a record of changing redox conditions in the northern peru basin during the late quaternary deduced from mn fe and growth rate variations in two diagenetic manganese nodules abstract two diagenetic manganese nodules from the peru basin were investigated by thermal ionization mass spectrometry and high resolution alpha spectrometry for uranium and thorium the tims concentrations for nodule 62kd 63kg vary as follows 0 12 1 01 ppb 0 06 0 59 230th 0 51 1 98 ppm 0 43 1 40 232th 0 13 0 80 ppb 0 09 0 49 234u and 1 95 13 47 ppm 1 66 8 24 238u both nodules have average growth rates of 110 mm per million years however from the variations of excess 230th with depth we estimate partial accumulation rates which range from 50 to 400 mm per million years the 234u dating method cannot be applied due to remobilization of u from the sediment and subsequent incorporation into the nodules crystal lattice reflected by decay corrected 234u values far above the ocean water value sections of fast nodule growth are related to those layers having high mn fe ratios up to 200 and higher densities as a possible explanation we develop a scenario that describes similar glacial interglacial trends in both nodules as a record of regional changes of sediment and or deep water chemistry

application of the global positioning system to crustal deformation measurement 2 the influence of errors in orbit determination networks global positioning system gps measurements of a geodetic network in southern and central california have been used to investigate the errors introduced by adopting different sets of stations as fixed such fixed points called fiducial stations are necessary to eliminate the errors of imprecise satellites orbits which otherwise would dominate the error budget for distances greater than tens of kilometers these fiducial stations also define the reference frame of the crustal deformation network establishing the magnitude of the effect of changing the fiducial network is essential for crustal deformation studies so that these artifacts of the differences between fiducial networks used for the data analyses are not interpreted as geophysical signals solutions for a crustal deformation network spanning distances up to 350 km were computed with a variety of fiducial networks we use fiducial coordinates determined from very long baseline interferometry vlbi we compare these solutions by computing the equivalent uniform strain and rotation that best maps one solution into another if we use a continental scale fiducial network with good geometry the distortions between the solutions are about 10 8 largely independent of the exact choice of stations the one case of a large scale fiducial network where the distortions are larger is when the three fiducial stations chosen all lie close to a great circle use of a fiducial network no larger than the crustal deformation network tan produce apparent strains of up to 10 7 our work suggests that fiducial coordinates determined from gps data analysis may be used although they should be determined using a consistent reference frame such as provided by vlbi and satellite laser ranging

earthquake mechanisms of the adriatic sea and western greece implications for the oceanic subduction continental collision transition summary we present 21 focal solutions magnitude 5 5 reliably computed by body wave modelling for the western hellenic arc from yugoslavia to the southern peloponnese mechanisms located within the aegean show normal faulting the t axis trending n s in the centre and parallel to the active boundary in the external part mechanisms associated with the keffalinia fault are consistent with dextral strike slip motion reverse mechanisms located along the active boundary are remarkably consistent and do not depend on the nature of the active boundary continental collision or oceanic subduction the consistency in azimuth of the slip vectors and of the gps velocity relative to africa all along the active boundary suggests that the deformation is related to the same motion the discrepancy between seismic energy release and the amount of shortening confirms that the continental collision is achieved by seismic slip on faults but the oceanic subduction is partially aseismic the northward decrease in velocity between continental collision and oceanic subduction suggests the continental collision to be a recent evolution of the active subduction

timing kinematics and cause of aegean extension a scenario based on a comparison with simple analogue experiments abstract since the early 1970s most geodynamic models proposed for the eastern mediterranean consider that the initiation of extension in the aegean during the late middle miocene or later was a direct consequence of the westward extrusion of anatolia away from the arabia eurasia collision front in the late 1990s a few models have taken into account the increasing evidence for an earlier initiation of aegean extension arising mostly from the analysis of deformation within the various alpine metamorphic complexes of the area based largely on our own investigations we first present a review of the data that reliably constrain the minimum age for the initiation of extension in these complexes it shows that regional scale extension with a pattern of stretching orientations similar to that of the pliocene pleistocene was already strongly active in the aegean before the onset of arabian indentation into eurasia lower miocene vs middle or upper miocene this implies that the initiation of aegean extension did not result from the lateral extrusion of anatolia instead extension may have started owing to a process of gravity spreading of the continental lithosphere that had previously been thickened during alpine collision the main arguments favouring this interpretation are presented and a preliminary scenario is proposed for the neogene evolution of the eastern mediterranean in which lateral extrusion of anatolia occurred lately during southward spreading of the aegean lithosphere in order to test this hypothesis further physical experiments simulating the horizontal spreading of a continental lithosphere toward a free boundary have been carried out the analysis of various elements of the deformation field displacements strain rotations fault pattern and kinematics both in the experiments and in the aegean domain reveals an excellent agreement between the two not only do early stages of aegean extension appear to fit the gravity spreading hypothesis but so does the recent to present internal deformation of the aegean transverse e w active shortening observed in the northern aegean is commonly taken as one of the most striking pieces of evidence that aegean extension results from the lateral extrusion of anatolia the experiments indicate that such transverse shortening may equally develop as a result of pure gravity spreading associated with a pattern of faults and rotations that compares well with that of the northern aegean pure dextral shearing along some strands of the north aegean trough fault system and the related development of an asymmetric pattern of faults in the northern aegean are eventually the only features that evidently arise from the extrusion of anatolia since less than 3 ma finally we argue that during the early stages of aegean extension since at least 21 ma and until ca 11 ma the distribution of extensional strain on a regional scale has been controlled by the distribution of earlier thickening post thickening thermal weakening through partial melting of deep levels of the crust probably accounts for the localization of extensional strain within the areas of thick crust restoring the aegean in its most likely configuration at the onset of bulk crustal extension suggests that 1 the extensional strain rate remained roughly constant or has eventually decreased since the onset of aegean extension and 2 the amounts of extension before and after 16 ma have been roughly equal

clarifying the interplate main tectonic elements of western anatolia turkey by using gnss velocities and bouguer gravity anomalies abstract in this study the gnss and gravity data were processed and compared together for examining the continental structures of the western anatolia region which has very complicated tectonism the gnss data of three national projects were processed and gnss velocities were found as approximately 25 mm per year towards southwest with respect to the eurasia fixed frame in order to investigate the interplate motions of the region the anatolian and aegean block solutions were calculated and the differences in directions and amplitudes of velocities were observed particularly in the anatolian block solution due to the anatolian block solutions the study area was grouped into three regions and compared with the tectonic structures as the first time for western anatolia by this study additionally w e and n s relative gnss solutions were obtained for observing the possible tectonic borders of the study area besides 2nd order horizontal derivative and low pass filter methods were applied to bouguer gravity anomalies and the results of the gravity applications and the changes on crustal mantle interface were compared with the gnss horizontal velocities

the distribution of rare earth and minor elements in manganese nodules and sediments from the equatorial and s w pacific abstract 62 manganese nodules and 17 associated sediments from the equatorial and s w pacific have been analyzed for a number of elements including the rare earth elements ree by instrumental neutron activation sc co as hf th and ree occur in higher concentrations in s w pacific than in equatorial pacific nodules reflecting the higher iron content of the s w pacific nodules these elements are probably incorporated nondiscriminantly into the iron oxyhydroxide structure by direct sorption from seawater because they are too large to be incorporated into the manganese oxide structure the highest ce la ratios are also found in the s w pacific nodules this may result from the fact that these nodules lie beneath the path of the fast flowing well oxygenated antarctic bottom water aabw which facilitates oxidation of ce to the tetravalent state if so this supports the idea that the ce la ratio of manganese nodules is an important redox indicator negative cerium anomalies were noted for nodules from areas f and g can be interpreted on the same model the ree contents in equatorial pacific siliceous oozes and s w pacific red clays are similar on a carbonate free basis the ce la ratio of the s w pacific red clays is however much higher than that of the equatorial pacific sediments possibly reflecting the preferential oxidation of ce to the tetravalent state beneath the aabw there appears to be no systematic relationship between the ree abundance in the nodules and their associated sediments although absolute ree abundances are higher in nodules than in their associated sediments nodules with the highest ce la ratios are however found on sediments with the highest ce la ratios the principal difference in the ree distribution pattern of the nodules and sediments lies in the well known cerium anomaly which is positive to slightly negative for nodules and always negative for sediments

sedimentation at manop site h eastern equatorial pacific over the past 400 000 years climatically induced redox variations and their effects on transition metal cycling gravity cores recovered from manganese nodule project site h 6 33 n 92 49 w show marked downcore variations in the abundance of calcium carbonate organic carbon opal manganese and other components deposited over the past 400 000 years variations in the downcore abundance of organic carbon which ranges from 0 2 to 1 0 can be used to hindcast redox conditions in the surface sediments over this time the results indicate that the depth to the manganese redox boundary varied from about 5 to 25 cm below the seafloor during four major cycles downcore variations in solid phase mn ni and cu can be produced by such changes in redox conditions a model which predicts that solid phase mn can be trapped and buried when the mn redox boundary migrates rapidly upward is consistent with the observed organic carbon and mn records and supports the reconstructed redox variations the history of redox variations at site h can be explained by changes with time in surface water productivity major productivity variations at the site occur over 100 kyr cycles with relatively higher productivity occurring during glacial stages thus quaternary climate changes influence surface water productivity redox conditions in sediments and the cycling of transition metals

molybdenum behavior during early diagenesis insights from mo isotopes 1 we present molybdenum isotope and concentration data from 14 sites in the eastern pacific from the central california to the peru margin the environments studied have been chosen to represent a broad range in oxidation reduction redox potential which provide a framework for the behavior of this redox sensitive element manganese rich hemipelagic sediments from the eastern tropical pacific have a mean characteristic mo isotope signature 98 95mo 0 49 0 04 two times the standard deviation of the mean 2 sdom with n 14 that reflects fractionation between ocean water and authigenic mo associated with mn oxides authigenic fe mo s deposits from reducing continental margin settings also have a characteristic mo isotopic signature 98 95mo 1 64 0 04 2 sdom with n 136 both of these values are in contrast to highly sulfidic 11 m h2saq restricted basin environments which contain mo isotope values analytically indistinguishable from seawater in terms of the mo isotope composition the modern oceanic mo sink is dominated by continental margin type environments where 98 95mo 1 6 and mn rich sediments where 98 95mo approximately 0 5 with a minor contribution from euxinic settings where h2saq 11 m

