the significance of clathrates in fluid inclusions and the evidence for overpressuring in the broadlands ohaaki geothermal system new zealand the broadlands ohaaki geothermal system is host to an epithermal environment where gold silver transport and deposition involves deeply derived fluids containing up to 3 3 wt percent co 2 and 0 1 wt percent cl earlier fluid inclusion investigations show that most microthermometric data reflect boiling and mixing in the upper 2 km of the system under modern p t x fluid conditions here we report the microthermometric results for a single quartz crystal from 1 258 m depth well br 25 in the upflow zone of the geothermal system that reveal the presence of clathrates upon freezing due to anomalous concentrations of co 2 7 9 to 14 3 wt these inclusions occupy the core of the quartz crystal and have homogenization temperatures from 291 to 365 c but the anomalous concentrations of co 2 are likely artifacts of deep boiling and heterogeneous trapping of the resulting coexisting gas and liquid phases only a few fluid inclusions t h 300 t m of 1 4 to 1 6 c which lack clathrate reveal more realistic conditions of early quartz precipitation from a modestly overpressured fluid 140 bars relative to the prevailing hydrodynamic boiling conditions 110 bars microthermometric data t h 300 t m of 0 2 to 0 8 c for fluid inclusions in a later formed overgrowth of the quartz crystal match the modern p t x conditions at 1 258 m depth in the well the overall results of the study show that the clathrates are artifacts of two phase trapping of steam and liquid and that the deep liquid became overpressured locally probably due to mineral deposition and sealing of a permeable channel

fluid inclusion evidence for minimum 11 km vertical offset on the wasatch fault utah the footwall of the wasatch fault in the corner creek area near salt lake city is hydrothermally altered and deformed quartz monzonite of the oligocene little cottonwood stock secondary fluid inclusions are associated with hydrothermal alteration minerals and structural deformation thermometric measurements of fluid inclusion characteristics indicate entrapment of a co2 h2o nacl fluid at minimum temperatures of 223 353 c and minimum fluid pressures of 900 2800 bar the 2800 bar fluid pressure is near lithostatic pressure at a depth of 11 km the minimum displacement of the fault that is required for exhumation of the observed alteration and fluid inclusions and more than three times greater than most previous estimates the large displacement estimate is supported by the occurrence of pyrophyllite in shales in the footwall by the petrology of metamorphosed shale surrounding an unroofed pluton in the footwall and by geologic reconstruction of the eroded footwall

quantifying fault zone activity in arid environments with high resolution topography 1 high resolution airborne laser swath mapping alsm topography illuminates active faulting with unprecedented clarity we contrast alsm topography of two dextral faults in arid regions of california with slip rates that differ by an order of magnitude the lenwood fault with rate of 1 mm yr and the clark fault a strand of the san jacinto fault with net slip rate 10 mm yr visualization of alsm data reveals abundant fault scarps and deflected channels that when reconstructed can yield powerful slip constraints though many of these features may also be detected in existing aerial photography these data are limited by stereo depth resolution and fixed illumination angle

a stable isotope and fluid inclusion study of the qaleh zaricu au ag deposit khorasan province iran abstract the qaleh zari copper deposit located in south khorasan in the central lut region of iran is a polymetallic vein deposit with major amounts of cu au ag and minor amounts of pb zn and bi mineralization occurs in a series of nw se trending fault planes and breccia zones in paleogene andesitic to basaltic volcanic rocks argillization sericitization and propylitization characterize alteration halos bordering mineral veins the main ore minerals are chalcopyrite pyrite galena and sphalerite with quartz calcite and minor chlorite as the main gangue phases microthermometric measurements of fluid inclusions in cogenetic quartz indicate homogenization temperatures between 160 and 300 c and salinities from 1 to 4 wt nacl equiv boiling occurred in the mineralising fluids at 160 1000 m below the paleo water table at pressures of approximately 15 80 bar at various stages in the formation of the ore body the wide range of pressures and temperatures reflects the multi stage nature of the mineralization at qaleh zari the 18 o values in quartz relative to smow and 34 s values in chalcopyrite and galena relative to cdt range from 6 5 to 7 5 and 0 0 1 5 mean 7 0 respectively at 300 c calculated fluid 18 o values are close to 0 these data suggest a magmatic origin for sulfur and a surficial origin for the mineralizing fluid mineralization at qaleh zari is interpreted as epithermal and low sulfidation in style and was probably related to a deep seated magmatic system ore deposition was the result of boiling cooling and pressure reduction

