late quaternary geological history of the dead sea area israel abstract a 34 5 m borehole which was drilled near the dead sea coast altitude 394 m in the southern part of the fan delta of wadi zeelim reveals the geological history of that area from the latest pleistocene to present the depositional time frame is based on six 14c dates and two u th dates an erosional or nondepositional period is implied by the hiatus between 21 100 yr b p u th age depth 33 m and 11 315 yr b p 14c age depth 32 m a subsequent arid phase is recorded by a 6 5 m thick layer of halite based on 14c dates this phase relates to the abrupt younger dryas cold period reported in temperate to polar regions the fragility of the environment in this region is indicated by the fact that the region experienced such a severe short aridification phase less than 1000 yr evidence of which is found widely in the desert fringes of the middle east and north africa the aragonite found in most of the holocene section indicates that the well site was covered by the lake for most of the holocene exceptions are the intervals at 0 3 and 10 14 m depths which represent low stands of the lake

formation deformation and chertification of systematic clastic dykes in a differentially lithified carbonate multilayer sw iberia algarve basin lower jurassic this work presents original field evidence for tectonically controlled calciclastic dyke injection and subsequent chertification in shelf carbonates during rifting in the south westernmost part of the eurasian continent in the early pliensbachian it is shown by the detailed description of tectonic structures faults and joints stratigraphic discontinuities and by the distribution orientation and morphology of the injected dykes of calciclastic sands into fine grained carbonates that these soft sediment deformation structures were tectonically controlled extensional tectonics developed vertical tensile joints in semi lithified fine grained limestones permitting upward and downward injection of loose calciclastic sands forming clastic dykes the frequency of injection structures along strata was constrained by the thickness of the layer into which the injection was occurring which implies an elastic behaviour however the curvi planar shapes of the dykes and drop like nodules attests the ductile behaviour of the fractured limestones indicating transition from elastic to ductile response to deformation with time the multi layered system consists of just two lithotypes the two display different mechanical behaviours which evolved in time to more brittle conditions as lithification progressed as shown by the cataclastic faulting and jointing of the previously formed soft sediment deformation structures and strata under an analogous stress regime the injection dykes were disrupted by a short lived episode of compression after which tectonic extension resumed still in the lower pliensbachian sometime before the deposition of the upper pliensbachian a pervasive selective event of chertification occurred only the calciclastic sandy layers dykes and nodules were substituted by silica thus enhancing the mechanical contrast between the primary sedimentary structures and the soft sediment deformation structures all the described events occurred during a time interval of approximately 2 myr as constrained by ammonoid stratigraphy

an 8000 year history of landscape climate and copper exploitation in the middle east the wadi faynan and the wadi dana national reserve in southern jordan abstract investigations of geomorphology geoarchaeology pollen palynofacies and charcoal indicate the comparative scales and significance of palaeoenvironmental changes throughout the holocene at the junction between the hyper arid hot wadi arabah desert and the front of the mediterranean belt mountains of edom in southern jordan through a series of climatic changes and episodes of intense mining and smelting of copper ores early holocene alluviation followed the impact of neolithic grazers but climate drove fluvial geomorphic change in the late holocene with a major arid episode corresponding chronologically with the little ice age causing widespread alluviation the harvesting of wood for charcoal may have been sufficiently intense and widespread to affect the capacity of intensively harvested tree species to respond to a period of greater precipitation deduced for the roman byzantine period a property that affects both taphonomic and biogeographical bases for the interpretation of palynological evidence from arid lands with substantial industrial histories studies of palynofacies have provided a record of human and climatic causes of soil erosion and the changing intensity of the use of fire over time the patterns of vegetational climatic change and geomorphic changes are set out for this area for the last 8000 years

the february 11 2004 dead sea earthquake ml 5 2 in jordan and its tectonic implication abstract a moderate sized m w 5 3 earthquake occurred in the dead sea basin on february 11 2004 a rigorous seismological analysis of the main shock and numerous aftershocks suggests that seismogenic structure was a secondary antithetic fault within the dead sea fault system the main shock is well located using all available regional seismic stations and 43 aftershocks were precisely located relative to the main shock using a double difference algorithm the first motion focal mechanism for this earthquake demonstrates nnw sse and ene wsw striking nodal planes and the aftershocks distribution is consistent with the latter indicating a right lateral sense of displacement this orientation and sense of shear are consistent with similarly oriented geological faults around the dead sea basin these structures are likely antithetic faults within the transform system although moderate in size earthquakes that occur very close to the large dead sea fault system warrant consideration in the earthquake hazard assessment of the region for example owing to the proximity to the main fault moderate earthquakes such as this may produce static changes in coulomb stress along the main fault

volcanic biotite sanidine 40ar 39ar age discordances reflect ar partitioning and pre eruption closure in biotite the 40 ar 39 ar radioisotope system is widely used to date eruption and cooling of volcanic tephra marker horizons that commonly provide the only means of correlating and assigning numerical ages to stratigraphy in which they are contained this chronometer bridges the gap between 14 c and longer lived isotopic systems that are too imprecise for dating young samples however 40 ar 39 ar ages obtained from coevally erupted biotite and sanidine do not always match here we use an independent chronometer 238 u 230 th disequilibrium to demonstrate that 40 ar 39 ar age disparity is not caused by differences in pre eruption crystallization times our findings indicate that the presence of extraneous 40 ar in biotite and its absence in sanidine may result from violations of two assumptions implicit in 40 ar 39 ar geochronology on volcanic samples 1 prior to eruption minerals are devoid of 40 ar due to rapid loss to an infinite reservoir such as the atmosphere and 2 closure to volume diffusion is geologically instantaneous and coincident with eruption we propose a mechanism whereby the presence of extraneous ar in certain minerals is explained by the relative sequence of four events in a magmatic system 1 crystallization 2 mineral closure with respect to ar diffusion 3 isotopic equilibration of magmatic and atmospheric ar and 4 quenching of the system by eruption these data have potentially far reaching implications for studies that depend on geochronological data necessitating re evaluation of interpretations based solely on biotite with no independent age control particularly in young samples where the effects are most pronounced

interpreting soft sediment deformation and mass transport deposits as seismites in the dead sea depocenter we have studied the history of earthquakes over the past 70 kyr by analyzing disturbed sedimentary layers around the margins of the dead sea however we know little about disturbances in the basin depocenter where water depth is 300 m and accessible only by drilling in this study we compare disturbances from the dead sea depocenter with the contemporaneous earthquake record 56 30 ka that was recovered on the western margin of the lake this comparison allows us to discern the characteristics of disturbance in the different subaqueous environments and identify the source and sedimentary process of mass transport deposits our observations indicate that i the long disturbance sequences in the dead sea depocenter are composed of in situ deformation slump and chaotic deposits ii earthquake triggered kelvin helmholtz instability is a plausible mechanism for the in situ deformation in the lake center iii the slump is slope area sourced iv the unit of chaotic deposits is lakeshore sourced and v earthquake triggered slope instability is a viable mechanism for the slump and chaotic deposits we further suggest that long sequences of disturbance in seismically active lake depocenters can be used to infer earthquake clusters

palynology sedimentology and palaeoecology of the late holocene dead sea abstract palynological and sedimentological studies were performed at two holocene profiles in erosion gullies ze elim and ein feshkha which dissect the retreating western shore of the dead sea the aim of the project was to analyse possible links between climate lithology and vegetation development the section in ze elim shows both lacustrine and fluvial sediments whereas sedimentation at ein feshkha is predominantly lacustrine the ze elim profile previously used for paleo lake reconstruction provides an opportunity to compare climate triggered lake levels as paleo hydrological indicators and vegetation history by use of palynology the vegetation development in ze elim and ein feshkha is influenced by both climate and human impact the pollen record of ze elim begins in the pottery neolithic the section of ein feshkha in the late bronze age both records end in the middle ages the ze elim section is characterized by sedimentary hiati between the beginning of the chalcolithic period until the middle bronze age and within the late bronze age settlement periods during the middle bronze age iron age and hellenistic roman byzantine period are indicated by high values of anthropogenic indicators and or mediterranean trees collapses of agriculture which can be related to climate effects are evident during the late bronze age during the iron age and at the end of the byzantine period when the lake level curve indicates arid conditions a comparison of the two pollen records from different environments illustrates a more prominent influence of mediterranean vegetation and cultivated plants in the pollen diagram of ein feshkha the southern dead sea region at the desert fringe is more vulnerable to regional climate change

modeling of seismic guided waves at the dead sea transform 1 on several recordings of linear seismometer arrays crossing the arava fault af in the middle east we see prominent wave trains emerging from in fault explosions which we interpret as waves being guided by a fault zone related low velocity layer the af is located in the arava valley and is considered the principal active fault of the mainly n s striking dead sea transform system in this section observations of these wave trains are confined to certain segments of the receiver lines and occur only for particular shot locations they exhibit large amplitudes and are almost monochromatic we model them by a two dimensional 2 d analytical solution for the scalar wave field in models with a vertical waveguide embedded in two quarter spaces a hybrid search scheme combining genetic algorithm and a local random search is employed to explore the multimodal parameter space resolution is investigated by synthetic tests the observations are adequately fit by models with a narrow only 3 12 m wide waveguide with s wave velocity reduced by 10 60 of the surrounding rock we relate this vertical low velocity layer with the damage zone of the af since the location of receivers observing and of shots generating the guided waves respectively match with the surface trace of the fault the thickness of the damage zone of the af at least at shallow depths seems to be much smaller than in other major fault zones this could be due to less total slip on this fault

earthquake magnitude frequency epicentral distance and soft sediment deformation in sedimentary basins abstract empirical equations available for earthquake magnitude frequency and the maximum epicentral distance of liquefied sites versus magnitude are combined with the characteristic instantaneous sediment deposition rate at a station in a sedimentary basin to form a model for the local stratigraphic frequency of earthquake induced soft sediment deformation structures both the style of sedimentation and the characteristics of the earthquake source combine to determine the pattern of incidence of the structures in a basin the model is probably most directly applicable to the geodynamic interpretation of fluvial basins in which substantial volumes of readily liquefied sands accumulate at high local short term rates

