fractal geometry based quantification of shock induced rock fragmentation in and around an impact crater shock induced fragmentation structures of basement rocks and their limestone cover in and around the ries impact crater germany were recorded on outcrop hand sample and thin section scale and quantified mainly by fractal geometry methods quantification was performed by automated procedures and in areas of square centimetres to square decametres with a maximum resolution of micrometre scale in 2d and on all scales the fragmentation structures form complex statistically self similar patterns fractals with specific characteristics i the pattern fractality is scale dependent ii three different power law relationships exist which reflect the effect of three fragmentation processes iii the fracture patterns are anisotropic and inhomogeneous over larger areas iv complexity and anisotropy of the fracture patterns vary systematically such systematic variation appears typical for impact related fragmentation

possible electrokinetic origin of large magnetic variations at la fournaise volcano abnormal time variations of the geomagnetic field related to volcanic activity have been reported for several decades1 10 two main candidates have been considered for the source mechanism of these volcanomagnetic variations piezomagnetism and electro kinetic effects we considered both of these mechanisms in our attempts to interpret the most spectacular volcanomagnetic variations observed on piton de la fournaise volcano reunion island 11 but now new analysis of the latest data which covers a time span of more than three years leads us to think that water circulation is the main agent of the strong magnetic signals observed on the volcano in addition to the signals that we correlated with the volcano activity11 12 longer period components also exist as shown here with amplitudes and characteristics that have not been reported before we propose that these magnetic variations are generated by electrokinetic effects in which case the water circulation system into this massif would be a sensor for detecting stress changes linked to the volcano activity

origin and morphology of limestone caves limestone caves form along ground water paths of greatest discharge and solutional aggressiveness flow routes that acquire increasing discharge accelerate in growth while others languish with negligible growth as discharge increases a maximum rate of wall retreat is approached typically about 0 01 0 1 cm yr determined by chemical kinetics but nearly unaffected by further increase in discharge the time required to reach the maximum rate is nearly independent of kinetics and varies directly with flow distance and temperature and inversely with initial fracture width discharge gradient and pco2 most caves require 104 105 yr to reach traversable size their patterns depend on the mode of ground water recharge sinkhole recharge forms branching caves with tributaries that join downstream as higher order passages maze caves form where 1 steep gradients and great undersaturation allow many alternate paths to enlarge at similar rates or 2 discharge or renewal of undersaturation is uniform along many alternate routes flood water can form angular networks in fractured rock anastomotic mazes along low angle partings or sponge work where intergranular pores are dominant diffuse recharge also forms networks and spongework often aided by mixing of chemically different waters ramiform caves with sequential outward branches are formed mainly by rising thermal or h2s rich water dissolution rates in cooling water increase with discharge co2 content temperature and thermal gradient but only at thermal gradients of more than 0 01 c m can normal ground water co2 form caves without the aid of hypogenic acids or mixing artesian flow has no inherent tendency to form maze caves geologic structure and stratigraphy influence cave orientation and extent but alone they do not determine branch work versus maze character

strong heterogeneity caused by deep mantle layering 1 numerical simulations are used to characterize the volumetric heterogeneity associated with proposed chemical layering in the deep mantle a globally continuous undulating layer generates enormous amounts of volumetric heterogeneity which is caused by lateral variations in the layer boundary depth and by strong hot upwellings arising from the top of the layer in the middle lower mantle region in contrast the heterogeneity in the deepest mantle is very weak partial cancellation of the temperature and compositional contributions to seismic velocity could mask the layer itself but the strong signatures of the thermochemical boundary layer and induced upwellings remain even when fields are filtered to approximate the resolution of global seismic tomographic models this distinctive heterogeneity is not observed in global seismic tomographic models dense material that is restricted to discontinuous piles generates heterogeneity that is more consistent although not entirely with seismic observations with strong heterogeneity at the core mantle boundary radial correlation functions display a characteristic narrowing in the vicinity of any chemical layer but are very sensitive to the applied seismic tomographic filtering

40ar 39ar laser probe age determination confirms the ries impact crater as the source of glass particles in graupensand sediments grimmelfingen formation north alpine foreland basin mineralogical and chemical characteristics of reworked suevite material recovered from graupensand deposits grimmelfingen formation north alpine foreland basin middle miocene are identical to those recorded in ries suevite 40ar 39ar laser probe analyses of two glass particles from graupensand components and of a glass fragment from the ries suevite yielded ages ranging between 14 3 and 14 4 ma identical within analytical uncertainties hitherto the ries impact event was dated at 15 ma conventional k ar and 40ar 39ar methods whereas the graupensande have been placed into the ottnangian around 18 5 ma on the basis of mammal biostratigraphy small sample masses involved in laser probe technique allowed rigorous preselection of highly pure glass particles thus reducing possible age determination errors through partly molten or even unmolten mineral fragments from the variscan crystalline basement our results reconfirm previous statements considering the graupensande as reworked products of the ries impact ejecta blanket thus placing the age of the grimmelfingen formation into the badenian of middle miocene rather than into the ottnangian early miocene

resistance to mantle flow inferred from the electromagnetic strike of the australian upper mantle seismic anisotropy is thought to result from the strain induced lattice preferred orientation of mantle minerals especially olivine1 2 owing to shear waves propagating faster along the a axis of olivine crystals than along the other axes this anisotropy results in birefringence or shear wave splitting 3 which has been investigated in numerous studies1 4 although olivine is also anisotropic with respect to electrical conductivity5 with the a axis being most conductive few studies of the electrical anisotropy of the upper mantle have been undertaken and these have been limited to relatively shallow depths in the lithospheric upper mantle6 7 theoretical models of mantle flow have been used to infer that for progressive simple shear imparted by the motion of an overriding tectonic plate the a axes of olivine crystals should align themselves parallel to the direction of plate motion8 9 here however we show that a significant discrepancy exists between the electromagnetic strike of the mantle below australia and the direction of present day absolute plate motion10 we infer from this discrepancy that the a axes of olivine crystals are not aligned with the direction of the present day plate motion of australia indicating resistance to deformation of the mantle by plate motion

precise determination of phase relations in pyrolite across the 660 km seismic discontinuity by in situ x ray diffraction and quench experiments abstract mineral assemblage changes in a pyrolite composition with increasing pressure were observed by in situ x ray diffraction and quench experiments at pressures near that of the 660 km seismic discontinuity and at a fixed temperature of 1600 c according to results obtained by in situ x ray diffraction experiments ringwoodite rw was observed with majorite garnet and casio 3 rich perovskite at pressures of about 20 22 gpa dissociation of ringwoodite to mgsio 3 rich perovskite and magnesiowustite mw was completed at 22 0 0 2 gpa according to matsui et al s periclase pressure scale and at 21 7 0 1 gpa according to shim et al s gold pressure scale majorite garnet persisted to about 24 gpa where pyrolite transformed to a lower mantle mineral assemblage i e mgsio 3 perovskite casio 3 rich perovskite and magnesiowustite thus majorite garnet coexists with the lower mantle assemblage at pressures of about 22 24 gpa in the quench experiments an assemblage of mgsio 3 perovskite magnesiowustite casio 3 rich perovskite and majorite garnet was synthesized at 22 5 gpa and 1600 c in which mg perovskite contained 2 8 wt al 2 o 3 and was significantly poorer in fe than coexisting magnesiowustite the fe mg partition coefficient between mg perovskite and magnesiowustite including ferric iron k app 0 27 0 06 is very close to that in the al free system which suggests that these p t conditions are in the vicinity of those of ringwoodite decomposition both the results of in situ x ray diffraction and quench experiments in the present study yield a convergent result that ringwoodite decomposes into mg perovskite and magnesiowustite before the garnet to perovskite transition at 1600 c in pyrolite the relation between the al content in mg perovskite and k app in pyrolite is non linear which is consistent with the fe mg partitioning between mg perovskite and magnesiowustite previously reported for a simpler mgo feo al 2 o 3 sio 2 system

karst landscape evolution in the littoral area of the bay of biscay north iberian peninsula the western pyrenean area contains extensive karst areas however their genesis and development are still mostly unknown in this work we make a general description of the karst landscape in different karst areas 1 rasa type 2 cone type karst and 3 alpine type karst the first two types are present in the littoral area where geomorphological evolution mostly depends on sea level and climatic changes we focused our study in two karst areas of the littoral cone type karst we correlate different caves created from different stable water table levels three representative caves are studied in detail studying their stratigraphic record based on allostratigraphy finally we dated the different phases of speleothem formation in the three caves using all this information we defined four stable paleowater table levels at 50 150 220 and 350 m asl controlled by sea level changes and isostatic uplift events the lowest level is the youngest with an age of c 1 ma we discovered that the interior of the three caves display very similar endokarst allostratigraphic sequences characterized firstly by an erosion phase a fluvio karst input flowstone speleothem formation and finally dripping speleothem formation the chronological data shows a correlation between these phases and pleistocene climatic phases the erosion phase is related to the falling sea level fluviokarst detrital input is related to cold glacial stages and the formation of speleothems is related to the warmest interglacial moments and high sea level periods

