quaternary tephrochronology helps define conditioning factors and triggering mechanisms of rock avalanches in nw argentina abstract ten previously defined quaternary tephra layers from northwestern argentina are described here in terms of electron microprobe analyses of glass shards in addition xrf analyses of three tephras alemania buey muerto and el paso ash were performed the alemania ash and buey muerto ash occur within 1 m of each other stratigraphically in several outcrops and exhibit identical glass chemistry as well xrf analyses show that both tephras have identical composition based on stratigraphic relations and age determinations these tephras can clearly be separated as two individual layers tephra ages were defined relatively by ams 14c dates of organic material by 10be surface exposure ages of landslides in stratigraphic association with these tephra layers or directly by 40ar 39ar ages of mineral separates or fission track dating of zircons ages of these tephra layers constrain the temporal distribution of large landslides rock avalanche type in northwestern argentina temporal distribution shows that these large collapses concentrated in deeply incised valleys during climate periods characterized by enhanced precipitation and run off in addition in the tonco valley tephra characteristics also suggest earthquake triggering of coeval landsliding in this valley four landslides one with a 10be age of 7820 830 yr lie in direct contact atop un redeposited paranilla ash showing the coeval age of these landslides the age of the dated landslide deposit coincides with the age of soft sediment deformation structures in nearby lake deposits with an ams 14c age of 7430 7570 cal yr bp

effect of the altiplano puna plateau south america on the regional intraplate stresses abstract a previous compilation of stress data for the sub andean region of northwest argentina is complemented with eight additional earthquake focal mechanisms seven events 5 3 5 5 mb had their mechanisms determined by inversion of teleseismic body waves short period p waves and long period sh waves all events had predominantly reverse faulting mechanisms five had almost pure dip slip motion and two had a component of oblique motion the other mechanism was a composite fault plane solution of the hualfin catamarca series of july 1986 maximum 4 mb determined with data from a local temporary network and the permanent inpres regional network the local data shows that the hualfin events occurred on a single fault plane oriented nw se with predominantly strike slip motion the stress data in the sub andean region suggests a radial pattern around the altiplano puna plateau with compressional stresses tending to be perpendicular to the eastern front of the plateau this indicates that local spreading stresses due to lateral density variations crustal thickening or lithospheric thinning of the plateau may be comparable or even exceed the plate wide regional stresses at the southeastern border of the puna plateau where a stress rotation of about 30 may be detected preliminary order of magnitude calculations indicate that the local plateau induced compression can be about 1 2 times greater than the regional horizontal deviatoric stress the present predominance of the local stress over the regional stress is consistent with the decrease of the nazca south america convergence rate observed since about 10 20 ma

structural styles and regional tectonic setting of the gela nappe and frontal part of the maghrebian thrust belt in sicily the gela nappe of south central sicily provides an example of a curved segment of an orogenic front that can be examined both onshore and offshore for deformational style and amount of shortening synorogenic sediments allow the deformation to be dated two distinct structural styles are observed in the gela nappe the central salient part of the nappe caltanissetta basin consists of a single thrust sheet containing a train of continuously tightening folds and the reentrant margins of the nappe sciacca and monte judica consist of a stack of several thrust sheets these different structural styles correspond to the pretectonic mesozoic stratigraphy of the foreland plate carbonate platforms exist on the adventure bank and hyblean plateau ahead of sciacca and monte judica respectively while the caltanissetta basin region appears to have accumulated basinal clay facies where the resistant carbonate stratigraphy provides a buttress to the propagation of the thrust front deformation is taken up by imbrication on steep ramps through the carbonates generating a relatively thick orogenic wedge in the basinal setting where no strong rheology exists the low angle of friction on the clay detachment levels requires the growing thrust wedge to be much thinner with a very low foreland dip hence the thrust front propagates much farther forward into the basin than it does in the adjacent platformal areas producing a nonlinear thrust front in the basinal region accretion of foreland material to the nappe by imbrication was only prominent during the messinian when subaerial exposure prevented low friction transport of the nappe across the highest levels of the stratigraphy a steady thickening of the nappe by internal folding suggests an increase in friction along the basal detachment possibly due to progressive compaction of the clays

amazonia during the last glacial abstract new data on the vegetational history and quaternary geology of amazonia permit an improved reconstruction of past environments in amazonia during the last glacial period although limited data from rondonia carajas and guyana show that in certain areas savanna type vegetation and savanna forest had replaced the rain forest during the late pleniglacial ca 22 000 13 000 yr b p the amazonian forest may have been split up into one major west amazonian and several other medium size forest areas this suggests a decline in rainfall of 500 to 1000 mm a reduction of 25 to 40 temperatures may also have been 2 to 6 c 4 2 c lower than today possibly substancially influencing amazonian vegetation during the humid middle pleniglacial 55 000 26 000 yr b p rivers carried a lot of water and sediment resulting in the deposition of lower terrace sediments with one dry interruption around 40 000 yr b p carajas and katira in carajas there is evidence of dry periods ocurring at about 40 000 yr b p and during the early pleniglacial ca 60 000 yr b p rivers carried little water and incised into the low terrace sediments during the dry late pleniglacial water levels rose during the late glacial 13 000 10 000 yr b p or at the beginning of the holocene 10 000 yr b p sedimentation in and of the present inundation valleys commenced after that

chronological and geomorphological approach to the holocene tephras from tafi and santa maria valleys nw argentina fil sampietro vattuone maria marta universidad nacional de tucuman facultad de ciencias naturales e instituto miguel lillo laboratorio de geoarqueologia argentina consejo nacional de investigaciones cientificas y tecnicas argentina

climate change and mass movements in the nw argentine andes abstract the chronology of multiple landslide deposits and related lake sediments in the eastern argentine cordillera suggests that major mass movements cluster in two time periods during the quaternary between 35 000 and 25 000 14 c yr bp and after 5000 14 c yr bp the older cluster may correspond to the minchin wet period 40 000 and 25 000 14 c yr bp identified in tropical and subtropical south america suggesting a causal relation between enhanced landslide activity and climate change the younger cluster predates the titicaca wet period that began at about 3900 14 c yr bp which also affected other regions in the andes and the amazon basin no landslide and associated lake sediments are documented during the tauca wet period between 16 000 and 8000 14 c yr bp however the two clusters correspond to periods where it assumed that the el nino southern oscillation enso and tropical atlantic sea surface temperature dipole tad were active the analysis of the present day precipitation patterns in nw argentina indicates significant spatial and temporal differences between the intra andean part of the study area and the andean foreland whereas the tad seems to consistently increase rainfall the intensity of precipitation during the el nino phase of the enso is reduced to only 25 of the mean annual average in the intra andean basins whereas the regions east of the andes receive more than 125 similar results but with an opposite sign characterize la nina events the comparison of this pattern with paleo precipitation data as inferred from varved lake sediments suggests that increased interannual climate variability and therefore increased fluctuations in rainfall and river discharge in narrow valleys may reduce landsliding thresholds

kinematics of the western africa eurasia plate boundary from focal mechanisms and gps data summary the western mediterranean displays a complex pattern of crustal deformation distributed along tectonically active belts developed in the framework of slow oblique plate convergence we used earthquake and global positioning system gps data to study the present day kinematics and tectonics of the africa eurasia plate boundary in this region crustal seismicity and focal mechanisms analysed in terms of seismic moment release and seismic deformation outline the geometry of major seismic belts and characterize their tectonics and kinematics continuous gps data have been analysed to determine euler vectors for the nubian and eurasian plates and to provide the global frame for a new mediterranean gps velocity field obtained by merging continuous and campaign observations collected in the 1991 2005 time span gps velocities and displacements predicted by the nubia eurasia rotation pole provide estimates of the deformation accommodated across the tectonically active belts the rather simple deformation occurring in the atlantic region characterized by extension about perpendicular to the middle atlantic and terceira ridges and right lateral motion along the gloria transform fault turns into a complex pattern of deformation occurring along broader seismic belts where continental lithosphere is involved our analysis reveals a more complex fragmentation of the plate boundary than previously proposed the roughly e w trending mainly compressive segments i e southwestern iberia northern algeria and southern tyrrhenian where plate convergence is largely accomodated across rather localized deformation zones and partially transferred northward to the adjacent domains i e the algero balearic and tyrrhenian basins are interrupted by regions of more distributed deformation i e the rif alboran betics tunisia libya and eastern sicily or limited seismicity i e the strait of sicily which are characterized by less homogeneous tectonics regimes mainly transcurrent to extensional in correspondence of the observed breaks tectonic structures with different orientation interfere and we find belts with only limited deformation i e the high and middle atlas the tunisian atlas and the offshore tunisia libya belt that extends from the plate boundary into the nubian plate along pre existing tectonic lineaments our analysis suggest that the sicilian pelagian domain is moving independently from nubia according to the presence of a right lateral and extensional decoupling zone corresponding to the tunisia libya and strait of sicily deformation zone despite the space variability of active tectonic regimes plate convergence still governs most of the seismotectonic and kinematic setting up to the central aeolian region in general local complexities derive from pre existing structural features inherited from the tectonic evolution of the mediterranean region on the contrary along calabria and the apennines the contribution of the subducted ionian oceanic lithosphere and the occurrence of microplates i e adria appear to substantially modify both tectonics and kinematics finally gps data across the gibraltar arc and the tyrrhenian calabria domain support the hypothesis that slab rollback in these regions is mostly slowed down or stopped

holocene history of deep seated landsliding in the north fork stillaguamish river valley from surface roughness analysis radiocarbon dating and numerical landscape evolution modeling documenting spatial and temporal patterns of past landsliding is a challenging step in quantifying the effect of landslides on landscape evolution while landslide inventories can map spatial distributions lack of dateable material landslide reactivations or time access and cost constraints generally limit dating large numbers of landslides to analyze temporal patterns here we quantify the record of the holocene history of deep seated landsliding along a 25 km stretch of the north fork stillaguamish river valley washington state usa including the 2014 oso landslide which killed 43 people we estimate the ages of more than 200 deep seated landslides in glacial sediment by defining an empirical relationship between landslide deposit age from radiocarbon dating and landslide deposit surface roughness we show that roughness systematically decreases with age as a function of topographic wavelength consistent with models of disturbance driven soil transport the age roughness model predicts a peak in landslide frequency 1 000 ybp with very few landslide deposits older than 7 000 ybp or younger than 100 ybp likely reflecting a combination of preservation bias and a complex history of changing climate base level and seismic shaking in the study area most recent landslides have occurred where channels actively interact with the toes of hillslopes composed of glacial sediments suggesting that lateral channel migration is a primary control on the location of large deep seated landslides in the valley

