fault interactions in the sea of marmara pull apart north anatolian fault earthquake clustering and propagating earthquake sequences summary knowledge on large earthquakes m 7 0 geology and fault kinematics is used to analyse conditions that favour isolated seismicity clustered earthquakes or propagating sequences along the north anatolian fault naf and the sea of marmara pull apart the overall naf marmara fault system is one of the most appropriate on earth to document fault interactions because reliable information covers almost completely two seismic cycles the past 500 yr coulomb stress analysis is used to characterize loading evolution in well identified fault segments including secular loading from below and lateral loading imposed by the occurrence of previous earthquakes earthquakes along the naf tend to occur where previous events have increased the stress but significant isolated events in the sea of marmara region 1894 1912 have occurred suggesting the secular loading has been the determining factor present day loading appears to be particularly high along the 70 km long segment located in the central marmara sea southwest of istanbul for the 18th century m 7 0 earthquake clusters we construct scenarios consistent with the tectonic and historical data we find that scenarios consistent with slip deficit and secular loading distributions from below clearly involve a sequence that propagates westward through the sea of marmara despite the structural complexity however the inference of a propagating sequence implies that each event has occurred in a segment previously stressed by lateral coulomb stress interactions the most likely scenarios for the propagating sequence are also consistent with coulomb stress interactions between faults with significant normal slip across the cinarcik basin propagating earthquake sequences do not occur every seismic cycle along the naf the loading has to be in a particular state of stress close to failure and uniform all along the fault segments to experience propagating earthquake sequences non uniform stress relief during the 18th century sequence explains the occurrence of isolated events in marmara in 1894 and 1912 as a consequence the wellknown 20th century sequence along the naf has not propagated as a sequence across the sea of marmara the most linear part of the naf across northern turkey behaves as a single fault segment accumulating stress during hundreds of years and rupturing entirely during very short periods the marmara pull apart fault system behaves as a major geometric complexity stopping or delaying the progression of earthquake clustering and propagating sequences fault zones interact with each other at a very large scale

pattern of opening rates along the axis of the mid atlantic ridge vine and wilson1 using the vine and matthews2 hypothesis were the first to try to relate the magnetic pattern over the crests of the mid ocean ridges to the known geomagnetic time scale to determine the spreading rate over the past few million years many determinations of spreading rate at the axis of the ridge during plio pleistocene times have been published le pichon3 and morgan4 for example used spreading rates computed for the axial magnetic pattern 10 myr anomaly 5 of heirtzler et al 5 or for the past 5 myr respectively even when trying to assess the properties of instantaneous plate kinematics likewise in the systematic inversion of minster et al 6 anomalies 3 and 5 were generally used thus averaging plate speeds over the past 5 10 myr minster and jordan7 sought to improve this and redetermined the spreading rates using magnetic anomalies 2 and 2 yielding a mean averaging interval of 3 myr here we examine plate behaviour over a shorter time scale in the reasonably well surveyed axial region of the mid atlantic ridge south of the azores the average opening rates we obtained for this region for magnetic anomalies 1 brunhes 2 and 2 using two different geomagnetic time scales indicate that 1 there was a relative slowing down of the opening between anomalies 1 and 2 which may be of global significance 2 the opening is compatible with a rigid plate model when it is averaged over 2 5 myr although for shorter averaging times 1 8 and 0 7 myr there is some evidence of non rigidity of the plates thus different segments of the mid atlantic ridge may display an independent behaviour and with respect to relatively short time intervals may show departures from characteristics typically associated with slow accretion

an active deep marine strike slip basin along the north anatolian fault in turkey the tekirdag depression within the marmara sea in the mediterranean region is an active rhomb shaped strike slip basin along the north anatolian fault with a basin floor at a water depth of 1150 m new multichannel seismic reflection data and on land geological studies indicate that the basin is forming along a releasing bend of the strike slip fault and is filled with syntransform sediments of pliocene quaternary age the basin is bounded on one side by the north anatolian fault and on the other side by a subparallel normal fault which forms the steep submarine slope in cross section the basin is strongly asymmetric with the thickness of the syntransform strata increasing from a few tens of meters on the submarine slope to over 2 5 km adjacent to the north anatolian fault seismic sections also show that the slope forming normal fault connects at depth to the north anatolian fault implying that the basin is completely detached from its substratum the whole structure can be envisaged as a huge rather flat negative flower structure the releasing bend of the north anatolian fault responsible for the formation of the basin is flanked by a constraining bend along the constraining bend the syntransform strata are being underthrust implying a recent change in the direction of the regional displacement vector this thrusting is responsible for the uplift of the submarine slope to a height of 924 m possibly by a mechanism of elastic rebound regional geology suggests that most of the syntransform strata are lacustrine with only the topmost few hundred meters consisting of deep marine clays the anomalous present depth of the tekirdag depression is due to reduced quaternary sedimentation coupled with high rates of displacement along the north anatolian fault which amounts to 20 mm yr in the marmara sea region

magmatic evolution of a volcano studied by 230th 238u disequilibrium and trace elements systematics the etna case age determinations of several lava flows from etna through 230th 238u disequilibrium internal isochrons yield a precise chronology of the volcano s history for the last 200 000 years and emphasize the main episodes in the formation of this huge complex strato volcano study of 230th232th 0 initial ratios of lavas together with their trace element compositions yields a consistent model of magmatic evolution implying the existence for 200 000 years of a deep reservoir of alkalic magma periodically mixed with magmas of tholeiitic affinity these short periods of mixing appear to be related to the formation of the large calderas of etna in addition to these processes affecting the deep reservoir fractional crystallization also occurred in more superficial levels of the volcanic edifice thereby yielding several series of differentiation of relatively short duration as for its geochemistry etna s volcanism is of oceanic type but with its own characteristics and in a peculiar geodynamic context at the edge of the african plate

propagating rifts and continental breakup a simple quantitative model is proposed whereby continental breakup starts with a phase of continental rifting and continues with the propagation of rifts toward locked zones these zones are deformed in the rifting process while oceanic crust is generated in the wake of the rift tip the deformed zones will cause overlaps when a continental reassembly is attempted the model accounts for the shape and distribution of magnetic quiet zones at ocean continent boundaries and for the detailed geometry of some v shaped zones of oceanic magnetic anomalies the former provide an estimate of the scale at which the hypothesis of rigid plates fails and the latter are used to measure the velocity of rift propagation illustrations are provided for present rifting in the red sea and gulf of aden and for early rifting of the south atlantic and breakup of pangea

plate tectonic development of the south west indian ocean a revised reconstruction of east antarctica and africa a revised sequence of reconstructions for east antarctica relative to africa is generated from published seafloor spreading and fracture zone anomalies these date from the cretaceous tertiary boundary to the late jurassic and lead to a revised predrift reconstruction for east and west gondwanaland euler pole 1 67 s 35 99 e rotation angle 53 43 this reconstruction derived wholly from marine data places east antarctica adjacent to the lebombo mountains and south of and subparallel to the sabi acid volcanic suite supporting the postulate that these rocks represent mesozoic plate boundaries this refit implies that part of the coastal plain of mozambique is underlain by oceanic or very highly extended continental crust the reconstruction is supported by the alignment of 1 the cape fold belt with its antarctic equivalents and 2 the western limit of pan african reactivation of the mozambique mobile belt with the western limit of the sverdrupfjella metamorphic suite antarctica initially moved along a transform fault lying immediately east of and subparallel to the lebombo mountains the eastern face of the tugela cone the southeastern face of the falkland plateau in its reconstructed position and the eastern flank of the agulhas plateau in its reconstructed position at m10 time a triple junction formed near the tip of the falkland plateau implying that the oldest lineated magnetic anomalies in the eastern weddell sea associated with this triple junction cannot predate m10 at m2 time the mozambique ridge rifted from the astrid ridge in a ridge jump episode such an event may also explain the presence of magnetic anomalies in the southern mozambique basin gunnerus ridge conrad rise and del cano rise are all tectonically associated with the madagascar ridge

development and applications of double difference seismic tomography double difference dd tomography is a generalization of dd location it simultaneously solves for the three dimensional velocity structure and seismic event locations dd tomography uses a combination of absolute and more accurate differential arrival times and hierarchically determines the velocity structure from larger scale to smaller scale this method is able to produce more accurate event locations and velocity structure near the source region than standard tomography which uses only absolute arrival times we conduct a stability and uncertainty analysis of dd tomography based on a synthetic data set currently three versions of the dd tomography algorithms exist tomodd tomofdd and tomoadd tomodd assumes a flat earth model and uses a pseudo bending ray tracing algorithm to find rays between events and stations while tomofdd uses a finite difference travel time algorithm and the curvature of the earth is considered both codes are based on a regularly distributed inversion grid with the former for a local scale and the latter for a regional scale in contrast tomoadd adapts the inversion mesh to match with the data distribution based on tetrahedral and voronoi diagrams we discuss examples of applying dd tomography to characterize fault zone structure image high resolution structure of subduction zones and determine the velocity structure of volcanoes

types and kinematic stability of triple junctions a triple junction is kinematically stable if the orientation of each plate boundary remains constant relative to other boundaries in the triple junction during a finite time interval instantaneous relative velocity vectors have been used elsewhere to indicate the relative motion of plates during a finite time interval a technique that is not generally valid where finite relative plate motion is not circular in the typical case in which all three plates have non zero velocities around different plate specific poles of rotation the direction and magnitude of relative plate velocity varies systematically with time five plate boundary types are considered in evaluating triple junction stability ridges r right lateral and left lateral transform faults fr and fl and trenches in which the overriding plate is clockwise tc or anticlockwise ta from the trench judged by a rotation around the triple junction one hundred twenty five triplet combinations of boundary types are possible some combinations display symmetry with other combinations grouping all similar configurations 25 types of triple junctions can be distinguished of which 19 types may be stable when finite relative motion is circular vectorial descriptors of the geometry of ridges transform faults and trenches permit the listing of general conditions for the kinematic stability of triple junctions under conditions of both circular and non circular relative motion the tj1 model for the evolution of rrr triple junctions provides estimates of the variation in the geometry of triple junctions in which spreading is orthogonal and near symmetric rrr triple junctions at which spreading is orthogonal and symmetric are always stable when the finite relative motion of all corresponding plates is circular however tj1 indicates that rrr triple junctions are not generally stable when relative motion is non circular in general triple junctions are not kinematically stable but evolve with changes in the finite relative motion of plates

