inverse kinematic and forward dynamic models of the 2002 denali fault earthquake alaska we perform inverse kinematic and forward dynamic models of the m 7 9 2002 denali fault alaska earthquake to shed light on the rupture process and dynamics of this event which took place on a geometrically complex fault system in central alaska we use a combination of local seismic and global positioning system gps data for our kinematic inversion and find that the slip distribution of this event is characterized by three major asperities on the denali fault the rupture nucleated on the susitna glacier thrust fault and after a pause propagated onto the strike slip denali fault approximately 216 km to the east the rupture abandoned the denali fault in favor of the more southwesterly directed totschunda fault three dimensional dynamic models of this event indicate that the abandonment of the denali fault for the totschunda fault can be explained by the totschunda fault s more favorable orientation with respect to the local stress field however a uniform tectonic stress field cannot explain the complex slip pattern in this event we also find that our dynamic models predict discontinuous rupture from the denali to totschunda fault segments such discontinuous rupture helps to qualitatively improve our kinematic inverse models two principal implications of our study are 1 a combination of inverse and forward modeling can bring insight into earthquake processes that are not possible with either technique alone and 2 the stress field on geometrically complex fault systems is most likely not due to a uniform tectonic stress field that is resolved onto fault segments of different orientations rather other forms of stress heterogeneity must be invoked to explain the observed slip patterns

effects of prestress state and rupture velocity on dynamic fault branching 1 we consider a mode ii rupture which propagates along a planar main fault and encounters an intersection with a branching fault using an elastodynamic boundary integral equation formulation allowing the failure path to be dynamically self chosen we study the following questions does the rupture initiate along the branch does it continue is the extensional or compressional side most favored for branching does rupture continue on the main fault too failure is described by a slip weakening law for which the strength at any amount of slip is proportional to normal stress our results show that dynamic stresses around the rupture tip which increase with rupture velocity at locations off the main fault plane relative to those on it could initiate rupture on a branching fault as suggested by prior work whether branched rupture can be continued to a larger scale depends on principal stress directions in the prestress state and on rupture velocity the most favored side for branching rupture switches from the extensional to the compressional side as we consider progressively shallower angles of the direction of maximum compressive prestress with the main fault simultaneous rupturing on both faults can be activated when the branching angle is wide but is usually difficult for a narrow branching angle due to strong stress interactions between faults however it can be also be activated by enhanced dynamic stressing when the rupture velocity is very near the rayleigh velocity natural examples seem consistent with the simulations that we present

the 1999 hector mine earthquake the dynamics of a branched fault system the 1999 m 7 1 hector mine earthquake ruptured a complex fault system with a branched structure in the north this fault geometry and slip pattern presents a puzzle because the northwest branch of this system should be in the stress shadow of the north branch upon which nucleation likely took place through 3d dynamic models of this event we show that the ability of rupture to propagate to the northwest branch most likely depends on the fact that rupture did not proceed to the surface on the north branch this slip pattern leads to part of the northwest branch being brought above its failure stress and to subsequent rupture propagation and slip occurring on that branch a similar effect can be seen in the case in which rupture is constrained not to propagate to the base of the north branch models with slip over the entire north branch do not produce rupture propagation and slip on the northwest branch the results are robust with respect to details of the prestress pattern and hypocenter location large heterogeneity over small length scales in the final stress pattern is a natural product of the models even when the initial stress field is quite homogeneous we also find that the interaction between fault geometry and stress pattern helps to explain other observations in this event including slow rupture propagation on the northwest branch the results help to show that 3d dynamic effects may be crucial in determining rupture propagation and slip behavior on geometrically complex fault systems although these effects may be hard to predict without detailed knowledge of the stress pattern and fault geometry prior to earthquakes manuscript received 31 january 2003

role of initial stress rotations in rupture dynamics and ground motion a case study with implications for the wenchuan earthquake 1 motivated by observations in the 2008 mw 7 9 wenchuan earthquake we study effects of systematic changes in the principal stress orientation along the fault strike on rupture dynamics and ground motion using a 3 d finite element method based on anderson s theory of faulting we set up the initial stress field with rotations in stress orientations along strike for a dynamic rupture model of a shallow dipping fault we find that initial stress rotations along strike can cause dramatic changes in rupture speed and produce distinct patterns in slip distribution and peak ground motion when a mismatch unfavorable for faulting between fault geometry and initial stress orientations is encountered rupture can spontaneously stop some first order features in the wenchuan event may be partially caused by rotations in the principal stress orientation along strike such as the rupture arrest at the northeast end and two severe destruction zones in the observed seismic intensity distribution these results may have important implications for assessing seismic hazards imposed by faults with changes in the initial stress field along strike worldwide

the 1999 mw 7 1 hector mine california earthquake sequence complex conjugate strike slip faulting the 1999 m w 7 1 hector mine mainshock showed right lateral strike slip faulting with an initial strike of n6 w and vertical dip the mainshock was preceded within 20 hours by 18 recorded foreshocks of 1 5 m 3 8 within a few kilometers distance of the mainshock hypocenter the aftershocks delineate how the hector mine earthquake ruptured with strike n6 w to the south for a distance of 15 km and possibly to the north for a distance of several kilometers the two largest aftershocks of m 5 9 and m 5 7 occurred near the north and south ends of the first mainshock rupture segment the second segment of rupture starting 15 km to the south away from the mainshock hypocenter delineated by strike slip and thrust faulting aftershocks extends 10 km farther away with a strike of s140 e along the bullion fault the aftershocks also outline an unusual third rupture segment extending from about 5 km south of the hypocenter with a strike of n30 w to n35 w for a distance of 20 km approximately 10 to 25 km farther to the north and west of the mainshock epicenter several clusters form a complex aftershock distribution three dimensional vp and vp vs models of the region exhibit only small regional changes as is typical for the mojave region nonetheless the mainshock rupture started within a region of rapidly varying vp and at least three regions of low vp vs are imaged within the aftershock zone the rate of decay for the hector mine earthquake sequence has been slightly above the mean for both p values and b values in southern california the focal mechanisms of the aftershocks and the state of stress are consistent with strike slip faulting including a component of normal faulting most prominent to the north the orientation of the regional maximum horizontal stress the variation in orientation of the mainshock fault segments by 30 and scattered distribution of aftershocks suggest that the mainshock and aftershock deformation field exhibit volumetric shear deformation accommodated by complex conjugate sets of strike slip faults

relationship of the kickapoo fault to the johnson valley and homestead valley faults san bernardino county california the 1992 mw 7 3 landers earthquake rupture propagated from the johnson valley fault to the homestead valley fault across homestead valley rupture was concentrated along the kickapoo fault a k a landers fault a previously unrecognized north south striking 5 km long fault in homestead valley and along small secondary fault traces east of the kickapoo fault to better understand the role of the kickapoo fault in accommodating slip between the johnson valley fault and the homestead valley fault we performed detailed aerial photograph interpretation and field mapping of alluvial deposits geomorphology and co seismic surface rupture evaluated existing water well data and conducted a gravity survey of the homestead valley area these data show that the kickapoo fault is a pre 1992 structure best interpreted as the northward continuation of the southern johnson valley fault the kickapoo fault merges northward with the northwest striking homestead valley fault thus we interpret that the johnson valley kickapoo and homestead valley faults form an interlinked system large ruptures similar to the 1992 landers rupture may have repeatedly propagated between the johnson valley and homestead valley faults along the kickapoo fault the kickapoo johnson valley fault intersection defines a 1 km wide left restraining bend uplifted alluvial deposits and pressure ridges are common within the bend indicating the bend is a long lived contractional feature homestead valley itself is underlain by relatively thin alluvial deposits over crystalline bedrock showing that no significant subsidence has occurred during the late quaternary these observations are consistent with the accommodation of north south right shear on the southern johnson valley and kickapoo faults in homestead valley

