angular velocities of nubia and somalia from continuous gps data implications on present day relative kinematics abstract this study focuses on the break up of the african tectonic plate into separate nubian and somalian blocks based on recent global positioning system gps data a new unique velocity field has been obtained by processing all available observations of permanent gps stations on africa since 1996 the quantity and distribution of the stations and the length of the time series of observations exceed that of previous studies by a considerable margin allowing one to derive a reliable estimate of the differential motion between the nubia and somalian plates which are considered as a single african block in the prevailing global tectonic plate models the estimated relative pole of rotation of somalia with respect to nubia is located at 54 8 s 37 0 e with magnitude 0 069 ma implying distinct opening in the ethiopian rift of magnitude 7 mm year and azimuth n94 e whereas in southeastern south africa this value is reduced to 2 mm year in almost the same direction this is in accordance with some of the independent geological and geophysical tectonic models of the nubia somalia plate boundary region however the spatial density of the current tracking network is still not optimal to establish the exact location of the entire somalia nubia plate boundary in particular the possible branch east of lake victoria and heading towards the mozambique channel is impossible to confirm or reject at this moment

initial indications of abiotic formation of hydrocarbons in the rainbow ultramafic hydrothermal system mid atlantic ridge in the presence of water olivine of ultramafic rock is oxidized during the process referred to as serpentinization water in contact with the olivine is reduced to molecular hydrogen h2 with the concomitant oxidation of fe ii the molecular hydrogen formed may be used as an energy source by lithotrophic bacteria but may at high temperature also be combined with co2 for the abiotic formation of organic compounds such as hydrocarbons and fatty acids through fischer tropsch type ftt synthesis our analyses of fluids from the peridotite hosted rainbow hydrothermal field on the mid atlantic ridge indicate de novo synthesis of linear saturated hydrocarbons the chain length of the hydrocarbons is between 16 and 29 carbon atoms the discovery of ftt reactions in ultramafic hydrothermal systems on earth provides an alternative pathway for the formation of early membranes and the origin of life

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

global geodesy using gps without fiducial sites baseline lengths and geocentric radii have been determined from gps data without the use of fiducial sites data from the first gps experiment for the iers and geodynamics gig 91 have been analyzed with a no fiducial strategy a baseline length daily repeatability of 2 mm 4 parts per billion was obtained for baselines in the northern hemisphere comparison of baseline lengths from gps and the global vlbi solution glb659 caprette et al 1990 show rms agreement of 2 1 parts per billion the geocentric radius mean daily repeatability for all sites was 15 cm comparison of geocentric radii from gps and sv5 murray et al 1990 show rms agreement of 3 8 cm given n globally distributed stations the n n 1 2 baseline lengths and n geocentric radii uniquely define a rigid closed polyhedron with a well defined center of mass geodetic information can be obtained by examining the structure of the polyhedron and its change with time

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

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

the relative motion between africa and eurasia as derived from itrf2000 and gps data 1 studies of intra and inter plate deformation typically need a model describing the motions of the stable part of the tectonic plates for reference purposes we have developed deos2k a model for the current motion of seven major tectonic plates derived from space geodetic observations this paper focuses on relative motion between africa and eurasia in the past this motion has been poorly established because of poor data coverage for africa deos2k is based on itrf2000 altamimi et al 2002 and new african gps observations it is an improvement over the nuvel 1a model for predicting the present day relative motions of these two plates deos2k predicts in northeastern africa that africa eurasia relative motion is about 40 smaller in magnitude than nuvel 1a and trends more to the northwest this is consistent with independent local geodetic observations a similar shift in orientation clockwise is observed at the western tip of the plate boundary

geodynamic models for the azores triple junction a contribution from tectonics abstract the american eurasian and african lithospheric plates meet at the azores triple junction the nature of the northern and southern branches of the junction is well known and uncontroversial the american plate is separated from eurasia and africa by the mid atlantic ridge mar the western group of islands of the azores archipelago flores and corvo lies on the american plate just west of the rift and their tectonic features agree with that location the nature of the third branch of the junction to the east of the mar is however still controversial some authors believe that a ridge ridge ridge junction occurs in the azores area and adopt the structure known as the terceira ridge working as a simple rift boundary as the third branch another model proposes a triangular microplate in the azores region bounded by the mid atlantic rift to the west the east azores fault zone to the south and a fault crossing s miguel and the terceira islands to the northeast in this model the fault zones are pure dextral strike slip boundaries both models would create space problems at gloria fault a well known pure dextral strike slip structure in the first model transtension would be necessary at gloria fault to accommodate plate motion while the second would require a transpressive regime on that structure neotectonic and seismotectonic data in the azores indicate a transtensile regime in the central and eastern island groups in present and recent times this is compatible with a leaky transform structure acting as the third branch of the junction in the azores area a model which has already been presented by several authors in the past stress trajectories deduced from neotectonic studies in some of the islands suggest that the main plate boundary passes between the islands of s jorge and pico south of s miguel and joins gloria fault east of santa maria this model and boundary location is also compatible with seismotectonic and magnetic data