the formation and failure of natural dams of the numerous kinds of dams that form by natural processes dams formed from landslides glacial ice and late neoglacial moraines present the greatest threat to people and property landslide dams form in a wide range of physiographic settings the most common types of mass movements that form landslide dams are rock and debris avalanches rock and soil slumps and slides and mud debris and earth flows the most common initiation mechanisms for dam forming landslides are excessive rainfall and snowmelt and earthquakes landslide dams can be classified into six categories based on their relation with the valley floor type i dams 11 of 184 landslide dams from around the world that we were able to classify do not reach from one valley side to the other type ii dams 44 span the entire valley floor in some cases depositing material high on opposite valley sides type iii dams 41 move considerable distances both upstream and downstream from the landslide failure type iv dams 1 are rare and involve the contemporaneous failure of material from both sides of a valley type v dams 1 also are rare and are created when a single landslide sends multiple tongues of debris into a valley and forms two or more landslide dams in the same reach of river type vi dams 3 involve one or more failure surfaces that extend under the stream or valley and emerge on the opposite valley side many landslide dams fail shortly after formation in our sample of 73 documented landslide dam failures 27 of the landslide dams failed less than 1 day after formation and about 50 failed within 10 days over topping is by far the most common cause of failure the timing of failure and the magnitude of the resulting floods are controlled by dam size and geometry material characteristics of the blockage rate of inflow to the impoundment size and depth of the impoundment bedrock control of flow and engineering controls such as artificial spill ways diversions tunnels and planned breaching by blasting or conventional excavation glacial ice dams can produce at least nine kinds of ice dammed lakes the most dangerous are lakes formed in main valleys dammed by tributary glaciers failure can occur by erosion of a drainage tunnel under or through the ice dam or by a channel over the ice dam cold polar ice dams generally drain supraglacially or marginally by downmelting of an outlet channel warmer temperate ice dams tend to fail by sudden englacial or subglacial breaching and drainage late neoglacial moraine dammed lakes are located in steep mountain areas affected by the advances and retreats of valley glaciers in the last several centuries these late neoglacial dams pose hazards because 1 they are sufficiently young that vegetation has not stabilized their slopes 2 many dam faces are steeper than the angle of repose 3 these dams and lakes are immediately downslope from steep crevassed glaciers and near vertical rock slopes and 4 downstream from these dams are steep canyons with easily erodible materials that can be incorporated in the flow and increase flood peaks the most common reported failure mechanism is overtopping and breaching by a wave or series of waves in the lake generated by icefalls rockfalls or snow or rock avalanches melting of ice cores or frozen ground and piping and seepage are other possible failure mechanisms natural dams may cause upstream flooding as the lake rises and downstream flooding as a result of failure of the dam although data are few for the same potential energy at the dam site ownstream flood peaks from the failure of glacier ice dams are smaller than those from landslide moraine and structed earth fill and rock fill dam failures moraine dam failures appear to produce some of the largest downstream flood peaks for potential energy at the dam site greater than 1011 1012 joules differences in flood peaks natural dam failures appear to be controlled by dam characteristics and failure mechanisms

kinematics of fault related folding derived from a sandbox experiment we analyze the kinematics of fault tip folding at the front of a fold and thrust wedge using a sandbox experiment the analog model consists of sand layers intercalated with low friction glass bead layers deposited in a glass sided experimental device and with a total thickness h 4 8 cm a computerized mobile backstop induces progressive horizontal shortening of the sand layers and therefore thrust fault propagation active deformation at the tip of the forward propagating basal decollement is monitored along the cross section with a high resolution ccd camera and the displacement field between pairs of images is measured from the optical flow technique in the early stage when cumulative shortening is less than about h 10 slip along the decollement tapers gradually to zero and the displacement gradient is absorbed by distributed deformation of the overlying medium in this stage of detachment tip folding horizontal displacements decrease linearly with distance toward the foreland vertical displacements reflect a nearly symmetrical mode of folding with displacements varying linearly between relatively well defined axial surfaces when the cumulative slip on the decollement exceeds about h 10 deformation tends to localize on a few discrete shear bands at the front of the system until shortening exceeds h 8 and deformation gets fully localized on a single emergent frontal ramp the fault geometry subsequently evolves to a sigmoid shape and the hanging wall deforms by simple shear as it overthrusts the flat ramp system as long as strain localization is not fully established the sand layers experience a combination of thickening and horizontal shortening which induces gradual limb rotation the observed kinematics can be reduced to simple analytical expressions that can be used to restore fault tip folds relate finite deformation to incremental folding and derive shortening rates from deformed geomorphic markers or growth strata

frictionite as evidence for a large late quaternary rockslide near kanchenjunga sikkim himalayas india implications for extreme events in mountain relief destruction abstract we present sedimentologic and petrographic field evidence of an extremely large 2 5 109 m3 late quaternary rockslide around dzongri 24 km s of kanchenjunga 8585 m a s l widespread occurrence of shattered leucogranites and migmatites deposited discordantly on top of undisturbed augen gneisses and separated by micro brecciated sliding surfaces indicate rapid movement during a large rockslide event occurrence of frictionite hyalomylonite in mineral samples indicates short term temperatures of 600 c in the moving rockslide mass along a 12 sliding plane from a sw direction of movement we infer a source 8 km ne of the deposit 5 km s of pandim 6691 m a s l where today a thick leucogranite intrusion marks a zone of weakness and failure of a postulated former mountain crest the mechanism of movement the dip of the sliding surface and the deposit preservation along ridge tops require that the dzongri rockslide ran out over an ice filled prek chu valley hence we prefer earthquake shaking over undercutting and glacial debuttressing as a possible trigger mechanism a regional review of other similarly large and catastrophic himalayan rockslides indicates that leucogranite intrusions are highly conducive to large scale failure in the higher himalayan crystalline hhc importantly high erosion rates have rendered this large rockslide deposit undetectable by remote sensing or digital elevation data which are commonly used for identifying evidence of such extreme events quantifying the contribution of such giant landslides in destroying some of the highest relief on earth will thus need further research attention

characterizing structural and lithologic controls on deep seated landsliding implications for topographic relief and landscape evolution in the oregon coast range usa in mountainous areas landslides regulate temporal variations in sediment production and may suppress simple linkages between topographic development and tectonic forcing rates and mechanisms of mass wasting depend on lithology bedrock structure and climatic and tectonic setting these factors tend to vary signifi cantly in active tectonic regions thus clouding our ability to predict how landsliding modulates topographic development over human and geological time scales here we use a novel dem based technique to document the distribution of large landslides in the oregon coast range ocr and quantify how they affect topographic relief we developed an automated algorithm that exploits the distinctive topographic signature specifi cally the relationship between curvature and gradient of large landslides to map their distribution within the gently folded tyee formation eocene deltaicsubmarine ramp sediments in contrast to steep and highly dissected terrain frequently identifi ed as characteristic of the ocr which exhibits steep planar sideslopes and highly curved low gradient ridgetops and valleys terrain prone to large landslides tends to have low values of both drainage density and curvature and gradient values that cluster between 0 16 and 0 44 the distribution of failure dominated terrain in our 10 000 km2 study area is infl uenced by systematic variations in sedimentary facies and bedrock structure the fraction of terrain altered by large landslides 0 1 km2 varies from 5 in the sand rich delta slope and proximal ramp facies southern section of our study area to 25 in the north distal ramp facies coincident with an increase in the thickness of siltstone beds and a decrease in the sandstone siltstone ratio local relief declines progressively northward suggesting that deep seated landsliding is sensitive to the thickness and frequency of low shearstrength siltstone beds and may serve to limit topographic development in the ocr structural controls are superimposed on facies related variations as deep seated landslides are frequently found on slopes whose downslope aspect corresponds to the bedrock dip direction for 1516 strike and dip measurements in our study area we calculated the fraction of proximal terrain 2 5 km altered by deep seated landsliding in the sand rich southern region the proportion of proximal slide dominated terrain increases modestly with bedrock dip in the silt rich northern region terrain altered by deep seated landsliding is pervasive and an increase in dip from 0 to 16 corresponds to a change in the fraction of slide prone terrain from 10 to 28 our technique for mapping large landslides has utility for hazard analysis and land management over million year time scales the progradational character of the tyee formation suggests that continued uplift and exhumation of the ocr should result in a southward propagation of slide prone silt rich distal facies as a result deep seated landsliding will become increasingly prominent and topographic relief in the central and southern ocr will progressively decline whereas spatial variability in climatic or tectonic forcing is often invoked to explain systematic variations in topographic development our results emphasize the importance of structural and intraformation lithologic controls on landsliding as such analyses linking surface processes climate tectonics and landscapes should be couched in the context of diverse geologic and topographic data

