comparing physiographic maps with different categorisations abstract this paper addresses the need for a robust map comparison method suitable for finding similarities between thematic maps with different forms of categorisations in our case the requirement was to establish the information content of newly derived physiographic maps with regards to set of reference maps for a study area in england and wales physiographic maps were derived from the 90 m resolution srtm dem using a suite of existing and new digital landform mapping methods with the overarching purpose of enhancing the physiographic unit component of the soil and terrain database soter reference maps were seven soil and landscape datasets mapped at scales ranging from 1 200 000 to 1 5 000 000 a review of commonly used statistical methods for categorical comparisons was performed and of these the cramer s v statistic was identified as the most appropriate for comparison of maps with different legends interpretation of multiple cramer s v values resulting from one by one comparisons of the physiographic and baseline maps was facilitated by multi dimensional scaling and calculation of average distances between the maps the method allowed for finding similarities and dissimilarities amongst physiographic maps and baseline maps and informed the recommendation of the most suitable methodology for terrain analysis in the context of soil mapping

desert pavement coated surfaces in extreme deserts present the longest lived landforms on earth all exposed rocks on earth s surface experience erosion the fastest rates are documented in rapidly uplifted monsoonal mountain ranges and the slowest occur in extreme cold or warm deserts millennial submeterscale erosion may be approached only in the latter the oldest previously reported exposure ages are from boulders and clasts of resistant lithologies lying at the surface and the slowest reported erosion rates are derived from bedrock outcrops or boulders that erode more slowly than their surroundings thus these oldest reported ages and slowest erosion rates relate to outstanding features in the landscape while the surrounding landscape may erode faster and be younger we present erosion rate and exposure age data from the paran plains a typical environment in the near east where vast abandoned alluvial surfaces 10 2 10 4 km 2 are covered by well developed desert pavements these surfaces may experience erosion rates that are slower than those documented elsewhere on our planet and can retain their original geometry for more than 2 m y major factors that reduce erosion converge in these regions extreme hyperaridity tectonic stability fl at and horizontal surfaces i e no relief and effective surface armoring by a clast mosaic of highly resistant lithology the 10 be concentrations in amalgamated desert pavement chert clasts collected from abandoned alluvial surfaces in the southern negev israel representing the sahara arabia deserts indicate simple exposure ages of 1 5 1 8 ma or correspond to maximum erosion rates of 0 25 0 3 m m y 1 the 36

climatic and tectonic forcing on alluvial fans in the southern central andes abstract mountainous regions and their forelands commonly support a suite of landforms sensitive to climate change and tectonics alluvial fans in particular are prominent geomorphological features in arid and semiarid regions which provide record for landscape climate and tectonic evolution we applied 10 be surface exposure dating on moraines and associated fan terraces of the ansilta range 31 6 s 69 8 w in the southern central andes with the aim of comparing both chronologies and examining the nature of alluvial fan development the alluvial fans yield minimum ages of 19 1 t1 120 9 t2 185 9 t3 389 22 t4 and 768 35 t5 ka minimum ages derived from moraines are 18 1 m1 27 1 m2 279 23 m3 and 410 28 m4 ka m1 t1 and m4 t4 seem to be geomorphic counterparts during mis2 and mis11 12 combining our glacial and alluvial database with that available from other published studies we recognized further glacial alluvial counterparts the distinct phases of alluvial fan aggradation mainly correlate with moraines or have a regional extension and fall into local cold and wet times so that climate seems to be the main forcing of alluvial fan formation at our study site even being a region with proofed neotectonic activity we interpret the presence of at least six cold and humid periods of alluvial aggradation which correlate with global mis 2 3 5d e 8 12 and 18 20 based on these results alluvial fans may allow landscape and climate reconstructions back to 750 ka in our study region

variations in late syn rift melt alignment inferred from shear wave splitting in crustal earthquakes beneath the ethiopian rift 1 the northern main ethiopian rift mer marks the transition from continental rifting to incipient seafloor spreading we constrain anisotropy of the upper crust in the mer and its uplifted rift flanks using shear wave splitting from 24 earthquakes located beneath 18 broadband stations along the axis of the mer the fast polarization direction is oriented between n and nne parallel to quaternary recent faults aligned cones and maximum horizontal stress delay times are highest 0 24 s where independent seismic studies show evidence of shallow partial melt we attribute anisotropy along the rift axis to aligned melt filled micro cracks and dikes at stations flanking the rift the fast polarization direction is oriented ne and delay times are smaller 0 04 0 14 s the lower amount of anisotropy is consistent with reduced melt away from the rift axis these results show melt induced anisotropy persists into the crust and magma injection localizes and accommodates strain just prior to continental break up

geology geochronology and rift basin development in the central sector of the main ethiopia rift based on stratigraphic relationships and k ar dating of volcanic rocks from both of the escarpments flanking plateaus and from the rift floor of the central sector of the main ethiopian rift six major volcanic episodes are recognized in the rift9s development over a time span from the late oligocene to the quaternary using the k ar data correlation of volcanic units from the six periods of activity throughout the study area forms the basis for establishing six time stratigraphic chronozones for the central sector that are related to volcanism in the ethiopian cenozoic volcanic province the oldest basalt and rhyolite flows exposed along the rift margins of the central sector are time correlative to or older than those in river canyons for example blue nile on the adjacent northwest plateau a thinned mesozoic stratigraphic sequence along the guraghe western rift margin suggests that doming may have preceded volcanism and rifting of the cenozoic by late miocene time at least by 8 3 ma and 9 7 ma the eastern and western faulted margins respectively of the rift had formed at guraghe and at agere selam as indicated by containment of flows of that age within the rift wall during eruption a paroxysm of calc alkaline ignimbrite activity produced voluminous flows nearly fully contained within the rift during the pliocene epoch the munesa crystal tuff 3 5 ma a prominent marker tuff exposed on both rift margins is present at depth in a geothermal well beneath the rift floor and indicates a minimum of 2 km of downthrow in the central sector since its eruption structural and stratigraphic relationships in the central sector indicate a two stage rift development this is characterized by an early phase late oligocene or early miocene of a series of alternating opposed half grabens along the rift with alternating polarity such as that in the present gregory and western rifts of east africa and symmetrical rifts that evolved from these grabens in late miocene or early pliocene time thus evolution from alternating half graben to a full symmetrical graben with a medially located neovolcanic zone that is bifurcated to marginal grabens in the northern part of the study area may be a fundamental part of the rifting process the study indicates that there are major petrologic and tectonic differences between the main ethiopian rift and the gregory kenyan rift

evolution of terrace risers along the upper rhine graben inferred from morphologic dating methods evidence of climatic and tectonic forcing summary we show that morphologic dating techniques that have been applied successfully in arid and semi arid areas are also suitable for slowly evolving scarps that are usually found in temperate climate environments we have attempted two morphologic approaches based on diffusion to relate the present day shape of an abandoned terrace riser to its age the first assumes a model of scarp degradation based on a diffusive process the d method the second evaluates the state of scarp degradation using the slope distribution the sd method along a topographic profile by using a manmade scarp of known age we have obtained a mass diffusivity close to 1 4 m2 ka 1 when the area experiences a temperate climate characterized by a continuous vegetation cover however this value decreases during glacial episodes probably on account of the permafrost even though the sd method requires an age correction that can be easily computed only this method reveals that at several profiles a later scarp reactivation event has occurred indeed along several profiles the slope distribution was best fitted by two offset gaussian curves suggesting that some scarps have undergone a complex evolution that cannot be modelled with a single diffusive process this scarp reactivation may correspond to a new incisive episode and allows one to estimate the vertical incision rate along the terrace riser applied to a wurmian terrace riser of the upper rhine valley ne france this approach reveals that the vertical incision rate ranges from 0 2 to 0 85 mm yr 1 between 35 and 15 ka and that the terrace bevelling occurred during two episodes related to climatic forcing moreover we can identify a component of tectonic forcing evidenced by an increase to the north of vertical incision rate and rhine stream power another major result is showing that this terrace riser is not isochronous along its strike and that younger portions result from lateral incision of a 30 ka pre existing scarp

landform classification and soil distribution in hummocky terrain saskatchewan canada this study presents a classification of distinct three dimensional landform elements and examines the relationship between these landform elements and selected soil morphological properties of udic boroll soils in southern saskatchewan canada the classification is based on defined ranges of three criteria derived from topographic data gradient profile downslope curvature and plan across slope curvature seven landform elements are recognized convergent shoulders divergent shoulders convergent backslopes divergent backslopes convergent footslopes divergent footslopes and level elements all of the elements are easily identified in the field the thicknesses of a horizons and depths to calcium carbonate of the soils were consistently greater in convergent versus divergent elements in the same profile group e g shoulders and showed an overall increase in the sequence shoulders backslopes level footslope elements distinct groups of elements emerge from a statistical analysis of the differences between individual and bivariate means of soil morphological properties associated with each landform element the differences in soil properties among the elements can be largely explained by differences in water movement and distribution in hillslope systems the results of the study highlight the need to consider land surface morphology during the development of research designs for soil related studies

