luminescence dating of sediment samples from white paintings rockshelter botswana luminescence dating of sediments from rockshelters is complicated by the possibility of incomplete sunlight bleaching in antiquity and uncertainties in the distribution of radioactivity yet such dating is important for the middle stone age in southern africa where rockshelters provide a large fraction of the known record sufficient bleaching is demonstrated for sediments at white paintings rockshelter in northwest botswana by comparing results from slowly bleaching thermoluminescence signals and rapidly bleaching optically stimulated luminescence radioactive disequilibrium is also shown to be present in these sediments and believed to result from fractionation between 238u and 234u requiring a small correction to the dose rate derived ages are in broad agreement with independent dating evidence and archaeological expectations

infra red stimulated luminescence dating of sands from the cronese basins mojave desert abstract potassium rich feldspars separated from aeolian sands from the east and west cronese basin have been dated by infra red stimulated luminescence sands from shoreline reworked aeolian dune ridges in the west cronese basin suggest that late holocene playa lakes have existed in the basin within the last 2000 years four dates from these ridges suggest that a phase of aeolian deposition and stabilisation occurred 150 250 years ago a date of 250 75 years on a yardang formed from horizontally bedded sand however implies that at least a metre of erosion in the west cronese basin has occurred since that time in response to a dominant southwesterly wind late pleistocene dates ranging from 18 850 to 23 350 years were obtained from an aeolian unit in the east cronese basin giving limiting ages on wavecut shorelines formed in the deposit this aeolian sand appears to have been deposited and stabilised at a similar time to part of the nearby cat dune sand ramp

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

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

uplift deformation and fluid involvement within an active normal fault zone in the gulf of corinth greece the active pisia fault zone is exposed close to the crest of a rotated carbonate fault block that forms part of the southern margin to the gulf of corinth half graben in central greece the crest of the fault block lies above sea level whilst in the hanging wall a marine basin exists as a result the diagenetic and structural characteristics of the fault zone record complex fluid involvement both early phreatic carbonate syn kinematic cements characterized by drusy fabrics baroque dolomites and crack seal textures and late vadose carbonate syn kinematic cements characterized by flowstones containing cave collapse debris exist in the uplifted footwall to the fault downward percolation of vadose meteoric waters and the upwelling of pore waters with elevated temperatures produced the diagenetic features observed within the fault zone the co existence of early phreatic and late vadose cements within the fault zone is related to footwall uplift across the water table and subsequent erosional unroofing the present day elevation of phreatic cements to c 650m above current sea level provides a minimum estimate of footwall uplift along the fault the wider implication is that temporal changes in deformation and fluid flow may typify fault block evolution

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

response of eolian geomorphic systems to minor climate change examples from the southern californian deserts abstract eolian processes and landforms are sensitive to changes in atmospheric parameters and surface conditions that affect sediment supply and mobility the response of eolian geomorphic systems to minor climate change can be examined through process response models based on a combination of relations between short term changes in climatic variables and eolian activity and the geologic and geomorphic record of holocene eolian activity at both time scales eolian activity in southern californian deserts is strongly controlled by variations in precipitation wind energy is not a limiting factor in this region formation of eolian deposits is a product of climatic changes that increase sediment supply from fluvial and lacustrine sources and may therefore be closely tied to periods of channel cutting and geomorphic instability during intervening periods eolian deposits migrate away from sediment source areas and are reworked modified and degraded remobilization of existing dormant dunes is a product of reduced vegetation cover and soil moisture in periods of drier climates the major control on these processes is decadal to annual changes in rainfall that determine vegetation cover and soil moisture content