long term quaternary uplift rates inferred from limestone caves in sarawak malaysia abstracttherateoflong term 2m y base levelloweringestimatedinanextensivesequenceoflimestonecavesinsarawak malaysia fromuraniumseries electronspinresonance andpaleomagneticdatingis0 19 1 0 03 2 0 04m ka thisratehasremainedconstantoveratleastthelast700ka asshownbycomparisonofthenumberandspacingofwallnotchesformedduringphasesofinterstadialandinterglacialaggradationwithpeaksinthedeep seaoxygenisotopecurve itisarguedthatbase levelloweringoccursinresponsetoepi rogenicupliftofthemoreresistantlimestonesduetoregionaldenudationofthesoftershales andto exuralisostacyassociatedwithhighratesofoffshoresedimentation introduction ratesofupliftareneededtoconstrainmodelsofreliefgeneration pazzagliaandgardiner 1994 andtectonicprocesses en glandandmolnar 1990 overgeologictimescales mostestimatesofuplifthavecomefromtectonicallyactivecoasts whereemer gentmarineterracescanbedatedusingura nium series and other techniques e g bloometal 1974 andstudiesofriverter racesusingradiocarbondating e g mer rittsetal 1994 however althoughlong termsequencesofbothcoastalandriverterraceshavebeenobtained pirazzolietal 1993 pazzagliaandgardiner 1994 thechronologicalcontrolontheseisoftenpoor furthermore uvialterracesarenotubiq uitous theirdevelopmentdependsoncrit icalinterrelationsbetweenupliftrate basinarea andtheeffectsofeustaticsealevel merrittsetal 1994 thusfewwell con strainedestimatesofratesofupliftoverthelongertimescaleareavailable herewepro videestimatesofthelong termrateofbase levellowering merrittsetal 1994 derivedfromuraniumseriesandpaleomagneticdat ingofdepositsfromextensivecavesystemsin the gunung mulu national park sarawak malaysia

evolution of multilevel caves in the sierra de atapuerca burgos spain and its relation to human occupation abstract the evolution of the torcas cave system sierra de atapuerca is analysed in order to shed light on the formation of the atapuerca archaeological sites and human occupation in the area critical for identifying the paths of the first human dispersal into europe the geomorphological analysis of the endokarst system and the regional base levels has revealed a multilevel cave system with drainage directions from south to north where old karst springs fed the pico river using morphological and topographic evidence we have correlated the fluvial terraces situated at relative heights of 84 80 m and 78 70 m above the arlanzon river main course with the first and second cave levels respectively both of early pleistocene age the fluvial levels t4 60 67 m and t5 50 54 m are linked with the third level early middle pleistocene which contains fluvial deposits probably related to terrace t6 44 46 m progressive fluvial incision allowed humans to gain access to the cave system through several entrances from 1 22 myr until the end of the middle pleistocene when these cave entrances became filled forming the most interesting hominid bearing deposits in europe

lateral variations in compressional shear velocities at the base of the mantle observations of core diffracted p p diff and sh sh diff waves recorded by the missouri to massachusetts moma seismic array show that the ratio of compressional p seismic velocities to horizontal shear sh velocities at the base of the mantle changes abruptly from beneath the mid pacific vp vs 1 88 also the value predicted by reference earth models to beneath alaska vp vs 1 83 this change signifies a sudden lateral variation in material properties that may have a mineralogical or textural origin a textural change could be a result of shear stresses induced during the arrival at the core of ancient lithosphere from the northern pacific paleotrench

sediments at the top of earth s core unusual physical properties at the core mantle boundary have been inferred from seismic and geodetic observations in recent years we show how both types of observations can be explained by a layer of silicate sediments which accumulate at the top of the core as earth cools compaction of the sediments expels most of the liquid iron but leaves behind a small amount of core material which is entrained in mantle convection and may account for the isotopic signatures of core material in some hot spot plumes extraction of light elements from the liquid core also enhances the vigor of convection in the core and may increase the power available to the geodynamo

lower mantle seismic discontinuities and the thermal morphology of subducted slabs abstract the nature of the lowermost few 100 km of the mantle holds insights into the scale of convection of the earth s mantle here we investigate the fine structure of this region using seismic migration of shear waves reflecting from velocity discontinuities near the core mantle boundary cmb recorded by a dense network of european seismic stations two main features are found one structure exhibits large scale topography and can be explained by a sharp increase in seismic velocity 206 316 km above the cmb the second structure lies 55 85 km above the cmb and marks a sharp reduction in velocity to explain the origin of these discontinuities we appeal to numerical simulations of three dimensional 3d mantle convection incorporating rigidly moving plates the plates organize the convective flow to allow for the development of large convection cells and cool sheet like downwellings at a convergent plate boundary the results suggest that in places observed seismic complexity in d discontinuity structure may be due to the thermal gradients resulting from the accumulation of cool subducted plate material at the cmb

alluvial terrace systems in zhangjiajie of northwest hunan china implications for climatic change tectonic uplift and geomorphic evolution abstract this paper reports the latest details from two comprehensive investigations of alluvial terrace sequences in zhangjiajie northwest hunan province china seven alluvial terrace units along the maoxi river and four terrace sequences along the suoxi river record significant regional geomorphic history rates of regional quaternary uplift and climate change are reconstructed using topographic and stratigraphic evidence from terrace and adjacent cave deposits along with electron spin resonance esr and thermo luminescence tl dating controls between 928 ka and 689 ka the time averaged uplift rate or incision rate was 0 16 m ka the rate decreased to 0 05 m ka between 689 ka and 347 ka and then increased slightly to 0 11 0 14 m ka after 347 ka the inferred incision rate increased roughly from 0 21 0 32 m ka to 0 51 m ka from the late pleistocene to present the seven alluvial phases t7 t1 and their associated chronology are consistent with climatic variations at regional and or global scales suggesting that these terraces represent climate driven pauses imprinted atop the record of long term tectonically induced incision by rivers insights from these alluvial terrace staircases and cave features indicate that the spectacular sandstone peak forest landscape of the study area has emerged since the middle period of the middle pleistocene

geographic correlation between hot spots and deep mantle lateral shear wave velocity gradients abstract hot spot volcanism may originate from the deep mantle in regions exhibiting the earth s most pronounced lateral s wave velocity gradients these strong gradient regions display an improved geographic correlation over s wave velocities to surface hot spot locations for the lowest velocities or strongest gradients occupying 10 of the surface area of the core mantle boundary cmb hot spots are nearly twice as likely to overlie the anomalous gradients if plumes arise in an isochemical lower mantle plume initiation should occur in the hottest thus lowest velocity regions or in the regions of strongest temperature gradients however if plume initiation occurs in the lowest velocity regions of the cmb lateral deflection of plumes or plume roots are required the average lateral deflections of hot spot root locations from the vertical of the presumed current hot spot location ranges from 300 to 900 km at the cmb for the 10 30 of the cmb covered by the most anomalous low s wave velocities the deep mantle may however contain strong temperature gradients or be compositionally heterogeneous with plume initiation in regions of strong lateral s wave velocity gradients as well as low s wave velocity regions if mantle plumes arise from strong gradient regions only half of the lateral deflection from plume root to hot spot surface location is required for the 10 30 of the cmb covered by the most anomalous strong lateral s wave velocities we find that strong gradient regions typically surround the large lower velocity regions in the base of the mantle which may indicate a possible chemical in addition to thermal component to these regions

coastal and inland karst morphologies driven by sea level stands a gis based method for their evaluation sea level is the base level for groundwater circulation in coastal aquifers the evolution of karst surface landforms and subsurface drainage systems in these aquifers has been conditioned in geological time by tectonics and glacio eustatic sea level changes present morpho structural settings and the type distribution of karst surface and subsurface forms have developed in different carbonate formations according to differences in lithology climate and exposure time all driving the intensity of morphologic and karst processes the repeated and significant changes of groundwater level linked to sea level changes have had the most important role in driving the continuous evolution of karstic drainage systems and has resulted in most cases in a multiphase karst this study aims at defining a general method for identifying in karst coastal settings the elevations of flat or low topographic gradient surfaces using morphometric analysis of digital elevation models dems and geographical information systems giss and their comparison with elevations of distinctive karstic levels passages lateral solution cavities observed in vertical shafts and horizontal caves of the elevations of flat or low topographic gradient surfaces only those agreeing within 10 m or 20 m with elevation ranges marked by the high frequency of distinctive karst levels were considered as representative of the more probable past sea level stands the method is applied to a regional coastal carbonate formation in southern italy by using a 10 m dem and information on 140 complex caves and 85 shafts of the 15 elevations indicated by dem analysis 620 600 470 450 425 385 355 315 270 250 205 180 150 110 and 70 m above sea level a s l 13 match clearly those highlighted by significant frequencies of distinctive karstic levels these elevations are validated by comparison to the elevation of terraces and karst plains indicated in the literature copyright 2012 john wiley sons ltd

evidence for a ubiquitous seismic discontinuity at the base of the mantle a sharp discontinuity at the base of earth s mantle has been suggested from seismic waveform studies the observed travel time and amplitude variations have been interpreted as changes in the depth of a spatially intermittent discontinuity most of the observed variations in travel times and the spatial intermittance of the seismic triplication can be reproduced by a ubiquitous first order discontinuity superimposed on global seismic velocity structure derived from tomography the observations can be modeled by a solid solid phase transition that has a 200 kilometer elevation above the core mantle boundary under adiabatic temperatures and a clapeyron slope of about 6 megapascal per kelvin

