horizontal surface velocity and strain patterns near thrust and normal faults during the earthquake cycle the importance of viscoelastic relaxation in the lower crust and implications for interpreting geodetic data in recent years more and more space geodetic data on the surface deformation associated with earthquakes on intracontinental normal and thrust faults have become available however numerical models investigating the coseismic and postseismic deformation near such faults in a general way i e not focused on a particular earthquake are still sparse here we use three dimensional finite element models that account for gravity far field regional extension shortening and postseismic relaxation in a viscoelastic lower crust to quantify the surface deformation caused by an mw 7 earthquake on a dip slip fault the coseismic deformation is characterized by horizontal shortening in the footwall of the normal fault and extension in the hanging wall of the thrust fault consistent with elastic dislocation models geological field observations and gps data from earthquakes in italy and taiwan during the postseismic phase domains of extensional and contractional strain exist next to each other near both fault types the spatiotemporal evolution of these domains as well as the postseismic velocities and strain rates strongly depend on the viscosity of the lower crust for viscosities of 1018 1020 pa s the signal from postseismic relaxation is detectible for 20 50 years after the earthquake if gps data containing a postseismic relaxation signal are used to derive regional rates the stations may show rates that are too high or too low or even an apparently wrong tectonic regime by quantifying the postseismic deformation through space and time our models help to interpret gps data and to identify the most suitable locations for gps stations

syndeformational fluid trapping in quartz determining the pressure temperature conditions of deformation from fluid inclusions and the formation of pure co2fluid inclusions during grain boundary migration observations and microthermometric data on fluid inclusions from a terrane that underwent deformation following peak metamorphic conditions show that grain boundary migration recrystallization favours the entrapment of carbonic inclusions whereas microfracturing during brittle deformation favours the infiltration and eventual entrapment of aqueous fluids our results imply that pure co2 fluid inclusions in metamorphic rocks are likely to be the residue of deformation recrystallization process rather than representing a primary metamorphic fluid where the temperature of deformation can be deduced by other means the densities of fluid inclusions trapped during recrystallization which we call recrystallization primary fluid inclusions can be used to constrain the ambient pressure during deformation using these constraints the data imply that the post metamorphic hercynian exhumation in sardinia brought rocks at 300 c to within 3km of the surface this conclusion is similar to that described for the rapidly uplifted southern alps in new zealand

redistribution of dynamic stress during coseismic ruptures evidence for fault interaction and earthquake triggering we investigate the spatiotemporal evolution of dynamic stress outside a rupturing extended fault the dynamic stress variations caused by a coseismic rupture in a half space are computed by using the discrete wavenumber and reflectivity methods after a transient phase the stress time history evolves to the final static stress value we compare the static stress changes resulting from this model with those computed from a static dislocation model we have applied this method to study the interactions between the first two normal faults which ruptured during the 1980 ms 6 9 irpinia earthquake these two subevents are separated in time by nearly 20 s while the third and last subevent occurred 40 s after the rupture onset we compute the dynamic stress changes caused by the rupture of the first subevent our modeling results show that the dynamic stress peak on the second subevent fault plane is reached between 7 s and 8 s after the rupture initiation on the main fault on the average the static stress level on the second subevent 20 s fault plane is reached nearly after 14 s the dynamic rupture did not jump from a rupturing segment to the adjacent one immediately but the triggering of the 20 s subevent is delayed by roughly 10 s with respect to the instant of occurrence of the dynamic stress peak induced by the 0 s event the dynamic stress pulse propagates along the strike direction of the second subevent fault plane at an average velocity of nearly 3 4 km s the delayed triggering of the second subevent can be interpreted in terms of the frictional properties of the faults in particular rate and state dependent frictional law can explain a delayed instability after a sudden change in stress using the estimated values of the subevent triggering delay and the shear stress change we attempt to constrain the parameter a on the 20 s fault the values here inferred agree well with those resulting from previous studies

integrated seismic hazard analysis of the wasatch front utah we examined the combined effects of different sources that influence earthquake hazard of the populated wasatch front utah we first evaluated the fault stress interaction of the two largest historic earthquakes of the intermountain seismic belt isb the 1959 hebgen lake montana m s 7 5 and the 1983 borah peak idaho m s 7 3 earthquakes which experienced multisegment normal faulting ruptures estimates of the static stress change for these events revealed an increase in coulomb failure stress in areas of extended aftershocks these observations suggested that fault stress analysis is applicable in evaluating the spatial distribution of aftershocks after large normal faulting earthquakes in the same extensional stress regime of the eastern basin range including the wasatch front utah which encompasses the 370 km long wasatch fault and surrounding faults on the basis of this result we applied the modeling technique to the historically seismically quiescent wasatch fault and examined the relation between the pattern of stress change and the space time distribution of paleoearthquakes ages and locations of the wasatch fault paleoseismic data imply 17 single segment or 11 multisegment ruptures in the past 5 6 kyr we prefer the multisegment model because almost all of the large historical normal faulting earthquakes in the isb were multisegment fitting the along fault displacements by an analytic half ellipse function provides a first order distribution of the displacement over an entire rupture length and allows new estimates of fault slip rates and seismic moment with these data we also estimated the occurrence rate of m w 6 6 wasatch paleoearthquakes and showed that the rate was about three times higher than that inferred by the historical seismicity this result along with new information from a megatrench on the wasatch fault near salt lake city that revealed no scarp forming earthquakes between ca 9 0 and 15 5 ka suggests that large wasatch fault events in the past 5 6 kyr may be clustered the recurrence rate of large earthquakes estimated by the geodetic measured strain on the other hand is three to four times higher than that estimated by the long term fault slip rate this difference together with the observation of a low regional strain rate from historical seismicity suggests that cumulative aseismic deformation may be significant on the wasatch fault we also examined a major consideration for along strike segmentation namely how stress contagion could affect the probability of failure of adjacent faults including paleoearthquake derived fault slip rates global positioning system derived geodetic moment rates and the effect of stress contagion in the earthquake hazard estimation for a specific location in the salt lake valley revealed an increase in the annual frequency of peak ground acceleration 0 25 g by a factor of 1 4 4 0 and 5 4 respectively compared with that derived from historical seismicity only manuscript received 31 may 2001

a geomorphological approach to the management of rivers contaminated by metal mining as the result of current and historical metal mining river channels and floodplains in many parts of the world have become contaminated by metal rich waste in concentrations that may pose a hazard to human livelihoods and sustainable development environmental and human health impacts commonly arise because of the prolonged residence time of heavy metals in river sediments and alluvial soils and their bioaccumulatory nature in plants and animals this paper considers how an understanding of the processes of sediment associated metal dispersion in rivers and the space and timescales over which they operate can be used in a practical way to help river basin managers more effectively control and remediate catchments affected by current and historical metal mining a geomorphological approach to the management of rivers contaminated by metals is outlined and four emerging research themes are highlighted and critically reviewed these are 1 response and recovery of river systems following the failures of major tailings dams 2 effects of flooding on river contamination and the sustainable use of floodplains 3 new developments in isotopic fingerprinting remote sensing and numerical modelling for identifying the sources of contaminant metals and for mapping the spatial distribution of contaminants in river channels and floodplains and 4 current approaches to the remediation of river basins affected by mining appraised in light of the european union s water framework directive 2000 60 ec future opportunities for geomorphologically based assessments of mining affected catchments are also identified

holocene vertical displacement on the central segments of the wasatch fault zone utah compiled per event vertical displacement observations from 17 paleoseismic sites along the six central segments of the wasatch fault zone wfz highlight possible biases and trends in displacement along the fault the displacement data are consistent with a model of characteristic type slip but anomalous and variable displacements indicate that significant natural variability in displacement occurs when combined into a composite distribution of displacement 79 of the data fit within a displacement envelope that shows displacement decreasing in a half ellipse shape from 1 4 3 5 m near the segment centers to 0 6 2 5 m near the ends additionally displacements normalized by the distance from the segment centers to ends decrease from means of 2 0 3 0 m near the segment centers to 1 3 1 9 m near the ends consistent with characteristic type slip termination although several paleoseismic sites exhibit repeated similar displacements the data are sparse and both low valued 0 5 0 8 m and high valued 4 2 4 7 m outliers suggest complex strain release possibly resulting from segment interaction and or noncharacteristic events although a global normal fault type surface rupture length srl average displacement regression underpredicts observed wfz displacements the largest displacements per segment correspond well with a srl maximum displacement regression this correlation as well as moderate variability in srl and displacement based moment magnitude suggests that the anomalous displacements represent the intrinsic variability in characteristic displacement per segment thus minor variations to the characteristic slip model to account for exceptional upper and lower bound displacements e g a hybrid characteristic variable slip model may be appropriate for the wfz additional paleoseismic data are necessary to address data gaps and biases to facilitate more robust tests of earthquake slip models and to reduce uncertainty in srl displacement and magnitude

intraplate extensional tectonics of the eastern basin range inferences on structural style from seismic reflection data regional tectonics and thermal mechanical models of brittle ductile deformation the general lack of a correlation between earthquakes and surface faulting in the interior of the western u s cordillera has motivated our efforts to evaluate the geometry structural style and mechanism of normal faulting characteristic of this region of intraplate extension to address the problem we have interpreted over 1500 km of seismic reflection data and constructed detailed cross sections of the upper crust rheological models of the continental crust were calculated to examine the possibility of shallow quasi plastic flow and its influence on faulting in the eastern basin range the western colorado plateau and the middle rocky mountains our data and interpretations have revealed the following styles of cenozoic deformation 1 steep to low angle dip normal faulting along the wasatch fault 2 low angle dip and listric normal faulting possibly associated with movement on preexisting thrusts 3 the occurrence of asymmetric mostly eastward tilted tertiary basins that are bounded by low to moderate dipping planar and listric faults and 4 at least three vertically stacked en echelon low angle reflections in the mid to upper crust that dip gently westward from 3 km beneath the wasatch plateau to over 15 km at the utah nevada border these reflections are interpreted as normal detachment faults the structural style of the pervasive low to moderate angle dipping faults cannot be easily reconciled with classic brittle failure theory but the interpreted termination of normal faults at or above the deeper low angle reflections suggests the presence of shallow zones of ductile deformation that may have accommodated slip an important observation based on interpretations of seismic reflection profiles is that normal fault zones dip more gently in the subsurface than their associated scarps in unconsolidated surficial deposits segment boundaries of the wasatch fault zone apparently coincide with the positions of east trending displacement transfer structures in thrust sheets and the position of the precambrian uinta aulacogen suggesting that preexisting crustal structure partly controls the geometry of extension to examine the influence of ductile deformation quasi plastic flow was modeled for appropriate geotherms of the basin range and colorado plateau crusts these models provide constraints on the depth to the frictional quasi plastic transition that occurs as shallow as 8 km in the eastern basin range this depth also corresponds to the approximate depth above which most accurately determined earthquake foci for small earthquakes m 5 5 appear to nucleate at 10 15 km in or near the brittle ductile transition the rheological modeling suggests that a thermally deforming continental lithosphere plays an important role in the evolution of this extending intraplate region large scale low angle reflections may represent decollements and normal faults at the top of upper crustal zones of reduced shearing strength and higher ductility

