on the hellenic subduction zone and the geodynamic evolution of crete since the late middle miocene abstract in recent syntheses of the geodynamic evolution of the aegean area the hellenic subduction zone and in particular its initiation plays a central role two basic aspects of the recent comprehensive model put forward by le pichon angelier and co workers are a initiation of subduction along the hellenic arc is inferred to have taken place approximately 13 ma ago whereas several others have suggested approximately 5 ma and b migration of the trench system to the south southwest giving rise to an extensional regime in the back arc region which led to general subsidence and formation of the present day aegean sea new data on the structure of the upper mantle underneath the aegean area indicate that the former aspect requires modification the seismic velocity structure indicating a northward dipping slab down to a depth of at least 600 km and the depth distribution of earthquake hypocenters can not be reconciled with straightforward initiation of subduction approximately 13 ma ago estimates of about 5 ma for the time of initiation of the present subduction zone are even more difficult to reconcile assuming 400 km as an upper bound for the effect of stretching of the aegean sea and of other processes contributing to the separation of crete from the eurasian mainland we arrive at an age for the hellenic subduction zone of at least 26 ma as to aspect b geological data of crete lend strong support to the idea that on crete compressional tectonics is of much greater importance than current models imply combining geophysical and geological data we propose a modification of the tectonic evolution for the cretan segment of the hellenic arc whereas the basic process of extension caused by a migrating trench system roll back in a land locked basin remains a very useful and sound concept the tectonics of the margins of a region subject to stretching in this case crete may be more complicated than hitherto thought in our model the documented fragmentation of crete into several basins which started about 12 ma ago is not attributed to initiation of subduction but to inception of the roll back process compressional tectonics on crete is taken to be associated with deformation of the crust resulting from the overall tensional stress regime

volcanology and petrology of volcanic products from the island of milos and neighbouring islets abstract new geochronological and volcanological data from volcanics of the island group of milos south aegean active volcanic arc allow four main cycles of volcanic activity to be distinguished ranging in age between 3 5 and 0 1 m y b p the oldest volcanic activity consists almost totally of pyroclastics and submarine products followed by subaerial ones the eruptive centers migrated in time and concentrated during the most recent volcanic phase in the central part of milos and on the island of antimilos the oldest products are dominated by andesites and dacites while the most recent ones mainly consist of rhyolites the volcanic evolution and the geochemical characters of the erupted products suggest that the feeding system of the oldest volcanism was located in the deep continental crust where contamination and fractional crystallization jointly occurred the younger cycle of volcanic activity was fed from small and relatively shallow magma chambers where contamination processes played a minor role these magma bodies are considered to responsible for the shallow thermal anomaly giving rise to the high enthalpy field on milos

evidence for transform faulting in the ionian sea the cephalonia island earthquake sequence of 1983 accurate locations of aftershocks of the january 17 1983 ms 7 0 main shock in the ionian islands have been determined as well as fault plane solutions for this main shock and its largest aftershock which are interpreted as a right lateral strike slip motion with a thrust component on a fault striking in about a ne sw direction

the mechanical state of the lithosphere in the altiplano puna segment of the andes abstract information about topography the shape of the geoid seismicity neogene deformation and volcanism in the region of altiplano puna of western south america is used to analyse the state of stress across the convergent plate margin in terms of the effects of topography and simple models of its compensation an average elevation near 4 km is consistent with compensation by a yet unresolved combination of crustal root and hot uppermost mantle producing a geoid high of 22 27 meters average horizontal compressive stress in excess of a reference sea level lithostatic value of 390 bars in a 150 km thick lithosphere and an average shear stress of 170 bars along a 30 dipping interplate boundary the basis for these estimates is evidence for a neutral to extensional stress regime within the high plateau contrasted with a compressional regime on the eastern slopes and along the interplate boundary itself comparison with other plateaus in a convergent plate tectonic setting suggests an evolutionary sequence from compressional to extensional tectonics as elevation of the plateau increases

plio quaternary stress state in the burdur basin sw turkey abstract this study defines the plio quaternary to present day stress regime in the burdur basin located at the northeastern end of the fethiye burdur fault zone in sw turkey this fault length which is considered the landward continuation of the pliny strabo trench is an important feature in sw turkey the inversion slip vectors measured on fault planes indicate a consistent normal faulting stress regime during plio quaternary time continuing into recent times as indicated by earthquake focal mechanism inversions both states have consistent nw se trending horizontal minimum stress axes 3 the orientation of fault sets is predominantly around the ne sw direction in the major fethiye burdur fault zone making the extension nw se the mean stress ratio is 0 74 indicating a triaxial stress state which is clearly different from radial extension the nw se extension is probably responsible for the formation of the burdur basin during plio quaternary time this extension which is probably caused by slab pull force due to the subduction process along the cyprus arc produces a dominant normal motion along the fbfz

tectonic stresses on the mainland of greece in situ measurements by overcoring abstract direct in situ measurements of the horizontal stresses in continental greece indicate a predominantly n s extensive stress considerable scatter of the azimuth of the axis of extension is found in thrace in contrast to a more homogeneous pattern in macedonia and peloponnesus these results are obtained with an overcoring technique in boreholes of a few meters they can be compared with neotectonic and seismic data to evaluate the present deformation process in this basin

late cenozoic stress distribution along the misis range in the anatolian arabian and african plate intersection region se turkey 1 this study defines the mio pliocene to present day stress regime acting at the northeastern mediterranean along the se border of the neogene adana basin along the misis range the inversion of earthquake focal mechanisms shows that the present day state of stress is dominantly a transtension combined the strike slip and extension with a consistent ene n83 e trending hmin 3 axis the inversion slip vectors measured on fault planes and chronologies between striations indicate a consistent strike slip stress regime that varied from transpressional initially to transtensional during pleistocene time with the latter continuing into recent times as indicated by earthquake focal mechanism inversions both states have consistent nnw n15 w trending compatible with nnw arabian drift direction and ene n75 e trending hmax 1 and hmin 3 axes respectively but have significantly different mean arithmetic stress ratio rm values rm 0 75 indicating transpression for the old regional stress regime and rm of 0 20 denoting transtensional for the younger regional stress regime the crosscutting of striations confirms also the change within the strike slip stress regime both stress regimes induce sinistral displacement along the major strike slip fault systems i e east anatolian fault karatas osmaniye fault the temporal stress regime change probably occurred during quaternary time and resulted from coeval influence of the superimposed forces owing to subduction processes in the southwest along the cyprus arc continental collision in the east and westward escape of the anatolian block in the north and west

complex rotational deformations in the serbo macedonian massif north greece structural and paleomagnetic evidence abstract structural data concerning the neotectonic deformation of the serbo macedonian massif suggest a possible counterclockwise rotation of the stress field which corresponds to a clockwise rotation of the geological structures such a rotation is confirmed by paleomagnetic data providing a new alternative interpretation of the geodynamic evolution of this area

the aegean region deep structures and seismological properties summary 3 d p wave velocity anomaly patterns the geometry of the hellenic wadatibenioff zone and of the seismically active fracture zones in the overlying continental wedge and the depth distribution of seismogenic properties seismic activity energy and b value for the aegean region are examined in this study the western and eastern parts of the area studied differ significantly in terms of the depth distribution of the considered seismological parameters and the velocity structures the results indicate different physical conditions in the western and eastern parts of the region in question data for the surface heat flow and the evolution of the volcanism in the aegean region since the early eocene are employed to interpret the results of the present study possible geodynamic processes at the plate boundaries between africa and eurasia are discussed

