a microearthquake study of the mygdonian graben northern greece during march and april 1984 a temporary network of 29 portable stations was operated in the region of the mygdonian graben near thessaloniki northern greece where a destructive earthquake ms 6 5 had occurred in the summer of 1978 during a period of six weeks we recorded 540 earthquakes with magnitudes ranging from 0 2 to 3 0 from this set of data 254 events are selected which according to us have a precision in epicenter and depth better than 1 5 km a total of 54 single event focal mechanisms have been determined the seismicity and focal mechanisms show a rather complex pattern there are no clear individual faults but the e w and nw se striking zones show n s extension zones striking nne ssw show dextral strike slip motion but nw se zones with sinistral strike slip are also observed in the center of the graben where the 1978 earthquake was located we observe several thrust mechanisms distributed in two groups showing either nw se or e w compression these earthquakes seem to be located 2 km above the earthquakes showing normal mechanisms the mean direction of the t axes found from the focal mechanisms trends n15 and dips sub horizontal we propose a model for the formation and evolution of a complex graben system comprising several stages in the initial stage the deformation occurs along pre existing nw se or nne ssw faults with normal or strike slip movements in the second stage a new e w trending group of normal faults is formed over the ancient fault network these new faults have a direction perpendicular to the mean t axis and accommodate better the actual state of stress at this stage the initial faults adjust to the deformation produced by the e w trending new faults and may constitute geometric barriers to the evolution of the new normal faults

relations between surface deformation fault geometry seismicity and rupture characteristics during the el asnam algeria earthquake of 10 october 1980 abstract the el asnam earthquake of october 10 1980 ms 7 3 produced surface faulting on a northeast trending thrust fault of 30 km length with displacements of up to 6 5 m though average displacements were about 3 m in addition widespread tensional features were formed some in clear association with folding above the thrust and others in an area beyond the exposure of the thrust at the surface which may be related to buried reverse faults the observed thrust fault is split into southern central and northern segments local and teleseismic data are examined to show that the main shock nucleated at the southwest end of the fault and propagated 12 km northeast where a second rupture of approximately equal moment occurred continuing the faulting a further 12 km northeast along the central segment both ruptures nucleated at about 8 10 km depth displacements were largest on the central segment where they were probably enlarged by aftershocks including one of mb 6 1 three hours after the main shock the northern segment was much shorter than the other two and showed smaller displacement the junctions between fault segments are marked by distinct geomorphological characteristics and a change in strike of the faulting as well as a sudden drop in the observed displacement it appears that the rupture development is influenced by the changes in fault geometry between segments and that such junctions or barriers have persisted through much of the late quaternary

seismicity normal faulting and the geomorphological development of the gulf of corinth greece the corinth earthquakes of february and march 1981 three major destructive earthquakes of m s 6 7 6 4 6 4 occurred in the eastern part of the gulf of corinth in february and march 1981 associated normal faulting was observed on both the north and the south sides of the gulf examination of teleseismic local seismic surface faulting and geomorpbological data suggests that the first and second of these shocks activated major north dipping normal faults these faults control the topography and bathymetry and are related to the recent uplift and subsidence of the coastline it is probable that the first earthquake occurred on a faultwhich outcrops underwater and the second on a fault which is visible on land it appears that the third shock activated an antithetic normal fault dipping southwards on the north side of the gulf and that the overall structure of the gulf of corinth graben is asymmetric the northern antithetic fault clearly demonstrates the geomorphological changes associated with developing young normal faulting in addition we suggest that observations of recent coastline movement provide a powerful tool for identifying major active fault systems and predicting their historical role in the paleogeography of an area

analyses of fault mechanisms and expansion of southwestern anatolia since the late miocene abstract neotectonic field studies and detailed analyses of neogene and quaternary fault mechanisms in southwestern anatolia enable us to recognize a succession of compressional and extensional events and to characterize the direction of corresponding regional stresses the three most important compressive phases occurred during the miocene and a much smaller one near the plio quaternary boundary the last one or two interrupted a widespread extension of much greater duration and amplitude the whole tectonic evolution resembles that of the aegean the large extension by normal faulting is consistent with a minimum stress along a nne ssw average direction it appears that this direction was n s during the pliocene and changed to ne sw sometime during the quaternary this dominant nne ssw extension which began during late miocene or earliest pliocene was related to the development of the southwestern anatolian graben system

late cenozoic extension in sw bulgaria a synthesis abstract southwest bulgaria forms the northern margin of the aegean extensional province since the early pliocene c 4 ma this region has accommodated southward or sse extension at several millimetres per year superimposed on c 400 m of post early pliocene regional uplift this sense of deformation superseded earlier extension oriented ene wsw which is estimated to have begun in the early late miocene c 10 9 ma and lasted until c 4 ma the regional topography is dominated by nnw sse striking grabens and normal fault escarpments relics from this time normal faults that are now active cut across these older structures although in some localities normal faults that were oriented obliquely to the earlier extension have remained active also oblique to the modern extension sense it is suggested that this present phase of extension relates to the modern sense of deformation throughout the aegean region and to the modern geometry of the north anatolian fault zone nafz which is independently inferred to have existed since c 4 ma the earlier ene wsw extension is inferred to have involved two phases the first predating the nafz and the second synkinematic with its initial phase of slip during c 7 4 ma when its geometry and the overall sense of deformation in the aegean region were different from at present some previous studies have inferred that sw bulgaria experienced large scale extension on low angle normal faults in the mid miocene or earlier however the limited evidence in support of this view is open to other interpretations and after due consideration can be discounted

neogene supra subduction zone extension in the polis graben system west cyprus the neotectonic polis graben and adjacent pegia half graben in west cyprus are extensional basins developed within the convergent tectonic regime of the eastern mediterranean both basins contain an early fill of miocene carbonates including reef limestones messinian extension oriented ene wsw produced the asymmetrically faulted polis graben structure evaporites were deposited in the south of the area while unconformity surfaces developed in the north pliocene mark and chalks were then deposited in a relatively quiescent phase in the north of the graben while faulting continued into the early pliocene in the south plio pleistocene to recent sediments record regional uplift of cyprus contemporaneous nne ssw oriented extension formed the pegia half graben and renewed minor faulting in the polis graben the extensional structures of the polis graben system are thought to result from extension above a subduction zone located south of cyprus driven by subduction 9roll back9 and trench migration accelerated convergence and rapid roll back during late miocene times caused the first stage of extension whilst the plio pleistocene faulting was driven by differential extension in the overriding plate as the eratosthenes seamount collided with the trench and locally impeded subduction the polis graben system may provide a model for the early stages of development of major suprasubduction zone extensional areas such as the aegean region

microseimicity and strain pattern in northwestern greece during a 7 week microearthquake experiment conducted in epirus akarnania and the ionian islands of western greece we located approximately 600 earthquakes with magnitudes between 2 and 4 2 no event was deeper than 40 km the seismicity cannot be clearly associated with any single fault except the lixourion right lateral fault located west of the ionian islands focal mechanisms of about 100 earthquakes show for a narrow band of earthquakes located along the coast ene wsw shortening consistent with the surface tectonics farther east focal mechanisms show nnw sse extension beneath the foothills of the pindus mountains which is unrelated to surface faulting but is consistent with the presently subsiding basins this strain pattern is seen far north and south of the lixourion fault and is similar to the one observed in the peloponnese it suggests that a large scale mechanism is responsible for the recent geodynamics of both the northwestern and southwestern aegean