epigenetic nature of the bif hosted gold mineralization at ajjanahalli southern india evidence from ore petrography and fluid inclusion studies abstract gold mineralization at ajjanahalli is bif hosted and structurally controlled ore petrographic studies revealed that gold was introduced as a consequence of focussed fluid flow and sulfidation of an oxide facies bif horizon ubiquitous syn kinematic quartz veins within the bif as well as in the associated metasedimentary units lay testimony to the high fluid flux during deformation fluid inclusion studies involving microthermometry and laser raman microspectroscopy on inclusions from quartz veins from different litho units were carried out the primary fluid preserved as aqueous carbonic inclusions within quartz veins in carbonaceous phyllites is found to be h2o co2 ch4 nacl type near isothermal decompression led to splitting of this fluid at greenschist facies conditions 0 8 kb 263 c to 1 15 kb 309 c and resulted in a low saline aqueous and a carbonic ch4 fluid the auriferous aqueous part reacted with the oxidic bif leading to epigenetic replacement of oxides to pyrite and concomitant precipitation of gold

the brittle plastic transition in experimentally deformed quartz aggregates deformation experiments have been conducted to provide constraints on the processes responsible for the brittle plastic transition in quartz aggregates a correlation between mechanical behavior and distinctive microstructural characteristics indicates that the brittle plastic transition in nonporous quartzite involves at least three transitions in deformation mechanism that occur with increasing temperature and or pressure first there is a transition from cataclastic faulting to semibrittle faulting microstructural observations indicate that this transition occurs due to the activation of dislocations in addition faulting is more stable in the semibrittle faulting regime due to the blunting of the stresses at the advancing fault tip by dislocation glide second there is a transition from semibrittle faulting to semibrittle flow this transition corresponds to a change from localized to distributed deformation microstructural observations indicate that microcracks nucleate in response to stress concentrations at dislocation pileups in the semibrittle flow regime we conclude that the transition to semibrittle flow occurs when the stress intensity at crack tips is insufficient to allow propagation across grain boundaries third there is a transition from semibrittle flow to dislocation creep microstructural observations suggest that this transition occurs as a result of an increase in grain boundary mobility with increasing temperature in addition microstructural observations indicate that a transition from dominantly mode i axial to mode ii shear microcracking occurs with an increase in confining pressure from 0 4 to 0 8 gpa regardless of temperature the differential stresses supported by the experimentally deformed samples are higher than those expected under geologic conditions however a comparison of the experimentally produced microstructures to those reported from natural fault zones suggests that similar processes are operative in the laboratory and in the earth the results of this study provide further evidence to indicate that the brittle plastic transition in the continental crust occurs over a relatively wide range of conditions

holocene paleoseismicity temporal clustering and probabilities of future large m 7 earthquakes on the wasatch fault zone utah the chronology of m 7 paleoearthquakes on the central five segments of the wasatch fault zone wfz is one of the best dated in the world and contains 16 earthquakes in the past 5600 years with an average repeat time of 350 years repeat times for individual segments vary by a factor of 2 and range from about 1200 to 2600 years four of the central five segments ruptured between 620 30 and 1230 60 calendar years b p the remaining segment brigham city segment has not ruptured in the past 2120 100 years comparison of the wfz space time diagram of paleoearthquakes with synthetic paleoseismic histories indicates that the observed temporal clusters and gaps have about an equal probability depending on model assumptions of reflecting random coincidence as opposed to intersegment contagion regional seismicity suggests that for exposure times of 50 and 100 years the probability for an earthquake of m 7 anywhere within the wasatch front region based on a poisson model is 0 16 and 0 30 respectively a fault specific wfz model predicts 50 and 100 year probabilities for an m 7 earthquake on the wfz itself based on a poisson model as 0 13 and 0 25 respectively in contrast segment specific earthquake probabilities that assume quasi periodic recurrence behavior on the weber provo and nephi segments are less 0 01 0 07 in 100 years than the regional or fault specific estimates 0 25 0 30 in 100 years due to the short elapsed times compared to average recurrence intervals on those segments the brigham city and salt lake city segments however have time dependent probabilities that approach or exceed the regional and fault specific probabilities for the salt lake city segment these elevated probabilities are due to the elapsed time being approximately equal to the average late holocene recurrence time for the brigham city segment the elapsed time is significantly longer than the segment specific late holocene recurrence time

grain boundary migration of water and carbon dioxide during uplift of garnet zone alpine schist new zealand deformed quartz veins in garnet zone schist adjacent to the active alpine fault new zealand have fluid inclusions trapped along quartz grain boundaries textures suggest that the inclusions formed in their present shapes during annealing of the deformed veins many of the inclusions are empty but some contain carbon dioxide with densities that range from 0 16 to 0 80 g cm 3 no water nitrogen or methane was detected the inclusions are considerably more co2 rich than either the primary metamorphic fluid 5 co2 or fluids trapped in fracture related situations in the same or related rocks 50 co2 enrichment of co2 is inferred to have resulted from selective migration wicking of saline water from the inclusions along water wet grain boundaries after cooling induced immiscibility of a water co2 mixture inclusion volumes changed after loss of water non wetting co2 remained trapped in the inclusions until further percolation progressively removed co2 in solution this mechanism of fluid migration dominated in ductile quartz rich rocks near but below the brittle ductile transition at deeper levels hydraulic fracturing is also an important mechanism for fluid migration whereas at shallower levels advection through open fractures dominates the fluid flow regime

a 3 d model of the crust and uppermost mantle beneath the central and western us by joint inversion of receiver functions and surface wave dispersion 1 rayleigh wave phase velocity maps from ambient noise and earthquake data are inverted jointly with receiver functions observed at 828 stations from the usarray transportable array west of 100 w longitude for data recorded in the years 2005 through 2010 to produce a 3 d model of shear wave speeds beneath the central and western us to a depth of 150 km eikonal tomography is applied to ambient noise data to produce about 300 000 rayleigh wave phase speed curves and helmholtz tomography is applied to data following 1550 ms 5 0 earthquakes so that rayleigh wave dispersion maps are constructed from 8 to 80 s period with associated uncertainties across the region harmonic stripping generates back azimuth independent receiver functions with uncertainty estimates for each of the stations a nonlinear bayesian monte carlo method is used to estimate a distribution of shear wave speed vs models beneath each station by jointly interpreting surface wave dispersion and receiver functions and their uncertainties the assimilation of receiver functions improves the vertical resolution of the model by reducing the range of estimated moho depths improving the determination of the shear velocity jump across moho and improving the resolution of the depth of anomalies in the uppermost mantle a great variety of geological and tectonic features are revealed in the 3 d model that form the basis for future detailed local to regional scale analysis and interpretation

temporal variation in fault friction and its effects on the slip evolution of a thrust fault over several earthquake cycles terra nova 24 357 362 2012 abstract the friction coefficient is a key parameter for the slip evolution of faults but how temporal changes in friction affect fault slip is still poorly known by using three dimensional numerical models with a thrust fault that is alternately locked and released we show that variations in the friction coefficient affect both coseismic and long term fault slip decreasing the friction coefficient by 5 while keeping the duration of the interseismic phase constant leads to a four fold increase in coseismic slip whereas a 5 increase nearly suppresses slip a gradual decrease or increase of friction over several earthquake cycles 1 5 per earthquake considerably alters the cumulative fault slip in nature the slip deficit surplus resulting from variations in the friction coefficient would presumably be compensated by a longer shorter interseismic phase but the magnitude of the changes required for compensation render variations of the friction coefficient of 5 unlikely

integration of paleoseismic data from multiple sites to develop an objective earthquake chronology application to the weber segment of the wasatch fault zone utah we present a method to evaluate and integrate paleoseismic data from multiple sites into a single objective measure of earthquake timing and recurrence on discrete segments of active faults we apply this method to the weber segment ws of the wasatch fault zone using data from four fault trench studies completed between 1981 and 2009 after systematically reevaluating the stratigraphic and chro nologic data from each trench site we constructed time stratigraphic oxcal models that yield site probability density functions pdfs of the times of individual earth quakes we next qualitatively correlated the site pdfs into a segment wide earthquake chronology which is supported by overlapping site pdfs large per event displace ments and prominent segment boundaries for each segment wide earthquake we computed the product of the site pdf probabilities in common time bins which emphasizes the overlap in the site earthquake times and gives more weight to the narrowest best defined pdfs the product method yields smaller earthquake timing uncertainties compared to taking the mean of the site pdfs but is best suited to earth quakes constrained by broad overlapping site pdfs we calculated segment wide earthquake recurrence intervals and uncertainties using a monte carlo model five surface faulting earthquakes occurred on the ws at about 5 9 4 5 3 1 1 1 and 0 6 ka with the exception of the 1 1 ka event we used the product method to define the earthquake times the revised ws chronology yields a mean recurrence interval of 1 3 kyr 0 7 1 9 kyr estimated two sigma 2 range based on interevent recurrence these data help clarify the paleoearthquake history of the ws including the important question of the timing and rupture extent of the most recent earthquake and are essential to the improvement of earthquake probability assessments for the wasatch front region

contemporary deformation of the wasatch fault utah from gps measurements with implications for interseismic fault behavior and earthquake hazard observations and kinematic analysis 1 contemporary strain accumulation rates of the 350 km long wasatch fault utah have been determined by gps measurements and provide key data for evaluating normal fault behavior and related earthquake hazard assessment this paper presents a complete description of the wasatch gps network data archiving and processing and the measured ground deformation the network spans the wasatch fault in an area 300 km long and 200 km wide in north and central utah and consists of 43 gps sites surveyed in 1992 1993 1994 1995 1999 2001 and 2003 plus 8 permanent gps stations operating continuously beginning 1997 observations across a 65 km wide area centered on the wasatch fault indicate the principal horizontal extension rate of 24 6 nstrain yr with the direction nearly perpendicular to the fault this strain rate corresponds to a horizontal displacement rate of 1 6 0 4 mm yr accommodating 50 of the crustal deformation across the 200 km wide eastern basin range analysis of the spatial variation of the strain rate field reveals that the strain accumulation is concentrated near the wasatch fault which suggests an abrupt transition in the horizontal deformation at the fault between the eastern basin range and the rocky mountains we employed a finite strain model that accounts for simple shear deformation of the hanging wall to compare horizontal extension rates measured by gps with vertical fault displacement rates determined by geologic data our results suggest that the average holocene strain release rate is higher than the contemporary strain loading rate for the wasatch fault if the fault dips less than 30 w but these two rates are consistent if the fault dips more steeply