in situ observations of phase transition between perovskite and cairo 3 type phase in mgsio 3 and pyrolitic mantle composition abstract in situ observations of the perovskite cairo3 phase transition in mgsio3 and in pyrolitic compositions were carried out using a laser heated diamond anvil cell interfaced with a synchrotron radiation source for pure mgsio3 the phase boundary between the orthorhombic mg perovskite and cairo3 type phases in the temperature range of 1300 3100 k was determined to be p gpa 130 3 0 0070 0 0030 t 2500 k using platinum as a pressure calibrant we confirmed that the cairo3 type phase remained stable up to pressures of at least 156 gpa and temperatures of 2600 k the consistency of our results with previous theoretical calculations leads us to conclude that the 2700 km seismic discontinuity at the bottom of the lower mantle can be attributed to a phase transition to the cairo3 type phase the phase change from an orthorhombic mg perovskite to a cairo3 type bearing assemblage in a pyrolitic mantle composition was also observed at p 125 gpa which corresponds to the same mantle depth as the seismic discontinuity the phase boundary between the orthorhombic mg perovskite and cairo3 type bearing assemblage was determined to be p gpa 124 4 0 008 0 005 t 2500 k using gold as a pressure calibrant this transition boundary indicates that the temperature at a depth of 2700 km is about 2600 k and the adiabatic temperature gradient in the lower mantle is estimated to be 0 31 k km the partition coefficients and the effect of some elements on the phase equilibrium between the orthorhombic mgsio3 perovskite and cairo3 type mgsio3 were estimated from ab initio calculations our experimental and theoretical results indicate that the d layer consists of a cairo3 type bearing assemblage which is likely to have significant effect on the chemical and thermal evolution of the earth s mantle

a comparison of electromagnetic distortion and resolution of upper mantle conductivities beneath continental europe and the mediterranean using islands as windows abstract to investigate the potential of utilising islands as windows through which oceanic mantle conductivities might be imaged simultaneous magnetotelluric mt measurements were carried out continuously over a 3 month duration at two continental stations one in the swabian alps southern germany the other in the bourgogne central france and on the mediterranean islands of montecristo mchr and mallorca mall the mt transfer functions to 1 5 cycles per day cpd and single site z h transfer functions for the first four harmonics of the solar quiet sq daily field variations are presented the transfer functions derived at the island sites are corrected for the distortive and inductive effects arising from the mediterranean bathymetry relative to the transfer functions calculated at the continental stations using three dimensional thin sheet modelling the corrections are formulated in terms of the magnetic perturbation tensor w static shifts in the mt transfer functions are corrected using the z h transfer functions and by comparison with hypothesised resistivity jumps at the transition zones models are derived jointly from the residual mt and z h transfer functions constraints on the resistivities of the upper mantle are investigated despite the widely different tectonic settings no significant differences in the conductivities of the upper mantle below 100 km are detected the disadvantages of utilising widely spaced islands as windows to the mantle are highlighted by departures from one dimensionality in the complex tectonic setting of the mediterranean region

carbon enhanced electrical conductivity during fracture of rocks changes in electrical resistance during rock fracture in the presence of a carbonaceous atmosphere have been investigated using nugget sandstone and westerly granite the experiments were performed in an internally heated gas pressure vessel with a load train that produced strain rates between 10 6 and 10 5 s 1 samples were deformed at temperatures of 354 to 502 c and pressures of 100 to 170 mpa in atmospheres of ar or mixtures of 95 co2 with 5 co or 5 ch4 compositions that are well within the field of graphite stability at the run conditions in experiments using nugget sandstone resistance reached a minimum value when the maximum temperature was achieved and good electrode contact was made the resistance then increased as the experiment continued probably due to dry out of the sample a change in the oxidation state of the fe oxide associated with the cement or destruction of current bearing pathways at approximately 200 mpa end load the rock sample failed plots of load and resistance versus time show several interesting features in one experiment for example as the end load reached about 175 mpa resistance stopped increasing and remained fairly constant for a period of approximately 0 5 hour during loading the end load displayed small decreases that were simultaneous with small decreases in resistance when the end load and the displacement indicated rock failure resistance decreased dramatically from 150 m to 100 m in a single experiment the westerly granite also showed a decrease in resistance during dilatancy the nature and distribution of carbon in the run products were studied by electron microprobe and time of flight secondary ion mass spectroscopy top sims carbon observed by mapping with the former is clearly observed on micro cracks that based on the microtexture are interpreted to have formed during the deformation the tof sims data confirm the electron probe observations that carbon is present on fracture surfaces these observations and experimental results lead to the hypothesis that as microfractures open in the time leading up to failure along a fracture carbon is deposited as a continuous film on the new reactive mineral surfaces and this produces a decrease in resistance subsequent changes in resistance occur as connectivity of the initial fracture network is altered by continued deformation such a process may explain some electromagnetic effects associated with earthquakes

role of sediment in speleogenesis sedimentation and paragenesis although the effects of sedimentation in caves have been recognised for many years its role in speleogenesis is frequently overlooked influxes of sediment into a cave system fundamentally alter the way cave passages develop either by alluviation in a vadose environment forcing lateral corrosion and the development of notches or by upwards dissolution in a phreatic environment through a process known as paragenesis sediment influxes affect the hydrological functioning of a karst aquifer by changing the way conduits behave and subsequently develop both in plan and long section here we give an overview of the mechanisms of cave sedimentation and describe how the process of alluviation and paragenesis affect speleogenesis a characteristic suite of meso and micro scale dissolutional features can be used to recognise paragenetic development which is reviewed here in a vadose environment these include alluvial notches whilst in a phreatic environment half tubes anastomoses and pendants bedrock fins and paragenetic dissolution ramps result using these to identify phases of sedimentation and paragenesis is crucial for reconstructing denudation chronologies from cave deposits we suggest that sedimentation and paragenesis are most likely to occur in certain geomorphological situations such as ice marginal and periglacial environments beneath thick residual soils and where rivers can transport fluvial sediment into a cave either via stream sinks or back flooding

resistivity and self potential changes associated with volcanic activity the july 8 2000 miyake jima eruption japan abstract the miyake jima volcano abruptly erupted on july 8 2000 after 17 years of quiet and gave birth to a crater 1 km in diameter and 250 m deep this expected unrest was monitored during the years 1995 2000 by electromagnetic methods including dc resistivity measurements and self potential sp surveys beneath the 2500 yr old hatcho taira summit caldera audio magnetotelluric soundings made in 1997 98 identified a conductive medium 200 500 m thick within the 50 m isoline located at a few hundred metres depth it was associated with the active steady state hydrothermal system centred close to the 1940 cone and extending southward a dc resistivity meter set in a schlumberger array with 600 1000 and 1400 m long injection lines evidenced strong resistivity changes between september 1999 and july 3 2000 in the vicinity of the newly formed crater the apparent resistivity has reached about three times its initial values on the 1400 m long line and has lowered to about 20 on the 600 m line just prior to the july 8 2000 eruption sp mapping made inside the summit hatcho taira caldera revealed negative anomalies where positive ones had occurred during the previous tens of years the largest negative anomaly 225 mv in amplitude mainly took place above the 1940 cone which collapsed in the crater formation a permanent 1 km long sp line across the caldera suggests accelerating changes during the 3 months preceding the eruption on a larger scale the comparison between 1995 and 2000 surveys has shown a global increase of the hydrothermal activity beneath the volcano its source could have been 250 m to the south of the crater these observations suggest that the hydrothermal system was slowly disturbed in the months preceding the eruption while drastic changes have occurred during the 2 weeks before the summit collapse when tectonic and volcanic swarms have appeared

a mid miocene to early pleistocene multi level cave as a gauge for tectonic uplift of the swabian alb southwest germany a recently discovered deep cave laierhohle within a plateau of upper jurassic limestone is the deepest 126 m of the southwest german swabian alb providing a unique gauge for crustal tilting and isostatic uplift of the southwest german crust from late mid miocene to earliest pleistocene horizontal levels are considered a product of a stationary palaeo water table vertical shafts are related to base level fall which in turn may be the result of uplift and or incision we correlate speleogenetic with dated geomorphic features and thus come to a chronology of events the laierhohle records five episodes of long term stability of the karst water table covering the time span from late middle miocene until the pliocene pleistocene transition the first two stable episodes can be dated to the late middle miocene and late miocene horizontal levels 1 and 2a an episode responsible for the formation of level 2b falls within early pliocene time levels 3a and 3b are spatially well separated but must have formed within a relatively short time span towards the end of the pliocene in the working area total depth of penetrative karstification was in the order of 120 m this penetration has been accomplished over a period of approximately 12 ma resulting in an average uplift rate of 0 01 mm a

monitoring resistivity changes prior to earthquakes in parkfield california with telluric arrays a telluric array has been designed to monitor long period changes of resistivity in parkfield prior to the next characteristic earthquake there the array straddles the san andreas fault and utilizes dipoles which range from 5 to 18 km long a method of data analysis using robust processing in the time domain and singular value decomposition yields daily estimates of telluric coefficients which are stable to within 1 the array has detected several fluctuations above the noise level of the measurements most of these fluctuations are uncorrelated with bursts of seismic activity changes in water levels anomalous strain and creep or magnetic storms however the largest fluctuation in 2 years coincided with a tensor strain anomaly and both of these preceded a m 3 7 earthquake by approximately 1 month this is the largest earthquake to occur in parkfield since the array was installed