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

evolution of the northwestern iblean mountains sicily uplift plicocene pleistocene sea level changes paleoenvironment and volcanism the late miocene to pleistocene evolution of the northwestern iblean plateau sicily is marked by a complex interplay of subaerial and submarine volcanism subsidence and uplift eustatic sea level changes and shallow water carbonate and clay sedimentation volcanic activity occurred in distinct phases differing drastically in volume chemical composition eruptive and depositional sites and eruptive mechanisms six of the newly defined formations in the northwestern iblean plateau are either entirely volcanic or contain significant amounts of volcanics the eastern part of a shallow marine basin was filled completely by late pliocene tholeiitic lava flows militello formation that had advanced subaerially from the south southeast lava deltas advanced southwestward on top of earlier pillow breccia debris flow deposits intertongued with soft trubi marls and chalks true submarine eruptions monte caliella formation simultaneously produced densely packed pillow piles up to 250 m thick inferred water depths based on volcanologic and paleoecologic criteria of interbedded and overlying calcarenites agree well

mid and late holocene limnogeology of laguna del negro francisco northern chile and its palaeoclimatic implications lacustrine sediments from the high elevation endorheic saline lake negro francisco 27 28 s 69 14 w 4125 m provide a detailed mid and late holocene environmental history of the southern chilean altiplano mineralogy chemical composition and sedimentary facies analyses of the deposits confirm the regional significance of mid holocene aridity between 6000 and 3800 bp precipitation rates were signifi cantly lower than the c 250 mm yr 1 of today fully arid conditions were interrupted by short term moist spells with an average return period of about 200 years effective moisture increased after 3800 bp and peaked between 3000 and 2600 bp and between 2200 and 1800 bp in two phases with conditions more humid than today comparison with regional palaeodata suggest that these two late holocene humid spells were most likely related to pacific moisture sources salinity levels increased again in laguna del negro francisco after 1800 bp the onset of modern climatic conditions was a stepwise nonlinear proce

active faulting and seismicity along the siculo calabrian rift zone southern italy abstract southern italy is dominated by extensional tectonics that in the calabrian arc and eastern sicily produced the development of the siculo calabrian rift zone scrz this zone is represented by a 370 km long fault belt consisting of 10 to 50 km long distinct fault segments which extend both offshore and on land being also responsible of the crustal seismicity of this region the geological and morphological observations indicate that the active normal faults of the scrz are characterized by throw rates ranging from 0 7 to 3 1 mm a they accommodate an almost uniform horizontal extension rate of about 3 0 mm a along a wnw ese regional extension direction based on our field observations and following empirical relationships between magnitude and surface rupture length connections between large crustal earthquakes and distinct fault segments of the scrz have been also tentatively tested our data indicate moreover that the magnitudes m of the historical and instrumental earthquakes are consistent with the estimated values and that the geometry and kinematics of the fault segments and the related different crustal features of the scrz control the different seismic behaviours of adjacent portions of the active rift zone

on the origin of an amphibole rich vein in a peridotite inclusion from the lunar crater volcanic field nevada u s a abstract late cenozoic alkali basaltic lavas of the lunar crater volcanic field lcvf located in the center of the great basin of the western u s a contain a diverse suite of nodule samples of the lower crust and upper mantle this paper documents a composite nodule from the marcath flow in which an amphibole bearing wehrlite 59 olivine 30 clinopyroxene 6 amphibole is cut by a 6 9 mm wide vein of andesine amphibolite 80 kaersutite 15 andesine 3 ilmenite aside from nodule basalt reaction at the nodule exterior there is little chemical variation either within or between individual grains of hydrous and anhydrous phases in the vein and host wehrlite furthermore there is no systematic compositional zoning in the wehrlite relative to vein proximity the whole rock major and trace element composition of the vein is similar to a primitive mg mg fe 0 692 basaltic liquid and has al fe mg ca mn na k zr y and sr contents similar to basalts observed in the lcvf in contrast to the sr isotopic equilibrium displayed by vein feldspar and vein amphibole sr isotopic disequilibrium is exhibited between the vein 0 70318 4 wehrlite 0 70322 4 and host basalt 0 70357 5 n 3 however the sr isotopic ratios of older lcvf basalts 0 7030 0 7038 n 14 overlap those of the vein and wehrlite and the magmatic activity leading to vein and wehrlite formation could be related to this older phase of lcvf volcanism petrographic and geochemical evidence is not consistent with a metasomatic origin for the vein and instead supports the view that the vein originated by the intrusion into a wehrlite mass and subsequent crystallization of a relatively primitive alkali basaltic magma in the lower crust or upper mantle the wehrlite contains olivine of fo71 and probably originated by crystal separation and accumulation from a relatively differentiated basaltic magma in the lower crust or upper mantle

kinematics and dynamics of the late quaternary rift flank deformation in the hyblean plateau se sicily abstract the southernmost branch of the siculo calabrian rift zone scrz in se sicily is flanked by an actively uplifting 31 km wide and 40 km long rectangular shaped crustal block siracusa domain sd whose late quaternary tectonic evolution has been controlled by the active nw verging thrusting along its northwestern margin accompanied by an extension on the opposite side within the mobile block a local extensional stress field has produced two n140 oriented late quaternary collapsed basins which opened roughly perpendicular to the direction of stretching along the scrz some tectonic peculiarities of the sd such as the occurrence of shortening in absence of a crustal back stop the coexistence of local extensional and contractional stress field and the primary role played by fluids in the deformational processes suggest a possible connection between the shallower crustal dynamics with a deep seated mantle intrusion beneath the region as it is commonly documented to occur along the rift zones where the rift flank volcanism develops similar dynamics and kinematics have been in fact described in the adjacent areas of the western flank of scrz which are affected by volcanism e g eolian islands and mt etna the results of our study in the hyblean region give thus the opportunity to detail on the mode and the mechanics of faulting that can be significant to interpret the seismicity and active deformation in the adjacent volcanic areas of sicily

correlation of upper cenozoic tephra layers between sediments of the western united states and eastern pacific ocean and comparison with biostratigraphic and magnetostratigraphic age data five widespread upper cenozoic tephra layers that are found within continental sediments of the western united states have been correlated with tephra layers in marine sediments in the humboldt and ventura basins of coastal california by similarities in major and trace element abundances four of these layers have also been identified in deep ocean sediments at dsdp sites 34 36 173 and 470 in the northeastern pacific ocean these layers erupted from vents in the yellowstone national park area of wyoming and idaho y the cascade range of the pacific northwest c and the long valley area california l are the huckleberry ridge ash bed 2 0 ma y rio dell ash bed ca 1 5 ma c bishop ash bed 0 74 ma l lava creek b ash bed 0 62 ma y and loleta ash bed ca 0 4 ma c the isochronous nature of these beds allows direct comparison of chronologic and climatic data in a variety of depositional environments for example the widespread bishop ash bed is correlated from proximal localities near bishop in east central california where it is interbedded with volcanic and glacial deposits to lacustrine beds near tecopa southeastern california to deformed on shore marine strata near ventura southwestern california to deep ocean sediments at site 470 in the eastern pacific ocean west of northern mexico the correlations allow us to compare isotopic ages determined for the tephra layers with ages of continental and marine biostratigraphic zones determined by magnetostratigraphy and other numerical age control and also provide iterative checks for available age control relative age variations of as much as 0 5 m y exist between marine biostratigraphic datums for example highest occurrence level of discoaster brouweri and calcidiscus tropicus c macintyrei as determined from sedimentation rate curves derived from other age control available at each of several sites these discrepancies may be due to several factors among which are 1 diachronism of the lowest and highest occurrence levels of marine faunal and floral species with latitude because of ecologic thresholds 2 upward reworking of older forms in hemipelagic sections adjacent to the tectonically active coast of the western united states and other similar analytical problems in identification of biostratigraphic and magnetostratigraphic datums 3 dissolution of microfossils or selective diagenesis of some taxa 4 lack of precision in isotopic age calibration of these datums 5 errors in isotopic ages of tephra beds and 6 large variations in sedimentation rates or hiatuses in stratigraphic sections that result in age errors of interpolated datums correlation of tephra layers between on land marine and deep ocean deposits indicates that some biostratigraphic datums diatom and calcareous nannofossil may be truly time transgressive because at some sites they are found above and at other sites below the same tephra layers

tectonics and climate of the southern central andes the history of the southern central andes including the world s second largest plateau and adjacent intermontane basins and ranges of the eastern cordillera and the northern sierras pampeanas of argentina and bolivia impressively documents the effects of tectonics and topography on atmospheric circulation patterns the development of orographic barriers and their influence on erosion and landscape evolution at various timescales protracted aridity in the orogen interior has facilitated the creation and maintenance of the puna altiplano plateau contraction and range uplift filling of basins and possibly wholesale uplift of the plateau increased gravitational stresses in the orogen interior which caused the eastward migration of deformation into the foreland and successive aridification the uplift of the andean orogen has also had a far reaching influence on atmospheric and moisture transport patterns in south america this is documented by the onset of humid climate conditions on the eastern side of the andes in late miocene time which was coupled with the establishment of dramatic precipitation gradients perpendicular to the orogen and changes in tectonic processes in the andean orogenic wedge

paleogeography and andean structural geometry northwest argentina neogene tectonic segmentation of the andean cordillera in northwestern argentina is a function of both the dip of the subducted plate and of major paleogeographic structures and sedimentary basins vergence fault dip and lateral continuity of neogene structures can be related to the character and pre existing geometries and structures of the materials in which they form south of 27 s the thick skinned sierras pampeanas which occur mostly over a flat segment of the subducted nazca plate formed where little sedimentary cover overlay crystalline basement north of 24 s the thin skinned subandean belt overlying an inclined slab segment formed within a thick elongate eastward tapering trough of paleozoic and mesozoic sediments that may represent a complex of pre andean foreland basin deposits the transitional region between 24 27 s the santa barbara system and cordillera oriental is characterized paleogeographically by complex cross trending structures and irregular basin geometries and the neogene structures are equally complex and variable the paleogeographic features of nw argentina are a product of compressional tectonism during much of the paleozoic that resulted in an orogenic belt oriented obliquely to the modern andes this earlier orogen was disrupted by several zones of transverse structures and by cretaceous extensional or pull apart basins these features clearly influence the geometry of the superposed andean structures more intriguing however is the possibility that preexisting structures of the continental lithosphere may in some way help to modify the geometry of the subducted plate

late cenozoic tectonism and landscape development in the foreland of the andes northern sierras pampeanas 26 28 s argentina the argentine sierras pampeanas are reverse fault bounded mountain blocks of precambrian to paleozoic basement rocks in the foreland of the central andes uplift in the northernmost sierras pampeanas fault blocks of sierra de quilmes sierra cumbres calchaquies and sierra aconquija started about 7 ma and became pronounced between 4 and 3 4 ma the movements culminated after 2 9 ma when the conformable mio pliocene santa maria group was overthrusted faulted and folded in the course of principal basement uplift these movements created climate and base level conditions that resulted in the formation of five pediment levels in the deformed basin strata between 2 5 and 0 3 ma tectonically induced base level changes in the piedmont resulted in three tectonism related pediment surfaces between 2 5 and 0 6 ma which attest to the neotectonic activity in the andean foreland the chronology of young tectonic uplift contradicts models in which early uplift between 20 and 13 ma is due to the interaction between high topography on the subducting nazca plate and the south american craton in conjunction with the principal uplift of the adjacent puna plateau the northernmost sierras pampeanas are better explained by e w compressional stresses superposed on a thinned lithosphere and inherited zones of structural weakness that facilitated uplift

