inverse square root dependence of mid ocean ridge flank roughness on spreading rate the topographic roughness of mid ocean ridge flanks is known to increase with decreasing spreading rate1 4 but the exact form of this relationship has not been established as the topographic features that make up ridge flank roughness abyssal hills are created near the axes of mid ocean ridges by faulting and volcan ism5 7 the relationship between roughness and spreading rate may shed light on the process of crustal accretion at spreading centres here i present measurements of ridge flank roughness on profiles crossing the world mid ocean ridge system which show that roughness is proportional to the inverse square root of the spreading rate this result is consistent with some very simple inferences of how the topographic roughness of mid ocean ridge flanks scales with the lithospheric thickness near ridge axes as determined by thermal models

the influence of surface and tectonic processes on landscape evolution of the iberian chain spain quantitative geomorphological analysis and geochronology abstract in tectonically active areas the landscape response to tectonic forcing is described and possibly quantified by regional topographic and hydrographic features as well as by spatial variation in rates of surface processes we investigated the recent landscape evolution of the iberian chain ne spain an intraplate thrust belt formed in cenozoic times and characterized by a dome shaped topography in its central sector the landscape is dominated by low relief surfaces late neogene in age presently standing at an average altitude of 1300 m a recent regional uplift controlled the organization of the present fluvial network and dissection of the landscape in this framework we investigated the geomorphic responses to tectonic forcing by the calculation of morphometric parameters focusing on topography map of local relief swath profiles and hydrography basin hypsometric curve and integral basin asymmetry factor river longitudinal profiles and relative indices and using srtm dem the results of morphometric analysis have been coupled with radiometric uranium series dating of calcareous tufas lying on fluvial strath terraces the obtained ages allow the estimation of incision rate along the high tajo and martin rivers our results indicate that uplift and rock type erodibility are the main factors influencing landscape evolution of the study area the incision rates are very similar throughout the central sector of the range indicating that despite subtle local variation the rivers are responding to a main tectonic input the regional uplift in conclusion the iberian chain landscape is in a transient state in response to a recent dome like uplift indeed the fluvial processes that weakly incised this landscape at a rate of 0 6 mm yr are approaching a radial pattern on the basis of geological and geomorphic constraints we hypothesize that the uplift started around or after 3 ma

interaction between a hotspot and a fracture zone the crustal structure of walvis ridge at 6 e highlights late stage volcanism covers old oceanic crust north of the florianopolis fracture zone no influence of fracture zone on formation of walvis ridge at 6 e walvis ridge at 6 e erupted in deep water environment abstract the walvis ridge is one of the major hotspot trails in the south atlantic and a classical example for volcanic island chains two models compete about the origin of the ridge it is either the result of a deep mantle plume or active fracture zones above mantle inhomogeneities among other things crustal information is needed to constrain the models here we provide such constraint with a 480 km long p wave velocity model of the deep crustal structure of the eastern walvis ridge at 6 e according to our data the walvis ridge stretches across the florianopolis fracture zone into the angola basin here we observe a basement high and thick basaltic layers covering the oceanic crust and the fracture zone we found two crustal roots along the profile one is located beneath the ridge crest the other one beneath the northern basement high in the angola basin the crustal thickness reaches 18 km and 12 km and the lower crustal velocities are 7 2 km s and 7 4 km s respectively the bathymetric expression of the ridge along the profile is less pronounced than closer to shore which is mainly attributable to the absence of a thick layer of volcanic debris rather than to reduced crustal thickness below the basement surface therefore this part of the ridge was never or only briefly subaerially exposed the crustal structure suggests that the ridge and the fracture zone formed independently of each other the oceanic crust north of the fracture zone which is buried underneath the basalt layer is younger than the reconstructed age of hotspot volcanism of the walvis ridge we interpret these structures north of the fracture zone to be at least partly a product of late stage volcanism

river drainage patterns in the new zealand alps primarily controlled by plate tectonic strain the persistence of dendritic drainage patterns implies that rivers reorganize after a tectonic perturbation preserving no long term record of that tectonic event numerical simulations of the evolution of drainage patterns in the southern alps new zealand however reveal rivers that resist reorganization and thus preserve a record of plate tectonic strain over 10 million years

active thrusting and folding along the northern tien shan and late cenozoic rotation of the tarim relative to dzungaria and kazakhstan we have studied geometries and rates of late cenozoic thrust faulting and folding along the northern piedmont of the tien shan mountain belt west of urumqi where the m 8 3 manas earthquake occurred on december 23 1906 the northern range of the tien shan rising above 5000 m overthrusts a flexural foredeep filled with up to 11 000 m of sediment of the dzungarian basement our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front within a 200 km long zone of neogene quaternary anticlines fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range in all the valleys the scarps offset vertically the highest terrace surface by the same amount 10 2 0 7 m inferring an early holocene age 10 2 kyr for this terrace which is continuous with the largest recent fans of the piedmont yields a rate of vertical throw of 1 0 0 3mm yr on the main active thrust at the surface a quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5 5 2 5 m 2 kyr a rather fresh surface scarp 0 8 0 15 m high that is unlikely to result from shallow earthquakes with 6 m 7 in the last 230 years is visible at the extremities of the main fold zone we associate this scarp with the 1906 manas earthquake and infer that a structure comprising a deep basement ramp under the range gently dipping flats in the foreland and shallow ramps responsible for the formation of the active fault propagation anticlines could have been activated by that earthquake if so the return period of a 1906 type event would be 850 380 years the small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth 2 3 is taken up by incremental folding near the surface comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising quaternary ranges such as the san gabriel mountains in california or the mont blanc aar massifs in the alps we estimate the finite cenozoic shortening of the folded dzungarian sediments to be of the order of 30 km and the cenozoic shortening rate to have been 3 1 5 mm yr assuming comparable shortening along the tarim piedmont and minor additional active thrusting within the mountain belt we infer the rate of shortening across the tien shan to be at least 6 3 mm yr at the longitude of manas 85 5 e a total shortening of 125 30 km is estimated from crustal thickening assuming local airy isostatic equilibrium under the same assumption serial n s sections imply that cenozoic shortening across the belt increases westwards to 203 50 km at the longitude of kashgar 76 e as reflected by the westward increase of the width of the belt this strain gradient implies a clockwise rotation of tarim relative to dzungaria and kazakhstan of 7 2 5 around a pole located near the eastern extremity of the tien shan west of hami 96 e 43 5 n comparable to that revealed by paleomagnetism between tarim and dzungaria 8 6 8 7 a 6 mm yr rate of shortening at the longitude of manas would imply a rate of rotation of 0 45 m y and would be consistent with a shortening rate of 12 mm yr north of kashgar taking such values to be representative of late cenozoic rates would place the onset of reactivation of the tien shan by the india asia collision in the early to middle miocene 16 22 9 m y in accord with the existence of particularly thick late neogene and quaternary deposits such reactivation would thus have started much later than the collision roughly at the time of the great mid miocene changes in tectonic regimes denudation and sedimentation rates observed in southeast asia the himalayas and the bay of bengal and of the correlative rapid change in seawater sr isotopic ratio 20 to 15 ma like these other changes the rise of the tien shan might be a distant consequence of the end of indochina s escape

wide angle seismic constraints on the internal structure of tenerife canary islands abstract we have used wide angle seismic data to constrain the internal structure of tenerife canary islands the experiment was designed as a seismic fan profile to detect azimuthal variations in the seismic structure of the volcanic edifice and its flanks seismic energy was generated using a 75 l airgun array on board the rrs charles darwin fired every 40 s along a quasi circular profile around the island of tenerife centered on teide volcano we present the results obtained from the data recorded by five portable land stations distributed on the island the travel times indicate that the averaged p wave velocity within the volcanic edifice is greater than 6 km s the observed travel times were reduced to residual travel times by removing the effects of variations in the bathymetry along the profile variations in the shot receiver distance and from local heterogeneities negative residual travel times up to 0 8 s in amplitude indicate that the southwestern part of tenerife is characterized by a high p wave velocity zone coincident with a gravity maximum that was previously modeled as a high density body forming the core of an old large mafic volcano we estimate velocities greater than 7 3 km s within the anomalous body suggesting that it represents an intrusive plutonic complex this high velocity high density body may have played an important role in the evolution of tenerife buttressing las canadas edifice and preventing the occurrence of landslides in the southern and western areas of tenerife the bathymetric high between tenerife and la gomera is associated with travel time delays up to 0 4 s suggesting that it may be composed of large deposits of lava flows and volcaniclastic materials probably erupted from the shield massifs of teno roque del conde and la gomera the post shield volcanic zones of santiago and dorsal rifts also seem to be characterized by moderate high p wave velocities

late pleistocene holocene right slip rate and paleoseismology of the nayband fault western margin of the lut block iran the 290 km long nayband strike slip fault bounds the western margin of the lut block and cuts across a region thought to have been quiescent during the last few millennia cl 36 cosmic ray exposure cre and optically stimulated luminescence osl dating of cumulative geomorphic offsets are used to derive the long term slip rate the measured offsets at two sites along the fault range between 9 1 m and 195 15 m with ages from 6 8 0 6 ka to 100 ka yielding minimum and maximum bounds of late pleistocene and holocene slip rates of 1 08 and 2 45 mm yr 1 respectively this moderate slip rate of 1 8 0 7 mm yr 1 averaged over several earthquake cycles is compared to the paleoseismic record retrieved from the first trench excavated across the fault combining the paleoseismic evidence with 18 osl ages obtained from this trench site demonstrates the occurrence of at least four large m 7 earthquakes during the last 17 4 1 3 ka and of two older wearthquakes one before 23 ka and another before 70 5 ka the exposed sediment succession also indicates a significant gap at the end of mis 2 and the beginning of mis 1 the age of the most recent regional incision is accurately bracketed between 6 1 ka and 7 4 ka sediments from the last 7 ka contain evidence of the three younger earthquakes interestingly the penultimate and antepenultimate events occurred between 6 5 0 4 ka and 6 7 0 4 ka within a time interval lasting at most 1 ka whereas the most recent earthquake occurred within the last millennium such an irregular earthquake occurrence suggests the seismic behavior of the nayband fault is not strictly time dependent but possibly related to clustering from this and taking into account the occurrence of the most recent earthquake within the last 800 years the imminence of an earthquake along the nayband fault cannot be discarded although the most recent surface rupturing event seems to have occurred after ad 1200 this event went unnoticed in the historical records this provides a marked illustration of the incompleteness of the historical seismic catalogs in central iran challenging any assessment of regional seismic hazard without appropriate geologic and geochronological information large and infrequent earthquakes are characteristic of the seismic behavior of the slow slipping strike slip faults slicing central and eastern iran also the slip rates summed across central and eastern iran from the iran plateau up to the afghan lowlands appear in agreement with the most recent gps data