genesis types and evolution of crevice type caves in the flysch belt of the western carpathians czech republic abstract crevice type caves are among the least investigated natural phenomena connected with the development of slope failures these caves present complex and peculiar underground systems with their own development and resulting landforms we investigated eight caves in the czech part of the outer western carpathians to determine their genesis types and evolution crevice formation is predisposed according to the lithological tectonic and morphological characteristics of the landslide body including the position and location of bedding planes joints and faults we performed several analyses including speleological mapping evaluation of high resolution topography above the caves geophysical ert measurements and structural investigations within cave passages in accordance with these analyses various mechanisms responsible for cave development were revealed an intra bed translation is responsible for the creation of regularly shaped passages with flat ceilings toppling as well as back and horizontal rotation of rock blocks determine the specific morphology and shapes of passages a relatively novel aspect of the current study is the identification of the subsidence of massive rock wedges due to the widening of cracks all of these mechanisms control the specific morphological characteristics within crevices e g typical shapes of passages cave level ordering and ceiling types some of these processes also influence topography above the caves finally the different phases of evolution of these caves were determined

lower mantle conductivity anomalies estimated from geomagnetic jerks 1 the occurrence epochs and duration periods of the 1969 1978 and 1991 geomagnetic jerks are estimated for 65 geomagnetic observatories by applying a statistical time series model to monthly means of the geomagnetic eastward component it is found for every jerk that the occurrence epochs around south africa and south pacific ocean are delayed several years from those in other regions moreover it is found for the 1969 and 1978 jerks that the duration times around south africa which are defined as the lengths of the duration periods are longer than those in other regions the distribution of these anomalous regions of the jerks i e south africa and south pacific ocean may imply the existence of higher conductivities in the lower mantle beneath these regions which possibly relates to the fact that the velocity of a seismic s wave in the d layer beneath these regions is slower than that in other regions the mantle conductivities beneath south africa south pacific ocean and other regions are estimated through a numerical simulation the magnetic diffusion equation in the mantle is solved for an abrupt magnetic change generated at the core mantle boundary comparing the results obtained by the simulation with those obtained by the data analysis it is plausible that the mantle conductivities beneath south africa and south pacific ocean are higher than that beneath other regions although there is an ambiguity in the estimated magnitudes of the mantle conductivity

electric potential changes prior to shear fracture in dry and saturated rocks electric potential changes before shear rupture were measured using darley dale sandstone quartz rich and icelandic basalt quartz free on both dry specimens and in the presence of pore fluid we find that electric potential changed markedly just prior to dynamic rupture in dry and saturated sandstones and saturated basalt but we did not detect precursory signals in dry basalt the absence of signals in dry basalt provides strong evidence that the piezoelectric effect and electrokinetic effect are dominant sources for precursory signals moreover we find that the amplitude of the precursory signals due to electrokinetic effect in saturated sandstone were as large as the coseismic signals we propose that this signal is caused by accelerating evolution of dilatancy as cracks grow in the rock before rupture resulting in water flow into the dilatant region with an electric current produced concurrently

steinheim suevite a first report of melt bearing impactites from the steinheim basin sw germany the 3 8 km steinheim basin in sw germany is a complex impact crater with central uplift hosted by a sequence of triassic to jurassic sedimentary rocks it exhibits a well preserved crater morphology intensely brecciated limestone blocks that form the crater rim as well as distinct shatter cones in limestones in addition an impact breccia mainly composed of middle to upper jurassic limestones marls mudstones and sandstones is known from drilling into the impact crater no impact melt lithologies however have so far been reported from the steinheim basin in samples of the breccia that were taken from the b 26 drill core we discovered small particles up to millimeters in size that are rich in sio2 50 wt and al2o3 28 wt and contain particles of fe ni co sulfides as well as target rock clasts shocked and unshocked quartz feldspar limestone and droplet shaped particles of calcite the particles exhibit distinct flow structures and relicts of schlieren and vesicles from the geochemical composition and the textural properties we interpret these particles as mixed silicate melt fragments widely recrystallized altered and or transformed into hydrous phyllosilicates furthermore we detected schlieren of lechatelierite and recrystallized carbonate melt on the basis of impactite nomenclature the melt bearing impact breccia in the steinheim basin can be denominated as steinheim suevite the geochemical character of the mixed melt particles points to middle jurassic sandstones eisensandstein formation that crop out at the center of the central uplift as the source for the melt fragments

eocene pliocene time scale and stratigraphy of the upper rhine graben urg and the swiss molasse basin smb we present a general stratigraphic synthesis for the upper rhine graben urg and the swiss molasse basin smb from eocene to pliocene times the stratigraphic data were compiled both from literature and from research carried out by the authors during the past 6 years an index of the stratigraphically most important localitites is provided we distinguish 14 geographical areas from the helvetic domain in the south to the hanau basin in the north for each geographical area we give a synthesis of the biostratigraphy lithofacies and chronostratigraphic ranges the relationships between this stratigraphic record and the global sea level changes are generally disturbed by the geodynamic e g subsidence evolution of the basins however global sea level changes probably affected the dynamic of transgression regression in the urg e g middle pechelbronn beds and serie grise corresponding with sea level rise between ru1 ru2 and ru2 ru3 sequences respectively as well as in the molasse basin regression of the umm corresponding with the sea level drop at the ch1 sequence the urgent project upper rhine graben evolution and neotectonics provided an unique opportunity to carry out and present this synthesis discussions with scientists addressing sedimentology tectonics geophysics and geochemistry permitted the comparison of the sedimentary history and stratigraphy of the basin with processes controlling its geodynamic evolution data presented here back up the palaeogeographic reconstructions presented in a companion paper by the same authors see berger et al in int j earth sci 2005

a fifty year perspective of magmatic evolution on ruapehu volcano new zealand verification of open system behaviour in an arc volcano geochemical and petrological data for samples from well documented eruptions that occurred at ruapehu volcano over the period 1945 1996 can be used to illustrate the complexity of short term geochemical variation in an arc type volcano collectively data from ruapehu volcano show trends with time of increasing sio2 abundance and rising 87sr 86sr ratios consistent with broad control by assimilation and crystal fractionation processes afc however the magmas emplaced during the past fifty years show geochemical variability that spans most of the range shown by lavas erupted over the entire history of the volcano magma compositions fluctuate through wide ranges over relatively short time intervals reflecting the effects of processes associated with magma recharge events within the volcano these complex trends are also manifested when the geochemistry and petrography of sequences of prehistoric lavas are examined in detail and they arise from short term effects that are imposed during recharge on the overall afc trend we show that the temporal geochemical and petrographic variations among erupted magmas are modulated by processes of mixing and mingling between fresh magma from below and stagnant melt and entrained crystals from earlier events remaining in the volcanic edifice probably in dikes and sills these processes are probably replicated over longer time periods hundreds to thousands of years as melts arrested at different levels in the near surface conduit system are progressively displaced by new magma batches arc type volcanoes such as ruapehu are characterised by pulsatory growth in which bursts of high magma production are superimposed on a background of subdued but more or less continuous activity this style of activity is difficult to predict through the usual seismicity ground deformation lake water geochemistry volcano monitoring techniques and petrology and geochemistry may provide the basis for an alternative strategy

normal mode and free air gravity constraints on lateral variations in velocity and density of earth s mantle with the use of a large collection of free oscillation data and additional constraints imposed by the free air gravity anomaly lateral variations in shear velocity compressional velocity and density within the mantle dynamic topography on the free surface and topography on the 660 km discontinuity and the core mantle boundary were determined the velocity models are consistent with existing models based on travel time and waveform inversions in the lowermost mantle near the core mantle boundary denser than average material is found beneath regions of upwellings centered on the pacific ocean and africa that are characterized by slow shear velocities these anomalies suggest the existence of compositional heterogeneity near the core mantle boundary

simultaneous inversion for 3 d variations in shear and bulk velocity in the mantle until recently most of the seismic tomographic modeling has been addressing the question of lateral heterogeneity either in p or s wave velocities the s wave velocity variations are larger and hence provide stronger signal on long period waveforms the direct p travel times being the first arrivals on the other hand are most frequently reported in the international seismological centre isc bulletins in mineral physics experiments the variation in bulk velocity is more often measured to better understand the differences between vp and vp patterns and better link the results from mineral physics to those of seismic tomography we formulate the inverse problem in terms of relative perturbations in the shear velocity vs 12 and bulk sound velocity v k 12 we use a large data set which consists of waveforms waveform derived travel times and travel times from the isc bulletins the earthquakes are relocated using corrections for lateral heterogeneity the events which cannot be reliably determined are discarded the model is defined as spherical harmonics to degree 12 horizontally and as chebyshev polynomials to order 13 radially for both shear and bulk sound velocity the inversion is performed under smoothness constraint the resolution tests and bootstrapping analysis indicate that the model is well recovered particularly at long wavelength the results indicate a much larger variability of shear than bulk sound velocity the model explains observations well the most intriguing result obtained in this study is that the variations in shear velocity and bulk sound velocity are negatively correlated in the lowermost mantle the explanation is not very clear from the mineral physics point of view it is not unlikely that this could be explained in terms of thermal variation even though we are unwilling to rule out the possibility of large wavelength compositional variations