inelastic response of compliant fault zones to nearby earthquakes 1 using dynamic rupture models we examine the response of compliant fault zones that surround pre existing faults to nearby earthquakes we find that some portions of a compliant fault zone can experience inelastic deformation due to dynamic stress perturbations while the remaining portions deform elastically inelastic response of the fault zone results in sympathetic fault parallel motion i e consistent with long term geologic slip across the fault while elastic response causes retrograde motion i e opposite to long term geologic slip in the static displacement field inelastic deformation signals along fault zones detected geodetically may be used to constrain the stress state in the crust because inelastic response occurs only when the prestress level is close to material strength which can be measured in the laboratory

the 2002 denali fault earthquake alaska a large magnitude slip partitioned event the mw moment magnitude 7 9 denali fault earthquake on 3 november 2002 was associated with 340 kilometers of surface rupture and was the largest strike slip earthquake in north america in almost 150 years it illuminates earthquake mechanics and hazards of large strike slip faults it began with thrusting on the previously unrecognized susitna glacier fault continued with right slip on the denali fault then took a right step and continued with right slip on the totschunda fault there is good correlation between geologically observed and geophysically inferred moment release the earthquake produced unusually strong distal effects in the rupture propagation direction including triggered seismicity

the effects of double fault bends on rupture propagation a geometrical parameter study we use the 2d finite element method to determine how geometrical parameters determine whether rupture will propagate across a linked stepover in a strike slip fault the end segments of the fault system are aligned in the direction of maximum shear and the length and angle of the linking segment are allowed to vary we observe that ruptures propagate through extensional stepovers with steeper angles and longer linking segments than otherwise equivalent compressional step overs these different rupture behaviors form distinct regions in angle stepover length parameter space the boundary between these regions takes the shape of an asymptotic curve in both the extensional and compressional cases models in which the size of the entire fault system was made larger or smaller revealed that the location of the bound aries between regions of different rupture behavior do not scale linearly with the system size it was easier to rupture steeper and relatively longer stepovers in fault systems that were larger overall a separate set of models in which the stress field is rotated so that the parallel end segments were optimally aligned for rupture significantly altered the rupture behavior curves in this stress field it was easier to rupture compressional stepovers with steeper angles and longer linking segments than it was to rupture equivalent extensional stepovers in both the case in which the end segments are aligned with the direction of maximum shear and the case in which the end segments are optimally oriented for rupture the angles at which rupture could no longer propagate through the entire fault corresponded with peaks in the fault s s value

dynamic slip transfer from the denali to totschunda faults alaska testing theory for fault branching we analyze the observed dynamic slip transfer from the denali to totschunda faults during the mw 7 9 3 november 2002 denali fault earthquake alaska this study adopts the theory and methodology of poliakov et al 2002 and kame et al 2003 in which it was shown that the propensity of the rupture path to follow a fault branch is determined by the preexisting stress state branch angle and incoming rupture velocity at the branch location here we check that theory on the denalitotschunda rupture process using 2d numerical simulations of processes in the vicinity of the branch junction the maximum compression direction with respect to the strike of the denali fault near the junction has been estimated to range from approximately 73 to 80 we use the values of 70 and 80 in our numerical simulations the rupture velocity at branching is not well constrained but has been estimated to average about 0 8 cs throughout the event we use 0 6 cs 0 8 cs 0 9 cs and even 1 4 cs as parameters in our simulations we simulate slip transfer by a 2d elastodynamic boundary integral equation model of mode ii slip weakening rupture with self chosen path along the branched fault system all our simulations except for 70 and 0 9 cs predict that the rupture path branches off along the totschunda fault without continuation along the denali fault in that exceptional case there is also continuation of rupture along the denali fault at a speed slower than that along the totschunda fault and with smaller slip

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

why the 2002 denali fault rupture propagated onto the totschunda fault implications for fault branching and seismic hazards 1 the propagation of the rupture of the mw7 9 denali fault earthquake from the central denali fault onto the totschunda fault has provided a basis for dynamic models of fault branching in which the angle of the regional or local prestress relative to the orientation of the main fault and branch plays a principal role in determining which fault branch is taken geoearthscope lidar and paleoseismic data allow us to map the structure of the denali totschunda fault intersection and evaluate controls of fault branching from a geological perspective lidar data reveal the denali totschunda fault intersection is structurally simple with the two faults directly connected at the branch point 227 2 km east of the 2002 epicenter the 2002 rupture diverges southeast to become the totschunda fault we use paleoseismic data to propose that differences in the accumulated strain on each fault segment which express differences in the elapsed time since the most recent event was one important control of the branching direction we suggest that data on event history slip rate paleo offsets fault geometry and structure and connectivity especially on high slip rate short recurrence interval faults can be used to assess the likelihood of branching and its direction analysis of the denali totschunda fault intersection has implications for evaluating the potential for a rupture to propagate across other types of fault intersections and for characterizing sources of future large earthquakes

three dimensional nonplanar simulation of the 1992 landers earthquake 1 we have simulated the rupture process of the 1992 landers california earthquake using a realistic nonplanar fault geometry including fault bends and branches through a three dimensional boundary integral equation method considering an external loading system due to local tectonics as well as a nonplanar fault structure we could reproduce the characteristic features of this earthquake such as spontaneous rupture transfer between faults pattern of slip distribution and propagation of rupture front without assuming any laterally heterogeneous distribution of parameters we could also reproduce seismic waveforms near the faults especially in the forward direction of rupture propagation where rupture directivity controlled by rupture transfer between faults significantly affects ground motion

thermochronology of isotopically zoned micas insights from the southwestern usa proterozoic orogen abstract we have used three different 40 ar 39 ar laser microprobe methods to explore the distribution of radiogenic 40 ar in 1 0 1 5 mm biotite crystals from the ca 1680 ma horse mountain monzogranite of central arizona incremental heating of two single crystals with a defocused laser beam produced flat age spectra with near plateau ages of 1190 ma showing no indication of intracrystalline 40 ar inhomogeneity in contrast total fusion of twenty five biotite fragments 100 pm yielded apparent ages ranging from 1006 7 to 1212 0 ma detailed age mapping in the 001 plane of two crystals with the laser focused to a minimum spot size confirms that the age dispersion in the fragment data reflects the existence of 200 m y age gradients in single crystals the two mapped crystals display very different age distribution patterns that suggest radiogenic 40 ar loss through two mechanisms volume diffusion on a scale comparable to that of the grain radius and more rapid diffusion along discrete zones of high crystal defect density simple inverse modeling of the overall age dispersion in the two mapped crystals and the fragment population is consistent with the development of the observed age gradients by slow cooling at an average rate of 0 5 k m y the horse mountain results as well as previously published studies indicate that conventional incremental heating of hydrous phases can homogenize intracrystalline gradients in 40 ar thereby masking important details of the thermal history of analyzed samples in contrast detailed isotopic mapping studies offer a wealth of information and will become more powerful with continued improvement in the spatial resolution of 40 ar 39 ar laser microprobes total fusion studies of crystal fragment populations can be readily automated making them less labor intensive than mapping studies our preliminary experiment on a limited horse mountain fragment population suggests that this procedure has great potential as a reconnaissance tool for thermal history research