geology fluid inclusion and stable isotope study of the yueyang ag au cu deposit zijinshan orefield fujian province china abstract the large yueyang ag au cu deposit is commonly regarded as a low sulfidation epithermal deposit in the zijinshan orefield fujian province southeastern china the ag ag cu orebodies hosted in the zijinshan granitic batholith are mainly stratoid and lens in shape and controlled by a series of nw trending listric faults with shallow dip angles four mineralization stages are recognized on the basis of mineral assemblage ore fabrics and crosscutting relationships of the ore veins namely pre ore pyrite sericite quartz chlorite main cu chalcopyrite pyrite sericite quartz bornite main ag au ag and au minerals pyrite quartz adularia calcite apatite chalcopyrite galena sphalerite and post ore quartz chalcedony calcite stages fluid inclusions fis in the deposit include aqueous liquid rich wl aqueous vapor rich wv and minor carbonic c and daughter mineral bearing s type ones wl subtype is the main inclusion type in the yueyang deposit accounting for more than 90 in proportion in each stage minor wv subtype inclusions occur in both the main cu and ag stages while the c type and s type ones are only observed in the main cu stage fluid inclusion and h o isotope study indicated that the ore forming fluid of the main cu stage is primarily magmatic vapor which further underwent fluid boiling and mixing with meteoric water while the ore forming fluid of the main ag stage is meteoric water dominated and the precipitation of silver and gold was mainly resulted from fluid boiling and the precipitation of other sulfides on the basis of the aforementioned geological fluid inclusion and stable isotope studies we proposed a two stage model for the yueyang deposit including a magmatic vapor related porphyry type cu mineralization and meteoric water related low sulfidation epithermal ag au cu mineralization although the porphyry cu mineralization is very limited in scale the mineralization and exhumation depths of the yueyang deposit are estimated to be 448 527 m and 18 97 m respectively by comparison with the exhumation depths of other deposits in the zijinshan orefield it is suggested that more epithermal deposits could be found in the southwest of the orefield due to less uplift and exhumation therein

hydro geochemical and isotopic fluid evolution of the los azufres geothermal field central mexico abstract hydrothermal alteration at los azufres geothermal field is mostly propylitic with a progressive dehydration with depth and temperature increase argillic and advanced argillic zones overlie the propylitic zone owing to the activity of gases in the system the deepest fluid inclusions proto fluid are liquid rich with low salinity with nacl dominant fluid type and ice melting temperatures t mi near zero 0 c and salinities of 0 8 wt nacl equivalent the homogenization temperature t h 325 5 c the boiling zone shows t h 300 c and apparent salinities between 1 and 4 9 wt nacl equivalent implying a vaporization process and a very important participation of non condensable gases ncgs mostly co 2 positive clathrate melting temperatures fusion with t h 150 c are observed in the upper part of the geothermal reservoir from 0 to 700 m depth these could well be the evidence of a high gas concentration the current water produced at the geothermal wells is nacl rich geothermal brine and is fully equilibrated with the host rock at temperatures between t 300 and 340 c the hot spring waters are acid sulfate indicating that they are derived from meteoric water heated by geothermal steam the ncgs related to the steam dominant zone are composed mostly of co 2 80 98 of all the gases the gases represent between 2 and 9 wt of the total mass of the fluid of the reservoir the authors interpret the evolution of this system as deep liquid water boiling when ascending through fractures connected to the surface boiling is caused by a drop of pressure which favors an increase in the steam phase within the brine ascending towards the surface during this ascent the fluid becomes steam dominant in the shallowest zone and mixes with meteoric water in perched aquifers stable isotope compositions 18 o d of the geothermal brine indicate mixing between meteoric water and a minor magmatic component the enrichment in 18 o is due to the rock water interaction at relatively high temperatures 13 c stable isotope data show a magmatic source with a minor meteoric contribution for co 2 the initial isotopic value 34 s res 2 3 which implies a magmatic source more negative values are observed for shallow pyrite and range from 34 s fes 2 4 to 4 9 indicating boiling the same fractionation tendencies are observed for fluids in the reservoir from results for 18 o

