geomorphic and biological indicators of paleoseismicity and holocene uplift rate at a coastal normal fault footwall western corinth gulf greece abstract the westernmost part of the gulf of corinth greece is an area of very fast extension and active normal faulting accompanied by intense coastal uplift and high seismicity this study presents geomorphic and biological evidence of holocene coastal uplift at the western extremity of the gulf where such evidence was previously unknown narrow shore platforms benches and rare notches occur mainly on holocene littoral conglomerates of uplifting small fan deltas they are perhaps the only primary paleoseismic evidence likely to provide information on earthquake recurrence on coastal faults in the specific part of the rift whereas dated marine fauna can provide constraints on the average holocene coastal uplift rate the types of geomorphic and biological evidence identified are not ideal and there are limitations and pitfalls involved in their evaluation in a first approach 5 uplifted paleoshorelines may be identified at 0 4 0 7 1 0 1 3 1 4 1 7 2 0 2 3 and 2 8 3 4 m a m s l probably forming after 1728 or 2250 cal b p a most conservative estimate for the average coastal uplift rate during the late holocene is 1 6 or 1 9 mm yr minimum with different amounts of reservoir correction some of the obtained radiocarbon ages of lithophaga sp allow for much higher holocene uplift rates of the order of 3 4 mm yr which cannot be discarded but require further research that the identified paleoshoreline record corresponds to episodes of coastal uplift only cannot be demonstrated beyond all doubt yet it appears the most likely interpretation given the geological and active tectonic context and present knowledge on eustatic sea level fluctuations in the mediterranean proving that the documented uplifts were abrupt i e arguably coseismic is equally difficult but rather probable five earthquakes in the last ca 2000 yr on the coastal fault zone that is responsible for the uplift compare well with historical seismicity and the results of recent on fault paleoseismological studies at the nearby eliki fault zone exact amounts of coseismic uplift cannot be determined precisely unless the rate of non seismic uplift of northern peloponnesus at the specific part of the corinth rift is somehow constrained

the 1986 kalamata south peloponnesus earthquake detailed study of a normal fault evidences for east west extension in the hellenic arc tectonic and seismological data collected in the field following the september 13 1986 kalamata earthquake south peloponnesus are presented and analyzed to discuss the earthquake rupture process and the regional tectonics the event occurred on the kalamata normal fault whose trace was mapped with spot images and topographic and field observations this fault is part of an approximately nnw sse en echelon system cutting through the hellenic nappes the fault striking n15 e on the average with a dip of about 50 has a minimum cumulated quaternary throw of the order of 1 km the measured coseismic slip is 6 18 cm over a length of 6 km the main shock focal mechanism obtained from long period waveform modeling strike 201 10 20 dip 45 5 rake 283 10 25 represents almost pure east west extension and is in good agreement with tectonic observations the centroid depth is constrained to 5 3 km and the seismic moment to 7 0 2 5 1017 n m over 700 aftershocks located by a 16 station network installed after the earthquake for a period of 2 weeks define two clusters separated by a gap of aftershock activity from the surface to a depth of about 10 km the main cluster to the south defines a 45 west dipping plane which lies on the downward extension of the fault mapped at the surface focal mechanisms of aftershocks on this fault plane are homogeneous and represent e w extension as the main shock in contrast the majority of focal mechanisms in the uppermost part of the foot wall show more or less e w compression probably corresponding to postseismic stress release the northern cluster of aftershocks is very dense and located away from the surface rupture within a relay zone between the kalamata and the next en echelon faults to the nw the thouria faults there focal mechanisms represent extension from about n115 to n70 and n20 corresponding mostly to fault reactivation in an area where nonrigid deformations prevail the main shock probably initiated in this relay zone 3 4 s before the rupture front reached the main fault plane and released most of the energy there the rupture presumably propagating southward the focal mechanism of the kalamata earthquake and that of the april 27 1965 earthquake located to the northwest of crete as well as the regional active normal fault pattern imply that e w extension oblique to the hellenic arc is presently the dominant tectonic regime e w stretching occurs partly on reactivated nw se faults parallel to the hellenic structures but mostly on newly formed n s normal faults across those structures the latter faults are responsible for the apparent segmentation of the hellenic belt from southern peloponnesus to crete the existence of active e w extension in this region implies a recent change in the tectonic regime and consequently a change in boundary conditions at the subduction zone probably in response to the incoming margin of africa

extensional tectonics of northwestern macedonia greece since the late miocene tectonic field studies in the florina ptolemais basin northwestern greece were carried out in an attempt to define the regional stress tensors in selected areas affected by neogene and quaternary faulting using recently proposed quantitative methods the analysis allows us to distinguish two extensional phases in the area a late miocene pliocene one with a ne sw average direction of extension and a pleistocene recent one with a nw se direction of extension we conclude that the principal stress axes 2 and 3 were interchanged in passing from one phase to the other these results are reasonably consistent with results of studies carried out in other parts of the aegean area especially the south aegean back arc domain

