aftershock decay productivity and stress rates in hawaii indicators of temperature and stress from magma sources 1 we examined dozens of aftershock sequences in hawaii in terms of gutenberg richter and modified omori law parameters we studied p the rate of aftershock decay ap the aftershock productivity defined as the observed divided by the expected number of aftershocks and c the time delay when aftershock rates begin to fall we found that for earthquakes shallower than 20 km p values 1 2 are near active magma centers we associate this high decay rate with higher temperatures and faster stress relaxation near magma reservoirs deep earthquakes near kilauea s inferred magma transport path show a range of p values suggesting the absence of a large deep magma reservoir aftershock productivity is 4 0 for flank earthquakes known to be triggered by intrusions but is normal 0 25 to 4 0 for isolated main shocks we infer that continuing post main shock stress from the intrusion adds to the main shock s stress step and causes higher ap high ap in other zones suggests less obvious intrusions and pulsing magma pressure near kilauea s feeding conduit we calculate stress rates and stress rate changes from pre main shock and aftershock rates stress rate increased after many intrusions but decreased after large m7 8 earthquakes stress rates are highest in the seismically active volcano flanks and lowest in areas far from volcanic centers we found sequences triggered by intrusions tend to have high ap high 0 10 day c values a stress rate increase and sometimes a peak in aftershock rate hours after the main shock we interpret these values as indicating continuing intrusive stress after the main shock

when and where the aftershock activity was depressed contrasting decay patterns of the proximate large earthquakes in southern california 1 seismic quiescence has attracted attention as a possible precursor to a large earthquake however sensitive detection of quiescence requires accurate modeling of normal aftershock activity we apply the epidemic type aftershock sequence etas model that is a natural extension of the modified omori formula for aftershock decay allowing further clusters secondary aftershocks within an aftershock sequence the hector mine aftershock activity has been normal relative to the decay predicted by the etas model during the 14 months of available data in contrast although the aftershock sequence of the 1992 landers earthquake m 7 3 including the 1992 big bear earthquake m 6 4 and its aftershocks fits very well to the etas up until about 6 months after the main shock the activity showed clear lowering relative to the modeled rate relative quiescence and lasted nearly 7 years leading up to the hector mine earthquake m 7 1 in 1999 specifically the relative quiescence occurred only in the shallow aftershock activity down to depths of 5 6 km the sequence of deeper events showed clear normal aftershock activity well fitted to the etas throughout the whole period we argue several physical explanations for these results among them we strongly suspect aseismic slips within the hector mine rupture source that could inhibit the crustal relaxation process within shadow zones of the coulomb s failure stress change furthermore the aftershock activity of the 1992 joshua tree earthquake m 6 1 sharply lowered in the same day of the main shock which can be explained by a similar scenario

deep magma body beneath the summit and rift zones of kilauea volcano hawaii a magnitude 7 2 earthquake in 1975 caused the south flank of kilauea volcano hawaii to move seaward in response to slippage along a deep fault since then a large part of the volcano s edifice has been adjusting to this perturbation the summit of kilauea extended at a rate of 0 26 meter per year until 1983 the south flank uplifted more than 0 5 meter and the axes of both the volcano s rift zones extended and subsided the summit continues to subside these ground surface motions have been remarkably steady and much more widespread than those caused by either recurrent inflation and deflation of the summit magma chamber or the episodic propagation of dikes into the rift zones kilauea s magmatic system is therefore probably deeper and more extensive than previously thought the summit and both rift zones may be underlain by a thick near vertical dike like magma system at a depth of 3 to 9 kilometers

frequency magnitude distribution of microearthquakes beneath the 9 50 n region of the east pacific rise october 2003 through april 2004 1 relocated hypocentral data from a 7 month deployment october 2003 to april 2004 of ocean bottom seismometers provide an opportunity to map microearthquake frequency magnitude distributions fmds along the 9 49 52 n region on the east pacific rise these analyses which incorporate more than 9000 earthquakes represent the first investigation of the 3 d spatial and temporal patterns of fmds along any mid ocean ridge spreading center the data are described well by a gutenberg richter model indicating a power law or fractal relationship between earthquake size and frequency the scaling exponent or b value shows significant spatial variability exceeding a value of 2 0 at the shallowest depths on axis and dropping below 1 0 away from the axial trough this spatial pattern is consistent with an inverse relationship between b value and ambient stress conditions with the lowest stress levels at shallow depths and relatively high stress levels or low pore pressures observed away from the axial zone intermediate b values are observed on axis above the ridge system s melt lens however within this region there also exists significant spatial variability this indicates that stress conditions and or structural heterogeneity may vary at subkilometer scales within the hydrothermal circulation cell although the observational period is characterized by increasing seismicity rates building toward an eruptive episode in january 2006 the first order spatial pattern of b values is sustained with no overall temporal trend as a byproduct of this b value analysis the detection capabilities of the array are assessed empirically

pressure transient analysis for two phase geothermal wells some numerical results a numerical geothermal reservoir simulator is used in a series of calculations to help devise interpretation techniques for analyzing pressure transient data from two phase geothermal reservoirs the investigations include 1 the drawdown buildup behavior of initially two phase liquid water steam reservoirs 2 the drawdown buildup response of initially single phase reservoirs which undergo flashing as a result of fluid production and 3 the effects of cold water injection into hot two phase reservoirs production drawdown buildup data from two phase either initially or due to production induced boiling reservoirs may be analyzed in the usual manner to yield kinematic mobility buildup data from reservoirs which undergo flashing on production also offer the possibility of determining absolute formation permeability injection data can be interpreted in a straightforward manner to yield absolute formation permeability the corresponding falloff data appear however to be of little value

seismicity rate changes in association with the evolution of the stress field in northern aegean sea greece summary seismicity rate changes in northern aegean area were studied by applying the dieterich 1994 rate state formulation the study area was divided into four smaller ones that exhibit seismotectonic homogeneity and accommodate strong events with similar to identical focal mechanisms seismicity rate evaluation concerns the study period between 1981 december 19 and 2010 august 31 whereas the reference seismicity rate was estimated for the learning period lasting from 1970 january 1 to 1981 december 19 the coseismic slip of the strongest events mw 5 8 that occurred during the study period was considered to contribute to the stress field evolution along with the continuous tectonic loading stress changes were calculated just before and after each strong event and their influence was then examined in connection with the occurrence rate of the smaller magnitude events above the individually determined magnitude of completeness in each subarea and for the respective time intervals after defining the probability density function of seismicity distribution a rate state model was used to combine static coulomb stress changes cff with seismicity rates and to compare the observed with the expected rates of earthquake production for each time period and subarea different parameter values combinations were tested to evaluate the model sensitivity qualitative and quantitative correlations were performed for each one of the selected study periods the modelling approach resulted to satisfactory correlation between real and synthetic seismicity rates and is expected to constitute a useful mean for the time dependent seismic hazard assessment

the krafla geothermal field iceland 1 analysis of well test data extensive modeling studies of the krafla geothermal field in iceland are presented in a series of four papers this first paper describes the geological settings of the field and the analysis of well test data the geothermal system at krafla is very complex with a single phase liquid reservoir overlying a two phase reservoir the reservoir rocks are volcanic with sequences of basalt flows hyloclastics and intrusions the fluid flow in the reservoir is fracture dominated considerable pressure transient data from injection tests have been gathered from the krafla wells these data are analyzed to yield the transmissivity distribution in the reservoir system as the data are complicated by various factors wellbore effects nonisothermal effects two phase flow and fractured rocks the applicability of conventional well test analysis methods is questionable the authors have developed a methodology to analyze injection tests for such systems the results obtained show that the transmissivity of the krafla reservoir is low averaging 2 darcy meters dm the average transmissivity of most commercially successful geothermal fields is an order of magnitude higher

the sequence and mechanism of low temperature dolomite formation calcian dolomites in a pennsylvanian echinoderm abstract middle pennsylvanian fossils from the buckhorn asphalt quarry of southern oklahoma are unusual in that early sealing by tar has preserved many of their original textural and mineralogic features and those of the earliest stages of diagenesis echinoderm fragments collected from this locality axe well preserved with original stereom morphology clearly visible optically one to five micrometer anhedral calcian dolomite grains occupy as much as 30 percent of the original stererom of the fragments as displayed by differential etching and mgk x my maps the composition of skeletal fragments is 75 percent ca 98mg 02co3 25 percent ca 54mg 46co3 single crystal x ray di fraction xrd empa tem and stem microanalysis were used to characterize the calcian dolomite phase tem micrographs revealed an approximate 100 a tweed structure identical to that reported by reeder and wenk 1979 our data imply that magnesium in the calcian dolomites was derived largely from the original magnesian calcite of the echinoderm stereom original biogenic high magnesium calcite is altered via local microdissolution reprecipitation to anhedral disordered calcian dolomite grains within low magnesium calcite the product phases low magnesium calcite and calcian dolomite retain the original crystallographic orientation of the stereom these products of early diagenesis are apparent precursors to well defined ordered euhedral microdolomites the relationships between the low magnesium calcite and calcian dolomite and the chemistry and complex ultrastructure of the calcian dolomites support the kind of low temperature mechanism of dolomite formation postulated by gains 1977 goldsm th and graf 1958 and others on the basis of hydrothermal experiments

