oxygen isotope and geochemical variations in the missouri river oxygen isotope ratios in streamflow of the missouri river basin vary geographically due to differences in source precipitation and the integration of waters from upstream regions average 18o values in the missouri river main stem systematically increase from less than 17 in the headwaters to about 9 in the lower basin seasonal variations at a given location result from fluctuations in meteoric precipitation residence time in reservoirs and groundwater systems evaporation and snowmelt average water chemistry values are successfully predicted for the upstream stations of two reaches on the lower missouri river based on changes in discharge along each reach and water quality measurements collected at the downstream stations source regions for some dissolved ions found in the lower missouri river are also identified sodium and sulfate originate predominantly from the basin above sioux city iowa while nitrate is largely derived from agricultural regions below sioux city

rapid nutrient load reduction during infiltration of managed aquifer recharge in an agricultural groundwater basin pajaro valley california artificial recharge of groundwater is an increasingly important method for augmenting groundwater supply and can have a positive or negative influence on the quality of water resources we instrumented a managed aquifer recharge mar pond in central coastal california to assess how patterns of infiltration and recharge affect the load of nitrate delivered to the underlying aquifer the concentration of nitrate in infiltrating water consistently decreased during passage through the first metre of subsurface soils enrichment of 18o and 15 n in the residual nitrate in infiltrating water proceeded in a ratio of 1 2 indicating that denitrification plays a significant role in the quantitative reduction of nutrients exported during infiltration through shallow soils the extent and rate of nitrate removal was spatially and temporally variable across the bottom of the recharge pond with 30 to 60 of the nitrate load being removed over the first 6 weeks of managed aquifer recharge operation during the period of highest n loading to the system when the average infiltration rate was 1 m day the recharge pond achieved a load reduction efficiency of 7 kg no3 n day ha which compares favourably to nitrate load reductions achieved by treatment wetlands groundwater mounding and water composition below the recharge pond suggest that recharge and subsequent lateral transport occur heterogeneously in the underlying aquifer nitrate concentrations in the aquifer following infiltration were lowered primarily by dilution with little evidence for additional denitrification occurring in the aquifer in comparison to high rates documented during shallow infiltration copyright 2011 john wiley sons ltd

characterization of hydraulic properties of rocks using probability of fluid induced microearthquakes the use of borehole fluid injections is typical for exploration and development of hydrocarbon or geothermal reservoirs such injections often induce small magnitude earthquakes the nature of processes leading to triggering of such microseismicity is still not completely understood here we consider induced microseismicity using as examples two case studies of geothermal reservoirs in crystalline rocks and one case study of a tight gas sandstone reservoir in all three cases we found that the probability of induced earthquakes occurring is very well described by the relaxation law of pressure perturbation in fluids filling the pore space in rocks this strongly supports the hypothesis of seismicity triggered by pore pressure moreover this opens additional possibilities of using passive seismic monitoring to characterize hydraulic properties of rocks on the reservoir scale with high precision

characterization of surface water and groundwater in the damascus ghotta basin hydrochemical and environmental isotopes approaches the hydrochemistry of major ions and environmental isotope compositions 18o 2h and tritium of water samples have been used to investigate the characteristics of rainfalls surface water and groundwater in the damascus ghotta basin the groundwater salinity in the damascus ghotta basin gradually increases as the groundwater moves from western to south eastern and north eastern parts of the basin a strong relationship exists between the barada river and the surrounded groundwaters mainly in terms of recharge by infiltration of surface waters the groundwater quality in the adra region has clearly become less saline as a result of establishment of the sewage water treatment station in this area since 1997 the uncommon depleted stable isotope concentrations in the vicinity of al ateibeh lake and adra valley could be interpreted as a result of sub flow recharge from the cenomanian turonian aquifer mostly prolonged along the damascus fault which forms direct contact between this complex and the quaternary alluvium aquifers the extensive exploitation of water from the cenomanian turonian aquifer for drinking water supply would shortly be reflected by a gradual decline of the groundwater table in the damascus ghotta basin amelioration of water quality in the damascus basin still requires further management strategies and efforts to be taken within the forthcoming years