crustal structure variations and transcurrent faulting at the eastern and western margins of the eastern mediterranean abstract crustal structure variations within the crust of the eastern mediterranean as well as within the continental crust of the land areas east and west of the basin have caused segmentation of the collision zones which extend from sicily through the calabrian arc the hellenic arc and the cyprian arc to the taurus chain on both sides of the eastern mediterranean in southeastern sicily and in the levant similar tectonic features have developed hinge faults exist along both continental margins due to the different modes of collision between the land areas and the adjacent oceanic areas landward of the margins two large transcurrent fault systems the scicli fault zone and the dead sea rift have developed due to the existence of unique crustal units within the continental crust adjacent to the margins on both sides these units are more buoyant than the adjacent crust and resist underthrusting the initial faulting along both transcurrent fault systems probably started at the collision zone in the north and propagated to the south where large extensional areas the pantelleria rift and the red sea exist

sedimentary and tectonic evolution of the eastern hyblean plateau southeastern sicily during late cretaceous to quaternary time abstract two palaeogeographic domains have been distinguished in the cretaceous quaternary sequences which crop out in the hyblean region of southeastern sicily in the northeast shallow water algal bryozoan calcarenites of oligocene miocene age overlie either cretaceous rudist limestones or volcanics further to the northeast the stratigraphic gap increases as the miocene limestone thins and in the a g i p well catania 10 plio pleistocene sediments and volcanics directly overlie upper jurassic rocks in the southwestern part of the hyblean plateau pelagic sediments occupy the cretaceous miocene interval they were deposited in a shallow basin dipping gently towards the southwest the transition between the two zones is marked by much evidence of synsedimentary tectonic activity such as widespread slumping and the development of megabreccias composed of cretaceous and eocene blocks the palaeogeographic picture is one of carbonate reefs and volcanic seamounts developing in the upper cretaceous they formed platforms fault bounded to the west and southwest from which were derived the detrital sediments found in the basin and occasional spectacular gravity slides in present day terms the structural high probably corresponds to the northeastern margin of the hyblean plateau and in part to the siracusa syracuse malta escarpment the pattern is little changed in the upper miocene with volcanoclastics of phreatomagmatic origin intercalated with coral bioherms overlying algal bryozoan calcarenites upper tortonian lower messinian limestones with a restricted fauna indicate a shallow water environment which grades up into continental conditions in the eastern hyblean plateau the tertiary sequence is capped by pliocene submarine to subaerial mafic lava flows lower pleistocene sediments consist of biocalcarenites and clays which fill deep graben delimited by plio pleistocene faults the inshore continuation of the malta syracuse escarpment system of faults from a tectonic standpoint the hyblean region a gently deformed segment of the african continental margin acted as a foreland during tertiary times a cretaceous eocene tectonic phase was responsible for the palaeogeographic pattern which existed during most of the cenozoic the present pattern is the result of three main tectonic phases following the regional upper miocene uplift of early middle pliocene plio pleistocene and middle pleistocene recent age which influenced the tectonic evolution of the present ionian coast and the malta syracuse escarpment

paleohydrology and paleoclimate of the past 33 000 years at the tamandua river central brazil abstract deposits of the tamandua river contain evidence for four major paleohydrologic stages in the last 33 000 years a wet period between 33 000 and 20 000 14 c yr b p produced a high water table that allowed organic rich deposition in the tamandua valley a dry interval 17 000 10 000 14 c yr b p produced sandy deposits of braided channels and alluvial fans river aggradation during this period probably resulted from a high sediment load promoted by intense slope erosion and from flash floods a wet period after 10 000 and before 6000 14 c yr b p was marked by reduced slope erosion and by high discharge that led to erosion of the valley fill during that time forests developed widely in brazil a drier climate after 6000 14 c yr b p caused a reduction of discharge but allowed a high water table to be maintained

chronology of a probable neotectonic pleistocene rock avalanche cordon del plata central andes mendoza argentina abstract placetas amarillas 1 rock avalanche located at 32 43 s 69 25 w was geomorphologically stratigraphically and chronologically studied this extraordinary event dammed a secondary gully causing the formation of a barrier lake indicated by relict lacustrine and diatomite deposits stratigraphically its deposit is overlain by alluvial fans where three tephra layers are intercalated dating using ar ar method of the middle ash level at 350 80 ka determined a middle pleistocene or older age for this event furthermore the younger age of placetas amarillas 2 is established by relative dating techniques such as soil development and rock varnish development the ages established in this research indicate that placetas amarillas 1 may be temporally correlated with the tigre dormido rock avalanche suggesting that the occurrence of these rock avalanches may be related to regional neotectonic activity nevertheless climatic conditions are not underestimated as the tigre dormido event occurred before formation of an outwash terrace related to a glaciation of early middle pleistocene age

palaeoenvironmental use of silicophytoliths in soils and palaeosols associated with holocene volcanic ash deposits in north western argentina abstract we compare the silicophytolith record of current soils and holocene palaeosols from two sedimentary sequences in a region between the chaco pampean plain and the puna tolombon section in santa maria valley and tafi del valle section in tafi valley nw argentina these two geographic areas are separated by the aconquija cumbres calchaquies ranges a climatic barrier to the wet atlantic winds these sequences contain volcanic ash deposits recording two large eruptions occurred during holocene in the southern puna in the central volcanic zone of the andes from the cueros de purulla volcano ca 7820 bp and the cerro blanco volcanic complex ca 4200 cal bp these ash fall deposits buried soils and preserved their silicophytolith record allowing the use of this palaeoenvironmental proxy to clarify the vegetation prior these two volcanic events the silicophytolith assemblages yield evidence for a desert shrubland when tolombon palaeosol was formed similar to the present day environment in the santa maria valley with presence of c4 grasses chloridoideae and panicoidae instead the climate was cooler and wetter ca 4200 cal bp than currently in the tafi valley increasing over time aridity and abundance of c4 grasses chloridoidae panicoideae and decreasing the quantity of c3 grasses pooideae prehistorical and historical land use also contributed to this change the impact of these large volcanic ash falls on vegetation did not translate in an abrupt change on phytodiversity results point out a stable arid environment during holocene in the santa maria valley whereas the tafi valley was more sensitive to environmental changes due to its location in the eastern slopes of aconquija cumbres calchaquies ranges more exposed to the wet atlantic winds

correlation of widespread holocene and pleistocene tephra layers from newberry volcano oregon usa using glass compositions and numerical analysis abstract during the last ca 500 000 years newberry volcano in oregon has produced at least 50 rhyolitic and dacitic tephras ranging from locally distributed pumice rings and cones to ignimbrites to widely dispersed plinian fallout deposits to date 13 tephra units with ages ranging from about 1525 14c years bp to 200 000 years bp have been traced to 20 sites across five western states of the usa correlations have been established by applying similarity coefficient and discriminant function analysis to major element compositions of tephra derived glasses determined by electron microprobe analysis newberry pumice correlates to four locations in oregon and idaho east lake or central pumice cone tephra correlates to two locations in oregon paulina creek ice quarry 9912d 9920c 984f 984g5 9917c and 9881c tephras correlate to ash beds at summer lake oregon paulina creek tephra also correlates to several locations in northern california and is equivalent to the olema ash bed tephra 9917c is very similar to tephras k and d at pringle falls oregon lava pass or a related tephra correlates to an unnamed tephra in the bonneville basin utah

patterns of tectonic stress in sicily from borehole breakout observations and finite element modeling the orientation of in situ tectonic stress was deduced from borehole breakout analysis of 22 wells from onshore sicily the results allow us to distinguish the stress field of different geological units 1 a nearly nnw 148 orientation is detected in the hyblean plateau 2 a nne shmax direction characterizes the gela area to the north within the thrust belt around mount judica the shmax direction swings to ne in the northeastern segment of the foredeep the catania plain the direction of shmax is roughly parallel to the ne trending grabens that mark the northern margin of the hyblean plateau 3 the southwestern segment of the foredeep has no preferential shmax orientation and may act as a transition zone with isotropic horizontal stresses 4 in western sicily a shmax orientation from n s to nw se is observed this fits well the kinematics of the se migrating egadi and adventure thrust belts and the direction of shortening inferred from the modern seismicity of the area a three dimensional finite element modeling including the most important tectonic features was performed modeling results of the stress field indicate that the nnw trending shmax is locally influenced by the variation of crustal thickness and local zones of weakness in addition the pantelleria rift causes a rotation of the regional nw se stress orientation to nne along the northern rim of the rift system including large on shore areas in the adjacent central south sicily

vertical gps ground motion rates in the euro mediterranean region new evidence of velocity gradients at different spatial scales along the nubia eurasia plate boundary we use 2 5 to 14 years long position time series from 800 continuous global positioning system gps stations to study vertical deformation rates in the euro mediterranean region we estimate and remove common mode errors in position time series using a principal component analysis obtaining a significant gain in the signal to noise ratio of the displacements data following the results of a maximum likelihood estimation analysis which gives a mean spectral index 0 7 we adopt a power law white noise stochastic model in estimating the final vertical rates and find 95 of the velocities within 2 mm yr with uncertainties from filtered time series 40 smaller than from the unfiltered ones we highlight the presence of statistically significant velocity gradients where the stations density is higher we find undulations of the vertical velocity field at different spatial scales both in tectonically active regions like eastern alps apennines and eastern mediterranean and in regions characterized by a low or negligible tectonic activity like central iberia and western alps a correlation between smooth vertical velocities and topographic features is apparent in many sectors of the study area glacial isostatic adjustment and weathering processes do not completely explain the measured rates and a combination of active tectonics and deep seated geodynamic processes must be invoked excluding areas where localized processes are likely or where subduction processes may be active mantle dynamics is the most likely process but regional mantle modeling is required for a better understanding

kinematic evolution of fault ramps and its role in development of landslides and lakes in the northwestern argentine andes the quebrada del toro and quebrada de las conchas in the cordillera oriental of northwestern argentina are notable for repeated landsliding and damming of major drainages both areas correspond to displacement transfer zones along major thrust systems that developed during the neogene uplift of the central andes during this period displacement transfer zones were areas of subdued relief that localized where rivers cross the fault systems however neotectonic deformation converted the transfer zones into restraining bends along strike slip systems resulting in enhanced uplift at river crossings the antecedent streams responded by rapidly downcutting into the ascending hanging wall blocks producing precipitous local relief the extreme local relief that was controlled by the kinematic evolution of faulting in both areas provides an effective precondition for landsliding which may have been ultimately triggered by seismicity and gravitational failure aided by enhanced undercutting during past humid conditions