river terrace systems in north west europe an archive of environmental change uplift and early human occupation abstract staircases of large scale aggradational river terraces are a notable feature of many valleys in the temperate lattitudes particularly in areas beyond the reach of the erosive activities of pleistocene ice sheets it is now recognized that the cyclic fluctuations of climate during the quaternary have driven the generation of terraces through the direct and indirect influence of both temperature and precipitation on fluviatile activity where fossiliferous deposits are preserved within terrace sequences it is often possible to date these and to correlate them with the oceanic record thus providing an important framework for the evidence of environmental change on land middle and late pleistocene terraces in different areas can commonly be seen to have formed in synchrony with glacial interglacial cycles or with longer periodicity megacycles climatic forcing alone is insufficient to cause terraces to form however uplift is also necessary so that terrace sequences can provide a useful record of crustal movement in northwest europe where some of the best known studies of river terrace sequences have been carried out the fluviatile deposits are also an important repository for palaeolithic artefacts from which a record of early human occupation can be reconstructed

geomorphological response of fluvial and coastal terraces to quaternary tectonics and climate as revealed by geostatistical topographic analysis geostatistical topographic analysis is widely recognized as a useful tool for the statistical reconstruction of planar geomorphic markers from relict surfaces this work is aimed at improving the geostatistical approach used in previous works and developing a method for evaluating the incision rates of rivers in their lower catchments during the late quaternary we chose the major valleys of the adriatic foothills central italy affected since late miocene by a differential tectonic uplift which is still active in particular i we applied the geostatistical analysis to reconstruct the original top surfaces of fluvial to coastal terrace bodies at the metauro river and cesano river mouths ii we performed correlations between the height distribution of the alluvial terrace sequences and the quaternary climatic curve to estimate the average long term fluvial incision rates in the lowermost reaches of the metauro cesano misa and esino rivers the obtained averaged incision rates have been interpreted also in the light of the stream length gradient index sl index steepness index ks and concavity index as proxies of the stream power per unit length results confirm that geostatistical and terrain analysis of topographic and geometric arrangements of fluvial and coastal terraces is an effective tool in detecting geomorphic and tectonic factors inducing perturbations on planar geomorphic markers in particular we better delineated the surface geometry and boundaries of well developed coastal fans at the mouths of the metauro and cesano rivers already recognized in previous works through sedimentological morphostratigraphic and chronological data moreover we found evidence for cut and fill phases that took place during and immediately after the river aggradation of the late quaternary glacial periods despite the slope area analysis evidenced a widespread influence of the regional differential uplift on single river basin configuration we observed some space and time variability of averaged incision rates for adjacent valleys mainly explained by physiographic configuration and dynamics of drainage network copyright 2011 john wiley sons ltd

geomorphic signal of active faulting at the northern edge of lut block insights on the kinematic scenario of central iran recent works documented neogene to quaternary dextral strike slip tectonics along the kuh e sarhangi and kuh e faghan intraplate strike slip faults at the northern edge of the lut block of central iran previously thought to be dominated by sinistral strike slip deformation this work focuses on the evidence of quaternary activity of one of these fault systems in order to provide new spatiotemporal constraints on their role in the active regional kinematic scenario through geomorphological and structural investigation integrated with optically stimulated luminescence dating of three generations of alluvial fans and fluvial terraces at 53 25 and 6 ka this study documents i the topographic inheritance of the long term myr punctuated history of fault nucleation propagation and exhumation along the northern edge of lut block ii the tectonic control on drainage network evolution pediment formation fluvial terraces and alluvial fan architecture iii the minimum holocene age of quaternary dextral strike slip faulting and iv the evidence of late quaternary fault related uplift localized along the different fault strands the documented spatial and temporal constraints on the active dextral strike slip tectonics at the northern edge of lut block provide new insights on the kinematic model for active faulting in central iran which has been reinterpreted in an escape tectonic scenario

evolution of the walvis ridge rio grande rise hot spot system implications for african and south american plate motions over plumes crystallization ages of volcanic rocks dredged or drilled from the walvis ridge ten sites and the rio grande rise one site have been determined by the 40ar 39ar incremental heating technique the fundamentally age progressive distribution of these basement ages suggests a common hot spot source for volcanism on the island of tristan da cunha along the walvis ridge and rio grande rise and for the formation of the continental flood basalts located in namibia africa and brazil south america the walvis ridge rio grande rise volcanic system evolved along a section of the south atlantic spreading axis as the african and south american plates migrated apart astride or in close proximity to an upwelling plume reconstructions of the spatial relationship between the spreading axis the tristan hot spot and the evolving walvis ridge rio grande rise volcanic feature show that at about 70 ma the spreading axis began to migrate westward away from the hot spot the resulting transition to intraplate hot spot volcanism along the walvis ridge and associated termination of rio grande rise formation also involved a northward migration of previously formed african seafloor over the hot spot rotation parameters for african motion over fixed hot spots i e absolute motion have been recalculated such that the predicted trail of the tristan hot spot agrees with the distribution of radiometric and fossil basement ages along the walvis ridge african absolute motion has been extended to the south and north american plates by the addition of relative motion reconstruction poles

landscape response to tectonic and climatic forcing in the foredeep of the southern apennines italy insights from quaternary stratigraphy quantitative geomorphic analysis and denudation rate proxies we present new data about the morphological and stratigraphic evolution and the rates of fluvial denudation of the tavoliere di puglia plain a low relief landscape representing the northernmost sector of the pliocene pleistocene foredeep of the southern apennines the study area is located between the easternmost part of the southern apennine chain and the gargano promontory and it is characterized by several orders of terraced fluvial deposits disconformably overlying lower pleistocene marine clay and organized in a staircase geometry which recorded the emersion and the long term incision history of this sector since mid pleistocene times we used the spatial and altimetric distribution of several orders of middle to late pleistocene fluvial terraces in order to perform paleotopographic reconstruction and gis aided eroded volumes estimates then we estimated denudation rates on the basis of the terraces chronostratigraphy supported by published osl and aar dating middle to upper pleistocene denudation rates estimated by means of such an approach are slightly lower than 0 1 mm yr 1 in good agreement with short term data from direct and indirect evaluation of suspended sediment yield the analysis of longitudinal river profiles using the stream power erosion model provided additional information on the incision rates of the studied area middle to late quaternary uplift rates about 0 15 mm yr 1 calculated on the basis of the elevation above sea level of marine deposits outcropping in the easternmost sector of the study area are quite similar to the erosion rates average value thus suggesting a steady state fluvial incision the approach adopted in this work has demonstrated that erosion rates traditionally obtained by quantitative geomorphic analysis and ksn estimations can be successfully integrated to quantify rates of tectonic or geomorphological processes of a landscape approaching steady state equilibrium copyright 2014 john wiley sons ltd

chronology and rates of faulting of ventura river terraces california new evidence concerning the chronology of four late pleistocene terraces of the ventura river near oak view california that are vertically offset and tilted by reverse and reverse flexural slip faults provides a means of estimating rates of fault movement and downcutting by the ventura river radiocarbon ages of charcoal contained within terrace deposits date two of the terraces correlation of soils that have developed on terrace deposits and extrapolation of the rate of vertical displacement of the arroyo parida santa ana fault not a flexural slip fault date the others resulting age estimates for the four main late pleistocene terraces are qt5b 30 000 qt6a 38 000 qt6b 54 000 and qt6c 92 000 yr b p vertical slip rates on flexural slip faults range from 0 3 to 1 1 mm yr and apparently are related to the rate form and mechanics of folding of the north limb of the ayers creek canada larga syncline average rates of downcutting of the ventura river for several intervals during the late pleistocene estimated from the chronology and relative elevation of river terraces north of the arroyo panda santa ana fault upstream from the zone of faulting vary from 0 5 to 1 3 mm yr the range in rates probably reflects variations in local uplift as well as adjustments to changing eustatic sea level climatic conditions and or regional deformation of the western transverse ranges the average rate of downcutting of the ventura river north of the zone of flexural slip faulting is 0 8 mm yr compared with 1 2 to 2 2 mm yr in the deformation zone immediately to the south this apparently indicates that during tectonic deformation there is an approximate balance between the rate of uplift due to faulting and folding and the rate of downcutting by the fluvial system

implications of updated magnetic anomalies for the late cretaceous tectonic evolution of walvis ridge in the south atlantic a reorganization of the mid atlantic ridge began before anomaly c34n 83 6 ma and ended before anomaly c30n 66 4 ma complicating tectonics of rio grande rise and older walvis ridge wr which formed together at the mid atlantic ridge this reorganization is poorly understood because magnetic anomalies c30n c34n are poorly defined near wr we interpreted these anomalies along westernwrto improve knowledge of rio grande rise wrtectonic development anomaly trends indicate that valdivia bank has an e w age progression perpendicular to that predicted by hot spot models anomaly spacing and width is irregular and anomalous near wr implying a series of ridge jumps and possibly a microplate between anomalies c34n and c32n eastward ridge jumps transferred microplate lithosphere to the south american plate this study shows that late cretaceous tectonic evolution of the rio grande rise wrlarge igneous provinces was more complex than previously understood

the structural evolution of active fault and fold systems in central otago new zealand evidence revealed by drainage patterns abstract central otago in new zealand is an area of active continental shortening in which a peneplain surface cut into schist has been deformed by folds which are developed above buried reverse faults we use the drainage patterns in this region to demonstrate various processes in fold and fault growth and interaction that would be difficult to identify by other means in particular we show 1 how simple asymmetric folds can develop into box folds 2 how apparently continuous ridges were formed by the coalescing of quite separate propagating fold and fault segments 3 evidence for the relative ages or relative uplift rates of adjacent structures and 4 evidence for the propagation direction of folds or faults as they grow the few quantitative estimates we obtain for fault propagation rates suggest an increase in length of 10 50 m per earthquake on faults about 20 km long these estimates are very uncertain but are similar in magnitude to an estimate made in nevada for a normal fault of similar size and are also similar to predicted estimates from theoretical growth models they raise the question of whether fault growth earthquake recurrence rates and climate change can interact to produce semi regular discrete features in an active landscape