reconciling tectonic shortening sedimentation and spatial patterns of erosion from 10 be paleo erosion rates in the argentine precordillera abstract the temporal evolution of erosion over million year timescales is key to understand the development of mountain ranges and adjacent fold and thrust belts while models of orogenic wedge dynamics predict an instantaneous response of erosion to pulses of rock uplift stream power based models predict that catchment wide erosion maxima significantly lag behind a pulse of rock uplift here we explore the relationships between rock uplift erosion and sediment deposition in the argentine precordillera fold and thrust belt at 30 s using a combination of 10be derived paleo erosion rates constraints on re exposure using 26al 10be ratios geomorphic observations and detrital zircon provenance we demonstrate that the attainment of maximum upland erosion rates lags the maximum rate of deformation over million year timescales the magnitudes and causes of the erosional delays shed new light on the catchment erosional response to tectonic deformation and rock uplift in orogenic wedges

morphological dating of cumulative reverse fault scarps examples from the gurvan bogd fault system mongolia morphological dating of cumulative reverse fault scarps

uniform postglacial slip rate along the central 600 km of the kunlun fault tibet from 26al 10be and 14c dating of riser offsets and climatic origin of the regional morphology late pleistocene holocene sinistral slip rates on several segments of the kunlun fault in northeastern tibet have been determined these determinations are based on the measured displacement of alluvial surfaces whose surface ages were determined by cosmogenic 2 6 al and 1 0 be dating of quartz pebbles and by 1 4 c dating of charcoal in the west at three sites along the xidatan dongdatan segment of the fault near 94 e terrace riser offsets ranging from 24 to 110 m with cosmogenic ages ranging from 1800 to 8200 yr yield a mean left lateral slip rate of 11 7 1 5 mm yr 1 field observations indicate minimum offsets of 9 12 m this offset when combined with the long term slip rate indicates that great earthquakes m 8 rupture this segment of the fault with a recurrence interval of 800 1000 yr at two sites along the dongxi anyemaqin segment of the fault near 99 e terrace riser offsets ranging from 57 to 400 m with 1 4 c ages ranging from 5400 to 37 000 yr bp yield a minimum slip rate of 10 mm yr 1 at one site the 1937 january 7 m 7 5 and the penultimate earthquakes produced 4 m of left slip and 0 4 m of reverse slip the maximum recurrence interval of earthquakes with such characteristic slip is thus 400 yr farther east near 100 5 e along the maqen segment of the fault the 180 m offset of a lateral moraine emplaced between the last glacial maximum 20 ka and 11 100 yr bp yields a mean slip rate of 12 5 2 5 mm yr 1 the slip rates are constant within uncertainty throughout the 600 km of the kunlun fault that we studied the average slip rate is 11 5 2 0 mm yr 1 extrapolating this rate to the reminder of the fault we conclude that most 80 per cent of the 300 morphological offsets measured in the field or on spot satellite images post date the last glacial maximum most of the terraces we studied were deposited during the humid period of the early holocene optimum 9 5 ka the formation of younger terraces reflects late holocene climate change

tephrochronologic constraints on temporal distribution of large landslides in northwest argentina abstract two morphologic settings in the northwestern argentine prone to giant mountain front collapse deeply incised narrow valleys and steep range fronts bordering broad piedmonts were analyzed through detailed investigations of fossil landslides and related fluvio lacustrine sediments nine different rhyodactic tephra layers were defined by geochemical fingerprinting of glass morphology of pumice stratigraphic relationships and mineralogy the age of three tephra could be determined either directly by 40ar 39ar dating or relatively by 14c dating of associated sediments paranilla ash documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont decl

rates and timing of earth surface processes from in situ produced cosmogenic be 10 beryllium 10 is the longest lived of the seven known unstable isotopes of be it results mostly from the interaction of cosmic radiation primarily neutrons with a variety of target atoms by spallation the splitting of nuclei lal 1988 it can also be produced at very low levels by radio disintegration of u and th sharma and middleton 1989 although all radioactive be isotopes are produced in the atmosphere via cosmic ray reactions arnold 1956 lal and peters 1967 morris et al chapter 5 this volume in this paper we are most interested in 10be produced in rock which we refer to as in situ produced such in situ produced 10be is a cosmic ray dosimeter functioning as a quantitative monitor of near surface residence time in some geologic situations 10be can be used as a chronometer allowing one to estimate the duration of surface exposure in other settings 10be can be used as a tracer allowing one to estimate the rate distribution and behavior of earth surface processes rates of 10be production are very low in rocks exposed at earth s surface 102 atoms g 1 y 1 resulting in typical in situ produced 10be concentrations termed activities of 103 to 107 atoms g 1 the development of accelerator mass spectrometry ams in the 1980s allowed routine measurement of 10be at levels typical of rocks exposed near earth s surface elmore and phillips 1987 analytical refinements in the 1990s lowered detection limits by an order of magnitude allowing dating of exposure periods 103 years in favorable geologic and geographic situations simple exposure histories at high altitude and latitude most in situ 10be is measured in quartz mineral separates where the primary spallation target is o lal and arnold 1985

modern crustal seismicity in the northern andean precordillera argentina abstract the precordillera in the andean backarc region of argentina has a long record of large and damaging earthquakes in the last century its northern part is not well known seismically neither its style of deformation in this work we study modern crustal seismicity occurring in the same epicentral area of the historical 1894 earthquake that earthquake caused deaths and severe damage even at large distances of about 500 km because of the unavailability of instrumental records to study this large earthquake not many details of its seismic source are known our study involves broadband and short period seismic data from modern seismicity to characterise the same epicentral area we used seismic records from the permanent argentine network inpres and from two temporary broadband experiments charge and siembra we determine 44 seismic locations and their focal depths which are in the range between 10 and 30 km and magnitudes 1 2 m 4 in addition we obtain 33 focal mechanism solutions for some of these earthquakes using p wave first motions and amplitude ratios between p and s waves for the same region five more moderate earthquakes have been ever observed globally and reported by the global centroid moment tensor catalogue in the last 55 years we note that epicentres are mainly distributed in the southern sector of the study region with a relatively greater concentration in the foothills of the frontal andes cordillera focal mechanisms show mainly reverse and in less proportion strike slip solutions overall these results agree with compression and shortening in an east west orientation of the andean northern precordilleran backarc region

eruption conditions of pele volcano on io inferred from chemistry of its volcanic plume we use thermodynamic models and published 1996 hubble space telescope hst observations of so2 so and monatomic sulfur gas in the pele volcanic plume on jupiter s moon io to evaluate the temperature 1440 k and oxidation state 3 3 log fo2 units below the ni nio buffer of pele s magma and exsolved volcanic gas combination of these results with 1999 hst data on the so2 s2 ratio in the pele plume allows us to calculate pressures 10 4 7 10 5 4 bar in the vicinity of volcanic vent and to present a detailed chemical model for the plume our model indicates that the pele plume represents volcanic gas which last equilibrated at magmatic temperature and was not significantly altered in the plume finally the redox state of pele plume indicates that io is differentiated and has an oxidized fe metal free mantle

holocene right slip rate determined by cosmogenic and osl dating on the anar fault central iran summary be cosmic ray exposure cre and optically stimulated luminescence osl dating of cumulative offset of alluvial fan surfaces have been performed to derive the long term sliprate of the anar fault at two sites the comparison between osl ages obtained within the latest sediments emplaced during the aggradation of the fan and cosmogenic exposure ages of the pebbles abandoned on the surface before its incision and subsequent dextral offset indicates a significant and variable cre inheritance combining offset risers with cre and osl dating implies the southern anar fault slips at a minimum rate of 0 8 mm yr 1 a little faster than formerly estimated by assuming the incision which created the risers was coeval with the onset of the holocene 12 2 ka the latest regional incision in the anar area appears rather coeval with the onset of the early middle holocene pluvial episode 6 10 5 ka evidenced in the neighbouring region of northern oman

