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

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several millimetres per year superimposed on c 400 m of post early pliocene regional uplift this sense of deformation superseded earlier extension oriented ene wsw which is estimated to have begun in the early late miocene c 10 9 ma and lasted until c 4 ma the regional topography is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

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

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

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

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

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

cenozoic prograding sequences of the antarctic continental margin a record of glacio eustatic and tectonic events abstract sedimentary sections up to 6 14 km thick lie beneath many areas of the antarctic continental margin the upper parts of the sections contain up to 6 km of cenozoic glacial and possibly non glacial sequences that have prograded the continental shelf up to 85 km we describe the cenozoic sequences using two general categories based on their acoustic geometries type ia sequences which account for most prograding of the antarctic continental shelf have complex sigmoidal geometries and some acoustic characteristics atypical of low latitude margins such as troughs and mounds lying parallel and normal to the shelf edge and high velocities 2 0 2 6 km s for flat layers within 150 m of the seafloor type iia sequences which principally aggrade the paleoshelf lie beneath type ia sequences and have mostly simple geometries and gently dipping reflections the prograding sequences are commonly located near the seaward edges of major mesozoic and older margin structures relatively rapid cenozoic subsidence has occured due to the probable rifting in the ross sea thermal subsidence in the antarctic peninsula and isostatic crustal flexure in wilkes land in prydz bay and the weddell sea prograding sequences cover mesozoic basins that have undergone little apparent cenozoic tectonism grounded ice sheets are viewed by us and others as the principal mechanism for depositing the antarctic prograding sequences during the initial advance of grounded ice the continental shelf is flexurally overdeepened the inner shelf is heavily eroded and gently dipping glacial strata are deposited on the shelf i e type iia sequences the overdeepened shelf profile is preserved a during glacial times by grounded ice sheets episodically crossing the shelf eroding sediments from onshore and inner shelf areas and depositing sediments at the front of the ice sheet as outer shelf topset banks and continental slope foreset aprons i e type ia sequences and b during interglacial times like today by little or no clastic sedimentation on the continental shelf other than beneath retreated ice shelves lying far from the continental sheld edge ice streams carve broad depressions across the shelf and carry abundant basal sediments directly to the continental shelf edge thereby creating troughmouth fans and sheet like prograding sequences i e type ia sequences numerous acoustic unconformities and multiple overcompacted layers within the prograding sequences suggest major fluctuations of the antarctic ice sheet the available drilling and seismic interpretations provide the following history 1 cenozoic ice sheets have existed in places near the continental shelf since middle to late eocene time 2 a grounded antarctic ice sheet first expanded to the continental shelf edge with probable overdeepening of the outer shelf in late eucene to early oligocene time in prydz bay possibly in early miocene time in the ross sea and at least by middle miocene time in the weddell sea 3 the relative amounts of shelf prograding and inferred ice volume variations and related sea level changes have increased since middle to late miocene time in the eastern ross sea prydz bay and possibly weddell sea our analysis is preliminary further acoustic surveys and scientific drilling are needed to resolve the proximal antarctic record of glacio eustatic climatic and tectonic events recorded by the prograding sequences

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

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

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

test of the partial bleach methodology as applied to the infra red stimulated luminescence of an alluvial sediment from the danube abstract a sample of fine grained distal sediment deposited by the river danube in romania was selected for luminescence measurements using infra red diodes for stimulation to obtain the equivalent dose ed a partial bleach approach was applied using a restricted spectrum in an attempt to replicate bleaching conditions underwater the results and those of the thermoluminescence measurements gave an age in agreement with the archaeological evidence suggesting that this sample was well bleached at deposition a more rigorous test was devised using a simulation experiment and the results suggested that the partial bleach method may not be able to date correctly sediments that have had only part of their infra red stimulated luminescence irsl signal removed at deposition additional types of measurement are required to detect incomplete resetting of the irsl signal at deposition

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

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

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