estimating growth rates of ferromanganese nodules from chemical compositions implications for nodule formation processes abstract using available information on the accretion rates and the bulk chemical compositions of oceanic ferromanganese nodules it can be shown that the accumulation rate of manganese is proportional to the square of the accumulation rate of iron this relationship has been used to derive an equation that predicts nodule growth rates from their chemical compositions the equation accurately predicts growth rates up to about 50 mm 10 6 yr but yields incorrect rates for faster growing concretions from this relationship nodules underneath water of high primary productivity grow most rapidly and accumulate transition metals most rapidly however nodules from regions of highest primary productivity do not have the highest concentrations of nickel and copper reduction of manganese within the sediment column and remobilization of a fraction to the surface sediments adds manganese to nodules without substantially augmenting the supply of other transition elements the addition of remobilized manganese to the nodule dilutes the concentrations of nickel copper and iron even though their rates of accumulation are also high

cgps time series and trajectories of crustal motion along the west hellenic arc summary western greece is one of the seismotectonically most active regions in europe the main tectonic structures are the west hellenic arc wha and the kephalonia fault zone in order to monitor and understand the crustal movements in space and time a continuous gps network was installed in this paper we present results of 6 yr 1995 2001 of measurements to ensure a consistent reference frame 54 mainly european igs and euref sites were included in the processing a selected subset was used to estimate an euler pole for the rotation of eurasia in order to obtain coordinate time series of high precision that are representative for crustal deformation special emphasis was given to the elimination of non tectonic effects four steps of improvement were pursued including a reprocessing after exclusion of poor data the removal of remaining outliers the correction of unknown phase centre offsets after antenna changes and weighted common mode filtering with this procedure non tectonic irregularities were reduced significantly and the precision was improved by an average of 40 per cent the final time series are used as a base for depicting trajectories of crustal motion interpreting the temporal behaviour of the sites and for estimating velocities for the first time height changes in the wha area were detected and quantified by gps sites that are located near the epicentres of the 1997 strofades mw 6 6 and the 1999 athens mw 6 0 earthquakes are particularly considered

the manganese nodules of the kane gap east atlantic indicators of sedimentation erosion changes manganese nodules from the kane gap a deep sea channel connecting the sierra leone and gambia basins off west africa were investigated chemically and dated by10be along cross sections comparing the nodule structure with the stratigraphy of the related sediments the following conclusions are drawn concerning the sedimentation processes during the last 4 to 6 106 years the growth of the nodules started about 4 to 4 5 ma before present during or near to the end of a period of erosion on a fossil free probably miocene sediment during the first phase of only a few hundred thousandyears the nodules grew very quickly 7 to 18 mm ma fe rich hydrogenetic material formed the internal sections of the nodules during this time slowing down of the bottom currents resulting in deposition of thin sediment covers for short intervals caused the character of the nodules to change to a more diagenetic composition the growth rates were reduced to about 1 to 2 mm ma the time of slowing is roughly 3 to 4 ma bp

seismic investigation of the transition from continental to oceanic subduction along the western hellenic subduction zone 1 the western hellenic subduction zone whsz exhibits well documented along strike variations in lithosphere density i e oceanic versus continental subduction rates and overriding plate extension differences in slab density are believed to drive deformation rates along the whsz however this hypothesis has been difficult to test given the limited seismic constraints on the structure of the whsz particularly beneath northern greece here we present high resolution seismic images across northern and southern greece to constrain the slab composition and mantle wedge geometry along the whsz data from two temporary arrays deployed across greece in a northern line nl and southern line sl are processed using a 2d teleseismic migration algorithm based on the generalized radon transform images of p and s wave velocity perturbations reveal n60e dipping low velocity layers beneath both nl and sl the 8 km thick layer beneath sl is interpreted as subducted oceanic crust while the 20 km thick layer beneath nl is interpreted as subducted continental crust the thickness of subducted continental crust inferred within the upper mantle suggests that 10 km of continental crust has accreted to the overriding plate the relative position of the two subducted crusts implies 70 85 km of additional slab retreat in the south relative to the north overall our seismic images are consistent with the hypothesis that faster sinking of the denser oceanic portion of the slab relative to the continental portion can explain the different rates of slab retreat and deformation in the overriding plate along the whsz

crustal strain in central greece from repeated gps measurements in the interval 1989 1997 summary a 66 station gps network spanning central greece first observed in 1989 has been occupied fully on three occasions june 1989 october 1991 and may 1993 subsets of this network bounding the gulf of korinthos have also been occupied in june 1995 october 1995 may 1996 and september october 1997 the first three occupations were processed using a fiducial gps methodology whereas later surveys were processed using code precise orbits combination of data from different surveys to yield smooth site velocities requires global network translations at each epoch to compensate for errors in the realization of the reference frame this method provides a posteriori estimates of the relative coordinate errors and reference frame noise only one earthquake the 1995 june 15 egion event has caused significant local coseismic displacement and its effects on the interseismic velocity field are removed using an elastic dislocation model we constrain the orientation of the 100 yr triangulation gps velocity estimates of davies et al 1997 using 14 sites common to the two networks the goodness of fit of this transformation indicates that the short term and 100 yr geodetic estimates of deformation are highly compatible we infer that short term geodetic studies are capable of determining longer term deformation rates provided that transient local effects can be modelled from the combined velocity field we estimate principal strains and rigid body rotation rates at points on a regular grid using data from neighbouring sites strain rates are high within the gulf of korinthos and much lower elsewhere the extension rate across the gulf of korinthos increases from east to west comparison of the extension rate with historical and recent rates of seismic release of strain reveals significant medium term seismic hazard in the western gulf of korinthos and may also indicate long term aseismic strain

global positioning system measurements of present day crustal movements in the arabia africa eurasia plate collision zone we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1994 at 54 sites extending east west from the caucasus mountains of southern russia georgia and armenia to the aegean coast of turkey and north south from the southern edge of the eurasian plate pontus block to the northern edge of the arabian platform viewed from a eurasia fixed reference frame sites on the northern arabian platform move n38 13 w at 20 3 mm yr roughly consistent with the velocity implied by nuvel 1a circuit closure n23 7 w at 24 2 mm yr the motion of arabia appears to be transferred directly to the region of turkey north of the suture however eastern turkey is characterized by distributed deformation while central western turkey is characterized by coherent plate motion involving westward displacement and counterclockwise rotation of the anatolian plate internal deformation within the central part of the anatolian plate is less than 2 mm yr the anatolian plate is decoupled from eurasia along the right lateral strike slip north anatolian fault naf this different response in eastern and western turkey to the collision of arabia may result from the different boundary conditions the hellenic arc forming a free boundary to the west and the asian continent and oceanic lithosphere of the black and caspian seas forming a resistant boundary to the north and east we derive a best fitting euler vector for anatolia eurasia motion of 29 2 0 8 n 32 9 0 4 1 3 0 1 m y the mapped surface trace of the naf corresponds well to a small circle about this pole the new euler vector implies an upper bound for naf slip rate of 30 2 mm yr i e assuming all relative motion is accommodated along the naf using the nuvel 1a euler vector for arabia eurasia and the gps euler vector for anatolia eurasia we determine an arabia anatolia euler vector of 31 2 n 45 2 e 0 9 0 1 m y and an upper bound on the east anatolian fault slip rate of 15 3 mm yr the aegean trough region of western turkey deviates significantly from coherent plate rotation in addition to rotating with anatolia this region shows roughly n s extension at a rate of 14 5 mm yr taken together with satellite laser ranging results along the hellenic arc the contemporary pattern of deformation indicates increasing motions toward the arc suggesting that the westward displacement and counterclockwise rotation of anatolia is driven both by pushing from the arabian plate and by pulling or basal drag associated with the foundering african plate along the hellenic subduction zone

a rigorous analysis of gps data to detect crustal deformations application in the area of the ionian sea an analysis of a deformation process in dynamic models is presented where time is considered as the essential part a rigorous adjustment model of unregularly spanned observations in space and time is proposed for the estimation of point velocities and strain rate parameters the problem of the reference frame definition and choices of deformation models are discussed finally an application is given in order to illustrate the method using real data from gps observations at the geodynamically unstable area of the ionian sea 1998 elsevier science b v all rights reserved

trajectories of crustal deformation of western greece from gps observations 1989 1994 the geodynamic processes in the alpine mediterranean area are reflected in the recent crustal movements determined by satellite geodesy there is counterclockwise rotation of africa relative to eurasia with complex deformation in between we report repeated gps measurements carried out between se italy and the island of crete in the period 1989 to 1994 the data reveal distinct crustal motion of the central ionian islands and sw greece over the time span of five years western greece has moved 200mm 10mm to the sw relative to se italy and epiros the trajectories constructed from the repeated observations show that the boundary zone against the sites of no significant motion relative to south italy coincides with the kephalonia fault zone kfz this intense deformation accounts in part for the earthquakes that have frequently devastated the central ionian islands

origin and role of major strike slip transfers during plate collision in the central mediterranean variations in the crustal structure along the northern african plate margin have caused different modes of collision with eurasia lateral density variations along the central mediterranean collision zone are expressed in a change of the angle of the downbending african plate and lead to the formation of strike slip transfers in these transition zones that are roughly perpendicular to the trend of the collisional zone in some cases these transfer zones are developed into hinge faults while in others they can be developed into transform faults this process governs the segmentation of the collision zone in the central mediterranean region south of the maghrebian thrust belt in tunisia and sicily through the calabrian arc to the northeastern hellenic arc extending further to the cyprian arc and to the taurus zagros chain

marine cobalt resources ferromanganese oxides in the open oceans are more enriched in cobalt than any other widely distributed sediments or rocks concentrations of cobalt exceed 1 percent in ferromanganese crusts on seamounts ocean ridges and other raised areas of the ocean the cobaltrich crusts may be the slowest growing of any earth material accumulating one molecular layer every 1 to 3 months attention has been drawn to crusts as potential resources because they contain cobalt manganese and platinum three of the four priority strategic metals for the united states moreover unlike abyssal nodules whose recovery is complicated by their dominant location in international waters some of the most cobalt rich crusts occur within the exclusive economic zone of the united states and other nations environmental impact statements for crust exploitation are under current development by the department of the interior

horizontal crustal motion in the central and eastern mediterranean inferred from satellite laser ranging measurements four campaigns to acquire satellite laser ranging slr measurements at sites in the mediterranean region have been completed these measurements to the lageos satellite made largely by mobile systems cover a time span beginning in november 1985 and ending in june 1993 the range data from 18 sites in the central and eastern mediterranean have been simultaneously analyzed with data acquired by the remainder of the global laser tracking network estimates of horizontal motion were placed into a regional northern europe fixed kinematic reference frame uncertainties are on the order of 5 mm yr for sites having at least four occupations by mobile systems and approach 1 mm yr for permanently located sites with long histories of tracking the resulting relative motion between sites in the aegean exhibit characteristics of broadly distributed pattern of radial extension but at rates that are about 50 larger than those implied from studies of seismic strain rates based on seismicity of magnitude 6 or greater or across the region the motion estimated for sites in turkey exhibit velocity components associated with the westward motion of the anatolian block relative to eurasia these results provide a present day snapshot of ongoing deformational processes as experienced by the locations occupiedmore by slr systems less