revealing the pace of river landscape evolution during the quaternary recent developments in numerical dating methods during the last twenty years several technical developments have considerably intensified the use of numerical dating methods for the quaternary the study of fluvial archives has greatly benefited from these enhancements opening new dating horizons for a range of archives at distinct time scales and thereby providing new insights into previously unanswered questions in this contribution we separately present the state of the art of five numerical dating methods that are frequently used in the fluvial context radiocarbon luminescence electron spin resonance esr 230th u and terrestrial cosmogenic nuclides tcn dating we focus on the major recent developments for each technique that are most relevant for new dating applications in diverse fluvial environments and on explaining these for non specialists therefore essential information and precautions about sampling strategies in the field and or laboratory procedures are provided for each method new and important implications for chronological reconstructions of quaternary fluvial landscapes are discussed and where necessary exemplified by key case studies a clear statement of the current technical limitations of these methods is included and forthcoming developments which might possibly open new horizons for dating fluvial archives in the near future are summarised

morphological dating of cumulative reverse fault scarps examples from the gurvan bogd fault system mongolia summary we relate reverse fault scarp morphology formed by several earthquake dislocations to the average deformation rate using a morphological dating model based on a diffusion analogue of erosion our scarp degradation model includes diffusive erosion during the interseismic period the gravitational collapse of the coseismic fault scarp just after formation and the variation of the surface rupture location interactions between thrusting and geomorphic processes acting on scarp morphology are analysed along the gurvan bogd range in mongolia four main processes acting on scarp morphology were distinguished i gravitational collapse of the frontal scarp resetting the diffusive scarp if fault offsets are big and faulting is localized 2 progressive erosion of the fault scarp during the interseismic period 3 folding associated with the frontal thrust and backthrusts 4 competing alluvial deposition on mountain piedmont slopes and abrasion of the fault scarp by wash processes the growth of cumulative reverse fault scarps is suppressed when they are located in the outwash of major drainage basins they can grow higher in distance from major catchment discharges the modelling suggests that the morphology of the scarp and its apparent degradation stage depend on the parameters controlling the amount of frontal collapse the magnitude of coseismic offsets the dip of the fault near the surface and the step distance between faults folding associated with thrusting creates a convexity on the upper part of the scarp and increases its height the comparison of different scarp profiles suggests that folding leads to an overestimate of the morphological age we estimate a diffusion coefficient at 3 3 1 7 m 2 ka l morphological ages calculated with our model confirm that slip rate along reverse faults of the gurvan bogd range has not been constant over the last 100 ka

delineating the major landforms of catchments using an objective hydrological terrain analysis method 1 the location and distribution of landform shape and size describe and categorize many features of a catchment landforms indicate soil types arability of land geological features hydrological influences and even shallow groundwater systems this paper describes an objective method for delineating major landforms of a catchment on the basis of hydrological terrain analysis it allows comparisons to be made within and between catchments the method uses the upness index from the fuzzy landscape analysis geographic information system flag model roberts et al 1997 that is derived from digital elevation data upness was developed as an index of surface and shallow subsurface water accumulation in the method presented in this paper we fit a five parameter sigmoidal function to the cumulative distribution function cdf of the natural log ln of upness the point of inflection of the cdf of the upness index is defined from the first derivative of the five parameter sigmoidal function as the point of maximum concavity the second and third points are defined by determining the maximum upward concavity and minimum downward concavity from the second derivative of a five parameter sigmoidal function referred to as break points the inflection and break points from the upness index are used to segment the cdf into three regions that represent four different landform elements landform categories based on these points represent ridge tops and upper slopes midslopes lower slope and in filled valley alluvial deposits the shape of the cdf curve indicates the dominance of major landforms within a catchment providing an objective means for classifying this catchment characteristic examples are given showing how landform discrimination compares to geological maps the landforms index presented in this study offers a useful technique for differentiating complex landforms from a landscape using terrain analysis that attempts to represent dominant hydrological soil formation processes

subsurface characterization of quaternary scarps and their possible connection to main structures of the western margin of precordillera san juan argentina abstract the el tigre fault provides a significant example of pliocene quaternary tectonic activity at the west of precordillera receiving considerable attention in the last years however longitudinal thrusts of the nearest sierra del tigre and a minor piedmont deformation belt identified in its western piedmont are still poorly understood the present work comprised a detailed map of the geomorphological features of tectonic origin and quaternary alluvial fan terraces located between the sierra del tigre and the el tigre fault several topographic and geoelectrical profiles across minor fault and fold scarps were surveyed to define the displacement scarps the geological structure geometries at subsurface and their relationship with main structures geoelectrical models allowed us to recognize three geoelectrical levels a 200 300 m correlated to pleistocene alluvial fan terraces q4 and q3 b ranging from 50 to 300 450 m under level a and correlated to the neogene substratum rodeo formation c

neogene structures overprinting palaeozoic thrust systems in the andean precordillera at 30 s latitude field studies along a 30 s latitude transect of the precordillera in nw argentina indicate that neogene to recent deformation caused high angle faulting that uplifted and breached a palaeozoic east verging thrust stack palaeozoic structures crop out in the higher linear ranges and intramontane neogene basins occur in the intervening valleys the palaeozoic rocks include three tectonic units with contrasting structural styles and differences in stratigraphy the western allochthon includes clastic ordovician rocks metamorphosed to lower greenschist facies and folded by large scale asymmetric east verging folds with a well developed axial planar cleavage this unit overthrusts a siluro devonian flysch type succession of the central imbricate thrust system and associated fault propagation folds in which the thrusts merge into a basal thrust beneath ordovician carbonates middle to upper carboniferous sediments unconformably overlie structures of this imbricate system in the frontal unit minor thrust faults are interpreted to explain the low angle unconformity within palaeozoic rocks neogene deformation causes only a minor overprint of the palaeozoic structure and large scale folding in the frontal unit appears to be mostly of neogene age the new data indicate that neogene intracontinental shortening may be smaller than previously proposed providing new perspectives on the present orogenic architecture along this andean section

a note of caution on the use of boulders for exposure dating of depositional surfaces abstract exposure dating of boulders has been widely applied to determine the age of depositional surfaces under the assumption that the pre depositional nuclide component in most boulders is negligible here we present a case study on fluvial terraces at the active mountain front of the eastern andes where this assumption is clearly invalid because sandstone boulders n 13 from terraces at two sites contain a highly variable inherited 10be component and have apparent 10be ages that exceed the age of the respective surface by up to 90 ka likewise boulders from active stream channels n 5 contain a substantial inherited 10be component equivalent to 5 48 ka of exposure the age of the fluvial terraces is well determined by two approaches that allow to correct for the pre depositional nuclide component 10be dating of amalgamated pebbles and 10be depth profiles on sand samples at site 1 three terraces have 10be ages of 3 5 ka t2 11 13 ka t3 and 16 20 ka t4 which are consistent with the terrace stratigraphy the age of terrace t3 is confirmed by a calibrated 14 c age of 12 61 0 20 ka bp obtained from a wood sample at site 2 terrace t3 has a 10be age of 13 16 ka the average inherited 10be concentration of sand grains determined from depth profiles and stream sediments is small and equivalent to 1 3 ka of exposure in contrast the mean inheritance of pebbles and boulders is higher and equivalent to exposure times of 10 ka and 30 ka respectively these differences in the pre depositional nuclide component are related to the different provenance and transport history of sand pebbles and boulders the sand is derived from rapidly eroding miocene sediments exposed near the mountain front whereas the pebbles and boulders originate from triassic sandstones in the internal part of the fold and thrust belt on their way to the mountain front boulders and pebbles were temporarily stored and irradiated in alluvial fans that are currently reworked as sediment deposition in intramontane basins and their subsequent excavation is common in the andes and other fold and thrust belts the presence of pre depositional nuclide components should be evaluated when applying exposure dating at active mountain fronts

morphologic evidence of active motion of the zambapala fault gulf of guayaquil ecuador abstract the zambapala fault zone zfz is located at the link between the offshore structures of the gulf of guayaquil and the guayaquil caracas megashear gcm that accommodates the northeastward motion of the north andean block we use morphological observations of drainage offset to assess the active motion of the zambapala fault the relation between the horizontal offset amount d of the stream channel and the upstream length l from the offset segment and offset of beach morphology provide a measurement of the average slip rate of the motion of the fault to an accuracy of a fraction of millimeters per year the drainage network is short running down the southeastern slopes of the zambapala cordillera 297 m a quaternary dome uplifted along a positive flower structure we measure the d drainage offset along the fault l drainage length from the fault relation for the upper and more recent part of the drainage network the relation suggests that the fault is active at present capture occurs along the middle slopes and channel straightening near the littoral plain hiding part or most of the fault offset the fault trace crosses the littoral plain showing 35 40 m offset of the inner beach ridge and delimiting variations of the beach morphology the attribution of a maximum age of 5000 6000 years to the oldest beach ridge the postglacial transgression allows us to calculate a minimal mean slip rate of 5 8 8 mm year 1 this result confirms that the guayaquil caracas megashear extends to the gulf of guayaquil through the zambapala fault zone which accommodate at least 60 80 of the slip motion of the guayaquil carcas megashear