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

earthquake faulting as a structural process abstract structural geology is concerned with the history of movement in the earth s crust and the processes by which displacements occur in the upper one third to one half of deforming continental crust displacement is accommodated largely by seismic slip increments on existing faults it follows that earthquakes and related processes are an integral part of structural geology traditionally structural geologists have been preoccupied with the complexity of the finite deformation within fault zones and with the stress states prevailing at the initiation of faults in intact crust future structural work should be directed more towards understanding the dynamic character of fault reactivation during incremental slip and related effects questions of interest include rheological and geometrical controls on the initiation perturbation and termination of ruptures directivity effects associated with rupture propagation the recognition of structures resulting from repeated stress cycling within seismogenic crust and identification of structural features diagnostic of shear stress levels during faulting structures arising from the inter relationships between slip episodes and induced fluid flow are of special importance because these dynamic fault processes appear influential in the development of much fault hosted mineralization mesothermal gold quartz lodes hosted in high angle reverse shear zones of mixed brittle ductile character form illustrative examples of structures that arguably can only be interpreted by seismo structural analysis embodying the concepts listed above

rift migration and lateral propagation evolution of normal faults and sediment routing systems of the western corinth rift greece the active corinth rift records hanging wall migration of faulting and slip rate accel eration the rift initiated at approximately 5 4 ma and older parts are well exposed in the northern peloponnese a new correlation of chrono and lithostratigraphy and structure across the onland central to westernmost rift with offshore data reveals westward rift propagation as well as north ward fault migration northward fault migration ended first in the east with the stabilization of major north dipping faults that now bound the gulf the basin then propagated to the wnw in two stages each involving the initiation of a new fault that propagated east to se to link to the sta ble fault system extension rates accelerated in distinct steps as the rift opened to the west the youngest faults in the westernmost rift are associated with high seismicity and highest geodetic extension due to rapid fault growth and linkage at depth the early synrift succession infilled substantial inherited palaeo relief antecedent rivers estab lished vigorous sediment routing systems that controlled facies distribution throughout rifting albeit with drainage reorganization during fault migration events multiple deepening events recorded in the stratigraphy can be due to lateral rift propagation the transition from rift initiation to rift climax is therefore diachronous along the rift axis

scaling properties of normal fault populations in the western corinth graben greece implications for fault growth in large strain settings abstract a variety of one dimensional and two dimensional map techniques of fractal analysis have been employed to investigate the scaling properties of the dominant wnw trending normal fault population of the western corinth graben in central greece to assess possible constraints on fault geometry during fault growth the data have been compiled separately from the northern and southern domains of the graben which have experienced differing amounts of finite strain based on power law distributions of the fault throw the applied extension is estimated at 30 and 22 for the northern and southern domains respectively however the fault spacing and fault length populations in both domains obey similar power law relationships these conclusions are also supported by maximum throw vs trace length data which demonstrate that the faults in the northern domain have systematically higher values for the slip to length ratios than those in the southern domain it is proposed that the corinth graben has reached fracture saturation that is the fault spacing stops evolving and displacement increases rather than faults lengthening to accommodate the increasing extension this growth process consistent with throw distributions along individual faults may be explained either in terms of a stress feedback mechanism or by the mechanical interaction between the wnw trending normal faults with a set of nne trending transverse faults

geometry of propagating continental rifts reconstruction of past plate configurations through palinspastic restoration of continental margins1 4 requires a detailed knowledge of the geometries of horizontal continental extension extension is often restricted to discrete linear zones termed rifts5 6 and rift models that invoke propagating vertical dykes and cracks7 10 are useful for assessing the relative significance and timing of uplift subsidence and extension in the tectonic evolution of rift basins however many models do not adequately account for the observed asymmetry of rifts i describe here the general three dimensional character of young and aborted continental rifts which can be used to derive a structural model for the propagation of rifts in continental lithosphere the rifts become asymmetric as a consequence of the role played by low angle normal faults in the overall rift geometry