modeling long term contamination in river systems from historical metal mining heavy metal contamination of sediments within river systems is a major environmental problem around the world deposited as a by product of metal mining contaminated sediments are persistent and widespread frequently affecting large areas of floodplains which makes precise assessments of contamination levels and patterns difficult this paper describes findings from a new generic catchment sediment model called tracer which uses historical mining records to accurately predict present day and future levels and patterns of contamination this model provides detailed views of the extent of contami nation and demonstrates how contaminated sediments form into hot spots which in turn become secondary sources of pollution the exceptional longevity of the contamina tion is also revealed 70 of the deposited contaminants remain within the river system for 200 yr after mine closure simulations of the impact of future climate changes in northern england show that increased flood magnitudes are likely to decrease surface contamination through dilution by cleaner sediment from hillslopes unaffected by mining activity

static coulomb stress changes on faults caused by the 2008 mw 7 9 wenchuan china earthquake abstract the 12 may 2008 mw 7 9 wenchuan earthquake has changed the regional tectonic stress field significantly it is important to know how such a change affects the tectonic loading processes of the faults and therefore the seismic potential of the region utilizing the slip distribution of the wenchuan earthquake as the driving source we compute the changes of coulomb failure stress cfs on the neighborhood faults assuming a friction coefficient of 0 4 our results show that the cfss have increased on average 1 6 104 and 1 8 104 pa at the sw and ne ends of the longmen shan 2 6 104 pa at the western segment of the qinling southern frontal 2 0 104 pa at the northernmost part of the longriba 1 4 104 pa at the southernmost part of the xianshuihe 1 3 104 pa at the southeast end of the east kunlun 9 0 103 pa at the southernmost part of the minjiang 2 9 103 pa at the baiyu and 3 5 103 pa at the longxian baoji faults recurring times of these faults are advanced about 39 and 230 years for the sw and ne segments of the longmen shan 5 5 years toward the east end of the east kunlun and 1 6 years for the se segments of the xianshuihe faults the quake also relaxed the cfs significantly on most part of the minjiang southwest segment of the longriba northwest segment of the xianshuihe southeast segment of the yushu maqu north part of the xiaojinhe daliangshan and anninghe faults with the cfs reductions ranging on average of 1 8 104 2 5 104 7 1 103 2 4 103 1 0 103 1 0 103 and 1 6 103 pa respectively recurring times of these faults are delayed up to 185 years for the south segment of the minjiang up to 18 years for the northeast of the longriba up to 9 8 years for the west qinling northern frontal and up to 2 7 years for the northwest segment of the xianshuihe faults respectively we test sensitivity of the changes of cfs to variations of apparent fiction coefficient and find that the senses of cfs change are almost invariant with except at the minjiang longriba and qinling southern frontal faults where large normal stresses on faults induced by the wenchuan earthquake could play an important role in manifesting cfs change when is large the cfs changes vary slowly along seismogenic depth on most of the receiver faults

comparison of geodetic and geologic data from the wasatch region utah and implications for the spectral character of earth deformation at periods of 10 to 10 million years the wasatch fault and adjacent fault zones provide an opportunity to compare present day deformation rate estimates obtained from space geodesy with geologic displacement rates over at least four temporal windows ranging from the last millennium up to 10 myr the three easternmost gps sites of the basin and range geodetic network bargen at this latitude define a 130 km wide region spanning three major normal faults extending east west at a total rate of 2 7 0 4 mm yr with an average regional strain rate estimated to be 21 4 nstrain yr about twice the basin and range average on the wasatch fault the vertical component of the geologic displacement rate is 1 7 0 5 mm yr since 6 ka 0 6 mm yr since 130 ka and 0 5 0 7 mm yr since 10 ma however it appears likely that at the longest timescale rates slowed over time from 1 0 to 1 4 mm yr between 10 and 6 ma to 0 2 to 0 3 mm yr since 6 ma the cumulative vertical displacement record across all three faults also shows time variable strain release ranging from 2 to 4 mm yr since 10 ka to 1 mm yr averaged over the past 130 kyr conventional earthquake recurrence models reid type behavior would require an accordingly large variation in strain accumulation or loading rate on a 10 kyr timescale for which there appears to be no obvious geophysical explanation alternatively seismic strain release given a wide range of plausible constitutive behaviors for frictional sliding may be clustered on the 10 kyr timescale resulting in the high holocene rates with comparatively low uniform strain accumulation rates on the 100 kyr timescale wallace type behavior the latter alternative combined with observations at the million year timescale and the likelihood of a significant contribution of postseismic transients implies maxima of spectral amplitude in the velocity field at periods of 10 myr variations in tectonic loading 10 kyr clustered strain release and of 100 years postseismic transients if so measurements of strain accumulation and strain release may be strongly timescale dependent for any given fault system

an elusive blind thrust fault beneath metropolitan los angeles seismic reflection profiles petroleum wells and relocated earthquakes reveal the presence of an active blind thrust fault beneath metropolitan los angeles a segment of this fault likely caused the 1987 whittier narrows magnitude 6 0 earthquake mapped sizes of other fault segments suggest that the system is capable of much larger magnitude 6 5 to 7 and more destructive earthquakes

holocene behavior of the brigham city segment implications for forecasting the next large magnitude earthquake on the wasatch fault zone utah the brigham city segment bcs the northernmost holocene active segment of the wasatch fault zone wfz is considered a likely location for the next big earthquake in northern utah we refine the timing of the last four surface rupturing m w 7 earthquakes at several sites near brigham city be1 2430 250 be2 3490 180 be3 4510 530 and be4 graphic 1 b p and calculate mean recurrence intervals 1060 1500 yr that are greatly exceeded by the elapsed time 2500 yr since the most recent surface rupturing earthquake mre an additional rupture observed at the pearsons canyon site pc1 graphic 2 b p near the southern segment boundary is probably spillover rupture from a large earthquake on the adjacent weber segment our seismic moment calculations show that the pc1 rupture reduced accumulated moment on the bcs about 22 a value that may have been enough to postpone the next large earthquake however our calculations suggest that the segment currently has accumulated more than twice the moment accumulated in the three previous earthquake cycles so we suspect that additional interactions with the adjacent weber segment contributed to the long elapse time since the mre on the bcs our moment calculations indicate that the next earthquake is not only overdue but could be larger than the previous four earthquakes displacement data show higher rates of latest quaternary slip 1 3 mm yr along the southern two thirds of the segment the northern third likely has experienced fewer or smaller ruptures which suggests to us that most earthquakes initiate at the southern segment boundary online material cross sections age estimates evaluation of box elder delta earthquake chronology code for oxcal models trench logs sources of surface offset data and description of call fort gravel pit fault exposures 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif

epigenetic nature of the bif hosted gold mineralization at ajjanahalli southern india evidence from ore petrography and fluid inclusion studies comment see nabarun pal and biswajit mishra 2003 gondwana research v 6 pp 531 540

heavy metal trends in floodplain sediments and valley fill river lahn germany abstract sampling along the river lahn a major tributary to the river rhine that flows through an agrarian region of west central germany reveals that heavy metal pollution occurs outside major industrial regions and mined landscapes along a 60 km reach of the river between marburg and wetzlar mean concentrations of cu pb and zn at depths of 5 and 15 cm in four floodplain transects were greater than background levels concentrations declined sharply between 15 and 25 cm laterally concentrations peaked at the bank top and in the near channel zone of the floodplain beyond the near channel zone generally up to 100 m from the channel concentrations were much less and fairly uniform to the valley wall the clustering of metals close to the channel suggests that they are a fluvial rather than an eolian deposit during floods of a moderate magnitude sediments and attached metals are deposited soon after the river overtops its banks although the overall store of metals in the valley is less than that along the rhine near channel metal concentrations are similar to those along rivers draining major industrial and mined areas

uniform california earthquake rupture forecast version 2 ucerf 2 the 2007 working group on california earthquake probabilities wgcep 2007 presents the uniform california earthquake rupture forecast version 2 ucerf 2 this model comprises a time independent poisson process earthquake rate model developed jointly with the national seismic hazard mapping program and a time dependent earthquake probability model based on recent earthquake rates and stress renewal statistics conditioned on the date of last event the models were developed from updated statewide earthquake catalogs and fault deformation databases using a uniform methodology across all regions and implemented in the modular extensible open seismic hazard analysis framework the rate model satisfies integrating measures of deformation across the plate boundary zone and is consistent with historical seismicity data an overprediction of earthquake rates found at intermediate magnitudes 6 5 m 7 0 in previous models has been reduced to within the 95 confidence bounds of the historical earthquake catalog a logic tree with 480 branches represents the epistemic uncertainties of the full time dependent model the mean ucerf 2 time dependent probability of one or more m 6 7 earthquakes in the california region during the next 30 yr is 99 7 this probability decreases to 46 for m 7 5 and to 4 5 for m 8 0 these probabilities do not include the cascadia subduction zone largely north of california for which the estimated 30 yr m 8 0 time dependent probability is 10 the m 6 7 probabilities on major strike slip faults are consistent with the wgcep 2003 study in the san francisco bay area and the wgcep 1995 study in southern california except for significantly lower estimates along the san jacinto and elsinore faults owing to provisions for larger multisegment ruptures important model limitations are discussed

a combined flood surface and geochemical analysis of metal fluxes in a historically mined region a case study from the new world mining district montana remediation of environmental damage due to mining activities requires distinguishing anthropogenic alteration from natural baseline conditions through icp oes analyses of the 63 m fraction of overbank sediments dating from 8 000 years to the present the development of a regional flood probability model traditional topographic surveying and the use of flood surface modeling it is shown that the combination of hydraulic modeling and geochemical analysis of sediments is an effective tool for determining remediation strategies this combination provides a means of distinguishing natural from anthropogenic sediments in a naturally metal rich region delineating zones of sediments with elevated metal concentrations and creating an accurate estimate for appropriate remediation specifically the distribution of metals in fisher creek of the new world mining district montana suggests the following 1 the glengarry adit is currently a point source of metal contamination the present surface distribution of metals in the 63 m fraction of overbank deposits is related to the probability of a surface being covered by water during a flood of a given recurrence probability 2 sediments with elevated metal concentrations pre date mining activity 3 pre mining overbank sediments contain metal concentrations as great or greater than post mining sediments 4 remediation of sediments with the highest concentration of metals requires assessment of sediments deposited above the 100 year flood surface