earthquake triggered soft sediment deformation structures seismites in travertine deposits abstract earthquakes related soft sediment deformations seismites are relevant structures to help reconstructing the palaeoseismicity in a region nevertheless although seismites have been described for a large variety of palaeo environments and stratigraphic settings they are rare and in some cases ambiguous structures in this paper we document for the first time impressive seismites affecting a latest quaternary travertine deposit located in southern tuscany serre di rapolano italy these structures are extremely relevant as seismites have been never described for this kind of terrestrial deposits the seismites developed within a 2 5 m thick stratigraphic succession made of alternating terrigenous and carbonate sediments embedded within the travertine deposits earthquake produced liquefaction and fluidization of some terrigenous levels and the injection of fluidized silty sediments dykes and sills into carbonate and terrigenous levels slumped levels and associated decollement surfaces produced highly non cylindrical folds overall induced by the loss of brittle shear strength along the basin slopes the occurrence of these soft sediment deformations implies an important seismic event that took place in a time spam encompassed between 84 8 and 48 92 5 08 ka in an area characterized by low seismicity and scarce knowledge of its seismotectonic setting their spectacular exposition and preservation in saw cuts of an abandoned quarry cava oliviera quarry highlights their relevance and importance

el ventorrillo a paleostructure of popocatepetl volcano insights from geochronology and geochemistry volcan popocatepetl mexico was constructed over the remains of a volcanic paleostructure based on fieldwork 40ar 39ar dating u pb dating and geochemistry we have determined the age chemistry and location of this paleostructure and named it el ventorrillo most remnants of el ventorrillo are covered by deposits from subsequent activity of popocatepetl except for the el abanico scarp and the barranca de nexpayantla where the stratigraphy of el ventorrillo eruptive products can be investigated inception of volcanism at el ventorrillo occurred at 331 10 ka with emission of the nexpayantla andesitic lavas and continued with extrusion of the yoloxochitl 267 31 ka and microwave 227 6 ka domes intrusion of dikes occurred at 298 94 and 230 3 ka activity at el ventorrillo continued with the emission of lavas that built the el abanico scarp 193 29 to 96 8 ka and continued until the tutti frutti eruption destroyed the cone 14 1 kyr ago el ventorrillo magmas produced rocks divided into two mineralogical groups the first group contains biotite amphibole rich rocks and the second group consists of biotite amphibole free lavas the rocks that contain biotite and amphibole are older than 198 13 ka whereas the rocks with no hydrous phases are younger than 227 6 ka and contain skarn and granodiorite xenoliths we interpret the change to an anhydrous mineral assemblage and the occurrence of skarn and granodiorite xenoliths as evidence for the formation of a new shallower reservoir a granodiorite xenolith was chosen for 40ar 39ar dating and u pb zircon analyses the u pb method yielded an age of 540 110 ka and the 40ar 39ar an age of 109 24 ka these ages are interpreted to indicate granodiorite crystallization 540 110 ka which metamorphosed the calcareous basement beneath popocatepetl into skarn and an influx of magma 109 24 ka that reheated the granodiorite major and trace elements sr nd and pb isotopic compositions and textural analyses of plagioclase show that el ventorrillo magmas were moderately modified by mixing with more mafic magmas and that assimilation of the calcareous basement was negligible

accuracy of post bomb 137cs and 14c in dating fluvial deposits abstract the accuracy and precision of 137cs and 14c for dating post 1950 alluvial deposits were evaluated for deposits from known floods on two rivers in arizona the presence of 137cs reliably indicates that deposition occurred after intensive above ground nuclear testing was initiated around 1950 there was a positive correlation between the measured level of 137cs activity and the clay content of the sediments although 137cs was detected even in sandy flood sediments with low clay content 137cs is a valuable dating tool in arid environments where organic materials for 14c or tree ring dating are scarce and observational records are limited the 14c activity measured in different types of fine organic detritus yielded dates within 1 to 8 yr of a 1980 flood deposit and the accuracy was species dependent however undifferentiated mixtures of fine organic materials from several post bomb deposits of various ages repeatedly yielded dates between 1958 and 1962 and detrital charcoal yielded a date range of 1676 1939 in semiarid environments the residence time of most types of organic debris precludes accurate annual resolution of post bomb 14c dates

holocene faulting and earthquake recurrence along the serghaya branch of the dead sea fault system in syria and lebanon an edited version of this paper was published in geophysical journal international by blackwell publishing blackwell publishing retains the copyright copyright 2003 blackwell publishing see also http www blackwell synergy com doi abs 10 1046 j 1365 246x 2003 01933 x http atlas geo cornell edu deadsea publications gomez2003 gji htm

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

the structure of the dead sea basin abstract the dead sea basin is located along the left lateral transform boundary between the arabian and sinai plates its structure and history are known from surface geology drilling seismic reflection and other geophysical data the basin comprises a large pull apart almost 150 km long and mostly 8 10 km wide which is flanked by a few kilometres wide zones of normal faulting the basin formed at about 15 ma or earlier close to the beginning of the transform motion and it reached about half its present length before the end of the miocene a strong negative gravity anomaly records a thick sediment basin fill 5 km under half its length reaching a maximum of 10 km the fill includes a few km of salt ca 6 4 ma which forms several diapirs at any one time large parts of the basin subsided simultaneously but the site of fastest subsidence seems to have shifted northward sedimentation rates reached at least hundreds of metres per million years or more in the miocene and 1 km myr in later periods the basin structure is dominated by longitudinal faults intrabasinal faults which delimit the pull apart and which are the extensions of the major strike slip faults north and south of the basin and normal faults which extend along the basin margins the latter faults express a small component of extension across the basin whereas the pull apart resulted from the much larger lateral motion along the basin in addition transverse faults divide the pull apart into several segments with somewhat different histories the pull apart grew by becoming longer parallel to the transform motion at shallow levels this was probably achieved by normal slip on transverse listric faults while the fill between them was little deformed the crust under the basin was stretched and thinned during basin lengthening which caused its subsidence basin formation was accompanied by uplifting of its flanks by 1 km sparse igneous activity occurred along the basin and its flanks its presence suggests a thermal anomaly in the lower lithosphere beneath the basin and adjacent parts of the transform

soft sediment deformation within seismogenic slumps of the dead sea basin abstract the late pleistocene lisan formation preserved next to the dead sea provides exceptional 3 d exposures of folds and faults generated during soft sediment slumping and deformation it is possible to generate a range of four different scenarios associated with overprinting in a single slump event the progressive evolution of slump systems may be broadly categorised into initiation translation cessation relaxation and compaction phases thrust packages typically define piggyback sequences during slump translation with back steepening of imbricate faults leading to collapse of folds back up the regional palaeoslope detailed evaluation of slumped horizons may also permit structures to be traced across apparently separate and distinct slumped units the recognition that slumps may be reworked by younger seismically triggered events suggests that in some cases the seismic recurrence interval may be shorter than previously anticipated

internal structure of the dead sea leaky transform rift in relation to plate kinematics abstract the structures along the dead sea transform rift are related to the motions of the sinai and arabia plates which border it and to the irregularities of their boundaries the total slip was 105 km left lateral but the present structures were formed mainly during the last 40 km of slip which probably occurred in the plio pleistocene along the southern half of the transform the strike slip motion takes place on en echelon faults this produces rhomb shaped grabens or pull aparts which are sometimes composite and in which there is local crustal separation thus much of the transform is leaky these structures occur in a morpho tectonic rift valley delimited by normal faults which express a small component of transverse extension along a few segments the shape of the transform is such that lateral motion produces local transverse compression the geometric relations of the structures along the transform define an eulerian pole of relative plate motions at 32 8 n 22 6 e 0 5 the older motion was somewhat different and is described by a pole located about 5 west of the above then the component of transverse extension and crustal separation was much smaller than now while local transverse compression was more important the northern half of the dead sea transform has an irregular shape and the bordering plates did not remain rigid as lateral motion continued here transverse compression is often important

using palynology to re assess the dead sea laminated sediments indeed varves lacustrine laminated sediments are often varves representing annual rhythmic deposition the dead sea high stand laminated sections consist of mm scale alternating detrital and authigenic aragonite laminae previous studies assumed these laminae were varves deposited seasonally however this assumption has never been robustly validated here we report an examination of the seasonal deposition of detrital aragonite couplets from two well known late holocene laminated sections at the ze elim fan delta using palynology and grain size distribution analyses these analyses are complemented by the study of contemporary flash flood samples and multivariate statistical analysis because transport affects the pollen preservation state well preserved mostly air borne transported pollen was analysed separately from badly preserved pollen and fungal spores which are more indicative of water transport and reworking from soils our results indicate that i both detrital and aragonite laminae were deposited during the rainy season ii aragonite laminae have significantly lower reworked and fungal spore concentrations than detrital and flash flood samples and iii detrital laminae are composed of recycling of local and distal sources with coarser particles that were initially deposited in the dead sea watershed and later transported via run off to the lake this is in line with previous carbon balance studies that showed that aragonite precipitation occurs after the massive input of tco2 associated with run off episodes consequently at least for the holocene ze elim formation laminated sediments cannot be considered as varves older quaternary laminated sequences should be re evaluated

seismically triggered soft sediment deformation structures close to a major strike slip fault system in the eastern alps hirlatz cave austria abstract we investigate episodic soft sediment deformation structures cross cut by normal faults preserved in unlithified finely laminated calcite rich sediments in the hirlatz cave in the northern calcareous alps austria these sediments comprise varve like alternations of brighter carbonate quartz rich layers and darker clay mineral rich layers the deformed sediments contain abundant millimeter to centimeter scale soft sediment structures load casts ball and pillow structures sheet slumps thrust faults and folds erosive channels filled with slides and chaotic slumps after deposition and soft sediment deformation normal faults developed within the entire sedimentary succession an event that probably correlates with an offset of c 10 cm of the passage wall above the outcrop our major conclusions are i the sediments have a glacial origin and were deposited in the hirlatz cave under phreatic fluvio lacustrine conditions the deposition and the soft sediment deformation occurred most likely during the last glaciation i e around 25 ka ago ii the liquefaction and formation of the soft sediment structures in water saturated stratified layers was triggered by episodic seismic events iii the internally deformed sediments were later displaced by normal faults iv a possible source for the seismic events is the active sinistral salzach ennstal mariazeller puchberger semp strike slip fault which is located about 10 km south of the outcrop and plays a major role in accommodating the extrusion of the eastern alps towards the pannonian basin to our knowledge the described structures are the first report of liquefaction and seismically induced soft sediment deformations in quaternary sediments in the eastern alps