the role of low angle normal faulting and isostatic response in the evolution of the suez rift egypt abstract a new geometric model for the suez rift suggests that isostatic uplift of an underlying low angle normal fault system accompanying early block faulting localized subsequent deep seated extension this in turn created a superimposed late stage graben system offset to the east from an earlier locus of extension initial extension in the oligocene and earliest miocene drove minor rotation on wide tilt blocks over an eastward dipping low angle normal fault system and formed a series of wide half grabens with increasing extension more closely spaced faults formed smaller rotating tilt blocks fragmenting the larger earlier half grabens and creating numerous sub basins in response to this brittle thinning of the upper crust isostatic uplift of the lower crust arched the underlying low angle fault surface limiting gravity driven tilt block movement in the west by flattening the low angle fault surface and creating a broad gulf parallel high in the fault surface and moho under the eastern portions of the rift this process diminished faulting in the west and localized continuing deep seated extension under the crest of the arch possibly through induced mantle convection through going faults thus initiated cut the old low angle fault system and bound a system of down dropped grabens offset to the east of the most extended portions of the older tilt block array in the red sea immediately to the south this process has continued with the increased separation allowing the formation of mantle derived oceanic crust this model suggests that early movement over low angle detachments and accompanying isostatic response may play an important role in localizing deformation within rifts and are probably critical elements in the early formation of passive margins

sequence stratigraphy in active extensional basins implications for the interpretation of ancient basin fills abstract systematic variations in sequences their component units and their stacking patterns exist within rift basins these variations can be related to displacement gradients associated with the large scale 12 50 km segmentation of normal fault zones which control accommodation sediment supply and basin physiography sediment supply is also strongly influenced by the nature of pre rift drainage networks and variations in bedrock lithology high rates of hangingwall subsidence close to the centre of normal fault segments may cancel out the effects of glacio eustatic sea level fall so that accommodation development is normally characterized by the continual addition of new space the resulting sequences lack type 1 sequence boundaries and lowstand systems tracts and stack into aggradational sequence sets the adjacent footwall is subject to uplift which may lead to subaerial exposure and incision generating a composite type 1 sequence boundary away from the fault zone and near segment boundaries slip rates are much lower and hence relative sea level change is dominated by eustasy here falls in relative sea level are important resulting in type 1 sequences sequence stacking patterns reflect not only eustasy and local fault controlled subsidence but also the interaction of these with adjacent uplifting footwalls and or regional uplift tectonic influence on sequence development will be more pronounced during greenhouse times than icehouse times

earthquake frequency distribution and the mechanics of faulting the level of intraplate seismicity in japan generally shows a positive correlation with the density of quaternary faulting in southwest japan where intraplate seismicity is concentrated on land rates of seismic moment release m 0 are similar when calculated from either the 400 year historical record of seismicity or geologically determined slip rates of quaternary faults a data set of 18 earthquakes with seismic moments m0 ranging from 0 01 to 3 1027 dyn cm shows a relationship between rupture lengthl and m0 log m0 23 5 1 94 log l when seismic moment on each quaternary fault is assumed to occur in discrete events every t m0 m 0g years where m0 is estimated for a rupture extended over the entire fault length and m 0g is proportional to the slip rate of each quaternary fault the moment frequency distribution of earthquakes log n a b log m0 predicted from the geologic record is virtually identical to that seen with the 400 year record of seismicity in contrast if it is assumed that earthquakes on each fault occur according to the gutenberg richter relation we obtain poor agreement with the observed seismicity thus while regional seismicity satisfies the relation log n a b log m0 or equivalently log n a b log m where m is magnitude it appears that seismicity on individual faults does not this further implies that the primary factor that leads to the magnitude frequency distribution in regional seismicity studies is the relative distribution of the slip rates and lengths of preexisting faults

displacement geometry in the volume containing a single normal fault fault displacements measured in coal mines and from seismic data are used to develop a model describing the near field displacements associated with an ideal single normal fault displacement on a fault surface ranges from a maximum at the center of the fault to zero at the edge or tip line the tip line is elliptical with the shorter axis of the ellipse parallel to the displacement direction contours of equal displacement form concentric ellipses centered on the point of maximum displacement displacement gradients vary with fault size and with mechanical properties of host rock fault radius to maximum displacement ratios range from 5 to 500 plotting of displacement contour diagrams and knowledge of displacement gradients are useful in interpreting seismic reflectio data both for quality control of interpretations and for quantitative extrapolation of limited data displacements associated with faulting decrease systematically with increasing distance along the normal to the fault surface this decrease is seen as reverse drag in both hanging wall and footwall hanging wall rollover and tilting of the reflectors cannot be used to distinguish listric from planar normal faults even where fault block rotation can be demonstrated neither listric fault geometry nor a flat detachment surface is geometrically necessary because faulting is accommodated by ductile deformation rigid fault bounded blocks cannot exist except in some special circumstances related to a free surface the displacements within the rock volume affected by a single fault are not simply related to regional extension apparent horizontal extension by faulting varies from one layer to another and a significant proportion of the extension in a basin may be due to ductile deformation