mine tailings dams characteristics failure environmental impacts and remediation on a global scale demand for the products of the extractive industries is ever increasing extraction of the targeted resource results in the concurrent production of a significant volume of waste material including tailings which are mixtures of crushed rock and processing fluids from mills washeries or concentrators that remain after the extraction of economic metals minerals mineral fuels or coal the volume of tailings is normally far in excess of the liberated resource and the tailings often contain potentially hazardous contaminants a priority for a reasonable and responsible mining organization must be to proactively isolate the tailings so as to forestall them from entering groundwaters rivers lakes and the wind there is ample evidence that should such tailings enter these environments they may contaminate food chains and drinking water furthermore the tailings undergo physical and chemical change after they have been deposited the chemical changes are most often a function of exposure to atmospheric oxidation and tends to make previously perhaps safely held contaminants mobile and available if the tailings are stored under water contact with the atmosphere is substantially reduced thereby forestalling oxygen mediated chemical change it is therefore accepted practice for tailings to be stored in isolated impoundments under water and behind dams however these dams frequently fail releasing enormous quantities of tailings into river catchments these accidents pose a serious threat to animal and human health and are of concern for extractive industries and the wider community it is therefore of importance to understand the nature of the material held within these dams what best safety practice is for these structures and should the worst happen what adverse effects such accidents might have on the wider environment and how these might be mitigated this paper reviews these factors covering the characteristics types and magnitudes environmental impacts and remediation of mine tailings dam failures

modeling the holocene slip history of the wasatch fault utah coseismic and postseismic coulomb stress changes and implications for paleoseismicity and seismic hazard

coulomb stress evolution in a diffuse plate boundary 1400 years of earthquakes in eastern california and western nevada usa diffuse plate boundaries are characterized by deformation distributed over a wide area in a complex network of active faults and by relatively low strain rates these characteristics make it difficult to understand the spatial and temporal distribution of seismicity the area east of the sierra nevada between longitudes 121 degrees w and 116 degrees w is part of a diffuse plate boundary at least 17 major surface rupturing earthquakes have happened here in the last 1400 years our purpose is to determine whether these events influence each other or whether they are randomly distributed in time and space we model the evolution of coseismic and postseismic coulomb failure stress changes delta cfs produced by these earthquakes and we also model interseismic stresses on the entire fault network our results show that 80 of the earthquake ruptures are located in areas of combined coseismic and postseismic delta cfs 0 2 bar this relationship is robust as shown by the control tests that we carried out using random earthquake sequences we also show that the fish lake valley pyramid lake and honey lake faults have accumulated 45 37 and 27 bars respectively of total delta cfs i e coseismic postseismic interseismic in the last 1400 years such values are comparable to the average stress drop in a major earthquake and these three faults may be therefore close to failure

crust and mantle structure across the basin and range colorado plateau boundary at 37 n latitude and implications for cenozoic extensional mechanism we present new evidence on the seismic velocity and density of the crust and upper mantle along a 200 km long transect across the eastern basin and range and western colorado plateau at 37 n latitude receiver functions computed from the p waveforms recorded with 10 portable broadband stations deployed along the transect were used to estimate crustal thickness variations the crust is 30 35 km thick within the eastern basin and range and increases over a distance of 100 km at the western edge of the colorado plateau reaching a maximum of approximately 45 km east of the hurricane fault the timing of crustal multiples within the reciever functions were used to estimate the v p v s of the crust along the profile and we found that the western colorado plateau crust is characterized by a high poisson s ratio 0 28 0 29 indicative of a crust with an average mafic composition we estimated the upper mantle lid thickness along our profile based on teleseismic p wave travel times and constraints provided by gravity data our data and available geophysical constraints are most consistent with a lithosphere that thickens from an average thickness of 60 km beneath the basin and range to 100 km beneath the western colorado plateau although the basin and range lithosphere may have significant thickness variations the thick strong mafic crust and thicker mantle lid under the colorado plateau can account for the relative geologic stability and subdued magmatism of the plateau during laramide compression and cenozoic extension compared to surrounding regions the crustal and lithospheric thinning across the tectonic boundary occurs over a short distance 100 km suggesting it is a geologically young feature produced by a predominantly mechanical response to late cenozoic extension our new lithosphere model at 37 n latitude is consistent with the existence in early cenozoic time of a flat subducted slab at 100 km depth and a relict sevier laramide 50 60 km thick crustal welt and 60 100 pure shear extension values of 1 6 2 0 during the late cenozoic

postglacial slip rate increase on the teton normal fault northern basin and range province caused by melting of the yellowstone ice cap and deglaciation of the teton range along the eastern front of the teton range wyoming prominent fault scarps offset pinedale deposits by up to 30 m and document that multiple earthquakes ruptured the range bounding teton normal fault after the last glacial period paleoseismological data suggest that 70 of the postglacial slip on the southern teton fault accumulated during or shortly after deglaciation before 8 ka here we use a three dimensional fi nite element model to show that melting of the yellowstone ice cap and the valley glaciers in the teton range may have caused the postglacial slip rate increase on the teton fault during deglaciation slip on our model fault accelerates by a factor of 6 with respect to the long term rate our model further shows that the impact of the melting yellowstone ice cap on fault slip increases along strike of the fault from south to north and is everywhere larger than the effect of the former valley glaciers in the teton range the results demonstrate that postglacial slip on faults in glaciated regions may not have been uniform through time rather a signifi cant fraction of slip may have accumulated within a few thousand years after the last glaciation we hypothesize that the rebound caused by the yellowstone ice cap has also triggered clusters of earthquakes on other normal faults in the surrounding basin and range province

large mid holocene and late pleistocene earthquakes on the oquirrh fault zone utah abstract the oquirrh fault zone is a range front normal fault that bounds the east side of tooele valley and it has long been recognized as a potential source for large earthquakes that pose a significant hazard to population centers along the wasatch front in central utah scarps of the oquirrh fault zone offset the provo shoreline of lake bonneville and previous studies of scarp morphology suggested that the most recent surface faulting earthquake occurred between 9000 and 13 500 years ago based on a potential rupture length of 12 to 21 km from previous mapping moment magnitude mw estimates for this event range from 6 3 to 6 6 in contrast our results from detailed mapping and trench excavations at two sites indicate that the most recent event actually occurred between 4300 and 6900 yr b p 4800 and 7900 cal b p and net vertical displacements were 2 2 to 2 7 m much larger than expected considering estimated rupture lengths for this event empirical relations between magnitude and displacement yield mw 7 0 to 7 2 a few short discontinuous fault scarps as far south as stockton utah have been identified in a recent mapping investigation and our results suggest that they may be part of the oquirrh fault zone increasing the total fault length to 32 km these results emphasize the importance of integrating stratigraphic and geomorphic information in fault investigations for earthquake hazard evaluations at both the big canyon and pole canyon sites trenches exposed faulted lake bonneville sediments and thick wedges of fault scarp derived colluvium associated with the most recent event bulk sediment samples from a faulted debris flow deposit at the big canyon site yield radiocarbon ages of 7650 90 yr b p and 6840 100 yr b p all lab errors are 1 a bulk sediment sample from unfaulted fluvial deposits that bury the fault scarp yield a radiocarbon age estimate of 4340 60 yr b p stratigraphic evidence for a pre bonneville lake cycle penultimate earthquake was exposed at the pole canyon site and although displacement is not well constrained the penultimate event colluvial wedge is comparable in size to the most recent event wedges charcoal from a marsh deposit which overlies the penultimate event colluvium and was deposited during the bonneville lake cycle transgression yields an ams radiocarbon age of 20 370 120 yr b p multiple charcoal fragments from fluvial deposits faulted during the penultimate event yield an ams radiocarbon age of 26 200 200 yr b p indirect stratigraphic evidence for an antepenultimate event was also exposed at pole canyon charcoal from fluvial sediments overlying the eroded free face for this event yields an ams age of 33 950 1160 yr b p providing a minimum limiting age on the antepenultimate event ages for the past two events on the oquirrh fault zone yield a recurrence interval of 13 300 to 22 100 radiocarbon years and estimated slip rates of 0 1 to 0 2 mm yr temporal clustering of earthquakes on the nearby wasatch fault zone in the late holocene does not appear to have influenced activity on the oquirrh fault zone however consistent with findings on the wasatch fault zone and with some other quaternary faults within the bonneville basin we found evidence for higher rates of activity during interpluvial periods than during the bonneville lake cycle if a causal relation between rates of strain release along faults and changes in loads imposed by the lake does exist it may have implications for fault dips and mechanics however our data are only complete for one deep lake cycle the past 32 000 radiocarbon years and whether this pattern persisted during the previous cutler dam and little valley deep lake cycles is unknown

transient stress coupling between the 1992 landers and 1999 hector mine california earthquakes a three dimensional finite element model fem of the mojave block region in southern california is constructed to investigate transient stress coupling between the 1992 landers and 1999 hector mine earthquakes the fem simulates a poroelastic upper crust layer coupled to a viscoelastic lower crust layer which is decoupled from the upper mantle fem predictions of the transient mechanical be havior of the crust are constrained by global positioning system gps data inter ferometric synthetic aperture radar insar images fluid pressure data from water wells and the dislocation source of the 1999 hector mine earthquake two time dependent parameters hydraulic diffusivity of the upper crust and viscosity of the lower crust are calibrated to 10 2 m 2 sec 1 and 5 10 18 pasec respectively the hydraulic diffusivity is relatively insensitive to heterogeneous fault zone permeabil ity specifications and fluid flow boundary conditions along the elastic free surface at the top of the problem domain the calibrated fem is used to predict the evolution of coulomb stress during the interval separating the 1992 landers and 1999 hector mine earthquakes the predicted change in coulomb stress near the hypocenter of the hector mine earthquake increases from 0 02 to 0 05 mpa during the 7 yr interval separating the two events this increase is primarily attributed to the recovery of decreased excess fluid pressure from the 1992 landers coseismic undrained strain field coulomb stress predictions are insensitive to small variations of fault plane dip and hypocentral depth estimations of the hector mine rupture

fluid inclusion record of the hypozonal orogenic renco gold deposit zimbabwe during the retrograde p t evolution the hypozonal renco gold deposit in zimbabwe is hosted by a shear zone system cutting granulite facies enderbites the geologic history of the region testifies to a polyphase tectonometamorphic evolution along the exhumation path three major events are notable during which fluid inclusions could have been formed detailed petrographic work and comparison of calculated isochores with the p t evolution allows correlation of inclusion formation with the tectonometamorphic evolution fluid inclusions in the mineralized lithologies of the renco gold mine are dominated by carbonic inclusions of highly variable densities the high density carbonic inclusions are related to the peak of metamorphism their lower density counterparts show a bimodal occurrence some are re equilibrated equivalents of the inclusions trapped at peak metamorphic conditions whereas others clearly post date this event and are related to gold mineralization the latter type of carbonic inclusions occurs in distinct microstructural domains of quartz crystals i e subgrain grain boundaries therefore these inclusions are interpreted to have formed because of selective trapping of co2 from a mixed h2o co2 low salinity ore fluid all the aqueous inclusions observed at renco can be attributed to a late retrograde greenschist facies overprint