aftershock tectonics of the 1978 tabas e golshan iran earthquake sequence a documented active thin and thick skinned tectonic case summary in this study a locally recorded aftershock sequence of the 1978 tabas e golshan earthquake m 7 4 was accurately located out of 1560 located events 329 best located aftershocks passed a strict quality criterion these well located aftershocks which have uncertainties in epicentre and in focal depth of about 1 and 2km respectively together with the wellconstrained focal mechanisms provided a detailed picture of active continental deformation during an aftershock sequence almost all aftershocks follow very closely the pattern of the earthquake faults at the surface and lie in the hanging wall block of the active fault the hypocentres occurred mainly at depths less than 23 km with a high concentration of seismic activity between 8 14 km depth the aftershocks clearly demonstrate an active imbricate listric thrust system with fault planes flattening into a basement decollement zone and the reactivation of different basement reverse faults in response to a considerable amount of shortening of the top sedimentary cover the sense of motion was almost universally thrusting and the aftershocks shared the same tectonic causes as the main shock the study indicates that the development of the young fold thrust mountain belts necessarily involves basement shortening thin and thick skinned tectonics and that the frontal reverse faults in young active fold thrust mountain belts are the most seismically active faults geological and seismic data propose that the active frontal reverse fault systems are possibly reactivated old normal faults and may add support to the contention of reversal of fault motion during rethickening of continental crust the active thinand thick skinned tectonics documented in this study may prevail in other young and active fold thrust mountain belts which are characterized by a thick sequence of telescoped top sedimentary cover over a decollement detachment zone

segmented african lithosphere beneath the anatolian region inferred from teleseismic p wave tomography summary lithospheric deformation throughout anatolia a part of the alpine himalayan orogenic belt is controlled mainly by collision related tectonic escape of the anatolian plate and subduction roll back along the aegean subduction zone we study the deeper lithosphere and mantle structure of anatolia using teleseismic finite frequency p wave traveltime tomography we use data from several temporary and permanent seismic networks deployed in the region approximately 34 000 p wave relative traveltime residuals measured in multiple frequency bands are inverted using approximate finite frequency sensitivity kernels our tomograms reveal segmented fast seismic anomalies beneath anatolia that corresponds to the subducted portion of the african lithosphere along the cyprean and the aegean trenches we identify these anomalies as the subducted aegean and the cyprus slabs that are separated from each other by a gap as wide as 300 km beneath western anatolia this gap is occupied by slow velocity perturbations that we interpret as hot upwelling asthenosphere the eastern termination of the subducting african lithosphere is located near the transition from central anatolia to the eastern anatolian plateau or arabian eurasian collision front that is underlain by large volumes of hot underplating asthenosphere marked by slow velocity perturbations our tomograms also show fast velocity perturbations at shallow depths beneath northwestern anatolia that sharply terminates towards the south at the north anatolian fault zone nafz the associated velocity contrast across the nafz persists down to a depth of 100 150 km hence our study is the first to investigate and interpret the vertical extent of deformation along this nascent transform plate boundary overall the resolved upper mantle structure of anatolia is directly related with the geology and tectonic features observed at the surface of the anatolian plate and suggest that the segmented nature of the subducted african lithosphere plays an important role in the evolution of anatolia and distribution of its tectonic provinces

seismological and sar signature of unrest at nisyros caldera greece abstract nisyros island a quaternary volcanic center located at the se of the aegean volcanic arc has been in the past characterized by periods of intense seismic activity accompanied sometimes by hydrothermal explosions the last one being in 1887 the recent long lasting episode of unrest 1995 1998 in the area is the first instrumentally documented providing information on the behavior of the volcano evidence from seismicity and sar interferometry suggests that the presently active part of the kos nisyros volcano tectonic complex is located at the nw coast of nisyros island defining an area much smaller than the whole volcano tectonic area seismicity patterns vary both temporally and spatially consistently with different rates of vertical ground deformation inferred from sar interferometry these observations help us to discuss the different elements controlling the behavior of the volcanic system such as the existence location and timing of magma chamber inflation the occurrence of tensile failure at the boundaries of the chamber and the possibility of magmatic fluids being expelled to form a shallow magmatic intrusion the seismic failure and migration of hypocenters indicating shallow magma transport

seismotectonics and the earthquake frequency magnitude distribution in the aegean area summary a study of aegean seismotectonics and the resulting frequency magnitude distribution on a broad scale is undertaken using the tectonic model of le pichon angelier this implies a tectonic moment release rate due to the spreading of the aegean of 17 8 times 1018 n m 1 yr 1 over the past 13 ma if stretching is due mainly to a series of normal faults dipping at about 45 in a seismogenic crust 10 20 km deep the moment magnitude relation from an instrumental magnitude catalogue is log m0 a bm with a 10 970 0 294 b 1 206 in si units this is established from 50 events of magnitude ms 5 3 whose scalar seismic moments m0 have been evaluated in a homogeneous manner for the region by spectral analysis of surface waves at 30 60 s period by contrast published body wave analyses from waveform modelling at 20 s period and moment tensor analyses seem to produce seismic moments which are lower by a factor of two or so on average this moment magnitude relation implies a seismogenic moment release rate due to stretching in the aegean of 14 times 1018 n m 1 yr 1 during the time period 1918 81 and 17 times 1018 n m 1 yr 1 for the period 1964 81 within a factor of two or so uncertainty this implies that the energy release in the brittle crust due to aegean spreading is substantially seismic within the stated accuracy and is also relatively stationary even when compared with the tectonic moment release rates a similar comparison using the same tectonic model shows that the subducting slab is sinking beneath the hellenic arc almost completely aseismically and that processes such as near vertical slab pull and confined thermal expansion could explain most of the observed seismic energy release by internal deformation of the slab the frequency magnitude statistics for the area of active extension has a characteristic earthquake of magnitude 7ms corresponding approximately to fault depths of 10 14 km for an aspect ratio of 2 and a strain drop of 10 4 this is close to the observed seismogenic depth 10 20 km for well determined earthquakes in the aegean area

the 1978 earthquake sequence near thessaloniki northern greece summary this paper presents a detailed study of teleseismically and locally recorded foreshocks and aftershocks of the 1978 thessaloniki earthquake sequence and discusses the relations between the locations and mechanisms of these shocks and the three dimensional geometry of faulting in the source region sixteen teleseismically recorded events were relocated using a relative relocation method and positioned geographically using the accurate locally determined location of the largest aftershock all these shocks had depths shallower than 15 km the spatial distribution of the foreshocks showed that the activity was initiated at the central part of the epicentral region progressed westwards and for about 20 days clustered in the region of the imminent mainshock no teleseismically recorded foreshock was located west of the mainshock location in less than 1 hr after the mainshock large aftershocks occurred west of it and in later stages spanned the entire western part of the epicentral region no teleseismically recorded aftershocks were located east of the mainshock locally recorded aftershocks were accurately located and provided a more detailed picture of the seismic deformation they occurred at depths between 3 and 12 km and in three distinct clusters separated by well defined gaps the largest foreshock on may 23 had a moment of 5 6 1024dyne cm and a mean displacement of 31cm the mainshock on june 20 had a moment of 5 2 1025dyne cm a strain drop of 4 0 10 5 static stress drop of 12 bar and a mean displacement of 64 cm these values are for one of the two possible interpretations of the aftershock distribution which suggests that the largest earthquakes of the sequence occurred on two different but adjacent fault segments the first event 1 on may 23 occurred along the central fault segment and was followed 28 days later by the second event 2 on june 20 along a western fault segment finally 61 days later another smaller earthquake event 3 occurred along another fault east of event 1

subsidence of the north aegean trough an alternative view the north aegean trough is a zone of deep water trending from northeast to southwest across the n aegean sea the western part of the trough the sporadhes basin contains a thick sequence of late cenozoic sediments le pichon et al 1984 suggested that the sporadhes basin coincides with a zone of extreme lithospheric stretching and that the crustal thickness is locally reduced to only 15 km we argue that the geophysical evidence cited by le pichon et al can be equally well explained by a crustal model involving a much smaller amount of local crustal thinning

inversion of field data in fault tectonics to obtain the regional stress i single phase fault populations a new method of computing the stress tensor summary we attempt a general definition of the inverse problem of computing the components of the regional stress tensor from a set of field data including the measurements of the strike and dip of several faults and the directions and senses of relative motion along these faults as indicated by slickenslides in previous treatments of this problem no experimental errors could be taken into account except those in measuring the pitch of slickenslides thus errors in the orientation of the fault strike and dip which have considerable practical importance were neglected in our work all experimental errors in the field measurements are taken into account so that the agreement between the computed stress tensor and the set of field measurements can be rigorously checked