quaternary tectonics in the gulf of patras western greece abstract air gun seismic and 3 5 khz profiling data from the gulf of patras western greece show that it is occupied by a small asymmetric graben with several geometric similarities to the larger scale graben in the gulf of corinth to the east major listric faulting characterizes the southern flank of the graben whilst the northern flank represents an associated rollover structure affected by antithetic and synthetic faulting the present phase of subsidence is of holocene age but buried growth faults suggest earlier subsidence in the gulf the average rate of subsidence through the holocene is estimated to be 10 mm year the gulf of patras graben together with the gulf of corinth graben and the megara basin represent a continuous system of wnw ese trending grabens in a broad zone of intense seismicity within the aegean domain individual grabens are offset and are interconnected by ne sw trending fault systems

interfering folds in constrictional deformation abstract experiments on buckle folding indicate that in pure constriction 2 3 2 3 there is an association of domes and basins with nonplane noncylindrical folds the areas of domes and basins are reduced with increasing deformation there is a dominant fold trend perpendicular to 3 with a less dominant trend perpendicular to 3 folds at an angle to these two sets may also occur the divergent folds link up in smooth arcs or join up at a dome or a basin over a relatively large domain the interference pattern produced by general constriction can be recognized by the association of domes and basins with nonplane noncylindrical folds by occurrence of hair pin bends of hinge lines of open folds by occurrence of amoeboid outcrop patterns and by absence of a consistent overprinting relation among different sets of folds layers subparallel to the 3 axis of general constriction may give rise to two or more sets of coaxial cylindrical folds with orthogonal axial surfaces

interaction of an antecedent fluvial system with early normal fault growth implications for syn rift stratigraphy western corinth rift greece continental overfilled conditions during rift initiation are conventionally explained as due to low creation of accommodation compared with sediment supply alternatively sediment supply can be relatively high from the onset of rifting due to an antecedent drainage system the alluvial lower group of the western plio pleistocene corinth rift is used to investigate the interac tion of fluvial sedimentation with early rifting this rift was obliquely super imposed on the hellenide mountain belt from which it inherited a significant palaeorelief detailed sedimentary logging and mapping of the well exposed syn rift succession document the facies distributions palaeocurrents and stratigraphic architecture magnetostratigraphy and bios tratigraphy are used to date and correlate the alluvial succession across and between fault blocks from 3 2 to 1 8 ma a transverse low sinuosity braided river system flowed north north east to east across east west striking active fault blocks 4 to 7 km in width deposits evolved downstream from coarse alluvial conglomerates to fine grained lacustrine deposits over 15 to 30 km the length scale of facies belts is much greater than and thus not directly controlled by the width of the fault blocks at its termination the distribu tive river system built small stacked deltas into a shallow lake margin the presence of a major antecedent drainage system is supported by i a single major sediment entry point ii persistence of a main channel belt axis iii downstream fining at the scale of the rift basin the zones of maximum sub sidence on individual faults are aligned with the persistent fluvial axis sug gesting that sediment supply influenced normal fault growth instead of low accommodation rate during the early rift phase this study proposes that facies progradation can be controlled by continuous and high sediment sup ply from antecedent rivers

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

kinematics of the central hellenides structural analysis along 24 cross sections crosscutting several windows in the central hellenides provides the sense of nappe movements as well as the location of destroyed oceans lying between the apulian and eurasian continents from the mesozoic orogeny took place in two phases the first phase the eo hellenic phase was initiated by convergence of the apulian and pelagonian plates with west directed subduction and closure of the pindos ocean late jurassic obduction of oceanic lithosphere over the western margin of the pelagonian plate was followed by footwall imbrication mylonites and sheath folds during the late cretaceous uplift was associated with ductile normal faulting at depth and tectonic unroofing at shallow crustal levels the second phase the meso hellenic phase comprised the closure of the ambelakia ocean at the eastern margin of the pelagonian plate and continental subduction along the eastern margin of the apulian plate west directed subduction of the ambelakia ocean was associated with eastward directed ductile thrusting folding and blueschist metamorphism blueschist formed within a simple duplex structure at depth and was subsequently overthrusted in the late eocene onto the olympos microcontinent which acted as a major obstacle to the eastward directed nappe movements up to 150 m thick cataclasites kink folds and a spaced cleavage were formed during the late stage of the continental collision a subduction along the eastern margin of the apulian plate caused kink folding and reimbrication of the western parts of the pelagonian basement since the oligocene the overthickened crust collapsed by means of low angle normal faults

