extension controls quaternary tectonics geomorphology and sedimentation of the n appennies foothills and adjacent po plain italy abstract in the middle pleistocene thrusting in the n apennine fold and thrust belt came to an end and foredeep sedimentation in the adjacent po plain basin ceased a new tectono sedimentary regime was installed extensional faults were activated in the foothills and are limited to the northeast by a major sw dipping normal fault the bologna fault for which a vertical displacement of 1000 m is estimated the region northeast of the fault i e its footwall was progressively tilted towards the po plain the sw sectors of the tilting region were progressively uplifted above sea level subjected to erosion thereby feeding a deltaic system which prograded towards the northeast in the subsiding regions compressional structures without major deformation are recorded in the zone of maximum curvature all these features are explained by the onset of extensional deformation along the bologna fault and consequent flexural unloading of its footwall the evidence therefore shows that the transition region between the n apennine foothills and po plain has been under a tensional stress regime since the middle pleistocene

a no net rotation model of present day surface motions a significant portion of the earth s surface consists of zones of diffuse deformation the interior regions of these diffuse zones of deformation move at distinctly different velocities from that of adjacent plates and because of their complexities have been ignored in previous no net rotation nnr models we have calculated a new nnr model from a continuous velocity field that incorporates both rigid plate motion and velocity gradients within plate boundary zones when compared with earlier nnr models we find significantly different angular velocities for many plates differences between the nnr model presented here and earlier nnr models can be attributed to the effect of including velocity gradients in diffuse plate boundary zones as well as to the actual differences between geodetically derived surface motions and geologic estimates

glacial isostatic adjustment observed using very long baseline interferometry and satellite laser ranging geodesy in global space geodetic solutions radial site motions are usually estimated relative to the geocenter the center of figure of the solid earth most geodesists estimate the motion of the geocenter assuming both that sites do not move radially and that sites move laterally as predicted by plate motion model nuvel 1a demets et al 1990 1994 here we estimate the motion of the geocenter assuming that the plate interiors deform radially and laterally as predicted by the postglacial rebound model of peltier 1994 or that of peltier 1996 without assuming a priori knowledge about relative plate motion radial site motions estimated relative to this rebound adjusted geocenter are in the same reference frame as the rebound model predictions whereas site motions estimated without adjusting for rebound are not we further constrain the motion of the rebound adjusted geocenter using satellite laser ranging s sensitivity to the center of mass of the solid earth the oceans and the atmosphere by assuming that the mean velocity between the rebound adjusted geocenter and the center of mass is negligible over the time period of geodetic measurement twenty years of observation with satellite laser ranging and very long baseline interferometry record the isostatic response of the solid earth to the unloading of the late pleistocene ice sheets the misfits of the postglacial rebound model of peltier 1994 and that of peltier 1996 are 34 and 16 less respectively than the misfit of the rigid plate model sites at onsala sweden and algonquin park ontario are observed to be rising at 3 mm yr and 2 mm yr respectively reflecting unloading of the fennoscandian and laurentide ice sheets sites along the east coast of the united states are subsiding at 2 mm yr indicating that the forebulge produced by the laurentide ice sheet is currently collapsing very slowly sites beneath the margins of the ice sheets during the last glacial maximum are currently moving laterally away from the ice sheet centers at 1 5 mm yr in disagreement with the moderately fast outward motion predicted by the model of peltier 1996

itrf2000 a new release of the international terrestrial reference frame for earth science applications 1 for the first time in the history of the international terrestrial reference frame the itrf2000 combines unconstrained space geodesy solutions that are free from any tectonic plate motion model minimum constraints are applied to these solutions solely in order to define the underlying terrestrial reference frame trf the itrf2000 origin is defined by the earth center of mass sensed by satellite laser ranging slr and its scale by slr and very long baseline interferometry its orientation is aligned to the itrf97 at epoch 1997 0 and its orientation time evolution follows conventionally that of the no net rotation nnr nuvel 1a model the itrf2000 orientation and its rate are implemented using a consistent geodetic method anchored over a selection of itrf sites of high geodetic quality ensuring a datum definition at the 1 mm level this new frame is the most extensive and accurate one ever developed containing about 800 stations located at about 500 sites with better distribution over the globe compared to past itrf versions but still with more site concentration in western europe and north america about 50 of station positions are determined to better than 1 cm and about 100 sites have their velocity estimated to at or better than 1 mm yr level the itrf2000 velocity field was used to estimate relative rotation poles for six major tectonic plates that are independent of the trf orientation rate a comparison to relative rotation poles of the nuvel 1a plate motion model shows vector differences ranging between 0 03 and 0 08 m y equivalent to approximately 1 7 mm yr over the earth s surface itrf2000 angular velocities for four plates relative to the pacific plate appear to be faster than those predicted by the nuvel 1a model the two most populated plates in terms of space geodetic sites north america and eurasia exhibit a relative euler rotation pole of about 0 056 0 005 m y faster than the pole predicted by nuvel 1a and located about 10 n 7 e more to the northwest compared to that model