tracing the decomposition of dissolved organic carbon in artificial groundwater recharge using carbon isotope ratios abstract reducing the concentration of dissolved organic c doc in water is one of the main challenges in the process of artificial groundwater recharge at the tuusula waterworks in southern finland surface water is artificially recharged into an esker by pond infiltration and an equal amount of groundwater is daily pumped from the aquifer this groundwater study was conducted to consider the role of redox processes in the decomposition of doc the isotopic composition of dissolved inorganic c 13 c dic in the recharged water was used as a tracer for redox reactions the isotopic composition of o and h in water was determined in order to calculate mixing ratios between the local groundwater and the infiltrated surface water three distinct processes in the reduction of the doc content were traced using isotopic methods and concentration analyses of dic and doc 1 the decomposition of doc 2 adsorption of doc on mineral matter and 3 the dilution of artificially recharged water by mixing with local groundwater the largest decrease 44 in the doc content occurred during the early stage of subsurface flow within 350 m of the infiltration ponds the reduction of doc was accompanied by an equal increase in dic and a significant drop in 13 c dic this change is attributed to the oxidative decomposition of doc a further 23 decrease in doc is attributed to adsorption and a final drop of 14 to dilution with local groundwater

laboratory investigations of compatibility of the kuwait group aquifer kuwait with possible injection waters a laboratory investigation of the compatibility of the kuwait group aquifer of kuwait with desalinated seawater and reverse osmosis processed treated wastewater was carried out in anticipation of the artificial recharge of the aquifer in future even with the use of wax coating and freezing with liquid nitrogen no core plugs could be extracted from the unconsolidated sections and only the consolidated to semi consolidated sections could be studied the aquifer consists of silty and gravelly sand and is often highly calcareous the clay minerals present in the aquifer mostly belong to the montmorillonite and illite groups with some palygorskite mercury injection porosimetry experiments on core plugs from the more cemented parts of the aquifer suggest that to avoid significant clogging from suspended solids particles down to a diameter of 8 m should be filtered out of the injection water core flow experiments suggest that for the samples examined loss of permeability due to clay swelling is not very important the blocking of pore throats by moving fines may be a more serious problem during injection the geochemical simulation indicates that the possibility of scale formation when the injection waters come in contact with the kuwait group formation water is remote rather there is a possibility of dissolution of carbonate minerals in the aquifer in contact with the injection waters

heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike slip faults 1 we combine a viscoelastic model for the interseismic process and an elastodynamic model for the coseismic process to explore the dynamics over multiple earthquake cycles of two parallel strike slip faults embedded in a two dimensional full space the step over fault geometry results in a buildup of heterogeneous fault stress near the step over this heterogeneous stress accumulates at the early stage of the evolution of the fault system and finally stabilizes after a number of earthquake cycles the heterogeneity in fault stress varies with the geometrical parameters e g width and along strike overlap gap of the step over as well as the rupture history of the fault system this heterogeneous fault stress from previous earthquakes has significant effects on earthquake rupture initiation propagation and termination the locations with a low normal stress level near a step over are favorable points for earthquake initiation rupture can jump a 4 km wide compressional step over and a 8 km or wider dilational step over if the fault system has historically experienced many earthquakes a young step over with less induced heterogeneity allows rupture to jump only smaller step over widths these results may have important implications for seismic hazard analysis in areas where segmented strikeslip faults predominate particularly for estimating maximum earthquake potential citation duan b and d d oglesby 2006 heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike slip faults j geophys res 111 b05309 doi 10 1029 2005jb004138

stable isotopes as an indicator of evaporation in the river murray australia the stable isotope composition of water d and 18o and chloride concentrations were measured monthly at 26 stations along the river murray australia and several major tributaries from december 1988 to june 1989 the first four months had low natural runoff plus large irrigation diversions from storage reservoirs the following three months had much higher up to a factor of 5 river discharge deuterium and oxygen 18 compositions had a maximum range of 50 and 9 respectively from headwaters to mouth chloride concentrations increased downstream with a maximum range from 1 to 180 10 3 kg m 3 these trends can be attributed to 1 evaporation from storage facilities and river channels 2 inflows of irrigation drainage water enriched in heavy isotopes and 3 inflows of saline groundwater water losses by evaporation from the river surface and irrigation areas amounted to about 40 15 of releases from reservoir storage based on the integrated enrichment of deuterium which is comparable to the total transpiration flux within the basin about half of the chloride acquired by the murray as it traversed the middle third of the basin during summer months appears to have resulted from return flows of irrigation drainage water

