anisotropy and transverse isotropy a number of authors in the exploration literature have written about anisotropy but have restricted their discussions to wave propagation through rock having transverse isotropy with a vertical symmetry axis this note shows that there are fundamental differences between transverse isotropy when the symmetry axis is vertical normal to the free surface and more general anisotropy with an azimuthal variation of properties these differences are important now that effective azimuthal shear wave anisotropy resulting from aligned cracks and pores is becoming recognized as a significant property of crustal rocks

rock glaciers and mountain hydrology a review abstract in mountainous regions climate change threatens cryospheric water resources and understanding all components of the hydrological cycle is necessary for effective water resource management rock glaciers are climatically more resilient than glaciers and contain potentially hydrologically valuable ice volumes and yet have received less attention even though rock glacier hydrological importance may increase under future climate warming in synthesising data from a range of global studies we provide the first comprehensive evaluation of the hydrological role played by rock glaciers we evaluate hydrological significance over a range of temporal and spatial scales alongside the complex multiple hydrological processes with which rock glaciers can interact diurnally seasonally annually decadally and both at local and regional extents we report that although no global extent complete inventory for rock glaciers exists currently recent research efforts have greatly elaborated spatial coverage using these research papers we synthesise information on rock glacier spatial distribution morphometric characteristics surface and subsurface features ice storage and hydrological flow dynamics water chemistry and future resilience from which we provide the first comprehensive evaluation of their hydrological contribution we identify and discuss long intermediate and short term timescales for rock glacier storage allowing a more balanced assessment of the contrasting perspectives regarding the relative significance of rock glacier derived hydrological contributions compared to other water sources we show that further empirical observations are required to gain a deeper hydrological understanding of rock glaciers in terms of i their genesis and geomorphological dynamics ii total ice water volume iii water discharge and iv water quality lastly we hypothesise that at decadal and longer timescales under future climate warming degradation of ice within rock glaciers may represent an increasing hydrological contribution to downstream regions and thus increased hydrological significance while rock glacier water stores persist

s local wave seismic anisotropy in the forearc above the subducted nazca plate between 33 s and 34 5 s s wave splitting from local earthquakes within the nazca plate that are deeper than the interplate seismogenic zone enabled the determination of the fast velocity direction and the lag time t in the forearc of the overriding plate data were collected from 20 seismic stations most of which were temporary deployed between 33 5 s and 34 5 s and included part of the normal subduction section to the south and part of the transitional section to flat subduction to the north the fast velocity direction has a complex pattern with three predominant directions northwest southeast north south and northeast southwest and relatively high t a quality evaluation of the highest measurements enabled us to identify possible cycle skipping in some of the measurements which could be responsible for the large observed lag time we consider that most of the anisotropy that was observed in the forearc is probably located in the mantle wedge and a minor part is located in the crust the complex pattern of splitting parameters when the anisotropy is associated at the mantle wedge could be the result of three dimensional variations in the subducting nazca plate at these latitudes also similarities between the splitting parameters and the principal compressional stress direction from pliocene and quaternary rocks suggest that the anisotropy in the crust could originate by tectonic local stress

the last 50 000 years in the neotropics southern brazil evolution of vegetation and climate abstract in the lagoa campestre lake of salitre 19 s 46 46 w 970 m elev there are plant taxa belonging to many ecological groups that are encountered nowhere else at this latitude frequent incursions of polar advections causing cooling and humidity a cool and foggy climate in the middle of the depression and warmer temperatures on the surrounding slopes help to maintain all these groups within a fairly restricted area late pleistocene holocene climatic change has had a considerable impact on the flora and vegetation of salitre the pollen record of the 6 m deep core lc3 shows how cold forest trees such as araucaria angustifolia and drimys brasiliensis semi deciduous forest halophytic plants and peat bog started to develop on this site the initial period between c 50 000 and 40 000 yr b p was an arid phase not recorded in any other neotropical lowland site it was followed by a period of high moisture levels 40 000 to 27 000 yr b p with a maximum estimated at c 35 000 yr b p the late glacial maximum is missing because of a gap in sedimentation humidity gradually increased during the late pleistocene between 16 000 and 11 000 yr b p the early holocene 9500 to 5000 yr b p is characterized by a more marked seasonal pattern and higher temperatures reaching a maximum c 5000 yr b p the spread of semi deciduous forest between 4000 and 3000 yr b p attests to a return of humidity comparison with the serra negra section 19 s 46 45 46 w 1170 m elev not far from salitre confirms the high moisture rates recorded at c 35 40 000 yr b p although temperatures were cooler at the altitude of serra negra as is attested by the presence of araucaria forest and also confirms the strong impact of polar advections on the climate of southeastern brazil

anisotropy detected in shallow clays using shear wave splitting in a vsp survey1 shear waves can provide valuable information about seismic anisotropy on entering an anisotropic medium a shear wave generally splits shear wave splitting into a fast and a slow quasi shear wave with polarizations fixed by the elastic properties of the medium and direction of travel if the medium contains planar discontinuities with common normals the fast shear wave will be suitably propagated if its polarization lies in the plane of the discontinuities measuring this polarization using a vsp geometry with oriented three component geophones in the borehole offers the possibility of monitoring the orientation and density of the discontinuities as a function of depth such a shear wave vsp was carried out in an uncased 0 3 m diameter borehole drilled to a depth of 120 m in the north of the netherlands the upper 80 m of the sequence consisting of a glacial till and sands and clays of pleistocene age was studied the clays in this sequence have been subjected to glacial deformation and as a result are overconsolidated and locally fissured in our shallow vsp experiment shear wave splitting and therefore anisotropy was identified at various geophone depths for one source offset hodograms showed a consistent polarization of the fast shear wave component over a large depth interval under the assumption that the anisotropy was caused by planar discontinuities with common normals this polarization direction gives the strike of the fissures in this interval the polarization direction of the fast s wave did not correspond exactly with the strike which was obtained from geological information on the fissures the geological information was from undisturbed oriented 70 mm core samples taken at 3 m intervals in the borehole the discrepancy however could be explained in terms of dipping fissures and such a dip was confirmed by the geological and geotechnical information the orientation of fissures is an important factor in the directional deformation and strength characteristics of clays as far as geotechnical behaviour is concerned this study thus illustrates a practical application of shear wave splitting observed in shallow shear wave vsp for geology and geotechnical engineering