40ar 39ar laser probe dating of the central european tektite producing impact event a new 40ar 39ar data set is presented for tektites from the central european strewn field moldavites this is the only strewn field that is entirely situated in a continental environment and still characterized by scattered ages 14 15 3 myr the main objectives of the study were to define more precisely the moldavite formation age and provide a good calibration for a glass standard proposed for fission track dating the laser total fusion ages obtained on chips from 7 individual specimens from the southern bohemian and moravian subfields are restricted to a narrow interval of time with an average of 14 34 0 08 myr relative to the 27 95 0 09 myr of the fish canyon tuff biotite this result gives a more precise age not only for the tektite field but also for its producing impact if the genetic link between the moldavites and the nordlinger ries impact crater is maintained then this new age has to be considered a reliable estimate for the ries crater also this new value places the formation of central european tektites within the lower serravallian period in the latest geologic timescales evidence of their impact products such as glass spherules or shocked minerals can therefore be sought in sedimentary marine formations in a more precisely defined age interval

feasibility of monitoring hydraulic fracturing using time lapse audio magnetotellurics abstracthydraulic fracturing is widely used for initiating and subsequently propagating fractures in reservoir strata by means of a pressurized fluid to release oil and gas or to store industry waste downhole or surface microseismic monitoring is commonly used to characterize the hydraulically induced fractures however in some cases downhole microseismic monitoring can be difficult due to the limitation imposed by boreholes surface microseismic monitoring often faces difficulties acquiring high signal to noise ratio data because of the on site noise from hydraulic fracturing process research and field observations indicate that injecting conductive slurry or water into a strata may generate distinct time lapse electromagnetic anomalies between pre and posthydraulic fracturing these anomalies provide a means for characterizing the hydraulic fracturing using time lapse electromagnetic methods we examined the time lapse variation over an hour one day one month and two years of observed audio magn

magnetic and electric field observations during the 2000 activity of miyake jima volcano central japan magnetic and electric field variations associated with the 2000 eruption of miyake jima volcano are summarized for about 1 week prior to the july 8 phreatic explosion significant changes in the total intensity were observed at a few stations which indicated uprising of a demagnetized area from a depth of 2 km towards the summit this nonmagnetic source can be regarded as a vacant space itself electric and magnetic field variations were observed simultaneously associated with the tilt step event which was the abrupt v50 s inflation at a few km depth within the volcano followed by gradual recovery vseveral hours the electric field is ascribed to the electrokinetic effect most probably due to forced injection of fluids from the source while the magnetic field to the piezomagnetic effect due to increased pressure large magnetic variations amounting to a few tens of nt were observed at several stations since july 8 and they turned almost flat after the august 18 largest eruption magnetic changes are explained mostly by the vanishing of magnetic mass in the summit and additionally by the thermal demagnetization at a rather shallow depth a large increase in the self potential by 130 mv was also observed near the summit caldera associated with the august 18 eruption which suggests that the hydrothermal circulation system sustained within the volcano for the past more than 10 years was destroyed by this eruption 9 2002 published by elsevier science b v

abrupt glacial valley incision at 0 8 ma dated from cave deposits in switzerland glacial erosion dramatically alters mountain landscapes but the pace at which glaciers carve a previously fluvial landscape remains poorly defined because long term valley incision rates are difficult to measure here we reconstruct the lowering history of the aare valley switzerland over the past 4 m y by dating cave sediments with cosmogenic 26al and 10be incision accelerated from 120 m m y to 1200 m m y at 0 8 1 0 ma at least 1 m y after the onset of local glaciation rapid incision may have been triggered by lowering of the equilibrium line altitude at the mid pleistocene climate transition

electromagnetic precursors to earthquakes in the ulf band a review of observations and mechanisms despite over 2 decades of international and national monitoring of electrical signals with the hope of detecting precursors to earthquakes the scientific community is no closer to understanding why precursors are observed only in some cases laboratory measurements have demonstrated conclusively that self potentials develop owing to fluid flow and that both resistivity and magnetization change when rocks are stressed however field experiments have had much less success many purported observations of low frequency electrical precursors are much larger than expectations based on laboratory results in some cases no precursors occurred prior to earthquakes or precursory signals were reported with no corresponding coseismic signals nonetheless the field experiments are in approximate agreement with laboratory measurements maximum resistivity changes of a few percent have been observed prior to some earthquakes in china but the mechanism causing those changes is still unknown anomalous electric and magnetic fields associated with fluid flow prior to earthquakes may have been observed finally piezomagnetic signals associated with stress release in earthquakes have been documented in measurements of magnetic fields

constraints on localized core mantle boundary structure from multichannel broadband sks coda analysis 1 in recent years a wide range of geophysical results have offered evidence that earth s lowermost mantle is characterized by strong lateral variations in material properties among the structures of particular interest are intermittent ultralow velocity zones ulvzs located directly above the core mantle boundary cmb which were originally inferred from the distortion of teleseismic spdks phases ulvzs have been modeled as layers with sharp boundaries and seismic velocity reductions 10 and interpreted as regions of partial melt in this study we further constrain local ulvz structure beneath north america by signal processing and waveform modeling of the sks coda recorded at broadband seismic arrays secondary phases in the sks coda are effectively isolated by eigenimage processing residual i e sks less data sections from various western pacific events display clear spdks arrivals followed by a secondary phase whose timing and slowness are consistent with cmb origins one dimensional modeling of these phases by reflectivity and generalized ray synthetics favors an asymmetric model with ulvz present at only one of the cmb intercepts the preferred ulvz is characterized by reductions in p and s velocities of 18 and 50 respectively and a diffuse upper boundary these characteristics are consistent with local production and gravitational sinking of dense e g iron rich partial melt above the cmb we postulate that a gradational ulvz beneath north america may mark a lateral transition domain between regions of mantle upwelling where more uniform ulvzs exist and regions of downwelling where ulvzs are either nonexistent or imperceptibly thin

geomorphological and sedimentological comparison of fluvial terraces and karst caves in zhangjiajie northwest hunan china an archive of sandstone landform development the zhangjiajie sandstone peak forest geopark zhangjiajie world geopark of northwest hunan china hosts a well preserved sequence of fluvial terraces and karst caves in this contribution a comparative study of fluvial terraces with karst caves along the middle lower suoxi river in zhangjiajie world geopark is presented to improve the understanding of the development of striking sandstone landscape in the upper suoxi river by integrating geomorphological sedimentological and geochronological techniques the possible correlation between fluvial terraces and karst caves as well as their climatic and tectonic implications is investigated the available electron spin resonance and thermo luminescence numerical ages coupled with morphostratigraphic analysis indicate that aggradation of fluvial terrace levels occurred at ca 347 34 ka t4 104 45 8 88 to 117 62 9 99 ka t3 60 95 5 18 ka t2 and holocene t1 followed by the stream incision fluvial terrace levels t4 to t1 correlate morphologically with the karst cave levels l1 to l4 yet the proposed chronology for the fluvial terrace levels is a bit later than the chronological data obtained from karst caves in northwest hunan where a unique sandstone peak forest landscape was extensively developed the fluvial terrace sequences as well as the cave systems are the important archives for studying the evolution of the sandstone landscape the beginning of the sandstone landscape development must be earlier than the aggradation of the fluvial terrace t4 allowing this unique landscape to occur in the middle pleistocene

the bolivian altiplano conductivity anomaly 1 a long period magnetotelluric study was carried out in the central andes between latitudes 19 5 s and 21 s along two almost parallel profiles of 220 and 380 km length respectively the investigation area extends from the pacific coast to the southern altiplano plateau in the back arc of the south american subduction zone the main geoelectrical structure resolved is a broad and probably deep reaching highly conductive zone in the middle and deeper crust beneath the high plateau although the data show deviations from two dimensionality a two dimensional approach is justified for large parts of the profiles sensitivity studies were carried out in order to constrain the depth extent another electrically conductive structure was resolved in the middle crust of the chilean forearc thought to be connected with the precordillera fault system the andean continental research program ancorp seismic reflection profile carried out along the same line at 21 s revealed highly reflective zones below the altiplano in good correlation with the upper boundary of the altiplano conductor this highly conductive domain also coincides with low seismic velocities and a zone of an elevated vp vs ratio and although not well resolved with low qp seismic quality factors taking into account the enhanced heat flow and a derived temperature model the most probable explanation lies in the assumption of granitic partial melts the good conductor below the volcanic arc which was found in regions farther south at 22 s gradually vanishes toward the north this is consistent with the results of seismic tomography concerning qp values and a gap of recent volcanism

a multi method approach for speleogenetic research on alpine karst caves torca la texa shaft picos de europa spain abstract speleogenetic research on alpine caves has advanced significantly during the last decades these investigations require techniques from different geoscience disciplines that must be adapted to the methodological constraints of working in deep caves the picos de europa mountains are one of the most important alpine karsts including 14 of the world s deepest caves caves with more than 1 km depth a speleogenetic research is currently being developed in selected caves in these mountains one of them named torca la texa shaft is the main goal of this article for this purpose we have proposed both an optimized multi method approach for speleogenetic research in alpine caves and a speleogenetic model of the torca la texa shaft the methodology includes cave surveying dye tracing cave geometry analyses cave geomorphological mapping uranium series dating 234u 230th and geomorphological structural and stratigraphical studies of the cave surroundings the speleodisc method was employed to establish the structural control of the cavity torca la texa 2653 m length 215 m depth is an alpine cave formed by two cave levels vadose canyons and shafts soutirage conduits and gravity modified passages the cave was formed prior to the middle pleistocene and its development was controlled by the drop of the base level producing the development of the two cave levels coevally to the cave levels formation soutirage conduits originated connecting phreatic and epiphreatic conduits and vadose canyons and shafts were formed most of the shafts were created before the local glacial maximum 43 45 ka and only two cave passages are related to dolines developed in recent times the cave development is strongly related to the structure locating the cave in the core of a gentle fold with the conduits geometry and orientation controlled by the bedding and five families of joints