3 d sediment basement tomography of the northern marmara trough by a dense obs network at the nodes of a grid of controlled source profiles along the north anatolian fault a 3 d tomographic inversion of first arrival times of shot profiles recorded by a dense 2 d obs network provides an unprecedented constraint on the p wave velocities heterogeneity of the upper crustal part of the north marmara trough nmt over a region of 180 km long by 50 km wide one of the specific aims of this controlled source tomography is to provide a 3 d initial model for the local earthquake tomography let hence in an original way the controlled source inversion has been performed by using a code dedicated to let after several tests to check the results trade off with the inversion parameters we build up a 3 d a priori velocity model in which the sea bottom topography the acoustic and the crystalline basements and the moho interfaces have been considered the reliability of the obtained features has been checked by checkerboard tests and also by their comparison with the deep penetration multichannel seismic profiles and with the wide angle reflection and refraction modelled profiles this study provides the first 3 d view of the basement topography along the active north anatolian fault beneath the marmara sea even beneath the deepest part of three sedimentary basins of nmt clear basement depressions reaching down 6 km depth below the sea level bsl have been found beneath these basins the north imrali basin located on the southern continental shelf is observed with a similar sedimentary thickness as its northern neighbours between central and cinarcik basins the central high rises up to 3 km depth below bsl its crest position is offset by 10 km northwestward relatively to the bathymetric crest on the contrary tekirdag and central basins appear linked forming a 60 km long basement depression beneath the bathymetric relief of western high low velocities are observed down to 6 km depth bsl and no basement high have been found the obtained 3 d vp heterogeneity model allows the consideration of the 3 d supracrustal heterogeneity into the future earthquake relocations in this region the topographic map of the pre kinematic basement offers the possibility to take into account the locking depth variations in future geohazard estimations by geomechanical modelling in this region

bouvet triple junction in the south atlantic geology and evolution the south american african and antarctic lithospheric plates meet in the bouvet triple junction btj located in the south atlantic near the island of bouvet multibeam magnetic gravimetric and seismic reflection data have been used to understand the evolution of the three accretionary transform boundaries that converge in the btj the easternmost segments of the american antarctic ridge aar have a spreading full rate of 19 5 mm yr for the last 8 m y they are oriented n s except for some ne sw segments probably created by magma poor extension the southernmost portion of mid atlantic ridge mar spreading full rate of 30 5 mm yr for the last 9 m y has elevated topographic anomalies it is segmented by transform and overlapping discontinuities and shows evidence of axial propagation the mar axial valley bifurcates at its southern tip in two branches oriented 115 o and 180 o that are or have been up to recently loci of crustal accretion the bifurcation represents a former ridge ridge ridge triple junction the westernmost segments of the southwest indian ridge swir are anomalously high the segment adjacent to the island of bouvet spreading rate 14 5 mm yr is shallower than normal by almost 1 km due to the influence of the bouvet hot spot the westernmost swir segment spiess ridge consists of a swollen volcanic ridge that reaches 320 rn below sea level and has a deep caldera on its summit spiess ridge narrows and deepens to the nw v shaped topographic and magnetic lineations suggest that it propagates nw at a rate of 40 to 50 mm yr the spiess magmatic event started at roughly 1 ma when it caused deactivation of the 115 o spreading branch therefore the antarctic south american and african plates meet presently not in a triple point but in a broad zone of diffuse deformation an area of extensional deformation observed east of spiess ridge may be caused by excess crustal formation at spiess ridge that cannot be accommodated by motion of rigid plates the evolution of the btj since 10 ma involves stages of rrr rff and rrf configurations with highly variable geometry of the accretionary transform boundaries topographic anomalies anomalously thick crust and excess volcanism suggest that the upper mantle below this region is affected by widespread strong thermal anomalies that have influenced the configuration of the btj and determined indirectly intraplate deformation in wide areas of the btj region the thermal anomaly that gave rise to the swir spiess excess magmatism is the prime cause of the recent disruption of a former rrr configuration and of the imminent establishment of a new rrr triple junction to the north

sea bottom observations from the western escarpment of the sea of marmara abstract the western escarpment of the sea of marmara has recently been recognized as the site of intensive gas emissions escaping from the seafloor visual observations with the nautile submersible indicate that gas escapes from elongated tensile cracks oriented to the northwest in the direction of the maximum principal stress here we report results from a 25 day test in 2007 with four ocean bottom seismometers obss showing that this area is also characterized by microseismic activity a cluster of 13 small magnitude earthquakes aligned northwest occurred in less than 30 hr at shallow crustal depth below the western slope of the tekirdag basin the only two focal mechanisms resolvable using land and sea bottom data reveal normal faulting with strike slip components consistent with the stress field expected in this area it is suggested that tectonic strain below the western slope of the tekirdag basin contributes to maintaining a high permeability in fault zones and that the fault network provides conduits for deep seated fluids to rise up to the seafloor

motion between the indian antarctic and african plates in the early cenozoic we used a three plate best fit algorithm to calculate four sets of euler rotations for motion between the india capricorn africa somali and antarctic plates for 14 time intervals in the early cenozoic each set of rotations had a different combination of data constraints the first set of rotations used a basic set of magnetic anomaly picks on the central indian ridge cir southeast indian ridge seir and southwest indian ridge swir and fracture zone constraints on the cir and seir but did not incorporate data from the carlsberg ridge and did not use fracture zones on the swir the second set added fracture zone constraints from the region of the bain fracture zone on the swir which were dated with synthetic flowlines based on the first data set the third set of rotations used the basic constraints from the first rotation set and added data from the carlsberg ridge the fourth set of rotations combined both the swir fracture zone constraints and the carlsberg ridge constraints data on the indian plate side of the carlsberg ridge arabian basin were rotated to the capricorn plate before being included in the constraints plate trajectories and spreading rate histories for the cir and swir based on the new rotations document the major early cenozoic changes in plate motion on the cir and seir there was a large but gradual slowdown starting around chron 23o 51 9 ma and continuing until chron 21y 45 3 ma followed 2 or 3 myr later by an abrupt change in spreading azimuth which started around chron 20o 42 8 ma and which was completed by chron 20y 41 5 ma no change in spreading rate accompanied the abrupt change in spreading direction on the swir there was a continuous increase in spreading rates between chrons 23o and 20o and large changes in azimuth around chrons 24 and 23 and again at chron 21 unexpectedly we found that the two sets of rotations constrained by the carlsberg ridge data diverged from the other two sets of rotations prior to anomaly 22o when compared to rotations for the cir that are simultaneously constrained by data from all three branches of the indian ocean triple junction there is a progressively larger separation of anomalies on the carlsberg ridge with a roughly 25 km misfit for anomaly 23o and increasing to over 100 km for anomaly 26y these data require that there was previously unrecognized convergence somewhere in the plate circuit linking the indian capricorn and somali plates prior to chron 22o we quantify this motion by summing our new capricorn somalia rotations with previously published rotations for neogene india capricorn motion and for early cenozoic somali india motion based solely on carlsberg ridge data the most likely possibility is that there was motion within the somalia plate due to a distinct seychelles microplate as young as chron 22o the sense of the misfit on the carlsberg ridge is consistent with roughly 100 150 km of convergence across a boundary passing through the amirante trench and extending north to the carlsberg ridge axis between anomalies 26y and 22o alternatively there may have been convergence within the indian plate either along the western margin of indian or east of the cir in the region of the current capricorn indian diffuse plate boundary our work sharpens the dating of the two major eocene changes in plate motion recognized in the indian ocean

evolution of the seismicity in the eastern marmara sea a decade before and after the 17 august 1999 izmit earthquake we review the long term evolution of seismicity in the eastern marmara sea over a decade before and after the 1999 mw 7 6 izmit earthquake we analyze large scale space time variations of seismicity in the region and illustrate the impact of the recent large strike slip earthquakes on the background activity composed of distinct pre existing seismic clusters two types of aftershocks activity are observed the first type of enhancement is on strike slip fault segments izmit fault princes island section of the main marmara fault gemlik fault immediately following the main shock and related to coulomb stress transfer the second type of enhancement is attached to extensional clusters yalova tuzla with a few days delay in the onset of strong activation probably related to pore pressure increase we observe a fast decay of the activity on strike slip segments and slower evolution of seismic clusters with extensional features two years after the izmit earthquake seismic activity returned to the pre earthquake pattern with most of the activity occurring within extensional clusters it appears that the influence of the last large strike slip event on the spatial seismicity distribution in the eastern marmara sea is less significant than the effect of the long term regional extension

the evolution of the bouvet triple junction implications of its absolute motion abstract consideration of the motion of the bouvet triple junction with respect to a mantle reference frame yields important kinematic information which provides the basis for a model that explains the junction s cyclical changes by utilizing minster and jordan s 1978 am1 2 absolute poles of rotation for the african afrc antarctic anta and south american soam plates we have located the locus along which relative velocity triangles are isosceles only along this isosceles line is the ridge fault fault rff configuration of the bouvet triple junction stable a rff junction becomes unstable as it moves away from this line because the relative velocity triangle of the bouvet is an obtuse isosceles triangle the junction is prone to migrating at relatively fast velocities across the surface of the earth significant changes in the shape and orientation of the relative velocity triangle at the junction accompany its migration such changes upset the stability condition and may lead to configuration changes a least squares algorithm is developed to quantify the geometric stability of any triple junction three linear equations of the form j a bh involving two unknowns describe the triple junction velocity with respect to the linear constraints imposed by each boundary in velocity space only a stable junction yields a unique solution otherwise the sum of the square of the residuals of a least squares regression may be taken as a measure of the degree of geometric instability in the case of the bouvet triple junction on the isosceles locus both ridge ridge ridge rrr and rff configurations are compatible with the same velocity triangle the stability of the rff configuration is less affected by the small changes in the relative velocities which arise during junction migration than the rrr mode this consideration may explain why the bouvet prefers rff when in the vicinity of the isosceles line prior to 31 m y b p a rrr version of the bouvet triple junction migrated toward the isosceles line at a velocity of 14 7 km m y at 373 at 31 m y b p the junction was close to the isosceles line when it switched to an rff junction in rff mode the junction migrated away from the isosceles locus with a velocity of 5 8 km m y at 157 until 12 5 m y b p when it reverted to rrr mode during this episode the mid atlantic ridge mar was extended 120 km in length and the conrad and bouvet paired transforms grew to their present length of 150 km from 12 5 to 5 m y b p the mar receded and the south american antarctica and the african antarctic ridges lengthened at about 5 m y b p the junction interesected the isosceles line again switched to rff mode and has been generating paired transforms until the present

tectonic evolution of the marmara sea and its surroundings abstract the basins in the marmara sea are the products of a superimposed evolutionary history defined by two different aged fault systems the early miocene early pliocene thrace eskisehir fault zone and its branches and the late pliocene recent north anatolian fault and its branches the thrace eskisehir fault and its westward branching secondary fault systems define the early neotectonic signature in the region the late neotectonic period started at the end of the early pliocene when the north anatolian fault divided the thrace eskisehir fault into four parts during the late neotectonic period the north anatolian fault extended westward as a number of splays by joining with the ganos bandirma behramkale and manyas edremit fault zones the branches of the north anatolian fault zone nafz caused the evolution of a number of basins which differ in character depending on the trend and past characteristics of the older branches that became connected since the northern branch of the north anatolian fault is connected to the n80 e trending ganos fault zone gfz in the west a single buried fault has developed in the marmara sea causing the well known troughs and ridges superimposed onto the negative flower structure formed by the gfz in the early neotectonic period the middle strand which extends from iznik lake to bandirma is oriented east west up to the n60 e trending bandirma behramkale fault zone then turns southward in the vicinity of bandirma forming a region dominated by compressional tectonics this bending caused n30 e trending tension in addition to the strike slip motion between the eastern part of gemlik bay and bandirma bay the southern branch of the nafz on the other hand produced three pull apart basins with different characteristics along the yenisehir bursa and manyas segments the southern branch of the nafz connected to the manyas edremit fault zone which is oriented n45 e to the south of manyas and the associated bending and rotation caused a n15 e trending extension in addition to the strike slip regime between manyas and uluabat the branches of north anatolian fault cut through the thrace eskisehir fault at three places the east marmara sea region in gemlik bay and to the east of bursa giving lateral offsets of 58 59 7 8 and 10 11 km respectively the cumulative motion is 75 78 km corresponding to the total lateral offset of the north anatolian fault in the region the correlation of these offsets with global positioning system slip vectors and with stratigraphic results implies that the north anatolian fault reached into the marmara sea region about 3 5 million yr ago tectonic processes forming the marmara sea and its environs were initiated by the thrace eskisehir fault and its splays have been most recently controlled by the north anatolian fault and its splays during the last 3 5 million yr