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

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

a re analysis of the late bronze age eruption and tsunami of santorini greece and the implications for the volcano tsunami hazard the paroxysmal eruption of santorini ca 3500 bp referred to as the late bronze age lba eruption probably generated multiple tsunami their occurrence and impacts being cited frequently in scientific papers and articles this paper examines what is known about any lba tsunami noting possible mechanisms of generation and identifying sedimentological traces firstly the eruption sequence is outlined providing the context in which tsunami genesis may have occurred secondly the arguments forwarded for the tsunami and a summary of the evidence is given thirdly results of a new geological investigation for lba tsunami deposits at 41 coastal sites from crete and kos are presented the data are used to test the hypothesis that the lba eruption generated an east mediterranean wide tsunami it will be seen that no terrestrial geological evidence is identified the paper re examines the original arguments presented for lba tsunami challenging them because their founding assumptions are flawed together the new data and the re analysis of the original tsunami hypothesis indicate that there is insufficient evidence to demonstrate that any significant far field tsunami propagated throughout the entire east mediterranean as frequently purported some terrestrial evidence exists to suggest localised near field tsunami inundation there is good submarine evidence however to suggest that a tsunami was focused to the w and wsw the results have important implications for understanding the volcano related tsunami hazard within the region and elsewhere

arc stresses determined by slabs implications for mechanisms of back arc spreading there is an anti correlation in stress field between the back arc area and the shallow portion of the slab generally slabs showing down dip compression have tensional back arcs and the reverse we explain this anti correlation by a force balance in the fore arc wedge between the slab pull collision force in the upper plate and the ridge push back arc spreading can occur as a passive response to the down dip compressional slab the mariana kyushu and aegean arcs are the exceptions to the anti correlation in these arcs the back arc is tensional although the slab is in down dip tension this may be because the fore arc is driven by the mantle drag toward the trench resulting in compression balanced with the slab pull the flow in the mantle would cause back arc spreading in this case

analysis of states of stress between provinces of constant stress recent studies have indicated the existence of crustal provinces or domains within which the state of stress shows little apparent horizontal variation between provinces the state of stress may undergo substantial changes often over remarkably short distances as analyzed here the transition in stress state between adjacent domains is caused by shear tractions acting on the base of the elastic brittle layer and is mediated by a stress field within a zone between the provinces that can be determined by solving the equations of force equilibrium and stress compatibility the component of horizontal stress oriented perpendicular to the provincial boundary changes smoothly across the transition zone from one province to the other whereas the horizontal stress oriented parallel to the boundary shows smaller but discontinuous changes the horizontal component of shear stress is unlikely to change from one province to another because of the implausible nature of the required basal traction thus in this regard states of stress in adjacent domains appear to be coupled the coincidence of a number of stress transition zones with boundaries defined by heat flow suggests that in many cases the basal tractions are the result of thermally induced mass transport below the elastic brittle layer in the direction of increasing horizontal compressive stress this analysis provides a quantitative relationship between changes in the stress field measured in the upper portion of the crust and shear stresses acting on the base of the elastic brittle layer

on crustal seismicity of the amazonian foothill of the central peruvian andes a microearthquake survey of crustal seismicity conducted in 1985 on the eastern cordillera and the amazonian foothills in central peru gives a description of the present tectonic activity related to the uplift of the andes hypocenters on the huaytapallana fault are shallower than 10 km and their focal mechanism is in agreement with the fault trace corresponding to the earthquakes of 1969 and suggests a reverse strike slip movement on a plane striking n130 an active tectonic zone is evidenced along a nw se direction passing through the amauta subandean region the vertical distribution of hypocenters and the comparison of shallow and deep focal mechanisms suggest a reverse fault dipping to the west depths vary between 0 and 20 km and never exceed 32 km the huaytapallana cordillera is uplifted by thrust faults on both sides

kinematics of cretaceous subduction and exhumation in the western rhodope chalkidiki block in the chalkidiki peninsula of northern greece a thrust complex made of a basement vertiskos unit a cover circum rhodope belt and arc back arc units chortiatis magmatic suite and eastern vardar ophiolites is exposed in the chalkidiki peninsula of northern greece the complex forms the western part of the rhodope metamorphic province and lies on the hanging wall of the kerdylion detachment the structure responsible for the exhumation of the southern rhodope core complex and the most prominent and visible ductile structure related to the tertiary aegean extension the chalkidiki thrust complex arguably preserves a complete record of cretaceous deformation and related fabrics in this contribution we describe the geometry of foliation stretching lineation and shear sense s on a regional scale the regional foliation strikes nw se and displays different patterns in the three studied units i dominantly dipping at low angle in the vertiskos unit ii affected by upright folding in the circum rhodope belt and iii systematically steeply dipping to the ne in the chortiatis magmatic suite stretching lineation trend dominantly sw ne in the three mentioned units on the basis of new mapping neglecting local perturbations and deformation related to tertiary extension we infer the regional kinematics of cretaceous syn metamorphic thrusting and subsequent exhumation of the metamorphic units thrusting took place toward the sw in present day coordination and the related fabrics are recorded throughout the metamorphic pile on the contrary exhumation related fabrics are related to shear toward the ne and are preferentially recorded in the uppermost part of the metamorphic pile suggesting that extension was more localised and of less finite intensity compared to thrusting

extensional compressional tectonics associated with the aegean arc comparison with the andean cordillera of south peru north bolivia extensional compressional tectonics are analysed along the convergent boundaries of the aegean arc and of the andean cordillera of south peru and north bolivia this paper deals only with deformations of miocene pliocene and pleistocene ages the prevailing regime in the aegean basin is extensional yet two compressional tectonic phases of u miocene l pliocene and of l pleistocene age have been recorded they are also known in many places all around the mediterranean thus forces that induce compressional tectonics in the aegean seem to have their origin outside the region they seem to be linked with changes in the conditions of convergence change in rate between the arabo african and eurasian plates beneath the andean cordillera of south peru north bolivia the subduction zone plunges at an angle of 25 30 as it does under the aegean arc there as in the aegean sea tectonics are predominantly extensional and several short lived compressional phases break up this extensional regime the latter may also be induced by changes of the conditions of convergence here between the nazca and south american plates beneath central peru north of the nazca ridge the subduction zone plunges at a small angle about 10 there neotectonic deformations are different in the recent they are essentially compressional or expressed by strike slip faulting geological data from the aegean and andes seem to demonstrate that the compressional deformation in the crust above subduction zones is strongly controlled by the stress conditions along convergent boundaries