geophysical imaging of alpine rock glaciers slope instabilities caused by the disappearance of ice within alpine rock glaciers are an issue of increasing concern design of suitable counter measures requires detailed knowledge of the internal structures of rock glaciers which can be obtained using geophysical methods we examine benefits and limitations of diffusive electromagnetics geoelectrics seismics and ground penetrating radar georadar for determining the depth and lateral variability of the active layer the distributions of ice and water the occurrence of shear horizons and the bedrock topography in particular we highlight new developments in data acquisition and data analysis that allow 2 d or even 3 d structures within rock glaciers to be imaged after describing peculiarities associated with acquiring appropriate geophysical datasets across rock glaciers and emphasizing the importance of state of the art tomographic inversion algorithms we demonstrate the applicability of 2 d imaging techniques using two case studies of rock glaciers in the eastern swiss alps we present joint interpretations of geoelectric seismic and georadar data appropriately constrained by information extracted from boreholes a key conclusion of our study is that the different geophysical images are largely complementary with each image resolving a different suite of subsurface features based on our results we propose a general template for the cost effective and reliable geophysical characterization of mountain permafrost

reflection seismology over azimuthally anisotropic media recent surveys have shown that azimuthal anisotropy due most plausibly to aligned fractures has an important effect on seismic shear waves previous work had discussed these effects on vsp data the same effects are seen in surface recording of reflections at small to moderate angles of incidence the anisotropic effects one different polarization components of vertically traveling shear waves permit the recognition and estimation of very small degrees of azimuthal anisotropy of order 2 1 percent as in an interferometer anisotropic effects on traveltime yield estimates of anisotropy which are averages over large depth intervals often raw field data must be corrected for these effects before the reflectors may be imaged two variations of a rotational algorithm to determine the principal time series are derived anisotropic effects on moveout lead to abnormal moveout unless the survey line is parallel to the fractures anisotropic effects on reflection amplitude permit the recognition and estimation of anisotropy hence fracture intensity differences at the reflecting horizon i e with high vertical resolution

core log integration studies in hole a of taiwan chelungpu fault drilling project summary taiwan chelungpu fault drilling project tcdp was initiated to understand the physical mechanisms involved in the large displacements of the 1999 taiwan chi chi earthquake continuous measurements of cores including laboratory work and a suite of geophysical downhole logs including p and s wave sonic velocity gamma ray electrical resistivity density temperature electrical borehole images and dipole shear sonic imager were acquired in hole a over the depth of 500 2003 m integrated studies of cores and logs facilitate qualitative and quantitative comparison of subsurface structures and physical properties of rocks a total of 10 subunits were divided on the basis of geophysical characteristics generally formation velocity and temperature increase with depth as a result of the overburden and thermal gradient respectively gamma ray resistivity formation density shear velocity anisotropy and density derived porosity are primarily dependent on the lithology zones with changes of percentage of shear wave anisotropy and the fast shear polarization azimuth deduced from dipole shear imager dsi are associated with the appearance of fractures steep bedding and shear zones the fast shear wave azimuth is in good agreement with overall dip of the bedding approximately 30 towards se and maximum horizontal compressional direction particularly in the kueichulin formation showing strong shear wave velocity anisotropy bedding parallel fractures are prevalent within cores whereas minor sets of high angle nnw sse trending with n and s dipping fractures are sporadically distributed the fault zone at depth 1111 m fza1111 is the chi chi earthquake slip zone and could be a fluid conduit after the earthquake the drastic change in fast shear wave polarization direction across the underlying non active sanyi thrust at depth 1710 m reflects changes in stratigraphy physical properties and structural geometry

interpretation of synthetic common depth point gathers for a single anisotropic layer analysis of synthetic traveltime gathers shows that anisotropy may have a large enough effect on p sh and sv propagation to alter significantly the interpretation of the subsurface below the anisotropic layers consequently if anisotropy exists below a seismic line it is important to estimate the anisotropic parameters correctly we discuss the effects of anisotropy on seismic waves and present a method for estimating the elastic constants of a transversely isotropic layer from p and sh arrival time gathers the technique may be extended to more general anisotropic symmetries by analyzing gathers from several azimuths to illustrate the possible effect of anisotropy on exploration surveys p sh and sv velocity variations are calculated for several types of anisotropic sedimentary fabrics alignments due to bedding shale lithology and dry parallel cracks may have similar velocity variations fabrics with other configurations of cracks may still possess overall transversely isotropic symmetry but t

evaluation of anisotropy by shear wave splitting the polarizations of three component shear wavetrains carry unique information about the internal structure of the rock through which they pass specifically commonly observed shear wave splitting may contain information about the orientation of crack distributions this information cannot usually be recovered from shear waves recorded at the free surface because of interference with the interaction of the shear wave with the surface even for nearly vertical incidence however shear wave splitting in synthetic three component vertical seismic profiles in some cases may be interpreted directly in terms of the direction of strike of vertical cracks because the human eye is not skilled at identifying the phase relationships between three component seismograms played out conventionally as parallel time series the polarizations are displayed in orthogonal sections of the particle displacements to facilitate recognition and evaluation of the shear wave splitting estimating the orientations of cracks an

measurements of seismic anisotropy and fracture compliances in synthetic fractured media ultrasonic velocities were measured on a stack of synthetic material plexiglass at low 90 120 khz long wavelength range and high 480 khz short wavelength range frequencies plates were pressed together with uniaxial normal stress these measurements were repeated under different uniaxial pressures for two cases 1without circular rubber inclusions between synthetic fractures and 2with circular rubber inclusions between fractures calculation of anisotropy parameters and also normal and shear interface fracture compliances using linear calculus show reasonable variations anisotropy and compliances decreases as overburden pressure increases suggesting that anisotropy is caused by compliances at higher frequencies synthetic fractures seem to be stiffer than at lower frequencies for the long and short wavelength ranges similar variations were observed for anisotropy parameters and fracture compliances vs measurements in different directions show that for the case without rubber inclusions there is a good approximation of vti medium whereas for the case with inclusions there is a significant difference between vs travelling in directions parallel and perpendicular to the plates