surface displacement field at terceira island deduced from repeated gps measurements abstract we present the results of six gps global positioning system campaigns held in terceira island azores between 1999 and 2006 for a group of 17 stations to estimate the surface displacement field induced by the eurasian nubian interplate motion and their relationship with the rifting along terceira rift and volcanic processes at the island scale we show that the whole island mainly behaves like a rigid body which absolute motion is closer to eurasia the magnitude of the computed intra island horizontal deformation field difference between the individual site velocities and the mean rigid body motion is still below the observation accuracy and so cannot be directly related with local processes we also show that the island is globally subsiding with an average rate close to 1 mm yr as it moves to the ne away from the terceira rift mostly attached to the eurasian plate the high subsidence rate can be the result of the volcanic processes that shaped the serreta ridge nw of terceira

organic acid metastability in sedimentary basins thermodynamic calculations indicate that co sub 2 in sedimentary basins may be in stable redox equilibrium with organic acids found in basinal brines but that ch sub 4 is not these calculations also show that the high concentrations of carboxylic acids are from equilibrium with decarboxylation reactions a compilation of recent analyses of carboxylic acids from aqueous solutions associated with petroleum reservoirs shows that there is no trend in acid concentrations with temperature however inspection of these data at approximately 100 c indicates that acetic and propanoic acids are in homogeneous metastable equilibrium oxygen fugacities indicated by this metastable assemblage are consistently lower than those set by iron oxide assemblages this is not surprising because both hematite and magnetite are unstable relative to siderite in the presence of detectable concentrations of acetic acid

recent geodetic results in the azores triple junction region gps global positioning system observations started to be carried out in the azores region under the scope of the tango transatlantic network for geodesy and oceanography project in 1988 the measurements carried out between 1993 and 2000 five campaigns on nine gps sites one per island were reprocessed using two state of the art software packages different methodologies were applied to compute each campaign solution and the derived velocity field the velocity fields including the motions of two permanent stations recently installed in the azores were computed within the most recent geodetic reference frame itrf2000 international terrestrial reference frame solution 2000 they are compared with the motions of the stable rigid tectonic plates using as reference deos2k a global tectonic model developed using geodetic data the relative motions between the western and central groups of islands yield to evaluate the opening rate of the mid atlantic ridge boundary between the north american plate and the eurasian and african plates concerning the boundary between the eurasian and african plates the motion of the tango sites in the central and eastern groups clearly identifies the transition pattern between those two plates two of the sites are considered to be located in the stable part of these plates whereas the remaining five are within the deformation region of the eurasia africa boundary the conclusions are analyzed in view of the different deformation models derived from geodynamic or geophysical data that have been proposed for the region

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

the itrf96 realization and its associated velocity field this text intends to present and to analyse the quality of the new 1996 edition of the international terrestrial reference system called the itrf96 the itrf96 represents a key step forward in the activity of the iers terrestrial system determinations a new physical combination model has been developed as well as a new stochastic model for the first time the level of accuracy has reached 1 cm or better in position for about 50 of itrf96 stations and 30 of the stations have their velocities determined free of any aditional tectonic plate model assumption with an uncertainty better than 3 mm yr the itrf96 also provides a more complete solution a new software has been developed which makes available the itrf96 full variance covariance matrix whereas this information was restricted to station positions in the previous itrf94 edition moreover the network coverage is clearly the largest set of globally distributed terrestrial space geodesy stations that have ever been computed 521 stations located among 290 sites in addition station velocities are also determined at a very accurate level allowing possible determination of kinematic plate motion models free of any geological assumption