geomorphic and structural variations along the doruneh fault system central iran 1 this paper focuses on the analysis of geomorphic structural and behavioral characteristics along the doruneh fault system dfs east of longitude 56 45 e detailed geomorphic and structural analyses of different scale satellite images and digital topographic data accompanied with field surveys allowed us to establish a fault segmentation model in which three discrete fault zones have been recognized 1 the western fault zone wfz characterized by reverse left lateral mechanism with left handed step over geometry 2 the central fault zone cfz which is pure left lateral strike slip and comprises nearly parallel faults and 3 the eastern fault zone efz that is a trailing imbricate fan fault termination characterized by reverse faulting and fault related folding each fault zone shows discrete geometry and kinematics implying that deformation is not uniformly accommodated along the dfs we propose a new kinematic model to explain how the dfs accommodate the arabia eurasia convergence normal to the overall fault orientation according to this model the dfs takes up the northward motion between central iran lut block relative to eurasia by a complex kinematics varying from pure reverse to pure left lateral strike slip faulting the kinematics of the wfz and efz corresponds to the direction of the ne trending regional compression while the partitioning of slip into strike slip and reverse component of faulting on parallel faults strain partitioning allows the cfz to remain pure left lateral strike slip such a model propose a way to explain how large strike slip faults such as the dfs accommodate tectonic block motions perpendicular to strike of the faults

morphology displacement and slip rates along the north anatolian fault turkey 1 geological and geomorphological offsets at different scales are used to constrain the localization of deformation total displacement and slip rates over various timescales along the central and eastern north anatolian fault naf in turkey the naf total displacement is reevaluated using large rivers valleys 80 15 km and structural markers pontide suture 85 25 km tosya vezirkopru basins 80 10 km these suggest a neogene slip rate of 6 5 mm yr over 13 myr the river network morphology shows offsets at a range of scales 20 m to 14 km across the main fault trace and is also used to estimate the degree to which deformation is localized at a smaller scale the morphology associated with small rivers is offset by 200 m along the naf the age of these features can be correlated with the holocene deglaciation and a slip rate of 18 3 5 mm yr is determined this is consistent with a rate of 18 5 mm yr deduced independently from the 14c dating of stream terrace offsets over the short term gps data gives a similar rate of 22 3 mm yr all our results tend to show that most of the deformation between the anatolian and eurasian lithospheric plates has been accommodated along or very close to the active trace of the naf the difference between the neogene and the holocene slip rate may be due to the recent establishment of the current plate geometry after the creation of the naf

geomorphic expression of active tectonics in a rapidly deforming forearc sila massif calabria southern italy we examine the tectonic geomorphology of la sila calabria southern italy a high standing 1500 m plateau surrounded by crustal extension with map dem and field data these data are used to constrain a simple geodynamic model that describes short wavelength deformation of the plateau rim topographic metrics including drainage patterns river longitudinal profiles and swath profiles are consistent with field stratigraphic relationships collectively suggesting that local tectonic deformation is embedded within a broader regional uplift that has increased the mean elevation of the sila plateau during the quaternary the concavity steepness and length gradient index of modeled river longitudinal profiles proved to be the most useful metrics for recording the effects of locally active faults a previously unrecognized horst on the northeastern portion of the plateau was identified with these data nevertheless the core of the sila plateau remains relatively undeformed with respect to its flanks which are characterized by steep fault bounded escarpments active extension has dropped base level for and unloaded the plateau rim causing deep fluvial incision and associated flexural uplift of the footwall this footwall uplift helps maintain a separate external and nearly radial drainage away from the plateau along its flanks and a nearly closed drainage for the plateau interior a drainage divide roughly correlates with the plateau rim inhibiting the process of drainage integration through the sila interior and subsequent landscape dissection as a result geomorphic processes driving erosion of the sila upland are lagging behind the tectonic processes that have driven rock uplift leading to an overall increase in mean surface elevation these results underscore the importance of the lag times a landscape may endure in transforming from one tectonic and base level condition to another we conclude that the calabrian forearc has a similar geomorphic evolution as the more northern apennines consistent with the emerging view that growth of apennine topography has been recent quaternary rapid and possibly decoupled from rock deformation in the orogenic wedge

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 architecture and deep structure of the ninetyeast ridge hotspot trail from active source ocean bottom seismology a 550 km long transect across the ninetyeast ridge a major indian ocean hotspot trail provided seismic refraction and wide angle reflection data recorded on 60 ocean bottom instruments about 24 000 crustal and 15 000 upper mantle arrivals have been picked and used to derive an image of the hotspot track two approaches have been chosen i a first arrival tomographic inversion yielding crustal properties and ii forward modelling of mantle phases revealing the structure at the crust mantle boundary region and of the uppermost mantle away from the volcanic edifice seismic recordings show the typical phases from oceanic crust that is two crustal refraction branches pg a wide angle reflection from the crust mantle boundary pmp and a wave group turning within the upper mantle pn approaching the edifice three additional phases have been detected we interpret these arrivals as a wide angle reflection from the base of material trapped under the pre hotspot crust pm2p and as a wide angle reflection pnp and its associated refraction branch pn from a layered upper mantle the resulting models indicate normal oceanic crust to the west and east of the edifice crustal thickness averages 6 5 7 km wide angle reflections from both the pre hotspot and the post hotspot crust mantle boundary suggest that the crust under the ridge has been bent downwards by loading the lithosphere and hotspot volcanism has underplated the pre existing crust with material characterized by seismic velocities intermediate between those of mafic lower crustal and ultramafic upper mantle rocks 7 5 7 6 km s 1 in total the crust is up to 24 km thick the ratio between the volume of subcrustal plutonism forming the underplate and extrusive and intrusive volcanism forming the edifice is about 0 7 an important observation is that underplating continued to the east under the wharton basin during the shield building phase however ninetyeast ridge was located adjacent to the broken ridge and was subsequently pulled apart along a transform fault boundary therefore underplating eastwards of the fracture zone separating the edifice from the wharton basin suggests that prolonged crustal growth by subcrustal plutonism occurred over millions of years after the major shield building stage this fact however requires mantle flow along the fossil hotspot trail the occurrence of pnp and pn arrivals is probably associated with a layered and anisotropic upper mantle due to the preferential alignment of olivine crystals and may have formed by rising plume material which spread away under the base of the lithosphere

seismicity in the vicinity of the tristan da cunha hot spot particular plate tectonics and mantle plume presence earthquake locations along the southern mid atlantic ridge have large uncertainties due to the sparse distribution of permanent seismological stations in and around the south atlantic ocean most of the earthquakes are associated with plate tectonic processes related to the formation of new oceanic lithosphere as they are located close to the ridge axis or in the immediate vicinity of transform faults a local seismological network of ocean bottom seismometers and land stations on and around the archipelago of tristan da cunha allowed for the first time a local earthquake survey for one year we relate intra plate seismicity within the african oceanic plate segment north of the island partly to extensional stresses induced by a bordering large transform fault and to the existence of the tristan mantle plume the temporal propagation of earthquakes within the segment reflects the prevailing stress field the strong extensional stresses in addition with the plume weaken the lithosphere and might hint at an incipient ridge jump an apparently aseismic zone coincides with the proposed location of the tristan conduit in the upper mantle southwest of the islands the margins of this zone describe the transition between the ductile and the surrounding brittle regime moreover we observe seismicity close to the islands of tristan da cunha and nearby seamounts which we relate to ongoing tectono magmatic activity

insights from scaled analogue modelling into the seismotectonics of the iranian region abstract we show how analogue modelling provides insights into complex crustal block kinematics and the seismotectonics of active areas undergoing contraction such as the iranian region the seismotectonic model deriving from this analysis is consistent with partitioning of the n directed arabia indentation into a composite system of collision oblique and collision parallel seismogenetic belts these features include 1 two main conjugate transpressive belts the dextral nw se trending zagros belt and the ne sw trending sinistral elburz aran torud eat belt and 2 a modest lateral escape of central iran towards the lut block along the nayband belt this cinematic model fits the seismic activity and the current fault pattern of the region also the velocity field scaled from the model to nature shows a good similarity with previous numerical modelling as well as with deformation rates along the first order seismogenetic belts determined by plate tectonic models and gps data

morphotectonic evolution of the adriatic piedmont of the apennines an advancement in the knowledge of the marche abruzzo border area abstract this study focuses on the morphotectonic evolution of the apennines central adriatic piedmont and in particular on the region along the marche abruzzo border stratigraphically the rocks of this area are typical of a marine environment which characterised the central periadriatic basin up to the early pleistocene a differential regional uplift produced a north eastward tilting of the area this led to the development of a parallel drainage network across the emerged coastal plain during the middle pleistocene these tectonic events along with a series of climatic changes during the quaternary caused alternating phases of fluvial incision and deposition which eventually produced four levels of fluvial terraces as outcropping lithologies seldom display a full record of significant tectonic deformation we carried out morphometric analysis along with a geomorphological survey in order to enhance our morphotectonic understanding of the area and to better define the role of neotectonics in the morphological evolution of the area we also analysed the morphological evidence of tectonics including field surveys focusing on fluvial and alluvial fan terraces as they are valuable indicators of neotectonic evolution finally we employed geostatistical analysis to facilitate the detection of fluvial terraces even when affected by neotectonics our results indicate an active control on drainage evolution by nw se to wnw ese tectonic lineaments intersected by sw ne and wsw ene ones these tectonic lines continued to be active up to the formation of the third level of terraces late pleistocene river captures and diversions followed during the late pleistocene and the holocene in some cases favoured by passive tectonic control