revised chronostratigraphy of the kenai group from 40ar 39ar dating of low potassium bearing minerals cook inlet basin alaska thirty seven tephra beds primarily from coal partings in the sterling and beluga formations were successfully dated by the 40ar 39ar method providing a new and revised understanding of the chronostratigraphy of late tertiary strata within cook inlet basin meticulous sample preparation multiple analyses and statistical evaluation of the data were required for these low k plagioclase and hornblende bearing tephras dating of subsurface core material provides the first subsurface to outcrop tie in cook inlet between well 212 24 in the beluga river unit and deposits in the clam gulch diamond creek and fox creek areas the new 40ar 39ar chronostratigraphic framework place the age of upper part of the kenai group strata between 4 6 and 9 4 ma and support the 8 ma interpretation of the boundary between the homerian and clamgulchian paleobotanical stages the 49 ma age from core data in pioneer unit suggests the tyonek formation is older than previously thought or that these units belong to an older form

episodic behavior of the jordan valley section of the dead sea fault inferred from a 14 ka long integrated catalog of large earthquakes the continuous record of large surface rupturing earthquakes along the dead sea fault brings unprecedented insights for paleoseismic and archaeoseismic research in most recent studies paleoseismic trenching documents the late holocene faulting activity while tectonic geomorphology addresses the long term behavior 10 ka with a tendency to smooth the effect of individual earthquake rupture events m w 7 here we combine historical archaeological and paleoseismic investigations to build a consolidated catalog of destructive surface rupturing earthquakes for the last 14 ka along the left lateral jordan valley fault segment the 120 km long fault segment limited to the north and the south by major pull apart basins the hula and the dead sea respectively is mapped in detail and shows five subsegments with narrow stepovers width 3 km we conducted quantitative geomorphology along the fault measured more than 20 offset drainages excavated four trenches at two sites and investigated archaeological sites with seismic damage in the jordan valley our results in paleoseismic trenching with 28 radiocarbon datings and the archaeoseismology at tell saydiyeh supplemented with a rich historical seismic record document 12 surface rupturing events along the fault segment with a mean interval of 1160 yr and an average 5 mm yr slip rate for the last 25 ka the most complete part of the catalog indicates recurrence intervals that vary from 280 yr to 1500 yr with a median value of 790 yr and suggests an episodic behavior for the jordan valley fault our study allows a better constraint of the seismic cycle and related short term variations late holocene versus long term behavior holocene and late pleistocene of a major continental transform fault

high resolution geological record of historic earthquakes in the dead sea basin a 2000 year paleoseismic record of the dead sea area was recovered from a lacustrine sedimentary section the section is being exposed at the ze elim terrace on the shores of the dead sea due to the fast retreat of the lake the section consists of laminated detrital and chemical mainly aragonite sediments that were deposited in the holocene paleo dead sea eight layers in the section show deformed sedimentary structures and are identified as seismites their chronology was determined by radiocarbon dating on organic remains the seismite ages are well correlated with the historically documented earthquakes of 64 and 31 b c and 33 363 1212 1293 1834 and 1927 a d the few historically documented earthquakes that have no correlatives in the ze elim seismite record occurred in times of sedimentary hiatuses at this site e g 749 a d based on modern analogues and the association of similar disturbed layers with syndepositional faults the ze elim terrace seismites indicate m 5 5 earthquakes the average recurrence interval is estimated as 100 300 years and represents slip events on different faults in the dead sea area the ze elim section provides a unique opportunity to correlate two independent and extensive data sets the historical and sedimentary records this study opens the way for better understanding of spatial and temporal distribution of earthquakes along the dead sea transform and elsewhere

the nature of the 660 kilometer upper mantle seismic discontinuity from precursors to the pp phase global seismic network data were used to image upper mantle seismic discontinuities stacks of phases that precede the pp phase thought to be underside reflections from the upper mantle discontinuities at depths of 410 and 660 kilometers show that the reflection from 410 kilometers is present but the reflection from 660 kilometers is not observed a continuous lame s constant lambda and seismic parameter at the 660 kilometer discontinuity explain the missing underside p reflections and lead to a p wave velocity jump of only 2 percent whereas the s wave velocity and density remain unchanged with respect to previous global models the model deemphasizes the role of lame s constant lambda with regard to the shear modulus and constrains the mineralogical composition across the discontinuity

seismic behaviour of the dead sea fault along araba valley jordan the dead sea fault zone is a major left lateral strike slip fault south of the dead sea basin the wadi araba fault extends over 160 km to the gulf of aqaba the dead sea fault zone is known to have produced several relatively large historical earthquakes however the historical events are unequally distributed along the fault and only four events have been reported in the araba valley over the last few thousands of years magnitudes estimated from the historical record are probably slightly smaller than that of the m w 7 3 earthquake that struck the gulf of aqaba in 1995 the fault cuts straight across pleistocene to holocene alluvium and shows morphologic evidence for essentially pure strike slip motion regional seismic monitoring reveals little microseismicity along the fault except around the dead sea and gulf of aqaba where the fault splays into complex pull apart basin fault systems we have investigated the fault zone at several sites selected from spot images and the study of aerial photography at the site of the now destroyed tilah castle a well preserved wall dated to be about 1200 yr bp 14 c age on charcoal is cut by the fault and offset by 2 2 m comparison with offset gullies at a nearby site 3 km to the north and at three other sites respectively 25 50 and 65 km to the south reveals that this specific fault displacement is probably related to the last seismic event that ruptured that fault segment possibly in ad 1458 moreover the offset gullies suggest a characteristic slip behaviour with recurring slip of about 1 5 m on average given the 4 2 mm yr 1 slip rate derived for this fault segment we infer that the fault should produce m w 7 earthquakes along some segment in the araba valley about every 200 years the historical period with only four well documented large earthquakes in ad 1068 ad 1212 ad 1293 and ad 1458 thus appears to have been relatively quiescent with a 20 per cent deficit of m w 7 earthquakes however our data do not exclude the possibility of larger m w 7 6 earthquakes or time clustering of earthquakes over longer timespans an alternative seismic behaviour involves m w 7 6 earthquakes about every 6000 years and m w 7 earthquakes about every 250 years the historical catalogue would then appear to be complete for m w 7 earthquakes

tropical daytime lower d region dependence on sunspot number 1 observed phases and amplitudes of vlf radio signals propagating on near tropical all sea paths both short 300 km and long 10 mm are used to find daytime parameter changes for the lowest edge of the d region of the earth s ionosphere as the solar cycle advanced from a very low sunspot number of 5 up to 60 in the period 2009 2011 the vlf phases relative to gps 1 s pulses and amplitudes were measured 100 km from the transmitter where the direct ground wave is very dominant 300 km from the transmitter near where the ionospherically reflected waves form a modal minimum with the ground wave and 10 mm away where the lowest order waveguide mode is fully dominant most of the signals came from the 19 8 khz 1 mw transmitter nwc north west cape australia propagating ene mainly over the sea to the vicinity of karratha and dampier on the nw coast of australia and then on to kauai hawaii 10 6 mm from nwc observations from the 8 1 mm path npm 21 4 khz hawaii to dunedin nz are also used the sunspot number increase from 5 to 60 was found to coincide with a decrease in the height h of the midday tropical ionosphere by 0 75 0 25 km from h 70 5 km to h 69 7 km while the sharpness increased by 0 025 0 01 km 1 from 0 47 km 1 to 0 49 km 1 where h and are the traditional height and sharpness parameters used by wait and by the u s navy in their earth ionosphere vlf radio waveguide programs

petrologic diversity in mount st helens dacites during the last 4 000 years implications for magma mixing mount st helens has explosively erupted dacitic magma discontinuously over the last 40 000 years and detailed stratigraphic data are available for the past 4 000 years during this last time period the major element composition of the dacites has ranged from mafic 62 64 wt sio2 to felsic 65 67 wt sio2 temperature has varied by about 150 c 770 920 c and crystallinity has ranged between 20 and 55 water content of these dacites has also fluctuated greatly although the source for the dacitic magmas is probably partial melting of lower crustal rocks there is strong physical evidence such as banded pumices thermal heterogeneities in single pumices phenocryst disequilibrium contrasts between compositions of glass inclusions and host matrix glass and amphibole reaction rims that suggests that magma mixing has been prominent in the dacitic reservoir indeed we suggest that the variations in major and trace element abundances in mount st helens dacites indicate that magma mixing between felsic dacite and mafic magma has controlled the petrologic diversity of the dacitic magmas magma mixing has also controlled the composition of andesites erupted at mount st helens and thus it appears that the continuum of magmatic composition erupted at the volcano is controlled by mixing between felsic dacite or possibly rhyodacite and basalt the flux of the felsic endmember to the reservior appears to have been relatively constant whereas the flux of basalt may have increased in the past 4 000 years as suggested by the apparently increased abundance of mafic dacite and andesite erupted in this period

inherited argon in a pleistocene andesite lava 40ar 39ar incremental heating and laser fusion analyses of plagioclase by using 40 ar 39 ar incremental heating and laser fusion techniques xenocrystic plagioclase was discovered in a late pleistocene andesitic lava that erupted through the andean cordillera inherited argon in the xenocrysts is as much as 450 times older than the host lava the age of which is independently known and is an obstacle to dating the lava by using a whole rock sample the xenocrysts are impossible to identify from petrography or chemical parameters such as their k ca ratios holocrystalline groundmass carefully separated from plagioclase and other phenocrysts gives an accurate 40 ar 39 ar age for the lava the xenocrysts could not have been degassed for more than several days in the magma and probably were assimilated from paleozoic rocks buried under kilometers of mesozoic and tertiary arc rocks composing the cordillera in central chile the required magma ascent velocity on the order of kilometers day is extraordinarily high compared to the 10 4 km day minimum implied by the 226 ra excess in continental arc lavas these data permit magma migration and storage in the mantle and lower crust for as much as thousands of years followed abruptly by rapid ascent to the surface

micropaleontological and taphonomic characteristics of mass transport deposits in the northern gulf of eilat aqaba red sea abstract submarine mass transport deposits mtds are a well known phenomenon in tectonically active regions evidence for such deposits is commonly found in the continental slope sedimentary records as distinct units with coarser grain size compared to the usual and continuous pelagic sedimentation the gulf of eilat aqaba is located between the southernmost end of the dead sea transform and the spreading center of the red sea and is considered as an active tectonic region in this study an innovative approach using symbiont bearing larger benthic foraminifera lbf to identify mtds in the gulf of eilat aqaba gea sedimentary record is presented the abundance size and preservation state of lbf shells were analyzed in two radiocarbon dated sediment cores collected at different deposition environments at water depth of 532 m and 316 m the microfaunal and taphonomic results show that the coarse units are characterized by a generally higher numerical abundance of lbf dominated by operculina ammonoides amphistegina papillosa and amphistegina bicirculata these benthic assemblages are found in deeper depths than their original habitat ranging between 50 and 120 m in accordance with their symbionts light requirements in the coarse units lbf 1 mm appear in high frequency up to 161 specimens per g sediment and poorly preserved shells are also abundant containing up to 247 specimens per g sediment in addition these units also contain high numbers of yellowish and blackish colored lbf shells as opposed to null in the non disturbed units and unlike their natural white color the large shell size indicates that high energy is involved in the displacement of the sediments the poor state of preservation also suggests a turbulent flow during transportation which requires a high energy triggering mechanism the color alteration is probably associated with a diagenetic process related to increasing burial time depth also supported by the stratigraphic older ages of the mtds suggesting a long burial before the sediments were displaced in addition according to the dating of the record some units correlate with historical and pre historical earthquakes reinforcing lbf species as a reliable proxy for mass transport events

