lithofacies analysis of colluvial sediments an aid in interpreting the recent history of quaternary normal faults in the basin and range province western united states inferring the frequency and magnitude of past earthquakes from the stratigraphy in exposures of normal faulted sediments is difficult because colluvial lithofacies assemblages adjacent to faults are complex similarities in facies assemblages adjacent to young fault scarps in arid to semiarid areas such as the basin and range province allow lithofacies to be grouped into two genetic architectural elements debris and wash elements upper and lower facies associations can commonly be recognized within each element a lithofacies code scheme similar to those used in the analysis of fluvial and glacial lithofacies sequences provides a concise way of illustrating lithofacies relations in fault exposures the source lithology of colluvial lithofacies is shown in the code and soil horizon symbols can be included the architecture of lithofacies assemblages near fault scarps in semiarid areas is explained by a model of colluvial sedimentation in response to a single surface faulting event analysis of lithofacies assemblages exposed in three trenches across normal faults in the eastern basin and range shows how the model can be used to interpret fault histories similar facies analysis methods may be useful in interpreting colluvial sequences formed by non tectonic processes

impact of riser reconstructions on estimation of secular variation in rates of strike slip faulting revisiting the cherchen river site along the altyn tagh fault nw china abstract slip rates are heavily contested for many of the first order strike slip faults within the indo asian collision zone rates determined geodetically are generally lower than those reported using reconstructions of offset landforms and it is unclear if this discrepancy reflects true secular variation in slip history systematic errors in interpretation or both here i examine the methods used to derive slip rates from reconstructions of displaced fluvial risers and show that such rates are subject to potentially important uncertainties that have largely been overlooked review of published data demonstrates that the slip rate can vary by a factor of 1 2 to 5 for the same site depending on whether the reconstruction uses the age of the upper or lower terrace for the initiation of riser offset to reduce this epistemic uncertainty i have developed six geomorphic indices that can be used to identify the most accurate end member reconstruction 1 comparison of riser offset with inset channel width 2 similarity of riser and tread displacements 3 morphological analysis of the scarp profile 4 riser deflection in plan view 5 diachroneity of terrace abandonment and 6 whether riser crests or bases yield the slip vector without the use of these geomorphic observations the epistemic uncertainty associated with current methods for determining slip rate from offset fluvial risers is likely to be so large that there is no resolvable discrepancy between the gps and geologic rates within the indo asian collision zone application of three of these indices to new field mapping of the cherchen he river site 86 4 e along the central altyn tagh fault yields a revised slip rate of 9 4 2 3 mm yr equivalent within error to the rates previously derived from gps and paleoseismic studies although reinterpretation of published data from the sulamu tagh site 87 4 is consistent with this revised rate additional work is needed to reconcile this result with some of the rates reported near aksay 94 e

the 2007 m5 4 alum rock california earthquake implications for future earthquakes on the central and southern calaveras fault 1 the similarity of seismograms recorded by two seismic stations demonstrate that the 31 october 2007 moment magnitude m5 4 alum rock earthquake is a repeat of a 1955 ml5 5 earthquake both occurred on oppenheimer et al s 1990 zone v stuck patch on the central calaveras fault providing new support for their model of calaveras fault earthquake activity we suggest that zone v fails only in a family of recurring m 5 4 5 5 earthquakes the 1955 and 2007 earthquakes are the penultimate and ultimate zone v events earthquakes in 1891 and 1864 are possible earlier zone v events the next zone v event is not expected in the next few decades assuming a time dependent recurrence model the mean forecast date is 2064 2035 2104 95 confidence range we further suggest that zones i ii iii and iv fail in recurring m 5 1 5 3 m 5 6 5 8 m 6 1 6 3 and m 4 9 5 0 earthquakes respectively if our earthquake recurrence model is correct the next zone i event is overdue and could occur anytime and m5 6 earthquakes should not occur on zones ii iii and iv before 2014 2012 and 2026 respectively we cannot rule out the possibility that zone vi which lies at the southern end of the mission seismic trend where the southern hayward and central calaveras faults appear to connect at depth fails aseismically or in large events on the southern hayward fault such as last occurred in 1868 or in large events on the adjoining northern calaveras fault segment

gully annealing by aeolian sediment field and remote sensing investigation of aeolian hillslope fluvial interactions colorado river corridor arizona usa abstract processes contributing to development of ephemeral gully channels are of great importance to landscapes worldwide and particularly in dryland regions where soil loss and land degradation from gully erosion pose long term land management problems whereas gully formation has been relatively well studied much less is known of the processes that anneal gullies and impede their growth this study of gully annealing by aeolian sediment spanning 95 km along the colorado river corridor in glen marble and grand canyon arizona usa employed field and remote sensing observations including digital topographic modelling results indicate that aeolian sediment activity can be locally effective at counteracting gully erosion gullies are less prevalent in areas where surficial sediment undergoes active aeolian transport and have a greater tendency to terminate in active aeolian sand although not common examples exist in the record of historical imagery of gullies that underwent infilling by aeolian sediment in past decades and evidently were effectively annealed we thus provide new evidence for a potentially important interaction of aeolian hillslope fluvial processes which could affect dryland regions substantially in ways not widely recognized moreover because the biologic soil crust plays an important role in determining aeolian sand activity and so in turn the extent of gully development this study highlights a critical role of geomorphic ecologic interactions in determining arid landscape evolution

potential for larger earthquakes in the east san francisco bay area due to the direct connection between the hayward and calaveras faults the hayward and calaveras faults two strike slip faults of the san andreas system located in the east san francisco bay area are commonly considered independent structures for seismic hazard assessment we use interferometric synthetic aperture radar to show that surface creep on the hayward fault continues 15 km farther south than previously known revealing new potential for rupture and damage south of fremont the extended trace of the hayward fault also illuminated by shallow repeating micro earthquakes documents a surface connection with the calaveras fault at depths greater than 3 5 km repeating micro earthquakes located 10 km north of the surface connection highlight the 3 d wedge geometry of the junction our new model of the hayward and calaveras faults argues that they should be treated as a single system with potential for earthquake ruptures generating events with magnitudes greater than 7 posing a higher seismic hazard to the east san francisco bay area than previously considered

