relic magma chamber structures preserved within the mesozoic north atlantic crust the north atlantic transect seismic reflection data collected southwest of bermuda have been reinterpreted following post stack migration and reveal two major intracrustal reflections the shallower of these two events located 1 s below the igneous basement is a subhorizontal undulating surface that in some places is continuous for as much as 10 km on the basis of its position within the section and its laterally discontinuous nature we believe that this upper crustal reflection corresponds to the intermittently sharp contact between the sheeted dikes and the underlying isotropic gabbro a second set of lower crustal reflections dipping 20 40 eastward is also prominent on the migrated profile and terminates downdip against the subhorizontal reflection moho several lines of evidence argue against these features being either artifacts or out of the plane events instead their presence may be ascribed either to crustal penetrating fault zones or to mafic ultramafic cumulate layers frozen into the oceanic crust at the time of formation at the paleo spreading center because of the laminated character of these events and their typical occurrence within 1 0 to 1 5 s of the reflection moho we prefer a compositional versus a structural interpretation for their origin the gradual thinning in the crust approaching the fracture zones is shown to be more complex than was originally inferred although the interpretation that the crust gradually thins toward fracture zones may still apply in a few localities significant departures are recognized elsewhere similarly the improved image on the migrated profile documents an increase in complexity across the localized region directly surrounding the blake spur fracture zone an interpretation advocating crustal thickening in this narrow zone is proposed as an alternative to the crustal thinning model of mutter and others

inversion of the horizontal to vertical spectral ratio in presence of strong lateral heterogeneity the horizontal to vertical spectral ratio hvsr method has recently gained a resurgence of interest because of its new interpretation through the diffuse field approach according to this theory the hvsr measurement is linked to the green s function retrieval while the hvsr method is traditionally used to evaluate simple and shallow velocity model we demonstrate that complex earth structure that includes composite geological layering can be assessed by choosing appropriate data processing and inversion scheme in particular we explore the effects of a strong lateral heterogeneity on the hvsr by using measurements along a vertical crater wall however wave propagation computation with lateral heterogeneity is inefficient to conduct an inversion then to accelerate the forward calculation we identified a simplified model consisting of an unbounded 2 d multilayer medium that allows describing the observed measurements with the use of a correction factor the 2 d character comes from a nonstandard noise illumination related to the wind blowing perpendicularly to the crater walls it is supported by several theoretical and experimental arguments we also show that the h and v components can be retrieved independently which may improve the sensitivity of the inversion at high frequency to reduce the non uniqueness of the problem we consider the joint inversion of the h and hvsr s at several positions where the thicknesses of the layers were evaluated thanks to a large geological outcrop the good agreement between the recovered velocity structure and the geology shows that the method is not limited to unbounded simple shallow structures which opens the domains of application of the method to exploration geophysics or to hazard assessment

overview of local site effects and seismic microzonation mapping in metropolitan vancouver british columbia canada abstract a multi year seismic microzonation project to map local variations of site response across metropolitan metro vancouver british columbia canada is currently underway this paper presents our progress in one dimensional site amplification hazard mapping of metro vancouver following our first field campaign we initiated our microzonation study by assembling relevant geological geophysical and geotechnical datasets from online and private sources to develop a regional 3d geodatabase we perform site characterization near 20 strong motion stations located on soft and stiff sediments using multiple non invasive in situ seismic methods including surface wave array and microtremor horizontal to vertical spectral ratio mhvsr techniques to retrieve shear wave velocity vs depth profiles we also compile all available earthquake recordings from 6 events of moment magnitude m 3 9 to assess earthquake site amplification across metro vancouver comparison of the limited earthquake horizontal to vertical spectral ratio ehvsr data with mhvsrs demonstrates consistent empirical site amplification supporting the use of mhvsrs as a valid proxy for earthquake site amplification in british columbia vertical array recordings in soft sediments from a m 4 7 earthquake further demonstrate consistency between these amplification measures to achieve spatial coverage for regional microzonation mapping the same vs profiling methods are applied in available open areas and more than 1100 mhvsr measurements are collected in a 600 m resolution grid three additional field campaigns will target validation of our non invasive seismic methods with co located invasive testing and fill in any spatial gaps this paper summarizes the developed and applied methodologies and challenges encountered in seismic amplification hazard mapping for the metro vancouver region