induced seismicity associated with fluid injection into a deep well in youngstown ohio 1 over 109 small earthquakes mw 0 4 3 9 were detected during january 2011 to february 2012 in the youngstown ohio area where there were no known earthquakes in the past these shocks were close to a deep fluid injection well the 14 month seismicity included six felt earthquakes and culminated with a mw 3 9 shock on 31 december 2011 among the 109 shocks 12 events greater than mw 1 8 were detected by regional network and accurately relocated whereas 97 small earthquakes 0 4 mw 1 8 were detected by the waveform correlation detector accurately located earthquakes were along a subsurface fault trending ene wsw consistent with the focal mechanism of the main shock and occurred at depths 3 5 4 0 km in the precambrian basement we conclude that the recent earthquakes in youngstown ohio were induced by the fluid injection at a deep injection well due to increased pore pressure along the preexisting subsurface faults located close to the wellbore we found that the seismicity initiated at the eastern end of the subsurface fault close to the injection point and migrated toward the west away from the wellbore indicating that the expanding high fluid pressure front increased the pore pressure along its path and progressively triggered the earthquakes we observe that several periods of quiescence of seismicity follow the minima in injection volumes and pressure which may indicate that the earthquakes were directly caused by the pressure buildup and stopped when pressure dropped

environmental isotope study of the major karst springs in damascus limestone aquifer systems case of the figeh and barada springs abstract the groundwaters of major karst springs and several piezometers and wells in the damascus limestone aquifer systems syria have been investigated using chemical and environmental isotope techniques the groundwater bodies of major karst springs mainly originate from direct infiltration of atmospheric water the groundwaters emerging from the figeh main spring have lower stable isotope concentrations than those emerging from the barada spring stable isotopes show that the elevation of the recharge zones of the figeh main spring 1750 m above sea level is higher than those for the figeh side spring 1500 m and the harouch spring 1300 m the groundwater in the barada spring seems to be recharged in a catchment area with a mean elevation of about 1250 m the temporal evolution of stable isotope concentrations tritium content and hydrochemistry show the existence of an interconnection between the aquifers of the figeh main spring and the figeh side spring especially during flood periods the distinct independent isotopic composition of harouch spring from those of figeh main and side springs suggests no interconnection with the figeh aquifers adopting a model with exponential time distribution the mean turnover time residence time of groundwater in figeh main spring was evaluated to be 50 years on the basis of this evaluation a value of about 3 9 billion m 3 was obtained for the maximum groundwater reservoir size 1997 elsevier science b v

deep injection and closely monitored induced seismicity at paradox valley colorado the u s bureau of reclamation s paradox valley unit pvu extracts aquifer brine from nine shallow wells along the dolores river paradox valley in southwestern colorado and after treating high pressure injects the brine 4 3 4 8 km below the surface pvu injects at rates between 800 and 1300 l min since 1991 pvu has emplaced over 4 106 m3 of fluid and induced more than 4000 surface recorded seismic events the events are recorded on the local 15 station paradox valley seismic network the induced seismicity at paradox separates into two distinct source zones a principle zone 95 of the events asymmetrically surrounding the injection well to a maximum radial distance of 3 km and a secondary ellipsoidal zone 2 5 km long and centered 8 km northwest of the injection well the expansion of these zones has stabilized since mid 1999 about three years after the onset of continuous injection within the principal zone hypocenters align in distinct linear patterns showing at depth stratigraphy and the local wray mesa fracture and fault system the primary faults of the wray mesa system are aseismic striking subparallel to the inferred maximum principal stress direction with one or more faults probably acting as fluid conduits to the secondary seismic zone individual seismic events in both zones do not discernibly correlate with short term injection parameters however a 0 5 km2 region immediately northwest of the injection well responds to long term large scale changes in injection rate and the surpassing of a threshold injection pressure focal mechanisms of the induced events are consistent with simple double couple strike slip moments and subhorizontal extension to the northeast in addition the fault planes are consistent with principal stress directions determined from borehole breakouts more than 99 9 of the pvu seismicity is below human detection m 2 5 however approximately 15 events have been felt locally with the largest being a magnitude m 4 3 because of the m 4 3 and two earlier felt m 3 5 events and injection economics pvu changed injection strategies three times since 1996 these changes reduced seismicity from 1100 events year to as low as 60 events year