geodetic constraints to the kinematics of the kapareli fault reactivated during the 1981 gulf of corinth earthquakes abstract comparison of historical and of post seismic triangulation data is used to model vertical crustal movements in the vicinity of the kapareli fault or the alkynonides earthquakes north fault one of the two antithetic normal faults which reactivated during the 1981 gulf of corinth ms 6 7 earthquakes this fault is characterized by a much smaller geomorphological signature than the south or perachora fault of the same seismic sequence analysis of geodetic data on the basis of polynomial filtering and elastic dislocation modelling as well as analysis of structural and coastal change data permits us to conclude that the upper bound in the uncertainty level of most of the available elevation changes is 20 30 cm usually lower than the corresponding dislocation signal in addition the available geodetic data have a systematic pattern and are consistent with structural data for this reason they permit more precise constraints on the geometry and the role of the kapareli fault or the alkyonides earthquakes north fault its total length is estimated about 17 km about 50 longer than its surface trace about 30 40 cm subsidence of its hanging wall as well as at least 15 cm maximum uplift of its footwall is also inferred this new evidence suggests that although in the long term the kapareli fault may represent a rather secondary antithetic fault to the alkyonides earthquakes south perachora fault during the 1981 earthquakes it probably had a more important structural role

luminescence dating of sand ramps in the eastern mojave desert abstract until recently the timing of the movement of sand and accumulation of sand by aeolian processes in the eastern mojave desert has remained the subject of speculation the results of a luminescence dating program involving 78 samples of material from nine sand ramp complexes have enabled recognition of regional and local patterns of sand accumulation in the eastern mojave the study area extends from lake manix in the west to the colorado river in the east the periods of accumulation have been identified on the basis of quartz tl dating and potassium feldspar tl and irsl dating at a regional scale two major depositional phases can be identified 1 late pleistocene 20 30 ka with sequences at hank s mountain balch dale lake and the big marias and 2 late pleistocene early holocene 15 7 ka with sequences at cat dune dale lake iron mountain big marias above palaeosol and at the western end of the study area at soldier mountain 20 7 ka late holocene sequences appear to be much more localized and are confined to the west cronese old dad mountain and balch sand ramps the earliest phases of sand accumulation on the ramps studied immediately predate the formation of pluvial lake mojave ca 24 5 ka the later main phases of accumulation coincide with the existence of lake mojave and the end of accumulation on the majority of the sand ramps immediately post dates the final end of intermittent lake mojave iii 9 7 ka the continuity of sand supply to potential deflation areas is seen as a critical condition for accumulation of material on the sand ramps during the late quaternary in the eastern mojave

the structures stratigraphy and evolution of the gulf of corinth rift greece summary a multichannel seismic and bathymetry survey of the central and eastern gulf of corinth goc greece reveals the offshore fault geometry seismic stratigraphy and basin evolution of one of earths most active continental rift systems active right stepping en echelon north dipping border faults trend ese along the southern gulf margin significantly overlapping along strike the basement offsets of three akrata derveni sithas and xylocastro are linked the faults are biplanar to listric typically intermediate angle 35 in the centre and 45 48 in the east near the surface but decreasing in dip and or intersecting a low or shallow angle 15 20 in the centre and 19 30 in the east curvi planar reflector in the basement major s dipping border faults were active along the northern margin of the central gulf early in the rift history and remain active in the western gulf and in the subsidiary gulf of lechaio but unlike the southern border faults are without major footwall uplift much of the eastern rift has a classic half graben architecture whereas the central rift has a more symmetric w or u shape the narrower and shallower western gulf that transects the 40 km thick crust of the hellenides is associated with a wider distribution of overlapping high angle normal faults that were formerly active on the peloponnesus peninsula the easternmost sector includes the subsidiary gulfs of lechaio and alkyonides with major faults and basement structures trending ne e w and nw the basement faults that control the rift architecture formed early in the rift history with little evidence other than the vrachonisida fault along the northern margin in the marine data for plan view evolution by subsequent fault linkage several have maximum offsets near one end crestal collapse graben formed where the hanging wall has pulled off the steeper onto the shallower downdip segment of the derveni fault the dominant strikes of the corinth rift faults gradually rotate from 090 120 in the basement and early rift to 090 100 in the latest rift reflecting a 10 rotation of the opening direction to the 005 presently measured by gps the sediments include a locally 1 5 km thick early rift section and a late rift section also locally 1 5 km thick that we subdivide into three sequences and correlate with seven 100 ka glacio eustatic cycles the gulf depocentre has deepened through time currently 700 mbsl as subsidence has outpaced sedimentation we measure the minimum total horizontal extension across the central and eastern gulf as varying along strike between 4 and 10 km and estimate full values of 6 11 km the rift evolution is strongly influenced by the inherited basement fabric the regional nnw structural fabric of the hellenic nappes changes orientation to ese in the parnassos terrane facilitating the focused north south extension observed offshore there the basement penetrating faults lose seismic reflectivity above the 4 14 km deep seismogenic zone multiple generations and dips of normal faults some cross cutting accommodate extension beneath the goc including low angle 15 20 interfaces in the basement nappes the thermally cool forearc setting and cross orogen structures unaccompanied by magmatism make this rift a poor analogue and unlikely precursor for metamorphic core complex formation