petrography and microanalysis of pennsylvanian coal ball concretions herrin coal illinois basin usa bearing on fossil plant preservation and coal ball origins abstract petrographic analyses of 25 coal balls from well studied paleobotanical profiles in the middle pennsylvanian herrin coal westphalian d illinois basin and five select coal balls from university collections indicate that herrin coal ball peats were permineralized by fibrous and non fibrous carbonates fibrous carbonates occur in fan like to spherulitic arrays in many intracellular within tissue pores and are best developed in relatively open extracellular between plant pore spaces acid etched fibrous carbonates appear white under reflected light and possess a microcrystalline texture attributable to abundant microdolomite scanning electron microscopy x ray diffraction and electron microprobe analysis demonstrate that individual fibers have a distinct trigonal prism morphology and are notable for their magnesium content 9 15 mol mgco 3 non fibrous carbonates fill intercrystalline spaces among fibers and pores within the peat as primary precipitates and neomorphic replacements in the immediate vicinity of plant cell walls non fibrous carbonates cut across fibrous carbonates as a secondary neomorphic phase attributed to coalification of plant cell walls dolomite occurs as diagenetic microdolomite associated with the fibrous carbonate phase as sparite replacements and as void filling cement maximum dolomite 50 59 wt is in the top of seam coal ball zone at the sahara mine which is overlain by the marine anna shale coal ball formation in the herrin coal began with the precipitation of fibrous high magnesium calcite the trigonal prism morphology of the carbonate fibers suggests rapid precipitation from super saturated meteoric pore waters carbonate precipitation from marine waters is discounted on the basis of stratigraphic paleobotanical and stable isotopic evidence most non fibrous carbonate is attributable to later diagenetic events including void fill replacements recrystallization and post depositional fracture fills evidence suggests that co 2 degassing was important in coal ball formation in the herrin coal which mainly occurred sequentially upward with peat accumulation in the sites studied

cement stratigraphy in triassic and jurassic limestones of the weserbergland northwestern germany abstract cement stratigraphy of the korallenoolith oxfordian and trochitenkalk upper muschelkalk formations southern lower saxony hills of germany is based on investigation of 232 carbonate samples by cathodoluminescence cl this enables subdivision of cements into four main generations generation 1 consisting of fine columnar equant and syntaxial cements with blotchy cl and or microdolomite inclusions that is interpreted as originally submarine mg calcitic precipitate generation 2 found in jurassic samples only these cements show intrinsic to non luminescent cl with thin bright orange subzones and they are interpreted as meteoric phreatic calcites generation 3 1 characterized by zoned calcites with variable cl colours these cements precipitated under shallow burial conditions in a phreatic environment during an incipient stage of late diagenesis generation 3 2 with relatively uniform orange cl indicative of precipitation in a stable chemical environment this cement generation is interpreted as late diagenetic deep burial calcites generation 3 3 partially strongly zoned and with a characteristically intense cl contrast it has been identified in only 17 of the 82 trochitenkalk samples deformation twins end within this generation indicating a post tectonic genesis for the subsequent younger cement zones the cements were probably precipitated in a near surface environment characterized by reducing or variable eh conditions generation 4 consisting of calcites that show intrinsic cl with bright orange subzones comparable to generation 2 but lacking deformation twins these cements are interpreted as post tectonic late diagenetic products of a meteoric phreatic environment based on detailed cl petrography fifteen diagenetic events three calcite cements three dolomite generations three fissure generations two stages of dedolomitization aragonite dissolution matrix recrystallization and two stages of hmc lmc transformation can be distinguished and timed relative to cement zonation the progressively decreasing 18o values for cement generations 1 to 3 2 likely reflect increasing temperatures caused by burial the low 18c values of cement generation 4 are probably a reflection of a meteoric diagenetic environment a time burial cementation pathway can be modelled combining cl patterns cement isotopic data and the subsidence history of the study area the main features of this model are 1 1 generation 1 cements are submarine precipitates and their age therefore coincides with sedimentation 2 2 cement generation 3 1 of the trochitenkalk commenced precipitation at a depth of about 120 m reached during late triassic time in case this minimum depth is also the formation depth of generation 3 1 in the korallenoolith formation then precipitation of these cements started during late jurassic time 3 3 cement generation 3 2 of both the trochitenkalk and the korallenoolith formation precipitated at assumed depths 1000 m reached during the doggerian and at the time of jurassic cretaceous transition respectively 4 4 cement generation 4 precipitated after the sediments had undergone telogenesis and must thus be younger than the intra senonian sub hercynian tectonic phase and possibly even younger than the paleocene tectonic pulse laramian phase

megathrust earthquake swarms indicate frictional changes which delimit large earthquake ruptures abstract using a recently constructed catalog of megathrust earthquake swarms we present results that illustrate how fault slip for m w 8 5 earthquakes with a publicly available finite fault rupture model is delimited along strike by swarm regions we further investigate this relationship for all m w 7 5 subduction zone megathrust earthquakes that have occurred over the last 40 years by estimating the rupture area from early aftershocks this extended comparison shows only 2 out of 42 earthquakes propagate through regions of the megathrust that have documented recurring earthquake swarm activity while about 40 17 out of 42 are terminate on at least one side near regions with swarm activity in japan chile sumatra and alaska earthquake swarms correlate with regions of the plate interface that exhibit low interseismic strain accumulation this suggests earthquake swarms are associated with reduced plate coupling and possibly aseismic moment release however earthquakes in chile and alaska ruptured through regions of weak coupling that do not show swarm activity we propose instead that stress heterogeneity on the megathrust can best explain why large earthquake ruptures terminate in swarm regions but not in regions with weak coupling alone earthquake swarms appear to be a proxy for along strike segmentation of subduction megathrusts at least on the time scale of one seismic cycle

implications of fault constitutive properties for earthquake prediction the rate and state dependent constitutive formulation for fault slip characterizes an exceptional variety of materials over a wide range of sliding conditions this formulation provides a unified representation of diverse sliding phenomena including slip weakening over a characteristic sliding distance dc apparent fracture energy at a rupture front time dependent healing after rapid slip and various other transient and slip rate effects laboratory observations and theoretical models both indicate that earthquake nucleation is accompanied by long intervals of accelerating slip strains from the nucleation process on buried faults generally could not be detected if laboratory values of dc apply to faults in nature however scaling of dc is presently an open question and the possibility exists that measurable premonitory creep may precede some earthquakes earthquake activity is modeled as a sequence of earthquake nucleation events in this model earthquake clustering arises from sensitivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and assigns physical interpretation to aftershock parameters the seismicity formulation predicts large changes of earthquake probabilities result from stress changes two mechanisms for foreshocks are proposed that describe observed frequency of occurrence of foreshock mainshock pairs by time and magnitude with the first mechanism foreshocks represent a manifestation of earthquake clustering in which the stress change at the time of the foreshock increases the probability of earthquakes at all magnitudes including the eventual mainshock with the second model accelerating fault slip on the mainshock nucleation zone triggers foreshocks

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

deep fault plane geometry inferred from multiplet relative relocation beneath the south flank of kilauea dense microearthquake swarms occur in the upper south flank of kilauea providing multiplets composed of hundreds of events the similarity of their waveforms and the quality of the data have been sufficient to provide accurate relative relocations of their hypocenters a simple and efficient method has been developed which allowed the relative relocation of more than 250 events with an average precision of about 50 m horizontally and 75 m vertically relocation of these events greatly improves the definition of the seismic image of the fault that generates them indeed relative relocations define a plane dipping about 6 northward although corresponding absolute locations are widely dispersed in the swarm a composite focal mechanism built from events providing a correct spatial sampling of the multiplet also gives a well constrained northward dip of about 5 to the near horizontal plane this technique thus collapses the clouds of hypocenters of single event locations to a plane coinciding with the slip plane revealed by previous focal mechanism studies we cannot conclude that all south flank earthquakes collapse to a single plane there may locally be several planes perhaps with different dips and depths throughout the south flank volume the 6 northward dipping plane we found is too steep to represent the overall flexure of the oceanic crust under the load of the island of hawaii this plane is probably an important feature that characterizes the basal slip layer below the upper south flank of kilauea volcano differences in seismicity rate and surface deformations between the upper and lower south flank could be related to the geometry of this deep fault plane the present work illustrates how high precision relative relocations of similar events in dense swarms combined with the analysis of geodetic measurements can help to describe deep fault plane geometry systematic selection and extensive relative relocation of similar earthquakes could be attempted in other well instrumented highly seismic areas to provide reliable basic information especially useful for understanding of earthquake generation processes

long term stress strain analysis of volcano flank instability the eastern sector of etna from 1980 to 2012 1 we investigated the evolution of seismicity and deformation in the unstable eastern flank of etna volcano over a 30 year period from 1980 to 2012 a significant temporal correlation has been revealed between periods of flank acceleration and intensified seismic activity by comparing seismicity along the northern border pernicana fault system of the sliding flank and the deformation of the eastern flank two marked phases have been observed in 1984 1986 and in the years following 2002 these two phases are separated by an intermediate phase from 1987 to 2001 in which the flank sliding slowed down and the seismicity dropped drastically this common temporal evolution in the deformation rate and seismic release supports the hypothesis that the seismicity in the northern border can be viewed as a marker of the response to accommodate the stress exerted by the traction of the eastern flank sliding this interplay has also been corroborated by finite element method numerical computations that highlight a good correlation between the seismicity pattern and areas of positive stress changes induced by the sliding surface the two intense phases of flank acceleration are representative of two main different sources volcano flank instability stretching the eastern sector in the first 1984 1986 phase and magmatic intrusions pushing the eastern flank seaward since the 2002 2003 eruption establishing the relationship between flank acceleration and seismic activation therefore contributes to understanding etna s mechanical behavior and provides insights into the processes regulating the unstable flank response

neotectonic implications and regional stress field constraints on mud volcanoes in offshore southwestern taiwan abstract recently discovered numerous mud volcanoes mvs and mud diapirs mds in sw taiwan both onshore and offshore show eruption lineaments suspected to be related to neotectonic processes spatial and temporal distribution of the mvs eruption events shows an obvious switch of the lineament orientation from nne ne n s nw and e w trending in n s direction the mud volcanoes have experienced multi stage eruptions and should have occurred