a probable earthquake scenario near istanbul determined from dynamic simulations abstract we perform numerical simulations of dynamic rupture processes along the north anatolian fault in the sea of marmara which poses a high risk to the nearby city of istanbul several fault geometry models nucleation points and initial stress states are tested the likelihood of each earthquake scenario is evaluated and a probabilistic assessment of the ground motion estimation is proposed the simulation results suggest that the fault geometrical configuration is not favorable for producing an earthquake of magnitude 6 7 as no scenario is found on the contrary the probability of occurrence of an earthquake of magnitude greater than 7 is high most of these large events are characterized by epicenters located in the central or eastern parts of the sea of marmara however the possibility of a western initiated rupture propagating eastward the worst scenario for the istanbul region cannot be ruled out many simulations led to supershear ruptures as observed for the nearby 1999 izmit earthquake and this significantly influences ground motion prediction in the region

travel time residuals of teleseismic p waves at the rodriguez triple junction in the indian ocean using ocean bottom seismometers we conducted three weeks of seismic observations at the rodriguez triple junction rtj in the indian ocean using 18 ocean bottom seismometers over an area of 90km 90km we identified six teleseismic events and obtained significant anomalies in the relative travel time residuals of the teleseismic p waves the residuals are positive at the rtj the northern part of the southeast indian ridge seir and the eastern side of the central indian ridge cir and are negative at and around the southwest indian ridge swir it is suggested that there is a relatively hotter mantle under the triple junction and the northern part of the seir segment along axis variations in mantle temperature along the seir segment and cooler mantle under the swir segment the cir segment has an asymmetrical distribution of relative residuals

the active main marmara fault abstract this paper presents selections from and a synthesis of a high resolution bathymetric sparker and deep towed seismic reflection data set recently acquired by the french ifremer r v le suroit in an e w deep trough that forms the northern half of the sea of marmara in nw turkey it includes the first high resolution complete bathymetric map of this area a single throughgoing dextral strike slip fault system which is the western continuation of the northern branch of the north anatolian fault cuts this trough lengthwise and joins the 1999 8 17 kocaeli earthquake fault with the 1912 8 09 arkoy murefte earthquake fault both of which display strike slip offset in its eastern one fourth the structure follows closely the northern margin of the deep trough whereas in the west it hugs its southern margin the eastern one fourth of the structure has a minor component of its displacement distributed across the deep trough owing to a possible original bend in the course of the dextral structure the present course of the north anatolian fault in the sea of marmara originated some 2 105 a ago by cutting across the older basin fabric generated by a dominant nne ssw extension before it began taking up major motion in the pliocene

southeast pacific tectonic evolution from early oligocene to present plate tectonic reconstructions of the nazca antarctic and pacific plates are presented from late oligocene to present these reconstructions document major plate boundary reorganizations in the southeast pacific at dirons 6c 24 ma 6 o 20 ma and 5a 12 ma and a smaller reorganization at chron 3 o 5 ma during the chron 6 o reorganization it appears that a ridge propagated into crust north of the northernmost pacific antarctic ridge between the chiloe fracture zone fz of the chile ridge and agassiz fz of the pacific nazca ridge which resulted in a northward jump of the pacific antarctic nazca pac ant naz mid ocean triple junction during the chron 5a reorganization the chile ridge propagated northward from the valdivia fz system to the challenger fz through lithosphere formed roughly 5 myr earlier at the pacific nazca ridge during this reorganization a short lived microplate the friday microplate existed at the pac ant naz triple junction the pac ant naz triple junction jumped northward 500 km as a result of this reorganization from a location along the valdivia fz to a location along the challenger fz the chron 5a reorganization also included a change in spreading direction of the chile and pacific antarctic ridges the reorganization at chron 3 o initiated the formation of the juan fernandez and easter microplates along the east pacific rise the manner of plate boundary reorganization at chron 6 o and chron 5a and possibly today at the juan fernandez microplate included a sequence of rift propagation transfer of lithosphere from one plate to another microplate formation and microplate abandonment and resulted in northward migration of the pac ant naz triple junction the associated microplate differs from previously studied microplates in that there is no failed ridge

plate tectonics and orogenic research after 25 years a tethyan perspective abstract orogeny the process by which the earth s prominent mountain ranges are constructed has been a central topic of interest in the earth sciences since at least the end of the 18th century the recognition that strains and displacements of very considerable magnitude occur along all of the three dimensions within an orogenic belt during its evolution has grown gradually during the last two centuries emphasis on primary vertical movements dominated the ideas on the nature of orogeny during the first half of the 19th century whereas compression and consequent uplift across mountain belts were believed to be the main cause for their origin during the subsequent one hundred years or so that were spent under the dominance of the fixist contraction theory mobilist tectonicians realised that continental drift in places also required motion along the trend of orogenic belts but this view did not gain general acceptance recognition of significant strike slip motion parallel or subparallel with mountain ranges evolved independently and mostly within the fixist camp by the 1960 s presence of important motions both along and across mountain belts had become common knowledge but no theoretical basis existed to account for them all

structural pattern of the galapagos microplate and evolution of the galapagos triple junctions a 13 000 km2 microplate intervenes to prevent the junction of the nazca cocos and pacific plates in the eastern equatorial pacific ocean west of the galapagos islands the microplate is rotating clockwise at 6 m y about an absolute pole 400 km southeast of its center so that although its northern margin has a similar motion to adjacent parts of the cocos plate its southern margin is 50 slower the perimeter of the galapagos microplate is best defined by bathymetry and has been surveyed with sea beam and examined by deep tow two of the three triple junctions on its margins are ridge ridge ridge rrr junctions 160 km apart on the crest of the east pacific rise epr the most like a classic rrr junction is the pacific nazca galapagos intersection at 1 10 n where the epr axis is joined by a narrow volcanic ridge 70 km long and 1 km high the cocos nazca galapagos junction at the west end of the cocos nazca spreading center is inferred to be of the rff type but the transform fault branches are represented by large nontransform offsets lack of stable transform faults is related to rapid westward migration of the junction caused by lengthening of the cocos nazca axis at 60 70 mm yr this rate which was once required to maintain a stable nazca cocos pacific rrr junction has persisted even after birth of the microplate about 1 ma continuing propagation of the cocos nazca axis has opened up the hess deep rift basin in the eastern epr flank in advance of the eruptive propagator tip this rift valley has a relief of more than 3 km from its uplifted rims to the floor where severe attenuation exposes basal layers of the epr crust the similar dietz deep rift basin at the southeastern margin of the microplate 70 km from hess deep was formed when a lengthening galapagos nazca spreading axis rifted through another part of the epr flank

paleoseismology of the north anatolian fault at guzelkoy ganos segment turkey size and recurrence time of earthquake ruptures west of the sea of marmara 1 the ganos fault is the westernmost segment of the north anatolian fault that experienced the mw 7 4 earthquake of 9 august 1912 the earthquake revealed 45 km long of surface ruptures inland trending n70 e and 5 5 m of maximum right lateral offset near guzelkoy the long term deformation of the fault is clearly expressed by several pull apart basins and sag ponds pressure and shutter ridges and offset streams in parallel with detailed geomorphologic investigations we measured co seismic and cumulative displacements along the fault and selected the guzelkoy site for paleoseismology a microtopographic survey at the site yields 10 5 0 5 m and 35 4 1 5 m cumulative lateral offsets of stream channels and geomorphologic features seven paleoseismic parallel and cross fault trenches document successive faulting events and provide the timing of past earthquakes on the ganos fault segment radiocarbon dating of successive colluvial wedges in trench t1 and the fresh scarplet above probably 1912 surface rupture indicate the occurrence of three faulting events since the 14th century parallel trenches 3 5 6 and 7 expose paleo channels and show a cumulative right lateral offset of 16 5 1 5 m next to the fault and 21 3 1 5 m total channel deflection radiocarbon dating of past channel units and fault scarp related colluvial deposits imply an average 17 5 mm year slip rate and 323 142 years recurrence interval of large earthquakes during the last 1000 years on the ganos fault the succession of past faulting events and inferred slip rate west of the marmara sea provide more constraint on the long term faulting behavior in the seismic gap of the north anatolian fault and may contribute to a better seismic hazard assessment in the istanbul region

1 ma east pacific rise oceanic crust and uppermost mantle exposed by rifting in hess deep equatorial pacific ocean abstract a series of dives with the french submersible nautile has been conducted in the region of the galapagos triple junction at the tip of the cocos nazca propagator most of the dives were devoted to the study of hess deep a rift valley produced by rifting of oceanic crust created at the axis of the very fast spreading east pacific rise the dives have enabled the structures and lithologies to be assessed and confirmed earlier dredging evidence for abundant basal crust and mantle rocks on an intra rift ridge located to the north of the axis of hess deep this shows that this situation is not specific not slow spreading ridges a nearly complete and unique log of young 1 ma crust and uppermost mantle representative of very fast accretion can be reconstructed even though the section is discontinuous and highly dismembered we propose two models that can explain the exposure on the ocean floor of the deep foundation of the oceanic crust one model stresses symmetry and vertical tectonics through isostasy diapirism of serpentinized mantle another model requires a larger amount of extension and emphasizes asymmetry with denudation of the upper crust through low angle detachment faulting in both models which differ mainly in the structure at depth amagmatic extension of east pacific rise crust by the cocos nazca propagator tip results in uplift and denudation of lower crust and upper mantle

episodic triple junction migration by rift propagation and microplates we describe a model for episodic open ocean triple junction migration based on observations of actual triple junction evolutions migration progresses by repeated episodes of rift propagation microplate formation and microplate accretion to an adjacent larger plate these episodes may be highly variable in space and time depending on triple junction geometry velocity triangle and other factors affecting local thermal and rheological conditions resulting tectonic features may include an abandoned transform fault straight and potentially curving pseudofaults sheared and potentially rotated abyssal hill fabric and a paleomicroplate with no associated failed rift this model developed mainly from the evolution of the pacific antarctic nazca triple junction may be relevant for other types of triple junctions such as the bouvet and azores triple junctions and ridge ridge ridge triple junctions in the indian and pacific oceans episodic migration is found to occur even when the triple junction is kinematically stable this model highlights the difference between predicted kinematic stability of triple junctions and observations of their true tectonic history