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

geochemistry of sediments from quaternary sand ramps in the southeastern mojave desert california abstract trace element analyses of sediment from sand ramps in the bristol trough and clark s pass aeolian corridors of the mojave desert california were conducted to determine their depositional history and relation to sources of sediment within sand transport corridors sand ramps are topographically controlled depositional systems consisting of amalgamated accumulations of aeolian fluvial and talus deposits these landforms contain a variety of deposits formed in different environments and are therefore a valuable source of paleoenvironmental information sediments were studied from three sand ramps the iron mountain big maria and dale lake sand ramps and from two sand sheets rice valley and cactus plain cactus plain is located on the eastern side of the colorado river in arizona but previous researchers have suggested that it is related to the corridors of the western california side geochemical data from units within individual sand ramps indicate that sources for each sand ramp changed through time probably as sediment availability from different local fluvial playa systems changed in response to climate fluctuations analyses also indicate that each sand ramp is composed of sediment from discrete local sources sand deposits in the bristol trough are not integrated and thus the corridor does not act as a coherent sand transport pathway comparisons of sand from cactus plain and sediment from the bristol trough and clark s pass corridors indicates that the cactus plain sand on the east side of the colorado river was not derived from sources on the west side of the river

luminescence dating of mojave desert sands abstract infra red stimulated luminescence has been used to date periods of sand deposition in the mojave desert california dates from the cronese basins kelso dunes and silver lake are compared with published irsl ages to provide evidence for discrete pulses of sand accretion during the late pleistocene and holocene linked to both arid and pluvial climates a critical factor in aeolian deposition throughout this area is shown to be the availability of sand from existing source areas

why large earthquakes do not nucleate at shallow depths although by definition tectonic earthquakes may nucleate anywhere within the seismogenic layer in almost all cases those earthquakes that become large nucleate near the base of the seismogenic layer because frictional strength and stress drop should increase with depth and in situ stress measurements suggest that the ambient stress increases with depth we have examined spontaneous rupture models with gradients of both average stress drop and average strength relative to ambient stress to determine whether this explains the observed phenomena we report here that ruptures that are nucleated with in the low stress drop shallow regions of the model are inhibited from propagating but those that are nucleated within the high stress drop regions can propagate over the entire fault plane

infra red stimulated luminescence ages from aeolian sand and alluvial fan deposits from the eastern mojave desert california abstract infra red stimulated luminescence irsl from coarse grained 180 212 m potassium rich feldspars has been used to date deposits associated with the western piedmont of the providence mountains in the eastern mojave desert these deposits consist of alluvial fans aeolian sand which exists in the form of lenses within the fan matrices and sand from the kelso dune field which abuts the distal end of the fan sequence deposition and subsequent stabilisation of these sand units appears to have occurred in both aird and intermittent climates associated with pluvial phases during the holocene and late pleistocene ages of 6600 870 and 7840 1790 years were obtained from dune sand bracketing the mazama ash at skull creek dunes oregon giving an independent age control on the single aliquot irsl method which was used on the mojave samples

interpretations and common challenges of aeolian records from north american dune fields abstract geomorphic and chronologic data for dune fields are evaluated for three contrasting areas of north america 1 the prairie parkland and boreal ecozones of the northern great plains in canada 2 the central great plains of the usa and 3 the deserts of southwestern usa and northern mexico luminescence and radiocarbon ages for periods of dune accumulation and stability are compared with palaeoenvironment proxies to provide an assessment of the boundary conditions of dune system response to changes in sediment supply availability and mobility dune fields in the northern great plains were formed from sediment originating from glaciofluvial or glaciolacustrine sediments deposited during deglaciation 16 11 ka subsequent aeolian deposition occurred in parkland and prairie dune fields as a result of mid holocene 8 5 ka and late holocene despite spatial and temporal gaps in chronometric data as a result of sampling biases the record from north american dune fields indicates the strong influence of sediment supply on dune construction with changes in sediment availability as a result of drought episodes resulting in dune field reactivation and reworking of pre existing sediment