history of faulting on the doruneh fault system implications for the kinematic changes of the central iranian microplate the doruneh fault system is one of the major transcurrent faults in central asia extending 900 km from western afghanistan into west central iran the left lateral doruneh fault system is also a key structure in the arabia eurasia collisional zone bounding the northern margin of the independent central iranian microplate the doruneh fault system exhibits a curved geometry and is divided here into three segments eastern central and western we present the results of geological structural and geomorphic studies into the nature of recent activity along the doruneh fault system segments a surprising observation is that small relatively young drainage systems often show recent systematic left lateral displacement across the fault whereas large rivers indicate a former more complex right lateral history furthermore the existence of right lateral offsets of pre pliocene rocks and s c fabrics confirm this earlier phase of right lateral movement on the fault we suggest that the early right lateral kinematics resulted from an earlier nw se directed regional shortening associated with the anticlockwise rotation of the central iranian microplate the shortening is characterized by the ne sw striking en echelon folds within the fault slivers the right lateral taknar imbricate fan and the superimposed folding exposed north of kashmar thus assuming an initiation age of eocene 55 8 ma for the fault we estimate a former right lateral slip rate of about 5 2 5 5 mm yr 1 which accompanied the 35 anticlockwise rotation of the central iranian microplate according to our study the youngest units exhibiting right lateral displacement are middle miocene in age suggesting a post middle miocene timing for the onset of slip sense inversion

kinematic evolution of the romanian carpathians abstract the regional pattern of contraction and extension directions and the evolution of the strain field from paleogene to neogene times enabled a reconstruction of the migration path of the carpathian collision front the carpathian nappes were thrust around the moesian plate during paleogene and early neogene times and protruded into a small oceanic embayment between the moesian and european plates the arc structure of the carpathian fold thrust belt was formed in late neogene times as a result of the eastward escaping tisza dacia block due to n directed convergence of the adriatic plate and the retreating subduction of an oceanic slab brittle deformation structures in the romanian carpathians suggest three tectonic events related to major plate motions 1 paleogene to middle miocene ne to ene contraction caused right lateral curved strike slip faults 2 middle miocene to pliocene fan shaped orientations of contraction directions were caused by right lateral oblique convergence in the southern carpathians frontal convergence in the southern eastern carpathians and left lateral convergence in the northern eastern carpathians 3 pleistocene to holocene general e w extension and n s contraction in the carpathian arc and local ese wnw contraction in the vrancea area is related to the late roll back stage and break off of the subducted slab in the bend area

subsidence and crustal roughness of ultra slow spreading ridges in the northern north atlantic and the arctic ocean summary five basin wide seismic reflection profiles of up to 550 km each were acquired in the arctic ocean and the northern north atlantic in 2001 and 2002 the main objective was to investigate the depth to the basement and to analyse the crustal structure morphology and roughness of ultra slow spreading ridges of the gakkel molloy and knipovich ridges to date little is known to date of the ultra slow spectrum of such spreading ridges the seismic profiles of all investigated ridges show similar morphological characteristics with deep axial valleys and rough basement topography magnetic data compilation and interpretation suggests that the ultra slow spreading systems are fairly stable and existed during the entire evolution of the basins to the north of the greenland fracture zone the thermal subsidence curve was calculated and corrected for sediment loads and crustal roughness values are estimated for all five profiles the resulting roughness values append the global roughness data set for ultra slow spreading systems the results are higher than those predicted by interpolating existing global roughness this study confirms the presence of a global relationship between crustal roughness ridge morphology and spreading rates new curve fits supporting the global relationship are discussed data on present spreading rates ridge morphology subsidence and roughness provide a better insight into the development of the axial ridge morphology in the study area the results show that the basins to the north of the greenland fracture zone were formed at ultra slow spreading axial rift valleys and continued spreading at ultra slow rates to the present day configuration

post neogene right lateral strike slip tectonics at the north western edge of the lut block kuh e sarhangi fault central iran abstract late cenozoic strike slip tectonics and active faulting in central iran have been extensively described in the last decades this study presents results of integrated structural and geomorphological analyses along the kuh e sarhangi fault a major ne sw striking brittle deformation zone that cuts across the basement and neogene quaternary cover successions at the north western edge of the lut block structural investigations document post neogene ne sw dextral transpressive tectonics and geomorphic evidence support a late quaternary age for the faulted alluvial fan deposits along the bedrock range fronts northward the nearly parallel great kavir doruneh fault is known to have active left lateral strike slip kinematics and its easternmost segment was considered as the northern margin of the lut block the new findings impose reconsideration of the current regional kinematic models with implications on the seismogenic fault networks of central iran

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

upper mantle density modelling for large scale moho gravity inversion case study on the atlantic ocean moho geometry is an important parameter in geodynamic understanding seismic methods can provide accurate burial depths but the coverage is low the widely used crust1 0 model under oceans is greatly restricted by a low coverage of seismic data gravity inversion can provide high coverage of moho undulations but the accuracy is relatively low observed gravity anomalies integrate gravity effects induced by 3 d density perturbations in the earth for studies of the geometry of a specific density interface based on gravity all gravity effects caused by other interfaces should be removed from the total anomaly map based on 3 d density distributions we use temperature based and velocity based methods to model the lithospheric upper mantle density two temperature calculation parameter models psm and gdh1 three thermal expansion coefficients alpha and three scaling ratio models are tested for each method psm and gdh1 result in a similar mantle gravity anomaly mga pattern but different mga average values when the alpha model is the same different alpha and scaling ratio models result in different moho inversion results and the optimal result from the temperature based method has an rms of 3 2 km with the crust1 0 model a comparison between this inversion result and the crust1 0 model shows that the temperature based method performs well in reproducing moho geometry in the main part of the atlantic ocean especially in the central basin the optimal result from the velocity based method has an rms of 4 3 km with the crust1 0 model compared with the temperature based method the velocity based method performs worse in the central basin but better in regions with low velocity and low density mantle away from the mid ocean ridge

the use of the stream length gradient index in morphotectonic analysis of small catchments a case study from central italy abstract the aim of this work is to test an integrated quantitative geomorphic approach based on stream length gradient index sl index analysis within the small catchment of the tarugo river in the northern marchean apennines central italy the tarugo river basin 92 km 2 wide strikes sw ne across the marchean ridge and the western sector of marchean piedmont the area is characterized by a series of nw se trending ne verging thrust folds affecting the meso cenozoic bedrock that pass upward from dominantly carbonate to dominantly terrigenous rocks the area investigated has been affected since the pliocene by extensional tectonics accompanying a regional uplift decreasing in rate north eastwards in this work the sl index analysis has been integrated with the spatial analysis of the amplitude of relief a r and compared to geological and geomorphological field data results of this work indicate that the sl index is a valid tool to detect the long wavelength structural effect on topography as well as the incipient local response to regional processes i e regional uplift that is often undetectable by other morphotectonic parameters in contrast the sl index analysis seems not be a valid tool for discriminating the local lithological influence from the tectonic one

present day kinematics and fault slip rates in eastern iran derived from 11 years of gps data we analyze new gps data spanning 11 years at 92 stations in eastern iran we use these data to analyze the present day kinematics and the slip rates on most seismogenic faults in eastern iran the east lut west lut kuhbanan anar dehshir and doruneh faults are confirmed as the major faults and are found to currently slip laterally at 5 6 0 6 4 4 0 4 3 6 1 3 2 0 0 7 1 4 0 9 and 1 3 0 8 mm yr respectively slip is right lateral on the ns striking east lut west lut kuhbanan anar and dehshir faults and left lateral on the ew doruneh fault the ns faults slice the eastern iranian crust into five blocks that are moving northward at 6 13 mm yr with respect to the stable afghan crust at the eastern edge of the collision zone the collective behavior of the ns faults might thus allow the arabian promontory to impinge northward into the eurasian crust the ns faults achieve additional ns shortening by rotating counterclockwise in the horizontal plane at current rates up to 0 8 ma modeling the gps and available geological data with a block rotation model suggests that the rotations have been going on at a similar rate 1 0 4 ma over the last 12 ma we identify large strains at the tips of the rotating east lut west lut and kuhbanan faults which we suspect to be responsible for the important historical and instrumental seismicity in those zones

spatial analysis of stream power using gis slk anomaly maps the stream length gradient index sl shows the variation in stream power along river reaches this index is very sensitive to changes in channel slope thus allowing the evaluation of recent tectonic activity and or rock resistance nevertheless the comparison of sl values from rivers of different length is biased due to the manner in which the index is formulated thus making correlations of sl anomalies along different rivers difficult therefore when undertaking a comparison of sl values of rivers of different lengths a normalization factor must be used the graded river gradient k has already been used in some studies to normalize the sl index in this work we explore the relationships between the graded river gradient k the sl index and the stream power proposing the use of a re named slk index which enables the comparison of variable length rivers as well as the drawing of slk anomaly maps we present here a gis based procedure to generate slk maps and to identify slk anomalies in order to verify the advantages of this methodology we compared an slk map of the ne border of the granada basin with both simple river profile knickpoint identification and with an sl map the results show that the slk map supplies good results with defined anomalies and suitably reflects the main tectonic and lithological features of the study area copyright 2008 john wiley sons ltd

mantle thermal structure and active upwelling during continental breakup in the north atlantic seismic reflection and refraction data acquired on four transects spanning the southeast greenland rifted margin and greenland iceland ridge gir provide new constraints on mantle thermal structure and melting processes during continental breakup in the north atlantic maximum igneous crustal thickness varies along the margin from s 30 km in the near hotspot zone 6 500 km from the hotspot track to v18 km in the distal zone 500 1100 km magmatic productivity on summed conjugate margins of the north atlantic decreases through time from 1800 300 to 600 50 km 3 km ma in the near hotspot zone and from 700 200 to 300 50 km 3 km ma in the distal zone comparison of our data with the british faeroe margins shows that both symmetric and asymmetric conjugate volcanic rifted margins exist joint consideration of crustal thickness and mean crustal seismic velocity suggests that along margin changes in magmatism are principally controlled by variations in active upwelling rather than mantle temperature the thermal anomaly vt at breakup was modest v100 125 c varied little along the margin and transient data along the gir indicate that the potential temperature anomaly 125 50 c and upwelling ratio v4 times passive of the iceland hotspot have remained roughly constant since 56 ma our results are consistent with a plume impact model in which 1 a plume of radius v300 km and vt of v125 c impacted the margin around 61 ma and delivered warm material to distal portions of the margin 2 at breakup 56 ma the lower half of the plume head continued to feed actively upwelling mantle into the proximal portion of the margin and 3 by 45 ma both the remaining plume head and the distal warm layer were exhausted with excess magmatism thereafter largely confined to a narrow 6 200 km radius zone immediately above the iceland plume stem alternatively the warm upper mantle layer that fed excess magmatism in the distal portion of the margin may have been a pre existing thermal anomaly unrelated to the plume fl 2001 elsevier science b v all rights reserved