simulated headward erosion of bank gullies in the dry hot valley region of southwest china although the development and migration of gully headcuts can increase soil loss and accelerate landscape degradation considerably little attention has been paid to the spatiotemporal variations of the morphological characteristics of bank gully heads in the dry hot valley region of southwest china this study explored the in situ variations in soil loss rates and morphological characteristics in active bank gully heads testing the overland flow discharge with a range of 30 to 120 l min 1 in response to this flow actively migrating headcuts developed with retreat rates ranging from 2 6 to 7 9 mm h 1 all experimental runs resulted in a gradual increase in soil loss volume incision depth and retreat distance over time due to set flow rates for the gully beds and upstream areas of gully heads the soil erosion rates were greatest at the beginning of each run and progressively decreased during the scouring test non steady state soil erosion rates were observed in the headwall for the flow discharge levels examined for this study this was due to an abrupt slope collapse after long term scouring effects as degradation progressed similar trends emerged for temporal variations within the fractal dimensions of topographic surfaces in both the gully heads and upstream areas after the scouring was run for a period of 90 min asymptotic fractal dimensions of topographic surfaces were attained in the upstream areas and gully heads suggesting that steady state morphological characteristics had been realised it should be noted that headwall collapses are typically associated with a substantial increase in sediment yield where no other obvious change in morphological characteristics occurs in the headwall therefore even though a significant difference in the soil erosion rates and fractal dimensions of topographic surface values could be found between the bank gully heads and upstream areas the temporal variation in the morphological characteristics of bank gully heads was similar to those observed in upstream areas where ephemeral gullies developed c 2013 elsevier b v all rights reserved

morphological characteristics and topographic thresholds of gullies in different agro ecological environments abstract gully erosion is an important sediment source and causes severe environmental degradation particularly in the drought prone regions of ethiopia we investigated the morphological characteristics of gullies the topographic thresholds of gully formation and estimated headcut retreat rates in three agro ecologies of the upper blue nile basin ethiopia highland guder midland aba gerima and lowland dibatie gully morphological characteristics were analyzed using data measured in the field whereas the topographic thresholds were estimated using slope and upslope drainage area average annual linear rl and volumetric ve headcut retreat rates were estimated by visual interpretation of very high resolution 0 5 1 5 m satellite images quickbird ikonos spot 7 and pleiades in a gis environment a significant power relationship fitted between gully volume v and length l for the three sites is v 8 097 l1 032 r2 0 902 n 94 the average annual rl ve and soil loss rates were estimated at 0 76 m yr 1 6 77 m3 yr 1 and 8 73 t ha 1 yr 1 in guder 2 09 m yr 1 19 58 m3 yr 1 and 20 76 t ha 1 yr 1 in aba gerima and 3 42 m yr 1 42 16 m3 yr 1 and 49 33 t ha 1 yr 1 in dibatie the higher gully headcut retreat rate in dibatie is mainly related to the highly erodible nature of vertisols the coefficients of the slope s drainage area a relationship s aa b were a 0 219 and b 0 139 in guder a 0 133 and b 0 234 in aba gerima and a 0 113 and b 0 216 in dibatie indicating that topographic thresholds for gully initiation varied among the agro ecologies the results of this study can be used to estimate gully erosion rates and identify areas for gully initiation thereby supporting the planning of appropriate gully control measures in the study sites and other areas with similar environmental settings

the earthquake cycle in the san francisco bay region a d 1600 2012 abstract stress changes produced by the 1906 san francisco earthquake had a profound effect on the seismicity of the san francisco bay region sfbr dramatically reducing it in the twentieth century whether the sfbr is still within or has emerged from this seismic quiescence is an issue of debate with implications for earthquake mechanics and seismic hazards historically the sfbr has not experienced one complete earthquake cycle i e the accumulation of stress its release primarily as coseismic slip during surface faulting earthquakes its re accumulation in the interval following and its subsequent rerelease the historical record of earthquake occurrence in the sfbr appears to be complete at about m 5 5 back to 1850 bakun 1999 for large events the record may be complete back to 1776 which represents about half a cycle paleoseismic data provide a more complete view of the most recent pre 1906 sfbr earthquake cycle extending it back to about 1600 using these we have developed estimates of magnitude and seismic moment for alternative sequences of surface faulting paleoearthquakes occurring between 1600 and 1776 on the region s major faults from these we calculate seismic moment and moment release rates for different time intervals between 1600 and 2012 these show the variability in moment release and suggest that in the sfbr regional plate boundary stress can be released on a single fault in great earthquakes such as that in 1906 and in multiple ruptures distributed on the regional plate boundary fault system on a decadal time scale

geomorphic threshold conditions for ephemeral gully incision abstract ephemeral gully erosion in cultivated land is an important source of sediment that is frequently being overlooked and not accounted for in soil erosion studies furthermore little is known about the factors controlling ephemeral gully erosion in this paper the available information on the initiation and location of ephemeral gullies is summarised focusing on the relationship between the upslope drainage area a and the critical slope gradient s cr for ephemeral gully initiation by plotting the non linear relationship between critical slope gradient measured immediately upstream of the incision head and drainage area at the incision head for gullied sites it was possible to draw a straight line on log log paper through the lower most points for each of the available datasets representing a critical slope area relationship for incision consequently below this line no incision occurs this line or critical relation can also be written as a power function between critical slope and area although many factors vary between the different datasets the exponent of the drainage area relationship 0 4 showed very little variation the observed critical slope area relationship can be related to a simple model of channel initiation by overland flow furthermore this relationship can be used to identify potentially unstable sites where control measures should be undertaken

slope and rainfall effects on the volume of sediment yield by gully erosion in the souar lithologic formation tunisia abstract the souar lithologic formation in semi arid tunisia is undergoing severe gully erosion which is threatening soil and water resources soil conservation strategies have focused more on terracing than on gully control techniques since the contribution of gully sediment yield in the overall soil loss from watersheds is unknown the paper reports investigations into the sediment yield provided by head cut as well as sidewall floor erosion of first order gullies on gentle and steep slope catchments underlined by the souar lithologic formation we measured mean field sediment volumes evacuated by different headward reaches of 10 and 9 gullies located on gentle and steep slope catchments respectively two equations between the length of the gully head cutting and the corresponding volume of evacuated sediment were established the treatment with a geographic information system arc view of air photographs of six flights from 1952 to 2000 allowed the calculation of the volume of sediment provided both by head cutting and gully sidewalls floor erosion through the following up of gully extension in eight catchments during the five periods separating the dates of these flights total gully erosion was on average 1 66 m3 ha 1 year 1 for the gentle slopes and 5 603 m3 ha 1 year 1 for the steep slopes sidewalls floor contribution in total erosion was on average 81 5 for the gentle slopes and 77 8 for the steep slopes we found out that the mean annual rainfall resulting from 40 mm daily rainfall threshold explained better the variation of annual head cutting sediment yield for these five periods than any other annual rainfall resulting from lower daily rainfall thresholds two equations between these two variables were established both for gentle and steep slope catchments

a global analysis of the morphology of linear erosion features abstract concentrated flow erosion poses a serious threat to agriculture across the world as it scours soils into linear features that can be wide and large which dramatically decreases land productivity and accessibility and causes serious downslope and downstream impacts despite the widespread occurrence of concentrated flow erosion features across the globe variations in their sizes have received limited attention their morphometric characteristics inform on the amount of fertile soil material eroded and transported to lower parts of landscapes and to river networks the main objective of this study was to elucidate the impacts of climate tropical sub tropical and temperate soil texture clayey loamy silty and sandy and land use cropland forest grassland and urban on the morphology length l width w depth d w d ratio of linear erosion features rills and gullies a total of 769 linear features from 53 published studies across the world were used in the current analysis the average length was 458 2 m for gullies and 114 7 m for rills width averaged 9 5 m for gullies and 1 0 m for rills and w d was respectively 4 0 and 6 7 which corresponded in all cases to significant difference at p