are mid latitude slopes sensitive to climatic oscillations implications from an early holocene sequence of slope deposits and buried soils from eastern germany abstract on a straight slope within the lake catchment of kleiner tornowsee brandenburg germany a sequence of slope sediments has been deposited during the late glacial the early holocene and around cal 4 2 ka before today 800 500 and 300 years ago the chronology is based on 21 radiocarbon dates and 11 osl dates and a deposition model including the numerical data as well as stratigraphic information has been calculated with oxcal 4 1 a comparison of the woody taxa of charcoal particles n 566 embedded within the sediments with the known regional vegetation history confirmed the reliability of the dates according to the age volume and distribution the deposition of the early holocene sediments at ca 10 3 kyrs ca 9 5 kyrs and ca 8 2 to 7 7 kyrs before today strongly suggests an influence of known climatic deteriorations phases on geomorphologic processes cold and dry climatic conditions probably promoted wildfires in pinus dominated forests and therefore triggered the observed repeated slope instability in consequence mid latitude slope deposits provide a potential to reconstruct the geomorphological response to climatic events at a high spatial resolution in contrast the recorded mid to late holocene soil erosion phases on the slope have been triggered by land use activities apart from traditional environmental archives slope deposits provide valuable information about the vegetation and climate history

reproduction of microseism h v spectral features using a three dimensional complex topographical model of the sediment bedrock interface in the osaka sedimentary basin summary estimating the velocity structure of microseisms based on the horizontal to vertical spectral ratio hvsr is an extremely practical means of modelling the subsurface structure necessary for strong ground motion predictions thus beyond the traditional framework of the 1 d velocity structure the hvsr derived from observation records of microseisms microtremors with a frequency of about 1 hz or lower originating from ocean waves in areas where the sediment bedrock interface has irregular topographies was reproduced by finite differential method fdm based simulation this study was conducted for the osaka sedimentary basin the sediment bedrock interface of which is three dimensionally complicated and contains grabens steps and ramps because high precision models for this basin have been constructed based on a wide range of existing exploration information the hvsrs of two components the east west direction and the north south direction to the vertical direction derived from the fdm simulations were both well reproduced in terms of not only the peak frequency hvfp but also the spectral curves for a number of observation sites above the sediment bedrock interface with complex geological features these results suggest that with a sufficient number of observation sites for microtremors and highly accurate a priori information on geophysical constants in the sedimentary layer that spatially serves as the reference the irregular shaped sediment bedrock interface may be estimated based on how well the hvsr curves and the hvfp agree between the observations and simulations furthermore the fdm simulations confirmed observed phenomena such as the polarization of the amplitude of horizontal motions and broad or plateau like hvsr peaks of microseisms in grabens and step structures it was determined that the hvfps in areas with these strong irregularities are higher than the peak frequency of rayleigh wave ellipticity for the fundamental mode rhvfp based on the 1 d velocity structure in addition there was a difference of about 20 per cent at most between the hvfp derived from fdm simulations and the rhvfp in areas where the depth of the sediment bedrock interface varies only slightly

from gullies to mountain belts a review of sediment budgets at various scales this paper reviews the state of the art in the concept as well as in the application of sediment budgets in sedimentary research sediments are a product of mass dispersal at the earth surface and take part in global cycles sediment budgets aim at quantifying this mass transfer based on the principle of mass conservation and are the key to determine ancient fluxes of solid matter at the earth surface this involves fundamental questions about the interplay of uplift climate and denudation in mountain belts and transfer of sediments from the continents to the oceans as well as applied issues such as soil and gully erosion reservoir siltation and coastal protection first after introducing basic concepts relevant scales and methodologies the different components of quaternary routing systems from erosion in headwaters river systems glacial and paraglacial systems lakes deltas estuaries coasts shelves epicontinental seas and deep sea fans are discussed in terms of their sediment budget most suitable are sedimentologically closed or semi closed depositional environments e g alluvial fans lakes deltas and deep sea fans in a second step the dynamics of passive active and collisional tectonic settings and sediment budgets in related sedimentary basins are explored and new concepts of sediment portioning at large geodynamic scales are introduced ancient routing systems are more or less incomplete and may be intensively fragmented or destroyed in active tectonic settings in terms of sedimentary basin types rifts intracontinental and epicontinental settings are preferred objects of sediment budgets because of their persistence and relatively simple overall sedimentary architecture however closing basins such as foreland forearc retroarc piggy back and wedge top basins may provide excellent snapshots of orogenic sediment fluxes in a third step the large long lived routing systems of the amazon the ganges brahmaputra and the rhine are reviewed for each system estimates of either sediment volumes mass or sediment fluxes of continental and marine subsystems have been compiled in order to receive a complete routing in terms of mass conservation for specific time periods since the late glacial maximum as well as the cenozoic following lessons can be taken from these case studies i depositional centers and fluxes show strong shifts in space and time and call for caution when simply looking at subsystems ii the response times of these large systems are within the milankovich time interval thus lower than predicted from diffusion models iii cyclic routing of sediments in continental basins is much more dominated by climate human control than by eustacy and iv at long time scales ultimate sinks win over intermittent storage it is concluded from this review that the quantitative understanding of global sediment cycling over historic and geologic time and its response to allogenic forcing is still in its infancy and further research is needed towards a holistic view of sediment routing systems at various temporal and spatial scales and their coupling with global biogeochemical cycles this includes i to better determine response times of large routing systems by linking quaternary with cenozoic sediment budgets and continental with marine sub systems ii to combine advanced provenance techniques with sediment budgets in order to reconstruct ancient systems iii to study sediment partitioning at the basin scale iv to reconcile continental supply dominated sequence stratigraphy with the eustatic dominated marine concept and iv to account for non actualism of ancient systems with respect to their erosion and transport mode in particular during glaciations and pronounced arid intervals glacial and eolian sediment routing may cross over hydrologic boundaries of drainage basins thus challenging the principle of mass conservation