coupled mantle dripping and lateral dragging controlling the lithosphere structure of the nw moroccan margin and the atlas mountains a numerical experiment abstract recent studies integrating gravity geoid surface heat flow elevation and seismic data indicate a prominent lithospheric mantle thickening beneath the nw moroccan margin lab 200 km depth followed by thinning beneath the atlas domain lab about 80 km depth such unusual configuration has been explained by the combination of mantle underthrusting due to oblique africa eurasia convergence together with viscous dripping fed by asymmetric lateral mantle dragging requiring a strong crust mantle decoupling in the present work we examine the physical conditions under which the proposed asymmetric mantle drip and drag mechanism can reproduce this lithospheric configuration we also analyse the influence of varying the kinematic boundary conditions as well as the mantle viscosity and the initial lithosphere geometry results indicate that the proposed drip drag mechanism is dynamically feasible and only requires a lateral variation of the lithospheric strength the further evolution of the gravitational instability can become either in convective removal of the lithospheric mantle mantle delamination or subduction initiation the model reproduces the main trends of the present day lithospheric geometry across the nw moroccan margin and the atlas mountains the characteristic time of the observed vertical movements the amplitude and rates of uplift in the atlas mountains and offers an explanation to the miocene to pliocene volcanism an abnormal constant tectonic subsidence rate in the margin is predicted

moment tensor inversion for iberia maghreb earthquakes 2005 2008 abstract we present and discuss a set of 77 moment tensor solutions for earthquakes in the iberia maghreb region from mid 2005 to the end of 2008 with moment magnitudes ranging from 3 2 to 6 0 inversion is based upon full three component intermediate period waveforms recorded at regional seismic broadband stations following the recent densification of permanent broadband networks and large scale temporary deployments at present more than 150 stations are recording in spain portugal and morocco this unprecedented station density allows analysis of small events from available short distance recordings and in general leads to more reliable source estimates due to data redundancies that permit elimination of waveforms affected by noise or complicated propagation effects the solutions for 2005 2008 constitute an important upgrade of the iberia maghreb moment tensor inventory to 225 solutions to date enhancing the image of seismotectonics at the compressive n algerian margin in the betic alboran shear zone and at the transpressive sw iberian margin as well as providing valuable constraints on seismic deformation in the western betics and the iberian foreland where little information has been previously available new solutions for the foreland and three recent seismic series in the western betics show strike slip and reverse faulting style contrasting with the dominance of normal faulting in the adjacent areas towards east in these areas as well as at the sw iberian margin faulting orientations are heterogeneous including solutions with opposite kinematics this indicates control by local stress conditions and points to fault interaction along the n algerian margin a counterclockwise rotation of slip vectors of thrust events from east to west becomes apparent several solutions for the area offshore cape st vincent are located at sub moho depths between 40 and 60 km supporting a large brittle layer thickness in the oceanic lithosphere

episodic tectonic plate reorganizations driven by mantle convection abstract periods of relatively uniform plate motion were interrupted several times throughout the cenozoic and mesozoic by rapid plate reorganization events r hey geol soc am bull 88 1977 1404 1420 p a rona e s richardson earth planet sci lett 40 1978 1 11 d c engebretson a cox r g gordon geol soc am spec pap 206 1985 r g gordon d m jurdy j geophys res 91 1986 12389 12406 d a clague g b dalrymple us geol surv prof pap 1350 1987 5 54 j m stock p molnar nature 325 1987 495 499 c lithgow bertelloni m a richards geophys res lett 22 1995 1317 1320 m a richards c lithgow bertelloni earth planet sci lett 137 1996 19 27 c lithgow bertelloni m a richards rev geophys 36 1998 27 78 it has been proposed that changes in plate boundary forces are responsible for these events m a richards c lithgow bertelloni earth planet sci lett 137 1996 19 27 c lithgow bertelloni m a richards rev geophys 36 1998 27 78 we present an alternative hypothesis convection driven plate motions are intrinsically unstable due to a buoyant instability that develops as a result of the influence of plates on an internally heated mantle this instability which has not been described before is responsible for episodic reorganizations of plate motion numerical mantle convection experiments demonstrate that high rayleigh number convection with internal heating and surface plates is sufficient to induce plate reorganization events changes in plate boundary forces or plate geometry are not required

intraplate deformation in western europe deduced from an analysis of the international terrestrial reference frame 1997 itrf97 velocity field although tectonic deformation in western europe is essentially concentrated in the appenines and alpine alps pyrenees mountain ranges several large historical and instrumentally recorded earthquakes m 6 are known in the supposedly stable part of europe because of its accuracy and internal consistency at a global scale the international terrestrial reference frame 1997 itrf97 velocity field allows testing of intraplate rigidity in western europe at a millimeter per year level using the full statistical information available on the itrf97 velocities we identify a subset of sites located in central europe that satisfies a rigid cap rotation with residual velocities 1 mm yr and therefore provide a stable europe reference frame serf in this reference frame we find residual velocities at european itrf sites that are consistent with known active tectonic features we identify a northward motion at sites located in italy with internal deformation of the adriatic block rather than rigid plate motion and a westward motion of the westernmost part of europe of the order of 1 2 mm yr relative to central europe the relative motion of the adriatic block and western europe agrees with the current extension known in the tyrrhenian sea and the apennines in central europe we find active deformation 1 mm yr in the eastern alps and western carpathians in the alpine range our results indicate e w extension across the western alps and n s compression across the central and eastern alps in agreement with the strain regime deduced from seismotectonic observations in belgium and the netherlands we find residual velocities of 1 1 5 mm yr to the northwest at all the sites most likely accommodated along the upper and lower rhine graben structures an important outcome of this study is the identification of internal deformation of the order of 1 2 mm yr in an area usually interpreted as stable europe this result should be further checked as new denser and more accurate space geodetic data sets with longer observation time spans become available for europe