premonitory seismicity changes prior to the parkfield and coalinga earthquakes in southern california abstract in this work we apply the pattern informatics technique for evaluating one surface expression of the underlying stress field the seismicity in order to study the parkfield coalinga interaction over the years preceding the 1983 coalinga earthquake we find that significant anomalous seismicity changes occur during the mid 1970s in this region prior to the coalinga earthquake that illustrate a reduction in the probability of an event at parkfield while the probability of an event at coalinga is seen to increase this suggests that the one event did not trigger or hinder the other rather that the dynamics of the earthquake system are a function of stress field changes on a larger spatial and temporal scale

a model for seismicity rates observed during the 1982 1984 unrest at campi flegrei caldera italy abstract we consider the space time distribution of seismicity during the 1982 1984 unrest at campi flegrei caldera italy where a correlation between seismicity and rate of ground uplift was suggested in order to investigate this effect we present a model based on stress transfer from the deformation source responsible for the unrest to potential faults we compute static stress changes caused by an inflating source in a layered half space stress changes are evaluated on optimally oriented planes for shear failure assuming a regional stress with horizontal extensional axis trending nne ssw the inflating source is modeled as inferred by previous studies from inversion of geodetic data with the same crustal model here assumed the magnitude of the regional stress is constrained by imposing an initial condition of close to failure to potential faults the resulting spatial distribution of stress changes is in agreement with observations we assume that the temporal evolution of ground displacement observed by a tide gauge at pozzuoli was due mainly to time dependent processes occurring at the inflating source we approximate this time dependence in piecewise linear way and we attribute it to each component of average stress change in the region interested by the observed seismicity then we evaluate the effect of a time dependent stressing rate on seismicity by following the approach indicated by dieterich 1994 on the basis of the rate and state dependent rheology of faults the seismicity rate history resulting from our model is in general agreement with data during the period 1982 1984 for reasonable values of unconstrained model parameters the initial value of the direct effect of friction and the reference shear stressing rate in particular this application shows that a decreasing stressing rate is effective in damping the seismicity rate

transformation of echinoid mg calcite skeletons by heating abstract interambularcral plates of echinoid heterocentrotus trigonarius composed of mg calcite 1 14 mol mgco3 were heated in three timed series of experiments at 300 c dried plate fragments and fragments with added water were heated separately in pressurized bombs x ray powder diffractometry unit cell dimensions and phase compositions are used to monitor reaction progress after 10 h heating in the bombs dolomite 43 5 mol mgco3 and mg calcite appear 4 7 mol mgco3 by 20 h all mg calcite 1 is consumed and at 120 h dolomite composition has evolved to 47 mol mgco3 and calcite to 2 mol mgco3 whole plates heated at 300 c in an open muffle furnace develop dolomite 42 mol mgco3 and mg calcite 2 6 mol mgco3 after 10 h and remain compositionally invariant throughout subsequent heating to 620 h limited skeletal water catalyzes the early reaction but escapes from the open furnace and consequently reaction ceases after 10 h the experimentally produced dolomite has relative mg ca ordering of 75 to 79 the stabilization of echinoid mg calcite by heating at 300 c to a mixture of dolomite and calcite occurs through a dissolution precipitation reaction the alteration fabric produced within the stereom consists of irregularly shaped branched dolomite crystals 5 m homoaxially set in a calcite 2 bomb or mg calcite 2 furnace matrix round and tubular pores 1 to 5 m are randomly distributed throughout this fabric the stereom pore system remains intact during furnace heating but is destroyed during heating in bombs the texture of experimentally stabilized echinoid skeletons is different from that of fossil echinoderms that are composed of microrhomic dolomite homoaxially set in a single calcite crystal

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

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

inversion of gps velocity and seismicity data to yield changes in stress in the japanese islands summary to estimate stress changes within the crust from observed displacement rates we have devised an ew stress inversion method for a 2 d plate subjected to a planar stress which uses airy s stress function the merits of this stress inversion method are that it allows us to estimate the stress field without full knowledge of the elastic properties of the object and it improves precision because it is not necessary to take derivatives of observed quantities we applied this stress inversion method to the japanese islands where the geographical survey institute has been operating a nationwide gps array called geonet we make the assumption that the inelastic deformation in the japanese islands has no dilatational component we used velocity data derived from 3 yr of gps observations we estimated the change in boundary traction from the seismic parameters of large earthquakes stress drop slip direction and recurrence interval we compared the observed total strain and estimated the elastic strain the results suggest that the latter looks larger than the former indicating that it is feasible to estimate the distribution of rigidity from the stress inversion comparison with seismicity data suggests that inland shallow earthquakes occur where rigidity is lower

stress shadows determined from a phase dynamical measure of historic seismicity the pattern informatics pi technique tiampo et al 2002 is founded on the premise that changes in the seismicity rate are a proxy for changes in the underlying stress these stress changes are correlated over large spatial regions and can be quantified using a phase dynamical analysis of the changes in historic seismicity rates this new approach to the study of seismicity quantifies its local and regional space time patterns and identifies regions of local quiescence or activation here we study those local changes in an attempt to objectively quantify short term stress shadow regions we determine that while persistent stress shadows are detectable with this method they do not occur uniformly throughout the spatio temporal region

petrography geochemistry and origin of burial diagenetic facies siluro devonian helderberg group carbonate rocks central appalachians petrographic and geochemical studies of pore filling cements and replacement products in the helderberg group upper silurian lower devonian central appalachians document the diagenetic history of these rocks shallow ramp skeletal limestones and buildups were partially lithified by marine cements however most pore filling cement formed under shallow 300 m to deep burial 300 4 000 m conditions regional cathodoluminescent zonation patterns in early calcite cements indicate meteoric ground waters were involved in shallow burial cementation early zoned calcite cements consist of updip nonluminescent cements with thin luminescent laminae in limestone or sandstone that pass downdip into subzoned dull cements interlayered bright and dull laminae and then into nonzoned dull cement in basinward limestone the regional distribution stable isotopic compositions and timing of early zoned cements relative to other diagenetic events suggest that all of the early cements formed synchronously from meteoric ground waters that became progressively more reducing as they flowed downdip at least 150 km helderberg sandstone tongues probably were preferential conduits for meteoric gro nd waters because early calcite cements formed only on scattered skeletal grains in sandstones late void filling dull cement formed from deep burial pore fluids at burial depths of 300 to 4 000 m deep burial pore fluids were dilute to saline na ca cl brines from primary fluid inclusion data with stable isotopic compositions that probably were similar to isotopic compositions of formation waters from modern oil fields void filling dull calcite cements occluded nearly all remaining porosity before late paleozoic fracturing and deformation latest diagenetic phases include dolomite fluorite silica and fracture filling dull calcite this study shows that integrated petrographic and geochemical approaches to diagenetic studies are useful for relating various diagenetic phases and fabrics to burial history and paleoaquifer distribution

detecting aseismic strain transients from seismicity data 1 aseismic deformation transients such as fluid flow magma migration and slow slip can trigger changes in seismicity rate we present a method that can detect these seismicity rate variations and utilize these anomalies to constrain the underlying variations in stressing rate because ordinary aftershock sequences often obscure changes in the background seismicity caused by aseismic processes we combine the stochastic epidemic type aftershock sequence model that describes aftershock sequences well and the physically based rate and state dependent friction seismicity model into a single seismicity rate model that models both aftershock activity and changes in background seismicity rate we implement this model into a data assimilation algorithm that inverts seismicity catalogs to estimate space time variations in stressing rate we evaluate the method using a synthetic catalog and then apply it to a catalog of m 1 5 events that occurred in the salton trough from 1990 to 2009 we validate our stressing rate estimates by comparing them to estimates from a geodetically derived slip model for a large creep event on the obsidian buttes fault the results demonstrate that our approach can identify large aseismic deformation transients in a multidecade long earthquake catalog and roughly constrain the absolute magnitude of the stressing rate transients our method can therefore provide a way to detect aseismic transients in regions where geodetic resolution in space or time is poor

biomineralisation in the palaeozoic oceans evidence for simultaneous crystallisation of high and low magnesium calcite by phacopine trilobites abstract the chemical composition and microstructure of the calcite cuticles of eleven species of phacopine trilobites have been investigated by electron beam imaging diffraction and microanalysis and results reveal that the lenses of their schizochroal eyes differed significantly in chemical composition from the rest of the cuticle in vivo apart from the eye lenses most cuticles are inferred to have escaped extensive recrystallisation because their constituent crystals are sub micrometre in size and have a preferred orientation that is consistent between species their current compositions of 1 4 to 2 4 mol mgco3 are likely to be close to original values although as they commonly luminesce and contain detectable manganese and iron some diagenetic alteration has taken place the associated lenses have a microstructure that is suitable for focusing light yet are optically turbid owing to the presence within calcite of micropores and crystals of microdolomite apatite celestite and pyrite the microdolomite indicates that lenses recrystallised from an original high mg calcite composition and this is supported by the presence of nanometre scale modulated microstructures in both the calcite and dolomite these lenses currently contain 1 to 6 mol mgco3 and by comparison with the proportion of magnesium lost from echinoderm stereom in the same thin sections may have contained 7 5 mol mgco3 in vivo in some samples more extensive diagenetic alteration is evidenced by recrystallisation of the cuticle including lenses to coarse equant calcite or enrichment of the cuticle but not necessarily the lenses in magnesium accompanying replacement by a mg fe phyllosilicate the phacopine trilobites had to modify partition coefficients for magnesium considerably in order to grow lenses with contrasting compositions to the rest of their cuticles and such a strong vital effect on biomineralisation suggests that incorporation of magnesium was essential for functioning of their calcite optical systems