rupture of the indian slab in the 2011 mw 6 9 sikkim himalaya earthquake and its tectonic implications unlike the other himalayan plate boundary segments the eastern nepal to bhutan himalayan region is not known to have generated prominent shallow thrust faulting earthquakes typical of the ongoing convergence this region features strike slip earthquakes over the depth ranges of 40 120 km indicating intraslab deformation here we present for the first time a slip distribution model for the largest recorded intraslab strike slip earthquake in this region the mw 6 9 sikkim event that occurred on 18 september 2011 relying on kinematic source process modeling our results indicate a ne sw trending steeply dipping sinistral source zone within the underthrusting indian slab the rupture propagated radially with a low rupture velocity of 1 7 km s breaking a large asperity of 20 a 20 km 2 with a maximum slip of 1 6 m the rupture nucleated at a depth of 45 km and reached upper mantle depths the computed coseismic stress drop value is 13 6 mpa we suggest that most of the aftershocks occurred on the conjugate plane possibly due to stress triggering stress inversion of focal mechanisms indicates a transpressive stress regime throughout the crust and pure strike slip regime in the upper mantle we observed a unimodal distribution of earthquakes beneath the higher himalaya this indicates a strong brittle indian slab and unravels a scenario of an eventual breakup of the lithosphere the key trigger might be variation in the convergence rates along the himalayan arc 2019 american geophysical union all rights reserved

dips of normal faults in british coal measures and other sedimentary sequences fault dip measurements n 3291 from 122 faults in british coalfields are presented two classes of normal fault are recognized a gently dipping 55 post coalification tectonic faults formed at depths of about 2 5 km which comprise 90 of the faults analysed dip data from the steeply dipping faults are variable standard deviation 9 both on single faults and between faults and 70 is a better approximation of fault dip than the commonly accepted value of 60 data on tectonic normal faults with comparable depths of formation using the modified griffith fracture criterion the dips of faults at varying depths up to 4 km are calculated for both unsaturated dry and saturated rocks the dips of normal faults are expected to vary from 90 at the surface to 60 at 3 4 km and this variation is consistent with the limited field data available the coalfield data are consistent with fault formation at standard hydrostatic pore fluid pressures at depths of about 2 5 km below depths of a few kilometres normal faults are expected to flatten out gradually to a dip of 45 but such flattening is not necessarily an indication of an underlying detachment

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

eolian sand transport pathways in the southwestern united states importance of the colorado river and local sources geomorphologists have long recognized that eolian sand transport pathways extend over long distances in desert regions along such pathways sediment transport by wind can surmount topographic obstacles and cross major drainages recent studies have suggested that three distinct eolian sand transport pathways exist or once existed in the mojave and sonoran desert regions of the southwestern united states one hypothesized pathway is eolian sand transport from the eastern mojave desert of california into western arizona near parker and would require sand movement across what must have been at least a seasonally dry colorado river valley we tested this hypothesis by mineralogical geochemical and magnetic analyses of eolian sands on both sides of the colorado river as well as sediment from the river itself results indicate that dunes on opposite sides of the colorado river are mineralogically distinct eastern california dunes are feldspar rich whereas western arizona dunes are quartz rich derived from quartz rich colorado river sediments because of historic vegetation changes little new sediment from the colorado river is presently available to supply the parker dunes based on this study and previous work the colorado river is now known to be the source of sand for at least three of the major dune fields of the sonoran desert of western arizona and northern mexico on the other hand locally derived alluvium appears to be a more important source of dune fields in the mojave desert of california although many geomorphologists have stressed the importance of large fluvial systems in the origin of desert dune fields few empirical data actually exist to support this theory the results presented here demonstrate that a major river system in the southwestern united states is a barrier to the migration of some dune fields but essential to the origin of others published by elsevier science ltd