synchronous deformation on orogenic plateau margins insights from the arabia eurasia collision abstract the temporal and spatial distribution of deformation during the early phases of plateau formation is poorly known the iranian plateau is developing in response to arabia eurasia convergence and is a potential analog to the early phases of tibetan plateau deformation previous studies document the onset of the iranian plateau growth based on the kinematic history of the zagros to the south and the alborz mountains to the north here we present new detrital apatite fission track aft data from 13 modern rivers of the talesh mountains northwestern iranian plateau these mountains lie immediately south west of the rigid south caspian block a total of 1233 single grain cooling ages were measured and range between 185 and 4 ma deconvolution of grain age data documents three main phases of exhumation including the oligocene 30 23 ma early to middle miocene 18 12 ma and early pliocene 5 ma comparison between cooling ages from the talesh mountains and elsewhere across the iranian plateau indicates widespread plateau formation in the oligocene earlier than previously suggested for the northwestern plateau margin these results highlight deformation on both the northern and southern margins of the plateau over almost the entire history of iranian plateau formation a similar pattern of synchronous deformation on the north northeastern and southern margins of the tibetan plateau has recently been documented and highlights the significance of rigid basement blocks focusing far field deformation for both plateaus

crustal structure of mauna loa volcano hawaii from seismic refraction and gravity data abstract in october 1978 the u s geological survey established a 100 km long seismic refraction profile normal to the kona coast of hawaii island analysis of these data along with available gravity data suggest that the oceanic crust dips about 3 landward under the submerged flank of the island increasing to 8 5 under the kona coast maximum vertical deflection of the base of crust from beneath the deep ocean to a point beneath the summit of mauna loa is about 9 km high velocity high density rocks vp about 7 1 km sec density about 2 9 gm cm 3 comprise the bulk of the volcanic edifice and reach to within a few kilometers of the surface beneath the north flank of mauna loa the data also suggest that an elongate high velocity high density body lies parallel to the kona coast just below the surface this body probably represents an extinct buried rift zone

hotspot volcanism in the southern south atlantic geophysical constraints on the evolution of the southern walvis ridge and the discovery seamounts abstract the southern atlantic hosts a variety of magmatic structures namely the walvis ridge the discovery seamounts and the shona ridge which are believed to be related to the evolution movement of hotspots although the basement of the walvis ridge has been sampled at different locations geophysical data are too sparse to provide sufficient information about its deeper structure to compare it with other hotspot tracks the discovery seamounts represent a completely different type feature in a way that it cannot be connected to any onshore volcanic feature however geological sampling of the volcanic basement indicates that the petrology of the discovery track is very similar to gough island and the southern branch of walvis ridge both structures erupted into already existing seafloor and so have been seismically investigated to document how if an associated thermal anomaly might have modified the underlying and surrounding oceanic crust seismic lines for both structures indicate rather normal seismic velocity distributions for oceanic crust both the walvis ridge and the largest volcano of the discovery seamounts have a maximum thickness in our research area of 13 km an interesting difference between these structures is a high velocity cone 6 km s at 2 4 km depth in the central part of discovery seamount this might indicate a primarily intrusional type of seamount such as has been reported for several similar structures in contrast the walvis ridge velocity structure does not show evidences for a shallow intrusional cone but seismic velocities typical for oceanic layer 3 at a more or less constant depth level along the entire profile this might indicate that the ridge s present day topography is built mainly by extrusive material

dynamic reorganization of river basins river networks evolve as migrating drainage divides reshape river basins and change network topology by capture of river channels we demonstrate that a characteristic metric of river network geometry gauges the horizontal motion of drainage divides assessing this metric throughout a landscape maps the dynamic states of entire river networks revealing diverse conditions drainage divides in the loess plateau of china appear stationary the young topography of taiwan has migrating divides driving adjustment of major basins and rivers draining the ancient landscape of the southeastern united states are reorganizing in response to escarpment retreat and coastal advance the ability to measure the dynamic reorganization of river basins presents opportunities to examine landscape scale interactions among tectonics erosion and ecology

uppermost mantle and crustal structure at tristan da cunha derived from ambient seismic noise abstract according to classical plume theory the tristan da cunha hotspot located 400 km east off the mid atlantic ridge is thought to have played a major role in the rifting while creating an aseismic walvis ridge during and after the breakup of the south atlantic margins volcanic activity on the tristan da cunha island shows that the hotspot might still be there influencing the upper mantle and crustal structure in this study we present ambient noise data from 24 broadband obs around tristan da cunha and a seismic station on nightingale island which provide first constraints on the crustal and uppermost mantle structure around the island by combining ambient noise techniques dispersion curve analysis of rayleigh waves 2d tomographic inversion of travel times and 3d depth inversion of dispersion data we derived a 3d v s velocity model around the archipelago of tristan da cunha the model shows an isolated vertically sharp bounded thickened and modified crust beneath the islands surrounded by thin oceanic crust

long term fault slip rates distributed deformation rates and forecast of seismicity in the iranian plateau in this paper the long term crustal flow of the iranian plateau is computed using a kinematic finite element model neokinema software based on the iterated weighted least squares method the models are fitted to the newest data set of iran including updated fault traces geologic fault offset rates geodetic benchmark velocities principal stress directions and velocity boundary conditions we are successful to find the best kinematic model in which geological slip rates geodetic velocities and interpolated stress directions are fitted at levels of 0 35 1 0 and 1 0 datum standard deviation respectively the best fitted model for the first time provides long term fault slip rates velocity and anelastic strain rate field in the iranian plateau from all available kinematic data in order to verify the model the estimates of fault slip rates are compared to slip rates from merely analyzing geodetic benchmark velocities or paleoseismological studies or published geological rates which have not been used in the model our estimated rates are all in the range of geodetic rates and are even more consistent with geological rates than previous gps based estimates using the selected model long term average seismicity maps and long term moment rates are produced on the basis of the shift hypothesis and previous global calibrations our kinematic model also provides a new constraint on ratio of seismic deformation to total deformation for different seismic zones of iran the resulting slip rates and the proposed seismic fraction of deformation provide the necessary input data for future time dependent hazard studies in iran moreover spatial distribution and total number of strong m 6 and major m 7 earthquakes which dominate the seismic hazard are all compatible with the regional seismic catalog

active tectonics and late cenozoic strain distribution in central and eastern iran 1 right lateral shear between central iran and afghanistan is accommodated on n s right lateral strike slip faults surrounding the aseismic dasht e lut north of 34 n the right lateral shear is accommodated on left lateral faults that rotate clockwise about vertical axes little is known of the late tertiary and younger offsets and slip rates on the active fault systems results that are important for understanding the regional tectonics we use observations from satellite imagery to identify displaced geological and geomorphological markers which we use in conjunction with the overall morphology and orientation of the active fault systems to estimate the total cumulative right lateral shear estimates of cumulative fault movements from offset features and inferred vertical axis rotation of fault bounded blocks suggest that the late cenozoic strain is concentrated toward the eastern margin of iran along the sistan shear zone where bedrock offsets of at least 70 km are observed across the active faults the geomorphology of the deh shir anar and great kavir strike slip faults in central iran suggest that although little shortening is accommodated across this region they might still be active and hence capable of producing earthquakes present day activity on these faults in central iran would not be expected from distributions of instrumental and historical earthquakes although speculative the late tertiary strain distribution described in this paper is consistent with what we know of the present day rates of shear in eastern iran and provides a framework to which later more detailed work can be added

influence of releasing step overs on surface fault rupture and fault segmentation examples from the 17 august 1999 izmit earthquake on the north anatolian fault turkey the 17 august 1999 izmit earthquake broke four distinct structural segments of the north anatolian fault from east to west the karadere sakarya sapanca and golcuk fault segments these segments are separated from one another and the adjoining yalova and duzce fault segments to the west and east respectively by distinct right releasing step over and or gaps in the fault trace these include from east to west the eften lake step over 2 4 km wide akyazi gap 6 13 km long sapanca step over 1 2 km wide golcuk step over 1 2 km wide and karamursel step over 4 5 km wide the earthquake nucleated within or near the golcuk step over with bilateral rupture propagation to the west and east to the west about 4 5 5 m of surface rupture up to 7 m of subsurface rupture on the golcuk segment was mostly if not entirely arrested by the 4 to 5 km wide karamursel step over to the east about 3 4 m of surface rupture about 4 m of subsurface rupture propagated through the 1 to 2 km wide sapanca step over triggering up to 4 5 5 5 m of surface rupture up to 5 6 m of subsurface rupture on the sakarya segment rupture on the sakarya segment stepped across the akyazi gap triggering 1 1 5 m of rupture on the karadere segment rupture on the karadere segment was arrested by the 2 to 4 km wide eften lake step over modeling of the transient stress field associated with the rupture propagation agrees well with the field observations the modeled fault rupture of 5 m on the golcuk segment appears to decrease the transient stress on the eastern tip of the adjoining yalova segment across the 4 to 5 km wide karamursel step over even if we allow rupture on the golcuk segment to extend along the entire southern margin of the step over our model shows that regardless of the amount of slip in a generic sense it is difficult to increase stress on the tip of an adjoining fault segment across a 5 km wide step over on the other hand fault rupture of 3 m on the western tip of the sapanca fault segment significantly increases the transient stress on the adjoining sakarya segment across the 1 to 2 km wide sapanca step over allowing rupture propagation across the basin an evaluation of 30 historical strike slip earthquakes involving 59 step over basins supports our field observations and stress modeling of the izmit fault rupture historical strike slip events with small to large displacements usually propagate through step overs less than 1 2 km wide with increasing displacement larger and larger step overs can be ruptured through the empirical data generally show a ratio ranging from 2 1 to 1 1 between step over width in kilometers and strike slip displacement in meters for a through going rupture however step overs of 4 to 5 km width appear to always arrest fault rupture regardless of the amount of displacement these results therefore provide important constraints for evaluating the probability of multisegment ruptures on segmented strike slip faults manuscript received 20 august 2000