gravitational viscoelastic postseismic relaxation on a layered spherical earth viscoelastic relaxation of a ductile asthenosphere underlying a purely elastic plate is a strong candidate process for explaining anomalous rates of crustal deformation observed following large earthquakes the nongravitational treatment of pollitz 1992 which is valid on a global scale and includes the effects of compressibility is here extended to permit the calculation of gravitational viscoelastic relaxation for a specified spherically layered viscoelastic rheology following an earthquake in an elastic layer the simple approximations we adopt make the resulting treatment particularly suitable for near field calculations for an asthenosphere with a maxwell rheology the effect of gravitational coupling is manifested only many relaxation times after the earthquake as obtained by previous investigators its effect is generally to speed up the long wavelength component of the relaxation process and attenuate the overall vertical displacement pattern several subtle features common to the relaxation behavior from several different fault types thrust rift and strike slip are identified the effect of gravitational coupling on horizontal displacements is consistent with flexure of the upper elastic plate driven by the corresponding effects on the vertical displacement stress diffusion away from the source region generally exhibits pulse like behavior which is dispersive in both space and time if the asthenosphere is confined to a relatively narrow channel then the dispersion branches governing relaxation are radically altered and stress diffusion effects far from the coseismic rupture zone exhibit a complicated time dependence reflecting the competing tendencies of toroidal and spheroidal mode relaxation

geothermal spring causes arsenic contamination in river waters of the southern tibetan plateau china large numbers of as enriched geothermal springs are distributed at the southern tibetan plateau and their influence on river water is still not clear lhasa river and its tributary duilong qu located at downstream of the largest geothermal spring of the tibetan plateau were selected for sampling during monsoon and non monsoon seasons dissolved trace elements b cr ni cu zn as cs ba and u were measured in river water samples by icp ms the results show that due to contribution of geothermal spring as levels of duilong qu 205 6 g l and lhasa river 12 7 g l were higher during non monsoon season than that of who guideline for drinking water 10 g l accordingly as level of river water was lower during the monsoon season than that of the non monsoon season due mainly to dilution process therefore although tibetan rivers are generally considered as free of contamination geothermal springs cause as contamination of river water at some local regions and may harm the local residents further research is needed in other parts of the plateau to determine whether as level of groundwater of the related region is high

use of mining contaminated sediment tracers to investigate the timing and rates of historical flood plain sedimentation abstract changes in land use practices following european settlement in the 1830s produced accelerated sedimentation on virtually all valley floors in the blue river watershed wisconsin the contamination of sediments by pb and zn mining allowed us to calculate cross valley rates of flood plain sedimentation for three time periods the pre mining period 1830 1900 the mining period 1900 1920 and the post mining period 1920 1997 most of the eight valley floors examined contained multiple presettlement surfaces significantly higher rates of sedimentation occurred on the lower flood plain surfaces while the terraces were high enough to prevent sedimentation from most floods higher rates of sedimentation on the lower surfaces eventually reduced valley floor relief and consequently lateral differences in sedimentation rates tributaries and larger valleys downstream exhibited differences in the timing and rates of historical flood plain sedimentation while rates of sedimentation were high during the pre mining period in tributary valleys the lower valleys were receiving little or no pre mining alluvium little pre mining alluvium was found in mid basin reaches suggesting that most of the pre mining sedimentation was limited to headwater locations during the mining period lateral channel migration and the development of meander belts increased the conveyance capacity of tributary and mid basin channels which decreased overbank flooding and produced lower rates of sedimentation during the post mining period the meander belt channels also had an effect on the lower portion of the watershed by increasing flood magnitudes and the transport of sediment downstream thereby shifting the locus of sedimentation from the tributaries to the larger lower valleys sedimentation rates in the largest most downstream site were an order of magnitude higher during the post mining period than any of the sites upstream

fluid immiscibility in natural processes use and misuse of fluid inclusion data ii interpretation of fluid inclusion data in terms of immiscibility abstract phase equilibrium analysis of the relevant systems together with the application of the principles of chemical equilibrium put severe constraints on the interpretation of fluid inclusion data in terms of immiscibility in part i following from that point the major limits on the accuracy and even the validity of fluid inclusion quantitative data and their interpretation in terms of fluid composition and density are briefly discussed the practical implications of the general constraints temperature pressure topology of the fluid systems are envisaged emphasis is laid on some important consequences such as the use of isochore intercepts and the possible resulting interpretation of fluid mixing rather than unmixing the case of highly saline inclusions the identification and interpretation of heterogeneous trapping the composition and density constraints on coexisting fluids are presented and illustrated by natural examples taking into account all the measurable parameters in fluid inclusions volume temperature and nature of phase transitions more or less complete individual spectroscopic analyses all the available experimental data and all the theoretical constraints may be long and difficult however it is most generally very informative and productive although part of these data is often sufficient to deny unmixing nevertheless a final example on metamorphic fluids demonstrates how such an approach can prove and also characterize a fluid unmixing during a geologic process

anisotropic shear strength characteristics of a tailings sand the deposition process of tailings in a tailings dam may lead to the anisotropy of mechanical properties of tailings to investigate the anisotropic shear strength characteristics of a tailings sand samples deposited under gravity were sheared in a modified direct shear apparatus along different orientations of the shear planes relative to the bedding plane the experimental results reveal that the anisotropy has a substantial effect on the peak shear strength of the tailings sand leading to a variation in peak friction angle of 10 it is found that the effect of anisotropy on the peak shear strength of the tailings sand is mainly attributed to the effect of anisotropy on soil dilatancy on the other hand the effect of anisotropy on the residual friction angle of the tailing sand is relatively smaller likely due to the partial erasure of anisotropy at large shear deformation the degree of anisotropy is reduced by an increase in normal stress to achieve more accurate stability analysis of tailings dams it is suggested to take into account the shear strength anisotropy of tailings soils

chronology of lake bonneville 30 000 to 10 000 yr b p abstract 368 radiocarbon ages between 30 and 10 cal ka for samples collected from outcrops and shorelines from the lake bonneville basin have been compiled for this paper samples include 1 organic materials from sources outside the lake such as wood charcoal plant fragments from emergent aquatics and dispersed wetland organics and 2 carbonate materials deposited in the lake such as mollusk shells tufa charophyte debris ooids and marl in general organic materials provide rather than precise ages for lacustrine events but their interpretation is less complicated than interpretation of results from carbonate samples the data set shows evidence of contamination of different carbonate samples with both younger carbon and older carbon for example a radiocarbon reservoir at certain places within the lake during the middle transgressive phase accounts for ages of mollusk shells that are older than basal wood ages at similar altitudes the large number of ages permits an accurate reconstruction of the lake chronology conflicts between ages can be detected and reliable ages can be meaningfully integrated in interpretations if fewer ages were available the chronology might look simpler but its accuracy would be unknown

structural analysis of the brigham city weber segment boundary zone wasatch normal fault utah implications for fault growth and structure we investigate the history kinematics principal stress orientations and geometry of deformation at the end of a bent normal fault segment of the wasatch fault zone utah three fault types developed in archean crystalline rocks reflect progressive uplift of fault related footwall rocks chlorite breccias and phyllonites reflect deep level reaction assisted plastic deformation along the north striking part of the segment planar fretted faults which formed by cataclasis cut the phyllonites and breccias and are developed throughout the footwall of the segment youngest faults are hematitecoated extremely narrow polished surfaces slip vectors and kinematic analyses of small faults developed in the footwall indicate oblique normal slip along the north striking portion of the segment slip vectors and fault orientation along the northwest striking portion of the segment reflect complexly oriented slip on faults which strike subparallel and at high angles to the main fault trace yet slip is confined to a broad fault parallel zone small faults at the southernmost tip of the segment indicate a strong influence of the north striking weber segment to the south inversion of fault data for principal stress orientations document complexly oriented principal stresses through the segment boundary zone and suggest that 3 may have reoriented approximately 60 over the life of the segment subsurface structure combined with small fault data indicate the segment boundary is comprised of a southwest plunging bedrock high which is reflected by a sharp bend in the brigham city segment the southern end of the brigham city segment may have started as a straight north striking fault which has bent due to changes in stress orientations and or interaction with the adjacent weber segment

slip rate variations on normal faults during glacial interglacial changes in surface loads geologic and palaeoseismological data document a marked increase in the slip rates of the wasatch fault and three adjacent normal faults in the basin and range province during the late pleistocene early holocene epochs the cause of this synchronous acceleration of fault slip and the subsequent clustering of earthquakes during the holocene has remained enigmatic although it has been suggested that the coincidence between the acceleration of slip and the shrinkage of lake bonneville after the last glacial maximum may indicate a causal relationship here we use finite element models of a discrete normal fault within a rheologically layered lithosphere to evaluate the relative importance of two competing processes that affect fault slip postglacial unloading the removal of mass which decreases the slip rate and lithospheric rebound which promotes faster slip we show that lithospheric rebound caused by regression of lake bonneville and deglaciation of adjacent mountain ranges provides a feasible mechanism for the high holocene rates of faulting in the wasatch region our analysis implies that climate controlled changes in loads applied to earth s surface may exert a fundamental control on the slip history of individual normal faults

aquifer deformation and active faulting in salt lake valley utah usa abstract aquifers and fault zones may interact through groundwater flow and stress redistribution yet their spatiotemporal relationship remains enigmatic here we quantify changes in water storage and associated stress along the wasatch fault zone in salt lake valley recently shaken by a m5 7 earthquake on march 18th 2020 ground deformation mapped by sentinel 1 sar imagery 2014 2019 reveals an elongated area with 50 mm seasonal uplift corresponding to 0 03 0 06 km3 water storage cycles phase shifts across active faults in both water level and deformation suggest control by the low permeability structures the seasonal stress changes on the adjoining faults from poroelastic volume strain are two orders of magnitude larger than those from hydrological surface loading but both are small compared to the annual increase of tectonic loading at seismogenic depths historic seismic events limited in number do not exhibit statistically significant annual periodicity and hydrological modulation of microseismicity or triggering of the recent m5 7 event is not evident

grouping and migration of surface faulting and variations in slip rates on faults in the great basin province abstract nonuniformity of the occurrence of large slip events producing surface ruptures on seismogenic faults and variations in slip rate probably characterize seismogenic faulting in the great basin province western united states examples include the grouping of faulting events along the lost river fault idaho changes in tilt rates of the east range and cortez mountains nevada extension of slip along a fault on the northwest flank of the humboldt range nevada and migration or shifting of slip back and forth from one fault to another along subparallel range front faults in dixie valley nevada

comment on the paper by schmidt mumm et al high co2 content of fluid inclusions in gold mineralisations in the ashanti belt ghana a new category of ore forming fluids mineralium deposita 32 107 118 1997