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

uranium series dating of the draining of an aquifer the example of wind cave black hills south dakota wind cave south dakota is a three dimensional rectilinear maze cave developed in 90 m of mississippian limestone and dolomite that is overlain by thick clastic cover strata beneath an area of 1 8 km 2 87 km of small drained phreatic passages are known exploration terminates at a water table 160 m below the highest parts of the cave as the cave was draining calcite precipitated from its waters uranium series measurements 85 were taken on fragments of broken calcite crusts collected in the lower 93 m of the cave the measurements reveal that it has been draining as a backwater for at least the past 300 000 yr 234 u 238 u ratios in the water were remarkably constant allowing estimation of ages beyond 400 ky b p after deducting glacial interglacial cyclic oscillations of 10 to 20 m amplitude the water table appears to have been lowered at a steady rate of 0 4 m per 10 3 yr since 400 ky b p most of this fall is attributed to the increase of hydraulic conductivity in the 260 m of cover strata that separates the carbonate aquifer from its spring discharge points a subaqueous calcite deposition zone extended to 70 m below the contemporary water table at all times where mean rates of deposition were 0 12 mm per 10 3 yr or less modeling of the precipitation kinetics suggests a well mixed water body with a ca 2 concentration close to the thermodynamic equilibrium value and variations of depositional rate being controlled by hydrostatic pressure

gravity induced deformation on the north flank and floor of the sporadhes basin of the north aegean sea trough pdr and continuous seismic profiling surveys in the sporadhes basin the western part of the north aegean sea trough reveal active gravity induced deformation of the postorogenic sedimentary sequence different deformational patterns in the uppermost sedimentary layers of the flanks and floor of the basin suggest that the layers are deformed by several gravity induced processes including slumping sliding and creep contemporaneous with sediment deposition antithetic faulting on the northern flank of the basin the thermaicos slope results from downslope creep of surface layers over deeper tilted bedding planes this process is a consequence of progressive slope development associated with the evolution of the sporadhes basin the morphology of the sea floor and the deformation of the upper layers clearly reflect synsedimentary tectonics in a subsiding basin environment

structural sketch of the hellenic continental margin between the western peloponnesus and eastern crete a structural sketch of the hellenic continental margin and adjacent areas based on numerous seismic profiles obtained in the past few years shows two distinct structural domains an inner extensional domain characterizes most of the continental margin the offshore regions as well as the cretan sea an outer compressional domain extends over the trenches and part of their outer slope we believe that this perplexing pattern is related to the presence of an underlying evaporitic series progressively deformed and piling up against a resistant continental margin the completion of subduction and subsequent continental collision are also involved in this structural framework

sequential rotation of stretching axes and block rotations a structural and paleomagnetic study along the north anatolian fault abstract fault kinematics of the western part of the north anatolian fault an active transcurrent fault were investigated consistent successive counterclockwise rotation of incremental stretching directions was derived from the seven areas investigated we assumed that the changes in stretching directions correlate to the consistent rotation of one or several blocks caused by interaction of major fault segments in order to test this hypothesis we compared magnetic remanence directions measured within tertiary calc alkaline volcanic rocks with the changes in stretching direction in spite of the successive changes in stretching systematic changes in remanence directions were not observed most of the latter show no or low angular distances to the reference direction of d 335 i 50 both positive and negative signs are inferred for movements about subhorizontal and subvertical axes where magnetic remanence directions suggest rotation we conclude that changes in the overall deformation explain the systematic changes in incremental directions better than consistent external rotation a deformation path is proposed that includes ne sw and n s shortening during the paleogene and possibly lower miocene nw se shortening and penecontemporaneous local n s extension for the miocene and nw se to e w shortening and sw ne to n s extension for the pliocene until the present

tectono sedimentary development of an extensional basin the neogene megara basin greece the miocene pliocene to pleistocene succession exposed in the megara basin comprises a grossly coarsening upwards sequence at least 1 km thick the oldest strata exposed in the nw record the establishment of alluvial fans and axial streams these drained into a lacustrine environment subject to minor wave and possibly tidal action the lower part of the central basin fill is comprised of marls siltstones sandstones and conglomerates they record the pulsed infill of the predominantly freshwater lake megara by progradation of a network of shallow multichannel streams which drained a western hinterland containing ultrabasic rocks cherts and limestones frequent examples of large scale soft sediment deformation structures and stratigraphic thickening into hangingwall rolloven indicate active fault control of sedimentation the lake river interface featured gilbert deltas which were subject to periodic transgression by climatically controlled lake expansions the upper part of the pliocene basin fill largely comprises fluviatile gravels but with two important marine transgressional horizons and renewed calcareous mar1 deposition including a basinwide tufa horizon towards the top the overlying pleistocene alluvial clastics were deposited by a nw flowing system and thicken markedly into a major basin bounding fault deposition of these fluvial deposits was interrupted towards the top of the sequence by the rapid deposition of monomict limestone breccias of debris flow origins which are believed to mark a catastrophic event at some time in the late pleistocene c 1 ma the basin bounding faults became inactive and the entire basin fill was inverted in response to uplift in the footwall of the active major fault strand that bounds the se margin of the alkyonides gulf

sliding and regional slope stability in active margins north aegean trough mediterranean continuous seismic air gun sub bottom profiling in the north aegean has revealed a large submarine slide the failure zone extends from a depth of about 300 m down to 850 m and covers an area of 85 km2 the mean thickness of the slide reaches about 55 m and an estimated total volume of 3 8 km3 of late pleistocene sediments has slid a distance of 6 7 km chronostratigraphic analysis of the acoustic reflectors imply that the major and secondary glide planes are the transitional zones between a lower sequence of strongly stratified reflectors stiff relatively coarser sediment layers and the overlying acoustically transparent and or poorly stratified sequence weaker muddy layers with higher water content and lower shear strength these weak transparent layers have been deposited during interglacial high sea level stands isotopic stages 7 5 3 the major glide plane is assumed to have been developed within a muddy layer that was deposited about 170 245 ka bp stratigraphic sedimentological data and ams dates indicate an early holocene age of the major failure event not earlier than about 5 5 ka bp and not later than 7 8 ka bp the regional seismic hazard and slope stability analysis shows that the north aegean marginal upper middle slopes are highly unstable the calculated values of horizontal ground acceleration able to initiate failures kc range from 80 to 300 gal downslope this is lower than what is expected within 50 yr especially in the upper middle slopes