new evidence for an extended occupation of the provo shoreline and implications for regional climate change pleistocene lake bonneville utah usa abstract lake bonneville was a climatically sensitive closed basin lake that occupied the eastern great basin during the late pleistocene ongoing efforts to refine the record of lake level history are important for deciphering climate conditions in the bonneville basin and for facilitating correlations with regional and global records of climate change radiocarbon data from this and other studies suggest that the lake oscillated at or near the provo level much longer than depicted by current models of lake level change radiocarbon data also suggest that the lake dropped from threshold control much more rapidly than previously supposed these revisions to the lake bonneville hydrograph coupled with independent evidence of climate change from vegetation and glacial records have important implications for conditions in the bonneville basin and during the pleistocene to holocene transition

the transition from porphyry to epithermal style gold mineralization at ladolam lihir island papua new guinea a reconnaissance study the exceptionally large gold resource at ladolam 1 300 metric tons of gold lihir island resulted from the transition of an early stage low grade porphyry gold system to a low sulfidation epithermal gold event this transition was probably triggered by rapid decompression during the partial slope failure of luise stratovolcano and accompanied by the ingress of seawater the original porphyry stage is indicated by remnant hydrothermal breccia clasts of strongly biotite magnetite altered monzodiorite with disseminated pyrite chalcopyrite and poorly developed pyrite quartz stockwork veins the breccias are overprinted by biotite magnetite alteration and their matrix is strongly mineralized with disseminated auriferous pyrite the breccias are cut by late stage epithermal quartz chalcedony illite adularia pyrite veins and associated illite adularia alteration that locally contain bonanza gold grades of up to 120 g t isotope data suggest a magmatic source of sulfur in the gold bearing fluids at ladolam electronic supplementary material to this paper can be obtained by using the springer link server located at http dx doi org 10 1007 s00126 001 0230 y

age and paleoclimatic significance of the stansbury shoreline of lake bonneville northeastern great basin abstract the stansbury shoreline one of the conspicuous late pleistocene shorelines of lake bonneville consists of tufa cemented gravel and barrier beaches within a vertical zone of about 45 m the lower limit of which is 70 m above the modern average level of great salt lake stratigraphic evidence at a number of localities including new evidence from crater island on the west side of the great salt lake desert shows that the stansbury shoreline formed during the transgressive phase of late pleistocene lake bonneville sometime between about 22 000 and 20 000 yr b p tufa cemented gravel and barrier beaches were deposited in the stansbury shorezone during one or more fluctuations in water level with a maximum total amplitude of 45 m we refer to the fluctuations as the stansbury oscillation the stansbury oscillation cannot have been caused by basin hypsometric factors such as stabilization of lake level at an external overflow threshold or by expansion into an interior subbasin or by changes in drainage basin size therefore changes in climate must have caused the lake level to reverse its general rise to drop about 45 m in altitude reducing its surface area by about 18 5000 km2 and later to resume its rise if the sizes of great basin lakes are controlled by the mean position of storm tracks and the jetstream which as recently postulated may be controlled by the size of the continental ice sheets the stansbury oscillation may have been caused by a shift in the jetstream during a major interstade of the laurentide ice sheet

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

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

evolution of the hydrothermal system at los azufres mexico based on petrologic fluid inclusion and isotopic data abstract the los azufres geothermal reservoir formed in a fractured upper miocene to pliocene andesite and basalt base complex is sealed to the surface by a silicic mainly rhyolitic sequence of pleistocene age almost the entire sequence is affected by hydrothermal alteration to varying extent petrological and fluid inclusion studies confirmed vertical zonation of the reservoir by secondary processes hydrothermal alteration processes under low temperature conditions at a depth of 1200 1500 m the maximum ice melting temperatures tmi values of 0 7 to 4 c and salinities of 6 4 wt nacl eq indicate boiling conditions of the geothermal brine in a vapor rich zone chlorite calcite quartz zeolite anhydrite albite sphene pyrite hematite and illite form the hydrothermal mineral paragenesis with maximum temperatures of 250 c and pressure conditions of 150 bar below 1500 m tmi reach maximum values of 0 1 c and low salinities of 0 2 wt nacl eq the minerals epidote amphibole prehnite and garnet indicate temperatures above 250 c and pressure conditions between 150 and 200 bar the measured homogenization temperatures th of fluid inclusions fi are consistently higher than the in situ measured temperatures which indicates retrograde cooling of the los azufres geothermal reservoir since the time of the hydrothermal mineral formation updoming temperature isotherms at the center of the geothermal field below well az 9 az 23 and az 25 indicate the heating up of the fluids by a shallow magma chamber stable isotope data 18o d of the geothermal brine indicates mixing processes between meteoric water and a minor magmatic component secondary reactions forming sericite may have caused a further positive shift in 18o in the shallow part of the geothermal reservoir

