenters neic catalog the aftershock epicenter maps are approximated by a two dimensional gaussian distribution the major ellipse axis is taken as a quantitative measure of the mainshock focal zone size the dependence of zone length l on earthquake size is studied for three representative focal mechanisms thrust normal and strike slip although the numbers of mainshocks available for analysis are limited maximum a few tens of events in each case all earthquakes show the same scaling m l 3 no observable scaling break or saturation occurs for the largest earthquakes m 10 21 n m m 8 therefore it seems that earthquake geometrical focal zone parameters are self similar

short term earthquake forecasting using early aftershock statistics abstract we present an alarm based earthquake forecast model that uses the early aftershock statistics east this model is based on the hypothesis that the time delay before the onset of the power law aftershock decay rate decreases as the level of stress and the seismogenic potential increase here we estimate this time delay from t g the time constant of the omori utsu law to isolate space time regions with a relative high level of stress the single local variable of our forecast model is the e a value the ratio between the long term and short term estimations of t g when and where the e a value exceeds a given threshold i e the c value is abnormally small an alarm is issued and an earthquake is expected to occur during the next time step retrospective tests show that the east model has better predictive power than a stationary reference model based on smoothed extrapolation of past seismicity the official prospective test for california started on 1 july 2009 in the testing center of the collaboratory for the study of earthquake predictability csep during the first nine months 44 m 4 earthquakes occurred in the testing area for this time period the east model has better predictive power than the reference model at a 1 level of significance because the east model has also a better predictive power than several time varying clustering models tested in csep at a 1 level of significance we suggest that our successful prospective results are not due only to the space time clustering of aftershocks

statistical properties of mine tremor aftershocks mine tremors and their aftershocks pose a risk to mine workers in the deep gold mines of south africa the statistical properties of mine tremor aftershocks were investigated as part of an endeavour to assess the hazard and manage the risk data from two gold mines in the carletonville mining district were used in the analysis main shocks were aligned in space and time and the aftershock sequences stacked and analysed the aftershocks were found to satisfy gutenberg richter scaling with a b value close to 1 aftershock activity diminished with time in accordance with the modified omori law with p values close to 1 however the relationship between the main shock and its biggest aftershock violated baths law with ml 1 9 for main shocks with ml 3 the aftershock density was found to fall off with distance as r 1 3 suggesting triggering by dynamic stress

fe isotope variations in the modern and ancient earth and other planetary bodies iron the fourth most abundant element in the earth s crust has four naturally occurring stable isotopes 54fe 5 84 56fe 91 76 57fe 2 12 and 58fe 0 28 and the natural mass dependent isotope variations of fe in the rock record span a range of 4 per mil in 56fe 54fe ratios fig 1 the field of fe isotope geochemistry is relatively new but has received considerable attention because it may allow us to gain a better understanding of how fe is cycled in different environments iron typically occurs as either reduced ferrous fe in oxygen poor environments or as oxidized ferric iron in oxygen rich environments notably only the reduced species is soluble in oxygenated aqueous solutions unless the ph is low in the archean and early proterozoic the earth may have been relatively oxygen poor e g kasting et al 1979 grandstaff 1980 holland 1994 suggesting that there may have been significant quantities of fe 0 9 millimolar dissolved in the oceans as fe ii aq e g ewers 1983 sumner 1997 the extensive iron formations of archean to early proterozoic age may have been deposited from such fe ii rich oceans e g beukes and klein 1992 in the modern oxic oceans however fe contents are exceedingly low 1 nanomolar in the open oceans e g martin and gordon 1988 bruland et al 1991 martin 1992 johnson et al 1997 and it is now recognized that marine productivity is fe limited in parts of the open oceans e g martin and fitzwater 1988 martin et al 1989 1994 the differences in the behavior of fe with redox state and the significant isotope fractionations 1 or more in 56fe 54fe that are associated with redox conditions suggests that fe isotope studies will be extremely useful for tracing