active tectonics of the north and central aegean sea summary in this paper we examine the connection between the westward motion of turkey relative to europe and the extension in and around the aegean sea the principal new data available since the last attempt to synthesize the tectonics of this region by mckenzie 1978 are much improved focal mechanisms of earthquakes constrained by p and sh body wave modelling as well as by first motions these mechanisms show that the faulting in the western part of the aegean region is mostly extensional in nature on normal faults with a nw to wnw strike and with slip vectors directed nnw to nne there is evidence from palaeomagnetism that this western region rotates clockwise relative to stable europe in the central and eastern aegean and in nw turkey distributed right lateral strike slip is more prevalent on faults trending ne to ene and with slip vectors directed ne palaeomagnetic data in this eastern region is more ambiguous but consistent with very small or no rotations in the northern part and possibly anticlockwise rotations relative to europe in the south the strike slip faulting that enters the central aegean from the east appears to end abruptly in the sw against the nw trending normal faults of greece the kinematics of the deformation is controlled by three factors the westward motion of turkey relative to europe the continental collision between nw greece albania and the apulia adriatic platform in the west and the presence of the hellenic subduction zone to the south as the right lateral slip on the north anatolian fault enters the aegean region it splays out becoming distributed on several parallel faults the continental shortening in nw greece and albania does not allow the rotation of the western margin of the region to be rapid enough to accommodate this distributed e w right lateral shear and thus leads to e w shortening in the northern aegean which is compensated by n s extension as the southern aegean margin can move easily over the hellenic subduction zone the dynamics of the system once initiated is self sustaining being driven by the high topography in eastern turkey and by the roll back of the subducted slab beneath the southern aegean the geometry of the deformation resembles the behaviour of a system of broken slats attached to margins that rotate in spite of its extreme simplicity a simple model of such broken slats is able to reproduce quantitatively most of the features of the instantaneous velocity field in the aegean region including the slip vectors and nature of the faulting in the eastern and western parts the senses and approximate rates of rotation the overall extensional velocity across the aegean and the distribution of strain rates as seen in the seismicity and topography or bathymetry and using geodetic measurements as part of this study we re examined the relation between the surface faulting and the focal parameters determined seismologically for the three large 1981 gulf of corinth earthquakes and reassessed the evidence for associating particular earthquakes in the sequence with observed surface faulting an important result is that in one of the events there is a resolvable discrepancy between the slip vector measured at the surface and that determined from the seismic body waves

aegean tectonics strain localisation slab tearing and trench retreat abstract we review the geodynamic evolution of the aegean anatolia region and discuss strain localisation there over geological times from late eocene to present crustal deformation in the aegean backarc has localised progressively during slab retreat extension started with the formation of the rhodope metamorphic core complex eocene and migrated to the cyclades and the northern menderes massif oligocene and miocene accommodated by crustal scale detachments and a first series of core complexes mccs extension then localised in western turkey the corinth rift and the external hellenic arc after messinian times while the north anatolian fault penetrated the aegean sea through time the direction and style of extension have not changed significantly except in terms of localisation the contributions of progressive slab retreat and tearing basal drag extrusion tectonics and tectonic inheritance are discussed and we favour a model 1 where slab retreat is the main driving engine 2 successive slab tearing episodes are the main causes of this stepwise strain localisation and 3 the inherited heterogeneity of the crust is a major factor for localising detachments the continental crust has an inherited strong heterogeneity and crustal scale contacts such as major thrust planes act as weak zones or as zones of contrast of resistance and viscosity that can localise later deformation the dynamics of slabs at depth and the asthenospheric flow due to slab retreat also have influence strain localisation in the upper plate successive slab ruptures from the middle miocene to the late miocene have isolated a narrow strip of lithosphere still attached to the african lithosphere below crete the formation of the north anatolian fault is partly a consequence of this evolution the extrusion of anatolia and the aegean extension are partly driven from below asthenospheric flow and from above extrusion of a lid of rigid crust

models of depth dependent bioturbation at manop site h in the eastern equatorial pacific the vertical distribution of excess 226ra sorbed to manganese rich sediments from a box core taken at manop site h 6 34 n 92 48 w in the eastern equatorial pacific can be modeled only if the rate of bioturbation decreases rapidly downward from the seafloor within the upper few centimeters of sediment independent bioturbation rates estimated by balancing dissolved and particulate diagenetic mn fluxes are compatible with the values obtained from the radium model such results are consistent with 210pb and 230th measurements reported here and with manop lander and porewater observations that rapid organic carbon degradation in these sediments consumes oxygen within a few centimeters of the sediment seawater interface the modeled decrease in bioturbation expressed as a biodiffusion coefficient is consistent with values of more than 25 cm2 kyr at the surface falling to less than 0 4 cm2 kyr at a depth of 14 cm

subcrustal microearthquake seismicity and fault plane solutions beneath the hellenic arc subcrustal seismicity recorded in the southern aegean sea during a 7 week microearthquake study was low compared with shallow seismicity most intermediate depth seismicity occurred beneath the western and eastern ends of the hellenic arc this distribution confirms that a slab of lithosphere is being subducted at a very shallow 15 angle for 200 km beneath the western end peloponnese but more steeply beneath the eastern end dodecanese we could locate only one intermediate depth event beneath the central pan of the arc where teleseimically located intermediate depth earthquakes also are infrequent t axes for most of the 22 focal mechanisms of subcrustal earthquakes are roughly parallel to the local dip direction of the seismic zone between depths of 40 and 80 km the mechanisms are more confused than at greater depth perhaps because some of these earthquakes did not occur within the downgoing slab earthquakes deeper than 80 km and within the subducted slab have nearly horizontal p axes that trend nne ssw in the eastern part and nnw sse in the western part of the arc these deeper mechanisms show horizontal p axes along strike perhaps in response to the contortion of the slab or to the westward motion of turkey as well as lengthening downdip probably in response to gravity acting on excess mass in the slab thus the short slab both downdip and along strike subducting beneath the aegean is subjected to a more complex set of forces than the long slabs of the pacific

characteristics of manganese nodules from the central indian basin relationship with the sedimentary environment the hydrogenetic and diagenetic manganese nodules from the cib show an unequivocal genetic relationship with neogene sedimentological patterns hydrogenetic nodules were observed at the top of the sedimentary column and interstratified in thin sequences of biosiliceous sediments and underlying miocene red clays in cores from topographic highs early to late pliocene radiolarian fauna were found at the base of the biosiliceous deposits these condensed biosiliceous sediments are less than 4 0 m thick and periods of non deposition and or erosion may have occurred in the central deep area 11 15 s significant biogenic deposition began during the early to late pliocene as a result of the development of a high biogenic productivity belt to the south producing the favourable conditions for diagenetic accretionary processes for mn nodules this indicates growth of hydrogenetic nodules prior to the late pliocene and the subsequent inception of diagenetic accretion formation of the most recent diagenetic nodules is associated with higher rates of sedimentation in the deep sea troughs where the siliceous sediments are much thicker this should promote the diagenetic mobilization of mn and its precipitation under oxic and suboxic conditions nevertheless diagenetic nodules are restricted to the upper 40 cm of sediments younger than 400 000 years suggesting fast growing diagenetic nodules and the dissolution of buried nodules below the first 50 cm of siliceous oozes hydrogenetic nodules are formed by dense layers of mno2 fe oh 3 and amorphous silica and they show smooth texture and botryoidal shapes analysis of bulk and selected portions of layered crust or rind shows very low mnfe ratios 2 and relatively high co and ti contents in most cases the cores of hydrogenetic nodules are fragments of altered ash layers from the indonesian volcanic arc which is located more than 2500 km to the east the ash layers are also interstratified with miocene red clays diagenetic nodules show a granular texture and comprise concentric layers with dendritic or columnar structures mainly of 10 a manganate higher mn ni and cu contents are observed in this phase late diagenetic enrichment of these nodules is continuous within the upper 40 cm of recent ni that enhances the stability of early diagenetic 10 a manganate buserite and c the formation of todorokite some nodules referred to as mixed in the literature show hydrogenetic internal layers which grade outward to a diagenetic crust this transitional character suggests slow changes in the sedimentary environment as growth advances the nodules of the cib and the east equatorial pacific eep are similar in terms of both metallic composition and accretionary patterns however the nodules of the cib are considerably younger and present a continuous accretionary history the history of the manganese nodules from the cib is related to the post late miocene sedimentary and geodynamic evolution of this basin

australasian microtektites in a substrate a new constraint on ferromanganese crust accumulation rates abstract microtektites belonging to the australasian tektite strewn field are found in the substrate of a ferromanganese crust dredged from the central indian basin they are identified on their physical appearance geographic occurrence and chemical composition the ferromanganese crust has a thickness range of 6 17 mm and its chemistry and mineralogy indicate hydrogenic accretion because the australasian strewn field has an age of 0 77 ma this finding implies that the overlying fe mn crust has minimum accretion rates of 7 8 22 1 mm myr which are much higher than the average growth rates of hydrogenic crusts

insights into present day crustal motion in the central mediterranean area from gps surveys summary in this paper we present observations of crustal motion related to a large gps network located in the central western mediterranean area velocities are obtained by the analysis of more than 30 observing sites at which at least three different gps campaigns were carried out in the time span 1991 1999 the results are presented both in the itrf96 reference frame and with respect to a eurasian fixed reference frame the sites located along the northern african margin in sicily and southern italy show prevalent northeastward movements with a mean velocity of roughly 0 7 cm yr 1 the relatively dense network available in the southern apennines led us to try a tentative estimate of the average strain rate in this zone resulting in a maximum extension of 0 021 0 006 10 6 yr 1 normal to the chain in ionian greece the two sites located south of the kephallinia discontinuity lefkas and kastro ilias consistently indicate a south to southwestward motion at an average rate of roughly 15 mm yr 1

establishment of a continuous gps network across the kephalonia fault zone ionian islands greece abstract we report on the establishment of a continuous gps network across the kephalonia fault zone kfz central ionian islands greece the kfz is an important segment of the boundary zone between the rapidly moving aegean microplate and the apulian platform italy repeated gps measurements carried out between the northern ionian islands and the island of crete have shown rates of crustal motion of the aegean reaching 35 mm a oriented sw relative to southern italy the kfz coincides with a maximum shear strain rate 180 nano strain a and a very high level of seismicity in order to monitor the ongoing deformation across the kfz and correlate the strain accumulation with earthquakes a continuous gps network has been installed operating at a sampling rate of 5 s this paper describes the instrumental set up the data logging strategy and first preliminary results