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

hydrothermal dolomitization of the bekhme formation upper cretaceous zagros basin kurdistan region of iraq record of oil migration and degradation abstract the common presence of oil seepages in dolostones is widespread in cretaceous carbonate successions of the kurdistan region of iraq this integrated field petrographic chemical stable c o and sr isotopes and fluid inclusion study aims to link dolomitization to the origin and geochemical evolution of fluids and oil migration in the upper cretaceous bekhme carbonates flux of hot basinal hydrothermal brines which is suggested to have occurred during the zagros orogeny resulted in dolomitization and cementation of vugs and fractures by coarse crystalline saddle dolomite equant calcite and anhydrite the saddle dolomite and host dolostones have similar stable isotopic composition and formed prior to oil migration from hot 81 115 c basinal nacl mgcl2 h2o brines with salinities of 18 22 wt nacl eq the equant calcite cement which surrounds and hence postdates saddle dolomite has precipitated during oil migration from cooler 60 110 c nacl cacl2 h2o brines 14 18 wt nacl eq the yellowish fluorescence color of oil inclusions in the equant calcite indicates that the oil had api gravity of 15 25 composition which is lighter than present day oil in the reservoirs api of 10 17 this difference in oil composition is attributed to oil degradation by the flux of meteoric water which is evidenced by the low 13c values 8 5 to 3 9 vpdb as well as by nil salinity and low temperature in fluid inclusions of late columnar calcite cement this study demonstrates that linking fluid flux history and related diagenesis to the tectonic evolution of the basin provides important clues to the timing of oil migration degradation and reservoir evolution

rift formation in the gokova region southwest anatolia implications for the opening of the aegean sea the time of the onset and the nature of the extension in the aegean area have been problematic owing to the confusion of neotectonic replacement structures with neotectonic revolutionary structures this paper concerns two rift systems of different ages and orientations in the gokova region of southwestern anatolia the first system has a northwest southeast trend with a middle to upper miocene infill whereas the second system is orientated in an east west direction and filled with plio quaternary rocks structural and palaeomagnetic data indicate that the first system originally had a north south trend and then bodily rotated anticlockwise to its present orientation before the end of the miocene both the orientations and the structural patterns of these cross cutting rift systems suggest that they resulted from two different and successive tectonic regimes regional geology suggests that the generative regime of the older system was characterized by north south compression and related to the palaeotectonic evolution of southwestern anatolia whereas that of the younger system is characterized by north south extension and relates to the neotectonic evolution of this region this inference contradicts at least in southwestern anatolia some recent claims that the extensional tectonics and the related rift formation in the aegean region began in the early miocene with the alleged demise of the compressional palaeotectonics during the late oligocene but is consistent with older views that placed the onset of north south extension into the later middle miocene the formation of the aegean sea seems to be the result of these two complicated and contrasting succesive tectonic regimes that have affected this region since middle miocene times

tectonics and sedimentation in the gulf of corinth and the zakynthos and kefallinia channels western greece abstract single channel seismic reflection profiling data are presented from the gulf of corinth and from the continental margin outside the gulf of patras different tectonic styles are exhibited in the two regions the gulf of corinth is occupied by a complex asymmetrical graben structure with major faults trending nearly perpendicular to the local tectonic zones of the internal hellenides the gulf is interpreted to have formed during the quaternary in response to approximately north south extensional stress the deep floor of the gulf is underlain by a sequence of turbidites up to 1 km thick affected by normal growth faulting that extends up to the sea floor the sea areas inside the ionian islands of zakynthos and kefallinia zakynthos and kefallinia channels occupy a broad structural depression that trends parallel to the local tectonic zones of the external hellenides and is situated on the continental side of the strophades continental margin rise the channels contain local nw se trending structural basins zakynthos and kefallinia basins whose geometry is controlled by reverse faults or thrusts with associated diapirism in triassic evaporites hydra bank is interpreted as a tilted fault block with a diapiric core and its faulted western margin can be traced into the zone of thrusting and diapirism in southeast kefallinia at the boundary between the ionian and pre apulian paxos zones of the external hellinides the zakynthos and kefallinia structural basins are filled with a variety of sediments including prodeltaic deposits in front of the modern delta complex of the acheloos river slumped masses and debris flow deposits and in the zakynthos basin occasional turbidites the boundary separating zones of extensional and compressional focal mechanisms for shallow earthquakes crosses the gulf of patras the inner part of which exhibits wnw ese trending graben tectonics apparently related to the gulf of corinth tectonic province onshore neotectonic studies around the gulf of patras are required in order to understand the nature and cause of the westward tectonic transition from wnw ese graben structures in the gulfs of corinth and patras to nw se oriented zones of subsidence with associated compressional tectonics and diapirism in the zakynthos and kefallinia channels

the eagle pass detachment southeastern arizona product of mid miocene listric normal faulting in the southern basin and range mid miocene low angle normal faulting is an integral part of the regional tectonic strain of the southern basin and range the distinguishing characteristic is the presence of detachments allochthons of moderately to steeply dipping hanging wall rocks resting in very low angle fault contact on structurally deeper generally older footwall rocks rotation of detachment strata was accomplished by imbricate listric normal faulting and coordinated tear faulting regional structural domains each thousands of kilometres in area contain detachments marked by uniform sense of detachment strata rotation the eagle pass detachment 70 km northeast of tucson arizona reveals informative structural details of parts of the system steeply southwest dipping mid miocene volcanic and sedimentary rocks several thousands of metres in thickness rest in very low angle 10 fault contact on precambrian granitic basement detachment strata were faulted into position by ne directed translation accompanied by rotation of strata to steep sw dips the detachment fault which underlies the 25 km2 detachment has the form of a large northeast trending mullion trough with relief of at least 500 m along the keel of the detachment precambrian quartz monzonite was transformed into a hydrothermally altered selvage of microbreccia the steep 80 northwest margin of the mullion trough served as a tear fault along which quartz monzonite was crushed volcanics were dragged and fanglomerate was locally sheared into flattened pebble conglomerate detachments like that at eagle pass resemble slump blocks on a grand scale they are elements of a regional system of extensional deformation which coincides with the belt of cordilleran metamorphic core complexes mid miocene detachment faulting post dates the formation of exposed mylonitic tectonites of core complex affinity but the direction of translation of the detachments is parallel to penetrative lineation in nearby and or underlying tectonite moreover in southeastern arizona examples the sense of translation of detachments matches the sense of simple shear movements disclosed by tectonite fabrics we speculate that large crustal displacements achieved during extension induced formation of tectonite produced a geometric and or dynamic condition which strongly influenced subsequent detachment faulting consequently with renewed or continued extension in mid miocene time deep upper crustal slumping was triggered and detachment rocks were translated along listric normal faults in the direction and sense of the earlier displacements which had accommodated the formation of tectonite

neotectonics of the pontides implications for incompatible structures along the north anatolian fault data for the post serravallian neotectonic evolution of the pontides in northern turkey indicate predominant ene wsw shortening with complementary nnw sse extension we present a new fault plane solution for the bartin earthquake 3 september 1968 and compare its mechanism with the movement picture of other neotectonic faults in the pontides and northern greece together with that of the thessaloniki earthquake 20 may 1978 the general strain pattern exhibited by these structures agrees remarkably well with that inferred from early tortonian early pleistocene structures reported from within the north anatolian fault zone which have been interpreted as indicating a possible reversal of the sense of movement along the north anatolian transform fault here we argue that such incompatible structures may be related to the overall e w shortening of anatolia and the southern parts of the black sea resulting from the sideways continental escape from around the african and the arabian promontories rather than to hypothetical reversal of motion along the north anatolian fault for which there is no evidence other than the above mentioned incompatible structures this new model also has important implications for seismicity and earthquake risk in regions contained within the southern part of the black sea plate

a thin viscous sheet model for continental deformation summary for the purposes of describing its large scale and long term deformation the continental lithosphere is regarded as a continuum obeying a newtonian or a power law rheology the flow of a thin sheet of power law material overlying an inviscid substrate is studied under the assumption that vertical gradients of the horizontal velocity are negligible a numerical model is used to investigate the deformation of such a sheet under conditions approximating those of continent continent collision the material flows in response to forces applied to its boundaries for example the indenting of one continent by another and to forces in its interior arising from gradients in crustal thickness the horizontal divergence of the flow produces changes in the crustal thickness and hence a time dependent form to the flow itself for a given set of boundary conditions the flow depends on the stress exponent in the power law rheology n and on the argand number which is a measure of the ratio between the stress arising from crustal thickness contrasts and the stress required to deform the material at the ambient strain rates when the effective viscosity of the medium is very high ar o crustal thickness variations do not influence the flow if the material is newtonian n l the deformation associated with an influx of material approximating an indenter is of much greater lateral dimension than the width of the indenter whereas when material has a power law rheology n 3 5 are used the deformation is confined to a region of lateral extent comparable to that of the indenter as ar increases the forces arising from crustal thickness contrasts exert more influence on the flow and the maximum crustal thickness that can be sustained by a given influx of material is related by a simple expression to the effective viscosity of the medium at the ambient strain rates in the limit of a very weak medium ar 10 the lithosphere is unable to sustain appreciable crustal elevation contrasts the results of these numerical experiments show that systems in which the effective viscosities are such that the maximum deviatoric stresses are between 1 kbar