geothermometry and circulation depth of groundwater in semnan thermal springs northern iran semnan thermal springs with high tds and moderate temperature are located northwest of semnan the northern part of iran the spatial and temporal variations of physicochemical characteristics of the thermal and cold springs were investigated for the recognition of origin and dominant hydrogeochemical processes results show that the thermal springs have the same origin but due to different ascending flow paths and different conductive cooling mechanism their temperatures vary the chemical composition of thermal waters is controlled by dolomite halite and sulfate minerals dissolution and calcite precipitation and bacterial sulfate reduction the concentration of major and trace elements in the thermal springs does not change in wet and dry seasons notably because they are derived from old groundwater with deep circulation and high temperature seasonal change in the concentration of some trace elements is due to the seasonal variation of ph eh temperature and dilution by shallow waters decreasing so4 and carbonate saturation index and increasing na cl ratios and ca content in the dry season show dilution effect caused by the previous heavy rainfall events the temperature of the heating reservoir based on k mg chalcedony quartz and chemical equilibrium approach was approximately estimated in the range of 60 80 c hydrogeologically a conceptual model was suggested for the thermal springs the general groundwater flow direction is probably from the dolomite lar formation in chenaran anticline toward the adjacent syncline in a confined condition and then a thrust fault acts as a conduit and redirects the thermal water to the emerging springs at the surface

catchment scale analysis of the effect of topography tillage direction and unpaved roads on ephemeral gully incision high resolution airphotographs and digital elevation models dems were used to study areas prone to gully incision in a small agricultural catchment in northern israel data are analyzed to understand better the integrated effect of environmental and human factors on gully incision the effect of flow accumulation slope unpaved roads density and tillage direction on gully width and length is found discontinuous and topography in the form of the topographic threshold was found to be the most dominant factor on gully incision in the catchment scale the topographic threshold coefficients observed in yehezkel catchment were lower than those found in previous studies due to the effect of large rainfall events during the early winter season when the soil in fields is still unprotected by crops in addition a survey of previous studies shows that in cultivated areas there is relationship between the topographic threshold coefficients a multiplier and b exponent the influence of unpaved roads and tillage direction on gully incision was also found significant and consistent during the two seasons observed while the non parametric test showed that it added to the prediction in 15 of the gullies incision points density plot show that of the two parameters the unpaved roads were found to have greater influence on gully head location than tillage direction studying the phenomenon on the catchment scale allows better understanding of the effect of spatial variation on gully head location copyright 2009 john wiley sons ltd

hydrogeochemical modeling of a thermal system and lessons learned for co2 geologic storage abstract geological storage of carbon dioxide is presently considered to be one of the main strategies to mitigate the impact of the emissions of this gas on global warming among the various alternatives considered for co 2 geological storage one of the main geological candidates for hosting injected co 2 in the long term are deep porous reservoir rock formations saturated with brackish or saline solutions although valuable information on the expected hydrogeochemical processes involved in the co 2 storage in such deep saline aquifers can be obtained in laboratory or modeling studies the only direct source of information about the long term behavior of geological storages for co 2 in deep aquifers is natural analogues in this work a classical and simple geochemical methodology is successfully applied to the study of the features and hydrogeochemical processes determining the evolution of a spanish thermal system the alhama jaraba complex which can be considered as a natural analogue for deep geological co 2 storage in carbonate rocks the geology structure depth and hydrogeochemistry of the alhama jaraba thermal system are very similar to the expected features of a potential co 2 reservoir in carbonate materials the processes determining the hydrogeochemical evolution in the alhama jaraba thermal system have been successfully identified and quantified with the assistance of ion ion plots speciation solubility calculations and mass balance calculations furthermore the feasibility of the proposed conceptual hydrogeochemical model for this system has been verified by using reaction path calculations mass balance calculation results have indicated that the observed hydrogeochemical evolution between springs is mainly due to halite dissolution and dedolomitization triggered by gypsum or anhydrite dissolution co 2 g mass transfer has been estimated to be negligible which suggests that the main processes responsible for the variation in the tic and the co 2 g pressure during deep circulation are dissolution and precipitation reactions for carbonate minerals all the processes identified in the alhama jaraba thermal system are relevant for the long term evolution of a deep co 2 storage site hosted by carbonate rocks as shown in this study the application of classical geochemical tools provides an excellent starting point for understanding the behavior of prospective storage systems moreover the existence of dedolomitization is very relevant for the hydraulic properties of carbonate aquifers potentially used for co 2 geological storage because of the effects on porosity and therefore permeability during the long term evolution of such systems furthermore dedolomitization may represent a mechanism of mineral trapping for co 2 sequestration under certain conditions

late holocene slip rate and earthquake history for the northern calaveras fault at welch creek eastern san francisco bay area california paleoseismic trenching was performed to assess the slip rate and earthquake history of the northern segment of the calaveras fault at a site along welch creek in the eastern san francisco bay area california at welch creek the northern calaveras fault crosses a series of fluvial terraces and displaces the intervening terrace risers we derive a late holocene slip rate using two independent methods 1 by measuring the offset of the back edge i e terrace angle of one of the offset terraces and 2 by using isopach contours to measure the offset of a debris flow unit within the terrace sediments the terrace back edge is offset 39 1 m and is between 5 and 13 ka old the debris flow deposit is offset 27 1 m the deposit age is estimated to be between 4840 and 5325 cal yr b p these findings suggest a late holocene slip rate of 6 1 mm yr for the northern calaveras fault we recognize as many as seven surface rupturing earthquakes at welch creek although the amount of terrace back edge displacement suggests that several more events must have occurred that are not discernable in the stratigraphic or structural record based on the maximum amount of time between age constrained paleoearthquakes that are preserved in the record at welch creek we derive an estimate of the maximum recurrence interval of between 1375 and 3425 yr using the assumption that additional events are required to account for the 39 1 m of back edge offset we derive a recurrence estimate of between 125 and 685 yr