palaeoclimates in central and south america since 18 000 bp based on pollen and lake level records abstract the last 18 ka of palaeoclimates are discussed at 3 ka intervals based on palaeoenvironmental changes shown in pollen and lake level records from central and south america a total of 61 pollen records fulfill the requirements of continuity and chronology to be used in this synthesis 8 records from tropical and subtropical lowlands in central and south america 7 records from the central american highlands 26 records from the high andes north and south of the equator 2 records from the southern subtropics and 18 from the southern andes and subantarctic islands palaeoclimatic interpretation of the pollen records is semiquantitative based on bioclimatic parameters such as e g elevational temperature gradients or latitudinal precipitation gradients that can be related to vegetation zonation additional palaeoclimatic information is obtained from lake level records derived either from dated shorelines or from the limnological history of lake sediment sections large scale palaeoclimatic comparison of the proxy data records indicates that full and late glacial climates throughout central and south america were cooler than today by about 4 to 5 c but that moisture patterns showed regional differentiation thus in both the southern subtropics and high latitudes in southern chile conditions were substantially moister than today during full and late glacial times whereas everywhere else conditions were far drier than today in terms of palaeocirculation this scenario can be interpreted as a poleward shift of the subtropical as well as the westerly circulation a scenario that has been suggested by palaeoclimatic simulations from general circulation models gcm another major palaeoclimatic aspect predicted by the gcm simulations is the suppressed early holocene summer monsoon in the southern subtropics although proxy records are few from this zone their palaeoenvironmental history during that time shows a period of aridity that would support the model one of the most controversial aspects of south american palaeoclimates concerns the existence of a younger dryas equivalent a cold period between 11 and 10 ka bp based on the existing data from south america that show a great diversity of palaeoclimatic trends the concept of an interval that is characterized by the same climatic signal as documented for the north atlantic seems too simplistic moreover at this point only very few records have been analysed in sufficient detail to yield unambiguous climatic information for the interval in question the principal outcome of this palaeoenvironmental and palaeoclimatic synthesis is the better understanding of the type and quality of data available at present and the realization of regions and periods where much more and concerted effort is needed to address problems of intra and interhemispheric palaeoclimatic correlations only then can questions concerning the mechanism of climatic change be tackled successfully

nature of environmental changes in south america at the last glacial maximum abstract a review is given of geomorphological evidence suggesting the nature of environmental changes in south america during the last glaciation maximum lgm the data are from glacial geocryogenic alluvial colluvial and aeolian systems and span 68 of latitude making the most complete land transect of major climatic systems in the southern hemisphere glaciers in the northern and central andes may have reached their maximal extent by 27 000 yr b p reduced precipitation at the lgm caused by lower temperatures and lower atmospheric humidity probably led to slight glacier recession in the tropical andes icefields in the southern andes were most expansive when global temperature and sea level were lowest because pacific westerlies supplied abundant moisture and western outlets advancing across the continental shelf were constrained by sea level low gradient river networks became incised by at least 100 m into narrow channels as global sea level fell by 120 m during the lgm draw down of water tables possibly impacted the forest cover enhancing the drying influence of reduced sea surface temperature and atmospheric humidity as forest and grass covers diminished in extent effecting greater atmospheric cooling because of reduced evapotranspiration and convective condensation colluvial and aeolian processes became more active and widespread almost 25 of the continent is covered with palaeo aeolian features presumed to have been active when airflow was stronger due to steeper atmospheric pressure and temperature gradients at the lgm substantial changes in precipitation totals and incidence and in ground water availability probably eliminated modern type tropical rainforest except in areas currently receiving ca 5000 mm of annual rainfall equivalent changes in vegetation cover spread across much of the guyana and brazilian highlands and throughout the southern temperate regions

seismic velocity anisotropy and fluid pressure in the barbados accretionary wedge from an offset vertical seismic profile with seabed sources 1 the state of compaction and fluid pressure in the barbados accretionary wedge near its toe at ocean drilling program site 949 were investigated by modeling travel times of seismic waves from ocean bottom shots to a borehole geophone array the model constrained by a three dimensional seismic survey and well logs shows 1 a velocity gradient of about 1 1 25 s 1 in the uppermost 180 230 m of the wedge 2 a zone of variable but no net change in velocity between 230 and 350 m depth 3 a low velocity zone 40 50 m thick just above the decollement at 391 m and 4 a displacement of the low velocity zone by thrust faults pore fluid pressure sections derived from p wave velocity show that the upper half of the wedge is normally pressured while the lower half is overpressured the 160 m thick underconsolidated basal zone shows anisotropy which increases downward the lowest 40 50 m has velocity varying 1 azimuthally 3 being fastest in the direction of plate convergence and 2 in the vertical plane 2 5 horizontal faster than vertical after correction for the effect of anisotropy in the derivation of effective stress from seismic velocity the calculated pore fluid pressure ratio does not exceed 0 9 and in the lowest 40 50 m of the basal zone is between 0 71 and 0 82 with fluid pressure hydrostatic lithostatic pressure hydrostatic between 0 5 and 0 65 in accordance with in situ measurements of fluid pressure in the decollement zone beneath these indicate that the accretionary wedge is stronger and less overpressured than was previously supposed

climatic events during the late pleistocene and holocene in the upper parana river correlation with ne argentina and south central brazil most quaternary studies in brazil are restricted to the atlantic coast and are mainly based on coastal morphology and sea level changes whereas research on inland areas is largely unexplored the study area lies along the parana river state of parana brazil at 22 43 s latitude and 53 10 w longitude where the river is as yet undammed paleoclimatological data were obtained from 10 vibro cores and 15 motor auger holes sedimentological and pollen analyses plus tl and 14c dating were used to establish the following evolutionary history of late pleistocene and holocene climates first drier episode 40 000 8000 bp first wetter episode 8000 3500 bp second drier episode 3500 1500 bp second present wet episode 1500 bp present full size table table options view in workspace download as csv climatic intervals are in agreement with prior studies made in southern brazil and in northeastern argentina

mountain permafrost development and challenges of a young research field an overview is given of the relatively short history important issues and primary challenges of research on permafrost in cold mountain regions the systematic application of diverse approaches and technologies contributes to a rapidly growing knowledge base about the existence characteristics and evolution in time of perennially frozen ground at high altitudes and on steep slopes these approaches and technologies include 1 drilling borehole measurement geophysical sounding photogrammetry laser altimetry gps sar surveying and miniature temperature data logging in remote areas that are often difficult to access 2 laboratory investigations e g rheology and stability of ice rock mixtures 3 analyses of digital terrain information 4 numerical simulations e g subsurface thermal conditions under complex topography and 5 spatial models e g distribution of permafrost where surface and microclimatic conditions are highly variable spatially a sound knowledge base and improved understanding of governing processes are urgently needed to deal effectively with the consequences of climate change on the evolution of mountain landscapes and especially of steep mountain slope hazards as the stabilizing permafrost warms and degrades interactions between glaciers and permafrost in cold mountain regions have so far received comparatively little attention and need more systematic investigation