evaluation of wasatch fault segmentation and slip rates using lake bonneville shorelines 1 analysis of lake bonneville shorelines using lidar digital elevation data challenges accepted models of wasatch fault deformation since the late pleistocene while footwall deformation of the weber segment of the wasatch fault is consistent with back rotation of the footwall block and greatest displacement rate toward the center of the segment shorelines along the footwall of the salt lake city segment decrease in elevation toward the interior and are highest at the segment boundaries an opposite pattern of footwall deformation than predicted for boundaries arresting or strongly inhibiting displacement during earthquakes the spatial pattern of footwall rebound implies that some of the proposed persistent fault segment boundaries do not stop earthquake ruptures that originate on adjacent fault segments nor constrain ruptures initiated within the salt lake city segment net vertical fault displacement at the boundary between the salt lake and provo segments is 16 20 m over the past 16 3 18 5 ka corresponding to a vertical displacement rate of 0 8 1 2 mm yr a net fault slip rate of 2 0 2 8 mm yr and horizontal extension rate of 1 8 2 6 mm yr on the 25 west southwest dipping fault that forms the southern salt lake city segment boundary shoreline analysis suggests isostatic rebound caused by a drop in lake level was concentrated during a relatively short 2000 year time period following the bonneville flood at 16 ka lidar derived topography in conjunction with robust geomorphic datums improves our ability to map deformation associated with lithospheric flexure and faulting while demonstrating the limitation of lacustrine shorelines in this type of analysis

a 12 000 year record of vertical deformation across the yellowstone caldera margin the shorelines of yellowstone lake the 600 ka yellowstone caldera exhibits several signs of unrest the most evident of which is historic ground deformation including both uplift and subsidence we document deformation in the area of the southeastern caldera across 12 000 years using the postglacial shoreline terraces of yellowstone lake raised shoreline elevations were interpreted from 230 leveling profiles surveyed across flights of terraces with an accuracy of 0 5 m of about 11 recognizable terraces the five most continuous raised shorelines were correlated around the lake basin to reveal deformation patterns shoreline ages are based on minimum and maximum limiting radiocarbon and obsidian hydration dates each terrace is interpreted as representing an episode of uplift 1 kyr 1 of the caldera interior and subsequent subsidence with little net volume change this cyclic behavior may result from magma emplacement and subsequent withdrawal or cooling and crystallization and or episodic trapping and release of magmatic fluids evolved during cooling and crystallization in a self sealing reservoir as hypothesized by dzurisin et al 1990 early postglacial shoreline deformation reveals substantial intracaldera subsidence possibly reflecting cooling and loss of trapped hydrothermal fluids extension along north south trending normal faults and related structures is also apparent in early to middle postglacial deformation both inside and outside of the caldera margin including downwarping and local faulting of hot weak intracaldera crust net deformation over the past 3 kyr has been dominantly up within the caldera interior and slightly down along the caldera rim relative to the extracaldera region this uplift is roughly similar to the historic pattern and may largely represent the effects of the most recent inflation episode subtraction of the total estimated magnitude of inflation in this episode suggests that the overall trend of postglacial deformation has been subsidence the cause of this trend is undetermined but is most likely related to the effects of regional extension and long term cooling within the yellowstone caldera

a general relation for standing normal jumps in both hydraulic and dry granular flows steady free surface flows can produce sudden changes in height and velocity namely standing jumps which demarcate supercritical from subcritical flows standing jumps have traditionally been observed and studied experimentally with water in order to mimic various hydraulic configurations for instance in the vicinity of energy dissipators more recently some studies have emerged that investigate standing jumps formed in flows of dry granular materials which are relevant to the design of protection dams against avalanches in the present paper we present a new explicit relation for the prediction of the height of standing jumps we demonstrate the robustness of the new relation proposed by revisiting and cross comparing a great number of data sets on standing jumps formed in water flows on horizontal and inclined smooth beds in water flows on horizontal rough beds and in flows of dry granular materials down smooth inclines our study reveals the limits of the traditional one to one relation between the sequent depth ratio of the jump and the froude number of the incoming supercritical flow namely the belanger equation the latter is a rankine hugoniot relation which does not take into account the gravitational and frictional forces acting within the jump volume over the jump length as well as the possible density change across the jump when the incoming fluid is compressible the newly proposed relation which is exact for grains and a reasonable approximation for water can solve all of these issues however this relation can predict the height of the standing jump only if another length scale namely the length of the jump is known we conclude our study by discussing empirical but simple closure relations to get a reasonable estimate of the jump length for water flows and dry granular flows these closure relations can be used to feed the general jump relation and then predict with accuracy the heights of the jumps in a number of situations provided that well calibrated friction laws described in the present study are considered