combining hvsr microtremor observations with the spac method for site resonance study of the tamar valley in launceston tasmania australia summary the presence of the deep and narrow tamar valley in the city of launceston tasmania australia in filled with soft sediments above hard dolerite bedrock induces a complex pattern of resonance across the city horizontal to vertical spectrum ratio hvsr microtremor observations are combined with 1 d shear wave velocity swv profiles evaluated from spatially averaged coherency spectra spac observations of the vertical component of the microtremor wavefield to complete a site resonance study in a valley environment such as the tamar valley using the methodology developed in a previous paper 1 d swv profiles are interpreted from observed coherency spectra axial coh above the deepest point of the tamar valley using pairs of sensors spatially separated parallel to the valley axis the 1 d swv profiles interpreted at five sites suggest the depth to bedrock interface varies from approximately z 25 m north of the city to z 250 m above the deepest point of the valley numerical simulations of the propagation of surface waves in a 2 d model representation of the tamar valley compare well with hvsr observations recorded on two profiles transverse to the valley axis hvsr observations can identify the in plane shear sv frequency of resonance above the deepest part of the valley on two separate profiles transverse to the valley axis by computing the ellipticity curves from the preferred swv profiles interpreted by the spac method the antiplane shear sh modes of resonance expected to develop in the tamar valley are identified modes which hvsr observations alone fail to locate with precision hvsr observations suggest a complex mix of 1 d and 2 d patterns of resonance develops across the valley the results from this paper suggest that hvsr microtremor observations can be combined with spac microtremor method to characterize the geology and the pattern of resonance in a 2 d narrow structure such as the tamar valley

topographic site effects and hvsr a comparison between observations and theory we present a comparison between observed and predicted amplification on a topographic feature our data come from an ad hoc experiment carried out during the summer of 1989 in epire northern greece ten digital autonomous three component stations recorded a total of 68 small earthquakes as these data were inadequate to compute empirical transfer functions using the standard spectral ratio ssr technique we explored the possible use of horizontal to vertical spectral ratios hvsr first we compare hvsr computed from theoretical transfer functions for incident p sv and rayleigh waves with the horizontal transfer function for each incidence type second we compute hvsr for our weak motion data set and show that the results are stable with a scatter not larger than that usually accepted in ssr studies we observe significant differences between n s and e w motion when we compare hvsr with theoretical transfer functions we obtain a better agreement for sv motion than for sh motion amplification levels are similar between hvsr and predicted amplification even for the sh case this suggests that discrepancies that have been signaled for the topographic amplification between observations and predictions could be due to site effects being present in the reference station used to computed ssr our results support the use of hvsr to determine topographic site effects thus hvsr may have a large potential to evaluate site effects in a wider variety of geological conditions than previously thought without the shortcomings of ssr finally we show that hvsr computed from noise recordings gives a reasonable estimate of hvsr computed from weak motion data although this conclusion should be better substantiated our preliminary results are encouraging