local and regional components of western aegean deformation extracted from 100 years of geodetic displacement measurements summary our objectives are as follows first we wish to develop a methodology to recover the long term component of deformation from any set of distributed time averaged geodetic strain measurements that were subject to seismic disturbance given a catalogue of local seismicity that occurred during the measurement period second using seismic and geodetic data sets that span approximately 100 years we apply this technique in the western aegean to assess the role of local seismicity in regional deformation the methodology is developed using a model for crustal deformation constructed from a long term smooth regional strain field combined with instantaneous local perturbations from upper crustal earthquakes approximated by static elastic dislocations by inverting geodetic displacements for the smooth field while simultaneously floating influential but uncertain earthquake source parameters an estimate of the regional component of deformation that is approximately independent of the seismicity can be made in the western aegean we find that the horizontal component of regional deformation can be described with minor inaccuracy by a quadratic relative displacement field the principal horizontal extensional axes calculated from the regionally smooth displacement field agree in orientation with the t axes of earthquakes in the region these observations indicate that the instantaneous elastic strain of the 10 km thick seismogenic layer is driven by a stress field that is smooth on the scale of the geodetic network as a whole 200 300 km

the seismicity geomorphology and structural evolution of the corinth area of greece in the eastern gulf of corinth geological structure is closely reflected in the topography in the 1981 corinth earthquakes ground deformation accentuated existing geomorphological patterns we explore the relationship between seismicity and landforms in space and time the area examined extends beyond the epicentral region of the 1981 events and its evolution is traced over the last 40000 years to understand the relation between deep and superficial structures we discuss processes that occurred in the 1981 earthquakes and go on to propose that surface faulting appears only above linear faults at depth that move in earthquakes with magnitudes m s greater than six where faults at depth intersect or bend the faulting becomes distributed and prim ary faulting does not reach the surface here the surface manifestation of faulting at depth is surface folding and secondary faulting such regions are identified in maps of the eastern gulf of corinth evidence for the evolution of the fault systems is provided by eyewitness accounts of shoreline changes following the recent earthquakes historical and archaeological data pertaining to old sea levels and 14 c dates for molluscs collected from fossil shorelines the results of these studies broadly confirm an earlier view of j a jackson et al earth planet sci lett 57 377 397 1982 that motion has shifted from faulting south of the city of corinth to faulting in the perachora peninsula but the transfer is not complete areas lying between the two fault systems have moved up and down in historical and archaeological times indicating that both systems are still active the evidence for activity of the northern system points to a repeat time of 300 years for earthquakes com parable with those of 1981 the work discussed in this paper suggests that some of the features previously described as m arine terraces are fault controlled continental surfaces furtherm ore beach deposits at a num ber of different levels long regarded as successive shorelines are in fact contemporaneous the critical ages were obtained by radiocarbon dating of shell carbonate a technique which yields dependable results if applied to samples which have been carefully selected and pretreated palaeontological dating of the terraces in contrast is found to be misleading because the faunas are environm entally controlled and consequently diachronous

source mechanisms of colombia aftershocks using digital surface wave data love and rayleigh wave signals recorded at stations of the global digital seismograph network were used to retrieve focal mechanism information for moderate magnitude mb 5 0 aftershocks that followed the large m s 7 7 colombia earthquake of 12 december 1979 source mechanisms compatible with the observed love rayleigh spectral amplitude ratios were identified following a comparison against theoretical values calculated for a suite of source models p wave first motions observed at worldwide stations were then used to remove ambiguities in the sense of slip and strike orientation for most of the events examined the focal depths of the events were fixed at values determined from depth phase arrival times in the surface wave comparison a reference earthquake with known focal mechanism and depth was used to calibrate the procedure and to minimize the path and size effects aftershocks whose epicenters lie within the asperity region from which most of the moment release originated during the large colombia earthquake denote thrust faulting similar to that of the main shock consistent with occurrence along the interplate zone the few near trench events in the vicinity of the asperity may have resulted from secondary deformation away from the major plane of rupture rather than from a propagation of interplate rupture seaward to the trench axis these near trench aftershocks which are seaward of the region of maximum energy release do not provide strong evidence for seismogenic failure of the plate interface at least one of the events is a normal faulting earthquake that occurred either above the interplate boundary or in the subducting nazca plate source mechanisms computed for aftershocks located northeast of the asperity but within the length of the rupture reported for the main shock are also consistent with interplate slip the aftershock activity observed north of this distance is associated with a separate and perhaps offset segment of the nazca south america plate boundary