results of ultra low frequency magnetic field measurements during the guam earthquake of 8 august 1993 we report the results of measurements of ultra low frequency magnetic noise during a large earthquake ms 7 1 at guam of 8 august 1993 depth 60 km the ulf observing system is located in the guam island about 65 km from the epicenter several distinct features of this analysis are summarized 1 we have proposed rather sophisticated statistical analyses monthly mean standard deviation in order to estimate the wave intensity and polarization i e ratio z h 2 a comparison between the ulf wave activity and kp is useful in distinguishing between the space geomagnetic pulsations and non space emissions 3 then the use of the ratio z h is found to be of essential importance in discrimating the emissions presumably of seismic origin from space plasma waves 4 the statistical analysis of the temporal evolution of this ratio has yielded that it shows a broad maximum only about one month before the earthquake and this suggests that the emissions during this period are very likely to be magnetic precursors 5 the temporal variation of z component is similar to that for the loma prieta earthquake such that it shows a broad maximum ten days two weeks before the earthquake and another increase a few days before the earthquake 6 the emissions presumably associated with the earthquake are of noise like nature and their main frequency is 0 02 0 05 hz with maximum intensity 0 1 nt

low frequency magnetic field measurements near the epicenter of the ms 7 1 loma prieta earthquake the authors report the results of measurements of low frequency magnetic noise by two independent monitoring systems prior to the occurrence of the m sub s 7 1 loma prieta earthquake of 17 october 1989 their measurements cover 25 narrow frequency bands in the more than six decade frequency range 0 01 hz 32 khz with a time resolution varying from a half hour in the ulf range 0 01 10 hz to one second in the elf vlf range 10 hz 32 khz the ulf system is located near corralitos about 7 km from the epicenter the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf data has revealed no precursor activity that they can identify at this time however the ulf data have some distinctive and anomalous features first a narrow band signal appeared in the range 0 05 0 2 hz around september 12 and persisted until the appearance of the second anomalous feature which consisted of a substantial increase in the noise background starting on 5 october and covering almost the entire frequency range of the ulf system third there was an anomalousmore dip in the noise background in the range 0 2 5 hz starting one day ahead of the earthquake finally and perhaps most compelling there was an increase to an exceptionally high level of activity in the range 0 01 0 5 hz starting approximately three hours before the earthquake there do not appear to have been any magnetic field fluctuations originating in the upper atmosphere that can account for this increase further while the systems are sensitive to motion seismic measurements indicate that there were no significant shocks preceding the quake thus the various anomalous features in the data and in particular the large amplitude increase in activity starting three hours before the quake may have been magnetic precursors less

estimation of electric fields in the conducting earth s crust for oscillating electric current dipole sources and implications for anomalous electric fields associated with earthquakes abstract electromagnetic radiation possibly associated with earthquake occurrences in the earth s crust can be treated as a problem of electromagnetic induction within a conducting half space representing the crust we estimated the magnitude of the electric field near the earth s surface for oscillating electric current dipole sources located at various depths this shows that the electric field highly attenuates as expected and the source must be stronger than 10 5 a m even if it is located at a depth of several kilometers for practically detecting signals at frequencies in the ulf ultra low frequency range we also examined the electric field near the earth s surface for a box car type source in uniform and non uniform crust models we found that the wave form of the source is rather well preserved in both models but signal amplitudes are very small and unlikely to be drastically enhanced even in a non uniform crustal structure although this discussion is based only on a specific non uniform model

dynamics of a phase change at the base of the mantle consistent with seismological observations the phase change model for the origin of the d seismic discontinuity is tested by comparing the results of convection modeling with seismic observations we compute a number of global dynamic models that incorporate a phase change at the base of the mantle with different characteristics and transform the resulting temperature field and the distribution of phases to seismic velocities over 900 two dimensional synthetic waveforms are computed for each of the models from which s scs and scd phases are picked the distribution of the relative amplitudes and differential travel time residuals for these phases are statistically compared with the distribution of data from four well studied regions northern siberia alaska india and central america in a search for the characteristics of a phase transition that best match these seismic observations we find that the best fit among the models considered is obtained for phase transitions characterized by a clapeyron slope of 6 mpa k 1 and an elevation above the core mantle boundary of 150 km under adiabatic temperature or 127 gpa and 2650 k on a p t diagram dynamic models demonstrate that the value of clapeyron slope and the density difference between the phases can have significant influence on the dynamics of plumes but probably only a minor influence on the dynamics of subducted slabs we find that the thermal structure of subducted slabs can be important in giving rise to the seismic triplication the strongest scd arrivals in our models are observed in the area of subduction the folding of the slab at the base of the mantle leads to patterns in differential travel time distributions consistent with seismic observations and suggests that the largest heterogeneity occurs at the top of the d layer or just above it analysis of the spatial autocorrelation functions of the differential travel time residuals suggests that their characteristic peaks reflect the patterns of slab folding and may provide constraints on the rheology of slabs at the base of the mantle

late cenozoic uplift history of the peak district central england inferred from dated cave deposits and integrated with regional drainage development a review and synthesis abstract the white peak upland in the peak district region of central england extends over an area of 100 km2 locally exceeding 400 m above sea level formed in extensively karstified limestone of early carboniferous age historically regarded as palaeo karst following the availability of u series dates since the 1980s it has become apparent that the superimposed cave levels in this region formed during the succession of pleistocene interglacials their differences in height reflecting downcutting by the river derwent and its tributaries in response to regional uplift however quantitative interpretation is complicated because of effects of glaciation most importantly glacial diversion of rivers in adjoining lowland regions making the determination of uplift from fluvial incision particularly difficult the derwent terrace dataset is also complicated by lithologically controlled knickpoints which can remain localized or propagate upstream depending on individual details cave fluvial and glacial datasets for this region are integrated to quantify the uplift history establishing the quaternary uplift history of a wide region of britain uplift of 100 m since the mid pleistocene revolution and by 300 400 m since the miocene is thus inferred these amounts exceed the uplift deduced over corresponding timescales in surrounding regions indicating that the quaternary uplift has slightly accentuated the overall domal form of this carboniferous limestone inlier the analysis supports the previous assignment of the wragby glaciation in the surrounding lowland regions to mis 8 and constrains the most recent glaciation within the peak district represented by the bakewell till also to mis 8 overall this work provides an important case study demonstrating integrated use of multi disciplinary datasets to quantify late cenozoic landscape development

results of ulf magnetic field measurements near the epicenters of the spitak ms 6 9 and loma prieta ms 7 1 earthquakes comparative analysis the characteristics of the ulf magnetic field emissions measured at two magnetic observatories in the republic of georgia prior to and after the ms 6 9 earthquake that occurred near spitak armenia on december 7 1988 are compared with the apparently similar emissions associated with the ms 7 1 earthquake that occurred near loma prieta california on october 17 1989 the main features of the spitak measurements according to observations made at the dusheti station 128 km to the spitak epicenter as compared with the loma prieta measurements which were made at corralitos california 7 km to the loma prieta epicenter are the following 1 the intensity of ulf background activity started growing 3 to 5 days before the spitak earthquake whereas the corresponding increase in activity began 12 days before the loma prieta earthquake 2 a substantial ulf emission burst was recorded at dusheti starting 4 hours prior to the main shock a similar large burst of ulf activity commenced 3 hours before the loma prieta event and continued until the occurrence of the main shock 3 ulf activity remained high for about two weeks after the spitak earthquake and for several months after the loma prieta earthquake 4 ulf noise bursts were observed 1 to 6 hours before powerful aftershocks at spitak during the period of enhanced activity but there was no conclusive link between the ulf noise at corralitos and the after shocks a major difference in the ulf activity preceding the two earthquakes is a difference in amplitude 0 2 nt at spitak and 5 nt at loma prieta but this is easily explained as being caused by the different distances of the observation stations from the epicenters

the equation of state of orthorhombic perovskite in a peridotitic mantle composition to 80 gpa implications for chemical composition of the lower mantle abstract in situ x ray diffraction of orthorhombic perovskite which is the dominant phase in the earth s lower mantle was carried out on a sample with a klb 1 peridotite composition up to a pressure of 80 gpa using a laser heated diamond anvil cell lhdac with x rays from a synchrotron radiation source at each pressure increment the sample was heated using a yag laser to relax the deviatoric stress in the sample the bulk modulus of the orthorhombic perovskite which contained feo al 2 o 3 tio 2 cao and na 2 o was nearly equal to or slightly larger than that of pure mgsio 3 perovskite the density of the klb 1 peridotite at the top of the lower mantle estimated using thermoelastic parameters is in good agreement with a density profile prem determined from seismic observations the klb 1 peridotite composition is therefore consistent with the bulk composition of the upper part of the lower mantle