interdisciplinary interpretation of challenging archives charcoal assemblages in drina valley alluvial and colluvial sediments jagnilo bosnia and herzegovina in connection to an archaeological project in bosnia and herzegovina charcoal fragments from several geomorphological profiles were analysed due to the lack of other archives for palaeoenvironmental reconstruction the major aim of the presented study was to systematically test the suitability of the documented colluvial and alluvial layers for charcoal analysis the profiles uncover main phases of sedimentation of drina valley holocene alluvial sedimentation and for the first time provide anthracological data from the area giving initial insight into the vegetation of the catchment areas and into dynamics of the drina for the late holocene the presence of several genera in the catchment areas of the investigated profiles was documented the most important genera are quercus and ostrya carpinus type fagus acer and pinus are also present light demanding genera such as corylus and the maloideae group indicate human activities alluvial elements such as ulmus fraxinus and alnus are present a major advantage of this investigation is the distinction of catchment areas for alluvial and colluvial layers by the means of charcoal analysis this interdisciplinary cooperation of botanists geoscientists and archaeologists yields new information about a rarely investigated region of southeastern europe and thus improves understanding of natural processes and human impact

from sedimentary records to sediment budgets multiple approaches to catchment sediment flux this paper reviews the traditional approach to sediment budget studies in geomorphology new approaches and more specifically the potential impact of new methodological advances each component of the budget is discussed including the spatial and volumetric estimations of erosion deposition and storage and the precision and accuracy of flux rate estimation examples are used from recent work in germany the netherlands and the uk and include the pedogenic approach to erosion estimation remote sensing lidar geophysics and sediment based dating techniques for flux rate estimation the precision and accuracy of catchment sediment flux estimates based upon sediment storage is not only dependant upon volumetric accuracy but also on the precision and accuracy of sediment dating in this area there has been a revolution with direct sediment dating techniques tl osl esr freeing budget studies from the constraints and biases of radiocarbon of particular importance is the use of cosmogenic nuclides for dating but which can also be used to derive long term erosion rates but only using a steady state assumption finally a tentative initial application of the sediment budget approach to pleistocene terrace staircase in unglaciated basins is discussed it is argued that only now do we have the techniques available to be able to produce accurate sediment budget estimations at spatial scales greater than that of zero order basins and over time periods greater than that covered by direct observations

osl dating of coarse grain fluvial quartz using single aliquot protocols on sediments from ne peloponnese greece abstract optical ages of quartz extracts in holocene sediments from the north eastern peloponnese greece are reported the single aliquot regenerative dose protocol proposed by murray and wintle 2000 radiation measurements 32 57 73 was used to estimate the equivalent dose in these samples a large inter aliquot scatter in d e values was observed for all samples this is ascribed to heterogeneous bleaching of the samples at deposition to estimate a d e for age calculation a technique is suggested based on the analysis of the d e scatter obtained from nine different quartz samples which were artificially bleached and irradiated this procedure is especially useful when the sample quantity is limited the optical age estimates increase with sampling depth an average aggradation rate of 1 5 mm yr is derived using the osl ages this value is consistent with the known uplift rate of 1 2 mm yr

the effect of lateral heterogeneity on horizontal to vertical spectral ratio of microtremors inferred from observation and synthetics abstract horizontal to vertical h v spectral ratios of microtremors hvrm have been traditionally interpreted as representing either the s wave amplification directly or the rayleigh wave ellipticity for a horizontally layered structure however based on the diffuse field theory we have derived an alternative theoretical basis that hvrm corresponds to the square root of the ratio between the imaginary part of the horizontal green s function and that of the vertical one under that condition the 1d horizontal layering assumption is not needed to interpret hvrm as observational evidence of such non 1d hvrm we discovered significant directional dependency at a site on the uji campus kyoto university japan the observed microtremor north south vertical spectral ratios are quite stable and have only one peak around 0 5 hz on the other hand the east west vertical spectral ratios are smaller in amplitude and have higher peak frequencies and sometimes two separated peaks the directional dependency of observed hvrm is aligned to the axis of the 2d basin structure we performed numerical analyses by spectral element method using a unit load on the surface to examine the effect of the 2d basin structure on the imaginary parts of the green s functions we found that the 2d basin structure clearly changes the characteristics of the h v spectral ratios in both perpendicular and parallel directions relative to the basin axis thus we succeeded in theoretically simulating the qualitative difference between the h v spectral ratios for two orthogonal horizontal components of the hvrm observed on the uji campus online material snapshots and animations of wave propagation