evidence for motion between nubia and somalia along the southwest indian ridge the east african rift marks the northern boundary of the nubian west african and somalian east african plates and has formed by horizontal stretching due to the separation of these plates1 south of 20 s any expression of deformation or seismicity due to the relative motion of these two distinct plates vanishes although the boundary must continue until it intersects another plate boundary the nearest such boundary is that of the antarctic plate marked by the southwest indian ridge but previous analyses of plate motion data have indicated no significant difference between nubia antarctica and somalia antarctica motion2 3 here we show using a large compilation of plate motion data that nubia antarctica motion does differ from somalia antarctica motion and we determine a relative angular velocity of the two plates that has compact confidence limits our analysis places the pole of rotation near to the southern limit of african seismicity implying that the southern part of the nubian somalian plate boundary is a diffuse zone of convergence up to 2 mm yr 1 whereas up to 6 mm yr 1 of separation is accommodated across the east african rift about half the separation rate of the slowest mid ocean ridge

geodetic constraints on the rigidity and relative motion of eurasia and north america gps observations in northeastern asia when combined with observations from the global network for the period 1992 1999 yield an angular rotation vector between eurasia and north america consistent with and a factor of two more precise than estimates derived using gps or vlbi data previously available from only western eurasia the new vector implies a pole of relative rotation 1200 km more to the northwest than predicted by the nuvel 1a global plate model suggesting a significant change in the relative motion of eurasia and north america over the past 3 myr the standard deviations of horizontal velocities from rigid plate motion for nineteen stations in eurasia and ten in north america are less than 1 mm yr the observations place an upper bound of 2 mm yr at 95 confidence for relative motion between western and eastern eurasia

revised history of early tertiary plate motion in the south west pacific reanalysis of early tertiary magnetic anomalies on the pacific plate south of the campbell plateau indicates that in early tertiary time there was a previously unrecognized triple junction of the pacific the antarctic and a third plate now beneath the bellingshausen sea corresponding revised parameters for pacific antarctica motion do not require early tertiary displacements within antarctica or new zealand but suggest a change in direction of the pacific plate over the hotspots of approximately the same sense and timing as the hawaiian emperor bend

east west extension and holocene normal fault scarps in the hellenic arc examination of surface fault traces with spot images and in the field corroborates the inference that the active tectonics of southern peloponnesus and crete are dominated by approximately north south normal faulting and approximately east west extension the heights of holocene normal fault scarps yield first order regional estimates of fault slip rates between 0 1 and 2 3 mm yr most of the surface scarps probably ruptured during past earthquakes such as that which destroyed sparta in 464 b c on the sparta fault the holocene average slip rate and the recurrence time of large earthquakes may be 1 mm yr and 3000 yr respectively the regional pattern of quaternary faulting suggests that the east west extension near the hellenic subduction zone is fast about 5 10 m y the change from north south to east west extension in the late pliocene 2 4 ma implies that the aegean is starting to collide with the northern margin of africa

seismic imaging of the eastern algerian margin off jijel integrating wide angle seismic modelling and multichannel seismic pre stack depth migration this study presents the results of a deep seismic survey across the north algerian margin based on the combination of 2 d multichannel and wide angle seismic data simultaneously recorded by 41 ocean bottom seismometers deployed along a north south line extending 180 km off jijel into the algerian offshore basin and 25 land stations deployed along a 100 km long line cutting through the lesser kabylia and the tellian thrust belt the final model obtained using forward modelling of the wide angle data and pre stack depth migration of the seismic reflection data provides an unprecedented view of the sedimentary and crustal structure of the margin the sedimentary layers in the algerian basin are 3 75 km thick to the north and up to 4 5 5 km thick at the foot of the margin they are characterized by seismic velocities from 1 9 to 3 8 km s 1 messinian salt formations are about 1 km thick in the study area and are modelled and imaged using a velocity between 3 7 and 3 8 km s 1 the crust in the deep sea basin is about 4 5 km thick and of oceanic origin presenting two distinct layers with a high gradient upper crust 4 7 6 1 km s 1 and a low gradient lower crust 6 2 7 1 km s 1 the upper mantle velocity is constrained to 7 9 km s 1 the ocean continent transition zone is very narrow between 15 and 20 km wide the continental crust reaches 25 km thickness as imaged from the most landward station and thins to 5 km over a less than 70 km distance the continental crust presents steep and asymmetric upper and lower crustal geometry possibly due to either asymmetric rifting of the margin an underplated body or flow of lower crustal material towards the ocean basin present time deformation as imaged from three additional seismic profiles is characterized by an interplay of gravity driven mobile salt creep and active thrusting at the foot of the tectonically inverted algerian margin