transport and release of transition elements during early diagenesis sequential leaching of sediments from manop sites m and h part i ph 5 acetic acid leach sediments from manop sites m and h in the eastern tropical pacific ocean can be partitioned into operationally defined phases by means of a sequential leach procedure this paper reports the results of the first leach in the sequence an acetic acid solution buffered as p h 5 with sodium acetate this leach is designed to remove carbonate bound and sorbed cations the only cation bound in a consistent ratio to calcium in the carbonate is strontium the molar ratio is 2 10 3 in contrast transition metals are sorbed onto the surfaces of other sedimentary particles the proportions sorbed range from 2 to 10 of the total manganese about 10 of the total nickel and copper and less than 1 of the total iron the pool of sorbed metals in surface sediments is sufficiently large and the rate of biological stirring is sufficiently rapid for this metal reservoir potentially to dominate the porewater reservoir in supplying metals to ferromanganese nodules a simple model for nodule growth based upon transfer of metals through this reservoir suggests that only 1 of the sedimentary sorbed metals within a radius of 2 to 9 cm is required to support typical nodule growth rates

contemporary global horizontal crustal motion summary an analysis of satellite laser ranging slr data to the lageos satellite has yielded improved estimates of the horizontal motion for a subset of 34 tracking sites within the global tracking network the analysis called sl8 3 utilized data acquired between 1980 january and 1993 june by the global network composed of 71 sites the solution design provides for the simultaneous estimation of site positions and their velocities within a pre defined kinematic frame the solution is statistically rigorous and retains the full correlation information content least squares estimates of relative poles of rotation which are used to model the motion of one plate relative to another were made based on the slr estimated velocities for sites known to be well away from deformation zones the resulting slr based relative rotation poles differ slightly from those of nuvel 1 but in general indicate that the magnitude of the slr implied velocities is slower than those implied by nuvel 1 consistent with the 4 5 per cent slowing in relative spherical rates noted in earlier comparisons spherical rates between sites in western north america support models of extension in the basin and range province and the rotation of the sierra nevada microplate an analysis of the spherical rates crossing the north atlantic shows that sl8 3 estimated extension between north america eurasia sites is generally smaller than those implied by nuvel 1 meanwhile sl8 3 rates between north america africa sites are in better agreement with nuvel 1 although they are not so well determined the maintenance and ongoing monitoring of global slr site kinematics provides a well defined global reference which will aid in combination global kinematic solutions where information from other technologies are merged e g very long baseline interferometry and global positioning system and in providing the context for densification studies of regional kinematics derived from terrestrial and global positioning system observations

fluxes of metals to a manganese nodule radiochemical chemical structural and mineralogical studies fluxes of metals to the top and bottom surfaces of a manganese nodule were determined by combining radiochemical 230th 231pa 232th 238u 234u and detailed chemical data the top of the nodule had been growing in its collected orientation at 4 7 mm myr 1 for at least 0 5 myr and accreting mn at 200 g cm 2 kyr 1 the bottom of the nodule had been growing in its collected orientation at about 12 mm myr 1 for at least 0 3 myr and accreting mn at about 700 g cm 2 yr 1 although the top of the nodule was enriched in iron relative to the bottom the nodule had been accreting fe 50 faster on the bottom 232th was also accumulating more rapidly in the bottom despite a 20 fold enrichment of230th on the top the distribution of alpha emitting nuclides calculated from detailed radiochemical measurements matched closely the pattern revealed by 109 day exposures of alpha sensitive film to the nodule however the shape and slope of the total alpha profile with depth into the nodule was affected strongly by226ra and222rn migrations making the alpha track technique alone an inadequate method of measuring nodule growth rates diffusion of radium in the nodule may have been affected by diagenetic reactions which produce barite phillipsite and todorokite within 1 mm of the nodule surface however our sampling interval was too broad to document the effect we have not been able to resolve the importance of nodule diagenesis on the gross chemistry of the nodule

tectonic evolution of fault bounded continental blocks comparison of paleomagnetic and gps data in the corinth and megara basins greece 1 we report on new paleomagnetic and anisotropy of magnetic susceptibility ams data from plio pleistocene sedimentary units from corinth and megara basins peloponnesus greece paleomagnetic results show that megara basin has undergone vertical axis cw rotation since the pliocene while corinth has rotated ccw during the same period of time these results indicate that the overall deformation in central greece has been achieved by complex interactions of mostly rigid rotating fault bounded crustal blocks the comparison of paleomagnetic results and existing gps data shows that the boundaries of the rigid blocks in central greece have changed over time with faulting migrating into the hanging walls sometimes changing in orientation the megara basin belonged to the beotia locris block in the past but has now been incorporated into the peloponnesus block possibly because the faulting in the gulf of corinth has propagated both north and east paleomagnetic and gps data from megara and corinth basins have significant implications for the deformation style of the continental lithosphere in areas of distributed deformation the continental lithosphere behaves instantaneously like a small number of rigid blocks with well defined boundaries this means that these boundaries could be detected with only few years of observations with gps however on a larger time interval the block boundaries change with time as the active fault moves paleomagnetic studies distinguishing differential rotational domains provide a useful tool to map how block boundaries change with time index terms 1208 geodesy and gravity crustal movements intraplate 8110 1518 geomagnetism and paleomagnetism magnetic fabrics and anisotropy 1525 geomagnetism and paleomagnetism paleomagnetism applied to tectonics regional global 8107 tectonophysics continental neotectonics 9335 information related to geographic region europe

contemporary kinematics of the southern aegean and the mediterranean ridge summary this study focuses on the kinematics of the southern aegean and the mediterranean ridge mr a quantification of the deformation of the mr is essential for both evaluating physical models of accretionary wedges in general and for obtaining a self consistent model of the surface deformation over the entire nubia eurasia nu eu plate boundary zone in the eastern mediterranean previous kinematic studies have not properly considered the deformation field south of the hellenic arc although this study focuses on the deformation field of the mr we also discuss the kinematics of the southern aegean because the geometry and movement of the hellenic arc determine to a large extent the kinematic boundary conditions for kinematic studies of the mr we calculate a continuous velocity and strain rate field by interpolating model velocities that are fitted in a least squares sense to published global positioning system gps velocities in the interpolation we use information from a detailed data set of onshore and offshore active faulting to place constraints on the expected style and direction of the model strain rate field in addition we use the orientations of tracks left by seamounts travelling into the wedge to further constrain the offshore deformation pattern our model results highlight the presence of active shear partitioning within the mediterranean ridge high compressional strain rates between the ridge crest and the deformation front accommodate approximately 60 70 per cent of the total motion over the wedge and the outward growth rate of the frontal thrust is 4m m yr 1 strain partitioning within the wedge leads to 19 23 mm yr 1 of dextral motion at the wedge backstop contact of the western mr whereas the pliny and strabo trenches in the eastern mr accommodate 21 23 mm yr 1 of sinistral motion the backstop of the western mr is kinematically part of the southern aegean which moves as a single block the aegean block ae at 33 34 mm yr 1 in the direction of s24 w 1 towards stable nubia nu our model confirms that there is a clear divergence between the western and eastern hellenic arc and we argue for a causal relation between the outward motion of the arc and the gradient in the regional geoid anomaly our results suggest that a significant driving source of the surface velocity field lies south of the hellenic arc and only for the southeastern aegean could there be some effect as a result of gravitational collapse associated with density differences within the overriding plate

gps derived strain rate field within the boundary zones of the eurasian african and arabian plates we use the gps velocity field 1988 1998 for eastern mediterranean and asia minor to determine the crustal deformation strain rate field in an area bounded by 35 n and 43 n and 20 e and 48 e we calculate the normal and shear strain rate components associated with the major faults and compare these qualitatively with seismological data uncertainties in the calculation of the strain rates reach 50 nstrain yr 1 in sparsely observed parts of anatolia whereas we estimate errors 20 nstrain yr 1 in the aegean and marmara regions the largest compressional strain rate components in the eastern part of the study area occur along the greater caucasus mountain front reaching 70 nstrain yr 1 1 nstrain yr 1 0 0317 10 15 s 1 the north anatolian fault zone is the clearest feature in the shear strain rate field it is expressed as a pronounced dextral strike slip fault zone reaching rates of up to 170 nstrain yr 1 this holds true also for the izmit area where the august 17 1999 earthquake occurred central anatolia is almost strain free whereas extension prevails in western anatolia the principal axes of extension vary around the n s direction with strain rates of up to 85 nstrain yr 1 these extensional areas coincide with graben features and normal faulting earthquakes the central and southwestern aegean sea is strain free with values far below 40 nstrain yr 1 the seismic cluster around the dodekanissa islands southeastern aegean sea coincides with nw se oriented extension attaining strain rates of up to 90 nstrain yr 1 this area of extension also exhibits recent active volcanism the entire hellenic arc shows compressional strain rates perpendicular to the arc the pliny strabo troughs along the eastern segment of the arc show left lateral shear strain rates reaching 80 nstrain yr 1 significant extension is found in central greece with a nne ssw oriented maximum of 120 nstrain yr 1 centered around the gulf of corinthos the kephalonia fault zone in nw greece is a distinct dextral fault zone separating apulia from the rapidly moving aegean microplate right lateral shear strain rates reach 150 nstrain yr 1

