quaternary palaeohydrological evolution of a playa lake salada mediana central ebro basin spain this research was partly funded by the national science foundation usa under the ear 941 8657 programme and by the eead csic project number z 5 96 this is limnological research center contribution number 527

the silence of the layers archaeological site visibility in the pleistocene holocene transition at the ebro basin abstract the ebro basin constitutes one of the most representative territories in sw europe for the study of prehistoric societies during the pleistocene holocene transition the correlation of palaeoenvironmental and geomorphological proxies obtained from sedimentary records with chronologically well constrained reference archaeological sites has allowed defining this time frame precisely such that three main pilot areas haven been broadly depicted the alavese region the pre pyrenees and the bajo aragon overall the human imprint in the ebro basin was rare during the upper palaeolithic but more visible from the upper magdalenian 14500 13500 cal bp to neolithic times up to 5500 cal bp local environmental resources were continuously managed by the prehistoric communities in the different areas of study in fact the ebro basin acted during those millennia as a whole developing the same cultural trends industrial techniques and settlement patterns in parallel throughout the territory however some gaps exist in the 14c frequency curve scdpd curve this is partially related to prehistoric sites in particular lithologies and geological structures that could have partly been lost by erosional processes especially during the early holocene in addition this gap also parallels the reconstructed climate trend for the pre pyrenean and the bajo aragon areas which are defined by high frequencies of xerophilous flora until ca 9500 cal bp suggesting that continental climate features could have hampered the presence of well established human communities in inland regions the interdisciplinary research archaeology geomorphology and palaeoclimatology discussed in this paper offers clues to understand the existence of fills and gaps in the archaeological record of the ebro basin and can be applied in other territories with similar geographic and climate patterns

a multi proxy record of holocene climatic change in southwestern spain the laguna de medina cadiz palaeolimnological data diatoms ostracods foraminifera molluscs aquatic pollen and lithology from a radiocarbon dated sediment core from a saline lake the laguna de medina provide the first complete record of holocene lake level change for southwest spain for the last c 9000 cal years the lake has always been relatively shallow but has exhibited marked fluctuations in salinity and water depth especially in the earlier record when oscillations culminate in maximum lake levels from c 6960 6680 cal bp c 6070 5830 bp indicating enhanced early to mid holocene humidity and a mid holocene humidity maximum prolonged shallowing thereafter reflects in part increased aridity in the later holocene lake desiccation followed by a c 800 yr phase zone 2 of major limnological change commencing at c 8000 cal bp c 7200 bp and a number of other abrupt desiccation events are also noteworthy the mid holocene maximum is consistent with widespread evidence for high lake levels around 6000 bp but t

lateglacial and late holocene environmental and vegetational change in salada mediana central ebro basin spain the salada mediana lacustrine sequence central ebro basin spain 41330 10an 0344 w 350 m a s l provides an example of the potential and limitations of saline lake records as palaeoclimate proxies in the semi arid mediterranean region sedimentary facies analyses chemical stratigraphy stable isotopes d18o and d13c of authigenic carbonates d13c values of bulk organic matter and pollen analyses from sediment cores provide paleohydrological and vegetation change reconstructions for the lateglacial and late holocene in the central ebro basin a preliminary chronology is based on 210pb and 14c ams dates the lacustrine sequence is composed of three sedimentary sections the lower section was deposited in a permanent saline to brackish lake this stage represents the most humid period in the record and it was accompanied by the expansion of temperate trees particularly corylus the middle section was deposited in an ephemeral playa lake complex frequent subaerial exposure conditions favour the colonisation of the playa lake oor by chenopodiaceae during a low water table period this interval re ects the most arid conditions in the salada mediana record including the current environment a secondary temperate tree expansion occurred after the maximum aridity period aquatic plants and cyanobacterial mats spread in the lake during periods of raised water tables this paleohydrological and vegetational evolution attests to large changes in e ective moisture during the lateglacial in the semi arid northeastern spain the abundance of corylus during the lateglacial indicates that refugia for temperate trees were located along the ebro valley during the last glacial maximum the holocene sediments in the salada mediana records have been eroded and the upper section represents deposition during the last few centuries 2000 elsevier science ltd and inqua all rights reserved

stress associated coda attenuation from ultrasonic waveform measurements 1 the theoretical and practical exploration of stress changes from seismic waves has been the focus of recent debate within the scientific community because of its direct implications on earthquake forecasts and seismic hazards propagating in underground structures wave velocity and attenuation contain information on stress changes of the earth s interior as a result of changes in the physical state of materials seismic coda which consists of a superposition of incoherent scattered waves is known to reflect small scale random heterogeneities in the earth medium in this article we investigate the coda attenuation under different effective stresses using laboratory measurements to increase our understanding of the dependence of acoustic coda attenuation on stress variations in rocks

sedimentary facies distribution and genesis of a recent carbonate rich saline lake gallocanta lake iberian chain ne spain abstract the study focuses on the holocene sedimentary infill of the gallocanta lacustrine basin in the iberian chain ne spain the gallocanta lake is a saline wetland with a maximum length of 7 5 km and a maximum width of 2 85 km the water depth varies significantly from a maximum depth of 2 m to completely dry in the central areas central subenvironment sapropels and salts develop with halite gypsum anhydrite dolomite aragonite calcite magnesite and lesser amounts of quartz and clay minerals cyanobacteria filaments are related to the aragonite and dolomite crystals the marginal subenvironment either has a gradual or a sharp change from that of the central subenvironment an inner area with desiccated light grey lutites is present in this marginal subenvironment in sem and x ray diffraction analyses quartz clay minerals aragonite calcite and small quantities of dolomite gypsum anhydrite and halite can be identified this inner area is surrounded by an external fringe composed of light brown lutites and a high concentration of salicornia meadwod and microbial mats this zone is only occasionally submerged and contains sandy and conglomerate islets active palustrine areas are flood zones where grey lutites with a significant quantity of vegetation such as reeds are common in general this entire sector is being modified by human action five sedimentary facies have been defined and this has enabled the identification of three distinct stages in the general evolution of the basin the first stage is an alluvial period developing during an arid climate after this a more humid stage facilitated the installation of a shallow carbonate rich lake a reduction of the water level probably due to a more arid stage induces a salinity increase of the lacustrine brine and the change to the third stage which corresponds to the present conditions the water level experienced frequent oscillations and alternations between humid conditions with a high production of organic matter which favors carbonate formation and water level dropdowns even to total dryness with saline sedimentation