mechanical response of the south flank of kilauea volcano hawaii to intrusive events along the rift systems abstract increased earthquake activity and compression of the south flank of kilauea volcano hawaii have been recognized by previous investigators to accompany rift intrusions we further detail the temporal and spatial changes in earthquake rates and ground strain along the south flank induced by six major rift intrusions which occurred between december 1971 and january 1981 the seismic response of the south flank to individual rift intrusions is immediate the increased rate of earthquake activity lasts from 1 to 4 weeks horizontal strain measurements indicate that compression of the south flank usually accompanies rift intrusions and eruptions emplacement of an intrusion at a depth greater than about 4 km such as the june 1982 southwest rift intrusion however results in a slight extension of the subaerial portion of the south flank horizontal strain measurements along the south flank are used to locate the january 1983 east rift intrusion which resulted in eruptive activity the intrusion is modeled as a vertical rectangular sheet with constant displacement perpendicular to the plane of the sheet this model suggests that the intrusive body that compressed the south flank in january 1983 extended from the surface to about 2 4 km depth and was aligned along a strike of n66 e the intrusion is approximately 11 km in length extended beyond the january 1983 eruptive fissures which are 8 km in length and is contained within the 14 km long region of shallow rift earthquakes

high magnesium calcite from sorgharwari limestone shale rhythmites of lower vindhyan proterozoic age lesser himalayas northwest india abstract the pink to gray micritic limestones of the sorgharwari rhythmites of lower vindhyan proterozoic age lesser himalayas northwest india are mainly composed of high mg calcite as shown by x ray diffraction study high mg calcites are not known to be preserved in ancient rocks the only known instances being of skeletal remains of pennsylvanian and cretaceous age sealed in impervious layers the sorgharwari rhythmites present field and petrographic features comparable with deeper water carbonates so well documented in the literature the high mg calcite could have been formed as 2 m micrite on the adjoining shelf as a physico chemical precipitate under hypersaline conditions and drifted to deeper waters as weak turbidity current deposits nephiloid layers or as contourites though this may be possible the preservation of high mg calcite in these micritic rocks is even more enigmatic it is presumed that the original shelf derived loose 2 m needles and plates of high mg calcite under the new deep water diagenetic environment neomorphosed to 2 m polyhedra thus giving a tight fabric to the rocks these in turn to coarser spar by aggrading neomorphism the alternative model of dissolution and reprecipitation proposed for the lithification of barbados limemud appears to be less probable

precursory seismic anomalies and transient crustal deformation prior to the 2008 mw 6 9 iwate miyagi nairiku japan earthquake 1 the epidemic type aftershock sequence etas model has been widely used for detecting seismicity anomalies such as quiescence and activation during aftershock sequences of large earthquakes and background levels of seismicity the causes of such anomalies are thought to be associated with spatiotemporal changes in stress even tiny perturbation of local stress here we analyze the seismic activity during the decade prior to the 2008 iwate miyagi inland earthquake of m7 2 mw6 9 to fit the etas model to the seismicity from various regions around the source over northern honshu japan from the viewpoint of the analyses with the etas model we find northern honshu is divided into three areas of distinctive behaviors increased seismicity decreased seismicity and normal seismicity relative to the etas prediction as in other previously published papers here we hypothesize that coulomb stress changes caused by a few years of precursory slip of the iwate miyagi earthquake resulted in the seismicity changes in and around the 2008 source region the confirmed significant seismic anomalies in respective regions are consistent with the increments of the coulomb failure stress of the corresponding regions that are calculated by the assumed slow slip on the southern part of the faults of the main shock the local crustal deformations observed from a dense global positioning system network including a station right above the focal fault supports that slow slip on the fault had been taking place for about 5 years prior to the occurrence of the focal earthquake and suggests that the slip terminated or migrated to down dip extension of the fault around 1 year before the rupture

influence of static stress changes on earthquake locations in southern california earthquakes induce changes in static stress on neighbouring faults that may delay hasten or even trigger subsequent earthquakes1 10 the length of time over which such effects persist has a bearing on the potential contribution of stress analyses to earthquake hazard assessment but is presently unknown here we use an elastic half space model11 to estimate the static stress changes generated by damaging magnitude m 5 earthquakes in southern california over the past 26 years and to investigate the influence of these changes on subsequent earthquake activity we find that in the 1 5 year period following a m 5 earthquake any subsequent nearby m 5 earthquake almost always ruptures a fault that is loaded towards failure by the first earthquake after this period damaging earthquakes are equally likely to rupture loaded and relaxed faults our results suggest that there is a short period of time following a damaging earthquake in southern california in which simple coulomb failure stress models could be used to identify regions of increased seismic hazard

evidence for syntectonic crystallization for the mudstone to slate transition at lehigh gap pennsylvania u s a data primarily for phyllosilicates have been obtained for the continuous transitional sequence from mudstone to slate with well developed slaty cleavage at lehigh gap pennsylvania and for slates from quarries in the same area samples were studied by optical microscopy powder x ray diffraction and electron microprobe analysis with emphasis on transmission and analytical electron microscopy mineral grains are virtually free of deformation induced strain concomitant with the gradual development of cleavage normal to bedding the following changes are observed or confirmed 1 the orientation of phyllosilicate grains changes discontinuously from being preferentially parallel to bedding to being parallel to cleavage 2 crystal imperfections as expressed in layer terminations low angle grain boundary like features and other defects decrease in density 3 complex mixed layering is replaced by homogeneous packets of layers of single phases and 4 illite transforms to muscovite with increase in k a1 and change from a lmd to 2m polytype slaty cleavage apparently develops due in part to pressure solution of phyllosilicates oriented parallel to bedding mass transport of components and crystallization to form new grains parallel to cleavage it reflects transitions from imperfect metastable phases toward ordered stable phases in a low temperature 225 c metamorphic environment

rapid deformation of the south flank of kilauea volcano hawaii the south flank of kilauea volcano has experienced two large magnitude m 7 2 and m 6 1 earthquakes in the past two decades global positioning system measurements conducted between 1990 and 1993 reveal seaward displacements of kilauea9s central south flank at rates of up to about 10 centimeters per year in contrast the northern side of the volcano and the distal ends of the south flank did not displace significantly the observations can be explained by slip on a low angle fault beneath the south flank combined with dilation deep within kilauea9s rift system both at rates of at least 15 centimeters per year

the use of earthquake rate changes as a stress meter at kilauea volcano stress changes in the earth s crust are generally estimated from model calculations that use near surface deformation as an observational constraint but the widespread correlation of changes of earthquake activity with stress has led to suggestions that stress changes might be calculated from earthquake occurrence rates obtained from seismicity catalogues although this possibility has considerable appeal because seismicity data are routinely collected and have good spatial and temporal resolution the method has not yet proven successful owing to the non linearity of earthquake rate changes with respect to both stress and time here however we present two methods for inverting earthquake rate data to infer stress changes using a formulation for the stress and time dependence of earthquake rates application of these methods at kilauea volcano in hawaii yields good agreement with independent estimates indicating that earthquake rates can provide a practical remote sensing stress meter

zigzag microstructure in rugose corals a possible indicator of relative seawater mg ca ratios low mg calcite lmc and high mg calcite hmc have been identified confidently as original biominerals in different rugose corals devonian tabulophyllum had a lmc skeleton whereas pennsylvanian lophophyllidium had a hmc skeleton zigzag microstructure a diagenetic microstructure in rugose corals may be related to early migration of mg2 ions during transformation of hmc into lmc therefore zigzag microstructure may indicate that the original mineral was hmc even in specimens that subsequently converted to lmc stratigraphically corals with zigzag microstructure are confined to the late paleozoic which is coincident with the aragonite sea of p a sandberg hence fluctuating mg ca ratios may have directly controlled oscillations in marine carbonate chemistry and the mineral composition of rugose corals so that hmc skeletons as indicated by zigzag microstructure formed during intervals with aragonite seas and lmc skeletons e g tabulophyllum formed during intervals with calcite seas

recent seismicity rate forecast for north east india an approach based on rate state friction law abstract in this study we have investigated the association of stress field disparities through earthquake production rate in both spatially and temporally for northeast region of india here we have implemented the rate and state dependent friction law for forecasting the seismicity rate over mw 5 0 earthquake events during the period 2013 2015 the most valuable input model parameter of forecasting seismicity rate is coulomb stresses changes cff which promote the seismicity rate the cff distributions that exhibit significant stress increase in the close proximity of the mainshock sources are found to be diminished with the inverse of the distance from the fault rupture plane basically background seismicity depends on the coulomb stress changes these coulomb stress changes amplify the background seismicity so a little change in stress can produce very low or high seismicity rate in areas of high ambient seismicity in several zones the high seismicity rate is revealed by the dominancy of the low b value the observed background seismicity rate lies between the ranges of 0 4 0 the significant b value is achieved in the range of 0 57 1 54 along with average value of 0 93 we have taken the value of constant consecutive parameters i e a 0 05 mpa and constant effective friction coefficient of 0 4 for all the faults however in the forecast model we have obtained the stress perturbations and heterogeneous b value to infer the reliable result in comparison to reference forecast model for the period of 1963 2012 in this study we have also adopted the relm experiment in csep testing centre to verify the consistency of the result related to forecast for the duration of 2013 2015 the statistical test provided the satisfactory result for this study region