sea level change and vertical land movements since the last two millennia along the coasts of southwestern turkey and israel abstract this paper provides new relative sea level data inferred from coastal archaeological sites located along the turkish coasts of the gulf of fethye 8 sites and israel between akziv and caesarea 5 sites the structures selected are those that for effective functioning can be accurately related to sea level at the time of their construction thus their positions with respect to present sea level provide a measure of the relative sea level change since their time of construction useful information was obtained from the investigated sites spanning an age range of 2 3 1 6 ka bp the inferred changes in relative sea level for the two areas are distinctly different from a rise of 2 41 to 4 50 m in turkey and from 0 to 0 18 m in israel sea level change is the combination of several processes including vertical tectonics glacio hydro isostatic signals associated with the last glacial cycle and changes in ocean volume for the israel section the present elevations of the mis 5 5 tyrrhenian terraces occur at a few meters above present sea level and vertical tectonic displacements are small data from gps and tide gauge measurements also indicate that any recent vertical movements are small the mis 5 5 shorelines are absent from the investigated section of the turkish coast consistent with crustal subsidence associated with the hellenic arc the isostatic signals for the israel section of the coast are also small ranging from 0 11 mm yr to 0 14 mm yr depending on site and earth model and the observed eustatic average sea level change corrected for this contribution is a rise of 13 5 2 6 cm during the past 2 ka this is attributed to the time integrated contribution to sea level from a combination of thermal expansion and other increases in ocean volume the observed sea levels from the turkish sites in contrast indicate a much greater rise of up to 2 2 mm yr since 2 3 ka bp occurring in a wide area between knidos and kekova the isostatic signal here is also one of a rising sea level of up to 1 mm yr and site and earth model dependent and the corrected tectonic rate of land subsidence is 1 48 mm yr this is the primary cause of dramatic relative sea level rise for this part of the coast

tests of the rigid plate hypothesis and bounds on intraplate deformation using geodetic data from very long baseline interferometry the geodetic results of ma et al 1994 from very long baseline interferometry are used to assess rates of intraplate deformation we analyze the resulting set of velocities of 18 plate interior sites nine on the north american plate four western european sites on the eurasian plate three on the pacific plate and two on the australian plate we formulate three alternative error budgets based partly on the work of ryan et al 1993a an optimistic error budget a conservative error budget and an upper bound error budget all three budgets assume the existence of a previously unmodeled error that is inversely proportional to the time span of observations at a site use of the conservative error budget indicates no significant motion between sites on any one of the four plates use of the upper bound error budget designed to be precisely large enough to be consistent with rigid plates places a usefully small upper bound on how fast any site might be moving relative to the rest of its plate speeds faster than 2 mm yr are excluded at the 95 confidence level for seven of the 18 plate interior sites adjustments of the site velocities for motion due to postglacial rebound as predicted from the model of tushingham and peltier 1991 give an insignificant improvement to the fit of the horizontal velocities to the rigid plate model the velocities of six sites near the western margin of the interior of the north american plate were also analyzed use of the conservative error budget indicates that a site near fairbanks alaska has an upper bound of 3 mm yr on its speed a site in nome alaska has an upper bound on its speed of 8 mm yr and a site in penticton british columbia has an upper bound on its speed of 4 mm yr of three sites on the colorado plateau two move marginally significantly and one moves insignificantly relative to stable north america upper limits on their speeds relative to stable north america range from 4 to 5 mm yr we conclude that the data do not yet demonstrate significant velocities between sites in the stable interior of any one plate but do provide useful and small upper bounds of 2 mm yr or less on the speeds of the best observed intraplate sites six sites near the western margin of the north american interior have upper bound speeds of 3 to 8 mm yr

global plate velocities from the global positioning system we have analyzed 204 days of global positioning system gps data from the global gps network spanning january 1991 through march 1996 on the basis of these gps coordinate solutions we have estimated velocities for 38 sites mostly located on the interiors of the africa antarctica australia eurasia nazca north america pacific and south america plates the uncertainties of the horizontal velocity components range from 1 2 to 5 0 mm yr with the exception of sites on the pacific and nazca plates the gps velocities agree with absolute plate model predictions within 95 confidence for most of the sites in north america antarctica and eurasia the agreement is better than 2 mm yr we find no persuasive evidence for significant vertical motions 3 standard deviations except at four sites three of these four were sites constrained to geodetic reference frame velocities the gps velocities were then used to estimate angular velocities for eight tectonic plates absolute angular velocities derived from the gps data agree with the no net rotation nnr nuvel 1a model within 95 confidence except for the pacific plate our pole of rotation for the pacific plate lies 11 5 west of the nnr nuvel 1a pole with an angular speed 10 faster our relative angular velocities agree with nuvel 1a except for some involving the pacific plate while our pacific north america angular velocity differs significantly from nuvel 1a our model and nuvel 1a predict very small differences in relative motion along the pacific north america plate boundary itself our pacific australia and pacific eurasia angular velocities are significantly faster than nuvel 1a predicting more rapid convergence at these two plate boundaries along the east pacific rise our pacific nazca angular velocity agrees in both rate and azimuth with nuvel 1a

seismotectonics of the lower cheliff basin structural background of the el asnam algeria earthquake the 1980 el asnam earthquake should be understood within its tectonic environment a seismotectonic map of the lower cheliff basin scale 1 500 000 has been synthesized from known geologic tectonic and seismological work on the region and from satellite photos the data set was integrated by a computer in order to handle different scales and projections several important tectonic features divide the region into 5 domains active faults and recent folds are consistent with a nnw sse direction of compression the cheliff basin is limited to the south by the relizane fault the basin is also crossed by three broken folds the eastern one being the one associated with the el asnam fault historical and instrumental seisinicity seems to be located at both ends of relizane fault it is suggested that the sites corresponding to folds and reverse faulting crossing the basin are relevant to seismic risk a simple tectonic model is proposed