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

submarine and coastal sediment failure triggered by the 1995 ms 6 1 r aegion earthquake gulf of corinth greece on june 15th 1995 a locally destructive earthquake of magnitude ms 6 1 on the richter scale occurred offshore 7 5 km nne of the town of aegion in the western gulf of corinth greece an offshore survey using 3 5 khz subbottom profiling system and a remote operated vehicle rov has shown that the earthquake caused small sized subaerial to submarine sediment failure in at least four sites in three fan delta deposits the rododafni the eliki and the tolofonas the fan deltas were located within a radius of about 9 km from the epicentre the areal size of the four sediment failure sites ranged from 2 104 m2 to 6 105 m2 whilst the volume of the failed masses ranged from 4 103 to 3 106 m3 the sediment deformation types identified at the failure sites consist of ground cracking rotational slides elongated slides sediment gravity flows and extrusion of mixtures of water and sand sand boils the sediment failure in the four sites affected the upper 5 6 m of well layered holocene topset and foreset fan delta deposits the failure occurred on slopes ranging from 0 2 to 23 and the slip planes were all bedding planes which have a gradient from 0 2 to 21 the dominant instability mechanism that caused the sediment failure in the rododafni and eliki fan deltas is considered to be liquefaction of a shallow sub surface horizon the liquefaction was caused by elevated pore pressure enhanced perhaps by the presence of gas resulting from the cyclic loading induced by the earthquake the liquefied layer is assumed to have temporarily provided a failure surface for sliding to take place on and caused movement of sand that was ejected onto the surface in the tolofonas fan delta the causative mechanism in the case of the multi block rotational slide is considered to be deformation of the underlying sediments caused by remoulding and or liquefaction while in the case of the elongated slide it is considered to be the result of a combination of shear stress increase and or strength degradation of the unconsolidated sediment both of these conditions could have been generated during the cyclic loading resulting from the aegion earthquake the study of historical documents reveals that sediment failure like those described above have also occurred at least four times during the past 2500 years in the same locations therefore it is suggested that they could be repeated in the future by any earthquake event with a magnitude greater than 6 r depending upon the proximity of the site to the earthquake epicentre

neotectonic evolution of northwestern continental greece the post miocene sedimentary and structural evolution of nw continental greece changes from west to east

alternating marine and lacustrine sedimentation during late quaternary in the gulf of corinth rift basin central greece abstract the gulf of corinth in central greece has a maximum depth of about 900 m and is separated from the open sea by the rion strait with a sill depth of 62 m marked by an extensive submarine terrace during eustatic sea level lowstands the gulf of corinth was a lake under lacustrine conditions stratified sediments accumulated in the deep water basins and turbid underflows from rivers eroded the basin slopes as the sea level rose marine waters flooded the gulf and deltas prograded across the shelves in shallow water areas two key reflectors termed z and x are terrace surfaces commonly erosional which mark the base of the overlying deltaic sequences in deep water basins z and x mark the top of the acoustically stratified sediments interpreted as lacustrine turbidites reflectors y and w mark the base of these stratified intervals and overlie acoustically transparent sections similar to the holocene section the last lacustrine conditions in the gulf z to y were during isotopic stage 2 and terminated about 12 000 yr ago age estimates based on sedimentation rates suggest that the x to w interval corresponds to the stage 4 lowstand of sea level in the western gulf of corinth shoreline transgressive surfaces corresponding to minor transgressions in stage 5 and to major transgression at the end of stage 6 are recognised this seismic stratigraphy permits a detailed interpretation of the history of the gulf of corinth in the past hundred thousand years it also provides a general model for sedimentation in rift basins in which marine and lacustrine sediments alternate

a new passive tomography of the aigion area gulf of corinth greece from the 2002 data set we present the results of a tomographic study performed in the framework of the 3f corinth project the aim of this work is to better understand the rifting process by imaging the crustal structure of the western gulf of corinth forty nine stations were deployed for a period of six months allowing us to monitor the microseismicity delayed p and s first arrival times have been simultaneously inverted for both hypocenter locations and 3 d velocity distributions we use an improved linearized tomography method based on an accurate finite difference travel time computation to invert the data set the obtained vp and vs models confirm the presence of a two layer vertical structure characterized by a sharp velocity gradient lying at 5 7 km depth which may be interpreted as a lithological contrast the shallower part of the crust down to 5 km depth is controlled by the n s extension and lacks seismicity the deeper part 7 13 km depth matches the seismogenic zone and is characterized by faster and more heterogeneous anomalies in this zone the background seismicity reveals a low angle active surface dipping about 20 toward the north and striking wnw ese the position of this active structure is consistent with both high vp vs and low vp vs anomalies identified at 8 12 km depth and suggesting a highly fracturated and fluid saturated zone both the geometry of the active structure beneath the gulf and the presence of fluids at 8 12 km depth are in accordance with a low angle detachment model for the western part of the gulf of corinth