the bouvet triple junction 20 to 10 ma and extensive transtensional deformation adjacent to the bouvet and conrad transforms the bouvet triple junction has been proposed to have evolved as a ridge fault fault rff type between 20 and 10 ma connecting the southernmost mid atlantic ridge smar with the bouvet and conrad transforms to the east and west respectively we surveyed immediately north of these two transforms with side scan and multibeam sonars on seafloor that would have originally been created at the smar close to its junction with the two transforms the sonar data reveal that smar fabrics on the bouvet and conrad sides when corrected for plate rotation are parallel to each other so they were most likely formed at the same spreading ridge and confirm that the triple junction was indeed rff our second major result is that the smar fabrics are extensively crosscut by normal faults over most of the 400 km surveyed along both transforms and most intensely north of the bouvet transform growth faults and faults affecting the sediment surface in multichannel seismic images show that the deformation has been long lived and is probably ongoing since the orientations of the crosscutting faults are similar to those of shear zone tension fractures we interpret these areas to be transtensional zones this extent of deformation adjacent to major oceanic transforms is rare and we develop a number of ideas to explain its origin

evolution of the southwest indian ridge from the late cretaceous anomaly 34 to the middle eocene anomaly 20 abstract the determination of the motion of antarctica relative to africa is particularly important when considering the breakup of gondwana two models have been proposed that describe the pattern of seafloor spreading between africa and antarctica during the late cretaceous starting at chron 34 84 ma through to the middle eocene chron 20 46 ma in the first model the motion of antarctica relative to africa can be simply described by a rotation about a single pole of rotation in the second model which we favor the relative motion of antarctica and africa is more complex and a major change in spreading direction between chron 32 74 ma and chron 24 56 ma times is required in this paper we present ten plate tectonic reconstructions of the southwest indian ridge that were produced using a new compilation of magnetic bathymetric and satellite altimetry data in combination with interactive computer graphics these reconstructions illustrate that spreading directions started to change at chron 32 74 ma between chrons 31 and 28 69 64 ma spreading was very slow

fault geometry rupture dynamics and ground motion from potential earthquakes on the north anatolian fault under the sea of marmara summary using the 3 d finite element method we develop dynamic spontaneous rupture models of earthquakes on the north anatolian fault system in the sea of marmara turkey considering the geometrical complexity of the fault system in this region we find that the earthquake size rupture propagation pattern and ground motion all strongly depend on the interplay between the initial static regional pre stress field and the dynamic stress field radiated by the propagating rupture by testing several nucleation locations we observe that those far from an oblique normal fault stepover segment near istanbul lead to large through going rupture on the entire fault system whereas nucleation locations closer to the stepover segment tend to produce ruptures that die out in the stepover however this pattern can change drastically with only a 10 rotation of the regional stress field our simulations also reveal that while dynamic unclamping near fault bends can produce a new mode of supershear rupture propagation this unclamping has a much smaller effect on the speed of the peak in slip velocity along the fault finally we find that the complex fault geometry leads to a very complex and asymmetric pattern of near fault ground motion including greatly amplified ground motion on the insides of fault bends the ground motion pattern can change significantly with different hypocentres even beyond the typical effects of directivity the results of this study may have implications for seismic hazard in this region for the dynamics and ground motion of geometrically complex faults and for the interpretation of kinematic inverse rupture models

submarine fault scarps in the sea of marmara pull apart north anatolian fault implications for seismic hazard in istanbul earthquake scarps associated with recent historical events have been found on the floor of the sea of marmara along the north anatolian fault naf the marmarascarps cruise using an unmanned submersible rov provides direct observations to study the fine scale morphology and geology of those scarps their distribution and geometry the observations are consistent with the diversity of fault mechanisms and the fault segmentation within the north marmara extensional step over between the strike slip ganos and izmit faults smaller strike slip segments and pull apart basins alternate within the main step over commonly combining strike slip and extension rapid sedimentation rates of 1 3 mm yr appear to compete with normal faulting components of up to 6 mm yr at the pull apart margins in spite of the fast sedimentation rates the submarine scarps are preserved and accumulate relief sets of youthful earthquake scarps extend offshore from the ganos and izmit faults on land into the sea of marmara our observations suggest that they correspond to the submarine ruptures of the 1999 izmit mw 7 4 and the 1912 ganos ms 7 4 earthquakes while the 1999 rupture ends at the immediate eastern entrance of the extensional cinarcik basin the 1912 rupture appears to have crossed the ganos restraining bend into the sea of marmara floor for 60 km with a right lateral slip of 5 m ending in the central basin step over from the gulf of saros to marmara the total 1912 rupture length is probably about 140 km not 50 km as previously thought the direct observations of submarine scarps in marmara are critical to defining barriers that have arrested past earthquakes as well as defining a possible segmentation of the contemporary state of loading incorporating the submarine scarp evidence modifies substantially our understanding of the current state of loading along the naf next to istanbul coulomb stress modeling shows a zone of maximum loading with at least 4 5 m of slip deficit encompassing the strike slip segment 70 km long between the cinarcik and central basins that segment alone would be capable of generating a large magnitude earthquake mw 7 2 other segments in marmara appear less loaded

recalculated probability of m 7 earthquakes beneath the sea of marmara turkey 1 new earthquake probability calculations are made for the sea of marmara region and the city of istanbul providing a revised forecast and an evaluation of time dependent interaction techniques calculations incorporate newly obtained bathymetric images of the north anatolian fault beneath the sea of marmara le pichon et al 2001 armijo et al 2002 newly interpreted fault segmentation enables an improved regional a d 1500 2000 earthquake catalog and interevent model which form the basis for time dependent probability estimates calculations presented here also employ detailed models of coseismic and postseismic slip associated with the 17 august 1999 m 7 4 izmit earthquake to investigate effects of stress transfer on seismic hazard probability changes caused by the 1999 shock depend on marmara sea fault stressing rates which are calculated with a new finite element model the combined 2004 2034 regional poisson probability of m 7 earthquakes is 38 the regional time dependent probability is 44 18 and incorporation of stress transfer raises it to 53 18 the most important effect of adding time dependence and stress transfer to the calculations is an increase in the 30 year probability of a m 7 earthquake affecting istanbul the 30 year poisson probability at istanbul is 21 and the addition of time dependence and stress transfer raises it to 41 14 the ranges given on probability values are sensitivities of the calculations to input parameters determined by monte carlo analysis 1000 calculations are made using parameters drawn at random from distributions sensitivities are large relative to mean probability values and enhancements caused by stress transfer reflecting a poor understanding of large earthquake aperiodicity index terms 7223 seismology seismic hazard assessment and prediction 7230 seismology seismicity and seismotectonics 8150 tectonophysics plate boundary general 3040 keywords earthquake probability sea of marmara seismic hazard turkey stress interaction north anatolian fault

a study of microearthquake seismicity and focal mechanisms within the sea of marmara nw turkey using ocean bottom seismometers obss we have carried out seismological observations within the sea of marmara nw turkey in order to investigate the seismicity induced after gflcqk iuzmit kocaeli earthquake mw 7 4 of august 17 1999 using ocean bottom seismometers obss high resolution hypocenters and focal mechanisms of microearthquakes have been investigated during this marmara sea obs project involving deployment of 10 obss within the cvnarcvk eastern marmara sea and central tekirdagu western marmara sea basins during april july 2000 little was known about microearthquake activity and their source mechanisms in the marmara sea we have detected numerous microearthquakes within the main basins of the sea of marmara along the imaged strands of the north anatolian fault naf we obtained more than 350 well constrained hypocenters and nine composite focal mechanisms during 70 days of observation microseismicity mainly occurred along the main marmara fault mmf in the marmara sea there are a few events along the southern shelf seismic activity along the main marmara fault is quite high and focal depth distribution was shallower than 20 km along the western part of this fault and shallower than 15 km along its eastern part from high resolution relative relocation studies of some of the microearthquake clusters we suggest that the western main marmara fault is subvertical and the eastern main marmara fault dips to south at 458 composite focal mechanisms show a strike slip regime on the western main marmara fault and complex faulting strike slip and normal faulting on the eastern main marmara fault d 2004 elsevier b v all rights reserved

constraints on fluid origins and migration velocities along the marmara main fault sea of marmara turkey using helium isotopes abstract fluids venting from the submarine portion of the marmara main fault part of the north anatolian fault system turkey were sampled in ti bottles deployed by submersible the fluids consist of mixtures of fault derived gases fault related cold seep fluids and ambient seawater these components can readily be distinguished using the isotopes of he and the he ne ratios 3he 4he ratios range between 0 03 0 1 and 4 9 0 4 ra indicating that both crustal and mantle derived sources of helium are sampled by the fault the dominant gas in all the samples analyzed is methane with the abundance of co2 below detection 2 in the mantle rich high 3he 4he fluids this is in contrast to nearly all mantle derived fluids where the c species are dominated by co2 while high ch4 co2 ratios may reflect organic or inorganic reactions within the crust which reduce mantle derived co2 to methane this is not a priori necessary we show that simple dilution of mantle fluids with methane produced within local sediments could result in the high 3he 4he methane rich gases currently emanating from the fault this observation is supported by an anticorrelation between 3he 4he and c 3he which is consistent with addition of c and 4he simultaneously to the fluids the highest 3he 4he ratios were found in the tekirdag basin at the foot of the escarpment bordering the western sea of marmara where seismic data are consistent with the presence of a fault network at depth which could provide conduits permitting deep seated fluids to rise to the surface the lack of recent volcanism or any evidence of underlying magmatism in the area along with low temperature fluids strongly suggests that the 3he rich helium in these fluids was derived from the mantle itself with the marmara main fault providing a high permeability conduit from the mantle to the surface assuming that the mantle source to the fluids originally had a 3he 4he ratio of 6 ra the minimum fluid velocities considering only vertical transport and no mixing with parentless 4he implied by the high 3he 4he ratios are of the order of 1 100 mm yr 1

nucleation and evolution of ridge ridge ridge triple junctions thermomechanical model and geometrical theory abstract ridge ridge ridge triple junctions are among the most remarkable features of global plate tectonics but their nucleation and evolution remains incompletely understood here we employ 3d numerical models to study the processes of the nucleation and evolution of triple junctions induced by multi directional lithospheric extension the simulations show that two major classes of junctions develop i transient quadruple and triple plate rifting junctions formed by the initial plate breakup that are gradually converted into ii stable triple oceanic spreading junctions formed by the accretion of new lithosphere quadruple junctions break into two diverging triple oceanic spreading junctions connected by a linear spreading center lengthening with time this process gradually decreases the length of deforming boundaries between four diverging rigid plates and thus the integral mechanical resistance of these boundaries to the spreading the geometry of triple oceanic spreading junctions varies from asymmetrical t junctions to ideal 120 junctions the structure of these junctions includes two crucial tectonic elements oceanic ridges spreading centers and intra plate ranges triple junction traces dividing crust accreted from different spreading centers the geometrical steady state is achieved within several million years we propose a new geometrical theory of a migrating steady state triple junction which describes its structure as a function of the relative plate velocities in a moving triple junction reference frame the relative plate velocities define the orientations and growth rates of respective intra plate ranges orientations and lengthening rates of oceanic ridges are in turn given by the average relative velocity of two adjacent plates the steady state triple junction migration velocity satisfies the condition of minimal cumulative ridge lengthening rate weighted by the square root of the spreading velocity our analytical theory agrees well with the results of the numerical simulations and natural data