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

differential dissolution of a pleistocene reef in the ground water mixing zone of coastal yucatan mexico a geochemical explanation is provided for the extensive dissolution observed along the carbonate coast of the yucatan peninsula mexico mixing of fresh ground water with subterranean caribbean seawater generates a highly reactive geochemical zone that enhances aragonite and calcite dissolution and permits neomorphism of aragonite mixing zone dissolution caused by ground water discharge is a major geomorphic process in developing caves coves and crescent shaped beaches along the yucatan coast such dissolution has probably been a significant control on permeability and porosity distribution in carbonate rocks in the geologic record

regional groundwater flow paths in trans pecos texas inferred from oxygen hydrogen and strontium isotopes summary stable isotopes radiogenic isotopes and major ion chemistry are used to constrain flow paths in a fracture controlled regional groundwater flow system in far west texas the flow system occurs in permian and cretaceous sedimentary rocks and cenozoic alluvial basin fill samples from springs and wells in the study area were analyzed for major ions and hydrogen oxygen and strontium isotopes d and 18o values fall close to the global meteoric water line indicating that these values have not been significantly affected by evaporation or mineral water reactions 18o values from samples along the regional flow path are lower by as much as 3 relative to local recharge values the distribution of stable isotope values throughout the study area suggests that lower 18o values represent recharge during cooler climatic conditions rather than latitude or altitude effects 87sr 86sr values for water samples from along the regional flow path range from 0 7093 to 0 7148 with the highest values at the upgradient end of the flow system these values are significantly higher than expected for groundwaters dominated by dissolution of permian and cretaceous marine carbonates and evaporites the high 87sr 86sr values reflect dissolution of minerals of precambrian and early paleozoic origin in the crystalline rocks of the carrizo and baylor mountains and alluvial basin fill at the upgradient end of the flow system contours of 87sr 86sr values indicate a zone of high 87sr 86sr water that corresponds to the regional groundwater flow paths mass balance mixing models and mineral reactions models indicate a three end member mixing system modified by dissolution of strontium bearing minerals in the alluvial fill at the upgradient end of the flow system

short term bank gully retreat rates in mediterranean environments abstract in this study short term headcut retreat was monitored from 46 active bank gullies selected in the guadalentin and the guadix basin in southeast spain the measurements were carried out manually using an orthogonal reference system fixed by erosion pins around the gully heads between april 1997 and april 1999 with a 1 year interval the average volumetric retreat rate for all gullies was 4 0 m 3 year 1 corresponding with an average linear retreat rate of 0 1 m year 1 but more erosion took place during the first monitored year 1997 1998 compared to the second 1998 1999 an interplay of spatial variations in rainfall distribution and tension crack activity is assumed to be responsible for the important difference in annual headcut retreat compared to the small difference in annual rainfall amounts statistical analysis showed that the present drainage basin area a p was the most important topographical factor explaining average gully headcut retreat rate both in terms of annual eroded volume v e and annual linear retreat r l and expressed by the power relationships v e 0 04 a p 0 38 r 2 0 39 and r l 0 01 a p 0 23 r 2 0 39 the v e a p relationship was compared with the relationship between original drainage basin area a o and total eroded bank gully volume vol i e vol 1 71 a o 0 60 r 2 0 65 the importance of runoff generation from a drainage basin is shown by the positive correlation of linear headcut retreat and the runoff curve number cn representative for the conditions in the drainage basin high cn values tend to coincide with higher annual eroded volumes in the relationship between present drainage basin area a p and annual eroded volume v e but this effect was not observed in the relationship between original drainage basin area a o and total eroded bank gully volume vol stepwise multiple regression selected the relevant environmental parameters explaining annual eroded volume and linear retreat in both equations the present drainage basin area explained the largest part of the variation the cn was selected as another common parameter height of the headcut was the second most important variable explaining annual eroded volume indicating the role of energy transfers and undercutting at the headcut linear retreat was further explained by the average slope of the present drainage basin area representing the effect of decreasing transmission losses and increasing flow velocity with steeper catchment slopes and by the sand content decreasing the cohesion of the soil material promoting soil fall and headcut retreat spatial extrapolation of the measured volumetric retreat rate of 4 0 m 3 year 1 revealed that active bank gully heads contribute up to 6 of the sediment yearly filling up the puentes reservoir estimated gully ages i based on the ergodic principle and ii by linear extrapolation of actual gully retreat rates in the past range between 63 years and 1539 and between 64 and 1720 years respectively the high correlation between the gully ages estimated by the two methods is attributed to the fact that most gullies have not reached the evolutionary stage of significantly declining retreat rates since medium term gully retreat rates are more dependent on drainage basin area compared to the short term retreat rates obtained in this study the estimated gully ages represent maximum values assuming that present land use and climate conditions prevailed over the last two millennia

holocene slip rate and earthquake recurrence of the northern calaveras fault at leyden creek northern california the northern calaveras fault traverses a heavily populated area in the eastern san francisco bay region and has not had a large earthquake in more than 130 years to obtain data on the number timing and recurrence of large paleoearthquakes we conducted paleoseismologic investigations at leyden creek which crosses the fault in the rugged southern east bay hills the site is characterized by a prominent west facing scarp and fivc fluvial terraces on the western upstream side of the fault on the eastern downstream side of the fault the creek flows through a narrow bedrock canyon that constricts the modern valley and has constrained the location of a late pleistocene palcovalley the margin of a buried bedrock valley west of the fault trends nearly perpendicular to the fault and is offset 54 18 14 m in a right lateral sense from the narrow bedrock canyon based on radiocarbon ages for alluvial sediments predating and postdating this paleovalley margin we estimate an age of 11 5 3 1 ka for the valley margin and a holocene slip rate of 5 2 mm yr for the fault at leyden creek slickensides exposed in multiple trenches across the fault show that the most recent movement was predominantly lateral with a minor component of down to the west slip multiple displaced scarp derived colluvial deposits are interpreted as results of five or six surface ruptures within the past 2500 years twenty one radiocarbon samples from scarp derived colluvium and interfingered alluvial deposits suggest an average interval between surface rupture carthquakes of 250 to 850 years

the mission link between the hayward and calaveras faults the left stepover between the calaveras and hayward faults gives rise to compressive strain that is accommodated by vertical deformation producing the highest hills bordering the east side of san francisco bay monument peak to mission peak the projection of the active trace of the hayward fault is separated 3 5 km from the junction of the northern and southern segments of the calaveras fault at calaveras reservoir for pure strike slip on the hayward and calaveras faults the stepover region is compressed in area at a rate given by the separation times the long term slip rate of 9 mm yr on the hayward fault assuming a seismogenic depth of 10 km the horizontal compression accumulated over 150 years is equivalent to a dip slip seismic moment of 2 8 1018 n m this moment if released in a single event would generate an earthquake of magnitude 6 3 due to dip slip alone dip slip may occur on buried faults throughout the stepover region the base of the southwest face of monument peak suggests a buried thrust or reverse fault dipping northeast the prominent scarp on mission peak has the same strike and sense of slip current microearthquakes between the calaveras and hayward faults align parallel to the mission fault but show only horizontal slip on a vertical fault plane a dipping fault is needed to satisfy the geometric constraint of the convergence therefore the mission fault zone must consist of two or more fault surfaces inclined at different dip angles as is observed in the san andreas fault zone in the loma prieta area horizontal slip is building up stress on the inclined fault which is currently locked growing compressive stress will increasingly impede horizontal slip until a thrust or reverse slip event occurs allowing then more horizontal slip to be transferred from the calaveras to the hayward fault the dip slip fault might be the unstable element governing slip in the larger system