moho topography beneath the corinth rift area greece from inversion of gravity data summary our aim is to understand better the rifting process by imaging the moho depth variation beneath corinth and evvia we present here the results of a gravity inversion analysis in the region of the corinth and evvia rift system and compare them to those obtained independently from teleseismic tomography and receiver function analyses the results of these different studies appear to be consistent and show 1 a 10 km crustal thickening in the western part of the area beneath the hellenides mountains 2 nw se trending periodic crustal thinning and 3 a maximum crustal thinning north of the gulf of corinth this 4 km thinning is unlikely to be the result of the rifting alone which seems to have been reactivated since only 1 ma we propose here a geodynamical scenario in two major steps to explain the evolution of corinth area aegean miocene extension involving boudinage resulted in periodic crustal thinning consistent with observations these lithospheric instabilities could have favoured rupture initiation in particular areas especially near the city of corinth then the reactivation of the corinth rift extension 1 myr ago led to westward rift propagation the offset observed between the maximum crustal thinning and the gulf of corinth could be accommodated by a lowangle normal fault at about 10 15 km depth the corinth rift is thus asymmetrical and was initiated in places of crustal weakness due to miocene lithospheric instabilities

the hellenic subduction zone a tomographic image and its geodynamic implications new tomographic images of the hellenic subduction zone demonstrate slab penetration in the aegean upper mantle to depths of at least 600 km beneath greece the lower part of the slab appears to be detached at a depth of about 200 km whereas it still seems to be unruptured beneath the southern aegean schematically we derive minimum time estimates for the duration of the hellenic subduction zone that range from 26 to 40 ma this is considerably longer than earlier estimates which vary between 5 and about 13 ma

geophysical monitoring of moisture induced landslides a review author s whiteley js chambers je uhlemann s wilkinson pb kendall jm abstract 2018 the authors geophysical monitoring of landslides can provide insights into spatial and temporal variations of subsurface properties associated with slope failure recent improvements in equipment data analysis and field operations have led to a significant increase in the use of such techniques in monitoring geophysical methods complement intrusive approaches which sample only a very small proportion of the subsurface and walk over or remotely sensed data which principally provide information only at the ground surface in particular recent studies show that advances in geophysical instrumentation data processing modeling and interpretation in the context of landslide monitoring are significantly improving the characterization of hillslope hydrology and soil and rock hydrology and strength and their dynamics over time this review appraises the state of the art of geophysical monitoring as applied to moisture induced landslides here we focus on technical and practical uses of time lapse methods in geophysics applied to monitoring moisture induced landslide the case studies identified in this review show that several geophysical techniques are currently used in the monitoring of subsurface landslide processes these geophysical contributions to monitoring and predicting the evolution of landslide processes are currently underrealized hence the further integration of multiple parametric and geotechnically coupled geophysical monitoring systems has considerable potential the complementary nature of certain methods to map the distribution of subsurface moisture and elastic moduli will greatly increase the predictive and monitoring capacity of early warning systems in moisture induced landslide settings

the tectonic development of the hellenic arc and the sea of crete a synthesis abstract we use field analyses together with interpretation of aerial photographs orbital imagery and sea beam data to define more accurately the geometry of fault systems in the hellenic arc the tectonics of the area are dominated by extensional processes related to normal faulting we then use sea beam data previous oceanographic studies and extrapolation of field analyses on surrounding islands to describe the fault pattern of the cretan sea basin which is found consistent with the land fault pattern the mechanisms of the late neogene and quaternary deformation of the central and southern aegean region are analysed in terms of stress trajectories as revealed by field studies of fault populations we then examine the subsidence of the sea of crete in terms of a model of uniform stretching of the lithosphere the opening of the sea of crete was cylindrical and did not result in bending of crete this leads us to modify the southern portion of an earlier kinematic reconstruction of aegea in agreement with recent paleomagnetic results the implications of the opening of the sea of crete on the tectonic evolution of the straits to the west and east of crete are discussed finally the uplift of the outer arc is explained by underplating due to subduction

determination of the pore fluid pressure ratio at seismogenic megathrusts in subduction zones implications for strength of asperities and andean type mountain building 1 we construct the differential stress profile across the fore arc in a subduction zone from the force balance between the shear stress at seismogenic megathrust and the lithostatic pressure we assume that is written by 1 n where is the pore fluid pressure ratio is the coefficient of static friction and n is the normal stress given a density structure of the fore arc wedge we determine by comparing calculated fore arc stresses with observed ones as 0 95 0 98 in shikoku miyagi peru north chile and south chile and 0 90 0 93 in south vancouver island and washington the parameter averaged over the seismogenic megathrust is of the order of 10 mpa stress drops of great earthquakes in these zones occupy 14 87 and not a constant fraction of they on the other hand increase linearly with 1 we propose a simple fault model in which the area of asperities as a fraction of the total fault area is proportional to 1 variation of fractional area of asperities thus may explain the observed correlation and the regional variation of assuming that the differential stress at summit of the andean mountains is zero not at the coast as observed at present we determine to be 0 84 in north chile in the mountain building stage such a smaller value of along with 0 9 in subduction zones would suggest that variation of controls the tectonic style of the earth

parallel thrust and normal faulting in peru and constraints on the state of stress abstract we present evidence for recent normal faulting in the cordillera blanca of peru along planes trending approximately n40 w parallel to the chain this type of faulting suggests that there is an important component of extension perpendicular to the chain and contrasts markedly with the underthrusting of the nazca plate on the west side of peru and with the folding and thrusting observed in the sub andes on the eastern flank of the chain these contrasting styles of deformation and associated stress fields can be explained by buoyancy forces due to the high mountains and crustal roots in so far as this explanation is correct the difference in elevation between zones of normal and thrust faulting can be used to place an upper bound of 500 bars on the average stress difference in the crust

neogene quaternary evolution of the offshore sector of the southern apennines accretionary wedge gulf of taranto italy abstract southern apennines represent a collisional orogenic belt whose compressional regime is commonly assumed to have ceased during middle quaternary on the other hand to the south the calabria arc is still characterized by subduction and the principal aim of the present research is to shed some light on the space and time transition from the ceased collision to the active subduction accordingly we investigated the offshore sector of the southern apennines accretionary wedge corresponding to the taranto gulf to gain insights into the offshore accretionary wedge we reconstructed a 3d geological and tectonic model by interpreting a grid of 40 seismic reflection lines 1100 km 80 intersections within an area of ca 104 km2 calibrated with 17 wells the geometric and chronological constraints allow documenting a systematic messinian quaternary thrust migration from internal towards external sectors of the wedge the migrating deformational process was essentially associated with a leading imbricate thrust system with a general ne younging direction where we could recognize and distinguish some major advancing phases characterized by alternating fast thrust propagation events and strain accumulation periods within the wedge this process is well emphasized by the jump of the foredeep and piggy back basins the ne wards wedge migration was also associated with a lithospheric scale flexural folding that generated a set of normal faults striking parallel to the coeval thrusts likely reactivating optimally oriented structures inherited from mesozoic events finally a persisting thrust activity up to the latest quaternary and possibly up to present in correspondence of the externalmost sector of the accretionary wedge has been documented and explained in terms of strain partitioning in the frame of a recent oblique convergence the results of this research have possible implications for the seismic hazard assessment of the broader region which is possibly greater than previously assumed

