alteration of hyaloclastites in the hsdp 2 phase 1 drill core 2 mass balance of the conversion of sideromelane to palagonite and chabazite this is the publisher s version also available electronically from http onlinelibrary wiley com

seafloor alteration of basaltic glass textures geochemistry and endolithic microorganisms 1 the incipient low temperature alteration of glassy margins of recent seafloor lavas from the mohns ridge is characterized by scanning electron microscopy and bulk chemical analyses of major and trace elements these investigations are designed to evaluate the endolithic microbial biomass to identify relations between alteration textures and microorganisms and to identify the chemical processes that take place during alteration the basaltic glass along intersecting fractures and around vesicles is typically altered to concentrically zoned yellow brown amorphous gel palagonite in most fractures microorganisms are observed at the outer surfaces of palagonite rims within porous zones of the rims and frequently also at the glass palagonite interfaces the cells act as nucleation sites for precipitation and become encrusted and embedded in palagonite with time zones of porous palagonite containing numerous hollow fossilized cells alternate with zones of compact palagonite lacking distinct cell structures which together indicate that the microbial growth is discontinuous the palagonite has an average organic carbon content of 0 9 wt 13corg 22 which derive from both living and fossilized biomass the microbial growth and biomineralization are major controls on the porosity and texture of the palagonite and thus likely on the chemical exchange between glass and seawater pit marks in the glass in fractures both with and without microbes indicate that microbial as well as abiotic processes mediate pitting elemental and isotope data show that the transformation of glass to gel palagonite at seafloor conditions with high water rock ratios results in near complete loss of si and alkali elements to seawater formation of fe and al oxyhydroxides complete exchange of alkaline earth elements like sr with seawater retention of v cu y pb th u and trivalent rees accompanied by a strong gain of these and other elements from seawater higher fe ti ratios in the gel palagonite compared to the parental glass suggest that the palagonite represents a mixture of fe ti oxyhydroxides derived from both the glass and seawater

importance of small earthquakes for stress transfers and earthquake triggering 1 we estimate the relative importance of small and large earthquakes for static stress changes and for earthquake triggering assuming that earthquakes are triggered by static stress changes and that earthquakes are located on a fractal network of dimension d this model predicts that both the number of events triggered by an earthquake of magnitude m and the stress change induced by this earthquake at the location of other earthquakes increase with m as similar to 10 dm 2 the stronger the spatial clustering the larger the influence of small earthquakes on stress changes at the location of a future event as well as earthquake triggering if earthquake magnitudes follow the gutenberg richter law with b d 2 small earthquakes collectively dominate stress transfer and earthquake triggering because their greater frequency overcomes their smaller individual triggering potential using a southern california catalog we observe that the rate of seismicity triggered by an earthquake of magnitude m increases with m as 10 alpha m where alpha 1 05 0 05 we also find that the magnitude distribution of triggered earthquakes is independent of the triggering earthquake s magnitude m when alpha approximate to b small earthquakes are roughly as important to earthquake triggering as larger ones we evaluate the fractal correlation dimension d of hypocenters using two relocated catalogs for southern california the value of d measured for distances 0 1 r 5 km is d 1 54 for the shearer et al catalog and d 1 73 for the hauksson et al catalog the value of d reflects both the structure of the fault network and the nature of earthquake interactions by considering only those earthquake pairs with interevent times larger than 1000 days we can largely remove the effects of short term clustering then d approximate to 2 close to the value d 2 alpha 2 1 predicted by assuming that earthquake triggering is due to static stress the value d approximate to 2b implies that small earthquakes are as important as larger ones for stress transfers between earthquakes and that considering stress changes induced by small earthquakes should improve models of earthquake interactions

microbes play an important role in the alteration of oceanic crust microbes have been identified within altered parts of the glass rims of pillow lavas in the upper oceanic crust 237 m below the top of the volcanic basement of odp hole 896a at the costa rica rift their presence is verified by spherical and vermicular microbodies containing dna the elemental composition of the microbially processed areas differ from the parent glass further the microbially processed parts showing different morphological forms also show different elemental composition extreme k enrichment indicate that microbes are presently active in the alteration process the carbon isotopic composition of disseminated carbonates within the basaltic section of the hole 504b 1 km distance from hole 896a also give evidence for microbial activity during rock alteration the 13c values of most of these trace carbonates are very low reflecting metabolic control of the carbon cycle in these rocks microbial alteration of basaltic glass comprising a substantial volume and surface area of the upper oceanic crust may thus play an important role in the element exchange between oceanic crust and seawater

chemical changes during progressive subaerial palagonitization of a subglacial olivine tholeiite hyaloclastite a microprobe study abstract the palagonite and parent sideromelane of the 6 7 mm thick reddish brown subaerial weathering zone w z as well as the less altered palagonite sideromelane inside the w z of an olivine tholeiite hyaloclastite have been investigated by xrd sem and the microprobe the light reddish brown to deep yellow palagonite rinds around the sideromelane grains in the outer part of the w z is 4 5 times thicker than the dark brown to nearly black palagonite 6 m thick inside the w z relative to the parent sideromelane the palagonite in the w z is considerably more depleted in sio 2 and mgo slightly more depleted in cao and considerably more enriched in al 2 o 3 and tio 2 than the palagonite inside the w z na 2 o is consistently depleted whereas feo t shows only minor variations in either direction k 2 o shows the largest variations by being strongly depleted in the outer part of the w z and strongly enriched inside the w z no authigenic minerals were observed in the palagonite and intergrain pores of the hyaloclastite the chemical variations within a palagonite rind or across the analysed profile are therefore assumed to have taken place in the amorphous state of palagonite through interaction with freshwater environment

alteration of hyaloclastites in the hsdp 2 phase 1 drill core 1 description and paragenesis this is the publisher s version copyright 2003 by chinese geophysical society all rights reserved

direct and indirect impact of the bacterial strain pseudomonas aeruginosa on the dissolution of synthetic fe iii and fe ii bearing basaltic glasses abstract this study investigates the direct and indirect bacterial contributions that influence the dissolution of basaltic glass in this regard three different types of glasses with or without fe in the reduced fe ii or oxidized fe iii states were prepared on the basis of a simplified basaltic glass composition in order to prevent the direct contact between the glasses and the model siderophore producing strain pseudomonas aeruginosa the glass samples were isolated in dialysis bags and immersed at 25 c and ph 6 5 in bacterial cultures throughout the dissolution experiments the following parameters were monitored determination of bacterial growth quantification of siderophore i e pyoverdine production microscopic observation of the glass surface and determination of dissolution kinetics isolating the glass from the bacterial suspension only triggered the biosynthesis of siderophores in the fe iii bearing glass dissolution experiments siderophores were produced in the presence of fe ii bearing and fe free glass independently on the experimental setup the siderophore production appeared to be either continuous in the absence of fe glass free control fe free glass dissolution experiments or stopped as soon as the bacteria entered their stationary phase when an fe source was present fe ii and fe iii bearing glass dissolution experiments the increase in the dissolution rates of each glass was correlated to the complex stability constants of the siderophore with the metallic cations in presence kfe2

seismically induced changes of the fluid signature detected by a multi isotope approach he co2 ch4 n2 at the wettinquelle bad brambach central europe 1 we present a study considering the systematics of gas and isotope compositions 3 he 4 he 13 c co2 13 c ch4 15 n of a permanent magmatic co 2 flux in the hydrothermal system of the spring wettinquelle in bad brambach and their relation to the seismic activity beneath the western eger rift the gas and isotope compositions were monitored for more than 3 years the time series includes periods before during and after a 4 month long seismically active period from the end of august to the end of december 2000 shifts due to admixture of crustal components were found for all monitored isotope ratios during and after the seismically active period in case of helium and nitrogen isotopic anomalies occurred already about 6 weeks before the beginning of the seismically active period contemporaneous with a water level anomaly of the well vl4 near the wettinquelle on the one hand preseismic deformations may be responsible for the observed isotope anomalies on the other hand coseismic fracturing processes in the surroundings of the hypocenters may play a role both effects produce greater permeability and result in the release of crustal fluids the migration and admixture of these crustal components to the permanent upper mantle derived fluid flux result in geochemical anomalies that persist for more than 2 years the results of the detailed isotope monitoring have proven to be an important contribution to understand the geodynamic processes that may presently be going on in the region vogtland nw bohemia