maximum earthquake magnitudes along different sections of the north anatolian fault zone abstract constraining the maximum likely magnitude of future earthquakes on continental transform faults has fundamental consequences for the expected seismic hazard since the recurrence time for those earthquakes is typically longer than a century such estimates rely primarily on well documented historical earthquake catalogs when available here we discuss the maximum observed earthquake magnitudes along different sections of the north anatolian fault zone nafz in relation to the age of the fault activity cumulative offset slip rate and maximum length of coherent fault segments the findings are based on a newly compiled catalog of historical earthquakes in the region using the extensive literary sources that exist owing to the long civilization record we find that the largest m7 8 8 0 earthquakes are exclusively observed along the older eastern part of the nafz that also has longer coherent fault segments in contrast the maximum observed events on the younger western part where the fault branches into two or more strands are smaller no first order relations between maximum magnitudes and fault offset or slip rates are found the results suggest that the maximum expected earthquake magnitude in the densely populated marmara istanbul region would probably not exceed m7 5 the findings are consistent with available knowledge for the san andreas fault and dead sea transform and can help in estimating hazard potential associated with different sections of large transform faults

seismicity distribution and locking depth along the main marmara fault turkey the seismicity along the main marmara fault mmf below the marmara sea is analyzed during the 2007 2012 period to provide insights on the recent evolution of this important regional seismic gap high precision locations show that seismicity is strongly varying along strike and depth providing fine details of the fault behavior that are inaccessible from geodetic observations the activity strongly clusters at the regions of transition between basins the central basin shows significant seismicity located below the shallow locking depth inferred from gps measurements its b value is low and the average seismic slip is high all observations are consistent with a deep creep of this segment on the contrary the kumburgaz basin at the center of the fault shows sparse seismicity with the hallmarks of a locked segment in the eastern marmara sea the seismicity distribution along the princes island segment in the cinarcik basin is consistent with the geodetic locking depth of 10 km and a low contribution to the regional seismic energy release the assessment of the locked segment areas provide an estimate of the magnitude of the main forthcoming event to be about 7 3 assuming that the rupture will not enter significantly within creeping domains

propagation of rifting along the arabia somalia plate boundary the gulfs of aden and tadjoura the localization and propagation of rifting between arabia and somalia are investigated by assessing the deformation geometry and kinematics at different scales between the eastern gulf of aden and the gulf of tadjoura using bathymetric magnetic seismological and structural evidence large scale southwestward propagation of the aden ridge markedly oblique to the arabia somalia relative motion vector began about 30 myr ago between the error and sharbithat ridges it was an episodic process with stages of rapid propagation mostly at rates 10 cm yr interrupted by million year pauses on transverse discontinuities coinciding with rheological boundaries between different crustal provinces of the arabia somalia plate the longest pause was at the shukra el sheik discontinuity 45 e where the ridge tip stalled for 13 myr between 17 and 4 ma west of that discontinuity rifting and spreading took place at an azimuth n25 10 e and rate 1 2 0 3 cm yr different from those of the global arabia somalia motion vector n39 1 73 cm yr implying an additional component of movement n65 10 e 0 7 0 2 cm yr due to rotation of the danakil microplate at shukra el sheik the typical oceanic ridge gives way to a narrow wsw trending axial trough resembling a large fissure across a shallow shelf this trough is composed of about eight rift segments which result from normal faulting and fissuring along n110 n130 e trends all the segments step to the left southwestward mostly through oblique transfer zones with en echelon normal faults only two segments show clear significant overlap there is one clear transform the maskali fault between the obock and tadjoura segments the latter segment which encroaches onland is composed of two parallel subrifts iboli ambabbo that propagated northwestward and formed in succession the most recent southwestern subrift ambabbo represents the current tip of the aden ridge we propose a mechanical model in which the large scale propagation of the ridge followed a wsw trending zone of maximum tensile stress while the small scale propagation of its nw trending segments was dictated by the orientation of that stress oblique propagation was a consequence of passive lithospheric necking of the arabia somalia plate along its narrow section in map view between socotra and the kink of the red sea ethiopian rift above the afar plume individual ridge segments oriented roughly perpendicular to plate motion like lithospheric cracks were forced to jump southward because of confinement within the necking zone self sustaining plate scale necking may explain why the aden ridge did not connect with the red sea through bab el mandeb but continued straight into afar

recent behavior of the north anatolian fault insights from an integrated paleoseismological data set 1 the north anatolian fault naf is a right lateral plate boundary fault that arcs across northern turkey for 1500 km almost the entire fault progressively ruptured in the 20th century its cascading style indicating that stress from one fault rupture triggers fault rupture of adjacent segments using published paleoseismic investigations this study integrates all of the existing information about the timing of paleoearthquakes on the naf paleoseismic investigation data are compiled into a database and for each site a bayesian ordering constrained age model is constructed in a consistent framework spatial variability of recurrence intervals suggests a spatial pattern in the behavior of earthquakes on the naf that may correspond to the tectonic provinces within the anatolian plate in the west the shear stress associated with the escaping anatolian plate interplays with the tensile stress associated with the aegean extensional province along this western transtensional section we recognize short recurrence intervals and switching between the furcated fault strands the central section of the naf is translational with little influence of fault normal stresses from other tectonic sources this section tends to rupture in unison or close succession the eastern section of the naf is transpressional due to the compressional fault normal stress associated with the indenting arabian plate along this section the recurrence intervals are bimodal which we attribute to variable normal stress although there are other possible causes

death and transfiguration of a triple junction in the south atlantic three major lithospheric plates antarctic south american and african meet in the south atlantic near bouvet island where the mid atlantic ridge mar the southwest indian ridge swir and the american antarctic ridge converge toward a fast evolving triple junction a major magmatic pulse has recently built a new swollen segment of the swir spiess ridge that is propagating toward the mar at a rate of 4 to 5 centimeters per year disrupting a former ridge ridge ridge rrr triple junction a new triple junction will be established about 70 kilometers to the north when the propagating swir spiess segment will impact with the mar probably within the next 1 million years the american antarctic ridge will take advantage of the mar swir duel by capturing an approximately 70 kilometer stretch of mar whereas the antarctic plate will increase its size

geomechanical model of the marmara sea region i 3 d contemporary kinematics summary we investigate by means of a 3 d geomechanical model the relationship between structural elements and contemporary kinematics in the marmara sea region northwest turkey the recently imaged fault system beneath the marmara sea is incorporated into the model as frictional surfaces with varying strike and dip the main marmara fault is implemented as through going and is accompanied by mostly non vertical second order faults topography basement topography and the moho become mechanically effective through changes in density and elastic parameters across these horizons the model is subjected to gravity and kinematic boundary conditions the ultimate goal of this study is to set up a 3 d model that is consistent with both kinematic observations and stress data the stress results are presented in a complementary paper in this paper we present the modelled long term 3 d kinematics in terms of fault slip rates rotations vertical motion and sense of fault slip the model results agree with global positioning system velocities geological fault slip rates palaeomagnetic measurements and with the observed pattern of subsidence and uplift furthermore our tectonically driven vertical velocities can be linked to landscape and basin evolution and to features of sedimentation our results indicate that the main marmara fault can be interpreted as a through going fault that slips almost purely in a strike slip sense nevertheless and not contradictory to the previous statement there is significant dip slip motion at some sections of the main marmara fault the agreement of the modelled 3 d kinematics with model independent observations supports that the main structural details of the fault system are accounted for sensitivity analysis of model parameters reveals that changes in rock properties and the initial stress state have minor influence on the 3 d kinematics we conclude that the 3 d structure of the fault system is the key control of the kinematics the slip rate of the main marmara fault from our model is lower than previous estimates and shows high variability along strike 12 8 17 8 mm a 1 the latter indicates that stress accumulation is non uniform along strike

triple junction kinematics accounts for the 2016 mw 7 8 kaikoura earthquake rupture complexity the 2016 moment magnitude mw 7 8 kaikoura earthquake generated the most complex surface ruptures ever observed although likely linked with kinematic changes in central new zealand the driving mechanisms of such complexity remain unclear here we propose an interpretation accounting for the most puzzling aspects of the 2016 rupture we examine the partitioning of plate motion and coseismic slip during the 2016 event in and around kaikoura and the large scale fault kinematics volcanism seismicity and slab geometry in the broader tonga kermadec region we find that the plate motion partitioning near kaikoura is comparable to the coseismic partitioning between strike slip motion on the kekerengu fault and subperpendicular thrusting along the offshore west hikurangi megathrust together with measured slip rates and paleoseismological results along the hope kekerengu and wairarapa faults this observation suggests that the west hikurangi thrust and kekerengu faults bound the southernmost tip of the tonga kermadec sliver plate the narrow region around kaikoura where the 3 fastest slipping faults of new zealand meet thus hosts a fault fault trench fft triple junction which accounts for the particularly convoluted 2016 coseismic deformation that triple junction appears to have migrated southward since the birth of the sliver plate around 5 to 7 million years ago this likely drove southward stepping of strike slip shear within the marlborough fault system and propagation of volcanism in the north island hence on a multimillennial time scale the apparently distributed faulting across southern new zealand may reflect classic plate tectonic triple junction migration rather than diffuse deformation of the continental lithosphere

distributed extension at the indian ocean triple junction the indian ocean triple junction is a ridge ridge ridge type joining two medium spreading ridges with one slow spreading ridge gloria long range side scan sonar images show that while the axial valleys of the two medium spreading ridges are almost colinear apart from a small 5 km offset the valley of the slow spreading third axis does not meet the other two in a simple fashion the axis of this slow spreading southwest indian ridge swir beyond the rift valley walls of the other two ridges steadily deepens by over 1000 m away from the triple junction to reach 5000 m at 35 km the gloria images show large normal faults around the deep swir rift valley which increase in heave away from the triple junction and crosscut the abyssal hills formed at the faster spreading central indian ridge indicating that extension across the swir is distributed over a zone 10 km or more wide this zone also shows no evidence for the formation of new oceanic crust suggesting that the extension may be amagmatic near the triple junction the high relief of the swir rift flanks containing tilted seafloor of the other two ridges may be an isostatic response of the lithosphere to the deep valley produced by this rifting these observations which suggest the progressive development of a propagating swir rift by the extension of preexisting seafloor may have general implications for the dynamics of oceanic spreading centers in particular the deepening and widening of the valley away from the triple junction is attributed to the competing effects of tectonic thinning and lithospheric cooling thermal models of mid ocean ridges spreading at 30 mm yr e g lin and parmentier 1989 predict that the depth to the 700 c isotherm increases with distance from the spreading axis by a proportion similar to the observed doubling in the total width of the deformation with distance from 10 to 35 km away from the triple junction this rate of widening of the deformation zone may therefore support lithospheric necking models for oceanic rift valleys if the width and depth of the deforming lithosphere are related in a simple manner