structural and lithological controls on large quaternary rock avalanches sturzstroms in arid northwestern argentina landsat thematic mapper tm analysis aerial photograph interpretation and field studies of the semiarid puna plateau adjacent eastern cordillera and sierras pampeanas of argentina lat 24 28 s have revealed the existence of at least 55 rock avalanche deposits with volumes larger than 10 6 m 3 that formed by the collapse of entire mountain fronts the spatial distribution of landslide deposits is not random but it clusters along mountain fronts bounded by active faults inspection in the field reveals five principal controls on the distribution of these events the source area of the rock avalanches has two topographic constraints 1 vertical relief contrasts between the breakaway zone and the mountain front must exceed a threshold of 400 m and 2 the slope inclinations must be steeper than 20 rock avalanches are restricted to three types of lithology granites low grade metamorphic rocks and coarse clastic sediments structural controls are very important rock avalanches are controlled by planar structures such as bedding planes exfoliation joints minor faults and cleavage that all dip toward the valley in addition major slide clusters occur along mountain fronts that underwent quaternary reverse fault reactivation of former transfer faults with strike slip kinematics the trigger mechanism for the majority of these landslides is interpreted to be seismic although the ages of some major slides are about 30 ka and they may correspond to a more humid interval in southern south america

late pleistocene climate change and erosion in the santa maria basin nw argentina present erosion and sediment flux in the semiarid intra montane santa maria basin nw argentina are compared with con ditions during a period of wetter and more variable climate at about 30 000 14 c yr ago the results suggest that the influence of climate change on the overall erosional sediment budget is significant mainly because of a change in the erosion regime coupled with an increase in mass movements the most effective mechanism to increase landslide activity in this environment is a highly variable climate on interannual timescales in contrast quaternary changes in erosional budgets due to variations in moisture regimes is small in the santa maria basin because the magnitude of a potential increase in background erosion as well as enhanced landsliding is smaller than typical levels of uncer tainty of erosional budgets for such large basins it is not likely that climate driven erosional unloading can influence tectonic style and rates in this semiarid environment on time scales of several thousands to a few tens of thousands of years

formation of landslide dammed lakes during a wet period between 40 000 and 25 000 yr b p in northwestern argentina abstract new ams radiocarbon data from the deposits of landslide dammed lakes in the santa maria basin 26 s 66 w and the quebrada del toro 25 s 66 w in the eastern argentine cordillera show that important mass movements occurred during a wet period between 40 000 and 25 000 yr b p in addition to increased humidity during this time detailed analysis of annual layered lacustrine strata suggests enhanced inter and intra annual fluctuations in precipitation as compared to the present variations in sediment characteristics and diatom assemblages with mean periodicities of 2 to 5 and 10 to 14 years respectively suggest an influence of the el nino southern oscillation enso and the atlantic sea surface temperature dipole the atlantic dipole slightly increased rainfall every 10 14 years as at present in contrast the weak modern enso influence in this area differs from the past situation where rainfall increased significantly with enso type periodicities both increased humidity and seasonality are believed to have reduced thresholds for the generation of catastrophic mass movements in northwestern argentina

36cl terrestrial cosmogenic nuclide dating suggests late pleistocene to early holocene mass movements on the south face of aconcagua mountain and in the las cuevas horcones valleys central andes argentina

investigation of earthquake triggering for deep seated landslides taranaki new zealand because large earthquakes can trigger landslides the landslide record has potential use for establishing the palaeoseismicity of a region however before this potential can be realized other possible landslide triggering mechanisms must be investigated in southeastern taranaki new zealand over 100 deep seated complex rock slumps occur in a region of steeply dissected gently dipping pliocene marine sediments three age populations can be detected by using relative and radiometric dating methods the youngest group of landslides displays a consistent depth of soil development lacks an integrated drainage network dams catchments to produce lakes and has well defined mass movement features this group covers an area of 1015 km2 yields radiocarbon dates of around 1300 bp and is clearly distinguishable from the two older groups of landslides the synchronicity of landslide formation over a wide area before new zealand was populated rules out human factors and slope undercutting as triggering agents comparison with modern analogues also rules out rainstorm as a triggering agent principally on the basis of depth of movement the distribution of landslides and the amount of failed surface is shown to be closely related to the location of active fault traces the increase in landsliding towards the fault cannot be explained by variation in lithology or structure limiting equilibrium analysis of one landslide further points to the need for earthquake shaking to induce movement together the lines of evidence investigated provide a strong case for earthquake triggering of prehistoric landslides in this region

the subsidence history of the northern hyblean plateau margin southeastern sicily abstract the southeastern corner of sicily is dominated by the hyblean plateau which is composed of carbonate rocks of triassic to miocene age the plateau forms part of the african foreland which collided during tertiary times with the calabrian arc giving rise to the maghrebian thrust belt the present study attempts to reconstruct the subsidence history of the northern hyblean plateau during the neogene climax of the plate collision this area has been a centre for widespread basaltic volcanic activity 8 1 ma and uplift at the close of the collisional events pliocene early pleistocene the area under consideration has been affected by subsidence and the progressive consumption of the northern margin of the hyblean plateau led to the development of the modern foredeep a quantitative analysis was done by one dimensional airy backstripping of seven deep wells located on this crucial part of the hyblean plateau the results of the analysis show that the subsidence history of the northern hyblean plateau area is characterized by four main phases similar to other domains in the central and eastern mediterranean basins these phases are a neotethyan rifting during late triassic early jurassic time b a slow thermal subsidence from early jurassic until late cretaceous time leading to the formation of a widespread mesozoic carbonate platform c compressional phase during late cretaceous palaeogene time which resulted in the formation of fold systems and d uplift and subsidence events during the middle tertiary which are probably the result of the continued collision of the european african plates after the early pleistocene unlike other terranes within the mediterranean an uplift occurred in the northern hyblean plateau following the upper miocene lower pleistocene massive volcanic activity this uplift is probably associated with the latest stages of thrusting along the frontal part of the maghrebian thrust belt

large rockslides in the southern central andes of chile 32 34 5 s tectonic control and significance for quaternary landscape evolution abstract the distribution and age of large 0 1 km2 pliocene to recent rockslides in the chilean cordillera principal 32 34 5 s the southern central andes has been analyzed to determine the rockslide triggering mechanisms and impact on regional landscape evolution most of the rockslides appear in the western cordillera principal and cluster along major geological structures variographic analyses show spatial correlation between rockslides geological structures and shallow seismicity a relative chronosequence was calibrated with existing 14c and 40ar 39ar dates and new cosmogenic nuclide exposure ages for selected rockslides rockslide induced sediment yield was estimated with empirical relations for rockslide area distributions throughout the quaternary rockslides have delivered sediment to streams at rates equivalent to denudation rates of 0 10 0 06 mm a 1 while estimates using short term 20 a seismicity records are 0 3 0 2 0 6 mm a 1 the estimates of sediment transfer and the spatial distribution of rockslides reflect a landscape in which tectonic and geological controls on denudation are more significant than climate

roots of etna volcano in faults of great earthquakes abstract results from several seismic methods allow us to sketch the deep structure of etna and its ionian margin under etna a volume of high velocity material is found in a structurally high position the emplacement of this suggests spreading of the surrounding medium just offshore down to the east normal faults penetrate through the upper crust the deeper crustal structure beneath appears upwarped from the basin towards etna juxtaposed with the crust of sicily a thinner crust reaches from the ionian basin under etna and the mantle is upwarped in such a structure magma can then be viewed as a melted lens capping a mantle upwarp at shallow depth rather than in an intracrustal chamber this reduces the conflict between estimates of its volume from excess output of volatiles and short residence times a link in time is indicated between volcanic and seismic activity at a large scale over the millennium the reported ends of episodes of high output rates of magma are followed by the reported occurrences of magnitude 7 earthquakes which caused destruction in southeastern sicily several steep active normal fault have been imaged to a depth of 10 km the crust up to 30 km offshore of the cities of catania and augusta which may be fault planes for such large earthquakes they expand and prolongate the system of the timpe faults on the eastern flank of etna thus linking large scale tectonics offshore with the volcano etna developed together with normal faulting upwarp and spreading during the recent evolution of the former ionian subduction activation of the material at depth at the lateral edge of the slab by vertical motion with extension above could produce the peculiar type of etna magmatism

earthquake dammed lakes in new zealand eleven small lakes were formed by landslides caused by the 1929 buller earthquake four others were formed by other historic earthquakes in new zealand at least nine other new zealand lakes are also dammed by landslides and were probably formed by prehistoric earthquakes when recognized by morphology synchronous age and areal distribution earthquake dammed lakes could provide an estimate of paleoseismicity for the past few hundred or thousand years

new gps constraints on the africa eurasia plate boundary zone in southern italy 1 southern italy is a key area for understanding the tectonic processes in the africa eurasia collision zone we analyze new gps measurements carried out between 1994 and 2001 the results are presented in terms of time series trajectories and velocities of crustal motion as well as a geodetic strain rate field while central italy corsica sardinia and the tyrrhenian sea move like the eurasian plate the overall motion of the sicily rift zone region matches african plate motion unexpected are the north northwest directed motions of northeastern sicily and the eolian islands most striking on the deformation field are a north south oriented compression along the northern sicilian coast compression between apulia and northwestern greece as well as extension in the sicily rift zone and the interior of sicily

active fault kinematics and crustal stresses along the ionian margin of southeastern sicily since the late cretaceous onset of plate convergence between africa and europe the malta escarpment has been converted from a mesozoic passive margin into a mega hinge fault system with an additional sinistral strike slip component the modern tectonic stress regime with nw se directed maximum horizontal stresses has been established since late messinian times since the pleistocene sinistral strike slip deformation and contemporaneous normal faulting along the malta escarpment have induced the opening of oblique trending onshore grabens at the eastern margin of the hyblean plateau in this study we focus on the kinematics the controlling state of stress and the temporal variation of the neotectonic to active strike slip and normal fault structures the stress tensor calculations reveals that the widespread map scaled to meso scaled normal fault structures are governed by the long term extensional state of stress during the quaternary this long term stress tensor is predominantly controlled by gravitational induced stresses due to vertical load 1 sv and lateral extension due to the topographic gradient of the malta escarpment 3 sh ne sw in this case the average tectonic stresses 2 sh nw se transmitted by the regional to plate tectonic stress field are significantly smaller than the gravitational induced stresses in contrast the clear localization of conjugate sets of meso scaled strike slip fault structures and shear zones without accompanying normal fault structures give strong indications for episodic seismotectonic strike slip faulting under critical stress conditions in this state tectonically induced maximum horizontal stresses are successively increased by ongoing plate convergence from low level stress magnitudes 1 sv 2 sh nw se up to critical stress magnitudes 1 sh nw se 2 sv which are significantly larger than gravitational stresses at the critical state seismotectonic stress release occurs by active strike slip faulting as recently indicated in mid crustal levels by the moderate 1990 augusta earthquake and re establishes the long term extensional state of stress because the strike slip faults and shear zones in the study area were formed as surface ruptures they additionally give indications of episodic large earthquakes in this region with magnitudes greater than 6 0 as reported by several large earthquakes devastating e and se sicily in historical times