re examination of crystal ages in recent mount st helens lavas implications for magma reservoir processes u series data for recent mount st helens lavas suggest that crystallization preceded eruption by more than 0 5 ka but are complicated by possible evidence of crystal recycling and or addition of radium to the liquid after crystallization we report new ion and electron microprobe trace and major element data for plagioclase and pyroxene in these recent mount st helens lavas and use these data to reassess 226ra 230th crystal ages by taking into account differences in the partitioning behavior of radium and barium and the effects of impurities in mineral separates revised 226ra 230th model crystallization ages are 2 4 ka for plagioclase with the exception of the 1982 dacite and 0 15 5 7 ka for pyroxene in contrast to previous interpretations no late stage addition of ra to the liquid after precipitation of the minerals is required the variability of ba concentrations measured in plagioclase is too large to be consistent with progressive crystallization from the same liquid or with diffusive re equilibration of xenocrysts with a new host liquid ba heterogeneity limits the residence time of the crystals in a magma at high temperatures and also suggests that in most cases ra th ages have not been significantly modified by ra diffusion into or out of the crystals high 226ra ba in plagioclase in the 1982 dacite relative to the host liquid likely reflects crystallization processes that precluded bulk crystal liquid chemical equilibrium one possibility is that of growth entrapment of surface enrichments during rapid crystallization which could lead to less discrimination between ra and ba than predicted by calculated bulk partition coefficients 226ra 230th crystal ages for the castle creek andesite and basalt that are younger than 230th 238u ages of the same crystals could be explained by mixing of crystals into melts with different 230th 232th ratios by combinations of older and younger crystal growth within the same magma or for the basalt by diffusion of ra into crystals at high magmatic temperatures average plagioclase ages in most of the samples of 2 ka imply that some significant mass fraction of the crystals in each flow was present simultaneously beneath the volcano this observation could be consistent either with simultaneous storage of physically distinct magma batches or with incorporation of a population of similarly aged crystals into each successive magma batch

soft sediment deformation structures from the diexi paleo dammed lakes in the upper reaches of the minjiang river east tibet abstract the north south trending upper reaches of the minjiang river run along the longmen shan min shan fault zone a zone of abrupt topographic change along the eastern margin of the tibetan plateau multiple levels of well preserved soft sediment deformation structures seismites occur in sediments deposited in paleo dammed lakes in the upper part of the minjiang river valley these deformation structures include liquefied convolute deformation water escape structures flame structures pseudonodules ball and pillow structures sedimentary dykes mud lenses and large scale folds several kilometers from the barrier bar of the diexi paleo dammed lakes seven deformed structural layers were identified at different heights in late quaternary stratigraphic sequences near shawan village maoxian county analyses of the deformation structures landforms and the structural environment indicate that these deformation structures were caused by earthquakes slumps and landslides osl optical stimulated luminescence and 14c dating of soft sediment layers from the shawan site indicate that intense earthquakes occurred during the period 25 20 ka b p therefore accurate geological dating of deformed features in dammed lake deposits in high mountains and canyons enables the record of moderate to large magnitude earthquakes to be extended to the late pleistocene holocene upon the eastern tibetan plateau

four thousand years of seismicity along the dead sea rift a study of major earthquake occurrence along the dead sea transform 35 5 36 5 e 27 2 37 5 n during the past four millenia has been attempted geological archaeological biblical historical and seismological evidence were integrated in an effort to quantify the space time distribution of seismicity in the said province the overall earthquake activity in the conterminous near east indicates a stable pattern and appeared to have been stationary over the examined time window about 110 earthquakes in the magnitude range 6 7 ml 8 3 affected the area during the past 2500 years of these 42 originated along the dead sea fault system itself while 68 were imported from the helenic cyprian arcs and the anatolian elburz zagros fault systems these events were responsible for the repeated destruction of many cultural centers in the dead sea region proper the major seismic activity since 2100 b c e before christian era has been confined to the vicinity of its eastern shore with extremal seismicity at its southern tip near the prehistorical site of bab a dara a 31 15 n 35 32 e this may constitute the first solid evidence that the biblical cities of the plain sodom gommorah etc were located there recent studies of earthquake deformations in the lisan deposits near bab a dara a agree with our findings at the present time a magnitude 6 earthquake is pending at the northern edge of the levant rift with its average recurrence interval 83 years exceeded by one standard deviation 32 years

geomorphological response of the lower jordan river basin to active tectonics of the dead sea transform abstract the lower jordan river ljr basin has been shaped on an active tectonic segment of the dead sea transform dst the jordan valley fault jvf which remains relatively unexplored due to its rough terrain conditions hyper arid climate and location along a political border where minefields are common the ability to detect the morphology of the valley surface by remote sensing methods provides an opportunity to follow the complex tectonic structure of the ljr basin and the spatial and temporal geomorphic processes that have shaped the basin since its exposure in the early holocene after the desiccation of lake lisan 14 5 ky bp in this study we use gis analyses and image processing to explore the relation between the geomorphology of the ljr basin and the active tectonics of the jvf the morphometric fluvial parameters of the basin are interpreted in relation to mapped faults geophysical gravity interpolation and seismic data we introduce morphometric gravity relations that show an increasing trend of the morphometric parameters standard deviation std as a function of the gravity anomaly increase which are consistent with stream power formulation studies and seismic measurements our results show that the active tectonics of the jvf is concentrated towards the basin s center and the dead sea fault location and that at the borders of the gravity highs sinuosity slope and width changes together with recent seismic activity all suggest on tectonic uplifting and active faulting in those areas

a critical evaluation of young near zero k ar ages an evaluation of the precision and resolution of the unspiked k ar dating method is presented with particular regard to the statistical significance of ages that are measured near or at the detection limit of the technique near zero historical ages can be measured by the unspiked k ar technique with a precision that is essentially controlled by the precision with which the 40ar 36ar of the sample can be resolved from the present day atmospheric value of 295 5 the best analytical precision on the isotopic ratio is 0 05 1 by this technique which currently limits the lower detection limit of unspiked k ar ages to samples featuring at least 0 14 of radiogenic 40ar the corresponding youngest resolvable k ar age depends on the k content and atmospheric contamination of the sample total fusion analysis of high k refractory minerals like sanidine is not practicable via k ar and the lowest resolvable age for medium k samples more amenable to complete fusion is around 1 5 ka on a single run basis it is argued that near zero age measured with a probability density straddling or narrowing the time origin cannot be handled without accounting for the non negativity constraint imposed by the physical requirement of a positive age the pertinent equations are derived both for the single run case and for the case of independent replicates made on a single sample we show that pooled k ar replicates can theoretically reduce the nominal uncertainty of individual unspiked ages typically 1 5 ka 2 to a value that is close to the smallest 40ar 39ar isochron age uncertainty achievable on sanidine in the 0 2 ka range 0 2 ka 2 however this performance is obtained at the cost of prohibitively large sample statistics n 15 for medium k feldspars datable via k ar coupled with the inability of the k ar approach to obviate the problems of excess fractionated 40ar and or xenocrystic contamination this makes the 40ar 39ar technique the method of choice for dating historical events by the k ar scheme

tree ring evidence for a two year interval between recent prehistoric explosive eruptions of mount st helens distinctive annual ring patterns in trees in a forest stand 10 km east of mount st helens indicate that the volcano9s voluminous layer we tephra was erupted after the a d 1481 growth season late in 1481 or early during 1482 combined with earlier research that established a d 1480 as the date of eruption of the underlying similar layer wn tephra the new tree ring data provide evidence that these two major explosive tephra eruptions about 500 yr ago were separated by about 2 yr during that eruptive sequence a voluminous explosive eruption was therefore followed by more than 1 yr of minor explosive activity before another voluminous eruption occurred this record suggests that mount st helens might produce a second large explosive eruption during its current period of activity examinations of the tephra deposits that correlate with narrowring patterns in trees at mount st helens also demonstrate that distinctive ring patterns can form in trees across a large range of tephra layer thicknesses the examinations also suggest that tephra coarseness interacts with tephra layer thickness in determining the effects that tephra fallout will have upon forest trees

the age of the steens reversal and the columbia river basalt group abstract the columbia river basalt group crbg eruptions have a well defined relative magnetostratigraphy but have not been definitively correlated to the geomagnetic polarity time scale 40 ar 39 ar ages are presented from lavas erupted in the r 0 through n 1 magnetozones of the crbg and in the transition between r 0 and n 0 four ages from transitionally magnetized lava flows at steens mountain catlow peak and poker jim ridge with a weighted mean age 16 58 0 10 ma 1 and the more precise age 16 654 0 025 ma of the normally magnetized oregon canyon tuff at the top of the catlow peak section show that the oldest crbg magnetozone r 0 correlates with the c5cr chron bayesian statistical analysis applied to data from four flows at catlow peak using the mean age of the steens reversal gives a best and preferred age of the steens reversal of 16 73 0 13 0 08 ma 95 confidence depending on the geomagnetic polarity time scale model the eruption rate from n 0 through r 2 0 34 0 45 ma in the middle and the bulk of the crbg emplacement averaged 0 30 0 41 km 3 a and peaked at a rate 1 1 2 to 4 1 2 times higher during r 2