asymmetric slip partitioning in the sea of marmara pull apart a clue to propagation processes of the north anatolian fault between 1939 and 1999 the north anatolian fault naf experienced a westward progression of eight large earthquakes over 800 km of its morphological trace the 2000 km long north anatolian transform fault has also grown by westward propagation through continental lithosphere over a much longer timescale 10 myr the sea of marmara is a large pull apart that appears to have been a geometrical mechanical obstacle encountered by the naf during its propagation the present paper focuses on new high resolution data on the submarine fault system that forms a smaller pull apart beneath the northern sea of marmara between two well known strike slip faults on land izmit and ganos faults the outstandingly clear submarine morphology reveals a segmented fault system including pull apart features at a range of scales which indicate a dominant transtensional tectonic regime there is no evidence for a single continuous purely strike slip fault this result is critical to understanding of the seismic behaviour of this region of the naf close to istanbul additionally morphological and geological evidence is found for a stable kinematics consistent both with the long term displacement field determined for the past 5 myr and with present day anatolia eurasia motion determined with gps however within the sea of marmara region the fault kinematics involves asymmetric slip partitioning that appears to have extended throughout the evolution of the pull apart the loading associated with the westward propagation process of the naf may have provided a favourable initial geometry for such a slip separation

the tectonic evolution of the indian ocean triple junction anomaly 6 to present the tectonic evolution of the indian ocean ridge ridge ridge triple junction the junction of the central indian ridge cir southeast indian ridge seir and southwest indian ridge swir is inferred by mapping structures along its traces on the three plates with a long range side scan sonar geological long range inclined asdic gloria the sonar images to the west of the triple junction show two different styles of tectonic evolution some sections of the trace on the african plate are marked by a swir facing scarp containing fine lineaments that are probably normal faults these correspond with sections of the trace on the antarctic plate of the same age that have a sharp intersection of swir and seir abyssal hills that is to be expected from a simple ridge ridge ridge triple junction evolution a herringbone pattern of isochrons in contrast there are other sections of the trace on the african plate that have a blocky structure with no definite termination of cir abyssal hills against those of the swir the corresponding regions of the antarctic plate show large 10 to 30 km long overlapping fault scarps tapering to the northeast and ending in asymmetric valleys to the southwest these major normal faults are each offset by 1 6 km forming an en echelon series the two different styles of tectonic structures indicate two different modes of evolution although why the triple junction has evolved with two different modes is unclear periods of asymmetric spreading in the cir magnetic anomaly sequence collected on the african plate may possibly indicate that the cir and seir have been offset by a fracture zone at the triple junction during one of these two modes echo sounder traverses on the antarctic and african plates commonly show a steady shallowing of the cir and seir seafloor toward the traces a steep scarp facing the swir and a broad marginal deep at the base of this scarp this rift flank shape resembles that of the swir valley s rift shoulders close to the present triple junction mitchell 1991a suggesting that the mechanical evolution has been similar to the present day and the relief due to the rift flank uplift has been preserved by the cooling and strengthening of the lithosphere with age away from the ridge axes if the shape of the rift shoulder uplift along the trace on the antarctic plate is interpreted with a simple flexural model involving an end loaded elastic plate the inferred rigidity 1019 1021 n m or 2 6 km effective elastic thickness is consistent with the suggestion that the isostatic uplift occurred in young weak lithosphere close to the triple junction interestingly the observed 1 km relief of the trace escarpment and the estimated rigidity suggest that the uplift was produced by a load 2 5 1011 n m that is equivalent to half the present cross sectional area of the swir valley 35 km from the triple junction

evolution of the indian ocean triple junction between 65 and 49 ma anomalies 28 to 21 reinterpretation of newly published geophysical data kamesh raju and ramprasad 1989 and older profiles of the central indian basin associated with similar studies of the madagascar and crozet basins shows that the indian ocean triple junction trace on the indian plate corresponds at anomalies 23 and 22 to a n38 e offset of the magnetic lineations oblique to both the southeast indian ridge seir and central indian ridge cir spreading directions the conjugate triple junction trace on the african plate identified in the madagascar basin is associated with a roughly north south offset parallel to the southwest indian ridge swir fracture zones in order to account for these observations and the velocity triangle of the indian african and antarctic plates close to the triple junction a ridge fault fault mode is proposed with a propagatorlike seir cir offset the triple junction jumped between anomalies 24 and 23 and between anomalies 22 and 21 restoring a ridge ridge ridge configuration which immediately turned to a pseudo ridge ridge fault and later to a true ridge fault fault configuration after the triple junction jump at anomaly 21 the former seir cir offset was accommodated by a new cir fracture zone the lack of such a fracture zone prior to anomaly 21 suggests that either a pseudo ridge ridge fault or an unstable ridge ridge ridge configuration prevailed before anomaly 24 in agreement with the velocity triangles which predict more unstable triple junction modes both modes support the creation of numerous swir fracture zones presently observed between 52 30 e and 59 30 e as a consequence of the triple junction evolution between anomalies 29 and 24 this result suggests that the physiography of the swir records the history of the triple junction

m 7 earthquake rupture forecast and time dependent probability for the sea of marmara region turkey we forecast time independent and time dependent earthquake ruptures in the marmara region of turkey for the next 30 years using a new fault segmentation model we also augment time dependent brownian passage time bpt probability with static coulomb stress changes cff from interacting faults we calculate mw 6 5 probability from 26 individual fault sources in the marmara region we also consider a multisegment rupture model that allows higher magnitude ruptures over some segments of the northern branch of the north anatolian fault zone beneath the marmara sea a total of 10 different mw 7 0 to mw 8 0 multisegment ruptures are combined with the other regional faults at rates that balance the overall moment accumulation we use gaussian random distributions to treat parameter uncertainties e g aperiodicity maximum expected magnitude slip rate and consequently mean recurrence time of the statistical distributions associated with each fault source we then estimate uncertainties of the 30 year probability values for the next characteristic event obtained from three different models poisson bpt and bpt cff using a monte carlo procedure the gerede fault segment located at the eastern end of the marmara region shows the highest 30 year probability with a poisson value of 29 and a time dependent interaction probability of 48 we find an aggregated 30 year poisson probability of m 7 3 earthquakes at istanbul of 35 which increases to 47 if time dependence and stress transfer are considered we calculate a twofold probability gain ratio time dependent to time independent on the southern strands of the north anatolian fault zone

southern ocean hotspot tracks and the cenozoic absolute motion of the african antarctic and south american plates abstract a detailed analysis based on an antarctica africa finite reconstruction at chron c29 64 ma an assumption of no relative wander between the marion prince edward and tristan hotspots and on recently revised bathymetric maps of the southern ocean region shows that the fixed hotspot reference frame is tenable for absolute plate motions bouvet hotspot and probably trinidade as well also shows little or no cenozoic relative motion contrary to previous models bouvet hotspot is unrelated to the meteor rise cape rise seamount chain instead the bathymetric data when compared with the predicted hotspot tracks indicate another hotspot exists near the southernmost south atlantic spreading ridge segment new geochemical evidence from the latter region supports this hypothesis in showing the effects of plume enrichment from a source that is compositionally distinct from bouvet the peculiar zig zag shape of the cape rise meteor rise lineament is the result of this hotspot crossing the active transform segment of the falkland agulhas fracture zone in late mesozoic times followed by an early cenozoic ridge jump to the pre weakened trace on the then south american plate from the averaged cenozoic absolute motions of the african antarctic and south american plates it is evident that antarctica has been most nearly stationary in an absolute motion sense

relationship of the central indian ridge segmentation with the evolution of the rodrigues triple junction for the past 8 myr located near 25 33 s 70 00 e the rodrigues triple junction is the joining point of the intermediate spreading southeast indian and central indian ridges with the ultraslow spreading southwest indian ridge bathymetric data and magnetic anomalies are used to analyze the relationship between the evolution of the central indian ridge segmentation and the evolution of the rodrigues triple junction for the past 8 myr the central indian ridge domain exhibits a complex morphotectonic pattern dominated by ridge normal and oblique bathymetric lows interpreted as the off axis traces of axial discontinuities the short lived nontransform discontinuities as well as the segments that lengthen or shorten along the ridge axis reveal that the central indian ridge segmentation is unstable near the rodrigues triple junction the combined study of the central indian ridge and southeast indian ridge domains shows that the triple junction evolves between two modes a continuous mode where the central indian ridge and southeast indian ridge axes are joined and a discontinuous mode where the two ridge axes are offset owing to spreading asymmetry and differences in axis direction or in lengthening rates of the central indian and southeast indian ridges the continuous mode is unstable and evolves rapidly 2 myr into a discontinuous mode this last one is more stable and can evolve into a continuous mode only through the formation of a new central indian ridge segment which takes place facing the northern southeast indian ridge segment the evolution of the rodrigues triple junction configuration and the evolution of the central indian ridge segmentation are thus closely related

a possible triple junction at 14 50 s on the north fiji basin ridge southwest pacific auzende j m grficia mont e bendel v huchon p lafoy y lagabrielle y de alteriis g and tanahashi m 1994 a possible triple junction at 14 50 s on the north fiji basin ridge southwest pacific in j m auzende and t urabe editors north fiji basin sxarner french japanese program mar geol 116 25 35 recent full coverage bathymetric and geophysical surveys yokosuka 90 and 91 carried out in the framework of the starmer japanese french joint project reveal details of the structure of the n160 segment of the north fiji basin ridge despite its intermediate spreading rate this segment shows a slow spreading type morphology with steep 1000 m high walls reaching an axial depth of 4000 m its northern tip at 14 50 s is a complex area involving several plates boundaries this domain can be interpreted either as a complex boundary between two plates or as a new triple junction symmetrical with the 16 50 s triple junction characterizing its southern tip in either case the complexity of the spreading ridge geometry in this area illustrates the instability of the accretionary geometry due to the deformation of the whole north fiji basin between the much larger indo australian and pacific plates

plates and their motions the last reviews which covered research in plate motions were those of herron and pitman 1975 on marine magnetic anomalies and dewey 1975 on plate tectonics both reporting on research for the period 1971 1974 in the last 12 years there has been considerable refinement of relative motion models as well as further development of global models also major effort has gone into defining reference frames for the study of plate motions and discriminating between them more recently the role of errors in individual plate rotations and the associated uncertainties in reconstructions have received attention in this report i concentrate on work published in the last 4 years 1983 1986 citing a minimum of publications from previous years however some papers in press for early 1987 have been included this report first reviews work on relative plate motions for the present and past and reconstructions and then models for these motions global ones for driving forces and local ones determining subduction history and back arc spreading the problem of reference frames both hotspot and paleomagnetic is discussed next i end with a review of work on the errors in plate motions