refractory element mobility in volcanic soils refractory trace element concentrations in strongly weathered hawaiian soils ranging in age from 20 to 4100 ka are highly elevated over parent rock values due to extensive mass loss of more soluble major elements during pedogenesis nb and ta exhibit virtually no mobility soil nb ta ratios are within the range of fresh bedrock even when soil nb concentrations are residually enriched by a factor of 10 in contrast al zr and hf are depleted relative to nb in surface soil horizons but are enriched at depth clearly indicating mobility of these elements variations in th nb ratios in soil profiles indicate significant th mobility within the soil column however mass balance calculations require that accretion of th enriched asian dust has resulted in a net increase in th in some soils soils developed on a 150 ka rainfall gradient show that the mobility and loss of zr increase with mean annual precipitation

triggering of the 1999 mw 7 1 hector mine earthquake by aftershocks of the 1992 mw 7 3 landers earthquake 1 there is strong observational evidence that the 1999 mw 7 1 hector mine earthquake in the mojave desert california was triggered by the nearby 1992 mw 7 3 landers earthquake many authors have proposed that the landers earthquake directly stressed the hector mine fault our model of the landers aftershock sequence however suggests there is an 85 chance that the hector mine hypocenter was actually triggered by a chain of smaller earthquakes that was initiated by the landers main shock we perform our model simulations using the monte carlo method based on the gutenberg richter relationship omori s law bath s law and assumptions that all earthquakes including aftershocks are capable of producing aftershocks and that aftershocks produce their own aftershocks at the same rate that other earthquakes do in general our simulations show that if it has been more than several days since an m 7 main shock most new aftershocks will be the result of secondary triggering these secondary aftershocks are not physically constrained to occur where the original main shock increased stress this may explain the significant fraction of aftershocks that have been found to occur in main shock stress shadows in static coulomb stress triggering studies

aftershock statistics of the 1999 chi chi taiwan earthquake and the concept of omori times in this paper we consider the statistics of the aftershock sequence of the m 7 65 20 september 1999 chi chi taiwan earthquake we first consider the frequency magnitude statistics we find good agreement with gutenberg richter scaling but find that the aftershock level is anomalously high this level is quantified using the difference in magnitude between the main shock and the largest inferred aftershock updelta m typically updelta m is in the range 0 8 1 5 but for the chi chi earthquake the value is updelta m 0 03 we suggest that this may be due to an aseismic slow earthquake component of rupture we next consider the decay rate of aftershock activity following the earthquake the rates are well approximated by the modified omori s law we show that the distribution of interoccurrence times between aftershocks follow a nonhomogeneous poisson process we introduce the concept of omori times to study the merging of the aftershock activity with the background seismicity the omori time is defined to be the mean interoccurrence time over a fixed number of aftershocks

a generalized omori s law for earthquake aftershock decay 1 earthquake aftershock sequences have been found to approximately satisfy three empirical scaling relations i the gutenberg richter frequency magnitude scaling ii bath s law for the difference in the magnitude of a mainshock and its largest aftershock and iii the modified omori s law for the temporal decay of aftershock rates the three laws are incorporated to give a generalized omori s law for aftershock decay rates that depend on several parameters specific for each given seismogenic region it is shown that the characteristic time c first introduced in the modified omori s law is no longer a constant but scales with a lower magnitude cutoff and a mainshock magnitude the generalized omori s law is tested against earthquake catalogs for the aftershock sequences of the landers northridge hector mine and san simeon earthquakes