holocene record of slip predictable earthquakes on the kenchreai fault gulf of corinth greece abstract we present the quaternary slip history of the kenchreai fault gulf of corinth based on geomorphological palaeoseismological geo archaeological data and literally determined events we also applied a series of geomorphic indices such as the hypsometric curve asymmetry factor the stream length gradient index sl the valley floor width to valley height ratio vf the drainage basin shape bs and the mountain front sinuosity smf in drainage basins flowing perpendicular to the fault these indices are representative for longer time period and are analyzed as follows values of sl are relatively high close to the fault trace smf values range from 1 01 to 1 85 vf mean values range between 0 29 and 1 07 bs values range from 1 16 to 4 78 lateral fault growth was likely achieved by propagation primarily towards east while its western end appears to act as persistent barrier the holocene palaeoseismic history of the fault investigated by a palaeoseismological trench and 14 c dating of ten samples suggest four linear morphogenic earthquakes in the last 10 ka the kenchreai fault displays a holocene slip rate in the order of 0 15 mm a 1 and a recurrence interval ranging between 1300 and 4700 years thus the fault is classified as a fault of moderate activity with moderate to well developed geomorphic evidence of activity and an overall slip predictable earthquake model

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

rates of uplift investigated through 230th dating in the gulf of corinth greece abstract the sr u and th isotope compositions of fourteen coral samples from raised terraces on the south side of the gulf of corinth greece have been analysed by high precision mass spectrometry 234u 230th ages of pure coral aragonite together with 87sr 86sr determinations provide the basis for an investigation of tectonic uplift rates in the w aegean over the last 350 ka the corinth basin is a continental fault bounded depression formed by crustal extension northeast of subduction along the hellenic trench and in the vicinity of the aegean volcanic arc the sr isotope composition of present day seawater in the gulf of corinth is indistinguishable from that in the north atlantic but this was not the case during earlier high stands 120 190 and 240 ka ago when 87sr 86sr ratios as estimated from the corals were apparently significantly lower than the ratios of their open ocean counterparts although the cause of the earlier discrepancy between the two reservoirs is unknown it is likely to result from one of two processes either circulation between the gulf of corinth and the open ocean may have been restricted at certain earlier highstands or the lower sr isotope compositions could be the result of diagenetic effects the latter hypothesis is favoured by large variations in the initial 234u 238u ratio of the corals by their unusually high th contents and by the observation that the underlying massive miocene carbonate is severely altered the ages of the corals as determined by mass spectrometry ranges between 70 2 and 385 5 ka for samples from terraces at elevations of 7 to 65 m above present sea level a mean uplift rate for this area of 0 3 mm yr over the last 350 ka has been estimated by combining the coral ages with terrace heights allowing for changes in sea level during this period the uplift here is probably caused by footwall uplift adjacent to large normal faults and put constraints on likely fault slip rates extension rates and the timescales of earthquake recurrence

cainozoic evolution of the state of stress and style of tectonism of the basin and range province of the western united states cainozoic evolution of the modern plate boundary along the western united states from subduction to a predominantly transform boundary coincided with a change from compressional to extensional deformation in the western united states extensions tectonism responsible for the modern basin and range province appears to represent a unique late stage episode of a much longer period of extension initiated in an in tra arc setting contemporaneously with calc alkaline magmatism basin range extension is distinguished from early extension on the basis of angular unconformities differences in fault trends and spacing and associated magmatism basaltic prebasin range extension i e extension preceding the break up of the region into ranges resembling the modern ones was under way locally by at least 30 ma and is now recognized by faulted and highly tilted strata exposed in uplifted range blocks by large regions of the crust underlain by passively emplaced subvolcanic batholiths and by the thickness and distribution of stratigraphic units locally high strain rates that accompanied early extensions of as much as 50 100 are implied data on preferentially orientated dyke swarms and fault slip vectors indicate a strikingly uniform wsw ene least principal stress orientation in the period ca 20 10 ma during this early extension the change from early extension to basin range style faulting of the upper 15 km of crust which resulted in broadly spaced ranges 25 35 km crest crest spacing was time transgressive and probably not abrupt locally both types occurred concurrently southern basin and range block faulting occurred largely in the period 13 10 ma in response to a stress field orientated similarly to that responsible for the early extension in contrast northern basin and range block faulting developed after 10 ma and continues to the present in response to a stress field orientated approximately 45 clockwise to the earlier stress field this modern stress field with a wnw ese to e w directed least principal stress characterizes the entire modern basin and range province and rio grande rift region the 45 change in least principal stress orientation is consistent with superposition of dextral shear associated with the development of the san andreas transform fault inclusion of pre basin range extension may help resolve the discrepancy between estimates of 15 30 for basin range block faulting and total extension estimates of 100 300 for the basin and range province

pliocene and quaternary regional uplift in western turkey the gediz river terrace staircase and the volcanism at kula abstract along the upper reaches of the gediz river in western turkey in the eastern part of the aegean extensional province the land surface has uplifted by 400 m since the middle pliocene this uplift is revealed by progressive gorge incision and its rate can be established because river terraces are capped by basalt flows that have been k ar and ar ar dated at present the local uplift rate is 0 2 mm a 1 uplift at this rate began around the start of the middle pleistocene following a span of time when the uplift was much slower this was itself preceded by an earlier uplift phase apparently in the late late pliocene and early early pleistocene when the uplift rate was comparable to the present the resulting regional uplift history resembles what is observed in other regions and is analogously interpreted as the isostatic response to changing rates of surface processes linked to global environmental change we suggest that this present phase of surface uplift amounting so far to 150 m is being caused by the nonsteady state thermal and isostatic response of the crust to erosion following an increase in erosion rates in the late early pleistocene most likely as a result of the first large northern hemisphere glaciation during oxygen isotope stage 22 at 870 ka we suggest that the earlier uplift phase responsible for the initial 250 m of uplift resulted from a similar increase in erosion rates caused by the deterioration in local climate at 3 1 ma this uplift thus has no direct relationship to the crustal extension occurring in western turkey the rate and sense of which are thought not to have changed significantly on this time scale our results thus suggest that the present often deeply incised landscape of western turkey has largely developed from the middle pleistocene onwards for reasons not directly related to the active normal faulting that is also occurring the local isostatic consequences of this active faulting are instead superimposed onto this background of regional surface uplift modelling of this surface uplift indicates that the effective viscosity of the lower continental crust beneath this part of turkey is of the order of 1019 pa s similar to a recent estimate for beneath central greece the lower uplift rates observed in western turkey compared with central greece result from the longer typical distances of fluvial sediment transport which cause weaker coupling by lower crustal flow between offshore depocentres and eroding onshore regions that provide the sediment source

sediment deformation structures and the palaeotectonic analysis of sedimentary basins with a case study from the carboniferous of northern england

rates of tectonic uplift in the corinth and megara basins central greece we present evidence of the rates of late quaternary tectonic uplift that have affected parts of central greece during this period of active extension and basin formation dual lines of evidence indicate upper pleistocene to holocene uplift rates of the order of 0 3 mm yr 1 for the corinth and megara basins first u series disequilibrium ages of acropora sp corals from uplifted marine sediments are used to derive minimum average rates of vertical displacement since deposition second the geometries of cyclical transgressive sequences and of erosional terraces are consistent with the radiometric evidence and the known history of late quaternary sea level fluctuations two types of uplift are distinguished on the basis of structural relationships 1 fault block rotation about a horizontal axis tilting in response to footwall uplift on the active normal fault bounding the alkyonides gulf and 2 a more regional uplift which affects the corinth basin and peloponnesos to the south the results of u series dating are discussed in the light of initial 234u 238u activity ratios derived from the coral samples which are higher than for average marine waters 1 17 1 31 compared to 1 14 these values may be related to a variable freshwater input to the structurally confined gulf of corinth or alternatively they may reflect a previously higher global 234u 238u activity ratio in marine waters or post mortem enrichment in 234u although the mechanism of the latter is not yet understood