rare earth elements ree and yttrium in stream waters stream sediments and fe mn oxyhydroxides fractionation speciation and controls over ree y patterns in the surface environment we have collected 500 stream waters and associated bed load sediments over an 400 km 2 region of eastern canada and analyzed these samples for fe mn and the rare earth elements ree y in addition to analyzing the stream sediments by total digestion multi acid dissolution with metaborate fusion we also leached the sediments with 0 25 m hydroxylamine hydrochloride in 0 05 m hcl to determine the ree y associated with amorphous fe and mn oxyhydroxide phases we are thus able to partition the ree into dissolved 0 45 lm labile hydroxylamine and detrital sediment fractions to investigate ree fractionation and in particular with respect to the development of ce and eu anomalies in oxygenated surface environments surface waters are typically lree depleted la sm nasc ranges from 0 16 to 5 84 average 0 604 n 410 where the ree are normalized to the north america shale composite have strongly negative ce anomalies ce ce nasc ranges from 0 02 to 1 25 average 0 277 n 354 and commonly have positive eu anomalies eu eu nasc ranges from 0 295 to 1 77 average 0 764 n 84 in contrast the total sediment have flatter ree y patterns relative to nasc la sm nasc ranges from 0 352 to 1 12 average 0 778 n 451 and are slightly middle ree enriched gd yb nasc ranges from 0 55 to 3 75 average 1 42 most total sediments have negative ce and eu anomalies ce ce nasc ranges from 0 097 to 2 12 average 0 799 and eu eu nasc ranges from 0 39 to 1 43 average 0 802 the partial extraction sediments are commonly less lree depleted than the total sediments la sm nasc ranges from 0 24 to 3 31 average 0 901 n 4537 more mree enriched gd yb nasc ranges from 0 765 to 6 28 average 1 97 and ce and eu anomalies negative and positive are more pronounced the partial extraction recovered on average 20 of the fe in the total sediment 80 of the mn and 21 29 of the rees ce 19 and y 32 comparison between rees in water partial extraction and total sediment analyses indicates that rees y in the stream sediments have two primary sources the host lithologies i e mechanical dispersion and hydromorphically transported the labile fraction furthermore eu appears to be more mobile than the other ree whereas ce is preferentially removed from solution and accumulates in the stream sediments in a less labile form than the other rees y despite poor statistical correlations between the rees y and mn in either the total sediment or partial extractions based on apparent distribution coefficients and the ph of the stream waters we suggest that either sediment organic matter and or possibly d mno2 feooh are likely the predominant sinks for ce and to a lesser extent the other ree in the stream sediments

rare earth elements as geochemical tracers of regional groundwater mixing abstract the rare earth elements ree were analyzed in a groundwater system from south central nevada i e ash meadows national wildlife refuge the spring mountains pahranagat national wildlife refuge and the nevada test site in order to investigate their potential use as tracers of regional groundwater flow previous investigations using conservative tracers e g deuterium and uranium isotopes identified recharge in local mountains as the primary source 60 70 of total discharge for the springs in the regional discharge zone i e ash meadows with the remaining contribution being interbasin flow from the northeast initial mixing calculations for these groundwaters using shale normalized ree patterns agreed well with the previous studies however because the rees are not expected to behave conservatively in natural waters the effect of both solution complexation which acts to enhance the stability of the rees in solution as well as surface complexation responsible for the particle reactive behavior of the rees were examined in subsequent mixing calculations in order to assess the roles of solution and surface complexation relative partitioning coefficients were estimated for each ree in each groundwater by evaluating the ratio of the ionic strength corrected co 3 1 ree co 3 2 ree and co 3 2 f to the first hydrolysis binding constants for the rees the relative partitioning coefficients were then used to calculate ree patterns expected to develop and persist in solution as a consequence of solution and surface complexation the calculated ree values closely resembled the actual measured ree concentrations suggesting that the rees are in fact controlled by solution and surface complexation in these groundwaters the calculated ree concentrations were subsequently used to determine mixing ratios the results of which coincided with the initial calculations as well as the previous studies the results of this study suggest that solution complexation of the rees is sufficient to overcome to a certain degree the affinity of the rees to be adsorbed onto surface sites in the aquifers such that distinctive ree signatures develop and persist in solution in groundwaters from different aquifers the ability of solution complexation to overcome surface complexation is likely related to the formation of the negatively charged dicarbonato complex i e ln co 3 2 where ln is any ree which accounts for significant fractions of each ree in these groundwaters

the equivalent strength of geometrical barriers to earthquakes we present a quantitative framework for evaluating the influence of non planar fault geometry on repeated seismic ruptures we model quasistatic ruptures on a non planar fault trace imbedded in a two dimensional elastic medium under in plane strain because of the presence of fault segments that are not parallel to the regional shear stress i e bends the apparent strength at a given point on the fault is not fixed but fluctuates with normal stress compressional features behave as increasingly strong barriers to fracture unless the stored normal stress is released in order to unlock the fault since slip on the fault itself cannot get rid of the normal stress this is achieved through the action of off fault morphological features such as secondary faulting folding and vertical motions that we introduce parametrically in the form of an aseismic relaxation the apparent strength of a fault bend will stabilize in a narrow interval of values after repeated ruptures characterized by a non dimensional hardness parameter whereby the relaxation rate is scaled by the tectonic loading rate on a fault structure having several small widely separated bends three families of events can be identified whose frequency and magnitude depend on the hardness relaxation parameter and the geometry small events that cluster in the tension zones of the bends intermediate size ruptures involving a single interbend segment and large ruptures that break through bends and link on or more interbend segments large multi segment events are most likely to occur for low values of the hardness i e fast relaxation and slow loading rate regions with compressional features act as barriers that stop most ruptures stress is stored at these sites until they themselves break and initiate motion on the smoother long reaches of the fault