thessaloniki gerakarou fault zone tgfz the western extension of the 1978 thessaloniki earthquake fault northern greece and seismic hazard assessment abstract active faulting and seismic properties are re investigated in the eastern precinct of the city of thessaloniki northern greece which was seriously affected by two large earthquakes during the 20th century and severe damage was done by the 1759 event it is suggested that the earthquake fault associated with the occurrence of the latest destructive 1978 thessaloniki earthquake continues westwards to the 20 km long thessaloniki gerakarou fault zone tgfz which extends from the gerakarou village to the city of thessaloniki this fault zone exhibits a constant dip to the n and is characterised by a complicated geometry comprised of inherited 100 trending faults that form multi level branching tree like fault geometry along with nne to ne trending faults the tgfz is compatible with the contemporary regional n s extensional stress field that tends to modify the pre existing nw se tectonic fabric prevailing in the mountainous region of thessaloniki both the 1978 earthquake fault and tgfz belong to a ca 65 km long e w trending rupture fault system that runs through the southern part of the mygdonia graben from the strymonikos gulf to thessaloniki this fault system here called thessaloniki rentina fault system trfs consists of two 17 20 km long left stepping 100 trending main fault strands that form underlapping steps bridged by 8 10 km long ene wsw faults the occurrence of large m 6 0 historical earthquakes in 620 677 and 700 a d demonstrates repeated activation and therefore the possible reactivation of the westernmost segment the tgfz could be a major threat to the city of thessaloniki changes in the coulomb failure function cff due to the occurrence of the 1978 earthquake calculated out in this paper indicate that the tgfz has been brought closer to failure a convincing argument for future seismic hazard along the tgfz

the koras sinclair ghanzi rift in southern africa volcanism sedimentation age relationships and geophysical signature of a late middle proterozoic rift system abstract a number of relatively undeformed late middle proterozoic volcano sedimentary basins are aligned along the western and northern margins of the kalahari craton although the assemblages of these basins have been compared and lithologically correlated by many authors radiometric ages partly contradict these interpretations attempts to incorporate all of these basins into a regional structural interpretation have been rare watters magmatic arc interpretation is contradicted by the overall geochemistry of the volcanic rocks the coarse continental red bed sediments and the structural style of the basins the depositional troughs were narrow fault bounded continental rift grabens with a structural style and sedimentation pattern controlled by strong vertical tectonism the development of the basins along two branches of a propagating continental rift system the koras sinclair ghanzi rift ksg rift is proposed radiometric ages reveal a distinct younging along the rift from the southern toward the northeastern branch the geophysical signature of the rift is dominated by positive bouguer gravity anomalies flanked by gravity lows which follow a linear trend the basins contain distinctly bimodal volcanic rocks with some intermediate volcanics in the sinclair basin contemporaneous with the extrusion of the volcanics granitic high level intrusions were emplaced along the rift the possible existence of a northern coastal branch of the ksg rift and the location of a triple junction is discussed the rift process possibly continued and led to the development of the early damara rift in swa namibia the african plate kalahari and congo cratons migrated southward between 1050 and 950 ma ago a stationary mantle plume probably caused the development of both the ksg and damara rift a comparison with rift migration in kenya is drawn the regional trends and structures of the ksg rift were reactivated several times undergoing both extension and compression the most prominent of these events was the development of the damara orogen which followed the regional trend of the late middle proterozoic rift but fault structures have been reactivated up to recent times

the geometrical evolution of normal fault systems abstract the purpose of this paper is to examine the kinematic behaviour of normal fault systems and see what general conditions govern their geometrical evolution we pay particular attention to seismological and surface data from regions of present day active normal faulting as the instantaneous three dimensional geometry at the time of fault movement is better known in active regions than in areas where the faults are now static most normal faults are concave upward or listric this shape can be produced by geometric constraints either because the faults reactivate curved thrusts or because they must be curved to accommodate rotations another effect which will produce curved faults is the variation of rheology with depth brittle failure at shallow depths produces less fault rotation than does distributed creep in the lower part of the crust an important geometric feature of normal faulting is the uplift of the footwall the amount of such uplift is related not only to the elastic properties of the lithosphere but also to the throw and dip of the fault a striking feature of active normal faults is that they occur in groups in which all the faults dip in the same direction this behaviour arises because the faults cannot intersect if they do one must cease to be active the rotation which such fault systems produce reduces the dip of the faults until a new steeply dipping fault is formed once a new fault cuts pre existing faults the earlier faults become locked and a new set of faults must propagate rapidly across the whole region involved many of these geometric constraints also apply to thrust faulting

aegean paleomagnetic inclination anomalies is there a tectonic explanation abstract more than a decade of paleomagnetic research in the aegean area mainly by french investigators c laj c kissel and their colleagues has provided a valuable data base for the evaluation of cenozoic aegean tectonics systematic rotations are documented and have been interpreted by the original investigators in the light of the evolution of the hellenic arc however less attention has been paid to the significance of the paleomagnetic inclinations which also are anomalous twenty one out of 22 paleomagnetic studies performed to date within the general aegean region have yielded paleolatitudes that are too shallow when compared with reference curves for either africa or eurasia suggesting northward relative transport with respect to both continents sedimentary volcanic and plutonic units are involved ages range from oligocene to pliocene some of these apparent paleolatitude anomalies may merely be the result of inclination flattening in certain kinds of clastic sedimentary rocks however shallow inclinations in igneous rocks cannot be so easily dismissed the explanation for these anomalously shallow inclinations does not appear to lie with the reference curves because several other reference curves calculated in several different ways yield essentially the same result we suggest that the paleomagnetic pattern may reflect real northward displacement of crustal blocks within the aegean region measured with respect to both europe and africa the amount of displacement appears to increase systematically to the west the pattern of local block rotations noticed by earlier investigators argues that the displacement did not involve a single coherent aegean block but rather a collection of smaller blocks moving quasi independently geological consequences of northward relative displacement of the aegean block ought to include mid tertiary and or later compressional structures in the north e g rhodope and extensional structures in the leading edge of the african plate