fault parameters of the 1980 mw 6 5 volos central greece earthquake from inversion of repeated leveling data the 1980 volos almyros seismic sequence the last of an unusual clustering of earthquakes with surface magnitude 6 0 7 0 which hit thessaly central greece between 1930 and 1980 is among the least studied recent earthquakes in greece repeated measurement of three first order spirit leveling traverses crossing the meizoseismal area of the seismic sequence indicates that between 1970 1971 and 1988 1989 a subsidence of about 35 cm is observed at the almyros neogene quaternary graben the observed displacements are significant against random and systematic errors and can be assigned to the 1980 earthquake sequence inversion of leveling data using an elastic dislocation model constrained by structural and seis mological data indicates that the mainshock mw 6 5 and the largest aftershock mw 6 1 were probably associated with reactivation of two subparallel homothetic nor mal faults marking the northern margin of the almyros neogene quaternary graben

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

lg wave attenuation in the isparta angle and anatolian plateau turkey we estimate lg wave attenuation using local and regional seismic phases in the isparta angle and the anatolian plateau turkey the isparta angle ia is a tectonically active zone forming the boundary between the african plate and the anatolian plateau and is currently undergoing n s extensional deformation the anatolian plateau contains many intra continental faults including the north anatolian fault zone and the east anatolian fault zone as well as the menderes massif a large waveform data set was compiled from a variety of local and regional seismic networks including 121 digital seismic stations broad band and short period between 1999 and 2008 spanning the ia the anatolian plateau and azerbaijan the data set was used to determine the nature of lg wave propagation and characterize the nature of seismic attenuation within the crust of these regions lg waveforms were used to calculate the frequency dependent lg qo and lg eta a wide range of lg qo values was obtained between 52 6 and 524 227 low lg qo values 90 155 are calculated towards the north of ia iskenderun gulf and its vicinity bingol karliova izmit and its vicinity lg qo values are especially low 90 along the menderes massif and the aksehir simav fault zones this may be due to intrinsic attenuation of lg associated with the partially molten crust and young volcanism the high lg qo values 350 are probably caused by the crust not being subject to large amounts of extensional deformation like the antalya gulf and apparently being thick enough to support lg propagation relatively higher values along the border of this subduction zone and plate boundary might be related to the taurus mountain belts and bitlis zagros suture zone the lateral frequency dependency lg eta is also consistent with high tectonic activity in this region

late palaeogene neogene evolution of the triple junction region near maras south central turkey the marao region of turkey includes the anatolian arabian african triple junction the african arabian margin is marked by left lateral transtension along the dead sea kara su rift motion on the anatolian arabian boundary is partitioned between the left lateral east anatolian fault and a fold thrust belt termed the engizek zone equivalent to the bitlis suture further east the african anatolian boundary lies along the cyprus misis andirin trend and is expressed near the triple junction as the aslantao iskenderun zone now undergoing slow left lateral transtension the neogene evolution of these boundaries is largely recorded in the stratigraphy and structure of the basins that lie along the anatolian arabian lice basin and anatolian african aslantao iskenderun basin boundaries these basins appear to have developed in the early miocene along major strike slip zones large half graben in the pre neogene 9basement9 of the western misis andirin block developed contemporaneously with motion on the anatolian african boundary these extensional features evolved subsequent to the intense shattering of the mesozoic carbonate sequence in the misis andirin block and its mixing with panels of deep water palaeogene strata to form an extensionally disrupted assemblage transpression and conversion of both anatolian african and anatolian arabian boundaries to fold thrust belts occurred in the late miocene transpression continues along the anatolian arabian boundary but transtension has recurred along the anatolian african boundary since the pliocene

the relationship between strain rates crustal thickening palaeomagnetism finite strain and fault movements within a deforming zone the deformation of continental lithosphere generally does not occur on a single fault but is distributed over a zone up to a few hundred kilometers wide if the deformation rate is constant throughout the zone and if the velocity is continuous everywhere and does not change with time the deformation gradient tensor can be obtained analytically this tensor directly determines the amount of crustal thickening and is related in a complicated manner to the finite strain tensor the declination of remnant magnetization measured within the zone can also be rotated by the deformation because palaeomagnetic measurements are generally made on rigid blocks which have not been deformed there is no simple relationship between such rotations and the finite strain expressions for all these quantities are obtained in terms of the velocity gradients which are taken to be constant the history of western north america is used to illustrate the relationship between the present deformation by strike slip and thrust motions the rotations of the remnant magnetization vectors and the shape of accreted terranes at the surface distributed deformation is taken up by motion on faults which separate the zone into blocks the displacement rate on the faults their strike and the finite rotations of the blocks are all controlled by the velocity gradients analytic expressions relating these quantities are obtained a deforming zone containing normal faults which crosses central greece takes up both strike slip and extension and illustrates the relationship between the structures within and the motion across the zone a similar but more complicated zone in northeastern iran involves both strike slip and shortening

the prina complex in eastern crete and its relationship to possible miocene strike slip tectonics abstract the basal neogene formations in the ierapetra region eastern crete are strongly influenced by a late serravallian tectonic phase which resulted in the breakup of pre existing palaeogeographic patterns important vertical movements caused the southward emplacement of neogene sediments together with parts of the underlying pre neogene nappe pile the resulting chaotic association of exotic blocks and sediments known as the prina complex has the properties of a sedimentary melange it can be traced for more than 15 km from north to south in the north a relatively coherent accumulation of large slide masses overlies deformed neogene coarse clastics and pre neogene rocks distally it comprises a poorly stratified sequence of breccias and intermixed finer grained sediments which locally contains olistostromes and debris flows and interfingers to the south with submarine fan deposits the intricate relation of faulting and gravity sliding in a rapidly subsiding basin can be explained by generation in a strike slip setting it is suggested that the ierapetra basin and its offshore extension the south cretan trough were initiated by sinistral movements along a ne sw oriented fault zone implications of this model for the geodynamic evolution of the south aegean area are discussed

active tectonics of the alpine himalayan belt between western turkey and pakistan summary over 80 new fault plane solutions combined with satellite imagery as well as both modern and historical observations of earthquake faulting are used to investigate the active tectonics of the middle east between western turkey and pakistan the deformation of the western part of this region is dominated by the movement of continental material laterally away from the lake van region in eastern turkey this movement helps to avoid crustal thickening in the van region and allows some of the shortening between arabia and eurasia to be taken up by the thrusting of continental material over oceanic type basement in the southern caspian mediterranean makran and black sea thus central turkey bounded by the north and east anatolian strike slip faults is moving west from the van region and overrides the eastern mediterranean at two intermediate depth seismic zones one extending between antalya bay and southern cyprus and the other further west in the hellenic trench the motion of northern iran eastwards from the van region is achieved mainly by a conjugate system of strike slip faults and leads to the low angle thrusting of iran over the southern caspian sea the seismicity of the caucasus shows predominantly shortening perpendicular to the regional strike but there is also some minor elongation along the strike of the belt as the causcasus overrides the caspian and black seas the deformation of the eastern part of this region is dominated by the shortening of iran against the stable borders of turkmenistan and afghanistan the north east direction of compression seen in zagros is also seen in north east iran and the kopet dag where the shortening is taken up by a combination of strike slip and thrust faulting large structural as well as palaeomagnetic rotations are likely to have occurred in ne iran as a result of this style of deformation north south strike slip faults in southern iran allow some movement of material away from the collision zone in ne iran towards the makran subduction zone where genuinely intermediate depth seismicity is seen within this broad deforming belt large areas such as central turkey nw iran azerbaijan central iran and the southern caspian appear to be almost aseismic and therefore to behave as relatively rigid blocks surrounded by active belts 200 300 km wide the motion of these blocks can usefully be described by poles of rotation the poles presented in this paper predict motions consistent with those observed and also predict the opening of the gulf of iskenderun ne of cyprus the change within the zagros mountains from strike slip faulting in the nw to intense thrusting in the se and the relatively feeble seismicity in se iran baluchistan this description also explains why the north south structures along the iran afghanistan border do not cut the east west ranges of the makran within the active belts surrounding the relatively aseismic blocks a continuum approach is needed for a description of the deformation even though motions at the surface may be concentrated on faults the evolution of fault systems within the active zones is controlled by geometric constraints such as the requirement that simultaneously active faults do not in general intersect many of the active processes discussed in this paper particularly large scale rotations and lateral movement along the regional strike are likely to have caused substantial complexities in older mountain belts and should be accounted for in any reconstructions of them