permafrost in steep bedrock slopes and its temperature related destabilization following climate change permafrost in steep bedrock is abundant in many cold mountain areas and its degradation can cause slope instability that is unexpected and unprecedented in location magnitude frequency and timing these phenomena bear consequences for the understanding of landscape evolution natural hazards and the safe and sustainable operation of high mountain infrastructure permafrost in steep bedrock is an emerging field of research knowledge of rock temperatures ice content mechanisms of degradation and the processes that link warming and destabilization is often fragmental in this article we provide a review and discussion of existing literature and pinpoint important questions ice filled joints are common in bedrock permafrost and possibly actively widened by ice segregation broad evidence of destabilization by warming permafrost exists despite problems of attributing individual events to this phenomenon with certainty convex topography such as ridges spurs and peaks is often subject to faster and deeper thaw than other areas permafrost degradation in steep bedrock can be strongly affected by percolating water in fractures this degradation by advection is difficult to predict and can lead to quick and deepdevelopment of thaw corridors along fractures in permafrost and potentially destabilize much greater volumes of rock than conduction would although most research on steep bedrock permafrost originates from the alps it will likely gain importance in other geographic regions with mountain permafrost

paleoenvironmental reconstruction of the lower mogi guacu river basin sao paulo state brazil morphopedosedimentary records and fluvial processes abstract the mogi guacu river rises in bom repouso minas gerais state brazil in the mantiqueira ridge and flows into the rio pardo river at an elevation of 483 m in pontal sao paulo state brazil after running a 530 km long course especially along the lower mogi guacu basin the river morphology is extremely sinuous characterized by intense processes of channel migration avulsion abandonment and reactivation of the channel producing an extensive alluvial plain composed of a series of associated relief forms and sedimentary facies among these forms point bar deposits by lateral accretion abandoned meanders paleo channels and fluvial terraces are notable features in this sense the objective of this work was to investigate whether these features could be linked to environmental changes to reach this goal soil properties of a catena of the jatai ecological station luiz antonio sao paulo state were analyzed in four sectors slope terrace i terrace ii and alluvial plain the results from grain size determination geochemical and isotopic studies dating paleopalynology coal fragments and micromorphology are presented in this paper from these analyses a paleo environmental evolution divided in three stages is proposed for the area 130 000 ybp upper pleistocene when the mogi guacu river base level was approximately 6 m above the present one a drier second phase 10 250 years bp lower holocene when an organic horizon was formed inside of an abandoned meander oxbow lake and a third phase 2096 ybp upper holocene of reactivation of a warm and humid climate that promoted the development of a two meters thick typic udifluvent in a sector where the mogi guacu river no more floods due to the incision of its thalweg reaching more than six meters depth in the last 130 000 years bp thus this paper used a fluvial geomorphologic approach and its interplay with climate to understand how the landscape was shaped from upper pleistocene to holocene however neotectonics might have played a relevant role as well not only in the mogi guacu river basin but also in the parana sedimentary basin

multidisciplinary geophysical investigations over an alpine rock glacier we have performed a multidisciplinary geophysical survey combined with geotechnical investigations over a degrading alpine rock glacier a dense grid of helicopter borne groundpenetrating radar data allowed the 3d shape of the bedrock topography and the gross transition from ice rich to ice poor parts of the rock glacier to be delineated the bedrock topography served as a 2d structural constraint for tomographic inversions of seismic and geoelectric data acquired on coincident profiles parallel and perpendicular to the rock glacier flow direction these profile data were complemented by a small 3d geoelectric tomography experiment only a combined interpretation of all the results allowed reliable and unambiguous interpretation of the tomograms we could distinguish between the active layer bedrock ice bearing rock glacier material and degraded permafrost within the rock glacier the latter could be further distinguished in areas where the ice must have melted only recently and regions that had degraded some time ago additionally high resolution cross hole radar tomography performed in an area of opening crevices allowed small scale structures to be resolved which were indicative of the dominant deformation mechanisms style of the rock glacier the success of our study was primarily based on the availability of 3d data sets that allowed important structures to be traced over larger areas and the integrated interpretation of several data types we have identified the internal structure of the rock glacier to be surprisingly heterogeneous with several small scale features that were judged to be critical for assessing its stability this underpinned the need for comprehensive 3d structural investigations to augment geotechnical measurements linearly with inclinometers or at points in boreholes

internal structure and composition of a rock glacier in the andes upper choapa valley chile using borehole information and ground penetrating radar this study uses boreholes ground temperature monitoring and ground penetrating radar gpr in order to understand the internal structure and composition of a rock glacier in the upper choapa valley northern chile the rock glacier is a small valley side feature 200 m long and ranging between 3710 and 3780 m a s l two boreholes were drilled down to depths of 20 and 25 m respectively using the diamond drillhole technique an ice rock mixture was encountered in the boreholes with heterogeneous ice content averaging 15 30 data from common midpoint cmp and constant offset co gpr surveys acquired respectively near the boreholes and across the whole rock glacier were processed to highlight the internal stratigraphy and variations in the radar wave velocity the gpr profiles depict a rock glacier constituted of stacked and generally concordant layers with a thickness ranging from 10 m in its upper part to 30 m towards its terminus the cmp analysis highlights radar wave velocities of 0 13 0 16 m ns 1 in the first 20 m of the structure larger vertical and lateral velocity variations are highlighted from co data reflecting the heterogeneous composition of the rock glacier and the likely presence of unfrozen water in the structure given the average air temperature registered at the site 0 58c the near melting point temperature registered in the boreholes over more than a year and the presence of locally high water content inferred from gpr data it is thought that the permafrost in the rock glacier is currently degrading