palaeovegetation and plate tectonics palaeophytogeography of north china during permian and triassic times abstract new evidence concerning the palaeovegetation of the upper permian and lower triassic shischienfeng group in north china reveals two distinctive floras a zechstein type vegetation in the lower part and a buntsandstein type flora in the middle and upper parts the traditional concept that north china is a component of the cathaysian floral province does not match with the newly confirmed palaeophytostratigraphical sequence from the early permian autunian saxonian flora passing via the zechstein and the buntsandstein vegetations to the late triassic keuper flora in north china corresponding to the sequence in western europe the sequence reveals that the former northern cathaysian province is thus to be considerably revised with north china now being assigned to the euramerican province rather than to the cathaysian province during late palaeozoic and early mesozoic times the eurasian arid province is suggested to comprise a specific scene of the euramerican province from the late permian to the early triassic the so called cathaysian floras in north china represent a mixed association of euramerican elements with some cathaysian components reflecting an origin when the south china plate drifted north ward and collided temporarily and repeatedly with the north china plate during the late palaeozoci time the evolution of south china and north china is briefly summarized in the light of the concept of continental drift

stress breakdown time and slip weakening distance inferred from slip velocity functions on earthquake faults we estimate the critical slip weakening distance on earthquake faults by using a new approach which is independent of the estimate of fracture energy or radiated seismic energy the approach is to find a physically based relation between the breakdown time of shear stress tb the time of peak slip velocity tpv and the slip weakening distance dc from the time histories of shear stress slip and slip velocity at each point on the fault which can be obtained from dynamic rupture calculations using a simple slip weakening friction law numerical calculations are carried out for a dynamic shear crack propagating either spontaneously or at a fixed rupture velocity on a vertical fault located in a 3d half space and a more realistic horizontally layered structure with finite difference schemes the results show that tpv is well correlated with tb for faults even with a heterogeneous stress drop dis tribution except at locations near strong barriers and the fault edges we also inves tigate this relation for different types of slip weakening behavior we have applied the method to two recent strike slip earthquakes in western japan the 2000 tottori and the 1995 kobe events we integrated the slip velocity functions on the vertical fault obtained from kinematic waveform inversion of strong motion and teleseismic records from the arrival time of rupture tr to the time of the peak slip velocity tpv and we then corrected the slip obtained at tpv for the errors expected from the dynamic calculations it was found that the slip weakening dis tance d c estimated in the frequency window between 0 05 and 0 5 hz ranges between 40 and 90 cm on the two earthquake faults however if we consider the limited frequency resolution of the observed waveforms probable time errors in the slip velocity functions obtained from kinematic inversion and the uncertainty of the slip weakening behavior the above estimates may be those located between the minimum resolvable limit and the upper bound of their real values the estimated dc values do not necessarily seem to indicate larger values in the shallower part and smaller values in the deeper part of the fault but rather a spatially heterogeneous distribution that appears to be dependent on the local maximum slip this possible dependence might be interpreted by the frictional properties of the fault such as the degree of roughness or the thickness of gouge layers in addition to stress heterogeneities

the dallas fort worth earthquake sequence october 2008 through may 2009 this paper describes a sequence of small earthquakes m b 3 3 that occurred at the dallas fort worth airport texas between 30 october 2008 and 31 may 2009 analysis of records at regional station wmok identified more than 180 earthquakes in the sequence about 90 percent occurred in four clusters on 30 october 1 november 20 november 26 december and 15 17 may after the sequence began a six station temporary local network obtained high quality three component records for 11 earthquakes occurring between 20 november and 1 december analysis of these data demonstrated that all 11 earthquakes originated from a focus near 32 855 n 97 051 w with an estimated depth 4 4 km this location is less than 0 5 km from a well completed in august 2008 that extends to a depth of 4 2 km drilled to dispose of brines collected during flowback of hydraulic fracturing fluids associated with the production of natural gas brine disposal commenced at the well on 12 september 2008 seismograms and s p intervals for the earthquakes are similar though not identical and relative locations indicate they occurred along a north northeast south southwest trend with horizontal and vertical dimensions of 1 1 km and 0 2 km respectively this trend is approximately coincident with that of a mapped normal fault in the subsurface and consistent with the maximum horizontal in situ stress direction because of the absence of previous historical earthquakes the proximity of the brine disposal well and the similarity with other documented cases of induced seismicity it seems likely that fluid injection induced the 2008 2009 sequence