the tectonic expression slab pull at continental convergent boundaries examination of five thrust belt systems developed at continental subduction boundaries suggests that they comprise two distinct groups that display pronounced and systematic differences in structural style topographic elevation denudation metamorphism postcollisional convergence and foredeep basin geometry and facies the distinctive geological features developed within each thrust belt group appear to be causally linked to the relative rates of subduction and convergence via the magnitude of horizontal compressional stress transmitted across the subduction boundary at subduction boundaries where the rate of overall plate convergence is less than the rate of subduction termed here retreating subduction boundaries the transmission of horizontal compressive stress across the plate boundary is small and regional deformation of the overriding plate is by horizontal extension the tectonic expression of these retreating subduction boundaries includes topographically low mountains little erosion or denudation low grade to no metamorphism little to no involvement of crystalline basement in shortening little to no postcollisional convergence anomalously deep foredeep basins and a protracted history of flysch deposition within the adjacent foredeep basin analysis of deflection and gravity data across three retreating subduction boundaries apennine carpathian and hellenic systems shows that subduction is driven by gravitational forces acting on dense subducted slabs at depths between about 40 and 80 km carpathians 50 and 150 km apennines and 50 and 250 km hellenides the total mass anomalies represented by the slabs are approximately 3 1012 6 1012 and 12 1012 n m respectively the slabs are partially supported by flexural stresses transmitted through the subducted lithosphere to the foreland and partially supported by dynamic viscous stresses in the asthenosphere at subduction boundaries where the rate of overall plate convergence is greater than the rate of subduction termed here advancing subduction boundaries the transmission of horizontal compressive stress across the plate boundary is large and regional deformation of the overriding plate is by horizontal shortening the tectonic expression of these advancing subduction boundaries includes topographically high mountains antithetic thrust belts large amounts of erosion and denudation exposure of high grade metamorphic rocks at the surface extensive deformation of crystalline basement to midcrustal depths protracted postcollisional convergence tens of millions of years and a protracted history of molasse deposition within the adjacent foredeep basins analysis of gravity and deflection data across two advancing subduction boundaries developed within the continental lithosphere western to eastern and southern alps and himalayas shows that the thrust sheets have been translated for great distances over the foreland lithosphere relative to the point at which the subduction forces are applied thus obscuring any flexural and gravity signals from the subducted slab however it appears that far field stresses presumably related to global plate motions drive most of the convergent motion across these subduction boundaries the concept that orogenic belts formed above retreating subduction boundaries have recognizable tectonic signatures that differ from those of orogenic belts formed above advancing subduction boundaries suggests that it may be possible to interpret the plate boundary settings in which ancient orogenic belts evolved appendix b is available with entire article on microfiche order from the american geophysical union 2000 floridaavenue n w washington d c 20009 document t92 004 2 50 payment must accompany order

ferromanganese nodules from manop sites h s and r control of mineralogical and chemical composition by multiple accretionary processes abstract the chemical composition of ferromanganese nodules from the three nodule bearing manop sites in the pacific can be accounted for in a qualitative way by variable contributions of distinct accretionary processes these accretionary modes are 1 1 hydrogenous i e direct precipitation or accumulation of colloidal metal oxides in seawater 2 2 oxic diagenesis which refers to a variety of ferromanganese accretion processes occurring in oxic sediments and 3 3 suboxic diagenesis which results from reduction of mn 4 by oxidation of organic matter in the sediments geochemical evidence suggests processes 1 and 2 occur at all three manop nodule bearing sites and process 3 occurs only at the hemipelagic site h which underlies the relatively productive waters of the eastern tropical pacific a normative model quantitatively accounts for the variability observed in nearly all elements zn and na however are not well explained by the three end member model and we suggest that an additional accretionary process results in greater variability in the abundances of these elements variable contributions from the three accretionary processes result in distinct top bottom compositional differences at the three sites nodule tops from h are enriched in ni cu and zn instead of the more typical enrichments of these elements in nodule bottoms in addition elemental correlations typical of most pelagic nodules are reversed at site h the three accretionary processes result in distinct mineralogies hydrogenous precipitation produces mno2 oxic diagenesis however produces cu ni rich todorokite and suboxic diagenesis results in an unstable todorokite which transforms to a 7 a phase birnessite upon dehydration the presence of cu and ni as charge balancing cations influence the stability of the todorokite structure in the bottoms of h nodules which accrete dominantly by suboxic diagenesis na and possibly mn 2 provide much of the charge balance for the todorokite structure limited growth rate data for h nodules suggest suboxic accretion is the fastest of the three processes with rates at least 200 mm 106 yr oxic accretion is probably 10 times slower and hydrogenous 100 times slower since these rates predict more suboxic component in bulk nodules than is calculated by the normative analysis we propose that suboxic accretion is a non steady state process variations in surface water productivity cause pulses of particulate flux to the sea floor which result in transient mn reduction in the surface sediments and reprecipitation on nodule surfaces

seismological and gps evidence for the aegean anatolia interaction seismological and gps data are used in order to examine the seismotectonic setting and the plate motions in the eastern mediterranean the main objective is to reevaluate the recently proposed idea of a single anatolia aegean microplate which performs a rigid body rotation about an euler pole located in northern africa both data sets show a more complicated setting south of the north anatolia fault naf the plate motion of anatolia relative to europe can be adequately described by a simple rigid body rotation with a dominant east west component and an average velocity of 22mm yr however both types of data show a significant increase of the deformation velocities in the aegean area 30 35mm yr and exhibit a much larger n s component up to 20mm yr than the one predicted from rigid body rotation this deformation pattern is more consistent with models which consider the aegean as a separate microplate

growth rates of manganese rich nodules at manop site h eastern north pacific abstract estimates of the growth rates of ferromanganese nodules at manop site h 6 33 n 92 49 w lie between 7 and 1200 mm my the most probable range estimated from nodule size distributions nodule chemistry accumulation rates of authigenic elements and u series modeling is 30 300 mm my such rates are much faster than measured values for most pelagic nodules the distributions of u series and stable elements suggest that a typical nodule consists of two compositionally distinct non detrital components one rich in mn u and sb and the other in fe co ree ni cu and th when the uncorrected u series data which do not show simple decay patterns with depth are normalized to the relative proportion of the fe rich component the data yield well constrained growth rates of 55 mm my for a nodule top and 200 mm my for its bottom the component enriched in mn which is most abundant on nodule bottoms appears to accrete much faster than the component enriched in fe

thorium and uranium isotopes in a manganese nodule from the peru basin determined by alpha spectrometry and thermal ionization mass spectrometry tims are manganese supply and growth related to climate thorium and uranium isotopes were measured in a diagenetic manganese nodule from the peru basin applying alpha and thermal ionization mass spectrometry tims alpha counting of 62 samples was carried out with a depth resolution of 0 4 mm to gain a high resolution230thexcess profile in addition 17 samples were measured with tims to obtain precise isotope concentrations and isotope ratios we got values of 0 06 0 59 ppb 230th 0 43 1 40 ppm 232th 0 09 0 49 ppb 234u and 1 66 8 24 ppm 238u the uranium activity ratio in the uppermost samples 1 6 mm and in two further sections in the nodule at 12 5 1 0 mm and 27 3 33 5 mm comes close to the present ocean water value of 1 144 0 004 in two other sections of the nodule this ratio is significantly higher probably reflecting incorporation of diagenetic uranium the upper 25 mm section of the mn nodule shows a relatively smooth exponential decrease in the230thexcess concentration tims the slope of the best fit yields a growth rate of 110 mm ma up to 24 5 mm depth the section from 25 to 30 3 mm depth shows constant230thexcess concentrations probably due to growth rates even faster than those in the top section of the nodule from 33 to 50 mm depth the growth rate is approximately 60 mm ma two layers in the nodule with distinct laminations 11 15 and 28 33 mm depth probably formed during the transition from isotopic stage 8 to 7 and in stage 5e respectively the mn fe ratio shows higher values during interglacials 5 and 7 and lower ones during glacials 4 and 6 a comparison of our data with data from adjacent sediment cores suggests a a variable supply of hydrothermal mn to sediments and mn nodules of the peru basin or b suboxic conditions at the water sediment interface during periods with lower mn fe ratios

the dynamics of the eastern mediterranean and eastern turkey summary in this study we investigate the dynamics of the region that includes greece the aegean sea and asia minor in a least squares inversion we solve for a continuous strain rate field and corresponding velocity field that satisfies 872 gps data the estimate of the geodetic strain rate field provides constraints for our dynamic analysis next we separately solve the depth integrated 3 d force balance equations for depth integrated deviatoric stresses within the lithosphere in which body force input comes from differences in vertically integrated vertical stress or differences in gravitational potential energy per unit area gpe these gpe estimates calibrate the absolute magnitudes of deviatoric stresses that are acting within the lithosphere further we investigate the sensitivity of our stress field solutions by using two different crustal structure models one from compiled crustal structure estimates obtained primarily from relatively recent seismic observations and the other from the crust 2 0 model in an iterative least squares inversion we then solve for stress field boundary conditions that when added to the contribution of deviatoric stresses associated with gpe differences provides a best fit to the directions of principal axes and relative magnitudes of the principal axes of the rates of strain obtained in the kinematic analysis robust features that arise from the boundary condition solution are nne forcing along the southern boundary east of about 33 e 0 5 1 2 1012 n m 1 with a rapid anticlockwise rotation of forces to the west of this along with an outward pulling force 0 4 1012 n m 1 directed ssw along the entire hellenic arc segment this force system along the hellenic arc can be interpreted as a result of slab rollback the total depth integrated 3 d deviatoric stresses in the final dynamic solution provides an excellent match to the deformation indicators throughout the region with vertically integrated stress magnitudes of order 0 5 2 5 1012 n m 1 we use constraints from derived stress magnitudes together with gps defined scalar values of strain rate magnitude to define bulk effective viscosities of the lithosphere depth averaged effective viscosities for the entire lithosphere are high within the black sea of order 0 7 3 1023 pa s relative to surrounding continental lithosphere north anatolian shear zone northern aegean sea and gulf of corinth are characterized by low depth averaged viscosities of order 1 5 1021 pa s deviatoric stresses from gpe differences and boundary condition effects combine in surprising ways in some regions resulting in near total stress cancellation in areas such as the southern aegean sea and portions of the central anatolian block gpe differences combine with boundary condition effects along the eastern segment of the north anatolian fault naf in a way that is compatible with the hypothesis that motion on the naf was facilitated by slab detachment beneath east anatolia and dynamic uplift of east anatolian plateau in general gpe differences play a nearly equal role as boundary condition influences in their contribution to the total deviatoric stress field the low depth integrated deviatoric stress magnitudes throughout the region suggest that zones of active deformation are facilitated by dramatic weakening mechanisms throughout the lithosphere

geochemical composition and inferred accretion rates of sediments and managanese nodules from a submarine hill in the madeira abyssal plain eastern north atlantic abstract the porewater and sediment composition of two boxcores and of a small gravity core taken on a manganese nodule covered hill and in the madeira abyssal plain proper respectively are compared the pore water study of the two boxcores indicates that oxic conditions prevail in both cores in addition it indicates that no detectable fluxes of mn or fe occur from the porewater to the ocean bottom water variations in the geochemical composition of the sediments can be explained by fluctuations in the amount of carbonate which acts as a diluting agent a clear carbonate minimum is observed at 20 22 cm depth in the two cores this minimum is likely to be associated with the last glacial period 10 20 kyr b p this association is supported by the sediment accumulation rate of 15 mm kyr as found by extrapolation from the rate for pelagic sediments in the madeira abyssal plain the bulk composition of the manganese nodules recovered from the submarine hill is chemically almost identical to the average composition of atlantic nodules the trace metal and rare earth elements composition indicate a hydrogenous origin for the manganese nodules of this study on the basis of the chemical composition and that of nodules relative to that of the adjacent sediments an average nodule accretian rate of 2 8 3 3 mm myr has been calculated although the analyses of the entire ferromanganese nodules that have been studied seem to indicate a homogenous composition internal structures of the nodules reveal great inhomogeneity both visually and chemically these fluctuations may be related to variations in the fluxes of mn and fe which in turn could be climate related