an assessment of human versus climatic impacts on holocene soil erosion in ne peloponnese greece soil erosion is a natural geomorphological process which can be triggered by both natural climate tectonics or both and anthropogenic e g agriculture perturbation of the ecosystem evidence has accrued that the holocene climate experienced large fluctuations in amplitude and suggestions of human impact on the ecosystem provided by the neolithic revolution dating back to the early holocene have been made the question of whether man or climate was the dominant factor responsible for holocene soil erosion remains unresolved to resolve the reasons for holocene sediment redistribution high resolution chronometric data on sediments derived from colluvial and alluvial archives from southern greece were obtained and combined with available archaeological and paleoclimatic data from the eastern mediterranean these data show a significant correlation between sedimentation rates and settlement history climatic fluctuations are only weakly correlated with sedimentation history the results show high sedimentation rates during the early neolithic 7th millennium bc in southern greece suggesting that holocene soil erosion was triggered by human activity and then amplified by enhanced precipitation this would explain the high sedimentation rates during the early neolithic in connection with enhanced precipitation in the eastern mediterranean which continued until the mid holocene

along axis variations in seafloor spreading in the mark area recent investigations with the manned submersible alvin and the angus deep towed camera sled greatly extended the known range of variations in the style of seafloor spreading along the axis of the mid atlantic ridge five transects of the spreading centre at intervals of10 20 km south of the kane fracture zone at 24 n latitude demonstrate dramatic changes in the style and magnitude of tectonic extension development of the neovolcanic zone expression of hydrothermal venting types oflithologic exposures and morphology of the median valley

present and past soil erosion rates in catchments of the kraichgau area sw germany abstract in four catchments of the kraichgau area sw germany all covered with loess and distinguished by different combinations of natural and manmade erosion risks total and recent soil losses from the hills were examined the total loss was calculated as difference of quantities of soil material of the mapped soil units compared with a profile under erosion protection the recent loss on the basis of young sediments in the depression using contents of cadmium and lead to distinguish between old and young soil deposits in the depressions in two of the catchments total soil loss from the hills came up to about 90 of the formerly existing luvisol material total soil loss did not correlate with the natural erosion risks inclination slope length but recent soil loss correlated with the manmade erosion risks land utilisation type this recent soil loss ranged from less than 14 t ha 1 yr 1 in the catchment with terraced slopes to 84 t ha 1 yr 1 in a catchment with a high percentage of corn and sugar beet on the cultivated area and with large fields cultivated downslope in a similarly endowed catchment but with transversally cultivated fields a recent soil erosion of 39 t ha 1 yr 1 was calculated methodical problems are discussed

historical soil erosion by water in germany scales and archives chronology research perspectives abstract the published record of historical soil erosion by water in germany as deduced from dated slope deposits n 306 alluvial sediments n 120 and lake sediments is summarized in this paper the number of sediments investigated reflects the state of knowledge chronology of historical soil erosion and to a certain degree the intensity of the human impact on german landscapes during the holocene even though few data of calculated historical soil erosion intensities exist an estimation of historical soil erosion in germany combining the available data has been calculated soil erosion in germany occurred first locally during the early holocene probably triggered by climatic variability from the neolithic onward the record reflects the human impact according to agricultural land use the observed variability indicates phases of weaker and regained intensity of agricultural land use in germany few records characterise the early and middle bronze age ca 2000 1600 bc and the migration period and the early medieval times ca 400 1000 ad surprisingly for the roman emperor times ca 1 400 ad a decreasing number of soil sediments is recorded even when the data from southern germany is examined separately phases characterised by an increase in soil erosion were the late bronze age and pre roman iron age ca 1600 bc 1 ad the high and late medieval times ca 1000 1350 ad and the modern times ca 1500 ad until today some extraordinary heavy precipitation events late 18th early 19th first half of 14th century pre roman iron age topped the even high soil erosion intensities research gaps as well as potential for future research as derived from the available data are outlined

on the limitation of the h v spectral ratio using seismic noise as an exploration tool application to the grenoble valley france a small apex ratio basin the h v spectral ratio method based on seismic noise hvsrn was used in the grenoble basin france an alpine valley characterized by a small apex ratio the resonance frequencies obtained in the experiments were compared to the thickness of the sediments deduced from a microgravimetric survey and to the 1 d theoretical assessment of site responses given the abundance of data on the sediments and depth of the basin the values of the theoretical resonance frequency fo can be determined quite accurately however it has been observed that the effects of basin geometry can disturb fo measurements using the hvsr method in particular for a case like the grenoble basin which has a small apex ratio w h and strong suspected 2 d and or 3 d effects interpretation of fo values in terms of bedrock depth gives rise to estimation errors of about 10 in certain cases with the most significant errors 50 occurring on the edges of the basin where subsurface layers are characterised by larger heterogeneities and where the basin topography is accentuated this study suggests that great care must be taken when using the hvsrn method as an exploration tool at least in valleys with a small apex ratio