nontrivial decay of aftershock density with distance in southern california the decay of the aftershock density with distance plays an important role in the discussion of the dominant underlying cause of earthquake triggering here we provide evidence that its form is more complicated than typically assumed and that in particular a transition in the power law decay occurs at length scales comparable to the thickness of the crust this is supported by an analysis of a very recent high resolution catalog for southern california sc and surrogate catalogs generated by the epidemic type aftershock sequence etas model which take into account inhomogeneous background activity short term aftershock incompleteness anisotropic triggering and variations in the observational magnitude threshold our findings indicate specifically that the asymptotic decay in the aftershock density with distance is characterized by an exponent larger than 2 which is much bigger than the observed exponent of approximately 1 35 observed for shorter distances ranging from the main shock rupture length up to a length scale comparable to the thickness of the crust this has also important consequences for time dependent seismic hazard assessment based on the etas model

quantitative description of induced seismic activity before and after the 2011 tohoku oki earthquake by nonstationary etas models 1 the epidemic type aftershock sequence etas model is extended for application to nonstationary seismic activity including transient swarm activity or seismicity anomalies in a seismogenic region the time dependent rates of both background seismicity and aftershock productivity in the etas model are optimally estimated from hypocenter data these rates can provide quantitative evidence for abrupt or gradual changes in shear stress and or fault strength due to aseismic transient causes such as triggering by remote earthquakes slow slips or fluid intrusions within the region this extended model is applied to data sets from several seismic events including swarms that were induced by the m9 0 tohoku oki earthquake of 2011

biological mediation in ocean crust alteration how deep is the deep biosphere abstract biological mediation has been suggested as a control of the chemical exchange between the oceanic crust and seawater but very little is known about its distribution within the oceanic crust and the relative importance of biotic and abiotic processes alteration textures in glassy pillow lava margins record the proportions of biotic and abiotic alteration and the fraction of biotic alteration may be determined by point counting methods we used this method at dsdp odp sites 417d and 418a 110 ma crust south of bermuda rise and holes 504b and 896a 5 9 ma costa rica rift biotic alteration dominates glass alteration in the upper 250 m of the oceanic crust 60 85 of the total glass alteration and steadily declines in importance down to 10 20 at 500 m the consistency of data between two crustal sections of very different age and tectonic setting suggest that microbially mediated glass alteration may be largely confined to the upper oceanic crust however both sites studied are sealed by thick sedimentary layers and thus are typical for ocean crust underlying the oceanic basins rather than crust at mid ocean ridges with possibly deep and rapid hydrothermal circulation down hole temperature measurements at the costa rica rift suggest that glass altering microbes are hyperthermophilic and thrive at least up to temperatures of about 90 c microbial activity does occur at higher temperatures up to about 110 c but with reduced apparent abundance

masking of earthquake triggering behavior by a high background rate and implications for epidemic type aftershock sequence inversions 1 we examine the effects of the spontaneous background event rate and aftershock triggering characteristics on the temporal statistics of seismicity in the epidemic type aftershock sequence model recent work has shown that the earthquake interevent time distribution is generally bimodal a superposition of a gamma component from triggered aftershocks at short time intervals and an exponential component at longer intervals from spontaneous events and the overlapping of independent aftershock sequences the relative size of these two components varies between catalogs so there is no simple universal scaling at the extreme of high spontaneous rate e g in large regions the high probability of temporally overlapping aftershock sequences causes the exponential component to dominate here we further explore the effects of both the spontaneous rate and the aftershock triggering parameters we show that the analytical theory of saichev and sornette 2007 although valid under their assumptions gives the impression of a more universal behavior if used outside its stated range of applicability we also show that within the high overlap high spontaneous rate regime a maximum likelihood inversion of the model s temporal parameters is both less accurate and biased specifically the background rate is systematically overestimated this has implications on the suitable range of region sizes for which parameter inversion may be reliable and must therefore be taken into account in any inversion for temporal variations in background rate in time dependent hazard calculation

quantitative earthquake forecasts resulting from static stress triggering 1 in recent years the triggering of earthquakes has been discussed controversially with respect to the underlying mechanisms and the capability to evaluate the resulting seismic hazard apart from static stress interactions other mechanisms including dynamic stress transfer have been proposed to be part of a complex triggering process exploiting the theoretical relation between long term earthquake rates and stressing rate we demonstrate that static stress changes resulting from an earthquake rupture allow us to predict quantitatively the aftershock activity without tuning specific model parameters these forecasts are found to be in excellent agreement with all first order characteristics of aftershocks in particular 1 the total number 2 the power law distance decay 3 the scaling of the productivity with the main shock magnitude 4 the foreshock probability and 5 the empirical bath law providing the maximum aftershock magnitude which supports the conclusion that static stress transfer is the major mechanism of earthquake triggering

a combined tem and nanosims study of endolithic microfossils in altered seafloor basalt abstract the incipient alteration of basaltic glass to palagonite in recent seafloor lavas from the arctic mohns ridge was studied by complimentary high spatial resolution geochemical techniques tem eds transmission electron microscopy energy dispersive x ray spectroscopy and nanosims nano scale secondary ion mass spectrometry rounded to elongated pores 0 5 2 m across were found embedded in compact palagonite that have sizes and shapes comparable to microbial cells in situ elemental mapping revealed that the micropore rims are comparable in composition to the bulk palagonite and that some are enriched in manganese elevated concentrations of carbon and nitrogen were also found in some of the micropores hence these structures are interpreted as fossilised bacteriomorphs of endolithic microorganisms that inhabited fractures in the basaltic glass the preferential accumulation of mn in some of the cell encrustations suggests the mineralisation of mn oxidising bacteria these data provide further evidence for the involvement of microorganisms in the colonisation and chemical alteration of recent seafloor volcanic glass and identify micro scale mn enrichments associated with micropores as a promising biosignature in such rocks

elemental abundance distributions in suboceanic basalt glass evidence of biogenic alteration 1 the alteration of subseafloor volcanic glass from three locations is qualitatively attributed to biological biotic or chemical abiotic reactions on the basis of microscopic morphology of the boundary between the unaltered and altered glass eleven element composition of fresh basalt glass sideromelane and its alteration products were determined by electron microprobe principal component analysis pca using these eleven elements as input na11 mg12 al13 si14 p15 cl17 k19 ca20 ti22 mn25 and fe26 extracts three factors accounting for 80 5 of the variance in the data these three factors can serve as inputs to a hierarchical cluster analysis hca algorithm for data driven discovery of three sample classes this autonomous classification agrees with the petrographic microscopic classification in 14 of 15 biotic clay analyses from a set of 34 analyses identified microscopically as abiotic clay the autonomous system identifies 4 with elemental abundance characteristics similar to the biotic clay and 4 similar to unaltered glass pca factors are then used as inputs to train an artificial neural network to produce a bayesian probability of correct classification using the classes discovered by hca mean bayesian probabilities of correct classification for abiotic clays biotic clays and glass were 76 1 8 5 64 9 9 0 and 77 0 7 2 respectively interestingly in the 9 of 74 cases where visual and elemental analysis disagree the bayesian probability estimate of correct classification using only elemental abundance data is low 60 0 11 7 compared to analyses where visual and elemental data agree 75 5 7 8 to our knowledge this is the first demonstration of a quantitative method for discrimination of biotic and abiotic alteration of subocean basalt glass as such the techniques make possible the systematic assessment of the impact of microbial life on subsurface basalts

sand rich turbidite system of the late oligocene northern apennines foredeep physical stratigraphy and architecture of the macigno costiero coastal tuscany italy

seafloor bioalteration of sulfide minerals results from in situ incubation studies we present results of incubation studies conducted at low temperatures 4 c in the vicinity of a seafloor hydrothermal vent system we reacted fe s cu and zn bearing minerals including pyrite marcasite chalcopyrite sphalerite elemental sulfur and a portion of a natural chimney sulfide structure for 2 months at the main endeavour segment of the juan de fuca ridge in the pacific ocean our study utilizes fluorescent in situ hybridizations fish scanning and transmission electron microscopy sem tem and light microscopic analysis the surfaces of these minerals are solely colonized by bacteria and not by archaea colonization densities vary over an order of magnitude with the following sequence elemental sulfur chimney sulfide marcasite pyrite sphalerite chalcopyrite and correspond well with the abiotic oxidation kinetics of these materials excepting elemental sulfur which is both the least reactive to oxidizing species and the most heavily colonized colonization densities also correspond with apparent degree of reaction dissolution pitting accumulation of secondary alteration products heavy accumulations of secondary fe oxides on fe bearing minerals most notably on the chimney sulfide form in situ as the result of mineral dissolution and the activity of neutrophilic fe oxidizing bacteria results suggest that mineral oxidizing bacteria play a prominent role in weathering of seafloor sulfide deposits and that microbial utilization of mineral substrates contributes to biomass production in seafloor hydrothermal environments