active layer and permafrost thickness in rock glaciers derived from geophysical methods in the semiarid andes of argentina abstract the argentinean central andes region 31 s to 35 s exhibits one of the largest densities of rock glaciers on earth however few studies have focused on the knowledge of the internal structure of these landforms in the present paper a characterization of the internal structure of two rock glaciers has been achieved by using seismic refraction tomography and vertical electrical sounding in one of the rock glaciers the thickness of the active layer is quite homogeneous while in the other said thickness diminishes towards the front in both rock glaciers near the top of the active layer the p wave velocity values vary between 350 and 600 m s while in the bottom of the layer the p values range from 800 to 1700 m s as regards the permafrost layer it shows an irregular thickness with values varying between 4 and 27 m approximately in addition p wave values ranging from 1600 to 3300 m s and a few k m values of electrical resistivity have been recorded the increase of geophysical surveys in rock glaciers in the andes region is expected to give a better understanding of the characteristics distribution and origin of the ice present in these landforms it should also allow researchers to estimate with certainty their ice content as solid state reserves

recent hydrologic change in a colorado alpine basin an indicator of permafrost thaw hydrologic and hydrochemical studies have been conducted in green lakes valley colorado front range usa above 3550 m since 1982 they show a classic seasonal hydrograph dominated by snowmelt and an earlier date for the start of spring flow and for peak flow over the period of record this is consistent with patterns found at lower elevations in colorado and throughout western north america they also show an increasing trend in flows in september and october of 2 6 0 7 mm a 1 which is not found elsewhere and cannot be accounted for by increased autumn precipitation and the melting of surface ice because this late season increase is not found at the highest elevations or in basins in which there is no evidence of permafrost it seems best explained by the thawing of alpine permafrost at intermediate elevations this is corroborated by an increase in the concentration of base cations and silica and particularly in ca 2 and so4 in the stream discharge starting in 2000 as with the physical hydrology the geochemical signals have not been detected at the higher elevations in the basin though they have previously been associated with streamflow from a small rock glacier in the valley the combined evidence suggests the degradation of ice rich permafrost on the north facing slopes of the valley below 3700 m where it has been detected at 3 m depth by geophysical surveys

rock glaciers and the geomorphological evolution of deglacierizing mountains abstract rock glaciers are an important geomorphic element of glaciated mountain landscapes but our understanding of their distribution and ages controls on their development and their importance in regional mountain hydrology and mountain geomorphic evolution is incomplete in part this incomplete knowledge arises through problems associated with identifying rock glaciers on a morphological basis alone amplified by the multiple ways in which rock glaciers can form in different glacial periglacial and paraglacial settings this study focuses on rock glaciers as a paraglacial mountain landscape element and considers the relationships between rock glaciers and glacial periglacial and paraglacial processes new geomorphic and sedimentary data on different rock glaciers from the khumbu region of nepal are presented these data show that even within a single region rock glaciers may have varied origins and thus likely ages and different climatic and environmental controls we argue that rock glaciers in deglacierizing mountains may have a long residence time in the landscape unlike many other glacially influenced mountain landforms and can undergo significant morphodynamic changes as glaciated landscapes transition into paraglacial landscapes

from the semiarid landscapes of southwestern usa to the wet tropical zone of southeastern brazil reflections on the development of cuestas pediments and talus abstract classical geomorphological models consider that escarpment retreat of cuesta landforms is fastest in arid and semiarid regions which would be expected to lead to increased talus production however this is in disagreement with the piedmont zone of the colorado plateau cliffs arid semiarid region of southwestern usa where talus is as inconspicuous as the deposits of the cuesta escarpment footslopes of the parana basin wet tropical region of southeastern brazil thus this paper discusses the evolutionary processes of cuesta escarpments pediments and piedmont deposits in both wet tropical regions and arid zones considering the key areas of the serra geral ridge in the parana basin and the eastern central colorado plateau as examples this manuscript constitutes a comprehensive and critical review of the principal literature on the landform development of such regions research has revealed that despite the production of sediment fine coarse from the escarpments in the arid southwestern usa geochemical weathering and freeze thaw cycles quickly destroy talus deposits furthermore chemical weathering dissolves minerals and forms caverns within the rock walls of mesas and in amphitheaters and canyons influencing escarpment retreat directly despite mechanical processes being the most important factors controlling landform development on the other hand in regions characterized by the wet tropical climate of brazil geochemical processes are more intense and they destroy the talus very quickly enhancing deep weathering however mechanical morphogenesis is also frequent in such regions forming in deforested areas features very similar to those found in the badlands of dry zones chemical and physical mechanical processes have very different intensities in dry arid and wet tropical areas but these processes are very relevant to landform development in both environments the rates of escarpment retreat are higher in the dry areas of the colorado plateau than estimated for the brazilian tropical zones which is in accordance with classical models these variations are probably related not only to climate but also to lithological differences the tops of the mesas on the colorado plateau are supported by thin strongly cemented conglomeratic fluvial sandstones whereas the caprocks of the brazilian cuesta landforms comprise thick basalt flows capped by ferruginous cuirasses in some cases lithological characteristics are more important than climate regarding escarpment retreat

stress induced upper crustal anisotropy in southern california 1 we use an automated method to analyze shear wave splitting from local earthquakes recorded by the southern california seismic network between 2000 and 2005 the observed fast directions of upper crustal anisotropy generally are consistent with the direction of maximum horizontal compression hmax suggesting that one major mechanism of anisotropy in the top 20 km of crust under southern california is regional stress however at other stations fast directions are aligned with the trends of regional faulting and local alignment of anisotropic bedrock splitting delay times range widely within 0 2 s these upper crustal anisotropy observations together with previous studies of sks shear wave splitting surface waves and receiver functions suggest different mechanisms of anisotropy at different depths under southern california anisotropy in the upper crust appears to be in response to the current horizontal maximum compression hmax which differs from the cause of anisotropy in the lower crust and mantle we also explore possible temporal variations in upper crustal anisotropy associated with preearthquake stress changes or stress changes excited by surface waves of great earthquakes but do not observe any clear temporal variations in fast directions or time delays