a microearthquake study in the gulf of patras region western greece and its seismotectonic interpretation summary the seismicity of the gulf of patras region was monitored from 1983 may to 1984 april by a six station microearthquake network with 30 km aperture over 650 events were located using the revised version of the hypo71 computer program for determining hypocentral locations of these a subset of 73 well located events was identified for detailed study analysis of these 73 events reveals a local pattern of seismicity with two main features firstly a gap in seismicity in the central and western parts of the gulf despite the local presence of active faulting affecting the seabed secondly a zone of high seismicity in the northeast part of the gulf where offshore seismic surveys reveal a zone of intense structural complexity a northeast dipping diffuse zone of seismicity extending to a depth of about 25 km has been identified in the northeastern corner of the gulf centred on the rio antirrio channel between the gulfs of patras and corinth it is postulated that the active faults in the central part of the gulf which are apparently aseismic are linked via a shallow decollement surface under the gulf to a deep wnw ese trending fault zone defining the southern margin of the corinth graben and extending westwards to trichonis lake the dipping zone of seismicity is related to the latter fault zone and aseismic faulting in the gulf of patras is attributed to the shallow surface of decollement into which the faults sole a transfer fault zone trending approximately ne sw is postulated to account for the offset of the corinth and patras grabens

fluid involvement in the active helike normal fault gulf of corinth greece abstract rock fabric and mineralogical composition from the fault core and the unaffected protolith have been used to define the role of the segmented helike fault to fluid flow sixty samples were investigated by xrd sem observation and sem eds microanalyses detrital smectite calcite and quartz represent the mineral assemblage at the crest of the footwall block in foniskaria sampling site in this site smectite is enriched at the rims of the fault core all other sampling sites located at the base of the fault scarp are characterized by detrital and newly formed minerals detrital minerals include plagioclase quartz calcite and illite in nikolaiika sampling site and smectite illite kaolinite quartz calcite in selinous sampling site in the latter sampling site erionite and cerussite are newly formed minerals with erionite considered as the hydrothermal alteration product of fluids at 80 100 c at the eastern fault segment illite quartz and calcite t13 site corresponds to detrital minerals mineralogy in the fault core reflects its high permeability to down flowing meteoric water and weak hydrothermal alteration the rock fabric suggests mineral alignment parallel to the fault plane mineralogy indicates that the aigion helike and pyrgaki faults in the gulf of corinth host hydrothermal activity at shallow levels

late holocene evolution of the east eliki fault gulf of corinth central greece abstract trench stratigraphy and morphotectonic analysis was used to examine the recent evolution of the helike eliki plain and eliki fault the entire alluvial plain of the kerynites and vouraikos rivers which cross the eliki fault has subsided at rate of 1 4 mm yr resulting in the burial of the late hellenistic roman occupation horizons under 3 m of fluvial and colluvial sediments along the eastern segment of the eliki fault five trenches have been excavated and their 5000 yr old fluvial and colluvial deposits have been studied in association with the fault strand imprinted on them the kerynites river crosses at high angle the eliki fault and appears to be sensitive in tectonic movements related with the eliki fault sedimentation in the alluvial plain and the fluvial geomorphology of the kerynites river is important for understanding the fault evolution and the burial of the ancient 4th century bc helike city the kerynites river course highlights breaching deformation is the more likely to connect east and west eliki fault segments and that postseismic deformation is a significant mechanism for stress accommodation for part of the west end of the gulf of corinth

late quaternary slip rate on the oak ridge fault transverse ranges california implications for seismic risk abstract the slip rate on the oak ridge fault at south mountain in the densely populated lower santa clara valley california is estimated as 6 15 to 12 3 mm yr since the end of saugus deposition at 0 4 to 0 2 ma slightly lower slip rate estimates result from a different projection of the top of the saugus in the hanging wall block of the fault an assumed displacement of 3 m per event gives an average recurrence interval of 250 to 500 yr with the major uncertainty being the age of the top of the saugus displacement of 2460 m of the top of the saugus at south mountain includes piercing point displacement and distributed displacement from drag folds near the fault both are the near surface expression of faulting at potential mainshock depths beneath well control slip rates for the nearby san cayetano and red mountain faults are not well constrained because post miocene strata are absent in their hanging wall blocks but available evidence suggests that their slip rates are about the same as that for the oak ridge fault earthquake return times measured in hundreds of years have been shown by others for the 1971 san fernando fault and a small fault near the red mountain fault and comparable return times are suggested for a normal fault in the hanging wall block of the oak ridge fault a trench on the harmon alluvial fan near the ventura county government center revealed evidence of cracks filled with sediments from below suggesting liquefaction during an earthquake the lower santa clara valley has not had a large damaging earthquake in 200 years of record keeping but one is expected there in the near future the december 21 1812 earthquake may have occurred on the offshore continuation of the oak ridge or red mountain fault