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

analysis of temporal and spatial heterogeneity of magnitude frequency distribution inferred from earthquake catalogues summary statistical models are introduced for the simultaneous estimation of the changes of the b value and detection rate of earthquakes in a catalogue which develops in time or varies in space the three characteristic parameters including b for the magnitude frequency distribution of detected earthquakes are represented by respective three b spline functions of time or location in a space an objective bayesian method is adopted for the optimal estimate of such functions with many unknown coefficients the present procedure is applied to earthquake catalogues for japanese seismic activity

diversity of life in ocean floor basalt abstract electron microscopy and biomolecular methods have been used to describe and identify microbial communities inhabiting the glassy margins of ocean floor basalts the investigated samples were collected from a neovolcanic ridge and from older sediment covered lava flows in the rift valley of the knipovich ridge at a water depth around 3500 m and an ambient seawater temperature of 0 7 c successive stages from incipient microbial colonisation to well developed biofilms occur on fracture surfaces in the glassy margins observed microbial morphologies are various filamentous coccoidal oval rod shaped and stalked forms etch marks in the fresh glass with form and size resembling the attached microbes are common precipitation of alteration products around microbes has developed hollow subspherical and filamentous structures these precipitates are often enriched in fe and mn the presence of branching and twisted stalks that resemble those of the iron oxidising gallionella indicate that reduced iron may be utilised in an energy metabolic process analysis of 16s rrna gene sequences from microbes present in the rock samples show that the bacterial population inhabiting these samples cluster within the and proteobacteria and the cytophaga flexibacter bacteroides subdivision of the bacteria while the archaea all belong to the crenarchaeota kingdom this microbial population appears to be characteristic for the rock and their closest relatives have previously been reported from cold marine waters in the arctic and antarctic deep sea sediments and hydrothermal environments

characteristics of earthquake clusters application to western corinth gulf greece abstract the western corinth gulf one of the most seismically active areas in greece with frequent earthquake sequences and a dense seismological network is an ideal region for investigating the properties of earthquake clusters we study 47 earthquake clusters identified using a high resolution earthquake catalog and the curate clustering algorithm based on the skewness and kurtosis of their moment release history 31 sequences are successfully distinguished as earthquake swarms and 13 as mainshock aftershock sequences three sequences could not be classified the relationship between skewness and kurtosis leads to a parabola where mainshock aftershock sequences are located to the right part high values of skewness and kurtosis whereas earthquake swarms to the center left low values of skewness and kurtosis this discrimination is validated by taking into consideration the occurrence time of the largest event in the sequence as well as the difference in magnitude between the largest event and other larger events twelve clusters which consist of several burst like repeaters show evidence of fluid driven activity with diffusivity ranging from 0 5 to 1 8 m2 s for the triggering front and 0 1 to 0 4 m2 s for the back front the observed temporal evolution of earthquake swarms compared to that expected from the etas stochastic model shows that they have distinct values for the model parameters and finally interevent time distributions for four clusters having at least 100 events show that a lognormal distribution fits best in all cases suggesting a degree of triggering between subsequent events

impact of aseismic transients on the estimation of aftershock productivity parameters abstract the epidemic type aftershock sequence etas model has been shown to describe successfully the statistical seismicity properties if earthquake triggering is related to tectonic forcing and earthquake induced stress changes however seismicity is locally often dominated by stress changes related to transient aseismic processes to avoid erroneous parameter estimations leading to biased forecasts it is important to account for those transients we apply a recently developed iterative algorithm based on the etas model to identify the time dependent background and etas parameters simultaneously we find that this procedure works well for synthetic data sets if catalog errors are appropriately considered however ignoring the time dependence leads to significantly biased parameter estimations in particular the value describing the magnitude dependence of the triggering kernel can be strongly underestimated if transients are ignored low values have been previously found for swarm activity for which transient aseismic processes are expected to play a major role these observed anomalously low values might thus indicate the importance of transient forcing rather than being due to differences in the earthquake earthquake trigger mechanism to explore this we apply the procedure systematically to earthquake clusters detected in southern california and to earthquake swarm activity in vogtland western bohemia while low values are mostly shown to be a consequence of catalog errors and time dependent forcing but not related to different earthquake earthquake interaction mechanisms some significant low values are observed in high heat flow areas in california confirming the existence of thermal control on earthquake triggering

earthquakes induced by water injection at 3 km depth within the rongchang gas field chongqing china 1 unwanted water amounting more than 1 million m 3 has been injected intermittently at a pumping pressure of 2 1 2 9 mpa over hydrostatic at 2 6 2 9 km depth within the rongchang gas field western chongqing china since july 1988 the injections have induced more than 32 000 surface recorded earthquakes including 2 of m l 5 14 of m l 4 and more than 100 of m l 3 up until the end of 2006 we examined the epidemic type aftershock sequence etas model and the temporal evolution of several statistics of the earthquake sequence the random component in the etas model can be considered as an indicator of fluid driven activity while the rate of omori law type aftershocks indicates stress triggering of the preceding earthquakes we observed three distinct seismic activity phases that were coincident with different injection periods phase i corresponds to initial injections with low injection rate long time interval and shows a vast majority of omori type events and only 8 externally forced activity phase ii corresponds to a period of high injection rates and shows intense earthquake activity characterized by a high percentage 45 of fluid driven earthquakes phase iii demonstrates decreasing seismicity as a result of a lowering in the injection rate more than 70 of earthquakes occurred randomly over time indicating the dominance of external triggering the physical mechanism that induced the rongchang earthquake sequence was a change in coulomb s failure stress caused by pore pressure diffusion and transformed from seismic slip of preceding earthquakes a pressure increase of 2 1 2 9 mpa at the injection well is more than sufficient to induce failure within the local formations

slow slip and aseismic deformation episodes associated with the subducting pacific plate offshore japan revealed by changes in seismicity 1 aseismic phenomena including slow slip can alter the surrounding seismicity we here investigate how seismicity can be used in order to reveal episodes of aseismic deformation an objective method is proposed that accounts for both earthquake interactions and transient loading applying it to the 1990 2011 pre tohoku seismicity of the japan subduction zone we find several significant instances of aseismic transients small scale and short duration transients are favored updip of the subducting plate large scale transients are mostly observed offshore ibaraki prefecture in a partly decoupled zone that extends downdip the four most intense of such transients have occurred periodically every 5 9years and are likely due to slow slip episodes other aseismic phenomena including possible fluid intrusion in the outer rise are also detected finally the seismicity in january and february 2011 close to the epicenter of the megathrust tohoku earthquake is found to be due to aseismic loading confirming previous studies although this transient is only one among others and is not the most intense nor the most significant for the 21year long period studied here

gradual unlocking of plate boundary controlled initiation of the 2014 iquique earthquake a long foreshock series unlocked the south american plate boundary until eventually initiating the m 8 1 iquique chile earthquake two groups publishing in this issue of nature analyse the seismic context of the iquique earthquake that occurred off the coast of northern chile on 1 april 2014 in a seismic zone that had been quiescent since a significant event in 1877 gavin hayes et al identify areas of remaining or elevated earthquake hazard along the megathrust fault in the region and conclude that the 2014 iquique event was not the earthquake that had been anticipated given that significant sections of the northern chile subduction zone have not ruptured in almost 150 years they suggest that it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 iquique sequence bernd schurr et al show that the april 2014 earthquake broke a central fraction of the northern chile seismic gap the last major segment of the south american plate boundary that had yet to rupture in the past century from july 2013 up to the april earthquake they identify three seismic clusters along this part of the plate boundary each lasting a few weeks with earthquakes of increasing peak magnitudes they conclude that these seismic clusters and their slip transients reflect a gradual weakening of the central part of the seismic gap that was instrumental in initiating the final failure on 1 april 2014 northern chile was struck by a magnitude 8 1 earthquake following a protracted series of foreshocks the integrated plate boundary observatory chile monitored the entire sequence of events providing unprecedented resolution of the build up to the main event and its rupture evolution here we show that the iquique earthquake broke a central fraction of the so called northern chile seismic gap the last major segment of the south american plate boundary that had not ruptured in the past century1 2 since july 2013 three seismic clusters each lasting a few weeks hit this part of the plate boundary with earthquakes of increasing peak magnitudes starting with the second cluster geodetic observations show surface displacements that can be associated with slip on the plate interface these seismic clusters and their slip transients occupied a part of the plate interface that was transitional between a fully locked and a creeping portion leading up to this earthquake the b value of the foreshocks gradually decreased during the years before the earthquake reversing its trend a few days before the iquique earthquake the mainshock finally nucleated at the northern end of the foreshock area which skirted a locked patch and ruptured mainly downdip towards higher locking peak slip was attained immediately downdip of the foreshock region and at the margin of the locked patch we conclude that gradual weakening of the central part of the seismic gap accentuated by the foreshock activity in a zone of intermediate seismic coupling was instrumental in causing final failure distinguishing the iquique earthquake from most great earthquakes finally only one third of the gap was broken and the remaining locked segments now pose a significant increased seismic hazard with the potential to host an earthquake with a magnitude of 8 5