geomorphology tectonism and quaternary landscape evolution of the central andes of san juan 30 s 69 w argentina abstract the north south trending valley of iglesia is a regional tectonic depression limited to the west by the cordillera frontal unit and to the east by precordillera occidental mountain units the forms of the resulting landscape in the region are the result of glacial periglacial fluvial and alluvial action aggradational and deggradational processes as well as neotectonic activity and climatic changes the generation of large quaternary alluvial fan aggradational surfaces is related to previous climatic conditions colder and more humid than the present ones abundant snowfalls and rains during the pleistocene made possible detritus deposition generating alluvial covers whose thickness increases toward the east these climatic conditions alternated with arid periods during which vertical erosion of streams prevailed forming a landscape of stepped levels in addition the presence of faults with quaternary tectonic activity indicates a strong structural control in the evolution of the landscape during the pleistocene holocene periods effectively starting vertical erosion and finishing a cycle of erosion accumulation and the beginning of the following one

do river profiles record along stream variations of low uplift rate environments 1m m yr 1 where climate changes may have erased tectonic features we evaluate the respective contribution of low uplift rate 0 1 mm yr 1 and pleistocene climate oscillations on gradient variations of two comparable river profiles crossing different uplift zones in the southern upper rhine graben we compare the observed points of discontinuity in river profile knickpoints and convex portions knickzones with those predicted by a detachment limited model that includes stochastic short term and cyclic long term variations in climate a bedrock detachment threshold and rock uplift the detachment limited model is chosen as it predicts the development of persistent knickpoints differing values of the shear stress exponent erosion threshold climate variability and uplift pattern have been checked our modeling suggests that climate changes had no significant effects on profiles and that anomalies are more likely due to anticline growth this surprising result arises from the combination of a very low regional uplift rate and the detachment limited assumption the detachment limited model implies an upstream propagation of knickpoints and knickzones generated by uplift at the outlet during dry climate periods of low erosion the greater the uplift rate the larger the variations in river bed elevation thus for high uplift rate knickpoints and knickzones generated by climate oscillations are more likely to hide tectonic features this result seems counterintuitive because it suggests that tectonic knickzones will be better preserved in low uplift rate environments provided that the lithology is homogeneous

a multiresolution index of valley bottom flatness for mapping depositional areas 1 valley bottoms function as hydrological buffers that significantly affect runoff behavior distinguishing valley bottoms from hillslopes is an important first step in identifying and characterizing sediment deposits for hydrologic and geomorphic purposes valley bottoms occur at a range of scales from a few meters to hundreds of kilometers in extent this paper describes an algorithm for using digital elevation models to identify valley bottoms based on their topographic signature as flat low lying areas the algorithm operates at a range of scales and combines the results at different scales into a single multiresolution index this index classifies degrees of valley bottom flatness which may be related to depth of deposit the index can also be used to identify groundwater constrictions and to delineate hydrologic and geomorphic units

fault growth and landscape development rates in otago new zealand using in situ cosmogenic 10be abstract we use in situ cosmogenic 10 be measurements in quartzites to examine the growth and propagation rates of a late quaternary anticline forming above a blind reverse fault in central otago new zealand we obtain average uplift and propagation rates of 0 10 0 15 mm yr 1 and 1 0 2 0 mm yr 1 respectively over the last 450 000 yr though it is probable that growth occurred episodically with more rapid development in the periods 600 400 kyr and 200 100 kyr and relative quiescence between about 400 and 200 kyr ago these results quantify and confirm a qualitative analysis of the fault evolution based on geomorphology and drainage patterns we obtain minimum 10 be exposure ages of up to 750 000 yr for the quartzites some of the oldest ages obtained by this method outside antarctica which are made possible by the extremely low erosion rates of less than 0 6 mm kyr 1 in the resistant quartzites these rocks consequently provide an opportunity to study geomorphic and tectonic processes in this region over unusually long time periods

calibrated late quaternary age indices using clast rubification and soil development on alluvial surfaces in pilot knob valley mojave desert southeastern california the orange coating varnish that forms on the undersides ventral sides of clasts in desert pavements constitutes a potential relative age indicator using munsell color notation we semiquantified the color of the orange ventral varnish on the undersides of clasts from 15 different alluvial fan and terrace surfaces of various ages ranging from less than 500 to about 25 000 yr all of the surfaces studied are located along the central portion of the left lateral garlock fault in the mojave desert of southern california the amount of left lateral offset may be used to determine the relative ages of the surfaces the previously published slip rate of the fault may also be used to estimate the absolute age of each surface the color of the ventral varnish is strongly correlated with surface age and appears to be a more reliable age indicator than the percentage coverage of dorsal varnish soil development indices also were not as strongly correlated with age as were the colors of the ventral varnish in particular rubification appears to be more useful than soils for distinguishing relative ages among holocene surfaces humidity sensors indicated that the undersides of clasts condensed moisture nightly for a period of several days to over a week after each rain these frequent wet dry cycles may be responsible for the rapid development of clast rubification on holocene surfaces

10be dating of alluvial deposits from southeastern iran the hormoz strait area abstract a key area for the understanding of the southeastern iran geodynamics the hormoz strait area was investigated tectonically active it provides useful sequences of quaternary deposits whose deposition may have ended either when the climate dried or when the tectonic activity uplifted the riverbed in situ produced cosmogenic 10be provides surface abandonment ages at 5 6 0 6 8 4 1 0 12 8 1 0 20 1 1 5 and 44 0 3 4 10be kyr located at the transition between the mediterranean winter rain and the indian monsoon domains and south of the northernmost position of the itcz intertropical convergence zone the studied area is very sensitive to climate changes some of the calculated 10be abandonment ages are within the entire investigated area coincidental with large scale climate shifts the offset of the mid holocene humid period 5 6 0 6 10be kyr the onset of the dry younger dryas cold and dry episode 12 8 1 010be kyr and the end of the last glacial maximum lgm 21 2 kyr at 20 1 1 5 10be kyr these events correspond to large scale changes in atmospheric circulation linked to global climate changes and or to sea level fluctuations in the persian gulf which was totally dry during the lgm locally observed abandonment ages at 8 4 1 0 and 44 0 3 4 10be kyr may likely be related to enhanced tectonic activity without regional impact

cumulative right lateral fault slip rate across the zagros makran transfer zone role of the minab zendan fault system in accommodating arabia eurasia convergence in southeast iran the zendan minab zone is the transition zone between the zagros collision to the west and makran subduction to the east it is also linked to the north with the nayband gowk fault system that bounds the lut block to the east the total convergence rate between arabia and eurasia is estimated to range between 23 and 35 mm yr 1 in a nne trending direction the deformation through the minab zendan system is accommodated within two fault systems the western n160 e trending minab zendan fault system and the eastern north south sabzevaran jiroft fault system the study area is characterized by a well defined succession of quaternary deposit levels the age of these deposits was estimated by archaeological data regional palaeoclimate correlations and constrained by additional in situ10be dating in another paper in this study these deposits exhibit offsets both lateral and vertical that are evaluated by satellite image analysis and gps profiles thanks to offsets and ages the strike slip rates associated with the minab zendan and the sabzevaran jiroft fault systems are calculated to be 5 1 1 3 or 6 6 1 5 and 6 2 0 7 mm yr 1 respectively these results allow an evaluation of the velocity vector of the musandam peninsula oman with respect to the lut block of 11 4 2 0 or 12 9 2 2 mm yr 1 in a n10 15 e direction close to the gps estimates this study also constrains the in plane slip rates for each fault previous works indicate that the zagros accommodates only 10 mm yr 1 of shortening while 10 mm yr 1 should be accommodated by the alborz mountains in northern iran this last 10 mm yr 1 may be accommodated through the nayband gowk system and the east iranian ranges implying that the two fault systems constituting the zagros makran transfer zone have different geodynamic roles the western minab zendan fault system links the makran and zagros deforming zones whereas the northwestern jiroft sabzevaran fault system is transmitting the deformation to the nayband gowk system and then to the alborz ranges the presence of another such strike slip zone within the makran seems to indicate that the accommodation zone between the zagros and makran is wide of the order of 400 km we interpret this deformation pattern that accompanies the genesis of the immature transform zone by a flexure of the slab under the zagros makran transfer zone instead of a tear in the slab that may be expected to induce a sharper transition zone