contemporary holocene and quaternary deformation of the asal rift djibouti implications for the mechanics of slow spreading ridges because the frequency and character of rifting events along mid ocean ridges are largely unknown how the repetition of such events gives rise to rift structures is unexplored the asal rift in the afar depression of djibouti africa provides the world s best subaerial analogue for young slow spreading mid ocean ridges seismic geodetic and field observations of a seismovolcanic event in 1978 at asal yield estimates of the fault and dike locations geometry displacement and volume of basalt extruded in a rifting event a 6 9 kyr old lake shore highstand at asal has been warped downward by 70 m providing a holocene measure of the vertical deformation across the rift the rift topography furnishes an older datum which we infer to be 34 6 kyr old using the holocene deformation rate we find that faults throughout the rift valley are active holocene slip rates diminish beyond 4 km from the rift axis late quaternary rates decrease beyond 6 7 km the holocene slip rates are used to estimate repeat times by taking the displacement on the faults which slipped in 1978 as characteristic we find tectonic events on individual faults recur every 200 300 years half the rift faults slipped together in the 1978 event if this is typical then groups of faults are activated every 100 150 years we suggest that half the events take place in the rift axis accompanied by volcanic extrusion the remainder occur peripheral to the neovolcanic zone and involve fault slip only both events having a repeat time of 200 300 years given the 10 km width of the rift and its 16 mm yr 1 spreading rate the mean age of the material in the rift should be 350 kyr an order of magnitude older than the inferred age of the formation of the rift topography the subsidence rate of the rift axis during the past 35 kyr is 8 9 mm yr 1 with the rate of infilling by volcanic extrusion 1 mm yr 1 the resulting net subsidence rate about equal to the half spreading rate of the rift could not be sustained for 300 kyr without significant infilling by lavas thus both observations suggest that the long term vertical deformation in the rift has not been steady state instead we suggest that there is a rifting filling cycle at asal with the most recent filling episode ending 35 kyr

marine tectonics processes at mid ocean ridges the use of multibeam echo sounders and various side looking sonar systems has greatly increased our knowledge and understanding of mid ocean ridge mor processes since the last iugg review on mid ocean ridge research macdonald 1983 the extensive use of swath mapping tools such as sea beam deep tow seamarc i and ii the application of multichannel seismic reflection techniques to the detection of axial magma chambers and the use of satellite data in the study of oceanic lithosphere have rejuvenated marine tectonics and have generated and stimulated a large number of important contributions this review will focus on what we feel were the major developments in marine tectonics with an emphasis on mid ocean ridges in the last four years certain topics such as marine seismicity and satellite studies are only briefly mentionned for reference and will be covered in greater detail in other reviews because of the exponential growth in the number of publications related to mors during 1982 1986 only a few references pertinent to each of the major research topics will be quoted in the text as examples but the reader will find an extensive bibliography at the end of the text references published prior to 1982 were added only where appropriate

evolution of the southwest indian ridge from 55 45 e to 62 e changes in plate boundary geometry since 26 ma from 55 45 e to 58 45 e and from 60 30 e to 62 00 e the ultraslow spreading southwest indian ridge swir consists of magmatic spreading segments separated by oblique amagmatic spreading segments transform faults and nontransform discontinuities off axis magnetic and multibeam bathymetric data permit investigation of the evolution of this part of the swir individual magmatic segments show varying magnitudes and directions of asymmetric spreading which requires that the shape of the plate boundary has changed significantly over time in particular since 26 ma the atlantis ii transform fault grew by 90 km to reach 199 km while a 45 km long transform fault at 56 30 e shrank to become an 11 km offset nontransform discontinuity conversely an oblique amagmatic segment at the center of a first order spreading segment shows little change in orientation with time these changes are consistent with the clockwise rotation of two 450 km wide first order spreading segments between the gallieni and melville transform faults 52 60 e to become more orthogonal to spreading we suggest that suborthogonal first order spreading segments reflect a stable configuration for mid ocean ridges that maximizes upwelling rates in the asthenospheric mantle and results in a hotter and weaker ridge axis that can more easily accommodate seafloor spreading

geometry and segmentation of the north anatolian fault beneath the marmara sea turkey deduced from long term ocean bottom seismographic observations both the geometry and the depth of the seismogenic zone of the north anatolian fault under the marmara sea the main marmara fault mmf are poorly understood in part because of the fault s undersea location we recorded 10 months of microseismic data with a dense array of ocean bottom seismographs and then applied double difference relocation and 3 d tomographic modeling to obtain precise hypocenters on the mmf beneath the central and western marmara sea the hypocenters show distinct lateral changes along the mmf 1 both the upper and lower crust beneath the western high are seismically active and the maximum focal depth reaches 26 km 2 seismic events are confined to the upper crust beneath the region extending from the eastern part of the central basin to the kumburgaz basin and 3 the magnitude and direction of dip of the main fault change under the central basin where there is also an abrupt change in the depth of the lower limit of the seismogenic zone we attribute this change to a segment boundary of the mmf our data show that the upper limit of the seismogenic zone corresponds to sedimentary basement we also identified several seismically inactive regions within the upper crust along the mmf their spatial extent beneath the kumburgaz basin is greater than beneath the western high from the comparison with seafloor extensometer data we consider that these regions might indicate zones of strong coupling that are accumulating stress for release during future large earthquakes

on the stability of triple junctions and its relation to episodicity in spreading a convenient representation of triple junctions that involve only ridges r and transform faults f is proposed this representation combines in a simple way information from geographic and velocity spaces the velocity triangle provides the budget of lithospheric surface change which directly results from interactions of the three plates a discussion of the relative positions of the triple junction with respect to the velocity triangle demonstrates that in general there are several triple junction configurations that are compatible with a given triangle this discussion stresses the importance of oblique and asymmetric spreading pairs of triple junction configurations that are of particular interest are rrr rrf and rrr ffr when the triple junction lies outside of the triangle at least one of the ridges will shorten leading to yet another type of potentially unstable configuration the present configurations of the bouvet galapagos and indian ocean triple junctions are reviewed a method is proposed to reconstruct past configurations of the indian ocean junction at the time of anomalies 23 and 28 the main parameters that influence triple junction evolution are the lengths of transform faults the availability of magma and related connectivity of magma chambers and the also related spreading velocities this study confirms an earlier suggestion that activity at constructive plate boundaries occurs in two preferred modes the effusive and tectonic modes corresponding here to rrr and to rrf rff configurations respectively these modes apparently alternate in episodes of typically 1 ma duration the significance of this time constant and consequences for lithospheric mechanics are briefly discussed

an integrated geophysical study east of the southern chagos laccadive ridge complex central indian ocean basin implications for the rodriguez triple junction dynamics in the late cretaceous abstract the central indian ocean basin east of the southern chagos laccadive ridge complex has evolved due to seafloor spreading in the n s direction since the late cretaceous the trace of the rodriguez triple junction rtj has been inferred in this basin but its exact location and dynamics prior to c29o are not known about 20 000 km of total magnetic intensity data along with satellite gravity mosaic were used to understand the dynamics of the rtj in the late cretaceous synthetic seafloor spreading models endorse the presence of late cretaceous to early palaeogene magnetic anomalies c34y to c24o in the study area half spreading rates are initially low 32 mm yr between c34y to c33y and increase up to 78 mm yr by c28y thereafter a decreasing trend is seen 57 mm yr towards the west in the study area higher spreading rates 120 mm yr between c33y and c32ay and distorted anomalies between chrons c32ay and c30y are observed detailed geophysical analysis suggests that the higher spreading rates are due to the presence of transferred crust and the distorted anomalies are caused by the presence of fragmented tectonic blocks depicting microplate formation and rotation plate reconstruction models suggest that the rtj at c34y time lay southwest of comorin ridge which coincided with the northern edge of the conrad rise until c33y the rtj left a linear trace parallel to the fracture zone trend on both the indian and antarctic plates while it gradually moved eastwards on the african plate the rtj migrated westwards until c31y causing the transfer of a considerable amount of crust from the african plate to both the indian and antarctic plates thereafter the rtj rapidly reversed its migration direction towards the east until c29o causing the formation and rotation of a microplate on the indian plate and lengthening of the southwest indian ridge the present study suggests that this episodic migration of the rtj may be due to ridge propagation under the influence of the marion hotspot which was in the vicinity during that period this rtj migration resulted in microplate formation lithospheric transfer and thickened lithosphere similar to the inferences made at many triple junctions in the pacific ocean thus the origin of anomalous structures such as the crozet bank may be related to triple junction dynamics under the influence of marion hotspot further the counter clockwise rotation of the southwest indian ridge between c33y and c29y may have a causal link with the formation and rotation of the microplate which occurred during the same period the present study thus facilitated the inference of the dynamics of the rtj trace between c34y and c29o on the three plates

displacement transfer between intersecting regional strike slip and extensional fault systems interaction and displacement transfer between active intersecting strike slip or transform and extensional fault systems are examined outcrop data from a well preserved strike slip fault and rift intersection in new zealand are compared to a global data set of 13 such intersections in both continental and oceanic crust displacement transfer between strike slip and normal faults is typically accomplished by gradual changes of fault orientations and slip vectors close to the intersection zone for two and three plate configurations these changes result in sub parallelism of the slip vectors of the component faults with their line of intersection the dimensions of the area over which fault strike and slip vectors change are principally controlled by the extent to which displacements on the dominant of the two intersecting fault systems are confined to a single slip surface or distributed across a zone where slip is spatially distributed the region in which the two displacement fields are superimposed produces transtension and associated oblique slip this distributed off fault deformation facilitates the development of a quasi stable configuration of the fault intersection region maintaining both the regional geometry and kinematics of the intersection zone which in many cases would not be possible for rigid block translations the dimensions of the transition zone are larger for continental crust than for oceanic crust because oceanic crust is thinner fault geometries in oceanic crust are simpler two plate configurations and the slip vectors of the component intersecting fault systems are sub parallel

moho crustal architecture and deep deformation under the north marmara trough from the seismarmara leg 1 offshore onshore reflection refraction survey abstract understanding further the nature and evolution at lithospheric scale of the sea of marmara on the north anatolian fault needs constraints on the deep crustal and moho spatial variation this has been probed here with offshore onshore and obs ocean bottom seismometer refraction seismics in addition to coincident mcs marine multichannel reflection seismic profiles over the whole north marmara trough the diverse strikes of mcs profiles in a dense grid allow to avoid misinterpretation of late echoes in the deep basin as moho reflections and attribute them to sidesweeps moho is instead positively identified from reversed observations of first arrival head and refracted waves at the top of the mantle obtained at large offset by land stations a significant and sharp reduction in its depth on the order of 5 km occurs beneath both the eastern and western rims of the north marmara trough with a more progressive crustal thinning from the south the wide angle reflections on obs and land stations document in addition to moho the top of a lower crustal reflective layer which is also sampled by mcs profiles and appears to follow moho topography the dense grid of mcs profiles along the southwestern margin of the north marmara trough reveals a dipping reflector through the upper crust with tilted basement blocks on top this low angle fault is suggested as a normal sense detachment extending in depth towards the reflective lower crust the upwarp of the moho and lower crustal layer towards the north marmara trough suggests that crustal thinning occurs mostly in the upper crustal part with lateral transport of the material towards wsw in the footwall of the detachment and possibly other features to the south in the motion of anatolia with respect to stable eurasia oblique to the north marmara trough thinning can be accommodated in an asymmetric partitioning of the displacement on several branching faults at lithospheric scale