fault zone migration by footwall shortcut and recumbent folding along an inverted fault example from the mosha fault central alborz northern iran the mosha fault is a multiply inverted fault in the central alborz field observations and structural data from this fault show that a footwall shortcut is the major mode of response of this fault to contractional deformation although the mosha fault is a basement involved fault there is no evidence of involvement of basement along its footwall shortcuts at least in the study area footwall shortcuts along this fault vary in size from several hundreds of metres to tens of kilometres suggesting that a footwall shortcut can be scale independent it is proposed that footwall shortcuts can also occur as blind thrusts under fault related folds in the terrains near the major inverted faults similar cases also exist in other regions such as japan some large footwall shortcuts may be the causative fault of devastating earthquakes in the active inverted terrains such as the south central alborz incompetent layers acting as detachments may play an important role in the development of footwall shortcuts recu

neotectonic development of the struma kraistid lineament southwest bulgaria and northern greece the struma kraistid lineament is a part of a fault belt of regional importance it strikes nnw sse and cuts through different alpine tectonic zones along the whole balkan peninsula normal and strike slip faults occurred in environments of extension and graben formation during collapse after or between collision epochs in the palaeogene and early neogene and in a back arc extensional environment during the neotectonic end of middle miocene quaternary stage the last alpine compression phase occurred in the beginning of the miocene and early middle miocene planation formed the initial peneplain new intense faulting marked the beginning of the neotectonic stage late badenian and the neotectonic development including sedimentation proceeded in four regional macrocycles badenian sarmatian maeotian pontian dacian and eopleistocene pleistocene the neotectonic development was marked by formation of the serbo macedonian swell as well as by rifting the vardar and struma rifts

fault and bed rotation during continental extension block rotation or vertical shear abstract for almost a century the view has existed that the tilting of blocks between closely spaced planar normal faults is rigid body rotation this interpretation requires only simple geometry and has consequently found widespread application however it is not consistent with the deformation expected around normal faults given the present knowledge of stress fields and rheology in basement in the brittle upper crust which is better regarded instead as distributed vertical simple shear rigid body rotation and vertical shear involve different relations between fault and bed tilting and thus predict different initial fault dips for particular present day dips of faults and beds these two schemes also predict different amounts of extension and it is consequently important to establish which is correct with this aim in mind we examine normal faults associated with neogene extension in western turkey and the western united states and with mesozoic extension in the north sea except where extension and the associated tilting are minimal rigid body rotation predicts unrealistically steep initial fault dips some extensional basins also exhibit reversals of normal fault polarity and tilt polarity of beds which are incompatible with rigid body rotation we therefore conclude that the general cause of the tilting is vertical shear not rigid body rotation this has three main observational consequences first the heave on any normal fault equals the amount of extension across it second no feature near a normal fault can rotate through the vertical a normal fault thus cannot rotate through the vertical and appear as a reverse fault third any initially vertical feature near a normal fault will remain vertical a vertical dyke in the tilted surroundings of a normal fault is thus not necessarily younger than the extension that caused the tilting

magnitude of crustal extension in the southern great basin strike slip faults in the southern great basin separate areas of cenozoic upper crustal extension from relatively stable tectonic blocks linear geologic features offset along the garlock fault las vegas valley shear zone and lake mead fault system allow reconstruction of the southern great basin to a pre extension configuration the sierra nevada mojave desert spring mountains and colorado plateau are treated as stable unextended blocks that have moved relative to each other in response to crustal extension with the spring mountains held fixed to the mojave block our reconstruction indicates a minimum of 65 extension 140 km between the southern sierra nevada and colorado plateau

block rotation in western turkey 1 observational evidence western turkey is a region of rapid continental extension where extension rate increasing westward causes counterclockwise vertical vorticity and hence counterclockwise rotation around vertical axes on a regional scale field observations and seismicity of the past century are used to deduce positions and slip senses of major active oblique normal faults in this region which take up extension in the upper crustal brittle layer and allow fault bounded blocks to rotate around vertical axes the principal active normal faults in western turkey strike roughly east west near the aegean coast turning gradually toward westnorthwest eastsoutheast strike across 200 km distance inland to the east slip vector azimuths indicate typical extension direction on these faults is s18 8w they truncate a second set of faults with smaller displacement and roughly orthogonal strike and slip vector azimuth as well as subdividing the brittle layer into blocks that show little internal deformation some major oblique normal faults subdivide it into domains that show different neogene rotation around vertical axes some domains contain sets of major active oblique normal faults that bound blocks that are elongated angular and shaped like tilted dominoes these faults take up extension and can also take up rotation around vertical axes provided they and the blocks between them rotate around vertical axes at the same rate where adequate paleomagnetic observations are available they indicate these domains have rotated counterclockwise as expected by up to 40 roughly equal to the change in strike of the principal set of active faults between the aegean coast and the eastern edge of the actively extending zone however evidence is scarce for the right lateral strike slip expected in some kinematic models on a set of oblique normal faults that takes up extension and counterclockwise rotation instead each fault appears to have the component of strike slip necessary to enable it given its local strike to slip in ue direction in which the region is extending two domains that have rotated clockwise are approximately circular in plan view with diameter 90 km and are bounded by faults with variable orientation each comprises a single block with no internal major active faults

tectonic interpretations of enigmatic structures in the north anatolian fault zone abstract two geometrically distinct groups of syn sedimentary and post depositional mesofaults and joints cut neogene quaternary sediments in basins situated along the convex northwards arc of the north anatolian fault zone between cerkes and erbaa one group comprises second order fractures interpreted as having developed during episodes of right lateral shear along the fault zone while the morphologically identical fractures in the other group have been interpreted as secondary products of left lateral shear thus apparently implying one or more former episodes of eastwards motion of the anatolian scholle because such a reversal of motion would be counter to the well established westward escape of anatolia the structures have been called anomalous or incompatible alternative hypotheses which have been advanced to explain the development of the anomalous mesofractures include localized reversals related to displacements of rigid blocks acting as buttresses within basins selective operation of intra pull apart strike slip faults stress release the coincidence of the present western sector of the fault with an older left lateral fault zone and the influence of a north turkish neotectonic stress regime

the neotectonics of the aegean an alternative view minor reverse faults in widely dispersed neogene outcrops in the central aegean have led several people to suggest that the regional extension which started in the lower pliocene or earlier was interrupted by short periods of compression the durations of these postulated compressional episodes are short compared to the time scale on which convective forces acting on the base of the lithosphere can change thus possible mechanisms for driving such motions are limited in this paper we offer alternative explanations for these observations and in particular show that these apparently compressional episodes are probably not regional in extent and may not be truly compressional in origin in some places they are more likely to be a consequence of the considerable rotation that is found in extensional terranes the plio quaternary paleogeography of the central aegean is satisfactorily explained by uplift in the footwall blocks of normal faults and does not require regional compression studies of the faulting associated with recent large earthquakes suggest that the sort of microtectonic analysis which is typically carried out on small faults in surficial sediments is more likely to reflect the internal deformation of blocks bounded by major fault structures than be a reliable indicator of regional stress patterns