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

mineralogy and geochemistry of trace metals and ree in volcanic massive sulfide host rocks stream sediments stream waters and acid mine drainage from the lousal mine area iberian pyrite belt portugal abstract acid mine drainage represents a major source of water pollution in the lousal area the concentrations of trace metals and the rare earth elements ree in the host rocks stream sediment surface waters and acid mine drainage amd associated with abandoned mine adits and tailings impoundments were determined in order to fingerprint their sources and to understand their mobility and water rock interaction the results show that the fe so4 rich acid waters vary substantially in composition both spatially and seasonally these waters include very low ph mostly in the range 1 9 3 0 extreme so4 concentrations 4635 20 070 mg l 1 so 4 2 high metal contents fe al cu zn and mn and very high ree contents the trace metal concentrations decrease downstream from the discharge points either due to precipitation of neoformed phases or to dilution the north american shale composite nasc normalized patterns corresponding to sediment from one stream corona stream show a flat tendency or are slightly enriched in light ree lree the nasc normalized patterns corresponding to acidic mine waters show enrichment in the middle ree mree with respect to the lree and heavy ree hree moreover the ree concentrations in acidic mine waters are 2 or 3 orders of magnitude higher than those of the surface waters changes of ree concentrations and variation of eu anomaly show two spatially distinct patterns a pond and spring waters with higher ree concentrations ranging from 375 to 2870 g l 1 that records conspicuous negative eu anomaly and b seeps from tailings impoundments corresponding to lower ree concentrations than the first pattern ranging from 350 to 1139 g l 1 with typically negative eu anomaly the stream water samples collected from the impacted stream during the spring show a low ph 2 8 3 1 and contain high concentrations of fe and trace elements up to 61 mg l 1 also temporal variations of the ree concentrations were observed in the corona waters the results obtained show that the ree concentrations increase during the winter spring transition stream waters draining the lousal mine area show high ree concentrations reaching a maximum value of about 2846 g l 1 spring the mree concentrations are usually enriched with respect to both the lree and hree a decrease in ree concentrations and a ph increase from 3 to 6 was observed downstream of the confluence of a tributary stream the geochemistry of the waters strongly influenced the mineralogy and geochemistry of efflorescent sulfates precipitated on the banks of the streams polluted by amd the mineralogy is dominated by hexahydrite rozenite szomolnokite alunite gypsum halotrychite coquimbite copiapite and schwertmannite the ree concentrations determined in the efflorescent sulfates suggest a selective partitioning of the hree onto mg al oxyhydroxides

hydrogeochemistry and rare earth element behavior in a volcanically acidified watershed in patagonia argentina abstract the rio agrio watershed in northern patagonia argentina is naturally acidic due to discharges of volcanic h 2 so 4 hcl and hf at its headwaters near the summit of copahue volcano a suite of water samples was collected from the summit of the volcano to a point roughly 40 km downstream where the ph of the rio agrio rose above 6 0 this suite included a sample of the hyperacidic ph the concentrations of ree in the rio agrio decreased by several orders of magnitude through the study area as a result of dilution and chemical attenuation a subtle shift in the slope of shale normalized profiles of dissolved ree concentration was observed from being weakly positive near the source of the rio agrio to showing a weak middle ree enrichment trend in lake caviahue to being weakly negative in the lower reaches of the river the trend to a negative slope across the lanthanide series in the lower river is explained by selective partitioning of the heavier ree to hydrous oxides of fe and al suspended in the water column and accumulating on the riverbed most of the decrease in ree load occurred immediately downstream of the confluence with a tributary that increased the ph of the rio agrio from 4 3 to 6 1 although the mixed water was supersaturated with ree phosphate compounds precipitation of lnpo 4 is not believed to have been a dominant process because the predicted pattern of inter element fractionation from phosphate deposition is inconsistent with the observed trends instead ree attenuation most likely occurred from adsorption onto freshly precipitated hydrous aluminum oxide the behavior of ree in the rio agrio watershed is broadly similar to what has been observed in watersheds that owe their acidity to oxidation of sulfide minerals

the 1999 izmit turkey earthquake nonplanar fault structure dynamic rupture process and strong ground motion we simulated dynamic rupture propagation along various nonplanar fault models of the 1999 izmit turkey earthquake using a boundary integral equation method these models were inferred from geological and geodetic observations based on these results we modeled seismic wave propagation around the fault system using a finite difference method we focused on the effect of different fault geometries on the rupture process and seismic wave propagation numerical simulation results imply a rapid and continuous rupture propagation from the izmit sapanca lake segment to the sapanca akyazi segment the rupture under sapanca lake appears to have propagated not on a disconnected fault segment but along a smooth fault structure with a bend of only a few degrees the observational complexity of the surface breaks however can be best simulated by a highly segmented fault model this infers that fault geometric characters observed in the field reflect near surface structure and that seismological and geodetic features are controlled by global fault structure at depth then we investigated the effect of frictional parameters and the initial stress field in order to explain near field seismograms at station skr located a distance of a few kilometers from the fault we had to force the rupture to propagate at shallow depth close to the station in order to obtain this we had to introduce a finite cohesive force in the friction law that allows stress accumulation and release in the shallow crust the external stress field had to be large enough for the rupture to propagate at very rapid speed our simulation results show that it is important to include detailed fault geometry in the numerical simulation and to constrain frictional parameters and the initial stress field for understanding of the full dynamic process of an earthquake

binding and transport of rare earth elements by organic and iron rich nanocolloids in alaskan rivers as revealed by field flow fractionation and icp ms abstract water samples were collected from six small rivers in the yukon river basin in central alaska to examine the role of nanocolloids 0 5 40 nm in the dynamics and transport of rare earth elements rees in northern high latitude watersheds influenced by permafrost total dissolved 40 nm colloids in a river sampled at higher altitude the

aftershocks of the 2014 south napa california earthquake complex faulting on secondary faults abstract we investigate the aftershock sequence of the 2014 m w 6 0 south napa california earthquake low magnitude aftershocks missing from the network catalog are detected by applying a matched filter approach to continuous seismic data with the catalog earthquakes serving as the waveform templates we measure precise differential arrival times between events which we use for double difference event relocation in a 3d seismic velocity model most aftershocks are deeper than the mainshock slip and most occur on the west of the mapped surface rupture although the mainshock coseismic and postseismic slip appears to have occurred on the near vertical strike slip west napa fault many of the aftershocks occur in a complex zone of secondary faulting earthquake locations in the main aftershock zone near the mainshock hypocenter delineate multiple dipping secondary faults composite focal mechanisms indicate strike slip and oblique reverse faulting on the secondary features the secondary faults were moved toward failure by coulomb stress changes from the mainshock slip clusters of aftershocks north and south of the main aftershock zone exhibit vertical strike slip faulting more consistent with the west napa fault the northern aftershocks correspond to the area of the largest mainshock coseismic slip whereas the main aftershock zone is adjacent to the fault area that has primarily slipped postseismically unlike most creeping faults the zone of postseismic slip does not appear to contain embedded stick slip patches that would have produced on fault aftershocks the lack of stick slip patches along this portion of the fault may contribute to the low productivity of the south napa aftershock sequence

rare earth elements ree of dissolved and suspended loads in the xijiang river south china abstract the xijiang river is the main channel of the zhujiang pearl river the second largest river in china in terms of water discharge and flows through one of the largest carbonate provinces in the world the rare earth element ree concentrations of the dissolved load and the suspended particulate matter spm load were measured in the xijiang river system during the high flow season the low dissolved ree concentration in the xijiang river is attributed to the interaction of high ph and low doc concentration the paas normalized ree patterns for the dissolved load show some common features negative ce anomaly progressively heavy ree hree enrichment relative to light ree lree similar to the world s major rivers the absolute concentration of the dissolved ree in the xijiang river are mainly ph controlled the degree of ree partitioning between the dissolved load and spm load is also strongly ph dependent the negative ce anomaly is progressively developed with increasing ph being consistent with the oxidation of ce iii to ce iv in the alkaline river waters and the lack of ce anomalies in several doc rich waters is presumably due to both ce iii and ce iv being strongly bound by organic matter the paas normalized ree patterns for the dissolved load and the spm load in rivers draining the carbonate rock area exhibit middle ree mree enrichment and a distinct maximum at eu indicating the preferential dissolution of phosphatic minerals during weathering of host lithologies compared to the xijiang river waters the mree enrichment with a maximum at eu disappeared and light ree were more depleted in the south china sea scs waters suggesting that the ree sourced from the xijiang river must be further fractionated and modified on entering the scs the river fluxes of individual dissolved ree introduced by the xijiang river into the scs vary from 0 04 to 4 36 10 4 mol a 1