rapid assessment of gully sidewall erosion rates in data poor catchments a case study in australia knowledge of erosion rates and sediment yields from gullies is critical for the effective prioritisation of management efforts aimed at reducing the impact of gully derived sediments on water quality this paper describes a rapid assessment method for estimating sidewall gully erosion rates for already established gully networks it combines a conceptual empirical model of the cycle of gully initiation and stabilisation with an easy to apply technique for assessing gully extent and dimensions the method is illustrated using a case study of the avon richardson catchment of north central victoria australia it is estimated that a total of 4 6 106tonnes of sediment have been generated in that catchment from gully erosion since the latest major phase of gullying in the mid 1800s this is equivalent to 8 9tha 1y 1 if sediment generation was evenly distributed spatially and temporally across the 3300km2 catchment over 160years prior to 2010 current rates of gully erosion are estimated to be 4700ty 1 equivalent to 1 4tha 1y 1 the results are comparable with observed rates of sidewall erosion in the avon richardson catchment further testing is required to build confidence in its applicability to assess sediment yields and for assisting regional authorities to plan remediation efforts

gully erosion in the siwalik hills nepal estimation of sediment production from active ephemeral gullies a simple field based monitoring programme was established in a small catchment area 4 6 km2 to find the rates of gully erosion in the siwalik hills nepal the rates are used to estimate the amount of sediment produced by gully erosion in the catchment three large and active gullies were selected with areas ranging from 0 44 to 0 78 ha aerial photographs taken in 1964 1978 and 1992 were ortho rectified and used to study the dynamics of gully heads the same gullies were also monitored manually using an orthogonal reference system fixed by erosion pins around the gully heads results from the aerial photos indicated that the gullies expanded remarkably over the period from 1964 to 1992 by 34 to 58 per cent head retreat rates during that period were 0 48 0 55 and 0 73 m a 1 and average annual sediment evacuation was estimated as 2534 171 959 60 and 2783 118 m3 a 1 for the three gullies respectively from the field measurement estimated volumes were found to vary from 731 57 to 2793 201 m3 a 1 over the monitoring period of two years it was also found that the gullies produce sediment which accounts for up to 59 per cent of the sediment produced from surface erosion in the headwater catchment the findings are useful for planning and executing appropriate control measures and constructing a sediment hazard map at the catchment scale copyright 2006 john wiley sons ltd

interseismic coupling and refined earthquake potential on the hayward calaveras fault zone interseismic strain accumulation and fault creep is usually estimated from gps and alignment arrays data which provide precise but spatially sparse measurements here we use interferometric synthetic aperture radar to resolve the interseismic deformation associated with the hayward and calaveras faults hf and cf in the east san francisco bay area the large 1992 2011 sar data set permits evaluation of short and long wavelength deformation larger than 2 mm yr without alignment of the velocity field to a gps based model our time series approach in which the interferogram selection is based on the spatial coherence enables deformation mapping in vegetated areas and leads to refined estimates of along fault surface creep rates creep rates vary from 0 2 mm yr on the northern cf to 14 2 mm yr on the central cf south of the hf surface junction we estimate the long term slip rates by inverting the long wavelength deformation and the distribution of shallow slip due to creep by inverting the remaining velocity field this distribution of slip reveals the locations of locked and slowly creeping patches with potential for a m6 8 0 3 on the hf near san leandro a m6 6 0 2 on the northern cf near dublin a m6 5 0 1 on the hf south of fremont and a m6 2 0 2 on the central cf near morgan hill with cascading multisegment ruptures the hf rupturing from berkeley to the cf junction could produce a m6 9 0 1 the northern cf a m6 6 0 1 the central cf a m6 9 0 2 from the junction to gilroy and a joint rupture of the hf and central cf could produce a m7 1 0 1

assessment of soil losses by ephemeral gully erosion using high altitude stereo aerial photographs the objective of this study is to explore in a critical way the potential of high altitude stereo aerial photographs for the assessment of ephemeral gully erosion rates on 28 may 1995 an intensive rainfall event 30 mm h 1 during 30 min return period 3 years occurred in central belgium ephemeral gullies formed within an area of 218 ha study area 1 were mapped and measured both in the field and by high altitude aerial photos taken at the same time comparison of these two methods shows that if only one of the two surveying techniques had been used only 75 per cent of the total ephemeral gully length would have been detected so that the combination of aerial and field data leads in fact to the best possible determination of total gully length within the selected area a correction factor c is proposed so that the results of an ephemeral gully erosion survey based on high altitude stereo aerial photos can be adjusted for the undetected gullies next a sequential series of high altitude stereo aerial photographs taken in six different years was analysed in order to determine ephemeral gully erosion rates in three selected study areas study areas 2 3 and 4 selection criteria were chosen so that these three areas were similar to study area 1 and representative for the cultivated areas in central belgium where intense soil erosion regularly occurs ephemeral gullies were mapped and their total length was measured from the aerial photos using a mean gully cross section of 0 2635 m2 determined in study area 1 the average eroded volume is 1 89 m3 ha 1 in six months for study area 1 0 86 m3 ha 1 in six months for area 2 1 44 m3 ha 1 in six months for area 3 and 2 37 m3 ha 1 in six months for area 4 according to the correction factor c these mean ephemeral gully erosion volumes have to be increased by 44 per cent the ephemeral gully erosion rates based on high altitude stereo aerial photos correspond well with the results of other surveys carried out in the belgian loess belt copyright 1999 john wiley sons ltd

testing crustal melting models for the origin of flood rhyolites a nd pb sr isotopic study of the tertiary davis mountains volcanic field west texas flood rhyolites are lavas that have areal extents similar to large ignimbrites the davis mountains volcanic field differs from most other cenozoic volcanic fields in the southwestern united states in that a major volume of the silicic rocks erupted there are flood rhyolites rather than ignimbrites a comparative isotopic study was made of a major flood rhyolite unit the star mountain and mafic to silicic rocks from three other magma systems the entire range in nd isotopic compositions found in the volcanic field is relatively small with n4 values ranging from about 2 in a basalt to between 1 0 and 1 5 in the silicic rocks including the star mountain rhyolite pb isotope ratios of the star mountain lavas 206 pb 204 pb 17 9 are considerably higher than those of xenoliths of proterozoic deep crustal granulites from the region 17 4 two types of crustal sources appear viable for the origin of the flood rhyolites first if the star mountain samples represent near primary melts from a crustal source then that source must have been cenozoic in age and silicic in composition second if the star mountain samples represent highly fractionated magmas then the crustal source could have been mafic but it could not have experienced the proterozoic granulite facies metamorphism known to have affected the basement the overall isotopic trends of the volcanic rocks are qualitatively consistent with the hypothesis that all the silicic rocks including the flood rhyolites evolved from mantle derived basalts with variable but generally small amounts of crustal contamination