the 16 september 1986 eruption of lascar volcano north chile satellite investigations landsat thematic mapper tm images acquired in 1984 and 1985 revealed a pronounced thermal anomaly on lascar volcano north chile subsequent images showed that the anomaly was persistent but variable and that after a significant eruption on 16 september 1986 it was weaker and divided into several sources tm studies and other observations of lascar indicate that the persistent thermal anomaly may be due to high temperature fumaroles within the summit crater goes weather satellite images and field investigations confirm that the 16 september event was a short lived vulcanian type eruption which produced an ash column that reached 15 km altitude the ash cloud can be tracked on geos images to about 400 km downwind and covered an area 112 000 km2 transport occurred in the upper troposphere at speeds up to 180 km h ash fall from the plume was well sorted and moderately fine grained md 200 m formation and fallout of ash as aggregates was unimportant in the deposition of the ash layer although small the lascar 16 september eruption is significant because few historic eruptions have been recorded in the central andes little would have been known of the eruption in the absence of remote sensed data

mesozoic and cenozoic rocks from malta escarpment central mediterranean sedimentary rocks of triassic neogene age are present on the malta escarpment of the eastern mediterranean upper triassic dolomitic limestones of shallow water origin at depths between 2 5 and 3 5 km are similar in lithofacies to coeval platform carbonates of the siracusa syracuse belt of southern sicily jurassic rocks include lower middle liassic shallow water limestones followed by condensed hemipelagic lime deposits indicative of sinking and starving of the former platform cretaceous materials are represented by both red marls rich in planktonic faunas and reworked volcaniclastic breccias including shallow water skeletal material paleogene rocks are both shallow water limestones with corals algae and bivalves and redeposited calcarenites of lithofacies similar to those from surface and subsurface of the ragusa zone oligocene lower miocene rocks from the escarpment are also similar in lithology to the coeval ragusa deposits tortonian is represented by hemipelagic marls indicating open marine environment pervasive dolomitization on lime crusts and on initial stage fissure fillings with strongly positive isotopic oxygen ratio is thought to be a product of messinian evaporitic drawdown pliocene sediments belong to the trubi facies and consist of pelagic foraminiferal chalk an impressive vertical relief existed by miocene times as attested by messinian crusts and veins on or in rocks as old as late triassic our data do not provide evidence that this morphologic feature necessarily coincides with a continent ocean transition the present escarpment was produced by faulting erosion and defacement

multiple landslide clusters record quaternary climate changes in the northwestern argentine andes the chronology of multiple landslide deposits and related lake sediments in the semi arid eastern argentine cordillera suggests that major mass movements cluster in two time periods during the quaternary i e between 40 and 25 and after 5 14 c kyr bp these clusters may correspond to the minchin maximum at around 28 27 14 c kyr bp and titicaca wet periods after 3 9 14 c kyr bp the more humid conditions apparently caused enhanced landsliding in this environment in contrast no landslide related damming and associated lake sediments occurred during the coipasa 11 5 10 14 c yr bp and tauca wet periods 14 5 11 14 c yr bp the two clusters at 40 25 and after 5 14 c kyr bp may correspond to periods where the el nin o southern oscillation enso and tropical atlantic sea surface temperature variability tav were active this however was not the case during the coipasa and tauca wet periods lake balance modelling of a landslide dammed lake suggests a 10 15 increase in precipitation and a 3 4 c decrease in temperature at v30 14 c kyr bp as compared to the present in addition time series analysis reveals a strong enso and tav during that time the landslide clusters in northwestern argentina are therefore best explained by periods of more humid and more variable climates 2003 elsevier science b v all rights reserved

neotectonics and catastrophic failure of mountain fronts in the southern intra andean puna plateau argentina new cosmogenic nuclide exposure ages of rock avalanche deposits in front of sierra laguna blanca in the arid argentine puna plateau demonstrate the effects of westward propagation of reverse faulting and the influence of active faulting on slope oversteepening and subsequent gravitational collapse the 21 ne exposure ages of 8 superposed landslides with volumes 0 3 km 3 are between ca 150 and 430 ka and indicate an average recurrence interval of large gravitational mountain front failures of 27 5 k y for the ultimate 7 landslides landsliding did not occur after 150 ka along this sector of the sierra laguna blanca the termination of landsliding activity correlates with reverse fault propagation into the piedmont area of the sierra laguna blanca the exposure age of ca 130 ka of a tectonically uplifted terrace postdates initiation of fault activity in the piedmont region and the fault scarp height of 120 m indicates important continued uplift in the piedmont no further offsets occurred at the mountain front due to this lack of tectonic activity at the mountain front no further collapse has occurred indicating that in this environment catastrophic mountain front failure is mainly controlled by tectonically driven slope oversteepening

plio quaternary tectonic evolution and structure of the catania foredeep the northern hyblean plateau and the ionian shelf se sicily abstract available multi and single channel seismic reflection profiles calibrated by onshore borehole data have been used for defining the structural styles in the shelf and slope of the ionian sea between catania and augusta se sicily the geological and geophysical data suggest that this area represents a segment of the foredeep foreland system which collapsed after late pliocene times the foundering was controlled by normal faults trending ne sw which flank the southern margin of the catania foredeep onland in outcrop these faults appear largely to be post dated by lower pleistocene sediments nearshore carbonates passing laterally into basinal clays which lie unconformably upon older substrata offshore close to the southern edge of the foredeep seismic lines allow recognition of two distinct units a syn rift wedge upper pliocene submarine tholeiites and sediments and a post rift sequence which can be correlated with lower pleistocene carbonates sands and clays recognisable on land both in outcrop and by borehole data the true frontal part of the thrust belt as detected by the seismic lines occupies the inner part of the area investigated and is buried by upper pliocene and lower pleistocene sediments however the compressive deformation seems to propagate toward the south southeast by means of growing detachment levels developing at depth within pleistocene marine clays for a length of about 10 km ahead of the present day thrust front offshore the faults trending ne sw are dissected towards the east by faults trending nnw sse subparallel to the malta escarpment which flank the edge of the submerged messina rise these faults originating in a steep scarp which drops eastwards to the deep ionian basin have triggered submarine slides and affected the present day seafloor sediments as shown by seismic lines and as stressed by the modern seismicity of the area some of the faults along the malta escarpment could be still active

subaqueous rock avalanche deposits exposed by post glacial isostatic rebound innfjorddalen western norway abstract this paper presents a detailed description of deposits and landforms of multiple rock avalanches in western norway one of which fell onto water saturated sediments in innfjorddalen below the former water level deposits of the latter are now exposed on the valley floor due to post glacial isostatic rebound at least three rock avalanches from the same source at grafonnfjellet mountain have occurred during late glacial and post glacial time and their deposits are distributed over an area of 1 44 km 2 in the valley these rock avalanches have volumes of 15 1 10 6 m 3 5 4 10 6 m 3 and 0 3 10 6 m 3 and yielded cosmogenic radionuclide 10 be ages of 14 3 1 4 ka 8 79 0 94 ka and 1 028 0 380 ka respectively the youngest event dates within uncertainty limits to a historic rock avalanche in the year 1611 12 ce the rock avalanches formed a stratified succession of deposits the rock avalanche deposits 1 38 m 2 have lobate forms have frontal rims and parallel ridges extend across the valley floor and up the opposite slope and form dams on the valley floor isolated hills comprised of rock boulders 0 61 km 2 interpreted to be toma hills are disconnected from the main rock avalanche deposits by a 520 m wide zone of deformed valley fill sediments trenches and a ground penetrating radar survey of these deposits indicate large scale deformation or liquefaction numerical runout modeling of the rock avalanches with the code dan3d supports the interpretation of their landforms and sources and highlights their runout behavior

prehistoric rock avalanches in the olympic mountains washington rock avalanches blocked streams in the olympic mountains southwest of puget sound during the past few thousand years limiting radiocarbon ages indicated that three or four of six avalanches occurred from 1000 to 1300 years ago or shortly thereafter most of the dates were from the outer preserved rings of trees drowned behind avalanche dams these three or four avalanches may be coeval not only with one another but also with abrupt tectonic deformation in western washington no rock avalanches in the olympic mountains are known to have resulted from storms or earthquakes during the past century the avalanches strengthen the case that a large prehistoric earthquake occurred in the puget sound region

the database of individual seismogenic sources diss version 3 summarizing 20 years of research on italy s earthquake geology abstract this paper describes the main characteristics the evolution and the structure of the database of individual seismogenic sources diss and particularly of its release of early 2007 the database contains the results of the investigations of the active tectonics in italy during the past 20 years the first two sections of this paper document the recent evolution in mapping and archiving italian active fault data in relation to important achievements in the understanding of italian tectonics some of which were spurred by significant earthquakes the central sections describe the current structure of the database the reasons for its assumptions and data categories its current contents its evolution through several years of improvements the last section describes how the current contents of the database correspond with the existing strain and stress data available from focal mechanism borehole breakout and gps data for the whole of italy the database supplies a fresh and unified view of active and seismogenic processes in italy by building on basic physical constraints concerning rates of crustal deformation on the continuity of deformation belts and on the spatial relationships between adjacent faults both at the surface and at depth