application of lidar to resolving bedrock structure in areas of poor exposure an example from the steep study area southern alaska an airborne lidar light detection and ranging data set is used to map bedrock structure in an area with poor outcrop and indistinct stratigraphy a 1 m bare earth filtered digital elevation model dem is used to construct multiple shaded relief images that show subtle topographic features suggestive of folded strata preliminary geologic interpretations exported to a field gis geographic information system with gps global positioning system identified the features as resistant beds beneath vegetation and allowed construction of a regional map of bedding and fault traces bedding traces and faults were then analyzed with several 3d software applications the ability to precisely map these features in 3d allowed projection onto cross section lines which helped define the structure as detachment folds cut by younger high angle faults comparison between aerial photography and shaded relief images of the bare earth dem indicates that structures beneath open forest and shrub are better revealed by shaded relief images the ability to create hillshade images using different sun angles supplements structural mapping with aerial photography even in open tundra with no significant vegetation canopy aerial photography would generally be more informative in areas of extensive outcrop and draping aerial photography on a lidar dem would produce spectacular visualization capabilities these techniques should yield good results where well bedded rocks lie beneath thin soil cover and open canopy forest but may not be successful in deeply weathered tropical forest or glaciated areas where glacial sculpting and deposition obscure bedrock structure we propose a mapping workflow that includes image processing of hillshade images together with 3d visualization and mapping methods

the anatomy of the 2009 l aquila normal fault system central italy imaged by high resolution foreshock and aftershock locations 1 on 6 april 01 32 utc 2009 a mw 6 1 normal faulting earthquake struck the axial area of the abruzzo region in central italy we study the geometry of fault segments using high resolution foreshock and aftershock locations two main sw dipping segments the l aquila and campotosto faults forming an en echelon system 40 km long nw trending the 16 km long l aquila fault shows a planar geometry with constant dip 48 through the entire upper crust down to 10 km depth the campotosto fault activated by three events with 5 0 mw 5 2 shows a striking listric geometry composed by planar segments with different dips along depth rather than a smoothly curving single fault surface the investigation of the spatiotemporal evolution of foreshock activity within the crustal volume where the subsequent l aquila main shock nucleated allows us to image the progressive activation of the main fault plane from the beginning of 2009 the foreshocks activated the deepest portion of the fault until a week before the main shock when the largest foreshock mw 4 0 triggered a minor antithetic segment seismicity jumped back to the main plane a few hours before the main shock secondary synthetic and antithetic fault segments are present both on the hanging and footwall of the system the stress tensor obtained by inverting focal mechanisms of the largest events reveals a ne trending extension and the majority of the aftershocks are kinematically consistent deviations from the dominant extensional strain pattern are observed for those earthquakes activating minor structures

volcanic stratigraphy of the los azufres geothermal area mexico abstract the los azufres volcanic center located 200 km northwest of mexico city is one of a number of pleistocene silicic volcanic centers with active geothermal systems that lie north of the axis of the mexican neovolcanic belt silicic volcanism began approximately 1 m y ago with eruption of the agua fria rhyodacite to high silica rhyolite lava domes and flows they are covered by rhyodacite and dacite lava domes and flows of the san andres volcano dated at 0 3 m y a north to northeast trending set of high angle normal faults is offset by a younger and more prominent east trending set that parallels the principal regional structural trend these faults cut all but the youngest volcanic rocks of the center the yerbabuena rhyodacites to high silica rhyolites these morphologically well preserved lava domes are approximately 0 15 m y old and are probably associated with air fall tuffs that blanket the western portion of the volcanic center two episodes of high heat flow suggested by studies of drill core samples and fluids from the los azufres geothermal field may correspond to two different episodes of magma injection to high levels the most recent one resulting in eruption of the yerbabuena lavas