refining fault slip rates using multiple displaced terrace risers an example from the honey lake fault ne california usa abstract faulted terrace risers are semi planar features commonly used to constrain quaternary slip rates along strike slip faults these landforms are difficult to date directly and therefore their ages are commonly bracketed by age estimates of the adjacent upper and lower terrace surfaces however substantial differences in the ages of the upper and lower terrace surfaces a factor of 2 4 difference observed globally produce large uncertainties in the slip rate estimate in this investigation we explore how the full range of displacements and bounding ages from multiple faulted terrace risers can be combined to yield a more accurate fault slip rate we use 0 25 m cell size digital terrain models derived from airborne lidar data to analyze three sites where terrace risers are offset right laterally by the honey lake fault in ne california usa we use ages for locally extensive subhorizontal surfaces to bracket the time of riser formation an upper surface is the bed of abandoned lake lahontan having an age of 15 8 0 6 ka and a lower surface is a fluvial terrace abandoned at 4 7 0 1 ka we estimate lateral offsets of the risers ranging between 6 6 and 28 3 m median values a greater than fourfold difference in values the amount of offset corresponds to the riser s position relative to modern stream meanders the smallest offset is in a meander cutbank position whereas the larger offsets are in straight channel or meander point bar positions taken in isolation the individual terrace riser offsets yield slip rates ranging from 0 3 to 7 1 mm a however when the offset values are collectively assessed in a probabilistic framework we find that a uniform linear slip rate of 1 6 mm a 1 4 1 9 mm a at 95 confidence can satisfy the data within their respective uncertainties this investigation demonstrates that integrating observations of multiple offset elements crest midpoint and base from numerous faulted and dated terrace risers at closely spaced sites can refine slip rate estimates on strike slip faults

tracing regional flow paths to major springs in trans pecos texas using geochemical data and geochemical models abstract san solomon giffin and phantom lake springs located in trans pecos texas have a high tds na cl so 4 baseflow component derived from a regional flow system and a low tds mixed cation mixed anion stormflow component derived from local precipitation events the hypothesis that the regional flow system maintaining baseflow spring discharge originates in the salt basin and flows through the apache mountains towards the springs is tested with historical geochemical data from wells and springs data from over 1400 wells in the study area over a 50 year period were analyzed and used to delineate 11 hydrochemical facies based on the predominant ions geochemical data from samples along the hypothesized regional flow path indicate a trend of increasing dissolved solids and cl hco 3 ratios and decreasing na cl ratios these are consistent with evolution of groundwater in an unconfined regional system dominated by carbonates and evaporites in the bicarbonate facies the waters represent recent recharge modified by mineral dissolution and cation exchange in the sulfate zones the hydrochemical facies are controlled by gypsum anhydrite and halite dissolution cation exchange and mixing with na cl waters in the chloride zones the hydrochemical facies are controlled by halite dissolution and irrigation return flow spring discharge chemistry is most similar to chloride zone waters na cl and ca so 4 ratios suggest that baseflow is derived from the chloride zone waters upgradient along the hypothesized flow path phreeqc modeled groundwater evolution along the hypothesized flow path and spring discharge under stormflow and baseflow conditions results indicate that 1 hydrochemistry along the regional flow path is controlled by dissolution of halite gypsum dolomite and co 2 and by precipitation of calcite 2 baseflow spring discharge is derived primarily from this regional flow system and 3 spring discharge after major storm events can constitute as much as 72 local recharge that is further modified by dissolution of calcite gypsum and co 2 data analysis and model results suggest that cave formation in this system is occurs during major storm events

correlation between groundwater flow and deformation in the fractured carbonate gran sasso aquifer infn underground laboratories central italy the gran sasso massif is a carbonate fractured aquifer with a spring discharge of more than 18 m3 s 1 the water table has been partially drained by two motorway tunnels and an underground laboratory ul located into the core aquifer karst features have limited role below the water table where groundwater flow is mainly regulated by the fracture network two paired laser extensometers ba and bc recorded ground deformation in the ul changes in deformation correlate with the seasonal recharge discharge cycle of groundwater flow and its long term changes hydrostatic conditions prevail during the recharge phases because of the low permeability of local fractures favoring compression and hydraulic gradient increase above the ul fast groundwater flow through the high permeability fault outcropping in the ul can enhance local dilatation for short periods spring discharge during exhaustion periods is fed by the low permeability fracture network fostering hydrodynamic conditions by hydraulic gradient decrease diminishing compression and consequently favoring dilatation independent support to this conceptual model comes from local tests and a numerical model which highlights the hydromechanical strain effects induced by the hydrological cycle on the jointed rock mass along ba and the role of the hydraulic gradient on the rock mass deformation

isotope hydrology and geochemical modeling new insights into the recharge processes and water rock interactions of a fissured carbonate aquifer gran sasso central italy the goal of this paper was to characterize the recharge process and water rock interactions in a regional homogeneous fractured carbonate aquifer in the mediterranean environment gran sasso central italy through isotope data 2h 18o and 13c dic collected between 2006 and 2010 samples were collected from the springs of the gran sasso aquifer and from the underground nuclear physics laboratories located within the aquifer additionally the hydrochemical data and the reference hydrogeological frameworks of previous studies have been used as a starting point for the geochemical modeling the gran sasso aquifer which is bounded by terrigenous and clastic units acting as aquitards accommodates a uniquely broad regional groundwater which feeds springs mainly at its border with high steady discharge in total these springs discharge of more than 18 m3 s at a local scale for the aquifer core and at a regional scale for the overall aquifer 2h 18o and 13c dic isotope data the geochemical inverse modeling through phreeqc and the 13c dic fractionation modeling through netpath 2 0 show the following 1 clear processes of evaporation and related isotope enrichment may be ruled out 2 groundwater flow is active and extends to the overall aquifer without clear signs of layering and partitioning 3 groundwater flowpaths radiate from the core toward the periphery 4 in l aquila plain gran sasso groundwater mixes with shallow quaternary water at a ratio of one half 5 the main geochemical processes are the dissolution of calcite and dolomite and in some cases ion exchange occurs mg2 and so42 release ca2 adsorption 6 in the less mineralized recharge groundwater the 13c dic value is influenced by the 13c dic value of rainfall while in more evolved groundwater the final 13c dic value is reached by fractionation during the flowpaths indicating a lengthy interaction with limestone