a bathymetry and altimetry profile across the southwest indian ridge crest at 31 s latitude abstract during march 1983 the m v marion dufresne obtained a bathymetry profile along more than 1500 km of a seasat altimeter sub track across the southwest indian ridge crest at 31 s latitude we have used these data to estimate the thermal and elastic thickness of the oceanic lithosphere in the vicinity of the ridge and to evaluate the performance of the seasat altimeter the thermal thickness appears to be in the range 72 109 km while the elastic thickness is about 2 5 km there is a good correlation between the geoid calculated from the bathymetry and its compensation and the observed geoid derived from seasat data the correlation is strongest for wavelengths greater than 45 km and poorest for shorter wavelengths we attribute the poor resolution at short wavelengths to instrument and oceanographic noise in the altimeter data combined with the reduced sensitivity of the geoid to bathymetric relief at very short wavelengths

paleogeographic maps of the continents bordering the indian ocean since the early jurassic paleomagnetic data from the african plate from the early jurassic onward are critically re evaluated and updated resulting in a set of 30 paleopoles from which an apparent polar wander path is derived using 20 ma intervals this path is then used in conjunction with kinematic models of the indian and atlantic oceans to place other continents bordering the indian ocean eurasia india islands and plateaus madagascar seychelles mascarene and blocks involved in the collision of india with eurasia south tibet indochina in an absolute paleogeographic frame fixed with respect to africa paleogeographic maps are presented for the early jurassic pre breakup the jurassic cretaceous boundary anomaly ml5 the early cretaceous m2 the late cretaceous a 34 the cretaceous tertiary boundary a 29 the early eocene a 24 the middle eocene a 21 and the oligocene miocene boundary a 6 observed and predicted paleomagnetic directions for landmasses other than africa i e for western europe china korea india and australia which are not used in deriving the maps are found to be in very satisfactory agreement the quality of reconstructions as measured by rms discrepancies between observed and predicted paleolatitudes is of the order of 5 the main features of the paleogeographic maps are discussed with the aim of relating oceanic and on land geodynamic events the constraints provided by tibetan data on the india asia collision and the 20 ma reorganization of geology and plate boundaries in a band extending from the south china sea through tibet to the red sea system are discussed in more detail we emphasize the episodic nature of the breakup of gondwanaland and formation of the indian ocean and subsequent interaction with eurasia in which six major discrete events are identified separated by 30 ma phases of rather uniform plate motion

relative positions of africa and antarctica in the upper cretaceous evidence for non stationary behaviour of fracture zones abstract new bathymetric and magnetic data have been collected in the enderby basin southern indian ocean during cruise md34 of the n o marion dufresne january february 1983 one can identify in this basin oceanic crust created along the same portion of the southwest indian ridge as the crust of the mozambique basin two sets of magnetic lineations with different amplitude split by a large offset fracture zone are localized in each basin and enable us to obtain accurate reconstructions of the africa antarctica plate boundary at the time of anomalies 34 33 and 32 the data west of prince edward fracture zone are taken into account to adjust the parameters of rotation these reconstructions of isochrons allow us to discuss the evolution of the geometry of accretionary plate boundaries and to emphasize the unstable behaviour of fractures zones in particular we give evidence for an important change in the spreading direction along prince edward fracture zone which demonstrates that stability of a pole of rotation is not guarantueed by major offset fracture zones

istanbul s earthquake hot spots geodetic constraints on strain accumulation along faults in the marmara seismic gap during the past century a series of predominantly westward migrating m 7 earthquakes broke an 1000 km section of the north anatolian fault naf the only major remaining seismic gap along the fault is under the sea of marmara main marmara fault mmf we use 20 years of gps observations to estimate strain accumulation on fault segments in the marmara sea seismic gap we report the first direct observations of strain accumulation on the princes islands segment of the mmf constraining the slip deficit rate to 10 15 mm yr in contrast the central segment of the mmf that was thought to be the most likely location for the anticipated gap filling earthquakes shows no evidence of strain accumulation suggesting that fault motion is accommodated by fault creep we conclude that the princes islands segment is most likely to generate the next m 7 earthquake along the sea of marmara segment of the naf

transient rifting north of the galapagos triple junction abstract seafloor bathymetry north of the galapagos microplate in the eastern pacific ocean contains evidence for a sequence of short lived rifts cross cutting abyssal hills adjacent to the east pacific rise these secondary rifts are sub parallel to the incipient rift that marks the current triple junction at 2 40 n and are nearly perpendicular to the direction of opening between the cocos and nazca plates secondary rifts likely initiated from the epr by lithospheric cracking eventually their activity stopped and they were carried away from the triple junction as part of the cocos plate we developed and analyzed numerical models of rift interaction to understand the evolution of rift configuration in this area by varying the geometry and locations of rifts we constrain the factors that have led to the location and orientation of secondary rifts at the northern galapagos triple junction interaction between secondary rifts and the cocos nazca rift results in 10 clockwise rotation of the secondary rift propagation direction as observed furthermore if a rift has become detached from the east pacific rise a zone of reduced tension is present ahead of the rift tip prohibiting its connection to the east pacific rise two zones of tensile stress enhancement develop along the east pacific rise next to the detached rift and control where new cracks are likely to form although the magnitude of tensile stress enhancement is controlled by the gap between the detached rift and the east pacific rise whether the new rift forms north or south of the detached rift is controlled by position of the cocos nazca rift therefore the sequence of ancient rifts found northeast of the current triple junction at 2 40 n represents the natural consequence of rift disconnection events and their position records the kinematic history of the gap between the east pacific rise and the cocos nazca rift

the seismic activity of the marmara sea region over the last 2000 years we examined the seismicity of the region of the sea of marmara in northwest turkey over the last 2000 yr using the historical record of the region we found no evidence for truly large earthquakes of a size comparable to those in the north anatolian fault zone in the marmara basin events are smaller in keeping with the known fault segmentation of the basin over the last 2000 yr seismic mo ment release accounted for the known right lateral shear velocity across the marmara region observed by global positioning system measurements its average rate is relatively constant and varies between 1 6 and 2 4 cm yr the long term seismicity in the marmara sea region shows that large earthquakes are less frequent than pre dicted from the 100 yr long instrumental period

the role of fluids in lower crustal earthquakes near continental rifts earthquakes in the lower continental crust of the earth are rare as the lower crust is thought to be too hot to allow brittle failure so it is surprising that they occasionally occur where continental crust is rifting apart a study of three dimensional crustal structure and seismicity in the taupo volcanic zone an active continental rift in new zealand has now provided insight into how these earthquakes arise the crustal earthquakes form a continuous band along the rift and often occur in swarms suggesting fluid movement in critically loaded fault zones seismic velocities within the band are consistent with the presence of fluids and the linking of upper and lower crust seismicity to crustal structure point to a common explanation for all of the seismicity probably the weakening of faults on the periphery of an otherwise dry crust by hot fluids a report on three dimensional tomographic imaging of seismic velocities and attenuation in the taupo volcanic zone an active continental rift where earthquakes are known to occur in the lower crust finds that crustal earthquakes form a continuous band along the rift and often occur in swarms suggesting fluid movement in critically loaded fault zones the occurrence of earthquakes in the lower crust near continental rifts has long been puzzling as the lower crust is generally thought to be too hot for brittle failure to occur1 2 such anomalous events have usually been explained in terms of the lower crust being cooler than normal3 4 but if the lower crust is indeed cold enough to produce earthquakes then the uppermost mantle beneath it should also be cold enough2 and yet uppermost mantle earthquakes are not observed5 numerous lower crustal earthquakes occur near the southwestern termination of the taupo volcanic zone tvz an active continental rift in new zealand6 here we present three dimensional tomographic imaging of seismic velocities and seismic attenuation in this region using data from a dense seismograph deployment7 we find that crustal earthquakes accurately relocated with our three dimensional seismic velocity model form a continuous band along the rift deepening from mostly less than 10 km in the central tvz to depths of 30 40 km in the lower crust 30 km southwest of the termination of the volcanic zone these earthquakes often occur in swarms suggesting fluid movement in critically loaded fault zones8 seismic velocities within the band are also consistent with the presence of fluids and the deepening seismicity parallels the boundary between high seismic attenuation interpreted as partial melt within the central tvz and low seismic attenuation in the crust to the southwest this linking of upper and lower crustal seismicity and crustal structure allows us to propose a common explanation for all the seismicity involving the weakening of faults on the periphery of an otherwise dry mafic crust by hot fluids including those exsolved from underlying melt such fluids may generally be an important driver of lower crustal seismicity near continental rifts

eddies advected by time dependent sverdrup circulation in the western boundary of the subarctic north pacific 1 it has been reported that several eddies frequently exist along the kuril kamchatka trench k k trench hereafter the western boundary of the subarctic north pacific lagged correlation maps of the altimeter derived sea level anomalies slas along the trench indicate that the southern eddies on the whole move northeastward along the k k trench and the northern eddies on the other hand move southwestward by tracking each anticyclonic eddy its propagating velocity along the trench is calculated the time series of the tracked 7 eddies shows similar seasonal variation to those of the first empirical orthogonal function eof of the sla maps and to those of the sverdrup transport at 40 n in addition when more than two eddies remotely exist in the studied area they show coherent moving patterns these results suggest that the eddies in the western boundary region of the subarctic north pacific are advected by the time dependent wind driven current

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

submarine earthquake history of the cinarcik segment of the north anatolian fault in the marmara sea turkey the north anatolian fault naf in the marmara sea is a significant hazard for the city of istanbul the use of paleoseismological data to provide an accurate seismic risk assessment for the area is constrained by the fact that the naf system is submarine thus a history of paleoearthquakes can be inferred only by using marine sediment cores here a record of turbidites was obtained in two cores and used to reconstruct the earthquake history along the cinarcik segment a main branch of the naf klg04 was collected from a berm north of the fault and klg03 was positioned in the cinarcik basin south of the fault the cores were correlated using long term geo chemical variations in the sediment and turbidites deposited simultaneously at both sites were then identified radionuclide measurements suggest the most recent turbi dite was triggered by the 1894 c e m w 7 3 earthquake we conclude that the turbidites identified at both sites are earthquake generated based on their particular sedimento logical and geochemical signatures the correlation of turbidites at berm and basin sites and the match of the most recent turbidite with a nineteenth century historical earthquake to date older turbidites we used carbon 14 and paleomagnetic data to build an oxcal model with a local reservoir correction of 400 50 yr the cinarcik segment is found to have ruptured in 1509 c e sometime in the fourteenth century in 989 c e and in 740 c e with a mean recurrence interval in the range of 256 321 years finally we used the earthquake record obtained to review the rupture history of the adjacent segments over the past 1500 years

active faults in the sea of marmara western turkey imaged by seismic reflection profiles turkey is moving westward relative to eurasia thereby accommodating the collision between arabia and eurasia this motion is mostly taken up by strike slip deformation along the north and east anatolian faults the sea of marmara lies over the direct westward continuation of the north anatolian fault zone just east of the sea of marmara the north anatolian fault splits into three strands two of which continue into the sea while the locations of the faults are well constrained on land it has not yet been determined how the deformation is transferred across the sea of marmara onto the faults on the west coast of turkey we present results from a seismic reflection survey undertaken to map the faults as they continue through the three deep marmara sea basins of clnarclk central marmara and tekirdag in order to determine how the deformation is distributed across the sea of marmara and how it is taken up on the western side of the sea the data show active dipping faults with associated tilting of sedimentary layers connecting the north anatolian fault to strike slip faults that cut the biga and gallipoli peninsulas