40ar39ar geochronology of rhyolites erupted following collapse of the yellowstone caldera yellowstone plateau volcanic field implications for crustal contamination abstract single crystal laser probe 40 ar 39 ar dating of 133 grains of sanidine and plagioclase has enabled us to resolve the eruption ages of the upper basin member rhyolites the lava flows and related tuffs that erupted within the yellowstone caldera shortly after its collapse 630 ky ago on eruption of the lava creek tuff two lavas and a tuff that erupted from the eastern ring fracture zone yield an eruptive age of 481 8 ka whereas two flows from the western ring fracture zone yield eruptive ages of 516 7 and 198 8 ka most of the units contain old xenocrysts explaining why previous attempts at dating these earliest post caldera units by the conventional k ar method yielded poorly resolved and in some cases anomalous ages the tuff shows the most severe contamination grains from a single pumice lapilli in the tuff show as large an age range as those from bulk vitrophyre indicating that the xenocrysts were incorporated in the magma prior to its near surface explosive fragmentation diffusion calculations indicate that the xenocrysts could not have remained in the magma for more than a few years without degassing and giving ages indistinguishable from the phenocrysts thus the contamination represented by the xenocrysts probably occurred during fracturing and conduit propagation rather than during caldera collapse which took place more than 100 ky earlier the apparent ages of xenocrysts and their compositions as determined by electron microprobe suggest that the eocene absaroka volcanics are the main contaminant with a single xenocryst probably coming from precambrian basement rocks most of the xenocrysts are difficult to distinguish optically or chemically from feldspar phenocrysts illustrating the necessity of single crystal to date many young volcanic rocks accurately

effects of strong seismic shaking in lake sediments and earthquake recurrence interval temiscaming quebec the magnitude 6 3 timiskaming earthquake of 1935 resulted in discoloration in small lakes in the epicentral region sonar profiles for lac tee have shown that organic rich gyttja has been removed from the sides and redeposited in the deep parts of the lake lake sediment cores from deep basins contain a 2 3 cm uppermost layer which is interpreted as the normal accumulation of sediment since 1935 this is followed by a 20 cm chaotic zone of black gyttja mixed with partly tabular fragments of a previously formed silt layer underlain by a dense 1 2 cm thick silt horizon the latter is interpreted as having formed by rapid settling of the denser silicate portion of the resuspended sediment this 20 cm zone is insufficient to account for the abnormal thickness of gyttja in the basins so events of this kind would have had to have occurred repeatedly since deglaciation the only major prehistoric event revealed by these 100 cm cores is at a depth equivalent to about 1500 years ago based on the amount of sed

holocene earthquakes inferred from a fan delta sequence in the dead sea graben abstract the holocene sequence of the fan delta of nahal darga in israel records deformation associated with earthquakes related to the dead sea transform in general and to the jericho fault in particular the fan delta sequence is well exposed and 20 radiocarbon ages help to date the earthquakes that are inferred from a displacement along faults b liquefaction features associated with 11 separate sandy and silty layers and c slumped allocthonous bodies of sediments located directly above one of the main splays of the jericho fault on average an earthquake larger than m 5 5 has occurred approximately every 600 years this estimate is based on the earthquake record of the complete stratigraphic sequence with erosional hiatuses omitted from the calculations the most recently deformed layer is related to the 1927 jericho m l 6 2 earthquake this layer provides a modern analog for the style of soft sediment deformation associated with earthquakes in the late pleistocene and holocene silty sand beds of the fan delta complexes of the dead sea and its predecessor lake lisan

active faulting in the dead sea rift abstract manifestations of late quaternary and holocene faulting were studied in a 500 km long segment of the dead sea transform rift most prominent are left slip faults whose characteristic physiographic features are recognizable along most of the studied segment where these faults bend or are stepped to the left rhomb shaped grabens or pull aparts are produced forming depressions in the reverse situation compressional features such as pressure ridges domes and folds form positive topographic features such structures are combined on a variety of scales ranging from a few hundred meters long to tens of kilometers normal faults sub parallel to the left slip faults produce a trough like valley along much of the dead sea transform but are most prominent along the margins of the large rhomb grabens e g the dead sea trough they apparently record a small component of transverse extension generally their motion is slow young slip did not occur along some segments during the last few 10 4 y elsewhere throws of 10 20 m at least occurred in this period the dead sea transform is seismically active the instrumental and historic records indicate a seismic slip rate of 0 15 0 35 cm y during the last 1000 1500 y while estimates of the average pliocene pleistocene rate are 0 7 1 0 cm y either much creep takes place or the slip rate varies over periods of a few 10 3 y

quantitative analysis of seismogenic shear induced turbulence in lake sediments spectacular deformations observed in lake sediments in an earthquake prone region lisan formation pre dead sea lake appear in phases of laminar moderate folds billow like asymmetric folds coherent vortices and turbulent chaotic structures power spectral analysis of the deformation indicates that the geometry robustly obeys a power law of 1 89 similar to the measured value of kelvin helmholtz kh turbulence in other environments numerical simulations are performed using properties of the layer materials based on measurements of the modern dead sea sediments which are a reasonable analogue of lake lisan the simulations show that for a given induced shear the smaller the thickness of the layers the greater is the turbulent deformation this is due to the fact that although the effective viscosity increases the reynolds number decreases the bulk richardson number becomes smaller with decrease in the layer thickness the latter represents the ratio between the gravitational potential energy of the stably stratified sediments and the shear energy generated by the earthquake therefore for thin layers the shear energy density is larger and the kh instability mechanism becomes more efficient the peak ground acceleration pga is related to the seismogenic shear established during the earthquake hence a link is made between the observed thickness and geometry of a deformed layer with its causative earthquake9s pga

prehistoric earthquake deformations near masada dead sea graben earthquake inducedfluidizations and suspensions of lake sediments associated with syndepositionalfaults formapaleoseismicrecordinthedeadseagraben theassociation offluidized beds with surface faulting supports the recognition of mixed layers as reliable earthquake indicators and provides a tool for the study of very long term 70 kar seismicity along the dead sea transform the faults compose a fault zone that offsets laminated sediments of the late pleistocene lake lisan they exhibit displacements of as much as 2 m layers of massive mixtures of laminated fragments are interpreted as disturbed beds each formed by an earthquake the undisturbed laminated layers between these mixed layers represent the interseismic interval a typical vertical slip of about 0 5 m per event is separated by several hundred years of quiescence the fault zone lies within the dead sea graben 2 km east of masada where archaeology and historical accounts indicate repeated strong earthquake damage the distribution of strikes in the fault zone resembles that of the faults exposed in and around the graben including the seismogenic ones the excellent exposures over hundreds of metres allow an unprecedented temporal and spatial resolution of slip events on faults

sedimentary earthquake records in the izmit gulf sea of marmara turkey abstract sedimentary earthquake records of the last 2400 a including that of the devastating 17 august 1999 izmit earthquake mw 7 4 were studied in cores from the 210 m deep central karamursel basin of the izmit gulf in the eastern sea of marmara using laser grain size physical properties stable o and c isotopes and xrf core scanner analyses and dated by radionuclide and radiocarbon methods the earthquake records are represented by turbidite homogenite mass flow units thu that commonly contain a basal coarse layer a middle laminated silt layer and an overlying homogeneous mud layer the coarse basal part has a sharp and sometimes scoured lower boundary and includes multiple coarse sand silt layers or laminae showing normal size grading multiple coarse layers and occasional bi directional cross bedding suggest deposition from a bed load during water column oscillations or seiche effect the grain size characteristics of the overlaying laminated silt and the homogeneous mud units indicate deposition from weak oscillating currents and homogeneous suspension respectively high mn value just below the base of thus suggests diagenetic enrichment at oxic anoxic redox boundary before the mass flow event sharp decrease in mn with very low values within the thus suggests transient redox conditions following the mass flow variable geochemical compositions of the basal coarse layers indicate different sediment sources for different thus eight sedimentary earthquake records observed in the last 2400 a in the izmit gulf can be confidently correlated with the historical earthquakes of 1999 1509 ad ms 7 2 1296 ad i vii 865 ad i viii 740 ad i viii 268 ad i viii 358 ad i ix and 427 bc this gives an earthquake recurrence time of ca 300 a with the interval between consecutive events ranging from 90 to 695 a

continental transforms a view from the alpine fault abstract continental transform faults are dominantly highly localized strike slip shear zones hundreds of kilometers long that accumulate tens to hundreds of kilometers of displacement from work on the alpine fault we pose the questions what is the deep structure of a continental transform and how does the displacement become localized we review research on the alpine fault and propose a model in which the fault partitions at depth into a steep zone extending into the mantle with largely fault parallel motion and a flat ductile decollement in the lower crust the fault localizes around two thirds of the plate motion within a 100 km wide zone of distributed deformation a review of other active continental fault systems suggests that variation between them may reflect their tectonic origins the nature of the crust in which they develop the presence of a significant oblique component of motion and the displacement rate all however have evidence for the development of a single principal fault zone that carries 50 of the total displacement and extends as a localized zone of shear into the upper mantle we review mechanisms of strain weakening and suggest that localization of a principal fault may be initiated in the seismogenic crust and through a series of positive feedbacks eventually extend through the lower crust into the upper mantle

strontium isotopic chemical and sedimentological evidence for the evolution of lake lisan and the dead sea precise strontium isotope ratios combined with chemical analyses and sedimentological information are used to monitor the water sources and the evolution of the dead sea and its late pleistocene precursor lake lisan 70 18 kyr b p the materials analyzed include bulk aragonite water leached soluble salts and residual aragonite and gypsum from the lisan formation in the perazim valley near the sw shore of the dead sea the residual aragonite and the associated soluble salts display systematic fluctuations in 17sr86sr ratios between 0 70803 and 0 70806 and from 0 70805 to 0 70807 respectively in individual soluble salt residual aragonite pairs the soluble salt displays a higher 87sr86sr ratio gypsum samples yield 17sr86sr ratios similar to the soluble salts from adjacent layers in the section this shows that in individual samples the source of sr in aragonite was distinct from that in soluble salts and the gypsum the sterility of the lisan sediments their strictly nonbioturbated fine lamination and their high content of chloride salts indicate that lake lisan was a saline or even hypersaline water body in the absence of alternative sources of hco3 and s042 the abundance of primary aragonite and gypsum in the lisan column reflects an import of very large volumes of freshwater into the otherwise saline lake resulting in a density stratification of this water body the history of the upper water layer and that of the lower brine is reflected in the chemical and strontium isotope composition of the aragonite and in that of the associated soluble salts and in the gypsum samples respectively whereas the bicarbonate and much of the ca2 required for aragonite crystallization were supplied by the freshwater the complementary ca2 and sr 2 were added by the lower brine the upper water layer of lake lisan acted as a so42 capacitor during the lake s rise periods it was removed therefrom as prominent gypsum beds upon climatic induced drier period mixing or even complete overturn of the lake the evolution of lake lisan took place between two distinct modes the first was characterized by an extensive supply of freshwater and resulted in a rise of the lake s level a density layered structure and precipitation of aragonite the second mode was marked by a diminishing freshwater input resulting in mixing or complete overturn of its water and precipitation of gypsum these two modes reflect the climatic evolution of the region in the late pleistocene which fluctuated between drier and wetter periods the transition to the holocene is accompanied by the dry up of lake lisan and its contraction to the present dead sea