deep structure of the west african continental margin congo zaire angola between 5 s and 8 s from reflection refraction seismics and gravity data summary the deep structure of the west african continental margin between 5 s and 8 s was investigated using vertical reflection and wide angle reflection refraction techniques during the zaiango project a joint programme conducted in 2000 april by ifremer and totalfinaelf to penetrate below the salt layer a non conventional low frequency seismic source was used in the single bubble mode together with ocean bottom instruments hydrophones and seismometers and a 4 5 km long streamer that recorded multichannel seismic reflection mcs the data show that the continental crust thins abruptly over a lateral distance of less than 50 km from 30 km thick below the continental platform based on gravity data to less than 4 km thick below the lower congo basin that formed prior to the aptian salt deposition this subsalt sedimentary basin 180 km wide 4 km thick with velocities varying from 4 7 km s 1 to 5 8 km s 1 at the bottom is located between the foot of the continental slope and the oceanic domain it is underlain by crust of an intermediary or transitional type between continental crust and what can be recognized as oceanic crust in the transitional zone a crustal upper layer is present below the pre salt sedimentary basin 3 to 7 km thick with velocities increasing from 5 8 km s 1 at the top to 6 8 km s 1 at the bottom of the layer this layer appears to thin regularly from 6 7 km thick below the depocentre of the pre salt sedimentary basin to 3 4 km thick below the western termination of the basin below this upper crustal layer an anomalous velocity layer 7 2 to 7 8 km s 1 is documented below the eastern side of the basin where the crustal thinning is at a maximum the origin of this layer is unknown several arguments like rifting duration between 15 ma and 30 ma or the absence of seaward dipping reflectors precludes the hypothesis of underplated mantle material but other hypotheses such as serpentinized material or high grade metamorphic crustal rocks or a mixture of mafic and ultramafic crustal rocks are plausible near the ocean termination of the basin the transitional zone is bounded to the west by a basement ridge that is clearly documented on two profiles 7 11 and 14 having a dense ocean bottom seismometer hydrophone obs obh spacing on these profiles an anomalous velocity layer is present in the westernmost part of the transitional zone below the basement ridge and in the oceanic domain this layer absent on profile 3 may be related either to oceanization and slow seafloor spreading processes or to a consequence of the rifting process

the role of the zagros orogeny in slowing down arabia eurasia convergence since 5 ma 1 large topographic belts along convergent margins have been recognized with the ability to slowdown the kinematics of subduction over geologically short time periods i e few myr because their associated gravitational spreading provides significant resistive force within the framework of plate tectonics the record of past and present day plate kinematics provides important constraints on the dynamics of the lithosphere because plate motion changes must reflect temporal changes in the balance of driving and resisting forces here we focus on the convergence between the arabian and eurasian plates across the zagros mountain belt relative motion across this plate boundary is reconstructed since 13 ma from published paleomagnetic and geodetic data and features a slowdown of 30 from 5 ma to the present day we employ global dynamic models of the mantle lithosphere system to test whether the most recent uplift across the arabia eurasia collision zone including the zagros orogeny may induce the observed slowdown since 5 ma specifically we use constraints from the geologic record to infer past topography and quantify its influence on the convergence rate between arabia and eurasia we test the sensitivity of our models to assumptions made in estimating the paleoelevation by perturbing the orogeny parameterization within reasonable ranges finally we speculate on the potential effects of tethys slab break off changes of the deformation style within the collision zone and the afar plume on the dynamics of convergence our results indicate that orogenic uplift across the arabia eurasia collision zone played a key role in slowing down convergence since 5 ma

building the zagros collisional orogen timing strain distribution and the dynamics of arabia eurasia plate convergence he zagros mountains are the result of the arabia eurasia collision initiated at 35 ma as the rifted arabian lithosphere was underthrusted beneath the iranian plate due to its negative buoyancy the onset of crustal thickening started at 25 ma as recorded by the hinterland exhumation and foreland clastic deposition deformation throughout the arabia eurasia collision zone and the uplift of the iranian plateau occurred after 15 12 ma as a result of shortening thickening of the thin iranian crust we emphasize that only 42 of the post 35 ma convergence is partitioned by shortening within central iran tomographic constraints show ongoing slab steepening or breakoff in the nw zagros whereas underthrusting of the arabian plate is observed beneath central zagros the current subduction dynamics can be explained by the original lateral difference in the buoyancy of the distal margin that promoted slab sinking in nw zagros and underthrusting in central zagros critical wedge approach applied to the zagros favors the hypothesis of strong brittle crust detached above a viscous lower crust in contrast the weak sedimentary cover deforms by buckling of a thick multilayered cover thrust faulting associated with folding occurs in the competent layers and is responsible for most of the earthquakes there is evidence that the role of the slab pull force in driving the arabian plate motion was reduced after 12 ma large scale mantle flow induced by mantle upwelling at the afar plume appears to be the main driver of the arabia plate motion we stress that the main kinematic change in the zagros region occurred at 15 12 ma as the zagros uplifted before the arabian slab detached the zagros appears key to investigate coupling between continental rheology plate driving forces and mountain building in which the role of rift inheritance appears to be central

thickness of the oceanic crust the lithosphere and the mantle transition zone in the vicinity of the tristan da cunha hot spot estimated from ocean bottom and ocean island seismometer receiver functions highlights receiver functions from ocean bottom seismometer stations reveal no significant crustal thickening in the surrounding of the tristan da cunha hot spot the mantle transition zone to the nw of tristan da cunha is thickened and cool the mantle transition zone is potentially thinned to the south southwest of tristan da cunha a thickness of 60 to 75 km beneath tristan da cunha argues for a compositional control on the seismological lithosphere in the south atlantic abstract the most prominent hotspot in the south atlantic is tristan da cunha which is widely considered to be underlain by a mantle plume but the existence location and size of this mantle plume have not been established due to the lack of regional geophysical observations a passive seismic experiment using ocean bottom seismometers aims to investigate the lithosphere and upper mantle structure beneath the hotspot using the ps receiver function method we calculate a thickness of 5 to 8 km for the oceanic crust at 17 ocean bottom stations deployed around the islands within the errors of the method the thickness of the oceanic crust is very close to the global mean the tristan hotspot seems to have contributed little additional magmatic material or heat to the melting zone at the mid oceanic ridge which could be detected as thickened oceanic crust magmatic activity on the archipelago and surrounding seamounts seems to have only effected the crustal thickness locally furthermore we imaged the mantle transition zone discontinuities by analysing receiver functions at the permanent seismological station tris and surrounding obs stations our observations provide evidence for a thickened cold mantle transition zone west and northwest of the islands which excludes the presence of a deep reaching mantle plume we have some indications of a thinned hot mantle transition zone south of tristan da cunha inferred from sparse and noisy observations which might indicate the location of a tristan mantle plume at mid mantle depths sp receiver functions image the base of lithosphere at about 60 to 75 km beneath the islands which argues for a compositionally controlled seismological lithosphere asthenosphere boundary beneath the study area

large river offsets and plio quaternary dextral slip rate on the red river fault yunnan china using multispectral spot images and 1 100 000 topographic data we present an improved map of the active red river fault zone between midu yunnan china and hanoi vietnam the fault zone is composed of parallel strands one of which the yuanjiang fault was previously undetected there also appears to be a component of extension all along the fault zone such extension increases toward the se from yunnan to the south china sea coast and the vector describing the motion of south china relative to indochina points within the n45 135 e quadrant we attempt to assess the plio quaternary dextral slip rate on the red river fault rrf by restoring large river offsets and searching for the largest plausible one across much of yunnan the fault is perpendicular to local catchments that drain into the red river from precise mapping of the river courses on spot satellite images and on 1 100 000 topographic maps numerous multiple offsets along the fault can be detected and reconstructed the lack of correlation between the apparent offsets and the lengths of the rivers upstream from the fault suggests either that the drainage system was in large part established prior to the onset of dextral slip along the fault or that frequent captures have occurred we thus try to find the best fit between series of river channels upstream and downstream from the fault by progressively restoring the dextral displacement in increments of 500 m up to an offset of 50 km for each increment we measure the misfits root mean squares rms between the upstream and downstream channels the best fit and smallest rms are obtained for an offset of 25 0 5 km that we interpret to represent the clearest large right lateral displacement recorded in the geomorphology along the active red river fault since dextral motion is likely to have started around 5 myr the most probable average plio quaternary slip rate on the fault is of order of 5 mm yr we attribute the apparent lack of seismic activity on a large stretch of the fault to millennial recurrence times between great earthquakes our study shows that relatively small drainage systems can keep a good record of fairly large cumulative fault offsets

comparisons of the kinematics and deep structures of the zagros and himalaya and of the iranian and tibetan plateaus and geodynamic implications 1 we compare the geologic histories the deep structures and the present day kinematics of deformation of the himalaya and the adjacent tibetan plateau with those of the zagros and iranian plateau to test geodynamic processes of continental collision shortly after india and arabia collided with eurasia horizontal shortening manifested itself by folding and thrust faulting of sedimentary rock detached from india s and arabia s underlying crystalline basement subsequently slip on thrust faults stacked slices of india s basement to build the himalaya on india s northern margin such faulting has not yet developed in the zagros where collision is more recent and arabia penetrates into eurasia more slowly than india does so that postcollision convergence with eurasia is less the greater elevation thicker crust and more marked heterogeneity of the upper mantle beneath the tibetan than beneath the iranian plateau also reflect a more advanced stage of development moreover while thrust or reverse faulting and crustal shortening continue on the margins of both plateaus normal faulting suggesting horizontal extension and crustal thinning occurs within tibet but not in iran hence the balance of forces that built the high tibetan plateau must have changed apparently some time since 15 ma removal of tibetan mantle lithosphere could have altered that balance if mantle lithosphere beneath the iranian plateau has been removed however the change in force balance has been too small to initiate normal faulting low seismic wave speeds in the uppermost mantle just beneath the moho of both plateaus suggest to us that lithosphere beneath both is thin consistent with late cenozoic removal of it but alternative explanations might account for these low speeds despite its apparently thin and hence presumably weak mantle lithosphere much of central iran undergoes little deformation it illustrates how a crustal block can behave rigidly not necessarily because it is strong but because deviatoric stresses can be small whereas differences between the two regions clearly depend on the amount that arabia and india have penetrated into eurasia which scales with both the dates of collision and rates of convergence we see no differences in the operative processes that depend on the present day rates of convergence