maximum earthquake size and seismicity rate from an etas model with slip budgetmaximum earthquake size and seismicity rate from an etas model with slip budget

foreshock rates from aftershock abundance the question whether foreshocks behave like mainshocks that happen to have larger aftershocks is important for the understanding of earthquake nucleation and the modeling of earthquake clustering many models including the short term earthquake probability step model for forecasting short term earthquake hazard in california and the epidemic type aftershock sequence etas model for the description of earthquake clustering imply that all earthquakes of magnitude m including foreshocks can trigger earthquakes according to a magnitude dependent triggering ability 10 m the magnitudes of the triggered earthquakes are proportional to 10 bm according to the gutenberg richter relation for the magnitude frequency distribution and therefore can be larger than the magnitude of the initiating event however numerous studies observe a lower foreshock occurrence than predicted from aftershock models in this article we show that for homogeneous earthquake catalogs and a consistent definition of foreshocks and aftershocks foreshock rates can be predicted from aftershock characteristics for southern california the probability that the initiating event of an earthquake cluster in the magnitude range 2 0 4 5 is followed by at least one larger event within one day is around 4 this agrees well with corresponding data from the global centroid moment tensor cmt catalog where the probability that the initiating earthquake of a cluster is followed by at least one larger event within 30 days is around 3 these foreshock rates are significantly lower than previously reported and we discuss possible reasons for this

alteration of oceanic volcanic glass textural evidence of microbial activity the subsurface biosphere may constitute as much as 50 percent of earth9s biomass direct and indirect evidence suggests that an extensive biosphere exists in the rocks below the sea floor this survey of basalts of the atlantic pacific and indian oceans supports the hypothesis that bacteria have colonized much of the upper oceanic crust which has a volume estimated at 1018 cubic meters although this is the largest habitat on earth its low abundance of bacteria constitutes much less than 1 percent of earth9s biomass

earthquake swarms in circum pacific subduction zones abstract we systematically and manually search through clusters of earthquakes along circum pacific subduction zones to identify potential earthquake swarms in total we find 266 potential earthquake swarms 180 we classify as megathrust and 68 we classify as volcanic due to their proximity to the megathrust or to volcanoes we focus on the megathrust swarms and demonstrate that 1 the number of events in a swarm is not a function of the largest earthquake in the swarm 2 swarms exhibit an approximately constant rate of seismicity that lasts until after the mean timing of events in the swarm 3 the timing of the largest earthquake in the sequence is no different than the timing of any other earthquake in the sequence 4 our catalogs of earthquakes comprising swarms 9000 events have high b values 1 5 to 2 and 5 when earthquake swarms are considered as single events using total duration and cumulative moment they appear to be consistent with the slow earthquake magnitude duration scaling law presented by ide et al 2007 the first three observations along with the observation that swarms can span very large areas compared to their cumulative seismic moment argue against static stress triggering as a driving mechanism for earthquake swarms along strike propagation velocities are observed for several swarms showing epicentral propagation of 10 km day similar to other documented slow slip events together this evidence implies that aseismic slip along the megathrust is likely an important mechanism for the generation of megathrust earthquake swarms in circum pacific subduction zones we then conduct a comparison of swarms and large megathrust earthquakes finding evidence that the two are broadly anti correlated megathrust segments with large earthquake swarm gaps are more likely to experience large mw 8 megathrust events we characterize the ubiquity of megathrust swarms at different margins and suggest that fault properties along marianas type margins may allow for earthquake swarms to occur regularly but other margins may rely on other variables such as the subduction of a ridge or seamount to facilitate the generation of megathrust earthquake swarms

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

evidence from the ad 2000 izu islands earthquake swarm that stressing rate governs seismicity magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat such swarm seismicity also migrates with time and often exhibits a dog bone shaped distribution the largest earthquakes in swarms produce aftershocks that obey an omori type exponential temporal decay but the duration of the aftershock sequences is drastically reduced relative to normal earthquake activity here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion a 1 000 fold increase in seismicity rate and a 1 000 fold decrease in aftershock duration occurred during the two month long dyke intrusion we find that the seismicity rate is proportional to the calculated stressing rate and that the duration of aftershock sequences is inversely proportional to the stressing rate this behaviour is in accord with a laboratory based rate state constitutive law suggesting an explanation for the occurrence of earthquake swarms any sustained increase in stressing rate whether due to an intrusion extrusion or creep event should produce such seismological behaviour

a new estimation of the decay of aftershock density with distance to the mainshock we investigate how aftershocks are spatially distributed relative to the mainshock compared to previous studies ours focuses on earthquakes causally related to the mainshock rather than on aftershocks of previous aftershocks we show that this distinction can be made objectively but becomes uncertain at long time scales and large distances analyzing a regional earthquake data set it is found that at time t following a mainshock of magnitude m the probability of finding an aftershock at distance r relative to the mainshock fault decays as r where is typically between 1 7 and 2 1 for 3 m 6 and is independent of m for r less than 10 to 20 km and t less than 1 day uncertainties on this probability at larger r and t do not allow for a correct estimation of this spatial decay we further show that a static stress model coupled with a rate and state friction model predicts a similar decay with an exponent 2 2 in the same space and time intervals this suggests that static stress changes could explain the repartition of aftershocks around the mainshock even at distances larger than 10 times the rupture length

submarine mass wasting deposits as an indicator of the onset of foreland thrust loading late permian bowen basin queensland australia in the eastern part of the permo triassic bowen basin of queensland australia a transition from passive thermal subsidence to flexural foreland basin subsidence is recorded within the upper permian stratigraphy two coarse grained intervals containing deposits of mass wasting processes occur within an otherwise siltstone dominated succession over 1500 m thick the moah creek beds and equivalents these intervals can be traced over at least 350 km north south along the structural eastern margin of the basin the lower of the coarse grained intervals is spectacularly exposed in the banks of the fitzroy river west of rockhampton here interbedded sandstones and siltstones of marine shelf origin are abruptly truncated by a mudrock succession containing evidence of slumping and contemporaneous magmatic activity this unit passes up section into packages of mass flow conglomerates and diamictites interpreted to have formed on an unstable submarine slope the character of the mass flow deposits their stratigraphic position and lateral extent are interpreted in terms of destabilization of a sloping marine surface by pulsed subsurface thrust propagation

indications for a successively triggered rupture growth underlying the 2000 earthquake swarm in vogtland nw bohemia 1 the characteristics of earthquake swarms can neither be described by simple laws nor are the underlying mechanisms presently understood swarm activity is often assumed to be caused by an intrusion of fluids into the seismogenic zone we have studied the earthquake catalog of the large earthquake swarm that occurred in the year 2000 in vogtland se germany and nw bohemia an area well known for its episodic swarm generation we observe a significant decrease of the gutenberg richter b value during the swarm evolution as well as a fractal temporal clustering of the earthquakes the spatial spreading of the swarm s activity which is approximately confined to one plane cannot simply be explained by a process of fluid diffusion instead we observe a simple relationship between the spatial spreading and the seismic moment release which is in good agreement with empirical relationships derived for tectonically driven earthquakes and theoretical crack growth models this observation points to a progressively growing main fracture underlying the swarm activity in addition we find that the swarm earthquakes themselves trigger aftershocks near the border of their rupture area the stick slip behavior of the rupture propagation can be explained by stress transfers and induced fluid flows due to earthquakes in a fluid permeated critically loaded fault zone however during the first phase the temporal behavior is found to be different pointing to intrusion of fluids initiating the swarm activity

biologically mediated dissolution of volcanic glass in seawater we studied the effects of biological mediation on the dissolution of basaltic glass in seawater experiments with typical seawater microbial populations were contrasted with a sterile control and reactions were monitored chemically and isotopically biologically mediated experiments produce twice the mass of authigenic phases than abiotic experiments and the phases are different abiotic alteration of glass dissolves basaltic si and ca and scavenges seawater mg while biotic alteration removes ca from seawater such opposing behavior of ca and mg in biotic and abiotic alteration of basaltic glass may have important implications for the carbon cycle and the exchange processes between ocean crust and seawater 87sr 86sr data of glass and alteration products suggest that biological mediation enhances both the diffusion of seawater sr into glass by a factor of 3 4 and the dissolution of basaltic sr into seawater by a factor of 20 40 the dependence of chemical exchange processes between seawater and glass on biological activity implies that chemical fluxes from water rock interaction at low temperatures may change as life on earth evolves