seismic cycles earthquakes landslides and sediment fluxes linking tectonics to surface processes using a reduced complexity model in tectonically active mountain ranges landslides triggered by earthquakes mobilise large volumes of sediment that affect river dynamics this sediment delivery can cause downstream changes in river geometry and transport capacity that affect the river efficiency to export this sediment out of the epicentre area the subsequent propagation of landslide deposits in the fluvial network has implications for the management of hazards downstream and for the long term evolution of topography over multiple seismic cycles a full understanding of the processes and time scales associated with the removal of landslide sediment by rivers following earthquakes however is still lacking here we propose a nested numerical approach to investigate the processes controlling the post seismic sediment evacuation at the mountain range scale informed by results from a reach scale model first we explore the river morphodynamic response to a landslide cascade at the reach scale using a 2d modelling approach the results are then used to describe empirically the evacuation of a landslide volume which avoids using a computationally extensive model in catchments which may have thousands of co seismic landslides second we propose a reduced complexity model to quantify evacuation times of earthquake triggered landslide clusters at the scale of a mountain range examining the hypothetical case of a mw 7 9 earthquake and its aftershocks occurring on the alpine fault new zealand our approach combines an empirical description of co seismic landslide clusters with the sediment export processes involved during the post seismic phase our results show that the inter seismic capacity of the mountain range to evacuate co seismic sediment is critical to assess the sediment budget of large earthquakes over one to several seismic cycles we show that sediment evacuation is controlled by two timescales 1 the transfer time of material from hillslopes to channels and 2 the evacuation time of the landslide deposits once it has reached the fluvial network in turn post seismic sediment evacuation can either be connectivity limited when sediment delivery along hillslopes is the main limiting process or transport limited when the transport by rivers is the limiting process despite high values of runoff we suggest that the southern alps of new zealand are likely to be in connectivity limited conditions for connection velocities 2 m yr 1 are sufficient to allow most of co seismic sediments to be mobilised and potentially exported out of the range within less than one seismic cycle because of the poorly constrained rate of sediment transfer along hillslopes our results potentially raise the issue of co seismic sediment accumulation within mountain ranges over several seismic cycles and of the imbalance between tectonic inputs and sediment export we therefore call for renewed observational efforts to better describe and quantify the physical processes responsible for the redistribution and mobilization of sediment from landslide scars and deposits

time dependent brittle creep as a mechanism for time delayed wellbore failure abstract by drilling a wellbore cavity high stresses arise at the wellbore wall leading to the formation of breakouts which enlarge the hole to an elongated shape oriented along the direction of the minimum principal stress if formation of breakouts is delayed rock debris falls on the drill bit which may lead to stuck pipe problems or even abandonment of the drill string reasons for such time delayed failure of the wellbore may be due to chemical fluid rock interaction especially in swelling clays however such delayed instabilities have also been observed e g in gneiss formations at the ktb borehole germany that are not known to exhibit a swelling behavior we propose to explain observations of delayed wellbore failure by time dependent brittle creep which has been observed for many types of rocks following this approach rock fails under loads less than their short time strength but after a long enough time span this time is in exponential relation to the load applied to the rock we implement a model developed for the creation of shear bands on the basis of time dependent brittle creep by amitrano and helmstetter 2006 here progressive damage of the formation is captured by a damage parameter d and the time to failure ttf young s modulus e is decreased by a factor every time ttf is expired i e when failure is reached subsequently stresses are redistributed according to the new distribution of e in the formation using this approach we obtain closure of the well with primary and secondary creep phases wellbore breakouts are formed progressively with deepening and widening of the initially damaged zone after a certain time the formation of breakouts comes to an end with an omori like decay of failure approaching a steady state

omori utsu law c values associated with recent moderate earthquakes in japan we investigate the early aftershock activity associated with four moderate earthquakes m w 6 6 6 7 that occurred recently in japan for each aftershock sequence we examine continuous high pass filtered seismograms recorded at seismic stations nearby the main fault to identify as many early events as possible the magnitude of these events is calibrated using aftershocks that are listed in the earthquake catalog of japan meteorological agency jma the analysis of the aftershock decay rates reveals a power law time dependence with a scaling exponent close to 1 0 that starts from about one minute from the mainshock our results demonstrate that the c value of the omori utsu law is very small although a lower bound is not established due to completeness problems in the first minute after the mainshock and statistical fluctuations

spatiotemporal correlations of aftershock sequences 1 aftershock sequences are of particular interest in seismic research because they may condition seismic activity in a given region over long time spans although they are typically identified with periods of enhanced seismic activity after a large earthquake as characterized by the omori law our knowledge of the spatiotemporal correlations between events in an aftershock sequence is limited here we study the spatiotemporal correlations of two aftershock sequences form california parkfield and hector mine using the recently introduced concept of recurrent events we find that both sequences have very similar properties and that most of them are captured by the space time epidemic type aftershock sequence etas model if one takes into account catalog incompleteness however the stochastic etas model does not capture those spatiotemporal correlations that give rise to the observed distribution of recurrent events on small spatial scales we also find that there is no clear evidence for stress shadows that have been observed for smaller earthquakes