tectonic deformation and microseismicity of the saronikos gulf greece we deployed an on offshore seismic network consisting of 36 three component stand alone digital stations in the saronikos gulf and surrounding area and observed the microseismic activity from 17 august to 9 december 2001 the geometry and location of the network were designed to observe the offshore activity to connect known active faults onshore with those offshore an average of 15 events per day were recorded by a minimum of six stations the focal parameters of 739 events could be defined within the network area we located 306 events with an rms travel time residual of about 0 2 sec the epicenters in the saronikos gulf are aligned mainly along an east west trending fault with a length of nearly 30 km this fault is located north of aegina and could produce earthquakes as large as ms 6 5 it is the offshore continuation of a seismic zone located in east corinthia a second active fault was identified east of aegina trending northeast southwest it is probably linked to the northeast southwest striking zone of the salamis fili seismic region activated by the september 1999 event of athens outside the network we mapped an active area at the parnis mountain still active after the ms 5 9 event and a second one further northeast at the western coast of evia this zone is close to chalkis and the recently active psachna area the network also mapped intense activity at the northeastern coast of evia close to the city of kymi and the area of skyros which was seriously damaged by an ms 5 8 earthquake in 2001 the onshore offshore local network identified several regions of very high seismic activity not detectable by regional networks and demonstrated once more the advantage of deploying local seismic networks for mapping active deformation in very short periods of time

new constraints on the rapid crustal motion of the aegean region recent results inferred from gps measurements 1993 1998 across the west hellenic arc greece abstract in this paper we present the most recent observations of crustal motion across the entire west hellenic arc wha these are based on repeated gps measurements carried out in the period from 1993 to 1998 the results are presented in terms of trajectories and rates relative to eurasia within these five years southwestern greece has moved to the southwest by an average rate of 30 mm a increasing from 10 mm a at the island of lefkada in the center of the ionian islands to nearly 40 mm a along the southwest part of the peloponnesus and to 35 mm a on the islands of crete and gavdhos the data provide strong evidence that distributed shear strain starts at the kephalonia fault zone kfz were an anomalously high earthquake activity is also observed a striking interruption of the motion is seen at the island of strofades at the southwest leading edge of the wha where a south oriented displacement of 12 cm was detected coincident with the m 6 4 strofades earthquake of nov 18 1997

active crustal deformation in the marmara sea region nw anatolia inferred from gps measurements deformation in the boundary zone between the anatolian and eurasian plates has been determined by means of repeated global positioning system gps measurements three campaigns 1990 1992 1994 were carried out around the marmara sea the network lies within the active earthquake belt of nw anatolia extending from the western part of the north anatolian fault zone nafz to the aegean extensional province results of the dense network consisting of 52 sites clearly reveal the westward motion of anatolia the rates amount to 17 mm a 3 mm a on average relative to istanbul located at the northeastern edge of the sea of marmara based on the trajectories for the displacements of the observation sites it is concluded that the marmara sea forms a transition zone between the europe fixed region of thrace black sea eurasia and nw anatolia at the western extremity of nw anatolia the motion bends from w to wsw 247 the strain field calculated yields an e w oriented right lateral strike slip movement average 0 12 ppm a maximum 0 41 ppm a accompanied by ne sw extension average 0 12 ppm a maximum 0 52 ppm a at the eastern end of the marmara sea and n s extension at the aegean shore line comparisons with the directions of t axes derived from 65 fault plane solutions of earthquakes show remarkable agreement

growth history of manganese nodules and crusts of the peru basin abstract in the nodule field of the peru basin situated south of the zone of high bioproductivity a relatively high flux of biogenic matter explains a distinct redox boundary at about 10 cm depth separating very soft oxic surface sediments from stiffer suboxic sediments maximum abundance 50 kg m 2 of diagenetic nodules is found near the calcite compensation depth ccd currently at 4250 m there the accretion rate of nodules is much higher 100 mm ma 1 than on ridges 5 mm ma 1 highest accretion rates are found at the bottom of large nodules that repeatedly sink to a level immediately above the redox boundary there distinct diagenetic growth conditions prevail and layers of dense laminated mn oxide of very pure todorokite are formed the layering of nodules is mainly the result of organisms moving nodules within the oxic surface sediment from diagenetic to hydrogenetic environments the frequency of such movements is much higher than that of climatic changes two types of nodule burial occur in the peru basin large nodules are less easily moved by organisms and become buried consequently buried nodules generally are larger than surface nodules this type of burial predominates in basins at ridges where smaller nodules prevail burial is mainly controlled by statistical selection where some nodules are not moved up by organisms

the kephalonia transform fault and the rotation of the apulian platform evidence from satellite geodesy this paper describes a collaborative gps project to determine recent crustal movements and deformations across the ne ionian sea this region is characterized by rifting in the african foreland pelagian sea subduction along the calabrian and west hellenic arcs rotation of the italian peninsula and distributed normal faulting in central greece from gps campaigns on the ionian islands and in nw greece performed in 1989 and 1991 a kinematic field is deduced which is controlled by the deep trough following the nw coast of kephalonia island it is concluded that this prominent bathymetric feature resembles an active fault system kephalonia fault which has the signature of a right lateral transform fault

western hellenic subduction and cephalonia transform local earthquakes and plate transport and strain abstract focal parameters of local earthquakes in the region of the ionian islands of western greece are constrained with a temporary dense array of three component seismographs operated jointly offshore and onshore seismic deformation is documented to be confined to the east of the n20 e striking steep continental slope west of cephalonia island the right lateral cephalonia transform fault ctf inferred from large earthquakes the pre apulian continental material appears to be only deforming east of the transform fault where it is in upper plate position to the hellenic subduction east of the transform fault the transmission velocity tomography from local earthquakes compared in depth section with a previous marine reflection profile provides evidence in support of a shallow landward dipping boundary around 12 km deep under the ionian islands along which they may override the lower plate on either side of this interface local earthquakes occur with different focal mechanisms in support with its interpretation as the interplate under cephalonia island reverse faulting deforms the upper plate along nw se structures which may also be affected by left lateral bookshelf faulting small earthquakes show normal faulting along the western coast of cephalonia and its extension 20 km ssw the trace of the ctf as inferred from the occurrence of the large strike slip earthquakes another group of normal fault earthquakes locates in the lower plate from under cephalonia to zante just outboard of a possible change of interplate dip suggested from reflection seismics landward under the islands these normal fault earthquakes appear to coincide in position with that of the load imposed by the upper plate transported over them rather than occurring in an outer rise outboard the plate boundary and trench as observed in other subductions and attributed to the control by the flexural bending of the lower plate under the pull of the sinking slab interpretation has to consider several peculiar features of plate interaction in western greece with respect to a steady state model for major subduction zones in particular a fast deformation of the upper plate in front of an orogenically overthickened crust and of the southwestward push of extruding anatolia its transport which is the cause of the migration of the plate boundary rather than the roll back of a slab which has been proposed to be detached possibly a flat and ramp shape of the interplate the geometrical complexity of the shear limit across the ctf between subduction and collision and the nearby variation of the nature of the foreland crust

the gps strain rate field in the aegean sea and western anatolia the gps velocity field of the aegean sea and western anatolia is used to determine crustal deformation strain rates for the period 1988 to 1996 the zone from the marmara sea to the north aegean trough is associated with strong right lateral shear motion with maximum strain rates of 170 nstrain a in the northern aegean sea the extensional deviatoric axes are oriented nne ssw associated with strain rates reaching 150 nstrain a and in western anatolia varying around n s with rates of up to 95 nstrain a the extensional areas mostly coincide with active graben features the south western aegean sea is almost strain free in general the areas of high geodetic strain rates are accompanied by distinct seismic clusters whereas the strain free regions are nearly aseismic

the strain field in northwestern greece and the ionian islands results inferred from gps measurements abstract recent crustal movements detected by the analysis of repeated satellite geodetic measurements reflect the ongoing geodynamic processes in the alpine mediterranean area superimposed on the large scale counterclockwise rotation of the african plate complex dynamic processes are affecting the lithospheric fragments between the african and eurasian plates key features to better understand the driving forces and associated seismic activity in the africa eurasia collision zone are the calabrian and hellenic arcs in this paper geodynamic investigations along the west hellenic arc are discussed they are based on two epochs 1989 and 1993 of satellite geodetic measurements carried out using the us global positioning system gps the results are presented in terms of relative displacements and strain rates within the time span of 4 years southwestern greece has moved to the southwest relative to southeastern italy by an average of 120 mm increasing from 80 mm at lefkada in the center of the ionian islands to 160 mm at the peloponnesus the maximum strain rate is 0 18 strain a located in the vicinity of lefkada where anomalously high earthquake activity is observed the data provide strong evidence for dextral strike slip motion on the order of 25 mm a along the kephalonia fault zone kfz the deformation field of the kfz is interpreted as a transition zone between the kinematics of the apulian platform and the west hellenic fold and thrust belts

evaluation of earthquake potential along the northern anatolian fault zone in the marmara sea using comparisons of gps strain and seismotectonic parameters abstract seismotectonic parameters including the gutenberg richter b value and multifractal dimensions d2 and d15 of seismicity patterns both spatial and temporal were compared to gps derived maximum shear and dilatation strains measured in the marmara sea region of western turkey along the northern anatolian fault zone nafz comparisons of seismotectonic parameters and gps derived maximum shear and dilatation strain along the nafz in the vicinity of the 1999 m7 4 izmit earthquake reveal a positive correlation r 0 5 p 0 05 between average dilatation and the gutenberg richter b value significant negative correlation r 0 56 p 0 03 and r 0 56 p 0 02 was also observed between the spatial fractal dimension d2 and gps derived maximum geodetic and shear strain this relationship suggests that as maximum geodetic and shear strains increase seismicity becomes increasingly clustered anomalous interrelationships are observed in the marmara sea region prior to the izmit event along a bend in the nafz near the eastern end of the marmara sea known as the northern boundary fault nbf an asperity is located near the northwest end of the nbf along the 50 km length of the nbf gps strains become slightly compressive the correlation between b value and gps derived dilatation suggests that regions in compression have increased probability of larger magnitude rupture the nbf appears to serve as an impediment to the transfer of strain from east to west along the nafz recurrence times for large earthquakes along the nbf are larger than in surrounding areas temporal clustering of seismicity in the vicinity of the nbf may represent foreshocks of an impending rupture