isotope evolution and contribution to geochemical investigations in aquifer storage and recovery a case study using reclaimed water at bolivar south australia aquifer storage and recovery asr is an important resource management tool whereby water from an available source is stored in a suitable aquifer for later use in periods of higher demand important issues in asr includemaintaining the injection rate and recovering water of suitable quality both of these depend on subsurface biogeochemical processes this paper investigates the use of deuterium 1 8 o 1 3 c 1 4 c and 3 4 s in understanding the reactions induced by reclaimed water injection in a carbonate aquifer at bolivar south australia additionally the injection scheme provides a natural laboratory to observe the process of carbon isotope exchange the injectant deuterium 6 4 2 9 versus vienna standard mean ocean water v smow and 1 8 o 0 9 0 5 v smow signature is more enriched and variable than the native groundwater signature of 26 1 and 4 4 0 1 respectively the variability of the injectant signature is maintained with injectant migration and is useful in constraining the portion of the injected end member reaching observation wells effluent treatment results in total dissolved inorganic carbon tdic enriched in 1 3 c 3 3 2 5 versus pee dee belemnite and modern carbon 100 7 per cent modem carbon pmc which is distinct from the native groundwater comparatively depleted in 1 3 c 11 1 and 1 4 c 5 6 2 1 pmc the carbon isotopic signature in groundwater 4 m from the asr well is dominated by the injectant signature modified by some organic matter oxidation and calcite dissolution however with further migration to the 50 m radius both 1 3 c and 1 4 c signatures are dominated by isotopic exchange with the matrix surface initially in equilibrium with the ambient groundwater and little overall dissolution during storage biogeochemical processes including sulphate reduction and methanogenesis are dominant near the asr well these are indicated by a sulphate decline of up to 1 5 mmol l 1 with around 12 enrichment in the residual sulphate versus canyon diablo troilite and the addition of tdic enriched in 1 3 c while maintaining a modern 1 4 c activity

triassic environments climates and reptile evolution abstract a consideration of all the available data on triassic vertebrate faunas and their stratigraphic location reveals a relatively sudden extinction event among the last of the mammal like reptiles and the herbivorous rhynchosaurs in the norian of the upper triassic this event was apparently quickly followed by the radiation of the dinosaurs also in the norian this conclusion suggests that competition was not the main factor in the initial success of the dinosaurs but opportunistic radiation following the extinction of major reptile groups a global review of triassic sedimentary facies shows that there were climatic and floral changes towards the end of the triassic it is envisaged that increasing aridity in the later triassic resulting from plate motions and particularly affecting gondwanaland and southwestern laurasia brought about floral changes and then the reptile extinctions with the rapid evolution of new floras of conifers and bennettitaleans the dinosaurs came to dominate all terrestrial faunas within the space of only a few million years

injection induced seismicity poroelastic and earthquake nucleation effects the standard model of injection induced seismicity considers changes in coulomb strength due solely to changes in pore pressure we consider two additional effects full poroelastic coupling of stress and pore pressure and time dependent earthquake nucleation we model stress and pore pressure due to specified injection rate in a homogeneous poroelastic medium stress and pore pressure are used to compute seismicity rate through the dieterich 1994 model for constant injection rate the time to reach a critical seismicity rate scales with t r2 cfc where r is distance from the injector c is hydraulic diffusivity and fc is a factor that depends on mechanical properties and weakly on r the seismicity rate decays following a peak consistent with some observations during injection poroelastic coupling may increase or decrease the seismicity rate depending on the orientation of the faults relative to the injector if injection induced stresses inhibit slip abrupt shut in can lead to locally sharp increases in seismicity rate tapering the flux mitigates this effect the maximum magnitude event has been observed to occur postinjection we suggest the seismicity rate at a given magnitude depends on the nucleation rate the size distribution of fault segments and if the background shear stress is low the time varying volume of perturbed crust this leads to a rollover in frequency magnitude distribution for larger events with a corner that increases with time larger events are absent at short times but approach the background frequency with time larger events occurring post shut in are thus not unexpected