three dimensional seismic imaging of a protoridge axis in the main ethiopian rift models of continental breakup remain uncertain because of a lack of knowledge of strain accommodation immediately before breakup our new three dimensional seismic velocity model from the main ethiopian rift clearly images mid crustal intrusions in this active transitional rift setting supporting breakup models based on dike intrusion and magma supply the most striking features of our velocity model are anomalously fast elongate bodies velocity v p 6 5 6 8 km s extending along the rift axis interpreted as cooled mafic intrusions these 20 km wide and 50 km long bodies are separated and laterally offset from one another in a right stepping en echelon pattern approximately mimicking surface segmentation of quaternary volcanic centers our crustal velocity model combined with results from geologic studies indicates that below a depth of 7 km extension is controlled by magmatic intrusion in a ductile middle to lower crust whereas normal faulting and dike intrusion in a narrow zone in the center of the rift valley control extension in the brittle upper crust this zone is inferred to be the protoridge axis for future seafloor spreading

timing and nature of alluvial fan and strath terrace formation in the eastern precordillera of argentina abstract sixty eight 10 be terrestrial cosmogenic nuclide tcn surface exposure ages are presented to define the timing of alluvial fan and strath terrace formation in the hyper arid san juan region of the argentine precordillera this region is tectonically active and numerous fault scarps traverse quaternary landforms the three study sites marquesado strath complex loma negra alluvial fan and carpinteria strath complex reveal a history of alluvial fan and strath terrace development over the past 225 ka the marquesado complex q3 m surface dates to 17 3 ka whereas the loma negra q1 ln q2 ln q3 ln q4 ln and q5 ln surfaces date to 24 3 ka 48 2 ka 65 13 ka 105 21 ka and 181 29 ka respectively the carpinteria complex comprises eight surfaces that have been dated and include the q1 c 23 3 ka q2 c 5 5 ka q3a c 25 12 ka q3b c 29 15 ka q4 c 61 12 ka q5 c 98 18 ka q6 c 93 18 ka and q7 c 212 37 ka 10 be tcn depth profile data for the loma negra alluvial fan complex and carpinteria strath terrace complex as well as osl ages on some carpinteria deposits aid in refining surface ages for comparison with local and global climate proxies and additionally offer insights into inheritance and erosion rate values for tcns 10 10 4 10 be atoms g of sio 2 and 5 m ma 1 respectively comparison with other alluvial fan studies in the region show that less dynamic and older preserved surfaces occur in the carpinteria and loma negra areas with only younger alluvial fan surfaces preserved both to the north and south these data in combination with that of other studies illustrate broad regional agreement between alluvial fan and strath terrace ages which suggests that climate is the dominant forcing agent in the timing of terrace formation in this region

dating offset fans along the mojave section of the san andreas fault using cosmogenic 26al and 10be analysis of cosmogenic 1 0 be and 2 6 al in samples collected from exposed boulders n 20 and from buried sediment n 3 from offset fans along the san andreas fault near little rock california yielded ages ranging from 16 to 413 ka which increase with dis lance from their source at the mouth of little rock creek in order to determine the age of the relatively younger fans the erosion rate of the boulders and the cosmogenic nuclide inheritance from exposure prior to deposition in the fan were established cosmogenic nuclide inheritance values that range between 8 5 x 10 3 and 196 10 3 atoms 1 0 be g 1 quartz were determined by measuring the concentrations and ratios of 1 0 be and 2 6 al in boulders n 10 and fine sediment n 7 at the outlet of the present active stream boulder erosion rate ranging between 17 and 160 mm k y 1 was estimated by measuring 1 0 be and 2 6 al concentrations in nearby bedrock outcrops n 8 since the boulders on the fans represent the most resistant rocks in this environment we used the lowest rate for the age calculations monte carlo simulations were used to determine ages of 16 5 and 29 7 ka for the two younger fan surfaces older fans older than 100 ka were dated by analyzing 1 0 be and 2 6 al concentrations in buried sand samples the ages of the three oldest fans range between 227 242 and 413 185 ka although fan age determinations are accompanied by large uncertainties the results of this study show a clear trend of increasing fan ages with increasing distance from the source near little rock creek and provide a long term slip rate along this section of the san andreas fault slip rate along the mojave section of the san andreas fault for the past 413 k y can be determined in several ways the average slip rate calculated from the individual fan ages is 4 2 0 9 cm yr 1 a linear regression through the data points implies a slip rate of 3 7 1 0 cm yr 1 a most probable slip rate of 3 0 1 0 cm yr 1 is determined by using a 2 test these rates suggest that the average slip along the mojave section of the san andreas fault has been relatively constant over this time period the slip rate along the mojave section of the san andreas fault determined in this study agrees well with previous slip rate calculations for the quaternary

a large and active debris rockslide in the central andes of argentina 30 26 s morphometry and triggering mechanisms abstract a large 0 1 km2 and complex mass movement in the central andes of argentina final portion of cordillera de olivares frontal cordillera was studied to identify the triggering factors and understand their relationship with geomorphic cryogenic and climatic dynamics this debris rockslide is composed of clast supported blocks of permian triassic volcanic breccias in order to characterize this feature high resolution satellite imagery interpretation was carried out together with the study of the landslide detachment zones and landslide bodies these debris rockslide events could have originated as a consequence of the combination of internal slow deformation and fragmentation under periglacial conditions followed by a sudden collapse of the rock mass pre and post slide digital elevation models dems were created from topographical data with the help of a geographic information system gis tool approximately 14 89 m m3 of rock and debris travelled nearly 2 km from an elevation of 5023 m 4325 m asl although usually the origin of such catastrophic movements is related to seismically active areas with earthquakes whose magnitude frequently exceed ms 6 our hypothesis is that this debris rockslide event has a climatic origin caused by large snow accumulations during winters and subsequent fast meltdown processes during spring which would have facilitated the sliding the paper outlines the important role that snowmelt can play in the genesis and evolution of rock displacements and the importance of meteorological data seismic catalogues historical aerial photography and satellite images in geomorphological back analysis

dating rupture events on alluvial fault scarps using cosmogenic nuclides and scarp morphology scarp morphology evolution has commonly been used to estimate the timing of fault scarp rupture events however rates of scarp degradation depend strongly on the geomorphic diffusivity a parameter that is difficult to constrain independently this difficulty may lead to large uncertainties in the estimated ages of rupture events in this study we have coupled the accumulation of the cosmogenic nuclide 36cl to a model for scarp morphology in order to constrain the value of the geomorphic diffusivity and thus determine a more accurate rupture chronology than a rupture history based solely on scarp morphology we measured depth profiles of 36cl accumulated in situ within alluvial sediments beneath the surface of the socorro canyon fault scarp in central new mexico the material analyzed consisted of 150 individual gravel clasts from each depth interval amalgamated into a single sample the alluvium was sampled in three vertical profiles 4 m deep the first profile was 1 5 m downslope of the fault plane on the hanging wall the second 1 5 m upslope of the fault plane on the footwall and the third 27 m upslope of the fault plane on the footwall the third profile which served as a control and which soil geomorphic evidence indicated was beneath a stable surface showed a simple exponential 36cl profile from which a depositional age of 122 18 ka was calculated the second profile on the footwall showed a 36cl deficit relative to the control profile indicating net erosion the first profile on the hanging wall showed a 36cl excess relative to the control profile indicating net deposition stratigraphic evidence in the hanging wall indicated two rupture events prior to the late holocene we modeled the accumulation of 36cl in the vicinity of the scarp simulating erosional redistribution using a diffusion equation for scarp morphology the model accounted for redistribution of 36cl along with the sediment and the effects of the changing fault scarp morphology on the 36cl production by matching both the observed hanging wall and footwall 36cl profiles to profiles calculated by the model as well as the observed topographic profile we obtained ages of 92 16 13 and 28 18 23 ka for the two ruptures the results of our study indicate that cosmogenic nuclides can be useful in constraining rupture chronologies of fault scarps in alluvium

the iglesia basin in the southern central andes a record of backarc extension before wedge top deposition in a foreland basin abstract the iglesia basin hosts a key sedimentary archive of the evolution of the southern central andes this basin is classically interpreted as recording the transition from an outer to an inner wedge top piggyback basin depozone in the early bermejo foreland basin system in this study we reevaluate the tectonic evolution of the iglesia basin based on the interpretation of 2d seismic reflection data structural geology zircon u pb geochronology and provenance analysis we report an extensional event that initiated the basin opening our results indicate normal faulting development and synextensional deposition from the latest oligocene earliest miocene to middle miocene since the middle miocene extensional activity experienced a progressive decrease in changing to shortening and basin inversion between the middle late miocene the latter stage coincided with the full development of pampean flat slab subduction indicating maximum plate coupling at that time our findings challenge the idea of uninterrupted paleogene to neogene flexural subsidence related to the andean orogenic load in the backarc area therefore the results of this study have important consequences for the early evolution of the bermejo foreland basin and ultimately for the growth of the southern central andes