detachment faulting and amagmatic extension at mid ocean ridges the josephine ophiolite as an example lithospheric extension at the josephine paleo spreading center occurred by a combination of magmatic and amagmatic processes the amount of extension by amagmatic processes appears at least as large as that from magmatic processes the structural processes responsible for amagmatic extension in the absence of a magma chamber appear to be normal faulting and block rotation in the brittle upper lithosphere and ductile flow in the lower lithosphere an extensive detachment shear zone occurs beneath the fault blocks approximately 1 km below the base of the crustal sequence the amount of amagmatic extension can be approximated from a simple geometric model relating extension to rotations of sheeted dikes similarly attenuated crustal thicknesses can be related to fault block rotations the results suggest that thin crustal sequences commonly observed in ophiolites and near fracture zones may result from attenuation during amagmatic extension furthermore detachment faulting and block rotation may be characteristic of spreading centers where the magma budget is low

an empirical site classification method for strong motion stations in japan using h v response spectral ratio having a reliable site classification scheme is vital for the development of robust strong motion attenuation models we discuss a promising empirical site classification scheme based on strong motion data from japan we assigned site classes according to the site classification defined in engineering design codes in japan for those k net sites where boreholes reached either to rock or to stiff soils with shear wave velocity of 600 m sec or larger using four site classes defined by dominant site period the average response spectral ratios of the horizontal and vertical components h v of earthquake records for all site classes were found not to be strongly affected by japan meteorological agency jma magnitude hypocentral distance and focal depth for all site classes we used h v ratios for records from the classified k net sites to establish a site classification index using the mean spectral ratios over a wide range of spectral period using the index we were able to classify both k net stations with soil layers thicker than 20 m and other strong motion stations in japan the peak period of the h v spectral ratio can also be used to identify soft soil sites the site amplification factors calculated from the site class terms based on the new site classification are consistent with the period bands defined for these site classes

an experimental topographic amplification study at los alamos national laboratory using ambient vibrations abstract an experimental study aimed at investigating potential topographic amplification of seismic waves was conducted on a 50 m tall and 185 m wide soft rock ridge located at los alamos national laboratory near los alamos new mexico ten portable broadband seismograph stations were placed in arrays across the ridge and left to record ambient vibration data for 9 hours clear evidence of topographic amplification was observed by comparing spectral ratios calculated from ambient noise recordings at the toe slope and crest of the instrumented ridge the inferred resonance frequency of the ridge obtained from the experimental recordings was found to agree well with several simple estimates of the theoretical resonance frequency based on its geometry and stiffness results support the feasibility of quantifying the frequency range of topographic amplification solely using ambient vibrations rather than strong or weak ground motions additionally comparisons have been made between a number of widely used experimental methods for quantifying topographic effects such as the standard spectral ratio median reference method and horizontal to vertical spectral ratio differences in the amplification and frequency range of topographic effects indicated by these methods highlight the importance of choosing a reference condition that is appropriate for the site specific conditions and goals associated with an experimental topographic amplification study

episodic magma chambers and amagmatic extension in the josephine ophiolite geochemical and structural aspects of the josephine ophiolite indicate that it formed by alternating cycles of magmatic and structural amagmatic extension episodic magma chambers are indicated by the presence of very primitive lavas in the lower pillow lavas which would have mixed into a magma chamber fe ti basalts that occur in the uppermost extrusive rocks and plagiogranites that occur along the sheeted dike gabbro contact represent highly fractionated magmas produced during the last stages of crystallization of a magma chamber during periods of amagmatic extension breccias accumulated and the entire crustal sequence was tilted 50 probably by faulting above an upper mantle detachment more than 1000 m of uplift and down dropping between magmatic cycles is suggested by the presence of out of place screens in the sheeted dike complex