using hydroacoustic stations as water column seismometers 1 getting seismic data from the deep oceans usually involves ocean bottom seismometers but hydrophone arrays may provide a practical alternative means of obtaining vector data we here explore this possibility using hydrophone stations of the international monitoring system which have been used to study icebergs and t wave propagation among others these stations consist of three hydrophones at about the depth of the deep sound channel in a horizontal triangle array with 2 km sides we use data from these stations in the very low frequency regime 0 01 0 05 hz band to demonstrate that these stations can also be used as water column seismometers by differencing the acoustic pressure we obtain vector quantities analogous to what a seismometer would record comparing processed hydrophone station records of the 2004 great sumatra andaman earthquake with broadband seismograms from a nearby island station we find that the differenced hydrophones are indeed a practical surrogate for seismometers

holocene climatic changes in the western mediterranean from south east france to south east spain abstract holocene climatic changes along coastal regions from south east france to south east spain were studied using pollen ratios comparing modern pollen rain vegetation and climate along selected transects from the atlantic ocean to the mediterranean we obtained threshold values of two different ratios corresponding to the different climatic conditions along the transects these pollen ratios and threshold values were employed to characterize the holocene climatic changes from nine mediterranean coastal sites the results were compared with data from marine and continental pollen sequences distributed in the western mediterranean basin and with additional regional data independent of human activity lake level fluctuations alpine glacier advance and retreat chronology 14 c anomaly and cooling phases in eastern france and central europe the role of anthropogenic activities and climate on the changes in vegetation is discussed six major changes in vegetation cover were identified they correspond to aridification phases that occurred around 9500 9000 yr bp 10 900 9700 cal bp 7500 7000 yr bp 8400 7600 cal bp 4500 4000 yr bp 5300 4200 cal bp 3700 3300 yr bp 4300 3400 cal bp 2600 1900 yr bp 2850 1730 cal bp and 1300 1000 yr bp 1300 750 cal bp these arid episodes were regional responses to more global climatic changes and determined the changes in the vegetation cover humans undoubtedly enhanced the vegetation changes but none the less had to adapt to these new climatic conditions

climatic change on the iberian peninsula recorded in a 30 000 yr pollen record from lake banyoles the banyoles lacustrine sequence shows that the vegetational history of the northeastern iberian peninsula during the last 30 000 yr follows the north atlantic pattern of climatic oscillations the banyoles pollen diagram supported by two calibrated 14c dates and nine u th dates shows a clear interstadial event between 30 000 and 27 000 yr b p a pleniglacial period with minor oscillations that ended abruptly ca 14 420 410 yr b p and a late glacial sequence that records the classical stages described in northern europe the bolling allerod interstade the younger dryas event at 12 000 yr b p u series age and a short warming phase between the younger dryas and the last cold event dated at 11 000 yr b p u series age

the holocene and upper pleistocene pollen record from padul granada spain a new study two borings were made at the site of padul granada pollen analysis of 200 spectra from two successive sequences 14 8 and 8 m deep enables a description of the vegetational and climatic history of this region the most southern one in europe from early wurmian times the chronology is supported by twenty one 14c dates original equivalents are found for the great european prewurm interstadials a markedly arid though thermically not extreme episode exactly equivalent to stage 4 of the marine isotopic stratigraphy closes this relatively temperate period the middle part of the last glacial shows climatic fluctuations that are poorly characterized as is often the case in europe for this period a long section very probably corresponding to the complete last pleniglacial does not show any climatic amelioration towards 15 000 yr b p a change in the diagram is noted that can only be interpreted as reflecting a larger expansion of a regional steppe cover this event also reported on three occasions in southeast france marks the beginning of the oldest dryas the climatic amelioration of ca 13 000 yr b p is far more pronounced here than anywhere else in europe whereas that at 10 000 yr b p is not so clearly marked this unexpected result may be accounted for by the fact that padul is the first continental site so far south and so near pleniglacial refuges to be known on the other hand this result is consistent with what is known from oceanic isotopic stratigraphy a quite new late glacial and holocene vegetational history is revealed characterized by the early appearance and dominance of quercus ilex oak forests of a southern type and the early occurrence of quercus suber and olea it is the first account of a complete history of the postglacial reafforestation in a region with a modern semi arid mediterranean climate from the palaeoclimatic point of view it shows that the hot and humid holocene optimum was attained slightly before 8000 yr b p and that the holocene climatic fluctuations were of but small amplitude

contrasting patterns of hydrological changes in europe in response to holocene climate cooling phases the quantitative reconstruction of climatic parameters from pollen and lake level data obtained at saint jorioz lake annecy eastern france gives evidence for cooler and wetter conditions during the 8 2 ka cold event a comparison of these regional data with other hydrological records reconstructed in europe for the same period suggests as a working hypothesis that mid latitudes between ca 50 and 43 underwent wetter conditions in response to the cooling whereas northern and southern europe were marked by drier climate in the latter case leading to an interruption of the sapropel 1 formation in the mediterranean a similar hydrological tri partition of europe can be observed during other holocene cooling phases associated with north atlantic ird events data indicate that the middle zone characterised by wetter climate conditions could have had a more extended latitudinal amplitude during phases of climate cooling weaker than the 8 2 ka event the differences in expansion of the wet mid european zone depending on holocene climate cooling phases could reflect variations in the strength of the atlantic westerly jet in relation with the thermal gradient between high and low latitudes

use of s wave attenuation from perforation shots to map the growth of the stimulated reservoir volume in the marcellus gas shale abstract water filled fractures stimulated by hydraulic fracturing will severely attenuate s waves by comparing the p and s wave amplitudes generated from perforation shots in the marcellus gas shale one can infer the existence and constrain the location of stimulated hydraulic fractures the waveforms of the perforation shots in unstimulated gas shale are first analyzed to define the prestimulation radiation pattern then the change of perforation shot s wave waveform is examined for information about the development of hydraulic fractures s wave attenuation validates the existence of offstage hydraulic fractures and the invasion of treatment fluid from another neighbor stage this method might have potential use in designing an active seismic survey to more effectively monitor hydraulic fracture stimulation beyond the current microseismic mapping techniques