insight on the crustal stress state in faial and pico islands azores from analysis of aftershocks of the 1998 earthquake the seismicity in the azores plateau can be of volcanic or tectonic origin the latter usually more destructive especially in the central group of islands in this study we aimed to obtain crustal stress indicators from seismic data collected in july 1998 following the july 9th m5 8 earthquake that struck near faial and pico islands the maximum horizontal stress shmax azimuth was obtained from two methods for the seismogenic volume the shmax was obtained from single and composite focal mechanisms whereas the state of stress beneath the seismic network was derived from shear wave splitting analysis of local earthquakes the composite focal mechanisms were obtained from a waveform clustering method applied to identify identical earthquakes the seismic anisotropy analysis could be applied to only six stations the polarization of the first s arrival being stable and with a secondary perpendicular pulse arriving 0 6 0 24 s later the focal mechanisms provided a nw se shmax with azimuth range of 96 114 and an associated transition of normal fault to strike slip dominant regime consistent with the estimated regional field of 110 120 and coherent with movement along three fault systems inland the shmax azimuths present greater variability in faial the stations located north of the caldeira present a stable azimuth of 151 153 and are consistent with the effect of a nnw sse fault system present in the islands rotating to 50 77 in the eastern sector of the pedro miguel graben probably due to a complex interaction of the wsw ene dominant fault system with old eroded volcanic complexes that segmented the island into several blocks in pico island the shmax direction azimuth ranges from 93 to 135 in a radial pattern around the island s main stratovolcano overlapping the regional stress field

closure of the africa eurasia north america plate motion circuit and tectonics of the gloria fault we examine the closure of the current plate motion circuit between the african north american and eurasian plates to test whether these plates are rigid and whether the gloria fault is an active transform fault we also investigate the possible existence of microplates that have been previously proposed to lie along these plate boundaries and compare the predicted direction of motion along the african eurasian plate boundary in the mediterranean with the direction of slip observed in earthquakes from marine geophysical data we obtain 13 transform fault azimuths and 40 3 m y average spreading rates 34 of which are determined from comparison of synthetic magnetic anomaly profiles to 140 observed profiles slip vectors from 32 earthquake focal mechanisms further describe plate motion detailed magnetic surveys north of iceland provide 11 rates in a region where prior plate motion models had few data magnetic profiles north of the azores triple junction record a rate of 24 mm yr 4 mm yr slower than used by prior models gloria and sea beam surveys accurately measure the azimuths of seven transform faults our plate motion model fits six of the seven within 2 two transform faults surveyed by gloria side scan sonar lie near famous area transform faults a and b and give azimuths 13 clockwise of them because recent studies show that short offset transforms such as transforms a and b are in many places oblique to the direction of plate motion we exclude azimuths from transforms with less than 35 km offset the best fitting and closure enforced vectors fit the data well except for a small systematic misfit to the slip vectors on right lateral slipping transforms slip vectors tend to be a few degrees clockwise of plate motion and mapped fault azimuths whereas on left lateral slipping transforms slip vectors tend to be a few degrees counterclockwise of plate motion and mapped fault azimuths we search the long eurasia north america boundary for evidence of an additional plate but find no systematic misfits to the data in particular if a spitsbergen plate exists and moves relative to eurasia its motion is less than 3 mm yr an africa eurasia euler vector determined by adding the eurasia north america and africa north america euler vectors is consistent with the gloria fault trend and with slip vectors from eastern azores gibraltar ridge focal mechanisms a small circle centered at the africa eurasia closure enforced pole fits the trace of the gloria fault the model in which closure was enforced predicts 4 mm yr slip across the azores gibraltar ridge and west northwest convergence near gibraltar 45 more oblique than suggested by a recent model based on compressive axes of focal mechanisms moreover our model predicts directions of plate motion that agree well with northwest trending slip vectors from thrust earthquakes between gibraltar and sicily because closure enforced vectors fit the data nearly as well as the best fitting vectors we conclude that the data are consistent with a rigid plate model and with the gloria fault being a transform fault

reduction of co2 during serpentinization of olivine at 300 c and 500 bar co 2 reduction processes occurring during experimental serpentinization of olivine at 300 c and 500 bar confirm that ultramafic rocks can play an important role in the generation of abiogenic hydrocarbon gas data reveal that conversion of fe ii in olivine to fe iii in magnetite during serpentinization leads to production of h 2 and conversion of dissolved co 2 to reduced c species including methane ethane propane and an amorphous carbonaceous phase hydrocarbon gases generated in the process fit a schulz flory distribution consistent with catalysis by mineral reactants or products magnetite is inferred to be the catalyst for methanization during serpentinization because it has been previously shown to accelerate fischer tropsch synthesis of methane in industrial applications involving mixtures of h 2 and co 2 the carbonaceous phase was predominantly aliphatic but had a significant aromatic component although this phase should ultimately be converted to hydrocarbon gases and graphite if full thermodynamic equilibrium were established its formation in these experiments indicates that the pathway for reduction of co 2 during serpentinization processes is complex and involves a series of metastable intermediates