a seafloor microbial biome hosted within incipient ferromanganese crusts exposed rocks on underwater mountains and ridges host abundant and diverse microbial communities x ray and microscopic analyses of volcanic rocks associated with loihi seamount in hawaii suggest that seafloor microbes may commonly be sustained by energy inputs from the water column exposed rocks at underwater volcanoes and ridges host complex abundant and diverse microbial communities1 2 3 the volcanic glasses associated with these features constitute one of the most geochemically reactive components of the earth s crust the most commonly held hypothesis is that their oxidation in sea water provides the energy necessary to establish a seafloor biosphere4 5 6 7 however this hypothesis has yet to be directly tested here we used synchrotron based x ray microprobe mapping x ray absorption spectroscopy and high resolution scanning and transmission electron microscopy techniques to examine the initial chemical changes that occur as the glassy rims of young pillow basalts are colonized by microbial organisms at loihi seamount hawaii we found little evidence of basalt dissolution instead microbial biofilms were intimately associated with fe iii and mn iv oxides that had precipitated from sea water onto the fresh basalt surfaces these accumulations of secondary minerals probably represent the earliest stages of ferromanganese crust formation we suggest that fluid derived energy sources such as dissolved and particulate fe ii mn ii and organic matter may support the microbial communities colonizing seafloor rocks to a greater degree than local rock dissolution

missing links in earthquake clustering models 1 many clustering models imply two kinds of earthquakes spontaneous ones and those triggered by previous earthquakes the pair wise links from earlier to later earthquakes control the estimates of the clustering parameters however earthquake catalogs are limited in time space and magnitude so that triggers of some cataloged earthquakes may be unknown thus some links are unrecognized and some triggered events appear spontaneous here we present a method for identifying such earthquakes and reducing the bias from missing links we treat earthquakes probably affected by missing links as potential triggers but we exclude them in evaluating modeled effects we use an epidemic type aftershock sequence etas model to examine specifics the most affected parameter is the proportion of spontaneous earthquakes the most important missing links apparently follow earthquakes below the magnitude threshold before the start and outside the spatial boundaries of the catalog in that order

bias in fitting the etas model a case study based on new zealand seismicity summary we fit various forms of the etas model to a large region that includes all of the most seismically active areas of new zealand the etas model contains two components a component describing background or immigrant events and a part describing aftershocks of the background events and aftershocks of the aftershocks we refer to the first part as the background part and the second as the etas part generally all of the sophistication and the bulk of the model parameters lies in the etas part of the model the background component is generally treated as a nuisance component and is often very simplistic while the main interest lies in the etas part of the model the poor model description of the background part imposes considerable bias on the etas part of the model for example a poorly specified spatial density of the background events causes many of the background events to be seen as etas events it can also cause the estimated omori power law decay p to be too small and hence the aftershock sequences appear to continue for too long on the other hand the boundary of the observation region can impose a reverse bias which causes aftershocks that are close but within the boundary to be seen as background events in almost all of the large nz event sequences since 1965 the model consistently under fits these sequences consequently it over fits those space time regions where there is normal seismicity with no major events present this may indicate that the space time region of a major event sequence is much closer to criticality in that aftershock events appear to be much more easily initiated the standard etas model does not reflect this observation

secular oscillations in the carbonate mineralogy of reef building and sediment producing organisms driven by tectonically forced shifts in seawater chemistry the primary mineralogy of oolites and early marine carbonate cements led sandberg nature 305 1983 19 22 to divide the phanerozoic eon into three intervals of aragonite seas and two intervals of calcite seas hardie geology 24 1996 279 283 has shown that these oscillations together with synchronous oscillations in the mineralogy of marine potash evaporites can be explained by secular shifts in the mg ca ratio of seawater driven by changes in spreading rates along mid ocean ridges the hardie model also predicts that high mg calcite should precipitate along with aragonite as it does in today s aragonite sea we have uncovered oscillations in the carbonate mineralogy of hypercalcifying organisms ones that have produced massive skeletons large reefs or voluminous bodies of sediment that correspond to sandberg s aragonite seas and calcite seas and that are predicted by the hardie model particular groups of corals sponges and algae appear to have been dominant reef builders only when favored by an appropriate mg ca ratio in seawater in early and middle paleozoic calcite seas calcite i reefs were dominated by calcitic tabulate heliolitid and rugose corals and calcitic stromatoporoids in contrast during the period of late paleozoic early mesozoic aragonite seas aragonite ii aragonitic groups of sponges scleractinian corals and phylloid algae as well as high mg calcitic red algae were principal reef builders during late cretaceous time at the acme of calcite ii massive rudists displaced aragonitic hermatypic corals in today s aragonite sea aragonite iii scleractinian corals are again dominant reef builders along with high mg calcitic coralline algae major sediment producing algae exhibit temporal patterns similar to those of reef builders calcitic receptaculitids flourished during calcite i whereas aragonitic dasycladaceans did not become dominant rock formers until aragonite ii during calcite ii calcitic nannoplankton formed massive coccolith chalks in warm shallow seas of the late cretaceous after the mg ca ratio of seawater had reached a very low value and calcium concentration a very high value as the mg ca ratio of seawater rose and calcium concentration fell during the cenozoic era individual coccoliths on average became less massive and encrusted cells less thickly by pliocene time during aragonite iii the prominent genus discoaster secreted only narrow rayed coccoliths that covered less than 25 of the cell surface also during aragonite iii the aragonitic green alga halimeda emerged as the dominant skeletal sediment producer in reef tracts the influence of seawater chemistry on skeletal secretion appears to have been especially strong for morphologically simple taxa that exert relatively weak control over their own calcification such groups include algae sponges corals and bryozoans morphological simplicity also permits these groups to adopt vegetative or colonial modes of growth that confer success in competition for space on reefs this linkage in addition to the basic chemical demands of hypercalcification has given the mg ca ratio of seawater strong control over the success of individual reef building taxa more generally this ratio appears to have strongly influenced evolutionary changes in the skeletal mineralogy of sponges and cheilostome bryozoans throughout their history we conclude that throughout phanerozoic time a chain of causation has extended from mid ocean ridge processes via seawater chemistry to the mineralogical and biological composition of reef communities and bioclastic carbonate deposits

impact of earthquake rupture extensions on parameter estimations of point process models abstract stochastic point processes are widely applied to model spatiotemporal earthquake occurrence in particular the epidemic type aftershock sequence etas model has been shown to successfully reproduce the short term clustering of earthquakes an important parameter of the model is the value describing the scaling of the aftershock productivity with magnitude of the triggering earthquake according to 10 m fitting of the space dependent etas model to empirical data yields values that are typically much smaller than the scaling inverted from more simple stacking of aftershock sequences we show by means of synthetic simulations that this is likely to result from assuming spatial isotropy of aftershock occurrence that in fact aligns along the mainshock rupture we fit the space dependent and space independent etas models to simulations where each earthquake is a line source with an empirical magnitude length relation although the space time model describes past activity quite well it overestimates the forecasted earthquake rate on the other hand the application of the space independent etas model predicts future seismicity well and can therefore be applied for forecasting purposes our test for the observed aftershock sequence following the 1992 m 7 3 landers earthquake supports these results

paleomagnetic data from the new england orogen eastern australia and implications for oroclinal bending orogenic curvatures oroclines are common in modern and ancient orogens but the geodynamic driving forces of many oroclines remain controversial here we focus on the new england oroclines of eastern australia the formation of which had been previously broadly constrained to the early middle permian this time interval encompasses periods of both back arc extension at 300 280 ma and subsequent contractional deformation hunter bowen orogeny that commenced at 270 ma along the paleo pacific and gondwanan subduction plate boundary we present new paleomagnetic data from volcanic rocks that were extruded during the transition from extension to contraction at 272 ma and we show that the oroclinal structure must have formed prior to the emplacement of the volcanic rocks our results thus indicate that oroclinal bending in the southernmost new england orogen has been completed prior to the onset of middle permian contractional deformation it is therefore concluded that the oroclines have likely formed during back arc extension and that a major contribution to the orogenic curvature was driven by trench retreat