evaluation of geochemical and hydrogeological processes by geochemical modeling in an area affected by evaporite karstification the ebro valley in the outskirts of zaragoza ne spain is severely affected by evaporite karstification leading to multiple problems related to subsidence and sinkhole formation in this work a combination of inverse mixing mass balance and forward reaction path geochemical calculations is applied for the quantification of the main karstification processes and seasonal variations in this area the obtained results prove the suitability of the applied methodology for the characterization of similar problems in other areas with scarce geological and hydrogeological information the hydrogeology and hydrochemistry of the system can be mainly attributed to the mixing of variable proportions of concentrated groundwater from the evaporitic aquifer and more dilute water from the overlying alluvial aquifer the existence of a good connection between these aquifers is supported by 1 the fast changes in the hydrochemistry of the karst aquifer related to recharge by irrigation and 2 the deduced input of evaporitic groundwater in the alluvial materials the evolution in some parts of the alluvial evaporitic aquifer system is clearly dominated by the seasonal variations in the recharge by dilute irrigation waters up to 95 of water volume in some sinkhole ponds whereas other points seem to be clearly determined by the hydrochemistry of the concentrated evaporitic aquifer groundwater up to 50 of the water volume in some springs the following reactions previous or superimposed to mixing processes explain the observed hydrochemistry in the studied area dissolution of halite naci gypsum caso4 2h 2 o anhydrite caso4 and dolomite camg co3 2 co2 b input and degassing and calcite caco3 dissolution precipitation the modeling results suggest the existence of a large spatial variability in the composition of the evaporitic groundwater mainly caused by large differences in the availability of halite in contact with the groundwater active subsidence associated with halite dissolution is expected to continue in the study area together with the episodic increase of gypsum dissolution associated with the input of dilute irrigation waters c 2015 elsevier b v all rights reserved

assessment of groundwater quality for irrigation and drinking purposes and identification of hydrogeochemical mechanisms evolution in northeastern tunisia oligocene and mio plio quaternary siliciclastic deposits constitute the most important deep aquifers of the kairouanai sahel region considering the over exploitation and contamination of the surface groundwater recourse to use deep groundwater was crucial these aquifers revealed three major hydrochemical facies hco3 mg hco3 na and so4 mg water types rock water interaction showed the main mechanisms are rock weathering and evaporation different parameters such as water quality index wqi sodium absorption ratio sar percentage of sodium residual sodium carbonate rsc magnesium hazard mh and permeability index pi were used to evaluate groundwater suitability for drinking and irrigation purposes results highlighted that groundwater is unsafe for irrigation based on pi mh rsc and salinity diagram according to the wqi values 10 25 of the water samples had good water quality 69 23 were considered as poor water 12 82 were very poor water and 7 69 were considered unsuitable for drinking purpose

geodetic constraints on san francisco bay area fault slip rates and potential seismogenic asperities on the partially creeping hayward fault 1 the hayward fault in the san francisco bay area sfba is sometimes considered unusual among continental faults for exhibiting significant aseismic creep during the interseismic phase of the seismic cycle while also generating sufficient elastic strain to produce major earthquakes imaging the spatial variation in interseismic fault creep on the hayward fault is complicated because of the interseismic strain accumulation associated with nearby faults in the sfba where the relative motion between the pacific plate and the sierra block is partitioned across closely spaced subparallel faults to estimate spatially variable creep on the hayward fault we interpret geodetic observations with a three dimensional kinematically consistent block model of the sfba fault system resolution tests reveal that creep rate variations with a length scale of 15 km are poorly resolved below 7 km depth in addition creep at depth may be sensitive to assumptions about the kinematic consistency of fault slip rate models differential microplate motions result in a slip rate of 6 7 0 8 mm yr on the hayward fault and we image along strike variations in slip deficit rate at 15 km length scales shallower than 7 km depth similar to previous studies we identify a strongly coupled asperity with a slip deficit rate of up to 4 mm yr on the central hayward fault that is spatially correlated with the mapped surface trace of the 1868 mw 6 9 7 0 hayward earthquake and adjacent to gabbroic fault surfaces

geochemical modeling of the madison aquifer in parts of montana wyoming and south dakota stable isotope data for dissolved carbonate sulfate and sulfide are combined with water compo sition data to construct geochemical reaction models along eight flow paths in the madison aquifer in parts of wyoming montana and south dakota the sulfur isotope data are treated as an isotope dilution problem whereas the carbon isotope data are treated as rayleigh distillations all reaction models reproduce the observed chemical and carbon and sulfur isotopic composition of the final waters and are partially validated by predicting the observed carbon and sulfur isotopic compositions of dolomite and anhydrite from the madison limestone the geochemical reaction models indicate that the dominant groundwater reaction in the madison aquifer is dedolomitization calcite precipita tion and dolomite dissolution driven by anhydrite dissolution sulfate reduction ca mg2 ina cation exchange and halite dissolution are locally important particularly in central montana the groundwater system is treated as closed to c02 gas from external sources such as the soil zone or cross formational leakage but open to c02 from oxidation of organic matter coupled with sulfate reduction and other redox processes occurring within the aquifer the computed mineral mass transfers and modeled sulfur isotopic composition of madison anhydrites are mapped throughout the study area carbon 14 groundwater ages adjusted for the modeled carbon mass transfer range from modem to about 23 000 years b p and indicate flow velocities of 7 7 ftlyr 2 1 26 5 rnlyr most horizontal hydraulic conductivities calculated from darcy s law using the average 14 c flow velocities are within a factor of 5 of those based on digital simulation the calculated mineral mass transfer and adjusted 14 c groundwater ages permit determination of apparent rates of reaction in the aquifer the apparent rate of organic matter oxidation is typically 0 12 jlidol uyr sulfate and to a lesser extent ferric iron are the predominant electron acceptors the kinetic biochemical fractionation of 34 s between sulfate and hydrogen sulfide is approximately 44 o at 25 c with a temperature variation of

a record of large earthquakes during the past two millennia on the southern green valley fault california we document evidence for surface rupturing earthquakes events at two trench sites on the southern green valley fault california sgvf the 75 80 km long dextral sgvf creeps 1 4 mm yr we identify stratigraphic horizons disrupted by upward flowering shears and infilled fissures unlikely to have formed from creep alone the mason rd site exhibits four events from 1013 ce to the present the lopes ranch site lr 12 km to the south exhibits three events from 18 bce to present including the most recent event mre 1610 52 yr ce 1 and a two event interval 18 bce 238 ce isolated by a millennium of low deposition using oxcal to model the timing of the four event earthquake sequence from radiocarbon data and the lr mre yields a mean recurrence interval ri or of 199 82 yr 1 and 35 yr standard error of the mean the first based on geologic data the time since the most recent earthquake open window since mre is 402 yr 52 yr well past 200 yr the shape of the probability density function pdf of the average ri from oxcal resembles a brownian passage time bpt pdf i e rather than normal that permits rarer longer ruptures potentially involving the berryessa and hunting creek sections of the northernmost gvf the model coefficient of variation cv is 0 41 but a larger value cv 0 6 fits better when using bpt a bpt pdf with of 250 and cv of 0 6 yields 30 yr rupture probabilities of 20 25 versus a poisson probability of 11 17 online material oxcal model for ages of paleoearthquakes lopes site 1998 logs and description of a model for estimation of rupture frequency