spatial variations in late quaternary slip rates along the doruneh fault system central iran the doruneh fault system dfs is one of the major active strike slip faults in the arabia eurasia collision zone despite its geological activity no large m 6 5 historical or instrumental earthquakes have been recorded along it to date the rate and distribution of slip as well as the seismic behavior of the dfs have been unknown we reconstructed 67 geomorphic offsets recorded by three successive alluvial abandonment surfaces q1 q2 and q3 displaced along the western wfz and central cfz fault zones the determined ages of 12 36 and 120 ka using in situ produced 10 be and 36 cl cosmogenic nuclides for theses surfaces allowed to estimate three sets of individual left lateral slip rates and consequently to describe the spatiotemporal distribution of slip along the cfz and wfz the slip rates averaged over time intervals of 36 and 120 ka reveal variable slip rates along length but similar slip rates at a point with a maximum rate of 8 2 mm yr during the holocene however the fault slip behavior appears more complex with a maximum rate of 5 3 mm yr the cfz is divided into two 4 km apart segments with symmetrical slip distributions relative to a persistent boundary which has not been ruptured over the last 12 ka the maximum length of seismic fault segments varies from 70 to 100 km which could produce earthquakes with a magnitude of m w 7 2 7 4 this emphasizes the necessity of segmentation models for long strike slip faults that may not necessarily rupture along their whole length during a single earthquake

deformation partitioning in flat subduction setting case of the andean foreland of western argentina 28 s 33 s 1 the andean foreland of western argentina 28 s 33 s corresponds to back arc deformations associated with the ongoing flat subduction of the nazca plate beneath the south american lithosphere in this paper short and long term tectonic regimes for this andean region are investigated and compared to nuvel 1 and the new gps derived velocity field for the andes mountains from this comparison it appears that 1 the slight convergence obliquity at the plate boundary is accommodated by the subduction zone itself precluding any deformation partitioning at lithospheric scale 2 clockwise rotation of 1 and p axes within the andean foreland of western argentina suggests that plio quaternary deformation partitioning may occur in the upper plate at crustal scale and 3 comparison of seismic rates of shallow deformations determined from moderate to large earthquakes localized between 22 s and 36 s shows that the amount of shortening is about the same 2 4 cm yr 1 between the forearcs of the 30 dipping slab segments and the back arc of the flat segment all together those observations are in close agreement with the idea that interplate coupling in flat subduction settings may play a key role in the present day transfer of plate boundary forces consequently the andean back arc of western argentina might be regarded as an obliquely converging foreland where plio quaternary deformations are partitioned between strike slip and thrust motions that are localized in the east verging thin skinned argentine precordillera and west verging thick skinned pampean ranges respectively

crustal motion in the southern andes 26 36 s do the andes behave like a microplate 1 a new global positioning system gps derived velocity field for the andes mountains 26 36 s allows analysis of instantaneous partitioning between elastic and anelastic deformation at the orogen s opposing sides adding an andes microplate to the traditional description of nazca south america plate convergence provides the kinematic framework for nearly complete explanation of the observed velocity field the results suggest the oceanic nazca boundary is fully locked while the continental backarc boundary creeps continuously at 4 5 mm yr the excellent fit of model to data 1 7 mm yr rms velocity misfit and the relative aseismicity of the upper crust in the interior andean region in comparison with its boundaries supports the notion that the mountains are not currently accruing significant permanent strains additionally the model implies permanent deformation is not accumulating throughout the backarc contractional wedge but rather that the deformation is accommodated only within a narrow deformational zone in the backarc

drainage anomalies as indicators of soft linked deformation zones between neotectonic structural highs in the precordillera central andes of argentina abstract between 31 45 32 15 s the western piedmont of the ansilta block in the precordillera of argentina has been uplifted in quaternary times through folds blind faults and faulted blocks that form discrete and evident areas of neotectonic deformation structural highs in between subtle tectonic perturbations of the fluvial landforms drainage anomalies such as diverted and entrenched streams asymmetric basins incision anomalies convex upward longitudinal stream profiles dammed rivers and broom shaped patterns allow the recognition of areas of incipient deformation we combined the analyses of both the structural highs and the drainage anomalies areas to investigate the role of the latest as an expression of soft linkage areas in fault systems the structural highs would be interpreted as isolated features without the consideration of the drainage anomalies areas between them moreover linking the structural highs using the drainage anomalies reveals the extent of major quaternary deformation belts in their initial development stages

evaluating the life expectancy of a desert pavement abstract this paper integrates prior scholarship on desert pavements with a case study of pavements on stream terraces in the sonoran desert to analyze the processes and site conditions that facilitate the survival of ancient desert pavements this synthesis identifies vital factors key factors and site specific factors promoting pavement stability hyperaridity is the vital factor in pavements surviving for 106 years or more aided by minimal bioturbation and clast size reduction three key factors aid in pavements surviving for 104 to 105 years accumulation of allochthonous dust underneath pavement cobbles a flat topography and a lack of headward retreating swales or gullies a unified explanation for pavement longevity however did not emerge from a literature review because a variety of site specific factors can also promote pavement antiquity including resistant bedrock beneath the pavement disk shaped cobbles to promote dust accumulation and microclimatological and ecological reasons for minimal bioturbation both key and site specific explanations for pavement longevity apply well to a case study of pavements on stream terraces in the sonoran desert central arizona the buildup of cosmogenic 10be and in situ 14c optically stimulated luminescence and varnish microlamination ages reveal stable pavements range in age between 30 and 332 ka with conditions for longevity including flat surface topography pavements underlain by consolidated granitic bedrock a lack of headward retreating gullies and swales 87sr 86sr analyses indicating the infiltration of allochthonous dust floating disk shaped pavement cobbles and a quartzite lithology resistant to disintegration however 10be ages also indicate evidence for the instability of desert pavements on stream terraces underlain by unconsolidated playa clays and unconsolidated fanglomerate these weaker materials allowed the growth of headward retreating swales that in turn promoted exposure of newer gravels by surface erosion

the aksay segment of the northern altyn tagh fault tectonic geomorphology landscape evolution and holocene slip rate 1 millennial slip rates have been determined for the altyn tagh fault atf at three sites near aksay 94 e in northeastern tibet by dating fluvial channels and terrace riser offsets with radiocarbon and 10be 26al surface exposure dating up to nine main surfaces are defined on the basis of morphology elevation and dating the abandonment age of some surfaces is constrained by radiocarbon dating which typically coincides with the youngest cosmogenic ages for a particular surface older surface exposure ages are taken to represent the duration of terrace emplacement cumulative offsets range from 20 to 260 m and fall in distinct groups indicative of climatically modulated regional landscape formation most samples are younger than 14 ka and postdate the last glacial maximum the end of the early holocene optimum marks the boundary between the ages of the two main terrace levels at 5 6 ka at this longitude the atf is divided into a northern and southern branch the northern atf should thus yield a minimum rate for the atf system slip rate estimates using the abandonment age of the overlying level for fill terraces or channels and the emplacement of the underlying level for strath terraces give 30 consistent results yielding an average holocene rate of 17 8 3 6 mm yr it is 9 mm yr less than the long term rate obtained near tura at 87 e 26 9 6 9 mm yr in keeping with the inference of an eastward decreasing rate on the atf due to increased thrusting to the south however it remains twice the rate determined by gps studies

cosmogenic dating ranging from 20 to 700 ka of a series of alluvial fan surfaces affected by the el tigre fault argentina it is crucial to date continental landforms to quantify processes involved in terrestrial surface evolution especially in regions affected by active tectonics andean quaternary alluvial fan surfaces affected by the el tigre strike slip fault have been studied using combined geomorphic and 10 be exposure age approaches field observations and spot french acronym for satellite for observation of the earth image analysis enable the identification of six alluvial fan units measurements of in situ produced cosmogenic 10 be concentrations in quartzite boulders exposed on the top of fan surfaces show that the depositional periods ended during successive major interglacial stages the calculated minimum exposure ages date the abandonments of the alluvial fan surface from 41 000 8500 yr for the youngest to 670 000 140 000 yr for the oldest unit when linked to the measured maximum cumulative right lateral displacement of stream channels the exposure ages yield a horizontal slip rate of about 1 mm yr on the el tigre fault this study shows that for arid regions where fan surface erosion is minimal in situ produced 10 be can be used to constrain the age of stratigraphically separate alluvial fan surfaces these fan surface exposure ages can be further used to calculate slip rates on active faults and infer depositional periods correlative with climatic events