iron isotope fractionation during microbial reduction of iron the importance of adsorption in experiments investigating the causes of fe isotope fractionation the d 56 54 fe value of fe ii remaining in solution fe ii aq after reduction of fe iii goethite by shewanella putrefaciens is 21 2 relative to the goethite in agreement with previous research the addition of an electron shuttle did not affect fractionation suggesting that fe isotope fractionation may not be related to the kinetics of the electron transfer furthermore in abiotic anaerobic fecl2 aq experiments in which approximately one third of fe ii aq is lost from solution due to adsorption of fe ii onto goethite the d 56 54 fe value of fe ii aq remaining in solution is shifted by 20 8 relative to fecl 2 this finding demonstrates that anaerobic nonbiological interaction between fe ii and goethite can generate signif icant fe isotope fractionation acid extraction of sorbed fe ii from goethite in experi ments reveals that heavy fe preferentially sorbs to goethite simple mass balance modeling indicates that the isotopic composition of the sorbed fe ii pool is 11 5 to 12 5 heavier than fe in the goethite 2 7 3 7 heavier than aqueous fe ii mass balance is also consistent with a pool of heavy fe that is not released to solution during acid extraction

the witputs diamictite in southern namibia and associated rocks constraints for a global glaciation the witputs section of the gariep belt s namibia comprises a sequence of clastic and chemical sediments which have been interpreted as representative of a late neoproterozoic global or near global ice age event and recent biostratigraphic work in the upper rocks of the witputs suggest a late ediacaran age to further characterise this sequence and provide additional age constraints a detailed sedimentological and detrital zircon study has been carried out the petrographic sedimentological and geochemical characteristics of the witputs diamictite determined in this study are homogenous and indicative of debris flow or palaeo valley infill sediments deposited in an oxic environment with no glaciogenic evidence this homogeneity is also reflected in the detrital zircon age spectra with most ages falling between 1 0 and 1 3 ga representing the local geology with the youngest grain at 1030 2 10 9 2 n 92 10 discordance despite the fact that mid and late neoproterozoic volcanic activity is known in the local region the overlying carbonate rocks often considered to be cap carbonates show high mn up to 60 mno with base metal precipitation zn v co and are recrystallised their 13cvpdb isotope ratios are homogeneous at around 3 major and trace element ratios reach values which indicate that c o isotopes may be disturbed and might not reflect primary global seawater composition thus questioning their use for global correlation and comparison with composite chemostratigraphic curves the contact to the overlying late ediacaran sanddrif member is not exposed and the rocks dip in a different direction than the underlying carbonate rocks the c 40 m thick section is characterised by rapid lithology changes including shales calcareous sandstones and wackes fine grained conglomerates and rare clean quartz rich sandstones all of which have strikingly similar detrital zircon populations and the youngest zircon is dated at 1082 8 10 ma 2 errors from 72 grains with 10 discordance acritarchs earlier found in the sanddrif member however indicate a post 570 ma depositional age if the diamictites are glacio marine deposits then an interesting conclusion is that the clastic sediments can display a very immature geochemical signature indicating a localised provenance with derivation purely from the local basement rocks which is also reflected in the detrital zircon populations however we would hesitate to assign a glacial origin to the deposits as no glacial indicators other than a diamictitic texture were observed clearly far more work on the detailed mapping and sedimentology of the neoproterozoic gariep belt deposits is required particularly as many are currently used for global correlation age constraints derived from extensive detrital zircon work can only constrain the deposits as being post 1 03 ma with the detritus being purely locally derived