on the formation of sand ramps a case study from the mojave desert sand ramps are dune scale sedimentary accumulations found at mountain fronts and consist of a combination of aeolian sands and the deposits of other geomorphological processes associated with hillslope and fluvial activity their complexity and their construction by wind water and mass movement means that sand ramps potentially hold a very rich store of palaeoenvironmental information however before this potential can be realised a full understanding of their formation is necessary this paper aims to provide a better understanding of the principal factors influencing the development of sand ramps it reviews the stratigraphic chronometric and sedimentological evidence relating to the past development of sand ramps focussing particularly on soldier mountain sand ramp in the mojave desert as well as using observations of the modern movement of slope material to elucidate the formation of stone horizons within sand ramps findings show that sand ramps cannot easily be interpreted in terms of a simple model of fluctuating palaeoenvironmental phases from aeolian dominated to soil fluvial dominated episodes they accumulate quickly perhaps in 5 ka probably in a single phase before becoming relict based on the evidence from soldier mountain they appear strongly controlled by a window of opportunity when sediment supply is plentiful and cease to develop when this sediment supply diminishes and or the accommodation space is filled up contemporary observations of stone movement both on rock and sandy sloping surfaces in the mojave region indicate movement rates in the order of 0 6 and 11 mm yr 1 which is insufficiently fast to explain how stone horizons could have been moved across and been incorporated into sand ramps on multiple occasions stone horizons found within the aeolian sediments lack evidence for soil development and are interpreted as very short term events in which small streams moved and splayed discontinuous stone horizons across the sand ramp surface before aeolian deposition resumed surface stone horizons may form by creep from mountain slope sources across sand ramps but require enhanced speed compared to measured rates of runoff creep we propose the mechanism of fluvio aeolian creep our study suggests that current models of alternating aeolian and colluvial deposition within sand ramps their palaeoenvironmental significance and indeed how sand ramps are distinguished from other dune forms require amendment

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

quaternary evolution of the corinth rift and its implications for the late cenozoic evolution of the aegean summary we present geological and morphological observations at different scales to constrain rates of faulting and the distribution of deformation in the seismically active aegean region we focus first on the 130 km long corinth rift an asymmetric graben where a flight of terraces of marine origin are uplifted we show that the edges of the terraces lie in the footwall of the normal fault bounding the corinth rift and correspond to sea level highstands of laic pleistocene age using a detailed analysis of aerial and spot imagery supported by field observations we have mapped 10 terrace platforms and strandlines ranging in elevation from 10 to 400 m over distances of 2 to 20 km from the fault the elevation of the terraces inner edges was estimated at 172 sites with an error of 5m this data set contains a precise description of the uplift and flexure of 10 different palaeohorizontal lines with respect to the present sea level to date the deformation we correlate the corinth terraces with late pleistocene oxygen isotope stages of high sea level stands and with global sea level fluctuations using a thick elastic plate model consistent with our current understanding of the earthquake cycle and a boundary element technique we reproduce the geometry of the shorelines to constrain both mechanical parameters and the slip on the fault we show that the seismogenic layer behaves over the long term as if its elastic modulus were reduced by a factor of about 1000 all the terraces are fitted for fault slip increasing in proportion to terrace age and the component of regional uplift is found to be less than 0 3 mm yr 1 the best fits give a slip rate of 11 3 mm yr 1 on the main rift bounding fault over the last 350 kyr other geological and morphologic information allows us to estimate the total age of the main fault 1 ma and to examine the mechanical evolution of the corinth rift the minimum observed sediment thickness in the gulf places an extreme check on the results of the modelling and a lower bound on slip rate of 6 7 mm yr 1 40 per cent less than estimated with modelling even this slip rate is nearly 10 times higher than for comparable features in most of the aegean and elsewhere in the world at a larger scale the spacing and asymmetry of the rift systems in the aegean suggest strain localization in the upper mantle with slow extension starting 15 myr ago or earlier the more recent 1 myr rapid phase of rifting in corinth partly reactivated this earlier phase of extension the younger faulting in corinth appears to result from its present location in the inhomogeneous stress field process zone of the south westward propagating tip of the southern branch of the north anatolian fault we extend these relations to propose a mechanical model for the late cenozoic evolution of the aegean as the arabia europe collision progressed in eastern turkey it caused anatolia to move to the west and the north anatolian fault to propagate into the aegean where the early slow extension started to be modified about 5 ma ago the process of propagation dramatically increased the activity of some but not all of the earlier rifts the model we present is compatible with tectonic observations as well as with the seismicity the palaeomagnetic rotations and the displacement field now observed with gps and slr