transpressive strain on the lipari vulcano volcanic complex and dynamics of the la fossa cone aeolian islands sicily revealed by gps surveys on a dense network abstract ground deformation resulting from the last two gps surveys carried out in march 2006 and september 2007 on the lipari vulcano volcanic complex are analyzed data inversion was performed by genetic algorithms approach using the horizontal strain measured on 258 gps baselines in order to avoid bias due to the ambiguity in fixing the reference system and to disregard the vertical deformation of the la fossa cone there are two networks in this area the main lipari vulcano network and the denser vulcano nord one surveying strategies adopted for the main network during the latest surveys allowed long baselines from lipari and vulcano to the surrounding permanent stations in the southern tyrrhenian to be processed with reliable accuracy the fast static strategy was instead adopted to survey the vulcano nord network data from the main lipari vulcano network has been processed in the itrf05 frame and also in a local reference frame together with the vulcano nord data a significant northward motion of vulcano island with respect to the itrf05 has been detected this motion abruptly decreases in the northern part of vulcano suggesting a decoupling of the main vulcano island from the rest of the volcanic complex the analysis in the local reference frame evidenced a relative sse ward motion of lipari and northern part of vulcano with respect to the central and southern vulcano this comparison also highlights a local uplift of the la fossa cone in addition a strain tensor analysis was performed which highlighted a main nne ssw contraction and a minor ese wnw extension detected only on the southern part of vulcano this results are in agreement with a transpressive kinematics of the lipari vulcano volcanic complex with a main dextral component of displacement along a nw se striking structure

spatiotemporal trends in erosion rates across a pronounced rainfall gradient examples from the southern central andes abstract the tectonic and climatic boundary conditions of the broken foreland and the orogen interior of the southern central andes of northwestern argentina cause strong contrasts in elevation rainfall and surface process regimes the climatic gradient in this region ranges from the wet windward eastern flanks 2 m yr rainfall to progressively drier western basins and ranges 0 1 m yr bordering the arid altiplano puna plateau in this study we analyze the impact of spatiotemporal climatic gradients on surface erosion first we present 41 new catchment mean erosion rates derived from cosmogenic nuclide inventories to document spatial erosion patterns second we re evaluate paleoclimatic records from the calchaquies basin 66 w 26 s a large intermontane basin bordered by high 4 5 km mountain ranges to demonstrate temporal variations in erosion rates associated with changing climatic boundary conditions during the late pleistocene and holocene three key observations in this region emphasize the importance of climatic parameters on the efficiency of surface processes in space and time 1 first order spatial patterns of erosion rates can be explained by a simple specific stream power ssp approach we explicitly account for discharge by routing high resolution satellite derived rainfall this is important as the steep climatic gradient results in a highly nonlinear relation between drainage area and discharge this relation indicates that erosion rates er scale with er ssp1 4 on cosmogenic nuclide time scales 2 we identify an intrinsic channel slope behavior in different climatic compartments channel slopes in dry areas 0 75 m yr with equal drainage areas thus compensating lower amounts of discharge with steeper slopes 3 erosion rates can vary by an order of magnitude between presently dry 0 05 mm yr and well defined late pleistocene humid 0 5 mm yr conditions within an intermontane basin overall we document a strong climatic impact on erosion rates and channel slopes we suggest that rainfall reaching areas with steeper channel slopes in the orogen interior during wetter climate periods results in intensified sediment mass transport which is primarily responsible for maintaining the balance between surface uplift erosion sediment routing and transient storage in the orogen

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

laacher see tephra a widespread isochronous late quaternary tephra layer in central and northern europe a late quaternary tephra layer widespread in central and northern europe resulted from explosive plinian and phreatomagmatic eruptions of the laacher see volcano 11 000 yr b p the tephra is distinguished from other late quaternary andesitic rhyolitic airfall tuff layers in northern europe and from basaltic or trachytic tuff deposits in southern europe by its phonolitic composition and abundance of sanidine plagioclase clinopyroxene amphibole and sphene the proximal tephia sequence at laacher see is divided into three main deposits the predominantly plinian deposits of lower and middle laacher see tephra llst and mlst and phreatomagmatic deposits of the upper laacher see tephra ulst the mlst member is further subdivided into beds a b and c1 c2 and c3 the chemical composition of the magma is highly differentiated phonolite in the llst to mlst b sections but mafic phonolite in the mlst c1 to ulst sections all deposits are considered to be isochronous the frequency maximum of 16 radiocarbon datings indicating an eruption about 11 000 50 yr b p distal ash was deposited in three main fans directed to the northeast lst traced up to 1 100 km distance south lst traced up to 600 km and southwest lst traced up to 100 km tephrostratigraphic correlation of the distal ash deposits is based on a the major element composition of glass shards b lithology and c heavy mineral analyses the northeastern fan consists of deposits from llst mlst b and mlst c1 eruptive phases the southern fan comprises mlst a mlst c2 and ulst deposits and the southwestern fan consists exclusively of ash from the ulst eruptive phase northeastern transport of ash during eruptive phases with high plinian eruption columns but southern and southwestern transport of ash along phases of relatively low eruption columns are interpreted in terms of prevailing southwesterly paleowinds at high altitudes tropopause level but northerly winds dominating in the lower atmosphere the laacher see eruption columns were emplaced into an atmosphere vertically zoned with respect to paleowind directions which also explains the near vent shifting of llst mlst b and mlst c1 iso pach axes from east southeast to northeast within the first 20 km of transport

millennial scale record of landslides in the andes consistent with earthquake trigger landslide deposits are often interpreted as the consequence of precipitation a millennial scale record of landslides inferred from river cobbles in the arid andes is instead consistent with earthquake triggering

the giant paleolandslide deposits of tafi del valle tucuman province argentina abstract in the present study seven landslide deposits that took place during the pleistocene in the northern part of tafi del valle tucuman province argentina are described the recognition and mapping of them were carried out using satellite images aerial photograph interpretation and field survey the analysis of the area covered by the deposits and their runout distances were undertaken using aerial photographs at a scale of 1 50 000 and the software image tool all the deposits overcome the 106 m3 of volume with smaller coefficients of friction at 0 22 that gives an idea of the great mobility that they had reaching average speeds 100 km h these deposits could have originated as a consequence of a combination of internal slow deformation and fragmentation under periglacial conditions followed by a sudden collapse of the rock mass generated by strong earthquakes of magnitudes 6 at the base of the cumbres calchaquies ranges

crustal motion along the eurasia nubia plate boundary in the calabrian arc and sicily and active extension in the messina straits from gps measurements 1 we investigate crustal deformation along the eurasia nubia plate boundary in calabria and sicily revealed by the gps velocity field obtained by the combination of continuous site velocities with previous results from episodic campaigns we recognize two distinct crustal domains characterized by different motions and styles of deformation convergence in sicily is taken up by crustal shortening along the former tyrrhenian back arc passive margin in agreement with seismological data and geological evidence of recent cessation of deformation along the plio pleistocene subduction front the analysis of the gps data and the consistency between earthquake slip vectors and convergence direction suggest that eu nu convergence in sicily does not require intermediate crustal blocks significant eurasia 3 mm yr to nne and nubia fixed 5 mm yr to ese residual velocities in calabria suggest instead the presence of an intermediate crustal block which can be interpreted as a forearc sliver or as an independent ionian block according to the first hypothesis subduction is still active in the ionian wedge although we find no evidence for active back arc spreading in the tyrrhenian sea the n115 e oriented sicily calabria gps relative motion is consistent with the extension observed during the 1908 mw 7 1 messina earthquake we suggest that up to 3 mm yr 80 of this estimated relative motion between sicily and the calabrian arc may be taken up in the messina straits

pedostratigraphy and pedological and geochemical characterization of las carreras loess paleosol sequence valle de tafi nw argentina abstract the las carreras loess paleosol sequence is considered the most complete quaternary pedostratigraphic record in south america it consists of 32 paleosols formed during the past 1 15 ma chronological control is provided by magnetostratigraphy sediment and paleosol characterization is based on a variety of methods including soil chemistry geochemistry and micromorphology the main pedogenic processes identified are carbonate leaching and reprecipitation ped formation and translocation of clay and organic matter in many cases the boundaries between individual paleosols are not clearly defined due to indistinct transitional zones based on both pedological and sedimentological characteristics the sequence was subdivided into three units with paleosols in units i and iii designated as luvisols and paleosols in unit ii tentatively classified as luvic kastanozems this subdivision reflects environmental changes associated with the mid pleistocene transition overall geochemical variability is low and largely related to pedogenesis the homogeneity suggests a rather constant provenance that seems to be linked to the central andes pursuant to the chaco model of iriondo 1997 models of deposition of loess and loessoids in the upper quaternary of south america journal of south american earth sciences 10 71 79 and includes direct volcanic ash falls and local sources in a subordinate manner in a paleoclimatic context loess paleosol alternation is interpreted to reflect climatic cycles that were primarily caused by the variability of the south american monsoon system

implications of quaternary volcanism at cerro tuzgle for crustal and mantle evolution of the puna plateau central andes argentina the high k tuzgle volcanic center 24 s 66 5 w along with several small shoshonitic centers developed along extensional quaternary faults of the el toro lineament on the east central puna plateau 275 km east of the main front of the andean central volcanic zone cvz these magmas formed by complex mixing processes in the mantle and thickened crust 50 km above a 200 km deep scismic zone tuzgle magmas are differentiated from shoshonitic series magmas by their more intraplate like ti group element characteristics lower incompatible element concentrations and lower 87sr 86sr ratios at a given end underlying mio pliocene volcanic rocks erupted in a compressional stress regime and have back arc like calc alkaline chemical characteristics the tuzgle rocks can be divided into two sequences with different mantle precursors a an older more voluminous rhyodacitic ignimbrite to mafic andestitic 56 to 71 sio2 sequence with la yb ratios 35 la yb ratios are controlled by the mafic components low ratios result from larger mantle melt percentages than high ratios shoshonitic series lavas 52 to 62 sio2 contain small percentage melts of more isotopically enriched arc like mantle sources some young tuzgle lavas have a shoshonitic like component variable thermal conditions and complex stress system are required to produce the tuzgle and shoshonitic series magmas in the same vicinity these conditions are consistent with the underlying mantle being in transition from the thick mantle lithosphere which produced rare shoshonitic flows in the altiplano to the thinner mantle lithosphere that produced back are calc alkaline and intraplate type flows in the southern puna substantial upper crustal type contamination in tuzgle lavas is indicated by decreasing end 2 5 to 6 7 with increasing 87sr 86sr 0 7063 to 0 7099 ratios and sio2 concentrations and by negative eu anomalies eu eu 0 78 in lavas that lack plagioclase phenocrysts trace element arguments indicate that the bulk contaminant was more silicic than the tuzgle ignimbrite and left a residue with a high pressure mineralogy crustal shortening processes transported upper crustal contaminants to depths where melting occurred these contaminants mixed with mafic magmas that were fractionating mafic phases at high pressure silicic melts formed at depth by these processes accumulated at a mid to upper crustal discontinuity decollement the tuzgle ignimbrite erupted from this level when melting rates were highest subsequent lavas are mixtures of contaminated mafic magmas and ponded silicic melts feldspar and quartz phenocrysts in the lavas are phenocrysts from the ponded silicic magmas