crustal velocity field of western europe from permanent gps array solutions 1996 2001 we derive a new geodetic velocity field for western europe and the western mediterranean by rigorously combining 1 a selection of 36 itrf2000 sites 2 a solution from a subset of sites of the european permanent gps network euref epn 3 a solution of the french national geodetic permanent gps network rgp and 4 a solution of a permanent gps network in the western alps regal the resulting velocity field describes horizontal crustal motion at 64 sites in western europe with an accuracy of the order of i mm yr 1 or better its analysis shows that central europe defined as east of the rhine graben and north of the alps and the carpathians behaves rigidly at a 0 4 mm yr 1 level and defines a stable europe reference frame in that reference frame we find no significant motion at sites located west of the rhine graben and on the iberian peninsula which sets an upper bound of 0 6 mm yr 1 on horizontal motion across the rhine graben and the pyrenees we find that the current strain pattern in the western alps combines e w extension and right lateral shear we confirm a counterclockwise rotation of the adriatic microplate which appears to control the strain pattern along its boundaries in the friuli area the alps and the apennines our results also suggest that the africa eurasia plate motion in the western mediterranean may be 40 50 per cent slower that the nuvel1a plate motion model and rotated 20 30 counterclockwise

magnetic parameters trace elements and multivariate statistical studies of river sediments from southeastern india a case study from the vellar river this contribution constitutes a new study using magnetic parameters and trace element determinations of pollutants in river sediments from the tamil nadu state the vellar river covers a total length of about 200 km and flows into the bay of bengal sediment samples were collected at different sediment depths up to 90 cm from 12 sites to investigate their magnetic properties 27 samples and the contents of trace elements 21 out of 27 samples along the river as well as to perform magnetic studies for various grain size fractions 16 sub samples the magnetic results of magnetic susceptibility and remanent magnetizations suggest that the magnetic signal of these sediments is controlled by ferrimagnetic minerals magnetite like minerals and a minor contribution of antiferromagnetic carriers such as hematite minerals detailed studies of selected samples showed a higher magnetic concentration in finer grain sized fractions and a slightly different magnetic mineralogy magnetic concentration dependent parameters evidenced high values which together with the background values allowed us to identify magnetic enhancement at some sites the pearson correlation and multivariate statistical studies principal component analysis canonical correlation analysis supported the relationship between the magnetic and chemical variables in particular magnetic susceptibility anhysteretic and isothermal remanent magnetization are closely correlated to co cr cu fe v zn and the pollution load index in addition principal coordinate analysis and fuzzy c means cluster analysis allowed us to make a classification and to perform a magnetic chemical characterization of the data into four groups thereby identifying critical possibly polluted sites from the vellar river

crustal velocity and strain rate fields in italy and surrounding regions new results from the analysis of permanent and non permanent gps networks summary we present a new geodetic velocity solution for italy and the surrounding areas obtained from an analysis of continuous and survey mode global positioning system observations collected between 1991 and 2002 we have combined local regional and global networks into a common reference frame velocity solution providing a new detailed picture of the regional scale deformation field in the central mediterranean our velocity estimates are computed with respect to a new stable eurasian reference frame constraining the kinematics of the greater african eurasian plate boundary system in the study area we provide strain rate values for the main seismotectonic districts which are in good agreement with the seismic deformation inferred from earthquake focal mechanisms the southern tyrrhenian area calabria the apennines the southeastern alps the southern dinarides and the albanides display deformation rates at the order of 20 30 nanostrain yr 1 the corsica sardinia block moves according to eurasian plate motions and there is no indication that the opening of the tyrrhenian is still active the pelagian and sicilian domains are separated by a northwest southeast discontinuity the sicily channel rifted area and marginally significant relative motion between the pelagian plateau and the african plate is also observed the southern tyrrhenian is affected by north south compression and accommodates up to 50 per cent of the africa eurasia relative plate motion whereas the calabrian arc exhibits 2 mm yr 1 northwest southeast extension the observed deformation pattern suggests the presence of a major approximately north south tectonic discontinuity separating the sicilian and calabrian domains an extensional boundary observed along peninsular italy coincides with the distribution of seismogenic faults along the axis of the apennines this boundary separates a tyrrhenian and an adriatic domain with diverging velocities orientated north nnw ward and northeastward respectively the apennines are extending perpendicularly to the chain axis at rates of less than 3 mm yr 1 and only in the outer northern apennines indications of active shortening are observed insignificant deformation is observed in the western po plain and the western alps while the central and eastern alps display north south shortening the eastern adriatic domain is shortening perpendicular to the dinaric front with strain rates increasing from north to south the locus of collision between the aegean balkan system and the adriatic and ionian domains is marked by the kephalonia fault system which accommodates up to 20 1 mm yr 1 of right lateral motion the deformation pattern observed in the peri adriatic domain is well described by a counter clockwise rotation of the adriatic microplate around a pole located in the western alps