the bronzewing lode gold deposit western australia p t x evidence for fluid immiscibility caused by cyclic decompression in gold bearing quartz veins abstract the bronzewing lode gold deposit is located in the yandal greenstone belt in the yilgarn craton of western australia gold mineralization is hosted in tholeiitic basalt that is metamorphosed to greenschist facies individual ore bodies are controlled by a complex gold bearing quartz vein system that comprises shear and extension veins formed during a progressive d2 deformation event gold is localized in quartz along fractures and deformed grain boundaries and is interpreted to have formed late in the formation of the veins detailed petrography and microthermometry on primary pseudosecondary and secondary fluid inclusions trapped in gold bearing shear and extension veins revealed five types of fluid inclusions 1 co2 ch4 h2o nacl inclusions of variable salinity 0 1 to 17 5 eq wt nacl containing between 10 and 99 mol co2 and molar volumes that range from 22 to 76 cm3 2 h2o nacl inclusions of variable salinity 0 4 to 22 1 eq wt nacl 3 co2 ch4 inclusions with up to 58 mol ch4 and molar volumes between 54 and 73 cm3 4 ch4 h2o inclusions with ch4 ranging from 80 to 90 mol and 5 ch4 inclusions with low molar volumes of 19 to 23 cm3 types 1 2 and 3 constitute a fluid inclusion assemblage that occurs consistently in primary pseudosecondary and secondary trails and clusters within the gold bearing quartz vein system these co existing fluids are interpreted to have formed by fluid immiscibility of a low salinity homogeneous parent fluid at about 300 c and 1500 bars locally type 2 fluid inclusions exhibit total homogenization temperatures that are on average 100 c less than the co genetically trapped type 1 aqueous carbonic inclusions this discrepancy is interpreted to have involved co2 effervescence in response to fluid pressure fluctuations types 4 and 5 fluid inclusions are rare and are only present locally in secondary trails and clusters in extension veins significant pressure fluctuations but relatively constant homogenization temperatures for types 1 2 and 3 fluid inclusions suggest that cyclic decompression of the hydrothermal fluids due to seismic activity along the shear zones that host the gold bearing veins triggered fluid immiscibility the process of fluid immiscibility and subsequent lowering of gold solubility is interpreted to be the most efficient precipitation mechanism for gold in the d2 shear zone hosted vein system at bronzewing

rheology of the lithosphere inferred from postseismic uplift following the 1959 hebgen lake earthquake 1 we have modeled the broad postseismic uplift measured by geodetic leveling in the epicentral area of the 1959 mw 7 3 hebgen lake montana earthquake a normal faulting event in the northern basin and range province to fit the observed uplift we calculate synthetic postseismic deformation using the relaxation response of a gravitational viscoelastic earth to the earthquake for a model with an elastic plate overlying a viscoelastic half space we find that the elastic thickness is 38 8 km which is close to the local crustal thickness the half space viscosity is estimated at 4 1018 0 5 pa s the leveling data do not require a viscous lower crust but permit a lower bound viscosity of 1020 pa s the observed broad uplift cannot be explained by physically plausible afterslip on and below the coseismic fault however local deformation across the coseismic surface rupture requires shallow afterslip reaching the surface the postseismic deformation induced by the estimated viscoelastic structure decays exponentially with a time constant of 15 years because of coupling between the elastic layer and the viscoelastic substrate this relaxation time is significantly longer than the 2 year maxwell relaxation time of the viscous half space itself our result suggests the importance of postseismic relaxation in interpreting high precision global positioning system velocities for example our model results suggest that postseismic transient velocities from both the 1959 hebgen lake and the 1983 mw 6 9 borah peak earthquakes are currently as large as 1 2 mm yr

fluids in metamorphic rocks abstract basic principles for the study of fluid inclusions in metamorphic rocks are reviewed and illustrated a major problem relates to the number of inclusions possibly formed on a wide range of p t conditions having also suffered in most cases extensive changes after initial trapping the interpretation of fluid inclusion data can only be done by comparison with independent p t estimates derived from coexisting minerals but this requires a precise knowledge of the chronology of inclusion formation in respect to their mineral host the three essential steps in any fluid inclusion investigation are described observation measurements and interpretation observation with a conventional petrographic microscope leads to the identification and relative chronology of a limited number of fluid types same overall composition eventually changes in fluid density for the chronology the notion of gis group of synchronous inclusions is introduced it should serve as a systematic basis for the rest of the study microthermometry measurements completed by nondestructive analyses mostly micro raman specify the composition and density of the different fluid types the major problem of density variability can be significantly reduced by simple considerations of the shape of density histograms allowing elimination of a great number of inclusions having suffered late perturbations finally the interpretation is based on the comparison between few isochores representative of the whole inclusion population and p t mineral data essential is a clear perception of the relative chronology between the different isochores when this is possible as illustrated by the complicated case of the granulites from central kola peninsula a good interpretation of the fluid inclusion data can be done if not fluid inclusions will not tell much about the metamorphic evolution of the rocks in which they occur

why earthquake hazard maps often fail and what to do about it abstract the 2011 tohoku earthquake is another striking example after the 2008 wenchuan and 2010 haiti earthquakes of highly destructive earthquakes that occurred in areas predicted by earthquake hazard maps to be relatively safe here we examine what went wrong for tohoku and how this failure illustrates limitations of earthquake hazard mapping we use examples from several seismic regions to show that earthquake occurrence is typically more complicated than the models on which hazard maps are based and that the available history of seismicity is almost always too short to reliably establish the spatiotemporal pattern of large earthquake occurrence as a result key aspects of hazard maps often depend on poorly constrained parameters whose values are chosen based on the mapmakers preconceptions when these are incorrect maps do poorly this situation will improve at best slowly owing to our limited understanding of earthquake processes however because hazard mapping has become widely accepted and used to make major decisions we suggest two changes to improve current practices first the uncertainties in hazard map predictions should be assessed and clearly communicated to potential users recognizing the uncertainties would enable users to decide how much credence to place in the maps and make them more useful in formulating cost effective hazard mitigation policies second hazard maps should undergo rigorous and objective testing to compare their predictions to those of null hypotheses including ones based on uniform regional seismicity or hazard such testing which is common and useful in similar fields will show how well maps actually work and hopefully help produce measurable improvements there are likely however limits on how well hazard maps can ever be made because of the intrinsic variability of earthquake processes

three dimensional numerical modeling of slip rate variations on normal and thrust fault arrays during ice cap growth and melting 1 changes in the volumes of ice caps considerably alter the stress state of the lithosphere by generating a transient signal that is added to the tectonic background stress field these stress field changes in turn affect crustal deformation and in particular the slip behavior of existing faults here we use three dimensional finite element models to investigate how arrays of normal and thrust faults near a growing and subsequently melting ice cap are influenced in their slip evolution the results show that regardless of fault dip both types of faults experience a decrease in their slip rate during ice cap advance and an increase in their slip rate during ice cap retreat if they are located beneath the ice cap in contrast faults outside the ice cap that are loaded on their footwall or hanging wall only show the opposite pattern their slip rate increases during glacial loading and decreases during subsequent unloading if the load is located along strike of the fault that is at one of its tips the slip behavior of normal and thrust faults is different the normal fault shows a slip rate increase during unloading the thrust fault during loading our results explain the location and timing of deglaciation induced paleoearthquakes in scandinavia and the contrasting slip histories reported from normal faults in the basin and range province which are located at different positions relative to the former yellowstone ice cap more generally our findings imply that a uniform slip behavior of faults in formerly glaciated regions should not be expected

fault segmentation new concepts from the wasatch fault zone utah usa the question of whether structural segment boundaries along multisegment normal faults such as the wasatch fault zone wfz act as persistent barriers to rupture is critical to seismic hazard analyses we synthesized late holocene paleoseismic data from 20 trench sites along the central wfz to evaluate earthquake rupture length and fault segmentation for the youngest 3 ka and best constrained earthquakes differences in earthquake timing across prominent primary segment boundaries especially for the most recent earthquakes on the north central wfz are consistent with segment controlled ruptures however broadly constrained earthquake times dissimilar event times along the segments the presence of smaller scale subsegment boundaries and areas of complex faulting permit partial segment and multisegment e g spillover ruptures that are shorter 20 40 km or longer 60 100 km than the primary segment lengths 35 59 km we report a segmented wfz model that includes 24 earthquakes since 7 ka and yields mean estimates of recurrence 1 1 1 3 kyr and vertical slip rate 1 3 2 0 mm yr for the segments however additional rupture scenarios that include segment boundary spatial uncertainties floating earthquakes and multisegment ruptures are necessary to fully address epistemic uncertainties in rupture length we compare the central wfz to paleoseismic and historical surface ruptures in the basin and range province and central italian apennines and conclude that displacement profiles have limited value for assessing the persistence of segment boundaries but can aid in interpreting prehistoric spillover ruptures our comparison also suggests that the probabilities of shorter and longer ruptures on the wfz need to be investigated

time dependent changes in failure stress following thrust earthquakes two dimensional 2 d viscoelastic finite element models were used to calculate the time dependent changes in coulomb failure stresses following thrust earthquakes due to respective effects of relaxation of viscous lower crust or upper mantle and postseismic creep on the main fault or its downdip extension results suggest that thrust earthquakes cause a coseismic increase in coulomb stress along antithetic lobes normal to the slip plane following a quake creep processes that reduce stresses in a ductile lower crust or upper mantle are calculated to cause a transfer of stress to the upper crust under certain conditions transfer of stress may lead to a further buildup of high coulomb stress along the base of the upper crust potentially shortening the time to failure of other faults in the region the conditions under which an antithetic lobe of high coulomb stress are favored to expand at the base of the upper crust postseismically within a few decades include the following the lower crust or upper mantle has an effective viscosity not greater than 1019 pa s the thrust fault has a moderate dip angle 40 50 the brittle ductile transition is deep enough to provide a corridor at the base of the upper crust for expansion and the crust has a low apparent coefficient of friction 0 2 postseismic increases in coulomb stress within the upper crust may also be caused by aseismic creep on the fault stress changes due to this mechanism are maximized with a high apparent coefficient of friction analysis of experimentally determined non newtonian flow laws suggests that wet granitic quartz and feldspar aggregates may have a viscosity of the order of 1019 pa s the calculated rate of stress transfer from a viscous lower crust or upper mantle to the upper crust becomes faster with increasing values of the power law exponent and the presence of a regional compressive strain rate results of this 2 d analysis suggest a potentially important role of viscous flow in controlling time dependent postseismic stress changes that warrant further investigation using 3 d viscoelastic analysis