late quaternary vegetation climate and fire history from the tropical mountain region of morro de itapeva se brazil late quaternary paleoenvironments have been interpreted from a 35 000 yr b p pollen and charcoal record from morro de itapeva 22 47 s 45 32 w 1850 m a s l in the se brazilian highlands changes in taxa composition and elevational shifts in high elevation grassland campos de altitude araucaria forest cloud forest and atlantic rain forest all of which can be found in the study area today indicate climatic changes in the past expanded high elevation grasslands absence of araucaria forest cloud forest and atlantic rain forest during the recorded last glacial period ca 35 000 17 000 yr b p suggest a climate markedly cooler and drier than today development of a sphagnum peat bog rare presence of araucaria forest taxa and existence of a narrow cloud forest and rain forest belt at lower elevations during the late glacial period 17 000 ca 10 000 yr b p indicate a change to a cool and somewhat moister climates during the early holocene cloud forest developed close to the study site reflecting a warm and moist climate on the east facing slopes but a drier climate on the highland plateau evidenced by the rare presence of araucaria and podocarpus only during the late holocene moisture increases in the highlands suggested by the higher frequency of araucaria and podocarpus fires were more frequent during the last glacial than during the holocene

the distribution of permafrost in rock glaciers of the southern alps france abstract forty electrical resistivity surveys were performed on ten rock glaciers in the southern alps of france in the summer of 1986 taking a resistivity value exceeding 25 000 m as indicative of a frozen layer suggests that seven of these rock glaciers still contain permafrost values up to 1 000 000 m were encountered in some cases the usual resistivity interpretation is inadequate because of the oversteepening effect due to the shape of the frozen bodies in general resistivity survey interpretation enables permafrost to be separated from massive glacier ice and gives information on the ice content of the permafrost and the thickness of the layer the resulting conclusion that these rock glaciers are essentially inherited forms testifying the passage of recent cold periods is confirmed by the discovery on three sites of rock glaciers with a heterogeneous structure a thawed central part and a accumulation of ice at the snout it suggests that the rock glaciers in the southern alps were formed for the most part during the subboreal period

radiation patterns of a shear wave vibrator in near surface shale two shallow surface to borehole field tests were conducted to investigate the radiation patterns of a shear wave vibrator in near surface shale in the in line direction for which baseplate motion is transverse to the source geophone raypath the vibrator produces a broadband high amplitude signal of the sh type and virtually no signal of the sv or p types the amplitude of the sh radiation is approximately constant as a function of polar angle but it falls off as the cosine of the azimuthal angle measured with respect to the in line direction in the broadside direction the vibrator produces a strong uncontaminated signal of the sv type the radiation pattern of the sv signature is lobate in the polar plane and peaks at an incident angle of 30 to 35 degrees in the horizontal plane the sv radiation varies as the sine of the azimuthal angle measured with respect to the in line direction the field tests were conducted on a permian shale in oklahoma and an eocene shale in east texas comparison between sh and sv wave surfaces indicates that both shales behave approximately like transversely isotropic solids with a vertical axis of symmetry theoretical wave surfaces are fit to the observed data by using elastic moduli determined from the field measurements and by making the assumption that the near surface shale at each field site is a single homogeneous inherently transversely isotropic material the analyses indicate that horizontal sh group velocity is about 30 percent greater than horizontal sv group velocity in the permian shale and about 25 percent greater in the eocene shale

modelling orthorhombic anisotropic effects for reservoir fracture characterization of a naturally fractured tight carbonate reservoir onshore texas usa in this study we present a step by step theoretical modelling approach using established seismic wave propagation theories in anisotropic media to generate unique anisotropic reflection patterns observed from three dimensional pure mode pressure 3d pp full azimuth and full offset seismic reflection data acquired over a naturally fractured tight carbonate field onshore texas usa our aim is to gain an insight into the internal structures of the carbonate reservoir responsible for the observed anisotropic reflection patterns from the generated model we were able to establish that the observed field seismic reflection patterns indicate azimuthal anisotropy in the form of crack induced shear wave splitting and variation in p wave velocity with offset and azimuth amplitude variation with azimuth avaz analysis also confirmed multi crack sets induced anisotropy which is characteristic of orthorhombic symmetry evident as multiple bright and dim amplitude azimuth directions as well as complete reversal of bright amplitude to dim amplitude azimuth direction as the angle of incidence increases from near 15 to mid 30 offsets finally we fitted the generated p wave velocity into an ellipse to determine the intensity and orientation n26e of the open crack set as well as the direction of the minimum in situ stress axis n116e within the reservoir the derived information served as an aid for the design of horizontal well paths that would intercept open fractures and ensure production optimization of the carbonate reservoir which was on production decline despite reservoir studies that indicate un depleted reserves

shear waves in lithosphere studies on the territory of the u s s r abstract thousands of kilometers of dss profiles were compiled with three component stations in the u s s r the results showed that the usual shots in holes or water basins normally create not only p waves but shear waves as well the most favourable condition for their generation is the presence of a sharp seismic boundary near the source for example the basement surface the s wave field as a rule contains all the types of reflected and refracted waves that are found in the p field the difference is in lower frequencies they are lower by one third somewhat higher intensity and greater variability of amplitudes of shear waves when recording the s waves the major information is obtained from the velocity relation v p v s with depth and laterally it reveals that three major factors are affecting this relation the degree of rock fissuring the composition of rocks and the temperatures at depth reduction of fissuring with depth i e with greater distances from the source results in an overall drop of as the composition of the uppermost crust changes the urals increases in blocks composed of basic rocks this value shows little changes on the baltic and ukrainian shields on the siberian platform first increases with depth from 1 71 up to 1 76 probably due to the dilatancy effect and then it decreases to values less than 1 7 in the lower crust and upper mantle in western siberia grows with depth reaching 1 79 in the lower crust it is somewhat reduced in the mantle but still above 1 7 this can be ascribed apparently to a higher temperature regime of the lower crust in western siberia in many regions a splitting of the shear waves of different polarization is observed due to velocity anisotropy this was found for the first refracted waves in the urals and for reflected waves from the m boundary on the siberian platform in both cases anisotropy is associated with the crust on the ukrainian and baltic shields the difference in the velocities of sh and sv waves was not recorded

climatic variations in the argentine plains during the last 18 000 years the last deglacial hemicycle was characterized by a general increase in temperature and precipitation in the region with a few significant departures from this general trend the present ne sw climatic gradient was maintained throughout the entire period except in the upper holocene the following sequence of events is apparent if the present climate is taken as a reference base 1 a 18 000 8500 yr b p arid and cool with aeolian sand ad loess deposition patagonian fauna climatic isolines temperature precipitation etc were located some 750 km northeast of their present positions 2 b 8500 3500 yr b p humid subtropical with brazilian fauna pedogenesis and fluvial dynamics climatic limits migrated about 800 900 km southwest of their former positions 3 c 3500 1000 yr b p dry subtropical aeolian dynamics the normal latitudinal climatic gradient was interrupted by the occurrence of an anticyclonic centre which stabilized the climate over an area of some 1 600 000 km2 4 d 1000 yr b p little ice age climate was similar to the present one over much of the plains but the northeastern extremity was warmer 5 e little ice age climatic deterioration in the southern belt was characterized by generalized aeolian activity and migration of isolines more than 150 km to the northeast in that area 6 f present climate 19th and 20th centuries subtropical humid in the east and dry in the west