travitonics using travertines in active fault studies abstract late quaternary travertines deposited from hot springs can reveal much about the neotectonic attributes and histories of structures on the basis of field studies in the aegean region turkey and greece the northern apennines italy and the basin and range province usa we conclude that the following relationships are of predictive value i travertine deposits are preferentially located along fracture traces either immediately above extensional fissures or in the hanging walls of normal faults ii the locations of many travertine fissure ridge deposits coincide with step over zones relay ramps between fault segments networks of intersecting tensional fissures reflecting the complex strains experienced in such settings are probably responsible for enhancing hydrothermal flow iii the morphology of travertine deposits overlying extensional fissures is controlled by the rheology of the underlying materials tufa cones towers pinnacles form on former and present lake floors where fissures underlie unconsolidated sediments whereas fissure ridges develop where fissures cut bedrocks at the surface iv fissure ridges comprise outwardly dipping bedded travertine flanking a central tensional fissure filled by vertically banded travertines fissures can be used to infer local stretching directions v where there are travertines datable by the u series method it is possible to calculate time averaged dilation and lateral propagation rates for individual fissures vi most fissures cutting fissure ridges comprise self similar angular segments with fractal dimensions in the range 1 00 1 12 the properties of bedded travertine combined with stress perturbations at fissure tips probably being responsible for such similar fractal dimensions being inferred from such a wide range of locations fissures gradually increasing in width with depth are products of continuous fracture dilation in contrast to those that form during episodic dilation which display stepped increases of width with depth vii travertine deposited from springs along fault zones accumulate in terraced mounds sited down slope of the spring line viii many post depositional fractures cutting travertine deposits are locally oriented at right angles to deposit margins and ix systematic joints in travertines are restricted to those parts of eroded sheet deposits that have been exhumed

evidence for late rifting of the cordilleran margin outlined by stratigraphic division of the lower cambrian gog group rocky mountain main ranges british columbia and alberta the lower cambrian mcnaughton formation of the gog group occupies a stratigraphic position transitional between the rift related rocks of the underlying upper proterozoic miette group and the overlying paleozoic passive margin succession a major regional unconformity overlain by a distinctive orthoquartzite marker has been traced within the mcnaughton formation this unconformity has been shown to truncate normal faults active during the deposition of the lower mcnaughton formation the lower mcnaughton formation consists of mature coarse grained fluvial sediments accumulated in hanging wall half grabens of active normal faults these faults represent the final stage of rifting on the continental margin the unconformity on the footwall blocks of these faults can be traced into the hanging wall and is overlain by the shoreface sediments of the transgressive upper mcnaughton formation formal subdivision of the mcnaughton formation into four lithostratigraphic members is proposed in order to describ

a formulation for reliable estimation of active crustal deformation and its application to central greece summary a procedure for the analysis of data concerning seismic moment release and fault plane solutions for the estimation of active crustal deformation is proposed the formulation takes advantage of all the available historical and instrumental data for the calculation of the size of the deformation in a seismic zone and of all the reliable fault plane solutions which are available for a broader seismic belt for the determination of the shape of the deformation a detailed analysis of the errors involved in each parameter based on a monte carlo numerical method is suggested the proposed procedure is applied to a region of extensional tectonics in central greece the resulting seismic strain rates show that the dominant mode of deformation in the area is extension at a rate of the order of 6 mm yr and a mean azimuth of n25 w a vertical contraction rate of about 1 mm yr has also been calculated the results from geodetic measurements performed by billiris et al 1991 declare that the calculated seismic deformation represents about 60 per cent of the total strain of this area

active folding in the algerian earthquake of 10 october 1980 a fold controlling the form of the local topography near el asnam algeria increased in amplitude at the time of the earthquake of 10 october 1980 the deformation occurred rapidly in an elastic brittle manner and not in the gradual ductile fashion in which folds are normally thought to develop

seismicity and associated strain of central greece between 1890 and 1988 summary we examined the seismicity of central greece between 1890 and 1988 using macroseismic and instrumental data to ask two questions 1 does the seismicity of this period reveal all the major tectonic structures that are known to be active and 2 what are the likely strains associated with the seismicity over this period many known active structures have been effectively aseismic for the last hundred years and even the inclusion of all known large events earlier than 1890 reveals no activity associated with the ne coast of evia gulf of argos or graben ne of mt parnassos it is clear that even 100 years data are inadequate for either a reasonable assessment of seismic risk or for a confident estimation of maximum magnitude however we are aware of no earthquakes in central greece during the last 200 yr that were larger than ms 7 0 it is probable that the maximum magnitude is restricted by the maximum length of fault segments which appears to be around 15 20 km the earthquakes of ms 5 8 during 1890 1988 can account for a n s displacement of around 45 70 cm with maximum and minimum estimates a factor of two greater and smaller than this across part of a 1890 1900 triangulation network in central greece that was resurveyed in 1988 the contribution of smaller events may increase this displacement by about 50 per cent this cumulative seismic displacement is similar to that estimated from the geodetic work about 100 cm but a detailed comparison of the two sets of observations will be reported elsewhere a re evaluation of all the important earthquakes of 1890 1988 in central greece is presented in the appendix which summarizes information of use to both earth scientists and engineers

a source study of the thessaloniki northern greece 1978 earthquake sequence summary the thessaloniki northern greece earthquake sequence appears to have occurred along faults forming a graben structure this graben situated in the border region between the serbomacedonian massif and the vardar zone is bounded to the south west by clearly exposed north west striking north east dipping normal faults relative hypocentre determinations fault plane solutions surface faulting and the aftershock distribution suggest that some of these faults have been reactivated during the 1978 earthquakes the source parameters of the mainshock mb 6 1 ms 6 4 were determined by computing body wave synthetic seismograms in the time domain and comparing them with the observed this modelling constrained the orientation of faulting determined by the p wave fault plane solution it also constrained the source depth to 6 mp 2 km similar depths were calculated by a relative relocation method for the other three large events of the sequence the dislocation time function required for the far field had a total duration of 9 mp 1 5 s the body wave moment was 5 2 mp 1 8 times 1025 dyne cm for a fault length of 35 km and a fault width of 17 km both estimated from the aftershock distribution the static stress drop was found to be 4 bar an accelerograph record of the mainshock shows two distinct events 3 4 s apart these two events were unresolved by the long period data in the far field but the unusually long duration of the mainshock time function suggests an overall slow energy release which probably occurred as a sequence of events close in space and time seismic energy released in this fashion can account for waveform complexities observed at some stations

optimal design of a regional seismological network for the arab countries the arab countries cover a large portion of the african and arabian plates a region characterized by seismic activity along complex continental collision zones active seafloor spreading rifting and intraplate earthquakes establishing a standardized regional seismic network in these countries then is of great importance considerable effort of some arab countries and unesco under project pamerar is under way to achieve this goal a design for the spatial distribution of a regional seismic network in the area based on a d optimal planning criterion is proposed in this paper the method which involves optimizing the geographical locations of stations is based on the probability of earthquake occurrence at a given point in the seismic region travel times of seismic waves and minimization of the ellipsoid volume of earthquake location errors

description and analysis of early faults based on geometry of fault bed intersections abstract the cross sectional configuration of dip slip faults in stratified rocks can be characterized in terms of sense of displacement relative age of faulted strata polarity hangingwall ramp flat type footwall ramp flat type hangingwall younging direction and footwall younging direction together these variables provide a descriptive framework for observations at single outcrops and a tool for kinematic analysis of deformed early faults contractional and extensional faults cutting strata that were flat lying when faulted can produce only 20 initial fault configurations including derivative configurations that result from fault propagation folding and post fault deformations as many as 120 fault configurations might be encountered in early faults application of these concepts is demonstrated through analysis of a major premetamorphic fault in the acadian orogen in maine which is reinterpreted as a contractional rather than an extensional structure