a reevaluation of coastal embayment rotation the dominance of cross shore versus alongshore sediment transport processes collaroy narrabeen beach southeast australia 1 over 30 years of wave and beach survey data at collaroy narrabeen beach in southeast australia are analyzed to investigate the extent to which shoreline variability within this coastal embayment is dominated by shoreline oscillations due to cross shore sediment exchange or shoreline rotations due to alongshore exchange between the beach s extremities offshore wave data are derived from both buoy measurements and era 40 reanalysis data eof analysis of the monthly shoreline data suggests that the dominant mode of shoreline variability 60 of variability is an onshore offshore sediment exchange that is greater at the more exposed northern end of the beach than at the predominantly sheltered southern end this mode is primarily associated with variability in wave energy storms which by the nature of the wave climate of this region chiefly occurs from the south southeast the secondary mode of shoreline variability 26 of variability is a rotational signal between either end of the beach which coincides with 24 of the offshore wave climate shifting between the south southeast and east as well as changes in the wave period and wave energy storms a distinct annual cycle is identified in this rotation signal it is concluded that alongshore sediment transport processes associated with embayment rotation is more subtle than previously thought and a refined conceptual model of coastal embayment variability in this region is presented highlighting the dominance of cross shore sediment exchange processes

large scale active slump of the southeastern flank of pico island azores we report evidence for ongoing lateral slump of part of the southeastern flank of the pico volcanic ridge in the azores data from a high resolution digital elevation model field work gps and radar interferometry show that 1 the slumping sector is several cubic kilometers in size 2 the structure involves several curved scars with normal fault kinematics 3 the central part is undergoing little horizontal displacement toward the southeast 1 6 1 3 mm yr but significant downward movement 5 12 mm yr and 4 the outer part of the southeastern flank of pico is subsiding faster than the inner parts this likely reflects recent individualization of a steep seaward dipping fault in the moving mass the slump shares similarities with active slumps recognized elsewhere although the studied area may represent only the proximal part of a much larger complex potentially affecting the deep submarine base of the island displacement of the subaerial part of the southeastern flank of pico seems to be accommodated by the movement and rotation of large blocks along listric normal faults

the azores triple junction evolution since 10 ma from an aeromagnetic survey of the mid atlantic ridge abstract in the past two decades several models have been presented to describe the evolution and the present structure of the azores triple junction these models were mainly based on morphological analysis of sea bottom topography sparse magnetic profiling sidescan sonar surveying over the plateaus and global plate kinematic considerations for the north atlantic in this paper we follow a different approach from a detailed aeromagnetic survey covering both sides of the mid atlantic ridge between 37 n and 40 30 n the magnetic anomalies up to anomaly 5 are accurately identified allowing careful modelling of the kinematics of this region for the past 10 ma and thus establishing a coherent framework for the design of geophysical models for the azores triple junction the analysis of magnetic anomalies and the use of fourier domain inversion techniques show that the ridge is made up of six segments each one varying in length from 50 to 60 km the more continuous section of the ridge can be defined from the first four northern segments although the north azores fracture zone right offsets the ridge at 39 30 n 29 40 w the fifth and sixth segments are respectively right offset by the acor fracture zone at 38 23 n 30 15 w and by the princess alice fracture zone at 38 00 n 30 50 w anomaly identifications using a two dimensional model and plate tectonics reconstruction techniques allowed the calculation of rotation pole parameters the results thus obtained reveal that at least between anomalies 5 and 3 10 3 85 ma the azores displayed an independent motion relative to the neighbouring plates and after anomaly 2a 2 45 ma the azores moved attached to the eurasian plate the triple junction azores north america africa or eurasia north america africa moved northward from 38 00 n 30 50 w to 38 20 n 30 15 w between 4 and 3a and probably to 38 50 n 30 00 w at anomaly 2a time a detailed reconstruction model is presented

analysis of geometry of volcanoes and faults in terceira island azores evidence for reactivation tectonics at the eur afr plate boundary in the azores triple junction abstract the late pliocene to quaternary 5 ma volcanism in the central and eastern azores archipelago is related to the eurasia africa divergence but a clear deformation pattern has not yet been established at this location this work focuses on the contribution of synthetic aperture radar sar scenes and digital elevation models dem complemented with geophysical geodetic and morpho structural data to establish the geometric relationships between volcanic edifices and tectonic structures in the central and eastern azores archipelago bathymetric data were also used to extend field observations to the significant submarine area of the azores plateau strikes of extension fractures directly observed or inferred from elongated volcanic vents or linear volcanic clusters in terceira island indicate that volcanism is mainly controlled by regional extension as given by nuvel 1a plate motion model additionally other directions were also detected for extension fractures around the santa barbara volcano defining a radial pattern and in the central part of the island exhibiting an s shape pattern although most of the volcanic vents are controlled by extension fractures some seem to be controlled by faulting such as the case of the ones rooted in releasing bends along strike slip or oblique slip faults in the central part of the island concerning the azores plateau most of the structures have directions that do not directly fit with present day direction of relative motion n70 between eurasia and africa directions ranging from n110 to n125 found mainly along the terceira rift are interpreted as ancient transform directions reactivating as transtensional fault zones due to the present day plate motion n s directions are also visible in the plateau being interpreted as former middle oceanic rift faults reactivated as left lateral fault zones these results contrast with the volcanic expression in other hotspot dominated oceanic islands such as the canaries or the hawaii islands chain probably due to the tectonic complexity promoted by the azores triple junction instability through time