a comparison of seismicity characteristics and fault structure between stick slip experiments and nature fault zones contain structural complexity on all scales this complexity influences fault mechanics including the dynamics of large earthquakes as well as the spatial and temporal distribution of small seismic events incomplete earthquake records unknown stresses and unresolved fault structures within the crust complicate a quantitative assessment of the parameters that control factors affecting seismicity to better understand the relationship between fault structure and seismicity we examined dynamic faulting under controlled conditions in the laboratory by creating saw cut guided natural fractures in cylindrical granite samples the resulting rough surfaces were triaxially loaded to produce a sequence of stick slip events during these experiments we monitored stress strain and seismic activity after the experiments fault structures were imaged in thin sections and using computer tomography the laboratory fault zones showed many structural characteristics observed in upper crustal faults including zones of localized slip embedded in a layer of fault gouge laboratory faults also exhibited a several millimeter wide damage zone with decreasing micro crack density at larger distances from the fault axis in addition to the structural similarities we also observed many similarities between our observed distribution of acoustic emissions aes and natural seismicity the aes followed the gutenberg richter and omori utsu relationships commonly used to describe natural seismicity moreover we observed a connection between along strike fault heterogeneity and variations of the gutenberg richter b value as suggested by natural seismicity studies areas of low b value marked the nucleation points of large slip events and were located at large asperities within the fault zone that were revealed by post experimental tomography scans our results emphasize the importance of stick slip experiments for the study of fault mechanics the direct correlation of acoustic activity with fault zone structure is a unique characteristic of our laboratory studies that has been impossible to observe in nature

ca cycling and isotopic fluxes in forested ecosystems in hawaii 1 biogeochemical processes fractionate ca isotopes in plants and soils along a 4 million year developmental sequence in the hawaiian islands we observed that plants preferentially take up 40ca relative to 44ca and that biological fractionation and changes in the relative contributions from volcanic and marine sources produce a significant increase in 44ca in soil exchangeable pools our results imply moderate fluxes enriched in 44ca from strongly nutrient depleted old soils in contrast with high 40ca fluxes in young and little weathered environments in addition biological fractionation controls divergent geochemical pathways of ca and sr in the plant soil system while ca depletes progressively with increasing soil age sr ca ratios increase systematically sr isotope ratios provide a valuable tracer for provenance studies of alkaline earth elements in forested ecosystems but its usefulness is limited when deciphering biogeochemical processes involved in the terrestrial ca cycle ca isotopes in combination with sr ca ratios reveal more complex processes involved in the biogeochemistry of ca and sr

ferrihydrite and allophane in four andepts from hawaii and implications for their classification abstract the mineralogy and composition of the waimea kukaiau akaka and hilo soils on the island of hawaii were studied using methods which included moessbauer spectroscopy and chemical dissolution the hilo soil which experiences 3000 mm year rainfall and the akaka soil 3800 mm year rainfall both contain large amounts about 25 of iron oxides of short range order together with other iron oxides gibbsite and allophane the iron oxides of short range order have characteristics similar to those of the reactive mineral ferrihydrite which is known to occur in a wide range of soils these characteristics however in two respects x ray diffraction and acid oxalate solubility do not rule out the presence or admixture of the much less known feroxyhite another closely related iron oxide of short range order most samples from these two soils dry irreversibly to give hard aggregates a property probably related to the presence of the iron oxides of shortrange order both the hilo and the akaka soils are classified as hydrandepts in the current usda soil taxonomy in the new proposed order of andisols these two soils would become hydrudands it is desirable to recognise the presence of short range order iron oxides in these soils the kukaiau soil currently classified as a dystrandept which occurs in a lower rainfall zone 1500 mm year contains about 25 allophane and lesser amounts of ferrihydrite other iron oxides and gibbsite the waimea soil occurs in the lowest rainfall zone 1000 mm year and the dominant mineral is halloysite but some allophane ferrihydrite and hematite are also present this soil is currently classified as a eutrandept under the andisol proposal the kukaiau and waimea soils would be a hapludand and a haplustand respectively quartz mica and other layer silicates were present in all four of the soils suggesting that there have been additions of eolian material