late quaternary pedogenesis of lacustrine terraces in gallocanta lake ne spain abstract transitional areas of lake margins are complex environments whose evolution is strongly controlled by flooding frequency and persistence the edaphic development of lacustrine marginal environments can be reconstructed by combining detailed geomorphological analysis with a systematic edaphic study of toposequences this approach has been applied to a set of recent lacustrine terraces in the downwind palustrine area of the gallocanta saline lake located in a semiarid area in ne spain up to five terraces from 1 6 to 4 5 m above the lake bottom have been identified and mapped using stereo photointerpretation and airborne lidar data several cycles of water level fluctuations as part of a general trend towards lake desiccation have generated stepped terrace levels the soils of these terraces have different morphological characteristics and provide evidences for the gallocanta paleolake being larger than that of the present day the soils have a sandy loam texture with variable clay content 1 to 46 and a predominantly carbonate composition mean 26 the soils are developed in a sequence of lacustrine carbonate rich mean 37 fine grained gray layers overlaying detrital mean 51 gravels and frequently erosive carbonate poor reddish layers the pedogenesis of the downwind palustrine area is mainly characterized by poorly developed carbonate accumulations and common redox mottles associated with water level fluctuations in the lake which continuously rejuvenate or truncate the soils integrating pedological and geomorphological features provides insight into recent complex lacustrine and soil forming processes and facilitates management strategies and plans for this protected saline environment

palynological evidence for climatic change and human activity during the holocene on minorca balearic islands four pollen diagrams from minorca balearic islands have been correlated with other previously studied sequences from majorca and minorca to define a holocene landscape sequence for the region from 8000 yr b p to the present the lower part of the pollen diagrams reflects a climatic phase with more rain and less marked seasonality than today significant quantities ofcorylus buxus and mesophilous taxa are found in the middle part between 5000 and 4000 yr b p a strong change is recorded in composition and structure of the vegetational landscape with vegetation appearing that was adapted to mediterranean conditions this episode coincided with the first human colonization of the island and also with a widespread climatic change in the western mediterranean region the change in taxa was complex and some sclerophyllous taxa sucholeaplayed an important role in the transformation of the landscape physiognomy from the mid holocene until the present although human activities have removed much of the mediterranean vegetation on the balearic islands it seems clear that the changes have been brought about in part by increasing dryness

stratigraphic architecture and alluvial geoarchaeology of an ephemeral fluvial infilling climatic versus anthropogenic factors controlling the holocene fluvial evolution in southeastern spain drylands abstract two stages of depositional high discharge fluvial environments are recorded in the infilling of a rock shelter in a canyon of the segura river namely 1 first stage aggradational alluvial gravels in the lower part interpreted as braided channel bars seventh millennium to 2030 cal bc and 2 second stage slackwater flood deposits in the upper part between 2030 cal bc and after 900 ad during a stage of main channel incision reconstructed flood discharges for the second stage were a minimum of 700 m 3 s extreme palaeofloods that inundated the cave from the canyon inlet were successively higher and are correlated to quick rising flash floods the characteristics of cultural remains preserved by flood deposits reveal long periods of human cave occupation and passage through the canyon without extreme floods occurring these long periods of low discharge fluvial flow punctuated by catastrophic flash floods are linked to a torrential fluvial regime the torrential regime is the current hydrologic and climatic scenario in the streams of semi arid southeastern spain it is discusses the climatic versus anthropogenic factors affecting the fluvial development we conclude that the archaeo fluvial record of the pozo rock shelter indicates that the present day semi arid conditions of the southeastern spain drylands extend back to circa 4000 yr bp methodologically the combination of fluvial palaeohydrology and geoarchaeology appears to be a robust tool to reconstruct long term holocene climate changes

using dual well seismic measurements to infer the mechanical properties of a hot dry rock geothermal system high frequency 8 15 khz seismic waves that travel between two boreholes are used to probe the detailed structure of rock in the los alamos national laboratory fenton hill hot dry rock geothermal energy reservoir we study travel times of direct p waves and spectral characteristics of waveforms in an effort to determine whether or not large fluid filled fractures are present in the rock between the two boreholes data from two experiments separated in time by 1 year are studied we find dramatic differences between the two experiments in p wave velocity and in spectral characteristics of waveforms that traversed the same region we also find variations in p wave velocity and spectra as a function of location during one experiment loss of high frequency content of direct arriving p waves during the second dual well seismic experiment is compared with q found by using the coda wave technique aki and chouet 1975 and also with theoretical results on frequency dependence of transmission through a water filled fracture to determine the minimum number of large fractures in the system two to four fractures with thickness about 4 mm and vertical extent of as much as 200 m are required to explain observations during the second experiment efficient transmission of high frequencies observed during the first experiment is interpreted as meaning that fracture thickness was less than 1 mm at that time increased fracture thickness during the second experiment is probably due to a 75 day period of heat extraction during which in situ temperature dropped by as much as 100 below the virgin temperature since the coefficient of linear thermal expansion of granite is approximately 10 5 c a decrease in temperature of 100 c in a region on the order of 1 m around the fracture is required to explain the increased fracture thickness

interaction of seismic waves with a viscous liquid layer abstract the interaction of seismic waves with a layer filled with a viscous fluid is studied this study is intended to provide the basis for designing active seismic experiments to detect the existence of hydraulically induced fractures in a hot dry rock geothermal energy system we compute transmission and reflection coefficients for p sv and sh waves incident at arbitrary angles onto a fluid layer embedded between two homogeneous half spaces we find that coefficients for sh waves at normal incidence can be written in terms of two dimensionless parameters one of these parameters i is the ratio of acoustic impedance of the fluid to the acoustic impedance of the solid the other dimensionless parameter d is a measure of the amount of energy the sh wave loses during one pass through the fluid layer we find that the amplitude of the sh wave transmitted through the fluid layer is equal to the amplitude of the incident sh wave if i is nearly 1 and d is small as d increases energy is lost due to viscous dissipation in the fluid and transmitted wave amplitude diminishes if i is not nearly 1 some energy is reflected by the fluid layer three dimensionless parameters are required for solution for the case of p waves normally incident on the fluid layer one parameter r is the ratio of the bulk modulus to effective shear modulus of the fluid the second parameter is the ratio of elastic impedance of the solid to the shear impedance of the fluid and the third is d we find that the value of r is a good measure of the importance of fluid viscosity on the propagation of p waves through the fluid detailed studies of the effects of fluid and solid physical properties on the amplitudes of transmitted and reflected waves when waves are normally incident provide valuable insight into the importance of physical properties in the calculations for non normal incidence finally reflection and transmission coefficients are computed for p and sv waves incident at arbitrary angle on a viscous fluid layer physical properties of fluid and rock are chosen to be those thought appropriate for the los alamos national laboratory hot dry rock geothermal test site located at fenton hill new mexico