earthquake scaling fault segmentation and structural maturity abstract slip and length measurements on earthquakes suggest large stress drop variability we analyze an extended set of slip length measurements for large earthquakes m 6 to seek for the possible origin s of this apparent variability we propose that such variability arises from earthquakes breaking a variable number of major fault segments that number depends on the strength of the inter segment zones which itself depends on the structural maturity of the faults we propose new d max l parameterizations based on that idea of multiple segment ruptures in such parameterizations each broken segment roughly scales as a crack while the total multi segment rupture does not stress drop on individual segments is roughly constant only varying between 3 5 to 9 mpa the slight variation that is still observed depends on fault structural maturity more mature faults have lower stress drops than immature ones the new d max l functions that we propose reduce uncertainties with respect to available relationships they thus provide a more solid basis to estimate seismic hazard by integrating fault properties revealed by geological studies

evolution of the bonneville shoreline scarp in west central utah comparison of scarp analysis methods and implications for the diffusion model of hillslope evolution abstract wave cut pluvial shoreline scarps are ideal natural experiments in hillslope evolution because the ages of these scarps are often precisely known and because they form with a range of heights alluvial textures and microclimates i e orientation previous work using midpoint slope methods on pluvial scarps in the basin and range concluded that scarp evolution is nonlinear and microclimatically controlled the purpose of this study was to further examine the influence of scarp height texture and microclimate in an attempt to calibrate a nonlinear model of scarp evolution to do this over 150 profiles of the bonneville shoreline in the adjacent snake and tule valleys west central utah were collected and analyzed by fitting the entire scarp profile to diffusion equation solutions taking into account uncertainty in the initial scarp angle in contrast to previous studies this analysis revealed no evidence for nonlinearity or microclimatic control to understand the reason for this discrepancy we undertook a systematic study of the accuracy of each scarp analysis method the midpoint slope inverse method was found to yield biased results with systematically higher diffusion ages for young tall scarps the slope offset method is unbiased but has limited resolution because it requires many scarp profiles to yield a single diffusion age a method that incorporates the full scarp profile and uncertainty in the initial scarp angle was found to be the most accurate technique the application of the full scarp method to the bonneville shoreline supports the use of a linear diffusion model for scarps up to 20 m in height scarp orientation had no discernable effect on diffusivity values soil texture was found to have a weak but significant inverse relationship with diffusivity values

the formation and distribution of co2 enriched fluid inclusions in epithermal environments abstract fluid inclusions from two geothermal systems associated with volcanic activity were studied to document the distribution of co 2 in modern epithermal environments the fluid inclusion data combined with mineral distributions and chemical analyses of the production fluids from both systems provide a record of steam and gas flux to depths in excess of 1 to 2 km and of transient variations in the gas contents of the reservoirs the liquid rich fluid inclusions can be grouped into two types on the basis of their co 2 contents inclusions with co 2 contents of less than about 4 wt typically have calculated gas contents that are higher than the present day reservoir fluids however the calculated pressures and temperatures of these inclusions are consistent with their depth of formation indicating that they may have formed in response to boiling and mixing processes in the reservoir liquid rich fluid inclusions with co 2 contents between approximately 4 and 6 wt are characterized by co 2 clathrate dissociation temperatures greater than 0 0 c these inclusions occur on the margins of the thermal systems where they define umbrella shaped caps around the main zones of upwelling the co 2 contents of the inclusions require that they formed at pressures several tens of bars above hydrostatic elevated pressures and gas contents may have developed through compression and condensation of co 2 enriched steam by tectonic stress

characterizing arid region alluvial fan surface roughness with airborne laser swath mapping digital topographic data 1 range front alluvial fan deposition in arid environments is episodic and results in multiple fan surfaces and ages these distinct landforms are often defined by descriptions of their surface morphology desert varnish accumulation clast rubification desert pavement formation soil development and stratigraphy although quantifying surface roughness differences between alluvial fan units has proven to be difficult in the past high resolution airborne laser swath mapping alsm digital topographic data are now providing researchers with an opportunity to study topography in unprecedented detail here we use alsm data to calculate surface roughness on two alluvial fans in northern death valley california we define surface roughness as the standard deviation of slope in a 5 m by 5 m moving window comparison of surface roughness values between mapped fan surfaces shows that each unit is statistically unique at the 99 confidence level furthermore there is an obvious smoothing trend from the presently active channel to a deposit with cosmogenic 10be and 36cl surface exposure ages of 70 ka beyond 70 ka alluvial landforms become progressively rougher with age these data suggest that alluvial fans in arid regions smooth out with time until a threshold is crossed where roughness increases at greater wavelength with age as a result of surface runoff and headward tributary incision into the oldest surfaces