dynamic 3d simulations of earthquakes on en echelon faults one of the mysteries of earthquake mechanics is why earthquakes stop this process determines the difference between small and devastating ruptures one possibility is that fault geometry controls earthquake size we test this hypothesis using a numerical algorithm that simulates spontaneous rupture propagation in a three dimensional medium and apply our knowledge to two california fault zones we find that the size difference between the 1934 and 1966 parkfield california earthquakes may be the product of a stepover at the southern end of the 1934 earthquake and show how the 1992 landers california earthquake followed physically reasonable expectations when it jumped across en echelon faults to become a large event if there are no linking structures such as transfer faults then strike slip earthquakes are unlikely to propagate through stepover s 5 km wide

finite element simulations of dynamic shear rupture experiments and dynamic path selection along kinked and branched faults we analyze the nucleation and propagation of shear cracks along nonplanar kinked and branched fault paths corresponding to the configurations used in recent laboratory fracture studies by rousseau and rosakis 2003 2009 the aim is to reproduce numerically those shear rupture experiments and from that provide an insight into processes which are active when a crack initially propagating in mode ii along a straight path interacts with a bend in the fault or a branching junction the experiments involved impact loading of thin homalite 100 a photoelastic polymer plates which had been cut along bent or branched paths and weakly glued back together everywhere except along a starter notch near the impact site strain gage recordings and high speed photography of isochromatic lines provided characterization of the transient deformation fields associated with the impact and fracture propagation we found that dynamic explicit 2 d plane stress finite element analyses with a simple linear slip weakening description of cohesive and frictional strength of the bonded interfaces can reproduce the qualitative rupture behavior past the bend and branch junctions in most cases and reproduce the principal features revealed by the photographs of dynamic isochromatic line patterns the presence of a kink or branch can cause an abrupt change in rupture propagation velocity additionally the finite element results allow comparison between total slip accumulated along the main and inclined fault segments we found that slip along inclined faults can be substantially less than slip along the main fault and the amount depends on the branch angle and kink or branch configuration

fault geometries and structures associated with the rupture endpoints of the 2008 mw 7 9 wenchuan earthquake eastern tibet plateau china

geochemical behaviour of rare earth elements ree along a river reach receiving inputs of acid mine drainage abstract total and dissolved rare earth elements ree were studied in a river reach affected by several inputs of acid mine drainage the first four acidic discharges were of lesser importance compared to the last agrio river coming from the rio tinto mines which transported high loads of fe and al 2 1 and 4 2 ton day respectively together with ree 16 4 kg day and other trace elements in the acid mine drainage amd sources practically all the ree were dissolved and the north american shale composite nasc normalized patterns showed an enrichment in medium ree although some differences exist between the patterns of each source the ph values in the river reach upstream of the confluence with the agrio river ranged between 8 01 and 7 03 and most of the fe and al from the amd sources precipitated downstream of this acidic discharge the ph decreased to 2 98 upstream of the first amd input the dissolved and total concentrations of ree were very low 7 concentrations of ree increased up to 25 g l mainly transported by the particulate phase in the reach downstream of the agrio river with acidic conditions ree behaved conservatively the ree nasc normalized patterns of the river samples resemble that of the amd sources although an enrichment of heavy ree in the dissolved phase is observed linked to complexation by carbonates cerium and particularly la also show higher dissolved percentages similar to hree which must be due to the lower affinity of these elements to be sorbed onto fe oxyhydroxides variations in ce and eu anomalies are observed along the river reach as a consequence of the different amd inputs however the values of the ce anomaly are higher in total samples than in dissolved samples speciation results indicate that these differences are not caused by differences in oxidation states but by slight differences in the hydrogeochemical behaviour of ce with respect to la and nd

influence of material contrast on fault branching behavior 1 material contrasts across faults are a common occurrence and it is important to understand if these material contrasts can influence the path of rupture propagation here we examine models solved numerically of rupture propagation through one type of geometric complexity that of a fault branch stemming from a planar main fault on which rupture initiates this geometry with a material contrast across the main fault could be representative of either a mature strike slip fault or a subduction zone interface we consider branches in both the compressional and extensional quadrants of the fault and material configurations in which the branch fault is in either the stiffer or the more compliant material as well as configurations with no material contrast we find that there are regimes in which this elastic contrast can influence the rupture behavior at a branching junction but there are also stress states for which the branch activation will not depend on the orientation of the mismatch for the scenarios presented here both compressional and extensional side branches are more likely to rupture if the branch is on the side of the fault with the more compliant material versus the stiffer material the stresses induced on the branch fault by rupture traveling on the main fault are different for the two orientations of material contrast we show how the interactions between rupture on the two faults determine which faults are activated

multicycle dynamics of nonplanar strike slip faults 1 we perform two dimensional dynamic models of strike slip faults with a change in strike a bend over multiple earthquake cycles to examine the long term effects of nonplanar fault geometry a viscoelastic model a proxy for off fault deformation and tectonic loading is introduced for the interseismic process to avoid pathological stress buildup around the bend a finite element method with an elastodynamic model is used to simulate dynamic earthquake ruptures we find that stresses near the bend differ strongly from the regional stress field and that the fault develops a relatively steady state in which the stress level and the event pattern on the fault are stable reduced normal stress on the dilatational side and increased normal stress on the compressive side of the bend during dynamic ruptures result in the bend serving as an initiation and or a termination point s for rupture typical events on such a fault consist of two classes unilateral events that rupture only the favorable segment and bilateral events that rupture the favorable segment and part of or the entire unfavorable segment in the latter class of events a time delay in rupture around the bend results from a high yield stress on the compressive side of the bend other effects of the bent fault geometry include higher displacement on the inward wall than on the outward wall higher slip on the more favorable segment than on the less favorable segment and a large slip velocity on the compressive side of the bend

dynamic rupture activation of backthrust fault branching we perform dynamic rupture simulations to investigate the possible reactivation of backthrust branches triggered by ruptures along a main thrust fault simulations with slip weakening fault friction and uniform initial stress show that fast propagation speed or long propagation distance of the main rupture promotes reactivation of backthrust over a range of branch angles the latter condition may occur separately from the former if rupture speed is limited by an increasing slip weakening distance towards the junction direction the results suggest a trade off between the amplitude and duration of the dynamic stress near the main rupture front for backthrust reactivation termination of the main rupture by a barrier can provide enhanced loading amplitude and duration along a backthrust rooted near the barrier facilitating its reactivation especially with a high frictional resistance the free surface and depth dependent initial stress can have several additional effects the sign of the triggered motion along the backthrust can be reversed from thrust to normal if a deeply nucleated main rupture breaks the free surface while it is preserved as thrust if the main rupture is terminated by a barrier at depth the numerical results are discussed in relation to several recent megathrust earthquakes in sumatra chile and japan and related topics such as branch feedbacks to the main fault the dynamic view on backthrust fault branching provided by the study fills a gap not covered by quasi static models or observations a specific examined case of antithetic fault branching may be useful for indicating a barrier like behavior along the main fault