the spatially extended 2006 april zakynthos ionian islands greece seismic sequence and evidence for stress transfer summary the seismic sequence at the southern part of zakynthos island ionian sea western greece during april and may of 2006 is investigated it consists of four moderate earthquakes 5 3 mw 5 7 that were followed by significant seismic activity source parameters of the significant events were determined using two different techniques teleseismic body wave modelling was employed for the major events of the sequence mw 5 6 although for the moderate ones the frequency wavenumber integration method was used the calculated fault plane solutions of the 2006 april seismic sequence revealed compressional regime in all cases more than 3500 microearthquakes were recorded and located using a local temporary network their spatial distribution indicated high concentration of seismic activity within an expanded area taking into account the magnitudes of the major events within this expanded area approximately 10 30 km 2 the focal depths varied between 10 and 25 km two main clusters were revealed the major events occurred in an area of low seismic activity that separates the two clusters seismic cross sections indicated a complex pattern of the hypocentre distribution with the activation of two nearly antithetical faults consistent with the determined focal mechanisms the northern cluster can be associated with a fault plane trending nnw sse and dipping towards sw although the southern cluster with a fault plane striking nw se and dipping towards ene finally coulomb stress analysis was performed to calculate the stress transfer and correlate it with the activated area positive lobes with stress more than 0 3 bars were obtained indicating that these values are large enough to increase the seismicity towards the observed nnw sse direction

stress variability and brittle tectonic structures the problem of stress variability both in space and time during brittle deformation of rocks is faced in this note several possible causes of the temporal and spatial variations of the stress tensor are reviewed and discussed a genetic partitioning of the stress tensor is proposed showing that any stress field within a crustal volume can be seen as the sum of relatively simple stress tensors associated to specific genetic components the genetic components discussed in this note are the gravitational the tectonic the fluid the thermal and the diagenetic one each genetic component is a function of several parameters but for all of them the possible important role played by the variable time is emphasised according to numerous researches based on theoretical and experimental grounds brittle deformation in a rock mass occurs when some critical conditions are reached starting from initial equilibrium conditions and leading to even different stress conditions as a consequence of failure field examples are presented and data from literature are discussed to exhibit evidences from complex tectonic structures and to argue about small and large scale spatial variations as well as about short and long term temporal variations of the stress trajectories and of the stress magnitudes that continuously occur during a brittle deformational event the relationships between local and temporal stress variations and what is commonly defined the regional stress field are discussed adding recommendations for future researches

the strain pattern in the western hellenic arc deduced from a microearthquake survey summary than loo0 earthquakes recorded during 7 weeks in 1986 in the peloponnese and surrounding areas show shallow seismicity spread over a wide area bounded by the hellenic trench the highest level in the energy release is for clusters located along the hellenic trench where changes in the morphology are seen a few clusters are also observed as at the intersection between the gulf of corinth and the gulf of patras near the lake trikhonis or between kythira and crete in the peloponnese the shallow earthquakes do not define single faults but are diffusely distributed a higher concentration and a deepening of the foci within the whole crust towards the west seem to reflect a higher strain rate there fault plane solutions exhibit a scattered pattern for earthquakes shallower than 11 km but for earthquakes deeper than 11 km they show some consistency in the orientation of p t and b axes gently dipping nodal planes are seen all over the peloponnese with the conjugate vertical plane striking in various directions and with no consistency in the sense of motion these earthquakes are located between 8 and 18 km deep and could reflect a decoupling between the lower and the upper crust reverse faulting is seen in the gulf of kefallinia and the western peloponnese the p axes trend ne sw to e w normal faulting is seen in the gulf of corinth and in central peloponnese with the t axes trending n s and in the southern peloponnese where the t axes trend nw se the deformation over the western hellenic arc revealed by fault plane solutions of earthquakes with depth between 11 and 40 km appears to be the superposition of two phenomena first throughout the aegean crustal extension with orientation roughly parallel to the trench dominates with crustal shortening and subduction along the aegean arc superimposed on this is a more local effect of the collision between the aegea and apulia which seems to induce horizontal compression roughly perpendicular to the aegean arc west of the peloponnese and epirus the compression due to this decays eastward at a distance comparable with the width of the collision zone the deepening of the brittleductile transition is likely to be due to an increase of the strain field towards the ionian islands

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

slab segmentation and late cenozoic disruption of the hellenic arc the hellenic subduction zone displays well defined temporal and spatial variations in subduction rate and offers an excellent natural laboratory for studying the interaction among slab buoyancy subduction rate and tectonic deformation in space the active hellenic subduction front is dextrally offset by 100 120 km across the kephalonia transform zone coinciding with the junction of a slowly subducting adriatic continental lithosphere in the north 5 10 mm yr and a rapidly subducting ionian oceanic lithosphere in the south 35 mm yr subduction rates can be shown to have decreased from late eocene time onward reaching 5 12 mm yr by late miocene time before increasing again along the southern portion of the subduction system geodynamic modeling demonstrates that the differing rates of subduction and the resultant trench offset arise naturally from subduction of oceanic pindos lithosphere until late eocene time followed by subduction of a broad tract of continental or transitional lithosphere hellenic external carbonate platform and then by miocene entry of high density oceanic ionian lithosphere into the southern hellenic trench model results yield an initiation age for the kephalonia transform of 6 8 ma in good agreement with observations consistency between geodynamic model results and geologic observations suggest that the middle miocene and younger deformation of the hellenic upper plate including formation of the central hellenic shear zone can be quantitatively understood as the result of spatial variations in the buoyancy of the subducting slab using this assumption we make late eocene middle miocene and pliocene reconstructions of the hellenic system that include quantitative constraints from subduction modeling and geologic constraints on the timing and mode of upper plate deformation

geodetic determination of tectonic deformation in central greece from 1900 to 1988 the global positioning system has been used to measure the relative displacements of fifteen monuments in a hundred year old triangulation network spanning part of the aegean extensional basin these displacements reflect the tectonic deformation of the region over the past century showing more than one metre of north south extension across the network the crust in this region appears to contain a few slowly deforming blocks separated by more rapidly deforming zones

modern tectonic stress field in the mediterranean region evidence for variation in stress directions at different scales summary a compilation of more than one thousand stress indicators which include in situ stress measurements focal mechanisms microtectonic and other geological data allowed us to reconstruct the modern stress field in the mediterranean region and the surrounding area average stress directions at different scales have been reconstructed by means of a linear interpolation method this method takes into account the distribution scale and quality of stress data the results of the interpolation at plate scale allow us to recognize slightly deformed regions such as the northwestern european platform where average maximum horizontal stress direction is oriented roughly nnw sse subparallel to absolute and relative plate velocity directions other regions such as the caucasus alps and pyrenees where recent tectonic deformation and seismicity are present display important variations of stress directions the reconstruction of the average stress directions at different scales within the french alps pointed out that the average stress field pattern may vary from one scale to another nevertheless variations of stress directions at a given scale are consistent with the kinematics of faults of the same scale

post seismic monitoring of cliff mass wasting using an unmanned aerial vehicle and field data at egremni lefkada island greece abstract on 17th november 2015 a strong earthquake affected lefkada island greece leading to extensive translational debris slides along the cliff overhanging egremni beach and the re activation of previously deposited slope material the cliff is crossed by the cephalonia fault zone with mass wasting processes inducing dry flows occurring in association with long term tectonic activity large scale co seismic and post seismic disturbance of the forest on top of the cliff has also resulted from the seismicity three years after the 2015 event the cliff had retreated due to active translational debris slides and the forest disturbance which represents a safety concern for the tourist beach below we aimed to qualitatively assess the transient evolution of debris slides at egremni and clarify the level of risk posed to the beach below annual monitoring was performed between 2015 and 2018 including extensive field measurements and unmanned aerial vehicle uav flight campaigns based on the high resolution images acquired by the uav we created orthophoto maps and digital surface models dsms of the cliff using structure from motion sfm photogrammetry the cliff slope models indicate that the overhanging cliff is progressively entering a stage of decline and approaching equilibrium due to climatic forcing alongside minor seismicity the dsms were combined with field survey data to further investigate the role of erosion and deposition across the cliff our results indicate that the cliff dynamics at egremni are primarily controlled by earthquake and storm induced debris slides with rock material moving within the cliff formation via rock falls and cliff inclination decreasing as a result of primitive slope self healing process mass wasting processes remained widespread across the western part of the lefkada coast three years after the 2015 earthquake sequence for safety reasons we suggest that pre emptive inspection of the cliffs should be carried annually after humid and winter periods and following strong earthquakes using a combination of field surveys and uav campaigns

character of active faulting in the north aegean sea abstract a re evaluation of the reprocessed seismic reflection data was made for the investigation of the presumed western continuation of the north anatolian fault naf in the aegean and mapping geometries of active faults in the aegean sea seismic data collected and processed by various national and international companies were selected from the data archives and they were reprocessed after stacking to bring them to the same processing and signal to noise ratio standards the total length of the selected lines is 8000 km we investigated the character of active faulting in the north aegean sea using seismic reflection data moreover the relations of active faults with earthquakes were examined using earthquake fault plane solutions fps we show that the active faults are dominantly normal in character in the nne aegean where fps for earthquakes with m 5 indicate strike slip movements along these faults we propose a simple mechanism that potentially explains this inconsistency active normal faults are oriented in a ne sw direction in alignment with the sw escape motion of the anatolian block in this region and this orientation facilitates instantaneously strike slip movements along these otherwise normal faults

strong tsunami impact on the bay of aghios nikolaos and its environs nw greece during classical hellenistic times abstract this paper presents for the first time detailed geomorphological sedimentological geoarchaeological geophysical and geochemical evidence of a strong tsunami impact on the bay of aghios nikolaos and its environs nw greece during classical hellenistic times tsunamigenically dislocated beachrock slabs found on top of the santa maura beach ridge complex are closely interrelated to adjacent coarse grained washover fan deposits encountered in vibracores and detected by earth resistivity measurements based on detailed topographic surveys and geomorphometric investigations it was possible to localize areas of high intensity overflow underwater studies revealed that the central and northern parts of the former plaka beach ridge were completely destroyed by tsunami impact loose littoral deposits were flushed into the bay of aghios nikolaos and mega blocks of the underlying beachrock structure were dislocated landwards tsunami landfall occurred all along the eastern and northern shores of the bay where deposits partly weathered and associated to archaeological findings were found runup was estimated to minimum values between 2 3 m and 4 6 m a s l crosschecking the results of radiocarbon analyses with archaeological ages from five sites allowed to date the strong tsunami event to the time period between 395 cal bc and 247 cal bc due to the funnel like contour of the coastline the area is extremely sensitive to tsunami events of mid to high magnitude and high frequency