holocene paleohydrology of playa lakes in northern and central spain a reconstruction based on the mineral composition of lacustrine sediments abstract the focus of this study is the reconstruction of holocene limnic conditions of playa lakes in central spain using inorganic components of their sediments it is demonstrated that the mineralogical sediment characters provide valuable paleoenvironmental information if dolomites originate from authigenic precipitation or early diagenetic dolomitization the mg ca ratio of dolomites derived from the position of dolomite s major x ray diffraction line turns out to be an indicator for the reconstruction of paleosalinity in contrast the concentrations of carbonates and sulphatic evaporites and their changing proportion to siliciclastic sediments point to changing depositional environments the comparison of investigations from different playa lakes and drainage basin systems shows that the interpretation of mineralogical sediment features always has to consider the petrographic hydrologic and geomorphic features of the catchment as for the lacustrine sediments investigated there are no data available yet a preliminary chronological framework is derived by comparison with results from neighbouring areas based on this the hypothesis is put forward that during the so called little ice age subhumid environmental conditions occurred over the central part of the iberian peninsula while today climatic conditions are dry subhumid to subarid also for times older than the subatlantic distinct changes of environmental conditions are noticed but various hiatuses in the sediments make correlation difficult

monte carlo simulation of stress associated scattering attenuation from laboratory ultrasonic measurements abstract seismic coda waves scattered by small scale heterogeneities contain information on stress changes of the medium because of changes in the physical state of materials based on the ultrasonic measurements under different stresses for a cylindrical sandstone sample we investigate the influence of stress changes on ultrasonic s coda attenuation and aim to characterize its stress frequency dependent pattern considering the complexity of ultrasonic coda waveforms measured from finite size rock samples in laboratory experiments the monte carlo simulation is employed to synthesize ultrasonic envelopes which act by incorporating the effect of multiple scatterings and boundary reflections on coda waves the optimal simulation parameters estimated by minimizing the residual between the observed and synthesized envelopes indicate that the rock sample under study presents moderate heterogeneities the relationship between attenuation and stress is similar for direct and coda s waves and remains stable in the range of high effective stresses around 30 60 mpa with less stress sensitivity enhanced attenuation for both types of waves occurs at lower effective stresses but with coda attenuation much faster and stronger presenting a quite different nonlinear behavior with respect to stress coda attenuation increases drastically at extremely low effective stresses below 15 mpa because of the increase in rock compliance showing much greater sensitivity to high pore pressure than intrinsic attenuation this study improves our understanding of the mechanism of ultrasonic coda attenuation and its scaling dependence on stress and frequency

paleohydrological fluctuations and steppe vegetation during the last glacial maximum in the central ebro valley ne spain combined analysis of sedimentary facies geochemistry and pollen from lake sediment records and sedimentological and palynological studies from slope deposits allow the characterization of vegetation and lake level status during the last glacial lgm in the central ebro valley ne spain these records show the presence of phases of increased effective moisture while regional vegetation was dominated by steppe species the longest lake record comes from la salineta one of the saline lakes in the los monegros area the other lake sequence comes from a sinkhole in the gallego river floodplain the slope deposit from valmadrid is the only periglacial deposit found in the central ebro valley our data indicate that at least for some intervals during full glacial times when cold steppe vegetation dominated the region some lakes experienced more positive water balance than today and run off was also high the data are coherent with the hypothesis that at least for some periods the ice age climate of the western mediterranean was characterized by cold winters with relatively higher effective moisture precipitation minus evaporation ratio and summer droughts increased flow from the pyrenean rivers during the early deglaciation could also have played a significant role in the paleohydrological cycle in the central ebro valley however la salineta records also show evidence for arid periods during glacial times indicating the complex evolution of hydrology and moisture availability in the central ebro valley during the lgm

effects of filling fluid type and composition and joint orientation on acoustic wave propagation across individual fluid filled rock joints abstract wave propagation and attenuation in subsurface rock masses could be highly affected by rock joints filled with fluids however the understanding of acoustic behaviours across fluid filled rock joints is still at its infancy to determine the effects of the type and composition of filling fluids as well as joint orientation on compressional wave propagation and attenuation across individual fluid filled rock joints extensive laboratory acoustic tests were conducted in this paper results showed that the existence of water in fluid filled rock joints results in higher wave velocity more wave transmission and less wave attenuation compared to light oils in most circumstances increasing liquid content in a single liquid filled joint enhances wave velocity and wave transmission for dual liquid filled joints both wave velocity and wave transmission increase with increasing water content joint orientation significantly affects wave characteristics of rock joints partially filled with liquids while it has slight influences on wave attributes of rock joints fully filled with liquids in addition wave velocity and attenuation across fluid filled rock joints increases with increasing central frequency of incident compressional waves