andean tectonics related to geometry of subducted nazca plate seismological and geological data show that tectonic segmentation of the andes coincides with segmentation of the subducted nazca plate which has nearly horizontal segments and 30 east dipping segments andean tectonics above a flat subducting segment between 28 s to 33 s are characterized by from west to east 1 a steady topographic rise from the coast to the crest of the andes 2 no significant quaternary and possibly neogene magmatism 3 a narrow belt of eastward migrating apparently thin skinned neogene to quaternary shortening of the andes and 4 plio pleistocene uplift of the crystalline basement on reverse faults in the pampeanas ranges from about 15 to 24 s over a 30 dipping subducted plate a west to east andes cross section includes 1 a longitudinal valley east of coastal mountains 2 an active neogene and holocene andesitic volcanic axis 3 the altiplano puna high plateau 4 a high neogene but inactive thrust belt eastern cordillera and 5 an active eastward migrating subandean thin skinned thrust belt tectonics above a steeply subducting segment south of 33 s are similar west of the volcanic axis but quite different to the east early cenozoic tectonics of western north america were quite similar to the neogene andes however duration of segmentation was longer and the width of deformation was greater in the western united states patterns of crustal seismicity are systematically related to plio quaternary structural provinces implying that current deformational processes have persisted since at least the pliocene horizontal compression parallel to the plate convergence direction is indicated to a distance of 800 km from the trench above flat subducting segments crustal seismicity occurs over a broad region whereas over steep segments it is confined to the narrow thrust belt strain patterns in the forearc region are complex and perhaps extensional and a broad region of the altiplano puna and eastern cordillera appears to be aseismic

application of the landsat thematic mapper to the identification of potentially active volcanoes in the central andes abstract landsat thematic mapper tm images have been used to make the first comprehensive study of the central andean volcanic province 14 s 28 s one of the world s largest zones of active volcanism more than 60 major volcanoes have been identified as potentially active whereas only 16 had been previously cataloged most of these are large composite cones up to 6000 m in height some of which threaten nearby settlements apart from its consistent coverage the chief merit of the landsat tm in making this study has been spatial resolution provided by the 30 m pixel size this has been particularly important for the recognition of subtle glacial morphological features such as valley and terminal moraines which can be used to determine relative ages of the volcanoes on the tm images we have classified a volcano as potentially active if it has i a well preserved summit crater ii pristine lava flow texture and morphology iii flank lava flows with low albedo and iv evidence of post glacial

late pleistocene landslide dammed lakes along the rio grande white rock canyon new mexico massive slump complexes composed of pliocene basaltic rocks and underlying miocene and pliocene sediments flank the rio grande along 16 km of northern white rock canyon new mexico the toe area of at least one slump complex was active in the late pleistocene damming the rio grande at least four times during the period from 18 to 12 sup 14 c ka and impounding lakes that extended 10 20 km upriver stratigraphic relationships and radiocarbon age constraints indicate that three separate lakes formed between 13 7 and 12 4 sup 14 c ka the age and dimensions of the ca 12 4 ka lake are best constrained it had an estimated maximum depth of approx 30 m a length of approx 13 km a surface area of approx 2 7 km sup 2 and an initial volume of approx 2 5 x 10 sup 7 m sup 3 the youngest landslide dammed lakes formed during a period of significantly wetter regional climate strongly suggesting that climate changes were responsible for reactivation of the slump complexes we are not certain about the exact triggering mechanisms for these landslides but they probably involved removal of lateral support due to erosion of the slope base by the rio grande during periods of exceptionally high flood discharge or rapid incision more increased pore pressures associated with higher water tables higher seepage forces at sites of ground water discharge or some combination of these processes seismic shaking could also have contributed to triggering of some of the landslides particularly if aided by wet antecedent conditions 54 refs 19 figs 3 tabs less

rock avalanches clusters along the northern chile coastal scarp abstract rock avalanche clusters can be relevant indicators of the evolution of specific regions they can be used to define the type and intensity of triggering events their recurrence and potential probability of occurrence the progressive damage of the rock mass the mechanisms of transport and deposition as well as the environmental conditions at the time of occurrence this paper tackles these subjects by analyzing two main clusters of rock avalanches each event between 0 6 and 30 mm 3 separated by few kilometers and located along the coastal scarp of northern chile south of iquique it lies hence within a seismic area characterized by a long seismic gap that ended on april 1st 2014 with a m w 8 2 earthquake the scar position high along the coastal cliff supports seismic triggering for these clusters the deposits relative positions are used to obtain the sequence of rock avalanching events for each cluster the progressive decrease of volume in the sequence of rock avalanches forming each cluster fits well the theoretical models for successive slope failures these sequences seem to agree with those derived by dating the deposits with ages spanning between 4 kyr and 60 kyr an average uplift rate of 0 2 mm yr in the last 40 kyr is estimated for the coastal plain giving a further constraint to the rock avalanche deposition considering the absence of reworking of the deposits volume estimates and datings allow the estimation of an erosion rate contribution of about 0 098 0 112 mm km 2 yr 1 which is well comparable to values presented in the literature for earthquake induced landslides we have carried out numerical modeling in order to analyze the mobility of the rock avalanches and examine the environmental conditions that controlled the runout in doing so we have considered the sequence of individual rock avalanches within the specific clusters thus including in the models the confining effect caused by the presence of previous deposits bingham rheology was the most successful at explaining both the distance and the geometry of the observed events

geological and geodetic constraints on the active deformation along the northern margin of the hyblean plateau se sicily abstract a geologic and geodetic integrated analysis of the northern margin of the hyblean plateau se sicily has been carried out in order to test the relationship between the active deformation recorded by gps data and the long term tectonic evolution reconstructed by the interpretation of structural and morphological data our study revealed the active growth of a large antiform as a consequence of the positive tectonic inversion of the previous flexure bordering the hyblean foreland the deformation of middle late pleistocene marine terraces and the evolution of the drainage system are consistent with a progressive regional tilting of the entire eastern sector of the hyblean plateau siracusa domain representing the southern limb of the active antiform the geometry of the late quaternary marine strandlines compared with the results of analogue models is compatible with the effects of the nw ward propagation of a detachment fault at depth the active deformation of the hyblean region coherent with the nubia eurasia plate convergence suggests to candidate the inverted tectonics at the northern border of the hyblean plateau as potential seismogenic sources of the area

seismicity and tectonics in jujuy province northwestern argentina the portable array for numerical digital analysis panda network a digitally recorded seismic array operated for nine months in jujuy province of northwestern argentina the network was deployed along the eastern edge of the altiplano puna plateau in a major n s thrust belt that is transitional in style between the thin skinned deformation of the bolivian foreland to the north and basement involved deformation of the pampean region to the south teleseismic locations of crustal earthquakes in the region indicate that seismicity is associated with compressional structures found near the eastern deformation front no crustal seismicity was detected beneath the puna plateau to the west peak seismicity levels beneath the foreland occurred between 20 and 25 km depth a sharp decrease in seismicity was observed below 25 km an estimate of 42 km for the thickness of the jujuy foreland crust was inferred from wide angle moho reflections observed on the digital seismograms the highest concentration of crustal seismicity was located beneath sierra de zapla a broad anticline immediately east of san salvador de jujuy many of the earthquakes in the 20 25 km depth range have a shallow west dipping nodal plane as does the focal mechanism solution for a moderately large 1973 earthquake inversion of focal mechanism data for the orientation of principal stresses shows that maximum compression is oriented at azimuth 74 closely paralleling both the current nazca south america convergence direction and the shortening direction derived from regional quaternary fault slip data we interpret the earthquakes as occurring on planes of weakness first produced during cretaceous rifting and later reactivated by neogene compressive stresses crustal seismicity patterns and fault plane solutions suggest the presence of a midcrustal detachment along which significant late cenozoic e w shortening has occurred

origin and deformation of the neogene recent maghrebian foredeep at the gela nappe se sicily se sicily contains one of the few exposures of orogenic foreland to the maghrebian apennine orogenic system in the central mediterranean here the african foreland is represented by the hyblean plateau adjacent to the frontal thrust structures of the maghrebian chain these structures include the disrupted foredeeps to earlier parts of the thrust system one of these the gela nappe is a major structure composed of late oligocene to early pliocene sediments emplaced onto pliocene pleistocene rocks of the buried foreland this paper presents a correlation of late miocene stratigraphic units between the foreland and the foredeep basin abrupt lithological and thickness variations of these units suggest that the foredeep basin was limited towards the foreland by normal faults in the hinterland these foredeep sediments lap back onto previously emplaced thrust sheets including the far travelled units of numidian flysch the precursor oligocene serravallian foredeep may also have been controlled by normal faulting compressional tectonics are reflected in folding and thrusting which post dates deposition of lower pliocene chalks trubi formation although minor folding and erosion preceded this unit larger thrusts repeat the basin stratigraphy and carry it out onto the adjacent foreland a minimum of 8 km shortening since messinian times can be demonstrated although a more realistic figure is c 25 km at a time averaged rate off 0 5cm a 1 the stratigraphic relationships on the foredeep sedimentary sequences may provide analogues for offshore areas of the thrust belt

geomorphological study of the cafayate dune field northwest argentina during the last millennium abstract the cafayate depression is a dry valley located in the pre andean region of northwest argentina the area shows the development of a large dune field its significance has been established from geomorphological and mineralogical evidence grain shape characteristics and chronological data osl dating archaeological remains and historical data the dating results were between 1000 1100 ad to1740 1830 ad showing that the aeolian dynamics remained active during the last millennium it was not possible to identify stabilised phases marked by ruptures or paleosol development nevertheless other regional and local proxies from northwest argentina archaeological documentary etc were used to complete the interpretative framework to propose the paleoenvironmental evolution of the area in addition human activity and land use must be considered as a complementary factor affecting aeolian dynamics during the most recent stage