the strain rate field in the eastern mediterranean region estimated by repeated gps measurements we use the combined gps velocity field of the eastern mediterranean for the period 1988 to 1996 to determine crustal deformation strain rates in a region comprising the hellenic arc the aegean sea and western anatolia we interpret the velocity field and determine the strain rate tensor by the spatial derivatives of the collocated motion vectors the region following the line marmara sea north aegean trough northern central greece and the central ionian islands is associated with strong right lateral shear motion with maximum shear strain rates of 180 nano strain a 180 10 9 a in the central aegean sea n s oriented extensional processes prevail reaching 100 nano strain a the southern aegean is characterized by relatively small strain rates maximum extensional components of the strain rate tensor reaching 150 nano strain a in a n s direction are found in central greece the hellenic arc is associated with moderate arc parallel extension and strong compression perpendicular to it projections of the strain rates parallel to the major fault zones reveal that the northern aegean is governed by the westward continuation of the north anatolian fault zone which is associated with strong dextral shearing maximum 220 nano strain a accompanied by numerous large earthquakes in this century

geochemistry and mineralogy of seafloor hydrothermal and hydrogenetic mn oxide deposits from the manus basin and bismarck archipelago region of the southwest pacific ocean abstract petrographic chemical and mineralogical data are presented for ferromanganese deposits from the manus basin bismarck archipelago region of the southwest pacific the samples were dredged from water depths of between 800 and 2700 m range up to 3 cm in thickness and occur on a variety of substrates including basalt and partially lithified sediments the physical appearance bulk composition and mineralogy of the majority of these samples suggest a hydrogenetic origin however one sample from northwest of manus island and two from inside the active spreading ridge of the manus basin show extreme fractionation of fe and mn depletion of minor trace metals and radiometric isotope compositions indicative of a hydrothermal origin the first report of such material from this region the co content in the deposits is low compared to crusts from other parts of the pacific basin and thus it would appear that the resource potential for co in the manus basin bismarck archipelago region may be limited the presence of mn rich crusts of hydrothermal origin does however suggest that further sampling in selected areas for potentially economic reserves of polymetallic sulphides may be warranted

deformation pattern in the central mediterranean and behavior of the african adriatic promontory abstract the adriatic platform has been described in the literature both as an africa promontory moving in close connection with the main continent and as an independent microplate this evident incongruity is mainly due to the wide spectrum of kinematic hypotheses proposed on the basis of paleomagnetic data and to the fact that the adriatic africa transition is not marked by any clear decoupling fracture or by any interruption of lithological facies along the marginal belts apennines maghrebides and dinarides hellenides in this work it is argued that the counterclockwise rotation of the adriatic plate driven by africa pushing beneath the calabrian arc and southern tyrrhenian may coherently account for all major plio quatemary events in the central mediterranean

a modified least squares collocation method for the determination of crustal deformation first results in the swiss alps summary the calculation of recent crustal movements and the associated crustal deformation rely on a suitable interpolation of geodetic measurements with repetition cycles of years or decades and modern gps permanent networks a common interpolation methods is the least square collocation lsc lsc requires some a priori assumptions about the characteristics of the velocity field that is stocasticity in moritz s definition of lsc we present a novel approach called adaptative lsc alsc to the interpolation of non stochastic fields which encompass the traditional lsc and the block model as special cases this modified collocation method is based on the empirical estimation of a anisotropic and inhomogeneous covariance function of the interpolated field the method has been tested on synthetic data that simulate geodetic measurements over a triple plate junction and with real data from precise levelling measurements over the swiss alps in both cases alsc gave better and more stable results compared to lsc and other interpolation methods such as smoothed splines

multi scale reasonable attenuation tomography analysis murat an imaging algorithm designed for volcanic regions abstract the attenuation of body wave amplitudes with propagation distance can be used to provide detailed tomographic images of seismic interfaces fluid reservoirs and melt batches in the crust the high sensitivity of body wave energies to high scattering structures becomes an obstacle when we try to apply attenuation tomography to small scale volcanic media where we must take into account the complexities induced by strong heterogeneous scattering topography and uncertain source modeling in the recorded wave fields the murat code uses a source and site independent coda normalization method to obtain frequency dependent measurements of p to coda and s to coda energy ratios the code inverts these data for both the geometrical spreading factor and the spatially dependent quality factors q providing additional attenuation information in the regions where velocity tomography is available the high sensitivity of coda waves to highly heterogeneous structures highlights zones of anomalous scattering which may corrupt amplitude dependent attenuation measurements and where basal assumptions of linear optics may go unfulfilled a multi step tomographic inversion increases the stability of the results obtained in regions of high heterogeneity e g the volcanic edifice by the inclusion of data corresponding to either sources or stations located in regions of lower heterogeneity on the other hand a mere increase in the number of rays entirely contained in the heterogeneous structures affects both the stability and the effective resolution of the results we apply the code to two small waveform datasets recorded at an active mount st helens and at a quiescent mount vesuvius volcano the results show that the seismicity located inside or under the volcanic edifice produces an increase of the low frequency energy ratios with travel time in both areas in our interpretation the anomalous concentration of energy which affects any waveform recorded on the cone produced inside the volcanic edifice or in the feeding system of the volcano is due to seismic source or medium dependent resonance the results also provide spatial and frequency limits on the feasibility of attenuation tomography in these two regions with larger datasets

scientific objectives of current and future wegener activities abstract the wegener group has promoted the development of scientific space geodetic activities in the mediterranean and in the european area for the last fifteen years and has contributed to the establishment of geodetic networks designed particularly for earth science research wegener currently has three scientific objectives which are related to plate boundary processes sea level and height changes and postglacial rebound in a full exploitation of the space geodetic techniques namely slr vlbi and gps the individual scientific projects do not only pursue these objectives but also contribute to improving and developing the observation techniques as well as the modelling theories in the past particularly slr observations within wegener medlas have provided a fundamental contribution to determine the regional kinematics of the tectonic plates in the mediterranean with high precision with gps spatially denser site distributions are feasible and in several wegener projects detailed studies of tectonically active areas were possible on the basis of repeated episodic gps observations current projects associated with wegener are successful in separating crustal movements and absolute sea level variations as well as in monitoring postglacial rebound these tasks require high precision height determinations a problem central to all of the present wegener activities in these projects continuously occupied gps sites are of increasing importance time series of heights observed with continuous gps can be determined with a few centimeters rms error thus enabling the reliable estimates of vertical rates over relatively short time intervals regional networks of continuous gps sites are already providing results relevant for example for the study of postglacial rebound the mediterranean area is an extraordinary natural laboratory for the study of seismotectonic processes and the wealth of observations acquired in previous wegener projects together with new space geodetic observations will allow the test of geophysical hypotheses linking three dimensional deformations of the earth s surface to the dynamics of the earth s interior in particular it is anticipated that wegener projects will aim at a test of the slab detachment hypothesis the complex investigations on sea level fluctuations presently carried out at basin scale from the strait of gibraltar to the black sea make it possible to study the present and recent past interactions of ocean atmosphere and solid earth as well as to develop appropriate models to assess future aspects

cerium anomaly variations in ferromanganese nodules and crusts from the indian ocean fifty analyses of rare earth elements as well as mineralogical studies have been carried out on a suite of manganese nodules and crusts from the central indian basin and the western indian ocean the aim was to identify the processes controlling the ree patterns of the phases hosting the ree in the manganese nodules with an emphasis on an understanding of the ce anomaly this has involved separating the encrusting layers and nuclei physically as well as fe mn oxides from the aluminosilicate phase chemically using a 2 m hcl leach prior to analysis the presence of nodule nuclei seems to have little influence mostly 5 to a maximum of 30 on the overall magnitude of the ce anomalies in these nodules the ratios of concentrations of elements in the acid leachates and the corresponding bulk values yield flat ree patterns indicating that the aluminosilicate phase contributes very little to the ce anomalies interelement relations indicate that the ce anomalies are largely controlled by the amorphous mineral phase feooh xh2o the relationship of fe ce anomaly and mno2 further suggests that ce is chemisorbed onto iron oxyhydroxides which are epitaxially intergrown with mno2 the regional distribution of the ce anomaly values appears to depend on many of the factors responsible for the uptake of other minor metals in nodules and crusts

moment tensor inversion of the 1983 january 17 kefallinia event of ionian islands greece summary the source parameters of the recent 1983 january 17 ionian island event are obtained by the inversion of body waves an optimum source depth of 8 km is determined and the source parameters of the major double couple are strike 60 dip 47 rake 174 and seismic moment m0 7 3 1025 dyne cm this mechanism implies a strike slip dextral fault with a small thrust component this solution ascertains the existence of a transform fault connecting the northwestern edge of the hellenic are with the compressional zone which is produced by the collision of the apulian plate with the eurasian plate along the adriatic north ionian coast this right lateral strike slip fault probably terminates the hellenic subduction zone

3d crustal structure from local earthquake tomography around the gulf of arta ionian region nw greece during summer of 1995 local seismicity was recorded in the area around the gulf of arta in northwestern greece by a dense temporary seismic network of the 441 local events observed at 37 stations 232 well locatable events with a total of 2776 p phase readings were selected applying the criteria of a minimum of 6 p observations and an azimuthal gap less than 180 this data set is used to compute a minimum 1d velocity model for the region several tests are conducted to estimate model stability and hypocenter uncertainties leading to the conclusion that relative hypocenter location accuracy is about 500 m in latitude and longitude and 1 km in depth the minimum 1d velocity model serves as initial model in the non linear inversion for three dimensional p velocity crustal structure by iteratively solving the coupled hypocenter velocity problem in a least squares sense careful analysis of the resolution capability of our data set outlines the well resolved features for interpretation the resulting 3d velocity model shows generally higher average crustal velocities in the east and the well resolved area of the eastern gulf of arta exhibits a homogeneous velocity around 6 km s for the whole upper crust a pronounced north south trending zone of low velocities in the upper 5 10 km is observed in the area of the katouna fault zone kfz at greater depths below 10 km the kfz is underlain by high velocity material e w profiles suggest a horst graben structure associated with the kfz

global positioning system gps estimates of crustal deformation in the marmara sea region northwestern anatolia abstract in the marmara sea region the relative motion between the anatolian and eurasian lithosphere has been measured by means of the modern techniques of space geodesy using the global positioning system gps in order to resolve in detail the kinematic field within the active earthquake belts of northwestern anatolia two gps campaigns were carried out across a dense network consisting of 45 sites preliminary results reveal horizontal westward motion of anatolia relative to eurasia of 2 4 cm y on average that runs along the western end of the north anatolian fault zone e w oriented right lateral strike slip movement average 0 06 ppm y maximum 0 13 ppm y 1ppm y 1 strain y and ne sw extension average 0 06 ppm y maximum 0 21 ppm y can be obtained from the calculated strain field in the west strike slip motion trending wsw ene is observed these findings are compared to the stress pattern derived from seismology and neotectonics