late pleistocene holocene palaeoenvironmental evolution of the anamaza river valley iberian range ne spain multidisciplinary approach on the study of carbonate fluvial systems abstract the uppermost pleistocene and holocene palaeoenvironmental evolution of the anamaza river valley iberian range ne spain is deduced using multidisciplinary approach including stratigraphical mineralogical palynological geochemical geophysical methods and drilling main changes were registered in distinct subenvironments of a carbonate fluvial system including the channelled zone and wetlands in the floodplain tufa barrages dominated although pools also existed geophysical survey and coring reveal tufa build ups and pool facies also in the subsoil lower water temperature and scarce evaporation are deduced for the pleistocene fluvial system that progressively changed through the holocene with more hydrologically closed areas and higher evaporation influence a general aggrading evolution during warm stages related with increasing base level and damming due to fast carbonate precipitation characterised the holocene detrital tufa indicates erosive high energy floods or colder stages when water level would decrease favouring erosion 14 c and 230 th 234 u dating reveal high sedimentation rates and three main discontinuities related with cold episodes younger dryas middle part of the holocene climate optimum and iron age epoch during the uppermost pleistocene tufa growth would be enhanced during warmer episodes as the bolling allerod in the younger dryas scarce vegetation favoured erosion of both slopes and tufa constructions subsequent warmer temperatures during the first part of the holocene favoured vegetated slopes enhanced tufa growing although interrupted in the middle part of the holocene climate optimum and development of wetlands with riparian vegetation in the floodplain where either siliciclastics or detrital tufa incoming alternated with low energy waters stages and mud settling progressive decline in tufa is deduced for the upper holocene but it is not possible to determine whether this and other palaeoenvironmental changes were related either to climate or increasing human activities during the roman and medieval warm periods more oxidizing conditions in the wetlands and increasing erosion prevailed probably conditioned by human activities the pollen record shows for the early holocene development of pinus forest with betula and expansion of deciduous quercus xerophilous and heliophilous grassland subsequent increasing moisture supported open forests with deciduous quercus ulmus corylus and evergreen quercus ilex pistacia species from ca 4000 yrbp a dominant deciduous quercus forest with groves of corylus ulmus acer fagus and taxus expanded and human activities grazing occurred from 1200 yrbp dry grassland expanded due to intensive land use agropastoral activities almost completely deforested plateaus surround the site today with slopes covered by patchy grass with junipers groves and screeds with little soil

edaphic and geomorphic evidences of water level fluctuations in gallocanta lake ne spain the pedological implications of lake water level fluctuations are complex especially in lake margin where topographical hydrological and sedimentary conditions are most variable lake water level fluctuations generate landscape elements which provide insights into the processes involved in soil development and the extent of the zones affected by flooding desiccation coupling information from detailed geomorphological inspections in the field the mapping of the lakeshore and the pedogenesis of each landscape element can provide a better understanding of these relationships which was used to study the saline gallocanta lake ne spain a semiarid intramontane lacustrine system that undergoes significant and rapid water level fluctuations geomorphic classification of the lake margin forms and environments served as a guide for soil sampling the geomorphological survey revealed high diversity and contrast in the lake margin environment from shores affected by coastal erosion to zones characterized by progradation aggradation two soil toposequences and 11 pedons that were on different geomorphic units were studied on two margins of the lake following gradients in elevation moisture and salinity soils showed a succession of inceptisols to aridisols with mollisols developed at intermediate positions and aquic soils at the lake floor and southern shore soils had a sandy loamy texture and a predominantly carbonatic composition high variation in cce mean 37 texture and coarse fragments throughout the soil profiles soil salinity was the highest at the lowest topographic position and in the upper soil horizons where mean ece 188 6 ds m 1 at 25 c in addition the highest organic matter 6 and gypsum 34 content occurred at the lake floor soil color characteristics and concentrations and depletions of fe and mn indicated redox changes associated with soil water saturation under carbonate and or saline conditions macro and micromorphological features of oxidized and reduced horizons indicated the alternation between palustrine reduced and non palustrine detrital emerged oxidized events at different geomorphic and topographic positions from the lake floor up to 7 m above it pedogenesis inferred and the littoral submerged forms located at permanently emerged areas confirmed the past and present trend towards the desiccation of the lake this study has improved our understanding of how soils form and develop within the context of geomorphic units and can be used in making land use decisions in the protected reserve and agricultural surroundings of the lake

gravity waves in mexico city ii coupling between an anelastic solid and a fluid layer abstract this paper completes a previous study of the role of gravity during the 19 september 1985 michoacan earthquake at mexico city it is assumed as suggested by lomnitz 1989 1990 that nonlinear mechanisms could bring the rheology of the mexico city soft clay layer nearer to a fluid than to a solid in order to test whether gravity waves in a viscous fluid could provide an explanation of exceedingly long duration observed at mexico city we have studied the motion on the surface of an irregular viscous fluid layer overlaying an elastic half space our formulation takes into account vertical displacement at the free surface of the fluid layer but requires a linearization of the corresponding boundary condition a decomposition of diffracted fields in terms of plane waves allows the use of aki larner9s method excitation is given by vertically incident sv waves we present results both for nonviscous and viscous fluids and show that an adequate free boundary condition is essential for this problem lacking data we have performed several simulations for values of viscosity going from 300 to 30 000 pa s in the case of a nonviscous fluid gravity surface waves are generated efficiently by diffraction of elastic waves on the irregular interface but attenuate rapidly when including viscosity and are not significant for viscosities above 3000 pa s the results presented in our companion paper and here allow us to conclude that gravity is not a likely explanation to the long duration of ground motion observed at mexico city in a more general context our model may be useful to study the interaction of seismic waves with water reservoirs such as dams

termination of the last glaciation in the iberian peninsula inferred from the pollen sequence of quintanar de la sierra abstract a 4 5 m thick late glacial pollen sequence supported by 17 ams14c dates has been investigated at the quintanar de la sierra marshland iberian cordillera north central spain pollen zones were defined that correspond to successive phases in vegetation history during the end of the late wurm late glacial interstade and younger dryas periods a transfer function approach has been adopted to derive quantitative climate estimates from the pollen assemblage data a first expansion ofjuniperusandhippophae about 13 50014c yr b p indicates the beginning of the late glacial interstade which is characterized by ajuniperus betula pinussuccession that suggests higher temperatures and moisture than during full glacial time the younger dryas interval is recorded by a 120 cm thick sediment unit that is dominated by herbaceous pollen transfer function estimates suggest that the climate during this period was cold with low precipitation during most of the year although not in summer the holocene arboreal recolonization in the area started about 10 00014c yr b p with a renewedjuniperus betula pinussuccession related to a strong increase in annual temperature and precipitation the start of this process was synchronous with mean sea surface temperature changes as recorded from the nearby su 81 18 marine core the strong affinity with other european late glacial pollen sequences demonstrates that the pattern of climatic changes during the last glacial interglacial transition was similar in both northwestern and southwestern europe