isotopes and geochemistry in a managed aquifer recharge scheme a case study of fresh water injection at the damascus university campus syria a combination of stable isotopes 18o and 2h and hydrochemistry has been applied to investigate storage processes in relation to aquifer storage and recovery asr of the shallow alluvial quaternary aquifer in damascus basin the stored water entirely taken from the figeh springs during flood periods was injected in a single well having a brackish groundwater water samples were collected from four observation wells drilled in the damascus university campus duc site during a 3 year period 2006 2008 the injectant water which deviates in its chemical and isotopic signatures from that of the ambient groundwater shows that the stored water plume remains within close proximity to the injection well iw 100 m thus only two wells w13 and w14 located at a distance less than 80 m from the injection point were affected by this injection the observation wells located at longer distances from the iw 145 m and 600 m for wells w15 and whz respectively were completely unaffected by the injection although most of the chemical and isotopic parameters usefully reflected the mixing process that occurs between the injectant water and ambient groundwater the stable isotope 18o and chloride cl were the most sensitive parameters that quickly reflect this signature using a simple mass balance the calculated proportion of injectant water reaching the well w13 was in the range of 50 90 this proportion was even lower 30 55 in the case of well w14 although the drought event prevailing during this study did not much help to inject further amounts of water higher than the injected volume 0 2416 m m3 and also not favourable to better evaluate the fate and subsurface hydrological processes these findings offer encouragement to continue the asr activities as an alternative way for better management of water resources in this basin facing intensive problems copyright 2010 john wiley sons ltd

preliminary phanerozoic polar wander paths for the north and south china blocks polar wander paths for the north and south china blocks suggest that 1 both were parts of gondwana in the palaeozoic 2 the north china block accreted to siberia in the late permian and 3 the south china block accreted to the north china block in the middle triassic to the early jurassic comparison of the polar wander path for the south china block with that for northern eurasia suggests that relative motion of over 4 000 km has occurred between them

helical burrow casts of therapsid origin from the beaufort group permian of south africa abstract large helical burrow casts of vertebrate origin have been discovered at several localities in the lowermost strata of the teekloof formation of the beaufort group permian in the southwestern karoo basin south africa they are not only the oldest but also the first vertebrate burrows of helical geometry to be found in rocks of pre mammalian age the burrow casts are vertically disposed spiralling tubes filled with fine grained sandstone or siltstone often with a calcareous cement tube diameters gradually increase from 60 mm in the upper entrance decline through two non contacting dextral coils to about 160 mm at the base of the spiral whereupon the tube straightens and widens into a horizontal terminal chamber burrow depths range from 0 5 0 75 m and the ramp angle ranges from 10 to 32 although within any single spiral it is constant articulated skeletons of the small dicynodont diictodon have been found within the terminal chambers and spirals of three sand filled burrows linear ridges preserved on the outer walls and floor of some of the terminal chambers resemble scratch marks possibly made by the claws and beak of diictodon during burrow excavation the sedimentary sequences at two separate localities are interpreted as having been deposited by episodic sheet floods and distributary splay fans in the proximal floodbasin areas flanking an aggrading meanderbelt rise comparison is drawn between helical burrow casts in the lower beaufort and other recorded occurrences in particular daimonelix a beaver burrow from the miocene of nebraska fundamental similarities far outweigh differences to the extent that the beaufort helical burrows may be grouped with the daimonelices it is concluded that the excavation of large helical burrows an activity usually attributed to rodents was pre empted by mammal like reptiles some 50 million years before the first anatomical mammals evolved