origin and deformation of holocene shoreline terraces yellowstone lake wyoming geodetic surveys within the yellowstone caldera have documented active uplift that is most likely caused by magmatic processes in the upper crust along the northeast shore of yellowstone lake maximum relative uplift rates are 10 mm yr for the period 1923 1975 however information on deformation prior to historic instrumental records has been lacking in this study closely spaced data on elevations of postglacial shoreline terraces around the north end of yellowstone lake reveal complex tilting though most holocene deformation is probably magma related the pattern of shoreline tilting deviates significantly from the historic pattern of roughly symmetric inflation of the caldera along the northeast shore where tilt directions of historic and shoreline deformation are similar differential uplift of a 2500 yr old terrace is roughly 10 m this gives a maximum uplift rate of 4 mm yr these unique holocene terraces may exist due to episodic deformation because vertical movements affecting the lake outlet directly control lake level

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

radiocarbon chronology of lake bonneville eastern great basin usa abstract lake bonneville occupied a series of connected topographically closed structural basins in the eastern great basin from about 30 ka to 12 ka the following synthesis of lake bonneville history is based on a critical evaluation of the stratigraphic and geomorphic contexts of 83 radiocarbon ages of a variety of samples including wood charcoal dispersed organic matter mollusk shells and tufa the lake began to rise from levels close to average holocene levels after about 28 ka by 22 ka it had transgressed approximately 100 m between 22 and 20 ka it regressed about 45 m in the stansbury oscillation and the stansbury shoreline was formed transgression after 20 ka proceeded in two phases a rapid phase from 20 to 18 ka and a slower phase from 18 to 15 ka the lake overflowed intermittently at its highest level the bonneville shoreline from about 15 to 14 5 ka then catastrophically dropped 100 m during the bonneville flood to the level of the provo shoreline which it occupied until about 14 ka subsequent closed basin regression was rapid and complete by 12 ka and was followed by a modest transgression to form the gilbert shoreline between 10 9 and 10 3 ka the lake bonneville record is an accurate proxy of the changing water balance in the bonneville basin during the late pleistocene although the nature of the climatic changes during this period are still uncertain

a healing reloading feedback control on the growth rate of seismogenic faults spatial and temporal variations in the growth rates of faults are explained in terms of a stress feedback mechanism operating in the seismogenic upper crust it is based on the idea that seismic rupture of a fault perturbs the surrounding stress field advancing the occurrence of future earthquakes on some faults that are optimally oriented while relaxing stress levels on others if post slip healing is geologically rapid then the earthquakes that are thus induced will contribute to reloading along the earlier rupture zone because of the symmetry of the optimal geometry a positive feedback is set up so that even in areas that are undergoing uniform tectonic straining some faults develop higher displacement rates and grow more rapidly while others experience reduced rates or become inactive using a thin plate elastic model for lithospheric scale faulting it is shown that this healing reloading feedback mechanism drives rapid localisation and the formation of major through going faults moving at plate boundary velocities enhanced displacement rates compared to an isolated fault develop shortly after the onset of deformation along those faults which are optimally positioned in the overall fault population thus the formation of a new plate boundary fault zone is predetermined and is a consequence of rather than the precursor of preferentially high displacement rates also fault segments located at points of rupture symmetry e g the central portion of a fault zone are reloaded more frequently and develop higher displacement rates and consequently have longer segment lengths and or larger displacement to length ratios episodic fault movement through time is a general feature of the model these predictions are consistent with available field observations over a wide range of scales thus elastic brittle failure and healing appear to be important rheological components of the lithosphere on long time scales 104 106 y as well as on the time scale of earthquake recurrence

the accommodation of large strains in the upper lithosphere of the earth and other solids by self similar fault systems the geometrical origin of b value plate tectonics has provided a method of visualizing the geometry of the deformation of the earth s lithosphere on a large scale the description is so concise that for many purposes it provides an explanation of geological processes that overshadows the need to understand the driving processes the mechanics of the zones between the plates are less well understood particularly in continental regions where large areas are subject to deformation both continuous and discontinuous models have been tried but both have obvious drawbacks