germanium sequestration by soil targeting the roles of secondary clays and fe oxyhydroxides abstract germanium is a trace element that behaves similarly to silicon and shows promise as a tracer of silicate weathering processes sequestration of ge by clay minerals is thought to be the dominant mechanism responsible for ge si fractionation during weathering in some environments ge may be sequestered by iron oxyhydroxides we examine ge behavior in soils along a well characterized climate gradient on the hawaiian island of maui to clarify the relationship between fe geochemistry and soil ge si ratios all of the sites are developed on basaltic lavas and tephras approximately 400 ky old are highly si depleted and have ge si ratios higher than parent material sites experiencing less than 3300 mm rain yr host oxidized highly weathered basaltic soils in which fe is present as secondary fe oxyhydroxide minerals in contrast the wetter sites 3340 mm yr show extensive fe reduction mobilization and loss we show that ge sequestration is independent of fe redox behavior along the gradient and thus precipitation of fe oxyhydroxides is not a major factor contributing to ge si fractionation during weathering instead elevated soil ge si ratios reflect partitioning of ge into secondary clay minerals plus additional retention of ge by refractory non silicates

how long is an aftershock sequence the occurrence of a mainschok is always followed by aftershocks spatially distributed within the fault area the aftershocks rate decay with time is described by the empirical omori law which was inferred by catalogues analysis the sequences discrimination within catalogues is not a straightforward operation especially for low magnitude mainshocks here we describe the rate decay of the omori law obtained using different sequence discrimination tools and we discover that when the background seismicity is excluded the sequences tend to last for the temporal extension of the catalogue

scaling properties of the parkfield aftershock sequence aftershock sequences present a unique opportunity to study the physics of earthquakes important questions concern the fundamental origin of three widely applicable scaling laws 1 gutenberg richter frequency magnitude scaling 2 omori s law for aftershock decay rates and 3 bath s law for the difference between the magnitude of the largest aftershock and a mainshock the high resolution parkfield seismic network provided the opportunity for detailed studies of the aftershock sequence following the 28 september 2004 m 6 0 parkfield earthquake in this article it is shown that aftershocks satisfy the gutenberg richter scaling relation only for relatively large times after the mainshock there is a systematic time delay for the establishment of this scaling law the temporal evolution of the rates of occurrence of aftershocks is quantified using the generalized omori s law this scaling law contains two characteristic times c and the analysis suggests that the parameter c plays the role of a characteristic time for the establishment of gutenberg richter scaling this time increases systematically with a decreasing lower magnitude cutoff the systematic time delay is attributed to a cascade of energy from long wavelengths to short wavelengths the parameter is a measure of the average time until the first aftershock occurs we find that slightly varies with the lower magnitude cutoff of the sequence we also note that the largest aftershock inferred from an extrapolation of gutenberg richter scaling m 5 0 is equal to the largest observed aftershock this scaling associated with the universal applicability of bath s law is attributed to a constant partitioning of energy between a mainshock and its associated aftershock sequence we also give in this article the distribution of interoccurrence times between successive aftershocks we show that this distribution is well approximated by a nonhomogeneous poissons process driven by the modified omori s law the self consistency between interoccurrence statistics and decay rates is taken as further evidence for the applicability of our studies

common dependence on stress for the two fundamental laws of statistical seismology the gutenberg richter relation and the omori utsu law both power laws are two of the long standing relationships of statistical seismology here aftershock sequences are described according to the faulting style of their main shocks showing that the time delay before the onset of the power law aftershock decay rate is on average shorter for thrust main shocks than for normal fault earthquakes these similar dependences on the faulting style indicate that both the fundamental power laws are governed by the state of stress

aspects of structure in earthquake networks analysis performed on multiple sets of earthquake networks created for the hawaii volcanic system reveals characteristics that can be associated with fundamental properties of seismicity the scale free behaviour of the connectivity distribution along the spectrum of the minimum weight values which can be used to discern the interrelated earthquakes from the rest of the data set is mirrored by a similar behaviour of the distribution of the number of linked neighbours the patterns found in the distributions of temporal and spatial intervals between earthquakes are similar from large to small networks similarities are found between the variation of the network clustering coefficient c and the variation of the exponents of the connectivity distribution and of the weight distribution their synchronous variation over successive temporal windows can be related to changes in seismicity and in the life of the volcanic system a zipf distribution is found for the ranked sets of magnitude values of successive network nodes the distribution of differences between the magnitude values of successive nodes is also governed by a power law