application of refraction seismics in alpine permafrost studies a review abstract refraction seismics is a common geophysical application to investigate permafrost in alpine studies this study reviews the physical basis of the use of refractions seismics and introduces the history of its application in alpine environments seismic properties are influenced by rock or soil properties and fluid or ice effects in laboratory measurements these influences are determined and linked to mechanical properties or used for calibration of field studies in field conditions supplementary environmental factors influence the seismic properties of landforms in this paper laboratory studies of rocks from different lithologies and with different properties as well as case studies on rock glaciers moraines talus slopes and debris covered slopes are collected and influencing factors quantitatively analyzed the data demonstrate how lithology porosity and anisotropy influence p wave velocity environmental factors result in a high variation of p wave velocities in landforms however p wave velocities enable the differentiation of active layer and permafrost in rock glaciers and moraines in talus slopes and debris covered slopes p wave velocity contrasts between active layer and permafrost layer might be insufficient and require the application of additional methods for a final differentiation

geomorphic response to rapid climatic and hydrologic change during the late pleistocene and early holocene in the humid and sub humid tropics abstract the data base concerning late quaternary environmental change in the humid tropics is dependent on records from scattered sites the intensity and duration of wet dry oscillations remain speculative and the responses of hillslopes and river systems are based on over simplified models however available evidence indicates that prolonged aridity affected all but a few favoured core areas of equatorial climate after 20 000 bp lasting 5 7 ka dry conditions at the lgm were marked by semi arid landforms and reduced steam activity large palaeofloods occurred after 13 000 be but dry conditions returned after 11 000 bp before the early holocene pluvial led to abundant sedimentation lasting nearly 2 ka after 9500 bp in africa amazonia and australasia erosion channel cutting and flood deposition occurred at the pleistocene holocene transition followed by multiple shifts from lateral to vertical accretion fill cut episodes during the early holocene while thick overbank deposits formed during the later holocene re establishment of the lowland rainforests was delayed until after 9000 bp in africa australia and brazil and several wet dry oscillations followed in the mid holocene period hillslope activity at the lgm was marked by local sediment transfers and fan formation at the termination sediment fluxes increased rapidly but mass movement probably peaked after 10 000 bp sediment delivery to stream channels was not immediate and large sediment stores remain on the landscape today many in areas of potential sensitivity of erosion

late quaternary environmental and climatic changes in central brazil paleoenvironmental changes dating back to 30 000 yr b p documented in a pollen record from central brazil lat 19 s permit the reconstruction of climatic changes related to shifts of the antarctic polar fronts the paleoclimatic inferences were obtained by a study of modern vegetation and pollen distribution taking into account present day climatic parameters at 30 000 yr b p the climate must have been warmer and moister than today judging from the high amount of tree pollen taxa characteristic of floodplain forest from 17 000 to 14 000 yr b p the climate was drier although tree pollen percentages were relatively high after 12 000 yr b p araucaria forest elements increased suggesting a moister and cooler climate the araucaria forest disappeared during a short interval between 11 000 and 10 000 yr b p this could be related to the younger dryas event at the beginning of the holocene the climate became cool and moist again as indicated by the reexpansion of the araucaria forest the latter was progressively replaced by a mesophytic semideciduous forest indicating warmer and drier climate after 8500 yr b p at 5000 yr b p an arid interval was followed by the expansion of mesophytic semideciduous forest elements

shallow seismic surveying of an alpine rock glacier to map the internal structure and lower boundary of an alpine rock glacier we recorded three shallow seismic profiles and drilled four 70 m deep holes through to the underlying bedrock although analysis of the seismic data using standard reflection processing schemes did not yield conclusive results because of the dominantly low frequency returned signals and the presence of strong source generated noise tomographic inversions of first arrival times were successful in mapping several critical subsurface features a thin low velocity layer of loose boulders air voids and snow was found to extend across the entire surveyed area below this layer two distinct velocity regimes superimposed on a general increase in velocity with depth were identified a broad regime of high velocities was interpreted to contain boulders with numerous ice filled voids whereas an adjacent regime of relatively low velocities was explained in terms of boulders with air and water filled voids this latter region of degrad

pebbly versus bouldery rock glaciers morphology structure and processes abstract differences in rockwall geology cause two types of rock glaciers a bouldery rock glacier having the active layer composed of matrix free boulders derived from crystalline rocks and massive limestone and a pebbly rock glacier consisting of matrix supported debris derived from less resistant shale and platy limestone such material composition controls transport processes responsible for the shape size and internal structure of the two types of rock glaciers this paper compares the major processes controlling the morphology and structure of the two types in the swiss alps based on mapping description of geological and morphological characteristics direct observation of stratigraphy and geophysical soundings of internal structure in the swiss alps pebbly rock glaciers are distinguished from bouldery rock glaciers by the clast size of 15 20 cm in the mean b axis diameter the former are fed by small scale rockfalls debris flows and solifluction whereas the latter mainly originate from large rockfalls pebbly rock glaciers are generally smaller 100 k m in bouldery rock glaciers appears to originate from snow banks buried with deposits of large rockfalls from the large source rockwall

the response of geomorphic systems to climatic and hydrological change during the late glacial and early holocene in the humid and sub humid tropics