estimation of arrival times in intense seismic sequences using a master events methodology based on waveform similarity summary intense seismic sequences involve a large number of earthquakes densely clustered in space and time their detailed analysis is important for the geometry of the activated faults which contributes to studies of the seismotectonic characteristics of an area the sheer number of small events as well as their low energy content renders their processing problematic in this work we have developed and applied a methodology to automatically pick the arrival times of p and s waves using a correlation detector event detection is performed using the waveform recordings of a reference station located close to the epicentral area of an intense seismic sequence such as aftershocks or swarms cross correlation matrices are constructed followed by nearest neighbour clustering and the formation of multiplets a master event is chosen from each cluster and its arrival times are picked manually the automatic algorithm uses the p o rs wave of each master event as a correlation detector searches the waveforms of the other events of the same multiplet and imposes the corresponding arrival time when the bestfit is achieved the picks are characterized by observation weights which derive from the quality of thefit the type of the available waveform components and the consistency between multiple measurements the proposed methodology was applied to an important seismic sequence that occurred between 2010 january 18 and 26 near the city of efpalio greece this procedure has the potential to increase 10 fold the amount of information and provide sufficient detail for a subsequent analysis of the spatiotemporal distribution of a seismic series

spatial structures in earthquakes and faults quantifying similarity in simulated stress fields and natural data sets abstract this paper presents an adaptation for fault analysis of the coherence method of kagan and knopoff kagan y y knopoff l 1985b the two point correlation function of the seismic moment tensor geophysical journal of the royal astronomical society 83 637 656 understanding coherence as a measure of the similarity between fault slip data for two faults which can be analytically computed from earthquake or fault moment tensors through the use of a customized gis routine the degree and distribution of similarity in synthetic and natural fault populations can be calculated as a function of distance between fault earthquake pairs and their relative orientation stress simulations using synthetic data sets reveal that fault populations which developed under homogeneous stress fields have a high degree of similarity that increases with the slip tendency of faults stress ratio variations and especially stress axis rotations lower the coherence values spatial analysis of natural earthquake and fault data sets from the umbria marche region northern apennines italy reveals a common pattern of coherence spatial cyclicities in faults earthquakes controlled by two consecutive tectonic phases miocene compression and plio pleistocene extension the proposed interpretation attributes the spatial cyclicities of miocene data to syn to post faulting folding in agreement with wavelengths derived from field data the observed periodicities in earthquakes 1997 colfiorito sellano umbria marche seismic sequence could in turn have been controlled by the miocene thrust structures with possible spatial stress field axis rotations and or stress ratio variations the spatial characteristics of younger fault earthquake populations are thus possibly controlled by the characteristics of older tectonic structures such as fold wavelength or fault spacing

late quaternary stratigraphy and luminescence geochronology of the northeastern mojave desert abstract the chronology of the holocene and late pleistocene deposits of the northeastern mojave desert have been largely obtained using radiocarbon ages our study refines and extends this framework using optically stimulated luminescence osl to date deposits from valjean valley silurian lake playa red pass and california valley of particular interest are eolian fine silts incorporated in ground water discharge gwd deposits bracketed at 185 140 and 20 50 ka alluvial fan deposits proved amenable for osl by dating both eolian sand lenses and reworked eolian sand in a matrix of gravel that occurs within the fan stratigraphy lacustrine sand in spits and bars also yielded acceptable osl ages these osl ages fill gaps in the geochronology of desert deposits which can provide data relevant to understanding the responses of several depositional systems to regional changes in climate this study identifies the most promising deposits for future luminescence dating and suggests that for several regions of the mojave desert sediments from previously undated landforms can be more accurately placed within correct geologic map units