normal faulting along the southern margin of the puna plateau northwest argentina 1 though orogen parallel shortening and vertical extension have dominated the tectonic evolution of the central andes a significant kinematic shift from horizontal contraction to extension appears to have occurred within the high puna altiplano plateau with the establishment of extension oblique to the orogen since late miocene time we present data from the southern margin of the puna plateau nw argentina where new normal faults have been documented in the fiambala punta negra and la quebrada areas the unifying characteristics of these areas are that young normal faults reactivate or crosscut older thrust and reverse faults the relationship between the faults and the late miocene pliocene punaschotter conglomerate suggests that the extensional faulting must be younger than 3 5 to 7 ma existing data are incomplete but indicate that similar horizontal extension has occurred in many regions throughout the puna altiplano plateau while shortening continues along the plateau margins given the spatial and temporal distribution of this late miocene to pliocene kinematic shift both lithospheric loss in the puna plateau and plateau wide gravitational extensional spreading enhanced by slowing of plate convergence rate could be responsible the young disorganized horizontal extension in the andes today may be the precursor to more pronounced extension such as observed on the tibetan plateau since mid miocene time

the bursa gonen depression nw turkey a complex basin developed on the north anatolian fault in this study we show that the southern branch of the north anatolian fault has been active since late pliocene time and that evidence of activity is supported by geological and seismological data the southern branch of the north anatolian fault consists of four segments from west to east yenice gonen manyas mustafakemalpasa uluabat and bursa these faults delimit the bursa gonen depression with the bandirma mudanya uplift to the north and uludag sularya uplift to the south the bursa gonen depression includes upper pliocene to recent sediments that thicken to the south suggesting a deposition pattern under active fault control study of fault kinematics suggests that the bursa gonen depression started as a small pull apart basin during late pliocene time and then evolved to a large depression the faults delimiting this depression are still active and capable of producing future earthquakes

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

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

empirical relationships among the convergence rate of plates rollback rate of trench axis and island arc tectonics laws of convergence rate of plates abstract the data on 27 recent arcs which were subducted by normal oceanic lithosphere were compiled among the compression extension rates for island arcs v a compression is defined as positive and the kinematic components of absolute plate motions parallel to the direction of backarc compression extension v on oceanward velocity of the overriding plate v sn continentward velocity of the subducting plate and v tn rollback rate of the trench axis the equations v a v on v sn 7 2 cm y 1 v tn 7 2 cm y v sn 2 are found to hold as for the convergent zones associated with a wadati benioff zone deeper than 200 km equation 1 suggests that backarc spreading and crustal shortening play the role of compensating the deviation of the convergence rate from the critical value of 7 2 cm y the equation 2 means that any subducting oceanic lithosphere has the potentiality of making the trench axis rollback at the rate of 7 2 cm y and that the virtual rollback rate v tn is determined by the balance between the potential rollback rate 7 2 cm y and v sn the present author calls the kinematic relationships represented by equations 1 and 2 laws of convergence rate of plates the convergent zones of plates associated with the wadati benioff zone shallower than 200 km also show a tendency that the greater and smaller values of v on v sn correspond to the backarc compression and extension however the critical value is 3 4 cm y instead of 7 2 cm y

the winter 1991 1992 earthquake sequence at cephalonia island western greece properties of the earthquake sequence of the 23 january 1992 5 8 ms earthquake in cephalonia island western greece are investigated the parameter b in the frequency magnitude relation is found equal to 1 084 while the decay parameter p of the time distribution of the aftershock sequence is found equal to 0 991 the principal parameters method is applied to the aftershock sequence and the average strikes of n156 e 20 and n61 e 10 were obtained denoting also very small dips the major strike which resulted from the aftershock epicentre distribution was nw se similar to miocene neogene basins on cephalonia island

changes in the tectonic regime above a subduction zone of andean type the andes of peru and bolivia during the pliocene pleistocene this paper adresses the changes in the tectonic regime in the peruvian and bolivian andes that have occurred since the upper miocene when the present day elevation of the cordillera above sea level has been almost reached the stress patterns are deduced essentially from a field study of fault kinematics and a numerical inversion of the slip vector data measured on the fault planes the cuzco fault system in southern peru is chosen as an example to illustrate the methodology used in this region striations on both active and holocene faults are in agreement with a n s extension but faults affecting early pleistocene deposits exhibit two families of striations the younger results from the previous n s extension the older involving reverse motions results from either an e w or a n s compression faults affecting pliocene formations often show an oldest family of striations resulting from a ne sw or an e w trending extension thus three tectonic regimes are demonstrated which are also supported by regional unconformities and sedimentological data 1 a pliocene extensional regime 2 a lower pleistocene compressional regime and 3 a mid pleistocene present day extensional regime similar analyses conducted in the pacific and sub andean lowlands allow sketching of the successive pliocene pleistocene stress patterns in the central andes the quaternary and present day stress pattern is characterized by a n s extension in the high andes and in the pacific lowlands and by an e w compression in the sub andean lowlands and at the contact between the nazca and south american plates this stress pattern is interpreted at a large wavelength 100 km as an effect of compensated topography this model supposes that the vertical lithospheric stress zz increases with the topography the crustal thickness and the low density mantle beneath and that the lithospheric maximum compressional horizontal stress hmax trending e w roughly parallel to the convergence is fairly constant on both edges of the andes the tectonics being compressional zz is 3 and hmax is 1 in the high andes zz becomes 1 then the e w trending hmax is 2 and hmin trending n s is 3 allowing extension to occur in this direction the pliocene stress pattern was characterized by a ne sw or an e w trending extension in the high andes in the pacific lowlands and possibly in the sub andean lowlands this stress pattern was clearly different from the present day one because the e w trending stress was hmin this required a weak push or eventually tractional boundary forces acting on the south american lithosphere it is suggested that this might result from a strong slab pull due to a long steeply dipping slab which decreased the value of the xx stress transmitted to the overriding plate the early pleistocene state of stress was compressional since the elevation of the andes had not markedly decreased during this period this required an increase of the e w trending stress value this resulted from a strong coupling between the two lithospheric plates possibly due to a rupture of a long slab under its own weight other spatial changes in the stress pattern are related to the particular situation of the forearc to the subduction of the buoyant nazca ridge and to the different dips of the slab extension in the high andes is of small magnitude of the order of 1 during the last 1 2 m y in a few basins it may have attained 40 during the pliocene 5 3 m y

north aegean core complexes the gravity spreading of a thrust wedge the north aegean core complexes developed in middle eocene soon after the end of continental block convergence and piling up of the hellenic thrust wedge they formed during back arc extension driven by the hellenic slab rollback at the back of the thrust wedge a series of scaled laboratory experiments was performed to test whether the gravity spreading of a thrust wedge is a suitable process for the development of the north aegean core complexes during back arc extension wedge shaped sand silicon models with variable boundary displacement velocities and different geometries of the upper sand layer were used to study the effects of variations in wedge rheology on the pattern of extension the models exemplify that extension either distributed wide rift mode or localized core complex mode is always located at the wedge rear core complex development was favored in models with thicker brittle layer higher frictional strength and low stretching rate lower ductile strength both core complex location at the wedge rear and detachment location and dip are interdependent and intrinsically related to the initial wedge shape of the extending system the experimental model displays striking similarities with the extensional pattern of the north aegean in terms of i location size and shape of core complexes as well as their sequence of development and ii detachment location and dip we conclude that it is the initial wedge geometry of the system and the weak nature of the crust at the onset of extension that controlled the extensional pattern of the north aegean domain