interaction of the south american monsoon system and the southern westerly wind belt during the last 14 kyr abstract surface currents and sediment distribution of the se south american upper continental margin are under the influence of the south american monsoon system sams and the southern westerly wind belt swwb both climatic systems determine the meridional position of the subtropical shelf front stsf and probably also of the brazil malvinas confluence bmc we reconstruct the changing impact of the sams and the swwb on sediment composition at the upper rio grande cone off southern brazil during the last 14 cal kyr bp combining sedimentological geochemical micropaleontological and rock magnetic proxies of marine sediment core geob 6211 2 sharp reciprocal changes in ferri and paramagnetic mineral content and prominent grain size shifts give strong clues to systematic source changes and transport modes of these mostly terrigenous sediments our interpretations support the assumption that the sams over se south america was weaker than today during most of the late glacial and entire early holocene while the swwb was contracted to more southern latitudes resembling modern austral summer like conditions in consequence the stsf and the bmc were driven to more southern positions than today s favoring the deposition of fe rich but weakly magnetic la plata river silts at the rio grande cone during the mid holocene the northern boundary of the swwb migrated northward while the stsf reached its northernmost position of the last 14 cal kyr bp and the bmc most likely arrived at its modern position this shift enabled the transport of antarctic diatoms and more strongly magnetic argentinean shelf sands to the rio grande cone while sediment contributions from the la plata river became less important during the late holocene the modern el nino southern oscillation set in and the sams and the austral tradewinds intensified causing a southward shift of the stsf to its modern position this reinforced a significant deposition of la plata river silts at the rio grande cone these higher magnetic silts with intermediate fe contents mirror the modern more humid terrestrial climatic conditions over se south america

three term taylor series for t2 x2 curves of p and s waves over layered transversely isotropic ground the arrival time curve of a reflection from a horizontal interface beneath a homogeneous isotropic layer is a hyperbola in the x t domain if the subsurface is one dimensionally inhomogeneous horizontally layered or if some or all of the layers are transversely isotropic with vertical axis of symmetry the statement is no longer strictly true though the arrival time curves are still hyperbola like in the case of transverse isotropy however classical interpretation of these curves fails interval velocities calculated from t 2 x 2 curves do not always approximate vertical velocities and therefore cannot be used to calculate depths of reflectors to study the relationship between velocities calculated from t 2 x 2 curves and the true velocities of a transversely isotropic layer we approximate t 2 x 2 curves over a vertically inhomogeneous transversely isotropic medium by a three term taylor series and calculate expressions for these terms as a function of the elastic parameters it is shown that both inhomogeneity and transverse isotropy affect slope and curvature of t 2 x 2 curves for p waves the effect of transverse isotropy is that the t 2 x 2 curves are convex upwards for sv waves the curves are convex downwards for sh waves transverse isotropy has no effect on curvature

the upper parana river brazil geomorphology sedimentology and paleoclimatology this study involves the geomorphological sedimentological and paleoclimatological aspects of the upper parana river at porto rico state of parana brazil the alluvial plain is composed of a braided system main channel with island and sandy bars and an anastomosing system involving secondary channels tributaries and a complex of swamps pools and natural levees river discharge in its upper course varies from 8400 to 13 000 m3 s minimum of 2550 m3 s and maximum of 33 740 m3 s solid discharge reaches 27 106 tons year for suspended sediments and 3 106 tons year for load sediments through echobathymetric survey bed forms were grouped in ripples megaripples dunes and sand waves a detailed study of the sedimentology heavy minerals and facies architecture was applied to the two major geomorphic provinces and their subenvironments channel province with sand bar and bed form deposits and overbank province with natural levee flood basin crevasse and island deposits palynological preliminary studies show that during the late pleistocene the area was dominated by grassland and savannas under drier climatic conditions since the beginning of the holocene there has been a generalized transition to a humid phase and the present broadleaf forest occupies the area some hypotheses can be formulated for the evolution of the area 1 the first order architectural element channel ch was generated during the pleistocene associated with climatic changes and tectonism the alluvial valley was filled up by alluvial colluvial deposits at the end of the pleistocene channel deposits present 40 ka bp 2 tectonism and climatic changes atlantic climatic optimum generated a new valley bottom 5 8 m below the former level and a wide meandering plain was built up 4000 4500 bp 3 a recent fluvial system created a new terrace 3 m above the normal water level

a review of shear wave splitting in the crack critical crust summary over the last 15 years it has become established that crack induced stress aligned shear wave splitting with azimuthal anisotropy is an inherent characteristic of almost all rocks in the crust this means that most in situ rocks are pervaded by fluid saturated microcracks and consequently are highly compliant the evolution of such stress aligned fluid saturated grain boundary cracks and pore throats in response to changing conditions can be calculated in some cases with great accuracy using anisotropic poro elasticity ape ape is tightly constrained with no free parameters yet dynamic modelling with ape currently matches a wide range of phenomena concerning anisotropy stress shear waves and cracks in particular ape has allowed the anisotropic response of a reservoir to injection to be calculated predicted with hindsight and the time and magnitude of an earthquake to be correctly stress forecast the reason for this calculability and predictability is that the microcracks in the crust are so closely spaced that they form critical systems this crack critical crust leads to a new style of geophysics that has profound implications for almost all aspects of pre fracturing deformation of the crust and for solid earth geophysics and geology we review past present and speculate about the future of shear wave splitting in the crack critical crust shear wave splitting is seen to be a dynamic measure of the deformation of the rock mass there is some good news and some bad news for conventional geophysics many accepted phenomena are no longer valid at high spatial and temporal resolution a major effect is that the detailed crack geometry changes with time and varies from place to place in response to very small previously negligible changes however at least in some circumstances the behaviour of the rock in the highly complex inhomogeneous earth may be calculated and the response predicted opening the way to possible control by feedback the need is to devise ways to exploit these new opportunities in the crack critical crust recent observations from the smsites project at husavik in northern iceland gathered while this review was being written display the extraordinarily sensitivity of in situ rock to small changes at great distances the effects are far too large to occur in a conventional elastic brittle crust and their presence confirms the highly compliant nature of the crack critical crust

the effect of the aspect ratio on crack induced anisotropy1 media containing aligned cracks show anisotropy with respect to elastic wave propagation there are several models describing the wave propagation in cracked media most of them only valid for cracks with small aspect ratios one of these models crampin s model is compared with a model valid for all aspect ratios nishizawa s model the elastic constants and the group velocities are compared for both dry and liquid filled inclusions with aspect ratios ranging from 0 0001 flat cracks up to 1 spheres the difference between both models is small for small aspect ratios but becomes larger for increasing aspect ratios at a crack density of 0 05 both models give within an error of 5 the same results for aspect ratios up to 0 3 therefore crampin s model can be applied to a large range of cracked media even if the aspect ratio of the inclusions is not small the variation of the anisotropy as a function of the aspect ratio can be studied using thomsen s dimensionless parameters e and y they show how inclusions with large aspect ratios result in elliptical anisotropy