medium term gully headcut retreat rates in southeast spain determined from aerial photographs and ground measurements this paper deals with gully retreat rates at different time scales whereby the short term time scale may span a time interval of 1 5 years the medium term time scale a time interval of 5 50 years and the long term time scale a time interval of more than 50 years an analysis of high altitude aerial photographs in combination with ground measurements allowed us to quantify volumetric gully head retreat rates for 12 permanent gullies in southeast spain guadalentin and guadix study areas over a 40 43 year time interval medium term time scale this resulted in an average retreat rate ve of 17 4 m3 year 1 a power relationship between drainage basin area a and medium term volumetric gully head retreat rate ve 0 069a0 380 r2 0 51 n 21 was found by combining the gully head retreat rates obtained in this study with those obtained by a dendrochronological method the exponent b and the coefficient of determination r2 of the power relationships ve aab increases from the short term to the long term time scale expressing the increasing importance of drainage basin area in gully development with time considerable differences between gully head retreat rates measured at the short and medium term time scales at individual gullies showed the importance of land use changes and unsuccessful management practices on gully head retreat and the episodic nature of gully head retreat when piping and tension cracking are involved higher gully head retreat rates are obtained at the medium term time scale compared to the short term time scale but the differences are not significantly different at 10 the medium term methods tend to measure proportionally more high gully retreat rates but less extreme values compared to the short term method this is explained by a more equal distribution of extreme rainfall events both in space and time at a longer term time scale and hence a higher probability of measuring the average effect of both small and extreme rainfall events at each gully

gully head erosion processes on a semi arid valley floor in kenya a case study into temporal variation and sediment budgeting a three year monitoring programme of gully head retreat was established to assess the significance of sediment production in a drainage network that expanded rapidly by gully head erosion on the low angled alluvio lacustrine njemps flats in semi arid baringo district kenya this paper discusses the factors controlling the large observed spatial and temporal variation in gully head retreat rates ranging from 0 to 15 m a 1 the selected gullies differed in planform and in runoff contributing catchment area but soil material and land use were similar the data were analysed at event and annual timescales the results show that at annual timescale rainfall amount appears to be a good indicator of gully head retreat while at storm event timescale rainfall distribution has to be taken into account a model is proposed including only rainfall p and the number of dry days dd between storms which explains 56 per cent of the variation in retreat rate of the single headed gully of lam1 a detailed sediment budget has been established for lam1 and its runoff contributing area rca by measuring sediment input from the rca the sediment output by channelized flow and linear retreat of the gully head for nine storms it can be seen that erosion shifts between different components of the budget depending on the duration of the dry period dd between storms sediment input from the rca was usually the largest component for the smaller storms the erosion of the gully head occurred as a direct effect of runoff falling over the edge ghwaterfall and of the indirect destabilization of the adjacent walls by the waterfall erosion and by saturation ghmass storage the latter component ghmass storage was usually much larger that the former ghwaterfall the sediment output from the gully was strongly related to the runoff volume while the linear retreat because of its complex behaviour was not overall the results show that the annual retreat is the optimal timescale to predict retreat patterns more detailed knowledge about relevant processes and interactions is necessary if gully head erosion is to be included in event based soil erosion models copyright 2001 john wiley sons ltd

slip partitioning of the calaveras fault california and prospects for future earthquakes examination of main shock and microearthquake data from the calaveras fault during the last 20 years reveals that main shock hypocenters occur at depths of 8 9 km near the base of the zone of microearthquakes the spatial pattern of pre main shock microseismicity surrounding the coyote lake and morgan hill hypocenters is similar to the pattern of the post main shock microseismicity microseismicity extends between depths of 4 and 10 km and defines zones of concentrated microseismicity and aseismic zones estimates of the fault regions which slipped during the coyote lake and morgan hill earthquakes as derived from seismic radiation coincide with zones which are otherwise aseismic we propose that these persistent aseismic zones represent stuck patches which slip only during moderate earthquakes from the pattern of microearthquake locations we recognize six aseismic zones where we expect future main shocks will rupture the calaveras fault from an analysis of historic seismic data we establish the main shock rupture history for each aseismic zone and identify two zones that are the most likely sites for the next m 5 earthquakes the first zone is located near gilroy and was last ruptured by a m5 2 earthquake in 1949 the second zone is located south of calaveras reservoir and north of the 1988 m5 1 alum rock earthquake it has not slipped seismically since at least 1903 and the size of the aseismic region is sufficiently large to sustain a m5 5 earthquake

distribution probability of large scale landslides in central nepal abstract large scale landslides in the himalaya are defined as huge deep seated landslide masses that occurred in the geological past they are widely distributed in the nepal himalaya the steep topography and high local relief provide high potential for such failures whereas the dynamic geology and adverse climatic conditions play a key role in the occurrence and reactivation of such landslides the major geoscientific problems related with such large scale landslides are 1 difficulties in their identification and delineation 2 sources of small scale failures and 3 reactivation only a few scientific publications have been published concerning large scale landslides in nepal in this context the identification and quantification of large scale landslides and their potential distribution are crucial therefore this study explores the distribution of large scale landslides in the lesser himalaya it provides simple guidelines to identify large scale landslides based on their typical characteristics and using a 3d schematic diagram based on the spatial distribution of landslides geomorphological geological parameters and logistic regression an equation of large scale landslide distribution is also derived the equation is validated by applying it to another area for the new area the area under the receiver operating curve of the landslide distribution probability in the new area is 0 699 and a distribution probability value could explain 65 of existing landslides therefore the regression equation can be applied to areas of the lesser himalaya of central nepal with similar geological and geomorphological conditions

hydrogeochemistry of volcanic hydrogeology based on cluster analysis of mount ciremai west java indonesia summary hydrogeochemical analysis has been conducted on 119 spring locations to portray volcanic hydrogeological system of mount ciremai west java indonesia cluster analysis on 14 parameters has extracted three clusters cluster 1 112 springs is distinguished by normal temperatures low tds ec and high bicarbonate concentrations cluster 2 five springs has moderately high temperature tds ec and high concentration of chloride cluster 3 two springs exhibits high temperature anomalous high tds ec and chloride concentration three hydrogeological systems have been pictured based on the 3 clusters consecutively the 1st system is developed in shallow unconfined aquifer with domination of high bicarbonate 4 2 me l meteoric water the 2nd system is predominated with mixing processes between groundwater in unconfined aquifer and hot groundwater from deeper aquifers the 3rd system is primarily dominated by groundwater flow from deep formation the hot deep seated groundwater flow also carries mud particles it has anomalous high tds 1000 mg l ec 515 s cm and chloride 99 me l from interaction between groundwater with clay formations interpreted as kaliwangu formation