on the scaling laws derived from ice beacon trajectories in the southern beaufort sea during the international polar year circumpolar flaw lead study 2007 2008 1 sea ice motion is an important element in mass balance calculations ice thermodynamic modeling ice management plans for industry and ecosystems studies in the historical literature sea ice motion in the beaufort sea was characterized by a predominantly anticyclonic motion during winter months with episodic reversals to cyclonic activity during summer however recent studies have shown an increase in cyclonic activity throughout the annual cycle in this paper we examine circulation in the beaufort sea based on the trajectories of 22 ice beacons launched in the franklin bay area during the international polar year circumpolar flaw lead ipy cfl study during an over wintering experiment in 2007 2008 dispersion characteristics of ice motion show that absolute zonal dispersion follows a t2 scaling law characteristic of advection associated with beaufort gyre circulation whereas absolute meridional dispersion follows a scaling law of t5 4 characteristic of floaters and dispersion in 2 d turbulence temporal autocorrelations of ice velocity fluctuations highlight definitive timescales with values of 1 2 0 7 days in the zonal meridional direction near gaussian behavior is reflected in higher order moments for ice velocity fluctuation probability density functions pdfs non gaussian behavior for absolute displacement pdfs indicates spatial heterogeneity in the ice motion fields atmospheric forcing of sea ice is explored through analysis of daily north american regional reanalysis and in situ wind data where it is shown that ice in the cfl study region travels with an average speed of approximately 0 2 and an average angle of 51 5 to the right of the surface winds during the 2007 2008 winter the results from this analysis further demonstrate seasonality in ice drift to wind ratios and angles that corresponds to stress buoy data indicative of increases in internal ice stress and connectivity due to consolidation of the seasonal ice zone to the coast and perennial ice pack during winter in the beaufort sea region

coseismic deformation of the may 21st 2003 mw 6 8 boumerdes earthquake algeria from gps measurements 1 on may 21st 2003 a mw 6 8 earthquake struck the central part of northern algeria causing extensive damage in the boumerdes area 40 km east of algiers it is among the largest events to occur in the western mediterranean over the past 25 years we present gps measurements of horizontal coseismic displacements that provide new constraints on the rupture geometry modeling the data with a uniform dislocation on a rectangular fault in an elastic half space we find that the rupture occurred on a reverse fault dipping 42 s with its upper edge 6 km offshore and lower edge 4 km inland the amplitude distribution of the coseismic displacements indicates that the rupture did not reach the surface at least in its western part and ended to the west around 3 4 e offshore faults like that of the boumerdes earthquake could account for part of the africa eurasia relative plate motion in the western mediterranean and represent a significant seismic threat for algeria

volcanic tectonic and mass wasting processes offshore terceira island azores revealed by high resolution seafloor mapping terceira island in the azores archipelago lies at the intersection of four submarine volcanic ridges new high resolution bathymetric and seismic reflection data have been used to analyze the main volcanic tectonic and mass wasting features of the island offshore volcanic features such as linear volcanic centers and pointy and flat topped cones are mainly concentrated on the narrow western and north western ridges characterized by an overall rugged morphology fault scarps dominate mainly the broad eastern and south eastern ridges which are characterized by an overall smooth and terrace like morphology on the eastern ridge faults form a series of horsts and grabens related to the onshore lajes graben the strikes of the fault scarps linear volcanic centers and alignment of volcanic cones on the ridges reveal two main structural trends wnw ese and nnw sse consistent with the main tectonic structures observed on the azores plateau in contrast a large variability of strike was observed in inter ridge areas reflecting the relative importance of regional and local stresses in producing these structures mass wasting features are subordinate and mostly represented by hundred meter wide scars that indent the edge of the insular shelf surrounding the island apart from two large deeper scars identified on the southern steep flank of the western ridge finally the remarkable morpho structural differences between the western and eastern ridges are discussed in the framework of the evolution of the terceira volcanic edifice and hypothesized to reflect successive stages of ridge evolution

gps and tectonic evidence for a diffuse plate boundary at the azores triple junction abstract we use gps bathymetric structural and seismic data to define the pattern of present deformation along the northern half of the azores plateau where the nubia eurasia plate boundary terminates at the axis of the mid atlantic ridge mar new and existing campaign gps velocities from the azores islands reveal extension oblique to a series of en echelon volcanic ridges occupied by terceira s jorge pico and faial islands in a frame of reference defined by 69 continuous gps stations on the eurasia plate terceira island moves 2 1 mm yr away from eurasia consistent with the island s location within the terceira rift and plate boundary structure the volcanic ridges south of the terceira rift move toward wsw at progressively faster rates reaching a maximum of 3 5 0 5 mm yr 2 for the pico faial volcanic ridge the hypothesis that the terceira rift accommodates all nubia eurasia plate motion is rejected at high confidence level based on the motions of sites on s jorge island just west of terceira rift all of the islands move relative to the nubia plate with pico island exhibiting the slowest motion only 1 0 5 mm yr 2 detailed bathymetry from the interior of the hypothesized azores microplate reveals faults that crosscut young mar seafloor fabric these observations and the gps evidence for distributed deformation described above argue against the existence of a rigid or semi rigid azores microplate and instead suggest that nubia eurasia plate motion is accommodated by extension across a 140 km wide zone east of the mar axis most likely bounded to the north by the northern shoulder of the terceira rift the mar spreading rate along the western end of the azores deformation zone 38 5 n 39 5 n is intermediate between the eurasia north america rate measured at 39 5 n and the nubia north america rate measured at 38 5 n consistent with the joint conclusions that the nubia eurasia boundary is broad where it intersects the mar and the azores triple junction is diffuse rather than discrete