aftershock patterns and main shock faulting we have compared aftershock patterns following several moderate to large earthquakes with the corresponding distributions of coseismic slip obtained from previous analyses of the recorded strong ground motion and teleseismic waveforms well located aftershock hypocenters are projected onto the main shock fault plane and their positions are examined relative to the zones of coseismic displacement indicated by the estimated distributions of main shock slip we also examine the aftershock focal mechanisms when these data are available in an attempt to identify possible patterns of secondary faulting within the aftershock zone our results are consistent with a hypothesis of aftershock occurrence that requires a secondary redistribution of stress following primary failure on the earthquake fault aftershocks following the earthquakes examined in this study occur mostly outside of or near the edges of the source areas indicated by the patterns of main shock slip the spatial distribution of aftershocks reflects either a continuation of slip in the outer regions of the areas of maximum coseismic displacement or the activation of subsidiary faults within the volume surrounding the boundaries of main shock rupture

luminescence dating of late quaternary aeolian deposits at dale lake and cronese mountains mojave desert california abstract relict aeolian deposits and landforms that can provide important information on the timing geographical extent and intensity of periods of aeolian sand accumulation are widespread in the mojave desert california the pleistocene part of the record is mostly undated the stratigraphy and sedimentology of sites near dale lake dale lake sand ramp and the cronese mountains cat dune were studied and luminescence dating techniques used to try to establish a chronological framework for the deposits the dating of these sites proved difficult with major disparities between the results of quartz and feldspar thermoluminescence tl dating particularly where the sediments comprised a mixture of aeolian and colluvial meterial however initial results based on quartz tl and feldspar infra red stimulated luminescence dating indicate the existence of two main periods of late pleistocene aeolian deposition between 35 to 25 ka and 15 to 10 ka

coseismic crustal deformation on a fault zone defined by microseismicity in the pavliani area central greece summary pavliani is an area of high microseismicity in northern central greece there is no evidence in the historical record of large damaging earthquakes in this area since at least 600 bc we examine contemporary crustal deformation in this area using microearthquake data recorded during 1983 84 by the volos seismic network principally and to a lesser extent by the patras seismic network the microseismicity 1 4 6 ml defines an approximately vertical fault zone trending wsw ene of 55 km length and 25 km depth the fault plane solution for the 4 6 m earthquake shows a strike consistent with the trend of the microseismicity zone and an extension direction consistent with many large earthquakes in central greece associated with the extensional greater aegean spectra of the microearthquakes are estimated using p waves obtained by selective windowing designed to exclude other p phases from the coda seismic moments in the range 1 95 x 10 n m are obtained accompanied by estimates of seismotectonic source parameters including source radii average stress drop and average coseismic slip of prime utility is an excellent correlation found between seismic moment and magnitude and with coseismic slip this allows heterogeneity in the distribution of individual microearthquake source parameters to be mapped onto the vertical fault zone plane and the history of coseismic deformation for the whole seismicity observed during 1983 84 to be examined using cumulative slip and moment release rate peaks of high moment release rate occur in the east and centre of the fault zone that in the east is dominated by a few large moment release events that in the centre by a large number of small events both moment release rate peaks despite their different component seismicity are associated with high cumulative coseismic slip only the eastern peak is also associated with high stress drop it is also shallower and therefore any surficial interaction is less likely to be attenuated the surface projection of this peak is within 3 km of a mapped normal fault coincident with an alpine thrust front delineated by a major scarp of mesozoic limestone surface evidence of recent movement on this normal fault is only slight friable fault gouge is seen at a few localities displacement could not be determined because the limestone surfaces are deeply weathered and lack kinematic indicators however considering the whole fault zone as a cohesive entity and using a brune estimate of slip at the current moment release rate throughout the present extensional tectonic regime suggests a total vertical displacement of order 175 m similar to the elevation of the scarp

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