from a black to a gray box a mass balance interpretation of pedogenesis we utilize chemical elements as tracers in a mass balance analysis that provides functional relationships among soil chemical composition bulk density and volume change in relation to parent material these analytical functions are based on the principle of conservation of mass and include a term quantifying mass flux into out of the soil and between horizons we apply the technique to the oldest member of a chronosequence developed on marine terraces in northern california it is an alfisol that evolved from beach sand to its present state nearly one third of its weight is composed of secondary clay minerals in about 240 ky aside from large increases in organic carbon desilication is the dominant factor in soil evolution 29 50 83 g cm 2 si was leached from the beach sand during pedogenesis the rate of desilication is roughly 2 1 t km 2 yr 1 0 21 g cm 2 ky 1 an order of magnitude slower than that implied by the si denudation rate calculated for the mattole river watershed weathering of primary minerals and synthesis of secondary minerals is relatively well advanced suggesting that the rate of desilication may be declining the local beach is composed of quartz and sodic plagioclase with smaller amounts of chlorite mica and kaolinite the soil has substantially different mineralogy sand is dominated by quartz and clay is dominated by kaolinite halloysite chloritic intergrades and gibbsite bases are also leached though the total mass was much less 57 2 55 g cm 2 of na in the beach sand was lost as plagioclase weathered by focusing on elemental and mineralogical gains and losses we emphasize the essential connection between the pedologic environment and the external hydrochemical environment

the impact of climate on the biogeochemical functioning of volcanic soils abstract rainfall and the amount of water available to leach ions from soil are among the most important features determining mineral weathering secondary mineral synthesis and soil chemical properties along an arid to humid climosequence on kohala mountain hawaii we sampled 16 soil profiles and found that weathering and soil properties change in a nonlinear fashion with increased rainfall the lavas are influenced by a strong rain shadow with mean annual precipitation map averaging 160 mm near the coast and rising to 3000 mm near the summit a temperature decline from 24 to 15 c with increasing elevation is matched by lower potential evapotranspiration et a water balance model monthly precipitation minus monthly et defines three broad climate zones along the sampling transect an arid zone with moisture deficit in every month an intermediate zone with moisture deficit during low rainfall summer months and moisture surplus during high rainfall winter months and a humid zone with moisture surplus during every month the annualized water balance can be ratioed with the integrated porosity of the top meter of soil to provide a leaching index the index reaches 1 total filling of the pore space on an annual basis at about 1400 mm map index values 1 imply intense leaching conditions because of pore water replacement in these 170 ka soils leaching losses of soluble base cations and si are nearly complete at index values 1 whereas only 60 of al has been lost at index values 1400 mm soil buffering capacity has been totally exhausted leading to low ph and low ecec the nonlinear decline in ecec is irreversible under natural conditions base cation depleted soils will remain so even if the climate shifts to drier conditions in contrast a climate shift to wetter conditions can drastically modify surface chemical properties existing in the drier soils as weathering depletes primary minerals elements are lost to leaching and surface chemistry is modified there is a time dimension implied in climate gradient studies soils forming in recently rejuvenated landscapes contain more primary minerals and should experience loss of buffering capacity at higher rainfall loss of buffering capacity means that biological acidity will move more deeply into the vadose zone or into the aquatic system the details of this transfer depend on present and past climate and the age and erosional stability of landscapes

bayesian confidence intervals for the magnitude of the largest aftershock aftershock sequences which follow large earthquakes last hundreds of days and are characterized by well defined frequency magnitude and spatio temporal distributions the largest aftershocks in a sequence constitute significant hazard and can inflict additional damage to infrastructure that is already affected by the main shock therefore the estimation of the magnitude of a possible largest aftershock in a sequence is of high importance in this work a bayesian predictive distribution and the corresponding confidence intervals for the magnitude of the largest expected aftershock in a sequence are derived using the framework of bayesian analysis and extreme value statistics the analysis is applied to 19 well known aftershock sequences worldwide to construct retrospectively the confidence intervals for the magnitude of the subsequent largest aftershock by using the statistics of early aftershocks in the sequences