cenozoic global plate motions cenozoic global plate motions relative to the hot spots are investigated and compared to plate motions in a mean lithosphere reference frame plate motions were analyzed over six time intervals divided by ages 10 25 43 48 and 56 ma chosen as much as possible to coincide with key plate reorganizations alternative motion circuits and rotational parameters were considered and evaluated with paleomagnetic data from the pacific and north american plates the circuit found to be in best agreement with the paleomagnetic data is one in which the hot spots in the atlantic region are assumed to be fixed relative to the hot spots in the pacific region throughout the cenozoic the hot spot and mean lithosphere reference frames have been in continual slow relative motion the rate of motion is nonuniform however most of the motion having occurred during the middle cenozoic the net cenozoic rotation of the lithosphere relative to the hot spots is described by a right handed rotation of 7 about a euler pole at 46 s 87 e which yields a 5 displacement of the north poles of the two reference frames this motion is small enough that inferences drawn about plate speeds in one reference frame should be valid in the other analysis of the global motions resulting from our preferred model showed that many characteristics of current plate motions have persisted throughout the cenozoic plate speeds correlate with latitude plates moving faster near the equator than near the poles throughout the cenozoic as at present continental plates except for the indian plate moved slower than oceanic plates throughout the cenozoic even the structure of the velocity fields as revealed in a contour of root mean square velocities in equatorial bands persists throughout the cenozoic the migration of the paleomagnetic axis over time is also compared to the hot spot and mean lithosphere reference frames the paleomagnetic axis has shifted 5 10 relative to the hot spot frame and a lesser amount relative to the mean lithosphere frame

kinematics of the iberia maghreb plate contact from seismic moment tensors and gps observations the iberian peninsula and the maghreb experience moderate earthquake activity and oblique nw se convergence between africa and eurasia at a rate of 5 mm yr coeval extension in the alboran basin and a n35 e trending band of active left lateral shear deformation in the alboran betic region are not straightforward to understand in the context of regional shortening and evidence complexity of deformation at the plate contact we estimate 86 seismic moment tensors mw 3 3 to 6 9 from time domain inversion of near regional waveforms in an intermediate period band those and previous moment tensors are used to describe regional faulting style and calculate average stress tensors the solutions associated to the trans alboran shear zone show predominantly strike slip faulting and indicate a clockwise rotation of the largest principal stress orientation compared to the regional convergence direction 1 at n350 e at the n algerian and sw iberian margins reverse faulting solutions dominate corresponding to n350 e and n310 e compression respectively over most of the betic range and intraplate iberia we observe predominately normal faulting and wsw ene extension 3 at n240 e from gps observations we estimate that more than 3 mm yr of african nubian eurasian plate convergence are currently accommodated at the n algerian margin 2 mm yr in the moroccan atlas and 2 mm yr at the sw iberian margin 2 mm yr is a reasonable estimate for convergence within the alboran region while alboran extension can be quantified as 2 5 mm yr along the stretching direction n240 e superposition of both motions explains the observed left lateral transtensional regime in the trans alboran shear zone two potential driving mechanisms of differential motion of the alboran betic gibraltar domain may coexist in the region a secondary stress source other than plate convergence related to regional scale dynamic processes in the upper mantle of the alboran region as well as drag from the continental scale motion of the nubian plate along the southern limit of the region in the atlantic ocean the 3 5 mm yr westward motion of the gibraltar arc relative to intraplate iberia can be accommodated at the transpressive sw iberian margin while available gps observations do not support an active subduction process in this area

evidence for a post 3 16 ma change in nubia eurasia north america plate motions we combine updated gps velocities from the nubian nu eurasian eu and north american na plates with 500 new 3 16 myr average seafloor spreading rates and nine transform fault azimuths from the northern atlantic and arctic basin seafloor spreading centers to estimate and test for changes in the relative motion between these plates the numerous new seafloor spreading rates and gps velocities improve our ability to detect recent changes in the relative motions of these plates the angular velocity vector that best fits the eu na gps velocities lies significantly north of the 3 ma average pole in accord with previously published geologic evidence that the eu na pole has migrated northward since v3 ma although we also find evidence for a significant post 3 ma change in nu na motion it is less compelling because the nubian plate gps velocity field is sparse and nu na seafloor spreading rates appear to have remained steady within the 1 mm yr 31 uncertainties if we systematically decrease the seafloor spreading rates to correct for outward displacement of seafloor spreading magnetic lineations the nu eu pole derived from gps site velocities lies more than 30 angular degrees south of the tightly constrained 3 ma average estimate and predicts significantly slower and more oblique present day nu eu convergence in the mediterranean both models for nu eu motion pass a key test for their accuracy namely they correctly predict strike slip motion along the well mapped gloria fault east of the azores the change to more oblique nu eu motion may reflect increasing difficulty in maintaining margin normal convergence within this continent continent collision zone 8 2003 published by elsevier b v

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

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

cenozoic plate driving forces past studies of plate driving forces have concluded that the forces due to subducted slabs in the upper mantle and those due to the thickening of the oceanic lithosphere are the principal driving forces we reexamine the balance of driving forces for the present day and extend our analysis through the cenozoic using an analytical torque balance method which accounts for interactions between plates via viscous coupling to the induced mantle flow we use an evolving mantle density heterogeneity field based on the last 200 myr of subduction to drive plate motions an approach which has proven successful in predicting the present day mantle heterogeneity field we find that for plausible upper mantle viscosities the forces due to subducted slabs in the cenozoic and mesozoic account for in excess of 90 of plate driving forces and those due to lithospheric thickening for less than 10