new insights into kilauea s volcano dynamics brought by large scale relative relocation of microearthquakes 1 we investigated the microseismicity recorded in an active volcano to infer information concerning the volcano structure and long term dynamics by using relative relocations and focal mechanisms of microearthquakes there were 32 000 earthquakes of the mauna loa and kilauea volcanoes recorded by more than eight stations of the hawaiian volcano observatory seismic network between 1988 and 1999 we studied 17 000 of these events and relocated more than 70 with an accuracy ranging from 10 to 500 m about 75 of these relocated events are located in the vicinity of subhorizontal decollement planes at a depth of 8 11 km however the striking features revealed by these relocation results are steep southeast dipping fault planes working as reverse faults clearly located below the decollement plane and which intersect it if this decollement plane coincides with the pre mauna loa seafloor as hypothesized by numerous authors such reverse faults rupture the pre mauna loa oceanic crust the weight of the volcano and pressure in the magma storage system are possible causes of these ruptures fully compatible with the local stress tensor computed by gillard et al 1996 reverse faults are suspected of producing scarps revealed by kilometer long horizontal slip perpendicular lineations along the decollement surface and therefore large scale roughness asperities and normal stress variations these are capable of generating stick slip large magnitude earthquakes the spatial microseismic pattern observed in the south flank of kilauea volcano and hilina type instabilities rupture intersecting the decollement surface causing its large scale roughness may be an important parameter controlling the growth of hawaiian volcanoes

dolomite carbonate replacement textures in veins cutting carboniferous rocks in east fife abstract carbonate veins cutting carboniferous sediments in fife scotland contain three apparently paragenetically equivalent types of ferroan dolomite all of which show somewhat unusual fabrics the most spectacular of these are fence textured crystals comprising an open rhombic network of inclusion rich dolomite which is partially filled by later syntaxial inclusion free ankerite the more common paragenetic equivalents to the fence textured dolomite are dolomite filled rhombic moulds and two dolomite intergrowth fabrics all three fabrics appear to indicate dolomite replacement of a rhombohedral carbonate precursor and seem to reflect different degrees of development in a common sequence of events 1 precipitation of a metastable phase 2 precipitation of dolomite 3 precipitation of dolomite coupled with dissolution of the metastable phase neomorphism 4 dissolution of the metastable phase this progression is compatible with gradual cooling within a series of hydrothermal systems centred on adjacent namurian volcanics and the range of fabrics developed by the dolomite may reflect differential cooling in different parts of these hydrothermal systems the ankerite which partially fills the fence texture and the rhombic moulds also occurs in veins cutting stephanian rocks indicating a much later origin

characteristics of deep 13 km hawaiian earthquakes and hawaiian earthquakes west of 155 55 w 1 high precision relocation of earthquakes recorded by the hawaiian volcano observatory hvo seismic network provides new information on the characteristics of seismic faulting at this oceanic hot spot using waveform cross correlation we have measured correlation coefficients and travel time differences for a set of 14 605 deep 13 km earthquakes recorded from 1988 to 1998 we find that about half of the analyzed earthquakes are in similar event clusters that delineate fault zones in the lower crust and upper mantle we suggest that much of this deep seismicity reflects rupture in the brittle lithosphere away from the magma pathways although at kilauea the stresses from magma movement may additionally help trigger mantle earthquakes on preexisting faults in regions with high differential ambient stresses focal mechanisms of similar event clusters throughout hawaii display characteristic patterns and appear consistent with the hypothesis that deep earthquakes on preexisting faults reflect the stresses due to volcano loading and flexure we also present the results of applying cross correlation analyses and relocation to 7000 earthquakes at all depths located west of 155 55 w and recorded from 1988 to 1998 the pattern of relocated earthquakes at the kealakekua fault zone is consistent with the presence of a low angle detachment on the west flank of mauna loa

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

review of the physical basis of laboratory derived relations for brittle failure and their implications for earthquake occurrence and earthquake nucleation a laboratory derived crack growth based constitutive relation for brittle faulting is developed the relation consists of two rheologic components a nonlinear arrhenius dependence of strain rate on temperature and stress corresponding to subcritical crack growth and a linear slip weakening behavior associated with dilatancy crack coalescence and supercritical crack growth the implications of this general behavior for the onset of rapid slip earthquake nucleation are considered laboratory observations of static fatigue and time dependent failure from rock fracture and rock friction experiments are consistent with this simple constitutive description as are the predictions of rate and state dependent equations for the onset of rapid frictional slip between bare rock surfaces i argue that crack growth is the physical process that controls time dependent rock fracture and the time dependent onset of unstable frictional sliding some similar and related arguments made in the past 1 2 century in the fields of rock mechanics and earthquake seismology are reviewed for stressing rates appropriate for the san andreas fault system the simple constitutive relation with lab derived constants predicts a minimum time for nucleation of 1 yr general predictions are a minimum nucleation patch radius of 0 06 to 0 2 m and a minimum earthquake moment of 8 5 x 107nm

carbon isotope excursions and crinoid dissolution at exposure surfaces in carbonates west texas u s a abstract carbonates from the horseshoe atoll reinecke field west texas u s a show four subaerial exposure events by the presence of rhizoliths alveolar septal fabric and thin calcretes that subdivide the pennsylvanian succession into five sequences vertical profiles of bulk rock 13c analyses show values that are generally 1 pdb but negative shifts of up to 2 occur beneath exposure surfaces the bulk rock 13c values 1 could be explained as a mixture of 63 marine carbonate 13c 4 and 37 pedogenic carbonate 13c 4 while a negative bulk rock excursion of 13c 1 can be explained as a mixture of 37 marine and 63 pedogenic calcite distinctive negative shifts in the 13c profiles do not occur under some exposure surfaces that contain soil generated features and one negative shift occurs that apparently is unrelated to an exposure surface bulk rock 13c values are difficult to interpret because the volume of their various components is unknown furthermore 13c profiles may miss subaerial exposure surfaces certain styles of crinoid alteration may indicate paleo subaerial exposure surfaces fossil crinoids can be preserved in a variety of ways but crinoids with dissolution holes that subsequently either become filled with calcite cement or were crushed during burial are restricted to 2 m below exposure surfaces dissolution of mg calcite crinoids is due to their relatively high mg composition 12 mole mgco3 combined with their location beneath soil capped surfaces from which meteoric waters greatly undersaturated with respect to calcite emerged late stage dissolution removed finely crystalline calcite but crinoids by this time had stabilized to coarsely crystalline calcite and dolomite and thus were unaffected evaluation of other stratigraphic systems is needed to determine whether the use of holey crinoids to identify subaerial exposure surfaces has broad application

petrography and significance of zoned dolomite cements from the cayman formation miocene of cayman brac british west indies abstract cavities in dolostones from the cayman formation miocene from cayman brac commonly contain complex cement successions that record three main phases of diagenesis phase i cements formed of low ca calcian dolomite lcd and high ca calcian dolomite hcd are divided into monomineralic lcd crystals oscillatory zoned lcd hcd crystals and step zoned hcd lcd crystals dissolution during phase ii produced dolomite crystals with hollow cores hollow growth zones and hollow crosscutting zones calcite precipitated during phase iii filled many of the cavities that had not been filled by the dolomite cements etching shows that the lcd is formed of blocky subcrystals that have their long axes perpendicular to the growth surfaces whereas hcd is characterized by a modulated structure that is evident as growth parallel slightly sinuous strands 10 20 nm wide the contrast in crystallographic microstructures supports the notion that lcd and hcd are distinct types of dolomite two levels of variability that operated on different time scales controlled diagenesis in the cayman formation of cayman brac long term variability controlled the evolution from dolomite precipitation to dolomite dissolution to calcite precipitation short term variability controlled variations in the physiochemical environments that characterized each phase of diagenesis thus during phase i diagenesis short term fluctuations in water chemistry and or crystal growth patterns controlled the mol caco3 in the dolomite cement crystals similarly short term variations in pore water compositions controlled the style of dolomite dissolution during the second phase of diagenesis

growth and persistence of hawaiian volcanic rift zones hawaiian volcanic rift zones are modeled by representing the rifts and adjacent volcano flanks as long ridges with the geometry of flattened triangular prisms the intrusion of dikes along the axis of a rift requires a mechanism to generate the appropriate dike trapping stress field within the prism possible factors that affect the state of stress in the prism include multiple dike intrusion along the ridge axis faulting and gravitational sagging of the topography in extreme models with very steep slopes and high poisson s ratio corresponding to the gelatin models of rift zones by fiske and jackson 1972 results of finite element calculations indicate that gravity induced stresses are sufficient to trap a dike into propagating within the prism and parallel to the rift zone as proposed by fiske and jackson however the mechanism does not work for gently sloping flanks or a more acceptable poisson s ratio of about 0 25 additionally trapping stresses in the gravity loading and density stratification models will not persist after a few dike injection episodes therefore in mature hawaiian rift zones with possibly thousands of dikes additional processes must act to control the stresses that permit continued dike intrusion and rift persistence it is proposed that accommodation to dike emplacement occurs by slip on deep faults possibly of the type proposed for the 1975 kalapana hawaii earthquake as suggested by others for this earthquake the faults could coincide with the contact of the volcano with the seafloor within the weak seafloor sediments such faulting not only provides a means for the flanks to adjust continuously to intrusions but also generates the stress patterns needed to constrain future dikes to propagate along the rift axis other possible faulting mechanisms such as shallow gravity slides and normal faulting of the flanks do not appear to favor rift zone persistence in this model the horizontal stress generated by a standing column of magma at the time of dike emplacement the stresses in the ridges and the fault strength are coupled this results in a feedback between the maximum height that magma can rise along the rift fault friction and fault width through this feedback the slope of the volcano flank is controlled by the fault friction when applied to kilauea volcano the model yields an estimate for the coefficient of fault friction as high as 0 39 assuming normal hydrostatic pore fluid pressure an implication of this model supported by other studies is that rift intrusion and lateral spreading could be major contributors to volcano growth