an improved equivalent viscoelastic medium method for wave propagation across layered rock masses abstract the behavior of waves propagating through a rock mass is complicated by the discontinuous nature posed by the joints in the rock mass however at large scale the jointed rock mass can be treated as an equivalent continuous medium the purpose of this paper is to establish a method to determine the equivalent viscoelastic property of rock masses with different seismic quality factors and to analyze seismic wave propagation across jointed rock masses each rock mass contains uniformly distributed joint sets with arbitrary orientation the equivalent viscoelastic parameters are calculated for a rock mass with different seismic quality factors the wave propagation equation is then derived for seismic wave across layered rock masses where the parallel layer interfaces are assumed to be welded comparison between the improved equivalent viscoelastic medium method evmm and the existing analytical methods is carried out for two specific cases reflection at free surface and transmission across a discontinuous interface between two media the effects of some parameters such as the incident angle the thickness of the layer and the rock mass seismic quality factor on wave propagation are discussed

lateglacial and holocene palaeohydrology in the western mediterranean region the lake estanya record ne spain abstract the multi proxy analysis of sediment cores recovered in karstic lake estanya 42 02 n 0 32 e 670 m a s l ne spain located in the transitional area between the humid pyrenees and the semi arid central ebro basin provides the first high resolution continuous sedimentary record in the region extending back the last 21 000 years the integration of sedimentary facies elemental and isotopical geochemistry and biogenic silica together with a robust age model based on 17 ams radiocarbon dates enables precise reconstruction of the main hydrological and environmental changes in the region during the last deglaciation arid conditions represented by shallow lake levels predominantly saline waters and reduced organic productivity occurred throughout the last glacial maximum 21 18 cal kyrs bp and the lateglacial reaching their maximum intensity during the period 18 14 5 cal kyrs bp including heinrich event 1 and the younger dryas 12 9 11 6 cal kyrs bp less saline conditions characterized the 14 5 12 6 cal kyrs bp period suggesting higher effective moisture during the bolling allerod the onset of more humid conditions started at 9 4 cal kyrs indicating a delayed hydrological response to the onset of the holocene which is also documented in several sites of the mediterranean basin higher although fluctuating holocene lake levels were punctuated by a mid holocene arid period between 4 8 and 4 0 cal kyrs bp a major lake level rise occurred at 1 2 cal kyrs bp conducive to the establishment of conditions similar to the present and interrupted by a last major water level drop occurring around 800 cal yrs bp which coincides with the medieval climate anomaly the main hydrological stages in lake estanya are in phase with most western mediterranean and north atlantic continental and marine records but our results also show similarities with other iberian and northern african reconstructions emphasizing peculiarities of palaeohydrological evolution of the iberian peninsula during the last deglaciation

interrelated continental sedimentary environments in the central iberian range spain facies characterization and main palaeoenvironmental changes during the holocene a complex holocene system in the central iberian range ne spain has been reconstructed on the basis of sediments recovered from cores and in situ observations small alluvial fans graded into a wide shallow lacustrine area anavieja lake that connected downstream with a carbonate fluvial system with associated vegetated zones the fluvial system was mainly characterized by the development of tufa barriers especially during the first part of the holocene that separated pools or small lakes oncolites detrital tufas calcarenites and marls were deposited in these pools adjacent vegetated areas were covered by macrophytes and were episodically reached by detrital tufa supplies indicating high flood stages high sedimentary rates existed in both the fluvial including the pools and vegetated areas suggesting that despite the common erosion of tufas a clear aggradating evolution existed by contrast very low sedimentary rates were registered in the anavieja lake all the environments but especially the vegetated areas registered the climate evolution during the holocene although the onset of the holocene was characterized by wide climate variability warm and humid conditions dominated during the first part and drier conditions during the second part a water level recovery seems to have been existed during the last millennium this is a good example of the potential of continental systems other than lakes to be useful for palaeoenvironmental and palaeoclimatic studies

avo inversion for a non welded interface estimating compliances of a fluid filled fracture though well known for layer boundaries the use of amplitude versus offset avo variations for non welded boundaries like fractures is not yet investigated depending on the seismic wavelength used fractures can be regarded as thin compliant zones in rocks in different scales we explore the potential of multiangle avo inversion of p p and p s reflections from a fracture to estimate fracture properties we conduct laboratory experiments to measure reflection responses of dry and wet fractures the observed p p reflections of the wet fracture and the fracture aperture are very well predicted by the non welded interface model we invert the angle dependent p p reflectivity of the fracture to estimate both normal and tangential fracture compliances the estimated value of the normal compliance is accurate and it is also possible to obtain the value of the non zero tangential compliance we find that supplementing the information of converted p s reflections in theavoinversion greatly improves the estimate of the tangential compliance the calculated compliance ratio clearly shows the existence of fluid in the fracture this finding can be crucial for new applications in a wide range of scale from earthquake seismology deep and shallow seismic exploration to non destructive material testing

equivalent medium representation of fractured rock a similarity may be found between various approaches for determining the effects of parallel fractures or aligned cracks on seismic wave propagation at wavelengths that are long compared with the scale length of the cracks fractures can be modeled using an empirical linear slip condition however natural fracture surfaces can also be simulated directly as planar distributions of small isolated areas of slip cracks model 1 or conversely as planar distributions of imperfect interfacial contacts model 2 an alternative is plane surfaces separated by thin continuous layers of viscous fluid or a soft material model 3 we present analytic expressions for the fracture compliances for these three models and using these analytic results compute the effective compliances and stiffnesses of the fractured material as a result it is possible to relate the measured compliances or stiffnesses directly to the statistics of the microstructural details of a fracture given appropriate a priori information on the fracture surfaces the results for model 1 are equivalent to a volume distribution of cracks as studied by hudson 1980 1981 for small crack density the results for model 2 are basically the same as those given by white 1983 for a packing of spheres and finally the results for model 3 are in agreement with those given by backus 1962 for combinations of two constituent layers these results can be extended to the case of nonaligned fractures and to allow for fluid flow between cracks and into a porous matrix rock finally it is shown that the ratio of the normal to shear fracture compliance is a good indicator of the properties of the fracture infill