late miocene early pliocene onset of n s extension along the southern margin of the central andean puna plateau evidence from magmatic geochronological and structural observations abstract extensional faulting typifies many of the earth s cenozoic orogenic plateaus the altiplano puna plateau in the southern central andes is the world s second largest orogenic plateau it contains a rich array of extensional fractures and normal faults with closely associated mafic volcanic flows dykes and cones this is in stark contrast to the foreland areas which record protracted shortening and continuous eastward growth of the mountain belt within the puna area a kinematic change over from shortening to extension has previously been inferred to have occurred during the quaternary however our research in the southern puna together with earlier petrologic investigations in the south central part of the plateau indicates an earlier onset for the extensional tectonism our analysis has focused on the eastern portion of the cordillera de san buenaventura in the southernmost part of the plateau where we mapped two upper miocene pliocene volcanic units associated with extensional faulting the aguada alumbrera ignimbrite and the la hoyada volcanic complex the structural inventory of these units records n s extensional deformation in the puna associated with the development of e w oriented fractures dykes normal and strike slip faults and folds new 40ar 39ar dating of magmatic rocks together with their relationships with the mapped structures reveal that widespread extension in the southern puna had already commenced by 5 ma and possibly as early as 7 ma although the extensional structures on the puna are typically associated with mafic volcanism the upper miocene pliocene la hoyada volcanic complex hosts dykes of intermediate compositions mafic to intermediate magmatism and extensional tectonism in this region is thus contemporaneous with and structurally akin to that in the central and northern parts of the plateau the ubiquitous cogenetic relationship between mafic volcanism and extensional tectonism both within the puna plateau and along its eastern flanks clearly indicates that the normal faulting is a regional phenomenon that is broadly coeval with an inferred rapid and large scale uplift of the altiplano puna plateau and a decrease in plate convergence rates these observations are compatible with a mantle delamination scenario in which the delamination of lithospheric mantle may have produced an ensuing weakening of the crust and regional uplift which may in turn have generated the conditions necessary to trigger gravitational extensional collapse beginning in the late miocene to early pliocene

late cenozoic stress field in the cameli basin sw turkey a history of deformation has been determined for the cameli basin located in the western part of the major fethiye burdur fault zone interpreted as the on land continuation of pliny strabo fault system e g eastern boundary of the hellenic arc inversion of fault slip vectors affecting mio pliocene to quaternary formations in the cameli basin in the southwestern segment of the transtensional fethiye burdur fault zone yields two different normal faulting stress regimes characterized by a roughly orthogonal set of extensional axes a nw se n129 19 e 3 axis and a ne sw n50 16 e 3 axis the orientation of fault sets is predominantly around the ne sw direction in the major fethiye burdur fault zone making the extension nw se the mean r values are 0 74 and 0 69 for both extensions indicating a triaxial stress state which is clearly different from radial extension and from transitional to strike slip stress state the nw se extension is probably responsible for the formation of the cameli basin during mio pliocene time in contrast the inversion of focal mechanism solutions of shallow earthquakes occurring within the cameli basin identifies a present day predominantly extensional stress regime characterized by an approximately n s n184 e 3 axis which has an r value of 0 637 indicating a triaxial stress state the nearly orthogonal extensional stress regimes seem to have been acting contemporaneously with each other at different intensities from the mio pliocene onwards in sw turkey this may be attributed to the geodynamic effects related to the subduction of the african plate beneath anatolia diffusing along hellenic and cyprus arcs and in the west southwestward extrusion of anatolia our hypothesis is that the cause of the early nw se extension is the slab pull force due to the subduction process along the cyprus arc considered to be dominant up to plio quaternary the later ne sw to present day n s extension dominant since the plio quaternary is related to the combined forces of the anatolian extrusion and the subduction process along the hellenic arc

counterclockwise rotation of the anatolian block abstract seismological and other data from the boundaries of anatolia are used to discuss the motion and plate tectonics of this block models which include a rotation of anatolia around a single pole are shown to be inconsistent with much of this data in particular a westward motion of anatolia which is the most commonly used model should be reconsidered models which use a single pole of rotation fail because they assume the north anatolian fault to be an ideal transform fault which describes all of the motion between anatolia and the black sea in effect internal deformation in the form of extension in western anatolia and for the most part strike slip faulting in eastern anatolia are important and account for some of the relative motion thus a more appropriate model for this region is one which not only stresses the dominance of the north anatolian fault but also recognises the importance of internal deformation and the limitation of classic plate tectonic models which this deformation implies the preferred model for the motion of anatolia is a nonuniform tight counterclockwise rotation approximated by the shape of the north anatolian fault as well as by the faults which splay from it to the south such a model is consistent with data from the boundaries of anatolia including the source mechanism of earthquakes and depth of benioff zone along the southern boundary of the block counterclockwise rotation of anatolia is the natural consequence of the collision of arabia with eastern anatolia coupled with subduction in the eastern mediterranean

microearthquake seismicity and fault plane solutions in the southern aegean and its geodynamic implications summary seismicity mi 3 5 in the southern aegean located using data collected during seven weeks of recording by a temporary network of seismological stations largely follows the hellenic arc the sea of crete is nearly aseismic and only little activity is located south of the hellenic trench within the african plate focal mechanisms exhibit reverse faulting in the external part of the arc and normal faulting inside it this normal faulting indicates n s extension in the northern aegean the gulf of corinth the cyclades and dodecanese islands but nw se extension in southern peloponnese and western crete and e w extension in eastern crete this non uniform strain pattern suggests that the aegean region not only extends in a n s sense with the hellenic arc moving south westward relative to the eurasian plate but also by e w extension of its southern margin so that there is a net divergence of material