seismicity and geodetic anomalies in a wide area preceding the niigata ken chuetsu earthquake of 23 october 2004 central japan 1 the ordinary short term occurrence rate of earthquakes in a region is predicted using the epidemic type aftershock sequence etas model of triggering seismicity any anomalous seismic activity such as quiescence and activation can be quantified by identifying significant deviation from the predicted rate such anomalies are revealed to have occurred during the three year period leading up to the 2004 chuetsu earthquake of m6 8 mw6 6 central japan the quiescence and activation which took place in the zone of negative and positive increments of the coulomb failure stress respectively were possibly caused by aseismic slip on or near the focal fault plane such slip is further supported by transient crustal movement around the rupture source time series records of the baseline distances between permanent gps stations deviated from the predicted trends with the deviations mostly consistent with the coseismic horizontal displacements of the stations due to the chuetsu earthquake the cumulated preceding slip is estimated to be roughly equivalent to mw6

triggered earthquakes suppressed by an evolving stress shadow from a propagating dyke the role of static versus dynamic stresses in earthquake clusters is unclear analysis of earthquakes triggered by a dyke intrusion at an icelandic volcano unambiguously demonstrates that static stresses are important for earthquake clustering large earthquakes can generate small changes in static stress increases that trigger aftershock swarms or reductions that create a region of reduced seismicity a stress shadow1 2 however seismic waves from large earthquakes also cause transient dynamic stresses that may trigger seismicity3 4 this makes it difficult to separate the relative influence of static and dynamic stress changes on aftershocks dyke intrusions do not generate dynamic stresses so provide an unambiguous test of the stress shadow hypothesis here we use gps and seismic data to reconstruct the intrusion of an igneous dyke that is 46 km long and 5 m wide beneath bar arbunga volcano central iceland in august 2014 we find that during dyke emplacement bursts of seismicity at a distance of 5 to 15 km were first triggered and then abruptly switched off as the dyke tip propagated away from the volcano we calculate the evolving static stress changes during dyke propagation and show that the stressing rate controls both the triggering and then suppression of earthquake rates in three separate areas adjacent to the dyke our results imply that static stress changes help control earthquake clustering similar small static stress changes may be important for triggering seismicity near geothermal areas regions being hydrofractured and deflating oil and gas fields

mineralogy nucleation and growth of dolomite in the laboratory and sedimentary environment a review dolomite camg co3 2 forms in numerous geological settings usually as a diagenetic replacement of limestone and is an important component of petroleum reservoir rocks rocks hosting base metal deposits and fresh water aquifers dolomite is a rhombohedral carbonate with a structure consisting of an ordered arrangement of alternating layers of ca2 and mg2 cations interspersed with co32 anion layers normal to the c axis dolomite has r3 symmetry lower than the caco3 r3 c symmetry of calcite primarily due to ca mg ordering high magnesium calcite also has r3 c symmetry and differs from dolomite in that ca2 and mg2 ions are not ordered high magnesium calcite with near dolomite stoichiometry 50 mol mgco3 has been observed both in nature and in laboratory products and is referred to in the literature as protodolomite or very high magnesium calcite many dolomites display some degree of cation disorder ca2 on mg2 sites and vice versa which is detectable using transmission electron microscopy and x ray diffractometry laboratory syntheses at high temperature and pressure as well as studies of natural dolomites show that factors affecting dolomite ordering stoichiometry nucleation and growth include temperature alkalinity ph concentration of mg and ca mg to ca ratio fluid to rock ratio mineralogy of the carbonate being replaced and surface area available for nucleation in spite of numerous attempts dolomite has not been synthesized in the laboratory under near surface conditions examination of published x ray diffraction data demonstrates that assertions of dolomite synthesis in the laboratory under near ambient conditions by microbial mediation are unsubstantiated these laboratory products show no evidence of cation ordering and appear to be very high magnesium calcite elevated temperature and elevated pressure experiments demonstrate that dolomite nucleation and growth always are preceded by very high magnesium calcite formation it remains to be demonstrated whether microbial mediated growth of very high magnesium calcite in nature provides a precursor to dolomite nucleation and growth analogous to reaction paths in high temperature experiments

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

seismic tremor at the 9 50 n east pacific rise eruption site ocean bottom seismic observations within the 9 50 n region of the east pacific rise indicate persistent low amplitude tremor activity throughout the october 2003 through february 2007 period of monitoring these signals exhibit either monochromatic or polychromatic spectral characteristics with a 6 hz fundamental frequency and up to two harmonics individual events cannot be correlated between nearby 1 km stations implying the presence of multiple small amplitude sources positioned within the shallow crust tremor exhibits a semidiurnal periodicity with some stations recording activity during times of increasing tidal extension and others detecting tremor signals during times of increasing compression the amplitude duration and rate of activity also correlate positively with fortnightly changes in the amplitude of the tides these spatiotemporal patterns are consistent with tremor generation in response to tidally modulated fluid flow within a network of shallow cracks tremor energy flux is spatially and temporally heterogeneous however there are extended periods of greater and lesser activity that can be tracked across portions of the array despite their shallow crustal origin changes in tremor amplitude and spectral character occur in the months prior to a major microearthquake swarm and inferred seafloor spreading event on 22 january 2006 with an increase in the degree of correlation between tremor activity and tidal strain in the weeks leading up to this event after the spreading event two eruption surviving stations near the axis continue to show high rates of tremor activity whereas these signals are suppressed at the single station recovered from the near axis flanks this off axis quiescence may result from the dike induced closing of cracks or perhaps from the emplacement of impermeable flows near the station

aftershock modeling based on uncertain stress calculations 1 we discuss the impact of uncertainties in computed coseismic stress perturbations on the seismicity rate changes forecasted through a rate and state dependent frictional model we aim to understand how the variability of coulomb stress changes affects the correlation between predicted and observed changes in the rate of earthquake production we use the aftershock activity following the 1992 m7 3 landers california earthquake as a case study to accomplish these tasks we first analyze the variability of stress changes resulting from the use of different published slip distributions we find that the standard deviation of the uncertainty is of the same size as the absolute stress change and that their ratio the coefficient of variation cv is approximately constant in space this uncertainty has a strong impact on the forecasted aftershock activity if a rate and state frictional model is considered we use the early aftershocks to invert for friction parameters and the coefficient of variation by means of the maximum likelihood method we show that when the uncertainties are properly taken into account the inversion yields stable results which fit the spatiotemporal aftershock sequence the analysis of the 1992 landers sequence demonstrates that accounting for realistic uncertainties in stress changes strongly improves the correlation between modeled and observed seismicity rate changes for this sequence we measure a friction parameter asn 0 017 mpa and a coefficient of stress variation cv 0 95

bridging great earthquake doublets through silent slip on and off fault aftershocks of the 2006 kuril island subduction earthquake toggled by a slow slip on the outer rise normal fault of the 2007 great earthquake 1 the november 2006 great thrust earthquake of moment magnitude m w 8 3 on the plate boundary in the kuril chishima islands triggered as many vigorous normal faulting aftershocks in the outer rise region seaward of the trench as on fault aftershocks here we show that the aftershocks for a 40 day period preceding the january 2007 m w 8 1 event in the outer rise were less frequently observed than the rate expected by both the omori utsu formula and the epidemic type aftershock sequence etas model while at the same time were more frequent along the plate boundary we discuss whether such simultaneous quiescence and activation in the pervasive 2006 aftershocks might have been initiated by the onset of aseismic slip on the 2007 rupture plane the stable fault sliding in an elastic half space demonstrates progressive stress shadowing in the outer rise and stress loading along the plate boundary furthermore the rate and state dependent friction of dieterich quantitatively simulates temporal changes in seismic behavior the same trends of the anomalous activities last in both zones after the 2007 rupture which suggests that the slips continuously take place in the similar region on the fault throughout the period before and after the rupture the kuril case implies that temporal seismic quiescence in an aftershock sequence is useful in evaluating the possibility of the subsequent triggered event thus suggesting itself as a potential earthquake forecasting model together with pervasive earthquake clustering models

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

hydrothermal replacement of biogenic and abiogenic aragonite by mg carbonates relation between textural control on effective element fluxes and resulting carbonate phase abstract dolomitization i e the secondary replacement of calcite or aragonite caco3 by dolomite camg co3 2 is one of the most volumetrically important carbonate diagenetic processes it occurs under near surface and shallow burial conditions and can significantly modify rock properties through changes in porosity and permeability dolomitization fronts are directly coupled to fluid pathways which may be related to the initial porosity permeability of the precursor limestone an existing fault network or secondary porosity permeability created through the replacement reaction in this study the textural control on the replacement of biogenic and abiogenic aragonite by mg carbonates that are typical precursor phases in the dolomitization process was experimentally studied under hydrothermal conditions aragonite samples with different textural and microstructural properties exhibiting a compact inorganic aragonite single crystal an intermediate bivalve shell of arctica islandica and open porous structure skeleton of coral porites sp were reacted with a solution of 0 9 m mgcl2 and 0 015 m srcl2 at 200 c the replacement of aragonite by a ca bearing magnesite and a mg ca carbonate of non stoichiometric dolomitic composition takes place via a dissolution precipitation process and leads to the formation of a porous reaction front that progressively replaces the aragonite precursor the reaction leads to the development of porosity within the reaction front and distinctive microstructures such as gaps and cavities at the reaction interface the newly formed reaction rim consists of chemically distinct phases separated by sharp boundaries it was found that the number of phases and their chemical variation decreases with increasing initial porosity and reactive surface area this observation is explained by variations in effective element fluxes that result in differential chemical gradients in the fluid within the pore space of the reaction rim observed reaction rates are highest for the replacement of the initially highly porous coral and lowest for the compact structure of a single aragonite crystal therefore the reaction progress equally depends on effective element fluxes between the fluid at the reaction interface and the bulk solution surrounding the test material as well as the reactive surface area this study demonstrates that the textural and microstructural properties of the parent material have a significant influence on the chemical composition of the product phase moreover our data highlight the importance of effective fluid mediated element exchange between the fluid at the reaction interface and the bulk solution controlled by the local microstructure