abiotic and candidate biotic micro alteration textures in subseafloor basaltic glass a high resolution in situ textural and geochemical investigation abstract the oceanic crust provides one of the largest habitats for subsurface microbial life on earth where lithoautotrophs utilize redox gradients between reduced elements in volcanic rocks and oxygenated seawater to form the basis of a deep microbial biosphere progressive alteration of the oceanic crust is argued to be in part microbially mediated but identifying robust textural and geochemical biosignatures with good fossilization potential is challenging this study investigates pillow basalts from the antarctic australian discordance aad at the south east indian ridge seir containing candidate textural biosignatures in alteration products of the glassy margins thorseth et al 2003 samples include 2 5 ma dredged seafloor basalts and 18 28 ma drill core samples from the ocean drilling program odp leg 187 the focused ion beam fib technique was used to prepare electron transparent foils across spherical microtextures in zeolite filled fractures and altered glass palagonite and across microtunnels at the interface of fresh and altered glass transmission electron microscopy tem was used to map chemical and ultrastructural variations and to evaluate both biotic and abiotic origins of the candidate textural biosignatures in the fib prepared foils three foils were cut from zeolite hosted hollow microspheres which comprise purely fe oxyhydroxides or mixed mn mg and fe mn oxyhydroxides the microspheres are 1 to 4 m across with a radiating ultrastructure and have a denser inner surface and a more porous outer surface suggesting outwards growth from a spherical initial surface amorphous organic carbon is associated with some of the microtextures both on the inner and outer walls these microtextures are interpreted as mineral encrusted microbial cells a fib foil was also cut from palagonite hosted microspheres which are more irregular in shape and partially infilled by palagonite amorphous organic carbon is abundant in the vicinity of the microtextures but is spatially unrelated and may be derived from several sources the results indicate that maturation of the palagonite involving dehydration and recrystallization overprints and destroys potential biosignatures in this alteration phase in contrast the zeolite hosted microtextures appear to have a higher preservation potential tubular microtextures in the glass at the alteration front comparable to argued bioalteration textures are also abundant in the aad basalts however their angular cross sectional shape and lack of bio elements in the palagonite infill mean that an abiotic origin cannot be excluded in summary fib tem provides multiple high resolution lines of information to characterize alteration textures in ocean floor basalts comparing the evidence obtained from glass hosted microtunnels zeolite and palagonite hosted microspheres we conclude that the zeolite hosted microtextures are the strongest candidate biosignature the combination of the size rim ultrastructure and elemental composition is consistent with an origin as cell encrustations resulting from the biologically induced mineralization of microbial cells that inhabited fractures in pillow lavas both at the seafloor and the subseafloor stage

short term properties of earthquake catalogs and models of earthquake source i review the short term properties of earthquake catalogs in particular the time and size distributions and the completeness of the early part of aftershock sequences for strong shallow earthquakes i determine the parameters of the omori and gutenberg richter laws for aftershocks close in time to a mainshock aftershock sequences of large earthquakes in southern california 1952 kern county 1992 joshua tree landers big bear sequence 1994 northridge and 1999 hector mine recorded in the caltech catalog are analyzed to demonstrate that at the beginning of these series many small earthquakes are absent from the catalog the number of missing earthquakes increases with the magnitude range of a catalog and for some data sets exceeds the number of aftershocks close to a mainshock listed in a catalog comparing global earthquake catalogs harvard centroid moment tensor and preliminary determination of epicenter with local data sets indicates that the catalogs based on longer period waves miss many early aftershocks even when their magnitudes are well above the stated magnitude threshold such short term incompleteness may introduce significant biases to the statistical analysis of the seismicity pattern in particular for branching models of earthquake occurrence incorporating the omori law for such models the likelihood function strongly depends on close aftershocks i review the techniques to alleviate this problem analyzing the source rupture process of several recent large earthquakes suggests that rupture propagation is highly inhomogeneous in space time and focal mechanism these random variations in the rupture process can be viewed as an extension of the aftershock stochastic generating mechanism toward the origin time of a mainshock i review various models of the earthquake rupture process and suggest that fractal distributions of microevents in time space and focal mechanism constitute the development of an earthquake the final identification of an individual earthquake depends on both objective and subjective factors manuscript received 21 may 2003

pathways for nitrogen cycling in earth s crust and upper mantle a review and new results for microporous beryl and cordierite figure 1 earth s atmosphere contains 27 30 of the planet s nitrogen and recent estimates are that about one half that amount 11 16 is located in the continental and oceanic crust combined the percentage of n in the mantle is more difficult to estimate but it is thought to be near 60 at very low concentrations knowledge of the behavior of n in various fluid melt rock settings is key to understanding pathways for its transfer among the major solid earth reservoirs nitrogen initially bound into various organic materials is transferred into silicate minerals during burial and metamorphism often as nh4 substituting for k in layer silicates clays and micas and feldspars low grade metamorphic rocks appear to retain much of this initial organic n signature in both concentrations and isotopic compositions thus in some cases providing a relatively un or little modified record of ancient biogeochemical cycling devolatilization can release significant fractions of the n initially fixed in crustal rocks through organic diagenesis during progressive metamorphism at temperatures of 350 550 c depending on pressure loss of fractionated n during devolatilization can impart an appreciable isotopic signature on the residual rocks producing shifts in 15n values mostly in the range of 2 to 5 these rocks then retain large fractions of the remaining n largely as nh4 despite further heating and ultimately partial melting with little additional change in 15n this retention leads to the storage of relatively large amounts of n largely as nh4 in the continental crust nitrogen can serve as a tracer of the mobility of organic sedimentary components into and within the upper mantle this contribution focuses on our growing but still fragmentary knowledge of the n pathways into shallow to deep continental crustal settings and the upper mantle we discuss the factors controlling the return of deeply subducted n to shallower reservoirs including the atmosphere via metamorphic devolatilization and arc magmatism we discuss observations from natural rock suites providing tests of calculated mineral fluid fractionation factors for n building on our discussion of n behavior in continental crust we present new measurements on the n concentrations and isotopic compositions of microporous beryl and cordierite from medium and high grade metamorphic rocks and pegmatites both phases containing molecular n2 and nh4 bearing micas coexisting with them we suggest some avenues of investigation that could be particularly fruitful toward obtaining a better understanding of the key n reservoirs and the more important pathways for n cycling in the solid earth 1 pending yes

modeling the foreshock sequence prior to the 2011 mw9 0 tohoku japan earthquake 1 the 2011 mw9 0 tohoku earthquake japan was preceded by a 2 day long foreshock sequence initiated by a mw7 3 earthquake we analyze this foreshock sequence with the aim of detecting possible aseismic deformation transients that could have driven its evolution continuous broad band recordings at f net stations are processed to identify as exhaustive a set of mjma 1 2 earthquakes as possible we moreover directly quantify with these recordings the changes in detection level associated with changes in seismic or environmental noise this earthquake data set is then modeled to show that the whole sequence can be readily explained without the need to invoke aseismic transients the observation of a 3 hour long low frequency noise increase concurrent with an apparent migration of seismicity toward the epicenter of the impending mw9 0 mega thrust earthquake however suggests that some premonitory slip could have played a role in loading the asperity which failure initiated the mw9 0 shock we thus propose that this aseismic slip if it really existed had only a minor role in triggering and southward displacing the foreshock sequence as compared to earthquake interaction mechanisms that allow earthquakes to trigger one another

iron and sulfide oxidation within the basaltic ocean crust implications for chemolithoautotrophic microbial biomass production microbial processes within the ocean crust are of potential importance in controlling rates of chemical reactions and thereby affecting chemical exchange between the oceans and lithosphere we here assess the oxidation state of altered ocean crust and estimate the magnitude of microbial biomass production that might be supported by oxidative and nonoxidative alteration compilations of fe2o3 feo and s concentrations from dsdp odp drill core samples representing upper basaltic ocean crust suggest that fe3 fe increases from 0 15 0 05 to 0 45 0 15 within the first 10 20 myr of crustal evolution within the same time frame 70 25 of primary sulfides in basalt are oxidized with an annual production of 4 0 1 8 1015 g of upper 500 200 m crust and average initial concentrations of 8 0 1 3 wt fe and 0 125 0 020 wt s we estimate annual oxidation rates of 1 7 1 2 1012 mol fe and 1 1 0 7 1011 mol s we estimate that 50 of fe oxidation may be attributed to hydrolysis producing 4 5 3 0 1011 mol h2 yr thermodynamic and bioenergetic calculations were used to estimate the potential chemolithoautotrophic microbial biomass production within ridge flanks combined aerobic and anaerobic fe and s oxidation may support production of up to 48 21 1010 g cellular carbon c hydrogen consuming reactions may support production of a similar or larger microbial biomass if iron reduction nitrate reduction or hydrogen oxidation by o2 aq are the prevailing metabolic reactions if autotrophic sulfate reduction or methanogenesis prevail the potential biomass production is 9 7 1010 g c yr and 3 2 1010 g c yr respectively combined primary biomass production of up to 1 1012 g c yr may be similar to that fueled by anaerobic oxidation of organic matter in deep seated heterotrophic systems these estimates suggest that water rock reactions may support significant microbial life within ridge flank hydrothermal systems these estimates suggest that water rock reactions may support significant microbial life within ridge flank hydrothermal systems