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

confirmation of the astronomical calibration of the magnetic polarity timescale from sea floor spreading rates the dating of the history of reversals of the earth s magnetic field since the jurassic period has been based primarily on radiometric dating of a small number of reversals with most ages of individual reversals interpolated or extrapolated on the basis of the widths of marine magnetic anomalies recently however pliocene and pleistocene reversals have been dated by an entirely independent method which relies on correlating climate proxies such as oxygen isotope ratios in sediments with calculated variations of the earth s orbit and inclination1 4 the dates obtained from this astronomical calibration are 3 8 older than radiometrically calibrated ages published between 1979 and 1989 see for example refs 5 and 6 although recent dating by the 40ar 39ar method tends to confirm the astronomical calibration7 10 at least for the past 3 3 myr here i use sea floor spreading rates determined from high precision plate rotation solutions for five plate pairs to test the astronomically calibrated timescale over the past 5 32 myr the results suggest that the errors in the astronomical calibration are no greater than 0 02 myr and also show that spreading rate can remain constant for several million years even for fast moving plates

seismic anisotropy of northeastern algeria from shear wave splitting analysis abstract there are few studies of internal deformation under northern africa here we present such a study we analyze teleseismic shear wave splitting for northeast algeria to improve our knowledge of lithospheric and asthenospheric deformation mechanisms in this region we study waveform data generated by tens of teleseismic events recorded at five recently installed broadband bb stations in algeria these stations cover an area 2 across extending from the tellian geological units in the north to the saharan atlas units in the south analysis of sks wave splitting results insignificant spatial variations in fast polarization orientation over a scale length of at most 100 km the seismic anisotropy shows three clear spatial patterns a general ene wsw orientation is observed under the stations in the north this polarization orientation follows the direction of the tell atlas mountain chain which is perpendicular to the convergence direction between africa and eurasia delay times vary significantly across the region between 0 6 and 2 0 s at several stations there is an indication of a wnw ese polarization orientation which is apparently related to a later geodynamic evolutionary phase in this region a third pattern of seismic anisotropy emerges in the south with an orientation of roughly n s we discuss these observations in light of geodynamic models and present day geodetic motion

waveform inversion of small to moderate earthquakes located offshore southwest iberia summary in this paper we apply the kinematic waveform inversion kiwi tools to the study of smallto moderate earthquakes in southwest sw iberia the earthquakes have magnitudes in the range ml 3 5 4 9 with the exception of one earthquake with magnitude ml 6 0 most events are located offshore are recorded with a large azimuthal gap and generate waves that travel throughastronglyheterogeneous crustalstructure weobtainnewestimatesofcentroid depth seismic moment strike dip and rake for 12 of the 29 studied events the earthquakes whose waveforms we cannot successfully model are 1 located too far from the stations 2 have small magnitude hence low signal to noise ratio or 3 are located within the cadiz basin which is a major sedimentary basin that affects wave propagation notably our results indicate that onshore earthquakes occur at shallow depths 15 km whereas offshore earthquakes occur deeper down to 46 km focal mechanisms indicate transpressive faulting

how rigid is the stable interior of the north american plate we analyze data from eight permanent gps stations broadly distributed through the interior of the north american plate and use the resulting velocities to estimate an euler vector describing motion of stable north america as a single rigid plate the site velocities fit the single plate model with a mean residual of 1 3 mm yr the residuals do not appear to reflect post glacial rebound and tests for differential motion between eastern and western north america at the new madrid seismic zone show no resolvable motion within uncertainties the residuals likely reflect observational error and thus our estimate of the stability of the plate interior is likely an upper bound

fragmentation of the adriatic promontory new chronological constraints from neogene shortening rates across the southern alps ne italy key points folded alluvial surfaces and balanced cross section constrain post lgm and neogene shortening rates decrease in shortening rate and change in compression direction are inferred at 1 2 ma kinematic reorganization is best explained by a shift from nubia driven to adria driven convergence abstract the eastern southern alps are located at the northern tip of the adria microplate which imposes 2 0 2 5 mm yr of n s convergence relative to stable eurasia we map surface evidence of recent folding faulting in this area from a 5 m dem in the eastern part of the belt observations reveal a 30 km wide zone of active folding composed of at least five growing anticlines the most recent ones warped the post glacial alluvial surface by 10m combining these findings with published geological and geophysical data allows us to infer that active thrusting occurs along a single deeply rooted thrust which accommodates the indentation of the adriatic crust resolving the observed pattern of uplift on the inferred fault geometry indicates that nne ssw shortening across the eastern southern alps has occurred at a rate of about 1 5 mm yr over the post glacial period on the other hand a balanced cross section for the eastern southern alps at the scale of the upper crust constrains a minimum of 43 km of finite shortening over the last 14ma yielding a shortening rate of about 3 mm yr which is two times higher than the post glacial shortening rate this decrease in the shortening rate is associated to the pleistocene activation of new thrusts that is compatible with a change in the direction of compression the inferred local change in the kinematics of thrusting during the pleistocene is consistent with a change from nubia imposed to adria imposed convergence indicating that the fragmentation of the adriatic promontory could have occurred 1 2 ma ago

the miocene to present kinematic evolution of the eastern mediterranean and middle east and its implications for dynamics the present kinematics in the eastern mediterranean and middle east is now well constrained by gps measurements and dominated by a circular counterclockwise motion while arabia rotates rigidly the rotational velocities increase from the levant to aegea causing extension in western anatolia we place the present pattern in light of the post middle miocene geological history and propose that in addition to the effects of the hellenic subduction and zagros collision subduction zones on driving the surface motion an underlying asthenospheric flow is also required this counterclockwise toroidal flow is expected to exist around the eastern edge of the african slab owing to subduction rollback and it helps explain the initiation of the north anatolia fault the extrusion and uplift of anatolia and the mid miocene to recent volcanism in eastern anatolia the afar plume had a similar effect on the acceleration of arabia at 40 mya