plio quaternary geodynamic evolution of a segment of the peruvian andean cordillera located above the change in the subduction geometry the cuzco region abstract the cuzco region which is located above a change in subduction geometry appears to be characterized by a variable plio quaternary tectono sedimentary evolution essentially located along the major fault system that separates the high plateaux from the eastern cordillera after the higher surface formation of the high plateaux a set of neogene basins were filled by miocene fluvio torrential series and by plio pleistocene fluvio lacustrine deposits the neogene series have been affected by compressional tectonic forces attributed to the late miocene this compression is followed by roughly e w trending syn sedimentary extensional tectonics attributed to the pliocene it is related to reactivation of the pre existing major faults basin evolution and volcanic activity concentrated along the faults in the early pleistocene fluvio lacustrine deposits are affected by syn and post sedimentary compressional tectonism it is characterized by shortening that trends both n s and e w and produces folding and faulting of the sedimentary cover extensional tectonism trending roughly n s has been taking place from the middle pleistocene to the present it is coeval with shoshonitic volcanic activity and with sedimentation of fluvio lacustrine terraces torrential fans and moraines quaternary and active normal faults due to this tectonism are located in a narrow zone more than 100 km long between the high plateaux and the eastern cordillera and two 15 km long fault sectors in the eastern cordillera characteristic pleistocene scarps 400 m or more high are due to the cumulative normal offset and there are also little scarps with heights ranging between 2 and 20 m which are related to holocene fault reactivations recent fault reactivation on the cuzco fault system during the april 5 1986 earthquake m b 5 3 is due to the n s trending extension this state of stress located at a mean elevation of roughly 3730 m is generally homogeneous to different scales the active cuzco normal faults may be a consequence of adjustment between the compensated western cordillera and the undercompensated eastern cordillera this latter being uplifted higher than its isostatic equilibrium due to compression acting on its eastern edge the variation of the state of stress during the plio quaternary is in agreement with the variations of the compressional boundary forces it may be explained by variation of the convergence rate or by the variation of pull slab forces

late cainozoic geodynamic evolution of thessaly and surroundings central northern greece abstract in the framework of the late alpide deformation of greece and of the recent and active extensional tectonism of the aegean region the geotectonic evolution of the thessaly region central northern greece has been examined using a quantitative and qualitative structural analysis stratigraphie sedimentological morphotectonic and seismological data the geometry of the faults their architecture and the knowledge of the stress pattern are used to explain some aspects of the tectonics and crustal dynamics of thessaly and the surrounding area the oldest compressional phases taken into account show a mean ene wsw trending direction of shortening and have been defined as late alpide early aquitanian and langhian a later late miocene pliocene ne sw oriented extensional phase has been related to the hellenic post orogenic collapse which developed behind the collisional front between the aegean eurasia and african plates this phenomenon diachronically migrated from the east central macedonia thermaikos basin towards the west epirus albania where it is still active as a consequence of this second phase the area forms a basin and range like structure the third and last phase middle pleistocene present is characterized by a n s direction of extension and affects the entire aegean region it generated new e w trending basins superimposed on the inherited ones this gave as a final result the complex block pattern we can see today the recent and active right lateral strike slip movements along the north aegean trough seem to stop in the sporades basin and do not affect the uppermost crust of mainland greece a further wnw ese directed extension observed occasionally in central and northern greece could be explained by local events or as block related deformation

variation in noble gas isotopic composition of gas samples from the aegean arc greece abstract in contrast to most other arcs with oceanic plate subduction the aegean arc is characterized by continent continent subduction noble gas abundances and isotopic compositions of 45 gas samples have been determined from 6 volcanoes along the arc 2 islands in the back arc region and 7 sites in the surrounding areas the 3he 4he ratios of the samples ranged from 0 027ra to 6 2ra ra denotes the atmospheric 3he 4he ratio of 1 4 10 6 demonstrating that even the maximum 3he 4he ratio in the region is significantly lower than the maximum ratios of most oceanic subduction systems which are equal to the morb value of 8 1 ra regional variations in the 3he 4he ratio were observed both along and across the arc the maximum 3he 4he ratio was obtained from nisyros volcano located in the eastern end of the arc and the ratio decreased westward possibly reflecting the difference in potential degree of crustal assimilation or the present magmatic activity in each volcano across the volcanic arc the 3he 4he ratio decreased with an increasing distance from the arc front reaching a low ratio of 0 063ra in macedonia which suggested a major contribution of radiogenic helium derived from the continental crust at nisyros a temporal increase in 3he 4he ratio due to ascending subsurface magma was observed after the seismic crisis of 1995 1998 and mantle neon was possibly detected the maximum 3he 4he ratio 6 2ra in the aegean region which is significantly lower than the morb value is not probably due to crustal assimilation at shallow depth or addition of slab derived helium to morb like mantle wedge but inherent characteristics of the subcontinental lithospheric mantle sclm beneath the aegean arc

extension of thickened and hot lithospheres inferences from laboratory modeling 1 the extension of a previously thickened lithosphere is studied through a series of analogue experiments the models deformed in free and boundary controlled gravity spreading conditions that simulate the development of wide rift type and core complex type structures in models the development of structures mainly depends on boundary velocity and therefore on bulk strain rate wide rifts are of tilted block type at high strain rate and of horst and graben type at low strain rate the development of metamorphic core complex type structures is enhanced by low strain rates and by the presence of weak heterogeneities within the ductile crust core complexes result from a necking instability of the upper crust creating a graben which further widens allowing the rise and exhumation of a ductile layer dome an upward convex detachment flat on top of the dome and steeper on dome limb appears not to be the primary cause of the core complex development but its consequence

the regional intraplate stress field in south america a compilation of lithospheric stress directions for continental south america and the inferred major patterns of the regional intraplate stress field are presented stress orientations are based primarily on earthquake focal mechanisms and quaternary fault slip inversion published in the literature four new focal mechanisms based on short period p wave modeling and selected centroid moment tensor solutions published by u s geological survey consistent with p wave first motions at south american and other world wide standard seismograph network stations are also included in the data base the observed patterns of intraplate stresses may be useful in constraining numerical models of the plate driving forces in the south american plate in the andean plateau altitudes greater than 3000 m n s extensional stresses predominate e w compressional stresses are observed in the sub andean and platform regions extending up to about 1000 km east of the andes the maximum horizontal stress shmax is uniformly oriented in the e w direction throughout western south america averages of the shmax direction at grid points spaced 2 5 o were taken as representing the regional field the e w direction of this regional field is not affected by the change of strike of the andean chain nor by the contact of a flat subducted slab underneath the regional shmax direction is oriented 15 o more clockwise than the direction of the nazca plate convergence the difference between the regional shmax orientations and the absolute plate motion may be only about 6 o this may indicate that contact forces with the nazca plate may not be the only major contributor to the intraplate stresses in western south america the eastern limit of this andean stress province seems to coincide with aseismic regions in the upper amazon basin and in the paraml basin in the central amazonian region seismicity and stress data suggest a seismic province with n s compressional stresses the origin of these stresses is not yet clearly understood but could possibly be related to lower crustal loading along the middle amazon basin in northeastern brazil seismicity is characterized by upper crustal strike slip earthquakes bordering the potiguar marginal basin a model is proposed for this region in which the stress field is the result of a superposition of regional e w compressional stresses and local extensional stresses oriented perpendicular to the continental margin possibly related to density contrasts and sediment loading in the continental shelf