deformation in a hyperslow oceanic rift insights from the tectonics of the sao miguel island terceira rift azores the evolution of hyperslow oceanic rifts like the terceira rift tr in the azores is still poorly understood here we examine the distribution of strain and magmatism in the portion of the tr making up the nubia eurasia plate boundary we use sao miguel island because it stretches most of the tr width which allows to investigate the tr s architecture and shedding light on tr s age and mode of deformation from topography and structural analysis and new measurements of 380 faults and dikes we show that 1 sao miguel has two main structural directions n150 and n110 mostly concentrated in the eastern part of the island as an onshore continuation of the faults observed offshore in the ne n110 faults and sw n140 tr walls 2 a new n50 n80 fault system is identified in sao miguel 3 fault and dike geometries indicate that eastern sao miguel comprises the tr s northern boundary and the lack of major faults in central and western sao miguel indicates that rifting is mostly concentrated at master faults bounding the tr based on tr s geometry structural observations and plate kinematics we estimate that the tr initiated between 1 4 and 2 7 ma ago and that there is no appreciable seafloor spreading associated with rifting based on plate kinematics on the new structural data and on sao miguel s structural and volcanic trends we propose that the eastern two thirds of sao miguel lie along a main tr related transform fault striking n70 n80 which connects two widely separated n130 n150 tr trending segments

seismicity source mechanisms and tectonics of the azores gibraltar plate boundary abstract a study and partial revision of the seismicity and source mechanisms of earthquakes are presented for the oceanic plate boundary of eurasia and africa from the azores islands to the strait of gibraltar focal mechanisms of 36 earthquakes wave form modelling of 4 and seismic moments and dimensions of 28 have been calculated these results indicate that the boundary is divided into three sections with different characteristics the azores the central section and the east section the azores section has high seismicity of moderate magnitude and a low slip rate 0 76 cm yr the predominant mechanism is normal or transform faulting with horizontal tensions on average in a n25 e direction in the central section large earthquakes occur with strike slip right lateral motion along faults in an e w direction there is a high slip rate 3 39 cm yr the east section is of more complex nature large earthquakes also occur but the predominant mechanism is reverse faulting with a horizontal pressure axis in the n30 w direction resulting in underthrusting of africa from the slip vectors the pole of rotation for the african plate is located at 28 2 n 21 1 w nearer to the boundary than previous locations close to the continent there is a continuation in the ocean crust of some structural features of the iberian peninsula

coseismic displacements of the mw 6 1 july 9 1998 faial earthquake azores north atlantic 1 on 9 july 1998 an earthquake occurred ne of faial island azores north atlantic the harvard cmt solution points to a sub vertical strike slip event corresponding to the strikes n241e and n151e here we use gps data to estimate the coseismic displacements and to constrain the geometry of the earthquake source gps observations collected between 1993 and 1999 are processed to separate the interseismic and coseismic movements additionally a displacement field is derived from a denser gps network of 30 stations we model the coseismic movements by a dislocation in a homogenous elastic half space the data do not allow to infer the fault strike direction which have helped to understand the relationships with the regional geodynamics however the models give consistent figures for the fault surface 40 km2 the coseismic slip 1 m and the depth of the upper and lower edges of the fault plane 2 and 6 km

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

defining the plate boundaries in the azores region abstract the azores archipelago occupies the boundary zone where three major tectonic plates eurasia nubia and north america meet to form the azores triple junction repeat observations from six campaigns carried out between 1993 and 2001 for the tango network of gps sites now allow reliable estimations of the current motions of the involved plates at millimeter scale resolution analysis of these space geodetic data demonstrates that during the observation period santa maria island followed the average nubian plate movement and graciosa island mimicked the average eurasian plate behavior all other gps sites display intermediate behavior consistent with their locations within the active inter plate deformation area the active deformation area is well modeled by an elastic half space approach with the segmentation of the eurasian nubian plate boundary constrained by other geophysical data