patterns of human occupation during the early holocene in the central ebro basin ne spain in response to the 8 2 ka climatic event abstract the central ebro river basin ne spain is the most northern area of truly semi arid mediterranean climate in europe and prehistoric human occupation there has been strongly influenced by this extreme environmental condition modern climate conditions single out this region due to the harsh environment characterised by the highest absolute summer temperatures of the ebro river basin the bajo aragon region se ebro river basin was intensively populated during the early holocene 9400 8200 cal yr bp but the settlements were abandoned abruptly at around 8200 cal yr bp we propose that this archaeological silence was caused by the regional impact of the global abrupt 8 2 ka cold event available regional paleoclimate archives demonstrate the existence of an aridity crisis then that interrupted the humid early holocene that environmental crisis would have forced hunter gatherer groups from the bajo aragon to migrate to regions with more favourable conditions i e more humid mountainous areas and only return in the neolithic coherently archaeological sites persist during this crisis in the nearby iberian range maestrazgo and the north ebro river area pre pyrenean mountains and along the northwestern ebro basin

younger dryas to mid holocene environmental history of the lowlands of nw transylvania romania pollen micro charcoal and total carbon analyses on sediments from the turbuta palaeolake in the transylvanian basin of nw romania reveal younger dryas to mid holocene environmental changes the chronostratigraphy relies on ams 14c measurements on organic matter and u th tims datings of snail shells results indicate the presence of pinus and betula open woodlands with small populations of picea ulmus alnus and salix before 12 000 cal yr bp a fairly abrupt replacement of pinus and betula by ulmus dominated woodlands at ca 11 900 cal yr bp likely represents competition effects of vegetation driven by climate warming at the onset of the holocene by 11 000 cal yr bp the woodlands were increasingly diverse and dense with the expansion of quercus fraxinus and tilia the establishment of corylus and the decline of upland herbaceous and shrubs taxa the marked expansion of quercus accompanied by tilia between 10 500 and 8000 cal yr bp could be the result of low effective moisture associated with both low elevation of the site and with regional change towards a drier climate at 10 000 cal yr bp corylus spread across the region and by 8000 cal yr bp it replaced quercus as a dominant forest constituent with only little representation of picea abies carpinus became established around 5500 cal yr bp but it was only a minor constituent in local woodlands until ca 5000 cal yr bp results from this study also indicate that the woodlands in the lowlands of turbuta were never closed

holocene flood histories in south western usa harden t macklin m g baker v r 2010 holocene flood histories in south western usa earth surface processes and landforms 35 6 707 716 sponsorship aberystwyth university university of arizona

reconstructing green s function by correlation of the coda of the correlation c3 of ambient seismic noise analysis of long range correlation of the microseisms has been shown to provide reliable measurements of surface wave speeds that can be used for seismic imaging and monitoring in the case of an even distribution of noise sources it has been theoretically demonstrated that the correlation is the exact green s function including all types of waves this method is limited in its application by the actual source distribution in practice the azimuthal distribution of energy flux of the noise is dominated by some particular directions resulting in a clear azimuthal dependence of the quality of the reconstruction of rayleigh waves with a poor reconstruction in some azimuths to solve this problem we use noise correlations measured on the entire network we consider two stations a and b for which the rayleigh waves could not be discerned in the in the correlation of continuous records of ambient noise we computed all correlations between the station a respectively b and all the 150 other stations located at regional distances theoretically these virtual seismograms contain direct waves and coda although they are clearly contaminated by the influence of the imperfect ambient noise field and most are inadequate for direct analysis we used these correlation functions as equivalents to seismograms produced by sources acting at the 150 stations locations and recorded in a respectively b we select time windows in those virtual seismograms that correspond to coda and compute correlations between them this metacorrelation is found to exhibit the surface wave part of the green s function that was not visible in the raw correlation of ambient noise we illustrate the legitimacy of the reconstruction by comparison with raw noise correlations this procedure can be used to assess seismic velocity between stations even in presence of a directive and poorly oriented ambient noise the result shows that in spite of the small signal to noise ratios often seen in correlations of ambient noise especially at large lag time corresponding to coda their codas are better equipartitioned than was the ambient noise upon which they were based they are therefore presumably multiply scattered and contain information on both direct surface waves and also on more complex travel paths