the impact of tailings dam spills and clean up operations on sediment and water quality in river systems the rios agrio guadiamar aznalcollar spain the aznalcollar tailings dam at boliden apirsa s aznalcollar los frailes ag cu pb zn mine 45 km west of seville spain was breached on 25 april 1998 flooding approximately 4600 hectares of land along the rios agrio and guadiamar with approximately 5 5 million m3 of acidic water and 1 3 106 m3 of heavy metal bearing tailings most of the deposited tailings and approximately 4 7 106 m3 of contaminated soils were removed to the aznalcollar open pit during clean up work undertaken immediately after the spill until january 1999 detailed geomorphological and geochemical surveys of the post clean up channel floodplain and valley floor and sediment and water sampling were carried out in january and may 1999 at 6 reaches representative of the types of river channel and floodplain environments in the rio guadiamar catchment affected by the spill the collected data show that the clean up operations removed enough spill deposited sediment to achieve pre spill metal ag as cd cu pb sb tl zn concentrations in surface sediment these concentrations however are still elevated above pre mining concentrations and emphasise that mining continues to contaminate the agrio guadiamar river system dilution by relatively uncontaminated sediment appears to reduce metal concentrations downstream but increases in metal and as concentrations occur downstream presumably as a result of factors such as sewage and agriculture river water samples collected in may 1999 have significantly greater dissolved concentrations of metals and as than those from january 1999 probably due to greater sulphide oxidation from residual tailings with concomitant release of metals in the warmer early summer months these concentrations are reduced downstream probably by a combination of dilution and removal of metals by mineral precipitation single chemical extractions de ionised water cacl2 0 01 mol l 1 ch3coonh4 1 m ch3coona 1 m and ammonium oxalate 0 2 m on alluvial samples from reaches 1 and 6 the tailings pre spill alluvium and marl have shown that the order of sediment borne contaminant mobility is generally zn cd cu pb as pb and as are relatively immobile except possibly under reducing conditions much of the highly contaminated sediment remaining in the floodplain and channel still contains a large proportion of tailings related sulphide minerals which are potentially reactive and may continue to release contaminants to the agrio guadiamar river system our work emphasises the need for pre mining geomorphological and geochemical data and an assessment of potential contributions of contaminants to river systems from other non mining sources

the 11 april 2012 east indian ocean earthquake triggered large aftershocks worldwide although strong remote aftershocks are exceedingly rare their rate increased fivefold during the six days following the 2012 east indian ocean earthquake perhaps as a result of the strike slip nature of the 2012 event or a build up of close to failure nucleation sites

fault geometry coseismic slip distribution and coulomb stress change associated with the 2009 april 6 mw 6 3 l aquila earthquake from inversion of gps displacements summary the 2009 april 6 mw 6 3 l aquila earthquake occurred within a complex system of nw se trending normal faults in the abruzzi central apennines italy we analyse the coseismic deformation as measured by 70 global positioning system gps stations both from continuous and survey mode networks providing unprecedented details for a moderate normal faulting earthquake in italy from gps measurements we use rectangular uniform slip dislocations embedded in an elastic homogeneous and isotropic half space and a constrained non linear optimization algorithm to solve for the best fitting rectangular dislocation geometry and coseismic slip distribution we use a bootstrap approach to investigate uncertainties in the model parameters and define confidence bounds for all the inverted parameters the rupture occurred on a n129 e striking and 50 southwestward dipping normal fault in agreement with geological observations of surface breaks along the paganica fault our distributed slip model exhibits a zone of relatively higher slip 60 cm between 1 5 and 11 km depth along a roughly downdip nw se elongated patch confined within the fault plane inverted assuming uniform slip the highest slip of the order of 1 m occurred on a 16 km2 area located at 5 km depth se of the mainshock epicentre the analysis of model resolution suggests that slip at depth below 5 km can be resolved only at a spatial scale larger than 2 km so a finer discretization of different asperities within the main patch of coseismic slip is not allowed by gps data we compute the coseismic coulomb stress changes in the crustal volume affected by the major aftershocks and compare the results obtained from the uniform slip and the heterogeneous slip models we find that most of the large aftershocks occurred in areas of coulomb stress increase of 0 2 13 bar and that a deepening of the slip distribution down to a depth greater than 6 km in the se part of the fault plane in agreement with the inverted slip model can explain the deepest april 7 mw 5 3 aftershock

mercury contamination of active channel sediment and floodplain deposits from historic gold mining at gold hill north carolina usa a reconnaissance investigation of mercury contamination associated with historic gold mining in north carolina usa revealed high concentrations of mercury in channel and floodplain sediments downstream from the gold hill mining district the most intense period of mining activities in this region occurred in the 1840s and 1850s when mercury amalgamation was used to recover fine gold particles from milled ore this paper evaluates mercury concentrations measured in active channel sediments and two cores recovered from historic floodplain deposits of the lower portion of dutch buffalo creek mercury concentrations in these cores range from 0 01 to 2 2 mg kg with maximum concentrations more than 35 times background levels a later peak in copper concentrations is associated with the operation of a large copper mine between 1899 and 1906 following the most intense periods of mining both mercury and copper concentrations decrease upcore to constant levels of about twice pre mining background concentrations results suggest that vertical trends in mercury and other trace metals provide a useful tool for interpreting rates of historic floodplain sedimentation in the piedmont of north carolina

an experimental study of the mechanism of the replacement of magnetite by pyrite up to 300 c abstract we present the results of an experimental study into the sulfidation of magnetite to form pyrite marcasite under hydrothermal conditions 90 300 c vapor saturated pressures a process associated with gold deposition in a number of ore deposits the formation of pyrite marcasite was studied as a function of reaction time temperature ph sulfide concentration solid weight to fluid volume ratio and geometric surface area of magnetite in polytetrafluoroethylene lined autoclaves ptfe and a titanium and stainless steel flow through cell marcasite was formed only at ph 21 c 21 c 1 11 while pyrite predominated at ph 21 c 2 and formed even under basic conditions up to ph 21 c 12 13 marcasite formation was favored at higher temperatures fine grained pyrrhotite formed in the initial stage of the reaction together with pyrite in some experiments with large surface area of magnetite grain size 120 c 0 96 4 42 and that rate of the transformation increased from 120 to 190 c scanning electron microscope sem imaging revealed that micro pores 0 1 5 m scale existed at the reaction front between the parent magnetite and the product pyrite and that the pyrite and or marcasite were euhedral at ph 21 c 155 c 4 42 the experimental results are in good agreement with sulfide phase assemblage and textures reported from sulfidized banded iron formations pyrite marcasite and pyrrhotite have been found to exist or co exist in different sulfidized banded iron formations and the microtextures show no evidence of sub m scale pseudomorphism of magnetite by pyrite

uncharted seismic risk the potential for earthquakes along the plate boundaries has been mapped with reasonable success our attention should now focus on the threat posed by unanticipated quakes located in the continental interiors

reservoir induced deformation and continental rheology in vicinity of lake mead nevada lake mead is a large reservoir in nevada formed by the construction of the 221 m high hoover dam in the black canyon of the colorado river the lake encompasses an area of 635 km2 and the total volume of the reservoir is 35 5 km3 filling started in february 1935 on the basis of a first order leveling in 1935 several levelings were carried out to measure the deformation induced by the load of the reservoir subsidence in the central parts of the lake relative to the first leveling was around 120 mm 1941 218 mm 1950 and 200 mm 1963 the subsidence pattern clearly shows relaxation of the underlying basement due to the water load of the lake which ceased after 1950 modeling of the relaxation process by means of layered viscoelastic compressible flat earth models with a detailed representation of the spatial and temporal distribution of the water load shows that the thickness of the elastic crust underneath lake mead is 30 3 km the data are also consistent with a 10 km thick elastic upper crust and a 20 km thick viscoelastic lower crust with 1020 pa s as a lower bound for its viscosity the subcrust has an average viscosity of 1018 0 2 pa s a surprisingly low value the leveling data constrain the viscosity profile down to 200 km depth

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

postseismic coulomb stress changes on intra continental dip slip faults due to viscoelastic relaxation in the lower crust and lithospheric mantle insights from 3d finite element modelling earthquakes in the brittle upper crust induce viscoelastic flow in the lower crust and lithospheric mantle which can persist for decades and lead to significant coulomb stress changes on receiver faults located in the surrounding of the source fault as most previous studies calculated the coulomb stress changes for a specific earthquake in nature a general investigation of postseismic coulomb stress changes independent of local geological conditions is still lacking for intra continental dip slip faults here we use finite element models with normal and thrust fault arrays respectively to show that postseismic viscoelastic flow considerably modifies the original coseismic coulomb stress patterns through space and time depending on the position of the receiver fault relative to the source fault areas with negative coseismic stress changes may exhibit positive postseismic stress changes and vice versa the lower the viscosity of the lower crust or lithospheric mantle the more pronounced are the transient stress changes in the 1st years with the lowest viscosity having the largest effect on the stress changes the evolution of postseismic coulomb stress changes is further controlled by the superposition of transient stress changes caused by viscoelastic relaxation leading to stress increase or decrease and the interseismic strain accumulation leading to a stress increase stress changes induced by viscoelastic relaxation can outweigh the interseismic stress increase such that negative coulomb stress changes can persist for decades on some faults postseismic relaxation and interseismic strain accumulation can act in concert to enhance already positive coulomb stress changes

postseismic mantle relaxation in the central nevada seismic belt holocene acceleration of deformation and postseismic relaxation are two hypotheses to explain the present day deformation in the central nevada seismic belt cnsb discriminating between these two mechanisms is critical for understanding the dynamics and seismic potential of the basin and range province interferometric synthetic aperture radar detected a broad area of uplift 2 to 3 millimeters per year that can be explained by postseismic mantle relaxation after a sequence of large crustal earthquakes from 1915 to 1954 the results lead to a broad agreement between geologic and geodetic strain indicators and support a model of a rigid basin and range between the cnsb and the wasatch fault

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

indonesian earthquake earthquake risk from co seismic stress last year s indonesian earthquake has increased seismic hazard in the region the scale of death and destruction caused by the recent sumatra andaman islands earthquake and its tsunami has raised concerns that another earthquake might be triggered on the contiguous sunda trench subduction zone a new calculation of stress distribution here and on the neighbouring sumatra fault reveals stress build up on both structures severe enough to increase the already high earthquake hazard this finding makes the need for an indian ocean tsunami warning system all the more pressing following the massive loss of life caused by the sumatra andaman earthquake in indonesia and its tsunami the possibility of a triggered earthquake on the contiguous sunda trench subduction zone is a real concern we have calculated the distributions of co seismic stress on this zone as well as on the neighbouring vertical strike slip sumatra fault and find an increase in stress on both structures that significantly boosts the already considerable earthquake hazard posed by them in particular the increased potential for a large subduction zone event in this region with the concomitant risk of another tsunami makes the need for a tsunami warning system in the indian ocean all the more urgent

slip rate variability and distributed deformation in the marmara sea fault system the slip rate along a fault controls the accumulation of strain that is eventually released during an earthquake estimates from a three dimensional geomechanical model of the slip rate on the main marmara fault near istanbul turkey reconcile geodetic and geological observations and indicate smaller values and higher variability than previously thought the slip rate along a fault controls the accumulation of strain that is eventually released during an earthquake1 along a 150 km long stretch of the north anatolian fault near istanbul turkey strain has been building up2 since the last large earthquake in 1766 estimates of the geodetic slip rates along the main marmara fault vary widely ranging between 17 and 27 9 mm yr 1 refs 2 3 4 5 this slip rate is difficult to quantify because of the lack of satellite observations offshore and the complexity of the submarine fault system that includes the main marmara fault2 6 7 here we estimate the right lateral slip rate on the main marmara fault using a three dimensional geomechanical model that incorporates these structural complexities from our simulations we infer slip rates between 12 8 and 17 8 mm yr 1 our estimates are smaller and more variable than previous results primarily because of slip partitioning and internal deformation our model results reconcile geodetic observations and geological fault slip rates8 9 10 which had been considered conflicting previously we suggest that the inferred variability in slip rate on the main marmara fault favours segmented release of seismic moment during consecutive events over the failure of the whole seismic gap in one large earthquake