landscape development in an hyperarid sandstone environment along the margins of the dead sea fault implications from dated rock falls in this study we explored the spatial and temporal relations between boulders and their original in situ locations on sandstone bedrock cliffs thiswas accomplished bycombining field observations withdating methods using cosmogenicisotopes 10 be and 14 c and optically stimulated luminescence osl our conclusions bear both on the landscape evolution and cliff retreat process in the hyperarid region of timna and on the methodology of estimating exposure ages using cosmogenic isotopes we recognize three discrete rock fall events at 31 ka 15 ka and 4 ka in this hyperarid region the most plausible triggering mechanism for rock fall events is strong ground acceleration caused by earthquakes generated by the nearby dead sea fault dsf our record however under represents the regional earthquake record implying that ongoing development of detachment cracks prior to the triggering event might be slower than the earthquake cycle cliff retreat rates calculated using the timing of rock fall events and estimated thickness of rock removed in each event range between 0 14 m ky 1 and 2 m ky 1 when only full cycles are considered we derive a more realistic range of 0 4 m ky 1 to 0 7 mk y 1 these rates are an order of magnitude faster than the calculated rate of surface lowering in the area we conclude that sandstone cliffs at timna retreat through episodic rock fall events that preserve the sharp imposing landscape characteristic to this region and that ongoing weathering of the cliff faces is minor a 10 20 difference in the 10 be concentrations in samples from matching boulder and cliff faces that have identical exposure histories and are located only a few meters apart indicates that cosmogenic nuclide production rates are sensitive to

a seismite in triassic gypsum deposits grabfeld formation ladinian southwestern germany an approximately 1 m thick gypsum bed and its underlying 45 cm dolomite bed with variable soft sediment deformation structures are described from the grundgips member of the grabfeld formation middle keuper ladinian in southwestern germany the deformation structures are mainly convolutions folds cusps domes and off shooting dykes and less common brecciation or faulting these deformation structures are interpreted to be caused by liquefaction and or fluidization of the semiconsolidated sediments by a seismic shock of approximately magnitude 6 7 palaeoseismicity is thought to be related with a nearby wrench fault system associated with a major suture zone of the variscan basement

calibration of the 14c time scale to 40 ka by 234u 230th dating of lake lisan sediments last glacial dead sea a new comparison of 14c dates with 234u 230th ages is presented of aragonites from lake lisan the last glacial dead sea between 20 52 cal ka bp the lisan data are coincident with the coral based 14c calendar age calibration through the continuous portion of the curve to 23 5 cal ka bp and with the additional checkpoints at 30 and 40 cal ka bp the agreement with the corals provides evidence for the accuracy of the u th and 14c ages and indicates that lisan aragonites can potentially be used to generate a nearly continuous record of the atmospheric 14c variations through this crucial time interval the lisan data are compared with other records older than 25 cal ka bp from lake suigetsu japan north atlantic foraminifera south african cave deposits and tufa from spain over some age intervals the records show broad agreement over other intervals they diverge all agree that 14c ages were 2 5 0 5 ka younger than calendar ages between 20 32 cal ka bp for ages 32 cal ka bp the lake suigetsu data indicate small differences between 14c ages and calendar ages of less than 1 5 ka the other records broadly agree that 14c ages are too young by 3 1 ka from 32 39 cal ka bp at 40 cal ka bp the foraminifera show equal 14c and calendar ages while the corals lisan aragonites and the spanish tufa indicate a large age difference of 4 5 ka a recent paleomagnetic study of the lisan formation indicates that the high calendar 14c age difference at 40 cal ka bp may be associated with the laschamp paleomagnetic excursion

under the volcano a new dimension in ar ar dating of volcanic ash a significant part of the history of the greek island of kos has been decoded from a handful of volcanic ash by argon argon laser probe dating of single crystals of the minerals sanidine plagioclase and quartz on a 3 d argon isotope plot the data define six straight lines corresponding to four distinct volcanic events from 161 to 1728 ka all four events produced plagioclase crystals whose ages and ca k ratios are consistent with the known evolution of the rest of the aegean arc sanidine appeared only in the final eruption at 161 ka the joint occurrence of quartz and plagioclase at a 925 ka event implies that quartz did not reside for millennia in the magma as has been suggested for quartz from the bishop tuff california the step heated cooling age of a schist fragment from the ash provides the first radiometric evidence for 250 ma crust under the volcano

excess argon in melt inclusions in zero age anorthoclase feldspar from mt erebus antarctica as revealed by the method abstract historically erupted 1984 anorthoclase phenocrysts from mt erebus yield k ar and 40 ar 40 ar apparent ages as old as 700 ka indicating the presence of excess argon 40 ar 39 ar furnace step heating results from anorthoclase reveal a positive correlation between the cl k ratio and apparent age because chlorine up to 1700 ppm is present in melt inclusions but not in the anorthoclase crystal lattice this correlation suggests that the excess argon is associated with melt inclusions trapped within the anorthoclase during rapid crystal growth confirmation of the source of excess argon comes from step heating experiments on multiple anorthoclase aliquots separated from two phenocrysts and one glass aliquot prepared from the matrix of a volcanic bomb the anorthoclase phenocrysts were crushed and hf etched to yield aliquots containing 30 10 and 1 melt inclusions the step heated anorthoclase with 30 and 10 melt inclusions yielded the highest cl k ratios and apparent integrated ages of 640 30 ka and 179 16 ka respectively the anorthoclase with i melt inclusions yielded significantly lower cl k ratios and apparent integrated ages of 48 8 ka and 50 30 ka the step heated volcanic glass yielded the least variable cl k ratios and a total gas age of 101 16 ka argon released from the anorthoclase and the trapped melt inclusions can be distinguished by differences in their degassing behavior allowing geologically more reasonable ages to be obtained melt inclusions exposed on the exterior of anorthoclase grains principally degas during furnace extraction at temperatures less than 1200 c inclusions entirely within anorthoclase grains principally degas at temperatures greater than 1200 c when incongruent melting of the anorthoclase allows melt inclusion hosted excess argon to escape anorthoclase aliquots prepared with less than 1 inclusions can be fitted with a plateau for heating steps below 1200 c to yield ages as young as 8 2 ka whereas steps above 1200 c yield ages in excess of 100 ka however anorthoclase aliquots containing 10 30 melt inclusions yield ages in excess of 200 ka for heating steps below 1200 c minimizing the effects of the excess argon from melt inclusions relies on sample preparation and step heating fine crushing and treatment with hydrofluoric acid removes many of the larger melt inclusions small melt inclusions which remain within the anorthoclase degas primarily at temperatures above 1200 c temperatures below 1200 c yield the most accurate ages attempts at post analytically correcting for the chlorine correlated excess argon are hindered by the variations in 40 ar e cl within and between samples elevated 40 ar e cl ratios in bubbles within the melt inclusions as deduced from in vacuo crushing experiments are the most likely cause for some or all of a sample s total 40 ar e cl variation in addition relative solubilities of argon and chlorine within phonolitic melts may be partly responsible for variations in 40 ar e cl

lake levels and sequence stratigraphy of lake lisan the late pleistocene precursor of the dead sea lake lisan the late pleistocene precursor of the dead sea existed from 70 000 to 15 000 yr b p it evolved through frequent water level fluctuations which reflected the regional hydrological and climatic conditions we determined the water level of the lake for the time interval 55 000 15 000 cal yr b p by mapping offshore nearshore and fan delta sediments by application of sequence stratigraphy methods and by dating with radiocarbon and u series methods during the studied time interval the lake level fluctuated between 340 and 160 m below mean sea level msl between 55 000 and 30 000 cal yr b p the lake evolved through short term fluctuations around 280 290 m below msl punctuated at 48 000 43 000 cal yr b p by a drop event to at least 340 m below msl at 27 000 cal yr b p the lake began to rise sharply reaching its maximum elevation of about 164 m below msl between 26 000 and 23 000 cal yr b p then it began dropping and reached 300 m below msl at 15 000 cal yr b p during the holocene the lake corresponding to the present dead sea stabilized at ca 400 m below msl with minor fluctuations the hypsometric curve of the basin indicates that large changes in lake area are expected at above 403 and 385 m below msl at these elevations the lake level is buffered lake lisan was always higher than 380 m below msl indicating a significantly large water contribution to the basin the long and repetitious periods of stabilization at 280 290 m below msl during lake lisan time indicate hydrological control combined with the existence of a physical sill at this elevation crossing this sill could not have been achieved without a dramatic increase in the total water input to the lake as occurred during the fast and intense lake rise from 280 to 160 m below msl at 27 000 cal yr b p

ar diffusion and solubility measurements in plagioclases using the ultra violet laser depth profiling technique we describe the first direct measurements of ar diffusion and solubility in plagioclases using ultra violet uv laser ablation depth profiling and noble gas mass spectrometer analyses of experimentallytreated 599 1000 8c 50 200 mpaofar crystalfragmentsoflabradoriteandoli goclase labradorite 40 ar gain diffusion profiles were measured yielding an activation energy of 26 72 4 58 kcal mol 21 118 0 19 16 kj mol 21 and a frequency factor of 9 77 10 29 8 79 10 28 28 79 10 29 c m 2 s 21 95 confidence the ar solubility in labradorite was measured yielding a value of 0 2 ppb bar 21 which is similar to or lower than many rock forming minerals the labradorite diffusion parameters indicate ar closure temperatures of 211 8c for a spherical diffusion geometry and 243 8c for a planar diffusion geometry for 100 mm diameter grains with cooling rates of 10 8 cm a 21 the data indicate that labradorite is less ar retentive than k feldspar at low temperatures but more ar retentive than k feldspar at high temperatures corroborating previous work on plagioclase the relatively slow ar diffusion rates in labradorite at magmatic temperatures may explain the common observation of older ages in large plagioclase grains in acidic volcanic systems supplementary material details of the uv laser depth profiles obtained from the labradorite and oligoclase samples used in this study are available at www geolsoc org uk sup18608