ichnotaxonomy of microbial trace fossils in volcanic glass abstract ancient microbial activity in volcanic glass creates micron sized cavities that can be regarded as trace fossils these are common in glassy rims of oceanic pillow lavas and volcanic breccias morphologically comparable mineralized traces are also found in meta volcanic glasses from ophiolites and precambrian greenstone belts multiple lines of evidence indicate microbial formation of these borings although the affinity of the trace maker s is poorly constrained two broad morphological types have been previously recognized and termed granular9 and tubular9 bioalteration textures here optical microscopy and sem observations are used to erect two new ichnogenera granulohyalichnus igen nov and tubulohyalichnus igen nov five ichnospecies are also defined granulohyalichnus vulgaris isp nov a granular species tubulohyalichnus simplus isp nov an unornamented tubular species tubulohyalichnus annularis isp nov an annulated tubular species tubulohyalichnus spiralis isp nov a helicoidal tubular species tubulohyalichnus stipes isp nov a branched tubular species this systematic taxonomy is advanced to allow reliable comparisons to be made between new and existing reports of these microbial borings moreover the adoption of a taxonomic framework will aid the development of these ichnofossils as palaeoenvironmental indicators and tracers of microbial evolution

thermal structure of oceanic transform faults we use three dimensional fi nite element simulations to investigate the temperature structure beneath oceanic transform faults we show that using a rheology that incorporates brittle weakening of the lithosphere generates a region of enhanced mantle upwelling and elevated temperatures along the transform the warmest temperatures and thinnest lithosphere are predicted to be near the center of the transform previous studies predicted that the mantle beneath oceanic transform faults is anomalously cold relative to adjacent intraplate regions with the thickest lithosphere located at the center of the transform these earlier studies used simplifi ed rheologic laws to simulate the behavior of the lithosphere and underlying asthenosphere we show that the warmer thermal structure predicted by our calculations is directly attributed to the inclusion of a more realistic brittle rheology this temperature structure is consistent with a wide range of observations from ridge transform environments including the depth of seismicity geochemical anomalies along adjacent ridge segments and the tendency for long transforms to break into small intratransform spreading centers during changes in plate motion

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

decay of aftershock density with distance does not indicate triggering by dynamic stress the most predictable earthquakes are aftershocks which invariably follow mainshocks so what triggers aftershocks it was recently argued controversially that the decay of aftershocks with distance from the main earthquake could only be explained by dynamic triggering keith richards dinger and colleagues have tested this hypothesis and conclude that the observed decay can be better explained by static triggering resolving whether static or dynamic stress triggers most aftershocks and subsequent mainshocks is essential to understand earthquake interaction and to forecast seismic hazard it has recently been argued that the decay of aftershocks with distance from the main earthquake could be explained only by dynamic triggering this hypothesis has now been tested the conclusion being that the observed decay can be better explained by static triggering resolving whether static1 2 3 or dynamic4 5 6 7 8 stress triggers most aftershocks and subsequent mainshocks is essential to understand earthquake interaction and to forecast seismic hazard9 felzer and brodsky10 examined the distance distribution of earthquakes occurring in the first five minutes after 2 m 3 and 3 m 4 mainshocks and found that their magnitude m 2 aftershocks showed a uniform power law decay with slope 1 35 out to 50 km from the mainshocks from this they argued that the distance decay could be explained only by dynamic triggering here we propose an alternative explanation for the decay and subject their hypothesis to a series of tests none of which it passes at distances more than 300 m from the 2 m 3 mainshocks the seismicity decay 5 min before the mainshocks is indistinguishable from the decay five minutes afterwards indicating that the mainshocks have no effect at distances outside their static triggering range omori temporal decay the fundamental signature of aftershocks is absent at distances exceeding 10 km from the mainshocks finally the distance decay is found among aftershocks that occur before the arrival of the seismic wave front from the mainshock which violates causality we argue that felzer and brodsky10 implicitly assume that the first of two independent aftershocks along a fault rupture triggers the second and that the first of two shocks in a creep or intrusion driven swarm triggers the second when this need not be the case

microbial endolithic colonization and the geochemical environment in young seafloor basalts the colonization and weathering of young seafloor basaltic glass from the mid atlantic ridge was examined microorganisms were localised to fractures in the surface of the basalt and grew on the surfaces of material in the fractures xas raman spectroscopy and nanosims analysis of the fracture filling material shows that it contains non crystallised iron enriched altered glass and poorly ordered iron oxides organisms which in places develop into contiguous biofilms develop on the surface of the material no putative biogenic alteration textures were observed in the basaltic glass at the fracture boundaries suggesting that the microbial community is restricted to the secondary alteration products microbial culturing shows the presence of heterotrophic bacteria including sufitobacter and halomonas consistent with observations of photic zone detritus associated with fracture filling material these data show that the interior of fresh basaltic glass is an endolithic habitat for microorganisms but that the glass itself is not a primary source of cations or energy for the developing communities

extending earthquakes reach through cascading earthquakes whatever their size can trigger other earthquakes mainshocks cause aftershocks to occur which in turn activate their own local aftershock sequences resulting in a cascade of triggering that extends the reach of the initial mainshock a long lasting difficulty is to determine which earthquakes are connected either directly or indirectly here we show that this causal structure can be found probabilistically with no a priori model nor parameterization large regional earthquakes are found to have a short direct influence in comparison to the overall aftershock sequence duration relative to these large mainshocks small earthquakes collectively have a greater effect on triggering hence cascade triggering is a key component in earthquake interactions

microbial alteration of 0 30 ma seafloor and sub seafloor basaltic glasses from the australian antarctic discordance scanning electron microscopic observations of alteration rims in basaltic glasses dredged from 0 2 5 ma seafloor and drilled from 18 28 ma ocean crust ocean drilling program odp leg 187 in the australian antarctic discordance aad document the presence of endolithic microbes in altered basalt glass in very young aad lavas 10 m thick alteration rims are developed along intersecting fractures and cracks and the altered glass contains numerous spherical rod and star shaped partially fossilised microbial cells similar to those from the arctic ridges 1 2 in 2 5 ma basalt glasses altered rims are up to 250 m thick and zeolite phillipsite is present within many fractures spherical cells occur in porous outer zones of alteration rims and on zeolite crystal surfaces within fractures indicating that microbial activity persists in the region for at least 2 5 ma mn rich microbial cell encrustations associated with zeolite suggest that mn is used in an energy yielding metabolic process combined with recent results from the arctic ridges the results from this study demonstrate that endolithic microbial growth is a persistent feature of mid ocean spreading ridges in glasses from odp cores 1 mm thick alteration rims are developed along the widest fractures lined with mn fe oxyhydroxides and or clay and filled by zeolite and calcite most common however are 10 200 m thick rims developed along zeolite filled more narrow fractures and cracks zeolite filled fractures with only minor to no alteration indicate several episodes of fracturing followed by relatively fast sealing there is no age progression in alteration thickness along fractures or other characteristics suggesting that alteration is essentially completed between 2 5 and 18 ma a comparison of alteration in the 2 5 ma glass with that in the odp samples indicates that a significant proportion of the glass alteration in the drilled samples developed prior to burial although one type of diffuse highly irregular front that is only observed in the odp samples most likely developed after burial these diffuse alteration fronts are caused by dissolution and alteration of the glass into minute globules 0 05 0 2 m in diameter with no associated microbial morphologies fossilised mn rich cells do occur within zeolite filled fractures possibly indicating that microbial activity continued in the fractures for as long as circulation continued the apparent non biological origin of diffuse irregular alteration fronts in buried aad glasses indicates that these textural features are not reliable as diagnostic criteria for the existence of a deep biosphere in the volcanic ocean crust