coeval argon 40 argon 39 ages of moldavites from the bohemian and lusatian strewn fields 40ar 39ar ages of four tektites moldavites from southern bohemia near cesk budejovice czech republic and a tektite from lusatia near dresden germany have been determined by 11 step degassing experiments the purpose of the study was to enlarge the 40ar 39ar data base of moldavites and to check the age relations of the bohemian and lusatian samples the mean plateau age of the bohemian samples which range from 14 42 to 14 70 ma is 14 50 0 16 0 42 2 ma errors in parentheses include age error and uncertainty of standard monitor age the plateau age of the lusatian sample of 14 38 0 26 0 44 2 ma confirms the previously published 40ar 39ar age of 14 52 0 08 0 40 2 ma and demonstrates that the fall of lusatian and bohemian tektites were contemporaneous because of their geochemistry and their ages there is no doubt that the lusatian tektites are moldavites accepting that moldavites are ejecta from the nrdlinger ries impact the new ages also date the impact event this age is slightly younger about 0 2 0 3 ma than the age suggested by earlier k ar determinations

inferences on flow at the base of earth s mantle based on seismic anisotropy we applied global waveform tomography to model radial anisotropy in the whole mantle we found that in the last few hundred kilometers near the core mantle boundary horizontally polarized s wave velocities vsh are on average faster by 1 than vertically polarized s wave velocities vsv suggesting a large scale predominance of horizontal shear this confirms that the d region at the base of the mantle is also a mechanical boundary layer for mantle convection a notable exception to this average signature can be found at the base of the two broad low velocity regions under the pacific ocean and under africa often referred to as superplumes where the anisotropic pattern indicates the onset of vertical flow

error propagation in electromagnetic transfer functions what role for the magnetotelluric method in detecting earthquake precursors summary whether electromagnetic precursors exist is a contentious issue that should be considered in the context of the focal depth and epicentral distance at which earthquakes nucleate and with due regard to externally driven changes in the electromagnetic fields recorded at the earth s surface if high frequency electromagnetic signals are generated by earthquakes then these signals may not be detectable because of attenuation occurring between the focal depth of the earthquake and the earth s surface this is particularly true in seismotectonic regions e g subduction zones where saline fluids including seawater raised heat flow and partial melts often lead to enhanced conductivities a technique for examining temporal variations in magnetotelluric mt spectra is presented which i considers both non inductive and inductive parts of the mt transfer function ii allows electromagnetic skin depths and adjustment distances to be calculated iii takes account of error propagation in the transfer functions and and iv acknowledges possible nonearthquake sources of observed variations in transfer functions and their errors data processing tends to eliminate non stationary electromagnetic disturbances of the source field hence the method is more suited to detecting hypothesized changes in subsurface conductivity than short lived electromagnetic bursts the technique is applied to mt data from seismotectonic regions in new zealand mt ruapehu the andes western cordillera and the mediterranean montecristo island and to a culturally quiet control site situated on a stable craton in central australia we demonstrate that the mt method can resolve apparent conductivity changes of the order of a few percent over 48 hr time intervals and give thresholds for other interval lengths comparison of the results obtained from seismotectonic regions with those from central australia and consideration of external source field effects highlight how temporal variations of electromagnetic fields might be speciously interpreted as earthquake precursors

speleogenesis in highly geodynamic contexts the quaternary evolution of monte corchia multi level karst system alpi apuane italy abstract the mt corchia karst system is one of the most important and famous caves in the world different from many other large caves here the geological structure has had only a minor role on the vertical multi level pattern of the cave a detailed geomorphic and morphometric analysis of the cave and a preliminary study of cave sediments along with new datings of speleothems allow us now to depict the multistage evolution of this cave which produced at least three major paleo phreatic levels related to different base level stages the analysis of the directions of cave passages shows that the three main phases have different orientations which can be attributed to the different surface morphology during speleogenesis in former times chronological constraints and geomorphic features suggest that the upper part of mt corchia cave developed during the end of pliocene in a stage of favourable climatic conditions and with a moderate tectonic uplift rate the morphological features and the nature of sediments in the upper paleo phreatic level at 1350 1450 m above present sea level apsl imply the occurrence of a wide allogenic catchment area this drainage pattern persisted also in the following stage during a significant but slow lowering of the base level which allowed the formation and the intense vadose rearrangement of the epi phreatic network around 1100 1250 m apsl an uplift stage in the early pleistocene caused the capture of the basins and the loss of allogenic feeding a third epi phreatic level was formed at around 900 m apsl when the catchment area was reduced to the present extent of carbonate rock more than 1 ma ago the recent evolution is due to rapid uplift and to the progressive incision of surrounding basins which led to the lowering of the local base level and to a readjustment of the cave system in order to adapt to a new equilibrium with the present elevation of the springs

plausibility of long distance electrotelluric precursors to earthquakes a systematic analysis of the plausibility of different classes of models which could account for low frequency precursory electrotelluric signals observable at large distances from a large earthquake is carried out first we consider linear models for which either a stationary electrical field is generated by a current dipole in the source volume or a static deformation field results from a precursory strain in the source volume linearly inducing a streaming potential effect near the electrode in the former case only the conjunction of very favorable circumstances may lead to an electrical field larger than 10 mv km at more than 100 km with the constraint that no anomaly exceeds a few volts per kilometer in the source area it indeed requires a powerful electrical dipole current 104 a length 1 km which might be produced by a streaming potential effect associated with the connection of nonhydrostatic fluid reservoirs pore pressure difference up to 100 mpa a two dimensional channeling of the electrical currents from the source to the electrode area which would result from high conductivity horizontal layers and finally a local amplification factor of typically 100 near the electrodes which might be produced by a narrowing of the conductive channel for an elastic long distance interaction an electric field of 10 mv km at a distance 10 times the source length 100 km away from a m 6 earthquake requires a precursory deformation larger than the coseismic deformation if no strong local amplification is considered alternatively nonlinear models are proposed and discussed assuming that the crust is stuffed with small scale local instabilities fractures and nonhydrostatic fluid reservoirs among which a number are close to their instability threshold these instabilities may follow their own evolutionary process inducing sporadic fluid flow and hence streaming potential effect in the vicinity of the electrodes without any relation to a remote tectonic activity however these instabilities may be sensitive to very small changes in the stress field and hence be triggered by the elastic precursory deformation of a remote seismic source this requires that the precursory deformation near the instability is at least larger than the tidal strain 10 7 this necessary condition is met at a distance of up to 10 times the source dimension when the precursory strain source is only 10 of the coseismic deformation provided that the strain source is double the size of the seismic fault itself this model could account for the absence of self potential anomalies related to the earthquake itself as a large proportion of the available instabilities could have been swept away by the precursory strain furthermore with such a model a precursory strain in the source area could induce a detectable change in the background seismic activity over a vast area which may give a new interpretation of the times of increased probability observations for short distances the triggering of fluid instabilities by strain perturbation and the associated streaming potential effect may well be a promising model for explaining low frequency electric and magnetic precursors

quaternary regional evolution based on karst cave geomorphology in picos de europa atlantic margin of the iberian peninsula abstract alpine caves have attracted considerable geomorphological paleoenvironmental and hydrogeological interest since climate glaciations relief uplift fluvial incision and karst aquifer control their evolution in the atlantic margin of the iberian peninsula picos de europa mountains is among of the most important karst areas of the world containing some of the deepest caves explored today in addition these mountains represent a reference site for the study of the last glacial cycle in the sw of europe this work aims to reconstruct the pliocene quaternary evolution of this region based on geomorphological and geochronological research u th and al be carried out in four alpine caves cave geomorphological mapping evidences that 12 km of studied caves are made up of 47 vadose canyons and shafts 45 phreatic epiphreatic conduits organised in six cave levels and 7 breakdown modified passages their deposits are characterized by speleothems including flowstones that represent ancient cave pavements fluvial terrace deposits with allochthonous clasts slackwater deposits related to cave floods and debris deposits produced by breakdown one 26al 10be burial age indicates a minimum age of 2 1 0 5 ma for the caves origin allowing estimation of the mountain uplift at 0 15 0 25 mm a 1 since the late pliocene twenty eight new 234u 230th ages and another six previous speleothem ages give ages ranging from mis 8 to 1 the speleogenetic model comprises six phases of regional evolution phase 1 main development of cave levels with se directed phreatic flow in the nw of picos de europa in a karst partially or totally covered by the detrital permian mesozoic cover presently eroded phase 2 erosion of the permian mesozoic cover and onset of vadose conditions before 260 ka in a karst affected by fluvial captures phase 3 cave infill during 220 145 ka probably caused by the erosion of stephanian detrital outcrops phase 4 erosion of cave infill during 125 45 ka phase 5 apparent pause in the speleothem formation during 45 25 ka related to dry and cold regional conditions phase 6 reactivation of the speleothem precipitation since 25 ka regional climate fluvial incision and the ancient presence of detrital outcrops at the surface appear to have been the main factors that controlled the cave evolution and regional geomorphological evolution throughout pliocene and quaternary times