early pliocene sedimentation in the cretan region implications for the timing and amount of vertical motion along the south hellenic arc eastern mediterranean abstract a boxcore taken from the top of a seamount south of crete on the outer south side of the hellenic trench contains allochtonous coarse clastics consisting mainly of rock fragments of alpine basement brecciated early middle pliocene marls and reworked older neogene sediments this mixture of lithologies is interpreted as an early middle pliocene mass flow deposit which can be correlated with similar deposits from adjoining on and offshore areas the wide distribution of these sediments may be related to a period of increased tectonic activity which caused substantial vertical movements in the south hellenic arc it is concluded that at the time of the formation of the mass flow deposits this part of the hellenic trench had not yet evolved

models for relative motion of crustal blocks within the carpathian region based on restorations of the outer carpathian thrust sheets details of the oligocene present day motion of the adriatic block with respect to europe can be determined by palinspastic restorations of the outer carpathians thrust sheets the arcuate nature of the carpathians poses problems for simple restorations of sections because they create converging restoration paths which require large amounts of strike parallel extension 40 50 such large amounts of extension are not seen on maps or in the field a combination of thrust transport directions changing with time between and within thrust sheets and divergent transport directions helps minimise the arc parallel extension necessary 18 25 the pannonian basin can be treated either as an area dominated by strike slip motion rigid block movements or as an area of back arc extension the differences in restoration geometry produced by these two scenarios help to indicate which of the two mechanisms was dominant the consequences of the rigid block restoration indicate the model is inappropriate because it requires approximately 20 clockwise rotation of the adriatic block during the late tertiary it also indicates at least 300 km strike slip motion distributed among the late tertiary faults of the dinaride balkanide and hellenide mountain belts the back arc extension model alleviates the the 20 clockwise rotation of the adriatic block and requires about 200 km distributed strike slip motion in yugoslavia and bulgaria

neotectonic and seismological data concerning major active faults and the stress regimes of northern greece northern greece is an intracontinental region behind the hellenic subduction zone with widespread seismic activity ranging from low to high with strong destructive earthquakes of mg6 0 in historical to recent times geological and seismological data indicate that recent seismic activity is mainly localized along large inherited fault zones which have transected northern greece since oligocene miocene times the main active fault zones in thrace and eastern and central macedonia strike approximately east west with lengths of 40 120 km fault segments strike wnw ese to ene wsw and range from 10 to 30 km in length in western macedonia the main active fault zones strike ne sw to ene wsw with lengths of 40 60 km and consist of 10 30 km segments the region s strong earthquakes are usually associated with reactivation of these fault segments and are estimated at m 5 6 6 5 focal mechanisms and fault slip data from the fault zones indicate a change in the trend of extension axes from nne ssw in eastern macedonia thrace to nnw sse in western macedonia thus neotectonic and seismological data suggest that variations in fault patterns as determined from the large inherited fault zones transecting northern greece are the major factor governing this change in the trend of maximum extension this interpretation is consistent with the long lived arcuate shape of the hellenic subduction zone of these the best known are the 1978 thessaloniki earthquake of m 6 5 papazachos et al 1979 and the 1995 kozani grevena earthquake pavlides et al 1995 mountrakis et al 1996c 1998 papazachos et al 1998a with the latter occurring in the low seismicity western macedonia region the rupture zones in northern greece need a thorough re examination in the light of recent advances in our understanding of active faulting and the new data provided by the aristotle university seismological network our aim is to identify the large active fault zones in northern greece from their geometric kinematic and seismotectonic features to define controlling stresses and to elucidate the continuity or extent of these zones the main aim is to better understand the active deformation of these areas and to determine whether fault deformation in northern greece is concentrated into relatively narrow bands or zones as one of the major issues in continental mechanics is how fault slips in the upper crust reflect more distributed flow in the lower lithosphere e g mckenzie jackson 1983 molnar gipson 1994 bourne et al 1998 information about active faulting and driving stresses in such areas is very useful brittle deformation within intracontinental regions is usually associated with distributed faulting and seismic activity however within such broad deforming regions some parts although transected by large faults are characterized by relatively less intense seismic activity and slip rates northern greece lies in the inner part of the continental collision region of nw greece and albania close to the intensely north south aegean extended sea this deformation is driven by the hellenic subduction zone and the westward extrusion of anatolia fig 1a in the older greek seismic code some large areas of macedonia e g western macedonia are classified as almost aseismic and other adjacent ones e g central macedonia as highly seismic recent instrumental data obtained from the regional seismological network of the aristotle university of thessaloniki after its installation in 1980 have confirmed the existence of significant seismicity in northern greece fig 1b particularly along narrow rupture zones papazachos et al 2001 furthermore large earthquakes have been reported in historical times papazachos papazachou 2003 and several strong and destructive ones have been recorded instrumentally during the last century 650 d mountrakis et al fig 1 a schematic map showing the position of northern greece in the broader eastern mediterranean geotectonic regime modified from papazachos papazachou 2003 b spatial distribution of instrumentally recorded earthquakes 1911 2004 with magnitudes mg3 0 for the broader study area ctf cephalonia transform fault rtf rhodes transform fault ptf paphos transform fault geology and seismotectonics of northern

the state of stress in an overriding plate situated above a flat slab the andes of central peru in the andes of central peru that are situated above a flat dipping slab analysis of both structural data collected in the field and available focal mechanisms show that the quaternary and recent state of stress is characterized by n s trending extension in the western cordillera and along the pacific coast whereas e w trending compression prevails in the sub andean lowlands and at the contact between the nazca and south american plates the eastern cordillera deformations suggest an intermediate state of stress i e strike slip faulting characterized by e w trending compression and n s trending extension thus major fault zones striking nw se i e parallel to the central peruvian andes are normal with a sinistral component in the western cordillera e g cordillera bianca and reverse sinistral in the eastern cordillera e g cordillera de huaytapallana this state of stress displays similarities with that of southern peru and may be also interpreted as an effect of compensated high topography in this model the vertical stress zz increases with the topography and hmax is considered as fairly constant trending e w roughly parallel to the convergence on both edges of the andes tectonics being compressional zz is 3 and hmax is 1 in the high andes zz becomes 1 then hmax is 2 allowing hmin striking n s to be 3 along the pacific coast tectonics is not compressional as expected and a nearly neutral state of stress may be due to a topographical effect related to the nearby deep peru chile trench however a conspicuous difference occurs in the andes of central peru in respect to the southern peru andes compressional strike slip tectonics is observed in the eastern cordillera indeed the mean elevation of the eastern cordillera is 3 7 km whereas that of the western cordillera is 4 2 km allowing an intermediate state of stress to occur therefore in central peru a lower mean andean topography and a stronger coupling consequence of the flat subduction seems to explain that compressional tectonics is distributed in a more widespread area than in southern peru superficial deformations related to the subduction of the aseismic nazca ridge are restricted to the coastal domain opposite to this ridge they support the fact that submarine topography of large extension may subduct without producing compressional deformation in the overriding plate which can be reminiscent of a collisional setting