background seismicity in boso peninsula japan long term acceleration and relationship with slow slip events slow slip events sses in subduction zones can trigger earthquake swarms especially at shallow depth the monitoring of seismicity rates has therefore the potential to help detect and characterize sses and transient changes in coupling however the relationship between seismicity rate and slow slip rate during a sse is unknown and made complicated by aftershock triggering within the swarm here we propose to complement geodetic methods with an objective measure of the seismicity rate that is directly associated with changes in slip rate we show that this measure applied to known occurrences of sses in the boso area japan yields an estimate albeit indirect of their seismic moment hence their slip rate we finally prove that the background rate in boso has been accelerating since 1990 this explains previous observations of the shortening of the recurrence time between sses in boso that clearly predate the 2011 mw9 0 tohoku oki earthquake

fractionation of fe isotopes by soil microbes and organic acids small natural variations in fe isotopes have been attributed to biological cycling however without understanding the mechanisms of fractionation it is impossible to interpret such variations here we show that the d 56 fe of fe dissolved from a silicate soil mineral by siderophore producing bacteria is as much as 0 8 lighter than bulk fe in the mineral a smaller isotopic shift is observed for fe released abiotically by two chelates and the magnitude of the shift increases with affinity of the ligand for fe consistent with a kinetic isotope effect during hydrolysis of fe at the mineral surface fe dissolved abiotically without chelates shows no isotopic shift the d 56 fe of the exchange fraction on soil grains is also lighter by 0 6 1 than fe from both hornblende and iron oxyhydroxides the kinetic isotope effect is therefore preserved in open systems such as soils when recorded in the rock record fe isotopic fractionation could document fe transport by organic molecules or by microbes where such entities were present in the geologic past

kinetic iron stable isotope fractionation between iron ii and iii complexes in solution abstract iron stable isotope fractionation between tris 2 2 bipyridine iron ii fe ii bipy 3 2 and iron iii chloride complexes has been measured using plasma source mass spectrometry the experimental protocol involves complexing fe ii ion with 2 2 bipyridine in a fe ii fe iii chloride solution and then separating the fe ii and fe iii solution species in 6 m hcl on an anion exchange resin large isotopic variations of 57 fe and 56 fe are experimentally measured in the two separated solution fractions with isotopic fractionations increasing from fe ii fe iii 25 to 174 units for 57 fe 54 fe and 17 to 117 units for 56 fe 54 fe the increase in fractionations correlates with a decrease in the mole fraction of fe ii in the solution fe fe ii fe ii fe iii that results from the dissociation and breakdown of fe ii bipy 3 2 complex in 6 m hcl solution the data variations are mainly ascribed to a kinetic fractionation occurring during this dissociation reaction mass balance calculations assuming that a rayleigh law describes the overall isotopic trends suggest a kinetic fractionation of ca 1 010 100 units the magnitude of this fractionation is attributed to the rupturing of the strong covalent bonds between 2 2 bipyridine and fe ii ion the experimental data confirm that the coordination chemistry of iron exhibits a profound control on its isotopic behaviour and that kinetic fractionations may play an important role in its isotope geochemistry as was also found in the pioneering experimental studies of the sulphur isotopic system in solution

iron isotope fractionation in river colloidal matter temporal variations in the iron isotopic composition 56fe between 0 13 and 0 31 have been measured in the suspended fraction in a boreal river the major mechanism behind these variations is temporal mixing between two types of particles colloids fe oxyhydroxides and fe c colloids data in this study indicate that these two types of colloids have different fe isotope composition the fe c colloid has a negative 56fe value whereas the fe oxyhydroxide colloid is enriched in 56fe these two types of colloidal matter have different hydrogeochemical origin the fe c colloid reaches the river during storm events when the upper sections of the soil profile o and e horizons are flooded by a rising water table colloidal fe oxyhydroxides reach the river via inflow and subsequent oxidation of groundwater enriched in dissolved fe ii