the relationship between microseismicity and high pore pressures during hydraulic stimulation experiments in low permeability granitic rocks several hundred microearthquakes with local magnitudes ranging between 4 and 2 were recorded during hydraulic stimulation experiments at the hot dry rock demonstration site fenton hill new mexico these events are probably caused by shear failure induced by high pore fluid pressures since the event locations seem to cluster in a narrow band near the hydraulic fracture we were able to use micro seismic techniques to locate the hydraulic fracture and monitor its growth we calculate the minimum pore pressure increase necessary to induce rock failure using a simple model of slippage on preexisting fractures by comparing a pore pressure distribution calculated using a one dimensional diffusion model with the distribution of event foci we demonstrate that high pore pressures are a probable cause for these microearthquakes stress drops for these microearthquakes calculated from spectral parameters increased by a factor of 3 during the course of the experiment the stress drop increase correlates with a migration of seismic activity away from the injection well bore which suggests relatively low in situ shear stresses near the well bore caused by strain release in this region during previous pressurizations

holocene environmental changes in the gallocanta lacustrine basin iberian range ne spain the sedimentological and palynological study of the gallocanta lake sediments in the ne of spain has allowed the holocene environmental evolution of this lacustrine basin to be established and several changes in the hydrological balance to be interpreted the chronology of the sequence is based on new radiocarbon datings and 210 pb radiometric techniques ten facies have been characterized which have been grouped into five sedimentary units two units a and b are interpreted as deposited in alluvial areas and three units c d and e in lacustrine environments moreover five pollen zones have been established for this succession from the stratigraphic correlation of the cores extracted in this lake three stages in the basin evolution have been interpreted stage 1 was characterized by a broad development of alluvial fans during the fullglacial or lateglacial times the sediments of this stage are lacking in pollen as they were exposed for most of the time stage 2 started around 10 100 yr bp and is characterized by the establishment of a brackish lake linked to a decrease in alluvial supplies and a more positive water balance the maximum lake level would have been reached around 8010 yr bp coinciding with the relatively moist period of the beginning of the holocene recorded in some spanish lakes although this dating would not match that of other areas of the iberian peninsula in which the maximum lake levels have been recorded around 6000 yr bp a sharp decrease in the lacustrine level has been registered at 3405 yr bp which may be correlated to a change to more arid conditions nevertheless the lake level recovered later stage 3 was linked to the development of an ephemeral shallow lake an age of ad 1840 yr has been calculated for this palaeogeographical change the data obtained suggest that the main vegetation changes during stage 2 were more related to climate variability whereas during stage 3 the anthropogenic impact became more significant

late quaternary lake level record from northern eurasia lake records from northern eurasia show regionally coherent patterns of changes during the late quaternary lakes peripheral to the scandinavian ice sheet were lower than those today but lakes in the mediterranean zone were high at the glacial maximum reflecting the dominance of glacial anticyclonic conditions in northern europe and a southward shift of the westerlies the influence of the glacial anticyclonic circulation attenuated through the late glacial period and the westerlies gradually shifted northward such that drier conditions south of the ice sheet were confined to a progressively narrower zone and the mediterranean became drier the early holocene shows a gradual shift to conditions wetter than present in central asia associated with the expanded asian monsoon and in the mediterranean in response to local monsoon type circulation there is no evidence of mid continental aridity in northern eurasia during the mid holocene in contrast the circum baltic region was drier reflecting the increased incidence of blocking anticyclones centered on scandinavia in summer there is a gradual transition to modern conditions after ca 5000 yr b p although these broad scale patterns are interrupted by shorter term fluctuations the long term trends in lake behavior show a clear response to changes in insolation and glaciation

an approach to detect afterslips in giant earthquakes in the normal mode frequency band summary an approach to detect afterslips in the source process of giant earthquakes is presented in the normal mode frequency band 0 3 2 0 mhz the method is designed to avoid a potential systematic bias problem in the determination of earthquake moment by a typical normal mode approach the source of bias is the uncertainties in q modal attenuation parameter which varies by up to about 10 per cent among published studies a choice of q values within this range affects amplitudes in synthetic seismograms significantly if a long time series of about 5 7 d is used for analysis we present an alternative time domain approach that can reduce this problem by focusing on a shorter time span with a length of about 1 d application of this technique to four recent giant earthquakes is presented 1 the tohoku japan earthquake of 2011 march 11 2 the 2010 maule chile earthquake 3 the 2004 sumatra andaman earthquake and 4 the solomon earthquake of 2007 april 1 the global centroid moment tensor gcmt solution for the tohoku earthquake explains the normal mode frequency band quite well the analysis for the 2010 chile earthquake indicates that the moment is about 7 10 per cent higher than the moment determined by its gcmt solution but further analysis shows that there is little evidence of afterslip the deviation in moment can be explained by an increase of the dip angle from 18 in the gcmt solution to 19 this may be a simple trade off problem between the moment and dip angle but it may also be due to a deeper centroid in the normal mode frequency band data as a deeper source could have steeper dip angle due to changes in geometry of the benioff zone for the 2004 sumatra andaman earthquake the five point source solution by tsai et al explains most of the signals but a sixth point source with long duration improves the fit to the normal mode frequency band data the 2007 solomon earthquake shows that the high frequency part of our analysis above 1 mhz is compatible with the gcmt solution but the low frequency part requires afterslip to explain the increasing amplitude ratios towards lower frequency the required slip has the moment about 19 per cent of the gcmt solution and the rise time of 260 s the total moment of these earthquakes are 5 31 1022 n m tohoku 1 86 1 96 1022 n m chile 1 33 1023 n m sumatra and 1 86 1021 n m solomon the moment magnitudes are 9 08 8 78 8 79 9 35 and 8 11 respectively using kanamori s original formula between the moment and the moment magnitude however the trade off problem between the moment and dip angle can modify these estimates for moment up to about 40 50 per cent and the corresponding magnitude 0 1