structural evolution of the east pacific rise axis from 13 10 n to 10 35 n interpretations from seamarc i data in 1983 the seamarc i and the sea beam systems imaged the east pacific rise epr and the clipperton transform fault from 13 10 n to 9 50 n revealing both magmatic and tectonic segmentation along the rise axis tectonic segments are defined by an undulating axial zone of extension which widens and narrows at an average wavelength of 45 km in addition axial fissure fault density and length curves reveal wavelengths of 30 and 56 km the narrowest axial zones 0 5 km in width correspond to regions of hydrothermal activity and are located atop regional morphologic highs quasi harmonically spaced at 155 km these highs define the major magma centers on the rise axis about which seamounts cluster superimposed on the intermediate wavelength highs are smaller highs from 10 to 50 km in length which are truncated by overlapping spreading centers osc s at their distal edges the rise axis widens near osc s while it narrows and disappears near the clipperton transform fault suggesting that transforms and osc s have different origins imagery on and adjacent to a few osc s reveals that in some cases osc s migrate along the axis forming relict off axial structural traces at oblique angles 285 330 to the axis off axial fault density and length curves have wavelengths similar to the axial curves however fault densities to the west of the axis are somewhat antisymmetric to fissure fault densities on the axis in contrast faults to the east of the axis nearly mimic fissure fault density and length curves on the axis suggesting that the fracture pattern is controlled by the state of deviatoric stress in the adjacent cocos plate to the east the data suggest that large deep seated magma diapirs may dominate the magmatic segmentation of the epr generating dynamically supported 155 km wavelength highs smaller shallower magma cupulas may rise as fingers to the seafloor above the large diapirs where the magma erupts may be a factor of the thin skin tectonic segmentation of the rise axis formed in response to the state of deviatoric stress in the upper crust small ocs s may form at crustal weak points and may migrate in response to magma body movement along the axis the instability of both the magmatic and tectonic segmentation is apparent from the oblique alignment of both seamount chains and relict osc s with their present day counterparts

are microtremors useful in site response evaluation we have reviewed the applicability of microtremor measurements to evaluate site response of soft soils to this end we evaluated three different techniques commonly used to estimate site effects from microtremor measurements interpretation of fourier amplitude spectra computation of spectral ratios relative to a firm reference station and finally computation of spectral ratios of horizontal components relative to the vertical component of ground motion nakamura s technique these techniques are applied to microtremor records obtained in three cities in mexico mexico city oaxaca and acapulco these cities differ in their local geological conditions and in their seismotectonic environment in order to evaluate the results obtained from microtremor measurements we compare them with standard spectral ratios of the intense s wave part of weak or strong motion records obtained at the same sites our results showed that microtremor measurements can be used to estimate the dominant period of a site with very acceptable reliability in the range 0 3 to 5 hz the best results were obtained with nakamura s technique which also gives a rough estimate of amplification of seismic waves when the local geology is relatively simple simple numerical simulations indicate that the underlying assumptions of nakamura s technique are consistent with the propagation of rayleigh waves these simple numerical simulations also explain why different researchers have been able to successfully characterize 1d site effects using microtremor records regardless of whether they consider microtremors to consist of surface or body waves our results strongly suggest that the technique by nakamura effectively compensates for source effects in microtremor measurements which eliminates a major limitation to their application in earthquake engineering

the seismic noise wavefield is not diffuse passive seismology is burgeoning under the apparent theoretical support of diffuse acoustics however basic physical arguments suggest that this theory may not be applicable to seismic noise a procedure is developed to establish the applicability of the diffuse field paradigm to a wavefield based on testing the latter for azimuthal isotropy and spatial homogeneity this procedure is then applied to the seismic noise recorded at 65 sites covering a wide variety of environmental and subsoil conditions considering the instantaneous oscillation vector measured at single triaxial stations the hypothesis of azimuthal isotropy is rejected in all cases with high confidence which makes the spatial homogeneity test unnecessary and leads directly to conclude that the seismic noise wavefield is not diffuse however such a conclusion has no practical effect on passive imaging which is also possible in non diffuse wavefields

holocene river and slope activity in the visoko basin bosnia herzegovina climate and land use effects alluvial and colluvial deposits were investigated at prehistoric tells close to the bosna river the chronology is based on ten radiocarbon ages five optically stimulated luminescence ages and on the archaeological record fluvial activity of the bosna river is indicated by overbank fines ca 5000 1000 bc 500 bc until today and a phase of lateral displacement of the river bed with subsequent channel fills ca 2000 500 bc early holocene fluvial activity was probably triggered by climatic variability but might have promoted the expansion of neolithic societies into the visoko basin mid to late holocene river activity occurred under increased climatic aridity but coincided with the expansion of prehistoric settlements to a wider area of the river basin on hard rocks in the adjacent mountainous areas the destruction of the thin soil cover in the mountains is discussed as a probable trigger for enduring subsequent river activity this is also indicated by a change in the geochemical signature of the alluvial sediments the proposed mechanism might explain the mid to late holocene river history in other regions the potential of geochemical analyses and diachronous high resolution archaeological records to make inferences regarding sediment sources and geomorphological processes is demonstrated copyright 2013 john wiley sons ltd