crustal structure of the main ethiopian rift from gravity data 3 dimensional modeling abstract a three dimensional interpretation of the newly compiled bouguer anomaly map of the main ethiopian rift is presented a high resolution 3 d model constrained with the seismic results reveals a possible crustal thickness and density distribution beneath the graben the bouguer anomalies along the axial portion of the rift floor as deduced from the results of the regional and residual separation are mainly caused by the deep seated structures the inferred zone of intrusion which is the main subject of the present study coincides with the maximum gravity anomaly of the rift floor the intrusion is displaced at several sectors along the east west direction and the two major displacements coincide with the locations of the major rift offsets on the surface because of the asthenospheric uplift the crust under the main ethiopian rift is slightly thinned the zone of crustal thinning 31 km coincides with the location of the intrusion beneath the rift floor and the maximum of which is attained in the northern and central sectors of the graben the trend of the crustal thinning zone which is from south to north is the same as the one obtained in the afar depression the southeastern and western plateaus on the other hand show by far the largest crustal thickness in the region 38 51 km in contrast to the afar depression where the crust is partly oceanized the thickness and density of the crust suggest that the main ethiopian rift is underlain by a purely continental crust the deep and relatively large nature of the intrusion leads to the conclusion that a large scale asthenospheric upwelling might be responsible for the thinning of the crust and subsequent rifting of the graben

vertical axis rotations and deformation along the active strike slip el tigre fault precordillera of san juan argentina assessed through palaeomagnetism and anisotropy of magnetic susceptibility palaeomagnetic data from poorly consolidated to non consolidated late cenozoic sediments along the central segment of the active el tigre fault central western precordillera of the san juan province argentina demonstrate broad cumulative deformation up to 450 m from the fault trace and reveal clockwise and anticlockwise vertical axis rotations of variable magnitude this deformation has affected in different amounts miocene to late pleistocene samples and indicates a complex kinematic pattern several inherited linear structures in the shear zone that are oblique to the el tigre fault may have acted as block boundary faults displacement along these faults may have resulted in a complex pattern of rotations the maximum magnitude of rotation is a function of the age of the sediments sampled with largest values corresponding to middle miocene lower pliocene deposits and minimum values obtained from late pleistocene deposits the kinematic study is complemented by low field anisotropy of magnetic susceptibility data to show that the local strain regime suggests a n s stretching direction subparallel to the strike of the main fault

first tectonic geomorphology study along the longmu gozha co fault system western tibet abstract the longmu gozha co left lateral strike slip fault system lgcf is located in remote western tibet forming a triple junction with both the altyn tagh fault atf and the karakorum fault kf the two major strike slip faults in the region the ashikule gozha co and longmu co faults are clear and distinct left stepping en echelon faults together forming the lgcf system although poorly documented quantifying its activity remains a key problem to understand the kinematics and the tectonic history of the westernmost tibetan plateau indeed the karakax fault nw segment of the atf lgcf and kf together control the tectonics of western tibet which itself controls the extrusion of tibet towards the east with the lgcf acting as a natural boundary for eastward motion of the tibetan plateau due to india s northward impingement the lgcf system shows clear and impressive morphological indications of left lateral active shear that we quantify using field measurements terrestrial lidar along with 10 be surface exposure dating our data suggest a slip rate 9 and 8 mm yr respectively yielding a few mm yr of extension accommodated most likely in the ashikule graben and surroundings located between the atf and karakax faults numerous evidences of recent tectonic related events are present in the vicinity such as the 1951 volcanic eruption as well as the 2008 and 2014 ms 7 3 yutian earthquakes attesting of its high activity in addition the lgcf s en echelon geometry and identical direction with the atf as well as smaller geological offsets and lower slip rate compared to those on the surrounding faults suggest that this segment of the atf may be the most recent

high slip rate for a low seismicity along the palu koro active fault in central sulawesi indonesia accurate chronological records are critical for understanding the landformsevolution and in particular of alluvial fan sequences emplaced during glocal global climatic changes toward this end we measured in situ produced 10be in quartz boulders exposed on top surfaces of sulawesian late quaternary alluvial fans combined geomorphic study spot image and field analyses indicate that this site is composed of twoalluvial fan units in situ produced 10be concentrations suggest that they were emplaced during two successive major climatic events the calculated minimum exposure ages date the younger unit abandonment at 11 000 2 000 years and seem consistent with a late interglacial abandonment age 120 000years for the older unit this study demonstrates that using both the neutron and muon components implicated in the production of in situ10be surficial erosion rates can be estimated 6 m ma in sulawesi and alluvial fan surfaces dated in particular it shows that10be may be used to date fan surface emplacement during the last 120 ka under humid tropical conditions significantly helping to constrain continental paleo climatology in these regions

tectonic implications of fluvial incision and pediment deformation at the northern margin of the central anatolian plateau based on multiple cosmogenic nuclides 1 we document quaternary fluvial incision driven by fault controlled surface deformation in the inverted intermontane gok rmak basin in the central pontide mountains along the northern margin of the central anatolian plateau in situ produced 10be 21ne and 36cl concentrations from gravel covered fluvial terraces and pediment surfaces along the trunk stream of the basin the gok rmak river yield model exposure ages ranging from 7 1 ka to 346 45 ka and average fluvial incision rates over the past 350 ka of 0 28 0 01 mm a 1 similarities between river incision rates and coastal uplift rates at the black sea coast suggest that regional uplift is responsible for the river incision model exposure ages of deformed pediment surfaces along tributaries of the trunk stream range from 60 5 ka to 110 10 ka demonstrating that the thrust faults responsible for pediment deformation were active after those times and were likely active earlier as well as explaining the topographic relief of the region together our data demonstrate cumulative incision that is linked to active internal shortening and uplift of 0 3 mm a 1 in the central pontide orogenic wedge which may ultimately contribute to the lateral growth of the northern anatolian plateau

the geometry of the active strike slip el tigre fault precordillera of san juan central western argentina integrating resistivity surveys with structural and geomorphological data the geometry and related geomorphological features of the right lateral strike slip el tigre fault one of the main morphostructural discontinuities in the central western precordillera of argentina were investigated achievements of this survey include recognition of structural and geometrical discontinuities along the fault trace identification and classification of landforms associated with local transpressional and transtensional sectors observation of significant changes in the fault strike and detection of right and left bends of different wavelength in the central segment of the el tigre fault 2d electrical resistivity tomography surveys were carried out across the fault zone the resistivity imaging permitted to infer the orientation of the main fault surface the presence of blind fault branches along the fault zone tectonic tilting of the quaternary sedimentary cover subsurface structure of pressure ridges and depth to the water table based on this information it is possible to characterize the el tigre fault also as an important hydro geological barrier our survey shows that the main fault surface changes along different segments from a high angle to a subvertical setting whilst the vertical slip component is either reverse or normal depending on the local transpressive or transtensive regime induced by major bends along the trace these local variations are expressed as sections of a few kilometres in length with relatively homogeneous behaviour and frequently separated by oblique or transversal structures

regional relative tectonic activity of structures in the pampean flat slab segment of argentina from 30 to 32 s abstract the pampean flat slab segment of the central andes in argentina is a broad active deformation zone subject to both plate boundary related and intraplate deformation to the west plate boundary related deformation is dominated by thin skinned fold and thrusts of the precordillera while to the east intraplate deformation involves thick skinned reverse faults of the sierras pampeanas gps data and absolute dating of displaced geomorphic features suggest that most of the active permanent deformation occurs between these two regions at the andean orogenic front and that there is a west to east trend of decreasing shortening rates however gps stations and sites with geomorphic slip rate measurements are currently too sparse and cover too short a time period to make reliable inferences about the longer term distribution and relative rates of deformation mountain range scale geomorphic indices on the other hand reflect tectonic activity since at least the pleistocene in this study we measured geomorphic indices hypsometric integral and curves basin elongation ratio basin volume to area ratio valley floor width to height ratio mountain front sinuosity and normalized steepness indices of rivers from 10 different n s striking range bounding faults that span both the precordillera and sierras pampeanas regions from west to east we use these data to assess the regional relative tectonic activity of major quaternary deformation features in the pampean segment of the central andes even when variations in climate and geology are considered mean values for each geomorphic index suggests uplift rates for the 10 mountain range bounding faults display local trends that are closely associated with the structural style and tectonic evolution of these structures although vertical uplift rates vary little horizontal shortening rates are higher for the precordillera fold and thrusts in the west than the thick skinned reverse faults of the sierras pampeanas in the east due to shallower fault dips for precordilleran structures the similarity with decadal slip rate gradients from gps studies could possibly indicate that the stress field has been constant since at least the pleistocene but further slip rate studies over broader time intervals in the late quaternary are necessary to confirm this variations observed in relative uplift rates along each fault point to sites that warrant further detailed study of slip rates and evaluation of associated seismic hazards