high salinity facilitates dolomite precipitation mediated by haloferax volcanii ds52 abstract although most modern dolomites occur in hypersaline environments the effects of elevated salinity on the microbial mediation of dolomite precipitation have not been fully evaluated here we report results of dolomite precipitation in association with a batch culture of haloferax volcanii ds52 a halophilic archaeon under various salinities from 120 to 360 and the impact of salinity on microbe mediated dolomite formation the mineral phases morphology and atomic arrangement of the precipitates were analyzed by xrd sem and tem respectively the amount of amino acids on the archaeal cell surface was quantified by hplc ms the xrd analysis indicated that disordered dolomite formed successfully with the facilitation of cells harvested from cultures with relatively high salinities 200 and 280 but was not observed in association with cells harvested from cultures with lower salinity 120 or the lysates of cells harvested from extremely high salinity 360 the tem analysis demonstrated that the crystals from cultures with a salinity of 200 closely matched that of dolomite importantly we found that more carboxyl groups were presented on the cell surface under high salinity conditions to resist the high osmotic pressure which may result in the subsequent promotion of dolomite formation our finding suggests a link between variations in the hydro chemical conditions and the formation of dolomite via microbial metabolic activity and enhances our understanding about the mechanism of microbially mediated dolomite formation under high salinity conditions

pre seismic anomalies in seismicity and crustal deformation case studies of the 2007 noto hanto earthquake of m6 9 and the 2007 chuetsu oki earthquake of m6 8 after the 2004 chuetsu earthquake of m6 8 summary if aseismic slip occured on a fault or its deeper extension both seismicity and crustal deformation around the source would be affected such anomalies are determined from earthquake occurrence data and geodetic records during the periods leading up to the 2007 march noto hanto earthquake of m6 9 and the 2007 july chuetsu oki earthquake of m6 8 which successively occurred after the 2004 october chuetsu earthquake of m6 8 on the japan sea coast assuming such aseismic slips seismic zones corresponding to negative and positive increments of the coulomb failure stress show seismic quiescence and activation respectively relative to the rate predicted by the epidemic type aftershock sequence model these interpretations are further supported by transient crustal movements around the sources preceding the ruptures for example the time series of baseline distances between permanent global positioning system stations deviated from their long term linear trends in a manner that is consistent with the assumed slip in particular this paper emphazes on the investigation of the interacting tectonic processes within such a narrow area and a short period considering the precursory slow slips on the focal faults or their downdip extensions based on the observed anomalies in seismicity and crustal movement

effects of a revised rate and state dependent friction law on aftershock triggering model abstract seismicity may be considered as a sequence of earthquake nucleation events controlled by regional loading history on the basis of this concept dieterich 1994 modeled aftershock seismicity following an imposed stress step by using a laboratory derived rate and state dependent friction law rsf although this model predicts the canonical 1 t decay of aftershock rate two huge gaps from observations are known the model with frictional parameters assumed to be laboratory observed values predicts too low aftershock productivity and also too long a delay before the decay onset these gaps are by orders of magnitude we suspected that the problem might be the incorrectness of traditional rsfs none of which was free from contradictions with laboratory data hence we modeled aftershock triggering with a revised rsf nagata et al 2012 which seems to have resolved the previously known flaws in reproducing laboratory data the original analytic approach of dieterich 1994 was found invalid for the revised rsf so we did an equivalent analysis by numerically tracking individual nucleation sources the revised rsf produced generally similar aftershock seismicity with the gaps mentioned above narrowed by a factor though these are far too small improvements of the huge gaps that is the revised rsf did not fully resolve the problem on the other hand our simulations found a counterintuitive response of a fault obeying the revised rsf if imposed during a certain stage in the seismic cycle a positive stress step can cause oscillatory slow slip events before eventual seismic instability instead of a usual response of further monotonic acceleration to seismic instability this delays the timing of the next earthquake due to this behavior the exponent of the aftershock decay can be greater than unity also the decay can once overshoot below the background seismicity before eventually returning to the background level

seismicity on a fault controlled by rate and state dependent friction with spatial variations of the critical slip distance 1 we perform systematic simulations of slip using a quasi dynamic continuum model of a two dimensional 2 d strike slip fault governed by rate and state dependent friction the depth dependence of the a b and l frictional parameters are treated in an innovative way that is consistent with available laboratory data and multidisciplinary field observations various realizations of heterogeneous l distributions are used to study effects of structural variations of fault zones on spatiotemporal evolution of slip we demonstrate that such realizations can produce within the continuum class of models realistic features of seismicity and slip distributions on a fault we explore effects of three types of variable l distributions 1 a depth dependent l profile accounting for the variable width of fault zones with depth 2 uncorrelated 2 d random distributions of l with different degrees of heterogeneity and 3 a hybrid distribution combining the depth dependent l profile with the 2 d random l distributions the first type of l distribution with relatively small l over the depth range corresponding to the seismogenic zone and larger l elsewhere generates stick slip events in the seismogenic zone and ongoing creep above and below that region the 2 d heterogeneous parameterizations generate frequency size statistics with event sizes spanning 4 orders of magnitude our results indicate that different degrees of heterogeneity of l distributions control 1 the number of simulated events and 2 the overall stress level and fluctuations other observable trends are 3 the dependency of hypocenter location on l and 4 different nucleation phases for small and large events in heterogeneous distributions

cold water injection into single and two phase geothermal reservoirs approximate analytical solutions are derived for cold water injection into single and two phase porous medium geothermal reservoirs a numerical geothermal reservoir simulator is used to verify the applicability of the analytical solutions for pressure transient analysis in accordance with these numerical results the analytical solutions indicate that the pressure buildup behavior during injection into either a single phase liquid or two phase reservoir is governed by the kinematic viscosity of the cold injected fluid the falloff pressures after cold water injection into a single phase liquid reservoir except for very early shut in times are primarily controlled by the kinematic viscosity of the in situ hot reservoir fluid for two phase reservoirs however the falloff behavior is considerably more complex and cannot be fully described by the analytical solution developed in this paper

comparison of deterministic and stochastic earthquake simulators for fault interactions in the lower rhine embayment germany time dependent probabilistic seismic hazard assessment requires a stochastic description of earthquake occurrences while short term seismicity models are well constrained by observations the recurrences of characteristic on fault earthquakes are only derived from theoretical considerations uncertain palaeo events or proxy data despite the involved uncertainties and complexity simple statistical models for a quasi period recurrence of on fault events are implemented in seismic hazard assessments to test the applicability of statistical models such as the brownian relaxation oscillator or the stress release model we perform a systematic comparison with deterministic simulations based on rate and state dependent friction high resolution representations of fault systems and quasi dynamic rupture propagation for the specific fault network of the lower rhine embayment germany we run both stochastic and deterministic model simulations based on the same fault geometries and stress interactions our results indicate that the stochastic simulators are able to reproduce the first order characteristics of the major earthquakes on isolated faults as well as for coupled faults with moderate stress interactions however we find that all tested statistical models fail to reproduce the characteristics of strongly coupled faults because multisegment rupturing resulting from a spatiotemporally correlated stress field is underestimated in the stochastic simulators our results suggest that stochastic models have to be extended by multirupture probability distributions to provide more reliable results

impact of the receiver fault distribution on aftershock activity 1 aftershock models are usually based either on purely empirical relations ignoring the physical mechanism or on deterministic calculations of stress changes on a predefined receiver fault orientation here we investigate the effect of considering more realistic fault systems in models based on static coulomb stress changes for that purpose we perform earthquake simulations with elastic half space stress interactions rate and state dependent frictional earthquake nucleation and extended ruptures with heterogeneous fractal slip distributions we find that the consideration of earthquake nucleation on multiple receiver fault orientations does not influence the shape of the temporal omori type aftershock decay but changes significantly the predicted spatial patterns and the total number of triggered events so called stress shadows with decreased activity almost vanish and activation decays continuously with increasing distance from the main shock rupture the total aftershock productivity which is shown to be almost independent of the assumed background rate increases significantly if multiple receiver fault planes exist the application to the 1992 m7 3 landers california aftershock sequence indicates a good agreement with the locations and the total productivity of the observed directly triggered aftershocks

motion of kilauea volcano during sustained eruption from the puu oo and kupaianaha vents 1983 1991 kilauea erupted almost continuously from january 1983 through 1991 although the summit began subsiding during the rift zone dike intrusion that initiated this eruption remarkably steady ground surface motions began in late 1983 after a magnitude 6 6 earthquake beneath the slopes of nearby mauna loa volcano and continued until the onset of brief upper east rift zone earthquake swarms in late 1990 during these 7 years the summit and upper rift zones subsided up to 10 11 and 4 8 cm yr 1 respectively and summit baselines contracted up to 6 cm yr 1 baselines directed northward from the summit to stations on mauna loa extended at rates up to 7 cm yr 1 and a baseline from south of the summit to mauna loa extended 4 cm yr 1 much of this extension is inconsistent with deformation caused solely by summit magma reservoir collapse and more likely reflects rifting as the south flank of the volcano moved seaward from the summit and rift zones farther from the summit baselines crossing the south flank extended up to 2 cm yr 1 and a south flank tide gauge rose 2 cm yr 1 the lower east rift zone 40 50 km from the summit subsided about 2 cm yr 1 motion on kilauea then is broadly consistent with slip along low angle south flank faults generating subsidence that is focused at the summit and along the rift system behind the faulting and uplift along the coastal south flank ahead of it dislocation models that combine these elements show that much of kilauea s edifice migrated seaward producing ground surface motions along the south flank of up to about 6 cm yr 1 the magnitude 6 1 earthquake of 1989 punctuated these motions along the eastern south flank producing more than 25 cm of seaward displacement and 15 km east of the epicenter up to 24 cm of subsidence south of the lower east rift zone unlike the magnitude 7 2 south flank earthquake of 1975 the 1989 event was preceded neither by summit magma reservoir inflation nor by rift zone dike intrusions and accompanying compression of the south flank deformation was probably caused by the weight of the volcanic overburden and by ongoing dilation and slip within the rift system