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

multi phased uplift of the southern margin of the central anatolian plateau turkey a record of tectonic and upper mantle processes abstract uplifted neogene marine sediments and quaternary fluvial terraces in the mut basin southern turkey reveal a detailed history of surface uplift along the southern margin of the central anatolian plateau from the late miocene to the present new surface exposure ages 10be 26al and 21ne of gravels capping fluvial strath terraces located between 28 and 135 m above the goksu river in the mut basin yield ages ranging from ca 25 to 130 ka corresponding to an average incision rate of 0 52 to 0 67 mm yr published biostratigraphic data combined with new interpretations of the fossil assemblages from uplifted marine sediments reveal average uplift rates of 0 25 to 0 37 mm yr since late miocene time starting between 8 and 5 45 ma and 0 72 to 0 74 mm yr after 1 66 to 1 62 ma together with the terrace abandonment ages the data imply 0 6 to 0 7 mm yr uplift rates from 1 6 ma to the present the different post late miocene and post 1 6 ma uplift rates can imply increasing uplift rates through time or multi phased uplift with slow uplift or subsidence in between longitudinal profiles of rivers in the upper catchment of the mut and ermenek basins show no apparent lithologic or fault control on some knickpoints that occur at 1 2 to 1 5 km elevation implying a transient response to a change in uplift rates projections of graded upper relict channel segments to the modern outlet together with constraints from uplifted marine sediments show that a slower incision uplift rate of 0 1 to 0 2 mm yr preceded the 0 7 mm yr uplift rate the river morphology and profile projections therefore reflect multi phased uplift of the plateau margin rather than steadily increasing uplift rates multi phased uplift can be explained by lithospheric slab break off and possibly also the arrival of the eratosthenes seamount at the collision zone south of cyprus

offset and evolution of the gowk fault s e iran a major intra continental strike slip system abstract we use drainage reconstructions to estimate long term offsets on the gowk fault an oblique right lateral strike slip fault in eastern iran on which there have been a number of recent large earthquakes a 3 km horizontal offset is inferred from well preserved geomorphology we further identify a total cumulative offset of 12 km which produces a simple reconstruction of geomorphology across the fault filling in pull apart basins restoring rivers to linear courses across the fault trace and aligning structural and bed rock features the probable age of the gowk fault and k ar dating of offset basalts north of the study region suggest an overall slip rate of 1 5 2 4 mm year this is small compared with the overall 10 20 mm year of shear expected between central iran and afghanistan and the deficit is likely to have been accommodated on other faults east of the gowk fault drainage displaced by dextral movement leads to the development of a series of basins along the fault and a longitudinal topographic profile that resembles an asymmetric saw tooth the geomorphic evolution of the fault zone at the surface includes both normal and reverse faulting components reflecting a probable ramp and flat structure in cross section this interpretation is consistent with evidence from the analysis of seismological radar and surface rupture data in recent earthquakes

crustal intrusion beneath the louisville hotspot track we report here the first detailed 2d tomographic image of the crust and upper mantle structure of a cretaceous seamount that formed during the interaction of the pacific plate and the louisville hotspot results show that at 1 5 km beneath the seamount summit the core of the volcanic edifice appears to be dominantly intrusive with velocities faster than 6 5 km s the edifice overlies both high lower crustal 7 2 7 6 km s and upper mantle 8 3 km s velocities suggesting that ultramafic rocks have been intruded as sills rather than underplated beneath the crust the results suggest that the ratio between the volume of intra crustal magmatic intrusion and extrusive volcanism is as high as 4 5 in addition the inversion of moho reflections shows that the pacific oceanic crust has been flexed downward by up to 2 5 km beneath the seamount the flexure can be explained by an elastic plate model in which the seamount emplaced upon oceanic lithosphere that was 10 myr at the time of loading intra crustal magmatic intrusion may be a feature of hotspot volcanism at young hot oceanic lithosphere whereas magmatic underplating below a pre existing moho may be more likely to occur where a hotspot interacts with oceanic lithosphere that is several tens of millions of years old

fluvial incision and tectonic uplift across the himalayas of central nepal the pattern of fluvial incision across the himalayas of central nepal is estimated from the distribution of holocene and pleistocene terraces and from the geometry of modern channels along major rivers draining across the range the terraces provide good constraints on incision rates across the himalayan frontal folds sub himalaya or siwaliks hills where rivers are forced to cut down into rising anticlines and have abandoned numerous strath terraces farther north and upstream in the lesser himalaya prominent fill terraces were deposited probably during the late pleistocene and were subsequently incised the amount of bedrock incision beneath the fill deposits is generally small suggesting a slow rate of fluvial incision in the lesser himalaya the terrace record is lost in the high range where the rivers are cutting steep gorges to complement the terrace study fluvial incision was also estimated from the modern channel geometries using an estimate of the shear stress exerted by the flowing water at the bottom of the channel as a proxy for river incision rate this approach allows quantification of the effect of variations in channel slope width and discharge on the incision rate of a river the determination of incision rates requires an additional lithological calibration the two approaches are shown to yield consistent results when applied to the same reach or if incision profiles along nearby parallel reaches are compared in the sub himalaya river incision is rapid with values up to 10 15 mm yr it does not exceed a few millimeters per year in the lesser himalaya and rises abruptly at the front of the high range to reach values of 4 8 mm yr within a 50 km wide zone that coincides with the position of the highest himalayan peaks sediment yield derived from the measurement of suspended load in himalayan rivers suggests that fluvial incision drives hillslope denudation of the landscape at the scale of the whole range the observed pattern of erosion is found to closely mimic uplift as predicted by a mechanical model taking into account erosion and slip along the flat ramp flat geometry of the main himalayan thrust fault the morphology of the range reflects a dynamic equilibrium between present day tectonics and surface processes the sharp relief together with the high uplift rates in the higher himalaya reflects thrusting over the midcrustal ramp rather than the isostatic response to reincision of the tibetan plateau driven by late cenozoic climate change or late miocene reactivation of the main central thrust

crustal structures of the boreas basin and the knipovich ridge north atlantic the boreas basin is located in the norwegian greenland sea between northeast greenland and svalbard towards the east it is bounded by the ultraslow mid ocean knipovich ridge here we present a 340 km long seismic refraction line acquired during the expedition ark xxiv 3 of research vessel polarstern in 2009 using 18 ocean bottom seismometers it crosses the central boreas basin from the knipovich ridge to the northeast greenland margin thus the line provides the first reliable crustal structure information of this basin in addition the gravity data acquired parallel to the seismic refraction line are used to calculate a 2 5 d gravity model the p wave velocity model shows an unusual 3 km thin oceanic crust with seismic velocities less than 6 3 km s 1 indicating the absence of a significant oceanic layer 3 mantle velocities vary between 7 5 kms 1 in the uppermost mantle and 8 0 km s 1 at approximately 15 km depth the low velocities within the upper mantle may be explained by 13 per cent serpentinisation which is negligible at about 15 km depth furthermore the s wave velocity model shows low vp vs ratios in the mantle indicating a highly serpentinised mantle at shallow depths the gravity model has crustal densities between 2 3 and 2 9 g cm 3 which also point towards the absence of a significant thick oceanic layer 3 the results of our seismic refraction line and other geophysical data indicate that the entire boreas basin opened at ultraslow spreading rates since at least 28 ma no evidence for an extinct spreading ridge in the centre of the boreas basin was found

solutions of the stream power equation and application to the evolution of river longitudinal profiles 1 erosion by bedrock river channels is commonly modeled with the stream power equation we present a two part approach to solving this nonlinear equation analytically and explore the implications for evolving river profiles first a method for non dimensionalizing the stream power equation transforms river profiles in steady state with respect to uniform uplift into a straight line in dimensionless distance elevation space second a method that tracks the upstream migration of slope patches which are mathematical entities that carry information about downstream river states provides a basis for constructing analytical solutions slope patch analysis explains why the transient morphology of dimensionless river profiles differs fundamentally if the exponent on channel slope n is less than or greater than one and why only concave up migrating knickpoints persist when n 1 at migrating knickpoints slope patches and the information they carry are lost a phenomenon that fundamentally limits the potential for reconstructing tectonic histories from bedrock river profiles stationary knickpoints which can arise from spatially varying uplift rates differ from migrating knickpoints in that slope patches and the information they carry are not lost counterparts to migrating knickpoints called stretch zones are created when closely spaced slope patches spread to form smooth curves in distance elevation space these theoretical results are illustrated with examples from the california king range and the central apennines

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

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

south atlantic opening a plume induced breakup upwelling hot mantle plumes are thought to disintegrate continental lithosphere and are considered to be drivers of active continental breakup the formation of the walvis ridge during the opening of the south atlantic is related to a putative plume induced breakup we investigated the crustal structure of the walvis ridge southeast atlantic ocean at its intersection with the continental margin and searched for anomalies related to the possible plume head the overall structure we identify suggests that no broad plume head existed during opening of the south atlantic and anomalous mantle melting occurred only locally we therefore question the importance of a plume head as a driver of continental breakup and further speculate that the hotspot was present before the rifting leaving a track of kimberlites in the african craton

crustal structure of a super slow spreading centre a seismic refraction study of mohns ridge 72 n summary a series of eight high resolution seismic refraction profiles from the ultra slow spreading 16 mm yr 1 full spreading rate mohns ridge in the norwegian greenland sea has been treated with modern inversion methods the profiles were shot parallel to the ridge at an off axis distance of 0 135 km corresponding to crustal ages of 0 22 ma the resulting models are constrained by synthetic seismograms and gravity modelling the crustal thickness in all profiles is well below the global average for typical oceanic crust and shows a high variability with a mean thickness of 4 0 0 5 km this is mainly due to a very thin and variable lower crustal layer layer 3 generally the crust is thicker beneath basement highs and thinner beneath basins implying local isostatic compensation the top of the basement layer 2a consists of a zone with low p wave velocities 2 5 3 0 km s 1 the mean thickness of this layer decreases with distance from the ridge beneath it lies a layer with slightly higher velocities layer 2b its thickness shows less variability along a given profile and an overall increase with age the combined average thickness of the upper two layers remains nearly constant indicating that the boundary between layer 2a and 2b may represent an alteration front upper mantle velocities are generally slow around 7 5 km s 1 for the profile directly within the rift valley a model without a third layer incorporating a constant gradient up to upper mantle velocities and a model with a moho depth inferred from neighbouring profiles and upper mantle velocity as slow as 7 2 km s 1 fit the seismic and gravity data equally well the crustal structure is not mature below the ridge these observations support previous models suggesting the presence of low densities and velocities at about 2 km below the rift axis poisson s ratios determined from converted s wave modelling are incompatible with a layer 3 consisting of purely serpentinized peridotite however a volume fraction of 10 40 per cent serpentinite cannot be ruled out

late cenozoic reorganization of the arabia eurasia collision and the comparison of short term and long term deformation rates the arabia eurasia collision deforms an area of 3 000 000 km2 of continental crust making it one of the largest regions of convergent deformation on earth there are now estimates for the active slip rates total convergence and timing of collision related deformation of regions from western turkey to eastern iran this paper shows that extrapolating the present day slip rates of many active fault systems for 3 7 million years accounts for their total displacement this result means that the present kinematics of the arabia eurasia collision are unlikely be the same as at its start which was probably in the early miocene 16 23 ma or earlier in some but not all active fault systems short term 10 year and long term 5 million year average deformation rates are consistent there is little active thickening across the turkish iranian plateau and possibly the interior of the greater caucasus these are two areas where present shortening rates would need more than 7 million years to account for the total crustal thickening and where there are structural and or stratigraphic data for pre late miocene deformation we suggest that once thick crust up to 60 km built up in the turkish iranian plateau and the greater caucasus convergence took place more easily by crustal shortening in less elevated regions such as the zagros simple folded zone the south caspian region and foothills of the greater caucasus or in other ways such as westward transport of turkey between the north and east anatolian faults the time and duration of this changeover are not known for certain and are likely be diachronous although deformation started or intensified in many of the currently active fault systems at 5 2 ma