holocene slip rate of the wasatch fault zone utah from geodetic data earthquake cycle effects 1 gps data define a broad zone of present day deformation in the eastern basin and range province western us using finite element models with elastic upper crust over viscoelastic lower crust upper mantle and incorporating earthquake cycle effects we show that these data are consistent with a model whereby most contemporary fault slip is focused on the wasatch fault zone modeled rates of horizontal extension are 3 0 4 5 mm yr in agreement with holocene geologic data the models are non unique in part because much of the wasatch fault is in the late stages of the earthquake cycle when surface velocity gradients across the fault are low

spatial distribution of trace elements in floodplain alluvium of the upper blackfoot river montana the mike horse mine tailings dam in western montana was partially breached in 1975 due to heavy rainfall and a failed drainage bypass approximately 90 000 tons of metal and arsenic enriched tailings flowed into beartrap creek and the blackfoot river the spatial distribution of trace elements as cd cu mn pb and zn in floodplain alluvium of the upper blackfoot river were examined along 20 transects in the upper 105 river kilometers downstream from the tailings dam trace element concentrations decrease with distance from the failed dam with as reaching background concentrations 15 km from the mike horse dam cd and pb at 21 km cu at 31 km and mn and zn at 37 km distance from the mike horse tailings dam and mine area is the dominating factor in explaining trace element levels with r 2 values ranging from 0 67 to 0 89 maximum floodplain trace element concentrations in the upper basin exceed us epa ecological screening levels for plants birds and other mammals and reflect adverse hazard quotients for exposure to as and mn for atv motorcycle use trace element concentrations in channel bank and bed alluvium are similar to concentrations in floodplain alluvium indicating active transport of trace elements through the river and deposition on the floodplain the fine fraction 2 mm of floodplain alluvium is dominated by sand sized particles 2 0 0 05 mm with cu and mn significantly correlated with silt sized 0 05 0 002 mm alluvium ongoing remediation in the headwaters area will not address metal contamination stored downstream in the channel banks and on the floodplain additionally some trace elements cu mn and zn were conveyed farther downstream than were others as cd pb

copper dispersion in ephemeral stream sediments sediment transport related parameters in ephemeral streams may be used to model and delineate 1 average dispersion patterns of copper laden sediments 2 differences in dispersion of copper in bedload and suspended sediments and 3 variability in the copper sediment dispersion patterns a model that effectively describes dispersion of copper in ephemeral stream sediments in a simple mixing model where cr is the resultant concentration beneath the confluence of the main channel with a tributary ct is the concentration of metal in sediments of the tributary cm is the metal concentration in main channel sediments and xm and xt are the basin areas or sediment yields of the main channel and tributary channel at their confluence variability in metal concentrations about values predicted by this model may be due to the different responses of bedload and suspended load to changes in stream hydraulics the dynamics of bedload transport the spatial and temporal variability rainfall within the drainage basin and chemical mobility of the copper

fluid immiscibility in natural processes use and misuse of fluid inclusion data abstract many occurrences of fluid immiscibility in natural geologic systems have been reported recently most often from fluid inclusion studies however the interpretation of fluid inclusion data in terms of immiscibility sometimes suffers from ambiguity of the vocabulary insufficient knowledge of the immiscibility constraints and insufficient knowledge of the topology in the tpx space of natural fluid systems for such reasons some authors have been misled to erroneous interpretations the term chemical immiscibility is unambiguously redefined as a multiphase multicomponent equilibrium the consequences of this definition are directly derived from the phase rule and concern the possible equations that relate the various parameters temperature pressure volumes compositions to each other these equations already put constraints on the topology of the phase equilibria in fluid systems a particular expression of the phase rule is proposed which takes into account the multiphase constant bulk volume constant bulk composition constraints in fluid inclusions the consequences of such an expression are of major importance in fluid inclusion studies the phase relations of some simple systems that approximate quite efficiently the natural complex fluids are then detailed h2o nacl co2 ch4 h2o co2 h2o co2 nacl the effects of these topologies and of the supplementary constraints constant bulk composition and constant bulk volume assumed for fluid inclusions isopleth isochoric systems are discussed

geochemical response to variable streamflow conditions in contaminated and uncontaminated streams 1 seasonal variations in stream inorganic geochemistry are not well documented or understood we sampled two mining impacted and two relatively pristine streams in western montana over a 12 month period collecting samples every 4 weeks with supplemental sampling at least weekly during spring runoff we analyzed all samples for dissolved operationally defined as 0 2 m and total recoverable concentrations generally the trace elements al as cu fe mn and zn did not correlate linearly with streamflow while the major elements e g ca k and mg did suspended sediment total recoverable metals and h followed clockwise hysteresis rotations driven by short term flushing events during the very early stages of spring runoff mining impacted sites had higher concentrations of many trace elements than did relatively pristine sites one of the mining impacted sites exhibited strong geochemical responses to spring rain events in the basin the results underscore the need to sample streams frequently during changing hydrologic and climatic conditions in order to accurately monitor surface water quality and to determine solute and particulate loads both contaminant and noncontaminant

slip rate variations on faults in the basin and range province caused by regression of late pleistocene lake bonneville and lake lahontan late pleistocene regression of two large pluvial lakes lake bonneville and lake lahontan caused considerable lithospheric rebound in the basin and range province usa here we use finite element models to show how lake growth and regression affect the temporal and spatial slip evolution on faults near the former lakes our results show that fluctuations in the volume of lake bonneville caused along strike slip variations on the wasatch normal fault with a pronounced slip rate increase on its northern and central parts during lake regression the response of normal and strike slip faults near the ring shaped lake lahontan depends on their location within the rebound area faults located in the centre of rebound show a slip rate increase during lake regression whereas strike slip faults at the periphery decelerate all slip rate variations are caused by differential stress changes owing to changing lake levels regardless of the individual fault response

stress transferred by the 1995 mw 6 9 kobe japan shock effect on aftershocks and future earthquake probabilities the kobe earthquake struck at the edge of the densely populated osaka kyoto corridor in southwest japan we investigate how the earthquake transferred stress to nearby faults altering their proximity to failure and thus changing earthquake probabilities we find that relative to the pre kobe seismicity kobe aftershocks were concentrated in regions of calculated coulomb stress increase and less common in regions of stress decrease we quantify this relationship by forming the spatial correlation between the seismicity rate change and the coulomb stress change the correlation is significant for stress changes greater than 0 2 1 0 bars 0 02 0 1 mpa and the nonlinear dependence of seismicity rate change on stress change is compatible with a state and rate dependent formulation for earthquake occurrence we extend this analysis to future mainshocks by resolving the stress changes on major faults within 100 km of kobe and calculating the change in probability caused by these stress changes transient effects of the stress changes are incorporated by the state dependent constitutive relation which amplifies the permanent stress changes during the aftershock period earthquake probability framed in this manner is highly time dependent much more so than is assumed in current practice because the probabilities depend on several poorly known parameters of the major faults we estimate uncertainties of the probabilities by monte carlo simulation this enables us to include uncertainties on the elapsed time since the last earthquake the repeat time and its variability and the period of aftershock decay we estimate that a calculated 3 bar 0 3 mpa stress increase on the eastern section of the arima takatsuki tectonic line attl near kyoto causes fivefold increase in the 30 year probability of a subsequent large earthquake near kyoto a 2 bar 0 2 mpa stress decrease on the western section of the attl results in a reduction in probability by a factor of 140 to 2000 the probability of a mw 6 9 earthquake within 50 km of osaka during 1997 2007 is estimated to have risen from 5 6 before the kobe earthquake to 7 11 afterward during 1997 2027 it is estimated to have risen from 14 16 before kobe to 16 22

fluid inclusion evidence for p v t x evolution of hydrothermal solutions in late alpine gold quartz veins at brusson val d ayas northwest italian alps

textural evolution of synthetic fluid inclusions in quartz during reequilibration with applications to tectonic reconstruction experimental reequilibration of synthetic 10 wt nacl h2o inclusions in natural quartz reveals that reequilibration textures show distinct differences depending upon the p t path followed by the inclusion after formation these differences combined with other geological information may be used to determine whether the sample rock followed a dominantly isothermal or isobaricp t path following entrapment the intensity and style of inclusion reequilibration features is related to the direction and magnitude of the departure of thep t path from the original isochore for the inclusion thus fluid inclusion reequilibration textures not only permit inclusionists to determine whether the rocks followed an isothermal or isobaric retrogradep t path but also the magnitude of departure of this path from one that is isochoric

viscosity estimates for the crust and upper mantle from patterns of lacustrine shoreline deformation in the eastern great basin the deformed shorelines of lake bonneville constitute a classic source of information on lithospheric elastic thickness and upper mantle viscosity we describe and apply a new model to a recently augmented data set new data better constrain both the complex spatio temporal pattern of the lake load and the crustal deformation response to that load the history of lake level fluctuations has been significantly refined and somewhat modified this is due to both more radiocarbon dates from within the bonneville basin and to an improved calibration of the radiocarbon timescale itself the data which constrain the crustal deformation pattern consist of ages and shoreline elevations from several hundred points which sample three major levels of lake bonneville and corresponding elevations from the high stands of three smaller lakes situated to the west of lake bonneville the data from the smaller lakes help elucidate the pattern of deflection which occurred beyond the edge of the big lake the geometry of the earth model incorporates an arbitrary number of layers overlying a half space and the rheology of each level can accommodate an arbitrary number of maxwell viscoelastic elements in parallel the inverse modeling comprises three complementary approaches for the simplest configurations we performed a direct search of the parameter space and delineated the irregular boundary of the subspace of acceptable models for more complex configurations we constrained the elastic parameters to their seismically determined values and then solved for viscosity versus depth profiles by either expressing the log viscosity versus log depth profile as a series of specially constructed orthogonal polynomials or by allowing each of 8 10 layers plus the half space to have an independently determined viscosity we found that the data do not strongly support nor can they conclusively exclude a more complex rheology than simple maxwell viscoelasticity the orthogonal polynomial solution exhibits an essentially monotonic decrease in viscosity with depth the most rapid change occurs at shallow depths decreasing from 1023 pa s at 3 km to 102o pa s at 30 km the decrease is much more gradual below with only another factor of 5 decrease between 30 and 300 km depth the unconstrained solution exhibits a rapid decrease in viscosity with depth from 2x 10 24 pa s in the top 10 km to 4x 1017 pa s at a depth of 40 km a nearly isoviscous asthenospheric region extends from 40 to 150 km and is underlain by a mantle lithospheric region with increased viscosity 2x 102o pa s extending from 150 to 300 km depth and by a uniform viscosity 1019 pa s half space below