dynamic path selection along branched faults experiments involving sub rayleigh and supershear ruptures building upon previous laboratory earthquake experiments of dynamic shear rupture growth taking place along faults with simple kinks new and complex fault geometries involving cohesively held fault branches are studied asymmetric impact at the specimen boundaries controls the incoming shear ruptures which are manipulated to propagate at either sub rayleigh or supershear velocities high speed photography and dynamic photoelasticity are used with a model material homalite 100 to monitor incoming and outgoing rupture propagation acceleration deceleration or arrest at the vicinity of the branch location differences and similarities of rupture velocity history between cases involving faults with either simple kinks or branches on the one hand and sub rayleigh and supershear incoming ruptures on the other are highlighted and explained results of the experiments show a clear general bias toward large branch inclination smaller branch angles appearing to be overshadowed and suppressed by the stress field associated with the main fault of great interest also is the sustenance of rupture propagation along a branch by the mach cone when the initial rupture is supershear driven generally higher rupture speeds favors larger arrays of branching angles to be triggered a companion analysis by templeton et al 2009 featuring detailed numerical simulations of these experiments provides further insight into the observed phenomena

the combined inversion of seismic and geodetic data for the source process of the 16 october 1999 mw 7 1 hector mine california earthquake we investigate the source process of the m w 7 1 hector mine earthquake by inverting broadband regional and local seismic displacement waveforms com bined with global positioning system gps and synthetic aperture radar interfer ometry insar geodetic measurements we find that the three data sets individually produce remarkably similar slip distributions over a multisegment fault a simulta neous inversion of the three data sets is presented and the sensitivity of the combined inversion to the weighting of the three independent data sets is examined the results indicate that the overall length of the fault that slipped is 42 km with a peak slip of 5 50 m and total scalar seismic moment of 6 8 10 19 n m the majority of slip is located on the western branch of the lavic lake fault to the northwest of the hypo center although the overall rupture is bilateral with appreciable slip on the bullion fault to the southeast some slip is located on an eastern branch of the lavic lake fault an apparent bifurcation which is also evident from aftershock locations the average slip and stress drops are 2 70 1 62 1 60 m and 78 36 and 55 bars for the western lavic lake the eastern lavic lake and bullion faults respectively the results also indicate that the overall rupture process is relatively slow which is char acterized by a several second delay before the onset of significant slip a 1 8 km sec rupture velocity of the primary asperity and long spatially variable dislocation rise times

surface ruptures on the transverse xiaoyudong fault a significant segment boundary breached during the 2008 wenchuan earthquake china abstract the 220 km long rupture of the 2008 mw 7 9 wenchuan earthquake breached several km scale geometric discontinuities along strike including the previously un mapped nw trending xiaoyudong fault connecting between the two major ne trending rupture planes on the beichuan and pengguan faults in this paper we present high resolution mapping of the 8 km long surface breaks and sinistral oblique thrusting coseismic slip on the xiaoyudong fault scarp height is the largest at the nw end reaching 3 5 m and decreases southward in steps to less than 0 2 m with an average slip gradient of 6 10 3 at a few tens of meters length scale but up to 50 10 3 locally left lateral offsets co vary with the vertical component the largest sinistral slip vector we observed is 2 2 m geological and geophysical evidence suggests that the xiaoyudong fault is likely a 30 sw dipping lateral ramp that soles into the pengguan fault and at its northwestern end intersects with the beichuan fault where the latter has a step in the fault plane kinematically the xiaoyudong fault functions as a tear and conjugate fault and coincides with significant coseismic slip rake rotations on both the beichuan and pengguan faults similar correlation of fault bends with sharp changes in faulting style occurs at other steps along the wenchuan rupture the xiaoyudong fault may have played a positive role in linking coseismic slip partitioning between parallel reverse fault planes facilitating the growth of a longer and more destructive rupture this highlights the role of tear faults in bridging ruptures between segments such that reverse type ruptures can breach steps wider than anticipated from strike slip fault examples transfer faults are common and perhaps poorly documented features in reverse fault systems and their roles in ruptures may increase the maximum potential earthquake magnitude for fold and thrust belts

applying wedge theory to dynamic rupture modeling of fault junctions wedges such as accretionary prisms and thin skinned fold and thrust belts occur frequently in nature and can be the site of devastating earthquakes critical wedge theory can be applied to these settings but this steady state description of wedge deformation is at odds with the periodic occurrence of earthquakes we discuss how critical wedge theory applies to the seismic cycle and we use elastic wedge theory to constrain realistic stress states our goal is to determine the rupture behavior of an earthquake in a wedge if rupture initiates on the basal sliding surface will it stay confined to the basal surface or will it propagate onto a fault branch interior to the wedge this information can significantly alter the seismic hazard in areas where fault intersections occur we answer this question using numerical models of dynamic rupture propagation through branched geometries for which the stress state is a pivotal input parameter we apply wedge theory to constrain the stress state but inherent to this theory is the assumption of a weak basal fault we investigate the role of this assumption and determine that rupture is unlikely to propagate from a weak basal fault onto a strong branch fault without the aid of a physical process such as pore fluid migration along the branch this framework is applied to the rupture of the 2008 wenchuan earthquake we find that we are able to reproduce the behavior at some fault intersections but our 2d model is not able to reproduce all the behaviors possibly due to the oblique nature of this event

rapid development of negative ce anomalies in surface waters and contrasting ree patterns in groundwaters associated with zn pb massive sulphide deposits ground and surface waters collected from two undisturbed zn pb massive sulphide deposits the halfmile lake and restigouche deposits and active mines in the bathurst mining camp bmc nb canada were analysed for the rare earth elements ree ree contents are highly variable in waters of the bmc with higher contents typical of waters with higher fe and lower ph there are significant differences between ground and surface waters and between groundwaters from different deposits the ree contents of surface waters are broadly similar within and between deposit areas although there are spatial variations reflecting differences in ph and redox conditions surface waters are characterised by strong negative ce anomalies ce ce nasc as low as 0 08 produced by oxidation of ce3 to ce4 and preferential removal of ce4 from solution upon leaving the shallow groundwater environment groundwaters and seeps typically lack significant ce anomalies reflecting generally more reducing conditions in the subsurface environment and indicating that ce oxidation is a rapid process in the surface waters deeper groundwaters at the halfmile lake deposit are characterised by ree patterns that are similar to the host lithologies whereas most groundwaters at the restigouche deposit have lree depleted patterns compared to nasc halfmile lake deposit groundwaters have generally lower ph values whereas restigouche deposit groundwaters show greater heavy ree complexation by carbonate ions shallow waters at the halfmile lake and stratmat main zone deposits have unusual patterns which reflect either the adsorption of light ree onto colloids and fracture zone minerals and or precipitation of ree phosphate minerals middle ree enrichment is typical for ground and surface waters and is highest for neutral ph waters the labile portion of stream sediments are generally more middle ree enriched than total sediment and surface waters indicating that the ree are removed from solution by adsorption to fe and mn oxyhydroxides in the order middle ree light ree heavy ree