distribution of holocene sediments and neotectonics in the deep north basin of the dead sea abstract the distribution of holocene sediments and active faults in the central portion of the northern dead sea basin was analyzed from high resolution seismic reflection data the seismic reflection profiles reveal that sediments buried at a shallow depth are flat lying continuous and unfaulted within the central basin floor four prominent subsurface seismic reflectors were identified that based on limited core data represent the contact between rock salt and marl layers isopach and structural maps of recent sediments indicate an asymmetry of active subsidence with thick accumulations located closer to the east margin of the basin sediment thickness increases within a rhomb shaped depression whose long axis is oriented approximately 20 30 counterclockwise to the regional basin bounding faults the morphology and trend of the locus of maximum subsidence suggests tectonic control of the depression however the proximity of the depocenter of recent sediments to the ein gedi diapir and rim depression suggests that local sub basinal subsidence may also be related to movement of rock salt at depth the basinal strata are deformed along the faults that form a bathymetric escarpment along the west east and south margins of the north basin of the dead sea thinning of recent sediments toward the faults indicates syntectonic deposition

long term earthquake clustering a 50 000 year paleoseismic record in the dead sea graben the temporal distribution of earthquakes in the dead sea graben is studied through a 50 000 year paleoseismic record recovered in laminated sediments of the late pleistocene lake lisan paleo dead sea the lisan represents more than 10 times the 4000 years of historical earthquake records it is the longest and most complete paleoseismic record along the dead sea transform and possibly the longest continuous record on earth it includes unique exposures of seismite beds earthquake induced structures associated with slip events on syndepositional faults the seismites are layers consisting of mixtures of fragmented and pulverized laminae the places where the seismites abut syndepositional faults are interpreted as evidence for their formation at the sediment water interface during slip events on these faults thicker sediment accumulation above the seismites in the downthrown blocks indicates that a seismite formed at the water sediment interface on both sides of the fault scarps modern analogs and the association with surface ruptures suggest that each seismite formed during a m l 5 5 earthquake the 230 th 234 u ages of a columnar section obtained by thermal ionization mass spectrometry give a mean recurrence time of 1600 years of m l 5 5 earthquakes in the dead sea graben the earthquakes cluster in 10 000 year periods separated by quiet periods of similar length this distribution implies that a long term behavior of the dead sea transform should be represented by a mean recurrence of at least 20 000 year record this observation has ramifications for seismic hazard assessment based on shorter records

geochemistry of the lisan and damya formations in jordan and implications for palaeoclimate abstract geochemical mineralogical and sedimentological investigations carried out on the lacustrine lisan and damya formations of the jordan rift valley reveal three major and several minor transgressive depositional cycles all terminating with massive gypsum precipitation the highest level of lake lisan is reported in the literature at 130 m below mean sea level b s l from 70 45 calibrated ka bp the lisan formation is characterised by a high gypsum aragonite ratio and a low lithogenic content implying a regression of an initially high water level caused by reduced water input in the following interval ca 45 36 cal ka bp two low water stands are marked by higher salt concentrations after recovery and a period of higher water level the lake lisan era ends with a strong regression at around 16 cal ka bp this date coincides with the period when lake van eastern turkey also fell dry thus marking a strong drought signal in the entire near east the overlying damya formation containing more lithogenics records lake level fluctuations at around 300 m b s l the existence of a north south precipitation gradient as present today is indicated by increasing sr ca ratios in aragonite and a decreasing lithogenic content in a n s direction secondary gypsum formed diagenetically and aragonite and low mg calcite was transformed into high mg fe calcite

a 3100 year history of argon isotopic and compositional variation at el chichon volcano abstract el chichon volcano has produced at least 11 eruptive events in the past 8000 years all of which display a relatively constant trachyandesitic composition the constancy of the eruptive products attests to the tapping of a long lived magma chamber and suggests a system held in steady state between the influx of basaltic magma and differentiation of resident magma we have sampled eruptive products from eight of these events subjecting their dominant phenocryst phases plagioclase and hornblende to argon isotopic analysis in order to investigate the dynamics of a steady state magmatic system plagioclase from the older eruptions 1500 yr bp 1600 yr bp 2000 yr bp and 3100 yr bp display variable enrichment of 40 ar excess argon whereas hornblende from the same eruptions shows little or no enrichment in contrast both plagioclase and hornblende phenocrysts from the younger eruptions in 1982 550 yr bp 900 yr bp and 1250 yr bp have argon isotopic ratios near atmospheric values isochron analysis of these mineral phases rules out xenocrystic contamination as the source of excess argon while mafic enclaves and isotopic and compositional zoning evidence frequent recharge events suggesting the source of this argon is most likely the same as the source of this basaltic magma correlation with cl points to melt vapor inclusions as the primary host for ar within the phenocrysts argon isotopic variations point to a disturbance of the system between 1500 yr bp and 1250 yr bp while compositional evidence for a major mafic input is present in the 900 yr bp eruption indicating a complex relationship between recharge and isotopic signature of eruptive products the amount of excess argon within a plagioclase phenocryst are a function of variations in melt and vapor inclusion abundance time elapsed between melt vapor inclusion entrapment and eruption variations in ar abundance in melt itself a function of vapor exsolution timing and time variations in ar isotopic composition of the melt subdued behavior of hornblende is due to slower diffusion and minimal inclusions

reevaluation of the lake sediment chronology in the dead sea basin israel based on new 230th u dates the dead sea is surrounded by chemical and detrital sediments that were deposited in its larger precursor lakes lake samra and lake lisan the sedimentary history of these lakes was recon structed by means of 230th234u ages of 30 samples mostly of argonite laminae from 8 columnar sections up to 110 km apart the general validity of the ages was demonstrated by subjecting them to tests of internal isotopic consistency agreement with stratigraphic order and concordance with 14c ages in the south only the part of the samra formation older than 170 000 yr is exposed while the aragonite detritus rhythmites found in the central and northern region are generally younger than 120 000 yr the lisan formation started accumulating about 63 000 yr b p with the clay and aragonite beds in the south central area reflecting a rise in water level to at least 280 m the upper part of the lisan formation the aragonite rich white cliff member started accumulating about 36 000 yr b p the lake probably reached its highest level sometime after this based on the ages of lisan sediments preserved in the southernmost reaches of the basin

40ar 39ar laser probe ages of bishop tuff quartz phenocrysts substantiate long lived silicic magma chamber at long valley united states laser probe ar 40 ar 39 dating of quartz phenocrysts with rhyolite glass inclusions from the bishop tuff air fall and ignimbrite deposits reveals that the long valley magma system existed as a long lived silicic magma chamber throughout most of the pleistocene sanidine phenocryst and matrix glass analyses show that the bishop tuff eruption occurred at 759 1 to 761 1 ha initial and radiogenic ar isotope ratios indicate isotopic equilibrium between the sanidine phenocrysts and their host melt at the time of eruption the quartz phenocrysts in contrast the most abundant phenocryst phase of the bishop rhyolite crystallized trapped their glass inclusions and became a closed system with respect to ar at 1 89 0 03 to 2 3 0 3 ma consequently the bishop rhyolite magma already resided in the long valley basement and had formed most of its quartz phenocrysts similar to 1 1 m y before its principal eruption providing important constraints on the longevity of large silicic magma chambers

extreme u th disequilibrium in rift related basalts rhyolites and granophyric granite and the timescale of rhyolite generation intrusion and crystallization at alid volcanic center eritrea received september 20 2005 accepted june 14 2006 advance access publication july 14 2006rhyolite pumices and co erupted granophyric granite xenolithsyield evidence for rapid magma generation and crystallization priorto their eruption at 15 2 2 9 ka at the alid volcanic center inthe danikil depression eritrea whole rock u and th isotopicanalyses show

tsunami and seiche triggered deformation within offshore sediments abstract most studies of tsunami and seiche related deposits have focussed on coastal and near coastal zones which are most readily accessible with few investigations of deeper water settings and the potential soft sediment deformation effects of such waves the late pleistocene lisan formation outcropping to the west of the dead sea contains superb examples of sedimentary slump folds formed in water depths of

petrology and fe ti oxide reequilibration of the 1991 mount unzen mixed magma a dacitic magma 64 5 wt sio2 a mixture of phenocryst rich rhyodacite and an aphyric mafic magma was erupted during the recent 1991 1995 mount unzen eruptive cycle the experimental and analytical results of this study reveal additional details about conditions in the premixing and postmixing magmas and the nature of the mixing process the preeruption rhyodacitic magma was at a temperature of 790 20 c according to fe ti oxide phenocryst cores and at a depth of 6 to 7 km 160 mpa according to al in hornblende geobarometry the mafic magma that mixed with the rhyodacite is found as andesitic 54 to 62 wt sio2 enclaves in the erupted magma and was essentially aphyric when intruded phase equilibria indicate that an aphyric andesite at 160 mpa is 1030 c h2o saturated and possibly as high as 1130 c 2 wt h2o the composition of the rhyodacite which was mixed with the andesite is estimated to lie between 67 and 69 wt sio2 using these compositions and temperatures the temperature of the unzen magma after mixing is estimated to be at least 850 to 870 c the groundmass fe ti oxide microphenocrysts and those in pargasite bearing reaction zones around biotite phenocrysts both give 890 20 c temperatures the oxide oxide contacts give temperatures of 910 20 c the 900 30 c postmixing temperatures are consistent with phase equilibria experiments which show that the magma was not above 930 c at 160 mpa our fe ti oxide reequilibration experiments suggest that the mixing of the two magmas began within a few weeks of the eruption which is a shorter time than is calculated using available diffusion data there is also evidence that some mixing took place much closer to the time of extrusion based on the presence of unrimmed biotite phenocrysts in the magma

abrupt aridities and salt deposition in the post glacial dead sea and their north atlantic connection abstract abrupt arid events in the post glacial 17 4 10 kyr bp dead sea basin dsb were recorded by significant lake level declines in lake lisan and massive deposition of gypsum and salt between 17 4 and 16 kyr cal bp the lake level dropped from its late mis2 stand of 260 m below mean sea level m bmsl to 330 m bmsl depositing a thick sequence of gypsum between 16 and 15 kyr cal bp the lake level recovered but dropped abruptly again at 14 kyr cal bp to below 465 m bmsl probably the lowest late pleistocene stand then between 13 and 11 kyr cal bp the younger dryas time interval the lake rose above 400 m bmsl and declined at 11 10 kyr cal bp depositing a thick sequence of salt the abrupt lake level drops and salt deposition coincided with times of ice and meltwater discharges into the north atlantic na heinrich event h1 and meltwater pulse mwp1a similar coincidence between ice and meltwater discharges in the na e g h events and arid episodes at the levant was recorded during the colder last glacial period demonstrating a persistent effect of the north atlantic hydrology and sea ice advances on the levant climate the climatically turmoil post glacial period was accompanied by significant developments in human culture the collapse of the natufian culture during the bolling allerod and the rise of the pre pottery neolithic cultures ppn a and b around the 11 10 kyr cal bp salt deposition interval marking the initiation of the neolithic revolution in the region