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

microstructures imply cataclasis and authigenic mineral formation control geomechanical properties of new zealand s alpine fault abstract the alpine fault is capable of generating large mw 8 earthquakes and is the main geohazard on south island nz and late in its 250 291 year seismic cycle to minimize its hazard potential it is indispensable to identify and understand the processes influencing the geomechanical behavior and strength evolution of the fault high resolution microstructural mineralogical and geochemical analyses of the alpine fault s core demonstrate wall rock fragmentation assisted by mineral dissolution and cementation resulting in the formation of a fine grained principal slip zone psz a complex network of anastomosing and mutually cross cutting calcite veins implies that faulting occurred during episodes of dilation slip and sealing fluid assisted dilatancy leads to a significant volume increase accommodated by vein formation in the fault core undeformed euhedral chlorite crystals and calcite veins that have cut footwall gravels demonstrate that these processes occurred very close to the earth s surface microstructural evidence indicates that cataclastic processes dominate the deformation and we suggest that powder lubrication and grain rolling particularly influenced by abundant nanoparticles play a key role in the fault core s velocity weakening behavior rather than frictional sliding this is further supported by the absence of smectite which is reasonable given recently measured geothermal gradients of more than 120 c km 1 and the impermeable nature of the psz which both limit the growth of this phase and restrict its stability to shallow depths our observations demonstrate that high temperature fluids can influence authigenic mineral formation and thus control the fault s geomechanical behavior and the cyclic evolution of its strength

exhumation of deep crustal metamorphic rocks and crustal extension in arc and back arc regions we adress the problem of exhumation of metamorphic rocks in arc and back arc positions based on observations of the aegean and tyrrhenian back arc regions in both regions back arc extension has been active for 25 ma at least while convergence and crustal thickening was going on at the thrust front compressional structures are reworked in the back arc domain as extensional flat lying detachments which allow unroofing of the metamorphic pile metamorphic rocks suffer first a dynamic burial during nappe stacking and then fast exhumation when they reach the extensional region we describe a continuous process of burial and exhumation that is contemporaneous with the migration of the thrust front toward external zones the front of extension follows behind at approximately one hundred kilometers at the convergence front continuous subduction of a cold oceanic slab or continuous accretion of continental units keeps a cool p t gradient and hp lt metamorphic rocks are formed at depth the overall cool environment leads to a deep brittle ductile transition and thus to a resistant crust which can sustain its large thickness while the thrust front propagates forward parts of the accretionary wedge which were formed earlier enter the back arc domain which can be already under extension and which is warmer because of a greater distance to the cold slab and the presence of the volcanic arc the brittle ductile transition rises in the thick crust which then becomes unstable and subsequently collapses the exhumation history of metamorphic rocks below detachments is two fold 1 a constantely thickening crust is unroofed by flat lying detachments which rework early thrusts this first period is characterized by a good preservation of hp lt parageneses 2 the second period is when rocks are in the zone of crustal scale extension of the back arc region deep crustal metamorphics are exhumed below flat lying detachements which affect the whole crust

macroscopic seismic anomalies and submarine pockmarks in the corinth patras rift greece prior to the aigion earthquake m 6 2 of 15 june 1995 in the western gulf of corinth people in the area observed anomalous phenomena including bubbling of the sea extraordinary behavior of animals earthquake lights ground deformation and the sound of wind immediately before the shock some precursory phenomena of this kind might be understood as symptoms of gas venting before an earthquake sonar observations made in 1988 showed a chain of submarine pockmarks tracing the aigion fault and evidently produced by the expulsion of fluids under pressure t hasiotis et al mar geol 130 333 344 reported that hot gas erupted from a field of giant submarine pockmarks in the neighboring bay of patras several hours prior to an earthquake in 1993 automated monitoring of bottom water temperature in submarine pockmark fields may detect outgassing events prior to earthquakes in this region