evaluation of the three dimensional configuration of a subsurface artificial fracture by the triaxial shear shadow method we have determined the three dimensional configuration of a single fracture in the hot dry rock model field at higashi hachimantai japan by the triaxial shear shadow method the crack was created by hydraulic fracturing in intact welded tuff at a depth of 370 m we have carried out crosshole seismic measurements by using a downhole air gun and a triaxial seismic detector extinction at a special polarization direction and the dependency of transmissivity in shear wave component on incident angle were determined by a triaxial hodogram analysis of detected signals we have evaluated the orientation and distribution of the fracture using the shear wave extinction and the three dimensional configuration of the fracture by a continuation of the evaluated orientations the results are in good agreement with the data obtained by independent experiments in the field

fragility of western mediterranean landscapes during holocene rapid climate changes abstract in this paper we explore the evidence for holocene rapid climate changes rccs in western mediterranean records examining similarities and differences in the timing and nature of impacts on different components of the natural environment vegetation fluvial and coastal sedimentation fire activity soil formation marine lacustrine and fluvial archives of the western mediterranean iberian peninsula and northwest africa provide evidence for both pervasive millennial scale climatic variability and abrupt decadal to centennial scale transitions we focus in particular on three rccs characterised by high latitude cooling glacier advances and north atlantic ice rafting events the mid holocene rcc interval 6 5 cal ka bp the late holocene rcc interval 3 5 2 5 cal ka bp and the historical rcc interval known as the little ice age lia 1300 1950 ad evidence from multiple records indicates wide ranging impacts of rccs in the western mediterranean region the three rcc intervals were characterised however by contrasting hydrological situations in the western mediterranean with prevailing dry conditions including marked aridification events during the rcc intervals 6 5 and 3 5 2 5 cal ka bp and prevailing or recurrent wet conditions during the lia we examine issues of proxy sensitivity in palaeoecological and geomorphological records and evaluate examples of contrasting geomorphological responses to regional climatic triggers between humid and semi arid sectors of the western mediterranean finally we consider the long term sensitivity of the region to rapid climate change the role of threshold changes and the extent to which this region represents a fragile landscape

stable isotope characterisation of co existing carbonates from the holocene gallocanta lake ne spain palaeolimnological implications the sedimentary succession of gallocanta lake a closed saline lake located in the iberian range ne spain documents two successive lacustrine stages 1 brackish lake stage and 2 shallow saline lake stage the saline stage corresponds to the present day situation in which the lake water properties are mainly controlled by a strongly negative annual water balance the carbonates of the brackish lake stage have relatively constant 18o values however they are rather high 18odo 2 4 and 18occ 4 5 mean values suggesting a hydrologically closed lake with a long residence time of the waters 18o values of carbonates from the saline stage vary greatly and are lighter than in the previous stage 18odo 0 5 18occ 0 7 18omgs 2 3 mean values these carbonates also precipitated in a hydrologically closed lake but in equilibrium with a lake water of more variable isotopic composition the 13c values for carbonates of both stages reflect a mixing of different pools of carbon but during saline stage 13c values have been more controlled by the equilibrium of the lake waters with atmospheric co2 during the current stage calcite and dolomite precipitate in gallocanta lake mainly during spring and summer although dolomite precipitation is more favoured towards the summer magnesite precipitates at the beginning of autumn when the first rainfall re dissolves the saline surface crust producing saline waters with a high mg2 content the isotopic composition of lake waters sampled in 2005 are far higher than those calculated from the carbonates it is considered that this could be due to two factors either because there have not been many extremely dry years like the year 2005 during the development of the lake or because the physical and chemical characteristics of the lake waters in such conditions are not appropriate for the development of these minerals

european lakes as palaeohydrological and palaeoclimatic indicators abstract lakes in temperate regions have fluctuated in size on annual to millenial time scales changes in water level or depth can be reconstructed by applying geomorphic sedimentological and biostratigraphic methods to transects of sediment cores this systematic field based approach has been used at a number of sites in europe it is illustrated by reconstructions of water level changes in lakes from southern sweden these lakes have shown broadly synchronous changes during the holocene such synchronous changes in water levels at several sites in a region reflect climatic changes inferences about the mechanism of the climatic change depend on identifying both synchronous changes within a region and differences in the direction magnitude and timing of lake level changes between regions continental compilations of lake level data are therefore necessary detailed studies are not available from enough sites but the interpretation of already existing stratigraphic and biostratigraphic data in terms of lake level changes has greatly increased the number of sites available for a continental scale synthesis in europe this eclectic literature based approach is illustrated with examples from southern europe lakes in the mediterranean region were high around the glacial maximum and again somtime during the first half of the holocene in the western mediterranean the peak of late glacial aridity occurred at 15 000 16 000 bp and the lakes were already high again by 12 000 bp in the east maximum late glacial aridity occurred between 13 000 and 11 000 bp and there was a gradual return to wetter climates during the early holocene such that 9000 bp was more arid than 6000 bp most lakes in the mediterranean region were high at 6000 bp the transition to arid conditions after 5000 bp occurred abruptly in the west and more gradually in the east the lakes of southern sweden indicate drier climates in the early holocene ca 9000 bp more effective moisture between 8000 and 6000 bp increased aridity between 5500 and 3500 bp and increased effective moisture again during the last 3000 years the history of lake level changes in southern sweden and the mediterranean region can be partially explained in terms of changes in the direct effects of insolation and in the strength and position of the westerlies and of the subtropical high pressure cell during the late quaternary

evolution from a freshwater to saline lake a climatic or hydrogeological change the case of gallocanta lake northeast spain sedimentological and hydrogeological studies are combined in order to investigate the environmental conditions of the lacustrine sedimentation during the holocene in gallocanta lake in spain six units have been identified in the sedimentary succession based on sedimentological facies and mineralogy and three depositional stages have been defined 1 alluvial 2 carbonate lake system 3 ephemeral carbonate saline lake system the transition between stages 2 and 3 implies a reduction in water inflows to the lake the 13c isotopical analysis of dolomites points to decaying organic matter as a source of carbon for the dissolved inorganic carbon and evinces that the 13c variations in the lake were probably controlled by organic processes on the other hand 18o values could be controlled by modifications in the hydrological system and not necessarily by climatic changes in this sense from the hydrological study three aquifers can be defined triassic jurassic cretaceous and cenozoic aquifers the lack of coincidence between the surface and subterranean watershed suggests that the transition between the second and third stages is controlled by a shift of the subterranean watershed copyright 2006 john wiley sons ltd