the holocene climatic record of the salt caves of mount sedom israel mount sedom is a salt diapir on the southwestern shore of the dead sea which has been rising above the local base level throughout the holocene karst development within the salt body has kept pace with the rise forming subhorizontal cave passages with vertical shafts wood fragments found embedded in flood sediments that were deposited in the cave passages yielded 14c ages ranging from c 7100 to 200 bp a palaeoclimatic sequence was constructed based on parameters that include relative abundance of plant types or floral communities the elevations of the corresponding cave passages and the ratio of their width to present passage width the results were correlated to the holocene sedimentary sequence of the dead sea basin and other features associated with shifting lake levels moister climatic stages are indicated by relatively abundant wood remains by wide cave passages and by elevated outlets indicating high dead sea level arid periods are marked by a scarcity of wood remains by narrow cave pa

earthquake damage history in israel and its close surrounding evaluation of spatial and temporal patterns abstract israel was hit by destructive earthquakes many times in the course of history to properly understand the hazard and support effective preparedness towards future earthquakes we examined the spatial and temporal distribution of the resulted damage we described in detail our systematic approach to searching the available literature collecting the data and screening the authenticity of that information we used gis geographic information system to map and evaluate the distribution of the damage and to search for recurring patterns overall it is found that 186 localities were hit 54 of them at least twice we also found that israel was affected by 4 17 8 and 2 damaging earthquakes that originated respectively from the southern central central northern and northern parts of the dead sea transform dst the temporal appearance of the northern earthquakes is clustered the central earthquakes are more regular in time whereas no damage from the north central and the central quakes with the exception of the year 363 earthquake seems to have occurred south of the dead sea region analyzing the distribution of the damage we realized that the number of the damage reports reflects only half of the incidents that actually happened attesting to incompleteness of the historical catalogue jerusalem is the most reported city with 14 entries followed by akko acre tiberias nablus and tyre with 8 7 7 and 6 reports respectively in general localities in the galilee and north of it suffered more severely than localities in central israel with the exception of nablus and the localities along the coastal plain of israel most probably due to local site effects for the sake of hazard management these observations should be considered for future planning and risk mitigation

summary of pre 1980 tephra fall deposits erupted from mount st helens washington state usa mount st helens has been a prolific source of tephra fall deposits for about 40 000 years these tephra deposits 1 record numerous explosive eruptions 2 form important regional time stratigraphic marker beds and 3 record repeated changes in composition within and between eruptive periods

recurrence pattern of holocene earthquakes along the dead sea transform revealed by varve counting and radiocarbon dating of lacustrine sediments abstract a high resolution holocene seismic history of the dead sea transform dst is established from laminated sedimentary cores recovered at the shores of the dead sea radiocarbon dating and annual laminae counting yield excellent agreement between disturbed sedimentary structures identified as seismites and the historical earthquake record all recent and historical strong events of the area were identified including the major earthquakes of a d 1927 1837 1212 1033 749 and 31 b c the total of 53 seismites recognized along the entire holocene profile indicate varying recurrence intervals of seismic activity between a few and 1000 years with a conspicuous minimum rate at 2100 31 b c and a noticeable maximum during the past six to eight centuries most of the epicenters of the correlated earthquakes are situated very close to the dead sea within 150 km or up to 400 km north of it along the dst between 1000 b c and a d 1063 and from a d 1600 to recent time the epicenters are all located on the northern segment of the dst whereas prior to 1000 b c and between a d 1000 and 1600 they appear to scatter along several segments of the dst we establish how the local intensity exerts a control on the formation of seismites at historically estimated intensities greater than vii all well documented earthquakes are correlated whereas at intensities smaller than vi none are matching the periods with enhanced earthquake rate along the dst correlate with those along the north anatolian fault as opposed to the intervening east anatolian fault this may indicate some elastic coupling on plate boundary scale that may also underlie escape and extrusion tectonics typical of continental collision

magmatic processes of unzen volcano revealed by excess argon distribution in zero age plagioclase phenocrysts abstract excess argon 40 ar is one of the most important problems in k ar geochronometry because it renders incorrect the simple assumption that all initial argon in rock samples is derived from the atmosphere using the laser microprobe analytical method we investigate and reveal the source and trapping site of excess argon in zero age plagioclase phenocrysts extracted from the lavas erupted during 1990 1995 activity of the unzen volcano kyushu japan by combining the results of laser microprobe analysis and conventional stepwise heating of separated plagioclase phenocrysts we reveal that the majority of the excess argon is retained in melt inclusions in the dusty zone of the phenocrysts we propose a model for the isotopic evolution of argon in the phenocryst bearing magma of the unzen volcano by taking into consideration the noble gas data from unzen volcanic gases and the chemical composition of the melt inclusions in the phenocrysts in our model plagioclase phenocrysts crystallize from or are captured by a low temperature t rhyodacitic magma this magma has a comparatively high 40 ar 36 ar ratio for an arc magma due to assimilation of old cretaceous granitic wall rock mantle derived argon is replenished in the rhyodacitic magma over the life of the volcano when the magma chamber is recharged at intervals by high t juvenile magma the plagioclase phenocrysts crystallize rapidly trapping excess argon 40 ar 36 ar 970 during successive dissolution crystallization events caused by intrusion of the high t magma or water rich fluids the phenocryst bearing mixed magma ascends at a relatively rapid rate following a final injection of the high t magma and interacts with shallow groundwater causing the 40 ar 36 ar ratio of the magma to decrease to the atmospheric ratio contamination of the phenocrysts by atmospheric argon in the surrounding magma is enhanced by rapid short circuit diffusion in which dislocations and or micro cracks in the plagioclase crystals are used for argon transport the remnant magma has been continuously degassing for a decade since the recent 1990 1995 eruptive activity without significant change to 3 he 4 he and 40 ar 36 ar ratios

provenance and earthquake signature of the last deglacial xinmocun lacustrine sediments at diexi east tibet abstract well preserved lacustrine sediments are found in some areas in east tibet this region is characterized by a windy and semi arid climate alpine valleys and frequent earthquakes measurements of rare earth elements observations from a scanning electron microscope and a high resolution record of grain size measurements allowed us to compare fine sediments from the xinmocun section in the diexi lake with loess from the chinese loess plateau and south china results indicate that fine grains of the xinmocun lacustrine sediments were transported by wind and trapped in the lake whereas the 16 m fraction was likely from local sources the grain size changes within the section repeatedly show abrupt coarsening and upward fining probably due to palaeoearthquake events large earthquakes in the study area often caused rockfalls and landslides exposing fine sediments that had accumulated on mountains slopes the fine grains were then retransported by wind to the diexi lake optically stimulated luminescence dating of the xinmocun section indicates continuous deposition from 18 65 to 10 63 ka these results indicate that palaeoearthquakes in the study area had a mean recurrence interval of 0 32 ka therefore we propose that lacustrine sediments in a tectonically active region have the potential to record a continuous history of palaeoearthquakes palaeoearthquakes probably produced numerous rockfalls and landslides in alpine valleys and provided significant sources of regional eolian dust

excess argon in mount st helens plagioclase as a recorder of magmatic processes excess argon in plagioclase crystals from young 4000 ybp tephra layers from mount st helens washington illustrates the importance of argon isotopes in understanding magmatic processes 40ar 39ar step heating identifies two distinct argon reservoirs in the plagioclase a high cl k low ca k reservoir with atmospheric 40ar 36ar and a low cl k higher ca k reservoir with variable 40ar 36ar the first is probably glass whereas the second is true plagioclase felsic dacite plagioclases have little or no excess argon but those from more mafic layers have significantly higher 40ar 36ar indicating a non atmospheric source these variations are seen within a layer that contains both mafic and felsic dacite and are inconsistent with either xenocrystic or restitic origin for plagioclase the magma chamber exhibits long term open system degassing behavior punctuated by short term fluctuations from influx of high 40ar 36ar basalt the relative timing between mixing and eruption can affect the amount of excess argon recorded in plagioclase

surface ruptures induced by the devastating 1068 ad earthquake in the southern arava valley dead sea rift israel abstract the elat fault a segment of the dead sea transform runs along the southern arava valley part of the dead sea rift israel forming a complex fault zone that displays a time dependent seismic behaviour paleoseismic evidence shows that this fault zone has generated at least 15 earthquakes of magnitude larger than m 6 during the late pleistocene and the holocene however at present the elat fault is one of the quietest segments of the dead sea transform lacking even microsesimicity the last event detected in the southern arava valley occurred in the avrona playa and was strong enough to have deformed the playa and to change it from a closed basin with internal drainage into an open basin draining to the south paleoseismological geophysical and archaeological evidences indicate that this event was the historical devastating earthquake which occurred in 1068 ad in the eastern mediterranean region according to the present study this event was strong enough to rupture the surface reactivate at least two fault branches of the elat fault and vertically displace the surface and an early islamic irrigation system by at least 1 m in addition the playa area was uplifted between 2 5 and 3 m along the eastern part of the elat fault shear zone such values are compatible with an earthquake magnitude ranging between m 6 6 and 7 since the average recurrence interval of strong earthquakes during the holocene along the elat fault is about 1 2 0 3 ky and the last earthquake occurred more about 1000 years ago the possibility of a very strong earthquake in this area in the future should be seriously considered in assessing seismic hazards

holocene seismic and tectonic activity in the dead sea area abstract the dead sea is a large active graben within the dead sea rift which is bounded by two major strike slip faults the jericho and the arava faults we investigated the young tectonic activity along the jericho fault by excavating trenches up to 3 5 m deep across its trace the trenches penetrate through late pleistocene and holocene sediments we found that a zone up to 15 m wide of disturbed sediments exists along the fault these disturbed sediments provide evidence for two periods of intensive activity or more likely for two major earthquakes that occurred during the last 2000 years the earthquakes are evident in small faults vertical throw of a few layers cracks unconformities and wide fissures we further documented evidence for recent sinistral shear along the jericho fault in deformed sediments and damage to an 8th century palace on a subsidiary fault we suggest that the two earthquakes may be correlated with the 31 b c earthquake and the 748 a d earthquake reported by the ancients