geometry and earthquake potential of the shoreline fault central california abstract the shoreline fault is a vertical strike slip fault running along the coastline near san luis obispo california much is unknown about the shoreline fault including its slip rate and the details of its geometry here i study the geometry of the shoreline fault at seismogenic depth as well as the adjacent section of the offshore hosgri fault using seismicity relocations and earthquake focal mechanisms the optimal anisotropic dynamic clustering oadc algorithm ouillon et al 2008 is used to objectively identify the simplest planar fault geometry that fits all of the earthquakes to within their location uncertainty the oadc results show that the shoreline fault is a single continuous structure that connects to the hosgri fault discontinuities smaller than about 1 km may be undetected but would be too small to be barriers to earthquake rupture the hosgri fault dips steeply to the east while the shoreline fault is essentially vertical so the hosgri fault dips towards and under the shoreline fault as the two faults approach their intersection the focal mechanisms generally agree with pure right lateral strike slip on the oadc planes but suggest a non planar hosgri fault or another structure underlying the northern shoreline fault the shoreline fault most likely transfers strike slip motion between the hosgri fault and other faults of the pacific north america plate boundary system to the east a hypothetical earthquake rupturing the entire known length of the shoreline fault would have a moment magnitude of 6 4 6 8 a hypothetical earthquake rupturing the shoreline fault and the section of the hosgri fault north of the hosgri shoreline junction would have a moment magnitude of 7 2 7 5

the effects of d0 on rupture propagation on fault stepovers abstract according to the slip weakening friction law andrews 1976a fault friction drops from a static value to a sliding value over some slip weakening distance d 0 laboratory studies of fault friction confirm this weakening but do not settle on a single value for d 0 however this parameter is a critical input in dynamic earthquake models as it affects rupture nucleation and propagation we use the 2d finite element method to test how the specific value of d 0 affects rupture behavior we consider the ability of rupture to jump from segment to segment of a disconnected stepover or to propagate through the double bends of a connected stepover as a way to gauge rupture energy and behavior we find the stepover width or bend angle through which rupture can propagate is affected by the choice of d 0 but it is not a linear relationship this is true regardless of whether the stepover is connected or disconnected compressional or extensional or whether the initial rupture velocity is supershear or subshear we do find however that scaling the intensity of the regional stress field up or down does linearly correspond to scaling d 0 down or up we interpret the nonlinearity of the d 0 scaling results to be related to the area of the secondary fault that intersects the lobe of failure level coulomb stress change induced by rupture of the first fault segment because 1 the d 0 controlled critical patch size for renucleation must be exceeded on the second segment and 2 the area of this overlap also does not change linearly with distance from the first fault

effects of low velocity fault zones on dynamic ruptures with nonelastic off fault response 1 using a finite element method for elastoplastic dynamic analysis we examine the effects of a low velocity fault zone lvfz surrounding a fault on a spontaneous dynamic earthquake rupture a mohr coulomb failure criterion is used to characterize nonelastic off fault response to earthquake ruptures we find that the presence of a lvfz alters the distribution of off fault plastic strain and results in larger final slip and larger peak slip velocities on the fault these effects show a lvfz width dependency a supershear relative to the shear wave velocity of country rocks rupture transition is observed with a lvfz width of 400 m or larger up to 2 km the presence of a lvfz increases the amplitude of ground shaking at stations within the lvfz and induces high frequency oscillations at stations within and near the lvfz

environmental tracers for elucidating the weathering process in a phosphogypsum disposal site implications for restoration summary this study provides geochemical data with the aim of identifying and tracing the weathering of phosphogypsum wastes stack piled directly on salt marshes of the tinto river estuary of huelva sw spain with that purpose different types of highly polluted acid solutions were collected in the stack connection between these solutions and the estuarine environment was studied by geochemical tracers such as rare earth elements ree and their north american shale composite nasc normalized patterns and cl br ratios phosphogypsum related wastewaters include process water stored on the surface pore water contained in the phosphogypsum profile and edge outflow water emerging from inside the stack edge outflow waters are produced by waterlogging at the contact between phosphogypsum and the nearly impermeable marsh surface and discharge directly into the estuary process water shows geochemical characteristics typical of phosphate fertilizers i e ree patterns with an evident enrichment of heavy ree hree with respect to middle ree mree and light ree lree by contrast ree patterns of deeper pore water and edge outflows are identical to those of tinto river estuary waters with a clear enrichment of mree relative to lree and hree denoting influence of acid mine drainage cl br ratios of these solutions are very close to that of seawater which also supports its estuarine origin these findings clearly show that process water is not chemically connected with edge outflows through pore waters as was previously believed phosphogypsum weathering likely occurs by an upward flow of seawater from the marsh because of overpressure and permeability differences several recommendations are put forward in this study to route restoration actions such as developing treatment systems to improve the quality of the edge outflow waters before discharging to the receiving environment

fault branching and rupture directivity 1 could the directivity of a complex earthquake be inferred from the ruptured fault branches it created typically branches develop in forward orientation making acute angles relative to the propagation direction direct backward branching of the same style as the main rupture e g both right lateral is disallowed by the stress field at the rupture front here we propose another mechanism of backward branching in that mechanism rupture stops along one fault strand radiates stress to a neighboring strand nucleates there and develops bilaterally generating a backward branch such makes diagnosing directivity of a past earthquake difficult without detailed knowledge of the branching process as a field example in the landers 1992 earthquake rupture stopped at the northern end of the kickapoo fault jumped onto the homestead valley fault and developed bilaterally there nnw to continue the main rupture but also sse for 4 km forming a backward branch we develop theoretical principles underlying such rupture transitions partly from elastostatic stress analysis and then simulate the landers example numerically using a two dimensional elastodynamic boundary integral equation formulation incorporating slip weakening rupture this reproduces the proposed backward branching mechanism based on realistic if simplified fault geometries prestress orientation corresponding to the region standard lab friction values for peak strength and fracture energies characteristic of the landers event we also show that the seismic s ratio controls the jumpable distance and that curving of a fault toward its compressional side like locally along the southeastern homestead valley fault induces near tip increase of compressive normal stress that slows rupture propagation

sensitivity study of physical limits on ground motion at yucca mountain abstract physical limits on ground motion parameters can be estimated from spontaneous rupture earthquake models but are subject to uncertainties in model parameters we investigate physical limits at yucca mountain nevada and assess sensitivities due to uncertainties in fault geometry off fault rock strength the seismogenic depth fault zone structure and undrained poroelastic response of the fluid pressure for the extreme scenario of nearly complete stress drop on the solitario canyon fault peak ground velocity pgv at a site near the fault is sensitive to deep fault geometry and cohesive strength of shallow geologic units while it is relatively insensitive to fault zone structure the seismogenic depth and pore pressure response taking previous estimates of andrews et al 2007 as a benchmark a 10 reduction in dip from 60 to 50 of the solitario canyon fault at depth combined with doubled cohesion of shallow units can increase both horizontal and vertical pgvs by over 1 m s to values exceeding 5 m s in a lower stress drop scenario constrained by regional extremes of coseismic slip inferred from the paleoseismic record pgv is most sensitive to fault geometry at depth is only modestly affected by fault zone structure and is insensitive to cohesion of shallow units and pore pressure response effects of rock strength on spectral acceleration are significant only at short periods i e less than 3 s the dipping normal fault models predict asymmetric inelastic strain distributions with respect to the fault plane with more intense inelastic deformation on the hanging wall though that asymmetry may be moderated by poroelastic effects