spatial variations in slip rate along the death valley fish lake valley fault system determined from lidar topographic data and cosmogenic 10be geochronology 1 the death valley fish lake valley fault zone dv flvfz is a prominent dextral fault system in the eastern california shear zone ecsz combining offset measurements determined with lidar topographic data for two alluvial fans with terrestrial cosmogenic nuclide 10be ages from the fan surfaces yields a late pleistocene slip rate of 2 5 to 3 mm yr for the northern part of the dv flvfz in fish lake valley these rates are slower than the late pleistocene rate determined for the system in northern death valley indicating that slip rates decrease northward along this major fault zone when summed with the slip rate from the white mountains fault the other major fault in this part of the ecsz our results suggest that either significant deformation is accommodated on structures east of fish lake valley or that rates of seismic strain accumulation and release have not remained constant over late pleistocene to holocene time

internal vein texture and vein evolution of the epithermal shila paula district southern peru the epithermal shila paula au ag district is characterized by numerous veins hosted in tertiary volcanic rocks of the western cordillera southern peru field studies of the ore bodies reveal a systematic association of a main e w vein with secondary n55 60 w veins two directions that are also reflected by the orientation of fluid inclusion planes in quartz crystals of the host rock in areas where this pattern is not recognized such as the apacheta sector vein emplacement seems to have been guided by regional n40 e and n40 w fractures two main vein filling stages are identified stage 1 is a quartz adularia pyrite galena sphalerite chalcopyrite electrum mn silicate carbonate assemblage that fills the main e w veins stage 2 which contains most of the precious metal mineralization is divided into pre bonanza and bonanza substages the pre bonanza substage consists of a quartz adularia carbonate assemblage that is observed within the secondary n45 60 w veins in veinlets that cut the stage 1 assemblage and in final open space fillings the two latter structures are finally filled by the bonanza substage characterized by a fe poor sphalerite chalcopyrite pyrite galena tennantite tetrahedrite polybasite pearceite electrum assemblage the ore in the main veins is systematically brecciated whereas the ore in the secondary veins and geodes is characteristic of open space crystallization microthermometric measurements on sphalerite from both stages and on quartz and calcite from stage 2 indicate a salinity range of 0 to 15 5 wt nacl equivalent and homogenization temperatures bracketed between 200 and 330 c secondary co2 n2 and h2s bearing fluid inclusions are also identified the age of vein emplacement based on 40ar 39ar ages obtained on adularia of different veins is estimated at around 11 ma with some overlap between adularia of stage 1 11 4 0 4 ma and of stage 2 10 8 0 3 ma a three phase tectonic model has been constructed to explain the vein formation phase 1 corresponds to the assumed development of e w sinistral shear zones and associated n60 w cleavages under the effects of a ne sw shortening direction that is recognized at andean scale these structures contain the stage 1 ore assemblage that was brecciated during ongoing deformation phase 2 is a reactivation of earlier structures under a nw se shortening direction that allowed the reopening of the preexisting schistosity and the formation of scarce n50 e striking s2 cleavage planes filled by the stage 2 pre bonanza minerals phase 3 coincides with the bonanza ore emplacement in the secondary n45 60 w veins and also in open space in the core of the main e w veins our combined tectonic textural mineralogical fluid inclusion and geochronological study presents a complete model of vein formation in which the reactivation of previously formed tectonic structures plays a significant role in ore formation

growth of faults by accumulation of seismic slip the accommodation of large strains in the upper crust is largely achieved by the accumulation of displacement on faults observation shows that as a fault accumulates displacement it grows in size i e its surface area and its length increase here we address the question for an increase in the amount of displacement on a fault by how much would the length of the fault change it is argued by cowie and scholz 1992a that the displacement on a fault is linearly related to the length of the fault this simple result is expanded upon in this paper by assuming that a fault accumulates displacement by repeated earthquakes two different approaches are presented the first approach considers the balance that must be achieved between the energy available for deformation and the work involved in creating new fault surface area as the fault grows the available energy is provided by changes in strain energy when the fault slips the second approach is to construct a geometrical model for fault growth using the scaling relationship between the slip during a single earthquake and the length of the rupture the total displacement on a fault is the sum of the slips contributed by many earthquakes the usefulness of these two approaches is that the growth of a fault over geologic time can be described by parameters that can be obtained from earthquake and fault data the models presented here predict that 1 the maximum amount a fault can grow in a single earthquake that ruptures the entire fault is of the order of 1 of its previous length and 2 the work of faulting may account for 10 of the total energy available during an earthquake the energy lost from the system is accounted for by work done against friction and seismic radiation consequences of fault growth for the segmentation and thus seismogenic potential of a fault over geologic time are discussed using predictions of the theory