evolution of moderate seismicity in the san francisco bay region 1850 to 1993 seismicity changes related to the occurrence of large and great earthquakes the rate of seismic activity of moderate size m 5 5 earthquakes in the san francisco bay sfb region has varied considerably during the past 150 years as measured by the rate of seismic moment release seismic activity in the sfb region is observed to accelerate prior to m 7 0 earthquakes in 1868 1906 and 1989 and then to decelerate following them we examine these seismicity changes in the context of the evolution of the stress field in the sfb region as a result of strain accumulation and release using a model of dislocations in an elastic halfspace we use a coulomb failure function cff to take into account changes in both shear and normal stresses on potential failure planes of varying strike and dip in the sfb region we find that the occurrence of a large or great earthquake creates a stress shadow a region where the stress driving earthquake deformation is decreased interseismic strain accumulation acts to reverse this process gradually bringing faults in the sfb region out of the stress shadow of a previous large or great earthquake and back into a state where earthquake failure is possible as the stress shadow generated by a large or great earthquake disappears it migrates inward toward the fault associated with that large or great event the observed changes in the rate of occurrence of moderate earthquakes in the sfb region are broadly consistent with this model in detail the decrease in seismicity throughout most of the sfb region and a localized increase in the monterey bay region following the great 1906 earthquake is consistent with our predicted stress changes the timing and location of moderate size earthquakes when the rate of seismicity increases again in the 1950s is consistent with areas in which the 1906 stress shadow had been eliminated by strain accumulation in the sfb region those earthquakes that are most inconsistent with our stress evolution model including the 1911 earthquake southeast of san jose are found to occur in regions where dip slip faulting is common in addition to strike slip the 1906 earthquake brought that zone of dip slip faulting closer to failure suggesting that the 1911 event may have been a reverse faulting earthquake rather than a strike slip one similar to the 1984 morgan hill earthquake the occurrence of activity on faults very close to the san andreas such as the lake elsman earthquakes of 1988 and 1989 appear to be associated with the last disappearence of the stress shadow on the loma prieta segment of the san andreas fault thus events of that type may represent an intermediate term precursor to a large earthquake such as the 1989 loma prieta event much of the moderate size earthquake activity in the sfb region appears to be modulated in time by the buildup and release of stress in large and great earthquakes a tensorial approach to earthquake prediction i e taking into account changes in the components of the stress tensor has several advantages over examining scalar changes such as those in seismic activity and moment release rates this tensorial approach allows for both activation and quiescence but in different subregions prior to as well as after large earthquakes

response of the san jacinto fault zone to static stress changes from the 1992 landers earthquake we perform an analysis of the seismicity response of the san jacinto fault zone to static coulomb stress changes from the 1992 landers earthquake sequence results show that in general stress changes forecast rate changes well we find a significant positive correlation between the change in rate and the magnitude of the coulomb stress change with a correlation coefficient of 0 76 equivalent to 5 6 when compared to a 0 null hypothesis furthermore although the correlations are less clear over negative than positive stress changes there is evidence of some coulomb stress dependent quiescence on stress shadows models that account for heterogeneity in reference seismicity show clear improvements in their predictions of spatial variability of aftershock rates compared to those that assume uniform reference we find also that better performance is obtained 1 using a time dependent coulomb rate state model compared to a time independent exponential model and 2 using structurally constrained rather than optimal target fault orientations these results are an important step in the validation of coulomb stress based methods for quantitative seismicity forecasting we conclude that the correspondence between the predictions of coulomb stress models for aftershock seismicity may be sensitive to strong heterogeneity in aftershock locations and orientations associated with the presence of large scale structure in aftershock study areas in these cases we suggest that where the regional structure is mapped incorporating it explicitly into coulomb stress models may improve the performance of quantitative coulomb stress based forecasts

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

detecting precursory earthquake migration patterns using the pattern informatics method 1 in this paper we analyze the evolution of seismic activity using a dynamic modification of the pattern informatics method this method identifies locations that have systematic fluctuations in seismicity on pi maps by investigating the evolution of hotspot configurations on the pi map and calculating the distance between hotspots and the epicenter of the impending large earthquake a migrating pattern of increasing or decreasing precursory change in seismicity is revealed we find that hotspots on the pi map appear increasingly closer to the epicenter as the time of the forthcoming earthquake is approached implying the existence of an earthquake preparation process the migration pattern and associated decreasing distance is confirmed by a stochastic test and therefore we conclude that a preparation process prior to large earthquakes can be detected

a typical evolution of seismicity patterns resulting from the coupled natural human induced and coseismic stresses in a longwall coal mining environment abstract a very unusual time space distribution of seismicity accompanying coal exploitation has been observed in a polish mine the earthquakes did not follow the depth of mining but exhibited changing depths from far below to close to the mined seam one of the deep events which occurred at close epicentral distance to the active mining front was m l 3 7 event this paper presents the study of possible coupling of natural human induced and coseismic stresses in a longwall coal mining environment the full moment tensor solution showed that the strong earthquake occurred on an almost vertical plane consistent with approximate strike of local tectonic structure the signal correlation analysis revealed some highly correlated pairs within both deep and shallow event groups to evaluate inducing factor of ongoing and past exploitation geomechanical modelling of its influence on strain and stress at the target depth has been performed the results exhibited a changing vertical stress regime which might have promoted failure on preexisting almost vertical planes of weakness the earthquakes rate variation in time showed no increase in activity right after the occurrence of m l 3 7 event the p s wave spectra corner frequency ratio had an average of 1 0 suggesting slow rupture however the coulomb stress change analysis showed that the magnitude of stress changes due to coseismic slip of m l 3 7 event at the hypocentral depth is of the same order as the stress changes caused by mining thus the distribution of seismicity at this level could have been driven by both exploitation and coseismic stresses moreover the seismicity which occurred within first few weeks after m l 3 7 event followed positive stress changes all the obtained results let us prove that the m l 3 7 event was a tectonic earthquake triggered by ongoing exploitation and that the distribution of following seismicity was affected by coupled natural exploitation induced and coseismic stresses

injection and thermal breakthrough in fractured geothermal reservoirs lbl 12698 preprint submitted to the journal of geophysical research injection and thermal breakthrough in fractured geothermal reservoirs gudmundur s bodvarsson and chin fu tsang may 1981 two week loan copy this is a library circulating copy which may be borrowed for two weeks for a personal retention copy call tech info division ext 6782 prepared for the u s department of energy under contract w 7405 eng 48

inference of coseismic slip via joint inversion of gps and aftershock data the 2004 parkfield example 1 in many coseismic slip inversions the number of model parameters is much larger than that of the independent observations and the problem is extremely underdetermined it is thus instructive to incorporate additional data sets into the slip inversion in this study i describe a new approach for coseismic slip inversion whereby both gps displacements and first day aftershock rate changes are used jointly to constrain the solution the joint inversion incorporates the dieterich s aftershock model which adopts a constitutive friction that depends logarithmically on the sliding rate the method is applied to the 2004 parkfield earthquake the joint inversion not only provides resolving power of slip at depths inaccessible to gps only inversions but it also helps to gain insight on the fault mechanical properties i show that the data are consistent with the adopted aftershock model being the dominant mechanism for aftershock production along the parkfield segment and i obtain an upper bound on the friction dependence on the log of rate of fault patches that have experienced aftershock activity a consequence of the irregular aftershock distribution is that the slip distribution is extremely nonsmooth with the aftershock zones acting as barriers

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

spatial variations in the stoichiometry and geochemistry of miocene dolomite from grand cayman implications for the origin of island dolostone abstract the cayman formation miocene 140 m thick on grand cayman is incompletely dolomitized with the most of the dolomite restricted to the peripheral part of the island these calcium rich dolomites with 50 60 mol caco 3 ca are divided into low calcium dolomite lcd ca 55 despite the small size of the island 6 8 km wide the percentages of lcd and hcd the ca and the geochemical properties of the dolomites show geographic variations relative to the surrounding shelf edge accordingly the cayman formation on the east end of the island is divided into the peripheral dolostone shelf edge 1 5 km inland transitional dolostone 1 5 2 7 km inland and the interior limestone and dolostone 2 7 km to island center from the peripheral dolostone to the interior limestone and dolostone there is an increase in the percentage of hcd and ca in the dolomite and decreases in the 18 o and 13 c values of the dolomite interpretations based on the oxygen and carbon isotopic compositions indicate that seawater is the source of mg for dolomitization the concentric pattern of dolomitization on the island reflects the fact that seawater flowed into the island from all directions during dolomitization the lateral inland variations in the dolomite stoichiometric and isotopic properties reflect the gradual modification of seawater by water rock interaction along the flow path from the shelf edge to the island center 87 sr 86 sr ratios indicate that two phases of dolomitization late miocene early pliocene and late pliocene early pleistocene were responsible for dolomitization of the cayman formation it is very likely that during both phases the carbonate platform was subaerially exposed and that the pump for circulating the seawater through the island was related to the seawater freshwater mixing zone the dolomitization model developed from grand cayman may be applicable to many other island dolostones affected by long term sea level changes given that the diagenetic potential of dolostone is directly linked to its stoichiometry the distribution of the lcd hcd will influence the petrographic properties geochemical signatures and reservoir potential of the dolostones