nonuniform prestress from prior earthquakes and the effect on dynamics of branched fault systems 1 to examine the effects of branched fault geometry on the dynamics of fault systems in the long term we perform multicycle simulations on generic faulting models an explicit finite element algorithm is used to simulate spontaneous dynamic rupture of earthquakes the fault stress during the interseismic period is evaluated by an analytical viscoelastic model we find that the fault prestress field becomes highly nonuniform near the branch point and on the two branch segments over multiple earthquake cycles owing to the branched fault geometry and stress interaction between the two segments the principal prestress on faults rotates over multiple earthquake cycles and departs from the regional stress field significantly near the branch point after a number of earthquake cycles the branched fault systems evolve to a steady state in which several patterns of the fault prestress and earthquake rupture repeat the nonuniform prestress developed from previous earthquakes has large effects on the rupture and slip patterns several different rupture scenarios can occur on a given branched fault system in addition backward branching can occur in the nonuniform prestress field either driven by slip on the stem of the fault system or through a triggering mechanism these modeling results may have important implications for understanding fault branching behavior observed in the 1992 landers the 1999 hector mine and the 2002 denali fault earthquakes and for seismic hazard analysis in the areas where branched fault systems exist

dynamic rupture through a branched fault configuration at yucca mountain and resulting ground motions we seek to characterize the likelihood of multiple fault activation along a branched normal fault system during earthquake rupture using dynamic finite element analyses this is motivated by the normal faults in the vicinity of yucca mountain nevada a potential site for a high level radioactive waste repository the solitario canyon fault scf a north south trending fault located approximately 1 km west of the crest of yucca mountain is the most active of these faults based on the results of previous branching work by kame et al 2003 branch activation in the hanging wall of a normal fault such as the scf may be possible for fast ruptures propagating near the rayleigh wave speed at the branch junction dynamic branch activation along a splay of the scf during a seismic event could have important effects on the rupture velocity and resulting ground motions at the proposed repository site we consider elastic as well as a pressure dependent elastic plastic response of the off fault material we find that based on the regional stress state in the area the only likely candidates for branch activation in the hanging wall of the scf are more steeply westward dipping intrablock splay faults we also find that the rupture velocity for an earthquake propagating updip along the scf must reach supershear speeds in order for dynamic branch activation to occur branch activation can have significant effects on the ground motions at the proposed repository site 1 km away from the scf beneath the crest of yucca mountain causing the repository site to experience a second peak in large vertical particle velocities elastic plastic response near the branch junction reduces peak ground velocities and accelerations at the proposed repository site

dynamic shear rupture interactions with fault bends and off axis secondary faulting 1 on the basis of elastodynamic stress fields for singular crack and nonsingular slip weakening models of propagating rupture we develop preliminary answers to such questions as follows if a rupturing fault is intersected by another providing a possible bend in the failure path when will stressing be consistent with rupture along the bend what secondary fault locations and orientations in a damaged region bordering a major fault will be stressed to failure by the main rupture stresses that could initiate rupture on a bend are shown to increase dramatically with crack speed especially near the limiting speed rayleigh for mode ii shear for mode iii whether a bend path once begun can be continued to larger scales depends on principal stress directions and ratios in the prestress field conditions should often be met in mode ii for which bend paths encouraged by stressing very near the rupture tip are discouraged by the larger scale stressing a basis for intermittent rupture propagation and spontaneous arrest secondary failure in the damage zone likewise increases markedly as the limiting speed is approached such may make the fracture energy much greater than for slip on a single surface the extent of secondary faulting is strongly affected by prestress directions and the ratio of residual to peak strength for mode ii prestress controls whether activation occurs primarily on the extensional side which we show to be the typical case or on the compressional side too natural examples are consistent with the concepts developed

rupture and ground motion models on the northern san jacinto fault incorporating realistic complexity we use the 3d finite element method to conduct dynamic models of rupture and resulting ground motion on the claremont casa loma stepover of the northern san jacinto fault we incorporate complex fault geometry from the u s geological survey usgs quaternary faults database see data and resources 1 a realistic velocity structure the southern california earthquake center community velocity model s a realistic regional stress field with an orientation taken from seismicity relocation literature and several stochastic self similar shear stress distributions as we incorporate more types of complexity the specific effects of any individual factor become less apparent within the overall rupture behavior we also find that the distribution of high and low shear stress that arises from combining regional and stochastic stress fields has the strongest control over where the rupture terminates using a regional stress field alone as well as with the combined regional and stochastic stress realization we find that the stepover presents a significant barrier to rupture regardless of our choice of initial nucleation point and that it is difficult for rupture to propagate the full length of either fault segment greater heterogeneity of stresses tends to produce shorter ruptures within this result we find that the claremont strand is more favorable for long ruptures than the casa loma clark strand low frequency ground motion intensity and distribution are controlled largely by the velocity structure rather than by stress heterogeneity the strongest motions produced in these models are in the san bernardino basin although directivity effects do contribute to the low frequency ground motion distribution particularly in the near field they are secondary to the effects of the velocity structure online material figures of ground motions from models used to calibrate the stress conditions for dynamic rupture propagation 1 sec 18

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

modeling the seismic cycle in subduction zones the role and spatiotemporal occurrence of off megathrust earthquakes shallow off megathrust subduction events are important in terms of hazard assessment and coseismic energy budget their role and spatiotemporal occurrence however remain poorly understood we simulate their spontaneous activation and propagation using a newly developed 2 d physically consistent continuum viscoelastoplastic seismo thermo mechanical modeling approach the characteristics of simulated normal events within the outer rise and splay and normal antithetic events within the wedge resemble seismic and seismological observations in terms of location geometry and timing their occurrence agrees reasonably well with both long term analytical predictions based on dynamic coulomb wedge theory and short term quasi static stress changes resulting from the typically triggering megathrust event the impact of off megathrust faulting on the megathrust cycle is distinct as more both shallower and slower megathrust events arise due to occasional off megathrust triggering and increased updip locking this also enhances tsunami hazards which are amplified due to the steeply dipping fault planes of especially outer rise events

the 1999 izmit turkey earthquake a 3d dynamic stress transfer model of intraearthquake triggering before the august 1999 izmit kocaeli turkey earthquake theoretical studies of earthquake ruptures and geological observations had provided estimates of how far an earthquake might jump to get to a neighboring fault both numerical simulations and geological observations suggested that 5 km might be the upper limit if there were no transfer faults the izmit earthquake appears to have followed these expectations it did not jump across any step over wider than 5 km and was instead stopped by a narrower step over at its eastern end and possibly by a stress shadow caused by a historic large earthquake at its western end our 3d spontaneous rupture simulations of the 1999 izmit earthquake provide two new insights 1 the west to east striking fault segments of this part of the north anatolian fault are oriented so as to be low stress faults and 2 the easternmost segment involved in the august 1999 rupture may be dipping an interesting feature of the izmit earthquake is that a 5 km long gap in surface rupture and an adjacent 25 restraining bend in the fault zone did not stop the earthquake the latter observation is a warning that significant fault bends in strike slip faults may not arrest future earthquakes manuscript received 30 august 2000