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

comparison of short term and time independent earthquake forecast models for southern california we have initially developed a time independent forecast for southern california by smoothing the locations of magnitude 2 and larger earthquakes we show that using small m 2 earthquakes gives a reasonably good prediction of m 5 earthquakes our forecast outperforms other time independent models kagan and jackson 1994 frankel et al 1997 mostly because it has higher spatial resolution we have then developed a method to estimate daily earthquake probabilities in south ern california by using the epidemic type earthquake sequence model kagan and knopoff 1987 ogata 1988 kagan and jackson 2000 the forecasted seismicity rate is the sum of a constant background seismicity proportional to our time independent model and of the aftershocks of all past earthquakes each earthquake triggers aftershocks with a rate that increases exponentially with its magnitude and decreases with time following omori s law we use an isotropic kernel to model the spatial distribution of aftershocks for small m 5 5 mainshocks for larger events we smooth the density of early aftershocks to model the density of future aftershocks the model also assumes that all earthquake magnitudes follow the gutenberg richter law with a uniform b value we use a maximum likelihood method to estimate the model parameters and test the short term and time independent forecasts a retro spective test using a daily update of the forecasts between 1 january 1985 and 10 march 2004 shows that the short term model increases the average probability of an earthquake occurrence by a factor 11 5 compared with the time independent forecast

stratigraphic imprint of the late palaeozoic ice age in eastern australia a record of alternating glacial and nonglacial climate regime stratigraphic and sedimentological data from new south wales and queensland eastern australia indicate that the late palaeozoic ice age comprised at least eight discrete glacial intervals each 1 8 ma in duration here termed glaciations separated by nonglacial intervals of comparable duration these events spanned an interval from mid carboniferous c 327 ma to the early late permian c 260 ma and illustrate a pattern of increasing climatic austerity and increasingly widespread glacial ice from initial onset until an acme in the late early permian followed by an opposite trend towards the final demise of glaciation in the late permian the alternating glacial nonglacial motif suggests that the late palaeozoic ice age was considerably more dynamic than previously thought these patterns are remarkably consistent with recent interpretations of palaeofloral change eustatic sea level fluctuations and co 2 climate glaciation relationships for this interval of time the detailed record of alternating glacial and nonglacial climate mode disclosed herein may facilitate more closely resolved evaluations of stratigraphic records elsewhere notably in far field ice distal northern hemisphere successions

alteration of submarine basaltic glass from the ontong java plateau a stxm and tem study frequent observations of tubular to vermicular microchannels in altered basalt glass have led to increasing appreciation of a possible significant role of microbes in the low temperature alteration of seafloor basalt we have examined such microchannel alteration features at the nanoscale in basalt glass shards from the ontong java plateau using a combination of focused ion beam milling transmission electron microscopy and scanning transmission x ray microscopy three types of materials were found in ultrathin cross sections cut through the microchannels by fib milling fresh basalt glass amorphous si rich rims surrounding the microchannels and palagonite within the microchannels x ray absorption spectroscopy at the c k edge and fe l2 3 edges showed the presence of organic carbon in association with carbonates within the microchannels and partial oxidation of iron in palagonite compared with basalt glass although these observations alone cannot discriminate between a biotic or abiotic origin for the microchannels they provide new information on their mineralogical and chemical composition and thus better constrain the physical and chemical conditions prevailing during the alteration process 2007 published by elsevier b v

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

bioalteration of basaltic glass in the oceanic crust 1 bioalteration of quaternary to early cretaceous basaltic glass from pillow lavas of the upper oceanic crust can be documented in deep sea drilling project ocean drilling program dsdp odp samples from shallow to deep drill holes from the north to central atlantic ocean lau basin and costa rica rift a wide range of marine settings biogenerated textures are rooted in fractures and occur as two main types a granular type and a tubular type the granular type common at all depths within the volcanic pile appears as solid bands semicircles or irregular patches of individual and or coalesced spherical bodies mostly 0 2 0 6 m in diameter with irregular protrusions into the fresh glass the tubular type is more common at deeper levels in the crust and consists of thin tubes sometime branching bodies mostly 20 30 m long and are more common at deeper levels the upper crust displays a large variability in the relative importance of biotic to abiotic alteration and the degree of bioalteration appears to decrease with depth thus the fraction of bioalteration of the total alteration of the glass ranges from 20 90 in the upper 300 m down to a maximum of 10 at about 500 m depth this might be due to a natural variability in the abundance of bioaltered glass or to biased sampling from low drilling recovery of relatively young crust the proportion of bioaltered to abiotically altered glass does not show any systematic variations with age of the crust thus bioalteration lasts as long as abiotic alteration i e for as long as water is available to the hydration of the oceanic crust evidence from heat flow measurements suggests that hydrothermal circulation lasts until at least 70 ma and thus the deep biosphere is likely to expand at least into crust of this age

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

evidence for microbial activity at the glass alteration interface in oceanic basalts a detailed microbiological and geochemical study related to the alteration of basaltic glass of pillow lavas from the oceanic crust recovered from hole 896a on the costa rica rift penetrating 290 m into the volcanic basement has been carried out a number of independent observations pointing to the influence of microbes may be summarized as follows 1 alteration textures are reminiscent of microbes in terms of form and shape 2 altered material contains appreciable amounts of c n and k and the n c ratios are comparable to those of nitrogen starved bacteria 3 samples stained with a dye dapi that binds specifically to nucleic acids show the presence of dna in the altered glass further staining with fluorescent labeled oligonucleotide probes that hybridize specifically to 16s ribosomal rna of bacteria and archaea demonstrate their presence in the altered part of the glass 4 disseminated carbonate in the glassy margin of the majority of pillows shows d 13 c values significantly lower than that of fresh basalt also suggests biological activity the majority of the samples have d 18 o values indicating temperatures of 20 100oc which is in the range of mesophilic and thermophilic micro organisms 1998 elsevier science b v all rights reserved

a comparison of long term changes in seismicity at the geysers salton sea and coso geothermal fields geothermal energy is an important source of renewable energy yet its production is known to induce seismicity here we analyze seismicity at the three largest geothermal fields in california the geysers salton sea and coso we focus on resolving the temporal evolution of seismicity rates which provides important observational constraints on how geothermal fields respond to natural and anthropogenic loading we develop an iterative regularized inversion procedure to partition the observed seismicity rate into two components 1 the interaction rate due to earthquake earthquake triggering and 2 the smoothly varying background rate controlled by other time dependent stresses including anthropogenic forcing we apply our methodology to compare long term changes in seismicity to monthly records of fluid injection and withdrawal at the geysers we find that the background seismicity rate is highly correlated with fluid injection with the mean rate increasing by approximately 50 and exhibiting strong seasonal fluctuations following construction of the santa rosa pipeline in 2003 in contrast at both salton sea and coso the background seismicity rate has remained relatively stable since 1990 though both experience short term rate fluctuations that are not obviously modulated by geothermal plant operation we also observe significant temporal variations in gutenberg richter b value earthquake magnitude distribution and earthquake depth distribution providing further evidence for the dynamic evolution of stresses within these fields the differing field wide responses to fluid injection and withdrawal may reflect differences in in situ reservoir conditions and local tectonics suggesting that a complex interplay of natural and anthropogenic stressing controls seismicity within california s geothermal fields

change in seismicity along the japan trench 1990 2011 and its relationship with seismic coupling we investigate the temporal evolution of the background seismicity rate related to the subduction of the pacific plate in northeast japan at latitudes 34o to 42o for the 1 1 1990 9 3 2011 period two declustering methods are used to identify robust features we find that the dominant behaviour is a lowering down of activity especially in the northern half of our studied area where changes appear related to the cycle of m7 5 earthquakes in particular the 1968 tokachi and the 1994 sanriku earthquakes acceleration of background seismicity is observed offshore the kanto region and could mark a long term decoupling of the pacific and the philippine sea plates over a 100 km long segment along the sagimi trough which cannot be simply explained by the earthquake cycle model our analysis further suggests that changes in background seismicity are plausibly related to changes in seismic coupling and thus further strengthens the recent observation that seismic coupling does vary at the time scales of tens of years for the japanese subduction zone

objective estimation of spatially variable parameters of epidemic type aftershock sequence model application to california the etas model is widely employed to model the spatio temporal distribution of earthquakes generally using spatially invariant parameters we propose an efficient method for the estimation of spatially varying parameters using the expectation maximization em algorithm and spatial voronoi tessellation ensembles we use the bayesian information criterion bic to rank inverted models given their likelihood and complexity and select the best models to finally compute an ensemble model at any location using a synthetic catalog we also check that the proposed method correctly inverts the known parameters we apply the proposed method to earthquakes included in the anss catalog that occurred within the time period 1981 2015 in a spatial polygon around california the results indicate significant spatial variation of the etas parameters we find that the efficiency of earthquakes to trigger future ones quantified by the branching ratio positively correlates with surface heat flow in contrast the rate of earthquakes triggered by far field tectonic loading or background seismicity rate shows no such correlation suggesting the relevance of triggering possibly through fluid induced activation furthermore the branching ratio and background seismicity rate are found to be uncorrelated with hypocentral depths indicating that the seismic coupling remains invariant of hypocentral depths in the study region additionally triggering seems to be mostly dominated by small earthquakes consequently the static stress change studies should not only focus on the coulomb stress changes caused by specific moderate to large earthquakes but also account for the secondary static stress changes caused by smaller earthquakes