fractal characteristics of active normal faults an example of the eastern gulf of corinth greece abstract we present a model proposing the evolution of segmented normal faults in a currently extended area allowing an explanation of strong earthquakes hosted by short faults active normal faults accommodating the current extension in the gulf of corinth result from the linkage of smaller component faults well exposed fault zones in the sofiko range are arranged as pairs of graben bounding faults and thus our structural analysis has implications for the evolution of active normal faults as well as graben evolution a basal strip of fresh bedrock at the base of fault scarps suggests continuous seismic or aseismic creep thus the structural analysis of component faults that show a power law length distribution describes an evolved fault zone of particular interest is that faulting in this region is self similar between limits distribution is characterized by a fractal dimension of d 1 and the limits in our study are between 10 m mapping resolution and double the maximum displacement of each fault zone component segments of any compartmentalized fault show a length to maximum displacement ratio of two basin architecture and structural analysis suggest that the nucleation points of faults are detectable over the entire evolution of the fault zone all analyzed faults evolved by an independent nucleation model morphotectonic and kinematic data as well as fractal dimension of trace length population plots all suggest that fault zones defining north and south dipping conjugates are active at least over the late stages of basin evolution although this study was focused on a relatively small area this pattern of fault growth appears to be applicable to the entire fault population in the gulf of corinth and is thus an important model for normal faults

geometry and kinematics of active faults and their seismotectonic significance in the western corinth patras rift greece abstract the western part of the corinth patras rift is formed in an area which is being uplifted rifted domains have subsided relative to the adjacent areas in nw peloponnesus and sterea hellas but subsidence rates rarely exceed uplift rates extension is mainly accomplished by wnw trending active faults with lengths up to 25 km most of these faults show an along strike segmentation and often terminate against transfer faults displacement analysis along 170 mesoscopic faults and 36 mappable faults has been carried out to assess slip rates and to estimate the magnitudes and recurrence time intervals of earthquakes occurring along them earthquake magnitude ranges between 5 and 6 7 only eight faults appear to be capable of producing earthquake magnitudes larger than 6 recurrence times of these large earthquakes vary between 80 and 1690 years upper crustal deformation in the western corinth graben can be described by six large asymmetric grabens which are inferred to bottom out to a n dipping curved ramp the asymmetric shape of most wnw trending rifts in the hellenic peninsula including the corinth patras rift promotes the simple shear model of extension against the pure shear model in the upper crustal layer

fault deformation mechanisms and fault rocks in micritic limestones examples from corinth rift normal faults abstract a multidisciplinary study investigates the influence of different parameters on fault rock architecture development along normal faults affecting non porous carbonates of the corinth rift southern margin here some fault systems cut the same carbonate unit pindus and the gradual and fast uplift since the initiation of the rift led to the exhumation of deep parts of the older faults this exceptional context allows superficial active fault zones and old exhumed fault zones to be compared our approach includes field studies micro structural optical microscope and cathodoluminescence geochemical analyses 13 c 18 o trace elements and fluid inclusions microthermometry of calcite sin kinematic cements our main results in a depth window ranging from 0 m to about 2500 m are i all cements precipitated from meteoric fluids in a close or open circulation system depending on depth ii depth in terms of p t condition determines the development of some structures and their sealing iii lithology marly levels influences the type of structures and its cohesive non cohesive nature iv early distributed rather than final total displacement along the main fault plane is the responsible for the fault zone architecture v petrophysical properties of each fault zone depend on the variable combination of these factors

displacement rates of normal faults previous estimates of displacement rates on individual faults have been limited to neotectonic faults and averaged over time intervals of about 200 kyr or less1 2 3 4 5 these estimates have been highly variable which has led to a belief that longer term displacement rates on individual faults are likely to be variable as well here we report estimates of long term normal fault displacement rates averaged over time intervals ranging from 1 to 40 myr and based on observed decreases in displacement of progressively younger horizons intersected by syn sedimentary faults we find that displacement rates are remarkably stable over these longer time periods and within a given fault system the rates are strongly dependent on the relative size of the fault as measured by cumulative vertical displacement taken together these results indicate that faults become large relative to nearby faults by having higher displacement rates even when small rather than as a consequence of having been active for longer our analyses also show that high regional strain rates tend to be accommodated by high fault displacement rates rather than high fault densities

the evolution of the gulf of corinth greece an aftershock study of the 1981 earthquakes summary a preliminary study of the aftershocks of three earthquakes that occurred near to corinth greece in 1981 is combined with observations of the morphology and faulting to understand the evolution of the eastern gulf of corinth the well located aftershocks form a zone 60km long and 20km wide they do not lie on the main fault planes and are mostly located between the north dipping faulting on which the first two earthquakes occurred and the south dipping faulting associated with the third event a cluster of aftershocks also lies in the footwall of the eastern end of the south dipping fault of the third event morphologically it is observed that in the evolution of the eastern gulf of corinth antithetic faulting apparently predates the appearance of the main faulting at the surface this evolution can be explained by motion on a deep seated shallow angle aseismic normal fault a model based on such a fault also accounts for the aftershock distribution of the 1981 earthquakes