elastodynamic analysis for slow tectonic loading with spontaneous rupture episodes on faults with rate and state dependent friction we present an efficient and rigorous numerical procedure for calculating the elastodynamic response of a fault subjected to slow tectonic loading processes of long duration within which there are episodes of rapid earthquake failure this is done for a general class of rate and state dependent friction laws with positive direct velocity effect the algorithm allows us to treat accurately within a single computational procedure loading intervals of thousands of years and to calculate for each earthquake episode initially aseismic accelerating slip prior to dynamic rupture the rupture propagation itself rapid post seismic deformation which follows and also ongoing creep slippage throughout the loading period in velocity strengthening fault regions the methodology is presented using the two dimensional 2 d antiplane spectral formulation and can be readily extended to the 2 d in plane and 3 d spectral formulations and with certain modifications to the space time boundary integral formulations as well as to their discretized development using finite difference or finite element methods the methodology can be used to address a number of important issues such as fault operation under low overall stress interaction of dynamic rupture propagation with pore pressure development patterns of rupture propagation in events nucleated naturally as a part of a sequence the earthquake nucleation process earthquake sequences on faults with heterogeneous frictional properties and or normal stress and others the procedure is illustrated for a 2 d crustal strike slip fault model with depth variable properties for lower values of the state evolution distance of the friction law small events appear the nucleation phases of the small and large events are very similar suggesting that the size of an event is determined by the conditions on the fault segments the event is propagating into rather than by the nucleation process itself we demonstrate the importance of incorporating slow tectonic loading with elastodynamics by evaluating two simplified approaches one with the slow tectonic loading but no wave effects and the other with all dynamic effects included but much higher loading rate

stress and aftershock constrained joint inversions for coseismic and postseismic slip applied to the 2004 m6 0 parkfield earthquake 1 both aftershocks and geodetically measured postseismic displacements are important markers of the stress relaxation process following large earthquakes postseismic displacements can be related to creep like relaxation in the vicinity of the coseismic rupture by means of inversion methods however the results of slip inversions are typically non unique and subject to large uncertainties therefore we explore the possibility to improve inversions by mechanical constraints in particular we take into account the physical understanding that postseismic deformation is stress driven and occurs in the coseismically stressed zone we do joint inversions for coseismic and postseismic slip in a bayesian framework in the case of the 2004 m6 0 parkfield earthquake we perform a number of inversions with different constraints and calculate their statistical significance according to information criteria the best result is preferably related to a physically reasonable model constrained by the stress condition namely postseismic creep is driven by coseismic stress and the condition that coseismic slip and large aftershocks are disjunct this model explains 97 of the coseismic displacements and 91 of the postseismic displacements during day 1 5 following the parkfield event respectively it indicates that the major postseismic deformation can be generally explained by a stress relaxation process for the parkfield case this result also indicates that the data to constrain the coseismic slip model could be enriched postseismically for the 2004 parkfield event we additionally observe asymmetric relaxation process at the two sides of the fault which can be explained by material contrast ratio across the fault of 1 15 in seismic velocity

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

three dimensional boundary integral modeling of spontaneous earthquake sequences and aseismic slip 1 fault processes involve complex patterns of seismic events and aseismic slip this work develops a three dimensional 3 d methodology for simulating long term history of spontaneous seismic and aseismic slip on a vertical planar strike slip fault subjected to slow tectonic loading our approach reproduces all stages of earthquake cycles from accelerating slip before dynamic instability to rapid dynamic propagation of earthquake rupture to postseismic slip and to interseismic creep including aseismic transients we use the developed 3 d methodology to study interaction of fault slip with a small patch of higher normal stress over long term slip history for uniform initial prestress dynamic rupture is significantly affected by the stronger patch in the first simulated event but not in subsequent ones the change in behavior is due to redistribution of shear stress by prior slip which demonstrates that distributions of fault strength and stress are related and illustrates the importance of simulating long slip histories even in studies of dynamic rupture despite no long term effect on dynamic rupture the small patch of higher normal stress influences nucleation processes and hence long term slip patterns in the model comparison of the fully dynamic simulations and a widely used quasi dynamic approach shows that the quasi dynamic approach modifies long term slip patterns in addition to resulting in much smaller slip velocities and rupture speeds during dynamic events we show that the response of quasi dynamic formulations with reduced radiation damping terms can be scaled to match the results of the standard quasi dynamic formulation and hence cannot improve the comparison