electrical conductivity variations around the palmdale section of the san andreas fault zone our analysis of a decade of observations from the palmdale california telluric array is presented the array is a system of large scale telluric field measurements used for the passive monitoring of electrical conductivity variations over a large region centered over the san andreas fault zone northeast of los angeles since 1985 systematic changes in the relationships between the telluric field measurements around the array have been observed these changes amounted to 1 to 2 by the time the array was closed down in 1989 with the fields measured along the fault and northeast of the fault showing signal decreases relative to the fields southwest of the fault because of the possible implications of these changes for conductivity variations related to tectonic activity on the san andreas we have attempted to sort out the geography of the zones that could cause the changes the simplest though nonunique interpretation of the observed variations in the telluric relationships is a steady increase in the conductivity of the lower crustal region of the fault zone from two dimensional models of the telluric response around the array we infer that an increase of about 60 milli siemens in the conductance of the lower crustal fault zone could account for the changes seen over the period 1985 to 1989 assuming changes were in a kilometer wide zone and that the lower crustal fluids were very conductive this could represent a strain of about 0 4 10 6 the surface strain would be much smaller and would be lost in surface strain noise because of the possibility that fluid pressure changes are involved these small strains could still be significant for earthquake cycle phenomena alternatively the observed changes could have been produced by increases in the conductivity of the upper crust of the mojave desert northeast of the fault or by decreases in the conductivity of the upper crust in the san gabriel mountains southwest of the fault to produce the observed telluric changes however the additional conductivity and the associated strain changes would have to be much larger the strain needed to accommodate the increased conductivity on the mojave side would have to be of the order of 6 10 4 which seems unrealistically high smaller strains could account for conductivity changes in the san gabriel mountains but these strains would have to be compressive water level changes are not considered to be a possible cause of the conductivity changes because the measurement scale is much larger than the typical scale of water level changes and no seasonally correlated changes in the telluric fields were observed

partial melting in a thermo chemical boundary layer at the base of the mantle abstract seismological detections of complex structures in the lowermost mantle boundary layer the d region motivate a conceptual model of a compositionally stratified thermo chemical boundary layer tcbl within which lateral temperature variations sustained by large scale mid mantle flow cause variations of partial melt fraction partial melt fractions of from 0 to 30 in the tcbl occur due to the eutectic of the boundary layer material lying below the high temperature at the core mantle boundary cmb coupled with the presence of steep thermal gradients across the boundary layer regions of the tcbl with the highest temperatures have extensive partial melting producing lateral chemical variations and strong effects on seismic velocities and boundary layer dynamics this tcbl concept provides a relatively simple framework that can plausibly account for diverse seismological observations such as predominance of large scale volumetric elastic wave velocity heterogeneity in the boundary layer laterally extensive but intermittent abrupt shear and compressional velocity increases and decreases at the top of the d region small scale topography of d velocity discontinuities thin ultra low velocity zones at the cmb widespread shear wave anisotropy in d bulk sound velocity anomalies detected in low shear velocity regions of d and large scale upwellings from the most extensively melted regions of the boundary layer neutral or negative buoyancy of the partial melt in the tcbl is required along with an increase in bulk modulus and some density increase of the boundary layer material relative to the overlying mantle more complex models in which the partially melted chemical boundary layer is laterally displaced by mid mantle downwellings are also viable but these appear to require additional special circumstances such as a phase change efficient segregation of slab crustal material or abrupt onset of anisotropy in order to account for rapid velocity increases at the top of d the precise nature of the compositional anomaly or anomalies in d and the eutectic composition of this zone are yet to be determined but it appears likely that partial melting within the lowermost mantle plays a paramount role in the observed seismic velocity heterogeneity increased resolution geodynamic calculations of dense boundary layer structures with partial melting and attendant viscosity reductions and chemical heterogeneity are needed to quantify this tcbl concept

paleogeography of the upper rhine graben urg and the swiss molasse basin smb from eocene to pliocene twenty paleogeographic maps are presented for middle eocene lutetian to late pliocene times according to the stratigraphical data given in the companion paper by berger et al this volume following a first lacustrine continental sedimentation during the middle eocene two and locally three rupelian transgressive events were identified with the first corresponding with the early rupelian middle pechelbronn beds and the second and third with the late rupelian serie grise fischschiefer and equivalents during the early rupelian middle pechelbronn beds a connection between north sea and urg is clearly demonstrated but a general connection between north sea urg and paratethys via the alpine sea is proposed but not proved during the late rupelian whereas in the southern urg a major hiatus spans early aquitanian to pliocene times early and middle miocene marine brackish and freshwater facies occur in the northern urg and in the molasse basin omm osm however no marine connections between these basins could be demonstrated during this time after the deposition of the molasse series a very complex drainage pattern developed during the late miocene and pliocene with a clear connection to the bresse graben during the piacenzian sundgau gravels during the late miocene pliocene and quaternary sedimentation persisted in the northern urg with hardly any interruptions the present drainage pattern of the rhine river from alpine area to the lower rhine embayment was not established before the early pleistocene

quantifying erosion over timescales of one million years a photogrammetric approach on the amount of rhenish erosion in southwestern germany abstract the lein valley in southwestern germany possesses well preserved pliocene to mid pleistocene land surfaces featuring a gentle relief and sediments accumulated by former tributaries of the danube this ancient danubian land surface was captured and incised by mid pleistocene to holocene tributaries of the river rhine in a photogrammetric approach we calculated the volume of material extracted by rhenish erosion providing a first quantification of the effects of stream piracy on timescales of about 1 ma using stereoscopic surface modelling software a dem was generated with a resolution of 5 m from borehole data literature geological maps and own field observations we determined the morphometric parameters of the ancient danubian ur lein valley the gradient was imported as a 3d breakline into the model where it controls the reinterpolation of surrounding data points the result is a high resolution dem of the valley of the ur lein subtraction of the dem of the actual landscape from the dem of the ancient ur lein valley yields a model representing the rock volume eroded by the rhenish lein which totals 1 39 km3 and converts into a rate of erosion between 63 and 74 mm ka over a period of 700 to 600 ka respectively in accordance with figures obtained elsewhere in central europe through cosmogenic nuclides it reflects the dominance of frequent fluctuations in climate and is considered to be mainly a product of strong changes in temperature and related processes during the transitional times between mid to late pleistocene warm and cold states a filtering procedure applied to cold and transitional state erosion rates of the middle and late pleistocene yielded peak values between 66 and 77 mm ka up to three times higher than the modern rate or the rate of warm state episodes an assessment of the contribution of rhenish stream piracy on long term mid pleistocene denudation under changing climate conditions resulted in a maximum 4 9 fold acceleration

development of finite strain in the convecting lower mantle and its implications for seismic anisotropy 1 seismological observations have revealed patches of seismic anisotropy in regions related to mantle upwelling and paleosubduction within an otherwise isotropic lower mantle a combination of numerical modeling and mineral physics is used to constrain the source of anisotropy in these regions in an effort to better understand lower mantle dynamics and mineral physics specifically it is investigated whether lattice preferred orientation lpo can explain the anisotropy observed in regions of paleosubduction since lpo is caused by dislocation creep and is destroyed by diffusion creep we can develop deformation mechanism maps to determine which regions allow for the development of a mineral fabric strain is then calculated in these regions and is related to mineral physics experiments combined with high pressure elastic constants of lower mantle minerals in order to assess the predicted seismic anisotropy uncertainties in rheological parameters such as the transition stress between dislocation creep and diffusion creep necessitate a full evaluation of the parameter range the effect of variations in transition stress activations parameters and strength of slabs on fabric development is investigated it is shown that lpo is a likely candidate for the cause of lowermost mantle anisotropy in regions of paleosubduction

discussion on the article coastal and inland karst morphologies driven by sea level stands a gis based method for their evaluation by canora f fidelibus d and spilotro g comments are presented on the article by canora et al 2012 dealing with karst morphologies driven by sea level stands in the murge plateau of apulia southern italy our comments start from cave levels that are considered in the cited article as a proof of sea level stands we argue that the presence of sub horizontal passages in cave systems is not a sufficient condition for correlating them with hypothetical past sea level stands such a correlation must be based upon identification of speleogenetic features within the karst systems and or geological field data the problems encountered when using cave surveys for scientific research and their low reliability especially in the case of old surveys are then treated since they represent a crucial point in the paper object of this discussion eventually we present some final consideration on cave levels and terraces and on the specific case study pointing out once again to the need in including geological field data to correctly find a correspondance between flat landforms and sea level fluctuations our main conclusion is that field data and information on speleogenesis of the underground karst landforms cannot be disregarded in a study that claims to deal with the influence of sea level changes on caves copyright 2013 john wiley sons ltd

noble gas constraints on the layered structure of the mantle several chemical models of mantle structure have been proposed1 6 based on isotopic data such as sr nd hf and pb in volcanic rocks from both oceanic and continental areas the most popular of these are two chemical models of the vertically layered mantle 1 that it is a depleted mantle from which mid oceanic ridge basalt morb is derived and 2 that it is a fertile mantle from which a mantle plume may arise1 5 however these models are almost always based on solid elements such as sr nd hf and pb isotopes and do not fully reflect the noble gas data because noble gases are liable to be lost from the solid earth when a mantle differentiation occurs on a global scale in the upper mantle the data on noble gas isotopes could give constraints on the structure of the mantle that differ from those by solid element isotopes based on a consideration 3he 4he and 40ar 36ar ratios of recent samples i argue here that the observed data suggest that mixing occurs between the source materials of a mantle plume and of morb the data seem to favour the model which assumes that the source of a typical mantle plume is deeper than that of morb

dc trains and pc3s source effects in mid latitude geomagnetic transfer functions magnetotelluric mt data from two sites 150 and 300 km southeast of san francisco california geomagnetic dipole latitude 43 degrees l approximately 1 9 show that the usual mt assumption of spatially uniform external magnetic fields is violated to a significant degree in the period range 10 30 s inter station transfer functions exhibit large systematic temporal variations which are consistent with a combination of two distinct sources electromagnetic noise due to the san francisco bay area rapid transit bart dc electric railway and pc3 geomagnetic pulsations there is a suggestion in the data that some of the pc activity may actually be excited by bart