studies of quaternary deformation zones through geomorphic and geophysical evidence a case in the precordillera sur central andes of argentina abstract at the northern sector of the precordillera sur 31 50 32 40 sl 68 45 69 20 wl central andes of argentina nw trending sinistral transpressive shear zones at different scales product of the late cenozoic andean deformation are recognized the most significant of them is the 120 km long barreal las penas belt and within it a small scale 7 km long quaternary sinistral transpressive shear zone called los avestruces has been detected from geomorphological and geophysical analysis 32 sl 69 21 wl geophysical techniques were applied to better characterize the shallow structure and kinematics of some representative structures in this shear zone in particular the use of tomography of electrical resistivity methods allowed characterizing the subsurface geometry of some areas of interest enabling the recognition of quaternary layers against their original slope the geometry of the reverse fault which uplifted the pleistocene deposits of one of the highs the geometry of a likely previous extensional fault reactivated and inverted during the quaternary as well as the presence of a reverse blind fault which has uplifted the quaternary deposits of the los avestruces bog the location of the above mentioned shear zones coincides with the northern branch of the nw trending extensional triassic cuyana basin thus their presence appears to be related to andean reactivation of older triassic mainly nw trending structures in the northern area of the precordillera sur as well as in other places of the world here discussed these kinds of paleotectonic oblique features play a major role in defining the geometry and kinematics of late cenozoic deformation

active basement uplift of sierra pie de palo northwestern argentina rates and inception from10be cosmogenic nuclide concentrations quaternary tectonic and denudation rates are investigated for an actively growing basement anticline the sierra pie de palo range which belongs to the andean foreland of northwestern argentina 28 s 33 s in this study a detailed morphometric analysis of the topography is combined with in situ produced cosmogenic10be concentrations measured in 1 surface boulders abandoned on alluvial terraces affected by fault activity along the north bounding fault and growth of the basement fold along the southeastern border 2 bedrock outcrops corresponding to an exhumed and folded regional erosion surface and 3 fluvial sediments sampled at the outlets of several watersheds along the eastern and northern borders of the range incision and uplift rates have been estimated at approximately 0 5 and 1 mm yr when integrated on holocene and pleistocene time scales in close agreement with both long term structural and basin evolution data and short term gps derived velocity field analyses cosmogenic derived denudation and uplift rates combined with geomorphic characteristics of watersheds and river channels allows estimating the onset of the uplift at 4 6 ma followed by a more recent period of topographic rejuvenation at roughly 1 2 ma probably synchronous with steepening of the eastern and northern flanks of the anticline

distribution of landslides along the andean active orogenic front argentinean precordillera 31 33 s abstract as one of the main environmental effects of earthquakes the distribution of landslides could reflect regional neotectonic activity to that end we carried out an inventory of landslides along the precordillera range 31 33 s comprising the most seismically active region of argentina main quaternary deformation is concentrated in this western central part of the country associated with active faults linked to intense shallow seismic activity

cosmic ray exposure cre dating in a wet tropical domain late quaternary fan emplacements in central sulawesi indonesia accurate chronological records are critical for studying the alluvial fan sequences emplaced during local global climatic changes but in general there are no satisfactory quantitative dating methods available in situ produced be 10 concentrations have been measured in quartz boulders exposed on sulawesian late quaternary fan surfaces these concentrations suggest that the two fan units evidenced by geomorphic study were emplaced during two distinct major climatic events the calculated minimum exposure ages imply abandonment ages of 11 kyr and 120 kyr for the younger and older units respectively this study demonstrates that using both the neutron and muon components implicated in the in situ be 10 production surficial erosion rates can be estimated and alluvial fans dated ln particular it shows that in situ be 10 may be used to date fan emplacement during the last 120 kyr under humid tropical conditions significantly helping to constrain continental palaeoclimatology

elementary forms for land surface segmentation the theoretical basis of terrain analysis and geomorphological mapping abstract land surface morphology is fundamental to geomorphological mapping and many gis applications review and comparison of various approaches to segmentation of the land surface reveals common features and permits development of a broad theoretical basis for segmentation and for characterization of segments and their boundaries within the context of defining landform units that maximise internal homogeneity and external differences this paper introduces the concept of elementary forms segments units defined by constant values of fundamental morphometric properties and limited by discontinuities of the properties the basic system of form defining properties represents altitude and its derivatives constant values of which provide elementary forms with various types of homogeneity every geometric type of elementary form can be characterized by a defining function which is a specific case of the general polynomial fitted function various types of boundary discontinuity and their connections and transformations into other types of morphological unit boundaries are analysed the wealth of types of elementary forms and their boundaries is potentially unbounded and thus is sufficient to cover the real variety of landforms elementary forms in the basic set proposed here have clear potential for genetic and dynamic interpretation a brief worked example documents the possibility of analytical computation of various models of ideal elementary forms for particular segments of landform ideal elementary forms can be considered as attractors to which the affinity of surface segments can be measured by multivariate statistical methods the use of the concept of elementary forms in landscape segmentation is promising and it could be adapted for elementary segmentation of various other spatial fields

seismic hazard reappraisal from combined structural geology geomorphology and cosmic ray exposure dating analyses the eastern precordillera thrust system nw argentina because earthquakes on large active thrust or reverse faults are not always accompanied with surface rupture paleoseismological estimation of their associated seismic hazard is a difficult task to improve the seismic hazard assessments in the andean foreland of western argentina san juan province this paper proposes a novel approach that combines structural geology geomorphology and exposure age dating the eastern precordillera of san juan is probably one of the most active zones of thrust tectonics in the world we concentrated on one major regional active reverse structure the 145 km long villic um pedernal thrust where this methodology allows one to 1 constrain the quaternary stress regime by inversion of geologically determined slip vectors on minor or major fault planes 2 analyse the geometry and the geomorphic characteristics of the villic um pedernal thrust and 3 estimate uplift and shortening rates through determination of in situ produced 1 0 be cosmic ray exposure cre ages of abandoned and uplifted alluvial terraces from a structural point of view the villic um pedernal thrust can be subdivided into three thrust portions constituting major structural segments separated by oblique n40 e trending fault branches along the three segments inversion of fault slip data shows that the development of the eastern precordillera between 31 s and 32 s latitude is dominated by a pure compressive reverse faulting stress regime characterized by a n110 10 e trending compressional stress axis 1 a geomorphic study realized along the 18 km long las tapias fault segment combined with cre ages shows that the minimum shortening rate calculated over the previous 20 kyr is at least of the order of 1 mm yr 1 an earthquake moment tensor sum has also been used to calculate a regional shortening rate caused by seismic deformation this analysis of the focal solutions available for the last 23 yr shows that the seismic contribution may be three times greater than the shortening rate we determined for the las tapias fault i e 3 mm yr 1 suggesting that the san juan region may have experienced a seismic crisis during the 20th century moreover the ramp that controls the development of the eastern precordillera appears to be one of the main seismic sources in the san juan area particularly the 65 km long villic um las tapias segment a first order evaluation of the seismic hazard parameters shows that this thrust segment can produce a maximum earthquake characterized by a moment magnitude of 7 3 0 1 and a recurrence interval of 2 4 1 5 kyr this part of the villic um pedernal ramp may have ruptured during the ms 7 4 1944 san juan earthquake producing very few surface ruptures and only distributed flexural slip deformation on to the neogene foreland bedding planes between the eastern precordillera and pie de palo

pleistocene alluvial deposits dating along frontal thrust of changhua fault in western taiwan the cosmic ray exposure point of view abstract to tackle the history of active thrusts it is necessary to open the observation window on time scales on the order of 104 105 years by studying the surface morphologies resulting from their activities because fluvial systems are particularly sensitive to recent environmental changes geomorphic features such as alluvial terraces are frequently used as markers to gauge tectonic deformation together with the measurement of cumulative displacements the chronological framework of emplacement and abandonment of these geomorphic markers is thus fundamental to determine long term fault slip rates in taiwan the geomorphic features associated with fault activity have been studied in detail with a high level of resolution however the use of deformed and partially preserved alluvial terraces is often hampered by the absence of well documented ages the purpose of this paper is two fold first we take the opportunity to review the chronological constraints that have been published in taiwan so far second we present how the cosmogenic dating method in situ produced 10be can be used to constraint the chronological framework of alluvial deposits over a pleistocene time scale thanks to a comparison of our cosmogenic derived ages with existing data we present a consistent regional chronological framework for the pakua tadu area along the changhua fault one of the most active frontal thrusts in the western foothills of the taiwan mountain belt we also discuss its relationships with global eustatism and its tectonic implications for the timing of propagation of the deformation front during the last 450 kyr