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

crustal thickness and earthquake distribution south of the logachev seamount knipovich ridge 1 during rv polarstern cruise ark xxiv 3 2009 a geophysical study along the ultraslow spreading knipovich ridge was conducted the survey located in the rift valley south of the logachev seamount 76 36 n provides a crustal thickness of 4 5 km in the amagmatic parts and 5 7 km underneath the seamount itself the velocity depth function indicates the presence of a thick oceanic layer 2 4 5 km but no indication for a thick oceanic layer 3 the only exception is the area underneath the logachev seamount where velocities higher than 6 km s are detected this indicates a stronger and focussed melt supply underneath the seamount local seismicity was analysed for two days in total 191 quakes were identified in the vicinity of the rift valley with magnitudes up to ml 2 6 at least 48 of them are located in the upper mantle up to 18 km below sea level supporting models predicting a cold mantle or conductive cooling underneath ultraslow ridges to explain the reduced melt supply

a fluvial record of active fault propagation folding salsomaggiore anticline northern apennines italy 1 fault propagation folds offer the potential to relate folding to underlying fault propagation and slip provided that fold kinematics can be established fluvial terraces have been recognized as kinematic indicators but precise relationships between surface uplift and various folding mechanisms remain largely unexplored this study takes advantage of a well preserved progressively deformed suite of middle pleistocene to recent fluvial terraces above a growing fault propagation fold at the apennine mountain front northern italy to constrain the recent fold kinematics and place them in the context of a longer growth history gleaned from older growth strata the geometry of straths and overlying terrace deposits defines a fixed anticlinal hinge a rolling synclinal hinge proxies for fault tip propagation rates rock uplift rates and tilting rates and how these features and rates vary over the last 800 ka along 15 km of strike length field studies are augmented with dem based quantitative geomorphic analyses that document catchment hypsometry mean anticlinal hinge elevation and long profile form notably long term rock uplift rates using incision as a proxy are uniformly correlated with fault propagation and associated synclinal hinge migration mean anticlinal hinge elevation and variations in catchment hypsometries channels that cross the forelimb at a high angle to the fold hinge generally have higher concavities but channel steepness commonly thought to reflect rock uplift is more strongly adjusted to rock type this study elucidates a new understanding of a complex fold growth history extending back at least 10 ma and provides a novel demonstration of how fluvial terraces may be utilized to constrain fault related fold kinematics

uplift driven valley incision and climate controlled river terrace development in the thames valley uk abstract the sequence of terraces of the river thames in southeast england has previously been shown to span the period from the earliest pleistocene to the present this terrace sequence contains biostratigraphical and sedimentary evidence that testifies to the high amplitude climatic changes of the quaternary large scale fluvial incision resulting in basin wide terrace formation appears to have been concentrated at the warming limbs of the major climatic glacial interglacial cycles when sediment supply was greatly reduced this incision and subsequent valley floor widening created the accommodation space for the later aggradation of the terrace sediments during the following warm cold transitions and during the cold stages when high sediment supply conditions prevailed although the timing of terrace aggradation may be controlled by climate change the progressive valley incision recorded by terrace staircases cannot easily be explained in terms of quaternary climatic change alone and recently developed models suggest that long term incision by the thames has been driven by uplift this paper presents an overview of the available terrace data and tabulates incision amounts and rates between key stratigraphic horizons superimposed upon these broad changes revealed by the complex internal sedimentary architecture of many terrace sediments are the geomorphological system responses to both higher frequency climate driven changes and more localized intrinsic fluvial system adjustments

gps constraints on continental deformation in the africa arabia eurasia continental collision zone and implications for the dynamics of plate interactions 1 the gps derived velocity field 1988 2005 for the zone of interaction of the arabian african nubian somalian and eurasian plates indicates counterclockwise rotation of a broad area of the earth s surface including the arabian plate adjacent parts of the zagros and central iran turkey and the aegean peloponnesus relative to eurasia at rates in the range of 20 30 mm yr this relatively rapid motion occurs within the framework of the slow moving 5 mm yr relative motions eurasian nubian and somalian plates the circulatory pattern of motion increases in rate toward the hellenic trench system we develop an elastic block model to constrain present day plate motions relative euler vectors regional deformation within the interplate zone and slip rates for major faults substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below 1 2 mm yr including central and eastern anatolia turkey the southwestern aegean peloponnesus the lesser caucasus and central iran geodetic slip rates for major block bounding structures are mostly comparable to geologic rates estimated for the most recent geological period 3 5 myr we find that the convergence of arabia with eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the caucasus and zagros mountain belts around the periphery of the collision zone in addition we find that the principal boundary between the westerly moving anatolian plate and arabia east anatolian fault is presently characterized by pure left lateral strike slip with no fault normal convergence this implies that extrusion is not presently inducing westward motion of anatolia on the basis of the observed kinematics we hypothesize that deformation in the africa arabia eurasia collision zone is driven in large part by rollback of the subducting african lithosphere beneath the hellenic and cyprus trenches aided by slab pull on the southeastern side of the subducting arabian plate along the makran subduction zone we further suggest that the separation of arabia from africa is a response to plate motions induced by active subduction

climatically controlled river terrace staircases a worldwide quaternary phenomenon a comparison of fluvial terrace sequences from around the world based on data collected as part of international geoscience programme igcp project no 449 has revealed significant patterns river terraces provide important records of uplift which is essential for their formation and of landscape evolution their cyclic formation however almost invariably seems to have been a response to climatic fluctuation sequences in the european core area of igcp 449 which has the longest and most extensive research history have been used as templates for worldwide comparison there is evidence for a global acceleration of uplift at the time of and perhaps in response to the mid pleistocene revolution when climatic fluctuation switched to 100 kyr milankovitch cycles terraces formed prior to this generally consist of wide aggradational sheets that probably each represent formation over several 41 kyr cycles subsequently river valleys became more steeply entrenched and terraces formed in response to the stronger 100 kyr climatic forcing in many cases at approximately one per cycle this paper uses the new data resource to explore differences between records in different climate zones between sequences with variable numbers of middle late pleistocene terraces and between systems in which the all important incision event has occurred in different parts of climatic cycles key records discussed include european examples from the rhine thames somme dniester dnieper don volga and aguas from asia the gediz turkey and orontes syria from north america the south platte and colorado from south africa the vaal and sundays from australia the shoalhaven and from south america the amazon paraguay and tributaries of the colorado and negro

the wide angle seismic image of a complex rifted margin offshore north namibia implications for the tectonics of continental breakup highlights up to 33 km thick dominantly gabbroic crust beneath walvis ridge massive gabbro addition with subjacent cumulates to the cob south of walvis ridge slow upper mantle at 35 km depth beneath etendeka plateau 4 6 km thick oceanic crust in the angola basin north of florianopolis transform velocity models suggest a dominant tectonic control on the location of magmatism abstract voluminous magmatism during the south atlantic opening has been considered as a classical example for plume related continental breakup we present a study of the crustal structure around walvis ridge near the intersection with the african margin two wide angle seismic profiles were acquired one is oriented nnw sse following the continent ocean transition and crossing walvis ridge a second amphibious profile runs nw se from the angola basin into continental namibia at the continent ocean boundary cob the mafic crust beneath walvis ridge is up to 33 km thick with a pronounced high velocity lower crustal body towards the south there is a smooth transition to 20 25 km thick crust underlying the cob in the walvis basin with a similar velocity structure indicating a gabbroic lower crust with associated cumulates at the base the northern boundary of walvis ridge towards the angola basin shows a sudden change to oceanic crust only 4 6 km thick coincident with the projection of the florianopolis fracture zone one of the most prominent tectonic features of the south atlantic ocean basin in the amphibious profile the cob is defined by a sharp transition from oceanic to rifted continental crust with a magmatic overprint landward of the intersection of walvis ridge with the namibian margin the continental crust beneath the congo craton is 40 km thick shoaling to 35 km further se the velocity models show that massive high velocity gabbroic intrusives are restricted to a narrow zone directly underneath walvis ridge and the cob in the south this distribution of rift related magmatism is not easily reconciled with models of continental breakup following the establishment of a large axially symmetric plume in the earth s mantle rift related lithospheric stretching and associated transform faulting play an overriding role in locating magmatism dividing the margin in a magma dominated southern and an essentially amagmatic northern segment

south pacific hotspot swells dynamically supported by mantle flows the dynamics of mantle plumes and the origin of their associated swells remain some of the most controversial topics in geodynamics here we construct a numerical model of the mantle flow beneath the french polynesia region our study is based on a new regional seismic tomography model which high resolution allows obtaining information at the scale of plumes we find excellent correlations between the observed and the modeled dynamic swells between the modeled flow pattern and the active volcanism and between the buoyancy fluxes obtained from our numerical model and the ones deduced from the swells morphology these outstanding fits reveal for the first time that a direct link exists between the surface observations and mantle flows